6,417 research outputs found
Integration of transthoracic focused cardiac ultrasound in the diagnostic algorithm for suspected acute aortic syndromes
Magnetic dipolar ordering and relaxation in the high-spin molecular cluster compound Mn6
Few examples of magnetic systems displaying a transition to pure dipolar
magnetic order are known to date, and single-molecule magnets can provide an
interesting example. The molecular cluster spins and thus their dipolar
interaction energy can be quite high, leading to reasonably accessible ordering
temperatures, provided the crystal field anisotropy is sufficiently small. This
condition can be met for molecular clusters of sufficiently high symmetry, as
for the Mn6 compound studied here. Magnetic specific heat and susceptibility
experiments show a transition to ferromagnetic dipolar order at T_{c} = 0.16 K.
Classical Monte-Carlo calculations indeed predict ferromagnetic ordering and
account for the correct value of T_{c}. In high magnetic fields we detected the
contribution of the ^{55}Mn nuclei to the specific heat, and the characteristic
timescale of nuclear relaxation. This was compared with results obtained
directly from pulse-NMR experiments. The data are in good mutual agreement and
can be well described by the theory for magnetic relaxation in highly polarized
paramagnetic crystals and for dynamic nuclear polarization, which we
extensively review. The experiments provide an interesting comparison with the
recently investigated nuclear spin dynamics in the anisotropic single molecule
magnet Mn12-ac.Comment: 19 pages, 11 eps figures. Contains extensive discussions on dipolar
ordering, specific heat and nuclear relaxation in molecular magnet
Observation of the single-electron regime in a highly tunable silicon quantum dot
We report on low-temperature electronic transport measurements of a silicon
metal-oxide-semiconductor quantum dot, with independent gate control of
electron densities in the leads and the quantum dot island. This architecture
allows the dot energy levels to be probed without affecting the electron
density in the leads, and vice versa. Appropriate gate biasing enables the dot
occupancy to be reduced to the single-electron level, as evidenced by
magnetospectroscopy measurements of the ground state of the first two charge
transitions. Independent gate control of the electron reservoirs also enables
discrimination between excited states of the dot and density of states
modulations in the leads.Comment: 4 pages, 3 figures, accepted for Applied Physics Letter
ab-plane resistivity and possible charge stripe ordering in strongly underdoped LaSrCuO single crystals
We have measured the ab-plane resistivity of LaSrCuO single
crystals with small Sr content (x=0.052 0.075) between 4.2 and 300 K by
using the AC Van der Pauw technique. As recently suggested by Ichikawa et al.,
the deviation from the linearity of the curve starting
at a temperature T can be interpreted as due to a progressive
slowing down of the fluctuations of pre-formed charge stripes. An electronic
transition of the stripes to a more ordered phase could instead be responsible
for some very sharp anomalies present in the of
superconducting samples just above .Comment: M2S-HTSC-VI Conference paper (2 pages, 2 figures), using Elsevier
style espcrc2.st
Simulation and performance of an artificial retina for 40 MHz track reconstruction
We present the results of a detailed simulation of the artificial retina
pattern-recognition algorithm, designed to reconstruct events with hundreds of
charged-particle tracks in pixel and silicon detectors at LHCb with LHC
crossing frequency of . Performances of the artificial retina
algorithm are assessed using the official Monte Carlo samples of the LHCb
experiment. We found performances for the retina pattern-recognition algorithm
comparable with the full LHCb reconstruction algorithm.Comment: Final draft of WIT proceedings modified according to JINST referee's
comment
The artificial retina for track reconstruction at the LHC crossing rate
We present the results of an R&D study for a specialized processor capable of
precisely reconstructing events with hundreds of charged-particle tracks in
pixel and silicon strip detectors at , thus suitable for
processing LHC events at the full crossing frequency. For this purpose we
design and test a massively parallel pattern-recognition algorithm, inspired to
the current understanding of the mechanisms adopted by the primary visual
cortex of mammals in the early stages of visual-information processing. The
detailed geometry and charged-particle's activity of a large tracking detector
are simulated and used to assess the performance of the artificial retina
algorithm. We find that high-quality tracking in large detectors is possible
with sub-microsecond latencies when the algorithm is implemented in modern,
high-speed, high-bandwidth FPGA devices.Comment: 3 pages, 3 figures, ICHEP14. arXiv admin note: text overlap with
arXiv:1409.089
A Specialized Processor for Track Reconstruction at the LHC Crossing Rate
We present the results of an R&D study of a specialized processor capable of
precisely reconstructing events with hundreds of charged-particle tracks in
pixel detectors at 40 MHz, thus suitable for processing LHC events at the full
crossing frequency. For this purpose we design and test a massively parallel
pattern-recognition algorithm, inspired by studies of the processing of visual
images by the brain as it happens in nature. We find that high-quality tracking
in large detectors is possible with sub-s latencies when this algorithm is
implemented in modern, high-speed, high-bandwidth FPGA devices. This opens a
possibility of making track reconstruction happen transparently as part of the
detector readout.Comment: Presented by G.Punzi at the conference on "Instrumentation for
Colliding Beam Physics" (INSTR14), 24 Feb to 1 Mar 2014, Novosibirsk, Russia.
Submitted to JINST proceeding
Impact of g-factors and valleys on spin qubits in a silicon double quantum dot
We define single electron spin qubits in a silicon MOS double quantum dot
system. By mapping the qubit resonance frequency as a function of gate-induced
electric field, the spectrum reveals an anticrossing that is consistent with an
inter-valley spin-orbit coupling. We fit the data from which we extract an
inter-valley coupling strength of 43 MHz. In addition, we observe a narrow
resonance near the primary qubit resonance when we operate the device in the
(1,1) charge configuration. The experimental data is consistent with a
simulation involving two weakly exchanged-coupled spins with a g-factor
difference of 1 MHz, of the same order as the Rabi frequency. We conclude that
the narrow resonance is the result of driven transitions between the T- and T+
triplet states, using an ESR signal of frequency located halfway between the
resonance frequencies of the two individual spins. The findings presented here
offer an alternative method of implementing two-qubit gates, of relevance to
the operation of larger scale spin qubit systems
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