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Search Results: 1 - 10 of 461984 matches for " A. Sezer "
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Exergetic Evaluation of Speed and Load Effects in Spark Ignition Engines évaluation exergétique des effets de la vitesse et de la charge dans les moteurs àallumage par étincelle
Sezer I.,Bilgin A.
Oil & Gas Science and Technology , 2012, DOI: 10.2516/ogst/2012002
Abstract: This study investigates the effects of various operating conditions in spark ignition engines via an exergy analysis. A thermodynamic cycle model including compression, combustion and expansion processes was used for investigation. Induction and exhaust processes were computed with a simple approximation method. The principles of the second law were applied to the cycle model to perform the exergy analysis. Exergetic variables, i.e., the exergy transfers with heat and work, irreversibilities, thermomechanical exergy, fuel chemical exergy and total exergy were calculated in the exergy analysis. Variation of the exergetic parameters and the distribution of them into the fuel exergy were determined for various operating conditions, i.e., engine speed and load. The first and second law efficiencies and specific fuel consumption were also computed to reveal the optimum operating conditions. The results show that the exergy transfer with heat decreases and the exergy transfer with exhaust gases increases with increasing engine speed. Engine speed of 3 000 rpm gives the maximum exergy transfer as work, the minimum irreversibility and the best efficiency and fuel consumption. Exergy transfers with heat, work and exhaust and irreversibilities increase with increasing engine load. Additionally, the first and second law efficiencies increase and fuel consumption decreases with increasing engine load, so a high engine load gives the best efficiency and fuel consumption. Cette étude examine les effets des différentes conditions de fonctionnement de moteurs à allumage commandé via une analyse exergétique. Un modèle de cycle thermodynamique comprenant les processus de compression, combustion et détente a été utilisé. Les processus d’admission et d’échappement sont modélisés à l’aide d’une méthode simple d’approximation. Les principes de la deuxième loi de la thermodynamique ont été appliqués au modèle de cycle pour effectuer l’analyse exergétique. Des variables exergétiques comme les transferts exergétiques de chaleur et de travail, les irréversibilités, l’exergie thermomécanique, l’exergie chimique du carburant et l’exergie totale ont été calculées dans l’analyse exergétique. La variation des paramètres exergétiques et leur distribution dans l’exergie du combustible ont été déterminées pour différentes conditions de fonctionnement, c’est à dire différentes vitesses du moteur et différentes charges. L’efficacité déduite, d’une part, de la première et la deuxième loi de la thermodynamique et, d’autre part, de la consommation spécifique de carburant ont également été ca
Ejecta detection in the middle-aged Galactic supernova remnant G296.1-0.5 observed with Suzaku
F. Gok,A. Sezer
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.19822.x
Abstract: In this paper, we report the detection of ejecta in the middle-aged Galactic supernova remnant G296.1-0.5 with the X-ray Imaging Spectrometer onboard the Suzaku satellite. The spectra of three lobes, north, southeast and southwest and inter-lobe regions, consist of soft (0.3-2.0 keV) emission originated from non-equilibrium ionization plasma. In north, southeast and inter-lobe regions, the thermal emission can be represented by a one-component, in southwest region it can be represented by two- component non-equilibrium ionization (VNEI) model. The spectra of studied regions have lines of N, O, Ne, Mg and Si elements. Si emission from this remnant is shown for the first time in this work. Enhanced abundances of Ne, Mg and Si elements obtained show the ejecta contribution in all regions. Assuming that the remnant is in Sedov phase, we obtained ambient density n0 ~ 0.45 cm-3, age t ~ 2.8 x 104 yr, shock velocity Vs ~ 320 km s-1, shock temperature Ts ~ 1.2 x 106 K, and swept-up mass Msw ~ 340 M at an adopted distance of d=3 kpc.
