51,610 research outputs found
Method of making impurity-type semiconductor electrical contacts Patent
Fabrication of sintered impurity semiconductor brushes for electrical energy transfe
Improved molybdenum disulfide-silver motor brushes have extended life
Motor brushes of proper quantities of molybdenum disulfide and copper or silver are manufactured by sintering techniques. Graphite molds are used. These brushes operate satisfactorily for long periods in normal atmosphere or in a high-vacuum environment
Mathematical modelling plant signalling networks
During the last two decades, molecular genetic studies and the completion of the sequencing of the Arabidopsis thaliana genome have increased knowledge of hormonal regulation in plants. These signal transduction pathways act in concert through gene regulatory and signalling networks whose main components have begun to be elucidated. Our understanding of the resulting cellular processes is hindered by the complex, and sometimes counter-intuitive, dynamics of the networks, which may be interconnected through feedback controls and cross-regulation. Mathematical modelling provides a valuable tool to investigate such dynamics and to perform in silico experiments that may not be easily carried out in a laboratory. In this article, we firstly review general methods for modelling gene and signalling networks and their application in plants. We then describe specific models of hormonal perception and cross-talk in plants. This sub-cellular analysis paves the way for more comprehensive mathematical studies of hormonal transport and signalling in a multi-scale setting
An interplanetary magnetic field ensemble at 1 AU
A method for calculation ensemble averages from magnetic field data is described. A data set comprising approximately 16 months of nearly continuous ISEE-3 magnetic field data is used in this study. Individual subintervals of this data, ranging from 15 hours to 15.6 days comprise the ensemble. The sole condition for including each subinterval in the averages is the degree to which it represents a weakly time-stationary process. Averages obtained by this method are appropriate for a turbulence description of the interplanetary medium. The ensemble average correlation length obtained from all subintervals is found to be 4.9 x 10 to the 11th cm. The average value of the variances of the magnetic field components are in the approximate ratio 8:9:10, where the third component is the local mean field direction. The correlation lengths and variances are found to have a systematic variation with subinterval duration, reflecting the important role of low-frequency fluctuations in the interplanetary medium
Trapped particle flux models at NSSDC/WDC-A-R/S
The data needed in the future for trapped particle modeling are summarized. A short summary of past and future modeling activities and a list of satellite data that have not yet been considered in the modeling efforts is included
Li I and K I Scatter in Cool Pleiades Dwarfs
We utilize high-resolution (R~60,000), high S/N (~100) spectroscopy of 17
cool Pleiades dwarfs to examine the confounding star-to-star scatter in the
6707 Li I line strengths in this young cluster. Our Pleiads, selected for their
small projected rotational velocity and modest chromospheric emission, evince
substantial scatter in the linestrengths of 6707 Li I feature that is absent in
the 7699 K I resonance line. The Li I scatter is not correlated with that in
the high-excitation 7774 O I feature, and the magnitude of the former is
greater than the latter despite the larger temperature sensitivity of the O I
feature. These results suggest that systematic errors in linestrength
measurements due to blending, color (or color-based T_eff) errors, or line
formation effects related to an overlying chromosphere are not the principal
source of Li I scatter in our stars. There do exist analytic spot models that
can produce the observed Li scatter without introducing scatter in the K I line
strengths or the color-magnitude diagram. However, these models predict factor
of >3 differences in abundances derived from the subordinate 6104 and resonance
6707 Li I features; we find no difference in the abundances determined from
these two features. These analytic spot models also predict CN line strengths
significantly larger than we observe in our spectra. The simplest explanation
of the Li, K, CN, and photometric data is that there must be a real abundance
component to the Pleiades Li dispersion. We suggest that this real abundance
component is the manifestation of relic differences in erstwhile
pre-main-sequence Li burning caused by effects of surface activity on stellar
structure. We discuss observational predictions of these effects.Comment: 35 pages, 7 figures; accepted by Ap
Age structure, dispersion and diet of a population of stoats (Mustela erminea) in southern Fiordland during the decline phase of the beechmast cycle
The dispersion, age structure and diet of stoats (Mustela erminea) in beech forest in the Borland and Grebe Valleys, Fiordland National Park, were examined during December and January 2000/01, 20 months after a heavy seed-fall in 1999. Thirty trap stations were set along a 38-km transect through almost continuous beech forest, at least 1 km apart. Mice were very scarce (nights, C/100TN) along two standard index lines placed at either end of the transect, compared with November 1999 (>60/100TN), but mice were detected (from footprints in stoat tunnels) along an 8 km central section of the transect (stations 14-22). Live trapping with one trap per station (total 317.5 trap nights) in December 2000 caught 2 female and 23 male stoats, of which 10 (including both females) were radio collared. The minimum range lengths of the two females along the transect represented by the trap line were 2.2 and 6.0 km; those of eight radio-tracked males averaged 2.9 ± 1.7 km. Stations 14-22 tended to be visited more often, by more marked individual stoats, than the other 21 stations.
