2,149 research outputs found
Possible Explanations for the NuTeV Weinberg Angle Measurement
The NuTeV collaboration has made an independent determination of the Weinberg
angle by measuring charged and neutral-current cross sections from neutrino and
antineutrino DIS on iron. Their value differs by 3 standard deviations from
that obtained from measurements at the Z pole. We review this experiment and
assess various possible explanations for this result, both within the Standard
Model ("old physics") and outside the Standard Model ("new physics").Comment: QCD Down Under Workshop, CSSM, Adelaide, Australia, Mar 10-19, 2004;
6 pages, 3 figs; updated references on QCD effect
Single-mode tunable erbium:ytterbium fibre Fabry-Perot laser
A compact tunable single-mode fiber laser is developed by using a novel combination of high-gain erbium: ytterbium (Er:Yb) phosphate fiber and fiber Fabry-Perot (FFP) cavity configurations. Experiments demonstrate the shortest Er:Yb phosphate FFP laser ever reported, which has a 100µm cavity length with a continuous wavelength tuning range over 4.52nm, as limited by the sharp fiber gain peak. In addition, an alternative 3-mirror laser design has also demonstrated single-mode lasing operation
Report on the Distribution of Dwarf Birches and Present Pollen Rain, Baffin Island, N.W.T., Canada
A distribution map for the dwarf birches is presented for the region from Frobisher Bay northward to Cumberland Peninsula. These shrubs are restricted to favourable habitats which, at the northern limit of the species (67 deg. 40 sec. N), are found on south-facing slopes above the immediate local cooling influence of the sea. Pollen studies within the zone of scattered dwarf birch indicate that pollen dispersal from these low, prostrate shrubs is minimal. Samples of moss collected beneath the bushes have 5-36% Betula pollen; whereas sites no more than 50 m away from Betula shrubs have percentages of <2%. These data will be useful in considering the Holocene and Pleistocene histories of these Low Arctic shrubs in the Eastern Canadian Arctic
Influence of temperature gradients on tunnel junction thermometry below 1 K: cooling and electron-phonon coupling
We have studied thermal gradients in thin Cu and AlMn wires, both
experimentally and theoretically. In the experiments, the wires were Joule
heated non-uniformly at sub-Kelvin temperatures, and the resulting temperature
gradients were measured using normal metal-insulator-superconducting tunnel
junctions. The data clearly shows that even in reasonably well conducting thin
wires with a short (m) non-heated portion, significant temperature
differences can form. In most cases, the measurements agree well with a model
which includes electron-phonon interaction and electronic thermal conductivity
by the Wiedemann-Franz law.Comment: J. Low Temp. Phys. in pres
SeaSoar data collected on RRS "Discovery" Cruise 198 (Sterna) across Drake Passage and in the Bellingshausen Sea
Transport of Surface States in the Bulk Quantum Hall Effect
The two-dimensional surface of a coupled multilayer integer quantum Hall
system consists of an anisotropic chiral metal. This unusual metal is
characterized by ballistic motion transverse and diffusive motion parallel
(\hat{z}) to the magnetic field. Employing a network model, we calculate
numerically the phase coherent two-terminal z-axis conductance and its
mesoscopic fluctuations. Quasi-1d localization effects are evident in the limit
of many layers. We consider the role of inelastic de-phasing effects in
modifying the transport of the chiral surface sheath, discussing their
importance in the recent experiments of Druist et al.Comment: 9 pages LaTex, 9 postscript figures included using eps
Comparison of multiple approaches to calculate time-varying biological reference points in climate-linked population-dynamics models
Fisheries managers use biological reference points (BRPs) as targets or limits on fishing and biomass to maintain productive levels of fish stock biomass. There are multiple ways to calculate BRPs when biological parameters are time varying. Using summer flounder (Paralichthys dentatus) as a case study, we investigated time-varying approaches in concert with climate-linked population models to understand the impact of environmentally driven variability in natural mortality, recruitment, and size-At-Age on two commonly used BRPs [B0(t) and F35%(t)]. We used the following two approaches to calculate time-varying BRPs: dynamic-BRP and moving-Average-BRP. We quantified the variability and uncertainty of different climate dependencies and estimation approaches, attributed BRP variation to variation in life-history processes, and evaluated how using different approaches impacts estimates of stock status. Results indicate that the dynamic-BRP approach using the climate-linked natural mortality model produced the least variable reference points compared to others calculated. Summer flounder stock status depended on the estimation approach and climate model used. These results emphasize that understanding climate dependencies is important for summer flounder reference points and perhaps other species, and careful consideration is warranted when considering what time-varying approach to use, ideally based upon simulation studies within a proposed set of management procedures
Charge Symmetry Violating Contributions to Neutrino Reactions
The NuTeV group has measured charged and neutral current reactions for
neutrinos on iron targets. Ratios of these cross sections provide an
independent measurement of the Weinberg angle. The NuTeV value for sin^2
theta_W is three standard deviations larger than the value measured in other
electroweak processes. By reviewing theoretical estimates of parton charge
symmetry violation (CSV), we study CSV contributions to the NuTeV measurement.
