Sustained Release Studies of Metformin Hydrochloride Drug Using Conducting Polymer/Gelatin-Based Composite Hydrogels.

The present work highlights the synthesis and characterization of conducting polymer (CP)-based composite hydrogels with gelatin (GL-B) for their application as drug delivery vehicles. The spectral, morphological, and rheological properties of the synthesized hydrogels were explored, and morphological studies confirmed formation of an intense interpenetrating network. Rheological measurements showed variation in the flow behavior with the type of conducting polymer. The hydrogels showed a slow drug release rate of about 10 h due to the presence of the conducting polymer. The release kinetics were fitted in various mathematical models and were best fit in first order for PNA-, POPD-, and PANI-based GL-B hydrogels, and the PVDF/GL-B hydrogel was best fit in the zero-order models. The drug release was found to follow the order: POPD/GL-B > PANI/GL-B > PVDF/GL-B.

Aging of cornstarch particles suspended in aqueous solvents at room temperature.

Starch suspensions are often used as model systems to demonstrate extreme shear-thickening effects. We study the aging of cornstarch particles in aqueous suspensions at room temperature by granulometry and rheological measurements. When starch is diluted in glycerol, no long-term changes are observed. The situation differs when water is used as solvent. For volume fractions up to 20 vol %, when the cornstarch suspensions in water are stored under continual agitation, we observe an increase in viscosity. When the cornstarch suspension is aged under quiescent conditions, no evolution of the particle size is observed. In the concentrated situation, the rheological properties vary independent of the storage condition. We show that the increase in viscosity is related to air trapped in the pore space and to the swelling of the granules and leakage of the amylopectin component of the starch into the surrounding water. The relative importance of the two processes depends upon the particle concentration and upon the energy brought to the system.

Integration of a soft dielectric composite into a cantilever beam for mechanical energy harvesting, comparison between capacitive and triboelectric transducers.

Flexible dielectrics that harvest mechanical energy via electrostatic effects are excellent candidates as power sources for wearable electronics or autonomous sensors. The integration of a soft dielectric composite (polydimethylsiloxane PDMS-carbon black CB) into two mechanical energy harvesters is here presented. Both are based on a similar cantilever beam but work on different harvesting principles: variable capacitor and triboelectricity. We show that without an external bias the triboelectric beam harvests a net density power of 0.3 [Formula: see text] under a sinusoidal acceleration of 3.9g at 40 Hz. In a variable capacitor configuration, a bias of 0.15 [Formula: see text] is required to get the same energy harvesting performance under the same working conditions. As variable capacitors' harvesting performance are quadratically dependent on the applied bias, increasing the bias allows the system to harvest energy much more efficiently than the triboelectric one. The present results make CB/PDMS composites promising for autonomous portable multifunctional systems and intelligent sensors.

Density waves in shear-thickening suspensions.

Shear thickening corresponds to an increase of the viscosity as a function of the shear rate. It is observed in many concentrated suspensions in nature and industry: water or oil saturated sediments, crystal-bearing magma, fresh concrete, silica suspensions, and cornstarch mixtures. Here, we reveal how shear-thickening suspensions flow, shedding light onto as yet non-understood complex dynamics reported in the literature. When shear thickening is important, we show the existence of density fluctuations that appear as periodic waves moving in the direction of flow and breaking azimuthal symmetry. They come with strong normal stress fluctuations of the same periodicity. The flow includes small areas of normal stresses of the order of tens of kilopascals and areas of normal stresses of the order of hundreds of pascals. These stress inhomogeneities could play an important role in the damage caused by thickening fluids in the industry.

Education and Training to Build Capacity in Total Worker Health®: Proposed Competencies for an Emerging Field.

OBJECTIVE: Establishment of core competencies for education and training of professionals entering the emerging field of Total Worker Health®. METHODS: Compilation and distillation of information obtained over a 5-year period from Total Worker Health symposia, workshops, and academic offerings, plus contributions from key stakeholders regarding education and training needs. RESULTS: A proposed set of Total Worker Health competencies aligns under six broad domains: Subject Matter Expertize; Advocacy and Engagement; Program Planning, Implementation and Evaluation; Communications and Dissemination; Leadership and Management; and Partnership Building and Coordination. CONCLUSIONS: Proposed set of core competencies will help standardize education and training for professionals being trained in Total Worker Health. It serves as an invitation for further input from stakeholders in academia, business, labor, and government.

Stress Field inside the Bath Determines Dip Coating with Yield-Stress Fluids in Cylindrical Geometry.

