50-nm Self-Aligned and “Standard” T-gate InP pHEMT Comparison: The Influence of Parasitics on Performance at the 50-nm Node

Continued research into the development of III-V high-electron mobility transistors (HEMTs), specifically the minimization of the device gate length, has yielded the fastest performance reported for any three terminal devices to date. In addition, more recent research has begun to focus on reducing the parasitic device elements such as access resistance and gate fringing capacitance, which become crucial for short gate length device performance maximization. Adopting a self-aligned T-gate architecture is one method used to reduce parasitic device access resistance, but at the cost of increasing parasitic gate fringing capacitances. As the device gate length is then reduced, the benefits of the self-aligned gate process come into question, as at these ultrashort-gate dimensions, the magnitude of the static fringing capacitances will have a greater impact on performance. To better understand the influence of these issues on the dc and RF performance of short gate length InP pHEMTs, the authors present a comparison between In_0.7Ga_0.3As channel 50-nm self-aligned and "standard" T-gate devices. Figures of merit for these devices include transconductance greater than 1.9 S/mm, drive current in the range 1.4 A/mm, and fT up to 490 GHz. Simulation of the parasitic capacitances associated with the self-aligned gate structure then leads a discussion concerning the realistic benefits of incorporating the self-aligned gate process into a sub-50-nm HEMT system     

Bandwidth correction for LED chromaticity

The spectral bandwidth formulae of Stearns and Stearns   are generalized for an arbitrary slit function. Correction coefficients are derived in terms of moments of the slit function. Application to model LED spectra measured with a compact, fiber‐coupled spectrometer having bandwidth of order 12 nm, and a nonlinear wavelength scale shows that accurate LED color measurements may be obtained with such an instrument. Fitting of the relatively broad slit function to line spectra for accurate wavelength calibration is also described. Such fitting, coupled consistently with the bandpass correction, improves the accuracy color measurements with a broad‐response spectrometer. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 374–380, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20242     

Isoproterenol evokes extracellular Ca2+ spikes due to secretory events in salivary gland cells

Secretory cells should in principle export substantial amounts of calcium via exocytosis since Ca2+ is sequestered in secretory granules. Based on a new technique for measurements of the extracellular calcium concentration in the vicinity of the cell membrane and on the droplet technique, we have monitored the rate of calcium extrusion from salivary gland acinar cells. Isoproterenol (ISP), a beta-adrenergic agonist and powerful secretogogue, evoked no change in the cytosolic free Ca2+ concentration ([Ca2+]i) but induced vigorous extracellular Ca2+ concentration ([Ca2+]i) spiking. The absence of [Ca2+]i elevation and the pulsatile nature of the changes in [Ca2+]i indicate that these spikes are most likely due to calcium release from secretory granules. The cholinergic agonist acetylcholine (ACh), which induces moderate secretion, evoked a marked rise in [Ca2+]i and a smooth rise in [Ca2+]i, most likely induced by plasma membrane calcium pumps, on which shortlasting [Ca2+]i spikes were superimposed. The rate of ISP-induced calcium efflux was very substantial. The calculated calcium loss during the first 100 s of supramaximal stimulation corresponded to a reduction of the total cellular calcium concentration of approximately 0.4 mM. We conclude that in salivary glands, calcium release via exocytosis is one of the main mechanisms extruding calcium from cells to the extracellular milieu.     

Global folds of highly deuterated, methyl-protonated proteins by multidimensional NMR

