Low leakage current Ni/CdZnTe/In diodes for X/ γ-ray detectors

NASA Astrophysics Data System (ADS)

Sklyarchuk, V. M.; Gnatyuk, V. A.; Pecharapa, W.

2018-01-01

The electrical characteristics of the Ni/Cd1-xZnxTe/In structures with a metal-semiconductor rectifying contact are investigated. The diodes, fabricated on the base of In-doped n-type Cd1-xZnxTe (CZT) crystals with resistivity of ∼1010 Ω ṡ cm, have low leakage current and can be used as X/ γ-ray detectors. The rectifying contact was obtained by vacuum deposition of Ni on the semiconductor surface pretreated with argon plasma. The high barrier rectifying contact allowed us to increase applied reverse bias voltage up to 2500 V at the CZT crystal thickness of 1 mm. Dark (leakage) currents of the diodes with the rectifying contact area of 4 mm2 did not exceed 3-5 nA at bias voltage of 2000 V and room temperature. The charge transport mechanisms in the Ni/CZT/In structures have been interpreted as generation-recombination in the space charge region within the range of reverse bias of 5-100 V and as currents limited by space charge at both forward and reverse bias at V >100 V.

The features of the Cosmic Web unveiled by the flip-flop field

NASA Astrophysics Data System (ADS)

Shandarin, Sergei F.; Medvedev, Mikhail V.

2017-07-01

Currently the dark matter environment is widely accepted as a framework for understanding of the observed structure in the universe. N-body simulations are indispensable for the analysis of the formation and evolution of the dark matter web. Two primary fields - density and velocity fields - are used in most of studies. Dark matter provides two additional fields that are unique for collisionless media only. They are the multistream field in Eulerian space and flip-flop field in Lagrangian space. The flip-flop field represents the number of sign reversals of an elementary volume of each collisionless fluid element. This field can be estimated by counting the sign reversals of the Jacobian at each particle at every time step of the simulation. The Jacobian is evaluated by numerical differentiation of the Lagrangian submanifold, I.e. the three-dimensional dark matter sheet in the six-dimensional space formed by three Lagrangian and three Eulerian coordinates. We present the results of the statistical study of the evolution of the flip-flop field from z = 50 to the present time z = 0. A number of statistical characteristics show that the pattern of the flip-flop field remains remarkably stable from z ≈ 30 to the present time. As a result the flip-flop field evaluated at z = 0 stores a wealth of information about the dynamical history of the dark matter web. In particular one of the most intriguing properties of the flip-flop is a unique capability to preserve the information about the merging history of haloes.

Modulation of the reaction cycle of the Na+:Ca2+, K+ exchanger.

PubMed

Vedovato, Natascia; Rispoli, Giorgio

2007-09-01

Ca(2+) concentration in retinal photoreceptor rod outer segment (OS) strongly affects the generator potential kinetics and the receptor light adaptation. The response to intense light stimuli delivered in the dark produce potential changes exceeding 40 mV: since the Ca(2+) extrusion in the OS is entirely controlled by the Na(+):Ca(2+), K(+) exchanger, it is important to assess how the exchanger ion transport rate is affected by the voltage and, in general, by intracellular factors. It is indeed known that the cardiac Na(+):Ca(2+) exchanger is regulated by Mg-ATP via a still unknown metabolic pathway. In the present work, the Na(+):Ca(2+), K(+) exchanger regulation was investigated in isolated OS, recorded in whole-cell configuration, using ionic conditions that activated maximally the exchanger in both forward and reverse mode. In all species examined (amphibia: Rana esculenta and Ambystoma mexicanum; reptilia: Gecko gecko), the forward (reverse) exchange current increased about linearly for negative (positive) voltages and exhibited outward (inward) rectification for positive (negative) voltages. Since hyperpolarisation increases Ca(2+) extrusion rate, the recovery of the dark level of Ca(2+) (and, in turn, of the generator potential) after intense light stimuli results accelerated. Mg-ATP increased the size of forward and reverse exchange current by a factor of approximately 2.3 and approximately 2.6, respectively, without modifying their voltage dependence. This indicates that Mg-ATP regulates the number of active exchanger sites and/or the exchanger turnover number, although via an unknown mechanism.

Distinct Roles of NMDAR and mGluR5 in Light Exposure Reversal of Feedforward Synaptic Strength in V1 of Juvenile Mice after Binocular Vision Deprivation.

PubMed

Tie, Xiaoxiu; Li, Shuo; Feng, Yilin; Lai, Biqin; Liu, Sheng; Jiang, Bin

2018-06-01

In the visual cortex, sensory deprivation causes global augmentation of the amplitude of AMPA receptor-mediated miniature EPSCs in layer 2/3 pyramidal cells and enhancement of NMDA receptor-dependent long-term potentiation (LTP) in cells activated in layer 4, effects that are both rapidly reversed by light exposure. Layer 2/3 pyramidal cells receive both feedforward input from layer 4 and intra-cortical lateral input from the same layer, LTP is mainly induced by the former input. Whether feedforward excitatory synaptic strength is affected by visual deprivation and light exposure, how this synaptic strength correlates with the magnitude of LTP in this pathway, and the underlying mechanism have not been explored. Here, we showed that in juvenile mice, both dark rearing and dark exposure reduced the feedforward excitatory synaptic strength, and the effects can be reversed completely by 10-12 h and 6-8 h light exposure, respectively. However, inhibition of NMDA receptors by CPP or mGluR5 by MPEP, prevented the effect of light exposure on the mice reared in the dark from birth, while only inhibition of NMDAR prevented the effect of light exposure on dark-exposed mice. These results suggested that the activation of both NMDAR and mGluR5 are essential in the light exposure reversal of feedforward excitatory synaptic strength in the dark reared mice from birth; while in the dark exposed mice, only activation of NMDAR is required. Copyright © 2018. Published by Elsevier Ltd.

Advances in the characterization of InAs/GaSb superlattice infrared photodetectors

NASA Astrophysics Data System (ADS)

Wörl, A.; Daumer, V.; Hugger, T.; Kohn, N.; Luppold, W.; Müller, R.; Niemasz, J.; Rehm, R.; Rutz, F.; Schmidt, J.; Schmitz, J.; Stadelmann, T.; Wauro, M.

2016-10-01

This paper reports on advances in the electro-optical characterization of InAs/GaSb short-period superlattice infrared photodetectors with cut-off wavelengths in the mid-wavelength and long-wavelength infrared ranges. To facilitate in-line monitoring of the electro-optical device performance at different processing stages we have integrated a semi-automated cryogenic wafer prober in our process line. The prober is configured for measuring current-voltage characteristics of individual photodiodes at 77 K. We employ it to compile a spatial map of the dark current density of a superlattice sample with a cut-off wavelength around 5 μm patterned into a regular array of 1760 quadratic mesa diodes with a pitch of 370 μm and side lengths varying from 60 to 350 μm. The different perimeter-to-area ratios make it possible to separate bulk current from sidewall current contributions. We find a sidewall contribution to the dark current of 1.2×10-11 A/cm and a corrected bulk dark current density of 1.1×10-7 A/cm2, both at 200 mV reverse bias voltage. An automated data analysis framework can extract bulk and sidewall current contributions for various subsets of the test device grid. With a suitable periodic arrangement of test diode sizes, the spatial distribution of the individual contributions can thus be investigated. We found a relatively homogeneous distribution of both bulk dark current density and sidewall current contribution across the sample. With the help of an improved capacitance-voltage measurement setup developed to complement this technique a residual carrier concentration of 1.3×1015 cm-3 is obtained. The work is motivated by research into high performance superlattice array sensors with demanding processing requirements. A novel long-wavelength infrared imager based on a heterojunction concept is presented as an example for this work. It achieves a noise equivalent temperature difference below 30 mK for realistic operating conditions.

Temperature-Dependent Detectivity of Near-Infrared Organic Bulk Heterojunction Photodiodes.

PubMed

Wu, Zhenghui; Yao, Weichuan; London, Alexander E; Azoulay, Jason D; Ng, Tse Nga

2017-01-18

Bulk heterojunction photodiodes are fabricated using a new donor-acceptor polymer with a near-infrared absorption edge at 1.2 μm, achieving a detectivity up to 10 12 Jones at a wavelength of 1 μm and an excellent linear dynamic range of 86 dB. The photodiode detectivity is maximized by operating at zero bias to suppress dark current, while a thin 175 nm active layer is used to facilitate charge collection without reverse bias. Analysis of the temperature dependence of the dark current and spectral response demonstrates a 2.8-fold increase in detectivity as the temperature was lowered from 44 to -12 °C, a relatively small change when compared to that of inorganic-based devices. The near-infrared photodiode shows a switching speed reaching up to 120 μs without an external bias. An application using our NIR photodiode to detect arterial pulses of a fingertip is demonstrated.

Universality of Non-Ohmic Shunt Leakage in Thin-Film Solar Cells

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

Dongaonkar, S.; Servaites, J.D.; Ford, G.M.

2010-01-01

We compare the dark current-voltage (IV) characteristics of three different thin-film solar cell types: hydrogenated amorphous silicon (a-Si:H) p-i-n cells, organic bulk heterojunction (BHJ) cells, and Cu(In,Ga)Se 2 (CIGS) cells. All three device types exhibit a significant shunt leakage current at low forward bias (V<~0.4) and reverse bias, which cannot be explained by the classical solar cell diode model. This parasitic shunt current exhibits non-Ohmic behavior, as opposed to the traditional constant shunt resistance model for photovoltaics. We show here that this shunt leakage (I sh) , across all three solar cell types considered, is characterized by the following commonmore » phenomenological features: (a) voltage symmetry about V=0 , (b) nonlinear (power law) voltage dependence, and (c) extremely weak temperature dependence. Based on this analysis, we provide a simple method of subtracting this shunt current component from the measured data and discuss its implications on dark IV parameter extraction. We propose a space charge limited (SCL) current model for capturing all these features of the shunt leakage in a consistent framework and discuss possible physical origin of the parasitic paths responsible for this shunt current mechanism.« less

Dark-matter QCD-axion searches.

PubMed

Rosenberg, Leslie J

2015-10-06

In the late 20th century, cosmology became a precision science. Now, at the beginning of the next century, the parameters describing how our universe evolved from the Big Bang are generally known to a few percent. One key parameter is the total mass density of the universe. Normal matter constitutes only a small fraction of the total mass density. Observations suggest this additional mass, the dark matter, is cold (that is, moving nonrelativistically in the early universe) and interacts feebly if at all with normal matter and radiation. There's no known such elementary particle, so the strong presumption is the dark matter consists of particle relics of a new kind left over from the Big Bang. One of the most important questions in science is the nature of this dark matter. One attractive particle dark-matter candidate is the axion. The axion is a hypothetical elementary particle arising in a simple and elegant extension to the standard model of particle physics that nulls otherwise observable CP-violating effects (where CP is the product of charge reversal C and parity inversion P) in quantum chromo dynamics (QCD). A light axion of mass 10(-(6-3)) eV (the invisible axion) would couple extraordinarily weakly to normal matter and radiation and would therefore be extremely difficult to detect in the laboratory. However, such an axion is a compelling dark-matter candidate and is therefore a target of a number of searches. Compared with other particle dark-matter candidates, the plausible range of axion dark-matter couplings and masses is narrowly constrained. This focused search range allows for definitive searches, where a nonobservation would seriously impugn the dark-matter QCD-axion hypothesis. Axion searches use a wide range of technologies, and the experiment sensitivities are now reaching likely dark-matter axion couplings and masses. This article is a selective overview of the current generation of sensitive axion searches. Not all techniques and experiments are discussed, but I hope to give a sense of the current experimental landscape of the search for dark-matter axions.

Dark-matter QCD-axion searches

PubMed Central

Rosenberg, Leslie J

2015-01-01

In the late 20th century, cosmology became a precision science. Now, at the beginning of the next century, the parameters describing how our universe evolved from the Big Bang are generally known to a few percent. One key parameter is the total mass density of the universe. Normal matter constitutes only a small fraction of the total mass density. Observations suggest this additional mass, the dark matter, is cold (that is, moving nonrelativistically in the early universe) and interacts feebly if at all with normal matter and radiation. There’s no known such elementary particle, so the strong presumption is the dark matter consists of particle relics of a new kind left over from the Big Bang. One of the most important questions in science is the nature of this dark matter. One attractive particle dark-matter candidate is the axion. The axion is a hypothetical elementary particle arising in a simple and elegant extension to the standard model of particle physics that nulls otherwise observable CP-violating effects (where CP is the product of charge reversal C and parity inversion P) in quantum chromo dynamics (QCD). A light axion of mass 10−(6–3) eV (the invisible axion) would couple extraordinarily weakly to normal matter and radiation and would therefore be extremely difficult to detect in the laboratory. However, such an axion is a compelling dark-matter candidate and is therefore a target of a number of searches. Compared with other particle dark-matter candidates, the plausible range of axion dark-matter couplings and masses is narrowly constrained. This focused search range allows for definitive searches, where a nonobservation would seriously impugn the dark-matter QCD-axion hypothesis. Axion searches use a wide range of technologies, and the experiment sensitivities are now reaching likely dark-matter axion couplings and masses. This article is a selective overview of the current generation of sensitive axion searches. Not all techniques and experiments are discussed, but I hope to give a sense of the current experimental landscape of the search for dark-matter axions. PMID:25583487

Tidal Debris from High-Velocity Collisions as Fake Dark Galaxies: A Numerical Model of VIRGOHI 21

NASA Astrophysics Data System (ADS)

Duc, Pierre-Alain; Bournaud, Frederic

2008-02-01

High-speed collisions, although current in clusters of galaxies, have long been neglected, as they are believed to cause little damages to galaxies except when they are repeated, a process called "harassment." In fact, they are able to produce faint but extended gaseous tails. Such low-mass, starless, tidal debris may become detached and appear as free-floating clouds in the very deep H I surveys that are currently being carried out. We show in this paper that these debris possess the same apparent properties as the so-called dark galaxies, objects originally detected in H I, with no optical counterpart, and presumably dark matter-dominated. We present a numerical model of the prototype of such dark galaxies—VIRGOHI 21—that is able to reproduce its main characteristics: the one-sided tail linking it to the spiral galaxy NGC 4254, the absence of stars, and above all the reversal of the velocity gradient along the tail originally attributed to rotation motions caused by a massive dark matter halo, which we find to be consistent with simple streaming motions plus projection effects. According to our numerical simulations, this tidal debris was expelled 750 Myr ago during a flyby at 1100 km s-1 of NGC 4254 by a massive companion that should now lie at a projected distance of about 400 kpc. A candidate for the intruder is discussed. The existence of galaxies that have never been able to form stars had already been challenged on the basis of theoretical and observational grounds. Tidal collisions, in particular those occurring at high speed, provide a much more simple explanation for the origin of such putative dark galaxies.

Dark-matter QCD-axion searches

DOE PAGES

Rosenberg, Leslie J.

2015-01-12

In the late 20th century, cosmology became a precision science. At the beginning of the next century, the parameters describing how our universe evolved from the Big Bang are generally known to a few percent. One key parameter is the total mass density of the universe. Normal matter constitutes only a small fraction of the total mass density. Observations suggest this additional mass, the dark matter, is cold (that is, moving nonrelativistically in the early universe) and interacts feebly if at all with normal matter and radiation. There’s no known such elementary particle, so the strong presumption is the darkmore » matter consists of particle relics of a new kind left over from the Big Bang. One of the most important questions in science is the nature of this dark matter. One attractive particle dark-matter candidate is the axion. The axion is a hypothetical elementary particle arising in a simple and elegant extension to the standard model of particle physics that nulls otherwise observable CP-violating effects (where CP is the product of charge reversal C and parity inversion P) in quantum chromo dynamics (QCD). A light axion of mass 10 -(6–3) eV (the invisible axion) would couple extraordinarily weakly to normal matter and radiation and would therefore be extremely difficult to detect in the laboratory. But, such an axion is a compelling dark-matter candidate and is therefore a target of a number of searches. Compared with other particle dark-matter candidates, the plausible range of axion dark-matter couplings and masses is narrowly constrained. This focused search range allows for definitive searches, where a nonobservation would seriously impugn the dark-matter QCD-axion hypothesis. Axion searches use a wide range of technologies, and the experiment sensitivities are now reaching likely dark-matter axion couplings and masses. Our paper is a selective overview of the current generation of sensitive axion searches. Finally, not all techniques and experiments are discussed, but I hope to give a sense of the current experimental landscape of the search for dark-matter axions.« less

Reversal of Fortune: Increased Star Formation Efficiencies in the Early Histories of Dwarf Galaxies?

NASA Astrophysics Data System (ADS)

Madau, Piero; Weisz, Daniel R.; Conroy, Charlie

2014-08-01

On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening potential well, characterized by a high SFE; and (2) a late, slow halo accretion phase where, perhaps as a consequence of reionization, the SFE is low. Nearby dwarfs have more old stars than predicted by assuming a constant or decreasing SFE with redshift, a behavior that appears to deviate qualitatively from the trends seen among more massive systems. Taken at face value, the data suggest that at sufficiently early epochs, dwarf galaxy halos above the atomic cooling mass limit can be among the most efficient sites of star formation in the universe.

Model-independent analyses of dark-matter particle interactions

DOE PAGES

Anand, Nikhil; Fitzpatrick, A. Liam; Haxton, W. C.

2015-03-24

A model-independent treatment of dark-matter particle elastic scattering has been developed, yielding the most general interaction for WIMP-nucleon low-energy scattering, and the resulting amplitude has been embedded into the nucleus, taking into account the selection rules imposed by parity and time-reversal. One finds that, in contrast to the usual spin-independent/spin-dependent (SI/SD) formulation, the resulting cross section contains six independent nuclear response functions, three of which are associated with possible velocity-dependent interactions. We find that current experiments are four orders of magnitude more sensitive to derivative couplings than is apparent in the standard SI/SD treatment, which necessarily associated such interactions withmore » cross sections proportional to v 2 T ~ 10⁻⁶, where v T is the WIMP velocity relative to the center of mass of the nuclear target.« less

Sequential decolorization of azo dye and mineralization of decolorization liquid coupled with bioelectricity generation using a pH self-neutralized photobioelectrochemical system operated with polarity reversion.

PubMed

Sun, Jian; Hu, Yongyou; Li, Wanjun; Zhang, Yaping; Chen, Jie; Deng, Feng

2015-05-30

A novel photobioelectrochemical system (PBES) was developed by acclimating algal-bacterial biofilm in both anode and cathode using Chlorella vulgaris and indigenous wastewater bacteria as inoculums. The PBES was operated in polarity reversion mode depend on dark/light alternate reaction to achieve simultaneous pH self-neutralization, azo dye degradation (Congo red) and bioelectricity generation. The anodic accumulated acidity and cathodic accumulated alkalinity were self-neutralized after polarity reversion and hence eliminate the membrane pH gradient. The Congo red was first decolored in the dark anode and the resultant decolorization liquid was subsequently mineralized after the dark anode changing to the photo-biocathode. The presence of C. vulgaris significantly enhanced the two-stage degradation of Congo red, with 93% increases in decolorization rates and 8% increases in mineralization compared to the algae-free BES. The PBES continuously generated stable voltage output over four months under repeatedly reversion of polarity. The maximum power density produced before and after polarity reversion was 78 and 61 mW/m(2), respectively. The synergy between C. vulgaris and mixed bacteria was responsible for the successful operation of the PBES which can be potentially applied to treat wastewater containing azo dye with benefits of enhanced azo dye degradation, high net power output and buffer minimization. Copyright © 2015 Elsevier B.V. All rights reserved.

[Effects of reversing the feeding cycle and the light period on the spontaneous activity of the rat (author's transl)].

PubMed

Ticca, M

1976-01-01

The amount and the circadian distribution of spontaneous activity in the rat are influenced by a number of factors, whose importance and interrelationships are still deeply discussed. In order to check the reliability of previous studies about the effects of meal-eating on the spontaneous activity (wheel running) of rats of our Sprague-Dawley strain, the adjustment to the modifications of the normal day-night cycle and of the normal nocturnal feeding rhythm have been controlled. Reversing the normal light and dark periods caused the rats, after a 24 hours period, to lower and to irregularly distribute their spontaneous activity. Rats shifted their pattern of maximal activity by 12 hours in the new period of darkness in about five days, and showed to have completely fixed the new reversed running habit. Also feeding habits changed in a similar way, but more slowly. The levels of mean daily activity did not change. In a second experiment, rats, received food during light hours, and were deprived during dark hours. Their activity increased considerably and irregularly during dark hours, while a very slight rise of wheel running was shown during light hours. Body weight gain and food consumption were similar to those of the control group. These results slightly differ from those obtained using other rat strains, and are an interesting example of reinforcement of a spontaneous behavior resulting more from the light-dark cycle than from cues provided by food deprivation.

Precision Laser Annealing of Focal Plane Arrays

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

Bender, Daniel A.; DeRose, Christopher; Starbuck, Andrew Lea

2015-09-01

We present results from laser annealing experiments in Si using a passively Q-switched Nd:YAG microlaser. Exposure with laser at fluence values above the damage threshold of commercially available photodiodes results in electrical damage (as measured by an increase in photodiode dark current). We show that increasing the laser fluence to values in excess of the damage threshold can result in annealing of a damage site and a reduction in detector dark current by as much as 100x in some cases. A still further increase in fluence results in irreparable damage. Thus we demonstrate the presence of a laser annealing windowmore » over which performance of damaged detectors can be at least partially reconstituted. Moreover dark current reduction is observed over the entire operating range of the diode indicating that device performance has been improved for all values of reverse bias voltage. Additionally, we will present results of laser annealing in Si waveguides. By exposing a small (<10 um) length of a Si waveguide to an annealing laser pulse, the longitudinal phase of light acquired in propagating through the waveguide can be modified with high precision, <15 milliradian per laser pulse. Phase tuning by 180 degrees is exhibited with multiple exposures to one arm of a Mach-Zehnder interferometer at fluence values below the morphological damage threshold of an etched Si waveguide. No reduction in optical transmission at 1550 nm was found after 220 annealing laser shots. Modeling results for laser annealing in Si are also presented.« less

Identification and Analysis of Partial Shading Breakdown Sites in CuIn xGa (1-x)Se 2 Modules

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

Palmiotti, Elizabeth; Johnston, Steven; Gerber, Andreas

In this paper, CuIn xGa (1-x) (CIGS) mini-modules are stressed under reverse bias, resembling partial shading conditions, to predict and characterize where failures occur. Partial shading can cause permanent damage in the form of 'wormlike' defects on thin-film modules due to thermal runaway. This results in module-scale power losses. We have used dark lock-in thermography (DLIT) to spatially observe localized heating when reverse-bias breakdown occurs on various CIGS mini-modules. For better understanding of how and where these defects originated and propagated, we have developed techniques where the current is limited during reverse-bias stressing. This allows for DLIT-based detection and detailedmore » studying of the region where breakdown is initiated before thermal runaway leads to permanent damage. Statistics of breakdown sites using current-limited conditions has allowed for reasonable identification of the as-grown defects where permanent breakdown will likely originate. Scanning electron microscope results and wormlike defect analysis show that breakdown originates in defects such as small pits, craters, or cracks in the CIGS layer, and the wormlike defects propagate near the top CIGS interface.« less

Identification and Analysis of Partial Shading Breakdown Sites in CuIn xGa (1-x)Se 2 Modules

DOE PAGES

Palmiotti, Elizabeth; Johnston, Steven; Gerber, Andreas; ...

2017-12-20

In this paper, CuIn xGa (1-x) (CIGS) mini-modules are stressed under reverse bias, resembling partial shading conditions, to predict and characterize where failures occur. Partial shading can cause permanent damage in the form of 'wormlike' defects on thin-film modules due to thermal runaway. This results in module-scale power losses. We have used dark lock-in thermography (DLIT) to spatially observe localized heating when reverse-bias breakdown occurs on various CIGS mini-modules. For better understanding of how and where these defects originated and propagated, we have developed techniques where the current is limited during reverse-bias stressing. This allows for DLIT-based detection and detailedmore » studying of the region where breakdown is initiated before thermal runaway leads to permanent damage. Statistics of breakdown sites using current-limited conditions has allowed for reasonable identification of the as-grown defects where permanent breakdown will likely originate. Scanning electron microscope results and wormlike defect analysis show that breakdown originates in defects such as small pits, craters, or cracks in the CIGS layer, and the wormlike defects propagate near the top CIGS interface.« less

High Performance CMOS Light Detector with Dark Current Suppression in Variable-Temperature Systems.

PubMed

Lin, Wen-Sheng; Sung, Guo-Ming; Lin, Jyun-Long

2016-12-23

This paper presents a dark current suppression technique for a light detector in a variable-temperature system. The light detector architecture comprises a photodiode for sensing the ambient light, a dark current diode for conducting dark current suppression, and a current subtractor that is embedded in the current amplifier with enhanced dark current cancellation. The measured dark current of the proposed light detector is lower than that of the epichlorohydrin photoresistor or cadmium sulphide photoresistor. This is advantageous in variable-temperature systems, especially for those with many infrared light-emitting diodes. Experimental results indicate that the maximum dark current of the proposed current amplifier is approximately 135 nA at 125 °C, a near zero dark current is achieved at temperatures lower than 50 °C, and dark current and temperature exhibit an exponential relation at temperatures higher than 50 °C. The dark current of the proposed light detector is lower than 9.23 nA and the linearity is approximately 1.15 μA/lux at an external resistance R SS = 10 kΩ and environmental temperatures from 25 °C to 85 °C.

High Performance CMOS Light Detector with Dark Current Suppression in Variable-Temperature Systems

PubMed Central

Lin, Wen-Sheng; Sung, Guo-Ming; Lin, Jyun-Long

2016-01-01

This paper presents a dark current suppression technique for a light detector in a variable-temperature system. The light detector architecture comprises a photodiode for sensing the ambient light, a dark current diode for conducting dark current suppression, and a current subtractor that is embedded in the current amplifier with enhanced dark current cancellation. The measured dark current of the proposed light detector is lower than that of the epichlorohydrin photoresistor or cadmium sulphide photoresistor. This is advantageous in variable-temperature systems, especially for those with many infrared light-emitting diodes. Experimental results indicate that the maximum dark current of the proposed current amplifier is approximately 135 nA at 125 °C, a near zero dark current is achieved at temperatures lower than 50 °C, and dark current and temperature exhibit an exponential relation at temperatures higher than 50 °C. The dark current of the proposed light detector is lower than 9.23 nA and the linearity is approximately 1.15 μA/lux at an external resistance RSS = 10 kΩ and environmental temperatures from 25 °C to 85 °C. PMID:28025530

Light induced changes of internal pH in a barnacle photoreceptor and the effect of internal pH on the receptor potential.

PubMed Central

Brown, H M; Meech, R W

1979-01-01

1. Intracellular pH (pH1) was measured in Balanus photoreceptors using pH-sensitive glass micro-electrodes. The average pH1 of twelve photoreceptors which had been dark adapted for at least 30 min was 7.3 +/- 0.07 (S.D.). 2. Illumination reduced the recorded pH1 by as much as 0.2 pH unit. The change in pH1 was graded with light intensity. 3. When the cells were exposed to CO2 in the dark, pH1 declined monophasically. Saline equilibrated with 2% CO2; 98% O2 produced a steady reduction in pH1 of about 0.25 unit in 2--3 min. The buffering capacity of the receptor cell cytoplasm calculated from such experiments is approximately 15 slykes. 4. In the presence of HCO3-1, CO2 saline produced smaller, biphasic changes in pH1. 5. The membrane depolarization produced by a bright flash (depolarizing receptor potential) was reversibly reduced in the presence of external CO2 or by injection of H+. Iontophoretic injection of HCO2- increased the amplitude of the receptor potential. 6. In individual cells there was a close correlation between the amplitude of the receptor potential and pH1. 7. Saline equilibrated with CO2 reduced the light induced current (recorded under voltage-clamp) by 40--50% without affecting its reversal potential. 8. Exposure of the receptor to 95% CO2 saline for several minutes (pH0 5.5) not only abolished the receptor potential but also reversibly decreased the K conductance of the membrane in the dark. These effects were not reproduced by pH0 5.5 buffered saline or by a 5 min exposure to saline equilibrated with N2. 9. It is suggested that changes in pH1 induced by light modulate the sensitivity of the receptor under physiological conditions. PMID:43890

Correlation of molecular expression with diel rhythm of oviposition in Calliphora vicina (Robineau-Desvoidy) (Diptera: Calliphoridae) and implications for forensic entomology.

PubMed

George, Kelly A; Archer, Melanie S; Toop, Tes

2015-01-01

This study explored the molecular mechanisms potentially underlying blow fly nocturnal oviposition. A behavioral study revealed that Calliphora vicina (Robineau-Desvoidy) (Diptera: Calliphoridae) possesses a diel rhythm of oviposition in light under 12:12 light/dark conditions. Reversal to 12:12 dark/light resulted in oviposition behavior changing to align with the adjusted regime in most females, but four of 59 experimental females lacked a diel rhythm of oviposition (were arrhythmic). Real-time PCR was used to monitor the molecular expression levels of known circadian genes per and tim in C. vicina to determine whether gene expression and behavior correlated. As with behavior, reversing light/dark conditions changed rhythmic gene expression to align with an adjusted light regime. This suggests that although it is unlikely that C. vicina will colonize dead bodies at night, arrhythmic females and oviposition in the dark was demonstrated. © 2014 American Academy of Forensic Sciences.

Product-to-parent reversion processes: Stream-hyporheic spiraling increases ecosystem exposure and environmental persistence

NASA Astrophysics Data System (ADS)

Ward, A. S.; Cwiertny, D. M.; Kolodziej, E. P.

2014-12-01

The product-to-parent reversion of metabolites of trenbolone acetate (TBA), a steroidal growth promoter used widely in beef cattle production, was recently observed to occur in environmental waters. The rapid forward reaction is by direct photolysis (i.e., photohydration), with the much slower reversion reaction occurring via dehydration in the dark. The objective of this study is to quantify the potential effect of this newly discovered reversible process on TBA metabolite concentrations and total bioactivity exposure in fluvial systems. Here, we demonstrate increased persistence of TBA metabolites in the stream and hyporheic zone due to the reversion process, increasing chronic and acute exposure to these endocrine-active compounds along a stream. The perpetually dark hyporheic zone is a key location for reversion in the system, ultimately providing a source of the parent compound to the stream and increasing mean in-stream concentration of 17α-trenbolone (17α-TBOH) by 40% of the input concentration under representative fluvial conditions. As such, regulatory frameworks for compounds undergoing product-to-parent reversion will require new approaches for assessing total exposure to bioactive compounds. Further, we demonstrate generalized cases for prediction of exposure for species with product-to-parent reversion in stream-hyporheic systems.

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

Fertig, Fabian, E-mail: fabian.fertig@ise.fraunhofer.de; Greulich, Johannes; Rein, Stefan

We present a spatially resolved method to determine the short-circuit current density of crystalline silicon solar cells by means of lock-in thermography. The method utilizes the property of crystalline silicon solar cells that the short-circuit current does not differ significantly from the illuminated current under moderate reverse bias. Since lock-in thermography images locally dissipated power density, this information is exploited to extract values of spatially resolved current density under short-circuit conditions. In order to obtain an accurate result, one or two illuminated lock-in thermography images and one dark lock-in thermography image need to be recorded. The method can be simplifiedmore » in a way that only one image is required to generate a meaningful short-circuit current density map. The proposed method is theoretically motivated, and experimentally validated for monochromatic illumination in comparison to the reference method of light-beam induced current.« less

Regulation of melatonin secretion in the pineal organ of the domestic duck--an in vitro study.

PubMed

Prusik, M; Lewczuk, B; Ziółkowska, N; Przybylska-Gornowicz, B

2015-01-01

The aim of study was to determine the mechanisms regulating melatonin secretion in the pineal organs of 1-day-old and 9-month-old domestic ducks. The pineals were cultured in a superfusion system under different light conditions. Additionally, some explants were treated with norepinephrine. The pineal glands of 1-day-old ducks released melatonin in a well-entrained, regular rhythm during incubation under a 12 hrs light:12 hrs dark cycle and adjusted their secretory activity to a reversed 12 hrs dark:12 hrs light cycle within 2 days. In contrast, the diurnal changes in melatonin secretion from the pineals of 9-month-old ducks were largely irregular and the adaptation to a reversed cycle lasted 3 days. The pineal organs of nestling and adult ducks incubated in a continuous light or darkness secreted melatonin in a circadian rhythm. The treatment with norepinephrine during photophases of a light-dark cycle resulted in: 1) a precise adjustment of melatonin secretion rhythm to the presence of this catecholamine in the culture medium, 2) a very high amplitude of the rhythm, 3) a rapid adaptation of the pineal secretory activity to a reversed light-dark cycle. The effects of norepinephrine were similar in the pineal organs of nestlings and adults. In conclusion, melatonin secretion in the duck pineal organ is controlled by three main mechanisms: the direct photoreception, the endogenous generator and the noradrenergic transmission. The efficiency of intra-pineal, photosensitivity-based regulatory mechanism is markedly lower in adult than in nestling individuals.

Computation of dark frames in digital imagers

NASA Astrophysics Data System (ADS)

Widenhorn, Ralf; Rest, Armin; Blouke, Morley M.; Berry, Richard L.; Bodegom, Erik

2007-02-01

Dark current is caused by electrons that are thermally exited into the conduction band. These electrons are collected by the well of the CCD and add a false signal to the chip. We will present an algorithm that automatically corrects for dark current. It uses a calibration protocol to characterize the image sensor for different temperatures. For a given exposure time, the dark current of every pixel is characteristic of a specific temperature. The dark current of every pixel can therefore be used as an indicator of the temperature. Hot pixels have the highest signal-to-noise ratio and are the best temperature sensors. We use the dark current of a several hundred hot pixels to sense the chip temperature and predict the dark current of all pixels on the chip. Dark current computation is not a new concept, but our approach is unique. Some advantages of our method include applicability for poorly temperature-controlled camera systems and the possibility of ex post facto dark current correction.

Understanding Mott-Schottky Measurements under Illumination in Organic Bulk Heterojunction Solar Cells

NASA Astrophysics Data System (ADS)

Zonno, Irene; Martinez-Otero, Alberto; Hebig, Jan-Christoph; Kirchartz, Thomas

2017-03-01

The Mott-Schottky analysis in the dark is a frequently used method to determine the doping concentration of semiconductors from capacitance-voltage measurements, even for such complex systems as polymer:fullerene blends used for organic solar cells. While the analysis of capacitance-voltage measurements in the dark is relatively well established, the analysis of data taken under illumination is currently not fully understood. Here, we present experiments and simulations to show which physical mechanisms affect the Mott-Schottky analysis under illumination. We show that the mobility of the blend has a major influence on the shape of the capacitance-voltage curve and can be obtained from data taken under reverse bias. In addition, we show that the apparent shift of the built-in voltage observed previously can be explained by a shift of the onset of space-charge-limited collection with illumination intensity.

Secondary Organic Aerosol Formation from Glyoxal: photochemical versus dark uptake and reversible versus irreversible SOA formation

NASA Astrophysics Data System (ADS)

Waxman, E.; Slowik, J. G.; Kampf, C. J.; Timkovsky, J.; Noziere, B.; Praplan, A. P.; Pfaffenberger, L.; Holzinger, R.; Hoffmann, T.; Dommen, J.; Prevot, A. S.; Baltensperger, U.; Volkamer, R.

2011-12-01

Glyoxal forms secondary organic aerosol (SOA) by partitioning to the aerosol aqueous phase according to Henry's law. The subsequent processing by heterogeneous and multiphase reactions shifts the partitioning towards aerosols. Currently it is not well understood whether these reactions result in reversible or irreversible SOA formation, and what parameters influence the rate limiting step of multiphase processing. We conducted a series of simulation chamber experiments at PSI in April and May 2011 to investigate processing under dark conditions, UV and/or visible light irradiated conditions, and in the presence and absence of OH radicals. Experiments used ammonium sulfate or ammonium sulfate/fulvic acid mixtures as seed aerosols, and were conducted between 50% and 85% relative humidity at approximately constant RH over the course of any given experiment. Glyoxal was produced photochemically from acetylene, using HONO photolysis as the OH radical source. Gas-phase glyoxal was measured by the CU LED-Cavity Enhanced-DOAS. The Thermal-Desorption Proton-Transfer-Reaction Mass Spectrometer (TD-PTR-MS) and Ion Chromatography Mass Spectrometer (IC-MS) monitored both gas and aerosol-phase organic reaction products. Particle composition was monitored by High-Resolution Time-of-Flight Aerosol Mass Spectrometry (HR-ToF-AMS), and HPLC-ESI MS/MS and LC-MS analysis of filter samples.

Secondary Organic Aerosol Formation from Glyoxal: photochemical versus dark uptake and reversible versus irreversible SOA formation

NASA Astrophysics Data System (ADS)

Waxman, E.; Slowik, J.; Kampf, C.; Timkovsky, J.; Noziere, B.; Praplan, A.; Pffafenberger, L.; Holzinger, R.; Hoffmann, T.; Dommen, J.; Prevot, A.; Baltensperger, U.; Volkamer, R.

2012-04-01

Glyoxal forms secondary organic aerosol (SOA) by partitioning to the aerosol aqueous phase according to Henry's law. The subsequent processing by heterogeneous and multiphase reactions shifts the partitioning towards aerosols. Currently it is not well understood whether these reactions result in reversible or irreversible SOA formation, and what parameters influence the rate limiting step of multiphase processing. We conducted a series of simulation chamber experiments at PSI in April and May 2011 to investigate processing under dark conditions, UV and/or visible light irradiated conditions, and in the presence and absence of OH radicals. Experiments used ammonium sulfate or ammonium sulfate/fulvic acid mixtures as seed aerosols, and were conducted between 50% and 85% relative humidity at approximately constant RH over the course of any given experiment. Glyoxal was produced photochemically from acetylene, using HONO photolysis as the OH radical source. Gas-phase glyoxal was measured by the CU LED-Cavity Enhanced-DOAS. The Thermal-Desorption Proton-Transfer-Reaction Mass Spectrometer (TD-PTR-MS) and Ion Chromatography Mass Spectrometer (IC-MS) monitored both gas and aerosol-phase organic reaction products. Particle composition was monitored by High-Resolution Time-of-Flight Aerosol Mass Spectrometry (HR-ToF-AMS), and HPLC-ESI MS/MS and LC-MS analysis of filter samples.

Circadian rhythm of intraocular pressure in the rat.

PubMed

Moore, C G; Johnson, E C; Morrison, J C

1996-02-01

To define the characteristics of the diurnal variation of intraocular pressure (IOP) in eyes of awake rats, ten male brown Norway rats were entrained to a 12-hour light:12-hour dark (12L:12D) lighting schedule and were conditioned to IOP measurement with the TonoPen XL tonometer while awake, using only 0.5% proparacaine HCl anesthesia. The IOP measurements were performed in 4 experiments: Preliminary-IOP was measured at 6-hour intervals in both eyes of each animal, to determine correlation between right and left eyes; Light:Dark-lighting remained the same as in the preliminary experiment, but the measurement schedule was altered so that measurements were obtained at 4-hour intervals in alternating eyes, over two 24-hour light cycles; Dark:Dark-animals were placed in constant dark (0L:24D) and, after 72 h, measurements were obtained at 4-hour intervals in alternating eyes. Animals were then re-entrained to the previous 12L:12D schedule for 7 days, after which they were returned to constant dark and the experiment was repeated; and Dark:Light-animals were entrained to a reversed light:dark cycle (12D:12L) for 28 days, after which measurements were obtained in the same fashion as in the Light:Dark experiment. Close agreement was found between right- and left-eye IOPs. Animals on a 12L:12D schedule exhibited lowest IOP while the lights were on (19.3 +/- 1.9 mm Hg), and highest (31.3 +/- 1.3 mm Hg) while the lights were off. Pressure changes anticipated the change from light to dark and dark to light. This pattern persisted in constant dark, and was reversed when the cycle was changed to 12D:12L. Brown Norway rats possess a regular rhythm of IOP that is entrained by the cycle of light and dark, and persistence of this rhythm in constant dark establishes it as a circadian rhythm. Furthermore, our results indicate that reliable and physiologically meaningful IOP measurements can be obtained in awake rats using the TonoPen XL tonometer.

Preparation of TNAs/NiO p-n heterojunction and their applications in UV photosensor

NASA Astrophysics Data System (ADS)

Yusoff, M. M.; Mamat, M. H.; Malek, M. F.; Abdullah, M. A. R.; Ismail, A. S.; Saidi, S. A.; Mohamed, R.; Suriani, A. B.; Khusaimi, Z.; Rusop, M.

2018-05-01

A nanocomposite consisted of n-type titanium dioxide (TiO2) nanorod arrays (TNAs) and p-type nickel oxide (NiO) were deposited using a novel facile low-temperature aqueous chemical route (ACR) in a Schott bottle with cap clamps and sol-gel spin coating method, respectively on a transparent conductive oxide (TCO) glass substrate for the application of ultraviolet (UV) photosensor. The p-n heterojunction photosensor exhibited an increase in photocurrent under UV light (365 nm, 750 µW/cm2) at applied reverse bias. The measured UV response also revealed an increase in photocurrent, and dark current with increasing applied reverse bias on the p-n heterojunction. In this study, the fabricated TNAs/NiO composite nanostructures showed potential applications for photosensor based on the steady photocurrent results obtained under UV irradiation

Recovery from the anatomical effects of long-term monocular deprivation in cat lateral geniculate nucleus.

PubMed

Duffy, Kevin R; Fong, Ming-Fai; Mitchell, Donald E; Bear, Mark F

2018-02-01

Monocular deprivation (MD) imposed early in postnatal life elicits profound structural and functional abnormalities throughout the primary visual pathway. The ability of MD to modify neurons within the visual system is restricted to a so-called critical period that, for cats, peaks at about one postnatal month and declines thereafter so that by about 3 months of age MD has little effect. Recovery from the consequences of MD likewise adheres to a critical period that ends by about 3 months of age, after which the effects of deprivation are thought to be permanent and without capacity for reversal. The attenuation of plasticity beyond early development is a formidable obstacle for conventional therapies to stimulate recovery from protracted visual deprivation. In the current study we examined the efficacy of dark exposure and retinal inactivation with tetrodotoxin to promote anatomical recovery in the dorsal lateral geniculate nuclues (dLGN) from long-term MD started at the peak of the critical period. Whereas 10 days of dark exposure or binocular retinal inactivation were not better at promoting recovery than conventional treatment with reverse occlusion, inactivation of only the non-deprived (fellow) eye for 10 days produced a complete restoration of neuron soma size, and also reversed the significant loss of neurofilament protein within originally deprived dLGN layers. These results reveal a capacity for neural plasticity and recovery that is larger than anything previously observed following protracted MD in cat, and they highlight a possibility for alternative therapies applied at ages thought to be recalcitrant to recovery. © 2017 Wiley Periodicals, Inc.

Estimation of dark and active dielectric constants in the sub-THz frequency domain of an optically tunable organic semiconductor blend of poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester

NASA Astrophysics Data System (ADS)

Andy, Andre S.; Kneller, James W. E.; Sushko, Oleksandr; Dubrovka, Rostyslav; Parini, Clive; Scott, Ken; Kreouzis, Theo; Donnan, Robert S.

2018-06-01

The dielectric properties of a 95% poly(3-hexylthiophene):5% phenyl-C61-butyric acid methyl ester blend are measured in the dark and under white light illumination by quasi-optical transmissometry and terahertz time-domain spectroscopy. The real part of the dielectric constant varies monotonically between 2.75 and 3.50, in agreement with the literature, and displays a reversible photoinduced drop of 0.05–0.55 at sub-THz. The imaginary part fluctuates between 0.1 and 1.5 in the dark and displays a reversible increase upon illumination of 0.10–0.52 at sub-THz. The corresponding charge carrier concentration under illumination (using transient and steady-state photoconduction) is 1014 to 1015 cm‑3.

Product-to-parent reversion increases ecosystem exposure to and environmental persistence of 17α-trenbolone

NASA Astrophysics Data System (ADS)

Ward, Adam; Cwiertny, David; Kolodziej, Edward; Brehm, Colleen

2016-04-01

The product-to-parent reversion of metabolites of trenbolone acetate (TBA), a steroidal growth promoter used widely in beef cattle production, was recently observed to occur in environmental waters. The rapid forward reaction is by direct photolysis (i.e., photohydration), with the much slower reversion reaction occurring via dehydration in the dark. The objective of this study is to quantify the potential effect of this newly discovered reversible process on TBA metabolite concentrations and total bioactivity exposure in fluvial systems. Here, we demonstrate increased persistence of TBA metabolites in the stream and hyporheic zone due to the reversion process, increasing chronic and acute exposure to these endocrine-active compounds along a stream. The perpetually dark hyporheic zone is a key location for reversion in the system, ultimately providing a source of the parent compound to the stream and increasing mean in-stream concentration of 17α-trenbolone (17α-TBOH) by 40% of the input concentration under representative fluvial conditions. We demonstrate generalized cases for prediction of exposure for species with product-to-parent reversion in stream-hyporheic systems. Recognizing this risk, regulatory frameworks for compounds undergoing product-to-parent reversion will require new approaches for assessing total exposure to bioactive compounds. We discuss the role of regulating "joint" or "mixture" bioactivity as an emerging paradigm for more meaningful management of micropollutants.

Dark solitons, breathers, and rogue wave solutions of the coupled generalized nonlinear Schrödinger equations.

PubMed

Priya, N Vishnu; Senthilvelan, M; Lakshmanan, M

2014-06-01

We construct dark-dark soliton, general breather (GB), Akhmediev breather (AB), Ma soliton (MS), and rogue wave (RW) solutions of a coupled generalized nonlinear Schrödinger (CGNLS) equation. While dark-dark solitons are captured in the defocusing regime of the CGNLS system, the other solutions, namely, GB, AB, MS, and RW, are identified in the focusing regime. We also analyze the structures of GB, AB, MS, and RW profiles with respect to the four-wave mixing parameter. We show that when we increase the value of the real part of the four-wave mixing parameter, the number of peaks in the breather profile increases and the width of each peak shrinks. Interestingly, the direction of this profile also changes due to this change. As far as the RW profile is concerned the width of the peak becomes very thin when we increase the value of this parameter. Further, we consider the RW solution as the starting point, derive AB, MS, and GB in the reverse direction, and show that the solutions obtained in both directions match each other. In the course of the reverse analysis we also demonstrate how to capture the RW solutions directly from AB and MS.

Dark Current Degradation of Near Infrared Avalanche Photodiodes from Proton Irradiation

NASA Technical Reports Server (NTRS)

Becker, Heidi N.; Johnston, Allan H.

2004-01-01

InGaAs and Ge avalanche photodiodes (APDs) are examined for the effects of 63-MeV protons on dark current. Dark current increases were large and similar to prior results for silicon APDs, despite the smaller size of InGaAs and Ge devices. Bulk dark current increases from displacement damage in the depletion regions appeared to be the dominant contributor to overall dark current degradation. Differences in displacement damage factors are discussed as they relate to structural and material differences between devices.

Infrared photodetectors with tailorable response due to resonant plasmon absorption in epitaxial silicide particles embedded in silicon

NASA Technical Reports Server (NTRS)

Fathauer, R. W.; Dejewski, S. M.; George, T.; Jones, E. W.; Krabach, T. N.; Ksendzov, A.

1993-01-01

Tailorable infrared photoresponse in the 1-2 micron range are demonstrated in a device incorporating electrically floating metal silicide particles. Photons absorbed by excitation of the metallic-particle surface plasmon are shown to contribute to the photoresponse. Quantum efficiencies of roughly 0.2 percent are measured at 77 K, with dark currents of less than 2 nA/sq cm at a reverse bias of 1 V and detectivities of 4 x 10 exp 9 - 8 x 10 exp 9 cm sq rt Hz/W are obtained.

Activation of violaxanthin cycle in darkness is a common response to different abiotic stresses: a case study in Pelvetia canaliculata

PubMed Central

2011-01-01

Background In the violaxanthin (V) cycle, V is de-epoxidized to zeaxanthin (Z) when strong light or light combined with other stressors lead to an overexcitation of photosystems. However, plants can also suffer stress in darkness and recent reports have shown that dehydration triggers V-de-epoxidation in the absence of light. In this study, we used the highly stress-tolerant brown alga Pelvetia canaliculata as a model organism, due to its lack of lutein and its non-photochemical quenching independent of the transthylakoidal-ΔpH, to study the triggering of the V-cycle in darkness induced by abiotic stressors. Results We have shown that besides desiccation, other factors such as immersion, anoxia and high temperature also induced V-de-epoxidation in darkness. This process was reversible once the treatments had ceased (with the exception of heat, which caused lethal damage). Irrespective of the stressor applied, the resulting de-epoxidised xanthophylls correlated with a decrease in Fv/Fm, suggesting a common function in the down-regulation of photosynthetical efficiency. The implication of the redox-state of the plastoquinone-pool and of the differential activity of V-cycle enzymes on V-de-epoxidation in darkness was also examined. Current results suggest that both violaxanthin de-epoxidase (VDE) and zeaxanthin-epoxidase (ZE) have a basal constitutive activity even in darkness, being ZE inhibited under stress. This inhibition leads to Z accumulation. Conclusion This study demonstrates that V-cycle activity is triggered by several abiotic stressors even when they occur in an absolute absence of light, leading to a decrease in Fv/Fm. This finding provides new insights into an understanding of the regulation mechanism of the V-cycle and of its ecophysiological roles. PMID:22269024

Lower-Dark-Current, Higher-Blue-Response CMOS Imagers

NASA Technical Reports Server (NTRS)

Pain, Bedabrata; Cunningham, Thomas; Hancock, Bruce

2008-01-01

Several improved designs for complementary metal oxide/semiconductor (CMOS) integrated-circuit image detectors have been developed, primarily to reduce dark currents (leakage currents) and secondarily to increase responses to blue light and increase signal-handling capacities, relative to those of prior CMOS imagers. The main conclusion that can be drawn from a study of the causes of dark currents in prior CMOS imagers is that dark currents could be reduced by relocating p/n junctions away from Si/SiO2 interfaces. In addition to reflecting this conclusion, the improved designs include several other features to counteract dark-current mechanisms and enhance performance.

A positively gravitropic mutant mirrors the wild-type protonemal response in the moss Ceratodon purpureus

NASA Technical Reports Server (NTRS)

Wagner, T. A.; Cove, D. J.; Sack, F. D.

1997-01-01

Wild-type Ceratodon purpureus (Hedw.) Brid. protonemata grow up in the dark by negative gravitropism. When upright wild-type protonemata are reoriented 90 degrees, they temporarily grow down soon after reorientation ("initial reversal") and also prior to cytokinesis ("mitotic reversal"). A positively gravitropic mutant designated wrong- way response (wwr-1) has been isolated by screening ultraviolet light-mutagenized Ceratodon protonemata. Protonemata of wwr-l reoriented from the vertical to the horizontal grow down with kinetics comparable to those of the wild-type. Protonemata of wwr-1 also show initial and mitotic reversals where they temporarily grow up. Thus, the direction of gravitropism, initial reversal, and mitotic reversal are coordinated though each are opposite in wwr-1 compared to the wild-type. Normal plastid zonation is still maintained in dark-grown wwr-1 apical cells, but the plastids are more numerous and plastid sedimentation is more pronounced. In addition, wwr-1 apical cells are wider and the tips greener than in the wild-type. These data suggest that a functional WWR gene product is not necessary for the establishment of some gravitropic polarity, for gravitropism, or for the coordination of the reversals. Thus, the WWR protein may normally transduce information about cell orientation.

Tunneling Diode Based on WSe2 /SnS2 Heterostructure Incorporating High Detectivity and Responsivity.

PubMed

Zhou, Xing; Hu, Xiaozong; Zhou, Shasha; Song, Hongyue; Zhang, Qi; Pi, Lejing; Li, Liang; Li, Huiqiao; Lü, Jingtao; Zhai, Tianyou

2018-02-01

van der Waals (vdW) heterostructures based on atomically thin 2D materials have led to a new era in next-generation optoelectronics due to their tailored energy band alignments and ultrathin morphological features, especially in photodetectors. However, these photodetectors often show an inevitable compromise between photodetectivity and photoresponsivity with one high and the other low. Herein, a highly sensitive WSe 2 /SnS 2 photodiode is constructed on BN thin film by exfoliating each material and manually stacking them. The WSe 2 /SnS 2 vdW heterostructure shows ultralow dark currents resulting from the depletion region at the junction and high direct tunneling current when illuminated, which is confirmed by the energy band structures and electrical characteristics fitted with direct tunneling. Thus, the distinctive WSe 2 /SnS 2 vdW heterostructure exhibits both ultrahigh photodetectivity of 1.29 × 10 13 Jones (I ph /I dark ratio of ≈10 6 ) and photoresponsivity of 244 A W -1 at a reverse bias under the illumination of 550 nm light (3.77 mW cm -2 ). © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Radiation detection measurements with a new ``Buried Junction'' silicon avalanche photodiode

NASA Astrophysics Data System (ADS)

Lecomte, R.; Pepin, C.; Rouleau, D.; Dautet, H.; McIntyre, R. J.; McSween, D.; Webb, P.

1999-02-01

An improved version of a recently developed "Buried Junction" avalanche photodiode (APD), designed for use with scintillators, is described and characterized. This device, also called the "Reverse APD", is designed to have a wide depletion layer and thus low capacitance, but to have high gain only for e-h pairs generated within the first few microns of the depletion layer. Thus it has high gain for light from scintillators emitting in the 400-600 nm range, with relatively low dark current noise and it is relatively insensitive to minimum ionizing particles (MIPs). An additional feature is that the metallurgical junction is at the back of the wafer, leaving the front surface free to be coupled to a scintillator without fear of junction contamination. The modifications made in this device, as compared with the earlier diode, have resulted in a lower excess noise factor, lower dark current, and much-reduced trapping. The electrical and optical characteristics of this device are described and measurements of energy and timing resolution of this device with several scintillators (BGO, LSO and GSO) of potential interest in high-energy physics and PET imaging systems are presented.

Design of InAs/GaSb superlattice infrared barrier detectors

NASA Astrophysics Data System (ADS)

Delmas, M.; Rossignol, R.; Rodriguez, J. B.; Christol, P.

2017-04-01

Design of InAs/GaSb type-II superlattice (T2SL) infrared barrier detectors is theoretically investigated. Each part of the barrier structures is studied in order to achieve optimal device operation at 150 K and 77 K, in the midwave and longwave infrared domain, respectively. Whatever the spectral domain, nBp structure with a p-type absorbing zone and an n-type contact layer is found to be the most favourable detector architecture allowing a reduction of the dark-current associated with generation-recombination processes. The nBp structures are then compared to pin photodiodes. The MWIR nBp detector with 5 μm cut-off wavelength can operate up to 120 K, resulting in an improvement of 20 K on the operating temperature compared to the pin device. The dark-current density of the LWIR nBp device at 77 K is expected to be as low as 3.5 × 10-4 A/cm2 at 50 mV reverse bias, more than one decade lower than the usual T2SL photodiode. This result, for a device having cut-off wavelength at 12 μm, is at the state of the art compared to the well-known MCT 'rule 07'.

