8,625 research outputs found
Subwavelength position sensing using nonlinear feedback and wave chaos
We demonstrate a position-sensing technique that relies on the inherent
sensitivity of chaos, where we illuminate a subwavelength object with a complex
structured radio-frequency field generated using wave chaos and a nonlinear
feedback loop. We operate the system in a quasi-periodic state and analyze
changes in the frequency content of the scalar voltage signal in the feedback
loop. This allows us to extract the object's position with a one-dimensional
resolution of ~\lambda/10,000 and a two-dimensional resolution of ~\lambda/300,
where \lambda\ is the shortest wavelength of the illuminating source.Comment: 4 pages, 4 figure
Ultra-high-frequency piecewise-linear chaos using delayed feedback loops
We report on an ultra-high-frequency (> 1 GHz), piecewise-linear chaotic
system designed from low-cost, commercially available electronic components.
The system is composed of two electronic time-delayed feedback loops: A primary
analog loop with a variable gain that produces multi-mode oscillations centered
around 2 GHz and a secondary loop that switches the variable gain between two
different values by means of a digital-like signal. We demonstrate
experimentally and numerically that such an approach allows for the
simultaneous generation of analog and digital chaos, where the digital chaos
can be used to partition the system's attractor, forming the foundation for a
symbolic dynamics with potential applications in noise-resilient communications
and radar
Coarse--graining, fixed points, and scaling in a large population of neurons
We develop a phenomenological coarse--graining procedure for activity in a
large network of neurons, and apply this to recordings from a population of
1000+ cells in the hippocampus. Distributions of coarse--grained variables seem
to approach a fixed non--Gaussian form, and we see evidence of scaling in both
static and dynamic quantities. These results suggest that the collective
behavior of the network is described by a non--trivial fixed point
Continuum of care for persons with common mental health disorders in Nunavik: a descriptive study.
BACKGROUND: Changing Directions, Changing Lives, the Mental Health Strategy for Canada, prioritizes the development of coordinated continuums of care in mental health that will bridge the gap in services for Inuit populations.
OBJECTIVE: In order to target ways of improving the services provided in these contexts to individuals in Nunavik with depression or anxiety disorders, this research examines delays and disruptions in the continuum of care and clinical, individual and organizational characteristics possibly associated with their occurrences.
DESIGN: A total of 155 episodes of care involving a common mental disorder (CMD), incident or recurring, were documented using the clinical records of 79 frontline health and social services (FHSSs) users, aged 14 years and older, living in a community in Nunavik. Each episode of care was divided into 7 stages: (a) detection; (b) assessment; (c) intervention; (d) planning the first follow-up visit; (e) implementation of the first follow-up visit; (f) planning a second follow-up visit; (g) implementation of the second follow-up visit. Sequential analysis of these stages established delays for each one and helped identify when breaks occurred in the continuum of care. Logistic and linear regression analysis determined whether clinical, individual or organizational characteristics influenced the breaks and delays.
RESULTS: More than half (62%) the episodes of care were interrupted before the second follow-up. These breaks mostly occurred when planning and completing the first follow-up visit. Episodes of care were more likely to end early when they involved anxiety disorders or symptoms, limited FHSS teams and individuals over 21 years of age. The median delay for the first follow-up visit (30 days) exceeded guideline recommendations significantly (1-2 weeks).
CONCLUSION: Clinical primary care approaches for CMDs in Nunavik are currently more reactive than preventive. This suggests that recovery services for those affected are suboptimal
Quality assessment of primary care for common mental disorders in isolated communities: Taking advantage of health records.
INTRODUCTION: This article is part of a research study on the organization of primary health care (PHC) for mental health in two of Quebec's remote regions. It introduces a methodological approach based on information found in health records, for assessing the quality of PHC offered to people suffering from depression or anxiety disorders.
METHODS: Quality indicators were identified from evidence and case studies were reconstructed using data collected in health records over a 2-year observation period. Data collection was developed using a three-step iterative process: (1) feasibility analysis, (2) development of a data collection tool, and (3) application of the data collection method. The adaptation of quality-of-care indicators to remote regions was appraised according to their relevance, measurability and construct validity in this context.
RESULTS: As a result of this process, 18 quality indicators were shown to be relevant, measurable and valid for establishing a critical quality appraisal of four recommended dimensions of PHC clinical processes: recognition, assessment, treatment and follow-up.
