58,902 research outputs found
A new species of Colletes (Hymenoptera: Apoidea: Colletidae) from northern Florida and Georgia, with notes on the Colletes of those states
Colletes ultravalidus Hall & Ascher, new species, is described from several sites in northwestern Florida and southeastern Georgia. It is a member of the inaequalis species group, very similar to C. validus Cresson, a specialist of Ericaceae, but can be distinguished by an even more elongate malar area and the absence of conspicuous tergal fascia. Colletes ultravalidus has been found flying from early winter to early spring when it forms nest aggregations in xeric sites adjacent to shrub bog or basin swamp, the habitat of Pieris phyllyreifolia (Hook.) DC. (Ericaceae), the most likely, but as yet unconfirmed, host plant of the new species. State records of Colletes for Florida and Georgia are reviewed and discrepancies in taxonomy and distributional limits between Stephen’s 1954 revision of the genus and Mitchell’s 1960 monograph of eastern North American bees are noted. We concur with Stephen that the distributions of several taxa in Colletes are more limited than that reported by Mitchell
Quantum fluctuations of a vortex in an optical lattice
Using a variational ansatz for the wave function of the Bose-Einstein
condensate, we develop a quantum theory of vortices and quadrupole modes in a
one-dimensional optical lattice. We study the coupling between the quadrupole
modes and Kelvin modes, which turns out to be formally analogous to the theory
of parametric processes in quantum optics. This leads to the possibility of
squeezing vortices. We solve the quantum multimode problem for the Kelvin modes
and quadrupole modes numerically and find properties that cannot be explained
with a simple linear-response theory.Comment: final version, minor change
The principle of equivalence and projective structure in space-times
This paper discusses the extent to which one can determine the space-time
metric from a knowledge of a certain subset of the (unparametrised) geodesics
of its Levi-Civita connection, that is, from the experimental evidence of the
equivalence principle. It is shown that, if the space-time concerned is known
to be vacuum, then the Levi-Civita connection is uniquely determined and its
associated metric is uniquely determined up to a choice of units of
measurement, by the specification of these geodesics. It is further
demonstrated that if two space-times share the same unparametrised geodesics
and only one is assumed vacuum then their Levi-Civita connections are again
equal (and so the other metric is also a vacuum metric) and the first result
above is recovered.Comment: 23 pages, submitted to Classical and Quantum Gravit
Barriers Inhibiting Industry from Partnering with Universities: Evidence from the Advanced Technology Program
A small sample of 38 Advanced Technology Projects funded between 1993 and 1996 are surveyed to explore the reasons for university non-participation, or, in the cases where they did participate, whether the partnerships encountered any difficulties from their participation. 32 percent report that intellectual property issues were an insurmountable barrier to university participation. Such barriers are more likely when the ATP share of funding is high and when the expected duration of the research is relatively short. They are also somewhat more likely for projects involving chemical technology, and when industrial participants have had previous experience with universities as research partners. These difficulties over IP may arise because the cultures in the two institutional forms differ, or because the original ATP guidelines do not recognize the existence of the Bayh-Dole Act (which grants universities title to inventions made by their employees using outside funding).
Universities as Research Partners
Universities are a key institution in the US innovation system and an important aspect of their involvement is the role they play in Private-Public Partnering activities. This study seeks to gain a better understanding of the performance of university-industry research partnerships using a sample survey of pre-commercial research projects funded the U.S. government's Advanced Technology Program. Although results must be interpreted cautiously due to the small size of the sample, the study finds that projects with university involvement tend to be in areas involving "new" science and therefore experience more difficulty and delay but also are more likely not to be aborted prematurely. We interpret this finding to imply that universities are contributing to basic research awareness and insight among the partners in ATP-funded projects.
Recent developments in the application of risk analysis to waste technologies.
