Theory of the Diamagnetism Above the Critical Temperature for Cuprates

Recently experiments on high critical temperature superconductors has shown that the doping levels and the superconducting gap are usually not uniform properties but strongly dependent on their positions inside a given sample. Local superconducting regions develop at the pseudogap temperature ($T^*$) and upon cooling, grow continuously. As one of the consequences a large diamagnetic signal above the critical temperature ($T_c$) has been measured by different groups. Here we apply a critical-state model for the magnetic response to the local superconducting domains between $T^*$ and $T_c$ and show that the resulting diamagnetic signal is in agreement with the experimental results.Comment: published versio

OLIA: An open-source digital lock-in amplifier

The Open Lock-In Amplifier (OLIA) is a microcontroller-based digital lock-in amplifier built from a small number of inexpensive and easily sourced electronic components. Despite its small credit card-sized form-factor and low build-cost of around US$35, OLIA is a capable instrument that offers many features associated with far costlier commercial devices. Key features include dual-phase lock-in detection at multiple harmonic frequencies up to 50 kHz, internal and external reference modes, adjustable levels of input gain, a choice between low-pass filtering and synchronous filtering, noise estimation, and a comprehensive programming interface for remote software control. OLIA comes with an optional optical breakout board that allows noise-tolerant optical detection down to the 40-pW level. OLIA and its breakout board are released here as open hardware, with technical diagrams, full parts-lists, and source-code for the firmware

Sub-millisecond Control of Neuronal Firing by Organic Light-Emitting Diodes.

Optogenetics combines optics and genetics to enable minimally invasive cell-type-specific stimulation in living tissue. For the purposes of bio-implantation, there is a need to develop soft, flexible, transparent and highly biocompatible light sources. Organic semiconducting materials have key advantages over their inorganic counterparts, including low Young's moduli, high strain resistances, and wide color tunability. However, until now it has been unclear whether organic light emitting diodes (OLEDs) are capable of providing sufficient optical power for successful neuronal stimulation, while still remaining within a biologically acceptable temperature range. Here we investigate the use of blue polyfluorene- and orange poly(p-phenylenevinylene)-based OLEDs as stimuli for blue-light-activated Sustained Step Function Opsin (SFFO) and red-light-activated ChrimsonR opsin, respectively. We show that, when biased using high frequency (multi-kHz) drive schemes, the OLEDs permit safe and controlled photostimulation of opsin-expressing neurons and were able to control neuronal firing with high temporal-resolution at operating temperatures lower than previously demonstrated

Supergravity Models for 3+1 Dimensional QCD

The most general black M5-brane solution of eleven-dimensional supergravity (with a flat R^4 spacetime in the brane and a regular horizon) is characterized by charge, mass and two angular momenta. We use this metric to construct general dual models of large-N QCD (at strong coupling) that depend on two free parameters. The mass spectrum of scalar particles is determined analytically (in the WKB approximation) and numerically in the whole two-dimensional parameter space. We compare the mass spectrum with analogous results from lattice calculations, and find that the supergravity predictions are close to the lattice results everywhere on the two dimensional parameter space except along a special line. We also examine the mass spectrum of the supergravity Kaluza-Klein (KK) modes and find that the KK modes along the compact D-brane coordinate decouple from the spectrum for large angular momenta. There are however KK modes charged under a U(1)xU(1) global symmetry which do not decouple anywhere on the parameter space. General formulas for the string tension and action are also given.Comment: 27 pages, LaTeX, 11 figures include

Comparing Local Starbursts to High-Redshift Galaxies: A Search for Lyman-Break Analogs

We compare the restframe far-ultraviolet (FUV) morphologies of 8 nearby interacting and starburst galaxies (Arp 269, M 82, Mrk 08, NGC 0520, NGC 1068, NGC 3079, NGC 3310, NGC 7673) with 54 galaxies at z approx.1.5 and 46 galaxies at z approx.4 in the Great Observatories Origins Deep Survey (GOODS) images taken with the Advanced Camera for Surveys onboard the Hubble Space Telescope. We calculate the Gini coefficient (G), the second order moment of 20% of the brightest pixels (M20), and the S ersic index (n). We find that 20% (11/54) of z approx.1.5 and 37% (17/46) of z approx.4 galaxies are bulge-like, using G and M20. We also find approx.70% of the z approx.1.5 and z approx.4 galaxies have exponential disks with n > 0.8. The 2D profile combined with the nonparametric methods provides more detail, concerning the nature of disturbed systems, such as merger and post-merger types. We also provide qualitative descriptions of each galaxy system and at each redshift. We conclude that Mrk 08, NGC 3079, and NGC 7673 have similar morphologies as the starburst FUV restframe galaxies and Lyman-break galaxies at z approx.1.5 and 4, and determine that they are Lyman-break analogs

Structures of Local Galaxies Compared to High Redshift Star-forming Galaxies

The rest-frame far-ultraviolet (FUV) morphologies of 8 nearby interacting and starburst galaxies (Arp 269, M 82, Mrk 8, NGC 520, NGC 1068, NGC 3079, NGC 3310, NGC 7673) are compared with 54 galaxies at z ~ 1.5 and 46 galaxies at z ~ 4 observed in the GOODS-ACS field. The nearby sample is artificially redshifted to z ~ 1.5 and 4. We compare the simulated galaxy morphologies to real z ~ 1.5 and 4 UV-bright galaxy morphologies. We calculate the Gini coefficient (G), the second-order moment of the brightest 20% of the galaxy's flux (M_20), and the Sersic index (n). We explore the use of nonparametric methods with 2D profile fitting and find the combination of M_20 with n an efficient method to classify galaxies as having merger, exponential disk, or bulge-like morphologies. When classified according to G and M_20, 20/30% of real/simulated galaxies at z ~ 1.5 and 37/12% at z ~ 4 have bulge-like morphologies. The rest have merger-like or intermediate distributions. Alternatively, when classified according to the Sersic index, 70% of the z ~ 1.5 and z ~ 4 real galaxies are exponential disks or bulge-like with n > 0.8, and ~30% of the real galaxies are classified as mergers. The artificially redshifted galaxies have n values with ~35% bulge or exponential at z ~ 1.5 and 4. Therefore, ~20-30% of Lyman-break galaxies (LBGs) have structures similar to local starburst mergers, and may be driven by similar processes. We assume merger-like or clumpy star-forming galaxies in the GOODS field have morphological structure with values n -1.7. We conclude that Mrk 8, NGC 3079, and NGC 7673 have structures similar to those of merger-like and clumpy star-forming galaxies observed at z ~ 1.5 and 4.Comment: Accepted by The Astronomical Journal May 2009. Changes include an added explanation of methods in Section

Tracing the String: BMN correspondence at Finite J^2/N

Employing the string bit formalism of hep-th/0209215, we identify the basis transformation that relates BMN operators in N=4 gauge theory to string states in the dual string field theory at finite g_2=J^2/N. In this basis, the supercharge truncates at linear order in g_2, and the mixing amplitude between 1 and 2-string states precisely matches with the (corrected) answer of hep-th/0206073 for the 3-string amplitude in light-cone string field theory. Supersymmetry then predicts the order g_2^2 contact term in the string bit Hamiltonian. The resulting leading order mass renormalization of string states agrees with the recently computed shift in conformal dimension of BMN operators in the gauge theory.Comment: 11 pages, 1 figur