Science.gov

Sample records for position sensitive photoconductive

  1. Photoconducting positions monitor and imaging detector

    DOEpatents

    Shu, Deming; Kuzay, Tuncer M.

    2000-01-01

    A photoconductive, high energy photon beam detector/monitor for detecting x-rays and gamma radiation, having a thin, disk-shaped diamond substrate with a first and second surface, and electrically conductive coatings, or electrodes, of a predetermined configuration or pattern, disposed on the surfaces of the substrate. A voltage source and a current amplifier is connected to the electrodes to provide a voltage bias to the electrodes and to amplify signals from the detector.

  2. Directly tailoring photon-electron coupling for sensitive photoconductance

    NASA Astrophysics Data System (ADS)

    Huang, Zhiming; Zhou, Wei; Huang, Jingguo; Wu, Jing; Gao, Yanqing; Qu, Yue; Chu, Junhao

    2016-03-01

    The coupling between photons and electrons is at the heart of many fundamental phenomena in nature. Despite tremendous advances in controlling electrons by photons in engineered energy-band systems, control over their coupling is still widely lacking. Here we demonstrate an unprecedented ability to couple photon-electron interactions in real space, in which the incident electromagnetic wave directly tailors energy bands of solid to generate carriers for sensitive photoconductance. By spatially coherent manipulation of metal-wrapped material system through anti-symmetric electric field of the irradiated electromagnetic wave, electrons in the metals are injected and accumulated in the induced potential well (EIW) produced in the solid. Respective positive and negative electric conductances are easily observed in n-type and p-type semiconductors into which electrons flow down from the two metallic sides under light irradiation. The photoconductivity is further confirmed by sweeping the injected electrons out of the semiconductor before recombination applied by sufficiently strong electric fields. Our work opens up new perspectives for tailoring energy bands of solids and is especially relevant to develop high effective photon detection, spin injection, and energy harvesting in optoelectronics and electronics.

  3. Directly tailoring photon-electron coupling for sensitive photoconductance

    PubMed Central

    Huang, Zhiming; Zhou, Wei; Huang, Jingguo; Wu, Jing; Gao, Yanqing; Qu, Yue; Chu, Junhao

    2016-01-01

    The coupling between photons and electrons is at the heart of many fundamental phenomena in nature. Despite tremendous advances in controlling electrons by photons in engineered energy-band systems, control over their coupling is still widely lacking. Here we demonstrate an unprecedented ability to couple photon-electron interactions in real space, in which the incident electromagnetic wave directly tailors energy bands of solid to generate carriers for sensitive photoconductance. By spatially coherent manipulation of metal-wrapped material system through anti-symmetric electric field of the irradiated electromagnetic wave, electrons in the metals are injected and accumulated in the induced potential well (EIW) produced in the solid. Respective positive and negative electric conductances are easily observed in n-type and p-type semiconductors into which electrons flow down from the two metallic sides under light irradiation. The photoconductivity is further confirmed by sweeping the injected electrons out of the semiconductor before recombination applied by sufficiently strong electric fields. Our work opens up new perspectives for tailoring energy bands of solids and is especially relevant to develop high effective photon detection, spin injection, and energy harvesting in optoelectronics and electronics. PMID:26964883

  4. Directly tailoring photon-electron coupling for sensitive photoconductance.

    PubMed

    Huang, Zhiming; Zhou, Wei; Huang, Jingguo; Wu, Jing; Gao, Yanqing; Qu, Yue; Chu, Junhao

    2016-01-01

    The coupling between photons and electrons is at the heart of many fundamental phenomena in nature. Despite tremendous advances in controlling electrons by photons in engineered energy-band systems, control over their coupling is still widely lacking. Here we demonstrate an unprecedented ability to couple photon-electron interactions in real space, in which the incident electromagnetic wave directly tailors energy bands of solid to generate carriers for sensitive photoconductance. By spatially coherent manipulation of metal-wrapped material system through anti-symmetric electric field of the irradiated electromagnetic wave, electrons in the metals are injected and accumulated in the induced potential well (EIW) produced in the solid. Respective positive and negative electric conductances are easily observed in n-type and p-type semiconductors into which electrons flow down from the two metallic sides under light irradiation. The photoconductivity is further confirmed by sweeping the injected electrons out of the semiconductor before recombination applied by sufficiently strong electric fields. Our work opens up new perspectives for tailoring energy bands of solids and is especially relevant to develop high effective photon detection, spin injection, and energy harvesting in optoelectronics and electronics. PMID:26964883

  5. Color-sensitive photoconductivity of nanostructured ZnO/fast green dye hybrid films

    NASA Astrophysics Data System (ADS)

    Rani, Mamta; Tripathi, S. K.

    2013-06-01

    Nanostructured ZnO/dye hybrid films prepared by sol gel method have been investigated in conductivity and photoconductivity measurements in view of applications in dye-sensitized solar cells (DSSC). The absorption of ZnO film sensitized by Fast Green dye (FGF) has been studied by UV spectroscopy which indicates that after the dye is adsorbed on the ZnO electrode, its absorption spectra showed red-shift in the peak position compared to the absorbance spectra of dye in ethanol. The films, in which dye molecules are located within the ZnO crystals, are found to show higher sensitivity to illumination with visible light in photoconductivity measurements due to a high proportion of surface dye molecules are being excited by π-electrons acting as sensitizers.

  6. New configuration of photoconductive-type diamond detector head for X-ray beam position monitors

    NASA Astrophysics Data System (ADS)

    Aoyagi, Hideki; Kudo, Togo; Tanida, Hajime; Kitamura, Hideo

    2004-05-01

    We designed and fabricated new diamond detector head for an X-ray beam position monitor (XBPM). This monitor operates in photoconductive mode, and is shaped into a blade in order to reduce heat load. A pair of aluminum electrodes is formed on both sides of the diamond blade. The profile of the detection efficiency inside the diamond detector head was measured. The signal current is generated only between the pair of electrodes. The bias voltage dependence of signal current along a section of the detector head is also measured. The results show that the detector head operates in photoconductive mode. We demonstrated that this detector head is feasible for the XBPM.

  7. Wavelength dependent negative and positive persistent photoconductivity in Sn δ-doped GaAs structures

    NASA Astrophysics Data System (ADS)

    Kulbachinskii, V. A.; Kytin, V. G.; Golikov, A. V.; Lunin, R. A.; van Schaijk, R. T. F.; de Visser, A.; Senichkin, A. P.; Bugaev, A. S.

    2000-09-01

    The photoconductivity of GaAs structures δ-doped by Sn has been investigated for wavelengths λ = 650-1200 nm in the temperature interval T = 4.2-300 K. The electron densities and mobilities, before and after illumination, have been determined by magnetoresistance, Shubnikov-de Haas effect and Hall effect measurements, in high magnetic fields. For the heavily doped structures (Hall density nH>2×1013 cm-2) we observe under illumination by light with wavelengths larger than the bandgap wavelength of the host material (λ = 815 nm at T = 4.2 K) first positive (PPPC) and then negative (NPPC) persistent photoconductivity. The NPPC is attributed to the ionization of DX centres and PPPC is explained by the excitation of electrons from Cr impurity states in the substrate. For λ<815 nm, in addition, the excitation of electrons over the bandgap of GaAs contributes to the PPPC. For the lightly doped structures (nH≤2×1013 cm-2) the photoconductivity effect is always positive.

  8. Broadband Phase-Sensitive Single InP Nanowire Photoconductive Terahertz Detectors.

    PubMed

    Peng, Kun; Parkinson, Patrick; Boland, Jessica L; Gao, Qian; Wenas, Yesaya C; Davies, Christopher L; Li, Ziyuan; Fu, Lan; Johnston, Michael B; Tan, Hark H; Jagadish, Chennupati

    2016-08-10

    Terahertz time-domain spectroscopy (THz-TDS) has emerged as a powerful tool for materials characterization and imaging. A trend toward size reduction, higher component integration, and performance improvement for advanced THz-TDS systems is of increasing interest. The use of single semiconducting nanowires for terahertz (THz) detection is a nascent field that has great potential to realize future highly integrated THz systems. In order to develop such components, optimized material optoelectronic properties and careful device design are necessary. Here, we present antenna-optimized photoconductive detectors based on single InP nanowires with superior properties of high carrier mobility (∼1260 cm(2) V(-1) s(-1)) and low dark current (∼10 pA), which exhibit excellent sensitivity and broadband performance. We demonstrate that these nanowire THz detectors can provide high quality time-domain spectra for materials characterization in a THz-TDS system, a critical step toward future application in advanced THz-TDS system with high spectral and spatial resolution.

  9. Position Sensitive Microcalorimeters

    NASA Technical Reports Server (NTRS)

    Sadleir, J. E.; Hammock, C.; Figueroa-Feliciano, E.; Stahle, C. K.; Bandler, S.; Saab, T.; Lindeman, M.; Porter, F. S.; Chervenak, J.; Brown, G.

    2004-01-01

    A Position Sensitive Transition-Edge Sensor (PoST) is a microcalorimeter device capable of one-dimensional imaging spectroscopy. The device consists of two Transition-Edge Sensors (TESs) connected to the ends of a long X-ray absorbing strip. The energy of a photon hitting the absorber and the position of the absorption event along the strip is measured from the response in the two sensors by analyzing the relative signal sizes, pulse rise times, and the sum of the pulses measured at each sensor, We report on the recent PoST effort at Goddard for applications to large field of view, high-energy- resolution, X-ray astrophysics.

  10. Understanding sensitization behavior of lead selenide photoconductive detectors by charge separation model

    SciTech Connect

    Zhao, Lihua E-mail: shi@ou.edu; Qiu, Jijun; Weng, Binbin; Chang, Caleb; Yuan, Zijian; Shi, Zhisheng E-mail: shi@ou.edu

    2014-02-28

    We introduce a charge separation model in this work to explain the mechanism of enhanced photoconductivity of polycrystalline lead salt photoconductors. Our results show that this model could clarify the heuristic fabrication processes of such lead salt detectors that were not well understood and often considered mysterious for nearly a century. The improved lifetime and performance of the device, e.g., responsivity, are attributed to the spatial separation of holes and electrons, hence less possibility of carrier recombination. This model shows that in addition to crystal quality the size of crystallites, the depth of outer conversion layer, and doping concentration could all affect detector performance. The simulation results agree well with experimental results and thus offer a very useful tool for further improvement of lead salt detectors. The model was developed with lead salt family of photoconductors in mind, but may well be applicable to a wider class of semiconducting films.

  11. Understanding sensitization behavior of lead selenide photoconductive detectors by charge separation model

    NASA Astrophysics Data System (ADS)

    Zhao, Lihua; Qiu, Jijun; Weng, Binbin; Chang, Caleb; Yuan, Zijian; Shi, Zhisheng

    2014-02-01

    We introduce a charge separation model in this work to explain the mechanism of enhanced photoconductivity of polycrystalline lead salt photoconductors. Our results show that this model could clarify the heuristic fabrication processes of such lead salt detectors that were not well understood and often considered mysterious for nearly a century. The improved lifetime and performance of the device, e.g., responsivity, are attributed to the spatial separation of holes and electrons, hence less possibility of carrier recombination. This model shows that in addition to crystal quality the size of crystallites, the depth of outer conversion layer, and doping concentration could all affect detector performance. The simulation results agree well with experimental results and thus offer a very useful tool for further improvement of lead salt detectors. The model was developed with lead salt family of photoconductors in mind, but may well be applicable to a wider class of semiconducting films.

  12. 32 CFR 154.13 - Sensitive positions.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... be categorized, with respect to security sensitivity, as either nonsensitive, noncritical-sensitive... shall designate each position within their jurisdiction as to its security sensitivity and...

  13. 32 CFR 154.13 - Sensitive positions.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... be categorized, with respect to security sensitivity, as either nonsensitive, noncritical-sensitive... shall designate each position within their jurisdiction as to its security sensitivity and...

  14. 32 CFR 154.13 - Sensitive positions.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... be categorized, with respect to security sensitivity, as either nonsensitive, noncritical-sensitive... shall designate each position within their jurisdiction as to its security sensitivity and...

  15. Photoconductivity of Activated Carbon Fibers

    DOE R&D Accomplishments Database

    Kuriyama, K.; Dresselhaus, M. S.

    1990-08-01

    The photoconductivity is measured on a high-surface-area disordered carbon material, namely activated carbon fibers, to investigate their electronic properties. Measurements of decay time, recombination kinetics and temperature dependence of the photoconductivity generally reflect the electronic properties of a material. The material studied in this paper is a highly disordered carbon derived from a phenolic precursor, having a huge specific surface area of 1000--2000m{sup 2}/g. Our preliminary thermopower measurements suggest that this carbon material is a p-type semiconductor with an amorphous-like microstructure. The intrinsic electrical conductivity, on the order of 20S/cm at room temperature, increases with increasing temperature in the range 30--290K. In contrast with the intrinsic conductivity, the photoconductivity in vacuum decreases with increasing temperature. The recombination kinetics changes from a monomolecular process at room temperature to a biomolecular process at low temperatures. The observed decay time of the photoconductivity is {approx equal}0.3sec. The magnitude of the photoconductive signal was reduced by a factor of ten when the sample was exposed to air. The intrinsic carrier density and the activation energy for conduction are estimated to be {approx equal}10{sup 21}/cm{sup 3} and {approx equal}20meV, respectively. The majority of the induced photocarriers and of the intrinsic carriers are trapped, resulting in the long decay time of the photoconductivity and the positive temperature dependence of the conductivity.

  16. Position sensitive solid state detectors

    NASA Astrophysics Data System (ADS)

    Schnatterly, S. E.; Husk, D.

    1986-05-01

    Solid state detectors have been used for years as high quantum efficiency detectors for visible light. In this paper the use of PDA and CCD, solid state detectors, in the X-ray region will be discussed. In particular examples of data in the soft X-ray region are presented. Finally the use of phosphor coatings to enhance the sensitivity of solid state detectors is described.

  17. Investigation on the photoconductive behaviors of an individual AlN nanowire under different excited lights

    PubMed Central

    2012-01-01

    Ultra-long AlN nanowire arrays are prepared by chemical vapor deposition, and the photoconductive performances of individual nanowires are investigated in our self-built measurement system. Individual ultra-long AlN nanowire (UAN) exhibits a clear photoconductive effect under different excited lights. We attribute the positive photocurrent response of individual UAN to the dominant molecular sensitization effect. It is found that they have a much faster response speed (a rise and decay time of about 1 ms), higher photocurrent response (2.7×106), and more reproductive working performance (the photocurrent fluctuation is lower than 2%) in the air environment. Their better photoconductive performances are comparable to many nanostructures, which are suggested to be a candidate for building promising photosensitive nanodevices in the future. PMID:22883472

  18. Position Sensitive Detection System for Charged Particles

    SciTech Connect

    Coello, E. A.; Favela, F.; Curiel, Q.; Chavez, E; Huerta, A.; Varela, A.; Shapira, Dan

    2012-01-01

    The position sensitive detection system presented in this work employs the Anger logic algorithm to determine the position of the light spark produced by the passage of charged particles on a 170 x 170 x 10 mm3 scintillator material (PILOT-U). The detection system consists of a matrix of nine photomultipliers, covering a fraction of the back area of the scintillators. Tests made with a non-collimated alpha particle source together with a Monte Carlo simulation that reproduces the data, suggest an intrinsic position resolution of up to 6 mm is achieved.

  19. A New Positioning Algorithm for Position-Sensitive Avalanche Photodiodes.

    PubMed

    Zhang, Jin; Olcott, Peter D; Levin, Craig S

    2007-06-01

    We are using a novel position sensitive avalanche photodiode (PSAPD) for the construction of a high resolution positron emission tomography (PET) camera. Up to now most researchers working with PSAPDs have been using an Anger-like positioning algorithm involving the four corner readout signals of the PSAPD. This algorithm yields a significant non-linear spatial "pin-cushion" distortion in raw crystal positioning histograms. In this paper, we report an improved positioning algorithm, which combines two diagonal corner signals of the PSAPD followed by a 45° rotation to determine the X or Y position of the interaction. We present flood positioning histogram data generated with the old and new positioning algorithms using a 3 × 4 array of 2 × 2 × 3 mm(3) and a 3 × 8 array of 1 × 1 × 3 mm(3) of LSO crystals coupled to 8 × 8 mm(2) PSAPDs. This new algorithm significantly reduces the pin-cushion distortion in raw flood histogram image. PMID:24307743

  20. Large area position sensitive β-detector

    NASA Astrophysics Data System (ADS)

    Vaintraub, S.; Hass, M.; Edri, H.; Morali, N.; Segal, T.

    2015-03-01

    A new conceptual design of a large area electron detector, which is position and energy sensitive, was developed. This detector is designed for beta decay energies up to 4 MeV, but in principle can be re-designed for higher energies. The detector incorporates one large plastic scintillator and, in general, a limited number of photomultipliers (7 presently). The current setup was designed and constructed after an extensive Geant4 simulation study. By comparison of a single hit light distribution between the various photomultipliers to a pre-measured accurate position-response map, the anticipated position resolution is around 5 mm. The first benchmark experiments have been conducted in order to calibrate and confirm the position resolution of the detector. The new method, results of the first test experiments and comparison to simulations are presented.

  1. 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.

  2. Photoconductivity in Dirac materials

    SciTech Connect

    Shao, J. M.; Yang, G. W.

    2015-11-15

    Two-dimensional (2D) Dirac materials including graphene and the surface of a three-dimensional (3D) topological insulator, and 3D Dirac materials including 3D Dirac semimetal and Weyl semimetal have attracted great attention due to their linear Dirac nodes and exotic properties. Here, we use the Fermi’s golden rule and Boltzmann equation within the relaxation time approximation to study and compare the photoconductivity of Dirac materials under different far- or mid-infrared irradiation. Theoretical results show that the photoconductivity exhibits the anisotropic property under the polarized irradiation, but the anisotropic strength is different between 2D and 3D Dirac materials. The photoconductivity depends strongly on the relaxation time for different scattering mechanism, just like the dark conductivity.

  3. Two-dimensional position sensitive radiation detectors

    DOEpatents

    Mihalczo, John T.

    1994-01-01

    Nuclear reaction detectors capable of position sensitivity with submillimeter resolution in two dimensions are each provided by placing arrays of scintillation or wave length shifting optical fibers formed of a plurality of such optical fibers in a side-by-side relationship in X and Y directions with a layer of nuclear reactive material operatively associated with surface regions of the optical fiber arrays. Each nuclear reaction occurring in the layer of nuclear reactive material produces energetic particles for simultaneously providing a light pulse in a single optical fiber in the X oriented array and in a single optical fiber in the Y oriented array. These pulses of light are transmitted to a signal producing circuit for providing signals indicative of the X-Y coordinates of each nuclear event.

  4. Two-dimensional position sensitive radiation detectors

    DOEpatents

    Mihalczo, J.T.

    1994-02-22

    Nuclear reaction detectors capable of position sensitivity with submillimeter resolution in two dimensions are each provided by placing arrays of scintillation or wavelength shifting optical fibers formed of a plurality of such optical fibers in a side-by-side relationship in X and Y directions with a layer of nuclear reactive material operatively associated with surface regions of the optical fiber arrays. Each nuclear reaction occurring in the layer of nuclear reactive material produces energetic particles for simultaneously providing a light pulse in a single optical fiber in the X oriented array and in a single optical fiber in the Y oriented array. These pulses of light are transmitted to a signal producing circuit for providing signals indicative of the X-Y coordinates of each nuclear event. 6 figures.

  5. 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.

  6. Photoconductive switch package

    SciTech Connect

    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 central portion to actuate the switch.

  7. Experiments on Photoconductivity

    ERIC Educational Resources Information Center

    Kraftmakher, Yaakov

    2012-01-01

    Computer-assisted experiments with CdS and CdSe photoresistors are described. The most important characteristics of the photoresistors are determined: (i) the spectral response, (ii) the photocurrent versus incident radiant power, (iii) the rise and decay time constants and (iv) the frequency response to modulated light. The photoconductivity gain…

  8. 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.

  9. 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.

  10. 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.

  11. 32 CFR 154.13 - Sensitive positions.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ...) Development or approval of war plans, plans or particulars of future major or special operations of war, or critical and extremely important items of war. (D) Investigative and certain investigative support duties...) Noncritical-sensitive. (A) Access to Secret or Confidential information. (B) Security police/provost...

  12. 32 CFR 154.13 - Sensitive positions.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...) Development or approval of war plans, plans or particulars of future major or special operations of war, or critical and extremely important items of war. (D) Investigative and certain investigative support duties...) Noncritical-sensitive. (A) Access to Secret or Confidential information. (B) Security police/provost...

  13. 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.

  14. Position sensitivity in gallium arsenide radiation detectors

    SciTech Connect

    Harper, R.; Hilko, R.A.

    1994-12-31

    For several years, the authors have studied the electrical output of GaAs detectors in response to MeV protons. Beams from the Los Alamos National Laboratory`s tandem Van de Graaff, bunched into pulses of about 0.7-ns width, have been used to drive detectors into the current mode, and fast electronics have enabled characterization of the impulse response shapes and the absolute sensitivities. Recently, the authors extended this line of investigation to measure output-charge spectra in response to low-current beams, in which the count rate was low and pulses due to individual ionizing particles were analyzed. The first part of the work was the measurement of spectra of the output charge of the detectors when bombarded by a beam of MeV-energy protons, which was collimated to a diameter of 0.1 mm. The GaAs detector was mounted on a microadjustable stage just behind the collimator, so that the site of irradiation on the detector could be varied. Output pulses originating from the impacts of individual protons were preamplified with charge-sensitive Lecroy 2004 preamplifiers, shaped with Lecroy 2011 amplifiers, and analyzed with a Lecroy 3500 multichannel analyzer. The second part was the measurement of the time response of the detector to a 0.1 mm-collimated bunched proton beam. The proton bunch width was less than 1 ns, during which time many protons struck the detector, driving it into the current mode where individual proton impacts are unresolved. A possible detector design is suggested by the results. In the past, GaAs time response has been improved by doping or radiation damaging, which introduces traps. The tails can be eliminated, but at the cost of a factor of a thousand in main peak sensitivity. It now appears that by masking off the region of the detector near the negative electrode, the tails can be eliminated with only a factor of about ten loss in peak gain.

  15. 43 CFR 422.11 - Position sensitivity and investigations.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 1 2011-10-01 2011-10-01 false Position sensitivity and investigations. 422.11 Section 422.11 Public Lands: Interior Regulations Relating to Public Lands BUREAU OF... Requirements § 422.11 Position sensitivity and investigations. Each law enforcement contract or...

  16. 43 CFR 422.11 - Position sensitivity and investigations.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 43 Public Lands: Interior 1 2010-10-01 2010-10-01 false Position sensitivity and investigations. 422.11 Section 422.11 Public Lands: Interior Regulations Relating to Public Lands BUREAU OF... Requirements § 422.11 Position sensitivity and investigations. Each law enforcement contract or...

  17. 43 CFR 422.11 - Position sensitivity and investigations.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 1 2012-10-01 2011-10-01 true Position sensitivity and investigations. 422.11 Section 422.11 Public Lands: Interior Regulations Relating to Public Lands BUREAU OF... Requirements § 422.11 Position sensitivity and investigations. Each law enforcement contract or...

  18. 43 CFR 422.11 - Position sensitivity and investigations.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 1 2014-10-01 2014-10-01 false Position sensitivity and investigations. 422.11 Section 422.11 Public Lands: Interior Regulations Relating to Public Lands BUREAU OF... Requirements § 422.11 Position sensitivity and investigations. Each law enforcement contract or...

  19. 43 CFR 422.11 - Position sensitivity and investigations.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 1 2013-10-01 2013-10-01 false Position sensitivity and investigations. 422.11 Section 422.11 Public Lands: Interior Regulations Relating to Public Lands BUREAU OF... Requirements § 422.11 Position sensitivity and investigations. Each law enforcement contract or...

  20. Photoconductivity spectra of nanodimensional structures on c-Si and GaAs substrates

    NASA Astrophysics Data System (ADS)

    Udovitskaya, Ruslana S.; Kondratenko, Sergey V.; Vakulenko, Oleg V.

    2005-08-01

    The photoconductivity spectra of the structure nanodimensional Ge/c-Si with Ge quantum wells on a single-crystal substrate surface were measured using infrared spectrophotometer IR-12. The same measurements were also made for the structures Al0.2Ga0.8As/In0.1Ga0.9As/GaAs with further comparison of received results to standard GaAs photodiode. The photoconductivity spectrum of nanodimensional Ge/c-S i structure was received at room temperature. The investigated samples are made by molecular - beam epitaxy method. rectangular frame type (5x5 micron) contact was generated on a surface of Ge layer. The thickness of a contact strip was equaled to 0,5 micron. The second contact was soldered to the back side of the singlecrystal surface. A shifting voltage U =1,5 V was switched in the opposite direction (negative potential to Ge slice) At measurements of photoconductivity of structure. It is necessary to note that photoconductive signal was 3 orders less, than at inverse displacement. It specifies presence heterotransitions between Ge and c-S i layer. The photosensitivity of a standard silicon photodiode was investigated for comparison of such assumption. For example the spectral dependence of photosensitivity of standard silicon photodiode FD-142Κ is represented. The spectral position of a photoconductivity curve was the same to standard silicon photodiode at room temperature. The value of photosensitivity of a researched sample was compared with the standard photodiode. Is established, that both these values are of the same order. It is possible to explain it by presence of a potential barrier between Ge and Si. It is known that longwave border of photoconductivity is defined by width of the forbidden zone of the semiconductor. The increase of photoconductivity is caused by increase of absorption at rising of quantums energy of the exited radiation (at reduction of wavelength). The form of a photoconductivity spectrum of the photodiode FD-142Κ and absence of a hole in

  1. Avalanche photoconductive switching

    SciTech Connect

    Pocha, M.D.; Druce, R.L.; Wilson, M.J.; Hofer, W.W.

    1989-01-01

    This paper describes work being done at Lawrence Livermore National Laboratory on the avalanche mode of operation of laser triggered photoconductive switches. We have been able to generate pulses with amplitudes of 2 kV--35 kV and rise times of 300--500 ps, and with a switching gain (energy of output electrical pulse vs energy of trigger optical pulse) of 10{sup 3} to over 10{sup 5}. Switches with two very different physical configurations and with two different illumination wavelengths (1.06 {mu}m, 890 nm) exhibit very similar behavior. The avalanche switching behavior, therefore, appears to be related to the material parameters rather than the optical wavelength or switch geometry. Considerable further work needs to be done to fully characterize and understand this mode of operation. 3 refs., 6 figs.

  2. Construction and commissioning of a position-sensitive ionization chamber

    NASA Astrophysics Data System (ADS)

    Kwag, M. S.; Chae, K. Y.; Cha, S. M.; Kim, A.; Kim, M. J.; Lee, E. J.; Lee, J. H.

    2016-05-01

    A position-sensitive ionization chamber has been constructed and commissioned at the Physics Department of Sungkyunkwan University to extract position information on incident charged particles for future nuclear reaction measurements. By utilizing the newly-designed position-sensitive anodes and the previously-commissioned portable gas-filled ionization chamber by Chae et al., position information on incident particles could be obtained. The device was tested with an 241Am α-emitting source, and the standard deviation of the fitted Gaussian distribution was measured to be 1.76 mm when a collimator with a 2 mm hole was used.

  3. Semiconducting-to-Metallic Photoconductivity Crossover and Temperature-Dependent Drude Weight in Graphene

    NASA Astrophysics Data System (ADS)

    Frenzel, A. J.; Lui, C. H.; Shin, Y. C.; Kong, J.; Gedik, N.

    2014-08-01

    We investigate the transient photoconductivity of graphene at various gate-tuned carrier densities by optical-pump terahertz-probe spectroscopy. We demonstrate that graphene exhibits semiconducting positive photoconductivity near zero carrier density, which crosses over to metallic negative photoconductivity at high carrier density. These observations can be accounted for by the interplay between photoinduced changes of both the Drude weight and carrier scattering rate. Our findings provide a complete picture to explain the opposite photoconductivity behavior reported in (undoped) graphene grown epitaxially and (doped) graphene grown by chemical vapor deposition. Notably, we observe nonmonotonic fluence dependence of the photoconductivity at low carrier density. This behavior reveals the nonmonotonic temperature dependence of the Drude weight in graphene, a unique property of two-dimensional massless Dirac fermions.

  4. Coexistence of negative photoconductivity and hysteresis in semiconducting graphene

    NASA Astrophysics Data System (ADS)

    Zhuang, Shendong; Chen, Yan; Xia, Yidong; Tang, Nujiang; Xu, Xiaoyong; Hu, Jingguo; Chen, Zhuo

    2016-04-01

    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. 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.

  5. InP:Fe Photoconducting device

    DOEpatents

    Hammond, Robert B.; Paulter, Nicholas G.; Wagner, Ronald S.

    1984-01-01

    A photoconducting device fabricated from Fe-doped, semi-insulating InP crystals exhibits an exponential decay transient with decay time inversely related to Fe concentration. Photoconductive gain as high as 5 is demonstrated in photoconducting devices with AuGe and AuSn contacts. Response times from 150 to 1000 picoseconds can be achieved.

  6. InP:Fe photoconducting device

    DOEpatents

    Hammond, R.B.; Paulter, N.G.; Wagner, R.S.

    A photoconducting device fabricated from Fe-doped, semi-insulating InP crystals exhibits an exponential decay transient with decay time inversely related to Fe concentration. Photoconductive gain as high as 5 is demonstrated in photoconducting devices with AuGe and AuSn contacts. Response times from 150 to 1000 picoseconds can be achieved.

  7. Dual Position Sensitive MWPC for tracking reaction products at VAMOS++

    NASA Astrophysics Data System (ADS)

    Vandebrouck, M.; Lemasson, A.; Rejmund, M.; Fremont, G.; Pancin, J.; Navin, A.; Michelagnoli, C.; Goupil, J.; Spitaels, C.; Jacquot, B.

    2016-03-01

    The characteristics and performance of a Dual Position Sensitive Multi-Wire Proportional Counter (DPS-MWPC) used to measure the scattering angle, the interaction position on the target and the velocity of reaction products detected in the VAMOS++ magnetic spectrometer, are reported. The detector consists of a pair of position sensitive low pressure MWPCs and provides both fast timing signals, along with the two-dimensional position coordinates required to define the trajectory of the reaction products. A time-of-flight resolution of 305(11) ps (FWHM) was measured. The measured resolutions (FWHM) were 2.5(3) mrad and 560(70) μm for the scattering angle and the interaction point at the target respectively. The subsequent improvement of the Doppler correction of the energy of the γ-rays, detected in the γ-ray tracking array AGATA in coincidence with isotopically identified ions in VAMOS++, is also discussed.

  8. Self-Balancing Position-Sensitive Detector (SBPSD)

    PubMed Central

    Porrazzo, Ryan; Lydecker, Leigh; Gattu, Suhasini; Bakhru, Hassaram; Tokranova, Natalya; Castracane, James

    2015-01-01

    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 technology, are inexpensive and provide a real-time, analog signal output corresponding to the position of the light spot. An innovative type of optical position sensor was developed using two back-to-back connected photodiodes. These so called self-balancing position-sensitive detectors (SBPSDs) eliminate the need for external readout circuitry entirely. Fabricated prototype devices demonstrate linear, symmetric coordinate characteristics and a spatial resolution of 200 μm for a 74 mm device. PSDs are commercially available only up to a length of 37 mm. Prototype devices were fabricated with various lengths up to 100 mm and can be scaled down to any size below that. PMID:26205266

  9. Self-Balancing Position-Sensitive Detector (SBPSD).

    PubMed

    Porrazzo, Ryan; Lydecker, Leigh; Gattu, Suhasini; Bakhru, Hassaram; Tokranova, Natalya; Castracane, James

    2015-01-01

    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 technology, are inexpensive and provide a real-time, analog signal output corresponding to the position of the light spot. An innovative type of optical position sensor was developed using two back-to-back connected photodiodes. These so called self-balancing position-sensitive detectors (SBPSDs) eliminate the need for external readout circuitry entirely. Fabricated prototype devices demonstrate linear, symmetric coordinate characteristics and a spatial resolution of 200 μm for a 74 mm device. PSDs are commercially available only up to a length of 37 mm. Prototype devices were fabricated with various lengths up to 100 mm and can be scaled down to any size below that.

  10. Development of a novel position-sensitive microchannel plate detector

    NASA Astrophysics Data System (ADS)

    Wiggins, Blake; Siwal, Davinder; Desouza, Romualdo

    2015-10-01

    Position sensitive microchannel plate (MCP) detectors which measure the position of an incident electron, ion, or photon, are useful in imaging applications. Recently, a novel detector, which utilizes an induced approach to provide position sensitivity, has been developed. In the prototype detector, using only the zero-crossing point of the inherently bipolar signals, a position resolution of 466 μm (FWHM) has been achieved. Implementing a differential readout may improve on this resolution. To realize this differential approach, a better understanding of the dependence of the induced signal shape on the position of the electron cloud is required. To characterize the dependence of the induced signal shape on position a resistive anode (RA) has been incorporated into the detector. The RA will allow determination of the centroid of the electron cloud. Factors impacting the position resolution obtained with the RA will be discussed and the achieved position resolution of 157 μm (FWHM) will be presented. Supported by the US DOE NNSA under Award No. DE-NA0002012.

  11. 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.

  12. Closing photoconductive semiconductor switches

    SciTech Connect

    Loubriel, G.M.; Zutavern, F.J.; Hjalmarson, H.P.; O'Malley, M.W.

    1989-01-01

    One of the most important limitations of Photoconductive Semiconductor Switches (PCSS) for pulsed power applications is the high laser powers required to activate the switches. In this paper, we discuss recent developments on two different aspects of GaAs PCSS that result in reductions in laser power by a factor of nearly 1000. The advantages of using GaAs over Si are many. First of all, the resistivity of GaAs can be orders of magnitude higher than that of the highest resistivity Si material, thus allowing GaAs switches to withstand dc voltages without thermal runaway. Secondly, GaAs has a higher carrier mobility than Si and, thus, is more efficient (per carrier). Finally, GaAs switches can have naturally fast (ns) opening times at room temperature and low fields, microsecond opening times at liquid nitrogen temperature of 77 K, or, on demand, closing and opening at high fields and room temperature by a mechanism called lock-on (see Ref. 1). By contrast, Si switches typically opening times of milliseconds. The amount of laser light required to trigger GaAs for lock-on, or at 77 K, is about three orders of magnitude lower than at room temperature. In this paper we describe the study of lock-on in GaAs and InP, as well as switching of GaAs at 77 K. We shall show that when GaAs is switched at 77 K, the carrier lifetime is about three orders of magnitude longer than it is at room temperature. We shall explain the change in lifetime in terms of the change in electron capture cross section of the deep levels in GaAs (these are defect or impurity levels in the band gap). In the second section, we describe the lock-on effect, now seen in GaAs and InP, and at fields as high as 70 kV/cm. We show how lock-on can be tailored by changing the GaAs temperature or by neutron bombardment. In the third section, we discuss possible lock-on mechanisms. 5 refs., 5 figs.

  13. Position sensitivity of the first SmartPET HPGe detector

    NASA Astrophysics Data System (ADS)

    Cooper, R. J.; Turk, G.; Boston, A. J.; Boston, H. C.; Cresswell, J. R.; Mather, A. R.; Nolan, P. J.; Hall, C. J.; Lazarus, I.; Simpson, J.; Berry, A.; Beveridge, T.; Gillam, J.; Lewis, R. A.

    2007-04-01

    In this paper we discuss the Smart Positron Emission Tomography (PET) imaging system being developed by the University of Liverpool in conjunction with CCLRC Daresbury Laboratory. We describe the motivation for the development of a semiconductor-based PET system and the advantages it will offer over current tomographs. Details of the detectors and associated electronics are discussed and results of high precision scans are presented. Analysis of this scan data has facilitated full characterization of the detector response function and calibration of the three-dimensional position sensitivity. This work presents the analysis of the depth sensitivity of the detector.

  14. 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.

  15. Development of a fast position-sensitive laser beam detector

    SciTech Connect

    Chavez, Isaac; Huang Rongxin; Henderson, Kevin; Florin, Ernst-Ludwig; Raizen, Mark G.

    2008-10-15

    We report the development of a fast position-sensitive laser beam detector. The detector uses a fiber-optic bundle that spatially splits the incident beam, followed by a fast balanced photodetector. The detector is applied to the study of Brownian motion of particles on fast time scales with 1 A spatial resolution. Future applications include the study of molecule motors, protein folding, as well as cellular processes.

  16. A novel method for assessing position-sensitive detector performance

    SciTech Connect

    Clinthorne, N.H.; Rogers, W.L.; Shao, L.; Hero, A.O. III; Koral, K.F.

    1989-02-01

    A marked point process model of a position-sensitive detector is developed which includes the effects of detector efficiency, spatial response, energy response, and source statistics. The average mutual information between the incident distribution of ..gamma.. rays and the detector response is derived and used as a performance index for detector optimization. A brief example is presented which uses this figure-of-merit for optimization of light guide dimensions for a modular scintillation camera.

  17. Two-dimensional position sensitive ionization chamber with GEM

    NASA Astrophysics Data System (ADS)

    Kitamura, Noritaka; Noro, Tetsuo; Sakaguchi, Satoshi; Takao, Hideaki; Nishio, Yasutaka

    2014-09-01

    We have been developing a multi-anode ionization chamber for Accelerator Mass Spectrometry (AMS) at Kyushu University. Furthermore, we are planning to construct a neutron detector with high position resolution by combining the chamber with Gas Electron Multiplier (GEM) and a neutron converter. One of purposes is the measurement of p-> , pn knockout reaction from unstable nuclei. The multi-anode ionization chamber is composed of subdivided multiple anodes, a cathode to produce an uniform electric field, and a Frisch grid. The chamber must have position sensitivity because obtaining a beam profile is required for AMS measurements, where counting loss should be avoided. Also in the case of the neutron detector, it is necessary to measure the position to deduce the scattering angles. We have recently established a two-dimensional position readout system by the following methods: the measurement of horizontal position is enabled by trimming some anodes into wedge-like shape, and vertical position can be determined by the ratio of induced charge on the grid to the total charge on anodes. In addition, improvement of S/N ratio is important for isotope separation and position resolution. We installed a rectangular-shaped GEM and tried improving S/N ratio by electron amplification.

  18. Wide Bandgap Extrinsic Photoconductive Switches

    SciTech Connect

    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 wide bandgap semiconductors 4H-SiC, 6H-SiC and 2H-GaN.

  19. 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.

  20. Wide Bandgap Extrinsic Photoconductive Switches

    SciTech Connect

    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 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.

  1. Development of the Position Sensitive Ionization Chamber for ANASEN

    NASA Astrophysics Data System (ADS)

    Gardiner, Hannah; Blackmon, Jeff; Deibel, Catherine; Gardiner, Emily; Lai, Jianping; Lauer, Amber; Linhardt, Laura; Macon, Kevin; Rasco, Charlie; Baby, Lagy; Koshchiy, Yevegn; Rogachev, Grigory; Santiago-Gonzales, Daniel; Wiedenhoever, Ingo; Bardayan, Dan; Matos, Milan

    2013-10-01

    The Array for Nuclear Astrophysics Studies with Exotic Nuclei (ANASEN) is a charged-particle detector array developed for reaction studies using radioactive ion beams to help improve understanding of the nuclear reactions important in stellar explosions. A gas-filled ionization chamber with two position-sensitive anode wire grid planes read out in 32 channels, and 12 alternating anode/cathode planes was developed and tested for use with ANASEN to identify the kinematic trajectory and atomic number of recoiling heavy ions by their relative energy loss. The position sensitive grids are arranged perpendicularly to each other in order to determine the x-y position of each ion with better than 4 mm resolution. This ionization chamber was tested using a stable beam of 12C at FSU. We report on the performance of this test experiment and plans for measurements with radioactive ion beams at FSU. Two other versions of the detector have been constructed and are now in place at the National Superconducting Cyclotron Laboratory and at the ATLAS accelerator facility at Argonne National Laboratory.

  2. Michrochannel plate for position sensitive alpha particle detection

    SciTech Connect

    Paul Hurley and James Tinsley

    2007-08-31

    This paper will describe the use of a microchannel plate (MCP) as the associated particle detector on a sealed tube neutron generator. The generator produces neutrons and associated alpha particles for use as a probe to locate and identify hidden explosives in associated particle imaging (API). The MCP measures the position in two dimensions and precise timing of the incident alpha particle, information which is then used to calculate the emission time and direction of the corresponding neutron. The MCP replaces the position-sensitive photomultipler tube (PSPMT) which, until recently, had been the only detector available for measuring position and timing for alpha particles in neutron generator applications. Where the PSPMT uses charge division for generating position information, a process that requires a first order correction to each pulse, the MCP uses delay-line timing, which requires no correction. The result is a device with an order of magnitude improvement in both position resolution and timing compared to the PSPMT. Hardware and software development and the measurements made to characterize the MCP for API applications are described.

  3. 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.

  4. Position-Sensitive Nuclear Spectroscopy with Pixel Detectors

    SciTech Connect

    Granja, Carlos; Vykydal, Zdenek; Jakubek, Jan; Pospisil, Stanislav

    2007-10-26

    State-of-the-art hybrid semiconductor pixel detectors such as Medipix2 are suitable for energy- and position-sensitive nuclear spectroscopy. In addition to excellent energy- and spatial-resolution, these devices can operate in spectroscopic, single-quantum counting and/or on-line tracking mode. A devoted compact USB-readout interface provides functionality and ease of operation. The compact and versatile Medipix2/USB radiation camera provides visualization, vacuum and room-temperature operation as a real-time portable active nuclear emulsion.

  5. Particle tracking with scintillating fibers and position sensitive photomultipliers

    SciTech Connect

    C.F. Perdrisat; R. Pourang; D. Koechner; D. Raine, III; B. Kross; S. Majewski; A. Weisenberger; R. Wojcik; K. Zorn; V. Punjabi; A. Day

    1991-11-01

    The use of position-sensitive phototubes in conjunction with scintillating plastic fibers for a particle tracking application in a future focal plane polarimeter (FPP) in the hadron arm of the hall A HRS 2 facility at the Continuous Electron Beam Accelerator Facility (CEBAF). Current results indicate that the design parameters of the FPP in the hadron arm of the double spectrometer facility HRS2 can be met with a design which couples round or square fibers 3 mm in size to Hamamatsu R4135 phototubes. Position resolutions {sigma}x or {sigma}y on the order of 0.6 mm are obtained in the phototubes. Detector structures with staggered double fiber layers lead to overall resolution of {sigma}=1 mm, and detection efficiencies close to 1. The characteristic speed of these detectors makes them particularly appropriate for the high rates which are expected with the 200-{micro}A continuous wave beam at CEBAF.

  6. Emulation workbench for position sensitive gaseous scintillation detectors

    NASA Astrophysics Data System (ADS)

    Pereira, L.; Margato, L. M. S.; Morozov, A.; Solovov, V.; Fraga, F. A. F.

    2015-12-01

    Position sensitive detectors based on gaseous scintillation proportional counters with Anger-type readout are being used in several research areas such as neutron detection, search for dark matter and neutrinoless double beta decay. Design and optimization of such detectors are complex and time consuming tasks. Simulations, while being a powerful tool, strongly depend on the light transfer models and demand accurate knowledge of many parameters, which are often not available. Here we describe an alternative approach based on the experimental evaluation of a detector using an isotropic point-like light source with precisely controllable light emission properties, installed on a 3D positioning system. The results obtained with the developed setup at validation conditions, when the scattered light is strongly suppressed show good agreement with simulations.

  7. Recent advances and future perspectives of position sensitive PMT

    NASA Astrophysics Data System (ADS)

    Pani, R.; Pellegrini, R.; Cinti, M. N.; Mattioli, M.; Trotta, C.; Montani, L.; Iurlaro, G.; Trotta, G.; D'Addio, L.; Ridolfi, S.; De Vincentis, G.; Weinberg, I. N.

    2004-01-01

    In recent years there has been a growing interest in developing compact gamma cameras to improve gamma ray imaging for application in nuclear medicine as well as in astrophysics, radiation physics and high energy physics. The gamma cameras based on position sensitive photomultipliers could be the best chance to obtain a realistic and low cost compact gamma camera. Since 1985 the development of position sensitive photo multiplier tubes (PSPMT) has shown the highest rate in technological advancement achieving very compact size (25 × 25 × 20 mm 3) by a novel charge multiplication system. The PSPMT shows the same advantages of a standard gamma camera with the additional possibility to utilize scintillation arrays with pixel dimension less than 1 mm, thus achieving sub-millimeter spatial resolution values. The last technological advance is a PSPMT with Flat Panel structure, named H8500. Its dimension is 50 × 50 mm 2 with a narrow peripheral dead zone to place closely different modules achieving large detection areas. In this paper the technological development of different PSPMT generations is reviewed and some measurements of the first Flat Panel PMT prototype are presented and compared with ones from previous generation. Flat Panel PMT could be the best trade-off between compactness, large detection areas, effective area (packing density) and imaging performance.

  8. Analysis of terahertz generation characteristic affected by injured photoconductive antenna

    NASA Astrophysics Data System (ADS)

    Li, Hui; Fan, Wen-hui; Liu, Jia

    2013-08-01

    In this paper, we deployed a home-made THz time-domain system and experimentally investigated the influence of impairment on photoconductive antenna. The low temperature grown GaAs photoconductive antenna (PCA) was used as THz emitter and a <110< ZnTe crystal modulating the probe beam to detect the THz field based on electro-optic sampling. By adjusting the position of laser spot on PCA gap, we found that the generated THz signal was quite different as the laser beam irradiating on different position of the antenna's gap. Moreover, we found that the small burned holes on the edge of both metal electrodes may affect the electric field of the antenna. Furthermore, we simulated the electric field of the PCA with a DC biased voltage applied across the electrodes, and found that the simulation results agreed with the experimental phenomenon, which can well demonstrated that the impairments on the antenna electrodes have a great influence on THz generation.

  9. 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

  10. 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.

  11. Photoconductive switching for high power microwave generation

    SciTech Connect

    Pocha, M.D.; Hofer, W.W.

    1990-10-01

    Photoconductive switching is a technology that is being increasingly applied to generation of high power microwaves. Two primary semiconductors used for these devices are silicon and gallium arsenide. Diamond is a promising future candidate material. This paper discusses the important material parameters and switching modes, critical issues for microwave generation, and future directions for this high power, photoconductive switching technology.

  12. Position sensitive detection of neutrons in high radiation background field

    SciTech Connect

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

    2014-01-15

    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) 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}.

  13. High gain photoconductive semiconductor switching

    SciTech Connect

    Zutavern, F.J.; Loubriel, G.M.; O'Malley, M.W.; Helgeson, W.D.; McLaughlin, D.L.

    1991-01-01

    Switching properties are reported for high gain photoconductive semiconductor switches (PCSS). A 200 ps pulse width laser was used in tests to examine the relations between electric field, rise time, delay, and minimum optical trigger energy for switches which reached 80 kV in a 50 {Omega} transmission line with rise times as short as 600 ps. Infrared photoluminescence was imaged during high gain switching providing direct evidence for current filamentation. Implications of these measurements for the theoretical understanding and practical development of these switches are discussed. 16 refs., 10 figs.

  14. ASIC for High Rate 3D Position Sensitive Detectors

    SciTech Connect

    Vernon, E.; De Geronimo, G.; Ackley, K.; Fried, J.; He, Z.; Herman, C.; Zhang, F.

    2010-06-16

    We report on the development of an application specific integrated circuit (ASIC) for 3D position sensitive detectors (3D PSD). The ASIC is designed to operate with pixelated wide bandgap sensors like Cadmium-Zinc-Telluride (CZT), Mercuric Iodide (Hgl2) and Thallium Bromide (TIBr). It measures the amplitudes and timings associated with an ionizing event on 128 anodes, the anode grid, and the cathode. Each channel provides low-noise charge amplification, high-order shaping with peaking time adjustable from 250 ns to 12 {micro}s, gain adjustable to 20 mV/fC or 120 mV/fC (for a dynamic range of 3.2 MeV and 530 keV in CZT), amplitude discrimination with 5-bit trimming, and positive and negative peak and timing detections. The readout can be full or sparse, based on a flag and single- or multi-cycle token passing. All channels, triggered channels only, or triggered with neighbors can be read out thus increasing the rate capability of the system to more than 10 kcps. The ASIC dissipates 330 mW which corresponds to about 2.5 mW per channel.

  15. Single photon emission imaging by position sensitive PMT

    NASA Astrophysics Data System (ADS)

    Pani, R.; Pellegrini, R.; Soluri, A.; De Vincentis, G.; Scafè, R.; Pergola, A.

    1998-02-01

    Position Sensitive Photo Multiplier Tube (PSPMT) represents a strong technological improvement for Nuclear Medicine imaging. Over the last 10 years Hamamatsu has developed a number of PSPMTs with different shapes and sizes, from 1 in. square up to more recent prototype of 8 in. diameter. The position is continuously detected by centroid method and spatial resolution represents its statistical uncertainty. By coupling PSPMTs to scintillating arrays it was possible to push PMTs near their intrinsic limit. A number of scintillating crystals arranged in a matrix were tested such as: YAP : Ce, NaI(Tl), CsI(Tl) and CsI(Na) with different pixel size (from 0.3×0.3 mm 2 to 2×2 mm 2) with overall dimension from 4×4 cm 2 up to 11 cm diameter. A number of applications in Nuclear Medicine were performed, such as miniature gamma cameras for radiopharmaceutical investigations on little animals where sub-millimeter spatial resolution values were carried out. More recently, the first prototype of dedicated gamma camera for scintimammography has been developed for small cancer detection in the breast.

  16. Next generation 1.5 microm terahertz antennas: mesa-structuring of InGaAs/InAlAs photoconductive layers.

    PubMed

    Roehle, H; Dietz, R J B; Hensel, H J; Böttcher, J; Künzel, H; Stanze, D; Schell, M; Sartorius, B

    2010-02-01

    Mesa-structuring of InGaAs/InAlAs photoconductive layers is performed employing a chemical assisted ion beam etching (CAIBE) process. Terahertz photoconductive antennas for 1.5 microm operation are fabricated and evaluated in a time domain spectrometer. Order-of-magnitude improvements versus planar antennas are demonstrated in terms of emitter power, dark current and receiver sensitivity. PMID:20174058

  17. READOUT ASIC FOR 3D POSITION-SENSITIVE DETECTORS.

    SciTech Connect

    DE GERONIMO,G.; VERNON, E.; ACKLEY, K.; DRAGONE, A.; FRIED, J.; OCONNOR, P.; HE, Z.; HERMAN, C.; ZHANG, F.

    2007-10-27

    We describe an application specific integrated circuit (ASIC) for 3D position-sensitive detectors. It was optimized for pixelated CZT sensors, and it measures, corresponding to an ionizing event, the energy and timing of signals from 121 anodes and one cathode. Each channel provides low-noise charge amplification, high-order shaping, along with peak- and timing-detection. The cathode's timing can be measured in three different ways: the first is based on multiple thresholds on the charge amplifier's voltage output; the second uses the threshold crossing of a fast-shaped signal; and the third measures the peak amplitude and timing from a bipolar shaper. With its power of 2 mW per channel the ASIC measures, on a CZT sensor Connected and biased, charges up to 100 fC with an electronic resolution better than 200 e{sup -} rms. Our preliminary spectral measurements applying a simple cathode/mode ratio correction demonstrated a single-pixel resolution of 4.8 keV (0.72 %) at 662 keV, with the electronics and leakage current contributing in total with 2.1 keV.

  18. Pulsed neutron imaging using 2-dimensional position sensitive detectors

    NASA Astrophysics Data System (ADS)

    Kiyanagi, Y.; Kamiyama, T.; Kino, K.; Sato, H.; Sato, S.; Uno, S.

    2014-07-01

    2-dimensional position sensitive detectors are used for pulsed neutron imaging and at each pixel of the detector a time of flight spectrum is recorded. Therefore, a transmission spectrum through the object has wavelength dependent structure reflecting the neutron total cross section. For such measurements, the detectors are required to have ability to store neutron events as a function of the flight time as well as to have good spatial resolution. Furthermore, high counting rate is also required at the high intensity neutron sources like J-PARC neutron source in Japan. We have developed several types of detectors with different characteristics; two counting type detectors for high counting rate with coarse spatial resolution and one camera type detector for high spatial resolution. One of counting type detectors is a pixel type. The highest counting rate is about 28 MHz. Better spatial resolution is obtained by a GEM detector. Effective area is 10 × 10 cm2, pixel size is 0.8 mm. The maximum counting rate is 3.65 MHz. To get higher spatial resolution we are now developing the camera type detector system using a neutron image intensifier, which have image integration function as a function of time of flight. We have succeeded to obtain time dependent images in this camera system. By using these detectors we performed transmission measurements for obtaining the crystallographic information and elemental distribution images.

  19. High resolution, position sensitive detector for energetic particle beams

    NASA Astrophysics Data System (ADS)

    Marsh, E. P.; Strathman, M. D.; Reed, D. A.; Morse, D. H.; Pontau, A. E.; Odom, R. W.

    1993-05-01

    The performance and design of an imaging position sensitive, particle beam detector will be presented. The detector is minimally invasive, operates over a wide dynamic range (> 10 10), and exhibits high spatial resolution. The secondary electrons produced when a particle beam passes through a thin foil are imaged using stigmatic ion optics onto a two-dimensional imaging detector. Due to the low scattering cross section of the 6 nm carbon foil the detector is a minimal perturbation on the primary beam. A prototype detector with an image resolution of approximately 5 μm for a field of view of 1 mm has been reported [R.W. Odom, M.D. Strathman, S.E. Buttrill, Jr., and S.M. Bauman, Nucl. Instr. and Meth. B44 (1990) 465]. A higher resolution detector for imaging small beams (< 50 μm) with an image resolution of better than 0.5 μm has since been developed and its design is presented.

  20. Carrier heating and negative photoconductivity in graphene

    SciTech Connect

    Heyman, J. N.; Stein, J. D.; Kaminski, Z. S.; Banman, A. R.; Massari, A. M.; Robinson, J. T.

    2015-01-07

    We investigated negative photoconductivity in graphene using ultrafast terahertz techniques. Infrared transmission was used to determine the Fermi energy, carrier density, and mobility of p-type chemical vapor deposition graphene samples. Time-resolved terahertz photoconductivity measurements using a tunable mid-infrared pump probed these samples at photon energies between 0.35 eV and 1.55 eV, approximately one-half to three times the Fermi energy of the samples. Although interband optical transitions in graphene are blocked for pump photon energies less than twice the Fermi energy, we observe negative photoconductivity at all pump photon energies investigated, indicating that interband excitation is not required to observe this effect. Our results are consistent with a thermalized free-carrier population that cools by electron-phonon scattering, but are inconsistent with models of negative photoconductivity based on population inversion.

  1. Persistent photoconductivity of ZnO

    NASA Astrophysics Data System (ADS)

    Laiho, R.; Stepanov, Yu. P.; Vlasenko, M. P.; Vlasenko, L. S.

    2009-12-01

    Persistent photoconductivity is observed in ZnO single crystals and ceramics together with persistence of electron paramagnetic resonance (EPR) spectra of defects and impurity centers. It is shown that when the light is switched on and off the microwave conductivity detected from absorption of the microwave field is well correlated with the dc-conductivity measured with electrical contacts applied to the sample. The microwave photoconductivity arises together with light-induced EPR spectra and persists after switching off the light. Coexistence of the conductivity and EPR spectra shows that the photoexcited electrons cannot return back to paramagnetic centers. The persistent photoconductivity in ZnO ceramics is large in comparison with the effect observed in powders prepared from the same material and in ZnO single crystals. This suggests that surface conductivity is the dominant mechanism of persistent photoconductivity in ZnO.

  2. 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

    ... MANAGEMENT Submission for Review: Information Collection; Questionnaire for Non-Sensitive Positions (SF 85...), Office of Management and Budget (OMB) Control No. 3206-NEW, for Questionnaire for Non-Sensitive Positions...@opm.gov . SUPPLEMENTARY INFORMATION: The Questionnaire for Non-Sensitive Positions, SF 85, housed in...

