13,639 research outputs found
Stationary structure of relativistic superfluid neutron stars
We describe recent progress in the numerical study of the structure of
rapidly rotating superfluid neutron star models in full general relativity. The
superfluid neutron star is described by a model of two interpenetrating and
interacting fluids, one representing the superfluid neutrons and the second
consisting of the remaining charged particles (protons, electrons, muons). We
consider general stationary configurations where the two fluids can have
different rotation rates around a common rotation axis. The previously
discovered existence of configurations with one fluid in a prolate shape is
confirmed.Comment: 5 pages, 2 figures. Conference proceedings for the 26th Spanish
Relativity Meeting (ERE 2002), Menorca, Spain, 22-24 Sept. 200
Radiative Transfer and Radiative driving of Outflows in AGN and Starbursts
To facilitate the study of black hole fueling, star formation, and feedback
in galaxies, we outline a method for treating the radial forces on interstellar
gas due to absorption of photons by dust grains. The method gives the correct
behavior in all of the relevant limits (dominated by the central point source;
dominated by the distributed isotropic source; optically thin; optically thick
to UV/optical; optically thick to IR) and reasonably interpolates between the
limits when necessary. The method is explicitly energy conserving so that
UV/optical photons that are absorbed are not lost, but are rather redistributed
to the IR where they may scatter out of the galaxy. We implement the radiative
transfer algorithm in a two-dimensional hydrodynamical code designed to study
feedback processes in the context of early-type galaxies. We find that the
dynamics and final state of simulations are measurably but only moderately
affected by radiative forces on dust, even when assumptions about the
dust-to-gas ratio are varied from zero to a value appropriate for the Milky
Way. In simulations with high gas densities designed to mimic ULIRGs with a
star formation rate of several hundred solar masses per year, dust makes a more
substantial contribution to the dynamics and outcome of the simulation. We find
that, despite the large opacity of dust to UV radiation, the momentum input to
the flow from radiation very rarely exceeds L/c due to two factors: the low
opacity of dust to the re-radiated IR and the tendency for dust to be destroyed
by sputtering in hot gas environments. We also develop a simplification of our
radiative transfer algorithm that respects the essential physics but is much
easier to implement and requires a fraction of the computational cost.Comment: 25 pages, 17 figures, submitted to MNRA
Detection of submillimeter polarization in the Orion Nebula
Linear polarization of the submillimeter (270 micron) continuum radiation from two regions of Orion was observed: one centered on the Kleinmann-Low Nebula and one centered on the 400 micron peak 1.5' south of the nebula. The polarizations measured for these regions are P = (1.7 +/-0.4)% at phi = 23 deg +/-7 deg and P=(1.7 +/- 0.5)% at phi = 27 deg +/- 7 deg respectively. A 2(sigma) upper limit, P or = 1.6%, was found for the nebular W3(OH). The position angle at KL is orthogonal to that measured at 11 microns by Dyck and Beichman and at 11 and 20 microns by Knacke and Capps. The far-IR values for KL reported by Gull et. al. (approx 2%) and by Cudlip et al. (1 to 2% level) are consistent with the submillimeter results
Active learning pedagogy: Structuring the pre-instruction assignment
Education research is changing the way teachers teach and students learn. In contrast with the lecture-based approach to instruction, centered on the teacher as "performer", teaching and learning activities now place equal emphasis on in-class and out-of-class work. Much of the interaction between at-home activity and classroom experience and is mediated by information technology tools. Students are technology savvy, comfortable in the world of on-line delivery of information and social media interactions. To be an effective player in this world, instructional design has to follow the students. Contrary to the opinion that the introduction of technology into the teaching and learning process will diminish the role of the teacher, we believe that the opposite could be the case. Communication technology can enable all students to be exposed to the best and most charismatic lecturers. Electronically enabled social media forums can give rise to much more individualized interactions between students and instructors and students and students than what was ever possible. In this paper, we focus on some pedagogical approaches that allow the students to prepare themselves for interactive classroom engagement. The techniques we describe are labelled Just-in-Time Teaching and Worked-Examples. These involve carefully crafted assignments that students complete before going to class. The results of these assignments, completed just before class-time and available to the instructor, prepare the both for a more productive in-class experience
