14,063 research outputs found
Quantum dot emission from site-controlled ngan/gan micropyramid arrays
InxGa1āxN quantum dots have been fabricated by the selective growth of GaN micropyramid arrays topped with InGaN/GaN quantum wells. The spatially, spectrally, and time-resolved emission properties of these structures were measured using cathodoluminescence hyperspectral imaging and low-temperature microphotoluminescence spectroscopy. The presence of InGaN quantum dots was confirmed directly by the observation of sharp peaks in the emission spectrum at the pyramid apices. These luminescence peaks exhibit decay lifetimes of approximately 0.5 ns, with linewidths down to 650 me
Technologies for imaging neural activity in large volumes
Neural circuitry has evolved to form distributed networks that act dynamically across large volumes. Collecting data from individual planes, conventional microscopy cannot sample circuitry across large volumes at the temporal resolution relevant to neural circuit function and behaviors. Here, we review emerging technologies for rapid volume imaging of neural circuitry. We focus on two critical challenges: the inertia of optical systems, which limits image speed, and aberrations, which restrict the image volume. Optical sampling time must be long enough to ensure high-fidelity measurements, but optimized sampling strategies and point spread function engineering can facilitate rapid volume imaging of neural activity within this constraint. We also discuss new computational strategies for the processing and analysis of volume imaging data of increasing size and complexity. Together, optical and computational advances are providing a broader view of neural circuit dynamics, and help elucidate how brain regions work in concert to support behavior
Prediction of far-field acoustic emissions from cavitation clouds during shock wave lithotripsy for development of a clinical device
This study presents the key simulation and decision stage of a multi-disciplinary project to develop a hospital device for monitoring the effectiveness of kidney stone fragmentation by shock wave lithotripsy (SWL). The device analyses, in real time, the pressure fields detected by sensors placed on the patient's torso, fields generated by the interaction of the incident shock wave, cavitation, kidney stone and soft tissue. Earlier free-Lagrange simulations of those interactions were restricted (by limited computational resources) to computational domains within a few centimetres of the stone. Later studies estimated the far-field pressures generated when those interactions involved only single bubbles. This study extends the free-Lagrange method to quantify the bubbleābubble interaction as a function of their separation. This, in turn, allowed identification of the validity of using a model of non-interacting bubbles to obtain estimations of the far-field pressures from 1000 bubbles distributed within the focus of the SWL field. Up to this point in the multi-disciplinary project, the design of the clinical device had been led by the simulations. This study records the decision point when the project's direction had to be led by far more costly clinical trials instead of the relatively inexpensive simulations. <br/
Nanotube Piezoelectricity
We combine ab initio, tight-binding methods and analytical theory to study
piezoelectric effect of boron nitride nanotubes. We find that piezoelectricity
of a heteropolar nanotube depends on its chirality and diameter and can be
understood starting from the piezoelectric response of an isolated planar
sheet, along with a structure specific mapping from the sheet onto the tube
surface. We demonstrate that coupling between the uniaxial and shear
deformation are only allowed in the nanotubes with lower chiral symmetry. Our
study shows that piezoelectricity of nanotubes is fundamentally different from
its counterpart in three dimensional (3D) bulk materials.Comment: 4 pages, with 3 postscript figures embedded. Uses REVTEX4 macros.
