2,428 research outputs found
Next-to-leading order QCD corrections to Z boson pair production via vector-boson fusion
Vector-boson fusion processes are an important tool for the study of
electroweak symmetry breaking at hadron colliders, since they allow to
distinguish a light Higgs boson scenario from strong weak boson scattering. We
here consider the channels WW->ZZ and ZZ->ZZ as part of electroweak Z boson
pair production in association with two tagging jets. We present the
calculation of the NLO QCD corrections to the cross sections for p p -> e+ e-
mu+ mu- + 2 jets and p p -> e+ e- nu_mu nubar_mu + 2 jets via vector-boson
fusion at order alpha_s alpha^6, which is performed in the form a NLO
parton-level Monte Carlo program. The corrections to the integrated cross
sections are found to be modest, while the shapes of some kinematical
distributions change appreciably at NLO. Residual scale uncertainties typically
are at the few percent level.Comment: 12 pages, 4 figure
Realization of a semiconductor-based cavity soliton laser
The realization of a cavity soliton laser using a vertical-cavity
surface-emitting semiconductor gain structure coupled to an external cavity
with a frequency-selective element is reported. All-optical control of bistable
solitonic emission states representing small microlasers is demonstrated by
injection of an external beam. The control scheme is phase-insensitive and
hence expected to be robust for all-optical processing applications. The
motility of these structures is also demonstrated
Morphological and biochemical variation in Sea buckthorn Hippophae rhamnoides ssp. turkestanica, a multipurpose plant for fragile mountains of Pakistan
Sea buckthorn (Hippophae rhamnoides ssp. turkestanica) a member of family Elaeagnaceae, is a very important multipurpose plant in the northern areas of Pakistan. It is an ideal plant for preventing soil erosion and land reclamation, can withstand extremes of temperature ranging from −43°C to 55°C and grows well under drought conditions and variable soil pH. The fruit is rich in nutrients and medicinal compounds such as vitamins, carotene, flavonoids, essential oil, carbohydrates, organic acids, amino acids, and soluble sugars. The plants are also important as fuel wood, fencing, fodder, soil erosion control, to make soil fertile by nitrogen fixation in roots and for the purpose of shelterbelts. In order to compare various populations of Sea buckthorn for morphological and biochemical composition, ten populations from different areas of northern Pakistan were compared using plant and fruit characters. The purpose of the investigation was to identify the variable populations for different valuable characteristics to develop improved varieties for commercial cultivation and easy fruit harvesting. The comparison indicated a significant amount of variability on morphological and biochemical basis. The variability will be utilised to develop commercial varieties of the plant utilising the conventional techniques of selection and hybridisation for economic activities on degraded land of mountainous regions of Pakistan
QCD Corrections to Vector-Boson Fusion Processes in Warped Higgsless Models
We discuss the signatures of a representative Higgsless model with ideal
fermion delocalization in vector-boson fusion processes, focusing on the gold-
and silver-plated decay modes of the gauge bosons at the CERN-Large Hadron
Collider. For this purpose, we have developed a fully-flexible parton-level
Monte-Carlo program, which allows for the calculation of cross sections and
kinematic distributions within experimentally feasible selection cuts at
NLO-QCD accuracy. We find that Kaluza-Klein resonances give rise to very
distinctive distributions of the decay leptons. Similar to the Standard Model
case, within the Higgsless scenario the perturbative treatment of the
vector-boson scattering processes is under excellent control.Comment: 22 pages, 20 figure
Vector Boson Pair Production via Vector Boson Fusion at NLO QCD
NLO QCD corrections to Vector Boson Pair Production via Vector Boson Fusion
have recently been calculated and implemented in a parton-level Monte-Carlo
program with full experimental cuts. We briefly sketch the elements of the
calculation and show numerical results for the Large Hadron Collider.Comment: 6 pages, 3 figures, presented by G.Bozzi at IFAE 2007 (Napoli, April
2007) and HEP 2007 (Manchester, July 2007
Three-dimensional structure of a mutant E.coli aspartate aminotransferase with increased enzymic activity
