911 research outputs found
Correlation functions, null polygonal Wilson loops, and local operators
We consider the ratio of the correlation function of n+1 local operators over
the correlator of the first n of these operators in planar N=4 super-Yang-Mills
theory, and consider the limit where the first n operators become pairwise null
separated. By studying the problem in twistor space, we prove that this is
equivalent to the correlator of a n-cusp null polygonal Wilson loop with the
remaining operator in general position, normalized by the expectation value of
the Wilson loop itself, as recently conjectured by Alday, Buchbinder and
Tseytlin. Twistor methods also provide a BCFW-like recursion relation for such
correlators. Finally, we study the natural extension where n operators become
pairwise null separated with k operators in general position. As an example, we
perform an analysis of the resulting correlator for k=2 and discuss some of the
difficulties associated to fixing the correlator completely in the strong
coupling regime.Comment: 34 pages, 6 figures. v2: typos corrected and references added; v3:
published versio
A study on occupational exposure of Sicilian farmers to Giardia and Cryptosporidium
Introduction. A cross-sectional study was undertaken to deter- mine the prevalence of Giardia and Cryptosporidium in calves of Palermo area (Sicily) and to evaluate the occupational risk associated with occurrence of zoonotic genotypes. Methods. A total of 217 faecal samples, from 149 calves (between 2 and 240 days of age) and 68 farmers, were collected in 19 cattle- farms of Palermo area. A questionnaire regarding demographic characteristics and personal hygienic measures was submitted to all farmers. All faecal samples were analyzed by Immunoflu- orescence assay and Polimerase Chain Reaction (PCR); geno- types were determined by DNA sequencing of Triose Phosphate Isomerase gene for Giardia and Small Subunit Ribosomal RNA gene for Cryptosporidium. Results. None farmer tested was positive for Giardia and Cryptosporidium, whereas these protozoa were respectively detected in 53 (including 5 with zoonotic G. duodenalis geno- type A) and 17 (of which 1 with zoonotic C. ubiquitum) of the examined calves. Discussion. The results indicate that the risk of transmitting both protozoa to farmers in Palermo area is negligible although it can- not be considered null because of identification of human geno- types/species in calves
Modelling the electronic structure and magnetic properties of LiFeAs and FeSe using hybrid-exchange density functional theory
The electronic structure and magnetic properties of LiFeAs and FeSe have been
studied using hybrid exchange density functional theory. The total energies for
a unit cell in LiFeAs and FeSe with different spin states including
non-magnetic and spin-2 are calculated. The spin-2 configuration has the lower
energy for both LiFeAs and FeSe. The computed anti-ferromagnetic exchange
interactions between spins on the nearest (next nearest) neighbouring Fe atoms
in LiFeAs and FeSe are approximately 14 (17) meV and 6 (13) meV respectively.
The total energies of the checkerboard and stripe-type anti-ferromagnetic
ordering for LiFeAs and FeSe are compared, yielding that for LiFeAs the
checkerboard is lower whereas for FeSe the stripe-type is lower. However, owing
to the fact that the exchange interaction of the next nearest neighbour is
larger than that of the nearest one, which means that the collinear ordering
might be the ground state. These results are in agreement with previous
theoretical calculations and experiments. Especially the calculations for
LiFeAs indicate a co-existence of conducting d-bands at the Fermi surface and
d-orbital magnetism far below the Fermi surface. The theoretical results
presented here might be useful for the experimentalists working on the
electronic structure and magnetism of iron-based superconductors.Comment: 7 pages, 4 figures, 1 table, accepted by Solid State Communication
Social stress increases the susceptibility to infection in the ant Harpegnathos saltator
Aggressive interactions between members of a social group represent an important source of social stress with all its negative follow-ups. We used the ponerine ant Harpegnathos saltator to study the effects of frequent aggressive interactions on the resistance to different stressors. In these ants, removal or death of reproducing animals results in a period of social instability within the colony that is characterized by frequent ritualized aggressive interactions leading to the establishment of a new dominance structure. Animals are more susceptible to infections during this period, whereas their resistance against other stressors remained unchanged. This is associated with a shift from glutathione-S-transferase activities towards glutathione peroxidase activities, which increases the antioxidative capacity at the expense of their immune competence
ERK2 phosphorylation of serine 77 regulates Bmf pro-apoptotic activity
B-cell lymphoma 2 (Bcl-2) homology 3 (BH3)-only proteins represent a class of pro-apoptotic factors that neutralize pro-survival Bcl-2 proteins, and, in some cases, directly activate Bax. The mechanisms of control and the role of BH3-only proteins, such as Bcl-2 like protein 11 extra large and Bad are well studied. By contrast, relatively little is known about the regulation and role of Bcl-2 modifying factor (Bmf). The B-RAF oncogene is mutated in âŒ8% of human tumors. We have previously shown that Bmf is upregulated at the transcript level and is required for apoptosis induced by targeting B-RAF signaling in tumor cells harboring mutant B-RAF. In this study, we show that Bmf is regulated at the post-translational level by mutant B-RAF-MEK-ERK2 signaling. Extracellular signal-regulated kinase (ERK2) directly phosphorylates Bmf on serine 74 and serine 77 residues with serine 77 being the predominant site. In addition, serine 77 phosphorylation reduces Bmf pro-apoptotic activity likely through a mechanism independent of altering Bmf localization to the mitochondria and/or interactions with dynein light chain 2 and the pro-survival proteins, B-cell lymphoma extra large, Bcl-2 and Mcl-1. These data identify a novel mode of regulation in Bmf that modulates its pro-apoptotic activity in mutant B-RAF tumor cells
Conformal higher spin scattering amplitudes from twistor space
We use the formulation of conformal higher spin (CHS) theories in twistor
space to study their tree-level scattering amplitudes, finding expressions for
all three-point anti-MHV amplitudes and all MHV amplitudes involving positive
helicity conformal gravity particles and two negative helicity higher spins.
