38,521 research outputs found
Dual frequency receiver system for Mariner 1967 to Venus Final engineering report
Dual frequency receiver system for inclusion in Mariner 1967 spacecraft payload for use in measuring Venusian ionosphere and atmosphere by radio occultatio
Effect of time delay on feedback control of a flashing ratchet
It was recently shown that the use of feedback control can improve the
performance of a flashing ratchet. We investigate the effect of a time delay in
the implementation of feedback control in a closed-loop collective flashing
ratchet, using Langevin dynamics simulations. Surprisingly, for a large
ensemble, a well-chosen delay time improves the ratchet performance by allowing
the system to synchronize into a quasi-periodic stable mode of oscillation that
reproduces the optimal average velocity for a periodically flashing ratchet.
For a small ensemble, on the other hand, finite delay times significantly
reduce the benefit of feedback control for the time-averaged velocity, because
the relevance of information decays on a time scale set by the diffusion time
of the particles. Based on these results, we establish that experimental use of
feedback control is realistic.Comment: 6 pages, 6 figures, to appear in Europhysics Letter
Children's brain injury : a postal follow-up of 525 children from one health region in the UK
Primary objectives: to follow-up a population of children admitted to one Hospital Trust with traumatic brain injury (TBI), and compare outcomes following mild TBI with outcomes following moderate or severe TBI.
Research design: population-based postal questionnaire survey.
Methods and procedures: questionnaires were mailed to parents of all 974 surviving children on a register of paediatric TBI admissions, 525 completed questionnaires were returned (56.2%). Most children (419) had suffered mild TBI, 57 moderate, and 49 severe.
Main outcomes and results: Thirty percent of parents received no information on post-injury symptoms, and clinical follow-up was limited. Statistically significant differences were observed between mild and moderate/severe groups for cognitive, social, emotional, and mobility problems. Nevertheless, approximately 20% of the mild group suffered from poor concentration, personality change, and educational problems post-injury. Few schools (20%) made special provision for children returning after injury.
Conclusions: children can have long lasting and wide ranging sequelae following TBI. Information should be routinely given to parents and schools after brain injury
Outcomes following childhood head injury : a population study
Objectives: To identify outcomes following head injury (HI) amongst a population of children admitted to one hospital centre and compare outcomes between different severity groups.
Methods:A postal follow-up of children admitted with HI to one NHS Trust, between 1992-1998, was carried out. Children were aged 5-15 years at injury (mean 9.8), followed-up at a mean of 2.2 years post-injury. Parents of 526 injured children (419 mild, 58 moderate, 49 severe) and 45 controls completed questionnaires. Outcomes were assessed using the King’s Outcome Scale for Childhood Head Injury (KOSCHI).
Results:Frequent behavioural, emotional, memory and attentional problems were reported by one third of the severe group, one quarter of the moderate, and 10-18% of the mild. Personality change since HI was reported for 148 children (28%) (21% mild HI, 46% moderate, 69% severe). There was a significant relationship between injury severity and KOSCHI outcomes. Following the HI, 252(48%) had moderate disability (43% mild HI, 64% moderate, 69% severe), 270(51%) made a good recovery (57% mild HI, 36% moderate, 22% severe). There was a significant association between social deprivation and poor outcome (p=0.002). Only 30%(158) of children received hospital follow-up after the HI. All children with severe disability received appropriate follow-up, but 64% of children with moderate disability received none. No evidence was found to suggest a threshold of injury severity below which the risk of late sequelae could be safely discounted.
Conclusions:Children admitted with mild HI may be at risk of poor outcomes, but often do not receive routine hospital follow-up. A postal questionnaire combined with the KOSCHI to assess outcomes after HI may be used to identify children who would benefit from clinical assessment. Further research is needed to identify factors which place children with mild HI at risk of late morbidity
Engineering handbook on the atmospheric environmental guidelines for use in wind turbine generator development
The guidelines are given in the form of design criteria relative to wind speed, wind shear, turbulence, wind direction, ice and snow loading, and other climatological parameters which include rain, hail, thermal effects, abrasive and corrosive effects, and humidity. This report is a presentation of design criteria in an engineering format which can be directly input to wind turbine generator design computations. Guidelines are also provided for developing specialized wind turbine generators or for designing wind turbine generators which are to be used in a special region of the United States
Parental stress and burden following traumatic brain injury amongst children and adolescents
Primary objectives: to assess parental stress following paediatric traumatic brain injury (TBI) and examine the relationship between self-reported problems and parental stress and general health.
