Techniques for Enhancing and Maintaining Electrical Efficiency of Photovoltaic Systems

Demand for electricity generation from solar energy, which is a clean and renewable resource, is increasing day by day. It is desirable that the panel surface temperature is not excessively hot while generating electricity with PVT panels. High temperature causes thermal degradation and panel electric efficiency decrease. There are many studies in the literature about active thermal cooling of PVT panels used for electricity generation as well as for storing thermal energy. In this study, a review was made on methods developed to increase the thermal and electrical efficiencies of PVT panels

Planetary migration in evolving planetesimals discs

In the current paper, we further improved the model for the migration of planets introduced in Del Popolo et al. (2001) and extended to time-dependent planetesimal accretion disks in Del Popolo and Eksi (2002). In the current study, the assumption of Del Popolo and Eksi (2002), that the surface density in planetesimals is proportional to that of gas, is released. In order to obtain the evolution of planetesimal density, we use a method developed in Stepinski and Valageas (1997) which is able to simultaneously follow the evolution of gas and solid particles for up to 10^7 yrs. Then, the disk model is coupled to migration model introduced in Del Popolo et al. (2001) in order to obtain the migration rate of the planet in the planetesimal. We find that the properties of solids known to exist in protoplanetary systems, together with reasonable density profiles for the disk, lead to a characteristic radius in the range 0.03-0.2 AU for the final semi-major axis of the giant planet.Comment: IJMP A in prin

Orbital migration and the period distribution of exoplanets

We use the model for the migration of planets introduced in Del Popolo, Yesilyurt & Ercan (2003) to calculate the observed mass and semimajor axis distribution of extra-solar planets. The assumption that the surface density in planetesimals is proportional to that of gas is relaxed, and in order to describe disc evolution we use a method which, using a series of simplifying assumptions, is able to simultaneously follow the evolution of gas and solid particles for up to $10^7 {\rm yr}$. The distribution of planetesimals obtained after $10^7 {\rm yr}$ is used to study the migration rate of a giant planet through the model of this paper. The disk and migration models are used to calculate the distribution of planets as function of mass and semimajor axis. The results show that the model can give a reasonable prediction of planets' semi-major axes and mass distribution. In particular there is a pile-up of planets at $a \simeq 0.05$ AU, a minimum near 0.3 AU, indicating a paucity of planets at that distance, and a rise for semi-major axes larger than 0.3 AU, out to 3 AU. The semi-major axis distribution shows that the more massive planets (typically, masses larger than $4 M_{\rm J}$) form preferentially in the outer regions and do not migrate much. Intermediate-mass objects migrate more easily whatever the distance they form, and that the lighter planets (masses from sub-Saturnian to Jovian) migrate easily.Comment: published in A&

On the nature of gravitational forces

In this paper I show how the statistics of the gravitational field is changed when the system is characterized by a non-uniform distribution of particles. I show how the distribution functions W(dF/dt) giving the joint probability that a test particle is subject to a force F and an associated rate of change of F given by dF/dt, are modified by inhomogeneity. Then I calculate the first moment of dF/dt to study the effects of inhomogenity on dynamical friction. Finally I test, by N-Body simulations, that the theoretical W(F) and dF/dt describes correctly the experimental data and I find that the stochastic force distribution obtained for the evolved system is in good agreement with theory. Moreover, I find that in an inhomogeneous background the friction force is actually enhanced relative to the homogeneous case

Cosmological constraints from clustering properties of galaxy clusters

In this paper, we discuss improvements of the Suto et al. (2000) model, in the light of recent theoretical developments (new theoretical mass functions, a more accurate mass-temperature relation and an improved bias model) to predict the clustering properties of galaxy clusters and to obtain constraints on cosmological parameters. We re-derive the two-point correlation function of clusters of galaxies for OCDM and LambdaCDM cosmological models, and we compare these results with the observed spatial correlation function for clusters in RASS1 (ROSAT All-Sky Survey 1), and in XBACs (X-RAY Brighest Abell-Type) samples. The comparison shows that the best agreement is obtained for the LambdaCDM model with Omega=0.3. The values of the correlation length obtained, (r_\simeq 28.2 \pm 5.2 \rm h^{-1}} Mpc for LambdaCDM), are larger than those found in the literature and comparable with the results found in Borgani, Plionis & Kolokotronis (1999). (REST IN THE PAPER ABSTRACT)Comment: printed in A&

