Passive scalar intermittency in low temperature helium flows

We report new measurements of turbulent mixing of temperature fluctuations in a low temperature helium gas experiment, spanning a range of microscale Reynolds number, $R_{\lambda}$, from 100 to 650. The exponents $\xi_{n}$ of the temperature structure functions $\sim r^{\xi_{n}}$ are shown to saturate to $\xi_{\infty} \simeq 1.45 \pm 0.1$ for the highest orders, $n \sim 10$. This saturation is a signature of statistics dominated by front-like structures, the cliffs. Statistics of the cliff characteristics are performed, particularly their width are shown to scale as the Kolmogorov length scale.Comment: 4 pages, with 4 figure

Antiferromagnetic correlations and impurity broadening of NMR linewidths in cuprate superconductors

We study a model of a d-wave superconductor with strong potential scatterers in the presence of antiferromagnetic correlations and apply it to experimental nuclear magnetic resonance (NMR) results on Zn impurities in the superconducting state of YBCO. We then focus on the contribution of impurity-induced paramagnetic moments, with Hubbard correlations in the host system accounted for in Hartree approximation. We show that local magnetism around individual impurities broadens the line, but quasiparticle interference between impurity states plays an important role in smearing out impurity satellite peaks. The model, together with estimates of vortex lattice effects, provides a semi-quantitative description of the impurity concentration dependence of the NMR line shape in the superconducting state, and gives a qualitative description of the temperature dependence of the line asymmetry. We argue that impurity-induced paramagnetism and resonant local density of states effects are both necessary to explain existing experiments.Comment: 15 pages, 23 figures, submitted to Phys. Rev.

Three-loop HTLpt thermodynamics at finite temperature and chemical potential

In this proceedings we present a state-of-the-art method of calculating thermodynamic potential at finite temperature and finite chemical potential, using Hard Thermal Loop perturbation theory (HTLpt) up to next-to-next-leading-order (NNLO). The resulting thermodynamic potential enables us to evaluate different thermodynamic quantities including pressure and various quark number susceptibilities (QNS). Comparison between our analytic results for those thermodynamic quantities with the available lattice data shows a good agreement.Comment: 5 pages, 6 figures, conference proceedings of XXI DAE-BRNS HEP Symposium, IIT Guwahati, December 2014; to appear in 'Springer Proceedings in Physics Series

Observation of twin beam correlations and quadrature entanglement by frequency doubling in a two-port resonator

We demonstrate production of quantum correlated and entangled beams by second harmonic generation in a nonlinear resonator with two output ports. The output beams at wavelength 428.5 nm exhibit 0.9 dB of nonclassical intensity correlations and 0.3 dB of entanglement.Comment: 5 pages, 7 figure

Temporal structure in neuronal activity during working memory in Macaque parietal cortex

A number of cortical structures are reported to have elevated single unit firing rates sustained throughout the memory period of a working memory task. How the nervous system forms and maintains these memories is unknown but reverberating neuronal network activity is thought to be important. We studied the temporal structure of single unit (SU) activity and simultaneously recorded local field potential (LFP) activity from area LIP in the inferior parietal lobe of two awake macaques during a memory-saccade task. Using multitaper techniques for spectral analysis, which play an important role in obtaining the present results, we find elevations in spectral power in a 50--90 Hz (gamma) frequency band during the memory period in both SU and LFP activity. The activity is tuned to the direction of the saccade providing evidence for temporal structure that codes for movement plans during working memory. We also find SU and LFP activity are coherent during the memory period in the 50--90 Hz gamma band and no consistent relation is present during simple fixation. Finally, we find organized LFP activity in a 15--25 Hz frequency band that may be related to movement execution and preparatory aspects of the task. Neuronal activity could be used to control a neural prosthesis but SU activity can be hard to isolate with cortical implants. As the LFP is easier to acquire than SU activity, our finding of rich temporal structure in LFP activity related to movement planning and execution may accelerate the development of this medical application.Comment: Originally submitted to the neuro-sys archive which was never publicly announced (was 0005002

Dopant-modulated pair interaction in cuprate superconductors

Comparison of recent experimental STM data with single-impurity and many-impurity Bogoliubov-de Gennes calculations strongly suggests that random out-of-plane dopant atoms in cuprates modulate the pair interaction locally. This type of disorder is crucial to understanding the nanoscale electronic structure inhomogeneity observed in BSCCO-2212, and can reproduce observed correlations between the positions of impurity atoms and various aspects of the local density of states such as the gap magnitude and the height of the coherence peaks. Our results imply that each dopant atom modulates the pair interaction on a length scale of order one lattice constant.Comment: 5 pages, 4 figure

Multiple and variable speed electrical generator systems for large wind turbines

A cost effective method to achieve increased wind turbine generator energy conversion and other operational benefits through variable speed operation is presented. Earlier studies of multiple and variable speed generators in wind turbines were extended for evaluation in the context of a specific large sized conceptual design. System design and simulation have defined the costs and performance benefits which can be expected from both two speed and variable speed configurations

A Method for Detection and Classification of Events in Neural Activity

We present a method for the real time prediction of punctuate events in neural activity, based on the time-frequency spectrum of the signal, applicable both to continuous processes like local field potentials (LFPs) as well as to spike trains. We test it on recordings of LFP and spiking activity acquired previously from the lateral intraparietal area (LIP) of macaque monkeys performing a memory-saccade task. In contrast to earlier work, where trials with known start times were classified, our method detects and classifies trials directly from the data. It provides a means to quantitatively compare and contrast the content of LFP signals and spike trains: we find that the detector performance based on the LFP matches the performance based on spike rates. The method should find application in the development of neural prosthetics based on the LFP signal. Our approach uses a new feature vector, which we call the 2d cepstrum

Mass Expansions of Screened Perturbation Theory

The thermodynamics of massless phi^4-theory is studied within screened perturbation theory (SPT). In this method the perturbative expansion is reorganized by adding and subtracting a mass term in the Lagrangian. We analytically calculate the pressure and entropy to three-loop order and the screening mass to two-loop order, expanding in powers of m/T. The truncated m/T-expansion results are compared with numerical SPT results for the pressure, entropy and screening mass which are accurate to all orders in m/T. It is shown that the m/T-expansion converges quickly and provides an accurate description of the thermodynamic functions for large values of the coupling constant.Comment: 22 pages, 10 figure