5,567 research outputs found
Perturbations of Dark Solitons
A method for approximating dark soliton solutions of the nonlinear
Schrodinger equation under the influence of perturbations is presented. The
problem is broken into an inner region, where core of the soliton resides, and
an outer region, which evolves independently of the soliton. It is shown that a
shelf develops around the soliton which propagates with speed determined by the
background intensity. Integral relations obtained from the conservation laws of
the nonlinear Schrodinger equation are used to approximate the shape of the
shelf. The analysis is developed for both constant and slowly evolving
backgrounds. A number of problems are investigated including linear and
nonlinear damping type perturbations
A comparison of the responses of mature and young clonal tea to drought.
To assist commercial producers with optimising the use of irrigation water, the
responses to drought of mature and young tea crops (22 and 5 years after field
planting respectively) were compared using data from two adjacent long-term
irrigation experiments in Southern Tanzania. Providing the maximum potential
soil water deficit was below about 400-500 mm for mature, and 200-250 mm for
young plants (clone 6/8), annual yields of dry tea from rainfed or partially
irrigated crops were similar to those from the corresponding well-watered crops.
At deficits greater than this, annual yields declined rapidly in young tea (up
to 22 kg (ha mm)-1) but relatively slowly in mature tea (up to 6.5 kg (ha mm)-
1). This apparent insensitivity of the mature crop to drought was due
principally to compensation that occurred during the rains for yield lost in the
dry season. Differences in dry matter distribution and shoot to root ratios
contributed to these contrasting responses. Thus, the total above ground dry
mass of well-irrigated, mature plants was about twice that for young plants.
Similarly, the total mass of structural roots (>1 mm diameter), to 3 m depth,
was four times greater in the mature crop than in the young crop and, for fine
roots (<1 mm diameter), eight times greater. The corresponding shoot to root
ratios (dry mass) were about 1:1 and 2:1 respectively. In addition, each unit
area of leaf in the canopy of a mature plant had six times more fine roots (by
weight) available to extract and supply water than did a young plant. Despite
the logistical benefits resulting from more even crop distribution during the
year when crops are fully irrigated, producers currently prefer to save water
and energy costs by allowing a substantial soil water deficit to develop prior
to the start of the rains, up to 250 mm in mature tea, knowing that yield
compensation will occur later
Understanding household preferences for alternative-fuel vehicles technologies
This report explores consumer preferences among four different alternative-fuel vehicles (AFVs): hybrid electric vehicles (HEVs), compressed natural gas (CNG) vehicles, hydrogen fuel cell (HFC) vehicles, and electric vehicles (EVs). Although researchers have been interested in understanding consumer preferences for AFVs for more than three decades, it is important to update our estimates of the trade-offs people are willing to make between cost, environmental performance, vehicle range, and refueling convenience. We conducted a nationwide, Internet-based survey to assess consumer preferences for AFVs. Respondents participated in a stated-preference ranking exercise in which they ranked a series of five vehicles (four AFVs and a traditional gasoline-fueled vehicle) that differ primarily in fuel type, price, environmental performance, vehicle range, and refueling convenience. Our findings indicate that, in general, gasoline-fueled vehicles are still preferred over AFVs, however there is a strong interest in AFVs. No AFV type is overwhelmingly preferred, although HEVs seem to have an edge. Using a panel rank-ordered mixed logit model, we assessed the trade-offs people make between key AFV characteristics. We found that, in order to leave a person’s utility unchanged, a 300 savings in driving cost over 12,000 miles; (2) a 17.5 mile increase in vehicle range; or (3) a 7.8-minute decrease in total refueling time (e.g. finding a gas station and refueling)
Placing the transfer of learning at the heart of HRD Practice
Training evaluation is a key area of Human Resource Development, however, measuring the effectiveness of training and the transfer of learning from a training programme to the workplace can be a challenging activity. This is even more problematic for a training provider who does not have the continuous relationship or access to performance measures of an in-house training department. This paper reports on the evaluation of a training model, assessing the impact from introduction to completion of the cycle. There are three partners in this research project: the training company, the client organisation and the university researchers.