We study experimentally and theoretically the thickness of the coating obtained by pulling out a rod from a reservoir of yield-stress fluid. Opposite to Newtonian fluids, the coating thickness for a fluid of large enough yield stress is determined solely by the flow inside the reservoir and not by the flow inside the meniscus. The stress field inside the reservoir determines the thickness of the coating layer. The thickness is observed to increase nonlinearly with the sizes of the rod and of the reservoir. We develop a theoretical framework that describes this behavior and allows us to precisely predict the coating thickness.

Molecular Insight into the Slipperiness of Ice.

Measurements of the friction coefficient of steel-on-ice over a large temperature range reveal very high friction at low temperatures (-100 °C) and a steep decrease in the friction coefficient with increasing temperature. Very low friction is only found over the limited temperature range typical for ice skating. The strong decrease in the friction coefficient with increasing temperature exhibits Arrhenius behavior with an activation energy of Ea ≈ 11.5 kJ mol-1. Remarkably, molecular dynamics simulations of the ice-air interface reveal a very similar activation energy for the mobility of surface molecules. Weakly hydrogen-bonded surface molecules diffuse over the surface in a rolling motion, their number and mobility increasing with increasing temperature. This correlation between macroscopic friction and microscopic molecular mobility indicates that slippery ice arises from the high mobility of its surface molecules, making the ice surface smooth and the shearing of the weakly bonded surface molecules easy.

Reduced Near-Resonant Vibrational Coupling at the Surfaces of Liquid Water and Ice.

We study the resonant interaction of the OH stretch vibrations of water molecules at the surfaces of liquid water and ice using heterodyne-detected sum-frequency generation (HD-SFG) spectroscopy. By studying different isotopic mixtures of H2O and D2O, we vary the strength of the interaction, and we monitor the resulting effect on the HD-SFG spectrum of the OH stretch vibrations. We observe that the near-resonant coupling effects are weaker at the surface than in the bulk, for both water and ice, indicating that for both phases of water the OH vibrations are less strongly delocalized at the surface than in the bulk.

Cross-linguistic vowel variation in trilingual speakers of Saterland Frisian, Low German, and High German.

The present study compares the acoustic realization of Saterland Frisian, Low German, and High German vowels by trilingual speakers in the Saterland. The Saterland is a rural municipality in northwestern Germany. It offers the unique opportunity to study trilingualism with languages that differ both by their vowel inventories and by external factors, such as their social status and the autonomy of their speech communities. The objective of the study was to examine whether the trilingual speakers differ in their acoustic realizations of vowel categories shared by the three languages and whether those differences can be interpreted as effects of either the differences in the vowel systems or of external factors. Monophthongs produced in a /hVt/ frame revealed that High German vowels show the most divergent realizations in terms of vowel duration and formant frequencies, whereas Saterland Frisian and Low German vowels show small differences. These findings suggest that vowels of different languages are likely to share the same phonological space when the speech communities largely overlap, as is the case with Saterland Frisian and Low German, but may resist convergence if at least one language is shared with a larger, monolingual speech community, as is the case with High German.

The Surface of Ice Is Like Supercooled Liquid Water.

The surface of ice has been reported to be disordered at temperatures well below the bulk melting point. However, the precise nature of this disorder has been a topic of intense debate. Herein, we study the molecular properties of the surface of ice as a function of temperatures using heterodyne-detected sum-frequency generation spectroscopy. We observe that, down to 245 K, the spectral response of the surface of ice contains a component that is indistinguishable from supercooled liquid water.

Observation and Identification of a New OH Stretch Vibrational Band at the Surface of Ice.

We study the signatures of the OH stretch vibrations at the basal surface of ice using heterodyne-detected sum-frequency generation and molecular dynamics simulations. At 150 K, we observe seven distinct modes in the sum-frequency response, five of which have an analogue in the bulk, and two pure surface-specific modes at higher frequencies (∼3530 and ∼3700 cm-1). The band at ∼3530 cm-1 has not been reported previously. Using molecular dynamics simulations, we find that the ∼3530 cm-1 band contains contributions from OH stretch vibrations of both fully coordinated interfacial water molecules and water molecules with two donor and one acceptor hydrogen bond.

A cross-dialectal acoustic study of Saterland Frisian vowels.

Previous investigations on Saterland Frisian report a large vowel inventory, including up to 20 monophthongs and 16 diphthongs in stressed position. Conducting a cross-dialectal acoustic study on Saterland Frisian vowels in Ramsloh, Scharrel, and Strücklingen, the objective is to provide a phonetic description of vowel category realization and to identify acoustic dimensions which may enhance the discrimination of neighboring categories within the crowded vowel space of the endangered minority language. All vowels were elicited in a /hVt/ frame. Acoustic measurements included vowel duration, mid-vowel F1 and F2, and the amount of spectral change and the spectral rate of change. The results suggest instances of phonetic attrition, i.e., merged categories, precisely where contrasts were reported to be on the retreat. The cross-dialectal comparison showed differences between the three dialects primarily within the F1 dimension at the 20% measurement point. The findings presented here contribute to the description of an endangered minority language and add to the question of which acoustic variables are used in languages with large vowel inventories to maintain or enhance the existing contrasts. Furthermore, the results underline the importance of the consideration of inter-speaker variability as well as measurements beyond the vowel target.

