Advanced memory effects in the aging of a polymer glass

A new kind of memory effect on low frequency dielectric measurements on plexiglass (PMMA) is described. These measurements show that cooling and heating the sample at constant rate give an hysteretic dependence on temperature of the dielectric constant $\epsilon$. A temporary stop of cooling produces a downward relaxation of $\epsilon$. Two main features are observed i) when cooling is resumed $\epsilon$ goes back to the values obtained without the cooling stop (i.e. the low temperature state is independent of the cooling history) ii) upon reheating $\epsilon$ keeps the memory of all the cooling stops({\it Advanced memory}). The dependence of this effect on frequency and on the cooling rate is analyzed. The memory deletion is studied too. Finally the results are compared with those of similar experiments done in spin glasses and with the famous experiments of Kovacs.Comment: to be published in the European Physical Journa

Analysis of Expedient Field Decontamination Methods for the XMX/2L-MIL High-Volume Aerosol Sampler

The XMX/2L-MIL is a high volume air sampler used by the Air Force Bioenvironmental Engineering community to collect biological aerosols. Without a verified decontamination technique, however, the XMX cannot be used effectively. The objective of this study was to evaluate several proposed methods for expedient field decontamination of the XMX. This study centered on the inactivation of Bacillus atrophaeus spores and vegetative Erwinia herbicola organisms from the XMX inner canister. The goals in this investigation were twofold: 1) to verify the antimicrobial efficacy of a 10% bleach solution and 2) to determine if wiping the components with a bleach-soaked paper towel or submerging the components directly in the bleach solution represents the optimal decontamination procedure. Data was gathered at the Dycor Technologies facility located in Edmonton, Alberta, Canada. Their Aerosol Test Chamber was used to disseminate the surrogate agents and then sample the aerosol using three XMX devices. Counts of the microbial population were calculated at each stage of the procedure to assess the efficacy of the two proposed methods. It was observed that 10% bleach solutions resulted in approximately 102-fold decreases in aggregate microbial contamination on XMX components. Of the methods tested, the submersion in a 10% bleach solution plus a 15-minute air purge showed the most efficiency. Contamination levels were consistent between all three devices during the trial and were measured at or below background levels after decontamination

Compaction dynamics of a granular media under vertical tapping

We report new experimental results on granular compaction under consecutive vertical taps. The evolution of the mean volume fraction and of the mean potential energy of a granular packing presents a slow densification until a final steady-state, and is reminiscent to usual relaxation in glasses via a stretched exponential law. The intensity of the taps seems to rule the characteristic time of the relaxation according to an Arrhenius's type relation >. Finally, the analysis of the vertical volume fraction profile reveals an almost homogeneous densification in the packing.Comment: 7 pages, 4 figures, to appear in Europhysics Letter

Pressure measurement in two-dimensional horizontal granular gases

International audienceA two-dimensional granular gas is produced by vibrating vertically a partial layer of beads on a horizontal plate. Measurements of the force applied by the granular gas to the sidewalls of the container, or granular pressure, are used to study the effect of the shaking strength, density, bead-plate restitution coefficient, and particle size on the steady properties of the gas

VHF discharges in storm cells producing microbursts

An experiment was carried out in which 3-D mapping of VHF sources was compared to a 3-D description of the reflectivity and dynamics of associated cloud cells observed by a radar network. Data from 61 microbursts were analyzed and it was found that, in 93 pct. of the cases, electrical activity precedes outflow development. The results confirm that the peak in intracloud activity precedes the maximum value of the outflow

Energy of a single bead bouncing on a vibrating plate: Experiments and numerical simulations

