3,273 research outputs found
Black hole solutions in 2+1 dimensions
We give circularly symmetric solutions for null fluid collapse in
2+1-dimensional Einstein gravity with a cosmological constant. The fluid
pressure and energy density are related by . The
long time limit of the solutions are black holes whose horizon structures
depend on the value of . The solution is the
Banados-Teitelboim-Zanelli black hole metric in the long time static limit,
while the solutions give other, `hairy' black hole metrics in this limit.Comment: 8 pages, RevTeX (to appear in Phys. Rev. D) References to Mann and
Ross, and Mann, Chan and Chan adde
Group study of an 'undercover' test for visuospatial neglect: Invisible cancellation can reveal more neglect than standard cancellation
Visual neglect is a relatively common deficit after brain damage, particularly strokes. Cancellation tests provide standard clinical measures of neglect severity and deficits in daily life. A recent single-case study introduced a new variation on standard cancellation. Instead of making a visible mark on each target found, the patient made invisible marks (recorded with carbon paper underneath, for later scoring). Such invisible cancellation was found to reveal more neglect than cancellation with visible marks. Here we test the generality of this. Twenty three successive cases with suspected neglect each performed cancellation with visible or invisible marks. Neglect of contralesional targets was more pronounced with invisible marks. Indeed, about half of the patients only showed neglect in this version. For cases showing more neglect with invisible marks, stronger neglect of contralesional targets correlated with more revisits to ipsilesional targets for making additional invisible marks upon them. These results indicate that cancellation with invisible marks can reveal more neglect than standard cancellation with visible marks, while still providing a practical bedside test. Our observations may be consistent with recent proposals that demands on spatial working memory (required to keep track of previously found items only when marked invisibly) can exacerbate spatial neglect
Two dimensional general covariance from three dimensions
A 3d generally covariant field theory having some unusual properties is
described. The theory has a degenerate 3-metric which effectively makes it a 2d
field theory in disguise. For 2-manifolds without boundary, it has an infinite
number of conserved charges that are associated with graphs in two dimensions
and the Poisson algebra of the charges is closed. For 2-manifolds with boundary
there are additional observables that have a Kac-Moody Poisson algebra. It is
further shown that the theory is classically integrable and the general
solution of the equations of motion is given. The quantum theory is described
using Dirac quantization, and it is shown that there are quantum states
associated with graphs in two dimensions.Comment: 10 pages (Latex), Alberta-Thy-19-9
Magnetotransport properties of lithographically defined lateral Co/Ni80Fe20 wires
In this article we have investigated the magnetization reversal process of laterally defined coupled magnetic structures consisting of micron-sized sputtered Co and Ni80Fe20 wires lying side by side at temperatures ranging from 3 to 300 K. We have used a microfabrication technique to create an array of planar, laterally coupled magnetic wires made of two ferromagnetic materials. We observed two distinct peaks in the magnetoresistance (MR) curves corresponding to the magnetization reversals of Co and Ni80Fe20 wires. Below a critical temperature of 20 K we observed an asymmetric shift in the Ni80Fe20 peak position for both forward and reverse field sweeps due to the exchange coupling between the ferromagnetic (Ni80Fe20) and antiferromagnetic (Co–oxide at the interface of Co and Ni80Fe20 formed during fabrication) parts. The Co peaks gradually disappeared as the temperature was reduced. At low temperature we also observed that the Ni80Fe20 peaks in the MR loops are considerably shifted to larger fields corresponding to the increase in coercivity
EFFECT OF PRESTRESSING FORCE ONTORSION RESISTANCE OF CONCRETE BEAMS
This study presents an experimental and theoretical investigation of torsion behavior of prestressed concrete rectangular beams without ordinary (or typical) reinforcement. Two concrete beams with concentric prestressing tendons (6-strands of 7 wires) and two plain concrete beams were tested in this investigation with f'c= 44MPa was used.
