5,758 research outputs found
Magnetism and Mott Transition: A Slave-rotor Study
Motivated by the debate of spin-density-wave (SDW) versus local-moment (LM)
picture in the iron-based superconducting (FeSC) materials, we consider a
two-band orbital-symmetric Hubbard model in which there is robust Fermi surface
nesting at . We obtain the phase diagram of such system by a
mean-field slave-rotor approach, in which the Fermi surface nesting and the SDW
order are explicitly taken into account via a natural separation of scale
between the Hund's coupling and the Coulomb interaction. We find that for a
sizable range of Hund's coupling the Mott transition acquires a strong
first-order character, but there also exists a small range of stronger Hund's
coupling in which an enhancement of magnetization can be observed on the SDW
side. We interpret the former scenario as one in which a sharp distinction can
be drawn between LM and the SDW picture, and the latter scenario as one in
which signs of LM physics begin to develop in the metallic phase. It is
tempting to suggest that some FeSC materials are in the vicinity of the latter
scenario.Comment: 7 pages, 5 figures; v2: Added discussions on anisotropy in
renormalized hopping, clarifications and discussions with regard to orbital
order, new inset in Fig. 3(d), expanded and revised bibliography, plus other
minor revisions. Accepted to PR
Observations and Analysis of High-Resolution Magnetic Field Structures in Molecular Clouds
Recent high-angular-resolution (up to 0.7") dust polarization observations
toward star forming regions are summarized. With the Sub-Millimeter Array, the
emission from the dense structures is traced and resolved. The detected
magnetic field morphologies vary from hourglass-like structures to isolated
patches depending on the evolutionary stage of the source. These observed
features have also served as a testbed to develop new analysis methods, with a
particular focus on quantifying the role of the magnetic field in the star
formation process.Comment: 4 pages, 2 figures; To appear in Proceedings of Magnetic Fields in
the Universe: From Laboratory and Stars to Primordial Structures Aug. 21st -
27th 2011, Zakopane, Poland Eds. M. Soida, K. Otmianowska-Mazur, E.M. de
Gouveia Dal Pino & A. Lazaria
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Fixing a 510(K) Loophole: In Support of The Sound Devices Act of 2012
The current medical device regulatory system contains a dangerous loophole. While the voluntary recall of a harmful medical device removes it from the market, new devices that claim they are substantially equivalent to the recalled device can still reach the market through the 510(k) premarket notification process. Devices that have gained regulatory clearance in this fashion have caused considerable harm and are much more likely to be recalled for safety reasons as well. The recently proposed Safety of Untested and New Devices Act of 2012 (the “SOUND Devices Act”) would fix this loophole. This paper describes the 510(k) clearance process and the recalled predicate loophole, summarizes the SOUND Devices Act’s proposed solution, and argues that Congress ought to enact the SOUND Devices Act
Raman signature of the U(1) Dirac spin-liquid state in spin-1/2 kagome system
We followed the Shastry--Shraiman formulation of Raman scattering in Hubbard
systems and considered the Raman intensity profile in the spin-1/2 "perfect"
kagome lattice herbertsmithite ZnCu_3(OH)_6Cl_2, assuming the ground state is
well-described by the U(1) Dirac spin-liquid state. In the derivation of the
Raman T-matrix, we found that the spin chirality term appears in the A_{2g}
channel in the kagome lattice at the t^4/(\omega_i-U)^3 order, but (contrary to
the claims by Shastry and Shraiman) vanishes in the square lattice to that
order. In the ensuing calculations on the spin-1/2 kagome lattice, we found
that the Raman intensity profile in the E_g channel is invariant under an
arbitrary rotation in the kagome plane, and that in all (A_{1g}, E_g, and
A_{2g}) symmetry channels the Raman intensity profile contains broad continua
that display power-law behaviors at low energy, with exponent approximately
equal to 1 in the A_{2g} channel and exponent approximately equal to 3 in the
E_g and the A_{1g} channels. For the A_{2g} channel, the Raman profile also
contains a characteristic 1/\omega singularity, which arose in our model from
an excitation of the emergent U(1) gauge field.Comment: 17 pages, 19 figures; Minor revisions, updated to be consistent with
the published versio
Infinitely many solutions to Kirchhoff double phase problems with variable exponents
In this work we deal with elliptic equations driven by the variable exponent
double phase operator with a Kirchhoff term and a right-hand side that is just
locally defined in terms of very mild assumptions. Based on an abstract
critical point result of Kajikiya (2005) and recent a priori bounds for
generalized double phase problems by the authors (2022), we prove the existence
of a sequence of nontrivial solutions whose -norms converge to zero
Aquaculture production and its environmental sustainability in Thailand : challenges and potential solutions
Though aquaculture plays an important role in providing foods and healthy diets, there are concerns regarding the environmental sustainability of prevailing practices. This study examines the trends and changes in fisheries originating from aquaculture production in Thailand and provides insights into such production’s environmental impacts and sustainability. Together with an extensive literature review, we investigated a time series of Thai aquaculture production data from 1995 to 2015. Overall, Thai aquaculture production has significantly increased during the last few decades and significantly contributed to socio-economic development. Estimates of total aquaculture production in Thailand have gradually grown from around 0.6 to 0.9 million tons over the last twenty years. Farmed shrimp is the main animal aquatic product, accounting for an estimated 40% of total yields of aquaculture production, closely followed by fish (38%) and mollusk (22%). Estimates over the past decades indicate that around 199470 ha of land is used for aquaculture farming. Out of the total area, 61% is used for freshwater farms, and 39% is used for coastal farms. However, this industry has contributed to environmental degradation, such as habitat destruction, water pollution, and ecological effects. Effective management strategies are urgently needed to minimize the environmental impacts of aquaculture and to ensure it maximally contributes to planetary health. Innovative and practical solutions that rely on diverse technology inputs and smart market-based management approaches that are designed for environmentally friendly aquaculture farming can be the basis for viable long-term solutions for the future
Ideal filter approximation and synthesis
Several methods are currently used for approximating the ideal low pass filter. Generally, those approximations relate only to the amplitude or phase characteristic of the ideal filter. A class of filters has been proposed as approximating both the amplitude and phase characteristics of the ideal filter. The characteristics of the first ten members of the proposed class are considered in this paper. The results indicate a much improved approximation to the ideal filter has been achieved --Abstract, page ii
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