Low-dark current 1024×1280 InGaAs PIN arrays

NASA Astrophysics Data System (ADS)

Yuan, Ping; Chang, James; Boisvert, Joseph C.; Karam, Nasser

2014-06-01

Photon counting imaging applications requires low noise from both detector and readout integrated circuit (ROIC) arrays. In order to retain the photon-counting-level sensitivity, a long integration time has to be employed and the dark current has to be minimized. It is well known that the PIN dark current is sensitive to temperature and a dark current density of 0.5 nA/cm2 was demonstrated at 7 °C previously. In order to restrain the size, weight, and power consumption (SWaP) of cameras for persistent large-area surveillance on small platforms, it is critical to develop large format PIN arrays with small pitch and low dark current density at higher operation temperatures. Recently Spectrolab has grown, fabricated and tested 1024x1280 InGaAs PIN arrays with 12.5 μm pitch and achieved 0.7 nA/cm2 dark current density at 15 °C. Based on our previous low-dark-current PIN designs, the improvements were focused on 1) the epitaxial material design and growth control; and 2) PIN device structure to minimize the perimeter leakage current and junction diffusion current. We will present characterization data and analyses that illustrate the contribution of various dark current mechanisms.

Three-Phase Morphology Evolution in Sequentially Solution-Processed Polymer Photodetector: Toward Low Dark Current and High Photodetectivity.

PubMed

Wang, Hanyu; Xing, Shen; Zheng, Yifan; Kong, Jaemin; Yu, Junsheng; Taylor, André D

2018-01-31

Sequentially solution-processed polymer photodetectors (SSP PPDs) based on poly(3-hexylthiophene-2,5-diyl) (P3HT)/[6,6]-phenyl C 71 -butyric acid methyl ester (PC 71 BM) are fabricated by depositing the top layers of PC 71 BM from an appropriate cosolvent of 2-chlorophenol (2-CP)/o-dichlorobenzene (ODCB) onto the predeposited bottom layers of P3HT. By adjusting the ratio of 2-CP/ODCB in the top PC 71 BM layers, the resulting SSP PPD shows a decreased dark current and an increased photocurrent, leading to a maximum detectivity of 1.23 × 10 12 Jones at a wavelength of 550 nm. This value is 5.3-fold higher than that of the conventional bulk heterojunction PPD. Morphology studies reveal that the PC 71 BM partially penetrates the predeposited P3HT layer during the spin-coating process, resulting in an optimal three-phase morphology with one well-mixed interdiffusion P3HT/PC 71 BM phase in the middle of the bulk and two pure phases of P3HT and PC 71 BM at the two electrode sides. We show that the pure phases form high Schottky barriers (>2.0 eV) at the active layer/electrodes interface and efficiently block unfavorable reverse charge carrier injection by significantly decreasing the dark current. The interdiffussion phase enlarges the donor-acceptor interfacial area leading to a large photocurrent. We also reveal that the improved performance of SSP PPDs is also due to the enhanced optical absorption, improved P3HT crystallinity, increased charge carrier mobilities, and suppressed bimolecular recombination.

Thermal annealing response following irradiation of a CMOS imager for the JUICE JANUS instrument

NASA Astrophysics Data System (ADS)

Lofthouse-Smith, D.-D.; Soman, M. R.; Allanwood, E. A. H.; Stefanov, K. D.; Holland, A. D.; Leese, M.; Turne, P.

2018-03-01

ESA's JUICE (JUpiter ICy moon Explorer) spacecraft is an L-class mission destined for the Jovian system in 2030. Its primary goals are to investigate the conditions for planetary formation and the emergence of life, and how does the solar system work. The JANUS camera, an instrument on JUICE, uses a 4T back illuminated CMOS image sensor, the CIS115 designed by Teledyne e2v. JANUS imager test campaigns are studying the CIS115 following exposure to gammas, protons, electrons and heavy ions, simulating the harsh radiation environment present in the Jovian system. The degradation of 4T CMOS device performance following proton fluences is being studied, as well as the effectiveness of thermal annealing to reverse radiation damage. One key parameter for the JANUS mission is the Dark current of the CIS115, which has been shown to degrade in previous radiation campaigns. A thermal anneal of the CIS115 has been used to accelerate any annealing following the irradiation as well as to study the evolution of any performance characteristics. CIS115s have been irradiated to double the expected End of Life (EOL) levels for displacement damage radiation (2×1010 protons, 10 MeV equivalent). Following this, devices have undergone a thermal anneal cycle at 100oC for 168 hours to reveal the extent to which CIS115 recovers pre-irradiation performance. Dark current activation energy analysis following proton fluence gives information on trap species present in the device and how effective anneal is at removing these trap species. Thermal anneal shows no quantifiable change in the activation energy of the dark current following irradiation.

Earth Observing-1 Advanced Imager Flight Performance Assessment: Investigating Dark Current Stability Over One-Half Orbit Period during the First 60 Days

NASA Technical Reports Server (NTRS)

Mendenhall, J. A.

2001-01-01

The stability of the EO-1 Advanced Land Imager dark current levels over the period of one-half orbit is investigated. A series of two-second dark current collections, over the course of 40 minutes, was performed during the first sixty days the instrument was in orbit. Analysis of this data indicates only two dark current reference periods, obtained entering and exiting eclipse, are required to remove ALI dark current offsets for 99.9% of the focal plane to within 1.5 digital numbers for any observation on the solar illuminated portion of the orbit.

Schottky x-ray detectors based on a bulk β-Ga2O3 substrate

NASA Astrophysics Data System (ADS)

Lu, Xing; Zhou, Leidang; Chen, Liang; Ouyang, Xiaoping; Liu, Bo; Xu, Jun; Tang, Huili

2018-03-01

β-Ga2O3 Schottky barrier diodes (SBDs) have been fabricated on a bulk (100) β-Ga2O3 substrate and tested as X-ray detectors in this study. The devices exhibited good rectification properties, such as a high rectification ratio and a close-to-unity ideality factor. A high photo-to-dark current ratio exceeding 800 was achieved for X-ray detection, which was mainly attributed to the low reverse leakage current in the β-Ga2O3 SBDs. Furthermore, transient response of the β-Ga2O3 X-ray detectors was investigated, and two different detection mechanisms, photovoltaic and photoconductive, were identified. The results imply the great potential of β-Ga2O3 based devices for X-ray detection.

Near-infrared photodetector with reduced dark current

DOEpatents

Klem, John F; Kim, Jin K

2012-10-30

A photodetector is disclosed for the detection of near-infrared light with a wavelength in the range of about 0.9-1.7 microns. The photodetector, which can be formed as either an nBp device or a pBn device on an InP substrate, includes an InGaAs light-absorbing layer, an InAlGaAs graded layer, an InAlAs or InP barrier layer, and an InGaAs contact layer. The photodetector can detect near-infrared light with or without the use of an applied reverse-bias voltage and is useful as an individual photodetector, or to form a focal plane array.

Photovoltaic retinal prosthesis for restoring sight to the blind: implant design and fabrication

NASA Astrophysics Data System (ADS)

Wang, Lele; Mathieson, Keith; Kamins, Theodore I.; Loudin, James; Galambos, Ludwig; Harris, James S.; Palanker, Daniel

2012-03-01

We have designed and fabricated a silicon photodiode array for use as a subretinal prosthesis aimed at restoring sight to patients who lost photoreceptors due to retinal degeneration. The device operates in photovoltaic mode. Each pixel in the two-dimensional array independently converts pulsed infrared light into biphasic electric current to stimulate remaining retinal neurons without a wired power connection. To enhance the maximum voltage and charge injection levels, each pixel contains three photodiodes connected in series. An active and return electrode in each pixel ensure localized current flow and are sputter coated with iridium oxide to provide high charge injection. The fabrication process consists of eight mask layers and includes deep reactive ion etching, oxidation, and a polysilicon trench refill for in-pixel photodiode separation and isolation of adjacent pixels. Simulation of design parameters included TSUPREM4 computation of doping profiles for n+ and p+ doped regions and MATLAB computation of the anti-reflection coating layers thicknesses. The main process steps are illustrated in detail, and problems encountered are discussed. The IV characterization of the device shows that the dark reverse current is on the order of 10-100 pA-negligible compared to the stimulation current; the reverse breakdown voltage is higher than 20 V. The measured photo-responsivity per photodiode is about 0.33A/W at 880 nm.

Development of Low Parasitic Light Sensitivity and Low Dark Current 2.8 μm Global Shutter Pixel †

PubMed Central

Yokoyama, Toshifumi; Tsutsui, Masafumi; Suzuki, Masakatsu; Nishi, Yoshiaki; Mizuno, Ikuo; Lahav, Assaf

2018-01-01

We developed a low parasitic light sensitivity (PLS) and low dark current 2.8 μm global shutter pixel. We propose a new inner lens design concept to realize both low PLS and high quantum efficiency (QE). 1/PLS is 7700 and QE is 62% at a wavelength of 530 nm. We also propose a new storage-gate based memory node for low dark current. P-type implants and negative gate biasing are introduced to suppress dark current at the surface of the memory node. This memory node structure shows the world smallest dark current of 9.5 e−/s at 60 °C. PMID:29370146

Development of Low Parasitic Light Sensitivity and Low Dark Current 2.8 μm Global Shutter Pixel.

PubMed

Yokoyama, Toshifumi; Tsutsui, Masafumi; Suzuki, Masakatsu; Nishi, Yoshiaki; Mizuno, Ikuo; Lahav, Assaf

2018-01-25

Abstract : We developed a low parasitic light sensitivity (PLS) and low dark current 2.8 μm global shutter pixel. We propose a new inner lens design concept to realize both low PLS and high quantum efficiency (QE). 1/PLS is 7700 and QE is 62% at a wavelength of 530 nm. We also propose a new storage-gate based memory node for low dark current. P-type implants and negative gate biasing are introduced to suppress dark current at the surface of the memory node. This memory node structure shows the world smallest dark current of 9.5 e - /s at 60 °C.

A sign-reversing pathway from rods to double and single cones in the retina of the tiger salamander.

PubMed

Attwell, D; Werblin, F S; Wilson, M; Wu, S M

1983-03-01

Signal transmission between rods and cones was studied by passing current into a rod and recording the voltage response in a nearby double or single cone and vice versa. Two types of rod-cone interaction were found. Between immediately adjacent rods and cones, passage of current into either receptor elicited in the other receptor a sustained voltage response of the same sign as the injected current. These signals were still seen in the presence of Co2+, and are probably mediated by the electrical synapses which have been seen anatomically between adjacent rods and cones. In addition to this short-range sign-preserving interaction, passing current into a rod elicited a transient sign-inverted signal in cones up to at least 80 micron from the injected rod. No such response was seen in rods for current injection into cones. This signal was greatly reduced by Co2+ ions. Hyperpolarization of the cone to about -65 mV, with about 0.1 nA current, reversed this signal, which is presumed to be mediated by a chemical synaptic input to cones. Light flashes suppressed the sign-inverted signal for a period which was longer for brighter flashes. The time of reappearance of the signal was correlated with the return of the rod and horizontal cell potentials to their dark levels. This suppression could also be produced by an annulus of light which produced no light response in the receptors at the centre of the annulus, but which did polarize horizontal cells under the centre of the annulus. The wave form of the sign-inverted signal was similar to that produced in horizontal cells by current injection into rods, but of opposite sign. If an electrode was left in a cone for some time, the normal hyperpolarizing light response diminished, leaving a depolarizing response produced, presumably, by feed-back from horizontal cells. This signal was reversed when the cone was hyperpolarized with about 0.1 nA current. These data suggest that the sign-inverted response is mediated by feed-back from horizontal cells and, assuming that depolarization increases the rate of release of horizontal cell synaptic transmitter, then the feed-back transmitter opens channels in the cone membrane whose currents have a reversal potential around -65 mV.

Correlation between morphological defects, electron beam-induced current imaging, and the electrical properties of 4H-SiC Schottky diodes

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

Wang, Y.; Ali, G.N.; Mikhov, M.K.

2005-01-01

Defects in SiC degrade the electrical properties and yield of devices made from this material. This article examines morphological defects in 4H-SiC and defects visible in electron beam-induced current (EBIC) images and their effects on the electrical characteristics of Schottky diodes. Optical Nomarski microscopy and atomic force microscopy were used to observe the morphological defects, which are classified into 26 types based on appearance alone. Forward and reverse current-voltage characteristics were used to extract barrier heights, ideality factors, and breakdown voltages. Barrier heights decrease about linearly with increasing ideality factor, which is explained by discrete patches of low barrier heightmore » within the main contact. Barrier height, ideality, and breakdown voltage all degrade with increasing device diameter, suggesting that discrete defects are responsible. Electroluminescence was observed under reverse bias from microplasmas associated with defects containing micropipes. EBIC measurements reveal several types of features corresponding to recombination centers. The density of dark spots observed by EBIC correlates strongly with ideality factor and barrier height. Most morphological defects do not affect the reverse characteristics when no micropipes are present, but lower the barrier height and worsen the ideality factor. However, certain multiple-tailed defects, irregularly shaped defects and triangular defects with 3C inclusions substantially degrade both breakdown voltage and barrier height, and account for most of the bad devices that do not contain micropipes. Micropipes in these wafers are also frequently found to be of Type II, which do not run parallel to the c axis.« less

Correlation Between Morphological Defects, Electron Beam Induced Current Imaging, and the Electrical Properties of 4H-SiC Schottky Diodes

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

Wang,Y.; Ali, G.; Mikhov, M.

2005-01-01

Defects in SiC degrade the electrical properties and yield of devices made from this material. This article examines morphological defects in 4H-SiC and defects visible in electron beam-induced current (EBIC) images and their effects on the electrical characteristics of Schottky diodes. Optical Nomarski microscopy and atomic force microscopy were used to observe the morphological defects, which are classified into 26 types based on appearance alone. Forward and reverse current-voltage characteristics were used to extract barrier heights, ideality factors, and breakdown voltages. Barrier heights decrease about linearly with increasing ideality factor, which is explained by discrete patches of low barrier heightmore » within the main contact. Barrier height, ideality, and breakdown voltage all degrade with increasing device diameter, suggesting that discrete defects are responsible. Electroluminescence was observed under reverse bias from microplasmas associated with defects containing micropipes. EBIC measurements reveal several types of features corresponding to recombination centers. The density of dark spots observed by EBIC correlates strongly with ideality factor and barrier height. Most morphological defects do not affect the reverse characteristics when no micropipes are present, but lower the barrier height and worsen the ideality factor. However, certain multiple-tailed defects, irregularly shaped defects and triangular defects with 3C inclusions substantially degrade both breakdown voltage and barrier height, and account for most of the bad devices that do not contain micropipes. Micropipes in these wafers are also frequently found to be of Type II, which do not run parallel to the c axis.« less

Rhythmic Larval Release in the Crab Dyspanopeus sayi: Entrainment by Light:Dark and Temperature Cycles

NASA Astrophysics Data System (ADS)

Sanchez, K.

2016-02-01

The release of larvae from the abdomen of the common subtidal crab Dyspanopeus sayi is not random, but instead is associated with several environmental rhythms, in particular light:dark rhythms. Previous work has given us a model which suggests the mother perceives the light:dark cycle and entrains this rhythm upon the embryos, which then stimulate release when the time is right. For this project the light:dark cycle and 24-hour temperature cycle were investigated. Crabs placed in constant conditions were able to display an endogenous circadian rhythm, with release occurring in the hours after sunset and with a period of 24.1 hours. Crabs with embryos of all stages without eye-slits were placed in a reversed light:dark cycle, and they were able to reset the entrainment and release in the hours following 06:00 hrs., the new sunset. The difference between the crabs in the altered cycle and the crabs in the field is significant. Finally, crabs placed in a reversed 24-hour temperature cycle were able to reset the entrainment after 4-5 days in the altered cycle, such that they also released in the hours after 06:00. The fact that the temperature is enough to cause entrainment suggests that maybe the female or embryos do not need to perceive the light in order to know when to induce larval release. In any event, this result opens up new areas of research involving decapod reproduction, in particular D. sayi.

Proteome-wide Light/Dark Modulation of Thiol Oxidation in Cyanobacteria Revealed by Quantitative Site-specific Redox Proteomics*

PubMed Central

Guo, Jia; Nguyen, Amelia Y.; Dai, Ziyu; Su, Dian; Gaffrey, Matthew J.; Moore, Ronald J.; Jacobs, Jon M.; Monroe, Matthew E.; Smith, Richard D.; Koppenaal, David W.; Pakrasi, Himadri B.; Qian, Wei-Jun

2014-01-01

Reversible protein thiol oxidation is an essential regulatory mechanism of photosynthesis, metabolism, and gene expression in photosynthetic organisms. Herein, we present proteome-wide quantitative and site-specific profiling of in vivo thiol oxidation modulated by light/dark in the cyanobacterium Synechocystis sp. PCC 6803, an oxygenic photosynthetic prokaryote, using a resin-assisted thiol enrichment approach. Our proteomic approach integrates resin-assisted enrichment with isobaric tandem mass tag labeling to enable site-specific and quantitative measurements of reversibly oxidized thiols. The redox dynamics of ∼2,100 Cys-sites from 1,060 proteins under light, dark, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (a photosystem II inhibitor) conditions were quantified. In addition to relative quantification, the stoichiometry or percentage of oxidation (reversibly oxidized/total thiols) for ∼1,350 Cys-sites was also quantified. The overall results revealed broad changes in thiol oxidation in many key biological processes, including photosynthetic electron transport, carbon fixation, and glycolysis. Moreover, the redox sensitivity along with the stoichiometric data enabled prediction of potential functional Cys-sites for proteins of interest. The functional significance of redox-sensitive Cys-sites in NADP-dependent glyceraldehyde-3-phosphate dehydrogenase, peroxiredoxin (AhpC/TSA family protein Sll1621), and glucose 6-phosphate dehydrogenase was further confirmed with site-specific mutagenesis and biochemical studies. Together, our findings provide significant insights into the broad redox regulation of photosynthetic organisms. PMID:25118246

Synergistic Effect of Light and Fusicoccin on Stomatal Opening 1

PubMed Central

Assmann, Sarah M.; Schwartz, Amnon

1992-01-01

Upon incubation of epidermal peels of Commelina communis in 1 millimolar KCl, a synergistic effect of light and low fusicoccin (FC) concentrations on stomatal opening is observed. In 1 millimolar KCl, stomata remain closed even in the light. However, addition of 0.1 micromolar FC results in opening up to 12 micrometers. The same FC concentration stimulates less than 5 micrometers of opening in darkness. The synergistic effect (a) decreases with increasing FC or KCl concentrations; (b) is dark-reversible; (c) like stomatal opening in high KCl concentrations (120 millimolar) is partially inhibited by the K+ channel blocker, tetraethyl-ammonium+ (20 millimolar). In whole-cell patch-clamp experiments with guard cell protoplasts of Vicia faba, FC (1 or 10 micromolar) stimulates an increase in outward current that is essentially voltage independent between - 100 and +60 millivolts, and occurs even when the membrane potential is held at a voltage (−60 millivolts) at which K+ channels are inactivated. These results are indicative of FC activation of a H+ pump. FC effects on the magnitude of inward and outward K+ currents are not observed. Epidermal peel and patch clamp data are both consistent with the hypothesis that the plasma membrane H+ ATPase of guard cells is a primary locus for the FC effect on stomatal apertures. PMID:16668799

Dark current of organic heterostructure devices with insulating spacer layers

NASA Astrophysics Data System (ADS)

Yin, Sun; Nie, Wanyi; Mohite, Aditya D.; Saxena, Avadh; Smith, Darryl L.; Ruden, P. Paul

2015-03-01

The dark current density at fixed voltage bias in donor/acceptor organic planar heterostructure devices can either increase or decrease when an insulating spacer layer is added between the donor and acceptor layers. The dominant current flow process in these systems involves the formation and subsequent recombination of an interfacial exciplex state. If the exciplex formation rate limits current flow, the insulating interface layer can increase dark current whereas, if the exciplex recombination rate limits current flow, the insulating interface layer decreases dark current. We present a device model to describe this behavior and illustrate it experimentally for various donor/acceptor systems, e.g. P3HT/LiF/C60.

Dark Currents and Their Effect on the Primary Beam in an X-band Linac

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

Bane, K.L.F.; Dolgashev, V.A.; Raubenheimer, T.

2005-05-27

We numerically study properties of primary dark currents in an X-band accelerating structure. For the H60VG3 structure considered for the Next Linear Collider (NLC) we first perform a fairly complete (with some approximations) calculation of dark current trajectories. These results are used to study properties of the dark current leaving the structure. For example, at accelerating gradient of 65 MV/m, considering two very different assumptions about dark current emission around the irises, we find that the fraction of emitted current leaving the structure to be a consistent {approx} 1%. Considering that {approx} 1 mA outgoing dark current is seen inmore » measurement, this implies that {approx} 100 mA (or 10 pC per period) is emitted within the structure itself. Using the formalism of the Lienard-Wiechert potentials, we then perform a systematic calculation of the transverse kick of dark currents on a primary linac bunch. The result is {approx} 1 V kick per mA (or per 0.1 pC per period) dark current emitted from an iris. For an entire structure we estimate the total kick on a primary bunch to be {approx} 15 V. For the NLC linac this translates to a ratio of (final) vertical beam offset to beam size of about 0.2. However, with the assumptions that needed to be made--particularly the number of emitters and their distribution within a structure--the accuracy of this result may be limited to the order of magnitude.« less

Optoelectronic characteristics of UV photodetector based on GaN/ZnO nanorods p- i- n heterostructures

NASA Astrophysics Data System (ADS)

Zhang, Lichun; Zhao, Fengzhou; Wang, Caifeng; Wang, Feifei; Huang, Ruizhi; Li, Qingshan

2015-07-01

We demonstrate an efficient ultraviolet (UV) photodetector operating at room temperature based on n-ZnO nanorods/ i-ZnO/ p-GaN heterojunctions. We employ x-ray diffraction and field-emission scanning electron microscopy to confirm the high quality of the ZnO nanorods using an undoped ZnO film as the interlayer. Then, we investigate the photoelectric properties of the fabricated photodetector with UV light illumination under a different reverse bias. Based on the current-voltage curve, the photocurrent to dark current ratio is approximately 73.3 at -4 V. At zerobias voltage, the peak responsivity was 138.9 mA/W at 362 nm under front-illumination conditions. Time-varying measurements indicate the reproducibility and stability of the heterojunction photodetector. [Figure not available: see fulltext.

Effects of temperature on the gas exchange of leaves in the light and dark.

PubMed

Hofstra, G; Hesketh, J D

1969-09-01

Evolution of CO2 into CO2-free air was measured in the light and in the dark over a range of temperatures from 15 to 50°. Photosynthetic rates were measured in air and O2-free air over the same range of temperatures. Respiration in the light had a different sensitivity to temperature compared with respiration in the dark. At the lower temperatures the rate of respiration in the light was higher than respiration in the dark, whereas at temperatures above 40° the reverse was observed. For any one species the maximum rates of photosynthesis and photorespiration occur at about the same temperature. The maximum rate for dark respiration generally is found at a temperature about 10° higher. Zea mays and Atriplex nummularia showed no enhancement of photosynthesis in O2-free air nor any evolution of CO2 in CO2-free air at any of the temperatures.

Earth Observing-1 Advanced Land Imager: Dark Current and Noise Characterization and Anomalous Detectors

NASA Technical Reports Server (NTRS)

Mendenhall, J. A.

2001-01-01

The dark current and noise characteristics of the Earth Observing-1 Advanced Land Imager measured during ground calibration at MIT Lincoln Laboratory are presented. Data were collected for the nominal focal plane operating temperature of 220 K as well as supplemental operating temperatures (215 and 225 K). Dark current baseline values are provided, and noise characterization includes the evaluation of white, coherent, low frequency, and high frequency components. Finally, anomalous detectors, characterized by unusual dark current, noise, gain, or cross-talk properties are investigated.

Effects of Extended Hypoxia on Night Vision

DTIC Science & Technology

1983-06-01

Continue on reverse aide it necessary and identify by block number) hypoxia, anoxia , night vision, dark adaptation, extended hypoxia /y虦 SABDST’RACT M=t...and his colleagues, who not only quantified significant aspects of the dark adaptation function due to anoxia (hypoxia) (12,13,14,16), but also...and his co-workers (7) conducted related and very significant research on bright- ness discrimination, and concluded that anoxia acts mainly on the

Long-range sound-mediated dark-soliton interactions in trapped atomic condensates

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

Allen, A. J.; Jackson, D. P.; Barenghi, C. F.

2011-01-15

A long-range soliton interaction is discussed whereby two or more dark solitons interact in an inhomogeneous atomic condensate, modifying their respective dynamics via the exchange of sound waves without ever coming into direct contact. An idealized double-well geometry is shown to yield perfect energy transfer and complete periodic identity reversal of the two solitons. Two experimentally relevant geometries are analyzed which should enable the observation of this long-range interaction.

Accounting for Dark Current Accumulated during Readout of Hubble's ACS/WFC Detectors

NASA Astrophysics Data System (ADS)

Ryon, Jenna E.; Grogin, Norman A.; Coe, Dan A.; ACS Team

2018-06-01

We investigate the properties of excess dark current accumulated during the 100-second full-frame readout of the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) detectors. This excess dark current, called "readout dark", gives rise to ambient background gradients and hot columns in each ACS/WFC image. While readout dark signal is removed from science images during the bias correction step in CALACS, the additional noise from the readout dark is currently not taken into account. We develop a method to estimate the readout dark noise properties in ACS/WFC observations. We update the error (ERR) extensions of superbias images to include the appropriate noise from the ambient readout dark gradient and stable hot columns. In recent data, this amounts to about 5 e-/pixel added variance in the rows farthest from the WFC serial registers, and about 7 to 30 e-/pixel added variance along the stable hot columns. We also flag unstable hot columns in the superbias data quality (DQ) extensions. The new reference file pipeline for ACS/WFC implements these updates to our superbias creation process.

An Exploration of WFC3/IR Dark Current Variation

NASA Astrophysics Data System (ADS)

Sunnquist, B.; Baggett, S.; Long, K. S.

2017-02-01

We use a collection of darks spanning September 2009 to June 2016 to study variations in the dark current in the IR detector on WFC3. Although the darks possess a similar signal pattern across the detector, we find that their median dark rates vary by as much as 0.014 DN/s (0.032 e-/s). The distribution of these median values has a triangular shape with a mean and standard deviation of 0.021 ± 0.0029 DN/s (0.049 ± 0.0069 e-/s). We observe a long term time-dependence in the inboard vertical reference pixel and zeroth read signals; however, these differences do not noticeably affect the calibrated dark signals, and we conclude that the WFC3/IR dark current levels continue to remain stable since launch. The inboard reference pixel signals exhibit a unique, but consistent, pattern around the detector, but this pattern does not evolve noticeably with the median of the science pixels, and a quadrant or row-based reference pixel subtraction strategy does not reduce the spread between the median dark rates. We notice a slight drift in the inboard reference pixel signals up the dark ramps, and the intensity of this drift is related to the median dark current in the science pixels. This holds true using either the horizontal or vertical reference pixels and for darks with a variety of sample sequences.

Small Bowel Follow-Through

MedlinePlus

... in size and shape and evaluate how waste matter moves through it. It also may be performed ... the area being examined by making it appear dark (or by electronically reversing the image contrast to ...

Pediatric Voiding Cystourethrogram

MedlinePlus

... the area being examined by making it appear dark (or by electronically reversing the image contrast to ... Disclaimer This information is copied from the RadiologyInfo Web site (http://www.radiologyinfo.org) which is dedicated ...

The influence of visible light on transparent zinc tin oxide thin film transistors

NASA Astrophysics Data System (ADS)

Görrn, P.; Lehnhardt, M.; Riedl, T.; Kowalsky, W.

2007-11-01

The characteristics of transparent zinc tin oxide thin film transistors (TTFTs) upon illumination with visible light are reported. Generally, a reversible decrease of threshold voltage Vth, saturation field effect mobility μsat, and an increase of the off current are found. The time scale of the recovery in the dark is governed by the persistent photoconductivity in the semiconductor. Devices with tuned [Zn]:[Sn] ratio show a shift of Vth of less 2V upon illumination at 5mW/cm2 (brightness >30000cd/m2) throughout the visible spectrum. These results demonstrate TTFTs which are candidates as pixel drivers in transparent active-matrix organic light emitting diode displays.

Dark current reduction of Ge photodetector by GeO₂ surface passivation and gas-phase doping.

PubMed

Takenaka, Mitsuru; Morii, Kiyohito; Sugiyama, Masakazu; Nakano, Yoshiaki; Takagi, Shinichi

2012-04-09

We have investigated the dark current of a germanium (Ge) photodetector (PD) with a GeO₂ surface passivation layer and a gas-phase-doped n+/p junction. The gas-phase-doped PN diodes exhibited a dark current of approximately two orders of magnitude lower than that of the diodes formed by a conventional ion implantation process, indicating that gas-phase doping is suitable for low-damage PN junction formation. The bulk leakage (Jbulk) and surface leakage (Jsurf) components of the dark current were also investigated. We have found that GeO₂ surface passivation can effectively suppress the dark current of a Ge PD in conjunction with gas-phase doping, and we have obtained extremely low values of Jbulk of 0.032 mA/cm² and Jsurf of 0.27 μA/cm.

SWIR HgCdTe avalanche photiode focal plane array performances evaluation

NASA Astrophysics Data System (ADS)

de Borniol, E.; Rothman, J.; Salveti, F.; Feautrier, P.

2017-11-01

One of the main challenges of modern astronomical instruments like adaptive optics (AO) systems or fringe trackers is to deal with the very low photons flux detection scenarios. The typical timescale of atmospheric turbulences being in the range of some tens of milliseconds, infrared wavefront sensors for AO systems needs frame rates higher than 1 KHz leading to integration times lower than 1 ms. This integration time associated with a low irradiance results in a few number of integrated photons per frame per pixel. To preserve the information coming from this weak signal, the focal plane array (FPA) has to present a low read out noise, a high quantum efficiency and a low dark current. Up to now, the output noise of high speed near infrared sensors is limited by the silicon read out circuit noise. The use of HgCdTe avalanche photodiodes with high gain at moderate reverse bias and low excess noise seems then a logical way to reduce the impact of the read noise on images signal to noise ratio. These low irradiance passive imaging applications with integration times in the millisecond range needs low photodiode dark current and low background current. These requirements lead to the choice of the photodiode cut off wavelength. The short wave infrared (SWIR) around 3 μm is a good compromise between the gain that can be obtain for a given APD bias and the background and dark current. The CEA LETI HgCdTe APD technology, and a fine analysis of the gain curve characteristic are presented in [1] and won't be detailed here. The response time of the APD is also a key factor for a high frame rate FPA. This parameter has been evaluated in [2] and the results shows cut off frequencies in the GHz range. In this communication we report the performances of a SWIR APD FPA designed and fabricated by CEA LETI and SOFRADIR for astrophysical applications. This development was made in the frame of RAPID, a 4 years R&D project funded by the French FUI (Fond Unique Interministériel). This project involves industrial and academic partners from the field of advanced infrared focal plane arrays fabrication (SOFRADIR and CEA LETI) and of astronomical/defense institutes (IPAG, LAM, ONERA). The goal of this program is to develop a fast and low noise SWIR camera for astronomical fast applications like adaptive optics wavefront sensing and fringe tracking for astronomical interferometers [3]. The first batch of FPA's was based on liquid-phase epitaxy (LPE) grown photodiode arrays with 3 μm cut off wavelength. In order to get higher avalanche gain for a given photodiode reverse bias voltage, we have made a second batch with a cadmium composition leading to 3.3 μm cut off wavelength (λc). This paper described the read out circuit in the next section. The aim section III is to find the critical parameter that has to be measured to evaluate the signal to noise ratio (SNR) of an APD FPA. The main electro optical characteristics of an FPA based on 3.3μm cut off wavelength APDs are reported in "Rapid FPAs characterisation" section. The dark current evolution with temperature of a 3 μm FPA high and low APD bias is also detailed in this section.

The interface modification for GNWs/Si Schottky junction with PEI/PEIE interlayers

NASA Astrophysics Data System (ADS)

Zhou, Quan; Liu, Xiangzhi; Luo, Wei; Shen, Jun; Wang, Yuefeng; Wei, Dapeng

2018-03-01

Polyethylenimine ethoxylated (PEIE) and polyethyl-enimine (PEI), the two kinds of interface buffer layer, are widely used in the organic light-emitting diodes and solar cells for band alignment adjustment. In this report, we carefully studied the influence of the inserting organic layer on the graphene nanowalls(GNWS)/Si junction quality and the photoresponse of the Schottky devices. We found that thinner layers of PEI could decrease the dark current and improve the photo-to-dark ratio to 105 for n-Si devices. The s-kink effect and degradation of open circuit voltage could be observed for thicker thickness and excessive doping. Relatively, PEIE with stable thin layer not only improve the rectifying characteristics of p-Si devices but also the incident photon conversion efficiency. The maximus IPCE could reach 44% and be adjusted to zero by the reverse bias. The tunneling inhibition for electrons can be alleviated by increasing the barrier height. Our results provide an attractive method to improve the efficiency of pristine GNWs/Si junction with interface doping and passivation.

Photoperiod Modulates Fast Delayed Rectifier Potassium Currents in the Mammalian Circadian Clock.

PubMed

Farajnia, Sahar; Meijer, Johanna H; Michel, Stephan

2016-10-01

One feature of the mammalian circadian clock, situated in the suprachiasmatic nucleus (SCN), is its ability to measure day length and thereby contribute to the seasonal adaptation of physiology and behavior. The timing signal from the SCN, namely the 24 hr pattern of electrical activity, is adjusted according to the photoperiod being broader in long days and narrower in short days. Vasoactive intestinal peptide and gamma-aminobutyric acid play a crucial role in intercellular communication within the SCN and contribute to the seasonal changes in phase distribution. However, little is known about the underlying ionic mechanisms of synchronization. The present study was aimed to identify cellular mechanisms involved in seasonal encoding by the SCN. Mice were adapted to long-day (light-dark 16:8) and short-day (light-dark 8:16) photoperiods and membrane properties as well as K + currents activity of SCN neurons were measured using patch-clamp recordings in acute slices. Remarkably, we found evidence for a photoperiodic effect on the fast delayed rectifier K + current, that is, the circadian modulation of this ion channel's activation reversed in long days resulting in 50% higher peak values during the night compared with the unaltered day values. Consistent with fast delayed rectifier enhancement, duration of action potentials during the night was shortened and afterhyperpolarization potentials increased in amplitude and duration. The slow delayed rectifier, transient K + currents, and membrane excitability were not affected by photoperiod. We conclude that photoperiod can change intrinsic ion channel properties of the SCN neurons, which may influence cellular communication and contribute to photoperiodic phase adjustment. © The Author(s) 2016.

Hot spots and dark current in advanced plasma wakefield accelerators

DOE PAGES

Manahan, G. G.; Deng, A.; Karger, O.; ...

2016-01-29

Dark current can spoil witness bunch beam quality and acceleration efficiency in particle beam-driven plasma wakefield accelerators. In advanced schemes, hot spots generated by the drive beam or the wakefield can release electrons from higher ionization threshold levels in the plasma media. Likewise, these electrons may be trapped inside the plasma wake and will then accumulate dark current, which is generally detrimental for a clear and unspoiled plasma acceleration process. The strategies for generating clean and robust, dark current free plasma wake cavities are devised and analyzed, and crucial aspects for experimental realization of such optimized scenarios are discussed.

Dark Current Reduction of IR Detectors

DTIC Science & Technology

2017-10-19

demonstrating a novel dark current reduction approach for dense infrared detector arrays. This technique is based on the diffusion control junction (DCJ...fabricate and test detector arrays with and without DCJs on the same wafer and demonstrate the effectiveness of the DCJ approach in reducing dark current...subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE

Morphological and electro optic studies of polymer dispersed liquid crystal in reverse mode

NASA Astrophysics Data System (ADS)

Sharma, Vandna; Kumar, Pankaj; Chinky, Malik, Praveen; Raina, K. K.

2018-05-01

Present work deals with reverse mode polymer dispersed liquid crystals (PDLCs) sensitive to electric field. Contrary to the conventional PDLCs operate from opaque (OFF state) to transparent state (ON state) with the application of field, reverse mode PDLCs work in transparent to opaque state. Reverse mode PDLC composed of nematic LC and UV curable optical adhesive polymer were prepared by the polymerization induced phase separation. The polarizing optical microscope study shows the vertical alignment of LCs within droplets with initial dark state under cross polarizers and confirms preliminary natural transparent state. The electro optic (EO) results show that the reverse mode PDLC lowered the threshold and operating voltages significantly compared with reported values. The contrast ratio of the film was also studied.

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

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

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

2012-07-01

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

The functional organization of the crayfish lamina ganglionaris. I. Nonspiking monopolar cells.

PubMed

Wang-Bennett, L T; Glantz, R M

1987-06-01

The light responses of the second order lamina monopolar neurons were examined in the crayfish compound eye. Single cartridge monopolar neurons (M1-M4) exhibited nonspiking hyperpolarizing light responses; for M1, M3 and M4 the transient 'on' response operated over the same intensity range as the receptor, 3.5 log units. M2 operated in a much narrower intensity range (1.5 log unit). The 'on' responses were associated with a 19% increase in conductance. The hyperpolarizing 'on' response can be reversed at 18 mV below the resting membrane potential. The half-angular sensitivity width of monopolar cells (in partially dark-adapted eyes) is 15 degrees X 8 degrees (horizontal by vertical). Off axis stimuli elicit attenuated hyperpolarizing responses associated with a diminished conductance increase or depolarizing responses associated with a net decrease in conductance. The latter result is consistent with the presynaptic inhibition of a 'back-ground' transmitter release which normally persists in the dark. Lateral inhibition is elicited from the area immediately surrounding the excitatory field, and it is associated with diminished transient responses and an accelerated decay of the response. Inhibitory stimuli decrease the conductance change associated with the hyperpolarizing response. The surround stimuli can also elicit depolarizing 'off' responses with reversal potentials positive to the membrane resting potential. It is concluded that the rapidly repolarizing monopolar cell response is modulated by both pre- and postsynaptic inhibitory mechanisms. A compartment model indicates that signal attenuation along a 500 microns length of monopolar cell axon is 22-34%. Simulation of steady-state signal transmission suggests that passive (decremental) conduction is sufficient to convey 66 to 78% of the monopolar cell signal from lamina to medulla. The current-voltage relation in current clamp is linear over the physiological operating range, and there is no evidence for rectification. Hyperpolarization of single monopolar cells (M1-M4) provides a polysynaptic excitatory signal to the medullary sustaining fibers.

Nonlinear time dependence of dark current in charge-coupled devices

NASA Astrophysics Data System (ADS)

Dunlap, Justin C.; Bodegom, Erik; Widenhorn, Ralf

2011-03-01

It is generally assumed that charge-coupled device (CCD) imagers produce a linear response of dark current versus exposure time except near saturation. We found a large number of pixels with nonlinear dark current response to exposure time to be present in two scientific CCD imagers. These pixels are found to exhibit distinguishable behavior with other analogous pixels and therefore can be characterized in groupings. Data from two Kodak CCD sensors are presented for exposure times from a few seconds up to two hours. Linear behavior is traditionally taken for granted when carrying out dark current correction and as a result, pixels with nonlinear behavior will be corrected inaccurately.

Low dark current InGaAs detector arrays for night vision and astronomy

NASA Astrophysics Data System (ADS)

MacDougal, Michael; Geske, Jon; Wang, Chad; Liao, Shirong; Getty, Jonathan; Holmes, Alan

2009-05-01

Aerius Photonics has developed large InGaAs arrays (1K x 1K and greater) with low dark currents for use in night vision applications in the SWIR regime. Aerius will present results of experiments to reduce the dark current density of their InGaAs detector arrays. By varying device designs and passivations, Aerius has achieved a dark current density below 1.0 nA/cm2 at 280K on small-pixel, detector arrays. Data is shown for both test structures and focal plane arrays. In addition, data from cryogenically cooled InGaAs arrays will be shown for astronomy applications.

Ultra-Fast Image Sensor Using Ge on Insulator MIS/Schottky Detectors

DTIC Science & Technology

2008-05-28

electronic system. The noise equivalent power is defined as in /R, where in is the current noise and R is the responsivity. At 1 V, the current noise ...is limited by the dark current and can be approximated as the shot noise 2eIdf1/2, where Id is the measured dark current. At 0 V, the dark current...approaches zero, and the current noise should be approximated as Johnson noise 4kTGf1/2, where G is the measured conductance. Therefore, D* can be

In Situ observation of dark current emission in a high gradient rf photocathode gun

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

Shao, Jiahang; Shi, Jiaru; Antipov, Sergey P.

Undesirable electron field emission (also known as dark current) in high gradient rf photocathode guns deteriorates the quality of the photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (~100 μm) dark current imaging experiment has been performed in an L-band photocathode gun operating at ~100 MV/m of surface gradient. Scattered strong emission areas with high current have been observed on the cathode. The field enhancement factor β of selected regions on the cathode has been measured. Finally, the postexaminations with scanning electron microscopy and white light interferometry reveal the origins ofmore » ~75% strong emission areas overlap with the spots where rf breakdown has occurred.« less

In Situ observation of dark current emission in a high gradient rf photocathode gun

DOE PAGES

Shao, Jiahang; Shi, Jiaru; Antipov, Sergey P.; ...

2016-08-15

Undesirable electron field emission (also known as dark current) in high gradient rf photocathode guns deteriorates the quality of the photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (~100 μm) dark current imaging experiment has been performed in an L-band photocathode gun operating at ~100 MV/m of surface gradient. Scattered strong emission areas with high current have been observed on the cathode. The field enhancement factor β of selected regions on the cathode has been measured. Finally, the postexaminations with scanning electron microscopy and white light interferometry reveal the origins ofmore » ~75% strong emission areas overlap with the spots where rf breakdown has occurred.« less

78 FR 18777 - Establishment of the Charles Young Buffalo Soldiers National Monument

Federal Register 2010, 2011, 2012, 2013, 2014

2013-03-28

... reverse the decision. The War Department's action in this matter was controversial, especially within the... Indians called the black cavalry troops ``buffalo soldiers'' because of their dark, curly hair, which...

Sleep in the nocturnal primate, Aotus trivirgatus.

NASA Technical Reports Server (NTRS)

Perachio, A. A.

1971-01-01

Measurement of the cycles of wakefulness and stages of sleep in owl monkeys during 24-hr periods divided into half dark and half light segments. Recordings of electrophysiological activity were used. Reversal of the sequence of light and dark served to test the influence of environmental lighting on the sleep-wakefulness cycles. The sleep patterns of owl monkeys expressed in percentage of rapid eye movement (REM) and nonrapid eye movement (NREM) were compared with those of a closely related New World monkey species, Saimiri Sciureus.

Recovery of photoinduced reversible dark States utilized for molecular diffusion measurements.

PubMed

Chmyrov, Andriy; Sandén, Tor; Widengren, Jerker

2010-12-15

For a spatially restricted excitation volume, the effective modulation of the excitation in time is influenced by the passage times of the molecules through the excitation volume. By applying an additional time-modulated excitation, the buildup of photoinduced reversible dark states in fluorescent molecules can be made to vary significantly with their passage times through the excitation volume. The variations in the dark state populations are reflected by the time-averaged fluorescence intensity, which thus can be used to characterize the mobilities of the molecules. The concept was experimentally verified by measuring the fluorescence response of freely diffusing cyanine fluorophores (Cy5), undergoing trans-cis isomerization when subject to time-modulated excitation in a focused laser beam. From the fluorescence response, and by applying a simple photodynamic model, the transition times of the Cy5 molecules could be well reproduced when applying different laminar flow speeds through the detection volume. The presented approach puts no constraints on sample concentration, no requirements for high time resolution or sensitivity in the detection, nor requires a high fluorescence brightness of the characterized molecules. This can make the concept useful for a broad range of biomolecular mobility studies.

Genetic analysis of the roles of phytochromes A and B1 in the reversed gravitropic response of the lz-2 tomato mutant

NASA Technical Reports Server (NTRS)

Behringer, F. J.; Lomax, T. L.

1999-01-01

The lz-2 mutation in tomato (Lycopersicon esculentum) causes conditional reversal of shoot gravitropism by light. This response is mediated by phytochrome. To further elicit the mechanism by which phytochrome regulates the lz-2 phenotype, phytochrome-deficient lz-2 plants were generated. Introduction of au alleles, which severely block chromophore biosynthesis, eliminated the reversal of hypocotyl gravitropism in continuous red and far-red light. The fri1 and tri1 alleles were introduced to specifically deplete phytochromes A and B1, respectively. In dark-grown seedlings, phytochrome A was necessary for response to high-irradiance far-red light, a complete response to low fluence red light, and also mediated the effects of blue light in a far-red reversible manner. Loss of phytochrome B1 alone did not significantly affect the behaviour of lz-2 plants under any light treatment tested. However, dark-grown lz-2 plants lacking both phytochrome A and B1 exhibited reduced responses to continuous red and were less responsive to low fluence red light and high fluence blue light than plants that were deficient for phytochrome A alone. In high light, full spectrum greenhouse conditions, lz-2 plants grew downward regardless of the phytochrome deficiency. These results indicate that phytochromes A and B1 play significant roles in mediating the lz-2 phenotype and that at least one additional phytochrome is involved in reversing shoot gravitropism in this mutant.

WFC3/UVIS Dark Calibration: Monitoring Results and Improvements to Dark Reference Files

NASA Astrophysics Data System (ADS)

Bourque, M.; Baggett, S.

2016-04-01

The Wide Field Camera 3 (WFC3) UVIS detector possesses an intrinsic signal during exposures, even in the absence of light, known as dark current. A daily monitor program is employed every HST cycle to characterize and measure this current as well as to create calibration files which serve to subtract the dark current from science data. We summarize the results of the daily monitor program for all on-orbit data. We also introduce a new algorithm for generating the dark reference files that provides several improvements to their overall quality. Key features to the new algorithm include correcting the dark frames for Charge Transfer Efficiency (CTE) losses, using an anneal-cycle average value to measure the dark current, and generating reference files on a daily basis. This new algorithm is part of the release of the CALWF3 v3.3 calibration pipeline on February 23, 2016 (also known as "UVIS 2.0"). Improved dark reference files have been regenerated and re-delivered to the Calibration Reference Data System (CRDS) for all on-orbit data. Observers with science data taken prior to the release of CALWF3 v3.3 may request their data through the Mikulski Archive for Space Telescopes (MAST) to obtain the improved products.

Radiometric and Radiation Response of Visible FPAs

NASA Technical Reports Server (NTRS)

Hubbs, John

2007-01-01

The readout integrated circuit (ROIC) used in these devices was originally developed for use in space based infrared systems operating at deep cryogenic temperatures and was selected because of its proven tolerance to total ionizing radiation? The detectors are a 128 x 128 array of 60 pm x 60 pm pixel elements that have been anti-reflection (AR) coated to improve the response at very short wavelengths. These visible focal plane arrays were operated at -40 C (233 K). Two focal planes were characterized using cobalt-60 radiation to produce ionizing total dose damage in the VFPAs. Both operational and performance data were obtained as functions of total dose. The first device tested showed no appreciable change in responsivity or noise up to 300 krad(Si). However, at the next dose level of 600 krad(Si), the readout was non-operational due to failure in the digital circuitry. The second device was characterized to a total dose of 750 krad(Si) with no observed change in responsivity. An increase dark current was observed in both devices, and in the second device, the dark current caused an increase in noise at low irradiance at 400 krad(Si) and above. The increase in dark current was somewhat un-expected for visible PIN detectors. The median dark current increased more than two orders of magnitude at 300 krad(Si) for the first device and a factor of 350 at 750 krad(Si) for pixels near the edge for the second device. The dark current was found to be a strong function of detector bias, with pixels near the edge of the array showing a greater increase in dark current with bias than those near the center. Since the optical response was not a function of bias, it is hypothesized that the dark current is a surface effect and that the variation in dark current with location is due to a variation in pixel bias, caused by a voltage drop across the pixel common lead. As the total dose increased, the dark current and the voltage drop increased

Dark Current Characterization of SW HgCdTe IRFPAs Detectors on Si Substrate with Long Time Integration

NASA Astrophysics Data System (ADS)

Song, P. Y.; Ye, Z. H.; Huang, A. B.; Chen, H. L.; Hu, X. N.; Ding, R. J.; He, L.

2016-09-01

The dark currents of two short wave (SW) HgCdTe infrared focal plane arrays (IRFPA) detectors hybridized with direct injection (DI) readout and capacitance transimpedance amplifier (CTIA) with long time integration were investigated. The cutoff wavelength of the two SW IRFPAs is about 2.6 μm at 84 K. The dark current densities of DI and CTIA samples are approximately 8.0 × 10-12 A/cm2 and 7.2 × 10-10 A/cm2 at 110 K, respectively. The large divergence of the dark current density might arise from the injection efficiency difference of the two readouts. The low injection efficiency of the DI readout, compared with the high injection efficiency of the CTIA readout at low temperature, makes the dark current density of the DI sample much lower than that of the CTIA sample. The experimental value of injection efficiency of the DI sample was evaluated as 1.1% which is consistent with its theoretical value.

Observation of dark pulses in 10 nm thick YBCO nanostrips presenting hysteretic current voltage characteristics

NASA Astrophysics Data System (ADS)

Ejrnaes, M.; Parlato, L.; Arpaia, R.; Bauch, T.; Lombardi, F.; Cristiano, R.; Tafuri, F.; Pepe, G. P.

2017-12-01

We have fabricated several 10 nm thick and 65 nm wide YBa2Cu3O7-δ (YBCO) nanostrips. The nanostrips with the highest critical current densities are characterized by hysteretic current voltage characteristics (IVCs) with a direct bistable switch from the zero-voltage to the finite voltage state. The presence of hysteretic IVCs allowed the observation of dark pulses due to fluctuations phenomena. The key role of the bistable behavior is its ability to transform a small disturbance (e.g. an intrinsic fluctuation) into a measurable transient signal, i.e. a dark pulse. On the contrary, in devices characterized by lower critical current density values, the IVCs are non-hysteretic and dark pulses have not been observed. To investigate the physical origin of the dark pulses, we have measured the bias current dependence of the dark pulse rate: the observed exponential increase with the bias current is compatible with mechanisms based on thermal activation of magnetic vortices in the nanostrip. We believe that the successful amplification of small fluctuation events into measurable signals in nanostrips of ultrathin YBCO is a milestone for further investigation of YBCO nanostrips for superconducting nanostrip single photon detectors and other quantum detectors for operation at higher temperatures.

Spectral response, dark current, and noise analyses in resonant tunneling quantum dot infrared photodetectors.

PubMed

Jahromi, Hamed Dehdashti; Mahmoodi, Ali; Sheikhi, Mohammad Hossein; Zarifkar, Abbas

2016-10-20

Reduction of dark current at high-temperature operation is a great challenge in conventional quantum dot infrared photodetectors, as the rate of thermal excitations resulting in the dark current increases exponentially with temperature. A resonant tunneling barrier is the best candidate for suppression of dark current, enhancement in signal-to-noise ratio, and selective extraction of different wavelength response. In this paper, we use a physical model developed by the authors recently to design a proper resonant tunneling barrier for quantum infrared photodetectors and to study and analyze the spectral response of these devices. The calculated transmission coefficient of electrons by this model and its dependency on bias voltage are in agreement with experimental results. Furthermore, based on the calculated transmission coefficient, the dark current of a quantum dot infrared photodetector with a resonant tunneling barrier is calculated and compared with the experimental data. The validity of our model is proven through this comparison. Theoretical dark current by our model shows better agreement with the experimental data and is more accurate than the previously developed model. Moreover, noise in the device is calculated. Finally, the effect of different parameters, such as temperature, size of quantum dots, and bias voltage, on the performance of the device is simulated and studied.

Prospects of direct search for dark photon and dark Higgs in SeaQuest/E1067 experiment at the Fermilab main injector

NASA Astrophysics Data System (ADS)

Liu, Ming Xiong

2017-03-01

In this review, we present the current status and prospects of the dark sector physics search program of the SeaQuest/E1067 fixed target dimuon experiment at Fermilab Main Injector. There has been tremendous excitement and progress in searching for new physics in the dark sector in recent years. Dark sector refers to a collection of currently unknown particles that do not directly couple with the Standard Model (SM) strong and electroweak (EW) interactions but assumed to carry gravitational force, thus could be candidates of the missing Dark Matter (DM). Such particles may interact with the SM particles through “portal” interactions. Two of the simple possibilities are being investigated in our initial search: (1) dark photon and (2) dark Higgs. They could be within immediate reach of current or near future experimental search. We show there is a unique opportunity today at Fermilab to directly search for these particles in a highly motivated but uncharted parameter space in high-energy proton-nucleus collisions in the beam-dump mode using the 120 GeV proton beam from the Main Injector. Our current search window covers the mass range 0.2-10 GeV/c2, and in the near future, by adding an electromagnetic calorimeter (EMCal) to the spectrometer, we can further explore the lower mass region down to about ˜1 MeV/c2 through the di-electron channel. If dark photons (and/or dark Higgs) were observed, they would revolutionize our understanding of the fundamental structures and interactions of our universe.

A Critical Evaluation of the Influence of the Dark Exchange Current on the Performance of Dye-Sensitized Solar Cells

PubMed Central

García-Rodríguez, Rodrigo; Villanueva-Cab, Julio; Anta, Juan A.; Oskam, Gerko

2016-01-01

The influence of the thickness of the nanostructured, mesoporous TiO2 film on several parameters determining the performance of a dye-sensitized solar cell is investigated both experimentally and theoretically. We pay special attention to the effect of the exchange current density in the dark, and we compare the values obtained by steady state measurements with values extracted from small perturbation techniques. We also evaluate the influence of exchange current density, the solar cell ideality factor, and the effective absorption coefficient of the cell on the optimal film thickness. The results show that the exchange current density in the dark is proportional to the TiO2 film thickness, however, the effective absorption coefficient is the parameter that ultimately defines the ideal thickness. We illustrate the importance of the exchange current density in the dark on the determination of the current–voltage characteristics and we show how an important improvement of the cell performance can be achieved by decreasing values of the total series resistance and the exchange current density in the dark. PMID:28787833

Temperature dependent electrical characterization of organic Schottky diode based on thick MgPc films

NASA Astrophysics Data System (ADS)

Singh, J.; Sharma, R. K.; Sule, U. S.; Goutam, U. K.; Gupta, Jagannath; Gadkari, S. C.

2017-07-01

Magnesium phthalocyanine (MgPc) based Schottky diode on indium tin oxide (ITO) substrate was fabricated by thermal evaporation method. The dark current voltage characteristics of the prepared ITO-MgPc-Al heterojunction Schottky diode were measured at different temperatures. The diode showed the non-ideal rectification behavior under forward and reverse bias conditions with a rectification ratio (RR) of 56 at  ±1 V at room temperature. Under forward bias, thermionic emission and space charge limited conduction (SCLC) were found to be the dominant conduction mechanisms at low (below 0.6 V) and high voltages (above 0.6 V) respectively. Under reverse bias conditions, Poole-Frenkel (field assisted thermal detrapping of carriers) was the dominant conduction mechanism. Three different approaches namely, I-V plots, Norde and Cheung methods were used to determine the diode parameters including ideality factor (n), barrier height (Φb), series resistance (R s) and were compared. SCLC mechanism showed that the trap concentration is 5.52  ×  1022 m-3 and it lies at 0.46 eV above the valence band edge.

