2,372 research outputs found
Fluctuations and Non-Hermiticity in the Stochastic Approach to Quantum Spins
We investigate the non-equilibrium dynamics of isolated quantum spin systems
via an exact mapping to classical stochastic differential equations. We show
that one can address significantly larger system sizes than recently obtained,
including two-dimensional systems with up to 49 spins. We demonstrate that the
results for physical observables are in excellent agreement with exact results
and alternative numerical techniques where available. We further develop a
hybrid stochastic approach involving matrix product states. In the presence of
finite numerical sampling, we show that the non-Hermitian character of the
stochastic representation leads to the growth of the norm of the time-evolving
quantum state and to departures for physical observables at late times. We
demonstrate approaches that correct for this and discuss the prospects for
further development.Comment: 5 pages, 4 figures, Supplementary Materia
Trajectory-Resolved Weiss Fields for Quantum Spin Dynamics
We explore the dynamics of quantum spin systems in two and three dimensions
using an exact mapping to classical stochastic processes. In recent work we
explored the effectiveness of sampling around the mean field evolution as
determined by a stochastically averaged Weiss field. Here, we show that this
approach can be significantly extended by sampling around the instantaneous
Weiss field associated with each stochastic trajectory taken separately. This
trajectory-resolved approach incorporates sample to sample fluctuations and
allows for longer simulation times. We demonstrate the utility of this approach
for quenches in the two-dimensional and three-dimensional quantum Ising model.
We show that the method is particularly advantageous in situations where the
average Weiss-field vanishes, but the trajectory-resolved Weiss fields are
non-zero. We discuss the connection to the gauge-P phase space approach, where
the trajectory-resolved Weiss field can be interpreted as a gauge degree of
freedom.Comment: 11 pages, 7 figure
Use of ERTS-1 data in identification, classification, and mapping of salt-affected soils in California
There are no author-identified significant results in this report
Stress patterns around distal angled implants in the all-on-four concept configuration
nonePurpose: The All-on-Four concept advocates immediate loading and the placement of distal implants
at an angle. The purpose of this study was to do a qualitative descriptive analysis of stress patterns
around the distal angled implant of the All-on-Four concept. Materials and Methods: Four photoelastic
acrylic resin models, each with four implants simulating the All-on-Four configuration, were prepared.
The two central implants were placed vertically and parallel in each model, and the distal implant on
each side was placed at an increasing angle (0, 15, 30, and 45 degrees) in each model. The four
implants were splinted by means of a cast metal bar. The photoelastic models were placed between
two parallel anvils. Pairs of abutments were systematically subjected to a load by suspending 5-, 10-,
and 15-kg weights from one of the anvils. Photoelastic analysis was accomplished using a circular
polariscope. The fringe patterns produced in the photoelastic resin for each implant and load were
photographed with a digital camera. Fringe concentrations and the highest fringe order were recorded
and described for the apical, central, and coronal regions of the distal angled implant for each load
scenario. Results: For the implants placed at 15- and 30-degree angles, little difference in stress patterns
was observed between the central straight implant and the distal angled implant. For every load
scenario and for all angulations, the lowest fringe order was recorded at the central region of the
implant. The highest fringe order for the apical region was always higher than the highest fringe order
for the coronal region of the implant. Markedly increased isochromatic fringe concentrations were
observed in model 4, which had the distal implants placed at a 45-degree angle. Conclusion: Periimplant
bone surrounding the 45-degree-angled distal abutment may be more prone to occlusal overload
than bone surrounding implants with lesser tilts.non
The Waipounamu Erosion Surface: questioning the antiquity of the New Zealand land surface and terrestrial fauna and flora
The Waipounamu Erosion Surface is a time-transgressive, nearly planar, wave-cut surface. It is not a peneplain. Formation of the Waipounamu Erosion Surface began in Late Cretaceous time following break-up of Gondwanaland, and continued until earliest Miocene time, during a 60 million year period of widespread tectonic quiescence, thermal subsidence and marine transgression. Sedimentary facies and geomorphological evidence suggest that the erosion surface may have eventually covered the New Zealand subcontinent (Zealandia). We can find no geological evidence to indicate that land areas were continuously present throughout the middle Cenozoic. Important implications of this conclusion are: (1) the New Zealand subcontinent was largely, or entirely, submerged and (2) New Zealand's present terrestrial fauna and flora evolved largely from fortuitous arrivals during the past 22 million years. Thus the modern terrestrial biota may not be descended from archaic ancestors residing on Zealandia when it broke away from Gondwanaland in the Cretaceous, since the terrestrial biota would have been extinguished if this landmass was submerged in Oligocene–Early Miocene time. We conclude that there is insufficient geological basis for assuming that land was continuously present in the New Zealand region through Oligocene to Early Miocene time, and we therefore contemplate the alternative possibility, complete submergence of Zealandia
EFFECTS OF STATIC STRETCHING ON MAXIMAL ISOKINETIC TORQUE
The effects of 20 seconds of agonist (AGO), antagonist (ANT) or no (NO) pre-exercise stretch on concentric (CON) and eccentric (ECC) maximal isokinetic torque produced at the knee were examined. Twelve male semi-pro rugby players performed dominant isokinetic knee extension following the specified stretch protocol. One-way Repeated Measures ANOVA revealed AGO to be significantly less (p < 0.05) than the other protocols for both CON (270 28 Nm) and ECC (309 42 Nm) torque. There was no difference between the ANT or NO for either CON (303 35 Nm and 304 38 Nm, respectively) or ECC (341 40 Nm and 33644 Nm). The results support the theory that pre-exercise agonist stretching may lead to performance decrements in maximal concentric torque production
Reproducibility of measurements of potential doubling time of tumour cells in the multicentre National Cancer Institute protocol T92-0045
We compared the flow cytometric measurement and analysis of the potential doubling time (Tpot) between three centres involved in the National Cancer Institute (NCI) protocol T92-0045. The primary purpose was to understand and minimize the variation within the measurement. A total of 102 specimens were selected at random from patients entered into the trial. Samples were prepared, stained, run and analysed in each centre and a single set of data analysed by all three centres. Analysis of the disc data set revealed that the measurement of labelling index (LI) was robust and reproducible. The estimation of duration of S-phase (Ts) was subject to errors of profile interpretation, particularly DNA ploidy status, and analysis. The LI dominated the variation in Tpot such that the level of final agreement, after removal of outliers and ploidy agreement, reached correlation coefficients of 0.9. The sample data showed poor agreement within each of the components of the measurement. There was some improvement when ploidy was in agreement, but correlation coefficients failed to exceed values of 0.5 for Tpot. The data suggest that observer-associated analysis of Ts and tissue processing and tumour heterogeneity were the major causes of variability in the Tpot measurement. The first two aspects can be standardized and minimized, but heterogeneity will remain a problem with biopsy techniques. © 1999 Cancer Research Campaig
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