8,256 research outputs found
Ka-band MMIC beam steered transmitter array
A 32-GHz six-element linear transmitter array utilizing monolithic microwave integrated circuit (MMIC) phase shifters and power amplifiers was designed and tested as part of the development of a spacecraft array feed for NASA deep-space communications applications. Measurements of the performance of individual phase shifters, power amplifiers, and microstrip radiators were carried out, and electronic beam steering of the linear array was demonstrated. The switched-line phase shifters were accurate to within 7 percent on average and the power amplifier 1-dB compressed output power varied over 0.3 dB. The array had a beamwidth of 7.5 deg and demonstrated acceptable beam steering over + or - 8 deg. From the results, it can be concluded that this MMIC phased array has adequate beam-scanning capability for use in the two-dimensional array. The areas that need to be improved are the efficiency of the MMIC power amplifier and the insertion loss of the MMIC phase shifter
Yukawa Scalar Self-Mass on a Conformally Flat Background
We compute the one loop self-mass-squared of a massless, minimally coupled
scalar which is Yukawa-coupled to a massless Dirac fermion in a general
conformally flat background. Dimensional regularization is employed and a fully
renormalized result is obtained. For the special case of a locally de Sitter
background our result is manifestly de Sitter invariant. By solving the
effective field equations we show that the scalar mode functions acquire no
significant one loop corrections. In particular, the phenomenon of
super-adiabatic amplification is not affected. One consequence is that the
scalar-catalyzed production of fermions during inflation should not be reduced
by changes in the scalar sector before it has time to go to completion.Comment: 23 pages, LaTeX 2epsilon, 3 figures (uses axodraw
Complementary and alternative medicine for victims of intimate partner abuse: A systematic review of use and efficacy
Objectives. To examine: (i) the extent to which victims of intimate partner abuse (IPA) use complementary and alternative medicine (CAM) and (ii) the effects of CAM on their mental health. Methods. Medline, Scopus, and Web of Science were searched for studies measuring the extent of CAM use amongst victims of IPA and trials assessing the impact of CAM on mental health amongst this population. Risk of bias was assessed using the Cochrane collaboration tool. Results. No studies measuring the level of CAM use amongst IPA victims, and only three studies assessing the effect of CAM on the mental health of this population were identified. Two studies looked at yogic breathing, while one assessed the effect of music therapy. All three studies showed some beneficial effects; however, each had a small sample, brief intervention period, and no follow-up measurement and were considered to be at high risk of bias. Conclusions. The review found little evidence for the benefits of CAM for IPA victims. Findings suggest positive effects of music therapy and yogic breathing; however, methodological limitations mean that these results should be interpreted with caution. It is important that more research into the use and effects of CAM amongst this population are undertaken. © 2014 Luke Duffy et al
The Caustic Ring Model of the Milky Way Halo
We present a proposal for the full phase space distribution of the Milky Way
halo. The model is axially and reflection symmetric and its time evolution is
self-similar. It describes the halo as a set of discrete dark matter flows with
stated densities and velocity vectors everywhere. We first discuss the general
conditions under which the time evolution of a cold collisionless
self-gravitating fluid is self-similar, and show that symmetry is not necessary
for self-similarity. When spherical symmetry is imposed, the model is the same
as described by Fillmore and Goldreich, and by Bertschinger, twenty-three years
ago. The spherically symmetric model depends on one dimensionless parameter
and two dimensionful parameters. We set = 0.3, a value
consistent with the slope of the power spectrum of density perturbations on
galactic scales. The dimensionful parameters are determined by the Galactic
rotation velocity (220 km/s) at the position of the Sun and by the age of the
Galaxy (13.7 Gyr). The properties of the outer caustics are derived in the
spherically symmetric model. The structure of the inner halo depends on the
angular momentum distribution of the dark matter particles. We assume that
distribution to be axial and reflection symmetric, and dominated by net overall
rotation. The inner caustics are rings whose radii are determined in terms of a
