2,972 research outputs found
The Herbertsmithite Hamiltonian: SR measurements on single crystals
We present transverse field muon spin rotation/relaxation measurements on
single crystals of the spin-1/2 kagome antiferromagnet Herbertsmithite. We find
that the spins are more easily polarized when the field is perpendicular to the
kagome plane. We demonstrate that the difference in magnetization between the
different directions cannot be accounted for by Dzyaloshinksii-Moriya type
interactions alone, and that anisotropic axial interaction is present.Comment: 8 pages, 3 figures, accepted to JPCM special issue on geometrically
frustrated magnetis
Perturbative Analysis of Nonabelian Aharonov-Bohm Scattering
We perform a perturbative analysis of the nonabelian Aharonov-Bohm problem to
one loop in a field theoretic framework, and show the necessity of contact
interactions for renormalizability of perturbation theory. Moreover at critical
values of the contact interaction strength the theory is finite and preserves
classical conformal invariance.Comment: 12 pages in LaTeX, uses epsf.sty, 5 uuencoded Postscript figures sent
separately. MIT-CTP-228
Striped instability of a holographic Fermi-like liquid
We consider a holographic description of a system of strongly-coupled
fermions in 2+1 dimensions based on a D7-brane probe in the background of
D3-branes. The black hole embedding represents a Fermi-like liquid. We study
the excitations of the Fermi liquid system. Above a critical density which
depends on the temperature, the system becomes unstable towards an
inhomogeneous modulated phase which is similar to a charge density and spin
wave state. The essence of this instability can be effectively described by a
Maxwell-axion theory with a background electric field. We also consider the
fate of zero sound at non-zero temperature.Comment: 16 pages, 9 figures; v2: added discussion and one figure. Typos
correcte
Holographic Nuclear Physics
We analyze the phases of the Sakai-Sugimoto model at finite temperature and
baryon chemical potential. Baryonic matter is represented either by 4-branes in
the 8-branes or by strings stretched from the 8-branes to the horizon. We find
the explicit configurations and use them to determine the phase diagram and
equation of state of the model. The 4-brane configuration (nuclear matter) is
always preferred to the string configuration (quark matter), and the latter is
also unstable to density fluctuations. In the deconfined phase the phase
diagram has three regions corresponding to the vacuum, quark-gluon plasma, and
nuclear matter, with a first-order and a second-order phase transition
separating the phases. We find that for a large baryon number density, and at
low temperatures, the dominant phase has broken chiral symmetry. This is in
qualitative agreement with studies of QCD at high density.Comment: 27 pages, 26 figures. v2: Added a comment about higher derivative
corrections to the DBI action in the smeared instanton in section 2.1. v3:
References added, version published in JHEP. v4: misprints correcte
Differences in lateral gene transfer in hypersaline versus thermal environments
<p>Abstract</p> <p>Background</p> <p>The role of lateral gene transfer (LGT) in the evolution of microorganisms is only beginning to be understood. While most LGT events occur between closely related individuals, inter-phylum and inter-domain LGT events are not uncommon. These distant transfer events offer potentially greater fitness advantages and it is for this reason that these "long distance" LGT events may have significantly impacted the evolution of microbes. One mechanism driving distant LGT events is microbial transformation. Theoretically, transformative events can occur between any two species provided that the DNA of one enters the habitat of the other. Two categories of microorganisms that are well-known for LGT are the thermophiles and halophiles.</p> <p>Results</p> <p>We identified potential inter-class LGT events into both a thermophilic class of Archaea (Thermoprotei) and a halophilic class of Archaea (Halobacteria). We then categorized these LGT genes as originating in thermophiles and halophiles respectively. While more than 68% of transfer events into Thermoprotei taxa originated in other thermophiles, less than 11% of transfer events into Halobacteria taxa originated in other halophiles.</p> <p>Conclusions</p> <p>Our results suggest that there is a fundamental difference between LGT in thermophiles and halophiles. We theorize that the difference lies in the different natures of the environments. While DNA degrades rapidly in thermal environments due to temperature-driven denaturization, hypersaline environments are adept at preserving DNA. Furthermore, most hypersaline environments, as topographical minima, are natural collectors of cellular debris. Thus halophiles would in theory be exposed to a greater diversity and quantity of extracellular DNA than thermophiles.</p
Predominance of deterministic microbial community dynamics in salterns exposed to different light intensities
