Complex Memory Formation in Frictional Granular Media.

Using numerical simulations it is shown that a jammed, random pack of soft frictional grains can store an arbitrary waveform that is applied as a small time-dependent shear while the system is slowly compressed. When the system is decompressed at a later time, an approximation of the input waveform is recalled in time-reversed order as shear stresses on the system boundaries. This effect depends on friction between the grains, and is independent of some aspects of the friction model. This type of memory could potentially be observable in other types of random media that form internal contacts when compressed.

Synthesis, characterization and magnetic properties of polymer-Fe3O4 nanocomposite.

The chemical stability of magnetic particles is of great importance for their applications in medicine and biotechnology. The most challenging problem in physics of disordered systems of magnetic nanoparticles is the investigation of their dynamic properties. The chemical coprecipitation process was used to synthesize spherical magnetite nanoparticles of 14 nm. The as-prepared magnetite nanoparticles have been aged in the matrix. Magnetic properties and aging effect were studied by Mössbauer spectroscopy at temperatures ranging from 77 to 300 K, and X-ray diffraction. At room temperature, the Mössbauer spectrum showed superparamagnetic behavior of the particles, while well-defined sextets were observed at 77K, indicating a blocked regime. The superparamagnetic magnetite nanoparticles can be used as microbead biosensors.

NMR study of the dynamics of 3He impurities in the proposed supersolid state of solid 4He.

The dynamics of (3)He atoms in solid (4)He have been investigated by measuring the NMR relaxation times T(1) and T(2) in the region where a significant nonclassical rotational inertia fraction has been reported. For (3)He concentrations x(3)=16 and 24 ppm, changes are observed for both the spin-lattice relaxation time T(1) and the spin-spin relaxation time T(2) at the temperatures corresponding to the onset of the nonclassical rotational inertia fraction and, at lower temperatures, to the (3)He-(4)He phase separation. The magnitudes of T(1) and T(2) at temperatures above the phase separation agree roughly with existing theory based on the tunneling of (3)He impurities in the elastic strain field due to isotopic mismatch. However, a distinct peak in T(1) and a less well-resolved feature in T(2) are observed near the reported nonclassical rotational inertia fraction onset temperature, in contrast to the temperature-independent relaxation times predicted by the tunneling theory.

Giant viscosity enhancement in a spin-polarized fermi liquid.

The viscosity is measured for a Fermi liquid, a dilute 3He-4He mixture, under extremely high magnetic field/temperature conditions (Bor=1.5 mK). The spin-splitting energy microB is substantially greater than the Fermi energy kBTF; as a consequence the polarization tends to unity and s-wave quasiparticle scattering is suppressed for T<

Interstitial gas and density segregation of vertically vibrated granular media.

We report experimental studies of the effect of interstitial gas on mass-density segregation in a vertically vibrated mixture of equal-sized bronze and glass spheres. Sufficiently strong vibration in the presence of interstitial gas induces vertical segregation into sharply separated bronze and glass layers. We find that the segregated steady state (i.e., bronze or glass layer on top) is a sensitive function of gas pressure and viscosity, as well as vibration frequency and amplitude. In particular, we identify distinct regimes of behavior that characterize the change from bronze-on-top to glass-on-top steady state.

NMR experiments on a three-dimensional vibrofluidized granular medium.

A three-dimensional granular system fluidized by vertical container vibrations was studied using pulsed field gradient NMR coupled with one-dimensional magnetic resonance imaging. The system consisted of mustard seeds vibrated vertically at 50 Hz, and the number of layers N(l)

Applications of controlled-flow laser-polarized xenon gas to porous and granular media study.

We report initial NMR studies of continuous flow laser-polarized xenon gas, both in unrestricted tubing, and in a model porous media. The study uses Pulsed Gradient Spin Echo-based techniques in the gas-phase, with the aim of obtaining more sophisticated information than just translational self-diffusion coefficients. Pulsed Gradient Echo studies of continuous flow laser-polarized xenon gas in unrestricted tubing indicate clear diffraction minima resulting from a wide distribution of velocities in the flow field. The maximum velocity experienced in the flow can be calculated from this minimum, and is seen to agree with the information from the complete velocity spectrum, or motion propagator, as well as previously published images. The susceptibility of gas flows to parameters such as gas mixture content, and hence viscosity, are observed in experiments aimed at identifying clear structural features from echo attenuation plots of gas flow in porous media. Gas-phase NMR scattering, or position correlation flow-diffraction, previously clearly seen in the echo attenuation data from laser-polarized xenon flowing through a 2 mm glass bead pack is not so clear in experiments using a different gas mixture. A propagator analysis shows most gas in the sample remains close to static, while a small portion moves through a presumably near-unimpeded path at high velocities.

