8,497 research outputs found
Exterior spacetime for stellar models in 5-dimensional Kaluza-Klein gravity
It is well-known that Birkhoff's theorem is no longer valid in theories with
more than four dimensions. Thus, in these theories the effective 4-dimensional
picture allows the existence of different possible, non-Schwarzschild,
scenarios for the description of the spacetime outside of a spherical star,
contrary to general relativity in 4D. We investigate the exterior spacetime of
a spherically symmetric star in the context of Kaluza-Klein gravity. We take a
well-known family of static spherically symmetric solutions of the Einstein
equations in an empty five-dimensional universe, and analyze possible stellar
exteriors that are conformal to the metric induced on four-dimensional
hypersurfaces orthogonal to the extra dimension. All these exteriors are
continuously matched with the interior of the star. Then, without making any
assumptions about the interior solution, we prove the following statement: the
condition that in the weak-field limit we recover the usual Newtonian physics
singles out an unique exterior. This exterior is "similar" to Scharzschild
vacuum in the sense that it has no effect on gravitational interactions.
However, it is more realistic because instead of being absolutely empty, it is
consistent with the existence of quantum zero-point fields. We also examine the
question of how would the deviation from the Schwarzschild vacuum exterior
affect the parameters of a neutron star. In the context of a model star of
uniform density, we show that the general relativity upper limit M/R < 4/9 is
significantly increased as we go away from the Schwarzschild vacuum exterior.
We find that, in principle, the compactness limit of a star can be larger than
1/2, without being a black hole. The generality of our approach is also
discussed.Comment: Typos corrected. Accepted for publication in Classical and Quantum
Gravit
Stellar models with Schwarzschild and non-Schwarzschild vacuum exteriors
A striking characteristic of non-Schwarzschild vacuum exteriors is that they
contain not only the total gravitational mass of the source, but also an {\it
arbitrary} constant. In this work, we show that the constants appearing in the
"temporal Schwarzschild", "spatial Schwarzschild" and
"Reissner-Nordstr{\"o}m-like" exteriors are not arbitrary but are completely
determined by star's parameters, like the equation of state and the
gravitational potential. Consequently, in the braneworld scenario the
gravitational field outside of a star is no longer determined by the total mass
alone, but also depends on the details of the internal structure of the source.
We show that the general relativistic upper bound on the gravitational
potential , for perfect fluid stars, is significantly increased in
these exteriors. Namely, , and for the
temporal Schwarzschild, spatial Schwarzschild and Reissner-Nordstr{\"o}m-like
exteriors, respectively. Regarding the surface gravitational redshift, we find
that the general relativistic Schwarzschild exterior as well as the braneworld
spatial Schwarzschild exterior lead to the same upper bound, viz., .
However, when the external spacetime is the temporal Schwarzschild metric or
the Reissner-Nordstr{\"o}m-like exterior there is no such constraint: . This infinite difference in the limiting value of is because for
these exteriors the effective pressure at the surface is negative. The results
of our work are potentially observable and can be used to test the theory.Comment: 19 pages, 3 figures and caption
Self-similar cosmologies in 5D: spatially flat anisotropic models
In the context of theories of Kaluza-Klein type, with a large extra
dimension, we study self-similar cosmological models in 5D that are
homogeneous, anisotropic and spatially flat. The "ladder" to go between the
physics in 5D and 4D is provided by Campbell-Maagard's embedding theorems. We
show that the 5-dimensional field equations determine the form of
the similarity variable. There are three different possibilities: homothetic,
conformal and "wave-like" solutions in 5D. We derive the most general
homothetic and conformal solutions to the 5D field equations. They require the
extra dimension to be spacelike, and are given in terms of one arbitrary
function of the similarity variable and three parameters. The Riemann tensor in
5D is not zero, except in the isotropic limit, which corresponds to the case
where the parameters are equal to each other. The solutions can be used as 5D
embeddings for a great variety of 4D homogeneous cosmological models, with and
without matter, including the Kasner universe. Since the extra dimension is
spacelike, the 5D solutions are invariant under the exchange of spatial
coordinates. Therefore they also embed a family of spatially {\it
inhomogeneous} models in 4D. We show that these models can be interpreted as
vacuum solutions in braneworld theory. Our work (I) generalizes the 5D
embeddings used for the FLRW models; (II) shows that anisotropic cosmologies
are, in general, curved in 5D, in contrast with FLRW models which can always be
embedded in a 5D Riemann-flat (Minkowski) manifold; (III) reveals that
