Small angle neutron scattering observation of chain retraction after a large step deformation

The process of retraction in entangled linear chains after a fast nonlinear stretch was detected from time-resolved but quenched small angle neutron scattering (SANS) experiments on long, well-entangled polyisoprene chains. The statically obtained SANS data cover the relevant time regime for retraction, and they provide a direct, microscopic verification of this nonlinear process as predicted by the tube model. Clear, quantitative agreement is found with recent theories of contour length fluctuations and convective constraint release, using parameters obtained mainly from linear rheology. The theory captures the full range of scattering vectors once the crossover to fluctuations on length scales below the tube diameter is accounted for

A bio-economic analysis of harvest control rules for the Northeast Arctic cod fishery

Harvest control rules (HCRs) have been implemented for many fisheries worldwide. However, in most instances, those HCRs are not based on the explicit feedbacks between stock properties and economic considerations. This paper develops a bio-economic model that evaluates the HCR adopted in 2004 by the Joint Norwegian-Russian Fishery Commission to manage the world's largest cod stock, Northeast Arctic cod (NEA). The model considered here is biologically and economically detailed, and is the firt to compare the performance of the stock's current HCR with that of alternative HCRs derived with optimality criteria. In particular, HCRs are optimized for economic objectives including fleet profit, economic welfare, and total yield and the emerging properties are analyzed. The performance of these optimal HCRs was compared with the currently used HCR. This paper show that the current HCR does in fact comes very close to maximizing profits. Furthermore, the results reveal that the HCR that maximizes profits is the most precautionary one among the considered HCRs. Finally, the HCR that maximizes yield leads to un-precautionary low levels of biomass. In these ways, the implementation of the HCR for NEA cod can be viewed as a success story that may provide valuable lessons for other fishries

A hybrid method for determining particle masses at the Large Hadron Collider with fully identified cascade decays

A new technique for improving the precision of measurements of SUSY particle masses at the LHC is introduced. The technique involves kinematic fitting of events with two fully identified decay chains. We incorporate both event ETmiss constraints and independent constraints provided by kinematic end-points in experiment invariant mass distributions of SUSY decay products. Incorporation of the event specific information maximises the information used in the fit and is shown to reduce the mass measurement uncertainites by ~30% compared to conventional fitting of experiment end-point constraints for the SPS1a benchmark model.Comment: 10 pages, 2 .eps figures, JHEP3 styl

Mass Determination in SUSY-like Events with Missing Energy

We describe a kinematic method which is capable of determining the overall mass scale in SUSY-like events at a hadron collider with two missing (dark matter) particles. We focus on the kinematic topology in which a pair of identical particles is produced with each decaying to two leptons and an invisible particle (schematically, $pp\to YY+jets$ followed by each $Y$ decaying via $Y\to \ell X\to \ell\ell'N$ where $N$ is invisible). This topology arises in many SUSY processes such as squark and gluino production and decay, not to mention t\anti t di-lepton decays. In the example where the final state leptons are all muons, our errors on the masses of the particles $Y$, $X$ and $N$ in the decay chain range from 4 GeV for 2000 events after cuts to 13 GeV for 400 events after cuts. Errors for mass differences are much smaller. Our ability to determine masses comes from considering all the kinematic information in the event, including the missing momentum, in conjunction with the quadratic constraints that arise from the $Y$, $X$ and $N$ mass-shell conditions. Realistic missing momentum and lepton momenta uncertainties are included in the analysis.Comment: 41 pages, 14 figures, various clarifications and expanded discussion included in revised version that conforms to the version to be publishe

Supersymmetric particle mass measurement with invariant mass correlations

The kinematic end-point technique for measuring the masses of supersymmetric particles in R-Parity conserving models at hadron colliders is re-examined with a focus on exploiting additional constraints arising from correlations in invariant mass observables. The use of such correlations is shown to potentially resolve the ambiguity in the interpretation of quark+lepton end-points and enable discrimination between sequential two-body and three-body lepton-producing decays. The use of these techniques is shown to improve the SUSY particle mass measurement precision for the SPS1a benchmark model by at least 20-30% compared to the conventional end-point technique.Comment: 29 pages, 23 .eps figures, JHEP3 style; v2 adds some references and small clarifications to text; v3 adds some more clarifications to the tex

