High-speed and high-efficiency superconducting nanowire single photon detector array

Superconducting nanowire single photon detectors (SNSPDs) have separately demonstrated high efficiency, low noise, and extremely high speed when detecting single photons. However, achieving all of these simultaneously has been limited by detector subtleties and tradeoffs. Here, we report an SNSPD system with <80 ps timing resolution, kHz noise count rates, and 76% fiber-coupled system detection efficiency in the low-flux limit at 1550 nm. We present a model for determining the detection efficiency penalty due to the detection recovery time, and we validate our method using experimental data obtained at high count rates. We demonstrate improved performance tradeoffs, such as 68% system detection efficiency, including losses due to detector recovery time, when coupled to a Poisson source emitting 100 million photons per second. Our system can provide limited photon number resolution, continuous cryogen-free operation, and scalability to future imaging and GHz-count-rate applications.

Ideal evolution of magnetohydrodynamic turbulence when imposing Taylor-Green symmetries

We investigate the ideal and incompressible magnetohydrodynamic (MHD) equations in three space dimensions for the development of potentially singular structures. The methodology consists in implementing the fourfold symmetries of the Taylor-Green vortex generalized to MHD, leading to substantial computer time and memory savings at a given resolution; we also use a regridding method that allows for lower-resolution runs at early times, with no loss of spectral accuracy. One magnetic configuration is examined at an equivalent resolution of 6144(3) points and three different configurations on grids of 4096(3) points. At the highest resolution, two different current and vorticity sheet systems are found to collide, producing two successive accelerations in the development of small scales. At the latest time, a convergence of magnetic field lines to the location of maximum current is probably leading locally to a strong bending and directional variability of such lines. A novel analytical method, based on sharp analysis inequalities, is used to assess the validity of the finite-time singularity scenario. This method allows one to rule out spurious singularities by evaluating the rate at which the logarithmic decrement of the analyticity-strip method goes to zero. The result is that the finite-time singularity scenario cannot be ruled out, and the singularity time could be somewhere between t=2.33 and t=2.70. More robust conclusions will require higher resolution runs and grid-point interpolation measurements of maximum current and vorticity.

Use of computed tomography adrenal gland measurement for differentiating ACTH dependence from ACTH independence in 64 dogs with hyperadenocorticism

BACKGROUND

The measurement of adrenal gland size on computed tomography (CT) scan has been proposed for the etiological diagnosis of hyperadrenocorticism (HAC) in dogs. Symmetric adrenal glands are considered to provide evidence for ACTH-dependent hyperadrenocorticism (ADHAC), whereas asymmetry suggests ACTH-independent hyperadrenocorticism (AIHAC). However, there are currently no validated criteria for such differentiation.

OBJECTIVE

The aim of this retrospective study was to compare various adrenal CT scan measurements and the derived ratios in ADHAC and AIHAC cases, and to validate criteria for distinguishing between these conditions in a large cohort of dogs.

ANIMALS

Sixty-four dogs with HAC (46 ADHAC, 18 AIHAC).

METHODS

Dogs with confirmed HAC and unequivocal characterization of its origin were included. Linear measurements of adrenal glands were made on both cross-sectional and reformatted images.

RESULTS

An overlap was systematically observed between the AIHAC and ADHAC groups for all measurements tested. Overlaps also were observed for ratios tested. For the maximum adrenal diameter ratio derived from reformatted images (rADR), only 1/18 AIHAC dogs had a rADR within the range for ADHAC. For a threshold of 2.08, the 95% confidence intervals for estimated sensitivity and specificity extended from 0.815 to 1.000 and from 0.885 to 0.999, respectively, for AIHAC diagnosis.

CONCLUSION AND CLINICAL IMPORTANCE

Measurements from cross-sectional or reformatted CT scans are of little use for determining the origin of HAC. However, rADR appears to distinguish accurately between ADHAC and AIHAC, with a rADR > 2.08 highly suggestive of AIHAC.

Conformal invariance in three-dimensional rotating turbulence

We examine turbulent flows in the presence of solid-body rotation and helical forcing in the framework of stochastic Schramm-Löwner evolution (SLE) curves. The data stem from a run with 1536³ grid points, with Reynolds and Rossby numbers of, respectively, 5100 and 0.06. We average the parallel component of the vorticity in the direction parallel to that of rotation and examine the resulting <ω(z)>(z) field for scaling properties of its zero-value contours. We find for the first time for three-dimensional fluid turbulence evidence of nodal curves being conformal invariant, belonging to a SLE class with associated Brownian diffusivity κ = 3.6 ± 0.1. SLE behavior is related to the self-similarity of the direct cascade of energy to small scales and to the partial bidimensionalization of the flow because of rotation. We recover the value of κ with a heuristic argument and show that this is consistent with several nontrivial SLE predictions.

