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Search Results: 1 - 10 of 326201 matches for " S. Kaiser "
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Corrosion Behaviour of Aluminium Engine Block in 3.5% NaCl Solution  [PDF]
M. S. Kaiser, Swagata Dutta
Journal of Materials Science and Chemical Engineering (MSCE) , 2014, DOI: 10.4236/msce.2014.210008

In the present work, the corrosion behavior of aluminium alloy engine block in 3.5% NaCl solution was studied. The work was carried out using conventional gravimetric measurements and complemented by scanning electron microscopy (SEM) and X-ray analyzer (EDX) investigations. The results obtained indicate that the main process the alloy undergoes, under the medium of exposure studied, is related to localized corrosion that takes place as a consequence of the process of alkalinization around the cathodic precipitates existing in the alloy. The alloy suffers a process of corrosion localized to the area surrounding the precipitates of the Al (Si, Mg) and Al-Mg, which resulted in hemispherical pits. This identification was confirmed by SEM and EDX analysis. No evidence was found of the formation of crystallographic pitting for exposure times up to 54 days. Gravimetric analysis confirmed that with varying exposure periods the weight loss of the alloy increases and the corrosion rate decreases with time.

Single-particle potential in a chiral approach to nuclear matter including short range NN-terms
S. Fritsch,N. Kaiser
Physics , 2002, DOI: 10.1140/epja/i2002-10149-x
Abstract: We extend a recent chiral approach to nuclear matter of Lutz et al. [Phys. Lett. B474 (2000) 7] by calculating the underlying (complex-valued) single-particle potential U(p,k_f) + i W(p,k_f). The potential for a nucleon at the bottom of the Fermi-sea, U(0,k_{f0})= - 20.0 MeV, comes out as much too weakly attractive in this approach. Even more seriously, the total single-particle energy does not rise monotonically with the nucleon momentum p, implying a negative effective nucleon mass at the Fermi-surface. Also, the imaginary single-particle potential, W(0,k_{f0}) = 51.1 MeV, is too large. More realistic single-particle properties together with a good nuclear matter equation of state can be obtained if the short range contributions of non-pionic origin are treated in mean-field approximation (i.e. if they are not further iterated with 1pi-exchange). We also consider the equation of state of pure neutron matter $bar E_n(k_n)$ and the asymmetry energy A(k_f) in that approach. The downward bending of these quantities above nuclear matter saturation density seems to be a generic feature of perturbative chiral pion-nucleon dynamics.
Chiral approach to nuclear matter: Role of explicit short-range NN-terms
S. Fritsch,N. Kaiser
Physics , 2003, DOI: 10.1140/epja/i2003-10179-x
Abstract: We extend a recent chiral approach to nuclear matter by including the most general (momentum-independent) NN-contact interaction. Iterating this two-parameter contact-vertex with itself and with one-pion exchange the emerging energy per particle exhausts all terms possible up-to-and-including fourth order in the small momentum expansion. The equation of state of pure neutron matter, $\bar E_n(k_n)$, can be reproduced very well up to quite high neutron densities of $\rho_n=0.5\fmd$ by adjusting the strength of a repulsive $nn$-contact interaction. Binding and saturation of isospin-symmetric nuclear matter is a generic feature of our perturbative calculation. Fixing the maximum binding energy per particle to $-\bar E(k_{f0})= 15.3 $MeV we find that any possible equilibrium density $\rho_0$ lies below $\rho_0^{\rm max}=0.191\fmd$. The additional constraint from the neutron matter equation of state leads however to a somewhat too low saturation density of $\rho_0 =0.134 \fmd$. We also investigate the effects of the NN-contact interaction on the complex single-particle potential $U(p,k_f)+i W(p,k_f)$. We find that the effective nucleon mass at the Fermi-surface is bounded from below by $M^*(k_{f0}) \geq 1.4 M$. This property keeps the critical temperature of the liquid-gas phase transition at somewhat too high values $T_c \geq 21 $MeV. The downward bending of the asymmetry energy $A(k_f)$ above nuclear matter saturation density is a generic feature of the approximation to fourth order. Altogether, there is within this complete fourth-order calculation no "magic" set of adjustable short-range parameters with which one could reproduce simultaneously and accurately all semi-empirical properties of nuclear matter.
Ense?anza de Temas Avanzados de Mecánica de Fluidos usando Dinámica de Fluidos Computacional
Zamora,Blas; Kaiser,Antonio S;
Formación universitaria , 2009, DOI: 10.4067/S0718-50062009000100005
Abstract: the experience gained in a course on selected topics of fluid mechanics course for the industrial engineer degree, polytechnic university of cartagena-spain employing numerical techniques as a motivating element for students. the mean objectives of the course are to provide an understanding of the analytical methods employed for selected topics in fluid mechanics and to bring a familiarity with some experimental and numerical techniques. to improve teaching-learning a pedagogical method based on problem-solving based learning is applied, using computational fluid dynamics. as a result, the motivation and the theoretical and technical abilities of the students have been improved. it can be concluded that now the method is efficient and has increase the satisfaction degree of the students.
A Comparison of the Performance of Cylindrical Lens Reflectors and Stepped-Indexed Cylindrical Luneburg Lens Reflectors: Simpler Is Better?
