Glasslike Arrest in Spinodal Decomposition as a Route to Colloidal Gelation

Colloid-polymer mixtures can undergo spinodal decomposition into colloid-rich and colloid-poor regions. Gelation results when interconnected colloid-rich regions solidify. We show that this occurs when these regions undergo a glass transition, leading to dynamic arrest of the spinodal decomposition. The characteristic length scale of the gel decreases with increasing quench depth, and the nonergodicity parameter exhibits a pronounced dependence on scattering vector. Mode coupling theory gives a good description of the dynamics, provided we use the full static structure as input.Comment: 14 pages, 4 figures; replaced with published versio

Ionic Coulomb blockade and anomalous mole fraction effect in NaChBac bacterial ion channels

We report an experimental study of the influences of the fixed charge and bulk ionic concentrations on the conduction of biological ion channels, and we consider the results within the framework of the ionic Coulomb blockade model of permeation and selectivity. Voltage clamp recordings were used to investigate the Na$^+$/Ca$^{2+}$ anomalous mole fraction effect (AMFE) exhibited by the bacterial sodium channel NaChBac and its mutants. Site-directed mutagenesis was used to study the effect of either increasing or decreasing the fixed charge in their selectivity filters for comparison with the predictions of the Coulomb blockade model. The model was found to describe well some aspects of the experimental (divalent blockade and AMFE) and simulated (discrete multi-ion conduction and occupancy band) phenomena, including a concentration-dependent shift of the Coulomb staircase. These results substantially extend the understanding of ion channel selectivity and may also be applicable to biomimetic nanopores with charged walls

sl(N) Onsager's Algebra and Integrability

We define an $sl(N)$ analog of Onsager's Algebra through a finite set of relations that generalize the Dolan Grady defining relations for the original Onsager's Algebra. This infinite-dimensional Lie Algebra is shown to be isomorphic to a fixed point subalgebra of $sl(N)$ Loop Algebra with respect to a certain involution. As the consequence of the generalized Dolan Grady relations a Hamiltonian linear in the generators of $sl(N)$ Onsager's Algebra is shown to posses an infinite number of mutually commuting integrals of motion

The magnetic field of IRAS 16293-2422 as traced by shock-induced H2O masers

Shock-induced H2O masers are important magnetic field tracers at very high density gas. Water masers are found in both high- and low-mass star-forming regions, acting as a powerful tool to compare magnetic field morphologies in both mass regimes. In this paper, we show one of the first magnetic field determinations in the low-mass protostellar core IRAS 16293-2422 at volume densities as high as 10^(8-10) cm^-3. Our goal is to discern if the collapsing regime of this source is controlled by magnetic fields or other factors like turbulence. We used the Very Large Array (VLA) to carry out spectro-polarimetric observations in the 22 GHz Zeeman emission of H2O masers. From the Stokes V line profile, we can estimate the magnetic field strength in the dense regions around the protostar. A blend of at least three maser features can be inferred from our relatively high spatial resolution data set (~ 0.1"), which is reproduced in a clear non-Gaussian line profile. The emission is very stable in polarization fraction and position angle across the channels. The maser spots are aligned with some components of the complex outflow configuration of IRAS 16293-2422, and they are excited in zones of compressed gas produced by shocks. The post-shock particle density is in the range of 1-3 x 10^9 cm^-3, consistent with typical water masers pumping densities. Zeeman emission is produced by a very strong line-of-sight magnetic field (B ~ 113 mG). The magnetic field pressure derived from our data is comparable to the ram pressure of the outflow dynamics. This indicates that the magnetic field is energetically important in the dynamical evolution of IRAS 16293-2422.Comment: 7 pages, 6 figures, accepted for publication in A&

High permeability explains the vulnerability of the carbon store in drained tropical peatlands

Tropical peatlands are an important global carbon (C) store but are threatened by drainage for palm oil and wood pulp production. The store's stability depends on the dynamics of the peatland water table, which in turn depend on peat permeability. We found that an example of the most abundant type of tropical peatland—ombrotrophic domes—has an unexpectedly high permeability similar to that of gravel. Using computer simulations of a natural peat dome (NPD) and a ditch-drained peat dome (DPD) we explored how such high permeability affects water tables and peat decay. High permeability has little effect on NPD water tables because of low hydraulic gradients from the center to the margin of the peatland. In contrast, DPD water tables are consistently deep, leaving the upper meter of peat exposed to rapid decay. Our results reveal why ditch drainage precipitates a rapid destabilization of the tropical peatland C store

Multi-threshold second-order phase transition

We present a theory of the multi-threshold second-order phase transition, and experimentally demonstrate the multi-threshold second-order phase transition phenomenon. With carefully selected parameters, in an external cavity diode laser system, we observe second-order phase transition with multiple (three or four) thresholds in the measured power-current-temperature three dimensional phase diagram. Such controlled death and revival of second-order phase transition sheds new insight into the nature of ubiquitous second-order phase transition. Our theory and experiment show that the single threshold second-order phase transition is only a special case of the more general multi-threshold second-order phase transition, which is an even richer phenomenon.Comment: 5 pages, 3 figure

New apparatus for DTA at 2000 bar: thermodynamic studies on Au, Ag, Al and HTSC oxides

A new DTA (Differential Thermal Analysis) device was designed and installed in a Hot Isostatic Pressure (HIP) furnace in order to perform high-pressure thermodynamic investigations up to 2 kbar and 1200C. Thermal analysis can be carried out in inert or oxidising atmosphere up to p(O2) = 400 bar. The calibration of the DTA apparatus under pressure was successfully performed using the melting temperature (Tm) of pure metals (Au, Ag and Al) as standard calibration references. The thermal properties of these metals have been studied under pressure. The values of DV (volume variation between liquid and solid at Tm), ROsm (density of the solid at Tm) and ALPHAm (linear thermal expansion coefficient at Tm) have been extracted. A very good agreement was found with the existing literature and new data were added. This HP-DTA apparatus is very useful for studying the thermodynamics of those systems where one or more volatile elements are present, such as high TC superconducting oxides. DTA measurements have been performed on Bi,Pb(2223) tapes up to 2 kbar under reduced oxygen partial pressure (p(O2) = 0.07 bar). The reaction leading to the formation of the 2223 phase was found to occur at higher temperatures when applying pressure: the reaction DTA peak shifted by 49C at 2 kbar compared to the reaction at 1 bar. This temperature shift is due to the higher stability of the Pb-rich precursor phases under pressure, as the high isostatic pressure prevents Pb from evaporating.Comment: 6 figures, 3 tables, Thermodynamics, Thermal property, Bi-2223, fundamental valu

Measurement of the 12C(e,e'p)11B Two-Body Breakup Reaction at High Missing Momentum Values

The five-fold differential cross section for the 12C(e,e'p)11B reaction was determined over a missing momentum range of 200-400 MeV/c, in a kinematics regime with Bjorken x > 1 and Q2 = 2.0 (GeV/c)2. A comparison of the results and theoretical models and previous lower missing momentum data is shown. The theoretical calculations agree well with the data up to a missing momentum value of 325 MeV/c and then diverge for larger missing momenta. The extracted distorted momentum distribution is shown to be consistent with previous data and extends the range of available data up to 400 MeV/c.Comment: 12 pages, 1 table and 3 figures for submission to Journal Physics

Fibromuscular Arterial Disease

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75604/1/j.1440-1673.1970.tb01633.x.pd