Efficient photoconductive terahertz detector with all-dielectric optical metasurface

NASA Astrophysics Data System (ADS)

Mitrofanov, Oleg; Siday, Thomas; Thompson, Robert J.; Luk, Ting Shan; Brener, Igal; Reno, John L.

2018-05-01

We designed an optically thin photoconductive channel as an all-dielectric metasurface comprising an array of low-temperature grown GaAs nanobeams and a sub-surface distributed Bragg reflector. The metasurface exhibited enhanced optical absorption, and it was integrated into a photoconductive THz detector, which showed high efficiency and sensitivity as a result. The detector produced photocurrents over one order of magnitude higher compared to a similar detector with an unstructured surface with only 0.5 mW of optical excitation while exhibiting high dark resistance required for low-noise detection in THz time-domain spectroscopy and imaging. At that level of optical excitation, the metasurface detector showed a high signal to noise ratio of 106. The detector showed saturation above that level.

Photoconductive switch package

DOEpatents

Ca[rasp, George J

2013-10-22

A photoconductive switch is formed of a substrate that has a central portion of SiC or other photoconductive material and an outer portion of cvd-diamond or other suitable material surrounding the central portion. Conducting electrodes are formed on opposed sides of the substrate, with the electrodes extending beyond the central portion and the edges of the electrodes lying over the outer portion. Thus any high electric fields produced at the edges of the electrodes lie outside of and do not affect the central portion, which is the active switching element. Light is transmitted through the outer portion to the central portion to actuate the switch.

Photoconductive switch package

DOE Office of Scientific and Technical Information (OSTI.GOV)

Caporaso, George J.

2015-10-27

A photoconductive switch is formed of a substrate that has a central portion of SiC or other photoconductive material and an outer portion of cvd-diamond or other suitable material surrounding the central portion. Conducting electrodes are formed on opposed sides of the substrate, with the electrodes extending beyond the central portion and the edges of the electrodes lying over the outer portion. Thus any high electric fields produced at the edges of the electrodes lie outside of and do not affect the central portion, which is the active switching element. Light is transmitted through the outer portion to the centralmore » portion to actuate the switch.« less

Stacked color image sensor using wavelength-selective organic photoconductive films with zinc-oxide thin film transistors as a signal readout circuit

NASA Astrophysics Data System (ADS)

Seo, Hokuto; Aihara, Satoshi; Namba, Masakazu; Watabe, Toshihisa; Ohtake, Hiroshi; Kubota, Misao; Egami, Norifumi; Hiramatsu, Takahiro; Matsuda, Tokiyoshi; Furuta, Mamoru; Nitta, Hiroshi; Hirao, Takashi

2010-01-01

Our group has been developing a new type of image sensor overlaid with three organic photoconductive films, which are individually sensitive to only one of the primary color components (blue (B), green (G), or red (R) light), with the aim of developing a compact, high resolution color camera without any color separation optical systems. In this paper, we firstly revealed the unique characteristics of organic photoconductive films. Only choosing organic materials can tune the photoconductive properties of the film, especially excellent wavelength selectivities which are good enough to divide the incident light into three primary colors. Color separation with vertically stacked organic films was also shown. In addition, the high-resolution of organic photoconductive films sufficient for high-definition television (HDTV) was confirmed in a shooting experiment using a camera tube. Secondly, as a step toward our goal, we fabricated a stacked organic image sensor with G- and R-sensitive organic photoconductive films, each of which had a zinc oxide (ZnO) thin film transistor (TFT) readout circuit, and demonstrated image pickup at a TV frame rate. A color image with a resolution corresponding to the pixel number of the ZnO TFT readout circuit was obtained from the stacked image sensor. These results show the potential for the development of high-resolution prism-less color cameras with stacked organic photoconductive films.

Photoconductivity, pH Sensitivity, Noise, and Channel Length Effects in Si Nanowire FET Sensors

NASA Astrophysics Data System (ADS)

Gasparyan, Ferdinand; Zadorozhnyi, Ihor; Khondkaryan, Hrant; Arakelyan, Armen; Vitusevich, Svetlana

2018-03-01

Silicon nanowire (NW) field-effect transistor (FET) sensors of various lengths were fabricated. Transport properties of Si NW FET sensors were investigated involving noise spectroscopy and current-voltage (I-V) characterization. The static I-V dependencies demonstrate the high quality of fabricated silicon FETs without leakage current. Transport and noise properties of NW FET structures were investigated under different light illumination conditions, as well as in sensor configuration in an aqueous solution with different pH values. Furthermore, we studied channel length effects on the photoconductivity, noise, and pH sensitivity. The magnitude of the channel current is approximately inversely proportional to the length of the current channel, and the pH sensitivity increases with the increase of channel length approaching the Nernst limit value of 59.5 mV/pH. We demonstrate that dominant 1/f-noise can be screened by the generation-recombination plateau at certain pH of the solution or external optical excitation. The characteristic frequency of the generation-recombination noise component decreases with increasing of illumination power. Moreover, it is shown that the measured value of the slope of 1/f-noise spectral density dependence on the current channel length is 2.7 which is close to the theoretically predicted value of 3.

Extreme sensitivity of graphene photoconductivity to environmental gases

PubMed Central

Docherty, Callum J.; Lin, Cheng-Te; Joyce, Hannah J.; Nicholas, Robin J.; Herz, Laura M.; Li, Lain-Jong; Johnston, Michael B.

2012-01-01

Graphene is a single layer of covalently bonded carbon atoms, which was discovered only 8 years ago and yet has already attracted intense research and commercial interest. Initial research focused on its remarkable electronic properties, such as the observation of massless Dirac fermions and the half-integer quantum Hall effect. Now graphene is finding application in touch-screen displays, as channels in high-frequency transistors and in graphene-based integrated circuits. The potential for using the unique properties of graphene in terahertz-frequency electronics is particularly exciting; however, initial experiments probing the terahertz-frequency response of graphene are only just emerging. Here we show that the photoconductivity of graphene at terahertz frequencies is dramatically altered by the adsorption of atmospheric gases, such as nitrogen and oxygen. Furthermore, we observe the signature of terahertz stimulated emission from gas-adsorbed graphene. Our findings highlight the importance of environmental conditions on the design and fabrication of high-speed, graphene-based devices. PMID:23187628

Extreme sensitivity of graphene photoconductivity to environmental gases.

PubMed

Docherty, Callum J; Lin, Cheng-Te; Joyce, Hannah J; Nicholas, Robin J; Herz, Laura M; Li, Lain-Jong; Johnston, Michael B

2012-01-01

Graphene is a single layer of covalently bonded carbon atoms, which was discovered only 8 years ago and yet has already attracted intense research and commercial interest. Initial research focused on its remarkable electronic properties, such as the observation of massless Dirac fermions and the half-integer quantum Hall effect. Now graphene is finding application in touch-screen displays, as channels in high-frequency transistors and in graphene-based integrated circuits. The potential for using the unique properties of graphene in terahertz-frequency electronics is particularly exciting; however, initial experiments probing the terahertz-frequency response of graphene are only just emerging. Here we show that the photoconductivity of graphene at terahertz frequencies is dramatically altered by the adsorption of atmospheric gases, such as nitrogen and oxygen. Furthermore, we observe the signature of terahertz stimulated emission from gas-adsorbed graphene. Our findings highlight the importance of environmental conditions on the design and fabrication of high-speed, graphene-based devices.

Effects of oxygen vacancy on the photoconductivity in BaSnO3

NASA Astrophysics Data System (ADS)

Park, Jisung; Char, Kookrin; Institute of Applied Physics, Department of Physics; Astronomy, Seoul National University Team

We have found the photoconductive behavior of BaSnO3, especially their magnitude and time dependence, is very sensitive to the oxygen vacancy concentration. We made epitaxial BaSnO3 film with BaHfO3 buffer layer by pulsed laser deposition. As we had reported before, MgO substrate with its large band gap size about 7.8 eV was used to exclude any photoconductance from the substrate. BaHfO3 layer was used to reduce the threading dislocation density in BaSnO3 film. To control the oxygen vacancy concentration in the BaSnO3 film, we annealed the sample in Ar or O2 atmosphere with varying annealing conditions. After each annealing process, photoconductivity of BaSnO3 was measured during illumination of UV light. The result showed that the magnitude of photoconductivity of BaSnO3 increased after annealing at higher temperature in Ar atmosphere, while the changes in the dark current remains minimal. The result can be explained by a hole trap mechanism. Higher Fermi level due to the increased oxygen vacancy concentration can cause occupation of deep acceptor levels in dislocations of the BaSnO3 film. These occupied deep acceptor levels in turn trap photo-generated holes so that the recombination of electron-hole pair is deterred. Samsung Science and Technology Foundation.

Controlling Photoconductivity in PBI Films by Supramolecular Assembly

PubMed Central

Archibald, Lewis J.; Nolan, Michael C.; Schweins, Ralf; Zwijnenburg, Martijn A.; Sproules, Stephen

2018-01-01

Abstract Perylene bisimides (PBIs) self‐assemble in solution. The solubility of the PBIs is commonly changed through the choice of substituents at the imide positions. It is generally assumed this substitution does not affect the electronic properties of the PBI, and that the properties of the self‐assembled aggregate are essentially that of the isolated molecule. However, substituents do affect the self‐assembly, resulting in potentially different packing in the formed aggregates. Here, we show that the photoconductivity of films formed from a library of substituted PBIs varies strongly with the substituent and demonstrate that this is due to the different ways in which they pack. Our results open the possibility for tuning the optoelectronic properties of self‐assembled PBIs by controlling the aggregate structure through careful choice of substituent, as demonstrated by us here optimising the photoconductivity of PBI films in this way. PMID:29405458

A 128×96 Pixel Stack-Type Color Image Sensor: Stack of Individual Blue-, Green-, and Red-Sensitive Organic Photoconductive Films Integrated with a ZnO Thin Film Transistor Readout Circuit

NASA Astrophysics Data System (ADS)

Seo, Hokuto; Aihara, Satoshi; Watabe, Toshihisa; Ohtake, Hiroshi; Sakai, Toshikatsu; Kubota, Misao; Egami, Norifumi; Hiramatsu, Takahiro; Matsuda, Tokiyoshi; Furuta, Mamoru; Hirao, Takashi

2011-02-01

A color image was produced by a vertically stacked image sensor with blue (B)-, green (G)-, and red (R)-sensitive organic photoconductive films, each having a thin-film transistor (TFT) array that uses a zinc oxide (ZnO) channel to read out the signal generated in each organic film. The number of the pixels of the fabricated image sensor is 128×96 for each color, and the pixel size is 100×100 µm2. The current on/off ratio of the ZnO TFT is over 106, and the B-, G-, and R-sensitive organic photoconductive films show excellent wavelength selectivity. The stacked image sensor can produce a color image at 10 frames per second with a resolution corresponding to the pixel number. This result clearly shows that color separation is achieved without using any conventional color separation optical system such as a color filter array or a prism.

Controlling Photoconductivity in PBI Films by Supramolecular Assembly.

PubMed

Draper, Emily R; Archibald, Lewis J; Nolan, Michael C; Schweins, Ralf; Zwijnenburg, Martijn A; Sproules, Stephen; Adams, Dave J

2018-03-15

Perylene bisimides (PBIs) self-assemble in solution. The solubility of the PBIs is commonly changed through the choice of substituents at the imide positions. It is generally assumed this substitution does not affect the electronic properties of the PBI, and that the properties of the self-assembled aggregate are essentially that of the isolated molecule. However, substituents do affect the self-assembly, resulting in potentially different packing in the formed aggregates. Here, we show that the photoconductivity of films formed from a library of substituted PBIs varies strongly with the substituent and demonstrate that this is due to the different ways in which they pack. Our results open the possibility for tuning the optoelectronic properties of self-assembled PBIs by controlling the aggregate structure through careful choice of substituent, as demonstrated by us here optimising the photoconductivity of PBI films in this way. © 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

High Current, Multi-Filament Photoconductive Semiconductor Switching

DTIC Science & Technology

2011-06-01

linear PCSS triggered with a 100 fs laser pulse . Figure 1. A generic photoconductive semiconductor switch rapidly discharges a charged capacitor...switching is the most critical challenge remaining for photoconductive semiconductor switch (PCSS) applications in Pulsed Power. Many authors have...isolation and control, pulsed or DC charging, and long device lifetime, provided the current per filament is limited to 20-30A for short pulse (10

Bias-switchable negative and positive photoconductivity in 2D FePS3 ultraviolet photodetectors.

PubMed

Gao, Yi; Lei, Shuijin; Kang, Tingting; Fei, Linfeng; Mak, Chee-Leung; Yuan, Jian; Zhang, Mingguang; Li, Shaojuan; Bao, Qiaoliang; Zeng, Zhongming; Wang, Zhao; Gu, Haoshuang; Zhang, Kai

2018-06-15

Metal-phosphorus-trichalcogenides (MPTs), represented by NiPS 3 , FePS 3 , etc, are newly developed 2D wide-bandgap semiconductors and have been proposed as excellent candidates for ultraviolet (UV) optoelectronics. In spite of having superior advantages for solar-blind UV photodetectors, including those free of surface trap states, being highly compatible with versatile integrations as well as having an appropriate band gap, to date relevant study is rare. In this work, the photoresponse characteristic of UV detectors based on few-layer FePS 3 has been comprehensively investigated. The responsivity of the photodetector, which is observed to be determined by bias gate voltage, may achieve as high as 171.6 mAW -1 under the illumination of 254 nm weak light, which is comparable to most commercial UV detectors. Notably, both negative and positive photoconductivities exist in the FePS 3 photodetectors and can be controllably switched with bias voltage. The eminent and novel photoresponse property paves the way for the further development and practical use of 2D MPTs in high-performance UV photodetections.

Bias-switchable negative and positive photoconductivity in 2D FePS3 ultraviolet photodetectors

NASA Astrophysics Data System (ADS)

Gao, Yi; Lei, Shuijin; Kang, Tingting; Fei, Linfeng; Mak, Chee-Leung; Yuan, Jian; Zhang, Mingguang; Li, Shaojuan; Bao, Qiaoliang; Zeng, Zhongming; Wang, Zhao; Gu, Haoshuang; Zhang, Kai

2018-06-01

Metal-phosphorus-trichalcogenides (MPTs), represented by NiPS3, FePS3, etc, are newly developed 2D wide-bandgap semiconductors and have been proposed as excellent candidates for ultraviolet (UV) optoelectronics. In spite of having superior advantages for solar-blind UV photodetectors, including those free of surface trap states, being highly compatible with versatile integrations as well as having an appropriate band gap, to date relevant study is rare. In this work, the photoresponse characteristic of UV detectors based on few-layer FePS3 has been comprehensively investigated. The responsivity of the photodetector, which is observed to be determined by bias gate voltage, may achieve as high as 171.6 mAW‑1 under the illumination of 254 nm weak light, which is comparable to most commercial UV detectors. Notably, both negative and positive photoconductivities exist in the FePS3 photodetectors and can be controllably switched with bias voltage. The eminent and novel photoresponse property paves the way for the further development and practical use of 2D MPTs in high-performance UV photodetections.

Impurity-induced photoconductivity of narrow-gap Cadmium–Mercury–Telluride structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozlov, D. V., E-mail: dvkoz@impras.ru; Rumyantsev, V. V.; Morozov, S. V.

2015-12-15

The photoconductivity (PC) spectra of CdHgTe (MCT) solid solutions with a Cd fraction of 17 and 19% are measured. A simple model for calculating the states of doubly charged acceptors in MCT solid solutions, which makes it possible to describe satisfactorily the observed photoconductivity spectra, is proposed. The found lines in the photoconductivity spectra of narrow-gap MCT structures are associated with transitions between the states of both charged and neutral acceptor centers.

Two-step photoconductivity in LiY x Lu1 - x F4:Ce,Yb crystals

NASA Astrophysics Data System (ADS)

Nurtdinova, L. A.; Korableva, S. L.; Leontiev, A. V.

2016-10-01

Photoconductivity of LiY x Lu1- x F4:Ce,Yb ( x = 0-1) crystals is measured under one- and two-step excitation. It is established that the photoconductivity is due to intra-center transitions from excited states of Ce3+ ions. The position of the ground 4 f-state of Ce3+ ion relative to the bottom of the conduction band is determined. The choice of pumping conditions to obtain the lasing on the 5 d-4 f transitions of trivalent cerium in these active media is substantiated.

Photoconductivity in BiFeO3 thin films

NASA Astrophysics Data System (ADS)

Basu, S. R.; Martin, L. W.; Chu, Y. H.; Gajek, M.; Ramesh, R.; Rai, R. C.; Xu, X.; Musfeldt, J. L.

2008-03-01

The optical properties of epitaxial BiFeO3 thin films have been characterized in the visible range. Variable temperature spectra show an absorption onset near 2.17eV, a direct gap (2.667±0.005eV at 300K), and charge transfer excitations at higher energy. Additionally, we report photoconductivity in BiFeO3 films under illumination from a 100mW /cm2 white light source. A direct correlation is observed between the magnitude of the photoconductivity and postgrowth cooling pressure. Dark conductivities increased by an order of magnitude when comparing films cooled in 760 and 0.1Torr. Large increases in photoconductivity are observed in light.

Solar-blind-ultraviolet extraordinary transmission for ultrasensitive photoconductive detector based on plasmonic subwavelength interdigital electrodes

NASA Astrophysics Data System (ADS)

Peng, Nan; Huang, Feng; Chu, Sheng; Chen, Hao

2016-12-01

The solar-blind-ultraviolet (SBUV) detection industry demands high sensitivity as well as easy processability for its semiconductor devices. Photoconductive detectors have the simplest structure. However, the electrodes covering the illuminated side cause optical shielding losses, resulting in a relatively low sensitivity of such devices. Through finite-difference time-domain (FDTD) simulation, we demonstrated that surface-plasmon-based enhanced SBUV transmission is achievable for Al interdigital electrodes (IDEs) with a period  ⩽200 nm and an interval  ⩾140 nm. Under this parameter setting, a larger interval and smaller period leads to further enhancement of SBUV transmission. Particularly, we have found that different possible dielectric environments, such as Ni insertion, Al oxidization, and MgF2 anti-oxidation, would not exert fatal effects on this enhancement. Besides, such an enhancement is maintained under the angle of incidence within 10°, which is large enough for practical SBUV detection. Our research reveals the feasibility of high sensitivity by a simple photoconductive device, showing profound significance for an applicable SBUV detector.

Wide Bandgap Extrinsic Photoconductive Switches

NASA Astrophysics Data System (ADS)

Sullivan, James Stephen

Wide Bandgap Extrinsic Photoconductive Switches Semi-insulating Gallium Nitride, 4H and 6H Silicon Carbide are attractive materials for compact, high voltage, extrinsic, photoconductive switches due to their wide bandgap, high dark resistance, high critical electric field strength and high electron saturation velocity. These wide bandgap semiconductors are made semi-insulating by the addition of vanadium (4H and 6H-SiC) and iron (2H-GaN) impurities that form deep acceptors. These deep acceptors trap electrons donated from shallow donor impurities. The electrons can be optically excited from these deep acceptor levels into the conduction band to transition the wide bandgap semiconductor materials from a semi-insulating to a conducting state. Extrinsic photoconductive switches with opposing electrodes have been constructed using vanadium compensated 6H-SiC and iron compensated 2H-GaN. These extrinsic photoconductive switches were tested at high voltage and high power to determine if they could be successfully used as the closing switch in compact medical accelerators. The successful development of a vanadium compensated, 6H-SiC extrinsic photoconductive switch for use as a closing switch for compact accelerator applications was realized by improvements made to the vanadium, nitrogen and boron impurity densities. The changes made to the impurity densities were based on the physical intuition outlined and simple rate equation models. The final 6H-SiC impurity 'recipe' calls for vanadium, nitrogen and boron densities of 2.5 e17 cm-3, 1.25e17 cm-3 and ≤ 1e16 cm-3, respectively. This recipe was originally developed to maximize the quantum efficiency of the vanadium compensated 6H-SiC, while maintaining a thermally stable semi-insulating material. The rate equation models indicate that, besides increasing the quantum efficiency, the impurity recipe should be expected to also increase the carrier recombination time. Three generations of 6H-SiC materials were tested. The

Design, fabrication, and experimental characterization of plasmonic photoconductive terahertz emitters.

PubMed

Berry, Christopher; Hashemi, Mohammad Reza; Unlu, Mehmet; Jarrahi, Mona

2013-07-08

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on photoconduction, which has been one of the most commonly used techniques for terahertz generation (1-8). Terahertz generation in a photoconductive emitter is achieved by pumping an ultrafast photoconductor with a pulsed or heterodyned laser illumination. The induced photocurrent, which follows the envelope of the pump laser, is routed to a terahertz radiating antenna connected to the photoconductor contact electrodes to generate terahertz radiation. Although the quantum efficiency of a photoconductive emitter can theoretically reach 100%, the relatively long transport path lengths of photo-generated carriers to the contact electrodes of conventional photoconductors have severely limited their quantum efficiency. Additionally, the carrier screening effect and thermal breakdown strictly limit the maximum output power of conventional photoconductive terahertz sources. To address the quantum efficiency limitations of conventional photoconductive terahertz emitters, we have developed a new photoconductive emitter concept which incorporates a plasmonic contact electrode configuration to offer high quantum-efficiency and ultrafast operation simultaneously. By using nano-scale plasmonic contact electrodes, we significantly reduce the average photo-generated carrier transport path to photoconductor contact electrodes compared to conventional photoconductors (9). Our method also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. By incorporating plasmonic contact electrodes, we demonstrate enhancing the optical-to-terahertz power conversion efficiency of a conventional photoconductive terahertz emitter by a factor of 50 (10).

Enhanced photoconductivity by melt quenching method for amorphous organic photorefractive materials

NASA Astrophysics Data System (ADS)

Tsujimura, S.; Fujihara, T.; Sassa, T.; Kinashi, K.; Sakai, W.; Ishibashi, K.; Tsutsumi, N.

2014-10-01

For many optical semiconductor fields of study, the high photoconductivity of amorphous organic semiconductors has strongly been desired, because they make the manufacture of high-performance devices easy when controlling charge carrier transport and trapping is otherwise difficult. This study focuses on the correlation between photoconductivity and bulk state in amorphous organic photorefractive materials to probe the nature of the performance of photoconductivity and to enhance the response time and diffraction efficiency of photorefractivity. The general cooling processes of the quenching method achieved enhanced photoconductivity and a decreased filling rate for shallow traps. Therefore, sample processing, which was quenching in the present case, for photorefractive composites significantly relates to enhanced photorefractivity.

Photoconductive circuit element reflectometer

DOEpatents

Rauscher, Christen

1990-01-01

A photoconductive reflectometer for characterizing semiconductor devices at millimeter wavelength frequencies where a first photoconductive circuit element (PCE) is biased by a direct current voltage source and produces short electrical pulses when excited into conductance by short first laser light pulses. The electrical pulses are electronically conditioned to improve the frequency related amplitude characteristics of the pulses which thereafter propagate along a transmission line to a device under test. Second PCEs are connected along the transmission line to sample the signals on the transmission line when excited into conductance by short second laser light pulses, spaced apart in time a variable period from the first laser light pulses. Electronic filters connected to each of the second PCEs act as low-pass filters and remove parasitic interference from the sampled signals and output the sampled signals in the form of slowed-motion images of the signals on the transmission line.

Photoconductive circuit element reflectometer

DOEpatents

Rauscher, C.

1987-12-07

A photoconductive reflectometer for characterizing semiconductor devices at millimeter wavelength frequencies where a first photoconductive circuit element (PCE) is biased by a direct current voltage source and produces short electrical pulses when excited into conductance by short first laser light pulses. The electrical pulses are electronically conditioned to improve the frequency related amplitude characteristics of the pulses which thereafter propagate along a transmission line to a device under test. Second PCEs are connected along the transmission line to sample the signals on the transmission line when excited into conductance by short second laser light pulses, spaced apart in time a determinable period from the first laser light pulses. Electronic filters connected to each of the second PCEs act as low-pass filters and remove parasitic interference from the sampled signals and output the sampled signals in the form of slowed-motion images of the signals on the transmission line. 4 figs.

Wide Bandgap Extrinsic Photoconductive Switches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sullivan, James S.

2012-01-20

Photoconductive semiconductor switches (PCSS) have been investigated since the late 1970s. Some devices have been developed that withstand tens of kilovolts and others that switch hundreds of amperes. However, no single device has been developed that can reliably withstand both high voltage and switch high current. Yet, photoconductive switches still hold the promise of reliable high voltage and high current operation with subnanosecond risetimes. Particularly since good quality, bulk, single crystal, wide bandgap semiconductor materials have recently become available. In this chapter we will review the basic operation of PCSS devices, status of PCSS devices and properties of the widemore » bandgap semiconductors 4H-SiC, 6H-SiC and 2H-GaN.« less

Negative Photoconductance in Heavily Doped Si Nanowire Field-Effect Transistors.

PubMed

Baek, Eunhye; Rim, Taiuk; Schütt, Julian; Baek, Chang-Ki; Kim, Kihyun; Baraban, Larysa; Cuniberti, Gianaurelio

2017-11-08

We report the first observation of negative photoconductance (NPC) in n- and p-doped Si nanowire field-effect transistors (FETs) and demonstrate the strong influence of doping concentrations on the nonconventional optical switching of the devices. Furthermore, we show that the NPC of Si nanowire FETs is dependent on the wavelength of visible light due to the phonon-assisted excitation to multiple conduction bands with different band gap energies that would be a distinct optoelectronic property of indirect band gap semiconductor. We attribute the main driving force of NPC in Si nanowire FETs to the photogenerated hot electrons trapping by dopants ions and interfacial states. Finally, comparing back- and top-gate modulation, we derive the mechanisms of the transition between negative and positive photoconductance regimes in nanowire devices. The transition is decided by the competition between the light-induced interfacial trapping and the recombination of mobile carriers, which is dependent on the light intensity and the doping concentration.

High frequency modulation circuits based on photoconductive wide bandgap switches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sampayan, Stephen

Methods, systems, and devices for high voltage and/or high frequency modulation. In one aspect, an optoelectronic modulation system includes an array of two or more photoconductive switch units each including a wide bandgap photoconductive material coupled between a first electrode and a second electrode, a light source optically coupled to the WBGP material of each photoconductive switch unit via a light path, in which the light path splits into multiple light paths to optically interface with each WBGP material, such that a time delay of emitted light exists along each subsequent split light path, and in which the WBGP materialmore » conducts an electrical signal when a light signal is transmitted to the WBGP material, and an output to transmit the electrical signal conducted by each photoconductive switch unit. The time delay of the photons emitted through the light path is substantially equivalent to the time delay of the electrical signal.« less

Failure mechanism of THz GaAs photoconductive antenna

NASA Astrophysics Data System (ADS)

Qadri, Syed B.; Wu, Dong H.; Graber, Benjamin D.; Mahadik, Nadeemullah A.; Garzarella, Anthony

2012-07-01

We investigated the failure mechanism of THz GaAs photoconductive antenna using high resolution x-ray diffraction topography. From these studies, it was found that grain boundaries are formed during the high frequency device operation. This results in the segregation of gold at the boundaries causing electromigration of the metal between the gold micro-strips. This disrupts the photocurrents from being produced by femtosecond laser thus preventing terahertz beam generation from the photoconductive antennae leading to device failure.

Negative terahertz photoconductivity in 2D layered materials.

PubMed

Lu, Junpeng; Liu, Hongwei; Sun, Jing

2017-11-17

The remarkable qualities of 2D layered materials such as wide spectral coverage, high strength and great flexibility mean that ultrathin 2D layered materials have the potential to meet the criteria of next-generation optoelectronic devices. Photoconductivity is one of the critical parameters of materials applied to optoelectronics. In contrast to traditional semiconductors, specific ultrathin 2D layers present anomalous negative photoconductivity. This opens a new avenue for designing novel optoelectronic devices. It is important to have a deep understanding of the fundamentals of this anomalous response, in order to design and optimize such devices. In this review, we provide an overview of the observation of negative photoconductivity in 2D layered materials including graphene, topological insulators and transitional metal dichalcogenides. We also summarize recent reports on investigations into the fundamental mechanism using ultrafast terahertz (THz) spectroscopies. Finally, we conclude the review by discussing the existing challenges and proposing the possible prospects of this direction of research.

Role of self-trapped holes in the photoconductive gain of β-gallium oxide Schottky diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Armstrong, Andrew M.; Crawford, Mary H.; Jayawardena, Asanka

Solar-blind photodetection and photoconductive gain > 50 corresponding to a responsivity > 8 A/W was observed for β-Ga 2O 3 Schottky photodiodes. We investigated the origin of photoconductive gain. Current-voltage characteristics of the diodes did not indicate avalanche breakdown, which excludes carrier multiplication by impact ionization as the source for gain. However, photocapacitance measurements indicated a mechanism for hole localization for above-band gap illumination, suggesting self-trapped hole formation. Comparison of photoconductivity and photocapacitance spectra indicated that self-trapped hole formation coincides with the strong photoconductive gain. We conclude that self-trapped hole formation near the Schottky diode lowers the effective Schottky barriermore » in reverse bias, producing photoconductive gain. Ascribing photoconductive gain to an inherent property like self-trapping of holes can explain the operation of a variety of β-Ga 2O 3 photodetectors.« less

Role of self-trapped holes in the photoconductive gain of β-gallium oxide Schottky diodes

DOE PAGES

Armstrong, Andrew M.; Crawford, Mary H.; Jayawardena, Asanka; ...

2016-03-10

Solar-blind photodetection and photoconductive gain > 50 corresponding to a responsivity > 8 A/W was observed for β-Ga 2O 3 Schottky photodiodes. We investigated the origin of photoconductive gain. Current-voltage characteristics of the diodes did not indicate avalanche breakdown, which excludes carrier multiplication by impact ionization as the source for gain. However, photocapacitance measurements indicated a mechanism for hole localization for above-band gap illumination, suggesting self-trapped hole formation. Comparison of photoconductivity and photocapacitance spectra indicated that self-trapped hole formation coincides with the strong photoconductive gain. We conclude that self-trapped hole formation near the Schottky diode lowers the effective Schottky barriermore » in reverse bias, producing photoconductive gain. Ascribing photoconductive gain to an inherent property like self-trapping of holes can explain the operation of a variety of β-Ga 2O 3 photodetectors.« less

Enhanced ultraviolet photoconductivity in porous GaN prepared by metal-assisted electroless etching

NASA Astrophysics Data System (ADS)

Guo, X. Y.; Williamson, T. L.; Bohn, P. W.

2006-10-01

The ultraviolet photoconductivity of porous GaN (PGaN) produced by Pt-assisted electroless etching has been investigated. The photoresponse of PGaN prepared from highly doped GaN ( n>1018 cm) shows enhanced ( 15×) magnitude and faster decay of persistent photoconductivity relative to bulk crystalline (CGaN), suggesting advantages for PGaN in photodetector applications. A space charge model for changes in photoconductivity is used to explain these observations. Heightened defect density in the etched material plays an important role in the enhanced photoconductivity in PGaN. Flux-dependent optical quenching (OQ) behavior, linked to the presence of metastable states, is also observed in PGaN as in CGaN.

Wide Bandgap Extrinsic Photoconductive Switches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sullivan, James S.

2013-07-03

Semi-insulating Gallium Nitride, 4H and 6H Silicon Carbide are attractive materials for compact, high voltage, extrinsic, photoconductive switches due to their wide bandgap, high dark resistance, high critical electric field strength and high electron saturation velocity. These wide bandgap semiconductors are made semi-insulating by the addition of vanadium (4H and 6HSiC) and iron (2H-GaN) impurities that form deep acceptors. These deep acceptors trap electrons donated from shallow donor impurities. The electrons can be optically excited from these deep acceptor levels into the conduction band to transition the wide bandgap semiconductor materials from a semi-insulating to a conducting state. Extrinsic photoconductivemore » switches with opposing electrodes have been constructed using vanadium compensated 6H-SiC and iron compensated 2H-GaN. These extrinsic photoconductive switches were tested at high voltage and high power to determine if they could be successfully used as the closing switch in compact medical accelerators.« less

Metal nanoparticles triggered persistent negative photoconductivity in silk protein hydrogels

NASA Astrophysics Data System (ADS)

Gogurla, Narendar; Sinha, Arun K.; Naskar, Deboki; Kundu, Subhas C.; Ray, Samit K.

2016-03-01

Silk protein is a natural biopolymer with intriguing properties, which are attractive for next generation bio-integrated electronic and photonic devices. Here, we demonstrate the negative photoconductive response of Bombyx mori silk protein fibroin hydrogels, triggered by Au nanoparticles. The room temperature electrical conductivity of Au-silk hydrogels is found to be enhanced with the incorporation of Au nanoparticles over the control sample, due to the increased charge transporting networks within the hydrogel. Au-silk lateral photoconductor devices show a unique negative photoconductive response under an illumination of 325 nm, with excitation energy higher than the characteristic metal plasmon resonance band. The enhanced photoconductance yield in the hydrogels over the silk protein is attributed to the photo-oxidation of amino groups in the β-pleated sheets of the silk around the Au nanoparticles followed by the breaking of charge transport networks. The Au-silk nanocomposite does not show any photoresponse under visible illumination because of the localization of excited charges in Au nanoparticles. The negative photoconductive response of hybrid Au-silk under UV illumination may pave the way towards the utilization of silk for future bio-photonic devices using metal nanoparticle platforms.

Giant Hall Photoconductivity in Narrow-Gapped Dirac Materials

NASA Astrophysics Data System (ADS)

Song, Justin C. W.; Kats, Mikhail A.

2016-12-01

Carrier dynamics acquire a new character in the presence of Bloch-band Berry curvature, which naturally arises in gapped Dirac materials (GDMs). Here we argue that photoresponse in GDMs with small band gaps is dramatically enhanced by Berry curvature. This manifests in a giant and saturable Hall photoconductivity when illuminated by circularly polarized light. Unlike Hall motion arising from a Lorentz force in a magnetic field, which impedes longitudinal carrier motion, Hall photoconductivity arising from Berry curvature can boost longitudinal carrier transport. In GDMs, this results in a helicity-dependent photoresponse in the Hall regime, where photoconductivity is dominated by its Hall component. We find that the induced Hall conductivity per incident irradiance is enhanced by up to six orders of magnitude when moving from the visible regime (with corresponding band gaps) to the far infrared. These results suggest that narrow-gap GDMs are an ideal test-bed for the unique physics that arise in the presence of Berry curvature, and open a new avenue for infrared and terahertz optoelectronics.

HgCdTe Photoconductive Mixers for 2-8 THz

NASA Technical Reports Server (NTRS)

Betz, A. L.; Boreiko, R. T.; Sivananthan, S.; Ashokan, R.

2001-01-01

Heterodyne spectroscopy has been taken to wavelengths as short as 63 micrometers with Schottky-diode mixers. Schottkys, however, are relatively insensitive compared to superconducting mixers such as the hot-electron microbolometer (HEB), which has an effective quantum efficiency of 3% at 120 micrometers (2.5 THz). Although HEB sensitivities are bound to improve, there will always be losses associated with antenna coupling of radiation into sub-micron size devices. Another approach to far infrared (FIR) mixer design is to use a photoconductive device which can be made much larger than a wavelength, and thus act as its own antenna. For example, HgCdTe photodiodes have been used as mixers in the lambda = 10 micrometers band for over 25 years, with sensitivities now only a factor of 2 from the quantum-noise-limit. HgCdTe can also be applied at FIR wavelengths, but surprisingly little work has been done to date. The exception is the pioneering work of Spears and Kostiuk and Spears, who developed HgCdTe photomixers for the 20-120 micrometer region. The spectral versatility of the HgCdTe alloy is well recognized for wavelengths as long as 8-20 micrometers. What is not so recognized, however, is that theoretically there is no long wavelength limit for appropriately composited HgCdTe. Although Spears successfully demonstrated a photoconductive response from HgCdTe at 120 micrometers, this initial effort was apparently never followed up, in part because of the difficulty of controlling the HgCdTe alloy composition with liquid-phase-epitaxy (LPE) techniques. With the availability of precise molecular-beam-epitaxy (MBE) since the early 1990's, it is now appropriate to reconsider HgCdTe for detector applications longward of lambda = 20 micrometers. We recently initiated an effort to fabricate detectors and mixers using II-VI materials for FIR wavelengths. Of particular interest are device structures called superlattices, which offer a number of advantages for high sensitivity

Nonlinear, anisotropic, and giant photoconductivity in intrinsic and doped graphene

NASA Astrophysics Data System (ADS)

Singh, Ashutosh; Ghosh, Saikat; Agarwal, Amit

2018-01-01

We present a framework to calculate the anisotropic and nonlinear photoconductivity for two band systems with application to graphene. In contrast to the usual perturbative (second order in the optical field strength) techniques, we calculate photoconductivity to all orders in the optical field strength. In particular, for graphene, we find the photoresponse to be giant (at large optical field strengths) and anisotropic. The anisotropic photoresponse in graphene is correlated with polarization of the incident field, with the response being similar to that of a half-wave plate. We predict that the anisotropy in the simultaneous measurement of longitudinal (σx x) and transverse (σy x) photoconductivity, with four probes, offers a unique experimental signature of the photovoltaic response, distinguishing it from the thermal-Seebeck and bolometric effects in photoresponse.

Steady-state photoconductivity and multi-particle interactions in high-mobility organic semiconductors.

PubMed

Irkhin, P; Najafov, H; Podzorov, V

2015-10-19

Fundamental understanding of photocarrier generation, transport and recombination under a steady-state photoexcitation has been an important goal of organic electronics and photonics, since these processes govern such electronic properties of organic semiconductors as, for instance, photoconductivity. Here, we discovered that photoconductivity of a highly ordered organic semiconductor rubrene exhibits several distinct regimes, in which photocurrent as a function of cw (continuous wave) excitation intensity is described by a power law with exponents sequentially taking values 1, 1/3 and ¼. We show that in pristine crystals this photocurrent is generated at the very surface of the crystals, while the bulk photocurrent is drastically smaller and follows a different sequence of exponents, 1 and ½. We describe a simple experimental procedure, based on an application of "gauge effect" in high vacuum, that allows to disentangle the surface and bulk contributions to photoconductivity. A model based on singlet exciton fission, triplet fusion and triplet-charge quenching that can describe these non-trivial effects in photoconductivity of highly ordered organic semiconductors is proposed. Observation of these effects in photoconductivity and modeling of the underlying microscopic mechanisms described in this work represent a significant step forward in our understanding of electronic properties of organic semiconductors.

Steady-state photoconductivity and multi-particle interactions in high-mobility organic semiconductors

PubMed Central

Irkhin, P.; Najafov, H.; Podzorov, V.

2015-01-01

Fundamental understanding of photocarrier generation, transport and recombination under a steady-state photoexcitation has been an important goal of organic electronics and photonics, since these processes govern such electronic properties of organic semiconductors as, for instance, photoconductivity. Here, we discovered that photoconductivity of a highly ordered organic semiconductor rubrene exhibits several distinct regimes, in which photocurrent as a function of cw (continuous wave) excitation intensity is described by a power law with exponents sequentially taking values 1, 1/3 and ¼. We show that in pristine crystals this photocurrent is generated at the very surface of the crystals, while the bulk photocurrent is drastically smaller and follows a different sequence of exponents, 1 and ½. We describe a simple experimental procedure, based on an application of “gauge effect” in high vacuum, that allows to disentangle the surface and bulk contributions to photoconductivity. A model based on singlet exciton fission, triplet fusion and triplet-charge quenching that can describe these non-trivial effects in photoconductivity of highly ordered organic semiconductors is proposed. Observation of these effects in photoconductivity and modeling of the underlying microscopic mechanisms described in this work represent a significant step forward in our understanding of electronic properties of organic semiconductors. PMID:26478121

Photoconduction in amorphous thin films of Se90Sb10-xAgx glassy alloys

NASA Astrophysics Data System (ADS)

Sharma, Suresh Kumar; Shukla, R. K.; Dwivedi, Prabhat K.; Kumar, A.

2017-10-01

The present paper reports the steady state photoconductivity and photosensitivity response of thermally evaporated amorphous thin films of Se90Sb10-xAgx(x = 2, 4, 6, 8, 10). Temperature dependence of dark conductivity is studied and activation energy is calculated for different samples. Temperature dependence of photoconductivity is also studied at different intensities. From temperature dependence of photoconductivity activation energy is computed at different intensities which are found to vary from 0.26 to 0.47 eV. Intensity dependence of photoconductivity has also been studied at different temperatures. These curves are plotted on logarithmic scale and found to be straight lines which show that photoconductivity follows a power law with intensity. Composition dependence of dark conductivity, activation energy of DC conduction and photosensitivity show that these parameters are highly. composition dependent and show a discontinuity at a particular composition when Ag concentration becomes 6 at. %. This is explained in terms of transition from floppy state to mechanically stabilized state at this composition.

Picosecond Transient Photoconductivity in Functionalized Pentacene Molecular Crystals Probed by Terahertz Pulse Spectroscopy

NASA Astrophysics Data System (ADS)

Hegmann, F. A.; Tykwinski, R. R.; Lui, K. P.; Bullock, J. E.; Anthony, J. E.

2002-11-01

We have measured transient photoconductivity in functionalized pentacene molecular crystals using ultrafast optical pump-terahertz probe techniques. The single crystal samples were excited using 800nm, 100fs pulses, and the change in transmission of time-delayed, subpicosecond terahertz pulses was used to probe the photoconducting state over a temperature range from 10 to 300K. A subpicosecond rise in photoconductivity is observed, suggesting that mobile carriers are a primary photoexcitation. At times longer than 4ps, a power-law decay is observed consistent with dispersive transport.

Photo-Ultrasonic Study of Extrinsic Photoconductivity in N-Gallium Arsenide

NASA Astrophysics Data System (ADS)

Bradshaw, Randall Grant

We have measured the velocity of piezoelectrically -active, ultrasonic shear waves between 1.5 K and 68 K for undoped and for oxygen-doped n-type GaAs, during and after illumination at 4.2 K. The results reveal photoconductivity, persistent photoconductivity, and thermally stimulated conductivity. In both samples the Fermi level in the dark is controlled by excess non-shallow donors near 0.2 eV below the conduction band. Analysis of these effects in oxygen-doped material indicates that there are mid-gap and much shallower photoionizable levels and that there is an electron trap near 20 meV below the conduction band. The undoped n-GaAs sample exhibits photoconductivity quenching with photons in the range 0.95-1.26 eV which, by analysis of the quenching rate, is attributed to the EL2 defect. In addition, levels with large hole capture coefficients have been detected.

Tellurium doping effect in avalanche-mode amorphous selenium photoconductive film

NASA Astrophysics Data System (ADS)

Park, Wug-Dong; Tanioka, Kenkichi

2014-11-01

Amorphous selenium (a-Se) high-gain avalanche rushing amorphous photoconductor (HARP) film has been used for highly sensitive imaging devices. To improve the spectral response of a-Se HARP photoconductive film at a long wavelength, the tellurium (Te) doping effect in an 8-μm-thick a-Se HARP film was investigated. The thickness of the Te-doped a-Se layer in the 8-μm-thick a-Se HARP films was varied from 60 to 120 nm. The signal current increases significantly due to the avalanche multiplication when the target voltage is increased over the threshold voltage. In the 8-μm-thick a-Se HARP film with a Te-doped layer, the spectral response at a long wavelength was improved in comparison with the a-Se HARP film without a Te-doped layer. In addition, the increase of the lag in the 8-μm-thick a-Se HARP target with a Te-doped layer of 120 nm is caused by the photoconductive lag due to the electrons trapped in the Te-doped layer. Based on the current-voltage characteristics, spectral response, and lag characteristics of the 8-μm-thick a-Se HARP targets, the Te-doped layer thickness of 90 nm is suitable for the 8-μm-thick a-Se HARP film.

Photoconductive properties of Bi{sub 2}S{sub 3} nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andzane, J., E-mail: jana.andzane@lu.lv; Kunakova, G.; Erts, D.

2015-02-14

The photoconductive properties of Bi{sub 2}S{sub 3} nanowires synthesized inside anodized alumina (AAO) membrane have been characterized as a function of illuminating photon energy between the wavelengths of 500 to 900 nm and at constant illumination intensity of 1–4 μW·cm{sup −2}. Photoconductivity spectra, photocurrent values, photocurrent onset/decay times of individual Bi{sub 2}S{sub 3} nanowires liberated from the AAO membrane were determined and compared with those of arrays of as-produced Bi{sub 2}S{sub 3} nanowires templated inside pores of AAO membrane. The alumina membrane was found to significantly influence the photoconductive properties of the AAO-hosted Bi{sub 2}S{sub 3} nanowires, when compared to liberated frommore » the AAO membrane individual Bi{sub 2}S{sub 3} nanowires, possibly due to charge carrier trapping at the interface between the nanowire surface and the pore walls.« less

Photoconductive circuit element pulse generator

DOEpatents

Rauscher, Christen

1989-01-01

A pulse generator for characterizing semiconductor devices at millimeter wavelength frequencies where a photoconductive circuit element (PCE) is biased by a direct current voltage source and produces short electrical pulses when excited into conductance by short laser light pulses. The electrical pulses are electronically conditioned to improve the frequency related amplitude characteristics of the pulses which thereafter propagate along a transmission line to a device under test.

Electric field detection of phase-locked near-infrared pulses using photoconductive antenna.

PubMed

Katayama, I; Akai, R; Bito, M; Matsubara, E; Ashida, M

2013-07-15

We have demonstrated that a photoconductive antenna gated with 5-fs ultrashort laser pulses can detect electric field transients of near-infrared pulses at least up to 180 THz. Measured sensitivity spectrum of the antenna shows a good agreement with a simple calculation, demonstrating the promising capability of the antenna to near infrared spectroscopy. Using this setup, near-infrared time-domain spectroscopy and characterization of phase controlled near-infrared pulses are demonstrated. Observed absorption spectrum of a polystyrene film and complex refractive index dispersion of a fused silica plate both agree well with those obtained by the conventional methods.

Ultrahigh photoconductivity of bandgap-graded CdSxSe1-x nanowires probed by terahertz spectroscopy

NASA Astrophysics Data System (ADS)

Liu, Hongwei; Lu, Junpeng; Yang, Zongyin; Teng, Jinghua; Ke, Lin; Zhang, Xinhai; Tong, Limin; Sow, Chorng Haur

2016-06-01

Superiorly high photoconductivity is desirable in optoelectronic materials and devices for information transmission and processing. Achieving high photoconductivity via bandgap engineering in a bandgap-graded semiconductor nanowire has been proposed as a potential strategy. In this work, we report the ultrahigh photoconductivity of bandgap-graded CdSxSe1-x nanowires and its detailed analysis by means of ultrafast optical-pump terahertz-probe (OPTP) spectroscopy. The recombination rates and carrier mobility are quantitatively obtained via investigation of the transient carrier dynamics in the nanowires. By analysis of the terahertz (THz) spectra, we obtain an insight into the bandgap gradient and band alignment to carrier transport along the nanowires. The demonstration of the ultrahigh photoconductivity makes bandgap-graded CdSxSe1-x nanowires a promising candidate as building blocks for nanoscale electronic and photonic devices.

High power telecommunication-compatible photoconductive terahertz emitters based on plasmonic nano-antenna arrays.

PubMed

Yardimci, Nezih Tolga; Lu, Hong; Jarrahi, Mona

2016-11-07

We present a high-power and broadband photoconductive terahertz emitter operating at telecommunication optical wavelengths, at which compact and high-performance fiber lasers are commercially available. The presented terahertz emitter utilizes an ErAs:InGaAs substrate to achieve high resistivity and short carrier lifetime characteristics required for robust operation at telecommunication optical wavelengths. It also uses a two-dimensional array of plasmonic nano-antennas to offer significantly higher optical-to-terahertz conversion efficiencies compared to the conventional photoconductive emitters, while maintaining broad operation bandwidths. We experimentally demonstrate pulsed terahertz radiation over 0.1-5 THz frequency range with the power levels as high as 300  μ W. This is the highest-reported terahertz radiation power from a photoconductive emitter operating at telecommunication optical wavelengths.

Holographic recording medium employing a photoconductive layer and a low molecular weight microcrystalline polymeric layer

NASA Technical Reports Server (NTRS)

Gange, Robert Allen (Inventor)

1977-01-01

A holographic recording medium comprising a conductive substrate, a photoconductive layer and an electrically alterable layer of a linear, low molecular weight hydrocarbon polymer has improved fatigue resistance. An acrylic barrier layer can be interposed between the photoconductive and electrically alterable layers.

Enhanced coherent terahertz beam with a photoconductive antenna containing a chaotic shape electrodes

NASA Astrophysics Data System (ADS)

Wu, Dong Ho; Kim, Christopher; Graber, Benjamin

2014-03-01

Photoconductive antenna is one of the most popular methods to produce a broadband terahertz beam. Our recent experiments indicate that a photoconductive antenna containing a pair of parallel micro-strip-line electrodes produces both incoherent and coherent terahertz beam. When we drive the antenna with a low bias voltage and a weak femto-second laser power, it produces mostly coherent terahertz beam. However, as the bias voltage and/or the femto-second laser power increase, the incoherent terahertz beam strength increases exponentially with the bias voltage.[1] When the bias voltage and/or the femto-second laser power exceeds critical values, heat associated with the incoherent beam eventually leads to a catastrophic antenna failure, resulting in a permanent damage on the antenna.[2] In order to improve our photoconductive antenna we have implemented a chaotic geometry in the photoconductive antenna's electrodes. Our experimental results show that the new antenna produces substantially more coherent terahertz beam and much less incoherent terahertz beam. We will present the details of our experimental results and discuss the merits of new antenna design. We will also examine some theory to understand our experimental results. Supported by DTRA.

Improving Photoconductance of Fluorinated Donors with Fluorinated Acceptors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garner, Logan E.; Larson, Bryon; Oosterhout, Stefan

2016-11-21

This work investigates the influence of fluorination of both donor and acceptor materials on the generation of free charge carriers in small molecule donor/fullerene acceptor BHJ OPV active layers. A fluorinated and non-fluorinated small molecule analogue were synthesized and their optoelectronic properties characterized. The intrinsic photoconductance of blends of these small molecule donors was investigated using time-resolved microwave conductivity. Blends of the two donor molecules with a traditional non-fluorinated fullerene (PC70BM) as well as a fluorinated fullerene (C60(CF3)2-1) were investigated using 5% and 50% fullerene loading. We demonstrate for the first time that photoconductance in a 50:50 donor:acceptor BHJ blendmore » using a fluorinated fullerene can actually be improved relative to a traditional non-fluorinated fullerene by fluorinating the donor molecule as well.« less

High power telecommunication-compatible photoconductive terahertz emitters based on plasmonic nano-antenna arrays

PubMed Central

Yardimci, Nezih Tolga; Lu, Hong; Jarrahi, Mona

2016-01-01

We present a high-power and broadband photoconductive terahertz emitter operating at telecommunication optical wavelengths, at which compact and high-performance fiber lasers are commercially available. The presented terahertz emitter utilizes an ErAs:InGaAs substrate to achieve high resistivity and short carrier lifetime characteristics required for robust operation at telecommunication optical wavelengths. It also uses a two-dimensional array of plasmonic nano-antennas to offer significantly higher optical-to-terahertz conversion efficiencies compared to the conventional photoconductive emitters, while maintaining broad operation bandwidths. We experimentally demonstrate pulsed terahertz radiation over 0.1–5 THz frequency range with the power levels as high as 300 μW. This is the highest-reported terahertz radiation power from a photoconductive emitter operating at telecommunication optical wavelengths. PMID:27916999

Optical and photoconductivity spectra of novel Ag₂In₂SiS₆ and Ag₂In₂GeS₆ chalcogenide crystals.

PubMed

Chmiel, M; Piasecki, M; Myronchuk, G; Lakshminarayana, G; Reshak, Ali H; Parasyuk, O G; Kogut, Yu; Kityk, I V

2012-06-01

Complex spectral studies of near-band gap and photoconductive spectra for novel Ag(2)In(2)SiS(6) and Ag(2)In(2)GeS(6) single crystals are presented. The spectral dependences of photoconductivity clearly show an existence of spectral maxima within the 450 nm-540 nm and 780 nm-920 nm. The fundamental absorption edge is analyzed by Urbach rule. The origin of the spectral photoconductivity spectral maxima is discussed. Temperature dependences of the spectra were done. The obtained spectral features allow to propose the titled crystals as photosensors. An analysis of the absorption and photoconductivity spectra is given within a framework of oversimplified spectroscopic model of complex chalcogenide crystals. Copyright © 2012 Elsevier B.V. All rights reserved.

High Sensitivity Terahertz Detection through Large-Area Plasmonic Nano-Antenna Arrays.

PubMed

Yardimci, Nezih Tolga; Jarrahi, Mona

2017-02-16

Plasmonic photoconductive antennas have great promise for increasing responsivity and detection sensitivity of conventional photoconductive detectors in time-domain terahertz imaging and spectroscopy systems. However, operation bandwidth of previously demonstrated plasmonic photoconductive antennas has been limited by bandwidth constraints of their antennas and photoconductor parasitics. Here, we present a powerful technique for realizing broadband terahertz detectors through large-area plasmonic photoconductive nano-antenna arrays. A key novelty that makes the presented terahertz detector superior to the state-of-the art is a specific large-area device geometry that offers a strong interaction between the incident terahertz beam and optical pump at the nanoscale, while maintaining a broad operation bandwidth. The large device active area allows robust operation against optical and terahertz beam misalignments. We demonstrate broadband terahertz detection with signal-to-noise ratio levels as high as 107 dB.

High Sensitivity Terahertz Detection through Large-Area Plasmonic Nano-Antenna Arrays

PubMed Central

Yardimci, Nezih Tolga; Jarrahi, Mona

2017-01-01

Plasmonic photoconductive antennas have great promise for increasing responsivity and detection sensitivity of conventional photoconductive detectors in time-domain terahertz imaging and spectroscopy systems. However, operation bandwidth of previously demonstrated plasmonic photoconductive antennas has been limited by bandwidth constraints of their antennas and photoconductor parasitics. Here, we present a powerful technique for realizing broadband terahertz detectors through large-area plasmonic photoconductive nano-antenna arrays. A key novelty that makes the presented terahertz detector superior to the state-of-the art is a specific large-area device geometry that offers a strong interaction between the incident terahertz beam and optical pump at the nanoscale, while maintaining a broad operation bandwidth. The large device active area allows robust operation against optical and terahertz beam misalignments. We demonstrate broadband terahertz detection with signal-to-noise ratio levels as high as 107 dB. PMID:28205615

High voltage photoconductive switch package

DOE Office of Scientific and Technical Information (OSTI.GOV)

Caporaso, George J.

2016-11-22

A photoconductive switch having a wide bandgap material substrate between opposing electrodes, and a doped dielectric filler that is in contact with both the electrodes and the substrate at the triple point. The dielectric filler material is doped with a conductive material to make it partially or completely conducting, to minimize the field enhancement near the triple point both when the substrate is not conducting in the "off" state and when the substrate is rendered conducting by radiation in the "on" state.

Numerical simulation of terahertz generation and detection based on ultrafast photoconductive antennas

NASA Astrophysics Data System (ADS)

Chen, Long-chao; Fan, Wen-hui

2011-08-01

The numerical simulation of terahertz generation and detection in the interaction between femtosecond laser pulse and photoconductive material has been reported in this paper. The simulation model based on the Drude-Lorentz theory is used, and takes into account the phenomena that photo-generated electrons and holes are separated by the external bias field, which is screened by the space-charge field simultaneously. According to the numerical calculation, the terahertz time-domain waveforms and their Fourier-transformed spectra are presented under different conditions. The simulation results indicate that terahertz generation and detection properties of photoconductive antennas are largely influenced by three major factors, including photo-carriers' lifetime, laser pulse width and pump laser power. Finally, a simple model has been applied to simulate the detected terahertz pulses by photoconductive antennas with various photo-carriers' lifetimes, and the results show that the detected terahertz spectra are very different from the spectra radiated from the emitter.

Characterization of memory and measurement history in photoconductivity of nanocrystal arrays

NASA Astrophysics Data System (ADS)

Fairfield, Jessamyn A.; Dadosh, Tali; Drndic, Marija

2010-10-01

Photoconductivity in nanocrystal films has been previously characterized, but memory effects have received little attention despite their importance for device applications. We show that the magnitude and temperature dependence of the photocurrent in CdSe/ZnS core-shell nanocrystal arrays depends on the illumination and electric field history. Changes in photoconductivity occur on a few-hour timescale, and subband gap illumination of nanocrystals prior to measurements modifies the photocurrent more than band gap illumination. The observed effects can be explained by charge traps within the band gap that are filled or emptied, which may alter nonradiative recombination processes and affect photocurrent.

Specific features of the spectra and relaxation kinetics of long-wavelength photoconductivity in narrow-gap HgCdTe epitaxial films and heterostructures with quantum wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rumyantsev, V. V., E-mail: rumyantsev@ipmras.ru; Ikonnikov, A. V.; Antonov, A. V.

2013-11-15

The spectra and relaxation kinetics of interband photoconductivity are investigated in narrow-gap Hg{sub 1-x}Cd{sub x}Te epitaxial films with x = 0.19-0.23 and in structures with HgCdTe-based quantum wells (QWs), having an interband-transition energy in the range of 30-90 meV, grown by molecular-beam epitaxy on GaAs (013) substrates. A long-wavelength sensitivity band caused by impurities or defects is found in the spectra of the structures with quantum wells in addition to the interband photoconductivity. It is shown that the lifetimes of nonequilibrium carriers in the structures with QWs is less than in bulk samples at the same optical-transition energy. From themore » measured carrier lifetimes, the ampere-watt responsivity and the equivalent noise power for a film with x = 0.19 at a wavelength of 19 {mu}m are estimated. When investigating the relaxation kinetics of the photoconductivity at 4.2 K in high excitation regime, it is revealed that radiative recombination is dominant over other mechanisms of nonequilibrium-carrier recombination.« less

Long wavelength, high gain InAsSb strained-layer superlattice photoconductive detectors

DOEpatents

Biefeld, Robert M.; Dawson, L. Ralph; Fritz, Ian J.; Kurtz, Steven R.; Zipperian, Thomas E.

1991-01-01

A high gain photoconductive device for 8 to 12 .mu.m wavelength radiation including an active semiconductor region extending from a substrate to an exposed face, the region comprising a strained-layer superlattice of alternating layers of two different InAs.sub.1-x Sb.sub.x compounds having x>0.75. A pair of spaced electrodes are provided on the exposed face, and changes in 8 to 12 .mu.m radiation on the exposed face cause a large photoconductive gain between the spaced electrodes.

Study of metal/ZnO based thin film ultraviolet photodetectors: The effect of induced charges on the dynamics of photoconductivity relaxation

NASA Astrophysics Data System (ADS)

Yadav, Harish Kumar; Sreenivas, K.; Gupta, Vinay

2010-02-01

Ultraviolet photoconductivity relaxation in ZnO thin films deposited by rf magnetron sputtering are investigated. Effect of oxygen partial pressure in the reactive gas mixture and film thickness on the photoconductivity transients is studied. A different photodetector configuration comprising ZnO thin film with an ultrathin overlayer of metals like Cu, Al, Sn, Au, Cr, and Te was designed and tested. Photoresponse signal were found to be stronger (four to seven times) in these configurations than the pure ZnO thin films. Sn(30 nm)/ZnO sample exhibits highest responsivity of ˜8.57 kV/W whereas Te(20 nm)/ZnO structure presents highest sensitivity of ˜31.3×103 compared to unloaded ZnO thin film. Enhancement in the photoresponse of ZnO thin films is attributed to the change in surface conductivity due to induced charge carriers at the interface because of the difference in work function and oxygen affinity values of metal overlayer with the underlying semiconducting layer. Charge carrier transfer from the metal layer to ZnO creates a surplus of electrons at the interface; a fraction of which are captured by the defect centers (traps) at the surface whereas the remaining one represents free carriers in the conduction band and are responsible for the enhanced photoconductivity.

Role of polymer matrix on photo-sensitivity of CdSe polymer nanocomposites

NASA Astrophysics Data System (ADS)

Kaur, Ramneek; Tripathi, S. K.

2018-04-01

This paper reports the effect of three different polymer matrices (PVP, PMMA and PVK) and Ag doping on the photo-sensitivity of CdSe polymer nanocomposites. The results reveal that the photoconductivity is high for linear chain polymer nanocomposites as compared to aromatic ones with decreasing trend as: CdSe-PMMA > CdSe-PVP > CdSe-PVK. The large substituents or branches along the polymer backbone hinder the stacking sequences in CdSe-PVK nanocomposites resulting in lowest photoconductivity. On contrary, CdSe-PVK nanocomposite exhibit highest photosensitivity. The reason behind it is the low value of dark conductivity in CdSe-PVK nanocomposite and photoconductive PVK matrix. With Ag doping, no considerable effect on the value of photosensitivity has been observed. The obtained results indicate that the photo-conducting properties of these polymer nanocomposites can be tuned by using different polymer matrices.

Digital radiography using amorphous selenium: photoconductively activated switch (PAS) readout system.

PubMed

Reznik, Nikita; Komljenovic, Philip T; Germann, Stephen; Rowlands, John A

2008-03-01

A new amorphous selenium (a-Se) digital radiography detector is introduced. The proposed detector generates a charge image in the a-Se layer in a conventional manner, which is stored on electrode pixels at the surface of the a-Se layer. A novel method, called photoconductively activated switch (PAS), is used to read out the latent x-ray charge image. The PAS readout method uses lateral photoconduction at the a-Se surface which is a revolutionary modification of the bulk photoinduced discharge (PID) methods. The PAS method addresses and eliminates the fundamental weaknesses of the PID methods--long readout times and high readout noise--while maintaining the structural simplicity and high resolution for which PID optical readout systems are noted. The photoconduction properties of the a-Se surface were investigated and the geometrical design for the electrode pixels for a PAS radiography system was determined. This design was implemented in a single pixel PAS evaluation system. The results show that the PAS x-ray induced output charge signal was reproducible and depended linearly on the x-ray exposure in the diagnostic exposure range. Furthermore, the readout was reasonably rapid (10 ms for pixel discharge). The proposed detector allows readout of half a pixel row at a time (odd pixels followed by even pixels), thus permitting the readout of a complete image in 30 s for a 40 cm x 40 cm detector with the potential of reducing that time by using greater readout light intensity. This demonstrates that a-Se based x-ray detectors using photoconductively activated switches could form a basis for a practical integrated digital radiography system.

Position-sensitive, fast ionization chambers

NASA Astrophysics Data System (ADS)

Lai, J.; Afanasieva, L.; Blackmon, J. C.; Deibel, C. M.; Gardiner, H. E.; Lauer, A.; Linhardt, L. E.; Macon, K. T.; Rasco, B. C.; Williams, C.; Santiago-Gonzalez, D.; Kuvin, S. A.; Almaraz-Calderon, S.; Baby, L. T.; Baker, J.; Belarge, J.; Wiedenhöver, I.; Need, E.; Avila, M. L.; Back, B. B.; DiGiovine, B.; Hoffman, C. R.

2018-05-01

A high-count-rate ionization chamber design with position-sensitivity has been developed and deployed at several accelerator facilities. Counting rates of ≥ 500 kHz with good Z-separation (up to 5% energy resolution) for particle identification have been demonstrated in a series of commissioning experiments. A position-sensitive capability, with a resolution of 3 mm, has been implemented for the first time to record position information and suppress pileup. The design and performance of the detectors are described.

GaAs photoconductive semiconductor switch

DOEpatents

Loubriel, Guillermo M.; Baca, Albert G.; Zutavern, Fred J.

1998-01-01

A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices.

Photoconductivity of CdS under high pressure

NASA Astrophysics Data System (ADS)

Savić, Pavle; Urošević, Vladeta

1987-04-01

The photoconductivity of the high-pressure (rocksalt) phase of CdS has been investigated over the 30-120 kbar pressure range. A decrease of the photo-threshold from 1.60 eV (at 30 kbar) to 1.49 eV (at 120 kbar) indicates an indirect gap semiconductor. The values obtained have been compared with the Savić-Kašanin theory.

Tuneable photoconductivity and mobility enhancement in printed MoS2/graphene composites

NASA Astrophysics Data System (ADS)

Kelly, Adam G.; Murphy, Conor; Vega-Mayoral, Victor; Harvey, Andrew; Sajad Esmaeily, Amir; Hallam, Toby; McCloskey, David; Coleman, Jonathan N.

2017-12-01

With the aim of increasing carrier mobility in nanosheet-network devices, we have investigated MoS2-graphene composites as active regions in printed photodetectors. Combining liquid exfoliation and inkjet-printing, we fabricated all-printed photodetectors with graphene electrodes and MoS2-graphene composite channels with various graphene mass fractions (0  ⩽  M f  ⩽  16 wt%). The increase in channel dark conductivity with M f was consistent with percolation theory for composites below the percolation threshold. While the photoconductivity increased with graphene content, it did so more slowly than the dark conductivity, such that the fractional photoconductivity decayed rapidly with increasing M f. We propose that both mobility and dark carrier density increase with graphene content according to percolation-like scaling laws, while photo-induced carrier density is essentially independent of graphene loading. This leads to percolation-like scaling laws for both photoconductivity and fractional photoconductivity—in excellent agreement with the data. These results imply that channel mobility and carrier density increase up to 100-fold with the addition of 16 wt% graphene.

A Real-Time Ultraviolet Radiation Imaging System Using an Organic Photoconductive Image Sensor†

PubMed Central

Okino, Toru; Yamahira, Seiji; Yamada, Shota; Hirose, Yutaka; Odagawa, Akihiro; Kato, Yoshihisa; Tanaka, Tsuyoshi

2018-01-01

We have developed a real time ultraviolet (UV) imaging system that can visualize both invisible UV light and a visible (VIS) background scene in an outdoor environment. As a UV/VIS image sensor, an organic photoconductive film (OPF) imager is employed. The OPF has an intrinsically higher sensitivity in the UV wavelength region than those of conventional consumer Complementary Metal Oxide Semiconductor (CMOS) image sensors (CIS) or Charge Coupled Devices (CCD). As particular examples, imaging of hydrogen flame and of corona discharge is demonstrated. UV images overlapped on background scenes are simply made by on-board background subtraction. The system is capable of imaging weaker UV signals by four orders of magnitude than that of VIS background. It is applicable not only to future hydrogen supply stations but also to other UV/VIS monitor systems requiring UV sensitivity under strong visible radiation environment such as power supply substations. PMID:29361742

GaAs photoconductive semiconductor switch

DOEpatents

Loubriel, G.M.; Baca, A.G.; Zutavern, F.J.

1998-09-08

A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device is disclosed. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices. 5 figs.

Quality Characterization of Silicon Bricks using Photoluminescence Imaging and Photoconductive Decay: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnston, S.; Yan, F.; Zaunbrecher, K.

2012-06-01

Imaging techniques can be applied to multicrystalline silicon solar cells throughout the production process, which includes as early as when the bricks are cut from the cast ingot. Photoluminescence (PL) imaging of the band-to-band radiative recombination is used to characterize silicon quality and defects regions within the brick. PL images of the brick surfaces are compared to minority-carrier lifetimes measured by resonant-coupled photoconductive decay (RCPCD). Photoluminescence images on silicon bricks can be correlated to lifetime measured by photoconductive decay and could be used for high-resolution characterization of material before wafers are cut. The RCPCD technique has shown the longest lifetimesmore » of any of the lifetime measurement techniques we have applied to the bricks. RCPCD benefits from the low-frequency and long-excitation wavelengths used. In addition, RCPCD is a transient technique that directly monitors the decay rate of photoconductivity and does not rely on models or calculations for lifetime. The measured lifetimes over brick surfaces have shown strong correlations to the PL image intensities; therefore, this correlation could then be used to transform the PL image into a high-resolution lifetime map.« less

Practical Considerations for Optimizing Position Sensitivity in Arrays of Position-sensitive TES's

NASA Technical Reports Server (NTRS)

Smith, Stephen J.; Bandler, Simon R.; Figueroa-Feliciano, Encetali; Iyomoto, Naoko; Kelley, Richard L.; Kilbourne, Caroline A.; Porder, Frederick S.; Sadleir, John E.