1300 nm wavelength InAs quantum dot photodetector grown on silicon.

PubMed

Sandall, Ian; Ng, Jo Shien; David, John P R; Tan, Chee Hing; Wang, Ting; Liu, Huiyun

2012-05-07

The optical and electrical properties of InAs quantum dots epitaxially grown on a silicon substrate have been investigated to evaluate their potential as both photodiodes and avalanche photodiodes (APDs) operating at a wavelength of 1300 nm. A peak responsivity of 5 mA/W was observed at 1280 nm, with an absorption tail extending beyond 1300 nm, while the dark currents were two orders of magnitude lower than those reported for Ge on Si photodiodes. The diodes exhibited avalanche breakdown at 22 V reverse bias which is probably dominated by impact ionisation occurring in the GaAs and AlGaAs barrier layers. A red shift in the absorption peak of 61.2 meV was measured when the reverse bias was increased from 0 to 22 V, which we attributed to the quantum confined stark effect. This shift also leads to an increase in the responsivity at a fixed wavelength as the bias is increased, yielding a maximum increase in responsivity by a factor of 140 at the wavelength of 1365 nm, illustrating the potential for such a structure to be used as an optical modulator.

Annual gonadal cycles in birds: modeling the effects of photoperiod on seasonal changes in GnRH-1 secretion.

PubMed

Dawson, Alistair

2015-04-01

This paper reviews current knowledge of photoperiod control of GnRH-1 secretion and proposes a model in which two processes act together to regulate GnRH1 secretion. Photo-induction controls GnRH1 secretion and is directly related to prevailing photoperiod. Photo-inhibition, a longer term process, acts through GnRH1 synthesis. It progresses each day during daylight hours, but reverses during darkness. Thus, photo-inhibition gradually increases when photoperiods exceed 12h, and reverses under shorter photoperiods. GnRH1 secretion on any particular day is the net result of these two processes acting in tandem. The only difference between species is their sensitivity to photo-inhibition. This can potentially explain differences in timing and duration of breeding seasons between species, why some species become absolutely photorefractory and others relatively photorefractory, why breeding seasons end at the same time at different latitudes within species, and why experimental protocols sometimes produce results that appear counter to what happens naturally. Copyright © 2014 The Author. Published by Elsevier Inc. All rights reserved.

Defect Related Dark Currents in III-V MWIR nBn Detectors

DTIC Science & Technology

2014-01-01

theory indicates a thermal activation energy of half the bandgap, and a direct proportionality between dark current density and defect density. 2.2...density due to defects maintains a full bandgap thermal activation energy , and is proportional to the square root of the defect density. Although neutral...photodiodes, and cooling is more efficient in reducing nBn’s dark current due to the full bandgap activation energy . Downloaded From: http

WIMP dark matter candidates and searches-current status and future prospects.

PubMed

Roszkowski, Leszek; Sessolo, Enrico Maria; Trojanowski, Sebastian

2018-06-01

We review several current aspects of dark matter theory and experiment. We overview the present experimental status, which includes current bounds and recent claims and hints of a possible signal in a wide range of experiments: direct detection in underground laboratories, gamma-ray, cosmic ray, x-ray, neutrino telescopes, and the LHC. We briefly review several possible particle candidates for a weakly interactive massive particle (WIMP) and dark matter that have recently been considered in the literature. We pay particular attention to the lightest neutralino of supersymmetry as it remains the best motivated candidate for dark matter and also shows excellent detection prospects. Finally we briefly review some alternative scenarios that can considerably alter properties and prospects for the detection of dark matter obtained within the standard thermal WIMP paradigm.

WIMP dark matter candidates and searches—current status and future prospects

NASA Astrophysics Data System (ADS)

Roszkowski, Leszek; Sessolo, Enrico Maria; Trojanowski, Sebastian

2018-06-01

We review several current aspects of dark matter theory and experiment. We overview the present experimental status, which includes current bounds and recent claims and hints of a possible signal in a wide range of experiments: direct detection in underground laboratories, gamma-ray, cosmic ray, x-ray, neutrino telescopes, and the LHC. We briefly review several possible particle candidates for a weakly interactive massive particle (WIMP) and dark matter that have recently been considered in the literature. We pay particular attention to the lightest neutralino of supersymmetry as it remains the best motivated candidate for dark matter and also shows excellent detection prospects. Finally we briefly review some alternative scenarios that can considerably alter properties and prospects for the detection of dark matter obtained within the standard thermal WIMP paradigm.

Investigation of 1/f Noise Mechanisms in Midwave Infrared HgCdTe Gated Photodiodes

NASA Astrophysics Data System (ADS)

Westerhout, R. J.; Musca, C. A.; Antoszewski, J.; Dell, J. M.; Faraone, L.

2007-08-01

In this work, gated midwave infrared (MWIR) Hg1 x Cd x Te photodiodes are used to investigate the physical origin of 1/f noise generation. Gated photodiodes were fabricated on liquid-phase epitaxy p-type HgCdTe MWIR material with a vacancy-doped concentration of 1.6 × 1016 cm-3 and x = 0.31. CdTe was thermally deposited and used as both a passivant and a mask for the plasma-based type conversion, and ZnS was used as an insulator. Fabricated devices show a R 0 A of 1 5 × 104 Ωcm2 with zero gate bias. Application of 2 V to the gate improves the R 0 A by more than two orders of magnitude to 6.0 × 106 Ωcm2, which corresponds to the p-type surface being at transition between depletion and weak inversion. Trap-assisted tunneling (TAT) current was observed at negative gate biases and reverse junction biases. For gate biases greater than 3 V, a field-induced junction breakdown was observed. An I n = α I β f -0.5 trend was observed above 200 pA reverse bias dark current, with α = 3.5 × 10-5 and β = 0.82, which corresponds to the TAT dominated region. Below 200 pA, junction generation-recombination (GR) current starts to dominate and this previously mentioned trend is no longer observed. Junction GR current was not seen to be correlated with 1/f noise in these photodiodes.

Observational constraints on variable equation of state parameters of dark matter and dark energy after Planck

NASA Astrophysics Data System (ADS)

Kumar, Suresh; Xu, Lixin

2014-10-01

In this paper, we study a cosmological model in general relativity within the framework of spatially flat Friedmann-Robertson-Walker space-time filled with ordinary matter (baryonic), radiation, dark matter and dark energy, where the latter two components are described by Chevallier-Polarski-Linder equation of state parameters. We utilize the observational data sets from SNLS3, BAO and Planck + WMAP9 + WiggleZ measurements of matter power spectrum to constrain the model parameters. We find that the current observational data offer tight constraints on the equation of state parameter of dark matter. We consider the perturbations and study the behavior of dark matter by observing its effects on CMB and matter power spectra. We find that the current observational data favor the cold dark matter scenario with the cosmological constant type dark energy at the present epoch.

Effect of different light-dark schedules on estrous cycle in mice, and implications for mitigating the adverse impact of night work.

PubMed

Yoshinaka, Kiichi; Yamaguchi, Ai; Matsumura, Ritsuko; Node, Koichi; Tokuda, Isao; Akashi, Makoto

2017-10-01

Approximately 20% of workers in developed countries are involved in night work. Nevertheless, many studies have strongly suggested that night-work-induced chronic circadian misalignment increases the risk of a diverse range of health problems. Although a relation between night work and irregular menstrual cycles has been indicated epidemiologically, a direct causal link remains elusive. Here, we report that repetitive reversal of light-dark (LD) cycles triggers irregular estrous cycles in mice. The findings showed that the estrous cycle remained irregular for more than four weeks after the mice were returned to regular LD cycles. Importantly, the magnitude of the negative impact of reversed LD cycles on the estrous cycle, or more specifically the decreased number of normal estrous cycles during the observation period, was dependent on the difference in the frequency of LD reversal. Presently, no clear solution to prevent night-work-mediated menstrual abnormalities is available, and reducing night work in modern society is difficult. Our findings indicate that optimizing work schedules could significantly prevent menstrual problems without reducing total night-work time. © 2017 Molecular Biology Society of Japan and John Wiley & Sons Australia, Ltd.

Sun glitter imaging analysis of submarine sand waves in HJ-1A/B satellite CCD images

NASA Astrophysics Data System (ADS)

Zhang, Huaguo; He, Xiekai; Yang, Kang; Fu, Bin; Guan, Weibing

2014-11-01

Submarine sand waves are a widespread bed-form in tidal environment. Submarine sand waves induce current convergence and divergence that affect sea surface roughness thus become visible in sun glitter images. These sun glitter images have been employed for mapping sand wave topography. However, there are lots of effect factors in sun glitter imaging of the submarine sand waves, such as the imaging geometry and dynamic environment condition. In this paper, several sun glitter images from HJ-1A/B in the Taiwan Banks are selected. These satellite sun glitter images are used to discuss sun glitter imaging characteristics in different sensor parameters and dynamic environment condition. To interpret the imaging characteristics, calculating the sun glitter radiance and analyzing its spatial characteristics of the sand wave in different images is the best way. In this study, a simulated model based on sun glitter radiation transmission is adopted to certify the imaging analysis in further. Some results are drawn based on the study. Firstly, the sun glitter radiation is mainly determined by sensor view angle. Second, the current is another key factor for the sun glitter. The opposite current direction will cause exchanging of bright stripes and dark stripes. Third, brightness reversal would happen at the critical angle. Therefore, when using sun glitter image to obtain depth inversion, one is advised to take advantage of image properties of sand waves and to pay attention to key dynamic environment condition and brightness reversal.

Minority carrier lifetime and dark current measurements in mid-wavelength infrared InAs 0.91Sb 0.09 alloy nBn photodetectors

DOE PAGES

Olson, B. V.; Kim, J. K.; Kadlec, E. A.; ...

2015-11-03

Carrier lifetime and dark current measurements are reported for a mid-wavelength infrared InAs 0.91Sb 0.09 alloy nBn photodetector. Minority carrier lifetimes are measured using a non-contact time-resolved microwave technique on unprocessed portions of the nBn wafer and the Auger recombination Bloch function parameter is determined to be |F 1F 2|=0.292. Moreover, the measured lifetimes are also used to calculate the expected diffusion dark current of the nBn devices and are compared with the experimental dark current measured in processed photodetector pixels from the same wafer. As a result, excellent agreement is found between the two, highlighting the important relationship betweenmore » lifetimes and diffusion currents in nBn photodetectors.« less

Prospects of direct search for dark photon and dark Higgs in SeaQuest/E1067 experiment at the Fermilab main injector

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

Liu, Ming Xiong

In this study, we present the current status and prospects of the dark sector physics search program of the SeaQuest/E1067 fixed target dimuon experiment at Fermilab Main Injector. There has been tremendous excitement and progress in searching for new physics in the dark sector in recent years. Dark sector refers to a collection of currently unknown particles that do not directly couple with the Standard Model (SM) strong and electroweak (EW) interactions but assumed to carry gravitational force, thus could be candidates of the missing Dark Matter (DM). Such particles may interact with the SM particles through “portal” interactions. Twomore » of the simple possibilities are being investigated in our initial search: (1) dark photon and (2) dark Higgs. They could be within immediate reach of current or near future experimental search. We show there is a unique opportunity today at Fermilab to directly search for these particles in a highly motivated but uncharted parameter space in high-energy proton–nucleus collisions in the beam-dump mode using the 120 GeV proton beam from the Main Injector. Our current search window covers the mass range 0.2–10 GeV/c 2, and in the near future, by adding an electromagnetic calorimeter (EMCal) to the spectrometer, we can further explore the lower mass region down to about ~1 MeV/c 2 through the di-electron channel. If dark photons (and/or dark Higgs) were observed, they would revolutionize our understanding of the fundamental structures and interactions of our universe.« less

Prospects of direct search for dark photon and dark Higgs in SeaQuest/E1067 experiment at the Fermilab main injector

DOE PAGES

Liu, Ming Xiong

2017-03-14

In this study, we present the current status and prospects of the dark sector physics search program of the SeaQuest/E1067 fixed target dimuon experiment at Fermilab Main Injector. There has been tremendous excitement and progress in searching for new physics in the dark sector in recent years. Dark sector refers to a collection of currently unknown particles that do not directly couple with the Standard Model (SM) strong and electroweak (EW) interactions but assumed to carry gravitational force, thus could be candidates of the missing Dark Matter (DM). Such particles may interact with the SM particles through “portal” interactions. Twomore » of the simple possibilities are being investigated in our initial search: (1) dark photon and (2) dark Higgs. They could be within immediate reach of current or near future experimental search. We show there is a unique opportunity today at Fermilab to directly search for these particles in a highly motivated but uncharted parameter space in high-energy proton–nucleus collisions in the beam-dump mode using the 120 GeV proton beam from the Main Injector. Our current search window covers the mass range 0.2–10 GeV/c 2, and in the near future, by adding an electromagnetic calorimeter (EMCal) to the spectrometer, we can further explore the lower mass region down to about ~1 MeV/c 2 through the di-electron channel. If dark photons (and/or dark Higgs) were observed, they would revolutionize our understanding of the fundamental structures and interactions of our universe.« less

Pixel pitch and particle energy influence on the dark current distribution of neutron irradiated CMOS image sensors.

PubMed

Belloir, Jean-Marc; Goiffon, Vincent; Virmontois, Cédric; Raine, Mélanie; Paillet, Philippe; Duhamel, Olivier; Gaillardin, Marc; Molina, Romain; Magnan, Pierre; Gilard, Olivier

2016-02-22

The dark current produced by neutron irradiation in CMOS Image Sensors (CIS) is investigated. Several CIS with different photodiode types and pixel pitches are irradiated with various neutron energies and fluences to study the influence of each of these optical detector and irradiation parameters on the dark current distribution. An empirical model is tested on the experimental data and validated on all the irradiated optical imagers. This model is able to describe all the presented dark current distributions with no parameter variation for neutron energies of 14 MeV or higher, regardless of the optical detector and irradiation characteristics. For energies below 1 MeV, it is shown that a single parameter has to be adjusted because of the lower mean damage energy per nuclear interaction. This model and these conclusions can be transposed to any silicon based solid-state optical imagers such as CIS or Charged Coupled Devices (CCD). This work can also be used when designing an optical imager instrument, to anticipate the dark current increase or to choose a mitigation technique.

Waveguide-integrated vertical pin photodiodes of Ge fabricated on p+ and n+ Si-on-insulator layers

NASA Astrophysics Data System (ADS)

Ito, Kazuki; Hiraki, Tatsurou; Tsuchizawa, Tai; Ishikawa, Yasuhiko

2017-04-01

Vertical pin structures of Ge photodiodes (PDs) integrated with Si optical waveguides are fabricated by depositing Ge epitaxial layers on Si-on-insulator (SOI) layers, and the performances of n+-Ge/i-Ge/p+-SOI PDs are compared with those of p+-Ge/i-Ge/n+-SOI PDs. Both types of PDs show responsivities as high as 1.0 A/W at 1.55 µm, while the dark leakage current is different, which is consistent with previous reports on free-space PDs formed on bulk Si wafers. The dark current of the p+-Ge/i-Ge/n+-SOI PDs is higher by more than one order of magnitude. Taking into account the activation energies for dark current as well as the dependence on PD area, the dark current of the n+-Ge/i-Ge/p+-SOI PDs is dominated by the thermal generation of carriers via mid-gap defect levels in Ge, while for the p+-Ge/i-Ge/n+-SOI PDs, the dark current is ascribed to not only thermal generation but also other mechanisms such as locally formed conduction paths.

Dark matter and dark energy interactions: theoretical challenges, cosmological implications and observational signatures.

PubMed

Wang, B; Abdalla, E; Atrio-Barandela, F; Pavón, D

2016-09-01

Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.

Current–voltage characteristics of organic heterostructure devices with insulating spacer layers

DOE PAGES

Yin, Sun; Nie, Wanyi; Mohite, Aditya D.; ...

2015-05-14

The dark current density in donor/acceptor organic planar heterostructure devices at a given forward voltage bias can either increase or decrease when an insulating spacer layer is added between the donor and acceptor layers. The dominant current flow process in these systems involves the formation and subsequent recombination of interfacial exciplex states. If the exciplex recombination rate limits current flow, an insulating interface layer decreases the dark current. However, if the exciplex formation rate limits the current, an insulating interface layer may increase the dark current. As a result, we present a device model to describe this behavior, and wemore » discuss relevant experimental data.« less

14 CFR 29.811 - Emergency exit marking.

Code of Federal Regulations, 2010 CFR

2010-01-01

... AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Design and Construction Personnel and Cargo... or in the dark. Such markings must be designed to remain visible for rotorcraft equipped for... colors may be reversed if this will increase the emergency illumination of the passenger compartment. (e...

Paecilomyces tabacinus

USDA-ARS?s Scientific Manuscript database

Culture characteristics - (in the dark, 25 °C after 7 d): Colonies on MEA 30–31 mm diam, velutinous to slightly floccose, mycelium white, sporulation abundant, cream-buff [R30; Ridgway (1912)], exudate clear, small droplets dominate, soluble pigments not observed, reverse cream-buff to chamois (R30)...

Rasamsonia columbiensis

USDA-ARS?s Scientific Manuscript database

Culture characteristics - (in the dark, 25 °C after 7 d): Colonies on MEA 30–31 mm diam, velutinous to slightly floccose, mycelium white, sporulation abundant, cream-buff [R30; Ridgway (1912)], exudate clear, small droplets dominate, soluble pigments not observed, reverse cream-buff to chamois (R30)...

Large Synoptic Survey Telescope: From Science Drivers to Reference Design

DTIC Science & Technology

2008-01-01

faint time domain. The LSST design is driven by four main science themes: constraining dark energy and dark matter , taking an inventory of the Solar...Energy and Dark Matter (2) Taking an Inventory of the Solar System (3) Exploring the Transient Optical Sky (4) Mapping the Milky Way Each of these four...Constraining Dark Energy and Dark Matter Current models of cosmology require the exis- tence of both dark matter and dark energy to match observational

GeV-scale dark matter: Production at the main injector

DOE PAGES

Dobrescu, Bogdan A.; Frugiuele, Claudia

2015-02-03

In this study, assuming that dark matter particles interact with quarks via a GeV-scale mediator, we study dark matter production in fixed target collisions. The ensuing signal in a neutrino near detector consists of neutral-current events with an energy distribution peaked at higher values than the neutrino background. We find that for a Z' boson of mass around a few GeV that decays to dark matter particles, the dark matter beam produced by the Main Injector at Fermilab allows the exploration of a range of values for the gauge coupling that currently satisfy all experimental constraints. The NOνA near detectormore » is well positioned for probing the presence of a dark matter beam, and future LBNF near detectors would provide more sensitive probes.« less

Light-dependent activation of phosphoenolpyruvate carboxylase by reversible phosphorylation in cluster roots of white lupin plants: diurnal control in response to photosynthate supply

PubMed Central

Feil, Regina; Lunn, John E.; Plaxton, William C.

2016-01-01

Background and Aims Phosphoenolpyruvate carboxylase (PEPC) is a tightly regulated enzyme that controls carbohydrate partitioning to organic acid anions (malate, citrate) excreted in copious amounts by cluster roots of inorganic phosphate (Pi)-deprived white lupin plants. Excreted malate and citrate solubilize otherwise inaccessible sources of mineralized soil Pi for plant uptake. The aim of this study was to test the hypotheses that (1) PEPC is post-translationally activated by reversible phosphorylation in cluster roots of illuminated white lupin plants, and (2) light-dependent phosphorylation of cluster root PEPC is associated with elevated intracellular levels of sucrose and its signalling metabolite, trehalose-6-phosphate. Methods White lupin plants were cultivated hydroponically at low Pi levels (≤1 µm) and subjected to various light/dark pretreatments. Cluster root PEPC activity and in vivo phosphorylation status were analysed to assess the enzyme’s diurnal, post-translational control in response to light and dark. Levels of various metabolites, including sucrose and trehalose-6-phosphate, were also quantified in cluster root extracts using enzymatic and spectrometric methods. Key Results During the daytime the cluster root PEPC was activated by phosphorylation at its conserved N-terminal seryl residue. Darkness triggered a progressive reduction in PEPC phosphorylation to undetectable levels, and this was correlated with 75–80 % decreases in concentrations of sucrose and trehalose-6- phosphate. Conclusions Reversible, light-dependent regulatory PEPC phosphorylation occurs in cluster roots of Pi-deprived white lupin plants. This likely facilitates the well-documented light- and sucrose-dependent exudation of Pi-solubilizing organic acid anions by the cluster roots. PEPC’s in vivo phosphorylation status appears to be modulated by sucrose translocated from CO2-fixing leaves into the non-photosynthetic cluster roots. PMID:27063365

An Integrative Model for Phytochrome B Mediated Photomorphogenesis: From Protein Dynamics to Physiology

PubMed Central

Kircher, Stefan; Kirchenbauer, Daniel; Timmer, Jens; Nagy, Ferenc; Schäfer, Eberhard; Fleck, Christian

2010-01-01

Background Plants have evolved various sophisticated mechanisms to respond and adapt to changes of abiotic factors in their natural environment. Light is one of the most important abiotic environmental factors and it regulates plant growth and development throughout their entire life cycle. To monitor the intensity and spectral composition of the ambient light environment, plants have evolved multiple photoreceptors, including the red/far-red light-sensing phytochromes. Methodology/Principal Findings We have developed an integrative mathematical model that describes how phytochrome B (phyB), an essential receptor in Arabidopsis thaliana, controls growth. Our model is based on a multiscale approach and connects the mesoscopic intracellular phyB protein dynamics to the macroscopic growth phenotype. To establish reliable and relevant parameters for the model phyB regulated growth we measured: accumulation and degradation, dark reversion kinetics and the dynamic behavior of different nuclear phyB pools using in vivo spectroscopy, western blotting and Fluorescence Recovery After Photobleaching (FRAP) technique, respectively. Conclusions/Significance The newly developed model predicts that the phyB-containing nuclear bodies (NBs) (i) serve as storage sites for phyB and (ii) control prolonged dark reversion kinetics as well as partial reversibility of phyB Pfr in extended darkness. The predictive power of this mathematical model is further validated by the fact that we are able to formalize a basic photobiological observation, namely that in light-grown seedlings hypocotyl length depends on the total amount of phyB. In addition, we demonstrate that our theoretical predictions are in excellent agreement with quantitative data concerning phyB levels and the corresponding hypocotyl lengths. Hence, we conclude that the integrative model suggested in this study captures the main features of phyB-mediated photomorphogenesis in Arabidopsis. PMID:20502669

n-ZnO/p-4H-SiC diode: Structural, electrical, and photoresponse characteristics

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

Guziewicz, M., E-mail: margu@ite.waw.pl; Jung, W.; Schifano, R.

Epitaxial n-type ZnO film has been grown, on a commercial 5 μm thick p-type 4H-SiC(00.1) Al doped epilayer, by atomic layer deposition. A full width at half maximum of the ZnO 00.2 diffraction peak rocking curve of 0.34°{sup  }± 0.02° has been measured. Diodes formed on the n-ZnO/p-4H-SiC heterostructure show rectifying behavior with a forward to reverse current ratio at the level of 10{sup 9} at ±4 V, a leakage current density of ∼6 × 10{sup −8} A/cm{sup 2}, and a low ideality factor equal to 1.17 ± 0.04. In addition, the diodes exhibit selective photoresponse with a maximum at 367 nm, and with a current increasemore » of ∼10{sup 3} under illuminations with respect to the dark value, which makes such devices prospective candidates for ultraviolet light sensors.« less

Comparison of dark energy models after Planck 2015

NASA Astrophysics Data System (ADS)

Xu, Yue-Yao; Zhang, Xin

2016-11-01

We make a comparison for ten typical, popular dark energy models according to their capabilities of fitting the current observational data. The observational data we use in this work include the JLA sample of type Ia supernovae observation, the Planck 2015 distance priors of cosmic microwave background observation, the baryon acoustic oscillations measurements, and the direct measurement of the Hubble constant. Since the models have different numbers of parameters, in order to make a fair comparison, we employ the Akaike and Bayesian information criteria to assess the worth of the models. The analysis results show that, according to the capability of explaining observations, the cosmological constant model is still the best one among all the dark energy models. The generalized Chaplygin gas model, the constant w model, and the α dark energy model are worse than the cosmological constant model, but still are good models compared to others. The holographic dark energy model, the new generalized Chaplygin gas model, and the Chevalliear-Polarski-Linder model can still fit the current observations well, but from an economically feasible perspective, they are not so good. The new agegraphic dark energy model, the Dvali-Gabadadze-Porrati model, and the Ricci dark energy model are excluded by the current observations.

Dark current suppression of MgZnO metal-semiconductor-metal solar-blind ultraviolet photodetector by asymmetric electrode structures.

PubMed

Wang, Ping; Zheng, Qinghong; Tang, Qing; Yang, Yintang; Guo, Lixin; Huang, Feng; Song, Zhenjie; Zhang, Zhiyong

2014-01-15

The application of asymmetric Schottky barrier and electrode area in an MgZnO metal-semiconductor-metal (MSM) solar-blind ultraviolet photodetector has been investigated by a physical-based numerical model in which the electron mobility is obtained by an ensemble Monte Carlo simulation combined with first principle calculations using the density functional theory. Compared with the experimental data of symmetric and asymmetric MSM structures based on ZnO substrate, the validity of this model is verified. The asymmetric Schottky barrier and electrode area devices exhibit reductions of 20 times and 1.3 times on dark current, respectively, without apparent photocurrent scarification. The plots of photo-to-dark current ratio (PDR) indicate that the asymmetric MgZnO MSM structure has better dark current characteristic than that of the symmetric one.

Using dark current data to estimate AVIRIS noise covariance and improve spectral analyses

NASA Technical Reports Server (NTRS)

Boardman, Joseph W.

1995-01-01

Starting in 1994, all AVIRIS data distributions include a new product useful for quantification and modeling of the noise in the reported radiance data. The 'postcal' file contains approximately 100 lines of dark current data collected at the end of each data acquisition run. In essence this is a regular spectral-image cube, with 614 samples, 100 lines and 224 channels, collected with a closed shutter. Since there is no incident radiance signal, the recorded DN measure only the DC signal level and the noise in the system. Similar dark current measurements, made at the end of each line are used, with a 100 line moving average, to remove the DC signal offset. Therefore, the pixel-by-pixel fluctuations about the mean of this dark current image provide an excellent model for the additive noise that is present in AVIRIS reported radiance data. The 61,400 dark current spectra can be used to calculate the noise levels in each channel and the noise covariance matrix. Both of these noise parameters should be used to improve spectral processing techniques. Some processing techniques, such as spectral curve fitting, will benefit from a robust estimate of the channel-dependent noise levels. Other techniques, such as automated unmixing and classification, will be improved by the stable and scene-independence noise covariance estimate. Future imaging spectrometry systems should have a similar ability to record dark current data, permitting this noise characterization and modeling.

Tart cherries improve working memory in aged rats

USDA-ARS?s Scientific Manuscript database

Aged rats show impaired performance on cognitive tasks that require the use of spatial learning and memory. In previous studies, we have shown the beneficial effects of various dark-colored berry fruits (blueberries, strawberries, and blackberries) in reversing age-related deficits in behavioral and...

Reversing the Course of Forgetting

ERIC Educational Resources Information Center

White, K. Geoffrey; Brown, Glenn S.

2011-01-01

Forgetting functions were generated for pigeons in a delayed matching-to-sample task, in which accuracy decreased with increasing retention-interval duration. In baseline training with dark retention intervals, accuracy was high overall. Illumination of the experimental chamber by a houselight during the retention interval impaired performance…

Realizing broad-bandwidth visible wavelength photodiode based on solution-processed ZnPc/PC71BM dyad

NASA Astrophysics Data System (ADS)

Zafar, Qayyum; Fatima, Noshin; Karimov, Khasan S.; Ahmed, Muhammad M.; Sulaiman, Khaulah

2017-02-01

Herein, we demonstrate a solution-processed visible wavelength organic photodiode (OPD) using donor/acceptor dyad of zinc phthalocyanine (ZnPc) and [6,6]-phenyl-C71-butyric-acid methyl ester (PC71BM), respectively. The synergic absorption profiles of both ZnPc and PC71BM moieties have been exploited to realize broader (350 and 800 nm) and consistent absorption spectrum of the photoactive film. The optimum loading ratio (by volume) of D/A dyad has been estimated to be 1:0.8, via quenching phenomenon in ZnPc photoluminescence spectrum. The performance of the OPD has been evaluated by detecting the photocurrent density with respect to varied illumination levels (0-150 mW/cm2) of impinging light at different reverse bias conditions. Under identical reverse bias mode, the photocurrent density has shown significant upsurge as the incident intensity of light is increased; ultimately leading to the significantly higher responsivity (162.4 μA/W) of the fabricated diode. The light to dark current density ratio (Jph/Jd) of the device at 3 V reverse bias has been calculated to be ∼20.12. The transient photocurrent density response of the fabricated OPD has also been characterized at -4 V operational bias under switch ON/OFF illumination. The measured response and recovery time for the fabricated OPD are ∼200 and 300 ms, respectively.

Pixelated Geiger-Mode Avalanche Photo-Diode Characterization Through Dark Current Measurement

NASA Astrophysics Data System (ADS)

Amaudruz, Pierre-Andre; Bishop, Daryl; Gilhully, Colleen; Goertzen, Andrew; James, Lloyd; Kozlowski, Piotr; Retiere, Fabrice; Shams, Ehsan; Sossi, Vesna; Stortz, Greg; Thiessen, Jonathan D.; Thompson, Christopher J.

2014-06-01

PIXELATED geiger-mode avalanche photodiodes (PPDs), often called silicon photomultipliers (SiPMs) are emerging as an excellent replacement for traditional photomultiplier tubes (PMTs) in a variety of detectors, especially those for subatomic physics experiments, which requires extensive test and operation procedures in order to achieve uniform responses from all the devices. In this paper, we show for two PPD brands, Hamamatsu MPPC and SensL SPM, that at room temperature, the dark noise rate, breakdown voltage and rate of correlated avalanches can be inferred from the sole measure of dark current as a function of operating voltage, hence greatly simplifying the characterization procedure. We introduce a custom electronics system that allows measurement for many devices concurrently, hence allowing rapid testing and monitoring of many devices at low cost. Finally, we show that the dark current of Hamamastu Multi-Pixel Photon Counter (MPPC) is rather independent of temperature at constant operating voltage, hence the current measure cannot be used to probe temperature variations. On the other hand, the MPPC current can be used to monitor light source conditions in DC mode without requiring strong temperature stability, as long as the integrated source brightness is comparable to the dark noise rate.

Dark Signal Characterization of 1.7 micron cutoff devices for SNAP

NASA Astrophysics Data System (ADS)

Smith, R. M.; SNAP Collaboration

2004-12-01

We report initial progress characterizing non-photometric sources of error -- dark current, noise, and zero point drift -- for 1.7 micron cutoff HgCdTe and InGaAs detectors under development by Raytheon, Rockwell, and Sensors Unlimited for SNAP. Dark current specifications can already be met with several detector types. Changes to the manufacturing process are being explored to improve the noise reduction available through multiple sampling. In some cases, a significant number of pixels suffer from popcorn noise, with a few percent of all pixels exhibiting a ten fold noise increase. A careful study of zero point drifts is also under way, since these errors can dominate dark current, and may contribute to the noise degradation seen in long exposures.

Electronic transport in a long wavelength infrared quantum cascade detector under dark condition

NASA Astrophysics Data System (ADS)

Li, L.; Zhou, X. H.; Lin, T.; Li, N.; Zhu, Z. Q.; Liu, F. Q.

2016-09-01

We present a joint experimental and theoretical investigation on a long wavelength infrared quantum cascade detector to reveal its dark current paths. The temperature dependence of the dark current is measured. It is shown that there are two different transport mechanisms, namely resonant tunneling at low temperatures and thermal excitation at higher temperature, dominate the carrier flow, respectively. Moreover, the experimental intersubband transition energies obtained by the magneto-transport measurements matches the theoretical predictions well. With the aid of the calculated band structures, we can explain the observed oscillation phenomena of the dark current under the magnetic field very well. The obtained results provide insight into the transport properties of quantum cascade detectors thus providing a useful tool for device optimization.

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

NASA Astrophysics Data System (ADS)

Frey, Joel Brandon

Recently, the world of diagnostic radiography has seen the integration of digital flat panel x-ray image detectors into x-ray imaging systems, replacing analog film screens. These flat panel x-ray imagers (FPXIs) have been shown to produce high quality x-ray images and provide many advantages that are inherent to a fully digital technology. Direct conversion FPXIs based on a photoconductive layer of stabilized amorphous selenium (a-Se) have been commercialized and have proven particularly effective in the field of mammography. In the operation of these detectors, incident x-ray photons are converted directly to charge carriers in the a-Se layer and drifted to electrodes on either side of the layer by a large applied field (10 V/microm). The applied field causes a dark current to flow which is not due to the incident radiation and this becomes a source of noise which can reduce the dynamic range of the detector. The level of dark current in commercialized detectors has been reduced by the deposition of thin n- and p- type blocking layers between the electrodes and the bulk of the a-Se. Despite recent research into the dark current in metal/a-Se/metal sandwich structures, much is still unknown about the true cause and nature of this phenomenon. The work in this Ph.D. thesis describes an experimental and theoretical study of the dark current in these structures. Experiments have been performed on five separate sets of a-Se samples which approximate the photoconductive layer in an FPXI. The dark current has been measured as a function of time, sample structure, applied field, sample thickness and contact metal used. This work has conclusively shown that the dark current is almost entirely due to the injection of charge carriers from the contacts and the contribution of Poole-Frenkel enhanced bulk thermal generation is negligible. There is also evidence that while the dark current is initially controlled by the injection of holes from the positive contact, several minutes after the application of the bias, the dark current due to hole injection may decay to the point where the electron current becomes significant and even dominant. These conclusions are supported by numerical calculations of the dark current transients which have been calibrated to match experimental results. Work detailed in this Ph.D. thesis also focuses on Monte Carlo modeling of the x-ray sensitivity of a-Se FPXIs. The higher the x-ray sensitivity of a detector, the lower the radiation dose required to acquire an acceptable image. FPXIs can experience a decrease in the x-ray sensitivity of the photoconductive layer with accumulating exposure, leading to a phenomenon known as "ghosting". Modeling this decrease in sensitivity can uncover the reasons behind it. The Monte Carlo model described in this thesis is a continuation of a previous model which now considers the effects of the n- and p-like blocking layers and the flow of dark current between x-ray exposures. The simulation results explain how deep trapping of photogenerated charge carriers, and the resulting effect on the electric field distribution, contribute to sensitivity loss. The model has shown excellent agreement with experimental data and has accurately predicted a sensitivity recovery once exposure has ceased which is due to primarily to the relaxation of metastable x-ray-induced carrier trap states.

NICMOS Temperature-specific Darks

NASA Astrophysics Data System (ADS)

Monroe, B.; Bergeron, E.

1999-11-01

The various components of NICMOS dark images have been modeled and combined to make synthetic dark calibration files which are intended for use with observations in a temperature range from 61 to ~75 K, currently available only for camera 2, with cameras 1 and 3 to follow in a few months. The amplifier glow and the true linear dark current have been constructed as temperature-independent quantities, while the “shading” component of the darks has been modeled as temperature-dependent. The data used to construct these models was taken with NIC 2, in a temperature range of 61 to 80 K during the recent warm-up of NICMOS due to cryogen exhaustion. The resulting synthetic darks are available through a web-based tool on the STScI NICMOS website http://www.stsci.edu/instruments/nicmos/NICMOS_tools/syndark.html.

The crystal structure of red fluorescent protein TagRFP-T reveals the mechanism of its superior photostability

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

Liu, Rui; Liang, Qing-Nan; Du, Shu-Qi

2016-08-19

The red fluorescent protein variant TagRFP-T has greatly improved photostability over its parent molecule, TagRFP, but the underlying mechanism leading to this improvement is to date unknown. The 1.95 Å resolution crystallographic structure of TagRFP-T showed that its chromophore exists as a mixture of cis and trans coplanar isomers in roughly equal proportions. Interestingly, both isomers are able to fluoresce, a property that has never been observed in any other fluorescent protein. We propose a “circular restoration model” for TagRFP-T to explain its superior photostability: There are four co-existing chromophore states (cis/trans protonated/ionized state) that can be driven by light tomore » transform from one state into another. This model also explains how TagRPF-T essentially eliminates the temporary dark state (reversible photobleaching). - Highlights: • The 1.95 Å resolution crystal structure of TagRFP-T was determined. • The chromophore of TagRFP-T contains a mixture of cis and trans coplanar isomers. • A “circular restoration model” was proposed to explain the superior photostability. • The chromophore can reversibly convert between cis/trans protonated/ionized states. • The light-driven conversion reduce the dark state (reversible photobleaching).« less

Interface-state density estimation of n-type nanocrystalline FeSi2/p-type Si heterojunctions fabricated by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Nopparuchikun, Adison; Promros, Nathaporn; Sittimart, Phongsaphak; Onsee, Peeradon; Duangrawa, Asanlaya; Teakchaicum, Sakmongkon; Nogami, Tomohiro; Yoshitake, Tsuyoshi

2017-09-01

By utilizing pulsed laser deposition (PLD), heterojunctions comprised of n-type nanocrystalline (NC) FeSi2 thin films and p-type Si substrates were fabricated at room temperature in this study. Both dark and illuminated current density-voltage (J-V) curves for the heterojunctions were measured and analyzed at room temperature. The heterojunctions demonstrated a large reverse leakage current as well as a weak near-infrared light response. Based on the analysis of the dark forward J-V curves, at the V value  ⩽  0.2 V, we show that a carrier recombination process was governed at the heterojunction interface. When the V value was  >  0.2 V, the probable mechanism of carrier transportation was a space-charge limited-current process. Both the measurement and analysis for capacitance-voltage-frequency (C-V-f ) and conductance-voltage-frequency (G-V-f ) curves were performed in the applied frequency (f ) range of 50 kHz-2 MHz at room temperature. From the C-V-f and G-V-f curves, the density of interface states (N ss) for the heterojunctions was computed by using the Hill-Coleman method. The N ss values were 9.19  ×  1012 eV-1 cm-2 at 2 MHz and 3.15  ×  1014 eV-1 cm-2 at 50 kHz, which proved the existence of interface states at the heterojunction interface. These interface states are the probable cause of the degraded electrical performance in the heterojunctions. Invited talk at 5th Thailand International Nanotechnology Conference (Nano Thailand-2016), 27-29 November 2016, Nakhon Ratchasima, Thailand.

Fabrication and testing of mis solar cells on a-Si:F:H. Final report, September 15, 1979-September 15, 1980

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

Han, M. K.; Anderson, W. A.

1980-11-03

Fabrication techniques and improved a-Si:H film processing have been achieved to produce a short circuit current density of 7.5 mA/cm/sup 2/ and open circuit voltage of 740 mV on large area (2cm/sup 2/) a-Si cells by the deposition of an inexpensive semitransparent metal (Cr) as a top electrode on a N-I-P structure. This corresponds to a 2% efficiency using AMl illumination. A V/sub oc/ of 830 mV and fill factor of 0.54 have also been separately obtained. A relatively simple and inexpensive deposition technique using a one pumpdown vacuum system, Al grid and thin metal film structure have been appliedmore » to reduce the cost of a-Si:H cell fabrication. A SEM study of a-Si film quality shows the substrate texture to greatly influence the film morphology. This in turn serves to influence the uniformity of photovoltaic response on completed solar cells. The studies of optical transmittance of various thin metal films promote the utilization of Cr and Cu as a top electrode. Dark and illuminated I-V characteristics show that current conduction mechanisms and recombination pheonomena are not the same under dark and illuminated conditions. Furthermore, spectral response analysis and reverse illuminated saturation current under different illumination levels show photoconductivity and collection efficiency to be a function of illumination level. Significant differences in spectral response are observed when comparing P-I-N, N-I-P and I-N structures. A Schottky barrier lowering effect is proposed to explain some spectral response data. The importance of the top junction region to carrier collection is also discussed.« less

Breakdown Degradation Associated with Elementary Screw Dislocations in 4H-SiC P(+)N Junction Rectifiers

NASA Technical Reports Server (NTRS)

Neudeck, P. G.; Huang, W.; Dudley, M.

1998-01-01

It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vector greater than 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = lc with no hollow core) in densities on the order of thousands per sq cm, nearly 100-fold micropipe densities. This paper describes an initial study into the impact of elementary screw dislocations on the reverse-bias current-voltage (I-V) characteristics of 4H-SiC p(+)n diodes. First, Synchrotron White Beam X-ray Topography (SWBXT) was employed to map the exact locations of elementary screw dislocations within small-area 4H-SiC p(+)n mesa diodes. Then the high-field reverse leakage and breakdown properties of these diodes were subsequently characterized on a probing station outfitted with a dark box and video camera. Most devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I-V knee, and no visible concentration of breakdown current. In contrast devices that contained at least one elementary screw dislocation exhibited a 5% to 35% reduction in breakdown voltage, a softer breakdown I-V knee, and visible microplasmas in which highly localized breakdown current was concentrated. The locations of observed breakdown microplasmas corresponded exactly to the locations of elementary screw dislocations identified by SWBXT mapping. While not as detrimental to SiC device performance as micropipes, the undesirable breakdown characteristics of elementary screw dislocations could nevertheless adversely affect the performance and reliability of 4H-SiC power devices.

Application of heat stress in situ demonstrates a protective role of irradiation on photosynthetic performance in alpine plants

PubMed Central

Buchner, Othmar; STOLL, Magdalena; Karadar, Matthias; Kranner, Ilse; Neuner, Gilbert

2015-01-01

The impact of sublethal heat on photosynthetic performance, photosynthetic pigments and free radical scavenging activity was examined in three high mountain species, Rhododendron ferrugineum, Senecio incanus and Ranunculus glacialis using controlled in situ applications of heat stress, both in darkness and under natural solar irradiation. Heat treatments applied in the dark reversibly reduced photosynthetic performance and the maximum quantum efficiency of photosystem II (Fv/Fm), which remained impeded for several days when plants were exposed to natural light conditions subsequently to the heat treatment. In contrast, plants exposed to heat stress under natural irradiation were able to tolerate and recover from heat stress more readily. The critical temperature threshold for chlorophyll fluorescence was higher under illumination (Tc′) than in the dark (Tc). Heat stress caused a significant de-epoxidation of the xanthophyll cycle pigments both in the light and in the dark conditions. Total free radical scavenging activity was highest when heat stress was applied in the dark. This study demonstrates that, in the European Alps, heat waves can temporarily have a negative impact on photosynthesis and, importantly, that results obtained from experiments performed in darkness and/or on detached plant material may not reliably predict the impact of heat stress under field conditions. PMID:25256247

Effects of 1- and 2-MeV electrons on photomultiplier tubes

NASA Technical Reports Server (NTRS)

Beatty, M. E., III; Debnam, W. J., Jr.; Meredith, B. D.

1976-01-01

Various types of photomultiplier tubes useful for space applications were irradiated with 1- and 2-MeV electrons at Van Allen radiation belt fluxes of 100,000 to 10 millions electrons/sq cm-sec. The increase in the dark current due to electron irradiation was observed at various bias voltages under worst-case conditions (no shielding). Results were presented in the form of dark current plotted against electron flux. All the tubes tested showed extremely large increases in dark current. Tube types 541A, 6217, 6199, and 6903 exhibited the largest increases under irradiation, whereas type 1P22 was affected the least. All the damage observed was transient. The luminescence produced in the optical window probably accounts for a large part of the dark-current increases, but there were some effects possibly due to direct irradiation of the photocathode and dynode chain.

Dilaton-assisted dark matter.

PubMed

Bai, Yang; Carena, Marcela; Lykken, Joseph

2009-12-31

A dilaton could be the dominant messenger between standard model fields and dark matter. The measured dark matter relic abundance relates the dark matter mass and spin to the conformal breaking scale. The dark matter-nucleon spin-independent cross section is predicted in terms of the dilaton mass. We compute the current constraints on the dilaton from LEP and Tevatron experiments, and the gamma-ray signal from dark matter annihilation to dilatons that could be observed by Fermi Large Area Telescope.

Weak mixing below the weak scale in dark-matter direct detection

NASA Astrophysics Data System (ADS)

Brod, Joachim; Grinstein, Benjamin; Stamou, Emmanuel; Zupan, Jure

2018-02-01

If dark matter couples predominantly to the axial-vector currents with heavy quarks, the leading contribution to dark-matter scattering on nuclei is either due to one-loop weak corrections or due to the heavy-quark axial charges of the nucleons. We calculate the effects of Higgs and weak gauge-boson exchanges for dark matter coupling to heavy-quark axial-vector currents in an effective theory below the weak scale. By explicit computation, we show that the leading-logarithmic QCD corrections are important, and thus resum them to all orders using the renormalization group.

NR-code: Nonlinear reconstruction code

NASA Astrophysics Data System (ADS)

Yu, Yu; Pen, Ue-Li; Zhu, Hong-Ming

2018-04-01

NR-code applies nonlinear reconstruction to the dark matter density field in redshift space and solves for the nonlinear mapping from the initial Lagrangian positions to the final redshift space positions; this reverses the large-scale bulk flows and improves the precision measurement of the baryon acoustic oscillations (BAO) scale.

Global limits and interference patterns in dark matter direct detection

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

Catena, Riccardo; Gondolo, Paolo

2015-08-13

We compare the general effective theory of one-body dark matter nucleon interactions to current direct detection experiments in a global multidimensional statistical analysis. We derive exclusion limits on the 28 isoscalar and isovector coupling constants of the theory, and show that current data place interesting constraints on dark matter-nucleon interaction operators usually neglected in this context. We characterize the interference patterns that can arise in dark matter direct detection from pairs of dark matter-nucleon interaction operators, or from isoscalar and isovector components of the same operator. We find that commonly neglected destructive interference effects weaken standard direct detection exclusion limitsmore » by up to one order of magnitude in the coupling constants.« less

Global limits and interference patterns in dark matter direct detection

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

Catena, Riccardo; Gondolo, Paolo, E-mail: riccardo.catena@theorie.physik.uni-goettingen.de, E-mail: paolo.gondolo@utah.edu

2015-08-01

We compare the general effective theory of one-body dark matter nucleon interactions to current direct detection experiments in a global multidimensional statistical analysis. We derive exclusion limits on the 28 isoscalar and isovector coupling constants of the theory, and show that current data place interesting constraints on dark matter-nucleon interaction operators usually neglected in this context. We characterize the interference patterns that can arise in dark matter direct detection from pairs of dark matter-nucleon interaction operators, or from isoscalar and isovector components of the same operator. We find that commonly neglected destructive interference effects weaken standard direct detection exclusion limitsmore » by up to one order of magnitude in the coupling constants.« less

Artificial night lighting inhibits feeding in moths

PubMed Central

van Grunsven, Roy H. A.; Veenendaal, Elmar M.

2017-01-01

One major, yet poorly studied, change in the environment is nocturnal light pollution, which strongly alters habitats of nocturnally active species. Artificial night lighting is often considered as driving force behind rapid moth population declines in severely illuminated countries. To understand these declines, the question remains whether artificial light causes only increased mortality or also sublethal effects. We show that moths subjected to artificial night lighting spend less time feeding than moths in darkness, with the shortest time under light conditions rich in short wavelength radiation. These findings provide evidence for sublethal effects contributing to moth population declines. Because effects are strong under various types of light compared with dark conditions, the potential of spectral alterations as a conservation tool may be overestimated. Therefore, restoration and maintenance of darkness in illuminated areas is essential for reversing declines of moth populations. PMID:28250209

Dirac dark matter and b →s ℓ+ℓ- with U(1) gauge symmetry

NASA Astrophysics Data System (ADS)

Celis, Alejandro; Feng, Wan-Zhe; Vollmann, Martin

2017-02-01

We revisit the possibility of a Dirac fermion dark matter candidate in the light of current b →s ℓ+ℓ- anomalies by investigating a minimal extension of the Standard Model with a horizontal U(1 ) ' local symmetry. Dark matter stability is protected by a remnant Z2 symmetry arising after spontaneous symmetry breaking of U(1 ) '. The associated Z' gauge boson can accommodate current hints of new physics in b →s ℓ+ℓ- decays, and acts as a vector portal between dark matter and the visible sector. We find that the model is severely constrained by a combination of precision measurements at flavor factories, LHC searches for dilepton resonances, as well as direct and indirect dark matter searches. Despite this, viable regions of the parameter space accommodating the observed dark matter relic abundance and the b →s ℓ+ℓ-anomalies still persist for dark matter and Z ' masses in the TeV range.

Dynamics of domain coverage of the protein sequence universe.

PubMed

Rekapalli, Bhanu; Wuichet, Kristin; Peterson, Gregory D; Zhulin, Igor B

2012-11-16

The currently known protein sequence space consists of millions of sequences in public databases and is rapidly expanding. Assigning sequences to families leads to a better understanding of protein function and the nature of the protein universe. However, a large portion of the current protein space remains unassigned and is referred to as its "dark matter". Here we suggest that true size of "dark matter" is much larger than stated by current definitions. We propose an approach to reducing the size of "dark matter" by identifying and subtracting regions in protein sequences that are not likely to contain any domain. Recent improvements in computational domain modeling result in a decrease, albeit slowly, in the relative size of "dark matter"; however, its absolute size increases substantially with the growth of sequence data.

Exploring the effects of overburden on the sublimation and transport of H2O on Iapetus

NASA Astrophysics Data System (ADS)

Rivera-Valentin, Edgard G.; Blackburn, David G.; Ulrich, Richard K.

2012-08-01

It has been shown through both measurements and simulations that there exists a measurable ice-free, porous, overburden overlaying water ice on Cassini Regio. Mass transfer through this porous media in a vacuum would occur in the Knudsen regime, which provides sublimation rates orders of magnitude smaller than Hertz-Langmuir sublimation. The availability of water ice for transport from this region is thus currently controlled by mass transfer through the dark material overburden. Thermal segregation suggests that Iapetus' polar regions have been brightened via ballistic transport of water and its subsequent cold trapping since exogenic deposition models predict dark high latitudes on the leading hemisphere. The limiting effect of the dark material on transport of water ice may thus greatly impact the current mass balance at the poles. The effects of the overburden on the global stability and transport of H2O is addressed in order to gain insight into its influence on the polar albedo distribution and current state of thermal segregation within the dark terrain. Results indicate that thermal segregation is currently an inactive or weak process within Cassini Regio, though it is an ongoing process at the inter-terrain regions. Modeling of polar accumulation suggests that even accounting for the current dark material cover within Cassini Regio there exists sufficient ballistically inbound water to overcome exogenic darkening mechanisms. Topographic effects on local albedo differences are also simulated to provide a more complete water stability study of Iapetus. Results suggest that topographically induced changes in heat flux may be sufficient to create the observed local albedo contrasts and also support ongoing dark exogenic deposition within Cassini Regio to explain the lack of bright slopes deep within the dark terrain.

Therapeutic perspectives for melatonin agonists and antagonists.

PubMed

Delagrange, P; Atkinson, J; Boutin, J A; Casteilla, L; Lesieur, D; Misslin, R; Pellissier, S; Pénicaud, L; Renard, P

2003-04-01

Melatonin is a neurohormone synthesized in the pineal gland during the dark period in all species, including humans. The diversity and differences in melatonin receptor distribution in the brain and extracerebral organs suggest multiple functional roles for melatonin. Administration of melatonin agonists reduces neophobia and treatment with a melatonin antagonist during the dark period reverses the anxiolytic-like effect of endogenous melatonin. Chronic treatment with agonists prevents various perturbations induced by chronic mild stress. Melatonin in vivo directly constricts cerebral arterioles in rats and decreases the lower limit of cerebral blood flow autoregulation, suggesting that melatonin may diminish the risk of hypoperfusion-induced cerebral ischemia. At the extracerebral level, melatonin regulates intestinal motility in rats. The intestinal postprandial motor response is shorter in the dark phase than in the light phase and this reduction is reversed in animals pretreated with a melatonin antagonist. Moreover, melatonin reduces the duration of cholecystokinin excitomotor effect. Endogenous melatonin may modulate intestinal motility to coordinate intestinal functions such as digestion and transit and control the metabolism of the animal. An adipocyte melatonin binding site may also participate in this control. Melatonin is involved in a wide range of physiological functions. The question remains as to whether evolution, adaptation and diurnal life have modified the physiological role of melatonin in humans. Moreover, the functional role of each of the receptor subtypes has to be characterized to design selective ligands to treat specific diseases.

Falsification of Dark Energy by Fluid Mechanics

NASA Astrophysics Data System (ADS)

Gibson, Carl H.

2012-03-01

The 2011 Nobel Prize in Physics was awarded for the discovery of accelerating super- novae dimness, suggesting a remarkable reversal in the expansion rate of the Universe from a decrease to an increase, driven by anti-gravity forces of a mysterious dark energy material comprising 70% of the Universe mass-energy. Fluid mechanics and Herschel- Planck-Spitzer-Hubble etc. space telescope observations falsify both the accelerating ex- pansion rate and dark energy concepts. Kinematic viscosity is neglected in models of self-gravitational structure formation. Large plasma photon viscosity predicts protosu- perclustervoid fragmentation early in the plasma epoch and protogalaxies at the end. At the plasma-gas transition, the gas protogalaxies fragment into Earth-mass rogue plan- ets in highly persistent, trillion-planet clumps (proto-globular-star-cluster PGCs). PGC planets freeze to form the dark matter of galaxies and merge to form their stars, giving the hydrogen triple-point (14 K) infrared emissions observed. Dark energy is a system- atic dimming error for Supernovae Ia caused by partially evaporated planets feeding hot white dwarf stars at the Chandrasekhar carbon limit. Planet atmospheres may or may not dim light from SNe-Ia events depending on the line of sight.

Pathway for recovery of photo-degraded polymer solar cells by post degradation thermal anneal

DOE PAGES

Bhattacharya, J.; Joshi, P. H.; Biswas, Rana; ...

