Category-specific enhancement of retrieval due to field perspective

Two memory perspectives have been distinguished: A field perspective where events are re-experienced in the first person, and an observer perspective where events are witnessed in the third person. Two experiments examined the influence of memory perspective on objective memory performance. In both experiments participants were presented with a series of verbal passages, each of which contained several different categories of information. For four of these categories (pertaining to affective reactions, physical sensations, psychological states, and associated ideas), recall was significantly higher when a field perspective was adopted than when an observer perspective was adopted, but for the five other categories (pertaining to physical actions, personal appearance, fine details, spatial relations, and peripheral details) there was no significant effect of perspective upon recall. The study is examined in the context of mental models and imagined episodic events

Poly silicon Contacted Emitter Bipolar Transistors: Fabrication Development

Traditionally bipolar transistors have monocrystalline emitters that are contacted by metal, usually aluminum. However, the current gain of conventional BJTs does not reach the highest values predicted by theory. This is due to the high doping effects which limit the emitter injection efficiency and/or high minority carrier recombination in the emitter Silicon bipolar technology has reached a state of advancement that the device characteristics and circuit performance are not only determined by the doping profiles but also by the emitter contact technology. In the last few years polycrystalline silicon has been used increasingly as the emitter contacting material. Polysilicon contacted devices have made it possible to achieve much greater emitter injection efficiencies, and possess the ability to greatly increase the current gain a t a given base impurity doping concentration. The performance of bipolar transistors has been considerably enhanced by the use of polysilicon as both a diffusion source and a contact for shallow emitter; devices. Improvements in packing density and switching speed have resulted from the self-aligned structure [2], which has reduced device parasitics, and the lower base current as compared to metal contacted shallow emitter devices. With a lower base current, the base doping level can be increased to reduce the intrinsic base resistance without sacrificing the current gain of the original device [3]. Several researchers have investigated enhanced gains in polysilicon emitter devices, suggested various models to explain their operations, fabricated devices, and obtained good results. However, none of them reported reproducible devices or data from the devices they made in terms of beta variability. The objective of this thesis lies not only in demonstrating that polysilicon emitter transistors have higher current gains than the conventional shallow emitter aluminum contacted devices but also in showing that the polysilicon emitter devices can be manufactured in a consistently reproducible manner. In fabricating n+pn transistors, either arsenic or phosphorus can be used as the dopant for the emitter region in monocrystalline silicon and for the polysilicon contact. Arsenic was chosen for our process due to the superior shallow doping profile that could be obtained. The shallow emitter was formed in the monocrystalline substrate before the polysilicon was deposited on that region to make a polysilicon contact, which is also doped with arsenic. The emitter is then composed of both a monocrystalline and polycrystalline region. The base currents of these shallow emitter devices are controlled by the material, which is polysilicon contacting the emitter, and the interface between the contacting material and the emitter region under the contact. There are three major different theories proposed to explain the improvement in emitter injection efficiency and hence beta of polysilicon contacted transistors. These theories and a model of the conduction mechanisms in polysilicon are discussed in chapter II. Polysilicon emitter contacted bipolar transistors were fabricated by the introduction of two extra masking steps into an existing four mask conventional shallow emitter bipolar process excluding isolation. The basic process and process development are discussed in chapter III. Before devices could be fabricated it was necessary to predict the device performance from the proposed fabrication sequence. The process simulators SUPREM II and SUPREM III have been useful in the design and optimization of integrated circuit technologies. SUPREM II, however, does not model structures that utilize polysilicon. SUPREM III, on the other hand, is an improved process simulator that can model up to five material layers, including polysilicon, and was available in the Engineering Computer Network at Purdue University. Using SUPREM III, the proposed bipolar junction transistor (BJT) structure was modeled and optimized with the existing implants, oxidations, and design rules. The program has predicted that an acceptable profile can be obtained by varying those parameters. This is also included in chapter III. Other processes that were performed for the purpose of developing the polysilicon emitter contacted devices are described. Their characteristics are explained and compared with the test results. Basic electrical measurements were made on both conventional devices and polysilicon emitter contacted devices that were fabricated in the same wafer and conditions except for the polysilicon contact part. Mainly enhanced current gain in the polysilicon emitter contacted devices, the deviation in the current gain values, and resistance values for the contacts over numerous devices are used as the evaluating criteria. The measurement method and results of measurements are discussed in chapter IV. Conclusions and recommendations are made in chapter V

Polysilicon Emitter Fabrication and Modeling

The research proposed for 1986 was to develop the technology for fabricating, measuring, and computer modeling the polysilicon emitter bipolar transistor. Fabrication consisted of producing three types of bipolar transistors; a regular bipolar device to act as the control, a polysilicon contacted emitter transistor, and a polysilicon emitter directly on the base region with a very thin oxide at the interface. The proposed fabrication research concentrated on investigating a new method of fabricating polysilicon contacted emitter bipolar transistors. The new fabrication technique uses plasma etching of the emitter location on the base region and, without breaking vacuum, depositing amorphous silicon (a-Si) on the cleaned interface. The a-Si was then to be doped by ion-implantation and heated to 600-700 C ° to produce the polysilicon emitter contact. The controlled interface and the fine grained polysilicon should lead to more uniform and predictable betas for the polycontacted transistors. Both polysilicon contacted emitters and polysilicon emitters were to be investigated over a range of base doping. We proposed the modeling work in two directions: l) 2-D simulation so that small geometry transistors can be accurately modeled and 2) simulation of polysilicon contacted emitter transistors. Measurements on the devices described above will be used to develop a polysilicon model. The objective of this part of the project is to develop a numerical device simulator with predictive capability, i.e. one that can be used with confidence in place of actual device fabrication. The numerical device models will be provided to Delco and should find many applications in development and manufacturing. The fabrication highlights of the 1986 work were the design and fabrication of preliminary bipolar transistors and polysilicon emitters, the design and layout of the test wafer, and the fabrication and measurements on shallow arsenic doped emitter devices. There were 22 sets of fabrication runs made beyond the preliminary devices. The last results of these runs show that the shallow Arsenic emitter (0.05 /i) and the very narrow base width (0.1 y) control devices with metal emitter contact, have an average peak beta of about 75. Poly contacted emitter devices fabricated at the same time on the same wafer show a beta enhancement to 232, a factor of about 2.7 to 3.0 in the average peak beta. The polysilicon was deposited in a standard way in a LPCVD tube. We are presently fabricating polysilicon devices for studying the effects of the methods used in treating the surfaces before the poly is deposited and the way the poly is formed (amorphous PELPCYD)

