
Citation: Enebe GC, Ukoba K, Jen T-C. Numerical modeling of effect of annealing on nanostructured CuO/TiO2 pn heterojunction solar cells using SCAPS[J]. AIMS Energy, 2019, 7(4): 527-538. doi: 10.3934/energy.2019.4.527
[1] | Julijana Gjorgjieva, Kelly Smith, Gerardo Chowell, Fabio Sánchez, Jessica Snyder, Carlos Castillo-Chavez . The Role of Vaccination in the Control of SARS. Mathematical Biosciences and Engineering, 2005, 2(4): 753-769. doi: 10.3934/mbe.2005.2.753 |
[2] | Fatmawati, Rashid Jan, Muhammad Altaf Khan, Yasir Khan, Saif ullah . A new model of dengue fever in terms of fractional derivative. Mathematical Biosciences and Engineering, 2020, 17(5): 5267-5287. doi: 10.3934/mbe.2020285 |
[3] | Alex Capaldi, Samuel Behrend, Benjamin Berman, Jason Smith, Justin Wright, Alun L. Lloyd . Parameter estimation and uncertainty quantification for an epidemic model. Mathematical Biosciences and Engineering, 2012, 9(3): 553-576. doi: 10.3934/mbe.2012.9.553 |
[4] | Konstantin Weise, Erik Müller, Lucas Poßner, Thomas R. Knösche . Comparison of the performance and reliability between improved sampling strategies for polynomial chaos expansion. Mathematical Biosciences and Engineering, 2022, 19(8): 7425-7480. doi: 10.3934/mbe.2022351 |
[5] | Qing Wu, Chunjiang Zhang, Mengya Zhang, Fajun Yang, Liang Gao . A modified comprehensive learning particle swarm optimizer and its application in cylindricity error evaluation problem. Mathematical Biosciences and Engineering, 2019, 16(3): 1190-1209. doi: 10.3934/mbe.2019057 |
[6] | Aili Wang, Xueying Zhang, Rong Yan, Duo Bai, Jingmin He . Evaluating the impact of multiple factors on the control of COVID-19 epidemic: A modelling analysis using India as a case study. Mathematical Biosciences and Engineering, 2023, 20(4): 6237-6272. doi: 10.3934/mbe.2023269 |
[7] | Tingting Zhao, Robert J. Smith? . Global dynamical analysis of plant-disease models with nonlinear impulsive cultural control strategy. Mathematical Biosciences and Engineering, 2019, 16(6): 7022-7056. doi: 10.3934/mbe.2019353 |
[8] | Xiaojing Wang, Yu Liang, Jiahui Li, Maoxing Liu . Modeling COVID-19 transmission dynamics incorporating media coverage and vaccination. Mathematical Biosciences and Engineering, 2023, 20(6): 10392-10403. doi: 10.3934/mbe.2023456 |
[9] | Tao-Li Kang, Hai-Feng Huo, Hong Xiang . Dynamics and optimal control of tuberculosis model with the combined effects of vaccination, treatment and contaminated environments. Mathematical Biosciences and Engineering, 2024, 21(4): 5308-5334. doi: 10.3934/mbe.2024234 |
[10] | Ridouan Bani, Rasheed Hameed, Steve Szymanowski, Priscilla Greenwood, Christopher M. Kribs-Zaleta, Anuj Mubayi . Influence of environmental factors on college alcohol drinking patterns. Mathematical Biosciences and Engineering, 2013, 10(5&6): 1281-1300. doi: 10.3934/mbe.2013.10.1281 |
The first COVID-19 infected case was identified in late 2019 in China and then spread around the globe with extraordinary speed. By March 11, 2021, the COVID-19 confirmed cases were registered in 213 countries, and the World Health Organization (WHO) declared this disease a global pandemic; see Ngo et al. [1]. Due to this pandemic, every aspect of life has been disturbed and almost every region around the globe has faced unexpected situations. In every region, among other sectors affected by this pandemic, the health sector is the most affected area; see Pfefferbaum and North [2], Kim et al. [3], Campion et al. [4], Gloster et al. [5], Talevi et al. [6], and Wastnedge et al. [7]. As of December 13, 2021, 09:09 GMT (Greenwich Mean Time), totally confirmed cases (TCC) have touched a figure of 270488249, the total number of deaths (TND) has reached 5324113, and 243235043 infected persons have been recovered. For the latest updates and details about the COVID-19 events; see https://www.worldometers.info/coronavirus/.
The top fifteen countries with the higher TND, include (ⅰ) America with 817956 deaths, (ⅱ) Brazil with 616941 deaths, (ⅲ) India with 475636 deaths, (ⅳ) Mexico with 296672 deaths, (ⅴ) Russia with 290604 deaths, (ⅵ) Peru with 201,650 deaths, (ⅶ) the United Kingdom with 146439 deaths, (ⅷ) Indonesia with 143936 deaths, (ⅸ) Italy with 134831 deaths, (ⅹ) Iran with 130722 deaths, (xi) Colombia with 129107 deaths, (xii) France with 120431 deaths, (xiii) Argentina with 116771 deaths, (ivx) Germany with 106331 deaths, and (xv) Ukraine with 91215 deaths. For a brief overview of country-wise statistics related to the COVID-19 pandemic, we refer to Bo et al. [8].
Due to the unprecedented situation of the COVID-19 pandemic, it is necessary to have the best description and efficient modeling of the COVID-19 events. Statistical methodologies are very useful in modeling and predicting lifetime events. Several statistical studies on this pandemic have appeared. For example, Moreau [9] predicted the COVID-19 phenomena in Brazil. Tuli et al. [10] predicted the growth trend of the COVID-19 pandemic. Rahman et al. [11] implemented the Weibull model for the COVID-19 data analysis. Almetwally [12] introduced a new inverted Topp-Leone (NITL) distribution and used it for modeling the COVID-19 mortality rate data.
These statistical studies are carried out either by implementing the existing models or by proposing new methodologies to update/modify the existing distributions. In the recent era of DT (distribution theory), the development of new methods to introduce new distributions is an important research topic. In this regard, numerous methods to update the distributional flexibility of the existing model have been introduced; see Alizadeh et al. [13] Chipepa et al. [14], Handique et al. [15], Tahir et al. [16], Zaidi et al. [17], Riad et al. [18], and Bakr et al. [19]. For more information about the applicability of statistical models in applied sectors, we refer to Xu et al. [20], and Luo et al. [21].
In this paper, we further contribute to the literature on DT by proposing a new approach, namely, a new extended exponential (NEExp) family. It can be used to obtain the updated versions of the classical/traditional (such as Weibull, beta, gamma, Gumble, Rayleigh, etc.) or other existing models. The NEExp family is proposed by incorporating the T-X distributions approach of Alzaatreh et al. [22] with the exponential distribution with probability density function (PDF) e−t, taken as a parent model.
The novelty and key motivations of the proposed method are the followings:
● The method introduced in this paper is new and has not been studied in the literature.
● The proposed method is a very simple and convenient approach of adding an extra parameter to obtain the updated versions of the existing models.
● The proposed approach helps to improve the flexibility and characteristics of the existing models.
● The proposed method provides a close fit to healthcare and other related data sets.
The reaming work carried out in this paper is organized as follows. In Section 2, we define the proposed family and discuss its special case. Certain mathematical properties of the NEExp family are provided in Section 3. The estimation of the parameters and a simulation study are provided in Section 4. To illustrate the NEExp family, two practical data sets are analyzed in Section 5. To forecast the COVID-19 data sets, the machine learning methods are discussed in Section 6. Finally, some concluding remarks, limitations of the proposed method, and future study plans are discussed in Section 7.
This section is divided into two subsections. In the very first subsection, we define the proposed NEExp family of distributions. Whereas, the second subsection is devoted to studying a special case of the NEExp family of distributions
Let V has a NEExp family, if its distribution function (DF) F(v;δ,ϑϑ) is given by
F(v;δ,ϑϑ)=1−δ[1−M(v;ϑϑ)]δ+M(v;ϑϑ),v∈R, | (2.1) |
where δ>0 is an additional parameter and ϑϑ is a vector of parameters associated with the baseline DF M(v;ϑϑ).
Furthermore, in link to F(v;δ,ϑϑ), the PDF f(v;δ,ϑϑ) of the NEExp family is
f(v;δ,ϑϑ)=δ(δ+1)m(v;ϑϑ)[δ+M(v;ϑϑ)]2,v∈R. | (2.2) |
For v∈R, the survival function (SF) S(v;δ,ϑϑ)=1−F(v;δ,ϑϑ), and hazard function (HF) h(v;δ,ϑϑ)=f(v;δ,ϑϑ)1−F(v;δ,ϑϑ) of the NEExp family are given by
S(v;δ,ϑϑ)=δ[1−M(v;ϑϑ)]δ+M(v;ϑϑ), |
and
h(v;δ,ϑϑ)=(δ+1)m(v;ϑϑ)[1−M(v;ϑϑ)][δ+M(v;ϑϑ)], |
respectively.
A special member of the NEExp family called, a new extended exponential Weibull (NEExp-Weibull) model is discussed in the next subsection. The NEExp-Weibull model is introduced by using the DF of the Weibull model in Eq (2.1). The DF M(v;ϑϑ) of the Weibull model is given by
M(v;ϑϑ)=1−e−φ2vφ1,v≥0,φ1>0,φ2>0, | (2.3) |
with PDF m(v;ϑϑ) given by
m(v;ϑϑ)=φ1φ2vφ1−1e−φ2vφ1,v>0,φ1>0,φ2>0, |
where ϑϑ=(φ1,φ2). By incorporating Eq (2.3) in Eq (2.1), we reach at the DF of the NEExp-Weibull model; see Subsection 2.2.
A random variable V has the NEExp-Weibull model with parameters φ1>0,φ2>0, and δ>0, if its DF F(v;δ,ϑϑ) and PDF F(v;δ,ϑϑ), are given by
F(v;δ,ϑϑ)=1−δe−φ2vφ1δ+1−e−φ2vφ1,v≥0, | (2.4) |
and
f(v;δ,ϑϑ)=δ(δ+1)φ1φ2vφ1−1e−φ2vφ1[δ+1−e−φ2vφ1]2,v>0, | (2.5) |
respectively.
For the NEExp-Weibull model with DF in Eq (2.4) and PDF in Eq (2.5), the SF ˉF(v;δ,ϑϑ)=1−F(v;δ,ϑϑ), HF h(v;δ,ϑϑ)=f(v;δ,ϑϑ)ˉF(v;δ,ϑϑ), and CHF H(v;δ,ϑϑ)=−log(ˉF(v;δ,ϑϑ)) are given by
ˉF(v;δ,ϑϑ)=δe−φ2vφ1δ+1−e−φ2vφ1,v>0, |
h(v;δ,ϑϑ)=(δ+1)φ1φ2vφ1−1[δ+1−e−φ2vφ1],v>0, |
and
H(v;δ,ϑϑ)=−log(δe−φ2vφ1δ+1−e−φ2vφ1),v>0, |
respectively.
