27,453 research outputs found
Classical and quantum anisotropic Heisenberg antiferromagnets
We study classical and quantum Heisenberg antiferromagnets with exchange
anisotropy of XXZ-type and crystal field single-ion terms of quadratic and
cubic form in a field. The magnets display a variety of phases, including the
spin-flop (or, in the quantum case, spin-liquid) and biconical (corresponding,
in the quantum lattice gas description, to supersolid) phases. Applying
ground-state considerations, Monte Carlo and density matrix renormalization
group methods, the impact of quantum effects and lattice dimension is analysed.
Interesting critical and multicritical behaviour may occur at quantum and
thermal phase transitions.Comment: 13 pages, 14 figures, conferenc
Sensitive gravity-gradiometry with atom interferometry: progress towards an improved determination of the gravitational constant
We here present a high sensitivity gravity-gradiometer based on atom
interferometry. In our apparatus, two clouds of laser-cooled rubidium atoms are
launched in fountain configuration and interrogated by a Raman interferometry
sequence to probe the gradient of gravity field. We recently implemented a
high-flux atomic source and a newly designed Raman lasers system in the
instrument set-up. We discuss the applications towards a precise determination
of the Newtonian gravitational constant G. The long-term stability of the
instrument and the signal-to-noise ratio demonstrated here open interesting
perspectives for pushing the measurement precision below the 100 ppm level
Improving the clinical value and utility of CGM systems: issues and recommendations: a joint statement of the European Association for the Study of Diabetes and the American Diabetes Association Diabetes Technology Working Group
The first systems for continuous glucose monitoring (CGM) became available over 15 years ago. Many then believed CGM would revolutionize the use of intensive insulin therapy in diabetes; however, progress toward that vision has been gradual. Although increasing, the proportion of individuals using CGM rather than conventional systems for self-monitoring of blood glucose on a daily basis is still low in most parts of the world. Barriers to uptake include cost, measurement reliability (particularly with earlier-generation systems), human factors issues, lack of a standardized format for displaying results, and uncertainty on how best to use CGM data to make therapeutic decisions. This Scientific Statement makes recommendations for systemic improvements in clinical use and regulatory (pre- and postmarketing) handling of CGM devices. The aim is to improve safety and efficacy in order to support the advancement of the technology in achieving its potential to improve quality of life and health outcomes for more people with diabetes
Improving the clinical value and utility of CGM systems: issues and recommendations : a joint statement of the European Association for the Study of Diabetes and the American Diabetes Association Diabetes Technology Working Group
The first systems for continuous glucose monitoring (CGM) became available over 15 years ago. Many then believed CGM would revolutionise the use of intensive insulin therapy in diabetes; however, progress towards that vision has been gradual. Although increasing, the proportion of individuals using CGM rather than conventional systems for self-monitoring of blood glucose on a daily basis is still low in most parts of the world. Barriers to uptake include cost, measurement reliability (particularly with earlier-generation systems), human factors issues, lack of a standardised format for displaying results and uncertainty on how best to use CGM data to make therapeutic decisions. This scientific statement makes recommendations for systemic improvements in clinical use and regulatory (pre- and postmarketing) handling of CGM devices. The aim is to improve safety and efficacy in order to support the advancement of the technology in achieving its potential to improve quality of life and health outcomes for more people with diabetes
Ionized Gas Kinematics and Morphology in Sgr B2 Main on 1000 AU Scales
We have imaged the Sgr B2 Main region with the Very Large Array in the BnA
configuration ( = 0\farcs13) in both the H52 (45.453
GHz) radio recombination line (RRL) and 7 mm continuum emission. At a distance
of 8500 pc, this spatial resolution corresponds to a physical scale of 0.005 pc
(1100 AU). The current observations detect H52 emission in 12
individual ultracompact (UC) and hypercompact (HC) HII regions. Two of the
sources with detected H52 emission have broad
(V50 \kms) recombination lines, and two of the sources
show lines with peaks at more than one velocity. We use line parameters from
the H52 lines and our previous H66 line observations to
determine the relative contribution of thermal, pressure and kinematic
broadening, and electron density. These new observations suggest that pressure
broadening can account for the broad lines in some of the sources, but that gas
motions (e.g. turbulence, accretion or outflow) contribute significantly to the
broad lines in at least one of the sources (Sgr B2 F3).Comment: 10 pages, 2 figure
Applying consumer responsibility principle in evaluating environmental load of carbon emissions
There is a need for a proper indicator in order to assess the environmental impact of international
