6,783 research outputs found
Peripheral and central mechanisms involved in hormonal control of male and female reproduction
Reproduction involves the integration of hormonal signals acting across multiple systems togenerate a synchronized physiological output. A critical component of reproduction is the luteinizinghormone (LH) surge, which is mediated by estradiol (E2) and neuroprogesterone interacting tostimulate kisspeptin release in the rostral periventricular nucleus of the third ventricle in rats. Recentevidence has shown that both classical and membrane E2 and progesterone signaling is involved inthis pathway. A metabolite of gonadotropin-releasing hormone (GnRH), GnRH-(1-5), has been shownto stimulate GnRH expression, secretion, and has a role in the regulation of lordosis. Additionally,gonadotropin-inhibitory hormone (GnIH) projects to and influences the activity of GnRH neurons inbirds. Stress-induced changes in GnIH have been shown to alter breeding behaviors in birds,demonstrating another molecular control of reproduction. Peripherally, paracrine and autocrineactions within the gonad have been suggested as therapeutic targets for infertility in both males andfemales. Dysfunction of testicular prostaglandin synthesis is a possible cause of idiopathic maleinfertility. Indeed, local production of melatonin and corticotropin-releasing hormone (CRH) couldinfluence spermatogenesis via immune pathways in the gonad. In females, vascular endothelialgrowth factor A (VEGF-A) has been implicated in an angiogenic process that mediates developmentof the corpus luteum and thus fertility via the Notch signaling pathway. Age-induced decreases infertility involve ovarian kisspeptin and its regulation of ovarian sympathetic innervation. Finally,morphological changes in the arcuate nucleus of the hypothalamus influence female sexualreceptivity in rats. The processes mediating these morphological changes have been shown toinvolve rapid effects of E2 controlling synaptogenesis in this hypothalamic nucleus. Together, thisreview highlights new research in these areas, focusing on recent findings in the molecularmechanisms of central and peripheral hormonal control of reproduction.Fil: Rudolph, L. M.. University of California at Los Angeles; Estados UnidosFil: Bentley, G. E.. University of California Berkeley; Estados UnidosFil: Calandra, Ricardo Saul. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de BiologĂa y Medicina Experimental. FundaciĂłn de Instituto de BiologĂa y Medicina Experimental. Instituto de BiologĂa y Medicina Experimental; ArgentinaFil: Paredes, A. H.. Universidad de Chile; ChileFil: Tesone, Marta. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de BiologĂa y Medicina Experimental. FundaciĂłn de Instituto de BiologĂa y Medicina Experimental. Instituto de BiologĂa y Medicina Experimental; ArgentinaFil: Wu, T. J.. Uniformed Services University; Estados UnidosFil: Micevych, P. E.. University of California at Los Angeles; Estados Unido
On the Importance to Economic Success of Property Rights in Finance and Innovation
This Essay surveys recent developments across the fields of finance and innovation to highlight some common themes concerning the importance of property rights to economic success. Society regularly makes choices when shaping the precise contours of the legal institutions that govern the behavior of market actors, often in response to high profile issues like the collapse of Enron and the patenting of life-saving AIDS drugs. Recognizing that no set of legal institutions or related enforcement mechanisms will be perfect, this Essay explores some particularly helpful institutional features based on property rights that too often are overlooked by policy makers and commentators, even though these property-based institutional features have long been associated with economic success in a number of diverse settings
Skyrmions in quantum Hall ferromagnets as spin-waves bound to unbalanced magnetic flux quanta
A microscopic description of (baby)skyrmions in quantum Hall ferromagnets is
derived from a scattering theory of collective (neutral) spin modes by a bare
quasiparticle. We start by mapping the low lying spectrum of spin waves in the
uniform ferromagnet onto that of free moving spin excitons, and then we study
their scattering by the defect of charge. In the presence of this disturbance,
the local spin stiffness varies in space, and we translate it into an
inhomogeneus metric in the Hilbert space supporting the excitons. An attractive
potencial is then required to preserve the symmetry under global spin
rotations, and it traps the excitons around the charged defect. The
quasiparticle now carries a spin texture. Textures containing more than one
exciton are described within a mean-field theory, the interaction among the
excitons being taken into account through a new renormalization of the metric.