Research design: controlled interview study
Methods and procedures: Parents of ninety-seven children admitted with a TBI (49 mild, 19 moderate, 29 severe) were identified from a case register of all paediatric admissions from 1992-1998. Parents of 31 uninjured children acted as controls. Structured interviews were carried out with families, and parents assessed on the Parenting Stress Index (PSI/SF) and General Health Questionnaire (GHQ-12) at recruitment, and repeated 12 months later.
Main outcomes and results: regardless of injury severity, parents of injured children suffered greater stress than control parents as measured by the PSI/SF (p = 0.001). There was a highly significant relationship between number of problems reported and level of parental stress (p = 0.001). Financial burden was related to severity of TBI.
Conclusions: improved information, follow-up, and support is likely to reduce parental stress and family burden
A New Linear Inductive Voltage Adder Driver for the Saturn Accelerator
Saturn is a dual-purpose accelerator. It can be operated as a large-area
flash x-ray source for simulation testing or as a Z-pinch driver especially for
K-line x-ray production. In the first mode, the accelerator is fitted with
three concentric-ring 2-MV electron diodes, while in the Z-pinch mode the
current of all the modules is combined via a post-hole convolute arrangement
and driven through a cylindrical array of very fine wires. We present here a
point design for a new Saturn class driver based on a number of linear
inductive voltage adders connected in parallel. A technology recently
implemented at the Institute of High Current Electronics in Tomsk (Russia) is
being utilized[1].
In the present design we eliminate Marx generators and pulse-forming
networks. Each inductive voltage adder cavity is directly fed by a number of
fast 100-kV small-size capacitors arranged in a circular array around each
accelerating gap. The number of capacitors connected in parallel to each cavity
defines the total maximum current. By selecting low inductance switches,
voltage pulses as short as 30-50-ns FWHM can be directly achieved.Comment: 3 pages, 4 figures. This paper is submitted for the 20th Linear
Accelerator Conference LINAC2000, Monterey, C
Single Z' production at CLIC based on e^- gamma collisions
We analyze the potential of CLIC based on e- gamma collisions to search for
new gauge boson. Single Z' production at e-gamma colliders in two SU(3)_C
X SU(3)_L X U(1)_N models: the minimal model and the model with right-handed
(RH) neutrinos is studied in detail. Results show that new Z' gauge bosons can
be observed at the CLIC, and the cross sections in the model with RH neutrinos
are bigger than those in the minimal one.Comment: 11 pages, 4 figures, To appear in JET
A quantitative evaluation of metallic conduction in conjugated polymers
As the periodicity in crystalline materials creates the optimal condition for
electronic delocalization, one might expect that in partially crystalline
conjugated polymers delocalization is impeded by intergrain transport. However,
for the best conducting polymers this presumption fails. Delocalization is
obstructed by interchain rather than intergrain charge transfer and we propose
a model of weakly coupled disordered chains to describe the physics near the
metal-insulator transition. Our quantitative calculations match the outcome of
recent broad-band optical experiments and provide a consistent explanation of
metallic conduction in polymers.Comment: 4 pages incl. 3 figure
The interpretation of the field angle dependence of the critical current in defect-engineered superconductors
We apply the vortex path model of critical currents to a comprehensive
analysis of contemporary data on defect-engineered superconductors, showing
that it provides a consistent and detailed interpretation of the experimental
data for a diverse range of materials. We address the question of whether
electron mass anisotropy plays a role of any consequence in determining the
form of this data and conclude that it does not. By abandoning this false
interpretation of the data, we are able to make significant progress in
understanding the real origin of the observed behavior. In particular, we are
able to explain a number of common features in the data including shoulders at
intermediate angles, a uniform response over a wide angular range and the
greater discrimination between individual defect populations at higher fields.
We also correct several misconceptions including the idea that a peak in the
angular dependence of the critical current is a necessary signature of strong
correlated pinning, and conversely that the existence of such a peak implies
the existence of correlated pinning aligned to the particular direction. The
consistency of the vortex path model with the principle of maximum entropy is
introduced.Comment: 14 pages, 7 figure
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