2,683 research outputs found
Calibration of a gamma-ray telescope using tagged position annihilation photons
Measurements of detection efficiency, angular resolution, and energy resolution properties of a gamma ray telescope used to study celestial gamma rays from balloon flight altitudes are described. Nearly monochromatic photons produced at the National Bureau of Standards tagged photon facility were used for the calibration. Details of the photon beam configuration and properties and results of the measurements made at photon energies of 15.1 and 31.1 MeV are presented. Finally, the data are compared with a Monte Carlo analysis of the instrument properties
From splashing to bouncing: the influence of viscosity on the impact of suspension droplets on a solid surface
We experimentally investigated the splashing of dense suspension droplets
impacting a solid surface, extending prior work to the regime where the
viscosity of the suspending liquid becomes a significant parameter. The overall
behavior can be described by a combination of two trends. The first one is that
the splashing becomes favored when the kinetic energy of individual particles
at the surface of a droplet overcomes the confinement produced by surface
tension. This is expressed by a particle-based Weber number . The second
is that splashing is suppressed by increasing the viscosity of the solvent.
This is expressed by the Stokes number , which influences the effective
coefficient of restitution of colliding particles. We developed a phase diagram
where the splashing onset is delineated as a function of both and .
A surprising result occurs at very small Stokes number, where not only
splashing is suppressed but also plastic deformation of the droplet. This leads
to a situation where droplets can bounce back after impact, an observation we
are able to reproduce using discrete particle numerical simulations that take
into account viscous interaction between particles and elastic energy
An investigation of vegetation and other earth resource/feature parameters using LANDSAT and other remote sensing data. A: LANDSAT. B: Remote sensing of volcanic emissions
There are no author-identified significant results in this report
Aircraft requirements for low/medium density markets
A study was conducted to determine the demand for and the economic factors involved in air transportation in a low and medium density market. The subjects investigated are as follows: (1) industry and market structure, (2) aircraft analysis, (3) economic analysis, (4) field surveys, and (5) computer network analysis. Graphs are included to show the economic requirements and the aircraft performance characteristics
Fluid physics, thermodynamics, and heat transfer experiments in space
An overstudy committee was formed to study and recommend fundamental experiments in fluid physics, thermodynamics, and heat transfer for experimentation in orbit, using the space shuttle system and a space laboratory. The space environment, particularly the low-gravity condition, is an indispensable requirement for all the recommended experiments. The experiments fell broadly into five groups: critical-point thermophysical phenomena, fluid surface dynamics and capillarity, convection at reduced gravity, non-heated multiphase mixtures, and multiphase heat transfer. The Committee attempted to assess the effects of g-jitter and other perturbations of the gravitational field on the conduct of the experiments. A series of ground-based experiments are recommended to define some of the phenomena and to develop reliable instrumentation
Puzzling It Out: The Current State of Scientific Knowledge on Pre-Kindergarten Effects - A Consensus Statement
Scientific research has established that if all children are to achieve their developmental potential, it is important to lay the foundation during the earliest years for lifelong health, learning, and positive behavior. A central question is how well our public pre-kindergarten (pre-K) programs are doing to build this foundation.Forty-two states and the District of Columbia, through 57 pre-K programs, have introduced substantial innovations in their early education systems by developing the infrastructure, program sites, and workforce required to accommodate pre-K education. These programs now serve nearly 30 percent of the nation's 4-year-olds and 5 percent of 3-year-olds
Experimental determination of the evolution of the Bjorken integral at low Q^2
We extract the Bjorken integral Gamma^{p-n}_1 in the range 0.17 < Q^2 < 1.10
GeV^2 from inclusive scattering of polarized electrons by polarized protons,
deuterons and 3He, for the region in which the integral is dominated by nucleon
resonances. These data bridge the domains of the hadronic and partonic
descriptions of the nucleon. In combination with earlier measurements at higher
Q^2, we extract the non-singlet twist-4 matrix element f_2.Comment: Quoted world data updated. Minor change in some results, Minor
rephrasin
Deviations from Matthiessen's Rule for and
We have measured the change in the resistivity of thin films of and upon introducing point defects by electron
irradiation at low temperatures, and we find significant deviations from
Matthiessen's rule. For a fixed irradiation dose, the induced change in
resistivity {\it decreases} with increasing temperature. Moreover, for a fixed
temperature, the increase in resistivity with irradiation is found to be {\it
sublinear}. We suggest that the observed behavior is due to the marked
anisotropic scattering of the electrons together with their relatively short
mean free path (both characteristic of many metallic oxides including cuprates)
which amplify effects related to the Pippard ineffectiveness condition
Physical Weight Loading Induces Expression of Tryptophan Hydroxylase 2 in the Brain Stem.
Sustaining brain serotonin is essential in mental health. Physical activities can attenuate mental problems by enhancing serotonin signaling. However, such activity is not always possible in disabled individuals or patients with dementia. Knee loading, a form of physical activity, has been found to mimic effects of voluntary exercise. Focusing on serotonergic signaling, we addressed a question: Does local mechanical loading to the skeleton elevate expression of tryptophan hydroxylase 2 (tph2) that is a rate-limiting enzyme for brain serotonin? A 5 min knee loading was applied to mice using 1 N force at 5 Hz for 1,500 cycles. A 5-min treadmill running was used as an exercise (positive) control, and a 90-min tail suspension was used as a stress (negative) control. Expression of tph2 was determined 30 min – 2 h in three brain regions ––frontal cortex (FC), ventromedial hypothalamus (VMH), and brain stem (BS). We demonstrated for the first time that knee loading and treadmill exercise upregulated the mRNA level of tph2 in the BS, while tail suspension downregulated it. The protein level of tph2 in the BS was also upregulated by knee loading and downregulated by tail suspension. Furthermore, the downregulation of tph2 mRNA by tail suspension can be partially suppressed by pre-application of knee loading. The expression of tph2 in the FC and VMH was not significantly altered with knee loading. In this study we provided evidence that peripheral mechanical loading can activate central tph2 expression, suggesting that physical cues may mediate tph2-cathalyzed serotonergic signaling in the brain
Observation of a narrow structure in p(gamma,K_s)X via interference with phi-meson production
We report observation of a narrow peak structure at ~1.54 GeV with a Gaussian
width sigma=6 MeV in the missing of K_s in the reaction gamma+p = pK_sK_L. The
observed structure may be due to the interference between a strange (or
anti-strange) baryon resonance in the pK_L system and the phi(K_sK_L)
photoproduction leading to the same final state. The statistical significance
of the observed excess of events estimated as the log likelihood ratio of the
resonant signal+background hypothesis and the phi-production based background
only hypothesis corresponds to 5.3 sigma.Comment: Accepted for publication in Physical Review C, 9 pages, 11 figures, 1
table added, revise
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