5,795 research outputs found
The Status of the Pion-Nucleon Coupling Constant
A review is given of the various determinations of the different piNN
coupling constants in analyses of the low-energy pp, np, pbarp, and pi-p
scattering data. The most accurate determinations are in the energy-dependent
partial-wave analyses of the NN data. The recommended value is f^2 = 0.075 . A
recent determination of f^2 by the Uppsala group from backward np cross
sections is shown to be model dependent and inaccurate, and therefore
completely uninteresting. We also argue that an accurate determination of f^2
using pp forward dispersion relations is not a realistic option.Comment: 19 pages, latex2e with a4wide.sty, more information is available at
http://NN-OnLine.sci.kun.nl . Invited talk at FBXV, Groningen, The
Netherlands, July 22-26, 1997. Invited talk at MENU97, Vancouver, B.C.,
Canada, July 28 - August 1, 199
Partial-Wave Analyses of all Proton-Proton and Neutron-Proton Data Below 500 MeV
In 1993 the Nijmegen group published the results of energy-dependent
partial-wave analyses (PWAs) of the nucleon-nucleon (NN) scattering data for
laboratory kinetic energies below Tlab=350 MeV (PWA93). In this talk some
general aspects, but also the newest developments on the Nijmegen NN PWAs are
reported. We have almost finished a new energy-dependent PWA and will discuss
some typical aspects of this new PWA; where it differs from PWA93, but also
what future developments might be, or should be.Comment: Presentation at the 19th European Conference on Few-Body Problems in
Physics, Groningen, The Netherlands, 23-27 August 2004. 4 pages REVTeX4, no
figure
Zero sound in a single component fermion - Bose Einstein Condensate mixture
The resonant dynamics of mediated interactions supports zero-sound in a cold
atom degenerate mixture of a single component fermion gas and a Bose-Einstein
condensate (BEC). We characterize the onset of instability in the phase
separation of an unstable mixture and we find a rich collective mode structure
for stable mixtures with one undamped mode that exhibits an avoided crossing
and a Landau-damped mode that terminates.Comment: 4 pages, 2 figure
Chiral two-pion exchange and proton-proton partial-wave analysis
The chiral two-pion exchange component of the long-range pp interaction is
studied in an energy-dependent partial-wave analysis. We demonstrate its
presence and importance, and determine the chiral parameters c_i (i=1,3,4). The
values agree well with those obtained from pion-nucleon amplitudes.Comment: 13 pages, no figure
Comment on piNN Coupling from High Precision np Charge Exchange at 162 MeV
In this updated and expanded version of our delayed Comment we show that the
np backward cross section, as presented by the Uppsala group, is seriously
flawed (more than 25 sd.). The main reason is the incorrect normalization of
the data. We show also that their extrapolation method, used to determine the
charged piNN coupling constant, is a factor of about 10 less accurate than
claimed by Ericson et al. The large extrapolation error makes the determination
of the coupling constant by the Uppsala group totally uninteresting.Comment: 5 pages, latex2e with a4wide.sty. This is an updated and extended
version of the Comment published in Phys. Rev. Letters 81, 5253 (1998
Degenerate fermion gas heating by hole creation
Loss processes that remove particles from an atom trap leave holes behind in
the single particle distribution if the trapped gas is a degenerate fermion
system. The appearance of holes increases the temperature and we show that the
heating is (i) significant if the initial temperature is well below the Fermi
temperature , and (ii) increases the temperature to
after half of the system's lifetime, regardless of the initial temperature. The
hole heating has important consequences for the prospect of observing
Cooper-pairing in atom traps.Comment: to be published in PR
Spin communication over 30 m long channels of chemical vapor deposited graphene on SiO
We demonstrate a high-yield fabrication of non-local spin valve devices with
room-temperature spin lifetimes of up to 3 ns and spin relaxation lengths as
long as 9 m in platinum-based chemical vapor deposition (Pt-CVD)
synthesized single-layer graphene on SiO/Si substrates. The spin-lifetime
systematically presents a marked minimum at the charge neutrality point, as
typically observed in pristine exfoliated graphene. However, by studying the
carrier density dependence beyond n ~ 5 x 10 cm, via
electrostatic gating, it is found that the spin lifetime reaches a maximum and
then starts decreasing, a behavior that is reminiscent of that predicted when
the spin-relaxation is driven by spin-orbit interaction. The spin lifetimes and
relaxation lengths compare well with state-of-the-art results using exfoliated
graphene on SiO/Si, being a factor two-to-three larger than the best values
reported at room temperature using the same substrate. As a result, the spin
signal can be readily measured across 30 m long graphene channels. These
observations indicate that Pt-CVD graphene is a promising material for
