Fractional crystallization of polypropylene

The development of a fractional crystallization technique for characterization of polypropylenes with respect to stereoregularity is described. It is a simple technique which is attractive for routine analysis and under suitable conditions yields quantitative data with good reproducibility. Separation by fractional crystallization from hot xylene solution is shown to take place according to polymer crystallizability and is relatively independent of molecular weight. It thus represents an alternative and in some ways superior approach to the more commonly used fractional extraction method. Preliminary work indicates that the fractional crystallization method may prove of value in establishing correlations between the stereoregular nature of polypropylenes and their physical properties.     

Effect of processing on the composition of dietary fibre and starch in some legumes

The effect of processing on the total dietary fibre (TDF) insoluble (IDF) and water-soluble (SDF) fractions as well as total (TS), available (AS) and resistant (RS) starch were studied in three legumes, viz. bengalgram (Cicer arietinum L.), Cowpea (Vigna unguiculata) and greengram (Vigna radiata). The processes studied were fermentation, germination, pressure-cooking and roasting. The dietary fibre (DF) content and its components were determined using the enzymatic-gravimetric method. The TS content was determined by the enzymatic method after solubilization with KOH. The DF content ranged from 23.2 to 25.6 g/100 g in the raw and 16.0 to 31.5 g/100 g in the processed legumes. All the processing treatments significantly decreased the SDF content and increased the IDF content of all the three legumes. The mean TS, AS and RS content of the raw legumes were similar, 46.9, 36.7 and 10.2 g/100 g respectively. AS content of all the legumes was reduced by the processing treatments, except pressure cooking. Correspondingly, higher amounts of RS were observed in the processed legumes, except pressure cooked, resulting in an increase in the TDF content.     

Impact of Ni Concentration on the Performance of Ni Silicide/HfO2/TiN Resistive RAM (RRAM) Cells

We present a study of Ni silicide as the bottom electrode in HfO₂-based resistive random-access memory cells. Various silicidation conditions were used for each device, yielding different Ni concentrations within the electrode. A higher concentration of Ni in the bottom electrode was found to cause a parasitic SET operation during certain RESET operation cycles, being attributed to field-assisted Ni cation migration creating a Ni filament. As such, the RESET is affected unless an appropriate RESET voltage is used. Bottom electrodes with lower concentrations of Ni were able to switch at ultralow currents (RESET current <1 nA) by using a low compliance current (<500 nA). The low current is attributed to the tunneling barrier formed by the native SiO₂ at the Ni silicide/HfO₂ interface.     

A Size‐Selective Intracellular Delivery Platform

Identifying and separating a subpopulation of cells from a heterogeneous mixture are essential elements of biological research. Current approaches require detailed knowledge of unique cell surface properties of the target cell population. A method is described that exploits size differences of cells to facilitate selective intracellular delivery using a high throughput microfluidic device. Cells traversing a constriction within this device undergo a transient disruption of the cell membrane that allows for cytoplasmic delivery of cargo. Unique constriction widths allow for optimization of delivery to cells of different sizes. For example, a 4 μm wide constriction is effective for delivery of cargo to primary human T‐cells that have an average diameter of 6.7 μm. In contrast, a 6 or 7 μm wide constriction is best for large pancreatic cancer cell lines BxPc3 (10.8 μm) and PANC‐1 (12.3 μm). These small differences in cell diameter are sufficient to allow for selective delivery of cargo to pancreatic cancer cells within a heterogeneous mixture containing T‐cells. The application of this approach is demonstrated by selectively delivering dextran‐conjugated fluorophores to circulating tumor cells in patient blood allowing for their subsequent isolation and genomic characterization.     

Procedure for evaluation of thermal management requirements in a laser diode structure

Temperature is either a direct catalyst or a precipitating factor in several common laser diode degradation mechanisms including dark-line defects, catastrophic optical destruction, metal diffusion and electrode delamination. This strong correlation between device temperature and performance degradation demonstrates the need for an efficient thermal management strategy. We have adopted a commonly used heat generation model to perform a finite element analysis to compute steady-state and transient thermal profiles for a laser diode structure. The flexibility of the FE model is utilized in performing a parametric study of selected variables affecting temperature in the structure. Taguchi principles are used in the set-up and analysis of this model, and quantitative correlations between the selected variables and temperature are derived. The combined interaction expression is then modeled as an optimization function that may be applied in thermal management analysis. The approach demonstrated here conforms to a general methodology for the development of physics of failure models for degradation in optoelectronic devices.     