Also available at
http://www.physics.upenn.edu/~nsai/preprints/bn_piezo/index.htm
Three-dimensional cephalometric evaluation of maxillary growth following in utero repair of cleft lip and alveolar-like defects in the mid-gestational sheep model
Objective: To evaluate maxillary growth following in utero repair of surgically created cleft lip and alveolar (CLA)-like defects by means of three-dimensional (3D) computer tomographic (CT) cephalometric analysis in the mid-gestational sheep model. Methods: In 12 sheep fetuses a unilateral CLA-like defect was created in utero (untreated control group: 4 fetuses). Four different bone grafts were used for the alveolar defect closure. After euthanasia, CT scans of the skulls of the fetuses, 3D re-constructions, and a 3D-CT cephalometric analysis were performed. Results: The comparisons between the operated and nonoperated skull sides as well as of the maxillary asymmetry among the experimental groups revealed no statistically significant differences of the 12 variables used. Conclusions: None of the surgical approaches used for the in utero correction of CLA-like defects seem to affect significantly postsurgical maxillary growth; however, when bone graft healing takes place, a tendency for almost normal maxillary growth can be observed. Copyright (c) 2006 S. Karger AG, Basel
Cross-Cultural Supervision: Racial/Ethnic Minority Supervisees\u27 Perspectives
Examining the clinical supervision experiences of minority supervisees with different backgrounds than their White supervisors is essential. Weak supervisory relationships can adversely affect a superviseeās professional competency, which in turn can negatively influence the client. This study explored the experiences of ten Racial/ethnic minority supervisees in a cross-cultural supervision setting. Using consensual qualitative research (CQR), three domains emerged: (a) cultural sensitivity, (b) cultural competency, and (c) relationship building. The outcome of this study highlights the types of training in counselor education that supervisors should consider when working with supervisees from different cultural backgrounds
Stable isotope relationships between apatite phosphate (Ī“18O), structural carbonate (Ī“18O, Ī“13C), and collagen (Ī“2H, Ī“13C, Ī“15N, Ī“34S) in modern human dentine
Rationale
The use of multiāisotopic analysis (Ī“2H, Ī“13C, Ī“15N, Ī“18O, and Ī“34S values) of modern human body tissues for provenancing of unknown individuals in forensics is increasing. Tooth dentine develops during childhood and adolescence, therefore providing geographical information from that period of life. Tooth apatite Ī“18O values are commonly used for the reconstruction of drinking water values, and HāCāNāS isotope ratios in collagen supply additional information about the composition of diet. We tested if dentine collagen Ī“2H values provide similar information to apatite Ī“18O values with a proofāofāconcept study.
Methods
Tooth samples were taken from modernāday individuals born in different regions of the world. Apatite and collagen were prepared from dentine. Stable isotope analyses were performed on apatite phosphate oxygen (Ī“18Ophos); oxygen and carbon of the structural carbonate (Ī“18Ocarb, Ī“13Ccarb); and hydrogen, carbon, nitrogen, and sulfur of the collagen (Ī“2Hcoll, Ī“13Ccoll, Ī“15N, Ī“34S).
Results
Ī“18Ophos, Ī“18Ocarb, and Ī“2Hcoll values are highly correlated in modern human dentine. There are significant relationships of Ī“18O values in the apatite fraction and Ī“2H values in the collagen fraction with local Ī“18O and Ī“2H precipitation values, respectively. Pearson correlation coefficients indicate no direct relationship between Ī“15N values and the isotope ratios of any other element. Weak relationships exist between collagen Ī“34S values and Ī“18Ocarb or Ī“18Ophos values.
Conclusions
The highly significant correlation of Ī“18Ophos, Ī“18Ocarb, and Ī“2Hcoll values in the modern human dentine implies that measurement of Ī“2H values in collagen or Ī“18O values in bioapatite will provide reliable information about the climate at the person's whereabouts
Estimating the furrow infiltration characteristic from a single advance point
Management and control of surface irrigation, in particular furrow irrigation, is limited by spatio-temporal soil infiltration variability as well as the high cost and time associated with collecting intensive field data for estimation of the infiltration characteristics. Recent work has proposed scaling the commonly used infiltration function by using a model infiltration curve and a single advance point for every other furrow in an irrigation event. Scaling factors were calculated for a series of furrows at two sites and at four points down the length of the field (0.25 L, 0.5 L, 0.75 L and L). Differences in the value of the scaling factor with distance were found to be a function of the shape of the advance curves. It is concluded that use of points early in the advance results in a substantial loss of accuracy and should be avoided. The scaling factor was also strongly correlated with the furrow-wetted perimeter suggesting that the scaling is an appropriate way of both predicting and accommodating the effect of the hydraulic variability
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