  3. Terahertz photoconductive antenna with metal nanoislands.

    PubMed

    Park, Sang-Gil; Choi, Yongje; Oh, Young-Jae; Jeong, Ki-Hun

    2012-11-01

    This work presents a nanoplasmonic photoconductive antenna (PCA) with metal nanoislands for enhancing terahertz (THz) pulse emission. The whole photoconductive area was fully covered with metal nanoislands by using thermal dewetting of thin metal film at relatively low temperature. The metal nanoislands serve as plasmonic nanoantennas to locally enhance the electric field of an ultrashort pulsed pump beam for higher photocarrier generation. The plasmon resonance of metal nanoislands was achieved at an excitation laser wavelength by changing the initial thickness of metal film. This nanoplasmonic PCA shows two times higher enhancement for THz pulse emission power than a conventional PCA. This work opens up a new opportunity for plasmon enhanced large-aperture THz photoconductive antennas. PMID:23187370

  4. Photoelectron imaging of cells: photoconductivity extends the range of applicability.

    PubMed Central

    Habliston, D L; Hedberg, K K; Birrell, G B; Rempfer, G F; Griffith, O H

    1995-01-01

    Photoelectron imaging is a sensitive surface technique in which photons are used to excite electron emission. This novel method has been applied successfully in studies of relatively flat cultured cells, viruses, and protein-DNA complexes. However, rounded-up cell types such as tumor cells frequently are more difficult to image. By comparing photoelectron images of uncoated and metal-coated MCF-7 human breast carcinoma cells, it is shown that the problem is specimen charging rather than a fundamental limitation of the electron imaging process. This is confirmed by emission current measurements on uncoated monolayers of MCF-7 carcinoma cells and flatter, normal Wi-38 fibroblasts. We report here that sample charging in photoelectron microscopy can be eliminated in most specimens by simultaneous use of two light sources--the standard UV excitation source (e.g., 254 nm) and a longer wavelength light source (e.g., 325 nm). The reduction in sample charging results largely from enhanced photoconduction in the bulk sample and greatly extends the range of cells that can be examined by photoelectron imaging. The contributions of photoconductivity, the electric field of the imaging system, and the short escape depths of the photoelectrons combine to make photoelectron imaging a uniquely sensitive technique for the study of biological surfaces. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 PMID:8534832

  5. 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.

  6. Parasitic mode losses versus signal sensitivity in beam position monitors

    NASA Astrophysics Data System (ADS)

    Denard, J. C.; Bane, K. L.; Bijleveld, J.; Hutton, A. M.; Pellegrin, J. I.; Rivkin, L.; Wang, P.; Weaver, J. N.

    1985-04-01

    A beam position monitor (BPM) for a storage or damping ring may be subject to heating problems due to the parasitic mode (PM) losses, beam interception and synchrotron radiation interception. In addition, high PM losses can cause beam instabilities under some conditions. Recessing and/or masking the BPM may increase the PM losses in the process of solving the latter two problems. Three complementary methods for estimating the PM losses and for improving the design of a stripline directional coupler type of BPM: bench measurements, computer modeling (TBCI), and an equivalent circuit representation are presented. These methods lead to a decrease in PM losses without significant reduction in output signal for the north Stanford Linear Collider (SLC) damping ring BPMs.

  7. Trap-induced photoconductivity in singlet fission pentacene diodes

    SciTech Connect

    Qiao, Xianfeng Zhao, Chen; Chen, Bingbing; Luan, Lin

    2014-07-21

    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, leading 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.

  8. Fielding and calibration issues for diamond photoconducting detectors

    SciTech Connect

    Spielman, R.B.; Ruggles, L.E.; Pepping, R.E.; Breeze, S.F.; McGurn, J.S.; Struve, K.W.

    1996-12-01

    Diamond photoconducting detectors are routinely fielded as soft x-ray diagnostics on Sandia`s Saturn facility. We have developed an improved detector mount that provides a 200-ps time response, is easily cleanable, and is very rugged. In addition, we have developed a new, fast insertion unit to apply bias voltage to the detectors. Absolute calibration of the PCDs is carried out either at the Brookhaven National Synchrotron Light Source or on Sandia`s laser calibration facility. We are now fielding diamond elements that have the dimensions 1x3x0.5 nun and 1x1xO.5 mm. We are neutron damaging some of the 1x1xO.5-mm detectors to reduce their sensitivity. We can tailor PCD sensitivity by adjusting element size and neutron damage level.

  9. Photoconductive terahertz near-field detector with a hybrid nanoantenna array cavity

    DOE PAGES

    Mitrofanov, Oleg; Brener, Igal; Luk, Ting S.; Reno, John L.

    2015-11-19

    Nanoscale structuring of optical materials leads to modification of their properties and can be used for improving efficiencies of photonic devices and for enabling new functionalities. In ultrafast optoelectronic switches for generation and detection of terahertz (THz) radiation, incorporation of nanostructures allows us to overcome inherent limitations of photoconductive materials. We propose and demonstrate a nanostructured photoconductive THz detector for sampling highly localized THz fields, down to the level of λ/150. The nanostructure that consists of an array of optical nanoantennas and a distributed Bragg reflector forms a hybrid cavity, which traps optical gate pulses within the photoconductive layer. Themore » effect of photon trapping is observed as enhanced absorption at a designed wavelength. This optically thin photoconductive THz detector allows us to detect highly confined evanescent THz fields coupled through a deeply subwavelength aperture as small as 2 μm (λ/150 at 1 THz). As a result, by monolithically integrating the THz detector with apertures ranging from 2 to 5 μm we realize higher spatial resolution and higher sensitivity in aperture-type THz near-field microscopy and THz time-domain spectroscopy.« less

  10. Photoconductive terahertz near-field detector with a hybrid nanoantenna array cavity

    SciTech Connect

    Mitrofanov, Oleg; Brener, Igal; Luk, Ting S.; Reno, John L.

    2015-11-19

    Nanoscale structuring of optical materials leads to modification of their properties and can be used for improving efficiencies of photonic devices and for enabling new functionalities. In ultrafast optoelectronic switches for generation and detection of terahertz (THz) radiation, incorporation of nanostructures allows us to overcome inherent limitations of photoconductive materials. We propose and demonstrate a nanostructured photoconductive THz detector for sampling highly localized THz fields, down to the level of λ/150. The nanostructure that consists of an array of optical nanoantennas and a distributed Bragg reflector forms a hybrid cavity, which traps optical gate pulses within the photoconductive layer. The effect of photon trapping is observed as enhanced absorption at a designed wavelength. This optically thin photoconductive THz detector allows us to detect highly confined evanescent THz fields coupled through a deeply subwavelength aperture as small as 2 μm (λ/150 at 1 THz). As a result, by monolithically integrating the THz detector with apertures ranging from 2 to 5 μm we realize higher spatial resolution and higher sensitivity in aperture-type THz near-field microscopy and THz time-domain spectroscopy.

  11. Understanding the effect of flower extracts on the photoconducting properties of nanostructured TiO2.

    PubMed

    Ansari, S G; Bhayana, Laitka; Umar, Ahmad; Al-Hajry, A; Al-Deyab, Salem S; Ansari, Z A

    2012-10-01

    Here we report an easy method to improve the optoelectronic properties of commercially available TiO2 nanopowder using extracts of various flowers viz. Calendula Orange (CO), Calendula Yellow (CY), Dahlia Violet (DV), Dahlia Yellow (DY), Rabbit flower (RF), Sweet Poppy (SP), Sweet Williams (SW) and their Mixed Extracts (ME). Various analysis techniques such as UV-Vis, FTIR, FESEM, XRD, and Raman spectroscopy were used to characterize for elemental, structural and morphological properties of the unmixed/mixed TiO2 nanopowder. TiO2 nanopowder was also calcined at 550 degrees C. Thick films of the these unmixed/mixed powder were printed, using conventional screen printing method, on fluorine doped tin oxide (FTO) substrate with organic binders and dried at 45 degrees C. The photoconducting properties are investigated as a function of wavelength from ultra-violet (UV) to infra-red (IR) region at a constant illumination intensity. Photocurrent gradually decreases when irradiated from UV to IR region. In case of unmixed and uncalcined TiO2, conductance decreased continuously whereas when extracts are added, a flat region of conductance is observed. The overall effect of extracts (colour pigments) is seen as an increase in the photoconductance. Highest photoconductance is observed in case of DY flower extract. Anthocyanins, present in flowers are known to have antioxidative properties and hence can contribute in photoconduction by reducing the surface adsorbed oxygen. This investigation indicates the potential use of flower extracts for dye sensitized solar cell (DSSC).

  12. Understanding the effect of flower extracts on the photoconducting properties of nanostructured TiO2.

    PubMed

    Ansari, S G; Bhayana, Laitka; Umar, Ahmad; Al-Hajry, A; Al-Deyab, Salem S; Ansari, Z A

    2012-10-01

    Here we report an easy method to improve the optoelectronic properties of commercially available TiO2 nanopowder using extracts of various flowers viz. Calendula Orange (CO), Calendula Yellow (CY), Dahlia Violet (DV), Dahlia Yellow (DY), Rabbit flower (RF), Sweet Poppy (SP), Sweet Williams (SW) and their Mixed Extracts (ME). Various analysis techniques such as UV-Vis, FTIR, FESEM, XRD, and Raman spectroscopy were used to characterize for elemental, structural and morphological properties of the unmixed/mixed TiO2 nanopowder. TiO2 nanopowder was also calcined at 550 degrees C. Thick films of the these unmixed/mixed powder were printed, using conventional screen printing method, on fluorine doped tin oxide (FTO) substrate with organic binders and dried at 45 degrees C. The photoconducting properties are investigated as a function of wavelength from ultra-violet (UV) to infra-red (IR) region at a constant illumination intensity. Photocurrent gradually decreases when irradiated from UV to IR region. In case of unmixed and uncalcined TiO2, conductance decreased continuously whereas when extracts are added, a flat region of conductance is observed. The overall effect of extracts (colour pigments) is seen as an increase in the photoconductance. Highest photoconductance is observed in case of DY flower extract. Anthocyanins, present in flowers are known to have antioxidative properties and hence can contribute in photoconduction by reducing the surface adsorbed oxygen. This investigation indicates the potential use of flower extracts for dye sensitized solar cell (DSSC). PMID:23421149

  13. Terahertz-frequency photoconductive detectors fabricated from metal-organic chemical vapor deposition-grown Fe-doped InGaAs

    NASA Astrophysics Data System (ADS)

    Hatem, O.; Cunningham, J.; Linfield, E. H.; Wood, C. D.; Davies, A. G.; Cannard, P. J.; Robertson, M. J.; Moodie, D. G.

    2011-03-01

    We report the detection of terahertz frequency radiation using photoconductive antennas fabricated from Fe-doped InGaAs, grown by metal-organic chemical vapor deposition. Coherent photoconductive detection is demonstrated using femtosecond laser pulses centered at either an 800 or a 1550 nm wavelength. The InGaAs resistivity and the sensitivity of photoconductive detection are both found to depend on the Fe-doping level. We investigate a wide range of probe laser powers, finding a peak in detected signal for ˜5 mW probe power, followed by a reduction at larger powers, attributed to screening of the detected THz field by photo-generated carriers in the material. The measured signal from Fe:InGaAs photoconductive detectors excited at 800 nm is four times greater than that from a low-temperature-grown GaAs photodetector with identical antenna design, despite the use of a ten times smaller probe power.

  14. 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.

  15. Selectively plated infrared-sensitive lead sulfide layers

    NASA Astrophysics Data System (ADS)

    Subramanian, V.; Murali, K. R.; Rangarajan, N.; Lakshmanan, A. S.

    1994-10-01

    Lead chalcogenides are well-known photoconductors in the infrared region. Lead sulfide detectors occupy an important position among infrared detectors owing to their high sensitivity in the near infrared region (1 - 3.2 microns), room temperature operation, low noise and ease of preparation. In this paper, we report for the first time the preparation of infrared sensitive photoconductive lead sulfide films by the swab plating technique. Adherent, non-porous `p' type lead sulfide films of thickness 3 - 4 microns were obtained. These films, after heat- treatment at 550 degree(s)C, showed a dark resistance of 25 - 30 kilo-ohms with a photosensitivity of 0.28. The films have been characterized by XRD, optical and photoconductivity measurements.

  16. Nano photoconductive switches for microwave applications

    NASA Astrophysics Data System (ADS)

    Tripon-Canseliet, C.; Faci, S.; Decoster, D.; Pagies, A.; Yoon, S. F.; Pey, K. L.; Chazelas, J.

    2013-01-01

    This paper addresses the interaction between light wave technologies and semiconductors devices at the nanoscale. Research works aiming at the development of emerging 1D and 2D nano materials such as nanodots, nanowires, nanotubes and nanoribbons open the way to overcome the performances bottleneck of conventional microwave photoconductive switches. Such new materials offer new opportunities for the confinement of light/matter interaction and exhibit interesting energy band diagram in an optical wavelength spectrum covering visible to NIR. Strong material interests stays for the generation of very high local density of carriers in contrast with a high dark resistivity, in association with a high carrier mobility. These challenges can be reached today thanks to nanotechnology processes with a high compatibility constraint with submicrometer light coupling solutions and microwave devices and circuits technologies. Modeling and design tools dedicated to photoconductive effect description at nanometer scale, for its implementation in passive and active components must be set up in order to exalt this effect for microwave signal processing functionalities such as switching, generation, amplification and emission over a large frequency bandwidth. This paper will report on latest demonstrations of high performance photoconductive switches for high frequency applications at 0.8μm and 1.5μm based on LT-GaAs, GaAs nanowires and GaInAsSb semiconductor materials.

  17. Effect of positive and negative defocus on contrast sensitivity in myopes and non-myopes.

    PubMed

    Radhakrishnan, Hema; Pardhan, Shahina; Calver, Richard I; O'Leary, Daniel J

    2004-01-01

    This study investigated the effect of lens induced defocus on the contrast sensitivity function in myopes and non-myopes. Contrast sensitivity for up to 20 spatial frequencies ranging from 1 to 20 c/deg was measured with vertical sine wave gratings under cycloplegia at different levels of positive and negative defocus in myopes and non-myopes. In non-myopes the reduction in contrast sensitivity increased in a systematic fashion as the amount of defocus increased. This reduction was similar for positive and negative lenses of the same power (p = 0.474). Myopes showed a contrast sensitivity loss that was significantly greater with positive defocus compared to negative defocus (p = 0.001). The magnitude of the contrast sensitivity loss was also dependent on the spatial frequency tested for both positive and negative defocus. There was significantly greater contrast sensitivity loss in non-myopes than in myopes at low-medium spatial frequencies (1-8 c/deg) with negative defocus. Latent accommodation was ruled out as a contributor to this difference in myopes and non-myopes. In another experiment, ocular aberrations were measured under cycloplegia using a Shack-Hartmann aberrometer. Modulation transfer functions were calculated using the second order term for defocus as well as the fourth order Zernike term for spherical aberration. The theoretical maximal contrast sensitivity based on aberration data predicted the measured asymmetry in contrast sensitivity to positive and negative defocus that was observed in myopic subjects. The observed asymmetry in contrast sensitivity with positive and negative defocus in myopes may be linked to the altered accommodative response observed in this group.

  18. Photoconductivity of organic polymer films doped with porous silicon nanoparticles and ionic polymethine dyes

    SciTech Connect

    Davidenko, N. A. Skrichevsky, V. A.; Ishchenko, A. A.; Karlash, A. Yu.; Mokrinskaya, E. V.

    2009-05-15

    Features of electrical conductivity and photoconductivity of polyvinylbutyral films containing porous silicon nanoparticles and similar films doped with cationic and anionic polymethine dyes are studied. Sensitization of the photoelectric effect by dyes with different ionicities in films is explained by the possible photogeneration of holes and electrons from dye molecules and the intrinsic bipolar conductivity of porous silicon nanoparticles. It is assumed that the electronic conductivity in porous silicon nanoparticles is higher in comparison with p-type conductivity.

  19. A position sensitive time of flight detector for heavy ion ERD

    NASA Astrophysics Data System (ADS)

    Eschbaumer, S.; Bergmaier, A.; Dollinger, G.

    2016-03-01

    A new 2D position sensitive time of flight detector for heavy ion ERD has been developed. The detector features separate time and position measurement in a straight geometry. An electrostatic lens focuses the secondary electrons ejected from a carbon foil onto a channel plate stack maintaining the position information despite the electron momentum distribution. For position readout a 2D Backgammon anode is used. A position resolution of <0.6 mm (FWHM) and a time resolution of 96 ps (FWHM) is demonstrated.

  20. DETECTORS AND EXPERIMENTAL METHODS: New test and analysis of position-sensitive-silicon-detector

    NASA Astrophysics Data System (ADS)

    Feng, Lang; Ge, Yu-Cheng; Wang, He; Fan, Feng-Ying; Qiao, Rui; Lu, Fei; Song, Yu-Shou; Zheng, Tao; Ye, Yan-Lin

    2009-01-01

    We have tested and analyzed the properties of two-dimensional Position-Sensitive-silicon-Detector (PSD) with new integrated preamplifiers. The test demonstrates that the best position resolution for 5.5 MeV α particles is 1.7 mm (FWHM), and the best energy resolution is 2.1%, which are notably better than the previously reported results. A scaling formula is introduced to make the absolute position calibration.

  1. Electronic interactions in metal complexed photoconducting polymers : a ZINDO study.

    SciTech Connect

    Manas, E. S.; Chen, L. X.; Chemistry; Univ. of Pennsylvania School of Medicine

    2000-12-01

    Semi-empirical (INDO/s) calculations have been conducted on molecular fragments with zero to three phenylenevinylene (PV) units attached to 4 and 4{prime} positions of a 2,2{prime}-bipyridine (bpy) group, with and without chelated metal ions, mimicking metal-free and metal-chelated photoconducting polymers 1 and 2 [Chen et al., J. Phys. Chem. B 104 (2000) 1950]. The calculations suggest that: (1) a global lowering of the molecular orbital energy levels due to metal-chelation is responsible for the observed red-shift in the lowest energy transitions; and (2) metal chelation attenuates {pi}-electron delocalization. The relevance of these effects to photoluminescence of metal-chelated polymers is also discussed.

  2. A method of monitoring the temperature of the photoconductive antenna

    NASA Astrophysics Data System (ADS)

    Liu, Hong; Wang, Yiqi; Li, Zhou; Bai, Yang; Pu, Ting; Kuang, Tingting; Chen, Kejian

    2014-11-01

    Photoconductive antenna (PCA), as the most widely used emitter (or detector) in Terahertz time-domain spectroscopy (TDS) system, virtually acts as a semiconductor switch, whose electrical conductivity controlled by pump light. At the same time, the heat caused by the pump light and the electrical bias will be stacked in a tiny area. Inevitably, the thermal effects, which may reduce the performance of PCA and the operational lifetime of device, need to be considered, especially for that generated by a compact package fiber-pigtailed photoconductive antenna. Nonetheless, there still lacks of relevant reports about real-time temperature monitoring for PCA. This paper proposes a method to obtain the temperature information by observing the temperature dependent frequency drifting of radiation spectroscopy. In other words, it converts the temperature information via analyzing the radiation spectrum of the conventional TDS system. In this work, we simulate a design of meta-atom-loaded PCA with indium antimonide (InSb). As a kind of temperature-dependent permittivity of the semiconductor, InSb is stuffed into the gap of split-ring resonator (SRR). When the temperature increases from 300K to 380 K, the resonance frequency shifts from 0.582THz to 0.678THz (a shift more than 16%), calculated by the commercial software-CST. The significant blue shift is caused by the SRR loading temperature sensitive materials, well analyzed by the LC resonant circuit model. Then, one can clearly obtain the actual antenna temperature from the radiation spectrum through the relationship between temperature and resonance frequency. Always, this simply method could be applied to shift the peak frequency of spectrum for various applications.

  3. Effect of diffusion on the photoconductivity of thin films

    SciTech Connect

    Hughes, R. C.; Sokel, R. J.

    1980-01-01

    The equations governing time dependent and steady state photoconductivity are solved analytically for some approxiations and numerically in exact form. The diffusion terms are shown to be important especially in thin films. Some data of Farmer and Lee on photoconductivity in MOS structures is reinterpreted with losses due to diffusion to the contacts included.

  4. A Beta-Particle Hodoscope Constructed Using Scintillating Optical Fibers and Position Sensitive Photomultiplier Tubes

    SciTech Connect

    Orrell, John L.; Aalseth, Craig E.; Day, Anthony R.; Fast, Jim; Hossbach, Todd W.; Lidey, Lance S.; Ripplinger, Mike D.; Schrom, Brian T.

    2006-09-19

    A hodoscopic detector was constructed using a position-sensitive plastic scintillator active area to determine the location of beta-active micron-sized particulates on air filters. The ability to locate beta active particulates on airsample filters is a tool for environmental monitoring of anthropogenic production of radioactive material. A robust, field-deployable instrument can provide localization of radioactive particulate with position resolution of a few millimeters. The detector employs a novel configuration of scintillating plastic elements usually employed at much higher charged particle energies. A filter is placed on this element for assay. The detector is intended to be sensitive to activity greater than 1 Bq. The physical design, position reconstruction method, and expected detector sensitivity are reported.

  5. Photoconductivities in monocrystalline layered V2O5 nanowires grown by physical vapor deposition

    PubMed Central

    2013-01-01

    Photoconductivities of monocrystalline vanadium pentoxide (V2O5) nanowires (NWs) with layered orthorhombic structure grown by physical vapor deposition (PVD) have been investigated from the points of view of device and material. Optimal responsivity and gain for single-NW photodetector are at 7,900 A W-1 and 30,000, respectively. Intrinsic photoconduction (PC) efficiency (i.e., normalized gain) of the PVD-grown V2O5 NWs is two orders of magnitude higher than that of the V2O5 counterpart prepared by hydrothermal approach. In addition, bulk and surface-controlled PC mechanisms have been observed respectively by above- and below-bandgap excitations. The coexistence of hole trapping and oxygen sensitization effects in this layered V2O5 nanostructure is proposed, which is different from conventional metal oxide systems, such as ZnO, SnO2, TiO2, and WO3. PMID:24160337

  6. 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.

  7. 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.

  8. 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.

  9. Sensitization to petrolatum: an unusual cause of false-positive drug patch-tests.

    PubMed

    Ulrich, G; Schmutz, J L; Trechot, Ph; Commun, N; Barbaud, A

    2004-09-01

    We report on an unexpected sensitization to petrolatum diagnosed with the occurrence of multiple nonrelevant and false-positive drug patch-tests performed while investigating a patient suffering from many cutaneous adverse drug reactions. All the positive drug patch-tests were prepared with GILBERT vaseline. This petrolatum reaction is positive as it was tested with five other brands of petrolatums a few months later. As the same petrolatums, but from different batches were tested, patch-tests with GILBERT petrolatum were doubtful, while other petrolatums were positive. White petrolatum is a mixture of semisolid hydrocarbons of the methane series. The sensitizing impurities of petrolatum are polycyclic aromatic hydrocarbons, e.g. phenanthrene derivatives. The purity of petrolatum depends on both the petroleum stock and on the production and packaging methods. Even if rare, contact sensitization to petrolatum can disturb the interpretation of drug patch-tests. It is necessary in the interpretation of drug patch-tests to test both in petrolatum and other vehicles and with all the different petrolatums used in preparing the material for drug patch-tests. So, it is essential to advise the patients sensitized to petrolatum to remove all the topical drugs, such as all the cosmetics, which contain petrolatum in their formulation.

  10. 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)…

  11. 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…

  12. Sensitivity of the ice-divide position in Greenland to climate change

    SciTech Connect

    Anandakrishnan, S.; Alley, R.B.; Waddington, E.D. |

    1994-03-01

    Model calculations of depth-age relations for deep ice cores in central Greenland are sensitive to stability of the ice-divide position. In addition, the folding of layers observed in the deep ice could be instigated by divide migration changing the velocity and particle paths of ice flow. We use simple steady-state calculations to show that lateral divide migration of between 10 km and 50 km and elevation change of approximately 100 m is likely on glacial-interglacial time scales, enough to affect model dating. The ice-divide location appears to be most sensitive to the position of the ice-sheet margins. By contrast, the ice-divide elevation is most sensitive to the accumulation rate, the temperature profile, and the ice-stiffness profile.

  13. Few layer graphene to graphitic films: infrared photoconductive versus bolometric response

    NASA Astrophysics Data System (ADS)

    Kurra, Narendra; Bhadram, Venkata Srinu; Narayana, Chandrabhas; Kulkarni, Giridhar U.

    2012-12-01

    We report a comparative study of the performance of infrared (IR) photoconductive and bolometric detectors fabricated from few layer graphene (FLG) to graphitic films obtained by different methods. FLG films grown directly on insulating substrates with the aid of residual hydrocarbons and polymethylmethacrylate (PMMA) carbon sources show an IR photoresponse of 73% which is far higher compared to the FLG films (6-14%) obtained by CVD and Scotch tape methods. The photoconductive nature of FLG films is due to generation of photoexcited charge carriers. On the other hand, the photoresponse of the bulk graphitic films is bolometric in nature where the resistance changes are due to thermal effects. The IR photoresponse from these graphitic films is correlated with the Raman peak intensities which are very sensitive to the nature of the FLG.We report a comparative study of the performance of infrared (IR) photoconductive and bolometric detectors fabricated from few layer graphene (FLG) to graphitic films obtained by different methods. FLG films grown directly on insulating substrates with the aid of residual hydrocarbons and polymethylmethacrylate (PMMA) carbon sources show an IR photoresponse of 73% which is far higher compared to the FLG films (6-14%) obtained by CVD and Scotch tape methods. The photoconductive nature of FLG films is due to generation of photoexcited charge carriers. On the other hand, the photoresponse of the bulk graphitic films is bolometric in nature where the resistance changes are due to thermal effects. The IR photoresponse from these graphitic films is correlated with the Raman peak intensities which are very sensitive to the nature of the FLG. Electronic supplementary information (ESI) available: The Raman spectrum of the FLG on the Ni surface (before etching) is shown in Fig. S1. The thickness and mobility of the FLG films are provided in Fig. S2 and S3 respectively. The sensitivity of the RHC-FLG towards the IR radiation emitted by an

  14. Photoconductivities in MoS2 Nanoflake Photoconductors

    NASA Astrophysics Data System (ADS)

    Shen, Wei-Chu; Chen, Ruei-San; Huang, Ying-Sheng

    2016-03-01

    Photoconductivities in molybdenum disulfide (MoS2) layered nanostructures with two-hexagonal crystalline structure prepared by mechanical exfoliation were investigated. The photoconductor-type MoS2 nanoflakes exhibit remarkable photoresponse under the above bandgap excitation wavelength of 532 nm at different optical intensity. The photocurrent responsivity and photoconductive gain of nanoflakes can reach, respectively, 30 AW-1 and 103 at the intensity of 50 Wm-2, which are several orders of magnitude higher than those of their bulk counterparts. The vacuum-enhanced photocurrent and power-independent responsivity/gain indicate a surface-controlled photoconduction mechanism in the MoS2 nanomaterial.

  15. Position-sensitive detectors of the detector group at Jülich

    NASA Astrophysics Data System (ADS)

    Engels, R.; Clemens, U.; Kemmerling, G.; Nöldgen, H.; Schelten, J.

    2009-06-01

    The detector group of the Central Institute of Electronics at the Forschungszentrum Jülich GmbH was founded in 1968. First developments aimed at a detector system with a position-sensitive BF 3 proportional counter for small-angle neutron scattering, which was later used at a beamline of the research reactor FRJ2. At the end of the 1970s first measurements were carried out with photomultiplier (PM)-based detector systems linked with a LiI crystal from Harshaw. Based on this experience we started with the spectrum of position-sensitive neutron scintillation detectors, which have been developed and designed in our institute during the last three decades comprising several high-resolution linear and two-dimensional detectors. The general design of those detectors is based on a modified Anger principle using an array of PMs and a 1 mm 6Li glass scintillator. The sensitive detector area varies on the type of the PMs used and is related to the spatial resolution of the detector type. The neutron sensitivity at 1 Å is about 65% and the remaining gamma sensitivity is less than 10 -4 with a maximum count rate up to 500 kHz depending on the used detector system.

  16. Position sensitivity in 3"×3" Spectroscopic LaBr3:Ce Crystals

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    The position sensitivity of a thick, cylindrical and continuous 3" × 3" (7.62 cm × 7.62 cm) LaBr3:Ce crystal with diffusive surfaces was investigated. Nuclear physics basic research uses thick LaBr3:Ce crystals (> 3cm) to measure medium or high energy gamma rays (0.5 MeV < Eγ< 20 MeV). In the first measurement the PMT photocathode entrance window was covered by black absorber except for a small window 1 cm × 1cm wide. A complete scan of the detector over a 0.5 cm step grid was performed. The data show that even in a 3" thick LaBr3:Ce crystal with diffusive surfaces the position of the full energy peak centroid depends on the source position. The position of the full energy peak centroids are sufficient to identify the collimated gamma source position. The crystal was then coupled to four Position Sensitive Photomultipliers (PSPMT). We acquired the signals from the 256 segments of the four PSPMTs grouping them into 16 elements. An event by event analysis shows a positon resolution of the order of 2 cm.

  17. 2 Dimensional position sensitive XAFS by using in-house X-ray spectrometer

    NASA Astrophysics Data System (ADS)

    Shinoda, Kozo; Suzuki, Shigeru; Kuribayashi, Masaru; Taguchi, Takeyoshi

    2009-09-01

    Position sensitive XAFS measurements by using the in-house X-ray spectrometer and the position sensitive X-ray detector were attempted. The in-house spectrometer produces monochromized divergent X-ray beam. Therefore, an extended direct-beam image projected on the detector can be taken, and its extension rate is depending on the arrangement of the sample and the detector. A position sensitive XAFS measurement was demonstrated by using Ni metal foil and NiO powder as a model sample. Ge(220) or Si(400) Johansson-type bent single-crystal was used as monochromator, and Mo and LaB6 were used as the target and filament, respectively. Tube voltage and current were operated at 16 kV and 100 mA (1.6 kW). XAFS spectra were measured by transmission-mode with sample set/reset method and required time of each experiment is about 6 hours in total. It was confirmed that metal and oxide spectra with enough quality for structural analysis were clearly separated by each position in the sample.

  18. Position sensitive x-ray spectrophotometer using microwave kinetic inductance detectors

    SciTech Connect

    Mazin, Benjamin A.; Bumble, Bruce; Day, Peter K.; Eckart, Megan E.; Golwala, Sunil; Zmuidzinas, Jonas; Harrison, Fiona A.

    2006-11-27

    The surface impedance of a superconductor changes when energy is absorbed and Cooper pairs are broken to produce single electron (quasiparticle) excitations. This change may be sensitively measured using a thin-film resonant circuit called a microwave kinetic inductance detector (MKID). The practical application of MKIDs for photon detection requires a method of efficiently coupling the photon energy to the MKID. The authors present results on position sensitive x-ray detectors made by using two aluminum MKIDs on either side of a tantalum photon absorber strip. Diffusion constants, recombination times, and energy resolution are reported. MKIDs can easily be scaled into large arrays.

  19. A multiplex readout method for position sensitive boron coated straw neutron detector

    NASA Astrophysics Data System (ADS)

    Yu, Hao; Gong, Hui; Li, Jianmin; Wang, Yongqiang; Wang, Xuewu; Li, Yuanjing; Kang, Kejun

    2015-10-01

    A 1 m×1 m boron coated straw neutron detector is expected to be used to build the small-angle neutron scattering (SANS) instrument of the Compact Pulsed Hadron Source (CPHS) in Tsinghua University. A multiplex readout method based on summing circuits in columns and rows is studied for this large area position sensitive detector. In this method, the outputs of charge sensitive preamplifiers are combined by columns and rows at two ends of the detector, and then the shaped signals are sampled by flash ADCs. With the position reconstructed algorithm implemented in FPGA which analyzes the charge division and column and row number of signals, the 3-D position information of neutron events can be obtained. The position resolution and counting rate performance of this method are analyzed, and the comparison to the delay-line readout method is also given. With the multiplex readout method, the scale of readout electronics can be greatly reduced and a good position resolution can be reached. A readout electronics system for a detector module which consists 4 × 10 straw tubes is designed based on this method, and the test with neutron beam shows an average 3-D spatial resolution of 4 × 4 × 6.8mm3.

  20. Compensation of optode sensitivity and position errors in diffuse optical tomography using the approximation error approach.

    PubMed

    Mozumder, Meghdoot; Tarvainen, Tanja; Arridge, Simon R; Kaipio, Jari; Kolehmainen, Ville

    2013-01-01

    Diffuse optical tomography is highly sensitive to measurement and modeling errors. Errors in the source and detector coupling and positions can cause significant artifacts in the reconstructed images. Recently the approximation error theory has been proposed to handle modeling errors. In this article, we investigate the feasibility of the approximation error approach to compensate for modeling errors due to inaccurately known optode locations and coupling coefficients. The approach is evaluated with simulations. The results show that the approximation error method can be used to recover from artifacts in reconstructed images due to optode coupling and position errors.

  1. Evaluation of a Compton scattering camera using 3-D position sensitive CdZnTe detectors

    NASA Astrophysics Data System (ADS)

    Du, Y. F.; He, Z.; Knoll, G. F.; Wehe, D. K.; Li, W.

    2001-01-01

    A CZT Compton Camera (CCC) is being built using two three-dimensional (3-D) position-sensitive CZT detectors. Expected system performance was analyzed by analytical and Monte Carlo approaches. Based on the measurement of detector energy and position resolution, the expected angular resolution is ˜3° and ˜2° for a ±30° FOV for 511 keV and 1 MeV γ-rays, respectively. The intrinsic efficiency for a point source 10 cm from the first detector surface ranges from 1.5×10 -4 to 8.8×10 -6 for 500 keV-3 MeV.

  2. Initial characterization of a position-sensitive photodiode/BGO detector for PET (positron emission tomography)

    SciTech Connect

    Derenzo, S.E.; Moses, W.W.; Jackson, H.G.; Turko, B.T.; Cahoon, J.L.; Geyer, A.B.; Vuletich, T.

    1988-11-01

    We present initial results of a position-sensitive photodiode/BGO detector for high resolution, multi-layer positron emission tomography (PET). Position sensitivity is achieved by dividing the 3 mm /times/ 20 mm rectangular photosensitive area along the diagonal to form two triangular segments. Each segment was individually connected to a low-noise amplifier. The photodiodes and crystals were cooled to /minus/100/degree/C to reduce dark current and increase the BGO signal. With an amplifier peaking time of 17 ..mu..sec, the sum of the signals (511 keV photopeak) was 3200 electrons with a full width at half maximum (fwhm) of 750 electrons. The ratio of one signal to the sum determined the depth of interaction with a resolution of 11 mm fwhm. 27 refs., 7 figs.

  3. Spectroscopy of highly-ionized atoms using position-sensitive detection

    NASA Astrophysics Data System (ADS)

    Kukla, K. W.; Livingston, A. E.; Serpa, F. G.; Zacarias, A. S.; Berry, H. G.; Dunford, R. W.; Kanter, E.; Cheng, S.; Suleiman, J.; Curtis, L. J.; Träbert, E.

    1993-06-01

    We report new results of atomic structure and atomic lifetime measurements in highly-ionized few electron atoms obtained using position-sensitive detection of extreme ultraviolet emission from excited fast ions. Data is presented from experiments run at the Notre Dame Tandem Accelerator and at the Argonne ATLAS facility using beam-foil spectroscopy with a photon-counting position-sensitive imaging detector. The results include excited state lifetimes in Si XI and Si XII involving both resonance transitions and Rydberg transitions, spectra of high-ionized He-like, Li-like, and Be-like nickel including comparisons of electron capture and excitation processes for charge selected beams and spectra and lifetimes in highly-charged bromine ions for both allowed and forbidden transitions.

  4. Photoconductive terahertz generation from textured semiconductor materials

    NASA Astrophysics Data System (ADS)

    Collier, Christopher M.; Stirling, Trevor J.; Hristovski, Ilija R.; Krupa, Jeffrey D. A.; Holzman, Jonathan F.

    2016-03-01

    Photoconductive (PC) terahertz (THz) emitters are often limited by ohmic loss and Joule heating—as these effects can lead to thermal runaway and premature device breakdown. To address this, the proposed work introduces PC THz emitters based on textured InP materials. The enhanced surface recombination and decreased charge-carrier lifetimes of the textured InP materials reduce residual photocurrents, following the picosecond THz waveform generation, and this diminishes Joule heating in the emitters. A non-textured InP material is used as a baseline for studies of fine- and coarse-textured InP materials. Ultrafast pump-probe and THz setups are used to measure the charge-carrier lifetimes and THz response/photocurrent consumption of the respective materials and emitters. It is found that similar temporal and spectral characteristics can be achieved with the THz emitters, but the level of photocurrent consumption (yielding Joule heating) is greatly reduced in the textured materials.

  5. Photoconductive terahertz generation from textured semiconductor materials.

    PubMed

    Collier, Christopher M; Stirling, Trevor J; Hristovski, Ilija R; Krupa, Jeffrey D A; Holzman, Jonathan F

    2016-01-01

    Photoconductive (PC) terahertz (THz) emitters are often limited by ohmic loss and Joule heating-as these effects can lead to thermal runaway and premature device breakdown. To address this, the proposed work introduces PC THz emitters based on textured InP materials. The enhanced surface recombination and decreased charge-carrier lifetimes of the textured InP materials reduce residual photocurrents, following the picosecond THz waveform generation, and this diminishes Joule heating in the emitters. A non-textured InP material is used as a baseline for studies of fine- and coarse-textured InP materials. Ultrafast pump-probe and THz setups are used to measure the charge-carrier lifetimes and THz response/photocurrent consumption of the respective materials and emitters. It is found that similar temporal and spectral characteristics can be achieved with the THz emitters, but the level of photocurrent consumption (yielding Joule heating) is greatly reduced in the textured materials.

  6. Using Berrys phase for position-sensitive acoustical and stress detection

    NASA Astrophysics Data System (ADS)

    Kuzyk, Mark G.

    2002-10-01

    Berry showed that a quantum system, upon an excursion around a closed path in phase space, can lead to a geometric phase. The polarization state of light in a fiber is a classical analog that is called the Pancharantnam phase. While most experiments have focused on esoteric issues, I show that, in theory, Berrys phase (or Pancharantnams phase) can be used to make a position-sensitive acoustical or stress sensor. 2002 Optical Society of America

  7. Exposure to an inflammatory challenge enhances neural sensitivity to negative and positive social feedback.

    PubMed

    Muscatell, Keely A; Moieni, Mona; Inagaki, Tristen K; Dutcher, Janine M; Jevtic, Ivana; Breen, Elizabeth C; Irwin, Michael R; Eisenberger, Naomi I

    2016-10-01

    Inflammation, part of the body's innate immune response, can lead to "sickness behaviors," as well as alterations in social and affective experiences. Elevated levels of pro-inflammatory cytokines have been associated with increased neural sensitivity to social rejection and social threat, but also decreased neural sensitivity to rewards. However, recent evidence suggests that inflammation may actually enhance sensitivity to certain social rewards, such as those that signal support and care. Despite a growing interest in how inflammation influences neural reactivity to positive and negative social experiences, no known studies have investigated these processes in the same participants, using a similar task. To examine this issue, 107 participants were randomly assigned to receive either placebo or low-dose endotoxin, which safely triggers an inflammatory response. When levels of pro-inflammatory cytokines were at their peak, participants were scanned using fMRI while they received positive, negative, and neutral feedback from an "evaluator" (actually a confederate) about how they came across in an audio-recorded interview. In response to negative feedback (vs. neutral), participants in the endotoxin condition showed heightened neural activity in a number of threat-related neural regions (i.e., bilateral amygdala, dorsal anterior cingulate cortex) and a key mentalizing-related region (i.e., dorsomedial PFC), compared to placebo participants. Interestingly, when receiving positive feedback (vs. neutral), endotoxin (vs. placebo) led to greater neural activity in the ventral striatum and ventromedial PFC, regions often implicated in processing reward, as well as greater activity in dorsomedial PFC. Together, these results reveal that individuals exposed to an inflammatory challenge are more "neurally sensitive" to both negative and positive social feedback, suggesting that inflammation may lead to a greater vigilance for both social threats and social rewards.

  8. 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.; Sad (eor. K/ E/); Figueroa-Feliciano, E.

    2008-01-01

    We report on the development of position-sensitive transition-edge sensors (PoST's) for future x-ray astronomy missions such as the International X-ray Observatory (IXO), currently under study by NASA and ESA. PoST's consist of multiple absorbers each with a different thermal coupling to one or more transition-edge sensor (TES). This differential thermal coupling between absorbers and TES's results in different characteristic pulse shapes and allows position discrimination between the different pixels. The development of PoST's is motivated by a desire to achieve maximum focal-plane area with the least number of readout channels and as such. PoST's are ideally suited to provide a focal-plane extension to the Constellation-X microcalorimeter array. We report the first experimental results of our latest one and two channel PoST's, which utilize fast thermalizing electroplated Au/Bi absorbers coupled to low noise Mo/Au TES's - a technology already successfully implemented in our arrays of single pixel TES's. We demonstrate 6 eV energy resolution coupled with spatial sensitivity in the keV energy range. We also report on the development of signal processing algorithms to optimize energy and position sensitivity of our detectors.

  9. Photoconductivity and photoconversion at a photorefractive thin crystal plate

    NASA Astrophysics Data System (ADS)

    Frejlich, Jaime; de Oliveira, Ivan; de Araujo, William R.; Carvalho, Jesiel F.; Montenegro, Renata; Georges, Marc; Fleury-Frenette, Karl

    2016-05-01

    We report on the photoconductivity and the photoelectric conversion measured on a thin photorefractive sillenite crystal plate, between transparent electrodes, in the longitudinal configuration where the current is measured along the same direction of the light beam through the sample. Its behavior is based on the already reported light-induced Schottky effect. The wavelength for optimal photoconductivity is determined. A specific parameter is formulated here for quantitatively determining the photoelectric conversion efficiency of the sandwiched material.

  10. Positive words or negative words: whose valence strength are we more sensitive to?

    PubMed

    Yang, Jiemin; Zeng, Jing; Meng, Xianxin; Zhu, Liping; Yuan, Jiajin; Li, Hong; Yusoff, Nasir

    2013-10-01

    The present study investigates the human brains' sensitivity to the valence strength of emotionally positive and negative chinese words. Event-Related Potentials were recorded, in two different experimental sessions, for Highly Positive (HP), Mildly Positive (MP) and neutral (NP) words and for Highly Negative (HN), Mildly Negative (MN) and neutral (NN) words, while subjects were required to count the number of words, irrespective of word meanings. The results showed a significant emotion effect in brain potentials for both HP and MP words, and the emotion effect occurred faster for HP words than MP words: HP words elicited more negative deflections than NP words in N2 (250-350 ms) and P3 (350-500 ms) amplitudes, while MP words elicited a significant emotion effect in P3, but not in N2, amplitudes. By contrast, HN words elicited larger amplitudes than NN words in N2 but not in P3 amplitudes, whereas MN words produced no significant emotion effect across N2 and P3 components. Moreover, the size of emotion-neutral differences in P3 amplitudes was significantly larger for MP compared to MN words. Thus, the human brain is reactive to both highly and mildly positive words, and this reactivity increased with the positive valence strength of the words. Conversely, the brain is less reactive to the valence of negative relative to positive words. These results suggest that human brains are equipped with increased sensitivity to the valence strength of positive compared to negative words, a type of emotional stimuli that are well known for reduced arousal.

  11. Toward a photoconducting semiconductor RF optical fiber antenna array.

    PubMed

    Davis, R; Rice, R; Ballato, A; Hawkins, T; Foy, P; Ballato, J

    2010-09-20

    Recently, optical fibers comprising a crystalline semiconductor core in a silica cladding have been successfully drawn by a conventional drawing process. These fibers are expected to exhibit a photoconductive response when illuminated by photons more energetic than the band gap of the core. In the photoconducting state, such a fiber can be expected to support driven RF currents so as to function as an antenna element, much as a plasma antenna. In this paper, we report the first device-related results on a crystalline semiconductor core optical fiber potentially useful in a photoconducting optical fiber antenna array; namely, optically induced changes to the electrical conductivity of a glass-clad germanium-core optical fiber. Since DC photoconduction measurements were masked by a photovoltaic effect, RF measurements at 5 MHz were used to determine the magnitude of the induced photoconductive effect. The observed photoconductivity, though not large in the present experiment, was comparable to that measured for the bulk crystals from which the fibers were drawn. The absorbed pumping light generated photo-carriers, thereby transforming the core from a dielectric material to a conductor. This technology could thus enable a class of transient antenna elements useful in low observable and reconfigurable antenna array applications.

  12. Head Position in the MEG Helmet Affects the Sensitivity to Anterior Sources

    PubMed Central

    Marinkovic, K; Cox, B; Reid, K; Halgren, E

    2013-01-01

    Current MEG instruments derive the whole-head coverage by utilizing a helmet-shaped opening at the bottom of the dewar. These helmets, however, are quite a bit larger than most people’s heads so subjects commonly lean against the back wall of the helmet in order to maintain a steady position. In such cases the anterior brain sources may be too distant to be picked up by the sensors reliably. Potential “invisibility” of the frontal and anterior temporal sources may be particularly troublesome for the studies of cognition and language, as they are subserved significantly by these areas. We examined the sensitivity of the distributed anatomically-constrained MEG (aMEG) approach to the head position (“front” vs. “back”) secured within a helmet with custom-tailored bite-bars during a lexical decision task. The anterior head position indeed resulted in much greater sensitivity to language-related activity in frontal and anterior temporal locations. These results emphasize the need to adjust the head position in the helmet in order to maximize the “visibility” of the sources in the anterior brain regions in cognitive and language tasks. PMID:16012659

  13. Exposure to an Inflammatory Challenge Enhances Neural Sensitivity to Negative and Positive Social Feedback

    PubMed Central

    Muscatell, Keely A.; Moieni, Mona; Inagaki, Tristen K.; Dutcher, Janine M.; Jevtic, Ivana; Breen, Elizabeth C.; Irwin, Michael R.; Eisenberger, Naomi I.

    2016-01-01

    Inflammation, part of the body’s innate immune response, can lead to “sickness behaviors,” as well as alterations in social and affective experiences. Elevated levels of pro-inflammatory cytokines have been associated with increased neural sensitivity to social rejection and social threat, but also decreased neural sensitivity to rewards. However, recent evidence suggests that inflammation may actually enhance sensitivity to certain social rewards, such as those that signal support and care. Despite a growing interest in how inflammation influences neural reactivity to positive and negative social experiences, no known studies have investigated these processes in the same participants, using a similar task. To examine this issue, 107 participants were randomly assigned to receive either placebo or low-dose endotoxin, which safely triggers an inflammatory response. When levels of pro-inflammatory cytokines were at their peak, participants were scanned using fMRI while they received positive, negative, and neutral feedback from an “evaluator” (actually a confederate) about how they came across in an audio-recorded interview. In response to negative feedback (vs. neutral), participants in the endotoxin condition showed heightened neural activity in a number of threat-related neural regions (i.e., bilateral amygdala, dorsal anterior cingulate cortex) and a key mentalizing-related region (i.e., dorsomedial PFC), compared to placebo participants. Interestingly, when receiving positive feedback (vs. neutral), endotoxin led to greater neural activity in the ventral striatum and ventromedial PFC, regions often implicated in processing reward, compared to placebo. Together, these results reveal that individuals exposed to an inflammatory challenge are more “neurally sensitive” to both negative and positive social feedback, suggesting that inflammation may lead to a greater vigilance for both social threats and social rewards. PMID:27032568

  14. 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.; Porter, F. S.; Figueroa-Feliciano, E.

    2008-01-01

    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. Using recently developed signal processing algorithms we have investigated the trade-off between position-sensitivity, energy resolution and pulse decay time. based on different device design parameters for PoST's. Our new generation of PoST's utilize technology successfully developed on high resolution (approximately 2.5eV) 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 these new one and two-channel PoST"s, consisting of all Au and composite Au/Bi absorbers, which are designed to achieve an energy resolution of < 10 eV. coupled with count-rates of 100's per pixel per second and position sensitivity over the energy range 0.3-10 keV.

  15. The position effect of electron-deficient quinoxaline moiety in porphyrin based sensitizers

    NASA Astrophysics Data System (ADS)

    Fan, Suhua; Lv, Kai; Sun, Hong; Zhou, Gang; Wang, Zhong-Sheng

    2015-04-01

    An electron-deficient group, 2,3-diphenylquinoxaline (DPQ), is incorporated as an auxiliary acceptor into the different positions of the porphyrin (Por) based donor-π bridge-acceptor (D-π-A) dye (FNE57) to construct D-A‧-Por-π-A (FNE58) and D-Por-A‧-π-A (FNE59) configurations. The incorporation of DPQ unit between the donor and porphyrin unit has negligible influence on the absorption property, whereas the DPQ unit located between the porphyrin unit and acceptor significantly increases the absorbance for the Soret band and the valley between the Soret and Q bands. Theoretical calculation reveals that incorporating the DPQ unit adjacent to the acceptor is more advantageous to delocalize the lowest unoccupied molecular orbital and enhance the electronic asymmetry, which facilitates the intramolecular charge transfer. The effect of DPQ unit and its linkage position on the performance of related quasi-solid-state dye-sensitized solar cells (DSSCs) is systematically investigated. The quasi-solid-state DSSC with sensitizer FNE59 displays a power conversion efficiency of 6.02%, which is 23% and 51% higher than those for FNE57 and FNE58 based DSSCs. Our studies facilitate the understanding of the crucial importance of molecular engineering and pave a new path to design novel porphyrin based sensitizers for highly efficient DSSCs.

  16. Sensitivity to abscisic acid modulates positive interactions between Arabidopsis thaliana individuals.

    PubMed

    Zhang, Hao; Shen, Zhuxia; Wang, Genxuan; Dai, Xinfeng; Huang, Qiaoqiao; Zheng, Kefeng

    2010-03-01

    The ability of abscisic acid (ABA) to modulate positive interactions between Arabidopsis thaliana individuals under salinity stress was investigated using abi1-1 (insensitive to ABA), era1-2 (hypersensitive to ABA) mutant and wild type plants. The results showed that sensitivity to ABA affects relative interaction intensity (RII) between Arabidopsis thaliana individuals. The neighbor removal experiments also confirmed the role of phenotypic responses in linking plant-plant interactions and sensitivity to ABA. For abi1-1 mutants, the absolute value differences between neighbor removal and control of stem length, root length, leaf area, leaf thickness, flower density, above biomass/belowground biomass (A/U), photosynthetic rate, stomatal conductance, leaf water content and water-use efficiency were smaller than those of the wild type, while for era1-2 mutants, these absolute value differences were larger than those of the wild type. Thus, it is suggested that positive interactions between Arabidopsis thaliana individuals are at least partly modulated by different sensitivity to ABA through different physiological and phenotypic plasticity. PMID:20377695

  17. Mammography outcomes in a practice setting by age: prognostic factors, sensitivity, and positive biopsy rate.

    PubMed

    Linver, M N; Paster, S B

    1997-01-01

    The separate unplanned analysis of women ages 40-49 in population-based randomized controlled trials has resulted in demonstration of statistically significant breast cancer mortality reduction due to screening mammography in only two of the individual trials, and in all such trials only through meta-analysis. Therefore, many researchers have utilized the surrogate endpoints of tumor size and axillary lymph node status to evaluate screening efficacy. For the present study, these endpoints were evaluated in an audit of 854 screen-detected cancers found in 147,125 mammographic examinations performed in women over 40 between 1988 and 1994 in a community practice setting. The concerns that mammography in the 40-49 group has a lower sensitivity and higher biopsy rate were also addressed. Median invasive tumor size and lymph node positivity were found to be equally small (1.0-1.1 cm and 13.5-12.2%, respectively), and the sensitivity and overall biopsy rate were found to be constant over all ages 40 and above. Positive biopsy rate (PBR) varied directly with increasing age, paralleling the measured cancer detection rate in each decade, with no abrupt change at age 50. We conclude that modern mammography in a community practice setting can successfully detect breast cancers with favorable prognostic factors and achieve constant sensitivity and acceptable PBRs in all women over 40. Our data also suggest that many of the large differences seen by inappropriately dividing data at age 50 decrease or disappear when analysis is performed by decade.

  18. A carbon nanotubes photoconductive detector for middle and far infrared regions based on porous silicon and a polyamide nylon polymer

    NASA Astrophysics Data System (ADS)

    Saleh, Wasan R.

    2015-06-01

    Sensitive and good response photoconductive detectors working in the middle and far infrared regions were fabricated. These detectors were fabricated based on multi and double walled carbon nanotube films and works at room temperature. The films were deposited on a porous silicon (PSi) nanosurface. The surfaces were functionalized by a thin layer of polyamide nylon polymer to improve the photoresponsivity of the fabricated detectors. The response time of the fabricated MWCNTs-PSi detectors were 30 and 0.22 ms for the middle and far IR region respectively. The functionalisation of the MWCNTs-PSi film surface by the polyamide nylon polymer improved the photoconductive gain, photoresponsivity, and specific conductivity in both MWCNTs-PSi and DWCNTs-PSi detectors. The designed carbon nanotube (CNT) based photodetector has low cost, high sensitivity and reasonable speed for the middle and far IR spectral range without cooling.

  19. Dorsal striatal D2-like receptor availability covaries with sensitivity to positive reinforcement during discrimination learning.

    PubMed

    Groman, Stephanie M; Lee, Buyean; London, Edythe D; Mandelkern, Mark A; James, Alex S; Feiler, Karen; Rivera, Ronald; Dahlbom, Magnus; Sossi, Vesna; Vandervoort, Eric; Jentsch, J David

    2011-05-18

    Deviations in reward sensitivity and behavioral flexibility, particularly in the ability to change or stop behaviors in response to changing environmental contingencies, are important phenotypic dimensions of several neuropsychiatric disorders. Neuroimaging evidence suggests that variation in dopamine signaling through dopamine D(2)-like receptors may influence these phenotypes, as well as associated psychiatric conditions, but the specific neurocognitive mechanisms through which this influence is exerted are unknown. To address this question, we examined the relationship between behavioral sensitivity to reinforcement during discrimination learning and D(2)-like receptor availability in vervet monkeys. Monkeys were assessed for their ability to acquire, retain, and reverse three-choice, visual-discrimination problems, and once behavioral performance had stabilized, they received positron emission tomography (PET) scans. D(2)-like receptor availability in dorsal aspects of the striatum was not related to individual differences in the ability to acquire or retain visual discriminations but did relate to the number of trials required to reach criterion in the reversal phase of the task. D(2)-like receptor availability was also strongly correlated with behavioral sensitivity to positive, but not negative, feedback during learning. These results go beyond electrophysiological findings by demonstrating the involvement of a striatal dopaminergic marker in individual differences in feedback sensitivity and behavioral flexibility, providing insight into the neural mechanisms that are affected in neuropsychiatric disorders that feature these deficits.

  20. An improved method of energy calibration for position-sensitive silicon detectors

    NASA Astrophysics Data System (ADS)

    Sun, Ming-Dao; Huang, Tian-Heng; Liu, Zhong; Ding, Bing; Yang, Hua-Bin; Zhang, Zhi-Yuan; Wang, Jian-Guo; Ma, Long; Yu, Lin; Wang, Yong-Sheng; Gan, Zai-Guo; Xiao-Hong, Zhou

    2016-04-01

    Energy calibration of resistive charge division-based position-sensitive silicon detectors is achieved by parabolic fitting in the traditional method, where the systematic variations of vertex and curvature of the parabola with energy must be considered. In this paper we extend the traditional method in order to correct the fitting function, simplify the procedure of calibration and improve the experimental data quality. Instead of a parabolic function as used in the traditional method, a new function describing the relation of position and energy is introduced. The energy resolution of the 8.088 MeV α decay of 213Rn is determined to be about 87 keV (FWHM), which is better than the result of the traditional method, 104 keV (FWHM). The improved method can be applied to the energy calibration of resistive charge division-based position-sensitive silicon detectors with various performances. Supported by ‘100 Person Project’ of the Chinese Academy of Sciences and the National Natural Science Foundation of China (11405224 and 11435014)

  1. Skin sensitization, false positives and false negatives: experience with guinea pig assays.

    PubMed

    Basketter, David A; Kimber, Ian

    2010-07-01

    The advent of the local lymph node assay (LLNA), and efforts to develop in vitro alternatives for the identification of skin sensitizing chemicals has focused attention on the issue of false positive and false negative results. In essence, the question becomes 'what is the gold standard?' In this context, attention has focused primarily on the LLNA as this is now the preferred assay for skin sensitization testing. However, for many years prior to introduction of the LLNA, the guinea pig maximization test and the occluded patch test of Buehler were the methods of choice. In order to encourage a more informed dialogue about the relative performance, accuracy and applicability of the LLNA and guinea pig tests, we have here considered the extent to which guinea pig methods were themselves subject to false positives and negative results. We describe and discuss here well-characterized examples of instances where both false negatives (including abietic acid and eugenol) or false positives (including vanillin and sulfanilic acid) have been recorded in guinea pig tests. These and other examples are discussed with particular reference to the fabrication of a gold standard dataset that is required for the validation of in vitro alternatives.

  2. Exploring the spatial resolution of position-sensitive microchannel plate detectors

    NASA Astrophysics Data System (ADS)

    Wiggins, Blake; Siwal, Davinder; Desouza, Romualdo

    2016-03-01

    High amplification and excellent timing make microchannel plate (MCP) detectors excellent devices for detection of photons, electrons, and ions. In addition to providing sub-nanosecond time resolution MCP detectors can also provide spatial resolution, thus making them useful in imaging applications. Use of a resistive anode (RA) is a routinely used approach to make an MCP position-sensitive. The spatial resolution of the RA associated with detection of a single incident electron was determined. Factors impacting the spatial resolution obtained with the RA will be discussed and the achieved spatial resolution of 64 μm (FWHM) will be presented. Recently, a novel approach has been developed to provide position-sensitivity for an MCP detector. In this approach, namely the induced signal approach, the position of the incident particle is determined by sensing the electron cloud emanating from a MCP stack. By utilizing the zero-crossing point of the inherently bipolar signals, a spatial resolution of 466 μm (FWHM) has been achieved. Work to improve the spatial resolution of the induced signal approach further will be presented. Supported by the US DOE NNSA under Award No. DE-NA0002012.

