611 research outputs found
A case study in the history of neurology
We review the case of a young man who developed a constellation of symptoms and signs—bizarre behavior, seizures, abnormal movements, and autonomic instability—that evaded diagnosis at the time of presentation. We use this case to explore the way medical knowledge changes over time. Despite the dramatic advances in our understanding of neurological diseases in recent decades, physicians tend to approach diseases and diagnoses as if they were immutable. Our case reinforces how the diagnosis and treatment of disease are determined by an ever-changing historical context driven by the rapid expansion of medical knowledge. We discuss the implications of this realization and present strategies for navigating the boundaries of knowledge, both in practice and in principle
Study of Doubly Heavy Baryon Spectrum via QCD Sum Rules
In this work, we calculate the mass spectrum of doubly heavy baryons with the
diquark model in terms of the QCD sum rules. The interpolating currents are
composed of a heavy diquark field and a light quark field. Contributions of the
operators up to dimension six are taken into account in the operator product
expansion. Within a reasonable error tolerance, our numerical results are
compatible with other theoretical predictions. This indicates that the diquark
picture reflects the reality and is applicable to the study of doubly heavy
baryons.Comment: 23 pages, 9 figures, minor corrections in expression
Independent Eigenstates of Angular Momentum in a Quantum N-body System
The global rotational degrees of freedom in the Schr\"{o}dinger equation for
an -body system are completely separated from the internal ones. After
removing the motion of center of mass, we find a complete set of
independent base functions with the angular momentum . These are
homogeneous polynomials in the components of the coordinate vectors and the
solutions of the Laplace equation, where the Euler angles do not appear
explicitly. Any function with given angular momentum and given parity in the
system can be expanded with respect to the base functions, where the
coefficients are the functions of the internal variables. With the right choice
of the base functions and the internal variables, we explicitly establish the
equations for those functions. Only (3N-6) internal variables are involved both
in the functions and in the equations. The permutation symmetry of the wave
functions for identical particles is discussed.Comment: 24 pages, no figure, one Table, RevTex, Will be published in Phys.
Rev. A 64, 0421xx (Oct. 2001
Ammonia in a time of COVID-19. A submission of evidence to Defra/AQEG
A submission to the Air Quality Expert Group (AQEG), an expert committee of the Department for Environment, Food and Rural Affairs (Defra) • Ammonia gas (NH3) is a priority pollutant both as a precursor to particulate matter and for ecosystem impacts. • Three scenarios for UK emission reductions during COVID-19 in emission sectors, where activity is likely reduced ,have been assessed. • Total UK emissions of NH3 are likely to have decreased slightly (~2%), which is within the uncertainty and meteorological variability of the UK atmosphere. • Urban background and urban on road and roadside emissions of NH3 are likely to have decreased, by as much as 30% and 90% respectively compared with usual emissions before COVID-19. • Unratified data from three of the five UK automatic NH3 analysers (Auchencorth Moss, Chilbolton Observatory, and Manchester OSCA Observatory) show typical springtime NH3 concentrations across the UK. •
Data from the non-automatic National Ammonia Monitoring Network will enable analysis at UK level in the months ahead. This includes roadside data from London Cromwell Rd. • Evidence gaps & future approaches are outlined. Future analysis of the Defra UKEAP rural networks proposed. • The key measurement gap is urban roadside NH3 (and PM ammonium) as there is only one long-term site in the UK measuring roadside NH3 concentrations. It is suggested that a roadside network of samplers and/or analysers are urgently put in place (perhaps aligned with the UK Urban NO2 Network; UUNN) to monitor NH3 at roadsides during and post COVID-19 lock down where possible
Friction force on a vortex due to the scattering of superfluid excitations in helium II
The longitudinal friction acting on a vortex line in superfluid He is
investigated within a simple model based on the analogy between such vortex
dynamics and that of the quantal Brownian motion of a charged point particle in
a uniform magnetic field. The scattering of superfluid quasiparticle
excitations by the vortex stems from a translationally invariant interaction
potential which, expanded to first order in the vortex velocity operator, gives
rise to vortex transitions between nearest Landau levels. The corresponding
friction coefficient is shown to be, in the limit of elastic scattering
(vanishing cyclotron frequency), equivalent to that arising from the Iordanskii
formula. Proposing a simple functional form for the scattering amplitude, with
only one adjustable parameter whose value is set in order to get agreement to
the Iordanskii result for phonons, an excellent agreement is also found with
the values derived from experimental data up to temperatures about 1.5 K.
