7,401 research outputs found
The Kepler problem and non commutativity
We investigate the Kepler problem using a symplectic structure consistent
with the commutation rules of the noncommutative quantum mechanics. We show
that a noncommutative parameter of the order of gives
observable corrections to the movement of the solar system. In this way,
modifications in the physics of smaller scales implies modifications at large
scales, something similar to the UV/IR mixing.Comment: 10 page
Delayed Scattering of Solitary Waves from Interfaces in a Granular Container
In granular media, the characterization of the behavior of solitary waves
around interfaces is of importance in order to look for more applications of
these systems. We study the behavior of solitary waves at both interfaces of a
symmetric granular container, a class of systems that has received recent
attention because it posses the feature of energy trapping. Hertzian contact is
assumed. We have found that the scattering process is elastic at one interface,
while at the other interface it is observed that the transmitted solitary wave
has stopped its movement during a time that gets longer when the ratio between
masses at the interfaces increases. The origin of this effect can be traced
back to the phenomenon of gaps opening, recently observed experimentally.Comment: To appear in Physical Review E, vol 7
Optically probing symmetry breaking in the chiral magnet Cu2OSeO3
We report on the linear optical properties of the chiral magnet Cu2OSeO3,
specifically associated with the absence of inversion symmetry, the chiral
crystallographic structure, and magnetic order. Through spectroscopic
ellipsometry, we observe local crystal-field excitations below the
charge-transfer gap. These crystal-field excitations are optically allowed due
to the lack of inversion symmetry at the Cu sites. Optical polarization
rotation measurements were used to study the structural chirality and magnetic
order. The temperature dependence of the natural optical rotation, originating
in the chiral crystal structure, provides evidence for a finite
magneto-electric effect in the helimagnetic phase. We find a large
magneto-optical susceptibility on the order of V(540nm)~10^4 rad/(T*m) in the
helimagnetic phase and a maximum Faraday rotation of ~165deg/mm in the
ferrimagnetic phase. The large value of V can be explained by considering spin
cluster formation and the relative ease of domain reorientation in this
metamagnetic material. The magneto-optical activity allows us to map the
magnetic phase diagram, including the skyrmion lattice phase. In addition to
this, we probe and discuss the nature of the various magnetic phase transitions
in Cu2OSeO3.Comment: 9 pages, 10 figure
Feature selection for chemical sensor arrays using mutual information
We address the problem of feature selection for classifying a diverse set of chemicals using an array of metal oxide sensors. Our aim is to evaluate a filter approach to feature selection with reference to previous work, which used a wrapper approach on the same data set, and established best features and upper bounds on classification performance. We selected feature sets that exhibit the maximal mutual information with the identity of the chemicals. The selected features closely match those found to perform well in the previous study using a wrapper approach to conduct an exhaustive search of all permitted feature combinations. By comparing the classification performance of support vector machines (using features selected by mutual information) with the performance observed in the previous study, we found that while our approach does not always give the maximum possible classification performance, it always selects features that achieve classification performance approaching the optimum obtained by exhaustive search. We performed further classification using the selected feature set with some common classifiers and found that, for the selected features, Bayesian Networks gave the best performance. Finally, we compared the observed classification performances with the performance of classifiers using randomly selected features. We found that the selected features consistently outperformed randomly selected features for all tested classifiers. The mutual information filter approach is therefore a computationally efficient method for selecting near optimal features for chemical sensor arrays
The Biological Relevance of NHERF1 Protein in Gynecological Tumors
Gynecological cancer management remains challenging and a better understanding of molecular mechanisms that lead to carcinogenesis and development of these diseases is needed to improve the therapeutic approaches. The Na+/H+ exchanger regulatory factor 1 (NHERF1) is a scaffold protein that contains modular protein-interaction domains able to interact with molecules with an impact on carcinogenesis and cancer progression. During recent years, its involvement in gynecological cancers has been explored, suggesting that NHERF1 could be a potential biomarker for the development of new targeted therapies suitable to the management of these tumors. This comprehensive review provides an update on the recent study on NHERF1 activity and its pathological role in cervical and ovarian cancer, as well as on its probable involvement in the therapeutic landscape of these cancer types
Residential mobility and childhood leukemia.
