504 research outputs found
Finite Theories and Marginal Operators on the Brane
We show how to use D and NS fivebranes in Type IIB superstring theory to
construct large classes of finite N=1 supersymmetric four dimensional field
theories. In this construction, the beta functions of the theories are directly
related to the bending of branes; in finite theories the branes are not bent,
and vice versa. Many of these theories have multiple dimensionless couplings. A
group of duality transformations acts on the space of dimensionless couplings;
for a large subclass of models, this group always includes an overall
SL(2,\ZZ) invariance. In addition, we find even larger classes of theories
which, although not finite, also have one or more marginal operators.Comment: 32 pages, 13 figures, uses revte
The microscopic effect of intramolecular vibrational energy redistribution
We investigate the effect of inter-mode coupling on the vibrational relaxation
dynamics of molecules in weak dissipative environments. The simulations are
performed within the reduced density matrix formalism in the Markovian regime,
assuming a Lindblad form for the system-bath interaction. The prototypical
two-dimensional model system representing two CO molecules approaching a
Cu(100) surface is adapted from an ab initio potential, while the diatom-
diatom vibrational coupling strength is systematically varied. In the weak
system-bath coupling limit and at low temperatures, only first order non-
adiabatic uni-modal coupling terms contribute to surface-mediated vibrational
relaxation. Since dissipative dynamics is non-unitary, the choice of
representation will affect the evolution of the reduced density matrix. Two
alternative representations for computing the relaxation rates and the
associated operators are thus compared: the fully coupled spectral basis, and
a factorizable ansatz. The former is well-established and serves as a
benchmark for the solution of Liouville-von Neumann equation. In the latter, a
contracted grid basis of potential-optimized discrete variable representation
is tailored to incorporate most of the inter-mode coupling, while the Lindblad
operators are represented as tensor products of one-dimensional operators, for
consistency. This procedure results in a marked reduction of the grid size and
in a much more advantageous scaling of the computational cost with respect to
the increase of the dimensionality of the system. The factorizable method is
found to provide an accurate description of the dissipative quantum dynamics
of the model system, specifically of the time evolution of the state
populations and of the probability density distribution of the molecular wave
packet. The influence of intra-molecular vibrational energy redistribution
appears to be properly taken into account by the new model on the whole range
of coupling strengths. It demontrates that most of the mode mixing during
relaxation is due to the potential part of the Hamiltonian and not to the
coupling among relaxation operator
ANALYTIC DETERMINATION OF THE REFERENCE TRIHEDRON POSITION RELATED TO THE PRINCIPAL PROJECTION PLANE AND OF THE PROJECTION DIRECTION OF AN OBLIQUE AXONOMETRIC PROJECTION FROM GIVEN AXIS AND VARIATION COEFFICIENTS
Surface mechanomyography and electromyography provide non-invasive indices of inspiratory muscle force and activation in healthy subjects
The current gold standard assessment of human inspiratory muscle function involves using invasive measures of transdiaphragmatic pressure (Pdi) or crural diaphragm electromyography (oesEMGdi). Mechanomyography is a non-invasive measure of muscle vibration associated with muscle contraction. Surface electromyogram and mechanomyogram, recorded transcutaneously using sensors placed over the lower intercostal spaces (sEMGlic and sMMGlic respectively), have been proposed to provide non-invasive indices of inspiratory muscle activation, but have not been directly compared to gold standard Pdi and oesEMGdi measures during voluntary respiratory manoeuvres. To validate the non-invasive techniques, the relationships between Pdi and sMMGlic, and between oesEMGdi and sEMGlic were measured simultaneously in 12 healthy subjects during an incremental inspiratory threshold loading protocol. Myographic signals were analysed using fixed sample entropy (fSampEn), which is less influenced by cardiac artefacts than conventional root mean square. Strong correlations were observed between: mean Pdi and mean fSampEn |sMMGlic| (left, 0.76; right, 0.81), the time-integrals of the Pdi and fSampEn |sMMGlic| (left, 0.78; right, 0.83), and mean fSampEn oesEMGdi and mean fSampEn sEMGlic (left, 0.84; right, 0.83). These findings suggest that sMMGlic and sEMGlic could provide useful non-invasive alternatives to Pdi and oesEMGdi for the assessment of inspiratory muscle function in health and disease.Peer ReviewedPostprint (published version
M5-brane geometries, T-duality and fluxes
We describe a duality relation between configurations of M5-branes in
M-theory and type IIB theory on Taub-NUT geometries with NSNS and RR 3-form
field strength fluxes. The flux parameters are controlled by the angles between
the M5-brane and the (T)duality directions. For one M5-brane, the duality leads
to a family of supersymmetric flux configurations which interpolates between
imaginary self-dual fluxes and fluxes similar to the Polchinski-Strassler kind.
