23,875 research outputs found
How is carer strain related to the recovery of stroke survivors with right hemisphere dysfunction? Implications for practice
Aim: Right hemisphere strokes are associated with neuro-behavioural impairments including hemi-inattention, impulsiveness and anosognosia, which can impede stroke recovery and adversely affect carer health. This study explored the impact of associated impairments on carer strain and depression through a mixed methods approach.
Method: Fifty-one carer-survivor dyads were recruited from inpatient rehabilitation units and followed-up for six months. Validated measures assessed survivors’ physical and cognitive function and carers’ strain and depression levels. Survey methods captured qualitative experiences of the caring role. Data collection occurred at baseline, discharge, six weeks post-discharge and six months. Multilevel-modelling and thematic data analysis, were employed.
Results: Carer strain median scores were within normal ranges of the Caregiver Strain Index scale. Carer strain was positively linked to carer depression, number of carers’ concerns reported and survivors’ anosognosia levels. Carer strain was negatively linked to the survivors’ functional and cognitive abilities. Carers’ experiences differed qualitatively with caring concerns increasing over time.
Conclusion: Carer strain worsens with increases in significant concerns about the rehabilitation process and poor survivor functioning skills, which potentially increase risk of depression in carers. Consequently, improving right-hemisphere stroke survivors’ recovery and nurturing the carer-survivor relationship are likely to enhance overall outcomes and caring experiences
Dynamic remapping decisions in multi-phase parallel computations
The effectiveness of any given mapping of workload to processors in a parallel system is dependent on the stochastic behavior of the workload. Program behavior is often characterized by a sequence of phases, with phase changes occurring unpredictably. During a phase, the behavior is fairly stable, but may become quite different during the next phase. Thus a workload assignment generated for one phase may hinder performance during the next phase. We consider the problem of deciding whether to remap a paralled computation in the face of uncertainty in remapping's utility. Fundamentally, it is necessary to balance the expected remapping performance gain against the delay cost of remapping. This paper treats this problem formally by constructing a probabilistic model of a computation with at most two phases. We use stochastic dynamic programming to show that the remapping decision policy which minimizes the expected running time of the computation has an extremely simple structure: the optimal decision at any step is followed by comparing the probability of remapping gain against a threshold. This theoretical result stresses the importance of detecting a phase change, and assessing the possibility of gain from remapping. We also empirically study the sensitivity of optimal performance to imprecise decision threshold. Under a wide range of model parameter values, we find nearly optimal performance if remapping is chosen simply when the gain probability is high. These results strongly suggest that except in extreme cases, the remapping decision problem is essentially that of dynamically determining whether gain can be achieved by remapping after a phase change; precise quantification of the decision model parameters is not necessary
Optimal dynamic remapping of parallel computations
A large class of computations are characterized by a sequence of phases, with phase changes occurring unpredictably. The decision problem was considered regarding the remapping of workload to processors in a parallel computation when the utility of remapping and the future behavior of the workload is uncertain, and phases exhibit stable execution requirements during a given phase, but requirements may change radically between phases. For these problems a workload assignment generated for one phase may hinder performance during the next phase. This problem is treated formally for a probabilistic model of computation with at most two phases. The fundamental problem of balancing the expected remapping performance gain against the delay cost was addressed. Stochastic dynamic programming is used to show that the remapping decision policy minimizing the expected running time of the computation has an extremely simple structure. Because the gain may not be predictable, the performance of a heuristic policy that does not require estimnation of the gain is examined. The heuristic method's feasibility is demonstrated by its use on an adaptive fluid dynamics code on a multiprocessor. The results suggest that except in extreme cases, the remapping decision problem is essentially that of dynamically determining whether gain can be achieved by remapping after a phase change. The results also suggest that this heuristic is applicable to computations with more than two phases
An optimal repartitioning decision policy
A central problem to parallel processing is the determination of an effective partitioning of workload to processors. The effectiveness of any given partition is dependent on the stochastic nature of the workload. The problem of determining when and if the stochastic behavior of the workload has changed enough to warrant the calculation of a new partition is treated. The problem is modeled as a Markov decision process, and an optimal decision policy is derived. Quantification of this policy is usually intractable. A heuristic policy which performs nearly optimally is investigated empirically. The results suggest that the detection of change is the predominant issue in this problem
Mechanisms of interpersonal sway synchrony and stability
Here we explain the neural and mechanical mechanisms responsible for synchronizing sway and improving postural control during physical contact with another standing person. Postural control processes were modelled using an inverted pendulum under continuous feedback control. Interpersonal interactions were simulated either by coupling the sensory feedback loops or by physically coupling the pendulums with a damped spring. These simulations precisely recreated the timing and magnitude of sway interactions observed empirically. Effects of firmly grasping another person's shoulder were explained entirely by the mechanical linkage. This contrasted with light touch and/or visual contact, which were explained by a sensory weighting phenomenon; each person's estimate of upright was based on a weighted combination of veridical sensory feedback combined with a small contribution from their partner. Under these circumstances, the model predicted reductions in sway even without the need to distinguish between self and partner motion. Our findings explain the seemingly paradoxical observation that touching a swaying person can improve postural control.This work was supported by two BBSRC grants (BB/100579X/1 and an Industry Interchange Award)
