Davies Model Research Articles

Study on the effect of semi-transparency on thermal insulation performance of silica aerogel composites

This paper centralizes its focus on elucidating the distinctive thermal insulation performance of silica aerogel composites, emphasizing their semitransparent attributes under diverse heating methodologies. Firstly, the theoretical prediction of conductive thermal conductivity is undertaken utilizing the spherical hollow cube model and Davies model. Subsequently, the radiative thermal conductivity is numerically derived employing the two-flux approximation model, integrating experimental measurements of optical radiation characteristic parameters. The prediction results under high-temperature are validated by the measured data via a Hot Disk instrument, utilizing the transient plane source method. Finally, the influence of semitransparent properties of the aerogel composites on thermal insulation performance is exhaustively investigated. This is conducted through a meticulous examination of temperature responses resulting from distinct heating modalities, namely contact heating, quartz lamp heating, and arc heated wind tunnel heating. The findings discernibly illustrate that these diverse heating mechanisms significantly impact the thermal insulation performance of aerogel composites endowed with semitransparent characteristics.

Evaluation of the Critical Times for the Crack Susceptibility Coefficient Calculation

The objective of the present study is to evaluate the hot tearing tendency based on the Clyne and Davies model by evaluating the critical times which can be obtained using a newly developed method. A method to determine the critical times required to calculate the crack susceptibility was presented based on the measurement results with Al–Si alloys, and the method to calculate the crack susceptibility coefficient was presented. In the newly developed method named “Signal intensity method,” signals were generated by tapping the edge of a waveguide which is immersed in molten and solidifying sample and the critical solid fractions were obtained from the signal intensity change. The conventional thermal analysis was also performed simultaneously and the corresponding critical points were identified. The method shown in the present study will enable the determination of the crack susceptibility coefficient with higher accuracy.

Optical and dispersion parameters of Ge-Zn-Se glassy films for VIS and FTIR Applications

Different chalcogenide films have been thermally evaporated onto cleaned glass substrates. The film transmission (T) and reflection (R) spectra have been measured over the wavelength spectral range (0.3–2.5 μm). The composition dependence of the optical band gap (E g ) has been illustrated and interpreted in the light of the Mott and Davies Model (MDM). The linear correlation between the changes in the optical band gap (ΔEg) and in the band tail parameter () confirmed the disorder’s decrease, which explains the observed increase in E g values with increasing Se concentrations. The dispersion and Sellmeier parameters have been determined and well discussed. A clear blueshift was observed throughout the observed decrease in values of λo and no and the observed shift of the absorption edge to the short wavelengths. The GZS films are transparent in the visible, near- and far-infrared, which makes these glasses suitable for VIS and infrared applications.

The Concept and the measurement of Strategic Leadership. The case of Greek Hotel Employees with the use of Exploratory Factor Analysis

Over the past two decades, scholars and practitioners are interested in the term of Strategic Leadership. Strategic Leadership is a leader’s ability to anticipate, envision, being flexible, and enable others to make strategic changes as required. There are several researches connecting strategic leadership with various variables of the Human Resource Management (HRM), such as: work stress, (Baysak and Yener, 2015), work commitment (Chiang & Wang, 2012) and role conflict (Palomino & Frezatti, 2016). Hence, it is very important to develop a reliable measurement tool which will explore the nature of strategic leadership and map its dimensions. Barbara Davies & Brent Davies (2004) have already developed a model which consists of both the organizational abilities and the individual characteristics of strategic leaders. The main purpose of the current paper is to study the application of Davies & Davies model (2004) in the hospitality industry. More thoroughly, the empirical data used on this paper has derived by a research consisted of 372 participants who work on Greek Hotel Companies. The method used to analyze the connections between the items of the strategic leadership was factor analysis. The findings support that Davies & Davies model (2004) can be used as a measurement tool in the hospitality industry. Thus, the current paper aims to contribute to the comprehension of the nature of strategic leadership on the hospitality and tourism industry, and trigger future empirical research in the field.