The aspartate and tyrosine aminotransferases from Escherichia coli have 43% sequence identity and nearly identical active sites. Both are equally good enzymes for dicarboxylate substrates, but the latter transaminates aromatic amino acids 1000 times faster. In an attempt to discover the critical residues for this differential substrate specificity, the aspartate aminotransferase mutant V39L has recently been prepared. It showed improved kcal/Km values for aspartate, glutamate and tyrosine and the corresponding oxo acids, mainly due to two to ten times lower Km values. For example, the Km values of V39L (wild type) for Asp and Glu are 0.12 (1.0) and 0.85 (2.7) mM respectively. The mutant was co-crystallized with 30 mM maleate from both polyethylene glycol and ammonium sulfate. Both structures were solved and refined to R-factors of 0.22 and 0.20 at 2.85 and 2.5 Å resolution respectively. They bear strong resemblance to the closed structure of the wild type enzyme complexed with maleate. The unexpected feature is that, for the first time, the closed form was produced in crystals grown from ammonium sulfate. It is concluded that the mutation has shifted the conformational equilibrium towards the closed form, which leads to generally reduced substrate Km
Biophysically motivated efficient estimation of the spatially isotropic R*2 component from a single gradient‐recalled echo measurement
Purpose
To propose and validate an efficient method, based on a biophysically motivated signal model, for removing the orientation‐dependent part of R*2 using a single gradient‐recalled echo (GRE) measurement.
Methods
The proposed method utilized a temporal second‐order approximation of the hollow‐cylinder‐fiber model, in which the parameter describing the linear signal decay corresponded to the orientation‐independent part of R*2. The estimated parameters were compared to the classical, mono‐exponential decay model for R*2 in a sample of an ex vivo human optic chiasm (OC). The OC was measured at 16 distinct orientations relative to the external magnetic field using GRE at 7T. To show that the proposed signal model can remove the orientation dependence of R*2, it was compared to the established phenomenological method for separating R*2 into orientation‐dependent and ‐independent parts.
Results
Using the phenomenological method on the classical signal model, the well‐known separation of R*2 into orientation‐dependent and ‐independent parts was verified. For the proposed model, no significant orientation dependence in the linear signal decay parameter was observed.
Conclusions
Since the proposed second‐order model features orientation‐dependent and ‐independent components at distinct temporal orders, it can be used to remove the orientation dependence of R*2 using only a single GRE measurement
Simulating local deformations in the human cortex due to blood flow-induced changes in mechanical tissue properties: Impact on functional magnetic resonance imaging
Investigating human brain tissue is challenging due to the complexity and the manifold interactions between structures across different scales. Increasing evidence suggests that brain function and microstructural features including biomechanical features are related. More importantly, the relationship between tissue mechanics and its influence on brain imaging results remains poorly understood. As an important example, the study of the brain tissue response to blood flow could have important theoretical and experimental consequences for functional magnetic resonance imaging (fMRI) at high spatial resolutions. Computational simulations, using realistic mechanical models can predict and characterize the brain tissue behavior and give us insights into the consequent potential biases or limitations of in vivo, high-resolution fMRI. In this manuscript, we used a two dimensional biomechanical simulation of an exemplary human gyrus to investigate the relationship between mechanical tissue properties and the respective changes induced by focal blood flow changes. The model is based on the changes in the brain’s stiffness and volume due to the vasodilation evoked by neural activity. Modeling an exemplary gyrus from a brain atlas we assessed the influence of different potential mechanisms: (i) a local increase in tissue stiffness (at the level of a single anatomical layer), (ii) an increase in local volume, and (iii) a combination of both effects. Our simulation results showed considerable tissue displacement because of these temporary changes in mechanical properties. We found that the local volume increase causes more deformation and consequently higher displacement of the gyrus. These displacements introduced considerable artifacts in our simulated fMRI measurements. Our results underline the necessity to consider and characterize the tissue displacement which could be responsible for fMRI artifacts
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