Chemical Association via Exact Thermodynamic Formulations

It can be fruitful to view two-component physical systems of attractive monomers, A and B, ``chemically'' in terms of a reaction A + B C, where C = AB is an associated pair or complex. We show how to construct free energies in the three-component or chemical picture which, under mass-action equilibration, exactly reproduce any given two-component or ``physical'' thermodynamics. Order-by-order matching conditions and closed-form chemical representations reveal the freedom available to modify the A-C, B-C, and C-C interactions and to adjust the association constant. The theory (in the simpler one-component, i.e., A = B, case) is illustrated by treating a van der Waals fluid.Comment: 15 double-spaced pages (RevTeX), including 1 eps figur

Transitions From Skilled Nursing Facility to Home: The Relationship of Early Outpatient Care to Hospital Readmission

BACKGROUND: Many adults are discharged to skilled nursing facilities (SNFs) prior to returning home from the hospital. Patient characteristics and factors that can help to prevent postdischarge adverse outcomes are poorly understood. OBJECTIVE: To identify whether early post-SNF discharge care reduces likelihood of 30-day hospital readmissions. DESIGN: Secondary data analysis using the Electronic Medical Record, Medicare, Medicaid and the Minimum Data Set. PARTICIPANTS/SETTING: Older (age > 65 years), community-dwelling adults admitted to a safety net hospital in the Midwest for 3 or more nights and discharged home after an SNF stay (n = 1543). MEASUREMENTS: The primary outcome was hospital readmission within 30 days of SNF discharge. The primary independent variables were either a home health visit or an outpatient provider visit within a week of SNF discharge. RESULTS: Out of 8754 community-dwelling, hospitalized older adults, 3025 (34.6%) were discharged to an SNF, of whom 1543 (51.0%) returned home. Among the SNF to home group, a home health visit within a week of SNF discharge was associated with reduced hazard of 30-day hospital readmission [adjusted hazard ratio (aHR) 0.61, P < .001] but outpatient provider visits were not associated with reduced risk of hospital readmission (aHR = 0.67, P = .821). CONCLUSION: For patients discharged from an SNF to home, the finding that a home health visit within a week of discharge is associated with reduced hazard of 30-day hospital readmissions suggests a potential avenue for intervention

Derivation of Hebb's rule

On the basis of the general form for the energy needed to adapt the connection strengths of a network in which learning takes place, a local learning rule is found for the changes of the weights. This biologically realizable learning rule turns out to comply with Hebb's neuro-physiological postulate, but is not of the form of any of the learning rules proposed in the literature. It is shown that, if a finite set of the same patterns is presented over and over again to the network, the weights of the synapses converge to finite values. Furthermore, it is proved that the final values found in this biologically realizable limit are the same as those found via a mathematical approach to the problem of finding the weights of a partially connected neural network that can store a collection of patterns. The mathematical solution is obtained via a modified version of the so-called method of the pseudo-inverse, and has the inverse of a reduced correlation matrix, rather than the usual correlation matrix, as its basic ingredient. Thus, a biological network might realize the final results of the mathematician by the energetically economic rule for the adaption of the synapses found in this article.Comment: 29 pages, LaTeX, 3 figure

Fractionation effects in phase equilibria of polydisperse hard sphere colloids

The equilibrium phase behaviour of hard spheres with size polydispersity is studied theoretically. We solve numerically the exact phase equilibrium equations that result from accurate free energy expressions for the fluid and solid phases, while accounting fully for size fractionation between coexisting phases. Fluids up to the largest polydispersities that we can study (around 14%) can phase separate by splitting off a solid with a much narrower size distribution. This shows that experimentally observed terminal polydispersities above which phase separation no longer occurs must be due to non-equilibrium effects. We find no evidence of re-entrant melting; instead, sufficiently compressed solids phase separate into two or more solid phases. Under appropriate conditions, coexistence of multiple solids with a fluid phase is also predicted. The solids have smaller polydispersities than the parent phase as expected, while the reverse is true for the fluid phase, which contains predominantly smaller particles but also residual amounts of the larger ones. The properties of the coexisting phases are studied in detail; mean diameter, polydispersity and volume fraction of the phases all reveal marked fractionation. We also propose a method for constructing quantities that optimally distinguish between the coexisting phases, using Principal Component Analysis in the space of density distributions. We conclude by comparing our predictions to perturbative theories for near-monodisperse systems and to Monte Carlo simulations at imposed chemical potential distribution, and find excellent agreement.Comment: 21 pages, 23 figures, 2 table

