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The effects of tensile strain and contact transmissivity on the performance limits of monolayer molybdenum disulfide ( MoS 2) nanoscale n-channel MOSFETs are studied using a semi-classical Monte Carlo method. Density functional theory calculations were performed to parametrize the electronic band structure of MoS 2 subject to tensile and shear strain. Tensile strain decreases the bandgap, increases the inter-valley band-edge energy separation between the light-mass K-valleys and heavier-mass Q-valleys, and decreases the K-valley effective mass in a way that depends on the direction and the amount of the applied strain. Biaxial tensile strain and uniaxial tensile strain along the x- or y-directions are found to have the largest effect. In bulk materials, low-field phonon-limited electron mobility is enhanced, peak and saturation drift velocities are increased, and high-field negative differential resistance becomes more pronounced. Both 200 and 15 nm gate length MoS 2 MOSFETs with end-contacts with ideal (unity) and more realistic (significantly sub-unity) contact interface transmissivity were simulated. These MoS 2 devices exhibited substantial sensitivity to strain with ideal contact transmissivity, and more so for the 15 nm quasi-ballistic device scale than 200 nm long-channel devices. However, the results showed much less strain sensitivity for devices with more realistic contact transmissivities, which may be good or bad depending on whether strain-insensitive or strain-sensitive performance is desired for a particular application and may be possible to modify with improved contact geometries. [ABSTRACT FROM AUTHOR]

Shear waves are employed in medical ultrasound imaging because they reveal variations in viscoelastic properties of soft tissue. Frequencies below 1 kHz are required due to the substantially higher attenuation and lower propagation speeds than for compressional waves. Shear waves exhibiting particle motion in the direction of propagation, referred to as longitudinal shear waves, can be generated with longitudinal motion of a circular disk on the surface of a soft elastic medium. This approach permits imaging of the longitudinal shear wave with a conventional ultrasound transducer that is coaxial with the source of the shear wave. Presented here is a mathematical model describing the complete wave field generated by displacement at the surface of an isotropic elastic half-space. Numerical simulations are shown for longitudinal, transverse, torsional, and radial source polarizations, with emphasis on focused longitudinal shear waves. Predictions are consistent with measurements of light beams revealing that the longitudinal electric field component produces a smaller focal spot than the transverse field component [Dorn, Quabis, and Leuchs, Phys. Rev. Lett. 91, 233901 (2003)]. Simulations are compared with preliminary measurements of a focused longitudinal shear wave beam generated in a soft tissue phantom by longitudinal motion of a spherically concave piston. [ABSTRACT FROM AUTHOR]

Pancreas volume, as measured by magnetic resonance imaging (MRI), is smaller in individuals with newly-diagnosed type 1 diabetes (T1D) and declines over the first year after diagnosis. However, the repeatability and reproducibility of these MRI measurements is not established, and for MRI to be utilized to measure pancreas volume, the variation between measurements of pancreas volume must be determined. To determine the test-retest repeatability of pancreas volume measurements by MRI, we performed two or three same-day repeat MRIs in the same individuals with or without T1D (n = 8, mean age 24 y, range 11-40 y). A single radiologist, blinded to whether the subject had T1D or not, outlined the pancreas on these repeat images. Pancreas volume was determined by multiplying the area of the pancreatic regions of interest by the MRI slice volume (5 mm). The repeatability of test-retest scans had an intraclass correlation coefficient (ICC) of 0.979 (95% CI 0.928 to 0.996). To determine the inter-reader reliability of pancreas volume measurements, the pancreas was independently outlined by two board-certified radiologists (n = 11). Comparing results from multiple radiologists yielded an ICC of 0.931 (95% CI 0.776 to 0.981), with greater differences in measurement in larger pancreases (p < 0.005). The mean DICE coefficient, a measurement of the degree overlap between pancreas regions of interest between the two readers, was 0.77. These data show that measurements of pancreas volume obtained using MRI are both repeatable and reproducible across multiple readers with ICCs corresponding to excellent clinical significance (ICC > 0.9). These results indicate that MRI measurements of T1D pancreatic volume can be reliably determined and could be useful for clinical investigation. Disclosure: J.M. Williams: None. M.A. Hilmes: None. B.T. Archer: None. L. Du: None. H. Kang: None. W.E. Russell: None. D.J. Moore: None. A.C. Powers: None. J. Virostko: None. Funding: JDRF (3-SRA-2015-102-M-B) [ABSTRACT FROM AUTHOR]