3,708 research outputs found
Pattern Reification as the Basis for Description-Driven Systems
One of the main factors driving object-oriented software development for
information systems is the requirement for systems to be tolerant to change. To
address this issue in designing systems, this paper proposes a pattern-based,
object-oriented, description-driven system (DDS) architecture as an extension
to the standard UML four-layer meta-model. A DDS architecture is proposed in
which aspects of both static and dynamic systems behavior can be captured via
descriptive models and meta-models. The proposed architecture embodies four
main elements - firstly, the adoption of a multi-layered meta-modeling
architecture and reflective meta-level architecture, secondly the
identification of four data modeling relationships that can be made explicit
such that they can be modified dynamically, thirdly the identification of five
design patterns which have emerged from practice and have proved essential in
providing reusable building blocks for data management, and fourthly the
encoding of the structural properties of the five design patterns by means of
one fundamental pattern, the Graph pattern. A practical example of this
philosophy, the CRISTAL project, is used to demonstrate the use of
description-driven data objects to handle system evolution.Comment: 20 pages, 10 figure
Modeling of Polymer Clay Nanocomposite for a Multiscale Approach
The mechanical property enhancement of polymer reinforced with nano-thin clay
platelets (of high aspect ratio) is associated with a high polymer-filler
interfacial area per unit volume. The ideal case of fully separated
(exfoliated) platelets is generally difficult to achieve in practice: a typical
nanocomposite also contains multilayer stacks of intercalated platelets. Here
we use numerical modelling to investigate how the platelet properties affect
the overall mechanical properties. The configuration of platelets is modelled
using a statistical interpretation of the Representative Volume Element (RVE)
approach, in which an ensemble of "sample" heterogeneous material is generated
(with periodic boundary conditions). A simple Monte Carlo algorithm is used to
place non-intersecting platelets in the RVE according to a specified set of
statistical distributions. The effective stiffness of the platelet-matrix
system is determined by measuring the stress (using standard Finite Element
analysis) produced as a result of applying a small deformation to the
boundaries, and averaging over the entire statistical ensemble. In this work we
determine the way in which the platelet properties (curvature, filling
fraction, stiffness, aspect ratio) and the number of layers in the stack affect
the overall stiffness enhancement of the nanocomposite. Thus, we bridge the gap
between behaviour on the macroscopic scale with that on the scale of the
nano-reinforcement, forming part of a multi-scale modelling framework.Comment: 39 pages, 19 figure
A reduced-order strategy for 4D-Var data assimilation
This paper presents a reduced-order approach for four-dimensional variational
data assimilation, based on a prior EO F analysis of a model trajectory. This
method implies two main advantages: a natural model-based definition of a mul
tivariate background error covariance matrix , and an important
decrease of the computational burden o f the method, due to the drastic
reduction of the dimension of the control space. % An illustration of the
feasibility and the effectiveness of this method is given in the academic
framework of twin experiments for a model of the equatorial Pacific ocean. It
is shown that the multivariate aspect of brings additional
information which substantially improves the identification procedure. Moreover
the computational cost can be decreased by one order of magnitude with regard
to the full-space 4D-Var method
Impact of Temporary Nitrogen Deprivation on Tomato Leaf Phenolics
Reducing the use of pesticides represents a major challenge of modern agriculture. Plants synthesize secondary metabolites such as polyphenols that participate in the resistance to parasites. The aim of this study was to test: (1) the impact of nitrogen deficiency on tomato (Solanum lycopersicum) leaf composition and more particularly on two phenolic molecules (chlorogenic acid and rutin) as well as on the general plant biomass; and (2) whether this effect continued after a return to normal nitrogen nutrition. Our results showed that plants deprived of nitrogen for 10 or 19 days contained higher levels of chlorogenic acid and rutin than control plants. In addition, this difference persisted when the plants were once again cultivated on a nitrogen-rich medium. These findings offer interesting perspectives on the use of a short period of deprivation to modulate the levels of compounds of interest in a plant
Influence of apical oxygen on the extent of in-plane exchange interaction in cuprate superconductors
In high Tc superconductors the magnetic and electronic properties are
determined by the probability that valence electrons virtually jump from site
to site in the CuO2 planes, a mechanism opposed by on-site Coulomb repulsion
and favored by hopping integrals. The spatial extent of the latter is related
to transport properties, including superconductivity, and to the dispersion
