1,088 research outputs found
Seesaw Neutrino Mass and New U(1) Gauge Symmetry
The three electroweak doublet neutrinos of the Standard
Model may acquire small seesaw masses, using either three Majorana fermion
singlets or three Majorana fermion triplets .
It is well-known that the former accommodates the U(1) gauge symmetry . It
has also been shown some years ago that the latter supports a new
gauge symmetry. Here we study two variations of this , one for two
and one , the other for one and two . Phenomenological
consequences are discussed.Comment: 16 pages, 3 figures, LaTex, 2 eps files,text adde
Radium ion: A possible candidate for measuring atomic parity violation
Single trapped and laser cooled Radium ion as a possible candidate for
measuring the parity violation induced frequency shift has been discussed here.
Even though the technique to be used is similar to that proposed by Fortson
[1], Radium has its own advantages and disadvantages. The most attractive part
of Radium ion as compared to that of Barium ion is its mass which comes along
with added complexity of instability as well as other issues which are
discussed hereComment: Conference proceedin
Quasi-static imaged-based immersed boundary-finite element model of human left ventricle in diastole
SUMMARY:
Finite stress and strain analyses of the heart provide insight into the biomechanics of myocardial function and dysfunction. Herein, we describe progress toward dynamic patient-specific models of the left ventricle using an immersed boundary (IB) method with a finite element (FE) structural mechanics model. We use a structure-based hyperelastic strain-energy function to describe the passive mechanics of the ventricular myocardium, a realistic anatomical geometry reconstructed from clinical magnetic resonance images of a healthy human heart, and a rule-based fiber architecture. Numerical predictions of this IB/FE model are compared with results obtained by a commercial FE solver. We demonstrate that the IB/FE model yields results that are in good agreement with those of the conventional FE model under diastolic loading conditions, and the predictions of the LV model using either numerical method are shown to be consistent with previous computational and experimental data. These results are among the first to analyze the stress and strain predictions of IB models of ventricular mechanics, and they serve both to verify the IB/FE simulation framework and to validate the IB/FE model. Moreover, this work represents an important step toward using such models for fully dynamic fluid–structure interaction simulations of the heart
Chiral Models of Weak Scale Supersymmetry
I discuss supersymmetric extensions of the Standard Model containing an extra
U(1)' gauge symmetry which provide a solution to the mu-problem and at the same
time protect the proton from decaying via dimension 4 operators. Moreover, all
fields are protected by chirality and supersymmetry from acquiring high scale
masses. The additional requirements of anomaly cancellation and gauge coupling
unification imply the existence of extra matter multiplets and that several
fields participate in U(1)' symmetry breaking simultaneously. While there are
several studies addressing subsets of these requirements, this work uncovers
simultaneous solutions to all of them. It is surprising and encouraging that
extending the Minimal Supersymmetric Standard Model by a simple U(1) factor
solves its major drawbacks with respect to the non-supersymmetric Standard
Model, especially as current precision data seem to offer a hint to the
existence of its corresponding Z' boson. It is also remarkable that there are
many solutions where the U(1)' charges of the known quarks and leptons are
predicted to be identical to those E_6 motivated Z' bosons which give the best
fit to the data. I discuss the solutions to these constraints including some
phenomenological implications.Comment: 19 page
Exposure to the tsunami disaster, PTSD symptoms and increased substance use – an Internet based survey of male and female residents of Switzerland
BACKGROUND: After the tsunami disaster in the Indian Ocean basin an Internet based self-screening test was made available in order to facilitate contact with mental health services. Although primarily designed for surviving Swiss tourists as well as relatives and acquaintances of the victims, the screening instrument was open to anyone who felt psychologically affected by this disaster. The aim of this study was to evaluate the influences between self-declared increased substance use in the aftermath of the tsunami disaster, trauma exposure and current PTSD symptoms. METHODS: One section of the screening covered addiction related behavior. We analyzed the relationship between increased substance use, the level of PTSD symptoms and trauma exposure using multivariable logistic regression with substance use as the dependent variable. Included in the study were only subjects who reported being residents of Switzerland and the analyses were stratified by gender in order to control for possible socio-cultural or gender differences in the use of psychotropic substances. RESULTS: In women PTSD symptoms and degree of exposure enlarged the odds of increased alcohol, pharmaceuticals and cannabis use significantly. In men the relationship was more specific: PTSD symptoms and degree of exposure only enlarged the odds of increased pharmaceutical consumption significantly. Increases in alcohol, cannabis and tobacco use were only significantly associated with the degree of PTSD symptoms. CONCLUSION: The tsunami was associated with increased substance use. This study not only replicates earlier findings but also suggests for a gender specificity of post-traumatic substance use increase
