500 research outputs found
Measurement of pressure and assessment of cavitation for a 22.5-kHz intra-arterial angioplasty device
This study was performed to understand better the mechanisms of action of an (22.5 kHz) ultrasonic wire catheter device used to remove atheromatous plaque in diseased blood vessels (ultrasonic angioplasty). During a clinical procedure, the wire acts as an acoustic waveguide to transfer acoustic energy from a generator outside the body to the ball tip of the wire, which is inserted in the blood vessel. The acoustic field radiated by the vibrating ball tip (1.5- to 3.0-mm diameter), was mapped in a relatively large (600 L) water tank and compared to the field from a well-characterized simple source. A dipolelike radiation pattern due to the translating ball tip was observed. At low power settings, standing wave effects in a smaller cylindrical volume (200-mm diameter, 350-mm height), which was used to simulate anthropometric dimensions, increase relative to the larger tank measurements. The standing wave ratio is dependent upon the pc characteristics of the medium and the dimensions of the volume, rather than on the absorption at this frequency. At high power-settings of the device, cavitation at the tip of the wire was measured using a 20-MHz passive cavitation detection scheme
Estimating the potential of rain-fed agriculture
Irrigation management / Water management / Irrigated farming / Rain-fed farming / Crop production / Food production / Irrigation effects / Climate / Models / Soil-water-plant relationships / Crop yield / Evapotranspiration
Developing effective institutions for water resources management: A case study in the Deduru Oya Basin, Sri Lanka
River basins / Water resource management / Water lifting / Wells / Domestic water / Population / Economic aspects / Income / Irrigation programs / Institutions / Policy / Groundwater / Agricultural development / Fish farming / Pumps / Ecology / Water supply / Drought / Poverty / Land use / Water scarcity / Natural resources / Agricultural production / Cropping systems
Spin-guides and spin-splitters: Waveguide analogies in one-dimensional spin chains
Here we show a direct mapping between waveguide theory and spin chain
transport, opening an alternative approach to quantum information transport in
the solid-state. By applying temporally varying control profiles to a spin
chain, we design a virtual waveguide or 'spin-guide' to conduct individual spin
excitations along defined space-time trajectories of the chain. We explicitly
show that the concepts of confinement, adiabatic bend loss and beamsplitting
can be mapped from optical waveguide theory to spin-guides (and hence
'spin-splitters'). Importantly, the spatial scale of applied control pulses is
required to be large compared to the inter-spin spacing, and thereby allowing
the design of scalable control architectures.Comment: 5 figure
Analytic solutions of the 1D finite coupling delta function Bose gas
An intensive study for both the weak coupling and strong coupling limits of
the ground state properties of this classic system is presented. Detailed
results for specific values of finite are given and from them results for
general are determined. We focus on the density matrix and concomitantly
its Fourier transform, the occupation numbers, along with the pair correlation
function and concomitantly its Fourier transform, the structure factor. These
are the signature quantities of the Bose gas. One specific result is that for
weak coupling a rational polynomial structure holds despite the transcendental
nature of the Bethe equations. All these new results are predicated on the
Bethe ansatz and are built upon the seminal works of the past.Comment: 23 pages, 0 figures, uses rotate.sty. A few lines added. Accepted by
Phys. Rev.
