58 research outputs found
Generation of scalar-tensor gravity effects in equilibrium state boson stars
Boson stars in zero-, one-, and two-node equilibrium states are modeled
numerically within the framework of Scalar-Tensor Gravity. The complex scalar
field is taken to be both massive and self-interacting. Configurations are
formed in the case of a linear gravitational scalar coupling (the Brans-Dicke
case) and a quadratic coupling which has been used previously in a cosmological
context. The coupling parameters and asymptotic value for the gravitational
scalar field are chosen so that the known observational constraints on
Scalar-Tensor Gravity are satisfied. It is found that the constraints are so
restrictive that the field equations of General Relativity and Scalar-Tensor
gravity yield virtually identical solutions. We then use catastrophe theory to
determine the dynamically stable configurations. It is found that the maximum
mass allowed for a stable state in Scalar-Tensor gravity in the present
cosmological era is essentially unchanged from that of General Relativity. We
also construct boson star configurations appropriate to earlier cosmological
eras and find that the maximum mass for stable states is smaller than that
predicted by General Relativity, and the more so for earlier eras. However, our
results also show that if the cosmological era is early enough then only states
with positive binding energy can be constructed.Comment: 20 pages, RevTeX, 11 figures, to appear in Class. Quantum Grav.,
comments added, refs update
A trick for passing degenerate points in Ashtekar formulation
We examine one of the advantages of Ashtekar's formulation of general
relativity: a tractability of degenerate points from the point of view of
following the dynamics of classical spacetime. Assuming that all dynamical
variables are finite, we conclude that an essential trick for such a continuous
evolution is in complexifying variables. In order to restrict the complex
region locally, we propose some `reality recovering' conditions on spacetime.
Using a degenerate solution derived by pull-back technique, and integrating the
dynamical equations numerically, we show that this idea works in an actual
dynamical problem. We also discuss some features of these applications.Comment: 9 pages by RevTeX or 16 pages by LaTeX, 3 eps figures and epsf-style
file are include
Structural changes induced by electric currents in a single crystal of PrCuO
We demonstrate a novel approach to the structural and electronic property
modification of perovskites, focusing on PrCuO, an undoped parent
compound of a class of electron-doped copper-oxide superconductors. Currents
were passed parallel or perpendicular to the copper-oxygen layers with the
voltage ramped up until a rapid drop in the resistivity was achieved, a process
referred to as "flash". The current was then further increased tenfold in
current-control mode. This state was quenched by immersion into liquid
nitrogen. Flash can drive many compounds into different atomic structures with
new properties, whereas the quench freezes them into a long-lived state.
Single-crystal neutron diffraction of as-grown and modified PrCuO
revealed a x superlattice due to oxygen-vacancy order.
The diffraction peak intensities of the superlattice of the modified sample
were significantly enhanced relative to the pristine sample. Raman-active
phonons in the modified sample were considerably sharper. Measurements of
electrical resistivity, magnetization and two-magnon Raman scattering indicate
that the modification affected only the Pr-O layers, but not the Cu-O planes.
These results point to enhanced oxygen-vacancy order in the modified samples
well beyond what can be achieved without passing electrical current. Our work
opens a new avenue toward electric field/quench control of structure and
properties of layered perovskite oxides
Role of Network Topology in the Synchronization of Power Systems
We study synchronization dynamics in networks of coupled oscillators with
bimodal distribution of natural frequencies. This setup can be interpreted as a
simple model of frequency synchronization dynamics among generators and loads
working in a power network. We derive the minimum coupling strength required to
ensure global frequency synchronization. This threshold value can be
efficiently found by solving a binary optimization problem, even for large
networks. In order to validate our procedure, we compare its results with
numerical simulations on a realistic network describing the European
interconnected high-voltage electricity system, finding a very good agreement.
Our synchronization threshold can be used to test the stability of frequency
synchronization to link removals. As the threshold value changes only in very
few cases when aplied to the European realistic network, we conclude that
network is resilient in this regard. Since the threshold calculation depends on
the local connectivity, it can also be used to identify critical network
partitions acting as synchronization bottlenecks. In our stability experiments
we observe that when a link removal triggers a change in the critical
partition, its limits tend to converge to national borders. This phenomenon,
which can have important consequences to synchronization dynamics in case of
cascading failure, signals the influence of the uncomplete topological
integration of national power grids at the European scale.Comment: The final publication is available at http://www.epj.org (see
http://www.springerlink.com/content/l22k574x25u6q61m/
Truncated post-Newtonian neutron star model
As a preliminary step towards simulating binary neutron star coalescing
problem, we test a post-Newtonian approach by constructing a single neutron
star model. We expand the Tolman-Oppenheimer-Volkov equation of hydrostatic
equilibrium by the power of , where is the speed of light, and
truncate at the various order. We solve the system using the polytropic
equation of state with index and 3, and show how this
approximation converges together with mass-radius relations. Next, we solve the
Hamiltonian constraint equation with these density profiles as trial functions,
and examine the differences in the final metric. We conclude the second
`post-Newtonian' approximation is close enough to describe general relativistic
single star. The result of this report will be useful for further binary
studies.
