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Distribution by Scientific Domains

Physics and Astronomy	40%

Selected Abstracts

Influence of the Weißenberg number on the stability of Oldroyd kind fluids

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010
N. Scurtu
Abstract This paper is concerned with nonlinear rheological fluids of Oldroyd type. We present a (formal) stability analysis of the corresponding system of equations, showing stability limits on the Weißenberg number in certain cases. To this end, we proceed in several steps, thus separating the possible sources for instabilities. First, a spectral analysis of the linearized Oldroyd system is presented. Then, the influence of the ,a -term on the stability of the constitutive stress equation and of the full Oldroyd system is examined. Moreover, because this stability analysis is of formal and linear nature, we complement it by numerical simulations for the system showing that the upper limit of the Weißenberg number found by the stability analysis is fairly sharp. We thereby try to shed some light on the high Weißenberg number problem, that is, the problem why in certain cases there seem to exist no solutions to the Oldroyd problem for large Weißenberg numbers. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Radial velocity and light curves analysis of the eclipsing binary NN Vir

ASTRONOMISCHE NACHRICHTEN, Issue 9 2004
R. Pazhouhesh
Abstract The eclipsing binary NN Vir is a short period system showing an EW-type light curve. Photometric observations of NN Vir were done by Gomez-Ferrellad & Garcia-Melendo (1997) at Esteve Duran Observatory. We used photometric data of NN Vir for light curve analysis. The available spectroscopic data of NN Vir is new and we also used the first radial velocity data of this system obtained by Rusinski & Lu (1999) for analysis. The radial velocity and light curves analysis was made with the latest version ofWilson program(1998) and the geometric and physical elements of the system are derived. By searching the simultaneous solutions of the system, we have determined the masses and radii of the components : 1.89(M,) and 1.65(R,) for the primary component; 0.93(M,) and 1.23(R,) for the secondary component. We estimated effective temperatures of 7030(K) for the primary and 6977(K) for the secondary component. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Signalization and cytoskeleton activity through myosin IB during the early steps of phagocytosis in Entamoeba histolytica: a proteomic approach

CELLULAR MICROBIOLOGY, Issue 10 2005
Sabrina Marion
Summary Phagocytosis of human cells is a crucial activity for the virulence of the human parasite Entamoeba histolytica. This protozoan invades and destroys the intestine by killing and phagocytosing epithelial cells, erythrocytes and cells from the immune system. In this study, we used magnetic beads covered with proteins from human serum as a model system to study the early events involved in phagocytosis by E. histolytica. We validated the system showing that the beads uptake triggered the activation of the actin-myosin cytoskeleton and involved a PI3-kinase as previously described for erythrophagocytosis. We purified early phagosomes from wild-type (WT) amoeba and from parasites that overproduced myosin IB (MyoIB+), the unique unconventional myosin of E. histolytica. The MyoIB+ cells exhibit a slower and more synchronized uptake process than the WT strain. Proteomic analysis by liquid chromatography and tandem mass spectroscopy (LC-MS/MS) of the WT and MyoIB+ phagosomes allowed us to identify, for the first time, molecular actors involved in the early step of the uptake process. These include proteins involved in cytoskeleton activity, signalling, endocytosis, lytic activity and cell surface proteins. Interestingly, the proteins that we found specifically recruited on the phagosomes from the MyoIB+ strain were previously described in other eukarytotic cells, as involved in the regulation of cortical F-actin dynamics, such as ,-actinin and formins. This proteomics approach allows a step further towards the understanding of the molecular mechanisms involved in phagocytosis in E. histolytica that revealed some interesting differences compared with phagocytosis in macrophages or Dictyostelium discoideum, and allowed to identify putative candidates for proteins linked to myosin IB activity during the phagocytic process [source]

Gaussian inputs: performance limits over non-coherent SISO and MIMO channels

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2007
Rasika R. Perera
Performance limits of information transfer over a discrete time memoryless Rayleigh fading channel with neither the receiver nor the transmitter knowing the fading coefficients except its statistics is an important problem in information theory. We derive closed form expressions for the mutual information of single input single output (SISO) and multiple input multiple output (MIMO) Rayleigh fading channels for any antenna number at any signal to noise ratio (SNR). Using these expressions, we show that the maximum mutual information of non-coherent Rayleigh fading MIMO channels is achieved with a single transmitter and multiple receivers when the input distribution is Gaussian. We show that the addition of transmit antennas for a fixed number of receivers result in a reduction of mutual information. Furthermore, we argue that the mutual information is bounded by the SNR in both SISO and MIMO systems showing the sub-optimality of Gaussian signalling in non-coherent Rayleigh fading channels. Copyright © 2006 AEIT [source]

On the reliability of the semi-empirical RR Lyrae period,V -band luminosity,blue amplitude relation

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2002
R. De Santis
Abstract We investigate the accuracy and reliability of the semi-empirical period,V -band luminosity,blue amplitude (PLA) relationship for ab-type RR Lyrae stars originally obtained by Castellani and De Santis in the mid-1990s. We infer that the zero-point of this relationship depends on the metallicity, by studying a sample of both field and cluster variables. We also show that the use of this relationship can still be useful for those stellar systems showing an intrinsic metallicity spread, since in this case the metallicity has a negligible effect on the final distance modulus estimate. We compare the adopted semi-empirical relationship with the fully empirical one recently provided by Kovács & Walker. When the zero-point of the latter relation is fixed consistently with the former one, the two equations are equivalent. By applying the semi-empirical period,V -band luminosity,blue amplitude relation, as well as the technique proposed recently by Cassisi, De Santis & Piersimoni, to the globular cluster , Cen, we show that the empirical slope of the relationship between the mass of the fundamental RR Lyrae pulsators and their metallicity is in fair agreement with the one predicted by updated evolutionary models for horizontal branch stars. [source]