1,529 research outputs found
Method of forming frozen spheres in a force-free drop tower
Hollow glass spheres are shaped by the effects of surface tension acting on bubbles of glass in its molten state. A downwardly flowing stream of air accelerated at a one-G rate of acceleration is established through a drop bubbles on molten glass are introduced into the stream of air and frozen and as they are accelerated at a one-G rate of acceleration
Improved cavity-type absolute total-radiation radiometer
Conical cavity-type absolute radiometer measures the intensity of radiant energy to an accuracy of one to two percent in a vacuum of ten to the minus fifth torr or lower. There is a uniform response over the ultraviolet, visible, and infrared range, and it requires no calibration or comparison with a radiation standard
Conically shaped cavity radiometer with a dual purpose cone winding Patent
Black body radiometer design with temperature sensing and cavity heat source cone windin
Free-stream noise and transition measurements on a cone in a Mach 3.5 pilot low-disturbance tunnel
A small scale Mach 3.5 wind tunnel incorporating certain novel design features and intended for boundary-layer-transition research has been tested. The free stream noise intensities and spectral distributions were determined throughout the test section for several values of unit Reynolds number and for nozzle boundary layer bleed on and off. The boundary layer transition location on a slender cone and the response of this to changes in the noise environment were determined. Root mean square free stream noise levels ranged from less than one tenth up to values approaching those for conventional nozzles, with the lowest values prevailing at upstream locations within the nozzle. For low noise conditions, cone transition Reynolds numbers were in the range of those for free flight; whereas for high noise conditions, they were in the range of those in conventional tunnels
Rocket calibration of the Nimbus 6 solar constant measurements
Total solar irradiance was observed simultaneously outside the earth's atmosphere by three types of absolute cavity radiometers and duplicates of four of the Nimbus 6 Earth Radiation Budget (ERB) solar channels in a June 1976 sounding rocket experiment. The preliminary average solar constant result from the cavity radiometers is 1367 Wm (-2) with an uncertainty of less than + or - 0.5% in S.I. units. The duplicate ERB channel 3 on the rocket gave a value of 1389 Wm (-2) which agreed exactly with the Nimbus 6 ERB channel 3 measurement made simultaneously with the rocket flight
Robust Inference of Trees
This paper is concerned with the reliable inference of optimal
tree-approximations to the dependency structure of an unknown distribution
generating data. The traditional approach to the problem measures the
dependency strength between random variables by the index called mutual
information. In this paper reliability is achieved by Walley's imprecise
Dirichlet model, which generalizes Bayesian learning with Dirichlet priors.
Adopting the imprecise Dirichlet model results in posterior interval
expectation for mutual information, and in a set of plausible trees consistent
with the data. Reliable inference about the actual tree is achieved by focusing
on the substructure common to all the plausible trees. We develop an exact
algorithm that infers the substructure in time O(m^4), m being the number of
random variables. The new algorithm is applied to a set of data sampled from a
known distribution. The method is shown to reliably infer edges of the actual
tree even when the data are very scarce, unlike the traditional approach.
Finally, we provide lower and upper credibility limits for mutual information
under the imprecise Dirichlet model. These enable the previous developments to
be extended to a full inferential method for trees.Comment: 26 pages, 7 figure
Ground-state properties of rutile: electron-correlation effects
Electron-correlation effects on cohesive energy, lattice constant and bulk
compressibility of rutile are calculated using an ab-initio scheme. A
competition between the two groups of partially covalent Ti-O bonds is the
reason that the correlation energy does not change linearly with deviations
from the equilibrium geometry, but is dominated by quadratic terms instead. As
a consequence, the Hartree-Fock lattice constants are close to the experimental
ones, while the compressibility is strongly renormalized by electronic
correlations.Comment: 1 figure to appear in Phys. Rev.
Electron attachment to valence-excited CO
The possibility of electron attachment to the valence state of CO
is examined using an {\it ab initio} bound-state multireference configuration
interaction approach. The resulting resonance has symmetry;
the higher vibrational levels of this resonance state coincide with, or are
nearly coincident with, levels of the parent state. Collisional
relaxation to the lowest vibrational levels in hot plasma situations might
yield the possibility of a long-lived CO state.Comment: Revtex file + postscript file for one figur
Global analyses of TetR family transcriptional regulators in mycobacteria indicates conservation across species and diversity in regulated functions
BACKGROUND: Mycobacteria inhabit diverse niches and display high metabolic versatility. They can colonise both humans and animals and are also able to survive in the environment. In order to succeed, response to environmental cues via transcriptional regulation is required. In this study we focused on the TetR family of transcriptional regulators (TFTRs) in mycobacteria. RESULTS: We used InterPro to classify the entire complement of transcriptional regulators in 10 mycobacterial species and these analyses showed that TFTRs are the most abundant family of regulators in all species. We identified those TFTRs that are conserved across all species analysed and those that are unique to the pathogens included in the analysis. We examined genomic contexts of 663 of the conserved TFTRs and observed that the majority of TFTRs are separated by 200 bp or less from divergently oriented genes. Analyses of divergent genes indicated that the TFTRs control diverse biochemical functions not limited to efflux pumps. TFTRs typically bind to palindromic motifs and we identified 11 highly significant novel motifs in the upstream regions of divergently oriented TFTRs. The C-terminal ligand binding domain from the TFTR complement in M. tuberculosis showed great diversity in amino acid sequence but with an overall architecture common to other TFTRs. CONCLUSION: This study suggests that mycobacteria depend on TFTRs for the transcriptional control of a number of metabolic functions yet the physiological role of the majority of these regulators remain unknown. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12864-015-1696-9) contains supplementary material, which is available to authorized users
Electron affinities of the first- and second- row atoms: benchmark ab initio and density functional calculations
A benchmark ab initio and density functional (DFT) study has been carried out
on the electron affinities of the first- and second-row atoms. The ab initio
study involves basis sets of and quality, extrapolations to
the 1-particle basis set limit, and a combination of the CCSD(T), CCSDT, and
full CI electron correlation methods. Scalar relativistic and spin-orbit
coupling effects were taken into account. On average, the best ab initio
results agree to better than 0.001 eV with the most recent experimental
results. Correcting for imperfections in the CCSD(T) method improves the mean
absolute error by an order of magnitude, while for accurate results on the
second-row atoms inclusion of relativistic corrections is essential. The latter
are significantly overestimated at the SCF level; for accurate spin-orbit
splitting constants of second-row atoms inclusion of (2s,2p) correlation is
essential. In the DFT calculations it is found that results for the 1st-row
atoms are very sensitive to the exchange functional, while those for second-row
atoms are rather more sensitive to the correlation functional. While the LYP
correlation functional works best for first-row atoms, its PW91 counterpart
appears to be preferable for second-row atoms. Among ``pure DFT'' (nonhybrid)
functionals, G96PW91 (Gill 1996 exchange combined with Perdew-Wang 1991
correlation) puts in the best overall performance. The best results overall are
obtained with the 1-parameter hybrid modified Perdew-Wang (mPW1) exchange
functionals of Adamo and Barone [J. Chem. Phys. {\bf 108}, 664 (1998)], with
mPW1LYP yielding the best results for first-row, and mPW1PW91 for second-row
atoms. Indications exist that a hybrid of the type mPW1LYP +
mPW1PW91 yields better results than either of the constituent functionals.Comment: Phys. Rev. A, in press (revised version, review of issues concerning
DFT and electron affinities added
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