4,181 research outputs found
Submillimeter, millimeter, and microwave spectral line catalogue
A computer accessible catalogue of submillimeter, millimeter, and microwave spectral lines in the frequency range between O and 3000 GHz (such as; wavelengths longer than 100 m) is discussed. The catalogue was used as a planning guide and as an aid in the identification and analysis of observed spectral lines. The information listed for each spectral line includes the frequency and its estimated error, the intensity, lower state energy, and quantum number assignment. The catalogue was constructed by using theoretical least squares fits of published spectral lines to accepted molecular models. The associated predictions and their estimated errors are based upon the resultant fitted parameters and their covariances
Submillimeter, millimeter, and microwave spectral line catalogue
This report describes a computer accessible catalogue of submillimeter, millimeter, and microwave spectral lines in the frequency range between 0 and 10000 GHz (i.e., wavelengths longer than 30 micrometers). The catalogue can be used as a planning guide or as an aid in the identification and analysis of observed spectral lines. The information listed for each spectral line includes the frequency and its estimated error, the intensity, lower state energy, and quantum number assignment. The catalogue has been constructed using theoretical least squares fits of published spectral lines to accepted molecular models. The associated predictions and their estimated errors are based upon the resultant fitted parameters and their covariances. Future versions of this catalogue will add more atoms and molecules and update the present listings (151 species) as new data appear. The catalogue is available from the authors as a magnetic tape recorded in card images and as a set of microfiche records
Submillimeter, millimeter, and microwave spectral line catalogue
A computer accessible catalogue of submillimeter, millimeter and microwave spectral lines in the frequency range between 0 and 3000 GHZ (i.e., wavelengths longer than 100 mu m) is presented which can be used a planning guide or as an aid in the identification and analysis of observed spectral lines. The information listed for each spectral line includes the frequency and its estimated error, the intensity, lower state energy, and quantum number assignment. The catalogue was constructed by using theoretical least squares fits of published spectral lines to accepted molecular models. The associated predictions and their estimated errors are based upon the resultant fitted parameters and their covariances. Future versions of this catalogue will add more atoms and molecules and update the present listings (133 species) as new data appear. The catalogue is available as a magnetic tape recorded in card images and as a set of microfiche records
Half metallic digital ferromagnetic heterostructure composed of a -doped layer of Mn in Si
We propose and investigate the properties of a digital ferromagnetic
heterostructure (DFH) consisting of a -doped layer of Mn in Si, using
\textit{ab initio} electronic-structure methods. We find that (i) ferromagnetic
order of the Mn layer is energetically favorable relative to antiferromagnetic,
and (ii) the heterostructure is a two-dimensional half metallic system. The
metallic behavior is contributed by three majority-spin bands originating from
hybridized Mn- and nearest-neighbor Si- states, and the corresponding
carriers are responsible for the ferromagnetic order in the Mn layer. The
minority-spin channel has a calculated semiconducting gap of 0.25 eV. Analysis
of the total and partial densities of states, band structure, Fermi surfaces
and associated charge density reveals the marked two-dimensional nature of the
half metallicity. The band lineup is found to be favorable for retaining the
half metal character to near the Curie temperature (). Being Si based
and possibly having a high as suggested by an experiment on dilutely
doped Mn in Si, the heterostructure may be of special interest for integration
into mature Si technologies for spintronic applications.Comment: 4 pages, 4 figures, Revised version, to appear in Phys. Rev. Let
The NASA integrated test facility and its impact on flight research
The Integrated Test Facility (ITF), being built at NASA Ames-Dryden Flight Research Facility, will provide new test capabilities for emerging research aircraft. An overview of the ITF and the challenges being addressed by this unique facility are outlined. The current ITF capabilities, being developed with the X-29 Forward Swept Wing Program, are discussed along with future ITF activities
Implications of the B20 Crystal Structure for the Magneto-electronic Structure of MnSi
Due to increased interest in the unusual magnetic and transport behavior of
MnSi and its possible relation to its crystal structure (B20) which has unusual
coordination and lacks inversion symmetry, we provide a detailed analysis of
the electronic and magnetic structure of MnSi. The non-symmorphic P2_13
spacegroup leads to unusual fourfold degenerate states at the zone corner R
point, as well as ``sticking'' of pairs of bands throughout the entire
Brillouin zone surface. The resulting Fermi surface acquires unusual features
as a result of the band sticking. For the ferromagnetic system (neglecting the
long wavelength spin spiral) with the observed moment of 0.4 \mu_B/Mn, one of
the fourfold levels at R in the minority bands falls at the Fermi energy (E_F),
and a threefold majority level at k=0 also falls at E_F. The band sticking and
presence of bands with vanishing velocity at E_F imply an unusually large phase