A deep X-ray observation of supernova remnant G304.6+0.1 (Kes 17) with Suzaku
F. Gok,A. Sezer
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.20948.x
Abstract: In this paper, we present the analysis of a deep (99.6 ks) observation of G304.6 + 0.1 with the X-ray Imaging Spectrometer on board {\it Suzaku} satellite. The X-ray spectral data are well-fitted with a plasma model consisting of a thermal component in collisional ionization equilibrium and a non-thermal component. The thermal emission is well fitted with VMEKAL model with an electron temperature of $kT_{\rm e}\sim 0.75$ keV, a high absorbing column density of $N_{\rm H}\sim 3.9\times10^{22}$ $\rm cm^{-2}$ and near/lower solar abundances which indicate that the X-ray emitting plasma of G304.6 + 0.1 is dominated by swept-up ambient medium. The non-thermal component is well fitted with a power-law model with photon index of $\Gamma \sim 1.4$. We found a relatively high electron density $n_{\rm e}\sim 2.3f^{-1/2}$ cm$^{-3}$, age $t$ $\sim 1.4\times10^4f^{1/2}$ yr, and X-ray emitting mass $M_{\rm x}\sim 380f^{1/2}$ {M\sun} at an adopted distance of d=10 kpc. Using the morphological and spectral X-ray data, we confirm that the remnant is a new member of mixed-morphology supernova remnants.
Suzaku study of centrally brightened supernova remnant G272.2-3.2
A. Sezer,F. Gok
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.20570.x
Abstract: In this work, the results from Suzaku observation of Galactic supernova remnant G272.2-3.2 are presented. Spectra of G272.2-3.2 are well fitted by a single-temperature variable abundances non-equilibrium ionization (VNEI) model with an electron temperature kTe \sim 0.77 keV, ionization timescale {\tau} \sim 6.5 \times 10^10 cm-3 s and absorbing column density NH \sim 1.1 \times 10^22 cm-2. We have detected enhanced abundances of Si, S, Ca, Fe and Ni in the center region indicating that the X-ray emission has ejecta origin. We estimated the electron density ne to be \sim0.48f^-1/2 cm-3, age \sim4300f^1/2 yr and the X-ray total mass Mx = 475f^1/2 M by taking the distance to be d=10 kpc. To understand the origin of the centrally-peaked X-ray emission of the remnant, we studied radial variations of the electron temperature and surface brightness. The relative abundances in the center region suggest that G272.2-3.2 is the result of a Type Ia supernova explosion.
Filtration shrinkage by level-crossings of a diffusion
A. Deniz Sezer
Mathematics , 2007, DOI: 10.1214/009117906000000683
Abstract: We develop the mathematics of a filtration shrinkage model that has recently been considered in the credit risk modeling literature. Given a finite collection of points $x_1<...
Exit densities of Super--Brownian motion as extreme X-harmonic functions
A. Deniz Sezer
Mathematics , 2013,
Abstract: Let $X$ be a super-Brownian motion (SBM) defined on a domain $E\subset R^n$ and $(X_D)$ be its exit measures indexed by sub-domains of $E$. The relationship between the equation $1/2 \Delta u=2 u^2$ and Super-Brownian motion (SBM) is analogous to the relationship between Brownian motion and the Laplace's equation, and substantial progress has been made on the study of the solutions of this semi-linear p.d.e. exploring this analogy. An area that remains to be explored is Martin boundary theory. Martin boundary in the semi-linear case is defined as the convex set of extreme $X$-harmonic functions which are functions on the space of finite measures supported in a domain $E$ of $R^d$ and characterized by a mean value property with respect to the Super-Brownian law. So far no probabilistic construction of Martin boundary is known. In this paper, we consider a bounded smooth domain $D$, and we investigate exit densities of SBM, a certain family of $X$ harmonic functions, $H^{\nu}$, indexed by finite measures $\nu$ on $\partial{D}$, These densities were first introduced by E.B. Dynkin and also identified by T.Salisbury and D. Sezer as the extended X-harmonic functions corresponding to conditioning SBM on its exit measure $X_D$ being equal to $\nu$. $H^{\nu}(\mu)$ can be thought as the analogue of the Poisson kernel for Brownian motion. It is well known that Poisson kernel for a smooth domain $D$ is equivalent to the so called Martin kernel, the class of extreme harmonic functions for $D$. We show that a similar result is true for Super-Brownian motion as well, that is $H^{\nu}$ is extreme for almost all $\nu$ with respect to a certain measure.
