Thermotropic liquid crystalline behavior of cholesterol‐linked hydroxyethyl cellulose

A series of monocholesterylsuccinate (ChMS) derivatives of hydroxyethyl cellulose (HEC) were prepared with degree of substitution ranging from 0.6 to 2.0. They were characterized by ChMS content, infrared spectroscopy, polarizing microscopy, and differential scanning calorimetry. All these polymers displayed thermotropic liquid crystalline behavior on heating as well as on cooling. The transformation temperature was found to be influenced by the degree of substitution. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 763–770, 1999     

Effect of Mg on Solidification Microstructures of Homogenous and Functionally Graded A390 Aluminum Alloys

Hypereutectic Al?CSi alloys are used in components that require high resistance wear and corrosion, good mechanical properties, low thermal expansion and less density. The size and morphology of hard primary silicon particles present in Al?CSi alloys greatly influences the mechanical properties. Addition of Mg leads to formation of intermetallic Mg₂Si phases, which contributes towards the properties of high silicon alloy as well as alters the nature and quantity of primary silicon formed. The high silicon alloy subjected to centrifugal casting leads to the formation of functionally gradient material, which provides variation in spatial and continuous distribution of primary phases in a definite direction exhibiting selective properties and functions within a component. The present study is to evaluate the effect of Mg on solidification microstructures of homogenous and functionally graded A390 aluminium alloys. The addition of Mg from 3 to 5?% in A390 alloy using Al?C20Mg master alloy has shown a transformation from primary silicon rich matrix to Mg₂Si rich matrix. Centrifugal casting shows the gradient distribution of primary silicon and Mg₂Si phases towards the inner periphery of the casting.     

Benefits of optical system diversity for multiplexed image reconstruction

Algorithms that use optical system diversity to improve multiplexed image reconstruction from multiple low-resolution images are analyzed and demonstrated. Compared with systems using identical imagers, systems using additional lower-resolution imagers can have improved accuracy and computation. The diverse system is not sensitive to boundary conditions and can take full advantage of improvements that decrease noise and allow an increased number of bits per pixel to represent spatial information in a scene.     

Quantum dots monitor TrkA receptor dynamics in the interior of neural PC12 cells

Can quantum dots (QDs) serve as physiologically relevant receptor probes in the interior of cells? We directly visualize endocytosis, redistribution, and shuttling of QD bound-TrkA receptors to PC12 neural processes and far-reaching growth cone tips. Internalized QDs are contained in microtubule-associated vesicles and possess transport properties that reflect TrkA receptor dynamics. This opens up new possibilities for the development of QD platforms as molecular tools to image biochemical signaling and transport cargo in the cell interior.     

Self-surface passivation of CdX (X = Se, Te) quantum dots

A small portion of a reaction mixture including unpurified CdX (X = Se or Te) quantum dots (QDs), in which unreacted Cd and Se ions were left together with coordinating solvents, was dropped into an organic solvent. The CdX QDs in this organic solution showed enhancement of photoluminescence (PL) efficiency, growth of particles, and focusing of size distribution for more than 10 h at room temperature (RT, -23 degrees C). These effects were attributed to passivation of QDs' surface by Cd and X ions present in the solution. No external energy source was used for these achievements; therefore, the process is termed as self-surface passivation. The self-surface passivation was reproduced using purified CdX QDs with additional Cd and X ions in an organic solvent. The self-surface passivation method was applied to RT-synthesized CdSe QDs, which is characterized by a broad PL spectrum (fwhm - 150 nm) for monodispersed QDs, to modify their emission characteristics. On self-surface passivation, the broad PL spectrum was narrowed (fwhm - 35 nm) and the QDs were grown. The X-ray diffraction measurements of RT-synthesized CdSe QDs and that subsequently aged in 1-butanol showed that crystallinity of the samples was improved on aging.     