Occlusion-aware 3D Morphable Models and an Illumination Prior for Face Image Analysis
Faces in natural images are often occluded by a variety of objects. We propose a fully automated, probabilistic and occlusion-aware 3D morphable face model adaptation framework following an analysis-by-synthesis setup. The key idea is to segment the image into regions explained by separate models. Our framework includes a 3D morphable face model, a prototype-based beard model and a simple model for occlusions and background regions. The segmentation and all the model parameters have to be inferred from the single target image. Face model adaptation and segmentation are solved jointly using an expectation-maximization-like procedure. During the E-step, we update the segmentation and in the M-step the face model parameters are updated. For face model adaptation we apply a stochastic sampling strategy based on the Metropolis-Hastings algorithm. For segmentation, we apply loopy belief propagation for inference in a Markov random field. Illumination estimation is critical for occlusion handling. Our combined segmentation and model adaptation needs a proper initialization of the illumination parameters. We propose a RANSAC-based robust illumination estimation technique. By applying this method to a large face image database we obtain a first empirical distribution of real-world illumination conditions. The obtained empirical distribution is made publicly available and can be used as prior in probabilistic frameworks, for regularization or to synthesize data for deep learning methods
Modular architecture of nucleotide-binding pockets
Recently, modularity has emerged as a general attribute of complex biological systems. This is probably because modular systems lend themselves readily to optimization via random mutation followed by natural selection. Although they are not traditionally considered to evolve by this process, biological ligands are also modular, being composed of recurring chemical fragments, and moreover they exhibit similarities reminiscent of mutations (e.g. the few atoms differentiating adenine and guanine). Many ligands are also promiscuous in the sense that they bind to many different protein folds. Here, we investigated whether ligand chemical modularity is reflected in an underlying modularity of binding sites across unrelated proteins. We chose nucleotides as paradigmatic ligands, because they can be described as composed of well-defined fragments (nucleobase, ribose and phosphates) and are quite abundant both in nature and in protein structure databases. We found that nucleotide-binding sites do indeed show a modular organization and are composed of fragment-specific protein structural motifs, which parallel the modular structure of their ligands. Through an analysis of the distribution of these motifs in different proteins and in different folds, we discuss the evolutionary implications of these findings and argue that the structural features we observed can arise both as a result of divergence from a common ancestor or convergent evolution
Can lepton flavor violating interactions explain the atmospheric neutrino problem?
We investigate whether flavor changing neutrino interactions (FCNIs) can be
sufficiently large to provide a viable solution to the atmospheric neutrino
problem. Effective operators induced by heavy boson exchange that allow for
flavor changing neutrino scattering off quarks or electrons are related by an
rotation to operators that induce anomalous tau decays. Since
violation is small for New Physics at or above the weak scale, one
can use the upper bounds on lepton flavor violating tau decays or on lepton
universality violation to put severe, model-independent bounds on the relevant
non-standard neutrino interactions. Also -induced flavor changing neutral
currents, due to heavy singlet neutrinos, are too small to be relevant for the
atmospheric neutrino anomaly. We conclude that the FCNI solution to the
atmospheric neutrino problem is ruled out.Comment: 16 pages, no figures, Late
Contributions of nitrogen deposition and forest regrowth to terrestrial carbon uptake
<p>Abstract</p> <p>Background</p> <p>The amount of reactive nitrogen deposited on land has doubled globally and become at least five-times higher in Europe, Eastern United States, and South East Asia since 1860 mostly because of increases in fertilizer production and fossil fuel burning. Because vegetation growth in the Northern Hemisphere is typically nitrogen-limited, increased nitrogen deposition could have an attenuating effect on rising atmospheric CO<sub>2 </sub>by stimulating the vegetation productivity and accumulation of carbon in biomass.</p> <p>Results</p> <p>This study shows that elevated nitrogen deposition would not significantly enhance land carbon uptake unless we consider its effects on re-growing forests. Our results suggest that nitrogen enriched land ecosystems sequestered 0.62–2.33 PgC in the 1980s and 0.75–2.21 PgC in the 1990s depending on the proportion and age of re-growing forests. During these two decades land ecosystems are estimated to have absorbed 13–41% of carbon emitted by fossil fuel burning.</p> <p>Conclusion</p> <p>Although land ecosystems and especially forests with lifted nitrogen limitations have the potential to decelerate the rise of CO<sub>2 </sub>concentrations in the atmosphere, the effect is only significant over a limited period of time. The carbon uptake associated with forest re-growth and amplified by high nitrogen deposition will decrease as soon as the forests reach maturity. Therefore, assessments relying on carbon stored on land from enhanced atmospheric nitrogen deposition to balance fossil fuel emissions may be inaccurate.</p
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