We use three glass material micromechanical properties (Young s modulus E, hardness H, and fracture toughness Kc) to describe the glass response to the lapping fabrication process. We discuss loose abrasive lapping of...
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We demonstrate the use of Monte Carlo simulations to generate photon scattering density functions (PSDFs) that represent the tissue volume sampled by steady-state and frequency-domain photon migration. We use these re...
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We demonstrate the use of Monte Carlo simulations to generate photon scattering density functions (PSDFs) that represent the tissue volume sampled by steady-state and frequency-domain photon migration. We use these results to illustrate how scaling laws can be developed to determine the mean sampling depth of the multiply scattered photons detected by photon migration methods that remain valid outside the bounds of the standard diffusion approximation, i.e., at small source-detector separations and in media where the optical absorption is significant relative to scattering. Using both the PSDF computation and the newly formulated scaling laws, we focus on a comprehensive description of the effects of source modulation frequency, optical absorption, and source-detector separation on the depth of the sampled tissue volume as well as the sensitivity of frequency-domain photon migration measurements to the presence of a localized absorption heterogeneity.
We demonstrate the growth of self-assembled nanowires of cobalt silicide on Si(111), (100), and (110) substrates during deposition of Co onto a heated Si substrate. Silicide islands form via an endotaxial mechanism, g...
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We demonstrate the growth of self-assembled nanowires of cobalt silicide on Si(111), (100), and (110) substrates during deposition of Co onto a heated Si substrate. Silicide islands form via an endotaxial mechanism, growing into the substrate along inclined Si{1¯11} planes, which breaks the symmetry of the surface and leads to a long, thin nanowire shape. During growth, both the length and width of the islands increase with time in a fixed proportion that varies strongly with growth temperature, which shows that the nanowire shape is kinetically determined. It is expected that nanowires could form in many other overlayer/substrate systems via this mechanism.
We present the first direct observations of tile-based DNA self-assembly in solution using fluorescent nanotubes composed of a single tile. The nanotubes reach tens of microns in length by end-to-end joining rather th...
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We present the first direct observations of tile-based DNA self-assembly in solution using fluorescent nanotubes composed of a single tile. The nanotubes reach tens of microns in length by end-to-end joining rather than by sequential addition of single tiles. Their exponential length distributions withstand dilution but decay via scission upon heating, with an energy barrier Esc∼180kBT. DNA nanotubes are thus uniquely accessible equilibrium polymers that enable new approaches to optimizing DNA-based programming and understanding the biologically programmed self-assembly of protein polymers.
Previous energetic considerations have led to the belief that carbon nanotubes (CNTs) of 4 Å in diameter are the smallest stable CNTs. Using high-resolution transmission electron microscopy, we find that a stabl...
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Previous energetic considerations have led to the belief that carbon nanotubes (CNTs) of 4 Å in diameter are the smallest stable CNTs. Using high-resolution transmission electron microscopy, we find that a stable 3 Å CNT can be grown inside a multiwalled carbon nanotube. Density functional calculations indicate that the 3 Å CNT is the armchair CNT(2,2) with a radial breathing mode at 787 cm−1. Each end can be capped by half of a C12 cage (hexagonal prism) containing tetragons.
Practical aspects of microfocal X‐ray image enhancement utilizing phase‐contrast effects are considered. Optimization of the experimental method to achieve phase contrast in the hard X‐ray regime is described for a...
Practical aspects of microfocal X‐ray image enhancement utilizing phase‐contrast effects are considered. Optimization of the experimental method to achieve phase contrast in the hard X‐ray regime is described for application to nondestructive evaluation of materials. To achieve this we simulate the diffraction field in an object from a small finite X‐ray source, and investigate effects of geometrical and material parameters on the X‐ray phase‐contrast image are investigated. Experimental phase‐contrast images of porosity and cylindrical pit obtained with a 5 micron microfocal X‐ray source are compared with those from computer simulation as a function of geometrical magnification and X‐ray energy. The phase‐contrast and absorption‐contrast images are compared demonstrating quantitative enhancement of image quality. The phase‐contrast X‐ray imaging provides enhanced contrast, improved edge definition and X‐ray phase information.
Results of isothermal magnetization and magnetic relaxation measurements are presented probing the nature of the magnetic-field-induced magnetostructural transition in the intermetallic compound Gd5Ge4. This transitio...
Results of isothermal magnetization and magnetic relaxation measurements are presented probing the nature of the magnetic-field-induced magnetostructural transition in the intermetallic compound Gd5Ge4. This transition shows the characteristics of a disorder-influenced first order transition including distinct metastable behavior. Below approximately 21K, the transition from the magnetic-field-induced ferromagnetic state back to the antiferromagnetic state shows additional interesting features. Similarities with other classes of magnetic systems exhibiting magnetostructural transitions are pointed out.
In the previous work, cordierite-based glass ceramics were successful prepared by optimising dispersants. In this paper, four different binders were investigated and their effects on the rheological behaviour of the s...
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In the previous work, cordierite-based glass ceramics were successful prepared by optimising dispersants. In this paper, four different binders were investigated and their effects on the rheological behaviour of the suspensions and on the microstructures of the green tapes were compared. Meanwhile, a good compatibility between the dispersant and binder was found to be a predominant factor to obtain an optimised cordierite glass ceramic tape. The microstructure of the green tapes was observed by SEM and the weight loss during binder burn out process was determined by DTA/TG The dielectric constant and dielectric loss of the sintered tapes (at 1150℃for 2h) was also measured.
Magnesium diboride is a new intermetallic superconductor with unique properties. Hot isostatic pressing (HIPing) is one of the most effective methods for the processing of bulk MgB2 from powder with excellent supercon...
Magnesium diboride is a new intermetallic superconductor with unique properties. Hot isostatic pressing (HIPing) is one of the most effective methods for the processing of bulk MgB2 from powder with excellent superconducting and mechanical properties. A high density of lattice defects is very desirable to increase the density of pinning centers which are crucial for high magnetic field applications. A combination of shock loading and subsequent hot isostatic pressing was employed to modify the microstructure and properties of bulk MgB2 as was successfully demonstrated earlier with another intermetallic material — titanium aluminide. Superconducting and mechanical properties, including elastic constants and Q measured with the DRS RUS method, of shock+HIPed material is presented and compared with properties of “as is” HIPed Alfa Aesar MgB2 powder.
Nanoindentation was used to assess the mechanical properties of lamellar and interlamellar tissue in dehydrated rabbit cancellous bone. The effects of surface roughness and maximum nanoindentation load on the measured...
Nanoindentation was used to assess the mechanical properties of lamellar and interlamellar tissue in dehydrated rabbit cancellous bone. The effects of surface roughness and maximum nanoindentation load on the measured mechanical properties were examined in two samples of differing surface roughness using maximum loads ranging from 250-3000 μN. As the ratio of indentation depth to surface roughness decreased below approximately 3:1, the variability in material properties increased substantially. At low loads, the indentation modulus of the lamellar bone was approximately 20% greater than that of the interlamellar bone, while at high loads the measured properties of both layers converged to an intermediate value. Relatively shallow indentations made on smooth surfaces revealed significant differences in the properties of lamellar and interlamellar bone that are consistent with microstructural observations of lamellar bone as more mineralized than interlamellar bone.
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