4,570 research outputs found
Bi-layer Kinetic Inductance Detectors for space observations between 80-120 GHz
We have developed Lumped Element Kinetic Inductance Detectors (LEKID)
sensitive in the frequency band from 80 to 120~GHz. In this work, we take
advantage of the so-called proximity effect to reduce the superconducting gap
of Aluminium, otherwise strongly suppressing the LEKID response for frequencies
smaller than 100~GHz. We have designed, produced and optically tested various
fully multiplexed arrays based on multi-layers combinations of Aluminium (Al)
and Titanium (Ti). Their sensitivities have been measured using a dedicated
closed-circle 100 mK dilution cryostat and a sky simulator allowing to
reproduce realistic observation conditions. The spectral response has been
characterised with a Martin-Puplett interferometer up to THz frequencies, and
with a resolution of 3~GHz. We demonstrate that Ti-Al LEKID can reach an
optical sensitivity of about ~ (best pixel), or
~ when averaged over the whole array. The optical
background was set to roughly 0.4~pW per pixel, typical for future space
observatories in this particular band. The performance is close to a
sensitivity of twice the CMB photon noise limit at 100~GHz which drove the
design of the Planck HFI instrument. This figure remains the baseline for the
next generation of millimetre-wave space satellites.Comment: 7 pages, 9 figures, submitted to A&
Spiral spin-liquid and the emergence of a vortex-like state in MnScS
Spirals and helices are common motifs of long-range order in magnetic solids,
and they may also be organized into more complex emergent structures such as
magnetic skyrmions and vortices. A new type of spiral state, the spiral
spin-liquid, in which spins fluctuate collectively as spirals, has recently
been predicted to exist. Here, using neutron scattering techniques, we
experimentally prove the existence of a spiral spin-liquid in MnScS by
directly observing the 'spiral surface' - a continuous surface of spiral
propagation vectors in reciprocal space. We elucidate the multi-step ordering
behavior of the spiral spin-liquid, and discover a vortex-like triple-q phase
on application of a magnetic field. Our results prove the effectiveness of the
- Hamiltonian on the diamond lattice as a model for the spiral
spin-liquid state in MnScS, and also demonstrate a new way to realize a
magnetic vortex lattice.Comment: 10 pages, 11 figure
A General Theory of Phase-Space Quasiprobability Distributions
We present a general theory of quasiprobability distributions on phase spaces
of quantum systems whose dynamical symmetry groups are (finite-dimensional) Lie
groups. The family of distributions on a phase space is postulated to satisfy
the Stratonovich-Weyl correspondence with a generalized traciality condition.
The corresponding family of the Stratonovich-Weyl kernels is constructed
explicitly. In the presented theory we use the concept of the generalized
coherent states, that brings physical insight into the mathematical formalism.Comment: REVTeX, 4 pages. More information on
http://www.technion.ac.il/~brif/science.htm
LEKID sensitivity for space applications between 80 and 600 GHz
We report the design, fabrication and testing of Lumped Element Kinetic
Inductance Detectors (LEKID) showing performance in line with the requirements
of the next generation space telescopes operating in the spectral range from 80
to 600 GHz. This range is of particular interest for Cosmic Microwave
Background (CMB) studies. For this purpose we have designed and fabricated
100-pixel arrays covering five distinct bands. These wafers have been measured
via multiplexing, where a full array is read out using a single pair of lines.
We adopted a custom cold black-body installed in front of the detectors and
regulated at temperatures between 1 K and 20 K. We will describe in the present
paper the main design considerations, the fabrication processes, the testing
and the data analysis
Fully-Renormalized QRPA fulfills Ikeda sum rule exactly
The renormalized quasiparticle-RPA is reformulated for even-even nuclei using
restrictions imposed by the commutativity of the phonon creation operator with
the total particle number operator. This new version, Fully-Renormalized QRPA
(FR-QRPA), is free from the spurious low-energy solutions. Analytical proof is
given that the Ikeda sum rule is fullfiled within the FR-QRPA.Comment: 9 page
A Hydrophobic Gate in an Ion Channel: The Closed State of the Nicotinic Acetylcholine Receptor
The nicotinic acetylcholine receptor (nAChR) is the prototypic member of the
`Cys-loop' superfamily of ligand-gated ion channels which mediate synaptic
neurotransmission, and whose other members include receptors for glycine,
gamma-aminobutyric acid, and serotonin. Cryo-electron microscopy has yielded a
three dimensional structure of the nAChR in its closed state. However, the
exact nature and location of the channel gate remains uncertain. Although the
transmembrane pore is constricted close to its center, it is not completely
occluded. Rather, the pore has a central hydrophobic zone of radius about 3 A.
