2,464 research outputs found
Topological surface transport in epitaxial SnTe thin films grown on Bi₂Te₃
The topological crystalline insulator SnTe has been grown epitaxially on a Bi₂Te₃ buffer layer by molecular beam epitaxy. In a 30-nm-thick SnTe film, p- and n-type carriers are found to coexist, and Shubnikov–de Haas oscillation data suggest that the n-type carriers are Dirac fermions residing on the SnTe (111) surface. This transport observation of the topological surface state in a p-type topological crystalline insulator became possible due to a downward band bending on the free SnTe surface, which appears to be of intrinsic origin
Lorentz-violating vs ghost gravitons: the example of Weyl gravity
We show that the ghost degrees of freedom of Einstein gravity with a Weyl
term can be eliminated by a simple mechanism that invokes local Lorentz
symmetry breaking. We demonstrate how the mechanism works in a cosmological
setting. The presence of the Weyl term forces a redefinition of the quantum
vacuum state of the tensor perturbations. As a consequence the amplitude of
their spectrum blows up when the Lorentz-violating scale becomes comparable to
the Hubble radius. Such a behaviour is in sharp contrast to what happens in
standard Weyl gravity where the gravitational ghosts smoothly damp out the
spectrum of primordial gravitational waves.Comment: 14 pages, 3 figures, REVTeX 4.
Ferromagnetism in Cr-doped topological insulator TlSbTe2
We have synthesized a new ferromagnetic topological insulator by doping Cr to the ternary topological-insulator material TlSbTe2. Single crystals of Tl1−x Cr x SbTe2 were grown by a melting method and it was found that Cr can be incorporated into the TlSbTe2 matrix only within the solubility limit of about 1%. The Curie temperature θC was found to increase with the Cr content but remained relatively low, with the maximum value of about 4 K. The easy axis was identified to be the c-axis and the saturation moment was 2.8 μB (Bohr magneton) at 1.8 K. The in-plane resistivity of all the samples studied showed metallic behavior with p-type carriers. Shubnikov-de Hass oscillations were observed in samples with the Cr-doping level of up to 0.76%. We also tried to induce ferromagnetism in TlBiTe2 by doping Cr, but no ferromagnetism was observed in Cr-doped TlBiTe2 crystals within the solubility limit of Cr which turned out to be also about 1%
Effect of partially purified fumonisins on cellular immune response in experimental murine paracoccidioidomycosis
Fumonisins are mycotoxins produced mainly by Fusarium verticillioides, which can modulate the immune response. Paracoccidioidomycosis (PCM), caused by the fungus Paracoccodioides brasiliensis (Pb), is one of the most important systemic mycoses in Latin America. The aim of this study was to evaluate the effect of the partially purified fumonisins on cellular immune response in mice infected with Pb. Four groups of male BALB/c mice were used. Groups PB and PB/FB were inoculated i.v. with 1 × 105 Pb yeast cells and, after 28 days, groups FB and PB/FB were inoculated (s.c.) with partially purified fumonisin B1 from F. verticillioides (5 × 2.25 mg FB1/kg body weight). After 7 days, cellular immune response was evaluated by delayed-type hypersensitivity (DTH) and lymphoproliferative assays (LA) using spleen cells. Nitric oxide (NO) production by spleen cells was also evaluated. The specific LA response to Pb antigen was higher in group PB than in FB and CTR groups (p< 0.05) but not significant with PB/FB. The DTH response was higher in infected than non infected groups (p<0.05) but also no significantly with PB and PB/FB groups. The lyphoproliferative response to ConA was decreased in FB or PB/FB in relation to CTR (p<0.05) but not with PB/FB and also a reduction of NO levels was observed in fumonisin treated in relation to control group FB1/kg (p<0.05). In conclusion, fumonisin B1 or other components of F. verticillioides extracts significantly suppress the unspecific cellular immune response and the NO production by splenocytes from P. brasiliensis infected or not infected BALB/c mice.Keywords: Fumonisin, Paracoccodioides brasiliensis, lymphoproliferative assay, nitric oxideAfrican Journal of Biotechnology Vol. 12(42), pp. 6126-613
Correlation Functions in 2-Dimensional Integrable Quantum Field Theories
In this talk I discuss the form factor approach used to compute correlation
functions of integrable models in two dimensions. The Sinh-Gordon model is our
basic example. Using Watson's and the recursive equations satisfied by matrix
elements of local operators, I present the computation of the form factors of
the elementary field and the stress-energy tensor of
the theory.Comment: 19pp, LATEX version, (talk at Como Conference on ``Integrable Quantum
Field Theories''
The Effective Field Theory of Multifield Inflation
We generalize the Effective Field Theory of Inflation to include additional
light scalar degrees of freedom that are in their vacuum at the time the modes
of interest are crossing the horizon. In order to make the scalars light in a
natural way we consider the case where they are the Goldstone bosons of a
global symmetry group or are partially protected by an approximate
supersymmetry. We write the most general Lagrangian that couples the scalar
mode associated to the breaking of time translation during inflation to the
additional light scalar fields. This Lagrangian is constrained by
diffeomorphism invariance and the additional symmetries that keep the new
scalars light. This Lagrangian describes the fluctuations around the time of
horizon crossing and it is supplemented with a general parameterization
describing how the additional fluctuating fields can affect cosmological
perturbations. We find that multifield inflation can reproduce the
