After a stroke, people often attempt to consciously control their motor actions, which, paradoxically, disrupts optimal performance. A learning strategy that minimizes the accrual of explicit ...knowledge may circumvent attempts to consciously control motor actions, thereby resulting in better performance. The purpose of this study was to examine the implicit learning of a dynamic balancing task after stroke by use of 1 of 2 motor learning strategies: learning without errors and discovery learning.
Ten adults with stroke and 12 older adults practiced a dynamic balancing task on a stabilometer under single-task (balance only) and concurrent-task conditions. Root-mean-square error (in degrees) from horizontal was used to measure balance performance.
The balance performance of the discovery (explicit) learners after stroke was impaired by the imposition of a concurrent cognitive task load. In contrast, the performance of the errorless (implicit) learners (stroke and control groups) and the discovery learning control group was not impaired.
The provision of explicit information during rehabilitation may be detrimental to the learning/relearning and execution of motor skills in some people with stroke. The application of implicit motor learning techniques in the rehabilitation setting may be beneficial.
The Ultra-Low Background Liquid Scintillation Counter developed by Pacific Northwest National Laboratory will expand the application of liquid scintillation counting by enabling lower detection ...limits and smaller sample volumes. By reducing the overall count rate of the background environment approximately 2 orders of magnitude below that of commercially available systems, backgrounds on the order of tens of counts per day over an energy range of ~3–3600keV can be realized. Initial test results of the ULB LSC show promising results for ultra-low background detection with liquid scintillation counting.
•Observed background is within a factor of 2 of the predictions from simulation.•Background achieved is 2 orders of magnitude below commercially available systems.•Backgrounds are in tens of counts per day over an energy range of ~3– 3600keV.•Initial results show promise for ultra-low background detection with the ULB LSC.
A search for Pauli-exclusion-principle-violating K
α
electron transitions was performed using 89.5 kg-d of data collected with a p-type point contact high-purity germanium detector operated at the ...Kimballton Underground Research Facility. A lower limit on the transition lifetime of
5.8
×
10
30
s at 90% C.L. was set by looking for a peak at 10.6 keV resulting from the X-ray and Auger electrons present following the transition. A similar analysis was done to look for the decay of atomic K-shell electrons into neutrinos, resulting in a lower limit of
6.8
×
10
30
s at 90% C.L. It is estimated that the
Majorana Demonstrator
, a 44 kg array of p-type point contact detectors that will search for the neutrinoless double-beta decay of
76
Ge, could improve upon these exclusion limits by an order of magnitude after three years of operation.
Pacific Northwest National Laboratory has recently opened a shallow underground laboratory intended for measurement of low-concentration levels of radioactive isotopes in samples collected from the ...environment. The development of a low-background liquid scintillation counter is currently underway to further augment the measurement capabilities within this underground laboratory. Liquid scintillation counting is especially useful for measuring charged particle (e.g., β and α) emitting isotopes with no (or very weak) gamma-ray yields. The combination of high-efficiency detection of charged particle emission in a liquid scintillation cocktail coupled with the low-background environment of an appropriately designed shield located in a clean underground laboratory provides the opportunity for increased-sensitivity measurements of a range of isotopes. To take advantage of the 35m-water-equivalent overburden of the underground laboratory, a series of simulations have evaluated the scintillation counter's shield design requirements to assess the possible background rate achievable. This report presents the design and background evaluation for a shallow underground, low background liquid scintillation counter design for sample measurements.
•Graded-shielding can produce an ultra-low-background liquid scintillation counter.•Location in a shallow underground cleanroom further enhances background reduction.•A novel light collection design and selected low background materials are utilized.•The background is predicted to be 10–100 times below typical commercial systems.•Simulations tentatively predict a background rate of order 10 counts per day.
Development of ultra low background gas proportional counters has made the contribution from naturally occurring radioactive isotopes – primarily α and β activity in the uranium and thorium decay ...chains – inconsequential to instrumental sensitivity levels when measurements are performed in above ground surface laboratories. Simple lead shielding is enough to mitigate against gamma rays as gas proportional counters are already relatively insensitive to naturally occurring gamma radiation. The dominant background in these surface laboratory measurements using ultra low background gas proportional counters is due to cosmic ray generated muons, neutrons, and protons. Studies of measurements with ultra low background gas proportional counters in surface and underground laboratories as well as radiation transport Monte Carlo simulations suggest a preferred conceptual design to achieve the highest possible sensitivity from an array of low background gas proportional counters when operated in a surface laboratory. The basis for a low background gas proportional counter array and the preferred shielding configuration is reported, especially in relation to measurements of radioactive gases having low energy decays such as 37Ar.
•Optimization of a cosmic ray shield to measure environmental radioactive gases.•Proportional counter sensitivity may reach ambient environmental 37Ar concentrations.•Variable length counter method evaluated for low concentration absolute gas counting.•Feasibility of several hour duration preparation of gas samples for 37Ar measurement.
The C-4 dark matter experiment Bonicalzi, R.M.; Collar, J.I.; Colaresi, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2013, Letnik:
712
Journal Article
Recenzirano
We describe the experimental design of C-4, an expansion of the CoGeNT dark matter search to four identical detectors each approximately three times the mass of the p-type point contact germanium ...diode presently taking data at the Soudan Underground Laboratory. Expected reductions of radioactive backgrounds and energy threshold are discussed, including an estimate of the additional sensitivity to low-mass dark matter candidates to be obtained with this search.
Argon-37 is an environmental signature of an underground nuclear explosion. Producing and quantifying low-level (37)Ar standards is an important step in the development of sensitive field measurement ...instruments. This paper describes progress at Pacific Northwest National Laboratory in developing a process to generate and quantify low-level (37)Ar standards, which can be used to calibrate sensitive field systems at activities consistent with soil background levels. This paper presents a discussion of the measurement analysis, along with assumptions and uncertainty estimates.
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