GaInP/GaAs HBTs for high-speed integrated circuit applications

The use of GaInP/GaAs heterojunction bipolar transistors (HBTs) for integrated circuit applications is demonstrated. The discrete devices fabricated showed excellent DC characteristics with low V_ce offset voltage and very low temperature sensitivity of the current gain. For a non-self-aligned device with a 3-μm×1.4-μm emitter area, f_T was extrapolated to 45 GHz and f_max was extrapolated to 70 GHz. The measured 1/f noise level was 20 dB better than that of AlGaAs HBTs and comparable to that of low-noise silicon bipolar junction transistors, and the noise bump (Lorentzian component) was not observed. The fabricated gain block circuits showed 8.5 dB gain with a 3-dB bandwidth of 12 GHz, and static frequency dividers (divide by 4) were operable up to 8 GHz     

Overexpression and kinetic characterization of the carboxyltransferase component of acetyl-CoA carboxylase

Acetyl-CoA carboxylase catalyzes the first committed step in the biosynthesis of fatty acids. The Escherichia coli form of the enzyme consists of a biotin carboxylase protein, a biotin carboxyl carrier protein, and a carboxyltransferase protein. In this report the overexpression of the genes for the carboxyltransferase component is described. The steady-state kinetics of the recombinant carboxyltransferase are characterized in the reverse direction, in which malonyl-CoA reacts with biocytin to form acetyl-CoA and carboxybiocytin. The initial velocity patterns indicated that the kinetic mechanism is equilibrium-ordered with malonyl-CoA binding before biocytin and the binding of malonyl-CoA to carboxyltransferase at equilibrium. The biotin analogs, desthiobiotin and 2-imidazolidone, inhibited carboxyltransferase. Both analogs exhibited parabolic noncompetitive inhibition, which means that two molecules of inhibitor bind to the enzyme. The pH dependence for both the maximum velocity (V) and the (V/K)biocytin parameters decreased at low pH. A single ionizing group on the enzyme with a pK of 6.2 or lower in the (V/K)biocytin profile and 7. 5 in the V profile must be unprotonated for catalysis. Carboxyltransferase was inactivated by N-ethylmaleimide, whereas malonyl-CoA protected against inactivation. This suggests that a thiol in or near the active site is needed for catalysis. The rate of inactivation of carboxyltransferase by N-ethylmaleimide decreased with decreasing pH and indicated that the pK of the sulfhydryl group had a pK value of 7.3. It is proposed that the thiolate ion of a cysteine acts as a catalytic base to remove the N1' proton of biocytin.     

Project management: Have we applied all that we know?

Information systems projects are often successfully justified but fail in their development. This is usually caused by ineffective management of the project during development combined with an overemphasis on coding techniques. A proven management methodology effectively applied to every project addresses the unpredictability of new objectives, personnel re-organizations, and changing priorities. Key management components include: obtaining management commitment, planning the work, organizing the staff, setting project standards, guiding the team, communicating with general management, documenting decisions, motivating staff, negotiating changes, and training the user. Thorough application of these principles during each project, combined with tracking the actual performance versus the schedule, provides a quality data base of estimating criteria for a data processing organization. Experience indicates proper management applied to any project significantly increases the probability of success.     

What Can Computational Modeling Tell Us about the Diversity of Odor-Capture Structures in the Pancrustacea?

A major transition in the history of the Pancrustacea was the invasion of several lineages of these animals onto land. We investigated the functional performance of odor-capture organs, antennae with olfactory sensilla arrays, through the use of a computational model of advection and diffusion of odorants to olfactory sensilla while varying three parameters thought to be important to odor capture (Reynolds number, gap-width-to-sensillum-diameter ratio, and angle of the sensilla array with respect to oncoming flow). We also performed a sensitivity analysis on these parameters using uncertainty quantification to analyze their relative contributions to odor-capture performance. The results of this analysis indicate that odor capture in water and in air are fundamentally different. Odor capture in water and leakiness of the array are highly sensitive to Reynolds number and moderately sensitive to angle, whereas odor capture in air is highly sensitive to gap widths between sensilla and moderately sensitive to angle. Leakiness is not a good predictor of odor capture in air, likely due to the relative importance of diffusion to odor transport in air compared to water. We also used the sensitivity analysis to make predictions about morphological and kinematic diversity in extant groups of aquatic and terrestrial crustaceans. Aquatic crustaceans will likely exhibit denser arrays and induce flow within the arrays, whereas terrestrial crustaceans will rely on more sparse arrays with wider gaps and little-to-no animal-induced currents.     