Effect of Ca/Al ratio on hot tearing susceptibility of Mg–Al–Ca alloy

The hot tearing susceptibility (HTS) of Mg–xAl–yCa (x + y = 8) alloys with different Ca/Al ratios (namely 0.06, 0.34, 0.63, 1.04, 1.75, and 2.82) is experimentally investigated using a “T-shaped” hot tearing measuring system. Additionally, the HTS of the alloys is determined using an optimized version of the Clyne–Davies model in conjunction with the solidification parameters of the alloys. The results of the optimized model, i.e., the fact that the HTS decreases with the increase in the Ca/Al ratio, are in good agreement with both the numerical simulations and experimental results. Furthermore, the hot tearing curves, thermal analysis curves, and microstructure of the alloys show that with the increase in the Ca/Al ratio, the intergranular bonding before the hot tearing initiation changes from relying on a liquid film only to involving both intergranular bridging and the liquid film, which enhances the intergranular bonding ability. In addition, the increase in the eutectic phase content, number of dendrite skeleton voids, and dendrite gap width result in an increase in the number of feeding channels and a decrease in the flow resistance of the residual liquid phase, thus increasing its filling efficiency against tears. Therefore, in alloys with high Ca/Al ratios, the large grain size results in a reduction in both the number and total length of grain boundaries, thereby reducing the number of locations where hot tears may initiate. Therefore, the HTS of alloys with a high Ca/Al ratio is significantly reduced.

Evaluation of the technical and economic aspects of solar photovoltaic plants under different climate conditions and feed-in tariff

In order to meet the energy demand and reduce the environmental pollution, it is necessary utilize photovoltaic (PV) module to produce electrical energy. There are many factors such as solar radiation, PV module material, wind energy, soiling factor, shading effect, geographical location, cell temperature is affecting the performance of the PV module. In this context, the performance of the multi crystalline based two PV plants has been examined. In this work, test is carried out in two solar plants installed at Kastoria, Greece (500kW, ground mounted) and Kocaeli, Turkey (110kW, roof mounted) and the results are compared with PVSYST software simulation results. From the results, it is found that the temperature losses for Kastoria and Kocaeli plants are obtained as 7.9% and 7.6% respectively. This leads to increase the performance ratio of 79% and 72.2% for Kastoria and Kocaeli plants respectively. Similarly, the maximum energy output is obtained for PVGIS database for all three models (Liu Jordan model, Hay Davies model and Perez model). The Internal Rate of Return for Kocaeli plant is 7.08% and for Kastoria plant is 6.71%. In addition, the Net Present Value for Kastoria and Kocaeli plant is obtained as 821900€ and 174072€ respectively.

Optical Characteristics of Thermally Evaporated Thin a-(Cu2ZnGe)50−xSe50+x Films

This article is allocated to study optical characteristics of a-(Cu2ZnGe)50−xSe50+x, CZGSe, films. The amorphous nature of films was affirmed via X-ray diffractograms. energy-dispersive X-ray spectroscopy confirmed the matching between selected compositional element percentages and those measured for all films. Many optical properties and parameters of CZGSe films were studied using UV–vis-INR spectroscopic transmission and reflection measurements. The envelope methods have been successfully applied on the measured transmission spectra according to Swanepoel technique, along with reflection spectra in accordance with Minkov method. Obtained results based on Swanepoel analysis are in excellent agreement with those inferred from Minkov method. A clear blueshift of the absorption edge was observed from 854 nm to 720 nm, in accordance with the increasing optical bandgap energy values from 1.456 eV to become 1.722 eV, as Se-content increases from 50 to 70 at wt%. The electronic transitions of (Cu2ZnGe)50−xSe50+x films arose from allowed indirect transitions. This observed energy gap increases was interpreted according to the Mott and Davies model. The absorption coefficient values have been estimated and discussed, it is found to be larger than 10−4 cm−1. All discussed parameters strongly depend on the Se-concentration. The bonding strength between the elements of samples strongly affects the optical properties.

EXAMINATION OF THE APPLICATION COURSE IN PRESCHOOL EDUCATIONAL INSTITUTIONS ACCORDING TO THE DAVIES MODEL

In this study, it is aimed to examine the application course in preschool educational institutions according to Davies Model, one of the program development models. In the study, one of the qualitative research methods, the document review method was used. According to the nature of the documents, the yare divided into four types: text-based, image-based, audiovisual-based and audio-visual-based. In this study, writing-based documents were used. In the selection of the sample from which the research data were collected, the Davies Model, one of the relevant program development models, was included in the study. In the analysis of the documents based on the writing of the application course in preschool educational institutions, the content analys is method was used. As a result of the analyzes conducted in this study, it was determined that the application course in preschool educational institutions studied is compatible with the work and task analysis of the Davies Model, one of the program development models, and alsow ith the 13 steps of the work and task analysis passed in this model.