Kaiser Lock;Sergei S. Vinogradova
PIER B , 2012, DOI: 10.2528/PIERB12053004
Abstract: This paper studies the characteristics of a constant-K lens when considered as a possible substitute for a Luneburg lens in a reflector. The competitiveness of the substitute lens is investigated in its 2D analogue, by comparing the backscattering radar cross section for the range of D/λ ∈ (0, 200). The performance of cylindrical reflectors with either a constant-K lens or a cylindrical Luneburg lens (approximated by a finite number of stepped-index dielectric layers) when illuminated by an electromagnetic plane wave is studied using the semi-analytic Method of Regularization. Because of similar underlying physical principles, these studies provide insight into the 3-D analogue. The radar cross section calculations of the two reflectors for incidence angles varying from normal to grazing incidence show that the cheaper-to-manufacture constant-K lens reflector is able to provide a more powerful and stable backscattering performance than the cylindrical Luneburg lens reflector, for electrical sizes in the range considered.
Symmetry Breaking in the Static Coordinate System of de Sitter Spacetime
András Kaiser,Alan Chodos
Physics , 1995, DOI: 10.1103/PhysRevD.53.787
Abstract: We study symmetry breaking in the static coordinate-system of de Sitter space. This is done with the help of the functional-Schr\"odinger approach used in previous calculations by Ratra [1]. We consider a massless, minimally coupled scalar field as the parameter of a continuous symmetry (the angular component of an O(2) symmetry). Then we study the correlation function of the massless scalar field, to derive the correlation function of the original field, which finally shows the restoration of the continuous symmetry.
From Caenorhabditis elegans to the Human Connectome: A Specific Modular Organisation Increases Metabolic, Functional, and Developmental Efficiency
Jinseop S. Kim,Marcus Kaiser
Quantitative Biology , 2014, DOI: 10.1098/rstb.2013.0529
Abstract: The connectome, or the entire connectivity of a neural system represented by network, ranges various scales from synaptic connections between individual neurons to fibre tract connections between brain regions. Although the modularity they commonly show has been extensively studied, it is unclear whether connection specificity of such networks can already be fully explained by the modularity alone. To answer this question, we study two networks, the neuronal network of C. elegans and the fibre tract network of human brains yielded through diffusion spectrum imaging (DSI). We compare them to their respective benchmark networks with varying modularities, which are generated by link swapping to have desired modularity values but otherwise maximally random. We find several network properties that are specific to the neural networks and cannot be fully explained by the modularity alone. First, the clustering coefficient and the characteristic path length of C. elegans and human connectomes are both higher than those of the benchmark networks with similar modularity. High clustering coefficient indicates efficient local information distribution and high characteristic path length suggests reduced global integration. Second, the total wiring length is smaller than for the alternative configurations with similar modularity. This is due to lower dispersion of connections, which means each neuron in C. elegans connectome or each region of interest (ROI) in human connectome reaches fewer ganglia or cortical areas, respectively. Third, both neural networks show lower algorithmic entropy compared to the alternative arrangements. This implies that fewer rules are needed to encode for the organisation of neural systems.
Genetic Architecture of Local Adaptation in Lunar and Diurnal Emergence Times of the Marine Midge Clunio marinus (Chironomidae, Diptera)
Tobias S. Kaiser, David G. Heckel
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0032092
Abstract: Circadian rhythms pre-adapt the physiology of most organisms to predictable daily changes in the environment. Some marine organisms also show endogenous circalunar rhythms. The genetic basis of the circalunar clock and its interaction with the circadian clock is unknown. Both clocks can be studied in the marine midge Clunio marinus (Chironomidae, Diptera), as different populations have different local adaptations in their lunar and diurnal rhythms of adult emergence, which can be analyzed by crossing experiments. We investigated the genetic basis of population variation in clock properties by constructing the first genetic linkage map for this species, and performing quantitative trait locus (QTL) analysis on variation in both lunar and diurnal timing. The genome has a genetic length of 167–193 centimorgans based on a linkage map using 344 markers, and a physical size of 95–140 megabases estimated by flow cytometry. Mapping the sex determining locus shows that females are the heterogametic sex, unlike most other Chironomidae. We identified two QTL each for lunar emergence time and diurnal emergence time. The distribution of QTL confirms a previously hypothesized genetic basis to a correlation of lunar and diurnal emergence times in natural populations. Mapping of clock genes and light receptors identified ciliary opsin 2 (cOps2) as a candidate to be involved in both lunar and diurnal timing; cryptochrome 1 (cry1) as a candidate gene for lunar timing; and two timeless (tim2, tim3) genes as candidate genes for diurnal timing. This QTL analysis of lunar rhythmicity, the first in any species, provides a unique entree into the molecular analysis of the lunar clock.
Energy Efficient System for St Martin s Island of Bangladesh
M. Shamim Kaiser,S.K. Aditya
Journal of Engineering and Applied Sciences , 2012,
Abstract: St Martin`s is one of the most beautiful Tourist Islands in Bangladesh where grid connected electric system for the inhabitants will not be possible to establish even in future. Diesel, Kerosene and wood are the main fuels for fulfilling the energy demand. Solar and Wind resources are the hybrid options for the Island. HOMER, a software for optimization of renewable based hybrid systems, has been used to find out the best technically viable renewable based energy efficient system for different numbers of households-1, 10, 20, 30, 40 and 50. It shows that per unit (KWh) cost of energy varies from 48 to 19 taka.
Phase readout of a charge qubit capacitively coupled to an open double quantum dot
C. Kreisbeck,F. J. Kaiser,S. Kohler
Physics , 2009, DOI: 10.1103/PhysRevB.81.125404
Abstract: We study the dynamics of a charge qubit that is capacitively coupled to an open double quantum dot. Depending on the qubit state, the transport through the open quantum dot may be resonant or off-resonant, such that the qubit affects the current through the open double dot. We relate the initial qubit state to the magnitude of an emerging transient current peak. The relation between these quantities enables the readout of not only the charge but also the phase of the qubit.
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