16,675 research outputs found
Thermotropic Nematic and Smectic Order in Silica Glass Nanochannels
Optical birefringence measurements on a rod-like liquid crystal (8OCB),
imbibed in silica channels (7 nm diameter), are presented and compared to the
thermotropic bulk behavior. The orientational and positional order of the
confined liquid evolves continuously at the paranematic-to-nematic and sizeably
broadened at the nematic-to-smectic order transition, resp., in contrast to the
discontinuous and well-defined second-order character of the bulk transitions.
A Landau-de-Gennes analysis reveals identical strengths of the nematic and
smectic ordering fields (imposed by the walls) and indicates that the smectic
order is more affected by quenched disorder (originating in channel tortuosity
and roughness) than the nematic transition.Comment: 3 pages, 4 figure
Crossover from weak localization to weak antilocalization in a disordered microbridge
We calculate the weak localization correction in the double crossover to
broken time-reversal and spin-rotational symmetry for a disordered microbridge
or a short disordered wire using a scattering-matrix approach. Whereas the
correction has universal limiting values in the three basic symmetry classes,
the functional form of the magnetoconductance is affected by eventual
non-homogeneities in the microbridge.Comment: 5 pages, RevTeX; 2 figure
Elastomer Compound Developed for High Wear Applications
The U.S. Army is currently spending 300 million dollars per year replacing rubber track pads. An experimental rubber compound has been developed which exhibits 2 to 3 times greater service life than standard production pad compounds. To improve the service life of the tank track pads various aspects of rubber chemistry were explored including polymer, curing and reinforcing systems. Compounds that exhibited superior physical properties based on laboratory data were then fabricated into tank pads and field tested. This paper will discuss the compounding studies, laboratory data and field testing that led to the high wear elastomer compound
Net energy analysis of solar and conventional domestic hot water systems in Melbourne, Australia
It is commonly assumed that solar hot water systems save energy and reduce greenhouse gas emissions. Very rarely has the life-cycle energy requirements of solar hot water systems been analysed, including their embodied energy. The extent to which solar hot water systems save energy compared to conventional systems in Melbourne, Australia, is shown through a comparative net energy analysis. The solar systems provided a net energy saving compared to the conventional systems after 0.5 to 2 years, for electricity and gas systems respectively.<br /
British digital game studies
This paper provides a short and potted recent history of digital games research in Great Britain. We begin this story in 2001. Though a substantial amount of research and writing on digital games was taking in Britain since at least the 1980s, for us the turn of the new millennium makes a logical starting point for our recent history. This is because this was not only the year that Aarseth (2001) marked as 'year one' for 'computer game research', but it was also the year that the first major international conference on digital games took place in the UK (in Bristol), and the first time a major British government grant was awarded to undertake research on digital gaming. The paper then charts the significant role Britain played in hosting major early international gatherings of (now leading) games researchers, such as those in Bristol and also Manchester. As well as the important crop of early British authored (text)books that helped shape the direction of this new emerging discipline. What we then see is a significant growth in British digital games studies focused around a number of key events, research clusters, and publications, and the development of a particular framing of digital games within a wider social, cultural, and political context. It is this, we would suggest, which has given British digital game studies its particular flavour and also its important global role in pushing forward research, theory, and key debates
Oxygen isotope effect on the superconductivity and stripe phase in LaNdSrCuO
The oxygen isotope effect on the superconductivity, stripe phase and
structure transition is systematically investigated in
LaNdSrCuO with static stripe phase. Substitution of
O by O leads to a decrease in superconducting transition
temperature T, while enhances the temperature of the structural transition
from low-temperature-orthorhombic (LTO) phase to low-temperature-tetragonal
(LTT) phase. Compared to the Nd free sample, a larger isotope effect on
is observed in LaNdSrCuO. These results indicate
that the distortion of CuO plane suppresses the superconductivity, giving a
direct evidence for the competing of stripe phase and superconductivity because
the distortion of CuO plane enhances the stripe phase.Comment: 4 pages, 5 figure
Quenching of lamellar ordering in an n-alkane embedded in nanopores
We present an X-ray diffraction study of the normale alkane nonadecane
C_{19}H_{40} embedded in nanoporous Vycor glass. The confined molecular crystal
accomplishes a close-packed structure by alignment of the rod-like molecules
parallel to the pore axis while sacrificing one basic principle known from the
bulk state, i.e. the lamellar ordering of the molecules. Despite this disorder,
the phase transitions observed in the confined solid mimic the phase behavior
of the 3D unconfined crystal, though enriched by the appearance of a true
rotator phase known only from longer alkane chains.Comment: 7 pages, 3 figure
Interstellar reddening towards six small areas in Puppis-Vela
We investigate the distribution of the interstellar dust towards six small
volumes of the sky in the region of the Gum nebula. New high-quality
four-colour uvby and H\beta\ Str\"omgren photometry obtained for 352 stars in
six selected areas of Kapteyn, complemented with data obtained in a previous
investigation for two of these areas, were used to estimate the colour excess
and distance to these objects. The obtained colour excess versus distance
diagrams, complemented with other information, when available, were analysed in
order to infer the properties of the interstellar medium permeating the
observed volumes. On the basis of the overall standard deviation in the
photometric measurements, we estimate that colour excesses and distances are
determined with an accuracy of 0.010 mag and better than 30%, respectively, for
a sample of 520 stars. A comparison with 37 stars in common with the new
Hipparcos catalogue attests to the high quality of the photometric distance
determination. The obtained colour excess versus distance diagrams testify to
the low density volume towards the observed lines-of-sight. Very few stars out
to distances of 1 kpc from the Sun have colour excesses larger than E(b-y) =
0.1 mag. In spite of the low density character of the interstellar medium
towards the Puppis-Vela direction, the obtained reddening as a function of the
distance indicates that two or more interstellar structures are crossed towards
the observed lines-of-sight. One of these structures may be associated with the
very low density wall of the Local Cavity, which has a distance of 100-150 pc
from the Sun. Another structure might be related to the Gum nebula, and if so,
its front face would be located at about 350 pc from the Sun.Comment: Accepted by Astronomy and Astrophysic
Classical simulation of noninteracting-fermion quantum circuits
We show that a class of quantum computations that was recently shown to be
efficiently simulatable on a classical computer by Valiant corresponds to a
physical model of noninteracting fermions in one dimension. We give an
alternative proof of his result using the language of fermions and extend the
result to noninteracting fermions with arbitrary pairwise interactions, where
gates can be conditioned on outcomes of complete von Neumann measurements in
the computational basis on other fermionic modes in the circuit. This last
result is in remarkable contrast with the case of noninteracting bosons where
universal quantum computation can be achieved by allowing gates to be
conditioned on classical bits (quant-ph/0006088).Comment: 26 pages, 1 figure, uses wick.sty; references added to recent results
by E. Knil
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