A visual behavior of f(v;δ,ϑϑ) for (i) φ1=5.5,φ2=0.2,δ=9.5 (red curve) (ii) φ1=4.5,φ2=0.6,δ=2.5, (green curve) (iii) φ1=0.5,φ2=1.6,δ=1.5, (blue curve) and (iv) φ1=1.9,φ2=2.6,δ=2.5, (gold curve) is provided in Figure 1.
From the visual illustration in Figure 1, we can see that f(v;δ,ϑϑ) possess different behaviors. For example, it takes (i) the left-skewed form (red curve), (ii) the symmetrical shape (green curve), (iii) the reverse-J shape (blue curve), and (iv) the right-skewed (gold curve).
Here, we obtain different mathematical properties of the NEExp family with PDF f(v;δ,ϑϑ). These properties include QF (quantile function) expressed by Q(u), rth moment denoted by μ/r, MGF (moment generating function) represented by MV(t), RL (residual life), and RRL (reverse residual life) functions.
The QF of the NEExp family can be obtained by inverting Eq (2.1). Let V have the NEExp family with DF F(v;δ,ϑϑ), then, its QF is given by
vq=Q(u)=F−1(δuδ+1−u), |
where u∈(0,1).
Suppose V follows the NEExp family of distributions, then the rth moment of the NEExp distributions is derived as
μ/r=∫Ωvrδ(δ+1)m(v;ϑϑ)[δ+M(v;ϑϑ)]2dv,μ/r=(δ+1)δ∫Ωvrm(v;ϑϑ)[1+M(v;ϑϑ)δ]2dv. | (3.1) |
Consider the series
1(1+k)2=∞∑a=1(−1)a−1aka−1. | (3.2) |
By implementing Eq (3.2) with k=M(v;ϑϑ)δ, we have
1(1+[M(v;ϑϑ)δ])2=∞∑a=1(−1)a−1a(M(v;ϑϑ)δ)a−1. | (3.3) |
Using Eq (3.3) in Eq (3.1), we get
μ/r=(δ+1)δa∞∑a=1(−1)a−1a∫Ωvrm(v;ϑϑ)M(v;ϑϑ)a−1dv,μ/r=(δ+1)δa∞∑a=1(−1)a−1∫Ωvrka(v;ϑϑ)dv, | (3.4) |
where ka(v;ϑϑ)=am(v;ϑϑ)M(v;ϑϑ)a−1 is the exponentiated PDF, and a is a power parameter. We can also write Eq (3.4), as follows
μ/r=(δ+1)δa∞∑a=1(−1)a−1λa,r, | (3.5) |
where
λa,r=∫Ωvrka(v;ϑϑ)dv. | (3.6) |
Using the DF and PDF of the Weibull model in Eq (3.6), we get
λa,r=∫∞0vrφ1φ2vφ1−1e−φ2vφ1(1−e−φ2vφ1)a−1dv. | (3.7) |
On solving Eq (3.7), we get
λa,r=a−1∑k=0(−1)k(a−1k)∫∞0vrφ1φ2vφ1−1e−φ2(k+1)vφ1dv,λa,r=a−1∑k=0(−1)k(a−1k)Γ(rφ1+1)(φ2)rφ1(k+1)rφ1+1. | (3.8) |
Using Eq (3.8) in Eq (3.5), we get the rth moment of the NEExp-Weibull model, given by
μ/r=(δ+1)δa∞∑a=1a−1∑k=0(−1)a+k−1(a−1k)Γ(rφ1+1)(φ2)rφ1(k+1)rφ1+1. | (3.9) |
Using r=1, in Eq (3.9), we get the first rth moment of the NEExp-Weibull model, given by
μ/1=(δ+1)δa∞∑a=1a−1∑k=0(−1)a+k−1(a−1k)Γ(1φ1+1)(φ2)1φ1(k+1)1φ1+1. |
Using r=2, in Eq (3.9), we obtain the second rth moment of the NEExp-Weibull model, given by
μ/2=(δ+1)δa∞∑a=1a−1∑k=0(−1)a+k−1(a−1k)Γ(2φ1+1)(φ2)2φ1(k+1)2φ1+1. |
Using r=3, in Eq (3.9), we obtain the third rth moment of the NEExp-Weibull model, given by
μ/3=(δ+1)δa∞∑a=1a−1∑k=0(−1)a+k−1(a−1k)Γ(3φ1+1)(φ2)3φ1(k+1)3φ1+1. |
Using r=4, in Eq (3.9), we obtain the second rth moment of the NEExp-Weibull model, given by
μ/4=(δ+1)δa∞∑a=1a−1∑k=0(−1)a+k−1(a−1k)Γ(4φ1+1)(φ2)4φ1(k+1)4φ1+1. |
Furthermore, the MGF of the NEExp-Weibull model is given by
MV(t)=(δ+1)δa∞∑a=1a−1∑k=0∞∑r=0(−1)a+k−1trr!(a−1k)Γ(rφ1+1)(φ2)rφ1(k+1)rφ1+1. |
The RL of the NEExp-Weibull model represented by Rt(v), is given by
Rt(v)=δe−φ2(v+t)φ1δ+1−e−φ2(v+t)φ1×δ+1−e−φ2vφ1δe−φ2vφ1. |
Furthermore, the RRL of the NEExp-Weibull model represented by ˉRt(v), is given by
ˉRt(v)=δe−φ2(v−t)φ1δ+1−e−φ2(v−t)φ1×δ+1−e−φ2vφ1δe−φ2vφ1. |
In this section, we obtain the estimators (^φ1,^φ2,ˆδ) of the parameters (φ1,φ2,δ) by implementing the maximum likelihood estimation approach. Furthermore, for the evaluation of ^φ1,^φ2, and ˆδ, a simulation is also provided.
Let V1,V2,...,Vp be a sample of size p observed from the PDF f(v;δ,ϑϑ). In link to f(v;δ,ϑϑ), the likelihood function (LH) λ(δ,ϑϑ|v1,v2,...,vp) is given by
λ(δ,ϑϑ|v1,v2,...,vp)=p∏a=1f(va;δ,ϑϑ). | (4.1) |
Using Eq (2.5) in Eq (4.1), we get
λ(δ,ϑϑ|v1,v2,...,vp)=p∏a=1δ(δ+1)φ1φ2vφ1−1ae−φ2vφ1a[δ+1−e−φ2vφ1a]2. | (4.2) |
Corresponding to λ(φ1,φ2,δ|v1,v2,...,vp), the log LH π(δ,ϑϑ|v1,v2,...,vp) is given by
π(δ,ϑϑ|v1,v2,...,vp)=plogδ+plog(δ+1)+plogφ1+plogφ2+(φ1−1)p∑a=1logva−p∑a=1φ2vφ1a−2p∑a=1log(δ+1−e−φ2vφ1a). |
The partial derivatives of π(δ,ϑϑ|v1,v2,...,vp) are given by
∂∂φ1π(δ,ϑϑ|v1,v2,...,vp)=pφ1+p∑a=1logva−φ2p∑a=1(logva)vφ1a−2φ2p∑a=1(logva)vφ1ae−φ2vφ1a(δ+1−e−φ2vφ1a), |
∂∂φ2π(δ,ϑϑ|v1,v2,...,vp)=pφ2−p∑a=1vφ1a−2p∑a=1vφ1ae−φ2vφ1a(δ+1−e−φ2vφ1a), |
and
∂∂δπ(δ,ϑϑ|v1,v2,...,vp)=pδ+p(δ+1)−2p∑a=11(δ+1−e−φ2vφ1a), |
respectively.
On solving ∂∂φ1π(δ,ϑϑ|v1,v2,...,vp)=0, ∂∂φ2π(δ,ϑϑ|v1,v2,...,vp)=0, and ∂∂δπ(δ,ϑϑ|v1,v2,...,vp), we get the estimators ^φ1,^φ2, and ˆδ, respectively.
Now, we evaluate the performances of ^φ1,^φ1, and ˆφ by conducting a SiSt (simulation study). The SiSt is performed by adopting the following steps
● To carry out the SiSt, the RNs (random numbers) from the NEExp-Weibull model are generated using the inverse DF, given by
vq=Q(u)=F−1(δuδ+1−u). |
● The SiSt is performed for two different combination sets of φ1,φ2, and δ, such as (a) φ1=0.7,φ2=0.9,δ=1.4, and (b) φ1=1.5,φ2=1.4,δ=1.25.
● For both two sets of φ1, φ2, and δ, RNs of sizes p=25,50,75,...,500 are generated using the inverse DF method.
● The numerical values of the maximum likelihood estimators (MLEs) (^φ1,^φ2,ˆδ) of the parameters (φ1,φ2,δ) are obtained.
● Two statistical quantities/measures such as (i) mean square errors (MSEs) and (ii) Bias, are selected for assessing ^φ1, ^φ2, and ˆδ. The values of these quantities are given by
MSE(ˆϕˆϕ)=1500500∑a=1(ˆϕˆϕa−ϕϕ)2, |
and
Bias(ˆϕˆϕ)=1500500∑a=1(ˆϕˆϕa−ϕϕ), |
respectively, where ϕϕ=(φ1,φ2,δ).
