442 research outputs found
Lagrangian description of world-line deviations
We introduce a Lagrangian which can be varied to give both the equation of
motion and world-line deviations of spinning particles simultaneously.Comment: to appear in IJT
General relativistic spinning fluids with a modified projection tensor
An energy-momentum tensor for general relativistic spinning fluids compatible
with Tulczyjew-type supplementary condition is derived from the variation of a
general Lagrangian with unspecified explicit form. This tensor is the sum of a
term containing the Belinfante-Rosenfeld tensor and a modified perfect-fluid
energy-momentum tensor in which the four-velocity is replaced by a unit
four-vector in the direction of fluid momentum. The equations of motion are
obtained and it is shown that they admit a Friedmann-Robertson-Walker
space-time as a solution.Comment: Submitted to General Relativity and Gravitatio
Enantioselective synthesis of non-proteinogenic 2-arylallyl-α-amino acids via Pd/In catalytic cascades
An efficient synthesis of both R- and S-enantiomers of 2-arylallyl-α-amino acids via a diastereoselective Pd/In mediated catalytic allylation of chiral N-sulfinyl-α-imino esters is described. The potential for further enhancement of molecular complexity and creating contiguous chiral centres by interfacing these processes with catalytic cyclisation–anion capture methodology is demonstrated
Comparison of 1-D Modelling Approaches for Wankel Engine Performance Simulation and Initial Study of the Direct Injection Limitations
Recent interest in the possible use of Wankel engines as range extenders for electric vehicles has prompted renewed investigations into the concept. While not presently used in the automotive industry, the type is well established in the unmanned aerial vehicles industry, and several innovative approaches to sealing and cooling have recently been developed which may result in improved performance for ground vehicle applications.One such UAV engine is the 225CS, a 225 cc/chamber single-rotor engine manufactured by Advanced Innovative Engineering (UK) Ltd. To be able to analyse the parameters, opportunities and limitations of this type of engine a model was created in the new dedicated Wankel modelling environment of AVL BOOST. For comparison a second model was created using the established method of modelling Wankel engines by specifying an ‘equivalent’ 3-cylinder 4-stroke reciprocating engine. The output from both of these models was evaluated using engine test data supplied by Advanced Innovative Engineering (UK) Ltd. The model created in the dedicated Wankel environment was found to fit the experimental data more closely.The model was then used to evaluate the impact on performance and fuel economy of applying direct injection to a Wankel rotary engine. This potential is because the nozzle can be situated in the cold side of the trochoid housing, taking advantage of the longer intake phase of the Wankel in turn permitting lower delivery pressures (the intake ‘stroke’ having 270 degrees of eccentric shaft rotation vs. 180 degrees for the reciprocating engine), plus the fact that the injector can be shielded from combustion pressure and hot burned gases. As it was found to be more accurate, the dedicated Wankel model was used to analyse the interrelationships between injector position, injection pressure and engine speed.Although a number of assumptions were required, and these will affect the accuracy of the model, the results provide a reasonable preliminary assessment of the feasibility of applying direct injection to the 225CS engine. A notable finding was that injection pressures of approximately 4.5 bar should be sufficient to supply fuel at all engine speeds and that the optimum position for the injector (for maximum fuel injection) corresponded to a position defined by the rotor apex tip at 597 degrees of eccentric shaft rotation after top dead centre firing. The advantage of both the injection pressure and injector location suggests a less complex fuel system design (compared to equivalent reciprocating systems) is possible at a reduced cost
Action principle formulation for motion of extended bodies in General Relativity
We present an action principle formulation for the study of motion of an
extended body in General Relativity in the limit of weak gravitational field.
This gives the classical equations of motion for multipole moments of arbitrary
order coupling to the gravitational field. In particular, a new force due to
the octupole moment is obtained. The action also yields the gravitationally
induced phase shifts in quantum interference experiments due to the coupling of
all multipole moments.Comment: Revised version derives Octupole moment force. Some clarifications
and a reference added. To appear in Phys. Rev.
Olfactory Jump Reflex Habituation in Drosophila and Effects of Classical Conditioning Mutations
Habituation is a nonassociative learning mechanism, in which an initial response toward repeated stimuli gradually wanes. This is amongst the simplest and most widespread forms of behavioral plasticity. So far, neither the underlying molecular mechanisms nor the precise neural networks of habituation are well understood. We have developed a novel paradigm to quantify habituation of the olfactory jump reflex in Drosophila. We present data demonstrating several behavioral properties of this phenomenon, generally observed in other species. We also show that the dunce and rutabaga memory mutants behave abnormally in this assay, suggesting that this assay might be used in behavioral screens for new mutants with defects in this simpler form of behavioral plasticity
Measurement of the partial widths of the Z into up- and down-type quarks
Using the entire OPAL LEP1 on-peak Z hadronic decay sample, Z -> qbarq gamma
decays were selected by tagging hadronic final states with isolated photon
candidates in the electromagnetic calorimeter. Combining the measured rates of
Z -> qbarq gamma decays with the total rate of hadronic Z decays permits the
simultaneous determination of the widths of the Z into up- and down-type
quarks. The values obtained, with total errors, were Gamma u = 300 ^{+19}_{-18}
MeV and Gamma d = 381 ^{+12}_{-12} MeV. The results are in good agreement with
the Standard Model expectation.Comment: 22 pages, 5 figures, Submitted to Phys. Letts.
Search for R-Parity Violating Decays of Scalar Fermions at LEP
A search for pair-produced scalar fermions under the assumption that R-parity
is not conserved has been performed using data collected with the OPAL detector
at LEP. The data samples analysed correspond to an integrated luminosity of
about 610 pb-1 collected at centre-of-mass energies of sqrt(s) 189-209 GeV. An
important consequence of R-parity violation is that the lightest supersymmetric
particle is expected to be unstable. Searches of R-parity violating decays of
charged sleptons, sneutrinos and squarks have been performed under the
assumptions that the lightest supersymmetric particle decays promptly and that
only one of the R-parity violating couplings is dominant for each of the decay
modes considered. Such processes would yield final states consisting of
leptons, jets, or both with or without missing energy. No significant
single-like excess of events has been observed with respect to the Standard
Model expectations. Limits on the production cross- section of scalar fermions
in R-parity violating scenarios are obtained. Constraints on the supersymmetric
particle masses are also presented in an R-parity violating framework analogous
to the Constrained Minimal Supersymmetric Standard Model.Comment: 51 pages, 24 figures, Submitted to Eur. Phys. J.
Measurement of the Hadronic Photon Structure Function F_2^gamma at LEP2
The hadronic structure function of the photon F_2^gamma is measured as a
function of Bjorken x and of the factorisation scale Q^2 using data taken by
the OPAL detector at LEP. Previous OPAL measurements of the x dependence of
F_2^gamma are extended to an average Q^2 of 767 GeV^2. The Q^2 evolution of
F_2^gamma is studied for average Q^2 between 11.9 and 1051 GeV^2. As predicted
by QCD, the data show positive scaling violations in F_2^gamma. Several
parameterisations of F_2^gamma are in agreement with the measurements whereas
the quark-parton model prediction fails to describe the data.Comment: 4 pages, 2 figures, to appear in the proceedings of Photon 2001,
Ascona, Switzerlan
A measurement of the tau mass and the first CPT test with tau leptons
We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV
using tau pairs from Z0 decays. To test CPT invariance we compare the masses of
the positively and negatively charged tau leptons. The relative mass difference
is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.
- …