Gravitino Dark Matter Scenarios with Massive Metastable Charged Sparticles at the LHC

We investigate the measurement of supersymmetric particle masses at the LHC in gravitino dark matter (GDM) scenarios where the next-to-lightest supersymmetric partner (NLSP) is the lighter scalar tau, or stau, and is stable on the scale of a detector. Such a massive metastable charged sparticle would have distinctive Time-of-Flight (ToF) and energy-loss ($dE/dx$) signatures. We summarise the documented accuracies expected to be achievable with the ATLAS detector in measurements of the stau mass and its momentum at the LHC. We then use a fast simulation of an LHC detector to demonstrate techniques for reconstructing the cascade decays of supersymmetric particles in GDM scenarios, using a parameterisation of the detector response to staus, taus and jets based on full simulation results. Supersymmetric pair-production events are selected with high redundancy and efficiency, and many valuable measurements can be made starting from stau tracks in the detector. We recalibrate the momenta of taus using transverse-momentum balance, and use kinematic cuts to select combinations of staus, taus, jets and leptons that exhibit peaks in invariant masses that correspond to various heavier sparticle species, with errors often comparable with the jet energy scale uncertainty.Comment: 23 pages, 10 figures, updated to version published in JHE

Homodyne detection for measuring internal quantum correlations of optical pulses

A new method is described for determining the quantum correlations at different times in optical pulses by using balanced homodyne detection. The signal pulse and sequences of ultrashort test pulses are superimposed, where for chosen distances between the test pulses their relative phases and intensities are varied from measurement to measurement. The correlation statistics of the signal pulse is obtained from the time-integrated difference photocurrents measured.Comment: 7 pages, A4.sty include

Mode structure and photon number correlations in squeezed quantum pulses

The question of efficient multimode description of optical pulses is studied. We show that a relatively very small number of nonmonochromatic modes can be sufficient for a complete quantum description of pulses with Gaussian quadrature statistics. For example, a three-mode description was enough to reproduce the experimental data of photon number correlations in optical solitons [S. Spalter et al., Phys. Rev. Lett. 81, 786 (1998)]. This approach is very useful for a detailed understanding of squeezing properties of soliton pulses with the main potential for quantum communication with continuous variables. We show how homodyne detection and/or measurements of photon number correlations can be used to determine the quantum state of the multi-mode field. We also discuss a possible way of physical separation of the nonmonochromatic modes.Comment: 14 pages, 4 figures; minor revisions of the text, new references; to appear in the Phys. Rev.

Mode structure and ray dynamics of a parabolic dome microcavity

We consider the wave and ray dynamics of the electromagnetic field in a parabolic dome microcavity. The structure of the fundamental s-wave involves a main lobe in which the electromagnetic field is confined around the focal point in an effective volume of the order of a cubic wavelength, while the modes with finite angular momentum have a structure that avoids the focal area and have correspondingly larger effective volume. The ray dynamics indicates that the fundamental s-wave is robust with respect to small geometrical deformations of the cavity, while the higher order modes are associated with ray chaos and short-lived. We discuss the incidence of these results on the modification of the spontaneous emission dynamics of an emitter placed in such a parabolic dome microcavity.Comment: 50 pages, 17 figure

Calculation of magnetic anisotropy energy in SmCo5

SmCo5 is an important hard magnetic material, due to its large magnetic anisotropy energy (MAE). We have studied the magnetic properties of SmCo5 using density functional theory (DFT) calculations where the Sm f-bands, which are difficult to include in DFT calculations, have been treated within the LDA+U formalism. The large MAE comes mostly from the Sm f-shell anisotropy, stemming from an interplay between the crystal field and the spin-orbit coupling. We found that both are of similar strengths, unlike some other Sm compounds, leading to a partial quenching of the orbital moment (f-states cannot be described as either pure lattice harmonics or pure complex harmonics), an optimal situation for enhanced MAE. A smaller portion of the MAE can be associated with the Co-d band anisotropy, related to the peak in the density of states at the Fermi energy. Our result for the MAE of SmCo5, 21.6 meV/f.u., agrees reasonably with the experimental value of 13-16 meV/f.u., and the calculated magnetic moment (including the orbital component) of 9.4 mu_B agrees with the experimental value of 8.9 mu_B.Comment: Submitted to Phys. Rev.