Stochastic honeycomb sandwich cores

This study presents a new type of cellular material that is simpler to make than conventional honeycombs and foams, while possessing many of the exceptional mechanical properties that make foams and honeycombs valuable as low density structural materials. The stochastic honeycombs had relative densities ranging from 7% to 13% with compressive strengths between 1 and 3 MPa, and compressive stiffnesses between 60 and 130 MPa. These values are comparable to those seen for commercial polypropylene honeycombs and significantly higher than those of commercial polypropylene foams. Rigid sandwich panels could be fabricated by reinforcing the stochastic honeycomb cores with external polypropylene face sheets. The panels could be assembled without adhesives, creating a rigid sandwich made entirely of a single material.     

Scan-Along Polygonal Approximation for Data Compression of Electrocardiograms

Three fast and efficient "scan-along" algorithms for compressing digitized electrocardiographic data are described. These algorithms are "scan-along" in the sense that they produce the compressed data in real time as the electrocardiogram is generated. The algorithms are based on the minimum perimeter polygonal approximation for digitized curves. The approximation restricts the maximum error to be no greater than a specified value. Our algorithms achieve a compression ratio of ten on a database of 8000 5-beat abnormal electrocardiograms sampled at 250 Hz and a compression ratio of eleven on a database of 600 3-beat normal electrocardiograms (different from the preceding database) sampled at 500 Hz.     

Role of the renin-angiotensin-aldosterone system in the progression of renal disease: a critical review

Interruption of the renin-angiotensin-aldosterone system (RAAS) by converting enzyme inhibition or angiotensin II (ANG II) receptor antagonism dramatically reduces injury in the remnant kidney model. Furthermore, converting enzyme inhibition reduces proteinuria and slows the decline in renal function in clinical disease. Hemodynamic actions of ANG II in the kidney in conjunction with a more poorly defined effect of the RAAS on systemic hypertension have been posited as the major mechanisms for maintenance of elevated glomerular pressure. Reductions in glomerular pressure have been attributed, at least in part, to removal of intrarenal effects of ANG II. Growth and fibrotic actions of ANG II may also contribute to progressive renal injury and relief from them reduce injury. The participation of circulating aldosterone in the remnant kidney model has been recently raised. Hyperaldosteronism and adrenal hypertrophy attend the hypertension, proteinuria, and glomerulosclerosis of this model. Although the hemodynamic actions of aldosterone probably account for some of the adverse effects it has in this model, other direct cellular actions may participate in its renal, as well as cardiac and fibrotic consequences. Thus, the RAAS, working through both ANG II and aldosterone, contributes to chronic progressive renal injury.     

The myosin coiled-coil is a truly elastic protein structure

Coiled-coils occur in a variety of proteins involved in mechanical and structural tasks in the cell. Their mechanical properties are important in various contexts ranging from hair elasticity to synaptic fusion. Beyond their importance in biology, coiled-coils have also attracted interest as programmable protein sequences for the design of novel hydrogels and materials. We have studied the elastic properties of the myosin coiled-coil at the single molecule level. The coiled-coil undergoes a massive structural transition at forces between 20 and 25 pN where the coil extends to about 2.5 times its original length. Unlike all other proteins investigated mechanically so far, this transition is reversible on a timescale of less than a second, making the coiled-coil a truly elastic protein.     

Additional comments on "On the Routh-Hurwitz criterion"

It is shown that the Routh-Hurwitz criterion may be used to determine the numbers of right- and left-half plane roots of a polynomial even in the case of a left-column zero.     

Access,utility, imperfection: The impact of videoconferencing on perceptions of social presence

The intent of the research study was to identify relationships between the use of videoconferencing in meetings and what perceptions of social presence may exist related to age, gender, and usage compared to face-to-face meetings. Employees from a large Midwestern University Information Technology division who utilize videoconferencing to facilitate meetings as an alternative to face-to-face meetings were surveyed to assess experiences, perceptions, and satisfaction. Female and male employees (N = 157), ranging in age from 18 to over 50 years of age, provided the frequency of usage, and responded to questions related to perceptions of social presence. Quantitative analysis of the resulting data supported the hypothesis that one of the independent variables, gender, had a positive impact on perceptions of social presence. Brief interviews further elucidated the quantitative findings. While videoconferencing seems to have drawbacks, accessibility, flexibility, and utility are important aspects that are clear from participants’ perceptions of videoconferencing.     

Primary non-Hodgkin's lymphoma of the common bile duct

Primary non-Hodgkin's lymphoma of the common bile duct is rare. To date, nine cases have been recorded in the literature. We report an additional case of a 39-yr-old woman presented with obstructive jaundice. Pathological studies of the surgical specimen disclosed that the wall of the common bile duct was transmurally infiltrated by non-Hodgkin's lymphoma of diffuse large cell type of B-cell lineage intimately associated with reticular fibers. The patient received postoperative brachytherapy, followed by six cycles of chemotherapy according to the CHOP regimen. There is no evidence of lymphoma recurrence 13 months after the surgery. Our analysis of the reported cases indicates that common bile duct non-Hodgkin's lymphoma is a rapidly progressive disease, terminating in death within a year. A complete surgical resection of the lymphoma followed by chemotherapy has shown a promising result.     

High order holds using polynomial spectral observation

New methods for generating high order data holds are developed that are especially attractive for digital controllers requiring substantial processing time between samples. The hold computations may be performed in parallel and need not represent an overhead to the stream of control computation. Both analog and digitally-based outputs are described, and numerical examples of each are given.