  3. Terahertz Bessel-Gauss beams of radial and azimuthal polarization from microstructured photoconductive antennas.

    PubMed

    Winnerl, S; Zimmermann, B; Peter, F; Schneider, H; Helm, M

    2009-02-01

    We report on emission and detection of pulsed terahertz radiation of radial and azimuthal polarization by microstructured photoconductive antennas. To this end the electrode geometry of the emitter is inverse to the desired THz field pattern and a second periodic structure prevents destructive interference effects. Beam profiles of freely propagating THz waves are studied for divergent and refocused beams. They can be well described as the lowest order Bessel-Gauss modes with a divergence comparable to linearly polarized Gaussian beams. Additionally, mode sensitive detection is demonstrated for radially polarized radiation. PMID:19188986

  4. Biological basis for increased sensitivity to radiation therapy in HPV-positive head and neck cancers.

    PubMed

    Bol, V; Grégoire, V

    2014-01-01

    Although development of head and neck squamous cell carcinomas (HNSCCs) is commonly linked to the consumption of tobacco and alcohol, a link between human papillomavirus (HPV) infection and a subgroup of head and neck cancers has been established. These HPV-positive tumors represent a distinct biological entity with overexpression of viral oncoproteins E6 and E7. It has been shown in several clinical studies that HPV-positive HNSCCs have a more favorable outcome and greater response to radiotherapy. The reason for improved prognosis of HPV-related HNSCC remains speculative, but it could be owned to multiple factors. One hypothesis is that HPV-positive cells are intrinsically more sensitive to standard therapies and thus respond better to treatment. Another possibility is that HPV-positive tumors uniquely express viral proteins that induce an immune response during therapy that helps clear tumors and prevents recurrence. Here, we will review current evidence for the biological basis of increased radiosensitivity in HPV-positive HNSCC.

  5. High-speed measurement of rotational anisotropy nonlinear optical harmonic generation using position-sensitive detection.

    PubMed

    Harter, J W; Niu, L; Woss, A J; Hsieh, D

    2015-10-15

    We present a method of performing high-speed rotational anisotropy nonlinear optical harmonic generation experiments at rotational frequencies of several hertz by projecting the harmonic light reflected at different angles from a sample onto a stationary position-sensitive detector. The high rotational speed of the technique, 10(3) to 10(4) times larger than existing methods, permits precise measurements of the crystallographic and electronic symmetries of samples by averaging over low frequency laser-power, beam-pointing, and pulse-width fluctuations. We demonstrate the sensitivity of our technique by resolving the bulk fourfold rotational symmetry of GaAs about its [001] axis using second-harmonic generation. PMID:26469591

  6. [CD11b-positive cells expression in rectal mucosa from ovalbumin sensitized and challenged rabbits].

    PubMed

    Bassan, Norberto; Vinuesa, Miguel; Roma, Stella

    2005-01-01

    Rabbit MAC-1 receptor, homologue to human CD11b is present in macrophages. The aim of the study was to determine quantitative and distributive modifications of CD11b-positive cells that participate in immune response at rectal mucosa, in an animal model of mucosal immunity. New Zealand rabbits were divided into three groups. G1: control; G2: ovalbumin (OVA) sensitized; G3: OVA-senstitized and rectal challenged. Animals were subcutaneously sensitized twice with 70 microg OVA and 30 ml aluminium hydroxide in 2 ml saline solution. Rectal challenge was developed with a solution of 50 mg OVA in 5 ml saline solution. Sensitized groups (G2 and G3) showed a positive PCA (Passive Cutaneous Anaphylaxis) at 1/160 fold dilutions. In G3 we observed a patchy mucosal edema, lymphangiectasis and eosinophil leucocyte infiltration. Cells were counted as the number of cells per high power field. G1: 9.64 (SE 0.22); G2: 18.10 (SE 0.09) and G3: 23.60 (SE 0.29). (G2 vs G1 p < 0.001; G3 vs G1 p < 0.001; G3 vs G2 p < 0.001). We conclude that there is a close relationship between the food antigen OVA penetration (after challenge) and the increase of CD11b positive cells in rectal mucosa. This fact could be due to the cellular influx to the inflammatory site by the action of chemotactic factors released after challenge.

  7. Array of 12 coils to measure the position, alignment, and sensitivity of magnetic sensors over temperature

    NASA Astrophysics Data System (ADS)

    Husstedt, Hendrik; Ausserlechner, Udo; Kaltenbacher, Manfred

    2012-04-01

    A measurement setup is presented that allows one to determine the position, alignment, and sensitivity of magnetic sensors over temperature. To this end, an array of 12 coils is used where the number of coils is larger than the number of unknowns to increase accuracy, and to ensure an adequate measurement signal for an arbitrary orientation of the magnetic sensors. With this coil array, a 3D sensing system is analyzed which is used during the testing of automotive magnetic sensors. In particular, the influence of assembly tolerances, and the variation of temperature are examined.

  8. Fast neutron spectrometry and dosimetry using a spherical moderator with position-sensitive detectors.

    PubMed

    Li, Taosheng; Yang, Lianzhen; Ma, Jizeng; Fang, Dong

    2007-01-01

    A neutron spectrometry and dosimetry measurement system has been developed based on a different design of the divided regions for a sphere, with three position-sensitive counters. The characteristics of the measurement system have been investigated in the reference radiation fields of Am-Be and (252)Cf sources. When realistic input spectra are used for the unfolding, the overall deviations of the calculated results for four dosimetric quantities are less than +/-10%. The results of other input spectra are also discussed in this report.

  9. 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.

  10. 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

  11. Demonstration of a high sensitivity GNSS software receiver for indoor positioning

    NASA Astrophysics Data System (ADS)

    Lin, Tao; Ma, Martin; Broumandan, Ali; Lachapelle, Gérard

    2013-03-01

    Advances in signal processing techniques contributed to the significant improvements of GNSS receiver performance in dense multipath environments and created the opportunities for a new category of high-sensitivity GNSS (HS-GNSS) receivers that can provide GNSS location services in indoor environments. The difficulties in improving the availability, reliability, and accuracy of these indoor capable GNSS receivers exceed those of the receivers designed for the most hostile urban canyon environments. The authors of this paper identified the vector tracking schemes, signal propagation statistics, and parallel processing techniques that are critical to a robust HS-GNSS receiver for indoor environments and successfully incorporated them into a fully functional high-sensitivity software receiver. A flexible vector-based receiver architecture is introduced to combine these key indoor signal processing technologies into GSNRx-hs™ - the high sensitivity software navigation receiver developed at the University of Calgary. The resulting receiver can perform multi-mode vector tracking in indoor environment at various levels of location and timing uncertainties. In addition to the obvious improvements in time-to-first-fix (TTFF) and signal sensitivity, the field test results in indoor environments surrounded by wood, glass, and concrete showed that the new techniques effectively improved the performance of indoor GNSS positioning. With fine GNSS timing, the proposed receiver can consistently deliver indoor navigation solution with the horizontal accuracy of 2-15 m depending on the satellite geometry and the indoor environments. If only the coarse GNSS timing is available, the horizontal accuracy of the indoor navigation solution from the proposed receiver is around 30 m depending on the coarse timing accuracy, the satellite geometry, and the indoor environments. From the preliminary field test results, it has been observed that the signal processing sensitivity is the

  12. 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).

  13. A diagnostic for micrometer sensitive positioning of solid targets in intense laser-matter interaction

    NASA Astrophysics Data System (ADS)

    Singh, Prashant Kumar; Kakolee, K. F.; Jeong, T. W.; Ter-Avetisyan, Sargis

    2016-09-01

    A target position monitoring diagnostic, relevant to intense laser-solid interaction, is presented. The alignment system, having a sensitivity of few micrometers, consist of an infinity corrected long working distance objective, a broadband illuminating source and a CCD camera. The imaging system, placed along the axis of incident laser pulse, serves the dual purpose of laser focus diagnosis and precise positioning of the target in three dimension axis. By employing this technique, solid targets with thickness varying from opaque micrometer thick foils to few nanometer thin transparent foils can be aligned precisely. The effectiveness of the entire alignment system is demonstrated in enhanced acceleration of ions in intense laser-matter interaction, with very high reproducibility.

  14. Resonant inelastic hard x-ray scattering with diced analyzer crystals and position-sensitive detectors

    SciTech Connect

    Huotari, S.; Albergamo, F.; Vanko, Gy.; Verbeni, R.; Monaco, G.

    2006-05-15

    A novel design of a high-resolution spectrometer is proposed for emission spectroscopy and resonant inelastic hard x-ray scattering applications. The spectrometer is based on a Rowland circle geometry with a diced analyzer crystal and a position-sensitive detector. The individual flat crystallites of the diced analyzer introduce a well-defined linear position-energy relationship within the analyzer focus. This effect can be exploited to measure emission spectra with an unprecedented resolution. For demonstration, a spectrometer was constructed using a diced Si(553) analyzer working at the Cu K edge with an intrinsic resolution of 60 meV. With the proposed design, spectrometers operating at the K edges of 3d transition metals can have intrinsic resolutions below 100 meV even with analyzer crystals not working in Bragg-backscattering conditions.

  15. CMOS color image sensor with overlaid organic photoconductive layers having narrow absorption band

    NASA Astrophysics Data System (ADS)

    Takada, Shunji; Ihama, Mikio; Inuiya, Masafumi; Komatsu, Takashi; Saito, Takahiro

    2007-02-01

    At EI2006, we proposed the CMOS image sensor, which was overlaid with organic photoconductive layers in order to incorporate in it large light-capturing ability of a color film owing to its multiple-layer structure, and demonstrated the pictures taken by the trial product of the proposed CMOS image sensor overlaid with an organic layer having green sensitivity. In this study, we have tried to get the optimized spectral sensitivity for the proposed CMOS image sensor by means of the simulation to minimize the color difference between the original Macbeth chart and its reproduction with the spectral sensitivity of the sensor as a parameter. As a result, it has been confirmed that the proposed CMOS image sensor with multiple-layer structure possesses high potential capability in terms of imagecapturing efficiency when it is provided with the optimized spectral sensitivity.

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

    SciTech Connect

    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 detection 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.

  17. A position-sensitive twin ionization chamber for fission fragment and prompt neutron correlation experiments

    NASA Astrophysics Data System (ADS)

    Göök, A.; Geerts, W.; Hambsch, F.-J.; Oberstedt, S.; Vidali, M.; Zeynalov, Sh.

    2016-09-01

    A twin position-sensitive Frisch grid ionization chamber, intended as a fission fragment detector in experiments to study prompt fission neutron correlations with fission fragment properties, is presented. Fission fragment mass and energies are determined by means of the double kinetic energy technique, based on conservation of mass and linear momentum. The position sensitivity is achieved by replacing each anode plate in the standard twin ionization chamber by a wire plane and a strip anode, both readout by means of resistive charge division. This provides information about the fission axis orientation, which is necessary to reconstruct the neutron emission process in the fully accelerated fragment rest-frame. The energy resolution compared to the standard twin ionization chamber is found not to be affected by the modification. The angular resolution of the detector relative to an arbitrarily oriented axis is better than 7° FWHM. Results on prompt fission neutron angular distributions in 235U(n,f) obtained with the detector in combination with an array of neutron scintillation detectors is presented as a proof of principle.

  18. Photoconductive terahertz generation from textured semiconductor materials

    PubMed Central

    Collier, Christopher M.; Stirling, Trevor J.; Hristovski, Ilija R.; Krupa, Jeffrey D. A.; Holzman, Jonathan F.

    2016-01-01

    Photoconductive (PC) terahertz (THz) emitters are often limited by ohmic loss and Joule heating—as these effects can lead to thermal runaway and premature device breakdown. To address this, the proposed work introduces PC THz emitters based on textured InP materials. The enhanced surface recombination and decreased charge-carrier lifetimes of the textured InP materials reduce residual photocurrents, following the picosecond THz waveform generation, and this diminishes Joule heating in the emitters. A non-textured InP material is used as a baseline for studies of fine- and coarse-textured InP materials. Ultrafast pump-probe and THz setups are used to measure the charge-carrier lifetimes and THz response/photocurrent consumption of the respective materials and emitters. It is found that similar temporal and spectral characteristics can be achieved with the THz emitters, but the level of photocurrent consumption (yielding Joule heating) is greatly reduced in the textured materials. PMID:26979292

  19. Photoconductive Semiconductor Switches for pulsed power applications

    SciTech Connect

    Loubriel, G.M.; Zutavern, F.J.; Denison, G.J.; Helgeson, W.D.; McLaughlin, D.L.; O`Malley, M.W.; Buttram, M.T.

    1993-08-01

    Photoconductive Semiconductor Switches (PCSS) are being used in, or tested for, many different pulsed power applications as diverse as ultrawideband (UWB) transmitters and high current pulsers. Some aspects of the switches that are relevant to most of the applications are: switch lifetime (longevity), switch opening time (related to the lifetime of carriers in the semiconductor), switching jitter, and the required laser energy. This paper will emphasize the results that we have obtained with Si switches for UWB applications. These include: measurement of switch longevity (a total of 80 Coulombs or 40 C/cm for a 2 cm wide switch and 18.4 Coulombs or 73 Coulombs/cm for a 0.25 cm wide switch), switching at high repetition rates (up to 540 Hz), measurement of carrier lifetime decay rates (a fast one of a few {mu}s, and a slow one of about 330 {mu}s), and measurements on the effect of neutron irradiation on carrier lifetimes. The total charge switched seems to be the highest ever reported for a PCSS. We have used these Si switches in a variety of circuits to produce: a monocycle with a period of about 10 ns corresponding to a center frequency of about 84 MHz, and ringing (many pulse) waveforms with periods of about 1 ns and 7.5 ns corresponding to center frequencies of 770 MHz and 133 MHz. We will also discuss recent studies on the switching properties of GaP.

  20. Vectorial photocurrents and photoconductivity in metalized chloroplasts

    SciTech Connect

    Greenbaum, E. )

    1990-08-09

    A novel photobiophysical phenomenon was observed in isolated spinach chloroplasts that were metalized by precipitating colloidal platinum onto the surface of the thylakoid membranes. A two-point irradiation and detection system was constructed in which a continuous-beam helium-neon laser ({lambda} = 632.8 nm) was used to irradiate the platinized chloroplasts at varying perpendicular distances (Figure 1) from a single linear platinum electrode in pressure contact with the platinized chloroplasts. No external voltage bias was applied to the system. The key objective of the experiments reported in this report was to measure the relative photoconductivity of the chloroplast-metal composite matrix. Unlike conventional photosynthetic electrochemical cells, in which irradiated chloroplasts are in close proximity to an electrode or linked to the electrode by an electrode-active mediator, the flow of photocurrent was through the biocomposite material. A sustained steady-state vectorial flow of current in the plane of the entrapped composite from the point of laser irradiation to the wire electrode was measured.

  1. A Study of Position-Sensitive Solid-State Photomultiplier Signal Properties

    PubMed Central

    Schmall, Jeffrey P.; Du, Junwei; Judenhofer, Martin S.; Dokhale, Purushottam; Christian, James; McClish, Mickel; Shah, Kanai S.; Cherry, Simon R.

    2014-01-01

    We present an analysis of the signal properties of a position-sensitive solid-state photomultiplier (PS-SSPM) that has an integrated resistive network for position sensing. Attractive features of PS-SSPMs are their large area and ability to resolve small scintillator crystals. However, the large area leads to a high detector capacitance, and in order to achieve high spatial resolution a large network resistor value is required. These inevitably create a low-pass filter that drastically slows what would be a fast micro-cell discharge pulse. Significant changes in the signal shape of the PS-SSPM cathode output as a function of position are observed, which result in a position-dependent time delay when using traditional time pick-off methods such as leading edge discrimination and constant fraction discrimination. The timing resolution and time delay, as a function of position, were characterized for two different PS-SSPM designs, a continuous 10 mm × 10 mm PS-SSPM and a tiled 2 × 2 array of 5 mm × 5 mm PS-SSPMs. After time delay correction, the block timing resolution, measured with a 6 × 6 array of 1.3 × 1.3 × 20 mm3 LSO crystals, was 8.6 ns and 8.5 ns, with the 10 mm PS-SSPM and 5 mm PS-SSPM respectively. The effect of crystal size on timing resolution was also studied, and contrary to expectation, a small improvement was measured when reducing the crystal size from 1.3 mm to 0.5 mm. Digital timing methods were studied and showed great promise for allowing accurate timing by implementation of a leading edge time pick-off. Position-dependent changes in signal shape on the anode side also are present, which complicates peak height data acquisition methods used for positioning. We studied the effect of trigger position on signal amplitude, flood histogram quality, and depth-of-interaction resolution in a dual-ended readout detector configuration. We conclude that detector timing and positioning can be significantly improved by implementation of digital timing

  2. A Study of Position-Sensitive Solid-State Photomultiplier Signal Properties.

    PubMed

    Schmall, Jeffrey P; Du, Junwei; Judenhofer, Martin S; Dokhale, Purushottam; Christian, James; McClish, Mickel; Shah, Kanai S; Cherry, Simon R

    2014-06-12

    We present an analysis of the signal properties of a position-sensitive solid-state photomultiplier (PS-SSPM) that has an integrated resistive network for position sensing. Attractive features of PS-SSPMs are their large area and ability to resolve small scintillator crystals. However, the large area leads to a high detector capacitance, and in order to achieve high spatial resolution a large network resistor value is required. These inevitably create a low-pass filter that drastically slows what would be a fast micro-cell discharge pulse. Significant changes in the signal shape of the PS-SSPM cathode output as a function of position are observed, which result in a position-dependent time delay when using traditional time pick-off methods such as leading edge discrimination and constant fraction discrimination. The timing resolution and time delay, as a function of position, were characterized for two different PS-SSPM designs, a continuous 10 mm × 10 mm PS-SSPM and a tiled 2 × 2 array of 5 mm × 5 mm PS-SSPMs. After time delay correction, the block timing resolution, measured with a 6 × 6 array of 1.3 × 1.3 × 20 mm(3) LSO crystals, was 8.6 ns and 8.5 ns, with the 10 mm PS-SSPM and 5 mm PS-SSPM respectively. The effect of crystal size on timing resolution was also studied, and contrary to expectation, a small improvement was measured when reducing the crystal size from 1.3 mm to 0.5 mm. Digital timing methods were studied and showed great promise for allowing accurate timing by implementation of a leading edge time pick-off. Position-dependent changes in signal shape on the anode side also are present, which complicates peak height data acquisition methods used for positioning. We studied the effect of trigger position on signal amplitude, flood histogram quality, and depth-of-interaction resolution in a dual-ended readout detector configuration. We conclude that detector timing and positioning can be significantly improved by implementation of digital timing

  3. 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

  4. Evidence for the sensitivity of a Great Basin terminal lake to storm track position

    NASA Astrophysics Data System (ADS)

    Hatchett, B.; Boyle, D. P.; Garner, C.; Kaplan, M. L.; Bassett, S.

    2014-12-01

    Arid, closed basin watersheds can serve as indicators of regional climate change. In this work we test the hypothesis that surface elevations of Walker Lake, a Great Basin terminal lake, are sensitive to storm track positions. To do so, we use historical climate records, numerically dated paleolakeshore elevations, global reanalysis products and a semi-distributed water balance model. Precipitation and temperature values from calculated wet and dry periods between 1920-2011 were used as input to the model. Storm track climatologies were developed using reanalysis products. Our results demonstrate that a strong relationship exists between historic wet and dry periods and storm track positions. Under the assumption of a stationary climate using these historic wet and dry climates with the model, we simulated lake levels that are consistent with recorded high and lowstands occurring during Heinrich Stadial 1, the Younger Dryas, the Medieval Climate Anomaly and the Little Ice Age. These findings provide direct support for the storm track migration hypothesis. The nonlinear relationship between changes in precipitation and runoff appears to play a critical role in determining why terminal lakes are particularly responsive to changes in storm track positions.

  5. Correlation of the plasmon-enhanced photoconductance and photovoltaic properties of core-shell Au@TiO2 network

    NASA Astrophysics Data System (ADS)

    Yang, Yiqun; Wu, Judy; Li, Jun

    2016-08-01

    This study reveals the contribution of hot electrons from the excited plasmonic nanoparticles in dye sensitized solar cells (DSSCs) by correlating the photoconductance of a core-shell Au@TiO2 network on a micro-gap electrode and the photovolatic properties of this material as photoanodes in DSSCs. The distinct wavelength dependence of these two devices reveals that the plasmon-excited hot electrons can easily overcome the Schottky barrier at Au/TiO2 interface in the whole visible wavelength range and transfer from Au nanoparticles into the TiO2 network. The enhanced charge carrier density leads to higher photoconductance and facilitates more efficient charge separation and photoelectron collection in the DSSCs.

  6. Intrinsic photo-conductance triggered by the plasmonic effect in graphene for terahertz detection.

    PubMed

    Wang, Lin; Chen, Xiaoshuang; Lu, Wei

    2016-01-22

    Terahertz (THz) technology is becoming more eminent for applications in diverse areas including biomedical imaging, communication, security and astronomy. However, THz detection still has some challenges due to the lack of sources and detectors despite decades of considerable effort. The appearance of graphene and its gapless spectrum enable their applications in sensitive detection of light over a very wide energy spectrum from ultraviolet, infrared to terahertz. Several mechanisms in graphene for THz detection have been proposed, such as photo-thermoelectric, Dyakonov-Shur (DS) and bolometric effects. Here, we propose a photoconductive mechanism assisted by plasma wave in a graphene field-effect transistor (FET). Sensitive response to THz radiation can be realized far below the interband transition at room temperature. The response is due to the contributions of both plasma drag and convection effects. The two effects can both trigger multiple potential wells along the channel, which are different from other quantum-transition mechanisms. The photoconductive effects can be explored in both periodic and non-periodic systems and can be substantially enhanced under the electric field. They could reduce the burden of structural complexity compared to other mechanisms like unilateral thermoelectric and DS detection. This paves the way for more judicious photo-detector design for versatile THz applications. PMID:26655800

  7. Intrinsic photo-conductance triggered by the plasmonic effect in graphene for terahertz detection

    NASA Astrophysics Data System (ADS)

    Wang, Lin; Chen, Xiaoshuang; Lu, Wei

    2016-01-01

    Terahertz (THz) technology is becoming more eminent for applications in diverse areas including biomedical imaging, communication, security and astronomy. However, THz detection still has some challenges due to the lack of sources and detectors despite decades of considerable effort. The appearance of graphene and its gapless spectrum enable their applications in sensitive detection of light over a very wide energy spectrum from ultraviolet, infrared to terahertz. Several mechanisms in graphene for THz detection have been proposed, such as photo-thermoelectric, Dyakonov-Shur (DS) and bolometric effects. Here, we propose a photoconductive mechanism assisted by plasma wave in a graphene field-effect transistor (FET). Sensitive response to THz radiation can be realized far below the interband transition at room temperature. The response is due to the contributions of both plasma drag and convection effects. The two effects can both trigger multiple potential wells along the channel, which are different from other quantum-transition mechanisms. The photoconductive effects can be explored in both periodic and non-periodic systems and can be substantially enhanced under the electric field. They could reduce the burden of structural complexity compared to other mechanisms like unilateral thermoelectric and DS detection. This paves the way for more judicious photo-detector design for versatile THz applications.

  8. Intrinsic photo-conductance triggered by the plasmonic effect in graphene for terahertz detection.

    PubMed

    Wang, Lin; Chen, Xiaoshuang; Lu, Wei

    2016-01-22

    Terahertz (THz) technology is becoming more eminent for applications in diverse areas including biomedical imaging, communication, security and astronomy. However, THz detection still has some challenges due to the lack of sources and detectors despite decades of considerable effort. The appearance of graphene and its gapless spectrum enable their applications in sensitive detection of light over a very wide energy spectrum from ultraviolet, infrared to terahertz. Several mechanisms in graphene for THz detection have been proposed, such as photo-thermoelectric, Dyakonov-Shur (DS) and bolometric effects. Here, we propose a photoconductive mechanism assisted by plasma wave in a graphene field-effect transistor (FET). Sensitive response to THz radiation can be realized far below the interband transition at room temperature. The response is due to the contributions of both plasma drag and convection effects. The two effects can both trigger multiple potential wells along the channel, which are different from other quantum-transition mechanisms. The photoconductive effects can be explored in both periodic and non-periodic systems and can be substantially enhanced under the electric field. They could reduce the burden of structural complexity compared to other mechanisms like unilateral thermoelectric and DS detection. This paves the way for more judicious photo-detector design for versatile THz applications.

  9. Parameter correction method for dual position-sensitive-detector-based unit.

    PubMed

    Mao, Shuai; Hu, Pengcheng; Ding, XueMei; Tan, JiuBin

    2016-05-20

    A dual position-sensitive-detector (PSD)-based unit can be used for angular measurements of a multi-degree-of-freedom measurement system and a laser interferometry-based sensing and tracking system. In order to ensure the precision of incident beam direction measurement for a PSD-based unit, model and autoreflection alignment methods for correction of PSD-based unit parameters are proposed. Experimental results demonstrate the deviations between the angular measurements obtained using a dual PSD-based unit and an autocollimator varied by 70″, 20″, and 1″ for three runs of the autoreflection alignment method, respectively, and the model method deviations all varied by 1″ in the 1000″ measurement range for three runs. It is therefore concluded that the model method is more reliable than the autoreflection alignment method for ensuring the accuracy of a dual PSD-based unit. PMID:27411134

  10. Development of a Position Sensitive Heavy Ion Detector for Nuclear Astrophysics

    NASA Astrophysics Data System (ADS)

    Need, Emily; Blackmon, J. C.; Deibel, C. M.; Lai, J.; Lindhart, L. E.; Macon, K. T.; Matos, M.; Rasco, B. C.; Rogachev, G.; Wiedenhover, I.

    2012-10-01

    The Array for Nuclear Astrophysics Studies with Exotic Nuclei (ANASEN) is a charged-particle detector array used to study reactions with radioactive beams at FSU and the NSCL. One of the main goals is to improve our understanding of nuclear reactions important in stellar explosions. One important component of ANASEN is a heavy ion detector located downstream of the target that is used to identify the atomic number of heavy ions based upon their energy loss through the gas-filled chamber. We have developed a new version of this detector with major design changes to improve data collection and allow much greater selectivity for the reactions of interest. These changes include anodes based on custom printed circuit boards that provide position sensitivity, larger grids to provide greater acceptance, and a change in wire spacing on the grids to improve transmission. We will present the new design and results from initial tests.

  11. Intensity-sensitive and position-resolving cavity for heavy-ion storage rings

    NASA Astrophysics Data System (ADS)

    Chen, X.; Sanjari, M. S.; Hülsmann, P.; Litvinov, Yu. A.; Nolden, F.; Piotrowski, J.; Steck, M.; Stöhlker, Th.; Walker, P. M.

    2016-08-01

    A heavy-ion storage ring can be adapted for use as an isochronous mass spectrometer if the ion velocity matches the transition energy of the ring. Due to the variety of stored ion species, the isochronous condition cannot be fulfilled for all the ions. In order to eliminate the measurement uncertainty stemming from the velocity spread, an intensity-sensitive and position-resolving cavity is proposed. In this paper we first briefly discuss the correction method for the anisochronism effect in the measurement with the cavity. Then we introduce a novel design, which is operated in the monopole mode and offset from the central beam orbit to one side. The geometrical parameters were optimized by analytic and numerical means in accordance with the beam dynamics of the future collector ring at FAIR. Afterwards, the electromagnetic properties of scaled prototypes were measured on a test bench. The results were in good agreement with the predictions.

  12. Parameter correction method for dual position-sensitive-detector-based unit.

    PubMed

    Mao, Shuai; Hu, Pengcheng; Ding, XueMei; Tan, JiuBin

    2016-05-20

    A dual position-sensitive-detector (PSD)-based unit can be used for angular measurements of a multi-degree-of-freedom measurement system and a laser interferometry-based sensing and tracking system. In order to ensure the precision of incident beam direction measurement for a PSD-based unit, model and autoreflection alignment methods for correction of PSD-based unit parameters are proposed. Experimental results demonstrate the deviations between the angular measurements obtained using a dual PSD-based unit and an autocollimator varied by 70″, 20″, and 1″ for three runs of the autoreflection alignment method, respectively, and the model method deviations all varied by 1″ in the 1000″ measurement range for three runs. It is therefore concluded that the model method is more reliable than the autoreflection alignment method for ensuring the accuracy of a dual PSD-based unit.

  13. Measuring Relative-Story Displacement and Local Inclination Angle Using Multiple Position-Sensitive Detectors

    PubMed Central

    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. PMID:22163434

  14. 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 °.

  15. Position sensitive detectors for the proposed AXAF imaging optical/UV monitor (AXIOM)

    NASA Astrophysics Data System (ADS)

    Allington-Smith, J. R.; Mason, I. M.; Schwarz, H. E.; Culhane, J. L.

    1985-02-01

    A description is given of the imaging detectors of the AXIOM instrument proposed for NASA's Advanced X-ray Astrophysics Facility (AXAF). The instrument is aligned with the X-ray telescope and consists of a diffraction limited, 30-cm aperture, telescope with redundant position sensitive detectors at the focus. This allows simultaneous imaging at optical and near UV wavelengths of the X-ray target objects. The proposed detectors cover a field of view of 8.5 x 8.5 sq arcmin with a resolution of 1 arcsec (= 50 microns FWHM). The quantum efficiency peaks at 30 percent and exceeds 10 percent over the wavelength range 125 to 540 nm. The detector design consists of a bi-alkali photocathode on a UV-transmitting window, proximity focussed onto a microchannel plate intensifier with a wedge and strip readout system, and is optimized for high count rates both from point sources and from the sky background.

  16. Position-sensitive detection of ultracold neutrons with an imaging camera and its implications to spectroscopy

    NASA Astrophysics Data System (ADS)

    Wei, Wanchun; Broussard, L. J.; Hoffbauer, M. A.; Makela, M.; Morris, C. L.; Tang, Z.; Adamek, E. R.; Callahan, N. B.; Clayton, S. M.; Cude-Woods, C.; Currie, S.; Dees, E. B.; Ding, X.; Geltenbort, P.; Hickerson, K. P.; Holley, A. T.; Ito, T. M.; Leung, K. K.; Liu, C.-Y.; Morley, D. J.; Ortiz, Jose D.; Pattie, R. W.; Ramsey, J. C.; Saunders, A.; Seestrom, S. J.; Sharapov, E. I.; Sjue, S. K.; Wexler, J.; Womack, T. L.; Young, A. R.; Zeck, B. A.; Wang, Zhehui

    2016-09-01

    Position-sensitive detection of ultracold neutrons (UCNs) is demonstrated using an imaging charge-coupled device (CCD) camera. A spatial resolution less than 15 μm has been achieved, which is equivalent to a UCN energy resolution below 2 pico-electron-volts through the relation δE =m0 gδx. Here, the symbols δE, δx, m0 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. This method allows different types of UCN spectroscopy and other applications.

  17. Imaging of β particle sources used in medical applications with position sensitive Silicon sensors

    NASA Astrophysics Data System (ADS)

    Caccia, M.; Alemi, M.; Bianchi, C.; Bulgheroni, A.; Cappellini, C.; Conte, L.; Kucewicz, W.; Prest, M.; Vallazza, E.; Sampietro, C.

    2004-06-01

    Real-time dosimetry is a critical issue in most radiotherapy applications. Silicon Ultra fast Cameras for electron and gamma sources In Medical Applications (Nucl. Phys. B 125 (2003) 133) is an EC project addressing the development of an imaging device for extended radioactive sources based on monolithic and hybrid-position-sensitive silicon sensors. Large-area Silicon strip detectors read out by low noise charge integrating chips were used to characterize a 90Sr intravascular brachytherapy source in terms of dose-depth curves in a tissue equivalent material and homogeneity of the activity. The results obtained with the Silicon sensor were compared to measurements with standard certified systems and are reported in the paper.

  18. Textured semiconductors for enhanced photoconductive terahertz emission

    NASA Astrophysics Data System (ADS)

    Collier, Christopher M.; Krupa, Jeffrey D. A.; Hristovski, Ilija R.; Stirling, Trevor J.; Bergen, Mark H.; Holzman, Jonathan F.

    2016-02-01

    There are severe limitations that photoconductive (PC) terahertz (THz) antennas experience due to Joule heating and ohmic losses, which cause premature device breakdown through thermal runaway. In response, this work introduces PC THz antennas utilizing textured InP semiconductors. These textured InP semiconductors exhibit high surface recombination properties and have shortened carrier lifetimes which limit residual photocurrents in the picoseconds following THz pulse emission—ultimately reducing Joule heating and ohmic losses. Fine- and coarse-textured InP semiconductors are studied and compared to a smooth-textured InP semiconductor, which provides a baseline. The surface area ratio (measuring roughness) of the smooth-, fine-, and coarse-textured InP semiconductors is resolved through a computational analysis of SEM images and found as 1.0 +/- 0.1, 2.9 +/- 0.4, and 4.3 +/- 0.6, respectively. The carrier lifetimes of the smooth-, fine-, and coarse-textured InP semiconductors are found as respective values of 200 +/- 6, 100 +/- 10, and 20 +/- 3 ps when measured with a pump-probe experimental system. The emitted THz electric fields and corresponding consumption of photocurrent are measured with a THz experimental setup. The temporal and spectral responses of PC THz antennas made with each of the textured InP semiconductors are found to be similar; however, the consumption of photocurrent (relating to Joule heating and ohmic losses) is greatly diminished for the semiconductors that are textured. The findings of this work can assist in engineering of small-scale PC THz antennas for high-power operation, where they are extremely vulnerable to premature device breakdown through thermal runaway.

  19. Imaging, Detection, and Identification Algorithms for Position-Sensitive Gamma-Ray Detectors

    NASA Astrophysics Data System (ADS)

    Wahl, Christopher G.

    Three-dimensional-position-sensitive semiconductors record both the locations and energies of gamma-ray interactions with high resolution, enabling spectroscopy and imaging of gamma-ray-emitting materials. Imaging enables the detection of point sources of gamma rays in an otherwise extended-source background, even when the background spectrum is unknown and may share the point source's spectrum. The generalized likelihood ratio test (GLRT) and source-intensity test (SIT) are applied to this situation to detect one-or-more unshielded point sources from a library of isotopes in a spectrally unknown or known background when the background intensity varies spatially by a factor of two or less. In addition to estimating the number of sources present, their activities, isotopes, and directions from the detector are estimated. Experimental and some simulated results are presented for a single detector and an 18-detector array of 2 cm by 2 cm by 1.5 cm CdZnTe crystals and compared with the performance of spectral-only detection when the background and source are assumed to be spectrally different. Furthermore, the expected detection performance of the 18-detector array system is investigated statistically using experimental data in the case where the background is distinct spectrally from the point source and the possible source location and isotopic identity are known. Including imaging gave at least 7% higher SNR compared to ignoring the image dimension. Also, imaging methods based on the maximum-likelihood, expectation-maximization method are introduced to determine the spatial distribution of isotopes and to find the activity distributions within targets moving with known motion through a radioactive background. Software has also been developed to support the analysis of the data from 3D-position-sensitive spectroscopic systems, for a range of detector designs and applications. The software design and unique features that allow fast multidimensional data analysis are

  20. New Developments in the Position Sensitive Detectors Based on Microchannel Plates

    NASA Astrophysics Data System (ADS)

    Tremsin, A. S.; Siegmund, O. H. W.

    2002-11-01

    We report on the latest developments in position sensitive photon counting detectors based on microchannel plates. Substantial improvement of the spatial resolution was achieved with introduction of new readout technology, namely crossed strip (XS) anode, and corresponding processing electronics. The spatial resolution of XS readout appeared to be as small as ~3-4 μm FWHM. Reduction of the total detector gain (down to 106 and potentially lower) without compromising the spatial accuracy allows detector operation at much higher local and global counting rates since the microchannel recharge time becomes smaller. Recent developments of novel microchannel plate technologies provide basis for substantial increase of the spectral sensitivity and quantum efficiency of MCP detectors. We have tested a number of new Silicon micromachined MCPs The new MCP technologies should allow deposition of completely new photocathode materials directly on the front surface of microchannel plates (opaque photocathodes). Opposite to standard glass MCPs new Silicon MCPs can sustain high temperatures (-800 C°) required for the photocathode deposition and activation processes.

  1. Fourier synthesis image reconstruction by use of one-dimensional position-sensitive detectors.

    PubMed

    Kotoku, Jun'ichi; Makishima, Kazuo; Okada, Yuu; Negoro, Hitoshi; Terada, Yukikatsu; Kaneda, Hidehiro; Oda, Minoru

    2003-07-10

    An improvement of Fourier synthesis optics for hard x-ray imaging is described, and the basic performance of the new optics is confirmed through numerical simulations. The original concept of the Fourier synthesis imager utilizes nonposition-sensitive hard x-ray detectors coupled to individual bigrid modulation collimators. The improved concept employs a one-dimensional position-sensitive detector (such as a CdTe strip detector) instead of the second grid layer of each bigrid modulation collimator. This improves the imaging performance in several respects over the original design. One performance improvement is a two-fold increase in the average transmission, from 1/4 to 1/2. The second merit is that both the sine and cosine components can be derived from a single grid-detector module, and hence the number of imaging modules can be halved. Furthermore, it provides information along the depth direction simultaneously. This in turn enables a three-dimensional imaging hard x-ray microscope for medical diagnostics, incorporating radioactive tracers. A conceptual design of such a microscope is presented, designed to provide a field of view of 4 mm and a spatial resolution of 400 microm.

  2. Position sensitivity of graphene field effect transistors to X-rays

    SciTech Connect

    Cazalas, Edward Moore, Michael E.; Jovanovic, Igor; Sarker, Biddut K.; Childres, Isaac; Chen, Yong P.

    2015-06-01

    Device architectures that incorporate graphene to realize detection of electromagnetic radiation typically utilize the direct absorbance of radiation by graphene. This limits their effective area to the size of the graphene and their applicability to lower-energy, less penetrating forms of radiation. In contrast, graphene-based transistor architectures that utilize the field effect as the detection mechanism can be sensitive to interactions of radiation not only with graphene but also with the surrounding substrate. Here, we report the study of the position sensitivity and response of a graphene-based field effect transistor (GFET) to penetrating, well-collimated radiation (micro-beam X-rays), producing ionization in the substrate primarily away from graphene. It is found that responsivity and response speed are strongly dependent on the X-ray beam distance from graphene and the gate voltage applied to the GFET. To develop an understanding of the spatially dependent response, a model is developed that incorporates the volumetric charge generation, transport, and recombination. The model is in good agreement with the observed spatial response characteristics of the GFET and predicts a greater response potential of the GFET to radiation interacting near its surface. The study undertaken provides the necessary insight into the volumetric nature of the GFET response, essential for development of GFET-based detectors for more penetrating forms of ionizing radiation.

  3. Lateral photoconductivity in structures with Ge/Si quantum dots

    SciTech Connect

    Panevin, V. Yu. Sofronov, A. N.; Vorobjev, L. E.; Firsov, D. A.; Shalygin, V. A.; Vinnichenko, M. Ya.; Balagula, R. M.; Tonkikh, A. A.; Werner, P.; Fuhrman, B.; Schmidt, G.

    2013-12-15

    The spectra of lateral photoconductivity and optical absorption caused by the intraband optical transitions of holes in Ge/Si quantum dots are studied at different lattice temperatures. Polarization-dependent spectral features related to the transitions of holes from the quantum dot (QD) ground state are revealed in the optical spectra. Temperature photoconductivity quenching caused by the reverse trapping of nonequilibrium free holes by the QD bound state is observed. The obtained experimental data make it possible to determine the height of the surface band bending at the QD heterointerface.

  4. Visible-light photoconductivity of Zn1-xCoxO and its dependence on Co2+ concentration

    SciTech Connect

    Johnson, Claire A.; Cohn, Alicia; Kaspar, Tiffany C.; Chambers, Scott A.; Salley, G. Mackay; Gamelin, Daniel R.

    2011-09-06

    Many metal oxides investigated for solar photocatalysis or photoelectrochemistry have band gaps that are too wide to absorb a sufficient portion of the solar spectrum. Doping with impurity ions has been extensively explored as a strategy to sensitize such oxides to visible light, but the electronic structures of the resulting materials are frequently complex and poorly understood. Here, we report a detailed photoconductivity investigation of the wide-gap II-VI semiconductor ZnO doped with Co2+ (Zn1-xCoxO), which responds to visible light in photoelectrochemical and photoconductivity experiments and thus represents a well-defined model system for understanding dopant-sensitized oxides. Variable-temperature scanning photoconductivity measurements have been performed on high-structural-quality Zn1-xCoxO epitaxial films to examine the relationship between dopant concentration (x) and visible-light photoconductivity, with particular focus on mid-gap d-d photoactivity. Excitation into the intense 4T1(P) d-d band at ~2.0 eV (620 nm) leads to Co2+/3+ ionization with a quantum efficiency that increases with decreasing cobalt concentration and increasing sample temperature. Both spontaneous and thermally assisted ionization from the Co2+ d-d excited state are found to become less effective as x is increased, attributed to an increasing conduction-band-edge potential. These trends counter the increasing light absorption with increasing x, explaining the experimental maximum in external photon-to-current conversion efficiencies at values well below the solid solubility of Co2+ in ZnO.

  5. Method of nonlinear correction of two-dimensional position sensitive detector

    NASA Astrophysics Data System (ADS)

    Mo, Changtao; Wang, Ming; Zhang, Guoyu

    2007-12-01

    The position sensitive detector (PSD) is photo-electronic sensor which can detect the position of a light spot incident on its surface. Many types of non-contact dynamic displacement monitoring instruments could be constructed using PSD. How to overcome the influence of non-linearity action is the most important problem to improve measuring precision and reliability of the instrument. The output characteristic of PSD is analyzed. It is found that the output response of sensor is non-linear when the measuring range is large. In this paper we propose a method for correcting non-linearity of PSD sensor based on high precision linearization sub-block integration neural network interpolation. By using conjugate gradient algorithm of neural network which have characteristic to approach arbitrary nonlinear function, the nonlinear mapping between detecting the voltage of sensor and the outputting results are obtained by training neural network under different nonlinear condition. Experiment results indicate that not only the influence of non-linearity is eliminated effectively, but also the output of nerve network is linear.

  6. Performance of BF{sub 3} Filled Position Sensitive Neutron Detector

    SciTech Connect

    Desai, Shraddha S.; Devan, Shylaja; Krishna, P. S. R.

    2011-07-15

    {sup 3}He filled position sensitive detectors (PSD)s developed in-house are successfully used for neutron scattering studies at Dhruva. However recent global scarcity of {sup 3}He has made it essential to find an alternative. It is very difficult to meet performance capabilities of {sup 3}He for neutron detection in any of the alternate materials. Among various alternatives, BF{sub 3} gas can be one. We have recently put an effort to evaluate performance of BF{sub 3} based PSD. For that a PSD filled with BF{sub 3} gas at 0.8 bar pressure is fabricated and characterized. Performances of the same with Pu-Be source and at Hi-Q Diffractometer, Dhruva are reported in this paper. Diffraction spectra from standard samples Fe and Si at wavelength 0.783 A were recorded. It is found that while position resolution of the BF{sub 3} filled PSD is comparable but the efficiency is 20 times less than that of a {sup 3}He(12 bar) filled PSD.

  7. Higher sensitivity of human auditory nerve fibers to positive electrical currents.

    PubMed

    Macherey, Olivier; Carlyon, Robert P; van Wieringen, Astrid; Deeks, John M; Wouters, Jan

    2008-06-01

    Most contemporary cochlear implants (CIs) stimulate the auditory nerve with trains of amplitude-modulated, symmetric biphasic pulses. Although both polarities of a pulse can depolarize the nerve fibers and generate action potentials, it remains unknown which of the two (positive or negative) phases has the stronger effect. Understanding the effects of pulse polarity will help to optimize the stimulation protocols and to deliver the most relevant information to the implant listeners. Animal experiments have shown that cathodic (negative) current flows are more effective than anodic (positive) ones in eliciting neural responses, and this finding has motivated the development of novel speech-processing algorithms. In this study, we show electrophysiologically and psychophysically that the human auditory system exhibits the opposite pattern, being more sensitive to anodic stimulation. We measured electrically evoked compound action potentials in CI listeners for phase-separated pulses, allowing us to tease out the responses to each of the two opposite-polarity phases. At an equal stimulus level, the anodic phase yielded the larger response. Furthermore, a measure of psychophysical masking patterns revealed that this polarity difference was still present at higher levels of the auditory system and was therefore not solely due to antidromic propagation of the neural response. This finding may relate to a particular orientation of the nerve fibers relative to the electrode or to a substantial degeneration and demyelination of the peripheral processes. Potential applications to improve CI speech-processing strategies are discussed.

  8. 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).

  9. Position-sensitive change in the transition metal L-edge fine structures

    SciTech Connect

    Gulec, Ahmet; Phillips, Patrick J.; Klie, Robert F.

    2015-10-05

    Studying the structure and composition of solid-state materials on the atomic scale has become nearly routine in transmission electron microscopy with the development of novel electron optics and electron sources. In particular, with spatial resolutions better than 0.1 nm and energy resolution smaller than 100 meV, the stoichiometry, bonding, and coordination can now be examined on similar scales. Aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) have played a crucial role in identifying charge ordering, valence, and as spin state transitions in transition metal perovskite oxides. In this letter, we investigate the effects of ever-decreasing electron-probe sizes on the measured near-edge fine-structure of the transition metal core-loss edge using EELS. We find that for certain transition metal perovskites, the position of the electron probe with respect to the atomic column is crucial in determining the correct valence state. Several reasons for the observed position-sensitive EELS fine-structure are discussed.

  10. A Simple Capacitive Charge-Division Readout for Position-Sensitive Solid-State Photomultiplier Arrays

    PubMed Central

    Du, Junwei; Schmall, Jeffrey P.; Yang, Yongfeng; Di, Kun; Dokhale, Purushottam A.; Shah, Kanai S.; Cherry, Simon R.

    2014-01-01

    A capacitive charge-division readout method for reading out a 2 × 2 array of 5 mm × 5 mm position-sensitive solid-state photomultipliers (PS-SSPM) was designed and evaluated. Using this analog multiplexing method, the 20 signals (16 position, 4 timing) from the PS-SSPM array are reduced to 5 signals (4 position, 1 timing), allowing the PS-SSPM array to be treated as an individual large-area PS-SSPM module. A global positioning approach can now be used, instead of individual positioning for each PS-SSPM in the array, ensuring that the entire light signal is utilized. The signal-to-noise ratio (SNR) and flood histogram quality at different bias voltages (27.5 V to 32.0 V at 0.5 V intervals) and a fixed temperature of 0 °C were evaluated by coupling a 6 × 6 array of 1.3 mm × 1.3 mm × 20 mm polished LSO crystals to the center of the PS-SSPM array. The timing resolution was measured at a fixed bias voltage of 31.0 V and a fixed temperature of 0 °C. All the measurements were evaluated and compared using capacitors with different values and tolerances. Capacitor values ranged from 0.051 nf to 10 nf, and the capacitance tolerance ranged from 1% to 20%. The results show that better performance was achieved using capacitors with smaller values and better capacitance tolerance. Using 0.2 nf capacitors, the SNR, energy resolution and timing resolution were 24.3, 18.2% and 8.8 ns at a bias voltage 31.0 V, respectively. The flood histogram quality was also evaluated by using a 10 × 10 array of 1 mm × 1 mm × 10 mm polished LSO crystals and a 10 × 10 array of 0.7 mm × 0.7 mm × 20 mm unpolished LSO crystals to determine the smallest crystal size resolvable. These studies showed that the high spatial resolution of the PS-SSPM was preserved allowing for 0.7 mm crystals to be identified. These results show that the capacitive charge-division analog signal processing method can significantly reduce the number of electronic channels, from 20 to 5, while retaining the

  11. New Data Collection Subsystem for Powder Neutron Diffractometer with Position Sensitive Detectors

    NASA Astrophysics Data System (ADS)

    Drab, Martin; Kalvoda, Ladislav; Vratislav, Stanislav; Dlouha, Maja

    2012-02-01

    Project INDECS (Integrated Neutron Diffraction Experiment Control System) is a newly developed software system created for the purpose of data acquisition from, and controlling of the upgraded version of the KSN-2 powder neutron diffractometer equipped with Position Sensitive Detectors. The KSN-2 neutron diffractometer (belonging to LND, DSSE, FNSPE, CTU in Prague, CZ, placed at the NRI, Řež near Prague, CZ) was recently upgraded with the possibility to contain up to three parallel linear PSDs which can be mounted on the detector arm instead of the original single counter detector. That was the motivation for the project INDECS to be started. For the actual data acquisition and initial data analysis of the raw sampled signals within the project INDECS a special modular structure called the PSD Acquisition Path (or PSDAP) was designed. Raw sampled signals from either end of the PSD are taken as the main input to the subsystem. The signals are then split into multiple events, analyzed for the position of the obtained events on the PSD, and a histogram of the diffraction events is created as the main output of this subsystem. Moreover, the PSDAP is capable of storing the raw signals either before event splitting or after, so that later the whole process of acquisition can be replayed in software, perhaps with different settings of the processing parameters or perhaps even algorithms. It can also be switched into a mode where under special conditions a correction curve specific for the given PSD can be constructed and later in normal operation it can be used to do the corrections of detected event positions to enhance the results on that particular PSD. This whole subsystem then acts as a single modular command unit (External Execution Module or EEM) within the entire system of project INDECS.

  12. Sensitivity of MJO propagation to a robust positive Indian Ocean dipole event in the superparameterized CAM

    NASA Astrophysics Data System (ADS)

    Benedict, James J.; Pritchard, Michael S.; Collins, William D.

    2015-12-01

    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 MJO 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 Niño-like conditions.

  13. Imatinib sensitizes endometrial cancer cells to cisplatin by targeting CD117-positive growth-competent cells.

    PubMed

    Zhang, Xiuzhi; Kyo, Satoru; Nakamura, Mitsuhiro; Mizumoto, Yasunari; Maida, Yoshiko; Bono, Yukiko; Takakura, Masahiro; Fujiwara, Hiroshi

    2014-04-01

    The use of molecular target therapy has not been established for endometrial cancer. The present study investigated the potential therapeutic strategy of targeting CD117-positive cancer cells as a novel molecular target therapy. FACS-sorted CD117(+) cells isolated from endometrial cancer cell lines (Ishikawa or MFE280 cells) exhibited higher proliferative capacity in vitro and colony forming activity on soft agar, and decreased sensitivity to cisplatin, compared to CD117(-) cells. Immunohistochemical analyses with surgical specimens of endometrial cancers showed that high CD117 expression was tightly linked to advanced FIGO stages, myometrial invasion and histological grade, and was significantly associated with poor overall survival and relapse-free survival (Kaplan-Meier analysis; p<0.001, log-rank test). The Cox-regression hazard model identified high CD117 expression to be an independent prognostic factor for survival (p<0.05). In vitro assay confirmed that stem cell factor (SCF), a ligand of CD117, was produced specifically in CD117(+) cells of endometrial cancer, and the colony-forming activity were abrogated by adding anti-SCF antibody, indicating an SCF-dependent growth property. Imatinib was confirmed to selectively target CD117(+) cells in vitro, and synergistically enhanced the anti-tumor effect of low dose cisplatin in vivo, which showed only modest effects when used as a single use. These findings suggest that CD117 can be a marker of aggressive behavior of cells as well as an independent prognostic marker in endometrial cancer. Targeting of the SCF/CD117 axis by imatinib sensitized endometrial cancer cells to cisplatin, proposing a novel therapeutic strategy for this tumor type. PMID:24333732

  14. 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.

  15. Metal nanoparticles triggered persistent negative photoconductivity in silk protein hydrogels.

    PubMed

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

    2016-04-14

    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. PMID:26996157

  16. Betabox: a beta particle imaging system based on a position sensitive avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Dooraghi, A. A.; Vu, N. T.; Silverman, R. W.; Farrell, R.; Shah, K. S.; Wang, J.; Heath, J. R.; Chatziioannou, A. F.

    2013-06-01

    A beta camera has been developed that allows planar imaging of the spatial and temporal distribution of beta particles using a 14 × 14 mm2 position sensitive avalanche photodiode (PSAPD). This camera system, which we call Betabox, can be directly coupled to microfluidic chips designed for cell incubation or other biological applications. Betabox allows for imaging the cellular uptake of molecular imaging probes labeled with charged particle emitters such as 18F inside these chips. In this work, we investigate the quantitative imaging capabilities of Betabox for 18F beta particles, in terms of background rate, efficiency, spatial resolution, and count rate. Measurements of background and spatial resolution are considered both at room temperature (21 °C ± 1 °C) and at an elevated operating temperature (37 °C ± 1 °C), as is often required for biological assays. The background rate measured with a 4 keV energy cutoff is below 2 cph mm-2 at both 21 and 37 °C. The absolute efficiency of Betabox for the detection of 18F positron sources in contact with a PSAPD with the surface passivated from ambient light and damage is 46% ± 1%. The lower detection limit is estimated using the Rose Criterion to be 0.2 cps mm-2 for 1 min acquisitions and a 62 × 62 µm2 pixel size. The upper detection limit is approximately 21 000 cps. The spatial resolution at both 21 and 37 °C ranges from 0.4 mm FWHM at the center of the field of view (FOV), and degrades to 1 mm at a distance of 5 mm away from center yielding a useful FOV of approximately 10 × 10 mm2. We also investigate the effects on spatial resolution and sensitivity that result from the use of a polymer based microfluidic chip. For these studies we place varying layers of low-density polyethylene (LDPE) between the detector and the source and find that the spatial resolution degrades by ˜180 µm for every 100 µm of LDPE film. Sensitivity is reduced by half with the inclusion of ˜200 µm of additional LDPE film. Lastly

  17. Betabox: a beta particle imaging system based on a position sensitive avalanche photodiode

    PubMed Central

    Dooraghi, AA; Vu, NT; Silverman, RW; Farrell, R; Shah, KS; Wang, J; Heath, JR; Chatziioannou, AF

    2013-01-01

    A beta camera has been developed that allows planar imaging of the spatial and temporal distribution of beta particles using a 14 × 14 mm2 position sensitive avalanche photodiode (PSAPD). This camera system, which we call Betabox, can be directly coupled to microfluidic chips designed for cell incubation or other biological applications. Betabox allows for imaging the cellular uptake of molecular imaging probes labeled with charged particle emitters such as 18F inside these chips. In this work, we investigate the quantitative imaging capabilities of Betabox for 18F beta particles, in terms of background rate, efficiency, spatial resolution, and count rate. Measurements of background and spatial resolution are considered both at room temperature (21 °C ± 1 °C) and at an elevated operating temperature (37 °C ± 1 °C), as is often required for biological assays. The background rate measured with a 4 keV energy cutoff is below 2 cph mm−2 at both 21 and 37 °C. The absolute efficiency of Betabox for the detection of 18F positron sources in contact with a PSAPD with the surface passivated from ambient light and damage is 46% ± 1%. The lower detection limit is estimated using the Rose Criterion to be 0.2 cps mm−2 for 1 min acquisitions and a 62 × 62 µm2 pixel size. The upper detection limit is approximately 21 000 cps. The spatial resolution at both 21 and 37 °C ranges from 0.4 mm FWHM at the center of the field of view (FOV), and degrades to 1 mm at a distance of 5 mm away from center yielding a useful FOV of approximately 10 × 10 mm2. We also investigate the effects on spatial resolution and sensitivity that result from the use of a polymer based microfluidic chip. For these studies we place varying layers of low-density polyethylene (LDPE) between the detector and the source and find that the spatial resolution degrades by ~180 µm for every 100 µm of LDPE film. Sensitivity is reduced by half with the inclusion of ~200 µm of additional LDPE film

  18. 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

    2012-11-01

    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. PMID:23187403

  19. Bandgap Density of States from Long-term Transient Photoconductivity in Thin-film TiO_2

    NASA Astrophysics Data System (ADS)

    Golego, Nickolay; Studenikin, S. A.; Cocivera, Michael

    1998-10-01

    Titanium dioxide thin films, stoichiometric and containing niobium, were prepared by spray pyrolysis from a peroxide solution.(J. Electrochem. Soc. 144), 736 (1997); Thin Solid Films, 322, 14 (1998); Chem. Mater., 10, 2000 (1998) Dark DC conductivity of the films was in the 10-11-10-9 (Ω\\cdotcm)-1 range; Hall effect measurements indicated that effective electron mobility was below 0.3 cm^2/(V\\cdots). Illumination increased the conductivity by several orders of magnitude; saturation was not attained after several hours of illumination at room temperature. The conductivity decay followed a non-exponential law extending beyond 10^7 s. Density-of-states distribution of sensitizing acceptor centres in the bandgap was calculated from photoconductivity transients using an improved Laplas transform method. Temperature, light intensity, and illumination time effects were studied in detail. Both transient and steady-state photoconductivity were dependent on oxygen partial pressure. The acceptor centres may be due to oxygen-related surface states; a model of photoconductivity is proposed.

