Study of hydrogen production and storage based on aluminum–water reaction

The rate and yield of hydrogen production from the reaction between activated aluminum and water has been investigated. The effect of different parameters such as water–aluminum ratio, water temperature and aluminum particle size and shape was studied experimentally. The aluminum activation method developed in-house involves 1%–2.5% of lithium-based activator which is diffused into the aluminum particles, enabling sustained reaction with tap water or sea water at room temperature. Hydrogen production rates in the range of 200–600 ml/min/g Al, at a yield of about 90%, depending on operating parameters, were demonstrated. The work further studied the application in proton exchange membrane (PEM) fuel cells in order to generate green electric energy, demonstrating theoretical specific electric energy storage that can exceed batteries by 10–20 folds.     

Digital Circuit Design Trends

This paper has described the different trends in the digital circuit design and changes over the past two decades moving from chips that contained tens of thousands of devices to today' s chips that may contain over a billion transistors. The job of the digital circuit designer has grown with the chips, moving from optimizing and validating gates, to working on functional units, to now designing complete systems. While the progress in digital design has clearly been tremendous, power challenges are an important issue in future VLSI designing system. Designers used considerable ingenuity to make CMOS compatible with the older bipolar ECL/TTL families, concentrating on meeting all aspects of the without requiring external components.     

Synthesis of Zirconia Colloids from Aqueous Salt Solutions

We monitor the synthesis of ZrO₂ colloids from dissolved ZrOCl₂·8H₂O using quasi-elastic light scattering and cryo-transmission electron microscopy (cryo-TEM). We investigate the effects of both precursor salt concentration and pH on the final size distribution. We find that the initial pH plays the most important role in the final particle size and yield. These trends and cryo-TEM observations help elucidate the roles of nucleation, aggregation, and recrystallization.     

Balancing sets of vectors

For n>0, d⩾0, n≡d (mod 2), let K(n, d) denote the minimal cardinality of a family V of ±1 vectors of dimension n, such that for any ±1 vector w of dimension n there is a v∈V such that |v- w|⩽d, where v-w is the usual scalar product of v and w. A generalization of a simple construction due to D.E. Knuth (1986) shows that K(n , d)⩽[n/(d+1)]. A linear algebra proof is given here that this construction is optimal, so that K(n, d)-[n/(d+1)] for all n≡d (mod 2). This construction and its extensions have applications to communication theory, especially to the construction of signal sets for optical data links     

The kinetics and shear threshold of transient and rolling interactions of L-selectin with its ligand on leukocytes

The kinetics of rolling and transient adhesions through selectins may depend on the kinetics and mechanical properties of the selectin:ligand bond, as well as on cellular properties including receptor-anchoring to the cell membrane and cytoskeleton. Kinetics are known to depend on the selectin and may also be ligand dependent. Here, we study the kinetics of transient and rolling interactions of leukocytes with L-selectin immobilized on a substrate. Remarkably, all properties examined are similar to those seen when the sidedness is opposite, i.e., when the L-selectin ligand is on the substrate and when the ligand is isolated from HEV rather than present on leukocytes. The similar properties include rolling velocity, a threshold shear stress above 0.4 dyn/cm2 required to support rolling, a k degreesoff of 7.0 to 6.8 s-1 for the L-selectin tether bond, and a mechanical bond length of 0.24 to 0.20 A. Our results argue against a model in which L-selectin shedding mediates rolling. Furthermore, the fast and force-resistant kinetic properties suggest that L-selectin is specialized dynamically for tethering leukocytes to vessel walls and adherent leukocytes.     

The regulation of the binding affinity of the luteinizing hormone/choriogonadotropin receptor by sodium ions is mediated by a highly conserved aspartate located in the second transmembrane domain of G protein-coupled receptors

Sequence alignment shows that there is a highly conserved aspartate in the second transmembrane helix of virtually all G protein-coupled receptors. A previous study on the alpha 2-adrenergic receptor demonstrated that substitution of this acidic residue for the corresponding amide slightly decreases the affinity of the receptor for agonists and completely abolishes the effect of Na+ on the affinity for agonists. Since we have previously shown that Na+ modulates the binding affinity of the LH/CG receptor for ovine LH (oLH) [but not for human CG (hCG)], the experiments described here were designed to determine if the corresponding residue (D383) of the rat LH/CG receptor also mediates this Na+ effect. We used site-directed mutagenesis to create an LH/CG receptor mutant in which D383 was substituted by N. The wild type and mutant receptor [designated rLHR(D383N)] were expressed in human embryonic kidney 293 cells, and the transfected cells were tested for their ability to bind hCG and oLH in medium containing Na+ or an isoosmolar concentration of an appropriate sodium substitute. The results presented here show that this single point mutation of the LH/CG receptor leads to a slight reduction in affinity for hCG and oLH but completely abolishes the effects of Na+ removal on the affinity for oLH. Thus, regardless of the presence or absence of Na+, cells expressing rLHR(D383N) bind oLH with a low affinity comparable to that of the wild type receptor assayed in the presence of Na+. We also measured the ability of hCG and oLH to increase cAMP accumulation in cells expressing the wild type and mutant receptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Source coding and graph entropies

A sender wants to accurately convey information to a receiver who has some, possibly related, data. We study the expected number of bits the sender must transmit for one and for multiple instances in two communication scenarios and relate this number to the chromatic and Korner (1973) entropies of a naturally defined graph     

Early experience with the contraceptive use of depot medroxyprogesterone acetate in an inner-city clinic population

There are few data on the experience of American women with the injectable depot medroxyprogesterone acetate (DMPA) since its recent approval by the Food and Drug Administration for contraceptive use in the United States. An exploratory study was conducted using chart reviews and telephone interviews of 261 women who initiated DMPA use between December 1992 and June 1994 at either a hospital-based (48%) or community-based (49%) clinic in New York City. Most DMPA users were single (70%), had had at least one birth (88%), had had at least one abortion (67%) and had ever practiced contraception (75% of those with available data). Life-table DMPA continuation rates were 63% at six months and 42% at 12 months and were not affected by the users' age, marital status, pregnancy history, clinic site or proximity of residence to the clinic. Among adults, the risk of DMPA discontinuation was highest during the three-month period following the second injection, while among adolescents, this risk increased throughout the duration of use. The most commonly reported reasons for method discontinuation were side effects, primarily menstrual irregularities (30%) and weight gain (24%).     

Finding and counting given length cycles

We present an assortment of methods for finding and counting simple cycles of a given length in directed and undirected graphs. Most of the bounds obtained depend solely on the number of edges in the graph in question, and not on the number of vertices. The bounds obtained improve upon various previously known results. This work was supported in part by The Basic Research Foundation administrated by The Israel Academy of Sciences and Humanities.