201 research outputs found
NMR quantum simulation of localization effects induced by decoherence
The loss of coherence in quantum mechanical superposition states limits the
time for which quantum information remains useful. Similarly, it limits the
distance over which quantum information can be transmitted, resembling Anderson
localization, where disorder causes quantum mechanical states to become
localized. Here, we investigate in a nuclear spin-based quantum simulator, the
localization of the size of spin clusters that are generated by a Hamiltonian
driving the transmission of information, while a variable-strength perturbation
counteracts the spreading. We find that the system reaches a dynamic
equilibrium size, which decreases with the square of the perturbation strength.Comment: 5 pages, 5 figure
Cryostratigraphy and the Sublimation Unconformity in Permafrost from an Ultraxerous Environment, University Valley, McMurdo Dry Valleys of Antarctica
The cryostratigraphy of permafrost in ultraxerous environments is poorly known. In this study, icy permafrost cores from University Valley (McMurdo Dry Valleys, Antarctica) were analyzed for sediment properties, ground-ice content, types and distribution of cryostructures, and presence of unconformities. No active layer exists in the valley, but the ice table, a sublimation unconformity, ranges from 0 to 60 cm depth. The sediments are characterized as a medium sand, which classifies them as low to non-frost susceptible. Computed tomography (CT) scan images of the icy permafrost cores revealed composite cryostructures that included the structureless, porous visible, suspended and crustal types. These cryostructures were observed irrespective of ground-ice origin (vapour deposited and freezing of snow meltwater), suggesting that the type and distribution of cryostructures could not be used as a proxy to infer the mode of emplacement of ground ice. Volumetric ice content derived from the CT scan images underestimated measured volumetric ice content, but approached measured excess ice content. A palaeo-sublimation unconformity could not be detected from a change in cryostructures, but could be inferred from an increase in ice content at the maximum predicted ice table depth. This study highlights some of the unique ground-ice processes and cryostructures in ultraxerous environments
The multiple quantum NMR dynamics in systems of equivalent spins with the dipolar ordered initial state
The multiple quantum (MQ) NMR dynamics in the system of equivalent spins with
the dipolar ordered initial state is considered. The high symmetry of the MQ
Hamiltonian is used in order to develop the analytical and numerical methods
for an investigation of the MQ NMR dynamics in the systems consisting of
hundreds of spins from "the first principles". We obtain the dependence of the
intensities of the MQ NMR coherences on their orders (profiles of the MQ NMR
coherences) for the systems of spins. It is shown that these
profiles may be well approximated by the exponential distribution functions. We
also compare the MQ NMR dynamics in the systems of equivalent spins having two
different initial states, namely the dipolar ordered state and the thermal
equilibrium state in the strong external magnetic field.Comment: 11 pages 4 figure
Origin, burial and preservation of late Pleistocene-age glacier ice in Arctic permafrost (Bylot Island, NU, Canada)
Over the past decades, observations of buried glacier ice exposed in coastal
bluffs and headwalls of retrogressive thaw slumps of the Arctic have
indicated that considerable amounts of late Pleistocene glacier ice survived
the deglaciation and are still preserved in permafrost. In exposures, relict
glacier ice and intrasedimental ice often coexist and look alike but their
genesis is strikingly different. This paper aims to present a detailed
description and infer the origin of a massive ice body preserved in the
permafrost of Bylot Island (Nunavut). The massive ice exposure and core
samples were described according to the cryostratigraphic approach, combining
the analysis of permafrost cryofacies and cryostructures, ice
crystallography, stable O-H isotopes and cation contents. The ice was clear
to whitish in appearance with large crystals (cm) and small gas inclusions
(mm) at crystal intersections, similar to observations of englacial ice
facies commonly found on contemporary glaciers and ice sheets. However, the
δ18O composition (-34.0Âą0.4 â°) of
the massive ice was markedly lower than contemporary glacier ice and was
consistent with the late Pleistocene age ice in the Barnes Ice Cap. This ice
predates the aggradation of the surrounding permafrost and can be used as an
archive to infer palaeo-environmental conditions at the study site. As most