relation of spin excitations (magnons). Here, for three antiferromagnetic
parent compounds (single-layer Bi2Sr0.99La1.1CuO6+delta, double-layer
Nd1.2Ba1.8Cu3O6 and infinite-layer CaCuO2) differing by the number of apical
atoms, we compare the magnetic spectra measured by resonant inelastic x-ray
scattering over a significant portion of the reciprocal space and with
unprecedented accuracy. We observe that the absence of apical oxygens increases
the in-plane hopping range and, in CaCuO2, it leads to a genuine 3D
exchange-bond network. These results establish a corresponding relation between
the exchange interactions and the crystal structure, and provide fresh insight
into the materials dependence of the superconducting transition temperature.Comment: 9 pages, 4 figures, 1 Table, 42 reference
Cutoff Suppresses RNA Polymerase II Termination to Ensure Expression of piRNA Precursors
Small non-coding RNAs called piRNAs serve as guides for an adaptable immune system that represses transposable elements in germ cells of Metazoa. In Drosophila the RDC complex, composed of Rhino, Deadlock and Cutoff (Cuff) bind chromatin of dual-strand piRNA clusters, special genomic regions, which encode piRNA precursors. The RDC complex is required for transcription of piRNA precursors, though the mechanism by which it licenses transcription remained unknown. Here, we show that Cuff prevents premature termination of RNA polymerase II. Cuff prevents cleavage of nascent RNA at poly(A) sites by interfering with recruitment of the cleavage and polyadenylation specificity factor (CPSF) complex. Cuff also protects processed transcripts from degradation by the exonuclease Rat1. Our work reveals a conceptually different mechanism of transcriptional enhancement. In contrast to other factors that regulate termination by binding to specific signals on nascent RNA, the RDC complex inhibits termination in a chromatin-dependent and sequence-independent manner
On the universality of density profiles
We use the secondary infall model described in Del Popolo (2009), which takes
into account the effect of dynamical friction, ordered and random angular
momentum, baryons adiabatic contraction and dark matter baryons interplay, to
study how in- ner slopes of relaxed LCDM dark matter (DM) halos with and
without baryons (baryons+DM, and pure DM) depend on redshift and on halo mass.
We apply the quoted method to structures on galactic scales and clusters of
galaxies scales. We find that the inner logarithmic density slope, of dark
matter halos with baryons has a significant dependence on halo mass and
redshift with slopes ranging from 0 for dwarf galaxies to 0.4 for objects of M
= 10^13M_solar and 0.94 for M = 10^15M_solar clusters of galaxies. Structures
slopes increase with increasing redshift and this trend reduces going from
galaxies to clusters. In the case of density profiles constituted just of dark
matter the mass and redshift dependence of slope is very slight. In this last
case, we used the Merrit et al. (2006) analysis who compared N-body density
profiles with various parametric models finding systematic variation in profile
shape with halo mass. This last analysis suggests that the galaxy-sized halos
obtained with our model have a different shape parameter, i.e. a different mass
distribution, than the cluster-sized halos, obtained with the same model. The
results of the present paper argue against universality of density profiles
constituted by dark matter and baryons and confirm claims of a systematic
variation in profile shape with halo mass, for dark matter halos.Comment: 11 pages, 5 figure
Vehicle localization by lidar point correlation improved by change detection
LiDAR sensors are proven sensors for accurate vehicle localization. Instead of detecting and matching features in the LiDAR data, we want to use the entire information provided by the scanners. As dynamic objects, like cars, pedestrians or even construction sites could lead to wrong localization results, we use a change detection algorithm to detect these objects in the reference data. If an object occurs in a certain number of measurements at the same position, we mark it and every containing point as static. In the next step, we merge the data of the single measurement epochs to one reference dataset, whereby we only use static points. Further, we also use a classification algorithm to detect trees. For the online localization of the vehicle, we use simulated data of a vertical aligned automotive LiDAR sensor. As we only want to use static objects in this case as well, we use a random forest classifier to detect dynamic scan points online. Since the automotive data is derived from the LiDAR Mobile Mapping System, we are able to use the labelled objects from the reference data generation step to create the training data and further to detect dynamic objects online. The localization then can be done by a point to image correlation method using only static objects. We achieved a localization standard deviation of about 5 cm (position) and 0.06° (heading), and were able to successfully localize the vehicle in about 93 % of the cases along a trajectory of 13 km in Hannover, Germany
Deciphering magnetospheric crossâfield currents
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94998/1/grl28658.pd
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