9,324 research outputs found
Boundary versus bulk behavior of time-dependent correlation functions in one-dimensional quantum systems
We study the influence of reflective boundaries on time-dependent responses
of one-dimensional quantum fluids at zero temperature beyond the low-energy
approximation. Our analysis is based on an extension of effective mobile
impurity models for nonlinear Luttinger liquids to the case of open boundary
conditions. For integrable models, we show that boundary autocorrelations
oscillate as a function of time with the same frequency as the corresponding
bulk autocorrelations. This frequency can be identified as the band edge of
elementary excitations. The amplitude of the oscillations decays as a power law
with distinct exponents at the boundary and in the bulk, but boundary and bulk
exponents are determined by the same coupling constant in the mobile impurity
model. For nonintegrable models, we argue that the power-law decay of the
oscillations is generic for autocorrelations in the bulk, but turns into an
exponential decay at the boundary. Moreover, there is in general a nonuniversal
shift of the boundary frequency in comparison with the band edge of bulk
excitations. The predictions of our effective field theory are compared with
numerical results obtained by time-dependent density matrix renormalization
group (tDMRG) for both integrable and nonintegrable critical spin- chains
with , and .Comment: 20 pages, 12 figure
Influence of shear stress applied during flow stoppage and rest period on the mechanical properties of thixotropic suspensions
We study the solid mechanical properties of several thixotropic suspensions
as a function of the shear stress history applied during their flow stoppage
and their aging in their solid state. We show that their elastic modulus and
yield stress depend strongly on the shear stress applied during their
solid-liquid transition (i.e., during flow stoppage) while applying the same
stress only before or only after this transition may induce only second-order
effects: there is negligible dependence of the mechanical properties on the
preshear history and on the shear stress applied at rest. We also found that
the suspensions age with a structuration rate that hardly depends on the stress
history. We propose a physical sketch based on the freezing of a microstructure
whose anisotropy depends on the stress applied during the liquid-solid
transition to explain why the mechanical properties depend strongly on this
stress. This sketch points out the role of the internal forces in the colloidal
suspensions' behavior. We finally discuss briefly the macroscopic consequences
of this phenomenon and show the importance of using a controlled-stress
rheometer
Sub-surface damage issues for effective fabrication of large optics
A new ultra precision large optics grinding machine, BoX®has been developed at
Cranfield University. BoX®islocated at the UK's Ultra Precision Surfaces
laboratory at the OpTIC Technium. This machine offers a rapidand economic
solution for grinding large off-axis aspherical and free-form optical
components.This paper presents an analysis of subsurface damage assessments of
optical ground materials produced usingdiamond resin bonded grinding wheels. The
specific materials used, Zerodur®and ULE®are currently understudy for making
extremely large telescope (ELT) segmented mirrors such as in the E-ELT
project.The grinding experiments have been conducted on the BoX®grinding machine
using wheels with grits sizes of76 μm, 46 μm and 25 μm. Grinding process data
was collected using a Kistler dynamometer platform. Thehighest material removal
rate (187.5 mm3/s) used ensures that a 1 metre diameter optic can be ground in
lessthan 10 hours. The surface roughness and surface profile were measured using
a Form Talysurf. The subsurfacedamage was revealed using a sub aperture
polishing process in combination with an etching technique.These results are
compared with the targeted form accuracy of 1 μm p-v over a 1 metre part,
surface roughnessof 50-150 nm RMS and subsurface damage in the range of 2-5 μm.
This process stage was validated on a 400mm ULE®blank and a 1 metre hexagonal Z
Variabilidade genética entre acessos de amendoim.
