Hard Spheres: Crystallization and Glass Formation

Motivated by old experiments on colloidal suspensions, we report molecular dynamics simulations of assemblies of hard spheres, addressing crystallization and glass formation. The simulations cover wide ranges of polydispersity s (standard deviation of the particle size distribution divided by its mean) and particle concentration. No crystallization is observed for s > 0.07. For 0.02 < s < 0.07, we find that increasing the polydispersity at a given concentration slows down crystal nucleation. The main effect here is that polydispersity reduces the supersaturation since it tends to stabilise the fluid but to destabilise the crystal. At a given polydispersity (< 0.07) we find three regimes of nucleation: standard nucleation and growth at concentrations in and slightly above the coexistence region; "spinodal nucleation", where the free energy barrier to nucleation appears to be negligible, at intermediate concentrations; and, at the highest concentrations, a new mechanism, still to be fully understood, which only requires small re-arrangement of the particle positions. The cross-over between the second and third regimes occurs at a concentration, around 58% by volume, where the colloid experiments show a marked change in the nature of the crystals formed and the particle dynamics indicate an "ideal" glass transition

Chandra Observations of A Galactic Supernova Remnant Vela Jr.: A New Sample of Thin Filaments Emitting Synchrotron X-Rays

A galactic supernova remnant (SNR) Vela Jr. (RX J0852.0$-$4622, G266.6$-$1.2) shows sharp filamentary structure on the north-western edge of the remnant in the hard X-ray band. The filaments are so smooth and located on the most outer side of the remnant. We measured the averaged scale width of the filaments ($w_u$ and $w_d$) with excellent spatial resolution of {\it Chandra}, which are in the order of the size of the point spread function of {\it Chandra} on the upstream side and 49.5 (36.0--88.8) arcsec on the downstream side, respectively. The spectra of the filaments are very hard and have no line-like structure, and were well reproduced with an absorbed power-law model with $\Gamma =$2.67 (2.55--2.77), or a {\tt SRCUT} model with $\nu_{rolloff}$ = 4.3 (3.4--5.3)$\times 10^{16}$ Hz under the assumption of $p=0.3$. These results imply that the hard X-rays are synchrotron radiation emitted by accelerated electrons, as mentioned previously. Using a correlation between a function ${\cal B} \equiv \nu_{rolloff}/w_d^2$ and the SNR age, we estimated the distance and the age of Vela Jr.: the estimated distance and age are 0.33 (0.26--0.50) kpc and 660 (420--1400) years, respectively. These results are consistent with previous reports, implying that ${\cal B}$--age relation may be a useful tool to estimate the distance and the age of synchrotron X-ray emitting SNRs.Comment: 19 pages, 8 figures, ApJ, in pres

Core-collapse model of broadband emission from SNR RX J1713.7-3946 with thermal X-rays and Gamma-rays from escaping cosmic rays

We present a spherically symmetric, core-collapse model of SNR RX J1713.7-3946 that includes a hydrodynamic simulation of the remnant evolution coupled to the efficient production of cosmic rays (CRs) by nonlinear diffusive shock acceleration (DSA). High-energy CRs that escape from the forward shock (FS) are propagated in surrounding dense material that simulates either a swept-up, pre-supernova shell or a nearby molecular cloud. The continuum emission from trapped and escaping CRs, along with the thermal X-ray emission from the shocked heated ISM behind the FS, integrated over the remnant, is compared against broadband observations. Our results show conclusively that, overall, the GeV-TeV emission is dominated by inverse-Compton from CR electrons if the supernova is isolated regardless of its type, i.e., not interacting with a >>100 Msun shell or cloud. If the SNR is interacting with a much larger mass >10^4 Msun, pion-decay from the escaping CRs may dominate the TeV emission, although a precise fit at high energy will depend on the still uncertain details of how the highest energy CRs are accelerated by, and escape from, the FS. Based on morphological and other constraints, we consider the 10^4 Msun pion-decay scenario highly unlikely for SNR RX J1713.7-3946 regardless of the details of CR escape. Importantly, even though CR electrons dominate the GeV-TeV emission, the efficient production of CR ions is an essential part of our leptonic model.Comment: 11 pages with 7 figures. Submitted to Ap

981-46 Impact of a Comprehensive Management Program on the Hospitalization Rate for Patients with Advanced Heart Failure