2007-01-01

We are developing Position-Sensitive Transitions-Edge Sensors (PoST's) for future X-ray astronomy missions such as NASA's Constellation-X. The PoST consists of one or more Transitions Edge Sensors (TES's) thermally connected to a large X-ray absorber, which through heat diffusion, gives rise to position dependence. The development of PoST's is motivated by the desire to achieve the largest the focal-plan coverage with the fewest number of readout channels. In order to develop a practical array, consisting of an inner pixellated core with an outer array of large absorber PoST's, we must be able to simultaneously read out all (-1800) channels in the array. This is achievable using time division multiplexing (TDM), but does set stringent slew rate requirements on the array. Typically, we must damp the pulses to reduce the slew rate of the input signal to the TDM. This is achieved by applying a low-pass analog filter with large inductance to the signal. This attenuates the high frequency components of the signal, essential for position discrimination in PoST's, relative to the white noise of the readout chain and degrades the position sensitivity. Using numerically simulated data, we investigate the position sensing ability of typical PoST designs under such high inductance conditions. We investigate signal-processing techniques for optimal determination of the event position and discuss the practical considerations for real-time implementation.

Optical absorption and photoconductivity in iodine-excess ionic liquids: the case of 1-alkyl-3-methyl imidazolium iodides.

PubMed

Aono, Masami; Miyazaki, Hisashi; Takekiyo, Takahiro; Tsuzuki, Seiji; Abe, Hiroshi

2018-02-21

We investigated the optical absorption and photoconductivity of iodine-excess ionic liquids (ILs) based on 1-alkyl-3-methyl imidazolium iodide ([C n mim][I]; n = 3, 4, and 6). The iodide concentration m was 2 ≦ m ≦ 8, which was determined by the molar fraction [C n mim] +  : [I m ] - = 1 : m. By adding iodine, an absorption edge shifted from 282 nm in the UV region to around 600 nm in the visible-light region. The optical bandgaps E o decreased gradually from 2.3 eV to 1.9 eV with increasing m from 2 to 8. The alkyl-side chain lengths of the cations have little effect on the E o . This experimental result was confirmed by ab initio molecular orbital calculations. The effects were reflected in the photoconductivity of the ILs, as expected. [C 4 mim][I m ] exhibited greater photo-induced electron generation compared with [C 3 mim][I m ] and [C 6 mim][I m ]. The photoconductivity in both [C 3 mim][I m ] and [C 6 mim][I m ] increased slightly with increasing m. The trend of photoconductivity in [C 4 mim][I m ] exhibited an N-shaped form. The highest photoconductivity 1.6 was observed in [C 4 mim][I 8 ].

Features of Stationary Photoconductivity of High-Ohmic Semiconductors Under Local Illumination

NASA Astrophysics Data System (ADS)

Lysenko, A. P.; Belov, A. G.; Kanevskii, V. E.; Odintsova, E. A.

2018-04-01

Photoconductivity has been thoroughly studied for a long time. However, most researchers have examined photoconductivity of semiconductors while illuminating the entire surface of samples. The present paper examines the effect of local exposure that ensures a high level of injection of free charge carriers upon the conductivity of high-ohmic cadmium telluride and semi-insulating gallium arsenide samples and upon the properties of ohmic contacts to samples. The authors found that regardless of the exposure area the value of transition resistance of ohmic contacts decreases and the concentration of the main charge carriers increases in the sample in proportion to radiation intensity. This research uncovered a number of previously unknown effects that are interesting from the physical point of view. This paper focuses on discussing these effects.

Optically controlled electrophoresis with a photoconductive substrate

NASA Astrophysics Data System (ADS)

Inami, Wataru; Nagashima, Taiki; Kawata, Yoshimasa

2018-05-01

A photoconductive substrate is used to perform electrophoresis. Light-induced micro-particle flow manipulation is demonstrated without using a fabricated flow channel. The path along which the particles were moved was formed by an illuminated light pattern on the substrate. Because the substrate conductivity and electric field distribution can be modified by light illumination, the forces acting on the particles can be controlled. This technique has potential applications as a high functionality analytical device.

Optimization Of Optoelectronic Characteristics Of Sintered Cadmium Sulphide Photoconductive Layers

NASA Astrophysics Data System (ADS)

Chockalingam, Mary J.; Suryanarayana, C. V.

1986-11-01

Photograde cadmium sulphide useful for sintered polycrystalline cadmium sulphide photoconductive cells as also for solar cells can be prepared by a simple chemical reaction between a soluble cadmium salt and thiourea in an aqueous alkaline solution by optimising the pH, temperature and concentration of the constituents in the bath. The precipitated cadmium-sulphide after drying at 120°C was found to result in a photograde quality of 99.999% pure cadmium sulphide as estimated by atomic absorption spectrophotometer. Details are given in this paper, of the process of preparation of CdS powder, screen printing and sintering the cadmium sulphide layers to give finally the photoconductive cell which gave on irradiation a change in the resistance of six to seven orders. The sintering technique and the mechanism of the reaction resulting in high photosensitivity of the layer obtained are discussed in detail.

Method and system for photoconductive detector signal correction

DOEpatents

Carangelo, Robert M.; Hamblen, David G.; Brouillette, Carl R.

1992-08-04

A corrective factor is applied so as to remove anomalous features from the signal generated by a photoconductive detector, and to thereby render the output signal highly linear with respect to the energy of incident, time-varying radiation. The corrective factor may be applied through the use of either digital electronic data processing means or analog circuitry, or through a combination of those effects.

Method and system for photoconductive detector signal correction

DOEpatents

Carangelo, R.M.; Hamblen, D.G.; Brouillette, C.R.

1992-08-04

A corrective factor is applied so as to remove anomalous features from the signal generated by a photoconductive detector, and to thereby render the output signal highly linear with respect to the energy of incident, time-varying radiation. The corrective factor may be applied through the use of either digital electronic data processing means or analog circuitry, or through a combination of those effects. 5 figs.

Control of the recombination time in photoconductive detectors

NASA Astrophysics Data System (ADS)

Pacheco, M. T. T.; Ghizoni, C. C.; Scolari, S. L.

1980-07-01

The current generated at a photoconductive cell depends upon the density of states of the electromagnetic field in the semiconductor film. This density of states is a function of the film geometry and dielectric properties. In this work we demonstrate that, for highly scattering substrate surfaces, which implies in a low density of states, the signal to noise ratio is better than that for smooth surfaces.

CMOS image sensor with organic photoconductive layer having narrow absorption band and proposal of stack type solid-state image sensors

NASA Astrophysics Data System (ADS)

Takada, Shunji; Ihama, Mikio; Inuiya, Masafumi

2006-02-01

Digital still cameras overtook film cameras in Japanese market in 2000 in terms of sales volume owing to their versatile functions. However, the image-capturing capabilities such as sensitivity and latitude of color films are still superior to those of digital image sensors. In this paper, we attribute the cause for the high performance of color films to their multi-layered structure, and propose the solid-state image sensors with stacked organic photoconductive layers having narrow absorption bands on CMOS read-out circuits.

Photoconductivity in organic thin films: From picoseconds to seconds after excitation

NASA Astrophysics Data System (ADS)

Day, J.; Subramanian, S.; Anthony, J. E.; Lu, Z.; Twieg, R. J.; Ostroverkhova, O.

2008-06-01

We present a detailed study, on time scales from picoseconds to seconds, of transient and continuous wave (cw) photoconductivity in solution-grown thin films of functionalized pentacene (Pc), anthradithiophene (ADT), and dicyanomethylenedihydrofuran (DCDHF). In all films, at temperatures of 285-350 K, we observe fast carrier photogeneration and nonthermally activated charge transport on picosecond time scales. At ˜30 ps after photoexcitation at room temperature and at applied electric field of 1.2×104 V/cm, values obtained for the product of mobility and photogeneration efficiency, μη, in ADT-tri-isoproplysilylethynyl-(TIPS)-F, Pc-TIPS, and DCDHF films are ˜0.018-0.025, ˜0.01-0.022, and ˜0.002-0.004 cm2/V s, respectively, depending on the film quality, and are weakly electric field dependent. In functionalized ADT and Pc films, the power-law decay dynamics of the transient photoconductivity is observed, on time scales of up to ˜1 μs after photoexcitation, in the best samples. In contrast, in DCDHF amorphous glass, most of the photogenerated carriers are trapped within ˜200 ps. Transport of photoexcited carriers on longer time scales is probed by cw illumination through an optical chopper, with a variable chopper frequency. In contrast with what is observed on picosecond time scales, charge carriers on millisecond and longer time scales are predominantly localized, and are characterized by a broad distribution of carrier lifetimes. Such carriers make the principal contributions to dc photoconductivity.

Photoconductivity in nanostructured sulfur-doped V2O5 thin films

NASA Astrophysics Data System (ADS)

Mousavi, M.; Yazdi, Sh. Tabatabai

2016-03-01

In this paper, S-doped vanadium oxide thin films with doping levels up to 40 at.% are prepared via spray pyrolysis method on glass substrates, and the effect of S-doping on the structural and photoconductivity related properties of β-V2O5 thin films is studied. The results show that most of the films have been grown in the tetragonal β-V2O5 phase structure with the preferred orientation along [200]. With increasing the doping level, the samples tend to be amorphous. The structure of the samples reveals to be nanobelt-shaped whose width decreases from nearly 100 nm to 40 nm with S concentration. The photoconductivity measurements show that by increasing the S-doping level, the photosensitivity increases, which is due to the prolonged electron’s lifetime as a result of enhanced defect states acting as trap levels.

Photoconductivity response time in amorphous semiconductors

NASA Astrophysics Data System (ADS)

Adriaenssens, G. J.; Baranovskii, S. D.; Fuhs, W.; Jansen, J.; Öktü, Ö.

1995-04-01

The photoconductivity response time of amorphous semiconductors is examined theoretically on the basis of standard definitions for free- and trapped-carrier lifetimes, and experimentally for a series of a-Si1-xCx:H alloys with x<0.1. Particular attention is paid to its dependence on carrier generation rate and temperature. As no satisfactory agreement between models and experiments emerges, a simple theory is developed that can account for the experimental observations on the basis of the usual multiple-trappping ideas, provided a small probability of direct free-carrier recombination is included. The theory leads to a stretched-exponential photocurrent decay.

Radiation-induced extrinsic photoconductivity in Li-doped Si.

NASA Technical Reports Server (NTRS)

Fenimore, E.; Mortka, T.; Corelli, J. C.

1972-01-01

Investigation of the effects of lithium on radiation-produced complexes having long-time stability by examining the localized energy levels in the forbidden gap which give rise to extrinsic photoconductivity. The levels are found to disappear and in some cases shift with annealing in the 100-450 C temperature range. Due to the complexity of the system and the present lack of adequate theory, no complete analysis of the data obtained could be made.

Study of the impurity photoconductivity in p-InSb using epitaxial p{sup +} contacts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eminov, Sh. O., E-mail: shikhamirem@gmail.com

2016-08-15

The optical absorption coefficient α in p{sup +}-InSb layers (with hole concentrations of p ≈ 1 × 10{sup 17}–1.2 × 10{sup 19} cm{sup –3}), grown by liquid-phase epitaxy on p-InSb substrates, is measured in the spectral range of 5-12 µm at 90 K, and the impurity photoconductivity is measured (at 60 and 90 K) in p{sup +}–p structures. It is found that a in the p{sup +} layers reaches a value of 7000 cm{sup –1} (at p ≈ 2 × 10{sup 19} cm{sup –1}). It is shown that the measured substrate value of (α ≈1–3 cm{sup –1}) is overestimated inmore » comparison with estimates (α ≈ 0.1 cm{sup –1}) based on comparing the photoconductivity data. This discrepancy is explained by the fact that the optical transitions of holes responsible for photoconductivity are obscured by the excitation of electrons to the conduction band. The photoionization cross section for these transitions does not exceed 1 × 10{sup –15} cm{sup 2}.« less

Light controlled prebreakdown characteristics of a semi-insulating GaAs photoconductive switch

NASA Astrophysics Data System (ADS)

Xiangrong, Ma; Wei, Shi; Weili, Ji; Hong, Xue

2011-12-01

A 4 mm gap semi-insulating (SI) GaAs photoconductive switch (PCSS) was triggered by a pulse laser with a wavelength of 1064 nm and a pulse energy of 0.5 mJ. In the experiment, when the bias field was 4 kV, the switch did not induce self-maintained discharge but worked in nonlinear (lock-on) mode. The phenomenon is analyzed as follows: an exciton effect contributes to photoconduction in the generation and dissociation of excitons. Collision ionization, avalanche multiplication and the exciton effect can supply carrier concentration and energy when an outside light source was removed. Under the combined influence of these factors, the SI-GaAs PCSS develops into self-maintained discharge rather than just in the light-controlled prebreakdown status. The characteristics of the filament affect the degree of damage to the switch.

A π-gel scaffold for assembling fullerene to photoconducting supramolecular rods

PubMed Central

Nair, Vishnu Sukumaran; Mukhopadhyay, Rahul Dev; Saeki, Akinori; Seki, Shu; Ajayaghosh, Ayyappanpillai

2016-01-01

Nonequilibrium self-assembly of molecules holds a huge prospect as a tool for obtaining new-generation materials for future applications. Crystallization of neutral molecules within a supramolecular gel matrix is one example in which two nonequilibrium processes occur orthogonal to each other. On the other hand, electronically interacting donor-acceptor two-component systems are expected to form phase-miscible hybrid systems. Contrary to the expectation, we report the behavior of a π-gel, derived from oligo(p-phenylenevinylene), OPVA, as a scaffold for the phase separation and crystallization of fullerene (C60) to supramolecular rods with increased transient photoconductivity (φƩμmax = 2.4 × 10−4 cm2 V−1 s−1). The C60 supramolecular rods in the π-gel medium exhibited high photocurrent in comparison to C60 loaded in a non–π-gel medium. This finding provides an opportunity for large-scale preparation of micrometer-sized photoconducting rods of fullerenes for device application. PMID:27679815

Transient photoconductivity in the ferromagnetic semiconductor CdCr2Se4

NASA Technical Reports Server (NTRS)

Walser, A. D.; Alfano, R. R.

1988-01-01

The transient photoconductive response time of the ferromagnetic semiconductor CdCr2Se4 was measured to be smaller than 90 ps, the response time of the scope. The measurements were performed at room temperature (300 K) for 0.53 and 1.06 microns excitations using a mode locked frequency-doubled YAG laser.

Transversely-illuminated high current photoconductive switches with geometry-constrained conductivity path

DOEpatents

Nelson, Scott D.

2016-05-10

A photoconductive switch having a wide bandgap semiconductor material substrate between opposing electrodes, with one of the electrodes having an aperture or apertures at an electrode-substrate interface for transversely directing radiation therethrough from a radiation source into a triple junction region of the substrate, so as to geometrically constrain the conductivity path to within the triple junction region.

Self-sorted photoconductive xerogels† †Electronic supplementary information (ESI) available: Full experimental details, rheological data, pK a titrations, further NMR data, full details of the photoconductivity set-up, further photoconductivity measurements. See DOI: 10.1039/c6sc02644c Click here for additional data file.

PubMed Central

Draper, Emily R.; Lee, Jonathan R.; Wallace, Matthew; Jäckel, Frank; Cowan, Alexander J.

2016-01-01

We show that a perylene bisimide (PBI)-based gelator forms self-sorted mixtures with a stilbene-based gelator. To form the self-sorted gels, we use a slow pH change induced by the hydrolysis of glucono-δ-lactone (GdL) to gluconic acid. We prove that self-sorting occurs using NMR spectroscopy, UV-Vis spectroscopy, rheology, and viscometry. The corresponding xerogels are photoconductive. Importantly, the wavelength dependence of the photoconductive films is different to that of the films formed from the perylene bisimide alone. Transient absorption spectroscopy of the xerogels reveals changes in the spectrum of the PBI on the picosecond timescale in the presence of stilbene with a PBI radical anion being formed within 10 ps when the stilbene is present. The ability to form the PBI radical anion under visible light leads to the enhanced spectral response of the multicomponent gels. These systems therefore have potential as useful visible-active optoelectronics. PMID:28451108

Generation-recombination noise in extrinsic photoconductive detectors

NASA Technical Reports Server (NTRS)

Brukilacchio, T. J.; Skeldon, M. D.; Boyd, R. W.

1984-01-01

A theory of generation-recombination noise is presented and applied to the analysis of the performance limitations of extrinsic photoconductive detectors. The theory takes account both of the photoinduced generation of carriers and of thermal generation that is due to the finite temperature of the detector. Explicit formulas are derived that relate the detector response time, responsivity, and noise equivalent power to the material properties of the photoconductor (such as the presence of compensating impurities) and to the detector's operating conditions, such as its temperature and the presence of background radiation. The detector's performance is shown to degrade at high background levels because of saturation effects.

High power operation of a nitrogen doped, vanadium compensated, 6H-SiC extrinsic photoconductive switch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sullivan, J. S.

2014-04-28

We report the high power operation of nitrogen doped, vanadium compensated, 6H-SiC, extrinsic photoconductive switches with improved vanadium and nitrogen dopant density. Photoconductive switching tests are performed on 1 mm thick, m-plane, switch substrates at switch voltage and currents up to 17 kV and 1.5 kA, respectively. Sub-ohm minimum switch on resistance is achieved for peak optical intensities ≥35 MW/cm{sup 2} at 532 nm applied to the switch facet. A reduction of greater than nine orders of magnitude is observed in switch material resistivity between dark and illuminated states.

Persistent photoconductivity due to trapping of induced charges in Sn/ZnO thin film based UV photodetector

NASA Astrophysics Data System (ADS)

Yadav, Harish Kumar; Sreenivas, K.; Gupta, Vinay

2010-05-01

Photoconductivity relaxation in rf magnetron sputtered ZnO thin films integrated with ultrathin tin metal overlayer is investigated. Charge carriers induced at the ZnO-metal interface by the tin metal overlayer compensates the surface lying trap centers and leads to the enhanced photoresponse. On termination of ultraviolet radiation, recombination of the photoexcited electrons with the valence band holes leaves the excess carriers deeply trapped at the recombination center and holds the dark conductivity level at a higher value. Equilibrium between the recombination centers and valence band, due to trapped charges, eventually stimulates the persistent photoconductivity in the Sn/ZnO photodetectors.

Extreme Carrier Depletion and Superlinear Photoconductivity in Ultrathin Parallel-Aligned ZnO Nanowire Array Photodetectors Fabricated by Infiltration Synthesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nam, Chang-Yong; Stein, Aaron

Ultrathin semiconductor nanowires enable high-performance chemical sensors and photodetectors, but their synthesis and device integration by standard complementary metal-oxide-semiconductor (CMOS)-compatible processes remain persistent challenges. This work demonstrates fully CMOS-compatible synthesis and integration of parallel-aligned polycrystalline ZnO nanowire arrays into ultraviolet photodetectors via infiltration synthesis, material hybridization technique derived from atomic layer deposition. The nanowire photodetector features unique, high device performances originating from extreme charge carrier depletion, achieving photoconductive on–off ratios of >6 decades, blindness to visible light, and ultralow dark currents as low as 1 fA, the lowest reported for nanostructure-based photoconductive photodetectors. Surprisingly, the low dark current is invariantmore » with increasing number of nanowires and the photodetector shows unusual superlinear photoconductivity, observed for the first time in nanowires, leading to increasing detector responsivity and other parameters for higher incident light powers. Temperature-dependent carrier concentration and mobility reveal the photoelectrochemical-thermionic emission process at grain boundaries, responsible for the observed unique photodetector performances and superlinear photoconductivity. Here, the results elucidate fundamental processes responsible for photogain in polycrystalline nanostructures, providing useful guidelines for developing nanostructure-based detectors and sensors. Lastly, the developed fully CMOS-compatible nanowire synthesis and device fabrication methods also have potentials for scalable integration of nanowire sensor devices and circuitries.« less

Extreme Carrier Depletion and Superlinear Photoconductivity in Ultrathin Parallel-Aligned ZnO Nanowire Array Photodetectors Fabricated by Infiltration Synthesis

DOE PAGES

Nam, Chang-Yong; Stein, Aaron

2017-11-15

Ultrathin semiconductor nanowires enable high-performance chemical sensors and photodetectors, but their synthesis and device integration by standard complementary metal-oxide-semiconductor (CMOS)-compatible processes remain persistent challenges. This work demonstrates fully CMOS-compatible synthesis and integration of parallel-aligned polycrystalline ZnO nanowire arrays into ultraviolet photodetectors via infiltration synthesis, material hybridization technique derived from atomic layer deposition. The nanowire photodetector features unique, high device performances originating from extreme charge carrier depletion, achieving photoconductive on–off ratios of >6 decades, blindness to visible light, and ultralow dark currents as low as 1 fA, the lowest reported for nanostructure-based photoconductive photodetectors. Surprisingly, the low dark current is invariantmore » with increasing number of nanowires and the photodetector shows unusual superlinear photoconductivity, observed for the first time in nanowires, leading to increasing detector responsivity and other parameters for higher incident light powers. Temperature-dependent carrier concentration and mobility reveal the photoelectrochemical-thermionic emission process at grain boundaries, responsible for the observed unique photodetector performances and superlinear photoconductivity. Here, the results elucidate fundamental processes responsible for photogain in polycrystalline nanostructures, providing useful guidelines for developing nanostructure-based detectors and sensors. Lastly, the developed fully CMOS-compatible nanowire synthesis and device fabrication methods also have potentials for scalable integration of nanowire sensor devices and circuitries.« less

Dark current in multilayer stabilized amorphous selenium based photoconductive x-ray detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frey, Joel B.; Belev, George; Kasap, Safa O.

2012-07-01

We report on experimental results which show that the dark current in n-i-p structured, amorphous selenium films is independent of i-layer thickness in samples with consistently thick blocking layers. We have observed, however, a strong dependence on the n-layer thickness and positive contact metal chosen. These results indicate that the dominant source of the dark current is carrier injection from the contacts and any contribution from carriers thermally generated in the bulk of the photoconductive layer is negligible. This conclusion is supported by a description of the dark current transients at different applied fields by a model which assumes onlymore » carrier emission over a Schottky barrier. This model also predicts that while hole injection is initially dominant, some time after the application of the bias, electron injection may become the dominant source of dark current.« less

Electronic transport in NbSe₂ two-dimensional nanostructures: semiconducting characteristics and photoconductivity.

PubMed

Huang, Y H; Chen, R S; Zhang, J R; Huang, Y S

2015-12-07

The electronic transport properties of two-dimensional (2D) niobium diselenide (NbSe2) layer materials with two-hexagonal single-crystalline structures grown by chemical vapor transport were investigated. Those NbSe2 nanostructures isolated simply using mechanical exfoliation were found to exhibit lower conductivity and semiconducting properties, compared with their bulk metallic counterparts. Benefiting from lower dark conductivity, NbSe2 nanoflakes exhibit a remarkable photoresponse under different wavelengths and intensity excitations. The photocurrent responsivity and photoconductive gain can reach 3.8 A W(-1) and 300, respectively; these values are higher than those of graphene and MoS2 monolayers and are comparable with those of GaS and GaSe nanosheets. The presence of electron trap states at the surface was proposed as an explanation for the reduced dark conductivity and enhanced photoconductivity in the 2D NbSe2 nanostructures. This work identifies another possibility for the application of a metallic layer material as an optoelectronic component in addition to an ultrathin transparent conducting material.

Negative differential photoconductance in gold nanoparticle arrays in the Coulomb blockade regime.

PubMed

Mangold, Markus A; Calame, Michel; Mayor, Marcel; Holleitner, Alexander W

2012-05-22

We investigate the photoconductance of gold nanoparticle arrays in the Coulomb blockade regime. Two-dimensional, hexagonal crystals of nanoparticles are produced by self-assembly. The nanoparticles are weakly coupled to their neighbors by a tunneling conductance. At low temperatures, the single electron charging energy of the nanoparticles dominates the conductance properties of the array. The Coulomb blockade of the nanoparticles can be lifted by optical excitation with a laser beam. The optical excitation leads to a localized heating of the arrays, which in turn gives rise to a local change in conductance and a redistribution of the overall electrical potential in the arrays. We introduce a dual-beam optical excitation technique to probe the distribution of the electrical potential in the nanoparticle array. A negative differential photoconductance is the direct consequence of the redistribution of the electrical potential upon lifting of the Coulomb blockade. On the basis of our model, we calculate the optically induced current from the dark current-voltage characteristics of the nanoparticle array. The calculations closely reproduce the experimental observations.

Persistent photoconductivity in two-dimensional Mo 1-xW xSe 2–MoSe 2 van der Waals heterojunctions

DOE PAGES

Puretzky, Alexander A.; Basile, Leonardo; Idrobo, Juan Carlos; ...

2016-02-16

Van der Waals (vdW) heterojunctions consisting of vertically-stacked individual or multiple layers of two-dimensional (2D) layered semiconductors, especially the transition metal dichalcogenides (TMDs), are fascinating new artificial solids just nanometers-thin that promise novel optoelectronic functionalities due to the sensitivity of their electronic and optical properties to strong quantum confinement and interfacial interactions. Here, monolayers of n-type MoSe 2 and p-type Mo 1-xW xSe 2–MoSe 2 are grown by vapor transport methods, then transferred and stamped to form artificial vdW heterostructures with different interlayer orientations. Atomic-resolution Z-contrast electron microscopy and electron diffraction are used to characterize both the individual monolayers andmore » the atomic registry between layers in the bilayer vdW heterostructures. These measurements are compared with photoluminescence and low-frequency Raman spectroscopy, which indicates strong interlayer coupling in heterostructures. Remarkably, the heterojunctions exhibit an unprecedented photoconductivity effect that persists at room temperature for several days. This persistent photoconductivity is shown to be tunable by applying a gate bias that equilibrates the charge distribution. Furthermore, these measurements indicate that such ultrathin vdW heterojunctions can function as rewritable optoelectronic switches or memory elements under time-dependent photo-illumination, an effect which appears promising for new monolayer TMDs-based optoelectronic devices applications.« less

Organic photovoltaic cells utilizing ultrathin sensitizing layer

DOEpatents

Forrest, Stephen R [Ann Arbor, MI; Yang, Fan [Piscataway, NJ; Rand, Barry P [Somers, NY

2011-09-06

A photosensitive device includes a plurality of organic photoconductive materials disposed in a stack between a first electrode and a second electrode, including a first continuous layer of donor host material, a second continuous layer of acceptor host material, and at least one other organic photoconductive material disposed as a plurality of discontinuous islands between the first continuous layer and the second continuous layer. Each of these other photoconductive materials has an absorption spectra different from the donor host material and the acceptor host material. Preferably, each of the discontinuous islands consists essentially of a crystallite of the respective organic photoconductive material, and more preferably, the crystallites are nanocrystals.

Vantage sensitivity: individual differences in response to positive experiences.

PubMed

Pluess, Michael; Belsky, Jay

2013-07-01

The notion that some people are more vulnerable to adversity as a function of inherent risk characteristics is widely embraced in most fields of psychology. This is reflected in the popularity of the diathesis-stress framework, which has received a vast amount of empirical support over the years. Much less effort has been directed toward the investigation of endogenous factors associated with variability in response to positive influences. One reason for the failure to investigate individual differences in response to positive experiences as a function of endogenous factors may be the absence of adequate theoretical frameworks. According to the differential-susceptibility hypothesis, individuals generally vary in their developmental plasticity regardless of whether they are exposed to negative or positive influences--a notion derived from evolutionary reasoning. On the basis of this now well-supported proposition, we advance herein the new concept of vantage sensitivity, reflecting variation in response to exclusively positive experiences as a function of individual endogenous characteristics. After distinguishing vantage sensitivity from theoretically related concepts of differential-susceptibility and resilience, we review some recent empirical evidence for vantage sensitivity featuring behavioral, physiological, and genetic factors as moderators of a wide range of positive experiences ranging from family environment and psychotherapy to educational intervention. Thereafter, we discuss genetic and environmental factors contributing to individual differences in vantage sensitivity, potential mechanisms underlying vantage sensitivity, and practical implications. 2013 APA, all rights reserved

Effect of cadmium-selenide quantum dots on the conductivity and photoconductivity of nanocrystalline indium oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Il’in, A. S., E-mail: as.ilin@physics.msu.ru; Fantina, N. P.; Martyshov, M. N.

The effect of cadmium-selenide quantum dots addition on the electrical and photoelectric properties of nanocrystalline indium oxide with nanocrystal dimensions in the range from 7 to 40 nm is studied. By impedance spectroscopy, it is shown that the addition of quantum dots substantially influences the resistance of interfaces between In{sub 2}O{sub 3} crystals. A change in the character of the photoconductivity spectrum of In{sub 2}O{sub 3} upon the addition of CdSe quantum dots is detected, and it is established that this change depends on the In{sub 2}O{sub 3}-nanocrystal dimensions. An energy band diagram is proposed to explain the observed changemore » in the photoconductivity spectrum of In{sub 2}O{sub 3} upon the addition of CdSe quantum dots.« less

Analytical expression for position sensitivity of linear response beam position monitor having inter-electrode cross talk

NASA Astrophysics Data System (ADS)

Kumar, Mukesh; Ojha, A.; Garg, A. D.; Puntambekar, T. A.; Senecha, V. K.

2017-02-01

According to the quasi electrostatic model of linear response capacitive beam position monitor (BPM), the position sensitivity of the device depends only on the aperture of the device and it is independent of processing frequency and load impedance. In practice, however, due to the inter-electrode capacitive coupling (cross talk), the actual position sensitivity of the device decreases with increasing frequency and load impedance. We have taken into account the inter-electrode capacitance to derive and propose a new analytical expression for the position sensitivity as a function of frequency and load impedance. The sensitivity of a linear response shoe-box type BPM has been obtained through simulation using CST Studio Suite to verify and confirm the validity of the new analytical equation. Good agreement between the simulation results and the new analytical expression suggest that this method can be exploited for proper designing of BPM.

Photoconductivity in reactively evaporated copper indium selenide thin films

NASA Astrophysics Data System (ADS)

Urmila, K. S.; Asokan, T. Namitha; Pradeep, B.; Jacob, Rajani; Philip, Rachel Reena

2014-01-01

Copper indium selenide thin films of composition CuInSe2 with thickness of the order of 130 nm are deposited on glass substrate at a temperature of 423 ±5 K and pressure of 10-5 mbar using reactive evaporation, a variant of Gunther's three temperature method with high purity Copper (99.999%), Indium (99.999%) and Selenium (99.99%) as the elemental starting materials. X-ray diffraction (XRD) studies shows that the films are polycrystalline in nature having preferred orientation of grains along the (112) plane. The structural type of the film is found to be tetragonal with particle size of the order of 32 nm. The structural parameters such as lattice constant, particle size, dislocation density, number of crystallites per unit area and strain in the film are also evaluated. The surface morphology of CuInSe2 films are studied using 2D and 3D atomic force microscopy to estimate the grain size and surface roughness respectively. Analysis of the absorption spectrum of the film recorded using UV-Vis-NIR Spectrophotometer in the wavelength range from 2500 nm to cutoff revealed that the film possess a direct allowed transition with a band gap of 1.05 eV and a high value of absorption coefficient (α) of 106 cm-1 at 570 nm. Photoconductivity at room temperature is measured after illuminating the film with an FSH lamp (82 V, 300 W). Optical absorption studies in conjunction with the good photoconductivity of the prepared p-type CuInSe2 thin films indicate its suitability in photovoltaic applications.

Characterization of opto-electrical enhancement of tandem photoelectrochemical cells by using photoconductive-AFM

NASA Astrophysics Data System (ADS)

Park, Sun-Young; Elbersen, Rick; Huskens, Jurriaan; Gardeniers, Han; Lee, Joo-Yul; Mul, Guido; Heo, Jinhee

2017-07-01

Solar-to-hydrogen conversion by water splitting in photoelectrochemical cells (PECs) is a promising approach to alleviate problems associated with intermittency in solar energy supply and demand. Several interfacial resistances in photoelectrodes limit the performance of such cells, while the properties of interfaces are not easy to analyze in situ. We applied photoconductive-AFM to analyze the performance of WO3/p+n Si photoanodes, containing an ultra-thin metal interface of either Au or Pt. The Au interface consisted of Au nanoparticles with well-ordered interspacing, while Pt was present in the form of a continuous film. Photoconductive-AFM data show that upon illumination significantly larger currents are measured for the WO3/p+n Si anode equipped with the Au interface, as compared to the WO3/p+n Si anode with the Pt interface, in agreement with the better performance of the former electrode in a photoelectrochemical cell. The remarkable performance of the Au-containing electrode is proposed to be the result of favorable electron-hole recombination rates induced by the Au nanoparticles in a plasmon resonance excited state.

Curved position-sensitive detector for X-ray crystallography

NASA Astrophysics Data System (ADS)

Izumi, T.

1980-11-01

A new curved position-sensitive proportional detector has been constructed for X-ray crystallography. A very hard steel wire 0.2 mm in diameter was used as a single anode wire. It was bent to a radius of 6.5 cm and was suspended elastically in a wide 160° 2θ angular aperture. An amplifier and ADC-per-cathode strip system was made in order to encode the position. The spatial resolution is better than 0.37 mm (fwhm) along the curved anode wire, and this value corresponds to an angular resolution of 0.28° in 2θ. It is shown that a thick hard anode wire is quite suitable for use as a curved position-sensitive detector.

Sensitivity of PbSnTe:In films to the radiation of free electron laser

NASA Astrophysics Data System (ADS)

Akimov, A. N.; Epov, V. S.; Klimov, A. E.; Kubarev, V. V.; Paschin, N. S.

2018-01-01

The analysis of experimental data on the observation of photoresponse in narrow gap semiconductor Pb1-x Sn x Te:In films grown by the method of molecular beam epitaxy, exposing samples to the powerful radiation of the Novosibirsk free electron laser (wavelength range of about 70-240 μm) under different measurement conditions, is presented in the paper. Both the positive and negative photoconductivities were detected. In a magnetic field, the resonance-type photoconductivity was observed. The results are discussed within the framework of the model taking into account the existence of different capture levels in PbSnTe.

Generation and detection of edge magnetoplasmons in a quantum Hall system using a photoconductive switch

NASA Astrophysics Data System (ADS)

Lin, Chaojing; Morita, Kyosuke; Muraki, Koji; Fujisawa, Toshimasa

2018-04-01

Edge magnetoplasmons (EMPs) are unidirectional charge density waves travelling in an edge channel of a two-dimensional electron gas in the quantum Hall regime. We present both generation and detection schemes with a photoconductive switch (PCS) for EMPs. Here, the conductance of the PCS is modulated by irradiation with a laser beam, whose amplitude can be modulated by an external signal. When the PCS is used as a generator, the electrical current from the PCS is injected into the edge channel to excite EMPs. When the PCS is used as a detector, the electronic potential induced by EMPs is applied to the PCS with a modulated laser beam so as to constitute a phase-sensitive measurement. For both experiments, we confirm that the time of flight for the EMPs increases with the magnetic field in agreement with the EMP characteristics. Combination of the two schemes would be useful in investigating and utilizing EMPs at higher frequencies.

Dual-wavelength photo-Hall effect spectroscopy of deep levels in high resistive CdZnTe with negative differential photoconductivity

NASA Astrophysics Data System (ADS)

Musiienko, A.; Grill, R.; Moravec, P.; Korcsmáros, G.; Rejhon, M.; Pekárek, J.; Elhadidy, H.; Šedivý, L.; Vasylchenko, I.

2018-04-01

Photo-Hall effect spectroscopy was used in the study of deep levels in high resistive CdZnTe. The monochromator excitation in the photon energy range 0.65-1.77 eV was complemented by a laser diode high-intensity excitation at selected photon energies. A single sample characterized by multiple unusual features like negative differential photoconductivity and anomalous depression of electron mobility was chosen for the detailed study involving measurements at both the steady and dynamic regimes. We revealed that the Hall mobility and photoconductivity can be both enhanced and suppressed by an additional illumination at certain photon energies. The anomalous mobility decrease was explained by an excitation of the inhomogeneously distributed deep level at the energy Ev + 1.0 eV, thus enhancing potential non-uniformities. The appearance of negative differential photoconductivity was interpreted by an intensified electron occupancy of that level by a direct valence band-to-level excitation. Modified Shockley-Read-Hall theory was used for fitting experimental results by a model comprising five deep levels. Properties of the deep levels and their impact on the device performance were deduced.

Anomalous photoconductive behavior of a single InAs nanowire photodetector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Junshuai; Yan, Xin; Sun, Fukuan

2015-12-28

We report on a bare InAs nanowire photodetector which exhibits an anomalous photoconductive behavior. Under low-power illumination, the current is smaller than the dark current, and monotonously decreases as the excitation power increases. When the excitation power is high enough, the current starts to increase normally. The phenomenon is attributed to different electron mobilities in the “core” and “shell” of a relatively thick nanowire originating from the surface effect, which result in a quickly dropped “core current” and slowly increased “shell current” under illumination.

Theoretical Noise Analysis on a Position-sensitive Metallic Magnetic Calorimeter

NASA Technical Reports Server (NTRS)

Smith, Stephen J.

2007-01-01

We report on the theoretical noise analysis for a position-sensitive Metallic Magnetic Calorimeter (MMC), consisting of MMC read-out at both ends of a large X-ray absorber. Such devices are under consideration as alternatives to other cryogenic technologies for future X-ray astronomy missions. We use a finite-element model (FEM) to numerically calculate the signal and noise response at the detector outputs and investigate the correlations between the noise measured at each MMC coupled by the absorber. We then calculate, using the optimal filter concept, the theoretical energy and position resolution across the detector and discuss the trade-offs involved in optimizing the detector design for energy resolution, position resolution and count rate. The results show, theoretically, the position-sensitive MMC concept offers impressive spectral and spatial resolving capabilities compared to pixel arrays and similar position-sensitive cryogenic technologies using Transition Edge Sensor (TES) read-out.

Cryocooled terahertz photoconductive detector system with background-limited performance in 1.5-4 THz frequency range.

PubMed

Aoki, Makoto; Hiromoto, Norihisa

2015-10-01

We describe a 4-K-cryocooled dual-band terahertz (THz) photoconductive detector system with background-limited performance. The detector system comprises two THz photoconductive detectors covering a response in a wide frequency range from 1.5 to 4 THz, low noise amplifiers, optical low-pass filters to eliminate input radiation of higher frequencies, and a mechanical 4 K Gifford-McMahon refrigerator that provides practical and convenient operation without a liquid He container. The electrical and optical performances of the THz detector system were evaluated at a detector temperature of 4 K under 300 K background radiation. We proved that the detector system can achieve background-limited noise-equivalent-power on the order of 10(-14) W/Hz(1/2) in the frequency range from 1.5 to 4 THz even if the vibration noise of the mechanical refrigerator is present.

Reconstruction-free sensitive wavefront sensor based on continuous position sensitive detectors.

PubMed

Godin, Thomas; Fromager, Michael; Cagniot, Emmanuel; Brunel, Marc; Aït-Ameur, Kamel

2013-12-01

We propose a new device that is able to perform highly sensitive wavefront measurements based on the use of continuous position sensitive detectors and without resorting to any reconstruction process. We demonstrate experimentally its ability to measure small wavefront distortions through the characterization of pump-induced refractive index changes in laser material. In addition, it is shown using computer-generated holograms that this device can detect phase discontinuities as well as improve the quality of sharp phase variations measurements. Results are compared to reference Shack-Hartmann measurements, and dramatic enhancements are obtained.

High speed curved position sensitive detector

DOEpatents

Hendricks, Robert W.; Wilson, Jack W.

1989-01-01

A high speed curved position sensitive porportional counter detector for use in x-ray diffraction, the detection of 5-20 keV photons and the like. The detector employs a planar anode assembly of a plurality of parallel metallic wires. This anode assembly is supported between two cathode planes, with at least one of these cathode planes having a serpentine resistive path in the form of a meander having legs generally perpendicular to the anode wires. This meander is produced by special microelectronic fabrication techniques whereby the meander "wire" fans outwardly at the cathode ends to produce the curved aspect of the detector, and the legs of the meander are small in cross-section and very closely spaced whereby a spatial resolution of about 50 .mu.m can be achieved. All of the other performance characteristics are about as good or better than conventional position sensitive proportional counter type detectors. Count rates of up to 40,000 counts per second with 0.5 .mu.s shaping time constants are achieved.

Surface State-Dominated Photoconduction and THz Generation in Topological Bi2Te2Se Nanowires

PubMed Central

2017-01-01

Topological insulators constitute a fascinating class of quantum materials with nontrivial, gapless states on the surface and insulating bulk states. By revealing the optoelectronic dynamics in the whole range from femto- to microseconds, we demonstrate that the long surface lifetime of Bi2Te2Se nanowires allows us to access the surface states by a pulsed photoconduction scheme and that there is a prevailing bolometric response of the surface states. The interplay of the surface and bulk states dynamics on the different time scales gives rise to a surprising physical property of Bi2Te2Se nanowires: their pulsed photoconductance changes polarity as a function of laser power. Moreover, we show that single Bi2Te2Se nanowires can be used as THz generators for on-chip high-frequency circuits at room temperature. Our results open the avenue for single Bi2Te2Se nanowires as active modules in optoelectronic high-frequency and THz circuits. PMID:28081604

Photoconductivity of few-layered p-WSe2 phototransistors via multi-terminal measurements

NASA Astrophysics Data System (ADS)

Pradhan, Nihar R.; Garcia, Carlos; Holleman, Joshua; Rhodes, Daniel; Parker, Chason; Talapatra, Saikat; Terrones, Mauricio; Balicas, Luis; McGill, Stephen A.

2016-12-01

Recently, two-dimensional materials and in particular transition metal dichalcogenides (TMDs) have been extensively studied because of their strong light-matter interaction and the remarkable optoelectronic response of their field-effect transistors (FETs). Here, we report a photoconductivity study from FETs built from few-layers of p-WSe2 measured in a multi-terminal configuration under illumination by a 532 nm laser source. The photogenerated current was measured as a function of the incident optical power, of the drain-to-source bias and of the gate voltage. We observe a considerably larger photoconductivity when the phototransistors were measured via a four-terminal configuration when compared to a two-terminal one. For an incident laser power of 248 nW, we extract 18 A W-1 and ˜4000% for the two-terminal responsivity (R) and the concomitant external quantum efficiency (EQE) respectively, when a bias voltage V ds = 1 V and a gate voltage V bg = 10 V are applied to the sample. R and EQE are observed to increase by 370% to ˜85 A W-1 and ˜20 000% respectively, when using a four-terminal configuration. Thus, we conclude that previous reports have severely underestimated the optoelectronic response of transition metal dichalcogenides, which in fact reveals a remarkable potential for photosensing applications.

Study of GaN nanowires converted from β-Ga2O3 and photoconduction in a single nanowire

NASA Astrophysics Data System (ADS)

Kumar, Mukesh; Kumar, Sudheer; Chauhan, Neha; Sakthi Kumar, D.; Kumar, Vikram; Singh, R.

2017-08-01

The formation of GaN nanowires from β-Ga2O3 nanowires and photoconduction in a fabricated single GaN nanowire device has been studied. Wurtzite phase GaN were formed from monoclinic β-Ga2O3 nanowires with or without catalyst particles at their tips. The formation of faceted nanostructures from catalyst droplets presented on a nanowire tip has been discussed. The nucleation of GaN phases in β-Ga2O3 nanowires and their subsequent growth due to interfacial strain energy has been examined using a high resolution transmission electron microscope. The high quality of the converted GaN nanowire is confirmed by fabricating single nanowire photoconducting devices which showed ultra high responsivity under ultra-violet illumination.

Humidity sensor and ultraviolet photodetector based on carrier trapping effect and negative photoconductivity in graphene quantum dots

NASA Astrophysics Data System (ADS)

Zhuang, ShenDong; Chen, Yan; Zhang, WeiChao; Chen, Zhuo; Wang, ZhenLin

2018-01-01

We report on the experimental realization of a graphene quantum dots (GQD)-based humidity sensor and ultraviolet (UV) photodetector. We demonstrate that the conductance of the GQD increases linearly with increasing relative humidity (RH) of the surrounding environment due to the carrier trapping effect, which forms the basis of a humidity sensor. When the sensor is operated in the dark state, the sensitivity can reach as high as 0.48 nS RH -1. The GQD are also found to exhibit light intensity dependent negative photoconductivity under the UV irradiation, which can be exploited for UV detection. As a result of these carrier trapping and de-trapping processes, the performance of the photodetector can be significantly improved with the increasing RH, and the photoresponsivity can reach a high value of -418.1 μA W-1 in the high humid state of RH=90%.

Multi-line triggering and interdigitated electrode structure for photoconductive semiconductor switches

DOEpatents

Mar, Alan [Albuquerque, NM; Zutavern, Fred J [Albuquerque, NM; Loubriel, Guillermo [Albuquerque, NM

2007-02-06

An improved photoconductive semiconductor switch comprises multiple-line optical triggering of multiple, high-current parallel filaments between the switch electrodes. The switch can also have a multi-gap, interdigitated electrode for the generation of additional parallel filaments. Multi-line triggering can increase the switch lifetime at high currents by increasing the number of current filaments and reducing the current density at the contact electrodes in a controlled manner. Furthermore, the improved switch can mitigate the degradation of switching conditions with increased number of firings of the switch.

Biotunable Nanoplasmonic Filter on Few-Layer MoS2 for Rapid and Highly Sensitive Cytokine Optoelectronic Immunosensing.

PubMed

Park, Younggeun; Ryu, Byunghoon; Oh, Bo-Ram; Song, Yujing; Liang, Xiaogan; Kurabayashi, Katsuo

2017-06-27

Monitoring of the time-varying immune status of a diseased host often requires rapid and sensitive detection of cytokines. Metallic nanoparticle-based localized surface plasmon resonance (LSPR) biosensors hold promise to meet this clinical need by permitting label-free detection of target biomolecules. These biosensors, however, continue to suffer from relatively low sensitivity as compared to conventional immunoassay methods that involve labeling processes. Their response speeds also need to be further improved to enable rapid cytokine quantification for critical care in a timely manner. In this paper, we report an immunobiosensing device integrating a biotunable nanoplasmonic optical filter and a highly sensitive few-layer molybdenum disulfide (MoS 2 ) photoconductive component, which can serve as a generic device platform to meet the need of rapid cytokine detection with high sensitivity. The nanoplasmonic filter consists of anticytokine antibody-conjugated gold nanoparticles on a SiO 2 thin layer that is placed 170 μm above a few-layer MoS 2 photoconductive flake device. The principle of the biosensor operation is based on tuning the delivery of incident light to the few-layer MoS 2 photoconductive flake thorough the nanoplasmonic filter by means of biomolecular surface binding-induced LSPR shifts. The tuning is dependent on cytokine concentration on the nanoplasmonic filter and optoelectronically detected by the few-layer MoS 2 device. Using the developed optoelectronic biosensor, we have demonstrated label-free detection of IL-1β, a pro-inflammatory cytokine, with a detection limit as low as 250 fg/mL (14 fM), a large dynamic range of 10 6 , and a short assay time of 10 min. The presented biosensing approach could be further developed and generalized for point-of-care diagnosis, wearable bio/chemical sensing, and environmental monitoring.

Photoluminescence and photoconductivity studies on amorphous and crystalline ZnO thin films obtained by sol-gel method

NASA Astrophysics Data System (ADS)

Valverde-Aguilar, G.; Manríquez Zepeda, J. L.

2015-03-01

Amorphous and crystalline ZnO thin films were obtained by the sol-gel process. A precursor solution of ZnO was synthesized by using zinc acetate dehydrate as inorganic precursor at room temperature. The films were spin-coated on silicon and glass wafers and gelled in humid air. The films were calcined at 450 °C for 15 min to produce ZnO nanocrystals with a wurtzite structure. Crystalline ZnO film exhibits an absorption band located at 359 nm (3.4 eV). Photoconductivity technique was used to determine the charge transport mechanism on both kinds of films. Experimental data were fitted with straight lines at darkness and under illumination at 355 and 633 nm wavelengths. This indicates an ohmic behavior. The photovoltaic and photoconductivity parameters were determined from the current density versus the applied electrical field results.

Surface state-dominated photoconduction and THz-generation in topological Bi2Te2Se-nanowires

NASA Astrophysics Data System (ADS)

Seifert, Paul; Vaklinova, Kristina; Kern, Klaus; Burghard, Marko; Holleitner, Alexander

Topological insulators constitute a fascinating class of quantum materials with non-trivial, gapless states on the surface and trivial, insulating bulk states. In revealing the optoelectronic dynamics in the whole range from femto- to microseconds, we demonstrate that the long surface lifetime of Bi2Te2Se-nanowires allows to access the surface states by a pulsed photoconduction scheme and that there is a prevailing bolometric response of the surface states. The interplay of the surface state dynamics on the different timescales gives rise to a surprising physical property of Bi2Te2Se-nanowires: their pulsed photoconductance changes polarity as a function of laser power. Moreover, we show that single Bi2Te2Se-nanowires can be used as THz-generators for on-chip high-frequency circuits at room temperature. Our results open the avenue for single Bi2Te2Se-nanowires as active modules in optoelectronic high-frequency and THz-circuits. We acknowledge financial support by the ERC Grant NanoReal (n306754).

Concept and design of a beam blanker with integrated photoconductive switch for ultrafast electron microscopy.

PubMed

Weppelman, I G C; Moerland, R J; Hoogenboom, J P; Kruit, P

2018-01-01

We present a new method to create ultrashort electron pulses by integrating a photoconductive switch with an electrostatic deflector. This paper discusses the feasibility of such a system by analytical and numerical calculations. We argue that ultrafast electron pulses can be achieved for micrometer scale dimensions of the blanker, which are feasible with MEMS-based fabrication technology. According to basic models, the design presented in this paper is capable of generating 100 fs electron pulses with spatial resolutions of less than 10 nm. Our concept for an ultrafast beam blanker (UFB) may provide an attractive alternative to perform ultrafast electron microscopy, as it does not require modification of the microscope nor realignment between DC and pulsed mode of operation. Moreover, only low laser pulse energies are required. Due to its small dimensions the UFB can be inserted in the beam line of a commercial microscope via standard entry ports for blankers or variable apertures. The use of a photoconductive switch ensures minimal jitter between laser and electron pulses. Copyright © 2017 Elsevier B.V. All rights reserved.

Photoconductive ZnO Films Printed on Flexible Substrates by Inkjet and Aerosol Jet Techniques

NASA Astrophysics Data System (ADS)

Winarski, D. J.; Kreit, E.; Heckman, E. M.; Flesburg, E.; Haseman, M.; Aga, R. S.; Selim, F. A.

2018-02-01

Zinc oxide (ZnO) thin films have remarkable versatility in sensor applications. Here, we report simple ink synthesis and printing methods to deposit ZnO photodetectors on a variety of flexible and transparent substrates, including polyimide (Kapton), polyethylene terephthalate, cyclic olefin copolymer (TOPAS), and quartz. X-ray diffraction analysis revealed the dependence of the film orientation on the substrate type and sintering method, and ultraviolet-visible (UV-Vis) absorption measurements revealed a band edge near 380 nm. van der Pauw technique was used to measure the resistivity of undoped ZnO and indium/gallium-codoped ZnO (IGZO) films. IGZO films showed lower resistivity and larger average grain size compared with undoped ZnO films due to addition of In3+ and Ga3+, which act as donors. A 365-nm light-emitting diode was used to photoirradiate the films to study their photoconductive response as a function of light intensity at 300 K. The results revealed that ZnO films printed by aerosol jet and inkjet techniques exhibited five orders of magnitude photoconductivity, indicating that such films are viable options for use in flexible photodetectors.

Enhancement of photovoltaic effects and photoconductivity observed in Co-doped amorphous carbon/silicon heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Y. C.; Gao, J., E-mail: jugao@hku.hk

2016-08-22

Co-doped amorphous carbon (Co-C)/silicon heterostructures were fabricated by growing Co-C films on n-type Si substrates using pulsed laser deposition. A photovoltaic effect (PVE) has been observed at room temperature. Open-circuit voltage V{sub oc} = 320 mV and short-circuit current density J{sub sc }= 5.62 mA/cm{sup 2} were measured under illumination of 532-nm light with the power of 100 mW/cm{sup 2}. In contrast, undoped amorphous carbon/Si heterostructures revealed no significant PVE. Based on the PVE and photoconductivity (PC) investigated at different temperatures, it was found that the energy conversion efficiency increased with increasing the temperature and reached the maximum at room temperature, while the photoconductivity showed amore » reverse temperature dependence. The observed competition between PVE and PC was correlated with the way to distribute absorbed photons. The possible mechanism, explaining the enhanced PVE and PC in the Co-C/Si heterostructures, might be attributed to light absorption enhanced by localized surface plasmons in Co nanoparticles embedded in the carbon matrix.« less

Cryocooled terahertz photoconductive detector system with background-limited performance in 1.5–4 THz frequency range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aoki, Makoto; Hiromoto, Norihisa, E-mail: dnhirom@ipc.shizuoka.ac

2015-10-15

We describe a 4-K-cryocooled dual-band terahertz (THz) photoconductive detector system with background-limited performance. The detector system comprises two THz photoconductive detectors covering a response in a wide frequency range from 1.5 to 4 THz, low noise amplifiers, optical low-pass filters to eliminate input radiation of higher frequencies, and a mechanical 4 K Gifford-McMahon refrigerator that provides practical and convenient operation without a liquid He container. The electrical and optical performances of the THz detector system were evaluated at a detector temperature of 4 K under 300 K background radiation. We proved that the detector system can achieve background-limited noise-equivalent-power onmore » the order of 10{sup −14} W/Hz{sup 1/2} in the frequency range from 1.5 to 4 THz even if the vibration noise of the mechanical refrigerator is present.« less

Photoconductive method for measuring light transmission to the root of metal-ceramic and all-ceramic restorations.

PubMed

Hsieh, Yun-Lin; Lai, Yu-Lin; Chen, Hui-Lin; Hung, Cheng-Yuan; Chen, Xiu-Ling; Lee, Shyh-Yuan

2008-09-01

In this study, the authors attempted to develop a photoconductive method for measuring light transmission through a crown restoration to the root dentin; metal-ceramic crowns with four coping designs (metal collar, and metal framework ending 0, 1, and 2mm coronal to the axiogingival line angle) and two all-ceramic crowns (Empress II and In-Ceram Alumina) were compared. According to pre-registered templates, 36 crowns were fabricated for an extracted central incisor. A cadmium sulfide (CdS) photoconductive cell was secured onto the root of a tooth, which was fixed in a light box. The validity and reliability of the experimental design were verified, and the impedance of the cell was recorded when the crowns were placed on the prepared tooth with or without try-in pastes under a constant luminance. A significant correlation (r= -0.99, p<0.001) was found between the light intensity and impedance of the CdS cell, and a 1.15% coefficient of variation between repeated measurements was observed. In this study, Empress II crowns had the smallest impedance, indicating that they provided the best light transmission. Conventional metal-ceramic crowns had the least light transmission, which was significantly improved by reducing the metal collar (p<0.05). The framework of metal-ceramic crowns which ended 2mm coronal to the axiogingival line angle showed as much light transmission as the In-Ceram crowns. The impedance increased when try-in pastes were employed in all test groups. The photoconductive method was proven to be a reliable technique for measuring the light transmitted through restorations into the adjacent tissue.

Highly efficient quantum dot-based photoconductive THz materials and devices

NASA Astrophysics Data System (ADS)

Rafailov, E. U.; Leyman, R.; Carnegie, D.; Bazieva, N.

2013-09-01

We demonstrate Terahertz (THz) signal sources based on photoconductive (PC) antenna devices comprising active layers of InAs semiconductor quantum dots (QDs) on GaAs. Antenna structures comprised of multiple active layers of InAs:GaAs PC materials are optically pumped using ultrashort pulses generated by a Ti:Sapphire laser and CW dualwavelength laser diodes. We also characterised THz output signals using a two-antenna coherent detection system. We discuss preliminary performance data from such InAs:GaAs THz devices which exhibit efficient emission of both pulsed and continuous wave (CW) THz signals and significant optical-to-THz conversion at both absorption wavelength ranges, <=850 nm and <=1300 nm.

Defective TiO 2 with high photoconductive gain for efficient and stable planar heterojunction perovskite solar cells

DOE PAGES

Li, Yanbo; Cooper, Jason K.; Liu, Wenjun; ...

2016-08-18

Formation of planar heterojunction perovskite solar cells exhibiting both high efficiency and stability under continuous operation remains a challenge. Here, we show this can be achieved by using a defective TiO 2 thin film as the electron transport layer. TiO 2 layers with native defects are deposited by electron beam evaporation in an oxygen-deficient environment. Deep-level hole traps are introduced in the TiO 2 layers and contribute to a high photoconductive gain and reduced photocatalytic activity. The high photoconductivity of the TiO 2 electron transport layer leads to improved efficiency for the fabricated planar devices. A maximum power conversion efficiencymore » of 19.0% and an average PCE of 17.5% are achieved. In addition, the reduced photocatalytic activity of the TiO 2 layer leads to enhanced long-Term stability for the planar devices. Under continuous operation near the maximum power point, an efficiency of over 15.4% is demonstrated for 100 h.« less

Sensitivity of GRETINA position resolution to hole mobility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prasher, V. S.; Cromaz, M.; Merchan, E.

The sensitivity of the position resolution of the gamma-ray tracking array GRETINA to the hole charge-carrier mobility parameter is investigated. The χ 2 results from a fit of averaged signal (“superpulse”) data exhibit a shallow minimum for hole mobilities 15% lower than the currently adopted values. Calibration data on position resolution is analyzed, together with simulations that isolate the hole mobility dependence of signal decomposition from other effects such as electronics cross-talk. Our results effectively exclude hole mobility as a dominant parameter for improving the position resolution for reconstruction of gamma-ray interaction points in GRETINA.

Sensitivity of GRETINA position resolution to hole mobility

DOE PAGES

Prasher, V. S.; Cromaz, M.; Merchan, E.; ...

2017-02-01

The sensitivity of the position resolution of the gamma-ray tracking array GRETINA to the hole charge-carrier mobility parameter is investigated. The χ 2 results from a fit of averaged signal (“superpulse”) data exhibit a shallow minimum for hole mobilities 15% lower than the currently adopted values. Calibration data on position resolution is analyzed, together with simulations that isolate the hole mobility dependence of signal decomposition from other effects such as electronics cross-talk. Our results effectively exclude hole mobility as a dominant parameter for improving the position resolution for reconstruction of gamma-ray interaction points in GRETINA.

Implementation of Complex Signal Processing Algorithms for Position-Sensitive Microcalorimeters

NASA Technical Reports Server (NTRS)

Smith, Stephen J.

2008-01-01

We have recently reported on a theoretical digital signal-processing algorithm for improved energy and position resolution in position-sensitive, transition-edge sensor (POST) X-ray detectors [Smith et al., Nucl, lnstr and Meth. A 556 (2006) 2371. PoST's consists of one or more transition-edge sensors (TES's) on a large continuous or pixellated X-ray absorber and are under development as an alternative to arrays of single pixel TES's. PoST's provide a means to increase the field-of-view for the fewest number of read-out channels. In this contribution we extend the theoretical correlated energy position optimal filter (CEPOF) algorithm (originally developed for 2-TES continuous absorber PoST's) to investigate the practical implementation on multi-pixel single TES PoST's or Hydras. We use numerically simulated data for a nine absorber device, which includes realistic detector noise, to demonstrate an iterative scheme that enables convergence on the correct photon absorption position and energy without any a priori assumptions. The position sensitivity of the CEPOF implemented on simulated data agrees very well with the theoretically predicted resolution. We discuss practical issues such as the impact of random arrival phase of the measured data on the performance of the CEPOF. The CEPOF algorithm demonstrates that full-width-at- half-maximum energy resolution of < 8 eV coupled with position-sensitivity down to a few 100 eV should be achievable for a fully optimized device.

Bulk lifetime characterization of corona charged silicon wafers with high resistivity by means of microwave detected photoconductivity

NASA Astrophysics Data System (ADS)

Engst, C. R.; Rommel, M.; Bscheid, C.; Eisele, I.; Kutter, C.

2017-12-01

Minority carrier lifetime (lifetime) measurements are performed on corona-charged silicon wafers by means of Microwave Detected Photoconductivity (MDP). The corona charge is deposited on the front and back sides of oxidized wafers in order to adjust accumulation conditions. Once accumulation is established, interface recombination is suppressed and bulk lifetimes are obtained. Neither contacts nor non-CMOS compatible preparation techniques are required in order to achieve accumulation conditions, which makes the method ideally suited for inline characterization. The novel approach, termed ChargedMDP (CMDP), is used to investigate neutron transmutation doped (NTD) float zone silicon with resistivities ranging from 6.0 to 8.2 kΩ cm. The bulk properties of 150 mm NTD wafers are analyzed in detail by performing measurements of the carrier lifetime and the steady-state photoconductivity at various injection levels. The results are compared with MDP measurements of uncharged wafers as well as to the established charged microwave detected Photoconductance Decay (charge-PCD) method. Besides analyzing whole wafers, CMDP measurements are performed on oxide test-structures on a patterned wafer. Finally, the oxide properties are characterized by means of charge-PCD as well as capacitance-voltage measurements. With CMDP, average bulk lifetimes up to 33.1 ms are measured, whereby significant variations are observed among wafers, which are produced out of the same ingot but oxidized in different furnaces. The observed lifetime variations are assumed to be caused by contaminations, which are introduced during the oxidation process. The results obtained by CMDP were neither accessible by means of conventional MDP measurements of uncharged wafers nor with the established charge-PCD method.

Mesoporous CdS via Network of Self-Assembled Nanocrystals: Synthesis, Characterization and Enhanced Photoconducting Property.

PubMed

Patra, Astam K; Banerjee, Biplab; Bhaumik, Asim

2018-01-01

Semiconduction nanoparticles are intensively studied due to their huge potential in optoelctronic applications. Here we report an efficient chemical route for hydrothermal synthesis of aggregated mesoporous cadmium sulfide (CdS) nanoparticles using supramolecular-assembly of ionic and water soluble sodium salicylate as the capping agent. The nanostructure, mesophase, optical property and photoconductivity of these mesoporous CdS materials have been characterized by using small and wide angle powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N2-sorption, Raman analysis, Fourier transformed infrared (FT-IR), UV-Visible DSR spectroscopy, and photoconductivity measurement. Wide angle XRD pattern and high resolution TEM image analysis suggested that the particle size of the materials is within 10 nm and the nanoparticles are in well-crystallized cubic phase. Mesoporous CdS nanoparticles showed drastically enhanced photoelectrochemical response under visible light irradiation on entrapping a photosensitizer (dye) molecule in the interparticle spaces. Efficient synthesis strategy and the enhanced photo response in the mesoporous CdS material could facilitate the designing of other porous semiconductor oxide/sulfide and their applications in photon-to-electron conversion processes.

Position-sensitive scanning fluorescence correlation spectroscopy.

PubMed

Skinner, Joseph P; Chen, Yan; Müller, Joachim D

2005-08-01

Fluorescence correlation spectroscopy (FCS) uses a stationary laser beam to illuminate a small sample volume and analyze the temporal behavior of the fluorescence fluctuations within the stationary observation volume. In contrast, scanning FCS (SFCS) collects the fluorescence signal from a moving observation volume by scanning the laser beam. The fluctuations now contain both temporal and spatial information about the sample. To access the spatial information we synchronize scanning and data acquisition. Synchronization allows us to evaluate correlations for every position along the scanned trajectory. We use a circular scan trajectory in this study. Because the scan radius is constant, the phase angle is sufficient to characterize the position of the beam. We introduce position-sensitive SFCS (PSFCS), where correlations are calculated as a function of lag time and phase. We present the theory of PSFCS and derive expressions for diffusion, diffusion in the presence of flow, and for immobilization. To test PSFCS we compare experimental data with theory. We determine the direction and speed of a flowing dye solution and the position of an immobilized particle. To demonstrate the feasibility of the technique for applications in living cells we present data of enhanced green fluorescent protein measured in the nucleus of COS cells.

Hybrid organic/inorganic position-sensitive detectors based on PEDOT:PSS/n-Si

NASA Astrophysics Data System (ADS)

Javadi, Mohammad; Gholami, Mahdiyeh; Torbatiyan, Hadis; Abdi, Yaser

2018-03-01

Various configurations like p-n junctions, metal-semiconductor Schottky barriers, and metal-oxide-semiconductor structures have been widely used in position-sensitive detectors. In this report, we propose a PEDOT:PSS/n-Si heterojunction as a hybrid organic/inorganic configuration for position-sensitive detectors. The influence of the thickness of the PEDOT:PSS layer, the wavelength of incident light, and the intensity of illumination on the device performance are investigated. The hybrid PSD exhibits very high sensitivity (>100 mV/mm), excellent nonlinearity (<3%), and a response correlation coefficient (>0.995) with a response time of <4 ms to the inhomogeneous IR illumination. The presented hybrid configuration also benefits from a straightforward low-temperature fabrication process. These advantages of the PEDOT:PSS/n-Si heterojunction are very promising for developing a new class of position-sensitive detectors based on the hybrid organic/inorganic junctions.

Photoluminescence and Photoconductivity to Assess Maximum Open-Circuit Voltage and Carrier Transport in Hybrid Perovskites and Other Photovoltaic Materials.

PubMed

Braly, Ian L; Stoddard, Ryan J; Rajagopal, Adharsh; Jen, Alex K-Y; Hillhouse, Hugh W

2018-06-06

Photovoltaic (PV) device development is much more expensive and time consuming than the development of the absorber layer alone. This perspective focuses on two methods that can be used to rapidly assess and develop PV absorber materials independent of device development. The absorber material properties of quasi-Fermi level splitting and carrier diffusion length under steady effective one-Sun illumination are indicators of a material's ability to achieve high VOC and JSC. These two material properties can be rapidly and simultaneously assessed with steady-state absolute intensity photoluminescence and photoconductivity measurements. As a result, these methods are extremely useful for predicting the quality and stability of PV materials prior to PV device development. Here, we summarize the methods, discuss their strengths and weaknesses, and compare photoluminescence and photoconductivity results with device performance for four hybrid perovskite compositions of various bandgaps (1.35 to 1.82 eV), CISe, CIGSe, and CZTSe.

Enhancing UV photoconductivity of ZnO nanobelt by polyacrylonitrile functionalization

NASA Astrophysics Data System (ADS)

He, J. H.; Lin, Yen H.; McConney, Michael E.; Tsukruk, Vladimir V.; Wang, Zhong L.; Bao, Gang

2007-10-01

UV photodetector fabricated using a single ZnO nanobelt (NB) has shown a photoresponse enhancement up to 750 times higher than that of a bare ZnO NB after coating with ˜20nm plasma polymerized acrylonitrile (PP-AN) nanoscale film. The mechanism for this colossal photoconductivity is suggested as a consequence of the efficient exciton dissociation under UV illumination due to enhanced electron transfer from valence band of ZnO NB to the PP-AN and then back to the conduction band of ZnO. This process has demonstrated an easy and effective method for improving the performance of the nanowire/NB-based devices, possibly leading to supersensitive UV detector for applications in imaging, photosensing, and intrachip optical interconnects.