2017-02-16

The photo-degradation of polymer solar cells is a critical challenge preventing its commercial deployment. We experimentally fabricate organic solar cells and characterize their degradation under solar simulators in an environmental chamber under nitrogen flow, without exposure to oxygen and moisture. We have developed a thermally stable inverted organic solar cell architecture in which light induced degradation of device characteristics can be reversibly annealed to the pristine values. The stable inverted cells utilized MoO x layers that are thermally treated immediately after their deposition on the organic layer, and before metal cathode deposition. Organic solar cells that are photo-degraded in themore » presence of oxygen, however show irreversible degradation that cannot be thermally recovered. The decrease of organic solar cell characteristics correlates with increases in mid-gap electronic states, measured using capacitance spectroscopy and dark current. It is likely the photo-induced defect states caused by local H motion from the alkyl chains to the aromatic backbone, can be reversibly annealed at elevated temperatures after photo-degradation. Finally, our results provide a pathway for improving the stability of organic photovoltaics.« less

Pathway for recovery of photo-degraded polymer solar cells by post degradation thermal anneal

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

Bhattacharya, J.; Joshi, P. H.; Biswas, Rana

The photo-degradation of polymer solar cells is a critical challenge preventing its commercial deployment. We experimentally fabricate organic solar cells and characterize their degradation under solar simulators in an environmental chamber under nitrogen flow, without exposure to oxygen and moisture. We have developed a thermally stable inverted organic solar cell architecture in which light induced degradation of device characteristics can be reversibly annealed to the pristine values. The stable inverted cells utilized MoO x layers that are thermally treated immediately after their deposition on the organic layer, and before metal cathode deposition. Organic solar cells that are photo-degraded in themore » presence of oxygen, however show irreversible degradation that cannot be thermally recovered. The decrease of organic solar cell characteristics correlates with increases in mid-gap electronic states, measured using capacitance spectroscopy and dark current. It is likely the photo-induced defect states caused by local H motion from the alkyl chains to the aromatic backbone, can be reversibly annealed at elevated temperatures after photo-degradation. Finally, our results provide a pathway for improving the stability of organic photovoltaics.« less

Al{sub x}Ga{sub 1-x}N-based back-illuminated solar-blind photodetectors with external quantum efficiency of 89%

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

Cicek, E.; McClintock, R.; Cho, C. Y.

2013-11-04

We report on high performance Al{sub x}Ga{sub 1−x}N-based solar-blind ultraviolet photodetector (PD) array grown on sapphire substrate. First, high quality, crack-free AlN template layer is grown via metalorganic chemical vapor deposition. Then, we systematically optimized the device design and material doping through the growth and processing of multiple devices. After optimization, uniform and solar-blind operation is observed throughout the array; at the peak detection wavelength of 275 nm, 729 μm{sup 2} area PD showed unbiased peak external quantum efficiency and responsivity of ∼80% and ∼176 mA/W, respectively, increasing to 89% under 5 V of reverse bias. Taking the reflection loses into consideration,more » the internal quantum efficiency of these optimized PD can be estimated to be as high as ∼98%. The visible rejection ratio measured to be more than six orders of magnitude. Electrical measurements yielded a low-dark current density: <2 × 10{sup −9} A/cm{sup 2}, at 10 V of reverse bias.« less

Eye Color as a Predictor of Outcomes in Behavior Therapy.

ERIC Educational Resources Information Center

Markle, Allan; And Others

1984-01-01

Examined the relationship between outcomes of behaviorally oriented treatment for children (N=366) and eye color. Findings were consistent with theoretical expectations: Dark-eyed children and teenagers responded better to reactive treatment programs than their light-eyed counterparts, while the reverse was true for self-paced treatment programs.…

Differential effects of blueberry polyphenols on age-associated neuroinflammation and cognition

USDA-ARS?s Scientific Manuscript database

Long-term effects of oxidative stress and inflammatory insults are thought to contribute to the decrements in cognitive performance seen in aging and neurodegenerative diseases. In previous studies, we have shown the beneficial effects of various dark-colored berry fruits in reversing age-related de...

Effects of dietary blueberry on cognition and in vivo and in vitro inflammatory status

USDA-ARS?s Scientific Manuscript database

Chronic inflammation is thought to play a role in age-related cognitive decline. Previous studies from our laboratory have shown that dietary intervention with darkly pigmented berry fruit can reduce systemic and central biomarkers of inflammation while reversing behavioral impairments in aged rats....

Evolution of separate screening soliton pairs in a biased series photorefractive crystal circuit.

PubMed

Liu, Jinsong; Hao, Zhonghua

2002-06-01

This paper presents calculations for an idea in photorefractive spatial soliton, namely, screening solitons form in a biased series photorefractive crystal circuit consisting of two photorefractive crystals connected electronically by electrode leads in a chain with a voltage source. A system of two coupled equations is derived under appropriate conditions for two-beam propagation in the crystal circuit. The possibility of obtaining steady-state bright and dark screening soliton solutions is investigated in one dimension and, the existence of dark-dark, bright-dark, and bright-bright separate screening soliton pairs in such a circuit is proved. The numerical results show that the two solitons in a soliton pair can affect each other by the light-induced current and their coupling can affect their spatial profiles, dynamical evolutions, stabilities, and self-deflection. Under the limit in which the optical wave has a spatial extent much less than the width of the crystal, only the dark soliton can affect the other soliton by the light-induced current, but the bright soliton cannot. For a bright-dark or dark-dark soliton pair, the dark soliton in a weak input intensity can be obtained for a larger nonlinearity than for a stronger input intensity. For a bright-dark soliton pair, increasing the input intensity of the dark soliton can increase the bending angle of the bright soliton. Some potential applications are discussed.

Electronic Properties of Grain Boundaries in GaAs: A Study of Oriented Bicrystals Prepared by Epitaxial Lateral Overgrowth.

DTIC Science & Technology

1984-05-10

overgrowth from a spoke 90 pattern of radial stripe openings at 1 intervals on an Si0 2 coated (110) surface. Bright regions are GaAs and dark regions are Si0...the dark current for such an ideal device is given by Idark - Io[exp(eVbi/AokT) - 1] , (11-l) where Io is a proportionality constant describing the...recombination and leakage currents which contribute to an increased dark current. The value of Voc is determined by the built-in junction barrier height and the

Stressed Ge:Ga photoconductors for space-based astronomy. (Is there life beyond 120 micron)

NASA Technical Reports Server (NTRS)

Beeman, J. W.; Haller, E. E.; Hansen, W. L.; Luke, P. N.; Richards, P. L.

1989-01-01

Information is given in viewgraph form. Information is given on the characteristics of stressed Ge:Ga, a spring type stress cavity, mounting hardware, materials parameters affecting dark current, and the behavior of low dark current stressed Ge:Ga. It is concluded that detectors exist today for background-limited detection at 200 microns, that researchers are narrowing in on the significant parameters that effect dark current in stressed photoconductors, that these findings may be applied to other photoconductor materials, and that some creative problem solving for an ionizing effect reset mechanism is needed.

UV detector based on InAlN/GaN-on-Si HEMT stack with photo-to-dark current ratio > 107

NASA Astrophysics Data System (ADS)

kumar, Sandeep; Pratiyush, Anamika Singh; Dolmanan, Surani B.; Tripathy, Sudhiranjan; Muralidharan, Rangarajan; Nath, Digbijoy N.

2017-12-01

We demonstrate an InAlN/GaN-on-Si high electron mobility transistor based UV detector with a photo-to-dark current ratio of >107. The Ti/Al/Ni/Au metal stack was evaporated and thermal annealed rapidly for Ohmic contacts to the 2D electron gas (2DEG) at the InAlN/GaN interface, while the channel + barrier was recess etched to a depth of 20 nm to pinch-off the 2DEG between Source-Drain pads. A spectral responsivity (SR) of 32.9 A/W at 367 nm was measured at 5 V. A very high photo-to-dark current ratio of >107 was measured at a bias of 20 V. The photo-to-dark current ratio at a fixed bias was found to be decreasing with an increase in the recess length of photodetectors. The fabricated devices were found to exhibit a UV-to-visible rejection ratio of >103 with a low dark current of < 32 pA at 5 V. Transient measurements showed rise and fall times in the range of 3-4 ms. The gain mechanism was investigated, and carrier lifetimes were estimated which matched well with those reported elsewhere.

Comparison of Measured Dark Current Distributions with Calculated Damage Energy Distributions in HgCdTe

NASA Technical Reports Server (NTRS)

Marshall, C. J.; Marshall, P. W.; Howe, C. L.; Reed, R. A.; Weller, R. A.; Mendenhall, M.; Waczynski, A.; Ladbury, R.; Jordan, T. M.

2007-01-01

This paper presents a combined Monte Carlo and analytic approach to the calculation of the pixel-to-pixel distribution of proton-induced damage in a HgCdTe sensor array and compares the results to measured dark current distributions after damage by 63 MeV protons. The moments of the Coulombic, nuclear elastic and nuclear inelastic damage distributions were extracted from Monte Carlo simulations and combined to form a damage distribution using the analytic techniques first described in [1]. The calculations show that the high energy recoils from the nuclear inelastic reactions (calculated using the Monte Carlo code MCNPX [2]) produce a pronounced skewing of the damage energy distribution. While the nuclear elastic component (also calculated using the MCNPX) contributes only a small fraction of the total nonionizing damage energy, its inclusion in the shape of the damage across the array is significant. The Coulombic contribution was calculated using MRED [3-5], a Geant4 [4,6] application. The comparison with the dark current distribution strongly suggests that mechanisms which are not linearly correlated with nonionizing damage produced according to collision kinematics are responsible for the observed dark current increases. This has important implications for the process of predicting the on-orbit dark current response of the HgCdTe sensor array.

Lateral amorphous selenium metal-insulator-semiconductor-insulator-metal photodetectors using ultrathin dielectric blocking layers for dark current suppression

NASA Astrophysics Data System (ADS)

Chang, Cheng-Yi; Pan, Fu-Ming; Lin, Jian-Siang; Yu, Tung-Yuan; Li, Yi-Ming; Chen, Chieh-Yang

2016-12-01

We fabricated amorphous selenium (a-Se) photodetectors with a lateral metal-insulator-semiconductor-insulator-metal (MISIM) device structure. Thermal aluminum oxide, plasma-enhanced chemical vapor deposited silicon nitride, and thermal atomic layer deposited (ALD) aluminum oxide and hafnium oxide (ALD-HfO2) were used as the electron and hole blocking layers of the MISIM photodetectors for dark current suppression. A reduction in the dark current by three orders of magnitude can be achieved at electric fields between 10 and 30 V/μm. The effective dark current suppression is primarily ascribed to electric field lowering in the dielectric layers as a result of charge trapping in deep levels. Photogenerated carriers in the a-Se layer can be transported across the blocking layers to the Al electrodes via Fowler-Nordheim tunneling because a high electric field develops in the ultrathin dielectric layers under illumination. Since the a-Se MISIM photodetectors have a very low dark current without significant degradation in the photoresponse, the signal contrast is greatly improved. The MISIM photodetector with the ALD-HfO2 blocking layer has an optimal signal contrast more than 500 times the contrast of the photodetector without a blocking layer at 15 V/μm.

Origin of large dark current increase in InGaAs/InP avalanche photodiode

NASA Astrophysics Data System (ADS)

Wen, J.; Wang, W. J.; Chen, X. R.; Li, N.; Chen, X. S.; Lu, W.

2018-04-01

The large dark current increase near the breakdown voltage of an InGaAs/InP avalanche photodiode is observed and analyzed from the aspect of bulk defects in the device materials. The trap level information is extracted from the temperature-dependent electrical characteristics of the device and the low temperature photoluminescence spectrum of the materials. Simulation results with the extracted trap level taken into consideration show that the trap is in the InP multiplication layer and the trap assisted tunneling current induced by the trap is the main cause of the large dark current increase with the bias from the punch-through voltage to 95% breakdown voltage.

Proton radiation effect on performance of InAs/GaSb complementary barrier infrared detector

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

Soibel, Alexander; Rafol, Sir B.; Khoshakhlagh, Arezou

In this work, we investigated the effect of proton irradiation on the performance of long wavelength infrared InAs/GaSb photodiodes (λ{sub c} = 10.2 μm), based on the complementary barrier infrared detector design. We found that irradiation with 68 MeV protons causes a significant increase of the dark current from j{sub d} = 5 × 10{sup −5} A/cm{sup 2} to j{sub d} = 6 × 10{sup −3} A/cm{sup 2}, at V{sub b} = 0.1 V, T = 80 K and fluence 19.2 × 10{sup 11 }H{sup +}/cm{sup 2}. Analysis of the dark current as a function of temperature and bias showed that the dominant contributor to the dark current in these devices changes from diffusion current to tunneling current after proton irradiation.more » This change in the dark current mechanism can be attributed to the onset of surface leakage current, generated by trap-assisted tunneling processes in proton displacement damage areas located near the device sidewalls.« less

A 4MP high-dynamic-range, low-noise CMOS image sensor

NASA Astrophysics Data System (ADS)

Ma, Cheng; Liu, Yang; Li, Jing; Zhou, Quan; Chang, Yuchun; Wang, Xinyang

2015-03-01

In this paper we present a 4 Megapixel high dynamic range, low dark noise and dark current CMOS image sensor, which is ideal for high-end scientific and surveillance applications. The pixel design is based on a 4-T PPD structure. During the readout of the pixel array, signals are first amplified, and then feed to a low- power column-parallel ADC array which is already presented in [1]. Measurement results show that the sensor achieves a dynamic range of 96dB, a dark noise of 1.47e- at 24fps speed. The dark current is 0.15e-/pixel/s at -20oC.

Figures of merit for present and future dark energy probes

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

Mortonson, Michael J.; Huterer, Dragan; Hu, Wayne

2010-09-15

We compare current and forecasted constraints on dynamical dark energy models from Type Ia supernovae and the cosmic microwave background using figures of merit based on the volume of the allowed dark energy parameter space. For a two-parameter dark energy equation of state that varies linearly with the scale factor, and assuming a flat universe, the area of the error ellipse can be reduced by a factor of {approx}10 relative to current constraints by future space-based supernova data and CMB measurements from the Planck satellite. If the dark energy equation of state is described by a more general basis ofmore » principal components, the expected improvement in volume-based figures of merit is much greater. While the forecasted precision for any single parameter is only a factor of 2-5 smaller than current uncertainties, the constraints on dark energy models bounded by -1{<=}w{<=}1 improve for approximately 6 independent dark energy parameters resulting in a reduction of the total allowed volume of principal component parameter space by a factor of {approx}100. Typical quintessence models can be adequately described by just 2-3 of these parameters even given the precision of future data, leading to a more modest but still significant improvement. In addition to advances in supernova and CMB data, percent-level measurement of absolute distance and/or the expansion rate is required to ensure that dark energy constraints remain robust to variations in spatial curvature.« less

Dynamics of domain coverage of the protein sequence universe

PubMed Central

2012-01-01

Background The currently known protein sequence space consists of millions of sequences in public databases and is rapidly expanding. Assigning sequences to families leads to a better understanding of protein function and the nature of the protein universe. However, a large portion of the current protein space remains unassigned and is referred to as its “dark matter”. Results Here we suggest that true size of “dark matter” is much larger than stated by current definitions. We propose an approach to reducing the size of “dark matter” by identifying and subtracting regions in protein sequences that are not likely to contain any domain. Conclusions Recent improvements in computational domain modeling result in a decrease, albeit slowly, in the relative size of “dark matter”; however, its absolute size increases substantially with the growth of sequence data. PMID:23157439

Effects of adsorbed pyridine derivatives and ultrathin atomic-layer-deposited alumina coatings on the conduction band-edge energy of TiO2 and on redox-shuttle-derived dark currents.

PubMed

Katz, Michael J; Vermeer, Michael J D; Farha, Omar K; Pellin, Michael J; Hupp, Joseph T

2013-01-15

Both the adsorption of t-butylpyridine and the atomic-layer deposition of ultrathin conformal coatings of insulators (such as alumina) are known to boost open-circuit photovoltages substantially for dye-sensitized solar cells. One attractive interpretation is that these modifiers significantly shift the conduction-edge energy of the electrode, thereby shifting the onset potential for dark current arising from the interception of injected electrons by solution-phase redox shuttle components such as Co(phenanthroline)(3)(3+) and triiodide. For standard, high-area, nanoporous photoelectrodes, band-edge energies are difficult to measure directly. In contrast, for flat electrodes they are readily accessible from Mott-Schottky analyses of impedance data. Using such electrodes (specifically TiO(2)), we find that neither organic nor inorganic electrode-surface modifiers shift the conduction-band-edge energy sufficiently to account fully for the beneficial effects on electrode behavior (i.e., the suppression of dark current). Additional experiments reveal that the efficacy of ultrathin coatings of Al(2)O(3) arises chiefly from the passivation of redox-catalytic surface states. In contrast, adsorbed t-butylpyridine appears to suppress dark currents mainly by physically blocking access of shuttle molecules to the electrode surface. Studies with other derivatives of pyridine, including sterically and/or electronically diverse derivatives, show that heterocycle adsorption and the concomitant suppression of dark current does not require the coordination of surface Ti(IV) or Al(III) atoms. Notably, the favorable (i.e., negative) shifts in onset potential for the flow of dark current engendered by organic and inorganic surface modifiers are additive. Furthermore, they appear to be largely insensitive to the identity of shuttle molecules.

Reversible superhydrophilicity and hydrophobicity switching of V2O5 thin films deposited by magnetron sputtering

NASA Astrophysics Data System (ADS)

Zhang, Chunzi; Peng, Zhiguang; Cui, Xiaoyu; Neil, Eric; Li, Yuanshi; Kasap, Safa; Yang, Qiaoqin

2018-03-01

V2O5 thin films are well-known "smart" materials due to their reversible wettability under UV irradiation and dark storage. Their surfaces are usually hydrophobic and turn into hydrophilic under UV irradiation. However, the V2O5 thin films deposited by magnetron sputtering in present work are superhydrophilic and turned into hydrophobic after days' of storage in air. This change can be recovered by heating. The effects of many factors including surface roughness, irradiation from visible light, UV, & X-ray, and storage in air & vacuum on the reversible switching of wettability were investigated. The results show that air absorption is the main factor causing the film surface change from superhydrophilicity to hydrophobicity.

THE NATURE OF FOVEAL DARK ADAPTATION

PubMed Central

Hecht, Selig

1921-01-01

1. After a discussion of the sources of error involved in the study of dark adaptation, an apparatus and a procedure are described which avoid these errors. The method includes a control of the initial light adaptation, a record of the exact beginning of dark adaptation, and an accurate means of measuring the threshold of the fovea after different intervals in the dark. 2. The results show that dark adaptation of the eye as measured by foveal vision proceeds at a very precipitous rate during the first few seconds, that most of the adaptation takes place during the first 30 seconds, and that the process practically ceases after 10 minutes. These findings explain much of the irregularity of the older data. 3. The changes which correspond to those in the fovea alone are secured by correcting the above results in terms of the movements of the pupil during dark adaptation. 4. On the assumption that the photochemical effect of the light is a linear function of the intensity, it is shown that the dark adaptation of the fovea itself follows the course of a bimolecular reaction. This is interpreted to mean that there are two photolytic products in the fovea; that they are disappearing because they are recombining to form anew the photosensitive substance of the fovea; and that the concentration of these products of photolysis in the sense cell must be increased by a definite fraction in order to produce a visual effect. 5. It is then suggested that the basis of the initial event in foveal light perception is some mechanism that involves a reversible photochemical reaction of which the "dark" reaction is bimolecular. Dark adaptation follows the "dark" reaction; sensory equilibrium is represented by the stationary state; and light adaptation by the shifting of the stationary state to a fresh point of equilibrium toward the "dark" side of the reaction. PMID:19871919

Numerical Device Modeling, Analysis, and Optimization of Extended-SWIR HgCdTe Infrared Detectors

NASA Astrophysics Data System (ADS)

Schuster, J.; DeWames, R. E.; DeCuir, E. A.; Bellotti, E.; Dhar, N.; Wijewarnasuriya, P. S.

2016-09-01

Imaging in the extended short-wavelength infrared (eSWIR) spectral band (1.7-3.0 μm) for astronomy applications is an area of significant interest. However, these applications require infrared detectors with extremely low dark current (less than 0.01 electrons per pixel per second for certain applications). In these detectors, sources of dark current that may limit the overall system performance are fundamental and/or defect-related mechanisms. Non-optimized growth/device processing may present material point defects within the HgCdTe bandgap leading to Shockley-Read-Hall dominated dark current. While realizing contributions to the dark current from only fundamental mechanisms should be the goal for attaining optimal device performance, it may not be readily feasible with current technology and/or resources. In this regard, the U.S. Army Research Laboratory performed physics-based, two- and three-dimensional numerical modeling of HgCdTe photovoltaic infrared detectors designed for operation in the eSWIR spectral band. The underlying impetus for this capability and study originates with a desire to reach fundamental performance limits via intelligent device design.

Searching for dark matter-dark energy interactions: Going beyond the conformal case

NASA Astrophysics Data System (ADS)

van de Bruck, Carsten; Mifsud, Jurgen

2018-01-01

We consider several cosmological models which allow for nongravitational direct couplings between dark matter and dark energy. The distinguishing cosmological features of these couplings can be probed by current cosmological observations, thus enabling us to place constraints on these specific interactions which are composed of the conformal and disformal coupling functions. We perform a global analysis in order to independently constrain the conformal, disformal, and mixed interactions between dark matter and dark energy by combining current data from: Planck observations of the cosmic microwave background radiation anisotropies, a combination of measurements of baryon acoustic oscillations, a supernova type Ia sample, a compilation of Hubble parameter measurements estimated from the cosmic chronometers approach, direct measurements of the expansion rate of the Universe today, and a compilation of growth of structure measurements. We find that in these coupled dark-energy models, the influence of the local value of the Hubble constant does not significantly alter the inferred constraints when we consider joint analyses that include all cosmological probes. Moreover, the parameter constraints are remarkably improved with the inclusion of the growth of structure data set measurements. We find no compelling evidence for an interaction within the dark sector of the Universe.

A monolithic 640 × 512 CMOS imager with high-NIR sensitivity

NASA Astrophysics Data System (ADS)

Lauxtermann, Stefan; Fisher, John; McDougal, Michael

2014-06-01

In this paper we present first results from a backside illuminated CMOS image sensor that we fabricated on high resistivity silicon. Compared to conventional CMOS imagers, a thicker photosensitive membrane can be depleted when using silicon with low background doping concentration while maintaining low dark current and good MTF performance. The benefits of such a fully depleted silicon sensor are high quantum efficiency over a wide spectral range and a fast photo detector response. Combining these characteristics with the circuit complexity and manufacturing maturity available from a modern, mixed signal CMOS technology leads to a new type of sensor, with an unprecedented performance spectrum in a monolithic device. Our fully depleted, backside illuminated CMOS sensor was designed to operate at integration times down to 100nsec and frame rates up to 1000Hz. Noise in Integrate While Read (IWR) snapshot shutter operation for these conditions was simulated to be below 10e- at room temperature. 2×2 binning with a 4× increase in sensitivity and a maximum frame rate of 4000 Hz is supported. For application in hyperspectral imaging systems the full well capacity in each row can individually be programmed between 10ke-, 60ke- and 500ke-. On test structures we measured a room temperature dark current of 360pA/cm2 at a reverse bias of 3.3V. A peak quantum efficiency of 80% was measured with a single layer AR coating on the backside. Test images captured with the 50μm thick VGA imager between 30Hz and 90Hz frame rate show a strong response at NIR wavelengths.

Application of heat stress in situ demonstrates a protective role of irradiation on photosynthetic performance in alpine plants.

PubMed

Buchner, Othmar; Stoll, Magdalena; Karadar, Matthias; Kranner, Ilse; Neuner, Gilbert

2015-04-01

The impact of sublethal heat on photosynthetic performance, photosynthetic pigments and free radical scavenging activity was examined in three high mountain species, Rhododendron ferrugineum, Senecio incanus and Ranunculus glacialis using controlled in situ applications of heat stress, both in darkness and under natural solar irradiation. Heat treatments applied in the dark reversibly reduced photosynthetic performance and the maximum quantum efficiency of photosystem II (Fv /Fm), which remained impeded for several days when plants were exposed to natural light conditions subsequently to the heat treatment. In contrast, plants exposed to heat stress under natural irradiation were able to tolerate and recover from heat stress more readily. The critical temperature threshold for chlorophyll fluorescence was higher under illumination (Tc (')) than in the dark (Tc). Heat stress caused a significant de-epoxidation of the xanthophyll cycle pigments both in the light and in the dark conditions. Total free radical scavenging activity was highest when heat stress was applied in the dark. This study demonstrates that, in the European Alps, heat waves can temporarily have a negative impact on photosynthesis and, importantly, that results obtained from experiments performed in darkness and/or on detached plant material may not reliably predict the impact of heat stress under field conditions. © 2014 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.

Proposal for Axion Dark Matter Detection Using an L C Circuit

DOE PAGES

Sikivie, P.; Sullivan, N.; Tanner, D. B.

2014-03-01

Here, we show that dark matter axions cause an oscillating electric current to flow along magnetic field lines. The oscillating current induced in a strong magnetic field B → 0 produces a small magnetic field B → a. We propose to amplify and detect B → a using a cooled LC circuit and a very sensitive magnetometer. This appears to be a suitable approach to searching for axion dark matter in the 10 –7 to 10 –9 eV mass range.

Comparison of dark energy models: A perspective from the latest observational data

NASA Astrophysics Data System (ADS)

Li, Miao; Li, Xiaodong; Zhang, Xin

2010-09-01

We compare some popular dark energy models under the assumption of a flat universe by using the latest observational data including the type Ia supernovae Constitution compilation, the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey, the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations and the determination of H 0 from the Hubble Space Telescope. Model comparison statistics such as the Bayesian and Akaike information criteria are applied to assess the worth of the models. These statistics favor models that give a good fit with fewer parameters. Based on this analysis, we find that the simplest cosmological constant model that has only one free parameter is still preferred by the current data. For other dynamical dark energy models, we find that some of them, such as the α dark energy, constant w, generalized Chaplygin gas, Chevalliear-Polarski-Linder parametrization, and holographic dark energy models, can provide good fits to the current data, and three of them, namely, the Ricci dark energy, agegraphic dark energy, and Dvali-Gabadadze-Porrati models, are clearly disfavored by the data.

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

Jiang, Zhenyu, E-mail: jiangzhenyu1201@hotmail.com, E-mail: jianxu@engr.psu.edu; Liu, Yan; Mo, Chen

In an attempt to suppress the dark current, the barrier layer engineer for solution-processed PbSe colloidal quantum-dot (CQD) photodetectors has been investigated in the present study. It was found that the dark current can be significantly suppressed by implementing two types of carrier blocking layers, namely, hole blocking layer and electron blocking layer, sandwiched in between two active PbSe CQD layers. Meanwhile no adverse impact has been observed for the photo current. Our study suggests that this improvement resides on the transport pathway created via carrier recombination at intermediate layer, which provides wide implications for the suppression of dark currentmore » for infrared photodetectors.« less

Novel Drift Structures for Silicon and Compound Semiconductor X-Ray and Gamma-Ray Detectors

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

Bradley E. Patt; Jan S. Iwanczyk

Recently developed silicon- and compound-semiconductor-based drift detector structures have produced excellent performance for charged particles, X rays, and gamma rays and for low-signal visible light detection. The silicon drift detector (SDD) structures that we discuss relate to direct X-ray detectors and scintillation photon detectors coupled with scintillators for gamma rays. Recent designs include several novel features that ensure very low dark current (both bulk silicon dark current and surface dark current) and hence low noise. In addition, application of thin window technology ensures a very high quantum efficiency entrance window on the drift photodetector.

Effects of Displacement Damage on the Time-Resolved Gain and Bandwidth of a Low Breakdown Voltage Si Avalanche Photodiode

NASA Technical Reports Server (NTRS)

Laird, Jamie S.; Onoda, Shinobu; Hirao, Toshio; Becker, Heidi; Johnston, Allan; Laird, Jamie S.; Itoh, Hisayoshi

2006-01-01

Effects of displacement damage and ionization damage induced by gamma irradiation on the dark current and impulse response of a high-bandwidth low breakdown voltage Si Avalanche Photodiode has been investigated using picosecond laser microscopy. At doses as high as 10Mrad (Si) minimal alteration in the impulse response and bandwidth were observed. However, dark current measurements also performed with and without biased irradiation exhibit anomalously large damage factors for applied biases close to breakdown. The absence of any degradation in the impulse response is discussed as are possible mechanisms for higher dark current damage factors observed for biased irradiation.

Direct Search for Dark Matter with DarkSide

NASA Astrophysics Data System (ADS)

Agnes, P.; Alexander, T.; Alton, A.; Arisaka, K.; Back, H. O.; Baldin, B.; Biery, K.; Bonfini, G.; Bossa, M.; Brigatti, A.; Brodsky, J.; Budano, F.; Cadonati, L.; Calaprice, F.; Canci, N.; Candela, A.; Cao, H.; Cariello, M.; Cavalcante, P.; Chavarria, A.; Chepurnov, A.; Cocco, A. G.; Crippa, L.; D'Angelo, D.; D'Incecco, M.; Davini, S.; De Deo, M.; Derbin, A.; Devoto, A.; Di Eusanio, F.; Di Pietro, G.; Edkins, E.; Empl, A.; Fan, A.; Fiorillo, G.; Fomenko, K.; Forster, G.; Franco, D.; Gabriele, F.; Galbiati, C.; Goretti, A.; Grandi, L.; Gromov, M.; Guan, M. Y.; Guardincerri, Y.; Hackett, B.; Herner, K.; Hungerford, E. V.; Ianni, Al; Ianni, An; Jollet, C.; Keeter, K.; Kendziora, C.; Kidner, S.; Kobychev, V.; Koh, G.; Korablev, D.; Korga, G.; Kurlej, A.; Li, P. X.; Loer, B.; Lombardi, P.; Love, C.; Ludhova, L.; Luitz, S.; Ma, Y. Q.; Machulin, I.; Mandarano, A.; Mari, S.; Maricic, J.; Marini, L.; Martoff, C. J.; Meregaglia, A.; Meroni, E.; Meyers, P. D.; Milincic, R.; Montanari, D.; Montuschi, M.; Monzani, M. E.; Mosteiro, P.; Mount, B.; Muratova, V.; Musico, P.; Nelson, A.; Odrowski, S.; Okounkova, M.; Orsini, M.; Ortica, F.; Pagani, L.; Pallavicini, M.; Pantic, E.; Papp, L.; Parmeggiano, S.; Parsells, R.; Pelczar, K.; Pelliccia, N.; Perasso, S.; Pocar, A.; Pordes, S.; Pugachev, D.; Qian, H.; Randle, K.; Ranucci, G.; Razeto, A.; Reinhold, B.; Renshaw, A.; Romani, A.; Rossi, B.; Rossi, N.; Rountree, S. D.; Sablone, D.; Saggese, P.; Saldanha, R.; Sands, W.; Sangiorgio, S.; Segreto, E.; Semenov, D.; Shields, E.; Skorokhvatov, M.; Smirnov, O.; Sotnikov, A.; Stanford, C.; Suvorov, Y.; Tartaglia, R.; Tatarowicz, J.; Testera, G.; Tonazzo, A.; Unzhakov, E.; Vogelaar, R. B.; Wada, M.; Walker, S.; Wang, H.; Wang, Y.; Watson, A.; Westerdale, S.; Wojcik, M.; Wright, A.; Xiang, X.; Xu, J.; Yang, C. G.; Yoo, J.; Zavatarelli, S.; Zec, A.; Zhu, C.; Zuzel, G.

2015-11-01

The DarkSide experiment is designed for the direct detection of Dark Matter with a double phase liquid Argon TPC operating underground at Laboratori Nazionali del Gran Sasso. The TPC is placed inside a 30 tons liquid organic scintillator sphere, acting as a neutron veto, which is in turn installed inside a 1 kt water Cherenkov detector. The current detector is running since November 2013 with a 50 kg atmospheric Argon fill and we report here the first null results of a Dark Matter search for a (1422 ± 67) kg.d exposure. This result correspond to a 90% CL upper limit on the WIMP-nucleon cross section of 6.1 × 10-44 cm2 (for a WIMP mass of 100 GeV/c2) and it's currently the most sensitive limit obtained with an Argon target.

The DarkSide direct dark matter search with liquid argon

NASA Astrophysics Data System (ADS)

Edkins, E.; Agnes, P.; Alexander, T.; Alton, A.; Arisaka, K.; Back, H. O.; Baldin, B.; Biery, K.; Bonfini, G.; Bossa, M.; Brigatti, A.; Brodsky, J.; Budano, F.; Cadonati, L.; Calaprice, F.; Canci, N.; Candela, A.; Cao, H.; Cariello, M.; Cavalcante, P.; Chavarria, A.; Chepurnov, A.; Cocco, A. G.; Crippa, L.; D'Angelo, D.; D'Incecco, M.; Davini, S.; De Deo, M.; Derbin, A.; Devoto, A.; Di Eusanio, F.; Di Pietro, G.; Empl, A.; Fan, A.; Fiorillo, G.; Fomenko, K.; Forster, G.; Franco, D.; Gabriele, F.; Galbiati, C.; Goretti, A.; Grandi, L.; Gromov, M.; Guan, M. Y.; Guardincerri, Y.; Hackett, B.; Herner, K.; Humble, P.; Hungerford, E. V.; Ianni, Al.; Ianni, An.; Jollet, C.; Keeter, K.; Kendziora, C.; Kobychev, V.; Koh, G.; Korablev, D.; Korga, G.; Kurlej, A.; Li, P. X.; Loer, B.; Lombardi, P.; Love, C.; Ludhova, L.; Luitz, S.; Ma, Y. Q.; Machulin, I.; Mandarano, A.; Mari, S.; Maricic, J.; Marini, L.; Martoff, C. J.; Meregaglia, A.; Meroni, E.; Meyers, P. D.; Milincic, R.; Montanari, D.; Montuschi, M.; Monzani, M. E.; Mosteiro, P.; Mount, B.; Muratova, V.; Musico, P.; Nelson, A.; Odrowski, S.; Okounkova, M.; Orsini, M.; Ortica, F.; Pagani, L.; Pallavicini, M.; Pantic, E.; Papp, L.; Parmeggiano, S.; Parsells, R.; Pelczar, K.; Pelliccia, N.; Perasso, S.; Pocar, A.; Pordes, S.; Pugachev, D.; Qian, H.; Randle, K.; Ranucci, G.; Razeto, A.; Reinhold, B.; Renshaw, A.; Romani, A.; Rossi, B.; Rossi, N.; Rountree, S. D.; Sablone, D.; Saggese, P.; Saldanha, R.; Sands, W.; Sangiorgio, S.; Segreto, E.; Semenov, D.; Shields, E.; Skorokhvatov, M.; Smirnov, O.; Sotnikov, A.; Stanford, C.; Suvorov, Y.; Tartaglia, R.; Tatarowicz, J.; Testera, G.; Tonazzo, A.; Unzhakov, E.; Vogelaar, R. B.; Wada, M.; Walker, S.; Wang, H.; Wang, Y.; Watson, A.; Westerdale, S.; Wojcik, M.; Wright, A.; Xiang, X.; Xu, J.; Yang, C. G.; Yoo, J.; Zavatarelli, S.; Zec, A.; Zhu, C.; Zuzel, G.

2017-11-01

The DarkSide-50 direct dark matter detector is a liquid argon time projection chamber (TPC) surrounded by a liquid scintillator neutron veto (LSV) and a water Cerenkov muon veto (WCV). Located under 3800 m.w.e. at the Laboratori Nazionali del Gran Sasso, Italy, it is the only direct dark matter experiment currently operating background free. The atmospheric argon target was replaced with argon from underground sources in April, 2015. The level of 39Ar, a β emitter present in atmospheric argon (AAr), has been shown to have been reduced by a factor of (1.4 ± 0.2) x 103. The combined spin-independent WIMP exclusion limit of 2.0 x 10-44 cm2 (mχ = 100 GeV/c2) is currently the best limit on a liquid argon target.

Repetitive Visual Stimulation Enhances Recovery from Severe Amblyopia

ERIC Educational Resources Information Center

Montey, Karen L.; Eaton, Nicolette C.; Quinlan, Elizabeth M.

2013-01-01

Severe amblyopia, characterized by a significant reduction in visual acuity through the affected eye, is highly resistant to reversal in adulthood. We have previously shown that synaptic plasticity can be reactivated in the adult rat visual cortex by dark exposure, and the reactivated plasticity can be harnessed to promote the recovery from severe…

Photojunction field-effect transistor based on a colloidal quantum dot absorber channel layer.

PubMed

Adinolfi, Valerio; Kramer, Illan J; Labelle, André J; Sutherland, Brandon R; Hoogland, S; Sargent, Edward H

2015-01-27

The performance of photodetectors is judged via high responsivity, fast speed of response, and low background current. Many previously reported photodetectors based on size-tuned colloidal quantum dots (CQDs) have relied either on photodiodes, which, since they are primary photocarrier devices, lack gain; or photoconductors, which provide gain but at the expense of slow response (due to delayed charge carrier escape from sensitizing centers) and an inherent dark current vs responsivity trade-off. Here we report a photojunction field-effect transistor (photoJFET), which provides gain while breaking prior photoconductors' response/speed/dark current trade-off. This is achieved by ensuring that, in the dark, the channel is fully depleted due to a rectifying junction between a deep-work-function transparent conductive top contact (MoO3) and a moderately n-type CQD film (iodine treated PbS CQDs). We characterize the rectifying behavior of the junction and the linearity of the channel characteristics under illumination, and we observe a 10 μs rise time, a record for a gain-providing, low-dark-current CQD photodetector. We prove, using an analytical model validated using experimental measurements, that for a given response time the device provides a two-orders-of-magnitude improvement in photocurrent-to-dark-current ratio compared to photoconductors. The photoJFET, which relies on a junction gate-effect, enriches the growing family of CQD photosensitive transistors.

Quantum Dot Detector Enhancement for Narrow Band Multispectral Applications

DTIC Science & Technology

2012-10-01

19 2.4.3 Dark Current and Noise Current Measurement of QDIPs.................................21 3 References...20 Figure 19: Dark Current of QDIPs Measured by Source Meter…………………………………………21 Figure 20: Schematic View of Noise Current Setup...temperature, higher photoconductive gain, carrier lifetimes 10-100 times longer than Quantum Well Infrared Photodetectors ( QWIPs ), and giving rise to a

Broadband and Resonant Approaches to Axion Dark Matter Detection.

PubMed

Kahn, Yonatan; Safdi, Benjamin R; Thaler, Jesse

2016-09-30

When ultralight axion dark matter encounters a static magnetic field, it sources an effective electric current that follows the magnetic field lines and oscillates at the axion Compton frequency. We propose a new experiment to detect this axion effective current. In the presence of axion dark matter, a large toroidal magnet will act like an oscillating current ring, whose induced magnetic flux can be measured by an external pickup loop inductively coupled to a SQUID magnetometer. We consider both resonant and broadband readout circuits and show that a broadband approach has advantages at small axion masses. We estimate the reach of this design, taking into account the irreducible sources of noise, and demonstrate potential sensitivity to axionlike dark matter with masses in the range of 10^{-14}-10^{-6}  eV. In particular, both the broadband and resonant strategies can probe the QCD axion with a GUT-scale decay constant.

Low dark current MCT-based focal plane detector arrays for the LWIR and VLWIR developed at AIM

NASA Astrophysics Data System (ADS)

Gassmann, Kai Uwe; Eich, Detlef; Fick, Wolfgang; Figgemeier, Heinrich; Hanna, Stefan; Thöt, Richard

2015-10-01

For nearly 40 years AIM develops, manufactures and delivers photo-voltaic and photo-conductive infrared sensors and associated cryogenic coolers which are mainly used for military applications like pilotage, weapon sights, UAVs or vehicle platforms. In 2005 AIM started to provide the competences also for space applications like IR detector units for the SLSTR instrument on board of the Sentinel 3 satellite, the hyperspectral SWIR Imager for EnMAP or pushbroom detectors for high resolution Earth observation satellites. Meanwhile AIM delivered more than 25 Flight Models for several customers. The first European pulse-tube cooler ever operating on-board of a satellite is made by AIM. AIM homes the required infrared core capabilities such as design and manufacturing of focal plane assemblies, detector housing technologies, development and manufacturing of cryocoolers and also data processing for thermal IR cameras under one roof which enables high flexibility to react to customer needs and assures economical solutions. Cryogenically cooled Hg(1-x)CdxTe (MCT) quantum detectors are unequalled for applications requiring high imaging as well as high radiometric performance in the infrared spectral range. Compared with other technologies, they provide several advantages, such as the highest quantum efficiency, lower power dissipation compared to photoconductive devices and fast response times, hence outperforming micro-bolometer arrays. However, achieving an excellent MCT detector performance at long (LWIR) and very long (VLWIR) infrared wavelengths is challenging due to the exponential increase in the thermally generated photodiode dark current with increasing cut-off wavelength and / or operating temperature. Dark current is a critical design driver, especially for LWIR / VLWIR multi-spectral imagers with moderate signal levels or hyper-spectral Fourier spectrometers operating deep into the VLWIR spectral region. Consequently, low dark current (LDC) technologies are the prerequisite for future scientific space and earth observation missions. Aiming, for example at exoplanet or earth atmospheric spectral analysis, significant improvement in LWIR / VLWIR detector material performance is mandatory. LDC material optimization can target different directions of impact: (i) reduction of dark current for a given operational temperature to increase SNR and reduce thermally induced signal offset variations. (ii) operation at elevated temperatures at a given dark current level to reduce mass and power budget of the required cryocooler and to reduce cryostat complexity. (iii) increase the accessible cut-off wavelength at constant detector temperature and dark current level. This paper presents AIM's latest results on n-on-p as well as p-on-n low dark current planar MCT photodiode focal plane detector arrays at cut-off wavelengths >11 μm at 80 K. Dark current densities below Tennant's `Rule07'1 have been demonstrated for n-on-p and p-on-n devices. This work has been carried out under ESA contract ESTEC 4000107414/13/NL/SFe².

One dark matter mystery: halos in the cosmic web

NASA Astrophysics Data System (ADS)

Gaite, Jose

2015-01-01

The current cold dark matter cosmological model explains the large scale cosmic web structure but is challenged by the observation of a relatively smooth distribution of matter in galactic clusters. We consider various aspects of modeling the dark matter around galaxies as distributed in smooth halos and, especially, the smoothness of the dark matter halos seen in N-body cosmological simulations. We conclude that the problems of the cold dark matter cosmology on small scales are more serious than normally admitted.

Development of 0.5-5 W, 10K Reverse Brayton Cycle Cryocoolers - Phase II Final Report

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

Doty, F. D.; Boman, A.; Arnold, S.

2001-10-15

Miniature cryocoolers for the 8-30 K range are needed to provide 0.5-5 w of cooling to high sensitivity detectors (for long-wave-length IR, magnetism, mm-wave, X-ray, dark matter, and possibly y-ray detection) while maintaining low mass, ultra-low vibration, and good efficiency. This project presents a new approach to eliminating the problems normally encountered in efforts to build low-vibration, fieldable, miniature cryocoolers. Using the reverse Brayton Cycle (RBC), the approach applies and expands on existing spinner technology previously used only in Nuclear Magnetic Resonance (NMR) probes.

Quantum field theory of interacting dark matter and dark energy: Dark monodromies

DOE PAGES

D’Amico, Guido; Hamill, Teresa; Kaloper, Nemanja

2016-11-28

We discuss how to formulate a quantum field theory of dark energy interacting with dark matter. We show that the proposals based on the assumption that dark matter is made up of heavy particles with masses which are very sensitive to the value of dark energy are strongly constrained. Quintessence-generated long-range forces and radiative stability of the quintessence potential require that such dark matter and dark energy are completely decoupled. However, if dark energy and a fraction of dark matter are very light axions, they can have significant mixings which are radiatively stable and perfectly consistent with quantum field theory.more » Such models can naturally occur in multi-axion realizations of monodromies. The mixings yield interesting signatures which are observable and are within current cosmological limits but could be constrained further by future observations« less

Quantum field theory of interacting dark matter and dark energy: Dark monodromies

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

D’Amico, Guido; Hamill, Teresa; Kaloper, Nemanja

We discuss how to formulate a quantum field theory of dark energy interacting with dark matter. We show that the proposals based on the assumption that dark matter is made up of heavy particles with masses which are very sensitive to the value of dark energy are strongly constrained. Quintessence-generated long-range forces and radiative stability of the quintessence potential require that such dark matter and dark energy are completely decoupled. However, if dark energy and a fraction of dark matter are very light axions, they can have significant mixings which are radiatively stable and perfectly consistent with quantum field theory.more » Such models can naturally occur in multi-axion realizations of monodromies. The mixings yield interesting signatures which are observable and are within current cosmological limits but could be constrained further by future observations« less

Gravitational Waves from Binary Mergers of Subsolar Mass Dark Black Holes

NASA Astrophysics Data System (ADS)

Shandera, Sarah; Jeong, Donghui; Gebhardt, Henry S. Grasshorn

2018-06-01

We explore the possible spectrum of binary mergers of subsolar mass black holes formed out of dark matter particles interacting via a dark electromagnetism. We estimate the properties of these dark black holes by assuming that their formation process is parallel to Population-III star formation, except that dark molecular cooling can yield a smaller opacity limit. We estimate the binary coalescence rates for the Advanced LIGO and Einstein telescope, and find that scenarios compatible with all current constraints could produce dark black holes at rates high enough for detection by Advanced LIGO.

Light-Induced Surface Reactions at the Bismuth Vanadate/Potassium Phosphate Interface.

PubMed

Favaro, Marco; Abdi, Fatwa F; Lamers, Marlene; Crumlin, Ethan J; Liu, Zhi; van de Krol, Roel; Starr, David E

2018-01-18

Bismuth vanadate has recently drawn significant research attention as a light-absorbing photoanode due to its performance for photoelectrochemical water splitting. In this study, we use in situ ambient pressure X-ray photoelectron spectroscopy with "tender" X-rays (4.0 keV) to investigate a polycrystalline bismuth vanadate (BiVO 4 ) electrode in contact with an aqueous potassium phosphate (KPi) solution at open circuit potential under both dark and light conditions. This is facilitated by the creation of a 25 to 30 nm thick electrolyte layer using the "dip-and-pull" method. We observe that under illumination bismuth phosphate forms on the BiVO 4 surface leading to an increase of the surface negative charge. The bismuth phosphate layer may act to passivate surface states observed in photoelectrochemical measurements. The repulsive interaction between the negatively charged surface under illumination and the phosphate ions in solution causes a shift in the distribution of ions in the thin aqueous electrolyte film, which is observed as an increase in their photoelectron signals. Interestingly, we find that such changes at the BiVO 4 /KPi electrolyte interface are reversible upon returning to dark conditions. By measuring the oxygen 1s photoelectron peak intensities from the phosphate ions and liquid water as a function of time under dark and light conditions, we determine the time scales for the forward and reverse reactions. Our results provide direct evidence for light-induced chemical modification of the BiVO 4 /KPi electrolyte interface.

Dark sequential Z ' portal: Collider and direct detection experiments

NASA Astrophysics Data System (ADS)

Arcadi, Giorgio; Campos, Miguel D.; Lindner, Manfred; Masiero, Antonio; Queiroz, Farinaldo S.

2018-02-01

We revisit the status of a Majorana fermion as a dark matter candidate when a sequential Z' gauge boson dictates the dark matter phenomenology. Direct dark matter detection signatures rise from dark matter-nucleus scatterings at bubble chamber and liquid xenon detectors, and from the flux of neutrinos from the Sun measured by the IceCube experiment, which is governed by the spin-dependent dark matter-nucleus scattering. On the collider side, LHC searches for dilepton and monojet + missing energy signals play an important role. The relic density and perturbativity requirements are also addressed. By exploiting the dark matter complementarity we outline the region of parameter space where one can successfully have a Majorana dark matter particle in light of current and planned experimental sensitivities.

Reduction in the critical dark length for flower induction during aging in the short-day plant Pharbitis nil var. Kidachi.

PubMed

Hasegawa, Hiroshi; Yamada, Mizuki; Iwase, Yuiko; Wada, Kaede C; Takeno, Kiyotoshi

2010-12-01

The stress-sensitive short-day plant Pharbitis nil var. Kidachi flowers under a 16-h light and 8-h dark regime and non-stress conditions when grown for long periods of time. Such flowering was found to occur from the third week, and the floral buds were formed from the eighth node of the main stem. When young plants were grafted onto aged plants, the scions were induced to flower early. This flower induction by grafting was more effective when older plants were used as rootstocks. Grafting experiments using a single leaf as a donor revealed that younger leaves are more responsive to flower induction, suggesting that this age-mediated flowering response is not induced by aging or senescence of individual leaves. Rather, the plant may obtain the ability to flower as the whole plant ages. Flowering does not occur under continuous light conditions. A night break given in the 8-h dark period inhibits flowering. These results suggest that 8-h dark conditions, which are normally considered to be long-day conditions, actually correspond to short-day conditions for this plant. The 8-h dark conditions caused early flowering more efficiently in older plants. The critical dark length determined by a single treatment was 12 h in 0-week-old plants and was reduced to 6 h in 2- and 4-week-old plants. These results suggest that the critical dark length becomes shorter when plants get older. The expression of PnFT1 and PnFT2, orthologs of the flowering gene flowering locus T, was analyzed by reverse transcription-polymerase chain reaction revealing that the expression of PnFT at the end of dark period is correlated with flowering.

Status and perspective of the DarkSide experiment at LNGS

DOE PAGES

Agnes, P.

2018-09-01

The DarkSide experiment aims to perform a background-free direct search for dark matter with a dual-phase argon TPC. The current phase of the experiment, DarkSide-50, is acquiring data at Laboratori Nazionali del Gran Sasso and produced the most sensitive limit on the WIMP-nucleon cross section ever obtained with a liquid argon target (2.0 × 10 -44 cm2 for a WIMP mass of 100 GeV/c 2). The future phase of the experiment will be a 20 t fiducial mass detector, designed to reach a sensitivity of ~1 × 10 -47 cm2 (at 1 TeV/c 2 WIMP mass) with a background-free exposuremore » of 100 ty. Here, this work contains a discussion of the current status of the DarkSide-50 WIMP search and of the results which are more relevant for the construction of the future detector.« less

Direct search for dark matter with DarkSide

DOE PAGES

Agnes, P.

2015-11-16

Here, the DarkSide experiment is designed for the direct detection of Dark Matter with a double phase liquid Argon TPC operating underground at Laboratori Nazionali del Gran Sasso. The TPC is placed inside a 30 tons liquid organic scintillator sphere, acting as a neutron veto, which is in turn installed inside a 1 kt water Cherenkov detector. The current detector is running since November 2013 with a 50 kg atmospheric Argon fill and we report here the first null results of a Dark Matter search for a (1422 ± 67) kg.d exposure. This result correspond to a 90% CL uppermore » limit on the WIMP-nucleon cross section of 6.1 × 10 -44 cm 2 (for a WIMP mass of 100 GeV/c 2) and it's currently the most sensitive limit obtained with an Argon target.« less

Status and perspective of the DarkSide experiment at LNGS

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

Agnes, P.

The DarkSide experiment aims to perform a background-free direct search for dark matter with a dual-phase argon TPC. The current phase of the experiment, DarkSide-50, is acquiring data at Laboratori Nazionali del Gran Sasso and produced the most sensitive limit on the WIMP-nucleon cross section ever obtained with a liquid argon target (2.0 × 10 -44 cm2 for a WIMP mass of 100 GeV/c 2). The future phase of the experiment will be a 20 t fiducial mass detector, designed to reach a sensitivity of ~1 × 10 -47 cm2 (at 1 TeV/c 2 WIMP mass) with a background-free exposuremore » of 100 ty. Here, this work contains a discussion of the current status of the DarkSide-50 WIMP search and of the results which are more relevant for the construction of the future detector.« less

Strain effects in Hg/sub 1-//sub x/Cd/sub x/Te (xapprox. 0. 2) photovoltaic arrays

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

Weiss, E.; Mainzer, N.

1989-03-01

The effect of stress and strain on the performance of Hg/sub 1-//sub x/Cd/sub x/Te (xapprox.0.2) photovoltaic arrays was studied both in the dark and under illumination. Stress, external as well as internal, affects the current--voltage characteristic of the photodiode. The combined action of illumination and strain yields an anomalous response to light absorption in the device. A model is conceived wherein the photodiode and guard ring are treated as a metal-insulator semiconductor field effect transistor (MISFET). Stress developed in the vicinity of small contact windows causes n-type damage, which brings about a forward bias in the device. The effect ofmore » strain on the reverse current of the photodiode is explained by a change in the n-channel conductivity of the MISFET. This change is caused by charges which are due either to a piezoelectric effect or n-type damage. Using this model observed phenomena in Hg/sub 1-//sub x/Cd/sub x/Te photovoltaic arrays are explained, as due to internal stresses originating from wafer deformation.« less

DarkBit: a GAMBIT module for computing dark matter observables and likelihoods

NASA Astrophysics Data System (ADS)

Bringmann, Torsten; Conrad, Jan; Cornell, Jonathan M.; Dal, Lars A.; Edsjö, Joakim; Farmer, Ben; Kahlhoefer, Felix; Kvellestad, Anders; Putze, Antje; Savage, Christopher; Scott, Pat; Weniger, Christoph; White, Martin; Wild, Sebastian

2017-12-01

We introduce DarkBit, an advanced software code for computing dark matter constraints on various extensions to the Standard Model of particle physics, comprising both new native code and interfaces to external packages. This release includes a dedicated signal yield calculator for gamma-ray observations, which significantly extends current tools by implementing a cascade-decay Monte Carlo, as well as a dedicated likelihood calculator for current and future experiments ( gamLike). This provides a general solution for studying complex particle physics models that predict dark matter annihilation to a multitude of final states. We also supply a direct detection package that models a large range of direct detection experiments ( DDCalc), and that provides the corresponding likelihoods for arbitrary combinations of spin-independent and spin-dependent scattering processes. Finally, we provide custom relic density routines along with interfaces to DarkSUSY, micrOMEGAs, and the neutrino telescope likelihood package nulike. DarkBit is written in the framework of the Global And Modular Beyond the Standard Model Inference Tool ( GAMBIT), providing seamless integration into a comprehensive statistical fitting framework that allows users to explore new models with both particle and astrophysics constraints, and a consistent treatment of systematic uncertainties. In this paper we describe its main functionality, provide a guide to getting started quickly, and show illustrative examples for results obtained with DarkBit (both as a stand-alone tool and as a GAMBIT module). This includes a quantitative comparison between two of the main dark matter codes ( DarkSUSY and micrOMEGAs), and application of DarkBit 's advanced direct and indirect detection routines to a simple effective dark matter model.

Comparison of Measured Leakage Current Distributions with Calculated Damage Energy Distributions in HgCdTe

NASA Technical Reports Server (NTRS)

Marshall, C. J.; Ladbury, R.; Marshall, P. W.; Reed, R. A.; Howe, C.; Weller, B.; Mendenhall, M.; Waczynski, A.; Jordan, T. M.; Fodness, B.

2006-01-01

This paper presents a combined Monte Carlo and analytic approach to the calculation of the pixel-to-pixel distribution of proton-induced damage in a HgCdTe sensor array and compares the results to measured dark current distributions after damage by 63 MeV protons. The moments of the Coulombic, nuclear elastic and nuclear inelastic damage distribution were extracted from Monte Carlo simulations and combined to form a damage distribution using the analytic techniques first described in [I]. The calculations show that the high energy recoils from the nuclear inelastic reactions (calculated using the Monte Car10 code MCNPX [2]) produce a pronounced skewing of the damage energy distribution. The nuclear elastic component (also calculated using the MCNPX) has a negligible effect on the shape of the damage distribution. The Coulombic contribution was calculated using MRED [3,4], a Geant4 [4,5] application. The comparison with the dark current distribution strongly suggests that mechanisms which are not linearly correlated with nonionizing damage produced according to collision kinematics are responsible for the observed dark current increases. This has important implications for the process of predicting the on-orbit dark current response of the HgCdTe sensor array.