Room temperature reversible colossal volto-magnetic effect in all-oxide metallicmagnet/topotactic-phase-transition material heterostructures

Multiferroic materials have undergone extensive research in the past two decades in an effort to produce a sizable room-temperature magneto-electric (ME) effect in either exclusive or composite materials for use in a variety of electronic or spintronic devices. These studies have looked into the ME effect by switching the electric polarization by the magnetic field or switching the magnetism by the electric field. Here, an innovative way is developed to knot the functional properties based on the tremendous modulation of electronics and magnetization by the electric field of the topotactic phase transitions (TPT) in heterostructures composed of metallic-magnet/TPT-material. It is divulged that application of a nominal potential difference of 2-3 Volts induces gigantic changes in magnetization by 100-250% leading to colossal Voltomagnetic effect, which would be tremendously beneficial for low-power consumption applications in spintronics. Switching electronics and magnetism by inducing TPT through applying an electric field requires much less energy, making such TPT-based systems promising for energy-efficient memory and logic applications as well as opening a plethora of tremendous opportunities for applications in different domains

Reactive Molecular Dynamics study on the first steps of DNA-damage by free hydroxyl radicals

We employ a large scale molecular simulation based on bond-order ReaxFF to simulate the chemical reaction and study the damage to a large fragment of DNA-molecule in the solution by ionizing radiation. We illustrate that the randomly distributed clusters of diatomic OH-radicals that are primary products of megavoltage ionizing radiation in water-based systems are the main source of hydrogen-abstraction as well as formation of carbonyl- and hydroxyl-groups in the sugar-moiety that create holes in the sugar-rings. These holes grow up slowly between DNA-bases and DNA-backbone and the damage collectively propagate to DNA single and double strand break.Comment: 6 pages and 8 figures. movies and simulations are available at: http://qmsimulator.wordpress.com

Sonic Hedgehog Is a Chemoattractant for Midbrain Dopaminergic Axons

Midbrain dopaminergic axons project from the substantia nigra (SN) and the ventral tegmental area (VTA) to rostral target tissues, including the striatum, pallidum, and hypothalamus. The axons from the medially located VTA project primarily to more medial target tissues in the forebrain, whereas the more lateral SN axons project to lateral targets including the dorsolateral striatum. This structural diversity underlies the distinct functions of these pathways. Although a number of guidance cues have been implicated in the formation of the distinct axonal projections of the SN and VTA, the molecular basis of their diversity remains unclear. Here we investigate the molecular basis of structural diversity in mDN axonal projections. We find that Sonic Hedgehog (Shh) is expressed at a choice point in the course of the rostral dopaminergic projections. Furthermore, in midbrain explants, dopaminergic projections are attracted to a Shh source. Finally, in mice in which Shh signaling is inactivated during late neuronal development, the most medial dopaminergic projections are deficient

X/Ka Celestial Frame Improvements: Vision to Reality

In order to extend the International Celestial Reference Frame from its S/X-band (2.3/8.4 GHz) basis to a complementary frame at X/Ka-band (8.4/32 GHz), we began in mid-2005 an ongoing series of X/Ka observations using NASA s Deep Space Network (DSN) radio telescopes. Over the course of 47 sessions, we have detected 351 extra-galactic radio sources covering the full 24 hours of right ascension and declinations down to -45 degrees. Angular source position accuracy is at the part-per-billion level. We developed an error budget which shows that the main errors arise from limited sensitivity, mismodeling of the troposphere, uncalibrated instrumental effects, and the lack of a southern baseline. Recent work has improved sensitivity by improving pointing calibrations and by increasing the data rate four-fold. Troposphere calibration has been demonstrated at the mm-level. Construction of instrumental phase calibrators and new digital baseband filtering electronics began in recent months. We will discuss the expected effect of these improvements on the X/Ka frame

Computational studies for reduced graphene oxide in hydrogen-rich environment

We employ molecular dynamic simulations to study the reduction process of graphene-oxide (GO) in a chemically active environment enriched with hydrogen. We examine the concentration and pressure of hydrogen gas as a function of temperature in which abstraction of oxygen is possible with minimum damage to C-sp$^2$ bonds hence preserving the integrity of the graphene sheet. Through these studies we find chemical pathways that demonstrate beneficiary mechanisms for the quality of graphene including formation of water as well as suppression of carbonyl pair holes in favor of hydroxyl and epoxy formation facilitated by hydrogen gas in the environment.Comment: 9 pages and 9 figures. Animations and movies are available at: http://qmsimulatorgojpc.wordpress.com