  20. Potential of sulfasalazine as a therapeutic sensitizer for CD44 splice variant 9-positive urogenital cancer.

    PubMed

    Takayama, Tatsuya; Kubo, Taro; Morikawa, Ai; Morita, Tatsuo; Nagano, Osamu; Saya, Hideyuki

    2016-05-01

    Cancer stem-like cells (CSCs) with high expression of CD44 splice variant (CD44v) have an enhanced capacity for intracellular reduced glutathione synthesis and defense against reactive oxygen species, resulting in resistance to various therapeutic stresses. Sulfasalazine (SSZ), a drug used in the treatment of rheumatoid arthritis (RA), inhibits glutamate-cystine transport, and suppressed CD44v-dependent tumor growth and increased sensitivity to cytotoxic drugs in an in vivo study. Here, we present two cases of CD44v9-positive urogenital cancer with concomitant treatment with SSZ for RA. Patient 1 was a 62-year-old man who had received SSZ for RA beginning 2 months before the diagnosis of urinary bladder cancer. Although he had multiple metastases to the bladder, abdominal, left cervical and left axillary lymph nodes, and brain, complete response with multidisciplinary therapy was maintained for more than 2 years. Patient 2 was a 74-year-old man with castration-resistant prostate cancer who was diagnosed with RA during chemotherapy and a gradual increase in prostate-specific antigen (PSA) level. When SSZ was added, his PSA value (ng/mL) decreased from 12.93 to 5.58 in only 2 weeks and then quickly rebounded, whereas levels of neuron-specific enolase, a neuroendocrine differentiator and CSC marker, remained almost unchanged. We therefore speculate that SSZ treatment may represent a new adjuvant treatment option for patients with CD44v9-positive urogenital cancer. PMID:27044355

  1. 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.

  2. Nanoscale Photoconductivity Imaging of Thin-film Semiconductors by Laser-assisted Microwave Impedance Microscopy

    NASA Astrophysics Data System (ADS)

    Chu, Zhaodong; Wu, Di; Ren, Yuan; Yang, Seungcheol; Sun, Liuyang; Li, Xiaoqin; Lai, Keji

    The photo-response of semiconductors is usually studied by detecting the photocurrent across source-drain electrodes under light illumination. By integrating the microwave impedance microscopy (MIM) technique with focused-laser stimulation, we are able to perform the real-space photoconductivity mapping of photo-sensitive materials without the need of patterning contact electrodes. Here, we report the MIM results of various thin-film materials, such as In2Se3 nano-sheets and transition metal dichalcogenides (TMD) flakes, illuminated by laser beams of different wavelengths in the ambient condition. With no or below-gap illumination, the samples were highly resistive, as indicated by the low MIM signals. The MIM contrast emerges under above-gap light and increases as increasing laser intensity, which clearly demonstrates the local imaging of photoconductivity rather than the transport photocurrent. Interestingly, clear domain structures with mesoscopic length scales were seen in the data due to the coexistence of multiple phases in In2Se3. The unique combination of MIM and laser stimulation thus provides a new direction to explore the microscopic origin of various light-driven phenomena in complex systems. We gratefully acknowledge financial support from NSF.

  3. 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.

  4. Tellurium doping effect in avalanche-mode amorphous selenium photoconductive film

    SciTech Connect

    Park, Wug-Dong; Tanioka, Kenkichi

    2014-11-10

    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.

  5. Reciprocal space mapping of epitaxial materials using position-sensitive x-ray detection

    SciTech Connect

    Lee, S.R.; Doyle, B.L.; Drummond, T.J.; Medernach, J.W.; Schneider, R.P. Jr.

    1994-10-01

    Reciprocal space mapping can be efficiently carried out using a position-sensitive x-ray detector (PSD) coupled to a traditional double-axis diffractometer. The PSD offers parallel measurement of the total scattering angle of all diffracted x-rays during a single rocking-curve scan. As a result, a two-dimensional reciprocal space map can be made in a very short time similar to that of a one-dimensional rocking-curve scan. Fast, efficient reciprocal space mapping offers numerous routine advantages to the x-ray diffraction analyst. Some of these advantages are the explicit differentiation of lattice strain from crystal orientation effects in strain-relaxed heteroepitaxial layers; the nondestructive characterization of the size, shape and orientation of nanocrystalline domains in ordered-alloy epilayers; and the ability to measure the average size and shape of voids in porous epilayers. Here, the PSD-based diffractometer is described, and specific examples clearly illustrating the advantages of complete reciprocal space analysis are presented.

  6. Characterization of two resistive anode encoder position sensitive detectors for use in ion microscopy

    NASA Astrophysics Data System (ADS)

    Brigham, Robert H.; Bleiler, Roger J.; McNitt, Paul J.; Reed, David A.; Fleming, Ronald H.

    1993-02-01

    Both the standard resistive anode encoder (RAE) position sensitive ion detector and a new faster version have been adapted for use with CAMECA IMS-3f/4f imaging secondary-ion mass spectroscopy instruments. Each detector includes a dual microchannel plate image intensifier mounted in front of a resistive anode. The conversion efficiencies of the standard and fast detectors are 60% and 55%, respectively. The high count rates attainable with the fast detector require high strip-current microchannel plates for optimum performance. The mass bias of these detectors is proportional to (mass)1/2 and can be compensated by adjustment of detector supply voltage. The response across the active area of these detectors is uniform to within 3% with the greatest deviations occurring at the periphery. Distortion and pixel-to-pixel bias are negligible with the standard RAE, but noticeable in the prototype of the fast RAE. Software has been developed that corrects pixel-to-pixel bias. The dead times of the standard and fast RAE systems are 4.3±0.1 μs and 330±2 ns which limit practical count rates to about 40 000 and 600 000 Hz, respectively. For many applications, the higher ion arrival rates and dynamic range of the fast RAE imaging system more than compensate for the increased pixel-to-pixel bias and distortion and the small decrease in conversion efficiency.

  7. Mathematical modelling and study of the encoding readout scheme for position sensitive detectors

    NASA Astrophysics Data System (ADS)

    Yue, Xiaoguang; Zeng, Ming; Zeng, Zhi; Wang, Yi; Wang, Xuewu; Zhao, Ziran; Cheng, Jianping; Kang, Kejun

    2016-04-01

    Encoding readout methods based on different schemes have been successfully developed and tested with different types of position-sensitive detectors with strip-readout structures. However, how to construct an encoding scheme in a more general and systematic way is still under study. In this paper, we present a graph model for the encoding scheme. With this model, encoding schemes can be studied in a more systematic way. It is shown that by using an encoding readout method, a maximum of n (n - 1)/2 + 1 strips can be processed with n channels if n is odd, while a maximum of n (n - 2)/2 + 2 strips can be processed with n channels if n is even. Furthermore, based on the model, the encoding scheme construction problem can be translated into a problem in graph theory, the aim of which is to construct an Eulerian trail such that the length of the shortest subcycle is as long as possible. A more general approach to constructing the encoding scheme is found by solving the associated mathematical problem. In addition, an encoding scheme prototype has been constructed, and verified with MRPC detectors.

  8. Development of position-sensitive time-of-flight spectrometer for fission fragment research

    SciTech Connect

    Arnold, C. W.; Tovesson, F.; Meierbachtol, K.; Bredeweg, T.; Jandel, M.; Jorgenson, H. J.; Laptev, A.; Rusev, G.; Shields, D. W.; White, M.; Blakeley, R. E.; Mader, D. M.; Hecht, A. A.

    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. Flight 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.

  9. Development of position-sensitive time-of-flight spectrometer for fission fragment research

    DOE PAGES

    Arnold, C. W.; Tovesson, F.; Meierbachtol, K.; Bredeweg, T.; Jandel, M.; Jorgenson, H. J.; Laptev, A.; Rusev, G.; Shields, D. W.; White, M.; et al

    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

  10. ROSAT Position Sensitive Proportional Counter spectra of six Seyfert 1 galaxies

    NASA Technical Reports Server (NTRS)

    Turner, T. J.; George, I. M.; Mushotzky, R. F.

    1993-01-01

    We present the results from ROSAT Position Sensitive Proportional Counter observations of six Seyfert 1 galaxies in the soft (0.1-2.0 keV) X-ray band. The sources (Mrk 335, ESO 198-G24, ESO 141-G55, Mrk 509, NGC 7469, and MCG-2-58-22) were chosen to have low absorbing column densities along the line of sight. As expected, it is found that all the sources possess significantly steeper spectra below about 1 keV than observed at higher X-ray energies. Assuming a simple absorbed power-law spectral model, the mean (photon) spectral index for the sample is Gamma = 2.38 +/- 0.25, compared to the canonical 1.7 typically observed in the 2-10 keV band. Furthermore, we find strong evidence for soft X-ray spectral features in half the sources. In NGC 7469 and ESO 198-G24, we find that the addition of a narrow emission line or an absorption edge to the underlying continuum is a significant improvement to the parameterization of the spectra. Mrk 335 also shows evidence for spectral complexity, but from these data it is not possible to unambiguously distinguish between an absorption edge and a steepening of the spectrum at low energies. We examine these results in the light of the accuracy of the PSPC spectral calibration.

  11. High-resolution and high-intensity neutron diffractometer with linear position-sensitive detector

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Hee; Moon, Myung-Kook; Em, V. T.; Choi, Young-Nam; Oh, Hwa-Suk; Nam, Uk-Won

    2003-08-01

    The characteristics of a neutron diffractometer using a 3He one-dimensional position-sensitive detector (PSD) with delay line readout, a 200 (length) × 100 (height) mm 2 active window and 2.5 mm spatial resolution have been studied and compared with those of the High-Resolution Powder Diffractometer (HRPD) of KAERI with 32 3He conventional tube (∅50 mm) detectors and Soller collimators (10') before detectors. For the sample to PSD distance R=1200 mm, the PSD subtends 8° angle of 2 θ and provides the resolution and the peak-to-background ratio close to that for HRPD. Time for scanning (with the same statistics) of a 0-160° interval is about 1.6 times longer and the multi-PSD system providing efficiency about 10 times higher than HRPD is proposed. Because of the small angle subtended by the PSD, the parasitic peaks from the sample environment are eliminated and operation without an oscillating radial collimator is possible. Additionally, the proposed diffractometer has an advantage for small samples.

  12. Pedunculopontine tegmental nucleus lesions impair probabilistic reversal learning by reducing sensitivity to positive reward feedback.

    PubMed

    Syed, Anam; Baker, Phillip M; Ragozzino, Michael E

    2016-05-01

    Recent findings indicate that pedunculopontine tegmental nucleus (PPTg) neurons encode reward-related information that is context-dependent. This information is critical for behavioral flexibility when reward outcomes change signaling a shift in response patterns should occur. The present experiment investigated whether NMDA lesions of the PPTg affects the acquisition and/or reversal learning of a spatial discrimination using probabilistic reinforcement. Male Long-Evans rats received a bilateral infusion of NMDA (30nmoles/side) or saline into the PPTg. Subsequently, rats were tested in a spatial discrimination test using a probabilistic learning procedure. One spatial location was rewarded with an 80% probability and the other spatial location rewarded with a 20% probability. After reaching acquisition criterion of 10 consecutive correct trials, the spatial location - reward contingencies were reversed in the following test session. Bilateral and unilateral PPTg-lesioned rats acquired the spatial discrimination test comparable to that as sham controls. In contrast, bilateral PPTg lesions, but not unilateral PPTg lesions, impaired reversal learning. The reversal learning deficit occurred because of increased regressions to the previously 'correct' spatial location after initially selecting the new, 'correct' choice. PPTg lesions also reduced the frequency of win-stay behavior early in the reversal learning session, but did not modify the frequency of lose-shift behavior during reversal learning. The present results suggest that the PPTg contributes to behavioral flexibility under conditions in which outcomes are uncertain, e.g. probabilistic reinforcement, by facilitating sensitivity to positive reward outcomes that allows the reliable execution of a new choice pattern. PMID:26976089

  13. Photoconductivity of composites based on CdSe quantum dots and low-band-gap polymers

    NASA Astrophysics Data System (ADS)

    Dayneko, Sergey; Linkov, Pavel; Martynov, Igor; Tameev, Alexey; Tedoradze, Marine; Samokhvalov, Pavel; Nabiev, Igor; Chistyakov, Alexander

    2016-05-01

    Photoconductivity of thin layers prepared by spin coating of blends of CdSe quantum dots (QDs) and a low-band-gap polymer PCDTBT or PTB7 has been studied. It has been found that photocurrent in the composites containing QDs of 10-nm in size is significantly higher than in those of containing 5-nm QDs. Analysis of the results showed that the photoresponse of the thin layers is mainly determined by the relative positions of the frontier energy levels of the materials used, organic semiconductors and QDs. Therefore, the ability to tune the relative positions of these levels by varying the QD size is of special importance, thus allowing the optimization of photodetectors and photovoltaic cells.

  14. N-Ethylmaleimide Sensitive Factor (NSF) Inhibition Prevents Vascular Instability following Gram-Positive Pulmonary Challenge

    PubMed Central

    Lee, Ji Young; Linge, Helena M.; Ochani, Kanta; Lin, Ke; Miller, Edmund J.

    2016-01-01

    Background The Acute Respiratory Distress Syndrome (ARDS), remains a significant source of morbidity and mortality in critically ill patients. Pneumonia and sepsis are leading causes of ARDS, the pathophysiology of which includes increased pulmonary microvascular permeability and hemodynamic instability resulting in organ dysfunction. We hypothesized that N-ethylmaleimide sensitive factor (NSF) regulates exocytosis of inflammatory mediators, such as Angiopoietin-2 (Ang-2), and cytoskeletal stability by modulating myosin light chain (MLC) phosphorylation. Therefore, we challenged pulmonary cells, in vivo and in vitro, with Gram Positive bacterial cell wall components, lipoteichoic acid (LTA), and peptidoglycan (PGN) and examined the effects of NSF inhibition. Methods Mice were pre-treated with an inhibitor of NSF, TAT-NSF700 (to prevent Ang-2 release). After 30min, LTA and PGN (or saline alone) were instilled intratracheally. Pulse oximetry was assessed in awake mice prior to, and 6 hour post instillation. Post mortem, tissues were collected for studies of inflammation and Ang-2. In vitro, pulmonary endothelial cells were assessed for their responses to LTA and PGN. Results Pulmonary challenge induced signs of airspace and systemic inflammation such as changes in neutrophil counts and protein concentration in bronchoalveolar lavage fluid and tissue Ang-2 concentration, and decreased physiological parameters including oxygen saturation and pulse distention. TAT-NSF700 pre-treatment reduced LTA-PGN induced changes in lung tissue Ang-2, oxygen saturation and pulse distention. In vitro, LTA-PGN induced a rapid (<2 min) release of Ang-2, which was significantly attenuated by TAT-NSF700 or anti TLR2 antibody. Furthermore, TAT-NSF700 reduced LTA-PGN-induced MLC phosphorylation at low concentrations of 1–10 nM. Conclusions TAT-NSF700 decreased Ang-2 release, improved oxygen saturation and pulse distention following pulmonary challenge by inhibiting MLC phosphorylation, an

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

    SciTech Connect

    Kozlov, D. V. Rumyantsev, V. V.; Morozov, S. V.; Kadykov, A. M.; Varavin, V. S.; Mikhailov, N. N.; Dvorestky, S. A.; Gavrilenko, V. I.; Teppe, F.

    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.

  16. Terahertz line detection by a microlens array coupled photoconductive antenna array.

    PubMed

    Pradarutti, B; Müller, R; Freese, W; Matthäus, G; Riehemann, S; Notni, G; Nolte, S; Tünnermann, A

    2008-10-27

    We present THz ultrashort pulse detection by a photoconductive antenna array consisting of 16 photoconductive antennas. The efficient excitation of the photoconductive antennas has been realized by a microlens array which generates 16 single spots from the exciting fs-laser beam. This combination of optoelectronics and microoptics improves the detection efficiency by an order of magnitude in comparison to an excitation by a line focus. PMID:18958123

  17. Steady-state photoconductivity of amorphous (As4S3Se3)1-x:Snx films

    NASA Astrophysics Data System (ADS)

    Iaseniuc, O. V.; Iovu, M. S.; Cojocaru, I. A.; Prisacar, A. M.

    2015-02-01

    Amorphous arsenic trisulfide (As2S3) and arsenic triselenide (As2Se3) are among widely investigated amorphous materials due to its interesting electrical, optical and photoelectrical properties. In order to improve the physical properties and recording characteristics, and to extend the spectral range of photosensibility, a special interest represents the mixed amorphous materials, like (As2S3):(As2Se3). Chalcogenide vitreous semiconductors (ChVS) of the As-S-Se system exhibit photostructural transformations with reversible and irreversible properties, and are promising materials as registration media for holography and optical information, for fabrication of diffractive elements, and other optoelectronic applications. Because many optoelectronic devices on amorphous semiconductors are based on the photoconductivity effect, special interests represent investigation of the stationary and non-stationary characteristics of photoconductivity. In this paper the experimental results of steady-state photoconductivity and holographic characteristics of amorphous (As4S3Se3)1-x:Snx thin films are presented. It was shown that the photoconductivity spectra depend on the polarity on the top illuminated electrode and on the Sn concentration in the host glass. The photosensitivity of amorphous ((As4S3Se3)1-x:Snx thin films is almost constant for all Sn-containing glasses. The Moss rule was used for determination of the optical forbidden gap Eg from the photoconductivity spectra. It was demonstrated that the investigated amorphous films are sensitive to the light irradiation and can be used as effective registration media for holographic information. The relaxation of photodarkening in amorphous (As4S3Se3)1-x:Snx thin films was investigated and was shown that the relaxation curves of transmittance T/T0 = f(t) can be described the stretch exponential function T(t)/T(0) = A0+Aexp[-(t-t0)/τ] (1-β) . The kinetics of diffraction efficiency growth η(t) was measured by registration of

  18. Persistent Photoconductivity Studies in Nanostructured ZnO UV Sensors

    PubMed Central

    2009-01-01

    The phenomenon of persistent photoconductivity is elusive and has not been addressed to an extent to attract attention both in micro and nanoscale devices due to unavailability of clear material systems and device configurations capable of providing comprehensive information. In this work, we have employed a nanostructured (nanowire diameter 30–65 nm and 5 μm in length) ZnO-based metal–semiconductor–metal photoconductor device in order to study the origin of persistent photoconductivity. The current–voltage measurements were carried with and without UV illumination under different oxygen levels. The photoresponse measurements indicated a persistent conductivity trend for depleted oxygen conditions. The persistent conductivity phenomenon is explained on the theoretical model that proposes the change of a neutral anion vacancy to a charged state. PMID:20652149

  19. Hybrid Computational Simulation and Study of Terahertz Pulsed Photoconductive Antennas

    NASA Astrophysics Data System (ADS)

    Emadi, R.; Barani, N.; Safian, R.; Nezhad, A. Zeidaabadi

    2016-08-01

    A photoconductive antenna (PCA) has been numerically investigated in the terahertz (THz) frequency band based on a hybrid simulation method. This hybrid method utilizes an optoelectronic solver, Silvaco TCAD, and a full-wave electromagnetic solver, CST. The optoelectronic solver is used to find the accurate THz photocurrent by considering realistic material parameters. Performance of photoconductive antennas and temporal behavior of the excited photocurrent for various active region geometries such as bare-gap electrode, interdigitated electrodes, and tip-to-tip rectangular electrodes are investigated. Moreover, investigations have been done on the center of the laser illumination on the substrate, substrate carrier lifetime, and diffusion photocurrent associated with the carriers temperature, to achieve efficient and accurate photocurrent. Finally, using the full-wave electromagnetic solver and the calculated photocurrent obtained from the optoelectronic solver, electromagnetic radiation of the antenna and its associated detected THz signal are calculated and compared with a measurement reference for verification.

  20. Photoconductivities in anatase TiO{sub 2} nanorods

    SciTech Connect

    Chen, Ruei-San; Liu, Yi-Ling; Chan, Ching-Hsiang; Huang, Ying-Sheng

    2014-10-13

    The photoconduction (PC) properties of single-crystalline titanium dioxide (TiO{sub 2}) nanorods (NRs) with anatase phase were investigated and compared. By examining the material's inherent properties, the anatase TiO{sub 2} NRs exhibit superior PC efficiency (quantitatively defined by normalized gain) which is near one order of magnitude higher than that of the rutile ones. The optimal photoconductive gain of the anatase NR device can also reach 1.6 × 10{sup 7} at the light intensity of 0.02 Wm{sup −2} and a low bias of 0.1 V. The power-dependent and time-resolved PC measurements were performed to investigate the physical mechanisms. The higher quantum efficiency and mobility product was confirmed to be responsible for the higher PC efficiency in the anatase TiO{sub 2} NRs in comparison to the rutile ones.

  1. Hybrid Computational Simulation and Study of Terahertz Pulsed Photoconductive Antennas

    NASA Astrophysics Data System (ADS)

    Emadi, R.; Barani, N.; Safian, R.; Nezhad, A. Zeidaabadi

    2016-11-01

    A photoconductive antenna (PCA) has been numerically investigated in the terahertz (THz) frequency band based on a hybrid simulation method. This hybrid method utilizes an optoelectronic solver, Silvaco TCAD, and a full-wave electromagnetic solver, CST. The optoelectronic solver is used to find the accurate THz photocurrent by considering realistic material parameters. Performance of photoconductive antennas and temporal behavior of the excited photocurrent for various active region geometries such as bare-gap electrode, interdigitated electrodes, and tip-to-tip rectangular electrodes are investigated. Moreover, investigations have been done on the center of the laser illumination on the substrate, substrate carrier lifetime, and diffusion photocurrent associated with the carriers temperature, to achieve efficient and accurate photocurrent. Finally, using the full-wave electromagnetic solver and the calculated photocurrent obtained from the optoelectronic solver, electromagnetic radiation of the antenna and its associated detected THz signal are calculated and compared with a measurement reference for verification.

  2. Photoconductive switch enhancements for use in Blumlein pulse generators

    NASA Astrophysics Data System (ADS)

    Davanloo, F.; Park, H.; Collins, C. B.; Agee, F. J.

    1999-06-01

    Stacked Blumlein pulse generators developed at the University of Texas at Dallas have produced high-power waveforms with risetimes and repetition rates in the range of 0.2-50 ns and 1-300 Hz, respectively, using a conventional thyratron, spark gap or photoconductive switch. Adaptation of the design has enabled the stacked Blumleins to produce 80 MW, nanosecond pulses with risetimes better than 200 ps into nominally matched loads. The device has a compact line geometry and is commutated by a single GaAs photoconductive switch triggered by a low power laser diode array. Our current investigations involve the switch characteristics that affect the broadening of the current channels in the avalanche, pre-avalanche seedings, the switch lifetime and the durability. This report presents the progress toward improving the GaAs switch operation and lifetime in stacked Blumlein pulsers. Advanced switch treatments including diamond film overcoating are implemented and discussed.

  3. Photoconductivity in donor-acceptor heterojunction organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Renshaw, C. K.; Zimmerman, J. D.; Lassiter, B. E.; Forrest, S. R.

    2012-08-01

    Organic photovoltaics (OPVs) differ from ideal inorganic solar cells due to their pronounced voltage dependence under reverse bias. This feature is commonly modeled in an ad hoc fashion by including a parallel junction resistance (Rp) that bypasses the heterojunction energy barrier between donor and acceptor. The existence of a finite Rp has variously been attributed to rough interfaces, pinhole defects, or to the electric field dependence of the dissociation of polaron pairs that are bound at the heterojunction. Here we show that the voltage dependence of the photocurrent can also arise from photoconductivity resulting from exciton generation followed by dissociation into free polarons within the bulk of the donor and acceptor layers. The presence of photoconductivity of the active layers does not result in an increase in power conversion efficiency, and places a constraint on the maximum fill factor that can be achieved in an OPV cell.

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

    SciTech Connect

    Cuddy-Walsh, SG; 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 optimizing 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.

  5. Semiconductor nanocrystals in photoconductive polymers: Charge generation and charge transport

    SciTech Connect

    Wang, Ying; Herron, Norman; Suna, A.

    1996-10-01

    A new class of photoconductive polymer composites, based on semiconductor nanocrystals (clusters) and carder-transporting polymers, have been developed. These materials are interesting for their potentials in laser printing, imaging, and photorefractives. We will describe material synthesis, charge transport and charge generation mechanisms. In particular, a model of field-dependent charge generation and separation in nonpolar media (e.g. polymers) will be discussed.

  6. 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.

  7. Time-resolved photoconductivity of PbSe nanocrystal arrays.

    PubMed

    Murphy, James E; Beard, Matthew C; Nozik, Arthur J

    2006-12-21

    We report the sub-picosecond photoconductivity dynamics of chemically treated PbSe nanocrystal arrays utilizing time-resolved terahertz spectroscopy (TRTS). TRTS allows both the degree of interdot electronic coupling and the carrier dynamics to be extracted simultaneously. The following capping ligands bonded to the quantum dot surface were studied: hydrazine, ethylenediamine, butlyamine, and aniline. In addition, the arrays were treated with NaOH. We find that the treatments affect both the degree of electronic coupling and the carrier dynamics.

  8. Magnetic and photoconductive repetitive rail-gun opening switches

    SciTech Connect

    Nunnally, W.C.

    1984-07-01

    This report investigates the use of a transformer with a saturable ferromagnetic core and a photoconductive element as a possible opening switch for a repetitive rail gun. A basic rail gun is first analyzed to determine the voltage, current, and power requirements for the switch. Then, each switch concept is analyzed to determine the characteristic size and operating parameters necessary to operate in the rail-gun system. The analysis is used to determine concept feasibility.

  9. 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…

  10. Plasmon enhanced photoconduction in porphyrin-gold nanoparticle assemblies

    NASA Astrophysics Data System (ADS)

    Conklin, David J.

    2011-07-01

    This thesis describes a series of experiments to both determine the origins of charge transport and enhanced photoconduction in metal nanoparticle arrays linked with zinc-porphyrin complexes, but to also determine the nucleation and growth mechanisms related to Ferroelectric Nanolithography (FNL) as a platform for hybrid devices. The development of test structures on glass substrates was undertaken to not only allow the study of the mechanisms controlling charge transport but the photoconduction of zinc-porphyrin linked gold nanoparticle (AuNP) arrays. In this study, the dominate charge transport mechanism was determined to be thermally assisted tunneling and the origins of enhanced photoconduction in these systems was attributed to three mechanisms: direct exciton formation in the molecules, hot electrons and a field effect (optical antenna) due to the excitation of surface plasmons. In the hope of developing a platform for hybrid devices, FNL was utilized to systematically vary the parameters that effect the deposition of metal nanoparticles through domain directed deposition on ferroelectric surfaces. The nucleation and growth mechanisms were determined through this work, where the integrated photon flux controlled the particle density and the interface between the particle and the ferroelectric surface determined the particles size. Finally, with the ability to control the deposition of AuNPs on a ferroelectric surface, hybrid devices of zinc-porphyrin linked AuNPs were realized with FNL.

  11. Proportional counter for X-ray analysis of lunar and planetary surfaces. [a position sensitive scintillating imaging proportional counter

    NASA Technical Reports Server (NTRS)

    1979-01-01

    A position sensitive proportional scintillation detector was developed and evaluated for use in applications involving X-ray imaging as well as spectroscopy. Topics covered include limitations of the proportional scintillation counter for use in space; purification of the xenon gas in the detector, and the operation of the detector system. Results show that the light signal in a proportional scintillation detector remains well localized. With modest electric fields in xenon, the primary electrons from a photoelectric absorption of an X-ray can be brought a distance of a few millimeters to a higher field region without spreading more than a millimeter or so. Therefore, it is possible to make a proportional scintillation detector with good position sensitivity that could be used to calibrate out the difference in light collection over its sensitive volume.

  12. 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.

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

    SciTech Connect

    Frey, Joel B.; Belev, George; Kasap, Safa O.; Tousignant, Olivier; Mani, Habib; Laperriere, Luc

    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 only 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.

  14. Sensitivity Analysis for Reactor Period Induced by Positive Reactivity Using One-point Adjoint Kinetic Equation

    NASA Astrophysics Data System (ADS)

    Chiba, G.; Tsuji, M.; Narabayashi, T.

    2014-04-01

    In order to better predict a kinetic behavior of a nuclear fission reactor, an improvement of the delayed neutron parameters is essential. The present paper specifies important nuclear data for a reactor kinetics: Fission yield and decay constant data of 86Ge, some bromine isotopes, 94Rb, 98mY and some iodine isotopes. Their importance is quantified as sensitivities with a help of the adjoint kinetic equation, and it is found that they are dependent on an inserted reactivity (or a reactor period). Moreover, dependence of sensitivities on nuclear data files is also quantified using the latest files. Even though the currently evaluated data are used, there are large differences among different data files from a view point of the delayed neutrons.

  15. Off-axis digital holographic particle positioning based on polarization-sensitive wavefront curvature estimation.

    PubMed

    Öhman, Johan; Sjödahl, Mikael

    2016-09-20

    Poor axial resolution in holographic particle imaging applications makes particle positioning in 3D space more complex since the positions are not directly obtained. In this paper we estimate the axial position of micrometer particles by finding the location where the wavefront curvature from the scattered light becomes zero. By recording scattered light at 90° using off-axis holography, the complex amplitude of the light is obtained. By reconstruction of the imaged scene, a complex valued volume is produced. From this volume, phase gradients are calculated for each particle and used to estimate the wavefront curvature. From simulations it is found that the wavefront curvature became zero at the true axial position of the particle. We applied this metric to track an axial translation experimentally using a telecentric off-axis holographic imaging system with a lateral magnification of M=1.33. A silicon cube with molded particles inside was used as sample. Holographic recordings are performed both before and after a 100 μm axial translation. From the estimated positions, it was found that the mean displacement of particles between recordings was 105.0 μm with a standard deviation of 25.3 μm. PMID:27661575

  16. Music training and empathy positively impact adults’ sensitivity to infant distress

    PubMed Central

    Parsons, Christine E.; Young, Katherine S.; Jegindø, Else-Marie E.; Vuust, Peter; Stein, Alan; Kringelbach, Morten L.

    2014-01-01

    Crying is the most powerful auditory signal of infant need. Adults’ ability to perceive and respond to crying is important for infant survival and in the provision of care. This study investigated a number of listener variables that might impact on adults’ perception of infant cry distress, namely parental status, musical training, and empathy. Sensitivity to infant distress was tested using a previously validated task, which experimentally manipulated distress by varying the pitch of infant cries. This task required that participants discriminate between pitch differences and interpret these as differences in infant distress. Parents with musical training showed a significant advantage on this task when compared with parents without. The extent of the advantage was correlated with the amount of self-reported musical training. For non-parents, individual differences in empathy were associated with task performance, with higher empathy scores corresponding to greater sensitivity to infant distress. We suggest that sensitivity to infant distress can be impacted by a number of listener variables, and may be amenable to training. PMID:25566122

  17. Music training and empathy positively impact adults' sensitivity to infant distress.

    PubMed

    Parsons, Christine E; Young, Katherine S; Jegindø, Else-Marie E; Vuust, Peter; Stein, Alan; Kringelbach, Morten L

    2014-01-01

    Crying is the most powerful auditory signal of infant need. Adults' ability to perceive and respond to crying is important for infant survival and in the provision of care. This study investigated a number of listener variables that might impact on adults' perception of infant cry distress, namely parental status, musical training, and empathy. Sensitivity to infant distress was tested using a previously validated task, which experimentally manipulated distress by varying the pitch of infant cries. This task required that participants discriminate between pitch differences and interpret these as differences in infant distress. Parents with musical training showed a significant advantage on this task when compared with parents without. The extent of the advantage was correlated with the amount of self-reported musical training. For non-parents, individual differences in empathy were associated with task performance, with higher empathy scores corresponding to greater sensitivity to infant distress. We suggest that sensitivity to infant distress can be impacted by a number of listener variables, and may be amenable to training. PMID:25566122

  18. Evaluation of a Compton scattering camera using 3D position-sensitive CdZnTe detectors

    NASA Astrophysics Data System (ADS)

    Du, Yanfeng; He, Zhong; Knoll, Glenn F.; Wehe, David K.; Li, Weiqi

    1999-10-01

    A CZT Compton Camera (CCC) is being built using two 3D position sensitive CZT detectors. Expected system performance was analyzed by analytical and Monte Carlo approaches. Based on the measurement of detector energy and position resolution, the expected angular resolution is approximately 3 degree and approximately 2 degrees for a +/- 30 degrees FOV for 511 keV and 1 MeV (gamma) -rays, respectively. The intrinsic efficiency for a point source 10 cm from the first detector surface ranges from 1.5 X 10-4 to 8.8 X 10-6 for 500 keV to 3 MeV.

  19. Observation of dynamics of impurity photoconductivity in n-GaAs caused by electron cooling

    SciTech Connect

    Aleshkin, V. Ya. Morozov, S. V.; Rumyantsev, V. V.; Tuzov, I. V.

    2015-01-15

    Experimental investigation of the time dependence of impurity photoconductivity in n-GaAs is carried out upon pulsed optical excitation. It is shown that a change in the photoconductivity is determined mainly by electron cooling in the first 20 ns after photoexcitation. A theoretical model for describing the dependences under observation is proposed.

  20. 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.

  1. Interfacial Electron Transfer and Transient Photoconductivity Studied with Terahertz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Milot, Rebecca Lee

    the porphyrin ring and degree of fluorination of ring substituents were analyzed. Due to the high reduction potentials of these sensitizers, injection into TiO2 was generally not observed. Injection timescales from the porphyrins into SnO2 depended strongly on the identity of the central substituent and were affected by competition with excited-state deactivation processes. The carboxylate anchoring group is commonly used to bind DSSC sensitizers to metal oxide surfaces but is typically not stable under the aqueous and oxidative conditions required for water oxidation. Electron injection efficiency and water stability of several alternative anchoring groups, including phosphonic acid, hydroxamic acid, acerylacetone, and boronic acid, were evaluated. While all of the anchoring groups exhibited water stability superior to carboxylate, the hydroxamate anchor had the best combination of ease of handling and electron injection efficiency. The effects on photoconductivity due to metal oxide morphology and the addition of dopants were also analyzed. Mixtures of anatase and rutile TiO 2 nanoparticles are known to exhibit cooperative effects which increase the efficiency of DSSCs and photocatalysis relative to the pure-phase materials. Through analysis of TRTS measurements, the mechanism of this synergistic effect was found to involve electron transfer from the lower-mobility, higher surface area rutile nanoparticles to anatase particles, resulting in a higher charge collection efficiency. In addition to morphology, doping has been investigated as a means of expanding the spectral range of visible absorption of photocatalysts. Doping ZnO nanowires with manganese(II) was found to significantly decrease the electron mobility, and doping with cobalt(II) increased the timescale for electron trapping. These differences can be understood by considering the changes to the band structure of ZnO effected by the dopants. Preliminary analyses of the solvent and electrolyte dependence on

  2. Bridging particle and wave sensitivity in a configurable detector of positive operator-valued measures.

    PubMed

    Puentes, Graciana; Lundeen, Jeff S; Branderhorst, Matthijs P A; Coldenstrodt-Ronge, Hendrik B; Smith, Brian J; Walmsley, Ian A

    2009-02-27

    We report an optical detector with tunable positive operator-valued measures. The device is based on a combination of weak-field homodyne techniques and photon-number-resolving detection. The resulting positive operator-valued measures can be continuously tuned from Fock-state projectors to a variety of phase-dependent quantum-state measurements by adjusting different system parameters such as local oscillator coupling, amplitude, and phase, allowing thus not only detection but also preparation of exotic quantum states. Experimental tomographic reconstructions of classical benchmark states are presented as a demonstration of the detector capabilities.

  3. Sensitivity of N170 and late positive components to social categorization and emotional valence.

    PubMed

    Montalan, B; Caharel, S; Personnaz, B; Le Dantec, C; Germain, R; Bernard, C; Lalonde, R; Rebaï, M

    2008-10-01

    Previous experiments have shown that categorization of people into two distinct fictive groups has an impact on cognitive processes. The main objective of the present study was to examine whether this mere categorization improves information processing speed and alters early and late onset ERPs during a social judgment task. In a group membership situation, in-group evaluation enhanced information processing speed and occipito-temporal N170 amplitudes, associated with orthographic processing, compared to out-group evaluation, more so for positive than negative attributes. Moreover, negative adjectives elicited larger N170 amplitudes and faster information processing speed than positive adjectives. In contrast, positive adjectives in a non-membership context enhanced a late positive component in prefrontal regions. These results reflect the existence of a motivational top-down influence due to social categorization in early perceptual stages of word processing. These findings are also in accord with the existence of two distinct systems of evaluation, the first implicating an automatic processing represented in occipito-temporal neocortex and the other a more controlled processing represented in PFC. PMID:18691559

  4. Sensitive low-pressure relief valve has positive seating against leakage

    NASA Technical Reports Server (NTRS)

    1964-01-01

    A pilot-operated relief valve which provides positive seating against leakage in cryogenic systems is described. The principal advantage is that the pilot poppet is unaffected by variations in control pressures in the pilot cavity, and results in a more accurate sensing of inlet pressure conditions.

  5. Sensitivity of Human Choice to Manipulations of Parameters of Positive and Negative Sound Reinforcement

    ERIC Educational Resources Information Center

    Lambert, Joseph M.

    2013-01-01

    The purpose of this study was to determine whether altering parameters of positive and negative reinforcement in identical ways could influence behavior maintained by each in different ways. Three undergraduate students participated in a series of assessments designed to identify preferred and aversive sounds with similar reinforcing values.…

  6. Organic Position-Sensitive Detectors Based on ZnO:Al and CuPc:C60.

    PubMed

    Morimune, Taichiro; Kajii, Hirotake; Nishimaru, Hiroki; Ono, Shinji

    2016-04-01

    Organic position-sensitive detector (OPSD) based on copper phthalocyanine CuPc:fullerene C60 bulk-heterojunction with an inverted structure have been fabricated using aluminum doped ZnO (ZnO:Al) as a resistive layer, which is prepared by sol-gel method. The resistance length of the one-dimensional PSD is fixed at 5 mm, and the Ag common electrode is fabricated by vacuum evaporation within the 100-µm width. The current density-voltage characteristics with different structures of photodetector, the influence of ZnO:Al resistivity on the thickness and the position characteristics of PSDs are investigated. The experimental results indicate that the architecture, which uses an inverted structure, increases sensitivity under red light illumination compared to the conventional structure. In addition, the thickness of the ZnO:Al has influence on the position characteristics. The resistivity of ZnO:A film with Al doping concentration of 2 mol% prepared in this study is around 150 Ωcm and it increases from less than approximately 400 nm-thickness. These characteristics seem to be correlated with the properties of ZnO:AI resistive layer. For a device with a 620 nm-thick ZnO:Al layer, the measured position values obtained from the output photocurrent agree with the actual position values under red laser light illumination. CuPc:C60 OPSD with an inverted structure exhibits red light sensitivity, high incident-photon-to-current conversion efficiency of above 80% at -3 V and linearity error of 5.9% at -2 V. PMID:27451643

  7. A position-sensitive germanium detector for gamma-ray astronomy

    NASA Technical Reports Server (NTRS)

    Varnell, L. S.; Ling, J. C.; Mahoney, W. A.; Jacobson, A. S.; Pehl, R. H.; Goulding, F. S.; Landis, D. A.; Luke, P. N.; Madden, N. W.

    1984-01-01

    The critical problem in high-resolution cosmic gamma-ray spectroscopy in the energy range from 0.02 to 10 MeV is the limited spectral sensitivity of the detectors used. This results from the small effective area of the detectors and the high background noise due to induced radioactivity and scattering in the detectors' high-energy particle environment. The effective area can be increased by increasing the number of detectors, but this becomes prohibitive because of the size and expense of the resulting instrument. We have taken a new approach: a segmented large-volume germanium gamma-ray detector which can effectively discriminate against internal background yet maintain the high spectral resolution and efficiency of conventional coaxial Ge detectors. To verify this concept, a planar detector divided into two segments has been fabricated and laboratory measurements agree well with Monte Carlo calculations. A large coaxial detector which will be divided into five segments is being built using the techniques developed for the planar detector. Monte Carlo calculations show that the sensitivity (minimum detectable flux) of the segmented coaxial detector is a factor of 2-3 better than conventional detectors because of the reduction in the internal background.

  8. Position sensitive photon detectors for nuclear physics, particle physics and healthcare applications

    NASA Astrophysics Data System (ADS)

    Seitz, B.

    2012-01-01

    Modern experiments in hadronic physics require detector systems capable of identifying and reconstructing all final-state particles and their momentum vectors. Imaging Cherenkov counters (RICH and DIRC) are frequently employed in nuclear and particle physics experiments. These detectors require high-rate, single-photon capable light detection system with sufficient granularity and position resolution. Several candidate systems are available, ranging from multi-anode photomultiplier tubes to micro-channel plate systems to silicon photomultipliers. Each of these detection solutions has particular advantages and disadvantages. Detailed studies of rate dependence, cross-talk, time-resolution and position resolution for a range of available photon detection solutions are presented. These properties make these photon detection systems ideal for radionuclide imaging applications. Cherenkov radiation can also be used for medical imaging applications. Two different applications using the Cherenkov effect for radionuclide imaging will be reviewed.

  9. Wedge-and-strip anodes for centroid-finding position-sensitive photon and particle detectors

    NASA Technical Reports Server (NTRS)

    Martin, C.; Jelinsky, P.; Lampton, M.; Malina, R. F.

    1981-01-01

    The paper examines geometries employing position-dependent charge partitioning to obtain a two-dimensional position signal from each detected photon or particle. Requiring three or four anode electrodes and signal paths, images have little distortion and resolution is not limited by thermal noise. An analysis of the geometrical image nonlinearity between event centroid location and the charge partition ratios is presented. In addition, fabrication and testing of two wedge-and-strip anode systems are discussed. Images obtained with EUV radiation and microchannel plates verify the predicted performance, with further resolution improvements achieved by adopting low noise signal circuitry. Also discussed are the designs of practical X-ray, EUV, and charged particle image systems.

  10. Two-dimensional position-sensitive detectors for small-angle neutron scattering

    SciTech Connect

    McElhaney, S.A.; Vandermolen, R.I.

    1990-05-01

    In this paper, various detectors available for small angle neutron scattering (SANS) are discussed, along with some current developments being actively pursued. A section has been included to outline the various methodologies of position encoding/decoding with discussions on trends and limitations. Computer software/hardware vary greatly from institute and experiment and only a general discussion is given to this area. 85 refs., 33 figs.

  11. Application of a One-Dimensional Position Sensitive Chamber on Synchrotron Radiation

    NASA Astrophysics Data System (ADS)

    Qi, Huirong; Liu, Mei

    2014-02-01

    In the last few years, wire chambers have been frequently used for X-ray detection because of their low cost, large area and reliability. X-ray diffraction is an irreplaceable method for powder crystal lattice measurements. A one-dimensional single-wire chamber has been developed in our lab to provide high position resolution for powder diffraction experiments using synchrotron radiation. There are 200 readout strips of 0.5 mm width with a pitch of 1.0 mm in the X direction, and the working gas is a mixture of Ar and CO2 (90/10). The one-dimensional position of the original ionization point is determined by the adjacent strip's distribution information using the center of gravity method. Recently, a study of the detector's performance and diffraction image was completed at the 1W1B laboratory of the Beijing Synchrotron Radiation Facility (BSRF) using a sample of SiO2. Most of the relative errors between the measured values of diffraction angles and existing data were less than 1%. The best position resolution achieved for the detector in the test was 71 μm (σ value) with a 20 μm slit collimator. Finally, by changing the detector height in incremental distances from the center of the sample, the one-dimensional detector achieved a two-dimensional diffraction imaging function, and the results are in good agreement with standard data.

  12. Enforced one-dimensional photoconductivity in core-cladding hexabenzocoronenes.

    PubMed

    Cohen, Yaron S; Xiao, Shengxiong; Steigerwald, Michael L; Nuckolls, Colin; Kagan, Cherie R

    2006-12-01

    Photoconductivity in contorted hexabenzocoronene liquid crystals is found to be exclusively one-dimensional. Spectroscopic measurements and density functional theory support the existence of two pi-systems attributed to a low-energy radialene-core and higher energy out-of-plane alkoxyphenyl rings. Persistent photocurrents, measured as a function of field, channel length, and intensity, fit a stretched exponential characteristic of intracolumnar transport, restricted through the radialene-core by the alkoxyphenyl-cladding. Bimolecular recombination is enhanced with increasing carrier concentration by the system's one-dimensionality.

  13. Large persistent photoconductivity in strontium titanate single crystals

    NASA Astrophysics Data System (ADS)

    Poole, Violet M.; McCluskey, Matthew D.

    2016-02-01

    Strontium titanate is a complex oxide with a range of interesting properties. Annealed samples show persistent photoconductivity at room temperature. When irradiated with sub-gap light, the resistivity drops significantly. The increased conductivity persists for days with negligible decay. This unusual effect is attributed to the excitation of an electron from an acceptor defect into the conduction band. A large barrier for recapture prevents electrons from returning to the defect level. Recent work suggests that optimized annealing conditions result in weakly p-type material prior to illumination.

  14. X-ray-induced persistent photoconductivity in vanadium dioxide

    SciTech Connect

    Dietze, S. H.; Marsh, M. J.; Wang, Siming; Ramírez, J. -G.; Cai, Z. -H.; Mohanty, J. R.; Schuller, Ivan K.; Shpyrko, O. G.

    2014-10-08

    The resistivity of vanadium dioxide (VO2) decreased by over one order of magnitude upon localized illumination with x rays at room temperature. Despite this reduction, the structure remained in the monoclinic phase and had no signature of the high-temperature tetragonal phase that is usually associated with the lower resistance. Once illumination ceased, relaxation to the insulating state took tens of hours near room temperature. However, a full recovery of the insulating state was achieved within minutes by thermal cycling. We show that this behavior is consistent with random local-potential fluctuations and random distribution of discrete recombination sites used to model residual photoconductivity.

  15. Electrical transport and photoconduction in ambipolar tungsten diselenide and n-type indium selenide

    NASA Astrophysics Data System (ADS)

    Fralaide, Michael Orcino

    In today's "silicon age" in which we live, field-effect transistors (FET) are the workhorse of virtually all modern-day electronic gadgets. Although silicon currently dominates most of these electronics, layered 2D transition metal dichalcogenides (TMDCs) have great potential in low power optoelectronic applications due to their indirect-to-direct band gap transition from bulk to few-layer and high on/off switching ratios. TMDC WSe2 is studied here, mechanically exfoliated from CVT-grown bulk WSe2 crystals, to create a few-layered ambipolar FET, which transitions from dominant p-type behavior to n-type behavior dominating as temperature decreases. A high electron mobility mu>150 cm2V-1s-1 was found in the low temperature region near 50 K. Temperature-dependent photoconduction measurements were also taken, revealing that both the application of negative gate bias and decreasing the temperature resulted in an increase of the responsivity of the WSe2 sample. Besides TMDCs, Group III-VI van der Waals structures also show promising anisotropic optical, electronic, and mechanical properties. In particular, mechanically exfoliated few-layered InSe is studied here for its indirect band gap of 1.4 eV, which should offer a broad spectral response. It was found that the steady state photoconduction slightly decreased with the application of positive gate bias, likely due to the desorption of adsorbates on the surface of the sample. A room temperature responsivity near 5 AW -1 and external quantum efficiency of 207% was found for the InSe FET. Both TMDC's and group III-VI chalcogenides continue to be studied for their remarkably diverse properties that depend on their thickness and composition for their applications as transistors, sensors, and composite materials in photovoltaics and optoelectronics.

  16. Nck adaptors are positive regulators of the size and sensitivity of the T-cell repertoire.

    PubMed

    Roy, Edwige; Togbe, Dieudonnée; Holdorf, Amy D; Trubetskoy, Dmitry; Nabti, Sabrina; Küblbeck, Günter; Klevenz, Alexandra; Kopp-Schneider, Annette; Leithäuser, Frank; Möller, Peter; Bladt, Friedhelm; Hämmerling, Günter; Arnold, Bernd; Pawson, Tony; Tafuri, Anna

    2010-08-31

    The size and sensitivity of the T-cell repertoire governs the effectiveness of immune responses against invading pathogens. Both are modulated by T-cell receptor (TCR) activity through molecular mechanisms, which remain unclear. Here, we provide genetic evidence that the SH2/SH3 domain containing proteins Nck lower the threshold of T-cell responsiveness. The hallmarks of Nck deletion were T-cell lymphopenia and hyporeactivity to TCR-mediated stimulation. In the absence of the Nck adaptors, peripheral T cells expressing a TCR with low avidity for self-antigens were strongly reduced, whereas an overall impairment of T-cell activation by weak antigenic stimulation was observed. Mechanistically, Nck deletion resulted in a significant decrease in calcium mobilization and ERK phosphorylation upon TCR engagement. Taken together, our findings unveil a crucial role for the Nck adaptors in shaping the T-cell repertoire to ensure maximal antigenic coverage and optimal T cell excitability.

  17. Nck adaptors are positive regulators of the size and sensitivity of the T-cell repertoire

    PubMed Central

    Roy, Edwige; Togbe, Dieudonnée; Holdorf, Amy D.; Trubetskoy, Dmitry; Nabti, Sabrina; Küblbeck, Günter; Klevenz, Alexandra; Kopp-Schneider, Annette; Leithäuser, Frank; Möller, Peter; Bladt, Friedhelm; Hämmerling, Günter; Arnold, Bernd; Pawson, Tony; Tafuri, Anna

    2010-01-01

    The size and sensitivity of the T-cell repertoire governs the effectiveness of immune responses against invading pathogens. Both are modulated by T-cell receptor (TCR) activity through molecular mechanisms, which remain unclear. Here, we provide genetic evidence that the SH2/SH3 domain containing proteins Nck lower the threshold of T-cell responsiveness. The hallmarks of Nck deletion were T-cell lymphopenia and hyporeactivity to TCR-mediated stimulation. In the absence of the Nck adaptors, peripheral T cells expressing a TCR with low avidity for self-antigens were strongly reduced, whereas an overall impairment of T-cell activation by weak antigenic stimulation was observed. Mechanistically, Nck deletion resulted in a significant decrease in calcium mobilization and ERK phosphorylation upon TCR engagement. Taken together, our findings unveil a crucial role for the Nck adaptors in shaping the T-cell repertoire to ensure maximal antigenic coverage and optimal T cell excitability. PMID:20709959

  18. Nck adaptors are positive regulators of the size and sensitivity of the T-cell repertoire.

    PubMed

    Roy, Edwige; Togbe, Dieudonnée; Holdorf, Amy D; Trubetskoy, Dmitry; Nabti, Sabrina; Küblbeck, Günter; Klevenz, Alexandra; Kopp-Schneider, Annette; Leithäuser, Frank; Möller, Peter; Bladt, Friedhelm; Hämmerling, Günter; Arnold, Bernd; Pawson, Tony; Tafuri, Anna

    2010-08-31

    The size and sensitivity of the T-cell repertoire governs the effectiveness of immune responses against invading pathogens. Both are modulated by T-cell receptor (TCR) activity through molecular mechanisms, which remain unclear. Here, we provide genetic evidence that the SH2/SH3 domain containing proteins Nck lower the threshold of T-cell responsiveness. The hallmarks of Nck deletion were T-cell lymphopenia and hyporeactivity to TCR-mediated stimulation. In the absence of the Nck adaptors, peripheral T cells expressing a TCR with low avidity for self-antigens were strongly reduced, whereas an overall impairment of T-cell activation by weak antigenic stimulation was observed. Mechanistically, Nck deletion resulted in a significant decrease in calcium mobilization and ERK phosphorylation upon TCR engagement. Taken together, our findings unveil a crucial role for the Nck adaptors in shaping the T-cell repertoire to ensure maximal antigenic coverage and optimal T cell excitability. PMID:20709959

  19. Position effect variegation and viability are both sensitive to dosage of constitutive heterochromatin in Drosophila.

    PubMed

    Berloco, Maria; Palumbo, Gioacchino; Piacentini, Lucia; Pimpinelli, Sergio; Fanti, Laura

    2014-09-01

    The dosage effect of Y-chromosome heterochromatin on suppression of position effect variegation (PEV) has long been well-known in Drosophila. The phenotypic effects of increasing the overall dosage of Y heterochromatin have also been demonstrated; hyperploidy of the Y chromosome produces male sterility and many somatic defects including variegation and abnormal legs and wings. This work addresses whether the suppression of position effect variegation (PEV) is a general feature of the heterochromatin (independent of the chromosome of origin) and whether a hyperdosage of heterochromatin can affect viability. The results show that the suppression of PEV is a general feature of any type of constitutive heterochromatin and that the intensity of suppression depends on its amount instead of some mappable factor on it. We also describe a clear dosage effect of Y heterochromatin on the viability of otherwise wild-type embryos and the modification of that effect by a specific gene mutation. Together, our results indicate that the correct balance between heterochromatin and euchromatin is essential for the normal genome expression and that this balance is genetically controlled.