space for long wavelength, low energy interband transitions that will be
important for understanding the unusual resistivity and far infrared optical
behavior.Comment: Nine two-column pages with eight figures include
Pest-predator spatial relationships in winter rape: implications for integrated crop management
Douglas Warner, Les J Allen-Williams, Andrew W Ferguson, and Ingrid H Williams, 'Pest–predator spatial relationships in winter rape: implications for integrated crop management', Pest Management Science, Vol. 56 (11): 977-982, November 2000, doi: 10.1002/1526-4998(200011)56:113.0.CO;2-U. Copyright © 2000 Society of Chemical IndustryThe brassica pod midge (Dasineura brassicae) is an important and widespread pest of winter and spring oilseed rape throughout Europe. Pods infested by D brassicae larvae split prematurely, releasing seeds, and the larvae drop to the soil into which they burrow to pupate. At this stage in its lifecycle D brassicae is potentially vulnerable to predation by carabid beetles foraging on the soil surface. This is the first study in the UK to focus on carabid beetles as predators of D brassicae in the oilseed rape crop. The spatio-temporal distributions of larvae of D brassicae dropping to the soil from the crop canopy and of adult carabid beetles active on the soil surface were analysed in two consecutive years. Insect samples were collected from spatially referenced sampling points across each crop. Counts of insects were mapped and analysed, and the degree of spatial association between predator and prey determined using Spatial Analysis by Distance Indices (SADIE). Carabid species abundant and active during peak drop of first generation D brassicae larvae included Agonum dorsale, Amara similata, Harpalus rufipes and Nebria brevicollis. The larvae of D brassicae had a marked edge distribution within the crop. SADIE analysis revealed significant spatial association between larvae of D brassicae and adult H rufipes (P <0.05) in 1998, but not with adults of A dorsale, A similata or N brevicollis. In 1999, there was strong spatial association only between larvae of D brassicae and adult A dorsale (P <0.01). Aggregation of N brevicollis adults occurred in some areas of greatest D brassicae larval counts in 1999, but overall spatial association was not signi®cant. The distributions are discussed in terms of their relevance to integrated crop management (ICM) strategies and spatial targeting of insecticides.Peer reviewe
A 163 micron laser heterodyne radiometer for OH
A 163 micron (1.836 THz) radiometer developed for airplane and/or balloon platforms is described. The laser local oscillator is a CO2 pumped methanol laser operating at a frequency which is approx. 1 GHz from the J = 3/2 - 1/2 transition of OH. The laser is used directly as a local oscillator or is translated in frequency to closer coincidence with the OH emission, depending on achieved detector IF bandwidth. Frequency translation techniques which are described are diode mixing and a method of single sideband generation using an external Stark modulated gas cell. The photoconductive mixer used is a strained Ge crystal, doped with Ga, originally used as an incoherent detector. The uniaxial strain on the Ga doped Ge crystal shifts the threshold for photoconduction from 100/cm to frequencies as low as 50/cm. These detectors are currently being characterized as mixers in the laboratory. Of particular interest are the effect of local oscillator power and strain on IF, bandwidth detector impedance, and conversion loss. Preliminary results of these tests are described and compared with theorectical expectations
Dynamical mean field study of the Mott transition in the half-filled Hubbard model on a triangular lattice
We employ dynamical mean field theory (DMFT) with a Quantum Monte Carlo (QMC)
atomic solver to investigate the finite temperature Mott transition in the
Hubbard model with the nearest neighbor hopping on a triangular lattice at
half-filling. We estimate the value of the critical interaction to be in units of the hopping amplitude through the evolution of the
magnetic moment, spectral function, internal energy and specific heat as the
interaction and temperature are varied. This work also presents a
comparison between DMFT and finite size determinant Quantum Monte Carlo (DQMC)
and a discussion of the advantages and limitations of both methods.Comment: 7 pages, 5 figure
First Principles Study of the Electronic and Vibrational Properties of LiNbO2
In the layered transition metal oxide LiNbO the Nb () ion is
trigonal-prismatically coordinated with O ions, with the resulting crystal
field leading to a single band system for low energy properties. A
tight-binding representation shows that intraplanar second neighbor hopping
meV dominates the first neighbor interaction ( meV). The
first and third neighbor couplings are strongly modified by oxygen
displacements of the symmetric Raman-active vibrational mode, and
electron-phonon coupling to this motion may provide the coupling mechanism for
superconductivity in Li-deficient samples (where K). We calculate all
zone-center phonon modes, identify infrared (IR) and Raman active modes, and
report LO-TO splitting of the IR modes. The Born effective charges for the
metal ions are found to have considerable anisotropy reflecting the degree to
which the ions participate in interlayer coupling and covalent bonding. Insight
into the microscopic origin of the valence band density, composed of Nb
states with some mixing of O states, is obtained from examining
Wannier functions for these bands.Comment: 12 pages, 7 figures; Updated with reviewer comments; Updated
reference
- …