Global sensitivity analysis of stochastic computer models with joint metamodels

The global sensitivity analysis method used to quantify the influence of uncertain input variables on the variability in numerical model responses has already been applied to deterministic computer codes; deterministic means here that the same set of input variables gives always the same output value. This paper proposes a global sensitivity analysis methodology for stochastic computer codes, for which the result of each code run is itself random. The framework of the joint modeling of the mean and dispersion of heteroscedastic data is used. To deal with the complexity of computer experiment outputs, nonparametric joint models are discussed and a new Gaussian process-based joint model is proposed. The relevance of these models is analyzed based upon two case studies. Results show that the joint modeling approach yields accurate sensitivity index estimatiors even when heteroscedasticity is strong

Outcomes from elective colorectal cancer surgery during the SARS-CoV-2 pandemic

This study aimed to describe the change in surgical practice and the impact of SARS-CoV-2 on mortality after surgical resection of colorectal cancer during the initial phases of the SARS-CoV-2 pandemic

Investigation of availability of raw perlite in refractory building material production

Perlite having rich reserves in Turkey is basic industrial raw material in line with sustainable development objectives. In recent years due to the thermal insulation properties expanded perlite has attracted the attention of researchers. It is started to use in some construction areas. Binder material is used to shape in the manufacturing of refractory bricks. Desired material was sintered at high temperature. In this study, perlite between 75-600 µm particle size was subjected to heat treatment at different temperatures and investigated to use in refractory construction materials production. Perlite grains clinging to each other engage a smooth shape. Gypsum is used as an activator in different proportions to achieve this objective. The samples were subjected to heat treatment at 1050-1200 °C for 30 minutes. In the 5% gypsum mixture highest compressive strength at 1150 °C was calculated as 47 MPa. Unit volume weight is considered as 1.95 g/cm3, water absorption by weight is determined as 0.30%. Superficial abrasion loss was determined to be 20 mm. Degree of porosity is calculated as 15%. Compactness was found to be 85%. Furthermore in the results of experiment of freezing of the obtained products was not found any damage or any strength loss. © 2018 Ergün Yesilyurt, Osman Simsek, Ahmet Bilgil

KOMPOZİT REZİNLERİN POLİMERİZASYONLARI ESNASINDA PULPA ODASINDAKİ ISI DEĞİŞİMLERİNİN İN VİTRO DEĞEİRLENDİRİLMESİ

Bu in vitro çal›şman›n amac›, kompozit rezin polimerizasyonu esnas›nda pulpa odas›nda oluşabilecek ›s› değişikliklerini değerlendirmektir. 40 adet çekilmiş maxiller santral insan dişi kullan›ld›. Dişlerin vestibul yüzeylerine 5 mm çap›nda, 2 mm yüksekliğinde standart kaviteler aç›ld›, dişler rasgele 4 gruba ayr›ld›. Dişlerin kökleri mine-sement birleşiminden yaklaş›k olarak 4 mm aşağ›da olacak şekilde kesildi, pulpa dokusu headström eğeler ile uzaklaşt›r›ld›. Her dişin pulpa odas›na digital termometrenin termocouple’› yerleştirildi ve radyografi ile kontrol edildi. Daha sonra bir ak›şkan Tetric-Flow , bir kondanse edilebilir Surefil ,bir hybrid Charisma ve bir ormoser esasl› Admira kompozit rezinler kavitelere yerleştirilerek 40 s ›ş›k cihaz› ile polimerize edildiler. Polimerizasyon esnas›ndaki ›s› art›şlar› kaydedildi. Sonuçlar istatistiksel olarak Varyans Analizi ve Duncan testi ile değerlendirildi. En yüksek ›s› art›ş› ak›şkan kompozit grubunda gözlendi. Diğer kompozit rezinler aras›nda istatistiksel olarak önemli farkl›l›k bulunmad›.