  20. Valproic Acid Increases CD133 Positive Cells that Show Low Sensitivity to Cytostatics in Neuroblastoma

    PubMed Central

    Khalil, Mohamed Ashraf; Hraběta, Jan; Groh, Tomáš; Procházka, Pavel; Doktorová, Helena; Eckschlager, Tomáš

    2016-01-01

    Valproic acid (VPA) is a well-known antiepileptic drug that exhibits antitumor activities through its action as a histone deacetylase inhibitor. CD133 is considered to be a cancer stem cell marker in several tumors including neuroblastoma. CD133 transcription is strictly regulated by epigenetic modifications. We evaluated the epigenetic effects of treatment with 1mM VPA and its influence on the expression of CD133 in four human neuroblastoma cell lines. Chemoresistance and cell cycle of CD133+ and CD133− populations were examined by flow cytometry. We performed bisulfite conversion followed by methylation-sensitive high resolution melting analysis to assess the methylation status of CD133 promoters P1 and P3. Our results revealed that VPA induced CD133 expression that was associated with increased acetylation of histones H3 and H4. On treatment with VPA and cytostatics, CD133+ cells were mainly detected in the S and G2/M phases of the cell cycle and they showed less activated caspase-3 compared to CD133− cells. UKF-NB-3 neuroblastoma cells which express CD133 displayed higher colony and neurosphere formation capacities when treated with VPA, unlike IMR-32 which lacks for CD133 protein. Induction of CD133 in UKF-NB-3 was associated with increased expression of phosphorylated Akt and pluripotency transcription factors Nanog, Oct-4 and Sox2. VPA did not induce CD133 expression in cell lines with methylated P1 and P3 promoters, where the CD133 protein was not detected. Applying the demethylating agent 5-aza-2’-deoxycytidine to the cell lines with methylated promoters resulted in CD133 re-expression that was associated with a drop in P1 and P3 methylation level. In conclusion, CD133 expression in neuroblastoma can be regulated by histone acetylation and/or methylation of its CpG promoters. VPA can induce CD133+ cells which display high proliferation potential and low sensitivity to cytostatics in neuroblastoma. These results give new insight into the possible

  1. Valproic Acid Increases CD133 Positive Cells that Show Low Sensitivity to Cytostatics in Neuroblastoma.

    PubMed

    Khalil, Mohamed Ashraf; Hraběta, Jan; Groh, Tomáš; Procházka, Pavel; Doktorová, Helena; Eckschlager, Tomáš

    2016-01-01

    Valproic acid (VPA) is a well-known antiepileptic drug that exhibits antitumor activities through its action as a histone deacetylase inhibitor. CD133 is considered to be a cancer stem cell marker in several tumors including neuroblastoma. CD133 transcription is strictly regulated by epigenetic modifications. We evaluated the epigenetic effects of treatment with 1mM VPA and its influence on the expression of CD133 in four human neuroblastoma cell lines. Chemoresistance and cell cycle of CD133+ and CD133- populations were examined by flow cytometry. We performed bisulfite conversion followed by methylation-sensitive high resolution melting analysis to assess the methylation status of CD133 promoters P1 and P3. Our results revealed that VPA induced CD133 expression that was associated with increased acetylation of histones H3 and H4. On treatment with VPA and cytostatics, CD133+ cells were mainly detected in the S and G2/M phases of the cell cycle and they showed less activated caspase-3 compared to CD133- cells. UKF-NB-3 neuroblastoma cells which express CD133 displayed higher colony and neurosphere formation capacities when treated with VPA, unlike IMR-32 which lacks for CD133 protein. Induction of CD133 in UKF-NB-3 was associated with increased expression of phosphorylated Akt and pluripotency transcription factors Nanog, Oct-4 and Sox2. VPA did not induce CD133 expression in cell lines with methylated P1 and P3 promoters, where the CD133 protein was not detected. Applying the demethylating agent 5-aza-2'-deoxycytidine to the cell lines with methylated promoters resulted in CD133 re-expression that was associated with a drop in P1 and P3 methylation level. In conclusion, CD133 expression in neuroblastoma can be regulated by histone acetylation and/or methylation of its CpG promoters. VPA can induce CD133+ cells which display high proliferation potential and low sensitivity to cytostatics in neuroblastoma. These results give new insight into the possible

  2. Valproic Acid Increases CD133 Positive Cells that Show Low Sensitivity to Cytostatics in Neuroblastoma.

    PubMed

    Khalil, Mohamed Ashraf; Hraběta, Jan; Groh, Tomáš; Procházka, Pavel; Doktorová, Helena; Eckschlager, Tomáš

    2016-01-01

    Valproic acid (VPA) is a well-known antiepileptic drug that exhibits antitumor activities through its action as a histone deacetylase inhibitor. CD133 is considered to be a cancer stem cell marker in several tumors including neuroblastoma. CD133 transcription is strictly regulated by epigenetic modifications. We evaluated the epigenetic effects of treatment with 1mM VPA and its influence on the expression of CD133 in four human neuroblastoma cell lines. Chemoresistance and cell cycle of CD133+ and CD133- populations were examined by flow cytometry. We performed bisulfite conversion followed by methylation-sensitive high resolution melting analysis to assess the methylation status of CD133 promoters P1 and P3. Our results revealed that VPA induced CD133 expression that was associated with increased acetylation of histones H3 and H4. On treatment with VPA and cytostatics, CD133+ cells were mainly detected in the S and G2/M phases of the cell cycle and they showed less activated caspase-3 compared to CD133- cells. UKF-NB-3 neuroblastoma cells which express CD133 displayed higher colony and neurosphere formation capacities when treated with VPA, unlike IMR-32 which lacks for CD133 protein. Induction of CD133 in UKF-NB-3 was associated with increased expression of phosphorylated Akt and pluripotency transcription factors Nanog, Oct-4 and Sox2. VPA did not induce CD133 expression in cell lines with methylated P1 and P3 promoters, where the CD133 protein was not detected. Applying the demethylating agent 5-aza-2'-deoxycytidine to the cell lines with methylated promoters resulted in CD133 re-expression that was associated with a drop in P1 and P3 methylation level. In conclusion, CD133 expression in neuroblastoma can be regulated by histone acetylation and/or methylation of its CpG promoters. VPA can induce CD133+ cells which display high proliferation potential and low sensitivity to cytostatics in neuroblastoma. These results give new insight into the possible

  3. Enhancing the sensitivity of a micro-diaphragm resonating sensor by effectively positioning the mass on the membrane

    PubMed Central

    Kim, Jinsik; Kim, Hye Jin; Cho, EunAe; Shin, Hyun-Joon; Park, Jung Ho; Hwang, Kyo Seon

    2015-01-01

    The detection of biomarkers in the liquid phase using mechanical sensors is difficult because of noise caused by the liquid. To reduce and verify the side effects of liquid loading, we performed calculations and experiments to determine the shift in resonant frequency according to the loading conditions. A 2-μm-thick piezoelectric rectangular micro-diaphragm with a 500 × 500 μm membrane was used. These dimensions were determined such that there would be an analogous resonant frequency shift ratio in both (1, 1) and (2, 2) modes. By calculating and measuring the resonant frequency, we verified that the resonant frequency of the sensor would change only through contact with the liquid, even the resonant frequency change by only liquid much higher than the changes caused by the nanoparticles. The real signal constituted only 0.017% of the initial resonant frequency. To enhance the sensitivity by reducing the unexpected surface stress in the liquid, the liquid was dropped onto the surface of the micro-diaphragm. This resulted in an improvement of more than 10 times the sensitivity in both modes. In addition, by controlling the position in the micro-diaphragm resonating sensor, more sensitive positions with large displacements were determined according to each mode. PMID:26594022

  4. 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.

  5. Multiple Chemical Sensitivity and the Workplace: Current Position and Need for an Occupational Health Surveillance Protocol

    PubMed Central

    Martini, A.; Iavicoli, S.; Corso, L.

    2013-01-01

    Multiple chemical sensitivity, commonly known as environmental illness, is a chronic disease in which exposure to low levels of chemicals causes correlated symptoms of varying intensity. With the continuous introduction of new substances, people with MCS suffer significant limitations to their living environment and frequently to their workplace. This paper describes the current situation as regards MCS and the critical points in its case definition, which is still not generally agreed upon; this makes it difficult to recognize with certainty, especially, its precise relationship with work. Other problems arise in relation to the occupational physician's role in diagnosing and managing the worker with the disorder, the question of low levels of exposure to chemicals, and the best measures possible to prevent it. A diagnostic “route” is proposed, useful as a reference for the occupational physician who is often called in first to identify cases suspected of having this disease and to manage MCS workers. Work-related problems for people with MCS depend not only on occupational exposure but also on the incompatibility between their illness and their work. More occupational physicians need to be “sensitive” to MCS, so that these workers are recognized promptly, the work is adapted as necessary, and preventive measures are promoted in the workplace. PMID:23844274

  6. 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.

  7. 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.

  8. Questionnaire for sensitive positions (QSP) version 4.0 -- Users guide document

    SciTech Connect

    Hausel, J.M.

    1996-05-21

    The US Government does background investigations and reinvestigations to establish that applicants are eligible for required security clearance. The QSP system is an automated Paradox application developed by Boeing in 1988 and used by DOE-RL for data collection, retention, and printing by facsimile of the Standard Form 86 containing a person`s data needed to conduct an investigation. In March 1991 the QSP form was revised by the Office of Personnel Management (OPM). The QSP system was modified and enhanced to QSP version 3.0 and released for use in 1992. Copies of QSP version 3.0 were provided to approximately 20 other sites when requested. In February 1995 the OPM approved the new Standard Form 86 ``Questionnaire for National Security Positions.`` The QSP system was modified and upgraded to QSP version 4.0 to agree with the revised form.

  9. [Determination of sensitivity of biofilm-positive forms of microorganisms to antibiotics].

    PubMed

    Holá, Veronika; Růzicka, Filip; Tejkalová, Renata; Votava, Miroslav

    2004-10-01

    Nosocomial infections caused by biofilm-positive microorganisms are a serious therapeutic problem. In the biofilm, microorganisms are protected against adverse effects of the external environment, including the action of antibiotics. It is well known that the values of minimum inhibitory concentrations (MIC) determined for planktonic forms do not correspond to the actual concentrations of antibiotics necessary for the eradication of bacteria in a biofilm. The purpose of the study was to propose a method of determining minimum biofilm inhibitory concentrations (MBIC) and minimum biofilm eradication concentrations (MBEC) and to compare these values with MIC values. Biofilm-positive strains of Staphylococcus epidermidis were cultured so as to form a biofilm layer on polystyrene pegs. The biofilm on the pegs was then exposed to the action of antibiotics and after 18 hours we determined the minimum biofilm inhibitory concentration (MBIC). The evaluation of minimum biofilm eradication concentrations was done colorimetrically from the metabolic activity of surviving cells. MBIC and MBEC values were many times higher than MIC values. We selected such a duration of the biofilms cultivation on the pegs of the plate, which ensured that the number of bacterial cells corresponded to standard MIC assessment. The MBEC values established in our study indicate that the currently used concentrations of tested antibiotics cannot be used in monotherapy for an efficacious eradication of a biofilm. The MBEC determination is a far more laborious and time-consuming method than the determination of MIC, but the use of plates with pegs facilitates the handling of biofilms. The advantage of our method is the possibility of standardization of the size of the inoculum and thus of the whole MBEC assessment.

  10. Dorsal Striatal D2-Like Receptor Availability Co-varies with Sensitivity to Positive Reinforcement during Discrimination Learning

    PubMed Central

    Groman, S.M.; Lee, B.; London, E.D.; Mandelkern, M.; James, A.S.; Feiler, K.; Rivera, R.; Dahlbom, M.; Sossi, V.; Vandervoort, E.; Jentsch, J.D.

    2011-01-01

    Deviations in reward sensitivity and behavioral flexibility, particularly in the ability to change or stop behaviors in response to changing environmental contingencies, are important phenotypic dimensions of several neuropsychiatric disorders. Neuroimaging evidence suggests that variation in dopamine signaling through dopamine D2-like receptors may influence these phenotypes, as well as associated psychiatric conditions, but the specific neurocognitive mechanisms through which this influence is exerted are unknown. To address this question, we examined the relationship between behavioral sensitivity to reinforcement during discrimination learning and D2-like receptor availability in vervet monkeys. Monkeys were assessed for their ability to acquire, retain and reverse three-choice, visual-discrimination problems, and once behavioral performance had stabilized, they received positron emission tomography (PET) scans. D2-like receptor availability in dorsal aspects of the striatum was not related to individual differences in the ability to acquire or retain visual discriminations but did relate to the number of trials required to reach criterion in the reversal phase of the task. D2-like receptor availability was also strongly correlated with behavioral sensitivity to positive, but not negative, feedback during learning. These results go beyond electrophysiological findings by demonstrating the involvement of a striatal dopaminergic marker in individual differences in feedback sensitivity and behavioral flexibility, providing insight into the neural mechanisms that are affected in neuropsychiatric disorders that feature these deficits. PMID:21593313

  11. Transient and local illumination of an organic photoconductive sensor

    NASA Astrophysics Data System (ADS)

    Woestenborghs, Wouter; De Visschere, Patrick; Beunis, Filip; Vetsuypens, Arnout; Neyts, Kristiaan

    2013-03-01

    In this paper we investigate the performance of a transparent photoconductive sensor based on a double layer of organic materials (m-MTDAB / PTCBI) which are deposited on two interdigitated transparent ITO electrodes. The performance of the sensor is demonstrated with electro-optical measurements: the I(V) curves consist of two linear sections meeting at a knee voltage Vt. Linear regression performed on the I(V) curves below Vt show that the conductance is a power law of the luminance incident on the device. We present a model to describe the behaviour of the sensor below Vt. We present measurements of I(t) for a transient illumination of the sensor. Plotting the inverse of the current as a function of time we find that the transient is consistent with the model for voltages below Vt. For voltages above Vt we find that the sensor behaves like a resistor in series with a space charge (SC) region. We present a local illumination experiment that confirms the existence of a SC region between the electrodes of the photoconductive sensor for V

  12. Amazingly resilient Indigenous people! Using transformative learning to facilitate positive student engagement with sensitive material.

    PubMed

    Jackson, Debra; Power, Tamara; Sherwood, Juanita; Geia, Lynore

    2013-12-01

    If health professionals are to effectively contribute to improving the health of Indigenous people, understanding of the historical, political, and social disadvantage that has lead to health disparity is essential. This paper describes a teaching and learning experience in which four Australian Indigenous academics in collaboration with a non-Indigenous colleague delivered an intensive workshop for masters level post-graduate students. Drawing upon the paedagogy of Transformative Learning, the objectives of the day included facilitating students to explore their existing understandings of Indigenous people, the impact of ongoing colonisation, the diversity of Australia's Indigenous people, and developing respect for alternative worldviews. Drawing on a range of resources including personal stories, autobiography, film and interactive sessions, students were challenged intellectually and emotionally by the content. Students experienced the workshop as a significant educational event, and described feeling transformed by the content, better informed, more appreciative of other worldviews and Indigenous resilience and better equipped to contribute in a more meaningful way to improving the quality of health care for Indigenous people. Where this workshop differs from other Indigenous classes was in the involvement of an Indigenous teaching team. Rather than a lone academic who can often feel vulnerable teaching a large cohort of non-Indigenous students, an Indigenous teaching team reinforced Indigenous authority and created an emotionally and culturally safe space within which students were allowed to confront and explore difficult truths. Findings support the value of multiple teaching strategies underpinned by the theory of transformational learning, and the potential benefits of facilitating emotional as well as intellectual student engagement when presenting sensitive material.

  13. Sensitivity of Allelic Divergence to Genomic Position: Lessons from the Drosophila tan Gene

    PubMed Central

    John, Alisha V.; Sramkoski, Lisa L.; Walker, Elizabeth A.; Cooley, Arielle M.; Wittkopp, Patricia J.

    2016-01-01

    To identify genetic variants underlying changes in phenotypes within and between species, researchers often utilize transgenic animals to compare the function of alleles in different genetic backgrounds. In Drosophila, targeted integration mediated by the ΦC31 integrase allows activity of alternative alleles to be compared at the same genomic location. By using the same insertion site for each transgene, position effects are generally assumed to be controlled for because both alleles are surrounded by the same genomic context. Here, we test this assumption by comparing the activity of tan alleles from two Drosophila species, D. americana and D. novamexicana, at five different genomic locations in D. melanogaster. We found that the relative effects of these alleles varied among insertion sites, with no difference in activity observed between them at two sites. One of these sites simply silenced both transgenes, but the other allowed expression of both alleles that was sufficient to rescue a mutant phenotype yet failed to reveal the functional differences between the two alleles. These results suggest that more than one insertion site should be used when comparing the activity of transgenes because failing to do so could cause functional differences between alleles to go undetected. PMID:27449514

  14. A Monte Carlo simulation comparing hydrocarbons as stopping gases for position sensitive neutron detectors

    NASA Astrophysics Data System (ADS)

    Doumas, A.; Smith, G. C.

    2009-12-01

    Various neutron detectors are being developed for the next generation user facilities, which incorporate new as well as existing approaches for the detection of thermal neutrons. Improvements in neutron detector efficiency, detector size and position resolution have occurred over the last three decades and further advances are expected in the next ten years. Since gas detectors are expected to continue in a key role for future thermal neutron experiments, it is advantageous to review some of the criteria for the choice of proton/triton stopping gases for gas-based detectors. Monte Carlo simulations, using the group of programs "Stopping and Range of Ions in Matter", have been run to determine key performance characteristics for neutron detectors which utilize the reaction 3He(n,p)t. This paper will focus on investigating the use of three common hydrocarbons and CF 4 as stopping gases for thermal neutron detectors. A discussion of these gases will include their behavior in terms of proton and triton range, ion distribution and straggle.

  15. 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

  16. Colossal photoconductivity in transparent perovskite semiconductor BaSnO3

    NASA Astrophysics Data System (ADS)

    Park, Jisung; Kim, Useong; Char, Kookrin

    2015-03-01

    We compare photoconductivities of BaSnO3 (BSO) and SrTiO3 (STO). Photoconductivity of STO has been intensively studied for its high potential for UV detector and optical devices. On the other hand, BSO has recently started to draw a large attention for its high electron mobility and thermal stability. BSO and STO have the same perovskite structure and similar band gap. Epitaxial thin films of BSO and STO were grown by pulsed laser ablation. The spectral responses measured by the monochromatic light showed peaks around the band gap of each film, an evidence that the electron-hole pair generation is the main mechanism for the photoconductivity in both materials. We have found the photoconductivity of BSO to be several orders of magnitude higher than that of STO. In addition, there exists a larger ``persistent'' photoconductivity in BSO. The high mobility of BSO, which is two orders of magnitude larger than that of STO at room temperature, should be partially responsible for the higher photoconductivity. The small difference between the direct gap and indirect gap of BSO may make band to band transition easier. We are also investigating the effect of dislocations on the ``persistent'' photoconductivity.

  17. A zero dead-time multi-particle time and position sensitive detector based on correlation between brightness and amplitude.

    PubMed

    Urbain, X; Bech, D; Van Roy, J-P; Géléoc, M; Weber, S J; Huetz, A; Picard, Y J

    2015-02-01

    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 H3 into two or three fragments, and the photo-double-ionization of Xenon atoms are presented, which illustrate the performances of the COBRA detection scheme. PMID:25725834

  18. A zero dead-time multi-particle time and position sensitive detector based on correlation between brightness and amplitude.

    PubMed

    Urbain, X; Bech, D; Van Roy, J-P; Géléoc, M; Weber, S J; Huetz, A; Picard, Y J

    2015-02-01

    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 H3 into two or three fragments, and the photo-double-ionization of Xenon atoms are presented, which illustrate the performances of the COBRA detection scheme.

  19. Ultraviolet photoconductive devices with an n-GaN nanorod-graphene hybrid structure synthesized by metal-organic chemical vapor deposition

    PubMed Central

    Kang, San; Mandal, Arjun; Chu, Jae Hwan; Park, Ji-Hyeon; Kwon, Soon-Yong; Lee, Cheul-Ro

    2015-01-01

    The superior photoconductive behavior of a simple, cost-effective n-GaN nanorod (NR)-graphene hybrid device structure is demonstrated for the first time. The proposed hybrid structure was synthesized on a Si (111) substrate using the high-quality graphene transfer method and the relatively low-temperature metal-organic chemical vapor deposition (MOCVD) process with a high V/III ratio to protect the graphene layer from thermal damage during the growth of n-GaN nanorods. Defect-free n-GaN NRs were grown on a highly ordered graphene monolayer on Si without forming any metal-catalyst or droplet seeds. The prominent existence of the undamaged monolayer graphene even after the growth of highly dense n-GaN NRs, as determined using Raman spectroscopy and high-resolution transmission electron microscopy (HR-TEM), facilitated the excellent transport of the generated charge carriers through the photoconductive channel. The highly matched n-GaN NR-graphene hybrid structure exhibited enhancement in the photocurrent along with increased sensitivity and photoresponsivity, which were attributed to the extremely low carrier trap density in the photoconductive channel. PMID:26028318

  20. Ultraviolet photoconductive devices with an n-GaN nanorod-graphene hybrid structure synthesized by metal-organic chemical vapor deposition.

    PubMed

    Kang, San; Mandal, Arjun; Chu, Jae Hwan; Park, Ji-Hyeon; Kwon, Soon-Yong; Lee, Cheul-Ro

    2015-06-01

    The superior photoconductive behavior of a simple, cost-effective n-GaN nanorod (NR)-graphene hybrid device structure is demonstrated for the first time. The proposed hybrid structure was synthesized on a Si (111) substrate using the high-quality graphene transfer method and the relatively low-temperature metal-organic chemical vapor deposition (MOCVD) process with a high V/III ratio to protect the graphene layer from thermal damage during the growth of n-GaN nanorods. Defect-free n-GaN NRs were grown on a highly ordered graphene monolayer on Si without forming any metal-catalyst or droplet seeds. The prominent existence of the undamaged monolayer graphene even after the growth of highly dense n-GaN NRs, as determined using Raman spectroscopy and high-resolution transmission electron microscopy (HR-TEM), facilitated the excellent transport of the generated charge carriers through the photoconductive channel. The highly matched n-GaN NR-graphene hybrid structure exhibited enhancement in the photocurrent along with increased sensitivity and photoresponsivity, which were attributed to the extremely low carrier trap density in the photoconductive channel.

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

    SciTech Connect

    Rumyantsev, V. V. Ikonnikov, A. V.; Antonov, A. V.; Morozov, S. V.; Zholudev, M. S.; Spirin, K. E.; Gavrilenko, V. I.; Dvoretskii, S. A.; Mikhailov, N. N.

    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 the 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.

  2. The sensitivity of soil O2 and redox biogeochemistry to landscape position and climate

    NASA Astrophysics Data System (ADS)

    Silver, W. L.; Ruan, L.; O'Connell, C.; Gutiérrez del Arroyo, O.

    2015-12-01

    Soil oxygen (O2) availability and associated redox dynamics are key drivers of carbon and nitrogen cycling and greenhouse gas emissions in terrestrial ecosystems. However, few studies have measured soil O2 availability, and even fewer have related this to biogeochemical cycling over space and time. Redox dynamics are likely to play a particularly important role in humid tropical forests characterized by high rainfall, near constant warm temperatures, high biological activity, and finely textured soils, all of which contribute to periodic O2 depletion throughout the soil profile. These ecosystems exhibit rapid C turnover and are a globally important source of the major greenhouse gases. We report on an extensive network of galvanic O2 sensors and time-domain reflectometry along topographic gradients in a lower montane wet tropical forest in Puerto Rico (n = 105 sensors). Within the sensor field we also installed three automated surface flux chambers in each topographic zone (ridge, slope and valley). A Cavity Ring-Down Spectroscopy (CRDS) gas analyzer was used to measure pseudo-continuous fluxes of CO2, N2O, and CH4. Soil O2 concentrations decrease nonlinearly from ridges to valleys along topographic gradients. Soil moisture was the best single predictor of soil O2 concentrations explaining over 50% of the variability in the data, even in these well-drained soils. Drought conditions dramatically altered soil O2 dynamics in both time and space, and showed that redox drivers differed by topographic position. Both ridges and slopes produced higher CO2 fluxes than valleys. Daily CH4 emissions went up to ~2000 g CH4 ha-1d-1 for valleys (hot spots and hot moments). Soil O2 dynamics also helped explain patterns in reactive Fe species and C storage, as well as pH along the catena. Our results highlight the potential for soil O2 concentrations as an integrator of biogeochemical dynamics in variable redox environments. They also provide a mechanism for identifying and

  3. Sensitivity of Solvation Environment to Oxidation State and Position in the Early Actinide Period.

    PubMed

    Clark, Aurora E; Samuels, Alex; Wisuri, Katy; Landstrom, Sarah; Saul, Tessa

    2015-07-01

    The aqueous solvation of U-Pu in the III-VI oxidation states has been examined using density functional theory and hydrated cluster models of the form An(H2O)30(4+/3+) and AnO2(H2O)30(2+/+) embedded within a polarizable continuum model to approximate the effect of bulk water. The structural features are compared to available data from extended X-ray absorption fine structure. Then, using a multiple-scattering approach, the X-ray absorption near-edge spectra (XANES) have been simulated and compared to experiment. These structural data are complemented by a detailed thermodynamic analysis using a recently benchmarked protocol. The structural, spectroscopic, and thermodynamic information has been used to assign the primary solvation environments in water, with an emphasis upon understanding how oxidation state and position in the period modifies the hydration number and equilibrium between different solvation shell environments. Tetravalent U is proposed to exist in equilibrium between the 8- and 9-coordinate species. Moving to the right of the period, Np(IV) and Pu(IV) exist solely as the octa-aquo species. Reduction to the trivalent ions leads to thermodynamic favorability for this solvation environment, whose features reproduce the XANES spectra. The actinyl dications (AnO2(2+)) of U and Np have a preferred environment in the equatorial plane consisting of 5 solvating waters; however, changes to the ionic radius and electronic structure at Pu leads to an equilibrium between the 4- and 5-coordinate species for PuO2(2+). Reduction of the dications to form the monocations generally leads to a preference for the 4-coordinate primary solvation shell, with an equilibrium existing for uranyl, while the neptunyl and plutonyl species exist solely as AnO2(H2O)4(+). These data provide accurate thermodynamic information for several rare species and the combined thermodynamic, structural, and spectroscopic approach reveals trends in hydration behavior across actinide oxidation

  4. TRPV1 expression level in isolectin B₄-positive neurons contributes to mouse strain difference in cutaneous thermal nociceptive sensitivity.

    PubMed

    Ono, Kentaro; Ye, Yi; Viet, Chi T; Dang, Dongmin; Schmidt, Brian L

    2015-05-01

    Differential thermal nociception across inbred mouse strains has genetic determinants. Thermal nociception is largely attributed to the heat/capsaicin receptor transient receptor potential vanilloid 1 (TRPV1); however, the contribution of this channel to the genetics of thermal nociception has not been revealed. In this study we compared TRPV1 expression levels and electrophysiological properties in primary sensory neurons and thermal nociceptive behaviors between two (C57BL/6 and BALB/c) inbred mouse strains. Using immunofluorescence and patch-clamp physiology methods, we demonstrated that TRPV1 expression was significantly higher in isolectin B4 (IB4)-positive trigeminal sensory neurons of C57BL/6 relative to BALB/c; the expression in IB4-negative neurons was similar between the strains. Furthermore, using electrophysiological cell classification (current signature method), we showed differences between the two strains in capsaicin sensitivity in IB4-positive neuronal cell types 2 and 13, which were previously reported as skin nociceptors. Otherwise electrophysiological membrane properties of the classified cell types were similar in the two mouse strains. In publicly available nocifensive behavior data and our own behavior data from the using the two mouse strains, C57BL/6 exhibited higher sensitivity to heat stimulation than BALB/c, independent of sex and anatomical location of thermal testing (the tail, hind paw, and whisker pad). The TRPV1-selective antagonist JNJ-17203212 inhibited thermal nociception in both strains; however, removing IB4-positive trigeminal sensory neurons with IB4-conjugated saporin inhibited thermal nociception on the whisker pad in C57BL/6 but not in BALB/c. These results suggest that TRPV1 expression levels in IB4-positive type 2 and 13 neurons contributed to differential thermal nociception in skin of C57BL/6 compared with BALB/c.

  5. [Photoexcitation mechanism of photoconductive device by organic/inorganic thin-film heteropairing].

    PubMed

    Jin, Hui; Teng, Feng; Liu, Jun-Feng; Meng, Xian-Guo; Xu, Zheng; Hou, Yan-Bing; Xu, Xu-Rong

    2004-08-01

    Photoconductive devices with organic (polyvinylcarbazole-PVK)/inorganic (zinc-sulfide--ZnS) thin-film heteropairing were fabricated. In external field, the excitation profile of the steady-state photoconductivity and the primary photoexcitation process of hybrid devices were presented and discussed. Comparison of photoconductivity of the devices and absorption spectra of PVK and ZnS implied that both layers absorption contributes to the photocurrent, but the effective part is at the interface of PVK and ZnS. The dependence of maximum photocurrent on the applied voltage and the dark and illuminated current spectra indicates the ultrafast charge transfer at the interface.

  6. Photorefractive effect in ferroelectric liquid crystal blends containing terthiophene photoconductive chiral dopants

    NASA Astrophysics Data System (ADS)

    Sasaki, Takeo; Yoshino, Masanori

    2016-04-01

    Ferroelectric liquid crystalline mixtures composed of a smectic liquid crystal, a photoconductive chiral dopant, and an electron trap reagent exhibit a large photorefractivity with a rapid response. It is expected that the photorefractive FLC blends can be utilized in dynamic amplification of moving optical signals. In the present study, the photorefractive properties of the ferroelectric liquid crystal blends containing different photoconductive chiral dopants were examined. The durability of the photoconductive chiral dopants during laser irradiation was investigated. Tthe effect of the conduction of photogenerated ionic species on the photorefractivity decay was clarified.

  7. Photorefractive amplification of dynamic light signals using photoconductive ferroelectric liquid crystals

    NASA Astrophysics Data System (ADS)

    Sasaki, Takeo

    2015-05-01

    The photorefractive effect in photoconductive ferroelectric liquid crystal blends containing photoconductive chiral compounds was investigated. Terthiophene compounds possessing chiral structures were mixed with an achiral smectic C liquid crystal mixture. The blends exhibit the ferroelectric chiral smectic C phase. The photorefractivity of the liquid crystal blends was investigated by two-beam coupling experiments. The photoconductive ferroelectric liquid crystal blends prepared in this study exhibited a large gain coefficient of over 1200 cm-1 and a fast response time shorter than 1 ms. Amplification of an moving optical image signal of over 30 fps using the photorefractive ferroelectric liquid crystal was demonstrated.

  8. 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.

  9. EGFR kinase domain mutation positive lung cancers are sensitive to intrapleural perfusion with hyperthermic chemotherapy (IPHC) complete treatment

    PubMed Central

    Zhang, Hongjuan; Zhan, Cheng; Ke, Ji; Xue, Zhiqiang; Zhang, Aiqun; Xu, Kaifeng; Shen, Zhirong; Yu, Lei; Chen, Liang

    2016-01-01

    Lung cancer is the global leading cause of cancer-related deaths. A significant portion of lung cancer patients harbor kinase domain mutations in the epidermal growth factor receptor (EGFR). While EGFR tyrosine kinase inhibitors (TKI) effectively shrink tumors harboring mutant EGFR, clinical efficacy is limited by the development of TKI resistance. Effective alternatives are desperately needed in clinic for treating EGFR kinase domain mutation positive lung cancer. In our clinic in treating M1a lung cancer patients through intrapleural perfusion with hyperthermic chemotherapy (IPHC) followed by cycles of systemic chemotherapy (we termed this procedure IPHC complete treatment, IPHC-CT), we found dramatic tumor shrinkage in mutant EGFR-positive patients. We further confirmed the sensitivity of EGFR mutation-positive lung cancer cell lines derived from patients to HC (hyperthermic chemotherapy) treatment. We found that hyperthermia promoted accumulation of cisplatin in lung cancer cells. Hyperthermia and cisplatin synergistically downregulated the EGFR protein level, leading to quenching of signal from EGFR and induction of apoptosis. Our work therefore showed IPHC-CT is an effective treatment for EGFR kinase domain mutation positive lung cancer patients. PMID:26654941

  10. 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.

  11. High gain photoconductive semiconductor switch having tailored doping profile zones

    SciTech Connect

    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.

  12. Photoconductive switching for HPM (high power microwave) generation

    SciTech Connect

    Pocha, M.D.; Hofer, W.W.

    1990-01-01

    Photoconductive switching has been explored at LLNL and demonstrated to be a viable technology for high power microwave (HPM) generation. This technology enables the development of compact, portable, and efficient HPM sources. At LLNL we have successfully switched 35 KV in <200 ps using laser triggered, 1 {times} 5 {times} 20 mm GaAs switches. Based on these results we are developing an HPM generator with applications for HPM weapons and high power, wideband radar. The paper will discuss the physics limits and tradeoffs in the application of this technology. Among the topics discussed will be switching efficiency, candidate switch materials, laser requirements, applicable laser technologies, generator configurations, and cooling requirements and techniques. In addition to presenting theoretical and practical considerations, the paper will discuss on-going work at LLNL and elsewhere. 11 refs., 2 figs., 1 tab.

  13. Photoconductive and nonlinear optical properties of composites based on metallophthalocyanines

    NASA Astrophysics Data System (ADS)

    Vannikov, A. V.; Grishina, A. D.; Gorbunova, Yu. G.; Tsivadze, A. Yu.

    2015-08-01

    The photoconductive, photorefractive and nonlinear optical properties of composites from polyvinylcarbazole or aromatic polyimide containing supramolecular ensembles of (tetra-15-crown-5) - phthalocyaninato gallium, indium, - phthalocyaninateacetato yttrium, - phthalocyaninato ruthenium with axially coordinated pyrazine molecules were investigated at 633, 1030 and 1064nmusing continuous and pulsed lasers. Supramolecular ensembles (SE) were prepared through dissolution of molecular metallophthalocyanines in tetrachloroethane (TCE) and subsequent treatment via three cycles of heating to 90∘C and slow cooling to room temperature. The zscan method in femtosecond and nanosecond regimeswas used for measuring nonlinear optical properties phthalocyaninato indium and yttrium in TCE solutions and polymer films. It was established that effect of heavy metallic atom is basic factor which determines the quantum yield, photorefractive amplification of laser object beam, dielectric susceptibility of third order and nonlinear optical properties of metallophthalocyanines.

  14. Photoconductive probing of the trap distribution in switchable interfaces.

    PubMed

    Tian, Ye; Zhang, Jianming; Guo, Chuan Fei; Zhang, Baoshun; Liu, Qian

    2016-01-14

    Interfacial resistive switching features are highly dependent on the distribution of the carrier traps in the interface. However, the lack of probing seriously restricts ways of offering physical insights into its mechanism and improving interfacial resistors. In this work, we investigated a resistive switching interface that consists of Bi2S3 nano networks (BSNN) and F-doped SnO2 (FTO), uncovering the relationship between the decay of the photoconductance in BSNN and interfacial trap distribution. Based on this, we suggest a general method to probe the distribution of various interface traps. This method provides us with a new tool to study the interfacial trap distribution in an interfacial resistor, and it might also be used to understand other interface problems. PMID:26660900

  15. Polycrystalline diamond photoconductive device with high UV-visible discrimination

    NASA Astrophysics Data System (ADS)

    McKeag, Robert D.; Chan, Simon S. M.; Jackman, Richard B.

    1995-10-01

    Planar metal-diamond-metal photoconductive devices have been fabricated from free standing large grain (20-30 μm) polycrystalline thin film diamond. An interdigitated electrode design with spacings of 20 μm was used to produce effective UV photodetecting devices at bias values in the range 0.1-10 V. A methane-air treatment has been used to modify the structures such that unprecedented performance characteristics have been recorded (106 higher response to 200 nm than visible wavelengths, <0.1 nA dark currents); spectral features similar to those observed in natural diamond crystals have been observed indicating that the treatment used led to near ideal electronic characteristics from polycrystalline material.

  16. Characteristics of current filamentation in high gain photoconductive semiconductor switching

    SciTech Connect

    Zutavern, F J; Loubriel, G M; O'Malley, M W; Helgeson, W D; McLaughlin, D L; Denison, G J

    1992-01-01

    Characteristics of current filamentation are reported for high gain photoconductive semiconductor switches (PCSS). Infrared photoluminescence is used to monitor carrier recombination radiation during fast initiation of high gain switching in large (1.5 cm gap) lateral GaAs PCSS. Spatial modulation of the optical trigger, a 200--300 ps pulse width laser, is examined. Effects on the location and number of current filaments, rise time, and delay to high gain switching, minimum trigger energy, and degradation of switch contacts are presented. Implications of these measurements for the theoretical understanding and practical development of these switches are discussed. Efforts to increase current density and reduce switch size and optical trigger energy requirements are described. Results from contact development and device lifetime testing are presented and the impact of these results on practical device applications is discussed.

  17. Effect of illumination uniformity on GaAs photoconductive switches

    SciTech Connect

    Donaldson, W.R.; Mu, L. . Lab. for Laser Energetics)

    1994-12-01

    The dynamic behavior of a GaAs photoconductive switch was studied with an electro-optic imaging system during the first 2 ns after optical illumination. The switch behavior changed as a function of the spatial distribution of the optical illumination. Symmetric and asymmetric illumination schemes were investigated experimentally with their electro-optic imaging system. The electric fields were significantly enhanced in the regions of low photo-carrier density. Approximately 1 ns after illumination the simple longitudinal variation of the electric field gave way to nonuniform transverse structure. The experimental results were modeled by treating the switch as an integral part of a transmission line consisting of discrete elements. The experimental results matched the predictions of the transmission-line model in terms of the electric-field enhancements and efficiency.

  18. Supralinear photoconductivity of copper doped semi-insulating gallium arsenide

    SciTech Connect

    Schoenbach, K.H.; Joshi, R.P.; Peterkin, F.; Druce, R.L.

    1995-05-15

    We report on the intensity dependent supralinear photoconductivity in GaAs:Si:Cu material. The results of our measurements show that the effective carrier lifetime can change over two orders of magnitude with variations in the intensity of the optical excitation. A threshold intensity level has been observed and can be related to the occupancy of the deep copper level. Numerical simulations have also been carried out to analyze the trapping dynamics. The intensity dependent lifetimes obtained from the simulations match the experimental data very well. Finally, based on the nonlinear intensity dependence of the effective lifetimes, a possible low-energy phototransistor application for the GaAs:Cu material system is presented. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  19. Microstructured gradient-index lenses for THz photoconductive antennas

    NASA Astrophysics Data System (ADS)

    Brincker, Mads; Karlsen, Peter; Skovsen, Esben; Søndergaard, Thomas

    2016-02-01

    A new type of substrate lens for photoconductive antennas (PCA's) based on sub-wavelength microstructuring is presented and studied theoretically by the use of Greens function integral equation methods (GFIEM's). By etching sub-wavelength trenches into a flat substrate, the effective dielectric constant can be designed to function like a gradient index (GRIN) lens. The proposed GRIN substrate lenses have sub-mm dimension, which is smaller than the dimensions of a typical hyper-hemispherical substrate lens (HSL), and could enable fabrication of arrays of closely packed PCA's with individual lenses integrated directly into the PCA substrate. The performance of different GRIN lenses is compared to a HSL and shown to be comparable with regards to the terahertz radiation extraction efficiency, and it is shown that the collimating properties of these GRIN lenses can be tailored by changing the parameters used for microstructuring.

  20. Stress induced long wavelength photoconductivity in doped silicon infrared detectors

    NASA Technical Reports Server (NTRS)

    Houck, J. R.

    1982-01-01

    The long wavelength cutoff of a Si:P detector was extended to 34 microns by the application of a uniaxial stress. An unstressed Si:P photoconductive detector responds to photons of up to 28 microns wavelength. By applying a uniaxial stress to a detector along the /100/ crystal axis, the response was extended to approximately 34 microns. The /100/ axis was chosen as the stress direction because theoretical calculations predicted that such a stress extends the wavelength response more than one along the /110/ axis. These theoretical calculations were based upon fits to experimental data obtained at stresses of up to approximately kbar, and indicated that the extension in wavelength response continues to increase at much larger stresses.

  1. Effect of surface scattering of carriers in the photoconductivity spectra of CdS

    SciTech Connect

    Batyrev, A. S. Bisengaliev, R. A.; Novikov, B. V.

    2013-05-15

    The effect caused by electron scattering at a semiconductor surface is revealed in the low-temperature (77 K) photoconductivity spectra of second-group CdS crystals subjected to the influence of an external enriching transverse electric field.

  2. Evolution of THz impulse imaging radar to 1550nm photoconductive switches

    NASA Astrophysics Data System (ADS)

    Brown, E. R.; Zhang, W.-D.; Feldman, A.; Harvey, T.; Mirin, R. P.; Sung, S.; Grundfest, W. S.; Taylor, Z. D.

    2016-05-01

    We present measurements of sub-bandgap photoconductivity and photoconductive switches using GaAs doped heavily with Er such that nanoparticles of ErAs are formed. In addition to strong resonant absorption centered around 1550 nm, the material provides strong sub-bandgap photoconductivity and >> μW average power levels when fabricated into an efficient (square spiral) THz antenna and driven by a 1550- nm ultrafast fiber laser. Photo-Hall measurements prove that the predominant photocarrier is the electron and the linearity of the 1550-nm photocurrent (with laser power) suggests that the photoconductivity is "extrinsic", not other possible mechanisms, such as two-photon absorption. These results have immediate relevance to the use of GaAs:Er switches as the transmitter in 1550-nm-driven THz imaging systems such as the "impulse imager" that we have successfully used for biomedical imaging applications.

  3. A new methodology for determining recombination parameters using an RF photoconductance instrument

    SciTech Connect

    Sinton, R.A.; Cuevas, A.

    1995-08-01

    Measurements of minority-carrier lifetime in silicon wafers provide an effective technique for process control and device-physics optimization. For example, detailed measurements of minority-carrier lifetime vs. injection level can allow a nearly complete experimental optimization of a solar cell design and process. This extended abstract describes a methodology that allows this fully characterization by using a relatively simple RF photoconductance-decay tool. By analyzing the quasi-steady-state photoconductance as a function of incident light intensity, information corresponding to an I{sub sc}-V{sub oc} curve can be obtained from a non-contacted silicon wafer. This information is available at various stages during the solar cell fabrication process. The use of steady-state photoconductance instead of transient photoconductance makes use of simple electronics and light sources, yet it has the capability to measure lifetimes down into the 100 ns range.

  4. Photoconductivity in reactively evaporated copper indium selenide thin films

    SciTech Connect

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

    2014-01-28

    Copper indium selenide thin films of composition CuInSe{sub 2} with thickness of the order of 130 nm are deposited on glass substrate at a temperature of 423 ±5 K and pressure of 10{sup −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 CuInSe{sub 2} 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 10{sup 6} cm{sup −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 CuInSe{sub 2} thin films indicate its suitability in photovoltaic applications.

  5. Paradoxes of photoconductive target and optical control of secondary ion yield

    SciTech Connect

    Rokakh, A. G. Matasov, M. D.

    2010-01-15

    This study of the photoconductivity of semiconductors, in particular, cadmium chalcogenides as materials for targets of vacuum image converters followed the path of overcoming paradoxes. The concepts developed by the classics of photoelectricity also help to understand the paradoxes of the new secondary-ion photoelectric effect, especially, its spectral characteristic. The optical channel of secondary ion yield control via a photoconductive target opens the way to a new branch of nanotechnology, i.e., optoionics.

  6. 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.

  7. Simulated Performance of Algorithms for the Localization of Radioactive Sources from a Position Sensitive Radiation Detecting System (COCAE)

    SciTech Connect

    Karafasoulis, K.; Zachariadou, K.; Seferlis, S.; Kaissas, I.; Potiriadis, C.; Lambropoulos, C.; Loukas, D.

    2011-12-13

    Simulation studies are presented regarding the performance of algorithms that localize point-like radioactive sources detected by a position sensitive portable radiation instrument (COCAE). The source direction is estimated by using the List Mode Maximum Likelihood Expectation Maximization (LM-ML-EM) imaging algorithm. Furthermore, the source-to-detector distance is evaluated by three different algorithms based on the photo-peak count information of each detecting layer, the quality of the reconstructed source image, and the triangulation method. These algorithms have been tested on a large number of simulated photons over a wide energy range (from 200 keV to 2 MeV) emitted by point-like radioactive sources located at different orientations and source-to-detector distances.

  8. Polarization analysis for the 2D position-sensitive detector of the HADAS reflectometer in Jülich

    NASA Astrophysics Data System (ADS)

    Rücker, U.; Bergs, W.; Alefeld, B.; Kentzinger, E.; Brückel, Th.

    2001-03-01

    A neutron reflectometer with polarization analysis is being built on the basis of the HADAS spectrometer in the neutron guide hall at the research reactor FRJ-2 (DIDO) in Jülich. The new instrument is optimized for reflectivity and diffuse scattering measurements under grazing incidence on layered magnetic structures with thicknesses in the nm range. In order to measure diffuse scattering with polarization analysis, the 2D position-sensitive detector has been equipped with a polarization analyser that consists of a stack of supermirrors parallel to the scattering plane. First tests have revealed that the resolution of the instrument is not reduced by the polarization analyser. A flipping ratio of 20 has been achieved already during the first experiment.

  9. Persistent photoconductivity in poly(p-phenylenevinylene): Spectral response and slow relaxation

    NASA Astrophysics Data System (ADS)

    Lee, C. H.; Yu, G.; Heeger, A. J.

    1993-06-01

    We report the spectral response and slow decay of the steady-state photoconductivity in poly(p-phenylenevinylene) (PPV) films. The spectral response of the photoconductivity is in good agreement with that calculated from the absorption data with the assumption of rapid recombination at the surface of the film; the results indicate direct photogeneration of free charge carriers via an interband transition. The photoconductivity is, therefore, consistent with a description of the electronic structure of PPV in terms of a semiconductor band model (rather than an exciton model). The very slow stretched-exponential relaxation of the photoinduced conductivity is reminiscent of the persistent photoconductivity observed in inorganic semiconductors. By assuming that the photocurrent is carried predominantly by mobile polarons near the surface, one can construct a model for the persistent photoconductivity in which the recombination of long-lived bipolarons is inhibited in the bulk where bipolarons have a lower free energy than polarons. The persistent photoconductivity, therefore, is caused by the slow dispersive diffusion of photogenerated bipolarons to the surface where they dissociate into polarons and where both polaron transport and recombination occur.

  10. Handy Compton camera using 3D position-sensitive scintillators coupled with large-area monolithic MPPC arrays

    NASA Astrophysics Data System (ADS)

    Kataoka, J.; Kishimoto, A.; Nishiyama, T.; Fujita, T.; Takeuchi, K.; Kato, T.; Nakamori, T.; Ohsuka, S.; Nakamura, S.; Hirayanagi, M.; Adachi, S.; Uchiyama, T.; Yamamoto, K.

    2013-12-01

    The release of radioactive isotopes (mainly 137Cs, 134Cs and 131I) from the crippled Fukushima Daiichi Nuclear Plant remains a serious problem in Japan. To help identify radiation hotspots and ensure effective decontamination operation, we are developing a novel Compton camera weighting only 1 kg and measuring just ∼10 cm2 in size. Despite its compactness, the camera realizes a wide 180° field of vision with a sensitivity about 50 times superior to other cameras being tested in Fukushima. We expect that a hotspot producing a 5 μSv/h dose at a distance of 3 m can be imaged every 10 s, with angular resolution better than 10° (FWHM). The 3D position-sensitive scintillators and thin monolithic MPPC arrays are the key technologies developed here. By measuring the pulse-height ratio of MPPC-arrays coupled at both ends of a Ce:GAGG scintillator block, the depth of interaction (DOI) is obtained for incident gamma rays as well as the usual 2D positions, with accuracy better than 2 mm. By using two identical 10 mm cubic Ce:GAGG scintillators as a scatterer and an absorber, we confirmed that the 3D configuration works well as a high-resolution gamma camera, and also works as spectrometer achieving typical energy resolution of 9.8% (FWHM) for 662 keV gamma rays. We present the current status of the prototype camera (weighting 1.5 kg and measuring 8.5×14×16 cm3 in size) being fabricated by Hamamatsu Photonics K.K. Although the camera still operates in non-DOI mode, angular resolution as high as 14° (FWHM) was achieved with an integration time of 30 s for the assumed hotspot described above.

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

    NASA Astrophysics Data System (ADS)

    Armstrong, Andrew M.; Crawford, Mary H.; Jayawardena, Asanka; Ahyi, Ayayi; Dhar, Sarit

    2016-03-01

    Solar-blind photodetection and photoconductive gain >50 corresponding to a responsivity >8 A/W were observed for β-Ga2O3 Schottky photodiodes. The origin of photoconductive gain was investigated. 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. It is concluded that self-trapped hole formation near the Schottky diode lowers the effective Schottky barrier 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-Ga2O3 photodetectors.

  12. 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; Ahyi, Ayayi; Dhar, Sarit

    2016-03-10

    Solar-blind photodetection and photoconductive gain > 50 corresponding to a responsivity > 8 A/W was observed for β-Ga2O3 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 barrier in reversemore » 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-Ga2O3 photodetectors.« less

  13. Comprehensive simulation of the response of a silicon strip detector for position-sensitive measurements of X-rays

    NASA Astrophysics Data System (ADS)

    Wiącek, P.; Dąbrowski, W.

    2005-10-01

    The paper describes a comprehensive simulation method to evaluate X-ray imaging response of a silicon strip detector with particular emphasis on the charge-sharing effects. The simulation steps include: generation of the initial charge distribution in the detector volume, transport of generated charge in the detector volume, calculation of charges induced in the readout strips, discrimination of noisy electronic signals, and finally determination of the count efficiency vs. photon position as a function of the discrimination threshold. The developed simulation tools are useful for optimising the designs and operating parameters of silicon strip detectors used as 1-D position sensitive devices in experimental techniques like X-ray powder diffraction, X-ray high-resolution diffraction and small angle X-ray scattering, using laboratory X-ray sources. The response of the detector as a function of the detector bias and discrimination threshold has been investigated for two measurement configurations: irradiation from the strip-side and from the back-side.

  14. 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

  15. The residual stress instrument with optimized Si(2 2 0) monochromator and position-sensitive detector at HANARO

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Hee; Moon, Myung-Kook; Em, Vyacheslav T.; Choi, Young-Hyun; Cheon, Jong-Kyu; Nam, Uk-Won; Kong, Kyung-Nam

    2005-06-01

    An upgraded residual stress instrument at the HANARO reactor of the KAERI is described. A horizontally focusing bent perfect crystal Si(2 2 0) monochromator (instead of a mosaic vertical focusing Ge monochromator) is installed in a drum with a tunable (2 θM=0-60°) take-off angle/wavelength. A specially designed position-sensitive detector (60% efficiency for λ=1.8 A) with 200 mm (instead of 100 mm) high-active area is used. There are no Soller type collimators in the instrument. The minimum possible monochromator to sample distance, L=2 m, and sample to detector distance, L=1.2 m, were found to be optimal. The new PSD and bent Si(2 2 0) monochromator combined with the possibility of selecting an appropriate wavelength resulted in about a ten-fold gain in data collection rate. The optimal reflections of austenitic and ferritic steels, aluminum and nickel for stress measurements with a Si(2 2 0) monochromator were chosen experimentally. The ability of the instrument to make strain measurements deep inside the austenitic and ferritic steels has been tested. For the chosen reflections and wavelengths, no shift of peak position (apparent strain) was observed up to 56 mm length of path.

  16. Cell patterning via diffraction-induced optoelectronic dielectrophoresis force on an organic photoconductive chip.

    PubMed

    Yang, Shih-Mo; Tseng, Sheng-Yang; Chen, Hung-Po; Hsu, Long; Liu, Cheng-Hsien

    2013-10-01

    A laser diffraction-induced dielectrophoresis (DEP) phenomenon for the patterning and manipulation of individual HepG2 cells and polystyrene beads via positive/negative DEP forces is reported in this paper. The optoelectronic substrate was fabricated using an organic photoconductive material, TiOPc, via a spin-coating process on an indium tin oxide glass surface. A piece of square aperture array grid grating was utilized to transform the collimating He-Ne laser beam into the multi-spot diffraction pattern which forms the virtual electrodes as the TiOPc-coating surface was illuminated by the multi-spot diffraction light pattern. HepG2 cells were trapped at the spot centers and polystyrene beads were trapped within the dim region of the illuminated image. The simulation results of light-induced electric field and a Fresnel diffraction image illustrated the distribution of trapped microparticles. The HepG2 morphology change, adhesion, and growth during a 5-day culture period demonstrated the cell viability through our manipulation. The power density inducing DEP phenomena, the characteristics of the thin TiOPc coating layer, the operating ac voltage/frequency, the sandwiched medium, the temperature rise due to the ac electric fields and the illuminating patterns are discussed in this paper. This concept of utilizing laser diffraction images to generate virtual electrodes on our TiOPc-based optoelectronic DEP chip extends the applications of optoelectronic dielectrophoretic manipulation. PMID:23925640

  17. Transport studies of conducting, semiconducting and photoconducting star polymers

    NASA Astrophysics Data System (ADS)

    Ferguson, John Baker

    Star polymers are studied for their transport properties in the highly conducting state doped with NOPF6 and iodine, the undoped semiconducting state and the photoconducting state. Doped star polymers exhibit variable range hopping of charge carriers. Transport dimensionality and conductivity depend intricately on the processing conditions for doping and casting films. The highest conducting diffusion doped film (room temperature conductivity 50 S/cm) exhibits 2-dimensional variable range for all doping levels. Polymers doped in solution, then cast to form films have 1.4 dimensional variable range hopping for the highest conducting samples with 10 S/cm at room temperature. The hopping dimensionality varies as the conductivity decreases. The doped star polymers remain on the insulator side of the insulator metal transition with localized carriers as revealed with Kramer-Kronig analysis. Optical and near infrared absorbance and photoluminescence reveal the core of the star polymers exist in a solid state solution of the arms with similar absorbance and luminescence for both solution and films. The arms retain the optical properties of their linear analogs indicating the core and arms do not interact quantum mechanically to produce a new state. Excitons created by absorption in the wider band gap cores rapidly migrate to the arms. Photoconductive time of flight mobility measurements reveal an almost field independent mobility at room temperature. This is due to a unique cancellation of on diagonal and off diagonal disorder in the Bassler disorder formalism. The cores introduce heterogeneous regions with a net lower mobility predicted by correlated disorder models. Space charge limited current reveals trap densities several orders of magnitude higher than the carrier density. Photovoltaic performance of star polymer and fullerene blend devices with both 20 nm and 100 nm thick layers are investigated. The thin devices have low open circuit voltages due to space charge

  18. A CdTe position sensitive detector for a hard X- and gamma-ray wide field camera

    SciTech Connect

    Caroli, E.; Cesare, G. de; Donati, A.; Dusi, W.; Landini, G.; Stephen, J.B.; Perotti, F.

    1998-12-31

    An important region of the electromagnetic spectrum for astrophysics is the hard X- and gamma ray band between 10 keV and a few MeV, where several processes occur in a wide variety of objects and with different spatial distribution and time scales. In order to fulfill the observational requirements in this energy range and taking into account the opportunities given by small/medium size missions (e.g., on the ISS), the authors have proposed a compact, wide field camera based on a thick (1 cm) position sensitive CdTe detector (PSD). The detector is made of an array of 128x96 CdTe microspectrometers with a pixel size of 2x2 mm{sup 2}. The basic element of the PSD is the linear module that is an independent detection unit with 32 CdTe crystals and monolithic front-electronics (ASIC) supported by a thin (300 {micro}m) ceramic layer. The expected performance of the PSD over the operative energy range and some of the required ASIC functionality are presented and discussed.

  19. A simple technique to increase the linearity and field-of-view in position sensitive photomultiplier tubes

    SciTech Connect

    Clancy, R.L.; Thompson, C.J.; Robar, J.L.; Bergman, A.M.

    1996-12-31

    Crossed anode wire position sensitive photomultiplier tubes (PS-PMTs) detect the location of a light source and provide the X and Y axis coordinates of the event. These coordinates are typically generated using Anger logic, where a resistor chain divides the current flow into two signals for each coordinate (X{sup +}, X{sup -} & Y{sup +}, Y{sup -}). In the standard readout, identical resistor values are used across the entire resistor chain. While this arrangement provides a linear readout in the central portion of the photomultiplier face, the readout is non-linear and sometimes even double valued near the edges of the PS-PMT due to the truncation of the charge beyond the last anode wire. To counter this effect, we have increased the value of the resistance near the ends of each resistor chain in order to compensate for the charge lost beyond the anode wires. Measurements were made using a Hamamatsu R-3941 PS-PMT coupled to a pixellated BGO matrix of cut crystals with a 2mm pitch in each direction. After changing the end resistors, the usable field-of-view increased by 39%. This simple modification should enhance the operation of PS-PMTs in applications such as positron emission mammography, and small animal PET imaging.

  20. High-Efficiency CdZnTe Position-Sensitive VFG Gamma-Ray Detectors for Safeguards Applications

    SciTech Connect

    Bolotnikov, Aleksey E.; James, Ralph B.; Cui, Y.; De Geronimo, G.; Vernon, E.; Camarda, G. S.; Hossain, A.; Yang, G.; Indusi, J.; Boyer, Brian

    2015-09-30

    The goal of this project is to incorporate a Cadmium-Zinc-Telluride (CdZnTe or CZT) detector (with 1% or better resolution) into a bench-top prototype for isotope identification and related safeguards applications. The bench-top system is based on a 2x2 array of 6x6x20 mm3 position-sensitive virtual Frisch-grid (VFG) CZT detectors. The key features of the array are that it allows for the use of average-grade CZT material with a moderate content of defects, and yet it provides high-energy resolution, 1% FWHM at 662 keV, large effective area, and low-power consumption. The development of this type of 3D detector and new instruments incorporating them is motivated by the high cost and low availability of large, > 1 cm3, CZT crystals suitable for making multi-pixel detectors with acceptable energy resolution and efficiency.

  1. Reciprocal-Space Analysis of Compositional Modulation in Short-Period Superlattices Using Position-Sensitive X-Ray Detection

    SciTech Connect

    Ahrenkiel, S.P.; Follstaedt, D.M.; Lee, S.R.; Millunchick, J.M.; Norman, A.G.; Reno, J.L.; Twesten, R.D.

    1998-11-10

    Epitaxial growth of AlAs-InAs short-period superlattices on (001) InP can lead to heterostructures exhibiting strong, quasi-periodic, lateral modulation of the alloy composition; transverse satellites arise in reciprocal space as a signature of the compositional modulation. Using an x-ray diffractometer equipped with a position-sensitive x-ray detector, we demonstrate reciprocal-space mapping of these satellites as an efficient, nondestructive means for detecting and characterizing the occurrence of compositional modulation. Systematic variations in the compositional modulation due to the structural design and the growth conditions of the short-period superlattice are characterized by routine mapping of the lateral satellites. Spontaneous compositional modulation occurs along the growth front during molecular-beam epitaxy of (AlAs) (InAs)n short-period superlattices. The modulation is quasi-periodic and forms a lateral superlattice superimposed on the intended SPS structure. Corresponding transverse satellites arise about each reciprocal lattice point, and x-ray diffraction can be routinely used to map their local reciprocal-space structure. The integrated intensity, spacing, orientation, and shape of these satellites provide a reliable means for nondestructively detecting and characterizing the compositional modulation in short-period superlattices. The analytical efficiency afforded by the use of a PSD has enabled detailed study of systematic vacations in compositional modulation as a function of the average composition, the period, and the growth rate of the short- period superlattice

  2. Charge integrating type position-sensitive proportional chamber for time-resolved measurements using intense X-ray sources

    NASA Astrophysics Data System (ADS)

    Mochiki, Koh-ichi; Hasegawa, Ken-ichi

    1985-02-01

    A position-sensitive detecting system for time-resolved diffraction measurements with very intensive X-ray sources has been developed. It consists of a charge integrating type gas-filled detector, multichannel analog multiplexers, a signal processor and a memory (120 ch.×128 phases×24 bits). The detector is 120 mm long in effective length by 10 mm×10 mm in cross section with a single anode of 20 μm diameter. One of the cathode planes consists of 120 cathode strips with a pitch of 1 mm. The spatial resolution is equal to the pitch under a certain detector current limit. The gas gain is adjustable to an appropriate value according to the X-ray intensity range of interest. For experiments with 8 keV X-ray sources, maximum absorption rates of 9×10 7 photons/s·mm with low applied voltage and minimum absorption rates of about 3 photons/s·mm with high applied voltage can be achieved. This system was applied to a time-resolved X-ray diffraction study on frog muscle using a synchrotron radiation source at the Photon Factory and we could collect diffraction patterns with a time resolution of 10 ms and only 10 stimulations.

