Interstitials, Vacancies and Dislocations in Flux-Line Lattices: A Theory of Vortex Crystals, Supersolids and Liquids

We study a three dimensional Abrikosov vortex lattice in the presence of an equilibrium concentration of vacancy, interstitial and dislocation loops. Vacancies and interstitials renormalize the long-wavelength bulk and tilt elastic moduli. Dislocation loops lead to the vanishing of the long-wavelength shear modulus. The coupling to vacancies and interstitials - which are always present in the liquid state - allows dislocations to relax stresses by climbing out of their glide plane. Surprisingly, this mechanism does not yield any further independent renormalization of the tilt and compressional moduli at long wavelengths. The long wavelength properties of the resulting state are formally identical to that of the ``flux-line hexatic'' that is a candidate ``normal'' hexatically ordered vortex liquid state.Comment: 21 RevTeX pgs, 7 eps figures uuencoded; corrected typos, published versio

Novel synovial fluid recovery method allows for quantification of a marker of arthritis in mice

SummaryObjectiveWe evaluated three methodologies – a calcium sodium alginate compound (CSAC), polyacrylate beads (PABs), and Whatman paper recovery (WPR) – for the ability to recover synovial fluid (SF) from mouse knees in a manner that facilitated biochemical marker analysis.MethodsPilot testing of each of these recovery vehicles was conducted using small volumes of waste human SF. CSAC emerged as the method of choice, and was used to recover and quantify SF from the knees of C57BL/6 mice (n=12), six of which were given left knee articular fractures. SF concentrations of cartilage oligomeric matrix protein (COMP) were measured by enzyme-linked immunosorbent assay.ResultsThe mean concentration ratio [(COMPleft knee)/(COMPright knee)] was higher in the mice subjected to articular fracture when compared to the non-fracture mice (P=0.026). The mean total COMP ratio (taking into account the quantitative recovery of SF) best discriminated between fracture and non-fracture knees (P=0.004).ConclusionsOur results provide the first direct evidence of accelerated joint tissue turnover in a mouse model responding to acute joint injury. These data strongly suggest that mouse SF recovery is feasible and that biomarker analysis of collected SF samples can augment traditional histological analyses in mouse models of arthritis

Different Ways of Reading, or Just Making the Right Noises?

What does reading look like? Can learning to read be reduced to the acquisition of a set of isolable skills, or proficiency in reading be equated with the independence of the solitary, silent reader of prose fiction? These conceptions of reading and reading development, which figure strongly in educational policy, may appear to be simple common sense. But both ethnographic data and evidence from literary texts suggest that such paradigms offer, at most, a partial and ahistorical picture of reading. An important dimension, neglected in the dominant paradigms, is the irreducibly social quality of reading practices

Evaluation of human chorionic gonadotropin as a replacement for GnRH in an ovulation synchronization protocol before fixed-time insemination

Two experiments were conducted to evaluate the difference between gonadotropinreleasing hormone (GnRH) and human chorionic gonadotropin (hCG) given at the beginning of a timed AI protocol and their effects on fertility. In Experiment 1, beef cows (n = 672) at six different locations were assigned randomly to treatments based on age, body condition, and days postpartum. On day −10, cattle were treated with GnRH or hCG and a progesterone-releasing controlled internal drug release (CIDR) insert was placed in the vagina. An injection of PGF2α was given and CIDR inserts were removed on day −3. Cows were inseminated at one fixed timed at 62 hr (day 0) after CIDR insert removal. Pregnancy was diagnosed at 33 days (range of 32 to 35) after insemination to determine pregnancy rates. For cows that were pregnant after the first insemination, a second pregnancy diagnosis was conducted 35 days (range of 33 to 37) after the first diagnosis to determine pregnancy survival. Pregnancy rates were reduced by the hCG injection compared with the GnRH injection (39.1 vs. 53.5%). In Experiment 2, cattle were assigned randomly to three treatments, balanced evenly across the two treatments (GnRH vs. hCG) applied in Experiment 1. Cows were injected with GnRH, hCG, or saline seven days before the first pregnancy diagnosis of cows inseminated in Experiment 1. At the time of pregnancy diagnosis, cattle found not pregnant (n = 328) were given PGF2α and inseminated 56 hours later. A second pregnancy diagnosis was conducted 35 days (range of 33 to 37) after the second insemination to determine pregnancy rate at the second AI. Injections of GnRH, hCG, or saline had no effect on pregnancy rates of cows already pregnant to the first insemination. Pregnancy rates after second insemination in cows given an injection of hCG or GnRH, however, tended to be reduced. Percentage of cows pregnant after two timed inseminations exceeded 60% without any need to detect estrus

