2,921 research outputs found
Pacifying the Fermi-liquid: battling the devious fermion signs
The fermion sign problem is studied in the path integral formalism. The
standard picture of Fermi liquids is first critically analyzed, pointing out
some of its rather peculiar properties. The insightful work of Ceperley in
constructing fermionic path integrals in terms of constrained world-lines is
then reviewed. In this representation, the minus signs associated with
Fermi-Dirac statistics are self consistently translated into a geometrical
constraint structure (the {\em nodal hypersurface}) acting on an effective
bosonic dynamics. As an illustrative example we use this formalism to study
1+1-dimensional systems, where statistics are irrelevant, and hence the sign
problem can be circumvented. In this low-dimensional example, the structure of
the nodal constraints leads to a lucid picture of the entropic interaction
essential to one-dimensional physics. Working with the path integral in
momentum space, we then show that the Fermi gas can be understood by analogy to
a Mott insulator in a harmonic trap. Going back to real space, we discuss the
topological properties of the nodal cells, and suggest a new holographic
conjecture relating Fermi liquids in higher dimensions to soft-core bosons in
one dimension. We also discuss some possible connections between mixed
Bose/Fermi systems and supersymmetry.Comment: 28 pages, 5 figure
Simultaneous lidar and airglow temperature measurements in the mesopause region
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94970/1/grl5512.pd
Is equal access to higher education in South Asia and sub-Saharan Africa achievable by 2030?
Higher education is back in the spotlight, with post-2015 sustainable development goals emphasising equality of access. In this paper, we highlight the long distance still to travel to achieve the goal of equal access to higher education for all, with a focus on poorer countries which tend to have lower levels of enrolment in higher education. Analysing Demographic and Health Survey data from 35 low- and middle-income countries in sub-Saharan Africa and South Asia, we show wide wealth inequalities in particular, with few if any of the poorest gaining access to higher education in some countries. We further identify that wealth and gender inequalities interact and tend to be wider in countries where levels of higher education are higher. This implies that expansion in access to higher education may predominantly benefit the rich, unless measures are taken to tackle inequalities. We find that that the rates of increase necessary for the attainment of the equal access goal by 2030 are particularly high. They pose a particularly difficult challenge given the access inequalities present from primary and secondary education in a wide majority of countries in our analysis. We therefore suggest that any measures aimed at attaining the goal need to tackle inequalities in access within a system-wide approach, focusing on the level of education at which inequalities initially manifest, alongside higher education.This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s10734-016-0039-
Predicting Allograft Requirement in the Management of Patients With Major Burn Injuries
âą Early debridement and coverage of burn wounds saves lives.
âą Allograft is the âgold-standardâ for temporary coverage of acute burns
Toward the End of Time
The null-brane space-time provides a simple model of a big crunch/big bang
singularity. A non-perturbative definition of M-theory on this space-time was
recently provided using matrix theory. We derive the fermion couplings for this
matrix model and study the leading quantum effects. These effects include
particle production and a time-dependent potential. Our results suggest that as
the null-brane develops a big crunch singularity, the usual notion of
space-time is replaced by an interacting gluon phase. This gluon phase appears
to constitute the end of our conventional picture of space and time.Comment: 31 pages, reference adde
Accelerating universe emergent from the landscape
We propose that the existence of the string landscape suggests the universe
can be in a quantum glass state, where an extremely large viscosity is
generated, and long distance dynamics slows down. At the same time, the short
distance dynamics is not altered due to the separation of time scales. This
scenario can help to understand some controversies in cosmology, for example
the natural existence of slow roll inflation and dark energy in the landscape,
the apparent smallness of the cosmological constant. We see also that moduli
stabilization is no longer necessary. We further identify the glass transition
point, where the viscosity diverges, as the location of the cosmic horizon. We
try to reconstruct the geometry of the accelerating universe from the structure
of the landscape, and find that the metric should have an infinite jump when
crossing the horizon. We predict that the static coordinate metric for dS space
breaks down outside the horizon.Comment: 20 pages, no figures, harvma
Proximity of the superconducting dome and the quantum critical point in the two-dimensional Hubbard model
We use the dynamical cluster approximation to understand the proximity of the superconducting dome to the quantum critical point in the two-dimensional Hubbard model. In a BCS formalism, Tc may be enhanced through an increase in the d-wave pairing interaction (Vd) or the bare pairing susceptibility (Ï0d). At optimal doping, where Vd is revealed to be featureless, we find a power-law behavior of Ï 0d(Ï=0), replacing the BCS log, and strongly enhanced T c. We suggest experiments to verify our predictions. © 2011 American Physical Society
Developed turbulence: From full simulations to full mode reductions
Developed Navier-Stokes turbulence is simulated with varying wavevector mode
reductions. The flatness and the skewness of the velocity derivative depend on
the degree of mode reduction. They show a crossover towards the value of the
full numerical simulation when the viscous subrange starts to be resolved. The
intermittency corrections of the scaling exponents of the pth order velocity
structure functions seem to depend mainly on the proper resolution of the
inertial subrange. Universal scaling properties (i.e., independent of the
degree of mode reduction) are found for the relative scaling exponents rho
which were recently defined by Benzi et al.Comment: 4 pages, 5 eps-figures, replaces version from August 5th, 199
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