Model calculations suggest that such a constriction may form a hydrophobic
gate, preventing movement of ions through a channel. We present a detailed and
quantitative simulation study of the hydrophobic gating model of the nicotinic
receptor, in order to fully evaluate this hypothesis. We demonstrate that the
hydrophobic constriction of the nAChR pore indeed forms a closed gate.
Potential of mean force (PMF) calculations reveal that the constriction
presents a barrier of height ca. 10 kT to the permeation of sodium ions,
placing an upper bound on the closed channel conductance of 0.3 pS. Thus, a 3 A
radius hydrophobic pore can form a functional barrier to the permeation of a 1
A radius Na+ ion. Using a united atom force field for the protein instead of an
all atom one retains the qualitative features but results in differing
conductances, showing that the PMF is sensitive to the detailed molecular
interactions.Comment: Accepted by Physical Biology; includes a supplement and a
supplementary mpeg movie can be found at
http://sbcb.bioch.ox.ac.uk/oliver/download/Movies/watergate.mp
Subgap Kinetic Inductance Detector Sensitive to 85-GHz Radiation
We have fabricated an array of subgap kinetic inductance detectors (SKIDs) made of granular aluminum (T∼2 K) sensitive in the 80–90 GHz frequency band and operating at 300 mK. We measure a noise equivalent power of 1.3×10-16W/Hz0.5 on average and 2.6×10W/Hz at best, for an illuminating power of 50 fW per pixel. Even though the circuit design of SKIDs is identical to that of the kinetic inductance detectors, the SKIDs operating principle is based on their sensitivity to subgap excitations. This detection scheme is advantageous because it avoids having to lower the operating temperature proportionally to the lowest detectable frequency. The SKIDs presented here are intrinsically selecting the 80–90 GHz frequency band, well below the superconducting spectral gap of the film, at approximately 180 GHz
Stochastic Resonance of Ensemble Neurons for Transient Spike Trains: A Wavelet Analysis
By using the wavelet transformation (WT), we have analyzed the response of an
ensemble of (=1, 10, 100 and 500) Hodgkin-Huxley (HH) neurons to {\it
transient} -pulse spike trains () with independent Gaussian noises.
The cross-correlation between the input and output signals is expressed in
terms of the WT expansion coefficients. The signal-to-noise ratio (SNR) is
evaluated by using the {\it denoising} method within the WT, by which the noise
contribution is extracted from output signals. Although the response of a
single (N=1) neuron to sub-threshold transient signals with noises is quite
unreliable, the transmission fidelity assessed by the cross-correlation and SNR
is shown to be much improved by increasing the value of : a population of
neurons play an indispensable role in the stochastic resonance (SR) for
transient spike inputs. It is also shown that in a large-scale ensemble, the
transmission fidelity for supra-threshold transient spikes is not significantly
degraded by a weak noise which is responsible to SR for sub-threshold inputs.Comment: 20 pages, 4 figure
Wigner function for twisted photons
A comprehensive theory of the Weyl-Wigner formalism for the canonical pair
angle-angular momentum is presented, with special emphasis in the implications
of rotational periodicity and angular-momentum discreteness.Comment: 6 pages, 4 figure
Two-body quantum mechanical problem on spheres
The quantum mechanical two-body problem with a central interaction on the
sphere is considered. Using recent results in representation
theory an ordinary differential equation for some energy levels is found. For
several interactive potentials these energy levels are calculated in explicit
form.Comment: 41 pages, no figures, typos corrected; appendix D was adde
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