All the numerical and simulation results are obtained using optim() R-function with the argument method="L-BFGS-B". The results of the SiSt of the NEExp-Weibull distribution are reported in Tables 1 and 2, and presented visually in Figures 2 and 3.
n | Parameters | MLEs | MSEs | Biases |
φ1 | 0.7439555 | 0.01816230 | 0.043955486 | |
20 | δ | 2.5224710 | 4.62452592 | 1.122470958 |
φ2 | 0.9819897 | 0.08933255 | 0.081989688 | |
φ1 | 0.7261523 | 0.00675241 | 0.026152290 | |
40 | δ | 2.2436960 | 3.50148162 | 0.843695947 |
φ2 | 0.9475541 | 0.04503070 | 0.047554140 | |
φ1 | 0.7174831 | 0.00469112 | 0.017483127 | |
60 | δ | 2.1504600 | 3.14461417 | 0.750459996 |
φ2 | 0.9382455 | 0.03002095 | 0.038245459 | |
φ1 | 0.7139450 | 0.00303585 | 0.013945008 | |
80 | δ | 2.0166510 | 2.71268772 | 0.616651319 |
φ2 | 0.9172897 | 0.02141037 | 0.017289700 | |
φ1 | 0.7118858 | 0.00250170 | 0.011885794 | |
100 | δ | 1.9587070 | 2.39162374 | 0.558707085 |
φ2 | 0.9215668 | 0.01819720 | 0.021566823 | |
φ1 | 0.7071069 | 0.00095725 | 0.007106915 | |
200 | δ | 1.6315320 | 1.20339825 | 0.231531527 |
φ2 | 0.8963361 | 0.00907772 | -0.003663932 | |
φ1 | 0.7059804 | 0.00056999 | 0.005980353 | |
300 | δ | 1.4947460 | 0.59116842 | 0.094745813 |
φ2 | 0.8942843 | 0.00510254 | -0.005715678 | |
φ1 | 0.7046970 | 0.00042009 | 0.004696986 | |
400 | δ | 1.4758080 | 0.42345175 | 0.075807616 |
φ2 | 0.8949554 | 0.00295727 | -0.005044638 | |
φ1 | 0.7026197 | 0.00015114 | 0.002619658 | |
500 | δ | 1.4191470 | 0.17256813 | 0.019147385 |
φ2 | 0.8958860 | 0.00155967 | -0.004113986 | |
φ1 | 0.7021186 | 0.00011673 | 0.002118624 | |
600 | δ | 1.3973690 | 0.05930217 | -0.002630857 |
φ2 | 0.8964089 | 0.00084446 | -0.003591110 |
n | Parameters | MLEs | MSEs | Biases |
φ1 | 0.6538964 | 1.61446e-02 | 0.053896399 | |
20 | δ | 2.3444560 | 3.753281849 | 0.844456065 |
φ2 | 0.8422871 | 0.074129355 | 0.042287133 | |
φ1 | 0.6335936 | 6.57586e-03 | 0.033593572 | |
40 | δ | 2.0966990 | 2.835106550 | 0.596698837 |
φ2 | 0.8114326 | 0.027465620 | 0.011432631 | |
φ1 | 0.6207884 | 3.08374e-03 | 0.020788424 | |
60 | δ | 1.9743140 | 2.393837599 | 0.474313588 |
φ2 | 0.8107312 | 0.022889902 | 0.010731190 | |
φ1 | 0.6195547 | 2.83132e-03 | 0.019554745 | |
80 | δ | 1.8076620 | 1.762573786 | 0.307661602 |
φ2 | 0.7912179 | 0.016246953 | -0.008782086 | |
φ1 | 0.6135883 | 1.52055e-03 | 0.013588293 | |
100 | δ | 1.7689760 | 1.451201967 | 0.268976369 |
φ2 | 0.7923297 | 0.011392565 | -0.007670316 | |
φ1 | 0.6062087 | 4.83673e-04 | 0.006208661 | |
200 | δ | 1.5338360 | 0.437971185 | 0.033836372 |
φ2 | 0.7870588 | 0.003783507 | -0.012941210 | |
φ1 | 0.6050252 | 2.87229e-04 | 0.005025202 | |
300 | δ | 1.4799110 | 0.134430960 | -0.020089413 |
φ2 | 0.7911718 | 0.001925689 | -0.008828233 | |
φ1 | 0.6021233 | 1.08930e-04 | 0.002123257 | |
400 | δ | 1.5034740 | 0.104238258 | 0.003473527 |
φ2 | 0.7954403 | 0.000832362 | -0.004559674 | |
φ1 | 0.6014035 | 6.62443e-05 | 0.001403539 | |
500 | δ | 1.4982590 | 0.048978064 | -0.001741474 |
φ2 | 0.7974116 | 0.000411811 | -0.002588439 | |
φ1 | 0.6009386 | 3.77904e-05 | 0.000938590 | |
600 | δ | 1.4899270 | 0.005002637 | -0.010072511 |
φ2 | 0.7976296 | 0.000242969 | -0.002370384 |
The primary aim of the introduction of the proposed distribution is its implementation for data analysis in the health and other related sectors. This section illustrates the respective fact by analyzing two data sets. The first data set (Data 1) represents the mortality rates of the COVID-19 infected persons in Mexico. Whereas, the second illustration is based on taking another COVID-19 data from Holland.
By analyzing these two COVID-19 data sets, the numerical results of the proposed model is compared with the
● Weibull model with SF given by
S(v;φ1,φ2)=e−φ2vφ1,v,φ1,φ2>0, |
● Logarithmic Weibull (L-Weibull) model with SF given by
S(v;φ1,φ2,θ,σ)=(1−σ[1−e−φ2vφ1]σ−[log(1−e−φ2vφ1)])α,v,φ1,φ2,α,σ>0, |
● Novel exponent power-Weibull (NEP-Weibull) model with SF given by
S(v;φ1,φ2,θ)=(1−1−e−φ2vφ1ee−φ2vφ1)θ,v,φ1,φ2,θ>0, |
and
● New modified Weibull (NM-Weibull) model with SF given by
S(v;φ1,φ2,σ)=1−(1−e−φ2vφ1)σ[σ−e−φ2vφ1],v,φ1,φ2,σ≥1,σ≤−1. |
To figure out the best competitive model for the COVID-19 data, certain statistical tests such as the (i) AD (Anderson-Darling) test statistic given by AD=−p−1pp∑a=1(2a−1)[logM(va)+log{1−M(vp−a+1)}], (ii) CM (Cramer-von Mises) test statistic expressed by CM=112p+p∑a=1[2a−12p−M(va)]2, and (iii) KS (Kolmogorov-Smirnov (KS) test statistic derived by KS=supv[Mp(v)−M(v)], are considered.
Here, we analyze the mortality rates of the patients infected by the COVID-19 pandemic in Mexico; see https://covid19.wh. It is also studied by Almongy et al. [23] using a new extension of the Rayleigh distribution. This data set consists of 106 observations and is recorded from March 4, 2020, to July 20, 2020. The data set is given by: 4.4130, 3.0525, 4.6955, 7.4810, 5.1915, 3.6335, 6.6100, 8.2490, 5.8325, 3.0075, 5.4275, 3.0610, 3.3280, 1.7200, 2.9270, 5.3425, 5.0175, 2.6210, 2.1720, 2.5715, 3.8150, 7.3020, 3.9515, 3.1850, 1.7685, 3.1635, 2.3650, 1.6075, 4.6420, 6.4390, 4.4065, 5.0215, 3.6300, 2.9925, 3.2060, 1.6975, 2.2120, 4.9675, 3.9200, 4.7750, 1.7495, 1.8755, 3.4840, 1.6430, 5.0790, 4.0540, 3.3485, 3.5755, 3.2800, 1.0385, 1.8890, 1.4940, 1.6680, 3.4070, 4.1625, 3.9270, 4.2755, 1.6140, 3.7430, 3.3125, 3.0700, 2.4545, 2.3305, 2.6960, 6.0210, 4.3480, 0.9075, 1.6635, 2.7030, 3.0910, 0.5205, 0.9000, 2.4745, 2.0445, 1.6795, 1.0350, 1.6490, 2.6585, 2.7210, 2.2785, 2.1460, 1.2500, 3.2675, 2.3240, 2.3485, 2.7295, 2.0600, 1.9610, 1.6095, 0.7010, 1.2190, 1.6285, 1.8160, 1.6165, 1.5135, 1.1760, 0.6025, 1.6090, 1.4630, 1.3005, 1.0325, 1.5145, 1.0290, 1.1630, 1.2530, 0.9615.
Corresponding to the COVID-19 data (mortality rate of the COVID-19 infected persons) of Mexico, the summary measures are: minimum = 0.5205, 1st quartile = 1.6445, median = 2.6397, mean = 2.9112, 3rd quartile = 3.7970, maximum = 8.2490, variance = 2.640433, range = 7.7285, standard deviation = 1.624941, skewness = 0.9732453, and kurtosis = 3.666136.
Corresponding to the mortality rate of the COVID-19 infected persons in Mexico, some basic plots are presented in Figure 4. The plots in Figure 4, show that the first data set is right-skewed and possesses the increasing failure rate behavior.
Corresponding to the Mexico data, the values of ^φ1, ^φ2, and ˆδ are presented in Table 3. The standard errors (SEs) (numerical values in the parentheses) of ^φ1, ^φ2, and ˆδ are also presented in Table 3.
Model | ^φ1 | ^φ2 | ˆδ | ˆα | ˆσ | ˆθ |
NEExp-Weibull | 2.53401 (0.31876) | 0.01723 (0.01562) | 0.26201 (0.24135) | - | - | - |
Weibull | 1.92738 (0.14019) | 0.09976 (0.02220) | - | - | - | - |
L-Weibull | 1.57117 (0.01001) | 1.20372 (0.00879) | - | 0.16022 (0.01580) | 0.45036 (0.01773) | - |
NEP-Weibull | 1.71906 (0.03634) | 0.95340 (0.03634) | - | - | - | 0.15201 (0.01503) |
NM-Weibull | 1.89237 (0.15734) | 0.11004 (0.03088) | - | - | 12.06058 (20.5532) | - |
For the Mexico data, the values of the selected tests CM, AD, and KS of the fitted models are reported in Table 4. The associated p-value of fitted models is also provided in Table 4. From the numerical illustration in Table 4, we can see that the proposed model has the smallest values of CM, AD, and KS, and the largest p-value. These facts show that the proposed model is the best competitor. Besides the numerical illustration, a visual display of the performances of the proposed model is also provided in Figure 5.
Model | CM | AD | KS | p-value |
NEExp-Weibull | 0.05834 | 0.33674 | 0.06266 | 0.79940 |
Weibull | 0.10264 | 0.66004 | 0.07147 | 0.65100 |
L-Weibull | 0.06002 | 0.36130 | 0.07091 | 0.66060 |
NEP-Weibull | 0.07017 | 0.43993 | 0.07862 | 0.52880 |
NM-Weibull | 0.10723 | 0.68969 | 0.07024 | 0.67240 |
Here, we provide a second illustration of the proposed model by analyzing another COVID-19 data taken from Holland; see Almongy et al. [23]. This data set consists of 30 observations and is recorded between March 31, 2020, and April 30, 2020. The second data set is given by: 7.4590, 3.7490, 3.4700, 5.3280, 1.4285, 1.1270, 6.1370, 5.1445, 5.4160, 3.5495, 1.7305, 1.8235, 2.9640, 6.6055, 3.9840, 3.7920, 2.6535, 2.5240, 2.7155, 2.7775, 3.0135, 2.0485, 1.8055, 2.4800, 2.2310, 1.9415, 0.9870, 0.6365, 0.7080, 2.1175.
The summary measures of the mortality rate of the COVID-19 infected persons in Holland are: minimum = 0.6365, 1st quartile = 1.8530, median = 2.6845, mean = 3.0783, 3rd quartile = 3.7812, maximum = 7.4590, variance = 3.121073, range = 6.8225, standard deviation = 1.766656, skewness = 0.8339708, and kurtosis = 2.953478.
In link to the mortality rate of the COVID-19 infected persons in Holland, some basic plots are sketched in Figure 6. From the plots in Figure 6, it is obvious that the second data set, related to the mortality rate of the COVID-19 infected persons, is skewed to the right and has increasing failure rate behavior.
Based on the Holland's COVID-19 data, the numerical values of estimators ^φ1,^φ2, and ˆδ are obtained in Table 5. Furthermore, the SEs of these estimators are also reported in Table 5.