The development of 15N, 13C, 2H multidimensional NMR spectroscopy has facilitated the assignment of backbone and side chain resonances of proteins and protein complexes with molecular masses of over 30 kDa. The success of these methods has been achieved through the production of highly deuterated proteins; replacing carbon-bound protons with deuterons significantly improves the sensitivity of many of the experiments used in chemical shift assignment. Unfortunately, uniform deuteration also radically depletes the number of interproton distance restraints available for structure determination, degrading the quality of the resulting structures. Here we describe an approach for improving the precision and accuracy of global folds determined from highly deuterated proteins through the use of deuterated, selectively methyl-protonated samples. This labeling profile maintains the efficiency of triple-resonance NMR experiments while retaining a sufficient number of protons at locations where they can be used to establish NOE-based contacts between different elements of secondary structure. We evaluate how this deuteration scheme affects the sensitivity and resolution of experiments used to assign 15N, 13C, and 1H chemical shifts and interproton NOEs. This approach is tested experimentally on a 14 kDa SH2/phosphopeptide complex, and a global protein fold is obtained from a set of methyl-methyl, methyl-NH, and NH-NH distance restraints. We demonstrate that the inclusion of methyl-NH and methyl-methyl distance restraints greatly improves the precision and accuracy of structures relative to those generated with only NH-NH distance restraints. Finally, we examine the general applicability of this approach by determining the structures of several proteins with molecular masses of up to 40 kDa from simulated distance and dihedral angle restraint tables.     

Hematopoietic precursor cell exhaustion is a cause of proliferative defect in primitive hematopoietic stem cells (PHSC) after chemotherapy

The aim of the present study is to determine the possibility of measuring the bone mineral density (BMD) around implants by dual energy X-ray absorptiometry (DEXA). Therefore, the trabecular BMD was measured close to 127-600 microns and at a distance from various uncoated and Ca-P-coated implants inserted into the femoral condyle of goals. The implants were left in situ for 12 weeks. In addition, the bone-implant interface was evaluated histologically. For comparative reasons the BMD of non-implanted lateral and medial femoral condyles was also measured. The reproducibility of the measurements, expressed as a coefficient of variation, was found to be 0.44%. Moreover, the regions closest to the implants exhibited a higher BMD than all other regions, and the regions located in the medial condyle showed a higher BMD than the lateral condylar regions. Although the histological sections of the implants in the medial condyle demonstrated more bone contact with the coated than with the uncoated implants, a higher density was measured around the uncoated implants. The results regarding the non-implanted condyles indicated a higher density in the medial than in the lateral condyle. In view of these results, we conclude that BMD around dental implants depends on the location of the implant and that DEXA appears to be an excellent tool for analysing bone-implant reactions.     

Cysteine adds to lipid hydroperoxide

Cysteine reacts with linoleic acid hydroperoxide to yield several products, some of which were identified as fatty acid-cysteine adducts. The addition was catalyzed by ferric chloride (10⁻⁵ M) by initiating free radical reactions. When isomerically pure 13-hydroperoxy-cis-9,trans-11-octadecadienoic acid and cysteine were reacted in 80% ethanol under N₂, the major adducts were 9-S-cysteine-13-hydroxy-10-ethoxy-trans-11-octadecenoic acid (I) and 9-S-cysteine-10,13-dihydroxy-trans-11-octadecenoic acid (II). When the reaction included both isomers of the hydroperoxide (13-and 9-hydroperoxide) and air, an adduct of 9-oxononanoic acid and cysteine also was isolated. Additional experiments gave information about possible mechanisms of I and II formation.     

Homolytic decomposition of linoleic acid hydroperoxide: Identification of fatty acid products