Patients with advanced heart failure have a course that is often characterized by frequent hospitalizations and progressive deterioration. These patients are commonly referred to specialized centers for consideration of heart transplantation (Tx). To assess the impact of the changes in therapy made in conjunction with heart transplantation evaluation on patient outcomes, we assessed the hospitalization rate and patient's functional status in the 6 months prior to referral compared to the 6 months after referral. Since 1/91, 214 patients were evaluated, accepted for Tx, and discharged having undergone adjustments in medical therapy and a comprehensive patient education program. At time of referral patients had mean LVEF 0.21, NYHA class 3.3, VO2 max 11.0ml/kg, and had undergone a total of 429 hospitalizations in the previous 6 months. During evaluation patients had their ACE inhibitor dose increased by a mean 91.5mg/day of captopril or the equivalent, were diuresed a mean 4.2 liters, were placed on a flexible regimen of loop diuretics, and were counseled on dietary management and home based progressive aerobic exercise. After 6 months of follow-up there were only 63 hospitalizations required (mean hospitalization rate per patient over the 6 months pre-evaluation 2.00±1.45 vs post-evaluation 0.29±0.53 p&lt;0.00001). Patient's NYHA class improved to 2.4 (p&lt;0.0001) and VO2 max increased to 15.2 (p&lt;0.001). Excluding the 12 elective status Tx, 14 urgent status Tx, and 9 deaths within 6 months yielded similar results (344 pre vs 34 post-evaluation hospitalizations). 64 patients (30%) improved their functional status to the point that transplantation was deferred in favor of sustained medical therapy.Referral to a heart failure specialty program is associated with a dramatic occurred between day 10±1 and 3 month. 4 patients died after hospital discharge (no death directly related to thromboembolic disease). Thus no higher risk of PE can be seen in patients with free floating prox-DVT and anticoagulant therapy should be efficient to prevent recurrent PE in such patient

On the interaction of a thin, supersonic shell with a molecular cloud

Molecular clouds (MCs) are stellar nurseries, however, formation of stars within MCs depends on the ambient physical conditions. MCs, over a free-fall time are exposed to numerous dynamical phenomena, of which, the interaction with a thin, dense shell of gas is but one. Below we present results from self-gravitating, 3-D smoothed particle hydrodynamics ({\small SPH}) simulations of the problem; seven realisations of the problem have been performed by varying the precollision density within the cloud, the nature of the post-collision shock, and the spatial resolution in the computational domain. Irrespective of the type of shock, a complex network of dense filaments, seeded by numerical noise, readily appears in the shocked cloud. Segregation of the dense and rarefied gas phases also manifests itself in a bimodal distribution of gas density. We demonstrate that the power-spectrum for rarefied gas is Kolomogorov like, while that for the denser gas is considerably steeper. As a corollary to the main problem, we also look into the possibly degenerative effect of the {\small SPH} artificial viscosity on the impact of the incident shell. It is observed that stronger viscosity leads to greater post-shock dissipation, that strongly decelerates the incident shock-front and promotes formation of contiguous structure, albeit on a much longer timescale. We conclude that too much viscosity is likely to enhance the proclivity towards gravitational boundedness of structure, leading to unphysical fragmentation.On the other hand, insufficient resolution appears to suppress fragmentation. Convergence of results is tested at both extremes, first by repeating the test case with more than a million particles and then with only half the number of particles in the original test case.Comment: 15 pages, 15 figures, and 1 Table; To appear in Monthly Notices to the RA

Nuclear structure of 30S and its implications for nucleosynthesis in classical novae

The uncertainty in the 29P(p,gamma)30S reaction rate over the temperature range of 0.1 - 1.3 GK was previously determined to span ~4 orders of magnitude due to the uncertain location of two previously unobserved 3+ and 2+ resonances in the 4.7 - 4.8 MeV excitation region in 30S. Therefore, the abundances of silicon isotopes synthesized in novae, which are relevant for the identification of presolar grains of putative nova origin, were uncertain by a factor of 3. To investigate the level structure of 30S above the proton threshold (4394.9(7) keV), a charged-particle spectroscopy and an in-beam gamma-ray spectroscopy experiments were performed. Differential cross sections of the 32S(p,t)30S reaction were measured at 34.5 MeV. Distorted wave Born approximation calculations were performed to constrain the spin-parity assignments of the observed levels. An energy level scheme was deduced from gamma-gamma coincidence measurements using the 28Si(3He,n-gamma)30S reaction. Spin-parity assignments based on measurements of gamma-ray angular distributions and gamma-gamma directional correlation from oriented nuclei were made for most of the observed levels of 30S. As a result, the resonance energies corresponding to the excited states in 4.5 MeV - 6 MeV region, including the two astrophysically important states predicted previously, are measured with significantly better precision than before. The uncertainty in the rate of the 29P(p,gamma)30S reaction is substantially reduced over the temperature range of interest. Finally, the influence of this rate on the abundance ratios of silicon isotopes synthesized in novae are obtained via 1D hydrodynamic nova simulations.Comment: 22 pages, 12 figure