This provides the on-shell analogue for the covariant coupling of CHS fields to
a conformal gravity background. We discuss the restriction of the theory to a
ghost-free unitary subsector, analogous to restricting conformal gravity to
general relativity with a cosmological constant. We study the flat-space limit
and show that the restricted amplitudes vanish, supporting the conjecture that
in the unitary sector the S-matrix of CHS theories is trivial. However, by
appropriately rescaling the amplitudes we find non-vanishing results which we
compare with chiral flat-space higher spin theories.Comment: 31 pages, no figures. v2: comments added, published versio
Short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms (SUNA) secondary to epidermoid cyst in the right cerebellopontine angle successfully treated with surgery
Short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) syndrome is a rare headache syndrome classified among the trigeminal autonomic cephalalgias. It is usually idiopathic, although infrequent secondary forms have been described. Recently, the term short-lasting unilateral headache with cranial autonomic symptoms (SUNA) has been defined by the International Headache Society (ICHD-2) as similar to SUNCT with less prominent absent conjunctival injection and lacrimation. We report a patient with paroxysmal orbito-temporal pains, phenotypically suggesting SUNA, secondary to epidermoid cyst in the cerebellopontine angle which disappeared after tumor resection. Neuroimaging should be considered in all patients with SUNA, notably in those with atypical presentation as our patient who presented on examination trigeminal hypoesthesia and tinnitus. Realization of a brain MRI would rule out injuries that causes this type of syndrome
Initial demonstration of AlGaAs-GaAsP-beta-Ga2O3 n-p-n double heterojunctions
Beta phase gallium oxides, an ultrawide-bandgap semiconductor, has great
potential for future power and RF electronics applications but faces challenges
in bipolar device applications due to the lack of p-type dopants. In this work,
we demonstrate monocrystalline AlGaAs_GaAsP_beta phase gallium oxides n-p-n
double-heterojunctions, synthesized using semiconductor grafting technology. By
transfer printing an n-AlGaAs_p-GaAsP nanomembrane to the n-beta
phase-GaO epitaxial substrate, we simultaneously achieved AlGaAs_GaAsP
epitaxial n-p junction diode with an ideality factor of 1.29 and a
rectification ratio of 2.57E3 at +/- 2 V, and grafted GaAsP_beta_phase_gallium
oxides p-n junction diode exhibiting an ideality factor of 1.36 and a
rectification ratio of 4.85E2 at +/- 2 V.Comment: 12 pages, 4 figure
Demonstration of a monocrystalline GaAs--GaO p-n heterojunction
In this work, we report the fabrication and characterizations of a
monocrystalline GaAs/-GaO p-n heterojunction by employing
semiconductor grafting technology. The heterojunction was created by lifting
off and transfer printing a p-type GaAs single crystal nanomembrane to an
AlO-coated n-type-GaO epitaxial substrate. The resultant
heterojunction diodes exhibit remarkable performance metrics, including an
ideality factor of 1.23, a high rectification ratio of 8.04E9 at +/- 4V, and a
turn on voltage of 2.35 V. Furthermore, at +5 V, the diode displays a large
current density of 2500 A/cm along with a low ON resistance of 2
mcm.Comment: 14 pages, 5 figure
Maximal Spontaneous Photon Emission and Energy Loss from Free Electrons
Free electron radiation such as Cerenkov, Smith--Purcell, and transition
radiation can be greatly affected by structured optical environments, as has
been demonstrated in a variety of polaritonic, photonic-crystal, and
metamaterial systems. However, the amount of radiation that can ultimately be
extracted from free electrons near an arbitrary material structure has remained
elusive. Here we derive a fundamental upper limit to the spontaneous photon
emission and energy loss of free electrons, regardless of geometry, which
illuminates the effects of material properties and electron velocities. We
obtain experimental evidence for our theory with quantitative measurements of
Smith--Purcell radiation. Our framework allows us to make two predictions. One
is a new regime of radiation operation---at subwavelength separations, slower
(nonrelativistic) electrons can achieve stronger radiation than fast
(relativistic) electrons. The second is a divergence of the emission
probability in the limit of lossless materials. We further reveal that such
divergences can be approached by coupling free electrons to photonic bound
states in the continuum (BICs). Our findings suggest that compact and efficient
free-electron radiation sources from microwaves to the soft X-ray regime may be
achievable without requiring ultrahigh accelerating voltages.Comment: 7 pages, 4 figure
- âŠ