Chiral soluble polymers and microspheres for enantioselective crystallization

A series of chiral polymers based on poly(N‐acryl) amino acids was synthesized using a convergent synthetic approach. These chiral polymers have been used as chiral additives to induce enantioselective crystallization of racemic or conglomerate amino acids in solutions. These polymeric additives showed strong capabilities to enhance highly enantioselective resolution during the crystallization of amino acids. In addition, these polymers caused unusual modifications of amino acid crystal morphologies. Furthermore, spherical microparticles of those same chiral polymers were also shown active in similar chiral discriminations during amino acid crystallizations occurring on microparticle surfaces. Our study demonstrates the high potential of chiral polymers and microparticles to resolve amino acids throughout crystallization processes. High enantiomeric excesses in one targeted enantiomer of amino acids can also be maximized via time‐dependent kinetic control of crystallizations. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3009–3017, 2006     

Dynamics of curved DNA molecules: prediction and experiment

We have developed a quantitative predictive model capable of describing the dynamics of migration of intrinsically curved DNA fragments on polyacrylamide gels. The model takes into account structural features of DNA, end-to-end distance, screening of hydrodynamic interactions, ionic strength of buffer, electrostatic persistence length, structural fluctuations of the macromolecule, counter condensation, and variation of dielectric constant and viscosity of water with MPD. In doing so, we have also addressed a decade old issue on the effect of the organic solvent 2-methyl-2,4-pentanediol on gel migration of phased A-tracts. We show here that A-tract-solvent interactions are less favored compared with A-tract-A-tract and solvent-solvent interactions.     

Applying the Voice Handicap Index (VHI) to Dysphonic and Nondysphonic Hebrew Speakers

OBJECTIVE: To evaluate a translated version of the Voice Handicap Index (VHI) as a diagnostic tool for people with and without a laryngeal pathology, among Hebrew speakers. STUDY DESIGN: Parallel group design. METHODS: The VHI was translated and adapted to Hebrew. The translated version was, then, administered to a group of 182 patients with various laryngeal pathologies and a control group of 171 people with no laryngeal pathology. Based on the participants' responses to the VHI, statistical analyses were, initially, performed to assess validity and reliability, and then to evaluate group differences between the pathological and control groups and among the different pathological groups included in the study. RESULTS: Statistical analyses showed high reliability values of the Hebrew version of the VHI (overall Cronbach's alpha r = 0.976). Participants' scores were not affected by their age (P = 0.156) or gender (P = 0.261). The participants in the control group obtained significantly lower scores on the overall VHI score, as well as on all three subscale scores, in comparison with the pathological group (P < 0.001). In addition, within the pathological group, patients with neurogenic pathologies received higher scores than all other pathological groups, whereas patients with laryngeal inflammation received lower scores than all other pathological groups (P < 0.05). CONCLUSION: The VHI is a powerful tool for quantifying patients' perceptions of their voice handicaps, and it maintained its power across translation. The VHI was shown to be valuable for the assessment of speakers with, as well as without laryngeal pathologies.     

Novel Thermal Flow Sensors Based on a Wheatstone Bridge Read-out

A novel thermal flow sensor transduction method is presented combining advantages of the calorimetric and the hot-film transduction principle. Four thin-film germanium thermistors are embedded in the silicon-nitride membrane acting as heat sources and as temperature sensors simultaneously. These devices operate in a Wheatstone bridge. The voltage across the bridge as well as the total dissipated power serves as output quantities. Two sensor configurations with different arrangement of the membrane thermistors were examined experimentally. Moreover, we investigated the influence of different layouts on the rise time, the sensitivity, and the usable flow range by means of two-dimensional finite element simulations.     

Micromachined Flow Sensors Enabling Electrocalorimetric and TOF Transduction

A novel thermal flow sensor is presented featuring three spatially separated micromachined silicon-nitride membranes. A thin-film heater is embedded in the central one, while the others carry thermistors. This advanced sensor structure enables two different transduction modes. The electrocalorimetric mode exhibits high resolution and quick response at the expense of high power consumption. For slowly varying flows, the Time-of-Flight mode with low duty-cycles allows for power-saving operation but suffers from less sensitivity and slower response.     

On expansion and topological overlap

We give a detailed and easily accessible proof of Gromov’s Topological Overlap Theorem. Let X be a finite simplicial complex or, more generally, a finite polyhedral cell complex of dimension d. Informally, the theorem states that if X has sufficiently strong higher-dimensional expansion properties (which generalize edge expansion of graphs and are defined in terms of cellular cochains of X) then X has the following topological overlap property: for every continuous map \(X\rightarrow \mathbb {R}^d\) there exists a point \(p\in \mathbb {R}^d\) that is contained in the images of a positive fraction \(\mu >0\) of the d-cells of X. More generally, the conclusion holds if \(\mathbb {R}^d\) is replaced by any d-dimensional piecewise-linear manifold M, with a constant \(\mu \) that depends only on d and on the expansion properties of X, but not on M.     

Preparation of graded materials by laterally controlled template synthesis

A novel scheme is presented for the synthesis of graded materials by electrodeposition in porous insulating templates. Lateral control of copper electrodeposition in nanoporous alumina membranes is achieved by application of a lateral potential gradient on a thin Au film evaporated on the membrane, used as the cathode. Formation of metal gradients in the membranes is shown to occur under conditions where essentially no gradient is formed on similar bare electrodes. This is attributed to the permanent resistivity of the thin Au film between the pores, which does not disappear upon Cu deposition, allowing a potential gradient to be maintained. Formation of a copper gradient in porous alumina membranes by uniform deposition followed by gradient dissolution is also demonstrated. These results establish the feasibility of controlled electrodeposition and gradient formation in nanoporous insulating templates.     

Synthesis and evaluation of a pseudocyclic tristhiourea-based anion host

A novel methodology for the evaluation of receptor arrangement in structurally flexible anion chemosensors was developed and applied to map the binding site of a new pseudocyclic tristhiourea chemosensor (6). The syntheses of 6 and related macrocyclic chemosensor 10 (a model of the folded monomeric structure of 6) are reported. Both chemosensors were evaluated by titration with a variety of structurally different anions in CH3Cl and DMSO, showing a common preference for F-, CH3CO2-, and H2PO4-. However, within this group of anions, the binding patterns of the chemosensors differed, indicating dissimilarity in the arrangement of the binding sites of 6 and 10.