The Effect of Splayed Pins on Vortex Creep and Critical Currents

We study the effects of splayed columnar pins on the vortex motion using realistic London Langevin simulations. At low currents vortex creep is strongly suppressed, whereas the critical current j_c is enhanced only moderately. Splaying the pins generates an increasing energy barrier against vortex hopping, and leads to the forced entanglement of vortices, both of which suppress creep efficiently. On the other hand splaying enhances kink nucleation and introduces intersecting pins, which cut off the energy barriers. Thus the j_c enhancement is strongly parameter sensitive. We also characterize the angle dependence of j_c, and the effect of different splaying geometries.Comment: 4 figure

Effects of columnar disorder on flux-lattice melting in high-temperature superconductors

The effect of columnar pins on the flux-lines melting transition in high-temperature superconductors is studied using Path Integral Monte Carlo simulations. We highlight the similarities and differences in the effects of columnar disorder on the melting transition in YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) and the highly anisotropic Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (BSCCO) at magnetic fields such that the mean separation between flux-lines is smaller than the penetration length. For pure systems, a first order transition from a flux-line solid to a liquid phase is seen as the temperature is increased. When adding columnar defects to the system, the transition temperature is not affected in both materials as long as the strength of an individual columnar defect (expressed as a flux-line defect interaction) is less than a certain threshold for a given density of randomly distributed columnar pins. This threshold strength is lower for YBCO than for BSCCO. For higher strengths the transition line is shifted for both materials towards higher temperatures, and the sharp jump in energy, characteristic of a first order transition, gives way to a smoother and gradual rise of the energy, characteristic of a second order transition. Also, when columnar defects are present, the vortex solid phase is replaced by a pinned Bose glass phase and this is manifested by a marked decrease in translational order and orientational order as measured by the appropriate structure factors. For BSCCO, we report an unusual rise of the translational order and the hexatic order just before the melting transition. No such rise is observed in YBCO.Comment: 32 pages, 13 figures, revte

Dynamic Vortex Phases and Pinning in Superconductors with Twin Boundaries

We investigate the pinning and driven dynamics of vortices interacting with twin boundaries using large scale molecular dynamics simulations on samples with near one million pinning sites. For low applied driving forces, the vortex lattice orients itself parallel to the twin boundary and we observe the creation of a flux gradient and vortex free region near the edges of the twin boundary. For increasing drive, we find evidence for several distinct dynamical flow phases which we characterize by the density of defects in the vortex lattice, the microscopic vortex flow patterns, and orientation of the vortex lattice. We show that these different dynamical phases can be directly related to microscopically measurable voltage - current V(I) curves and voltage noise. By conducting a series of simulations for various twin boundary parameters we derive several vortex dynamic phase diagrams.Comment: 5 figures, to appear in Phys. Rev.

Vortex Plastic Flow, B(x,y,H(t)),M(H(t)),Jc(B(t))B(x,y,H(t)), M(H(t)), J_c(B(t)), Deep in the Bose Glass and Mott-Insulator Regimes

We present simulations of flux-gradient-driven superconducting vortices interacting with strong columnar pinning defects as an external field $H(t)$ is quasi-statically swept from zero through a matching field $B_{\phi}$. We analyze several measurable quantities, including the local flux density $B(x,y,H(t))$, magnetization $M(H(t))$, critical current $J_{c}(B(t))$, and the individual vortex flow paths. We find a significant change in the behavior of these quantities as the local flux density crosses $B_{\phi}$, and quantify it for many microscopic pinning parameters. Further, we find that for a given pin density $J_c(B)$ can be enhanced by maximizing the distance between the pins for $B < B_{\phi}$.Comment: 4 pages, 4 PostScript Figure

Phase Behavior of Bent-Core Molecules

Recently, a new class of smectic liquid crystal phases (SmCP phases) characterized by the spontaneous formation of macroscopic chiral domains from achiral bent-core molecules has been discovered. We have carried out Monte Carlo simulations of a minimal hard spherocylinder dimer model to investigate the role of excluded volume interations in determining the phase behavior of bent-core materials and to probe the molecular origins of polar and chiral symmetry breaking. We present the phase diagram as a function of pressure or density and dimer opening angle $\psi$. With decreasing $\psi$, a transition from a nonpolar to a polar smectic phase is observed near $\psi = 167^{\circ}$, and the nematic phase becomes thermodynamically unstable for $\psi < 135^{\circ}$. No chiral smectic or biaxial nematic phases were found.Comment: 4 pages Revtex, 3 eps figures (included