4,509 research outputs found
The National Forest Management Act in a Changing Society, 1976-1996: How Well Has It Worked in the Past 20 Years? Will It Work in the 21st Century?
12 pages
Stability and Control Characteristics at Subsonic Speeds of a Flat-Top Arrowhead Wing-Body Combination
A wind-tunnel investigation was made to determine the longitudinal- and lateral-stability derivatives of a flat-top wing-body configuration at Mach numbers from 0.22 to 0.90 and Reynolds numbers of 3.5 and 17 million. The wing had a leading-edge sweepback of 78.9 deg and a cathedral of 45 deg on the outer panels. The tests included the determination of the effectiveness of elevon and rudder controls and also an investigation of ground effects. The model was tested at angles of attack up to 28 deg and angles of sideslip up to 18 deg. The dynamic response of this configuration has been determined from the wind-tunnel data for a simulated airplane having a wing loading of 17.7 pounds per square foot. The longitudinal data show a forward shift in aerodynamic center of 10 percent of the mean aerodynamic chord as the lift coefficient is increased above 0.1. Although flown in the lift range of decreasing stability, the simulated airplane did not encounter pitch-up in maneuvers initiated from steady level flight with zero static margin unless a load factor of 2.2 was exceeded. This maneuver margin was provided by a large value of pitching moment due to pitching velocity. The number of cycles to damp the Dutch roll mode to half amplitude, the time constants of the roll subsidence and spiral divergence modes, and control effectiveness in roll are computed. The lateral stability is shown to be positive but is marginal in meeting the military specifications for today's aircraft. An analog computer study has been made in five degrees of freedom (constant velocity) which illustrates that the handling characteristics are satisfactory. Several programed rolling maneuvers and coordinated turns also illustrate the handling qualities of the airplane
ARPES in the normal state of the cuprates: comparing the marginal Fermi liquid and spin fluctuation scenarios
We address the issue whether ARPES measurements of the spectral function near the Fermi surface in the normal state of near optimally doped
cuprates can distinguish between the marginal Fermi liquid scenario and the
spin-fluctuation scenario. We argue that the data for momenta near the Fermi
surface are equally well described by both theories, but this agreement is
nearly meaningless as in both cases one has to add to a large constant of yet unknown origin. We show that the data can be
well fitted by keeping only this constant term in the self-energy. To
distinguish between the two scenarios, one has to analyze the data away from
the Fermi surface, when the intrinsic piece in becomes
dominant.Comment: Accepted for publication in Europhysics Letters, Incorrect
interpretation of reference 10 correcte
Recollection, Familiarity, and Cortical Reinstatement: A Multivoxel Pattern Analysis
SummaryEpisodic memory retrieval is thought to involve reinstatement of the neurocognitive processes engaged when an episode was encoded. Prior fMRI studies and computational models have suggested that reinstatement is limited to instances in which specific episodic details are recollected. We used multivoxel pattern-classification analyses of fMRI data to investigate how reinstatement is associated with different memory judgments, particularly those accompanied by recollection versus a feeling of familiarity (when recollection is absent). Classifiers were trained to distinguish between brain activity patterns associated with different encoding tasks and were subsequently applied to recognition-related fMRI data to determine the degree to which patterns were reinstated. Reinstatement was evident during both recollection- and familiarity-based judgments, providing clear evidence that reinstatement is not sufficient for eliciting a recollective experience. The findings are interpreted as support for a continuous, recollection-related neural signal that has been central to recent debate over the nature of recognition memory processes
World Species of the Genus Chromoteleia Ashmead (Hymenoptera, Platygastridae, Scelioninae)
The genus Chromoteleia was originally described by William H. Ashmead (1893), based on the colorful type species Chromoteleia semicyanea from the Caribbean island of Saint Vincent. Currently, six species have been recorded from the New World and a single species from Africa. One fossil species, C. theobaldi Maneval, was reported from Baltic amber (from 40~60 mya), but the status of this species is not clear. These creatures are parasites of insect eggs, but which host they attack is still unclear. Since its original description Chromoteleia has never been comprehensively reviewed. In this study, a total of 27 species are recognized worldwide, of which 21 are new to science. All species are described and illustrated. Several important morphological characters are provided for the identification of the species of Chromoteleia and the geographical distribution records of the genus are expanded to 29 countries in Central and South America, the Caribbean, and Africa. The documentation of the species diversity is crucial to the understanding of the evolution and interrelationships in this genus, as well as informing conservation policies
Isolation of Bartonella sp. from Sheep Blood
A Bartonella sp. was isolated from sheep blood. Bacterial identification was conducted by using electron microscopy and DNA sequencing of the 16S rRNA, citrate synthase, riboflavin synthase, and RNAase P genes. To our knowledge, this is the first report of ovine Bartonella infection
Measurement of the dynamic charge response of materials using low-energy, momentum-resolved electron energy-loss spectroscopy (M-EELS)
One of the most fundamental properties of an interacting electron system is
its frequency- and wave-vector-dependent density response function, . The imaginary part, , defines the
fundamental bosonic charge excitations of the system, exhibiting peaks wherever
collective modes are present. quantifies the electronic compressibility
of a material, its response to external fields, its ability to screen charge,
and its tendency to form charge density waves. Unfortunately, there has never
been a fully momentum-resolved means to measure at the
meV energy scale relevant to modern elecronic materials. Here, we demonstrate a
way to measure with quantitative momentum resolution by applying
alignment techniques from x-ray and neutron scattering to surface
high-resolution electron energy-loss spectroscopy (HR-EELS). This approach,
which we refer to here as "M-EELS," allows direct measurement of with meV resolution while controlling the momentum with an accuracy
better than a percent of a typical Brillouin zone. We apply this technique to
finite-q excitations in the optimally-doped high temperature superconductor,
BiSrCaCuO (Bi2212), which exhibits several phonons
potentially relevant to dispersion anomalies observed in ARPES and STM
experiments. Our study defines a path to studying the long-sought collective
charge modes in quantum materials at the meV scale and with full momentum
control.Comment: 26 pages, 10 sections, 7 figures, and an appendi
Open questions in the study of population III star formation
The first stars were key drivers of early cosmic evolution. We review the
main physical elements of the current consensus view, positing that the first
stars were predominantly very massive. We continue with a discussion of
important open questions that confront the standard model. Among them are
uncertainties in the atomic and molecular physics of the hydrogen and helium
gas, the multiplicity of stars that form in minihalos, and the possible
existence of two separate modes of metal-free star formation.Comment: 15 pages, 2 figures. To appear in the conference proceedings for IAU
Symposium 255: Low-Metallicity Star Formation: From the First Stars to Dwarf
Galaxie
The Amateur Sky Survey Mark III Project
The Amateur Sky Survey (TASS) is a loose confederation of amateur and
professional astronomers. We describe the design and construction of our Mark
III system, a set of wide-field drift-scan CCD cameras which monitor the
celestial equator down to thirteenth magnitude in several passbands. We explain
the methods by which images are gathered, processed, and reduced into lists of
stellar positions and magnitudes. Over the period October, 1996, to November,
1998, we compiled a large database of photometric measurements. One of our
results is the "tenxcat" catalog, which contains measurements on the standard
Johnson-Cousins system for 367,241 stars; it contains links to the light curves
of these stars as well.Comment: 20 pages, including 4 figures; additional JPEG files for Figures 1,
2. Submitted to PAS
- ā¦