A novel trench-defined MISIM CCD structure for X-ray imaging andother applications

A charge-coupled device (CCD) utilizing a trench-defined metal-insulator-semiconductor-insulator-metal (MISIM) sandwich structure is proposed and analyzed. The CCD features high charge capacity and a deep photogenerated carrier collection depth. The trench CCD structure has potential application in X-ray imaging as well as in high-density visible and infrared imaging     

What do successful computer science students know? An integrative analysis using card sort measures and content analysis to evaluate graduating students' knowledge of programming concepts

Abstract: This paper describes a multi‐institutional study that used a repeated single‐criterion card sort to investigate graduating computer science students' knowledge of programming concepts. The study seeks to improve computer science instruction by gaining insight into how graduating students retain and assimilate introductory programming knowledge into their broader understanding of the discipline. A total of 291 card sorts was elicited from 65 undergraduate students in their final year of study at eight colleges and universities throughout the USA. To fully exploit the rich qualitative and quantitative aspects of the card sort data, an integrative analysis process was used that combined content analysis with two measures, normalized minimum spanning tree and edit distance, both developed specifically to analyze card sort data.     

Analysis and control of floating-body bipolar effects in fullydepleted submicrometer SOI MOSFET's

Floating-body effects triggered by impact ionization in fully depleted submicrometer silicon-on-insulator (SOI) MOSFETs are analyzed based on two-dimensional device simulations. The parasitic bipolar junction transistor (BJT) effects are emphasized, but the kink effect and its disappearance in the fully depleted device are first explained physically to provide a basis for the BJT analysis. The results of simulations of the BJT-induced breakdown and latch phenomena are given, and parametric dependences are examined to give physical insight for optimal design. The analysis further relates the DC breakdown and latch mechanisms in the fully depleted submicrometer SOI MOSFET to actual BJT-related problems in an operating SOI CMOS circuit. A comprehensive understanding of the floating-body effects is attained, and a device design to control them utilizing a lightly doped source (LDS) is suggested and shown to be feasible     

A physical model for the dependence of carrier lifetime on doping density in nondegenerate silicon

A theoretical model that describes the dependence of carrier lifetime on doping density, which is based on the equilibrium solubility of a single defect in nondegenerately doped silicon, is developed. The model predictions are consistent with the longest measured hole and electron lifetimes reported for n-type and p-type silicon, and hence imply a possibly “fundamental” (unavoidable) defect in silicon. The defect is acceptor-type and is more soluble in n-type than in p-type silicon, which suggests a longer fundamental limit for electron lifetime than for hole lifetime at a given nondegenerate doping density. The prevalent, minimum density of the defect, which defines these limits, occurs at the processing temperature below which the defect is virtually immobile in the silicon lattice. The analysis reveals that this temperature is in the range 300–400°C, and thus emphasizes, when related also to common non-fundamental defects, the significance of low-temperature processing in the fabrication of silicon devices requiring long or well-controlled carrier lifetimes.     

Numerical simulation of temperature-dependent minority-hole transport in n silicon emitters

A one-dimensional numerical computer simulation of minority-hole transport in heavily doped n⁺ silicon emitters is developed accounting for significant temperature dependences. The model includes the most recent insights regarding heavy-doping effects, which indeed facilitate the accounting for the temperature dependences. Measurements of base current in polysilicon-contacted n⁺pn transistors over a wide temperature range, carefully interpreted by accounting for unavoidable device/ambient temperature discrepancies, support the model and demonstrate its utility, for example in characterizing the electrical properties of the polysilicon emitter contact.     

Benchtop Energetics: Hyperthermal Species Detection

We propose a novel scheme for monitoring the transition between deflagration and “detonation‐like” behavior of small‐scale explosive samples‐in‐vacuum subjected to short duration shock stimuli. Our approach relies on measuring the chemical identities and velocity distributions of the gaseous species produced by such samples; e.g. the relatively low velocity expansion‐quenched reaction intermediates produced by deflagration versus the hyperthermal thermodynamically stable molecules generated by the termination of a detonation wave at an explosive‐vacuum interface. We demonstrate our ability to detect such species by time‐of‐flight mass spectrometry (TOFMS) using fast Al atoms produced by laser ablation of aluminum metal. Extensive SIMION simulations of ion trajectories in our mass spectrometer lead to a semi‐quantitative model connecting the system operating parameters and the velocity‐dependent neutral species detection efficiency. We present a method for correcting our data for these detection biases, and for transforming them into neutral species velocity and kinetic energy distributions. We also present preliminary TOFMS data of hyperthermal organic molecular species produced by direct laser ablation/ignition of thin‐film nitrocellulose samples.     

