780 research outputs found
Ferruleless coupled-cavity traveling-wave tube cold-test characteristics simulated with micro-SOS
The three-dimensional, electromagnetic circuit analysis code, Micro-SOS, can be used to reduce expensive and time consuming experimental 'cold-testing' of traveling-wave tube (TWT) circuits. The frequency-phase dispersion and beam interaction impedance characteristics of a ferruleless coupled-cavity traveling-wave tube slow-wave circuit were simulated using the code. Computer results agree closely with experimental data. Variations in the cavity geometry dimensions of period length and gap-to-period ratio were modeled. These variations can be used in velocity taper designs to reduce the radiofrequency (RF) phase velocity in synchronism with the decelerating electron beam. Such circuit designs can result in enhanced TWT power and efficiency
Smartphone Medical Applications Useful for the Rural Practitioner
Like other similarly situated rural states, West Virginiaâs patients and practitioners often experience access barriers to current medical expertise for multiple disciplines. This article was generated to help bridge this gap and highlights the best-rated mobile medical applications (Apps) for smartphone use. From finding drug interactions and dosing schedules to discussing patients in HIPAA-compliant formats, Apps are becoming integral to the practice of 21st Century medicine. The increased use of these Apps by physicians-in-training and established practitioners highlights the shift from reliance upon the medical library to the easy to use mobile-based technology platforms. This article provides our practitioners, physician extenders, medical trainees, and office staff a guide to access and assess the utility of some of the best rated medical and HIPAA compliant Apps
Diastolic Ventricular Interaction in Heart Failure With Preserved Ejection Fraction
Background Exerciseâinduced pulmonary hypertension is common in heart failure with preserved ejection fraction (HFpEF). We hypothesized that this could result in pericardial constraint and diastolic ventricular interaction in some patients during exercise. Methods and Results Contrast stress echocardiography was performed in 30 HFpEF patients, 17 hypertensive controls, and 17 normotensive controls (healthy). Cardiac volumes, and normalized radius of curvature (NRC) of the interventricular septum at endâdiastole and endâsystole, were measured at rest and peakâexercise, and compared between the groups. The septum was circular at rest in all 3 groups at endâdiastole. At peakâexercise, endâsystolic NRC increased to 1.47±0.05 (P<0.001) in HFpEF patients, confirming development of pulmonary hypertension. Endâdiastolic NRC also increased to 1.54±0.07 (P<0.001) in HFpEF patients, indicating septal flattening, and this correlated significantly with endâsystolic NRC (Ï=0.51, P=0.007). In hypertensive controls and healthy controls, peakâexercise endâsystolic NRC increased, but this was significantly less than observed in HFpEF patients (HFpEF, P=0.02 versus hypertensive controls; P<0.001 versus healthy). There were also small, nonâsignificant increases in endâdiastolic NRC in both groups (hypertensive controls, +0.17±0.05, P=0.38; healthy, +0.06±0.03, P=0.93). In HFpEF patients, peakâexercise endâdiastolic NRC also negatively correlated (r=â0.40, P<0.05) with the change in left ventricular endâdiastolic volume with exercise (ie, the FrankâStarling mechanism), and a trend was noted towards a negative correlation with change in stroke volume (r=â0.36, P=0.08). Conclusions Exercise pulmonary hypertension causes substantial diastolic ventricular interaction on exercise in some patients with HFpEF, and this restriction to left ventricular filling by the right ventricle exacerbates the preâexisting impaired FrankâStarling response in these patients
3-He in the Milky Way Interstellar Medium: Ionization Structure
The cosmic abundance of the 3-He isotope has important implications for many
fields of astrophysics. We are using the 8.665 GHz hyperfine transition of
3-He+ to determine the 3-He/H abundance in Milky Way HII regions and planetary
nebulae. This is one in a series of papers in which we discuss issues involved
in deriving accurate 3-He/H abundance ratios from the available measurements.
