1,157 research outputs found
Efficient Searches for r-Process-Enhanced, Metal-Poor Stars
Neutron-capture-enhanced, metal-poor stars are of central importance to
developing an understanding of the operation of the r-process in the early
Galaxy, thought to be responsible for the formation of roughly half of all
elements beyond the iron peak. A handful of neutron-capture-rich, metal-poor
stars with [Fe/H] < -2.0 have already been identified, including the well known
r-process-enhanced stars CS 22892-052 and CS 31082-001. However, many questions
of fundamental interest can only be addressed with the assemblage of a much
larger sample of such stars, so that general properties can be distinguished.
We describe a new effort, HERES: The Hamburg/ESO R-Process-Enhanced Star
survey, nearing completion, which will identify on the order of 5-10 additional
highly r-process-enhanced, metal-poor stars, and in all likelihood, a similar
or greater number of mildly r-process-enhanced, metal-poor stars in the halo of
the Galaxy. HERES is based on rapid "snapshot" spectra of over 350 candidate
halo giants with [Fe/H] < -2.0, obtained at moderately high resolution, and
with moderate signal-to-noise ratios, using the UVES spectrograph on the
European VLT 8m telescope.Comment: Contributed paper to The Eighth Nuclei in the Cosmos conference, to
appear (in refereed form) in Nuclear Physics
Inhibition of transforming growth factor alpha signaling slows progression of osteoarthritis in a dmm model
Assessing the phenology of southern tropical Africa:A comparison of hemispherical photography, scatterometry, and optical/NIR remote sensing
Violation of the Wiedemann-Franz Law in a Large-N Solution of the t-J Model
We show that the Wiedemann-Franz law, which holds for Landau Fermi liquids,
breaks down in a large-n treatment of the t-J model. The calculated ratio of
the in-plane thermal and electrical conductivities agrees quantitatively with
experiments on the normal state of the electron-doped Pr_{2-x}Ce_xCuO_4 (x =
0.15) cuprate superconductor. The violation of the Wiedemann-Franz law in the
uniform phase contrasts with other properties of the phase that are Fermi
liquid like.Comment: 4 pages, 2 figures. Typos corrected, one added reference, revised
discussion of experiment on 214 cuprate material (x = 0.06
Statistical characterisation of bio-aerosol background in an urban environment
In this paper we statistically characterise the bio-aerosol background in an
urban environment. To do this we measure concentration levels of naturally
occurring microbiological material in the atmosphere over a two month period.
Naturally occurring bioaerosols can be considered as noise, as they mask the
presence of signals coming from biological material of interest (such as an
intentionally released biological agent). Analysis of this 'biobackground' was
undertaken in the 1-10 um size range and a 3-9% contribution was found to be
biological in origin - values which are in good agreement with other studies
reported in the literature. A model based on the physics of turbulent mixing
and dispersion was developed and validated against this analysis. The Gamma
distribution (the basis of our model) is shown to comply with the scaling laws
of the concentration moments of our data, which enables us to universally
characterise both biological and non-biological material in the atmosphere. An
application of this model is proposed to build a framework for the development
of novel algorithms for bio-aerosol detection and rapid characterisation.Comment: 14 Pages, 8 Figure
Temperature-dependent NMR features of the Al65Cu20Ru15 icosahedral alloy
The Al65Cu20Ru15 icosahedral alloy was studied by Al27 nuclear magnetic resonance from 150 to 1110 K. The Knight shift of the unresolved resonance line was observed to significantly increase above 500 K. This uncommon temperature dependence of the Knight shift is interpreted in terms of the presence of a pseudogap at the Fermi level. The spin-lattice relaxation rate deviates from the linear temperature dependence of Korringa relaxation below 500 K, and above 500 K it is dominated by a thermally activated process with a small activation energy of 0.48 eV. This energy is distinctly different from the activation energy observed in simple metallic alloys
Quantum teleportation of entangled coherent states
We propose a simple scheme for the quantum teleportation of both bipartite
and multipartite entangled coherent states with the successful probability 1/2.