Model | ^φ1 | ^φ2 | ˆδ | ˆα | ˆσ | ˆθ |
NEExp-Weibull | 2.20197 (0.48765) | 0.03704 (0.04876) | 0.75896 (0.10983) | - | - | - |
Weibull | 1.92738 (0.14019) | 0.09976 (0.02220) | - | - | - | - |
L-Weibull | 1.42252 (0.51193) | 0.12239 (0.05844) | - | 2.85548 (0.97654) | 0.89686 (2.15028) | - |
NEP-Weibull | 1.77603 (0.07305) | 1.03756 (0.07304) | - | - | - | 0.11297 (0.02890) |
NM-Weibull | 2.00489 (0.28946) | 0.06377 (0.04170) | - | - | -2.41345 (3.47713) |
Corresponding to the Holland data, the p-value and values of CM, AD, and KS are reported in Table 6. From the numerical comparison of the fitted models in Table 6, it is obvious that the proposed model performs better than the other competitors as it has the largest p-value and smallest CM, AD, and KS values. In support of Table 6, the performances of the proposed model are also illustrated visually by plotting the estimated DF, PP, PDF, QQ, and SF; see Figure 7.
Model | CM | AD | KS | p-value |
NEExp-Weibull | 0.03088 | 0.20437 | 0.08557 | 0.96710 |
Weibull | 0.04794 | 0.29434 | 0.10236 | 0.88030 |
L-Weibull | 0.05165 | 0.31630 | 0.10144 | 0.88660 |
NEP-Weibull | 0.03423 | 0.22143 | 0.10418 | 0.86740 |
NM-Weibull | 0.03926 | 0.24960 | 0.08981 | 0.95100 |
In this section, we implement three different machine learning algorithms, namely, SVR, NNAR, and RF to forecast the data set analyzed in Section 5. Before modeling, we split the data set into two parts; 80 percent as training data and 20 percent as testing data, followed by Qi and Zhang [24]. We apply all the models to training data and compare their forecasting performances using the testing data. To assess the out-of-sample (also known as post-sample) prediction accuracy, multistep ahead forecasts with RMSE and MAE are calculated.
The SVR is a popular ML approach, which is used for regression as well as classification problems. The SVR was first developed by Cortes and Vapnik [25], and to date, it is one of the most widely used supervised learning methods that is based on structured risk minimization rule and statistical theory. The structured risk minimization rule maximizes prediction accuracy and mitigates the likelihood of over fitting.
In practice, it can effectively approximate linear and nonlinear problems and work well for numerous problems. The SVR uses various kernel functions to figure out the similarity between two data points to tackle the non-linear situations. The main advantage of SVR lies in its potential to capture the predictors' nonlinearity and then utilize it to enhance forecasting accuracy. In our case, the set of predictors contains the lagged values. The SVR assists to detect the margin of error which is bearable in the model; see Ribeiro et al. [26] and Bibi et al. [27]. The SVR equation with kernel function can be expressed as
Ft=h∑k=1(λk−λ∗k)N(ck,c)+μ, | (6.1) |
where Ft is the outcome variable. The kernel function, N(ck,c) denotes the inner product, while μ is accommodated within the kernel function. In the literature, several kernel functions have been developed. Among them, the radial basis function (RBF) is the most popular, which can be illustrated as
N(ck,c)=exp{−||ck−cN||22τ2}, | (6.2) |
where the Euclidean distance between the two predictors squared vectors is represented by ||ck−cN||2 and τ2 is basically the width of RBF; see Lu et al. [28]. Hence, in this study, we focus on the RBF kernel function for the SVR. Tuning the SVR model enable us to arrive at optimal parameters.
Another ML approach is RF which is also known as the random decision forest. It falls within the supervised learning category. The RF is a very effective algorithm that is used for both regression and classification problems as proposed by Breiman [29]. Dietterich [30] argued that RF is considered the most efficient ensemble technique appearing in ML and fulfills good forecasting properties. The RF approach is employed in different areas, including stock trading, finance, e-commerce, and health care. It provides a forest out of a collection of decision trees that are usually estimated (trained) by employing the bagging approach.
The RF approach discovers the output based on the decision trees' forecasts. The forecasts are computed by averaging the output of several trees. The improvement is achieved in prediction by expanding the number of trees. In other words, as the number of trees in the forest grows, a more accurate forecast is obtained and circumvents the issue of over fitting as well. To estimate the RF, we use three hyper parameters i.e., the number of trees, number of nodes, and sample repetition. The number of nodes and trees are utilized as 3 and 500, respectively.
In general, neural networks (NNs) are basically a network or circuit of neurons. The artificial neural network (ANNs) is composed of nodes or artificial neurons. NNs are highly flexible computing frameworks for analyzing a wide range of nonlinear problems. A key advantage of such networks is that they have not required prior information regarding the functional form in the model establishing process, rather highly determined by the characteristics of data; see Peng et al. [31].
A feedback NN is established with lagged realization as predictors and hidden layer(s) with dimension nodes. The neural network autoregression (NNAR) contains three layers such as (i) the input layer, (ii) the hidden layer, and (iii) the output layer. The NNAR model is fitted to forecast a time series by utilizing its past information as inputs Ft,Ft−1,...,Ft−m, the entire process refers to feedback delay, where t indicates the time delay parameter. The NNAR (m, n) entails that the hidden layer consists of m delayed inputs and n nodes. The mathematical form of NNAR can be illustrated as
Ft=ω0+m∑c=1θωc(ℵc+z∑n=1ℵcnFt−i)+μ, | (6.3) |
where ℵcn(c=1,2,3,...,m,n=1,2,3,...,z) and ωc(c=1,2,3,...,m) are the weights of interconnection, and z is the length of input layers, and m is the length of hidden layers.
The prediction accuracy of all ML techniques is quantified by using two statistical accuracy criteria computed from a testing data set. Statistically, the forecast errors are more appropriate criteria to evaluate the predictive power and to finalize the best approach. In general, the most popular measures are MAE and RMSE. Hence, we compare the forecasting performance of ML techniques using these two measures in our study. Their mathematical expressions are given by
MAE=mean(|Ft−^Ft|), |
and
RMSE=√mean(Ft−^Ft)2, |
respectively.
This subsection is further divided into two parts. In the first part, we deal with the mortality rates of the patients infected by the COVID-19 pandemic in Mexico. In the second part, we deal with the death rates of the patients infected by the COVID-19 pandemic in Holland.
From Figure 8, it can be observed that the entire trajectory of the mortality rate has experienced many ups and downs in the last few months, but the trend of data is decreasing over time. The mortality rate series is plotted in Figure 8, where the vertical blue dotted line splits the estimation and post-sample forecasting periods. The histogram plot and box plot are also provided in Figure 8, which reveal that the underlying time series is right skewed.
The two statistical accuracy measures for the Mexico data set are given in Table 7. The MAE and RMSE are calculated for ML algorithms such as SVR, RF, and NNAR. It is inferred that the RF outperformed the other competitor counterparts. For the RF method, the RMSE and MAE values are given by 0.066 and 0.039, respectively. Whereas, for the SVR, the values of the RMSE and MAE are given by 0.073 and 0.043, respectively. On the other hand, the RMSE and MAE values for the NNAR are, respectively, given by 0.198 and 0.149. From the values of the RMSE and MAE for the NNAR approach, it is clear that the values of NNAR are higher than the values of the RMSE and MAE computed for RF and SVR.
Criteria | SVR | RF | NNAR |
RMSE | 0.073 | 0.066 | 0.198 |
MAE | 0.043 | 0.039 | 0.149 |
Furthermore, the visual illustration of forecast errors is porvided in Figure 9. The plots in Figure 9 show that the ML algorithms, specifically, the RF remained an efficient tool in forecasting the mortality rates of COVID-19 patients.
We also plot the prediction curves for COVID-19 deaths under the three machine learning algorithms to get a more intuitive picture of the prediction accuracy and results. In this regard, the line chart has been constructed, for the representation of predicted and actual values; see Figure 10. Some predicted values of the NNAR approach are very close, but few are substantially far away from the actual data. On the other hand, SVR prediction is highly stable over time and therefore beat the rival algorithms in predictive modeling.
Here, we estimate and predict the daily death data of COVID-19 for Holland. It can be observed from Figure 11 that the entire trajectory of mortality rate has experienced numerous episodes in several months, but the times series is declining over time. The mortality rate series is plotted in Figure 11, where the vertical blue dotted line represents the estimation and post-sample forecasting periods. The histogram plot and box plot are also presented in Figure 10, which demonstrates that the underlying series is right skewed.
The two considered statistical accuracy measures for the Holland data set are reported in Table 8. The MAE and RMSE are computed for ML algorithms, namely SVR, RF, and NNAR. From Table 8, we can observe that the SVR showed superior forecast performance as compared to the rival counterparts. For the SVR method, the RMSE and MAE values are 0.16 and 0.118, respectively. On the other hand, for the RF approach, these values are given by 0.191 and 0.139, respectively. Whereas, the forecast errors (RMSE and MAE) of NNAR are given by 0.444 and 0.398, respectively. From the above discussion, it is obvious that the forecast errors of the NNAR approach are substantially higher than the forecast errors of RF and SVR.
Criteria | SVR | RF | NNAR |
RMSE | 0.160 | 0.191 | 0.444 |
MAE | 0.118 | 0.139 | 0.398 |
The graphical comparison of forecast errors is also depicted in Figure 12. It manifests that the ML algorithms, specifically SVR remained an effective tool in forecasting the post-sample trajectory of the mortality rate of COVID-19 patients.
We portray the prediction curves for COVID-19 deaths using these three ML algorithms to get a more clear picture of the models performances. In this regard, we use the line chart for the representation of forecasted and observed data; see Figure 13. From the plots in Figure 13, it can be seen that the observed test series is highly volatile and noisy. Despite this volatility, SVR and RF have shown good results, particularly the RF performance is highly satisfactory.
The efforts in this paper added another useful approach to the literature on statistical methodologies by introducing a new family of distributions. The new family was named a NEExp family of distributions. Based on a NEExp family, an updated version of the Weibull model called, a NEExp-Weibull model was studied. The MLEs of the NEExp-Weibull model were obtained. The evaluation of the MLEs of the NEExp-Weibull distribution was carried out through a brief SiSt. The usefulness of the NEExp-Weibull model was shown by analyzing two data sets taken from the healthcare sector. The first data set was representing the mortality rate of COVID-19 patients in Mexico. Whereas, the second data was also related to the COVID-19 events taken from Holland. Using these two COVID-19 data sets, the NEExp-Weibull distribution was compared with the Weibull and three other well-known models such as the L-Weibull, NEP-Weibull, and NM-Weibull distributions. Based on four well-known comparative tools, it is observed that the NEExp-Weibull distribution was the best competitive model as compared to the Weibull and other well-known modified forms of the Weibull distribution. Therefore, based on the numerical results and findings of this study, it is observed that the NEExp-Weibull distribution may be the best suitable choice to use for analyzing the medical and other related data sets. Besides the statistical modeling, for prediction purposes, we further implemented three ML methods including SVR, RF, and NNAR using the same data sets. To compare their forecasting performances, two well-known statistical accuracy quantities such as the RMSE and MAE were computed. We found that the RF algorithm was very efficient in forecasting using the first data. However, for the second data set, the SVR showed superior performance in contrast to other methods.