We conclude that charge symmetry violating effects should remove roughly 30% of
the discrepancy between the NuTeV result and other determinations of sin^2
theta_W.Comment: 15 pages, 2 figures; Fig 2 replaced [CSV distribution calculated at
low Q^2, evolved to 20 GeV^2]; table II change
Implementing two-dimensional autocorrelation in either survival or natural mortality improves a state-space assessment model for Southern New England-Mid Atlantic yellowtail flounder
Survival is an important population process in fisheries stock assessment models and is typically treated as deterministic. Recently developed state-space assessment models can estimate stochastic deviations in survival, which represent variability in some ambiguous combination of natural mortality (M), fishing mortality (F), and migration. These survival deviations are generally treated as independent by age and year, despite our understanding that many population processes can be autocorrelated and that not accounting for autocorrelation can result in notable bias. We address these concerns, as well as the strong retrospective pattern found in the last assessment of Southern New England yellowtail flounder (Limanda ferruginea), by incorporating two-dimensional (2D, age and year) first-order autocorrelation in survival and M. We found that deviations were autocorrelated among both years (0.53 ± 0.09, 0.63 ± 0.16) and ages (0.33 ± 0.12, 0.40 ± 0.16) when estimated for survival or M, respectively. Models with 2D autocorrelation on survival or M fit the data better and had reduced retrospective pattern than models without autocorrelation. The best fit model included 2D autocorrelated deviations in survival as well as independent deviations in M and altered estimates of spawning stock biomass by 18 % and F by 21 % in model years. In short-term projections with F = 0, including 2D autocorrelation in survival or M reduced spawning stock biomass by 48 %. We conclude that incorporating 2D autocorrelated variation in survival or M could improve the assessment of Southern New England yellowtail flounder in terms of model fit and consistency of biomass projections
Partially fluidized shear granular flows: Continuum theory and MD simulations
The continuum theory of partially fluidized shear granular flows is tested
and calibrated using two dimensional soft particle molecular dynamics
simulations. The theory is based on the relaxational dynamics of the order
parameter that describes the transition between static and flowing regimes of
granular material. We define the order parameter as a fraction of static
contacts among all contacts between particles. We also propose and verify by
direct simulations the constitutive relation based on the splitting of the
shear stress tensor into a``fluid part'' proportional to the strain rate
tensor, and a remaining ``solid part''. The ratio of these two parts is a
function of the order parameter. The rheology of the fluid component agrees
well with the kinetic theory of granular fluids even in the dense regime. Based
on the hysteretic bifurcation diagram for a thin shear granular layer obtained
in simulations, we construct the ``free energy'' for the order parameter. The
theory calibrated using numerical experiments with the thin granular layer is
applied to the surface-driven stationary two dimensional granular flows in a
thick granular layer under gravity.Comment: 20 pages, 19 figures, submitted to Phys. Rev.
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