2,980 research outputs found
Uses of a small field value which falls from a metastable maximum over cosmological times
We consider a small, metastable maximum vacuum expectation value of
order of a few eV, for a pseudoscalar Goldstone-like field, which is related to
the scalar inflaton field in an idealized model of a cosmological,
spontaneously-broken chiral symmetry. The b field allows for relating
semi-quantitatively three distinct quantities in a cosmological context.
(1) A very small, residual vacuum energy density or effective cosmological
constant of ~ lambda b_0^4 ~ 2.7 x 10^{-47}GeV^4, for lambda ~ 3 x 10^{-14},
the same as an empirical inflaton self-coupling.
(2) A tiny neutrino mass, less then b_0.
(3) A possible small variation downward of the proton to electron mass ratio
over cosmological time. The latter arises from the motion downward of the
field over cosmological time, toward a nonzero limiting value as . Such behavior is consistent with an equation of motion.
We argue that hypothetical b quanta, potentially inducing new long-range
forces, are absent, because of negative, effective squared mass in an equation
of motion for -field fluctuations.Comment: version accepted for publication in Mod.Phys.Lett.
Content addressable memory project
A parameterized version of the tree processor was designed and tested (by simulation). The leaf processor design is 90 percent complete. We expect to complete and test a combination of tree and leaf cell designs in the next period. Work is proceeding on algorithms for the computer aided manufacturing (CAM), and once the design is complete we will begin simulating algorithms for large problems. The following topics are covered: (1) the practical implementation of content addressable memory; (2) design of a LEAF cell for the Rutgers CAM architecture; (3) a circuit design tool user's manual; and (4) design and analysis of efficient hierarchical interconnection networks
Initial data for black hole-neutron star binaries: a flexible, high-accuracy spectral method
We present a new numerical scheme to solve the initial value problem for
black hole-neutron star binaries. This method takes advantage of the
flexibility and fast convergence of a multidomain spectral representation of
the initial data to construct high-accuracy solutions at a relatively low
computational cost. We provide convergence tests of the method for both
isolated neutron stars and irrotational binaries. In the second case, we show
that we can resolve the small inconsistencies that are part of the
quasi-equilibrium formulation, and that these inconsistencies are significantly
smaller than observed in previous works. The possibility of generating a wide
variety of initial data is also demonstrated through two new configurations
inspired by results from binary black holes. First, we show that choosing a
modified Kerr-Schild conformal metric instead of a flat conformal metric allows
for the construction of quasi-equilibrium binaries with a spinning black hole.
Second, we construct binaries in low-eccentricity orbits, which are a better
approximation to astrophysical binaries than quasi-equilibrium systems.Comment: 19 pages, 11 figures, Modified to match final PRD versio
A kidney transplant recipient with recurrent trichilemmal carcinoma and multiple other primary malignancies
Kidney transplant recipients are at increased risk of developing malignancy, with prolonged immunosuppressive therapy being a strong risk factor. Non-melanoma skin cancers are most commonly reported and multiple primary malignancies are also described. This is the first report of a recurrent trichilemmal carcinoma, a rare cutaneous tumour, in a kidney transplant recipient. This case, and the associated literature, indicate that regular screening, thorough examination, and tailored immunosuppressive regimens are critical in managing these patients
Spectral methods for the wave equation in second-order form
Current spectral simulations of Einstein's equations require writing the
equations in first-order form, potentially introducing instabilities and
inefficiencies. We present a new penalty method for pseudo-spectral evolutions
of second order in space wave equations. The penalties are constructed as
functions of Legendre polynomials and are added to the equations of motion
everywhere, not only on the boundaries. Using energy methods, we prove
semi-discrete stability of the new method for the scalar wave equation in flat
space and show how it can be applied to the scalar wave on a curved background.
Numerical results demonstrating stability and convergence for multi-domain
second-order scalar wave evolutions are also presented. This work provides a
foundation for treating Einstein's equations directly in second-order form by
spectral methods.Comment: 16 pages, 5 figure
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 CientÃficas y Técnicas. Instituto de BiologÃa y Medicina Experimental. Fundación de Instituto de BiologÃa y Medicina Experimental. Instituto de BiologÃa y Medicina Experimental; ArgentinaFil: Paredes, A. H.. Universidad de Chile; ChileFil: Tesone, Marta. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Instituto de BiologÃa y Medicina Experimental. Fundación de Instituto de BiologÃa y Medicina Experimental. Instituto de BiologÃa y Medicina Experimental; ArgentinaFil: Wu, T. J.. Uniformed Services University; Estados UnidosFil: Micevych, P. E.. University of California at Los Angeles; Estados Unido
From time-series to complex networks: Application to the cerebrovascular flow patterns in atrial fibrillation
A network-based approach is presented to investigate the cerebrovascular flow
patterns during atrial fibrillation (AF) with respect to normal sinus rhythm
(NSR). AF, the most common cardiac arrhythmia with faster and irregular
beating, has been recently and independently associated with the increased risk
of dementia. However, the underlying hemodynamic mechanisms relating the two
pathologies remain mainly undetermined so far; thus the contribution of
modeling and refined statistical tools is valuable. Pressure and flow rate
temporal series in NSR and AF are here evaluated along representative cerebral
sites (from carotid arteries to capillary brain circulation), exploiting
reliable artificially built signals recently obtained from an in silico
approach. The complex network analysis evidences, in a synthetic and original
way, a dramatic signal variation towards the distal/capillary cerebral regions
during AF, which has no counterpart in NSR conditions. At the large artery
level, networks obtained from both AF and NSR hemodynamic signals exhibit
elongated and chained features, which are typical of pseudo-periodic series.
These aspects are almost completely lost towards the microcirculation during
AF, where the networks are topologically more circular and present random-like
characteristics. As a consequence, all the physiological phenomena at
microcerebral level ruled by periodicity - such as regular perfusion, mean
pressure per beat, and average nutrient supply at cellular level - can be
strongly compromised, since the AF hemodynamic signals assume irregular
behaviour and random-like features. Through a powerful approach which is
complementary to the classical statistical tools, the present findings further
strengthen the potential link between AF hemodynamic and cognitive decline.Comment: 12 pages, 10 figure
Solving Einstein's Equations With Dual Coordinate Frames
A method is introduced for solving Einstein's equations using two distinct
coordinate systems. The coordinate basis vectors associated with one system are
used to project out components of the metric and other fields, in analogy with
the way fields are projected onto an orthonormal tetrad basis. These field
components are then determined as functions of a second independent coordinate
system. The transformation to the second coordinate system can be thought of as
a mapping from the original ``inertial'' coordinate system to the computational
domain. This dual-coordinate method is used to perform stable numerical
evolutions of a black-hole spacetime using the generalized harmonic form of
Einstein's equations in coordinates that rotate with respect to the inertial
frame at infinity; such evolutions are found to be generically unstable using a
single rotating coordinate frame. The dual-coordinate method is also used here
to evolve binary black-hole spacetimes for several orbits. The great
flexibility of this method allows comoving coordinates to be adjusted with a
feedback control system that keeps the excision boundaries of the holes within
their respective apparent horizons.Comment: Updated to agree with published versio
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