2,053,562 research outputs found
Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope
We analyze the first two years of data from the Fermi Gamma Ray Space
Telescope from the direction of the inner 10 degrees around the Galactic Center
with the intention of constraining, or finding evidence of, annihilating dark
matter. We find that the morphology and spectrum of the emission between 1.25
degrees and 10 degrees from the Galactic Center is well described by a the
processes of decaying pions produced in cosmic ray collisions with gas, and the
inverse Compton scattering of cosmic ray electrons in both the disk and bulge
of the Inner Galaxy, along with gamma rays from known points sources in the
region. The observed spectrum and morphology of the emission within
approximately 1.25 degrees (~175 parsecs) of the Galactic Center, in contrast,
departs from the expectations for by these processes. Instead, we find an
additional component of gamma ray emission that is highly concentrated around
the Galactic Center. The observed morphology of this component is consistent
with that predicted from annihilating dark matter with a cusped (and possibly
adiabatically contracted) halo distribution (density proportional to
r^{-gamma}, with gamma=1.18 to 1.33). The observed spectrum of this component,
which peaks at energies between 1-4 GeV (in E^2 units), can be well fit by a
7-10 GeV dark matter particle annihilating primarily to tau leptons with a
cross section in the range of 4.6 x 10^-27 to 5.3 x 10^-26 cm^3/s, depending on
how the dark matter distribution is normalized. We also discuss other sources
for this emission, including the possibility that much of it originates from
the Milky Way's supermassive black hole.Comment: 23 pages, 16 figure
Evidence for Extremely High Dust Polarization Efficiency in NGC 3184
Recent studies have found the Type II-plateau supernova (SN) 1999gi to be
highly polarized (p_max = 5.8%, where p_max is the highest degree of
polarization measured in the optical bandpass; Leonard & Filippenko 2001) and
minimally reddened (E[B-V] = 0.21 +/- 0.09 mag; Leonard et al. 2002). From
multiple lines of evidence, including the convincing fit of a ``Serkowski''
interstellar polarization (ISP) curve to the continuum polarization shape, we
conclude that the bulk of the observed polarization is likely due to dust along
the line of sight (l-o-s), and is not intrinsic to SN 1999gi. We present new
spectropolarimetric observations of four distant Galactic stars close to the
l-o-s to SN 1999gi (two are within 0.02 degrees), and find that all are null to
within 0.2%, effectively eliminating Galactic dust as the cause of the high
polarization. The high ISP coupled with the low reddening implies an
extraordinarily high polarization efficiency for the dust along this l-o-s in
NGC 3184: ISP / E(B-V) = 31^{+22}_{-9} % mag^{-1}. This is inconsistent with
the empirical Galactic limit (ISP / E[B-V] < 9% mag^{-1}), and represents the
highest polarization efficiency yet confirmed for a single sight line in either
the Milky Way or an external galaxy.Comment: 27 pages, accepted for publication by the Astronomical Journa
Does the Boltzmann principle need a dynamical correction?
In an attempt to derive thermodynamics from classical mechanics, an
approximate expression for the equilibrium temperature of a finite system has
been derived [M. Bianucci, R. Mannella, B. J. West, and P. Grigolini, Phys.