Besides the certain advantages of the NEExp-Weibull distribution over the Weibull and other competitive distributions, the NEExp-Weibull distribution has also some certain limitations, for example
● The proposed NEExp-Weibull model is a continuous probability distribution, and it is employed to analyze the mortality rates of COVID-19 patients. Therefore, the NEExp-Weibull model could not be implemented to analyze other forms of the COVID-19 data that are discrete in nature, for example, (i) the number of deaths, (ii) the number of confirmed cases, or (iii) the number of recovered cases, etc.
● Due to the introduction of the additional parameter, the NEExp-Weibull distribution has a complicated form of its PDF. Therefore, the expressions for the estimators of its parameters are not in explicit forms. Therefore, computer software must be used to obtain the estimated values of the parameters.
● Since, the PDF of the NEExp family has a complicated form, therefore, more computational efforts are needed to derive the key mathematical properties.
In the future, we are motivated to obtain the discrete version of the proposed NEExp-Weibull distribution to counter the discrete data sets. In this work, we only used the maximum likelihood estimation method to estimate the parameters of the NEExp-Weibull distribution. In the future, we are intended to estimate the parameters of the NEExp-Weibull distribution using other classical methods such as ordinary least square, weighted ordinary least square, maximum product spacing methods, etc. Neutrosophic statistics is a generalization of classical statistics and is implemented when the data sets are generated from a complex process. In the future, we are also motivated to study the neutrosophic extension of the NEExp-Weibull distribution.
[1] |
Akhsassi M, El Fathi A, Erraissi N, et al. (2018) Experimental investigation and modeling of the thermal behavior of a solar PV module. Sol Energy Mater Sol Cells 180: 271–279. doi: 10.1016/j.solmat.2017.06.052
![]() |
[2] |
Covill D, Blayden A, Coren D, et al. (2015) Parametric finite element analysis of steel bicycle frames: the influence of tube selection on frame stiffness. Procedia Eng 112: 34–39. doi: 10.1016/j.proeng.2015.07.172
![]() |
[3] | Ukoba K, Imoisili PE, Adgidzi D (2015) Finite element analysis of bamboo bicycle frame. J Adv Math Compu Sci 5: 583–594. |
[4] | Marchal PC, Ortega JG, García JG (2019) Production Planning, Modeling and Control of Food Industry Processes. Springer. |
[5] | Biemans H, Speelman LH, Ludwig F, et al. (2013) Future water resources for food production in five South Asian river basins and potential for adaptation-A modeling study. Sci Total Environ 468: S117–S131. |
[6] |
Younas R, Imran H, Shah SIH, et al. (2019) Computational modeling of polycrystalline silicon on oxide passivating contact for silicon solar cells. IEEE Trans Electron Devices 66: 1819–1826. doi: 10.1109/TED.2019.2900691
![]() |
[7] |
Fantacci S, De Angelis F (2019) Ab initio modeling of solar cell dye sensitizers: The hunt for red photons continues. Eur J Inorg Chem 2019: 743–750. doi: 10.1002/ejic.201801258
![]() |
[8] | Verma A, Asthana P (2020) Modeling of thin film solar photovoltaic based on ZnO/SnS Oxide-absorber substrate configuration. Int J Eng Res Appl 4: 12–18. |
[9] |
Tyagi A, Ghosh K, Kottantharayil A, et al. (2019) An analytical model for the electrical characteristics of passivated Carrier-Selective Contact (CSC) solar cell. IEEE Trans Electron Devices 66: 1377–1385. doi: 10.1109/TED.2019.2893998
![]() |
[10] |
D'Alpaos C, Moretto M (2019) Do smart grid innovations affect real estate market values? AIMS Energy 7: 141–150. doi: 10.3934/energy.2019.2.141
![]() |
[11] |
Asumadu-Sarkodie S, Owusu PA (2016) A review of Ghana's solar energy potential. Aims Energy 4: 675–696. doi: 10.3934/energy.2016.5.675
![]() |
[12] |
Ludin GA, Amin MA, Aminzay A, et al. (2016) Theoretical potential and utilization of renewable energy in Afghanistan. AIMS Energy 5: 1–19. doi: 10.3934/energy.2017.1.1
![]() |
[13] |
Ukoba KO, Eloka-Eboka AC, Inambao FL (2018) Review of nanostructured NiO thin film deposition using the spray pyrolysis technique. Renewable Sustainable Energy Rev 82: 2900–2915. doi: 10.1016/j.rser.2017.10.041
![]() |
[14] |
Tao J, Hu X, Guo Y, et al. (2019) Solution-processed SnO2 interfacial layer for highly efficient Sb2Se3 thin film solar cells. Nano Energy 60: 802–809. doi: 10.1016/j.nanoen.2019.04.019
![]() |
[15] | Ukoba KO, Inambao FL, Eloka-Eboka AC (2018) Fabrication of affordable and sustainable solar cells using NiO/TiO2 PN heterojunction. Int J Photoenergy 2018. |
[16] |
Ge M, Cao C, Huang J, et al. (2016) A review of one-dimensional TiO2 nanostructured materials for environmental and energy applications. J Mater Chem A 4: 6772–6801. doi: 10.1039/C5TA09323F
![]() |
[17] |
Minami T, Nishi Y, Miyata T (2015) Heterojunction solar cell with 6% efficiency based on an n-type aluminum–gallium–oxide thin film and p-type sodium-doped Cu2O sheet. Appl Phys Express 8: 022301. doi: 10.7567/APEX.8.022301
![]() |
[18] |
Wick R, Tilley SD (2015) Photovoltaic and photoelectrochemical solar energy conversion with Cu2O. J Phys Chem C 119: 26243–26257. doi: 10.1021/acs.jpcc.5b08397
![]() |
[19] |
Ukoba OK, Inambao FL, Eloka-Eboka AC (2017) Influence of annealing on properties of spray deposited nickel oxide films for solar cells. Energy Procedia 142: 244–252. doi: 10.1016/j.egypro.2017.12.039
![]() |
[20] |
Liu H, Avrutin V, Izyumskaya N, et al. (2010) Transparent conducting oxides for electrode applications in light emitting and absorbing devices. Superlattices Microstruct 48: 458–484. doi: 10.1016/j.spmi.2010.08.011
![]() |
[21] |
Ahmed S, Reuter KB, Gunawan O, et al. (2012) A high efficiency electrodeposited Cu2ZnSnS4solar cell. Adv Energy Mater 2: 253–259. doi: 10.1002/aenm.201100526
![]() |
[22] |
Maeda K, Tanaka K, Fukui Y, et al. (2011) Influence of H2S concentration on the properties of Cu2ZnSnS4 thin films and solar cells prepared by sol–gel sulfurization. Solar Energy Mater Solar Cells 95: 2855–2860. doi: 10.1016/j.solmat.2011.05.050
![]() |
[23] |
Katagiri H, Jimbo K, Yamada S, et al. (2008) Enhanced conversion efficiencies of Cu2ZnSnS4-based thin film solar cells by using preferential etching technique. Appl Phys Express 1: 041201. doi: 10.1143/APEX.1.041201
![]() |
[24] |
Shabu R, Raj AME, Sanjeeviraja C, et al. (2015) Assessment of CuO thin films for its suitablity as window absorbing layer in solar cell fabrications. Mater Res Bull 68: 1–8. doi: 10.1016/j.materresbull.2015.03.016
![]() |
[25] |
Ooi PK, Ng SS, Abdullah MJ, et al. (2013) Effects of oxygen percentage on the growth of copper oxide thin films by reactive radio frequency sputtering. Mater Chem Phys 140: 243–248. doi: 10.1016/j.matchemphys.2013.03.028
![]() |
[26] |
Valladares LDLS, Salinas DH, Dominguez AB, et al. (2012) Crystallization and electrical resistivity of Cu2O and CuO obtained by thermal oxidation of Cu thin films on SiO2/Si substrates. Thin Solid Films 520: 6368–6374. doi: 10.1016/j.tsf.2012.06.043
![]() |
[27] |
Liu M, Lin MC, Wang C (2011) Enhancements of thermal conductivities with Cu, CuO, and carbon nanotube nanofluids and application of MWNT/water nanofluid on a water chiller system. Nanoscale Res Lett 6: 297. doi: 10.1186/1556-276X-6-297
![]() |
[28] | Cutter A (2011) The Electricians Green Handbook, Delmar, New York, 288. |
[29] | Singla V, Garg VK (2013) Modeling of solar photovoltaic module & effect of insolation variation using Matlab/Simulink. Int J Adv Eng Tech 4: 5–9. |
[30] | Gray JL (1991) Adept: a general purpose numerical device simulator for modeling solar cells in one-, two-, and three-dimensions. The Conference Record of the Twenty-Second IEEE Photovoltaic Specialists Conference-1991 436–438. |
[31] | Lee YJ, Gray JL (1993) Numerical modeling of polycrystalline CdTe and CIS solar cells. In Conference Record of the Twenty Third IEEE Photovoltaic Specialists Conference-1993 586–591. |
