2,828 research outputs found
Eight-band calculations of strained InAs/GaAs quantum dots compared with one, four, and six-band approximations
The electronic structure of pyramidal shaped InAs/GaAs quantum dots is
calculated using an eight-band strain dependent Hamiltonian. The
influence of strain on band energies and the conduction-band effective mass are
examined. Single particle bound-state energies and exciton binding energies are
computed as functions of island size. The eight-band results are compared with
those for one, four and six bands, and with results from a one-band
approximation in which m(r) is determined by the local value of the strain. The
eight-band model predicts a lower ground state energy and a larger number of
excited states than the other approximations.Comment: 8 pages, 7 figures, revtex, eps
AUTONOMOUS MANEUVERING: A DEFENSE ADVANTAGE FOR AFSOC AIRCRAFT
The U.S. military continues to operate in increasingly complex security environments and can no longer expect uncontested or dominant superiority in every domain. Aircraft operated by special operations forces (SOF) need improved defensive capabilities to support missions in non-permissive environments. Integrating automation and human-machine teaming into existing defensive capabilities may reduce threat reaction time and increase the effectiveness of defensive maneuvers in manned and unmanned aircraft configurations. This thesis examines the value of aircraft maneuvering as part of a threat reaction to identify situations where human intervention negatively affects timing and accuracy. It also considers opportunities to replicate Merlin Labs' approach to flight automation and incorporate a machine-trained system capable of performing defensive maneuvers into existing aircraft. The analysis indicates aircraft maneuvering is critical to an effective threat reaction, and automating select operator actions can increase survivability against certain surface-to-air threats. This thesis recommends a renewed focus on defensive capabilities for SOF aircraft and endorses integrating onboard autonomous systems into traditionally manned platforms to improve defensive threat reactions. It also advocates for continued research into the use of optionally manned aircraft in SOF missions to refine their operational utility and expand capabilities across a variety of mission platforms.Major, United States Air ForceMajor, United States Air ForceApproved for public release. Distribution is unlimited
The GEOS-3 orbit determination investigation
The nature and improvement in satellite orbit determination when precise altimetric height data are used in combination with conventional tracking data was determined. A digital orbit determination program was developed that could singly or jointly use laser ranging, C-band ranging, Doppler range difference, and altimetric height data. Two intervals were selected and used in a preliminary evaluation of the altimeter data. With the data available, it was possible to determine the semimajor axis and eccentricity to within several kilometers, in addition to determining an altimeter height bias. When used jointly with a limited amount of either C-band or laser range data, it was shown that altimeter data can improve the orbit solution
Absence of correlation between built-in electric dipole moment and quantum Stark effect in InAs/GaAs self-assembled quantum dots
We report significant deviations from the usual quadratic dependence of the
ground state interband transition energy on applied electric fields in
InAs/GaAs self-assembled quantum dots. In particular, we show that conventional
second-order perturbation theory fails to correctly describe the Stark shift
for electric field below kV/cm in high dots. Eight-band calculations demonstrate this effect is predominantly due to
the three-dimensional strain field distribution which for various dot shapes
and stoichiometric compositions drastically affects the hole ground state. Our
conclusions are supported by two independent experiments.Comment: 4 pages, 4 figure
Electronic structure of strained InP/GaInP quantum dots
We calculate the electronic structure of nm scale InP islands embedded in
. The calculations are done in the envelope approximation
and include the effects of strain, piezoelectric polarization, and mixing among
6 valence bands. The electrons are confined within the entire island, while the
holes are confined to strain induced pockets. One pocket forms a ring at the
bottom of the island near the substrate interface, while the other is above the
island in the GaInP. The two sets of hole states are decoupled. Polarization
dependent dipole matrix elements are calculated for both types of hole states.Comment: Typographical error corrected in strain Hamiltonia
Intuitionistc probability and the Bayesian objection to dogmatism
Given a few assumptions, the probability of a conjunction is raised, and the probability of its negation is lowered, by conditionalising upon one of the conjuncts. This simple result appears to bring Bayesian confirmation theory into tension with the prominent dogmatist view of perceptual justification â a tension often portrayed as a kind of âBayesian objectionâ to dogmatism. In a recent paper, David Jehle and Brian Weatherson observe that, while this crucial result holds within classical probability theory, it fails within intuitionistic probability theory. They conclude that the dogmatist who is willing to take intuitionistic logic seriously can make a convincing reply to the Bayesian objection. In this paper, I argue that this conclusion is premature â the Bayesian objection can survive the transition from classical to intuitionistic probability, albeit in a slightly altered form. I shall conclude with some general thoughts about what the Bayesian objection to dogmatism does and doesnât show