The interfacial structure of water droplets in a hydrophobic liquid.

Nanoscopic and microscopic water droplets and ice crystals embedded in liquid hydrophobic surroundings are key components of aerosols, rocks, oil fields and the human body. The chemical properties of such droplets critically depend on the interfacial structure of the water droplet. Here we report the surface structure of 200 nm-sized water droplets in mixtures of hydrophobic oils and surfactants as obtained from vibrational sum frequency scattering measurements. The interface of a water droplet shows significantly stronger hydrogen bonds than the air/water or hexane/water interface and previously reported planar liquid hydrophobic/water interfaces at room temperature. The observed spectral difference is similar to that of a planar air/water surface at a temperature that is ∼50 K lower. Supercooling the droplets to 263 K does not change the surface structure. Below the homogeneous ice nucleation temperature, a single vibrational mode is present with a similar mean hydrogen-bond strength as for a planar ice/air interface.

Excess Hydrogen Bond at the Ice-Vapor Interface around 200 K.

Phase-resolved sum-frequency generation measurements combined with molecular dynamics simulations are employed to study the effect of temperature on the molecular arrangement of water on the basal face of ice. The topmost monolayer, interrogated through its nonhydrogen-bonded, free O-H stretch peak, exhibits a maximum in surface H-bond density around 200 K. This maximum results from two competing effects: above 200 K, thermal fluctuations cause the breaking of H bonds; below 200 K, the formation of bulklike crystalline interfacial structures leads to H-bond breaking. Knowledge of the surface structure of ice is critical for understanding reactions occurring on ice surfaces and ice nucleation.

Experimental and theoretical evidence for bilayer-by-bilayer surface melting of crystalline ice.

On the surface of water ice, a quasi-liquid layer (QLL) has been extensively reported at temperatures below its bulk melting point at 273 K. Approaching the bulk melting temperature from below, the thickness of the QLL is known to increase. To elucidate the precise temperature variation of the QLL, and its nature, we investigate the surface melting of hexagonal ice by combining noncontact, surface-specific vibrational sum frequency generation (SFG) spectroscopy and spectra calculated from molecular dynamics simulations. Using SFG, we probe the outermost water layers of distinct single crystalline ice faces at different temperatures. For the basal face, a stepwise, sudden weakening of the hydrogen-bonded structure of the outermost water layers occurs at 257 K. The spectral calculations from the molecular dynamics simulations reproduce the experimental findings; this allows us to interpret our experimental findings in terms of a stepwise change from one to two molten bilayers at the transition temperature.

Functional representation of tissue phantom ratios for photon fields.

PURPOSE: The tissue phantom ratio (TPR) is a common dosimetric quantity used in photon dose calculations. For small photon fields with side lengths less than 4 cm, TPR data hardly exist in literature. In this work, a self-contained functional representation of TPR is proposed, valid for the whole range of clinically relevant depth and field sizes. This is especially useful for small fields shaped by multileaf collimators. METHODS: TPRs were measured for quadratic fields with side lengths between 0.4 and 18 cm. The measured data were fitted to a physically meaningful function taking electron buildup, buildup of scattered photons, beam attenuation, and beam hardening into account. The achievable accuracy was tested against measurement and data from the literature. RESULTS: A set of parameters for the proposed function was derived for 6 and 10 MV beams. The comparison of the calculated and the measured data generally yielded a difference of less than 1%. For field sizes below 2 cm, a systematic discrepancy between the author's data and those from Cheng et al. [Med. Phys 34, 3149-3157 (2007)] was found. CONCLUSIONS: With the proposed model, TPRs can be calculated for the full range of field sizes and depths required by treatment planning system algorithms and monitor unit check programs with very high accuracy. The method is also useful in detecting and reducing errors in measurement.

Under-utilization of mechanical circulatory support in Canada: why and what can be done?

In October of 2002, a workshop was held as part of the Canadian Cardiovascular Congress in Edmonton, Canada, entitled "Under-Utilization of Mechanical Circulatory Support in Canada. Why and What Can Be Done?" The workshop examined various issues related to the use of mechanical circulatory support devices in the Canadian context. Representatives from all Canadian centers with active mechanical circulatory support programs were invited to participate and participants included surgeons and cardiologists, as well as other affiliated health professionals. Opinions were solicited from the workshop participants and a series of recommendations were formulated.