In vitro digestibility of proteins in black gram (Phaseolus mungo) and green gram (Phaseolus radiatus) papads

‘Papads’, a traditional food of India, were prepared with decorticated black gram and green gram flours and toasted, microwaved or deep fat fried. Toasting was done by holding the papads over direct flame for 1–2 min. Sharp carousal microwave oven was used for microwaving at high temperature for 30 – 40 s. Deep fat frying was done by immersing the product in preheated refined groundnut oil for 5 – 10 s. In vitro digestibility of proteins in prepared papads was investigated by pepsin and pepsin + pancreatin. The percent protein hydrolysed in black gram papads was 80.5, 75.3 and 72.5 for toasted, microwaved and fried papads respectively. They were not significantly different from each other. Green gram papads exhibited significantly higher hydrolysis in microwaved product (79.3%) when compared to toasted (65.2%) or fried products (65.0%). Pepsin digestibilities were not influenced to a significant extent by cooking method and were in the range of 51.4 – 54.6% for black gram papads and 34.4 – 35.6% for green gram papads.     

Determination of fixed electron-beam-induced positive oxide charge

Contrary to previous beliefs, electron-beam-induced positive charges in insulators persist where created for at least several weeks without discernible movement. Formerly, coating with a thin metal overlay was thought to allow the charge to leak away. Coating with a conductor is shown to shield electric fields from affecting the imaging probe, but to remove no charge from the specimen. A new technique is introduced for the evaluation of the properties of electron-beam-induced positive charges in metal-oxide-semiconductor (MOS) capacitors. MOS structures were subjected to partial area exposure in a scanning electron microscope. These exposures resulted in the creation of areas of localized positive charge within the oxide, which was observed as steps in the capacitance-voltage data. A systematic study was performed. It related the exposed area to the step height and the amount of induced charge to the voltage shift of the step. A model describing the observed phenomenon is presented, followed by a comparison of theoretical and experimental results. The progress of the charge over time was studied by performing capacitance-voltage analysis 30 min after electron beam exposure and up to 4 weeks later.     

Quantum capture times at room temperature in high-speed In0.4Ga0.6As-GaAs self-organized quantum-dot lasers

The quantum capture times in high-speed single-mode self-organized quantum-dot (QD) lasers with I_th=15-30 mA, and small-signal modulation bandwidth f_{-3 dB}=4.5 GHz, have been estimated from high frequency electrical impedance measurements. The effective carrier capture times, determined from this relatively simple measurement technique, vary in the range of 20-40 ps, depending on bias current, and are in excellent agreement with theoretical predictions. The results suggest that carrier capture, not damping, may prove to be the limiting factor in the modulation bandwidths of QD lasers     

Surface wettability of human hair. I. Effect of deposition of polymers and surfactants

Monitoring the wetting force exerted on a single fiber while the fiber is slowly and continuously immersed in a liquid and then withdrawn can provide several kinds of information about the physicochemical heterogeneity of the fiber surface. This method for scanning the fiber surface with an appropriate liquid has been found useful for studying the distribution of materials deposited on the surface of human hair to improve hair assembly properties, such as cationic polymers used in hair conditioners. It is shown how wetting force vs. immersion depth curves can reflect not only the average distribution of the material on the surface, but also the degree of uniformity of the deposit; further, wetting force curves for multiple immersions of the same treated fiber indicate the ease of desorption of the surface material. The results for the systems studied, which include mildly oxidized hair and smooth nylon fibers for comparison, show how the relation between the critical surface tension of the fiber and the surface tension of the treating solution influences distribution and substantivity. Finally, data on the difference between advancing and receding wettability indicate how this hysteresis is related to the nature of the surface and to surface coverage by treating agents.     

Electrochemical synthesis of calcium carbonate coatings on stainless steel substrates

Calcite CaCO₃ has been electrocrystallized on stainless steel substrates by the galvanostatic cathodic reduction of aqueous calcium bicarbonate solutions. The deposition is controlled by pH changes occurring close to the cathode due to electrogeneration of base. The deposit morphology varies from facetted rhombs observed at low (1-20 mA cm⁻²) current densities to corner-rounded particles observed at high (40 mA cm⁻²) current densities.