754 research outputs found
Internuclear gene silencing in Phytophthora infestans is established through chromatin remodelling
In the plant pathogen Phytophthora infestans, nuclear integration of inf1 transgenic DNA sequences results in internuclear gene silencing of inf1. Although silencing is regulated at the transcriptional level, it also affects transcription from other nuclei within heterokaryotic cells of the mycelium. Here we report experiments exploring the mechanism of internuclear gene silencing in P. infestans. The DNA methylation inhibitor 5-azacytidine induced reversion of the inf1-silenced state. Also, the histone deacetylase inhibitor trichostatin-A was able to reverse inf1 silencing. inf1-expression levels returned to the silenced state when the inhibitors were removed except in non-transgenic inf1-silenced strains that were generated via internuclear gene silencing, where inf1 expression was restored permanently. Therefore, inf1-transgenic sequences are required to maintain the silenced state. Prolonged culture of non-transgenic inf1-silenced strains resulted in gradual reactivation of inf1 gene expression. Nuclease digestion of inf1-silenced and non-silenced nuclei showed that inf1 sequences in silenced nuclei were less rapidly degraded than non-silenced inf1 sequences. Bisulfite sequencing of the endogenous inf1 locus did not result in detection of any cytosine methylation. Our findings suggest that the inf1-silenced state is based on chromatin remodelling
Development of a novel 3D simulation modelling system for distributed manufacturing
This paper describes a novel 3D simulation modelling system for supporting our distributed machine design and control paradigm with respect to simulating and emulating machine behaviour on the Internet. The system has been designed and implemented using Java2D and Java3D. An easy assembly concept of drag-and-drop assembly has been realised and implemented by the introduction of new connection features (unified interface assembly features) between two assembly components (modules). The system comprises a hierarchical geometric modeller, a behavioural editor, and two assemblers. During modelling, designers can combine basic modelling primitives with general extrusions and integrate CAD geometric models into simulation models. Each simulation component (module) model can be visualised and animated in VRML browsers.
It is reusable. This makes machine design re-configurable and flexible. A case study example is given to support our conclusions
Constrained generalized supersymmetries and superparticles with tensorial central charges. A classification
We classify the admissible types of constraint (hermitian, holomorphic, with
reality conditions on the bosonic sectors, etc.) for generalized
supersymmetries in the presence of complex spinors. We further point out which
constrained generalized supersymmetries admit a dual formulation. For both real
and complex spinors generalized supersymmetries are constructed and classified
as dimensional reductions of supersymmetries from {\em oxidized} space-times
(i.e. the maximal space-times associated to -component Clifford irreps). We
apply these results to sistematically construct a class of models describing
superparticles in presence of bosonic tensorial central charges, deriving the
consistency conditions for the existence of the action, as well as the
constrained equations of motion. Examples of these models (which, in their
twistorial formulation, describe towers of higher-spin particles) were first
introduced by Rudychev and Sezgin (for real spinors) and later by Bandos and
Lukierski (for complex spinors).Comment: 32 pages, LaTe
Tentacle probes: eliminating false positives without sacrificing sensitivity
The majority of efforts to increase specificity or sensitivity in biosensors result in trade-offs with little to no gain in overall accuracy. This is because a biosensor cannot be more accurate than the affinity interaction it is based on. Accordingly, we have developed a new class of reagents based on mathematical principles of cooperativity to enhance the accuracy of the affinity interaction. Tentacle probes (TPs) have a hairpin structure similar to molecular beacons (MBs) for enhanced specificity, but are modified by the addition of a capture probe for increased kinetics and affinity. They produce kinetic rate constants up to 200-fold faster than MB with corresponding stem strengths. Concentration-independent specificity was observed with no false positives at up to 1 mM concentrations of variant analyte. In contrast, MBs were concentration dependent and experienced false positives above 3.88 μM of variant analyte. The fast kinetics of this label-free reagent may prove important for extraction efficiency, hence sensitivity and detection time, in microfluidic assays. The concentration-independent specificity of TPs may prove extremely useful in assays where starting concentrations and purities are unknown as would be the case in bioterror or clinical point of care diagnostics
The Effect of Knee Angle on Force Production, in Swimming Starts, using the OSB11 Block
