36,874 research outputs found
Epitaxial gallium arsenide wafers
The preparation of GaAs epitaxial layers by a vapor transport process using AsCl3, Ga and H2 was pursued to provide epitaxial wafers suitable for the fabrication of transferred electron oscillators and amplifiers operating in the subcritical region. Both n-n(+) structures, and n(++)-n-n(+) sandwich structures were grown using n(+) (Si-doped) GaAs substrates. Process variables such as the input AsCl3 concentration, gallium temperature, and substrate temperature and temperature gradient and their effects on properties are presented and discussed
Are cocaine-seeking “habits” necessary for the development of addiction-like behavior in rats?
Drug self-administration models of addiction typically require animals to make the same response (e.g., a lever-press or nose-poke) over and over to procure and take drugs. By their design, such procedures often produce behavior controlled by stimulus-response (S-R) habits. This has supported the notion of addiction as a “drug habit”, and has led to considerable advances in our understanding of the neurobiological basis of such behavior. However, for addicts to procure drugs, like cocaine, often requires considerable ingenuity and flexibility in seeking behavior, which, by definition, precludes the development of habits. To better model drug-seeking behavior in addicts we first developed a novel cocaine self-administration procedure (the Puzzle Self-Administration Procedure; PSAP) that required rats to solve a new puzzle every day to gain access to cocaine, which they then self-administered on an Intermittent Access (IntA) schedule. Such daily problem-solving precluded the development of S-R seeking habits. We then asked whether prolonged PSAP/IntA experience would nevertheless produce ‘symptoms of addiction’. It did, including escalation of intake, sensitized motivation for drug, continued drug use in the face of adverse consequences and very robust cue-induced reinstatement of drug-seeking, especially in a subset of ‘addiction-prone’ rats. Furthermore, drug-seeking behavior continued to require dopamine neurotransmission in the core of the nucleus accumbens (but not the dorsolateral striatum). We conclude that the development of S-R seeking habits is not necessary for the development of cocaine addiction-like behavior in rats
Field research on the spectral properties of crops and soils, volume 1
The experiment design, data acquisition and preprocessing, data base management, analysis results and development of instrumentation for the AgRISTARS Supporting Research Project, Field Research task are described. Results of several investigations on the spectral reflectance of corn and soybean canopies as influenced by cultural practices, development stage and nitrogen nutrition are reported as well as results of analyses of the spectral properties of crop canopies as a function of canopy geometry, row orientation, sensor view angle and solar illumination angle are presented. The objectives, experiment designs and data acquired in 1980 for field research experiments are described. The development and performance characteristics of a prototype multiband radiometer, data logger, and aerial tower for field research are discussed
Atlas of soil reflectance properties
A compendium of soil spectral reflectance curves together with soil test results and site information is presented in an abbreviated manner listing those soil properties most important in influencing soil reflectance. Results are presented for 251 soils from 39 states and Brazil. A narrative key describes relationships between soil parameters and reflectance curves. All soils are classified according to the U.S. soil taxonomy and soil series name for ease of identification
Some exact solutions with torsion in 5-D Einstein-Gauss-Bonnet gravity
Exact solutions with torsion in Einstein-Gauss-Bonnet gravity are derived.
These solutions have a cross product structure of two constant curvature
manifolds. The equations of motion give a relation for the coupling constants
of the theory in order to have solutions with nontrivial torsion. This relation
is not the Chern-Simons combination. One of the solutions has a structure and is so the purely gravitational analogue of the
Bertotti-Robinson space-time where the torsion can be seen as the dual of the
covariantly constant electromagnetic field.Comment: 19 pages, LaTex, no figures. References added, notation clarified.
Accepted for publication on Physical Review
Critical current of a Josephson junction containing a conical magnet
We calculate the critical current of a
superconductor/ferromagnetic/superconductor (S/FM/S) Josephson junction in
which the FM layer has a conical magnetic structure composed of an in-plane
rotating antiferromagnetic phase and an out-of-plane ferromagnetic component.
In view of the realistic electronic properties and magnetic structures that can
be formed when conical magnets such as Ho are grown with a polycrystalline
structure in thin-film form by methods such as direct current sputtering and
evaporation, we have modeled this situation in the dirty limit with a large
magnetic coherence length (). This means that the electron mean free
path is much smaller than the normalized spiral length which in
turn is much smaller than (with as the length a complete
spiral makes along the growth direction of the FM). In this physically
reasonable limit we have employed the linearized Usadel equations: we find that
the triplet correlations are short ranged and manifested in the critical
current as a rapid oscillation on the scale of . These rapid
oscillations in the critical current are superimposed on a slower oscillation
which is related to the singlet correlations. Both oscillations decay on the
scale of . We derive an analytical solution and also describe a
computational method for obtaining the critical current as a function of the
conical magnetic layer thickness.Comment: Extended version of the published paper. Additional information about
the computational method is included in the appendi
The Relationship Between Molecular Gas Tracers and Kennicutt-Schmidt Laws
We provide a model for how Kennicutt-Schmidt (KS) laws, which describe the
correlation between star formation rate and gas surface or volume density,
depend on the molecular line chosen to trace the gas. We show that, for lines
that can be excited at low temperatures, the KS law depends on how the line
critical density compares to the median density in a galaxy's star-forming
molecular clouds. High critical density lines trace regions with similar
physical properties across galaxy types, and this produces a linear correlation
between line luminosity and star formation rate. Low critical density lines
probe regions whose properties vary across galaxies, leading to a star
formation rate that varies superlinearly with line luminosity. We show that a
simple model in which molecular clouds are treated as isothermal and homogenous
can quantitatively reproduce the observed correlations between galactic
luminosities in far infrared and in the CO(1->0) and HCN(1->0) lines, and
naturally explains why these correlations have different slopes. We predict
that IR-line luminosity correlations should change slope for galaxies in which
the median density is close to the line critical density. This prediction may
be tested by observations of lines such as HCO^+(1->0) with intermediate
critical densities, or by HCN(1->0) observations of intensely star-forming high
redshift galaxies with very high densities. Recent observations by Gao et al.
hint at just such a change in slope. We argue that deviations from linearity in
the HCN(1->0)-IR correlation at high luminosity are consistent with the
assumption of a constant star formation efficiency.Comment: Accepted to ApJ. 11 pages, 4 figures, emulateapj format. This version
has some additional models exploring the effects of varying metallicity and
temperature. The conclusions are unchange
A multiband radiometer and data acquisition system for remote sensing field research
Specifications are described for a recently developed prototype multispectral data acquisition system which consists of multiband radiometer with 8 bands between 0.4 and 12.5 micrometers and a data recording module to record data from the radometer and ancillary sources. The systems is adaptable to helicopter, truck, or tripod platforms, as well as hand-held operation. The general characteristics are: (1) comparatively inexpensive to acquire, maintain and operate; (2) simple to operate and calibrate; (3) complete with data hardware and software; and (4) well documented for use by researchers. The instrument system is to be commercially available and can be utilized by many researchers to obtain large numbers of accurate, calibrated spectral measurements. It can be a key element in improving and advancing the capability for field research in remote sensing
- …