Fenn trapping at the same 30 sites, but with multiple traps per station (1333.5 trap nights), in late January 2001 collected carcasses of 35 males and 28 females (including 12 of the marked live-trapped ones). Another two marked males were recovered dead. The stoat population showed no sign of chronic nutritional stress (average fat reserve index = 2.8 on a scale of 1-4 where 4 = highest fat content); and only one of 63 guts analysed was empty. Nevertheless, all 76 stoats handled were adults with 1-3 cementum annuli in their teeth, showing that reproduction had failed that season. Prey categories recorded in descending frequency of occurrence were birds, carabid beetle (ground beetle), weta, possum, rat, and mouse. The frequencies of occurrence of mice and birds in the diet of these stoats (10% and 48%, respectively) were quite different from those in stoats collected in Pig Creek, a tributary of the Borland River (87%, 5%), 12 months previously when mice were still abundant. Five of the six stoat guts containing mice were collected within 1 km of stations 14-22
Atmospheric nitrogen oxides (NO and NO2) at Dome C, East Antarctica, during the OPALE campaign
Mixing ratios of the atmospheric nitrogen oxides NO and NO2 were measured as part of the OPALE (Oxidant Production in Antarctic Lands & Export) campaign at Dome C, East Antarctica (75.1 degrees S, 123.3 degrees E, 3233 m), during December 2011 to January 2012. Profiles of NOx mixing ratios of the lower 100m of the atmosphere confirm that, in contrast to the South Pole, air chemistry at Dome C is strongly influenced by large diurnal cycles in solar irradiance and a sudden collapse of the atmospheric boundary layer in the early evening. Depth profiles of mixing ratios in firn air suggest that the upper snowpack at Dome C holds a significant reservoir of photolytically produced NO2 and is a sink of gas-phase ozone (O-3). First-time observations of bromine oxide (BrO) at Dome C show that mixing ratios of BrO near the ground are low, certainly less than 5 pptv, with higher levels in the free troposphere. Assuming steady state, observed mixing ratios of BrO and RO2 radicals are too low to explain the large NO2 : NO ratios found in ambient air, possibly indicating the existence of an unknown process contributing to the atmospheric chemistry of reactive nitrogen above the Antarctic Plateau. During 2011-2012, NOx mixing ratios and flux were larger than in 2009-2010, consistent with also larger surface O-3 mixing ratios resulting from increased net O-3 production. Large NOx mixing ratios at Dome C arise from a combination of continuous sunlight, shallow mixing height and significant NOx emissions by surface snow (F-NOx). During 23 December 2011-12 January 2012, median F-NOx was twice that during the same period in 20092010 due to significantly larger atmospheric turbulence and a slightly stronger snowpack source. A tripling of F-NOx in December 2011 was largely due to changes in snowpack source strength caused primarily by changes in NO3- concentrations in the snow skin layer, and only to a secondary order by decrease of total column O-3 and associated increase in NO3- photolysis rates. A source of uncertainty in model estimates of F-NOx is the quantum yield of NO3- photolysis in natural snow, which may change over time as the snow ages
Sprayable low density ablator and application process
A sprayable, low density ablative composition is described consisting esentially of: (1) 100 parts by weight of a mixture of 25-65% by weight of phenolic microballoons, 0-20% by weight of glass microballoons, 4-10% by weight of glass fibers, 25-45% by weight of an epoxy-modified polyurethane resin, 2-4% by weight of a bentonite dispersing aid, and 1-2% by weight of an alcohol activator for the bentonite; (2) 1-10 parts by weight of an aromatic amine curing agent; and (3) 200-400 parts by weight of a solvent
The Wolf-Rayet counterpart of Cygnus X-3
We present orbital-phase resolved I and K-band spectroscopy of Cygnus X-3.
All spectra show emission lines characteristic of Wolf-Rayet stars of the WN
subclass. On time scales longer than about one day, the line strengths show
large changes, both in flux and in equivalent width. In addition, the line
ratios change, corresponding to a variation in spectral subtype of WN6/7 to
WN4/5. We confirm the finding that at times when the emission lines are weak,
they shift in wavelength as a function of orbital phase, with maximum blueshift
coinciding with infrared and X-ray minimum, and maximum redshift half an orbit
later. Furthermore, we confirm the prediction -- made on the basis of previous
observations -- that at times when the emission lines are strong, no clear
wavelength shifts are observed. We describe a simplified, but detailed model
for the system, in which the companion of the X-ray source is a Wolf-Rayet star
whose wind is at times ionised by the X-ray source, except for the part in the
star's shadow. With this model, the observed spectral variations can be
reproduced with only a small number of free parameters. We discuss and verify
the ramifications of this model, and find that, in general, the observed
properties can be understood. We conclude that Cyg X-3 is a Wolf-Rayet/X-ray
binary.Comment: 22 pages, 13 figures. Accepted by A&A. Uses l-aa.sty. A complete
20-page postscript file using the correct postscript fonts is available at
http://astro.caltech.edu/~mhvk/bigcyg.ps.
- …