Development of Position-sensitive Transition-edge Sensor X-ray Detectors

NASA Technical Reports Server (NTRS)

Smith, S. J.; Bandler, S. R.; Brekosky, R. P.; Brown, A.-D.; Chervenak, J. A.; Eckard, M. E.; Finkbeiner, F. M.; Kelley, R. L.; Kilbourne, C. A.; Porter, F. s.;

Optically thin hybrid cavity for terahertz photo-conductive detectors

DOE PAGES

Thompson, Robert J.; Siday, T.; Glass, S.; ...

2017-01-23

Here, the efficiency of photoconductive (PC) devices, including terahertz detectors, is constrained by the bulk optical constants of PC materials. Here, we show that optical absorption in a PC layer can be modified substantially within a hybrid cavity containing nanoantennas and a Distributed Bragg Reflector. We find that a hybrid cavity, consisting of a GaAs PC layer of just 50 nm, can be used to absorb >75% of incident photons by trapping the light within the cavity. We provide an intuitive model, which describes the dependence of the optimum operation wavelength on the cavity thickness. We also find that themore » nanoantenna size is a critical parameter, small variations of which lead to both wavelength shifting and reduced absorption in the cavity, suggesting that impedance matching is key for achieving efficient absorption in the optically thin hybrid cavities.« less

Studies on organic semiconductors. 15: Effects of the substituents on the photoconductivities of substituted anthracenes

NASA Technical Reports Server (NTRS)

Sugimoto, A.; Kato, S.; Inoue, H.; Imoto, E.

1985-01-01

The photocurrents of the substituted anthracenes, 1,5-diacetylanthracene (2), 1-acetylanthracene (3), 9-acetylanthracene (4), 1,5-dichloroanthracene (5), 1,5-diethylanthracene (6), 1,5-dimethoxyanthracene (7), 9-cyanoanthracene (8), and anthracene (1) were measured by using their surface type cells in nitrogen. The compounds of (1), (5), (6), (7), and (8) showed the photocurrent spectra which corresponded to the absorption spectra of their evaporated films. In the cases of (2) and (3), however, the anomalous photocurrent appeared in the threshold region of their absorption spectra. The appearance of the anomalous photocurrent was characteristic of anthracenes having the acetyl group at 1- and/or 5-position. The magnitude of the photocurrents of the 1,5-disubstituted anthracenes was similar to that of (1). The photocurrents of the monosubstituted anthracenes were smaller than that of (1). Among the monosubstituted anthracenes, the compound (4) showed no photocurrent under the same conditions. Contrary to the results obtained in the cases of phenazines, the photoconductivities of the anthracene derivatives became better in air.

Photoconductivity of Low-Bandgap Polymer and Polymer: Fullerene Bulk Heterojunction Studied by Constant Photocurrent Method

NASA Astrophysics Data System (ADS)

Malov, V. V.; Tameev, A. R.; Novikov, S. V.; Khenkin, M. V.; Kazanskii, A. G.; Vannikov, A. V.

2015-08-01

Optical and photoelectric properties of modern photosensitive polymers are of great interest due to their prospects for photovoltaic applications. In particular, an investigation of absorption and photoconductivity edge of these materials could provide valuable information. For these purpose we applied the constant photocurrent method which has proved its efficiency for inorganic materials. PCDTBT and PTB7 polymers were used as objects for the study as well as their blends with a fullerene derivative PC71BM. The measurements by constant photocurrent method (CPM) show that formation of bulk heterojunction (BHJ) in the blends increases photoconductivity and results in a redshift of the photocurrent edge in the doped polymers compared with that in the neat polymers. Obtained from CPM data, spectral dependences of absorption coefficient were approximated using Gaussian distribution of density-of-states within HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) bands. The approximation procedure allowed us to evaluate rather optical than electrical bandgaps for the studied materials. Moreover, spectra of polymer:PC71BM blends were fitted well by the sum of two Gaussian peaks which reveal both the transitions within the polymer and the transitions involving charge transfer states at the donor-acceptor interface in the BHJ.

Preparation, characterization, physical properties, and photoconducting behaviour of anthracene derivative nanowires

NASA Astrophysics Data System (ADS)

Xiao, Jinchong; Yin, Zongyou; Yang, Bo; Liu, Yi; Ji, Li; Guo, Jun; Huang, Ling; Liu, Xuewei; Yan, Qingyu; Zhang, Hua; Zhang, Qichun

2011-11-01

Organic nanowires of 9,10-dibromoanthracene (DBA) and 9,10-dicyanoanthracene (DCNA) were obtained by adding the THF solution of DBA/DCNA into water containing P123 surfactants. The as-prepared nanowires were characterized by UV-vis, fluorescence spectra, Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM). We found that DBA and DCNA nanowires emitted green light rather than blue light for molecules in THF solution. The red-shift UV and fluorescent spectra of DBA and DCNA nanowires implied that these nanowires were formed through J-aggregation. The photoconducting study of DBA/DCNA nanowire-based network on rGO/SiO2/Si shows different photocurrent behaviors upon irradiation, which displayed that electron transfer from DCNA nanowire to rGO was stronger than that of DBA nanowires to rGO.Organic nanowires of 9,10-dibromoanthracene (DBA) and 9,10-dicyanoanthracene (DCNA) were obtained by adding the THF solution of DBA/DCNA into water containing P123 surfactants. The as-prepared nanowires were characterized by UV-vis, fluorescence spectra, Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM). We found that DBA and DCNA nanowires emitted green light rather than blue light for molecules in THF solution. The red-shift UV and fluorescent spectra of DBA and DCNA nanowires implied that these nanowires were formed through J-aggregation. The photoconducting study of DBA/DCNA nanowire-based network on rGO/SiO2/Si shows different photocurrent behaviors upon irradiation, which displayed that electron transfer from DCNA nanowire to rGO was stronger than that of DBA nanowires to rGO. Electronic supplementary information (ESI) available: XRD patterns and simulations, and FT-IR spectra. CCDC reference numbers 840471. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c1nr10655d

Improving the efficiency and directivity of THz photoconductive antennas by using a defective photonic crystal substrate

NASA Astrophysics Data System (ADS)

Rahmati, Ehsan; Ahmadi-Boroujeni, Mehdi

2018-04-01

One of the shortcomings of photoconductive (PC) antennas in terahertz (THz) generation is low effective radiated power in the desirable direction. In this paper, we propose a defective photonic crystal (DPC) substrate consisting of a customized 2D array of air holes drilled into a solid substrate in order to improve the radiation characteristics of THz PC antennas. The effect of the proposed structure on the performance of a conventional THz PC antenna has been examined from several aspects including radiation efficiency, directivity, and field distribution. By comparing the radiation performance of the THz antenna on the proposed DPC substrate to that of the conventional solid substrate, it is shown that the proposed technique can significantly improve the efficiency and directivity of the THz PC antenna over a wide frequency range. It is achieved by reducing the amount of power coupled to the substrate surface waves and limiting the radiation in undesirable directions. In addition, it is found that the sensitivity of directivity to the substrate thickness is considerably decreased and the adverse Fabry-Perot effects of the thick substrate are reduced by the application of the proposed DPC substrate.

Metal-to-metal charge transfer between dopant and host ions: Photoconductivity of Yb-doped CaF{sub 2} and SrF{sub 2} crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barandiarán, Zoila, E-mail: zoila.barandiaran@uam.es; Seijo, Luis; Instituto Universitario de Ciencia de Materiales Nicolás Cabrera and Condensed Matter Physics Center

2015-10-14

Dopant-to-host electron transfer is calculated using ab initio wavefunction-based embedded cluster methods for Yb/Ca pairs in CaF{sub 2} and Yb/Sr pairs in SrF{sub 2} crystals to investigate the mechanism of photoconductivity. The results show that, in these crystals, dopant-to-host electron transfer is a two-photon process mediated by the 4f{sup N−1}5d excited states of Y b{sup 2+}: these are reached by the first photon excitation; then, they absorb the second photon, which provokes the Y b{sup 2+} + Ca{sup 2+} (Sr{sup 2+}) → Y b{sup 3+} + Ca{sup +} (Sr{sup +}) electron phototransfer. This mechanism applies to all the observed Ymore » b{sup 2+} 4f–5d absorption bands with the exception of the first one: Electron transfer cannot occur at the first band wavelengths in CaF{sub 2}:Y b{sup 2+} because the Y b{sup 3+}–Ca{sup +} states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in SrF{sub 2}:Y b{sup 2+} at the wavelengths of the first 4f–5d absorption band, but the mechanism is different from that described above: first, the two-photon excitation process occurs within the Y b{sup 2+} active center, then, non-radiative Yb-to-Sr electron transfer can occur. All of these features allow to interpret consistently available photoconductivity experiments in these materials, including the modulation of the photoconductivity by the absorption spectrum, the differences in photoconductivity thresholds observed in both hosts, and the peculiar photosensitivity observed in the SrF{sub 2} host, associated with the lowest 4f–5d band.« less

High gain photoconductive semiconductor switch having tailored doping profile zones

DOEpatents

Baca, Albert G.; Loubriel, Guillermo M.; Mar, Alan; Zutavern, Fred J; Hjalmarson, Harold P.; Allerman, Andrew A.; Zipperian, Thomas E.; O'Malley, Martin W.; Helgeson, Wesley D.; Denison, Gary J.; Brown, Darwin J.; Sullivan, Charles T.; Hou, Hong Q.

2001-01-01

A photoconductive semiconductor switch with tailored doping profile zones beneath and extending laterally from the electrical contacts to the device. The zones are of sufficient depth and lateral extent to isolate the contacts from damage caused by the high current filaments that are created in the device when it is turned on. The zones may be formed by etching depressions into the substrate, then conducting epitaxial regrowth in the depressions with material of the desired doping profile. They may be formed by surface epitaxy. They may also be formed by deep diffusion processes. The zones act to reduce the energy density at the contacts by suppressing collective impact ionization and formation of filaments near the contact and by reducing current intensity at the contact through enhanced current spreading within the zones.

Photoconductivity of high-voltage space insulating materials

NASA Technical Reports Server (NTRS)

Coffey, H. T.; Nanevicz, J. E.; Adamo, R. C.

1975-01-01

The dark and photoconductivities of four high voltage spacecraft insulators, Kapton-H, FEP Teflon, Parylene, and fused quartz, were studied under a variety of conditions intended to simulate a space environment. All measurements were made in a vacuum of less than .00001 torr while the temperature was varied from 22 C to 100 C. Some of the samples used employed conventional deposited metal electrodes--others employed electrodes composed either of an electron beam or a plasma formed by ionization of the residual gas in the test chamber. Test results show: (1) Kapton had unusual conduction properties; it conductivity decreased by more than an order of magnitude when heated at 100 C in a vacuum, but ultimately attained a stable and reproducible value. (2) Both Teflon and fused quartz had high dark resistivities but low photoresistivities when exposed to UV. Optical-density measurements revealed that both materials transmitted UV with little attenuation. (3) Parylene was found to have a low but relatively stable resistivity--comparatively minor changes occurred upon heating or illuminating the sample. Optical-density measurements showed that Parylene was absorbent in the UV and would prevent photoemission from the metal electrode on the back surface.

Structural, thermal, laser damage, photoconductivity, NLO and mechanical properties of modified vertical Bridgman method grown AgGa0.5In0.5Se2 single crystal

NASA Astrophysics Data System (ADS)

Vijayakumar, P.; Ramasamy, P.

2016-08-01

AgGa0.5In0.5Se2 single crystal was grown using modified vertical Bridgman method. The structural perfection of the AgGa0.5In0.5Se2 single crystal has been analyzed by high-resolution X-ray diffraction rocking curve measurements. The structural and compositional uniformities of AgGa0.5In0.5Se2 were studied using Raman scattering spectroscopy at room temperature. The FWHM of the Γ1 (W1) and Γ5L (Γ15) measured at different regions of the crystal confirms that the composition throughout its length is fairly uniform. Thermal properties of the as-grown crystal, including specific heat, thermal diffusivity and thermal conductivity have been investigated. The multiple shot surface laser damage threshold value was measured using Nd:YAG laser. Photoconductivity measurements with different temperatures have confirmed the positive photoconducting behavior. Second harmonic generation (SHG) on powder samples has been measured using the Kurtz and Perry technique and the results display that AgGa0.5In0.5Se2 is a phase-matchable NLO material. The hardness behavior has been measured using Vickers micro hardness measurement and the indentation size effect has been observed. The classical Meyer's law, propositional resistance model and modified propositional resistance model have been used to analyse the micro hardness behavior.

Dynamic amplification of light signals in photorefractive ferroelectric liquid crystal blends containing photoconductive chiral dopant

NASA Astrophysics Data System (ADS)

Sasaki, T.; Hafuri, M.; Suda, T.; Nakano, M.; Funada, K.; Ohta, M.; Terazono, T.; Le, K. V.; Naka, Y.

2017-08-01

Effect of ferroelectricity on the photorefractive effect of ferroelectric liquid crystal blends was investigated. The photorefractive effect of ferroelectric liquid crystal blends strongly depend on the ferroelectricity of the blend. We have prepared a series of ferroelectric liquid crystal blends that contains several concentrations of a chiral compound while keeping a constant concentration of a photoconductive moiety. The photorefractive properties of the ferroelectric liquid crystal blends were discussed with relations to the ferroelectric properties of the blends.

Position sensitive radioactivity detection for gas and liquid chromatography

DOEpatents

Cochran, Joseph L.; McCarthy, John F.; Palumbo, Anthony V.; Phelps, Tommy J.

2001-01-01

A method and apparatus are provided for the position sensitive detection of radioactivity in a fluid stream, particularly in the effluent fluid stream from a gas or liquid chromatographic instrument. The invention represents a significant advance in efficiency and cost reduction compared with current efforts.

Development of an amorphous selenium based photoconductor and its application in a high-sensitivity photodetector (Conference Presentation)

NASA Astrophysics Data System (ADS)

Masuzawa, Tomoaki; Ebisudani, Taishi; Ochiai, Jun; Saito, Ichitaro; Yamada, Takatoshi; Chua, Daniel H. C.; Mimura, Hidenori; Okano, Ken

2016-09-01

Although present imaging devices are mostly silicon-based devices such as CMOS and CCD, these devices are reaching their sensitivity limit due to the band gap of silicon. Amorphous selenium (a-Se) is a promising candidate for high- sensitivity photo imaging devices, because of its low thermal noise, high spatial resolution, as well as adaptability to wide-area deposition. In addition, internal signal amplification is reported on a-Se based photodetectors, which enables a photodetector having effective quantum efficiency over 100 % against visible light. Since a-Se has sensitivity to UV and soft X-rays, the reported internal signal amplification should be applicable to UV and X-ray detection. However, application of the internal signal amplification required high voltage, which caused unexpected breakdown at the contact or thin-film transistor-based signal read-out. For this reason, vacuum devices having electron-beam read-out is proposed. The advantages of vacuum-type devices are vacuum insulation and its extremely low dark current. In this study, we present recent progresses in developing a-Se based photoconductive films and photodetector using nitrogen-doped diamond electron beam source as signal read-out. A novel electrochemical method is used to dope impurities into a-Se, turning the material from weak p-type to n-type. A p-n junction is formed within a-Se photoconductive film, which has increased the sensitivity of a-Se based photodetector. Our result suggests a possibility of high sensitivity photodetector that can potentially break the limit of silicon-based devices.

Supramolecular core-shell nanoparticles for photoconductive device applications

NASA Astrophysics Data System (ADS)

Cheng, Chih-Chia; Chen, Jem-Kun; Shieh, Yeong-Tarng; Lee, Duu-Jong

2016-08-01

We report a breakthrough discovery involving supramolecular-based strategies to construct novel core-shell heterojunction nanoparticles with hydrophilic adenine-functionalized polythiophene (PAT) as the core and hydrophobic phenyl-C61-butyric acid methyl ester (PCBM) as the shell, which enables the conception of new functional supramolecular assemblies for constructing functional nanomaterials for applications in optoelectronic devices. The generated nanoparticles exhibit uniform spherical shape, well-controlled tuning of particle size with narrow size distributions, and excellent electrochemical stability in solution and the solid state owing to highly efficient energy transfer from PAT to PCBM. When the PAT/PCBM nanoparticles were fabricated into a photoconducting layer in an electronic device, the resulting device showed excellent electric conduction characteristics, including an electrically-tunable voltage-controlled switch, and high short-circuit current and open-circuit voltage. These observations demonstrate how the self-assembly of PAT/PCBM into specific nanostructures may help to promote efficient charge generation and transport processes, suggesting potential for a wide variety of applications as a promising candidate material for bulk heterojunction polymer devices.

Measurement of optical-beat frequency in a photoconductive terahertz-wave generator using microwave higher harmonics.

PubMed

Murasawa, Kengo; Sato, Koki; Hidaka, Takehiko

2011-05-01

A new method for measuring optical-beat frequencies in the terahertz (THz) region using microwave higher harmonics is presented. A microwave signal was applied to the antenna gap of a photoconductive (PC) device emitting a continuous electromagnetic wave at about 1 THz by the photomixing technique. The microwave higher harmonics with THz frequencies are generated in the PC device owing to the nonlinearity of the biased photoconductance, which is briefly described in this article. Thirteen nearly periodic peaks in the photocurrent were observed when the microwave was swept from 16 to 20 GHz at a power of -48 dBm. The nearly periodic peaks are generated by the homodyne detection of the optical beat with the microwave higher harmonics when the frequency of the harmonics coincides with the optical-beat frequency. Each peak frequency and its peak width were determined by fitting a Gaussian function, and the order of microwave harmonics was determined using a coarse (i.e., lower resolution) measurement of the optical-beat frequency. By applying the Kalman algorithm to the peak frequencies of the higher harmonics and their standard deviations, the optical-beat frequency near 1 THz was estimated to be 1029.81 GHz with the standard deviation of 0.82 GHz. The proposed method is applicable to a conventional THz-wave generator with a photomixer.

Development of a one-dimensional Position Sensitive Detector for tracking applications

NASA Astrophysics Data System (ADS)

Lydecker, Leigh Kent, IV

Optical Position Sensitive Detectors (PSDs) are a non-contact method of tracking the location of a light spot. Silicon-based versions of such sensors are fabricated with standard CMOS processing, are inexpensive and provide a real-time, analog signal output corresponding to the position of the light spot. Because they are non-contact, they do not degrade over time from surface friction due to repetitive sliding motion associated with standard full contact sliding potentiometers. This results in long, reliable device lifetimes. In this work, an innovative PSD was developed to replace the linear hard contact potentiometer currently being used in a human-computer interface architecture. First, a basic lateral effect PSD was developed to provide real-time positioning of the mouthpiece used in the interface architecture which tracks along a single axis. During the course of this work, multiple device geometries were fabricated and analyzed resulting in a down selection of a final design. This final device design was then characterized in terms of resolution and responsivity and produced in larger quantities as initial prototypes for the test product integration. Finally, an electronic readout circuit was developed in order to interface the dual- line lateral effect PSD developed in this thesis with specifications required for product integration. To simplify position sensing, an innovative type of optical position sensor was developed using a linear photodiodes with back-to-back connections. This so- called Self-Balancing Position Sensitive Detector (SBPSD) requires significantly fewer processing steps than the basic lateral effect position sensitive detector discussed above and eliminates the need for external readout circuitry entirely. Prototype devices were fabricated in this work, and the performance characteristics of these devices were established paving the way for ultimate integration into the target product as well as additional applications.

Vantage Sensitivity: Environmental Sensitivity to Positive Experiences as a Function of Genetic Differences.

PubMed

Pluess, Michael

2017-02-01

A large number of gene-environment interaction studies provide evidence that some people are more likely to be negatively affected by adverse experiences as a function of specific genetic variants. However, such "risk" variants are surprisingly frequent in the population. Evolutionary analysis suggests that genetic variants associated with increased risk for maladaptive development under adverse environmental conditions are maintained in the population because they are also associated with advantages in response to different contextual conditions. These advantages may include (a) coexisting genetic resilience pertaining to other adverse influences, (b) a general genetic susceptibility to both low and high environmental quality, and (c) a coexisting propensity to benefit disproportionately from positive and supportive exposures, as reflected in the recent framework of vantage sensitivity. After introducing the basic properties of vantage sensitivity and highlighting conceptual similarities and differences with diathesis-stress and differential susceptibility patterns of gene-environment interaction, selected and recent empirical evidence for the notion of vantage sensitivity as a function of genetic differences is reviewed. The unique contribution that the new perspective of vantage sensitivity may make to our understanding of social inequality will be discussed after suggesting neurocognitive and molecular mechanisms hypothesized to underlie the propensity to benefit disproportionately from benevolent experiences. © 2015 Wiley Periodicals, Inc.

Development of arrays of position-sensitive microcalorimeters for Constellation-X

NASA Technical Reports Server (NTRS)

Smith, S. J.; Bandler, S. R.; Brekosky, R. P.; Brown, A.-D.; Chervenak, J. A.; Eckart, M. E.; Finkbeiner, F. M.; Iyomoto, N.; Kelley, R. L.; Kolbourne, C. A.;

Ga2O3-In2O3 thin films on sapphire substrates: Synthesis and ultraviolet photoconductivity

NASA Astrophysics Data System (ADS)

Muslimov, A. E.; Butashin, A. V.; Kolymagin, A. B.; Nabatov, B. V.; Kanevsky, V. M.

2017-11-01

The structure and electrical and optical properties of β-Ga2O3-In2O3 thin films on sapphire substrates with different orientations have been investigated. The samples have been prepared by annealing of gallium-indium metallic films on sapphire substrates in air at different gallium-to-indium ratios in the initial mixture. The photoconductivity of these structures in the solar-blind ultraviolet spectral region has been examined.

Quantitative analysis of the persistent photoconductivity effect in Cu(In,Ga)Se2

NASA Astrophysics Data System (ADS)

Maciaszek, Marek; Zabierowski, Paweł

2018-04-01

The magnitude of the persistent photoconductivity effect (PPC) in two sets of Cu(In,Ga)Se2 samples, differing in the amount of cadmium and sodium, was measured. Using equations describing the magnitude of PPC, metastable defect and shallow acceptor densities were calculated. The method of the analysis of PPC in the presence of a deep acceptor level was presented. Based on obtained results, we drew conclusions about reasons of decreased PPC in Cu(In,Ga)Se2 without sodium as well as the role of (VSe-VCu) complexes in establishing the carrier concentration in Cu(In,Ga)Se2 with and without sodium.

Uncovering the density of nanowire surface trap states hidden in the transient photoconductance.

PubMed

Xu, Qiang; Dan, Yaping

2016-09-21

The gain of nanoscale photoconductors is closely correlated with surface trap states. Mapping out the density of surface trap states in the semiconductor bandgap is crucial for engineering the performance of nanoscale photoconductors. Traditional capacitive techniques for the measurement of surface trap states are not readily applicable to nanoscale devices. Here, we demonstrate a simple technique to extract the information on the density of surface trap states hidden in the transient photoconductance that is widely observed. With this method, we found that the density of surface trap states of a single silicon nanowire is ∼10(12) cm(-2) eV(-1) around the middle of the upper half bandgap.

Gamma ray measurements with photoconductive detectors using a dense plasma focus.

PubMed

May, M J; Brown, G V; Halvorson, C; Schmidt, A; Bower, D; Tran, B; Lewis, P; Hagen, C

2014-11-01

Photons in the MeV range emitted from the dense plasma focus (DPF) at the NSTec North Las Vegas Facility have been measured with both neutron-damaged GaAs and natural diamond photoconductive detectors (PCDs). The DPF creates or "pinches" plasmas of various gases (e.g., H2, D2, Ne, Ar., etc.) that have enough energy to create MeV photons from either bremsstrahlung and/or (n,n(')) reactions if D2 gas is used. The high bandwidth of the PCDs enabled the first ever measurement of the fast micro-pinches present in DPF plasmas. Comparisons between a slower more conventional scintillator/photomultiplier tube based nuclear physics detectors were made to validate the response of the PCDs to fast intense MeV photon signals. Significant discrepancies in the diamond PCD responses were evident.

A position sensitive microchannel photomultiplier for ultraviolet space astronomy

NASA Technical Reports Server (NTRS)

Lampton, M.; Siegmund, O. H. W.; Bixler, J.; Bowyer, S.

1986-01-01

The 25-mm microchannel-plate, position-sensitive UV astronomy photomultiplier tube presented is intended for the EOM-1 Spacelab Mission's FAUST payload and conducts wide-field imaging surveys in the VUV over the 1400-1800-A range. The sealed detector encompasses a CsI photocathode deposited on the inner surface of a MgF2 window, a stack of microchannel plates, and a wedge-and-strip two-dimensional position-sensing anode. Since the wedge-and-strip principle requires only three anode signals, flight electronics can be reduced to three charge amplifiers and three analog-to-digital converters.

Hall mobility and photoconductivity in TlGaSeS crystals

NASA Astrophysics Data System (ADS)

Qasrawi, A. F.; Gasanly, N. M.

2013-01-01

In this work, the fundamental properties of the TlGaSeS single crystals are investigated by means of temperature dependent electrical resistivity and Hall mobility. The crystal photo-responsibility as function of illumination intensity and temperature is also tested in the temperature range of 350-160 K. The study allowed the determination of acceptor centers as 230 and 450 meV below and above 260 K, and recombination centers as 181, 363, and 10 meV at low, moderate, and high temperatures, respectively. While the temperature-dependent Hall mobility behaved abnormally, the photoconductivity analysis reflected an illumination intensity dependent recombination center. Namely, the recombination center increased from 10 to 90 meV as the light intensity increased from 27.9 to 76.7 mW cm-2, respectively. That strange behavior was attributed to the temporary shift in Fermi level caused by photoexcitation.

Similar cisplatin sensitivity of HPV-positive and -negative HNSCC cell lines

PubMed Central

Kriegs, Malte; Gatzemeier, Fruzsina; Krüger, Katharina; Möckelmann, Nikolaus; Fritz, Gerhard; Petersen, Cordula; Knecht, Rainald; Rothkamm, Kai; Rieckmann, Thorsten

2016-01-01

Patients with HPV-positive head and neck squamous cell carcinoma (HNSCC) show better survival rates than those with HPV-negative HNSCC. While an enhanced radiosensitivity of HPV-positive tumors is clearly evident from single modality treatment, cisplatin is never administered as monotherapy and therefore its contribution to the enhanced cure rates of HPV-positive HNSCC is not known. Both cisplatin and radiotherapy can cause severe irreversible side effects and therefore various clinical studies are currently testing deintensified regimes for patients with HPV-positive HNSCC. One strategy is to omit cisplatin-based chemotherapy or replace it by less toxic treatments but the risk assessment of these approaches remains difficult. In this study we have compared the cytotoxic effects of cisplatin in a panel of HPV-positive and -negative HNSCC cell lines alone and when combined with radiation. While cisplatin-treated HPV-positive strains showed a slightly stronger inhibition of proliferation, there was no difference regarding colony formation. Cellular responses to the drug, namely cell cycle distribution, apoptosis and γH2AX-induction did not differ between the two entities but assessment of cisplatin-DNA-adducts suggests differences regarding the mechanisms that determine cisplatin sensitivity. Combining cisplatin with radiation, we generally observed an additive but only in a minority of strains from both entities a clear synergistic effect on colony formation. In summary, HPV-positive and -negative HNSCC cells were equally sensitive to cisplatin. Therefore replacing cisplatin may be feasible but the substituting agent should be of similar efficacy in order not to jeopardize the high cure rates for HPV-positive HNSCC. PMID:27127883

Single crystal CVD diamond membranes as Position Sensitive X-ray Detector

NASA Astrophysics Data System (ADS)

Desjardins, K.; Menneglier, C.; Pomorski, M.

2017-12-01

Transparent X-ray Beam Position Monitor (XBPM) has been specifically developed for low energy X-ray beamlines (1.4 keV < E < 5 keV) allowing to transmit more than 80% of 2 keV energy beam. The detector is based on a free-standing single crystal CVD diamond membrane of 4 μm thickness with position-sensitive DLC (Diamond-Like Carbon) resistive electrodes in duo-lateral configuration. The measured X-ray beam induced current (XBIC) due to the interaction of X-rays with diamond membrane allows precise monitoring of the absolute beam flux and the beam position (by the reconstruction of its center-of-gravity) at beam transmissions reaching 95%. This detector has been installed at SOLEIL synchrotron on the SIRIUS beamline monochromator output and it has shown charge collection efficiency (CCE) reaching 100% with no lag-effects and excellent beam intensity sensitivity monitoring. X-ray beam mapping of the detector showed an XBIC response inhomogeneity of less than 10% across the membrane, corresponding mainly to the measured variation of the diamond plate thickness. The measured beam position resolution is at sub-micron level depending on the beam flux and the readout electronics bandwidth.

Nanoparticle-assisted high photoconductive gain in polymer/fullerene matrix

PubMed Central

Chen, Hsiang-Yu; Lo, Michael K. F.; Yang, Guanwen; Monbouquette, Harold G.; Yang, Yang

2014-01-01

Polymer/inorganic nanocrystal composites1–10 offer an attractive means to combine the merits of organic and inorganic materials into novel electronic and photonic systems. However, many applications of these composites are limited by the solubility11 and distribution of nanocrystals (NCs) in polymer matrices. Here, a high photoconductive gain has been achieved by blending cadmium telluride (CdTe) nanoparticles (NPs) into a polymer/fullerene matrix followed by a solvent annealing12 process. The NP surface capping ligand, N-phenyl-N’-methyldithiocarbamate, renders the NPs highly soluble in the polymer blend thereby enabling high nanocrystal loadings. An external quantum efficiency (EQE) as high as ~8000% (at 350nm) is reached at −4.5V. Hole-dominant devices coupled with AFM images are studied to uncover the probable mechanism. We observe a higher concentration of CdTe NPs is located near the cathode/polymer interface. These NPs with trapped electrons assist hole injection into the polymer under reverse bias, which contributes to greater than 100% EQE. PMID:18772915

Development of Position-Sensitive Magnetic Calorimeters for X-Ray Astronomy

NASA Technical Reports Server (NTRS)

Bandler, SImon; Stevenson, Thomas; Hsieh, Wen-Ting

2011-01-01

Metallic magnetic calorimeters (MMC) are one of the most promising devices to provide very high energy resolution needed for future astronomical x-ray spectroscopy. MMC detectors can be built to large detector arrays having thousands of pixels. Position-sensitive magnetic (PoSM) microcalorimeters consist of multiple absorbers thermally coupled to one magnetic micro calorimeter. Each absorber element has a different thermal coupling to the MMC, resulting in a distribution of different pulse shapes and enabling position discrimination between the absorber elements. PoSMs therefore achieve the large focal plane area with fewer number of readout channels without compromising spatial sampling. Excellent performance of PoSMs was achieved by optimizing the designs of key parameters such as the thermal conductance among the absorbers, magnetic sensor, and heat sink, as well as the absorber heat capacities. Micro fab ri - cation techniques were developed to construct four-absorber PoSMs, in which each absorber consists of a two-layer composite of bismuth and gold. The energy resolution (FWHM full width at half maximum) was measured to be better than 5 eV at 6 keV x-rays for all four absorbers. Position determination was demonstrated with pulse-shape discrimination, as well as with pulse rise time. X-ray microcalorimeters are usually designed to thermalize as quickly as possible to avoid degradation in energy resolution from position dependence to the pulse shapes. Each pixel consists of an absorber and a temperature sensor, both decoupled from the cold bath through a weak thermal link. Each pixel requires a separate readout channel; for instance, with a SQUID (superconducting quantum interference device). For future astronomy missions where thousands to millions of resolution elements are required, having an individual SQUID readout channel for each pixel becomes difficult. One route to attaining these goals is a position-sensitive detector in which a large continuous or

Functionalised hexagonal-domain graphene for position-sensitive photodetectors

NASA Astrophysics Data System (ADS)

De Sanctis, Adolfo; Barnes, Matthew D.; Amit, Iddo; Craciun, Monica F.; Russo, Saverio

2017-03-01

Graphene’s unique photoresponse has been largely used in a multitude of optoelectronics applications ranging from broadband photodetectors to wave-guide modulators. In this work we extend the range of applications to position-sensitive photodetectors (PSDs) using FeCl3-intercalated hexagonal domains of graphene grown by atmospheric pressure chemical vapour deposition (APCVD). The FeCl3-based chemical functionalisation of APCVD graphene crystals is affected by the presence of wrinkles and results in a non-uniform doping of the graphene layers. This doping profile creates multiple p-p+ photoactive junctions which show a linear and bipolar photoresponse with respect to the position of a focused light spot, which is ideal for the realization of a PSD. Our study paves the way towards the fabrication of flexible and transparent PSDs that could be embedded in smart textile and wearable electronics.

Polarization-sensitive nanowire photodetectors based on solution-synthesized CdSe quantum-wire solids.

PubMed

Singh, Amol; Li, Xiangyang; Protasenko, Vladimir; Galantai, Gabor; Kuno, Masaru; Xing, Huili Grace; Jena, Debdeep

2007-10-01

Polarization-sensitive photodetectors are demonstrated using solution-synthesized CdSe nanowire (NW) solids. Photocurrent action spectra taken with a tunable white light source match the solution linear absorption spectra of the NWs, showing that the NW network is responsible for the device photoconductivity. Temperature-dependent transport measurements reveal that carriers responsible for the dark current through the nanowire solids are thermally excited across CdSe band gap. The NWs are aligned using dielectrophoresis between prepatterned electrodes using conventional optical photolithography. The photocurrent through the NW solid is found to be polarization-sensitive, consistent with complementary absorption (emission) measurements of both single wires and their ensembles. The range of solution-processed semiconducting NW materials, their facile synthesis, ease of device fabrication, and compatibility with a variety of substrates make them attractive for potential nanoscale polarization-sensitive photodetectors.

Influence of N incorporation on persistent photoconductivity in GaAsN alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Field III, R. L.; Jin, Y.; Cheng, H.

2013-04-08

We examine the role of N environment on persistent photoconductivity (PPC) in GaAs 1-xN x films. For x > 0.006, significant PPC is observed at cryogenic temperatures, with the PPC magnitude increasing with increasing x due to an increase in the density of N-induced levels. Interestingly, rapid thermal annealing suppresses the PPC magnitude and reduces the N interstitial fraction; thus, the N-induced level is likely associated with N interstitials. PPC is attributed to the photogeneration of carriers from N-induced levels to the conduction-band edge, leading to a modified N molecular bond configuration. With the addition of thermal energy, the groundmore » state configuration is restored; the N-induced level is then able to accept carriers and the conductivity decays to its preillumination value.« less

Influence of N incorporation on persistent photoconductivity in GaAsN alloys

NASA Astrophysics Data System (ADS)

Field, R. L., III; Jin, Y.; Cheng, H.; Dannecker, T.; Jock, R. M.; Wang, Y. Q.; Kurdak, C.; Goldman, R. S.

2013-04-01

We examine the role of N environment on persistent photoconductivity (PPC) in GaAs1-xNx films. For x > 0.006, significant PPC is observed at cryogenic temperatures, with the PPC magnitude increasing with increasing x due to an increase in the density of N-induced levels. Interestingly, rapid thermal annealing suppresses the PPC magnitude and reduces the N interstitial fraction; thus, the N-induced level is likely associated with N interstitials. PPC is attributed to the photogeneration of carriers from N-induced levels to the conduction-band edge, leading to a modified N molecular bond configuration. With the addition of thermal energy, the ground state configuration is restored; the N-induced level is then able to accept carriers and the conductivity decays to its preillumination value.

Photoconductive detector of circularly polarized radiation based on a MIS structure with a CoPt layer

NASA Astrophysics Data System (ADS)

Kudrin, A. V.; Dorokhin, M. V.; Zdoroveishchev, A. V.; Demina, P. B.; Vikhrova, O. V.; Kalent'eva, I. L.; Ved', M. V.

2017-11-01

A photoconductive detector of circularly polarized radiation based on the metal-insulator-semiconductor structure of CoPt/(Al2O3/SiO2/Al2O3)/InGaAs/GaAs is created. The efficiency of detection of circularly polarized radiation is 0.75% at room temperature. The operation of the detector is based on the manifestation of the effect of magnetic circular dichroism in the CoPt layer, that is, the dependence of the CoPt transmission coefficient on the sign of the circular polarization of light and magnetization.

Delay-Line Three-Dimensional Position Sensitive Radiation Detection

NASA Astrophysics Data System (ADS)

Jeong, Manhee

High-resistivity silicon(Si) in large volumes and with good charge carrier transport properties has been produced and achieved success as a radiation detector material over the past few years due to its relatively low cost as well as the availability of well-established processing technologies. One application of that technology is in the fabrication of various position-sensing topologies from which the incident radiation's direction can be determined. We have succeeded in developing the modeling tools for investigating different position-sensing schemes and used those tools to examine both amplitude-based and time-based methods, an assessment that indicates that fine position-sensing can be achieved with simpler readout designs than are conventionally deployed. This realization can make ubiquitous and inexpensive deployment of special nuclear materials (SNM) detecting technology becomes more feasible because if one can deploy position-sensitive semiconductor detectors with only one or two contacts per side. For this purpose, we have described the delay-line radiation detector and its optimized fabrication. The semiconductor physics were simulated, the results from which guided the fabrication of the guard ring structure and the detector electrode, both of which included metal-field-plates. The measured improvement in the leakage current was confirmed with the fabricated devices, and the structures successfully suppressed soft-breakdown. We also demonstrated that fabricating an asymmetric strip-line structure successfully minimizing the pulse shaping and increases the distance through which one can propagate the information of the deposited charge distribution. With fabricated delay-line detectors we can acquire alpha spectra (Am-241) and gamma spectra (Ba-133, Co-57 and Cd-109). The delay-line detectors can therefore be used to extract the charge information from both ion and gamma-ray interactions. Furthermore, standard charge-sensitive circuits yield high SNR

Nanoparticle-assisted high photoconductive gain in composites of polymer and fullerene.

PubMed

Chen, Hsiang-Yu; Lo, Michael K F; Yang, Guanwen; Monbouquette, Harold G; Yang, Yang

2008-09-01

Polymer-inorganic nanocrystal composites offer an attractive means to combine the merits of organic and inorganic materials into novel electronic and photonic systems. However, many applications of these composites are limited by the solubility and distribution of the nanocrystals in the polymer matrices. Here we show that blending CdTe nanoparticles into a polymer-fullerene matrix followed by solvent annealing can achieve high photoconductive gain under low applied voltages. The surface capping ligand renders the nanoparticles highly soluble in the polymer blend, thereby enabling high CdTe loadings. An external quantum efficiency as high as approximately 8,000% at 350 nm was achieved at -4.5 V. Hole-dominant devices coupled with atomic force microscopy images show a higher concentration of nanoparticles near the cathode-polymer interface. The nanoparticles and trapped electrons assist hole injection into the polymer under reverse bias, contributing to efficiency values in excess of 100%.

An experimental and theoretical study of the dark current and x-ray sensitivity of amorphous selenium x-ray photoconductors

NASA Astrophysics Data System (ADS)

Frey, Joel Brandon

Recently, the world of diagnostic radiography has seen the integration of digital flat panel x-ray image detectors into x-ray imaging systems, replacing analog film screens. These flat panel x-ray imagers (FPXIs) have been shown to produce high quality x-ray images and provide many advantages that are inherent to a fully digital technology. Direct conversion FPXIs based on a photoconductive layer of stabilized amorphous selenium (a-Se) have been commercialized and have proven particularly effective in the field of mammography. In the operation of these detectors, incident x-ray photons are converted directly to charge carriers in the a-Se layer and drifted to electrodes on either side of the layer by a large applied field (10 V/microm). The applied field causes a dark current to flow which is not due to the incident radiation and this becomes a source of noise which can reduce the dynamic range of the detector. The level of dark current in commercialized detectors has been reduced by the deposition of thin n- and p- type blocking layers between the electrodes and the bulk of the a-Se. Despite recent research into the dark current in metal/a-Se/metal sandwich structures, much is still unknown about the true cause and nature of this phenomenon. The work in this Ph.D. thesis describes an experimental and theoretical study of the dark current in these structures. Experiments have been performed on five separate sets of a-Se samples which approximate the photoconductive layer in an FPXI. The dark current has been measured as a function of time, sample structure, applied field, sample thickness and contact metal used. This work has conclusively shown that the dark current is almost entirely due to the injection of charge carriers from the contacts and the contribution of Poole-Frenkel enhanced bulk thermal generation is negligible. There is also evidence that while the dark current is initially controlled by the injection of holes from the positive contact, several

Low temperature grown GaNAsSb: A promising material for photoconductive switch application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tan, K. H.; Yoon, S. F.; Wicaksono, S.

2013-09-09

We report a photoconductive switch using low temperature grown GaNAsSb as the active material. The GaNAsSb layer was grown at 200 °C by molecular beam epitaxy in conjunction with a radio frequency plasma-assisted nitrogen source and a valved antimony cracker source. The low temperature growth of the GaNAsSb layer increased the dark resistivity of the switch and shortened the carrier lifetime. The switch exhibited a dark resistivity of 10{sup 7} Ω cm, a photo-absorption of up to 2.1 μm, and a carrier lifetime of ∼1.3 ps. These results strongly support the suitability of low temperature grown GaNAsSb in the photoconductivemore » switch application.« less

Interband Photoconductivity of Metamorphic InAs/InGaAs Quantum Dots in the 1.3-1.55-μm Window

NASA Astrophysics Data System (ADS)

Golovynskyi, Sergii; Datsenko, Oleksandr I.; Seravalli, Luca; Trevisi, Giovanna; Frigeri, Paola; Babichuk, Ivan S.; Golovynska, Iuliia; Qu, Junle

2018-04-01

Photoelectric properties of the metamorphic InAs/In x Ga1 - x As quantum dot (QD) nanostructures were studied at room temperature, employing photoconductivity (PC) and photoluminescence spectroscopies, electrical measurements, and theoretical modeling. Four samples with different stoichiometry of In x Ga1 - x As cladding layer have been grown: indium content x was 0.15, 0.24, 0.28, and 0.31. InAs/In0.15Ga0.85As QD structure was found to be photosensitive in the telecom range at 1.3 μm. As x increases, a redshift was observed for all the samples, the structure with x = 0.31 was found to be sensitive near 1.55 μm, i.e., at the third telecommunication window. Simultaneously, only a slight decrease in the QD PC was recorded for increasing x, thus confirming a good photoresponse comparable with the one of In0.15Ga0.75As structures and of GaAs-based QD nanostructures. Also, the PC reduction correlate with the similar reduction of photoluminescence intensity. By simulating theoretically the quantum energy system and carrier localization in QDs, we gained insight into the PC mechanism and were able to suggest reasons for the photocurrent reduction, by associating them with peculiar behavior of defects in such a type of structures. All this implies that metamorphic QDs with a high x are valid structures for optoelectronic infrared light-sensitive devices.

Nonequilibrium Green's function theory of resonant steady state photoconduction in a double quantum well FET subject to THz radiation at plasmon frequency

NASA Astrophysics Data System (ADS)

Morgenstern Horing, Norman J.; Popov, Vyacheslav V.

2006-04-01

Recent experimental observations by X.G. Peralta and S.J. Allen, et al. of dc photoconductivity resonances in steady source-drain current subject to terahertz radiation in a grid-gated double-quantum well FET suggested an association with plasmon resonances. This association was definitively confirmed for some parameter ranges in our detailed electrodynamic absorbance calculations. In this paper we propose that the reason that the dc photoconductance resonances match the plasmon resonances in semiconductors is based on a nonlinear dynamic screening mechanism. In this, we employ a shielded potential approximation that is nonlinear in the terahertz field to determine the nonequilibrium Green's function and associated density perturbation that govern the nonequilibrium dielectric polarization of the medium. This ''conditioning'' of the system by the incident THz radiation results in resonant polarization response at the plasmon frequencies which, in turn, causes a sharp drop of the resistive shielded impurity scattering potentials and attendant increase of the dc source-drain current. This amounts to disabling the impurity scattering mechanism by plasmon resonant behavior in nonlinear screening.

Absolute and angular efficiencies of a microchannel-plate position-sensitive detector

NASA Technical Reports Server (NTRS)

Gao, R. S.; Gibner, P. S.; Newman, J. H.; Smith, K. A.; Stebbings, R. F.

1984-01-01

This paper presents a characterization of a commercially available position-sensitive detector of energetic ions and neutrals. The detector consists of two microchannel plates followed by a resistive position-encoding anode. The work includes measurement of absolute efficiencies of H(+), He(+), and O(+) ions in the energy range between 250 and 5000 eV, measurement of relative detection efficiencies as a function of particle impact angle, and a simple method for accurate measurement of the time at which a particle strikes the detector.

Application of an Al-doped zinc oxide subcontact layer on vanadium-compensated 6H-SiC photoconductive switches

NASA Astrophysics Data System (ADS)

Zhou, Tian-Yu; Liu, Xue-Chao; Huang, Wei; Dai, Chong-Chong; Zheng, Yan-Qing; Shi, Er-Wei

2015-04-01

Al-doped ZnO thin film (AZO) is used as a subcontact layer in 6H-SiC photoconductive semiconductor switches (PCSSs) to reduce the on-state resistance and optimize the device structure. Our photoconductive test shows that the on-state resistance of lateral PCSS with an n+-AZO subcontact layer is 14.7% lower than that of PCSS without an n+-AZO subcontact layer. This occurs because a heavy-doped AZO thin film can improve Ohmic contact properties, reduce contact resistance, and alleviate Joule heating. Combined with the high transparance characteristic at 532 nm of AZO film, vertical structural PCSS devices are designed and their structural superiority is discussed. This paper provides a feasible route for fabricating high performance SiC PCSS by using conductive and transparent ZnO-based materials. Project supported by the Innovation Program of the Shanghai Institute of Ceramics (Grant No. Y39ZC1110G), the Innovation Program of the Chinese Academy of Sciences (Grant No. KJCX2-EW-W10), the Industry-Academic Joint Technological Innovations Fund Project of Jiangsu Province, China (Grant No. BY2011119), the Natural Science Foundation of Shanghai (Grant No. 14ZR1419000), the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61404146), and the National High-tech R & D Program of China (Grant Nos. 2013AA031603 and 2014AA032602).

Improved performance of photoconductive gain hybrid UV detector by trap state engineering of ZnO nanoparticles

NASA Astrophysics Data System (ADS)

Azadinia, M.; Fathollahi, M. R.; Mosadegh, M.; Boroumand, F. A.; Mohajerani, E.

2017-10-01

With the purpose of examining the impact of donor polymer on the performance of nanocomposite photodetectors (PDs) and to better understand the underlying physics, different wide-bandgap semiconducting polymers, poly(N-vinylcarbazole), poly(9, 9-di-n-octylfluorenyl-2, 7-diyl) , and [9,9'-dioctyl-fluorene-2,7-diyl]-copoly[diphenyl-p-tolyl-amine-4,4'-diyl] (BFE), are mixed with ZnO nanoparticles (NPs) to fabricate hybrid UV PDs. Three different polymer matrix nanocomposites were investigated that differ in the electron-trap depth in the nanocomposite and also the carrier tunneling energy at the interface. All the fabricated PDs exhibit strong photoconductive gain characteristics which can be attributed to trapped electron accumulation and band bending at the cathode interface. Experimental results show that the manipulation of the photoactive nanocomposite improves the PD properties simultaneously, namely, the external quantum efficiency (EQE, ˜104%), the maximum detectivity (D*, ˜1013 Jones), and the linear dynamic range (LDR, ˜85 dB). In addition, the gain bandwidth product of the device improves more than 50 times. Furthermore, the effect of the photogenerated carrier profile within the active layer is investigated experimentally by changing the direction of the incident light using a transparent cathode. Interestingly, under illumination through the Al cathode, faster photocurrent response, wider spectral range toward the deep UV region, and higher EQE in relatively low voltages are observed. These considerations might provide a general strategy to fabricate low-cost photoconductive PDs with a reasonably good combination of gain, response speed, LDR, and selectivity.

Structural, photoconductivity, and dielectric studies of polythiophene-tin oxide nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murugavel, S., E-mail: starin85@gmail.com; Malathi, M., E-mail: mmalathi@vit.ac.in

2016-09-15

Highlights: • Synthesis of polythiophene-tin oxide nanocomposites confirmed by FTIR and EDAX. • SEM shows SnO{sub 2} nanoparticles embedded within polythiophene matrix. • Stability and isoelectric point suggest nanoparticle–matrix interaction. • High dielectric constant due to high Maxwell–Wagner interfacial polarization. - Abstract: Polythiophene-tinoxide (PT-SnO{sub 2}) nanocomposites were prepared by in situ chemical oxidative polymerization, in the presence of various concentrations of SnO{sub 2} nanoparticles. Samples were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and Zeta potential measurements. Morphologies and elemental compositions were investigated by transmission electron microscopy, field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy.more » The photoconductivity of the nanocomposites was studied by field-dependent dark and photo conductivity measurements. Their dielectric properties were investigated using dielectric spectroscopy, in the frequency range of 1kHz–1 MHz. The results indicated that the SnO{sub 2} nanoparticles in the PT-SnO{sub 2} nanocomposite were responsible for its enhanced dielectric performance.« less

Results with OECD recommended positive control sensitizers in the maximization, Buehler and local lymph node assays.

PubMed

Basketter, D A; Selbie, E; Scholes, E W; Lees, D; Kimber, I; Botham, P A

1993-01-01

The guinea pig maximization test and the Buehler occluded patch test are used widely to identify the sensitization potential of new chemicals. This information enables toxicologists and/or regulatory authorities to determine whether a chemical should be classified formally as a skin sensitizer. Both to improve and to harmonize these assessments internationally, the OECD has recommended recently that moderate rather than strong contact sensitizers are used as positive control substances. The purpose is to ensure an adequate level of sensitivity in sensitization assays performed at specific testing establishments. Results from two laboratories reported here show that the minimum acceptable standard laid down by the OECD can be achieved and indeed commonly exceeded by a substantial margin. Furthermore, results with these positive controls in a new method, the local lymph node assay, also appear to satisfy similar criteria, suggesting results from this assay, including negative data, should be acceptable for classification purposes. However, a review of the way in which results with new chemicals will be interpreted for regulatory purposes, in the context of positive control data, reveals that considerable inadequacies still exist. It is recommended that ultimately, sensitization data can only be interpreted meaningfully (i.e. to protect humans from sensitization hazards) by considering the potency of the contact allergen in the context of the sensitivity of the assay performed at the particular testing institution.

Sensitivity to Social Contingency and Positive Emotion in 2-Month-Olds

ERIC Educational Resources Information Center

Soussignan, Robert; Nadel, Jacqueline; Canet, Pierre; Gerardin, Priscille

2006-01-01

This study was aimed at sorting out conflicting results in the literature concerning 2-month-olds' sensitivity to interpersonal contingency, and investigated the potential role of infants' positive emotion in contingency detection. Infants were randomly assigned to an experimental group (EG) that was presented an uninterrupted live-replay-live…

Investigation of high-voltage pulse trigger generator based on photo-conductive semiconductor switch

NASA Astrophysics Data System (ADS)

Chu, Xu; Liu, Jin-Liang; Wang, Lang-Ning; Qiu, Yong-Feng

2018-06-01

The trigger to generate high-voltage pulse is one of the most important parts in a pulsed-power system, especially for the conduction characteristics of the main switch. However, traditional triggers usually have the drawbacks of large structure and worse long-term working stability, which goes against the demands of pulsed-power system miniaturization and stability. In the paper, a pulse trigger using photo-conductive semiconductor switch was developed, which is of small size, stable performance and steep leading edge of the output pulse rise. It is found that the output trigger pulse rise time is 14 ns, and the jitter of 20 shots is 330 ps. Applying the designed pulsed trigger in a field distortion switch and a triggered vacuum switch, experiments show that the switches could be triggered stably with reduced jitter.

Use of Opioid Medications for Employees in Critical Safety or Security Positions and Positions with Safety Sensitive Duties

DTIC Science & Technology

2017-01-30

workers function while on the job must be thoroughly evaluated by a competent healthcare provider and fitness for duty must be determined. Treatment...performance of job functions with or without accommodation. D. Prior to recommending an employee’s return to a safety sensitive position, the healthcare

Sci—Thur PM: Imaging — 01: Position-sensitive noise characteristics in multi-pinhole cardiac SPECT imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cuddy-Walsh, SG; University of Ottawa Heart Institute; Wells, RG

2014-08-15

Myocardial perfusion imaging (MPI) with Single Photon Emission Computed Tomography (SPECT) is invaluable in the diagnosis and management of heart disease. It provides essential information on myocardial blood flow and ischemia. Multi-pinhole dedicated cardiac-SPECT cameras offer improved count sensitivity, and spatial and energy resolutions over parallel-hole camera designs however variable sensitivity across the field-of-view (FOV) can lead to position-dependent noise variations. Since MPI evaluates differences in the signal-to-noise ratio, noise variations in the camera could significantly impact the sensitivity of the test for ischemia. We evaluated the noise characteristics of GE Healthcare's Discovery NM530c camera with a goal of optimizingmore » the accuracy of our patient assessment and thereby improving outcomes. Theoretical sensitivity maps of the camera FOV, including attenuation effects, were estimated analytically based on the distance and angle between the spatial position of a given voxel and each pinhole. The standard deviation in counts, σ was inferred for each voxel position from the square root of the sensitivity mapped at that position. Noise was measured experimentally from repeated (N=16) acquisitions of a uniform spherical Tc-99m-water phantom. The mean (μ) and standard deviation (σ) were calculated for each voxel position in the reconstructed FOV. Noise increased ∼2.1× across a 12 cm sphere. A correlation of 0.53 is seen when experimental noise is compared with theory suggesting that ∼53% of the noise is attributed to the combined effects of attenuation and the multi-pinhole geometry. Further investigations are warranted to determine the clinical impact of the position-dependent noise variation.« less

Enhanced excitonic photoconductivity due to built-in internal electric field in TlGaSe{sub 2} layered semiconductor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seyidov, MirHasan Yu., E-mail: smirhasan@gyte.edu.tr; Suleymanov, Rauf A.; Institute of Physics Azerbaijan National Academy of Sciences, AZ-1143 Baku

2014-12-07

The strong enhancement, by several orders of magnitude, of the excitonic peak within the photoconductivity spectrum of TlGaSe{sub 2} semiconductor was observed. The samples were polarized in external dc electric field, which was applied prior to the measurements. Due to the accumulation of charges near the surface, an internal electric field was formed. Electron-hole pairs that were created after the absorption of light are fallen in and then separated by the built-in electric field, which prevents radiative recombination process.

Conformable large-area position-sensitive photodetectors based on luminescence-collecting silicone waveguides

NASA Astrophysics Data System (ADS)

Bartu, Petr; Koeppe, Robert; Arnold, Nikita; Neulinger, Anton; Fallon, Lisa; Bauer, Siegfried

2010-06-01

Position sensitive detection schemes based on the lateral photoeffect rely on inorganic semiconductors. Such position sensitive devices (PSDs) are reliable and robust, but preparation with large active areas is expensive and use on curved substrates is impossible. Here we present a novel route for the fabrication of conformable PSDs which allows easy preparation on large areas, and use on curved surfaces. Our device is based on stretchable silicone waveguides with embedded fluorescent dyes, used in conjunction with small silicon photodiodes. Impinging laser light (e.g., from a laser pointer) is absorbed by the dye in the PSD and re-emitted as fluorescence light at a larger wavelength. Due to the isotropic emission from the fluorescent dye molecules, most of the re-emitted light is coupled into the planar silicone waveguide and directed to the edges of the device. Here the light signals are detected via embedded small silicon photodiodes arranged in a regular pattern. Using a mathematical algorithm derived by extensive using of models from global positioning system (GPS) systems and human activity monitoring, the position of light spots is easily calculated. Additionally, the device shows high durability against mechanical stress, when clamped in an uniaxial stretcher and mechanically loaded up to 15% strain. The ease of fabrication, conformability, and durability of the device suggests its use as interface devices and as sensor skin for future robots.

Effective photoconductivity of exfoliated black phosphorus for optoelectronic switching under 1.55 μm optical excitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Penillard, A., E-mail: anne.penillard@espci.fr; Tripon-Canseliet, C.; Maksimovic, I.

2016-01-14

We present a microwave photoconductive switch based on exfoliated black phosphorus and strongly responding to a 1.55 μm optical excitation. According to its number of atomic layers, exfoliated black phosphorus presents unique properties for optoelectronic applications, like a tunable direct bandgap from 0.3 eV to 2 eV, strong mobilities, and strong conductivities. The switch shows a maximum ON/OFF ratio of 17 dB at 1 GHz, and 2.2 dB at 20 GHz under 1.55-μm laser excitation at 50 mW, never achieved with bidimensional materials.

Topography of eye-position sensitivity of saccades evoked electrically from the cat's superior colliculus.

PubMed

McIlwain, J T

1990-03-01

Saccades evoked electrically from the deep layers of the superior colliculus have been examined in the alert cat with its head fixed. Amplitudes of the vertical and horizontal components varied linearly with the starting position of the eye. The slopes of the linear-regression lines provided an estimate of the sensitivity of these components to initial eye position. In observations on 29 sites in nine cats, the vertical and horizontal components of saccades evoked from a given site were rarely influenced to the same degree by initial eye position. For most sites, the horizontal component was more sensitive than the vertical component. Sensitivities of vertical and horizontal components were lowest near the representations of the horizontal and vertical meridians, respectively, of the collicular retinotopic map, but otherwise exhibited no systematic retinotopic dependence. Estimates of component amplitudes for saccades evoked from the center of the oculomotor range also diverged significantly from those predicted from the retinotopic map. The results of this and previous studies indicate that electrical stimulation of the cat's superior colliculus cannot yield a unique oculomotor map or one that is in register everywhere with the sensory retinotopic map. Several features of these observations suggest that electrical stimulation of the colliculus produces faulty activation of a saccadic control system that computes target position with respect to the head and that small and large saccades are controlled differently.

Two Carrier Analysis of Persistent Photoconductivity in Modulation-Doped Structures

NASA Technical Reports Server (NTRS)

Schacham, S. E.; Mena, R. A.; Haugland, E. J.; Alterovitz, S. A.

1995-01-01

A simultaneous fit of Hall and conductivity data gives quantitative results on the carrier concentration and mobility in both the quantum well and the parallel conduction channel. In this study this method was applied to reveal several new findings on the effect of persistent photoconductivity (PPC) on free-carrier concentrations and mobilities. The increase in the two-dimensional electron-gas (2DEG) concentration is significantly smaller than the apparent one derived from single carrier analysis of the Hall coefficient. In the two types of structures investigated, delta doped and continuously doped barrier, the apparent concentration almost doubles following illumination, while analysis reveals an increase of about 20% in the 2DEG. The effect of PPC on mobility depends on the structure. For the sample with a continuously doped barrier the mobility in the quantum well more than doubles. This increase is attributed to the effective screening of the ionized donors by the large electron concentration in the barrier. In the delta doped barrier sample the mobility is reduced by almost a factor of 2. This decrease is probably caused by strong coupling between the two wells, as is demonstrated by self-consistent analysis.

A position-sensitive X-ray detector for the HEAO-A satellite.

NASA Technical Reports Server (NTRS)

Held, D.; Weisskopf, M. C.

1973-01-01

A position-sensitive, low-energy proportional counter system is described which will be used on the High-Energy Astronomical Observatory, Mission A, spacecraft. The associated system incorporates the capability to employ pulse-shape discrimination for background rejection and interpolation circuitry to locate the centroid of an X-ray event with an accuracy of approximately one eighth the cathode-wire spacing.

Position Sensitive Proximity Charge Sensing Readout of HPGe Detectors

NASA Astrophysics Data System (ADS)

Priest, Anders Peterson

Electrode segmentation is a necessity to achieve position sensitivity in semicon- ductor radiation detectors. Traditional segmentation requires decreasing electrode sizes while increasing channel numbers to achieve very fine position resolution. These electrodes can be complicated to fabricate, and many electrodes with individual electronic channels are required to instrument large detector areas. To simplify the fabrication process, we have moved the readout electrodes onto a printed circuit board that is positioned above the ionization type detection material. In this scheme, charge from radiation interactions will be shared amongst several electrodes, allowing for position interpolation. Because events can be reconstructed in between electrodes, fewer electrodes are needed to instrument large detector areas. The proximity charge sensing method of readout promises to simplify detector fabrication while maintaining the position resolution that is required by fields such as homeland security, astrophysics, environmental remediation, nuclear physics, and medical imaging. We performed scanning measurements on a proof of principle detector that we fabricated at Lawrence Berkeley National Laboratory (LBNL). These measurements showed that position resolution much finer than the strip pitch was achievable using the proximity charge readout method. We performed analytic calculations and Monte Carlo modeling to optimize the readout electrode geometry for a larger detector to test the limits of this technology. We achieved an average position resolution of 288 microm with eight proximity electrodes at a 5 mm pitch and 1 mm strip width, set 100 microm away from the detector surface by a Kapton spacer. To achieve this resolution using standard technologies, 300 microm pitch strips are necessary, and would require 100 channels to instrument the same area. Through our optimization calculations, we found that there is a trade-off between position resolution and energy resolution

Study of positive and negative feedback sensitivity in psychosis using the Wisconsin Card Sorting Test.

PubMed

Farreny, Aida; Del Rey-Mejías, Ángel; Escartin, Gemma; Usall, Judith; Tous, Núria; Haro, Josep Maria; Ochoa, Susana

2016-07-01

Schizophrenia involves marked motivational and learning deficits that may reflect abnormalities in reward processing. The purpose of this study was to examine positive and negative feedback sensitivity in schizophrenia using computational modeling derived from the Wisconsin Card Sorting Test (WCST). We also aimed to explore feedback sensitivity in a sample with bipolar disorder. Eighty-three individuals with schizophrenia and 27 with bipolar disorder were included. Demographic, clinical and cognitive outcomes, together with the WCST, were considered in both samples. Computational modeling was performed using the R syntax to calculate 3 parameters based on trial-by-trial execution on the WCST: reward sensitivity (R), punishment sensitivity (P), and choice consistency (D). The associations between outcome variables and the parameters were investigated. Positive and negative sensitivity showed deficits, but P parameter was clearly diminished in schizophrenia. Cognitive variables, age, and symptoms were associated with R, P, and D parameters in schizophrenia. The sample with bipolar disorder would show cognitive deficits and feedback abnormalities to a lesser extent than individuals with schizophrenia. Negative feedback sensitivity demonstrated greater deficit in both samples. Idiosyncratic cognitive requirements in the WCST might introduce confusion when supposing model-free reinforcement learning. Negative symptoms of schizophrenia were related to lower feedback sensitivity and less goal-directed patterns of choice. Copyright © 2016 Elsevier Inc. All rights reserved.

Bistability of hydrogen in ZnO: origin of doping limit and persistent photoconductivity.

PubMed

Nahm, Ho-Hyun; Park, C H; Kim, Yong-Sung

2014-02-18

Substitutional hydrogen at oxygen site (HO) is well-known to be a robust source of n-type conductivity in ZnO, but a puzzling aspect is that the doping limit by hydrogen is only about 10(18) cm(-3), even if solubility limit is much higher. Another puzzling aspect of ZnO is persistent photoconductivity, which prevents the wide applications of the ZnO-based thin film transistor. Up to now, there is no satisfactory theory about two puzzles. We report the bistability of HO in ZnO through first-principles electronic structure calculations. We find that as Fermi level is close to conduction bands, the HO can undergo a large lattice relaxation, through which a deep level can be induced, capturing electrons and the deep state can be transformed into shallow donor state by a photon absorption. We suggest that the bistability can give explanations to two puzzling aspects.

Canadian Penning Trap Mass Measurements using a Position Sensitive MCP

NASA Astrophysics Data System (ADS)

Kuta, Trenton; Aprahamian, Ani; Marley, Scott; Nystrom, Andrew; Clark, Jason; Perez Galvan, Adrian; Hirsh, Tsviki; Savard, Guy; Orford, Rodney; Morgan, Graeme

2015-10-01

The primary focus of the Canadian Penning Trap (CPT) located at Argonne National Lab is to determine the masses of various isotopes produced in the spontaneous fission of Californium. Currently, the CPT is operating in conjunction with CARIBU at the ATLAS facility in an attempt to measure neutron-rich nuclei produced by a 1.5 Curie source of Californium 252. The masses of nuclei produced in fission is accomplished by measuring the cyclotron frequency of the isotopes circling within the trap. This frequency is determined by a position sensitive MCP, which records the relative position of the isotope in the trap at different times. Using these position changes over time in connection with a center spot, angles between these positions are calculated and used to determine the frequency. Most of the work currently being conducted on the CPT is focused on the precision of these frequency measurements. The use of traps has revolutionized the measurements of nuclear masses to very high precision. The optimization methods employed here include focusing the beam in order to reduce the spread on the position of the isotope as well as the tuning of the MR-ToF, a mass separator that is intended on removing contaminants in the beam. This work was supported by the nuclear Grant PHY-1419765 for the University of Notre Dame.

Infrared photoconductivity and photovoltaic response from nanoscale domains of PbS alloyed with thorium and oxygen

NASA Astrophysics Data System (ADS)

Arad-Vosk, N.; Beach, R.; Ron, A.; Templeman, T.; Golan, Y.; Sarusi, G.; Sa'ar, A.

2018-03-01

Thin films of lead sulfide alloyed with thorium and oxygen were deposited on GaAs substrates and processed to produce a photo-diode structure. Structural, optical and electrical characterizations indicate the presence of small nanoscale domains (NDs) that are characterized by dense packaging, high quality interfaces and a blue-shift of the energy bandgap toward the short wavelength infrared range of the spectrum. Photocurrent spectroscopy revealed a considerable photoconductivity that is correlated with excitation of carriers in the NDs of lead sulfide alloyed with thorium and oxygen. Furthermore, the appearance of a photovoltaic effect under near infrared illumination indicates a quasi-type II band alignment at the interface of the GaAs and the film of NDs.

Infrared photoconductivity and photovoltaic response from nanoscale domains of PbS alloyed with thorium and oxygen.

PubMed

Arad-Vosk, N; Beach, R; Ron, A; Templeman, T; Golan, Y; Sarusi, G; Sa'ar, A

2018-03-16

Thin films of lead sulfide alloyed with thorium and oxygen were deposited on GaAs substrates and processed to produce a photo-diode structure. Structural, optical and electrical characterizations indicate the presence of small nanoscale domains (NDs) that are characterized by dense packaging, high quality interfaces and a blue-shift of the energy bandgap toward the short wavelength infrared range of the spectrum. Photocurrent spectroscopy revealed a considerable photoconductivity that is correlated with excitation of carriers in the NDs of lead sulfide alloyed with thorium and oxygen. Furthermore, the appearance of a photovoltaic effect under near infrared illumination indicates a quasi-type II band alignment at the interface of the GaAs and the film of NDs.

The local lymph node assay: current position in the regulatory classification of skin sensitizing chemicals.

PubMed

Basketter, David A; Gerberick, G Frank; Kimber, Ian

2007-01-01

The local lymph node assay (LLNA) is being used increasingly in the identification of skin sensitizing chemicals for regulatory purposes. In the context of new chemicals legislation (REACH) in Europe, it is the preferred assay. The rationale for this is that the LLNA quantitative and objective approach to skin sensitization testing allied with the important animal welfare benefits that the method offers. However, as with certain guinea pig sensitization tests before it, this increasing use also brings experience with an increasingly wide range of industrial and other chemicals where the outcome of the assay does not always necessarily meet with the expectations of those conducting it. Sometimes, the result appears to be a false negative, but rather more commonly, the complaint is that the chemical represents a false positive. Against this background we have here reviewed a number of instances where false positive and false negative results have been described and have sought to reconcile science with expectation. Based on these analyses, it is our conclusion that false positives and false negatives do occur in the LLNA, as they do with any other skin sensitization assay (and indeed with all tests used for hazard identification), and that this occurs for a number of reasons. We further conclude, however, that false positive results in the LLNA, as with the guinea pig maximization test, arise most commonly via failure to distinguish what is scientifically correct from that which is unpalatable. The consequences of this confusion are discussed in the article, particularly in relation to the need to integrate both potency measurement and risk assessments into classification and labelling schemes that aim to manage potential risks to human health.

