Dynamic properties of lung parenchyma: mechanical contributions of fiber network and interstitial cells

We investigated the contributions of the connective tissue fiber network and interstitial cells to parenchymal mechanics in a surfactant-free system. In eight strips of uniform dimension from guinea pig lung, we assessed the storage (G') and loss (G") moduli by using pseudo-random length oscillations containing a specially designed set of seven frequencies from 0.07 to 2.4 Hz at baseline, during methacholine (MCh) challenge, and after death of the interstitial cells. Measurements were made at mean forces of 0.5 and 1 g and strain amplitudes of 5, 10, and 15% and were repeated 12 h later in the same, but nonviable samples. The results were interpreted using a linear viscoelastic model incorporating both tissue damping (G) and stiffness (H). The G' and G" increased linearly with the logarithm of frequency, and both G and H showed negative strain amplitude and positive mean force dependence. After MCh challenge, the G' and G" spectra were elevated uniformly, and G and H increased by < 15%. Tissue stiffness, strain amplitude, and mean force dependence were virtually identical in the viable and nonviable samples. The G and hence energy dissipation were approximately 10% smaller in the nonviable samples due to absence of actin-myosin cross-bridge cycling. We conclude that the connective tissue network may also dominate parenchymal mechanics in the intact lung, which can be influenced by the tone or contraction of interstitial cells.     

Suppression of buried oxide induced variability on digital performance of GeOI pMOSFETs using substrate bias scheme

Random variation in buried oxide thickness strongly affects the digital performance of ultra-thin body germanium-on-insulator MOSFETs. Dependencies of threshold voltage, ON-current, OFF-current and subthreshold slope of ultra-thin body germanium-on-insulator MOSFETs on three different BOX dielectrics are examined by employing well-calibrated Synopsys TCAD. The variation of threshold voltage and ON-current becomes less sensitive with high-k BOX dielectrics whereas smaller variation of OFF-current is observed for the device with low-k BOX dielectrics. The subthreshold slope remains almost unaltered for all BOX dielectrics. Furthermore, a positive substrate bias is found to suppress variability of digital performance parameters of GeOI p-MOSFETs.

     

Step multiple quantum well enabled performance enhancement in InGaN/GaN based light-emitting diodes

In this work, we propose and investigate numerically InGaN/GaN based multiple quantum well (QW) blue light-emitting diodes (LEDs) with step quantum well (InGaN)/barrier (GaN) structures. We design four LED structures—(LED-A) InGaN/GaN rectangular quantum well, (LED-B) one down step in the middle of the QW created using sharp increase in In contents, (LED-C) one down step in the middle of the QW and the other down step in the right barrier away from QW and (LED-D) similar to LED-C barring one down step in the left barrier facing the QW. Using well-calibrated APSYS simulation program we compare the variation of output power and internal quantum efficiency of LEDs with input injection current and analyze them in the light of energy band diagram, electric field distribution, carrier concentration and radiative recombination rate. The proposed LED-D exhibits significant improvement in optical output power ~ 180.7% compared to conventional LED-A. Furthermore unlike other three LED structures, LED-D shows a very low internal quantum efficiency droop of 5.1% only at injection current of 120 mA.

     

Quasi-dynamic Load Balanced Clustering Protocol for Energy Efficient Wireless Sensor Networks

Wireless Personal Communications - Miscellaneous issues related to wireless sensor networks (WSN) like clustering of sensor nodes, load balancing amongst the cluster heads, energy efficient...     

Providing Software as a Service: a design decision(s) model

We examine how Software as a Service (SaaS) providers make different design decisions using a theoretical model. We consider two non-functional attributes: modularity of the software architecture and the architectural performance of the software. We model the relationship of these two attributes with factors such as user preferences, user demand, and the price of the service. In a significant departure from traditional models of IS product development, we considered marginal cost and maintenance cost of providing SaaS service to recognize that the SaaS service has characteristics of both a product and a service. We show how to find the optimal values of design attributes that maximize SaaS provider’s profits, taking into account relevant factors such as user preferences, user demand and service price. Our research provides one of the first analytical models of optimal design decision making by SaaS providers. We use the model to further show how the SaaS providers should adjust the service design in response to changes in user preferences, associated costs and other relevant factors.     

Preparation and characterization of nanocomposites based on thermoplastic elastomers from rubber–plastic blends

In the present work, thermoplastic elastomer (TPE)–clay nanocomposites (TPN) based on different rubber–plastic blends from ethylene–octene copolymer [Engage]–Polypropylene and brominated poly(isobutylene‐co‐paramethyl styrene)–nylon 6 were prepared by melt blending. Hexadecyltrimethylammonium bromide and octadecyl amine‐modified sodium montmorillonite were used as organoclays. The nanocomposites were prepared by adding the nanoclay separately into the rubber and plastic phases. The TPNs were characterized with the help of transmission electron microscopy (TEM) and X‐ray diffraction. The X‐ray diffraction peaks observed in the range of 3–10° for the modified clays disappeared in the thermoplastic elastomeric nanocomposites. TEM photographs showed exfoliation and intercalation of the clays in the range of 20–30 nm in the particular phase where the clay was added. Excellent improvement in mechanical properties like tensile strength, elongation at break, and modulus was observed on incorporation of the nanoclays in the rubber phase of TPN. When the nanoclay was added to the plastic phase, the mechanical reinforcement is comparatively poorer due to partial destruction of the crystallinity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1645–1656, 2006     

