77,797 research outputs found
Electron pockets and pseudogap asymmetry observed in the thermopower of underdoped cuprates
We calculate the diffusion thermoelectric power of high-Tc cuprates using the
resonating-valence-bond spin-liquid model developed by Yang, Rice and Zhang
(YRZ). In this model, reconstruction of the energy-momentum dispersion results
in a pseudogap in the density of states that is heavily asymmetric about the
Fermi level. The subsequent asymmetry in the spectral conductivity is found to
account for the large magnitude and temperature dependence of the thermopower
observed in underdoped cuprates. In addition we find evidence in experimental
data for electron pockets in the Fermi surface, arising from a YRZ-like
reconstruction, near the onset of the pseudogap in the slightly overdoped
regime.Comment: 6 pages, 7 figures, accepted for publication in EP
Circadian clocks and breast cancer
Circadian clocks respond to environmental time cues to coordinate 24-hour oscillations in almost every tissue of the body. In the breast, circadian clocks regulate the rhythmic expression of numerous genes. Disrupted expression of circadian genes can alter breast biology and may promote cancer. Here we overview circadian mechanisms, and the connection between the molecular clock and breast biology. We describe how disruption of circadian genes contributes to cancer via multiple mechanisms, and link this to increased tumour risk in women who work irregular shift patterns. Understanding the influence of circadian rhythms on breast cancer could lead to more efficacious therapies, reformed public health policy and improved patient outcome
Creation of a molecular condensate by dynamically melting a Mott-insulator
We propose creation of a molecular Bose-Einstein condensate (BEC) by loading
an atomic BEC into an optical lattice and driving it into a Mott insulator (MI)
with exactly two atoms per site. Molecules in a MI state are then created under
well defined conditions by photoassociation with essentially unit efficiency.
Finally, the MI is melted and a superfluid state of the molecules is created.
We study the dynamics of this process and photoassociation of tightly trapped
atoms.Comment: minor revisions, 5 pages, 3 figures, REVTEX4, accepted by PRL for
publicatio
Natural Resource Information System, remote sensing studies
Potential applications of remote sensing data were reviewed, and available imagery was interpreted to provide input to a demonstration data base. A literature review was conducted to determine the types and qualities of imagery required to satisfy identified data needs. Ektachrome imagery available over the demonstration areas was reviewed to establish the feasibility of interpreting cultural features, range condition, and timber type. Using the same imagery, a land use map was prepared for the demonstration area. The feasibility of identifying commercial timber areas using a density slicing technique was tested on multispectral imagery available for a portion of the demonstration area
Exploring the value of Scotland's environment
Protection of the environment can be regarded as representing a substantial cost to business. However, it is typically considered from the point of view of effect on company profitability, rather than its relative importance to human kind. This paper estimates the value of Scotland's natural environment by applying the methodology developed by Costanza et al (1997a and b) for estimation of the value of the earth's ecosystem services. Ecosystem services provide the vital functions to support life on Earth, such as flows of materials and energy. Since the study's publication, further research has sought to apply this global methodology to a regional and national level (for example Loomis et al, 2000, Farber and Griner, 2000 and Stevens et al, 2000). The value derived for Scotland provides a useful context for understanding the scale and importance of Scotland's natural habitats and it helps to reinforce the message that the environment is central to human welfare (Williams et al, 2003). The valuation of ecosystem services in monetary terms provokes theoretical, practical and philosophical arguments. This paper does not seek to revisit in depth these debates; rather the valuation should be taken as a starting point for setting the importance of Scotland's ecosystems in an interesting perspective. A recent edition of the journal Ecological Economics (Costanza and Farber, 2002) was devoted to considering some of these issues and providing many avenues for further exploration
Evidence for two electronic components in high-temperature superconductivity from NMR
A new analysis of 63Cu and 17O NMR shift data on La1.85Sr0.15CuO4 is reported
that supports earlier work arguing for a two-component description of this
material, but conflicts with the widely held view that the cuprates are a
one-component system. The data are analyzed in terms of two components A and B
with susceptibilities Chi(A), Chi(B), and Chi(AB)=Chi(BA) . We find that above
Tc, Chi(AB) and Chi(BB) are independent of temperature and obtain for the first
time the temperature dependence of all three susceptibilities above Tc as well
as the complete temperature dependence of Chi(AA)+Chi(AB) and of
Chi(AB)+Chi(BB) below Tc. The form of the results agrees with that recently
proposed by Barzykin and Pines.Comment: 14 pages, 4 figure
Nanoindentation-induced deformation of Ge
The deformation mechanisms of crystalline (100) Ge were studied using nanoindentation, cross sectional transmission electron microscopy (XTEM) and Raman microspectroscopy. For a wide range of indentation conditions using both spherical and pointed indenters, multiple discontinuities were found in the force–displacement curves on loading, but no discontinuities were found on unloading. Raman microspectroscopy, measured from samples which had plastically deformed on loading, showed a spectrum shift from that in pristine Ge, suggesting only residual strain. No evidence (such as extra Raman bands) was found to suggest that any pressure-induced phase transformations had occurred, despite the fact that the material had undergone severe plastic deformation.Selected area diffraction pattern studies of the mechanically damaged regions also confirmed the absence of additional phases. Moreover, XTEM showed that, at low loads, plastic deformation occurs by twinning and dislocation motion. This indicates that the hardness of Gemeasured by indentation is not primarily dominated by phase transformation, rather by the nucleation and propagation of twin bands and/or dislocations
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