AimsStudies of environmental exposures and childhood leukemia studies do not usually account for residential mobility. Yet, in addition to being a potential risk factor, mobility can induce selection bias, confounding, or measurement error in such studies. Using data collected for California Powerline Study (CAPS), we attempt to disentangle the effect of mobility.MethodsWe analyzed data from a population-based case-control study of childhood leukemia using cases who were born in California and diagnosed between 1988 and 2008 and birth certificate controls. We used stratified logistic regression, case-only analysis, and propensity-score adjustments to assess predictors of residential mobility between birth and diagnosis, and account for potential confounding due to residential mobility.ResultsChildren who moved tended to be older, lived in housing other than single-family homes, had younger mothers and fewer siblings, and were of lower socioeconomic status. Odds ratios for leukemia among non-movers living <50 meters (m) from a 200+ kilovolt line (OR: 1.62; 95% CI: 0.72-3.65) and for calculated fields ≥ 0.4 microTesla (OR: 1.71; 95% CI: 0.65-4.52) were slightly higher than previously reported overall results. Adjustments for propensity scores based on all variables predictive of mobility, including dwelling type, increased odds ratios for leukemia to 2.61 (95% CI: 1.76-3.86) for living < 50 m from a 200 + kilovolt line and to 1.98 (1.11-3.52) for calculated fields. Individual or propensity-score adjustments for all variables, except dwelling type, did not materially change the estimates of power line exposures on childhood leukemia.ConclusionThe residential mobility of childhood leukemia cases varied by several sociodemographic characteristics, but not by the distance to the nearest power line or calculated magnetic fields. Mobility appears to be an unlikely explanation for the associations observed between power lines exposure and childhood leukemia
Espondilitis tuberculosa no es una metástasis vertebral: diagnóstico diferencial y tratamiento quirúrgico. A propósito de un caso
Presentamos el caso de una paciente con dorsalgia y clÃnica neurológica de varios meses de evolución
que ante las pruebas de imagen fue erróneamente diagnosticada de metástasis vertebral sin confirmación previa
con biopsia. El deterioro progresivo neurológico y las nuevas pruebas de imagen confirmaron el diagnóstico de tuberculosis
vertebral. La paciente fue tratada mediante curetaje, desbridamiento, fusión intersomática y osteosÃntesis anterior
además del tratamiento médico. Hubo una recuperación neurológica de la función sensitiva, motora y esfinteriana
prácticamente completa al mes de la intervención. Tras 20 meses de evolución la paciente está asintomática sin
evidencia de progresión de la enfermedadWe report a patient with back pain and neurological symptoms several months of evolution to the test
image was wrongly diagnosed with spinal metastases without prior confirmation with biopsy. The progressive deterioration
of neurological and new imaging confirmed the diagnosis of spinal tuberculosis. The patient was treated by
curettage, debridement, anterior interbody fusion and internal fixation in addition to medical treatment. There neurological
recovery of sensory function, motor and sphincter almost complete month after the intervention. After 20
months of evolution, the patient is asymptomatic without evidence of disease progressio
Characterization of Sequential Collagen-Poly(Ethylene Glycol) Diacrylate Interpenetrating Networks and Initial Assessment of Their Potential for Vascular Tissue Engineering
Collagen hydrogels have been widely investigated as scaffolds for vascular tissue engineering due in part to the capacity of collagen to promote robust cell adhesion and elongation. However, collagen hydrogels display relatively low stiffness and strength, are thrombogenic, and are highly susceptible to cell-mediated contraction. In the current work, we develop and characterize a sequentially-formed interpenetrating network (IPN) that retains the benefits of collagen, but which displays enhanced mechanical stiffness and strength, improved thromboresistance, high physical stability and resistance to contraction. In this strategy, we first form a collagen hydrogel, infuse this hydrogel with poly(ethylene glycol) diacrylate (PEGDA), and subsequently crosslink the PEGDA by exposure to longwave UV light. These collagen-PEGDA IPNs allow for cell encapsulation during the fabrication process with greater than 90% cell viability via inclusion of cells within the collagen hydrogel precursor solution. Furthermore, the degree of cell spreading within the IPNs can be tuned from rounded to fully elongated by varying the time delay between the formation of the cell-laden collagen hydrogel and the formation of the PEGDA network. We also demonstrate that these collagen-PEGDA IPNs are able to support the initial stages of smooth muscle cell lineage progression by elongated human mesenchymal stems cells
The Hopf Algebra of Renormalization, Normal Coordinates and Kontsevich Deformation Quantization
Using normal coordinates in a Poincar\'e-Birkhoff-Witt basis for the Hopf
algebra of renormalization in perturbative quantum field theory, we investigate
the relation between the twisted antipode axiom in that formalism, the Birkhoff
algebraic decomposition and the universal formula of Kontsevich for quantum
deformation.Comment: 21 pages, 15 figure
- …