585 research outputs found
Improved AdS/QCD Model with Matter
We study an improved AdS/QCD model at finite temperature and chemical
potential. An Ansatz for the beta-function for the boundary theory allows for
the derivation of a charged dilatonic black hole in bulk. The solution is
asymptotically RN-AdS in the UV and AdS2 * R3 in the IR. We discuss the
thermodynamical aspects of the solution. The fermionic susceptibilities are
shown to deviate from the free fermionic limits at asymptotic temperatures
despite the asymptotically free nature of the gauge coupling at the boundary.
The Polyakov line, the temporal and spatial string tensions dependence on both
temperature and chemical potential are also discussed
Holographic Pomeron: Saturation and DIS
We briefly review the approach to dipole-dipole scattering in holographic QCD
developed in ARXIV:1202.0831. The Pomeron is modeled by exchanging closed
strings between the dipoles and yields Regge behavior for the elastic
amplitude. We calculate curvature corrections to this amplitude in both a
conformal and confining background, identifying the holographic direction with
the virtuality of the dipoles. The it wee-dipole density is related to the
string tachyon diffusion in both virtuality and the transverse directions. We
give an explicit derivation of the dipole saturation momentum both in the
conformal and confining metric. Our holographic result for the dipole-dipole
cross section and the it wee-dipole density in the conformal limit are shown to
be identical in form to the BFKL pomeron result when the non-critical string
transverse dimension is . The total dipole-dipole cross section is
compared to DIS data from HERA
Jet quenching in shock waves
We study the propagation of an ultrarelativistic light quark jet inside a
shock wave using the holographic principle. The maximum stopping distance and
its dependency on the energy of the jet is obtained
Algorithmic Complexity for Short Binary Strings Applied to Psychology: A Primer
Since human randomness production has been studied and widely used to assess
executive functions (especially inhibition), many measures have been suggested
to assess the degree to which a sequence is random-like. However, each of them
focuses on one feature of randomness, leading authors to have to use multiple
measures. Here we describe and advocate for the use of the accepted universal
measure for randomness based on algorithmic complexity, by means of a novel
previously presented technique using the the definition of algorithmic
probability. A re-analysis of the classical Radio Zenith data in the light of
the proposed measure and methodology is provided as a study case of an
application.Comment: To appear in Behavior Research Method
Parallel Retention of Pdx2 Genes in Cartilaginous Fish and Coelacanths
The Pdx1 or Ipf1 gene encodes an important homeodomain-containing protein with key roles in pancreas development and function. Mutations in human PDX1 are implicated in developmental defects and disease of the pancreas. Extensive research, including genome sequencing, has indicated that Pdx1 is the only member of its gene family in mammals, birds, amphibians, and ray-finned fish, and with the exception of teleost fish, this gene forms part of the ParaHox gene cluster along with Gsx1 and Cdx2. The ParaHox cluster, however, is a remnant of a 4-fold genome duplication; the three other ParaHox paralogues lack a Pdx-like gene in all vertebrate genomes examined to date. We have used bacterial artificial chromosome cloning and synteny analysis to show that the ancestor of living jawed vertebrates in fact had more ParaHox genes, including two Pdx genes (Pdx1 and Pdx2). Surprisingly, the two Pdx genes have been retained in parallel in two quite distantly related lineages, the cartilaginous fish (sharks, skates, and chimeras) and the Indonesian coelacanth, Latimeria menadoensis. The Pdx2 gene has been lost independently in ray-finned fish and in tetrapods
First observations of high-temperature submarine hydrothermal vents and massive anhydrite deposits off the north coast of Iceland
High-temperature (250°C) hydrothermal vents and massive anhydrite deposits have been found in a shallow water, sediment-filled graben near 66°36âČN in the Tjornes Fracture Zone north of Iceland. The site is located about 30 km offshore, near the small island of Grimsey. The main vent field occurs at a depth of 400 m and consists of about 20 large-diameter (up to 10 m) mounds and 1â3 m chimneys and spires of anhydrite and talc. A northâsouth alignment of the mounds over a 1-km strike length of the valley floor suggests that their distribution is controlled by a buried fault. Widespread shimmering water and extensive white patches of anhydrite in the sediment between the mounds indicates that the entire 1-km2 area occupied by the vents is thermally active. A 2-man research submersible JAGO was used to map the area and to sample vent waters, gases, and chimneys. Actively boiling hydrothermal vents occur on most of the mounds, and extensive two-phase venting indicates that the field is underlain by a large boiling zone (200Ă300 m). The presence of boiling fluids in shallow aquifers beneath the deposits was confirmed by sediment coring. The highest-temperature pore fluids were encountered in talc- and anhydrite-rich sedimentary layers that occur up to 7 m below the mounds. Baked muds underlie the talc and anhydrite layers, and pyrite is common in stockwork-like fractures and veins in the hydrothermally altered sediments. However, massive sulfides (pyriteâmarcasite crusts) were found in only one relict mound. Subseafloor boiling has likely affected the metal-carrying capacity of the hydrothermal fluids, and deposition of sulfides may be occurring at greater depth. Although the mounds and chimneys at Grimsey resemble other deposits at sedimented ridges (e.g. Middle Valley, Escanaba Trough, Guaymas Basin), the shallow water setting and extensive boiling of the hydrothermal fluids represent a distinctive new type of seafloor hydrothermal system
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