8,167 research outputs found
Antenna Impedance in a Warm Plasma
Impedance of biconical and cylindrical dipoles in warm isotropic plasm
Propulsion/flight control integration technology (PROFIT) software system definition
The Propulsion Flight Control Integration Technology (PROFIT) program is designed to develop a flying testbed dedicated to controls research. The control software for PROFIT is defined. Maximum flexibility, needed for long term use of the flight facility, is achieved through a modular design. The Host program, processes inputs from the telemetry uplink, aircraft central computer, cockpit computer control and plant sensors to form an input data base for use by the control algorithms. The control algorithms, programmed as application modules, process the input data to generate an output data base. The Host program formats the data for output to the telemetry downlink, the cockpit computer control, and the control effectors. Two applications modules are defined - the bill of materials F-100 engine control and the bill of materials F-15 inlet control
Antiferromagnetic Dimers of Ni(II) in the S=1 Spin-Ladder Na_2Ni_2(C_2O_4)_3(H_2O)_2
We report the synthesis, crystal structure and magnetic properties of the S=1
2-leg spin-ladder compound Na_2Ni_2(C_2O_4)_3(H_2O)_2. The magnetic properties
were examined by magnetic susceptibility and pulsed high field magnetization
measurements. The magnetic excitations have been measured in high field high
frequency ESR. Although the Ni(II) ions form structurally a 2-leg ladder, an
isolated dimer model consistently describes the observations very well. The
analysis of the temperature dependent magnetization data leads to a magnetic
exchange constant of J=43 K along the rungs of the ladder and an average value
of the g-factor of 2.25. From the ESR measurements, we determined the single
ion anisotropy to D=11.5 K. The validity of the isolated dimer model is
supported by Quantum Monte Carlo calculations, performed for several ratios of
interdimer and intradimer magnetic exchange and taking into account the
experimentally determined single ion anisotropy. The results can be understood
in terms of the different coordination and superexchange angles of the oxalate
ligands along the rungs and legs of the 2-leg spin ladder.Comment: 8 pages, 10 figure
Optimal, reliable estimation of quantum states
Accurately inferring the state of a quantum device from the results of
measurements is a crucial task in building quantum information processing
hardware. The predominant state estimation procedure, maximum likelihood
estimation (MLE), generally reports an estimate with zero eigenvalues. These
cannot be justified. Furthermore, the MLE estimate is incompatible with error
bars, so conclusions drawn from it are suspect. I propose an alternative
procedure, Bayesian mean estimation (BME). BME never yields zero eigenvalues,
its eigenvalues provide a bound on their own uncertainties, and it is the most
accurate procedure possible. I show how to implement BME numerically, and how
to obtain natural error bars that are compatible with the estimate. Finally, I
briefly discuss the differences between Bayesian and frequentist estimation
techniques.Comment: RevTeX; 14 pages, 2 embedded figures. Comments enthusiastically
welcomed
Solving spin quantum-master equations with matrix continued-fraction methods: application to superparamagnets
We implement continued-fraction techniques to solve exactly quantum master
equations for a spin with arbitrary S coupled to a (bosonic) thermal bath. The
full spin density matrix is obtained, so that along with relaxation and
thermoactivation, coherent dynamics is included (precession, tunnel, etc.). The
method is applied to study isotropic spins and spins in a bistable anisotropy
potential (superparamagnets). We present examples of static response, the
dynamical susceptibility including the contribution of the different relaxation
modes, and of spin resonance in transverse fields.Comment: Resubmitted to J. Phys. A: Math. Gen. Some rewriting here and there.
Discussion on positivity in App.D3 at request of one refere
Electrodynamics of Media
Contains reports on six research projects.Joint Services Electronics Program (Contract DAABO7-71-C-0300)U. S. Army Research Office - Durham (Contract DAHC04-72-C-0044)National Science Foundation (Grant GK-31012X), Cornell Universit
Early frontotemporal dementia targets neurons unique to apes and humans
Objective: Frontotemporal dementia (FTD) is a neurodegenerative disease that erodes uniquely human aspects of social behavior and emotion. The illness features a characteristic pattern of early injury to anterior cingulate and frontoinsular cortex. These regions, though often considered ancient in phylogeny, are the exclusive homes to the von Economo neuron (VEN), a large bipolar projection neuron found only in great apes and humans. Despite progress toward understanding the genetic and molecular bases of FTD, no class of selectively vulnerable neurons has been identified.
Methods: Using unbiased stereology, we quantified anterior cingulate VENs and neighboring Layer 5 neurons in FTD (n = 7), Alzheimer's disease (n = 5), and age‐matched nonneurological control subjects (n = 7). Neuronal morphology and immunohistochemical staining patterns provided further information about VEN susceptibility.
Results: FTD was associated with early, severe, and selective VEN losses, including a 74% reduction in VENs per section compared with control subjects. VEN dropout was not attributable to general neuronal loss and was seen across FTD pathological subtypes. Surviving VENs were often dysmorphic, with pathological tau protein accumulation in Pick's disease. In contrast, patients with Alzheimer's disease showed normal VEN counts and morphology despite extensive local neurofibrillary pathology.
Interpretation: VEN loss links FTD to its signature regional pattern. The findings suggest a new framework for understanding how evolution may have rendered the human brain vulnerable to specific forms of degenerative illness
Lowering the energy threshold in COSINE-100 dark matter searches
COSINE-100 is a dark matter detection experiment that uses NaI(Tl) crystal
detectors operating at the Yangyang underground laboratory in Korea since
September 2016. Its main goal is to test the annual modulation observed by the
DAMA/LIBRA experiment with the same target medium. Recently DAMA/LIBRA has
released data with an energy threshold lowered to 1 keV, and the persistent
annual modulation behavior is still observed at 9.5. By lowering the
energy threshold for electron recoils to 1 keV, COSINE-100 annual modulation
results can be compared to those of DAMA/LIBRA in a model-independent way.
Additionally, the event selection methods provide an access to a few to sub-GeV
dark matter particles using constant rate studies. In this article, we discuss
the COSINE-100 event selection algorithm, its validation, and efficiencies near
the threshold
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