An isomeric mixture of linoleic acid hydroperoxides, 13-hydroperoxy-cis-9,trans-11-octadecadienoic acid (79%) and 9-hydroperoxy-cis-12,trans-10-octadecadienoic acid (21%), was decomposed homolytically by Fe(II) in an ethanol-water solution. In one series of experiments, the hydroperoxides were decomposed by catalytic concentrations of Fe(II). The 10⁻⁵ M Fe(III) used to initiate the decomposition was kept reduced as Fe(II) by a high concentration of cysteine added to the reaction in molar excess of the hydroperoxides. Nine different monomeric (no detectable dimeric) fatty acids were identified from the reaction. Analyses of these fatty acids revealed that they were mixtures of positional isomers identified as follows: (I) 13-oxo-trans,trans-(andcis,trans-) 9,11-octadecadienoic and 9-oxo-trans,trans- (andcis,trans-) 10,12-octadecadienoic acids; (II) 13-oxo-trans-9,10-epoxy-trans-11-octadecenoic and 9-oxo-trans-12, 13-epoxy-trans-10-octadecenoic acids; (III) 13-oxo-cis-9,10-epoxy-trans-11-octadecenoic and 9-oxo-cis-12, 13-epoxy-trans-10-octadecenoic acids; (IV) 13-hydroxy-9,11-octadecadienoic and 9-hydroxy-10,12-octadecadienoic acids; (V) 11-hydroxy-trans-12, 13-epoxy-cis-9-octadecenoic and 11-hydroxy-trans-9, 10-epoxy-cis-12-octadecenoic acids; (VI) 11-hydroxy-trans-12, 13-epoxy-trans-9-octadecenoic and 11-hydroxy-trans-9,10-epoxy-trans-12-octadecenoic acids; (VII) 13-oxo-9-hydroxy-trans-10-octadecenoic acids; (VIII) isomeric mixtures of 9, 12, 13-dihydroxyethoxy-trans-10-octadecenoic and 9, 10, 13-dihydroxyethoxy-trans-11-octadecenoic acids; and (IX) 9, 12, 13-trihydroxy-trans-10-octadecenoic and 9, 10, 13-trihydroxy-trans-11-octadecenoic acids. In another experiment, equimolar amounts of Fe(II) and hydroperoxide were reacted in the absence of cysteine. A large proportion of dimeric fatty acids and a smaller amount of monomeric fatty acids resulted. The monomeric fatty acids were examined by gas liquid chromatography-mass spectroscopy. Spectra indicated that the monomers were largely similar to those produced by the Fe(III)-cysteine reaction. Presented in part at the American Chemical Society Meeting, Los Angeles, March 1974. ARS, USDA.     

Molar absorptivity of poly(methyl methacrylate) in the near-ultraviolet region

The molar absorptivities of methyl methacrylate monomer and of thermally polymerized, monomer-free poly(methyl methacrylate) have been measured in the range 2200–3000 Å, and smoothed values are presented at wavelength intervals of 20 Å over much of this range. Typical amounts of monomer present in a thermally polymerized bulk polymer and in films cast from CH₂Cl₂ solutions of the bulk polymer have been ascertained. The use of such absorptivity values to determine the amount of monomer present in polymer samples is evaluated.     

Comparing Public Perceptions of Alternative Water Sources for Potable Use: The Case of Rainwater,Stormwater, Desalinated Water,and Recycled Water

This research investigated how people’s perceptions of alternative water sources compare with their perceptions of other technologies, and identified significant predictors of comfort with different alternative water sources. We drew on data from four questionnaire survey studies with a total sample of more than 1200 Australian participants. Relative levels of comfort with the alternative water sources was consistent across the four studies: comfort was always highest for drinking rainwater and lowest for drinking recycled water, with comfort with drinking treated stormwater and desalinated water sitting between these two. Although comfort with drinking recycled water was always lowest of the four alternative water sources, participants were significantly more comfortable with drinking recycled water than they were with nuclear energy, or with using genetically modified plants and animals for food. In general, demographic variables were less important predictors of comfort with alternative water sources than were psychological variables; only age and gender emerged as relatively consistent predictors for recycled water, stormwater, and desalinated water, with older participants and males more comfortable with drinking these water sources. Of the psychological variables, participants’ comfort with technology in general, trust in science and trust in government emerged consistently as significant positive predictors of comfort with drinking recycled water, stormwater, and desalinated water.

     

Considerations for linking seatpan and backrest angles

Modern ergonomic chairs typically have several dimensions that can be adjusted independently of one another. Finding a desirable setting for any one dimension can depend on how other dimensions are set, thereby confronting users with a significant control problem. One design strategy for dealing with this problem has been to link changes in seatpan and backrest angles in some ratio, such that a one‐degree change in seatpan angle is associated with a two‐ or three‐degree change in backrest angle. However, there is no evidence to justify the choice of a particular ratio. This article presents data that addresses this issue. Subjects, performing either an entry or verification task, could adjust the chair to any position. Backrest and seatpan angles were plotted over time and analyzed using both graphical and statistical methods. The resulting scatter plots do not support the industry standard, 1:2 or 1:3 ratio, of changes in seatpan to backrest angles. The possibility of a variable linkage is discussed; however, problems associated with such a solution raise the possibility that control issues might be best addressed through training and exploration.