O objetivo deste trabalho foi avaliar a variabilidade genética entre 29 acessos de amendoim (Arachis hypogaea L.), por meio de marcadores moleculares randômicos (DNA polimórfico amplificado ao acaso - RAPD). O ensaio molecular foi realizado com 31 iniciadores, dos quais 12 (39%) mostraram polimorfismo. Observou-se o total de 145 fragmentos amplificados, dos quais 35 (24%) foram polimórficos, com média de 4,67 fragmentos por iniciador e 1,13 fragmento polimórfico por iniciador. Pelo dendrograma, observou-se que os acessos foram separados em dois grupos com 89% de similaridade. Esta distribuição mostra a variabilidade existente entre os acessos das diferentes variedades botânicas, uma vez que acessos da subespécie fastigiata estão presentes nos dois grupos principais, e os acessos da subespécie hypogaea estão distribuídos pelos subgrupos A e B do grupo II do dendograma. The objective of this study was to evaluate the genetic variability among 29 accessions of peanut (Arachis hypogaea L.) by means of random molecular markers (random amplified polimorphic DNA - RAPD). The molecular assay was performed with 31 primers, of which 12 (39%) revealed polymorphism. It was observed a total of 145 amplified fragments, of which 35 (24%) were polymorphic, with an average of 4.67 fragments by primer and 1.13 polymorphic fragment by primer. It was observed through the dendrogram that the accessions were separated into two groups with 89% of similarity. This distribution shows the variability among the accessions of the different botanical varieties, since the accessions of subspecie fastigiata are present in two principal groups, and the accessions of subspecie hypogaea are distributed in subgroups A and B from dendrogram group II
Three Dimensional (3D) Reconstruction of Subterranean Clover
Three dimensional (3D) plant reconstructions, extended to four dimensions with the use of time series and accompanied by visual modelling, is being used for a number of purposes including the estimation of biovolume and as the basis for functional structural plant modelling (FSPM). This has been successfully applied to crop species such as cotton (Paproki et al. 2012). Measuring the growth pattern and arrangement of a pasture sward is a difficult task but can be used as an indirect measure of other variables of interest, such as growth rate, light interception, nutritional quality, herbivore intake, etc. (Laca and Lemaire 2000). Digital representation of individual plants in three dimensions is one way to determine sward structure. The High Resolution Plant Phenomics Centre (HRPPC) has developed PlantScan™ which combines robotics, image analysis and computing advances, to accelerate and automate the measurement of plant growth characteristics and allow discrimination of differences between individual plants within species. Image silhouettes and LiDAR (Light Detection And Ranging) are used and combined to digitise plant architecture in three dimensions with a high level of detail. Colour information, extracted from multispectral sensors, and thermal imaging from infra-red (IR) cameras are then overlaid on these 3D plant representations, thus providing a tool to link plant structure to plant function. Successful reconstructions using data collected by PlantScan™ in controlled conditions, have been conducted for a range of grasses such as wheat (Triticum aestivum), rice (Oryza sativa), corn (Zea mays) and broadleaf species such as canola (Brassica napus), cotton (Gossypium hirsutum) and tobacco (Nicotiana tabacum). This suggests that modelling the sward structure of grass and legume pasture species should be equally achievable. This study explores the use of PlantScanTM to reconstruct 3D images of the important and common pasture legume, subterranean clover (Trifolium subterraneum) with a view to analysing their 3D structure in-silico
The Trajectory Synthesizer Generalized Profile Interface
The Trajectory Synthesizer is a software program that generates aircraft predictions for Air Traffic Management decision support tools. The Trajectory Synthesizer being used by researchers at NASA Ames Research Center was restricted in the number of trajectory types that could be generated. This limitation was not sufficient to support the rapidly changing Air Traffic Management research requirements. The Generalized Profile Interface was developed to address this issue. It provides a flexible approach to describe the constraints applied to trajectory generation and may provide a method for interoperability between trajectory generators. It also supports the request and generation of new types of trajectory profiles not possible with the previous interface to the Trajectory Synthesizer. Other enhancements allow the Trajectory Synthesizer to meet the current and future needs of Air Traffic Management research
Upwelling regime off the Cabo Frio region in Brazil and impact on acoustic propagation
This work introduces a description of the complex upwelling regime off the Cabo Frio region in Brazil and shows that ocean modeling, based on the feature-oriented regional modeling system (FORMS) technique, can produce reliable predictions of sound speed fields for the corresponding shallow water environment. This work also shows, through the development of simulations, that the upwelling regime can be responsible for the creation of shadow coastal zones, in which the detection probability is too low for an acoustic source to be detected. The development of the FORMS technique and its validation with real data, for the particular region of coastal upwelling off Cabo Frio, reveals the possibility of a sustainable and reliable forecast system for the corresponding (variable in space and time) underwater acoustic environment. (C) 2018 Acoustical Society of AmericaBrazilian Navy; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)/Ciencias Sem Fronteiras [400671/2014-0]; European Union [OAEX-230855]; Fundacao de Amparo a Pesquisa (FAPERJ) [E-26/110.327/2012
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