Proper motions and membership probabilities of stars in the region of globular cluster NGC 6809
NGC 6809 is a luminous metal-poor halo globular cluster that is relatively
easy to study due to its proximity and low concentration. Because of its high
Galactic latitude (b = -23deg), interstellar reddening and contamination is not
very high. We aim to determine the relative proper motion and membership
probability of the stars in the wide area of globular cluster NGC 6809. To
target cluster members reliably during spectroscopic surveys and both spatial
and radial distributions in the cluster outskirts without including field
stars, a good proper motion and membership probability catalogue of NGC 6809 is
required.The archival data of two epochs with a time-base line of 7.1 years
have been collected with Wide Field Imager (WFI) mounted on the 2.2m MPG/ESO
telescope. The CCD images of both epochs have been reduced using the
astrometric techniques as described in Anderson et al. (2006). The calibrated
UBVI magnitudes have been derived using Stetson's secondary standard stars. We
derived the relative proper motion and membership probabilities for \sim 12600
stars in the field of globular cluster NGC 6809. The measurement error in
proper motions for the stars of V \sim 17 mag is 2.0 mas/yr, gradually
increasing up to \sim 3 mas/yr at V = 20 mag. We also provide the membership
probability for the published different types of sources in NGC 6809. An
electronic catalogue with proper motion and membership probability for the
stars will be available to the astronomical community.Comment: Accepted for publication in The A&A. 11 pages. 11 figures,5 Table
The characteristics of sexual abuse in sport: A multidimensional scaling analysis of events described in media reports
Most research on sexual abuse has been conducted within family settings (Fergusson & Mullen, 1999). In recent years, following several high profile convictions and scandals, research into sexual abuse has also encompassed institutional and community settings such as sport and the church (Gallagher, 2000; Wolfe et al., 2003). Research into sexual abuse in sport, for example, began with both prevalence studies (Kirby & Greaves, 1996; Leahy, Pretty & Tenenbaum, 2002) and qualitative analyses of the processes and experiences of athlete sexual abuse (Brackenridge, 1997; Cense & Brackenridge, 2001, Toftegaard Nielsen, 2001). From such work, descriptions of the modus operandi of abusers in sport, and the experiences and consequences for athlete victims, have been provided, informing both abuse prevention work and coach education. To date, however, no study has provided empirical support for multiple associations or identified patterns of sex offending in sport in ways that might allow comparisons with research-generated models of offending outside sport. This paper reports on an analysis of 159 cases of criminally defined sexual abuse, reported in the print media over a period of 15 years. The main aim of the study was to identify the nature of sex offending in sport focusing on the methods and locations of offences. The data were analysed using multidimensional scaling (MDS), as a data reduction method, in order to identify the underlying themes within the abuse and explore the inter-relationships of behaviour, victim and context variables. The findings indicate that there are specific themes that can be identified within the perpetrator strategies that include âintimateâ, âaggressiveâ, and ââdominantâ modes of interaction. The same patterns that are described here within the specific context of sport are consistent with themes that emerge from similar behavioural analyses of rapists (Canter & Heritage, 1990; Bishopp, 2003) and child molester groups (Canter, Hughes & Kirby, 1998). These patterns show a correspondence to a broader behavioural model â the interpersonal circumplex (e.g., Leary 1957). Implications for accreditation and continuing professional education of sport psychologists are noted
Theory of band gap bowing of disordered substitutional II-VI and III-V semiconductor alloys
For a wide class of technologically relevant compound III-V and II-VI
semiconductor materials AC and BC mixed crystals (alloys) of the type
A(x)B(1-x)C can be realized. As the electronic properties like the bulk band
gap vary continuously with x, any band gap in between that of the pure AC and
BC systems can be obtained by choosing the appropriate concentration x, granted
that the respective ratio is miscible and thermodynamically stable. In most
cases the band gap does not vary linearly with x, but a pronounced bowing
behavior as a function of the concentration is observed. In this paper we show
that the electronic properties of such A(x)B(1-x)C semiconductors and, in
particular, the band gap bowing can well be described and understood starting
from empirical tight binding models for the pure AC and BC systems. The
electronic properties of the A(x)B(1-x)C system can be described by choosing
the tight-binding parameters of the AC or BC system with probabilities x and
1-x, respectively. We demonstrate this by exact diagonalization of finite but
large supercells and by means of calculations within the established coherent
potential approximation (CPA). We apply this treatment to the II-VI system
Cd(x)Zn(1-x)Se, to the III-V system In(x)Ga(1-x)As and to the III-nitride
system Ga(x)Al(1-x)N.Comment: 14 pages, 10 figure
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