AbstractWork presented in this paper discusses the effect of knee angle, during the block phase of the start, on overall start performance using the Omega OSB11 block. Omega claims that the footrest enables the athlete to push-off with a rear knee angle of 90°, which is beneficial to starting performance. Published work to date supports the positive effect of starting performance using the footrest, compared to blocks without a footrest, however, reference is not specifically made to the knee angle of the athlete beyond set-up. Ten male, national-level, sprint swimmers were asked to perform maximal start trials using three different footrest configurations. Force and video data were collected for each trial at a rate of 125Hz. Analysis of the data focused on the effect of knee angle at set-up, on horizontal and vertical peak forces. For these data the best starts produced a peak vertical force at a rear knee angle of 80°-90°. More interestingly, this study suggests that, for the best starts, peak horizontal force production occurred with an obtuse knee angle of 100°-110°
New insulating phases of two-dimensional electrons in high Landau levels: observation of sharp thresholds to conduction
The intriguing re-entrant integer quantized Hall states recently discovered
in high Landau levels of high-mobility 2D electron systems are found to exhibit
extremely non-linear transport. At small currents these states reflect
insulating behavior of the electrons in the uppermost Landau level. At larger
currents, however, a discontinuous and hysteretic transition to a conducting
state is observed. These phenomena, found only in very narrow magnetic field
ranges, are suggestive of the depinning of a charge density wave state, but
other explanations can also be constructed.Comment: 5 pages, 5 figure
A framework of web-based conceptual design
A web-based conceptual design prototype system is presented. The system consists of four parts which interpret on-line sketches as 2D and 3D geometry, extract 3D hierarchical configurations, allow editing of component behaviours, and produce VRML-based behavioural simulations for design verification and web-based application. In the first part, on-line freehand sketched input is interpreted as 2D and 3D geometry, which geometrically represents conceptual design. The system then infers 3D configuration by analysing 3D modelling history. The configuration is described by a parent–child hierarchical relationship and relative positions between two geometric components. The positioning information is computed with respect to the VRML97 specification. In order to verify the conceptual design of a product, the behaviours can be specified interactively on different components. Finally, the system creates VRML97 formatted files for behavioural simulation and collaborative design application over the Internet. The paper gives examples of web-based applications. This work forms a part of a research project into the design and establishing of modular machines for automation manufacture. A consortium of leading automotive companies is collaborating on the research project
Supersymmetric Euler-Heisenberg effective action: Two-loop results
The two-loop Euler-Heisenberg-type effective action for N = 1 supersymmetric
QED is computed within the background field approach. The background vector
multiplet is chosen to obey the constraints D_\a W_\b = D_{(\a} W_{\b)} =
const, but is otherwise completely arbitrary. Technically, this calculation
proves to be much more laborious as compared with that carried out in
hep-th/0308136 for N = 2 supersymmetric QED, due to a lesser amount of
supersymmetry. Similarly to Ritus' analysis for spinor and scalar QED, the
two-loop renormalisation is carried out using proper-time cut-off
regularisation. A closed-form expression is obtained for the holomorphic sector
of the two-loop effective action, which is singled out by imposing a relaxed
super self-duality condition.Comment: 27 pages, 2 eps figures, LaTeX; V2: typos corrected, comments and
reference adde
Curvature corrections and Kac-Moody compatibility conditions
We study possible restrictions on the structure of curvature corrections to
gravitational theories in the context of their corresponding Kac--Moody
algebras, following the initial work on E10 in Class. Quant. Grav. 22 (2005)
2849. We first emphasize that the leading quantum corrections of M-theory can
be naturally interpreted in terms of (non-gravity) fundamental weights of E10.
We then heuristically explore the extent to which this remark can be
generalized to all over-extended algebras by determining which curvature
corrections are compatible with their weight structure, and by comparing these
curvature terms with known results on the quantum corrections for the
corresponding gravitational theories.Comment: 27 page
Geometric Dequantization
Dequantization is a set of rules which turn quantum mechanics (QM) into
classical mechanics (CM). It is not the WKB limit of QM. In this paper we show
that, by extending time to a 3-dimensional "supertime", we can dequantize the
system in the sense of turning the Feynman path integral version of QM into the
functional counterpart of the Koopman-von Neumann operatorial approach to CM.
Somehow this procedure is the inverse of geometric quantization and we present
it in three different polarizations: the Schroedinger, the momentum and the
coherent states ones.Comment: 50+1 pages, Late
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