While the dynamics of microbial community assembly driven by environmental perturbations have been extensively studied, our understanding is far from complete, particularly for lightâinduced perturbations. Extremely halophilic communities thriving in coastal solar salterns are mainly influenced by two environmental factorsâsalt concentrations and high sunlight irradiation. By experimentally manipulating light intensity through the application of shading, we showed that light acts as a deterministic factor that ultimately drives the establishment of recurrent microbial communities under nearâsaturation salt concentrations. In particular, the stable and highly changeâresistant communities that established under highâlight intensities were dominated (>90% of metagenomic reads) by Haloquadratum spp. and Salinibacter spp. On the other hand, under 37âfold lower light intensity, different, less stable and changeâresistant communities were established, mainly dominated by yet unclassified haloarchaea and relatively diverse photosynthetic microorganisms. These communities harboured, in general, much lower carotenoid pigment content than their highâirradiation counterparts. Both assemblage types appeared to be highly resilient, reâestablishing when favourable conditions returned after perturbation (i.e. highâirradiation for the former communities and lowâirradiation for the latter ones). Overall, our results revealed that stochastic processes were of limited significance to explain these patterns.This study was funded by the Spanish Ministry of Economy projects CGL2012-39627-C03-03 CLG2015_66686-C3-1-P and PGC2018-096956-B-C41 (to R.R.M.), CGL2015_66686-C3-3-P (to J.A.) and CGL2015_66686-C3-2-P (to J.E.G.P.), which were also supported with European Regional Development Fund (FEDER) funds. R.A. was funded by the Max Planck Society. KTKâs research was supported, in part, by the U.S. National Science Foundation (Award No. 1831582). T.V.P. received a pre-doctoral fellowship (No. BES-2013-064420) from the Spanish Government Ministry for Finance and Competition. R.R.M. acknowledges the financial support of the sabbatical stay at Georgia Tech supported by the Grant PRX18/00048 of the Ministry of Sciences, Innovation and Universities
String Bit Models for Superstring
We extend the model of string as a polymer of string bits to the case of
superstring. We mainly concentrate on type II-B superstring, with some
discussion of the obstacles presented by not II-B superstring, together with
possible strategies for surmounting them. As with previous work on bosonic
string we work within the light-cone gauge. The bit model possesses a good deal
less symmetry than the continuous string theory. For one thing, the bit model
is formulated as a Galilei invariant theory in dimensional
space-time. This means that Poincar\'e invariance is reduced to the Galilei
subgroup in space dimensions. Naturally the supersymmetry present in the
bit model is likewise dramatically reduced. Continuous string can arise in the
bit models with the formation of infinitely long polymers of string bits. Under
the right circumstances (at the critical dimension) these polymers can behave
as string moving in dimensional space-time enjoying the full
Poincar\'e supersymmetric dynamics of type II-B superstring.Comment: 43 pages, phyzzx require
Response of Holographic QCD to Electric and Magnetic Fields
We study the response of the Sakai-Sugimoto holographic model of large N_c
QCD at nonzero temperature to external electric and magnetic fields. In the
electric case we find a first-order insulator-conductor transition in both the
confining and deconfining phases of the model. In the deconfining phase the
conductor is described by the parallel 8-brane-anti-8-brane embedding with a
current of quarks and anti-quarks. We compute the conductivity and show that it
agrees precisely with a computation using the Kubo formula. In the confining
phase we propose a new kind of 8-brane embedding, corresponding to a baryonic
conductor. In the magnetic field case we show that the critical temperature for
chiral-symmetry restoration in the deconfined phase increases with the field
and approaches a finite value in the limit of an infinite magnetic field. We
also illustrate the nonlinear behavior of the electric and magnetic
susceptibilities in the different phases.Comment: 18 pages, 19 figures; reference added, version published in JHE
Graphene transistors are insensitive to pH changes in solution
We observe very small gate-voltage shifts in the transfer characteristic of
as-prepared graphene field-effect transistors (GFETs) when the pH of the buffer
is changed. This observation is in strong contrast to Si-based ion-sensitive
FETs. The low gate-shift of a GFET can be further reduced if the graphene
surface is covered with a hydrophobic fluorobenzene layer. If a thin Al-oxide
layer is applied instead, the opposite happens. This suggests that clean
graphene does not sense the chemical potential of protons. A GFET can therefore
be used as a reference electrode in an aqueous electrolyte. Our finding sheds
light on the large variety of pH-induced gate shifts that have been published
for GFETs in the recent literature
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