Filter for biomedical imaging and image processing

Image filtering techniques have numerous potential applications in biomedical imaging and image processing. The design of filters largely depends on the a priori, knowledge about the type of noise corrupting the image. This makes the standard filters application specific. Widely used filters such as average, Gaussian, and Wiener reduce noisy artifacts by smoothing. However, this operation normally results in smoothing of the edges as well. On the other hand, sharpening filters enhance the high-frequency details, making the image nonsmooth. An integrated general approach to design a finite impulse response filter based on Hebbian learning is proposed for optimal image filtering. This algorithm exploits the interpixel correlation by updating the filter coefficients using Hebbian learning. The algorithm is made iterative for achieving efficient learning from the neighborhood pixels. This algorithm performs optimal smoothing of the noisy image by preserving high-frequency as well as low-frequency features. Evaluation results show that the proposed finite impulse response filter is robust under various noise distributions such as Gaussian noise, salt-and-pepper noise, and speckle noise. Furthermore, the proposed approach does not require any a priori knowledge about the type of noise. The number of unknown parameters is few, and most of these parameters are adaptively obtained from the processed image. The proposed filter is successfully applied for image reconstruction in a positron emission tomography imaging modality. The images reconstructed by the proposed algorithm are found to be superior in quality compared with those reconstructed by existing PET image reconstruction methodologies.     

Characterization of centrifugal cast functionally graded aluminum-silicon carbide metal matrix composites

The present investigation is on characterization of functionally graded composites based on 356 cast and 2124 wrought aluminum alloys reinforced with SiC particles of 23 μm average particle size processed by liquid metal stir casting followed by horizontal centrifugal casting. A maximum of 45 and 40% SiC particles are obtained at the outer periphery of the Al(356)-SiC and Al(2124)-SiC FGMMC casting respectively. The maximum hardness obtained at the outer periphery after heat treatment for Al(356)-SiC and Al(2124)-SiC FGMMC are 155 BHN and 145 BHN respectively. The freezing range of the matrix alloy has been found to dictate the nature of transition from particle enriched to depleted zone. These composites are suitable for making engineering components, which require very high surface hardness and wear resistances with high specific strength.     

Numerical simulation of ceramic composite armor subjected to ballistic impact

Armor systems made of ceramic and composite materials are widely used in ballistic applications to defeat armor piercing (AP) projectiles. Both the designers and users of body armor face interesting choices – how best to balance the competing requirements posed by weight, thickness and cost of the armor package for a particular threat level. A finite element model with a well developed material model is indispensible in understanding the various nuances of projectile–armor interaction and finding effective ways of developing lightweight solutions. In this research we use the explicit finite element analysis and explain how the models are built and the results verified. The Johnson–Holmquist material model in LS-DYNA is used to model the impact phenomenon in ceramic material. A user defined material model is developed to characterize the ductile backing made of ultra high molecular weight polyethylene (UHMWPE) material. An ad hoc design optimization is carried out to design a thin, light and cost-effective armor package. Laboratory testing of the prototype package shows that the finite element predictions of damage are excellent though the back face deformations are under predicted.     

Study of the effect of source signal bandwidth on ratiometric wavelength measurement

We derive an analytic equation for a ratiometric wavelength measurement system and analyze the influence of the optical source signal bandwidth. Our investigation shows that in a particular optical sensing system, the higher the bandwidth of the optical signal, the better resolution the system will achieve. Experiments based on two types of optical signals (output signal of a tunable laser and a fiber Bragg grating) were carried out, and experimental results verified both the simulation results and the theoretical analysis.     

Temperature dependence of 1∕f noise mechanisms in silicon nanowire biochemical field effect transistors

The 1∕f noise of silicon nanowire biochemical field effect transistors is fully characterized from weak to strong inversion in the temperature range 100-300 K. At 300 K, our devices follow the correlated Δn-Δμ model. As the temperature is lowered, the correlated mobility fluctuations become insignificant and the low frequency noise is best modeled by the Δn-model. For some devices, evidence of random telegraph signals is observed at low temperatures, indicating that fewer traps are active and that the 1∕f noise due to number fluctuations is further resolved to fewer fluctuators, resulting in a Lorentzian spectrum.