Low energy universality and scaling of Van der Waals forces

At long distances interactions between neutral ground state atoms can be described by the Van der Waals potential V(r) =-C6/r^6-C8/r^8 - ... . In the ultra-cold regime atom-atom scattering is dominated by s-waves phase shifts given by an effective range expansion p cot d0 (p) = -1/a0 + r0 p^2/2 + ... in terms of the scattering length a0 and the effective range r0. We show that while for these potentials the scattering length cannot be predicted, the effective range is given by the universal low energy theorem r0 = A + B/a0+ C/a0^2 where A,B and C depend on the dispersion coefficients Cn and the reduced di-atom mass. We confront this formula to about a hundred determinations of r0 and a0 and show why the result is dominated by the leading dispersion coefficient C6. Universality and scaling extends much beyond naive dimensional analysis estimates.Comment: 4 pages, 3 figure

Long-term material compatibility testing system

System includes procedure for hermetically sealing solid materials and fluids in glass ampoule and use of temperature-controlled facility containing sample holder, which permits sample containers to be retrieved safely and conveniently. Solid material and fluid are sealed within chemically-clean glass ampoule according to highly detailed procedure

Characterizing the Low-Redshift Intergalactic Medium towards PKS1302-102

We present a detailed analysis of the intergalactic metal-line absorption systems in the archival HST/STIS and FUSE ultraviolet spectra of the low-redshift quasar PKS1302-102 (z_QSO = 0.2784). We supplement the archive data with CLOUDY ionization models and a survey of galaxies in the quasar field. There are 15 strong Lya absorbers with column densities logN_HI > 14. Of these, six are associated with at least CIII 977 absorption (logN(C^++) > 13); this implies a redshift density dN_CIII/dz = 36+13/-9 (68% confidence limits) for the five detections with rest equivalent width W_r > 50 mA. Two systems show OVI 1031,1037 absorption in addition to CIII (logN(O^+5) > 14). One is a partial Lyman limit system (logN_HI = 17) with associated CIII, OVI, and SiIII 1206 absorption. There are three tentative OVI systems that do not have CIII detected. For one OVI doublet with both lines detected at 3 sigma with W_r > 50 mA, dN_OVI/dz = 7+9/-4. We also search for OVI doublets without Lya absorption but identify none. From CLOUDY modeling, these metal-line systems have metallicities spanning the range -4 < [M/H] < -0.3. The two OVI systems with associated CIII absorption cannot be single-phase, collisionally-ionized media based on the relative abundances of the metals and kinematic arguments. From the galaxy survey, we discover that the absorption systems are in a diverse set of galactic environments. Each metal-line system has at least one galaxy within 500 km/s and 600 h^-1 kpc with L > 0.1 L_*.Comment: 21 pages in emulatepj form, 24 figures, 10 tables, accepted to Ap

A characterization of multiple (n-k)-blocking sets in projective spaces of square order

In [10], it was shown that small t-fold (n - k)-blocking sets in PG(n, q), q = p(h), p prime, h >= 1, intersect every k-dimensional space in t (mod p) points. We characterize in this article all t-fold (n k)-blocking sets in PG(n, q), q square, q >= 661, t < c(p)q(1/6)/2, vertical bar B vertical bar < tq(n-k) + 2tq(n-k-1) root q, intersecting every k-dimensional space in t (mod root q) points

A mean field description of jamming in non-cohesive frictionless particulate systems

A theory for kinetic arrest in isotropic systems of repulsive, radially-interacting particles is presented that predicts exponents for the scaling of various macroscopic quantities near the rigidity transition that are in agreement with simulations, including the non-trivial shear exponent. Both statics and dynamics are treated in a simplified, one-particle level description, and coupled via the assumption that kinetic arrest occurs on the boundary between mechanically stable and unstable regions of the static parameter diagram. This suggests the arrested states observed in simulations are at (or near) an elastic buckling transition. Some additional numerical evidence to confirm the scaling of microscopic quantities is also provided.Comment: 9 pages, 3 figs; additional clarification of different elastic moduli exponents, plus typo fix. To appear in PR

Controlled biomineralization of magnetite (Fe₃O₄) by <i>Magnetospirillum gryphiswaldense</i>

Results from a study of the chemical composition and micro-structural characteristics of bacterial magnetosomes extracted from the magnetotactic bacterial strain Magnetospirillum gryphiswaldense are presented here. Using high-resolution transmission electron microscopy combined with selected-area electron diffraction and energy dispersive X-ray microanalysis, biogenic magnetite particles isolated from mature cultures were analysed for variations in crystallinity and particle size, as well as chain character and length. The analysed crystals showed a narrow size range (∼14-67 nm) with an average diameter of 46±6.8 nm, cuboctahedral morphologies and typical Gamma type crystal size distributions. The magnetite particles exhibited a high chemical purity (exclusively Fe3O4) and the majority fall within the single-magnetic-domain range

Tuning of Crystal Nucleation and Growth by Proteins: Molecular Interactions at Solid-Liquid Interfaces in Biomineralization

The mineralized tissues of a bivalve mollusk and a sea urchin are both composed of calcium carbonate crystals that are intimately associated with acidic glycoproteins. In vitro studies in which carboxylate-, carbonate- and phosphate-containing crystals are grown in the presence of partially purified acidic glycoproteins from these two tissues show that some of these macro- molecules are able to interact specifically with certain crystal faces. Significantly all the affected crystal faces contain a common stereochemical motif. Interesting differences, however, were observed in the modes of interaction between the mollusk and sea urchin derived acidic glycoproteins. Only the former can induce oriented calcite nucleation in vitro and only the latter can interact from solution with specific calcite crystal faces. These differences are ascribed in part to the fact that the mollusk macromolecules are much more acidic than those from the sea urchin. Some of the acidic glycoproteins are also occluded inside the growing crystals. In the case of the sea urchin, and not of the mollusk, the proteins are preferentially located at specific crystal planes and their presence influences the mechanical properties of the crystal. A detailed study of these composite crystals by X-ray synchrotron radiation shows how the presence of the protein influences the crystal mosaicity. The interactions revealed by these studies follow well defined stereochemical rules, tuned by electrostatic forces. They, in turn, provide new \u27insight into some of the basic underlying processes occurring in biomineralization

Second order equation of motion for electromagnetic radiation back-reaction

We take the viewpoint that the physically acceptable solutions of the Lorentz--Dirac equation for radiation back-reaction are actually determined by a second order equation of motion, the self-force being given as a function of spacetime location and velocity. We propose three different methods to obtain this self-force function. For two example systems, we determine the second order equation of motion exactly in the nonrelativistic regime via each of these three methods, the three methods leading to the same result. We reveal that, for both systems considered, back-reaction induces a damping proportional to velocity and, in addition, it decreases the effect of the external force.Comment: 13 page

Deciphering nonfemtoscopic two-pion correlations in p+pp+p collisions with simple analytical models

A simple model of nonfemtoscopic particle correlations in proton-proton collisions is proposed. The model takes into account correlations induced by the conservation laws as well as correlations induced by minijets. It reproduces well the two-pion nonfemtoscopic correlations of like-sign and unlike-sign pions in proton-proton collision events at $\sqrt{s} = 900$ GeV analyzed by the ALICE Collaboration. We also argue that similar nonfemtoscopic correlations can appear in the hydrodynamic picture with event-by-event fluctuating nonsymmetric initial conditions that are typically associated with nonzero higher-order flow harmonics.Comment: 21 pages, 10 figures, misprints correcte