3,586 research outputs found
Alignment transition in a nematic liquid crystal due to field-induced breaking of anchoring
We report on the alignment transition of a nematic liquid crystal from
initially homeotropic to quasi-planar due to field-induced anchoring breaking.
The initial homeotropic alignment is achieved by Langmuir-Blodgett monolayers.
In this geometry the anchoring strength can be evaluated by the Frederiks
transition technique. Applying an electric field above a certain threshold
provokes turbulent states denoted DSM1 and DSM2. While DSM1 does not affect the
anchoring, DSM2 breaks the coupling between the surface and the liquid crystal:
switching off the field from a DSM2 state does not immediately restore the
homeotropic alignment. Instead, we obtain a quasi-planar metastable alignment.
The cell thickness dependence for the transition is related to theComment: 7 pages, LaTeX2e article, 4 figures, 7 EPS files, added references,
accepted for publication in Europhysics Letter
Engineering human cell-based, functionally integrated osteochondral grafts by biological bonding of engineered cartilage tissues to bony scaffolds
In this study, we aimed at developing and validating a technique for the engineering of osteochondral grafts based on the biological bonding of a chondral layer with a bony scaffold by cell-laid extracellular matrix. Osteochondral composites were generated by combining collagen-based matrices (Chondro-Gide) containing human chondrocytes with devitalized spongiosa cylinders (Tutobone) using a fibrin gel (Tisseel). We demonstrate that separate pre-culture of the chondral layer for 3 days prior to the generation of the composite allows for (i) more efficient cartilaginous matrix accumulation than no pre-culture, as assessed histologically and biochemically, and (ii) superior biological bonding to the bony scaffold than 14 days of pre-culture, as assessed using a peel-off mechanical test, developed to measure integration of bilayered materials. The presence of the bony scaffold induced an upregulation in the infiltrated cells of the osteoblast-related gene bone sialoprotein, indicative of the establishment of a gradient of cell phenotypes, but did not affect per se the quality of the cartilaginous matrix in the chondral layer. The described strategy to generate osteochondral plugs is simple to be implemented and--since it is based on clinically compliant cells and materials--is amenable to be readily tested in the clinic
Sensitive methods for estimating the anchoring strength of nematic liquid crystals on Langmuir-Blodgett monolayers of fatty acids
The anchoring of the nematic liquid crystal
N-(p-methoxybenzylidene)-p-butylaniline (MBBA) on Langmuir-Blodgett monolayers
of fatty acids (COOHCH) was studied as a function of the length
of the fatty acid alkyl chains, (). The monolayers were
deposited onto ITO-coated glass plates which were used to assemble sandwich
cells of various thickness that were filled with MBBA in the nematic phase. The
mechanism of relaxation from the flow-induced quasi-planar to the
surface-induced homeotropic alignment was studied for the four decreases
linearly with increasing the length of the alkyl chains which suggests that
the Langmuir-Blodgett film plays a role in the phenomenon. This fact was
confirmed by a sensitive estimation of the anchoring strength of MBBA on the
fatty acid monolayers after anchoring breaking which takes place at the
transition between two electric-field--induced turbulent states, denoted as
DSM1 and DSM2. It was found that the threshold electric field for the anchoring
breaking, which can be considered as a measure of the anchoring strength, also
decreases linearly as increases. Both methods thus possess a high
sensitivity in resolving small differences in anchoring strength. In cells
coated with mixed Langmuir-Blodgett monolayers of two fatty acids ( and
) a maximum of the relaxation speed was observed when the two acids were
present in equal amount. This observation homeotropic cells by changing the
ratio between the components of the surfactant film.Comment: LaTeX article, 20 pages, 15 figures, 17 EPS files. 1 figure added,
references moved. Submitted to Phys. Rev.