CONCLUSIONS: There is not only an interest in the use of health records to assess the quality of PHC for mental health in remote regions but also a scientific value for the rigorous and meticulous methodological approach developed in this study. From the perspective of stakeholders in the PHC system of care in remote areas, quality indicators are credible and provide potential for transferability to other contexts. This study brings information that has the potential to identify gaps in and implement solutions adapted to the context
Sound velocity and absorption measurements under high pressure using picosecond ultrasonics in diamond anvil cell. Application to the stability study of AlPdMn
We report an innovative high pressure method combining the diamond anvil cell
device with the technique of picosecond ultrasonics. Such an approach allows to
accurately measure sound velocity and attenuation of solids and liquids under
pressure of tens of GPa, overcoming all the drawbacks of traditional
techniques. The power of this new experimental technique is demonstrated in
studies of lattice dynamics, stability domain and relaxation process in a
metallic sample, a perfect single-grain AlPdMn quasicrystal, and rare gas, neon
and argon. Application to the study of defect-induced lattice stability in
AlPdMn up to 30 GPa is proposed. The present work has potential for application
in areas ranging from fundamental problems in physics of solid and liquid
state, which in turn could be beneficial for various other scientific fields as
Earth and planetary science or material research
Tropical and subtropical actinorhizal plants
A maioria dos paĂses tropicais enfrenta dois grandes problemas: o aumento constante da exploração das reservas florestais para extração de madeira ou lenha e a diminuição da fertilidade do solo para produção agrĂcola. O conceito geral Ă© o de que plantas fixadoras de N2 podem evitar a propalada crise de madeira e alimentos. Juntas com um grande nĂșmero de leguminosas fixadoras de N2, plantas actinorrĂzicas podem ter um papel importante na produção de madeira e recuperação de solos. As plantas actinorrĂzicas compreendem oito famĂlias de dicotiledĂŽneas, todas elas representadas nos trĂłpicos. Neste trabalho, as mais promissoras plantas actinorrĂzicas tropicais sĂŁo brevemente apresentadas e a ĂȘnfase Ă© dada principalmente Ă famĂlia Casuarinaceae. Esta famĂlia compreende quatro gĂȘneros (Casuarina, Allocasuarina, Gymnostoma e gĂȘnero C), com 82 espĂ©cies, incluindo muitas ĂĄrvores que podem produzir madeira de boa qualidade. As estirpes de Frankia que tĂȘm sido isoladas das Casuarinaceae crescem lentamente e sĂŁo capazes de reduzir acetileno in vitro sob ar, o que indica uma capacidade de proteção contra o O2 muito mais eficiente do que no Rhizobium. Apenas as espĂ©cies do gĂȘnero Casuarina podem ser noduladas pela estirpe ORS 021001, isolada de Casuarina junghuhniana, o que sugere a existĂȘncia de grupos de inoculação dentro da famĂlia Casuarinaceae. A fixação de N2 de Casuarina equisetifolia, crescida em microparcelas de 1 m2, na estação experimental de ORSTM, em Dakar, foi estimada atravĂ©s da comparação do N total em plantas nĂŁo-inoculadas e plantas inoculadas com a estirpe ORS 021001. Extrapolando para um hectare, a fixação de N2 foi de 131 kg/N em um perĂodo de 6,5 meses. Usando o mĂ©todo de equivalĂȘncia com adubo nitrogenado, a inoculação parece ser equivalente Ă aplicação de 288 kg de N/ha-1.Most tropical countries face two major problems: increasing overexploitation of wood reserves for timber or fuel wood and diminishing soil fertility for agricultural production. The present consensus is that N2 -fixing plants can help prevent the forthcoming wood and food crisis. Together with the vast group of N2 -fixing Leguminoseae, actinorhizal plants (AP) can play a major role in wood production and land regeneration. AP comprise eight families of dicotyledonous plants all of which are represented in the tropics. In this paper the most promising tropical AP are briefly presented and the emphasis is put mainly on Casuarinaceae. This family forms a group of four genera (Casuarina, Allocasuarina, Gymnostoma and genus C) with 82 species, including many trees that can yield wood of good quality. The Frankia strains that have been isolated from Casuarinaceae grow slowly and are able to reduce acetylene in vitro under air, which indicates that the protection against O2 is much more efficient in Frankia than in rhizobia. Only the species belonging to the Casuarina genus could be nodulated by strain ORS 021001, isolated from Casuarina junghuhniana, suggesting the existence of crossinoculation groups within the family Casuarinaceae. N2 fixation of Casuarina equisetifolia, grown in 1 m2 microplots at the ORSTOM experimental station of Dakar, was estimated by comparing total N in non-inoculated plants and plants inoculated with Frankia strain ORS 021001. Extrapolating to 1 hectare, N2 fixation was 131 kg for a 6.5-month period. Using the N fertilizer equivalence method, inoculation appeared to be equivalent to the application of 288 kg of N fertilizer per hectare
Heat transport by turbulent Rayleigh-B\'enard convection for $\Pra\ \simeq 0.83\times 10^{12} \alt \Ra\ \alt 10^{15}\Gamma = 0.50$
We report experimental results for heat-transport measurements, in the form
of the Nusselt number \Nu, by turbulent Rayleigh-B\'enard convection in a
cylindrical sample of aspect ratio ( m is
the diameter and m the height). The measurements were made using
sulfur hexafluoride at pressures up to 19 bars as the fluid. They are for the
Rayleigh-number range 3\times 10^{12} \alt \Ra \alt 10^{15} and for Prandtl
numbers \Pra\ between 0.79 and 0.86. For \Ra < \Ra^*_1 \simeq 1.4\times
10^{13} we find \Nu = N_0 \Ra^{\gamma_{eff}} with , consistent with classical turbulent Rayleigh-B\'enard convection in a
system with laminar boundary layers below the top and above the bottom plate.
