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We derive a relation between the static structure factor for a mixture and experimental quantities that can be extracted from a Rayleigh-Brillouin light scattering experiment: the Landau-Placzek ratio and Brillouin shift. Partial structure factors are related to the thermodynamic quantities that characterize a mixture in a similar way as the Kirkwood-Buff integrals. In a He + Xe noble gas mixture, the spectrum is dominated by the contribution due to the XtXe correlations in the mixture. We compare experimental results to calculations using the van der Waals equation of state. The other two partial structure factors can be obtained in an approximate way from a mixing rule for the partial static structure factors. Thus, it is possible to obtain approximate values for the isothermal compressibility, the osmotic compressibility, and th...
We present the Rayleigh-Brillouin light scattering data for He + Xe mixtures of various compositions and pressures between 2 and 10 MPa. We compare our experimental data to calculations for a mixture that behaves according to the van der Waals equation of state. Our analysis shows that the contribution of concentration fluctuations to the Landau-Placzek ratio is very important. Furthermore, we demonstrate experimentally the relation between the Landau-Placzek ratio, the adiabatic velocity of sound, and the reduced second moment of the dynamic light scattering spectrum. We show that the van der Waals equation of state can be used to predict the Landau-Placzek ratio in these mixtures quantitatively for mixtures with compositions xu < 0.9. For mixtures with higher xenon concentrations, experimental results agreed quantitatively up to 5 M...
Spectra of fluctuations in the total intensity of laser light deflected by supercooled water show that even under carefully controlled conditions large samples give convection when cooled below -0%. This is in agreement with the Rayleigh versus Prandtl number relation for supercooled water. Localisation of the temperatures at which transitions in thermal convection occur allows an estimate of the temperature at which the samples should become fully turbulent. Since the samples always freeze before that point is reached and a turbulent situation is never observed, one is led to the surmise that turbulence drives the transition out of the metastable state.
We present new data on Hz + Xe mixtures that support the existence of a fast sound mode in binary gas mixtures. In addition we show that using an approriate scaling, the behaviour of the slow sound mode in systems with different mass ratios, i.e. Hz + Xe, H, + Ar and He + Xe, is identical.
Accurate control of the balance of the T1 and T2 cells during antiviral immunity is essential for optimizing immune effector functions and for avoiding potentially severe immunopathology. We examined the in vivo role of the signal transducer and activator of transcription (STAT) 4 in regulating the T1/T2 balance during the response to live influenza virus and isolated viral proteins. We found that the differentiation of gamma interferon (IFN-γ)-producing Th1 and Tc1 cells after inoculation of live virus occurred independently of STAT 4 expression. Influenza virus-specific T2 and Tc2 responses were well controlled in such STAT 4-deficient mice unless IFN-γ was eliminated as well. In contrast, the STAT 4-dependent signaling pathway played a more essential role in regulating the T1/T2 balance after immunization with viral proteins and, in...
We investigated the role of different lymphocyte subpopulations in the host defense reaction against influenza virus infection, taking advantage of various immunodeficient mouse strains. Whereas, following immunization, wild-type animals showed complete protection against challenge with a lethal dose of A/PR8/34 (PR8) virus, mice that lack both B and T cells but not NK cells (namely, scid and RAG2(-/-) mice) did not display any protective effect in similar conditions. By contrast, J(H)D(-/-) mice devoid of B cells and immunized with virus showed a protective response after challenge with a lethal dose. The immunized J(H)D(-/-) mice that survived completely recovered from the influenza virus infection. Immunized J(H)D(-/+) mice exhibited a more complete protection, suggesting the role of specific antibodies in resistance to infection. T...
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