Rev. E 51, 3002 (1995)] which differs from the one that follows from the
Boltzmann principle S = k log (Omega(E)) via the thermodynamic relation 1/T=
dS/dE by additional terms of "dynamical" character, which are argued to correct
and generalize the Boltzmann principle for small systems (here Omega(E) is the
area of the constant-energy surface). In the present work, the underlying
definition of temperature in the Fokker-Planck formalism of Bianucci et al. is
investigated and shown to coincide with an approximate form of the
equipartition temperature. Its exact form, however, is strictly related to the
"volume" entropy S = k log (Phi(E)) via the thermodynamic relation above for
systems of any number of degrees of freedom (Phi(E) is the phase space volume
enclosed by the constant-energy surface). This observation explains and
clarifies the numerical results of Bianucci et al. and shows that a dynamical
correction for either the temperature or the entropy is unnecessary, at least
within the class of systems considered by those authors. Explicit analytical
and numerical results for a particle coupled to a small chain (N~10) of quartic
oscillators are also provided to further illustrate these facts.Comment: REVTeX 4, 10 pages, 2 figures. Accepted to J. Stat. Phy
Spring coccolithophore production and dispersion in the temperate eastern North Atlantic Ocean
Production and dispersion of coccolithophores are assessed within their ecologic and hydrographic context across enhanced spring chlorophyll production in the surface eastern North Atlantic. Within a 4 day period from 12 to 16 March 2004, a N-S transect from 47 degrees N to 33 degrees N was sampled along 20 degrees W. Water samples from defined depths down to 200 m were analyzed for coccolithophores from 0.45 mu m polycarbonate filters by scanning electron microscopy. At 47 degrees N coccolithophores flourished when euphotic conditions allowed new production at deep mixing, low temperatures, and high nutrient concentrations. Emiliania huxleyi flourished at high turbulence during an early stage of the phytoplankton succession and contributed half of the total coccolithophore assemblage, with up to 150 x 10(3) cells L(-1) and up to 12 x 10(9) cells m(-2) when integrated over the upper 200 m of the water column. Maximum chlorophyll concentrations occurred just north of the Azores Front, at 37 degrees N-39 degrees N, at comparatively low numbers of coccolithophores. To the south, at 35 degrees N-33 degrees N, coccolithophores were abundant within calm and stratified Subtropical Mode Waters, and E. huxleyi was the dominant species again. Although the cell densities of coccolithophores observed here remained below those typical of plankton blooms visible from satellite images, the depth-integrated total mass makes them significant producers of calcite and contributors to the total carbon sedimentation at a much wider range of ecological conditions during late winter and early spring than hitherto assumed
Wind-aligned Drainage in Loess in Iowa
Analysis of stream valley alignment reveals that first-order valleys, which are formed entirely within Wisconsinan loess, show a strongly preferred orientation of N40-50 degrees W, within an otherwise random distribution. This alignment is present in NW, W Central, and Central Iowa. It is not apparent in S Iowa. In NE and E Iowa wind-aligned features change to a N60-70 degree W orientation. This is interpreted as wind-alignment of the low-order valleys within the loess, created by prevailing NW winds during or shortly after loess deposition. Higher order streams are controlled by the till landscape beneath the loess. The four directions of preferred orientation in these higher order valleys are coincident with till joints
Promoting Emotional and Social Well-Being and a Sense of Belonging in Adolescents through Participation in Volunteering
This research received external funding from Research Group (SEJ 131): Analysis of Social
Life.The data presented in this study are available on request from the first
author, e-mail: [email protected] (M.L.-S.).The aim of this study was to analyze the differences within education-related degrees with respect to participation in volunteering. Volunteering motivation promotes and encourages emotional and social well-being and a sense of belonging in university students. This study was based on a total sample of 985 students undertaking Degrees in Early Childhood Education, Primary Education, and Social Education who attended higher education institutions in Northern Africa (Spain) and Eastern Spain. Once the quality parameters of the instrument were determined, the reliability was confirmed, and data collection was initiated. In order to analyze the results, a multilevel study (ANOVA) was conducted by interacting the variables for degrees with three levels (PE = Primary Education; EC = Early Childhood Education; SE = Social Education) and the variable "volunteering is my motivation to feel better", with five levels (strongly disagree, disagree, unsure, agree, and strongly agree). From the data obtained, it was concluded that there were significant differences between the different degree paths, the assessment covering sociodemographic variables and areas of interest showing that volunteering benefits university students both socially and in their decision-making processes.Research Group: Analysis of Social Life