The scheme is based on only linear optical devices such as beam splitters and
phase shifters, and two-mode photon number measurements. The quantum channels
described by multipartite maximally entangled coherent states are readily made
by the beam splitters and phase shifters.Comment: 4 pages, no figure
Net ecosystem exchange from two formerly afforested peatlands undergoing restoration in the Flow Country of northern Scotland
Northern peatlands are important in the global carbon (C) cycle as they help regulate local, regional and global C budgets through high atmospheric carbon dioxide (CO2) uptake and low net CO2 losses to the atmosphere. Since the 1900s (but particularly the 1950s) land-use change has affected many peatland areas, driven in part by attempts to improve their commercial value. During this period, many peatlands in the UK were drained and planted with non-native conifer plantations. Efforts are now underway to restore the ecosystem functioning of these peatlands to those characteristic of pristine peatlands, in particular C flux dynamics. A lack of ecosystem level measurements means that the timescales of restoration and the degree to which they are successful remains poorly determined. In this research, we present the first year-round study of net ecosystem CO2 exchange (NEE) from peatlands undergoing restoration from forestry. Annual NEE was measured from two sites between March 2014 and June 2015, where restoration commenced 10 years and 16 years prior to the start of this study, and the results were then compared to existing measurements from a near-pristine peatland. Existing NEE data (expressed as CO2-C) from the near-pristine peatland indicated a C sink of 114 g m-2 yr-1, and our estimates suggest that the older restored site (16 years) was also a NEE sink (71 g m-2 yr-1). In contrast, the younger site (10 years) was a NEE source (80 g m-2 yr-1). We critically assess the confidence of these measurements and also present these data in relation to other northern hemisphere peatlands to better understand the timeframe in which a peatland site can turn from a C source to a C sink after restoration
Generation of atom-photon entangled states in atomic Bose-Einstein condensate via electromagnetically induced transparency
In this paper, we present a method to generate continuous-variable-type
entangled states between photons and atoms in atomic Bose-Einstein condensate
(BEC). The proposed method involves an atomic BEC with three internal states, a
weak quantized probe laser and a strong classical coupling laser, which form a
three-level Lambda-shaped BEC system. We consider a situation where the BEC is
in electromagnetically induced transparency (EIT) with the coupling laser being
much stronger than the probe laser. In this case, the upper and intermediate
levels are unpopulated, so that their adiabatic elimination enables an
effective two-mode model involving only the atomic field at the lowest internal
level and the quantized probe laser field. Atom-photon quantum entanglement is
created through laser-atom and inter-atomic interactions, and two-photon
detuning. We show how to generate atom-photon entangled coherent states and
entangled states between photon (atom) coherent states and atom-(photon-)
macroscopic quantum superposition (MQS) states, and between photon-MQS and
atom-MQS states.Comment: 9 pages, 1 figur
Particle Dark Matter Constraints from the Draco Dwarf Galaxy
It is widely thought that neutralinos, the lightest supersymmetric particles,
could comprise most of the dark matter. If so, then dark halos will emit radio
and gamma ray signals initiated by neutralino annihilation. A particularly
promising place to look for these indicators is at the center of the local
group dwarf spheroidal galaxy Draco, and recent measurements of the motion of
its stars have revealed it to be an even better target for dark matter
detection than previously thought. We compute limits on WIMP properties for
various models of Draco's dark matter halo. We find that if the halo is nearly
isothermal, as the new measurements indicate, then current gamma ray flux
limits prohibit much of the neutralino parameter space. If Draco has a moderate
magnetic field, then current radio limits can rule out more of it. These
results are appreciably stronger than other current constraints, and so
acquiring more detailed data on Draco's density profile becomes one of the most
promising avenues for identifying dark matter.Comment: 13 pages, 6 figure
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