  3. Photoconductive Semiconductor Switch Technology for Short Pulse Electromagnetics and Lasers

    SciTech Connect

    Denison, Gary J.; Helgeson, Wesley D.; Hjalmarson, Harold P.; Loubriel, Guillermo M.; Mar, Alan; O'Malley, Martin W.; Zutavern, Fred J.

    1999-08-05

    High gain photoconductive semiconductor switches (PCSS) are being used to produce high power electromagnetic pulses foc (1) compact, repetitive accelerators, (2) ultra-wide band impulse sources, (3) precision gas switch triggers, (4) optically-activated firesets, and (5) high power optical pulse generation and control. High power, sub-nanosecond optical pulses are used for active optical sensors such as compact optical radars and range-gated hallistic imaging systems. Following a brief introduction to high gain PCSS and its general applications, this paper will focus on PCSS for optical pulse generation and control. PCSS technology can be employed in three distinct approaches to optical pulse generation and control: (1) short pulse carrier injection to induce gain-switching in semiconductor lasers, (2) electro-optical Q-switching, and (3) optically activated Q-switching. The most significant PCSS issues for these applications are switch rise time, jitter, and longevity. This paper will describe both the requirements of these applications and the most recent results from PCSS technology. Experiments to understand and expand the limitations of high gain PCSS will also be described.

  4. Simulating photoconductive atomic-force microscopy on disordered photovoltaic materials

    NASA Astrophysics Data System (ADS)

    Blakesley, James C.; Castro, Fernando A.

    2015-04-01

    We present a tool for simulating photoconductive atomic-force microscopy (Pc-AFM) on bulk heterojunction (BHJ) materials with a minimal set of empirical parameters. The simulation is a master-equation solution of a three-dimensional hopping charge transport model which includes donor-acceptor domain morphology, energetic and spatial disorder, exciton transport and splitting, charge-pair generation and recombination, and tip-substrate electrostatics. A simplifying aspect of the model is that electron transport, hole transport, and electron-hole recombination are treated as the same electron-transfer process. The model recreates realistic bulk recombination rates, without requiring short-range Coulombic effects to be calculated. We demonstrate the tool by simulating line scans of a Pc-AFM tip passing over the surface of a buried or exposed acceptor cluster in a BHJ film. The simulations confirm experimental observations that such defects can be detected by open-circuit mode Pc-AFM imaging, even when the clusters are buried below the surface.

  5. 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.

  6. Structural and Photoconductivity Properties of Tellurium/PMMA Films

    NASA Astrophysics Data System (ADS)

    Carotenuto, Gianfranco; Palomba, Mariano; De Nicola, Sergio; Ambrosone, Giuseppina; Coscia, Ubaldo

    2015-08-01

    Owing to the very brittle nature of tellurium powder, nanoscopic grains with an average size of 4.8 ± 0.8 nm were produced by dry vibration milling technique using a mixer/mill apparatus. A novel material was obtained by binding the nanosized tellurium grains with poly(methyl methacrylate) (PMMA) polymer. The morphology, elemental composition, and structural and optical properties of Te/PMMA films were investigated. The prepared material was composed of hexagonal tellurium and α-phase of tellurium oxide. The electrical properties of the films were studied, for different electrode contact configurations, in dark condition and under white light illumination varying the optical power density from 2 to 170 mW/cm2 and turning the light on and off cyclically. Data analysis shows that the photoconductivity of the film with sandwich contact configuration is a linear function of the light power density and increases more than 2 orders of magnitude as compared to the photoresponse of the film with coplanar contact configuration.

  7. Cryogenic silicon photoconductive power switches for high-power applications

    SciTech Connect

    Petr, R.A.

    1987-01-01

    The silicon photoconductive power switch (PCPS) is an attractive switch technology because it is capable of switching extremely large energy pulses of short duration with good efficiency and precise timing control. At high operating frequencies, there are enormous advantages to be gained by operating at liquid nitrogen temperatures. For example, the mechanical properties of silicon at 77K are such that its power-dissipation limit due to stress fracture is an order of magnitude higher than at 300K. Also, its thermal conductivity is improved at lower temperatures. Another important characteristic of 77K silicon is that its optical absorption depth at 1.06um extends out to 13cm, as compared to 0.1cm at 300K. Important aspects of operating a cryogenic silicon PCPS at high average power levels are addressed here. Electrical and optical properties of silicon at both 77K and 300K are developed, along with its thermomechanical properties when switching high peak and average power. In addition, experimental data concerning PCPS electrical-switching characteristics, optical trigger uniformity, and thermal stress response during conduction are presented. Finally, a system study compares the silicon PCPS to the thyratron.

  8. 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.

  9. Subnanosecond, high voltage photoconductive switching in GaAs

    SciTech Connect

    Druce, R.L.; Pocha, M.D.; Griffin, K.L. ); O'Bannon, B.J. )

    1990-01-01

    We are conducting research on the switching properties of photoconductive materials to explore their potential for generating high-power microwaves (HPM) and for high rep-rate switching. We have investigated the performance of Gallium Arsenide (GaAs) in linear mode (the conductivity of the device follows the optical pulse) as well as an avalanche-like mode (the optical pulse only controls switch closing). Operating in the linear mode, we have observed switch closing times of less than 200 ps with a 100 ps duration laser pulse and opening times of less than 400 ps at several kV/cm fields using neutron irradiated GaAs. In avalanche and lock-on modes, high fields are switched with lower laser pulse energies, resulting in higher efficiencies; but with measurable switching delay and jitter. We are currently investigating both large area (1 cm{sup 2}) and small area (<1 mm{sup 2}) switches illuminated by AlGaAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 {mu}m.

  10. Time- and spectrally resolved terahertz photoconductivity of quantum Hall systems

    NASA Astrophysics Data System (ADS)

    Stellmach, C.; Vasile, G.; Hirsch, A.; Bonk, R.; Vasilyev, Yu. B.; Hein, G.; Becker, C. R.; Nachtwei, G.

    2007-07-01

    We present terahertz photoconductivity measurements on GaAs/AlGaAs and HgTe/HgCdTe heterostructures. The photoresponse is investigated time and spectrally resolved under quantum Hall conditions. The samples are excited by a pulsed p-Ge laser, which emits photons of frequencies around 2THz (corresponding to photon energies around 10meV ). Corbino-shaped GaAs/AlGaAs samples show relaxation times τ down to 10ns . The dependence of τ on the applied source-drain voltage is explained by a two-level picture after normalizing the data. All spectrally resolved measurements show contributions of the cyclotron resonance and the bolometric effect. These results are compared to numerical calculations based on a self-consistent Born approximation method. The measurements on HgTe/HgCdTe samples show comparable results. However, the effective mass in these samples is only mc=0.026m0 (approximately 1/3 of the mass in GaAs/AlGaAs ). Thus the cyclotron resonance is shifted to smaller magnetic fields around 2T . This fact makes HgTe/HgCdTe systems especially interesting for terahertz detector applications.

  11. 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.

  12. Structural and Photoconductivity Properties of Tellurium/PMMA Films.

    PubMed

    Carotenuto, Gianfranco; Palomba, Mariano; De Nicola, Sergio; Ambrosone, Giuseppina; Coscia, Ubaldo

    2015-12-01

    Owing to the very brittle nature of tellurium powder, nanoscopic grains with an average size of 4.8 ± 0.8 nm were produced by dry vibration milling technique using a mixer/mill apparatus. A novel material was obtained by binding the nanosized tellurium grains with poly(methyl methacrylate) (PMMA) polymer. The morphology, elemental composition, and structural and optical properties of Te/PMMA films were investigated. The prepared material was composed of hexagonal tellurium and α-phase of tellurium oxide. The electrical properties of the films were studied, for different electrode contact configurations, in dark condition and under white light illumination varying the optical power density from 2 to 170 mW/cm(2) and turning the light on and off cyclically. Data analysis shows that the photoconductivity of the film with sandwich contact configuration is a linear function of the light power density and increases more than 2 orders of magnitude as compared to the photoresponse of the film with coplanar contact configuration. PMID:26245856

  13. Deep donor model for the persistent photoconductivity effect

    SciTech Connect

    Hjalmarson, H.P.; Drummond, T.J.

    1986-03-10

    It is proposed that a persistent photoconductivity (PPC) effect is universally produced by deep donors. The general requirements of a class of models which explains the PPC effect in semiconductors are discussed. In particular, donor dopants such as Si and Te in Ga/sub 1-x/Al/sub x/As with xapprox.0.3 are conjectured to be deep and responsible for the PPC effect attributed to DX centers consisting of donor-vacancy pairs. It is shown that the Si donor has properties which explain the known data attributed to the DX center; these data include (1) the slow capture rate at low temperatures, (2) the thermally activated capture rate at high temperatures, and (3) the shape of the photoexcitation cross section. However, in contrast with the DX-center model, the deep donor model does not require a high trapped vacancy concentration ((V)approx.10/sup 18/ cm/sup -3/) to explain the PPC effect in highly doped semiconductors.

  14. Supramolecular core-shell nanoparticles for photoconductive device applications.

    PubMed

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

    2016-08-12

    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. PMID:27353003

  15. 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

  16. Strain-induced photoconductivity in thin films of Co doped amorphous carbon.

    PubMed

    Jiang, Y C; Gao, J

    2014-01-01

    Traditionally, strain effect was mainly considered in the materials with periodic lattice structure, and was thought to be very weak in amorphous semiconductors. Here, we investigate the effects of strain in films of cobalt-doped amorphous carbon (Co-C) grown on 0.7PbMg(1/3)Nb(2/3)O3-0.3PbTiO3 (PMN-PT) substrates. The electric transport properties of the Co-C films were effectively modulated by the piezoelectric substrates. Moreover, we observed, for the first time, strain-induced photoconductivity in such an amorphous semiconductor. Without strain, no photoconductivity was observed. When subjected to strain, the Co-C films exhibited significant photoconductivity under illumination by a 532-nm monochromatic light. A strain-modified photoconductivity theory was developed to elucidate the possible mechanism of this remarkable phenomenon. The good agreement between the theoretical and experimental results indicates that strain-induced photoconductivity may derive from modulation of the band structure via the strain effect. PMID:25338641

  17. Strain-induced photoconductivity in thin films of Co doped amorphous carbon

    PubMed Central

    Jiang, Y. C.; Gao, J.

    2014-01-01

    Traditionally, strain effect was mainly considered in the materials with periodic lattice structure, and was thought to be very weak in amorphous semiconductors. Here, we investigate the effects of strain in films of cobalt-doped amorphous carbon (Co-C) grown on 0.7PbMg1/3Nb2/3O3-0.3PbTiO3 (PMN-PT) substrates. The electric transport properties of the Co-C films were effectively modulated by the piezoelectric substrates. Moreover, we observed, for the first time, strain-induced photoconductivity in such an amorphous semiconductor. Without strain, no photoconductivity was observed. When subjected to strain, the Co-C films exhibited significant photoconductivity under illumination by a 532-nm monochromatic light. A strain-modified photoconductivity theory was developed to elucidate the possible mechanism of this remarkable phenomenon. The good agreement between the theoretical and experimental results indicates that strain-induced photoconductivity may derive from modulation of the band structure via the strain effect. PMID:25338641

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    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.

  20. Reduced sensitivity to both positive and negative reinforcement in mice over-expressing the 5-hydroxytryptamine transporter.

    PubMed

    Line, Samantha J; Barkus, Chris; Rawlings, Nancy; Jennings, Katie; McHugh, Stephen; Sharp, Trevor; Bannerman, David M

    2014-12-01

    The 5-hydroxytryptamine (5-HT) transporter (5-HTT) is believed to play a key role in both normal and pathological psychological states. Much previous data suggest that the s allele of the polymorphic regulatory region of the 5-HTT gene promoter is associated with reduced 5-HTT expression and vulnerability to psychiatric disorders, including anxiety and depression. In comparison, the l allele, which increases 5-HTT expression, is generally considered protective. However, recent data link this allele to both abnormal 5-HT signalling and psychopathic traits. Here, we studied the processing of aversive and rewarding cues in transgenic mice that over-express the 5-HTT (5-HTTOE mice). Compared with wild-type mice, 5-HTTOE mice froze less in response to both a tone that had previously been paired with footshock, and the conditioning context. In addition, on a decision-making T-maze task, 5-HTTOE mice displayed reduced preference for a larger, delayed reward and increased preference for a smaller, immediate reward, suggesting increased impulsiveness compared with wild-type mice. However, further inspection of the data revealed that 5-HTTOE mice displayed a relative insensitivity to reward magnitude, irrespective of delay. In contrast, 5-HTTOE mice appeared normal on tests of spatial working and reference memory, which required an absolute choice between options associated with either reward or no reward. Overall, the present findings suggest that 5-HTT over-expression results in a reduced sensitivity to both positive and negative reinforcers. Thus, these data show that increased 5-HTT expression has some maladaptive effects, supporting recent suggestions that l allele homozygosity may be a potential risk factor for disabling psychiatric traits.

  1. A data acquisition system for two-dimensional position sensitive micropattern gas detectors with delay-line readout

    NASA Astrophysics Data System (ADS)

    Hanu, A. R.; Prestwich, W. V.; Byun, S. H.

    2015-04-01

    We present a data acquisition (DAQ) system for two-dimensional position sensitive micropattern gas detectors using the delay-line method for readout. The DAQ system consists of a field programmable gate array (FPGA) as the main data processor and our time-to-digital (TDC) mezzanine card for making time measurements. We developed the TDC mezzanine card around the Acam TDC-GPX ASIC and it features four independent stop channels referenced to a common start, a typical timing resolution of ~81 ps, and a 17-bit measurement range, and is compliant with the VITA 57.1 standard. For our DAQ system, we have chosen the Xilinx SP601 development kit which features a single Spartan 6 FPGA, 128 MB of DDR2 memory, and a serial USB interface for communication. Output images consist of 1024×1024 square pixels, where each pixel has a 32-bit depth and corresponds to a time difference of 162 ps relative to its neighbours. When configured for a 250 ns acquisition window, the DAQ can resolve periodic event rates up to 1.8×106 Hz without any loses and will report a maximum event rate of 6.11×105 Hz for events whose arrival times follow Poisson statistics. The integral and differential non-linearities have also been measured and are better than 0.1% and 1.5%, respectively. Unlike commercial units, our DAQ system implements the delay-line image reconstruction algorithm entirely in hardware and is particularly attractive for its modularity, low cost, ease of integration, excellent linearity, and high throughput rate.

  2. Reduced sensitivity to both positive and negative reinforcement in mice over-expressing the 5-hydroxytryptamine transporter.

    PubMed

    Line, Samantha J; Barkus, Chris; Rawlings, Nancy; Jennings, Katie; McHugh, Stephen; Sharp, Trevor; Bannerman, David M

    2014-12-01

    The 5-hydroxytryptamine (5-HT) transporter (5-HTT) is believed to play a key role in both normal and pathological psychological states. Much previous data suggest that the s allele of the polymorphic regulatory region of the 5-HTT gene promoter is associated with reduced 5-HTT expression and vulnerability to psychiatric disorders, including anxiety and depression. In comparison, the l allele, which increases 5-HTT expression, is generally considered protective. However, recent data link this allele to both abnormal 5-HT signalling and psychopathic traits. Here, we studied the processing of aversive and rewarding cues in transgenic mice that over-express the 5-HTT (5-HTTOE mice). Compared with wild-type mice, 5-HTTOE mice froze less in response to both a tone that had previously been paired with footshock, and the conditioning context. In addition, on a decision-making T-maze task, 5-HTTOE mice displayed reduced preference for a larger, delayed reward and increased preference for a smaller, immediate reward, suggesting increased impulsiveness compared with wild-type mice. However, further inspection of the data revealed that 5-HTTOE mice displayed a relative insensitivity to reward magnitude, irrespective of delay. In contrast, 5-HTTOE mice appeared normal on tests of spatial working and reference memory, which required an absolute choice between options associated with either reward or no reward. Overall, the present findings suggest that 5-HTT over-expression results in a reduced sensitivity to both positive and negative reinforcers. Thus, these data show that increased 5-HTT expression has some maladaptive effects, supporting recent suggestions that l allele homozygosity may be a potential risk factor for disabling psychiatric traits. PMID:25283165

  3. Fast x-ray scattering measurements on molten alumina using a 120{degree} curved position sensitive detector.

    SciTech Connect

    Hennet, L.; Thiaudiere, D.; Gailhanou, M.; Landron, C.; Coutures, J.-P.; Price, D. L.; C.R.M.H.T.; LURE; Univ. de Perpignan

    2002-01-01

    Fast x-ray scattering measurements on molten alumina were performed on the H10 beam line at the DCI Synchrotron of LURE (Orsay, France). A high-temperature chamber with a levitation device was coupled with the four-circle goniometer of the beam line. A 100 W CO{sub 2} laser was used to melt the sample and the temperature was measured using an optical pyrometer operating at 0.85 {mu}m. Usually, measurements of the total structure factor S(Q) on molten materials are performed using a fixed detector scanned over an angular range. In this work, in order to reduce the total scan duration, x-ray scattered intensities were measured with a 120{sup o} position sensitive detector (INEL CPS120). We performed several measurements with different acquisition times varying from 10 s to 5 min. In 5 min it was possible to obtain a good determination of S(Q) with a usable signal up to the Q range limit (13 Angstroms{sup -1}). The intensity was comparable with a 1 h measurement with a NaI (Tl) scintillator scanned over the 120 2{theta} range. On reducing the counting time the statistics are degraded and the data are noisier, especially in the high Q region. Nevertheless, even with 10 s, the S(Q) data remain usable and give good results. Performing the Fourier transformation of S(Q), we obtain similar reliable pair-correlation functions with both 5 min and 10 s acquisition times.

  4. One-dimensional organic photoconductive nanoribbons built on Zn-Schiff base complex

    SciTech Connect

    Liu Li; Shao Mingwang; Wang Xiuhua

    2010-03-15

    One-dimensional organic nanoribbons built on N-p-nitrophenylsalicylaldimine zinc complex were synthesized via a facile solvothermal route. The scanning electron microscope images revealed that the as-synthesized products were ribbon-like with width mainly of 300-600 nm, thickness of about 50 nm, and length of up to tens of micrometers. Fourier transform infrared spectrum was employed to characterize the structure. Ultraviolet-visible absorption and photoluminescence spectra showed that the products had good photoluminescent property and exhibited blue emission. The conductivity of a bundle of nanoribbons was also measured, which showed that the Schiff base zinc nanoribbons had good photoconductive property. This work might enrich the organic photoconductive materials and be applicable in light-controlled micro-devices or nano-devices in the future. - Graphical abstract: The Schiff base zinc nanoribbons nanowires exhibited good photoresponse under an incandescent lamp, which indicated their potential application as organic semiconductive or photoconductive nanodevices in the future.

  5. Photoconducting properties of a unit nanostructure of ZnO assembled between microelectrodes.

    PubMed

    Kulkarni, Atul; Wahab, Rizwan; Ansari, S G; Kim, Tae-Sung; Al-Deyab, Salem S; Ansari, Z A

    2012-03-01

    The photoconducting properties of a unit microflower of zinc oxide are investigated as a function of wavelength from UV to IR region at constant illumination intensity. Synthesized flowers were trapped in 2 microm gap, between pre-prepared gold microelectrodes, using AC dielectrophoresis. Photocurrent drastically increases upon illumination in the UV region, whereas it gradually reduces when irradiated in visible and IR region. Higher photoconductivity in UV region is correlated to band to band transition upon illumination. In visible region, deep level transitions are expected which intern exhibits comparatively low photocurrent. Photoconduction in IR region is only due to the adsorbed surface oxygen species. This investigation suggests the potential application of ZnO nanostructures for various optoelectronic device applications.

  6. Impact of substrate characteristics on performance of large area plasmonic photoconductive emitters.

    PubMed

    Yardimci, Nezih T; Salas, Rodolfo; Krivoy, Erica M; Nair, Hari P; Bank, Seth R; Jarrahi, Mona

    2015-12-14

    We present a comprehensive analysis of terahertz radiation from large area plasmonic photoconductive emitters in relation with characteristics of device substrate. Specifically, we investigate the radiation properties of large area plasmonic photoconductive emitters fabricated on GaAs substrates that exhibit short carrier lifetimes through low-temperature substrate growth and through epitaxially embedded rare-earth arsenide (ErAs and LuAs) nanoparticles in superlattice structures. Our analysis indicates that the utilized substrate composition and growth process for achieving short carrier lifetimes are crucial in determining substrate resistivity, carrier drift velocity, and carrier lifetime, which directly impact optical-to-terahertz conversion efficiency, radiation power, radiation bandwidth, and reliability of large area plasmonic photoconductive emitters.

  7. Photoconductive detection of hydrogen in ZnO and rutile TiO2

    NASA Astrophysics Data System (ADS)

    Lavrov, E. V.; Mchedlidze, T.; Herklotz, F.

    2016-08-01

    Hydrogen donors in ZnO and rutile TiO2 are probed by means of photoconductivity and IR absorption. It is shown that the O-H bonds giving rise to the local vibrational modes (LVMs) of interstitial hydrogen at 3611 and 3290 cm-1 in the case of ZnO and TiO2, respectively, also occur in the photoconductivity spectra as Fano resonances. The effects of isotope substitution, concentration, sample thickness, influence of other donors present in both oxides are considered. Based on the shape and frequency of these resonances, it is concluded that the apparent ionization energy of interstitial hydrogen in rutile TiO2 is less than 300 meV. By a direct comparison, we also demonstrate that photoconductive detection of LVMs of defects in thin semiconductor films is superior to the standard IR absorption.

  8. Nano-thermometers with thermo-sensitive polymer grafted USPIOs behaving as positive contrast agents in low-field MRI

    NASA Astrophysics Data System (ADS)

    Hannecart, Adeline; Stanicki, Dimitri; Vander Elst, Luce; Muller, Robert N.; Lecommandoux, Sébastien; Thévenot, Julie; Bonduelle, Colin; Trotier, Aurélien; Massot, Philippe; Miraux, Sylvain; Sandre, Olivier; Laurent, Sophie

    2015-02-01

    Two commercial statistical copolymers of ethylene oxide and propylene oxide, Jeffamine® M-2005 (PEO5-st-PPO37) and M-2070 (PEO46-st-PPO13), exhibiting lower critical solution temperature (LCST) in water, were grafted onto the surface of ultra-small superparamagnetic iron oxide nanoparticles (USPIOs) using silanization and amide-bond coupling reactions. The LCSTs of the polymers in solution were measured by dynamic light scattering (DLS) and nuclear magnetic resonance (NMR). In accordance with the compositions of EO vs. PO, the transition temperature was measured to be 22 +/- 2 °C for M-2005 by both DLS and NMR, while the LCST was much higher, 52 +/- 2 °C, for M-2070 (a second transition was also detected above 80 °C by NMR in that case, ascribed to the full dehydration of chains at the molecular level). The resulting polymer-grafted USPIOs exhibit a temperature-responsive colloidal behaviour, their surface reversibly changing from hydrophilic below LCST to hydrophobic above it. This phenomenon was utilised to design thermo-sensitive contrast agents for MRI. Transverse relaxivities (r2) of the USPIO@PEO5-st-PPO37 core-shell nanoparticles were measured at 8.25, 20, 60, and 300 MHz. Nuclear magnetic resonance dispersion (NMRD) profiles, giving longitudinal relaxivities (r1) between 0.01 and 60 MHz, were acquired at temperatures ranging from 15 to 50 °C. For all tested frequencies except 300 MHz, both r1 and r2 decrease with temperature and show an inflection point at 25 °C, near the LCST. To illustrate the interest of such polymer-coated USPIOs for MRI thermometry, sample tubes were imaged on both low-field (8.25 MHz/0.194 Tesla) and high-field (300 MHz/7.05 Tesla) MRI scanners with either T1- or T2*-weighted spin echo sequences. The positive contrast on low-field MR images and the perfect linearity of the signal with a T2*-weighted sequence over the entire temperature range 15-50 °C render these LCST polymer coated USPIOs interesting positive contrast agents

  9. High Infrared Photoconductivity in Films of Arsenic-Sulfide-Encapsulated Lead-Sulfide Nanocrystals

    PubMed Central

    2014-01-01

    Highly photoconductive thin films of inorganic-capped PbS nanocrystal quantum dots (QDs) are reported. Stable colloidal dispersions of (NH4)3AsS3-capped PbS QDs were processed by a conventional dip-coating technique into a thin homogeneous film of electronically coupled PbS QDs. Upon drying at 130 °C, (NH4)3AsS3 capping ligands were converted into a thin layer of As2S3, acting as an infrared-transparent semiconducting glue. Photodetectors obtained by depositing such films onto glass substrates with interdigitate electrode structures feature extremely high light responsivity and detectivity with values of more than 200 A/W and 1.2 × 1013 Jones, respectively, at infrared wavelengths up to 1400 nm. Importantly, these devices were fabricated and tested under ambient atmosphere. Using a set of time-resolved optoelectronic experiments, the important role played by the carrier trap states, presumably localized on the arsenic-sulfide surface coating, has been elucidated. Foremost, these traps enable a very high photoconductive gain of at least 200. The trap state density as a function of energy has been plotted from the frequency dependence of the photoinduced absorption (PIA), whereas the distribution of lifetimes of these traps was recovered from PIA and photoconductivity (PC) phase spectra. These trap states also have an important impact on carrier dynamics, which led us to propose a kinetic model for trap state filling that consistently describes the experimental photoconductivity transients at various intensities of excitation light. This model also provides realistic values for the photoconductive gain and thus may serve as a useful tool to describe photoconductivity in nanocrystal-based solids. PMID:25470412

  10. High infrared photoconductivity in films of arsenic-sulfide-encapsulated lead-sulfide nanocrystals.

    PubMed

    Yakunin, Sergii; Dirin, Dmitry N; Protesescu, Loredana; Sytnyk, Mykhailo; Tollabimazraehno, Sajjad; Humer, Markus; Hackl, Florian; Fromherz, Thomas; Bodnarchuk, Maryna I; Kovalenko, Maksym V; Heiss, Wolfgang

    2014-12-23

    Highly photoconductive thin films of inorganic-capped PbS nanocrystal quantum dots (QDs) are reported. Stable colloidal dispersions of (NH4)3AsS3-capped PbS QDs were processed by a conventional dip-coating technique into a thin homogeneous film of electronically coupled PbS QDs. Upon drying at 130 °C, (NH4)3AsS3 capping ligands were converted into a thin layer of As2S3, acting as an infrared-transparent semiconducting glue. Photodetectors obtained by depositing such films onto glass substrates with interdigitate electrode structures feature extremely high light responsivity and detectivity with values of more than 200 A/W and 1.2×10(13) Jones, respectively, at infrared wavelengths up to 1400 nm. Importantly, these devices were fabricated and tested under ambient atmosphere. Using a set of time-resolved optoelectronic experiments, the important role played by the carrier trap states, presumably localized on the arsenic-sulfide surface coating, has been elucidated. Foremost, these traps enable a very high photoconductive gain of at least 200. The trap state density as a function of energy has been plotted from the frequency dependence of the photoinduced absorption (PIA), whereas the distribution of lifetimes of these traps was recovered from PIA and photoconductivity (PC) phase spectra. These trap states also have an important impact on carrier dynamics, which led us to propose a kinetic model for trap state filling that consistently describes the experimental photoconductivity transients at various intensities of excitation light. This model also provides realistic values for the photoconductive gain and thus may serve as a useful tool to describe photoconductivity in nanocrystal-based solids.

  11. Electrical Breakdown Physics in Photoconductive Semiconductor Switches (PCSS).

    SciTech Connect

    Mar, Alan; Zutavern, Fred J.; Vawter, Gregory A.; Hjalmarson, Harold P.; Gallegos, Richard Joseph; Bigman, Verle Howard

    2016-01-01

    Advanced switching devices with long lifetime will be critical components for Linear Transformer Drivers (LTDs) in next-generation accelerators. LTD designs employ high switch counts. With current gas switch technology at %7E10e3 shot life, a potential game-changer would be the development of a reliable low-impedance (%3C35nh) optically-triggered compact solid-state switch capable of switching 200kV and 50kA with 10e5 shotlife or better. Other applications of this technology, are pulse shaping programmable systems for dynamic material studies (Z-next, Genesis), efficient pulsed power systems for biofuel feedstock, short pulse (10 ns) accelerator designs for the Defense Threat Reduction Agency (DTRA), and sprytron replacements in NW firing sets. This LDRD project has succeeded in developing new optically-triggered photoconductive semiconductor switch (PCSS) designs that show great promise for scaling to modules capable of 200kV (DC) and 5kA current that can be stacked in parallel to achieve 100's of kA with 10e5 shot lifetime. . Executive Summary Advanced switching devices with long lifetime will be critical components for Linear Transformer Drivers (LTDs) in next-generation accelerators. LTD designs employ high switch counts. With current gas switch technology at %7E10e3 shot life, a potential game-changer would be the development of a reliable low-impedance (%3C35nh) optically-triggered compact solid-state switch capable of switching 200kV and 50kA with 10e5 shotlife or better. Other applications of this technology, are pulse shaping programmable systems for dynamic material studies (Z-next, Genesis), efficient pulsed power systems for biofuel feedstock, short pulse (10 ns) accelerator designs for the Defense Threat Reduction Agency (DTRA), and sprytron replacements in NW firing sets. This LDRD project has succeeded in developing new optically-triggered photoconductive semiconductor switch (PCSS) designs that show great promise for scaling to modules capable

  12. Nanostructured donor-acceptor self assembly with improved photoconductivity.

    PubMed

    Saibal, B; Ashar, A Z; Devi, R Nandini; Narayan, K S; Asha, S K

    2014-11-12

    Nanostructured supramolecular donor-acceptor assemblies were formed when an unsymmetrical N-substituted pyridine functionalized perylenebisimide (UPBI-Py) was complexed with oligo(p-phenylenevinylene) (OPVM-OH) complementarily functionalized with hydroxyl unit and polymerizable methacrylamide unit at the two termini. The resulting supramolecular complex [UPBI-Py (OPVM-OH)]1.0 upon polymerization by irradiation in the presence of photoinitiator formed well-defined supramolecular polymeric nanostructures. Self-assembly studies using fluorescence emission from thin film samples showed that subtle structural changes occurred on the OPV donor moiety following polymerization. The 1:1 supramolecular complex showed red-shifted aggregate emission from both OPV (∼500 nm) and PBI (∼640 nm) units, whereas the OPV aggregate emission was replaced by intense monomeric emission (∼430 nm) upon polymerizing the methacrylamide units on the OPVM-OH. The bulk structure was studied using wide-angle X-ray diffraction (WXRD). Complex formation resulted in distinct changes in the cell parameters of OPVM-OH. In contrast, a physical mixture of 1 mol each of OPVM-OH and UPBI-Py prepared by mixing the powdered solid samples together showed only a combination of reflections from both parent molecules. Thin film morphology of the 1:1 molecular complex as well as the supramolecular polymer complex showed uniform lamellar structures in the domain range <10 nm. The donor-acceptor supramolecular complex [UPBI-Py (OPVM-OH)]1.0 exhibited space charge limited current (SCLC) with a bulk mobility estimate of an order of magnitude higher accompanied by a higher photoconductivity yield compared to the pristine UPBI-Py. This is a very versatile method to obtain spatially defined organization of n and p-type semiconductor materials based on suitably functionalized donor and acceptor molecules resulting in improved photocurrent response using self-assembly.

  13. Nanostructured donor-acceptor self assembly with improved photoconductivity.

    PubMed

    Saibal, B; Ashar, A Z; Devi, R Nandini; Narayan, K S; Asha, S K

    2014-11-12

    Nanostructured supramolecular donor-acceptor assemblies were formed when an unsymmetrical N-substituted pyridine functionalized perylenebisimide (UPBI-Py) was complexed with oligo(p-phenylenevinylene) (OPVM-OH) complementarily functionalized with hydroxyl unit and polymerizable methacrylamide unit at the two termini. The resulting supramolecular complex [UPBI-Py (OPVM-OH)]1.0 upon polymerization by irradiation in the presence of photoinitiator formed well-defined supramolecular polymeric nanostructures. Self-assembly studies using fluorescence emission from thin film samples showed that subtle structural changes occurred on the OPV donor moiety following polymerization. The 1:1 supramolecular complex showed red-shifted aggregate emission from both OPV (∼500 nm) and PBI (∼640 nm) units, whereas the OPV aggregate emission was replaced by intense monomeric emission (∼430 nm) upon polymerizing the methacrylamide units on the OPVM-OH. The bulk structure was studied using wide-angle X-ray diffraction (WXRD). Complex formation resulted in distinct changes in the cell parameters of OPVM-OH. In contrast, a physical mixture of 1 mol each of OPVM-OH and UPBI-Py prepared by mixing the powdered solid samples together showed only a combination of reflections from both parent molecules. Thin film morphology of the 1:1 molecular complex as well as the supramolecular polymer complex showed uniform lamellar structures in the domain range <10 nm. The donor-acceptor supramolecular complex [UPBI-Py (OPVM-OH)]1.0 exhibited space charge limited current (SCLC) with a bulk mobility estimate of an order of magnitude higher accompanied by a higher photoconductivity yield compared to the pristine UPBI-Py. This is a very versatile method to obtain spatially defined organization of n and p-type semiconductor materials based on suitably functionalized donor and acceptor molecules resulting in improved photocurrent response using self-assembly. PMID:25283356

  14. 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.

  15. On-Chip Picosecond Pulse Detection and Generation Using Graphene Photoconductive Switches

    PubMed Central

    2015-01-01

    We report on the use of graphene for room temperature on-chip detection and generation of pulsed terahertz (THz) frequency radiation, exploiting the fast carrier dynamics of light-generated hot carriers, and compare our results with conventional low-temperature-grown gallium arsenide (LT-GaAs) photoconductive (PC) switches. Coupling of picosecond-duration pulses from a biased graphene PC switch into Goubau line waveguides is also demonstrated. A Drude transport model based on the transient photoconductance of graphene is used to describe the mechanism for both detection and generation of THz radiation. PMID:25710079

  16. Study of photoconductivity in Ni doped CdS thin films prepared by spray pyrolysis technique

    SciTech Connect

    Patidar, Manju Mishra Gangrade, Mohan; Nath, R.; Ganesan, V.; Ajay, Akhil; Wala, Arwa Dewas; N, Kiran; Panda, Richa

    2014-04-24

    Ni-doped cadmium sulphide [Cd{sub 1−x}Ni{sub x}S, (x=0, 0.03, 0.05 and 0.20)] thin films were investigated for photoconductive properties. The films were prepared by spray Pyrolysis technique (SPT). AFM and two probe resistivity measurements were carried out to analyze the morphological and electrical properties of the films. AFM shows the note worthy changes in the morphology where the nanorod structures in CdS is changed into nano particles with the Ni doping. The presence of persistence photo current is demonstrated and extensive photoconductivity analysis has been studied on these films.

  17. Coherent and incoherent terahertz beams measured from a terahertz photoconductive antenna

    SciTech Connect

    Ho Wu, Dong; Graber, Benjamin; Kim, Christopher; Qadri, S. B.; Garzarella, Anthony

    2014-02-03

    We have systematically measured and analyzed the terahertz beams of a photoconductive antenna fabricated on a GaAs substrate. Our data indicate that the antenna produces both coherent and incoherent terahertz beams. The former is produced largely by the plasmon, and the latter is believed to be due to the black body radiation resulting from the thermal excitations and Joule heating by both the femto-second laser and the bias voltage, applied across the electrodes of the antenna. The terahertz-beam property is greatly affected by the operating condition of the photoconductive antenna.

  18. Light-soaking effects on photoconductivity in a-Si:H thin films

    SciTech Connect

    Morgado, E.; Da Silva, M.R.; Henriques, R.T.

    1997-07-01

    Metastable defects have been created by light exposure in thin films of a-Si:H. The samples have been characterized by Photothermal Deflection Spectroscopy, Electron Spin Resonance, dark- and photo-conductivity. The experimental results are consistent with numerical calculations with a recombination model involving band tails and one class of correlated dangling-bond states. The effects of light-soaking on the light intensity and defect density dependences of photoconductivity are reproduced by the calculations. The model allows to explain the experimental trends by changes in the electronic occupation of the gap states produced by light-induced defects.

  19. Photorefractive amplification of moving light signals by photoconductive ferroelectric liquid crystal blends

    NASA Astrophysics Data System (ADS)

    Sasaki, Takeo; Yoshino, Masanori

    2015-09-01

    Ferroelectric liquid crystal blends composed of a smectic liquid crystalline mixture, a photoconductive chiral dopant, and an electron trap reagent exhibit significant photorefractivity together with rapid responses. As such, they allow the dynamic amplification of moving optical signals. In the present work, the durability of a photorefractive ferroelectric liquid crystal blend was investigated. A series of photoconductive chiral dopants was prepared and the durability of blends incorporating these dopants during laser irradiation was examined. In addition, the effect of the conduction of photogenerated ionic species on the photorefractivity decay was clarified.

  20. Nano-thermometers with thermo-sensitive polymer grafted USPIOs behaving as positive contrast agents in low-field MRI

    NASA Astrophysics Data System (ADS)

    Hannecart, Adeline; Stanicki, Dimitri; Vander Elst, Luce; Muller, Robert N.; Lecommandoux, Sébastien; Thévenot, Julie; Bonduelle, Colin; Trotier, Aurélien; Massot, Philippe; Miraux, Sylvain; Sandre, Olivier; Laurent, Sophie

    2015-02-01

    Two commercial statistical copolymers of ethylene oxide and propylene oxide, Jeffamine® M-2005 (PEO5-st-PPO37) and M-2070 (PEO46-st-PPO13), exhibiting lower critical solution temperature (LCST) in water, were grafted onto the surface of ultra-small superparamagnetic iron oxide nanoparticles (USPIOs) using silanization and amide-bond coupling reactions. The LCSTs of the polymers in solution were measured by dynamic light scattering (DLS) and nuclear magnetic resonance (NMR). In accordance with the compositions of EO vs. PO, the transition temperature was measured to be 22 +/- 2 °C for M-2005 by both DLS and NMR, while the LCST was much higher, 52 +/- 2 °C, for M-2070 (a second transition was also detected above 80 °C by NMR in that case, ascribed to the full dehydration of chains at the molecular level). The resulting polymer-grafted USPIOs exhibit a temperature-responsive colloidal behaviour, their surface reversibly changing from hydrophilic below LCST to hydrophobic above it. This phenomenon was utilised to design thermo-sensitive contrast agents for MRI. Transverse relaxivities (r2) of the USPIO@PEO5-st-PPO37 core-shell nanoparticles were measured at 8.25, 20, 60, and 300 MHz. Nuclear magnetic resonance dispersion (NMRD) profiles, giving longitudinal relaxivities (r1) between 0.01 and 60 MHz, were acquired at temperatures ranging from 15 to 50 °C. For all tested frequencies except 300 MHz, both r1 and r2 decrease with temperature and show an inflection point at 25 °C, near the LCST. To illustrate the interest of such polymer-coated USPIOs for MRI thermometry, sample tubes were imaged on both low-field (8.25 MHz/0.194 Tesla) and high-field (300 MHz/7.05 Tesla) MRI scanners with either T1- or T2*-weighted spin echo sequences. The positive contrast on low-field MR images and the perfect linearity of the signal with a T2*-weighted sequence over the entire temperature range 15-50 °C render these LCST polymer coated USPIOs interesting positive contrast agents

  1. Color image sensor using stacked organic photoconductive films with transparent readout circuits separated by thin interlayer insulator

    NASA Astrophysics Data System (ADS)

    Sakai, Toshikatsu; Seo, Hokuto; Aihara, Satoshi; Ohtake, Hiroshi; Kubota, Misao; Furuta, Mamoru

    2014-03-01

    We have been working on developing an image sensor with three stacked organic photoconductive films (OPFs) sensitive to only one primary color component (red—R, green—G, or blue—B); each OPF has a signal readout circuit. This type of stacked sensor is advantageous for the manufacture of compact color cameras with high-quality pictures, since color separation systems, such as prisms or color filter arrays, are eliminated because of the color selectivity of OPFs. To achieve a high-resolution stacked sensor, its total thickness should be reduced to less than 10 μm. In this study, we fabricated a color image sensor with R and G-sensitive OPFs by applying amorphous In-Ga-Zn-O thin-film transistor (TFT) readout circuits. A 10 μm-thick interlayer insulator separated the R and G-sensitive layers. The entire fabrication process for the device was implemented below 150°C to avoid damaging the OPFs. Output signals were successfully read from each OPF through the TFT circuit, and multi-color images were reproduced from the fabricated sensor.

  2. Rapid and sensitive quantification of levoglucosan in aerosols by high-performance anion-exchange chromatography with positive electrospray ionization mass spectrometry (HPAEC-positive ESI-MS)

    NASA Astrophysics Data System (ADS)

    Asakawa, Daichi; Furuichi, Yuko; Yamamoto, Atsushi; Oku, Yuichiro; Funasaka, Kunihiro

    2015-12-01

    A convenient quantification method for underivatized levoglucosan, which is a tracer for biomass burning influenced particulate matter (PM), has been established using high-performance anion-exchange chromatography (HPAEC) coupled to positive electrospray ionization mass spectrometry ((+)ESI-MS). Levoglucosan was chromatographically separated from its isomers (mannosan and galactosan) and detected selectively with positive ESI-MS. Limits of detection and quantification for this method were 0.40 and 1.3 ng mL-1, respectively. A comparison of simultaneous measurements by this method and conventional derivatization gas chromatography/mass spectrometry showed a good linearity with a slope of 1.008 and a determination coefficient of 0.9932. The developed method was applied to ambient suspended particulate matter hourly collected by continuous particulate monitors at 10 stations. The hourly concentration of levoglucosan during August 9-11, 2011, was 1.7-918 ng m-3 and its distribution indicated the transportation of biomass burning aerosols of a forest fire. This is the first report of horizontal distribution of the hourly levoglucosan concentration in Japan.

  3. 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.

  4. Anomalous high photoconductivity in short channel indium-zinc-oxide photo-transistors

    SciTech Connect

    Choi, Hyun-Sik; Jeon, Sanghun

    2015-01-05

    Upon light exposure, an indium-zinc-oxide (IZO) thin-film transistor (TFT) presents higher photoconductivity by several orders of magnitude at the negative gate bias region. Among various device geometrical factors, scaling down the channel length of the photo-transistor results in an anomalous increase in photoconductivity. To probe the origin of this high photoconductivity in short-channel device, we measured transient current, current–voltage, and capacitance–voltage characteristics of IZO–TFTs with various channel lengths and widths before and after illumination. Under the illumination, the equilibrium potential region which lies far from front interface exists only in short-channel devices, forming the un-depleted conducting back channel. This region plays an important role in carrier transport under the illumination, leading to high photoconductivity in short-channel devices. Photon exposure coupled with gate-modulated band bending for short-channel devices leads to the accumulation of V{sub o}{sup ++} at the front channel and screening negative gate bias, thereby generating high current flow in the un-depleted back-channel region.

  5. 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.

  6. Anomalous high photoconductivity in short channel indium-zinc-oxide photo-transistors

    NASA Astrophysics Data System (ADS)

    Choi, Hyun-Sik; Jeon, Sanghun

    2015-01-01

    Upon light exposure, an indium-zinc-oxide (IZO) thin-film transistor (TFT) presents higher photoconductivity by several orders of magnitude at the negative gate bias region. Among various device geometrical factors, scaling down the channel length of the photo-transistor results in an anomalous increase in photoconductivity. To probe the origin of this high photoconductivity in short-channel device, we measured transient current, current-voltage, and capacitance-voltage characteristics of IZO-TFTs with various channel lengths and widths before and after illumination. Under the illumination, the equilibrium potential region which lies far from front interface exists only in short-channel devices, forming the un-depleted conducting back channel. This region plays an important role in carrier transport under the illumination, leading to high photoconductivity in short-channel devices. Photon exposure coupled with gate-modulated band bending for short-channel devices leads to the accumulation of Vo++ at the front channel and screening negative gate bias, thereby generating high current flow in the un-depleted back-channel region.

  7. Improvement in thermal barriers to intense terahertz generation from photoconductive antennas

    SciTech Connect

    Ropagnol, X.; Bouvier, Marcel; Reid, M.; Ozaki, T.

    2014-07-28

    We study the generation of free-space terahertz (THz) pulses at low THz frequencies using 6H-SiC and 4H-SiC photoconductive antennas. We investigate the dependence of the THz electric field radiated from the biased SiC emitters on the applied bias field and on the incident optical fluence. In this work, bias fields as high as 32 kV/cm, and optical fluences up to 2.5 mJ/cm{sup 2} (for the 400 nm laser), and 7.5 mJ/cm{sup 2} (for the 800 nm laser) were used. THz generation with back- and front-side illumination of the antennas is also examined. It is found that the SiC antenna, when illuminated from the backside, generates higher THz electric fields. The performance of 6H-SiC and ZnSe photoconductive antennas are compared. We show that, taking advantage of the superior thermal properties of SiC compare with ZnSe, the THz output power generated with the 6H-SiC photoconductive antenna under optimum conditions is 2.3 times larger that with a ZnSe photoconductive antenna.

  8. The temporal dynamics of impurity photoconductivity in quantum wells in GaAs

    SciTech Connect

    Aleshkin, V. Ya. E-mail: aleshkin@ipm.sci-nnov.ru

    2015-10-15

    A theory of cascade capture at charged donors in quantum wells (QWs) is developed without using the Fokker-Planck approximation, which is not valid in QWs. The time dependences of impurity photoconductivity and photoelectron concentration in GaAs QWs are determined. The cascade capture time as a function of the charge donor concentration is calculated.

  9. Anisotropic picosecond photoconductivity caused by optical alignment of electron momenta in cubic semiconductors

    SciTech Connect

    Malevich, Y. V. Adomavičius, R.; Krotkus, A.; Malevich, V. L.

    2014-02-21

    Transient photoconductivity in cubic semiconductors InGaAs and InAs excited by a femtosecond laser pulse in the presence of a uniform dc electric field has been studied with the use of the Monte Carlo simulation by taking into account optical alignment of photoexcited electrons over their momenta. Simulations show that due to the optical alignment effect and energy dependence of the electron mobility, the transient photoconductivity in cubic semiconductors becomes anisotropic during the first few picoseconds after optical excitation. The magnitude of this anisotropy reaches its peak when the excess energy of the optically excited electrons approaches the threshold for the intervalley transfer. It has also been found that when the electrons are excited near the threshold energy for the intervalley transfer, the component of the transient photocurrent directed along the dc field for a short time after the end of the femtosecond optical pulse can become negative. The anisotropy of the transient photoconductivity has been investigated experimentally on (001) InGaAs sample by the optical pump - terahertz-probe technique. Optically induced changes in terahertz pulse amplitude were found to be dependent on the direction of terahertz field relative to the polarization of the optical pump pulse and to the crystallographic axes of the semiconductor. Experimental data have been explained in terms of the transient anisotropic photoconductivity and correlate with the results of the Monte Carlo simulation.

  10. Temperature dependence of photoconductivity in Zn-doped GaN

    SciTech Connect

    Reshchikov, Michael A.

    2014-02-21

    In agreement with predictions from a model that explained an abrupt thermal quenching of the blue luminescence (BL) band in high-resistivity Zn-doped GaN [Reshchikov et al., Phys. Rev. B 84, 075212 (2011) and Phys. Rev. B 85, 245203 (2012)], we observed the stepwise decrease of photoconductivity in this material with increasing temperature. For the sample studied in this work, the decrease in photoconductivity occurred in two steps at characteristic temperatures T{sub 1} and T{sub 2}. The characteristic temperatures increased with increasing excitation intensity, very similar to the photoluminescence (PL) behavior. The steps in photoconductivity at about 100 K and 200 K are attributed to drop in the concentration of free electrons due to the thermal emission of holes from a shallow acceptor and the Zn{sub Ga} acceptor, respectively, to the valence band and their recombination with electrons via nonradiative centers. This finding supports the model suggested previously and helps to explain other examples of tunable photoconductivity reported in literature.

  11. Electro-optic imagery of high-voltage GaAs photoconductive switches

    SciTech Connect

    Falk, R.A.; Adams, J.C.; Capps, C.D.; Ferrier, S.G.; Krinsky, J.A. )

    1995-01-01

    The authors present electro-optic images of GaAs high-voltage photoconductive switches utilizing the electro-optic effect of the semi-insulating GaAs substrate. Experimental methodology for obtaining the images is described along with a self-calibrating data reduction algorithm. Use of the technique for observing fabrication defects is shown.

  12. Persistent photoconductivity in two-dimensional Mo1-xW xSe2–MoSe2 van der Waals heterojunctions

    DOE PAGES

    Puretzky, Alexander A.; Basile, Leonardo; Idrobo, Juan Carlos; Rouleau, Christopher M.; Geohegan, David B.; Xiao, Kai; Li, Xufan; Lin, Ming -Wei; Wang, Kei

    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 MoSe2 and p-type Mo1-xW xSe2–MoSe2 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 and the atomic registry betweenmore » 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

  13. 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.

  14. Photoconductivity and dark-conductivity studies of CdS1-xSex(Cu) sintered layers

    NASA Astrophysics Data System (ADS)

    Pillai, P. K. C.; Shroff, Niloufer; Nanda Kumar, N.; Tripathi, A. K.

    1985-12-01

    The photoconductivity and dark conductivity of CdS1-xSex(Cu) layers sintered at 773 K have been studied in a configuration similar to that under actual use in a solid-state image intensifier. The dark current shows linear dependence on voltage at lower voltages. At higher voltages the current shows non-Ohmic behavior. The photocurrent is found to be space-charge limited at the lowest voltage studied; this behavior is explained by the nonuniform illumination of the sample. Supralinearity and subsequent sublinearity in the photocurrent dependence on light intensity indicate the presence of sensitizing centers near the valence band as well as an exponential trap distribution nearer the conduction band. The thermal quenching of the photocurrent seems to confirm this. The unusual decrease in the dark current with increase in temperature around room temperature (313 K) can be explained on the basis of these centers. The spectral studies indicate the filtering effect of selective absorption because of the particular configuration. Infrared spectral studies indicate the presence of sensitizing centers about 1 eV above the valence band.

  15. Positive but variable sensitivity of August surface ozone to large-scale warming in the southeast United States

    NASA Astrophysics Data System (ADS)

    Fu, Tzung-May; Zheng, Yiqi; Paulot, Fabien; Mao, Jingqiu; Yantosca, Robert M.

    2015-05-01

    Surface ozone, a major air pollutant toxic to humans and damaging to ecosystems, is produced by the oxidation of volatile organic compounds in the presence of nitrogen oxides (NOx = NO + NO2) and sunlight. Climate warming may affect future surface ozone levels even in the absence of anthropogenic emission changes, but the direction of ozone change due to climate warming remains uncertain over the southeast US and other polluted forested areas. Here we use observations and simulations to diagnose the sensitivity of August surface ozone to large-scale temperature variations in the southeast US during 1988-2011. We show that the enhanced biogenic emissions and the accelerated photochemical reaction rates associated with warmer temperatures both act to increase surface ozone. However, the sensitivity of surface ozone to large-scale warming is highly variable on interannual and interdecadal timescales owing to variation in regional ozone advection. Our results have important implications for the prediction and management of future ozone air quality.

  16. Effects of Detector Thickness on Geometric Sensitivity and Event Positioning Errors in the Rectangular PET/X Scanner

    PubMed Central

    MacDonald, Lawrence R.; Hunter, William C. J.; Kinahan, Paul E.; Miyaoka, Robert S.

    2015-01-01

    We used simulations to investigate the relationship between sensitivity and spatial resolution as a function of crystal thickness in a rectangular PET scanner intended for quantitative assessment of breast cancers. The system had two 20 × 15-cm2 and two 10 × 15-cm2 flat detectors forming a box, with the larger detectors separated by 4 or 8 cm. Depth-of-interaction (DOI) resolution was modeled as a function of crystal thickness based on prior measurements. Spatial resolution was evaluated independent of image reconstruction by deriving and validating a surrogate metric from list-mode data (dFWHM). When increasing crystal thickness from 5 to 40 mm, and without using DOI information, the dFWHM for a centered point source increased from 0.72 to 1.6 mm. Including DOI information improved dFWHM by 12% and 27% for 5- and 40-mm-thick crystals, respectively. For a point source in the corner of the FOV, use of DOI information improved dFWHM by 20% (5-mm crystal) and 44% (40-mm crystal). Sensitivity was 7.7% for 10-mm-thick crystals (8-cm object). Increasing crystal thickness on the smaller side detectors from 10 to 20 mm (keeping 10-mm crystals on the larger detectors) boosted sensitivity by 24% (relative) and degraded dFWHM by only ~3%/8% with/without DOI information. The benefits of measuring DOI must be evaluated in terms of the intended clinical task of assessing tracer uptake in small lesions. Increasing crystal thickness on the smaller side detectors provides substantial sensitivity increase with minimal accompanying loss in resolution. PMID:26160982

  17. Over-the-Counter Relief From Pains and Pleasures Alike: Acetaminophen Blunts Evaluation Sensitivity to Both Negative and Positive Stimuli.

    PubMed

    Durso, Geoffrey R O; Luttrell, Andrew; Way, Baldwin M

    2015-06-01

    Acetaminophen, an effective and popular over-the-counter pain reliever (e.g., the active ingredient in Tylenol), has recently been shown to blunt individuals' reactivity to a range of negative stimuli in addition to physical pain. Because accumulating research has shown that individuals' reactivity to both negative and positive stimuli can be influenced by a single factor (an idea known as differential susceptibility), we conducted two experiments testing whether acetaminophen blunted individuals' evaluations of and emotional reactions to both negative and positive images from the International Affective Picture System. Participants who took acetaminophen evaluated unpleasant stimuli less negatively and pleasant stimuli less positively, compared with participants who took a placebo. Participants in the acetaminophen condition also rated both negative and positive stimuli as less emotionally arousing than did participants in the placebo condition (Studies 1 and 2), whereas nonevaluative ratings (extent of color saturation in each image; Study 2) were not affected by drug condition. These findings suggest that acetaminophen has a general blunting effect on individuals' evaluative and emotional processing, irrespective of negative or positive valence. PMID:25862546

  18. Over-the-Counter Relief From Pains and Pleasures Alike: Acetaminophen Blunts Evaluation Sensitivity to Both Negative and Positive Stimuli

    PubMed Central

    Durso, Geoffrey R. O.; Luttrell, Andrew; Way, Baldwin M.

    2015-01-01

    Acetaminophen, an effective and popular over-the-counter pain reliever (e.g., the active ingredient in Tylenol), has recently been shown to blunt individuals’ reactivity to a range of negative stimuli in addition to physical pain. Because accumulating research has shown that individuals’ reactivity to both negative and positive stimuli can be influenced by a single factor (an idea known as differential susceptibility), we conducted two experiments testing whether acetaminophen blunted individuals’ evaluations of and emotional reactions to both negative and positive images from the International Affective Picture System. Participants who took acetaminophen evaluated unpleasant stimuli less negatively and pleasant stimuli less positively, compared with participants who took a placebo. Participants in the acetaminophen condition also rated both negative and positive stimuli as less emotionally arousing than did participants in the placebo condition (Studies 1 and 2), whereas nonevaluative ratings (extent of color saturation in each image; Study 2) were not affected by drug condition. These findings suggest that acetaminophen has a general blunting effect on individuals’ evaluative and emotional processing, irrespective of negative or positive valence. PMID:25862546

  19. Count rate studies of a box-shaped PET breast imaging system comprised of position sensitive avalanche photodiodes utilizing monte carlo simulation.

    PubMed

    Foudray, Angela M K; Habte, Frezghi; Chinn, Garry; Zhang, Jin; Levin, Craig S

    2006-01-01

    We are investigating a high-sensitivity, high-resolution positron emission tomography (PET) system for clinical use in the detection, diagnosis and staging of breast cancer. Using conventional figures of merit, design parameters were evaluated for count rate performance, module dead time, and construction complexity. The detector system modeled comprises extremely thin position-sensitive avalanche photodiodes coupled to lutetium oxy-orthosilicate scintillation crystals. Previous investigations of detector geometries with Monte Carlo indicated that one of the largest impacts on sensitivity is local scintillation crystal density when considering systems having the same average scintillation crystal densities (same crystal packing fraction and system solid-angle coverage). Our results show the system has very good scatter and randoms rejection at clinical activity ranges ( approximately 200 muCi). PMID:17645997

  20. 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.

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

    PubMed Central

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

    2016-01-01

    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. PMID:27263861

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

    PubMed

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

    2016-06-06

    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.

