3,248 research outputs found
Real-space anisotropy of the superconducting gap in the charge-density wave material 2H-NbSe2
We present a scanning tunneling microscopy (STM) and ab-initio study of the anisotropic superconductivity of 2H-NbSe2 in the charge-density-wave (CDW) phase. Differential-conductance spectra show a clear double-peak structure, which is well reproduced by density functional theory simulations enabling full k- and real-space resolution of the superconducting gap. The hollow-centered (HC) and chalcogen-centered (CC) CDW patterns observed in the experiment are mapped onto separate van der Waals layers with different electronic properties. We identify the CC layer as the high-gap region responsible for the main STM peak. Remarkably, this region belongs to the same Fermi surface sheet that is broken by the CDW gap opening. Simulations reveal a highly anisotropic distribution of the superconducting gap within single Fermi sheets, setting aside the proposed scenario of a two-gap superconductivity. Our results point to a spatially localized competition between superconductivity and CDW involving the HC regions of the crystal
Situational Awareness: Detecting Critical Dependencies and Devices in a Network
Large-scale networks consisting of thousands of connected devices are like a living organism, constantly changing and evolving. It is very difficult for a human administrator to orient in such environment and to react to emerging security threats. With such motivation, this PhD proposal aims to find new methods for automatic identification of devices, the services they provide, their dependencies and importance. The main focus of the proposal is to find novel approaches to building cyber situational awareness in an unknown network for the purpose of computer security incident response. Our research is at the initial phase and will contribute to a PhD thesis in four years
Difficult Scenarios for NMSSM Higgs Discovery at the LHC
We identify scenarios not ruled out by LEP data in which NMSSM Higgs
detection at the LHC will be particularly challenging. We first review the
`no-lose' theorem for Higgs discovery at the LHC that applies if Higgs bosons
do not decay to other Higgs bosons - namely, with L=300 fb^-1, there is always
one or more `standard' Higgs detection channel with at least a 5 sigma signal.
However, we provide examples of no-Higgs-to-Higgs cases for which all the
standard signals are no larger than 7 sigma implying that if the available L is
smaller or the simulations performed by ATLAS and CMS turn out to be overly
optimistic, all standard Higgs signals could fall below 5 sigma even in the
no-Higgs-to-Higgs part of NMSSM parameter space. In the vast bulk of NMSSM
parameter space, there will be Higgs-to-Higgs decays. We show that when such
decays are present it is possible for all the standard detection channels to
have very small significance. In most such cases, the only strongly produced
Higgs boson is one with fairly SM-like couplings that decays to two lighter
Higgs bosons (either a pair of the lightest CP-even Higgs bosons, or, in the
largest part of parameter space, a pair of the lightest CP-odd Higgs bosons). A
number of representative bench-mark scenarios of this type are delineated in
detail and implications for Higgs discovery at various colliders are discussed.Comment: 31 pages, 5 figure
About direct Dark Matter detection in Next-to-Minimal Supersymmetric Standard Model
Direct dark matter detection is considered in the Next-to-Minimal
Supersymmetric Standard Model (NMSSM). The effective neutralino-quark
Lagrangian is obtained and event rates are calculated for the Ge-73 isotope.
Accelerator and cosmological constraints on the NMSSM parameter space are
included. By means of scanning the parameter space at the Fermi scale we show
that the lightest neutralino could be detected in dark matter experiments with
sizable event rate.Comment: latex, 12 pages, 2 ps-figures; extra LEP constraint is included,
extra figure is added, recorrected version, resubmitted to Phys.Rev.
Denominators of Eisenstein cohomology classes for GL_2 over imaginary quadratic fields
We study the arithmetic of Eisenstein cohomology classes (in the sense of G.
Harder) for symmetric spaces associated to GL_2 over imaginary quadratic
fields. We prove in many cases a lower bound on their denominator in terms of a
special L-value of a Hecke character providing evidence for a conjecture of
Harder that the denominator is given by this L-value. We also prove under some
additional assumptions that the restriction of the classes to the boundary of
the Borel-Serre compactification of the spaces is integral. Such classes are
interesting for their use in congruences with cuspidal classes to prove
connections between the special L-value and the size of the Selmer group of the
Hecke character.Comment: 37 pages; strengthened integrality result (Proposition 16), corrected
statement of Theorem 3, and revised introductio
Spontaneous Violation of the CP Symmetry in the Higgs Sector of the Next-to-Minimal Supersymmetric Model
The spontaneous violation of the CP symmetry in the next-to-minimal
supersymmetric standard Model (NMSSM) is investigated. It is found that the
spontaneous violation of the CP symmetry can occur in the Higgs sector of the
NMSSM for a wide region of the parameter space of the model, at the 1-loop
level where the radiative corrections due to the top quark and scalar-top quark
loops are found to generate the scalar-pseudoscalar mixings between the two
Higgs doublets of the NMSSM. In our model, we assume that the masses of the
left-handed and the right-handed scalar-top quarks are not degenerate. And we
investigate our model anaytically: We derive analytical formulae of the 1-loop
mass matrix for the neutral Higgs bosons. We calculate the upper bound on the
lightest neutral Higgs boson mass under the assumption. It is found to be about
140 GeV for our choice of parameter values in the presence of the spontaneous
violation of the CP symmetry in the NMSSM. Thus, the possibility of the
spontaneous violation of the CP symmetry is not completely ruled out in the
Higgs sector of the NMSSM if the masses of the left-handed and the right-handed
scalar-top quarks are not degenerate. Further, the phenomenology of the
- mixing within the context of our model is studied. The lower
bound on CP violating phase in the - mixing is found to increase
if either decreases or increases.Comment: 21 pages, 5 figures, To appear in Phys. Rev.
