2,656 research outputs found
On Multiple Zeta Values of Even Arguments
For k <= n, let E(2n,k) be the sum of all multiple zeta values with even
arguments whose weight is 2n and whose depth is k. Of course E(2n,1) is the
value of the Riemann zeta function at 2n, and it is well known that E(2n,2) =
(3/4)E(2n,1). Recently Z. Shen and T. Cai gave formulas for E(2n,3) and
E(2n,4). We give two formulas form E(2n,k), both valid for arbitrary k <=n, one
of which generalizes the Shen-Cai results; by comparing the two we obtain a
Bernoulli-number identity. We also give explicit generating functions for the
numbers E(2n,k) and for the analogous numbers E*(2n,k) defined using multiple
zeta-star values of even arguments.Comment: DESY number added; misprints fixed; reference added. Second revision
(2016): New result on multiple zeta-star values adde
Mechanical Evidence of the Orbital Angular Momentum to Energy Ratio of Vortex Beams
We measure, in a single experiment, both the radiation pressure and the torque due to a wide variety of
propagating acoustic vortex beams. The results validate, for the first time directly, the theoretically
predicted ratio of the orbital angular momentum to linear momentum in a propagating beam. We
experimentally determine this ratio using simultaneous measurements of both the levitation force and
the torque on an acoustic absorber exerted by a broad range of helical ultrasonic beams produced by a
1000-element matrix transducer array. In general, beams with helical phase fronts have been shown to
contain orbital angular momentum as the result of the azimuthal component of the Poynting vector around
the propagation axis. Theory predicts that for both optical and acoustic helical beams the ratio of the
angular momentum current of the beam to the power should be given by the ratio of the beam’s
topological charge to its angular frequency. This direct experimental observation that the ratio of the
torque to power does convincingly match the expected value (given by the topological charge to angular
frequency ratio of the beam) is a fundamental result
Equilibrium Current and Orbital Magnetization in a Quantum Hall Fluid
We present a general theory for the equilibrium current distribution in an
interacting two-dimensional electron gas subjected to a perpendicular magnetic
field, and confined by a potential that varies slowly on the scale of the
magnetic length. The distribution is found to consist of strips or channels of
current, which alternate in direction, and which have universal integrated
strength.Comment: 13 pages, Revtex, to appear in the proceedings of the "Workshop on
Novel Physics in Low-Dimensional Electron Systems" held in Madra
Wind Effects on Near- and Midfield Mixing in Tidally Pulsed River Plumes
River plumes transport and mix land-based tracers into the ocean. In tidally pulsed river plumes, wind effects have long been considered negligible in modulating interfacial mixing in the energetic nearfield region. This research tests the influence of variable, realistic winds on mixing in the interior plume. A numerical model of the Merrimack River plume-shelf system is utilized, with an application of the salinity variance approach employed to identify spatial and temporal variation in advection, straining, and dissipation (mixing) of vertical salinity variance (stratification). Results indicate that moderate wind stresses (∼0.5 Pa) with a northward component countering the downcoast rotation of the plume are most effective at decreasing stratification in the domain relative to other wind conditions. Northward winds advect plume and ambient shelf stratification offshore, allowing shelf water salinity to increase in the nearshore, which strengthens the density gradient at the plume base. Straining in the plume increases with winds enhancing offshore-directed surface velocities, leading to increased shear at the plume base. Increased straining and larger density gradients at the plume base enhance variance dissipation in the near- and midfield plume, and dissipation remains enhanced if the shelf is clear of residual stratification. The smaller spatial and temporal scales of the Merrimack plume allow the mechanisms to occur at tidal time scales in direct response to instantaneous winds. This is the first study to show tidal time scale wind-induced straining and advection as controlling factors on near- and midfield mixing rates in river plumes under realistic winds
Freshwater Composition and Connectivity of the Connecticut River Plume During Ambient Flood Tides
The Connecticut River plume interacts with the strong tidal currents of the ambient receiving waters in eastern Long Island Sound. The plume formed during ambient flood tides is studied as an example of tidal river plumes entering into energetic ambient tidal environments in estuaries or continental shelves. Conservative passive freshwater tracers within a high-resolution nested hydrodynamic model are applied to determine how source waters from different parts of the tidal cycle contribute to plume composition and interact with bounding plume fronts. The connection to source waters can be cut off only under low-discharge conditions, when tides reverse surface flow through the mouth after max ambient flood. Upstream plume extent is limited because ambient tidal currents arrest the opposing plume propagation, as the tidal internal Froude number exceeds one. The downstream extent of the tidal plume always is within 20 km from the mouth, which is less than twice the ambient tidal excursion. Freshwaters in the river during the preceding ambient ebb are the oldest found in the new flood plume. Connectivity with source waters and plume fronts exhibits a strong upstream-to- downstream asymmetry. The arrested upstream front has high connectivity, as all freshwaters exiting the mouth immediately interact with this boundary. The downstream plume front has the lowest overall connectivity, as interaction is limited to the oldest waters since younger interior waters do not overtake this front. The offshore front and inshore boundary exhibit a downstream progression from younger to older waters and decreasing overall connectivity with source waters. Plume-averaged freshwater tracer concentrations and variances both exhibit an initial growth period followed by a longer decay period for the remainder of the tidal period. The plume-averaged tracer variance is increased by mouth inputs, decreased by entrainment, and destroyed by internal mixing. Peak entrainment velocities for younger waters are higher than values for older waters, indicating stronger entrainment closer to the mouth. Entrainment and mixing time scales (1–4 h at max ambient flood) are both shorter than half a tidal period, indicating entrainment and mixing are vigorous enough to rapidly diminish tracer variance within the plume
