5,796 research outputs found
Refined Kirby calculus for integral homology spheres
A theorem of Kirby states that two framed links in the 3-sphere produce
orientation-preserving homeomorphic results of surgery if they are related by a
sequence of stabilization and handle-slide moves.
The purpose of the present paper is twofold: First, we give a sufficient
condition for a sequence of handle-slides on framed links to be able to be
replaced with a sequences of algebraically canceling pairs of handle-slides.
Then, using the first result, we obtain a refinement of Kirby's calculus for
integral homology spheres which involves only +/-1-framed links with zero
linking numbers.Comment: This is the version published by Geometry & Topology on 18 September
200
Equation of state of cubic boron nitride at high pressures and temperatures
We report accurate measurements of the equation of state (EOS) of cubic boron
nitride by x-ray diffraction up to 160 GPa at 295 K and 80 GPa in the range
500-900 K. Experiments were performed on single-crystals embedded in a
quasi-hydrostatic pressure medium (helium or neon). Comparison between the
present EOS data at 295 K and literature allows us to critically review the
recent calibrations of the ruby standard. The full P-V-T data set can be
represented by a Mie-Gr\"{u}neisen model, which enables us to extract all
relevant thermodynamic parameters: bulk modulus and its first
pressure-derivative, thermal expansion coefficient, thermal Gr\"{u}neisen
parameter and its volume dependence. This equation of state is used to
determine the isothermal Gr\"{u}neisen mode parameter of the Raman TO band. A
new formulation of the pressure scale based on this Raman mode, using
physically-constrained parameters, is deduced.Comment: 8 pages, 7 figure
The Impact of Tax Incentives to Stimulate Investment in South Africa
The purpose of this paper is, very generally, to provide a framework and potential methodology of analysis of tax incentives in one country — South Africa. As incentives are often specific and targeted, the precise methods needed to analyze the effectiveness of incentives may well differ among types of incentives. However, by positing a framework for evaluation based on basic economic principles, we believe that transparency, accountability and rigorous evaluation of individual incentives or regarding the choice of incentives may be enhanced
A High Pressure Distorted a-Uranium (Pnma) Structure in Plutonium
Under pressure many rare earths and actinide metals transform to a-U
structure or its lower symmetry distorted forms. We have reinterpreted the
diffraction data of Dabos et al for Pu (reference 4) and find that a Am IV type
distorted a-U structure in Pnma space group can explain this for its high
pressure phase. The structures of this phase and a-Pu are both shown to have a
distorted hcp topology. The upturn in the atomic volume of Pu at 0.1 MPa can
also be rationalized on the basis of this proposalComment: 10pages,3 figure
Low-temperature effective potential of the Ising model
We study the low-temperature effective potential of the Ising model. We
evaluate the three-point and four-point zero-momentum renormalized coupling
constants that parametrize the expansion of the effective potential near the
coexistence curve. These results are obtained by a constrained analysis of the
-expansion that uses accurate estimates for the two-dimensional Ising
model.Comment: 16 pages, RevTex, few minor change
Mid-infrared laser light nulling experiment using single-mode conductive waveguides
Aims: In the context of space interferometry missions devoted to the search
of exo-Earths, this paper investigates the capabilities of new single mode
conductive waveguides at providing modal filtering in an infrared and
monochromatic nulling experiment; Methods: A Michelson laser interferometer
with a co-axial beam combination scheme at 10.6 microns is used. After
introducing a Pi phase shift using a translating mirror, dynamic and static
measurements of the nulling ratio are performed in the two cases where modal
filtering is implemented and suppressed. No additional active control of the
wavefront errors is involved. Results: We achieve on average a statistical
nulling ratio of 2.5e-4 with a 1-sigma upper limit of 6e-4, while a best null
of 5.6e-5 is obtained in static mode. At the moment, the impact of external
vibrations limits our ability to maintain the null to 10 to 20 seconds.;
Conclusions: A positive effect of SM conductive waveguide on modal filtering
has been observed in this study. Further improvement of the null should be
possible with proper mechanical isolation of the setup.Comment: Accepted in A&A, 7 pages, 5 figure
Effective potential in three-dimensional O(N) models
We consider the effective potential in three-dimensional models with O(N)
symmetry. For generic values of N, and in particular for the physically
interesting cases N=0,1,2,3, we determine the six-point and eight-point
renormalized coupling constants which parametrize its small-field expansion.
These estimates are obtained from the analysis of their -expansion,
taking into account the exact results in one and zero dimensions, and, for the
Ising model (i.e. N=1), the accurate high-temperature estimates in two
dimensions. They are compared with the available results from other approaches.
We also obtain corresponding estimates for the two-dimensional O() models.Comment: 22 pages, revtex, 2 fig
eXtended Color Cell Compression -- A Runtime-efficient Compression Scheme for Software Video
Multimedia applications require a compression and decompression scheme for digital video. The standardized and widely used techniques JPEG and MPEG provide very good compression ratios, but are computationally quite complex and demanding. We propose to use an extension to the much simpler Color Cell Compression scheme as an alternative. Our extension includes the use of variable block sizes, the reuse of color index values from previously encoded blocks, and Huffman encoding of the stream of blocks. We present experimental results showing that our scheme provides much better runtime performance than MPEG, at the cost of a slightly inferior compression ratio. It is thus especially suited for software videos in high-speed networks
Indexing, browsing and searching of digital video
Video is a communications medium that normally brings together moving pictures with a synchronised audio track into a discrete piece or pieces of information. The size of a “piece ” of video can variously be referred to as a frame, a shot, a scene, a clip, a programme or an episode, and these are distinguished by their lengths and by their composition. We shall return to the definition of each of these in section 4 this chapter. In modern society, video is ver
Analysis of the instantaneous Bethe-Salpeter equation for -bound-states
We investigate the structure of the instantaneous Bethe-Salpeter equation for
-bound states in the general case of unequal quark masses and
develop a numerical scheme for the calculation of mass spectra and
Bethe-Salpeter amplitudes. In order to appreciate the merits of the various
competing models beyond the reproduction of the mass spectra we present
explicit formulas to calculate electroweak decays. The results for an explicit
quark model will be compared to experimental data in a subsequent paperComment: 11 pages, RevTeX, TK-93-1
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