trade, therefore using the carbon footprint as an indicator can be relevant and useful. The aim of this
study is to show from a methodological perspective how the carbon footprint, combined with input-
output models can be used for analysing the impacts of international trade on the sustainable use
of national resources in a country. The use of the input-output approach has the essential advantage
of being able to track the transformation of goods through the economy. The study examines the environmental
impact of consumption related to international trade, using the consumer responsibility
principle. In this study the use of the carbon footprint and input-output methodology is shown on the
example of the Hungarian consumption and the impact of international trade. Moving from a production-
based approach in climate policy to a consumption-perspective principle and allocation,
would also help to increase the efficiency of emission reduction targets and the evaluation of the
ecological impacts of international trade
A Deep ROSAT HRI Observation of NGC 1313
We describe a series of observations of NGC 1313 using the ROSAT HRI with a
combined exposure time of 183.5 ksec. The observations span an interval between
1992 and 1998; the purpose of observations since 1994 was to monitor the X-ray
flux of SN1978K, one of several luminous sources in the galaxy. No diffuse
emission is detected in the galaxy to a level of ~1-2x10^37 ergs/s/arcmin^-2. A
total of eight sources are detected in the summed image within the D_25
diameter of the galaxy. The luminosities of five of the eight range from
\~6x10^37 to ~6x10^38 erg/s; these sources are most likely accreting X-ray
binaries, similar to sources obseved in M31 and M33. The remaining three
sources all emit above 10^39 erg/s. We present light curves of the five
brightest sources. Variability is detected at the 99.9% level from four of
these. We identify one of the sources as an NGC 1313 counterpart of a Galactic
X-ray source. The light curve, though crudely sampled, most closely resembles
that of a Galactic black hole candidate such as GX339-4, but with considerably
higher peak X-ray luminosity. An additional seven sources lie outside of the
D_25 diameter and are either foreground stars or background AGN.Comment: 18 pages, 9 figures; accepted AJ, scheduled for November 200
A Compact Supermassive Binary Black Hole System
We report on the discovery of a supermassive binary black hole system in the
radio galaxy 0402+379, with a projected separation between the two black holes
of just 7.3 pc. This is the closest black hole pair yet found by more than two
orders of magnitude. These results are based upon recent multi-frequency
observations using the Very Long Baseline Array (VLBA) which reveal two
compact, variable, flat-spectrum, active nuclei within the elliptical host
galaxy of 0402+379. Multi-epoch observations from the VLBA also provide
constraints on the total mass and dynamics of the system. Low spectral
resolution spectroscopy using the Hobby-Eberly Telescope indicates two velocity
systems with a combined mass of the two black holes of ~1.5 x 10^8 solar
masses. The two nuclei appear stationary while the jets emanating from the
weaker of the two nuclei appear to move out and terminate in bright hot spots.
The discovery of this system has implications for the number of close binary
black holes that might be sources of gravitational radiation. Green Bank
Telescope observations at 22 GHz to search for water masers in this interesting
system are also presented.Comment: 34 pages, 7 figures, Accepted to The Astrophysical Journa
Flickering of 1.3 cm Sources in Sgr B2: Towards a Solution to the Ultracompact HII Region Lifetime Problem
Accretion flows onto massive stars must transfer mass so quickly that they
are themselves gravitationally unstable, forming dense clumps and filaments.
These density perturbations interact with young massive stars, emitting
ionizing radiation, alternately exposing and confining their HII regions. As a
result, the HII regions are predicted to flicker in flux density over periods
of decades to centuries rather than increasing monotonically in size as
predicted by simple Spitzer solutions. We have recently observed the Sgr B2
region at 1.3 cm with the VLA in its three hybrid configurations (DnC, CnB and
BnA) at a resolution of 0.25''. These observations were made to compare in
detail with matched continuum observations from 1989. At 0.25'' resolution, Sgr
B2 contains 41 UC HII regions, 6 of which are hypercompact. The new
observations of Sgr B2 allow comparison of relative peak flux densites for the
HII regions in Sgr B2 over a 23 year time baseline (1989-2012) in one of the
most source-rich massive star forming regions in the Milky Way. The new 1.3 cm
continuum images indicate that four of the 41 UC HII regions exhibit
significant changes in their peak flux density, with one source (K3) dropping
in peak flux density, and the other 3 sources (F10.303, F1 and F3) increasing
in peak flux density. The results are consistent with statistical predictions
from simulations of high mass star formation, suggesting that they offer a
solution to the lifetime problem for ultracompact HII regions.Comment: 12 pages, 3 figures, Accepted for publication in the Astrophysical
Journal Letter
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