3,491 research outputs found
Limiting stable currents in bounded electron and ion streams
The classical static analysis of the infinite planar diode has been extended to include the effects of finite transverse beam size. Simple expressions have been found for the increase in maximum stable current density over that of an infinite stream for finite cylindrical and strip streams flowing between plates of infinite diodes. The results are also given in terms of stream perveance. The effect of a nonuniform distribution of current across the stream is shown to be relatively small. Experimental values of maximum stable current agree with those obtained from the analysis. A further extension of the static analysis has been made to include the effects of additional conducting plane boundaries parallel to the stream motion. For length-to-width ratios L/D less than 0.25 the tube is adequately described by the results for the infinite planar diode and for L/D greater than 4, the infinitely-long drift tube theory suffices. At intermediate values of L/D, the maximum amount of current that can be stably passed through the tube is greater than that predicted by either asymptotic theory
B-R Colors of Globular Clusters in NGC 6166 (A2199)
We have analysed new R-band photometry of globular clusters in NGC 6166, the
cD galaxy in the cooling flow cluster A2199. In combination with the earlier B
photometry of Pritchet \& Harris (1990), we obtain BR colours for 40
globular clusters in NGC 6166. The mean BR is 1.26 0.11, corresponding
to a mean [Fe/H] = 1 0.4. Given that NGC 6166 is one of the most
luminous cD galaxies studied to date, our result implies significant scatter in
the relationship between mean cluster [Fe/H] and parent galaxy luminosity. We
obtain a globular cluster specific frequency of S 9, with a possible
range between 5 and 18. This value is inconsistent with the value of S
4 determined earlier by Pritchet \& Harris (1990) from B-band
photometry, and we discuss possible reasons for the discrepancy. Finally, we
reassess whether or not cooling flows are an important mechanism for forming
globular clusters in gE/cD galaxies.Comment: 8 pages, uuencoded, gzipped tar file with latex file, 6 figures (Fig
1 omitted because of size), and mn.sty file. Figures will be embedded into
the postscript file. Accepted (March 1996) for publication in MNRA
Complementing PABITRA high-island studies by examining terrestrial plant diversity on atolls
The Pacific-Asia Biodiversity Transect (PABITRA) studies are based on a network of high-island biodiversity sites. These sites are structurally and historically complex. The majority of Pacific islands, in contrast, are low atolls with a common and simple flora and structure. As a result, atolls may serve as "controls" that may provide a way to assess impact of the upland high-island ecosystems on coastal regions of Pacific islands. Atoll studies can complement the PABITRA network because the gateway sites are near each other or separated from one another by one or more atolls. Such an addition will enhance interpretation of high-island ecosystems and their coastal zones because ecosystem surveys can be conducted quickly and accurately in atoll environments. We present results from quantitative studies of plant diversity from seven islets at Ailinginae Atoll in the northern Marshall Islands and discuss the value of this methodology as a way to enhance interpretation of the PABITRA data
A computer operated mass spectrometer system
Digital computer system for processing mass spectrometer output dat
Evaluation of SIR-A space radar for geologic interpretation: United States, Panama, Colombia, and New Guinea
Comparisons between LANDSAT MSS imagery, and aircraft and space radar imagery from different geologic environments in the United States, Panama, Colombia, and New Guinea demonstrate the interdependence of radar system geometry and terrain configuration for optimum retrieval of geologic information. Illustrations suggest that in the case of space radars (SIR-A in particular), the ability to acquire multiple look-angle/look-direction radar images of a given area is more valuable for landform mapping than further improvements in spatial resolution. Radar look-angle is concluded to be one of the most important system parameters of a space radar designed to be used for geologic reconnaissance mapping. The optimum set of system parameters must be determined for imaging different classes of landform features and tailoring the look-angle to local topography
Is anterior N2 enhancement a reliable electrophysiological index of concealed information?