Here we describe the ionization correction we use to convert the 3-He+/H+
abundance, y3+, to the 3-He/H abundance, y3. In principle the nebular
ionization structure can significantly influence the y3 derived for individual
sources. We find that in general there is insufficient information available to
make a detailed ionization correction. Here we make a simple correction and
assess its validity. The correction is based on radio recombination line
measurements of H+ and 4-He+, together with simple core-halo source models. We
use these models to establish criteria that allow us to identify sources that
can be accurately corrected for ionization and those that cannot. We argue that
this effect cannot be very large for most of the sources in our observational
sample. For a wide range of models of nebular ionization structure we find that
the ionization correction factor varies from 1 to 1.8. Although large
corrections are possible, there would have to be a conspiracy between the
density and ionization structure for us to underestimate the ionization
correction by a substantial amount.Comment: 36 pages, 4 figures To appear Astrophysical Journal, 20 August 2007,
vol 665, no
Structure of the first representative of Pfam family PF04016 (DUF364) reveals enolase and Rossmann-like folds that combine to form a unique active site with a possible role in heavy-metal chelation.
The crystal structure of Dhaf4260 from Desulfitobacterium hafniense DCB-2 was determined by single-wavelength anomalous diffraction (SAD) to a resolution of 2.01â
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using the semi-automated high-throughput pipeline of the Joint Center for Structural Genomics (JCSG) as part of the NIGMS Protein Structure Initiative (PSI). This protein structure is the first representative of the PF04016 (DUF364) Pfam family and reveals a novel combination of two well known domains (an enolase N-terminal-like fold followed by a Rossmann-like domain). Structural and bioinformatic analyses reveal partial similarities to Rossmann-like methyltransferases, with residues from the enolase-like fold combining to form a unique active site that is likely to be involved in the condensation or hydrolysis of molecules implicated in the synthesis of flavins, pterins or other siderophores. The genome context of Dhaf4260 and homologs additionally supports a role in heavy-metal chelation
HII Region Metallicity Distribution in the Milky Way Disk
The distribution of metals in the Galaxy provides important information about
galaxy formation and evolution. HII regions are the most luminous objects in
the Milky Way at mid-infrared to radio wavelengths and can be seen across the
entire Galactic disk. We used the NRAO Green Bank Telescope (GBT) to measure
radio recombination line and continuum emission in 81 Galactic HII regions. We
calculated LTE electron temperatures using these data. In thermal equilibrium
metal abundances are expected to set the nebular electron temperature with high
abundances producing low temperatures. Our HII region distribution covers a
large range of Galactocentric radius (5 to 22 kpc) and samples the Galactic
azimuth range 330 degree to 60 degree. Using our highest quality data (72
objects) we derived an O/H Galactocentric radial gradient of -0.0383 +/- 0.0074
dex/kpc. Combining these data with a similar survey made with the NRAO 140 Foot
telescope we get a radial gradient of -0.0446 +/- 0.0049 dex/kpc for this
larger sample of 133 nebulae. The data are well fit by a linear model and no
discontinuities are detected. Dividing our sample into three Galactic azimuth
regions produced significantly different radial gradients that range from -0.03
to -0.07 dex/kpc. These inhomogeneities suggest that metals are not well mixed
at a given radius. We stress the importance of homogeneous samples to reduce
the confusion of comparing data sets with different systematics. Galactic
chemical evolution models typically derive chemical evolution along only the
radial dimension with time. Future models should consider azimuthal evolution
as well.Comment: Accepted for publication in Ap
The structure of BVU2987 from Bacteroides vulgatus reveals a superfamily of bacterial periplasmic proteins with possible inhibitory function.
Proteins that contain the DUF2874 domain constitute a new Pfam family PF11396. Members of this family have predominantly been identified in microbes found in the human gut and oral cavity. The crystal structure of one member of this family, BVU2987 from Bacteroides vulgatus, has been determined, revealing a ÎČ-lactamase inhibitor protein-like structure with a tandem repeat of domains. Sequence analysis and structural comparisons reveal that BVU2987 and other DUF2874 proteins are related to ÎČ-lactamase inhibitor protein, PepSY and SmpA_OmlA proteins and hence are likely to function as inhibitory proteins
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