SEJ 13
The Energy Spectrum of TeV Gamma-Rays from the Crab Nebula as measured by the HEGRA system of imaging air Cherenkov telescopes
The Crab Nebula has been observed by the HEGRA (High-Energy Gamma-Ray
Astronomy) stereoscopic system of imaging air Cherenkov telescopes (IACTs) for
a total of about 200 hrs during two observational campaigns: from September
1997 to March 1998 and from August 1998 to April 1999. The recent detailed
studies of system performance give an energy threshold and an energy resolution
for gamma-rays of 500 GeV and ~ 18%, respectively. The Crab energy spectrum was
measured with the HEGRA IACT system in a very broad energy range up to 20 TeV,
using observations at zenith angles up to 65 degrees. The Crab data can be
fitted in the energy range from 1 to 20 TeV by a simple power-law, which yields
dJg/dE = (2.79+/-0.02 +/- 0.5) 10^{-7} E^{-2.59 +/- 0.03 +/- 0.05}, ph m^{-2}
s^{-1} TeV^{-1} The Crab Nebula energy spectrum, as measured with the HEGRA
IACT system, agrees within 15% in the absolute scale and within 0.1 units in
the power law index with the latest measurements by the Whipple, CANGAROO and
CAT groups, consistent within the statistical and systematic errors quoted by
the experiments. The pure power-law spectrum of TeV gamma-rays from the Crab
Nebula constrains the physics parameters of the nebula environment as well as
the models of photon emission.Comment: to appear in ApJ, 29 pages, 6 figure
Bromine, iodine and sodium in surface snow along the 2013 Talos Dome-GV7 traverse (northern Victoria Land, East Antarctica)
Halogen chemistry in the polar regions occurs through the release of halogen elements from different sources. Bromine is primarily emitted from sea salt aerosols and other saline condensed phases associated with sea ice surfaces, while iodine is affected by the release of organic compounds from algae colonies living within the sea ice environment. Measurements of halogen species in polar snow samples are limited to a few sites although there is some evidence that they are related to sea ice extent. We examine here total bromine, iodine and sodium concentrations in a series of 2m cores collected during a traverse from Talos Dome (72 degrees 48'S, 159 degrees 06'E) to GV7 (70 degrees 41'S, 158 degrees 51'E) analyzed by inductively coupled plasma-sector field mass spectrometry (ICP-SFMS) at a resolution of 5 cm.We find a distinct seasonality of the bromine enrichment signal in most of the cores, with maxima during the austral spring. Iodine shows average concentrations of 0.04 ppb with little variability. No distinct seasonality is found for iodine and sodium.The transect reveals homogeneous air-to-snow fluxes for the three chemical species along the transect due to competing effects of air masses originating from the Ross Sea and the Southern Ocean
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Shear-Wave Splitting and Mantle Flow Beneath the Colorado Plateau and its Boundary with the Great Basin
Shear-wave splitting measurements from SKS and SKKS phases show fast polarization azimuths that are subparallel to North American absolute plate motion within the central Rio Grande Rift (RGR) and Colorado Plateau (CP) through to the western rim of the CP, with anisotropy beneath the CP and central RGR showing a remarkably consistent pattern with a mean fast azimuth of 4 degrees +/- degrees 6 E of N. Approaching the rim from the southeast, fast anisotropic directions become north-northeast-south-southwest (NNE-SSW), rotate counter clockwise to north-south in the CP-GB transition, and then to NNW-SSE in the western Great Basin ( GB). This change is coincident with uppermost mantle S-wave velocity perturbations that vary from +4% beneath the western CP and the eastern edge of the Marysvale volcanic field to about -8% beneath the GB. Corresponding delay times average 1.5 sec beneath the central CP, decrease to approximately 0.8 sec near the CP-GB transition, and increase to about 1.2 sec beneath the GB. For the central CP, we suggest anisotropy predominantly controlled by North American plate motion above the asthenosphere. The observed pattern of westward-rotating anisotropy from the western CP through the CP-GB transition may be influenced to asthenospheric flow around a CP lithospheric keel and/or by vertical flow arising from edge-driven small-scale convection. The anisotropic transition from the CP to the GB thus marks a first-order change from absolute plate motion dominated lithosphere-asthenosphere shear to a new regime controlled by regional flow processes. The NNW-SSE anisotropic fast directions of split SKS waves in the eastern GB area are part of a broad circular pattern of seismic anisotropic fast direction in the central GB that has recently been hypothesized to be due to toroidal flow around the sinking Juan de Fuca-Gorda slab.National Science Foundation EAR 9706094, 9707188, 9707190, 0207812Los Alamos National Laboratory Institute of Geophysics and Planetary PhysicsNational Science Foundation Cooperative EAR-000430Department of Energy National Nuclear Security AdministrationGeological Science
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