Impulse response measurement in the HgCdTe avalanche photodiode

NASA Astrophysics Data System (ADS)

Singh, Anand; Pal, Ravinder

2018-04-01

HgCdTe based mid-wave infrared focal plane arrays (MWIR FPAs) are being developed for high resolution imaging and range determination of distant camouflaged targets. Effect of bandgap grading on the response time in the n+/ν/p+ HgCdTe electron avalanche photodiode (e-APD) is evaluated using impulse response measurement. Gain normalized dark current density of 2 × 10-9 A/cm2 at low reverse bias for passive mode and 2 × 10-4 A/cm2 at -8 V for active mode is measured in the fabricated APD device, yielding high gain bandwidth product of 2.4 THZ at the maximum gain. Diffusion of carriers is minimized to achieve transit time limited impulse response by introducing composition grading in the HgCdTe epilayer. The noise equivalent photon performance less than one is achievable in the FPA that is suitable for active cum passive imaging applications.

Sol-gel synthesis of Cu-doped p-CdS nanoparticles and their analysis as p-CdS/n-ZnO thin film photodiode

NASA Astrophysics Data System (ADS)

Arya, Sandeep; Sharma, Asha; Singh, Bikram; Riyas, Mohammad; Bandhoria, Pankaj; Aatif, Mohammad; Gupta, Vinay

2018-05-01

Copper (Cu) doped p-CdS nanoparticles have been synthesized via sol-gel method. The as-synthesized nanoparticles were successfully characterized and implemented for fabrication of Glass/ITO/n-ZnO/p-CdS/Al thin film photodiode. The fabricated device is tested for small (-1 V to +1 V) bias voltage. Results verified that the junction leakage current within the dark is very small. During reverse bias condition, the maximum amount of photocurrent is obtained under illumination of 100 μW/cm2. Electrical characterizations confirmed that the external quantum efficiency (EQE), gain and responsivity of n-ZnO/p-CdS photodiode show improved photo response than conventional p-type materials for such a small bias voltage. It is therefore revealed that the Cu-doped CdS nanoparticles is an efficient p-type material for fabrication of thin film photo-devices.

Effect of the polymeric coating thickness on the photocurrent performance of titanium dioxide nanorod arrays-polyaniline composite-based UV photosensor

NASA Astrophysics Data System (ADS)

Yusoff, M. M.; Mamat, M. H.; Malek, M. F.; Othman, , N.; Ismail, A. S.; Saidi, S. A.; Mohamed, R.; Suriani, A. B.; Khusaimi, Z.; Rusop, M.

2018-05-01

Titanium dioxide (TiO2) nanorod arrays (TNAs) were synthesized and deposited on fluorine tin oxide (FTO)-coated glass substrate using a one-step immersion method in a glass container. The effect of the polymeric coating thickness of p-type polyaniline (PANI) on the n-type TNAs was investigated in the p-n heterojunction photodiode (PD) for the application of ultraviolet (UV) photosensor. The fabricated photosensor demonstrated an increased photocurrent under UV irradiation in correlation with the thickness layer of PANI. The measured UV response showed the highest photocurrent of 0.014 µA at 1.0 V of reverse bias with low dark current under the UV radiation (365 nm, 750 µW/cm2). The thickness of the PANI film improved the photocurrent of the fabricated TNAs/PANI composite-based UV photosensor.

Si⁺-implanted Si-wire waveguide photodetectors for the mid-infrared

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

Souhan, Brian; Lu, Ming; Grote, Richard R.

2014-10-28

CMOS-compatible Si⁺-implanted Si-waveguide p-i-n photodetectors operating at room temperature and at mid-infrared wavelengths from 2.2 to 2.3 µm are demonstrated. Responsivities of 9.9 ± 2.0 mA/W are measured at a 5 V reverse bias with an estimated internal quantum efficiency of 2.7 – 4.5%. The dark current is found to vary from a few microamps down to less than a nanoamp after a post-implantation annealing of 350°C. The measured photocurrent dependence on input power shows a linear correspondence over more than three decades, and the frequency response of a 250 µm-length p-i-n device is measured to be ~1.7 GHz formore » a wavelength of λ = 2.2 µm, thus potentially opening up new communication bands for photonic integrated circuits.« less

Fabrication of InP-pentacene inorganic-organic hybrid heterojunction using MOCVD grown InP for photodetector application

NASA Astrophysics Data System (ADS)

Sarkar, Kalyan Jyoti; Pal, B.; Banerji, P.

2018-04-01

We fabricated inorganic-organic hybrid heterojunction between indium phosphide (InP) and pentacene for photodetector application. InP layer was grown on n-Si substrate by atmospheric pressure metal organic chemical vapour deposition (MOCVD) technique. Morphological properties of InP and pentacene thin film were characterized by atomic force microscopy (AFM). Current-voltage characteristics were investigated in dark and under illumination condition at room temperature. During illumination, different wavelengths of visible and infrared light source were employed to perform the electrical measurement. Enhancement of photocurrent was observed with decreasing in wavelength of incident photo radiation. Ideality factor was found to be 1.92. High rectification ratio of 225 was found at ± 3 V in presence of infrared light source. This study provides new insights of inorganic-organic hybrid heterojunction for broadband photoresponse in visible to near infrared (IR) region under low reverse bias condition.

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

Byrne, James; Klueglein, Nicole; Pearce, Carolyn I.

Despite the regular occurrence of both magnetite and iron-metabolizing bacteria in the same environments, it is currently unknown whether the iron(II) and iron(III) in magnetite can be cycled between different bacteria and whether or how magnetic properties are affected by this metabolic activity. We show through magnetic and spectroscopic measurements that the phototrophic Fe(II)-oxidizer Rhodopseudomonas palustris TIE-1 can oxidize solid-phase magnetite nanoparticles using light energy, leading to a decrease in the measured magnetic susceptibility (MS). This process likely occurs at the surface and is reversible in the dark by the Fe(III)-reducer Geobacter sulfurreducens resulting in an increase in MS. Thesemore » results show that iron ions bound in highly crystalline mineral magnetite are bioavailable as electron stores and electron sinks under varying environmental conditions, making magnetite a potential “biogeobattery” during day/night cycles. These findings are relevant for environmental studies and reinforce the impact of microbial redox processes on the global iron cycle.« less

Dark sector shining through 750 GeV dark Higgs boson at the LHC

NASA Astrophysics Data System (ADS)

Ko, P.; Nomura, Takaaki

2016-07-01

We consider a dark sector with SU(3)C × U(1)Y × U(1)X and three families of dark fermions that are chiral under dark U(1)X gauge symmetry, whereas scalar dark matter X is the SM singlet. U(1)X dark symmetry is spontaneously broken by nonzero VEV of dark Higgs field 〈 Φ 〉, generating the masses of dark fermions and dark photon Z‧. The resulting dark Higgs boson ϕ can be produced at the LHC by dark quark loop (involving 3 generations) and will decay into a pair of photon through charged dark fermion loop. Its decay width can be easily ∼ 45 GeV due to its possible decays into a pair of dark photon, which is not strongly constrained by the current LHC searches pp → ϕ →Z‧Z‧ followed by Z‧ decays into the SM fermion pairs. The scalar DM can achieve thermal relic density without conflict with direct detection bound or the invisible ϕ decay into a pair of DM.

Proton effects on low noise and high responsivity silicon-based photodiodes for space environment

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

Pedroza, Guillaume; Gilard, Olivier; Bourqui, Marie-Lise

A series of proton irradiations has been carried out on p-n silicon photodiodes for the purpose of assessing the suitability of these devices for the European Galileo space mission. The irradiations were performed at energies of 60, 100, and 150 MeV with proton fluences ranging from 1.7x10{sup 10} to 1x10{sup 11} protons/cm{sup 2}. Dark current, spectral responsivity, and dark current noise were measured before and after each irradiation step. We observed an increase in both dark current, dark current noise, and noise equivalent power and a drop of the spectral responsivity with increasing displacement damage dose. An analytical model hasmore » been developed to investigate proton damage effects through the modeling of the electro-optical characteristics of the photodiode. Experimental degradations were successfully explained taking into account the degradation of the minority carrier diffusion length in the N-region of the photodiode. The degradation model was then applied to assess the end-of-life performance of these devices in the framework of the Galileo mission.« less

Analysis of Dark Current in BRITE Nanostellite CCD Sensors †

PubMed Central

Popowicz, Adam

2018-01-01

The BRightest Target Explorer (BRITE) is the pioneering nanosatellite mission dedicated for photometric observations of the brightest stars in the sky. The BRITE charge coupled device (CCD) sensors are poorly shielded against extensive flux of energetic particles which constantly induce defects in the silicon lattice. In this paper we investigate the temporal evolution of the generation of the dark current in the BRITE CCDs over almost four years after launch. Utilizing several steps of image processing and employing normalization of the results, it was possible to obtain useful information about the progress of thermal activity in the sensors. The outcomes show a clear and consistent linear increase of induced damage despite the fact that only about 0.14% of CCD pixels were probed. By performing the analysis of temperature dependencies of the dark current, we identified the observed defects as phosphorus-vacancy (PV) pairs, which are common in proton irradiated CCD matrices. Moreover, the Meyer-Neldel empirical rule was confirmed in our dark current data, yielding EMN=24.8 meV for proton-induced PV defects. PMID:29415471

Photo-controllable thermoelectric properties with reversibility and photo-thermoelectric effects of tungsten trioxide accompanied by its photochromic phenomenon

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

Azuma, Chiori; Kawano, Takuto; Kakemoto, Hirofumi

2014-11-07

The addition of photo-controllable properties to tungsten trioxide (WO{sub 3}) is of interest for developing practical applications of WO{sub 3} as well as for interpreting such phenomena from scientific viewpoints. Here, a sputtered crystalline WO{sub 3} thin film generated thermoelectric power due to ultraviolet (UV) light-induced band-gap excitation and was accompanied by a photochromic reaction resulting from generating W{sup 5+} ions. The thermoelectric properties (electrical conductivity (σ) and Seebeck coefficient (S)) and coloration of WO{sub 3} could be reversibly switched by alternating the external stimulus between UV light irradiation and dark storage. After irradiating the film with UV light, σmore » increased, whereas the absolute value of S decreased, and the photochromic (coloration) reaction was detected. Notably, the opposite behavior was exhibited by WO{sub 3} after dark storage, and this reversible cycle could be repeated at least three times. Moreover, photo-thermoelectric effects (photo-conductive effect (photo-conductivity, σ{sub photo}) and photo-Seebeck effect (photo-Seebeck coefficient, S{sub photo})) were also detected in response to visible-light irradiation of the colored WO{sub 3} thin films. Under visible-light irradiation, σ{sub photo} and the absolute value of S{sub photo} increased and decreased, respectively. These effects are likely attributable to the excitation of electrons from the mid-gap visible light absorption band (W{sup 5+} state) to the conduction band of WO{sub 3}. Our findings demonstrate that the simultaneous, reversible switching of multiple properties of WO{sub 3} thin film is achieved by the application of an external stimulus and that this material exhibits photo-thermoelectric effects when irradiated with visible-light.« less

Global color variations on the Martian surface

USGS Publications Warehouse

Soderblom, L.A.; Edwards, K.; Eliason, E.M.; Sanchez, E.M.; Charette, M.P.

1978-01-01

Surface materials exposed throughout the equatorial region of Mars have been classified and mapped on the basis of spectral reflectance properties determined by the Viking II Orbiter vidicon cameras. Frames acquired at each of three wavelengths (0.45 ?? 0.03 ??m, 0.53 ?? 0.05 ??m, and 0.59 ?? 0.05 ??m) during the approach of Viking Orbiter II in Martian summer (Ls = 105??) were mosaicked by computer. The mosaics cover latitudes 30??N to 63??S for 360?? of longitude and have resolutions between 10 and 20 km per line pair. Image processing included Mercator transformation and removal of an average Martian photometric function to produce albedo maps at three wavelengths. The classical dark region between the equator and ???30??S in the Martian highlands is composed of two units: (i) and ancient unit consisting of topographic highs (ridges, crater rims, and rugged plateaus riddled with small dendritic channels) which is among the reddest on the planet (0.59/0.45 ??m {reversed tilde equals} 3); and (ii) intermediate age, smooth, intercrater volcanic plains displaying numerous mare ridges which are among the least red on Mars (0.59/0.45 ??m {reversed tilde equals} 2). The relatively young shield volcanoes are, like the oldest unit, dark and very red. Two probable eolian deposits are recognized in the intermediate and high albedo regions. The stratigraphically lower unit is intermediate in both color (0.59/ 0.45 ??m {reversed tilde equals} 2.5) and albedo. The upper unit has the highest albedo, is very red (0.59/0.45 ??m {reversed tilde equals} 3), and is apparently the major constituent of the annual dust storms as its areal extent changes from year to year. The south polar ice cap and condensate clouds dominate the southernmost part of the mosaics. ?? 1978.

Optimization of Visual Training for Full Recovery from Severe Amblyopia in Adults

ERIC Educational Resources Information Center

Eaton, Nicolette C.; Sheehan, Hanna Marie; Quinlan, Elizabeth M.

2016-01-01

The severe amblyopia induced by chronic monocular deprivation is highly resistant to reversal in adulthood. Here we use a rodent model to show that recovery from deprivation amblyopia can be achieved in adults by a two-step sequence, involving enhancement of synaptic plasticity in the visual cortex by dark exposure followed immediately by visual…

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

Domengie, F., E-mail: florian.domengie@st.com; Morin, P.; Bauza, D.

We propose a model for dark current induced by metallic contamination in a CMOS image sensor. Based on Shockley-Read-Hall kinetics, the expression of dark current proposed accounts for the electric field enhanced emission factor due to the Poole-Frenkel barrier lowering and phonon-assisted tunneling mechanisms. To that aim, we considered the distribution of the electric field magnitude and metal atoms in the depth of the pixel. Poisson statistics were used to estimate the random distribution of metal atoms in each pixel for a given contamination dose. Then, we performed a Monte-Carlo-based simulation for each pixel to set the number of metalmore » atoms the pixel contained and the enhancement factor each atom underwent, and obtained a histogram of the number of pixels versus dark current for the full sensor. Excellent agreement with the dark current histogram measured on an ion-implanted gold-contaminated imager has been achieved, in particular, for the description of the distribution tails due to the pixel regions in which the contaminant atoms undergo a large electric field. The agreement remains very good when increasing the temperature by 15 °C. We demonstrated that the amplification of the dark current generated for the typical electric fields encountered in the CMOS image sensors, which depends on the nature of the metal contaminant, may become very large at high electric field. The electron and hole emissions and the resulting enhancement factor are described as a function of the trap characteristics, electric field, and temperature.« less

SU-F-T-554: Dark Current Effect On CyberKnife Beam Dosimetry

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

Kim, H; Chang, A

Purpose: All RF linear accelerators produce dark current to varying degrees when an accelerating voltage and RF input is applied in the absence of electron gun injection. This study is to evaluate how dark current from the linear accelerator of CyberKnife affect the dose in the reference dosimetry. Methods: The G4 CyberKnife system with 6MV photon beam was used in this study. Using the ion chamber and the diode detector, the dose was measured in water with varying time delay between acquiring charges and staring beam-on after applying high-voltage into the linear accelerator. The dose was measured after the timemore » delay with over the range of 0 to 120 seconds in the accelerating high-voltage mode without beam-on, applying 0, 10, 50, 100, and 200 MUs. For the measurements, the collimator of 60 mm was used and the detectors were placed at the depths of 10 cm with the source-to-surface distance of 80 cm. Results: The dark current was constant over time regardless of MU. The dose due to the dark current increased over time linearly with the R-squared value of 0.9983 up to 4.4 cGy for the time 120 seconds. In the dose rate setting of 720 MU/min, the relative dose when applying the accelerating voltage without beam-on was increased over time up to 0.6% but it was less than the leakage radiation resulted from the accelerated head. As the reference dosimetry condition, when 100 MU was delivered after 10 seconds time delay, the relative dose increased by 0.7% but 6.7% for the low MU (10 MU). Conclusion: In the dosimetry using CyberKnife system, the constant dark current affected to the dose. Although the time delay in the accelerating high-voltage mode without beam-on is within 10 seconds, the dose less than 100 cGy can be overestimated more than 1%.« less

Dark gauge bosons: LHC signatures of non-abelian kinetic mixing

DOE PAGES

Argüelles, Carlos A.; He, Xiao-Gang; Ovanesyan, Grigory; ...

2017-04-20

We consider non-abelian kinetic mixing between the Standard Model and a dark sector gauge group associated with the presence of a scalar triplet. The magnitude of the resulting dark photon coupling ϵ is determined by the ratio of the triplet vacuum expectation value, constrained to by by electroweak precision tests, to the scale Λ of the effective theory. The corresponding effective operator Wilson coefficient can be while accommodating null results for dark photon searches, allowing for a distinctive LHC dark photon phenomenology. After outlining the possible LHC signatures, we illustrate by recasting current ATLAS dark photon results into the non-abelianmore » mixing context.« less

Dark matter and the equivalence principle

NASA Technical Reports Server (NTRS)

Frieman, Joshua A.; Gradwohl, Ben-Ami

1993-01-01

A survey is presented of the current understanding of dark matter invoked by astrophysical theory and cosmology. Einstein's equivalence principle asserts that local measurements cannot distinguish a system at rest in a gravitational field from one that is in uniform acceleration in empty space. Recent test-methods for the equivalence principle are presently discussed as bases for testing of dark matter scenarios involving the long-range forces between either baryonic or nonbaryonic dark matter and ordinary matter.

76 FR 70190 - Self-Regulatory Organizations; Financial Industry Regulatory Authority, Inc.; Order Approving...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-11-10

... concern about dark pools and their potential impact on the fairness and transparency of the national market system.\\12\\ One of these commenters suggested that dark pools be prohibited entirely.\\13\\ FINRA... transparency that currently exists.\\14\\ FINRA stated that all trades executed on an ATS, including a dark pool...

Reverse leakage current characteristics of InGaN/GaN multiple quantum well ultraviolet/blue/green light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhou, Shengjun; Lv, Jiajiang; Wu, Yini; Zhang, Yuan; Zheng, Chenju; Liu, Sheng

2018-05-01

We investigated the reverse leakage current characteristics of InGaN/GaN multiple quantum well (MQW) near-ultraviolet (NUV)/blue/green light-emitting diodes (LEDs). Experimental results showed that the NUV LED has the smallest reverse leakage current whereas the green LED has the largest. The reason is that the number of defects increases with increasing nominal indium content in InGaN/GaN MQWs. The mechanism of the reverse leakage current was analyzed by temperature-dependent current–voltage measurement and capacitance–voltage measurement. The reverse leakage currents of NUV/blue/green LEDs show similar conduction mechanisms: at low temperatures, the reverse leakage current of these LEDs is attributed to variable-range hopping (VRH) conduction; at high temperatures, the reverse leakage current of these LEDs is attributed to nearest-neighbor hopping (NNH) conduction, which is enhanced by the Poole–Frenkel effect.

Directly detecting isospin-violating dark matter

NASA Astrophysics Data System (ADS)

Kelso, Chris; Kumar, Jason; Marfatia, Danny; Sandick, Pearl

2018-03-01

We consider the prospects for multiple dark matter direct detection experiments to determine if the interactions of a dark matter candidate are isospin-violating. We focus on theoretically well-motivated examples of isospin-violating dark matter (IVDM), including models in which dark matter interactions with nuclei are mediated by a dark photon, a Z , or a squark. We determine that the best prospects for distinguishing IVDM from the isospin-invariant scenario arise in the cases of dark photon-or Z -mediated interactions, and that the ideal experimental scenario would consist of large exposure xenon- and neon-based detectors. If such models just evade current direct detection limits, then one could distinguish such models from the standard isospin-invariant case with two detectors with of order 100 ton-year exposure.

n-B-pi-p Superlattice Infrared Detector

NASA Technical Reports Server (NTRS)

Ting, David Z.; Bandara, Sumith V.; Hill, Cory J.; Gunapala, Sarath D.

2011-01-01

A specially designed barrier (B) is inserted at the n-pi junction [where most GR (generation-recombination) processes take place] in the standard n-pi-p structure to substantially reduce generation-recombination dark currents. The resulting n-Bpi- p structure also has reduced tunneling dark currents, thereby solving some of the limitations to which current type II strained layer superlattice infrared detectors are prone. This innovation is compatible with common read-out integrated circuits (ROICs).

Thin film assembly of nano-sized Zn(II)-8-hydroxy-5,7-dinitroquinolate by using successive ion layer adsorption and reaction (SILAR) technique: characterization and optical-electrical-photovoltaic properties.

PubMed

Farag, A A M; Haggag, Sawsan M S; Mahmoud, Mohamed E

2012-07-01

A method is described for thin film assembly of nano-sized Zn(II)-8-hydroxy-5,7-dinitroquinolate complex, Zn[((NO(2))(2)-8HQ)(2)] by using successive ion layer adsorption and reaction (SILAR) technique. Highly homogeneous assembled nano-sized metal complex thin films with particle size distribution in the range 27-47nm was identified by using scanning electron microscopy (SEM). Zn[((NO(2))(2)-8HQ)(2)] and [(NO(2))(2)-8HQ] ligand were studied by thermal gravimetric analysis (TGA). Graphical representation of temperature dependence of the dark electrical conductivity produced two distinct linear parts for two activation energies at 0.377eV and 1.11eV. The analysis of the spectral behavior of the absorption coefficient in the intrinsic absorption region reveals a direct allowed transition with a fundamental band gap of 2.74eV. The dark current density-voltage (J-V) characteristics showed the rectification effect due to the formation of junction barrier of Zn[((NO(2))(2)-8HQ)(2)] complex film/n-Si interface. The photocurrent in the reverse direction is strongly increased by photo-illumination and the photovoltaic characteristics were also determined and evaluated. Copyright © 2012 Elsevier B.V. All rights reserved.

Antimatter cosmic rays from dark matter annihilation: First results from an N-body experiment

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

Lavalle, J.; Nezri, E.; Athanassoula, E.

2008-11-15

While the particle hypothesis for dark matter may be very soon investigated at the LHC, and as the PAMELA and GLAST satellites are currently taking new data on charged and gamma cosmic rays, the need of controlling the theoretical uncertainties affecting the possible indirect signatures of dark matter annihilation is of paramount importance. The uncertainties which originate from the dark matter distribution are difficult to estimate because current astrophysical observations provide rather weak dynamical constraints and because, according to cosmological N-body simulations, dark matter is neither smoothly nor spherically distributed in galactic halos. Some previous studies made use of N-bodymore » simulations to compute the {gamma}-ray flux from dark matter annihilation, but such a work has never been performed for the antimatter (positron and antiproton) primary fluxes, for which transport processes complicate the calculations. We take advantage of the galaxylike 3D dark matter map extracted from the Horizon Project results to calculate the positron and antiproton fluxes from dark matter annihilation, in a model-independent approach as well as for dark matter particle benchmarks relevant at the LHC scale (from supersymmetric and extradimensional theories). We find that the flux uncertainties arise mainly from fluctuations of the local dark matter density, and are of {approx}1 order of magnitude. We compare our results to analytic descriptions of the dark matter halo, showing how the latter can well reproduce the former. The overall antimatter predictions associated with our benchmark models are shown to lie far below the existing measurements and, in particular, that of the positron fraction recently reported by PAMELA, and far below the background predictions as well. Finally, we stress the limits of the use of an N-body framework in this context.« less

Probing the sign-changeable interaction between dark energy and dark matter with current observations

NASA Astrophysics Data System (ADS)

Guo, Juan-Juan; Zhang, Jing-Fei; Li, Yun-He; He, Dong-Ze; Zhang, Xin

2018-03-01

We consider the models of vacuum energy interacting with cold dark matter in this study, in which the coupling can change sigh during the cosmological evolution. We parameterize the running coupling b by the form b( a) = b 0 a+ b e(1- a), where at the early-time the coupling is given by a constant b e and today the coupling is described by another constant b 0. We explore six specific models with (i) Q = b( a) H 0 ρ 0, (ii) Q = b( a) H 0 ρ de, (iii) Q = b( a) H 0 ρ c, (iv) Q = b( a) Hρ 0, (v) Q = b( a) H ρ de, and (vi) Q = b( a) Hρ c. The current observational data sets we use to constrain the models include the JLA compilation of type Ia supernova data, the Planck 2015 distance priors data of cosmic microwave background observation, the baryon acoustic oscillations measurements, and the Hubble constant direct measurement. We find that, for all the models, we have b 0 < 0 and b e > 0 at around the 1 σ level, and b 0 and b e are in extremely strong anti-correlation. Our results show that the coupling changes sign during the evolution at about the 1 σ level, i.e., the energy transfer is from dark matter to dark energy when dark matter dominates the universe and the energy transfer is from dark energy to dark matter when dark energy dominates the universe.

Solar terrestrial relationships related to thunderstorms and BUV dark current and ozone data

NASA Technical Reports Server (NTRS)

Herman, J. R.

1980-01-01

Solar terrestrial interactions as they affect Nimbus 4 BUV dark current and possibly affect thunderstorm occurrence are investigated. A solar wind index is calculated for 1970 to 1971. Dark current enhancements appear to be associated in some way with solar proton events and the solar wind index, but additional investigations by GSFC are required before conclusions can be drawn. Superposed epoch analysis of an index of North American thunderstorm occurrence reveals a discernible increase in the index magnitude on days 1 and 2 following solar proton events. There appears to be little or no 27 day recurrence tendency in thunderstorm occurrence frequency and no association with vorticity area index on a day to day basis.

Probing leptophilic dark sectors with hadronic processes

NASA Astrophysics Data System (ADS)

D'Eramo, Francesco; Kavanagh, Bradley J.; Panci, Paolo

2017-08-01

We study vector portal dark matter models where the mediator couples only to leptons. In spite of the lack of tree-level couplings to colored states, radiative effects generate interactions with quark fields that could give rise to a signal in current and future experiments. We identify such experimental signatures: scattering of nuclei in dark matter direct detection; resonant production of lepton-antilepton pairs at the Large Hadron Collider; and hadronic final states in dark matter indirect searches. Furthermore, radiative effects also generate an irreducible mass mixing between the vector mediator and the Z boson, severely bounded by ElectroWeak Precision Tests. We use current experimental results to put bounds on this class of models, accounting for both radiatively induced and tree-level processes. Remarkably, the former often overwhelm the latter.

Probing leptophilic dark sectors with hadronic processes

DOE PAGES

D'Eramo, Francesco; Kavanagh, Bradley J.; Panci, Paolo

2017-05-29

We study vector portal dark matter models where the mediator couples only to leptons. In spite of the lack of tree-level couplings to colored states, radiative effects generate interactions with quark fields that could give rise to a signal in current and future experiments. We identify such experimental signatures: scattering of nuclei in dark matter direct detection; resonant production of lepton–antilepton pairs at the Large Hadron Collider; and hadronic final states in dark matter indirect searches. Furthermore, radiative effects also generate an irreducible mass mixing between the vector mediator and the Z boson, severely bounded by ElectroWeak Precision Tests. Wemore » use current experimental results to put bounds on this class of models, accounting for both radiatively induced and tree-level processes. Remarkably, the former often overwhelm the latter.« less

Fast light-induced reversible wettability of a zinc oxide nanorod array coated with a thin gold layer

NASA Astrophysics Data System (ADS)

Wei, Yuefan; Du, Hejun; Kong, Junhua; Tran, Van-Thai; Koh, Jia Kai; Zhao, Chenyang; He, Chaobin

2017-11-01

Zinc oxide (ZnO) has gained much attention recently due to its excellent physical and chemical properties, and has been extensively studied in energy harvesting applications such as photovoltaic and piezoelectric devices. In recent years, its reversible wettability has also attracted increasing interest. The wettability of ZnO nanostructures with various morphologies has been studied. However, to the best of our knowledge, there is still a lack of investigations on further modifications on ZnO to provide more benefits than pristine ZnO. Comprehensive studies on the reversible wettability are still needed. In this study, a ZnO nanorod array was prepared via a hydrothermal process and subsequently coated with thin gold layers with varied thickness. The morphologies and structures, optical properties and wettability were investigated. It is revealed that the ZnO-Au system possesses recoverable wettability upon switching between visible-ultraviolet light and a dark environment, which is verified by the contact angle change. The introduction of the thin gold layer to the ZnO nanorod array effectively increases the recovery rate of the wettability. The improvements are attributed to the hierarchical structures, which are formed by depositing thin gold layers onto the ZnO nanorod array, the visible light sensitivity due to the plasmonic effect of the deposited gold, as well as the fast charge-induced surface status change upon light illumination or dark storage. The improvement is beneficial to applications in environmental purification, energy harvesting, micro-lenses, and smart devices.

Blue light- and genetically-reversed gravitropic response in protonemata of the moss Ceratodon purpureus.

PubMed

Lamparter, T; Hughes, J; Hartmann, E

1998-09-01

In darkness, protonemal filaments of Ceratodon purpureus (Brid.) grow negatively gravitropically (upwards). Red light induces a positive phototropic response mediated by the photoreceptor phytochrome. A red light treatment also has an inhibitory effect on the gravitropic response, an effect also mediated by phytochrome. In this study the effects of blue light on phototropism and on gravitropism were analysed. Unilateral blue light resulted in only a weak phototropic response, but markedly randomised growth direction. Blue light given together with a gravitropic stimulus reversed the gravitropism, changing it from negative to positive (filaments grow downward). The effect of blue light was also analysed with the mutant ptr116, which is defective in the biosynthesis of the phytochrome chromophore, and in a newly isolated mutant wwr2, which is positively gravitropic in darkness. Blue light induced the same reversal of gravitropism in ptrll6 as in the wild type, indicating that phytochrome is not involved in this process. In wwr2 the direction of gravitropism was unaltered by the blue light treatment. Light also affects chlorophyll content and the size of plastids, potential statoliths for gravitropism. Red light induced an increase in plastid size and chlorophyll content in the wild type but not in ptr116. Blue light induced a similar change in wild type plastids. It seems as though light-induced alterations of gravitropism are not simply mediated by alterations in plastid properties, and that red light and blue light evoke fundamentally different responses.

Regulatory mechanisms of metabolic flexibility in the dark-eyed junco (Junco hyemalis).

PubMed

Stager, Maria; Swanson, David L; Cheviron, Zachary A

2015-03-01

Small temperate birds reversibly modify their aerobic performance to maintain thermoregulatory homeostasis under seasonally changing environmental conditions and these physiological adjustments may be attributable to changes in the expression of genes in the underlying regulatory networks. Here, we report the results of an experimental procedure designed to gain insight into the fundamental mechanisms of metabolic flexibility in the dark-eyed junco (Junco hyemalis). We combined genomic transcriptional profiles with measures of metabolic enzyme activities and whole-animal thermogenic performance from juncos exposed to four 6-week acclimation treatments that varied in temperature (cold, 3°C; warm, 24°C) and photoperiod (short day, 8 h light:16 h dark; long day, 16 h light:8 h dark). Cold-acclimated birds increased thermogenic capacity compared with warm-acclimated birds, and this enhanced performance was associated with upregulation of genes involved in muscle hypertrophy, angiogenesis, and lipid transport and oxidation, as well as with catabolic enzyme activities. These physiological changes occurred over ecologically relevant timescales, suggesting that birds make regulatory adjustments to interacting, hierarchical pathways in order to seasonally enhance thermogenic capacity. © 2015. Published by The Company of Biologists Ltd.

Searching for dark absorption with direct detection experiments

DOE PAGES

Bloch, Itay M.; Essig, Rouven; Tobioka, Kohsaku; ...

2017-06-16

We consider the absorption by bound electrons of dark matter in the form of dark photons and axion-like particles, as well as of dark photons from the Sun, in current and next-generation direct detection experiments. Experiments sensitive to electron recoils can detect such particles with masses between a few eV to more than 10 keV. For dark photon dark matter, we update a previous bound based on XENON10 data and derive new bounds based on data from XENON100 and CDMSlite. We find these experiments to disfavor previously allowed parameter space. Moreover, we derive sensitivity projections for SuperCDMS at SNOLAB formore » silicon and germanium targets, as well as for various possible experiments with scintillating targets (cesium iodide, sodium iodide, and gallium arsenide). The projected sensitivity can probe large new regions of parameter space. For axion-like particles, the same current direction detection data improves on previously known direct-detection constraints but does not bound new parameter space beyond known stellar cooling bounds. However, projected sensitivities of the upcoming SuperCDMS SNOLAB using germanium can go beyond these and even probe parameter space consistent with possible hints from the white dwarf luminosity function. We find similar results for dark photons from the sun. For all cases, direct-detection experiments can have unprecedented sensitivity to dark-sector particles.« less

Searching for dark absorption with direct detection experiments

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

Bloch, Itay M.; Essig, Rouven; Tobioka, Kohsaku

We consider the absorption by bound electrons of dark matter in the form of dark photons and axion-like particles, as well as of dark photons from the Sun, in current and next-generation direct detection experiments. Experiments sensitive to electron recoils can detect such particles with masses between a few eV to more than 10 keV. For dark photon dark matter, we update a previous bound based on XENON10 data and derive new bounds based on data from XENON100 and CDMSlite. We find these experiments to disfavor previously allowed parameter space. Moreover, we derive sensitivity projections for SuperCDMS at SNOLAB formore » silicon and germanium targets, as well as for various possible experiments with scintillating targets (cesium iodide, sodium iodide, and gallium arsenide). The projected sensitivity can probe large new regions of parameter space. For axion-like particles, the same current direction detection data improves on previously known direct-detection constraints but does not bound new parameter space beyond known stellar cooling bounds. However, projected sensitivities of the upcoming SuperCDMS SNOLAB using germanium can go beyond these and even probe parameter space consistent with possible hints from the white dwarf luminosity function. We find similar results for dark photons from the sun. For all cases, direct-detection experiments can have unprecedented sensitivity to dark-sector particles.« less

Calcium regulates vesicle replenishment at the cone ribbon synapse

PubMed Central

Babai, Norbert; Bartoletti, Theodore M.; Thoreson, Wallace B.

2010-01-01

Cones release glutamate-filled vesicles continuously in darkness and changing illumination modulates this release. Because sustained release in darkness is governed by vesicle replenishment rates, we analyzed how cone membrane potential regulates replenishment. Synaptic release from cones was measured by recording post-synaptic currents in Ambystoma tigrinum horizontal or OFF bipolar cells evoked by depolarization of simultaneously voltage-clamped cones. We measured replenishment after attaining a steady-state between vesicle release and replenishment using trains of test pulses. Increasing Ca2+ currents (ICa) by changing the test step from −30 to −10 mV increased replenishment. Lengthening −30 mV test pulses to match the Ca2+ influx during 25 ms test pulses to −10 mV produced similar replenishment rates. Reducing Ca2+ driving force by using test steps to +30 mV slowed replenishment. Using UV flashes to reverse inhibition of ICa by nifedipine accelerated replenishment. Increasing [Ca2+]i by flash photolysis of caged Ca2+ also accelerated replenishment. Replenishment, but not the initial burst of release, was enhanced by using an intracellular Ca2+ buffer of 0.5 mM EGTA rather than 5 mM EGTA, and diminished by 1 mM BAPTA. This suggests that although release and replenishment and release exhibited similar Ca2+-dependencies, release sites are <200 nm from Ca2+ channels but replenishment sites are >200 nm away. Membrane potential thus regulates replenishment by controlling Ca2+ influx, principally by effects on replenishment mechanisms but also by altering releasable pool size. This in turn provides a mechanism for converting changes in light intensity into changes in sustained release at the cone ribbon synapse. PMID:21106825

New integration concept of PIN photodiodes in 0.35μm CMOS technologies

NASA Astrophysics Data System (ADS)

Jonak-Auer, I.; Teva, J.; Park, J. M.; Jessenig, S.; Rohrbacher, M.; Wachmann, E.

2012-06-01

We report on a new and very cost effective way to integrate PIN photo detectors into a standard CMOS process. Starting with lowly p-doped (intrinsic) EPI we need just one additional mask and ion implantation in order to provide doping concentrations very similar to standard CMOS substrates to areas outside the photoactive regions. Thus full functionality of the standard CMOS logic can be guaranteed while the photo detectors highly benefit from the low doping concentrations of the intrinsic EPI. The major advantage of this integration concept is that complete modularity of the CMOS process remains untouched by the implementation of PIN photodiodes. Functionality of the implanted region as host of logic components was confirmed by electrical measurements of relevant standard transistor as well as ESD protection devices. We also succeeded in establishing an EPI deposition process in austriamicrosystems 200mm wafer fabrication which guarantees the formation of very lowly p-doped intrinsic layers, which major semiconductor vendors could not provide. With our EPI deposition process we acquire doping levels as low as 1•1012/cm3. In order to maintain those doping levels during CMOS processing we employed special surface protection techniques. After complete CMOS processing doping concentrations were about 4•1013/cm3 at the EPI surface while the bulk EPI kept its original low doping concentrations. Photodiode parameters could further be improved by bottom antireflective coatings and a special implant to reduce dark currents. For 100×100μm2 photodiodes in 20μm thick intrinsic EPI on highly p-doped substrates we achieved responsivities of 0.57A/W at λ=675nm, capacitances of 0.066pF and dark currents of 0.8pA at 2V reverse voltage.

Revealing the nonadiabatic nature of dark energy perturbations from galaxy clustering data

NASA Astrophysics Data System (ADS)

Velten, Hermano; Fazolo, Raquel

2017-10-01

We study structure formation using relativistic cosmological linear perturbation theory in the presence of intrinsic and relative (with respect to matter) nonadiabatic dark energy perturbations. For different dark energy models we assess the impact of nonadiabaticity on the matter growth promoting a comparison with growth rate data. The dark energy models studied lead to peculiar signatures of the (non)adiabatic nature of dark energy perturbations in the evolution of the f σ8(z ) observable. We show that nonadiabatic dark energy models become close to be degenerated with respect to the Λ CDM model at first order in linear perturbations. This would avoid the identification of the nonadiabatic nature of dark energy using current available data. Therefore, such evidence indicates that new probes are necessary to reveal the nonadiabatic features in the dark energy sector.

Reducing current reversal time in electric motor control

DOEpatents

Bredemann, Michael V

2014-11-04

The time required to reverse current flow in an electric motor is reduced by exploiting inductive current that persists in the motor when power is temporarily removed. Energy associated with this inductive current is used to initiate reverse current flow in the motor.

Near-Infrared Photon-Counting Camera for High-Sensitivity Observations

NASA Technical Reports Server (NTRS)

Jurkovic, Michael

2012-01-01

The dark current of a transferred-electron photocathode with an InGaAs absorber, responsive over the 0.9-to-1.7- micron range, must be reduced to an ultralow level suitable for low signal spectral astrophysical measurements by lowering the temperature of the sensor incorporating the cathode. However, photocathode quantum efficiency (QE) is known to reduce to zero at such low temperatures. Moreover, it has not been demonstrated that the target dark current can be reached at any temperature using existing photocathodes. Changes in the transferred-electron photocathode epistructure (with an In- GaAs absorber lattice-matched to InP and exhibiting responsivity over the 0.9- to-1.7- m range) and fabrication processes were developed and implemented that resulted in a demonstrated >13x reduction in dark current at -40 C while retaining >95% of the approximately equal to 25% saturated room-temperature QE. Further testing at lower temperature is needed to confirm a >25 C predicted reduction in cooling required to achieve an ultralow dark-current target suitable for faint spectral astronomical observations that are not otherwise possible. This reduction in dark current makes it possible to increase the integration time of the imaging sensor, thus enabling a much higher near-infrared (NIR) sensitivity than is possible with current technology. As a result, extremely faint phenomena and NIR signals emitted from distant celestial objects can be now observed and imaged (such as the dynamics of redshifting galaxies, and spectral measurements on extra-solar planets in search of water and bio-markers) that were not previously possible. In addition, the enhanced NIR sensitivity also directly benefits other NIR imaging applications, including drug and bomb detection, stand-off detection of improvised explosive devices (IED's), Raman spectroscopy and microscopy for life/physical science applications, and semiconductor product defect detection.

Exponential Potential versus Dark Matter

DTIC Science & Technology

1993-10-15

scale of the solar system. Galaxy, Dark matter , Galaxy cluster, Gravitation, Quantum gravity...A two parameter exponential potential explains the anomalous kinematics of galaxies and galaxy clusters without need for the myriad ad hoc dark ... matter models currently in vogue. It also explains much about the scales and structures of galaxies and galaxy clusters while being quite negligible on the

Effects of rat sex differences and lighting on locomotor exploration of a circular open field with free-standing central corners and without peripheral walls.

PubMed

Alstott, Jeff; Timberlake, William

2009-01-23

A typical open field consists of a square enclosure, bounded by four straight walls joined by identical corners. For decades behavioral researchers have used the open center and more sheltered perimeter of such fields to examine the effects of drugs, sex differences, and illumination on the behavioral expression of fear and anxiety. The present study "reversed" the relative security of the center and periphery of a circular field to re-examine the functional relation of open field behavior to experience, sex differences and lighting. Across six daily exposures, males in both the light and dark rapidly increased their preference for the center. Females in the light developed a similar pattern, though more slowly; females in the dark continued to spend the great majority of their time in the open periphery, including the edge of the field. The behavior of all groups, but especially the dark females, strongly supports the continued importance of environmental assessment in open field behavior.

Switchable Pickering Emulsions Stabilized by Awakened TiO2 Nanoparticle Emulsifiers Using UV/Dark Actuation.

PubMed

Zhang, Qing; Bai, Rui-Xue; Guo, Ting; Meng, Tao

2015-08-26

In this work, switchable Pickering emulsions that utilize UV/dark manipulation employ a type of smart TiO2 nanoparticle as emulsifiers. The emulsifiers can be awakened when needed via UV-induced degradation of grafted silanes on TiO2 nanoparticles. By tuning the surface wettability of TiO2 nanoparticles in situ via UV/dark actuation, emulsions stabilized by the nanoparticles can be reversibly switched between the water-in-oil (W/O) type and oil-in-water (O/W) type for several cycles. Due to the convertible wettability, the smart nanoparticle emulsifiers can be settled in either the oil phase or the water phase as desired during phase separation, making it convenient for recycling. The present work provides a facile and noninvasive method to freely manipulate the formation, breakage, and switching of the emulsion; this method has promising potential as a powerful technique for use in energy-efficient and environmentally friendly industries.

Search for Muonic Dark Forces at BABAR

NASA Astrophysics Data System (ADS)

Godang, Romulus

2017-04-01

Many models of physics beyond Standard Model predict the existence of light Higgs states, dark photons, and new gauge bosons mediating interactions between dark sectors and the Standard Model. Using a full data sample collected with the BABAR detector at the PEP-II e+e- collider, we report searches for a light non-Standard Model Higgs boson, dark photon, and a new muonic dark force mediated by a gauge boson (Z') coupling only to the second and third lepton families. Our results significantly improve upon the current bounds and further constrain the remaining region of the allowed parameter space.

Warm dark matter effects in a spherical collapse model with shear and angular momentum

NASA Astrophysics Data System (ADS)

Marciu, Mihai

2016-03-01

This paper investigates the nonlinear structure formation in a spherical top-hat collapse model based on the pseudo-Newtonian approximation. The system is composed of warm dark matter and dark energy and the dynamical properties of the collapsing region are analyzed for various parametrizations of the dark matter equation of state which are in agreement with current observations. Concerning dark energy, observational constraints of the Chevallier-Polarski-Linder model and the Jassal-Bagla-Padmanabhan equation of state have been considered. During the collapse, the positive dark matter pressure leads to an increase of growth for dark matter and dark energy perturbations and an accelerated expansion for the spherical region. Hence, in the warm dark matter hypothesis, the structure formation is accelerated and the inconsistencies of the Λ CDM model at the galactic scales could be solved. The results obtained are applicable only to adiabatic warm dark matter physical models which are compatible with the pseudo-Newtonian approach.

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

Blennow, Mattias; Clementz, Stefan, E-mail: emb@kth.se, E-mail: scl@kth.se

Current problems with the solar model may be alleviated if a significant amount of dark matter from the galactic halo is captured in the Sun. We discuss the capture process in the case where the dark matter is a Dirac fermion and the background halo consists of equal amounts of dark matter and anti-dark matter. By considering the case where dark matter and anti-dark matter have different cross sections on solar nuclei as well as the case where the capture process is considered to be a Poisson process, we find that a significant asymmetry between the captured dark particles andmore » anti-particles is possible even for an annihilation cross section in the range expected for thermal relic dark matter. Since the captured number of particles are competitive with asymmetric dark matter models in a large range of parameter space, one may expect solar physics to be altered by the capture of Dirac dark matter. It is thus possible that solutions to the solar composition problem may be searched for in these type of models.« less

Ultrahigh sensitivity and gain white light photodetector based on GaTe/Sn : CdS nanoflake/nanowire heterostructures

NASA Astrophysics Data System (ADS)

Zhou, Weichang; Zhou, Yong; Peng, Yuehua; Zhang, Yong; Yin, Yanling; Tang, Dongsheng

2014-11-01

Optoelectronic diode based on PN heterostructure is one of the most fundamental device building blocks with extensive applications. Here we reported the fabrication and optoelectronic properties of GaTe/Sn : CdS nanoflake/nanowire PN heterojunction photodetectors. With high quality contacts between metal electrodes and Sn : CdS or GaTe, the electrical measurement of GaTe/Sn : CdS hybrid heterojunction under dark condition demonstrates an excellent diode characteristic with well-defined current rectification behavior. The photocurrent increases drastically under LED white light as well as red, green, UV illumination. The on-off ratio of current is about 100 for forward bias and 3000 for reverse bias, which clearly indicates the ultrahigh sensitivity of the heterostructure photodetector to white light. The responsivity and optical gain are determined to be 607 A W-1 and (1.06-2.16) × 105%, which is higher than previous reports of single GaTe or CdS nanostructures. Combination the Ids-Vds curves under different illumination power with energy band diagrams, we assign that both the light modulation effect under forward and reverse bias and the surface molecular oxygen adsorption/desorption mechanism are dominant to the electrical transport behavior of GaTe/Sn : CdS heterojunction. This heterostructure photodetector also shows good stability and fast response speed. Both the high photosensibility and fast response time described in the present study suggest strongly that the GaTe/Sn : CdS hybrid heterostructure is a promising candidate for photodetection, optical sensing and switching devices.

Characterization of gallium arsenide X-ray mesa p-i-n photodiodes at room temperature

NASA Astrophysics Data System (ADS)

Lioliou, G.; Meng, X.; Ng, J. S.; Barnett, A. M.

2016-03-01

Two GaAs mesa p+-i-n+ photodiodes intended for photon counting X-ray spectroscopy, having an i layer thickness of 7 μm and diameter of 200 μm, have been characterized electrically, for their responsivity at the wavelength range 580 nm to 980 nm and one of them for its performance at detection of soft X-rays, at room temperature. Dark current and capacitance measurements as a function of applied forward and reverse bias are presented. The results show low leakage current densities, in the range of nA/cm2 at the maximum internal electric field (22 kV/cm). The unintentional doping concentration of the i layer, calculated from capacitance measurements, was found to be <1014 cm-3. Photocurrent measurements were performed under visible and near infrared light illumination for both diodes. The analysis of these measurements suggests the presence of a non-active (dead) layer (0.16 μm thickness) at the p+ side top contact interface, where the photogenerated carriers do not contribute to the photocurrent, possibly due to recombination. One of the diodes, D1, was also characterized as detector for room temperature photon counting X-ray spectroscopy; the best energy resolution achieved (FWHM) at 5.9 keV was 745 eV. The noise analysis of the system, based on spectra obtained at different shaping times and applied reverse biases, showed that the dominant source of noise is the dielectric noise. It was also calculated that there was at least (165±24) eV charge trapping noise at 0 V.

New LUX result constrains exotic quark mediators with the vector dark matter

NASA Astrophysics Data System (ADS)

Chen, Chuan-Ren; Li, Ming-Jie

2016-12-01

The scenario of the compressed mass spectrum between heavy quark and dark matter is a challenge for LHC searches. However, the elastic scattering cross-section between dark matter and nuclei in dark matter direct detection experiments can be enhanced with nearly degenerate masses between heavy quarks and dark matter. In this paper, we illustrate such scenario with a vector dark matter, using the latest result from LUX 2016. The mass constraints on heavy quarks can be more stringent than current limits from LHC, unless the coupling strength is very small. However, the compress mass spectrum with allowed tiny coupling strength makes the decay lifetime of heavy quarks longer than the timescale of QCD hadronization.

Rapid dark-blood carotid vessel-wall imaging with random bipolar gradients in a radial SSFP acquisition.

PubMed

Lin, Hung-Yu; Flask, Chris A; Dale, Brian M; Duerk, Jeffrey L

2007-06-01

To investigate and evaluate a new rapid dark-blood vessel-wall imaging method using random bipolar gradients with a radial steady-state free precession (SSFP) acquisition in carotid applications. The carotid artery bifurcations of four asymptomatic volunteers (28-37 years old, mean age = 31 years) were included in this study. Dark-blood contrast was achieved through the use of random bipolar gradients applied prior to the signal acquisition of each radial projection in a balanced SSFP acquisition. The resulting phase variation for moving spins established significant destructive interference in the low-frequency region of k-space. This phase variation resulted in a net nulling of the signal from flowing spins, while the bipolar gradients had a minimal effect on the static spins. The net effect was that the regular SSFP signal amplitude (SA) in stationary tissues was preserved while dark-blood contrast was achieved for moving spins. In this implementation, application of the random bipolar gradient pulses along all three spatial directions nulled the signal from both in-plane and through-plane flow in phantom and in vivo studies. In vivo imaging trials confirmed that dark-blood contrast can be achieved with the radial random bipolar SSFP method, thereby substantially reversing the vessel-to-lumen contrast-to-noise ratio (CNR) of a conventional rectilinear SSFP "bright-blood" acquisition from bright blood to dark blood with only a modest increase in TR (approximately 4 msec) to accommodate the additional bipolar gradients. Overall, this sequence offers a simple and effective dark-blood contrast mechanism for high-SNR SSFP acquisitions in vessel wall imaging within a short acquisition time.

High Detectivity Graphene-Silicon Heterojunction Photodetector.

PubMed

Li, Xinming; Zhu, Miao; Du, Mingde; Lv, Zheng; Zhang, Li; Li, Yuanchang; Yang, Yao; Yang, Tingting; Li, Xiao; Wang, Kunlin; Zhu, Hongwei; Fang, Ying

2016-02-03

A graphene/n-type silicon (n-Si) heterojunction has been demonstrated to exhibit strong rectifying behavior and high photoresponsivity, which can be utilized for the development of high-performance photodetectors. However, graphene/n-Si heterojunction photodetectors reported previously suffer from relatively low specific detectivity due to large dark current. Here, by introducing a thin interfacial oxide layer, the dark current of graphene/n-Si heterojunction has been reduced by two orders of magnitude at zero bias. At room temperature, the graphene/n-Si photodetector with interfacial oxide exhibits a specific detectivity up to 5.77 × 10(13) cm Hz(1/2) W(-1) at the peak wavelength of 890 nm in vacuum, which is highest reported detectivity at room temperature for planar graphene/Si heterojunction photodetectors. In addition, the improved graphene/n-Si heterojunction photodetectors possess high responsivity of 0.73 A W(-1) and high photo-to-dark current ratio of ≈10(7) . The current noise spectral density of the graphene/n-Si photodetector has been characterized under ambient and vacuum conditions, which shows that the dark current can be further suppressed in vacuum. These results demonstrate that graphene/Si heterojunction with interfacial oxide is promising for the development of high detectivity photodetectors. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Simultaneous wood and metal particle detection on dark-field radiography.

PubMed

Braig, Eva-Maria; Birnbacher, Lorenz; Schaff, Florian; Gromann, Lukas; Fingerle, Alexander; Herzen, Julia; Rummeny, Ernst; Noël, Peter; Pfeiffer, Franz; Muenzel, Daniela

2018-01-01

Currently, the detection of retained wood is a frequent but challenging task in emergency care. The purpose of this study is to demonstrate improved foreign-body detection with the novel approach of preclinical X-ray dark-field radiography. At a preclinical dark-field x-ray radiography, setup resolution and sensitivity for simultaneous detection of wooden and metallic particles have been evaluated in a phantom study. A clinical setting has been simulated with a formalin fixated human hand where different typical foreign-body materials have been inserted. Signal-to-noise ratios (SNR) have been determined for all test objects. On the phantom, the SNR value for wood in the dark-field channel was strongly improved by a factor 6 compared to conventional radiography and even compared to the SNR of an aluminium structure of the same size in conventional radiography. Splinters of wood < 300 μm in diameter were clearly detected on the dark-field radiography. Dark-field radiography of the formalin-fixated human hand showed a clear signal for wooden particles that could not be identified on conventional radiography. x-ray dark-field radiography enables the simultaneous detection of wooden and metallic particles in the extremities. It has the potential to improve and simplify the current state-of-the-art foreign-body detection.

Red Shoe-Blue Shoe: An Acid-Base Demonstration with a Fashionable Twist.

ERIC Educational Resources Information Center

Breyer, Arthur C.; Uzelmeier, Calvin E.

1998-01-01

Illustrates that acid-base indicators come in many forms and the reversible effects that acids and bases have on the colors of such indicators. An object is dyed in an indicator, which causes the object to turn dark blue at pH less than 3.0 to 5.0. Suggests using dyeable fabric shoes and other cotton articles. (PVD)

DarkSide search for dark matter

NASA Astrophysics Data System (ADS)

Alexander, T.; Alton, D.; Arisaka, K.; Back, H. O.; Beltrame, P.; Benziger, J.; Bonfini, G.; Brigatti, A.; Brodsky, J.; Bussino, S.; Cadonati, L.; Calaprice, F.; Candela, A.; Cao, H.; Cavalcante, P.; Chepurnov, A.; Chidzik, S.; Cocco, A. G.; Condon, C.; D'Angelo, D.; Davini, S.; De Vincenzi, M.; De Haas, E.; Derbin, A.; Di Pietro, G.; Dratchnev, I.; Durben, D.; Empl, A.; Etenko, A.; Fan, A.; Fiorillo, G.; Franco, D.; Fomenko, K.; Forster, G.; Gabriele, F.; Galbiati, C.; Gazzana, S.; Ghiano, C.; Goretti, A.; Grandi, L.; Gromov, M.; Guan, M.; Guo, C.; Guray, G.; Hungerford, E. V.; Ianni, Al; Ianni, An; Joliet, C.; Kayunov, A.; Keeter, K.; Kendziora, C.; Kidner, S.; Klemmer, R.; Kobychev, V.; Koh, G.; Komor, M.; Korablev, D.; Korga, G.; Li, P.; Loer, B.; Lombardi, P.; Love, C.; Ludhova, L.; Luitz, S.; Lukyanchenko, L.; Lund, A.; Lung, K.; Ma, Y.; Machulin, I.; Mari, S.; Maricic, J.; Martoff, C. J.; Meregaglia, A.; Meroni, E.; Meyers, P.; Mohayai, T.; Montanari, D.; Montuschi, M.; Monzani, M. E.; Mosteiro, P.; Mount, B.; Muratova, V.; Nelson, A.; Nemtzow, A.; Nurakhov, N.; Orsini, M.; Ortica, F.; Pallavicini, M.; Pantic, E.; Parmeggiano, S.; Parsells, R.; Pelliccia, N.; Perasso, L.; Perasso, S.; Perfetto, F.; Pinsky, L.; Pocar, A.; Pordes, S.; Randle, K.; Ranucci, G.; Razeto, A.; Romani, A.; Rossi, B.; Rossi, N.; Rountree, S. D.; Saggese, P.; Saldanha, R.; Salvo, C.; Sands, W.; Seigar, M.; Semenov, D.; Shields, E.; Skorokhvatov, M.; Smirnov, O.; Sotnikov, A.; Sukhotin, S.; Suvarov, Y.; Tartaglia, R.; Tatarowicz, J.; Testera, G.; Thompson, J.; Tonazzo, A.; Unzhakov, E.; Vogelaar, R. B.; Wang, H.; Westerdale, S.; Wojcik, M.; Wright, A.; Xu, J.; Yang, C.; Zavatarelli, S.; Zehfus, M.; Zhong, W.; Zuzel, G.

