Description: Accurately measuring the bulk minority carrier lifetime is one of the greatest challenges in evaluating photoactive materials used in photovoltaic cells. One-photon time-resolved photoluminescence decay measurements are commonly used to measure lifetimes of direct bandgap materials. However, because the incident photons have energies higher than the bandgap of the semiconductor, most carriers are generated close to the surface, where surface defects cause inaccurate lifetime measurements. Here we show that two-photon absorption permits sub-surface optical excitation, which allows us to decouple surface and bulk recombination processes even in unpassivated samples. Thus with two-photon microscopy we probe the bulk minority carrier lifetime of photovoltaic semiconductors. We demonstrate how the traditional one-photon technique can underestimate the bulk lifetime in a CdTe crystal by 10× and show that two-photon excitation more accurately measures the bulk lifetime. Finally, we generate multi-dimensional spatial maps of optoelectronic properties in the bulk of these materials using two-photon excitation. Scientific Reports 3 doi: 10.1038/srep02098

Description: In dynamic MRI, spatial and temporal parallel imaging can be exploited to reduce scan time. Real-time reconstruction enables immediate visualization during the scan. Commonly used view-sharing techniques suffer from limited temporal resolution, and many of the more advanced reconstruction methods are either retrospective, time-consuming, or both. A Kalman filter model capable of real-time reconstruction can be used to increase the spatial and temporal resolution in dynamic MRI reconstruction. The original study describing the use of the Kalman filter in dynamic MRI was limited to non-Cartesian trajectories because of a limitation intrinsic to the dynamic model used in that study. Here the limitation is overcome, and the model is applied to the more commonly used Cartesian trajectory with fast reconstruction. Furthermore, a combination of the Kalman filter model with Cartesian parallel imaging is presented to further increase the spatial and temporal resolution and signal-to-noise ratio. Simulations and experiments were conducted to demonstrate that the Kalman filter model can increase the temporal resolution of the image series compared with view-sharing techniques and decrease the spatial aliasing compared with TGRAPPA. The method requires relatively little computation, and thus is suitable for real-time reconstruction. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

Description: Receiver functions sampling the Sierra Nevada batholith and adjacent regions exhibit significant variations in the structure of the crust and upper mantle. Crustal Vp/Vs values are lower in the core of the batholith and higher in the northern Sierra Nevada, portions of the Basin and Range, and near young volcanic fields in the eastern Sierra Nevada and Owens Valley. P- to S-wave conversions from the Moho vary from high amplitude and shallow (〉25% of the direct P-arrival amplitude, 25-35 km depth) along the eastern Sierra Nevada to low amplitude and deep (

Description: Purpose To develop and assess a three-dimensional refocused turbo spin-echo (rTSE) sequence for generating peripheral angiograms. This sequence combines the rapid T 2 -weighting of TSE and the better flow performance of the fully-refocused gradients of balanced steady state free precession (bSSFP), along with bSSFP-style phase alternation of refocusing radiofrequency (RF) pulses. Materials and Methods The signal behavior generated by such a sequence was explored through Bloch equation simulations. The rTSE and TSE sequences were both used to generate peripheral angiograms in nine normal volunteers. The signal to noise ratio, contrast resolution, and vessel sharpness of the resulting images were used as bases for comparison. Additionally, the rTSE sequence was applied in four patients with peripheral artery disease to preliminarily assess its efficacy in a clinical setting through quality scoring by two experienced radiologists. Results The rTSE's RF phase alternation approach out-performs a simple balanced-gradient CPMG (Carr-Purcell-Meiboom-Gill) -style TSE sequence in the presence of B 0 and B 1 inhomogeneities. In volunteers, the rTSE sequence yielded better arterial–venous contrast (0.378 ± 0.145 versus 0.155 ± 0.202; P 〈 0.01) and increased vessel sharpness (0.340 ± 0.034 versus 0.263 ± 0.034; P 〈 0.005) over TSE images. Stenoses visible in conventional angiographic images in patients were successfully imaged with the rTSE sequence; however, image quality scores in patients were lower than in volunteers (1.2 ± 0.38 versus 3.0 ± 1.0; P 〈 0.05). Conclusion The rTSE sequence generates nonsubtractive, flow-independent, peripheral MR angiograms with better arterial–venous contrast and vessel sharpness in normal volunteers than a conventional TSE sequence. J. Magn. Reson. Imaging 2013 . © 2013 Wiley Periodicals, Inc .

Description: Nature Genetics 45, 1134 (2013). doi:10.1038/ng.2760 Authors: Travis I Zack, Steven E Schumacher, Scott L Carter, Andrew D Cherniack, Gordon Saksena, Barbara Tabak, Michael S Lawrence, Cheng-Zhong Zhang, Jeremiah Wala, Craig H Mermel, Carrie Sougnez, Stacey B Gabriel, Bryan Hernandez, Hui Shen, Peter W Laird, Gad Getz, Matthew Meyerson & Rameen Beroukhim

