21,010 research outputs found
Looking for CP Violation in W Production and Decay
We describe CP violating observables in resonant and plus one
jet production at the Tevatron. We present simple examples of CP violating
effective operators, consistent with the symmetries of the Standard Model,
which would give rise to these observables. We find that CP violating effects
coming from new physics at the scale could in principle be observable at
the Tevatron with decays.Comment: 15 pgs with standard LATEX, 7 ps figures embedded with eps
Uranium(III) coordination chemistry and oxidation in a flexible small-cavity macrocycle
U(III) complexes of the conformationally flexible, small-cavity macrocycle trans-calix[2]benzene[2]pyrrolide (L)2–, [U(L)X] (X = O-2,6-tBu2C6H3, N(SiMe3)2), have been synthesized from [U(L)BH4] and structurally characterized. These complexes show binding of the U(III) center in the bis(arene) pocket of the macrocycle, which flexes to accommodate the increase in the steric bulk of X, resulting in long U–X bonds to the ancillary ligands. Oxidation to the cationic U(IV) complex [U(L)X][B(C6F5)4] (X = BH4) results in ligand rearrangement to bind the smaller, harder cation in the bis(pyrrolide) pocket, in a conformation that has not been previously observed for (L)2–, with X located between the two ligand arene rings
Integrability of one degree of freedom symplectic maps with polar singularities
In this paper, we treat symplectic difference equations with one degree of
freedom. For such cases, we resolve the relation between that the dynamics on
the two dimensional phase space is reduced to on one dimensional level sets by
a conserved quantity and that the dynamics is integrable, under some
assumptions. The process which we introduce is related to interval exchange
transformations.Comment: 10 pages, 2 figure
Barbell back squat:How do resistance bands affect muscle activation and knee kinematics?
ObjectivesThis study aimed to determine whether looped resistance bands affect knee kinematics and lower body muscle activation during the barbell back squat.MethodsTwenty-six healthy participants (13 female, 13 male) calculated their one repetition maximum (RM) prior to data collection. Each participant performed three squats at both 80% and 40% 1RM wearing a light resistance band, an extra-heavy resistance band and no resistance band.Vicon 3D motion analysis cameras were used to collect the kinematic data, and Delsys Trigno Lab wireless electromyography (EMG) system was used to measure vastus medialis, vastus lateralis, gluteus maximus, gluteus medius and biceps femoris muscle activity. Peak knee flexion angle, peak knee valgus angle and maximum tibial rotation values were examined. Peak EMG values were also analysed after being normalised and expressed as a percentage of maximum voluntary contraction (MVC).ResultsGluteus maximus (GM) activity is significantly increased when a resistance band is used during squatting. However, squatting with a resistance band is detrimental to knee kinematics as it leads to an increase in knee valgus angle and maximum tibial rotation angle. A direct correlation is recorded between an increase in resistance and an increase in these two angles.ConclusionsSquatting with resistance bands is likely to increase the risk of knee injury. Coaches and clinicians who already implement this technique are advised to remove resistance band squats from training and rehabilitation programmes. Further research evaluating the long-term effects of using resistance bands during the barbell back squat should be considered
Semiclassical Spectrum of Small Bose-Hubbard Chains: A Normal Form Approach
We analyze the spectrum of the 3-site Bose-Hubbard model with periodic
boundary conditions using a semiclassical method. The Bohr-Sommerfeld
quantization is applied to an effective classical Hamiltonian which we derive
using resonance normal form theory. The derivation takes into account the 1:1
resonance between frequencies of a linearized classical system, and brings
nonlinear terms into a corresponding normal form. The obtained expressions
reproduce the exact low-energy spectrum of the system remarkably well even for
a small number of particles N corresponding to fillings of just two particles
per site. Such small fillings are often used in current experiments, and it is
inspiring to get insight into this quantum regime using essentially classical
calculations.Comment: Minor corrections to the coefficients of the effective Hamiltonian in
Eqs 14,15,18,19. Figs 1,2 are slightly modified, correspondingl
Comparison of Monomethylhydrazine/Hydroxypropylcellulose and Hydrocarbon/Silica Gels
Experimental studies have been performed to investigate rheology and droplet burning with different types of gelled propellants. Monomethylhydrazine has been gelled with organic hydroxypropylcellulose. JP-8 and RP-1 hydrocarbon gels have been produced with inorganic fumed silica particles. Rheological characterization showed the differences in terms of viscosity and yield stress behavior due to different types of gelling agents. Herschel-Bulkley and Carreau-Yasuda models have been used to characterize the gels with inorganic and organic gelling agents, respectively. First experiments with the Monomethylhydrazine/hydroxypropylcellulose gels showed a typical swelling process during combustion with a flexible viscous droplet surface. Contrary to that, the hydrocarbon/silica gels burned while a rigid silica structure was built, which remained unburned. Burning drop measurements have been compared to the d^2-squared law
Identities among relations for higher-dimensional rewriting systems
We generalize the notion of identities among relations, well known for
presentations of groups, to presentations of n-categories by polygraphs. To
each polygraph, we associate a track n-category, generalizing the notion of
crossed module for groups, in order to define the natural system of identities
among relations. We relate the facts that this natural system is finitely
generated and that the polygraph has finite derivation type.Comment: 16 pages, corrected version after review, to appear in S\'eminaires
et Congr\`e
Gravitational Techniwaves
We investigate the production and possible detection of gravitational waves
stemming from the electroweak phase transition in the early universe in models
of minimal walking technicolor. In particular we discuss the two possible
scenarios in which one has only one electroweak phase transition and the case
in which the technicolor dynamics allows for multiple phase transitions.Comment: 30 pages, 5 figures. v2: minor changes, references added, title
changed in journa
Simulating hot Abelian gauge dynamics
The time evolution of soft modes in a quantum gauge field theory is to first
approximation classical, but the equations of motion are non-local. We show how
they can be written in a local and Hamiltonian way in an Abelian theory, and
that this formulation is particularly suitable for numerical simulations. This
makes it possible to simulate numerically non-equilibrium processes such as the
phase transition in the Abelian Higgs model and and to study, for instance,
bubble nucleation and defect formation. Such simulations would also help to
understand phase transitions in more complicated gauge theories. Moreover, we
show that the existing analytical results for the time-evolution in a
pure-gauge theory correspond to a special class of initial conditions and that
different initial conditions can lead to qualitatively different behavior. We
compare the results of the simulations to analytical calculations and find an
excellent agreement.Comment: 18 pages, 5 figures, REVTe
Transport coefficients in high temperature gauge theories: (II) Beyond leading log
Results are presented of a full leading-order evaluation of the shear
viscosity, flavor diffusion constants, and electrical conductivity in high
temperature QCD and QED. The presence of Coulomb logarithms associated with
gauge interactions imply that the leading-order results for transport
coefficients may themselves be expanded in an infinite series in powers of
1/log(1/g); the utility of this expansion is also examined. A
next-to-leading-log approximation is found to approximate the full
leading-order result quite well as long as the Debye mass is less than the
temperature.Comment: 38 pages, 6 figure
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