12,523 research outputs found
General Analysis of U-Spin Breaking in B Decays
We analyse the breaking of U-spin on a group theoretical basis. Due to the
simple behaviour of the weak effective hamiltonian under U-spin and the unique
structure of the breaking terms such a group theoretical analysis leads to a
manageable number of parameters. Several applications are discussed, including
the decays B -> J/psi K and B -> D K.Comment: 18 pages, 2 figures; Paragraph added on decays of B0 to P+P- with
P=(pi,K), and several minor corrections performed. Version matches the one to
appear in Phys. Rev.
Confined Multilamellae Prefer Cylindrical Morphology
By evaporating a drop of lipid dispersion we generate the myelin morphology
often seen in dissolving surfactant powders. We explain these puzzling
nonequilibrium structures using a geometric argument: The bilayer repeat
spacing increases and thus the repulsion between bilayers decreases when a
multilamellar disk is converted into a myelin without gain or loss of material
and with number of bilayers unchanged. Sufficient reduction in bilayer
repulsion can compensate for the cost in curvature energy, leading to a net
stability of the myelin structure. A numerical estimate predicts the degree of
dehydration required to favor myelin structures over flat lamellae.Comment: 6 pages, 3 figures, submitted to Euro. Phys. J.
Unusual Beaver, Castor canadensis, Dams in Central Yukon
North American Beavers (Castor canadensis) are remarkable for their ability to build dams and modify their habitat. Dams are typically made of the boles and branches of trees and large shrubs, and reinforced with mud and rocks. Here, we report two unusual Beaver dams in central Yukon, Canada, that are made primarily of medium-sized rocks. This observation points to the adaptability of Beavers in using available materials to build their dams
Sequential Flavour Symmetry Breaking
The gauge sector of the Standard Model (SM) exhibits a flavour symmetry which
allows for independent unitary transformations of the fermion multiplets. In
the SM the flavour symmetry is broken by the Yukawa couplings to the Higgs
boson, and the resulting fermion masses and mixing angles show a pronounced
hierarchy. In this work we connect the observed hierarchy to a sequence of
intermediate effective theories, where the flavour symmetries are broken in a
step-wise fashion by vacuum expectation values of suitably constructed spurion
fields. We identify the possible scenarios in the quark sector and discuss some
implications of this approach.Comment: 22 pages latex, no figure
Full QED+QCD Low-Energy Constants through Reweighting
The effect of sea quark electromagnetic charge on meson masses is
investigated, and first results for full QED+QCD low-energy constants are
presented. The electromagnetic charge for sea quarks is incorporated in
quenched QED+full QCD lattice simulations by a reweighting method. The
reweighting factor, which connects quenched and unquenched QED, is estimated
using a stochastic method on 2+1 flavor dynamical domain-wall quark ensembles.Comment: 5 pages, 9 figures, REVTeX 4.1, v2: published versio
Reduction of the contact resistance by doping in pentacene few monolayers thin film transistors and self-assembled nanocrystals
The authors study the contact resistance of gold-pentacene interface by applying the transmission-line method to a few monolayers thick pentacene films in thin film transistor geometry. It was found that tetrafluorotetracyanoquinodimethane (F(4)TCNQ) doping reduces the contact resistance by more than a factor of 20. In addition, a significant improvement of the conductance of pentacene nanocrystals self-assembled on 10 nm gap Au nanojunction devices by F(4)TCNQ doping is observed. The result demonstrates the importance of doping on the performance of organic electronic devices from 10 nm scale up to 100 mu m scale. (C) 2007 American Institute of Physics
Temperature dependent charge-injection at the metal-organic semiconductor interface and density of states in pristine and doped pentacene
The authors study temperature dependent electrical transport in pristine and tetrafluorotetracyanoquinodimethane (F(4)TCNQ)-doped pentacene to explore the physical mechanism of the doping-induced reduction in the contact resistance at the metal-organic semiconductor interface. It was found that the F(4)TCNQ-doping induces an apparent lowering of the hole injection barrier at gold-pentacene interfaces. In addition, characteristic changes in the density of states (DOS) induced by the F(4)TCNQ-doping in a thin-film transistor geometry have been observed. The correlation between the doping-induced DOS and the carrier injection process is discussed
Electron transfer at electrode interfaces via a straightforward quasiclassical fermionic mapping approach
Electron transfer at electrode interfaces to molecules in solution or at the
electrode surface plays a vital role in numerous technological processes.
However, treating these processes requires a unified and accurate treatment of
the fermionic states of the electrode and their coupling to the molecule being
oxidized or reduced in the electrochemical processes and, in turn, the way the
molecular energy levels are modulated by the bosonic nuclear modes of the
molecule and solvent. Here we present a physically transparent quasiclassical
scheme to treat these electrochemical electron transfer processes in the
presence of molecular vibrations by using an appropriately chosen mapping of
the fermionic variables. We demonstrate that this approach, which is exact in
the limit of non-interacting fermions, is able to accurately capture the
electron transfer dynamics from the electrode even when the process is coupled
to vibrational motions in regimes of weak coupling. This approach thus provides
a scalable strategy to explicitly treat electron transfer from electrode
interfaces in condensed-phase molecular systems
Using NWP to assess the influence of the Arctic atmosphere on mid-latitude weather and climate
The influence of the Arctic atmosphere on Northern Hemisphere mid-latitude tropospheric weather and climate is explored by comparing the skill of two sets of 14-day weather forecast experiments using the ECMWF model with and without relaxation of the Arctic atmosphere towards ERA-Interim reanalysis data during the integration. Two pathways are identified along which the Arctic influences mid-latitude weather: a pronounced one over Asia and Eastern Europe, and a secondary one over North America. In general, linkages are found to be strongest (weakest) during boreal winter (summer) when the amplitude of stationary planetary waves over the Northern Hemisphere is strongest (weakest). No discernible Arctic impact is found over the North Atlantic and North Pacific region, which is consistent with predominantly southwesterly flow. An analysis of the flow-dependence of the linkages shows that anomalous northerly flow conditions increase the Arctic influence on mid-latitude weather over the continents. Specifically, an anomalous northerly flow from the Kara Sea towards West Asia leads to cold surface temperature anomalies not only over West Asia but also over Eastern and Central Europe. Finally, the results of this study are discussed in the light of potential mid-latitude benefits of improved Arctic prediction capabilities
Melanistic Tundra Voles, Microtus oeconomus, from Central Yukon
Colour aberrations are not commonly observed in voles (e.g., Microtus and Myodes); thus, individual observations are of interest. We report two observations of melanism in Tundra Voles, Microtus oeconomus, collected from central Yukon. These are the second and third records of melanistic Tundra Voles, and the first reports from non-insular populations
- …