For \Ra^*_1 < \Ra < \Ra^*_2 (with \Ra^*_2 \simeq 5\times 10^{14})
gradually increases up to . We argue that above
\Ra^*_2 the system is in the ultimate state of convection where the boundary
layers, both thermal and kinetic, are also turbulent. Several previous
measurements for are re-examined and compared with the present
results.Comment: 44 pages, 18 figures, submitted to NJ
Mackenzie Inuit Lithic Raw Material Procurement in the Lower Mackenzie Valley: The Importance of Social Factors
Oral and written historical records indicate that the Mackenzie Inuit traveled up the Mackenzie River from the Arctic Coast to procure lithic raw material in the interior from a quarry at the mouth of the Thunder River, which is known locally by the Gwichâin of the lower Mackenzie Valley as Vihtrâii Tshik. We evaluate this proposition using non-destructive polarized energy dispersive X-ray fluorescence to compare the geochemical signatures of the lithic raw material from Vihtrâii Tshik (MiTi-1) and flakes and tools from the Mackenzie Inuit village of Kuukpak (NiTs-1), which is located more than 400 km downriver of the quarry source. The concentrations of nine selected elementsâthree major elements expressed as oxides (SiO2, Fe2O3T, and K2O) and six trace elements expressed as metals (Rb, Sr, Y, Zr, Ba, and Ce)âare compared using descriptive statistics, spider diagrams, and principal components analysis. The geochemical effects of chemical weathering on the surfaces of artifacts are evaluated by measuring element concentrations before and after removal of the weathering rind from select artifacts. The results of our analyses demonstrate that the lithic raw material available at Vihtrâii Tshik is best characterized as chert, and that 86% of the flakes and tools from Kuukpak analyzed in this study are chemically similar to the raw material from Vihtrâii Tshik. Historical records and archaeological data indicate that the people of Kuukpak traversed a complex social landscape to obtain stone from Vihtrâii Tshik through direct procurement.Les traditions orales et Ă©crites historiques indiquent que les Inuits du Mackenzie remontaient le fleuve Mackenzie en quittant la cĂŽte arctique et allant vers lâintĂ©rieur des terres afin dâobtenir de la matiĂšre premiĂšre lithique dâune carriĂšre qui se trouvait prĂšs de lâembouchure de la riviĂšre Thunder. Les Gwichâin de la basse vallĂ©e du Mackenzie appellent cet endroit Vihtrâii Tshik. Nous Ă©valuons ces rĂ©vĂ©lations en utilisant la technique de fluorescence par rayons X en mode dispersion dâĂ©nergie (gĂ©omĂ©trie polarisante, mĂ©thode non destructive) afin de comparer les signatures gĂ©ochimiques des roches trouvĂ©es Ă la carriĂšre Vihtrâii Tshik (MiTi-1) avec celles des Ă©clats et des outils en pierre provenant dâun site villageois inuit appelĂ© Kuukpak (NiTs-1) qui se trouve Ă 400 km en aval de la carriĂšre. Les concentrations de neuf Ă©lĂ©ments chimiques â trois Ă©lĂ©ments majeurs exprimĂ©s sous la forme dâoxydes (SiO2, Fe2O3T et K2O) et six Ă©lĂ©ments traces exprimĂ©s sous la forme de mĂ©taux (Rb, Sr, Y, Zr, Ba et Ce) â sont utilisĂ©es pour calculer des statistiques descriptives et des diagrammes-araignĂ©es, et rĂ©aliser une analyse multivariĂ©e par composantes principales. Nous Ă©valuons aussi les effets gĂ©ochimiques causĂ©s par lâintempĂ©risation de la surface des artefacts en mesurant les concentrations dâĂ©lĂ©ments avant et aprĂšs lâenlĂšvement de celle-ci sur des artefacts sĂ©lectionnĂ©s. Les rĂ©sultats de nos analyses chimiques dĂ©montrent que la roche provenant de la carriĂšre Vihtrâii Tshik est un chert, et que 86 % des Ă©clats et outils analysĂ©s dans cette Ă©tude provenant du site villageois Kuukpak montrent des affinitĂ©s gĂ©ochimiques au chert de cette carriĂšre. Les documents historiques et les donnĂ©es archĂ©ologiques nous indiquent que les gens de Kuukpak devaient naviguer Ă travers une gĂ©ographie culturelle complexe afin de se procurer directement le chert de la carriĂšre de Vihtrâii Tshik
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