Fluorescence visualization of a convective instability which modulates the spreading of volatile surface films

The spontaneous spreading of a thin liquid film along the surface of a deep liquid layer of higher surface tension is a ubiquitous process which provides rapid and efficient surface transport of organic or biological material. For a source of constant concentration, the leading edge of a nonvolatile, immiscible film driven to spread by gradients in surface tension is known to advance as t^3/4 in time. Recent experiments using laser shadowgraphy to detect the advancing front of spreading films indicate, however, that immiscible but volatile sources of constant concentration spread with a reduced exponent according to t^1/2. Using a novel technique whereby fluorescent lines are inscribed in water, we have detected the evolution of a thermal instability beneath the leading edge of volatile films which strongly resembles a Rayleigh-Bénard roll. We propose that the increased dissipation from this rotational flow structure is likely responsible for the reduction in spreading exponent. This observation suggests a conceptual framework for coupling the effects of evaporation to the dynamics of spreading

Theory of the Spin Excitations of Rb\u3csub\u3e2\u3c/sub\u3eMn\u3csub\u3ex\u3c/sub\u3eNi\u3csub\u3e1−x\u3c/sub\u3eF\u3csub\u3e4\u3c/sub\u3e

We give a systematic treatment of the spin excitations of a family of disordered quasi-two-dimensional Heisenberg antiferromagnets, Rb2MnxNi1−xF4, for arbitrary values of x. The density of states, static response functions, and the dynamic susceptibility are calculated numerically. Results at several concentrations are presented graphically. We derive simple analytic theories which give an adequate description of the calculated quantities. The static response functions characterize excitations at low energy and long wave length, and enable us to predict the concentration dependence of the anisotropy gap frequency and the temperature dependence of the magnetization. The dynamic susceptibility is in good agreement with recent neutron-scattering experiments on Rb2Mn0.5Ni0.5F4. The spin-wave density of states for 0.

Low-Frequency Response Functions of Random Magnetic Systems

The frequencies of long-wavelength spin waves in random magnets are studied through their relation to the static magnetic elastic constants A, the domain-wall stiffness, and (for antiferromagnets) χ⊥, the perpendicular susceptibility. We treat the classical limit of large spin and low temperature. In the case of random dilution A and χ⊥ are evaluated numerically as a function of magnetic concentration p for common lattices. Exact analytic results for the static susceptibility, χ(q), where q is the wave vector, are given for some models of disorder in one dimension and, for higher dimensionality, in the limit of low concentrations of vacancies. One general conclusion is that local fluctuations in the spin magnitude significantly affect χ⊥, causing it to diverge for isotropic random systems in two or fewer dimensions. If critical exponents are defined for p→pc by A~|p−pc|σ, χ⊥~|p−pc|−τ, P~|p−pc|β, and ξ~|p−pc|−ν, where pc is the percolation threshold, P is the percolation probability, and ξ is the correlation length, then our numerical results in three dimensions yield σ=1.6±0.1 and τ=0.5±0.2. A simple physical argument shows that τ≥σ−β+(2−d)ν. Our data are consistent with the possibility that this is an equality. Using mean-field-theory values for the exponents in this relation leads to a critical dimensionality dc=6. We study pc, A, and χ⊥ in diluted YIG and mixed garnets and give a detailed discussion of the regime near angular momentum compensation, where a low-frequency optical mode with both ω∝q and ω∝q2 regimes occurs. Our work contradicts the common assumption of a concentration-independent relationship between Tc and A or D, the spin-wave stiffness. We also present nonlinear calculations which allow us to study the dependence of χ⊥ on magnetic field. Our calculations agree with the experimental results on diluted KMnF3 and K2MnF4 and show that the observed nonlinearity is largely the result of local ferrimagnetic fluctuations. A novel configuration for elastic neutron scattering in the presence of a transverse magnetic field is proposed to permit direct observation of the magnitude and characteristic length scale of these fluctuations

Is the way to man's heart (and lung) through the abdomen?

Intra-abdominal hypertension is increasingly recognized to be both prevalent and clinically important in medical and surgical intensive care units. Intra-abdominal pressure (IAP) can impact organ function throughout the body, and it can also complicate standard measurements used in intensive care units. The article by Krebs and colleagues reports the effect of IAP on respiratory function, gas exchange and hemodynamic function. Their results show a relatively small effect of modestly elevated IAP on these variables in their patient population. However, their work raises several questions for clinicians and researchers regarding the pathophysiology and management of IAP

Cryogenic microstripline-on-Kapton microwave interconnects

Simple broadband microwave interconnects are needed for increasing the size of focal plane heterodyne radiometer arrays. We have measured loss and cross-talk for arrays of microstrip transmission lines in flex circuit technology at 297 and 77 K, finding good performance to at least 20 GHz. The dielectric constant of Kapton substrates changes very little from 297 to 77 K, and the electrical loss drops. The small cross-sectional area of metal in a printed circuit structure yields overall thermal conductivities similar to stainless steel coaxial cable. Operationally, the main performance tradeoffs are between crosstalk and thermal conductivity. We tested a patterned ground plane to reduce heat flux.Comment: 3 pages, 3 figures, submitted to The Review of Scientific Instrument

