22,381 research outputs found
On the response to ocean surface currents in synthetic aperture radar imagery
The balance of wave action spectral density for a fixed wave-number is expressed in terms of a new dimensionless function, the degree of saturation, b, and is applied to an analysis of the variations of this quantity (and local spectral level) at wave-numbers large compared to that of the spectral peak, that are produced by variations in the ocean surface currents in the presence of wind input and wave breaking. Particular care is taken to provide physically based representations of wind input and loss by wave breaking and a relatively convenient equation is derived that specifies the distribution of the degree of saturation in a current field, relative to its ambient (undisturbed) background in the absence of currents. The magnitude of the variations in b depends on two parameters, U(o)/c, where U/(o) is the velocity scale of the current and c the phase speed of the surface waves at the (fixed) wave-number considered or sampled by SAR, and S = (L/lambda) (u*/c)(2), where L is the length scale of the current distribution, lambda the wavelength of the surface waves the length scale of the current distribution, lambda the wavelength of the surface waves and u* the friction velocity of the wind
Results of an experimental program to provide low cost computer searches of the NASA information file to university graduate students in the southeast Final report
Experimental program to provide low cost computer searches of NASA information files to university graduate student
A comprehensive WebCT integration system
Murdoch University, in collaboration with industry partners, has developed a sophisticated middleware application (WebCTMan) between WebCT and other corporate systems, such as the Callista student records system, the Concept 1 human resources system and Murdochās own authentication system. This presentation will describe the architecture and functionality of this system.
The impetus for WebCTMan was to enable Murdoch to change its student records database with minimal impact on our WebCT installation. However, WebCTMan now gives us great flexibility in managing our WebCT installation, enabling us to manage courses across teaching periods, and upgrade easily. This paper describes the context in which this system was built and gives an overview of its architecture.
Courses in WebCTMan can have a status of active (where student details are updated nightly), inactive (where all students are orphans), and static (where student accounts are valid but not updated). Tools are available to change this status, and easily activate and deactivate courses. Different versions of courses are maintained for each teaching period, resolving the problem of overlap between semesters, when some students still have deferred examinations after the start of a new semester.
In addition to managing students, WebCTMan provides functionality to manage staff and courses. Staff can request courses to be created or cloned from other courses. They can also create their own guest accounts and allocate tutors and markers to courses, and download class lists. Operators can create or rename courses on demand, as well as changing the roles of staff, including primary and secondary designers. A subset of functions is available to helpdesk operators, who can lookup details of both students and staff within the system
On some properties of the spectrum of wind-generated ocean waves; Comments on Dr. Phillip\u27s paper
The resonance theory of wave generation predicts that
Mottness: Identifying the Propagating Charge Modes in doped Mott Insulators
High-temperature superconductivity in the copper-oxide ceramics remains an
unsolved problem because we do not know what the propagating degrees of freedom
are in the normal state. As a result, we do not know what are the weakly
interacting degrees of freedom which pair up to form the superconducting
condensate. That the electrons are not the propagating degrees of freedom in
the cuprates is seen most directly from experiments that show spectral weight
redistributions over all energy scales. Of course, the actual propagating
degrees of freedom minimize such spectral rearrangements. This review focuses
on the range of epxerimental consequences such UV-IR mixings have on the normal
state of the cuprates, such as the pseudogap, mid-infrared band, temperature
dependence of the Hall number, the superfluid density, and a recent theoretical
advance which permits the identification of the weakly interacting degrees of
freedom in a doped Mott insulator. Within this theory, we show how the wide
range of phenomena which typify the normal state of the cuprates arises
including linear resistivity.Comment: To appear as a Colloquium in the April issue of Rev. Mod. Phys
Updated version contains new references and a clarification concerning Fig.
8
The low frequency components of the spectrum of wind-generated waves
This paper is concerned with the dynamical processes involved in the growth of the lower frequency spectral components of wind-generated waves. Some calculations of Miles (1960) are extended, leading to the concept of a transition frequency for a given fetch as the frequency above which energy is supplied to the waves by the instability (or sheltering) mechanism and below which it is supplied by the resonance mechanism...
n-CdSe/p-ZnTe based wide band-gap light emitters: Numerical simulation and design
The only IIāVI/IIāVI wide bandāgap heterojunction to provide both good lattice match and pā and nātype dopability is CdSe/ZnTe. We have carried out numerical simulations of several light emitter designs incorporating CdSe, ZnTe, and Mg alloys. In the simulations, Poissonās equation is solved in conjunction with the hole and electron current and continuity equations. Radiative and nonradiative recombination in bulk material and at interfaces are included in the model. Simulation results show that an nāCdSe/pāZnTe heterostructure is unfavorable for efficient wide bandāgap light emission due to recombination in the CdSe and at the CdSe/ZnTe interface. An nāCdSe/Mg_(x)Cd_(1āx)Se/pāZnTe heterostructure significantly reduces interfacial recombination and facilitates electron injection into the pāZnTe layer. The addition of a Mg_(y)Zn_(1āy)Te electron confining layer further improves the efficiency of light emission. Finally, an nāCdSe/Mg_(x)Cd_(1āx)Se/Mg_(y)Zn_(1āy)Te/pāZnTe design allows tunability of the wavelength of light emission from green into the blue wavelength regime
Photoluminescence upconversion at GaAs/InGaP2 interfaces driven by a sequential two-photon absorption mechanism
This paper reports on the results of an investigation into the nature of photoluminescence upconversion at
GaAs/InGaP2 interfaces. Using a dual-beam excitation experiment, we demonstrate that the upconversion in our
sample proceeds via a sequential two-photon optical absorption mechanism. Measurements of photoluminescence
and upconversion photoluminescence revealed evidence of the spatial localization of carriers in the InGaP2
material, arising from partial ordering of the InGaP2. We also observed the excitation of a two-dimensional electron
gas at the GaAs/InGaP2 heterojunction that manifests as a high-energy shoulder in the GaAs photoluminescence
spectrum. Furthermore, the results of upconversion photoluminescence excitation spectroscopy demonstrate that
the photon energy onset of upconversion luminescence coincides with the energy of the two-dimensional electron
gas at the GaAs/InGaP2 interface, suggesting that charge accumulation at the interface can play a crucial role in
the upconversion process
X-ray photoelectron spectroscopy measurement of valence-band offsets for Mg-based semiconductor compounds
We have used x-ray photoelectron spectroscopy to measure the valence-band offsets for the lattice matched MgSe/Cd0.54Zn0.46Se and MgTe/Cd0.88Zn0.12Te heterojunctions grown by molecular beam epitaxy. By measuring core level to valence-band maxima and core level to core level binding energy separations, we obtain values of 0.56+/-0.07 eV and 0.43+/-0.11 eV for the valence-band offsets of MgSe/Cd0.54Zn0.46Se and MgTe/Cd0.88Zn0.12Te, respectively. Both of these values deviate from the common anion rule, as may be expected given the unoccupied cation d orbitals in Mg. Application of our results to the design of current II-VI wide band-gap light emitters is discussed
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