publisher: Elsevier articletitle: Is anterior N2 enhancement a reliable electrophysiological index of concealed information? journaltitle: NeuroImage articlelink: http://dx.doi.org/10.1016/j.neuroimage.2016.08.042 content_type: article copyright: © 2016 Elsevier Inc. All rights reserved
Evidence for Magnetic Field Induced Changes of the Phase of Tunneling States: Spontaneous Echoes in (KBr)(KCN) in Magnetic Fields
Recently, it has been discovered that in contrast to expectations the
low-temperature dielectric properties of some multi-component glasses depend
strongly on magnetic fields. In particular, the low-frequency dielectric
susceptibility and the amplitude of coherent polarization echoes show striking
non-monotonic magnetic field dependencies. The low-temperature dielectric
response of these materials is governed by atomic tunneling systems. We now
have investigated the coherent properties of tunneling states in a crystalline
host in magnetic fields up to 230mT. Two-pulse echo experiments have been
performed on a KBr crystal containing about 7.5% CN. Like in glasses, but
perhaps even more surprising in the case of a crystalline system, we observe a
very strong magnetic field dependence of the echo amplitude. Moreover, for the
first time we have direct evidence that magnetic fields change the phase of
coherent tunneling systems in a well-defined way. We present the data and
discuss the possible origin of this intriguing effect.Comment: 4 pages, 3 figures, submitted to PR
A Self-Consistent Model of the Circumstellar Debris Created by a Giant Hypervelocity Impact in the HD172555 System
Spectral modeling of the large infrared excess in the Spitzer IRS spectra of
HD 172555 suggests that there is more than 10^19 kg of sub-micron dust in the
system. Using physical arguments and constraints from observations, we rule out
the possibility of the infrared excess being created by a magma ocean planet or
a circumplanetary disk or torus. We show that the infrared excess is consistent
with a circumstellar debris disk or torus, located at approximately 6 AU, that
was created by a planetary scale hypervelocity impact. We find that radiation
pressure should remove submicron dust from the debris disk in less than one
year. However, the system's mid-infrared photometric flux, dominated by
submicron grains, has been stable within 4 percent over the last 27 years, from
IRAS (1983) to WISE (2010). Our new spectral modeling work and calculations of
the radiation pressure on fine dust in HD 172555 provide a self-consistent
explanation for this apparent contradiction. We also explore the unconfirmed
claim that 10^47 molecules of SiO vapor are needed to explain an emission
feature at 8 um in the Spitzer IRS spectrum of HD 172555. We find that unless
there are 10^48 atoms or 0.05 Earth masses of atomic Si and O vapor in the
system, SiO vapor should be destroyed by photo-dissociation in less than 0.2
years. We argue that a second plausible explanation for the 8 um feature can be
emission from solid SiO, which naturally occurs in submicron silicate "smokes"
created by quickly condensing vaporized silicate.Comment: Accepted to the Astrophysical Journa
Assessing the Benefits of Misting–Cooling Systems for Growing/Finishing Swine as Affected by Environment and Pig Placement Date
The NCPIG swine growth model was used to evaluate swine growth performance for Wilmington, North Carolina; Bardstown and Mayfield, Kentucky; and Oklahoma City, Oklahoma as influenced by the use of a misting–cooling system. Five pig placement dates (Julian days 106, 126, 146, 166, and 186) were evaluated for each location using 22 years of weather data (1978–1999). The use of a misting system, while quite variable, was found to be generally profitable, reducing the length of the time to reach market weight. As the placement date increased, the average return to misting (8.12 to 6.00 to 4.14 to 3.07 to 1.39 per pig/per year for the cost of a misting system, probabilities for recovering the initial investment amount were determined for each pig placement date and location. These probabilities decreased as the pig placement date increased, except for Oklahoma City, which remained above 98% regardless of the date. For the locations other than Oklahoma City, the probabilities indicated that the earlier placement dates were more favorable for recovering the initial investment
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