Deep Inspiration and the Emergence of Ventilation Defects during Bronchoconstriction: A Computational Study

Deep inspirations (DIs) have a dilatory effect on airway smooth muscle (ASM) that helps to prevent or reduce more severe bronchoconstriction in healthy individuals. However, this bronchodilation appears to fail in some asthmatic patients or under certain conditions, and the reason is unclear. Additionally, quantitative effects of the frequency and magnitude of DIs on bronchodilation are not well understood. In the present study, we used a computational model of bronchoconstriction to study the effects of DI volumes, time intervals between intermittent DIs, relative speed of ASM constriction, and ASM activation on bronchoconstriction and the emergence of ventilation defects (VDefs). Our results showed a synergistic effect between the volume of DIs and the time intervals between them on bronchoconstriction and VDefs. There was a domain of conditions with sufficiently large volumes of DIs and short time intervals between them to prevent VDefs. Among conditions without VDefs, larger volumes of DIs resulted in greater airway dilation. Similarly, the time interval between DIs, during which the activated ASM re-constricts, affected the amplitude of periodic changes in airway radii. Both the relative speed of ASM constriction and ASM activation affected what volume of DIs and what time interval between them could prevent the emergence of VDefs. In conclusion, quantitative characteristics of DIs, such as their volume and time interval between them, affect bronchoconstriction and may contribute to difficulties in asthma. Better understanding of the quantitative aspects of DIs may result in novel or improved therapeutic approaches

A Deep ROSAT HRI Observation of NGC 1313

We describe a series of observations of NGC 1313 using the ROSAT HRI with a combined exposure time of 183.5 ksec. The observations span an interval between 1992 and 1998; the purpose of observations since 1994 was to monitor the X-ray flux of SN1978K, one of several luminous sources in the galaxy. No diffuse emission is detected in the galaxy to a level of ~1-2x10^37 ergs/s/arcmin^-2. A total of eight sources are detected in the summed image within the D_25 diameter of the galaxy. The luminosities of five of the eight range from \~6x10^37 to ~6x10^38 erg/s; these sources are most likely accreting X-ray binaries, similar to sources obseved in M31 and M33. The remaining three sources all emit above 10^39 erg/s. We present light curves of the five brightest sources. Variability is detected at the 99.9% level from four of these. We identify one of the sources as an NGC 1313 counterpart of a Galactic X-ray source. The light curve, though crudely sampled, most closely resembles that of a Galactic black hole candidate such as GX339-4, but with considerably higher peak X-ray luminosity. An additional seven sources lie outside of the D_25 diameter and are either foreground stars or background AGN.Comment: 18 pages, 9 figures; accepted AJ, scheduled for November 200

Generic local distinguishability and completely entangled subspaces

A subspace of a multipartite Hilbert space is completely entangled if it contains no product states. Such subspaces can be large with a known maximum size, S, approaching the full dimension of the system, D. We show that almost all subspaces with dimension less than or equal to S are completely entangled, and then use this fact to prove that n random pure quantum states are unambiguously locally distinguishable if and only if n does not exceed D-S. This condition holds for almost all sets of states of all multipartite systems, and reveals something surprising. The criterion is identical for separable and for nonseparable states: entanglement makes no difference.Comment: 12 page

Effect of varying the concentrations of carbohydrate and milk protein in rehydration solutions ingested after exercise in the heat

The present study investigated the relationship between the milk protein content of a rehydration solution and fluid balance after exercise-induced dehydration. On three occasions, eight healthy males were dehydrated to an identical degree of body mass loss (BML, approximately 1.8 %) by intermittent cycling in the heat, rehydrating with 150 % of their BML over 1 h with either a 60 g/l carbohydrate solution (C), a 40 g/l carbohydrate, 20 g/l milk protein solution (CP20) or a 20 g/l carbohydrate, 40 g/l milk protein solution (CP40). Urine samples were collected pre-exercise, post-exercise, post-rehydration and for a further 4 h. Subjects produced less urine after ingesting the CP20 or CP40 drink compared with the C drink (P<0.01), and at the end of the study, more of the CP20 (59 (SD 12) %) and CP40 (64 (SD 6) %) drinks had been retained compared with the C drink (46 (SD 9) %) (P,0.01). At the end of the study, whole-body net fluid balance was more negative for trial C (2470 (SD 154) ml) compared with both trials CP20 (2181 (SD 280) ml) and CP40 (2107 (SD 126) ml) (P<0.01). At 2 and 3 h after drink ingestion, urine osmolality was greater for trials CP20 and CP40 compared with trial C (P<0.05). The present study further demonstrates that after exercise-induced dehydration, a carbohydrate–milk protein solution is better retained than a carbohydrate solution. The results also suggest that high concentrations of milk protein are not more beneficial in terms of fluid retention than low concentrations of milk protein following exercise-induced dehydration