anisotropic cosmologies can be curved and devoid of matter, both in 5D and 4D,
even when the metric in 5D explicitly depends on the extra coordinate, which is
quite different from the isotropic case.Comment: Typos corrected. Minor editorial changes and additions in the
Introduction and Summary section
The Effective Energy-Momentum Tensor in Kaluza-Klein Gravity With Large Extra Dimensions and Off-Diagonal Metrics
We consider a version of Kaluza-Klein theory where the cylinder condition is
not imposed. The metric is allowed to have explicit dependence on the "extra"
coordinate(s). This is the usual scenario in brane-world and space-time-matter
theories. We extend the usual discussion by considering five-dimensional
metrics with off-diagonal terms. We replace the condition of cylindricity by
the requirement that physics in four-dimensional space-time should remain
invariant under changes of coordinates in the five-dimensional bulk. This
invariance does not eliminate physical effects from the extra dimension but
separates them from spurious geometrical ones. We use the appropriate splitting
technique to construct the most general induced energy-momentum tensor,
compatible with the required invariance. It generalizes all previous results in
the literature. In addition, we find two four-vectors, J_{m}^{mu} and
J_{e}^{mu}, induced by off-diagonal metrics, that separately satisfy the usual
equation of continuity in 4D. These vectors appear as source-terms in equations
that closely resemble the ones of electromagnetism. These are Maxwell-like
equations for an antisymmetric tensor {F-hat}_{mu nu} that generalizes the
usual electromagnetic one. This generalization is not an assumption, but
follows naturally from the dimensional reduction. Thus, if {F-hat}_{mu nu}
could be identified with the electromagnetic tensor, then the theory would
predict the existence of classical magnetic charge and current. The splitting
formalism used allows us to construct 4D physical quantities from
five-dimensional ones, in a way that is independent on how we choose our
space-time coordinates from those of the bulk.Comment: New title, editorial changes made as to match the version to appear
in International Journal of Modern Physics
Pinworms of the red howler monkey (Alouatta seniculus) in Colombia. Gathering the pieces of the pinworm-primate puzzle
Pinworms of primates are believed to be highly host specific parasites, forming co-evolutionary associations with their hosts. In order to assess the strength and reach of such evolutionary links, we need to have a broad understanding of the pinworm diversity associated with primates. Here, we employed an integrative taxonomic approach to assess pinworm diversity in red howler monkeys in Colombia. Molecular and morphological evidence validate the presence of at least four different species of Trypanoxyuris occurring in red howler monkeys: T. minutus, a widely distributed species, and three new species, T. seunimiii n. sp., T. kemuimae n. sp. and T. kotudoi n. sp. The mitochondrial COI gene and the 28S ribosomal gene were used for phylogenetic assessments through Bayesian inference. The three new species were morphologically distinct and formed reciprocally monophyletic lineages. Further molecular lineage subdivision in T. minutus and T. kotudoi n. sp. without morphological correspondence, suggests the potential scenario for the existence of cryptic species. Phylogenetic relationships imply that the different species of Trypanoxyuris occurring in each howler monkey species were acquired through independent colonization events. On-going efforts to uncover pinworm diversity will allow us to test the degree of host specificity and the co-phylogenetic hypothesis, as well as to further unravel the primate-pinworm evolutionary history puzzle
Social Media Technologies and Its Role in Sustainable Tourism Development of Asik-Asik Falls
Asik-Asik Falls remained hidden from the public until it was introduced through social media. Since then, it has become a tourist attraction in Alamada, North Cotabato. This research envisions contributing to the sustainable development of Asik-Asik Falls. Specifically, it aims to assess the respondents’ perception of the potential impact of tourism in Alamada using sustainable tourism development literature. The research was conducted by examining online posts of previous travelers, key informant interviews (KII), and online surveys among 150 previous travelers. The findings provide a greater understanding of tourist perceptions, which can be used as guidelines for future sustainable developments. Asik-Asik Falls as a tourist attraction has an apparent impact on the local economy, and the quality of life of the residents has generally improved. The findings also revealed that consumers and tourism suppliers shared a common interest to maintain the natural beauty of the Asik-Asik Falls. The study recommends that the local government support the development of ecotourism by allocating a budget for maintenance and promotion. The residents should also participate in the implementation of the tourism development plan.