of the glaciated Arctic landscapes are still strongly determined by their
glacial legacy, the melting of these large ice bodies could lead to extensive
slope failures and settlement of the ground surface, with significant impact
on permafrost geosystem landscape dynamics, terrestrial and aquatic
ecosystems and infrastructure.</p
The Icebreaker Life Mission to Mars: A Search for Biomolecular Evidence for Life
The search for evidence of life on Mars is the primary motivation for the exploration of that planet. The results from previous missions, and the Phoenix mission in particular, indicate that the ice-cemented ground in the north polar plains is likely to be the most recently habitable place that is currently known on Mars. The near-surface ice likely provided adequate water activity during periods of high obliquity, ~ 5 Myr ago. Carbon dioxide and nitrogen is present in the atmosphere, and nitrates may be present in the soil. Perchlorate in the soil together with iron in basaltic rock provides a possible energy source for life. Furthermore, the presence of organics must once again be considered, as the results of the Viking GCMS are now suspect given the discovery of the thermally reactive perchlorate. Ground-ice may provide a way to preserve organic molecules for extended periods of time, especially organic biomarkers. The Mars Icebreaker Life mission focuses on the following science goals: 1. Search for specific biomolecules that would be conclusive evidence of life. 2. A general search for organic molecules in the ground ice. 3. Determine the processes of ground ice formation and the role of liquid water. 4. Understand the mechanical properties of the Mars polar ice-cemented soil. 5. Assess the recent habitability of the environment with respect to required elements to support life, energy sources, and possible toxic elements. And 6. Compare the elemental composition of the northern plains with mid-latitude sites. The Icebreaker Life payload has been designed around the Phoenix spacecraft and is targeted to a site near the Phoenix landing site. However, the Icebreaker payload could be supported on other Mars landing systems. Preliminary studies of the SpaceX Dragon lander show that it could support the Icebreaker payload for a landing either at the Phoenix site or at mid-latitudes. Duplicate samples could be cached as a target for possible return by a Mars Sample Return mission. If the samples were shown to contain organic biomarkers interest in returning them to Earth would be high
Palliative care in advanced dementia; A mixed methods approach for the development of a complex intervention
There is increasing interest in improving the quality of care that patients with advanced dementia receive when they are dying. Our understanding of the palliative care needs of these patients and the natural history of advanced disease is limited. Many people with advanced dementia have unplanned emergency admissions to the acute hospital; this is a critical event: half will die within 6 months. These patients have complex needs but often lack capacity to express their wishes. Often carers are expected to make decisions. Advance care planning discussions are rarely performed, despite potential benefits such more consistent supportive healthcare, a reduction in emergency admissions to the acute hospital and better resolution of carer bereavement
Validation of an advanced practice physiotherapy model of care in an orthopaedic outpatient clinic
Validation of Doloplus-2 among nonverbal nursing home patients - an evaluation of Doloplus-2 in a clinical setting
In the present study, more patients were categorized as having pain while using Doloplus-2 compared with nurses' estimation of pain without using any tools. The fact that nurses could not report if the patients were in pain in one third of the patients supports the claim that Doloplus-2 is a useful supplement for estimating pain in this population. However, nurses must use their clinical experience in addition to the use of Doloplus-2, as behaviour can have different meaning for different patients. Further research is still needed about the use of Doloplus-2 in patients not able to self-report their pain.THE WORK (AS DEFINED BELOW) IS PROVIDED UNDER THE TERMS OF THIS BIOMED CENTRAL OPEN ACCESS LICENSE ("LICENSE"). THE WORK IS PROTECTED BY COPYRIGHT AND/OR OTHER APPLICABLE LAW. ANY USE OF THE WORK OTHER THAN AS AUTHORIZED UNDER THIS LICENSE IS PROHIBITED.BY EXERCISING ANY RIGHTS TO THE WORK PROVIDED HERE, YOU ACCEPT AND AGREE TO BE BOUND BY THE TERMS OF THIS LICENSE. THE LICENSOR GRANTS YOU THE RIGHTS CONTAINED HERE IN CONSIDERATION OF YOUR ACCEPTANCE OF SUCH TERMS AND CONDITIONS
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