32,346 research outputs found
Elevation scanning laser/multi-sensor hazard detection system controller and mirror/mast speed control components
The electro-mechanical and electronic systems involved with pointing a laser beam from a roving vehicle along a desired vector are described. A rotating 8 sided mirror, driven by a phase-locked dc motor servo system, and monitored by a precision optical shaft encoder is used. This upper assembly is then rotated about an orthogonal axis to allow scanning into all 360 deg around the vehicle. This axis is also driven by a phase locked dc motor servo-system, and monitored with an optical shaft encoder. The electronics are realized in standard TTL integrated circuits with UV-erasable proms used to store desired coordinates of laser fire. Related topics such as the interface to the existing test vehicle are discussed
Social Security and Medicare : the impending fiscal challenge
Social Security—and the solvency of its Trust Fund—have increasingly become a focus of discussion in the media and policy circles. The basic problem is that promised benefits will soon exceed program revenues. Without changes in benefits or funding, the Trustees of Social Security project that assets in the Trust Fund will be depleted in 2041. While Social Security is a serious problem for taxpayers and beneficiaries, Medicare poses an even greater challenge. Together, the two programs’ benefits currently amount to about 6 percent of GDP. By 2080 they are projected to swell to 20 percent. With spending on these two programs projected to grow faster than the nation’s GDP, the Board of Trustees of Social Security and Medicare have concluded that “We do not believe the currently projected long-run growth rates of Social Security and Medicare are sustainable under current financing arrangements.” To keep the programs solvent without slashing benefits or increasing tax revenues, the federal budget deficit would need to grow drastically. Thus changes will likely be needed to the structure of the two programs. In fact, any viable solution is likely to involve changes in government spending and taxes. Hakkio and Wiseman provide a framework for understanding the nature of the fiscal challenges posed by Social Security and Medicare—a prerequisite for finding specific solutionsSocial security ; Medicare
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Addressing the needs of international postgraduate students: the role of social capital
Self-evidently, international students are likely to have considerable informational and social needs when coming to study in the UK. This paper reports the findings of a small study of such needs among international postgraduate students in the School of Health Sciences. It was an interview study, with twelve students participating. Though the study was designed to support the creation of an online resource, the findings suggest that meeting those needs satisfactorily requires a multi-faceted approach. Both face-to-face and online processes are needed to help students to develop the social capital necessary to success in undertaking the course, getting to know the university, and adjusting to life in England
Spectral isolation of bi-invariant metrics on compact Lie groups
We show that a bi-invariant metric on a compact connected Lie group is
spectrally isolated within the class of left-invariant metrics. In fact, we
prove that given a bi-invariant metric on there is a positive integer
such that, within a neighborhood of in the class of left-invariant
metrics of at most the same volume, is uniquely determined by the first
distinct non-zero eigenvalues of its Laplacian (ignoring multiplicities).
In the case where is simple, can be chosen to be two.Comment: 10 pages, new title, revised abstract and introduction, minor typos
corrected, to appear in Ann. Inst. Fourier (Grenoble
Flexible synthesis of polyfunctionalised 3-fluoropyrroles
An efficient and selective approach for the synthesis of polyfunctionalised 3-fluoropyrroles has been developed starting from commercial aldehydes. The methodology is concise, efficient and allows for the modular and systematic assembly of polysubstituted 3-fluoropyrroles. This synthesis provides an alternative and highly convergent strategy for the generation of these chemically and biologically important units
Highly Efficient Modeling of Dynamic Coronal Loops
Observational and theoretical evidence suggests that coronal heating is
impulsive and occurs on very small cross-field spatial scales. A single coronal
loop could contain a hundred or more individual strands that are heated
quasi-independently by nanoflares. It is therefore an enormous undertaking to
model an entire active region or the global corona. Three-dimensional MHD codes
have inadequate spatial resolution, and 1D hydro codes are too slow to simulate
the many thousands of elemental strands that must be treated in a reasonable
representation. Fortunately, thermal conduction and flows tend to smooth out
plasma gradients along the magnetic field, so "0D models" are an acceptable
alternative. We have developed a highly efficient model called Enthalpy-Based
Thermal Evolution of Loops (EBTEL) that accurately describes the evolution of
the average temperature, pressure, and density along a coronal strand. It
improves significantly upon earlier models of this type--in accuracy,
flexibility, and capability. It treats both slowly varying and highly impulsive
coronal heating; it provides the differential emission measure distribution,
DEM(T), at the transition region footpoints; and there are options for heat
flux saturation and nonthermal electron beam heating. EBTEL gives excellent
agreement with far more sophisticated 1D hydro simulations despite using four
orders of magnitude less computing time. It promises to be a powerful new tool
for solar and stellar studies.Comment: 34 pages, 8 figures, accepted by Astrophysical Journal (minor
revisions of original submitted version
Flatfish herding behavior in response to trawl sweeps: a comparison of diel responses to conventional sweeps and elevated sweeps
Commercial bottom trawls often have sweeps to herd fish into
the net. Elevation of the sweeps off the seaf loor may reduce seafloor disturbance, but also reduce herding
effectiveness. In both field and laboratory experiments, we examined the behavior of flatfish in response to sweeps. We tested the hypotheses that 1) sweeps are more effective at
herding flatfish during the day than at night, when fish are unable to see approaching gear, and that 2) elevation
of sweeps off the seafloor reduces herding during the day, but not at night. In sea trials, day catches were greater than night catches for four out of six flatfish species examined. The elevation of sweeps 10 cm significantly
decreased catches during the day, but not at night. Laboratory experiments revealed northern rock sole (Lepidopsetta polyxystra) and Pacific halibut (Hippoglossus stenolepis) were more likely to be herded\ud
by the sweep in the light, whereas in the dark they tended to pass under or over the sweep. In the light, elevation
of the sweep reduced herding, and more fish passed under the sweep. In contrast, in the dark, sweep elevation
had little effect upon the number of fish that exhibited herding behavior. The results of both field and laboratory
experiments were consistent with the premise that vision is the principle sensory input that controls fish behavior and orientation to trawl gear, and gear performance will differ
between conditions where flatfish can see, in contrast to where they cannot see, the approaching gear
Refraction of shear zones in granular materials
We study strain localization in slow shear flow focusing on layered granular
materials. A heretofore unknown effect is presented here. We show that shear
zones are refracted at material interfaces in analogy with refraction of light
beams in optics. This phenomenon can be obtained as a consequence of a recent
variational model of shear zones. The predictions of the model are tested and
confirmed by 3D discrete element simulations. We found that shear zones follow
Snell's law of light refraction.Comment: 4 pages, 3 figures, minor changes, jounal ref. adde
A sensitive genetic-based detection capability for Didymosphenia geminata
It is now well recognized that the increase in global transportation over the last two decades has brought with it an increased potential for the introduction of unwanted microorganisms (aquatic or terrestrial) that may have drastic effects on human and ecosystem health and agriculture. We have developed and validated a unique genetic fingerprinting tool for D. geminata. In concert, we developed field collection and preservation techniques specific for D. geminata along with genetic-based procedures that can now reliably detect D. geminate from a complex environmental community with a high degree of sensitivity. Recent work (Phase 2) has shown that the described methods will provide detection levels from <1 – 10,000 cells ml-1. We contend that the genetic based detection approaches used in this study offer great promise to meet the increasing demands to monitor the global threat from invasive micro-organisms
Measurement of pilot describing functions in single-controller multiloop tasks
Measurement of pilot describing functions in single controller multiloop task
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