1,514 research outputs found
DIAPHRAGM MUSCLE STRIP PREPARATION FOR EVALUATION OF GENE THERAPIES IN mdx MICE
1.â Duchenne muscular dystrophy (DMD), a severe muscle wasting disease of young boys with an incidence of one in every 3000, results from a mutation in the gene that encodes dystrophin. The absence of dystrophin expression in skeletal muscles and heart results in the degeneration of muscle fibres and, consequently, severe muscle weakness and wasting. The mdx mouse discovered in 1984, with some adjustments for differences, has proven to be an invaluable model for scientific investigations of dystrophy. 2.â The development of the diaphagm strip preparation provided an ideal experimental model for investigations of skeletal muscle impairments in structure and function induced by interactions of disease- and age-related factors. Unlike the limb muscles of the mdx mouse, which show adaptive changes in structure and function, the diaphragm strip preparation reflects accurately the deterioration in muscle structure and function observed in boys with DMD. 3.â The advent of sophisticated servo motors and force transducers interfaced with state-of-the-art software packages to drive complex experimental designs during the 1990s greatly enhanced the capability of the mdx mouse and the diaphragm strip preparation to evaluate more accurately the impact of the disease on the structureâfunction relationships throughout the life span of the mouse. 4.â Finally, during the 1990s and through the early years of the 21st century, many promising, sophisticated genetic techniques have been designed to ameliorate the devastating impact of muscular dystrophy on the structure and function of skeletal muscles. During this period of rapid development of promising genetic therapies, the combination of the mdx mouse and the diaphragm strip preparation has provided an ideal model for the evaluation of the success, or failure, of these genetic techniques to improve dystrophic muscle structure, function or both. With the 2 year life span of the mdx mouse, the impact of age-related effects can be studied in this model.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72970/1/j.1440-1681.2007.04865.x.pd
Stellar spectroscopy: Fermions and holographic Lifshitz criticality
Electron stars are fluids of charged fermions in Anti-de Sitter spacetime.
They are candidate holographic duals for gauge theories at finite charge
density and exhibit emergent Lifshitz scaling at low energies. This paper
computes in detail the field theory Green's function G^R(w,k) of the
gauge-invariant fermionic operators making up the star. The Green's function
contains a large number of closely spaced Fermi surfaces, the volumes of which
add up to the total charge density in accordance with the Luttinger count.
Excitations of the Fermi surfaces are long lived for w <~ k^z. Beyond w ~ k^z
the fermionic quasiparticles dissipate strongly into the critical Lifshitz
sector. Fermions near this critical dispersion relation give interesting
contributions to the optical conductivity.Comment: 38 pages + appendices. 9 figure
Lattice potentials and fermions in holographic non Fermi-liquids: hybridizing local quantum criticality
We study lattice effects in strongly coupled systems of fermions at a finite
density described by a holographic dual consisting of fermions in
Anti-de-Sitter space in the presence of a Reissner-Nordstrom black hole. The
lattice effect is encoded by a periodic modulation of the chemical potential
with a wavelength of order of the intrinsic length scales of the system. This
corresponds with a highly complicated "band structure" problem in AdS, which we
only manage to solve in the weak potential limit. The "domain wall" fermions in
AdS encoding for the Fermi surfaces in the boundary field theory diffract as
usually against the periodic lattice, giving rise to band gaps. However, the
deep infrared of the field theory as encoded by the near horizon AdS2 geometry
in the bulk reacts in a surprising way to the weak potential. The hybridization
of the fermions bulk dualizes into a linear combination of CFT1 "local quantum
critical" propagators in the bulk, characterized by momentum dependent
exponents displaced by lattice Umklapp vectors. This has the consequence that
the metals showing quasi-Fermi surfaces cannot be localized in band insulators.
