484 research outputs found
Evaluation of on-board hydrogen storage methods for hypersonic vehicles
Hydrogen is the foremost candidate as a fuel for use in high speed transport. Since any aircraft moving at hypersonic speeds must have a very slender body, means of decreasing the storage volume requirements below that for liquid hydrogen are needed. The total performance of the hypersonic plane needs to be considered for the evaluation of candidate fuel and storage systems. To accomplish this, a simple model for the performance of a hypersonic plane is presented. To allow for the use of different engines and fuels during different phases of flight, the total trajectory is divided into three phases: subsonic-supersonic, hypersonic and rocket propulsion phase. The fuel fraction for the first phase is found be a simple energy balance using an average thrust to drag ratio for this phase. The hypersonic flight phase is investigated in more detail by taking small altitude increments. This approach allowed the use of flight profiles other than the constant dynamic pressure flight. The effect of fuel volume on drag, structural mass and tankage mass was introduced through simplified equations involving the characteristic dimension of the plane. The propellant requirement for the last phase is found by employing the basic rocket equations. The candidate fuel systems such as the cryogenic fuel combinations and solid and liquid endothermic hydrogen generators are first screened thermodynamically with respect to their energy densities and cooling capacities and then evaluated using the above model
Numerical study of two-body correlation in a 1D lattice with perfect blockade
We compute the dynamics of excitation and two-body correlation for two-level
"pseudoatoms" in a 1D lattice. We adopt a simplified model where pair
excitation within a finite range is perfectly blocked. Each superatom is
initially in the ground state, and then subjected to an external driving laser
with Rabi frequency satisfying a Poissonian distribution, mimicking the
scenario as in Rydberg gases. We find that two-body quantum correlation drops
very fast with the distance between pseudoatoms. However, the total correlation
decays slowly even at large distance. Our results may be useful to the
understanding of Rydberg gases in the strong blockade regime
Design, development and deployment of a hand/wrist exoskeleton for home-based rehabilitation after stroke - SCRIPT project
YesChanges in world-wide population trends have provided new demands for new technologies in areas
such as care and rehabilitation. Recent developments in the the field of robotics for neurorehabilitation
have shown a range of evidence regarding usefulness of these technologies as a tool to augment
traditional physiotherapy. Part of the appeal for these technologies is the possibility to place a
rehabilitative tool in one’s home, providing a chance for more frequent and accessible technologies
for empowering individuals to be in charge of their therapy.
Objective: this manuscript introduces the Supervised Care and Rehabilitation Involving Personal
Tele-robotics (SCRIPT) project. The main goal is to demonstrate design and development steps
involved in a complex intervention, while examining feasibility of using an instrumented orthotic
device for home-based rehabilitation after stroke.
Methods: the project uses a user-centred design methodology to develop a hand/wrist
rehabilitation device for home-based therapy after stroke. The patient benefits from a dedicated
user interface that allows them to receive feedback on exercise as well as communicating with
the health-care professional. The health-care professional is able to use a dedicated interface
to send/receive communications and remote-manage patient’s exercise routine using provided
performance benchmarks. Patients were involved in a feasibility study (n=23) and were instructed to
use the device and its interactive games for 180 min per week, around 30 min per day, for a period of
6 weeks, with a 2-months follow up. At the time of this study, only 12 of these patients have finished
their 6 weeks trial plus 2 months follow up evaluation.
Results: with the “use feasibility” as objective, our results indicate 2 patients dropping out due
to technical difficulty or lack of personal interests to continue. Our frequency of use results indicate
that on average, patients used the SCRIPT1 device around 14 min of self-administered therapy a day.
The group average for the system usability scale was around 69% supporting system usability.
Conclusions: based on the preliminary results, it is evident that stroke patients were able to use the
system in their homes. An average of 14 min a day engagement mediated via three interactive games
is promising, given the chronic stage of stroke. During the 2nd year of the project, 6 additional games
with more functional relevance in their interaction have been designed to allow for a more variant context for interaction with the system, thus hoping to positively influence the exercise duration.