Finite values of the cyclotron frequency arising from recent theories are shown
to yield similar results. The incidence of vortex-induced quasiparticle
transitions on the friction process is estimated to be, in the roton dominated
regime, about 50 % of the value of the friction coefficient, 8 % of which
corresponds to roton-phonon transitions and 42 % to roton
ones.Comment: 15 pages, 4 figures; typos corrected, to be published in PR
Development of a high sensitivity ammonia sensor: Phase 1 feasibility study report (01/05/18 – 31/08/18)
Gas sensor technologies for monitoring atmospheric concentrations of ammonia gas are reviewed and summarised in this report
Development of a new model DELTA sampler and assessment of potential sampling artefacts in the UKEAP AGANet DELTA system: summary and technical report
Measurement of ammonia emissions from temperate and sub-polar seabird colonies
The chemical breakdown of marine derived reactive nitrogen transported to the land as seabird guano represents a significant source of ammonia (NH3) in areas far from other NH3 sources. Measurements made at tropical and temperate seabird colonies indicate substantial NH3 emissions, with emission rates larger than many anthropogenic point sources. However, several studies indicate that thermodynamic processes limit the amount of NH3 emitted from guano, suggesting that the percentage of guano volatilizing as NH3 may be considerably lower in colder climates. This study undertook high resolution temporal ammonia measurements in the field and coupled results with modelling to estimate NH3 emissions at a temperate puffin colony and two sub-polar penguin colonies (Signy Island, South Orkney Islands and Bird Island, South Georgia) during the breeding season. These emission rates are then compared with NH3 volatilization rates from other climates. Ammonia emissions were calculated using a Lagrangian atmospheric dispersion model, resulting in mean emissions of 5 μg m-2 s-1 at the Isle of May, 12 μg m-2 s-1 at Signy Island and 9 μg m-2 s-1 at Bird Island. The estimated percentage of total guano nitrogen volatilized was 5% on the Isle of May, 3% on Signy and 2% on Bird Island. These values are much smaller than the percentage of guano nitrogen volatilized in tropical contexts (31-65%). The study confirmed temperature, wind speed and water availability have a significant influence on the magnitude of NH3 emissions, which has implications for reactive nitrogen in both modern remote regions and pre-industrial atmospheric composition and ecosystem interactions
Pulsar-wind nebulae and magnetar outflows: observations at radio, X-ray, and gamma-ray wavelengths
We review observations of several classes of neutron-star-powered outflows:
pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe
interacting directly with interstellar medium (ISM), and magnetar-powered
outflows. We describe radio, X-ray, and gamma-ray observations of PWNe,
focusing first on integrated spectral-energy distributions (SEDs) and global
spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering
array of morphologies, with jets, trails, and other structures. Several of the
23 so far identified magnetars show evidence for continuous or sporadic
emission of material, sometimes associated with giant flares, and a few
possible "magnetar-wind nebulae" have been recently identified.Comment: 61 pages, 44 figures (reduced in quality for size reasons). Published
in Space Science Reviews, "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray
Bursts and Blazars: Physics of Extreme Energy Release
Measurements of the Mass and Full-Width of the Meson
In a sample of 58 million events collected with the BES II detector,
the process J/ is observed in five different decay
channels: , , (with ), (with
) and . From a combined fit of all five
channels, we determine the mass and full-width of to be
MeV/ and
MeV/.Comment: 9 pages, 2 figures and 4 table. Submitted to Phys. Lett.
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