Experimental results showed that the ultimate torsional strengths increased by about 70% for the tested beams containing concentric prestressed strands over the plain concrete beams. Also the angle of twist decreased (68.8%).Crack patterns and the effect of compressive force due to prestressing tendons and high strength concrete can be denoted from the helical mode of single crack at midspan of the beams under testing and from the sudden failure mode. In the analytical work P3DNFEA (Program, three-dimensional nonlinear finite element analysis), by Al-Shaarbaf has been utilized. Three dimensional nonlinear quadratic 20 -node brick elements were used to model the concrete, while, the prestressing strands were modeled by embedded representation. Reinforcing bars (Prestressing strands) were assumed to be capable of transmitting axial forces only. It was found that the general behavior of the finite element showed good agreement with
observations and results from the experimental tests
Background independent quantization and the uncertainty principle
It is shown that polymer quantization leads to a modified uncertainty
principle similar to that obtained from string theory and non-commutative
geometry. When applied to quantum field theory on general background
spacetimes, corrections to the uncertainty principle acquire a metric
dependence. For Friedmann-Robertson-Walker cosmology this translates to a scale
factor dependence which gives a large effect in the early universe.Comment: 6 page
Einstein's equations and the chiral model
The vacuum Einstein equations for spacetimes with two commuting spacelike
Killing field symmetries are studied using the Ashtekar variables. The case of
compact spacelike hypersurfaces which are three-tori is considered, and the
determinant of the Killing two-torus metric is chosen as the time gauge. The
Hamiltonian evolution equations in this gauge may be rewritten as those of a
modified SL(2) principal chiral model with a time dependent `coupling
constant', or equivalently, with time dependent SL(2) structure constants. The
evolution equations have a generalized zero-curvature formulation. Using this
form, the explicit time dependence of an infinite number of
spatial-diffeomorphism invariant phase space functionals is extracted, and it
is shown that these are observables in the sense that they Poisson commute with
the reduced Hamiltonian. An infinite set of observables that have SL(2) indices
are also found. This determination of the explicit time dependence of an
infinite set of spatial-diffeomorphism invariant observables amounts to the
solutions of the Hamiltonian Einstein equations for these observables.Comment: 22 pages, RevTeX, to appear in Phys. Rev.
A Novel Hybrid Notch (HN) Substrate Integrated Waveguide (SIW) Bandstop Filter
The advent of substrate integrated waveguide has seen an influx of researches on the study and design of microwave filters employing such a technique[1]-[4]. This technique provides an excellent avenue to design millimeter wave circuits such as filters, resonators and antennae [5]. A great advantage is that these devices can be easily connected to other planar microwave transmission lines and devices by using very simple transitions [6]. While many researches on SIW primarily focused on bandpass filters, researches on SIW bandstop filters for the GHz frequency ranges are gaining momentum working on the big list of advantages of SIW over microstrips. This paper presents the analysis and design of a novel Hybrid Notch Bandstop Filter working in the X-Band of the Frequency Spectrum
Canonical Quantization of the Gowdy Model
The family of Gowdy universes with the spatial topology of a three-torus is
studied both classically and quantum mechanically. Starting with the Ashtekar
formulation of Lorentzian general relativity, we introduce a gauge fixing
procedure to remove almost all of the non-physical degrees of freedom. In this
way, we arrive at a reduced model that is subject only to one homogeneous
constraint. The phase space of this model is described by means of a canonical
set of elementary variables. These are two real, homogeneous variables and the
Fourier coefficients for four real fields that are periodic in the angular
coordinate which does not correspond to a Killing field of the Gowdy
spacetimes. We also obtain the explicit expressions for the line element and
reduced Hamiltonian. We then proceed to quantize the system by representing the
elementary variables as linear operators acting on a vector space of analytic
functionals. The inner product on that space is selected by imposing Lorentzian
reality conditions. We find the quantum states annihilated by the operator that
represents the homogeneous constraint of the model and construct with them the
Hilbert space of physical states. Finally, we derive the general form of the
quantum observables of the model.Comment: 13 pages, Revte
Decision-support system for risk management of produced water in the offshore petroleum industry
A decision-support system for produced water management
(DISSPROWM) in offshore operations is being developed. The system
determines the risk and hazards to human and marine species from
non-carcinogenic and carcinogenic pollutants, including radionuclides present
in produced water. The DISSPROWM also evaluates the best available
treatment technology for treating the produced water whose properties are
in the database. The system consists of a Windows-based Graphical User
Interface (GUI) developed with Microsoft Visual Basic, which integrates a
SQL Server database, a risk assessment model and a dilution model for
produced water contaminants. The database contains most produced water
pollutants and their important properties that are required in dispersion and risk
assessment modelling. The database also contains current produced water
regulations and information on some of the selected existing treatment
technologies with typical cost data required in the decision-support system
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