Modeling combined global, beam, and diffuse clear-sky indices with Markov-chain mixture distribution models

This study uses the N-state Markov-chain mixture distribution model and the multiple-component N-state Markov-chain mixture distribution model to simulate global, beam, and diffuse horizontal clear-sky index. The models are data-driven such that when trained on single or multiple clear-sky index time-series, the models generate arbitrarily long synthetic clear-sky index time-series for the same components. The models were tested on solar irradiance datasets from two different climatic regions: Norrköping, Sweden, and Oahu, Hawaii, USA. The results show high probability distribution and temporal autocorrelation goodness-of-fit for all models and high cross correlation goodness-of-fit as well as accurate correlation between the component datasets for the multiple component model simulations. When combined with, e.g., the Hay and Davies model, the output from this model could, for example, be used to generate realistic time-series of incident solar irradiance on tilted planes.

Effects of Y and Addition of Refiners on Hot Tearing Susceptibility of MgZn-Based Alloy

On the basis of studying the effect of rare earth elements on hot tearing susceptibility (HTS) of Mg–Zn alloys, further exploring effective ways to reduce HTS of Mg–Zn–Y alloys are very important for the development and application of magnesium alloys. In this paper, the effects of 2 at% Y on HTS of MgZn1 alloy and several grain refiners on HTS of MgZn1Y2 alloy were studied. The modified Clyne–Davies model is used to predict the HTS of the investigated alloys, which are found in the descending order: MgZn1 > MgZn1Y2 > MgZn1Y2–0.5 wt% Na2CO3 > MgZn1Y2–0.5 wt% Ti > MgZn1Y2–0.5 wt% Zr. By means of XRD, SEM, TEM and EBSD, the evolution of the microstructure during solidification is revealed. The results show that the addition of 2 at% Y can not refine α-Mg grains, but it can change the precipitation type of the second phase. When the precipitation type of the second phase changes from Mg7Zn3 to Mg12ZnY (LPSO phase) and Mg3Zn3Y2 (W-phase), the solidification end temperature of the alloy increases by more than 100 °C, and the coherent lattice of LPSO and α-Mg has a better bridging effect on the grain boundary, which reduces the HTS by 28.4%. Moreover, the addition of 0.5 wt% Na2CO3, 0.5 wt% Ti or 0.5 wt% Zr is an effective method for α-Mg grain refinement, equiaxation and dendrite coherent delay of MgZn1Y2 alloy. In particular, the addition of 0.5 wt% Zr can reduce the α-Mg grain size of MgZn1Y2 alloy by 89.1% and increase the solid fraction by 45% when dendrites are coherent, which results in a 77.1% reduction in HTS.

Strain-dependent wicking behavior of cotton/lycra elastic woven fabric for sportswear

Abstract The strain-dependent vertical and horizontal wicking of as-prepared cotton/lycra elastic woven fabric was systematically studied. The experimental results revealed that the fabric exhibited a strain strengthening effect. A higher tensile strain results in a higher equilibrium wicking height, and vice versa. Moreover, the results indicated that the proposed Laughlin–Davies model is capable of tracking well the experimental data and replicating the wicking characteristics of fabric under different levels of stretch. In addition, the wetting time and wicking area of fabric under different strains and height regimes were examined during horizontal wicking. It was found that the wetting time decreased with an increase of strain and/or water drop height. The strain-enhanced and height-weakened effects of wicking area were revealed. The spreading mechanism of water drop in elastic fabric was also proposed. Such fundamental work provides a basic support for the in-depth investigation of wicking behavior of complex stretchable textile structures.

Fabrication of toughened plastic using styrene butadiene rubber-poly (methyl methacrylate) interpenetrating polymer networks

A standard set of interpenetrating polymeric networks (IPNs) has been contrived using an elastomer-styrene butadiene rubber and a thermoplastic poly (methyl methacrylate) through sequential polymerization protocol. This low-cost material can be hopefully engaged as a toughened plastic with co-continuous morphology. Different morphological protocols including Raman imaging are effectively utilized to envisage the effect of blend ratio in IPN fabrication. The different mechanical properties of IPNs revealed that the cross-linking in phases have their own impact. Thermogravimetric analysis is used as an efficient tool to prove the extra thermal stability of IPNs. Of seven different composites theoretical models, the Davies model showed better fit to the experimental data. The etiquette of characterization adopted in this work including mechanical, morphological, and thermal protocols and their correlation with theoretical predictions can definitely be act as a platform for the synthesis of low-cost toughened plastic.

