Effect of Shear Flow on the Stability of Domains in Two Dimensional Phase-Separating Binary Fluids

We perform a linear stability analysis of extended domains in phase-separating fluids of equal viscosity, in two dimensions. Using the coupled Cahn-Hilliard and Stokes equations, we derive analytically the stability eigenvalues for long wavelength fluctuations. In the quiescent state we find an unstable varicose mode which corresponds to an instability towards coarsening. This mode is stabilized when an external shear flow is imposed on the fluid. The effect of the shear is seen to be qualitatively similar to that found in experiments.Comment: 13 pages, RevTeX, 8 eps figures included. Submitted to Phys. Rev.

Life-Detection Technologies for the Next Two Decades

Since its inception six decades ago, astrobiology has diversified immensely to encompass several scientific questions including the origin and evolution of Terran life, the organic chemical composition of extraterrestrial objects, and the concept of habitability, among others. The detection of life beyond Earth forms the main goal of astrobiology, and a significant one for space exploration in general. This goal has galvanized and connected with other critical areas of investigation such as the analysis of meteorites and early Earth geological and biological systems, materials gathered by sample-return space missions, laboratory and computer simulations of extraterrestrial and early Earth environmental chemistry, astronomical remote sensing, and in-situ space exploration missions. Lately, scattered efforts are being undertaken towards the R&D of the novel and as-yet-space-unproven life-detection technologies capable of obtaining unambiguous evidence of extraterrestrial life, even if it is significantly different from Terran life. As the suite of space-proven payloads improves in breadth and sensitivity, this is an apt time to examine the progress and future of life-detection technologies.Comment: 6 pages, the white paper was submitted to and cited by the National Academy of Sciences in support of the Astrobiology Science Strategy for the Search for Life in the Univers

Improved high-temperature expansion and critical equation of state of three-dimensional Ising-like systems

High-temperature series are computed for a generalized $3d$ Ising model with arbitrary potential. Two specific ``improved'' potentials (suppressing leading scaling corrections) are selected by Monte Carlo computation. Critical exponents are extracted from high-temperature series specialized to improved potentials, achieving high accuracy; our best estimates are: $\gamma=1.2371(4)$, $\nu=0.63002(23)$, $\alpha=0.1099(7)$, $\eta=0.0364(4)$, $\beta=0.32648(18)$. By the same technique, the coefficients of the small-field expansion for the effective potential (Helmholtz free energy) are computed. These results are applied to the construction of parametric representations of the critical equation of state. A systematic approximation scheme, based on a global stationarity condition, is introduced (the lowest-order approximation reproduces the linear parametric model). This scheme is used for an accurate determination of universal ratios of amplitudes. A comparison with other theoretical and experimental determinations of universal quantities is presented.Comment: 65 pages, 1 figure, revtex. New Monte Carlo data by Hasenbusch enabled us to improve the determination of the critical exponents and of the equation of state. The discussion of several topics was improved and the bibliography was update

Size of third and fourth ventricle in obstructive and communicating acute hydrocephalus after aneurysmal subarachnoid hemorrhage

In patients with acute hydrocephalus after aneurysmal subarachnoid haemorrhage (SAH), lumbar drainage is possible if the obstruction is in the subarachnoid space (communicating hydrocephalus). In case of intraventricular obstruction (obstructive hydrocephalus), ventricular drainage is the only option. A small fourth ventricle is often considered a sign of obstructive hydrocephalus. We investigated whether the absolute or relative size of the fourth ventricle can indeed distinguish between these two types of hydrocephalus. On CT-scans of 76 consecutive patients with acute headache but normal CT and CSF, we measured the cross-sectional surface of the third and fourth ventricle to obtain normal planimetric values. Subsequently we performed the same measurements on 117 consecutive SAH patients with acute hydrocephalus. These patients were divided according to the distribution of blood on CT-scan into three groups: mainly intraventricular blood (n = 15), mainly subarachnoid blood (n = 54) and both intraventricular and subarachnoid blood (n = 48). The size of the fourth ventricle exceeded the upper limit of normal in 2 of the 6 (33%) patients with intraventricular blood but without haematocephalus, and in 15 of the 54 (28%) patients with mainly subarachnoid blood. The mean ratio between the third and fourth ventricle was 1.45 (SD 0.66) in patients with intraventricular blood and 1.42 (SD 0.91) in those with mainly subarachnoid blood. Neither fourth ventricular size nor the ratio between the third and fourth ventricles discriminates between the two groups. A small fourth ventricle does not necessarily accompany obstructive hydrocephalus and is therefore not a contraindication for lumbar drainage

Block of death-receptor apoptosis protects mouse cytomegalovirus from macrophages and is a determinant of virulence in immunodeficient hosts.

The inhibition of death-receptor apoptosis is a conserved viral function. The murine cytomegalovirus (MCMV) gene M36 is a sequence and functional homologue of the human cytomegalovirus gene UL36, and it encodes an inhibitor of apoptosis that binds to caspase-8, blocks downstream signaling and thus contributes to viral fitness in macrophages and in vivo. Here we show a direct link between the inability of mutants lacking the M36 gene (ΔM36) to inhibit apoptosis, poor viral growth in macrophage cell cultures and viral in vivo fitness and virulence. ΔM36 grew poorly in RAG1 knockout mice and in RAG/IL-2-receptor common gamma chain double knockout mice (RAGγC(-/-)), but the depletion of macrophages in either mouse strain rescued the growth of ΔM36 to almost wild-type levels. This was consistent with the observation that activated macrophages were sufficient to impair ΔM36 growth in vitro. Namely, spiking fibroblast cell cultures with activated macrophages had a suppressive effect on ΔM36 growth, which could be reverted by z-VAD-fmk, a chemical apoptosis inhibitor. TNFα from activated macrophages synergized with IFNγ in target cells to inhibit ΔM36 growth. Hence, our data show that poor ΔM36 growth in macrophages does not reflect a defect in tropism, but rather a defect in the suppression of antiviral mediators secreted by macrophages. To the best of our knowledge, this shows for the first time an immune evasion mechanism that protects MCMV selectively from the antiviral activity of macrophages, and thus critically contributes to viral pathogenicity in the immunocompromised host devoid of the adaptive immune system