Measurement of the analyzing power in p-->d-->(p p)n with a fast forward 1S0 proton pair

A measurement of the analyzing power A(y) of the p-->d--> (p p) + n reaction was carried out at the ANKE spectrometer at COSY at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy E(pp) < 3 MeV. The S-wave dominance in the fast diproton is experimentally demonstrated in this reaction. While at T(p) = 0.8 GeV the measured analyzing power almost vanishes, it rises to nearly unity at T(p) = 0.5 GeV for neutrons emitted at theta(c.m.)(n) = 167 degrees. The results are compared with a model taking into account one-nucleon exchange, single scattering, and Delta(1232) excitation in the intermediate state. The model describes fairly well the unpolarized cross section obtained earlier and the analyzing power at 0.8 GeV; it fails to reproduce A(y) at 0.5 GeV.     

Surface-charge-governed ion transport in nanofluidic channels

A study of ion transport in aqueous-filled silica channels as thin as 70 nm reveals a remarkable degree of conduction at low salt concentrations that departs strongly from bulk behavior: In the dilute limit, the electrical conductances of channels saturate at a value that is independent of both the salt concentration and the channel height. Our data are well described by an electrokinetic model parametrized only by the surface-charge density. Using chemical surface modifications, we further demonstrate that at low salt concentrations, ion transport in nanochannels is governed by the surface charge.     

Differential inhibition of postnatal brain,spinal cord and body growth by a growth hormone antagonist

Background  

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.     

Steady shear rate rheology of suspensions, as described by the giant floc model

The break-down of a particle network by shear is described as the development of shear planes: a region able to withstand low shear stresses may break down under a larger stress; thus with increasing shear stress and shear rate, the mutual distance (A) between successive shear planes decreases until, at very high shear rates, A approaches the particle diameter. The shear planes are idealised as flat planes. Energy dissipation during shear is predominantly due to the energy dissipated through the movement of the particles; the energy dissipation due to breakage and renewed formation of bonds between particles is relatively small. A consideration of the energy dissipated during the encounters of particles during shear, including that dissipated by entrained particles, then leads to a relation between this energy dissipation and the average fraction L, over which a moving particle entrains a neighbour. L includes the effect of parts of the network which are rotating under the influence of the shear. In the limit of large shear rates, L is found to depend only to a small extent on whether the suspension is coagulated or not.     

The Electroviscous Behavior of Aqueous Dispersions of Amorphous Silica (Ludox)

The electroviscous effects in very dilute aqueous dispersions of amorphous silica (Ludox) were investigated at various levels of salt, pH, and volume fraction (<0.01) of solids. Viscosities were much higher than predicted from existing theories, which is ascribed to the formation of a thick, gel-like surface layer on the particle. The volume of a particle adjusts itself almost reversibly to the salt and pH levels of the liquid and can grow up to four times the dry volume. This explains the apparent discrepancy between published dry and wet particle sizes and also the reported anomalously large number of bound water layers around a particle. The existence of a gel layer leads to an abnormally large amount of surface conductance; this may explain the anomalities found in electrophoresis. The validity of the model is also supported by published results of the amount of nonbulk water as found with NMR. Copyright 2001 Academic Press.     

Aging in 1D discrete spin models and equivalent systems

We derive exact expressions for a number of aging functions that are scaling limits of nonequilibrium correlations, R(t(w),t(w)+t) as t(w)-->infinity, t/t(w)-->theta, in the 1D homogenous q-state Potts model for all q with T = 0 dynamics following a quench from T = infinity. One such quantity is (0)(t(w));sigma-->(n)(t(w)+t)> when n/square root of ([t(w))-->z. Exact, closed-form expressions are also obtained when an interlude of T = infinity dynamics occurs. Our derivations express the scaling limit via coalescing Brownian paths and a "Brownian space-time spanning tree," which also yields other aging functions, such as the persistence probability of no spin flip at 0 between t(w) and t(w)+t.     

Analysis of the Xedni Calculus Attack

The xedni calculus attack on the elliptic curve discrete logarithm problem (ECDLP) involves lifting points from the finite field to the rational numbers and then constructing an elliptic curve over that passes through them. If the lifted points are linearly dependent, then the ECDLP is solved. Our purpose is to analyze the practicality of this algorithm. We find that asymptotically the algorithm is virtually certain to fail, because of an absolute bound on the size of the coefficients of a relation satisfied by the lifted points. Moreover, even for smaller values of p experiments show that the odds against finding a suitable lifting are prohibitively high.     

Ratchet driven by quasimonochromatic noise

The currents generated by noise-induced activation processes in a periodic potential are investigated analytically, by digital simulation and by performing analog experiments. The noise is taken to be quasimonochromatic and the potential to be a smoothed sawtooth. Two analytic approaches are studied. The first involves a perturbative expansion in inverse powers of the frequency characterizing quasimonochromatic noise and the second is a direct numerical integration of the deterministic differential equations obtained in the limit of weak noise. These results, together with the digital and analog experiments, show that the system does indeed give rise, in general, to a net transport of particles. All techniques also show that a current reversal exists for a particular value of the noise parameters.     

Symmetry breaking of fluctuation dynamics by noise color

Activated escape is investigated for systems that are driven by noise whose power spectrum peaks at a finite frequency. Analytic theory and analog and digital experiments show that the system dynamics during escape exhibit a symmetry-breaking transition as the width of the fluctuational spectral peak is varied. For double-well potentials, even a small asymmetry may result in a parametrically large difference of the activation energies for escape from different wells.