8,986 research outputs found
The Hopf algebra structure of the Z-graded quantum supergroup GL
In this work, we give some features of the Z-graded quantum supergroup
Towards a physical interpretation for the Stephani Universes
A physicaly reasonable interpretation is provided for the perfect fluid,
sphericaly symmetric, conformally flat ``Stephani Universes''. The free
parameters of this class of exact solutions are determined so that the ideal
gas relation is identicaly fulfiled, while the full equation of state
of a classical monatomic ideal gas and a matter-radiation mixture holds up to a
good approximation in a near dust, matter dominated regime. Only the models
having spacelike slices with positive curvature admit a regular evolution
domain that avoids an unphysical singularity. In the matter dominated regime
these models are dynamicaly and observationaly indistinguishable from
``standard'' FLRW cosmology with a dust source.Comment: 17 pages, 2 figures, LaTeX with revtex style, submitted to General
Relativity and Gravitatio
On Spinors Transformations
We begin showing that for even dimensional vector spaces all
automorphisms of their Clifford algebras are inner. So all orthogonal
transformations of are restrictions to of inner automorphisms of the
algebra. Thus under orthogonal transformations and - space and time
reversal - all algebra elements, including vectors and spinors ,
transform as and for some
algebra element . We show that while under combined spinor remain in its spinor space, under or separately
goes to a 'different' spinor space and may have opposite chirality.
We conclude with a preliminary characterization of inner automorphisms with
respect to their property to change, or not, spinor spaces.Comment: Minor changes to propositions 1 and
UV Dichroism in Vertically Aligned Nematic Displays
Vertically aligned negative nematics are employed in high-end projection applications, where extremely high light fluxes are employed. Under these conditions, the UV photochemical stability of the material becomes an issue that must be included in the characterization process of such devices. Photochemical aging tests for vertically aligned microdisplay, however, must take into account the linear dichroism shown by the liquid crystal material upon switching. In this work a method to evaluate UV linear dichroism is described. The method is included in a comparative study of the electrooptical performance of two negative nematic mixtures, one experimental and one commercial
The trends and dependencies between air and water temperatures in lakes in northern Poland in 1961?2000
International audienceOver 40 years, from 1961?2000, daily mean values of surface lake water temperatures at 0.4 m depth in six lakes in northern Poland were recorded with nearby mean daily air temperatures at 2 m. Air temperatures increased on average from 0.020 to 0.025°C year?1 while lake-water temperatures varied more but increased by 0.005 to 0.028°C year-1. For shorter periods (for instance, for 10 days) the pattern of trend directions and values was more complex, depending on the morphometric and trophic conditions of the lakes. It has been concluded that changes in lake water temperatures during climate warming may be documented by studies of lakes located relatively closely together (up to 300 kilometres). Keywords: physical limnology, climate changes, lake water, temperatur
Non-linear sigma-models in noncommutative geometry: fields with values in finite spaces
We study sigma-models on noncommutative spaces, notably on noncommutative
tori. We construct instanton solutions carrying a nontrivial topological charge
q and satisfying a Belavin-Polyakov bound. The moduli space of these instantons
is conjectured to consists of an ordinary torus endowed with a complex
structure times a projective space .Comment: Latex, 10 page
Electro-optical properties of an orthoconic liquid crystal mixture (W-182) and its molecular dynamics
We observed that the perfect dark state problem could be solved by using orthoconic antiferroelectric liquid crystal (OAFLC) instead of normal AFLC by comparing the properties of isocontrast and dispersion chromaticity of W-182 OAFLC and normal AFLC CS-4001. We electro-optically observed that several subphases such as SmCγ*, SmC*β, SmC*α and antiferroelectric SmI*A phases exist in W-182 OAFLC. We dielectrically observed in 4 μm thin cell that during heating, several new phases appeared. In the high temperature antiferroelectric region, a higher order than SmC* phase could be detected dielectrically, in the temperature range of 91–98 °C, behaving similar to SmCγ* and also, another phase below SmC* region could be dielectrically detected in the temperature range of 103–1100 °C, behaving similar to SmCα*, and an antiferroelectric, similar to SmIA* phase, was observed in the lower temperature region of the antiferroelectric phase; those are definitely arising due to surface force and interfacial charges interactions. We observed both PH and PL relaxation modes in both cells, although they differed in their strength and relaxation frequency. We studied extensively our observations of PH and PL modes in the antiferroelectric region, a Goldstone mode in the ferroelectric region and a soft mode in the ferroelectric region and SmA* phases
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