The number of excitons actually bound depends on the Zeeman coupling, that
plays the same role as a chemical potencial. For small Zeeman energies, the
defect binds many excitons which condensate. As the bound excitons have a unit
of angular momentum, provided by the quantum of magnetic flux left unbalanced
by the defect of charge, the resulting texture turns out to be a topological
excitation of charge 1. Its energy is that given by the non-linear sigma model
for the ground state in this topological sector, i.e. the texture is a
skyrmion.Comment: 17 pages, 1 figur
Zero-Shot Hashing via Transferring Supervised Knowledge
Hashing has shown its efficiency and effectiveness in facilitating
large-scale multimedia applications. Supervised knowledge e.g. semantic labels
or pair-wise relationship) associated to data is capable of significantly
improving the quality of hash codes and hash functions. However, confronted
with the rapid growth of newly-emerging concepts and multimedia data on the
Web, existing supervised hashing approaches may easily suffer from the scarcity
and validity of supervised information due to the expensive cost of manual
labelling. In this paper, we propose a novel hashing scheme, termed
\emph{zero-shot hashing} (ZSH), which compresses images of "unseen" categories
to binary codes with hash functions learned from limited training data of
"seen" categories. Specifically, we project independent data labels i.e.
0/1-form label vectors) into semantic embedding space, where semantic
relationships among all the labels can be precisely characterized and thus seen
supervised knowledge can be transferred to unseen classes. Moreover, in order
to cope with the semantic shift problem, we rotate the embedded space to more
suitably align the embedded semantics with the low-level visual feature space,
thereby alleviating the influence of semantic gap. In the meantime, to exert
positive effects on learning high-quality hash functions, we further propose to
preserve local structural property and discrete nature in binary codes.
Besides, we develop an efficient alternating algorithm to solve the ZSH model.
Extensive experiments conducted on various real-life datasets show the superior
zero-shot image retrieval performance of ZSH as compared to several
state-of-the-art hashing methods.Comment: 11 page
New universality class for the three-dimensional XY model with correlated impurities: Application to He in aerogels
Encouraged by experiments on He in aerogels, we confine planar spins in
the pores of simulated aerogels (diffusion limited cluster-cluster aggregation)
in order to study the effect of quenched disorder on the critical behavior of
the three-dimensional XY model. Monte Carlo simulations and finite-size scaling
are used to determine critical couplings and exponents. In agreement with
experiments, clear evidence of change in the thermal critical exponents
and is found at nonzero volume fractions of impurities. These changes
are explained in terms of {\it hidden} long-range correlations within disorder
distributions.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Statistical analysis of Ni nanowires breaking processes: a numerical simulation study
A statistical analysis of the breaking behavior of Ni nanowires is presented.
Using molecular dynamic simulations, we have determined the time evolution of
both the nanowire atomic structure and its minimum cross section (Sm(t)).
Accumulating thousands of independent breaking events, Sm histograms are built
and used to study the influence of the temperature, the crystalline stretching
direction and the initial nanowire size. The proportion of monomers, dimers and
more complex structures at the latest stages of the breaking process are
calculated, finding important differences among results obtained for different
nanowire orientations and sizes. Three main cases have been observed. (A) [111]
stretching direction and large nanowire sizes: the wire evolves from more
complex structures to monomers and dimers prior its rupture; well ordered
structures is presented during the breaking process. (B) Large nanowires
stretched along the [100] and [110] directions: the system mainly breaks from
complex structures (low probability of finding monomers and dimers), having
disordered regions during their breakage; at room temperature, a huge histogram
peak around Sm=5 appears, showing the presence of long staggered pentagonal Ni
wires with ...-5-1-5-... structure. (C) Initial wire size is small: strong size
effects independently on the temperature and stretching direction. Finally, the
local structure around monomers and dimmers do not depend on the stretching
direction. These configurations differ from those usually chosen in static
studies of conductance.Comment: 18 pages, 13 figure
Approximate evolution for a system composed by two coupled Jaynes-Cummings Hamiltonians
In this work we construct an approximate time evolution operator for a system
composed by two coupled Jaynes-Cummings Hamiltonians. We express the full time
evolution operator as a product of exponentials and we analyze the validity of
our approximations contrasting our analytical results with those obtained by
purely numerical methods.Comment: 15 pages, 3 figures, 1 tabl
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