Toward a microscopic description of flow near the jamming threshold

We study the relationship between microscopic structure and viscosity in non-Brownian suspensions. We argue that the formation and opening of contacts between particles in flow effectively leads to a negative selection of the contacts carrying weak forces. We show that an analytically tractable model capturing this negative selection correctly reproduces scaling properties of flows near the jamming transition. In particular, we predict that (i) the viscosity {\eta} diverges with the coordination z as {\eta} ~ (z_c-z)^{-(3+{\theta})/(1+{\theta})}, (ii) the operator that governs flow displays a low-frequency mode that controls the divergence of viscosity, at a frequency {\omega}_min\sim(z_c-z)^{(3+{\theta})/(2+2{\theta})}, and (iii) the distribution of forces displays a scale f* that vanishes near jamming as f*/\sim(z_c-z)^{1/(1+{\theta})} where {\theta} characterizes the distribution of contact forces P(f)\simf^{\theta} at jamming, and where z_c is the Maxwell threshold for rigidity.Comment: 6 pages, 4 figure

Cosine and Sine Operators Related with Orthogonal Polynomial Sets on the Intervall [-1,1]

The quantization of phase is still an open problem. In the approach of Susskind and Glogower so called cosine and sine operators play a fundamental role. Their eigenstates in the Fock representation are related with the Chebyshev polynomials of the second kind. Here we introduce more general cosine and sine operators whose eigenfunctions in the Fock basis are related in a similar way with arbitrary orthogonal polynomial sets on the intervall [-1,1]. To each polynomial set defined in terms of a weight function there corresponds a pair of cosine and sine operators. Depending on the symmetry of the weight function we distinguish generalized or extended operators. Their eigenstates are used to define cosine and sine representations and probability distributions. We consider also the inverse arccosine and arcsine operators and use their eigenstates to define cosine-phase and sine-phase distributions, respectively. Specific, numerical and graphical results are given for the classical orthogonal polynomials and for particular Fock and coherent states.Comment: 1 tex-file (24 pages), 11 figure

Emission of volatile halogenated organic compounds over various Dead Sea landscapes

Volatile halogenated organic compounds (VHOCs), such as methyl halides (CH3X; X is Br, Cl and I) and very short-lived halogenated substances (VSLSs; bromoform-CHBr3, dibromomethane-CH2Br2, bromodichloromethane-CHBrCl2, trichloroethylene-C2HCl3, chloroform-CHCl3- A nd dibromochloromethane-CHBr2Cl) are well known for their significant influence on ozone concentrations and oxidation capacity of the troposphere and stratosphere and for their key role in aerosol formation. Insufficient characterization of the sources and the emission rate of VHOCs limits our ability to understand and assess their impact in both the troposphere and stratosphere. Over the last two decades, several natural terrestrial sources for VHOCs, including soil and vegetation, have been identified, but our knowledge of emission rates from these sources and their responses to changes in ambient conditions remains limited. Here we report measurements of the mixing ratios and fluxes of several chlorinated and brominated VHOCs from different landscapes and natural and agricultural vegetated sites at the Dead Sea during different seasons. Fluxes were generally positive (emission into the atmosphere), corresponding to elevated mixing ratios, but were highly variable. Fluxes (and mixing ratios) for the investigated VHOCs ranged as follows: CHBr3 from 79 to 187 nmolm2 d1 (1.9 to 22.6 pptv), CH2Br2 from 55 to 71 nmolm2 d1 (0.7 to 19 pptv), CHBr2Cl from 408 to 768 nmolm2 d1 (0.4 to 11 pptv), CHBrCl2 from 29 to 45 nmolm2 d1 (0.5 to 9.6 pptv), CHCl3 from 577 to 883 nmolm2 d1 (15 to 57 pptv), C2HCl3 from 74 to 884 nmolm2 d1 (0.4 to 11 pptv), methyl chloride (CH3Cl) from-5300 to 10,800 nmolm2 d1 (530 to 730 pptv), methyl bromide (CH3Br) from 111 to 118 nmolm2 d1 (7.5 to 14 pptv) and methyl iodide (CH3I) from 25 to 17 nmolm2 d1 (0.4 to 2.8 pptv). Taking into account statistical uncertainties, the coastal sites (particularly those where soil is mixed with salt deposits) were identified as sources of all VHOCs, but this was not statistically significant for CHCl3. Further away from the coastal area, the bare soil sites were sources for CHBrCl2, CHBr2Cl, CHCl3, and probably also for CH2Br2 and CH3I, and the agricultural sites were sources for CHBr3, CHBr2Cl and CHBrCl2. In contrast to previous reports, we also observed emissions of brominated trihalomethanes, with net molar fluxes ordered as follows: CHBr2Cl > CHCl3 > CHBr3 > CHBrCl2 and lowest positive flux incidence for CHCl3 among all trihalomethanes; this finding can be explained by the soil's enrichment with Br. Correlation analysis, in agreement with recent studies, indicated common controls for the emission of CHBr2Cl and CHBrCl2 and likely also for CHBr3. There were no indications for correlation of the brominated trihalomethanes with CHCl3. Also in line with previous reports, we observed elevated emissions of CHCl3 and C2HCl3 from mixtures of soil and different salt-deposited structures; the flux correlations between these compounds and methyl halides (particularly CH3I) suggested that at least CH3I is also emitted via similar mechanisms or is subjected to similar controls. Overall, our results indicate elevated emission of VHOCs from bare soil under semiarid conditions. Along with other recent studies, our findings point to the strong emission potential of a suite of VHOCs from saline soils and salt lakes and call for additional studies of emission rates and mechanisms of VHOCs from saline soils and salt lakes