International audienceThe energy of a single bead bouncing on a vibrating plate is determined in simulations and experiments by tracking the bead-plate collision times. The plate oscillates sinusoidally along the vertical with the dimension-less peak acceleration ⌫, and the bead-plate collisions are characterized by the velocity restitution coefficient ⑀. Above the threshold dimensionless peak acceleration ⌫ s Ӎ0.85, which does not depend on the restitution coefficient, the bead energy is shown to initially increase linearly with the vibration amplitude A, whereas it is found to scale like v p 2 /(1Ϫ⑀), where v p is the peak velocity of the plate, only in the limit ⌫ӷ⌫ s. The threshold ⌫ s is shown to decrease when the bead is subjected, in simulations, to additional nondissipative collisions occurring with the typical frequency ␯ c. As a consequence, the bead energy scales like v p 2 /(1Ϫ⑀) for all vibration strengths in the limit ␯ c ӷ␯ c *. From the experimental and numerical findings, an analytical expression of the bead energy as a function of the experimental parameters is proposed. As they exhibit a wide range of unusual behaviors, granu-lar materials are the subject of intensive investigations ͓1–3͔. Because of the inelastic nature of the contacts between the grains, these systems are intrinsically dissipative. In order to explore experimentally the effects of the dissipation on the properties of granular systems, it is convenient to produce stationary states; they are achieved by continuously providing the system with energy, compensating the energy intrin-sically lost when the grains are in motion. Among these studies , one can note the experimental realization of two-dimensional (2D) granular gases, consisting of inelastic beads constituting less than one-layer coverage on a vertically shaken, horizontal plate ͓4 –8͔ ͑the experimental situation has been the framework of molecular-dynamics simulations by Nie et al. ͓9͔͒. The velocity distributions, granular temperature, pressure, as well as phase transitions have been studied as functions of the vibration strength, usually characterized by the peak plate acceleration ⌫. Nevertheless, detailed analysis of the clustering transition and of the pressure indicates that the vibrating boundary becomes inefficient to thermalize the system when the acceleration or the density of the gas are decreased. The energy input by the vibrating boundary has been the subject of several theoretical studies ͓10–13͔; the scaling law for the energy as a function of the vibration strength has been shown to depend on the shape of the boundary vibration ͑sinusoidal, sawtooth, etc.͒ and on the nature of the dissipation within the gas ͑viscous, inelastic͒. In these studies, the assumption was made that the bead impinges randomly on the boundary; we note that this is not the case when the bead collides more than once with the boundary between two collisions with another bead. One can easily show that the velocity is exponentially correlated between two successive collisions in this case. It is hence relevant to study the dynamical behavior of a single bead bouncing on a vibrating plate, and to determine the mean energy ͗E͘ of th

Co-Branding Internationally: Everyone Wins?

Co-branding is an increasingly popular technique used primarily in domestic markets to transfer the positive associations of the partner brands to a newly formed co-brand.  This exploratory study investigates the relative impact of the brand equity of the constituent brands on co-branding efforts internationally using a sample of 1,203 Philippine housewives.  Findings indicate the co-branding of two high-equity brands was mutually beneficial, but the co-branding of high-equity and low-equity brands can be potentially dangerous for the high equity partner

Survival of Campylobacter spp. on inoculated pork skin or meat.

Campylobacter is one of the main causes of human foodborne bacterial zoonoses due to food consumption in developed countries. Nine to 32% of pig carcasses are contaminated by Campylobacter. The purpose of the study was to improve our knowledge of the survival of implanted campylobacters from the two kinds of pork matrix meat (skin, muscle) during meat cold domestic storage. One hundred and twenty pork skin and 120 skinless chine samples (25 cm2/sample) were inoculated with two C. jejuni and four C. coli strains and stored in closed box at 4 oc for 1, 4, 8, 15 and 22 days. Campylobacter were isolated from sample suspensions after mechanical pummeling and numbered by direct plating. We calculated the shoulder time (ST), the D value (the time for one log decrease} and the R, value (the time to reach 10% of the initial population R, = ST +D). We compared them in a stratified approach according to pork matrix and strain. According to matrixes, mean D, TS and R, value varied significantly between pork skin (4.3 days, 1.3 days, 5.6 days, respectively} and spare rib (7 .2 days, 3.5 days, 10.8 days, respectively}. On spare rib, R1 was higher (16 days) with one C. coli strain (CCV55). Statistical effects between TS and R, value on spare rib and strain were noticed. This study shows that the survival of campylobacters on pork meat is similar to the survival of Campylobacter on poultry meat. Consequently, good hygiene practices are needed to manage the risk of pork Campylobacter contamination and further studies focusing on survival factors may complete this risk analysis on the pork food chain

Formation and transportation of sand-heap in an inclined and vertically vibrated container

We report the experimental findings of formation and motion of heap in granular materials in an inclined and vertically vibrated container. We show experimentally how the transport velocity of heap up container is related to the driving acceleration as well as the driving frequency of exciter. An analogous experiment was performed with a heap-shaped Plexiglas block. We propose that cohesion force resulted from pressure gradient in ambient gas plays a crucial role in enhancing and maintaining a heap, and ratchet effect causes the movement of the heap. An equation which governs the transport velocity of the heap is presented.Comment: 9 pages, 5 figures, submitted to PR