The system usability was tested and provided supporting evidence for this parameter. Additional
improvements to the system are planned based on formative feedback throughout the project and
during the evaluations. These include a new orthosis that allows a more active control of the amount
of assistance and resistance provided, thus aiming to provide a more challenging interaction.This work has been partially funded under Grant FP7-ICT-288698(SCRIPT) of the European Community Seventh Framework Programme
Tunable Indistinguishable Photons From Remote Quantum Dots
Single semiconductor quantum dots have been widely studied within devices
that can apply an electric field. In the most common system, the low energy
offset between the InGaAs quantum dot and the surrounding GaAs material limits
the magnitude of field that can be applied to tens of kVcm^-1, before carriers
tunnel out of the dot. The Stark shift experienced by the emission line is
typically 1 meV. We report that by embedding the quantum dots in a quantum well
heterostructure the vertical field that can be applied is increased by over an
order of magnitude whilst preserving the narrow linewidths, high internal
quantum efficiencies and familiar emission spectra. Individual dots can then be
continuously tuned to the same energy allowing for two-photon interference
between remote, independent, quantum dots
Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering: Determined by the OLYMPUS Experiment
The OLYMPUS collaboration reports on a precision measurement of the
positron-proton to electron-proton elastic cross section ratio, ,
a direct measure of the contribution of hard two-photon exchange to the elastic
cross section. In the OLYMPUS measurement, 2.01~GeV electron and positron beams
were directed through a hydrogen gas target internal to the DORIS storage ring
at DESY. A toroidal magnetic spectrometer instrumented with drift chambers and
time-of-flight scintillators detected elastically scattered leptons in
coincidence with recoiling protons over a scattering angle range of to . The relative luminosity between the two beam species
was monitored using tracking telescopes of interleaved GEM and MWPC detectors
at , as well as symmetric M{\o}ller/Bhabha calorimeters at
. A total integrated luminosity of 4.5~fb was collected. In
the extraction of , radiative effects were taken into account
using a Monte Carlo generator to simulate the convolutions of internal
bremsstrahlung with experiment-specific conditions such as detector acceptance
and reconstruction efficiency. The resulting values of , presented
here for a wide range of virtual photon polarization ,
are smaller than some hadronic two-photon exchange calculations predict, but
are in reasonable agreement with a subtracted dispersion model and a
phenomenological fit to the form factor data.Comment: 5 pages, 3 figures, 2 table
Laparoscopic correction of perforated peptic ulcer: first choice? A review of literature
Background Perforated peptic ulcer (PPU), despite antiulcer medication and Helicobacter eradication, is still the most common indication for emergency gastric surgery associated with high morbidity and mortality. Outcome might be improved by performing this procedure laparoscopically, but there is no consensus on whether the benefits of laparoscopic closure of perforated peptic ulcer outweigh the disadvantages such as prolonged surgery time and greater expense. Methods An electronic literature search was done by using PubMed and EMBASE databases. Relevant papers written between January 1989 and May 2009 were selected and scored according to Effective Public Health Practice Project guidelines. Results Data were extracted from 56 papers, as summarized in Tables 1-7. The overall conversion rate for laparoscopic correction of perforated peptic ulcer was 12.4%, with main reason for conversion being the diameter of perforation. Patients presenting with PPU were predominantly men (79%), with an average age of 48 years. Onethird had a history of peptic ulcer disease, and one-fifth took nonsteroidal anti-inflammatory drugs (NSAIDs). Only 7% presented with shock at admission. There seems to be no consensus on the perfect setup for surgery and/or operating technique. In the laparoscopic groups, operating time was significant longer and incidence of recurrent leakage at the repair site was higher. Nonetheless there was significant less postoperative pain, lower morbidity, less mortality, and shorter hospital stay. Conclusion There are good arguments that laparoscopic correction of PPU should be first treatment of choice. A Boey score of 3, age over 70 years, and symptoms persisting longer than 24 h are associated with higher morbidity and mortality and should be considered contraindications for laparoscopic intervention
Modulation of Sn concentration in ZnO nanorod array: intensification on the conductivity and humidity sensing properties
Tin (Sn)-doped zinc oxide (ZnO) nanorod arrays (TZO) were synthesized onto aluminum-doped ZnO-coated glass substrate via a facile sonicated sol–gel immersion method for humidity sensor applications. These nanorod arrays were grown at different Sn concentrations ranging from 0.6 to 3 at.%. X-ray diffraction patterns showed that the deposited TZO arrays exhibited a wurtzite structure. The stress/strain condition of the ZnO film metamorphosed from tensile strain/compressive stress to compressive strain/tensile stress when the Sn concentrations increased. Results indicated that 1 at.% Sn doping of TZO, which has the lowest tensile stress of 0.14 GPa, generated the highest conductivity of 1.31 S cm− 1. In addition, 1 at.% Sn doping of TZO possessed superior sensitivity to a humidity of 3.36. These results revealed that the optimum performance of a humidity-sensing device can be obtained mainly by controlling the amount of extrinsic element in a ZnO film
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