Low-lying spectrum of the Y-string three-quark potential using hyper-spherical coordinates

We calculate the energies of three-quark states with definite permutation symmetry (i.e. of SU(6) multiplets) in the N=0,1,2 shells, confined by the Y-string three-quark potential. The exact Y-string potential consists of one, so-called three-string term, and three angle-dependent two-string terms. Due to this technical complication we treat the problem at three increasingly accurate levels of approximation: 1) the (approximate) three-string potential expanded to first order in trigonometric functions of hyper-spherical angles; 2) the (approximate) three-string potential to all orders in the power expansion in hyper-spherical harmonics, but without taking into account the transition(s) to two-string potentials; 3) the exact minimal-length string potential to all orders in power expansion in hyper-spherical harmonics, and taking into account the transition(s) to two-string potentials. We show the general trend of improvement %convergence of these approximations: The exact non-perturbative corrections to the total energy are of the order of one per cent, as compared with approximation 2), yet the exact energy differences between the $[20,1^{+}], [70,2^{+}], [56,2^{+}], [70,0^{+}]$-plets are shifted to 2:2:0.9, from the Bowler and Tynemouth separation rule 2:2:1, which is obeyed by approximation 2) at the one per cent level. The precise value of the energy separation of the first radial excitation ("Roper") $[56^{\prime},0^{+}]$-plet from the $[70,1^{-}]$-plet depends on the approximation, but does not become negative, i.e. the "Roper" remains heavier than the odd-parity $[70,1^{-}]$-plet in all of our approximations.Comment: 19 pages, 6 figure

948-46 Preserved Cardiac Baroreflex Control of Renal Cortical Blood Flow in Advanced Heart Failure Patients: A Positron Emission Tomography Study

Cardiac baroreflex (CBR) control of forearm blood flow (FBF) is blunted or reversed in humans with heart failure (HF). but little is known about CBR control of renal cortical blood flow (RCBF) in HF due to technical limitations. Positron emission tomography (PET) 0–15 water is a new, precise method to measure RCBF quantitatively. We compared CBR control of RCBF and FBF (venous plethysmography) in 8 patients with HF (mean age, 47±3 y, ejection fraction 0.25±0.02) and 10 normal humans (mean age 35±5 y) during CBR unloading with phlebotomy (450ml). In 5 normals, cold pressor test was used as a strong, non-baroreflex mediated stimulus to vasoconstriction.ResultsPhlebotomy decreased central venous pressure (p &lt;0.001), but did not change mean arterial pressure or heart rate in HF patients or controls. The major findings of the study are: 1) At rest, RCBF is markedly diminished in HF vs normals (2.4±0.1 vs 4.3±0.2ml/min/g, p &lt; 0.001). 2) In normal humans during phlebotomy, FBF decreased substantially (basal vs phlebotomy: 3.3±0.4 vs 2.6±0.3 ml/min/100 ml, p=0.021, and RCBF decreased slightly, but significantly (basal vs phlebotomy: 4.3±0.2 vs 4.0±0.3 ml/min/g, p=0.01). 3) The small magnitude of reflex renal vasoconstriction is not explained by the inability of the renal circulation to vasoconstrict since the cold pressor stimulus induced substantial decreases in RCBF in normals (basal vs cold pressor: 4.4±0.1 vs 3.7±0.1 ml/min/g, p=0.003). 4) In humans with heart failure during phlebotomy, FBF did not change (basal vs phlebotomy: 2.6±0.3 vs 2.7±0.2 ml/min/100 ml, p=NS), but RCBF decreased slightly but significantly (basal vs phlebotomy: 2.4±0.1 vs 2.1±0.1 ml/min/g, p=0.01). Thus, in patients with heart failure, there is an abnormality in cardiopulmonary baroreflex control of the forearm circulation, but not the renal circulationConclusionThis study 1) shows the power of PET to study physiologic and pathophysiologic reflex control of the renal circulation in humans, and 2) describes the novel finding of selective dysfunction of cardiac baroreflex control of the forearm circulation, but its preservation of the renal circulation, in patients with heart failur