A novel interfacial thermodynamic model for predicting solubility of nanoparticles coated by stabilizers

To improve the stability of nanoparticles in aqueous solution, polymer or surfactant, etc. are often added in solutions during the preparation process of nanoparticles, which can induce new interfaces that influence the solubility of nanoparticles. In this work, a novel interfacial thermodynamic model for describing the Gibbs energy of the nanoparticles coated by stabilizers was proposed to predict the solubility of nanoparticles. Within the developed model, the activity coefficient of nano metal system was determined by Davies model and that of nano drug system by Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT). The Gibbs energy of the interface was established as a function of molecular parameters via the application for nano metal system. Furthermore, the model was further used to predict the solubility of nano drugs itraconazole, fenofibrate, and griseofulvin. It was found that the Gibbs energy of the interface plays an important role especially when the radius of nano metal is less than 40 nm, and the developed model can predict the solubility of nano drug with high accuracy in comparison with the experimental data as well as predict the changing trend of solubility of nano drugs that increases as the particle size decreases. Meanwhile, the stabilization mechanism of stabilizers on nano drugs was studied which provided theoretical guidance for the selection of polymer or surfactant stabilizer. These findings showed that the developed model can provide a reliable prediction of the solubility of nanoparticles and help to comprehend the stabilization mechanism of the stabilizers on nano drugs with different particle sizes, which is expected to provide important information for the design of nano drugs formulations.

Influence of Nd on Hot Tearing Susceptibility and Mechanism of Mg-Zn-Y-Zr Alloys

The influence of Nd on the hot tearing susceptibility(HTS) of Mg-4.5Zn-1Y-xNd-0.5Zr (x = 0, 1, 2, 3 wt.%) alloy was systematically studied by using Clyne–Davies model, the Newton baseline method based on the thermal analysis and the “T” hot tearing die with temperature and force testing system. The HTS of the alloy decreased first and then increased with Nd content increase, reaching the minimum value at the Nd content of 2 wt.%. Based on the results of thermal analysis, the solidification path of multi-component alloy was studied, and the evolution of phase precipitation and microstructure was discussed by SEM, EBD and TEM. It was found that the precipitation of W-phase, which has a relatively high precipitation temperature and a certain coherent relationship with the parent phase, and reduced the intergranular hot tearing tendency. The results show that with the increase in Nd content to 2 wt.%, the decrease in HTS was due to α-Mg grain refinement, and the entry of Nd atoms into phase I and phase W, so that the ratio of phase I with low melting point to phase W decreases. When the content reaches 3 wt.%, the reason of HTS decrease was α-Mg grain turn to coarsening and the appearance of another T-phase with much lower melting point than W-phase, i.e., ternary (MgZn)92Nd8 phase. It was considered that the smooth feeding channels caused by fine and uniform α-Mg grains and the high grain boundary bridging strength from the higher precipitation temperature of W-phase with a certain crystallographic relationship to the matrix leads to the lowest HTS of the Mg-4.5Zn-1Y-2Nd-0.5Zr alloy.

Unlocking UK COVID-19 policy

Unlocking UK COVID-19 policy

Effect of Cu on the Hot Tearing Susceptibility of Al–6Zn–2.5Mg–xCu Alloy

Based on the modified Clyne–Davies model and the “T”-type hot tearing test system, the hot tearing susceptibility of Al–6Zn–2.5Mg–xCu (x = 0, 1, 2, 3 wt%) alloy was predicted and verified. The results showed that the hot tearing susceptibility first decreased and then increased with the increase in the content of Cu, and the smallest was at the content of 2 wt%. It was found that dendrite coherence temperature (Tcoh) measured by double-couple test and hot tearing initiation temperature (Thi) measured by cooling stress–strain curve of T-type specimen are important parameters to characterize hot tearing susceptibility of alloys. The lower Tcoh and Thi, the lower the hot tearing susceptibility of alloys. The effect of different Cu contents on the crystallization of the parent phase and the precipitation of the second phase was analyzed by optical microscopy, scanning electron microscopy and X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The results show that the cooling structure of Al–6Zn–2.5Mg–2Cu alloy with the lowest hot tearing susceptibility corresponds to the finest grains, and a suitable amount of S (Al2CuMg) and T (Al2Mg3Zn3) phases is distributed on the grain boundary.