non-Gaussianities that can be generated in single field inflation but can also
give rise to new kinds of non-Gaussianities. We find several new three-point
function shapes. We show that in multifield inflation it is possible to
naturally suppress the three-point function making the four-point function the
leading source of detectable non-Gaussianities. We find that under certain
circumstances, i.e. if specific shapes of non-Gaussianities are detected in the
data, one could distinguish between single and multifield inflation and
sometimes even among the various mechanisms that kept the additional fields
light.Comment: 62 pages, 1 figure; v2: JHEP published version, minor corrections,
comments and references adde
Effective theories of single field inflation when heavy fields matter
We compute the low energy effective field theory (EFT) expansion for
single-field inflationary models that descend from a parent theory containing
multiple other scalar fields. By assuming that all other degrees of freedom in
the parent theory are sufficiently massive relative to the inflaton, it is
possible to derive an EFT valid to arbitrary order in perturbations, provided
certain generalized adiabaticity conditions are respected. These conditions
permit a consistent low energy EFT description even when the inflaton deviates
off its adiabatic minimum along its slowly rolling trajectory. By generalizing
the formalism that identifies the adiabatic mode with the Goldstone boson of
this spontaneously broken time translational symmetry prior to the integration
of the heavy fields, we show that this invariance of the parent theory dictates
the entire non-perturbative structure of the descendent EFT. The couplings of
this theory can be written entirely in terms of the reduced speed of sound of
adiabatic perturbations. The resulting operator expansion is distinguishable
from that of other scenarios, such as standard single inflation or DBI
inflation. In particular, we re-derive how certain operators can become
transiently strongly coupled along the inflaton trajectory, consistent with
slow-roll and the validity of the EFT expansion, imprinting features in the
primordial power spectrum, and we deduce the relevant cubic operators that
imply distinct signatures in the primordial bispectrum which may soon be
constrained by observations.Comment: (v1) 25 pages, 1 figure; (v2) references added and typos corrected,
to appear in Journal of High Energy Physic
On Non-linear Action for Gauged M2-brane
We propose a non-linear extension of U(1) \times U(1) (abelian) ABJM model
including T_{M2} (higher derivative) corrections. The action proposed here is
expected to describe a single M2-brane proving C^4/Z_k target space. The model
includes couplings with the 3-form background in the eleven-dimensional
supergravity which is consistent with the orbifold projection. We show that the
novel higgs mechanism proposed by Mukhi and Papageorgakis does work even in the
presence of higher derivative corrections and couplings with the background
field, giving the correct structure of the Dirac-Born-Infeld action with
Wess-Zumino term for a D2-brane. We also find half BPS solutions in the full
non-linear theory which is interpreted as an another M2-brane intersecting with
the original M2-brane. A possible generalization to U(N) \times U(N) gauge
group is briefly discussed.Comment: 19 pages, no figure, references added, typos correcte
Quantum phase transition in a single-molecule quantum dot
Quantum criticality is the intriguing possibility offered by the laws of
quantum mechanics when the wave function of a many-particle physical system is
forced to evolve continuously between two distinct, competing ground states.
This phenomenon, often related to a zero-temperature magnetic phase transition,
can be observed in several strongly correlated materials such as heavy fermion
compounds or possibly high-temperature superconductors, and is believed to
govern many of their fascinating, yet still unexplained properties. In contrast
to these bulk materials with very complex electronic structure, artificial
nanoscale devices could offer a new and simpler vista to the comprehension of
quantum phase transitions. This long-sought possibility is demonstrated by our
work in a fullerene molecular junction, where gate voltage induces a crossing
of singlet and triplet spin states at zero magnetic field. Electronic tunneling
from metallic contacts into the quantum dot provides here the
necessary many-body correlations to observe a true quantum critical behavior.Comment: 8 pages, 5 figure
5-Hydroxymethylfurfural (HMF) formation during subcritical water extraction
The aim of this study was to investigate the
effect of material type (artichoke leave, lemon peel, flaxseed meal), extraction temperature (50, 100, 120, 140, 160,
180, 200 C) and static extraction time (5, 15, 30, 45 min)
on 5-hydroxymethylfurfural (5-HMF) formation during
subcritical water extraction. 5-HMF content of artichoke
leave and lemon peel extracts increased 7.2 and 26.1 times
with the rise of extraction temperature from 160 to 180 C
for 5 min during subcritical water extraction, respectively.
Besides, 5-HMF content of artichoke leave, lemon peel and
flaxseed meal extracts increased 1.4, 2.0 and 4.5 times as
static extraction time increased from 15 to 45 min at
180 C during subcritical water extraction, respectively.
The highest 5-HMF content of artichoke leave and lemon
peel extracts were obtained as 58.83 and 231.21 mg/L at
180 C and 45 min, respectively. However, for flaxseed
meal, the highest 5-HMF content (222.94 mg/L) was
obtained at 200 C and 15 min during subcritical water
extraction.Project Nos. 2014.M80.02.03, 2014.M80.02.04 by Artvin Coruh University Scientific Research Project Uni
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