293 research outputs found
Buerger's disease manifesting nodular erythema with livedo reticularis
ArticleINTERNAL MEDICINE. 46(21):1815-1819(2007)journal articl
Dissecting early regulatory relationships in the lamprey neural crest gene network
The neural crest, a multipotent embryonic cell type, originates at the border between neural and nonneural ectoderm. After neural tube closure, these cells undergo an epithelial–mesenchymal transition, migrate to precise, often distant locations, and differentiate into diverse derivatives. Analyses of expression and function of signaling and transcription factors in higher vertebrates has led to the proposal that a neural crest gene regulatory network (NC-GRN) orchestrates neural crest formation. Here, we interrogate the NC-GRN in the lamprey, taking advantage of its slow development and basal phylogenetic position to resolve early inductive events, 1 regulatory step at the time. To establish regulatory relationships at the neural plate border, we assess relative expression of 6 neural crest network genes and effects of individually perturbing each on the remaining 5. The results refine an upstream portion of the NC-GRN and reveal unexpected order and linkages therein; e.g., lamprey AP-2 appears to function early as a neural plate border rather than a neural crest specifier and in a pathway linked to MsxA but independent of ZicA. These findings provide an ancestral framework for performing comparative tests in higher vertebrates in which network linkages may be more difficult to resolve because of their rapid development
The Chiral Model of Sakai-Sugimoto at Finite Baryon Density
In the context of holographic QCD we analyze Sakai-Sugimoto's chiral model at
finite baryon density and zero temperature. The baryon number density is
introduced through compact D4 wrapping S^4 at the tip of D8-\bar{D8}. Each
baryon acts as a chiral point-like source distributed uniformly over R^3, and
leads a non-vanishing U(1)_V potential on the brane. For fixed baryon charge
density n_B we analyze the bulk energy density and pressure using the canonical
formalism. The baryonic matter with point like sources is always in the
spontaneously broken phase of chiral symmetry, whatever the density. The
point-like nature of the sources and large N_c cause the matter to be repulsive
as all baryon interactions are omega mediated. Through the induced DBI action
on D8-\bar{D8}, we study the effects of the fixed baryon charge density n_B on
the pion and vector meson masses and couplings. Issues related to vector
dominance in matter in the context of holographic QCD are also discussed.Comment: V3: 39 pages, 16 figures, minor corrections, version to appear in
JHEP. V2: references added, typos correcte
Stringy NJL and Gross-Neveu models at finite density and temperature
Nonlocal stringy versions of the Nambu-Jona-Lasinio and Gross-Neveu models
arise in a certain limit of holographic QCD. We analyze the phase structure at
finite density and temperature at strong coupling in terms of probe branes in
the gravity dual. Comparison with the phase structure of the local field theory
models shows qualitative agreement with some aspects, and disagreement with
others. Finally, we explain how to construct the Landau potentials for these
models by taking the probe branes off-shell.Comment: 32 pages, uses JHEP3.cls; v2, references added, version to be
submitted to JHE
Holographic Thermodynamics at Finite Baryon Density: Some Exact Results
We use the AdS/CFT correspondence to study the thermodynamics of massive N=2
supersymmetric hypermultiplets coupled to N=4 supersymmetric SU(Nc) Yang-Mills
theory in the limits of large Nc and large 't Hooft coupling. In particular, we
study the theory at finite baryon number density. At zero temperature, we
present an exact expression for the hypermultiplets' leading-order contribution
to the free energy, and in the supergravity description we clarify which
D-brane configuration is appropriate for any given value of the chemical
potential. We find a second-order phase transition when the chemical potential
equals the mass. At finite temperature, we present an exact expression for the
hypermultiplets' leading-order contribution to the free energy at zero mass.Comment: 21 pages, 1 figure; v2 corrected typos, added comments to sections
2.2 and 2.
Notes on Properties of Holographic Matter
Probe branes with finite worldvolume electric flux in the background created
by a stack of Dp branes describe holographically strongly interacting
fundamental matter at finite density. We identify two quantities whose leading
low temperature behavior is independent of the dimensionality of the probe
branes: specific heat and DC conductivity. This behavior can be inferred from
the dynamics of the fundamental strings which provide a good description of the
probe branes in the regime of low temperatures and finite densities. We also
comment on the speed of sound on the branes and the temperature dependence of
DC conductivity at vanishing charge density.Comment: 18 pages, 2 figures; v2: corrected error in Section 6, conclusions
unchanged; v3: improved figures and added clarifying comment
Reconstitution into liposomes of membrane proteins involved in ribosome binding on rough endoplasmic reticulum. Ribosome-binding capacity
Holographic phase transitions at finite baryon density
We use holographic techniques to study SU(Nc) super Yang-Mills theory coupled
to Nf << Nc flavours of fundamental matter at finite temperature and baryon
density. We focus on four dimensions, for which the dual description consists
of Nf D7-branes in the background of Nc black D3-branes, but our results apply
in other dimensions as well. A non-zero chemical potential mu or baryon number
density n is introduced via a nonvanishing worldvolume gauge field on the
D7-branes. Ref. [1] identified a first order phase transition at zero density
associated with `melting' of the mesons. This extends to a line of phase
transitions for small n, which terminates at a critical point at finite n.
Investigation of the D7-branes' thermodynamics reveals that (d mu / dn)_T <0 in
a small region of the phase diagram, indicating an instability. We comment on a
possible new phase which may appear in this region.Comment: 33 pages, 22 figure
Criticality, Scaling and Chiral Symmetry Breaking in External Magnetic Field
We consider a D7-brane probe of in the presence of pure
gauge -field. The dual gauge theory is flavored Yang-Mills theory in
external magnetic field. We explore the dependence of the fermionic condensate
on the bare quark mass and study the discrete self-similar behavior of
the theory near the origin of the parametric space. We calculate the critical
exponents of the bare quark mass and the fermionic condensate. A study of the
meson spectrum supports the expectation based on thermodynamic considerations
that at zero bare quark mass the stable phase of the theory is a chiral
symmetry breaking one. Our study reveals the self-similar structure of the
spectrum near the critical phase of the theory, characterized by zero fermionic
condensate and we calculate the corresponding critical exponent of the meson
spectrum.Comment: 29 pages, 9 figures. Accepted in JHEP. Updated to mach the published
version. One figure added, some definitions improve
Baryonic Response of Dense Holographic QCD
The response function of a homogeneous and dense hadronic system to a
time-dependent (baryon) vector potential is discussed for holographic dense QCD
(D4/D8 embedding) both in the confined and deconfined phases. Confined
holographic QCD is an uncompressible and static baryonic insulator at large N_c
and large \lambda, with a gapped vector spectrum and a massless pion.
Deconfined holographic QCD is a diffusive conductor with restored chiral
symmetry and a gapped transverse baryonic current. Similarly, dense D3/D7 is
diffusive for any non-zero temperature at large N_c and large \lambda. At zero
temperature dense D3/D7 exhibits a baryonic longitudinal visco-elastic mode
with a first sound speed \lambda/\sqrt{3} and a small width due to a shear
viscosity to baryon ratio \eta/n_B=\hbar/4. This mode is turned diffusive by
arbitrarily small temperatures, a hallmark of holography.Comment: V2: 47 pages, 7 figures, references added, typos correcte
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