Carrier transport performance of Cd0.9Zn0.1Te detector by direct current photoconductive technology

NASA Astrophysics Data System (ADS)

Ling, Yunpeng; Min, Jiahua; Liang, Xiaoyan; Zhang, Jijun; Yang, Liuqing; Zhang, Ying; Li, Ming; Liu, Zhaoxin; Wang, Linjun

2017-01-01

In this paper, based on the derivation of the Hecht model and Many model, we establish a new theoretical model and deduce its mathematical equation by considering an even-distributed charged center of certain concentration under constant illumination. This model helps us deeply understand the carrier transport performance of Cd0.9Zn0.1Te (CZT) under various illuminations and non-uniform distribution of the internal electric field in CZT. In our research, direct current photoconductive technology (DCPT) is applied to assess the electrical transport properties of carriers in CZT crystals, which is verified by room temperature Am-241 alpha-particle responses and charge collection efficiency test. The mobility-lifetime product ( μτ ) for carriers is extracted from fitting the Hecht model by DCPT for CZT radiated from the cathode and anode by a constant laser, respectively. Moreover, the carrier transport properties of CZT under various light intensities and during a wide range of temperatures are also taken and analyzed in detail, which enable us to develop the best performance of CZT. In addition, we figure out a method for estimating μeτe and μhτh on different positions of CZT wafer on the basis of the pixel detector that collects single polarity charge, and several corrective actions have improved the accuracy of the measurement.

Bistability of Hydrogen in ZnO: Origin of Doping Limit and Persistent Photoconductivity

PubMed Central

Nahm, Ho-Hyun; Park, C. H.; Kim, Yong-Sung

2014-01-01

Substitutional hydrogen at oxygen site (HO) is well-known to be a robust source of n-type conductivity in ZnO, but a puzzling aspect is that the doping limit by hydrogen is only about 1018 cm−3, even if solubility limit is much higher. Another puzzling aspect of ZnO is persistent photoconductivity, which prevents the wide applications of the ZnO-based thin film transistor. Up to now, there is no satisfactory theory about two puzzles. We report the bistability of HO in ZnO through first-principles electronic structure calculations. We find that as Fermi level is close to conduction bands, the HO can undergo a large lattice relaxation, through which a deep level can be induced, capturing electrons and the deep state can be transformed into shallow donor state by a photon absorption. We suggest that the bistability can give explanations to two puzzling aspects. PMID:24535157

Nano-antenna in a photoconductive photomixer for highly efficient continuous wave terahertz emission

PubMed Central

Tanoto, H.; Teng, J. H.; Wu, Q. Y.; Sun, M.; Chen, Z. N.; Maier, S. A.; Wang, B.; Chum, C. C.; Si, G. Y.; Danner, A. J.; Chua, S. J.

2013-01-01

We report highly efficient continuous-wave terahertz (THz) photoconductive antenna based photomixer employing nano-gap electrodes in the active region. The tip-to-tip nano-gap electrode structure provides strong THz field enhancement and acts as a nano-antenna to radiate the THz wave generated in the active region of the photomixer. In addition, it provides good impedance matching to the THz planar antenna and exhibits a lower RC time constant, allowing more efficient radiation especially at the higher part of the THz spectrum. As a result, the output intensity of the photomixer with the new nano-gap electrode structure in the active region is two orders of magnitude higher than that of a photomixer with typical interdigitated electrodes. Significant improvement in the THz emission bandwidth was also observed. An efficient continuous wave THz source will greatly benefit compact THz system development for high resolution THz spectroscopy and imaging applications. PMID:24100840

Persistent photoconductivity in oxygen-ion implanted KNbO3 bulk single crystal

NASA Astrophysics Data System (ADS)

Tsuruoka, R.; Shinkawa, A.; Nishimura, T.; Tanuma, C.; Kuriyama, K.; Kushida, K.

2016-12-01

Persistent Photoconductivity (PPC) in oxygen-ion implanted KNbO3 ([001] oriented bulk single crystals; perovskite structure; ferroelectric with a band gap of 3.16 eV)　is studied in air at room temperature to prevent the degradation of its crystallinity caused by the phase transition. The residual hydrogens in un-implanted samples are estimated to be 5×1014 cm-2 from elastic recoil detection analysis (ERDA). A multiple-energy implantation of oxygen ions into KNbO3 is performed using energies of 200, 400, and 600 keV (each ion fluence:1.0×1014 cm-2). The sheet resistance varies from >108 Ω/□ for an un-implanted sample to 1.9×107 Ω/□ for as-implanted one, suggesting the formation of donors due to hydrogen interstitials and oxygen vacancies introduced by the ion implantation. The PPC is clearly observed with ultraviolet and blue LEDs illumination rather than green, red, and infrared, suggesting the release of electrons from the metastable conductive state below the conduction band relating to the charge states of the oxygen vacancy.

Enhanced emission and photoconductivity due to photo-induced charge transfer from Au nanoislands to ZnO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Shang-Hsuan; Chan, Ching-Hsiang; Liang, Ching-Tarng

2016-01-25

We report systematic studies based on photoluminescence, Hall, and photoconductivity measurements together with theoretical modeling in order to identify mechanisms for the photo-induced charge transfer effects in ZnO thin film incorporated with the Au nano-islands (AuNIs). Significant enhancement of near band edge emission and improvement in conductivity of ZnO/AuNIs samples after illumination are observed, which are attributed to the photo-induced hot electrons in Au which are then transferred into the conduction band of ZnO as long as the excitation energy is higher than the offset between the ZnO conduction-band minimum and Au Fermi level. Our experimental results are consistent withmore » the general features predicted by first principles calculations.« less

Sensitivity of the Positive and Negative Syndrome Scale (PANSS) in Detecting Treatment Effects via Network Analysis.

PubMed

Esfahlani, Farnaz Zamani; Sayama, Hiroki; Visser, Katherine Frost; Strauss, Gregory P

2017-12-01

Objective: The Positive and Negative Syndrome Scale is a primary outcome measure in clinical trials examining the efficacy of antipsychotic medications. Although the Positive and Negative Syndrome Scale has demonstrated sensitivity as a measure of treatment change in studies using traditional univariate statistical approaches, its sensitivity to detecting network-level changes in dynamic relationships among symptoms has yet to be demonstrated using more sophisticated multivariate analyses. In the current study, we examined the sensitivity of the Positive and Negative Syndrome Scale to detecting antipsychotic treatment effects as revealed through network analysis. Design: Participants included 1,049 individuals diagnosed with psychotic disorders from the Phase I portion of the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) study. Of these participants, 733 were clinically determined to be treatment-responsive and 316 were found to be treatment-resistant. Item level data from the Positive and Negative Syndrome Scale were submitted to network analysis, and macroscopic, mesoscopic, and microscopic network properties were evaluated for the treatment-responsive and treatment-resistant groups at baseline and post-phase I antipsychotic treatment. Results: Network analysis indicated that treatment-responsive patients had more densely connected symptom networks after antipsychotic treatment than did treatment-responsive patients at baseline, and that symptom centralities increased following treatment. In contrast, symptom networks of treatment-resistant patients behaved more randomly before and after treatment. Conclusions: These results suggest that the Positive and Negative Syndrome Scale is sensitive to detecting treatment effects as revealed through network analysis. Its findings also provide compelling new evidence that strongly interconnected symptom networks confer an overall greater probability of treatment responsiveness in patients with

Children's Reward and Punishment Sensitivity Moderates the Association of Negative and Positive Parenting Behaviors in Child ADHD Symptoms.

PubMed

Li, James J

2018-03-20

Atypical reward processing, including abnormal reward responsivity and sensitivity to punishment, has long been implicated in the etiology of ADHD. However, little is known about how these facets of behavior interact with positive (e.g., warmth, praise) and negative (e.g., hostility, harsh discipline) parenting behavior in the early expression of ADHD symptoms in young children. Understanding the interplay between children's reward processing and parenting may be crucial for identifying specific treatment targets in psychosocial interventions for ADHD, especially given that not all children benefit from contingency-based treatments (e.g., parent management training). The study consisted of a sample of kindergarten children (N = 201, 55% male) and their parents, who completed questionnaires about their parenting practices, their child's behaviors and participated in an observed parent-child play task in the laboratory. Children's reward responsivity and sensitivity to punishment were positively associated with child ADHD symptoms. However, children with high reward responsivity had more symptoms of ADHD but only under conditions of low negative parenting (self-reported and observed) and high self-reported positive parenting, compared to children with low reward responsivity. Children with high sensitivity to punishment had more ADHD symptoms relative to children with low sensitivity to punishment, but only under conditions in which observed praise was infrequent. Results provide evidence that individual differences in sensitivity to reward/punishment may be an important of marker of risk for ADHD, but also highlights how children's responses to positive and negative parenting behavior may vary by children's sensitivities. Clinical and treatment implications are discussed.

Analysis of photoconductive mechanisms of organic-on-inorganic photodiodes

NASA Astrophysics Data System (ADS)

Ocaya, R. O.; Dere, A.; Al-Sehemi, Abdullah G.; Al-Ghamdi, Ahmed A.; Soylu, M.; Yakuphanoglu, F.

2017-09-01

In this work, it is shown that choosing an organic-on-inorganic Schottky diode for photoconductive sensing by a using a power law exponent (PLE or γ) determined at a single bias point is a limited approach. The standard literature approach does not highlight any bias voltage effects on the distribution of interface state density and other operationally important parameters. In this paper we suggest a new empirical method that holistically highlights the variation of γ with voltage, irradiance and temperature to reach a more informed choice of photosensor for real applications. We obtain a simple, plausible relation of the variation of barrier height, Φ, with voltage, irradiance and temperature. The method is evaluated with data collected previously for Schottky diodes of structure Al/p-Si/organic-semiconductor (OSC)/Au, where OSC is Coumarin-doped with graphene oxide (GO), Cobalt Phthacyanine (CoPC) doped with GO or PCBM doped with GO, respectively. The method reproduces published data for the three diodes reported at specific bias and provides for the first time some qualitative evidence of barrier height variation with light intensity, for which a possible physical basis is also given. Typically, Schottky barrier height is characterized using dark current leading to an under reporting of the effect of illumination on barrier height. Finally, since recombination mechanisms are gauged on the basis of the magnitude of PLE, the method facilitates the identification of the recombination mechanism at a given bias.

Origins of Persistent Photoconductivity in GaAsN Alloys

NASA Astrophysics Data System (ADS)

Field, R. L., III; Wang, Y. Q.; Kurdak, C.; Goldman, R. S.

2013-03-01

In GaAs1-xNx alloys, we observe significant persistent photoconductivity (PPC) at cryogenic temperatures for x > 0.006, with the PPC strength increasing with increasing x and decreasing upon rapid-thermal annealing (RTA). Since the RTA-induced suppression is accompanied by a reduction of the interstitial N fraction, the N-induced donor state is likely associated with N pairs. PPC is attributed to the promotion of carriers from a ground N-pair state to the conduction band edge, inducing modifications in the N-pair molecular bond configuration. When illumination is terminated, an energy barrier hinders the return of carriers to the N-pair induced complex. With the addition of thermal energy, the original N-pair configuration is restored and the N-pair induced complex is then able to accept carriers. We use PPC at cryogenic temperatures to go through a metal-insulator transition in GaAsN by increasing the carrier density with illumination. For different illumination durations we determine the minimum metallic conductivity, giving us the critical carrier density, nc, at the transition point. We then determine the effective mass, m * , using the Mott criterion nc1 / 3 aH = 0.26 where aH = (4 πɛ h2) /(e2 m *) is the Bohr radius. We use PPC to induce a metal-insulator transition in GaAsN. We will discuss the effective mass as a function of N concentration and compare to the predictions of the band anticrossing model.

Position sensitivity in large spectroscopic LaBr3:Ce crystals for Doppler broadening correction

NASA Astrophysics Data System (ADS)

Blasi, N.; Giaz, A.; Boiano, C.; Brambilla, S.; Camera, F.; Million, B.; Riboldi, S.

2016-12-01

The position sensitivity of a large LaBr3:Ce crystal was investigated with the aim of correcting for the Doppler broadening in nuclear physics experiments. The crystal was cylindrical, 3 in×3 in (7.62 cm x 7.62 cm) and with diffusive surfaces as typically used in nuclear physics basic research to measure medium or high energy gamma rays (0.5 MeVPosition Sensitive Photomultipliers (PSPMT). The signals from the 256 segments of the four PSPMTs were acquired grouping them into 16 elements. An event by event analysis was performed and a positon resolution of the order of 2 cm was found. It was verified that this allows an important reduction of the Doppler broadening induced by relativistic beams in Nuclear Physics experiments.

Observation of spin-polarized photoconductivity in (Ga,Mn)As/GaAs heterojunction without magnetic field

PubMed Central

Wu, Qing; Liu, Yu; Wang, Hailong; Li, Yuan; Huang, Wei; Zhao, Jianhua; Chen, Yonghai

2017-01-01

In the absent of magnetic field, we have observed the anisotropic spin polarization degree of photoconduction (SPD-PC) in (Ga,Mn)As/GaAs heterojunction. We think three kinds of mechanisms contribute to the magnetic related signal, (i) (Ga,Mn)As self-producing due to the valence band polarization, (ii) unequal intensity of left and right circularly polarized light reaching to GaAs layer to excite unequal spin polarized carriers in GaAs layer, and (iii) (Ga,Mn)As as the spin filter layer for spin transport from GaAs to (Ga,Mn)As. Different from the previous experiments, the influence coming from the Zeeman splitting induced by an external magnetic field can be avoided here. While temperature dependence experiment indicates that the SPD-PC is mixed with the magnetic uncorrelated signals, which may come from current induced spin polarization. PMID:28084437

Photoconductivity induced by nanoparticle segregated grain-boundary in spark plasma sintered BiFeO3

NASA Astrophysics Data System (ADS)

Nandy, Subhajit; Mocherla, Pavana S. V.; Sudakar, C.

2017-05-01

Photoconductivity studies on spark plasma sintered BiFeO3 samples with two contrasting morphologies, viz., nanoparticle-segregated grain boundary (BFO-AP) and clean grain boundary (BFO-AA), show that their photo-response is largely influenced by the grain boundary defects. Impedance analyses at 300 K and 573 K clearly demarcate the contributions from grain, grain-boundary, and the nanoparticle-segregated grain-boundary conductivities. I-V characteristics under 1 sun illumination show one order of higher conductivity for BFO-AP, whereas conductivity decreases for BFO-AA sample. Larger photocurrent in BFO-AP is attributed to the extra conduction path provided by oxygen vacancies on the nanoparticle surfaces residing at the grain boundaries. Creation of photo-induced traps under illumination and the absence of surface conduction channels in BFO-AA are surmised to result in a decreased conductivity on illumination.

Coexistence of positive and negative refractive index sensitivity in the liquid-core photonic crystal fiber based plasmonic sensor.

PubMed

Shuai, Binbin; Xia, Li; Liu, Deming

2012-11-05

We present and numerically characterize a liquid-core photonic crystal fiber based plasmonic sensor. The coupling properties and sensing performance are investigated by the finite element method. It is found that not only the plasmonic mode dispersion relation but also the fundamental mode dispersion relation is rather sensitive to the analyte refractive index (RI). The positive and negative RI sensitivity coexist in the proposed design. It features a positive RI sensitivity when the increment of the SPP mode effective index is larger than that of the fundamental mode, but the sensor shows a negative RI sensitivity once the increment of the fundamental mode gets larger. A maximum negative RI sensitivity of -5500nm/RIU (Refractive Index Unit) is achieved in the sensing range of 1.50-1.53. The effects of the structural parameters on the plasmonic excitations are also studied, with a view of tuning and optimizing the resonant spectrum.

New uses of position-sensitive photomultiplier tubes

NASA Astrophysics Data System (ADS)

Gordon, Jeffrey S.; Redus, Robert H.; Nagarkar, Vivek V.; Squillante, Michael R.

1992-12-01

Recent advances in photomultiplier tube technology have led to the availability of position sensitive photomultiplier tubes (PSPMTs). These tubes make it possible to build a new generation of imaging instruments for gamma rays and other types of ionizing radiation. We have investigated the use of these tubes for the construction of several prototype instruments. The first application investigated measures the quantity and distribution of radioactive compounds on filter papers used in microbiology research. The intent of this instrument is to replace film autoradiography with an electronic imaging system which can analyze samples 75 to 110 times faster than film. The second application involved the development of an intraoperative imaging probe to help surgeons identify cancerous tissue and ensure its complete removal. This instrument will replace a non-imaging probe now in use at many hospitals. A third prototype instrument under evaluation is an imaging nuclear survey system which obtains both a video and gamma ray image for the purpose of locating and quantifying radioactive materials. This system would be used at nuclear power plants and radioactive materials preparation facilities. A modification of this system could be built into robots used for inspecting and repairing power plants.

Range position and climate sensitivity: The structure of among-population demographic responses to climatic variation

USGS Publications Warehouse

Amburgey, Staci M.; Miller, David A. W.; Grant, Evan H. Campbell; Rittenhouse, Tracy A. G.; Benard, Michael F.; Richardson, Jonathan L.; Urban, Mark C.; Hughson, Ward; Brand, Adrianne B,; Davis, Christopher J.; Hardin, Carmen R.; Paton, Peter W. C.; Raithel, Christopher J.; Relyea, Rick A.; Scott, A. Floyd; Skelly, David K.; Skidds, Dennis E.; Smith, Charles K.; Werner, Earl E.

2018-01-01

Species’ distributions will respond to climate change based on the relationship between local demographic processes and climate and how this relationship varies based on range position. A rarely tested demographic prediction is that populations at the extremes of a species’ climate envelope (e.g., populations in areas with the highest mean annual temperature) will be most sensitive to local shifts in climate (i.e., warming). We tested this prediction using a dynamic species distribution model linking demographic rates to variation in temperature and precipitation for wood frogs (Lithobates sylvaticus) in North America. Using long-term monitoring data from 746 populations in 27 study areas, we determined how climatic variation affected population growth rates and how these relationships varied with respect to long-term climate. Some models supported the predicted pattern, with negative effects of extreme summer temperatures in hotter areas and positive effects on recruitment for summer water availability in drier areas. We also found evidence of interacting temperature and precipitation influencing population size, such as extreme heat having less of a negative effect in wetter areas. Other results were contrary to predictions, such as positive effects of summer water availability in wetter parts of the range and positive responses to winter warming especially in milder areas. In general, we found wood frogs were more sensitive to changes in temperature or temperature interacting with precipitation than to changes in precipitation alone. Our results suggest that sensitivity to changes in climate cannot be predicted simply by knowing locations within the species’ climate envelope. Many climate processes did not affect population growth rates in the predicted direction based on range position. Processes such as species-interactions, local adaptation, and interactions with the physical landscape likely affect the responses we observed. Our work highlights the

Face Inversion Disproportionately Disrupts Sensitivity to Vertical over Horizontal Changes in Eye Position

ERIC Educational Resources Information Center

Crookes, Kate; Hayward, William G.

2012-01-01

Presenting a face inverted (upside down) disrupts perceptual sensitivity to the spacing between the features. Recently, it has been shown that this disruption is greater for vertical than horizontal changes in eye position. One explanation for this effect proposed that inversion disrupts the processing of long-range (e.g., eye-to-mouth distance)…

Enhanced optical-to-THz conversion efficiency of photoconductive antenna using dielectric nano-layer encapsulation

NASA Astrophysics Data System (ADS)

Gupta, Abhishek; Rana, Goutam; Bhattacharya, Arkabrata; Singh, Abhishek; Jain, Ravikumar; Bapat, Rudheer D.; Duttagupta, S. P.; Prabhu, S. S.

2018-05-01

Photoconductive antennas (PCAs) are among the most conventional devices used for emission as well as detection of terahertz (THz) radiation. However, due to their low optical-to-THz conversion efficiencies, applications of these devices in out-of-laboratory conditions are limited. In this paper, we report several factors of enhancement in THz emission efficiency from conventional PCAs by coating a nano-layer of dielectric (TiO2) on the active area between the electrodes of a semi-insulating GaAs-based device. Extensive experiments were done to show the effect of thicknesses of the TiO2 layer on the THz power enhancement with different applied optical power and bias voltages. Multiphysics simulations were performed to elucidate the underlying physics behind the enhancement of efficiency of the PCA. Additionally, this layer increases the robustness of the electrode gaps of the PCAs with high electrical insulation as well as protect it from external dust particles.

Position-sensitive radiation monitoring (surface contamination monitor). Innovative technology summary report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1999-06-01

The Shonka Research Associates, Inc. Position-Sensitive Radiation Monitor both detects surface radiation and prepares electronic survey map/survey report of surveyed area automatically. The electronically recorded map can be downloaded to a personal computer for review and a map/report can be generated for inclusion in work packages. Switching from beta-gamma detection to alpha detection is relatively simple and entails moving a switch position to alpha and adjusting the voltage level to an alpha detection level. No field calibration is required when switching from beta-gamma to alpha detection. The system can be used for free-release surveys because it meets the federal detectionmore » level sensitivity limits requires for surface survey instrumentation. This technology is superior to traditionally-used floor contamination monitor (FCM) and hand-held survey instrumentation because it can precisely register locations of radioactivity and accurately correlate contamination levels to specific locations. Additionally, it can collect and store continuous radiological data in database format, which can be used to produce real-time imagery as well as automated graphics of survey data. Its flexible design can accommodate a variety of detectors. The cost of the innovative technology is 13% to 57% lower than traditional methods. This technology is suited for radiological surveys of flat surfaces at US Department of Energy (DOE) nuclear facility decontamination and decommissioning (D and D) sites or similar public or commercial sites.« less

Light-Induced Peroxide Formation in ZnO: Origin of Persistent Photoconductivity

PubMed Central

Kang, Youngho; Nahm, Ho-Hyun; Han, Seungwu

2016-01-01

The persistent photoconductivity (PPC) in ZnO has been a critical problem in opto-electrical devices employing ZnO such as ultraviolet sensors and thin film transistors for the transparent display. While the metastable state of oxygen vacancy (VO) is widely accepted as the microscopic origin of PPC, recent experiments on the influence of temperature and oxygen environments are at variance with the VO model. In this study, using the density-functional theory calculations, we propose a novel mechanism of PPC that involves the hydrogen-zinc vacancy defect complex (2H-VZn). We show that a substantial amount of 2H-VZn can exist during the growth process due to its low formation energy. The light absorption of 2H-VZn leads to the metastable state that is characterized by the formation of (peroxide) around the defect, leaving the free carriers in the conduction band. Furthermore, we estimate the lifetime of photo-electrons to be ~20 secs, which is similar to the experimental observation. Our model also explains the experimental results showing that PPC is enhanced (suppressed) in oxygen-rich (low-temperature) conditions. By revealing a convincing origin of PPC in ZnO, we expect that the present work will pave the way for optimizing optoelectronic properties of ZnO. PMID:27748378

Low temperature grown photoconductive antennas for pulsed 1060 nm excitation: Influence of excess energy on the electron relaxation

NASA Astrophysics Data System (ADS)

Dietz, R. J. B.; Brahm, A.; Velauthapillai, A.; Wilms, A.; Lammers, C.; Globisch, B.; Koch, M.; Notni, G.; Tünnermann, A.; Göbel, T.; Schell, M.

2015-01-01

We investigate properties of MBE grown photoconductive terahertz (THz) antennas based on the InGaAs/InAlAs/InP material system aimed for an excitation wavelength of approx. 1060 nm. Therefore, we analyze several different approaches concerning growth parameters, layer and material compositions as well as doping. The carrier dynamics are probed via transient white-light pump-probe spectroscopy as well as THz Time Domain Spectroscopy (TDS) measurements. We find that the electron capture probability is reduced for higher electron energies. By adjusting the material band gap this can be resolved and lifetimes of 1.3 ps are obtained. These short lifetimes enable the detection of THz TDS spectra with a bandwidth exceeding 4 THz.

Suppression of persistent photo-conductance in solution-processed amorphous oxide thin-film transistors

NASA Astrophysics Data System (ADS)

Lee, Minkyung; Kim, Minho; Jo, Jeong-Wan; Park, Sung Kyu; Kim, Yong-Hoon

2018-01-01

This study offers a combinatorial approach for suppressing the persistent photo-conductance (PPC) characteristic in solution-processed amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) in order to achieve rapid photo-recovery. Various analyses were used to examine the photo-instability of indium-gallium-zinc-oxide (IGZO) TFTs including negative-bias-illumination-stress (NBIS) and transient photo-response behaviors. It was found that the indium ratio in metallic components had a significant impact on their PPC and photo-recovery characteristics. In particular, when the indium ratio was low (51.5%), the PPC characteristic was significantly suppressed and achieving rapid photo-recovery was possible without significantly affecting the electrical performance of AOSs. These results imply that the optimization of the indium composition ratio may allow achieving highly photo-stable and near PPC-free characteristics while maintaining high electrical performance of AOSs. It is considered that the negligible PPC behavior and rapid photo-recovery observed in IGZO TFTs with a lower indium composition are attributed to the less activation energy required for the neutralization of ionized oxygen vacancies.

Position-sensitive proportional counter with low-resistance metal-wire anode

DOEpatents

Kopp, Manfred K.

1980-01-01

A position-sensitive proportional counter circuit is provided which allows the use of a conventional (low-resistance, metal-wire anode) proportional counter for spatial resolution of an ionizing event along the anode of the counter. A pair of specially designed active-capacitance preamplifiers are used to terminate the anode ends wherein the anode is treated as an RC line. The preamplifiers act as stabilized active capacitance loads and each is composed of a series-feedback, low-noise amplifier, a unity-gain, shunt-feedback amplifier whose output is connected through a feedback capacitor to the series-feedback amplifier input. The stabilized capacitance loading of the anode allows distributed RC-line position encoding and subsequent time difference decoding by sensing the difference in rise times of pulses at the anode ends where the difference is primarily in response to the distributed capacitance along the anode. This allows the use of lower resistance wire anodes for spatial radiation detection which simplifies the counter construction and handling of the anodes, and stabilizes the anode resistivity at high count rates (>10.sup.6 counts/sec).

Dye characteristics of Zingiber officinale var rubrum, Cinnamomum zaylanicum, Curcuma longa L., Oryza sativa L. Indica in dye sensitized solar cell (DSSC)

NASA Astrophysics Data System (ADS)

Cari; Mahfudli Fadli, U.; Bayu Prasada, A.; Supriyanto, A.

2017-01-01

The aims of the research to were know performance of DSSC using the dye of Zingiber, Cinnamomum, Curcuma, and Oryza as a photosensitizer with a variation of dye deposition area with spin coating techniques. The structure of the samples as a sandwich consisting of the working electrode (TiO2), dye, electrodes of platinum (Pt) and the electrolyte sandwiched between two electrodes. Test absorbance dye using UV-Visible Spectrophotometer Lambda 25, using a two-point conductivity test probes El Kahfi 100 and characterization test IV using a Keithley 2602A. For Zingiber results showed that absorbance at 243 nm and 279 nm, photoconductivity of 0.29 Ω-1m-1 and the efficiency is 0.015% on 0.5 cm2. Cinnamomum results showed that absorbance at 253 nm and 403 nm, photoconductivity of 0.11 Ω-1m-1 and the efficiency is 0.002% on 3 cm2. Curcuma results showed that absorbance at 243 nm and 422 nm, photoconductivity of 0.177 Ω-1m-1 and the efficiency is 0.072% on 3 cm2. Oryza results showed that absorbance at 240 nm and 423 nm, photoconductivity of 0.21 Ω-1m-1 and the efficiency is 0.04% on 2.25 cm2. Best absorbance value was obtained from Oryza dye; the highest photoconductivity was obtained from Zingiber dye, and the highest efficiency was obtained from Curcuma dye.

System and method of modulating electrical signals using photoconductive wide bandgap semiconductors as variable resistors

DOEpatents

Harris, John Richardson; Caporaso, George J; Sampayan, Stephen E

2013-10-22

A system and method for producing modulated electrical signals. The system uses a variable resistor having a photoconductive wide bandgap semiconductor material construction whose conduction response to changes in amplitude of incident radiation is substantially linear throughout a non-saturation region to enable operation in non-avalanche mode. The system also includes a modulated radiation source, such as a modulated laser, for producing amplitude-modulated radiation with which to direct upon the variable resistor and modulate its conduction response. A voltage source and an output port, are both operably connected to the variable resistor so that an electrical signal may be produced at the output port by way of the variable resistor, either generated by activation of the variable resistor or propagating through the variable resistor. In this manner, the electrical signal is modulated by the variable resistor so as to have a waveform substantially similar to the amplitude-modulated radiation.

Penicillin sensitivity among children without a positive history for penicillin allergy.

PubMed

Cetinkaya, Feyzullah; Cag, Yakup

2004-06-01

To establish the prevalence of positive penicillin skin tests among outpatients without any drug reaction history. Skin testing was performed in 147 children (aged 6-13 years) who had had received a penicillin preparation at least three times in the last 12 months without any allergic reaction. Before testing, detailed pediatric and allergy history were learned and then all children were tested with benzyl penicilloyl polylysin (PPL) and mixture of minor antigenic determinants. The test procedures were made epidermally and intradermally subsequently in every subject. The overall frequency of positive skin reactions to penicillin antigens was 10.2%. A mild systemic reaction was observed in one of the children during testing with PPL. We concluded that frequent use of penicillin and other beta-lactam antibiotics leads to sensitization of children in our study population despite these children seem to be asymptomatic during testing time. Copyright 2004 Blackwell Munksgaard

Designing a chevron unit for a microelectronic position-sensitive detector with two microchannel plates

NASA Astrophysics Data System (ADS)

Kosulya, A. V.; Verbitskii, V. G.

2017-09-01

The dependence of the transverse section of an electron beam on the distance between plates and on the accelerating potential difference is determined for a chevron unit of a microelectronic position-sensitive detector (MPSD) with two microchannel plates. The geometry of the MPSD chevron unit is designed and optimized.

GRIDSS: sensitive and specific genomic rearrangement detection using positional de Bruijn graph assembly

PubMed Central

Do, Hongdo; Molania, Ramyar

2017-01-01

The identification of genomic rearrangements with high sensitivity and specificity using massively parallel sequencing remains a major challenge, particularly in precision medicine and cancer research. Here, we describe a new method for detecting rearrangements, GRIDSS (Genome Rearrangement IDentification Software Suite). GRIDSS is a multithreaded structural variant (SV) caller that performs efficient genome-wide break-end assembly prior to variant calling using a novel positional de Bruijn graph-based assembler. By combining assembly, split read, and read pair evidence using a probabilistic scoring, GRIDSS achieves high sensitivity and specificity on simulated, cell line, and patient tumor data, recently winning SV subchallenge #5 of the ICGC-TCGA DREAM8.5 Somatic Mutation Calling Challenge. On human cell line data, GRIDSS halves the false discovery rate compared to other recent methods while matching or exceeding their sensitivity. GRIDSS identifies nontemplate sequence insertions, microhomologies, and large imperfect homologies, estimates a quality score for each breakpoint, stratifies calls into high or low confidence, and supports multisample analysis. PMID:29097403

Sensitivity, specificity, positive and negative predictive values: diagnosing purple mange.

PubMed

Collier, Jill; Huebscher, Roxana

2010-04-01

To shed light on several epidemiological terms for better understanding of diagnostic testing measures by using a mythical condition, "purple mange." Scientific literature related to epidemiology and statistical tests. Nurse practitioners (NPs) use the concepts of sensitivity (SEN), specificity (SPEC), positive predictive value (PPV), and negative predictive value (NPV) daily in primary care and specialty areas. In addition, PPV and NPV vary with the prevalence of a condition. At times, NPs misunderstand the meaning of these terms. In order to develop appropriate treatment plans, an understanding of the concepts of SEN, SPEC, PPV, and NPV is important for interpreting test results. The authors have used this mythical condition purple mange as a teaching tool for NP students.

Estimated SLR station position and network frame sensitivity to time-varying gravity

NASA Astrophysics Data System (ADS)

Zelensky, Nikita P.; Lemoine, Frank G.; Chinn, Douglas S.; Melachroinos, Stavros; Beckley, Brian D.; Beall, Jennifer Wiser; Bordyugov, Oleg

2014-06-01

This paper evaluates the sensitivity of ITRF2008-based satellite laser ranging (SLR) station positions estimated weekly using LAGEOS-1/2 data from 1993 to 2012 to non-tidal time-varying gravity (TVG). Two primary methods for modeling TVG from degree-2 are employed. The operational approach applies an annual GRACE-derived field, and IERS recommended linear rates for five coefficients. The experimental approach uses low-order/degree coefficients estimated weekly from SLR and DORIS processing of up to 11 satellites (tvg4x4). This study shows that the LAGEOS-1/2 orbits and the weekly station solutions are sensitive to more detailed modeling of TVG than prescribed in the current IERS standards. Over 1993-2012 tvg4x4 improves SLR residuals by 18 % and shows 10 % RMS improvement in station stability. Tests suggest that the improved stability of the tvg4x4 POD solution frame may help clarify geophysical signals present in the estimated station position time series. The signals include linear and seasonal station motion, and motion of the TRF origin, particularly in Z. The effect on both POD and the station solutions becomes increasingly evident starting in 2006. Over 2008-2012, the tvg4x4 series improves SLR residuals by 29 %. Use of the GRGS RL02 series shows similar improvement in POD. Using tvg4x4, secular changes in the TRF origin Z component double over the last decade and although not conclusive, it is consistent with increased geocenter rate expected due to continental ice melt. The test results indicate that accurate modeling of TVG is necessary for improvement of station position estimation using SLR data.

Reduced photoconductivity observed by time-resolved terahertz spectroscopy in metal nanofilms with and without adhesion layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alberding, Brian G.; Heilweil, Edwin J., E-mail: edwin.heilweil@nist.gov; Kushto, Gary P.

2016-05-30

Non-contact, optical time-resolved terahertz spectroscopy has been used to study the transient photoconductivity of nanometer-scale metallic films deposited on the fused quartz substrates. Samples of 8 nm thick gold or titanium show an instrument-limited (ca. 0.5 ps) decrease in conductivity following photoexcitation due to electron-phonon coupling and subsequent increased lattice temperatures which increases charge carrier scattering. In contrast, for samples of 8 nm gold with a 4 nm adhesion layer of titanium or chromium, a ca. 70 ps rise time for the lattice temperature increase is observed. These results establish the increased transient terahertz transmission sign change of metallic compared to semiconductor materials.more » The results also suggest nanoscale gold films that utilize an adhesion material do not consist of distinct layers.« less

Time and position sensitive single photon detector for scintillator read-out

NASA Astrophysics Data System (ADS)

Schössler, S.; Bromberger, B.; Brandis, M.; Schmidt, L. Ph H.; Tittelmeier, K.; Czasch, A.; Dangendorf, V.; Jagutzki, O.

2012-02-01

We have developed a photon counting detector system for combined neutron and γ radiography which can determine position, time and intensity of a secondary photon flash created by a high-energy particle or photon within a scintillator screen. The system is based on a micro-channel plate photomultiplier concept utilizing image charge coupling to a position- and time-sensitive read-out anode placed outside the vacuum tube in air, aided by a standard photomultiplier and very fast pulse-height analyzing electronics. Due to the low dead time of all system components it can cope with the high throughput demands of a proposed combined fast neutron and dual discrete energy γ radiography method (FNDDER). We show tests with different types of delay-line read-out anodes and present a novel pulse-height-to-time converter circuit with its potential to discriminate γ energies for the projected FNDDER devices for an automated cargo container inspection system (ACCIS).

[Sensitivity and specificity of the breast screening program in the Isere region based on positive results between 1991 and 1999].

PubMed

Garnier, A; Poncet, F; Billette De Villemeur, A; Exbrayat, C; Bon, M F; Chevalier, A; Salicru, B; Tournegros, J M

2009-06-01

The screening program guidelines specify that the call back rate of women for additional imaging (positive mammogram) should not exceed 7% at initial screening, and 5% at subsequent screening. Materials and methods. Results in the Isere region (12%) have prompted a review of the correlation between the call back rate and indicators of quality (detection rate, sensitivity, specificity, positive predictive value) for the radiologists providing interpretations during that time period. Three groups of radiologists were identified: the group with call back rate of 10% achieved the best results (sensitivity: 92%, detection rate: 0.53%, specificity: 90%). The group with lowest call back rate (7.7%) showed insufficient sensitivity (58%). The last group with call back rate of 18.3%, showed no improvement in sensitivity (82%) and detection rate (0.53%), but showed reduced specificity (82%). The protocol update in 2001 does not resolve this problematic situation and national results continue to demonstrate a high percentage of positive screening mammograms. A significant increase in the number of positive screening examinations compared to recommended guidelines is not advantageous and leads to an overall decrease in the quality of the screening.

Antibiotic sensitivity pattern in blaNDM-1-positive and carbapenemase-producing Enterobacteriaceae

PubMed Central

Mulla, Summaiya; Charan, Jaykaran; Rajdev, Sangita

2016-01-01

Background: Some studies published in recent time revealed that many bacteria from Enterobacteriaceae group are multi-antibiotic-resistant because of the production enzymes carbapenemase particularly New Delhi metallo-beta-lactamase encoded by gene called blaNDM-1. Looking at public health importance of this issue there is a need for studies at other centers to confirm or refute published findings. Objectives: This study was designed with the aim of exploring antibiotic resistance in Enterobacteriaceae group of bacteria and also to explore gene and enzyme responsible for it. Materials and Methods: Samples of Enterobacteriaceae were collected from wards and outpatient departments. Antibiotic sensitivity was checked by an automated system (VITEK 2 COMPACT). Carbapenemase production was assessed by Modified Hodge Test. Presence of blaNDM-1 was assessed by polymerase chain reaction. Statistics: Frequency and percentage were used to describe the data. Frequency of sensitivity was compared between carbapenemase producers and noncarbapenemase producers by Fisher's exact test. Results: Forty-seven percent bacteria were found to be producing carbapenemase enzyme. These bacteria were significantly less sensitive to cefoperazone, cefepime, and amikacin. Among carbapenemase-producing organisms, 3% and 6% were resistant to tigecycline and colistin, respectively. Forty percent bacteria were found to be having blaNDM-1 gene. There was a significant difference between blaNDM-1-positive and blaNDM-1-negative for sensitivity toward cefoperazone + sulbactam, imipenem, meropenem, amikacin, tobramycine, ciprofloxacin, and levofloxacin. Conclusion: Presence of carbapenemase enzyme and blaNDM-1 gene is associated with high level of resistance in Enterobacteriaceae group of bacteria and only few antibiotics have good sensitivity for these organisms. PMID:26958516

Host-guest chemistry for tuning colloidal solubility, self-organization and photoconductivity of inorganic-capped nanocrystals

NASA Astrophysics Data System (ADS)

Bodnarchuk, Maryna I.; Yakunin, Sergii; Piveteau, Laura; Kovalenko, Maksym V.

2015-12-01

Colloidal inorganic nanocrystals (NCs), functionalized with inorganic capping ligands, such as metal chalcogenide complexes (MCCs), have recently emerged as versatile optoelectronic materials. As-prepared, highly charged MCC-capped NCs are dispersible only in highly polar solvents, and lack the ability to form long-range ordered NC superlattices. Here we report a simple and general methodology, based on host-guest coordination of MCC-capped NCs with macrocyclic ethers (crown ethers and cryptands), enabling the solubilization of inorganic-capped NCs in solvents of any polarity and improving the ability to form NC superlattices. The corona of organic molecules can also serve as a convenient knob for the fine adjustment of charge transport and photoconductivity in films of NCs. In particular, high-infrared-photon detectivities of up to 3.3 × 1011 Jones with a fast response (3 dB cut-off at 3 kHz) at the wavelength of 1,200 nm were obtained with films of PbS/K3AsS4/decyl-18-crown-6 NCs.

Characterization of the VEGA ASIC coupled to large area position-sensitive Silicon Drift Detectors

NASA Astrophysics Data System (ADS)

Campana, R.; Evangelista, Y.; Fuschino, F.; Ahangarianabhari, M.; Macera, D.; Bertuccio, G.; Grassi, M.; Labanti, C.; Marisaldi, M.; Malcovati, P.; Rachevski, A.; Zampa, G.; Zampa, N.; Andreani, L.; Baldazzi, G.; Del Monte, E.; Favre, Y.; Feroci, M.; Muleri, F.; Rashevskaya, I.; Vacchi, A.; Ficorella, F.; Giacomini, G.; Picciotto, A.; Zuffa, M.

2014-08-01

Low-noise, position-sensitive Silicon Drift Detectors (SDDs) are particularly useful for experiments in which a good energy resolution combined with a large sensitive area is required, as in the case of X-ray astronomy space missions and medical applications. This paper presents the experimental characterization of VEGA, a custom Application Specific Integrated Circuit (ASIC) used as the front-end electronics for XDXL-2, a large-area (30.5 cm2) SDD prototype. The ASICs were integrated on a specifically developed PCB hosting also the detector. Results on the ASIC noise performances, both stand-alone and bonded to the large area SDD, are presented and discussed.

Identifying Moderators of the Link between Parent and Child Anxiety Sensitivity: The Roles of Gender, Positive Parenting, and Corporal Punishment

PubMed Central

Graham, Rebecca A.; Weems, Carl F.

2014-01-01

A substantial body of literature suggests that anxiety sensitivity is a risk factor for the development of anxiety problems and research has now begun to examine the links between parenting, parent anxiety sensitivity and their child’s anxiety sensitivity. However, the extant literature has provided mixed findings as to whether parent anxiety sensitivity is associated with child anxiety sensitivity, with some evidence suggesting that others factors may influence the association. Theoretically, specific parenting behaviors may be important to the development of child anxiety sensitivity and also in understanding the association between parent and child anxiety sensitivity. In this study, 191 families (n = 255 children and adolescents aged 6–17 and their parents) completed measures of child anxiety sensitivity (CASI) and parenting (APQ-C), and parents completed measures of their own anxiety sensitivity (ASI) and their parenting (APQ-P). Corporal punishment was associated with child anxiety sensitivity and the child’s report of their parent’s positive parenting behaviors moderated the association between parent and child anxiety sensitivity. The child’s gender was also found to moderate the association between parent and child anxiety sensitivity, such that there was a positive association between girls and parent anxiety sensitivity and a negative association in boys. The findings advance the understanding of child anxiety sensitivity by establishing a link with corporal punishment and by showing that the association between parent and child anxiety sensitivity may depend upon the parenting context and child’s gender. PMID:25301177

Identifying Moderators of the Link Between Parent and Child Anxiety Sensitivity: The Roles of Gender, Positive Parenting, and Corporal Punishment.

PubMed

Graham, Rebecca A; Weems, Carl F

2015-07-01

A substantial body of literature suggests that anxiety sensitivity is a risk factor for the development of anxiety problems and research has now begun to examine the links between parenting, parent anxiety sensitivity and their child's anxiety sensitivity. However, the extant literature has provided mixed findings as to whether parent anxiety sensitivity is associated with child anxiety sensitivity, with some evidence suggesting that other factors may influence the association. Theoretically, specific parenting behaviors may be important to the development of child anxiety sensitivity and also in understanding the association between parent and child anxiety sensitivity. In this study, 191 families (n = 255 children and adolescents aged 6-17 and their parents) completed measures of child anxiety sensitivity (CASI) and parenting (APQ-C), and parents completed measures of their own anxiety sensitivity (ASI) and their parenting (APQ-P). Corporal punishment was associated with child anxiety sensitivity and the child's report of their parent's positive parenting behaviors moderated the association between parent and child anxiety sensitivity. The child's gender was also found to moderate the association between parent and child anxiety sensitivity, such that there was a positive association between girls' and their parents anxiety sensitivity and a negative association in boys. The findings advance the understanding of child anxiety sensitivity by establishing a link with corporal punishment and by showing that the association between parent and child anxiety sensitivity may depend upon the parenting context and child's gender.

78 FR 42982 - Submission for Review: Information Collection; Questionnaire for Non-Sensitive Positions (SF 85)

Federal Register 2010, 2011, 2012, 2013, 2014

2013-07-18

... OFFICE OF PERSONNEL MANAGEMENT Submission for Review: Information Collection; Questionnaire for... collection request (ICR), Office of Management and Budget (OMB) Control No. 3206-NEW, for Questionnaire for... Questionnaire for Non-Sensitive Positions, SF 85, housed in a system named e-QIP (Electronic Questionnaires for...

Phase I - Final report: Improved position sensitive detectors for thermal neutrons. Design, fabrication, and results of testing the Phase I - Proof-of-Principal Improved Position Sensitive Thermal Neutron Detector Prototype in the laboratory and at the Intense Pulsed Neutron Source (IPNS), Argonne National Laboratory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hull, Carter D.

A position sensitive neutron detector was designed and fabricated with bundles of individual detector elements with diameters of 120 mm. These neutron scintillating fibers were coupled with optoelectronic arrays to produce a ''Fiber Detector.'' A fiber position sensitive detector was completed and tested with scattered and thermal neutrons. Deployment of improved 2D PSDs with high signal to noise ratios at lower costs per area was the overall objective of the project.

Persistent photoconductivity in ZnO nanowires: Influence of oxygen and argon ambient

NASA Astrophysics Data System (ADS)

Madel, M.; Huber, F.; Mueller, R.; Amann, B.; Dickel, M.; Xie, Y.; Thonke, K.

2017-03-01

ZnO nanowires typically show persistent photoconductivity (PPC), which depends in their temporal behaviour on the ambient. We investigate ZnO nanowires in oxygen and argon ambient and analyze the PPC both on the short and on the long time scale to sort out the underlying mechanisms. Wavelength dependent excitation shows the energy barrier for the PPC to be around 150 meV below the band gap of ZnO, independent of the ambient atmosphere. In photocurrent measurements at constant wavelength, a log-logistic dependence of the conductivity on the partial oxygen pressure is observed. The experimental results are compared to a model of Bonasewicz et al. [J. Electrochem. Soc. 133, 2270 (1986)] and can be explained by oxygen adsorption processes occurring on the surface of the ZnO nanowires. From temperature dependent measurements of the decay times in oxygen and argon ambient, the related activation energies for the fast and slow decay processes are determined. Comparing our results to theoretical calculations of energy levels of intrinsic defects [Janotti and Van de Walle, Phys. Status Solidi B 248, 799 (2011)], we find oxygen vacancies to be related to the fast decay processes, whereas adsorption and desorption processes of oxygen on the ZnO nanowire surface account for the slow part.

A front end readout electronics ASIC chip for position sensitive solid state detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kravis, S.D.; Tuemer, T.O.; Visser, G.J.

1998-12-31

A mixed signal Application Specific Integrated Circuit (ASIC) chip for front end readout electronics of position sensitive solid state detectors has been manufactured. It is called RENA (Readout Electronics for Nuclear Applications). This chip can be used for both medical and industrial imaging of X-rays and gamma rays. The RENA chip is a monolithic integrated circuit and has 32 channels with low noise high input impedance charge sensitive amplifiers. It works in pulse counting mode with good energy resolution. It also has a self triggering output which is essential for nuclear applications when the incident radiation arrives at random. Different,more » externally selectable, operational modes that includes a sparse readout mode is available to increase data throughput. It also has externally selectable shaping (peaking) times.« less

High sensitive position-dependent photodetection observed in Cu-covered Si nanopyramids.

PubMed

Mei, Chunlian; Zou, Jiaren; Huang, Xu; Zou, Bugao; Zhou, Peiqi; Gan, Zhikai; Hu, Jieqiong; Zhang, Qian; Wang, Hui

2018-05-18

Silicon nanopyramids with the excellent ability of light absorption have been mostly reported in solar cells. Here, we report an obviously enhanced lateral photovoltaic effect (LPE) in copper-nanoparticle-covered random Si nanopyramids (Cu@Si-pyramid). Remarkable photoelectric responses are achieved in broadband from 405 to 780 nm. Furthermore, a prominent LPE is double-enhanced from 74.0 to 157.9 mV mm -1 when the linear region decreases from 3 to 1 mm. Finite-difference time-domain simulation is applied to investigate the origin of the exceptional results. This work declares a position-sensitive property of Si-nanopyramid systems and proposes promising applications to photodetections based on LPE.

High sensitive position-dependent photodetection observed in Cu-covered Si nanopyramids

NASA Astrophysics Data System (ADS)

Mei, Chunlian; Zou, Jiaren; Huang, Xu; Zou, Bugao; Zhou, Peiqi; Gan, Zhikai; Hu, Jieqiong; Zhang, Qian; Wang, Hui

2018-05-01

Silicon nanopyramids with the excellent ability of light absorption have been mostly reported in solar cells. Here, we report an obviously enhanced lateral photovoltaic effect (LPE) in copper-nanoparticle-covered random Si nanopyramids (Cu@Si-pyramid). Remarkable photoelectric responses are achieved in broadband from 405 to 780 nm. Furthermore, a prominent LPE is double-enhanced from 74.0 to 157.9 mV mm‑1 when the linear region decreases from 3 to 1 mm. Finite-difference time-domain simulation is applied to investigate the origin of the exceptional results. This work declares a position-sensitive property of Si-nanopyramid systems and proposes promising applications to photodetections based on LPE.

Development of arrays of position-sensitive microcalorimeters for Constellation-X

NASA Astrophysics Data System (ADS)

Smith, Stephen J.; Bandler, Simon R.; Brekosky, Regis P.; Brown, Ari-D.; Chervenak, James A.; Eckart, Megan E.; Figueroa-Feliciano, Enectali; Finkbeiner, Fred M.; Kelley, Richard L.; Kilbourne, Caroline A.; Porter, F. Scott; Sadleir, John E.

2008-07-01

We are developing arrays of position-sensitive transition-edge sensor (PoST) X-ray detectors for future astronomy missions such as NASA's Constellation-X. The PoST consists of multiple absorbers thermally coupled to one or more transition-edge sensor (TES). Each absorber element has a different thermal coupling to the TES. This results in a distribution of different pulse shapes and enables position discrimination between the absorber elements. PoST's are motivated by the desire to achieve the largest possible focal plane area with the fewest number of readout channels and are ideally suited to increasing the Constellation-X focal plane area, without comprising on spatial sampling. Optimizing the performance of PoST's requires careful design of key parameters such as the thermal conductances between the absorbers, TES and the heat sink, as well as the absorber heat capacities. Our new generation of PoST's utilizes technology successfully developed on high resolution (~ 2.5 eV) single pixels arrays of Mo/Au TESs, also under development for Constellation-X. This includes noise mitigation features on the TES and low resistivity electroplated absorbers. We report on the first experimental results from new one-channel, four-pixel, PoST's or 'Hydras', consisting of composite Au/Bi absorbers. We have achieved full-width-at-half-maximum energy resolution of between 5-6 eV on all four Hydra pixels with an exponential decay time constant of 620 μs. Straightforward position discrimination by means of rise time is also demonstrated.

Serial position effects are sensitive predictors of conversion from MCI to Alzheimer's disease dementia.

PubMed

Egli, Simone C; Beck, Irene R; Berres, Manfred; Foldi, Nancy S; Monsch, Andreas U; Sollberger, Marc

2014-10-01

It is unclear whether the predictive strength of established cognitive variables for progression to Alzheimer's disease (AD) dementia from mild cognitive impairment (MCI) varies depending on time to conversion. We investigated which cognitive variables were best predictors, and which of these variables remained predictive for patients with longer times to conversion. Seventy-five participants with MCI were assessed on measures of learning, memory, language, and executive function. Relative predictive strengths of these measures were analyzed using Cox regression models. Measures of word-list position-namely, serial position scores-together with Short Delay Free Recall of word-list learning best predicted conversion to AD dementia. However, only serial position scores predicted those participants with longer time to conversion. Results emphasize that the predictive strength of cognitive variables varies depending on time to conversion to dementia. Moreover, finer measures of learning captured by serial position scores were the most sensitive predictors of AD dementia. Copyright © 2014 The Alzheimer's Association. Published by Elsevier Inc. All rights reserved.

Development of a new signal processor for tetralateral position sensitive detector based on single-chip microcomputer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang Meizhen; Shi Longzhao; Wang Yuxing

2006-08-15

An inherently nonlinear relation between the output current of the tetralateral position sensitive detector (PSD) and the position of the incident light spot has been found theoretically. Based on single-chip microcomputer and the theoretical relation between output current and position, a new signal processor capable of correcting nonlinearity and reducing position measurement deviation of tetralateral PSD was developed. A tetralateral PSD (S1200, 13x13 mm{sup 2}, Hamamatsu Photonics K.K.) was measured with the new signal processor, a linear relation between the output position of the PSD, and the incident position of the light spot was obtained. In the 60% range ofmore » a 13x13 mm{sup 2} active area, the position nonlinearity (rms) was 0.15% and the position measurement deviation (rms) was {+-}20 {mu}m. Compared with traditional analog signal processor, the new signal processor is of better compatibility, lower cost, higher precision, and easier to be interfaced.« less

Development of a new signal processor for tetralateral position sensitive detector based on single-chip microcomputer

NASA Astrophysics Data System (ADS)

Huang, Mei-Zhen; Shi, Long-Zhao; Wang, Yu-Xing; Ni, Yi; Li, Zhen-Qing; Ding, Hai-Feng

2006-08-01

An inherently nonlinear relation between the output current of the tetralateral position sensitive detector (PSD) and the position of the incident light spot has been found theoretically. Based on single-chip microcomputer and the theoretical relation between output current and position, a new signal processor capable of correcting nonlinearity and reducing position measurement deviation of tetralateral PSD was developed. A tetralateral PSD (S1200, 13×13mm2, Hamamatsu Photonics K.K.) was measured with the new signal processor, a linear relation between the output position of the PSD, and the incident position of the light spot was obtained. In the 60% range of a 13×13mm2 active area, the position nonlinearity (rms) was 0.15% and the position measurement deviation (rms) was ±20μm. Compared with traditional analog signal processor, the new signal processor is of better compatibility, lower cost, higher precision, and easier to be interfaced.

Environmental gram-positive mastitis treatment: in vitro sensitivity and bacteriologic cure.

PubMed

Cattell, M B; Dinsmore, R P; Belschner, A P; Carmen, J; Goodell, G

2001-09-01

A clinical trial was conducted in a large dairy herd to determine the efficacy of intramammary pirlimycin hydrochloride administration during lactation for bacteriologic clearance of gram-positive environmental clinical and subclinical mastitis infections. Quarters infected with environmental streptococci that received pirlimycin therapy (13/28) were 1.8 times more likely to resolve infection than untreated quarters (5/14). The small numbers of quarters infected with coagulase-negative staphylococci resulted in inadequate power to assess treatment differences in cure rate. Although the association was not statistically significant, quarters from cows with sensitive environmental streptococci isolates from composite samples (8/13) resolved infection with treatment at approximately twice the rate of treated quarters with resistant isolates (3/10).

High voltage photo switch package module

DOEpatents

Sullivan, James S; Sanders, David M; Hawkins, Steven A; Sampayan, Stephen E

2014-02-18

A photo-conductive switch package module having a photo-conductive substrate or wafer with opposing electrode-interface surfaces, and at least one light-input surface. First metallic layers are formed on the electrode-interface surfaces, and one or more optical waveguides having input and output ends are bonded to the substrate so that the output end of each waveguide is bonded to a corresponding one of the light-input surfaces of the photo-conductive substrate. This forms a waveguide-substrate interface for coupling light into the photo-conductive wafer. A dielectric material such as epoxy is then used to encapsulate the photo-conductive substrate and optical waveguide so that only the metallic layers and the input end of the optical waveguide are exposed. Second metallic layers are then formed on the first metallic layers so that the waveguide-substrate interface is positioned under the second metallic layers.

Soft x-ray measurements using photoconductive type-IIa and single-crystal chemical vapor deposited diamond detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, A. S.; Bentley, C. D.; Foster, J. M.

2008-10-15

Photoconductive detectors (PCDs) are routinely used alongside vacuum x-ray diodes (XRDs) to provide an alternative x-ray flux measurement at laser facilities such as HELEN at AWE Aldermaston, UK, and Omega at the Laboratory for Laser Energetics. To evaluate diamond PCDs as an alternative to XRD arrays, calibration measurements made at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory are used to accurately calculate the x-ray flux from a laser-heated target. This is compared to a flux measurement using the Dante XRD diagnostic. Estimates indicate that the photoinduced conductivity from measurements made at Omega are too large, and calculationsmore » using the radiometric calibrations made at the NSLS agree with this hypothesis. High-purity, single-crystal, chemical vapor deposited (CVD) diamond samples are compared to natural type-IIa PCDs and show promising high resistivity effects, the corollary of which preliminary results show is a slower response time.« less

Pulsed characterization of a UV LED for pulsed power applications on a silicon carbide photoconductive semiconductor switch

NASA Astrophysics Data System (ADS)

Wilson, Nicholas; Mauch, Daniel; Meyers, Vincent; Feathers, Shannon; Dickens, James; Neuber, Andreas

2017-08-01

The electrical and optical characteristics of a high-power UV light emitting diode (LED) (365 nm wavelength) were evaluated under pulsed operating conditions at current amplitudes several orders of magnitude beyond the LED's manufacturer specifications. Geared towards triggering of photoconductive semiconductor switches (PCSSs) for pulsed power applications, measurements were made over varying pulse widths (25 ns-100 μs), current (0 A-250 A), and repetition rates (single shot-5 MHz). The LED forward voltage was observed to increase linearly with increasing current (˜3.5 V-53 V) and decrease with increasing pulse widths. The peak optical power observed was >30 W, and a maximum system efficiency of 23% was achieved. The evaluated LED and auxiliary hardware were successfully used as the optical trigger source for a 4H-SiC PCSS. The lowest measured on-resistance of SiC was approximately 67 kΩ.

Pulsed characterization of a UV LED for pulsed power applications on a silicon carbide photoconductive semiconductor switch.

PubMed

Wilson, Nicholas; Mauch, Daniel; Meyers, Vincent; Feathers, Shannon; Dickens, James; Neuber, Andreas

2017-08-01

The electrical and optical characteristics of a high-power UV light emitting diode (LED) (365 nm wavelength) were evaluated under pulsed operating conditions at current amplitudes several orders of magnitude beyond the LED's manufacturer specifications. Geared towards triggering of photoconductive semiconductor switches (PCSSs) for pulsed power applications, measurements were made over varying pulse widths (25 ns-100 μs), current (0 A-250 A), and repetition rates (single shot-5 MHz). The LED forward voltage was observed to increase linearly with increasing current (∼3.5 V-53 V) and decrease with increasing pulse widths. The peak optical power observed was >30 W, and a maximum system efficiency of 23% was achieved. The evaluated LED and auxiliary hardware were successfully used as the optical trigger source for a 4H-SiC PCSS. The lowest measured on-resistance of SiC was approximately 67 kΩ.

Host-guest chemistry for tuning colloidal solubility, self-organization and photoconductivity of inorganic-capped nanocrystals.

PubMed

Bodnarchuk, Maryna I; Yakunin, Sergii; Piveteau, Laura; Kovalenko, Maksym V

2015-12-09

Colloidal inorganic nanocrystals (NCs), functionalized with inorganic capping ligands, such as metal chalcogenide complexes (MCCs), have recently emerged as versatile optoelectronic materials. As-prepared, highly charged MCC-capped NCs are dispersible only in highly polar solvents, and lack the ability to form long-range ordered NC superlattices. Here we report a simple and general methodology, based on host-guest coordination of MCC-capped NCs with macrocyclic ethers (crown ethers and cryptands), enabling the solubilization of inorganic-capped NCs in solvents of any polarity and improving the ability to form NC superlattices. The corona of organic molecules can also serve as a convenient knob for the fine adjustment of charge transport and photoconductivity in films of NCs. In particular, high-infrared-photon detectivities of up to 3.3 × 10(11) Jones with a fast response (3 dB cut-off at 3 kHz) at the wavelength of 1,200 nm were obtained with films of PbS/K3AsS4/decyl-18-crown-6 NCs.

Host–guest chemistry for tuning colloidal solubility, self-organization and photoconductivity of inorganic-capped nanocrystals

PubMed Central

Bodnarchuk, Maryna I.; Yakunin, Sergii; Piveteau, Laura; Kovalenko, Maksym V.

2015-01-01

Colloidal inorganic nanocrystals (NCs), functionalized with inorganic capping ligands, such as metal chalcogenide complexes (MCCs), have recently emerged as versatile optoelectronic materials. As-prepared, highly charged MCC-capped NCs are dispersible only in highly polar solvents, and lack the ability to form long-range ordered NC superlattices. Here we report a simple and general methodology, based on host–guest coordination of MCC-capped NCs with macrocyclic ethers (crown ethers and cryptands), enabling the solubilization of inorganic-capped NCs in solvents of any polarity and improving the ability to form NC superlattices. The corona of organic molecules can also serve as a convenient knob for the fine adjustment of charge transport and photoconductivity in films of NCs. In particular, high-infrared-photon detectivities of up to 3.3 × 1011 Jones with a fast response (3 dB cut-off at 3 kHz) at the wavelength of 1,200 nm were obtained with films of PbS/K3AsS4/decyl-18-crown-6 NCs. PMID:26647828

Improved instrumentation for intensity-, wavelength-, temperature-, and magnetic field-resolved photoconductivity spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cottingham, Patrick, E-mail: pcotting@usc.edu; Morey, Jennifer R.; Institute for Quantum Matter, Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218

2016-10-15

We report instrumentation for photovoltage and photocurrent spectroscopy over a larger continuous range of wavelengths, temperatures, and applied magnetic fields than other instruments described in the literature: 350 nm≤λ≤1700 nm, 1.8 K≤T≤300 K, and B≤9 T. This instrument uses a modulated monochromated incoherent light source with total power<30 μW in combination with an LED in order to probe selected regions of non-linear responses while maintaining low temperatures and avoiding thermal artifacts. The instrument may also be used to measure a related property, the photomagnetoresistance. We demonstrate the importance of normalizing measured responses for variations in light power and describe amore » rigorous process for performing these normalizations. We discuss several circuits suited to measuring different types of samples and provide analysis for converting measured values into physically relevant properties. Uniform approaches to measurement of these photoproperties are essential for reliable quantitative comparisons between emerging new materials with energy applications. - Highlights: • A novel instrument for measuring photoconductivity and photocurrents of materials and devices. • Continuous parameter space: 350 nm≤λ≤1700, 1.8 K≤T≤300 K, and B≤9 T. • Methodology for treating non-linear responses and variable lamp intensity. • Mathematical detail for extracting properties of materials from measured values is provided.« less

Sensitivity and specificity of oral HPV detection for HPV-positive head and neck cancer.

PubMed

Gipson, Brooke J; Robbins, Hilary A; Fakhry, Carole; D'Souza, Gypsyamber

2018-02-01

The incidence of HPV-related head and neck squamous cell carcinoma (HPV-HNSCC) is increasing. Oral samples are easy and non-invasive to collect, but the diagnostic accuracy of oral HPV detection methods for classifying HPV-positive HNSCC tumors has not been well explored. In a systematic review, we identified eight studies of HNSCC patients meeting our eligibility criteria of having: (1) HPV detection in oral rinse or oral swab samples, (2) tumor HPV or p16 testing, (3) a publication date within the last 10 years (January 2007-May 2017, as laboratory methods change), and (4) at least 15 HNSCC cases. Data were abstracted from each study and a meta-analysis performed to calculate sensitivity and specificity. Eight articles meeting inclusion criteria were identified. Among people diagnosed with HNSCC, oral HPV detection has good specificity (92%, 95% CI = 82-97%) and moderate sensitivity (72%, 95% CI = 45-89%) for HPV-positive HNSCC tumor. Results were similar when restricted to studies with only oropharyngeal cancer cases, with oral rinse samples, or testing for HPV16 DNA (instead of any oncogenic HPV) in the oral samples. Among those who already have HNSCC, oral HPV detection has few false-positives but may miss one-half to one-quarter of HPV-related cases (false-negatives). Given these findings in cancer patients, the utility of oral rinses and swabs as screening tests for HPV-HNSCC among healthy populations is probably limited. Copyright © 2017 Elsevier Ltd. All rights reserved.

Breakover mechanism of GaAs photoconductive switch triggering spark gap for high power applications

NASA Astrophysics Data System (ADS)

Tian, Liqiang; Shi, Wei; Feng, Qingqing

2011-11-01

A spark gap (SG) triggered by a semi-insulating GaAs photoconductive semiconductor switch (PCSS) is presented. Currents as high as 5.6 kA have been generated using the combined switch, which is excited by a laser pulse with energy of 1.8 mJ and under a bias of 4 kV. Based on the transferred-electron effect and gas streamer theory, the breakover characteristics of the combined switch are analyzed. The photoexcited carrier density in the PCSS is calculated. The calculation and analysis indicate that the PCSS breakover is caused by nucleation of the photoactivated avalanching charge domain. It is shown that the high output current is generated by the discharge of a high-energy gas streamer induced by the strong local electric field distortion or by overvoltage of the SG resulting from quenching of the avalanching domain, and periodic oscillation of the current is caused by interaction between the gas streamer and the charge domain. The cycle of the current oscillation is determined by the rise time of the triggering electric pulse generated by the PCSS, the pulse transmission time between the PCSS and the SG, and the streamer transit time in the SG.

Photoconductivity enhancement and charge transport properties in ruthenium-containing block copolymer/carbon nanotube hybrids.

PubMed

Lo, Kin Cheung; Hau, King In; Chan, Wai Kin

2018-04-05

Functional polymer/carbon nanotube (CNT) hybrid materials can serve as a good model for light harvesting systems based on CNTs. This paper presents the synthesis of block copolymer/CNT hybrids and the characterization of their photocurrent responses by both experimental and computational approaches. A series of functional diblock copolymers was synthesized by reversible addition-fragmentation chain transfer polymerizations for the dispersion and functionalization of CNTs. The block copolymers contain photosensitizing ruthenium complexes and modified pyrene-based anchoring units. The photocurrent responses of the polymer/CNT hybrids were measured by photoconductive atomic force microscopy (PCAFM), from which the experimental data were analyzed by vigorous statistical models. The difference in photocurrent response among different hybrids was correlated to the conformations of the hybrids, which were elucidated by molecular dynamics simulations, and the electronic properties of polymers. The photoresponse of the block copolymer/CNT hybrids can be enhanced by introducing an electron-accepting block between the photosensitizing block and the CNT. We have demonstrated that the application of a rigorous statistical methodology can unravel the charge transport properties of these hybrid materials and provide general guidelines for the design of molecular light harvesting systems.

Intense THz Pulses with large ponderomotive potential generated from large aperture photoconductive antennas.

PubMed

Ropagnol, X; Khorasaninejad, M; Raeiszadeh, M; Safavi-Naeini, S; Bouvier, M; Côté, C Y; Laramée, A; Reid, M; Gauthier, M A; Ozaki, T

2016-05-30

We report the generation of free space terahertz (THz) pulses with energy up to 8.3 ± 0.2 µJ from an encapsulated interdigitated ZnSe Large Aperture Photo-Conductive Antenna (LAPCA). An aperture of 12.2 cm² is illuminated using a 400 nm pump laser with multi-mJ energies at 10 Hz repetition rate. The calculated THz peak electric field is 331 ± 4 kV/cm with a spectrum characterized by a median frequency of 0.28 THz. Given its relatively low frequency, this THz field will accelerate charged particles efficiently having very large ponderomotive energy of 15 ± 1 eV for electrons in vacuum. The scaling of the emission is studied with respect to the dimensions of the antenna, and it is observed that the capacitance of the LAPCA leads to a severe decrease in and distortion of the biasing voltage pulse, fundamentally limiting the maximum applied bias field and consequently the maximum energy of the radiated THz pulses. In order to demonstrate the advantages of this source in the strong field regime, an open-aperture Z-scan experiment was performed on n-doped InGaAs, which showed significant absorption bleaching.

