1,215 research outputs found
Current legal and institutional issues in the commercialization of phosphoric acid fuel cells
Legal and institutional factors affecting the development and commercial diffusion of phosphoric acid fuel cells are assessed. Issues for future research and action are suggested. Perceived barriers and potential opportunities for fuel cells in central and dispersed utility operations and on-site applications are reviewed, as well as the general concept of commercialization as applied to emerging energy technologies
Pairing of a trapped resonantly-interacting fermion mixture with unequal spin populations
We consider the phase separation of a trapped atomic mixture of fermions with
unequal spin populations near a Feshbach resonance. In particular, we determine
the density profile of the two spin states and compare with the recent
experiments of Partridge et al. (cond-mat/0511752). Overall we find quite good
agreement. We identify the remaining discrepancies and pose them as open
problems.Comment: 4 figures, 4+ pages, revtex
Teaching word recognition to children with severe learning difficulties: an exploratory comparison of teaching methods
Background: Some children with severe learning difficulties fail to begin word recognition. For these children there is a need for an effective and appropriate pedagogy. However, conflicting advice can be found regarding this derived from teaching approaches that are not based on a shared understanding of how reading develops or the skills that the non-reader needs to master.
Purpose: In this research, three techniques for teaching word recognition in this context are described and compared: (1) the handle technique, (2) morphing method and (3) word alone. It also discusses whether it is appropriate for such small-scale research to influence pedagogy.
Programme description: The handle technique uses an abstract mnemonic cue used to teach word recognition, and previous research indicates it is more successful than the presentation of words alone. The morphing method transforms a word into a photographic picture and a previous study suggested that it might also be more effective that presenting words alone.
Sample: Six children between 11 and 13 years of age were selected. The criterion for selection was being unable to recognise any words from the British Ability Scales Reading Test. All the children attended a school for children with severe learning difficulties.
Design and methods: A three-condition related design was used. The order in which the conditions were presented was counterbalanced and each child was taught 12 words, four words in each experimental condition. The children encountered each of the three methods and overall each word was taught via each method. Within conditions (teaching methods), the presentation of words was randomised. The number of words that the children could read (without cues) before each session was recorded, following the presentation of the uncued words in a random order. The difference in the number of words recognised between the three conditions was considered using a non-parametric statistical analysis.
Results: The results suggest that the handle approach might be a more effective method of teaching word recognition.
Conclusion: Research in this area is necessarily small in scale. However, it is ongoing and cumulative, and can give insights into potentially beneficial changes in classroom practice
Density of states in d-wave superconductors disordered by extended impurities
The low-energy quasiparticle states of a disordered d-wave superconductor are
investigated theoretically. A class of such states, formed via tunneling
between the Andreev bound states that are localized around extended impurities
(and result from scattering between pair-potential lobes that differ in sign)
is identified. Its (divergent) contribution to the total density of states is
determined by taking advantage of connections with certain one-dimensional
random tight-binding models. The states under discussion should be
distinguished from those associated with nodes in the pair potential.Comment: 5 pages, 1 figur
Asymmetric Fermi superfluid with different atomic species in a harmonic trap
We study the dilute fermion gas with pairing between two species and unequal
concentrations in a harmonic trap using the mean field theory and the local
density approximation. We found that the system can exhibit a superfluid shell
structure sandwiched by the normal fermions. This superfluid shell structure
occurs if the mass ratio is larger then certain critical value which increases
from the weak-coupling BCS region to the strong-coupling BEC side. In the
strong coupling BEC regime, the radii of superfluid phase are less sensitive to
the mass ratios and are similar to the case of pairing with equal masses.
However, the lighter leftover fermions are easier to mix with the superfluid
core than the heavier ones. A partially polarized superfluid can be found if
the majority fermions are lighter, whereas phase separation is still found if
they are heavier.Comment: 12 pages, 7 figure
Metastability in spin polarised Fermi gases and quasiparticle decays
We investigate the metastability associated with the first order transition from normal to superfluid phases in the phase diagram of two-component polarised Fermi gases.We begin by detailing the dominant decay processes of single quasiparticles.Having determined the momentum thresholds of each process and calculated their rates, we apply this understanding to a Fermi sea of polarons by linking its metastability to the stability of individual polarons, and predicting a region of metastability for the normal partially polarised phase. In the limit of a single impurity, this region extends from the interaction strength at which a polarised phase of molecules becomes the groundstate, to the one at which the single quasiparticle groundstate changes character from polaronic to molecular. Our argument in terms of a Fermi sea of polarons naturally suggests their use as an experimental probe. We propose experiments to observe the threshold of the predicted region of metastability, the interaction strength at which the quasiparticle groundstate changes character, and the decay rate of polarons
High harmonic generation at long wavelengths
High harmonic radiation spectra up to 19th order in alkali metal vapors excited by an intense, picosecond mid-infrared (3 -4 mu m) laser are reported and compared to theory. The strong-field dynamics in the alkali metal atoms exhibit significant differences from all previously studied systems due to the strong coupling between their ground and first excited states
USING BIRD STRIKE DATA TO MONITOR BIRD-HAZARD CONTROL
An effective definition of a bird strike is the basis for quantifying the scale of bird hazard problems. Here we present a working definition of a bird strike, which in turn forms the basis of an analysis of 32 years’ data collected at Dublin Airport, Ireland. A variety of datasets are analysed including the number of bird strikes per ten thousand aircraft movements, the mass of the bird species being struck, the time of year at which bird strikes occur and the dimensions of the aircraft utilising the airfield. In addition, we have analysed the mean number of strikes per year and the mean number of birds struck per bird strike. Following a very serious incident involving a Boeing 737-200 which struck a flock of gulls in the mid -1980’s, a new regime of control measures was put in place. Therefore our study permits us to evaluate the effectiveness of this management programme. The results suggest that the most significant impact of control measures is to reduce the number of birds being struck per bird strike
Microwave conductivity of a d-wave superconductor disordered by extended impurities: a real-space renormalization group approach
Using a real-space renormalization group (RSRG) technique, we compute the
microwave conductivity of a d-wave superconductor disordered by extended
impurities. To do this, we invoke a semiclassical approximation which naturally
accesses the Andreev bound states localized near each impurity. Tunneling
corrections (which are captured using the RSRG) lead to a delocalization of
these quasiparticles and an associated contribution to the microwave
conductivity.Comment: 8 pages, 4 figures. 2 figures added to previous versio
Pamela: development of the RF system for a non-relativistic non-scaling FFAG
The PAMELA project(Particle Accelerator For MEdical
Applications) currently consists of the design of a particle
therapy facility. The project, which is in the design phase,
contains Non-Scaling FFAG, particle accelerator capable
of rapid beam acceleration, giving a pulse repetition rate of
1kHz, far beyond that of a conventional synchrotron. To
realise the repetition rate, a key component of the accelerator
is the rf accelerating system. The combination of a high
energy gain per turn and a high repetition rate is a significant
challenge. In this paper, options for the rf system of
the proton ring and the status of development are presented
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