838 research outputs found
Completely localized gravity with higher curvature terms
In the intersecting braneworld models, higher curvature corrections to the
Einstein action are necessary to provide a non-trivial geometry (brane tension)
at the brane junctions. By introducing such terms in a Gauss-Bonnet form, we
give an effective description of localized gravity on the singular
delta-function branes. There exists a non-vanishing brane tension at the
four-dimensional brane intersection of two 4-branes. Importantly, we give
explicit expressions of the graviton propagator and show that the
Randall-Sundrum single-brane model with a Gauss-Bonnet term in the bulk
correctly gives a massless graviton on the brane as for the RS model. We
explore some crucial features of completely localized gravity in the solitonic
braneworld solutions obtained with a choice (\xi=1) of solutions. The no-go
theorem known for Einstein's theory may not apply to the \xi=1 solution. As
complementary discussions, we provide an effective description of the power-law
corrections to Newtonian gravity on the branes or at the common intersection
thereof.Comment: 19 pages, LaTeX, Revised/Published Versio
Thermodynamic Relations in Correlated Systems
Several useful thermodynamic relations are derived for metal-insulator
transitions, as generalizations of the Clausius-Clapeyron and Eherenfest
theorems. These relations hold in any spatial dimensions and at any
temperatures. First, they relate several thermodynamic quantities to the slope
of the metal-insulator phase boundary drawn in the plane of the chemical
potential and the Coulomb interaction in the phase diagram of the Hubbard
model. The relations impose constraints on the critical properties of the Mott
transition. These thermodynamic relations are indeed confirmed to be satisfied
in the cases of the one- and two-dimensional Hubbard models. One of these
relations yields that at the continuous Mott transition with a diverging charge
compressibility, the doublon susceptibility also diverges. The constraints on
the shapes of the phase boundary containing a first-order metal-insulator
transition at finite temperatures are clarified based on the thermodynamic
relations. For example, the first-order phase boundary is parallel to the
temperature axis asymptotically in the zero temperature limit. The
applicability of the thermodynamic relations are not restricted only to the
metal-insulator transition of the Hubbard model, but also hold in correlated
systems with any types of phases in general. We demonstrate such examples in an
extended Hubbard model with intersite Coulomb repulsion containing the charge
order phase.Comment: 10 pages, 9 figure
Erratum: Causal Knowledge Promotes Behavioral Self-Regulation: An Example using Climate Change Dynamics (PLoS ONE (2017) 12:9 (E0184480) DOI: 10.1371/Journal.pone.0184480)
In the Task overview: Managing a dynamic human-climate system subsection of the Introduction, there is an error in equation 4. There is a factor of Ï„ that is missing from the denominator of the first term that appears on the right-hand side of the equation. Please view the complete, correct equation here [Formula Presented]
Ab initio Derivation of Low-energy Model for Iron-Based Superconductors LaFeAsO and LaFePO
Effective Hamiltonians for LaFeAsO and LaFePO are derived from the
downfolding scheme based on first-principles calculations and provide insights
for newly discovered superconductivity in the family of LnFeAsOF,
Ln = La, Ce, Pr, Nd, Sm, and Gd. Extended Hubbard Hamiltonians for five
maximally localized Wannier orbitals per Fe are constructed dominantly from
five-fold degenerate iron-3 bands. They contain parameters for effective
Coulomb and exchange interactions screened by the polarization of other
electrons away from the Fermi level. The onsite Coulomb interaction estimated
as 2.2-3.3 eV is compared with the transfer integrals between the
nearest-neighbor Fe-3 Wannier orbitals, 0.2-0.3 eV, indicating moderately
strong electron correlation. The Hund's rule coupling is found to be 0.3-0.6
eV. The derived model offers a firm basis for further studies on physics of
this family of materials. The effective models for As and P compounds turn out
to have very similar screened interactions with slightly narrower bandwidth for
the As compound.Comment: 5 pages, 3 figures, 1 table; to appear in J. Phys. Soc. Jpn. Vol. 77
No.9: Revised version contains corrected table values and discussions of
quantitative accuracy of constrained random-phase approximatio
A standardisation proof for algebraic pattern calculi
This work gives some insights and results on standardisation for call-by-name
pattern calculi. More precisely, we define standard reductions for a pattern
calculus with constructor-based data terms and patterns. This notion is based
on reduction steps that are needed to match an argument with respect to a given
pattern. We prove the Standardisation Theorem by using the technique developed
by Takahashi and Crary for lambda-calculus. The proof is based on the fact that
any development can be specified as a sequence of head steps followed by
internal reductions, i.e. reductions in which no head steps are involved.Comment: In Proceedings HOR 2010, arXiv:1102.346
Effects of the COVID-19 pandemic on medical students: a multicenter quantitative study