Position sensitive detection of neutrons in high radiation background field.

PubMed

Vavrik, D; Jakubek, J; Pospisil, S; Vacik, J

2014-01-01

We present the development of a high-resolution position sensitive device for detection of slow neutrons in the environment of extremely high γ and e(-) radiation background. We make use of a planar silicon pixelated (pixel size: 55 × 55 μm(2)) spectroscopic Timepix detector adapted for neutron detection utilizing very thin (10)B converter placed onto detector surface. We demonstrate that electromagnetic radiation background can be discriminated from the neutron signal utilizing the fact that each particle type produces characteristic ionization tracks in the pixelated detector. Particular tracks can be distinguished by their 2D shape (in the detector plane) and spectroscopic response using single event analysis. A Cd sheet served as thermal neutron stopper as well as intensive source of gamma rays and energetic electrons. Highly efficient discrimination was successful even at very low neutron to electromagnetic background ratio about 10(-4).

Sensitivity and positive predictive values of presurgical clinical diagnosis of excised benign and malignant skin tumors: a prospective study of 835 lesions in 778 patients.

PubMed

Har-Shai, Y; Hai, N; Taran, A; Mayblum, S; Barak, A; Tzur, E; Schafer, I; David, R; David, E; Linn, S

2001-12-01

This article reports on the sensitivity and positive predictive value of clinical diagnosis of benign and malignant skin tumors by expert plastic surgeons in an Israeli clinic. Most published reports have focused on the sensitivity of clinicians' diagnoses, a general measure of the physician's skill that does not predict the rate of accuracy of a physician's diagnoses. Our study of 835 lesions in 778 patients, one of the largest Israeli series, assesses the clinical diagnosis of malignant and benign skin tumors and is one of the few that provide information on the positive predictive value, the measure that is of interest to both physicians and patients. The majority of tumors were benign (56.8 percent), 31.6 percent were malignant, and 11.6 percent were premalignant. Among the 474 benign lesions, 46 percent were nevi. The most common nevi subclass was compound nevi (53 percent), 9 percent of the nevi were dysplastic, and 5 percent were blue nevi. The most common malignant tumor was basal cell carcinoma, accounting for 78 percent of malignant tumors. Although sensitivity for clinical diagnosis of malignancy was 91.3 percent, the positive predictive value for clinical diagnosis of malignancy was 71.3 percent. The sensitivity rate for clinically diagnosing premalignant tumors was 42.3 percent, whereas the positive predictive value for these diagnoses was higher (64.1 percent). The sensitivity rate for diagnosis of all benign lesions was 85.9 percent, and the positive predictive value was 94.2 percent. The sensitivity rate for diagnosis of all nevi was 87.6 percent, and the positive predictive value was 85.7 percent: i.e., only seven of the 218 pathologically proven diagnoses of nevi (3.2 percent) were falsely diagnosed as malignant lesions. Even more interestingly, five of the 223 clinical diagnoses of nevi (2.2 percent) were pathologically proven to be malignant melanomas, and seven were found to be premalignant lesions (3.1 percent). It was concluded that

Roll-to-roll light directed electrophoretic deposition system and method

DOEpatents

Pascall, Andrew J.; Kuntz, Joshua

2017-06-06

A roll-to-roll light directed electrophoretic deposition system and method advances a roll of a flexible electrode web substrate along a roll-to-roll process path, where a material source is positioned to provide on the flexible electrode web substrate a thin film colloidal dispersion of electrically charged colloidal material dispersed in a fluid. A counter electrode is also positioned to come in contact with the thin film colloidal dispersion opposite the flexible electrode web substrate, where one of the counter electrode and the flexible electrode web substrate is a photoconductive electrode. A voltage source is connected to produce an electric potential between the counter electrode and the flexible electrode web substrate to induce electrophoretic deposition on the flexible electrode web substrate when the photoconductive electrode is rendered conductive, and a patterned light source is arranged to illuminate the photoconductive electrode with a light pattern and render conductive illuminated areas of the photoconductive electrode so that a patterned deposit of the electrically charged colloidal material is formed on the flexible electrode web substrate.

Positioning system for single or multi-axis sensitive instrument calibration and calibration system for use therewith

NASA Technical Reports Server (NTRS)

Finley, Tom D. (Inventor); Parker, Peter A. (Inventor)

2008-01-01

A positioning and calibration system are provided for use in calibrating a single or multi axis sensitive instrument, such as an inclinometer. The positioning system includes a positioner that defines six planes of tangential contact. A mounting region within the six planes is adapted to have an inclinometer coupled thereto. The positioning system also includes means for defining first and second flat surfaces that are approximately perpendicular to one another with the first surface adapted to be oriented relative to a local or induced reference field of interest to the instrument being calibrated, such as a gravitational vector. The positioner is positioned such that one of its six planes tangentially rests on the first flat surface and another of its six planes tangentially contacts the second flat surface. A calibration system is formed when the positioning system is used with a data collector and processor.

Sensitivity and specificity of CT colonography for the detection of colonic neoplasia after positive faecal occult blood testing: systematic review and meta-analysis.

PubMed

Plumb, Andrew A; Halligan, Steve; Pendsé, Douglas A; Taylor, Stuart A; Mallett, Susan

2014-05-01

CT colonography (CTC) is recommended after positive faecal occult blood testing (FOBt) when colonoscopy is incomplete or infeasible. We aimed to estimate the sensitivity and specificity of CTC for colorectal cancer and adenomatous polyps following positive FOBt via systematic review. The MEDLINE, EMBASE, AMED and Cochrane Library databases were searched for CTC studies reporting sensitivity and specificity for colorectal cancer and adenomatous polyps. Included subjects had tested FOBt-positive by guaiac or immunochemical methods. Per-patient detection rates were summarized via forest plots. Meta-analysis of sensitivity and specificity was conducted using a bivariate random effects model and the average operating point calculated. Of 538 articles considered, 5 met inclusion criteria, describing results from 622 patients. Research study quality was good. CTC had a high per-patient average sensitivity of 88.8 % (95 % CI 83.6 to 92.5 %) for ≥6 mm adenomas or colorectal cancer, with low between-study heterogeneity. Specificity was both more heterogeneous and lower, at an average of 75.4 % (95 % CI 58.6 to 86.8 %). Few studies have investigated CTC in FOBt-positive individuals. CTC is sensitive at a ≥6 mm threshold but specificity is lower and variable. Despite the limited data, these results suggest that CTC may adequately substitute for colonoscopy when the latter is undesirable. • FOBt is the most common mass screening test for colorectal cancer. • Few studies evaluate CT colonography after positive FOBt. • CTC is approximately 89 % sensitive for ≥6 mm adenomas/cancer in this setting. • Specificity is lower, at approximately 75 %, and more variable. • CT colonography is a good alternative when colonoscopy is undesirable.

Novel method for minority-carrier mobility measurement using photoconductance decay with chemically passivated and plasma damaged surfaces

NASA Astrophysics Data System (ADS)

Stephens, A. W.; Green, M. A.

1996-10-01

A method for measuring minority-carrier mobility using microwave-detected photoconductance decay without requiring bulk lifetime, estimates is presented. Three different measurements on a single sample yield values for surface recombination velocity, bulk lifetime, and diffusivity. For each measurement the surface conditions of the sample are changed, allowing extraction of different parameters. The usefulness of 0.08 molar ethanol/iodine solution as a means of achieving such good surface passivation is demonstrated. The following procedure was used to achieve high surface recombination. A CF4 plasma surface etch was shown to achieve the same level of surface damage as mechanical abrasion. The advantage of the new method is that it completely eliminates the chance of breaking samples during the abrasion process, which is of particular advantage for thin samples. The new experimental method for minority-carrier mobility measurement is evaluated using carrier lifetime measurements made on a commercially available Leo Giken ``Wafer-τ'' lifetime tester.

MiX: a position sensitive dual-phase liquid xenon detector

NASA Astrophysics Data System (ADS)

Stephenson, S.; Haefner, J.; Lin, Q.; Ni, K.; Pushkin, K.; Raymond, R.; Schubnell, M.; Shutty, N.; Tarlé, G.; Weaverdyck, C.; Lorenzon, W.

2015-10-01

The need for precise characterization of dual-phase xenon detectors has grown as the technology has matured into a state of high efficacy for rare event searches. The Michigan Xenon detector was constructed to study the microphysics of particle interactions in liquid xenon across a large energy range in an effort to probe aspects of radiation detection in liquid xenon. We report the design and performance of a small 3D position sensitive dual-phase liquid xenon time projection chamber with high light yield (Ly122=15.2 pe/keV at zero field), long electron lifetime (τ > 200 μs), and excellent energy resolution (σ/E = 1% for 1,333 keV gamma rays in a drift field of 200 V/cm). Liquid xenon time projection chambers with such high energy resolution may find applications not only in dark matter direct detection searches, but also in neutrinoless double beta decay experiments and other applications.

Position sensitive detection of neutrons in high radiation background field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vavrik, D., E-mail: vavrik@itam.cas.cz; Institute of Theoretical and Applied Mechanics, Academy of Sciences of the Czech Republic, Prosecka 76, 190 00 Prague 9; Jakubek, J.

We present the development of a high-resolution position sensitive device for detection of slow neutrons in the environment of extremely high γ and e{sup −} radiation background. We make use of a planar silicon pixelated (pixel size: 55 × 55 μm{sup 2}) spectroscopic Timepix detector adapted for neutron detection utilizing very thin {sup 10}B converter placed onto detector surface. We demonstrate that electromagnetic radiation background can be discriminated from the neutron signal utilizing the fact that each particle type produces characteristic ionization tracks in the pixelated detector. Particular tracks can be distinguished by their 2D shape (in the detector plane)more » and spectroscopic response using single event analysis. A Cd sheet served as thermal neutron stopper as well as intensive source of gamma rays and energetic electrons. Highly efficient discrimination was successful even at very low neutron to electromagnetic background ratio about 10{sup −4}.« less

A sensitive ultraviolet light photodiode based on graphene-on-zinc oxide Schottky junction

NASA Astrophysics Data System (ADS)

Zhang, Teng-Fei; Wu, Guo-An; Wang, Jiu-Zhen; Yu, Yong-Qiang; Zhang, Deng-Yue; Wang, Dan-Dan; Jiang, Jing-Bo; Wang, Jia-Mu; Luo, Lin-Bao

2017-08-01

In this study, we present a simple ultraviolet (UV) light photodiode by transferring a layer of graphene film on single-crystal ZnO substrate. The as-fabricated heterojunction exhibited typical rectifying behavior, with a Schottky barrier height of 0.623 eV. Further optoelectronic characterization revealed that the graphene-ZnO Schottky junction photodiode displayed obvious sensitivity to 365-nm light illumination with good reproducibility. The responsivity and photoconductive gain were estimated to be 3×104 A/W and 105, respectively, which were much higher than other ZnO nanostructure-based devices. In addition, it was found that the on/off ratio of the present device can be considerably improved from 2.09 to 12.1, when the device was passivated by a layer of AlOx film. These results suggest that the present simply structured graphene-ZnO UV photodiode may find potential application in future optoelectronic devices.

RF switching network: a novel technique for IR sensing

NASA Astrophysics Data System (ADS)

Mechtel, Deborah M.; Jenkins, R. Brian; Joyce, Peter J.; Nelson, Charles L.

2016-05-01

Rapid sensing of near infrared (IR) energy on a composite structure would provide information that could mitigate damage to composite structures. This paper describes a novel technique that implements photoconductive sensors in a radio frequency (RF) switching network designed to locate in real time the position and intensity of IR radiation incident on a composite structure. In the implementation described here, photoconductive sensors act as rapid response switches in a two layer RF network embedded in an FR-4 laminate. To detect radiation, phosphorous doped silicon photoconductive sensors are inserted in GHz range RF transmission lines. Photoconductive sensors use semiconductor materials that are optically sensitive at material dependent wavelengths. Incident radiation at the appropriate wavelength produces hole-electron pairs, so that the semiconductor becomes a conductor. By permitting signal propagation only when a sensor is illuminated, the RF signals are selectively routed from the lower layer transmission lines to the upper layer lines, thereby pinpointing the location and strength of incident radiation on a structure. Simulations based on a high frequency 3D planar electromagnetics model are presented and compared to experimental results. Experimental results are described for GHz range RF signal control for 300 mW and 180 mW incident energy from 975 nm and 1060 nm wavelength lasers respectively, where upon illumination, RF transmission line signal output power doubled when compared to non-illuminated results. Experimental results are reported for 100 W incident energy from a 1060 nm laser. Test results illustrate that real-time signal processing would permit a structure or vehicle to be controlled in response to incident radiation

Single-Photon Computed Tomography With Large Position-Sensitive Phototubes*

NASA Astrophysics Data System (ADS)

Feldmann, John; Ranck, Amoreena; Saunders, Robert S.; Welsh, Robert E.; Bradley, Eric L.; Saha, Margaret S.; Kross, Brian; Majewski, Stan; Popov, Vladimir; Weisenberger, Andrew G.; Wojcik, Randolph

2000-10-01

Position-sensitive photomultiplier tubes (PSPMTs) coupled to pixelated CsI(Tl) scintillators have been used with parallel-hole collimators to view the metabolism in small animals of radiopharmaceuticals tagged with ^125I. We report here our preliminary results analyzed using a tomography program^1 written in IDL programming language. The PSPMTs are mounted on a rotating gantry so as to view the subject animal from any azimuth. Preliminary results to test the tomography algorithm have been obtained by placing a variety of plastic mouse-brain phantoms (loaded with Na^125I) in front of one of the detectors and rotating the phantom in steps through 360 degrees. Results of this simulation taken with a variety of collimator hole sizes will be compared and discussed. Extentions of this technique to the use of very small PSPMTs (Hamamatsu M-64) which are capable of a very close approach to those parts of the animal of greatest interest will be described. *Supported in part by The Department of Energy, The National Science Foundation, The American Diabetes Association, The Howard Hughes Foundation and The Jeffress Trust. 1. Tomography algorithm kindly provided by Dr. S. Meikle of The Royal Prince Albert Hospital, Sydney, Australia

Radio frequency coupling apparatus and method for measuring minority carrier lifetimes in semiconductor materials

DOEpatents

Johnston, Steven W.; Ahrenkiel, Richard K.

2002-01-01

An apparatus for measuring the minority carrier lifetime of a semiconductor sample using radio-frequency coupling. The measuring apparatus includes an antenna that is positioned a coupling distance from a semiconductor sample which is exposed to light pulses from a laser during sampling operations. A signal generator is included to generate high frequency, such as 900 MHz or higher, sinusoidal waveform signals that are split into a reference signal and a sample signal. The sample signal is transmitted into a sample branch circuit where it passes through a tuning capacitor and a coaxial cable prior to reaching the antenna. The antenna is radio-frequency coupled with the adjacent sample and transmits the sample signal, or electromagnetic radiation corresponding to the sample signal, to the sample and receives reflected power or a sample-coupled-photoconductivity signal back. To lower impedance and speed system response, the impedance is controlled by limiting impedance in the coaxial cable and the antenna reactance. In one embodiment, the antenna is a waveguide/aperture hybrid antenna having a central transmission line and an adjacent ground flange. The sample-coupled-photoconductivity signal is then transmitted to a mixer which also receives the reference signal. To enhance the sensitivity of the measuring apparatus, the mixer is operated to phase match the reference signal and the sample-coupled-photoconductivity signal.

Neutral vs positive oral contrast in diagnosing acute appendicitis with contrast-enhanced CT: sensitivity, specificity, reader confidence and interpretation time

PubMed Central

Naeger, D M; Chang, S D; Kolli, P; Shah, V; Huang, W; Thoeni, R F

2011-01-01

Objective The study compared the sensitivity, specificity, confidence and interpretation time of readers of differing experience in diagnosing acute appendicitis with contrast-enhanced CT using neutral vs positive oral contrast agents. Methods Contrast-enhanced CT for right lower quadrant or right flank pain was performed in 200 patients with neutral and 200 with positive oral contrast including 199 with proven acute appendicitis and 201 with other diagnoses. Test set disease prevalence was 50%. Two experienced gastrointestinal radiologists, one fellow and two first-year residents blindly assessed all studies for appendicitis (2000 readings) and assigned confidence scores (1=poor to 4=excellent). Receiver operating characteristic (ROC) curves were generated. Total interpretation time was recorded. Each reader's interpretation with the two agents was compared using standard statistical methods. Results Average reader sensitivity was found to be 96% (range 91–99%) with positive and 95% (89–98%) with neutral oral contrast; specificity was 96% (92–98%) and 94% (90–97%). For each reader, no statistically significant difference was found between the two agents (sensitivities p-values >0.6; specificities p-values>0.08), in the area under the ROC curve (range 0.95–0.99) or in average interpretation times. In cases without appendicitis, positive oral contrast demonstrated improved appendix identification (average 90% vs 78%) and higher confidence scores for three readers. Average interpretation times showed no statistically significant differences between the agents. Conclusion Neutral vs positive oral contrast does not affect the accuracy of contrast-enhanced CT for diagnosing acute appendicitis. Although positive oral contrast might help to identify normal appendices, we continue to use neutral oral contrast given its other potential benefits. PMID:20959365

Growth and characterization of AgGa0.5In0.5Se2 single crystals by modified vertical Bridgman method

NASA Astrophysics Data System (ADS)

Vijayakumar, P.; Ramasamy, P.

2016-05-01

AgGa0.5In0.5Se2 single crystal was grown using a double wall quartz ampoule with accelerated crucible rotation technique by modified vertical Bridgman method. The structural perfection was measured using HRXRD. The grown single crystal composition was measured using ICP-OES analysis and compositional uniformities were measured using Raman spectroscopy analysis. Photoconductivity measurements confirm the positive photoconducting nature.

Photo-conductive detection of continuous THz waves via manipulated ultrafast process in nanostructures

NASA Astrophysics Data System (ADS)

Moon, Kiwon; Lee, Eui Su; Lee, Il-Min; Park, Dong Woo; Park, Kyung Hyun

2018-01-01

Time-domain and frequency-domain terahertz (THz) spectroscopy systems often use materials fabricated with exotic and expensive methods that intentionally introduce defects to meet short carrier lifetime requirements. In this study, we demonstrate the development of a nano-photomixer that meets response speed requirements without using defect-incorporated, low-temperature-grown (LTG) semiconductors. Instead, we utilized a thin InGaAs layer grown on a semi-insulating InP substrate by metal-organic chemical vapor deposition (MOCVD) combined with nano-electrodes to manipulate local ultrafast photo-carrier dynamics via a carefully designed field-enhancement and plasmon effect. The developed nano-structured photomixer can detect continuous-wave THz radiation up to a frequency of 2 THz with a peak carrier collection efficiency of 5%, which is approximately 10 times better than the reference efficiency of 0.4%. The better efficiency results from the high carrier mobility of the MOCVD-grown InGaAs thin layer with the coincidence of near-field and plasmon-field distributions in the nano-structure. Our result not only provides a generally applicable methodology for manipulating ultrafast carrier dynamics by means of nano-photonic techniques to break the trade-off relation between the carrier lifetime and mobility in typical LTG semiconductors but also contributes to mass-producible photo-conductive THz detectors to facilitate the widespread application of THz technology.

High field CdS detector for infrared radiation

NASA Technical Reports Server (NTRS)

Tyagi, R. C.; Boer, K. W.; Hadley, H. C.; Robertson, J. B.

1972-01-01

New and highly sensitive method of detecting infrared irradiation makes possible solid state infrared detector which is more sensitive near room temperature than usual photoconductive low band gap semiconductor devices. Reconfiguration of high field domains in cadmium sulphide crystals provides basis for discovery.

Neutron position-sensitive scintillation detector

DOEpatents

Strauss, Michael G.; Brenner, Raul

1984-01-01

A device is provided for mapping one- and two-dimensional distributions of neutron-positions in a scintillation detector. The device consists of a lithium glass scintillator coupled by an air gap and a light coupler to an array of photomultipliers. The air gap concentrates light flashes from the scintillator, whereas the light coupler disperses this concentrated light to a predetermined fraction of the photomultiplier tube array.

Effect of substrate nitridation temperature on the persistent photoconductivity of unintentionally-doped GaN layer grown by PAMBE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prakash, Nisha, E-mail: prakasnisha@gmail.com; Barvat, Arun; Anand, Kritika

2016-05-23

The surface roughness and defect density of GaN epitaxial layers grown on c-plane sapphire substrate are investigated and found to be dependent on nitridation temperature. GaN epitaxial layers grown after nitridation of sapphire at 200°C have a higher defect density and higher surface roughness compared to the GaN layers grown at 646°C nitridation as confirmed by atomic force microscopy (AFM). The persistent photoconductivity (PPC) was observed in both samples and it was found to be decreasing with decreasing temperature in the range 150-300°C due to long carrier lifetime and high electron mobility at low temperature. The photoresponse of the GaNmore » films grown in this study exhibit improved PPC due to their better surface morphology at 646°C nitrided sample. The point defects or extended microstructure defects limits the photocarrier lifetime and electron mobility at 200°C nitrided sample.« less

Sensitivity to the Positional Information of Morphemes inside Chinese Compound Words and Its Relationship with Word Reading

ERIC Educational Resources Information Center

Liu, Duo; Chung, Kevin Kien Hoa; Zhang, Yimin; Lu, Zheng

2014-01-01

The purpose of the present study was to investigate developmental differences in lexical processing and sensitivity to the positional information of constituent morphemes with reference to Chinese word-reading ability. One hundred mainland Chinese children (50 second graders and 50 third graders) and 22 high school students were tested with a…

Stress sensitivity mediates the relationship between traumatic life events and attenuated positive psychotic symptoms differentially by gender in a college population sample.

PubMed

Gibson, Lauren E; Anglin, Deidre M; Klugman, Joshua T; Reeves, Lauren E; Fineberg, Anna M; Maxwell, Seth D; Kerns, Connor M; Ellman, Lauren M

2014-06-01

The purpose of this study was to investigate whether stress sensitivity mediates the relationship between traumatic life events and total attenuated positive psychotic symptoms, as well as the relationship between traumatic life events and endorsement of 8 or more attenuated positive psychotic symptoms as distressing (a threshold that has been associated with higher risk for psychosis in clinical groups). Participants (n = 671, aged 17-35, 29% male) were college students who were administered the Prodromal Questionnaire, the Perceived Stress Scale and the Life Events Checklist. Bootstrapping results indicated that stress sensitivity significantly mediated the relationships between traumatic life events and the number of attenuated positive psychotic symptoms endorsed and between traumatic life events and those who endorsed 8 or more distressing attenuated positive psychotic symptoms. Stratified gender analyses indicated the findings were specific to females. Results suggest that stress sensitivity may represent a specific vulnerability factor for risk of attenuated psychotic symptoms in those previously exposed to traumatic life events and that this liability appears stronger in females. Copyright © 2014 Elsevier Ltd. All rights reserved.

A Broadband THz-TDS System Based on DSTMS Emitter and LTG InGaAs/InAlAs Photoconductive Antenna Detector

PubMed Central

Zhang, Ying; Zhang, Xiaoling; Li, Shaoxian; Gu, Jianqiang; Li, Yanfeng; Tian, Zhen; Ouyang, Chunmei; He, Mingxia; Han, Jiaguang; Zhang, Weili

2016-01-01

We demonstrate a 4-f terahertz time-domain spectroscopy (THz-TDS) system using an organic crystal DSTMS as the THz emitter and a low temperature grown (LTG) InGaAs/InAlAs photoconductive antenna as the receiver. The system covers a frequency range from 0.2 up to 8 THz. The influences of the pump laser power, the probe laser power and the azimuthal angle of the DSTMS crystal on the time-domain THz amplitude are experimentally analyzed. The frequency accuracy of the system is verified by measuring two metamaterial samples and a lactose film in this THz-TDS system. The proposed combination of DSTMS emission and PC antenna detection realizes a compact and low-cost THz-TDS scheme with an ultra-broad bandwidth, which may promote the development and the applications of THz-TDS techniques. PMID:27244689

A Broadband THz-TDS System Based on DSTMS Emitter and LTG InGaAs/InAlAs Photoconductive Antenna Detector.

PubMed

Zhang, Ying; Zhang, Xiaoling; Li, Shaoxian; Gu, Jianqiang; Li, Yanfeng; Tian, Zhen; Ouyang, Chunmei; He, Mingxia; Han, Jiaguang; Zhang, Weili

2016-05-31

We demonstrate a 4-f terahertz time-domain spectroscopy (THz-TDS) system using an organic crystal DSTMS as the THz emitter and a low temperature grown (LTG) InGaAs/InAlAs photoconductive antenna as the receiver. The system covers a frequency range from 0.2 up to 8 THz. The influences of the pump laser power, the probe laser power and the azimuthal angle of the DSTMS crystal on the time-domain THz amplitude are experimentally analyzed. The frequency accuracy of the system is verified by measuring two metamaterial samples and a lactose film in this THz-TDS system. The proposed combination of DSTMS emission and PC antenna detection realizes a compact and low-cost THz-TDS scheme with an ultra-broad bandwidth, which may promote the development and the applications of THz-TDS techniques.

32 CFR 154.13 - Sensitive positions.

Code of Federal Regulations, 2013 CFR

2013-07-01

... misconduct, malfeasance, or nonfeasance of an incumbent in any such position could result in an unacceptably... the extent feasible, the Top Secret billet structure into the component Manpower Unit Manning Document...

32 CFR 154.13 - Sensitive positions.

Code of Federal Regulations, 2010 CFR

2010-07-01

... misconduct, malfeasance, or nonfeasance of an incumbent in any such position could result in an unacceptably... the extent feasible, the Top Secret billet structure into the component Manpower Unit Manning Document...

32 CFR 154.13 - Sensitive positions.

Code of Federal Regulations, 2012 CFR

2012-07-01

... misconduct, malfeasance, or nonfeasance of an incumbent in any such position could result in an unacceptably... the extent feasible, the Top Secret billet structure into the component Manpower Unit Manning Document...

32 CFR 154.13 - Sensitive positions.

Code of Federal Regulations, 2011 CFR

2011-07-01

... misconduct, malfeasance, or nonfeasance of an incumbent in any such position could result in an unacceptably... the extent feasible, the Top Secret billet structure into the component Manpower Unit Manning Document...

32 CFR 154.13 - Sensitive positions.

Code of Federal Regulations, 2014 CFR

2014-07-01

... misconduct, malfeasance, or nonfeasance of an incumbent in any such position could result in an unacceptably... the extent feasible, the Top Secret billet structure into the component Manpower Unit Manning Document...

Development of LLNA:DAE: a new local lymph node assay that includes the elicitation phase, discriminates borderline-positive chemicals, and is useful for cross-sensitization testing.

PubMed

Yamashita, Kunihiko; Shinoda, Shinsuke; Hagiwara, Saori; Itagaki, Hiroshi

2014-02-01

We developed a new local lymph node assay (LLNA) that includes the elicitation phase termed LLNA:DAE for discrimination of borderline-positive chemicals as classified by the LLNA modified by Daicel based on ATP content (LLNA:DA) and for cross-sensitization testing. Although the LLNA:DA method could help identify skin sensitizers, some skin irritants classified as non-sensitizers by the LLNA were classified as borderline positive. In addition, the evaluation for the cross-sensitization potential between chemicals was impossible. In the LLNA:DAE procedure, test group of mice received four applications of chemicals on the dorsum of the right ear for induction and one application on the dorsum of the left ear for elicitation. Control group of mice received one chemical application on the dorsum of the left ear. We evaluated the sensitizing potential by comparing the weights of the lymph nodes from the left ears between the two groups. The results of using the LLNA:DAE method to examine 24 chemicals, which contained borderline-positive chemicals, were consistent with those from the LLNA method, except for nickel chloride (NiCl2). Two chemical pairs, 2,4-dinitrochlorobenzene (DNCB) with 2,4-dinitrofluorobenzene (DNFB) and hydroquinone (HQ) with p-benzoquinone (p-BQ), showed clear cross-sensitization with each other, while another chemical pair, DNFB with hexylcinnamic aldehyde (HCA) did not. Taken together, our results suggest that the LLNA:DAE method is useful for discriminating borderline-positive chemicals and for determining chemical cross-sensitization.

Monolithic echo-less photoconductive switches as a high-resolution detector for terahertz time-domain spectroscopy

NASA Astrophysics Data System (ADS)

Maussang, K.; Palomo, J.; Manceau, J.-M.; Colombelli, R.; Sagnes, I.; Li, L. H.; Linfield, E. H.; Davies, A. G.; Mangeney, J.; Tignon, J.; Dhillon, S. S.

2017-04-01

Interdigitated photoconductive (iPC) switches are powerful and convenient devices for time-resolved spectroscopy, with the ability to operate both as sources and detectors of terahertz (THz) frequency pulses. However, reflection of the emitted or detected radiation within the device substrate itself can lead to echoes that inherently limit the spectroscopic resolution achievable for their use in time-domain spectroscopy (TDS) systems. In this work, we demonstrate a design of low-temperature-grown-GaAs (LT-GaAs) iPC switches for THz pulse detection that suppresses such unwanted echoes. This is realized through the growth of a buried multilayer LT-GaAs structure that retains its ultrafast properties, which, after wafer bonding to a metal-coated host substrate, results in an iPC switch with a metal plane buried at a subwavelength depth below the LT-GaAs surface. Using this device as a detector, and coupling it to an echo-less iPC source, enables echo-free THz-TDS and high-resolution spectroscopy, with a resolution limited only by the temporal length of the measurement governed by the mechanical delay line used. As a proof-of-principle, the 212-221 and the 101-212 rotational lines of water vapor have been spectrally resolved, demonstrating a spectral resolution below 10 GHz.

Infrared emitting and photoconducting colloidal silver chalcogenide nanocrystal quantum dots from a silylamide-promoted synthesis.

PubMed

Yarema, Maksym; Pichler, Stefan; Sytnyk, Mykhailo; Seyrkammer, Robert; Lechner, Rainer T; Fritz-Popovski, Gerhard; Jarzab, Dorota; Szendrei, Krisztina; Resel, Roland; Korovyanko, Oleksandra; Loi, Maria Antonietta; Paris, Oskar; Hesser, Günter; Heiss, Wolfgang

2011-05-24

Here, we present a hot injection synthesis of colloidal Ag chalcogenide nanocrystals (Ag(2)Se, Ag(2)Te, and Ag(2)S) that resulted in exceptionally small nanocrystal sizes in the range between 2 and 4 nm. Ag chalcogenide nanocrystals exhibit band gap energies within the near-infrared spectral region, making these materials promising as environmentally benign alternatives to established infrared active nanocrystals containing toxic metals such as Hg, Cd, and Pb. We present Ag(2)Se nanocrystals in detail, giving size-tunable luminescence with quantum yields above 1.7%. The luminescence, with a decay time on the order of 130 ns, was shown to improve due to the growth of a monolayer thick ZnSe shell. Photoconductivity with a quantum efficiency of 27% was achieved by blending the Ag(2)Se nanocrystals with a soluble fullerene derivative. The co-injection of lithium silylamide was found to be crucial to the synthesis of Ag chalcogenide nanocrystals, which drastically increased their nucleation rate even at relatively low growth temperatures. Because the same observation was made for the nucleation of Cd chalcogenide nanocrystals, we conclude that the addition of lithium silylamide might generally promote wet-chemical synthesis of metal chalcogenide nanocrystals, including in as-yet unexplored materials.

Dense Ge nanocrystals embedded in TiO2 with exponentially increased photoconduction by field effect.

PubMed

Lepadatu, A-M; Slav, A; Palade, C; Dascalescu, I; Enculescu, M; Iftimie, S; Lazanu, S; Teodorescu, V S; Ciurea, M L; Stoica, T

2018-03-20

Si and Ge nanocrystals in oxides are of a large interest for photo-effect applications due to the fine-tuning of the optical bandgap by quantum confinement in nanocrystals. In this work, dense Ge nanocrystals suitable for enhanced photoconduction were fabricated from 60% Ge in TiO 2 amorphous layers by low temperature rapid thermal annealing at 550 °C. An exponential increase of the photocurrent with the applied voltage was observed in coplanar structure of Ge nanocrystals composite films deposited on oxidized Si wafers. The behaviour was explained by field effect control of the Fermi level at the Ge nanocrystals-TiO 2 layer/substrate interfaces. The blue-shift of the absorption gap from bulk Ge value to 1.14 eV was evidenced in both photocurrent spectra and optical reflection-transmission experiments, in good agreement with quantum confinement induced bandgap broadening in Ge nanocrystal with sizes of about 5 nm as found from HRTEM and XRD investigations. A nonmonotonic spectral dependence of the refractive index is associated to the Ge nanocrystals formation. The nanocrystal morphology is also in good agreement with the Coulomb gap hopping mechanism of T -1/2 -type explaining the temperature dependence of the dark conduction.

Using focus groups to develop a culturally sensitive videotape intervention for HIV-positive women.

PubMed

Murdaugh, C; Russell, R B; Sowell, R

2000-12-01

Research-based interventions for women with the human immunodeficiency virus (HIV) are usually developed without input from the women who receive the intervention. An exploratory study was performed using focus group methodology to develop a culturally sensitive videotape intervention for educating HIV-positive women about pregnancy and antiretroviral use. Women who met the study criteria were HIV-positive and of childbearing age. These women volunteered to participate in the focus groups to provide information on decisions concerning pregnancy and antiretroviral use during pregnancy to decrease perinatal transmission. A total of five focus groups were conducted in 1998. Responses to three questions that were relevant to the video are presented in this article. Information gained from the focus groups was used successfully to develop a videotape currently being used in a multisite intervention study. Focus group methodology is a useful strategy to develop culturally and content relevant educational interventions for research and practice.

Toward an Empirical Multidimensional Structure of Anhedonia, Reward Sensitivity, and Positive Emotionality: An Exploratory Factor Analytic Study.

PubMed

Olino, Thomas M; McMakin, Dana L; Forbes, Erika E

2016-11-20

Positive emotionality, anhedonia, and reward sensitivity share motivational and experiential elements of approach motivation and pleasure. Earlier work has examined the interrelationships among these constructs from measures of extraversion. More recently, the Research Domain Criteria introduced the Positive Valence Systems as a primary dimension to better understand psychopathology. However, the suggested measures tapping this construct have not yet been integrated within the structural framework of personality, even at the level of self-report. Thus, this study conducted exploratory factor and exploratory bifactor analyses on 17 different dimensions relevant to approach motivation, spanning anhedonia, behavioral activation system functioning, and positive emotionality. Convergent validity of these dimensions is tested by examining associations with depressive symptoms. Relying on multiple indices of fit, our preferred model included a general factor along with specific factors of affiliation, positive emotion, assertiveness, and pleasure seeking. These factors demonstrated different patterns of association with depressive symptoms. We discuss the plausibility of this model and highlight important future directions for work on the structure of a broad Positive Valence Systems construct. © The Author(s) 2016.

Sensitive detection of trimethylamine based on dopant-assisted positive photoionization ion mobility spectrometry.

PubMed

Cheng, Shasha; Li, Haitao; Jiang, Dandan; Chen, Chuang; Zhang, Tan; Li, Yong; Wang, Haitao; Zhou, Qinghua; Li, Haiyang; Tan, Mingqian

2017-01-01

Biogenic amines are degradation products generated through enzymatic and microbial processes during food spoilage, which may pose a health hazard to consumers at elevated levels. Trimethylamine (TMA) is a good target for the detection of biogenic amines due to its volatility and fishy odor. In this study, we developed a stand-alone dopant-assisted positive photoionization ion mobility spectrometry (DAPP-IMS) for rapid and sensitive detection of TMA. Response of TMA was enhanced by the addition of dopants and characteristic product ions with reduced mobility 2.26cm 2 V -1 s -1 were formed. 2-Butaone was chosen as the dopant for better separation between reagent ion peak and TMA product ion peak as well as higher sensitivity and the limit of detections (LODs) for TMA standard sample was 1ppb. The potential application of DAAP-IMS was evaluated by the detection of TMA generated by oyster and shrimp during 4°C storage. Analysis of two kinds of seafood showed the same characteristic peak to TMA standard sample, and the intensity of TMA increased over the storage time. The results of this study testify to the potential of DAPP-IMS for qualitative and quantitative determination of TMA in real food samples. Copyright © 2016 Elsevier B.V. All rights reserved.

A multiplexed TOF and DOI capable PET detector using a binary position sensitive network.

PubMed

Bieniosek, M F; Cates, J W; Levin, C S

2016-11-07

Time of flight (TOF) and depth of interaction (DOI) capabilities can significantly enhance the quality and uniformity of positron emission tomography (PET) images. Many proposed TOF/DOI PET detectors require complex readout systems using additional photosensors, active cooling, or waveform sampling. This work describes a high performance, low complexity, room temperature TOF/DOI PET module. The module uses multiplexed timing channels to significantly reduce the electronic readout complexity of the PET detector while maintaining excellent timing, energy, and position resolution. DOI was determined using a two layer light sharing scintillation crystal array with a novel binary position sensitive network. A 20 mm effective thickness LYSO crystal array with four 3 mm  ×  3 mm silicon photomultipliers (SiPM) read out by a single timing channel, one energy channel and two position channels achieved a full width half maximum (FWHM) coincidence time resolution of 180  ±  2 ps with 10 mm of DOI resolution and 11% energy resolution. With sixteen 3 mm  ×  3 mm SiPMs read out by a single timing channel, one energy channel and four position channels a coincidence time resolution 204  ±  1 ps was achieved with 10 mm of DOI resolution and 15% energy resolution. The methods presented here could significantly simplify the construction of high performance TOF/DOI PET detectors.

Influence of polymer:sensitizer ratio on photoelectric properties of organic composite photoconductor

NASA Astrophysics Data System (ADS)

Aleman, K.; Sanchez Juarez, A.; Kosarev, A.; Mansurova, S.; Koeber, S.; Meerholz, K.

2010-06-01

The results on characterization of the main photoelectric properties of the polymer:fulleren based composite material by using the non-steady-state photo-electromotive force (p-EMF) and modulated photocurrent technique are presented. By measuring this current under different experimental conditions, important material photoelectric parameters such as drift L0 and diffusion length LD, photocarrier's lifetime τ ; quantum efficiency of charge generation φ can be determined. The 50% of the composite weight consists of a mixture of the hole-conducting polymer PF6:TPD (poly-hexyle-triophene:N,N'-bis(4-methylphenyl)-N,N'-bis-(phenyl)-benzidine) sensitized with the highly soluble C60 derivative PCBM (phenyl-C61-butyric acid methyl ester) . Seven samples with varied polymer:sensitizer weight ratio (49:1wt.-%, 45:5wt.-%, 40:10wt.-%, 15:35wt.-%, 25:25wt.-%, 10:40wt.-%, 5:45wt.-%) where prepared. The remaining 50% were two azo-dyes 2,5-dimethyl-(4-p-nitrophenylazo)-anisole (DMNPAA) and 3- methoxy-(4-p-nitrophenylazo)-anisole (MNPAA) (25wt.-% each). Photoconductive composite film was sandwiched between two glass plates covered by transparent ITO electrodes. Two counter-propagating beams derived from a cw HeNe laser (λ = 633nm) intersected inside the detector creating an interference pattern. The output photo-EMF current (SEE MANUSCRIPT FOR EQUATION) was detected as a voltage drop by a lock-in amplifier. At polymer sensitizer ratio 25:25wt.-% the signal sign changes to the opposite revealing that the majority carriers at this and higher concentration of sensitizer are electrons. Our results show that the majority carrier's lifetime τ is only slightly affected by the variations of sensitizer concentration. Mobility-lifetime product μhτh of holes, on its turn decreases at the increasing sensitizer concentration, while μeτe of electrons keeps increasing. All this indicates that the carrier's mobility is strongly influenced by the changes on sensitizer concentrations.

Sensitive Infrared Photodetectors: Optimized Electron Kinetics for Room-Temperature Operation

DTIC Science & Technology

2010-12-20

QD levels; (iii) High photoconductive gain and responsivity; (iv) Low generation-recombination noise due to the long photoelectron lifetime. The...etc. [1-6]. For example, quantum-well infrared photodetectors ( QWIPs ) is currently a well-established technology, which is widely employed in...various imaging devices working at liquid nitrogen temperatures and below [7,8]. At 77K, modern QWIPs operating around λ = 10 μm demonstrate the

A position- and time-sensitive photon-counting detector with delay- line read-out

NASA Astrophysics Data System (ADS)

Jagutzki, Ottmar; Dangendorf, Volker; Lauck, Ronald; Czasch, Achim; Milnes, James

2007-05-01

We have developed image intensifier tubes with delay-anode read-out for time- and position-sensitive photon counting. The timing precision is better than 1 ns with 1000x1000 pixels position resolution and up to one megacounts/s processing rate. Large format detectors of 40 and 75 mm active diameter with internal helical-wire delay-line anodes have been produced and specified. A different type of 40 and 25 mm tubes with semi-conducting screen for image charge read-out allow for an economic and robust tube design and for placing the read-out anodes outside the sealed housing. Two types of external delay-line anodes, i.e. pick-up electrodes for the image charge, have been tested. We present tests of the detector and anode performance. Due to the low background this technique is well suited for applications with very low light intensity and especially if a precise time tagging for each photon is required. As an example we present the application of scintillator read-out in time-of-flight (TOF) neutron radiography. Further applications so far are Fluorescence Life-time Microscopy (FLIM) and Astronomy.

Single n+-i-n+ InP nanowires for highly sensitive terahertz detection.

PubMed

Peng, Kun; Parkinson, Patrick; Gao, Qian; Boland, Jessica L; Li, Ziyuan; Wang, Fan; Mokkapati, Sudha; Fu, Lan; Johnston, Michael B; Tan, Hark Hoe; Jagadish, Chennupati

2017-03-24

Developing single-nanowire terahertz (THz) electronics and employing them as sub-wavelength components for highly-integrated THz time-domain spectroscopy (THz-TDS) applications is a promising approach to achieve future low-cost, highly integrable and high-resolution THz tools, which are desirable in many areas spanning from security, industry, environmental monitoring and medical diagnostics to fundamental science. In this work, we present the design and growth of n + -i-n + InP nanowires. The axial doping profile of the n + -i-n + InP nanowires has been calibrated and characterized using combined optical and electrical approaches to achieve nanowire devices with low contact resistances, on which the highly-sensitive InP single-nanowire photoconductive THz detectors have been demonstrated. While the n + -i-n + InP nanowire detector has a only pA-level response current, it has a 2.5 times improved signal-to-noise ratio compared with the undoped InP nanowire detector and is comparable to traditional bulk THz detectors. This performance indicates a promising path to nanowire-based THz electronics for future commercial applications.

Photoconductivity of ultra-thin Ge(GeSn) layers grown in Si by low-temperature molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Talochkin, A. B., E-mail: tal@isp.nsc.ru; Novosibirsk State University, Novosibirsk 630090; Chistokhin, I. B.

2016-04-07

Photoconductivity (PC) spectra of Si/Ge(GeSn)/Si structures with the ultra-thin (1.0–2.3 nm) Ge and GeSn alloy layers grown by the low-temperature (T = 100 °C) molecular beam epitaxy are studied. Photoresponse in the range of 1.2–0.4 eV related to light absorption in the buried Ge(GeSn) layer is observed. It is shown that in case of lateral PC, a simple diffusion model can be used to determine the absorption coefficient of this layer α ∼ 10{sup 5 }cm{sup −1}. This value is 100 times larger than that of a single Ge quantum dot layer and is reached significantly above the band gap of most bulk semiconductors. The observedmore » absorption is caused by optical transitions between electron and hole states localized at the interfaces. The anomalous high value of α can be explained by the unusual state of Ge(GeSn) layer with high concentration of dangling bonds, the optical properties of which have been predicted theoretically by Knief and von Niessen (Phys. Rev. B 59, 12940 (1999)).« less

Positive alcohol use expectancies moderate the association between anxiety sensitivity and alcohol use across adolescence.

PubMed

Borges, Allison M; Lejuez, Carl W; Felton, Julia W

2018-06-01

Anxiety sensitivity (AS), or the fear of anxious symptoms and the belief that these symptoms may have negative physical, social, and cognitive consequences, is one personality trait that emerges in early adolescence and may be linked to alcohol use. However, findings are equivocal as to whether elevated AS during adolescence directly predicts alcohol use. Adolescents do report increases in positive alcohol use expectancies during this developmental period, and these expectancies have been found to be significantly associated with alcohol use. The current study examined whether positive alcohol use expectancies and AS in early adolescence predicted changes in alcohol use throughout adolescence. This aim was examined via secondary data analyses from a longitudinal study examining the development of risk behaviors in adolescents. Results of univariate latent growth curve modeling suggest that AS alone was not a significant predictor of baseline alcohol use or change in use over time after controlling for gender, age, and self-reported anxiety. However, AS in early adolescence was found to be a significant predictor of increases in alcohol use across adolescence for youth who reported greater positive alcohol use expectancies. These results indicate that beliefs regarding the positive effects of alcohol use are an important moderator in the relation between AS and change in alcohol use during adolescence. Copyright © 2018 Elsevier B.V. All rights reserved.

MiR-129-5p Sensitizes the Response of Her-2 Positive Breast Cancer to Trastuzumab by Reducing Rps6.

PubMed

Lu, Xiangdong; Ma, Jingjing; Chu, Jiahui; Shao, Qing; Zhang, Yao; Lu, Guangping; Li, Jun; Huang, Xiang; Li, Wei; Li, Yongfei; Ling, Yang; Zhao, Tao

2017-01-01

Trastuzumab is an important treatment used for patients with Her-2-positive breast cancer, but an increasing incidence of trastuzumab resistance has been observed clinically during the past decade. Aberrant microRNA (miR) expression levels are correlated with prognosis and response to trastuzumab in breast cancer. MiR-129-5p is downregulated in trastuzumab-resistant human breast cancer cells (JIMT-1), but its potential function and underlying mechanism remain unclear. Quantitative RT-PCR (qRT-PCR) was used to determine the expression levels of miR-129-5p and its potential target genes. The effects of miR-129-5p on cell responses to trastuzumab were analyzed by CCK-8 and flow cytometry assays in Her-2-positive breast cancer cells (SKBR-3 and JIMT-1). Bio-informatics analyses were performed to predict target genes of miR-129-5p, and luciferase assays were carried out to confirm the binding of miR-129-5p and rpS6. MiR-129-5p, which was downregulated and predicted to target rpS6 in trastuzumab-resistant breast cancer cells, enhanced the sensitivity of breast cancer cells to trastuzumab by reducing the expression of rpS6. Moreover, the overexpression of rpS6 reversed the sensitivity of cells to trastuzumab induced by miR-129-5p. MiR-129-5p sensitized Her-2-positive breast cancer to trastuzumab by downregulating rpS6. These findings provide novel insights into the common role of rpS6 and its related molecular mechanisms in mediating trastuzumab-resistance in Her-2-positive breast cancers. © 2017 The Author(s). Published by S. Karger AG, Basel.

Sensitivity and positive predictive value of CT, MRI and 123I-MIBG scintigraphy in localizing pheochromocytomas: a prospective study.

PubMed

Lumachi, Franco; Tregnaghi, Alberto; Zucchetta, Pietro; Cristina Marzola, Maria; Cecchin, Diego; Grassetto, Gaia; Bui, Franco

2006-07-01

To establish a standardized non-invasive imaging protocol for patients with pheochromocytoma undergoing surgery. A series of 32 consecutive patients (16 men, 16 women; median age 43 years, range 15-71 years) with biochemically confirmed pheochromocytoma underwent computed tomography (CT) scanning, magnetic resonance imaging (MRI) and meta-[I]iodobenzylguanidine (MIBG) whole-body scintigraphy prior to adrenalectomy or excision of extra-adrenal tumour (paraganglioma). At final pathology no malignant pheochromocytomas were found. The tumour was right-sided in 16 (50%) patients, left-sided in 13 (41%), extra-adrenal (sympathetic ganglia, upper abdomen) in two (6%) and bilateral in one (3%) patient. Overall, the median greatest diameter (size) of the tumour was 35 mm (range, 15-90 mm). The sensitivity of CT, MRI and MIBG scintigraphy was 90%, 93% and 91%, and the specificity was 93%, 93% and 100%, respectively. The three patients with false negative scintigraphy had an intra-adrenal tumour, ranging from 20 to 50 mm in size. The presence of necrosis within the mass might justify the lack of significant uptake of radiopharmaceutical in two patients, and the small size (15 mm) of the mass in the other. There were two false positive results with both CT and MRI, and no false positive MIBG scintigraphy, which had the highest (100%) positive predictive value. The combination of MRI+MIBG scintigraphy reached 100% sensitivity and positive predictive value. Our data suggest that this imaging protocol should be used in all patients with biochemically confirmed pheochromocytoma.

Photoconductivity in the chalcohalide semiconductor, SbSeI: a new candidate for hard radiation detection.

PubMed

Wibowo, Arief C; Malliakas, Christos D; Liu, Zhifu; Peters, John A; Sebastian, Maria; Chung, Duck Young; Wessels, Bruce W; Kanatzidis, Mercouri G

2013-06-17

We investigated an antimony chalcohalide compound, SbSeI, as a potential semiconductor material for X-ray and γ-ray detection. SbSeI has a wide band gap of 1.70 eV with a density of 5.80 g/cm(3), and it crystallizes in the orthorhombic Pnma space group with a one-dimensional chain structure comprised of infinite zigzag chains of dimers [Sb2Se4I8]n running along the crystallographic b axis. In this study, we investigate conditions for vertical Bridgman crystal growth using combinations of the peak temperature and temperature gradients as well as translation rate set in a three-zone furnace. SbSeI samples grown at 495 °C peak temperature and 19 °C/cm temperature gradient with 2.5 mm/h translation rate produced a single phase of columnar needlelike crystals aligned along the translational direction of the growth. The ingot sample exhibited an n-type semiconductor with resistivity of ∼10(8) Ω·cm. Photoconductivity measurements on these specimens allowed us to determine mobility-lifetime (μτ) products for electron and hole carriers that were found to be of similar order of magnitude (∼10(-4) cm(2)/V). Further, the SbSeI ingot with well-aligned, one-dimensional columnar needlelike crystals shows an appreciable response of Ag Kα X-ray.

Light Enhanced Hydrofluoric Acid Passivation: A Sensitive Technique for Detecting Bulk Silicon Defects

PubMed Central

Grant, Nicholas E.

2016-01-01

A procedure to measure the bulk lifetime (>100 µsec) of silicon wafers by temporarily attaining a very high level of surface passivation when immersing the wafers in hydrofluoric acid (HF) is presented. By this procedure three critical steps are required to attain the bulk lifetime. Firstly, prior to immersing silicon wafers into HF, they are chemically cleaned and subsequently etched in 25% tetramethylammonium hydroxide. Secondly, the chemically treated wafers are then placed into a large plastic container filled with a mixture of HF and hydrochloric acid, and then centered over an inductive coil for photoconductance (PC) measurements. Thirdly, to inhibit surface recombination and measure the bulk lifetime, the wafers are illuminated at 0.2 suns for 1 min using a halogen lamp, the illumination is switched off, and a PC measurement is immediately taken. By this procedure, the characteristics of bulk silicon defects can be accurately determined. Furthermore, it is anticipated that a sensitive RT surface passivation technique will be imperative for examining bulk silicon defects when their concentration is low (<1012 cm-3). PMID:26779939

Impact of variation in the BDNF gene on social stress sensitivity and the buffering impact of positive emotions: replication and extension of a gene-environment interaction.

PubMed

van Winkel, Mark; Peeters, Frenk; van Winkel, Ruud; Kenis, Gunter; Collip, Dina; Geschwind, Nicole; Jacobs, Nele; Derom, Catherine; Thiery, Evert; van Os, Jim; Myin-Germeys, Inez; Wichers, Marieke

2014-06-01

A previous study reported that social stress sensitivity is moderated by the brain-derived-neurotrophic-factor(Val66Met) (BDNF rs6265) genotype. Additionally, positive emotions partially neutralize this moderating effect. The current study aimed to: (i) replicate in a new independent sample of subjects with residual depressive symptoms the moderating effect of BDNF(Val66Met) genotype on social stress sensitivity, (ii) replicate the neutralizing impact of positive emotions, (iii) extend these analyses to other variations in the BDNF gene in the new independent sample and the original sample of non-depressed individuals. Previous findings were replicated in an experience sampling method (ESM) study. Negative Affect (NA) responses to social stress were stronger in "Val/Met" carriers of BDNF(Val66Met) compared to "Val/Val" carriers. Positive emotions neutralized the moderating effect of BDNF(Val66Met) genotype on social stress sensitivity in a dose-response fashion. Finally, two of four additional BDNF SNPs (rs11030101, rs2049046) showed similar moderating effects on social stress-sensitivity across both samples. The neutralizing effect of positive emotions on the moderating effects of these two additional SNPs was found in one sample. In conclusion, ESM has important advantages in gene-environment (GxE) research and may attribute to more consistent findings in future GxE research. This study shows how the impact of BDNF genetic variation on depressive symptoms may be explained by its impact on subtle daily life responses to social stress. Further, it shows that the generation of positive affect (PA) can buffer social stress sensitivity and partially undo the genetic susceptibility. Copyright © 2014 Elsevier B.V. and ECNP. All rights reserved.

Positive association between high-sensitivity C-reactive protein level and diabetes mellitus among US non-Hispanic black adults.

PubMed

Shankar, A; Li, J

2008-08-01

Previous epidemiologic studies have demonstrated a positive association between serum C-reactive protein (CRP) level and diabetes mellitus. However among US race-ethnicities, the putative association between CRP and diabetes mellitus in non-Hispanic Blacks is not clear. We specifically examined the association between high-sensitivity CRP level and diabetes mellitus in a representative sample of US non-Hispanic blacks. Cross-sectional study among 1,479 National Health and Nutrition Examination Survey 1999-2002 non-Hispanic black participants aged > or = 20 years. Main outcome-of-interest was the presence of diabetes mellitus (fasting plasma glucose > or = 126 mg/dL, non-fasting plasma glucose > or = 200 mg/dL, or self-reported current use of oral hypoglycemic medication or insulin) (n=204). Higher CRP levels were positively associated with diabetes mellitus, independent of smoking, waist circumference, hypertension, and other confounders. Multivariable odds ratio (OR) [95% confidence intervals (CI)] comparing elevated CRP level (>3 mg/L) to low CRP level (<1 mg/L) was 3.12 (1.77-5.48), p-trend<0.0001. This association persisted in separate analysis among men and women. The results were consistent in subgroup analyses by categories of age, smoking, body mass index, and hypertension status. In nonparametric models, the positive association between serum CRP and diabetes mellitus appeared to be present across the full range of CRP, without any threshold effect. Higher serum high-sensitivity CRP levels are positively associated with diabetes mellitus in a sample of US non-Hispanic blacks. Inflammatory processes previously shown to be related to diabetes mellitus in other race-ethnicities may be involved in non-Hispanic blacks also.

Effective preventive interventions to support parents of young children: Illustrations from the Video-feedback Intervention to promote Positive Parenting and Sensitive Discipline (VIPP-SD).

PubMed

Juffer, Femmie; Struis, Estelle; Werner, Claudia; Bakermans-Kranenburg, Marian J

2017-01-01

Secure attachment relationships are essential for children's current and later development. From attachment theory and research, it can be derived that sensitive parenting is the key to positive parent-child relationships. Is it possible to design effective interventions to enhance sensitive parenting? In this article, we review elements that are crucial for effective attachment-based interventions, and we proceed with illustrations from the Video-feedback Intervention to promote Positive Parenting and Sensitive Discipline (VIPP-SD). We describe how this intervention program was developed, how it has been implemented in practice in different types of families and in daycare settings, and how effective the program is. We conclude that intervention programs like the VIPP-SD could play an important role in the community by serving families in need of parenting support.

On determining dead layer and detector thicknesses for a position-sensitive silicon detector

NASA Astrophysics Data System (ADS)

Manfredi, J.; Lee, Jenny; Lynch, W. G.; Niu, C. Y.; Tsang, M. B.; Anderson, C.; Barney, J.; Brown, K. W.; Chajecki, Z.; Chan, K. P.; Chen, G.; Estee, J.; Li, Z.; Pruitt, C.; Rogers, A. M.; Sanetullaev, A.; Setiawan, H.; Showalter, R.; Tsang, C. Y.; Winkelbauer, J. R.; Xiao, Z.; Xu, Z.

2018-04-01

In this work, two particular properties of the position-sensitive, thick silicon detectors (known as the "E" detectors) in the High Resolution Array (HiRA) are investigated: the thickness of the dead layer on the front of the detector, and the overall thickness of the detector itself. The dead layer thickness for each E detector in HiRA is extracted using a measurement of alpha particles emitted from a 212Pb pin source placed close to the detector surface. This procedure also allows for energy calibrations of the E detectors, which are otherwise inaccessible for alpha source calibration as each one is sandwiched between two other detectors. The E detector thickness is obtained from a combination of elastically scattered protons and an energy-loss calculation method. Results from these analyses agree with values provided by the manufacturer.

Application of gamma imaging techniques for the characterisation of position sensitive gamma detectors

NASA Astrophysics Data System (ADS)

Habermann, T.; Didierjean, F.; Duchêne, G.; Filliger, M.; Gerl, J.; Kojouharov, I.; Li, G.; Pietralla, N.; Schaffner, H.; Sigward, M.-H.

2017-11-01

A device to characterize position-sensitive germanium detectors has been implemented at GSI. The main component of this so called scanning table is a gamma camera that is capable of producing online 2D images of the scanned detector by means of a PET technique. To calibrate the gamma camera Compton imaging is employed. The 2D data can be processed further offline to obtain depth information. Of main interest is the response of the scanned detector in terms of the digitized pulse shapes from the preamplifier. This is an important input for pulse-shape analysis algorithms as they are in use for gamma tracking arrays in gamma spectroscopy. To validate the scanning table, a comparison of its results with a second scanning table implemented at the IPHC Strasbourg is envisaged. For this purpose a pixelated germanium detector has been scanned.

Primary Data Treatment Software for Position-Sensitive Detector of Small-Angle Neutron Scattering Spectrometer in the Isotropic Pattern Scattering Case

NASA Astrophysics Data System (ADS)

Soloviev, Alexei; Kutuzov, Sergei; Ivankov, Olexander; Kuklin, Alexander

2018-02-01

A new data converter has been created for the new position-sensitive detector (PSD) of small-angle neutron scattering (SANS) spectrometer YuMO. In the isotropic pattern scattering case, it provides the possibility for processing PSD data with the SAS data processing program that has already been in use.

Reduced graphene oxide-ZnO self-assembled films: tailoring the visible light photoconductivity by the intrinsic defect states in ZnO.

PubMed

Kavitha, M K; Gopinath, Pramod; John, Honey

2015-06-14

ZnO is a wide direct bandgap semiconductor; its absorption can be tuned to the visible spectral region by controlling the intrinsic defect levels. Combining graphene with ZnO can improve its performance by photo-induced charge separation by ZnO and electronic transport through graphene. When reduced graphene oxide-ZnO is prepared by a hydrothermal method, the photophysical studies indicate that oxygen vacancy defect states are healed out by diffusion of oxygen from GO to ZnO during its reduction. Because of the passivation of oxygen vacancies, the visible light photoconductivity of the hybrid is depleted, compared to pure ZnO. In order to overcome this reduction in photocurrent, a photoelectrode is fabricated by layer-by-layer (LBL) self-assembly of ZnO and reduced graphene oxide. The multilayer films are fabricated by the electrostatic LBL self-assembly technique using negatively charged poly(sodium 4-styrene sulfonate)-reduced graphene oxide (PSS-rGO) and positively charged polyacrylamide-ZnO (PAM-ZnO) as building blocks. The multilayer films fabricated by this technique will be highly interpenetrating; it will enhance the interaction between the ZnO and rGO perpendicular to the electrode surface. Upon illumination under bias voltage defect assisted excitation occurs in ZnO and the photogenerated charge carriers can transfer to graphene. The electron transferred to graphene sheets can recombine in two ways; either it can recombine with the holes in the valence band of ZnO in its bilayer or the ZnO in the next bilayer. This type of tunnelling of electrons from graphene to the successive bilayers will result in efficient charge transfer. This transfer and propagation of electron will enhance as the number of bilayers increases, which in turn improve the photocurrent of the multilayer films. Therefore this self-assembly technique is an effective approach to fabricate semiconductor-graphene films with excellent conductivity.

The development and test of ultra-large-format multi-anode microchannel array detector systems

NASA Technical Reports Server (NTRS)

Timothy, J. G.

1984-01-01

The specific tasks that were accomplished with each of the key elements of the multi-anode microchannel array detector system are described. The modes of operation of position-sensitive electronic readout systems for use with high-gain microchannel plates are described and their performance characteristics compared and contrasted. Multi-anode microchannel array detector systems with formats as large as 256 x 1024 pixels are currently under evaluation. Preliminary performance data for sealed ultraviolet and visible-light detector tubes show that the detector systems have unique characteristics which make them complementary to photoconductive array detectors, such as CCDs, and superior to alternative pulse-counting detector systems employing high-gain MCPs.

Measuring relative-story displacement and local inclination angle using multiple position-sensitive detectors.

PubMed

Matsuya, Iwao; Katamura, Ryuta; Sato, Maya; Iba, Miroku; Kondo, Hideaki; Kanekawa, Kiyoshi; Takahashi, Motoichi; Hatada, Tomohiko; Nitta, Yoshihiro; Tanii, Takashi; Shoji, Shuichi; Nishitani, Akira; Ohdomari, Iwao

2010-01-01

We propose a novel sensor system for monitoring the structural health of a building. The system optically measures the relative-story displacement during earthquakes for detecting any deformations of building elements. The sensor unit is composed of three position sensitive detectors (PSDs) and lenses capable of measuring the relative-story displacement precisely, even if the PSD unit was inclined in response to the seismic vibration. For verification, laboratory tests were carried out using an Xθ-stage and a shaking table. The static experiment verified that the sensor could measure the local inclination angle as well as the lateral displacement. The dynamic experiment revealed that the accuracy of the sensor was 150 μm in the relative-displacement measurement and 100 μrad in the inclination angle measurement. These results indicate that the proposed sensor system has sufficient accuracy for the measurement of relative-story displacement in response to the seismic vibration.

Development of position-sensitive time-of-flight spectrometer for fission fragment research

DOE PAGES

Arnold, C. W.; Tovesson, F.; Meierbachtol, K.; ...

2014-07-09

A position-sensitive, high-resolution time-of-flight detector for fission fragments has been developed. The SPectrometer for Ion DEtermination in fission Research (SPIDER) is a 2E–2v spectrometer designed to measure the mass of light fission fragments to a single mass unit. The time pick-off detector pairs to be used in SPIDER have been tested with α-particles from 229Th and its decay chain and α-particles and spontaneous fission fragments from 252Cf. Each detector module is comprised of thin electron conversion foil, electrostatic mirror, microchannel plates, and delay-line anodes. Particle trajectories on the order of 700 mm are determined accurately to within 0.7 mm. Flightmore » times were measured with 250 ps resolution FWHM. Computed particle velocities are accurate to within 0.06 mm/ns corresponding to a precision of 0.5%. As a result, an ionization chamber capable of 400 keV energy resolution coupled with the velocity measurements described here will pave the way for modestly efficient measurements of light fission fragments with unit mass resolution.« less

Substrate effects in high gain, low operating voltage SnSe2 photoconductor

NASA Astrophysics Data System (ADS)

Krishna, Murali; Kallatt, Sangeeth; Majumdar, Kausik

2018-01-01

High gain photoconductive devices find wide spread applications in low intensity light detection. Ultra-thin layered materials have recently drawn a lot of attention from researchers in this regard. However, in general, a large operating voltage is required to obtain large responsivity in these devices. In addition, the characteristics are often confounded by substrate induced trap effects. Here we report multi-layer SnSe2 based photoconductive devices using two different structures: (1) SiO2 substrate supported inter-digitated electrode (IDE), and (2) suspended channel. The IDE device exhibits a responsivity of ≈ {10}3 A W-1 and ≈ 8.66× {10}4 A W-1 at operating voltages of 1 mV and 100 mV, respectively—a superior low voltage performance over existing literature on planar 2D structures. However, the responsivity reduces by more than two orders of magnitude, while the transient response improves for the suspended device—providing insights into the critical role played by the channel-substrate interface in the gain mechanism. The results, on one hand, are promising for highly sensitive photoconductive applications consuming ultra-low power, and on the other hand, show a generic methodology that could be applied to other layered material based photoconductive devices as well for extracting the intrinsic behavior.

Cardiac Position Sensitivity Study in the Electrocardiographic Forward Problem Using Stochastic Collocation and Boundary Element Methods

PubMed Central

Swenson, Darrell J.; Geneser, Sarah E.; Stinstra, Jeroen G.; Kirby, Robert M.; MacLeod, Rob S.

2012-01-01

The electrocardiogram (ECG) is ubiquitously employed as a diagnostic and monitoring tool for patients experiencing cardiac distress and/or disease. It is widely known that changes in heart position resulting from, for example, posture of the patient (sitting, standing, lying) and respiration significantly affect the body-surface potentials; however, few studies have quantitatively and systematically evaluated the effects of heart displacement on the ECG. The goal of this study was to evaluate the impact of positional changes of the heart on the ECG in the specific clinical setting of myocardial ischemia. To carry out the necessary comprehensive sensitivity analysis, we applied a relatively novel and highly efficient statistical approach, the generalized polynomial chaos-stochastic collocation method, to a boundary element formulation of the electrocardiographic forward problem, and we drove these simulations with measured epicardial potentials from whole-heart experiments. Results of the analysis identified regions on the body-surface where the potentials were especially sensitive to realistic heart motion. The standard deviation (STD) of ST-segment voltage changes caused by the apex of a normal heart, swinging forward and backward or side-to-side was approximately 0.2 mV. Variations were even larger, 0.3 mV, for a heart exhibiting elevated ischemic potentials. These variations could be large enough to mask or to mimic signs of ischemia in the ECG. Our results suggest possible modifications to ECG protocols that could reduce the diagnostic error related to postural changes in patients possibly suffering from myocardial ischemia. PMID:21909818

Food Approach and Food Avoidance in Young Children: Relation with Reward Sensitivity and Punishment Sensitivity

PubMed Central

Vandeweghe, Laura; Vervoort, Leentje; Verbeken, Sandra; Moens, Ellen; Braet, Caroline

2016-01-01

It has recently been suggested that individual differences in Reward Sensitivity and Punishment Sensitivity may determine how children respond to food. These temperamental traits reflect activity in two basic brain systems that respond to rewarding and punishing stimuli, respectively, with approach and avoidance. Via parent-report questionnaires, we investigate the associations of the general motivational temperamental traits Reward Sensitivity and Punishment Sensitivity with Food Approach and Food Avoidance in 98 preschool children. Consistent with the conceptualization of Reward Sensitivity in terms of approach behavior and Punishment Sensitivity in terms of avoidance behavior, Reward Sensitivity was positively related to Food Approach, while Punishment Sensitivity was positively related to Food Avoidance. Future research should integrate these perspectives (i.e., general temperamental traits Reward Sensitivity and Punishment Sensitivity, and Food Approach and Avoidance) to get a better understanding of eating behavior and related body weight. PMID:27445898

Small field measurements with a novel silicon position sensitive diode array.