Synaptic Change Ltd is a training consultancy delivering bespoke training to organisations. Utilising a case study approach, this project reports on the evaluation of their training model through its introduction at Connect Housing, a charitable housing and support provider. This presents an interesting context for the study as researchers have suggested the distinctive value led culture of the Voluntary Sector can support a strong learning culture within the organisation. The project seeks to assess the value of learning to the organisation derived from the introduction of the model. The paper explores theoretical and empirical research concerning the evaluation of training and discusses the context of the case study organisation. It then positions the methodology employed and how data will be collected. As a working paper, the findings are not available at this time but will be presented and discussed at the UFHRD conference
Big Impacts and Transient Oceans on Titan
We have studied the thermal consequences of very big impacts on Titan [1]. Titan's thick atmosphere and volatile-rich surface cause it to respond to big impacts in a somewhat Earth-like manner. Here we construct a simple globally-averaged model that tracks the flow of energy through the environment in the weeks, years, and millenia after a big comet strikes Titan. The model Titan is endowed with 1.4 bars of N2 and 0.07 bars of CH4, methane lakes, a water ice crust, and enough methane underground to saturate the regolith to the surface. We assume that half of the impact energy is immediately available to the atmosphere and surface while the other half is buried at the site of the crater and is unavailable on time scales of interest. The atmosphere and surface are treated as isothermal. We make the simplifying assumptions that the crust is everywhere as methane saturated as it was at the Huygens landing site, that the concentration of methane in the regolith is the same as it is at the surface, and that the crust is made of water ice. Heat flow into and out of the crust is approximated by step-functions. If the impact is great enough, ice melts. The meltwater oceans cool to the atmosphere conductively through an ice lid while at the base melting their way into the interior, driven down in part through Rayleigh-Taylor instabilities between the dense water and the warm ice. Topography, CO2, and hydrocarbons other than methane are ignored. Methane and ethane clathrate hydrates are discussed quantitatively but not fully incorporated into the model
Plasmon Evolution and Charge-Density Wave Suppression in Potassium Intercalated Tantalum Diselenide
We have investigated the influence of potassium intercalation on the
formation of the charge-density wave (CDW) instability in 2H-tantalum
diselenide by means of Electron Energy-Loss Spectroscopy and density functional
theory. Our observations are consistent with a filling of the conduction band
as indicated by a substantial decrease of the plasma frequency in experiment
and theory. In addition, elastic scattering clearly points to a destruction of
the CDW upon intercalation as can be seen by a vanishing of the corresponding
superstructures. This is accompanied by a new superstructure, which can be
attributed to the intercalated potassium. Based on the behavior of the c-axis
upon intercalation we argue in favor of interlayer-sites for the alkali-metal
and that the lattice remains in the 2H-modification
New Measurements of Fine-Scale CMB Polarization Power Spectra from CAPMAP at Both 40 and 90 GHz
We present new measurements of the cosmic microwave background (CMB)
polarization from the final season of the Cosmic Anisotropy Polarization MAPper
(CAPMAP). The data set was obtained in winter 2004-2005 with the 7 m antenna in
Crawford Hill, New Jersey, from 12 W-band (84-100 GHz) and 4 Q-band (36-45 GHz)
correlation polarimeters with 3.3' and 6.5' beamsizes, respectively. After
selection criteria were applied, 956 (939) hours of data survived for analysis
of W-band (Q-band) data. Two independent and complementary pipelines produced
results in excellent agreement with each other. A broad suite of null tests as
well as extensive simulations showed that systematic errors were minimal, and a
comparison of the W-band and Q-band sky maps revealed no contamination from
galactic foregrounds. We report the E-mode and B-mode power spectra in 7 bands
in the range 200 < l < 3000, extending the range of previous measurements to
higher l. The E-mode spectrum, which is detected at 11 sigma significance, is
in agreement with cosmological predictions and with previous work at other
frequencies and angular resolutions. The BB power spectrum provides one of the
best limits to date on B-mode power at 4.8 uK^2 (95% confidence).Comment: 19 pages, 17 figures, 2 tables, submitted to Ap
The longitudinal conductance of mesoscopic Hall samples with arbitrary disorder and periodic modulations
We use the Kubo-Landauer formalism to compute the longitudinal (two-terminal)
conductance of a two dimensional electron system placed in a strong
perpendicular magnetic field, and subjected to periodic modulations and/or
disorder potentials. The scattering problem is recast as a set of
inhomogeneous, coupled linear equations, allowing us to find the transmission
probabilities from a finite-size system computation; the results are exact for
non-interacting electrons. Our method fully accounts for the effects of the
disorder and the periodic modulation, irrespective of their relative strength,
as long as Landau level mixing is negligible. In particular, we focus on the
interplay between the effects of the periodic modulation and those of the
disorder. This appears to be the relevant regime to understand recent
experiments [S. Melinte {\em et al}, Phys. Rev. Lett. {\bf 92}, 036802 (2004)],
and our numerical results are in qualitative agreement with these experimental
results. The numerical techniques we develop can be generalized
straightforwardly to many-terminal geometries, as well as other multi-channel
scattering problems.Comment: 13 pages, 11 figure
Variability in Short Gamma-ray Bursts: Gravitationally Unstable Tidal Tails
Short gamma-ray bursts are thought to result from the mergers of two neutron
stars or a neutron star and stellar mass black hole. The final stages of the
merger are generally accompanied by the production of one or more tidal "tails"
of ejecta, which fall back onto the remnant-disc system at late times. Using
the results of a linear stability analysis, we show that if the material
comprising these tails is modeled as adiabatic and the effective adiabatic
index satisfies , then the tails are gravitationally unstable
and collapse to form small-scale knots. We analytically estimate the properties
of these knots, including their spacing along the tidal tail and the total
number produced, and their effect on the mass return rate to the merger
remnant. We perform hydrodynamical simulations of the disruption of a
polytropic (with the polytropic and adiabatic indices equal), neutron star by a black hole, and find agreement between the predictions of
the linear stability analysis and the distribution of knots that collapse out
of the instability. The return of these knots to the black hole induces
variability in the fallback rate, which can manifest as variability in the
lightcurve of the GRB and -- depending on how rapidly the instability operates
-- the prompt emission. The late-time variability induced by the return of
these knots is also consistent with the extended emission observed in some
GRBs.Comment: Small corrections, additional references included to reflect ApJL
published versio
Electron-beam propagation in a two-dimensional electron gas
A quantum mechanical model based on a Green's function approach has been used
to calculate the transmission probability of electrons traversing a
two-dimensional electron gas injected and detected via mode-selective quantum
point contacts. Two-dimensional scattering potentials, back-scattering, and
temperature effects were included in order to compare the calculated results
with experimentally observed interference patterns. The results yield detailed
information about the distribution, size, and the energetic height of the
scattering potentials.Comment: 7 pages, 6 figure
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