Preliminary Estimate of the Reservoir Age in the Lagoon of Venice
The Lagoon of Venice was formed about 6000 years ago due to the marine transgression associated with the late Pleistocene sea level rise. Already by the time of the Republic of Venice (727–1797 AD) it was recognized that the future of the city and its many historical buildings was strongly correlated with the future of the lagoon itself. During the centuries many engineering projects such as modification of the fluvial systems, construction of coastal barriers, and dredging of navigation channels were carried out to preserve the lagoonal environment. The present-day lagoon is the result of all these processes and covers an area of 540 km2 with an average depth of 0.6 m. A series of radiocarbon age determinations carried out on material obtained from cores collected in the Lagoon of Venice indicate within the sedimentary units the existence of a number of discontinuities and slumping events due to the highly active lagoonal environment. The evaluation of data obtained from a variety of different materials—both terrestrial and marine—allowed us to determine for the first time the marine reservoir effect in the lagoon of Venice. The discussion includes a comparison with other relevant measurements and a possible explanation to the relatively high reservoir age (1200–1300 yr)
Renormalization Group Analysis of a Quivering String Model of Posture Control
Scaling concepts and renormalization group (RG) methods are applied to a
simple linear model of human posture control consisting of a trembling or
quivering string subject to damping and restoring forces. The string is driven
by uncorrelated white Gaussian noise intended to model the corrections of the
physiological control system. We find that adding a weak quadratic nonlinearity
to the posture control model opens up a rich and complicated phase space
(representing the dynamics) with various non-trivial fixed points and basins of
attraction. The transition from diffusive to saturated regimes of the linear
model is understood as a crossover phenomenon, and the robustness of the linear
model with respect to weak non-linearities is confirmed. Correlations in
posture fluctuations are obtained in both the time and space domain. There is
an attractive fixed point identified with falling. The scaling of the
correlations in the front-back displacement, which can be measured in the
laboratory, is predicted for both the large-separation (along the string) and
long-time regimes of posture control.Comment: 20 pages, 13 figures, RevTeX, accepted for publication in PR
Geometric Approach to Pontryagin's Maximum Principle
Since the second half of the 20th century, Pontryagin's Maximum Principle has
been widely discussed and used as a method to solve optimal control problems in
medicine, robotics, finance, engineering, astronomy. Here, we focus on the
proof and on the understanding of this Principle, using as much geometric ideas
and geometric tools as possible. This approach provides a better and clearer
understanding of the Principle and, in particular, of the role of the abnormal
extremals. These extremals are interesting because they do not depend on the
cost function, but only on the control system. Moreover, they were discarded as
solutions until the nineties, when examples of strict abnormal optimal curves
were found. In order to give a detailed exposition of the proof, the paper is
mostly self\textendash{}contained, which forces us to consider different areas
in mathematics such as algebra, analysis, geometry.Comment: Final version. Minors changes have been made. 56 page
A High Throughput Configurable SDR Detector for Multi-user MIMO Wireless Systems
Spatial division multiplexing (SDM) in
MIMO technology significantly increases the spectral
efficiency, and hence capacity, of a wireless communication
system: it is a core component of the next generation
wireless systems, e.g. WiMAX, 3GPP LTE and
other OFDM-based communication schemes. Moreover,
spatial division multiple access (SDMA) is one
of the widely used techniques for sharing the wireless
medium between different mobile devices. Sphere detection
is a prominent method of simplifying the detection
complexity in both SDM and SDMA systems
while maintaining BER performance comparable with
the optimum maximum-likelihood (ML) detection. On
the other hand, with different standards supporting
different system parameters, it is crucial for both base
station and handset devices to be configurable and
seamlessly switch between different modes without the
need for separate dedicated hardware units. This challenge
emphasizes the need for SDR designs that target
the handset devices. In this paper, we propose the
architecture and FPGA realization of a configurable
sort-free sphere detector, Flex-Sphere, that supports
4, 16, 64-QAM modulations as well as a combination of 2, 3 and 4 antenna/user configuration for handsets.
The detector provides a data rate of up to 857.1 Mbps
that fits well within the requirements of any of the next
generation wireless standards. The algorithmic optimizations
employed to produce an FPGA friendly realization
are discussed.Xilinx Inc.National Science Foundatio
Search for the h_c meson in B^+- ->h_c K^+-
We report a search for the meson via the decay chain , \etac \gamma with and
. No significant signals are observed. We obtain upper limits on the
branching fractions for in bins of the
invariant mass. The results are based on an analysis of 253
fb of data collected by the Belle detector at the KEKB
collider.Comment: 12 pages, 6 figures, submitted to Phys. Rev.
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