[32] | Gloeckler M, Fahrenbruch AL, Sites JR (2003) Numerical modeling of CIGS and CdTe solar cells: setting the baseline. In 3rd World Conference on Photovoltaic Energy Conversion, 2003. Proceedings of 1: 491–494. |
[33] | Muthuswamy G (2005) Numerical modeling of CdS/CdTe thin film solar cell using MEDICI. Graduate theses, University of South Florida. |
[34] | Ganvir R (2016) Modelling of the nanowire CdS-CdTe device design for enhanced quantum efficiency in Window-absorber type solar cells. Master's thesis, University of Kentucky. |
[35] | Burgelman M, Nollet P, Degrave S (2000) Modelling polycrystalline semiconductor solar cells. Thin Solid Films 361: 527–532. |
[36] | Ukoba KO, Inambao FL (2018) Modeling of fabricated NiO/TiO2 PN heterojunction solar cells. Int J Appl Eng Res 13: 9701–9705. |
[37] | Schwartz R, Gray J, Lundstrom M (1985) Current status of one-and two-dimensional numerical models: Successes and limitations. |
[38] |
Hossain MI, Alharbi FH, Tabet N (2015) Copper oxide as inorganic hole transport material for lead halide perovskite based solar cells. Solar Energy 120: 370–380. doi: 10.1016/j.solener.2015.07.040
![]() |
[39] |
Li BS, Akimoto K, Shen A (2009) Growth of Cu2O thin films with high hole mobility by introducing a low-temperature buffer layer. J Cryst Growth 311: 1102–1105. doi: 10.1016/j.jcrysgro.2008.11.038
![]() |
[40] |
Tripathi AK, Singh MK, Mathpal MC, et al. (2013) Study of structural transformation in TiO2 nanoparticles and its optical properties. J Alloys Compd 549: 114–120. doi: 10.1016/j.jallcom.2012.09.012
![]() |
[41] |
Kırbıyık Ç, Kara DA, Kara K, et al. (2019) Improving the performance of inverted polymer solar cells through modification of compact TiO2 layer by different boronic acid functionalized self-assembled monolayers. Appl Surf Sci 479: 177–184. doi: 10.1016/j.apsusc.2019.01.268
![]() |
[42] |
Sawicka-Chudy P, Sibiński M, Wisz G, et al. (2018) Numerical analysis and optimization of Cu2O/TiO2, CuO/TiO2, heterojunction solar cells using SCAPS. J Phys: Conference Series 1033: 012002. doi: 10.1088/1742-6596/1033/1/012002
![]() |
[43] |
Ichimura M, Kato Y (2013) Fabrication of TiO2/Cu2O heterojunction solar cells by electrophoretic deposition and electrodeposition. Mater Sci in Semicond Process 16: 1538–1541. doi: 10.1016/j.mssp.2013.05.004
![]() |
[44] | Tao J, Liu J, Chen L, et al. (2016) 7.1% efficient co-electroplated Cu2ZnSnS4 thin film solar cells with sputtered CdS buffer layers. Green Chem 18: 550–557. |
[45] | Zhao W, Zhou W, Miao X (2012) Numerical simulation of CZTS thin film solar cell. 2012 7th IEEE International Conference on Nano/Micro Engineered and Molecular Systems (NEMS) 502–505. |
[46] |
Dussan A, Bohórquez A, Quiroz HP (2017) Effect of annealing process in TiO2 thin films: Structural, morphological, and optical properties. Appl Surf Sci 424: 111–114. doi: 10.1016/j.apsusc.2017.01.269
![]() |
[47] | Sahrul Saehana, Muslimin (2013) Performance Improvement of Cu2O/TiO2 Heterojunction Solar Cell by Employing Polymer Electrolytes. Int J Eng Techno 13: 83–86 |
[48] |
Mahato S, Kar AK (2017) The effect of annealing on structural, optical and photosensitive properties of electrodeposited cadmium selenide thin films. J Sci: Adv Mater Devices 2: 165–171. doi: 10.1016/j.jsamd.2017.04.001
![]() |
[49] |
Sundqvist A, Sandberg OJ, Nyman M, et al. (2016) Origin of the S-Shaped JV curve and the Light-Soaking issue in inverted organic solar cells. Adv Energy Mater 6: 1502265. doi: 10.1002/aenm.201502265
![]() |
[50] |
Tan K, Lin P, Wang G, et al. (2016) Controllable design of solid-state perovskite solar cells by SCAPS device simulation. Solid-State Electron 126: 75–80. doi: 10.1016/j.sse.2016.09.012
![]() |
[51] |
Iqbal K, Ikram M, Afzal M, et al. (2018) Efficient, low-dimensional nanocomposite bilayer CuO/ZnO solar cell at various annealing temperatures. Mater Renewable Sustainable Energy 7: 4. doi: 10.1007/s40243-018-0111-2
![]() |
[52] |
Masudy-Panah S, Dalapati GK, Radhakrishnan K, et al. (2015) p-CuO/n-Si heterojunction solar cells with high open circuit voltage and photocurrent through interfacial engineering. Prog Photovoltaic: Res Appl 23: 637–645. doi: 10.1002/pip.2483
![]() |
1. | A. O. Egonmwan, D. Okuonghae, Analysis of a mathematical model for tuberculosis with diagnosis, 2019, 59, 1598-5865, 129, 10.1007/s12190-018-1172-1 | |
2. | Fumin Zhang, Zhipeng Qiu, Aijun Huang, Xin Zhao, Optimal control and cost-effectiveness analysis of a Huanglongbing model with comprehensive interventions, 2021, 90, 0307904X, 719, 10.1016/j.apm.2020.09.033 | |
3. | CHANDRA N. PODDER, ABBA B. GUMEL, CHRIS S. BOWMAN, ROBERT G. MCLEOD, MATHEMATICAL STUDY OF THE IMPACT OF QUARANTINE, ISOLATION AND VACCINATION IN CURTAILING AN EPIDEMIC, 2007, 15, 0218-3390, 185, 10.1142/S0218339007002180 | |
4. | Folashade B. Agusto, Optimal control and cost-effectiveness analysis of a three age-structured transmission dynamics of chikungunya virus, 2017, 22, 1553-524X, 687, 10.3934/dcdsb.2017034 | |
5. | Mohammad A. Safi, Mudassar Imran, Abba B. Gumel, Threshold dynamics of a non-autonomous SEIRS model with quarantine and isolation, 2012, 131, 1431-7613, 19, 10.1007/s12064-011-0148-6 | |
6. | Mohammad A. Safi, Global Stability Analysis of Two-Stage Quarantine-Isolation Model with Holling Type II Incidence Function, 2019, 7, 2227-7390, 350, 10.3390/math7040350 | |
7. | Jianyong Wu, Radhika Dhingra, Manoj Gambhir, Justin V. Remais, Sensitivity analysis of infectious disease models: methods, advances and their application, 2013, 10, 1742-5689, 20121018, 10.1098/rsif.2012.1018 | |
8. | N. Hussaini, J. M-S Lubuma, K. Barley, A.B. Gumel, Mathematical analysis of a model for AVL–HIV co-endemicity, 2016, 271, 00255564, 80, 10.1016/j.mbs.2015.10.008 | |
9. | Govind Prasad Sahu, Joydip Dhar, Dynamics of an SEQIHRS epidemic model with media coverage, quarantine and isolation in a community with pre-existing immunity, 2015, 421, 0022247X, 1651, 10.1016/j.jmaa.2014.08.019 | |
10. | Mohammad A. Safi, Dessalegn Y. Melesse, Abba B. Gumel, Dynamics Analysis of a Multi-strain Cholera Model with an Imperfect Vaccine, 2013, 75, 0092-8240, 1104, 10.1007/s11538-013-9845-2 | |
11. | Abba B. Gumel, Enahoro A. Iboi, Calistus N. Ngonghala, Elamin H. Elbasha, A primer on using mathematics to understand COVID-19 dynamics: Modeling, analysis and simulations, 2021, 6, 24680427, 148, 10.1016/j.idm.2020.11.005 | |
12. | Folashade B. Agusto, Shamise Easley, Kenneth Freeman, Madison Thomas, Mathematical Model of Three Age-Structured Transmission Dynamics of Chikungunya Virus, 2016, 2016, 1748-670X, 1, 10.1155/2016/4320514 | |
13. | Mohammad A. Safi, Abba B. Gumel, Qualitative study of a quarantine/isolation model with multiple disease stages, 2011, 218, 00963003, 1941, 10.1016/j.amc.2011.07.007 | |
14. | F. B. Agusto, J. Cook, P. D. Shelton, M. G. Wickers, Mathematical Model of MDR-TB and XDR-TB with Isolation and Lost to Follow-Up, 2015, 2015, 1085-3375, 1, 10.1155/2015/828461 | |
15. | C. N. Podder, O. Sharomi, A. B. Gumel, E. Strawbridge, Mathematical Analysis of a Model for Assessing the Impact of Antiretroviral Therapy, Voluntary Testing and Condom Use in Curtailing the Spread of HIV, 2011, 19, 0971-3514, 283, 10.1007/s12591-011-0090-6 | |
16. | Folashade B Agusto, Miranda I Teboh-Ewungkem, Abba B Gumel, Mathematical assessment of the effect of traditional beliefs and customs on the transmission dynamics of the 2014 Ebola outbreaks, 2015, 13, 1741-7015, 10.1186/s12916-015-0318-3 | |
17. | F.B. Agusto, M.C.A. Leite, Optimal control and cost-effective analysis of the 2017 meningitis outbreak in Nigeria, 2019, 4, 24680427, 161, 10.1016/j.idm.2019.05.003 | |
18. | Farinaz Forouzannia, Abba B. Gumel, Mathematical analysis of an age-structured model for malaria transmission dynamics, 2014, 247, 00255564, 80, 10.1016/j.mbs.2013.10.011 | |
19. | Adnan Khan, Sultan Sial, Mudassar Imran, Transmission Dynamics of Hepatitis C with Control Strategies, 2014, 2014, 2314-5080, 1, 10.1155/2014/654050 | |