large-scale spin-based logic-in-memory applications
Three-Fluid Description of the Sympathetic Cooling of a Boson-Fermion Mixture
We present a model for sympathetic cooling of a mixture of fermionic and
bosonic atomic gases in harmonic traps, based on a three-fluid description. The
model confirms the experimentally observed cooling limit of about 0.2 T_F when
only bosons are pumped. We propose sequential cooling -- first pumping of
bosons and afterwards fermions -- as a way to obtain lower temperatures. For
this scheme, our model predicts that temperatures less than 0.1 T_F can be
reached.Comment: 9 pages, 6 figure
Calibration of aerodynamic roughness over the Tibetan Plateau with Ensemble Kalman Filter analysed heat flux
Abstract. Aerodynamic roughness height (Zom) is a key parameter required in several land surface hydrological models, since errors in heat flux estimation are largely dependent on optimization of this input. Despite its significance, it remains an uncertain parameter which is not readily determined. This is mostly because of non-linear relationship in Monin-Obukhov similarity (MOS) equations and uncertainty of vertical characteristic of vegetation in a large scale. Previous studies often determined aerodynamic roughness using a minimization of cost function over MOS relationship or linear regression over it, traditional wind profile method, or remotely sensed vegetation index. However, these are complicated procedures that require a high accuracy for several other related parameters embedded in serveral equations including MOS. In order to simplify this procedure and reduce the number of parameters in need, this study suggests a new approach to extract aerodynamic roughness parameter from single or two heat flux measurements analyzed via Ensemble Kalman Filter (EnKF) that affords non-linearity. So far, to our knowledge, no previous study has applied EnKF to aerodynamic roughness estimation, while the majority of data assimilation study have paid attention to updates of other land surface state variables such as soil moisture or land surface temperature. The approach of this study was applied to grassland in semi-arid Tibetan Plateau and maize on moderately wet condition in Italy. It was demonstrated that aerodynamic roughness parameter can be inversely tracked from heat flux EnKF final analysis. The aerodynamic roughness height estimated in this approach was consistent with eddy covariance method and literature value. Through a calibration of this parameter, this adjusted the sensible heat previously overestimated and latent heat flux previously underestimated by the original Surface Energy Balance System (SEBS) model. It was considered that this improved heat flux estimation especially during the summer Monsoon period, based upon a comparison with precipitation and soil moisture field measurement. For an advantage of this approach over other previous methodologies, this approach is useful even when eddy covariance data are absent at a large scale and is time-variant over vegetation growth, as well as is not directly affected by saturation problem of remotely sensed vegetation index
Are track recommendations dependent on schools and school boards? A study of trends in the level of track recommendations, number of double recommendations and reconsiderations in Dutch urban and rural areas
Track recommendations provided to students in the final grade of primary education lead the allocation to specific school tracks in secondary education in the Netherlands. Where the results of a standardised test indicate that students are able to go to a higher track level, primary schools are required to reconsider and potentially adjust the track recommendation to a higher level. The current research aimed to (1) investigate trends in the level of track recommendations, double track recommendations and reconsiderations over the years 2014–2015 to 2018–2019, (2) explore the variation in (trends of) track recommendations between Dutch primary schools and their school boards, and (3) assess the association between track recommendations and the school level variables degree of urbanisation and type of primary education. We used multilevel growth curve modelling for continuous and count data based on publicly available school-level population data regarding track recommendations and school leavers tests from 2014–2015 to 2018–2019. The number of double track recommendations has increased over the cohorts, with a slightly decreasing gap between schools in rural and urban areas. The number of reconsiderations first decreased and then increased. The differences in reconsiderations between rural and urban areas are increasing over time. An initial trend towards higher average recommendations stabilising in the later cohorts appeared with no clear pattern for degree of urbanisation. The current study adds to the existing knowledge by assessing longitudinal trends instead of cross-sectional analyses and including multiple stakeholders and factors simultaneously.</p
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