For multiple M5-branes, the IIB configurations are related to fluxes for
twisted sector fields in orbifolds. The dual M5-brane picture also provides a
geometric interpretation for several properties of flux configurations (like
the supersymmetry conditions, their contribution to tadpoles, etc), and for
many non-trivial effects in the IIB side. Among the latter, the dielectric
effect for probe D3-branes is dual to the recombination of probe M5-branes with
background ones; also, a picture of a decay channel for non-supersymmetric
fluxes is suggested.Comment: 30 pages, 3 figure
Quantum-ionic features in the absorption spectra of homonuclear diatomic molecules
Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).We show that additional features can emerge in the linear absorption spectra of homonuclear diatomic molecules when the ions are described quantum mechanically. In particular, the widths and energies of the peaks in the optical spectra change with the initial configuration, mass, and charge of the molecule. We introduce a model that can describe these features and we provide a quantitative analysis of the resulting peak energy shifts and width broadenings as a function of the mass.We acknowledge financial support from the European Research Council Advanced Grant DYNamo (Grant No. ERC-2010-AdG-267374), Spanish Grants No. FIS2013-46159-C3-1-P and No. PIB2010US-00652, and Grupo Consolidado UPV/EHU del Gobierno Vasco (Grant No. IT578-13). A.C.-U. acknowledges financial
support from the Departamento de Educacion, Universidades e Investigacion del Gobierno Vasco (Reference No. BFI-2011-26).Peer Reviewe
Orientifolding the conifold
In this paper we study the N=1 supersymmetric field theories realized on the
world-volume of type IIB D3-branes sitting at orientifolds of non-orbifold
singularities (conifold and generalizations). Several chiral models belong to
this family of theories. These field theories have a T-dual realization in
terms of type IIA configurations of relatively rotated NS fivebranes, D4-branes
and orientifold six-planes, with a compact direction, along which the
D4-branes have finite extent. We compute the spectrum on the D3-branes directly
in the type IIB picture and match the resulting field theories with those
obtained in the type IIA setup, thus providing a non-trivial check of this
T-duality. Since the usual techniques to compute the spectrum of the model and
check the cancellation of tadpoles, cannot be applied to the case orientifolds
of non-orbifold singularities, we use a different approach, and construct the
models by partially blowing-up orientifolds of C^3/(Z_2 x Z_2) and C^3/(Z_2 x
Z_3) orbifolds.Comment: 52 pages, Latex 7 eps figure
N=1 Type IIA brane configurations, Chirality and T-duality
We consider four-dimensional N=1 field theories realized by type IIA brane
configurations of NS-branes and D4-branes, in the presence of orientifold
six-planes and D6-branes. These configurations are known to present interesting
effects associated to the appearance of chiral symmetries and chiral matter in
the four-dimensional field theory. We center on models with one compact
direction (elliptic models) and show that, under T-duality, the configurations
are mapped to a set of type IIB D3-branes probing N=1 orientifolds of C^2/Z_N
singularities. We explicitly construct these orientifolds, and show the field
theories on the D3-brane probes indeed reproduces the field theories
constructed using the IIA brane configurations. This T-duality map allows to
understand the type IIB realization of several exotic brane dynamics effects on
the type IIA side: Flavour doubling, the splitting of D6-branes and O6-planes
in crossing a NS-brane and the effect of a non-zero type IIA cosmological
constant turn out to have surprisingly standard type IIB counterparts.Comment: 39 pages, Latex, 7 eps figures. References adde
Mucosal delivery of tuberculosis vaccines: a review of current approaches and challenges.
Introduction: Tuberculosis (TB) remains a major health threat and it is now clear that the current vaccine, BCG, is unable to arrest the global TB epidemic. A new vaccine is needed to either replace or boost BCG so that a better level of protection could be achieved. The route of entry of Mycobacterium tuberculosis, the causative organism, is via inhalation making TB primarily a respiratory disease. There is therefore good reason to hypothesize that a mucosally delivered vaccine against TB could be more effective than one delivered via the systemic route.Areas covered: This review summarizes the progress that has been made in the area of TB mucosal vaccines in the last few years. It highlights some of the strengths and shortcomings of the published evidence and aims to discuss immunological and practical considerations in the development of mucosal vaccines.Expert opinion: There is a growing body of evidence that the mucosal approach to vaccination against TB is feasible and should be pursued. However, further key studies are necessary to both improve our understanding of the protective immune mechanisms operating in the mucosa and the technical aspects of aerosolized delivery, before such a vaccine could become a feasible, deployable strategy
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