© 2021, The Author(s). Background: The COVID-19 pandemic disrupted the United States (US) medical education system with the necessary, yet unprecedented Association of American Medical Colleges (AAMC) national recommendation to pause all student clinical rotations with in-person patient care. This study is a quantitative analysis investigating the educational and psychological effects of the pandemic on US medical students and their reactions to the AAMC recommendation in order to inform medical education policy. Methods: The authors sent a cross-sectional survey via email to medical students in their clinical training years at six medical schools during the initial peak phase of the COVID-19 pandemic. Survey questions aimed to evaluate students’ perceptions of COVID-19’s impact on medical education; ethical obligations during a pandemic; infection risk; anxiety and burnout; willingness and needed preparations to return to clinical rotations. Results: Seven hundred forty-one (29.5%) students responded. Nearly all students (93.7%) were not involved in clinical rotations with in-person patient contact at the time the study was conducted. Reactions to being removed were mixed, with 75.8% feeling this was appropriate, 34.7% guilty, 33.5% disappointed, and 27.0% relieved. Most students (74.7%) agreed the pandemic had significantly disrupted their medical education, and believed they should continue with normal clinical rotations during this pandemic (61.3%). When asked if they would accept the risk of infection with COVID-19 if they returned to the clinical setting, 83.4% agreed. Students reported the pandemic had moderate effects on their stress and anxiety levels with 84.1% of respondents feeling at least somewhat anxious. Adequate personal protective equipment (PPE) (53.5%) was the most important factor to feel safe returning to clinical rotations, followed by adequate testing for infection (19.3%) and antibody testing (16.2%). Conclusions: The COVID-19 pandemic disrupted the education of US medical students in their clinical training years. The majority of students wanted to return to clinical rotations and were willing to accept the risk of COVID-19 infection. Students were most concerned with having enough PPE if allowed to return to clinical activities
A rigorous treatment of the perturbation theory for many-electron systems
Four point correlation functions for many electrons at finite temperature in
periodic lattice are analyzed by the perturbation theory with respect to the
coupling constant. The correlation functions are characterized as a limit of
finite dimensional Grassmann integrals. A lower bound on the radius of
convergence and an upper bound on the perturbation series are obtained. The
perturbation series up to second order is numerically implemented along with
the volume-independent upper bounds on the sum of the higher order terms in 2
dimensional case.Comment: 61 page
Ground State Properties and Optical Conductivity of the Transition Metal Oxide
Combining first-principles calculations with a technique for many-body
problems, we investigate properties of the transition metal oxide from the microscopic point of view. By using the local density
approximation (LDA), the high-energy band structure is obtained, while screened
Coulomb interactions are derived from the constrained LDA and the GW method.
The renormalization of the kinetic energy is determined from the GW method. By
these downfolding procedures, an effective Hamiltonian at low energies is
derived. Applying the path integral renormalization group method to this
Hamiltonian, we obtain ground state properties such as the magnetic and orbital
orders. Obtained results are consistent with experiments within available data.
We find that is close to the metal-insulator transition.
Furthermore, because of the coexistence and competition of ferromagnetic and
antiferromgnetic exchange interactions in this system, an antiferromagnetic and
orbital-ordered state with a nontrivial and large unit cell structure is
predicted in the ground state. The calculated optical conductivity shows
characteristic shoulder structure in agreement with the experimental results.
This suggests an orbital selective reduction of the Mott gap.Comment: 38pages, 22figure
What is Minimal Model of 3He Adsorbed on Graphite? -Importance of Density Fluctuations in 4/7 Registered Solid -
We show theoretically that the second layer of 3He adsorbed on graphite and
solidified at 4/7 of the first-layer density is close to the fluid-solid
boundary with substantial density fluctuations on the third layer. The solid
shows a translational symmetry breaking as in charge-ordered insulators of
electronic systems. We construct a minimal model beyond the multiple-exchange
Heisenberg model. An unexpectedly large magnetic field required for the
measured saturation of magnetization is well explained by the density
fluctuations. The emergence of quantum spin liquid is understood from the same
mechanism as in the Hubbard model and in \kappa-(ET)_2Cu_2(CN)_3 near the Mott
transitions.Comment: 9 pages, 5 figure
Quantum Mott Transition and Multi-Furcating Criticality
Phenomenological theory of the Mott transition is presented. When the
critical temperature of the Mott transition is much higher than the quantum
degeneracy temperature, the transition is essentially described by the Ising
universality class. Below the critical temperature, phase separation or
first-order transition occurs. However, if the critical point is involved in
the Fermi degeneracy region, a marginal quantum critical point appears at zero
temperature. The originally single Mott critical point generates subsequent
many unstable fixed points through various Fermi surface instabilities induced
by the Mott criticality characterized by the diverging charge susceptibility or
doublon susceptibility. This occurs in marginal quantum-critical region.
Charge, magnetic and superconducting instabilitites compete severely under
these critical charge fluctuations. The quantum Mott transition triggers
multi-furcating criticality, which goes beyond the conventional concept of
multicriticality in quantum phase transitions. Near the quantum Mott
transition, the criticality generically drives growth of inhomogeneous
structure in the momentum space with singular points of flat dispersion on the
Fermi surface. The singular points determine the quantum dynamics of the Mott
transition by the dynamical exponent . We argue that many of
filling-control Mott transitions are classified to this category. Recent
numerical results as well as experimental results on strongly correlated
systems including transition metal oxides, organic materials and He layer
adsorbed on a substrate are consistently analyzed especially in two-dimensional
systems.Comment: 28 pages including 2 figure
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