In the AdS2 metal regime, where the conformal dimension of the fermionic
operator is large and no Fermi surfaces are present at low T/\mu, the lattice
gives rise to a characteristic dependence of the energy scaling as a function
of momentum. We predict crossovers from a high energy standard momentum AdS2
scaling to a low energy regime where exponents found associated with momenta
"backscattered" to a lower Brillioun zone in the extended zone scheme. We
comment on how these findings can be used as a unique fingerprint for the
detection of AdS2 like "pseudogap metals" in the laboratory.Comment: 42 pages, 5 figures; v2, minor correction, to appear in JHE
Mixed RG Flows and Hydrodynamics at Finite Holographic Screen
We consider quark-gluon plasma with chemical potential and study
renormalization group flows of transport coefficients in the framework of
gauge/gravity duality. We first study them using the flow equations and compare
the results with hydrodynamic results by calculating the Green functions on the
arbitrary slice. Two results match exactly. Transport coefficients at arbitrary
scale is ontained by calculating hydrodynamics Green functions. When either
momentum or charge vanishes, transport coefficients decouple from each other.Comment: 22 pages, 6 figure
Holographic fermions in charged Gauss-Bonnet black hole
We study the properties of the Green's functions of the fermions in charged
Gauss-Bonnet black hole. What we want to do is to investigate how the presence
of Gauss-Bonnet coupling constant affects the dispersion relation,
which is a characteristic of Fermi or non-Fermi liquid, as well as what
properties such a system has, for instance, the Particle-hole (a)symmetry. One
important result of this research is that we find for , the behavior of
this system is different from that of the Landau Fermi liquid and so the system
can be candidates for holographic dual of generalized non-Fermi liquids. More
importantly, the behavior of this system increasingly similar to that of the
Landau Fermi liquid when is approaching its lower bound. Also we find
that this system possesses the Particle-hole asymmetry when , another
important characteristic of this system. In addition, we also investigate
briefly the cases of the charge dependence.Comment: 22 pages, 6 figures; version published in JHE
Prioritising surveillance for alien organisms transported as stowaways on ships travelling to South Africa
The global shipping network facilitates the transportation and introduction of marine and terrestrial organisms to regions where they are not native, and some of these organisms become invasive. South Africa was used as a case study to evaluate the potential for shipping to contribute to the introduction and establishment of marine and terrestrial alien species (i.e. establishment debt) and to assess how this varies across shipping routes and seasons. As a proxy for the number of species introduced (i.e. 'colonisation pressure') shipping movement data were used to determine, for each season, the number of ships that visited South African ports from foreign ports and the number of days travelled between ports. Seasonal marine and terrestrial environmental similarity between South African and foreign ports was then used to estimate the likelihood that introduced species would establish. These data were used to determine the seasonal relative contribution of shipping routes to South Africa's marine and terrestrial establishment debt. Additionally, distribution data were used to identify marine and terrestrial species that are known to be invasive elsewhere and which might be introduced to each South African port through shipping routes that have a high relative contribution to establishment debt. Shipping routes from Asian ports, especially Singapore, have a particularly high relative contribution to South Africa's establishment debt, while among South African ports, Durban has the highest risk of being invaded. There was seasonal variation in the shipping routes that have a high relative contribution to the establishment debt of the South African ports. The presented method provides a simple way to prioritise surveillance effort and our results indicate that, for South Africa, port-specific prevention strategies should be developed, a large portion of the available resources should be allocated to Durban, and seasonal variations and their consequences for prevention strategies should be explored further. (Résumé d'auteur
A soliton menagerie in AdS
We explore the behaviour of charged scalar solitons in asymptotically global
AdS4 spacetimes. This is motivated in part by attempting to identify under what
circumstances such objects can become large relative to the AdS length scale.
We demonstrate that such solitons generically do get large and in fact in the
planar limit smoothly connect up with the zero temperature limit of planar
scalar hair black holes. In particular, for given Lagrangian parameters we
encounter multiple branches of solitons: some which are perturbatively
connected to the AdS vacuum and surprisingly, some which are not. We explore
the phase space of solutions by tuning the charge of the scalar field and
changing scalar boundary conditions at AdS asymptopia, finding intriguing
critical behaviour as a function of these parameters. We demonstrate these
features not only for phenomenologically motivated gravitational Abelian-Higgs
models, but also for models that can be consistently embedded into eleven
dimensional supergravity.Comment: 62 pages, 21 figures. v2: added refs and comments and updated
appendice
Cooper pairing near charged black holes
We show that a quartic contact interaction between charged fermions can lead
to Cooper pairing and a superconducting instability in the background of a
charged asymptotically Anti-de Sitter black hole. For a massless fermion we
obtain the zero mode analytically and compute the dependence of the critical
temperature T_c on the charge of the fermion. The instability we find occurs at
charges above a critical value, where the fermion dispersion relation near the
Fermi surface is linear. The critical temperature goes to zero as the marginal
Fermi liquid is approached, together with the density of states at the Fermi
surface. Besides the charge, the critical temperature is controlled by a four
point function of a fermionic operator in the dual strongly coupled field
theory.Comment: 1+33 pages, 4 figure
Dipole Coupling Effect of Holographic Fermion in the Background of Charged Gauss-Bonnet AdS Black Hole
We investigate the holographic fermions in the charged Gauss-Bonnet
black hole background with the dipole coupling between fermion and gauge field
in the bulk. We show that in addition to the strength of the dipole coupling,
the spacetime dimension and the higher curvature correction in the gravity
background also influence the onset of the Fermi gap and the gap distance. We
find that the higher curvature effect modifies the fermion spectral density and
influences the value of the Fermi momentum for the appearance of the Fermi
surface. There are richer physics in the boundary fermion system due to the
modification in the bulk gravity.Comment: 16 pages, accepted for publication in JHE
Holographic Fermi and Non-Fermi Liquids with Transitions in Dilaton Gravity
We study the two-point function for fermionic operators in a class of
strongly coupled systems using the gauge-gravity correspondence. The gravity
description includes a gauge field and a dilaton which determines the gauge
coupling and the potential energy. Extremal black brane solutions in this
system typically have vanishing entropy. By analyzing a charged fermion in
these extremal black brane backgrounds we calculate the two-point function of
the corresponding boundary fermionic operator. We find that in some region of
parameter space it is of Fermi liquid type. Outside this region no well-defined
quasi-particles exist, with the excitations acquiring a non-vanishing width at
zero frequency. At the transition, the two-point function can exhibit non-Fermi
liquid behaviour.Comment: 52 pages, 6 figures. v3: Appendix F added showing numerical
interpolation between the near-horizon region and AdS4. Additional minor
comments also adde
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