Negative differential resistance of AlGaAs/GaAs heterojunctionbipolar transistors: influence of emitter edge current

We report an electrical characterisation of AlGaAs/GaAs heterojunction bipolar transistors over a temperature range of 250 to 400 K in which the emitter edge current contribution to the negative differential output resistance (NDR) effect is determined. A quantitative analysis of the DC gain versus temperature and perimeter to area ratio indicates that emitter edge current has a major influence on the NDR magnitude     

Multitasking in the olfactory system: context-dependent responses to odors reveal dual GABA-regulated coding mechanisms in single olfactory projection neurons

Studies of olfaction have focused mainly on neural processing of information about the chemistry of odors, but olfactory stimuli have other properties that also affect central responses and thus influence behavior. In moths, continuous and intermittent stimulation with the same odor evokes two distinct flight behaviors, but the neural basis of this differential response is unknown. Here we show that certain projection neurons (PNs) in the primary olfactory center in the brain give context-dependent responses to a specific odor blend, and these responses are shaped in several ways by a bicuculline-sensitive GABA receptor. Pharmacological dissection of PN responses reveals that bicuculline blocks GABAA-type receptors/chloride channels in PNs, and that these receptors play a critical role in shaping the responses of these glomerular output neurons. The firing patterns of PNs are not odor-specific but are strongly modulated by the temporal pattern of the odor stimulus. Brief repetitive odor pulses evoke fast inhibitory potentials, followed by discrete bursts of action potentials that are phase-locked to the pulses. In contrast, the response to a single prolonged stimulus with the same odor is a series of slow oscillations underlying irregular firing. Bicuculline disrupts the timing of both types of responses, suggesting that GABAA-like receptors underlie both coding mechanisms. These results suggest that glomerular output neurons could use more than one coding scheme to represent a single olfactory stimulus. Moreover, these context-dependent odor responses encode information about both the chemical composition and the temporal pattern of the odor signal. Together with behavioral evidence, these findings suggest that context-dependent odor responses evoke different perceptions in the brain that provide the animal with important information about the spatiotemporal variations that occur in natural odor plumes.     

Cardiac hypertrophy alters myocardial response to ischaemia and reperfusion in vivo

The impact of cardiac hypertrophy on myocardial biochemical and physiological responses to ischaemia-reperfusion (I-R) was investigated in vivo. Hypertrophy was produced by aortic constriction (PH) or swimming training (TH). Open-chest rat hearts in PH, TH and a sedentary control group (SC) were subjected: (1) to ischaemia, by surgical occlusion of the main descending branch of the left coronary artery for 30 min; (2) to I-R, by releasing the occluded blood vessel for 15 min; or (3) to a sham operation. Ischaemia per se had little effect on heart oxidative and antioxidant status, or lipid peroxidation. However, I-R significantly decreased glutathione (GSH) content, increased glutathione disulfide (GSSG) content, and reduced GSH/GSSG ratio in the SC hearts. These alterations were associated with decreased activities of GSH peroxidase and GSSG reductase, and an increase in lipid peroxidation. Myocardial ATP, total adenine nucleotide content and energy charge in SC were significantly decreased after ischaemia, whereas levels of purine nucleotide derivatives, particularly adenosine, were elevated. No significant alteration of GSH status of adenine nucleotide metabolism occurred after ischaemia or I-R in hypertrophied hearts. In both PH and TH, glutathione content was significantly higher than in SC, whereas activities of GSH peroxidase and GSSG reductases were lower. TH rats maintained a higher heart rate (HR), peak systolic pressure, and energy charge during I-R. These data indicate that hypertrophied but well-functioned hearts may be more resistant to I-R induced disturbances of myocardial oxidative and antioxidant functions.     

Changes in body image, depression, and anxiety levels among women with human papillomavirus infection

In the present study, we examined the expression of CD44 variant exons in human oral squamous cell carcinoma (OSCC). Of ten cell lines from OSCCs, two (KB and H357), as well as the HeLa cell line, failed to express CD44 variant exons. In surgical specimens, all normal mucosa expressed CD44v9 (both mRNA and protein). Of 40 primary OSCCs, 19 (47.5%) showed downregulation of CD44v9, which correlated with tumor cell differentiation, primary metastasis to lymph nodes and secondary metastasis to lymph nodes. The results suggest that the downregulation of CD44v9 may play a role in lymphatic metastasis of OSCC and changes in its expression may be a useful diagnostic tool to determine the metastatic potential of OSCC to lymph nodes. Moreover, three cell lines that failed to express CD44 variant exons might become a useful experimental model to study the role of variant exons in the progression of OSCC.     

Prospective assessment of triage in an urban emergency department

BACKGROUND: This study examined the effectiveness of a triage system based on patient complaints, medical history, vital signs, and triage nurse impression. Measurements included recognizing patients needing admission, in correlating with disposition, and its effectiveness in all age groups. METHODS: Data were collected prospectively on all patients coming to a general emergency department (ED) of an urban teaching hospital from October 1, 1992, through November 30, 1992. Data included assigned triage acuity, disposition waiting time to physician examination, and disposition, as well as return to the ED within 2 weeks. The patients were divided into age groups: 0 to 16 years, 17 years to 25 years, 25 years to 50 years, 50 years to 65 years, and >65 years of age. RESULTS: There were five patients (n = 4,993, 0.4%) who were triaged nonemergently and subsequently admitted. The sensitivity and specificity of an assigned triage 3 acuity assignment in correlating with lack of admission were 99% and 56%, respectively. Mean waiting time to physician examination was 61 +/- 14 minutes for triage 1, 129 +/- 19 for triage 2, and 182 +/- 22 for triage 3. Mean time to admission from sign-in was 246 +/- 10 minutes for triage 1 and 372 +/- 16 minutes for triage 2. CONCLUSIONS: This triage system accurately correlated with disposition and determined waiting time to examination.