Keywords: Social media · information technology · sustainable tourism development · ecotourism · economic sustainability · environmental sustainabilit
Negative Acculturation Conditions, Wellbeing, and the Mediating Role of Separation in the Workplace
This article reports on the results of research which assessed adverse acculturation conditions in the workplace. Acculturation conditions such as racism, discrimination, segregation and separation were evaluated as predictors to ascertain how they affect acculturation outcomes such as intentions to quit and ill-health, both physical and psychological, of workers in the workplace. A convenience sample (N = 327) was taken from various sectors, for example retail, banking, mining, police service, and the municipality. The study aimed to test the mediating role of separation in the relation between adverse acculturation conditions and wellbeing as measured by ill-health and intentions to quit. The results indicated that racism, discrimination, segregation and separation, ill-health and intentions to quit were positively related. The hypothesized model was confirmed in a structural equation modelling analysis. This meant that more mainstream segregation demands, discrimination, and subtle racism, coupled with a dominant ethnic separation acculturation strategy and co-ethnics demanding that their members keep to themselves at work (with limited or no intercultural contact), were associated with the experiences of higher physical and psychological ill-health, and frequent thoughts of intentions to quit. In addition, mainstream segregation demands, compared to subtle racism and discrimination, were much more strongly associated with ethnic preference to separate. Blacks reported higher segregation demands and discrimination experiences at work (conditions), an individual separation acculturation strategy and physical ill-health at work (outcomes) compared to Whites, although the effects were relatively small. Recommendations for future research are provided
Late time cosmic acceleration from vacuum Brans-Dicke theory in 5D
We show that the scalar-vacuum Brans-Dicke equations in 5D are equivalent to
Brans-Dicke theory in 4D with a self interacting potential and an effective
matter field. The cosmological implication, in the context of FRW models, is
that the observed accelerated expansion of the universe comes naturally from
the condition that the scalar field is not a ghost, i.e., . We
find an effective matter-dominated 4D universe which shows accelerated
expansion if . We study the question of whether
accelerated expansion can be made compatible with large values of ,
within the framework of a 5D scalar-vacuum Brans-Dicke theory with variable,
instead of constant, parameter . In this framework, and based on a
general class of solutions of the field equations, we demonstrate that
accelerated expansion is incompatible with large values of .Comment: In V2 the summary section is expanded. To be published in Classical
and Quantum Gravity
Analog test interface for IEEE 1687 employing split SAR architecture to support embedded instrument dependability applications
Embedded instruments have become ubiquitous in modern day System-on-Chips for test and monitoring purposes. IEEE 1687 or IJTAG addresses the standardization of access and operation of these embedded instruments. Recently, there has been a lot of interest in employing embedded instruments for dependability purposes. Many of these embedded instruments are required to monitor physical quantities which are analog in nature. A cost-effective architecture to integrate these analog instruments into the IEEE 1687 infrastructure is a bottleneck and has not yet been standardized. This paper presents a time and area efficient architecture to interface analog embedded instruments onto the IEEE 1687 network especially for dependability applications. The architecture mitigates the drawbacks associated with utilizing an analog test bus and enables periodic sampling with minimal hardware overhead. The simulations to illustrate the concept have been conducted with TSMC 40nm CMOS technology
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