  3. The Development of Sensitivity to Sublexical Orthographic Constraints: An Investigation of Positional Frequency and Consistency Using a Wordlikeness Choice Task

    ERIC Educational Resources Information Center

    O'Brien, Beth A.

    2014-01-01

    The developmental sequence of the types of orthographic knowledge that children acquire early in reading development is unclear. Following findings of skilled reading, the orthographic constraints of positional frequency and feedback consistency were explored with a wordlikeness judgement task for grades 1-3 English-speaking children. The data…

  4. [Differences in antibiotic sensitivity in biofilm-positive and biofilm-negative strains of Staphylococcus epidermidis isolated from blood cultures].

    PubMed

    Holá, V; Růzicka, F; Votava, M

    2004-01-01

    The adhering capability and biofilm growth facilitate staphylococcal colonization of surfaces of damaged tissues and foreign bodies. Biofilm-forming bacteria are more resistant to immune system activities, mechanical effects of blood flow and other adverse effects, e.g. those due to antibiotics. Minimal inhibitory concentrations (MICs) were compared for two groups of Staphylococcus epidermidis strains isolated from blood cultures. Group 1 included biofilm positive strains whose biofilm-forming potential was revealed by both phenotypic and genotypic methods. Group 2 included strains without biofilm-forming potential. The comparison of MICs for selected antibiotics showed higher resistance of biofilm positive compared to biofilm negative strains. The difference was evident particularly for oxacillin, tetracycline, co-trimoxazole and gentamicin.

  5. Zero-order and first-order theory of the formation of space-charge gratings in photoconductive polymers

    NASA Astrophysics Data System (ADS)

    Schildkraut, Jay S.; Cui, Yiping

    1992-12-01

    When a photoconducting polymer is illuminated by light with an intensity that varies sinusoidally with position, the space-charge electric field, hole density, ionized photosensitizer density, hole trap density, and other properties, will also vary with position. We derive an expression for the zero-order Fourier component of the hole density and a linear system of equations for the first-order Fourier component of a number of variables. The system of equations is solved for the steady-state first-order Fourier component of the electric field for the case in which hole untrapping is negligible or no hole traps are present. Next, the equations are simplified for the case in which the initial trap density is far greater than the density of holes, and for the case of no hole traps. Finally, we compare the zero-order hole density and first-order electric field calculated from our equations to values obtained by Fourier transforming the results of numerical calculations.

  6. Note: A large open ratio, time, and position sensitive detector for time of flight measurements in UHV

    SciTech Connect

    Lupone, S.; Damoy, S.; Husseen, A.; Briand, N.; Debiossac, M.; Tall, S.; Roncin, P.

    2015-12-15

    We report on the construction of an UHV compatible 40 mm active diameter detector based on micro channel plates and assembled directly on the feed-throughs of a DN63CF flange. It is based on the charge division technique and uses a standard 2 inch Si wafer as a collector. The front end electronic is placed directly on the air side of the flange allowing excellent immunity to noise and a very good timing signal with reduced ringing. The important aberrations are corrected empirically providing an absolute positioning accuracy of 500 μm while a 150 μm resolution is measured in the center.

  7. 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.

  8. 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.

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

    SciTech Connect

    Tan, K. H.; Yoon, S. F.; Wicaksono, S.; Loke, W. K.; Li, D. S.; Saadsaoud, N.; Tripon-Canseliet, C.; Lampin, J. F.; Decoster, D.; Chazelas, J.

    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 photoconductive switch application.

  10. 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.

  11. Computer simulation of photoconductivity decay in AgBr microcrystals: Relaxation model

    NASA Astrophysics Data System (ADS)

    Hailstone, R. K.; Erdtmann, D. E.

    1994-10-01

    Previous workers have explained photoconductivity decay in AgBr microcrystals by proposing a model involving lattice relaxation following shallow surface trapping of electrons. This model is investigated using Monte Carlo simulations in which the electron and hole undergo a random walk in the volume of the microcrystals and are shallowly trapped at the surface. The decay rate is controlled by the thermal barrier that must be overcome to achieve a lower-energy lattice configuration, as well as by the density and cross section of the shallow surface traps. The simulation results lend support to the lattice relaxation model, but also suggest a significant role of free-electron/trapped-hole recombination in the photoconductivity decay. The experimentally observed increase in decay time with increasing microcrystal size is also seen in the simulations. This size dependence is due to the effect of the surface-to-volume ratio on the distribution between free and shallowly trapped states for the electron.

  12. Investigation of deep levels in porous silicon by photoconductivity decay and thermally stimulated depolarization current methods

    NASA Astrophysics Data System (ADS)

    Borowski, P.; Bratkowski, A.; Bala, Waclaw; Bartkiewicz, K.

    2003-10-01

    The photoconductivity measurements of porous silicon were made using the visible light in wavelength range of 450 nm - 1200 nm. Obtained photoconductivity spectra were decomposed as a sum of Gaussian. The deep level energies are calculated for these peaks at about 1.24 eV, 1.33 eV, 1.55 eV, 1.84 eV, 2.17 eV and 2.54 eV at room temperature. To characterizing the deep levels we used also thermally stimulated depolarizaton current method (TSDC). In this case we used a thermal stimulation in temperature range of about 90 K - 300 K in vaccuum. After multigaussian decomposing of the current-temperature characteristic we calculated the thermal deep levels energies (0.4 eV and 0.8 eV). From the voltage-current measurements ideality factor was also calculated.

  13. Low Temperature-Induced 30 (LTI30) positively regulates drought stress resistance in Arabidopsis: effect on abscisic acid sensitivity and hydrogen peroxide accumulation.

    PubMed

    Shi, Haitao; Chen, Yinhua; Qian, Yongqiang; Chan, Zhulong

    2015-01-01

    As a dehydrin belonging to group II late embryogenesis abundant protein (LEA) family, Arabidopsis Low Temperature-Induced 30 (LTI30)/XERO2 has been shown to be involved in plant freezing stress resistance. However, the other roles of AtLTI30 remain unknown. In this study, we found that the expression of AtLTI30 was largely induced by drought stress and abscisic acid (ABA) treatments. Thereafter, AtLTI30 knockout mutants and overexpressing plants were isolated to investigate the possible involvement of AtLTI30 in ABA and drought stress responses. AtLTI30 knockout mutants were less sensitive to ABA-mediated seed germination, while AtLTI30 overexpressing plants were more sensitive to ABA compared with wild type (WT). Consistently, the AtLTI30 knockout mutants displayed decreased drought stress resistance, while the AtLTI30 overexpressing plants showed improved drought stress resistance compared with WT, as evidenced by a higher survival rate and lower leaf water loss than WT after drought stress. Moreover, manipulation of AtLTI30 expression positively regulated the activities of catalases (CATs) and endogenous proline content, as a result, negatively regulated drought stress-triggered hydrogen peroxide (H2O2) accumulation. All these results indicate that AtLTI30 is a positive regulator of plant drought stress resistance, partially through the modulation of ABA sensitivity, H2O2 and proline accumulation. PMID:26539205

  14. 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.

  15. Low Temperature-Induced 30 (LTI30) positively regulates drought stress resistance in Arabidopsis: effect on abscisic acid sensitivity and hydrogen peroxide accumulation.

    PubMed

    Shi, Haitao; Chen, Yinhua; Qian, Yongqiang; Chan, Zhulong

    2015-01-01

    As a dehydrin belonging to group II late embryogenesis abundant protein (LEA) family, Arabidopsis Low Temperature-Induced 30 (LTI30)/XERO2 has been shown to be involved in plant freezing stress resistance. However, the other roles of AtLTI30 remain unknown. In this study, we found that the expression of AtLTI30 was largely induced by drought stress and abscisic acid (ABA) treatments. Thereafter, AtLTI30 knockout mutants and overexpressing plants were isolated to investigate the possible involvement of AtLTI30 in ABA and drought stress responses. AtLTI30 knockout mutants were less sensitive to ABA-mediated seed germination, while AtLTI30 overexpressing plants were more sensitive to ABA compared with wild type (WT). Consistently, the AtLTI30 knockout mutants displayed decreased drought stress resistance, while the AtLTI30 overexpressing plants showed improved drought stress resistance compared with WT, as evidenced by a higher survival rate and lower leaf water loss than WT after drought stress. Moreover, manipulation of AtLTI30 expression positively regulated the activities of catalases (CATs) and endogenous proline content, as a result, negatively regulated drought stress-triggered hydrogen peroxide (H2O2) accumulation. All these results indicate that AtLTI30 is a positive regulator of plant drought stress resistance, partially through the modulation of ABA sensitivity, H2O2 and proline accumulation.

  16. Low Temperature-Induced 30 (LTI30) positively regulates drought stress resistance in Arabidopsis: effect on abscisic acid sensitivity and hydrogen peroxide accumulation

    PubMed Central

    Shi, Haitao; Chen, Yinhua; Qian, Yongqiang; Chan, Zhulong

    2015-01-01

    As a dehydrin belonging to group II late embryogenesis abundant protein (LEA) family, Arabidopsis Low Temperature-Induced 30 (LTI30)/XERO2 has been shown to be involved in plant freezing stress resistance. However, the other roles of AtLTI30 remain unknown. In this study, we found that the expression of AtLTI30 was largely induced by drought stress and abscisic acid (ABA) treatments. Thereafter, AtLTI30 knockout mutants and overexpressing plants were isolated to investigate the possible involvement of AtLTI30 in ABA and drought stress responses. AtLTI30 knockout mutants were less sensitive to ABA-mediated seed germination, while AtLTI30 overexpressing plants were more sensitive to ABA compared with wild type (WT). Consistently, the AtLTI30 knockout mutants displayed decreased drought stress resistance, while the AtLTI30 overexpressing plants showed improved drought stress resistance compared with WT, as evidenced by a higher survival rate and lower leaf water loss than WT after drought stress. Moreover, manipulation of AtLTI30 expression positively regulated the activities of catalases (CATs) and endogenous proline content, as a result, negatively regulated drought stress-triggered hydrogen peroxide (H2O2) accumulation. All these results indicate that AtLTI30 is a positive regulator of plant drought stress resistance, partially through the modulation of ABA sensitivity, H2O2 and proline accumulation. PMID:26539205

  17. A matter of symmetry: terahertz polarization detection properties of a multi-contact photoconductive antenna evaluated by a response matrix analysis.

    PubMed

    Niehues, Gudrun; Funkner, Stefan; Bulgarevich, Dmitry S; Tsuzuki, Satoshi; Furuya, Takashi; Yamamoto, Koji; Shiwa, Mitsuharu; Tani, Masahiko

    2015-06-15

    While terahertz time domain spectroscopy (THz-TDS) is a well-established technique, polarization sensitive measurements are challenging due to the need of broadband polarization devices. Here, we characterize our recently introduced multi-contact photoconductive detector antenna with a response matrix analysis. We show that the lead lines attached to electrodes reduce the antenna symmetry and thereby influence the properties of the response matrices. With a wire grid polarizer, we simulate a sample influencing the polarization angle and the intensity of the incident THz pulse. Evaluating the measurements with the response matrix analysis, our results show a well agreement of the adjusted and measured polarization angles and intensities over a frequency range from 0.25 to 0.8 THz.

  18. Features of the long-wavelength impurity photoconductivity spectrum in compensated germanium

    SciTech Connect

    Druzhinin, Y.P.; Chirkova, E.G.

    1995-09-01

    This paper discusses the impurity photoconductivity spectra of compensated Ge: (Cu, Sb) in the photoheating regime, in which the photon energy is comparable to the scale of the random potential well, and the temperature is 4.2 K. Three sections are distinguished in the long-wavelength cutoff region, corresponding to different energy relaxation and charge-carrier transport mechanisms, including a mechanism that involves the participation of optical phonons. 6 refs., 1 fig.

  19. 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. PMID:18404939

  20. Control of terahertz emission in photoconductive antennas through an additional optical continuous wave.

    PubMed

    Bockelt, A; Palací, J; Vidal, B

    2013-08-15

    The manipulation of the operating conditions of photoconductive antennas by means of an additional continuous wave (CW) is reported. It is used to control a fiber-based terahertz (THz) time-domain-spectroscopy system at telecom wavelengths. The injection of an optical CW into the transmitter allows the control of the THz amplitude without causing major degradation to the system performance. This, for instance, can be exploited to perform modulation of the THz signal. PMID:24104665

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

    SciTech Connect

    Johnston, S.; Yan, F.; Zaunbrecher, K.; Al-Jassim, M.; Sidelkheir, O.; Ounadjela, 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 lifetimes 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.

  2. Exclusive-OR Encryption by Photoconduction and Two-Photon Absorption in Carbon Nanotubes.

    PubMed

    Torres-Torres, C; Rebollo, N R; Castañeda, L; Trejo-Valdez, M; Torres-Marínez, R

    2015-02-01

    A two-wave photoconductive system dependent on the nonlinear optical absorption in carbon nano-tubes is presented. Optical irradiation at 532 nm wavelength and 1 nanosecond pulse duration was employed for performing the experiments. A vectorial two-wave mixing configuration was used in order to measure the absorptive and refractive nonlinearities. A single-beam transmittance technique was carried out to evaluate the photoconductivity and also it allows us to confirm the participation of the nonlinear optical absorption displayed by the samples. A two-photon absorption effect was identified as the main physical mechanism associated to the third order absorptive nonlinearity. The exclusive disjunctive logic function was achieved by the optoelectronic response of an interferometric configuration. An ultrasonic spray pyrolysis processing route was utilized for the preparation of the samples. The morphology of the nanotubes was estimated by using scanning electronic microscopy. By combining the photoconductive response of two different carbon nanotubes thin film samples, a straightforward XOR encryption was performed. PMID:26353707

  3. Photoconductivity oscillations in surface state of three-dimensional topological insulator subjected to a magnetic field

    SciTech Connect

    Shao, J. M.; Yao, J. D.; Yang, G. W.

    2015-05-21

    We describe a theoretical study of the terahertz (THz) radiation field-induced dc transport response of the surface state of a 3D topological insulator that has been subjected to a perpendicular magnetic field. Using the Landau–Floquet state and linear response theory, we obtain the photoconductivity characteristics for various types of polarized THz field. The longitudinal photoconductivity shows a clear oscillatory dependence on ω/ω{sub B}, where ω{sub B}=v{sub F}√(2eB/ℏ). This oscillation occurs because of the oscillatory structure of the Landau density of states and occurs in agreement with the photon-assisted transitions between the different Landau levels. The THz field's polarization has a major influence on the photoconductivity. A linear transverse polarization will lead to the most obvious oscillation, while the circular polarization is next to it, but the longitudinal polarization has no influence. We also discuss the broadening effect on the impurity potential and its influence. The findings with regard to the interactions between topological insulators and THz fields actually open a path toward the development of THz device applications of topological insulators.

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

    SciTech Connect

    Andzane, J. Kunakova, G.; Erts, D.; Varghese, J.; Holmes, J. 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 from 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.

  5. Sensitivity analysis of the position of the intervertebral centres of reaction in upright standing--a musculoskeletal model investigation of the lumbar spine.

    PubMed

    Zander, Thomas; Dreischarf, Marcel; Schmidt, Hendrik

    2016-03-01

    The loads between adjacent vertebrae can be generalised as a single spatial force acting at the intervertebral centre of reaction. The exact position in vivo is unknown. However, in rigid body musculoskeletal models that simulate upright standing, the position is generally assumed to be located at the discs' centres of rotation. The influence of the antero-posterior position of the centre of reaction on muscle activity and joint loads remains unknown. Thus, by using an inverse dynamic model, we varied the position of the centre of reaction at L4/L5 (i), simultaneously at all lumbar levels (ii), and by optimisation at all lumbar levels (iii). Variation of the centres of reaction can considerably influence the activities of lumbar muscles and the joint forces between vertebrae. The optimisation of the position of the centre of reaction reduced the maximum lumbar muscle activity and axial joint forces at L4/L5 from 17.5% to 1.5% of the muscle strength and from 490 N to 390 N, respectively. Thus, when studying individual postures, such as for therapeutic or preventive evaluations, potential differences between the centre of reaction and the centre of rotation might influence the study results. These differences could be taken into account by sensitivity analyses.

  6. Analysis of Sensitivity, Specificity, and Positive and Negative Predictive Values of Smear and Colposcopy in Diagnosis of Premalignant and Malignant Cervical Lesions

    PubMed Central

    Barut, Mert Ulaş; Kale, Ahmet; Kuyumcuoğlu, Umur; Bozkurt, Murat; Ağaçayak, Elif; Özekinci, Server; Gul, Talip

    2015-01-01

    Background This study aimed to examine the positive and negative predictive value in the diagnosis of premalignant and malignant lesions of cervical colposcopy, the sensitivity and specificity of smear, and to evaluate the correlation with histopathology of abnormal cytology and colposcopy. Material/Methods The criteria for inclusion of patients with unhealthy cervix in the study were: Erosion, Chronic cervicitis, and Healed lacerations, Hypertrophied cervix, bleeding on touch, suspicious growth/ulcer/polyp on the cervix, and abnormal discharges from the cervix. Women with frank carcinoma cervix, pregnant females, patients with bleeding per vaginum at the time of examination, and those who had used vaginal medications, vaginal contraceptives or douches in the last 48 h of examination were excluded from the study. Demographic analysis was performed for 450 patients who were admitted to the clinic. Sensitivity, specificity, positive predictive value and negative predictive values of patients to identify cervical pathologies of smear and colposcopy were histopathologically calculated. The statistical software package SPSS 15.0 (SPSS Inc., Chicago, IL, USA) and Spearman‘s and Chi-Square tests were used for statistical analysis. Results Sensitivity, specificity, PPD and NDP of smear were 0.57%, 0.76%, 0.26%, 0.92% respectively. Sensitivity, specificity, PPD and NDP of colposcopy were 0.92%, 0.67%, 0.52%, 0.96% respectively. A statistically significant correlation was found between abnormal cytology and histopathology, and abnormal colposcopy finding and histopathology. Conclusions Women with clinical diagnosis of unhealthy cervix should be evaluated by cytology to detect any premalignant or malignant lesions. It was concluded that Pap smear, colposcopy and histopathology should be collectively evaluated to evaluate cervical findings in low socio-economic regions. PMID:26655816

  7. Lateral photovoltaic effect in flexible free-standing reduced graphene oxide film for self-powered position-sensitive detection

    NASA Astrophysics Data System (ADS)

    Moon, In Kyu; Ki, Bugeun; Yoon, Seonno; Oh, Jungwoo

    2016-09-01

    Lightweight, simple and flexible self-powered photodetectors are urgently required for the development and application of advanced optical systems for the future of wearable electronic technology. Here, using a low-temperature reduction process, we report a chemical approach for producing freestanding monolithic reduced graphene oxide papers with different gradients of the carbon/oxygen concentration ratio. We also demonstrate a novel type of freestanding monolithic reduced graphene oxide self-powered photodetector based on a symmetrical metal–semiconductor–metal structure. Upon illumination by a 633-nm continuous wave laser, the lateral photovoltage is observed to vary linfearly with the laser position between two electrodes on the reduced graphene oxide surface. This result may suggest that the lateral photovoltaic effect in the reduced graphene oxide film originates from the built-in electric field by the combination of both the photothermal electric effect and the gradient of the oxygen-to-carbon composition. These results represent substantial progress toward novel, chemically synthesized graphene-based photosensors and suggest one-step integration of graphene-based optoelectronics in the future.

  8. The anti-malarial chloroquine overcomes Primary resistance and restores sensitivity to Trastuzumab in HER2-positive breast cancer

    PubMed Central

    Cufí, Sílvia; Vazquez-Martin, Alejandro; Oliveras-Ferraros, Cristina; Corominas-Faja, Bruna; Cuyàs, Elisabet; López-Bonet, Eugeni; Martin-Castillo, Begoña; Joven, Jorge; Menendez, Javier A.

    2013-01-01

    Autophagy may control the de novo refractoriness of HER2 gene-amplified breast carcinomas to the monoclonal antibody trastuzumab (Herceptin). Tumor cells originally obtained from a patient who rapidly progressed on trastuzumab ab initio display increased cellular levels of the LC3-II protein—a finding that correlates with increased numbers of autophagosomes—and decreased levels of the autophagy receptor p62/SQSTM1, a protein selectively degraded by autophagy. Trastuzumab-refractory cells are in a state of “autophagy addiction” because genetic ablation of autophagy-specific genes (ATG8, ATG5, ATG12) notably reduces intrinsic refractoriness to trastuzumab. When the anti-malarial lysosomotropic drug chloroquine impedes autophagic resolution of the accumulation of autophagolysosomes formed in the presence of trastuzumab, cells commit to die by apoptosis. Accordingly, combination treatment with trastuzumab and chloroquine radically suppresses tumor growth by > 90% in a tumor xenograft completely refractory to trastuzumab. Adding chloroquine to trastuzumab-based regimens may therefore improve outcomes among women with autophagy-addicted HER2-positive breast cancer. PMID:23965851

  9. Lateral photovoltaic effect in flexible free-standing reduced graphene oxide film for self-powered position-sensitive detection.

    PubMed

    Moon, In Kyu; Ki, Bugeun; Yoon, Seonno; Oh, Jungwoo

    2016-01-01

    Lightweight, simple and flexible self-powered photodetectors are urgently required for the development and application of advanced optical systems for the future of wearable electronic technology. Here, using a low-temperature reduction process, we report a chemical approach for producing freestanding monolithic reduced graphene oxide papers with different gradients of the carbon/oxygen concentration ratio. We also demonstrate a novel type of freestanding monolithic reduced graphene oxide self-powered photodetector based on a symmetrical metal-semiconductor-metal structure. Upon illumination by a 633-nm continuous wave laser, the lateral photovoltage is observed to vary linfearly with the laser position between two electrodes on the reduced graphene oxide surface. This result may suggest that the lateral photovoltaic effect in the reduced graphene oxide film originates from the built-in electric field by the combination of both the photothermal electric effect and the gradient of the oxygen-to-carbon composition. These results represent substantial progress toward novel, chemically synthesized graphene-based photosensors and suggest one-step integration of graphene-based optoelectronics in the future. PMID:27634110

  10. Lateral photovoltaic effect in flexible free-standing reduced graphene oxide film for self-powered position-sensitive detection

    PubMed Central

    Moon, In Kyu; Ki, Bugeun; Yoon, Seonno; Oh, Jungwoo

    2016-01-01

    Lightweight, simple and flexible self-powered photodetectors are urgently required for the development and application of advanced optical systems for the future of wearable electronic technology. Here, using a low-temperature reduction process, we report a chemical approach for producing freestanding monolithic reduced graphene oxide papers with different gradients of the carbon/oxygen concentration ratio. We also demonstrate a novel type of freestanding monolithic reduced graphene oxide self-powered photodetector based on a symmetrical metal–semiconductor–metal structure. Upon illumination by a 633-nm continuous wave laser, the lateral photovoltage is observed to vary linfearly with the laser position between two electrodes on the reduced graphene oxide surface. This result may suggest that the lateral photovoltaic effect in the reduced graphene oxide film originates from the built-in electric field by the combination of both the photothermal electric effect and the gradient of the oxygen-to-carbon composition. These results represent substantial progress toward novel, chemically synthesized graphene-based photosensors and suggest one-step integration of graphene-based optoelectronics in the future. PMID:27634110

  11. Sensitive detection of miRNA by using hybridization chain reaction coupled with positively charged gold nanoparticles.

    PubMed

    Miao, Xiangmin; Ning, Xue; Li, Zongbing; Cheng, Zhiyuan

    2016-01-01

    Positively charged gold nanoparticles (+)AuNPs can adsorb onto the negatively charged surface of single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA). Herein, long-range dsDNA polymers could form based on the hybridization chain reaction (HCR) of two hairpin probes (H1 and H2) by using miRNA-21 as an initiator. (+)AuNPs could adsorb onto the negatively charged surface of such long-range dsDNA polymers based on the electrostatic adsorption, which directly resulted in the precipitation of (+)AuNPs and the decrease of (+)AuNPs absorption spectra. Under optimal conditions, miRNA-21 detection could be realized in the range of 20 pM-10 nM with a detection limit of 6.8 pM. In addition, (+)AuNPs used here are much more stable than commonly used negatively charged gold nanoparticles ((-)AuNPs) in mixed solution that contained salt, protein or other metal ions. Importantly, the assay could realize the detection of miRNA in human serum samples. PMID:27576601

  12. Lateral photovoltaic effect in flexible free-standing reduced graphene oxide film for self-powered position-sensitive detection.

    PubMed

    Moon, In Kyu; Ki, Bugeun; Yoon, Seonno; Oh, Jungwoo

    2016-09-16

    Lightweight, simple and flexible self-powered photodetectors are urgently required for the development and application of advanced optical systems for the future of wearable electronic technology. Here, using a low-temperature reduction process, we report a chemical approach for producing freestanding monolithic reduced graphene oxide papers with different gradients of the carbon/oxygen concentration ratio. We also demonstrate a novel type of freestanding monolithic reduced graphene oxide self-powered photodetector based on a symmetrical metal-semiconductor-metal structure. Upon illumination by a 633-nm continuous wave laser, the lateral photovoltage is observed to vary linfearly with the laser position between two electrodes on the reduced graphene oxide surface. This result may suggest that the lateral photovoltaic effect in the reduced graphene oxide film originates from the built-in electric field by the combination of both the photothermal electric effect and the gradient of the oxygen-to-carbon composition. These results represent substantial progress toward novel, chemically synthesized graphene-based photosensors and suggest one-step integration of graphene-based optoelectronics in the future.

  13. Sensitive detection of miRNA by using hybridization chain reaction coupled with positively charged gold nanoparticles

    PubMed Central

    Miao, Xiangmin; Ning, Xue; Li, Zongbing; Cheng, Zhiyuan

    2016-01-01

    Positively charged gold nanoparticles (+)AuNPs can adsorb onto the negatively charged surface of single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA). Herein, long-range dsDNA polymers could form based on the hybridization chain reaction (HCR) of two hairpin probes (H1 and H2) by using miRNA-21 as an initiator. (+)AuNPs could adsorb onto the negatively charged surface of such long-range dsDNA polymers based on the electrostatic adsorption, which directly resulted in the precipitation of (+)AuNPs and the decrease of (+)AuNPs absorption spectra. Under optimal conditions, miRNA-21 detection could be realized in the range of 20 pM-10 nM with a detection limit of 6.8 pM. In addition, (+)AuNPs used here are much more stable than commonly used negatively charged gold nanoparticles ((−)AuNPs) in mixed solution that contained salt, protein or other metal ions. Importantly, the assay could realize the detection of miRNA in human serum samples. PMID:27576601

  14. The anti-malarial chloroquine overcomes primary resistance and restores sensitivity to trastuzumab in HER2-positive breast cancer.

    PubMed

    Cufí, Sílvia; Vazquez-Martin, Alejandro; Oliveras-Ferraros, Cristina; Corominas-Faja, Bruna; Cuyàs, Elisabet; López-Bonet, Eugeni; Martin-Castillo, Begoña; Joven, Jorge; Menendez, Javier A

    2013-01-01

    Autophagy may control the de novo refractoriness of HER2 gene-amplified breast carcinomas to the monoclonal antibody trastuzumab (Herceptin). Tumor cells originally obtained from a patient who rapidly progressed on trastuzumab ab initio display increased cellular levels of the LC3-II protein--a finding that correlates with increased numbers of autophagosomes--and decreased levels of the autophagy receptor p62/SQSTM1, a protein selectively degraded by autophagy. Trastuzumab-refractory cells are in a state of "autophagy addiction" because genetic ablation of autophagy-specific genes (ATG8, ATG5, ATG12) notably reduces intrinsic refractoriness to trastuzumab. When the anti-malarial lysosomotropic drug chloroquine impedes autophagic resolution of the accumulation of autophagolysosomes formed in the presence of trastuzumab, cells commit to die by apoptosis. Accordingly, combination treatment with trastuzumab and chloroquine radically suppresses tumor growth by > 90% in a tumor xenograft completely refractory to trastuzumab. Adding chloroquine to trastuzumab-based regimens may therefore improve outcomes among women with autophagy-addicted HER2-positive breast cancer. PMID:23965851

  15. Blocking the NOTCH pathway can inhibit the growth of CD133-positive A549 cells and sensitize to chemotherapy

    SciTech Connect

    Liu, Juntao; Mao, Zhangfan; Huang, Jie; Xie, Songping; Liu, Tianshu; Mao, Zhifu

    2014-02-21

    Highlights: • Notch signaling pathway members are expressed lower levels in CD133+ cells. • CD133+ cells are not as sensitive as CD133− cells to chemotherapy. • GSI could inhibit the growth of both CD133+ and CD133− cells. • Blockade of Notch signaling pathway enhanced the effect of chemotherapy with CDDP. • DAPT/CDDP co-therapy caused G2/M arrest and elimination in CD133+ cells. - Abstract: Cancer stem cells (CSCs) are believed to play an important role in tumor growth and recurrence. These cells exhibit self-renewal and proliferation properties. CSCs also exhibit significant drug resistance compared with normal tumor cells. Finding new treatments that target CSCs could significantly enhance the effect of chemotherapy and improve patient survival. Notch signaling is known to regulate the development of the lungs by controlling the cell-fate determination of normal stem cells. In this study, we isolated CSCs from the human lung adenocarcinoma cell line A549. CD133 was used as a stem cell marker for fluorescence-activated cell sorting (FACS). We compared the expression of Notch signaling in both CD133+ and CD133− cells and blocked Notch signaling using the γ-secretase inhibitor DAPT (GSI-IX). The effect of combining GSI and cisplatin (CDDP) was also examined in these two types of cells. We observed that both CD133+ and CD133− cells proliferated at similar rates, but the cells exhibited distinctive differences in cell cycle progression. Few CD133+ cells were observed in the G{sub 2}/M phase, and there were half as many cells in S phase compared with the CD133− cells. Furthermore, CD133+ cells exhibited significant resistance to chemotherapy when treated with CDDP. The expression of Notch signaling pathway members, such as Notch1, Notch2 and Hes1, was lower in CD133+ cells. GSI slightly inhibited the proliferation of both cell types and exhibited little effect on the cell cycle. The inhibitory effects of DPP on these two types of cells were

  16. Improved sensitivity by use of gas chromatography-positive chemical ionization triple quadrupole mass spectrometry for the analysis of drug related substances.

    PubMed

    Van Gansbeke, Wim; Polet, Michael; Hooghe, Fiona; Devos, Christophe; Van Eenoo, Peter

    2015-09-15

    In 2013, the World Anti-Doping Agency (WADA) drastically lowered the minimum required performance levels (MRPLs) of most doping substances, demanding a substantial increase in sensitivity of the existing methods. For a number of compounds, conventional electron impact ionization gas chromatography tandem mass spectrometry (GC-EI-MS/MS) is often no longer sufficient to reach these MRPLs and new strategies are required. In this study, the capabilities of positive ion chemical ionization (PICI) GC-MS/MS are investigated for a wide range of drug related compounds of various classes by injection of silylated reference standards. Ammonia as PICI reagent gas had superior characteristics for GC-MS/MS purposes than methane. Compared to GC-EI-MS/MS, PICI (with ammonia as reagent gas) provided more selective ion transitions and consequently, increased sensitivity by an average factor of 50. The maximum increase (by factor of 500-1000) was observed in the analysis of stimulants, namely chlorprenaline, furfenorex and phentermine. In total, improved sensitivity was obtained for 113 out of 120 compounds. A new GC-PICI-MS/MS method has been developed and evaluated for the detection of a wide variety of exogenous doping substances and the quantification of endogenous steroids in urine in compliance with the required MRPLs established by WADA in 2013. The method consists of a hydrolysis and extraction step, followed by derivatization and subsequent 1μL pulsed splitless injection on GC-PICI-MS/MS (16min run). The increased sensitivity allows the set up of a balanced screening method that meets the requirements for both quantitative and qualitative compounds: sufficient capacity and resolution in combination with high sensitivity and short analysis time. This resulted in calibration curves with a wide linear range (e.g., 48-9600ng/mL for androsterone and etiochanolone; all r(2)>0.99) without compromising the requirements for the qualitative compounds.

  17. Improved sensitivity by use of gas chromatography-positive chemical ionization triple quadrupole mass spectrometry for the analysis of drug related substances.

    PubMed

    Van Gansbeke, Wim; Polet, Michael; Hooghe, Fiona; Devos, Christophe; Van Eenoo, Peter

    2015-09-15

    In 2013, the World Anti-Doping Agency (WADA) drastically lowered the minimum required performance levels (MRPLs) of most doping substances, demanding a substantial increase in sensitivity of the existing methods. For a number of compounds, conventional electron impact ionization gas chromatography tandem mass spectrometry (GC-EI-MS/MS) is often no longer sufficient to reach these MRPLs and new strategies are required. In this study, the capabilities of positive ion chemical ionization (PICI) GC-MS/MS are investigated for a wide range of drug related compounds of various classes by injection of silylated reference standards. Ammonia as PICI reagent gas had superior characteristics for GC-MS/MS purposes than methane. Compared to GC-EI-MS/MS, PICI (with ammonia as reagent gas) provided more selective ion transitions and consequently, increased sensitivity by an average factor of 50. The maximum increase (by factor of 500-1000) was observed in the analysis of stimulants, namely chlorprenaline, furfenorex and phentermine. In total, improved sensitivity was obtained for 113 out of 120 compounds. A new GC-PICI-MS/MS method has been developed and evaluated for the detection of a wide variety of exogenous doping substances and the quantification of endogenous steroids in urine in compliance with the required MRPLs established by WADA in 2013. The method consists of a hydrolysis and extraction step, followed by derivatization and subsequent 1μL pulsed splitless injection on GC-PICI-MS/MS (16min run). The increased sensitivity allows the set up of a balanced screening method that meets the requirements for both quantitative and qualitative compounds: sufficient capacity and resolution in combination with high sensitivity and short analysis time. This resulted in calibration curves with a wide linear range (e.g., 48-9600ng/mL for androsterone and etiochanolone; all r(2)>0.99) without compromising the requirements for the qualitative compounds. PMID:26296082

  18. A BGO/GSO position sensitive block detector for a high resolution positron emission tomography with depth of interaction detection capability

    SciTech Connect

    Yamamoto, S.

    1996-12-31

    We developed a position sensitive block detector with depth of interaction detection capability for positron emission tomography (PET). The detector consists of 6 x 8 array of GSO scintillators, 6 x 8 array of BGO scintillators and two dual photomultiplier tubes (PMT). The GSO scintillators are optically coupled to front surface of the BGO scintillators. The position of 6 x 8 scintillators are determined by the Anger principle and depth of interaction position is determined by using the pulse shape analysis of GSOs and BGOs. Performance of the block detector was measured. Position distribution of the developed BGO/GSO block detector was little distorted. However the separation of the spots was still enough to distinguish the scintillators in transaxial and axial directions. Since pulse shape distribution using a developed simple pulse shape analyzer had two peaks, it is possible to separate the GSOs and BGOs for depth of interaction detection. With these results, a high resolution PET with depth of interaction detection capability will be possible using the developed BGO/GSO block detectors.

  19. A transformer of molecular beacon for sensitive and real-time detection of phosphatases with effective inhibition of the false positive signals.

    PubMed

    Zhang, Chen; Su, Xin; Liang, Yuan; Zhu, Xiaocui; Song, Chen; Zhao, Meiping

    2011-10-15

    Molecular beacons (MBs) have shown great potential in measurement of enzyme activities. However, currently available methods for monitoring of phosphatases only use MBs as a signal reporter. Extra substrates for the phosphatases are needed to hybridize to the MB either as a primer or as a template. Moreover, few MB-based methods have been used to detect enzyme activities in real biological samples due to insufficient sensitivity or false positive interference signals caused by nonspecific nucleases. In this work, a novel type of fluorescent probe was designed and synthesized for monitoring of phosphatases by integrating the DNA substrate and the signaling structures into a single molecule. Such a new design not only significantly simplified the probing system and greatly enhanced the sensitivity, but also offered a practical way to guard against the false-positive signal problems in the application to real samples. The unique design of the assay format should be widely applicable to many other enzymatic assays using oligonucleotide fluorescent probes.

  20. 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. PMID

  1. Positive or negative allosteric modulation of metabotropic glutamate receptor 5 (mGluR5) does not alter expression of behavioral sensitization to methamphetamine.

    PubMed

    Kufahl, Peter R; Nemirovsky, Natali E; Watterson, Lucas R; Zautra, Nicholas; Olive, M Foster

    2013-01-01

    We investigated the role of metabotropic glutamate receptor type 5 (mGluR5) in methamphetamine-induced behavioral sensitization. The mGluR5 positive allosteric modulator (3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl) benzamide (CDPPB) and negative allosteric modulator fenobam were tested in separate experiments. Sprague-Dawley rats were repeatedly injected with 1 mg/kg methamphetamine or saline, and then given a locomotor challenge test using a dose of 0.5 mg/kg methamphetamine. Prior to the challenge test session, rats were injected with CDPPB, fenobam, or a vehicle.  Doses from previous studies showed reduced drug-conditioned behavior; however in this study neither CDPPB nor fenobam pretreatment resulted in an altered expression of behavioral sensitization, indicating a lack of mGluR5 involvement in sensitized methamphetamine-induced locomotion. Additionally, the high dose (30 mg/kg) of fenobam resulted in decreased methamphetamine-induced locomotion in rats regardless of drug exposure history, which suggests evidence of nonspecific behavioral inhibition.

  2. Evaluation of an integrated Fourier-transform spectrometer utilizing a lateral effect position sensitive detector with a multi-channel Fabry Perot interferometer

    NASA Astrophysics Data System (ADS)

    Andersson, H. A.; Manuilskiy, A.; Thungström, G.; Nilsson, H.-E.

    2008-04-01

    The basis of this paper is the evaluation of an integrated multi-channel Fourier-transform (FT) spectrometer based on a multi-channel wedge Fabry-Perot interferometer and a one-dimensional lateral effect position sensitive detector (PSD). The use of a PSD for an interferogram readout allows for a simple scanning mechanism with no requirement for any position reference. The use of a wedge-shaped interferometer makes it possible to integrate it directly onto the PSD surface, thus producing a very compact spectrometer. The capabilities of the spectrometer are demonstrated by absorption spectral measurements using a reference sample. In addition, spectral measurements on 532 nm DPSS and 632.8 nm He-Ne lasers are presented. The resolution of the spectrometer is approximately 5 nm. The evaluated spectrometer set-up can be used in applications where compact and low cost spectrometers are required, such as in process control and in education. Further, it is shown that there are deteriorations in very high accuracy position measurements, which are caused by changes in incident light intensity. A model describing the above-mentioned nonlinearities was developed based on analysing the equivalent circuit for PSDs and parameters such as leakage current and serial resistance. Additionally, a method is proposed to assist in the reduction of the nonlinearity caused by this effect.

  3. Development and applications of a new neutron single-crystal diffractometer based on a two-dimensional large-area curved position-sensitive detector

    PubMed Central

    Lee, Chang-Hee; Noda, Yukio; Ishikawa, Yoshihisa; Kim, Shin Ae; Moon, Myungkook; Kimura, Hiroyuki; Watanabe, Masashi; Dohi, Yuki

    2013-01-01

    A new single-crystal neutron diffractometer based on a large-area curved two-dimensional position-sensitive detector (C-2DPSD) has been developed. The diffractometer commissioning is almost complete, together with development of the measurement methodology and the raw data processing software package, the Reciprocal Analyzer, and the instrument is now ready to be launched for users. Position decoding of the C-2DPSD is via a delay-line readout method with an effective angular range of 110 × 54° in the horizontal and vertical directions, respectively, with a nominal radius of curvature of 530 mm. The diffractometer is equipped with a Ge(311) mosaic monochromator and two supermirror vacuum guide paths, one before and one after the monochromator position. The commissioning incorporates corrections and calibration of the instrument using an NaCl crystal, various applications such as crystallographic and magnetic structure measurements, a crystallinity check on large crystals, and a study on the composition or dopant content of a mixed crystal of (TmxYb1−x)Mn2O5. The installation of the diffractometer and the measurement method, the calibration procedure and results, the raw data treatment and visualization, and several applications using the large C-2DPSD-based diffractometer are reported. PMID:23682194

  4. Deep level centers and their role in photoconductivity transients of InGaAs/GaAs quantum dot chains

    SciTech Connect

    Kondratenko, S. V. Vakulenko, O. V.; Mazur, Yu. I. Dorogan, V. G.; Marega, E.; Benamara, M.; Ware, M. E.; Salamo, G. J.

    2014-11-21

    The in-plane photoconductivity and photoluminescence are investigated in quantum dot-chain InGaAs/GaAs heterostructures. Different photoconductivity transients resulting from spectrally selecting photoexcitation of InGaAs QDs, GaAs spacers, or EL2 centers were observed. Persistent photoconductivity was observed at 80 K after excitation of electron-hole pairs due to interband transitions in both the InGaAs QDs and the GaAs matrix. Giant optically induced quenching of in-plane conductivity driven by recharging of EL2 centers is observed in the spectral range from 0.83 eV to 1.0 eV. Conductivity loss under photoexcitation is discussed in terms of carrier localization by analogy with carrier distribution in disordered media.

  5. MRI compatibility of position-sensitive photomultiplier depth-of-interaction PET detectors modules for in-line multimodality preclinical studies

    NASA Astrophysics Data System (ADS)

    Vaquero, J. J.; Sánchez, J. J.; Udías, J. M.; Cal-González, J.; Desco, M.

    2013-02-01

    This work addresses the feasibility of a small-animal, in-line PET/MR system based on Position-Sensitive Photo Multiplier Tubes (PS-PMTs). To this end, we measured the effects of static magnetic fields on the PS-PMTs performance in order to explore the minimal tandem separation between the PET and MR subsystems to preserve their respective performances. We concluded that it is possible to achieve minimal degradation of the PET scanner performance (after a system recalibration) if the magnetic field strength influencing the PET detectors is less than 1 mT and if it is oriented perpendicularly to the longitudinal axis of the tube. Therefore, we predict that it will be possible to maintain the PET image quality if it is placed outside the 1 mT line.

  6. Performance and field tests of a handheld Compton camera using 3-D position-sensitive scintillators coupled to multi-pixel photon counter arrays

    NASA Astrophysics Data System (ADS)

    Kishimoto, A.; Kataoka, J.; Nishiyama, T.; Fujita, T.; Takeuchi, K.; Okochi, H.; Ogata, H.; Kuroshima, H.; Ohsuka, S.; Nakamura, S.; Hirayanagi, M.; Adachi, S.; Uchiyama, T.; Suzuki, H.

    2014-11-01

    After the nuclear disaster in Fukushima, radiation decontamination has become particularly urgent. To help identify radiation hotspots and ensure effective decontamination operation, we have developed a novel Compton camera based on Ce-doped Gd3Al2Ga3O12 scintillators and multi-pixel photon counter (MPPC) arrays. Even though its sensitivity is several times better than that of other cameras being tested in Fukushima, we introduce a depth-of-interaction (DOI) method to further improve the angular resolution. For gamma rays, the DOI information, in addition to 2-D position, is obtained by measuring the pulse-height ratio of the MPPC arrays coupled to ends of the scintillator. We present the detailed performance and results of various field tests conducted in Fukushima with the prototype 2-D and DOI Compton cameras. Moreover, we demonstrate stereo measurement of gamma rays that enables measurement of not only direction but also approximate distance to radioactive hotspots.

  7. De-Li-DAQ-2D - a new data acquisition system for position-sensitive neutron detectors with delay-line readout

    NASA Astrophysics Data System (ADS)

    Levchanovskiy, F. V.; Murashkevich, S. M.

    2016-09-01

    Software for a data acquisition system of modern one- and two-dimensional position-sensitive detectors with delay-line readout, which includes a software interface to a new electronic module De-Li-DAQ-2D with a USB interface, is presented. The new system after successful tests on the stand and on several spectrometers of the IBR-2 reactor has been integrated into the software complex SONIX+ [1]. The De-Li- DAQ-2D module [2] contains an 8-channel time-code converter (TDC-GPX) with a time resolution of 80 ps, field programmable gate array (FPGA), 1 Gbyte histogram memory and high-speed interface with a fiber-optic communication line. A real count rate is no less than 106 events/s. The De-Li-DAQ-2D module is implemented in the NIM standard. The De-Li-DAQ-2D module can operate in two modes: histogram mode and list mode.

  8. Determination of (235)U, (239)Pu, (240)Pu, and (241)Am in a nuclear bomb particle using a position-sensitive α-γ coincidence technique.

    PubMed

    Peräjärvi, Kari A; Ihantola, Sakari; Pöllänen, Roy C; Toivonen, Harri I; Turunen, Jani A

    2011-02-15

    A nuclear bomb particle containing 1.6 ng of Pu was investigated nondestructively with a position-sensitive α detector and a broad-energy HPGe γ-ray detector. An event-mode data acquisition system was used to record the data. α-γ coincidence counting was shown to be well suited to nondestructive isotope ratio determination. Because of the very small background, the 51.6 keV γ rays of (239)Pu and the 45.2 keV γ rays of (240)Pu were identified, which enabled isotopic ratio calculations. In the present work, the (239)Pu/((239)Pu+(240)Pu) atom ratio was determined to be 0.950 ± 0.010. The uncertainties were much smaller than in the previous more conventional nondestructive studies on this particle. Obtained results are also in good agreement with the data from the destructive mass spectrometric studies obtained previously by other investigators.

  9. Discovery of Novel Cell Wall-Active Compounds Using PywaC, a Sensitive Reporter of Cell Wall Stress, in the Model Gram-Positive Bacterium Bacillus subtilis

    PubMed Central

    Czarny, T. L.; Perri, A. L.; French, S.

    2014-01-01

    The emergence of antibiotic resistance in recent years has radically reduced the clinical efficacy of many antibacterial treatments and now poses a significant threat to public health. One of the earliest studied well-validated targets for antimicrobial discovery is the bacterial cell wall. The essential nature of this pathway, its conservation among bacterial pathogens, and its absence in human biology have made cell wall synthesis an attractive pathway for new antibiotic drug discovery. Herein, we describe a highly sensitive screening methodology for identifying chemical agents that perturb cell wall synthesis, using the model of the Gram-positive bacterium Bacillus subtilis. We report on a cell-based pilot screen of 26,000 small molecules to look for cell wall-active chemicals in real time using an autonomous luminescence gene cluster driven by the promoter of ywaC, which encodes a guanosine tetra(penta)phosphate synthetase that is expressed under cell wall stress. The promoter-reporter system was generally much more sensitive than growth inhibition testing and responded almost exclusively to cell wall-active antibiotics. Follow-up testing of the compounds from the pilot screen with secondary assays to verify the mechanism of action led to the discovery of 9 novel cell wall-active compounds. PMID:24687489

  10. DNA double strand break repair defect and sensitivity to poly ADP-ribose polymerase (PARP) inhibition in human papillomavirus 16-positive head and neck squamous cell carcinoma

    PubMed Central

    Weaver, Alice N.; Cooper, Tiffiny S.; Rodriguez, Marcela; Trummell, Hoa Q.; Bonner, James A.; Rosenthal, Eben L.; Yang, Eddy S.

    2015-01-01

    Patients with human papillomavirus-positive (HPV+) head and neck squamous cell carcinomas (HNSCCs) have increased response to radio- and chemotherapy and improved overall survival, possibly due to an impaired DNA damage response. Here, we investigated the correlation between HPV status and repair of DNA damage in HNSCC cell lines. We also assessed in vitro and in vivo sensitivity to the PARP inhibitor veliparib (ABT-888) in HNSCC cell lines and an HPV+ patient xenograft. Repair of DNA double strand breaks (DSBs) was significantly delayed in HPV+ compared to HPV− HNSCCs, resulting in persistence of γH2AX foci. Although DNA repair activators 53BP1 and BRCA1 were functional in all HNSCCs, HPV+ cells showed downstream defects in both non-homologous end joining and homologous recombination repair. Specifically, HPV+ cells were deficient in protein recruitment and protein expression of DNA-Pk and BRCA2, key factors for non-homologous end joining and homologous recombination respectively. Importantly, the apparent DNA repair defect in HPV+ HNSCCs was associated with increased sensitivity to the PARP inhibitor veliparib, resulting in decreased cell survival in vitro and a 10–14 day tumor growth delay in vivo. These results support the testing of PARP inhibition in combination with DNA damaging agents as a novel therapeutic strategy for HPV+ HNSCC. PMID:26336991

  11. Preparation of Hydrogenated Amorphous Silicon and its Characterization by Transient Photoconductivity

    NASA Astrophysics Data System (ADS)

    Walker, Christopher Morgan

    1992-01-01

    Hydrogenated amorphous silicon (a-Si:H) is a semiconductor material that has generated recent widespread interest because of its low manufacturing and processing costs compared with other semiconducting materials. The performance of devices incorporating a-Si:H depends to a large extent on the photoresponse of the a-Si:H. The work in this thesis involves the construction of an a-Si:H plasma-enhanced chemical vapor deposition (PECVD) system, characterization of the quality of the a-Si:H produced by this system, and measurement of the transient photoconductivity in response to pulses of laser illumination with different durations. The relationship of the design of the PECVD system to the quality of the a-Si:H is treated, emphasizing the features included in the system to reduce the incorporation of defects in the a-Si:H layers. These features include an ultra-high-vacuum deposition chamber, a load-lock chamber enabling samples to be loaded under vacuum, and an electrode assembly designed to produce a uniform electric field for decomposing the reactant gases used in the system. The quality of the a-Si:H films is examined. The dark conductivity activation energy, optical absorption, and photoconductivity are measured to characterize intrinsic, p-doped, and n-doped a-Si:H layers. Results from these measurements indicate our system produces good-quality a-Si:H films. The current vs. voltage characteristics under illuminated and dark conditions, and the quantum efficiency are measured on a-Si:H p-i-n diodes made in our system, and the results show that these diodes compare favorably to similar high-quality p-i-n diodes produced at other laboratories. An investigation into the effect of the light-induced degradation associated with a-Si:H on the performance of OASLMs is also presented. Finally, the transient photoresponse to laser pulses ranging in duration from 1 mus to 1 s over a range of temperatures from 100 to 300 K is investigated. We have discovered that the

  12. Surface photoconductivity of organosilicate glass dielectrics induced by vacuum-ultraviolet radiation

    NASA Astrophysics Data System (ADS)

    Zheng, H.; Nichols, M. T.; Pei, D.; Nishi, Y.; Shohet, J. L.

    2013-08-01

    The temporary increase in the electrical surface conductivity of low-k organosilicate glass (SiCOH) during exposure to vacuum-ultraviolet radiation (VUV) is investigated. To measure the photoconductivity, patterned "comb structures" are deposited on dielectric films and exposed to synchrotron radiation in the range of 8-25 eV, which is in the energy range of most plasma vacuum-ultraviolet radiation. The change in photo surface conductivity induced by VUV radiation may be beneficial in limiting charging damage of dielectrics by depleting the plasma-deposited charge.

  13. Oxygen vacancies induced DX center and persistent photoconductivity properties of high quality ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Xie, Yong; Madel, Manfred; Feneberg, Martin; Neuschl, Benjamin; Jie, Wanqi; Hao, Yue; Ma, Xiaohua; Thonke, Klaus

    2016-04-01

    Ultraviolet sensors based on homoepitaxially grown ZnO nanorods were fabricated using clean room technology. We study the spectral dependence and frequency dependence of the photoresponse of these rods at different temperatures and ambient conditions. Whereas the response for above-bandgap light is fast, we find a slow response to light below band gap and clear signatures of persistent photoconductivity. These findings are explained by switching oxygen vacancies by light from nonconductive to conductive state, whereas the oxygen vacancies undergo a large lattice relaxation. The threshold photon energy for this process is found to be 2.6 eV at room temperature.

  14. Laser Plasma Vapour Deposition Of Photoconducting And High Tc Superconducting Films

    NASA Astrophysics Data System (ADS)

    Popescu, Mihai A.; Apostol, Ileana; Mihailescu, Ion N.; Botila, T.; Pentia, E.; Ciurea, M. L.; Dinescu, M.; Jaklovsky, J.; Aldica, Gheorghe V.; Miu, L.; Rusu, C.; Hening, Al. A.; Mihai, S.; Constantin, C.; Stoica, Mihaela; Pausescu, P.; Cruceanu, Eugen; Pompe, Wolfgang; Wuensch, R.; Richter, Asta; Scheibe, H. J.

    1989-05-01

    Device quality PbS photoconducting films were obtained by laser plasma vapour deposition on special glass substrates at room temperature and their structure was investigated by X-ray diffraction. High Tc superconducting films of composition Dy0.2Y0.8Ba2Cu3O~7 and YBa2Cu3O~7 were deposited on sapphire substrate. It was shown for laser deposited YBa2Cu3O~7 that a buffer layer of the same composition predeposited by rf sputtering allows for getting high quality superconducting films.

  15. Crystallographic, luminescence and photoconductive characteristics of chemically tailored ZnO nanorods

    SciTech Connect

    Bayan, Sayan Chakraborty, Purushottam

    2014-04-24

    The optoelectronic properties of zinc oxide (ZnO) nanorods synthesized using two different chemical methods have been explored in the light of microstructural features. The presence/absence of band edge emission in the luminescence spectra of the nanorods is found to be governed by the crystallographic properties. Moreover, we observed a pronounced effect of variation in crystallite size on the UV photoconductivity of the nanorods. Understanding the influence of microstructural aspects on the optical and electronic properties of the nanostructures may help in the fabrication of prototype, miniaturized optoelectronic devices.

  16. Negative infrared photoconductivity in CdS1-xSex films

    NASA Astrophysics Data System (ADS)

    Abdinov, A. S.; Jafarov, M. A.; Mamedov, H. M.; Nasirov, E. F.

    2003-09-01

    The negative infrared photoconductivity (NPH) has been observed for the first time in CdS1-xSex films, in the wavelength region of 0.700 - 1.23 μm. at values of stimulating light intensity Φ = 100 - 400 Lk. electrical field E = 0.5 - 130 V/cm and temperature T = 265 - 310 Κ. It is established, that basic laws of NPH explains on the basis of two-barrier model and in the considered conditions a charge carriers, overcome a barrier by tunneling. A films of CdS1-xSex can be used in IR engineering and negatronics.

  17. Anomalous photoconductive behavior of a single InAs nanowire photodetector

    SciTech Connect

    Li, Junshuai; Yan, Xin; Sun, Fukuan; Zhang, Xia Ren, Xiaomin

    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.

  18. Surface photoconductivity of organosilicate glass dielectrics induced by vacuum-ultraviolet radiation

    SciTech Connect

    Zheng, H.; Nichols, M. T.; Pei, D.; Shohet, J. L.; Nishi, Y.

    2013-08-14

    The temporary increase in the electrical surface conductivity of low-k organosilicate glass (SiCOH) during exposure to vacuum-ultraviolet radiation (VUV) is investigated. To measure the photoconductivity, patterned “comb structures” are deposited on dielectric films and exposed to synchrotron radiation in the range of 8–25 eV, which is in the energy range of most plasma vacuum-ultraviolet radiation. The change in photo surface conductivity induced by VUV radiation may be beneficial in limiting charging damage of dielectrics by depleting the plasma-deposited charge.

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

    DOEpatents

    Mar, Alan; Zutavern, Fred J.; Loubriel, Guillermo

    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.

  20. X-ray effects in charge-ordered manganites: A magnetic mechanism of persistent photoconductivity

    SciTech Connect

    Keimer, B.; Casa, D.; Kiryukhin, V.; Saleh, O.A.; Hill, J.P.; Tomioka, Y.; Tokura, Y. |

    1998-12-31

    Charge-ordered manganites of composite Pr{sub 1{minus}x}(Ca{sub 1{minus}y}Sr{sub y}){sub x}MnO{sub 3} exhibit persistent photoconductivity when illuminated by x-rays. The authors review transport and x-ray diffraction data as functions of x-ray exposure, magnetic field, and temperature which shed light on the origin of this unusual behavior. The experimental evidence suggests that the mechanism primarily involves a ferromagnetic polarization of local spins by hot electrons generated by the x-rays.

  1. Tunable narrowband THz pulse generation in scalable large area photoconductive antennas.

    PubMed

    Krause, Johannes; Wagner, Martin; Winnerl, Stephan; Helm, Manfred; Stehr, Dominik

    2011-09-26

    The generation and characterization of narrowband THz pulses by means of chirped pulse difference frequency generation in Auston-switch type photoconductive antennas is reported. Using optical pulses with energies in the range from 1 nJ to 1 µJ, we generate THz pulses with up to 50 pJ in energy and electric field strengths on the order of 1 kV/cm. Two emitter concepts are investigated and circumvention of the fast saturation for small area excitation by scaling of the THz emitter is demonstrated. PMID:21996852

  2. High Dynamics and Precision Optical Measurement Using a Position Sensitive Detector (PSD) in Reflection-Mode: Application to 2D Object Tracking over a Smart Surface

    PubMed Central

    Ivan, Ioan Alexandru; Ardeleanu, Mihai; Laurent, Guillaume J.