Structures in magnetohydrodynamic turbulence: detection and scaling

We present a systematic analysis of statistical properties of turbulent current and vorticity structures at a given time using cluster analysis. The data stem from numerical simulations of decaying three-dimensional magnetohydrodynamic turbulence in the absence of an imposed uniform magnetic field; the magnetic Prandtl number is taken equal to unity, and we use a periodic box with grids of up to 1536³ points and with Taylor Reynolds numbers up to 1100. The initial conditions are either an X -point configuration embedded in three dimensions, the so-called Orszag-Tang vortex, or an Arn'old-Beltrami-Childress configuration with a fully helical velocity and magnetic field. In each case two snapshots are analyzed, separated by one turn-over time, starting just after the peak of dissipation. We show that the algorithm is able to select a large number of structures (in excess of 8000) for each snapshot and that the statistical properties of these clusters are remarkably similar for the two snapshots as well as for the two flows under study in terms of scaling laws for the cluster characteristics, with the structures in the vorticity and in the current behaving in the same way. We also study the effect of Reynolds number on cluster statistics, and we finally analyze the properties of these clusters in terms of their velocity-magnetic-field correlation. Self-organized criticality features have been identified in the dissipative range of scales. A different scaling arises in the inertial range, which cannot be identified for the moment with a known self-organized criticality class consistent with magnetohydrodynamics. We suggest that this range can be governed by turbulence dynamics as opposed to criticality and propose an interpretation of intermittency in terms of propagation of local instabilities.

Neuronal release of D-serine: a physiological pathway controlling extracellular D-serine concentration

D-serine is thought to be a glia-derived transmitter that activates N-methyl D-aspartate receptors (NMDARs) in the brain. Here, we investigate the pathways for D-serine release using primary cultures, brain slices, and in vivo microdialysis. In contrast with the notion that D-serine is exclusively released from astrocytes, we found that D-serine is released by neuronal depolarization both in vitro and in vivo. Veratridine (50 microM) or depolarization by 40 mM KCl elicits a significant release of endogenous D-serine from primary neuronal cultures. Controls with astrocyte cultures indicate that glial cells are insensitive to veratridine, but release D-serine mainly by the opening of volume-regulated anion channels. In cortical slices perfused with veratridine, endogenous D-serine release is 10-fold higher than glutamate receptor-evoked release. Release of D-serine from slices does not require internal or external Ca(2+), suggesting a nonvesicular release mechanism. To confirm the neuronal origin of D-serine, we selectively loaded neurons in cortical slices with D-[(3)H]serine or applied D-alanine, which specifically releases D-serine from neurons. Depolarization with veratridine promotes D-serine release in vivo monitored by high temporal resolution microdialysis of the striatum. Our data indicate that the neuronal pool of D-serine plays a major role in D-serine dynamics, with implications for the regulation of NMDAR transmission.

Thyroid function and infertility in the dog: a survey in five breeds

In our study, a clinical and reproductive examination was undertaken in 204 dogs of five different breeds. Thyroxine and thyroid-stimulating hormone plasma concentrations were assayed in order to assess the real incidence of hypothyroidism associated with reproductive disease. Among these animals, only two breeds were affected by hypothyroidism (4.5% of the Dogue de Bordeaux and 2.4% of the Leonbergers). Moreover, these animals did not suffer from any reproductive disease. Our study showed also that 70% of the male Dogue de Bordeaux were hypothyroxinemic compared with Great Danes, English Mastiff and Leonbergers whose male population was 100% normothyroidic. We found the same tendency in bitches. In our data, there was no difference in thyroxin plasma concentrations between normo- and hypofertile dogs, but our results were not statistically significant.

Lack of universality in decaying magnetohydrodynamic turbulence

Using computations of three-dimensional magnetohydrodynamic (MHD) turbulence with a Taylor-Green flow, whose inherent time-independent symmetries are implemented numerically, and in the absence of either a forcing function or an imposed uniform magnetic field, we show that three different inertial ranges for the energy spectrum may emerge for three different initial magnetic fields, the selecting parameter being the ratio of nonlinear eddy to Alfvén time. Equivalent computational grids range from 128(3) to 2048(3) points with a unit magnetic Prandtl number and a Taylor Reynolds number of up to 1500 at the peak of dissipation. We also show a convergence of our results with Reynolds number. Our study is consistent with previous findings of a variety of energy spectra in MHD turbulence by studies performed in the presence of both a forcing term with a given correlation time and a strong, uniform magnetic field. However, in contrast to the previous studies, here the ratio of characteristic time scales can only be ascribed to the intrinsic nonlinear dynamics of the paradigmatic flows under study.