exoMMR: a New Python Package to Confirm and Characterize Mean Motion Resonances
The study of orbital resonances allows for the constraint of planetary
properties of compact systems. We can predict a system's resonances by
observing the orbital periods of the planets, as planets in or near mean motion
resonance have period ratios that reduce to a ratio of small numbers. However,
a period ratio near commensurability does not guarantee a resonance; we must
study the system's dynamics and resonant angles to confirm resonance. Because
resonances require in-depth study to confirm, and because two-body resonances
require a measurement of the eccentricity vector which is quite challenging,
very few resonant pairs or chains have been confirmed. We thus remain in the
era of small number statistics, not yet able to perform large population
synthesis or informatics studies. To address this problem, we build a python
package to find, confirm, and analyze mean motion resonances, primarily through
N-body simulations. We then analyze all near-resonant planets in the Kepler/K2
and TESS catalogues, confirming over 60 new resonant pairs and various new
resonant chains. We additionally demonstrate the package's functionality and
potential by characterizing the mass-eccentricity degeneracy of Kepler-80g,
exploring the likelihood of an exterior giant planet in Kepler-80, and
constraining the masses of planets in Kepler-305. We find that our methods
overestimate the libration amplitudes of the resonant angles and struggle to
confirm resonances in systems with more than three planets. We identify various
systems that are likely resonant chains but that we are unable to confirm, and
highlight next steps for exoplanetary resonances.Comment: 19 pages, 3 figures, 8 tables, accepted for publication in A
Peak oxygen uptake measured during a perceptually-regulated exercise test is reliable in community-based manual wheelchair users
This study aimed to compare test-retest reliability and peak exercise responses from
ramp-incremented (RAMP) and maximal perceptually-regulated (PRETmax) exercise
tests during arm crank exercise in individuals reliant on manual wheelchair
propulsion (MWP). Ten untrained participants (9 male) completed four trials over a
2-week period, performing two RAMP (0-40 W + 5-10 W·min-1) trials one week followed by two PRETmax trials the next, or vice versa. PRETmax consisted of five, 2-min stages performed at Ratings of Perceived Exertion (RPE) 11, 13, 15, 17 and 20. Participants freely changed the power output to match the required RPE. Gas exchange variables, heart rate, power output, RPE and affect were determined throughout trials. The V̇ O2peak from RAMP (14.8 ± 5.5 ml·kg-1 ·min-1 ) and PRETmax (13.9 ± 5.2 ml·kg-1 ·min-1) trials were not different (P = 0.08). Measurement error was 1.7 and 2.2 ml·kg-1 ·min-1 and coefficient of variation 5.9% and 8.1% for
measuring V̇ O2peak from RAMP and PRETmax, respectively. Affect was more positive at RPE 13 (P = 0.02), 15 (P = 0.01) and 17 (P = 0.01) during PRETmax. This study shows the PRETmax can be used to measure V̇ O2peak in participants reliant on MWP and leads to a more positive affective response compared to RAMP
The Role of the Private Sector in Supporting Malaria Control in Resource Development Settings.
Industrial operations of the private sector, such as extraction, agriculture, and construction, can bring large numbers of people into new settlement areas and cause environmental change that promotes the transmission of vector-borne diseases. Industry-related workers and communities unduly exposed to infection risk typically lack the knowledge and means to protect themselves. However, there is a strong business rationale for protecting local resident employees through integrated vector control programs, as well as an ethical responsibility to care for these individuals and the affected communities. We discuss the role and challenges of the private sector in developing malaria control programs, which can include extensive collaborations with the public sector that go on to form the basis of national vector control programs or more broadly support local healthcare systems
Universal Equilibrium Currents in the Quantum Hall Fluid
The equilibrium current distribution in a quantum Hall fluid that is
subjected to a slowly varying confining potential is shown to generally consist
of strips or channels of current, which alternate in direction, and which have
universal integrated strengths. A measurement of these currents would yield
direct independent measurements of the proper quasiparticle and quasihole
energies in the fractional quantum Hall states.Comment: 4 pages, Revte
Fusion products, Kostka polynomials, and fermionic characters of su(r+1)_k
Using a form factor approach, we define and compute the character of the
fusion product of rectangular representations of \hat{su}(r+1). This character
decomposes into a sum of characters of irreducible representations, but with
q-dependent coefficients. We identify these coefficients as (generalized)
Kostka polynomials. Using this result, we obtain a formula for the characters
of arbitrary integrable highest-weight representations of \hat{su}(r+1) in
terms of the fermionic characters of the rectangular highest weight
representations.Comment: 21 pages; minor changes, typos correcte
- …