Performance evaluation of different photovoltaic technologies in the region of Ifrane, Morocco

This study aims at analyzing and comparing several indices that evaluate the performance of different grid connected photovoltaic technologies, namely amorphous silicon (a-Si), Polycrystalline silicon (pc-Si), and Monocrystalline silicon (mc-Si) generating around 2 kWp each and set up a forecast studies for future perspectives. These technologies are connected to a low voltage (400 V) three phase electrical grid of Al Akhawayn University (33° North, 5° West) facing south on a flat surface, 32° tilted with zero azimuth, and without including any tracking system. This work is done within the framework of Propre.ma project aiming at establishing a photovoltaic yield maps throughout Morocco. The experimental and theoretical horizontal irradiances of Ifrane’s region, simulated with the Davies and Hay model on the MATLAB’s software, are compared in the following study. Besides, the evaluation of different technologies is based on the (annual/monthly/daily) AC energy output, the performance ratio, the system efficiency, and the capacity factor that are calculated and measured from data gathered between October 2014 and the end of 2018. An economic analysis was carried out in order to define the levelized cost of electricity of the three technologies. Eventually, the obtained results confirm that the polycrystalline technology is the most cost-effective technology for the region of Ifrane.

Exposure Levels of Adult Patients during Radiographic Examinations: Sinuses and Coastal Grill Cases at the Ngaoundere Regional Hospital, Cameroon.

Background The purpose of this study was to estimate the doses delivered to adult patients during explorations of the sinuses and coastal grill whose attention in dosimetric terms is neglected because of the low demand for diagnosis. But yet dosimetric values are very high. Materials and Methods The present study was transversely descriptive and was conducted between April and July 2016. The data were collected on 50 adult patients of mass of 70±10kg at the Regional Hospital of Ngaoundere (HRN). The dose at the entrance of the patients' skin was evaluated through the theoretical methods derived from the Davies model according to the 75th percentile calculations. Results and Discussion The entrance skin doses obtained in mGy were, respectively, of 7.2±0.2 for sinuses and 5.27±0.1 for coastal grill. The present study found many variations in doses during radiological investigations. These variations allowed us to understand that the notions of quality of the radiographic image, insurance, and quality control of the radiological equipment are tributary, abstract, and often theoretical because doses delivered are not sufficiently optimized. Conclusion The dosimetric analysis remains very worrying because the various procedures show that an improvement of the practices especially with respect to the technical parameters and the protocols must be considered. Therefore a strengthening of radiological protection skills of radiological manipulators (continuing education and retraining) would contribute to a better protection of patients.

An Assessment of Effective Factors in Technology Acceptance Model: A Meta- Analysis Study

Purpose: The main object of this study is to identify the main factors which cause the acceptance or rejection of technology by the users. Methodology: In the present study; the results of studies conducted in the mentioned field were analyzed using statistical methods. The method applied in the current study was meta-analysis. In this study, all studies done in the mentioned field have been searched from three citation databases of ISI, Scopus and ISC, based on the presence of keywords TAM and Technology Acceptance Model in titles, abstracts, keywords, texts and references. For meta-analysis of the studies, means and standard error of variables in the studies were collected and their significance level was measured with the use of means differences. Then, based on tests applied in the studies, the effects size of the variables was calculated based on Hedges approach. Also, Cohen approach was used for their interpretation. Findings: Totally, 164 researches had the property of measuring the effect size. Given the obtained results, twenty-one-dimensional variables with different values are effective in the technology acceptance in environments and based on the type of samples in the studies. Given that all main variables in Davies model had high means and high effect size, it can be concluded that components of Davis’ Technology Acceptance Model (TAM) are still considered as the ideal components in this field. Originality/value: the article have a new methodology to technology acceptance or rejection causes.

Effects of Copper Content and Mold Temperature on the Hot Tearing Susceptibility of Mg-7Zn-xCu-0.6Zr Alloys

The effects of copper (Cu) content and mold temperature on the hot tearing susceptibility (HTS) of Mg-7Zn-xCu-0.6Zr (x = 0, 1, 2) alloys were investigated experimentally using a T-type hot tearing mold. The crack volumes were measured by paraffin permeation method, and the solidification process was analyzed by thermal analysis and by using the Clyne and Davies model. The microstructure and morphology of the crack zone of Mg-7Zn-xCu-0.6Zr alloys were characterized by scanning electron microscopy, and the composition of alloys was analyzed by X-ray diffraction. The results showed the formation of a new phase of MgZnCu in the alloys with Cu addition. Moreover, addition of Cu also led to the refinement of microstructures of Mg-7Zn-xCu-0.6Zr alloys. The HTS of Mg-7Zn-xCu-0.6Zr alloys decreased with the increase in both the content of Cu and the mold temperature.