Particle spectrum in the modified NMSSM in the strong Yukawa coupling limit
A theoretical analysis of solutions of renormalisation group equations in the
MSSM corresponding to the quasi-fixed point conditions shows that the mass of
the lightest Higgs boson in this case does not exceed . It
means that a substantial part of the parameter space of the MSSM is practically
excluded by existing experimental data from LEP II. In the NMSSM the upper
bound on the lightest Higgs boson mass reaches its maximum in the strong Yukawa
coupling regime, when Yukawa constants are considerably larger the gauge ones
on the Grand Unification scale. In this paper a particle spectrum in a simple
modification of NMSSM which leads to a self-consistent solution in the
considered region of the parameter space is studied. This model allows one to
get even for comparatively low values of . For an analysis of the Higgs boson spectrum and neutralino spectrum a
method for diagonalisation of mass matrices proposed formerly is used. The mass
of the lightest Higgs boson in this model does not exceed .Comment: 34 pages, 5 figures included, LaTeX 2
Light dark matter in the NMSSM: upper bounds on direct detection cross sections
In the Next-to-Minimal Supersymmetric Standard Model, a bino-like LSP can be
as light as a few GeV and satisfy WMAP constraints on the dark matter relic
density in the presence of a light CP-odd Higgs scalar. We study upper bounds
on the direct detection cross sections for such a light LSP in the mass range
2-20 GeV in the NMSSM, respecting all constraints from B-physics and LEP. The
OPAL constraints on e^+ e^- -> \chi^0_1 \chi^0_i (i > 1) play an important role
and are discussed in some detail. The resulting upper bounds on the
spin-independent and spin-dependent nucleon cross sections are ~ 10^{-42}
cm^{-2} and ~ 4\times 10^{-40} cm^{-2}, respectively. Hence the upper bound on
the spin-independent cross section is below the DAMA and CoGeNT regions, but
could be compatible with the two events observed by CDMS-II.Comment: 17 pages, 3 figure
Anisotropic expansion of hepatocyte lumina enforced by apical bulkheads
Lumen morphogenesis results from the interplay between molecular pathways and mechanical forces. In several organs, epithelial cells share their apical surfaces to form a tubular lumen. In the liver, however, hepatocytes share the apical surface only between adjacent cells and form narrow lumina that grow anisotropically, generating a 3D network of bile canaliculi (BC). Here, by studying lumenogenesis in differentiating mouse hepatoblasts in vitro, we discovered that adjacent hepatocytes assemble a pattern of specific extensions of the apical membrane traversing the lumen and ensuring its anisotropic expansion. These previously unrecognized structures form a pattern, reminiscent of the bulkheads of boats, also present in the developing and adult liver. Silencing of Rab35 resulted in loss of apical bulkheads and lumen anisotropy, leading to cyst formation. Strikingly, we could reengineer hepatocyte polarity in embryonic liver tissue, converting BC into epithelial tubes. Our results suggest that apical bulkheads are cell-intrinsic anisotropic mechanical elements that determine the elongation of BC during liver tissue morphogenesis
The P2 Receptor Antagonist PPADS Supports Recovery from Experimental Stroke In Vivo
BACKGROUND: After ischemia of the CNS, extracellular adenosine 5'-triphosphate (ATP) can reach high concentrations due to cell damage and subsequent increase of membrane permeability. ATP may cause cellular degeneration and death, mediated by P2X and P2Y receptors. METHODOLOGY/PRINCIPAL FINDINGS: The effects of inhibition of P2 receptors by pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) on electrophysiological, functional and morphological alterations in an ischemia model with permanent middle cerebral artery occlusion (MCAO) were investigated up to day 28. Spontaneously hypertensive rats received PPADS or vehicle intracerebroventricularly 15 minutes prior MCAO for up to 7 days. The functional recovery monitored by qEEG was improved by PPADS indicated by an accelerated recovery of ischemia-induced qEEG changes in the delta and alpha frequency bands along with a faster and sustained recovery of motor impairments. Whereas the functional improvements by PPADS were persistent at day 28, the infarct volume measured by magnetic resonance imaging and the amount of TUNEL-positive cells were significantly reduced by PPADS only until day 7. Further, by immunohistochemistry and confocal laser scanning microscopy, we identified both neurons and astrocytes as TUNEL-positive after MCAO. CONCLUSION: The persistent beneficial effect of PPADS on the functional parameters without differences in the late (day 28) infarct size and apoptosis suggests that the early inhibition of P2 receptors might be favourable for the maintenance or early reconstruction of neuronal connectivity in the periinfarct area after ischemic incidents
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