2013-11-01

The DarkSide staged program utilizes a two-phase time projection chamber (TPC) with liquid argon as the target material for the scattering of dark matter particles. Efficient background reduction is achieved using low radioactivity underground argon as well as several experimental handles such as pulse shape, ratio of ionization over scintillation signal, 3D event reconstruction, and active neutron and muon vetos. The DarkSide-10 prototype detector has proven high scintillation light yield, which is a particularly important parameter as it sets the energy threshold for the pulse shape discrimination technique. The DarkSide-50 detector system, currently in commissioning phase at the Gran Sasso Underground Laboratory, will reach a sensitivity to dark matter spin-independent scattering cross section of 10-45 cm2 within 3 years of operation.

Mechanisms of the passage of dark currents through Cd(Zn)Te semi-insulating crystals

NASA Astrophysics Data System (ADS)

Sklyarchuk, V.; Fochuk, P.; Rarenko, I.; Zakharuk, Z.; Sklyarchuk, O.; Nykoniuk, Ye.; Rybka, A.; Kutny, V.; Bolotnikov, A. E.; James, R. B.

2014-09-01

We investigated the passage of dark currents through semi-insulating crystals of Cd(Zn)Te with weak n-type conductivity that are used widely as detectors of ionizing radiation. The crystals were grown from a tellurium solution melt at 800 оС by the zone-melting method, in which a polycrystalline rod in a quartz ampoule was moved through a zone heater at a rate of 2 mm per day. The synthesis of the rod was carried out at ~1150 оС. We determined the important electro-physical parameters of this semiconductor, using techniques based on a parallel study of the temperature dependence of current-voltage characteristics in both the ohmic and the space-charge-limited current regions. We established in these crystals the relationship between the energy levels and the concentrations of deep-level impurity states, responsible for dark conductivity and their usefulness as detectors.

Short-wavelength infrared imaging using low dark current InGaAs detector arrays and vertical-cavity surface-emitting laser illuminators

NASA Astrophysics Data System (ADS)

Macdougal, Michael; Geske, Jon; Wang, Chad; Follman, David

2011-06-01

We describe the factors that go into the component choices for a short wavelength IR (SWIR) imager, which include the SWIR sensor, the lens, and the illuminator. We have shown the factors for reducing dark current, and shown that we can achieve well below 1.5 nA/cm2 for 15 μm devices at 7 °C. In addition, we have mated our InGaAs detector arrays to 640×512 readout integrated integrated circuits to make focal plane arrays (FPAs). The resulting FPAs are capable of imaging photon fluxes with wavelengths between 1 and 1.6 μm at low light levels. The dark current associated with these FPAs is extremely low, exhibiting a mean dark current density of 0.26 nA/cm2 at 0 °C. Noise due to the readout can be reduced from 95 to 57 electrons by using off-chip correlated double sampling. In addition, Aerius has developed laser arrays that provide flat illumination in scenes that are normally light-starved. The illuminators have 40% wall-plug efficiency and provide low-speckle illumination, and provide artifact-free imagery versus conventional laser illuminators.

Review on Dark Photon

NASA Astrophysics Data System (ADS)

Curciarello, Francesca

2016-04-01

e+e- collider experiments at the intensity frontier are naturally suited to probe the existence of a force beyond the Standard Model between WIMPs, the most viable dark matter candidates. The mediator of this new force, known as dark photon, should be a new vector gauge boson very weakly coupled to the Standard Model photon. No significant signal has been observed so far. I will report on current limits set on the coupling factor ɛ2 between the photon and the dark photon by e+e- collider experiments.

Dark matter in the coming decade: Complementary paths to discovery and beyond

DOE PAGES

Bauer, Daniel; Buckley, James; Cahill-Rowley, Matthew; ...

2015-05-27

Here, we summarize the many dark matter searches currently being pursued through four complementary approaches: direct detection, indirect detection, collider experiments, and astrophysical probes. The essential features of broad classes of experiments are described, each with their own strengths and weaknesses. Furthermore, we discuss the complementarity of the different dark matter searches qualitatively and illustrated quantitatively in two simple theoretical frameworks. Our primary conclusion is that the diversity of possible dark matter candidates requires a balanced program drawing from all four approaches.

Asymmetric capture of Dirac dark matter by the Sun

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

Blennow, Mattias; Clementz, Stefan

2015-08-18

Current problems with the solar model may be alleviated if a significant amount of dark matter from the galactic halo is captured in the Sun. We discuss the capture process in the case where the dark matter is a Dirac fermion and the background halo consists of equal amounts of dark matter and anti-dark matter. By considering the case where dark matter and anti-dark matter have different cross sections on solar nuclei as well as the case where the capture process is considered to be a Poisson process, we find that a significant asymmetry between the captured dark particles andmore » anti-particles is possible even for an annihilation cross section in the range expected for thermal relic dark matter. Since the captured number of particles are competitive with asymmetric dark matter models in a large range of parameter space, one may expect solar physics to be altered by the capture of Dirac dark matter. It is thus possible that solutions to the solar composition problem may be searched for in these type of models.« less

The combination of gas-phase fluorophore technology and automation to enable high-throughput analysis of plant respiration.

PubMed

Scafaro, Andrew P; Negrini, A Clarissa A; O'Leary, Brendan; Rashid, F Azzahra Ahmad; Hayes, Lucy; Fan, Yuzhen; Zhang, You; Chochois, Vincent; Badger, Murray R; Millar, A Harvey; Atkin, Owen K

2017-01-01

Mitochondrial respiration in the dark ( R dark ) is a critical plant physiological process, and hence a reliable, efficient and high-throughput method of measuring variation in rates of R dark is essential for agronomic and ecological studies. However, currently methods used to measure R dark in plant tissues are typically low throughput. We assessed a high-throughput automated fluorophore system of detecting multiple O 2 consumption rates. The fluorophore technique was compared with O 2 -electrodes, infrared gas analysers (IRGA), and membrane inlet mass spectrometry, to determine accuracy and speed of detecting respiratory fluxes. The high-throughput fluorophore system provided stable measurements of R dark in detached leaf and root tissues over many hours. High-throughput potential was evident in that the fluorophore system was 10 to 26-fold faster per sample measurement than other conventional methods. The versatility of the technique was evident in its enabling: (1) rapid screening of R dark in 138 genotypes of wheat; and, (2) quantification of rarely-assessed whole-plant R dark through dissection and simultaneous measurements of above- and below-ground organs. Variation in absolute R dark was observed between techniques, likely due to variation in sample conditions (i.e. liquid vs. gas-phase, open vs. closed systems), indicating that comparisons between studies using different measuring apparatus may not be feasible. However, the high-throughput protocol we present provided similar values of R dark to the most commonly used IRGA instrument currently employed by plant scientists. Together with the greater than tenfold increase in sample processing speed, we conclude that the high-throughput protocol enables reliable, stable and reproducible measurements of R dark on multiple samples simultaneously, irrespective of plant or tissue type.

Direct detection of sub-GeV dark matter with semiconductor targets

DOE PAGES

Essig, Rouven; Fernández-Serra, Marivi; Mardon, Jeremy; ...

2016-05-09

Dark matter in the sub-GeV mass range is a theoretically motivated but largely unexplored paradigm. Such light masses are out of reach for conventional nuclear recoil direct detection experiments, but may be detected through the small ionization signals caused by dark matter-electron scattering. Semiconductors are well-studied and are particularly promising target materials because their O(1 eV) band gaps allow for ionization signals from dark matter particles as light as a few hundred keV. Current direct detection technologies are being adapted for dark matter-electron scattering. In this paper, we provide the theoretical calculations for dark matter-electron scattering rate in semiconductors, overcomingmore » several complications that stem from the many-body nature of the problem. We use density functional theory to numerically calculate the rates for dark matter-electron scattering in silicon and germanium, and estimate the sensitivity for upcoming experiments such as DAMIC and SuperCDMS. We find that the reach for these upcoming experiments has the potential to be orders of magnitude beyond current direct detection constraints and that sub-GeV dark matter has a sizable modulation signal. We also give the first direct detection limits on sub-GeV dark matter from its scattering off electrons in a semiconductor target (silicon) based on published results from DAMIC. We make available publicly our code, QEdark, with which we calculate our results. Our results can be used by experimental collaborations to calculate their own sensitivities based on their specific setup. In conclusion, the searches we propose will probe vast new regions of unexplored dark matter model and parameter space.« less

Toward (finally!) ruling out Z and Higgs mediated dark matter models

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

Escudero, Miguel; Berlin, Asher; Hooper, Dan

2016-12-01

In recent years, direct detection, indirect detection, and collider experiments have placed increasingly stringent constraints on particle dark matter, exploring much of the parameter space associated with the WIMP paradigm. In this paper, we focus on the subset of WIMP models in which the dark matter annihilates in the early universe through couplings to either the Standard Model Z or the Standard Model Higgs boson. Considering fermionic, scalar, and vector dark matter candidates within a model-independent context, we find that the overwhelming majority of these dark matter candidates are already ruled out by existing experiments. In the case of Zmore » mediated dark matter, the only scenarios that are not currently excluded are those in which the dark matter is a fermion with an axial coupling and with a mass either within a few GeV of the Z resonance ( m {sub DM} ≅ m {sub Z} /2) or greater than 200 GeV, or with a vector coupling and with m {sub DM} > 6 TeV . Several Higgs mediated scenarios are currently viable if the mass of the dark matter is near the Higgs pole ( m {sub DM} ≅ m {sub H} /2). Otherwise, the only scenarios that are not excluded are those in which the dark matter is a scalar (vector) heavier than 400 GeV (1160 GeV) with a Higgs portal coupling, or a fermion with a pseudoscalar (CP violating) coupling to the Standard Model Higgs boson. With the exception of dark matter with a purely pseudoscalar coupling to the Higgs, it is anticipated that planned direct detection experiments will probe nearly the entire range of models considered in this study.« less

Toward (finally!) ruling out Z and Higgs mediated dark matter models

DOE PAGES

Escudero, Miguel; Fermi National Accelerator Lab.; Berlin, Asher; ...

2016-12-15

In recent years, direct detection, indirect detection, and collider experiments have placed increasingly stringent constraints on particle dark matter, exploring much of the parameter space associated with the WIMP paradigm. In this paper, we focus on the subset of WIMP models in which the dark matter annihilates in the early universe through couplings to either the Standard Model Z or the Standard Model Higgs boson. Considering fermionic, scalar, and vector dark matter candidates within a model-independent context, we find that the overwhelming majority of these dark matter candidates are already ruled out by existing experiments. In the case of Zmore » mediated dark matter, the only scenarios that are not currently excluded are those in which the dark matter is a fermion with an axial coupling and with a mass either within a few GeV of the Z resonance (m DM ≃ m Z/2) or greater than 200 GeV, or with a vector coupling and with m DM > 6 TeV . Several Higgs mediated scenarios are currently viable if the mass of the dark matter is near the Higgs pole (m DM ≃ m H/2). Otherwise, the only scenarios that are not excluded are those in which the dark matter is a scalar (vector) heavier than 400 GeV (1160 GeV) with a Higgs portal coupling, or a fermion with a pseudoscalar (CP violating) coupling to the Standard Model Higgs boson. Furthermore, with the exception of dark matter with a purely pseudoscalar coupling to the Higgs, it is anticipated that planned direct detection experiments will probe nearly the entire range of models considered in this study.« less

Toward (finally!) ruling out Z and Higgs mediated dark matter models

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

Escudero, Miguel; Fermi National Accelerator Lab.; Berlin, Asher

In recent years, direct detection, indirect detection, and collider experiments have placed increasingly stringent constraints on particle dark matter, exploring much of the parameter space associated with the WIMP paradigm. In this paper, we focus on the subset of WIMP models in which the dark matter annihilates in the early universe through couplings to either the Standard Model Z or the Standard Model Higgs boson. Considering fermionic, scalar, and vector dark matter candidates within a model-independent context, we find that the overwhelming majority of these dark matter candidates are already ruled out by existing experiments. In the case of Zmore » mediated dark matter, the only scenarios that are not currently excluded are those in which the dark matter is a fermion with an axial coupling and with a mass either within a few GeV of the Z resonance (m DM ≃ m Z/2) or greater than 200 GeV, or with a vector coupling and with m DM > 6 TeV . Several Higgs mediated scenarios are currently viable if the mass of the dark matter is near the Higgs pole (m DM ≃ m H/2). Otherwise, the only scenarios that are not excluded are those in which the dark matter is a scalar (vector) heavier than 400 GeV (1160 GeV) with a Higgs portal coupling, or a fermion with a pseudoscalar (CP violating) coupling to the Standard Model Higgs boson. Furthermore, with the exception of dark matter with a purely pseudoscalar coupling to the Higgs, it is anticipated that planned direct detection experiments will probe nearly the entire range of models considered in this study.« less

Analytic study of the effect of dark energy-dark matter interaction on the growth of structures

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

Marcondes, Rafael J.F.; Landim, Ricardo C.G.; Costa, André A.

2016-12-01

Large-scale structure has been shown as a promising cosmic probe for distinguishing and constraining dark energy models. Using the growth index parametrization, we obtain an analytic formula for the growth rate of structures in a coupled dark energy model in which the exchange of energy-momentum is proportional to the dark energy density. We find that the evolution of f σ{sub 8} can be determined analytically once we know the coupling, the dark energy equation of state, the present value of the dark energy density parameter and the current mean amplitude of dark matter fluctuations. After correcting the growth function formore » the correspondence with the velocity field through the continuity equation in the interacting model, we use our analytic result to compare the model's predictions with large-scale structure observations.« less

Generation-recombination and trap-assisted tunneling in long wavelength infrared minority electron unipolar photodetectors based on InAs/GaSb superlattice

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

Callewaert, F.; Hoang, A. M.; Razeghi, M., E-mail: razeghi@eecs.northwestern.edu

2014-02-03

A long wavelength infrared minority electron unipolar photodetector based on InAs/GaSb type-II superlattices is demonstrated. At 77 K, a dark current of 3 × 10{sup −5} A/cm{sup 2} and a differential resistance-area of 3700 Ω.cm{sup 2} are achieved at the turn-on bias, with a 50%-cutoff of 10.0 μm and a specific detectivity of 6.2 × 10{sup 11} Jones. The dark current is fitted as a function of bias and temperature using a model combining generation-recombination and trap-assisted tunneling. Good agreement was observed between the theory and the experimental dark current.

Dark matter universe.

PubMed

Bahcall, Neta A

2015-10-06

Most of the mass in the universe is in the form of dark matter--a new type of nonbaryonic particle not yet detected in the laboratory or in other detection experiments. The evidence for the existence of dark matter through its gravitational impact is clear in astronomical observations--from the early observations of the large motions of galaxies in clusters and the motions of stars and gas in galaxies, to observations of the large-scale structure in the universe, gravitational lensing, and the cosmic microwave background. The extensive data consistently show the dominance of dark matter and quantify its amount and distribution, assuming general relativity is valid. The data inform us that the dark matter is nonbaryonic, is "cold" (i.e., moves nonrelativistically in the early universe), and interacts only weakly with matter other than by gravity. The current Lambda cold dark matter cosmology--a simple (but strange) flat cold dark matter model dominated by a cosmological constant Lambda, with only six basic parameters (including the density of matter and of baryons, the initial mass fluctuations amplitude and its scale dependence, and the age of the universe and of the first stars)--fits remarkably well all the accumulated data. However, what is the dark matter? This is one of the most fundamental open questions in cosmology and particle physics. Its existence requires an extension of our current understanding of particle physics or otherwise point to a modification of gravity on cosmological scales. The exploration and ultimate detection of dark matter are led by experiments for direct and indirect detection of this yet mysterious particle.

Dark matter universe

PubMed Central

Bahcall, Neta A.

2015-01-01

Most of the mass in the universe is in the form of dark matter—a new type of nonbaryonic particle not yet detected in the laboratory or in other detection experiments. The evidence for the existence of dark matter through its gravitational impact is clear in astronomical observations—from the early observations of the large motions of galaxies in clusters and the motions of stars and gas in galaxies, to observations of the large-scale structure in the universe, gravitational lensing, and the cosmic microwave background. The extensive data consistently show the dominance of dark matter and quantify its amount and distribution, assuming general relativity is valid. The data inform us that the dark matter is nonbaryonic, is “cold” (i.e., moves nonrelativistically in the early universe), and interacts only weakly with matter other than by gravity. The current Lambda cold dark matter cosmology—a simple (but strange) flat cold dark matter model dominated by a cosmological constant Lambda, with only six basic parameters (including the density of matter and of baryons, the initial mass fluctuations amplitude and its scale dependence, and the age of the universe and of the first stars)—fits remarkably well all the accumulated data. However, what is the dark matter? This is one of the most fundamental open questions in cosmology and particle physics. Its existence requires an extension of our current understanding of particle physics or otherwise point to a modification of gravity on cosmological scales. The exploration and ultimate detection of dark matter are led by experiments for direct and indirect detection of this yet mysterious particle. PMID:26417091

75 FR 10740 - New Car Assessment Program (NCAP); Safety Labeling

Federal Register 2010, 2011, 2012, 2013, 2014

2010-03-09

... separated from each other by a dark line that is a minimum of 3 points in width. Also as is currently required, the entire safety rating label would be required to be surrounded by a solid dark line that is a... dark background. \\4\\ The full study report is available at http://www.regulations.gov in Docket No...

NASA and Dark Energy

NASA Astrophysics Data System (ADS)

Rhodes, Jason

2014-03-01

Dark energy, the name given to the cause of the accelerating expansion of the Universe, is one of the most profound mysteries in modern science. Current cosmological models hold that dark energy is currently the dominant component of the Universe, but the exact nature of dark energy remains poorly understood. There are ambitious ground-based surveys underway that seek to understand dark energy and NASA is participating in the development of significantly more ambitious space-based surveys planned for the next decade. NASA has provided mission enabling technology to the European Space Agency's (ESA) Euclid mission in exchange for US scientists to participate in the Euclid mission. NASA is also developing the Wide Field Infrared Survey Telescope-Astrophysics Focused Telescope Asset (WFIRST-AFTA) mission for possible launch in ~2023. WFIRST was the highest ranked space mission in the Astro2010 Decadal Survey and the AFTA incarnation of the WFIRST design uses a 2.4 m space telescope to go beyond what the Decadal Survey envisioned for WFIRST. Understanding dark energy is one of the primary science goals of WFIRST-AFTA. I'll discuss the status of Euclid and WFIRST and comment on the complementarity of the two missions.

Redshift drift constraints on holographic dark energy

NASA Astrophysics Data System (ADS)

He, Dong-Ze; Zhang, Jing-Fei; Zhang, Xin

2017-03-01

The Sandage-Loeb (SL) test is a promising method for probing dark energy because it measures the redshift drift in the spectra of Lyman- α forest of distant quasars, covering the "redshift desert" of 2 ≲ z ≲ 5, which is not covered by existing cosmological observations. Therefore, it could provide an important supplement to current cosmological observations. In this paper, we explore the impact of SL test on the precision of cosmological constraints for two typical holographic dark energy models, i.e., the original holographic dark energy (HDE) model and the Ricci holographic dark energy (RDE) model. To avoid data inconsistency, we use the best-fit models based on current combined observational data as the fiducial models to simulate 30 mock SL test data. The results show that SL test can effectively break the existing strong degeneracy between the present-day matter density Ωm0 and the Hubble constant H 0 in other cosmological observations. For the considered two typical dark energy models, not only can a 30-year observation of SL test improve the constraint precision of Ωm0 and h dramatically, but can also enhance the constraint precision of the model parameters c and α significantly.

Measuring Dark Energy with CHIME

NASA Astrophysics Data System (ADS)

Newburgh, Laura; Chime Collaboration

2015-04-01

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a new radio transit interferometer currently being built at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC, Canada. We will use the 21 cm emission line of neutral hydrogen to map baryon acoustic oscillations between 400-800 MHz across 3/4 of the sky. These measurements will yield sensitive constraints on the dark energy equation of state between redshifts 0.8 - 2.5, a fascinating but poorly probed era corresponding to when dark energy began to impact the expansion history of the Universe. I will describe theCHIME instrument, the analysis challenges, the calibration requirements, and current status.

Make dark matter charged again

NASA Astrophysics Data System (ADS)

Agrawal, Prateek; Cyr-Racine, Francis-Yan; Randall, Lisa; Scholtz, Jakub

2017-05-01

We revisit constraints on dark matter that is charged under a U(1) gauge group in the dark sector, decoupled from Standard Model forces. We find that the strongest constraints in the literature are subject to a number of mitigating factors. For instance, the naive dark matter thermalization timescale in halos is corrected by saturation effects that slow down isotropization for modest ellipticities. The weakened bounds uncover interesting parameter space, making models with weak-scale charged dark matter viable, even with electromagnetic strength interaction. This also leads to the intriguing possibility that dark matter self-interactions within small dwarf galaxies are extremely large, a relatively unexplored regime in current simulations. Such strong interactions suppress heat transfer over scales larger than the dark matter mean free path, inducing a dynamical cutoff length scale above which the system appears to have only feeble interactions. These effects must be taken into account to assess the viability of darkly-charged dark matter. Future analyses and measurements should probe a promising region of parameter space for this model.

Dark matter haloes: a multistream view

NASA Astrophysics Data System (ADS)

Ramachandra, Nesar S.; Shandarin, Sergei F.

2017-09-01

Mysterious dark matter constitutes about 85 per cent of all masses in the Universe. Clustering of dark matter plays a dominant role in the formation of all observed structures on scales from a fraction to a few hundreds of Mega-parsecs. Galaxies play a role of lights illuminating these structures so they can be observed. The observations in the last several decades have unveiled opulent geometry of these structures currently known as the cosmic web. Haloes are the highest concentrations of dark matter and host luminous galaxies. Currently the most accurate modelling of dark matter haloes is achieved in cosmological N-body simulations. Identifying the haloes from the distribution of particles in N-body simulations is one of the problems attracting both considerable interest and efforts. We propose a novel framework for detecting potential dark matter haloes using the field unique for dark matter-multistream field. The multistream field emerges at the non-linear stage of the growth of perturbations because the dark matter is collisionless. Counting the number of velocity streams in gravitational collapses supplements our knowledge of spatial clustering. We assume that the virialized haloes have convex boundaries. Closed and convex regions of the multistream field are hence isolated by imposing a positivity condition on all three eigenvalues of the Hessian estimated on the smoothed multistream field. In a single-scale analysis of high multistream field resolution and low softening length, the halo substructures with local multistream maxima are isolated as individual halo sites.

Constraining the interaction between dark sectors with future HI intensity mapping observations

NASA Astrophysics Data System (ADS)

Xu, Xiaodong; Ma, Yin-Zhe; Weltman, Amanda

2018-04-01

We study a model of interacting dark matter and dark energy, in which the two components are coupled. We calculate the predictions for the 21-cm intensity mapping power spectra, and forecast the detectability with future single-dish intensity mapping surveys (BINGO, FAST and SKA-I). Since dark energy is turned on at z ˜1 , which falls into the sensitivity range of these radio surveys, the HI intensity mapping technique is an efficient tool to constrain the interaction. By comparing with current constraints on dark sector interactions, we find that future radio surveys will produce tight and reliable constraints on the coupling parameters.

Characterization and Analysis of Integrated Silicon Photonic Detectors for High-Speed Communications

DTIC Science & Technology

2015-03-26

17 2.2.1.1 Depletion Region and Dark Current . . . . . . . . . . . . . . . . . 18 2.2.1.2 Photocurrent, Quantum ...facilitate a greater consciousness for the RF spectrum from MHz to ∼1 THz demonstrating an advantage over any purely electronic approach. Electronic... Quantum Efficiency and Responsivity. Extrapolating the established model from the dark current section provides the photodiode’s response when light

The dark side of cosmology: dark matter and dark energy.

PubMed

Spergel, David N

2015-03-06

A simple model with only six parameters (the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation) fits all of our cosmological data . Although simple, this standard model is strange. The model implies that most of the matter in our Galaxy is in the form of "dark matter," a new type of particle not yet detected in the laboratory, and most of the energy in the universe is in the form of "dark energy," energy associated with empty space. Both dark matter and dark energy require extensions to our current understanding of particle physics or point toward a breakdown of general relativity on cosmological scales. Copyright © 2015, American Association for the Advancement of Science.

Novel dark matter phenomenology at colliders

NASA Astrophysics Data System (ADS)

Wardlow, Kyle Patrick

While a suitable candidate particle for dark matter (DM) has yet to be discovered, it is possible one will be found by experiments currently investigating physics on the weak scale. If discovered on that energy scale, the dark matter will likely be producible in significant quantities at colliders like the LHC, allowing the properties of and underlying physical model characterizing the dark matter to be precisely determined. I assume that the dark matter will be produced as one of the decay products of a new massive resonance related to physics beyond the Standard Model, and using the energy distributions of the associated visible decay products, develop techniques for determining the symmetry protecting these potential dark matter candidates from decaying into lighter Standard Model (SM) particles and to simultaneously measure the masses of both the dark matter candidate and the particle from which it decays.

Reverse Current in Solar Flares

NASA Technical Reports Server (NTRS)

Knight, J. W., III

1978-01-01

An idealized steady state model of a stream of energetic electrons neutralized by a reverse current in the pre-flare solar plasma was developed. These calculations indicate that, in some cases, a significant fraction of the beam energy may be dissipated by the reverse current. Joule heating by the reverse current is a more effective mechanism for heating the plasma than collisional losses from the energetic electrons because the Ohmic losses are caused by thermal electrons in the reverse current which have much shorter mean free paths than the energetic electrons. The heating due to reverse currents is calculated for two injected energetic electron fluxes. For the smaller injected flux, the temperature of the coronal plasma is raised by about a factor of two. The larger flux causes the reverse current drift velocity to exceed the critical velocity for the onset of ion cyclotron turbulence, producing anomalous resistivity and an order of magnitude increase in the temperature. The heating is so rapid that the lack of ionization equilibrium may produce a soft X-ray and EUV pulse from the corona.

Suppression of dark current radiation in step-and-shoot intensity modulated radiation therapy by the initial pulse-forming network.

PubMed

Cheng, Chee-Wai; Das, Indra J; Ndlovu, Alois M

2002-09-01

The effect of the initial pulse forming network (IPFN) on the suppression of dark current is investigated for a Siemens Primus accelerator. The dark current produces a spurious radiation, which is referred to as dark current radiation (DCR) in this study. In the step-and-shoot delivery of an intensity modulated radiation therapy (IMRT), the DCR could be of some concern for whole body dose along with leakage radiation through collimator jaws or multileaf collimator. By adjusting the IPFN-to-PFN ratio to >0.8, the DCR can be measured with an ion chamber during the "PAUSE" state of the accelerator in the IMRT mode. For 15 MV x rays, the magnitude of the DCR is approximately equal to 0.7% of the dose at dmax for a 10 x 10 cm2 field. The DCR has a similar central axis depth dose as a 15 MV beam as determined from a water phantom scan. When the IPFN-to-PFN ratio is lowered to <0.8, no DCR is detected. For low energy x rays (6 MV), no DCR is detected regardless of the IPFN-to-PFN ratio. Although the DCR is studied only for the Siemens Primus model accelerator, the same precaution applies to other models of modern accelerators from other vendors. Due to the large number of field segments used in a step-and-shoot IMRT, it is imperative therefore, that dark current evaluation be part of machine commissioning and annual calibration for high-energy photon beams. Should DCR be detected, the medical physicist should work with a service engineer to rectify the problem. In view of DCR and whole body dose, low-energy photon beams are advisable for IMRT.

Cosmic history of chameleonic dark matter in F (R ) gravity

NASA Astrophysics Data System (ADS)

Katsuragawa, Taishi; Matsuzaki, Shinya

2018-03-01

We study the cosmic history of the scalaron in F (R ) gravity with constructing the time evolution of the cosmic environment and discuss the chameleonic dark matter based on the chameleon mechanism in the early and current Universe. We then find that the scalaron can be a dark matter. We also propose an interesting possibility that the F (R ) gravity can address the coincidence problem.

Dark Chocolate Intake Acutely Enhances Neutrophil Count in Peripheral Venous Blood.

PubMed

Montagnana, Martina; Danese, Elisa; Lima-Oliveira, Gabriel; Salvagno, Gian Luca; Lippi, Giuseppe

2017-01-01

Beside the well-established impact on decreasing the risk of cardiovascular diseases (1), recent attention has been paid to the relationship between cocoa-containing foods and the immune system (2), showing that dark chocolate consumption enhances the systemic defense against bacterial (3) and viral (4) infections. Hence, the current study aimed at investigating the acute effect of dark chocolate intake on peripheral blood leukocytes.

Study on the performance of 2.6 μm In0.83Ga0.17As detector with different etch gases

NASA Astrophysics Data System (ADS)

Li, Ping; Tang, Hengjing; Li, Tao; Li, Xue; Shao, Xiumei; Ma, Yingjie; Gong, Haimei

2017-09-01

In order to obtain a low-damage recipe in the ICP processing, ICP-induced damage using Cl2/CH4 etch gases in extended wavelength In0.83Ga0.17As detector materials was studied in this paper. The effect of ICP etching on In0.83Ga0.17As samples was characterized qualitatively by the photoluminescence (PL) technology. The etch damage of In0.83Ga0.17As samples was characterized quantitatively by the Transmission Line Model (TLM), current voltage (IV) measurement, signal and noise testing and the Fourier Transform Infrared Spectroscopy (FTIR) technologies. The results showed that the Cl2/CH4 etching processing could lead better detector performance than that Cl2/N2, such as a larger square resistance, a lower dark current, a lower noise voltage and a higher peak detectivity. The lower PL signal intensity and lower dark current could be attributed to the hydrogen decomposed by the CH4 etch gases in the plasma etching process. These hydrogen particles generated non-radiative recombination centers in inner materials to weaken the PL intensity and passivated dangling bond at the surface to reduce the dark current. The larger square resistance resulted from the lower etch damage. The lower dark current meant that the detectors have less dangling bonds and leakage channels.

Neutrino Oscillations as a Probe of Light Scalar Dark Matter.

PubMed

Berlin, Asher

2016-12-02

We consider a class of models involving interactions between ultralight scalar dark matter and standard model neutrinos. Such couplings modify the neutrino mass splittings and mixing angles to include additional components that vary in time periodically with a frequency and amplitude set by the mass and energy density of the dark matter. Null results from recent searches for anomalous periodicities in the solar neutrino flux strongly constrain the dark matter-neutrino coupling to be orders of magnitude below current and projected limits derived from observations of the cosmic microwave background.

Probing light nonthermal dark matter at the LHC

NASA Astrophysics Data System (ADS)

Dutta, Bhaskar; Gao, Yu; Kamon, Teruki

2014-05-01

This paper investigates the collider phenomenology of a minimal nonthermal dark matter model with a 1-GeV dark matter candidate, which naturally explains baryogenesis. Since the light dark matter is not parity protected, it can be singly produced at the LHC. This leads to large missing energy associated with an energetic jet whose transverse momentum distribution is featured by a Jacobian-like shape. The monojet, dijet, paired dijet, and two jets + missing energy channels are studied. Currently existing data at the Tevatron and LHC offer significant bounds on our model.

Constraints on the holographic dark energy model via type Ia supernovae, baryon acoustic oscillation, and WMAP7

NASA Astrophysics Data System (ADS)

Xu, Lixin

2012-06-01

In this paper, the holographic dark energy model, where the future event horizon is taken as an IR cutoff, is confronted by using currently available cosmic observational data sets which include type Ia supernovae, baryon acoustic oscillation, and cosmic microwave background radiation from full information of WMAP 7-yr data. Via the Markov chain Monte Carlo method, we obtain the values of model parameter c=0.696-0.0737-0.132-0.190+0.0736+0.159+0.264 with 1, 2, 3σ regions. Therefore, one can conclude that at at least 3σ level the future Universe will be dominated by phantom-like dark energy. It is not consistent with positive energy condition, however this condition must be satisfied to derive the holographic bound. It implies that the current cosmic observational data points disfavor the holographic dark energy model.

Maerua angolensis stem bark extract reverses anxiety and related behaviours in zebrafish-Involvement of GABAergic and 5-HT systems.

PubMed

Benneh, Charles Kwaku; Biney, Robert Peter; Mante, Priscilla Kolibea; Tandoh, Augustine; Adongo, Donatus Wewura; Woode, Eric

2017-07-31

Maerua angolensis DC (Capparaceae) has been employed in the management of several central nervous system (CNS) disorders including anxiety. This study evaluated the anxiolytic effects of the petroleum ether/ethyl acetate fraction stem bark extract and its possible mechanism(s) using zebrafish anxiety models. Adult zebrafish, tested in the novel tank and light dark tests, have shown by previous authors to be sensitive to the anxiolytic effects of known anxiolytic drugs. Adult zebrafish were treated with M. angolensis extract, fluoxetine, desipramine, and diazepam followed by testing in the novel tank and light dark tests. We further assessed the effect of the extract on anxiety after inducing an anxiogenic phenotype using the ethanol-withdrawal and chronic unpredictable stress (CUS) tests. The anxiolytic effect was further investigated after pretreatment with flumazenil, granisetron, cyproheptadine, methysergide and pizotifen. M. angolensis extract, similar to fluoxetine and desipramine, demonstrated significant anxiolytic behaviour at doses that did not reduce locomotor activity significantly. Similar anxiolytic effects were recorded in the ethanol withdrawal-induced anxiety test. Furthermore, the anxiogenic effects induced by the CUS paradigm were significantly reversed by treatment M. angolensis extract and fluoxetine. The anxiolytic effects of M. angolensis extract were however reversed after pre-treatment with flumazenil, granisetron, cyproheptadine, methysergide and pizotifen. Taken together, this suggests that the petroleum ether/ ethyl acetate fraction of M. angolensis possesses significant anxiolytic activity, which could partly be accounted for by an interaction with the serotoninergic system and the GABA A receptor. Copyright © 2017 Elsevier Ireland Ltd. All rights reserved.

Sustained Photobiological Hydrogen Gas Production upon Reversible Inactivation of Oxygen Evolution in the Green Alga Chlamydomonas reinhardtii1

PubMed Central

Melis, Anastasios; Zhang, Liping; Forestier, Marc; Ghirardi, Maria L.; Seibert, Michael

2000-01-01

The work describes a novel approach for sustained photobiological production of H2 gas via the reversible hydrogenase pathway in the green alga Chlamydomonas reinhardtii. This single-organism, two-stage H2 production method circumvents the severe O2 sensitivity of the reversible hydrogenase by temporally separating photosynthetic O2 evolution and carbon accumulation (stage 1) from the consumption of cellular metabolites and concomitant H2 production (stage 2). A transition from stage 1 to stage 2 was effected upon S deprivation of the culture, which reversibly inactivated photosystem II (PSII) and O2 evolution. Under these conditions, oxidative respiration by the cells in the light depleted O2 and caused anaerobiosis in the culture, which was necessary and sufficient for the induction of the reversible hydrogenase. Subsequently, sustained cellular H2 gas production was observed in the light but not in the dark. The mechanism of H2 production entailed protein consumption and electron transport from endogenous substrate to the cytochrome b6-f and PSI complexes in the chloroplast thylakoids. Light absorption by PSI was required for H2 evolution, suggesting that photoreduction of ferredoxin is followed by electron donation to the reversible hydrogenase. The latter catalyzes the reduction of protons to molecular H2 in the chloroplast stroma. PMID:10631256

Extra-high short-circuit current for bifacial solar cells in sunny and dark-light conditions.

PubMed

Duan, Jialong; Duan, Yanyan; Zhao, Yuanyuan; He, Benlin; Tang, Qunwei

2017-09-05

We present here a symmetrically structured bifacial solar cell tailored by two fluorescent photoanodes and a platinum/titanium/platinum counter electrode, yielding extra-high short-circuit current densities as high as 28.59 mA cm -2 and 119.9 μA cm -2 in simulated sunlight irradiation (100 mW cm -2 , AM1.5) and dark-light conditions, respectively.

Measured and Simulated Dark J-V Characteristics of a-Si:H Single Junction p-i-n Solar Cells Irradiated with 40 keV Electrons

NASA Technical Reports Server (NTRS)

Lord, Kenneth; Woodyard, James R.

2002-01-01

The effect of 40 keV electron irradiation on a-Si:H p-i-n single-junction solar cells was investigated using measured and simulated dark J-V characteristics. EPRI-AMPS and PC-1D simulators were explored for use in the studies. The EPRI-AMPS simulator was employed and simulator parameters selected to produce agreement with measured J-V characteristics. Three current mechanisms were evident in the measured dark J-V characteristics after electron irradiation, namely, injection, shunting and a term of the form CV(sup m). Using a single discrete defect state level at the center of the band gap, good agreement was achieved between measured and simulated J-V characteristics in the forward-bias voltage region where the dark current density was dominated by injection. The current mechanism of the form CV(sup m) was removed by annealing for two hours at 140 C. Subsequent irradiation restored the CV(sup m) current mechanism and it was removed by a second anneal. Some evidence of the CV(sup m) term is present in device simulations with a higher level of discrete density of states located at the center of the bandgap.

Action spectra of chlorophyll a biosynthesis in cyanobacteria: dark-operative protochlorophyllide oxidoreductase-deficient mutants.

PubMed

Gao, Yang; Xiong, Wei; He, Ming J; Tang, Li; Xiang, Jin Y; Wu, Qing Y

2009-01-01

Both light-dependent and light-independent (dark) protochlorophyllide (Pchlide) reductase account for catalyzing the reduction of Pchlide to chlorophyllide during the biosynthesis of Mg-tetrapyrrole pigments in cyanobacteria. To gain more insight into the interaction between the wavelength of the light and these two chlorophyll synthetic pathways in Synechocystis sp. PCC 6803, the spectral effectiveness of the formation of chlorophyll a was investigated during the regreening process in chlL(-) and chlN(-) mutants, which could not synthesize chlorophyll during growth in the dark. The action spectra showed obvious maxima around 450 nm and 650 nm, similar to those of higher plants except that the intensities of two peaks are reversed. The mRNA levels of chlL and chlN and chlorophyll a content under different wavelengths of light in the wild-type strain were also measured. The RT-PCR analysis revealed that the transcripts of chlL and chlN were up-regulated in red light but simultaneously down-regulated in green light which resulted in corresponding changes of the chlorophyll content. This fact indicates that the regulation of dark-operative protochlorophyllide oxidoreductase (DPOR) in the transcriptional level is essential for cyanobacteria to synthesize appropriate chlorophyll for acclimating in various light colour environments.

Detector Simulation and WIMP Search Analysis for the Cryogenic Dark Matter Search Experiment

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

McCarthy, Kevin

2013-06-01

Astrophysical and cosmological measurements on the scales of galaxies, galaxy clusters, and the universe indicate that 85% of the matter in the universe is composed of dark matter, made up of non-baryonic particles that interact with cross-sections on the weak scale or lower. Hypothetical Weakly Interacting Massive Particles, or WIMPs, represent a potential solution to the dark matter problem, and naturally arise in certain Standard Model extensions. The Cryogenic Dark Matter Search (CDMS) collaboration aims to detect the scattering of WIMP particles from nuclei in terrestrial detectors. Germanium and silicon particle detectors are deployed in the Soudan Underground Laboratory inmore » Minnesota. These detectors are instrumented with phonon and ionization sensors, which allows for discrimination against electromagnetic backgrounds, which strike the detector at rates orders of magnitude higher than the expected WIMP signal. This dissertation presents the development of numerical models of the physics of the CDMS detectors, implemented in a computational package collectively known as the CDMS Detector Monte Carlo (DMC). After substantial validation of the models against data, the DMC is used to investigate potential backgrounds to the next iteration of the CDMS experiment, known as SuperCDMS. Finally, an investigation of using the DMC in a reverse Monte Carlo analysis of WIMP search data is presented.« less

Origins and challenges of viral dark matter.

PubMed

Krishnamurthy, Siddharth R; Wang, David

2017-07-15

The accurate classification of viral dark matter - metagenomic sequences that originate from viruses but do not align to any reference virus sequences - is one of the major obstacles in comprehensively defining the virome. Depending on the sample, viral dark matter can make up from anywhere between 40 and 90% of sequences. This review focuses on the specific nature of dark matter as it relates to viral sequences. We identify three factors that contribute to the existence of viral dark matter: the divergence and length of virus sequences, the limitations of alignment based classification, and limited representation of viruses in reference sequence databases. We then discuss current methods that have been developed to at least partially circumvent these limitations and thereby reduce the extent of viral dark matter. Copyright © 2017 Elsevier B.V. All rights reserved.

The DarkSide awakens

DOE PAGES

Davini, S.; Agnes, P.; Agostino, L.; ...

2016-06-09

Here, the DarkSide program at LNGS aims to perform background-free WIMP searches using two phase liquid argon time projection chambers, with the ultimate goal of covering all parameters down to the so-called neutrino floor. One of the distinct features of the program is the use of underground argon with has a reduced content of the radioactive 39Ar compared to atmospheric argon. The DarkSide Collaboration is currently operating the DarkSide-50 experiment, the first such WIMP detector using underground argon. Operations with underground argon indicate a suppression of 39Ar by a factor (1.4 ± 0.2) × 10 3 relative to atmospheric argon.more » The new results obtained with DarkSide-50 and the plans for the next steps of the DarkSide program, the 20t fiducial mass DarkSide-20k detector and the 200 t fiducial Argo, are reviewed in this proceedings.« less

Genome research elucidating environmental adaptation: Dark-fly project as a case study.

PubMed

Fuse, Naoyuki

2017-08-01

Organisms have the capacity to adapt to diverse environments, and environmental adaptation is a substantial driving force of evolution. Recent progress of genome science has addressed the genetic mechanisms underlying environmental adaptation. Whole genome sequencing has identified adaptive genes selected under particular environments. Genome editing technology enables us to directly test the role(s) of a gene in environmental adaptation. Genome science has also shed light on a unique organism, Dark-fly, which has been reared long-term in the dark. We determined the whole genome sequence of Dark-fly and reenacted environmental selections of the Dark-fly genome to identify the genes related to dark-adaptation. Here I will give an overview of current progress in genome science and summarize our study using Dark-fly, as a case study for environmental adaptation. Copyright © 2017 Elsevier Ltd. All rights reserved.

The DarkSide awakens

NASA Astrophysics Data System (ADS)

Davini, S.; Agnes, P.; Agostino, L.; Albuquerque, I. F. M.; Alexander, T.; Alton, A. K.; Arisaka, K.; Back, H. O.; Baldin, B.; Biery, K.; Bonfini, G.; Bossa, M.; Bottino, B.; Brigatti, A.; Brodsky, J.; Budano, F.; Bussino, S.; Cadeddu, M.; Cadonati, L.; Cadoni, M.; Calaprice, F.; Canci, N.; Candela, A.; Cao, H.; Cariello, M.; Carlini, M.; Catalanotti, S.; Cavalcante, P.; Chepurnov, A.; Cocco, A. G.; Covone, G.; D'Angelo, D.; D'Incecco, M.; De Cecco, S.; De Deo, M.; De Vincenzi, M.; Derbin, A.; Devoto, A.; Di Eusanio, F.; Di Pietro, G.; Edkins, E.; Empl, A.; Fan, A.; Fiorillo, G.; Fomenko, K.; Foster, G.; Franco, D.; Gabriele, F.; Galbiati, C.; Giganti, C.; Goretti, A. M.; Granato, F.; Grandi, L.; Gromov, M.; Guan, M.; Guardincerri, Y.; Hackett, B. R.; Herner, K. R.; Hungerford, E. V.; Ianni, Aldo; Ianni, Andrea; James, I.; Jollet, C.; Keeter, K.; Kendziora, C. L.; Kobychev, V.; Koh, G.; Korablev, D.; Korga, G.; Kubankin, A.; Li, X.; Lissia, M.; Lombardi, P.; Luitz, S.; Ma, Y.; Machulin, I. N.; Mandarano, A.; Mari, S. M.; Maricic, J.; Marini, L.; Martoff, C. J.; Meregaglia, A.; Meyers, P. D.; Miletic, T.; Milincic, R.; Montanari, D.; Monte, A.; Montuschi, M.; Monzani, M. E.; Mosteiro, P.; Mount, B. J.; Muratova, V. N.; Musico, P.; Napolitano, J.; Orsini, M.; Ortica, F.; Pagani, L.; Pallavicini, M.; Pantic, E.; Parmeggiano, S.; Pelczar, K.; Pelliccia, N.; Perasso, S.; Pocar, A.; Pordes, S.; Pugachev, D. A.; Qian, H.; Randle, K.; Ranucci, G.; Razeto, A.; Reinhold, B.; Renshaw, A. L.; Romani, A.; Rossi, B.; Rossi, N.; Rountree, S. D.; Sablone, D.; Saggese, P.; Saldanha, R.; Sands, W.; Sangiorgio, S.; Savarese, C.; Segreto, E.; Semenov, D. A.; Shields, E.; Singh, P. N.; Skorokhvatov, M. D.; Smirnov, O.; Sotnikov, A.; Stanford, C.; Suvorov, Y.; Tartaglia, R.; Tatarowicz, J.; Testera, G.; Tonazzo, A.; Trinchese, P.; Unzhakov, E. V.; Vishneva, A.; Vogelaar, B.; Wada, M.; Walker, S.; Wang, H.; Wang, Y.; Watson, A. W.; Westerdale, S.; Wilhelmi, J.; Wojcik, M. M.; Xiang, X.; Xu, J.; Yang, C.; Yoo, J.; Zavatarelli, S.; Zec, A.; Zhong, W.; Zhu, C.; Zuzel, G.

2016-05-01

The DarkSide program at LNGS aims to perform background-free WIMP searches using two phase liquid argon time projection chambers, with the ultimate goal of covering all parameters down to the so-called neutrino floor. One of the distinct features of the program is the use of underground argon with has a reduced content of the radioactive 39Ar compared to atmospheric argon. The DarkSide Collaboration is currently operating the DarkSide-50 experiment, the first such WIMP detector using underground argon. Operations with underground argon indicate a suppression of 39Ar by a factor (1.4 ± 0.2) × 103 relative to atmospheric argon. The new results obtained with DarkSide-50 and the plans for the next steps of the DarkSide program, the 20t fiducial mass DarkSide-20k detector and the 200 t fiducial Argo, are reviewed in this proceedings.

The fraternal WIMP miracle

DOE PAGES

Craig, Nathaniel; Katz, Andrey

2015-10-27

We identify and analyze thermal dark matter candidates in the fraternal twin Higgs model and its generalizations. The relic abundance of fraternal twin dark matter is set by twin weak interactions, with a scale tightly tied to the weak scale of the Standard Model by naturalness considerations. As such, the dark matter candidates benefit from a "fraternal WIMP miracle'', reproducing the observed dark matter abundance for dark matter masses between 50 and 150 GeV . However, the couplings dominantly responsible for dark matter annihilation do not lead to interactions with the visible sector. The direct detection rate is instead setmore » via fermionic Higgs portal interactions, which are likewise constrained by naturalness considerations but parametrically weaker than those leading to dark matter annihilation. Finally, the predicted direct detection cross section is close to current LUX bounds and presents an opportunity for the next generation of direct detection experiments.« less

Enhanced bioelectricity generation and azo dye treatment in a reversible photo-bioelectrochemical cell by using novel anthraquinone-2,6-disulfonate (AQDS)/MnOx-doped polypyrrole film electrodes.

PubMed

Sun, Jian; Cai, Bihai; Xu, Wenjing; Huang, Yu; Zhang, Yaping; Peng, Yenping; Chang, Kenlin; Kuo, Jiahong; Chen, Kufan; Ning, Xunan; Liu, Guoguang; Wang, Yujie; Yang, Zuoyi; Liu, Jingyong

2017-02-01

A novel anthraquinone-2,6-disulfonate/MnO x -doped polypyrrole film (AQDS/Mn/PPy) electrode was prepared by one-step electropolymerization method and was used to improve performance of a reversible photo-bioelectrochemical cell (RPBEC). The RPBEC was operated in polarity reversion depended on dark/light reaction of alga Chlorella vulgaris by which sequential decolorization of azo dye and mineralization of decolorization products coupled with bioelectricity generation can be achieved. The results showed that formation of uniform AQDS/Mn/PPy film significantly enhanced electroactive surface area and electrocatalytic activity of carbon electrode. The RPBEC with AQDS/Mn/PPy electrodes demonstrated 77% increases in maximum power and 73% increases in Congo red decolorization rate before polarity reversion, and 198% increases in maximum power and 138% increases in decolorization products mineralization rate after polarity reversion, respectively, compared to the RPBEC with bare electrode. This was resulted from simultaneous dynamics improvement in half-reaction rate of anode and photo-biocathode due to enhanced electron transfer and algal-bacterial biofilm formation. Copyright © 2016 Elsevier Ltd. All rights reserved.

Thin-Film Quantum Dot Photodiode for Monolithic Infrared Image Sensors.

PubMed

Malinowski, Pawel E; Georgitzikis, Epimitheas; Maes, Jorick; Vamvaka, Ioanna; Frazzica, Fortunato; Van Olmen, Jan; De Moor, Piet; Heremans, Paul; Hens, Zeger; Cheyns, David

2017-12-10

Imaging in the infrared wavelength range has been fundamental in scientific, military and surveillance applications. Currently, it is a crucial enabler of new industries such as autonomous mobility (for obstacle detection), augmented reality (for eye tracking) and biometrics. Ubiquitous deployment of infrared cameras (on a scale similar to visible cameras) is however prevented by high manufacturing cost and low resolution related to the need of using image sensors based on flip-chip hybridization. One way to enable monolithic integration is by replacing expensive, small-scale III-V-based detector chips with narrow bandgap thin-films compatible with 8- and 12-inch full-wafer processing. This work describes a CMOS-compatible pixel stack based on lead sulfide quantum dots (PbS QD) with tunable absorption peak. Photodiode with a 150-nm thick absorber in an inverted architecture shows dark current of 10 -6 A/cm² at -2 V reverse bias and EQE above 20% at 1440 nm wavelength. Optical modeling for top illumination architecture can improve the contact transparency to 70%. Additional cooling (193 K) can improve the sensitivity to 60 dB. This stack can be integrated on a CMOS ROIC, enabling order-of-magnitude cost reduction for infrared sensors.

Second-order processing of four-stroke apparent motion.

PubMed

Mather, G; Murdoch, L

1999-05-01

In four-stroke apparent motion displays, pattern elements oscillate between two adjacent positions and synchronously reverse in contrast, but appear to move unidirectionally. For example, if rightward shifts preserve contrast but leftward shifts reverse contrast, consistent rightward motion is seen. In conventional first-order displays, elements reverse in luminance contrast (e.g. light elements become dark, and vice-versa). The resulting perception can be explained by responses in elementary motion detectors turned to spatio-temporal orientation. Second-order motion displays contain texture-defined elements, and there is some evidence that they excite second-order motion detectors that extract spatio-temporal orientation following the application of a non-linear 'texture-grabbing' transform by the visual system. We generated a variety of second-order four-stroke displays, containing texture-contrast reversals instead of luminance contrast reversals, and used their effectiveness as a diagnostic test for the presence of various forms of non-linear transform in the second-order motion system. Displays containing only forward or only reversed phi motion sequences were also tested. Displays defined by variation in luminance, contrast, orientation, and size were effective. Displays defined by variation in motion, dynamism, and stereo were partially or wholly ineffective. Results obtained with contrast-reversing and four-stroke displays indicate that only relatively simple non-linear transforms (involving spatial filtering and rectification) are available during second-order energy-based motion analysis.

Review of indirect detection of dark matter with neutrinos

NASA Astrophysics Data System (ADS)

Danninger, Matthias

2017-09-01

Dark Matter could be detected indirectly through the observation of neutrinos produced in dark matter self-annihilations or decays. Searches for such neutrino signals have resulted in stringent constraints on the dark matter self-annihilation cross section and the scattering cross section with matter. In recent years these searches have made significant progress in sensitivity through new search methodologies, new detection channels, and through the availability of rich datasets from neutrino telescopes and detectors, like IceCube, ANTARES, Super-Kamiokande, etc. We review recent experimental results and put them in context with respect to other direct and indirect dark matter searches. We also discuss prospects for discoveries at current and next generation neutrino detectors.

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

Dunach, M.; Marti, T.; Khorana, H.G.

The light-dark adaptation reactions of a set of bacteriorhodopsin (bR) mutants that affect function and color of the chromophore were examined by using visible absorption spectroscopy. The absorbance spectra of the mutants Arg-82 in equilibrium Ala (Gln), Asp-85 in equilibrium Ala (Asn, Glu), Tyr-185 in equilibrium Phe, and Asp-212 in equilibrium Ala (Asn, Glu) were measured at different pH values during and after illumination. None of these mutants exhibited a normal dark-light adaptation, which in wild-type bR causes a red shift of the visible absorption maximum from 558 nm (dark-adapted bR) to 568 nm (light-adapted bR). Instead a reversible lightmore » reaction occurs in the Asp-85 and Asp-212 mutants from a blue form with lambda max near 600 nm to a pink form with lambda max near 480 nm. This light-induced shift explains the appearance of a reversed light adaptation previously observed for the Asp-212 mutants. In the case of the Tyr-185 and Arg-82 mutants, light causes a purple-to-blue transformation similar to the effect of lowering the pH. However, the blue forms observed in these mutants are not identical to those formed by acid titration or deionization of wild-type bR. It is suggested that in all of these mutants, the chromophore has lost the ability to undergo the normal 13-cis, 15-syn to all-trans, 15-anti light-driven isomerization, which occurs in native bR. Instead these mutants may have as stable forms all-trans,syn and 13-cis,anti chromophores, which are not allowed in native bR, except transiently.« less

Photocontrol of germination in Amaranthus caudatus.