Evaluation of cell culture in microfluidic chips for application in monoclonal antibody production

Microfluidic chips are useful devices for cell culture that allow cell growth under highly controlled conditions, as is required for production of therapeutic recombinant proteins. To understand the optimal conditions for growth of cells amenable of recombinant protein expression in these devices,we culturedHEK-293T cells under different microfluidic experimental conditions. The cells were cultured in polymethyl methacrylate (PMMA) and polydi-methylsiloxane (PDMS)microdevices, in the absence or presence of the cell adhesion agent poly-D-lysine. Different microchannel geometries and thicknesses, as well as the influence of the flow rate have also been tested, showing their great influence in cell adhesion and growth. Results show that the presence of poly-D-lysine improves the adhesion and viability of the cells in continuous or discontinuous flow. Moreover, the optimal adhesion of cells was observed in the corners of themicrochannels, as well as in wide channels possibly due to the decrease in the flow rate in these areas. These studies provide insight into the optimal architecture of microchannels for long-term culture of adherent cells in order to use microfluidics devices as bioreactors for monoclonal antibodies production.Fil: Peñaherrera Pazmiño, Ana Belén. Universidad Tecnológica Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Payés, Cristian. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; ArgentinaFil: Sierra Rodero, Marina. Universidad Tecnológica Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Vega, M.. Universidad Tecnológica Nacional; ArgentinaFil: Rosero, G.. Universidad Tecnológica Nacional; Argentina. Universidad de Buenos Aires; ArgentinaFil: Lerner, Betiana. Universidad Tecnológica Nacional; Argentina. Universidad de Buenos Aires; ArgentinaFil: Helguera, Gustavo Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; ArgentinaFil: Pérez, M. S.. Universidad Tecnológica Nacional; Argentina. Universidad de Buenos Aires; Argentin

Unified Theory of Inertial Granular Flows and Non-Brownian Suspensions

Rheological properties of dense flows of hard particles are singular as one approaches the jamming threshold where flow ceases, both for aerial granular flows dominated by inertia, and for over-damped suspensions. Concomitantly, the lengthscale characterizing velocity correlations appears to diverge at jamming. Here we introduce a theoretical framework that proposes a tentative, but potentially complete scaling description of stationary flows. Our analysis, which focuses on frictionless particles, applies {\it both} to suspensions and inertial flows of hard particles. We compare our predictions with the empirical literature, as well as with novel numerical data. Overall we find a very good agreement between theory and observations, except for frictional inertial flows whose scaling properties clearly differ from frictionless systems. For over-damped flows, more observations are needed to decide if friction is a relevant perturbation or not. Our analysis makes several new predictions on microscopic dynamical quantities that should be accessible experimentally.Comment: 13 pages + 3 pages S

Low temperature sintering of electroexplosive nanopowders

By means of the methods of conductivity measurement and transmitting electron microscopy of sintered metal layer it has been shown that electroexplosive copper and zink powders are sintered with the formation of strong aggregates of corresponding compact metals. It has been also shown that sels-sintereing is a cause of below reduction of metal powder particle size obtained by the method of semiconductor electrical explosion

Determination of biomembrane bending moduli in fully atomistic simulations.

The bilayer bending modulus (Kc) is one of the most important physical constants characterizing lipid membranes, but precisely measuring it is a challenge, both experimentally and computationally. Experimental measurements on chemically identical bilayers often differ depending upon the techniques employed, and robust simulation results have previously been limited to coarse-grained models (at varying levels of resolution). This Communication demonstrates the extraction of Kc from fully atomistic molecular dynamics simulations for three different single-component lipid bilayers (DPPC, DOPC, and DOPE). The results agree quantitatively with experiments that measure thermal shape fluctuations in giant unilamellar vesicles. Lipid tilt, twist, and compression moduli are also reported

Spin Relaxation in a Quantized Hall Regime in Presence of a Disorder

We study the spin relaxation (SR) of a two-dimensional electron gas (2DEG) in the quantized Hall regime and discuss the role of spatial inhomogeneity effects on the relaxation. The results are obtained for small filling factors ($\nu\ll 1$) or when the filling factor is close to an integer. In either case SR times are essentially determined by a smooth random potential. For small $\nu$ we predict a "magneto-confinement" resonance manifested in the enhancement of the SR rate when the Zeeman energy is close to the spacing of confinement sublevels in the low-energy wing of the disorder-broadened Landau level. In the resonant region the $B$-dependence of the SR time has a peculiar non-monotonic shape. If $\nu\simeq 2n+1$, the SR is going non-exponentially. Under typical conditions the calculated SR times range from $10^{-8}$ to $10^{-6}$s.Comment: 10 pages, 1 figure. To appear in JETP Letter

Ejection Energy of Photoelectrons in Strong Field Ionization

We show that zero ejection energy of the photoelectrons is classically impossible for hydrogen-like ions, even when field ionization occurs adiabatically. To prove this we transform the basic equations to those describing two 2D anharmonic oscillators. The same method yields an alternative way to derive the anomalous critical field of hydrogen-like ions. The analytical results are confirmed and illustrated by numerical simulations. PACS Number: 32.80.RmComment: 7 pages, REVTeX, postscript file including the figures is available at http://www.physik.th-darmstadt.de/tqe/dieter/publist.html or via anonymous ftp from ftp://tqe.iap.physik.th-darmstadt.de/pub/dieter/publ_I_pra_pre.ps, accepted for publication in Phys. Rev.