PubMed

Manolopoulos, S; Wojnecki, C; Hugtenburg, R; Jaafar Sidek, M A; Chalmers, G; Heyes, G; Green, S

2009-02-07

DOSI, a novel dosimeter based on position sensitive detectors for particle physics experiments, was used for relative clinical dosimetry measurements in small radiotherapy fields. The device is capable of dynamic measurements in real time and provides sub-millimetre spatial resolution. The basic beam data for a stereotactic radiotherapy collimator system (BrainLAB) using 6 MV photons were measured and compared with the corresponding data acquired with a small diamond detector and a PinPoint ionization chamber. All measurements showed an excellent agreement between DOSI and the diamond detector. There was an increasing discrepancy between the relative output factors (ROF) measured with DOSI and those measured with the ionization chamber with decreasing field size, specifically for collimators with a diameter smaller than 15 mm. The percentage depth doses (PDD) were in agreement to better than 1% for all depths. The agreement on off-axis ratios (OAR) was better than 3% for all collimators, whereas the agreement on relative output factors (ROF) was at the 1% level. DOSI's fast read-out electronics made it possible for all measurements to be recorded within 45 min including time to change collimators. This should reduce the overall time for commissioning and QA measurements, an important factor especially for busy radiotherapy departments.

Environmental Sensitivity in Children: Development of the Highly Sensitive Child Scale and Identification of Sensitivity Groups

ERIC Educational Resources Information Center

Pluess, Michael; Assary, Elham; Lionetti, Francesca; Lester, Kathryn J.; Krapohl, Eva; Aron, Elaine N.; Aron, Arthur

2018-01-01

A large number of studies document that children differ in the degree they are shaped by their developmental context with some being more sensitive to environmental influences than others. Multiple theories suggest that "Environmental Sensitivity" is a common trait predicting the response to negative as well as positive exposures.…

A zero dead-time multi-particle time and position sensitive detector based on correlation between brightness and amplitude

DOE Office of Scientific and Technical Information (OSTI.GOV)

Urbain, X., E-mail: xavier.urbain@uclouvain.be; Bech, D.; Van Roy, J.-P.

A new multi-particle time and position sensitive detector using only a set of microchannel plates, a waveform digitizer, a phosphor screen, and a CMOS camera is described. The assignment of the timing information, as taken from the microchannel plates by fast digitizing, to the positions, as recorded by the camera, is based on the COrrelation between the BRightness of the phosphor screen spots, defined as their integrated intensity and the Amplitude of the electrical signals (COBRA). Tests performed by observing the dissociation of HeH, the fragmentation of H{sub 3} into two or three fragments, and the photo-double-ionization of Xenon atomsmore » are presented, which illustrate the performances of the COBRA detection scheme.« less

3D scanning characteristics of an amorphous silicon position sensitive detector array system.

PubMed

Contreras, Javier; Gomes, Luis; Filonovich, Sergej; Correia, Nuno; Fortunato, Elvira; Martins, Rodrigo; Ferreira, Isabel

2012-02-13

The 3D scanning electro-optical characteristics of a data acquisition prototype system integrating a 32 linear array of 1D amorphous silicon position sensitive detectors (PSD) were analyzed. The system was mounted on a platform for imaging 3D objects using the triangulation principle with a sheet-of-light laser. New obtained results reveal a minimum possible gap or simulated defect detection of approximately 350 μm. Furthermore, a first study of the angle for 3D scanning was also performed, allowing for a broad range of angles to be used in the process. The relationship between the scanning angle of the incident light onto the object and the image displacement distance on the sensor was determined for the first time in this system setup. Rendering of 3D object profiles was performed at a significantly higher number of frames than in the past and was possible for an incident light angle range of 15 ° to 85 °.

Micro Cantilever Movement Detection with an Amorphous Silicon Array of Position Sensitive Detectors

PubMed Central

Contreras, Javier; Costa, Daniel; Pereira, Sonia; Fortunato, Elvira; Martins, Rodrigo; Wierzbicki, Rafal; Heerlein, Holger; Ferreira, Isabel

2010-01-01

The movement of a micro cantilever was detected via a self constructed portable data acquisition prototype system which integrates a linear array of 32 1D amorphous silicon position sensitive detectors (PSD). The system was mounted on a microscope using a metal structure platform and the movement of the 30 μm wide by 400 μm long cantilever was tracked by analyzing the signals acquired by the 32 sensor array electronic readout system and the relevant data algorithm. The obtained results show a linear behavior of the photocurrent relating X and Y movement, with a non-linearity of about 3%, a spatial resolution of less than 2 μm along the lateral dimension of the sensor as well as of less than 3 μm along the perpendicular dimension of the sensor, when detecting just the micro-cantilever, and a spatial resolution of less than 1 μm when detecting the holding structure. PMID:22163648

Assessment of skin sensitization under REACH: A case report on vehicle choice in the LLNA and its crucial role preventing false positive results.

PubMed

Watzek, Nico; Berger, Franz; Kolle, Susanne Noreen; Kaufmann, Tanja; Becker, Matthias; van Ravenzwaay, Bennard

2017-04-01

In the EU, chemicals with a production or import volume in quantities of one metric ton per year or more have to be tested for skin sensitizing properties under the REACH regulation. The murine Local Lymph Node Assay (LLNA) and its modifications are widely used to fulfil the data requirement, as it is currently considered the first-choice method for in vivo testing to cover this endpoint. This manuscript describes a case study highlighting the importance of understanding the chemistry of the test material during testing for 'skin sensitization' of MCDA (mixture of 2,4- and 2,6-diamino-methylcyclohexane) with particular focus on the vehicle used. While the BrdU-ELISA modification of the LLNA using acetone/olive oil (AOO) as vehicle revealed expectable positive results. However, the concentration control analysis unexpectedly revealed an instability of MCDA in the vehicle AOO. Further studies on the reactivity showed MCDA to rapidly react with AOO under formation of various imine structures, which might have caused the positive LLNA result. The repetition of the LLNA using propylene glycol (PG) as vehicle did not confirm the positive results of the LLNA using AOO. Finally, a classification of MCDA as skin sensitizer according to the Globally Harmonized System (GHS) was not justified. Copyright © 2017 Elsevier Inc. All rights reserved.

School, Supervision and Adolescent-Sensitive Clinic Care: Combination Social Protection and Reduced Unprotected Sex Among HIV-Positive Adolescents in South Africa.

PubMed

Toska, Elona; Cluver, Lucie D; Boyes, Mark E; Isaacsohn, Maya; Hodes, Rebecca; Sherr, Lorraine

2017-09-01

Social protection can reduce HIV-risk behavior in general adolescent populations, but evidence among HIV-positive adolescents is limited. This study quantitatively tests whether social protection is associated with reduced unprotected sex among 1060 ART-eligible adolescents from 53 government facilities in South Africa. Potential social protection included nine 'cash/cash-in-kind' and 'care' provisions. Analyses tested interactive/additive effects using logistic regressions and marginal effects models, controlling for covariates. 18 % of all HIV-positive adolescents and 28 % of girls reported unprotected sex. Lower rates of unprotected sex were associated with access to school (OR 0.52 95 % CI 0.33-0.82 p = 0.005), parental supervision (OR 0.54 95 % CI 0.33-0.90 p = 0.019), and adolescent-sensitive clinic care (OR 0.43 95 % CI 0.25-0.73 p = 0.002). Gender moderated the effect of adolescent-sensitive clinic care. Combination social protection had additive effects amongst girls: without any provisions 49 % reported unprotected sex; with 1-2 provisions 13-38 %; and with all provisions 9 %. Combination social protection has the potential to promote safer sex among HIV-positive adolescents, particularly girls.

Cherenkov radiation-based three-dimensional position-sensitive PET detector: A Monte Carlo study.

PubMed

Ota, Ryosuke; Yamada, Ryoko; Moriya, Takahiro; Hasegawa, Tomoyuki

2018-05-01

Cherenkov radiation has recently received attention due to its prompt emission phenomenon, which has the potential to improve the timing performance of radiation detectors dedicated to positron emission tomography (PET). In this study, a Cherenkov-based three-dimensional (3D) position-sensitive radiation detector was proposed, which is composed of a monolithic lead fluoride (PbF 2 ) crystal and a photodetector array of which the signals can be readout independently. Monte Carlo simulations were performed to estimate the performance of the proposed detector. The position- and time resolution were evaluated under various practical conditions. The radiator size and various properties of the photodetector, e.g., readout pitch and single photon timing resolution (SPTR), were parameterized. The single photon time response of the photodetector was assumed to be a single Gaussian for the simplification. The photo detection efficiency of the photodetector was ideally 100% for all wavelengths. Compton scattering was included in simulations, but partly analyzed. To estimate the position at which a γ-ray interacted in the Cherenkov radiator, the center-of-gravity (COG) method was employed. In addition, to estimate the depth-of-interaction (DOI) principal component analysis (PCA), which is a multivariate analysis method and has been used to identify the patterns in data, was employed. The time-space distribution of Cherenkov photons was quantified to perform PCA. To evaluate coincidence time resolution (CTR), the time difference of two independent γ-ray events was calculated. The detection time was defined as the first photon time after the SPTR of the photodetector was taken into account. The position resolution on the photodetector plane could be estimated with high accuracy, by using a small number of Cherenkov photons. Moreover, PCA showed an ability to estimate the DOI. The position resolution heavily depends on the pitch of the photodetector array and the radiator

Behavior of temperature-dependent dc-photoconductivity in hot-wall deposited CaAl2Se4 layers

NASA Astrophysics Data System (ADS)

Jeong, J. W.; Hong, K. J.; Jeong, T. S.; Youn, C. J.

2017-10-01

The dc-photoconductive characteristic on the hot-wall grown CaAl2Se4 (CAS) layers was explored as a function of temperature. From the photocurrent (PC) measurement, three PC peaks A, B, and C corresponded to the intrinsic transitions, which represent the band-to-band transitions from the valence-band states of Γ2(A), Γ3 + Γ4(B), and Γ3 + Γ4(C) to the conduction-band state of Γ1, respectively. Based on these PC results, the optical band-gap energy was well matched by E g ( T) = E g (0) - 4.94 × 10-3 T 2/( T + 552), where E g (0) is found to be 3.8239, 3.8716, and 3.8801 eV for three peaks A, B, and C, respectively. Thus, the effect of the crystal field and spin-orbit splitting (These values were extracted out to be 47.7 and 8.5 meV, respectively.) was observed and calculated by means of the PC spectroscopy. However, PC intensity gradually decreased with decreasing temperature unlike an ordinary behavior. In the log J ph vs 1/ T plot, two dominant traplevels were observed to be 20.81 meV at temperatures of 300 - 70 K and 1.18 meV at temperatures below 70 K. Consequently, we extract out that these trapping centers caused by native defects in CAS confine the PC intensity as temperature decreases.

Sensitivity of Fermi level position at Ga-polar, N-polar, and nonpolar m-plane GaN surfaces to vacuum and air ambient

NASA Astrophysics Data System (ADS)

Janicki, Łukasz; Ramírez-López, Manolo; Misiewicz, Jan; Cywiński, Grzegorz; Boćkowski, Michał; Muzioł, Grzegorz; Chèze, Caroline; Sawicka, Marta; Skierbiszewski, Czesław; Kudrawiec, Robert

2016-05-01

Ga-polar, N-polar, and nonpolar m-plane GaN UN+ structures have been examined in air and vacuum ambient by contactless electroreflectance (CER). This technique is very sensitive to the surface electric field that varies with the Fermi level position at the surface. For UN+ GaN structures [i.e., GaN (undoped)/GaN (n-type)/substrate], a homogeneous built-in electric field is expected in the undoped GaN layer that is manifested by Franz-Keldysh oscillation (FKO) in CER spectra. A clear change in FKO has been observed in CER spectra for N-polar and nonpolar m-plane structures when changing from air to vacuum ambient. This means that those surfaces are very sensitive to ambient atmosphere. In contrast to that, only a small change in FKO can be seen in the Ga-polar structure. This clearly shows that the ambient sensitivity of the Fermi level position at the GaN surface varies with the crystallographic orientation and is very high for N-polar and nonpolar m-plane surfaces. This feature of the N-polar and nonpolar m-plane surfaces can be very important for GaN-based devices grown on these crystallographic orientations and can be utilized in some of the devices, e.g., sensors.

The psychology of psychiatric genetics: evidence that positive emotions in females moderate genetic sensitivity to social stress associated with the BDNF Val-sup-6-sup-6Met polymorphism.

PubMed

Wichers, Marieke; Kenis, Gunter; Jacobs, Nele; Myin-Germeys, Inez; Schruers, Koen; Mengelers, Ron; Delespaul, Philippe; Derom, Catherine; Vlietinck, Robert; van Os, Jim

2008-08-01

Previous work indicated protective effects of positive emotions on genetically influenced stress sensitivity. Given the fact that expression of brain-derived-neurotrophic-factor (BDNF) is associated with stress-induced behavioral changes, it was hypothesized that the BDNF Val-sup-6-sup-6Met genotype may mediate genetic effects on stress sensitivity, conditional on the level of concurrent positive emotions. Subjects (n=446) participated in a momentary assessment study, collecting appraisals of stress and affect in the flow of daily life. Multilevel regression analyses examined moderation of daily life stress-induced negative affect (NA) by BDNF genotype, and to what degree this was conditional on concurrent positive emotions. Results showed that heterozygous BDNF "Met" carriers exhibited an increased NA response to social stress compared with "Val/Val" subjects. Positive emotions at the time of the stressor decreased BDNF genetic moderation of the NA response to social stress in a dose-response fashion. This effect was most pronounced in BDNF Met carriers. Thus, the impact of BDNF genotype on stress sensitivity is conditional on the experience of positive emotions. Interdisciplinary research in psychology and psychiatric genetics may lead to the improvement of treatment choices in stress-related disorders. Copyright (c) 2008 APA, all rights reserved.

Intermediate type excitons in Schottky barriers of A3B6 layer semiconductors and UV photodetectors

NASA Astrophysics Data System (ADS)

Alekperov, O. Z.; Guseinov, N. M.; Nadjafov, A. I.

2006-09-01

Photoelectric and photovoltaic spectra of Schottky barrier (SB) structures of InSe, GaSe and GaS layered semiconductors (LS) are investigated at quantum energies from the band edge excitons of corresponding materials up to 6.5eV. Spectral dependences of photoconductivity (PC) of photo resistors and barrier structures are strongly different at the quantum energies corresponding to the intermediate type excitons (ITE) observed in these semiconductors. It was suggested that high UV photoconductivity of A3B6 LS is due to existence of high mobility light carriers in the depth of the band structure. It is shown that SB of semitransparent Au-InSe is high sensitive photo detector in UV region of spectra.

Position-sensitive detection of ultracold neutrons with an imaging camera and its implications to spectroscopy

DOE PAGES

Wei, Wanchun; Broussard, Leah J.; Hoffbauer, Mark Arles; ...

2016-05-16

Position-sensitive detection of ultracold neutrons (UCNs) is demonstrated using an imaging charge-coupled device (CCD) camera. A spatial resolution less than 15μm has been achieved, which is equivalent to a UCN energy resolution below 2 pico-electron-volts through the relation δE=m 0gδx. Here, the symbols δE, δx, m 0 and g are the energy resolution, the spatial resolution, the neutron rest mass and the gravitational acceleration, respectively. A multilayer surface convertor described previously is used to capture UCNs and then emits visible light for CCD imaging. Particle identification and noise rejection are discussed through the use of light intensity profile analysis. Asmore » a result, this method allows different types of UCN spectroscopy and other applications.« less

Position-sensitive detection of ultracold neutrons with an imaging camera and its implications to spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, Wanchun; Broussard, Leah J.; Hoffbauer, Mark Arles

Position-sensitive detection of ultracold neutrons (UCNs) is demonstrated using an imaging charge-coupled device (CCD) camera. A spatial resolution less than 15μm has been achieved, which is equivalent to a UCN energy resolution below 2 pico-electron-volts through the relation δE=m 0gδx. Here, the symbols δE, δx, m 0 and g are the energy resolution, the spatial resolution, the neutron rest mass and the gravitational acceleration, respectively. A multilayer surface convertor described previously is used to capture UCNs and then emits visible light for CCD imaging. Particle identification and noise rejection are discussed through the use of light intensity profile analysis. Asmore » a result, this method allows different types of UCN spectroscopy and other applications.« less

Three-dimensional, position-sensitive radiation detection

DOEpatents

He, Zhong; Zhang, Feng

2010-04-06

Disclosed herein is a method of determining a characteristic of radiation detected by a radiation detector via a multiple-pixel event having a plurality of radiation interactions. The method includes determining a cathode-to-anode signal ratio for a selected interaction of the plurality of radiation interactions based on electron drift time data for the selected interaction, and determining the radiation characteristic for the multiple-pixel event based on both the cathode-to-anode signal ratio and the electron drift time data. In some embodiments, the method further includes determining a correction factor for the radiation characteristic based on an interaction depth of the plurality of radiation interactions, a lateral distance between the selected interaction and a further interaction of the plurality of radiation interactions, and the lateral positioning of the plurality of radiation interactions.

A sensitive assay for urinary cocaine metabolite benzoylecgonine shows more positive results and longer half‐lives than those using traditional cut‐offs

PubMed Central

Nickley, Joyce; Krock, Kevin

2017-01-01

Cocaine is a common drug of abuse. To detect its use, a screening detection concentration for the cocaine metabolite benzoylecgonine is commonly set at 150 ng/mL and its confirmatory cut‐off is set at 100 ng/mL. Studies have suggested that these cut‐offs may be set too high, allowing some patients with this substance abuse problem to be missed or improperly monitored. With the advent of liquid chromatography–tandem mass spectrometry (LC–MS/MS) technology it is possible to reliably detect and quantify lower concentrations of its metabolite benzoylecgonine as part of a larger drug panel. One purpose of the study was to establish if there was a significant increase in detection of cocaine use with a ten‐fold more sensitive cut‐off. A very sensitive dilute and shoot assay for benzoylecgonine was developed with a lower limit of quantitation of 5 ng/mL. Validation of the 5 ng/mL cut‐off was achieved by plotting all the positive cocaine observations as a frequency distribution on a logarithmic scale. The number of positive results with measurable concentrations below the typical industry 100 ng/mL cut‐off level but above the high sensitivity 5 ng/mL cut‐off level was observed to be 51.9% of the observed positives. The lower cut‐off also allowed a re‐evaluation of the window of detection after cessation of use. It was observed to be between 17 and 22 days. © 2016 Precision Diagnostics, LLC. Drug Testing and Analysis published by John Wiley & Sons, Ltd. PMID:28024167

A comparative study of photoconductivity in LaTiO3/SrTiO3 and LaAlO3/SrTiO3 2-DEG heterostructures

NASA Astrophysics Data System (ADS)

Rastogi, A.; Hossain, Z.; Budhani, R. C.

2013-02-01

Here we compare the growth temperature dependence of the response of LaTiO3/SrTiO3 and LaAlO3/SrTiO3 2D-electron gas (2-DEG) field effect structure to the optical radiation of near ultraviolet frequency and electrostatic gate field. For both the films the resistance of the channel increases significantly as growth temperature is lowered from 800 to 700 °C. These heterostructures show the photoconductivity (PC) simulated by UV light of λ ≤ 400 nm. The PC follows the stretched exponential dynamics. It is found that photo-response of the LaTiO3 films is prominent and has larger decay time constant as compare to LaAlO3 films. The effect of electric field on the photo-induced conducting state is also studied.

Position-sensitive ``movie'' in situ neutron detector for the UCN τ experiment

NASA Astrophysics Data System (ADS)

Weaver, Hannah; UCNTau Collaboration

2016-09-01

Precision measurements of neutron β-decay parameters provide tests of fundamental theories in elementary particle physics and cosmology such as the Standard Model and Big Bang nucleosynthesis. In particular, the UCN τ experiment aims to measure the mean lifetime of ultracold neutrons confined in an asymmetric magneto-gravitational trap using an in situ neutron detector. This detector consists of a 20 nm film of 10B on top of a ZnS:Ag scintillating screen. The screen is readout using two photomultipliers which view an array of wavelength shifting fibers optically coupled to the scintillator. When the detector is lowered into the loaded trap, light is emitted due to the charged particles recoiling into the ZnS:Ag when neutrons absorb on the 10B. Phase space evolution in the stored neutron population can lead to apparent shifts in the measured neutron lifetime with the detector height. In order to quantify this systematic uncertainty, we are implementing a supplemental 64-channel position-sensitive PMT module with high quantum efficiency and fast time response to image the entire detector in situ during measurements. We have characterized a prototype using a ZnS screen and an α-particle source along with a prototype lens system and will report the results and future plans.

Development of a position sensitive X-ray detector for use in a light weight X-ray diffractometer

NASA Technical Reports Server (NTRS)

Semmler, R. A.

1971-01-01

A position sensitive proportional counter for use in an X-ray diffractometer is developed to permit drastic reductions in the power and weight requirements of the X-ray source and the elimination of the power, weight, and complexity of a moving slit. The final detector constructed and tested has a window spanning 138 and a free standing anode curved along an arc of 7.1 cm radius. Demonstration spectra of a quartz sample in a Debye-Sherrer geometry indicate a spatial resolution of 0.4 - 0.5 mm (0.3 - 0.4 theta). The lunar diffractometer consumed 25 watts in the X-ray generator and weighed about 20 pounds.

Associations between sensitivity to punishment, sensitivity to reward, and gambling.

PubMed

Gaher, Raluca M; Hahn, Austin M; Shishido, Hanako; Simons, Jeffrey S; Gaster, Sam

2015-03-01

The majority of individuals gamble during their lifetime; however only a subset of these individuals develops problematic gambling. Gray's Reinforcement Sensitivity Theory may be relevant to understanding gambling problems. Differences in sensitivity to punishments and rewards can influence an individual's behavior and may be pertinent to the development of gambling problems. This study examined the functional associations between sensitivity to punishment (SP), sensitivity to reward (SR), and gambling problems in a sample of 2254 college students. Zero-inflated negative binomial regression was used to predict gambling problems as well as the absence of gambling problems. Gambling problems were hypothesized to be positively associated with SR and inversely associated with SP. In addition, SP was hypothesized to moderate the association between SR and gambling problems, attenuating the strength of the association. As hypothesized, SR was positively associated with gambling problems. However, SP did not moderate the relationship between SR and gambling problems. SP did, however, moderate the relationship between SR and the likelihood of never experiencing gambling problems. The results demonstrate that individual differences in SP and SR are functionally associated with gambling problems. Copyright © 2014 Elsevier Ltd. All rights reserved.

A sensitive assay for urinary cocaine metabolite benzoylecgonine shows more positive results and longer half-lives than those using traditional cut-offs.

PubMed

Nickley, Joyce; Pesce, Amadeo J; Krock, Kevin

2017-08-01

Cocaine is a common drug of abuse. To detect its use, a screening detection concentration for the cocaine metabolite benzoylecgonine is commonly set at 150 ng/mL and its confirmatory cut-off is set at 100 ng/mL. Studies have suggested that these cut-offs may be set too high, allowing some patients with this substance abuse problem to be missed or improperly monitored. With the advent of liquid chromatography-tandem mass spectrometry (LC-MS/MS) technology it is possible to reliably detect and quantify lower concentrations of its metabolite benzoylecgonine as part of a larger drug panel. One purpose of the study was to establish if there was a significant increase in detection of cocaine use with a ten-fold more sensitive cut-off. A very sensitive dilute and shoot assay for benzoylecgonine was developed with a lower limit of quantitation of 5 ng/mL. Validation of the 5 ng/mL cut-off was achieved by plotting all the positive cocaine observations as a frequency distribution on a logarithmic scale. The number of positive results with measurable concentrations below the typical industry 100 ng/mL cut-off level but above the high sensitivity 5 ng/mL cut-off level was observed to be 51.9% of the observed positives. The lower cut-off also allowed a re-evaluation of the window of detection after cessation of use. It was observed to be between 17 and 22 days. © 2016 Precision Diagnostics, LLC. Drug Testing and Analysis published by John Wiley & Sons, Ltd. © 2016 Precision Diagnostics, LLC. Drug Testing and Analysis published by John Wiley & Sons, Ltd.

Drama-induced affect and pain sensitivity.

PubMed

Zillmann, D; de Wied, M; King-Jablonski, C; Jenzowsky, S

1996-01-01

This study was conducted to examine the pain-ameliorating and pain-sensitizing effects of exposure to emotionally engaging drama. Specifically, the consequences for pain sensitivity of exposure to dramatic expositions differing in both excitatory and hedonic qualities were determined. Hedonically negative, neutral, and positive affective states were induced in male respondents by exposure to excerpts from cinematic drama. Pain sensitivity was assessed by the cuff-pressure procedure before and after exposure and by the cold pressor test after exposure only. When compared against the control condition, pain sensitivity diminished under conditions of hedonically positive affect. An inverse effect was suggested for hedonically negative conditions, but proved tentative and statistically unreliable. The findings are consistent with earlier demonstrations of mood effects on pain sensitivity. Unlike inconclusive earlier findings concerning the magnitude of directional effects, however, they suggest an asymmetry that emphasizes the pain-ameliorating effect of positive affects while lending little, if any, support to the proposal of a pain-sensitizing effect of negative affects. The investigation did not accomplish the intended creation of conditions necessary to test the proposal that heightened sympathetic activity diminishes pain sensitivity. The utility of a rigorous determination of this hypothesized relationship is emphasized, and procedures for a viable test of the proposal are suggested.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhuang, Shendong; Tang, Nujiang; Chen, Zhuo, E-mail: zchen@nju.edu.cn

Solution-processed graphene quantum dots (GQDs) possess a moderate bandgap, which make them a promising candidate for optoelectronics devices. However, negative photoconductivity (NPC) and hysteresis that happen in the photoelectric conversion process could be harmful to performance of the GQDs-based devices. So far, their origins and relations have remained elusive. Here, we investigate experimentally the origins of the NPC and hysteresis in GQDs. By comparing the hysteresis and photoconductance of GQDs under different relative humidity conditions, we are able to demonstrate that NPC and hysteresis coexist in GQDs and both are attributed to the carrier trapping effect of surface adsorbed moisture.more » We also demonstrate that GQDs could exhibit positive photoconductivity with three-order-of-magnitude reduction of hysteresis after a drying process and a subsequent encapsulation. Considering the pervasive moisture adsorption, our results may pave the way for a commercialization of semiconducting graphene-based and diverse solution-based optoelectronic devices.« less

Study of Retinal Nerve Fibre Layer Thickness and Visual Contrast Sensitivity in HIV Positive Individuals.

PubMed

Paul, Rudrajit; Ghosh, Asim K; Nag, Adwaita; Biswas, Shyamapada; Naiya, Britisundar; Mondal, Jayati

2017-06-01

Measurement of Retinal Nerve Fibre Layer Thickness (RNFLT) by Optical Coherence Tomography (OCT) is a sensitive, non invasive and cheap method of detecting early retinal changes in a variety of diseases. In HIV infection, RNFLT is altered and this may have effect on other visual functions like Contrast Sensitivity (CS) and visual acuity. Such ocular pathology can affect the daily life and profession (especially driving) of HIV infected individuals. However, studies on this topic in HIV infected population are rare from India. To study RNFLT, CS and their correlation in a sample of HIV positive Indian population. The present cross-sectional study was done in a tertiary care medical college hospital of Eastern India between May 2016 and September 2016. We did this study on HIV positive subjects with no clinically apparent ocular infection or other pathology. In this study, we have measured the RNFLT using the HRA-OCT Spectralis machine. The CS was tested using a smartphone version of the Pellie-Robson chart. CD4 count, visual acuity and colour vision were also tested. The data was analysed using SPSS version 20.0 for any correlation between these parameters. Pearson coefficient was used for continuous data and Spearman rank correlation was used for categorical data. A p-value <0.05 was considered significant. We had 17 patients, that is 34 eyes. RNFLT loss was found in 21% of the eyes and borderline thinning was found in a further 26%. Predominantly, the temporal quadrant was involved. The mean of log CS was 1.33±0.38. Taking 1.5 as the cut-off value for normalcy, 47% of the eyes tested showed decreased CS. Log CS showed significant correlation with RNFLT of the temporal quadrant only (r=0.37; 95% C.I. 0.041 to 0.631; p=0.02). Temporal RNFLT also showed statistical correlation with the CD4 count. The low CS was also significantly correlated with low visual acuity (r=0.5). In HIV infected persons, subtle ocular changes may occur and this may affect visual functions

Theory and Development of Position-Sensitive Quantum Calorimeters. Degree awarded by Stanford Univ.

NASA Technical Reports Server (NTRS)

Figueroa-Feliciano, Enectali; White, Nicholas E. (Technical Monitor)

2001-01-01

Quantum calorimeters are being developed as imaging spectrometers for future X-ray astrophysics observatories. Much of the science to be done by these instruments could benefit greatly from larger focal-plane coverage of the detector (without increasing pixel size). An order of magnitude more area will greatly increase the science throughput of these future instruments. One of the main deterrents to achieving this goal is the complexity of the readout schemes involved. We have devised a way to increase the number of pixels from the current baseline designs by an order of magnitude without increasing the number of channels required for readout. The instrument is a high energy resolution, distributed-readout imaging spectrometer called a Position-Sensitive Transition-Edge Sensor (POST). A POST is a quantum calorimeter consisting of two Transition-Edge Sensors (TESS) on the ends of a long absorber capable of one-dimensional imaging spectroscopy. Comparing rise time and energy information from the two TESS, the position of the event in the POST is determined. The energy of the event is inferred from the sum of the two pulses. We have developed a generalized theoretical formalism for distributed-readout calorimeters and apply it to our devices. We derive the noise theory and calculate the theoretical energy resolution of a POST. Our calculations show that a 7-pixel POST with 6 keV saturation energy can achieve 2.3 eV resolution, making this a competitive design for future quantum calorimeter instruments. For this thesis we fabricated 7- and 15-pixel POSTS using Mo/Au TESs and gold absorbers, and moved from concept drawings on scraps of napkins to a 32 eV energy resolution at 1.5 keV, 7-pixel POST calorimeter.

Landscape position influences soil respiration variability and sensitivity to physiological drivers in mixed-use lands of Southern California, USA

NASA Astrophysics Data System (ADS)

Crum, Steven M.; Liang, Liyin L.; Jenerette, G. Darrel

2016-10-01

Linking variation in ecosystem functioning to physiological and landscape drivers has become an important research need for understanding ecosystem responses to global changes. We investigate how these contrasting scale-dependent ecosystem drivers influence soil respiration (Rs), a key ecosystem process, using in situ landscape surveys and experimental subsidies of water and labile carbon. Surveys and experiments were conducted in summer and winter seasons and were distributed along a coastal to desert climate gradient and among the dominant land use classes in Southern California, USA. We found that Rs decreased from lawn to agricultural and wildland land uses for both seasons and along the climate gradient in the summer while increasing along the climate gradient in the winter. Rs variation was positively correlated with soil temperature and negatively to soil moisture and substrate. Water additions increased Rs in wildland land uses, while urban land uses responded little or negatively. However, most land uses exhibited carbon limitation, with wildlands experiencing largest responses to labile carbon additions. These findings show that intensively managed land uses have increased rates, decreased spatial variation, and decreased sensitivity to environmental conditions in Rs compared to wildlands, while increasing aridity has the opposite effect. In linking scales, physiological drivers were correlated with Rs but landscape position influenced Rs by altering both the physiological drivers and the sensitivity to the drivers. Systematic evaluation of physiological and landscape variation provides a framework for understanding the effects of interactive global change drivers to ecosystem metabolism across multiple scales.

SU-G-BRB-03: Assessing the Sensitivity and False Positive Rate of the Integrated Quality Monitor (IQM) Large Area Ion Chamber to MLC Positioning Errors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boehnke, E McKenzie; DeMarco, J; Steers, J

2016-06-15

Purpose: To examine both the IQM’s sensitivity and false positive rate to varying MLC errors. By balancing these two characteristics, an optimal tolerance value can be derived. Methods: An un-modified SBRT Liver IMRT plan containing 7 fields was randomly selected as a representative clinical case. The active MLC positions for all fields were perturbed randomly from a square distribution of varying width (±1mm to ±5mm). These unmodified and modified plans were measured multiple times each by the IQM (a large area ion chamber mounted to a TrueBeam linac head). Measurements were analyzed relative to the initial, unmodified measurement. IQM readingsmore » are analyzed as a function of control points. In order to examine sensitivity to errors along a field’s delivery, each measured field was divided into 5 groups of control points, and the maximum error in each group was recorded. Since the plans have known errors, we compared how well the IQM is able to differentiate between unmodified and error plans. ROC curves and logistic regression were used to analyze this, independent of thresholds. Results: A likelihood-ratio Chi-square test showed that the IQM could significantly predict whether a plan had MLC errors, with the exception of the beginning and ending control points. Upon further examination, we determined there was ramp-up occurring at the beginning of delivery. Once the linac AFC was tuned, the subsequent measurements (relative to a new baseline) showed significant (p <0.005) abilities to predict MLC errors. Using the area under the curve, we show the IQM’s ability to detect errors increases with increasing MLC error (Spearman’s Rho=0.8056, p<0.0001). The optimal IQM count thresholds from the ROC curves are ±3%, ±2%, and ±7% for the beginning, middle 3, and end segments, respectively. Conclusion: The IQM has proven to be able to detect not only MLC errors, but also differences in beam tuning (ramp-up). Partially supported by the Susan Scott

Targeting Notch1 signaling pathway positively affects the sensitivity of osteosarcoma to cisplatin by regulating the expression and/or activity of Caspase family

PubMed Central

2014-01-01

Background The introduction of cisplatin has improved the long-term survival rate in osteosarcoma patients. However, some patients are intrinsically resistant to cisplatin. This study reported that the activation of Notch1 is positively correlated with cisplatin sensitivity, evidenced by both clinical and in vitro data. Results In this study, a total 8 osteosarcoma specimens were enrolled and divided into two groups according to their cancer chemotherapeutic drugs sensitivity examination results. The relationship between Notch1 expression and cisplatin sensitivity of osteosarcoma patients was detected by immunohistochemistry and semi-quantitative analysis. Subsequently, two typical osteosarcoma cell lines, Saos-2 and MG63, were selected to study the changes of cisplatin sensitivity by up-regulating (NICD1 plasmid transfeciton) or decreasing (gamma-secretase complex inhibitor DAPT) the activation state of Notch1 signaling pathway. Our results showed a significant correlation between the expression of Notch1 and cisplatin sensitivity in patient specimens. In vitro, Saos-2 with higher expression of Notch1 had significantly better cisplatin sensitivity than MG63 whose Notch1 level was relatively lower. By targeting regulation in vitro, the cisplatin sensitivity of Saos-2 and MG63 had significantly increased after the activation of Notch1 signaling pathway, and vice versa. Further mechanism investigation revealed that activation/inhibition of Notch1 sensitized/desensitized cisplatin-induced apoptosis, which probably depended on the changes in the activity of Caspase family, including Caspase 3, Caspase 8 and Caspase 9 in these cells. Conclusions Our data clearly demonstrated that Notch1 is critical for cisplatin sensitivity in osteosarcoma. It can be used as a molecular marker and regulator for cisplatin sensitivity in osteosarcoma patients. PMID:24894297

Vanadium supersaturated silicon system: a theoretical and experimental approach

NASA Astrophysics Data System (ADS)

Garcia-Hemme, Eric; García, Gregorio; Palacios, Pablo; Montero, Daniel; García-Hernansanz, Rodrigo; Gonzalez-Diaz, Germán; Wahnon, Perla

2017-12-01

The effect of high dose vanadium ion implantation and pulsed laser annealing on the crystal structure and sub-bandgap optical absorption features of V-supersaturated silicon samples has been studied through the combination of experimental and theoretical approaches. Interest in V-supersaturated Si focusses on its potential as a material having a new band within the Si bandgap. Rutherford backscattering spectrometry measurements and formation energies computed through quantum calculations provide evidence that V atoms are mainly located at interstitial positions. The response of sub-bandgap spectral photoconductance is extended far into the infrared region of the spectrum. Theoretical simulations (based on density functional theory and many-body perturbation in GW approximation) bring to light that, in addition to V atoms at interstitial positions, Si defects should also be taken into account in explaining the experimental profile of the spectral photoconductance. The combination of experimental and theoretical methods provides evidence that the improved spectral photoconductance up to 6.2 µm (0.2 eV) is due to new sub-bandgap transitions, for which the new band due to V atoms within the Si bandgap plays an essential role. This enables the use of V-supersaturated silicon in the third generation of photovoltaic devices.

Increased sensitivity to positive social stimuli in monozygotic twins at risk of bipolar vs. unipolar disorder.

PubMed

Kærsgaard, S; Meluken, I; Kessing, L V; Vinberg, M; Miskowiak, K W

2018-05-01

Abnormalities in affective cognition are putative endophenotypes for bipolar and unipolar disorders but it is unclear whether some abnormalities are disorder-specific. We therefore investigated affective cognition in monozygotic twins at familial risk of bipolar disorder relative to those at risk of unipolar disorder and to low-risk twins. Seventy monozygotic twins with a co-twin history of bipolar disorder (n = 11), of unipolar disorder (n = 38) or without co-twin history of affective disorder (n = 21) were included. Variables of interest were recognition of and vigilance to emotional faces, emotional reactivity and -regulation in social scenarios and non-affective cognition. Twins at familial risk of bipolar disorder showed increased recognition of low to moderate intensity of happy facial expressions relative to both unipolar disorder high-risk twins and low-risk twins. Bipolar disorder high-risk twins also displayed supraliminal attentional avoidance of happy faces compared with unipolar disorder high-risk twins and greater emotional reactivity in positive and neutral social scenarios and less reactivity in negative social scenarios than low-risk twins. In contrast with our hypothesis, there was no negative bias in unipolar disorder high-risk twins. There were no differences between the groups in demographic characteristics or non-affective cognition. The modest sample size limited the statistical power of the study. Increased sensitivity and reactivity to positive social stimuli may be a neurocognitive endophenotype that is specific for bipolar disorder. If replicated in larger samples, this 'positive endophenotype' could potentially aid future diagnostic differentiation between unipolar and bipolar disorder. Copyright © 2018 Elsevier B.V. All rights reserved.

GammadeltaT cells positively regulate contact sensitivity (CS) reaction via modulation of INF-gamma, IL-12 and TNF-alpha production.

PubMed

Strzepa, Anna; Majewska-Szczepanik, Monika; Szczepanik, Marian

2013-01-01

The gammadeltaT cells were identified as positive as well as negative regulators of immune responses. They take part in pathogen clearance, modulation of innate and adaptive immunity as well as in healing and tissue maintenance. The course of many pathological conditions such as collagen induced arthritis (CIA), experimental autoimmune encephalomyelitis (EAE) and airway hyperresponsiveness is positively regulated by gammadeltaT cells. It was shown previously that contact sensitivity (CS), an example of antigen-specific cell-mediated immune response, is also positively regulated by gammadeltaT cells. The current work confirmed the regulatory function of gammadeltaT cells in CS response as their depletion with anti-TCRdelta monoclonal antibody and complement significantly decreased adoptive transfer of the CS reaction. In vitro study showed that removal of gammadeltaT cells with magnetic beads significantly decreased the production of the proinflammatory cytokines IFN-gamma, IL-12 and TNF-alpha. Reconstitution of gammadeltaT-depleted cells with gammadeltaT-enriched cells restored cytokine production, proving the reversibility of the investigated process. In summary, gammadeltaT cells positively regulate the CS reaction via modulation of proinflammatory cytokine production.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiao, Xianfeng, E-mail: qiaoxianfeng@hotmail.com; Zhao, Chen; Chen, Bingbing

This paper reports a trap-induced photoconductivity in ITO/pentacene/Al diodes by using current-voltage and magneto-conductance measurements. The comparison of photoconductivity between pentacene diodes with and without trap clearly shows that the traps play a critical role in generating photoconductivity. It shows that no observable photoconductivity is detected for trap-free pentacene diodes, while significant photoconductivity is observed in diodes with trap. This is because the initial photogenerated singlet excitons in pentacene can rapidly split into triplet excitons with higher binding energy prior to dissociating into free charge carriers. The generated triplet excitons react with trapped charges to release charge-carriers from traps, leadingmore » to a trap-induced photoconductivity in the single-layer pentacene diodes. Our studies elucidated the formation mechanisms of photoconductivity in pentacene diodes with extremely fast singlet fission rate.« less

Front-end circuit for position sensitive silicon and vacuum tube photomultipliers with gain control and depth of interaction measurement

NASA Astrophysics Data System (ADS)

Herrero, Vicente; Colom, Ricardo; Gadea, Rafael; Lerche, Christoph W.; Cerdá, Joaquín; Sebastiá, Ángel; Benlloch, José M.

2007-06-01

Silicon Photomultipliers, though still under development for mass production, may be an alternative to traditional Vacuum Photomultipliers Tubes (VPMT). As a consequence, electronic front-ends initially designed for VPMT will need to be modified. In this simulation, an improved architecture is presented which is able to obtain impact position and depth of interaction of a gamma ray within a continuous scintillation crystal, using either kind of PM. A current sensitive preamplifier stage with individual gain adjustment interfaces the multi-anode PM outputs with a current division resistor network. The preamplifier stage allows to improve front-end processing delay and temporal resolution behavior as well as to increase impact position calculation resolution. Depth of interaction (DOI) is calculated from the width of the scintillation light distribution, which is related to the sum of voltages in resistor network input nodes. This operation is done by means of a high-speed current mode scheme.

Kinematic sensitivity of robot manipulators

NASA Technical Reports Server (NTRS)

Vuskovic, Marko I.

1989-01-01

Kinematic sensitivity vectors and matrices for open-loop, n degrees-of-freedom manipulators are derived. First-order sensitivity vectors are defined as partial derivatives of the manipulator's position and orientation with respect to its geometrical parameters. The four-parameter kinematic model is considered, as well as the five-parameter model in case of nominally parallel joint axes. Sensitivity vectors are expressed in terms of coordinate axes of manipulator frames. Second-order sensitivity vectors, the partial derivatives of first-order sensitivity vectors, are also considered. It is shown that second-order sensitivity vectors can be expressed as vector products of the first-order sensitivity vectors.

Photodiode array for position-sensitive detection using high X-ray flux provided by synchrotron radiation

NASA Astrophysics Data System (ADS)

Jucha, A.; Bonin, D.; Dartyge, E.; Flank, A. M.; Fontaine, A.; Raoux, D.

1984-09-01

Synchrotron radiation provides a high intensity source over a large range of wavelengths. This is the prominent quality that has laid the foundations of the EXAFS development (Extended X-ray Absorption Fine Structure). EXAFS data can be collected in different ways. A full scan requires 5 to 10 min, compared to the one-day data collection of a conventional Bremsstrahlung X-ray tube. Recently, by using the new photodiode array (R 1024 SFX) manufactured by Reticon, it has been possible to reduce the data collection time to less than 100 ms. The key elements of this new EXAFS method are a dispersive optics combined with a position sensitive detector able to work under very high flux conditions. The total aperture of 2500 μm × 25 μm for each pixel is well suited to spectroscopic applications. Besides its high dynamic range (> 10 4) and its linearity, the rapidity of the readout allows a flux of 10 9-10 10 photons/s over the 1024 sensing elements.

Position-sensitive coincidence detection of nuclear reaction products at the Prague Van-de-Graaff accelerator

NASA Astrophysics Data System (ADS)

Granja, Carlos; Kraus, Vaclav; Pugatch, Valery; Kohout, Zdenek

2017-06-01

In low-energy nuclear reactions of astrophysical interest or fusion studies the spatial- and time-correlated detection of two and more reaction products can be a valuable tool in studies of reaction mechanisms, resolving reaction channels and measuring angular distributions of reaction products. For this purpose we constructed a configurable array of position-sensitive detectors based on the hybrid semiconductor pixel detector Timepix. Additional analog-signal electronics provide self-trigger together with extended multi-device control and synchronized readout electronics by a customized control and coincidence unit. The instrumentation, developed and used for detection of fission fragments in spontaneous and neutron induced fission as well as in charged particle detection in neutron induced reactions, is being implemented for low-energy light-ion induced nuclear reactions. Application and demonstration of the technique with two Timepix detectors on p+p elastic scattering at the Van-de-Graaff (VdG) accelerator in Prague is given.

Sensitivity to punishment and sensitivity to reward and traffic violations.

PubMed

Castellà, Josep; Pérez, Jorge

2004-11-01

The aim of our study consists of contributing information on the relationship between the personality variables derived from Gray's model and the conduct that accompanies the infringement of the road traffic rules. Seven hundred and ninety-two adults of both sexes took part in the study (389 men and 403 women), all of whom had driving licences and drove frequently. The subjects answered "The Sensitivity to Punishment and Sensitivity to Reward Questionnaire", a scale of monotony avoidance, and two Likert scales of attitude and behaviour in connection with traffic violations. We found a high positive relationship between attitude and behaviour, with the men infringing the rules more than the women. Hypotheses regarding a relationship between traffic offences and sensibility to reward and monotony avoidance were confirmed. Those people with high scores in sensitivity to punishment and low ones in sensitivity to reward were those who drove within the law, while those with low sensitivity to punishment and high sensitivity to reward were those who broke it more. Sensitivity to reward was a stronger determinant in encouraging infringement of the rules than was sensitivity to punishment in discouraging the subjects to do so.

Nucleation kinetics, crystal growth and optical studies on lithium hydrogen oxalate monohydrate single crystal

NASA Astrophysics Data System (ADS)

Chandran, Senthilkumar; Paulraj, Rajesh; Ramasamy, P.

2017-06-01

Semi-organic lithium hydrogen oxalate monohydrate non-linear optical single crystals have been grown by slow evaporation solution technique at 40 °C. The nucleation parameters such as critical radius, interfacial tension, and critical free energy change have been evaluated using the experimental data. The solubility and the nucleation curve of the crystal at different temperatures have been analyzed. The crystal has a positive temperature coefficient of solubility. The metastable zone width and induction period have been determined for the aqueous solution growth of lithium hydrogen oxalate monohydrate. The UV-vis-NIR spectrum showed this crystal has high transparency. The photoconductivity studies indicate lithium hydrogen oxalate monohydrate has positive photoconductivity behaviour. The low etch pit density observed on (0 0 1) crystal surface and the high resolution x-ray difraction analysis indicate the good quality of the grown crystals

Positive lusitropic effect and diminished myofibrillar sensitivity to calcium produced by cAMP on toad (Bufo arenarum Hensel) ventricle.

PubMed

Vila Petroff, M; Vittone, L; Mundiña, C; Chiappe de Cingolani, G; Alicia, M

1992-01-01

In intact ventricular strips from toad heart, we studied the relaxant or positive lusitropic effect of different interventions known to increase intracellular cAMP levels. Isoproterenol increased developed tension (DT), maximal rate of contraction (+T), and maximal velocity of relaxation (-T). From 10(-8) to 10(-4)M isoproterenol, -T increased proportionally more than +T being the ratio +T/-T significantly decreased. A single dose of isoproterenol (3 x 10(-8)M) increased cAMP levels from 0.174 +/- 0.022 to 0.329 +/- 0.039 pmoles/mg ww (P < 0.05), increased contractility by 69 +/- 13% and decreased +T/-T by 18.5 +/- 4.55%. Administration of 10(-3)M of dibutyryl cyclic AMP (dcAMP) significantly increased DT and +T and decreased the ratio +T/-T. Similar effects were obtained with milrinone, a specific cAMP phosphodiesterase inhibitor. Papaverine, a non selective phosphodiesterase inhibitor, failed to increase +T but significantly increased -T. In chemically skinned ventricular trabeculae, calcium sensitivity of the myofibrils was significantly increased by 10(-5)M of the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (IBMX). 10(-3)M dcAMP failed to affect calcium sensitivity of chemically skinned ventricular trabeculae when given alone, but produced a decrease in calcium sensitivity of the myofibrils in the presence of 10(-5)M of either IBMX or papaverine. The results would indicate that the relaxant effect of isoproterenol is mediated in toad ventricle by an increase in intracellular cAMP levels. They furthermore suggest that a decrease in myofilament sensitivity to calcium may be a mechanism by which cAMP produces its relaxant effect.

Sensitive Mid-Infrared Detection in Wide-Bandgap Semiconductors Using Extreme Non-Degenerate Two-Photon Absorption

DTIC Science & Technology

2011-08-07

cutting and imaging, with p- and i -GaN regions estimated to be ,1 mm in thickness36. This detector was used in photoconductive mode, with a preamplifier...D., Khoo, I . C., Salamo, G. J., Stegeman, G. I . & Van Straland, E. W. Nonlinear refraction and absorption: mechanisms and magnitudes. Adv. Opt...Am. B 9, 2065–2074 (1992). 14. Sheik- Bahae , M., Wang, J., DeSalvo, R., Hagan, D. J. & Van Styland, E. W. Measurement of nondegenerate nonlinearities

Dandelions, tulips and orchids: evidence for the existence of low-sensitive, medium-sensitive and high-sensitive individuals.

PubMed

Lionetti, Francesca; Aron, Arthur; Aron, Elaine N; Burns, G Leonard; Jagiellowicz, Jadzia; Pluess, Michael

2018-01-22

According to empirical studies and recent theories, people differ substantially in their reactivity or sensitivity to environmental influences with some being generally more affected than others. More sensitive individuals have been described as orchids and less-sensitive ones as dandelions. Applying a data-driven approach, we explored the existence of sensitivity groups in a sample of 906 adults who completed the highly sensitive person (HSP) scale. According to factor analyses, the HSP scale reflects a bifactor model with a general sensitivity factor. In contrast to prevailing theories, latent class analyses consistently suggested the existence of three rather than two groups. While we were able to identify a highly sensitive (orchids, 31%) and a low-sensitive group (dandelions, 29%), we also detected a third group (40%) characterised by medium sensitivity, which we refer to as tulips in keeping with the flower metaphor. Preliminary cut-off scores for all three groups are provided. In order to characterise the different sensitivity groups, we investigated group differences regarding the Big Five personality traits, as well as experimentally assessed emotional reactivity in an additional independent sample. According to these follow-up analyses, the three groups differed in neuroticism, extraversion and emotional reactivity to positive mood induction with orchids scoring significantly higher in neuroticism and emotional reactivity and lower in extraversion than the other two groups (dandelions also differed significantly from tulips). Findings suggest that environmental sensitivity is a continuous and normally distributed trait but that people fall into three distinct sensitive groups along a sensitivity continuum.

Long-Term Associations of Justice Sensitivity, Rejection Sensitivity, and Depressive Symptoms in Children and Adolescents

PubMed Central

Bondü, Rebecca; Sahyazici-Knaak, Fidan; Esser, Günter

2017-01-01

Depressive symptoms have been related to anxious rejection sensitivity, but little is known about relations with angry rejection sensitivity and justice sensitivity. We measured rejection sensitivity, justice sensitivity, and depressive symptoms in 1,665 9-to-21-year olds at two points of measurement. Participants with high T1 levels of depressive symptoms reported higher anxious and angry rejection sensitivity and higher justice sensitivity than controls at T1 and T2. T1 rejection, but not justice sensitivity predicted T2 depressive symptoms; high victim justice sensitivity, however, added to the stabilization of depressive symptoms. T1 depressive symptoms positively predicted T2 anxious and angry rejection and victim justice sensitivity. Hence, sensitivity toward negative social cues may be cause and consequence of depressive symptoms and requires consideration in cognitive-behavioral treatment of depression. PMID:28955257

Conductive Photo-Activated Porphyrin-ZnO Nanostructured Gas Sensor Array.

PubMed

Magna, Gabriele; Catini, Alexandro; Kumar, Raj; Palmacci, Massimo; Martinelli, Eugenio; Paolesse, Roberto; di Natale, Corrado

2017-04-01

Chemoresistors working at room temperature are attractive for low-consumption integrated sensors. Previous studies show that this feature can be obtained with photoconductive porphyrins-coated ZnO nanostructures. Furthermore, variations of the porphyrin molecular structure alter both the chemical sensitivity and the photoconductivity, and can be used to define the sensor characteristics. Based on these assumptions, we investigated the properties of an array of four sensors made of a layer of ZnO nanoparticles coated with porphyrins with the same molecular framework but different metal atoms. The array was tested with five volatile organic compounds (VOCs), each measured at different concentrations. Results confirm that the features of individual porphyrins influence the sensor behavior, and the differences among sensors are enough to enable the discrimination of volatile compounds disregarding their concentration.

Fundamental Investigations into the Infrared Properties of Carbon Nanotubes

DTIC Science & Technology

2013-01-23

Judy Wu. Development of Nanopatterned Fluorine-Doped Tin Oxide Electrodes for Dye-Sensitized Solar Cells with Improved Light Trapping, ACS Applied...heterojunction solar cell photocurrent enhancement, Nanoscale, (06 2012): 0. doi: 10.1039/c2nr30735a 08/30/2011 1.00 Rongtao Lu, Rayyan Kamal, Judy Z Wu...Jun Li, Judy Wu. The effect of annealing on the photoconductivity of carbon nanofiber/TiO2core-shell nanowires for use in dye-sensitized solar cells

Optimal design of a high accuracy photoelectric auto-collimator based on position sensitive detector

NASA Astrophysics Data System (ADS)

Yan, Pei-pei; Yang, Yong-qing; She, Wen-ji; Liu, Kai; Jiang, Kai; Duan, Jing; Shan, Qiusha

2018-02-01

A kind of high accuracy Photo-electric auto-collimator based on PSD was designed. The integral structure composed of light source, optical lens group, Position Sensitive Detector (PSD) sensor, and its hardware and software processing system constituted. Telephoto objective optical type is chosen during the designing process, which effectively reduces the length, weight and volume of the optical system, as well as develops simulation-based design and analysis of the auto-collimator optical system. The technical indicators of auto-collimator presented by this paper are: measuring resolution less than 0.05″; a field of view is 2ω=0.4° × 0.4° measuring range is +/-5' error of whole range measurement is less than 0.2″. Measuring distance is 10m, which are applicable to minor-angle precise measuring environment. Aberration analysis indicates that the MTF close to the diffraction limit, the spot in the spot diagram is much smaller than the Airy disk. The total length of the telephoto lens is only 450mm by the design of the optical machine structure optimization. The autocollimator's dimension get compact obviously under the condition of the image quality is guaranteed.

Position sensitive and energy dispersive x-ray detector based on silicon strip detector technology

NASA Astrophysics Data System (ADS)

Wiącek, P.; Dąbrowski, W.; Fink, J.; Fiutowski, T.; Krane, H.-G.; Loyer, F.; Schwamberger, A.; Świentek, K.; Venanzi, C.

2015-04-01

A new position sensitive detector with a global energy resolution for the entire detector of about 380 eV FWHM for 8.04 keV line at ambient temperature is presented. The measured global energy resolution is defined by the energy spectra summed over all strips of the detector, and thus it includes electronic noise of the front-end electronics, charge sharing effects, matching of parameters across the channels and other system noise sources. The target energy resolution has been achieved by segmentation of the strips to reduce their capacitance and by careful optimization of the front-end electronics. The key design aspects and parameters of the detector are discussed briefly in the paper. Excellent noise and matching performance of the readout ASIC and negligible system noise allow us to operate the detector with a discrimination threshold as low as 1 keV and to measure fluorescence radiation lines of light elements, down to Al Kα of 1.49 keV, simultaneously with measurements of the diffraction patterns. The measurement results that demonstrate the spectrometric and count rate performance of the developed detector are presented and discussed in the paper.

Highly sensitive derivatization reagents possessing positively charged structures for the determination of oligosaccharides in glycoproteins by high-performance liquid chromatography electrospray ionization tandem mass spectrometry.

PubMed

Min, Jun Zhe; Nagai, Keisuke; Shi, Qing; Zhou, Wenjun; Todoroki, Kenichiro; Inoue, Koichi; Lee, Yong-Ill; Toyo'oka, Toshimasa

2016-09-23

We have developed three kinds of novel derivatization reagents (4-CEBTPP, 4-CBBTPP, 5-COTPP) with triphenylphosphine (TPP) as a basic structure carrying a permanent positive charge for resolution of the oligosaccharides in glycoprotein using high-performance liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The synthesized reagents reacted with the sialylglycosylamine of the sialylglycopeptide after treatment by PNGase F. The final derivatives were analyzed by ESI-MS and sensitively detected in the selected reaction monitoring (SRM) mode. Furthermore, the limits of detection (S/N=3) on the SRM chromatograms were at the fmol level (30fmol). Therefore, we used the limit of detection of the reagent products detected by the SRM and evaluated the utility of each reagent. Among the reagents, the positively charged 4-CEBTPP derivative's peak area was the highest; 4-CEBTPP with a positively charged structure showed about a 20 times greater sensitivity for the glycosylamine of the SGP product compared to the conventional fluorescence reagent, Fmoc-Cl. In addition, various fragment ions based on the carbohydrate units also appeared in the MS/MS spectra. Among the fragment ions, m/z 627.37 (CE=40eV) corresponding to 4-CEBTPP-GlcNAc and m/z 120.09 (CE=100eV) corresponding to 4-CEBTPP are the most important ones for identifying the oligosaccharide. 4-CEBTPP-SGA was easily identified by the selected-ion chromatogram in the product ion scan (m/z 120.09) and in the precursor ion scan (m/z 627.37) by MS/MS detection. The derivatized analytes have a high ionization efficiency and they are detected with a high sensitivity in the electrospray ionization. The novel derivatization reagent with a multi-function provided a higher sensitivity for the oligosaccharide analysis, as well as a better specificity and feasibility. Furthermore, several oligosaccharides in fetuin and ribonuclease B were successfully identified by the proposed procedure

Sensitivity and specificity of clinician administered screening instruments in detecting depression among HIV-positive individuals in Uganda.

PubMed

Akena, Dickens; Joska, John; Obuku, Ekwaro A; Stein, Dan J

2013-01-01

Depressive disorders are highly prevalent in Africa where diseases such as HIV/AIDS are common. The aim of this study was to assess the validity of commonly used depression screening instruments in a setting characterized by low literacy, where patients may not be able to self-administer depression scales. We explored the validity of the Patient Health Questionaire-9 (PHQ-9), Centre for Epidemiological Surveys for Depression (CES-D), and the Kessler-10 (K-10), using the Mini International Neuropsychiatric Instrument (MINI) as a gold standard in 368 persons living with HIV/AIDS (PLWHA) in Uganda. The shorter versions of the K-10 and PHQ-9 were extracted to assess their performance in comparison to the longer versions. We used STATA 11.2 to analyze the data. The prevalence of a MINI defined depression in this patient sample was 17.4%. The three instruments all performed well, with areas under the curve (AUC) ranging from 0.82 to 0.96. The PHQ-9 showed the best performance characteristics with an AUC of 0.96, a sensitivity of 91.6%, and specificity 81.2%. The extracted versions performed more modestly. All three instruments showed good properties as screening tools; the PHQ-9 has particularly high sensitivity and specificity, and so can be considered useful for screening HIV-positive patients for depression.

Mapping nanoscale effects of localized noise-source activities on photoconductive charge transports in polymer-blend films.

PubMed

Shekhar, Shashank; Cho, Duckhyung; Cho, Dong-Guk; Yang, Myungjae; Hong, Seunghun

2018-05-18

We develolped a method to directly image the nanoscale effects of localized noise-source activities on photoconducting charge transports in domain structures of phase-separated polymer-blend films of Poly(9,9-di-n-octylfluorenyl-2,7-diyl) and Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole). For the imaging, current and noise maps of the polymer-blend were recorded using a conducting nanoprobe in contact with the surface, enabling the conductivity (σ) and noise-source density (N T ) mappings under an external stimulus. The blend-films exhibited the phase-separation between the constituent polymers at domains level. Within a domain, high σ (low N T ) and low σ (high N T ) regions were observed, which could be associated with the ordered and disordered regions of a domain. In the N T maps, we observed that noise-sources strongly affected the conduction mechanism, resulting in a scaling behavior of σ ∝ [Formula: see text] in both ordered and disordered regions. When a blend film was under an influence of an external stimulus such as a high bias or an illumination, an increase in the σ was observed, but that also resulted in increases in the N T as a trade-off. Interestingly, the Δσ versus ΔN T plot exhibited an unusual scaling behavior of Δσ ∝ [Formula: see text] which is attributed to the de-trapping of carriers from deep traps by the external stimuli. In addition, we found that an external stimulus increased the conductivity at the interfaces without significantly increasing their N T , which can be the origin of the superior performances of polymer-blend based devices. These results provide valuable insight about the effects of noise-sources on nanoscale optoelectronic properties in polymer-blend films, which can be an important guideline for improving devices based on polymer-blend.

Mapping nanoscale effects of localized noise-source activities on photoconductive charge transports in polymer-blend films

NASA Astrophysics Data System (ADS)

Shekhar, Shashank; Cho, Duckhyung; Cho, Dong-Guk; Yang, Myungjae; Hong, Seunghun

2018-05-01

We develolped a method to directly image the nanoscale effects of localized noise-source activities on photoconducting charge transports in domain structures of phase-separated polymer-blend films of Poly(9,9-di-n-octylfluorenyl-2,7-diyl) and Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole). For the imaging, current and noise maps of the polymer-blend were recorded using a conducting nanoprobe in contact with the surface, enabling the conductivity (σ) and noise-source density (N T) mappings under an external stimulus. The blend-films exhibited the phase-separation between the constituent polymers at domains level. Within a domain, high σ (low N T) and low σ (high N T) regions were observed, which could be associated with the ordered and disordered regions of a domain. In the N T maps, we observed that noise-sources strongly affected the conduction mechanism, resulting in a scaling behavior of σ ∝ {{N}{{T}}}-0.5 in both ordered and disordered regions. When a blend film was under an influence of an external stimulus such as a high bias or an illumination, an increase in the σ was observed, but that also resulted in increases in the N T as a trade-off. Interestingly, the Δσ versus ΔN T plot exhibited an unusual scaling behavior of Δσ ∝ {{Δ }}{{N}{{T}}}0.5, which is attributed to the de-trapping of carriers from deep traps by the external stimuli. In addition, we found that an external stimulus increased the conductivity at the interfaces without significantly increasing their N T, which can be the origin of the superior performances of polymer-blend based devices. These results provide valuable insight about the effects of noise-sources on nanoscale optoelectronic properties in polymer-blend films, which can be an important guideline for improving devices based on polymer-blend.

[An oral sensitization food allergy model in Brown-Norway rats].

PubMed

Huang, Juan; Zhong, Yan; Cai, Wei; Zhang, Hongbo

2009-01-01

To develop an oral-sensitized animal model of food allergy using Brown-Norway (BN) rats and evaluate the sensitivity of ELISA and passive cutaneous anaphylaxis (PCA) in detecting ovalbumin-specific IgE antibody (OVA-IgE) level in sensitized animals. Sixteen 3-week old female BN rats were randomly divided into 3 groups: negative control group orally gavaged with saline, positive control group sensitized by intraperitoneal injection of 0. lmg/d OVA, and, study group sensitized by daily gavage of 1 mg/d ovalbumin (OVA). OVA-IgE was analyzed by ELISA and PCA method at week 4, 5, 6, 7, 8 and 9. At week 13, OVA-IgE level was analyzed after orally challenged by 1.0 ml of 100 mg/ml OVA. The ELISA result showed that the OVA-IgE level in study group was significantly increased at week 6, 7 and week 8 compared with negative control group (P < 0.05), and the highest level was found at week 6. There was no significant difference for the level of OVA-IgE between study group and positive control group. The sensitization rate in study group was 60%, 80% and 80% at week 6, 7 and 8 respectively, which was similar to positive control group. All PCA results in study group were negative, while in positive control group it was positive. Oral sensitization could be used as a suitable method to establish an animal model of food allergy, which is more comparable with the natural sensitization process in food allergy patients. ELISA method is more sensitive in detecting OVA-IgE level in oral sensitized animal model than PCA method.

Sensitivity of MJO propagation to a robust positive Indian Ocean dipole event in the superparameterized CAM

DOE PAGES

Benedict, James J.; Pritchard, Michael S.; Collins, William D.

2015-11-23

The superparameterized Community Atmosphere Model (SPCAM) is used to investigate the impact and geographic sensitivity of positive Indian Ocean Dipole (+IOD) sea-surface temperatures (SSTs) on Madden-Julian oscillation (MJO) propagation. The goal is to clarify potentially appreciable +IOD effects on MJO dynamics detected in prior studies by using a global model with explicit convection representation. Prescribed climatological October SSTs and variants of the SST distribution from October 2006, a +IOD event, force the model. Modest MJO convection weakening over the Maritime Continent occurs when either climatological SSTs, or +IOD SST anomalies restricted to the Indian Ocean, are applied. However, severe MJOmore » weakening occurs when either +IOD SST anomalies are applied globally or restricted to the equatorial Pacific. MJO disruption is associated with time-mean changes in the zonal wind profile and lower moist static energy (MSE) in subsiding air masses imported from the Subtropics by Rossby-like gyres. On intraseasonal scales, MJO disruption arises from significantly smaller MSE accumulation, weaker meridional advective moistening, and overactive submonthly eddies that mix drier subtropical air into the path of MJO convection. These results (1) demonstrate that SPCAM reproduces observed time-mean and intraseasonal changes during +IOD episodes, (2) reaffirm the role that submonthly eddies play in MJO propagation and show that such multiscale interactions are sensitive to interannual SST states, and (3) suggest that boreal fall +IOD SSTs local to the Indian Ocean have a significantly smaller impact on Maritime Continent MJO propagation compared to contemporaneous Pacific SST anomalies which, for October 2006, resemble El Ninõ-like conditions.« less

Sensitivity of MJO propagation to a robust positive Indian Ocean dipole event in the superparameterized CAM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benedict, James J.; Pritchard, Michael S.; Collins, William D.

The superparameterized Community Atmosphere Model (SPCAM) is used to investigate the impact and geographic sensitivity of positive Indian Ocean Dipole (+IOD) sea-surface temperatures (SSTs) on Madden-Julian oscillation (MJO) propagation. The goal is to clarify potentially appreciable +IOD effects on MJO dynamics detected in prior studies by using a global model with explicit convection representation. Prescribed climatological October SSTs and variants of the SST distribution from October 2006, a +IOD event, force the model. Modest MJO convection weakening over the Maritime Continent occurs when either climatological SSTs, or +IOD SST anomalies restricted to the Indian Ocean, are applied. However, severe MJOmore » weakening occurs when either +IOD SST anomalies are applied globally or restricted to the equatorial Pacific. MJO disruption is associated with time-mean changes in the zonal wind profile and lower moist static energy (MSE) in subsiding air masses imported from the Subtropics by Rossby-like gyres. On intraseasonal scales, MJO disruption arises from significantly smaller MSE accumulation, weaker meridional advective moistening, and overactive submonthly eddies that mix drier subtropical air into the path of MJO convection. These results (1) demonstrate that SPCAM reproduces observed time-mean and intraseasonal changes during +IOD episodes, (2) reaffirm the role that submonthly eddies play in MJO propagation and show that such multiscale interactions are sensitive to interannual SST states, and (3) suggest that boreal fall +IOD SSTs local to the Indian Ocean have a significantly smaller impact on Maritime Continent MJO propagation compared to contemporaneous Pacific SST anomalies which, for October 2006, resemble El Ninõ-like conditions.« less

Photoconductive and electro-optic effects in (Cd,Mg)Te single crystals measured in an experiment-on-chip configuration

NASA Astrophysics Data System (ADS)

Serafini, John; Hossain, A.; James, R. B.; Guziewicz, M.; Kruszka, R.; Słysz, W.; Kochanowska, D.; Domagala, J. Z.; Mycielski, A.; Sobolewski, Roman

2017-07-01

We present our studies on both photoconductive (PC) and electro-optic (EO) responses of (Cd,Mg)Te single crystals. In an In-doped Cd0.92Mg0.08Te single crystal, subpicosecond electrical pulses were optically generated via a PC effect, coupled into a transmission line, and, subsequently, detected using an internal EO sampling scheme, all in the same (Cd,Mg)Te material. For photo-excitation and EO sampling, we used femtosecond optical pulses generated by the same Ti:sapphire laser with the wavelengths of 410 and 820 nm, respectively. The shortest transmission line distance between the optical excitation and EO sampling points was 75 μm. By measuring the transient waveforms at different distances from the excitation point, we calculated the transmission-line complex propagation factor, as well as the THz frequency attenuation factor and the propagation velocity, all of which allowed us to reconstruct the electromagnetic transient generated directly at the excitation point, showing that the original PC transient was subpicosecond in duration with a fall time of ˜500 fs. Finally, the measured EO retardation, together with the amount of the electric-field penetration, allowed us to determine the magnitude of the internal EO effect in our (Cd,Mg)Te crystal. The obtained THz-frequency EO coefficient was equal to 0.4 pm/V, which is at the lower end among the values reported for CdTe-based ternaries, apparently, due to the disorientation of the tested crystal that resulted in the non-optimal EO measurement condition.