PubMed

Kendrick, R E; Frankland, B

1969-12-01

Germination of Amaranthus caudatus is inhibited by light, far-red being the most effective part of the spectrum. At temperatures of 25° and below there is a low final germination percentage under continuous far-red whereas above 25° there is only a delaying effect. In the presence of a saturating concentration of gibberellic acid (GA3) at 25° seeds germinate under continuous far-red although they are delayed. At 25° seeds exposed to 48 hr far-red fail to germinate when transferred to darkness. This induced dormancy can be broken by a single short exposure to red light given at any time after the far-red illumination. This effect of short red can be reversed by a subsequent short period of far-red indicating that the seeds are phytochrome controlled. Although most seeds have escaped from the reversing effect of short far-red after an intervening dark period of 5 hours, germination is greatly reduced by continuous far-red at this time. Results of exposing seeds to varying periods of far-red before and after dark imbibition are interpreted in terms of a continual production of phytochrome in its active P fr form and a requirement for P fr action over a long period of time. Effects of intermittent and continuous low intensity far-red on the inhibition of germination provides further evidence for a low energy photoreaction involving phytochrome. Effects on Germination Index of continuous illumination with various light sources maintaining different P fr /P total ratios have been investigated. The results suggest that the proportion of phytochrome in the P fr form is the most important factor in the regulation of germination. A scheme for the phytochrome control of germination in Amaranthus caudatus is presented and possible explanations for the dependence on P fr /P total ratio are discussed.

Searching for a dark photon with DarkLight

DOE PAGES

Corliss, R.

2016-07-30

Here, we describe the current status of the DarkLight experiment at Jefferson Laboratory. DarkLight is motivated by the possibility that a dark photon in the mass range 10 to 100 MeV/c 2 could couple the dark sector to the Standard Model. DarkLight will precisely measure electron proton scattering using the 100 MeV electron beam of intensity 5 mA at the Jefferson Laboratory energy recovering linac incident on a windowless gas target of molecular hydrogen. We will detect the complete final state including scattered electron, recoil proton, and e +e - pair. A phase-I experiment has been funded and is expectedmore » to take data in the next eighteen months. The complete phase-II experiment is under final design and could run within two years after phase-I is completed. The DarkLight experiment drives development of new technology for beam, target, and detector and provides a new means to carry out electron scattering experiments at low momentum transfers.« less

Absorption of light dark matter in semiconductors

DOE PAGES

Hochberg, Yonit; Lin, Tongyan; Zurek, Kathryn M.

2017-01-01

Semiconductors are by now well-established targets for direct detection of MeV to GeV dark matter via scattering off electrons. We show that semiconductor targets can also detect significantly lighter dark matter via an absorption process. When the dark matter mass is above the band gap of the semiconductor (around an eV), absorption proceeds by excitation of an electron into the conduction band. Below the band gap, multiphonon excitations enable absorption of dark matter in the 0.01 eV to eV mass range. Energetic dark matter particles emitted from the sun can also be probed for masses below an eV. We derivemore » the reach for absorption of a relic kinetically mixed dark photon or pseudoscalar in germanium and silicon, and show that existing direct detection results already probe new parameter space. Finally, with only a moderate exposure, low-threshold semiconductor target experiments can exceed current astrophysical and terrestrial constraints on sub-keV bosonic dark matter.« less

Caulonemal gravitropism and amyloplast sedimentation in the moss Funaria

NASA Technical Reports Server (NTRS)

Schwuchow, J. M.; Kim, D.; Sack, F. D.

1995-01-01

Caulonemata of the moss Funaria were examined to determine whether they are gravitropic. Funaria and Physcomitrella were also evaluated to compare amyloplast sedimentation with that of Ceratodon. Protonemata were either chemically fixed in place or examined alive using infrared timelapse videomicroscopy. Funaria caulonemata were found to be negatively gravitropic, i.e., they grew upwards in the dark. Upward curvature reversed temporarily before cytokinesis in Funaria, a phenomenon already known for Ceratodon and Physcomitrella. Most horizontal and upward-curving Funaria tip cells contained a broad subapical zone where plastid sedimentation occurred. In dark-grown Physcomitrella caulonemata, sedimentation was detected by the presence of a thin, amyloplast-free strip of cytoplasm at the top of the cell. These results suggest that gravitropism and subapical amyloplast sedimentation may be relatively common in moss caulonemata.

Dark Chocolate Intake Acutely Enhances Neutrophil Count in Peripheral Venous Blood

PubMed Central

Montagnana, Martina; Danese, Elisa; Lima-Oliveira, Gabriel; Salvagno, Gian Luca; Lippi, Giuseppe

2017-01-01

Beside the well-established impact on decreasing the risk of cardiovascular diseases (1), recent attention has been paid to the relationship between cocoa-containing foods and the immune system (2), showing that dark chocolate consumption enhances the systemic defense against bacterial (3) and viral (4) infections. Hence, the current study aimed at investigating the acute effect of dark chocolate intake on peripheral blood leukocytes. PMID:29531561

Current status of direct dark matter detection experiments

NASA Astrophysics Data System (ADS)

Liu, Jianglai; Chen, Xun; Ji, Xiangdong

2017-03-01

Much like ordinary matter, dark matter might consist of elementary particles, and weakly interacting massive particles are one of the prime suspects. During the past decade, the sensitivity of experiments trying to directly detect them has improved by three to four orders of magnitude, but solid evidence for their existence is yet to come. We overview the recent progress in direct dark matter detection experiments and discuss future directions.

Performance of the STIS CCD Dark Rate Temperature Correction

NASA Astrophysics Data System (ADS)

Branton, Doug; STScI STIS Team

2018-06-01

Since July 2001, the Space Telescope Imaging Spectrograph (STIS) onboard Hubble has operated on its Side-2 electronics due to a failure in the primary Side-1 electronics. While nearly identical, Side-2 lacks a functioning temperature sensor for the CCD, introducing a variability in the CCD operating temperature. Previous analysis utilized the CCD housing temperature telemetry to characterize the relationship between the housing temperature and the dark rate. It was found that a first-order 7%/°C uniform dark correction demonstrated a considerable improvement in the quality of dark subtraction on Side-2 era CCD data, and that value has been used on all Side-2 CCD darks since. In this report, we show how this temperature correction has performed historically. We compare the current 7%/°C value against the ideal first-order correction at a given time (which can vary between ~6%/°C and ~10%/°C) as well as against a more complex second-order correction that applies a unique slope to each pixel as a function of dark rate and time. At worst, the current correction has performed ~1% worse than the second-order correction. Additionally, we present initial evidence suggesting that the variability in pixel temperature-sensitivity is significant enough to warrant a temperature correction that considers pixels individually rather than correcting them uniformly.

Basic corrections to predictions of solar cell performance required by nonlinearities

NASA Technical Reports Server (NTRS)

Lindholm, F. A.; Fossum, J. G.; Burgess, E. L.

1976-01-01

The superposition principle is used to derive the approximation that the current-voltage characteristic of an illuminated solar cell is the dark current-voltage characteristic shifted by the short-circuit photocurrent. The derivation requires the linearity of the boundary value problems that underlie the electrical characteristics. The shifting approximation is invalid if considerable photocurrent and considerable dark current both occur within the junction space-charge region; it is invalid also if sizable series resistance is present or if high-injection concentrations of holes and electrons exist within the quasi-neutral regions.

Signatures of dark radiation in neutrino and dark matter detectors

NASA Astrophysics Data System (ADS)

Cui, Yanou; Pospelov, Maxim; Pradler, Josef

2018-05-01

We consider the generic possibility that the Universe's energy budget includes some form of relativistic or semi-relativistic dark radiation (DR) with nongravitational interactions with standard model (SM) particles. Such dark radiation may consist of SM singlets or a nonthermal, energetic component of neutrinos. If such DR is created at a relatively recent epoch, it can carry sufficient energy to leave a detectable imprint in experiments designed to search for very weakly interacting particles: dark matter and underground neutrino experiments. We analyze this possibility in some generality, assuming that the interactive dark radiation is sourced by late decays of an unstable particle, potentially a component of dark matter, and considering a variety of possible interactions between the dark radiation and SM particles. Concentrating on the sub-GeV energy region, we derive constraints on different forms of DR using the results of the most sensitive neutrino and dark matter direct detection experiments. In particular, for interacting dark radiation carrying a typical momentum of ˜30 MeV /c , both types of experiments provide competitive constraints. This study also demonstrates that non-standard sources of neutrino emission (e.g., via dark matter decay) are capable of creating a "neutrino floor" for dark matter direct detection that is closer to current bounds than is expected from standard neutrino sources.

Dark Matter Decays from Nonminimal Coupling to Gravity.

PubMed

Catà, Oscar; Ibarra, Alejandro; Ingenhütt, Sebastian

2016-07-08

We consider the standard model extended with a dark matter particle in curved spacetime, motivated by the fact that the only current evidence for dark matter is through its gravitational interactions, and we investigate the impact on the dark matter stability of terms in the Lagrangian linear in the dark matter field and proportional to the Ricci scalar. We show that this "gravity portal" induces decay even if the dark matter particle only has gravitational interactions, and that the decay branching ratios into standard model particles only depend on one free parameter: the dark matter mass. We study in detail the case of a singlet scalar as a dark matter candidate, which is assumed to be absolutely stable in flat spacetime due to a discrete Z_{2} symmetry, but which may decay in curved spacetimes due to a Z_{2}-breaking nonminimal coupling to gravity. We calculate the dark matter decay widths and we set conservative limits on the nonminimal coupling parameter from experiments. The limits are very stringent and suggest that there must exist an additional mechanism protecting the singlet scalar from decaying via this gravity portal.

Make dark matter charged again

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

Agrawal, Prateek; Cyr-Racine, Francis-Yan; Randall, Lisa

2017-05-01

We revisit constraints on dark matter that is charged under a U(1) gauge group in the dark sector, decoupled from Standard Model forces. We find that the strongest constraints in the literature are subject to a number of mitigating factors. For instance, the naive dark matter thermalization timescale in halos is corrected by saturation effects that slow down isotropization for modest ellipticities. The weakened bounds uncover interesting parameter space, making models with weak-scale charged dark matter viable, even with electromagnetic strength interaction. This also leads to the intriguing possibility that dark matter self-interactions within small dwarf galaxies are extremely large,more » a relatively unexplored regime in current simulations. Such strong interactions suppress heat transfer over scales larger than the dark matter mean free path, inducing a dynamical cutoff length scale above which the system appears to have only feeble interactions. These effects must be taken into account to assess the viability of darkly-charged dark matter. Future analyses and measurements should probe a promising region of parameter space for this model.« less

Analysis of high reverse currents of 4H-SiC Schottky-barrier diodes

NASA Astrophysics Data System (ADS)

Okino, Hiroyuki; Kameshiro, Norifumi; Konishi, Kumiko; Shima, Akio; Yamada, Ren-ichi

2017-12-01

Nickel (Ni), titanium (Ti), and molybdenum (Mo) 4H-silicon carbide Schottky-barrier diodes (SiC SBDs) were fabricated and used to investigate the relation between forward and reverse currents. Temperature dependence of reverse current follows a theory that includes tunneling in regard to thermionic emission, namely, temperature dependence is weak at low temperature but strong at high temperatures. On the other hand, the reverse currents of the Ni and Mo SBDs are higher than their respective currents calculated from their Schottky barrier heights (SBHs), whereas the reverse current of the Ti SBD agrees well with that calculated from its SBH. The cause of the high reverse currents was investigated from the viewpoints of low barrier patch, Gaussian distribution of barrier height (GD), thin surface barrier, and electron effective mass. The high reverse current of the Ni and Mo SBDs can be explained not in terms of a low-barrier patch, GD, or thin surface barrier but in terms of small effective masses. Investigation of crystal structures at the Schottky interface revealed a large lattice mismatch between the metals (Ni, Ti, or Mo) and SiC for the Ni and Mo SBDs. The small effective mass is possibly attributed to the large lattice mismatch, which might generate transition layers at the Schottky interface. It is concluded from these results that the lattice constant as well as the work function is an important factor in selecting the metal species as the Schottky metal for wide band-gap SBDs, for which tunneling current dominates reverse current.

Mechanism of the AppABLUF Photocycle Probed by Site-Specific Incorporation of Fluorotyrosine Residues: Effect of the Y21 pKa on the Forward and Reverse Ground-State Reactions.

PubMed

Gil, Agnieszka; Haigney, Allison; Laptenok, Sergey P; Brust, Richard; Lukacs, Andras; Iuliano, James; Jeng, Jessica; Melief, Eduard; Zhao, Rui-Kun; Yoon, EunBin; Clark, Ian; Towrie, Michael; Greetham, Gregory M; Ng, Annabelle; Truglio, James; French, Jarrod; Meech, Stephen R; Tonge, Peter J

2016-01-27

The transcriptional antirepressor AppA is a blue light using flavin (BLUF) photoreceptor that releases the transcriptional repressor PpsR upon photoexcitation. Light activation of AppA involves changes in a hydrogen-bonding network that surrounds the flavin chromophore on the nanosecond time scale, while the dark state of AppA is then recovered in a light-independent reaction with a dramatically longer half-life of 15 min. Residue Y21, a component of the hydrogen-bonding network, is known to be essential for photoactivity. Here, we directly explore the effect of the Y21 pKa on dark state recovery by replacing Y21 with fluorotyrosine analogues that increase the acidity of Y21 by 3.5 pH units. Ultrafast transient infrared measurements confirm that the structure of AppA is unperturbed by fluorotyrosine substitution, and that there is a small (3-fold) change in the photokinetics of the forward reaction over the fluorotyrosine series. However, reduction of 3.5 pH units in the pKa of Y21 increases the rate of dark state recovery by 4000-fold with a Brønsted coefficient of ∼ 1, indicating that the Y21 proton is completely transferred in the transition state leading from light to dark adapted AppA. A large solvent isotope effect of ∼ 6-8 is also observed on the rate of dark state recovery. These data establish that the acidity of Y21 is a crucial factor for stabilizing the light activated form of the protein, and have been used to propose a model for dark state recovery that will ultimately prove useful for tuning the properties of BLUF photosensors for optogenetic applications.

Dark matter and neutrino mass from the smallest non-Abelian chiral dark sector

NASA Astrophysics Data System (ADS)

Berryman, Jeffrey M.; de Gouvêa, André; Kelly, Kevin J.; Zhang, Yue

2017-10-01

All pieces of concrete evidence for phenomena outside the standard model (SM)—neutrino masses and dark matter—are consistent with the existence of new degrees of freedom that interact very weakly, if at all, with those in the SM. We propose that these new degrees of freedom organize themselves into a simple dark sector, a chiral S U (3 )×S U (2 ) gauge theory with the smallest nontrivial fermion content. Similar to the SM, the dark S U (2 ) is spontaneously broken while the dark S U (3 ) confines at low energies. At the renormalizable level, the dark sector contains massless fermions—dark leptons—and stable massive particles—dark protons. We find that dark protons with masses between 10 and 100 TeV satisfy all current cosmological and astrophysical observations concerning dark matter even if dark protons are a symmetric thermal relic. The dark leptons play the role of right-handed neutrinos and allow simple realizations of the seesaw mechanism or the possibility that neutrinos are Dirac fermions. In the latter case, neutrino masses are also parametrically different from charged-fermion masses and the lightest neutrino is predicted to be massless. Since the new "neutrino" and "dark-matter" degrees of freedom interact with one another, these two new-physics phenomena are intertwined. Dark leptons play a nontrivial role in early Universe cosmology while indirect searches for dark matter involve, decisively, dark-matter annihilations into dark leptons. These, in turn, may lead to observable signatures at high-energy neutrino and gamma-ray observatories, especially once one accounts for the potential Sommerfeld enhancement of the annihilation cross section, derived from the low-energy dark-sector effective theory, a possibility we explore quantitatively in some detail.

Conservation of Information: Reverse Engineering Dark Social Systems

DTIC Science & Technology

2010-01-01

Factbook, retrieved 5/20/10 from www.cia.gov). 25 For example, Air- America , a politically liberal talk radio network, said that it would cease operations...attractive targets than mid- America ; see Reding, 2009). Obama Clinton Clinton Obama Lawless et al.: Conservation of Information 13 approached it...indefinitely sustain the control of the Communist Party--i.e., censoring Google--is increasingly at odds with Network China, which is thriving by

Effect of diet textural characteristics on the temporal rhythms of feeding in rats.

PubMed

Mok, E; Thibault, L

To examine whether the diurnal rhythms of protein-rich and carbohydrate-rich diet ingestion can be altered by presenting the diets in different textural forms, adult male Wistar rats were assigned to two dietary groups. One group received a two-way choice between high-protein powder and high-carbohydrate granular (HPP-HCG) diets. In the other group the textures were reversed [high-protein granular and high-carbohydrate powder (HPG-HCP) diets]. Rats fed HPP-HCG diets selected significantly less protein (kcal) vs. rats fed HPG-HCP diets, during the 24-h and 12-h dark phase and during the 4-h early and late dark phases. Carbohydrate intakes of the two dietary groups were not significantly different. Total caloric intake for the HPG-HCP dietary group was significantly higher than that of the HPP-HCG dietary group during the 24-h and 12-h dark phase. Body weight was significantly lower in rats fed HPP-HCG diets. In conclusion, macronutrient-rich diets presented in different textural forms alter protein-rich diet ingestion and total energy intake.

Corticosterone-responsive and -unresponsive metabolic characteristics of adrenalectomized rats.

PubMed

Hamelink, C R; Currie, P J; Chambers, J W; Castonguay, T W; Coscina, D V

1994-09-01

Glucocorticoids are important in influencing substrate flux through the metabolic pathways. This study was designed to answer the question "Does adrenalectomy (ADX) cause a shift toward fat metabolism as measured by a decrease in respiratory quotient (RQ)?" Male Sprague-Dawley rats were divided into four groups, ADX, ADX + 20% corticosterone (Cort) (ADX-20%), ADX + 40% Cort (ADX-40%), or sham-operated controls (Sham). ADX-20% received 50 mg and ADX-40% 100 mg Cort dissolved in 250-mg cholesterol pellets and placed subcutaneously. Each rat was monitored for 90 min four times both during a preoperative period and again after a 1-wk postsurgical recovery period in an indirect calorimeter. Cort prevented ADX-induced suppression of weight gain and food intake. ADX decreased motoric activity in both the light and dark periods. Cort restored activity to Sham levels. ADX decreased RQ only in the dark (0.858 ADX vs. 0.891 Sham) and was reversed only in the ADX-40% group. Energy expenditure (EE) was depressed in both the light and dark by ADX; Cort partially restored EE to Sham values in the light period.

Effect of photoperiod change on chronobiology of cercarial emergence of Schistosoma japonicum derived from hilly and marshy regions of China.

PubMed

Wang, Su-Rong; Zhu, Yuan-Jian; Ge, Qing-Peng; Yang, Meng-Jia; Huang, Ji-Lei; Huang, Wen-Qiao; Zhuge, Hong-Xiang; Lu, Da-Bing

2015-12-01

The chronobiology of cercarial emergence appeared to be a genetically controlled behavior, adapted to definitive host species, for schistosome. However, a few physiological and ecological factors, for example the change of photoperiod, were reported to affect the rhythmic emergence of cercariae. Therefore, the effect of photoperiod change on cercarial emergence of two Schistosoma japonicum isolates, the hilly and the marshland, was investigated. Four shedding experiments each under a different photoperiod were conducted. Under a natural photoperiod, two distinct shedding modes, one from the hilly region and one from the marshland, were observed. Under a reversed photoperiod, the regular pattern (i.e. under a natural photoperiod) of S. japonicum cercarial emergence was reversed for the marshland isolate and disappeared for the hilly isolate. With an input of a 2 h darkness from 7am to 9am, the cercarial emergence peak were delayed for the two isolates; whereas with an input of a 2 h darkness from 5pm to 7pm, neither effect on the cercarial emergence rhythm was observed. The total cercariae emerged for both parasite isolates varied with a different photoperiod. The results indicate that the change of photoperiod could affect the chronobiology of S japonicum cercarial emergence. Copyright © 2015 Elsevier Inc. All rights reserved.

Breaking the current density threshold in spin-orbit-torque magnetic random access memory

NASA Astrophysics Data System (ADS)

Zhang, Yin; Yuan, H. Y.; Wang, X. S.; Wang, X. R.

2018-04-01

Spin-orbit-torque magnetic random access memory (SOT-MRAM) is a promising technology for the next generation of data storage devices. The main bottleneck of this technology is the high reversal current density threshold. This outstanding problem is now solved by a new strategy in which the magnitude of the driven current density is fixed while the current direction varies with time. The theoretical limit of minimal reversal current density is only a fraction (the Gilbert damping coefficient) of the threshold current density of the conventional strategy. The Euler-Lagrange equation for the fastest magnetization reversal path and the optimal current pulse is derived for an arbitrary magnetic cell and arbitrary spin-orbit torque. The theoretical limit of minimal reversal current density and current density for a GHz switching rate of the new reversal strategy for CoFeB/Ta SOT-MRAMs are, respectively, of the order of 105 A/cm 2 and 106 A/cm 2 far below 107 A/cm 2 and 108 A/cm 2 in the conventional strategy. Furthermore, no external magnetic field is needed for a deterministic reversal in the new strategy.

Laser damage tests on InSb photodiodes at 1.064 micron and 0.532 micron

NASA Technical Reports Server (NTRS)

Bearman, G. H.; Staller, C.; Mahoney, C.

1992-01-01

InSb photodiodes were examined for performance degradation after pulsed laser illumination at 0.532 micron and 1.064 micron. Incident laser powers ranged from 6 x 10 exp-18 micron-watts to 16 micron-watts in a 50 pm diameter spot. Dark current and spectral response were both measured before and after illumination. Dark current measurements were taken with the diode blanked off and viewing only 77 K surfaces. Long term stability tests demonstrated that the blackbody did not exhibit long term drifts. Other tests showed that room temperature variations did not affect the diode signal chain or the digitization electronics used in data acquisition. Results of the experiment show that the diodes did not exhibit changes in dark current or spectral response performance as a result of the laser illumination. A typical change in diode spectral response (before/after laser exposure) was about 0.2 percent +/- 0.2 percent.

New Models and Methods for the Electroweak Scale

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

Carpenter, Linda

2017-09-26

This is the Final Technical Report to the US Department of Energy for grant DE-SC0013529, New Models and Methods for the Electroweak Scale, covering the time period April 1, 2015 to March 31, 2017. The goal of this project was to maximize the understanding of fundamental weak scale physics in light of current experiments, mainly the ongoing run of the Large Hadron Collider and the space based satellite experiements searching for signals Dark Matter annihilation or decay. This research program focused on the phenomenology of supersymmetry, Higgs physics, and Dark Matter. The properties of the Higgs boson are currently beingmore » measured by the Large Hadron collider, and could be a sensitive window into new physics at the weak scale. Supersymmetry is the leading theoretical candidate to explain the natural nessof the electroweak theory, however new model space must be explored as the Large Hadron collider has disfavored much minimal model parameter space. In addition the nature of Dark Matter, the mysterious particle that makes up 25% of the mass of the universe is still unknown. This project sought to address measurements of the Higgs boson couplings to the Standard Model particles, new LHC discovery scenarios for supersymmetric particles, and new measurements of Dark Matter interactions with the Standard Model both in collider production and annihilation in space. Accomplishments include new creating tools for analyses of Dark Matter models in Dark Matter which annihilates into multiple Standard Model particles, including new visualizations of bounds for models with various Dark Matter branching ratios; benchmark studies for new discovery scenarios of Dark Matter at the Large Hardon Collider for Higgs-Dark Matter and gauge boson-Dark Matter interactions; New target analyses to detect direct decays of the Higgs boson into challenging final states like pairs of light jets, and new phenomenological analysis of non-minimal supersymmetric models, namely the set of Dirac Gaugino Models.« less

Radial oscillations of strange quark stars admixed with condensed dark matter

NASA Astrophysics Data System (ADS)

Panotopoulos, G.; Lopes, Ilídio

2017-10-01

We compute the 20 lowest frequency radial oscillation modes of strange stars admixed with condensed dark matter. We assume a self-interacting bosonic dark matter, and we model dark matter inside the star as a Bose-Einstein condensate. In this case the equation of state is a polytropic one with index 1 +1 /n =2 and a constant K that is computed in terms of the mass of the dark matter particle and the scattering length. Assuming a mass and a scattering length compatible with current observational bounds for self-interacting dark matter, we have integrated numerically first the Tolman-Oppenheimer-Volkoff equations for the hydrostatic equilibrium, and then the equations for the perturbations ξ =Δ r /r and η =Δ P /P . For a compact object with certain mass and radius we have considered here three cases, namely no dark matter at all and two different dark matter scenarios. Our results show that (i) the separation between consecutive modes increases with the amount of dark matter, and (ii) the effect is more pronounced for higher order modes. These effects are relevant even for a strange star made of 5% dark matter.

Deep diode arrays for X-ray detection

NASA Technical Reports Server (NTRS)

Zemel, J. N.

1984-01-01

Temperature gradient zone melting process was used to form p-n junctions in bulk of high purity silicon wafers. These diodes were patterned to form arrays for X-ray spectrometers. The whole fabrication processes for these X-ray detectors are reviewed in detail. The p-n junctions were evaluated by (1) the dark diode I-V measurements, (2) the diode C sub I - V measurements, and (3) the MOS C-V measurements. The results showed that these junctions were linearly graded in charge distribution with low reverse bias leakage current flowing through them (few nA at -10 volts). The X-ray detection experiments showed that an FWHM of 500 eV was obtained from these diodes with a small bias of just -5 volts (for X-ray source Fe55). A theoretical model was proposed to explain the extra peaks found in the energy spectra and a very interesting point - cross talk effect was pointed out. This might be a solution to the problem of making really high resolution X-ray spectrometers.

Degradation mechanisms of gamma irradiated LWIR HgCdTe photovoltaic detectors

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

Sarusi, G.; Eger, D.; Zemel, A.

1990-12-01

Planar n{sup +}p Hg{sub 1{minus}x}Cd{sub x}Te (x = 0.23) photodiodes passivated with ZnS were irradiated by Co{sup 60} gamma source. A strong increase in the reverse dark current was observed for doses above 0.3 Mrad(air). A similar effect was found by exposing the photodiodes to U.V illumination from a high pressure mercury lamp. By filtering the U.V light it is shown that the degradation in the performance of the photodiodes is caused by the light or radiation absorbed in the ZnS layer above the implanted n-type region. C-V measurements of irradiated MIS devices showed a significant increase in the fastmore » surface state density. Galvanomagnetic and lifetime measurements made on irradiated p-type HgCdTe layer showed no significant changes in the bulk transport parameters. Based on these findings, a model for the degradation mechanism is proposed.« less

Chlorine doped graphene quantum dots: Preparation, properties, and photovoltaic detectors

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

Zhao, Jianhong; Xiang, Jinzhong, E-mail: jzhxiang@ynu.edu.cn; Tang, Libin, E-mail: scitang@163.com

Graphene quantum dots (GQDs) are becoming one of the hottest advanced functional materials because of the opening of the bandgap due to quantum confinement effect, which shows unique optical and electrical properties. The chlorine doped GQDs (Cl-GQDs) have been fabricated by chemical exfoliation of HCl treated carbon fibers (CFs), which were prepared from degreasing cotton through an annealing process at 1000 °C for 30 min. Raman study shows that both G and 2D peaks of GQDs may be redshifted (softened) by chlorine doping, leading to an n-type doping. The first vertical (Cl)-GQDs based photovoltaic detectors have been demonstrated, both the light absorbingmore » and electron-accepting roles for (Cl)-GQDs in photodetection have been found, resulting in an exceptionally big ratio of photocurrent to dark current as high as ∼10{sup 5} at room temperature using a 405 nm laser irradiation under the reverse bias voltage. The study expands the application of (Cl)-GQDs to the important optoelectronic detection devices.« less

Generalized Optoelectronic Model of Series-Connected Multijunction Solar Cells

DOE PAGES

Geisz, John F.; Steiner, Myles A.; Garcia, Ivan; ...

2015-10-02

The emission of light from each junction in a series-connected multijunction solar cell, we found, both complicates and elucidates the understanding of its performance under arbitrary conditions. Bringing together many recent advances in this understanding, we present a general 1-D model to describe luminescent coupling that arises from both voltage-driven electroluminescence and voltage-independent photoluminescence in nonideal junctions that include effects such as Sah-Noyce-Shockley (SNS) recombination with n ≠ 2, Auger recombination, shunt resistance, reverse-bias breakdown, series resistance, and significant dark area losses. The individual junction voltages and currents are experimentally determined from measured optical and electrical inputs and outputs ofmore » the device within the context of the model to fit parameters that describe the devices performance under arbitrary input conditions. Furthermore, our techniques to experimentally fit the model are demonstrated for a four-junction inverted metamorphic solar cell, and the predictions of the model are compared with concentrator flash measurements.« less

High-performance Ge p-i-n photodetector on Si substrate

NASA Astrophysics Data System (ADS)

Chen, Li-qun; Huang, Xiang-ying; Li, Min; Huang, Yan-hua; Wang, Yue-yun; Yan, Guang-ming; Li, Cheng

2015-05-01

High-performance and tensile-strained germanium (Ge) p-i-n photodetector is demonstrated on Si substrate. The epitaxial Ge layers were prepared in an ultrahigh vacuum chemical vapor deposition (UHV-CVD) system using low temperature Ge buffer technique. The devices were fabricated by in situ doping and using Si as passivation layer between Ge and metal, which can improve the ohmic contact and realize the high doping. The results show that the dark current of the photodetector with diameter of 24 μm is about 2.5×10-7 μA at the bias voltage of -1 V, and the optical responsivity is 0.1 A/W at wavelength of 1.55 μm. The 3 dB bandwidth (BW) of 4 GHz is obtained for the photodetector with diameter of 24 μm at reverse bias voltage of 1 V. The long diffusion time of minority carrier in n-type Ge and the large contact resistance in metal/Ge contacts both affect the performance of Ge photodetectors.

Observation of a photoinduced, resonant tunneling effect in a carbon nanotube–silicon heterojunction

PubMed Central

Ambrosio, Antonio; Boscardin, Maurizio; Castrucci, Paola; Crivellari, Michele; Cilmo, Marco; De Crescenzi, Maurizio; De Nicola, Francesco; Fiandrini, Emanuele; Grossi, Valentina; Maddalena, Pasqualino; Passacantando, Maurizio; Santucci, Sandro; Scarselli, Manuela; Valentini, Antonio

2015-01-01

Summary A significant resonant tunneling effect has been observed under the 2.4 V junction threshold in a large area, carbon nanotube–silicon (CNT–Si) heterojunction obtained by growing a continuous layer of multiwall carbon nanotubes on an n-doped silicon substrate. The multiwall carbon nanostructures were grown by a chemical vapor deposition (CVD) technique on a 60 nm thick, silicon nitride layer, deposited on an n-type Si substrate. The heterojunction characteristics were intensively studied on different substrates, resulting in high photoresponsivity with a large reverse photocurrent plateau. In this paper, we report on the photoresponsivity characteristics of the device, the heterojunction threshold and the tunnel-like effect observed as a function of applied voltage and excitation wavelength. The experiments are performed in the near-ultraviolet to near-infrared wavelength range. The high conversion efficiency of light radiation into photoelectrons observed with the presented layout allows the device to be used as a large area photodetector with very low, intrinsic dark current and noise. PMID:25821710

Observation of a photoinduced, resonant tunneling effect in a carbon nanotube-silicon heterojunction.

PubMed

Aramo, Carla; Ambrosio, Antonio; Ambrosio, Michelangelo; Boscardin, Maurizio; Castrucci, Paola; Crivellari, Michele; Cilmo, Marco; De Crescenzi, Maurizio; De Nicola, Francesco; Fiandrini, Emanuele; Grossi, Valentina; Maddalena, Pasqualino; Passacantando, Maurizio; Santucci, Sandro; Scarselli, Manuela; Valentini, Antonio

2015-01-01

A significant resonant tunneling effect has been observed under the 2.4 V junction threshold in a large area, carbon nanotube-silicon (CNT-Si) heterojunction obtained by growing a continuous layer of multiwall carbon nanotubes on an n-doped silicon substrate. The multiwall carbon nanostructures were grown by a chemical vapor deposition (CVD) technique on a 60 nm thick, silicon nitride layer, deposited on an n-type Si substrate. The heterojunction characteristics were intensively studied on different substrates, resulting in high photoresponsivity with a large reverse photocurrent plateau. In this paper, we report on the photoresponsivity characteristics of the device, the heterojunction threshold and the tunnel-like effect observed as a function of applied voltage and excitation wavelength. The experiments are performed in the near-ultraviolet to near-infrared wavelength range. The high conversion efficiency of light radiation into photoelectrons observed with the presented layout allows the device to be used as a large area photodetector with very low, intrinsic dark current and noise.

Focal switching of photochromic fluorescent proteins enables multiphoton microscopy with superior image contrast.

PubMed

Kao, Ya-Ting; Zhu, Xinxin; Xu, Fang; Min, Wei

2012-08-01

Probing biological structures and functions deep inside live organisms with light is highly desirable. Among the current optical imaging modalities, multiphoton fluorescence microscopy exhibits the best contrast for imaging scattering samples by employing a spatially confined nonlinear excitation. However, as the incident laser power drops exponentially with imaging depth into the sample due to the scattering loss, the out-of-focus background eventually overwhelms the in-focus signal, which defines a fundamental imaging-depth limit. Herein we significantly improve the image contrast for deep scattering samples by harnessing reversibly switchable fluorescent proteins (RSFPs) which can be cycled between bright and dark states upon light illumination. Two distinct techniques, multiphoton deactivation and imaging (MPDI) and multiphoton activation and imaging (MPAI), are demonstrated on tissue phantoms labeled with Dronpa protein. Such a focal switch approach can generate pseudo background-free images. Conceptually different from wave-based approaches that try to reduce light scattering in turbid samples, our work represents a molecule-based strategy that focused on imaging probes.

Focal switching of photochromic fluorescent proteins enables multiphoton microscopy with superior image contrast

PubMed Central

Kao, Ya-Ting; Zhu, Xinxin; Xu, Fang; Min, Wei

2012-01-01

Probing biological structures and functions deep inside live organisms with light is highly desirable. Among the current optical imaging modalities, multiphoton fluorescence microscopy exhibits the best contrast for imaging scattering samples by employing a spatially confined nonlinear excitation. However, as the incident laser power drops exponentially with imaging depth into the sample due to the scattering loss, the out-of-focus background eventually overwhelms the in-focus signal, which defines a fundamental imaging-depth limit. Herein we significantly improve the image contrast for deep scattering samples by harnessing reversibly switchable fluorescent proteins (RSFPs) which can be cycled between bright and dark states upon light illumination. Two distinct techniques, multiphoton deactivation and imaging (MPDI) and multiphoton activation and imaging (MPAI), are demonstrated on tissue phantoms labeled with Dronpa protein. Such a focal switch approach can generate pseudo background-free images. Conceptually different from wave-based approaches that try to reduce light scattering in turbid samples, our work represents a molecule-based strategy that focused on imaging probes. PMID:22876358

High-Temperature Characteristics of an InAsSb/AlAsSb n+Bn Detector

NASA Astrophysics Data System (ADS)

Ting, David Z.; Soibel, Alexander; Höglund, Linda; Hill, Cory J.; Keo, Sam A.; Fisher, Anita; Gunapala, Sarath D.

2016-09-01

The high-temperature characteristics of a mid-wavelength infrared (MWIR) detector based on the Maimon-Wicks InAsSb/AlAsSb nBn architecture was analyzed. The dark current characteristics are examined in reference to recent minority carrier lifetime results. The difference between the responsivity and absorption quantum efficiency (QE) at shorter wavelengths is clarified in terms of preferential absorption of higher-energy photons in the top contact layer, which cannot provide reverse-bias photo-response due to the AlAsSb electron blocking layer and strong recombination. Although the QE does not degrade when the operating temperature increases to 325 K, the turn-on bias becomes larger at higher temperatures. This behavior was originally attributed to the change in the valence band alignment between the absorber and top contact layers caused by the shift in Fermi level with temperature. In this work, we demonstrated the inadequacy of the original description, and offer a more likely explanation based on temperature-dependent band-bending effects.

On the Generation of the Hubble Sequence Through an Internal Secular Dynamical Process

DTIC Science & Technology

2004-01-01

is apparently brought about by the fact that spiral galaxies still have varying reserves of baryonic dark matter to form stars, therefore as the...central baryonic dark matter supply, thus the ellipticals in more advanced stage of evolution (which also generally have larger L) will experi- ence...This view is particularly favored by the currently popular hierarchical clustering/cold dark matter (CDM) paradigm of structure formation and evolution

The maximal-density mass function for primordial black hole dark matter

NASA Astrophysics Data System (ADS)

Lehmann, Benjamin V.; Profumo, Stefano; Yant, Jackson

2018-04-01

The advent of gravitational wave astronomy has rekindled interest in primordial black holes (PBH) as a dark matter candidate. As there are many different observational probes of the PBH density across different masses, constraints on PBH models are dependent on the functional form of the PBH mass function. This complicates general statements about the mass functions allowed by current data, and, in particular, about the maximum total density of PBH. Numerical studies suggest that some forms of extended mass functions face tighter constraints than monochromatic mass functions, but they do not preclude the existence of a functional form for which constraints are relaxed. We use analytical arguments to show that the mass function which maximizes the fraction of the matter density in PBH subject to all constraints is a finite linear combination of monochromatic mass functions. We explicitly compute the maximum fraction of dark matter in PBH for different combinations of current constraints, allowing for total freedom of the mass function. Our framework elucidates the dependence of the maximum PBH density on the form of observational constraints, and we discuss the implications of current and future constraints for the viability of the PBH dark matter paradigm.

Probing dark energy dynamics from current and future cosmological observations

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

Zhao Gongbo; Department of Physics, Simon Fraser University, Burnaby, BC, V5A 1S6; Zhang Xinmin

2010-02-15

We report the constraints on the dark energy equation-of-state w(z) using the latest 'Constitution' SNe sample combined with the WMAP5 and Sloan Digital Sky Survey data. Assuming a flat Universe, and utilizing the localized principal component analysis and the model selection criteria, we find that the {Lambda}CDM model is generally consistent with the current data, yet there exists a weak hint of the possible dynamics of dark energy. In particular, a model predicting w(z)<-1 at z is an element of [0.25,0.5) and w(z)>-1 at z is an element of [0.5,0.75), which means that w(z) crosses -1 in the range ofmore » z is an element of [0.25,0.75), is mildly favored at 95% confidence level. Given the best fit model for current data as a fiducial model, we make future forecast from the joint data sets of Joint Dark Energy Mission, Planck, and Large Synoptic Survey Telescope, and we find that the future surveys can reduce the error bars on the w bins by roughly a factor of 10 for a 5-w-bin model.« less

Differences in the locomotor-activating effects of indirect serotonin agonists in habituated and non-habituated rats.

PubMed

Halberstadt, Adam L; Buell, Mahálah R; Price, Diana L; Geyer, Mark A

2012-07-01

The indirect serotonin (5-HT) agonist 3,4-methylenedioxymethamphetamine (MDMA) produces a distinct behavioral profile in rats consisting of locomotor hyperactivity, thigmotaxis, and decreased exploration. The indirect 5-HT agonist α-ethyltryptamine (AET) produces a similar behavioral profile. Using the Behavioral Pattern Monitor (BPM), the present investigation examined whether the effects of MDMA and AET are dependent on the novelty of the testing environment. These experiments were conducted in Sprague-Dawley rats housed on a reversed light cycle and tested during the dark phase of the light/dark cycle. We found that racemic MDMA (RS-MDMA; 3 mg/kg, SC) increased locomotor activity in rats tested in novel BPM chambers, but had no effect on locomotor activity in rats habituated to the BPM chambers immediately prior to testing. Likewise, AET (5 mg/kg, SC) increased locomotor activity in non-habituated animals but not in animals habituated to the test chambers. These results were unexpected because previous reports indicate that MDMA has robust locomotor-activating effects in habituated animals. To further examine the influence of habituation on MDMA-induced locomotor activity, we conducted parametric studies with S-(+)-MDMA (the more active enantiomer) in habituated and non-habituated rats housed on a standard or reversed light cycle. Light cycle was included as a variable due to reported differences in sensitivity to serotonergic ligands during the dark and light phases. In confirmation of our initial studies, rats tested during the dark phase and habituated to the BPM did not show an S-(+)-MDMA (3 mg/kg, SC)-induced increase in locomotor activity, whereas non-habituated rats did. By contrast, in rats tested during the light phase, S-(+)-MDMA increased locomotor activity in both non-habituated and habituated rats, although the response in habituated animals was attenuated. The finding that habituation and light cycle interact to influence MDMA- and AET-induced hyperactivity demonstrates that there are previously unrecognized complexities associated with the behavioral effects of these drugs. Copyright © 2012 Elsevier Inc. All rights reserved.

[Identification of early irreversible damage area in a rat model of cerebral ischemia and reperfusion].

PubMed

Liu, S; Guo, Y

2000-02-01

To observe the early neuron ischemic damage in focal cerebral ischemia/reperfusion with histostaining methods of argyrophil III (AG III), Toludine blue(TB), and H&E, and to make out the 'separating line' between the areas of reversible and irreversible early ischemic damage. Forty-two male Wistar rats were randomly divided into the following groups: pseudo-surgical, blank-control, O2R0(occluded for 2 hours and reperfused for 0 hour), O2R0.5, O2R2, O2R4, O2R24. There were 6 rats in each group. Rats in experimental groups were suffered focal cerebral ischemia/reperfusion through a nylon suture method. After a special processor for tissue manage, the brain were coronal sectioned and stained with H&E, TB, and AG III. The area where dark neurons dwell in (ischemic core) were calculated with image analysis system. The success rate of ischemic model for this experiment is 90%. After being stained with argyrophil III method, normal neurons appear yellow or pale brown, which is hardly distinguished from the pale brown background. The ischemic neuron stained black, and has collapsed body and "corkscrew-like" axon or dentries, which were broken to some extent. The neuropil in the dark neurons dwelt area appears gray or pale black, which is apparently different from the pale brown neighborhood area. The distribution of dark neurons in cortex varies according to different layers, and has a character of columnar form. The dark neurons present as early as 2 hours ischemia without reperfusion with AG III method. AG III stain could selectively display early ischemic neurons, the area dwelt by dark neurons represent early ischemic core. Dark neuron is possibly the irreversibly damaged neuron. Identification of dark neurons could be helpful in the discrimination between early ischemic center and penumbra.

Dark matter admixed strange quark stars in the Starobinsky model

NASA Astrophysics Data System (ADS)

Lopes, Ilídio; Panotopoulos, Grigoris

2018-01-01

We compute the mass-to-radius profiles for dark matter admixed strange quark stars in the Starobinsky model of modified gravity. For quark matter, we assume the MIT bag model, while self-interacting dark matter inside the star is modeled as a Bose-Einstein condensate with a polytropic equation of state. We numerically integrate the structure equations in the Einstein frame, adopting the two-fluid formalism, and we treat the curvature correction term nonperturbatively. The effects on the properties of the stars of the amount of dark matter as well as the higher curvature term are investigated. We find that strange quark stars (in agreement with current observational constraints) with the highest masses are equally affected by dark matter and modified gravity.

Characterization of the rod photoresponse isolated from the dark-adapted primate ERG.

PubMed

Jamison, J A; Bush, R A; Lei, B; Sieving, P A

2001-01-01

The a-wave of the human dark-adapted ERG is thought to derive from activity of rod photoreceptors. However, other sources within the retina could potentially perturb this simple equation. We investigated the extent to which the short-latency dark-adapted rod a-wave of the primate ERG is dominated by the rod photoresponse and the applicability of the phototransduction model to fit the rod a-wave. Dark-adapted Ganzfeld ERGs were elicited over a 5-log-unit intensity range using short bright xenon flashes, and the light-adapted cone responses were subtracted to isolate the rod ERG a-wave. Intravitreal 4-phosphono-butyric acid (APB) and cis-2,3-piperidine-dicarboxylic acid (PDA) were applied to isolate the photoreceptor response. The Hood and Birch version of the phototransduction model, Rmax[1 - e(-I x S x (t-t(eff)))2], was fitted to the a-wave data while allowing Rmax and S to vary. Three principle observations were made: (1) At flash intensities > or =0.77 log sc-td-s the leading edge of the normalized rod ERG a-wave tracks the isolated photoreceptor response across the first 20 ms or up to the point of b-wave intrusion. The rod ERG a-wave was essentially identical to the isolated receptor response for all intensities that produce peak responses within 14 ms after the flash. (2) The best fit of sensitivity (S) was not affected by APB and/or PDA, suggesting that the inner retina contributes very little to the dark-adapted a-wave. (3) APB always reduced the maximum dark-adapted a-wave amplitude (by 15-30%), and PDA always increased it (by 7-15%). Using the phototransduction model, both events can be interpreted as a scaling of the photoreceptor dark current. This suggests that activity of postreceptor cells somehow influences the rod dark current, possibly by feedback through horizontal cells (although currently not demonstrated for the rod system), or by altering the ionic concentrations near the photoreceptors, or by neuromodulator effects mediated by dopamine or melatonin.

Exploring fermionic dark matter via Higgs boson precision measurements at the Circular Electron Positron Collider

NASA Astrophysics Data System (ADS)

Xiang, Qian-Fei; Bi, Xiao-Jun; Yin, Peng-Fei; Yu, Zhao-Huan

2018-03-01

We study the impact of fermionic dark matter (DM) on projected Higgs precision measurements at the Circular Electron Positron Collider (CEPC), including the one-loop effects on the e+e-→Z h cross section and the Higgs boson diphoton decay, as well as the tree-level effects on the Higgs boson invisible decay. As illuminating examples, we discuss two UV-complete DM models, whose dark sector contains electroweak multiplets that interact with the Higgs boson via Yukawa couplings. The CEPC sensitivity to these models and current constraints from DM detection and collider experiments are investigated. We find that there exist some parameter regions where the Higgs measurements at the CEPC will be complementary to current DM searches.

Structural, electrical and photovoltaic properties of CoS/Si heterojunction prepared by spray pyrolysis

NASA Astrophysics Data System (ADS)

El Radaf, I. M.; Nasr, Mahmoud; Mansour, A. M.

2018-01-01

Au/p-CoS/n-Si/Al heterojunction device was fabricated by spray pyrolysis technique. The structural and morphological features were examined by x-ray diffraction, scanning electron microscope and energy dispersive x-ray analysis. The capacitance-voltage characteristics of the prepared heterojunction were analyzed at room temperature in the dark. The current-voltage characteristics were examined under dark and different incident light intensities 20-100 mW cm-2. The rectification ratio, series resistance, shunt resistance, diode ideality factor and the effective barrier height were determined at dark and illumination conditions. The photovoltaic parameters such as short circuit current density, open circuit voltage, fill factor and power conversion efficiency were calculated at different incident light intensities.

Reversing into Meritocracy: Shifting the Culture of Physics

NASA Astrophysics Data System (ADS)

Bertschinger, Edmund

Culture is the dark energy of our lives: it is an invisible force that shapes our environment for work and life. Physics culture often includes the assumption that people have equal access to resources and opportunities regardless of gender, race, or any other demographic characteristic. Numerous studies show this is false, yet the invisible force of meritocracy shapes many departments, and its passive acceptance can foster inequitable working environments. Department chairs and other leaders play a key role in shifting institutional culture to leverage the power of diversity, improve student and employee success, and enhance the quality of life for everyone. I will describe steps taken at MIT to shift our cultural direction so that we are not driving in reverse on the highway of meritocracy.

Charting the Unknown: A Hunt in the Dark

NASA Astrophysics Data System (ADS)

Mohlabeng, Gopolang Mokoka

Astrophysical and cosmological observations have pointed strongly to the existence of dark matter in the Universe, yet its nature remains elusive. It may be hidden in a vast unknown parameter space in which exhaustively searching for a signal is not feasible. We are, therefore, compelled to consider a robust program based on a wide range of new theoretical ideas and complementary strategies for detection. The aim of this dissertation is to investigate the phenomenology of diverse dark sectors with the objective of understanding and characterizing dark matter. We do so by exploring dark matter phenomenology under three main frameworks of study: (I) the model dependent approach, (II) model independent approach and (III) considering simplified models. In each framework we focus on unexplored and well motivated dark matter scenarios as well as their prospects of detection at current and future experiments. First, we concentrate on the model dependent method where we consider minimal dark matter in the form of mixed fermionic stable states in a gauge extension of the standard model. In particular, we incorporate the fermion mixings governed by gauge invariant interactions with the heavier degrees of freedom. We find that the manner of mixing has an impact on the detectability of the dark matter at experiments. Pursuing this model dependent direction, we explore a space-time extension of the standard model which houses a vector dark matter candidate. We incorporate boundary terms arising from the topology of the model and find that these control the way dark matter may interact with baryonic matter. Next we investigate the model independent approach in which we examine a non-minimal dark sector in the form of boosted dark matter. In this study, we consider an effective field theory involving two stable fermionic states. We probe the sensitivity of this type of dark matter coming from the galactic center and the center of the Sun, and investigate its detection prospects at current and future large volume experiments. Finally, we explore an intermediate approach in the form of a simplified model. Here we analyze a different non-minimal dark sector in which its interactions with the standard model sector are mediated primarily by the Higgs Boson. We discuss for the first time a vector and fermion dark matter preserved under the same stabilization symmetry. We find that the presence of both species in the early Universe results in rare processes contributing to the dark matter relic abundance. We conclude that connecting these three frameworks under one main dark matter program, instead of concentrating on them individually, could help us understand what we are missing, and may assist us to produce ground breaking ideas which lead to the discovery of a signal in the near future.

SiC-based Photo-detectors for UV, VUV, EUV and Soft X-ray Detection

NASA Technical Reports Server (NTRS)

Yan, Feng

2006-01-01

A viewgraph presentation describing an ideal Silicon Carbide detector for ultraviolet, vacuum ultraviolet, extreme ultraviolet and soft x-ray detection is shown. The topics include: 1) An ideal photo-detector; 2) Dark current density of SiC photodiodes at room temperature; 3) Dark current in SiC detectors; 4) Resistive and capacitive feedback trans-impedance amplifier; 5) Avalanche gain; 6) Excess noise; 7) SNR in single photon counting mode; 8) Structure of SiC single photon counting APD and testing structure; 9) Single photon counting waveform and testing circuit; 10) Amplitude of SiC single photon counter; 11) Dark count of SiC APD photon counters; 12) Temperature-dependence of dark count rate; 13) Reduce the dark count rate by reducing the breakdown electric field; 14) Spectrum range for SiC detectors; 15) QE curves of Pt/4H-SiC photodiodes; 16) QE curve of SiC; 17) QE curves of SiC photodiode vs. penetration depth; 18) Visible rejection of SiC photodiodes; 19) Advantages of SiC photodiodes; 20) Competitors of SiC detectors; 21) Extraterrestrial solar spectra; 22) Visible-blind EUV detection; 23) Terrestrial solar spectra; and 24) Less than 1KeV soft x-ray detection.

Top-philic dark matter within and beyond the WIMP paradigm

NASA Astrophysics Data System (ADS)

Garny, Mathias; Heisig, Jan; Hufnagel, Marco; Lülf, Benedikt

2018-04-01

We present a comprehensive analysis of top-philic Majorana dark matter that interacts via a colored t -channel mediator. Despite the simplicity of the model—introducing three parameters only—it provides an extremely rich phenomenology allowing us to accommodate the relic density for a large range of coupling strengths spanning over 6 orders of magnitude. This model features all "exceptional" mechanisms for dark matter freeze-out, including the recently discovered conversion-driven freeze-out mode, with interesting signatures of long-lived colored particles at colliders. We constrain the cosmologically allowed parameter space with current experimental limits from direct, indirect and collider searches, with special emphasis on light dark matter below the top mass. In particular, we explore the interplay between limits from Xenon1T, Fermi-LAT and AMS-02 as well as limits from stop, monojet and Higgs invisible decay searches at the LHC. We find that several blind spots for light dark matter evade current constraints. The region in parameter space where the relic density is set by the mechanism of conversion-driven freeze-out can be conclusively tested by R -hadron searches at the LHC with 300 fb-1 .

HgCdTe APD-based linear-mode photon counting components and ladar receivers

NASA Astrophysics Data System (ADS)

Jack, Michael; Wehner, Justin; Edwards, John; Chapman, George; Hall, Donald N. B.; Jacobson, Shane M.

2011-05-01

Linear mode photon counting (LMPC) provides significant advantages in comparison with Geiger Mode (GM) Photon Counting including absence of after-pulsing, nanosecond pulse to pulse temporal resolution and robust operation in the present of high density obscurants or variable reflectivity objects. For this reason Raytheon has developed and previously reported on unique linear mode photon counting components and modules based on combining advanced APDs and advanced high gain circuits. By using HgCdTe APDs we enable Poisson number preserving photon counting. A metric of photon counting technology is dark count rate and detection probability. In this paper we report on a performance breakthrough resulting from improvement in design, process and readout operation enabling >10x reduction in dark counts rate to ~10,000 cps and >104x reduction in surface dark current enabling long 10 ms integration times. Our analysis of key dark current contributors suggest that substantial further reduction in DCR to ~ 1/sec or less can be achieved by optimizing wavelength, operating voltage and temperature.

X-ray bright points and He I lambda 10830 dark points

NASA Technical Reports Server (NTRS)

Golub, L.; Harvey, K. L.; Herant, M.; Webb, D. F.

1989-01-01

Using near-simultaneous full disk Solar X-ray images and He I 10830 lambda, spectroheliograms from three recent rocket flights, dark points identified on the He I maps were compared with X-ray bright points identified on the X-ray images. It was found that for the largest and most obvious features there is a strong correlation: most He I dark points correspond to X-ray bright points. However, about 2/3 of the X-ray bright points were not identified on the basis of the helium data alone. Once an X-ray feature is identified it is almost always possible to find an underlying dark patch of enhanced He I absorption which, however, would not a priori have been selected as a dark point. Therefore, the He I dark points, using current selection criteria, cannot be used as a one-to-one proxy for the X-ray data. He I dark points do, however, identify the locations of the stronger X-ray bright points.

X-ray bright points and He I lambda 10830 dark points

NASA Technical Reports Server (NTRS)

Golub, L.; Harvey, K. L.; Herant, M.; Webb, D. F.

1989-01-01

Using near-simultaneous full disk Solar X-ray images and He I 10830 lambda, spectroheliograms from three recent rocket flights, dark points identified on the He I maps were compared with x-ray bright points identified on the X-ray images. It was found that for the largest and most obvious features there is a strong correlation: most He I dark points correspond to X-ray bright points. However, about 2/3 of the X-ray bright points were not identified on the basis of the helium data alone. Once an X-ray feature is identified it is almost always possible to find an underlying dark patch of enhanced He I absorption which, however, would not a priori have been selected as a dark point. Therefore, the He I dark points, using current selection criteria, cannot be used as a one-to-one proxy for the X-ray data. He I dark points do, however, identify the locations of the stronger X-ray bright points.

Dark energy two decades after: observables, probes, consistency tests.