single additional parameter . We summarize the observational
evidence in support of the model. The evidence is consistent with
= 0.18 in Concordance Cosmology, equivalent to = 0.26 in
Einstein - de Sitter cosmology. We give formulas to estimate the flow densities
and velocity vectors anywhere in the Milky Way halo. The properties of the
first forty flows at the location of the Earth are listed.Comment: 35 pages, 6 figure
Fully automated segmentation and tracking of the intima media thickness in ultrasound video sequences of the common carotid artery
Abstract—The robust identification and measurement of the intima media thickness (IMT) has a high clinical relevance because it represents one of the most precise predictors used in the assessment of potential future cardiovascular events. To facilitate the analysis of arterial wall thickening in serial clinical investigations, in this paper we have developed a novel fully automatic algorithm for the segmentation, measurement, and tracking of the intima media complex (IMC) in B-mode ultrasound video sequences. The proposed algorithm entails a two-stage image analysis process that initially addresses the segmentation of the IMC in the first frame of the ultrasound video sequence using a model-based approach; in the second step, a novel customized tracking procedure is applied to robustly detect the IMC in the subsequent frames. For the video tracking procedure, we introduce a spatially coherent algorithm called adaptive normalized correlation that prevents the tracking process from converging to wrong arterial interfaces. This represents the main contribution of this paper and was developed to deal with inconsistencies in the appearance of the IMC over the cardiac cycle. The quantitative evaluation has been carried out on 40 ultrasound video sequences of the common carotid artery (CCA) by comparing the results returned by the developed algorithm with respect to ground truth data that has been manually annotated by clinical experts. The measured IMTmean ± standard deviation recorded by the proposed algorithm is 0.60 mm ± 0.10, with a mean coefficient of variation (CV) of 2.05%, whereas the corresponding result obtained for the manually annotated ground truth data is 0.60 mm ± 0.11 with a mean CV equal to 5.60%. The numerical results reported in this paper indicate that the proposed algorithm is able to correctly segment and track the IMC in ultrasound CCA video sequences, and we were encouraged by the stability of our technique when applied to data captured under different imaging conditions. Future clinical studies will focus on the evaluation of patients that are affected by advanced cardiovascular conditions such as focal thickening and arterial plaques
Overdiagnosis in breast cancer screening: the importance of length of observation period and lead time
PMCID: PMC3706885This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
Hydrodynamic theory of de-wetting
A prototypical problem in the study of wetting phenomena is that of a solid
plunging into or being withdrawn from a liquid bath. In the latter, de-wetting
case, a critical speed exists above which a stationary contact line is no
longer sustainable and a liquid film is being deposited on the solid.
Demonstrating this behavior to be a hydrodynamic instability close to the
contact line, we provide the first theoretical explanation of a classical
prediction due to Derjaguin and Levi: instability occurs when the outer, static
meniscus approaches the shape corresponding to a perfectly wetting fluid
Ultrahigh magnetic field spectroscopy reveals the band structure of the 3D topological insulator BiSe
We have investigated the band structure at the point of the
three-dimensional (3D) topological insulator BiSe using
magneto-spectroscopy over a wide range of energies (\,eV) and in
ultrahigh magnetic fields up to 150\,T. At such high energies (\,eV) the
parabolic approximation for the massive Dirac fermions breaks down and the
Landau level dispersion becomes nonlinear. At even higher energies around 0.99
and 1.6 eV, new additional strong absorptions are observed with a temperature
and magnetic-field dependence which suggest that they originate from higher
band gaps. Spin orbit splittings for the further lying conduction and valence
bands are found to be 0.196 and 0.264 eV
Granular Elasticity without the Coulomb Condition
An self-contained elastic theory is derived which accounts both for
mechanical yield and shear-induced volume dilatancy. Its two essential
ingredients are thermodynamic instability and the dependence of the elastic
moduli on compression.Comment: 4pages, 2 figure
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