The European waste sector is undergoing a period of unprecedented change driven
by business consolidation, new legislation and heightened public and government
scrutiny. One feature is the transition of the sector towards a process industry
with increased pre-treatment of wastes prior to the disposal of residues and the
co-location of technologies at single sites, often also for resource recovery
and residuals management. Waste technologies such as in-vessel composting, the
thermal treatment of clinical waste, the stabilisation of hazardous wastes,
biomass gasification, sludge combustion and the use of wastes as fuel, present
operators and regulators with new challenges as to their safe and
environmentally responsible operation. A second feature of recent change is an
increased regulatory emphasis on public and ecosystem health and the need for
assessments of risk to and from waste installations. Public confidence in waste
management, secured in part through enforcement of the planning and permitting
regimes and sound operational performance, is central to establishing the
infrastructure of new waste technologies. Well-informed risk management plays a
critical role. We discuss recent developments in risk analysis within the sector
and the future needs of risk analysis that are required to respond to the new
waste and resource management agenda
Comparison of Material Properties and Microstructure of Specimens Built Using the 3D Systems Vanguard HS and Vanguard HiQ+HSSLS Systems
The HiQ upgrade to the 3D Systems Vanguard selective laser sintering (SLS) machine incorporates a revised thermal calibration system and new control software. The paper compares
the tensile modulus, tensile strength, elongation at break, flexural modulus, Izod impact resistance and microstructure of two batteries of standard specimens built from recycled Duraform
PA (Nylon 12). The first set is built on a Vanguard HS system and the second on the same
system with the HiQ upgrade installed. The upgrade reduces user intervention, decreases total build time and improves surface finish. However, using the default processing parameters,
tensile, flexure and impact properties are all found to decline after the upgrade is installed.Mechanical Engineerin
Conditional Spectral Analysis of Replicated Multiple Time Series with Application to Nocturnal Physiology
This article considers the problem of analyzing associations between power
spectra of multiple time series and cross-sectional outcomes when data are
observed from multiple subjects. The motivating application comes from sleep
medicine, where researchers are able to non-invasively record physiological
time series signals during sleep. The frequency patterns of these signals,
which can be quantified through the power spectrum, contain interpretable
information about biological processes. An important problem in sleep research
is drawing connections between power spectra of time series signals and
clinical characteristics; these connections are key to understanding biological
pathways through which sleep affects, and can be treated to improve, health.
Such analyses are challenging as they must overcome the complicated structure
of a power spectrum from multiple time series as a complex positive-definite
matrix-valued function. This article proposes a new approach to such analyses
based on a tensor-product spline model of Cholesky components of
outcome-dependent power spectra. The approach flexibly models power spectra as
nonparametric functions of frequency and outcome while preserving geometric
constraints. Formulated in a fully Bayesian framework, a Whittle likelihood
based Markov chain Monte Carlo (MCMC) algorithm is developed for automated
model fitting and for conducting inference on associations between outcomes and
spectral measures. The method is used to analyze data from a study of sleep in
older adults and uncovers new insights into how stress and arousal are
connected to the amount of time one spends in bed
Depletion isolation effect in Vertical MOSFETS during transition from partial to fully depleted operation
A simulation study is made of floating-body effects (FBEs) in vertical MOSFETs due to depletion isolation as the pillar thickness is reduced from 200 to 10 nm. For pillar thicknesses between 200–60 nm, the output characteristics with and without impact ionization are identical at a low drain bias and then diverge at a high drain bias. The critical drain bias Vdc for which the increased drain–current is observed is found to decrease with a reduction in pillar thickness. This is explained by the onset of FBEs at progressively lower values of the drain bias due to the merging of the drain depletion regions at the bottom of the pillar (depletion isolation). For pillar thicknesses between 60–10 nm, the output characteristics show the opposite behavior, namely, the critical drain bias increases with a reduction in pillar thickness. This is explained by a reduction in the severity of the FBEs due to the drain debiasing effect caused by the elevated body potential. Both depletion isolation and gate–gate coupling contribute to the drain–current for pillar thicknesses between 100–40 nm
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