The first optical light from the supernova remnant G182.4+4.3 located in the Galactic anti-centre region
A. Sezer,F. Gok,E. Aktekin
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.22015.x
Abstract: We report the discovery of optical filamentary and diffuse emission from G182.4+4.3 using 1.5-m Russian-Turkish telescope. We present the optical CCD images obtained with Halpha filter revealing the presence of mainly filamentary structure at the northwest, filamentary and diffuse structure at the centre, south and north regions of the remnant. The bright optical filaments located in northwest and south regions are well correlated with the prominent radio shell of the remnant strongly suggesting their association. From the flux-calibrated CCD imaging, the average [SII]/Halpha ratio is found to be ~0.9 and ~1.1 for south and northwest regions, which clearly indicates that the emission originates from the shock heated gas. We also present the results of X-ray data obtained from XMM-Newton that show diffuse emission with a very low luminosity of ~7.3x10^31 erg s^-1 at a distance of 3 kpc in 0.3-10 keV energy band. Furthermore, we find a surprisingly young age of ~4400 yr for this remnant with such a large radius of ~22 pc.
Conditioning super-Brownian motion on its boundary statistics, and fragmentation
Thomas S. Salisbury,A. Deniz Sezer
Mathematics , 2012, DOI: 10.1214/12-AOP778
Abstract: We condition super-Brownian motion on "boundary statistics" of the exit measure $X_D$ from a bounded domain $D$. These are random variables defined on an auxiliary probability space generated by sampling from the exit measure $X_D$. Two particular examples are: conditioning on a Poisson random measure with intensity $\beta X_D$ and conditioning on $X_D$ itself. We find the conditional laws as $h$-transforms of the original SBM law using Dynkin's formulation of $X$-harmonic functions. We give explicit expression for the (extended) $X$-harmonic functions considered. We also obtain explicit constructions of these conditional laws in terms of branching particle systems. For example, we give a fragmentation system description of the law of SBM conditioned on $X_D=\nu$, in terms of a particle system, called the backbone. Each particle in the backbone is labeled by a measure $\tilde{\nu}$, representing its descendants' total contribution to the exit measure. The particle's spatial motion is an $h$-transform of Brownian motion, where $h$ depends on $\tilde{\nu}$. At the particle's death two new particles are born, and $\tilde{\nu}$ is passed to the newborns by fragmentation.
Moment densities of super-Brownian motion, and a Harnack estimate for a class of X-harmonic functions
Thomas S. Salisbury,A. Deniz Sezer
Mathematics , 2012,
Abstract: This paper features a comparison inequality for the densities of the moment measures of super-Brownian motion. These densities are defined recursively for each $n \ge 1$ in terms of the Poisson and Green's kernels, hence can be analyzed using the techniques of classical potential theory. When $n = 1$, the moment density is equal to the Poisson kernel, and the comparison is simply the classical inequality of Harnack. For $n > 1$ we find that the constant in the comparison inequality grows at most exponentially with $n$. We apply this to a class of $X$-harmonic functions $H^\nu$ of super-Brownian motion, introduced by Dynkin. We show that for a.e. $H^\nu$ in this class, $H^\nu(\mu)<\infty$ for every $\mu$.
The Effect of Simulated Transportation on Biochemical Plasma Parameters of Japanese Quails
O. Tekelioglu,M. Sezer,F. Ekici,O. Atis,A. Akbas
Journal of Animal and Veterinary Advances , 2012, DOI: 10.3923/javaa.2010.892.895
Abstract: The effect of the duration of simulated transportation on blood SOD (Superoxide Dismutase), GSH-Px (Glutathione Peroxidase), AST (Aspartate Transaminase), ALT (Alanine Transaminase), GGT (Gamma-Glutamyl Transpeptidase), LDH (Lactic Dehydrogenase) enzyme levels and NO (Nitric Oxide) and MDA (Malondialdehyde) product levels was investigated in Japanese quails. Simulated transportation was carried out with a road simulator which was calibrated for Turkish roads conditions. Animals were loaded into well ventilated carrier boxes and carried at 2 and 5 h on the simulator. Blood samples were collected from 10-weeks-old Japanese Quails just after transportation. A significant (p<0.05) increase in all measured plasma parameters (except GGT) at 5 h transportation was observed. However, all of the plasma parameters have not shown a significant increase at 2 h transportation. This transportation duration might be the evidence of the time duration in still safe zone for Japanese Quails for that condition.
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