High performance GaAs MESFETs with molecular implanted and optimized lowly-doped drain structure for maximized speed, gain and breakdown performance

GaAs MESFETs with novel lowly-doped drain structures have been developed utilizing molecular implants of silicon trifluoride. Short-channel effects in the 1/4 μm enhancement- and depletion-mode transistors have been suppressed with drain-induced barrier height lowering of less than 70 mV/V and pinch-off voltage shifts of less than 220 mV as the gate length was scaled from 1.0 to 1/4 μm. The 3-terminal breakdown, the transconductance to output conductance ratio, and the unity current gain, cut-off frequency were simultaneously optimized. The E-mode device possessed breakdown of >10 V, G_m · R_ds > 9.5, F_t > 55 GHz, and nominal on-resistance of 2.1 Ω mm while the D-mode device had breakdown >10 V, G_m · R_ds > 6.0, F_t > 45 GHz, and nominal on-resistance of 1.9 Ω mm. These optimized transistors enabled the realization of a variety of low-power digital and high-power mixed signal circuits, using 3-level source-coupled transistor and common-mode logic, such as laser and electro-optic drivers, highly integrated transceivers, multiplexers, demultiplexers, and clock data recover circuits.     

The pedagogic paradox (or why no didactics in England?)

This article has been written for two purposes. First, it explores a paradox: that recent Anglo-American usage of 'pedagogy' mirrors the mainland European use of 'didactic'. Secondly, it is a comment on the current status of curriculum studies. In particular, it relates curriculum analysis to the fields of didactic and pedagogic analysis.     

Bone cell attachment and growth on well‐characterized chitosan films

Chitosan has been widely researched for bone tissue and implant applications. While initial results are promising, there are inconsistent reports regarding the biological responses. This may be due to inadequate evaluation of chitosan material properties. This study evaluated normal human osteoblast precursor cell attachment and proliferation on a series of well‐characterized chitosan films. The chitosan films exhibited a range of properties: 76–96% degree of de‐acetylation (DDA), 2400–8200 kDa viscosity‐average molecular weight, 62–90° contact angle, 0.24–2.46% residual ash, 5.3–287 µg cm^?2 residual protein and 23–40% crystallinity. There was no trend or correlation between DDA, crystallinity, contact angle, molecular weight, residual ash or protein content and the attachment or growth of bone cells on chitosan films. All films supported higher levels of bone cell proliferation than tissue culture plastic, which supports the general hypothesis that chitosans are osteocompatible. The 78 and 92% DDA chitosan films supported the most cell proliferation, approximately 16 times that of tissue culture plastic controls, but no chitosan physiochemical property correlated with the increased cell growth. The lack of correlation is hindered since more than one physiochemical property changed for each chitosan material. Data do indicate that there may be much variability in chitosan materials, and this variability may make understanding and comparing biological performance of chitosan materials difficult. These results highlight the need for systematic characterizations of chitosan materials for predictable biomedical applications. Copyright © 2006 Society of Chemical Industry     

Far infrared measurements of bulk and surface phonons in GaAs/AlAs superlattices

We have used far-infrared oblique-incidence reflection spectroscopy to study bulk phonon polaritons, and attenuated total reflection (ATR) spectroscopy to study surface phonon polaritons, in long-period GaAs/Al_xGa_1?xAs and short-period GaAs/AlAs superlattices. Results on the former are in good agreement with an effective-medium bulk-slab model of the dielectric tensor of the superlattice; results on the latter are analysed in terms of a model that contains dielectric-tensor contributions from the confined optic phonons.     

Problematic aspects of diagnosing premenstrual phase dysphoria: Recommendations for psychological research and practice.

A gender-specific psychiatric diagnosis, named after an aspect of normal menstrual cycle physiology ("Late Luteal Phase" Dysphoric Disorder, or LLPD), is currently being considered for full diagnostic status in the upcoming catalog of psychiatric disorders, the DSM-IV. Psychologists have had surprisingly little voice in the ongoing debate about LLPD, despite the severe methodological difficulties involved in establishing reliability and validity for the proposed diagnosis. To stimulate research contributions by psychologists, we discuss the risks for over- and underdiagnosis, identify gaps in knowledge, and highlight specific empirical questions that require attention if the debate is to be informed by assessments with demonstrated and acceptable levels of reliability and validity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of nordihydroguaiaretic acid on luteal phase length and oxytocin-induced release of prostaglandin F2 alpha in heifers

Two experiments were conducted to determine if intrauterine infusion of nordihydroguaiaretic acid, a lipoxygenase pathway inhibitor, would delay luteolysis (Experiment 1) and inhibit oxytocin-induced release of prostaglandin F2 alpha (as measured by the stable prostaglandin F2 alpha metabolite, 15-keto-13,14-dihydroprostaglandin F2 alpha) in plasma on d 16 (d 0 = estrus) of the estrous cycle (Experiment 2). Nordihydroguaiaretic acid (20 mg) or saline was infused twice daily into the uterus on d 14 to 23 (Experiment 1) or d 14 to 20 (Experiment 2) postestrus, respectively. In Experiment 1 and 2, mean concentration of progesterone was higher and luteolysis was delayed in nordihydroguaiaretic acid-infused heifers compared with saline-infused heifers. In Experiment 2, saline or oxytocin (100 IU, i.v.) was injected into each heifer on d 16 postestrus to stimulate the release of prostaglandin F2 alpha from the uterus. Mean concentration of 15-keto-13,14-dihydroprostaglandin F2 alpha increased within 1.5 h postinjection in heifers infused with saline, whereas concentration of 15-keto-13,14-dihydroprostaglandin F2 alpha in nordihydroguaiaretic acid-infused heifers did not increase within the same time period. Thus, nordihydroguaiaretic acid may inhibit both the lipoxygenase and cyclooxygenase pathways of arachidonic acid metabolism and therefore delay luteolysis.     

Attribution difficulty and memory for attribution-relevant information.

Compared the processing and retrieval of attribution-relevant information when the attributional inference is easy or difficult to make. Ss attributed behavioral events to the person or to the situation, based on several items of context information. Each context sentence implied either the person or the entity as causal agent. When the attributional inference was difficult to make (an equal number of context sentences implied actor and entity as the causal agent), Ss recalled more of the behavioral events, recalled more context sentences, and were less confident in their attributions than when the attributional inference was easy to make (most context sentences implied the same causal agent). Ss also recalled context information that was implicationally incongruent with the majority of the other context sentences with a higher probability than when that same information was implicationally congruent. (PsycINFO Database Record (c) 2010 APA, all rights reserved)