20. | Mudassar Imran, Muhammad Hassan, Muhammad Dur-E-Ahmad, Adnan Khan, A comparison of a deterministic and stochastic model for Hepatitis C with an isolation stage, 2013, 7, 1751-3758, 276, 10.1080/17513758.2013.859856 | |
21. | Aliya A. Alsaleh, Abba B. Gumel, Analysis of Risk-Structured Vaccination Model for the Dynamics of Oncogenic and Warts-Causing HPV Types, 2014, 76, 0092-8240, 1670, 10.1007/s11538-014-9972-4 | |
22. | A. Nwankwo, D. Okuonghae, A Mathematical Model for the Population Dynamics of Malaria with a Temperature Dependent Control, 2019, 0971-3514, 10.1007/s12591-019-00466-y | |
23. | Abba B. Gumel, Ahmed Abdelrazec, Kamaldeen Okuneye, Mathematical analysis of a weather-driven model for the population ecology of mosquitoes, 2017, 15, 1551-0018, 57, 10.3934/mbe.2018003 | |
24. | S. I. Kabanikhin, O. I. Krivorotko, Mathematical Modeling of the Wuhan COVID-2019 Epidemic and Inverse Problems, 2020, 60, 0965-5425, 1889, 10.1134/S0965542520110068 | |
25. | A. S. Hassan, S. M. Garba, A. B. Gumel, J. M.-S. Lubuma, Dynamics ofMycobacteriumandbovine tuberculosisin a Human-Buffalo Population, 2014, 2014, 1748-670X, 1, 10.1155/2014/912306 | |
26. | Mohammad A. Safi, Abba B. Gumel, Dynamics analysis of a quarantine model in two patches, 2015, 38, 01704214, 349, 10.1002/mma.3072 | |
27. | ALIYA A. ALSALEH, ABBA B. GUMEL, DYNAMICS ANALYSIS OF A VACCINATION MODEL FOR HPV TRANSMISSION, 2014, 22, 0218-3390, 555, 10.1142/S0218339014500211 | |
28. | Nafiu Hussaini, Kamaldeen Okuneye, Abba B. Gumel, Mathematical analysis of a model for zoonotic visceral leishmaniasis, 2017, 2, 24680427, 455, 10.1016/j.idm.2017.12.002 | |
29. | F.B. Agusto, M.A. Khan, Optimal control strategies for dengue transmission in pakistan, 2018, 305, 00255564, 102, 10.1016/j.mbs.2018.09.007 | |
30. | Mohammad A. Safi, Abba B. Gumel, The effect of incidence functions on the dynamics of a quarantine/isolation model with time delay, 2011, 12, 14681218, 215, 10.1016/j.nonrwa.2010.06.009 | |
31. | F. Nazari, A.B. Gumel, E.H. Elbasha, Differential characteristics of primary infection and re-infection can cause backward bifurcation in HCV transmission dynamics, 2015, 263, 00255564, 51, 10.1016/j.mbs.2015.02.002 | |
32. | F.B. Agusto, S. Bewick, W.F. Fagan, Mathematical model of Zika virus with vertical transmission, 2017, 2, 24680427, 244, 10.1016/j.idm.2017.05.003 | |
33. | Pei-Yu Liu, Sha He, Li-Bin Rong, San-Yi Tang, The effect of control measures on COVID-19 transmission in Italy: Comparison with Guangdong province in China, 2020, 9, 2049-9957, 10.1186/s40249-020-00730-2 | |
34. | Zuiyuan Guo, Dan Xiao, Dongli Li, Xiuhong Wang, Yayu Wang, Tiecheng Yan, Zhiqi Wang, Zhen Jin, Predicting and Evaluating the Epidemic Trend of Ebola Virus Disease in the 2014-2015 Outbreak and the Effects of Intervention Measures, 2016, 11, 1932-6203, e0152438, 10.1371/journal.pone.0152438 | |
35. | Lindsay Simpson, Abba B. Gumel, Mathematical assessment of the role of pre-exposure prophylaxis on HIV transmission dynamics, 2017, 293, 00963003, 168, 10.1016/j.amc.2016.07.043 | |
36. | KAMALDEEN O. OKUNEYE, JORGE X. VELASCO-HERNANDEZ, ABBA B. GUMEL, THE “UNHOLY” CHIKUNGUNYA–DENGUE–ZIKA TRINITY: A THEORETICAL ANALYSIS, 2017, 25, 0218-3390, 545, 10.1142/S0218339017400046 | |
37. | A. O. Egonmwan, D. Okuonghae, Mathematical analysis of a tuberculosis model with imperfect vaccine, 2019, 12, 1793-5245, 1950073, 10.1142/S1793524519500736 | |
38. | Kamaldeen Okuneye, Steffen E. Eikenberry, Abba B. Gumel, Weather-driven malaria transmission model with gonotrophic and sporogonic cycles, 2019, 13, 1751-3758, 288, 10.1080/17513758.2019.1570363 | |
39. | Mohammad A. Safi, Abba B. Gumel, Dynamics of a model with quarantine-adjusted incidence and quarantine of susceptible individuals, 2013, 399, 0022247X, 565, 10.1016/j.jmaa.2012.10.015 | |
40. | Jan M. Baetens, Bernard De Baets, 2016, Chapter 9, 978-3-319-44364-5, 91, 10.1007/978-3-319-44365-2_9 | |
41. | I. Santamaría-Holek, V. Castaño, Possible fates of the spread of SARS-CoV-2 in the Mexican context, 2020, 7, 2054-5703, 200886, 10.1098/rsos.200886 | |
42. | Nasser Al-Salti, Ibrahim M. Elmojtaba, Jaqueline Mesquita, Dayse Pastore, Maryam Al-Yahyai, 2021, Chapter 11, 978-981-16-2449-0, 219, 10.1007/978-981-16-2450-6_11 | |
43. | Fumin Zhang, Zhipeng Qiu, Aijun Huang, Yan Cheng, Guihong Fan, Global dynamics and bifurcation analysis of an insect-borne plant disease model with two transmission routes, 2022, 15, 1793-5245, 10.1142/S1793524522500553 | |
44. | Baoquan Zhou, Bingtao Han, Daqing Jiang, Tasawar Hayat, Ahmed Alsaedi, Ergodic stationary distribution and extinction of a hybrid stochastic SEQIHR epidemic model with media coverage, quarantine strategies and pre-existing immunity under discrete Markov switching, 2021, 410, 00963003, 126388, 10.1016/j.amc.2021.126388 | |
45. | Sandra Cole, Stephen Wirkus, Modeling the Dynamics of Heroin and Illicit Opioid Use Disorder, Treatment, and Recovery, 2022, 84, 0092-8240, 10.1007/s11538-022-01002-w | |
46. | Theophilus Kwofie, Matthias Dogbatsey, Stephen E. Moore, Curtailing crime dynamics: A mathematical approach, 2023, 8, 2297-4687, 10.3389/fams.2022.1086745 | |
47. | Calistus N. Ngonghala, Abba B. Gumel, 2023, 9780323950640, 221, 10.1016/B978-0-323-95064-0.00013-0 | |
48. | Buddhi Pantha, Folashade B. Agusto, Ibrahim M. Elmojtaba, Optimal control applied to a visceral leishmaniasis model, 2020, 2020, 1072-6691, 80, 10.58997/ejde.2020.80 | |
49. | Queen Tollett, Salman Safdar, Abba B. Gumel, Dynamics of a two-group model for assessing the impacts of pre-exposure prophylaxis, testing and risk behaviour change on the spread and control of HIV/AIDS in an MSM population, 2023, 24680427, 10.1016/j.idm.2023.11.004 | |
50. | Shuaibu Ahijo Abdullahi, Abdulrazaq Garba Habib, Nafiu Hussaini, Mathematical analysis for the dynamics of snakebite envenoming, 2024, 35, 1012-9405, 10.1007/s13370-023-01156-3 | |
51. | Salman Safdar, Abba B. Gumel, 2023, Chapter 10, 978-3-031-40804-5, 243, 10.1007/978-3-031-40805-2_10 | |
52. | Binod Pant, Abba B. Gumel, Mathematical assessment of the roles of age heterogeneity and vaccination on the dynamics and control of SARS-CoV-2, 2024, 24680427, 10.1016/j.idm.2024.04.007 | |
53. | Adel Alatawi, Abba B. Gumel, Mathematical assessment of control strategies against the spread of MERS-CoV in humans and camels in Saudi Arabia, 2024, 21, 1551-0018, 6425, 10.3934/mbe.2024281 | |
54. | Alice Oveson, Michelle Girvan, Abba B. Gumel, Modeling the impact of hospitalization-induced behavioral changes on the spread of COVID-19 in New York City, 2025, 24680427, 10.1016/j.idm.2025.05.001 |
n | Parameters | MLEs | MSEs | Biases |
φ1 | 0.7439555 | 0.01816230 | 0.043955486 | |
20 | δ | 2.5224710 | 4.62452592 | 1.122470958 |
φ2 | 0.9819897 | 0.08933255 | 0.081989688 | |
φ1 | 0.7261523 | 0.00675241 | 0.026152290 | |
40 | δ | 2.2436960 | 3.50148162 | 0.843695947 |
φ2 | 0.9475541 | 0.04503070 | 0.047554140 | |
φ1 | 0.7174831 | 0.00469112 | 0.017483127 | |
60 | δ | 2.1504600 | 3.14461417 | 0.750459996 |
φ2 | 0.9382455 | 0.03002095 | 0.038245459 | |
φ1 | 0.7139450 | 0.00303585 | 0.013945008 | |
80 | δ | 2.0166510 | 2.71268772 | 0.616651319 |
φ2 | 0.9172897 | 0.02141037 | 0.017289700 | |
φ1 | 0.7118858 | 0.00250170 | 0.011885794 | |
100 | δ | 1.9587070 | 2.39162374 | 0.558707085 |
φ2 | 0.9215668 | 0.01819720 | 0.021566823 | |
φ1 | 0.7071069 | 0.00095725 | 0.007106915 | |
200 | δ | 1.6315320 | 1.20339825 | 0.231531527 |
φ2 | 0.8963361 | 0.00907772 | -0.003663932 | |
φ1 | 0.7059804 | 0.00056999 | 0.005980353 | |
300 | δ | 1.4947460 | 0.59116842 | 0.094745813 |
φ2 | 0.8942843 | 0.00510254 | -0.005715678 | |
φ1 | 0.7046970 | 0.00042009 | 0.004696986 | |
400 | δ | 1.4758080 | 0.42345175 | 0.075807616 |
φ2 | 0.8949554 | 0.00295727 | -0.005044638 | |
φ1 | 0.7026197 | 0.00015114 | 0.002619658 | |
500 | δ | 1.4191470 | 0.17256813 | 0.019147385 |