    2012-01-01

    When related to a single and good contrast object or a laser spot, position sensing, or sensitive, detectors (PSDs) have a series of advantages over the classical camera sensors, including a good positioning accuracy for a fast response time and very simple signal conditioning circuits. To test the performance of this kind of sensor for microrobotics, we have made a comparative analysis between a precise but slow video camera and a custom-made fast PSD system applied to the tracking of a diffuse-reflectivity object transported by a pneumatic microconveyor called Smart-Surface. Until now, the fast system dynamics prevented the full control of the smart surface by visual servoing, unless using a very expensive high frame rate camera. We have built and tested a custom and low cost PSD-based embedded circuit, optically connected with a camera to a single objective by means of a beam splitter. A stroboscopic light source enhanced the resolution. The obtained results showed a good linearity and a fast (over 500 frames per second) response time which will enable future closed-loop control by using PSD. PMID:23223078

  3. High dynamics and precision optical measurement using a position sensitive detector (PSD) in reflection-mode: application to 2D object tracking over a Smart Surface.

    PubMed

    Ivan, Ioan Alexandru; Ardeleanu, Mihai; Laurent, Guillaume J

    2012-01-01

    When related to a single and good contrast object or a laser spot, position sensing, or sensitive, detectors (PSDs) have a series of advantages over the classical camera sensors, including a good positioning accuracy for a fast response time and very simple signal conditioning circuits. To test the performance of this kind of sensor for microrobotics, we have made a comparative analysis between a precise but slow video camera and a custom-made fast PSD system applied to the tracking of a diffuse-reflectivity object transported by a pneumatic microconveyor called Smart-Surface. Until now, the fast system dynamics prevented the full control of the smart surface by visual servoing, unless using a very expensive high frame rate camera. We have built and tested a custom and low cost PSD-based embedded circuit, optically connected with a camera to a single objective by means of a beam splitter. A stroboscopic light source enhanced the resolution. The obtained results showed a good linearity and a fast (over 500 frames per second) response time which will enable future closed-loop control by using PSD. PMID:23223078

  4. Direct-Coated Photoconducting Nanocrystalline PbS Thin Films with Tunable Band Gap

    NASA Astrophysics Data System (ADS)

    Vankhade, Dhaval; Kothari, Anjana; Chaudhuri, Tapas K.

    2016-06-01

    Nanocrystalline PbS thin films are deposited on glass by direct coating from a precursor solution of lead acetate and thiourea in methanol. A single coating has a thickness of 50 nm and greater thicknesses are obtained from layer by layer deposition. The films are smooth and shiny with roughness (rms) of about 1.5 nm. X-ray diffraction studies show that films are cubic PbS with crystallite size about 10 nm. The films are p-type with dark electrical conductivities in the range of 0.4-0.5 S/cm. These films are basically photoconducting. Photoconductivity monotonically increases with increase in thickness. The band gap of the films strongly depends on the thickness of the films. The band gap decreases from 2.4 eV to 1.6 eV as the thickness is increased from 50 nm to 450 nm. The tunability of the band gap is useful for technical applications, such as solar cells and photodetectors.

  5. 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.

  6. 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.

  7. DX centers and persistent photoconductivity in CdTe In films

    NASA Astrophysics Data System (ADS)

    Rivera-Alvarez, Z.; Hernández, L.; Becerril, M.; Picos-Vega, A.; Zelaya-Angel, O.; Ramírez-Bon, R.; Vargas-García, J. R.

    2000-02-01

    In this work, we study the nature and behavior of the persistent photoconductivity (PPC) in CdTe-In films grown by co-sputtering of CdTe-In-Cd targets. It was found that only when In atoms are substantially incorporated into CdTe films, the persistent photoconductivity is observed with a quenching temperature of about 270 K. We have also investigated the trapping centers in the CdTe films by using the thermally stimulated conductivity technique. Two localized deep levels were determined. One of them, with an activation energy of 0.42 eV, has been ascribed as a direct evidence of DX centers that are formed by Cd vacancies and In donors complexes. By formulating the PPC build-up and decay kinetics, we have associated the PPC effect in our films to the photoionization of this deep level (DX like centers). Up to date, the existence of DX centers in CdTe-In polycrystalline films have not been previously reported.

  8. In situ studies of transient photoconductivity in PbSe quantum dot solar cells

    NASA Astrophysics Data System (ADS)

    Gao, Jianbo; Koh, Weon-Kyu; Makarov, Nikolay; Pietryga, Jeffrey; Klimov, Victor

    2014-03-01

    PbSe quantum dot (QD) solar cells have attracted significant interest due to their band gap tunability, easy-processing and flexibility. Efficiencies have risen from 1% just a few years ago to nearly 9% today. Furthermore, the novel concept of multiple exciton generation (MEG) resulting from quantum confinement makes these materials scientifically interesting counterparts to bulk semiconductors. Recent observations of more than 100% external quantum efficiency in PbSe QD solar cells confirm direct relevance of MEG to practical photovoltaics. However, in order to take full advantage of this effect, one needs a better understanding of photogeneration dynamics and carrier transport in QD solar cells. In this talk, we discuss a new technique for in situ measurements of transient photoconductivity with fast response time (<50 ps) applied to study carrier transport and photogeneration dynamics in PbSe QD solar cells. These measurements complement traditional photoconductivity techniques such as time-resolved microwave conductivity and time-of-flight. Based on the analysis of temperature, excitation wavelength and electrical field dependence measurements, we derive parameters such as MEG efficiency, carrier lifetime, trap-free mobility and carrier emission rate from trap states.

  9. 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

  10. Enhanced photoconductivity and fine response tuning in nanostructured porous silicon microcavities

    NASA Astrophysics Data System (ADS)

    Urteaga, R.; Marín, O.; Acquaroli, L. N.; Comedi, D.; Schmidt, J. A.; Koropecki, R. R.

    2009-05-01

    We used light confinement in optical microcavities to achieve a strong enhancement and a precise wavelength tunability of the electrical photoconductance of nanostructured porous silicon (PS). The devices consist of a periodic array of alternating PS layers, electrochemically etched to have high and low porosities - and therefore distinct dielectric functions. A central layer having a doubled thickness breaks up the symmetry of the one-dimensional photonic structure, producing a resonance in the photonic band gap that is clearly observed in the reflectance spectrum. The devices were transferred to a glass coated with a transparent SnO2 electrode, while an Al contact was evaporated on its back side. The electrical conductance was measured as a function of the photon energy. A strong enhancement of the conductance is obtained in a narrow (17nm FWHM) band peaking at the resonance. We present experimental results of the angular dependence of this photoconductance peak energy, and propose an explanation of the conductivity behaviour supported by calculations of the internal electromagnetic field. These devices are promising candidates for finely tuned photoresistors with potential application as chemical sensors and biosensors.

  11. Transport and photoconduction characteristics of metal-graphene-4H-SiC(0001) heterojunction devices

    SciTech Connect

    Hosseini, T.; Kouklin, N.; Tomer, D.; Rajput, S.; Li, L.

    2014-12-01

    Vertically integrated graphene-semiconductor systems remain of significant technological importance for their promise to captivate new device physics and propel the development of advanced carbon-based opto-electronic devices. In this study, we carry out a series of bias-dependent transport, gate-dependent transport, and photoconduction measurements to probe the opto-electronic characteristics of metal-graphene-4H-SiC (0001) (Si-face) heterojunctions. The forward bias transport is found to deviate strongly from thermionic emission one as being controlled by the device circuitry and minority carrier injection mechanisms. An improved analytical model is offered and used to extract key junction parameters including series resistance of ∼80 kΩ, interface barrier height of ∼0.6 eV, and ideality factor of ∼6.1. The results of the photocurrent tests point to a light-assisted minority carrier injection as a key mechanism behind the photoconductive gain obtained in the devices subject to a weak, sub-bandgap cw-excitation.

  12. Photoconductivity on nanocrystalline ZnO/TiO2 thin films obtained by sol-gel

    NASA Astrophysics Data System (ADS)

    Valverde-Aguilar, G.; García-Macedo, J. A.; Juárez-Arenas, R.

    2008-08-01

    In this paper we report results on the synthesis, characterization and photoconductivity behaviour of amorphous and nanocrystalline ZnO/TiO2 thin films. They were produced by the sol-gel process at room temperature by using the spin-coating method and deposited on glass substrates. The ZnO/TiO2 films were synthesized by using tetrabutyl orthotitanate and zinc nitrate hexahydrate as the inorganic precursors. The samples were sintered at 520°C for 1 hour. The obtained films were characterized by X-ray diffraction (XRD), optical absorption (OA), infrared spectroscopy (IR) and scanning electronic microscopy (SEM) studies. Photoconductivity studies were performed on amorphous and nanocrystalline (anatase phase) films to determine the charge transport parameters. The experimental data were fitted with straight lines at darkness and under illumination at 310 nm, 439 nm and 633 nm. This indicates an ohmic behavior. The Φμτ and Φl0 parameters were fitted by least-squares with straight lines (nanocrystalline films) and polynomial fits (amorphous films).

  13. Transient photoconductivity in polymer bulk heterojunction solar cells. Competition between sweep-out and recombination

    SciTech Connect

    Cowan, Sarah; Street, R. A.; Cho, Shinuk; Heeger, Alan

    2011-01-18

    Transient photoconductivity measurements carried out on bulk heterojunction (BHJ) solar cells demonstrate the competition between carrier sweep-out by the internal field and the loss of photogenerated carriers by recombination. The transient photoconductance data imply the existence of a well-defined internal field; carrier sweep-out is proportional to the magnitude of the internal field and limited by the carrier mobility. At external voltages near open circuit where the internal field approaches zero, the photocurrent decays because of the recombination of photogenerated mobile carriers. Mobility and recombination lifetimes are evaluated for carriers in poly[3-hexylthiophene] (P3HT): [6,6]-phenyl-C61 -butyric acid methyl ester (PC60 BM) and poly[N -9''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT): [6,6]-phenyl-C71 -butyric acid methyl ester (PC71 BM) solar cells.

  14. 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.

  15. Increased photorefractive sensitivity in double-doped KTa(1-x)Nb(x)O(3):Fe,Ti.

    PubMed

    Leyva, V; Agranat, A; Yariv, A

    1993-06-15

    Double-doped KTN:Fe,Ti exhibits increased photorefractive sensitivity compared with single-doped KTN:Fe and KTN:Ti. Absorption and photoconductivity measurements correlate the increase with an increased concentration of Fe in the reduced Fe(2+) valence state and to an increased fraction of Fe incorporated into the crystal from the flux.

  16. A combination of positive dielectrophoresis driven on-line enrichment and aptamer-fluorescent silica nanoparticle label for rapid and sensitive detection of Staphylococcus aureus.

    PubMed

    Shangguan, Jingfang; Li, Yuhong; He, Dinggeng; He, Xiaoxiao; Wang, Kemin; Zou, Zhen; Shi, Hui

    2015-07-01

    Staphylococcus aureus (S. aureus) is an important human pathogen that causes several diseases ranging from superficial skin infections to life-threatening diseases. Here, a method combining positive dielectrophoresis (pDEP) driven on-line enrichment and aptamer-fluorescent silica nanoparticle label has been developed for the rapid and sensitive detection of S. aureus in microfluidic channels. An aptamer, having high affinity to S. aureus, is used as the molecular recognition tool and immobilized onto chloropropyl functionalized fluorescent silica nanoparticles through a click chemistry approach to obtain S. aureus aptamer-nanoparticle bioconjugates (Apt(S.aureus)/FNPs). The pDEP driven on-line enrichment technology was used for accumulating the Apt(S.aureus)/FNP labeled S. aureus. After incubating with S. aureus, the mixture of Apt(S.aureus)/FNP labeled S. aureus and Apt(S.aureus)/FNPs was directly introduced into the pDEP-based microfluidic system. By applying an AC voltage in a pDEP frequency region, the Apt(S.aureus)/FNP labelled S. aureus moved to the electrodes and accumulated in the electrode gap, while the free Apt(S.aureus)/FNPs flowed away. The signal that came from the Apt(S.aureus)/FNP labelled S. aureus in the focused detection areas was then detected. Profiting from the specificity of aptamer, signal amplification of FNP label and pDEP on-line enrichment, this assay can detect as low as 93 and 270 cfu mL(-1)S. aureus in deionized water and spiked water samples, respectively, with higher sensitivities than our previously reported Apt(S.aureus)/FNP based flow cytometry. Moreover, without the need for separation and washing steps usually required for FNP label involved bioassays, the total assay time including sample pretreatment was within 2 h.

  17. Inhibition of miR-146b expression increases radioiodine-sensitivity in poorly differential thyroid carcinoma via positively regulating NIS expression

    SciTech Connect

    Li, Luchuan; Lv, Bin; Chen, Bo; Guan, Ming; Sun, Yongfeng; Li, Haipeng; Zhang, Binbin; Ding, Changyuan; He, Shan; Zeng, Qingdong

    2015-07-10

    Dedifferentiated thyroid carcinoma (DTC) with the loss of radioiodine uptake (RAIU) is often observed in clinical practice under radioiodine therapy, indicating the challenge for poor prognosis. MicroRNA (miRNA) has emerged as a promising therapeutic target in many diseases; yet, the role of miRNAs in RAIU has not been generally investigated. Based on recent studies about miRNA expression in papillary or follicular thyroid carcinomas, the expression profiles of several thyroid relative miRNAs were investigated in one DTC cell line, derived from normal DTC cells by radioiodine treatment. The top candidate miR-146b, with the most significant overexpression profiles in dedifferentiated cells, was picked up. Further research found that miR-146b could be negatively regulated by histone deacetylase 3 (HDAC3) in normal cells, indicating the correlation between miR-146b and Na{sup +}/I{sup −} symporter (NIS)-mediated RAIU. Fortunately, it was confirmed that miR-146b could regulate NIS expression/activity; what is more important, miR-146b interference would contribute to the recovery of radioiodine-sensitivity in dedifferentiated cells via positively regulating NIS. In the present study, it was concluded that NIS-mediated RAIU could be modulated by miR-146b; accordingly, miR-146b might serve as one of targets to enhance efficacy of radioactive therapy against poorly differential thyroid carcinoma (PDTC). - Highlights: • Significant upregulated miR-146b was picked up from thyroid relative miRNAs in DTC. • MiR-146b was negatively regulated by HDAC3 in normal thyroid carcinoma cells. • NIS activity and expression could be regulated by miR-146b in thyroid carcinoma. • MiR-146b inhibition could recover the decreased radioiodine-sensitivity of DTC cells.

  18. A sensitive one-step real-time PCR for detection of avian influenza viruses using a MGB probe and an internal positive control

    PubMed Central

    Di Trani, Livia; Bedini, Barbara; Donatelli, Isabella; Campitelli, Laura; Chiappini, Barbara; De Marco, Maria Alessandra; Delogu, Mauro; Buonavoglia, Canio; Vaccari, Gabriele

    2006-01-01

    Background Avian influenza viruses (AIVs) are endemic in wild birds and their introduction and conversion to highly pathogenic avian influenza virus in domestic poultry is a cause of serious economic losses as well as a risk for potential transmission to humans. The ability to rapidly recognise AIVs in biological specimens is critical for limiting further spread of the disease in poultry. The advent of molecular methods such as real time polymerase chain reaction has allowed improvement of detection methods currently used in laboratories, although not all of these methods include an Internal Positive Control (IPC) to monitor for false negative results. Therefore we developed a one-step reverse transcription real time PCR (RRT-PCR) with a Minor Groove Binder (MGB) probe for the detection of different subtypes of AIVs. This technique also includes an IPC. Methods RRT-PCR was developed using an improved TaqMan technology with a MGB probe to detect AI from reference viruses. Primers and probe were designed based on the matrix gene sequences from most animal and human A influenza virus subtypes. The specificity of RRT-PCR was assessed by detecting influenza A virus isolates belonging to subtypes from H1–H13 isolated in avian, human, swine and equine hosts. The analytical sensitivity of the RRT-PCR assay was determined using serial dilutions of in vitro transcribed matrix gene RNA. The use of a rodent RNA as an IPC in order not to reduce the efficiency of the assay was adopted. Results The RRT-PCR assay is capable to detect all tested influenza A viruses. The detection limit of the assay was shown to be between 5 and 50 RNA copies per reaction and the standard curve demonstrated a linear range from 5 to 5 × 108 copies as well as excellent reproducibility. The analytical sensitivity of the assay is 10–100 times higher than conventional RT-PCR. Conclusion The high sensitivity, rapidity, reproducibility and specificity of the AIV RRT-PCR with the use of IPC to monitor

  19. Aqueous Solution Processed Photoconductive Cathode Interlayer for High Performance Polymer Solar Cells with Thick Interlayer and Thick Active Layer.

    PubMed

    Nian, Li; Chen, Zhenhui; Herbst, Stefanie; Li, Qingyuan; Yu, Chengzhuo; Jiang, Xiaofang; Dong, Huanli; Li, Fenghong; Liu, Linlin; Würthner, Frank; Chen, Junwu; Xie, Zengqi; Ma, Yuguang

    2016-09-01

    An aqueous-solution-processed photoconductive cathode interlayer is developed, in which the photoinduced charge transfer brings multiple advantages such as increased conductivity and electron mobility, as well as reduced work function. Average power conversion efficiency over 10% is achieved even when the thickness of the cathode interlayer and active layer is up to 100 and 300 nm, respectively.

  20. Influence of Surface Mobility of Charge Carriers on Cdx Hg1-x Te (x=0,2-0,3) Photoconductivity

    NASA Astrophysics Data System (ADS)

    Salaev, Eldar; Guseýnov, Emil; Ýsmaýlov, Namýk; Tezer, Ateþ

    1997-10-01

    Experimental data on the photoconductivity of CdxHg1-xTe with different surface states are presented. The results are interpreted by he influence of surface mobility of charge carriers on photoeffect phenomena and the value of surface mobility for chemically treated, for polished surface and for aluminium covered surfaces of CdxHg1-xTe crystals are given.

  1. Balancing activity and tolerability of neoadjuvant paclitaxel- and docetaxel-based chemotherapy for HER2-positive early stage breast cancer: sensitivity analysis of randomized trials.

    PubMed

    Carbognin, Luisa; Sperduti, Isabella; Nortilli, Rolando; Brunelli, Matteo; Vicentini, Cecilia; Pellini, Francesca; Pollini, Giovanni Paolo; Giannarelli, Diana; Tortora, Giampaolo; Bria, Emilio

    2015-03-01

    Paclitaxel and docetaxel represent the most adopted taxanes in the neoadjuvant treatment of HER2-positive breast cancer. Questions still remain with regard to their difference in terms of activity and tolerability. Events for pathological complete response (pCR), severe and febrile neutropenia (FN), and severe neurotoxicity were pooled by adopting a fixed- and random-effect model. A sensitivity analysis to test for the interaction between paclitaxel and docetaxel was accomplished. Absolute differences with 95% confidence intervals (CIs) and the number of patients needed to treat/harm (NNT/NNH) were calculated to derive the Likelihood of being Helped or Harmed (LHH). Data from 15 trials (3601 patients) were included. Paclitaxel significantly increases pCR rate by 6.8% in comparison with docetaxel (43.4%, 95% CI 41.1-45.7% versus 36.6%, 95% CI 34.3-39.0%, p=0.0001), regardless of the chemotherapy backbone, with an absolute difference of 9% and 9.2% for anthracycline-based or free-regimens. Paclitaxel significantly improves pCR versus docetaxel with a single HER2-inhibition by 6.7% (p=0.0012), with no difference if combined with a dual HER2-inhibition. Severe neutropenia and FN are significantly lower with paclitaxel, with an absolute difference of 32.4% (p<0.0001) and 2.5% (p=0.0059), respectively. Conversely, severe neurotoxicity is slightly higher with paclitaxel (3%, p=0.0001). The LHH ratio calculated for pCR and severe neutropenia is 2.0 and 0.7 for paclitaxel and docetaxel. Although the activity of neoadjuvant paclitaxel and docetaxel HER2-positive breast cancer is considered similar, the slight advantage in pCR, the significantly lower neutropenia and FN, do favor paclitaxel (in the weekly fashion) over docetaxel, despite the slightly worst neurotoxicity.

  2. THz generation at 1.55 µm excitation: six-fold increase in THz conversion efficiency by separated photoconductive and trapping regions.

    PubMed

    Dietz, Roman J B; Gerhard, Marina; Stanze, Dennis; Koch, Martin; Sartorius, Bernd; Schell, Martin

    2011-12-19

    We present first results on photoconductive THz emitters for 1.55µm excitation. The emitters are based on MBE grown In0.53Ga0.47As/In0.52Al0.48As multilayer heterostructures (MLHS) with high carrier mobility. The high mobility is achieved by spatial separation of photoconductive and trapping regions. Photoconductive antennas made of these MLHS are evaluated as THz emitters in a THz time domain spectrometer (THz TDS). The high carrier mobility and effective absorption significantly increases the optical-to-THz conversion efficiency with THz bandwidth in excess of 3 THz. PMID:22274179

  3. Positive feedback loops for factor V and factor VII activation supply sensitivity to local surface tissue factor density during blood coagulation.

    PubMed

    Balandina, A N; Shibeko, A M; Kireev, D A; Novikova, A A; Shmirev, I I; Panteleev, M A; Ataullakhanov, F I

    2011-10-19

    Blood coagulation is triggered not only by surface tissue factor (TF) density but also by surface TF distribution. We investigated recognition of surface TF distribution patterns during blood coagulation and identified the underlying molecular mechanisms. For these investigations, we employed 1), an in vitro reaction-diffusion experimental model of coagulation; and 2), numerical simulations using a mathematical model of coagulation in a three-dimensional space. When TF was uniformly immobilized over the activating surface, the clotting initiation time in normal plasma increased from 4 min to >120 min, with a decrease in TF density from 100 to 0.7 pmol/m(2). In contrast, surface-immobilized fibroblasts initiated clotting within 3-7 min, independently of fibroblast quantity and despite a change in average surface TF density from 0.5 to 130 pmol/m(2). Experiments using factor V-, VII-, and VIII-deficient plasma and computer simulations demonstrated that different responses to these two TF distributions are caused by two positive feedback loops in the blood coagulation network: activation of the TF-VII complex by factor Xa, and activation of factor V by thrombin. This finding suggests a new role for these reactions: to supply sensitivity to local TF density during blood coagulation.

  4. Characterization of a sub-assembly of 3D position sensitive cadmium zinc telluride detectors and electronics from a sub-millimeter resolution PET system

    NASA Astrophysics Data System (ADS)

    Abbaszadeh, Shiva; Gu, Yi; Reynolds, Paul D.; Levin, Craig S.

    2016-09-01

    Cadmium zinc telluride (CZT) offers key advantages for small animal positron emission tomography (PET), including high spatial and energy resolution and simple metal deposition for fabrication of very small pixel arrays. Previous studies have investigated the intrinsic spatial, energy, and timing resolution of an individual sub-millimeter resolution CZT detector. In this work we present the first characterization results of a system of these detectors. The 3D position sensitive dual-CZT detector module and readout electronics developed in our lab was scaled up to complete a significant portion of the final PET system. This sub-system was configured as two opposing detection panels containing a total of twelve 40~\\text{mm}× 40~\\text{mm}× 5 mm monolithic CZT crystals for proof of concept. System-level characterization studies, including optimizing the trigger threshold of each channel’s comparators, were performed. 68Ge and 137Cs radioactive isotopes were used to characterize the energy resolution of all 468 anode channels in the sub-system. The mean measured global 511 keV photopeak energy resolution over all anodes was found to be 7.35+/- 1.75 % FWHM after correction for photon interaction depth-dependent signal variation. The measured global time resolution was 37 ns FWHM, a parameter to be further optimized, and the intrinsic spatial resolution was 0.76 mm FWHM.

  5. Time-Resolved Imaging of the MALDI Linear-TOF Ion Cloud: Direct Visualization and Exploitation of Ion Optical Phenomena Using a Position- and Time-Sensitive Detector

    NASA Astrophysics Data System (ADS)

    Ellis, Shane R.; Soltwisch, Jens; Heeren, Ron M. A.

    2014-05-01

    In this study, we describe the implementation of a position- and time-sensitive detection system (Timepix detector) to directly visualize the spatial distributions of the matrix-assisted laser desorption ionization ion cloud in a linear-time-of-flight (MALDI linear-ToF) as it is projected onto the detector surface. These time-resolved images allow direct visualization of m/z-dependent ion focusing effects that occur within the ion source of the instrument. The influence of key parameters, namely extraction voltage ( E V ), pulsed-ion extraction (PIE) delay, and even the matrix-dependent initial ion velocity was investigated and were found to alter the focusing properties of the ion-optical system. Under certain conditions where the spatial focal plane coincides with the detector plane, so-called x-y space focusing could be observed (i.e., the focusing of the ion cloud to a small, well-defined spot on the detector). Such conditions allow for the stigmatic ion imaging of intact proteins for the first time on a commercial linear ToF-MS system. In combination with the ion-optical magnification of the system (~100×), a spatial resolving power of 11-16 μm with a pixel size of 550 nm was recorded within a laser spot diameter of ~125 μm. This study demonstrates both the diagnostic and analytical advantages offered by the Timepix detector in ToF-MS.

  6. In the blink of an eye: relating positive-feedback sensitivity to striatal dopamine D2-like receptors through blink rate.

    PubMed

    Groman, Stephanie M; James, Alex S; Seu, Emanuele; Tran, Steven; Clark, Taylor A; Harpster, Sandra N; Crawford, Maverick; Burtner, Joanna Lee; Feiler, Karen; Roth, Robert H; Elsworth, John D; London, Edythe D; Jentsch, James David

    2014-10-22

    For >30 years, positron emission tomography (PET) has proven to be a powerful approach for measuring aspects of dopaminergic transmission in the living human brain; this technique has revealed important relationships between dopamine D2-like receptors and dimensions of normal behavior, such as human impulsivity, and psychopathology, particularly behavioral addictions. Nevertheless, PET is an indirect estimate that lacks cellular and functional resolution and, in some cases, is not entirely pharmacologically specific. To identify the relationships between PET estimates of D2-like receptor availability and direct in vitro measures of receptor number, affinity, and function, we conducted neuroimaging and behavioral and molecular pharmacological assessments in a group of adult male vervet monkeys. Data gathered from these studies indicate that variation in D2-like receptor PET measurements is related to reversal-learning performance and sensitivity to positive feedback and is associated with in vitro estimates of the density of functional dopamine D2-like receptors. Furthermore, we report that a simple behavioral measure, eyeblink rate, reveals novel and crucial links between neuroimaging assessments and in vitro measures of dopamine D2 receptors.

  7. Sensitive monitoring of monoterpene metabolites in human urine using two-step derivatisation and positive chemical ionisation-tandem mass spectrometry.

    PubMed

    Schmidt, Lukas; Belov, Vladimir N; Göen, Thomas

    2013-09-01

    A gas chromatographic-positive chemical ionisation-tandem mass spectrometric (GC-PCI-MS/MS) method for the simultaneous determination of 10 oxidative metabolites of the monoterpenoid hydrocarbons α-pinene, (R)-limonene, and Δ(3)-carene ((+)-3-carene) in human urine was developed and tested for the monoterpene biomonitoring of the general population (n=36). The method involves enzymatic cleavage of the glucuronides followed by solid-supported liquid-liquid extraction and derivatisation using a two-step reaction with N,O-bis(trimethylsilyl)-trifluoroacetamide and N-(trimethylsilyl)imidazole. The method proved to be both sensitive and reliable with detection limits ranging from 0.1 to 0.3 μg L(-1). In contrast to the frequent and distinct quantities of (1S,2S,4R)-limonene-1,2-diol, the (1R,2R,4R)-stereoisomer could not be detected. The expected metabolite of (+)-3-carene, 3-caren-10-ol was not detected in any of the samples. All other metabolites were detected in almost all urine samples. The procedure enables for the first time the analysis of trace levels of a broad spectrum of mono- and bicyclic monoterpenoid metabolites (alcohols, diols, and carboxylic acids) in human urine. This analytical procedure is a powerful tool for population studies as well as for the discovery of human metabolism and toxicokinetics of monoterpenes. PMID:23953203

  8. Preparation of hydrogenated amorphous silicon and its characterization by transient photoconductivity

    SciTech Connect

    Walker, C.M.

    1992-12-31

    Hydrogenated amorphous silicon (a-Si:H) is a semiconductor material that has generated recent widespread interest because of its low manufacturing and processing costs compared with other semiconducting materials. The performance of devices incorporating a-Si:H depends to a large extent on the photoresponse of the a-Si:H. The work in this thesis involves the construction of an a-Si:H plasma-enhanced chemical vapor deposition (PECVD) system, characterization of the quality of the a-Si:H produced by this system, and measurement of the transient photoconductivity n response to pulses of laser illumination with different durations. The relationship of the design of the PECVD system to the quality of the a-Si:H is treated, emphasizing the features included in the system to reduce the incorporation of defects in the a-Si:H layers. These features include an ultra-high-vacuum deposition chamber, a load-lock chamber enabling samples to be loaded under vacuum, and an electrode assembly designed to produce a uniform electric field for decomposing the reactant gases. The quality of the A-Si:H films is examined. The dark conductivity activation energy, optical absorption, and photoconductivity are measured to characterize intrinsic, p-doped, and n-doped a-Si:H layers. The current vs. voltage characteristics under illuminated and dark conditions, and the quantum efficiency are measured on a-Si:H p-i-n diodes made in our system, and the results show that these diodes compare favorably to similar high-quality p-i-n diodes produced at other laboratories. An investigation into the effect of the light-induced degradation associated with a-Si:H on the performance of OASLMs is also presented. Finally, the transient photoresponse to laser pulses ranging in duration from 1 {mu}s to 1 s over a range of temperatures from 100 to 300 K is investigated. We have discovered that the response time of the initial photoconductivity decay increases as the excitation-pulse duration increases.

  9. 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.

  10. Influence of temperature and bias voltage on the performance of a high resolution PET detector built with position sensitive avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Vandenbroucke, A.; McLaughlin, T. J.; Levin, C. S.

    2012-08-01

    We evaluate the performance of an 8 × 8 array of 0.9 × 0.9 × 1 mm3 cerium doped lutetium oxyothosilicate (LSO) crystals coupled to a position sensitive avalanche photodiode (PSAPD) as a function of bias voltage and temperature. We use this detector to develop a general methodology to optimize bias voltage, temperature, and gain for PET detectors using semiconductor photodetectors. This detector module will be used in a novel high resolution positron emission tomography (PET) camera dedicated to breast imaging under construction in our lab. Due to the tight packing of many PSAPDs in the system a thermal gradient is expected across the imaging heads. Data were collected for 11 PSAPD temperatures between 5°C and 40°C using a thermo-electric (Peltier) device. At each temperature the bias voltage was varied in steps of 5 V over a 50 V range. We present three methods to predict the optimal bias voltage at every temperature: one based on optimizing the coincidence time resolution, the others based on the relative change in PSAPD gain and leakage current due to the onset of hole multiplication. Optimal gain could also be predicted based on the quality of the flood histogram. At optimal bias voltage, the energy resolution degrades as (10.5±0.1)+((0.038±0.006)/ °C·T)%. Time resolution stays constant at 2.37±0.02 ns below 15°C. Above this temperature, time resolution deteriorates as (1.67±0.06)+((0.042±0.002)/°C·T)ns. Even at high temperatures, all 64 crystal position peaks in the flood histogram are still clearly visible. The width of the peaks in the flood histogram show a quadratic degradation with temperature: (2.6±0.1)·10-2+(1.6±0.2)·10-5/(°C)2·T2. We conclude that both the quality of the flood histogram as well as the coincidence time resolution are better parameters to estimate the optimal bias voltage, than energy resolution. Optimal bias voltage is found to be dependent on the value of k, the ratio between hole and electron multiplication. We

  11. 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

  12. Deep-ultraviolet solar-blind photoconductivity of individual gallium oxide nanobelts.

    PubMed

    Li, Liang; Auer, Erwin; Liao, Meiyong; Fang, Xiaosheng; Zhai, Tianyou; Gautam, Ujjal K; Lugstein, Alois; Koide, Yasuo; Bando, Yoshio; Golberg, Dmitri

    2011-03-01

    We designed solar-blind deep-ultraviolet semiconductor photodetectors using individual Ga2O3 nanobelts. The photoconductive behavior was systematically studied. The photodetectors demonstrate high selectivity towards 250 nm light, fast response times of less than 0.3 s, and a large photocurrent to dark current ratio of up to 4 orders of magnitude. The photoresponse parameters such as photocurrent, response time, and quantum efficiency depend strongly on the intensity of light, the detector environment, and the nanobelt size. The photoresponse mechanism was discussed, which was mainly attributed to the band bending, surface traps, and distribution of traps in the bandgap. Present Ga2O3 nanobelts can be exploited for future applications in photo sensing, light-emitting diodes, and optical switches.

  13. Horizontal transfer of aligned Si nanowire arrays and their photoconductive performance

    PubMed Central

    2014-01-01

    An easy and low-cost method to transfer large-scale horizontally aligned Si nanowires onto a substrate is reported. Si nanowires prepared by metal-assisted chemical etching were assembled and anchored to fabricate multiwire photoconductive devices with standard Si technology. Scanning electron microscopy images showed highly aligned and successfully anchored Si nanowires. Current-voltage tests showed an approximately twofold change in conductivity between the devices in dark and under laser irradiation. Fully reversible light switching ON/OFF response was also achieved with an ION/IOFF ratio of 230. Dynamic response measurement showed a fast switching feature with response and recovery times of 10.96 and 19.26 ms, respectively. PMID:25520603

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

    SciTech Connect

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

    2014-11-15

    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., H{sub 2}, D{sub 2}, Ne, Ar., etc.) that have enough energy to create MeV photons from either bremsstrahlung and/or (n,n{sup ′}) reactions if D{sub 2} 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.

  15. Gamma ray measurements with photoconductive detectors using a dense plasma focusa)

    NASA Astrophysics Data System (ADS)

    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.

  16. High effective terahertz radiation from semi-insulating-GaAs photoconductive antennas with ohmic contact electrodes

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Hou, Lei; Wang, Xinmei

    2011-07-01

    Terahertz (THz) radiation efficiency of a photoconductive antenna with Schottky contact electrodes is low because the electrical field is limited to a narrow region close to the anode. However, the electrical field in the gap of an antenna with ohmic contact electrodes is more uniform, which contributes to improving THz generation efficiency. In this paper, the semi-insulating (SI)-GaAs antennas with ohmic contact electrodes and SI-GaAs antennas with Schottky contact electrodes were fabricated by using AuGeNi alloy electrodes and Ti/Au electrodes, respectively. The voltage-ampere characteristic and the distribution of electrical field of the two kinds of antennas were tested. At the same condition, the THz intensity from the antenna with ohmic contact electrodes was 3-8 times higher than that from the antenna with Schottky contact electrodes, and the larger gap antennas with ohmic contact electrodes have higher optical and electrical energy to THz intensity conversion efficiency.

  17. Dark and photo-conductivity of doctor-bladed CZTS films above room temperature

    NASA Astrophysics Data System (ADS)

    Ghediya, Prashant R.; Chaudhuri, Tapas K.

    2015-11-01

    The temperature variation of electrical conductivity of Cu2ZnSnS4 (CZTS) films in the dark and under light has been studied in the temperature range of 350-500 K. CZTS films were deposited on glass substrates by doctor-blade printing from microwave-processed nanoparticle ink. X-ray diffraction and Raman spectroscopy confirm the formation of kesterite CZTS. Thermoelectric measurements show the films are basically p-type. The electrical conductivity of CZTS films increases with temperature and it is found to be thermally activated. An analysis of the temperature variation of dark and illuminated conductivity reveals that the transport of holes in these films is due to the thermionic emission over grain boundary barriers. The films are photoconducting in nature. Under illumination, the grain boundary barrier height of these films decreases due to photogenerated charge carriers.

  18. 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.

  19. Transient photoconductivity of a -Si sub 1 minus x Ge sub x :H alloys

    SciTech Connect

    Kunst, M.; Neitzert, H.C. ); Ruebel, H. )

    1991-07-15

    Contactless measurements of the transient photoconductivity in {ital a}-Si:H and in {ital a}-Si{sub 1{minus}{ital x}}Ge{sub {ital x}}:H alloys are reported. A decrease of the effective electron mobility with increasing Ge content is observed. Because of a difference of dependence of the excitation density, two different processes are distinguished that lead to this decrease of the mobility. One is attributed to trapping and the other one leads to a decrease of the drift mobility. No increase of the recombination rate upon alloying of {ital a}-Si:H with Ge is observed as, on the contrary, the long-time decay in alloys is slower than in pure {ital a}-Si:H.

  20. Photoconductivity of PbSe quantum-dot solids: dependence on ligand anchor group and length.

    PubMed

    Gao, Yunan; Aerts, Michiel; Sandeep, C S Suchand; Talgorn, Elise; Savenije, Tom J; Kinge, Sachin; Siebbeles, Laurens D A; Houtepen, Arjan J

    2012-11-27

    The assembly of quantum dots is an essential step toward many of their potential applications. To form conductive solids from colloidal quantum dots, ligand exchange is required. Here we study the influence of ligand replacement on the photoconductivity of PbSe quantum-dot solids, using the time-resolved microwave conductivity technique. Bifunctional replacing ligands with amine, thiol, or carboxylic acid anchor groups of various lengths are used to assemble quantum solids via a layer-by-layer dip-coating method. We find that when the ligand lengths are the same, the charge carrier mobility is higher in quantum-dot solids with amine ligands, while in quantum-dot solids with thiol ligands the charge carrier lifetime is longer. If the anchor group is the same, the charge carrier mobility is ligand length dependent. The results show that the diffusion length of charge carriers can reach several hundred nanometers.

  1. Synthesis, characterization and enhanced photoconductivity from a mesoporous titania on dye doping.

    PubMed

    Pal, Nabanita; Paul, Manidipa; Bera, Ashoke; Basak, Durga; Bhaumik, Asim

    2010-07-26

    New wormhole-like mesoporous TiO(2) material has been synthesized through a convenient sol-gel method in the presence of a Schiff base secondary amine hexadecyl-2-pyrrole-methylamine (HPMA) containing chelating donor sites as template or structure directing agent (SDA). SDA molecules can be easily removed from the composite to generate mesoporosity and upon removal of the SDA molecule, this mesoporous TiO(2) material showed very high surface area (480+/-10 m(2)/g) with an average pore diameter of 2.57+/-0.05 nm. When Rose Bengal dye is entrapped inside the nanopores of this material, it showed a drastic enhancement (ca. 40-folds) in the photoconductivity vis-à-vis mesoporous TiO(2) alone under white light illumination.

  2. Synchronization of two GaAs photoconductive semiconductor switches triggered by two laser diodes.

    PubMed

    Xu, Ming; Bian, Kangkang; Ma, Cheng; Jia, Hangjuan; An, Xin; Shi, Wei

    2016-09-15

    In this Letter, we show the synchronization of two 2-mm-gap gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS), which are in parallel and triggered by two laser diodes (LDs) independently. The comparison of the synchronization is measured by varying the bias electric field and optical excitation energy, respectively. An optimum synchronization is achieved as low as 200.5 ps, while the GaAs PCSS are biased at 1.2 kV with optical excitation energy of 1.91 μJ. The simulations demonstrate the relationship between the synchronization, the carriers average drift velocity, and the number of carriers undergoing intervalley scattering. PMID:27628404

  3. Interfacial Donor-Acceptor Engineering of Nanofiber Materials To Achieve Photoconductivity and Applications.

    PubMed

    Zang, Ling

    2015-10-20

    Self-assembly of π-conjugate molecules often leads to formation of well-defined nanofibril structures dominated by the columnar π-π stacking between the molecular planes. These nanofibril materials have drawn increasing interest in the research frontiers of nanomaterials and nanotechnology, as the nanofibers demonstrate one-dimensionally enhanced exciton and charge diffusion along the long axis, and present great potential for varying optoelectronic applications, such as sensors, optics, photovoltaics, and photocatalysis. However, poor electrical conductivity remains a technical drawback for these nanomaterials. To address this problem, we have developed a series of nanofiber structures modified with different donor-acceptor (D-A) interfaces that are tunable for maximizing the photoinduced charge separation, thus leading to increase in the electrical conductivity. The D-A interface can be constructed with covalent linker or noncovalent interaction (e.g., hydrophobic interdigitation between alkyl chains). The noncovalent method is generally more flexible for molecular design and solution processing, making it more adaptable to be applied to other fibril nanomaterials such as carbon nanotubes. In this Account, we will discuss our recent discoveries in these research fields, aiming to provide deep insight into the enabling photoconductivity of nanofibril materials, and the dependence on interface structure. The photoconductivity generated with the nanofibril material is proportional to the charge carriers density, which in turn is determined by the kinetics balance of the three competitive charge transfer processes: (1) the photoinduced electron transfer from D to A (also referred to as exciton dissociation), generating majority charge carrier located in the nanofiber; (2) the back electron transfer; and (3) the charge delocalization along the nanofiber mediated by the π-π stacking interaction. The relative rates of these charge transfer processes can be tuned by

  4. Giant persistent photoconductivity in BaTiO{sub 3}/TiO{sub 2} heterostructures

    SciTech Connect

    Plodinec, Milivoj; Šantić, Ana; Gajović, Andreja; Zavašnik, Janez; Čeh, Miran

    2014-10-13

    The persistent photoconductivity (PPC) effect in nanotube arrays of barium titanate and TiO{sub 2} (BTO/TiO{sub 2}NT) was studied at room temperature under daylight illumination. The BTO/TiO{sub 2}NT heterostructures exhibited a giant PPC effect that was six orders of magnitude higher than the dark conductivity, followed by a slow relaxation for 3 h. The PPC in this material was explained by the existence of defects at the surfaces and the interfaces of the investigated heterostructures. The sample was prepared using a two-step synthesis: the anodization of a Ti-foil and a subsequent hydrothermal synthesis. The structural and electrical characteristics were studied by micro-Raman spectroscopy, field-emission-gun scanning electron microscopy, and impedance spectroscopy.

  5. Toward a 1550 nm InGaAs photoconductive switch for terahertz generation.

    PubMed

    Williams, Kimani K; Taylor, Z D; Suen, J Y; Lu, Hong; Singh, R S; Gossard, A C; Brown, E R

    2009-10-15

    We report a terahertz (THz) photoconductive switch made from a composite of metal ErAs nanoparticles embedded in In(0.53)Ga(0.47)As and coupled to a square spiral antenna. The THz output power was measured in a 77 K cryostat by using a standard hyperhemisphere-lens package, a Golay cell outside the cryostat, and a quasi-optical filter bank for spot frequency spectral measurements. Results indicate an average output power of approximately 12 microW at 22 V bias using 140 mW of optical pump power from a subpicosecond fiber mode-locked laser. In addition, the THz spectra displayed invariance to bias voltage despite operating near impact ionization.

  6. Improved efficiency of photoconductive THz emitters by increasing the effective contact length of electrodes

    SciTech Connect

    Singh, Abhishek; Surdi, Harshad; Nikesh, V. V.; Prabhu, S. S.; Döhler, G. H.

    2013-12-15

    We study the effect of a surface modification at the interface between metallic electrodes and semiconducting substrate in Semi-Insulating GaAs (SI-GaAs) based photoconductive emitters (PCE) on the emission of Tera-Hertz (THz) radiation. We partially etch out a 500 nm thick layer of SI-GaAs in grating like pattern with various periods before the contact deposition. By depositing the electrodes on the patterned surface, the electrodes follow the contour of the grating period. This increases the effective contact length of the electrodes per unit area of the active regions on the PCE. The maxima of the electric field amplitude of the THz pulses emitted from the patterned surface are enhanced by up to more than a factor 2 as compared to an un-patterned surface. We attribute this increase to the increase of the effective contact length of the electrode due to surface patterning.

  7. Synchronization of two GaAs photoconductive semiconductor switches triggered by two laser diodes.

    PubMed

    Xu, Ming; Bian, Kangkang; Ma, Cheng; Jia, Hangjuan; An, Xin; Shi, Wei

    2016-09-15

    In this Letter, we show the synchronization of two 2-mm-gap gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS), which are in parallel and triggered by two laser diodes (LDs) independently. The comparison of the synchronization is measured by varying the bias electric field and optical excitation energy, respectively. An optimum synchronization is achieved as low as 200.5 ps, while the GaAs PCSS are biased at 1.2 kV with optical excitation energy of 1.91 μJ. The simulations demonstrate the relationship between the synchronization, the carriers average drift velocity, and the number of carriers undergoing intervalley scattering.

  8. Ultrabroadband terahertz field detection by proton-bombarded InP photoconductive antennas.

    PubMed

    Liu, Tze-An; Tani, Masahiko; Nakajima, Makoto; Hangyo, Masanori; Sakai, Kiyomi; Nakashima, Shin-Ichi; Pan, Ci-Ling

    2004-06-28

    Photoconductive (PC) antennas fabricated on InP bombarded with 180 keV protons of different dosages (InP:H+) all exhibit a useful bandwidth of about 30 THz, comparable to that of the LT-GaAs PC antenna. The peak signal current of the best InP: H+ device (dosage of 10;15 ions/cm;2) is slightly higher than that of the LT-GaAs one, while the signal-to-noise ratio (SNR) of the former is about half of that of the latter due to lower resistivity. This suggests that InP: H+ can be a good substrate for THz PC antennas with proper annealing and/or implantation recipe. PMID:19483812

  9. Terahertz near-field microscopy with subwavelength spatial resolution based on photoconductive antennas.

    PubMed

    Bitzer, Andreas; Ortner, Alex; Walther, Markus

    2010-07-01

    Imaging and sensing applications based on pulsed terahertz radiation have opened new possibilities for scientific and industrial applications. Many exploit the unique features of the terahertz (THz) spectral region, where common packaging materials are transparent and many chemical compounds show characteristic absorptions. Because of their diffraction limit, THz far-field imaging techniques lack microscopic resolution and, if subwavelength features have to be resolved, near-field techniques are required. Here, we present a THz near-field microscopy approach based on photoconductive antennas as the THz emitter and as a near-field probe. Our system allows us to measure amplitude, phase, and polarization of the electric fields in the vicinity of a sample with a spatial resolution on the micrometer scale (approximately lambda/20). Using a dielectric (plant leaf) and a metallic structure (microwire) as examples, we demonstrate the capabilities of our approach. PMID:20648112

  10. Photoconductive response in organic charge transfer interfaces with high quantum efficiency.

    PubMed

    Alves, Helena; Pinto, Rui M; Maçôas, Ermelinda S

    2013-01-01

    Organic semiconductors have unique optical, mechanical and electronic properties that can be combined with customized chemical functionality. In the crystalline form, determinant features for electronic applications, such as molecular purity, the charge mobility or the exciton diffusion length, reveal a superior improved performance when compared with materials in a more disordered form. However, the use of organic single crystals in devices is still limited to a few applications, such as field-effect transistors. Here we report the first example of photoconductive behaviour of single-crystal charge-transfer interfaces. The system composed of rubrene and 7,7,8,8-tetracyanoquinodimethane presents a responsivity reaching 1 AW(-1), corresponding to an external quantum efficiency of nearly 100%. This result opens the possibility of using organic single-crystal interfaces in photonic applications. PMID:23673627

  11. Multi-bands photoconductive response in AlGaN/GaN multiple quantum wells

    SciTech Connect

    Chen, G.; Rong, X.; Xu, F. J.; Tang, N.; Wang, X. Q. Shen, B.; Fu, K.; Zhang, B. S.; Hashimoto, H.; Yoshikawa, A.; Ge, W. K.

    2014-04-28

    Based on the optical transitions among the quantum-confined electronic states in the conduction band, we have fabricated multi-bands AlGaN/GaN quantum well infrared photodetectors. Crack-free AlGaN/GaN multiple quantum wells (MQWs) with atomically sharp interfaces have been achieved by inserting an AlN interlayer, which releases most of the tensile strain in the MQWs grown on the GaN underlayer. With significant reduction of dark current by using thick AlGaN barriers, photoconductive responses are demonstrated due to intersubband transition in multiple regions with center wavelengths of 1.3, 2.3, and 4 μm, which shows potential applications on near infrared detection.

  12. Emission characteristics of photoconductive antennas based on low-temperature-grown GaAs and semi-insulating GaAs.

    PubMed

    Tani, M; Matsuura, S; Sakai, K; Nakashima, S

    1997-10-20

    Terahertz radiation was generated with several designs of photoconductive antennas (three dipoles, a bow tie, and a coplanar strip line) fabricated on low-temperature-grown (LT) GaAs and semi-insulating (SI) GaAs, and the emission properties of the photoconductive antennas were compared with each other. The radiation spectrum of each antenna was characterized with the photoconductive sampling technique. The total radiation power was also measured by a bolometer for comparison of the relative radiation power. The radiation spectra of the LT-GaAs-based and SI-GaAs-based photoconductive antennas of the same design showed no significant difference. The pump-power dependencies of the radiation power showed saturation for higher pump intensities, which was more serious in SI-GaAs-based antennas than in LT-GaAs-based antennas. We attributed the origin of the saturation to the field screening of the photocarriers. PMID:18264312

  13. Fine Tuning of CaV1.3 Ca2+ Channel Properties in Adult Inner Hair Cells Positioned in the Most Sensitive Region of the Gerbil Cochlea

    PubMed Central

    Zampini, Valeria; Johnson, Stuart L.; Franz, Christoph; Knipper, Marlies; Holley, Matthew C.; Magistretti, Jacopo; Russo, Giancarlo; Marcotti, Walter; Masetto, Sergio

    2014-01-01

    Hearing relies on faithful signal transmission by cochlear inner hair cells (IHCs) onto auditory fibres over a wide frequency and intensity range. Exocytosis at IHC ribbon synapses is triggered by Ca2+ inflow through CaV1.3 (L-type) Ca2+ channels. We investigated the macroscopic (whole-cell) and elementary (cell-attached) properties of Ca2+ currents in IHCs positioned at the middle turn (frequency ∼2 kHz) of the adult gerbil cochlea, which is their most sensitive hearing region. Using near physiological recordings conditions (body temperature and a Na+ based extracellular solution), we found that the macroscopic Ca2+ current activates and deactivates very rapidly (time constant below 1 ms) and inactivates slowly and only partially. Single-channel recordings showed an elementary conductance of 15 pS, a sub-ms latency to first opening, and a very low steady-state open probability (Po: 0.024 in response to 500-ms depolarizing steps at ∼−18 mV). The value of Po was significantly larger (0.06) in the first 40 ms of membrane depolarization, which corresponds to the time when most Ca2+ channel openings occurred clustered in bursts (mean burst duration: 19 ms). Both the Po and the mean burst duration were smaller than those previously reported in high-frequency basal IHCs. Finally, we found that middle turn IHCs are likely to express about 4 times more Ca2+ channels per ribbon than basal cells. We propose that middle-turn IHCs finely-tune CaV1.3 Ca2+ channel gating in order to provide reliable information upon timing and intensity of lower-frequency sounds. PMID:25409445

  14. Highly sensitive and selective analysis of urinary steroids by comprehensive two-dimensional gas chromatography combined with positive chemical ionization quadrupole mass spectrometry

    PubMed Central

    Zhang, Ying; Tobias, Herbert J.; Brenna, J. Thomas

    2014-01-01

    Comprehensive two dimensional gas chromatography (GC×GC) provides greater separation space than conventional GC. Because of fast peak elution, a time of flight mass spectrometer (TOFMS) is the usual structure-specific detector of choice. The quantitative capabilities of a novel GC×GC fast quadrupole MS were investigated with electron ionization (EI), and CH4 or NH3 positive chemical ionization (PCI) for analysis of endogenous urinary steroids targeted in anti-doping tests. Average precisions for steroid quantitative analysis from replicate urine extractions were 6% (RSD) for EI and 8% for PCI-NH3. The average limits of detection (LOD) calculated by quantification ions for 12 target steroids spiked into steroid-free urine matrix (SFUM) were 2.6 ng mL−1 for EI, 1.3 ng mL−1 for PCI-CH4, and 0.3 ng mL−1 for PCI-NH3, all in mass scanning mode. The measured limits of quantification (LOQ) with full mass scan GC×GC-qMS were comparable with the LOQ values measured by one-dimensional GC-MS in single ion monitoring (SIM) mode. PCI-NH3 yields fewer fragments and greater (pseudo)molecular ion abundances than EI or PCI-CH4. These data show a benchtop GC×GC-qMS system has the sensitivity, specificity, and resolution to analyze urinary steroids at normal urine concentrations, and that PCI-NH3, not currently available on most GC×GC-TOFMS instruments, is of particular value for generation of structure-specific ions. PMID:22606686

  15. 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

  16. Coexistence of electron-glass phase and persistent photoconductivity in GeSbTe compounds

    NASA Astrophysics Data System (ADS)

    Ovadyahu, Z.

    2015-03-01

    It is demonstrated that persistent photoconductivity (PPC), well studied in lightly-doped semiconductors, is observable in GeSbTe compounds using infrared excitation at cryogenic temperatures. The low levels of energy flux necessary to induce an appreciable effect seems surprising given the high carrier concentration n of these ternary alloys (n >1020cm-3 ). On the other hand, their high density of carriers makes GeSbTe films favorable candidates for exhibiting intrinsic electron-glass effects with long relaxation times. These are indeed observed in GeSbTe thin films that are Anderson-localized. In particular, a memory dip is observed in samples with sheet resistances larger than ≈105Ω at T ≈4 K with similar characteristics as in other systems that exhibit intrinsic electron-glass effects. Persistent photoconductivity, however, is observable in GeSbTe films even for sheet resistances of the order of 103Ω , well below the range of disorder required for observing electron-glass effects. These two nonequilibrium phenomena, PPC and electron glass, are shown to be of different nature in terms of other aspects as well. In particular, their relaxation dynamics is qualitatively different; the excess conductance Δ G associated with PPC decays with time as a stretched exponential whereas a logarithmic relaxation law characterizes Δ G (t ) of all electron glasses studied to date. Surprisingly, the magnitude of the memory dip is enhanced when the system is in the PPC state. This counter-intuitive result may be related to the compositional disorder in these materials extending over mesoscopic scales. Evidence in support of this scenario is presented and discussed.

  17. Interaction of light with the ZnO surface: Photon induced oxygen “breathing,” oxygen vacancies, persistent photoconductivity, and persistent photovoltage

    SciTech Connect

    Gurwitz, Ron; Cohen, Rotem; Shalish, Ilan

    2014-01-21

    ZnO surfaces adsorb oxygen in the dark and emit CO{sub 2} when exposed to white light, reminiscent of the lungs of living creatures. We find that this exchange of oxygen with the ambient affects the integrity of the ZnO surface. Thus, it forms a basis for several interesting surface phenomena in ZnO, such as photoconductivity, photovoltage, and gas sensing, and has a role in ZnO electrical conduction. Using x-ray photoelectron spectroscopy on ZnO nanowires, we observed a decomposition of ZnO under white light and formation of oxygen-depleted surface, which explains photoconductivity by the electron donation of oxygen vacancies. Our findings suggest that the observed decomposition of the ZnO lattice may only take place due to photon-induced reduction of ZnO by carbon containing molecules (or carbo-photonic reduction), possibly from the ambient gas, accounting in a consistent way for both the reduced demands on the energy required for decomposition and for the observed emission of lattice oxygen in the form of CO{sub 2}. The formation of oxygen-vacancy rich surface is suggested to induce surface delta doping, causing accumulation of electrons at the surface, which accounts for both the increase in conductivity and the flattening of the energy bands. Using surface photovoltage spectroscopy in ultra high vacuum, we monitored changes in the deep level spectrum. We observe a wide optical transition from a deep acceptor to the conduction band, which energy position coincides with the position of the so called “green luminescence” in ZnO. This green transition disappears with the formation of surface oxygen vacancies. Since the oxygen vacancies are donors, while the green transition involves surface acceptors, the results suggest that the initial emission of oxygen originates at the defect sites of the latter, thereby eliminating each other. This suggests that the green transition originates at surface Zn vacancy acceptors. Removing an oxygen atom from a Zn vacancy

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

    SciTech Connect

    Aoki, Makoto; Hiromoto, Norihisa

    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 on 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.

  19. The Effect of Deposition Temperature to Photoconductivity Properties of Amorphous Carbon Thin Films Deposited By Thermal CVD

    NASA Astrophysics Data System (ADS)

    Mohamad, F.; Suriani, A. B.; Noor, U. M.; Rusop, M.

    2010-07-01

    Amorphous carbon (a-C) thin films were deposited by thermal chemical vapor deposition (CVD) using camphor oil on quartz substrates. The photoconductivity and optical properties of the thin films were studied with varying the deposition temperatures ranging from 650 to 900 °C. The film deposited at 750 °C shows large photoconductivity compare to other films. The optical characterization shows that the optical band gap of the thin films decreased from 0.65 to ˜0.0eV with increasing the deposition temperature due to the increase of sp2 bonded carbon configuration. The electrical conductivity of the thin films grown at higher temperature is much higher compared with the thin films deposited at low temperature.

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

    SciTech Connect

    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.