Phase Behavior and Micro-Structure of Fat–Oil Mixtures: Engineering the Shape of Fat Clusters

The mechanical properties of fat–oil mixtures are dictated by the morphology of the fat crystal network, which in turn is strongly affected by the processing conditions. In this work the effect of uniform (linear) cooling rates on the size and shape of tribehenin (fat) clusters in isopropyl myristate (oil) was studied. The state of the fat–oil mixtures was comprehensively analyzed by establishing pseudo‐phase diagrams via visual observations, brightfield and polarization microscopy at various cooling rates and fat concentrations. The microstructure of the constituent fat clusters undergo a shape transition from bundles of needles at low cooling rates to spherical clusters at high cooling rates. The network structures formed with these different shaped fat clusters were examined using rheology. At a given cooling rate, the storage modulus (G?) of fat–oil mixtures versus fat concentration followed a power law relationship. For a given fat concentration, the fat crystal networks comprising of bundles of needles showed higher G? values as compared to fat networks made of spherical clusters. While the fractal dimension of networks cooled at different cooling rates varied over a small range of 2.78–2.86, considerable change in the pre‐exponential factor (γ) was observed. The results show the critical importance of processing conditions on the shape and size of fat clusters and its impact on the rheological properties of the fat crystal network.     

Evolution of mechanical and electrical properties of tin-lead and lead free solder to copper joint interface

Cu-(Sn37Pb) and Cu-(Sn3.5Ag0.5Cu) solder joints were prepared at the same reflow temperature of 230 °C. The microstructural observation of the solder assemblies in scanning and transmission electron microscopes confirmed the presence of η-Cu₆Sn₅ in case of the former, and Cu₃Sn + η-Cu₆Sn₅ for the latter in the reaction zone. The findings are correlated with the electrical and mechanical properties of the joints. Lead free solder-Cu joint exhibited lower reaction zone thickness and improved electrical conductivity (0.28 × 10⁶Ω^− 1 cm^− 1) and shear strength ∼ 68MPa compared to conventional lead-tin solder-Cu joint. The latter showed electrical conductivity and shear strength of 0.22 × 10⁶Ω^− 1 cm^− 1 and ∼ 55 MPa, respectively. The difference in reaction zone thickness is explained on the basis of melt superheat, with Sn being the primary diffusing species in the intermetallic layer.     

Automatic target recognition employing signal compression

Quadratic correlation filters (QCFs) have been used successfully to detect and recognize targets embedded in background clutter. Recently, a QCF called the Rayleigh quotient quadratic correlation filter (RQQCF) was formulated for automatic target recognition (ATR) in IR imagery. Using training images from target and clutter classes, the RQQCF explicitly maximized a class separation metric. What we believe to be a novel approach is presented for ATR that synthesizes the RQQCF using compressed images. The proposed approach considerably reduces the computational complexity and storage requirements while retaining the high recognition accuracy of the original RQQCF technique. The advantages of the proposed scheme are illustrated using sample results obtained from experiments on IR imagery.     

A fluorogenic peptide containing the processing site of human SARS corona virus S-protein: kinetic evaluation and NMR structure elucidation

Human severe acute respiratory syndrome coronavirus (hSARS-CoV) is the causative agent for SARS infection. Its surface glycoprotein (spike protein) is considered to be one of the prime targets for SARS therapeutics and intervention because its proteolytic maturation by a host protease is crucial for host-virus fusion. Using intramolecularly quenched fluorogenic (IQF) peptides based on hSARS-CoV spike protein (Abz-(755)Glu-Gln-Asp-Arg-Asn-Thr-Arg-Glu-Val-Phe-Ala-Gln(766)-Tyx-NH(2)) and in vitro studies, we show that besides furin, other PCs, like PC5 and PC7, might also be involved in this cleavage event. Through kinetic measurements with recombinant PCs, we observed that the peptide was cleaved efficiently by both furin and PC5, but very poorly by PC7. The cleavage could be blocked by a PC-inhibitor, alpha1-PDX, in a dose-dependent manner. Circular dichroism spectra indicated that this peptide possesses a high degree of sheet structure. Following cleavage by furin, the sheet content increased, possibly at the expense of turn and random structures. (1)H NMR spectra from 2D COSY and ROESY experiments under physiological buffer and pH conditions indicated that this peptide possesses a structure with a turn at its C-terminal segment, close to the cleavage site. The data suggest that the cleavable peptide bond is located within the most exposed domain; this is supported by the nearby turn structure. Several strong to weak NMR ROESY correlations were detected, and a 3D structure of the spike IQF peptide that contains the crucial cleavage site R(761) E has been proposed.