Effect of antibiotic growth promoters and anticoccidials on growth of Clostridium perfringens in the caeca and on performance of broiler chickens

The purpose of this study was to analyze atomizer performance in the production of respirable spray-dried particles. An ultrasonic nebulizer and a plain-jet airblast atomizer were evaluated in an open cycle, cocurrent spray-drying tower using a 0.5% w/v disodium fluorescein solution. The plain-jet airblast atomizer produced smaller initial droplet sizes (D32 = 4.5-4.8 microns) relative to the ultrasonic nebulizer (D32 = 20-48 microns) over a range of atomizer operating conditions. The airblast atomizer was selected for further analysis in two spray-drying tower configurations: grounded and electrostatically charged. The spray-dried particles produced by the airblast atomizer were of a size range (mass median aerodynamic diameter [MMAD] < 1.6 microns) suitable for inhalation. Significant differences were observed for the grounded and electrostatically charged tower configurations, the latter producing the smaller median particle size at the expense of decreased collection efficiency. The electrostatically charged tower was size selective because of diffusion charging, retaining particles with an aerodynamic diameter (Dae) in the range 1 < Dae < 2 microns. The particle size was reduced with decreasing ambient relative humidity, although a controlled study of this parameter would be required to explicitly define its effects.     

Constant temperature monitoring: a study of temperature patterns in the postanesthesia care unit

Our previous research has demonstrated that with the more aciduric oral bacteria, an acid shock to sub-lethal pH values results in the induction of an acid tolerance response that protects the cells at extremely low pH (pH 3.0-4.0) that kills unadapted control cells maintained at pH 7.5 (Oral Microbiol Immunol 1997: 12: 266-273). In this study, we were interested in comparing the protein profiles of acid-shocked and control cells of nine organisms from three acid-ogenic genera that could be categorized as strong, weak and non-acid responders in an attempt to identify proteins that could be classified as acid-regulated proteins and which may be important in the process of survival at very low pH. For this, log-phase cultures were rapidly acidified from pH 7.5 to 5.5 in the presence of [14C]-amino acids for varying periods up to 2 h, the period previously shown to be required for maximum induction of the acid response. The cells were extracted for total protein and subjected to one-dimensional sodium dodecyl sulfate-polyacrylamide chromatography with comparable control and acid-shocked protein profiles compared by scanning and computer analysis. Of particular interest were the proteins in the acid-shocked cells that showed enhanced labeling (i.e., synthesis) over the control cells, since these were considered acid-regulated proteins of importance in pH homeostasis. Streptococcus mutans LT11 generated the most rapid and complex pattern: a total of 36 acid-regulated proteins showing enhanced synthesis, with 25 appearing within the first 30 min of acid shock. The enhanced synthesis was transient with all proteins, with the exception of two with molecular weights of 50/49 and 33/32 kDa. Within the acid-regulated proteins were proteins having molecular weights comparable to the heat shock proteins and the various subunits of the membrane H+/ATPase. By comparison, the strong responder, Lactobacillus casei 151, showed the enhanced formation of only nine proteins within the first 30 min of the acid shock, with a total of 11 acid-regulated proteins formed during the 2-h adaptation period with enhanced synthesis transient for seven of these proteins. Streptococcus salivarius AT2 and Streptococcus gordonii TH12 had the formation of 6 and 8 proteins enhanced, while the weakly responding organisms, Streptococcus sanguis ATCC 10,556 and Streptococcus oralis ATCC 10,557, exhibited 8 and 6 such proteins, respectively. Even non-responding strains unable to survive at very low pH, such as Streptococcus sobrinus CH125/43, Streptococcus mitis ATCC 12,261 and Actinomyces naeslundii 301-13 showed the initial formation of 3-9 acid-regulated proteins, but protein synthesis was not sustained over the entire adaptation period. Clearly, the survival of oral bacteria at very low pH is related, not to the total number of the acid-regulated proteins induced per se but to the formation of key proteins that function to augment normal pH homeostasis.     

Deep cryogenic noise and electrical characterization of thecomplementary heterojunction field-effect transistor (CHFET)

This paper discusses a characterization at 4 K of the complementary heterojunction field-effect transistor (CHFET), to examine its suitability for deep cryogenic (<10 K) readout electronics applications. The CHFET is a GaAs-based transistor analogous in structure and operation to silicon CMOS. The electrical properties including the gate leakage current, subthreshold transconductance, and input-referred noise voltage were examined. It is shown that both n-channel and p-channel CHFET's are fully functional at 4 K, with no anomalous behavior, such as hysteresis or kinks. Complementary circuit designs are possible, and a simple CHFET-based multiplexed op-amp is presented and characterized at 4 K. The noise and gate leakage current of the CHFET are presently several orders of magnitude too large for readout applications, however. The input-referred noise is on the order of 1 μV/√(Hz) at 100 Hz for a 50×50 μm n-channel CHFET. The gate current is strongly dependent on the doping at the gate edge, and is on the order of 10^-14 A for a 10×10 μm ² n-channel CHFET with light gate-edge region doping