Photoconductive and electro-optic effects in (Cd,Mg)Te single crystals measured in an experiment-on-chip configuration

DOE PAGES

Serafini, John; Hossain, A.; James, R. B.; ...

2017-07-03

We present our studies on both photoconductive (PC) and electro-optic (EO) responses of (Cd,Mg)Te single crystals. In an In-doped Cd 0.92Mg 0.08Te single crystal, subpicosecond electrical pulses were optically generated via a PC effect, coupled into a transmission line, and, subsequently, detected using an internal EO sampling scheme, all in the same (Cd,Mg)Te material. For photo-excitation and EO sampling, we used femtosecond optical pulses generated by the same Ti:sapphire laser with the wavelength 410 and 820 nm, respectively. The shortest transmission line distance between the optical excitation and EO sampling points was 75 μm. By measuring the transient waveforms atmore » different distances from the excitation point, we calculated the transmission-line complex propagation factor, as well as the THz frequency attenuation factor and the propagation velocity, all of which allowed us to reconstruct the electromagnetic transient generated directly at the excitation point, showing that the original PC transient was subpicosecond in duration with a fall time of ~500 fs. Finally, the measured EO retardation, together with the amount of the electric-field penetration, allowed us to determine the magnitude of the internal EO effect in our (Cd,Mg)Te crystal. The obtained THz-frequency EO coefficient was equal to 0.4 pm/V, which is at the lower end among the values reported for CdTe-based ternaries, due to a twinned structure and misalignment of the tested (Cd,Mg)Te crystal.« less

Crystal growth and characterization of semi organic nonlinear optical (NLO) piperazinium tetrachlorozincate monohydrate (PTCZ) single crystal

NASA Astrophysics Data System (ADS)

Karuppasamy, P.; Pandian, Muthu Senthil; Ramasamy, P.

2018-04-01

The semi-organic single crystal of piperazinium tetrachlorozincate monohydrate (PTCZ) was successfully grown by slow evaporation solution technique (SEST). The grown crystal was subjected to the single crystal XRD studies for confirming the unit cell parameters. The optical quality of the grown crystal was identified by the UV-Vis NIR spectrum analysis and the optical band gap energy was calculated. The photoconductivity study reveals that the grown crystal has positive photoconductive nature. The mechanical stability of the grown crystal was analyzed using Vickers microhardness analyzer. The third-order nonlinear optical properties such as nonlinear refractive index (n2), absorption co-efficient (β) and susceptibility (χ(3)) were studied by Z-scan technique at 640 nm using solid state laser.

Evolutionary Analysis Predicts Sensitive Positions of MMP20 and Validates Newly- and Previously-Identified MMP20 Mutations Causing Amelogenesis Imperfecta

PubMed Central

Gasse, Barbara; Prasad, Megana; Delgado, Sidney; Huckert, Mathilde; Kawczynski, Marzena; Garret-Bernardin, Annelyse; Lopez-Cazaux, Serena; Bailleul-Forestier, Isabelle; Manière, Marie-Cécile; Stoetzel, Corinne; Bloch-Zupan, Agnès; Sire, Jean-Yves

2017-01-01

Amelogenesis imperfecta (AI) designates a group of genetic diseases characterized by a large range of enamel disorders causing important social and health problems. These defects can result from mutations in enamel matrix proteins or protease encoding genes. A range of mutations in the enamel cleavage enzyme matrix metalloproteinase-20 gene (MMP20) produce enamel defects of varying severity. To address how various alterations produce a range of AI phenotypes, we performed a targeted analysis to find MMP20 mutations in French patients diagnosed with non-syndromic AI. Genomic DNA was isolated from saliva and MMP20 exons and exon-intron boundaries sequenced. We identified several homozygous or heterozygous mutations, putatively involved in the AI phenotypes. To validate missense mutations and predict sensitive positions in the MMP20 sequence, we evolutionarily compared 75 sequences extracted from the public databases using the Datamonkey webserver. These sequences were representative of mammalian lineages, covering more than 150 million years of evolution. This analysis allowed us to find 324 sensitive positions (out of the 483 MMP20 residues), pinpoint functionally important domains, and build an evolutionary chart of important conserved MMP20 regions. This is an efficient tool to identify new- and previously-identified mutations. We thus identified six functional MMP20 mutations in unrelated families, finding two novel mutated sites. The genotypes and phenotypes of these six mutations are described and compared. To date, 13 MMP20 mutations causing AI have been reported, making these genotypes and associated hypomature enamel phenotypes the most frequent in AI. PMID:28659819

Evolutionary Analysis Predicts Sensitive Positions of MMP20 and Validates Newly- and Previously-Identified MMP20 Mutations Causing Amelogenesis Imperfecta.

PubMed

Gasse, Barbara; Prasad, Megana; Delgado, Sidney; Huckert, Mathilde; Kawczynski, Marzena; Garret-Bernardin, Annelyse; Lopez-Cazaux, Serena; Bailleul-Forestier, Isabelle; Manière, Marie-Cécile; Stoetzel, Corinne; Bloch-Zupan, Agnès; Sire, Jean-Yves

2017-01-01

Amelogenesis imperfecta (AI) designates a group of genetic diseases characterized by a large range of enamel disorders causing important social and health problems. These defects can result from mutations in enamel matrix proteins or protease encoding genes. A range of mutations in the enamel cleavage enzyme matrix metalloproteinase-20 gene ( MMP20 ) produce enamel defects of varying severity. To address how various alterations produce a range of AI phenotypes, we performed a targeted analysis to find MMP20 mutations in French patients diagnosed with non-syndromic AI. Genomic DNA was isolated from saliva and MMP20 exons and exon-intron boundaries sequenced. We identified several homozygous or heterozygous mutations, putatively involved in the AI phenotypes. To validate missense mutations and predict sensitive positions in the MMP20 sequence, we evolutionarily compared 75 sequences extracted from the public databases using the Datamonkey webserver. These sequences were representative of mammalian lineages, covering more than 150 million years of evolution. This analysis allowed us to find 324 sensitive positions (out of the 483 MMP20 residues), pinpoint functionally important domains, and build an evolutionary chart of important conserved MMP20 regions. This is an efficient tool to identify new- and previously-identified mutations. We thus identified six functional MMP20 mutations in unrelated families, finding two novel mutated sites. The genotypes and phenotypes of these six mutations are described and compared. To date, 13 MMP20 mutations causing AI have been reported, making these genotypes and associated hypomature enamel phenotypes the most frequent in AI.

The MAGIC Touch: Combining MAGIC-Pointing with a Touch-Sensitive Mouse

NASA Astrophysics Data System (ADS)

Drewes, Heiko; Schmidt, Albrecht

In this paper, we show how to use the combination of eye-gaze and a touch-sensitive mouse to ease pointing tasks in graphical user interfaces. A touch of the mouse positions the mouse pointer at the current gaze position of the user. Thus, the pointer is always at the position where the user expects it on the screen. This approach changes the user experience in tasks that include frequent switching between keyboard and mouse input (e.g. working with spreadsheets). In a user study, we compared the touch-sensitive mouse with a traditional mouse and observed speed improvements for pointing tasks on complex backgrounds. For pointing task on plain backgrounds, performances with both devices were similar, but users perceived the gaze-sensitive interaction of the touch-sensitive mouse as being faster and more convenient. Our results show that using a touch-sensitive mouse that positions the pointer on the user’s gaze position reduces the need for mouse movements in pointing tasks enormously.

Low noise optical position sensor

DOEpatents

Spear, J.D.

1999-03-09

A novel optical position sensor is described that uses two component photodiodes electrically connected in parallel, with opposing polarities. A lens provides optical gain and restricts the acceptance angle of the detector. The response of the device to displacements of an optical spot is similar to that of a conventional bi-cell type position sensitive detector. However, the component photodiode design enables simpler electronic amplification with inherently less electrical noise than the bi-cell. Measurements by the sensor of the pointing noise of a focused helium-neon laser as a function of frequency demonstrate high sensitivity and suitability for optical probe beam deflection experiments. 14 figs.

Low noise optical position sensor

DOEpatents

Spear, Jonathan David

1999-01-01

A novel optical position sensor is described that uses two component photodiodes electrically connected in parallel, with opposing polarities. A lens provides optical gain and restricts the acceptance angle of the detector. The response of the device to displacements of an optical spot is similar to that of a conventional bi-cell type position sensitive detector. However, the component photodiode design enables simpler electronic amplification with inherently less electrical noise than the bi-cell. Measurements by the sensor of the pointing noise of a focused helium-neon laser as a function of frequency demonstrate high sensitivity and suitability for optical probe beam deflection experiments.

Diagnosing periprosthetic infection: false-positive intraoperative Gram stains.

PubMed

Oethinger, Margret; Warner, Debra K; Schindler, Susan A; Kobayashi, Hideo; Bauer, Thomas W

2011-04-01

Intraoperative Gram stains have a reported low sensitivity but high specificity when used to help diagnose periprosthetic infections. In early 2008, we recognized an unexpectedly high frequency of apparent false-positive Gram stains from revision arthroplasties. The purpose of this report is to describe the cause of these false-positive test results. We calculated the sensitivity and specificity of all intraoperative Gram stains submitted from revision arthroplasty cases during a 3-month interval using microbiologic cultures of the same samples as the gold standard. Methods of specimen harvesting, handling, transport, distribution, specimen processing including tissue grinding/macerating, Gram staining, and interpretation were studied. After a test modification, results of specimens were prospectively collected for a second 3-month interval, and the sensitivity and specificity of intraoperative Gram stains were calculated. The retrospective review of 269 Gram stains submitted from revision arthroplasties indicated historic sensitivity and specificity values of 23% and 92%, respectively. Systematic analysis of all steps of the procedure identified Gram-stained but nonviable bacteria in commercial broth reagents used as diluents for maceration of periprosthetic membranes before Gram staining and culture. Polymerase chain reaction and sequencing showed mixed bacterial DNA. Evaluation of 390 specimens after initiating standardized Millipore filtering of diluent fluid revealed a reduced number of positive Gram stains, yielding 9% sensitivity and 99% specificity. Clusters of false-positive Gram stains have been reported in other clinical conditions. They are apparently rare related to diagnosing periprosthetic infections but have severe consequences if used to guide treatment. Even occasional false-positive Gram stains should prompt review of laboratory methods. Our observations implicate dead bacteria in microbiologic reagents as potential sources of false-positive Gram

Sensitivity, specificity and predictive probability values of serum agglutination test titres for the diagnosis of Salmonella Dublin culture-positive bovine abortion and stillbirth.

PubMed

Sánchez-Miguel, C; Crilly, J; Grant, J; Mee, J F

2018-06-01

The objective of this study was to determine the diagnostic value of maternal serology for the diagnosis of Salmonella Dublin bovine abortion and stillbirth. A retrospective, unmatched, case-control study was carried out using twenty year's data (1989-2009) from bovine foetal submissions to an Irish government veterinary laboratory. Cases (n = 214) were defined as submissions with a S. Dublin culture-positive foetus from a S. Dublin unvaccinated dam where results of maternal S. Dublin serology were available. Controls (n = 415) were defined as submissions where an alternative diagnosis other than S. Dublin was made in a foetus from an S. Dublin unvaccinated dam where the results of maternal S. Dublin serology were available. A logistic regression model was fitted to the data: the dichotomous dependent variable was the S. Dublin foetal culture result, and the independent variables were the maternal serum agglutination test (SAT) titre results. Salmonella serology correctly classified 87% of S. Dublin culture-positive foetuses at a predicted probability threshold of 0.44 (cut-off at which sensitivity and specificity are at a maximum, J = 0.67). The sensitivity of the SAT at the same threshold was 73.8% (95% CI: 67.4%-79.5%), and the specificity was 93.2% (95% CI: 90.3%-95.4%). The positive and negative predictive values were 84.9% (95% CI: 79.3%-88.6%) and 87.3% (95% CI: 83.5%-91.3%), respectively. This study illustrates that the use of predicted probability values, rather than the traditional arbitrary breakpoints of negative, inconclusive and positive, increases the diagnostic value of the maternal SAT. Veterinary laboratory diagnosticians and veterinary practitioners can recover from the test results, information previously categorized, particularly from those results declared to be inconclusive. © 2017 Blackwell Verlag GmbH.

Apparatus and method for measuring minority carrier lifetimes in semiconductor materials

DOEpatents

Ahrenkiel, Richard K.; Johnston, Steven W.

2001-01-01

An apparatus for determining the minority carrier lifetime of a semiconductor sample includes a positioner for moving the sample relative to a coil. The coil is connected to a bridge circuit such that the impedance of one arm of the bridge circuit is varied as sample is positioned relative to the coil. The sample is positioned relative to the coil such that any change in the photoconductance of the sample created by illumination of the sample creates a linearly related change in the input impedance of the bridge circuit. In addition, the apparatus is calibrated to work at a fixed frequency so that the apparatus maintains a consistently high sensitivity and high linearity for samples of different sizes, shapes, and material properties. When a light source illuminates the sample, the impedance of the bridge circuit is altered as excess carriers are generated in the sample, thereby producing a measurable signal indicative of the minority carrier lifetimes or recombination rates of the sample.

Apparatus for measuring minority carrier lifetimes in semiconductor materials

DOEpatents

Ahrenkiel, R.K.

1999-07-27

An apparatus for determining the minority carrier lifetime of a semiconductor sample includes a positioner for moving the sample relative to a coil. The coil is connected to a bridge circuit such that the impedance of one arm of the bridge circuit is varied as sample is positioned relative to the coil. The sample is positioned relative to the coil such that any change in the photoconductance of the sample created by illumination of the sample creates a linearly related change in the input impedance of the bridge circuit. In addition, the apparatus is calibrated to work at a fixed frequency so that the apparatus maintains a consistently high sensitivity and high linearly for samples of different sizes, shapes, and material properties. When a light source illuminates the sample, the impedance of the bridge circuit is altered as excess carriers are generated in the sample, thereby producing a measurable signal indicative of the minority carrier lifetimes or recombination rates of the sample. 17 figs.

Apparatus for measuring minority carrier lifetimes in semiconductor materials

DOEpatents

Ahrenkiel, Richard K.

1999-01-01

An apparatus for determining the minority carrier lifetime of a semiconductor sample includes a positioner for moving the sample relative to a coil. The coil is connected to a bridge circuit such that the impedance of one arm of the bridge circuit is varied as sample is positioned relative to the coil. The sample is positioned relative to the coil such that any change in the photoconductance of the sample created by illumination of the sample creates a linearly related change in the input impedance of the bridge circuit. In addition, the apparatus is calibrated to work at a fixed frequency so that the apparatus maintains a consistently high sensitivity and high linearly for samples of different sizes, shapes, and material properties. When a light source illuminates the sample, the impedance of the bridge circuit is altered as excess carriers are generated in the sample, thereby producing a measurable signal indicative of the minority carrier lifetimes or recombination rates of the sample.

Observations of Local Positive Low Cloud Feedback Patterns and Their Role in Internal Variability and Climate Sensitivity

NASA Astrophysics Data System (ADS)

Yuan, Tianle; Oreopoulos, Lazaros; Platnick, Steven E.; Meyer, Kerry

2018-05-01

Modeling studies have shown that cloud feedbacks are sensitive to the spatial pattern of sea surface temperature (SST) anomalies, while cloud feedbacks themselves strongly influence the magnitude of SST anomalies. Observational counterparts to such patterned interactions are still needed. Here we show that distinct large-scale patterns of SST and low-cloud cover (LCC) emerge naturally from objective analyses of observations and demonstrate their close coupling in a positive local SST-LCC feedback loop that may be important for both internal variability and climate change. The two patterns that explain the maximum amount of covariance between SST and LCC correspond to the Interdecadal Pacific Oscillation and the Atlantic Multidecadal Oscillation, leading modes of multidecadal internal variability. Spatial patterns and time series of SST and LCC anomalies associated with both modes point to a strong positive local SST-LCC feedback. In many current climate models, our analyses suggest that SST-LCC feedback strength is too weak compared to observations. Modeled local SST-LCC feedback strength affects simulated internal variability so that stronger feedback produces more intense and more realistic patterns of internal variability. To the extent that the physics of the local positive SST-LCC feedback inferred from observed climate variability applies to future greenhouse warming, we anticipate significant amount of delayed warming because of SST-LCC feedback when anthropogenic SST warming eventually overwhelm the effects of internal variability that may mute anthropogenic warming over parts of the ocean. We postulate that many climate models may be underestimating both future warming and the magnitude of modeled internal variability because of their weak SST-LCC feedback.

Crystal growth, perfection, linear and nonlinear optical, photoconductivity, dielectric, thermal and laser damage threshold properties of 4-methylimidazolium picrate: an interesting organic crystal for photonic and optoelectronic devices

NASA Astrophysics Data System (ADS)

Rajesh, K.; Arun, A.; Mani, A.; Praveen Kumar, P.

2016-10-01

The 4-methylimidazolium picrate has been synthesized and characterized successfully. Single and powder x-ray diffraction studies were conducted which confirmed the crystal structure, and the value of the strain was calculated. The crystal perfection was determined by a HRXR diffractometer. The transmission spectrum exhibited a better transmittance of the crystal in the entire visible region with a lower cut-off wavelength of 209 nm. The linear absorption value was calculated by the optical limiting method. A birefringence study was also carried out. Second and third order nonlinear optical properties of the crystal were found by second harmonic generation and the z-scan technique. The crystals were also characterized by dielectric measurement and a photoconductivity analyzer to determine the dielectric property and the optical conductivity of the crystal. The laser damage threshold activity of the grown crystal was studied by a Q-switched Nd:YAG laser beam. Thermal studies established that the compound did not undergo a phase transition and was stable up to 240 °C.

Efficacy of direct Gram stain in differentiating staphylococci from streptococci in blood cultures positive for gram-positive cocci.

PubMed Central

Agger, W A; Maki, D G

1978-01-01

A preponderance of clusters seen on direct Gram stain of blood cultures positive for gram-positive cocci was 98% sensitive and 100% specific for identification of staphylococcal species or of Peptococcus. A preponderance of chains, pairs, or both was 100% sensitive and 98% specific for identifying streptococci. Further presumptive identification of either staphylococci or streptococci based on microscopic morphology was unreliable. The direct Gram stain is highly reliable for differentiating staphylococci from streptococci and should be of considerable value to clinicians selecting initial antimicrobial therapy. PMID:75888

Electrical Transport Mechanisms and Photoconduction in Undoped Crystalline Flash-Evaporated Lead Iodide Thin Films

NASA Astrophysics Data System (ADS)

Al-Daraghmeh, Tariq M.; Saleh, Mahmoud H.; Ahmad, Mais Jamil A.; Bulos, Basim N.; Shehadeh, Khawla M.; Jafar, Mousa M. Abdul-Gader

2018-03-01

The flash-evaporation technique was utilized to fabricate undoped 1.35-μm and 1.2-μm thick lead iodide films at substrate temperatures T_{{s}} = 150 °C and 200°C, respectively. The films were deposited onto a coplanar comb-like copper (Cu-) electrode pattern, previously coated on glass substrates to form lateral metal-semiconductor-metal (MSM-) structures. The as-measured constant- temperature direct-current (dc)-voltage ( I( {V;T} ) - V ) curves of the obtained lateral coplanar Cu-PbI2-Cu samples (film plus electrode) displayed remarkable ohmic behavior at all temperatures ( T = 18 - 90°C). Their dc electrical resistance R_{{dc}} (T ) revealed a single thermally-activated conduction mechanism over the temperature range with activation energy E_{{act}} ≈ 0.90 - 0.98 {eV} , slightly less than half of room-temperature bandgap energy E_{{g}} ( ≈ 2.3 {eV} ) of undoped 2H-polytype PbI2 single crystals. The undoped flash-evaporated {PbI}_{{x}} thin films were homogeneous and almost stoichiometric ( x ≈ 1.87 ), in contrast to findings on lead iodide films prepared by other methods, and were highly crystalline hexagonal 2H-polytypic structure with c-axis perpendicular to the surface of substrates maintained at T_{s} ≳ 150°C. Photoconductivity measurements made on these lateral Cu-PbI2-Cu-structures under on-off visible-light illumination reveal a feeble photoresponse for long wavelengths ( λ > 570 {nm} ), but a strong response to blue light of photon energy E_{{ph}} ≈ 2.73 {eV} ( > E_{{g}} ), due to photogenerated electron-hole (e-h) pairs via direct band-to-band electronic transitions. The constant-temperature/dc voltage current-time I( {T,V} ) - t curves of the studied lateral PbI2 MSM-structures at low ambient temperatures ( T < 50°C), after cutting off the blue-light illumination, exhibit two trapping mechanisms with different relaxation times. These strongly depend on V and T , with thermally generated charge carriers in the PbI2 mask photogenerated

Metal cation detection in positive ion mode electrospray ionization mass spectrometry using a tetracationic salt as a gas-phase ion-pairing agent: evaluation of the effect of chelating agents on detection sensitivity.

PubMed

Xu, Chengdong; Dodbiba, Edra; Padivitage, Nilusha L T; Breitbach, Zachary S; Armstrong, Daniel W

2012-12-30

The detection of metal cations continues to be essential in many scientific and industrial areas of interest. The most common electrospray ionization mass spectrometry (ESI-MS) approach involves chelating the metal ions and detecting the organometallic complex in the negative ion mode. However, it is well known that negative ion mode ESI-MS is generally less sensitive than the positive ion mode. To achieve greater sensitivity, it is necessary to examine the feasibility of detecting the chelated metal cations in positive ion mode ESI-MS. Since highly solvated native metal cations have relatively low ionization efficiency in ESI-MS, and can be difficult to detect in the positive ion mode, a tetracationic ion-pairing agent was added to form a complex with the negatively charged metal chelate. The use of the ion-pairing agent leads to the generation of an overall positively charged complex, which can be detected at higher m/z values in the positive ion mode by electrospray ionization linear quadrupole ion trap mass spectrometry. Thirteen chelating agents with diverse structures were evaluated in this study. The nature of the chelating agent played as important a role as was previously determined for cationic pairing agents. The detection limits of six metal cations reached sub-picogram levels and significant improvements were observed when compared to negative ion mode detection where the metal-chelates were monitored without adding the ion-pairing reagent (IPR). Also, selective reaction monitoring (SRM) analyses were performed on the ternary complexes, which improved detection limits by one to three orders of magnitude. With this method it was possible to analyze the metal cations in the positive ion mode ESI-MS with the advantage of speed, sensitivity and selectivity. The optimum solution pH for this type of analysis is 5-7. Tandem mass spectrometry (MS/MS) further increases the sensitivity. Speciation is straightforward making this a broadly useful approach for the

DUX4 Immunohistochemistry Is a Highly Sensitive and Specific Marker for CIC-DUX4 Fusion-positive Round Cell Tumor.

PubMed

Siegele, Bradford; Roberts, Jon; Black, Jennifer O; Rudzinski, Erin; Vargas, Sara O; Galambos, Csaba

2017-03-01

The histologic differential diagnosis of pediatric and adult round cell tumors is vast and includes the recently recognized entity CIC-DUX4 fusion-positive round cell tumor. The diagnosis of CIC-DUX4 tumor can be suggested by light microscopic and immunohistochemical features, but currently, definitive diagnosis requires ancillary genetic testing such as conventional karyotyping, fluorescence in situ hybridization, or molecular methods. We sought to determine whether DUX4 expression would serve as a fusion-specific immunohistochemical marker distinguishing CIC-DUX4 tumor from potential histologic mimics. A cohort of CIC-DUX4 fusion-positive round cell tumors harboring t(4;19)(q35;q13) and t(10;19)(q26;q13) translocations was designed, with additional inclusion of a case with a translocation confirmed to involve the CIC gene without delineation of the partner. Round cell tumors with potentially overlapping histologic features were also collected. Staining with a monoclonal antibody raised against the C-terminus of the DUX4 protein was applied to all cases. DUX4 immunohistochemistry exhibited diffuse, crisp, strong nuclear staining in all CIC-DUX4 fusion-positive round cell tumors (5/5, 100% sensitivity), and exhibited negative staining in nuclei of all of the other tested round cell tumors, including 20 Ewing sarcomas, 1 Ewing-like sarcoma, 11 alveolar rhabdomyosarcomas, 9 embryonal rhabdomyosarcomas, 12 synovial sarcomas, 7 desmoplastic small round cell tumors, 3 malignant rhabdoid tumors, 9 neuroblastomas, and 4 clear cell sarcomas (0/76, 100% specificity). Thus, in our experience, DUX4 immunostaining distinguishes CIC-DUX4 tumors from other round cell mimics. We recommend its use when CIC-DUX4 fusion-positive round cell tumor enters the histologic differential diagnosis.

Use of side-chain incompatibility for tailoring long-range p/n heterojunctions: photoconductive nanofibers formed by self-assembly of an amphiphilic donor-acceptor dyad consisting of oligothiophene and perylenediimide.

PubMed

Li, Wei-Shi; Saeki, Akinori; Yamamoto, Yohei; Fukushima, Takanori; Seki, Shu; Ishii, Noriyuki; Kato, Kenichi; Takata, Masaki; Aida, Takuzo

2010-07-05

To tailor organic p/n heterojunctions with molecular-level precision, a rational design strategy using side-chain incompatibility of a covalently connected donor-acceptor (D-A) dyad has been successfully carried out. An oligothiophene-perylenediimide dyad, when modified with triethylene glycol side chains at one terminus and dodecyl side chains at the other (2(Amphi)), self-assembles into nanofibers with a long-range D/A heterojunction. In contrast, when the dyad is modified with dodecyl side chains at both termini (2(Lipo)), ill-defined microfibers result. In steady-state measurements using microgap electrodes, a cast film of the nanofiber of 2(Amphi) displays far better photoconducting properties than that of the microfiber of 2(Lipo). Flash-photolysis time-resolved microwave conductivity measurements, in conjunction with transient absorption spectroscopy, clearly indicate that the nanofiber of 2(Amphi) intrinsically allows for better carrier generation and transport properties than the microfibrous assembly of 2(Lipo).

Effects of transcriptional start site sequence and position on nucleotide-sensitive selection of alternative start sites at the pyrC promoter in Escherichia coli.

PubMed Central

Liu, J; Turnbough, C L

1994-01-01

In Escherichia coli, expression of the pyrC gene is regulated primarily by a translational control mechanism based on nucleotide-sensitive selection of transcriptional start sites at the pyrC promoter. When intracellular levels of CTP are high, pyrC transcripts are initiated predominantly with CTP at a site 7 bases downstream of the Pribnow box. These transcripts form a stable hairpin at their 5' ends that blocks ribosome binding. When the CTP level is low and the GTP level is high, conditions found in pyrimidine-limited cells, transcripts are initiated primarily with GTP at a site 9 bases downstream of the Pribnow box. These shorter transcripts are unable to form a hairpin at their 5' ends and are readily translated. In this study, we examined the effects of nucleotide sequence and position on the selection of transcriptional start sites at the pyrC promoter. We characterized promoter mutations that systematically alter the sequence at position 7 or 9 downstream of the Pribnow box or vary the spacing between the Pribnow box and wild-type transcriptional initiation region. The results reveal preferences for particular initiating nucleotides (ATP > or = GTP > UTP >> CTP) and for starting positions downstream of the Pribnow box (7 >> 6 and 8 > 9 > 10). The results indicate that optimal nucleotide-sensitive start site switching at the wild-type pyrC promoter is the result of competition between the preferred start site (position 7) that uses the poorest initiating nucleotide (CTP) and a weak start site (position 9) that uses a good initiating nucleotide (GTP). The sequence of the pyrC promoter also minimizes the synthesis of untranslatable transcripts and provides for maximum stability of the regulatory transcript hairpin. In addition, the results show that the effects of the mutations on pyrC expression and regulation are consistent with the current model for translational control. Possible effects of preferences for initiating nucleotides and start sites on the

Tend to Compare and Tend to Be Fair: The Relationship between Social Comparison Sensitivity and Justice Sensitivity

PubMed Central

Zhen, Shanshan; Yu, Rongjun

2016-01-01

Social comparison is a prerequisite for processing fairness, although the two types of cognition may be associated with different emotions. Whereas social comparison may induce envy, the perception of unfairness may elicit anger. Yet, it remains unclear whether people who tend to have a strong sense of fairness also tend to compare themselves more with others. Here, Study 1 used a modified ultimatum game (UG) and a social comparison game (SCG) to examine the relationship between justice sensitivity and social comparison sensitivity in 51 young adults. Study 2 examined self-reported social comparison and justice sensitivity in 142 young adults. Both studies showed a positive correlation between social comparison sensitivity and justice sensitivity. We reason that social comparison and justice sensitivity have an important positive correlation in human decision-making. The rejection of self-disadvantageous inequality offers may be due to the social comparison effect, which suggests that the tendency to compare oneself with others may contribute to having a strong sense of justice. Our findings suggest that the predictions of game theory may vary depending on the social culture context and incorporating notions of fairness and social comparison tendency may be essential to better predict the actual behavior of players in social interactive situations. PMID:27214372

The Case for Frequency Sensitivity in Orthographic Learning

ERIC Educational Resources Information Center

McMurray, Sharon; McVeigh, Claire

2016-01-01

This paper positions the importance of frequency sensitivity in the development of orthographic knowledge throughout childhood and promotes learning to spell as a vehicle which may be used effectively to develop this sensitivity. It is suggested that orthographic knowledge is advanced via a process of "frequency sensitivity" to…

Sources of sensitization, cross-reactions, and occupational sensitization to topical anaesthetics among general dermatology patients.

PubMed

Jussi, Liippo; Lammintausta, Kaija

2009-03-01

Contact sensitization to local anaesthetics is often from topical medicaments. Occupational sensitization to topical anaesthetics may occur in certain occupations. The aim of the study was to analyse the occurrence of contact sensitization to topical anaesthetics in general dermatology patients. Patch testing with topical anaesthetics was carried out in 620 patients. Possible sources of sensitization and the clinical histories of the patients are analysed. Positive patch test reactions to one or more topical anaesthetics were seen in 25/620 patients. Dibucaine reactions were most common (20/25), and lidocaine sensitization was seen in two patients. Six patients had reactions to ester-type and/or amide-type anaesthetics concurrently. Local preparations for perianal conditions were the most common sensitizers. One patient had developed occupational sensitization to procaine with multiple cross-reactions and with concurrent penicillin sensitization from procaine penicillin. Dibucaine-containing perianal medicaments are the major source of contact sensitization to topical anaesthetics. Although sensitization to multiple anaesthetics can be seen, cross-reactions are possible. Contact sensitization to lidocaine is not common, and possible cross-reactions should be determined when reactions to lidocaine are seen. Occupational procaine sensitization from veterinary medicaments is a risk among animal workers.

Lupin sensitization and clinical allergy in food allergic children in Norway.

PubMed

Lindvik, Helene; Holden, Lise; Løvik, Martinus; Cvancarova, Milada; Halvorsen, Ragnhild

2008-01-01

The aim of the present pilot study was to investigate to what extent children in Norway sensitized to lupin had clinical lupin allergy, and to compare sensitization to lupin with sensitization to other legumes. Thirty-five children with food allergy referred to a national referral hospital were evaluated with skin prick test (SPT) and analysis of serum-specific IgE to lupin, peanut, pea and soy. The children with positive SPTs to lupin were offered oral food challenges with lupin flour. Fifteen children (43%) had positive SPT and 17 children (49%) had serum-specific IgE to lupin. Ten SPT-positive children underwent oral food challenges and one experienced an allergic reaction to lupin flour. This child was one of six challenged children with IgE antibodies to peanut >15 kU(A)/L. There was a strong relationship between positive SPT to lupin flour and positive SPT to soy and between positive SPT to lupin and specific IgE to soy, pea and peanut. Children with sensitization to lupin are not likely to have a clinical lupin allergy. Avoidance of lupin on the basis of lupin sensitization or peanut allergy would lead to unnecessarily strict diets. Food challenge is currently necessary to diagnose lupin allergy.

Symbol-String Sensitivity and Children's Reading

ERIC Educational Resources Information Center

Pammer, Kristen; Lavis, Ruth; Hansen, Peter; Cornelissen, Piers L.

2004-01-01

In this study of primary school children, a novel "symbol-string" task is used to assess sensitivity to the position of briefly presented non-alphabetic but letter-like symbols. The results demonstrate that sensitivity in the symbol-string task explains a unique proportion of the variability in children's contextual reading accuracy. Moreover,…

75 FR 77783 - Designation of National Security Positions

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-14

... requiring eligibility for access to Top Secret or ``Q'' classified information; (ii) Positions involving... at the Top Secret or ``Q'' level; (xix) Positions working with significant life-critical/mission... Sensitive information, requiring involvement in Top Secret Special Access Programs (SAP), or positions which...

The Positive Inotropic Effect of Pyruvate Involves an Increase in Myofilament Calcium Sensitivity

PubMed Central

Torres, Carlos A. A.; Varian, Kenneth D.; Canan, Cynthia H.; Davis, Jonathan P.; Janssen, Paul M. L.

2013-01-01

Pyruvate is a metabolic fuel that is a potent inotropic agent. Despite its unique inotropic and antioxidant properties, the molecular mechanism of its inotropic mechanism is still largely unknown. To examine the inotropic effect of pyruvate in parallel with intracellular calcium handling under near physiological conditions, we measured pH, myofilament calcium sensitivity, developed force, and calcium transients in ultra thin rabbit heart trabeculae at 37 °C loaded iontophoretically with the calcium indicator bis-fura-2. By contrasting conditions of control versus sarcoplasmic reticulum block (with either cyclopiazonic acid and ryanodine or with thapsigargin) we were able to characterize and isolate the effects of pyruvate on sarcoplasmic reticulum calcium handling and developed force. A potassium contracture technique was subsequently utilized to assess the force-calcium relationship and thus the myofilament calcium sensitivity. Pyruvate consistently increased developed force whether or not the sarcoplasmic reticulum was blocked (16.8±3.5 to 24.5±5.1 vs. 6.9±2.6 to 12.5±4.4 mN/mm2, non-blocked vs. blocked sarcoplasmic reticulum respectively, p<0.001, n = 9). Furthermore, the sensitizing effect of pyruvate on the myofilaments was demonstrated by potassium contractures (EC50 at baseline versus 20 minutes of pyruvate infusion (peak force development) was 701±94 vs. 445±65 nM, p<0.01, n = 6). This study is the first to demonstrate that a leftward shift in myofilament calcium sensitivity is an important mediator of the inotropic effect of pyruvate. This finding can have important implications for future development of therapeutic strategies in the management of heart failure. PMID:23691074

Compliance and stress sensitivity of spur gear teeth

NASA Technical Reports Server (NTRS)

Cornell, R. W.

1983-01-01

The magnitude and variation of tooth pair compliance with load position affects the dynamics and loading significantly, and the tooth root stressing per load varies significantly with load position. Therefore, the recently developed time history, interactive, closed form solution for the dynamic tooth loads for both low and high contact ratio spur gears was expanded to include improved and simplified methods for calculating the compliance and stress sensitivity for three involute tooth forms as a function of load position. The compliance analysis has an improved fillet/foundation. The stress sensitivity analysis is a modified version of the Heywood method but with an improvement in the magnitude and location of the peak stress in the fillet. These improved compliance and stress sensitivity analyses are presented along with their evaluation using test, finite element, and analytic transformation results, which showed good agreement.

Positive selection of a duplicated UV-sensitive visual pigment coincides with wing pigment evolution in Heliconius butterflies

PubMed Central

Briscoe, Adriana D.; Bybee, Seth M.; Bernard, Gary D.; Yuan, Furong; Sison-Mangus, Marilou P.; Reed, Robert D.; Warren, Andrew D.; Llorente-Bousquets, Jorge; Chiao, Chuan-Chin

2010-01-01

The butterfly Heliconius erato can see from the UV to the red part of the light spectrum with color vision proven from 440 to 640 nm. Its eye is known to contain three visual pigments, rhodopsins, produced by an 11-cis-3-hydroxyretinal chromophore together with long wavelength (LWRh), blue (BRh) and UV (UVRh1) opsins. We now find that H. erato has a second UV opsin mRNA (UVRh2)—a previously undescribed duplication of this gene among Lepidoptera. To investigate its evolutionary origin, we screened eye cDNAs from 14 butterfly species in the subfamily Heliconiinae and found both copies only among Heliconius. Phylogeny-based tests of selection indicate positive selection of UVRh2 following duplication, and some of the positively selected sites correspond to vertebrate visual pigment spectral tuning residues. Epi-microspectrophotometry reveals two UV-absorbing rhodopsins in the H. erato eye with λmax = 355 nm and 398 nm. Along with the additional UV opsin, Heliconius have also evolved 3-hydroxy-DL-kynurenine (3-OHK)-based yellow wing pigments not found in close relatives. Visual models of how butterflies perceive wing color variation indicate this has resulted in an expansion of the number of distinguishable yellow colors on Heliconius wings. Functional diversification of the UV-sensitive visual pigments may help explain why the yellow wing pigments of Heliconius are so colorful in the UV range compared to the yellow pigments of close relatives lacking the UV opsin duplicate. PMID:20133601

Positive selection of a duplicated UV-sensitive visual pigment coincides with wing pigment evolution in Heliconius butterflies.

PubMed

Briscoe, Adriana D; Bybee, Seth M; Bernard, Gary D; Yuan, Furong; Sison-Mangus, Marilou P; Reed, Robert D; Warren, Andrew D; Llorente-Bousquets, Jorge; Chiao, Chuan-Chin

2010-02-23

The butterfly Heliconius erato can see from the UV to the red part of the light spectrum with color vision proven from 440 to 640 nm. Its eye is known to contain three visual pigments, rhodopsins, produced by an 11-cis-3-hydroxyretinal chromophore together with long wavelength (LWRh), blue (BRh) and UV (UVRh1) opsins. We now find that H. erato has a second UV opsin mRNA (UVRh2)-a previously undescribed duplication of this gene among Lepidoptera. To investigate its evolutionary origin, we screened eye cDNAs from 14 butterfly species in the subfamily Heliconiinae and found both copies only among Heliconius. Phylogeny-based tests of selection indicate positive selection of UVRh2 following duplication, and some of the positively selected sites correspond to vertebrate visual pigment spectral tuning residues. Epi-microspectrophotometry reveals two UV-absorbing rhodopsins in the H. erato eye with lambda(max) = 355 nm and 398 nm. Along with the additional UV opsin, Heliconius have also evolved 3-hydroxy-DL-kynurenine (3-OHK)-based yellow wing pigments not found in close relatives. Visual models of how butterflies perceive wing color variation indicate this has resulted in an expansion of the number of distinguishable yellow colors on Heliconius wings. Functional diversification of the UV-sensitive visual pigments may help explain why the yellow wing pigments of Heliconius are so colorful in the UV range compared to the yellow pigments of close relatives lacking the UV opsin duplicate.

An efficient fast response and high-gain solar-blind flexible ultraviolet photodetector employing hybrid geometry

NASA Astrophysics Data System (ADS)

Hussain, Amreen A.; Pal, Arup R.; Patil, Dinkar S.

2014-05-01

We report high performance flexible hybrid ultraviolet photodetector with solar-blind sensitivity using nanocomposite film of plasma polymerized aniline-titanium dioxide. A facile solvent-free plasma technique is used to synthesize superior quality hybrid material with high yield. The hybrid photodetector exhibited high photoconductive gain of the order of ˜105 and fast speed with response and recovery time of 22.87 ms and 34.23 ms. This is an excellent result towards getting a balance in the response speed and photoconductive gain trade-off of the photodetectors reported so far. In addition, the device has the advantages of enhanced photosensitivity ((Ilight - Idark)/Idark) of the order of ˜102 and high responsivity of ˜104 AW-1. All the merits substantiates that, to prepare hybrid material, plasma based method holds potential to be an easy way for realizing large scale nanostructured photodetectors for practical applications.

Sensitivity of Podosphaera aphanis isolates to DMI fungicides: distribution and reduced cross-sensitivity.

PubMed

Sombardier, Audrey; Dufour, Marie-Cécile; Blancard, Dominique; Corio-Costet, Marie-France

2010-01-01

Management of strawberry powdery mildew, Podopshaera aphanis (Wallr.), requires numerous fungicide treatments. Limiting epidemics is heavily dependent on sterol demethylation inhibitors (DMIs) such as myclobutanil or penconazole. Recently, a noticeable reduction in the efficacy of these triazole fungicides was reported by strawberry growers in France. The goal of this study was to investigate the state of DMI sensitivity of French P. aphanis and provide tools for improved pest management. Using leaf disc sporulation assays, sensitivity to myclobutanil and penconazole of 23 isolates of P. aphanis was monitored. Myclobutanil EC(50) ranged from less than 0.1 to 14.67 mg L(-1) and for penconazole from 0.04 to 4.2 mg L(-1). A cross-analysis and a Venn diagram showed that there was reduced sensitivity and a positive correlation between the less sensitive myclobutanil and penconazole isolates; 73.9% of isolates were less sensitive to a DMI and 47.8% exhibited less sensitivity to both fungicides. The results show that sensitivity to myclobutanil and, to a lesser extent, penconazole has become less efficient in strawberry powdery mildew in France. Therefore, urgent action is required in order to document its appearance and optimise methods of control.

Interpersonal sensitivity and persistent attenuated psychotic symptoms in adolescence.

PubMed

Masillo, Alice; Brandizzi, M; Valmaggia, L R; Saba, R; Lo Cascio, N; Lindau, J F; Telesforo, L; Venturini, P; Montanaro, D; Di Pietro, D; D'Alema, M; Girardi, P; Fiori Nastro, P

2018-03-01

Interpersonal sensitivity defines feelings of inner-fragility in the presence of others due to the expectation of criticism or rejection. Interpersonal sensitivity was found to be related to attenuated positive psychotic symptom during the prodromal phase of psychosis. The aims of this study were to examine if high level of interpersonal sensitivity at baseline are associated with the persistence of attenuated positive psychotic symptoms and general psychopathology at 18-month follow-up. A sample of 85 help-seeking individuals (mean age = 16.6, SD = 5.05) referred an Italian early detection project, completed the interpersonal sensitivity measure and the structured interview for prodromal symptoms (SIPS) at baseline and were assessed at 18-month follow-up using the SIPS. Results showed that individuals with high level of interpersonal sensitivity at baseline reported high level of attenuated positive psychotic symptoms (i.e., unusual thought content) and general symptoms (i.e., depression, irritability and low tolerance to daily stress) at follow-up. This study suggests that being "hypersensitive" to interpersonal interactions is a psychological feature associated with attenuated positive psychotic symptoms and general symptoms, such as depression and irritability, at 18-month follow-up. Assessing and treating inner-self fragilities may be an important step of early detection program to avoid the persistence of subtle but very distressing long-terms symptoms.

The ultrafast dynamics and conductivity of photoexcited graphene at different Fermi energies

PubMed Central

Turchinovich, Dmitry; Kläui, Mathias; Hendry, Euan; Polini, Marco

2018-01-01

For many of the envisioned optoelectronic applications of graphene, it is crucial to understand the subpicosecond carrier dynamics immediately following photoexcitation and the effect of photoexcitation on the electrical conductivity—the photoconductivity. Whereas these topics have been studied using various ultrafast experiments and theoretical approaches, controversial and incomplete explanations concerning the sign of the photoconductivity, the occurrence and significance of the creation of additional electron-hole pairs, and, in particular, how the relevant processes depend on Fermi energy have been put forward. We present a unified and intuitive physical picture of the ultrafast carrier dynamics and the photoconductivity, combining optical pump–terahertz probe measurements on a gate-tunable graphene device, with numerical calculations using the Boltzmann equation. We distinguish two types of ultrafast photo-induced carrier heating processes: At low (equilibrium) Fermi energy (EF ≲ 0.1 eV for our experiments), broadening of the carrier distribution involves interband transitions (interband heating). At higher Fermi energy (EF ≳ 0.15 eV), broadening of the carrier distribution involves intraband transitions (intraband heating). Under certain conditions, additional electron-hole pairs can be created [carrier multiplication (CM)] for low EF, and hot carriers (hot-CM) for higher EF. The resultant photoconductivity is positive (negative) for low (high) EF, which in our physical picture, is explained using solely electronic effects: It follows from the effect of the heated carrier distributions on the screening of impurities, consistent with the DC conductivity being mostly due to impurity scattering. The importance of these insights is highlighted by a discussion of the implications for graphene photodetector applications. PMID:29756035

Sensitivity of ring growth and carbon allocation to climatic variation vary within ponderosa pine trees.

PubMed

Kerhoulas, Lucy P; Kane, Jeffrey M

2012-01-01

Most dendrochronological studies focus on cores sampled from standard positions (main stem, breast height), yet vertical gradients in hydraulic constraints and priorities for carbon allocation may contribute to different growth sensitivities with position. Using cores taken from five positions (coarse roots, breast height, base of live crown, mid-crown branch and treetop), we investigated how radial growth sensitivity to climate over the period of 1895-2008 varies by position within 36 large ponderosa pines (Pinus ponderosa Dougl.) in northern Arizona. The climate parameters investigated were Palmer Drought Severity Index, water year and monsoon precipitation, maximum annual temperature, minimum annual temperature and average annual temperature. For each study tree, we generated Pearson correlation coefficients between ring width indices from each position and six climate parameters. We also investigated whether the number of missing rings differed among positions and bole heights. We found that tree density did not significantly influence climatic sensitivity to any of the climate parameters investigated at any of the sample positions. Results from three types of analyses suggest that climatic sensitivity of tree growth varied with position height: (i) correlations of radial growth and climate variables consistently increased with height; (ii) model strength based on Akaike's information criterion increased with height, where treetop growth consistently had the highest sensitivity and coarse roots the lowest sensitivity to each climatic parameter; and (iii) the correlation between bole ring width indices decreased with distance between positions. We speculate that increased sensitivity to climate at higher positions is related to hydraulic limitation because higher positions experience greater xylem tensions due to gravitational effects that render these positions more sensitive to climatic stresses. The low sensitivity of root growth to all climatic variables

Symbol-string sensitivity and children's reading.

PubMed

Pammer, Kristen; Lavis, Ruth; Hansen, Peter; Cornelissen, Piers L

2004-06-01

In this study of primary school children, a novel 'symbol-string' task is used to assess sensitivity to the position of briefly presented non-alphabetic but letter-like symbols. The results demonstrate that sensitivity in the symbol-string task explains a unique proportion of the variability in children's contextual reading accuracy. Moreover, developmental dyslexic readers show reduced sensitivity in this task, compared to chronological age controls. The results suggest that limitations set by visuo-spatial processes and/or attentional iconic memory resources may constrain children's reading accuracy.

Franz-Keldysh effect in epitaxial ZnO thin films

NASA Astrophysics Data System (ADS)

Bridoux, G.; Villafuerte, M.; Ferreyra, J. M.; Guimpel, J.; Nieva, G.; Figueroa, C. A.; Straube, B.; Heluani, S. P.

2018-02-01

Photoconductance spectroscopy has been studied in epitaxial ZnO thin films with different thicknesses that range between 136 and 21 nm. We report a systematic decrease in photoconductivity and a red shift in band edge photoconductance spectra when the thickness is reduced. For thinner films, it is found that the effective energy gap value diminishes. By time dependent photoconductivity measurements, we found an enhanced contribution of the slow relaxation times for thicker films. These effects are interpreted in terms of a band-bending contribution where the Franz-Keldysh effect and the polarization of ZnO play a major role in thinner films.

CPRA for allocation of kidneys in the US: More candidates ≥98% CPRA, lower positive crossmatch rates and improved transplant rates for sensitized patients.

PubMed

Baxter-Lowe, Lee Ann; Kucheryavaya, Anna; Tyan, Dolly; Reinsmoen, Nancy

2016-05-01

In 2009 calculated panel reactive antibody (CPRA) replaced PRA as the metric for HLA sensitization in the US kidney allocation system. During the next four years, registrants with at least one unacceptable antigen increased (34-40%) and registrants with ≥98% PRA/CPRA increased from 7% to 9% of the waitlist. These changes were accompanied by a reduction in kidney offers refused for positive crossmatch: 14,137 (1.7%) in 2009 and 3,310 in 2013 (0.4%). Registrants with ≥98% PRA/CPRA had highest rates of refusal but also showed substantial improvement (20% in 2009 vs 8% in 2013). For registrants with ≥98% PRA/CPRA, 45% of accepted offers in 2009 were not transplanted into the intended recipient compared to 11% in 2013. Transplant rates remained low for these patients (∼50/1000 active patient-years), but rates improved for patients with 80-97% PRA/CPRA (223/1000 active patient-years in 2009 vs 354/1000 in 2013). In 2013, 40% regraft candidates had CPRA ≥98% compared to 4% of primary graft candidates. More females than males were ≥98% CPRA (14% vs 7%) and more females had CPRA above 0 (50% vs 28%). In the CPRA era, listing of unacceptable antigens increased, positive crossmatches were diminished and transplant rates for sensitized patients improved. Copyright © 2016 American Society for Histocompatibility and Immunogenetics. All rights reserved.

Phosphatidylglycerol and Chilling Sensitivity in Plants

PubMed Central

Roughan, P. Grattan

1985-01-01

The hypothesis that molecular species of thylakoid phosphatidylglycerol containing two saturated fatty acids (disaturated phosphatidylglycerol) confer chilling sensitivity upon plants was tested by analyzing the fatty acid composition of phosphatidylglycerols isolated from leaves of a range of plants expected to have different sensitivities to chilling temperatures. `Saturated' fatty acids (palmitate plus stearate plus hexadeca-trans-3-enoate) as a proportion of total phosphatidylglycerol fatty acids varied from 51 to 80 mole per cent in the plants analyzed but appeared to be rigidly fixed for a given plant species, being unaffected by leaf maturity or by environment. Hexadeca-trans-3-enoate occurred only at the sn-2 position, whereas C-18 fatty acids occurred only at the sn-1 position of thylakoid phosphatidylglycerol. Therefore, the proportion of disaturated molecular species could be predicted accurately from the total fatty acids of phosphatidylglycerol. Disaturated molecular species accounted for <25% of the total phosphatidylglycerol from leaves of chilling-resistant plants and for 50 to 60% of the phosphatidylglycerol in leaves from some of the most chilling-sensitive plants. However, not all chilling-sensitive plants contained high proportions of disaturated phosphatidylglycerol; solanaceous and other 16:3-plants and C4 grasses may be important exceptions. Nonetheless, proportions of disaturated phosphatidylglycerol increased concomitantly with increasing chilling sensitivity of plants within a genus. PMID:16664127

Evaluation of the LightCycler Staphylococcus MGRADE Kits on Positive Blood Cultures That Contained Gram-Positive Cocci in Clusters

PubMed Central

Shrestha, Nabin K.; Tuohy, Marion J.; Padmanabhan, Ravindran A.; Hall, Gerri S.; Procop, Gary W.

2005-01-01

We evaluated the Roche LightCycler Staphylococcus MGRADE kits to differentiate between Staphylococcus aureus and coagulase-negative staphylococci in blood cultures growing clusters of gram-positive cocci. Testing 100 bottles (36 containing S. aureus), the assay was 100% sensitive and 98.44% specific for S. aureus and 100% sensitive and specific for coagulase-negative staphylococci. PMID:16333115

Radiation sensitive devices and systems for detection of radioactive materials and related methods

DOEpatents

Kotter, Dale K

2014-12-02

Radiation sensitive devices include a substrate comprising a radiation sensitive material and a plurality of resonance elements coupled to the substrate. Each resonance element is configured to resonate responsive to non-ionizing incident radiation. Systems for detecting radiation from a special nuclear material include a radiation sensitive device and a sensor located remotely from the radiation sensitive device and configured to measure an output signal from the radiation sensitive device. In such systems, the radiation sensitive device includes a radiation sensitive material and a plurality of resonance elements positioned on the radiation sensitive material. Methods for detecting a presence of a special nuclear material include positioning a radiation sensitive device in a location where special nuclear materials are to be detected and remotely interrogating the radiation sensitive device with a sensor.

Terahertz-radiation generation and detection in low-temperature-grown GaAs epitaxial films on GaAs (100) and (111)A substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galiev, G. B.; Pushkarev, S. S., E-mail: s-s-e-r-p@mail.ru; Buriakov, A. M.

The efficiency of the generation and detection of terahertz radiation in the range up to 3 THz by LT-GaAs films containing equidistant Si doping δ layers and grown by molecular beam epitaxy on GaAs (100) and (111)Ga substrates is studied by terahertz spectroscopy. Microstrip photoconductive antennas are fabricated on the film surface. Terahertz radiation is generated by exposure of the antenna gap to femtosecond optical laser pulses. It is shown that the intensity of terahertz radiation from the photoconductive antenna on LT-GaAs/GaAs (111)Ga is twice as large as the intensity of a similar antenna on LT-GaAs/GaAs(100) and the sensitivity ofmore » the antenna on LT-GaAs/GaAs (111)Ga as a terahertz-radiation detector exceeds that of the antenna on LT-GaAs/GaAs(100) by a factor of 1.4.« less

Contact sensitivity to preservatives in Singapore: frequency of sensitization to 11 common preservatives 2006-2011.

PubMed

Cheng, Suzanne; Leow, Yung Hian; Goh, Chee Leok; Goon, Anthony

2014-01-01

Preservatives are indispensable agents used to prevent bacterial and fungal contamination of cosmetics, personal care products, domestic preparations, and industrial products. We evaluated patch-test data at the National Skin Centre, Singapore, from 2006 to 2011 to identify the trends in preservative contact allergies. All patients with suspected contact dermatitis were patch tested to 4 preservatives within the modified European standard series. Patients were also tested with 7 preservatives from our special series if clinically indicated. Three thousand one hundred seventy-seven patients were tested to preservatives in the standard series. Sensitization frequencies were all greater than 1%: parabens (2.58%), methylchloroisothiazolinone/methylisothiazolinone (1.75%), quaternium 15 (1.43%), and methyldibromoglutaronitrile (1.2%). There was no change in trends in sensitization frequencies from 2006 to 2011, with no increase in sensitization frequency to methylchloroisothiazolinone/methylisothiazolinone. The sensitization frequencies for methyldibromoglutaronitrile/phenoxyethanol and diazolidinylurea were 2.03% and 1.37%, respectively, and remained less than 1% for bronopol, imidazolidinyl urea, and 2-phenoxyethanol. A rate of 0% was seen for 1,3-dimethylol-5,5-dimethyl hydantoin and formaldehyde; 9.4% of positive patch-test results became positive only at day 7. Preservatives are common causes of allergic contact dermatitis. This should be considered when introducing new preservatives into the market. Day 7 readings are important to detect late reactions.

Rejection Sensitivity, Jealousy, and the Relationship to Interpersonal Aggression.

PubMed

Murphy, Anna M; Russell, Gemma

2018-07-01

The development and maintenance of interpersonal relationships lead individuals to risk rejection in the pursuit of acceptance. Some individuals are predisposed to experience a hypersensitivity to rejection that is hypothesized to be related to jealous and aggressive reactions within interpersonal relationships. The current study used convenience sampling to recruit 247 young adults to evaluate the relationship between rejection sensitivity, jealousy, and aggression. A mediation model was used to test three hypotheses: Higher scores of rejection sensitivity would be positively correlated to higher scores of aggression (Hypothesis 1); higher scores of rejection sensitivity would be positively correlated to higher scores of jealousy (Hypothesis 2); jealousy would mediate the relationship between rejection sensitivity and aggression (Hypothesis 3). Study results suggest a tendency for individuals with high rejection sensitivity to experience higher levels of jealousy, and subsequently have a greater propensity for aggression, than individuals with low rejection sensitivity. Future research that substantiates a link between hypersensitivity to rejection, jealousy, and aggression may provide an avenue for prevention, education, or intervention in reducing aggression within interpersonal relationships.

Improving the Sensitivity and Positive Predictive Value in a Cystic Fibrosis Newborn Screening Program Using a Repeat Immunoreactive Trypsinogen and Genetic Analysis.

PubMed

Sontag, Marci K; Lee, Rachel; Wright, Daniel; Freedenberg, Debra; Sagel, Scott D

2016-08-01

To evaluate the performance of a new cystic fibrosis (CF) newborn screening algorithm, comprised of immunoreactive trypsinogen (IRT) in first (24-48 hours of life) and second (7-14 days of life) dried blood spot plus DNA on second dried blood spot, over existing algorithms. A retrospective review of the IRT/IRT/DNA algorithm implemented in Colorado, Wyoming, and Texas. A total of 1 520 079 newborns were screened, 32 557 (2.1%) had abnormal first IRT; 8794 (0.54%) on second. Furthermore, 14 653 mutation analyses were performed; 1391 newborns were referred for diagnostic testing; 274 newborns were diagnosed; and 201/274 (73%) of newborns had 2 mutations on the newborn screening CFTR panel. Sensitivity was 96.2%, compared with sensitivity of 76.1% observed with IRT/IRT (105 ng/mL cut-offs, P < .0001). The ratio of newborns with CF to heterozygote carriers was 1:2.5, and newborns with CF to newborns with CFTR-related metabolic syndrome was 10.8:1. The overall positive predictive value was 20%. The median age of diagnosis was 28, 30, and 39.5 days in the 3 states. IRT/IRT/DNA is more sensitive than IRT/IRT because of lower cut-offs (∼97 percentile or 60 ng/mL); higher cut-offs in IRT/IRT programs (>99 percentile, 105 ng/mL) would not achieve sufficient sensitivity. Carrier identification and identification of newborns with CFTR-related metabolic syndrome is less common in IRT/IRT/DNA compared with IRT/DNA. The time to diagnosis is nominally longer, but diagnosis can be achieved in the neonatal period and opportunities to further improve timeliness have been enacted. IRT/IRT/DNA algorithm should be considered by programs with 2 routine screens. Copyright © 2016 Elsevier Inc. All rights reserved.

[Antibiotics sensitivity and characteristics of the esculin-positive Pseudomonas aeruginosa biovar].

PubMed

Sivolodskiĭ, E P

2000-01-01

Strains of Pseudomonas aeruginosa hydrolyzing esculin were isolated for the first time. They amount to 17.1 +/- 2.0% (60 from 325) of the investigated P. aeruginosa strains isolated from the clinical material in St. Petersburg. Esculin hydrolysis was measured by micromethod in plates, results were analysed after 3-hours incubation at 37 degrees C. Esculin-positive strains possesed biovar properties: they are widely spread, demonstrated other characteristic features (absence of triethylamine odour, specific colonies lysis), are stable on ability to hydrolyse esculin while culture storage and after repeated culturing. Typical strain of esculinolytica biovar was deposited into the culture collection of the National Research Institute of Agricultural Microbiology as P. aeruginosa ARRIAM 64-A. Susceptibility testing of the esculin-positive strains by disk-diffusion method revealed that most strains were inhibited by imipenem (86.6%), amikacin (75.0%), ceftazidime (65.0%), meropenem (60.0%), aztreonam (51.6%). The percent of strains susceptible to other antibiotics was lower: azlocillin--33.3%, netilmycin--33.3%, piperacillin--26.6%, ceftriaxon--18.3%. Only small number of strains were inhibited by ciprofloxacin (8.3%), gentamycin (3.4%), cefoperazone (1.7%) and carbenicillin (1.7%). The results may be used for empiric therapy before the isolated strain susceptibility is tested but only according to positive esculin-hydrolysis express-test evaluated in 3-hours period.

Complement activation and liver impairment in trichloroethylene-sensitized BALB/c mice.

PubMed

Zhang, Jiaxiang; Zha, Wansheng; Wang, Feng; Jiang, Tao; Xu, Shuhai; Yu, Junfeng; Zhou, Chengfan; Shen, Tong; Wu, Changhao; Zhu, Qixing

2013-01-01

Our recent studies have shown that trichloroethylene (TCE) was able to induce multisystem injuries in the form of occupational medicamentosa-like dermatitis, including skin, kidney, and liver damages. However, the role of complement activation in the immune-mediated liver injury is not known. This study examined the role of complement activation in the liver injury in a mouse model of TCE-induced sensitization. Treatment of female BALB/c mice with TCE under specific dosing protocols resulted in skin inflammation and sensitization. Skin edema and erythema occurred in TCE-sensitized groups. Trichloroethylene sensitization produced liver histopathological lesions, increased serum alanine aminotransferase, aspartate transaminase activities, and the relative liver weight. The concentrations of serum complement components C3a-desArg, C5a-desArg, and C5b-9 were significantly increased in 24-hour, 48-hour, and 72-hour sensitization-positive groups treated with TCE and peaked in the 72-hour sensitization-positive group. Depositions of C3a, C5a, and C5b-9 into the liver tissue were also revealed by immunohistochemistry. Immunofluorescence further verified high C5b-9 expression in 24-hour, 48-hour, and 72-hour sensitization-positive groups in response to TCE treatment. Reverse transcription-polymerase chain reaction detected C3 messenger RNA expression in the liver, and this was significantly increased in 24-hour and 48-hour sensitization-positive groups with a transient reduction at 72 hours. These results provide the first experimental evidence that complement activation may play a key role in the generation and progression of immune-mediated hepatic injury by exposure to TCE.

Radio frequency switching network: a technique for infrared sensing

NASA Astrophysics Data System (ADS)

Mechtel, Deborah M.; Jenkins, R. Brian; Joyce, Peter J.; Nelson, Charles L.

2016-10-01

This paper describes a unique technique that implements photoconductive sensors in a radio frequency (RF) switching network designed to locate in real-time the position and intensity of IR radiation incident on a composite structure. In the implementation described here, photoconductive sensors act as rapid response switches in a two-layer RF network embedded in an FR-4 laminate. To detect radiation, phosphorous-doped silicon photoconductive sensors are inserted in GHz range RF transmission lines. By permitting signal propagation only when a sensor is illuminated, the RF signals are selectively routed from lower layer transmission lines to upper layer lines, thereby pinpointing the location and strength of incident radiation. Simulations based on a high frequency three-dimensional planar electromagnetics model are presented and compared to the experimental results. The experimental results are described for GHz range RF signal control for 300- and 180-mW incident energy from 975- to 1060-nm wavelength lasers, respectively, where upon illumination, RF transmission line signal output power doubled when compared to nonilluminated results. The experimental results are also reported for 100-W incident energy from a 1060-nm laser. Test results illustrate real-time signal processing would permit a structure to be controlled in response to incident radiation.

The relevance of memory sensitivity for psychological well-being in aging.

PubMed

Toffalini, Enrico; Borella, Erika; Cornoldi, Cesare; De Beni, Rossana

2016-08-01

In the present study, we investigated the relationship between memory sensitivity, which describes a positive attitude to autobiographical memory and the presence of behaviors devoted to saving memories of the personal past, and psychological well-being; in particular, we tested whether their relationship would change across age groups. Three hundred eighteen participants, divided in four groups: young to middle-aged adults (20-55 years old), young-old adults (65-74 years old), old adults (75-84 years old), and old-old adults (85-97 years old), completed questionnaires on their memory sensitivity and psychological well-being. Memory sensitivity slightly decreased with age and had a positive relationship with psychological well-being that was critically moderated by age. Specifically, the relationship between memory sensitivity and psychological well-being became increasingly stronger as age increased. While memory sensitivity may have little or no particular relevance in the case of young to middle-aged adults, it has an increasingly important positive relationship with psychological well-being at later age. It is thus suggested that memory sensitivity represents a dimension that should be considered in the study and interventions on quality of life in the elderly population.

Arrays of Position-Sensitive Virtual Frisch-Grid CdZnTe Detectors: Results From a $$4\\times 4$$ Array Prototype

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ocampo Giraldo, L. A.; Bolotnikov, A. E.; Camarda, G. S.

Position-sensitive virtual Frisch-grid (VFG) CdZnTe (CZT) detectors offer a unique capability for correcting the response nonuniformities caused by crystal defects. This allowed us to achieve high energy resolution, while using typical-grade commercial CZT crystals with relaxed requirements to their quality, thus reducing the overall cost of detectors. Another advantage of the VFG detectors is that they can be integrated into arrays and used in small compact hand-held instruments or large-area gamma cameras that will enhance detection capability for many practical applications, including nonproliferation, medical imaging, and gamma-ray astronomy. Here in this paper, we present the results from testing small arraymore » prototypes coupled with front-end application-specified integrated circuit. Each detector in the array is furnished with 5-mm-wide charge-sensing pads placed near the anode. The pads signals are converted into XY coordinates, which combined with the cathode signals (for Z coordinates) provide 3-D position information of all interaction points. The basic array consists of a number of detectors grouped into 2×2 subarrays, each having a common cathode made by connecting together the cathodes of the individual detectors. Lastly, these features can significantly improve the performance of detectors while using typical-grade low-cost CZT crystals to reduce the overall cost of the proposed instrument.« less

Arrays of Position-Sensitive Virtual Frisch-Grid CdZnTe Detectors: Results From a $$4\\times 4$$ Array Prototype

DOE PAGES

Ocampo Giraldo, L. A.; Bolotnikov, A. E.; Camarda, G. S.; ...

2017-08-22

Position-sensitive virtual Frisch-grid (VFG) CdZnTe (CZT) detectors offer a unique capability for correcting the response nonuniformities caused by crystal defects. This allowed us to achieve high energy resolution, while using typical-grade commercial CZT crystals with relaxed requirements to their quality, thus reducing the overall cost of detectors. Another advantage of the VFG detectors is that they can be integrated into arrays and used in small compact hand-held instruments or large-area gamma cameras that will enhance detection capability for many practical applications, including nonproliferation, medical imaging, and gamma-ray astronomy. Here in this paper, we present the results from testing small arraymore » prototypes coupled with front-end application-specified integrated circuit. Each detector in the array is furnished with 5-mm-wide charge-sensing pads placed near the anode. The pads signals are converted into XY coordinates, which combined with the cathode signals (for Z coordinates) provide 3-D position information of all interaction points. The basic array consists of a number of detectors grouped into 2×2 subarrays, each having a common cathode made by connecting together the cathodes of the individual detectors. Lastly, these features can significantly improve the performance of detectors while using typical-grade low-cost CZT crystals to reduce the overall cost of the proposed instrument.« less

Food intake is influenced by sensory sensitivity.