Description: Non-invasive imaging techniques are highly desirable as an alternative to conventional biopsy for the characterization of the remodeling of tissues associated with disease progression, including end-stage heart failure. Cardiac diffusion tensor imaging (DTI) has become an established method for the characterization of myocardial microstructure. However, the relationships between diffuse myocardial fibrosis, which is a key biomarker for staging and treatment planning of the failing heart, and measured DTI parameters have yet to be investigated systematically. In this study, DTI was performed on left ventricular specimens collected from patients with chronic end-stage heart failure as a result of idiopathic dilated cardiomyopathy ( n  = 14) and from normal donors ( n  = 5). Scalar DTI parameters, including fractional anisotropy (FA) and mean (MD), primary ( D 1 ), secondary ( D 2 ) and tertiary ( D 3 ) diffusivities, were correlated with collagen content measured by digital microscopy. Compared with hearts from normal subjects, the FA in failing hearts decreased by 22%, whereas the MD, D 2 and D 3 increased by 12%, 14% and 24%, respectively ( P  〈 0.01). No significant change was detected for D 1 between the two groups. Furthermore, significant correlation was observed between the DTI scalar indices and quantitative histological measurements of collagen (i.e. fibrosis). Pearson's correlation coefficients ( r ) between collagen content and FA, MD, D 2 and D 3 were –0.51, 0.59, 0.56 and 0.62 ( P  〈 0.05), respectively. The correlation between D 1 and collagen content was not significant ( r  = 0.46, P  = 0.05). Computational modeling analysis indicated that the behaviors of the DTI parameters as a function of the degree of fibrosis were well explained by compartmental exchange between myocardial and collagenous tissues. Combined, these findings suggest that scalar DTI parameters can be used as metrics for the non-invasive assessment of diffuse fibrosis in failing hearts. Copyright © 2014 John Wiley & Sons, Ltd. Myocardial diffuse fibrosis has been linked to arrhythmias and sudden cardiac death. Although diffusion tensor imaging (DTI) is increasingly being used to characterize cardiac diseases, quantitative correlation between DTI scalar metrics and diffuse fibrosis remains lacking. In this study, DTI parameters obtained on heart specimens from patients with idiopathic dilated cardiomyopathy and from normal donors were correlated with histological collagen content measurements. The results indicated that diffuse fibrosis is significantly correlated with water diffusivity and inversely correlated with diffusion anisotropy. Computational analysis showed that the behaviors of the DTI parameters are well explained by compartmental exchange between myocardial and collagenous tissues.

Description: Purpose The major hurdle to widespread adoption of spiral trajectories has been their poor off-resonance performance. Here we present a self-correcting spiral k-space trajectory that avoids much of the well-known spiral blurring during data acquisition. Theory and Methods In comparison with a traditional spiral-out trajectory, the spiral-in/out trajectory has improved off-resonance performance. By combining two spiral-in/out acquisitions, one rotated 180° in k-space compared with the other, multishot spiral-in/out artifacts are eliminated. A phantom was scanned with the center frequency manually tuned 20, 40, 80, and 160 Hz off-resonance with both a spiral-out gradient echo sequence and the redundant spiral-in/out sequence. The phantom was also imaged in an oblique orientation in order to demonstrate improved concomitant gradient field performance of the sequence. Additionally, the trajectory was incorporated into a spiral turbo spin echo sequence for brain imaging. Results Phantom studies with manually tuned off-resonance agree well with theoretical calculations, showing that moderate off-resonance is well-corrected by this acquisition scheme. Blur due to concomitant fields is reduced, and good results are obtained in vivo. Conclusion The redundant spiral-in/out trajectory results in less image blur for a given readout length than a traditional spiral-out scan, reducing the need for complex off-resonance correction algorithms. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.

Description: Nature Medicine 20, 231 (2014). doi:10.1038/nm0314-231 Author: Craig H Lipset A growing number of participants in clinical trials are sharing information about their health online. It's time that the drug development community starts to examine how this social media use might compromise the integrity of research studies and how it might also offer new opportunities.

Description: [1]  To investigate the physical basis for support of topography in the western U.S., we construct a sub-continent scale, 3D density model using ~1000 estimated crustal thicknesses and S -velocity profiles to 150 km depth at each of 947 seismic stations. Seismic signatures of temperature and composition are considered in the crust, but we assume that mantle velocity variations are thermal in origin. From these densities, we calculate crustal and mantle topographic contributions. Typical 2 σ uncertainty of topography is ~500 meters, and elevations in 84% of the region are reproduced within error. Remaining deviations from observed elevations are attributed to melt, variations in crustal quartz content, and dynamic topography; compositional variations in the mantle, while plausible, are not necessary to reproduce topography. Support for western U.S topography is heterogeneous, with each province having a unique combination of mechanisms. Topography due to mantle buoyancy is nearly constant (within ~250 m) across the Cordillera; relief there (〉2 km) results from variations in crustal chemistry and thickness. Cold mantle provides ~1.5 km of ballast to the thick crust of the Great Plains and Wyoming craton. Crustal temperature variations and dynamic pressures have smaller magnitude and/or more localized impacts. Positive gravitational potential energy (GPE) anomalies (~2x10 12 N/m) calculated from our model promote extension in the northern Basin and Range and near the Sierra Nevada. Negative GPE anomalies (-3x10 12 N/m) along the western North American margin and Yakima fold and thrust belt add compressive stresses. We thus argue that stresses derived from lithospheric density variations may strongly modulate edge and basal force-derived stresses in many regions in the western U.S. continental interior.

Description: Author(s): D. Heinert, K. Craig, H. Grote, S. Hild, H. Lück, R. Nawrodt, D. A. Simakov, D. V. Vasilyev, S. P. Vyatchanin, and H. Wittel Current gravitational-wave detectors rely on the use of Michelson interferometers. One crucial limitation of their sensitivity is the thermal noise of their optical components. Thus, for example, fluctuational deformations of the mirror surface are probed by a laser beam being reflected from the mir... [Phys. Rev. D 90, 042001] Published Thu Aug 07, 2014