Quantum phase transitions in photonic cavities with two-level systems
Systems of coupled photonic cavities have been predicted to exhibit quantum
phase transitions by analogy with the Hubbard model. To this end, we have
studied topologies of few (up to six) photonic cavities each containing a
single two-level system. Quantum phase space diagrams are produced for these
systems, and compared to mean-field results. We also consider finite effective
temperature, and compare this to the notion of disorder. We find the extent of
the Mott lobes shrink analogously to the conventional Bose-Hubbard model.Comment: 11 pages, 11 figures, updated typo
Estimation Model of Site Quality of Teak (Tectona grandis) Using Very High-Resolution Imagery from Unmanned Aerial Vehicle in KPH Nganjuk
Site quality is one of the main information needed in forest stand management. Site quality classes need to be evaluated every certain period because the quality of forest stands may change as a result of management applied. This study describes the use of very high-resolution imagery derived from unmanned aerial vehicle (UAV) for estimating the site quality of teak (Tectona grandis). The UAV imagery used was taken from 400 m above datum (the average land surface elevation) with ground spatial resolution of 15 cm. Site quality estimation models was built using discriminant analysis. The study found that the best accuracy from discriminant function using multiple variables canopy density (C) and average of crown diameter (Dc Ì
Ì
Ì
) is 60.9%
Making sense of phantom limb pain
Phantom limb pain (PLP) impacts the majority of individuals who undergo limb amputation. The PLP experience is highly heterogenous in its quality, intensity, frequency and severity. This heterogeneity, combined with the low prevalence of amputation in the general population, has made it difficult to accumulate reliable data on PLP. Consequently, we lack consensus on PLP mechanisms, as well as effective treatment options. However, the wealth of new PLP research, over the past decade, provides a unique opportunity to re-evaluate some of the core assumptions underlying what we know about PLP and the rationale behind PLP treatments. The goal of this review is to help generate consensus in the field on how best to research PLP, from phenomenology to treatment. We highlight conceptual and methodological challenges in studying PLP, which have hindered progress on the topic and spawned disagreement in the field, and offer potential solutions to overcome these challenges. Our hope is that a constructive evaluation of the foundational knowledge underlying PLP research practices will enable more informed decisions when testing the efficacy of existing interventions and will guide the development of the next generation of PLP treatments
Symmetry perception for patterns defined by colour and luminance
Perception of visual symmetry is fast, efficient and relies on both early, low-level and late, mid- and
high-level neural mechanisms. To test for potential influences of early, low-level mechanisms on
symmetry perception, we used isoluminant, achromatic and combined (colour + luminance) patterns
in a psychophysical and an event-related potential (ERP) experiment. In the psychophysical
experiment, pattern contrast was fixed at individual symmetry discrimination threshold. Participants
then judged whether a pattern was symmetric or random. Stimuli at isoluminance were associated
with a large bias towards symmetry, achromatic stimuli introduced the opposite bias, while stimuli
containing a balance of both colour and luminance were perceived without bias. These findings are
in line with distinct contrast sensitivity functions for colour and luminance, with colour providing low
frequency information useful for symmetry detection and luminance providing high frequency
information useful for detection of detail. The subsequent ERP experiment was run at high contrasts
to assess processing of symmetry in suprathreshold conditions. Sustained Posterior Negativity, a
symmetry-sensitive ERP component, was observed in all conditions and showed the expected
dependence on symmetry. However, interactions between symmetry and contrast type were not
observed. In conclusion, while our findings at threshold support models that propose an important
contribution of low-level mechanisms to symmetry perception, at suprathreshold, these low-level
contributions do not persist. Therefore, under everyday viewing conditions, symmetry perception
engages a relatively broad cortical network that is not constrained by low-level inputs
Band Structure, Phase transitions and Semiconductor Analogs in One-Dimensional Solid Light Systems
The conjunction of atom-cavity physics and photonic structures (``solid
light'' systems) offers new opportunities in terms of more device functionality
and the probing of designed emulators of condensed matter systems. By analogy
to the canonical one-electron approximation of solid state physics, we propose
a one-polariton approximation to study these systems. Using this approximation
we apply Bloch states to the uniformly tuned Jaynes-Cummings-Hubbard model to
analytically determine the energy band structure. By analyzing the response of
the band structure to local atom-cavity control we explore its application as a
quantum simulator and show phase transition features absent in mean field
theory. Using this novel approach for solid light systems we extend the
analysis to include detuning impurities to show the solid light analogy of the
semiconductor. This investigation also shows new features with no semiconductor
analog.Comment: 7 page
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