New evidence for zero-temperature relaxation in a spin-polarized fermi liquid.

Spin-echo experiments are reported for 3He-4He solutions under extremely high B/T conditions, B=14.75 T and T>or=1.73 mK. The 3He concentration x(3) was adjusted close to the value x(c) approximately 3.8% at which the spin-rotation parameter muM0 vanishes. In this way the transverse and longitudinal spin-diffusion coefficients D( perpendicular ),D( parallel ) were measured while keeping |muM(0)|<1. It is found that the temperature dependence of D( perpendicular ) deviates strongly from 1/T(2), with anisotropy temperature T(a)=4.26(+0.18)(-0.44) mK. This value is close to the theoretical prediction for dilute solutions and suggests that spin current relaxation remains finite as the temperature tends to zero.

Measurements of grain motion in a dense, three-dimensional granular fluid.

We have used an NMR technique to measure the short-time, three-dimensional displacement of grains in a system of mustard seeds vibrated vertically at 15 g. The technique averages over a time interval in which the grains move ballistically, giving a direct measurement of the granular temperature profile. The dense, lower portion of the sample is well described by a recent hydrodynamic theory for inelastic hard spheres. Near the free upper surface the mean free path is longer than the particle diameter and the hydrodynamic description fails.

Potential energy in a three-dimensional vibrated granular medium measured by NMR imaging

Fast NMR imaging was used to measure the density profile of a three-dimensional granular medium fluidized by vertical vibrations of the container. For container acceleration much larger than gravity, the rise in center of mass of the granular medium is found to scale as v(alpha)(0)/N(beta)(l) with alpha = 1.0+/-0.2 and beta = 0.5+/-0.1, where v(0) is the vibration velocity, and N(l) is the number of layers of grains in the container. This value for alpha is significantly less than found previously for experiments and simulations in one dimension ( alpha = 2) and two dimensions ( alpha = 1.3-1.5).

[Normal values of hemoglobin, hematocrit, blood coagulation factors, and fibrinolysis in New Zealand white rabbits]. / Valores normales de hemoglobina, hematocrito, factores de coagulación y fibrinolisis en conejos Nueva Zelanda blancos.

PURPOSE: To assess the normal rates of several haematological parameters along with coagulation and fibrinolysis values. MATERIAL AND METHODS: Male white New Zealand rabbits weighting between 1.5 and 2.5 kg. were used in variable amounts for each test (117-102). The following haematological determinations were carried out: haemoglobin, haematocrit, platelet count, and peripheral blood cell morphology. Prothrombin time, kaolin-activated partial thromboplastin time and thrombin time were assessed as well. Fibrinogen, plasminogen, prothrombin, factor V, factor X and factor XIII assays were also performed, along with tests for fibrinolytic activity and assay of fibrin and fibrinogen degradation products. All tests were compared with samples of pooled human and rabbit plasma. A statistical study was carried out including mean, mode, standard deviation, variation coefficient, confidence interval and chi square test plus Kolmogorow-Smirnoff test for normality assessment. RESULTS: The curves attained after plotting the figures for haematocrit, haemoglobin, platelet count, kaolin-activated partial thromboplastin time, thrombin time and factors II and X approached the normal values (p > 0.05). Asymmetric curves were achieved for fibrinogen, prothrombin time and plasminogen (p < 0.005). Rabbit anti-fibrinogen serum reacted with rabbit plasma and fibrinogen, but failed to react against human samples. No fibrin and/or fibrinogen degradation products were detected and no fibrinolytic activity was observed on fibrin plate assays. CONCLUSIONS: White New Zealand rabbits have values for haemoglobin, haematocrit and fibrinogen similar to the human ones. On the contrary, factors V, X and XIII, along with plasminogen, are in higher concentration, especially the former. Factor II is present at about half the human concentration. No fibrinolytic activity could be demonstrated with the methods used here.