(Note to readers) This paper was accepted for publication in Physical Review
D. [access code dsj637]. However, since I was strongly suggested that the
contents of this paper should be included as a section in our group's future
paper, I gave up the publication.Comment: 5 pages, RevTeX, 3 eps figs, epsf.sty, accepted for publication in
PRD (Brief Report), but will not appea
Dynamical evolution of boson stars in Brans-Dicke theory
We study the dynamics of a self-gravitating scalar field solitonic object
(boson star) in the Jordan-Brans-Dicke (BD) theory of gravity. We show
dynamical processes of this system such as (i) black hole formation of
perturbed equilibrium configuration on an unstable branch; (ii) migration of
perturbed equilibrium configuration from the unstable branch to stable branch;
(iii) transition from excited state to a ground state. We find that the
dynamical behavior of boson stars in BD theory is quite similar to that in
general relativity (GR), with comparable scalar wave emission. We also
demonstrate the formation of a stable boson star from a Gaussian scalar field
packet with flat gravitational scalar field initial data. This suggests that
boson stars can be formed in the BD theory in much the same way as in GR.Comment: 13 pages by RevTeX, epsf.sty, 16 figures, comments added, refs
updated, to appear in Phys. Rev.
Inactivation of a Single Copy of Crebbp Selectively Alters Pre-mRNA Processing in Mouse Hematopoietic Stem Cells
Global expression analysis of fetal liver hematopoietic stem cells (FL HSCs) revealed the presence of unspliced pre-mRNA for a number of genes in normal FL HSCs. In a subset of these genes, Crebbp+/â FL HSCs had less unprocessed pre-mRNA without a corresponding reduction in total mRNA levels. Among the genes thus identified were the key regulators of HSC function Itga4, Msi2 and Tcf4. A similar but much weaker effect was apparent in Ep300+/â FL HSCs, indicating that, in this context as in others, the two paralogs are not interchangeable. As a group, the down-regulated intronic probe sets could discriminate adult HSCs from more mature cell types, suggesting that the underlying mechanism is regulated with differentiation stage and is active in both fetal and adult hematopoiesis. Consistent with increased myelopoiesis in Crebbp hemizygous mice, targeted reduction of CREBBP abundance by shRNA in the multipotent EML cell line triggered spontaneous myeloid differentiation in the absence of the normally required inductive signals. In addition, differences in protein levels between phenotypically distinct EML subpopulations were better predicted by taking into account not only the total mRNA signal but also the amount of unspliced message present. CREBBP thus appears to selectively influence the timing and degree of pre-mRNA processing of genes essential for HSC regulation and thereby has the potential to alter subsequent cell fate decisions in HSCs
Dokumentasi etnobotani-linguistik tumbuhan sagu: laboran awal dari etnis marori di taman nasional wasur Merauke [The ethnobotanical-linguistic documentation of Sago: a preliminary report from Merauke]
This paper discusses the ethnobotanical-linguistic documentation of sago (sago Metroxylon Rottb.) in Marori. Sago is a plant of high socio-cultural and economic values for the Papuan people in general and for the Marori ethnic group in particular. Socio-culturally, sago plays a central role in everyday life: it is used in a variety of important rituals, from birth to funeral ceremonies, which involve certain social obligation and responsibility. It is the identity of the Mahuze clan. Traditionally sago has a high economic value too, as staple food. However, there has been a widespread process of acculturation and change resulting in a shift, among other things, in the consumption patterns of staple food, from sago to rice. In addition, the Marori language is highly endangered; the local indigenous knowledge related to sago (and also other plants) is also increasingly endangered. This is mainly due to external socio-historicalcultural factors that have affected and shaped the current ecology in Merauke and in modern Indonesia. The role of language is central in the intergenerational transmission of indigenous knowledge. Collaborative efforts of all stakeholders are therefore urgently needed to do language and cultural documentation, as part of the conservation and preservation of language and culture of this ethnic group. The discussion on the entholinguistics of sago in this paper addresses two related aspects, namely documentation aspects and ethnobotanical-linguistic aspects. The discussion on the folk taxonomy and lexical items in relation to sago plants and sago processing highlights rich vocabulary related to socio-cultural knowledge of sago. The paper also discusses the socio-cultural and economic significance of sago, outlining a sago-trading taboo posing a delicate problem in maximizing the economic potential of sago, and the efforts so far done to address the issues by relevant stakeholders
Low expression of FGF1 (Fibroblast growth factor-1) in rat parasympathetic preganglionic neurons
Fibroblast growth factor-1 (FGF1), a member
of the FGF family of growth factors, is localized in
cholinergic neurons where it has trophic activity. We
recently reported that cholinergic neurons in the dorsal
motor nucleus of the vagus (DMNV) contain little
FGF1, raising the possibility that FGF1 is not localized
to parasympathetic preganglionic cholinergic neurons.
To clarify this issue, we investigated the co-localization
of FGF1 with cholinergic neuron markers in the
Edinger-Westphal nucleus (EWN), salivatory nucleus,
DMNV, and sacral parasympathetic nucleus by double
immunofluorescence using antibodies to FGF1 and
choline acetyltransferase (ChAT). The neurons in the
EWN were devoid of FGF1. In the salivatory nucleus,
13% of ChAT-positive neurons were also positive for
FGF1. In the DMNV, only 8% of ChAT-positive neurons
contained FGF1, and in the sacral parasympathetic
nucleus, 18% of ChAT-positive neurons were FGF1-
positive. We also confirmed that a large number of
ChAT-positive motor neurons in the oculomotor nucleus,
facial nucleus, hypoglossal nucleus, and spinal motor
neurons contained FGF1. The results confirmed that
parasympathetic preganglionic neurons are largely
devoid of FGF1, which is a unique feature among
cholinergic neurons
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