φ2 | 0.8958860 | 0.00155967 | -0.004113986 | |
φ1 | 0.7021186 | 0.00011673 | 0.002118624 | |
600 | δ | 1.3973690 | 0.05930217 | -0.002630857 |
φ2 | 0.8964089 | 0.00084446 | -0.003591110 |
n | Parameters | MLEs | MSEs | Biases |
φ1 | 0.6538964 | 1.61446e-02 | 0.053896399 | |
20 | δ | 2.3444560 | 3.753281849 | 0.844456065 |
φ2 | 0.8422871 | 0.074129355 | 0.042287133 | |
φ1 | 0.6335936 | 6.57586e-03 | 0.033593572 | |
40 | δ | 2.0966990 | 2.835106550 | 0.596698837 |
φ2 | 0.8114326 | 0.027465620 | 0.011432631 | |
φ1 | 0.6207884 | 3.08374e-03 | 0.020788424 | |
60 | δ | 1.9743140 | 2.393837599 | 0.474313588 |
φ2 | 0.8107312 | 0.022889902 | 0.010731190 | |
φ1 | 0.6195547 | 2.83132e-03 | 0.019554745 | |
80 | δ | 1.8076620 | 1.762573786 | 0.307661602 |
φ2 | 0.7912179 | 0.016246953 | -0.008782086 | |
φ1 | 0.6135883 | 1.52055e-03 | 0.013588293 | |
100 | δ | 1.7689760 | 1.451201967 | 0.268976369 |
φ2 | 0.7923297 | 0.011392565 | -0.007670316 | |
φ1 | 0.6062087 | 4.83673e-04 | 0.006208661 | |
200 | δ | 1.5338360 | 0.437971185 | 0.033836372 |
φ2 | 0.7870588 | 0.003783507 | -0.012941210 | |
φ1 | 0.6050252 | 2.87229e-04 | 0.005025202 | |
300 | δ | 1.4799110 | 0.134430960 | -0.020089413 |
φ2 | 0.7911718 | 0.001925689 | -0.008828233 | |
φ1 | 0.6021233 | 1.08930e-04 | 0.002123257 | |
400 | δ | 1.5034740 | 0.104238258 | 0.003473527 |
φ2 | 0.7954403 | 0.000832362 | -0.004559674 | |
φ1 | 0.6014035 | 6.62443e-05 | 0.001403539 | |
500 | δ | 1.4982590 | 0.048978064 | -0.001741474 |
φ2 | 0.7974116 | 0.000411811 | -0.002588439 | |
φ1 | 0.6009386 | 3.77904e-05 | 0.000938590 | |
600 | δ | 1.4899270 | 0.005002637 | -0.010072511 |
φ2 | 0.7976296 | 0.000242969 | -0.002370384 |
Model | ^φ1 | ^φ2 | ˆδ | ˆα | ˆσ | ˆθ |
NEExp-Weibull | 2.53401 (0.31876) | 0.01723 (0.01562) | 0.26201 (0.24135) | - | - | - |
Weibull | 1.92738 (0.14019) | 0.09976 (0.02220) | - | - | - | - |
L-Weibull | 1.57117 (0.01001) | 1.20372 (0.00879) | - | 0.16022 (0.01580) | 0.45036 (0.01773) | - |
NEP-Weibull | 1.71906 (0.03634) | 0.95340 (0.03634) | - | - | - | 0.15201 (0.01503) |
NM-Weibull | 1.89237 (0.15734) | 0.11004 (0.03088) | - | - | 12.06058 (20.5532) | - |
Model | CM | AD | KS | p-value |
NEExp-Weibull | 0.05834 | 0.33674 | 0.06266 | 0.79940 |
Weibull | 0.10264 | 0.66004 | 0.07147 | 0.65100 |
L-Weibull | 0.06002 | 0.36130 | 0.07091 | 0.66060 |
NEP-Weibull | 0.07017 | 0.43993 | 0.07862 | 0.52880 |
NM-Weibull | 0.10723 | 0.68969 | 0.07024 | 0.67240 |
Model | ^φ1 | ^φ2 | ˆδ | ˆα | ˆσ | ˆθ |
NEExp-Weibull | 2.20197 (0.48765) | 0.03704 (0.04876) | 0.75896 (0.10983) | - | - | - |
Weibull | 1.92738 (0.14019) | 0.09976 (0.02220) | - | - | - | - |
L-Weibull | 1.42252 (0.51193) | 0.12239 (0.05844) | - | 2.85548 (0.97654) | 0.89686 (2.15028) | - |
NEP-Weibull | 1.77603 (0.07305) | 1.03756 (0.07304) | - | - | - | 0.11297 (0.02890) |
NM-Weibull | 2.00489 (0.28946) | 0.06377 (0.04170) | - | - | -2.41345 (3.47713) |
Model | CM | AD | KS | p-value |
NEExp-Weibull | 0.03088 | 0.20437 | 0.08557 | 0.96710 |
Weibull | 0.04794 | 0.29434 | 0.10236 | 0.88030 |
L-Weibull | 0.05165 | 0.31630 | 0.10144 | 0.88660 |
NEP-Weibull | 0.03423 | 0.22143 | 0.10418 | 0.86740 |
NM-Weibull | 0.03926 | 0.24960 | 0.08981 | 0.95100 |
Criteria | SVR | RF | NNAR |
RMSE | 0.073 | 0.066 | 0.198 |
MAE | 0.043 | 0.039 | 0.149 |
Criteria | SVR | RF | NNAR |
RMSE | 0.160 | 0.191 | 0.444 |
MAE | 0.118 | 0.139 | 0.398 |
n | Parameters | MLEs | MSEs | Biases |
φ1 | 0.7439555 | 0.01816230 | 0.043955486 | |
20 | δ | 2.5224710 | 4.62452592 | 1.122470958 |
φ2 | 0.9819897 | 0.08933255 | 0.081989688 | |
φ1 | 0.7261523 | 0.00675241 | 0.026152290 | |
40 | δ | 2.2436960 | 3.50148162 | 0.843695947 |
φ2 | 0.9475541 | 0.04503070 | 0.047554140 | |
φ1 | 0.7174831 | 0.00469112 | 0.017483127 | |
60 | δ | 2.1504600 | 3.14461417 | 0.750459996 |
φ2 | 0.9382455 | 0.03002095 | 0.038245459 | |
φ1 | 0.7139450 | 0.00303585 | 0.013945008 | |
80 | δ | 2.0166510 | 2.71268772 | 0.616651319 |
φ2 | 0.9172897 | 0.02141037 | 0.017289700 | |
φ1 | 0.7118858 | 0.00250170 | 0.011885794 | |
100 | δ | 1.9587070 | 2.39162374 | 0.558707085 |
φ2 | 0.9215668 | 0.01819720 | 0.021566823 | |
φ1 | 0.7071069 | 0.00095725 | 0.007106915 | |
200 | δ | 1.6315320 | 1.20339825 | 0.231531527 |
φ2 | 0.8963361 | 0.00907772 | -0.003663932 | |
φ1 | 0.7059804 | 0.00056999 | 0.005980353 | |
300 | δ | 1.4947460 | 0.59116842 | 0.094745813 |
φ2 | 0.8942843 | 0.00510254 | -0.005715678 | |
φ1 | 0.7046970 | 0.00042009 | 0.004696986 | |
400 | δ | 1.4758080 | 0.42345175 | 0.075807616 |
φ2 | 0.8949554 | 0.00295727 | -0.005044638 | |
φ1 | 0.7026197 | 0.00015114 | 0.002619658 | |
500 | δ | 1.4191470 | 0.17256813 | 0.019147385 |
φ2 | 0.8958860 | 0.00155967 | -0.004113986 | |
φ1 | 0.7021186 | 0.00011673 | 0.002118624 | |
600 | δ | 1.3973690 | 0.05930217 | -0.002630857 |
φ2 | 0.8964089 | 0.00084446 | -0.003591110 |
n | Parameters | MLEs | MSEs | Biases |
φ1 | 0.6538964 | 1.61446e-02 | 0.053896399 | |
20 | δ | 2.3444560 | 3.753281849 | 0.844456065 |
φ2 | 0.8422871 | 0.074129355 | 0.042287133 | |
φ1 | 0.6335936 | 6.57586e-03 | 0.033593572 | |
40 | δ | 2.0966990 | 2.835106550 | 0.596698837 |
φ2 | 0.8114326 | 0.027465620 | 0.011432631 | |
φ1 | 0.6207884 | 3.08374e-03 | 0.020788424 | |
60 | δ | 1.9743140 | 2.393837599 | 0.474313588 |
φ2 | 0.8107312 | 0.022889902 | 0.010731190 | |
φ1 | 0.6195547 | 2.83132e-03 | 0.019554745 | |
80 | δ | 1.8076620 | 1.762573786 | 0.307661602 |
φ2 | 0.7912179 | 0.016246953 | -0.008782086 | |
φ1 | 0.6135883 | 1.52055e-03 | 0.013588293 | |
100 | δ | 1.7689760 | 1.451201967 | 0.268976369 |
φ2 | 0.7923297 | 0.011392565 | -0.007670316 | |
φ1 | 0.6062087 | 4.83673e-04 | 0.006208661 | |
200 | δ | 1.5338360 | 0.437971185 | 0.033836372 |
φ2 | 0.7870588 | 0.003783507 | -0.012941210 | |
φ1 | 0.6050252 | 2.87229e-04 | 0.005025202 | |
300 | δ | 1.4799110 | 0.134430960 | -0.020089413 |
φ2 | 0.7911718 | 0.001925689 | -0.008828233 | |
φ1 | 0.6021233 | 1.08930e-04 | 0.002123257 | |
400 | δ | 1.5034740 | 0.104238258 | 0.003473527 |
φ2 | 0.7954403 | 0.000832362 | -0.004559674 | |
φ1 | 0.6014035 | 6.62443e-05 | 0.001403539 | |
500 | δ | 1.4982590 | 0.048978064 | -0.001741474 |
φ2 | 0.7974116 | 0.000411811 | -0.002588439 | |
φ1 | 0.6009386 | 3.77904e-05 | 0.000938590 | |
600 | δ | 1.4899270 | 0.005002637 | -0.010072511 |
φ2 | 0.7976296 | 0.000242969 | -0.002370384 |
Model | ^φ1 | ^φ2 | ˆδ | ˆα | ˆσ | ˆθ |
NEExp-Weibull | 2.53401 (0.31876) | 0.01723 (0.01562) | 0.26201 (0.24135) | - | - | - |
Weibull | 1.92738 (0.14019) | 0.09976 (0.02220) | - | - | - | - |
L-Weibull | 1.57117 (0.01001) | 1.20372 (0.00879) | - | 0.16022 (0.01580) | 0.45036 (0.01773) | - |
NEP-Weibull | 1.71906 (0.03634) | 0.95340 (0.03634) | - | - | - | 0.15201 (0.01503) |
NM-Weibull | 1.89237 (0.15734) | 0.11004 (0.03088) | - | - | 12.06058 (20.5532) | - |
Model | CM | AD | KS | p-value |
NEExp-Weibull | 0.05834 | 0.33674 | 0.06266 | 0.79940 |
Weibull | 0.10264 | 0.66004 | 0.07147 | 0.65100 |
L-Weibull | 0.06002 | 0.36130 | 0.07091 | 0.66060 |
NEP-Weibull | 0.07017 | 0.43993 | 0.07862 | 0.52880 |
NM-Weibull | 0.10723 | 0.68969 | 0.07024 | 0.67240 |
Model | ^φ1 | ^φ2 | ˆδ | ˆα | ˆσ | ˆθ |
NEExp-Weibull | 2.20197 (0.48765) | 0.03704 (0.04876) | 0.75896 (0.10983) | - | - | - |
Weibull | 1.92738 (0.14019) | 0.09976 (0.02220) | - | - | - | - |
L-Weibull | 1.42252 (0.51193) | 0.12239 (0.05844) | - | 2.85548 (0.97654) | 0.89686 (2.15028) | - |
NEP-Weibull | 1.77603 (0.07305) | 1.03756 (0.07304) | - | - | - | 0.11297 (0.02890) |
NM-Weibull | 2.00489 (0.28946) | 0.06377 (0.04170) | - | - | -2.41345 (3.47713) |
Model | CM | AD | KS | p-value |
NEExp-Weibull | 0.03088 | 0.20437 | 0.08557 | 0.96710 |
Weibull | 0.04794 | 0.29434 | 0.10236 | 0.88030 |
L-Weibull | 0.05165 | 0.31630 | 0.10144 | 0.88660 |
NEP-Weibull | 0.03423 | 0.22143 | 0.10418 | 0.86740 |
NM-Weibull | 0.03926 | 0.24960 | 0.08981 | 0.95100 |
Criteria | SVR | RF | NNAR |
RMSE | 0.073 | 0.066 | 0.198 |
MAE | 0.043 | 0.039 | 0.149 |
Criteria | SVR | RF | NNAR |
RMSE | 0.160 | 0.191 | 0.444 |
MAE | 0.118 | 0.139 | 0.398 |