800 research outputs found
Nuclear translocation of Cyclin B1 marks the restriction point for terminal cell cycle exit in G2 phase
Effects of training on sand or hard surfaces on sprint and jump performance of team-sport players: a systematic review with meta-analysis
We examined the effectiveness of training on sand and compared the effects of sand and hard surface training programs on the sprint and jump performance of team-sport players. PubMed MEDLINE, SPORTDiscus, and Web of Science databases were used in the literature search. A total of 377 records were initially identified and six studies comprising 136 athletes were included in the meta-analysis. Pre- and post-comparisons showed that sand training interventions were effective at improving both jump and sprint capacities. When comparing sand and hard surfaces, no significant differences in favor of any of the interventions were observed. In summary, this review revealed that sand training is an efficient strategy to improve jump and sprint performances in team-sport players. Moreover, sand surfaces produced similar gains to those observed after hard surface training schemes. Strength and conditioning coaches and sport scientists who work with team-sports can use both sand and hard surface training programs as part of their regular training practices, during distinct phases of the season
Branes on Generalized Calibrated Submanifolds
We extend previous results on generalized calibrations to describe
supersymmetric branes in supergravity backgrounds with diverse fields turned
on, and provide several new classes of examples. As an important application,
we show that supersymmetric D-branes in compactifications with field strength
fluxes, and on SU(3)-structure spaces, wrap generalized calibrated
submanifolds, defined by simple conditions in terms of the underlying globally
defined, but non-closed, 2- and 3-forms. We provide examples where the
geometric moduli of D-branes (for instance D7-branes in 3-form flux
configurations) are lifted by the generalized calibration condition. In
addition, we describe supersymmetric D6-branes on generalized calibrated
3-submanifolds of half-flat manifolds, which provide the mirror of B-type
D-branes in IIB CY compactifications with 3-form fluxes. Supersymmetric sets of
such D-branes carrying no homology charges are mirror to supersymmetric sets of
D-branes which are homologically non-trivial, but trivial in K-theory. As an
additional application, we describe models with chiral gauge sectors, realized
in terms of generalized calibrated brane box configurations of NS- and
D5-branes, which are supersymmetric but carry no charges, so that no
orientifold planes are required in the compactification.Comment: 40 pages, 3 figures, references adde
Building MSSM Flux Vacua
We construct N=1 and N=0 chiral four-dimensional vacua of flux
compactification in Type IIB string theory. These vacua have the common
features that they are free of tadpole instabilities (both NSNS and RR) even
for models with N=0 supersymmetry. In addition, the dilaton/complex structure
moduli are stabilised and the supergravity background metric is warped. We
present an example in which the low energy spectrum contains the MSSM spectrum
with three generations of chiral matter. In the N=0 models, the background
fluxes which stabilise the moduli also induce soft supersymmetry breaking terms
in the gauge and chiral sectors of the theory, while satisfying the equation of
motion. We also discuss some phenomenological features of these three
generation MSSM flux vacua. Our techniques apply to other closed string
backgrounds as well and, in fact, also allow to find new N=1 D-brane models
which were believed not to exist. Finally, we discuss in detail the consistency
conditions of these flux compactifications. Cancellation of K-theory charges
puts additional constraints on the consistency of the models, which render some
chiral D-brane models in the literature inconsistent.Comment: 33 pages, 1 figure. Minor correction
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
Fluxes, moduli fixing and MSSM-like vacua in a simple IIA orientifold
We study the effects of adding RR, NS and metric fluxes on a T^6/(\Omega
(-1)^{F_L} I_3) Type IIA orientifold. By using the effective flux-induced
superpotential we obtain Minkowski or AdS vacua with broken or unbroken
supersymmetry. In the Minkowski case some combinations of real moduli remain
undetermined, whereas all can be stabilized in the AdS solutions. Many flux
parameters are available which are unconstrained by RR tadpole cancellation
conditions allowing to locate the minima at large volume and small dilaton. We
also find that in AdS supersymmetric vacua with metric fluxes, the overall flux
contribution to RR tadpoles can vanish or have opposite sign to that of
D6-branes, allowing for new model-building possibilities. In particular, we
construct the first N=1 supersymmetric intersecting D6-brane models with
MSSM-like spectrum and with all closed string moduli stabilized. Some
axion-like fields remain undetermined but they are precisely required to give
St\"uckelberg masses to (potentially anomalous) U(1) brane fields. We show that
the cancellation of the Freed-Witten anomaly guarantees that the axions with
flux-induced masses are orthogonal to those giving masses to the U(1)'s.
Cancellation of such anomalies also guarantees that the D6-branes in our N=1
supersymmetric AdS vacua are calibrated so that they are forced to preserve one
unbroken supersymmetry.Comment: 61 pages, Latex, v2: added references, v3: minor correction
On the Taxonomy of Flux Vacua
We investigate several predictions about the properties of IIB flux vacua on
Calabi-Yau orientifolds, by constructing and characterizing a very large set of
vacua in a specific example, an orientifold of the Calabi-Yau hypersurface in
. We find support for the prediction of Ashok and Douglas
that the density of vacua on moduli space is governed by where and are curvature and K\"ahler forms on the moduli
space. The conifold point on moduli space therefore serves as an
attractor, with a significant fraction of the flux vacua contained in a small
neighborhood surrounding . We also study the functional dependence of
the number of flux vacua on the D3 charge in the fluxes, finding simple power
law growth.Comment: 22 pages, harvmac; v2 typos corrected, refs added; v3 minor error
correcte
Moduli Stabilization with Long Winding Strings
Stabilizing all of the modulus fields coming from compactifications of string
theory on internal manifolds is one of the outstanding challenges for string
cosmology. Here, in a simple example of toroidal compactification, we study the
dynamics of the moduli fields corresponding to the size and shape of the torus
along with the ambient flux and long strings winding both internal directions.
It is known that a string gas containing states with non-vanishing winding and
momentum number in one internal direction can stabilize the radius of this
internal circle to be at self-dual radius. We show that a gas of long strings
winding all internal directions can stabilize all moduli, except the dilaton
which is stabilized by hand, in this simple example.Comment: title changed, improved presentation; reference added. 18 pages, JHEP
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NUEVOS CASOS TERATOLÓGICOS EN APOIDEA (HYMENOPTERA)
This work deals with three teratological specimens of Apoidea that belong to the families Halictidae,
Anthophoridae and Apidae and the genera Lasioglossum Curtis, 1833, Nomada Scopoli, 1770 and Bombus Latreille, 1802. According to BALAZUC (1948, 1958) these cases are local and preimaginal abnormalities produced in gaster segmentation, in two of the specimens, and in the third the malformations appear in head and the mesothoracic legs. Every possible ethiology is studied too.Se estudian varias conformaciones teratológicas que afectan a tres individuos de la superfamilia Apoidea, pertenecientes a las familias Halictidae, Anthophoridae y Apidae y que corresponden a los géneros Lasioglossum Curtis, 1833, Nomada Scopoli, 1770 y Bombus Latreille, 1802. De acuerdo con BALAZUC (1948, 1958), tales alteraciones se clasifican dentro de las anomalías locales preimaginales: en dos de los ejemplares se trata de errores en la segmentación del gáster y en el tercer ejemplar las malformaciones afectan a la cabeza y patas mesotorácicas. Se indica, asimismo, la posible etiología de estas particularidades morfológicas
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