The identification and distribution of major biogenic amines in the central nervous system of Aedes triseriatus (Say) (Diptera: Culicidae) and studies on their regulation of adult mosquito behavior
The major biogenic amines of the insect nervous system (dopamine, octopamine, and serotonin) were identified and quantified by high performance liquid chromatography in the brain and thoracic ganglia of female Aedes triseriatus mosquitoes. Octopamine was quantitatively dominant in both tissues while dopamine and serotonin were found in smaller but generally similar amounts. Noradrenaline was not found in measurable quantities. Amine levels in the brain and thoracic ganglia increased significantly between days 1-14 of adult life while total protein content remained unchanged. No statistically significant circadian changes in brain amine levels were observed. When brains were divided by region (midbrain, optic lobes, subesophageal ganglion), octopamine was more abundant in the optic lobes, relative to the distribution of dopamine and serotonin;Biogenic amine concentrations were depleted in A. triseriatus when administered a single oral dose (approximately 4 [mu]g) of [alpha]-methyl tyrosine (AMT) or [alpha]-methyl tryptophan (AMTP). AMTP treatment selectively lowered the brain concentration of serotonin through the 14 days monitored following treatment. During the first week, serotonin levels in AMTP-treated mosquitoes were approximately 10% of control levels. Administration of AMT significantly depleted dopamine through 14 days post-treatment; dopamine was reduced by 50% in AMT-treated mosquitoes during the first week. Octopamine concentration was also lowered by AMT (determined on Day 3 post-treatment), but not to the degree of dopamine depression. Treatment with AMT or AMTP elicited statistically significant decreases in the spontaneous, circadian flight-activity of A. triseriatus for several days but flight activity of treated mosquitoes returned to control levels prior to evidence of amine pool repletion. Amine reductions did not alter the circadian pattern of flight activity;Host-seeking ability (evaluated with an olfactometer) was not altered by treatment with either AMT or AMTP. However, bloodfeeding success was significantly reduced by either oral administration or injection of AMTP. AMTP-treated mosquitoes responded positively when placed in close proximity to a host (rabbit) but fewer mosquitoes fed to repletion or fed at all. Those that fed to repletion took longer to do so. No differences were observed between control and AMT-treated mosquitoes. These observations suggest that serotonin plays a role in modulating bloodfeeding behavior in A. triseriatus
Determination of the magnetic anisotropy axes of single-molecule magnets
Simple methods are presented allowing the determination of the magnetic
anisotropy axes of a crystal of a single-molecule magnet (SMM). These methods
are used to determine an upper bound of the easy axis tilts in a standard
Mn12-Ac crystal. The values obtained in the present study are significately
smaller than those reported in recent high frequency electron paramagnetic
resonance (HF-EPR) studies which suggest distributions of hard-axes tilts.Comment: 10 pages, 6 figure
Inviscid analysis of the plume created by multiple rocket engines. Part II - Description of the computer programs
Computer program for calculation of single jet and five jet interaction regimes associated with multiple rocket engine
Biases in the In Situ Measurement of Particulate Organic Carbon and Its Effect on the Calibration and Validation of Ocean Color Sensors
Particulate organic carbon (POC) plays an oversize role, relative to its standing stock in the global carbon (C) cycle. Accurate measurement of POC is central to understanding the ocean C flux and its sensitivity to climate forcing. POC is a standard NASA ocean color data product, which lacks a consensus, quality-assured measurement protocol for satellite validation. Thus, algorithms based on field measurements lacking verified uncertainties have limited applicability towards climate data records. Different sampling and filtration protocols, and blank corrections, introduce biases in the magnitude of POC measured from the field. A significant filter blank attributable to dissolved organic C (DOC) adsorption that, until recently has been seldom corrected for, likely has introduced biases in POC global datasets
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