Thermoradiation inactivation of naturally occurring organisms in soil
Samples of soil collected from Kennedy Space Center near spacecraft assembly facilities were found to contain microorganisms very resistant to conventional sterilization techniques. The inactivation behavior of the naturally occurring spores in soil was investigated using dry heat and ionizing radiation, first separately, then in combination. Dry heat inactivation rates of spores were determined for 105 and 125 C. Radiation inactivation rates were determined for dose rates of 660 and 76 krad/hr at 25 C. Simultaneous combinations of heat and radiation were then investigated at 105, 110, 115, 120, and 125 C. Combined treatment was found to be highly synergistic requiring greatly reduced radiation doses to accomplish sterilization
An X-ray-UV correlation in Cen X-4 during quiescence
Quiescent emission from the neutron star low-mass X-ray binary Cen X-4 is
seen to be variable on timescales from hundreds of seconds to years, suggesting
that at least in this object, low-level accretion is important during
quiescence. Here we present results from recent XMM-Newton and Swift
observations of Cen X-4, where the X-ray flux (0.5 - 10 keV) varies by a factor
of 6.5 between the brightest and faintest states. We find a positive
correlation between the X-ray flux and the simultaneous near-UV flux, where as
there is no significant correlation between the X-ray and simultaneous optical
(V, B) fluxes. This suggests that while the X-ray and UV emitting regions are
somehow linked, the optical region originates elsewhere. Comparing the
luminosities, it is plausible that the UV emission originates due to
reprocessing of the X-ray flux by the accretion disk, with the hot inner region
of the disk being a possible location for the UV emitting region. The optical
emission, however, could be dominated by the donor star. The X-ray/UV
correlation does not favour the accretion stream-impact point as the source of
the UV emission.Comment: 8 pages, 3 figures, accepted for publication in MNRA
X-ray and UV correlation in the quiescent emission of Cen X-4, evidence of accretion and reprocessing
We conducted the first long-term (60 days), multiwavelength (optical,
ultraviolet, and X-ray) simultaneous monitoring of Cen X-4 with daily Swift
observations, with the goal of understanding variability in the low mass X-ray
binary Cen X-4 during quiescence. We found Cen X-4 to be highly variable in all
energy bands on timescales from days to months, with the strongest quiescent
variability a factor of 22 drop in the X-ray count rate in only 4 days. The
X-ray, UV and optical (V band) emission are correlated on timescales down to
less than 110 s. The shape of the correlation is a power law with index gamma
about 0.2-0.6. The X-ray spectrum is well fitted by a hydrogen NS atmosphere
(kT=59-80 eV) and a power law (with spectral index Gamma=1.4-2.0), with the
spectral shape remaining constant as the flux varies. Both components vary in
tandem, with each responsible for about 50% of the total X-ray flux, implying
that they are physically linked. We conclude that the X-rays are likely
generated by matter accreting down to the NS surface. Moreover, based on the
short timescale of the correlation, we also unambiguously demonstrate that the
UV emission can not be due to either thermal emission from the stream impact
point, or a standard optically thick, geometrically thin disc. The spectral
energy distribution shows a small UV emitting region, too hot to arise from the
accretion disk, that we identified as a hot spot on the companion star.
Therefore, the UV emission is most likely produced by reprocessing from the
companion star, indeed the vertical size of the disc is small and can only
reprocess a marginal fraction of the X-ray emission. We also found the
accretion disc in quiescence to likely be UV faint, with a minimal contribution
to the whole UV flux.Comment: 5 pages, 4 figures, submitted to Proc. Int. Conf. Physics at the
Magnetospheric Boundary, Geneva, Switzerland (25-28 June, 2013
Daily, multiwavelength Swift monitoring of the neutron star low-mass X-ray binary Cen X-4: evidence for accretion and reprocessing during quiescence
We conducted the first long-term (60 days), multiwavelength (optical,
ultraviolet, and X-ray) simultaneous monitoring of Cen X-4 with daily Swift
observations from June to August 2012, with the goal of understanding
variability in the low mass X-ray binary Cen X-4 during quiescence. We found
Cen X-4 to be highly variable in all energy bands on timescales from days to
months, with the strongest quiescent variability a factor of 22 drop in the
X-ray count rate in only 4 days. The X-ray, UV and optical (V band) emission
are correlated on timescales down to less than 110 s. The shape of the
correlation is a power law with index gamma about 0.2-0.6. The X-ray spectrum
is well fitted by a hydrogen NS atmosphere (kT=59-80 eV) and a power law (with
spectral index Gamma=1.4-2.0), with the spectral shape remaining constant as
the flux varies. Both components vary in tandem, with each responsible for
about 50% of the total X-ray flux, implying that they are physically linked. We
conclude that the X-rays are likely generated by matter accreting down to the
NS surface. Moreover, based on the short timescale of the correlation, we also
unambiguously demonstrate that the UV emission can not be due to either thermal
emission from the stream impact point, or a standard optically thick,
geometrically thin disc. The spectral energy distribution shows a small UV
emitting region, too hot to arise from the accretion disk, that we identified
as a hot spot on the companion star. Therefore, the UV emission is most likely
produced by reprocessing from the companion star, indeed the vertical size of
the disc is small and can only reprocess a marginal fraction of the X-ray
emission. We also found the accretion disc in quiescence to likely be UV faint,
with a minimal contribution to the whole UV flux.Comment: 19 pages, 6 figures, 4 table
- …