219 research outputs found
Isotropic-nematic transition in liquid crystals confined between rough walls
The effect of rough walls on the phase behaviour of a confined liquid crystal
(LC) fluid is studied using constant pressure Monte Carlo simulations. The LC
is modelled as a fluid of soft ellipsoidal molecules and the rough walls are
represented as a hard wall with a number of molecules randomly embedded in
them. It is found that the isotropic-nematic (IN) transition is shifted to
higher pressures for rougher walls.Comment: 4 pages, 4 figures Accepted in Chemical Physics Letter
Irrigation management for double-cropped fresh-market tomatoes on a high-water-table soil
Two tomato (Lycopersicon esculentum, Mill.)
experiments were conducted for two years on a southeastern
Coastal Plain soil that has a high, fluctuating water
table. In one experiment, two methods for managing
microirrigation were compared to a treatment that received
only rainfall by measuring marketable fruit yields for
spring and fall cropping seasons. Irrigation increased yields
for both seasons in the second year because of low rainfall.
Measurements among seven shallow wells on the site
showed no consistent differences for either water table
depth or gradient between adjacent wells. Two cultivars
were evaluated in the second year, primarily because frost
severely damaged the tomato plants about three weeks
after transplanting. In the second experiment, two
excessively irrigated treatments were evaluated in an effort
to induce a "soft-fruit" storage and shipping problem
experienced by many growers in this region. Although
extremely large quantities of irrigation water were applied,
these symptoms were not observed in this study. There
were no differences in fruit yield between the two water
management treatments in either spring or fall. Fruit
quality measurements showed no significant differences.
The 'Sunny' cultivar performed better than 'Walter' during
the fall season for the extremely wet soil condition. A
double-crop, microirrigation management system has
higher input costs but provides increased profitability for
fresh-market tomato production, particularly where
markets are available for both spring and fall crops
Experiences with microirrigation for agronomic crops in the southeastern USA
Microirrigation offers several advantages over sprinkler irrigation in humid areas, including
ease of automation; lower water pressure and flow rate; improved management of water and
nutrients; and easy seasonal start-up, especially for subsurface placement. Microirrigation
system cost could be reduced and made more profitable for agronomic crops by using wider
spacing and subsurface placement of microirrigation laterals. Results are reviewed from five
experiments involving microirrigation of agronomic crops (corn, soybean, and cotton) and
including 14 site-years of data. Agronomic crops can be effectively and efficiently irrigated
in the southeastern Coastal Plain with microirrigation systems. In three experiments involving
nine site-years of data, both normal (0.76 - 1.0 m) and wide (1.5 - 2.0 m) lateral spacings
were used to irrigate corn and cotton; yields were equal except in one year when corn yield
was reduced by about 10% for the wide spacing. With corn, there was no yield difference
between surface and subsurface placement of laterals at the normal spacing (every row).
Other data indicate that wider spacing of laterals in subsurface installations produces cotton
lint yields similar to those for the same spacing in surface placements. Consequently, it
appears that surface or subsurface placement of laterals at wider spacings (alternate furrow,
1.5 - 2.0 m) has significant potential for profitable irrigation of agronomic crops such as corn,
cotton, and soybean in the southeastern USA
Surface tension of the isotropic-nematic interface
We present the first calculations of the pressure tensor profile in the
vicinity of the planar interface between isotropic liquid and nematic liquid
crystal, using Onsager's density functional theory and computer simulation.
When the liquid crystal director is aligned parallel to the interface, the
situation of lowest free energy, there is a large tension on the nematic side
of the interface and a small compressive region on the isotropic side. By
contrast, for perpendicular alignment, the tension is on the isotropic side.
There is excellent agreement between theory and simulation both in the forms of
the pressure tensor profiles, and the values of the surface tension.Comment: Minor changes; to appear in Phys. Rev.
Clustering transitions in vibro-fluidized magnetized granular materials
We study the effects of long range interactions on the phases observed in
cohesive granular materials. At high vibration amplitudes, a gas of magnetized
particles is observed with velocity distributions similar to non-magnetized
particles. Below a transition temperature compact clusters are observed to form
and coexist with single particles. The cluster growth rate is consistent with a
classical nucleation process. However, the temperature of the particles in the
clusters is significantly lower than the surrounding gas, indicating a
breakdown of equipartition. If the system is quenched to low temperatures, a
meta-stable network of connected chains self-assemble due to the anisotropic
nature of magnetic interactions between particles.Comment: 4 pages, 5 figure
Phylogeny of snakes (Serpentes): combining morphological and molecular data in likelihood Bayesian and parsimony analyses
Copyright © 2007 The Natural history MuseumThe phylogeny of living and fossil snakes is assessed using likelihood and parsimony approaches and a dataset combining 263 morphological characters with mitochondrial (2693 bp) and nuclear (1092 bp) gene sequences. The ‘no common mechanism’ (NCMr) and ‘Markovian’ (Mkv) models were employed for the morphological partition in likelihood analyses; likelihood scores in the NCMr model were more closely correlated with parsimony tree lengths. Both models accorded relatively less weight to the molecular data than did parsimony, with the effect being milder in the NCMr model. Partitioned branch and likelihood support values indicate that the mtDNA and nuclear gene partitions agree more closely with each other than with morphology. Despite differences between data partitions in phylogenetic signal, analytic models, and relative weighting, the parsimony and likelihood analyses all retrieved the following widely accepted groups: scolecophidians, alethinophidians, cylindrophiines, macrostomatans (sensu lato) and caenophidians. Anilius alone emerged as the most basal alethinophidian; the combined analyses resulted in a novel and stable position of uropeltines and cylindrophiines as the second-most basal clade of alethinophidians. The limbed marine pachyophiids, along with Dinilysia and Wonambi, were always basal to all living snakes. Other results stable in all combined analyses include: Xenopeltis and Loxocemus were sister taxa (fide morphology) but clustered with pythonines (fide molecules), and Ungaliophis clustered with a boine-erycine clade (fide molecules). Tropidophis remains enigmatic; it emerges as a basal alethinophidian in the parsimony analyses (fide molecules) but a derived form in the likelihood analyses (fide morphology), largely due to the different relative weighting accorded to data partitions.Michael S. Y. Lee, Andrew F. Hugall, Robin Lawson & John D. Scanlo
Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET
The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR
Relationship of edge localized mode burst times with divertor flux loop signal phase in JET
A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM
All-sky search for long-duration gravitational wave transients with initial LIGO
We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society
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