49,856 research outputs found
Reparametrization invariance of B decay amplitudes and implications for new physics searches in B decays
When studying B decays within the Standard Model, it is customary to use the
unitarity of the CKM matrix in order to write the decay amplitudes in terms of
only two of the three weak phases which appear in the various diagrams.
Occasionally, it is mentioned that those two weak phases can be used in order
to describe any decay amplitude, even beyond the Standard Model. Here we point
out that, when describing a generic decay amplitude, the two weak phases can be
chosen completely at will, and we study the behavior of the decay amplitudes
under changes in the two weak phases chosen as a basis. Of course, physical
observables cannot depend on such reparametrizations. This has an impact in
discussions of the SM and in attempts to parametrize new physics effects in the
decay amplitudes. We illustrate these issues by looking at B --> psi K_S and
the isospin analysis in B --> pi pi.Comment: 16 pages, RevTe
Vortex rectification effects in films with periodic asymmetric pinning
We study the transport of vortices excited by an ac current in an Al film
with an array of nanoengineered asymmetric antidots. The vortex response to the
ac current is investigated by detailed measurements of the voltage output as a
function of ac current amplitude, magnetic field and temperature. The
measurements revealed pronounced voltage rectification effects which are mainly
characterized by the two critical depinning forces of the asymmetric potential.
The shape of the net dc voltage as a function of the excitation amplitude
indicates that our vortex ratchet behaves in a way very different from standard
overdamped models. Rather, as demonstrated by the observed output signal, the
repinning force, necessary to stop vortex motion, is considerably smaller than
the depinning force, resembling the behavior of the so-called inertia ratchets.
Calculations based on an underdamped ratchet model provide a very good fit to
the experimental data.Comment: 5 pages, 4 figure
Universal Magnetic-Field-Driven Metal-Insulator-Metal Transformations in Graphite and Bismuth
Applied magnetic field induces metal - insulator and re-entrant
insulator-metal transitions in both graphite and rhombohedral bismuth. The
corresponding transition boundaries plotted on the magnetic field - temperature
(B - T) plane nearly coincide for these semimetals and can be best described by
power laws T ~ (B - B_c)^k, where B_c is a critical field at T = 0 and k = 0.45
+/- 0.05. We show that insulator-metal-insulator (I-M-I) transformations take
place in the Landau level quantization regime and illustrate how the IMT in
quasi-3D graphite transforms into a cascade of I-M-I transitions, related to
the quantum Hall effect in quasi-2D graphite samples. We discuss the possible
coupling of superconducting and excitonic correlations with the observed
phenomena, as well as the signatures of quantum phase transitions associated
with the M-I and I-M transformations.Comment: 23 pages including 14 figure
Neuronal glucose transporter isoform 3 deficient mice demonstrate features of autism spectrum disorders.
Neuronal glucose transporter (GLUT) isoform 3 deficiency in null heterozygous mice led to abnormal spatial learning and working memory but normal acquisition and retrieval during contextual conditioning, abnormal cognitive flexibility with intact gross motor ability, electroencephalographic seizures, perturbed social behavior with reduced vocalization and stereotypies at low frequency. This phenotypic expression is unique as it combines the neurobehavioral with the epileptiform characteristics of autism spectrum disorders. This clinical presentation occurred despite metabolic adaptations consisting of an increase in microvascular/glial GLUT1, neuronal GLUT8 and monocarboxylate transporter isoform 2 concentrations, with minimal to no change in brain glucose uptake but an increase in lactate uptake. Neuron-specific glucose deficiency has a negative impact on neurodevelopment interfering with functional competence. This is the first description of GLUT3 deficiency that forms a possible novel genetic mechanism for pervasive developmental disorders, such as the neuropsychiatric autism spectrum disorders, requiring further investigation in humans
Reentrant Metallic Behavior of Graphite in the Quantum Limit
Magnetotransport measurements performed on several well-characterized highly
oriented pyrolitic graphite and single crystalline Kish graphite samples reveal
a reentrant metallic behavior in the basal-plane resistance at high magnetic
fields, when only the lowest Landau levels are occupied. The results suggest
that the quantum Hall effect and Landau-level-quantization-induced
superconducting correlations are relevant to understand the metallic-like
state(s) in graphite in the quantum limit.Comment: 4 pages, 5 figure
Bed and suspended sediment-associated rare earth element concentrations and fluxes in a polluted Brazilian river system
Rare earth elements (REEs) have been recently recognized as emergent pollutants in rivers. However, data regarding REE fluxes in association with either bed or suspended are scarce. To address this knowledge gap, we determined the concentrations and fluxes of La, Ce, Pr, Nd, Sm, Eu, Gd, Yb, Lu, Dy, Er, Ho, Tb, and Tm in bed and suspended sediment samples of a representative polluted Brazilian River. Sediment-associated data on REEs were placed in the context of corresponding background concentrations in soils under natural conditions along the Ipojuca watershed. Light rare earth elements (LREEs) comprised more than 94% of the total REEs associated with bed and suspended sediments. Suspended sediments accounted for more than 95% of the total REE flux. The Ce and Nd fluxes of about 7 t year−1 underscore the importance of including REEs in future estimations of
global suspended sediment-associated element fluxes. In contrast, bedload often transported less than 0.0007 t year−1 of each REE. The main sources of pollution in the Ipojuca River are anthropogenic, likely due to domestic effluent and waste water from industrial and agricultural operations—major causes of sediment-associated Gd transport in polluted streams
ForÃdeos cleptoparasitas de abelhas-sem-ferrão: sazonalidade, distribuição espacial e atratividade de iscas de vinagre.
Este estudo teve como objetivos verificar a abundância e a sazonalidade de moscas cleptoparasitas de abelhas-sem-ferrão da famÃlia Phoridae, em Rio Branco, AC, assim como a eficácia de diferentes iscas de vinagre na captura dessas moscas. Três métodos de amostragem foram utilizados: a) armadilhas instaladas a diferentes distâncias do meliponário, contendo pólen de abelha-sem-ferrão, ou vinagre de vinho tinto ou ambos; b) armadilhas instaladas ao lado de colmeias com isca de vinagre de vinho tinto, de maçã ou álcool; c) contagem do número de forÃdeos dentro das colmeias. Foram amostrados 1.050 espécimes, sendo a maioria (92%) coletada em armadilhas. A espécie Pseudohypocera kerteszi representou 98% dos espécimes capturados nas armadilhas. A maior abundância de forÃdeos capturados ocorreu na estação chuvosa, com pico em dezembro. Verificou-se uma correlação positiva entre o número de forÃdeos contados dentro das colônias e o número de forÃdeos capturados nas armadilhas. Estes foram mais frequentes nas armadilhas com pólen colocadas na área do meliponário, apresentando uma distribuição agregada. Em função disso, recomenda-se a manutenção das colônias enfraquecidas a, pelo menos, 20 metros dos locais de criação de abelhas-sem-ferrão. Os vinagres de vinho tinto ou de maçã apresentaram atratividade semelhante, podendo ambos ser usados como isca.bitstream/item/64718/1/24346.pd
Produção de tambaquis com diferentes densidades de estocagem em tanques-rede instalados em lago abastecido com água pluvial.
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