Atypical Chryseobacterium meningosepticum and meningitis and sepsis in newborns and the immunocompromised, Taiwan.

From 1996 to 1999, 17 culture-documented systemic infections due to novel, atypical strains of Chryseobacterium meningosepticum occurred in two newborns and 15 immunocompromised patients in a medical center in Taiwan. All clinical isolates, which were initially misidentified as Aeromonas salmonicida by an automated bacterial identification system, were resistant to a number of antimicrobial agents. The isolates were characterized as atypical strains of C. meningosepticum by complete biochemical investigation, 16S rRNA gene sequence analysis, cellular fatty acid analysis, and random amplified polymorphic DNA fingerprinting (RAPD). This is the first report of a cluster of atypically variant strains of C. meningosepticum, which may be an emerging pathogen in newborns and the immunocompromised

Phase separation in mixtures of colloids and long ideal polymer coils

Colloidal suspensions with free polymer coils which are larger than the colloidal particles are considered. The polymer-colloid interaction is modeled by an extension of the Asakura-Oosawa model. Phase separation occurs into dilute and dense fluid phases of colloidal particles when polymer is added. The critical density of this transition tends to zero as the size of the polymer coils diverges.Comment: 5 pages, 3 figure

Parity forbidden excitations of Sr2CuO2Cl2 revealed by optical third-harmonic spectroscopy

We present the first study of nonlinear optical third harmonic generation in the strongly correlated charge-transfer insulator Sr2CuO2Cl2. For fundamental excitation in the near-infrared, the THG spectrum reveals a strongly resonant response for photon energies near 0.7 eV. Polarization analysis reveals this novel resonance to be only partially accounted for by three-photon excitation to the optical charge-transfer exciton, and indicates that an even-parity excitation at 2 eV, with a_1g symmetry, participates in the third harmonic susceptibility.Comment: Requires RevTeX v4.0beta

Phase transitions in a ferrofluid at magnetic field induced microphase separation

In the presence of a magnetic field applied perpendicular to a thin sample layer, a suspension of magnetic colloidal particles (ferrofluid) can form spatially modulated phases with a characteristic length determined by the competition between dipolar forces and short-range forces opposing density variations. We introduce models for thin-film ferrofluids in which magnetization and particle density are viewed as independent variables and in which the non-magnetic properties of the colloidal particles are described either by a lattice-gas entropy or by the Carnahan-Starling free energy. Our description is particularly well suited to the low-particle density regions studied in many experiments. Within mean-field theory, we find isotropic, hexagonal and stripe phases, separated in general by first-order phase boundaries.Comment: 12 pages, RevTex, to appear in PR

Structure of ternary additive hard-sphere fluid mixtures

Monte Carlo simulations on the structural properties of ternary fluid mixtures of additive hard spheres are reported. The results are compared with those obtained from a recent analytical approximation [S. B. Yuste, A. Santos, and M. Lopez de Haro, J. Chem. Phys. 108, 3683 (1998)] to the radial distribution functions of hard-sphere mixtures and with the results derived from the solution of the Ornstein-Zernike integral equation with both the Martynov-Sarkisov and the Percus-Yevick closures. Very good agreement between the results of the first two approaches and simulation is observed, with a noticeable improvement over the Percus-Yevick predictions especially near contact.Comment: 11 pages, including 8 figures; A minor change; accepted for publication in PR