PubMed

Naish, Katherine R; Harris, Gillian

2012-01-01

Wide availability of highly palatable foods is often blamed for the rising incidence of obesity. As palatability is largely determined by the sensory properties of food, this study investigated how sensitivity to these properties affects how much we eat. Forty females were classified as either high or low in sensory sensitivity based on their scores on a self-report measure of sensory processing (the Adult Sensory Profile), and their intake of chocolate during the experiment was measured. Food intake was significantly higher for high-sensitivity compared to low-sensitivity individuals. Furthermore, individual scores of sensory sensitivity were positively correlated with self-reported emotional eating. These data could indicate that individuals who are more sensitive to the sensory properties of food have a heightened perception of palatability, which, in turn, leads to a greater food intake.

Electrochromic projection and writing device

DOEpatents

Branz, Howard M.; Benson, David K.

2002-01-01

A display and projection apparatus includes an electrochromic material and a photoconductive material deposited in tandem used in conjunction with a light filtering means for filtering light transmitted through the electrochromic material. When an electric field is applied across the electrochromic material and the photoconductive material, light that is incident onto the photoconductive material through the surface of the projection apparatus causes the photoconductive material to conduct current locally in proportion to the amount of light incident on the photoconductive material. The flow of current causes the underlying portions of the electrochromic material to switch from an opaque state to a clear or transmissive state, thereby allowing back-light to propagate through the electrochromic material to create a visible image on the surface of the projection apparatus. Reversal of the electric field causes the electrochromic material to revert back to its opaque state, thereby blocking the transmission of back-light and effectively erasing the image from the surface of the projection apparatus.

Race-based rejection sensitivity partially accounts for the relationship between racial discrimination and distressing attenuated positive psychotic symptoms.

PubMed

Anglin, Deidre M; Greenspoon, Michelle; Lighty, Quenesha; Ellman, Lauren M

2016-10-01

Self-reported experiences of racial discrimination have been associated with a continuum of psychotic experiences in racial and ethnic minority populations; however, the underlying mechanisms of this relationship are not yet clear. Race-based rejection sensitivity (RS-race) has been associated with thought intrusions about being the target of racial discrimination; therefore, the present study aimed to determine whether RS-race accounts for the relationship between racial discrimination and psychotic-like experiences in racial and ethnic minority populations. A sample of 644 young adults from a US urban, predominantly immigrant, and racial and ethnic minority population was administered a self-report inventory of psychosis risk (i.e. Prodromal Questionnaire (PQ) ), providing a dimensional assessment of the total number of attenuated positive psychotic symptoms experienced as distressing (APPS-distress). Participants also completed the Experiences of Discrimination Questionnaire and the Rejection Sensitivity Questionnaire-Race. Hierarchical linear regression analyses revealed that RS-race and racial discrimination were both significantly related to higher levels of APPS-distress. Bootstrapping analyses of indirect effects indicated that RS-race partially accounted for the relationship between racial discrimination and APPS-distress. Although the cross-sectional nature of the data limits conclusions about causal inference, our findings do suggest that racial discrimination and RS-race may both be important for understanding risk for distress in the psychotic spectrum among racial and ethnic minority young adults. Some individuals who report racial discrimination may be more vulnerable to APPS-distress in part because they are anxiously anticipating being racially slighted, and this should be explored further in prospective clinical high-risk studies. © 2014 Wiley Publishing Asia Pty Ltd.

Evaluation of the LightCycler Staphylococcus M GRADE kits on positive blood cultures that contained gram-positive cocci in clusters.

PubMed

Shrestha, Nabin K; Tuohy, Marion J; Padmanabhan, Ravindran A; Hall, Gerri S; Procop, Gary W

2005-12-01

We evaluated the Roche LightCycler Staphylococcus M(GRADE) kits to differentiate between Staphylococcus aureus and coagulase-negative staphylococci in blood cultures growing clusters of gram-positive cocci. Testing 100 bottles (36 containing S. aureus), the assay was 100% sensitive and 98.44% specific for S. aureus and 100% sensitive and specific for coagulase-negative staphylococci.

Perspectives on MEMS in bioengineering: a novel capacitive position microsensor.

PubMed

Pedrocchi, A; Hoen, S; Ferrigno, G; Pedotti, A

2000-01-01

We describe a novel capacitive position sensor using micromachining to achieve high sensitivity and large range of motion. These sensors require a new theoretical framework to describe and optimize their performance. Employing a complete description of the electrical fields, the sensor should deviate from the standard geometries used for capacitive sensors. By this optimization, the sensor gains a twofold increase in sensitivity. Results on a PC board 10x model imply that the micromachined sensor should achieve a sensitivity of less than 10 nm over 500-micron range of travel. Some bioengineering applications are addressed, including positioning of micromirrors for laser surgery and dose control for implantable drug delivery systems.

CDK4/6 Inhibitors Sensitize Rb-positive Sarcoma Cells to Wee1 Kinase Inhibition through Reversible Cell-Cycle Arrest.

PubMed

Francis, Ashleigh M; Alexander, Angela; Liu, Yanna; Vijayaraghavan, Smruthi; Low, Kwang Hui; Yang, Dong; Bui, Tuyen; Somaiah, Neeta; Ravi, Vinod; Keyomarsi, Khandan; Hunt, Kelly K

2017-09-01

Research into the biology of soft tissue sarcomas has uncovered very few effective treatment strategies that improve upon the current standard of care which usually involves surgery, radiation, and chemotherapy. Many patients with large (>5 cm), high-grade sarcomas develop recurrence, and at that point have limited treatment options available. One challenge is the heterogeneity of genetic drivers of sarcomas, and many of these are not validated targets. Even when such genes are tractable targets, the rarity of each subtype of sarcoma makes advances in research slow. Here we describe the development of a synergistic combination treatment strategy that may be applicable in both soft tissue sarcomas as well as sarcomas of bone that takes advantage of targeting the cell cycle. We show that Rb-positive cell lines treated with the CDK4/6 inhibitor palbociclib reversibly arrest in the G 1 phase of the cell cycle, and upon drug removal cells progress through the cell cycle as expected within 6-24 hours. Using a long-term high-throughput assay that allows us to examine drugs in different sequences or concurrently, we found that palbociclib-induced cell-cycle arrest poises Rb-positive sarcoma cells (SK-LMS1 and HT-1080) to be more sensitive to agents that work preferentially in S-G 2 phase such as doxorubicin and Wee1 kinase inhibitors (AZD1775). The synergy between palbociclib and AZD1775 was also validated in vivo using SK-LMS1 xenografts as well as Rb-positive patient-derived xenografts (PDX) developed from leiomyosarcoma patients. This work provides the necessary preclinical data in support of a clinical trial utilizing this treatment strategy. Mol Cancer Ther; 16(9); 1751-64. ©2017 AACR . ©2017 American Association for Cancer Research.

Asymmetric Zinc Phthalocyanines as Dye-Sensitized Solar Cells

NASA Astrophysics Data System (ADS)

Tunc, Gulenay; Yavuz, Yunus; Gurek, Aysegul; Canimkurbey, Betul; Kosemen, Arif; San, Sait Eren; Ahsen, Vefa

Dye-sensitized solar cells (DSSCs) have received increasing attention due to their high incident to photon efficiency, easy fabrication and low production cost . Tremendous research efforts have been devoted to the development of new and efficient sensitizers suitable for practical use. In TiO2-based DSSCs, efficiencies of up to 11.4% under simulated sunlight have been obtained with rutheniumepolypyridyl complexes. However, the main drawback of ruthenium complexes is the lack of absorption in the red region of the visible light and the high cost. For this reason, dyes with large and stable p-conjugated systems such as porphyrins and phthalocyanines are important classes of potential sensitizers for highly efficient DSSCs. Phthalocyanines (Pcs) have been widely used as sensitizers because of their improved light-harvesting properties in the far red- and near-IR spectral regions and their extraordinary robustness [1]. In this work, a series of asymmetric Zn(II) Pcs bearing a carboxylic acid group and six hexylthia groups either at the peripheral or non-peripheral positions have been designed and synthesized to investigate the influence of the COOH group and the positions of hexylthia groups on the dye-sensitized solar cell (DSSC) performance.

Sensitivity and Specificity of Histoplasma Antigen Detection by Enzyme Immunoassay.

PubMed

Cunningham, Lauren; Cook, Audrey; Hanzlicek, Andrew; Harkin, Kenneth; Wheat, Joseph; Goad, Carla; Kirsch, Emily

2015-01-01

The objective of this study was to evaluate the sensitivity and specificity of an antigen enzyme immunoassay (EIA) on urine samples for the diagnosis of histoplasmosis in dogs. This retrospective medical records review included canine cases with urine samples submitted for Histoplasma EIA antigen assay between 2007 and 2011 from three veterinary institutions. Cases for which urine samples were submitted for Histoplasma antigen testing were reviewed and compared to the gold standard of finding Histoplasma organisms or an alternative diagnosis on cytology or histopathology. Sensitivity, specificity, negative predictive value, positive predictive value, and the kappa coefficient and associated confidence interval were calculated for the EIA-based Histoplasma antigen assay. Sixty cases met the inclusion criteria. Seventeen cases were considered true positives based on identification of the organism, and 41 cases were considered true negatives with an alternative definitive diagnosis. Two cases were considered false negatives, and there were no false positives. Sensitivity was 89.47% and the negative predictive value was 95.35%. Specificity and the positive predictive value were both 100%. The kappa coefficient was 0.9207 (95% confidence interval, 0.8131-1). The Histoplasma antigen EIA test demonstrated high specificity and sensitivity for the diagnosis of histoplasmosis in dogs.

[Sensitivity and antibiotic resistance in infections of the musculoskeletal system].

PubMed

Mata-Hernández, Argenis; Rivera-Villa, Adrián Huematzin; Miguel-Pérez, Adrián; Pérez-Atanasio, José Manuel; Torres-González, Rubén

2016-01-01

Infections of the musculoskeletal system are a devastating complication for patients, due to it's long rehabilitation process and even sometimes the removal of the implant, the chronicity of infection, is often due to lack of coverage in empirical antibiotics. A retrospective, observational, descriptive cohort study was performed. All cultures form musculoskeletal system infected patients reported of sensitivity and resistance of germs isolated were analyzed. A total of 143 positive results were included. Reported more frequent germ Staphylococcus aureus accounted for 75 positive cases, followed by Escherichia coli with 31 positive results. Antibiotics with better sensitivity according to the type of microorganisms were trimethoprim-sulfamethoxazole and vancomycin, levofloxacin and linezolid, gentamicin, erythromycin and amikacin. Regarding antibiotic resistance, those reported with the highest percentage were penicillin G, amoxicillin with clavulanic acid and ampicillin. We recommend using empirical treatments in musculoskeletal system infections, trimethoprim-sulfamethoxazole are the best choice because they have the same sensitivity compare with vancomycin and a resistance rate of 7.6%. Betalactamics have a high percentage of resistance and low sensitivity so we must consider alternatives.

Numerical Simulation and Mechanical Design for TPS Electron Beam Position Monitors

NASA Astrophysics Data System (ADS)

Hsueh, H. P.; Kuan, C. K.; Ueng, T. S.; Hsiung, G. Y.; Chen, J. R.

2007-01-01

Comprehensive study on the mechanical design and numerical simulation for the high resolution electron beam position monitors are key steps to build the newly proposed 3rd generation synchrotron radiation research facility, Taiwan Photon Source (TPS). With more advanced electromagnetic simulation tool like MAFIA tailored specifically for particle accelerator, the design for the high resolution electron beam position monitors can be tested in such environment before they are experimentally tested. The design goal of our high resolution electron beam position monitors is to get the best resolution through sensitivity and signal optimization. The definitions and differences between resolution and sensitivity of electron beam position monitors will be explained. The design consideration is also explained. Prototype deign has been carried out and the related simulations were also carried out with MAFIA. The results are presented here. Sensitivity as high as 200 in x direction has been achieved in x direction at 500 MHz.

[An analysis of spectrum of allergen sensitization among patients with tree pollen allergy in Beijing].

PubMed

Wang, X Y; Ning, H Y; Chu, S M; Jiang, L; Pang, Y J; Jin, W T; Wang, S Q; Wang, X Y

2017-12-05

Objective: To explore the feature of allergic sensitization of tree pollen and the relationship between tree pollen and airborne pollen in Beijing. Method: Two thousand five hundred and twenty-one patients with allergic diseases were enrolled between January to July in 2017 in an allergy department. All patients received SPT of 8 kinds of tree pollen. Result: ①The overall tree pollen positive rate of SPT was 49.3% (1 244/2 521). Male had a higher positive rate than female (56.4% vs 45.0%, P <0.01) while child group had a higher positive rate than adult group (55.9% vs 48.6%, P <0.05). The poly sensitization was observed with a rate of 26.3%, take the percentage of 53.3% of the overall positive subjects. ②The highest sensitization rate was found in March (62.2%), followed by May (52.1%), the lowest was January (27.9%). There was a positive correlation between tree pollen sensitization rate and pollen count of each month ( r =0.929, P <0.01). ③Cypress had the highest positive rate (34.6%), followed by poplar (21.3%), the lowest was sophora (13.3%). The sensitization rate was positively correlated with pollen count among different tree pollen ( r =0.714, P <0.05). Conclusion: The main allergic pollen in Beijing was cypress. The tree pollen sensitization showed a seasonality with the peak in March. The sensitization status was tightly associated with the amount of airborne pollen. Copyright© by the Editorial Department of Journal of Clinical Otorhinolaryngology Head and Neck Surgery.

The sensitivity of direct identification from positive BacT/ALERT™ (bioMérieux) blood culture bottles by matrix-assisted laser desorption ionization time-of-flight mass spectrometry is low.

PubMed

Szabados, F; Michels, M; Kaase, M; Gatermann, S

2011-02-01

Recently, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been presented as a novel method for the direct identification of bacteria from positive blood culture bottles. The rate of the MALDI TOF MS-based identification in the present study from positive BacT/ALERT (bioMérieux, Marcy l'Etoile, France) blood culture bottles was 30%, which is far below the previously reported sensitivities using the BACTEC (Becton Dickinson, Franklin Lakes, NJ, USA) system. We also found evidence that the Biotyper algorithm did not identify a second pathogen in cases of positive BacT/ALERT blood culture bottles containing two different species. © 2010 The Authors. Journal Compilation © 2010 European Society of Clinical Microbiology and Infectious Diseases.

Large angle solid state position sensitive x-ray detector system

DOEpatents

Kurtz, D.S.; Ruud, C.O.

1998-03-03

A method and apparatus for x-ray measurement of certain properties of a solid material are disclosed. In distinction to known methods and apparatus, this invention employs a specific fiber-optic bundle configuration, termed a reorganizer, itself known for other uses, for coherently transmitting visible light originating from the scintillation of diffracted x-radiation from the solid material gathered along a substantially one dimensional linear arc, to a two-dimensional photo-sensor array. The two-dimensional photodetector array, with its many closely packed light sensitive pixels, is employed to process the information contained in the diffracted radiation and present the information in the form of a conventional x-ray diffraction spectrum. By this arrangement, the angular range of the combined detector faces may be increased without loss of angular resolution. Further, the prohibitively expensive coupling together of a large number of individual linear diode photodetectors, which would be required to process signals generated by the diffracted radiation, is avoided. 7 figs.

Large angle solid state position sensitive x-ray detector system

DOEpatents

Kurtz, David S.; Ruud, Clay O.

1998-01-01

A method and apparatus for x-ray measurement of certain properties of a solid material. In distinction to known methods and apparatus, this invention employs a specific fiber-optic bundle configuration, termed a reorganizer, itself known for other uses, for coherently transmitting visible light originating from the scintillation of diffracted x-radiation from the solid material gathered along a substantially one dimensional linear arc, to a two-dimensional photo-sensor array. The two-dimensional photodetector array, with its many closely packed light sensitive pixels, is employed to process the information contained in the diffracted radiation and present the information in the form of a conventional x-ray diffraction spectrum. By this arrangement, the angular range of the combined detector faces may be increased without loss of angular resolution. Further, the prohibitively expensive coupling together of a large number of individual linear diode photodetectors, which would be required to process signals generated by the diffracted radiation, is avoided.

Large angle solid state position sensitive x-ray detector system

DOEpatents

Kurtz, D.S.; Ruud, C.O.

1998-07-21

A method and apparatus are disclosed for x-ray measurement of certain properties of a solid material. In distinction to known methods and apparatus, this invention employs a specific fiber-optic bundle configuration, termed a reorganizer, itself known for other uses, for coherently transmitting visible light originating from the scintillation of diffracted x-radiation from the solid material gathered along a substantially one dimensional linear arc, to a two-dimensional photo-sensor array. The two-dimensional photodetector array, with its many closely packed light sensitive pixels, is employed to process the information contained in the diffracted radiation and present the information in the form of a conventional x-ray diffraction spectrum. By this arrangement, the angular range of the combined detector faces may be increased without loss of angular resolution. Further, the prohibitively expensive coupling together of a large number of individual linear diode photodetectors, which would be required to process signals generated by the diffracted radiation, is avoided. 7 figs.

[Tuberculin sensitivity in infants and preschool children].

PubMed

Guseva, E M; Efimova, E P; Stepankina, T T; Chernyshova, L V

2001-01-01

Marked fluctuations in sensitivity to tuberculin related to the time of nonspecific vaccinations were found in children aged 1 to 7 years vaccinated with BCG within the first week of life in annual Mantoux test (2 tuberculin units). At the age of 3 and 7 years vaccinations raise sensitivity to tuberculin causing a rise in positive reactions to tuberculin. This indicates changes in postvaccination allergy to BCG.

Sealed position sensitive hard X-ray detector having large drift region for all sky camera with high angular resolution

NASA Technical Reports Server (NTRS)

Gorenstein, P.; Perlman, D.; Parsignault, D.; Burns, R.

1979-01-01

A sealed position sensitive proportional counter filled with two atmospheres of 95% xenon and 5% methane, and containing a drift region of 24 atm cm, has operated in a stable manner for many months. The detector contains G-10 frames to support the anode and cathode wires. The detector was sealed successfully by a combination of vacuum baking the G-10 frames at 150 C for two weeks followed by assembly into the detector in an environment of dry nitrogen, and the use of passive internal getters. The counter is intended for use with a circumferential cylindrical collimator. Together they provide a very broad field of view detection system with the ability to locate cosmic hard X-ray and soft gamma ray sources to an angular precision of a minute of arc. A set of instruments based on this principle have been proposed for satellites to detect and precisely locate cosmic gamma ray bursts.

Maternal sensitivity: a concept analysis.

PubMed

Shin, Hyunjeong; Park, Young-Joo; Ryu, Hosihn; Seomun, Gyeong-Ae

2008-11-01

The aim of this paper is to report a concept analysis of maternal sensitivity. Maternal sensitivity is a broad concept encompassing a variety of interrelated affective and behavioural caregiving attributes. It is used interchangeably with the terms maternal responsiveness or maternal competency, with no consistency of use. There is a need to clarify the concept of maternal sensitivity for research and practice. A search was performed on the CINAHL and Ovid MEDLINE databases using 'maternal sensitivity', 'maternal responsiveness' and 'sensitive mothering' as key words. The searches yielded 54 records for the years 1981-2007. Rodgers' method of evolutionary concept analysis was used to analyse the material. Four critical attributes of maternal sensitivity were identified: (a) dynamic process involving maternal abilities; (b) reciprocal give-and-take with the infant; (c) contingency on the infant's behaviour and (d) quality of maternal behaviours. Maternal identity and infant's needs and cues are antecedents for these attributes. The consequences are infant's comfort, mother-infant attachment and infant development. In addition, three positive affecting factors (social support, maternal-foetal attachment and high self-esteem) and three negative affecting factors (maternal depression, maternal stress and maternal anxiety) were identified. A clear understanding of the concept of maternal sensitivity could be useful for developing ways to enhance maternal sensitivity and to maximize the developmental potential of infants. Knowledge of the attributes of maternal sensitivity identified in this concept analysis may be helpful for constructing measuring items or dimensions.

Relationships between psychological state, abuse, somatization and visceral pain sensitivity in irritable bowel syndrome

PubMed Central

Grinsvall, Cecilia; Törnblom, Hans; Tack, Jan; Van Oudenhove, Lukas; Simrén, Magnus

2018-01-01

Background and objective Psychological states may interfere with visceral sensitivity. Here we investigate associations between psychosocial factors and visceral sensitivity in irritable bowel syndrome (IBS). Methods Two IBS patient cohorts (Cohort 1: n = 231, Rome II; Cohort 2: n = 141, Rome III) underwent rectal barostat testing, and completed questionnaires for anxiety, depression, somatization, and abuse. The associations between questionnaire measures and visceral sensitivity parameters were analyzed in three-step general linear models (step1: demographic and abuse variables; step 2: anxiety and depression; step 3: somatization). Results Cohort 1. Pain threshold was positively associated with age and female gender, and negatively with adult sexual abuse and somatization. Pain referral area was negatively associated with age and positively with somatization and GI-specific anxiety, the latter effect mediated by somatization. Cohort 2. Pain threshold was positively associated with age and male gender, and negatively with adult sexual abuse. Pain intensity ratings were positively associated with somatization, female gender and depression, the latter effect mediated by somatization. Conclusion Somatization is associated with most visceral sensitivity parameters, and mediates the effect of some psychological factors on visceral sensitivity. It may reflect a psychobiological sensitization process driving symptom generation in IBS. In addition, abuse history was found to independently affect some visceral sensitivity parameters. PMID:29511560

Moiré deflectometry-based position detection for optical tweezers.

PubMed

Khorshad, Ali Akbar; Reihani, S Nader S; Tavassoly, Mohammad Taghi

2017-09-01

Optical tweezers have proven to be indispensable tools for pico-Newton range force spectroscopy. A quadrant photodiode (QPD) positioned at the back focal plane of an optical tweezers' condenser is commonly used for locating the trapped object. In this Letter, for the first time, to the best of our knowledge, we introduce a moiré pattern-based detection method for optical tweezers. We show, both theoretically and experimentally, that this detection method could provide considerably better position sensitivity compared to the commonly used detection systems. For instance, position sensitivity for a trapped 2.17 μm polystyrene bead is shown to be 71% better than the commonly used QPD-based detection method. Our theoretical and experimental results are in good agreement.

Determining the prevalence of inv-positive and ail-positive Yersinia enterocolitica in pig tonsils using PCR and culture methods.

PubMed

Stachelska, Milena Alicja

2017-01-01

Yersiniosis is believed to be the third most common intestinal zoonosis in the European Union, after campylobacteriosis and salmonellosis. Yersinia enterocolitica is the most common species responsible for human infections. Pigs are regarded as the biggest reservoir of pathogenic Y. enterocolitica strains, which are mainly isolated from pig tonsils. The aim of this paper is to examine the prevalence of inv-positive and ail-positive Y. enterocolitica in pigs which were slaughtered in a Polish abattoir. Real-time PCR and culture methods were used to assess the prevalence of patho- genic Y. enterocolitica strains in pig tonsils. Real-time PCR was applied to detect inv-positive and ail-positive Y. enterocolitica. Y. enterocolitica was also isolated by applying direct plating, unselective (tryptic soy broth) and selective (irgasan-ticarcillin-potassium chlorate bouillon) enrichment. A total of 180 pigs were studied, of which 85% and 32% respectively were found to be infected with inv-positive and ail-positive Y. enterocolitica. The 92 inv-positive and ail-positive isolates, from 57 culture- positive tonsils, underwent bio- and serotyping. The most common was bioserotype 4/O:3, which was found in 53 (93%) out of 57 culture-positive tonsils. Strains of bioserotypes 2/O:5, 2/O:9 and 2/O:5.27 occurred in significantly lower numbers. The prevalence of inv-positive and ail-positive Y. enterocolitica was found to be high in the ton- sils of slaughtered pigs, using real-time PCR. The real-time PCR method for the detection and identification of pathogenic Y. enterocolitica is sensitive and specific, which has been verified by specificity and sensitivity tests using the pure cultures. Serotypes were distinguished from each other using PCR serotyping. The PCR method was essential in forming our conclusions.

Spectrum and Sensitivity of Bacterial Keratitis Isolates in Auckland.

PubMed

Marasini, S; Swift, S; Dean, S J; Ormonde, S E; Craig, J P

2016-01-01

Background. The bacteria isolated from severe cases of keratitis and their antibiotic sensitivity are recognised to vary geographically and over time. Objectives. To identify the most commonly isolated bacteria in keratitis cases admitted over a 24-month period to a public hospital in Auckland, New Zealand, and to investigate in vitro sensitivity to antibiotics. Methods. Hospital admissions for culture-proven bacterial keratitis between January 2013 and December 2014 were identified. Laboratory records of 89 culture positive cases were retrospectively reviewed and antibiotic sensitivity patterns compared with previous studies from other NZ centres. Results. From 126 positive cultures, 35 species were identified. Staphylococcus was identified to be the most common isolate (38.2%), followed by Pseudomonas (21.3%). Over the last decade, infection due to Pseudomonas species, in the same setting, has increased (p ≤ 0.05). Aminoglycosides, cefazolin, ceftazidime, erythromycin, tetracycline, and doxycycline were 100% effective against tested isolates in vitro. Amoxicillin (41.6%), cefuroxime (33.3%), and chloramphenicol (94.7%) showed reduced efficacy against Gram-negative bacteria, whereas penicillin (51%) and ciprofloxacin (98.8%) showed reduced efficacy against Gram-positive bacteria. Conclusions. Despite a shift in the spectrum of bacterial keratitis isolates, antibiotic sensitivity patterns have generally remained stable and show comparability to results within the last decade from NZ centres.

Spectrum and Sensitivity of Bacterial Keratitis Isolates in Auckland

PubMed Central

Swift, S.; Dean, S. J.; Ormonde, S. E.

2016-01-01

Background. The bacteria isolated from severe cases of keratitis and their antibiotic sensitivity are recognised to vary geographically and over time. Objectives. To identify the most commonly isolated bacteria in keratitis cases admitted over a 24-month period to a public hospital in Auckland, New Zealand, and to investigate in vitro sensitivity to antibiotics. Methods. Hospital admissions for culture-proven bacterial keratitis between January 2013 and December 2014 were identified. Laboratory records of 89 culture positive cases were retrospectively reviewed and antibiotic sensitivity patterns compared with previous studies from other NZ centres. Results. From 126 positive cultures, 35 species were identified. Staphylococcus was identified to be the most common isolate (38.2%), followed by Pseudomonas (21.3%). Over the last decade, infection due to Pseudomonas species, in the same setting, has increased (p ≤ 0.05). Aminoglycosides, cefazolin, ceftazidime, erythromycin, tetracycline, and doxycycline were 100% effective against tested isolates in vitro. Amoxicillin (41.6%), cefuroxime (33.3%), and chloramphenicol (94.7%) showed reduced efficacy against Gram-negative bacteria, whereas penicillin (51%) and ciprofloxacin (98.8%) showed reduced efficacy against Gram-positive bacteria. Conclusions. Despite a shift in the spectrum of bacterial keratitis isolates, antibiotic sensitivity patterns have generally remained stable and show comparability to results within the last decade from NZ centres. PMID:27213052

Multiplex Identification of Gram-Positive Bacteria and Resistance Determinants Directly from Positive Blood Culture Broths: Evaluation of an Automated Microarray-Based Nucleic Acid Test

PubMed Central

Buchan, Blake W.; Ginocchio, Christine C.; Manii, Ryhana; Cavagnolo, Robert; Pancholi, Preeti; Swyers, Lettie; Thomson, Richard B.; Anderson, Christopher; Kaul, Karen; Ledeboer, Nathan A.

2013-01-01

Background A multicenter study was conducted to evaluate the diagnostic accuracy (sensitivity and specificity) of the Verigene Gram-Positive Blood Culture Test (BC-GP) test to identify 12 Gram-positive bacterial gene targets and three genetic resistance determinants directly from positive blood culture broths containing Gram-positive bacteria. Methods and Findings 1,252 blood cultures containing Gram-positive bacteria were prospectively collected and tested at five clinical centers between April, 2011 and January, 2012. An additional 387 contrived blood cultures containing uncommon targets (e.g., Listeria spp., S. lugdunensis, vanB-positive Enterococci) were included to fully evaluate the performance of the BC-GP test. Sensitivity and specificity for the 12 specific genus or species targets identified by the BC-GP test ranged from 92.6%–100% and 95.4%–100%, respectively. Identification of the mecA gene in 599 cultures containing S. aureus or S. epidermidis was 98.6% sensitive and 94.3% specific compared to cefoxitin disk method. Identification of the vanA gene in 81 cultures containing Enterococcus faecium or E. faecalis was 100% sensitive and specific. Approximately 7.5% (87/1,157) of single-organism cultures contained Gram-positive bacteria not present on the BC-GP test panel. In 95 cultures containing multiple organisms the BC-GP test was in 71.6% (68/95) agreement with culture results. Retrospective analysis of 107 separate blood cultures demonstrated that identification of methicillin resistant S. aureus and vancomycin resistant Enterococcus spp. was completed an average of 41.8 to 42.4 h earlier using the BC-GP test compared to routine culture methods. The BC-GP test was unable to assign mecA to a specific organism in cultures containing more than one Staphylococcus isolate and does not identify common blood culture contaminants such as Micrococcus, Corynebacterium, and Bacillus. Conclusions The BC-GP test is a multiplex test capable of detecting most

In vivo sensitivity estimation and imaging acceleration with rotating RF coil arrays at 7 Tesla.

PubMed

Li, Mingyan; Jin, Jin; Zuo, Zhentao; Liu, Feng; Trakic, Adnan; Weber, Ewald; Zhuo, Yan; Xue, Rong; Crozier, Stuart

2015-03-01

Using a new rotating SENSitivity Encoding (rotating-SENSE) algorithm, we have successfully demonstrated that the rotating radiofrequency coil array (RRFCA) was capable of achieving a significant reduction in scan time and a uniform image reconstruction for a homogeneous phantom at 7 Tesla. However, at 7 Tesla the in vivo sensitivity profiles (B1(-)) become distinct at various angular positions. Therefore, sensitivity maps at other angular positions cannot be obtained by numerically rotating the acquired ones. In this work, a novel sensitivity estimation method for the RRFCA was developed and validated with human brain imaging. This method employed a library database and registration techniques to estimate coil sensitivity at an arbitrary angular position. The estimated sensitivity maps were then compared to the acquired sensitivity maps. The results indicate that the proposed method is capable of accurately estimating both magnitude and phase of sensitivity at an arbitrary angular position, which enables us to employ the rotating-SENSE algorithm to accelerate acquisition and reconstruct image. Compared to a stationary coil array with the same number of coil elements, the RRFCA was able to reconstruct images with better quality at a high reduction factor. It is hoped that the proposed rotation-dependent sensitivity estimation algorithm and the acceleration ability of the RRFCA will be particularly useful for ultra high field MRI. Copyright © 2014 Elsevier Inc. All rights reserved.

In vivo sensitivity estimation and imaging acceleration with rotating RF coil arrays at 7 Tesla

NASA Astrophysics Data System (ADS)

Li, Mingyan; Jin, Jin; Zuo, Zhentao; Liu, Feng; Trakic, Adnan; Weber, Ewald; Zhuo, Yan; Xue, Rong; Crozier, Stuart

2015-03-01

Using a new rotating SENSitivity Encoding (rotating-SENSE) algorithm, we have successfully demonstrated that the rotating radiofrequency coil array (RRFCA) was capable of achieving a significant reduction in scan time and a uniform image reconstruction for a homogeneous phantom at 7 Tesla. However, at 7 Tesla the in vivo sensitivity profiles (B1-) become distinct at various angular positions. Therefore, sensitivity maps at other angular positions cannot be obtained by numerically rotating the acquired ones. In this work, a novel sensitivity estimation method for the RRFCA was developed and validated with human brain imaging. This method employed a library database and registration techniques to estimate coil sensitivity at an arbitrary angular position. The estimated sensitivity maps were then compared to the acquired sensitivity maps. The results indicate that the proposed method is capable of accurately estimating both magnitude and phase of sensitivity at an arbitrary angular position, which enables us to employ the rotating-SENSE algorithm to accelerate acquisition and reconstruct image. Compared to a stationary coil array with the same number of coil elements, the RRFCA was able to reconstruct images with better quality at a high reduction factor. It is hoped that the proposed rotation-dependent sensitivity estimation algorithm and the acceleration ability of the RRFCA will be particularly useful for ultra high field MRI.

Developmental Aspects of Reaction to Positive Inducements

ERIC Educational Resources Information Center

Lindskold, Svenn; And Others

1970-01-01

Probes children's behavioral sensitivity to variation in reward probability and magnitude (bribes) and suggests that preadolescent children do respond to promises of positive inducements for cooperation in a mixed-motive situation. (WY)

Coupling influence on the sensitivity of microfiber resonator sensors

NASA Astrophysics Data System (ADS)

Guo, Wei; Chen, Ye; Kou, Jun-long; Xu, Fei; Lu, Yan-qing

2011-12-01

By modifying the resonant condition of microfiber resonator sensors while taking the coupling effect into account, we theoretically investigate coupling influence on the resonant wavelength and sensitivity. Numerical calculation shows significant difference in resonant wavelength and sensitivity with different coupling strength. Tuning the coupling can shift the resonant position as far as several nanometers and change the sensitivity as large as 30 nm/RIU in an all-coupling microfiber coil resonator.

Attachment Insecurity Predicts Punishment Sensitivity in Anorexia Nervosa.

PubMed

Keating, Charlotte; Castle, David J; Newton, Richard; Huang, Chia; Rossell, Susan L

2016-10-01

Individuals with anorexia nervosa (AN) experience insecure attachment. We investigated whether insecure attachment is associated with punishment and reward sensitivity in women with AN. Women with AN (n = 24) and comparison women (n = 26) (CW) completed The Eating Disorder Examination Questionnaire, Depression Anxiety Stress Scale, The Attachment Style Questionnaire, and Sensitivity to Punishment/Sensitivity to Reward Questionnaire. Participants with AN returned higher ratings for insecure attachment (anxious and avoidant) experiences and greater sensitivity to punishment (p = 0.001) than CW. In AN, sensitivity to punishment was positively correlated with anxious attachment and negative emotionality but not eating disorder symptoms. Regression analysis revealed that anxious attachment independently predicted punishment sensitivity in AN. Anxious attachment experiences are related to punishment sensitivity in AN, independent of negative emotionality and eating disorder symptoms. Results support ongoing investigation of the contribution of attachment experiences in treatment and recovery.

Scanning Probe Microscopy of Organic Solar Cells

NASA Astrophysics Data System (ADS)

Reid, Obadiah G.

Nanostructured composites of organic semiconductors are a promising class of materials for the manufacture of low-cost solar cells. Understanding how the nanoscale morphology of these materials affects their efficiency as solar energy harvesters is crucial to their eventual potential for large-scale deployment for primary power generation. In this thesis we describe the use of optoelectronic scanning-probe based microscopy methods to study this efficiency-structure relationship with nanoscale resolution. In particular, our objective is to make spatially resolved measurements of each step in the power conversion process from photons to an electric current, including charge generation, transport, and recombination processes, and correlate them with local device structure. We have achieved two aims in this work: first, to develop and apply novel electrically sensitive scanning probe microscopy experiments to study the optoelectronic materials and processes discussed above; and second, to deepen our understanding of the physics underpinning our experimental techniques. In the first case, we have applied conductive-, and photoconductive atomic force (cAFM & pcAFM) microscopy to measure both local photocurrent collection and dark charge transport properties in a variety of model and novel organic solar cell composites, including polymer/fullerene blends, and polymer-nanowire/fullerene blends, finding that local heterogeneity is the rule, and that improvements in the uniformity of specific beneficial nanostructures could lead to large increases in efficiency. We have used scanning Kelvin probe microscopy (SKPM) and time resolved-electrostatic force microscopy (trEFM) to characterize all-polymer blends, quantifying their sensitivity to photochemical degradation and the subsequent formation of local charge traps. We find that while trEFM provides a sensitive measure of local quantum efficiency, SKPM is generally unsuited to measurements of efficiency, less sensitive than tr

The Use of a Contract to Facilitate Sensitivity Training.

ERIC Educational Resources Information Center

Drennen, Will; Pugh, Marta

1979-01-01

This study assessed Egan's hypothesis that a contract, spelling out in advance sensitivity group goals and member behaviors, facilitates positive interaction and interpersonal growth. Although results were not definitive, the contract group did seem to receive some additional benefits from sensitivity training, when compared to the non-contract…

Nano-biosensor for highly sensitive detection of HER2 positive breast cancer.

PubMed

Salahandish, Razieh; Ghaffarinejad, Ali; Naghib, Seyed Morteza; Majidzadeh-A, Keivan; Zargartalebi, Hossein; Sanati-Nezhad, Amir

2018-05-25

Nanocomposite materials have provided a wide range of conductivity, sensitivity, selectivity and linear response for electrochemical biosensors. However, the detection of rare cells at single cell level requires a new class of nanocomposite-coated electrodes with exceptional sensitivity and specificity. We recently developed a construct of gold nanoparticle-grafted functionalized graphene and nanostructured polyaniline (PANI) for high-performance biosensing within a very wide linear response and selective performance. Further, replacing the expensive gold nanoparticles with low-cost silver nanoparticles as well as optimizing the nanocomposite synthesis and functionalization protocols on the electrode surface in this work enabled us to develop ultrasensitive nanocomposites for label-free detection of breast cancer cells. The sensor presented a fast response time of 30 min within a dynamic range of 10 - 5 × 10 6 cells mL -1 and with a detection limit of 2 cells mL -1 for the detection of SK-BR3 breast cancer cell. The nano-biosensor, for the first time, demonstrated a high efficiency of > 90% for the label-free detection of cancer cells in whole blood sample without any need for sample preparation and cell staining. The results demonstrated that the optimized nanocomposite developed in this work is a promising nanomaterial for electrochemical biosensing and with the potential applications in electro-catalysis and super-capacitances. Copyright © 2018 Elsevier B.V. All rights reserved.

The sensitivity of the QuantiFERON®-TB Gold Plus assay in Zambian adults with active tuberculosis.

PubMed

Telisinghe, L; Amofa-Sekyi, M; Maluzi, K; Kaluba-Milimo, D; Cheeba-Lengwe, M; Chiwele, K; Kosloff, B; Floyd, S; Bailey, S-L; Ayles, H

2017-06-01

To investigate the sensitivity of the new interferon-gamma release assay (IGRA), QuantiFERON®-TB Gold Plus (QFT-Plus), for active TB (used as a surrogate for latent tuberculous infection) in a Zambian TB clinic. Consecutive smear or Xpert® MTB/RIF-positive adult (age 18 years) pulmonary TB patients were recruited between June 2015 and March 2016. Venous blood was tested using QFT-Plus. The sensitivity was defined as the number positive divided by the total number tested. Using logistic regression, factors associated with positive QFT-Plus results were explored. Of 108 patients (median age 32 years, interquartile range 27-38; 73% male; 63% human immunodeficiency virus [HIV] positive), 90 were QFT-Plus-positive, 11 were negative and seven had indeterminate results; sensitivity was 83% (95%CI 75-90). There was no difference in sensitivity by HIV status (HIV-positive 85%, 95%CI 75-93; n = 68 vs. HIV-negative 80%, 95%CI 64-91; n = 40; P = 0.59). In models adjusted for age alone, CD4 cell count <100 cells/μl (OR 0.15, 95%CI 0.02-0.96; P = 0.05) and body mass index <18.5 kg/m2 (OR 0.27, 95%CI 0.08-0.91; P = 0.02) were associated with decreased odds of positive QFT-Plus results. Overall, the sensitivity of QFT-Plus is similar to that of the tuberculin skin test and other IGRAs. While overall sensitivity is not affected by HIV status, QFT-Plus sensitivity was lower among people living with HIV/acquired immune-deficiency syndrome with severe immunosuppression.

Body position-dependent shift in odor percept present only for perithreshold odors.

PubMed

Lundström, Johan N; Boyle, Julie A; Jones-Gotman, Marilyn

2008-01-01

We recently demonstrated that a supine position causes a decrease in olfactory sensitivity compared with an upright position. We pursued that initial finding in 3 separate experiments in which we explored the extent of, and mechanism underlying, this phenomenon. In Experiment 1, we replicated the decrease in olfactory sensitivity when in a supine compared with an upright position. In Experiment 2, we measured body position-dependent shifts in physiological variables and sniff measures while smelling suprathreshold odorants and performing a perithreshold odor intensity discrimination task. Olfactory performances were reduced while supine. However, no relationships between the shift in olfactory performances and either the physiological variables or sniff measures were found. In Experiment 3, we determined that there were no position-dependent shifts in ability to discriminate or identify suprathreshold odors or rate them for pleasantness, intensity, or familiarity. However, a drop in scores was observed, and performance was slowed, on a cognitive skill while supine. These results demonstrate a body position-dependent shift in olfactory sensitivity only for perithreshold odors that appears to be mediated by cognitive rather than physiological factors. Implications for olfactory imaging studies are discussed.

Inductance position sensor for pneumatic cylinder

NASA Astrophysics Data System (ADS)

Ripka, Pavel; Chirtsov, Andrey; Mirzaei, Mehran; Vyhnanek, Jan

2018-04-01

The position of the piston in pneumatic cylinder with aluminum wall can be measured by external inductance sensor without modifications of the aluminum piston and massive iron piston rod. For frequencies below 20 Hz the inductance is increasing with inserting rod due to the rod permeability. This mode has disadvantage of slow response to piston movement and also high temperature sensitivity. At the frequency of 45 Hz the inductance is position independent, as the permeability effect is compensated by the eddy current effect. At higher frequencies eddy current effects in the rod prevail, the inductance is decreasing with inserting rod. In this mode the sensitivity is smaller but the sensor response is fast and temperature stability is better. We show that FEM simulation of this sensor using measured material properties gives accurate results, which is important for the sensor optimization such as designing the winding geometry for the best linearity.

Sensitivity of mouse bioassay in clinical wound botulism.

PubMed

Wheeler, Charlotte; Inami, Gregory; Mohle-Boetani, Janet; Vugia, Duc

2009-06-15

California has an ongoing epidemic of wound botulism (WB) among injection drug users (IDUs). We retrospectively studied a cohort of patients with WB and determined the sensitivity of the mouse bioassay-the gold standard laboratory test for confirmation of botulism-in verifying WB. We defined a clinical case of WB as an acute, bilateral, descending, flaccid paralysis starting with 1 cranial nerve palsies in an IDU with no other explainable diagnosis. We calculated the sensitivity of the mouse bioassay as the proportion of clinical WB cases that had positive serum toxin test results by mouse bioassay. We compared serum toxin-positive with serum toxin-negative patients. Of 73 patients with WB, 50 tested serum toxin positive, yielding a sensitivity of 68%. Serum toxin-positive patients did not differ significantly from serum toxin-negative patients with respect to demographic characteristics or injection drug use practices or in days from patient symptom onset to collection of specimens for testing. Patients did not differ significantly by clinical characteristics, except that serum toxin-positive patients were more likely than serum toxin-negative patients to have required mechanical ventilation during their hospital courses (74% vs. 43%; P = .01). In this study, the mouse bioassay failed to detect botulinum toxin in the serum samples of nearly one-third of IDUs with characteristic WB. Such patients should be considered to have probable WB. Physicians should be aware of the test's limitations and base their final diagnosis of suspected WB on clinical criteria when the mouse bioassay produces negative results.

Design and Performance of a 1 mm3 Resolution Clinical PET System Comprising 3-D Position Sensitive Scintillation Detectors.

PubMed

Hsu, David F C; Freese, David L; Reynolds, Paul D; Innes, Derek R; Levin, Craig S

2018-04-01

We are developing a 1-mm 3 resolution, high-sensitivity positron emission tomography (PET) system for loco-regional cancer imaging. The completed system will comprise two cm detector panels and contain 4 608 position sensitive avalanche photodiodes (PSAPDs) coupled to arrays of mm 3 LYSO crystal elements for a total of 294 912 crystal elements. For the first time, this paper summarizes the design and reports the performance of a significant portion of the final clinical PET system, comprising 1 536 PSAPDs, 98 304 crystal elements, and an active field-of-view (FOV) of cm. The sub-system performance parameters, such as energy, time, and spatial resolutions are predictive of the performance of the final system due to the modular design. Analysis of the multiplexed crystal flood histograms shows 84% of the crystal elements have>99% crystal identification accuracy. The 511 keV photopeak energy resolution was 11.34±0.06% full-width half maximum (FWHM), and coincidence timing resolution was 13.92 ± 0.01 ns FWHM at 511 keV. The spatial resolution was measured using maximum likelihood expectation maximization reconstruction of a grid of point sources suspended in warm background. The averaged resolution over the central 6 cm of the FOV is 1.01 ± 0.13 mm in the X-direction, 1.84 ± 0.20 mm in the Y-direction, and 0.84 ± 0.11 mm in the Z-direction. Quantitative analysis of acquired micro-Derenzo phantom images shows better than 1.2 mm resolution at the center of the FOV, with subsequent resolution degradation in the y-direction toward the edge of the FOV caused by limited angle tomography effects.

Amoxicillin rash in patients with infectious mononucleosis: evidence of true drug sensitization.

PubMed

Ónodi-Nagy, Katinka; Kinyó, Ágnes; Meszes, Angéla; Garaczi, Edina; Kemény, Lajos; Bata-Csörgő, Zsuzsanna

2015-01-01

It hasn't been clearly understood yet whether sensitization to antibiotics, the virus itself or transient loss of drug tolerance due to the virus, is responsible for the development of maculopapular exanthems following amoxicillin intake in patients with infectious mononucleosis. We aimed to examine whether sensitization to penicillin developed among patients with skin rash following amoxicillin treatment within infectious mononucleosis. Ten patients were investigated for drug sensitization by lymphocyte transformation test and six patients were further tested by prick-, intradermal and patch tests employing the penicillin's main antigens. Lymphocyte transformation test showed negative results with amoxicillin, while one patient had positive reaction to cefixime. Six patients with suspected sensitization to amoxicillin were then investigated by in vivo tests. Prick tests were negative in all six patients, but the intradermal tests showed positive reactions in four patients. Our data demonstrate that in vitro testing is not sensitive enough in determining drug sensitization to penicillin. In vivo tests should be performed to detect sensitization and indeed with skin tests our results confirmed that sensitization to aminopenicillin may develop within infectious mononucleosis.

Positive Maladjustment as a Transition from Chaos to Order

ERIC Educational Resources Information Center

Laycraft, Krystyna

2009-01-01

Dabrowski's theory of positive disintegration describes patterns and explains mechanisms of human development and has been successfully applied to understanding of gifted individuals. This article shows how the concepts of chaos theory and self-organization such as the sensitivity to initial conditions, positive and negative feedback, bifurcation…

New Ultra-High Sensitivity, Absolute, Linear, and Rotary Encoders

NASA Technical Reports Server (NTRS)

Leviton, Douglas B.

1998-01-01

Several new types of absolute optical encoders of both rotary and linear function are discussed. The means for encoding are complete departures from conventional optical encoders and offer advantages of compact form, immunity to damage-induced dropouts of position information, and about an order of magnitude higher sensitivity over what is commercially available. Rotary versions have sensitivity from 0.02 arcseconds down to 0.003 arcsecond while linear models have sensitivity of 10 nm.

Differences in sensitivity to parenting depending on child temperament: A meta-analysis.

PubMed

Slagt, Meike; Dubas, Judith Semon; Deković, Maja; van Aken, Marcel A G

2016-10-01

Several models of individual differences in environmental sensitivity postulate increased sensitivity of some individuals to either stressful (diathesis-stress), supportive (vantage sensitivity), or both environments (differential susceptibility). In this meta-analysis we examine whether children vary in sensitivity to parenting depending on their temperament, and if so, which model can best be used to describe this sensitivity pattern. We tested whether associations between negative parenting and negative or positive child adjustment as well as between positive parenting and positive or negative child adjustment would be stronger among children higher on putative sensitivity markers (difficult temperament, negative emotionality, surgency, and effortful control). Longitudinal studies with children up to 18 years (k = 105 samples from 84 studies, Nmean = 6,153) that reported on a parenting-by-temperament interaction predicting child adjustment were included. We found 235 independent effect sizes for associations between parenting and child adjustment. Results showed that children with a more difficult temperament (compared with those with a more easy temperament) were more vulnerable to negative parenting, but also profited more from positive parenting, supporting the differential susceptibility model. Differences in susceptibility were expressed in externalizing and internalizing problems and in social and cognitive competence. Support for differential susceptibility for negative emotionality was, however, only present when this trait was assessed during infancy. Surgency and effortful control did not consistently moderate associations between parenting and child adjustment, providing little support for differential susceptibility, diathesis-stress, or vantage sensitivity models. Finally, parenting-by-temperament interactions were more pronounced when parenting was assessed using observations compared to questionnaires. (PsycINFO Database Record (c) 2016 APA, all

Reinforcement Sensitivity and Social Anxiety in Combat Veterans

PubMed Central

Kimbrel, Nathan A.; Meyer, Eric C.; DeBeer, Bryann B.; Mitchell, John T.; Kimbrel, Azure D.; Nelson-Gray, Rosemery O.; Morissette, Sandra B.

2017-01-01

Objective The present study tested the hypothesis that low behavioral approach system (BAS) sensitivity is associated with social anxiety in combat veterans. Method Self-report measures of reinforcement sensitivity, combat exposure, social interaction anxiety, and social observation anxiety were administered to 197 Iraq/Afghanistan combat veterans. Results As expected, combat exposure, behavioral inhibition system (BIS) sensitivity, and fight-flight-freeze system (FFFS) sensitivity were positively associated with both social interaction anxiety and social observation anxiety. In contrast, BAS sensitivity was negatively associated with social interaction anxiety only. An analysis of the BAS subscales revealed that the Reward Responsiveness subscale was the only BAS subscale associated with social interaction anxiety. BAS-Reward Responsiveness was also associated with social observation anxiety. Conclusion The findings from the present research provide further evidence that low BAS sensitivity may be associated with social anxiety over and above the effects of BIS and FFFS sensitivity. PMID:28966424

Reinforcement Sensitivity and Social Anxiety in Combat Veterans.

PubMed

Kimbrel, Nathan A; Meyer, Eric C; DeBeer, Bryann B; Mitchell, John T; Kimbrel, Azure D; Nelson-Gray, Rosemery O; Morissette, Sandra B

2016-08-01

The present study tested the hypothesis that low behavioral approach system (BAS) sensitivity is associated with social anxiety in combat veterans. Self-report measures of reinforcement sensitivity, combat exposure, social interaction anxiety, and social observation anxiety were administered to 197 Iraq/Afghanistan combat veterans. As expected, combat exposure, behavioral inhibition system (BIS) sensitivity, and fight-flight-freeze system (FFFS) sensitivity were positively associated with both social interaction anxiety and social observation anxiety. In contrast, BAS sensitivity was negatively associated with social interaction anxiety only. An analysis of the BAS subscales revealed that the Reward Responsiveness subscale was the only BAS subscale associated with social interaction anxiety. BAS-Reward Responsiveness was also associated with social observation anxiety. The findings from the present research provide further evidence that low BAS sensitivity may be associated with social anxiety over and above the effects of BIS and FFFS sensitivity.

High-sensitivity detection of breast tumors in vivo by use of a pH-sensitive near-infrared fluorescence probe

NASA Astrophysics Data System (ADS)

Mathejczyk, Julia Eva; Pauli, Jutta; Dullin, Christian; Resch-Genger, Ute; Alves, Frauke; Napp, Joanna

2012-07-01

We investigated the potential of the pH-sensitive dye, CypHer5E, conjugated to Herceptin (pH-Her) for the sensitive detection of breast tumors in mice using noninvasive time-domain near-infrared fluorescence imaging and different methods of data analysis. First, the fluorescence properties of pH-Her were analyzed as function of pH and/or dye-to-protein ratio, and binding specificity was confirmed in cell-based assays. Subsequently, the performance of pH-Her in nude mice bearing orthotopic HER2-positive (KPL-4) and HER2-negative (MDA-MB-231) breast carcinoma xenografts was compared to that of an always-on fluorescent conjugate Alexa Fluor 647-Herceptin (Alexa-Her). Subtraction of autofluorescence and lifetime (LT)-gated image analyses were performed for background fluorescence suppression. In mice bearing HER2-positive tumors, autofluorescence subtraction together with the selective fluorescence enhancement of pH-Her solely in the tumor's acidic environment provided high contrast-to-noise ratios (CNRs). This led to an improved sensitivity of tumor detection compared to Alexa-Her. In contrast, LT-gated imaging using LTs determined in model systems did not improve tumor-detection sensitivity in vivo for either probe. In conclusion, pH-Her is suitable for sensitive in vivo monitoring of HER2-expressing breast tumors with imaging in the intensity domain and represents a promising tool for detection of weak fluorescent signals deriving from small tumors or metastases.

Negative urgency and reward/punishment sensitivity in intermittent explosive disorder.

PubMed

Puhalla, Alexander A; Ammerman, Brooke A; Uyeji, Lauren L; Berman, Mitchell E; McCloskey, Michael S

2016-09-01

Intermittent explosive disorder (IED) is the sole psychiatric diagnosis in which affective aggression is the cardinal symptom. Previous research has been equivocal with regard to the relationship between IED and impulsivity. This inconsistency may reflect the varied facets of impulsivity, with some aspects of impulsivity (e.g. negative urgency) as well as some overlapping, albeit distinct constructs (e.g. reward and punishment sensitivity) yet to be studied. The present study compared individuals diagnosed with IED (n=81) with psychiatric controls (PCs; n=52) and healthy volunteers (HVs; n=58) on the impulsivity domains of negative and positive urgency, perseverance, sensation seeking, and premeditation, as well as on reward and punishment sensitivity. We hypothesized that individuals with IED would show greater negative and positive urgency, reward sensitivity, punishment sensitivity, with negative urgency independently predicting IED status. We also hypothesized that negative urgency would predict levels of anger, aggression, and aggression control among those with IED. The IED participants reported greater negative urgency than both comparison groups, and greater levels of positive urgency, reward sensitivity, and punishment sensitivity compared to HVs. Further, heightened negative urgency was the sole predictor an IED diagnosis. Within the IED group negative urgency uniquely predicted decreased aggression control and increased trait anger. Limitations included reliance on self-report measures to assess RS/PS, impulsivity, and aggression. These findings suggest that negative urgency is a key factor associated with IED and is associated with dampened control of aggression within those with IED. Copyright © 2016 Elsevier B.V. All rights reserved.

Thermal Neutron Imaging Using A New Pad-Based Position Sensitive Neutron Detector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dioszegi I.; Vanier P.E.; Salwen C.

2016-10-29

Thermal neutrons (with mean energy of 25 meV) have a scattering mean free path of about 20 m in air. Therefore it is feasible to find localized thermal neutron sources up to ~30 m standoff distance using thermal neutron imaging. Coded aperture thermal neutron imaging was developed in our laboratory in the nineties, using He-3 filled wire chambers. Recently a new generation of coded-aperture neutron imagers has been developed. In the new design the ionization chamber has anode and cathode planes, where the anode is composed of an array of individual pads. The charge is collected on each of themore » individual 5x5 mm2 anode pads, (48x48 in total, corresponding to 24x24 cm2 sensitive area) and read out by application specific integrated circuits (ASICs). The high sensitivity of the ASICs allows unity gain operation mode. The new design has several advantages for field deployable imaging applications, compared to the previous generation of wire-grid based neutron detectors. Among these are the rugged design, lighter weight and use of non-flammable stopping gas. For standoff localization of thermalized neutron sources a low resolution (11x11 pixel) coded aperture mask has been fabricated. Using the new larger area detector and the coarse resolution mask we performed several standoff experiments using moderated californium and plutonium sources at Idaho National Laboratory. In this paper we will report on the development and performance of the new pad-based neutron camera, and present long range coded-aperture images of various thermalized neutron sources.« less

Sensory Processing Sensitivity: Factors of the Highly Sensitive Person Scale and Their relationships to Personality and Subjective Health Complaints.

PubMed

Listou Grimen, Hanne; Diseth, Åge

2016-12-01

The aim of the present study was to examine the factor structure of a Norwegian version of the Highly Sensitive Person Scale (HSPS) and to investigate how sensory processing sensitivity (SPS) is related to personality traits of neuroticism, extraversion, and openness and to subjective health complaints (SHC) in a sample of 167 undergraduate psychology students. The results showed that the variance in a shortened version of the HSPS was best described by three separate factors: ease of excitation (EOE), aesthetic sensitivity (AES), and low sensory threshold (LST). Furthermore, the result showed than an overall SPS factor (EOE, LST, and AES combined) was predicted positively by neuroticism and openness and negatively by extraversion. With respect to SHC, the results showed that EOE and LST were positively associated with psychological health complaints. However, the personality trait of neuroticism contributed more than the SPS factors as predictor of SHC. In conclusion, the present study supported a shortened version of the HSPS and its relation to personality factors and SHC. © The Author(s) 2016.

The sensitivity of the QuantiFERON®-TB Gold Plus assay in Zambian adults with active tuberculosis

PubMed Central

Amofa-Sekyi, M.; Maluzi, K.; Kaluba-Milimo, D.; Cheeba-Lengwe, M.; Chiwele, K.; Kosloff, B.; Floyd, S.; Bailey, S-L.; Ayles, H.

2017-01-01

SUMMARY SETTING AND OBJECTIVE: To investigate the sensitivity of the new interferon-gamma release assay (IGRA), QuantiFERON®-TB Gold Plus (QFT-Plus), for active TB (used as a surrogate for latent tuberculous infection) in a Zambian TB clinic. DESIGN: Consecutive smear or Xpert® MTB/RIF-positive adult (age ⩾18 years) pulmonary TB patients were recruited between June 2015 and March 2016. Venous blood was tested using QFT-Plus. The sensitivity was defined as the number positive divided by the total number tested. Using logistic regression, factors associated with positive QFT-Plus results were explored. RESULTS: Of 108 patients (median age 32 years, interquartile range 27–38; 73% male; 63% human immunodeficiency virus [HIV] positive), 90 were QFT-Plus-positive, 11 were negative and seven had indeterminate results; sensitivity was 83% (95%CI 75–90). There was no difference in sensitivity by HIV status (HIV-positive 85%, 95%CI 75–93; n = 68 vs. HIV-negative 80%, 95%CI 64–91; n = 40; P = 0.59). In models adjusted for age alone, CD4 cell count <100 cells/μl (OR 0.15, 95%CI 0.02–0.96; P=0.05) and body mass index <18.5 kg/m2 (OR 0.27, 95%CI 0.08–0.91; P = 0.02) were associated with decreased odds of positive QFT-Plus results. CONCLUSION: Overall, the sensitivity of QFT-Plus is similar to that of the tuberculin skin test and other IGRAs. While overall sensitivity is not affected by HIV status, QFT-Plus sensitivity was lower among people living with HIV/acquired immune-deficiency syndrome with severe immunosuppression. PMID:28482964

Comparisons of LET distributions measured in low-earth orbit using tissue-equivalent proportional counters and the position-sensitive silicon-detector telescope (RRMD-III)

NASA Technical Reports Server (NTRS)

Doke, T.; Hayashi, T.; Borak, T. B.; Chatterjee, A. (Principal Investigator)

2001-01-01

Determinations of the LET distribution, phi(L), of charged particles within a spacecraft in low-Earth orbit have been made. One method used a cylindrical tissue-equivalent proportional counter (TEPC), with the assumption that for each measured event, lineal energy, y, is equal to LET and thus phi(L) = phi(y). The other was based on the direct measurement of LETs for individual particles using a charged-particle telescope consisting of position-sensitive silicon detectors called RRMD-III. There were differences of up to a factor of 10 between estimates of phi(L) using the two methods on the same mission. This caused estimates of quality factor to vary by a factor of two between the two methods.

Reinforcement Sensitivity Underlying Treatment-Seeking Smokers’ Affect, Smoking Reinforcement Motives, and Affective Responses

PubMed Central

Cui, Yong; Robinson, Jason D.; Engelmann, Jeffrey M.; Lam, Cho Y.; Minnix, Jennifer A.; Karam-Hage, Maher; Wetter, David W.; Dani, John A.; Kosten, Thomas R.; Cinciripini, Paul M.

2014-01-01

Nicotine dependence has been suggested to be related to reinforcement sensitivity, which encompasses behavioral predispositions either to avoid aversive (behavioral inhibition) or to approach appetitive (behavioral activation) stimuli. Reinforcement sensitivity may shape motives for nicotine use and offer potential targets for personalized smoking cessation therapy. However, little is known regarding how reinforcement sensitivity is related to motivational processes implicated in the maintenance of smoking. Additionally, women and men differ in reinforcement sensitivity, and such difference may cause distinct relationships between reinforcement sensitivity and motivational processes for female and male smokers. In this study, we characterized reinforcement sensitivity in relation to affect, smoking-related reinforcement motives, and affective responses, using self-report and psychophysiological measures, in over 200 smokers before treating them. The Behavioral Inhibition/Activation Scales (BIS/BAS; Carver & White, 1994) was used to measure reinforcement sensitivity. In female and male smokers, BIS was similarly associated with negative affect and negative reinforcement of smoking. But positive affect was positively associated with BAS Drive scores in male smokers, and this association was reversed in female smokers. BIS was positively associated with corrugator electromyographic reactivity towards negative stimuli and left frontal electroencephalogram alpha asymmetry. Female and male smokers showed similar relationships for these physiological measures. These findings suggest that reinforcement sensitivity underpins important motivational processes (e.g., affect), and gender is a moderating factor for these relationships. Future personalized smoking intervention, particularly among more dependent treatment-seeking smokers, may experiment to target individual differences in reinforcement sensitivity. PMID:25621416

Molecular engineering of cyanine dyes to design a panchromatic response in Co-sensitized dye-sensitized solar cells

DOE PAGES

Pepe, Giulio; Cole, Jacqueline M.; Waddell, Paul G.; ...

2016-04-05

Cyanines are optically tunable dyes with high molar extinction coefficients, suitable for applications in co-sensitized dye-sensitized solar cells (DSCs); yet, barely thus applied. This might be due to the lack of a rational molecular design strategy that efficiently exploits cyanine properties. This study computationally re-designs these dyes, to broaden their optical absorption spectrum and create dye···TiO 2 binding and co-sensitization functionality. This is achieved via a stepwise molecular engineering approach. Firstly, the structural and optical properties of four parent dyes are experimentally and computationally investigated: 3,3’-diethyloxacarbocyanine iodide, 3,3’-diethylthiacarbocyanine iodide, 3,3’-diethylthiadicarbocyanine iodide and 3,3’-diethylthiatricarbocyanine iodide. Secondly, the molecules are theoretically modifiedmore » and their energetics are analyzed and compared to the parent dyes. A dye···TiO 2 anchoring group (carboxylic or cyanoacrylic acid), absent from the parent dyes, is chemically substituted at different molecular positions to investigate changes in optical absorption. We find that cyanoacrylic acid substitution at the para-quinoidal position affects the absorption wavelength of all parent dyes, with an optimal bathochromic shift of ca. 40 nm. The theoretical lengthening of the polymethine chain is also shown to effect dye absorption. Two molecularly engineered dyes are proposed as promising co-sensitizers. Finally, corresponding dye···TiO 2 adsorption energy calculations corroborate their applicability, demonstrating the potential of cyanine dyes in DSC research.« less

Laser-controlled optical transconductance varistor system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Hoang T.; Stuart, Brent C.

2017-07-11

An optical transconductance varistor system having a modulated radiation source configured to provide modulated stimulus, a wavelength converter operably connected to the modulated radiation source to produce a modulated stimulus having a predetermined wavelength, and a wide bandgap semiconductor photoconductive material in contact between two electrodes. The photoconductive material is operably coupled, such as by a beam transport module, to receive the modulated stimulus having the predetermined wavelength to control a current flowing through the photoconductive material when a voltage potential is present across the electrodes.

Ultrafast Spectral Photoresponse of Bilayer Graphene: Optical Pump-Terahertz Probe Spectroscopy.

PubMed

Kar, Srabani; Nguyen, Van Luan; Mohapatra, Dipti R; Lee, Young Hee; Sood, A K

2018-02-27

Photoinduced terahertz conductivity Δσ(ω) of Bernal stacked bilayer graphene (BLG) with different dopings is measured by time-resolved optical pump terahertz probe spectroscopy. The real part of photoconductivity Δσ(ω) (Δσ Re (ω)) is positive throughout the spectral range 0.5-2.5 THz in low-doped BLG. This is in sharp contrast to Δσ(ω) for high-doped bilayer graphene where Δσ Re (ω) is negative at low frequency and positive on the high frequency side. We use Boltzmann transport theory to understand quantitatively the frequency dependence of Δσ(ω), demanding the energy dependence of different scattering rates such as short-range impurity scattering, Coulomb scattering, carrier-acoustic phonon scattering, and substrate surface optical phonon scattering. We find that the short-range disorder scattering dominates over other processes. The calculated photoconductivity captures very well the experimental conductivity spectra as a function of lattice temperature varying from 300 to 4 K, without any empirical fitting procedures adopted so far in the literature. This helps us to understand the intraband conductivity of photoexcited hot carriers in 2D materials.

Food sensitivity in reflux esophagitis.

PubMed

Price, S F; Smithson, K W; Castell, D O

1978-08-01

We examined 66 patients with pain of possible esophageal origin for sensitivity to intraesophageal infusions of coffee, orange juice, spicy tomato drink, or HCl of varying concentrations as an addendum to their acid infusion (Bernstein) tests. Compared to Berstein-negative subjects, acid-sensitive patients were sensitive to infusion of coffee (P less than 0.01), orange juice (P less than 0.001), and tomato drink (P less than 0.001). Patients were largely insensitive to HCl solutions with a titratable acidity of 1 mEq per liter or less, less than the least acidic food solution tested. However, Berstein-positive patients were still highly sensitive to infusions of coffee, orange juice, and tomato drink adjusted to pH 7 (P less than 0.001). Patients were unable to differentiate symptoms caused by acid or food infusions, and solutions did not differ in the duration of infusion needed either to cause symptoms or to relieve them by saline. We conclude that the pain of esophagitis is nonspecific and can be precipitated by variety of seemingly unrelated substances.

Sensitivity of Gram stain in the diagnosis of urethritis in men.

PubMed

Orellana, M Angeles; Gómez-Lus, M Luisa; Lora, David

2012-06-01

Acute urethritis is among the most common types of sexually transmitted diseases in men. The diagnosis usually requires microscopic evidence of urethritis, but sometimes urethral pathogens are detected in asymptomatic men without such evidence. The aims of this study were to assess the sensitivity of Gram stain in men with urethral symptoms and to relate it to the microorganisms isolated. Between January 2006 and December 2007, 491 urethral samples were analysed. The authors assessed the presence of leukocytes by Gram stain and tested specifically for Chlamydia trachomatis, Ureaplasma urealyticum, Mycoplasma hominis and Trichomonas vaginalis, as well as analysing the results of conventional culture. The percentages of positive samples as a function of Gram category were two or less polymorphonuclear leukocytes (PMNLs)/high-power field (HPF) 25% (92/364), three to four PMNLs/HPF 32% (18/57) and five or more PMNLs/HPF 54% (38/70). Classing samples with more than two PMNLs/HPF as positive, the sensitivity, specificity and positive likelihood ratio for Gram stain were 38% (95% CI 30 to 46), 79% (95% CI 75 to 84) and 1.8 (95% CI 1.4 to 2.4), respectively. On the other hand, taking as positive five or more PMNLs/HPF, the sensitivity, specificity and positive likelihood ratio for Gram stain were 26% (95% CI 18 to 33), 91% (95% CI 87 to 94) and 2.7 (95% CI 1.8 to 4.2), respectively. The sensitivity of Gram stain to Neisseria gonorrhoeae, Chlamydia trachomatis and Ureaplasma urealyticum were 80% (95% CI 64 to 96), 23% (95% CI 8 to 39) and 11% (95% CI 2 to 20), respectively. The low sensitivity of Gram stain means that negative results do not exclude the presence of urethritis in symptomatic patients.