PubMed

Huterer, Dragan; Shafer, Daniel L

2018-01-01

The discovery of the accelerating universe in the late 1990s was a watershed moment in modern cosmology, as it indicated the presence of a fundamentally new, dominant contribution to the energy budget of the universe. Evidence for dark energy, the new component that causes the acceleration, has since become extremely strong, owing to an impressive variety of increasingly precise measurements of the expansion history and the growth of structure in the universe. Still, one of the central challenges of modern cosmology is to shed light on the physical mechanism behind the accelerating universe. In this review, we briefly summarize the developments that led to the discovery of dark energy. Next, we discuss the parametric descriptions of dark energy and the cosmological tests that allow us to better understand its nature. We then review the cosmological probes of dark energy. For each probe, we briefly discuss the physics behind it and its prospects for measuring dark energy properties. We end with a summary of the current status of dark energy research.

Explaining dark matter and B decay anomalies with an L μ - L τ model

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

Altmannshofer, Wolfgang; Gori, Stefania; Profumo, Stefano

We present a dark sector model based on gauging the L μ - L τ symmetry that addresses anomalies in b→ sμ +μ - decays and that features a particle dark matter candidate. The dark matter particle candidate is a vector-like Dirac fermion coupled to the Z' gauge boson of the L μ - L τ symmetry. We compute the dark matter thermal relic density, its pair-annihilation cross section, and the loop-suppressed dark matter-nucleon scattering cross section, and compare our predictions with current and future experimental results. We demonstrate that after taking into account bounds from Bs meson oscillations, darkmore » matter direct detection, and the CMB, the model is highly predictive: B physics anomalies and a viable particle dark matter candidate, with a mass of ~ (5 - 23) GeV, can be accommodated only in a tightly-constrained region of parameter space, with sharp predictions for future experimental tests. The viable region of parameter space expands if the dark matter is allowed to have L μ - L τ charges that are smaller than those of the SM leptons.« less

Explaining dark matter and B decay anomalies with an L μ - L τ model

DOE PAGES

Altmannshofer, Wolfgang; Gori, Stefania; Profumo, Stefano; ...

2016-12-20

We present a dark sector model based on gauging the L μ - L τ symmetry that addresses anomalies in b→ sμ +μ - decays and that features a particle dark matter candidate. The dark matter particle candidate is a vector-like Dirac fermion coupled to the Z' gauge boson of the L μ - L τ symmetry. We compute the dark matter thermal relic density, its pair-annihilation cross section, and the loop-suppressed dark matter-nucleon scattering cross section, and compare our predictions with current and future experimental results. We demonstrate that after taking into account bounds from Bs meson oscillations, darkmore » matter direct detection, and the CMB, the model is highly predictive: B physics anomalies and a viable particle dark matter candidate, with a mass of ~ (5 - 23) GeV, can be accommodated only in a tightly-constrained region of parameter space, with sharp predictions for future experimental tests. The viable region of parameter space expands if the dark matter is allowed to have L μ - L τ charges that are smaller than those of the SM leptons.« less

Revamping Newtonian Gravity

NASA Astrophysics Data System (ADS)

Eckhardt, Donald H.; Garrido Pestaña, José Luis

2014-06-01

The nineteenth century's quest for the missing matter (Vulcan) ended with the publication of Einstein's General Theory of Relativity. We contend that the current quest for the missing matter is parallel in its perseverance and in its ultimate futility. After setting the search for dark matter in its historic perspective, we critique extant dark matter models and offer alternative explanations -- derived from a Lorentz-invariant Lagrangian -- that will, at the very least, sow seeds of doubt about the existence of dark matter.

Cosmological Signature of the Standard Model Higgs Vacuum Instability: Primordial Black Holes as Dark Matter

NASA Astrophysics Data System (ADS)

Espinosa, J. R.; Racco, D.; Riotto, A.

2018-03-01

For the current central values of the Higgs boson and top quark masses, the standard model Higgs potential develops an instability at a scale of the order of 1 011 GeV . We show that a cosmological signature of such instability could be dark matter in the form of primordial black holes seeded by Higgs fluctuations during inflation. The existence of dark matter might not require physics beyond the standard model.

Gravitational vacuum energy in our recently accelerating universe

NASA Astrophysics Data System (ADS)

Bludman, Sidney

2009-04-01

We review current observations of the homogeneous cosmological expansion which, because they measure only kinematic variables, cannot determine the dynamics driving the recent accelerated expansion. The minimal fit to the data, the flat ACDM model, consisting of cold dark matter and a cosmological constant, interprets 4? geometrically as a classical spacetime curvature constant of nature, avoiding any reference to quantum vacuum energy. (The observed Uehling and Casimir effects measure forces due to QED vacuum polarization, but not any quantum material vacuum energies.) An Extended Anthropic Principle, that Dark Energy and Dark Gravity be indistinguishable, selects out flat ACDM. Prospective cosmic shear and galaxy clustering observations of the growth of fluctuations are intended to test whether the 'dark energy' driving the recent cosmological acceleration is static or moderately dynamic. Even if dynamic, observational differences between an additional negative-pressure material component within general relativity (Dark Energy) and low-curvature modifications of general relativity (Dark Gravity) will be extremely small.

Gravity-mediated dark matter annihilation in the Randall-Sundrum model

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

Rueter, T. D.; Rizzo, T. G.; Hewett, J. L.

Observational evidence for dark matter stems from its gravitational interactions, and as of yet there has been no evidence for dark matter interacting via other means. We examine models where dark matter interactions are purely gravitational in a Randall-Sundrum background. In particular, the Kaluza-Klein tower of gravitons which result from the warped fifth dimension can provide viable annihilation channels into Standard Model final states, and we find that we can achieve values of the annihilation cross section, < σv >, which are consistent with the observed relic abundance in the case of spin-1 dark matter. As a result, we examinemore » constraints on these models employing both the current photon line and continuum indirect dark matter searches, and assess the prospects of hunting for the signals of such models in future direct and indirect detection experiments.« less

Gravity-mediated dark matter annihilation in the Randall-Sundrum model

DOE PAGES

Rueter, T. D.; Rizzo, T. G.; Hewett, J. L.

2017-10-13

Observational evidence for dark matter stems from its gravitational interactions, and as of yet there has been no evidence for dark matter interacting via other means. We examine models where dark matter interactions are purely gravitational in a Randall-Sundrum background. In particular, the Kaluza-Klein tower of gravitons which result from the warped fifth dimension can provide viable annihilation channels into Standard Model final states, and we find that we can achieve values of the annihilation cross section, < σv >, which are consistent with the observed relic abundance in the case of spin-1 dark matter. As a result, we examinemore » constraints on these models employing both the current photon line and continuum indirect dark matter searches, and assess the prospects of hunting for the signals of such models in future direct and indirect detection experiments.« less

Complexity in pH-Dependent Ribozyme Kinetics: Dark pKa Shifts and Wavy Rate-pH Profiles.

PubMed

Frankel, Erica A; Bevilacqua, Philip C

2018-02-06

Charged bases occur in RNA enzymes, or ribozymes, where they play key roles in catalysis. Cationic bases donate protons and perform electrostatic catalysis, while anionic bases accept protons. We previously published simulations of rate-pH profiles for ribozymes in terms of species plots for the general acid and general base that have been useful for understanding how ribozymes respond to pH. In that study, we did not consider interaction between the general acid and general base or interaction with other species on the RNA. Since that report, diverse small ribozyme classes have been discovered, many of which have charged nucleobases or metal ions in the active site that can either directly interact and participate in catalysis or indirectly interact as "influencers". Herein, we simulate experimental rate-pH profiles in terms of species plots in which reverse protonated charged nucleobases interact. These analyses uncover two surprising features of pH-dependent enzyme kinetics. (1) Cooperativity between the general acid and general base enhances population of the functional forms of a ribozyme and manifests itself as hidden or "dark" pK a shifts, real pK a shifts that accelerate the reaction but are not readily observed by standard experimental approaches, and (2) influencers favorably shift the pK a s of proton-transferring nucleobases and manifest themselves as "wavy" rate-pH profiles. We identify parallels with the protein enzyme literature, including reverse protonation and wavelike behavior, while pointing out that RNA is more prone to reverse protonation. The complexities uncovered, which arise from simple pairwise interactions, should aid deconvolution of complex rate-pH profiles for RNA and protein enzymes and suggest veiled catalytic devices for promoting catalysis that can be tested by experiment and calculation.

A realization of sound focused personal audio system using acoustic contrast control.

PubMed

Chang, Ji-Ho; Lee, Chan-Hui; Park, Jin-Young; Kim, Yang-Hann

2009-04-01

A personal audio system that does not use earphone or any wire would have great interest and potential impact on the audio industries. In this study, a line array speaker system is used to localize sound in the listening zone. The contrast control [Choi, J.-W. and Kim, Y.-H. (2002). J. Acoust. Soc. Am. 111, 1695-1700] is applied, which is a method to make acoustically bright zone around the user and acoustically dark zone in other regions by maximizing the ratio of acoustic potential energy density between the bright and the dark zone. This ratio is regarded as acoustic contrast, analogous with what is used for optical devices. For the evaluation of the performance of acoustic contrast control, experiments are performed and the results are compared with those of uncontrolled case and time reversal array.

PDF-modulated visual inputs and cryptochrome define diurnal behavior in Drosophila.

PubMed

Cusumano, Paola; Klarsfeld, André; Chélot, Elisabeth; Picot, Marie; Richier, Benjamin; Rouyer, François

2009-11-01

Morning and evening circadian oscillators control the bimodal activity of Drosophila in light-dark cycles. The lateral neurons evening oscillator (LN-EO) is important for promoting diurnal activity at dusk. We found that the LN-EO autonomously synchronized to light-dark cycles through either the cryptochrome (CRY) that it expressed or the visual system. In conditions in which CRY was not activated, flies depleted for pigment-dispersing factor (PDF) or its receptor lost the evening activity and displayed reversed PER oscillations in the LN-EO. Rescue experiments indicated that normal PER cycling and the presence of evening activity relied on PDF secretion from the large ventral lateral neurons and PDF receptor function in the LN-EO. The LN-EO thus integrates light inputs and PDF signaling to control Drosophila diurnal behavior, revealing a new clock-independent function for PDF.

Algorithm for Detecting a Bright Spot in an Image

NASA Technical Reports Server (NTRS)

2009-01-01

An algorithm processes the pixel intensities of a digitized image to detect and locate a circular bright spot, the approximate size of which is known in advance. The algorithm is used to find images of the Sun in cameras aboard the Mars Exploration Rovers. (The images are used in estimating orientations of the Rovers relative to the direction to the Sun.) The algorithm can also be adapted to tracking of circular shaped bright targets in other diverse applications. The first step in the algorithm is to calculate a dark-current ramp a correction necessitated by the scheme that governs the readout of pixel charges in the charge-coupled-device camera in the original Mars Exploration Rover application. In this scheme, the fraction of each frame period during which dark current is accumulated in a given pixel (and, hence, the dark-current contribution to the pixel image-intensity reading) is proportional to the pixel row number. For the purpose of the algorithm, the dark-current contribution to the intensity reading from each pixel is assumed to equal the average of intensity readings from all pixels in the same row, and the factor of proportionality is estimated on the basis of this assumption. Then the product of the row number and the factor of proportionality is subtracted from the reading from each pixel to obtain a dark-current-corrected intensity reading. The next step in the algorithm is to determine the best location, within the overall image, for a window of N N pixels (where N is an odd number) large enough to contain the bright spot of interest plus a small margin. (In the original application, the overall image contains 1,024 by 1,024 pixels, the image of the Sun is about 22 pixels in diameter, and N is chosen to be 29.)

Developmental pathways of childhood dark traits.

PubMed

De Clercq, Barbara; Hofmans, Joeri; Vergauwe, Jasmine; De Fruyt, Filip; Sharp, Carla

2017-10-01

The dark triad of personality has traditionally been defined by 3 interrelated constructs, defined as Narcissism, Machiavellianism, and Psychopathy. Although the content of each of these constructs is clearly represented in childhood maladaptive trait measures, no studies have jointly addressed the prospective developmental course of this core set of maladaptive characteristics throughout childhood and adolescence. The current study uses latent growth modeling to explore how early dark traits develop over time, relying on a selected set of 6 childhood maladaptive traits that conceptually cover the adult dark triad. Across a 5-wave multi-informant design spanning 10 years of childhood, adolescence, and emerging adulthood (Nwave 1 = 717, 54.4% girls, age range T1 = 8-14.7 years, mean age = 10.73), results indicate that childhood dark traits show to some extent shared growth across time, although notable unique growth variance was also observed. Early dark traits further demonstrate significant association patterns with an adult dark triad measure across informants and are increasingly able to discriminate among more and less prototypical profiles of adult dark triad scores. Findings are discussed from a developmental psychopathology framework, underscoring that the proposed set of childhood dark traits represents a meaningful developmental precursor of the adult dark triad. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

Illuminated to dark ratio improvement in lateral SOI PIN photodiodes at high temperatures

NASA Astrophysics Data System (ADS)

Novo, C.; Giacomini, R.; Doria, R.; Afzalian, A.; Flandre, D.

2014-07-01

This work presents a study of the illuminated to dark ratio (IDR) of lateral SOI PIN photodiodes. Measurements performed on fabricated devices show a fivefold improvement of the IDR when the devices are biased in accumulation mode and under high temperatures of operation, independently of the anode voltage. The obtained results show that the doping concentration of the intrinsic region has influence on the sensitivity of the diodes: the larger the doping concentration, the smaller the IDR. Furthermore, the photocurrent and dark current present lower values as the silicon film thickness is decreased, resulting in a further increase in the illuminated to dark ratio.

Chloride equilibrium potential in salamander cones

PubMed Central

Thoreson, Wallace B; Bryson, Eric J

2004-01-01

Background GABAergic inhibition and effects of intracellular chloride ions on calcium channel activity have been proposed to regulate neurotransmission from photoreceptors. To assess the impact of these and other chloride-dependent mechanisms on release from cones, the chloride equilibrium potential (ECl) was determined in red-sensitive, large single cones from the tiger salamander retinal slice. Results Whole cell recordings were done using gramicidin perforated patch techniques to maintain endogenous Cl- levels. Membrane potentials were corrected for liquid junction potentials. Cone resting potentials were found to average -46 mV. To measure ECl, we applied long depolarizing steps to activate the calcium-activated chloride current (ICl(Ca)) and then determined the reversal potential for the current component that was inhibited by the Cl- channel blocker, niflumic acid. With this method, ECl was found to average -46 mV. In a complementary approach, we used a Cl-sensitive dye, MEQ, to measure the Cl- flux produced by depolarization with elevated concentrations of K+. The membrane potentials produced by the various high K+ solutions were measured in separate current clamp experiments. Consistent with electrophysiological experiments, MEQ fluorescence measurements indicated that ECl was below -36 mV. Conclusions The results of this study indicate that ECl is close to the dark resting potential. This will minimize the impact of chloride-dependent presynaptic mechanisms in cone terminals involving GABAa receptors, glutamate transporters and ICl(Ca). PMID:15579212

Design and Varactors: Operational Considerations. A Reliability Study for Robust Planar GaAs

NASA Technical Reports Server (NTRS)

Maiwald, Frank; Schlecht, Erich; Ward, John; Lin, Robert; Leon, Rosa; Pearson, John; Mehdi, Imran

2003-01-01

Preliminary conclusions include: Limits for reverse currents cannot be set. Based on current data we want to avoid any reverse bias current. We know 1 micro-A is too high. Leakage current gets suppressed when operated at 120K. Migration and verification: a) Reverse Bias Voltage will be limited; b) Health check with I/V curve: 1) Minimal reverse voltage shall be x0.75 of the calculated voltage breakdown Vbr; 2) Degradation of the Reverse Bias voltage at given current will be used as indication of ESD incidents or other Damages (high RF power, heat); 3) Calculation of diodes parameter to verify initial health check result in forward direction. RF output power starts to degrade when diode I/V curve is very strongly degraded only. Experienced on 400GHz doubler and 200GHz doubler

Effect of self assembled quantum dots on carrier mobility, with application to modeling the dark current in quantum dot infrared photodetectors

NASA Astrophysics Data System (ADS)

Youssef, Sarah; El-Batawy, Yasser M.; Abouelsaood, Ahmed A.

2016-09-01

A theoretical method for calculating the electron mobility in quantum dot infrared photodetectors is developed. The mobility calculation is based on a time-dependent, finite-difference solution of the Boltzmann transport equation in a bulk semiconductor material with randomly positioned conical quantum dots. The quantum dots act as scatterers of current carriers (conduction-band electrons in our case), resulting in limiting their mobility. In fact, carrier scattering by quantum dots is typically the dominant factor in determining the mobility in the active region of the quantum dot device. The calculated values of the mobility are used in a recently developed generalized drift-diffusion model for the dark current of the device [Ameen et al., J. Appl. Phys. 115, 063703 (2014)] in order to fix the overall current scale. The results of the model are verified by comparing the predicted dark current characteristics to those experimentally measured and reported for actual InAs/GaAs quantum dot infrared photodetectors. Finally, the effect of the several relevant device parameters, including the operating temperature and the quantum dot average density, is studied.

A kinetic Monte Carlo model with improved charge injection model for the photocurrent characteristics of organic solar cells

NASA Astrophysics Data System (ADS)

Kipp, Dylan; Ganesan, Venkat

2013-06-01

We develop a kinetic Monte Carlo model for photocurrent generation in organic solar cells that demonstrates improved agreement with experimental illuminated and dark current-voltage curves. In our model, we introduce a charge injection rate prefactor to correct for the electrode grid-size and electrode charge density biases apparent in the coarse-grained approximation of the electrode as a grid of single occupancy, charge-injecting reservoirs. We use the charge injection rate prefactor to control the portion of dark current attributed to each of four kinds of charge injection. By shifting the dark current between electrode-polymer pairs, we align the injection timescales and expand the applicability of the method to accommodate ohmic energy barriers. We consider the device characteristics of the ITO/PEDOT/PSS:PPDI:PBTT:Al system and demonstrate the manner in which our model captures the device charge densities unique to systems with small injection energy barriers. To elucidate the defining characteristics of our model, we first demonstrate the manner in which charge accumulation and band bending affect the shape and placement of the various current-voltage regimes. We then discuss the influence of various model parameters upon the current-voltage characteristics.

Ultra compact 45 GHz CMOS compatible Germanium waveguide photodiode with low dark current.

PubMed

DeRose, Christopher T; Trotter, Douglas C; Zortman, William A; Starbuck, Andrew L; Fisher, Moz; Watts, Michael R; Davids, Paul S

2011-12-05

We present a compact 1.3 × 4 μm2 Germanium waveguide photodiode, integrated in a CMOS compatible silicon photonics process flow. This photodiode has a best-in-class 3 dB cutoff frequency of 45 GHz, responsivity of 0.8 A/W and dark current of 3 nA. The low intrinsic capacitance of this device may enable the elimination of transimpedance amplifiers in future optical data communication receivers, creating ultra low power consumption optical communications.

Could Mars be dark and altered?

USGS Publications Warehouse

Calvin, Wendy M.

1998-01-01

There is a long known dichotomy in the martian albedo, with an associated, but mostly assumed, mineralogical split as well. The bright red regions are inferred to be weathered, oxidized dust and the dark grey regions unaltered volcanic material. A number of recent analyses suggest this division is unnaturally simplistic and the association of many dark regions with the former presence of water requires a re‐examination of the spectra in light of potential alteration minerals. I present an alternate interpretation of the reflectance spectral characteristics of some dark regions on Mars that includes dark layer silicates. If their presence is confirmed on Mars this will have implications for sequestration of current and past volatile inventories, clues to the extent and type of geochemical weathering, and potential zones where bacterial life forms may have emerged.

Significant gamma lines from inert Higgs dark matter.

PubMed

Gustafsson, Michael; Lundström, Erik; Bergström, Lars; Edsjö, Joakim

2007-07-27

One way to unambiguously confirm the existence of particle dark matter and determine its mass would be to detect its annihilation into monochromatic gamma-rays in upcoming telescopes. One of the most minimal models for dark matter is the inert doublet model, obtained by adding another Higgs doublet with no direct coupling to fermions. For a mass between 40 and 80 GeV, the lightest of the new inert Higgs particles can give the correct cosmic abundance of cold dark matter in agreement with current observations. We show that for this scalar dark matter candidate, the annihilation signal of monochromatic gammagamma and Zgamma final states would be exceptionally strong. The energy range and rates for these gamma-ray line signals make them ideal to search for with the soon upcoming GLAST satellite.

Measurements of the reverse current of highly irradiated silicon sensors to determine the effective energy and current related damage rate

NASA Astrophysics Data System (ADS)

Wiehe, Moritz; Wonsak, S.; Kuehn, S.; Parzefall, U.; Casse, G.

2018-01-01

The reverse current of irradiated silicon sensors leads to self heating of the sensor and degrades the signal to noise ratio of a detector. Precise knowledge of the expected reverse current during detector operation is crucial for planning and running experiments in High Energy Physics. The dependence of the reverse current on sensor temperature and irradiation fluence is parametrized by the effective energy and the current related damage rate, respectively. In this study 18 n-in-p mini silicon strip sensors from companies Hamamatsu Photonics and Micron Semiconductor Ltd. were deployed. Measurements of the reverse current for different bias voltages were performed at temperatures of -32 ° C, -27 ° C and -23 ° C. The sensors were irradiated with reactor neutrons in Ljubljana to fluences ranging from 2 × 1014neq /cm2 to 2 × 1016neq /cm2. The measurements were performed directly after irradiation and after 10 and 30 days of room temperature annealing. The aim of the study presented in this paper is to investigate the reverse current of silicon sensors for high fluences of up to 2 × 1016neq /cm2 and compare the measurements to the parametrization models.

Distributed Control of a Swarm of Autonomous Unmanned Aerial Vehicles

DTIC Science & Technology

2003-03-01

wisdom, and love have provided a firm anchor in rough times, and a light in the darkness . “Come to me, all you who are weary and burdened, and I will...time. The light-gray trails represent the area that has been covered in the past 50 timesteps. The dark -gray areas are overlapping areas calculated...during the current timestep. The dark line encloses the total contigu- ous sensor area for this example. Note that while agent 1’s footprint does not

Cosmological Signature of the Standard Model Higgs Vacuum Instability: Primordial Black Holes as Dark Matter.

PubMed

Espinosa, J R; Racco, D; Riotto, A

2018-03-23

For the current central values of the Higgs boson and top quark masses, the standard model Higgs potential develops an instability at a scale of the order of 10^{11}  GeV. We show that a cosmological signature of such instability could be dark matter in the form of primordial black holes seeded by Higgs fluctuations during inflation. The existence of dark matter might not require physics beyond the standard model.

Cold dark matter plus not-so-clumpy dark relics

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

Diamanti, Roberta; Ando, Shin'ichiro; Weniger, Christoph

Various particle physics models suggest that, besides the (nearly) cold dark matter that accounts for current observations, additional but sub-dominant dark relics might exist. These could be warm, hot, or even contribute as dark radiation. We present here a comprehensive study of two-component dark matter scenarios, where the first component is assumed to be cold, and the second is a non-cold thermal relic. Considering the cases where the non-cold dark matter species could be either a fermion or a boson, we derive consistent upper limits on the non-cold dark relic energy density for a very large range of velocity dispersions,more » covering the entire range from dark radiation to cold dark matter. To this end, we employ the latest Planck Cosmic Microwave Background data, the recent BOSS DR11 and other Baryon Acoustic Oscillation measurements, and also constraints on the number of Milky Way satellites, the latter of which provides a measure of the suppression of the matter power spectrum at the smallest scales due to the free-streaming of the non-cold dark matter component. We present the results on the fraction f {sub ncdm} of non-cold dark matter with respect to the total dark matter for different ranges of the non-cold dark matter masses. We find that the 2σ limits for non-cold dark matter particles with masses in the range 1–10 keV are f {sub ncdm}≤0.29 (0.23) for fermions (bosons), and for masses in the 10–100 keV range they are f {sub ncdm}≤0.43 (0.45), respectively.« less

Development of an Electromagnetic Microscope for Eddy Current Evaluation of Materials

DTIC Science & Technology

1991-08-01

headed a laboratory investigating cryogenic detectors for astro-particle physics applications including the search for dark matter candidates and weakly...and L. Stodolsky, Studies of single superconducting grains for a neutrino and dark matter detector, Nucl. Inst. and Meth. A287, 583, 1990. Frank, M

Current-voltage characteristics and increase in the quantum efficiency of three-terminal gate and avalanche-based silicon LEDs.

PubMed

Xu, Kaikai

2013-09-20

In this paper, the emission of visible light by a monolithically integrated silicon p-n junction under reverse-bias is discussed. The modulation of light intensity is achieved using an insulated-gate terminal on the surface of the p-n junction. By varying the gate voltage, the breakdown voltage of the p-n junction will be adjustable so that the reverse current I(sub) flowing through the p-n junction at a fixed reverse-bias voltage is changed. It is observed that the light, which is emitted from the defects located at the p-n junction, depends closely on the reverse current I(sub). In regard to the phenomenon of electroluminescence, the relationship between the optical emission power and the reverse current I(sub) is linear. On the other hand, it is observed that both the quantum efficiency and the power conversion efficiency are able to have obvious enhancement, although the reverse-bias of the p-n junction is reduced and the corresponding reverse-current is much lower. Moreover, the successful fabrication on monolithic silicon light source on the bulk silicon by means of standard silicon complementary metal-oxide-semiconductor process technology is presented.

Tailored Electrospinning of WO₃ Nanobelts as Efficient Ultraviolet Photodetectors with Photo-Dark Current Ratios up to 1000.

PubMed

He, Zhiyang; Liu, Qiao; Hou, Huilin; Gao, Fengmei; Tang, Bin; Yang, Weiyou

2015-05-27

In this work, polycrystalline WO3 nanobelts were fabricated via an electrospinning process combined with subsequent air calcination. The resultant products were characterized by X-ray diffraction, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy in regard to the structures. It has been found that the applied voltage during the electrospinning process played the determined role in the formation of the WO3 nanobelts, allowing the controlled growth of the nanobelts. The ultraviolet (UV) photodetector assembled by an individual WO3 nanobelt exhibits a high sensitivity and a precise selectivity to the different wavelength lights, with a very low dark current and typical photo-dark current ratio up to 1000, which was the highest for any WO3 photodectectors ever reported. This work could not only push forward the facile preparation of WO3 nanobelts but also represent, for the first time, the possibility that the polycrystalline WO3 nanobelts could be a promising building block for the highly efficient UV photodetectors.

Low dark current photovoltaic multiquantum well long wavelength infrared detectors

NASA Technical Reports Server (NTRS)

Wu, C. S.; Wen, Cheng P.; Sato, R. N.; Hu, M.

1990-01-01

The authors have, for the first time, demonstrated photovoltaic detection for an multiple quantum well (MQW) detector. With a blocking layer, the MQW detector exhibits Schottky I-V characteristics with extremely low dark current and excellent ideality factor. The dark current is 5 times 10(exp -14) A for an 100x100 square micron 10 micron detector at 40 K, 8 to 9 orders of magnitude lower than that of a similar 10 micron MQW detector without blocking layer. The ideality factor is about 1.01 to 1.05 at T = 40 to 80 K. The measured barrier height is consistent with the energy difference between first excited states and ground states, or the peak of spectral response. The authors also, for the first time, report the measured effective Richardson constant (A asterisk asterisk) for the GaAs/AlGaAs heterojunction using this blocking layer structure. The A asterisk asterisk is low approx. 2.3 A/sq cm/K(exp 2).

Searching for dark matter with single phase liquid argon

NASA Astrophysics Data System (ADS)

Caldwell, Thomas S., Jr.

The first hint that we fail to understand the nature of a large fraction of the gravitating matter in the universe came from Fritz Zwicky's measurements of the velocity distribution of the Coma cluster in 1933. Using the Virial theorem, Zwicky found that galaxies in the cluster were orbiting far too fast to remain gravitationally bound when their mass was estimated by the brightness of the visible matter. This led to the postulation that some form of non-luminous dark matter is present in galaxies comprising a large fraction of the galactic mass. The nature of this dark matter remains yet unknown over 80 years after Zwicky's measurements despite the efforts of many experiments. Dark matter is widely believed to be a beyond the Standard Model particle which brings the dark matter problem into the realm of particle physics. Supersymmetry is one widely explored extension of the Standard model, from which particles meeting the constraints on dark matter properties can naturally arise. These particles are generically termed weakly interacting massive particles (WIMPs), and are a currently favored dark matter candidate. A variety of experimental efforts are underway aimed towards direct detection of dark matter through observation of rare scattering of WIMPs in terrestrial detectors. Single phase liquid argon detectors are an appealing WIMP detection technique due to the scintillation properties of liquid argon and the scalability of the single phase approach. The MiniCLEAN dark matter detector is a single phase liquid argon scintillation scintillation detector with a 500 kg active mass. The modular design offers 4pi coverage with 92 optical cassettes, each containing TPB coated acrylic and a cryogenic photomultiplier tube. The MiniCLEAN detector has recently completed construction at SNOLAB. The detector is currently being commissioned, and will soon begin operation with the liquid argon target. Utilizing advanced pulse-shape discrimination techniques, MiniCLEAN will probe the WIMP-nucleon cross section parameter space to the level of 10--44 cm2 and demonstrate the pulse-shape discrimination required for next generation experiments capable of further probing the WIMP parameter space in search of WIMP dark matter.

Gravitational collapse of dark energy field configurations and supermassive black hole formation

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

Jhalani, V.; Kharkwal, H.; Singh, A., E-mail: anupamsingh.iitk@gmail.com

Dark energy is the dominant component of the total energy density of our Universe. The primary interaction of dark energy with the rest of the Universe is gravitational. It is therefore important to understand the gravitational dynamics of dark energy. Since dark energy is a low-energy phenomenon from the perspective of particle physics and field theory, a fundamental approach based on fields in curved space should be sufficient to understand the current dynamics of dark energy. Here, we take a field theory approach to dark energy. We discuss the evolution equations for a generic dark energy field in curved space-timemore » and then discuss the gravitational collapse for dark energy field configurations. We describe the 3 + 1 BSSN formalism to study the gravitational collapse of fields for any general potential for the fields and apply this formalism to models of dark energy motivated by particle physics considerations. We solve the resulting equations for the time evolution of field configurations and the dynamics of space-time. Our results show that gravitational collapse of dark energy field configurations occurs and must be considered in any complete picture of our Universe. We also demonstrate the black hole formation as a result of the gravitational collapse of the dark energy field configurations. The black holes produced by the collapse of dark energy fields are in the supermassive black hole category with the masses of these black holes being comparable to the masses of black holes at the centers of galaxies.« less

MCT-Based LWIR and VLWIR 2D Focal Plane Detector Arrays for Low Dark Current Applications at AIM

NASA Astrophysics Data System (ADS)

Hanna, S.; Eich, D.; Mahlein, K.-M.; Fick, W.; Schirmacher, W.; Thöt, R.; Wendler, J.; Figgemeier, H.

2016-09-01

We present our latest results on n-on- p as well as on p-on- n low dark current planar mercury cadmium telluride (MCT) photodiode technology long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) two-dimensional focal plane arrays (FPAs) with quantum efficiency (QE) cut-off wavelength >11 μm at 80 K and a 512 × 640 pixel format FPA at 20 μm pitch stitched from two 512 × 320 pixel photodiode arrays. Significantly reduced dark currents as compared with Tennant's "Rule 07" are demonstrated in both polarities while retaining good detection efficiency ≥60% for operating temperatures between 30 K and 100 K. This allows for the same dark current performance at 20 K higher operating temperature than with previous AIM INFRAROT-MODULE GmbH (AIM) technology. For p-on- n LWIR MCT FPAs, broadband photoresponse nonuniformity of only about 1.2% is achieved at 55 K with low defective pixel numbers. For an n-on- p VLWIR MCT FPA with 13.6 μm cut-off at 55 K, excellent photoresponse nonuniformity of about 3.1% is achieved at moderate defective pixel numbers. This advancement in detector technology paves the way for outstanding signal-to-noise ratio performance infrared detection, enabling cutting-edge next-generation LWIR/VLWIR detectors for space instruments and devices with higher operating temperature and low size, weight, and power for field applications.

Progress of MCT Detector Technology at AIM Towards Smaller Pitch and Lower Dark Current

NASA Astrophysics Data System (ADS)

Eich, D.; Schirmacher, W.; Hanna, S.; Mahlein, K. M.; Fries, P.; Figgemeier, H.

2017-09-01

We present our latest results on cooled p-on- n planar mercury cadmium telluride (MCT) photodiode technology. Along with a reduction in dark current for raising the operating temperature ( T op), AIM INFRAROT-MODULE GmbH (AIM) has devoted its development efforts to shrinking the pixel size. Both are essential requirements to meet the market demands for reduced size, weight and power and high-operating temperature applications. Detectors based on the p-on- n technology developed at AIM now span the spectrum from the mid-wavelength infrared (MWIR) to the very long wavelength infrared (VLWIR) with cut-off wavelengths from 5 μm to about 13.5 μm at 80 K. The development of the p-on- n technology for VLWIR as well as for MWIR is mainly implemented in a planar photodetector design with a 20- μm pixel pitch. For the VLWIR, dark currents significantly reduced as compared to `Tennant's Rule 07' are demonstrated for operating temperatures between 30 K and 100 K. This allows for the same dark current performance at a 20 K higher operating temperature than with previous AIM technology. For MWIR detectors with a 20- μm pitch, noise equivalent temperature differences of less than 30 mK are obtained up to 170 K. This technology has been transferred to our small pixel pitch high resolution (XGA) MWIR detector with 1024 × 768 pixels at a 10- μm pitch. Excellent performance at an operating temperature of 160 K is demonstrated.

Reversing the Course of Forgetting

PubMed Central

White, K. Geoffrey; Brown, Glenn S

2011-01-01

Forgetting functions were generated for pigeons in a delayed matching-to-sample task, in which accuracy decreased with increasing retention-interval duration. In baseline training with dark retention intervals, accuracy was high overall. Illumination of the experimental chamber by a houselight during the retention interval impaired performance accuracy by increasing the rate of forgetting. In novel conditions, the houselight was lit at the beginning of a retention interval and then turned off partway through the retention interval. Accuracy was low at the beginning of the retention interval and then increased later in the interval. Thus the course of forgetting was reversed. Such a dissociation of forgetting from the passage of time is consistent with an interference account in which attention or stimulus control switches between the remembering task and extraneous events. PMID:21909163

Radio for hidden-photon dark matter detection

DOE PAGES

Chaudhuri, Saptarshi; Graham, Peter W.; Irwin, Kent; ...

2015-10-08

We propose a resonant electromagnetic detector to search for hidden-photon dark matter over an extensive range of masses. Hidden-photon dark matter can be described as a weakly coupled “hidden electric field,” oscillating at a frequency fixed by the mass, and able to penetrate any shielding. At low frequencies (compared to the inverse size of the shielding), we find that the observable effect of the hidden photon inside any shielding is a real, oscillating magnetic field. We outline experimental setups designed to search for hidden-photon dark matter, using a tunable, resonant LC circuit designed to couple to this magnetic field. Ourmore » “straw man” setups take into consideration resonator design, readout architecture and noise estimates. At high frequencies, there is an upper limit to the useful size of a single resonator set by 1/ν. However, many resonators may be multiplexed within a hidden-photon coherence length to increase the sensitivity in this regime. Hidden-photon dark matter has an enormous range of possible frequencies, but current experiments search only over a few narrow pieces of that range. As a result, we find the potential sensitivity of our proposal is many orders of magnitude beyond current limits over an extensive range of frequencies, from 100 Hz up to 700 GHz and potentially higher.« less

Search for sterile neutrinos in holographic dark energy cosmology: Reconciling Planck observation with the local measurement of the Hubble constant

NASA Astrophysics Data System (ADS)

Zhao, Ming-Ming; He, Dong-Ze; Zhang, Jing-Fei; Zhang, Xin

2017-08-01

We search for sterile neutrinos in the holographic dark energy cosmology by using the latest observational data. To perform the analysis, we employ the current cosmological observations, including the cosmic microwave background temperature power spectrum data from the Planck mission, the baryon acoustic oscillation measurements, the type Ia supernova data, the redshift space distortion measurements, the shear data of weak lensing observation, the Planck lensing measurement, and the latest direct measurement of H0 as well. We show that, compared to the Λ CDM cosmology, the holographic dark energy cosmology with sterile neutrinos can relieve the tension between the Planck observation and the direct measurement of H0 much better. Once we include the H0 measurement in the global fit, we find that the hint of the existence of sterile neutrinos in the holographic dark energy cosmology can be given. Under the constraint of the all-data combination, we obtain Neff=3.76 ±0.26 and mν,sterile eff<0.215 eV , indicating that the detection of Δ Neff>0 in the holographic dark energy cosmology is at the 2.75 σ level and the massless or very light sterile neutrino is favored by the current observations.

Last electroweak WIMP standing: pseudo-dirac higgsino status and compact stars as future probes

NASA Astrophysics Data System (ADS)

Krall, Rebecca; Reece, Matthew

2018-04-01

Electroweak WIMPs are under intense scrutiny from direct detection, indirect detection, and collider experiments. Nonetheless the pure (pseudo-Dirac) higgsino, one of the simplest such WIMPs, remains elusive. We present an up-to-date assessment of current experimental constraints on neutralino dark matter. The strongest bound on pure higgsino dark matter currently may arise from AMS-02 measurements of antiprotons, though the interpretation of these results has sizable uncertainty. We discuss whether future astrophysical observations could offer novel ways to test higgsino dark matter, especially in the challenging regime with order MeV mass splitting between the two neutral higgsinos. We find that heating of white dwarfs by annihilation of higgsinos captured via inelastic scattering could be one useful probe, although it will require challenging observations of distant dwarf galaxies or a convincing case to be made for substantial dark matter content in ω Cen, a globular cluster that may be a remnant of a disrupted dwarf galaxy. White dwarfs and neutron stars give a target for astronomical observations that could eventually help to close the last, most difficult corner of parameter space for dark matter with weak interactions. Supported by NSF (PHY-1415548) and NASA ATP (NNX16AI12G)

Light-dependent reversion gravitropism of the moss Pohlia nutans

NASA Astrophysics Data System (ADS)

Khorkavtsiv, O.

Plants have evolved highly sensitive mechanisms adapting their growth to the environmental conditions. Light and gravity are critical importance factors, which exerts an essential and specific influence on the determination of the growth direction and regulation of the early stages of plants ontogeny, sometimes effects of these factors being independent. The negative gravitropic resp onse of moss protonemata causes their spatial orientation towards light, which in its turn is the source of photosynthetic efficiency and phototropism. The gravitropism system does not function independently of other sensory response systems in plants. The competence of protonemata to gravity might be altered and the gravitropic response be reversed from negative to positive by light. It has been shown that response of apical cells to light depend on wavelenght: red light (max = 660 nm) represses the gravitropism and blue ( = 450 nm) inverts the protonemal gravitropism. Light, has also been shown for seed plants to modulate gravitropism of roots and stems through the action of phy B in red/far-red reversible way and by phy A in a non-reversible, very - low-fluence response (Hangarter, 1997). In P. nutans blue light reversed the gravitropism protonemal filaments. The mean angle after 24 h blue irradiation was 83 0, like that of negative gravitropic protonemata in darkness. We compared the effect of blue light on gravitropism of chloronemal filaments of Funaria hygrometrica having very low sensitivity to gravity. After action of blue light, however, the positive gravitropism of F. hygrometrica chloronemata was fairly high - 370 . Among blue light spectrum the highest reversion effectiveness in P. nutans had the UV light ( = 350 nm) initiated bends in 90% of protonemata. If a far-red pulse (5 min per h) was added to the blue/UV the gravitropic growth of protonemata resembled that in the dark control. Phytochrome has maxima of absorption in blue and red spectrum region and in our experiments far-red pulse removed the action of the blue/UV light. This indicates to a participation of phytochrome in changing direction of gravitropism. Since red light inhibited the gravitropism it may be suggested that phytochrome is not directly responsible for positive direction of gravitropism. Probably phytochrome only modifies the activity of other receptors or signal systems participating in realization of the gravitropic reaction. Moveover, the competence of apical cells protonemata to grow in opposite directions might be genetically controlled via blue-light - dependent repressor proteins (Lamparter et al., 1998).

Tuning the Colors of the Dark Isomers of Photochromic Boron Compounds with Fluoride Ions: Four-State Color Switching.

PubMed

Mellerup, Soren K; Rao, Ying-Li; Amarne, Hazem; Wang, Suning

2016-09-02

Combining a three-coordinated boron (BMes2) moiety with a four-coordinated photochromic organoboron unit leads to a series of new diboron compounds that undergo four-state reversible color switching in response to stimuli of light, heat, and fluoride ions. Thus, these hybrid diboron systems allow both convenient color tuning/switching of such photochromic systems, as well as visual fluoride sensing by color or fluorescent emission color change.

Sub-MeV bosonic dark matter, misalignment mechanism, and galactic dark matter halo luminosities

NASA Astrophysics Data System (ADS)

Yang, Qiaoli; Di, Haoran

2017-04-01

We explore a scenario that dark matter is a boson condensate created by the misalignment mechanism, in which a spin 0 boson (an axionlike particle) and a spin 1 boson (the dark photon) are considered, respectively. We find that although the sub-MeV dark matter boson is extremely stable, the huge number of dark matter particles in a galaxy halo makes the decaying signal detectable. A galaxy halo is a large structure bounded by gravity with a typical ˜1 012 solar mass, and the majority of its components are made of dark matter. For the axionlike particle case, it decays via ϕ →γ γ , therefore the photon spectrum is monochromatic. For the dark photon case, it is a three body decay A'→γ γ γ . However, we find that the photon spectrum is heavily peaked at M /2 and thus can facilitate observation. We also suggest a physical explanation for the three body decay spectrum by comparing the physics in the decay of orthopositronium. In addition, for both cases, the decaying photon flux can be measured for some regions of parameter space using current technologies.

An ecological approach to problems of Dark Energy, Dark Matter, MOND and Neutrinos

NASA Astrophysics Data System (ADS)

Zhao, Hong Sheng

2008-11-01

Modern astronomical data on galaxy and cosmological scales have revealed powerfully the existence of certain dark sectors of fundamental physics, i.e., existence of particles and fields outside the standard models and inaccessible by current experiments. Various approaches are taken to modify/extend the standard models. Generic theories introduce multiple de-coupled fields A, B, C, each responsible for the effects of DM (cold supersymmetric particles), DE (Dark Energy) effect, and MG (Modified Gravity) effect respectively. Some theories use adopt vanilla combinations like AB, BC, or CA, and assume A, B, C belong to decoupled sectors of physics. MOND-like MG and Cold DM are often taken as antagnising frameworks, e.g. in the muddled debate around the Bullet Cluster. Here we argue that these ad hoc divisions of sectors miss important clues from the data. The data actually suggest that the physics of all dark sectors is likely linked together by a self-interacting oscillating field, which governs a chameleon-like dark fluid, appearing as DM, DE and MG in different settings. It is timely to consider an interdisciplinary approach across all semantic boundaries of dark sectors, treating the dark stress as one identity, hence accounts for several "coincidences" naturally.

Search for right-handed neutrinos from dark matter annihilation with gamma-rays

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

Campos, Miguel D.; Queiroz, Farinaldo S.; Yaguna, Carlos E.

Several extensions of the Standard Model contain right-handed (sterile) neutrinos in the GeV-TeV mass range. Due to their mixing with the active neutrinos, they may give rise to novel effects in cosmology, neutrino physics, and collider searches. In addition, right-handed neutrinos can also appear as final states from dark matter annihilations, with important implications for dark matter indirect detection searches. In this paper, we use current data from the Fermi Large Area Telescope (6-year observation of dwarf spheroidal galaxies) and H.E.S.S. (10-year observation of the Galactic center) to constrain the annihilation of dark matter into right-handed neutrinos. We consider right-handedmore » neutrino with masses between 10 GeV and 1 TeV, including both two-body and three-body decays, to derive bounds on the dark matter annihilation rate, ( σ v ), as a function of the dark matter mass. Our results show, in particular, that the thermal dark matter annihilation cross section, 3× 10{sup −26} cm{sup 3} s {sup −1} , into right-handed neutrinos is excluded for dark matter masses smaller than 200 GeV.« less

Non-thermal production of minimal dark matter via right-handed neutrino decay

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

Aoki, Mayumi; Toma, Takashi; Vicente, Avelino

2015-09-29

Minimal Dark Matter (MDM) stands as one of the simplest dark matter scenarios. In MDM models, annihilation and co-annihilation processes among the members of the MDM multiplet are usually very efficient, pushing the dark matter mass above O(10) TeV in order to reproduce the observed dark matter relic density. Motivated by this little drawback, in this paper we consider an extension of the MDM scenario by three right-handed neutrinos. Two specific choices for the MDM multiplet are studied: a fermionic SU(2){sub L} quintuplet and a scalar SU(2){sub L} septuplet. The lightest right-handed neutrino, with tiny Yukawa couplings, never reaches thermalmore » equilibrium in the early universe and is produced by freeze-in. This creates a link between dark matter and neutrino physics: dark matter can be non-thermally produced by the decay of the lightest right-handed neutrino after freeze-out, allowing to lower significantly the dark matter mass. We discuss the phenomenology of the non-thermally produced MDM and, taking into account significant Sommerfeld corrections, we find that the dark matter mass must have some specific values in order not to be in conflict with the current bounds from gamma-ray observations.« less

Non-thermal production of minimal dark matter via right-handed neutrino decay

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

Aoki, Mayumi; Toma, Takashi; Vicente, Avelino, E-mail: mayumi@hep.s.kanazawa-u.ac.jp, E-mail: takashi.toma@th.u-psud.fr, E-mail: Avelino.Vicente@ulg.ac.be

2015-09-01

Minimal Dark Matter (MDM) stands as one of the simplest dark matter scenarios. In MDM models, annihilation and co-annihilation processes among the members of the MDM multiplet are usually very efficient, pushing the dark matter mass above O(10) TeV in order to reproduce the observed dark matter relic density. Motivated by this little drawback, in this paper we consider an extension of the MDM scenario by three right-handed neutrinos. Two specific choices for the MDM multiplet are studied: a fermionic SU(2){sub L} quintuplet and a scalar SU(2){sub L} septuplet. The lightest right-handed neutrino, with tiny Yukawa couplings, never reaches thermalmore » equilibrium in the early universe and is produced by freeze-in. This creates a link between dark matter and neutrino physics: dark matter can be non-thermally produced by the decay of the lightest right-handed neutrino after freeze-out, allowing to lower significantly the dark matter mass. We discuss the phenomenology of the non-thermally produced MDM and, taking into account significant Sommerfeld corrections, we find that the dark matter mass must have some specific values in order not to be in conflict with the current bounds from gamma-ray observations.« less

Searching for light dark matter with the SLAC millicharge experiment.

PubMed

Diamond, M; Schuster, P

2013-11-27

New sub-GeV gauge forces ("dark photons") that kinetically mix with the photon provide a promising scenario for MeV-GeV dark matter and are the subject of a program of searches at fixed-target and collider facilities around the world. In such models, dark photons produced in collisions may decay invisibly into dark-matter states, thereby evading current searches. We reexamine results of the SLAC mQ electron beam dump experiment designed to search for millicharged particles and find that it was strongly sensitive to any secondary beam of dark matter produced by electron-nucleus collisions in the target. The constraints are competitive for dark photon masses in the ~1-30 MeV range, covering part of the parameter space that can reconcile the apparent (g-2)(μ) anomaly. Simple adjustments to the original SLAC search for millicharges may extend sensitivity to cover a sizable portion of the remaining (g-2)(μ) anomaly-motivated region. The mQ sensitivity is therefore complementary to ongoing searches for visible decays of dark photons. Compared to existing direct-detection searches, mQ sensitivity to electron-dark-matter scattering cross sections is more than an order of magnitude better for a significant range of masses and couplings in simple models.

Dark stars: a review.

PubMed

Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

2016-06-01

Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >[Formula: see text] and luminosities  >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

Dark stars: a review

NASA Astrophysics Data System (ADS)

Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

2016-06-01

Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only ≲ 0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (˜10 AU) and cool (surface temperatures  ˜10 000 K) objects. We follow the evolution of dark stars from their inception at  ˜1{{M}⊙} as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >{{10}6}{{M}⊙} and luminosities  >{{10}10}{{L}⊙} , making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

DARKNESS: A Microwave Kinetic Inductance Detector Integral Field Spectrograph for High-contrast Astronomy

NASA Astrophysics Data System (ADS)

Meeker, Seth R.; Mazin, Benjamin A.; Walter, Alex B.; Strader, Paschal; Fruitwala, Neelay; Bockstiegel, Clint; Szypryt, Paul; Ulbricht, Gerhard; Coiffard, Grégoire; Bumble, Bruce; Cancelo, Gustavo; Zmuda, Ted; Treptow, Ken; Wilcer, Neal; Collura, Giulia; Dodkins, Rupert; Lipartito, Isabel; Zobrist, Nicholas; Bottom, Michael; Shelton, J. Chris; Mawet, Dimitri; van Eyken, Julian C.; Vasisht, Gautam; Serabyn, Eugene

2018-06-01

We present DARKNESS (the DARK-speckle Near-infrared Energy-resolving Superconducting Spectrophotometer), the first of several planned integral field spectrographs to use optical/near-infrared Microwave Kinetic Inductance Detectors (MKIDs) for high-contrast imaging. The photon counting and simultaneous low-resolution spectroscopy provided by MKIDs will enable real-time speckle control techniques and post-processing speckle suppression at frame rates capable of resolving the atmospheric speckles that currently limit high-contrast imaging from the ground. DARKNESS is now operational behind the PALM-3000 extreme adaptive optics system and the Stellar Double Coronagraph at Palomar Observatory. Here, we describe the motivation, design, and characterization of the instrument, early on-sky results, and future prospects.

Testing for Dark Matter Trapped in the Solar System

NASA Technical Reports Server (NTRS)

Krisher, Timothy P.

1996-01-01

We consider the possibility of dark matter trapped in the solar system in bound solar orbits. If there exist mechanisms for dissipating excess kinetic energy by an amount sufficient for generating bound solar orbits, then trapping of galactic dark matter might have taken place during formation of the solar system, or could be an ongoing process. Possible locations for acumulation of trapped dark matter are orbital resonances with the planets or regions in the outer solar system. It is posible to test for the presence of unseen matter by detecting its gravitational effects. Current results for dynamical limits obtained from analyses of planetary ephemeris data and spacecraft tracking data are presented. Possible future improvements are discussed.

Light-regulated phosphorylation of maize phosphoenolpyruvate carboxykinase plays a vital role in its activity.

PubMed

Chao, Qing; Liu, Xiao-Yu; Mei, Ying-Chang; Gao, Zhi-Fang; Chen, Yi-Bo; Qian, Chun-Rong; Hao, Yu-Bo; Wang, Bai-Chen

2014-05-01

Phosphoenolpyruvate carboxykinase (PEPCK)-the major decarboxylase in PEPCK-type C4 plants-is also present in appreciable amounts in the bundle sheath cells of NADP-malic enzyme-type C4 plants, such as maize (Zea mays), where it plays an apparent crucial role during photosynthesis (Wingler et al., in Plant Physiol 120(2):539-546, 1999; Furumoto et al., in Plant Mol Biol 41(3):301-311, 1999). Herein, we describe the use of mass spectrometry to demonstrate phosphorylation of maize PEPCK residues Ser55, Thr58, Thr59, and Thr120. Western blotting indicated that the extent of Ser55 phosphorylation dramatically increases in the leaves of maize seedlings when the seedlings are transferred from darkness to light, and decreases in the leaves of seedlings transferred from light to darkness. The effect of light on phosphorylation of this residue is opposite that of the effect of light on PEPCK activity, with the decarboxylase activity of PEPCK being less in illuminated leaves than in leaves left in the dark. This inverse relationship between PEPCK activity and the extent of phosphorylation suggests that the suppressive effect of light on PEPCK decarboxylation activity might be mediated by reversible phosphorylation of Ser55.

Suppressing the Neurospora crassa circadian clock while maintaining light responsiveness in continuous stirred tank reactors

PubMed Central

Cockrell, Allison L.; Pirlo, Russell K.; Babson, David M.; Cusick, Kathleen D.; Soto, Carissa M.; Petersen, Emily R.; Davis, Miah J.; Hong, Christian I.; Lee, Kwangwon; Fitzgerald, Lisa A.; Biffinger, Justin C.

2015-01-01

Neurospora crassa has been utilized as a model organism for studying biological, regulatory, and circadian rhythms for over 50 years. These circadian cycles are driven at the molecular level by gene transcription events to prepare for environmental changes. N. crassa is typically found on woody biomass and is commonly studied on agar-containing medium which mimics its natural environment. We report a novel method for disrupting circadian gene transcription while maintaining light responsiveness in N. crassa when held in a steady metabolic state using bioreactors. The arrhythmic transcription of core circadian genes and downstream clock-controlled genes was observed in constant darkness (DD) as determined by reverse transcription-quantitative PCR (RT-qPCR). Nearly all core circadian clock genes were up-regulated upon exposure to light during 11hr light/dark cycle experiments under identical conditions. Our results demonstrate that the natural timing of the robust circadian clock in N. crassa can be disrupted in the dark when maintained in a consistent metabolic state. Thus, these data lead to a path for the production of industrial scale enzymes in the model system, N. crassa, by removing the endogenous negative feedback regulation by the circadian oscillator. PMID:26031221

Dark Higgs bosons at the ForwArd Search ExpeRiment

NASA Astrophysics Data System (ADS)

Feng, Jonathan L.; Galon, Iftah; Kling, Felix; Trojanowski, Sebastian

2018-03-01

FASER, ForwArd Search ExpeRiment at the LHC, has been proposed as a small, very far forward detector to discover new, light, weakly-coupled particles. Previous work showed that with a total volume of just ˜0.1 - 1 m3 , FASER can discover dark photons in a large swath of currently unconstrained parameter space, extending the discovery reach of the LHC program. Here we explore FASER's discovery prospects for dark Higgs bosons. These scalar particles are an interesting foil for dark photons, as they probe a different renormalizable portal interaction and are produced dominantly through B and K meson decays, rather than pion decays, leading to less collimated signals. Nevertheless, we find that FASER is also a highly sensitive probe of dark Higgs bosons with significant discovery prospects that are comparable to, and complementary to, much larger proposed experiments.

Probing sub-GeV dark matter-baryon scattering with cosmological observables

NASA Astrophysics Data System (ADS)

Xu, Weishuang Linda; Dvorkin, Cora; Chael, Andrew

2018-05-01

We derive new limits on the elastic scattering cross section between baryons and dark matter using cosmic microwave background data from the Planck satellite and measurements of the Lyman-alpha forest flux power spectrum from the Sloan Digital Sky Survey. Our analysis addresses generic cross sections of the form σ ∝vn , where v is the dark matter-baryon relative velocity, allowing for constraints on the cross section independent of specific particle physics models. We include high-ℓ polarization data from Planck in our analysis, improving over previous constraints. We apply a more careful treatment of dark matter thermal evolution than previously done, allowing us to extend our constraints down to dark matter masses of ˜MeV . We show in this work that cosmological probes are complementary to current direct detection and astrophysical searches.

Enlightening Students about Dark Matter

NASA Astrophysics Data System (ADS)

Hamilton, Kathleen; Barr, Alex; Eidelman, Dave

2018-01-01

Dark matter pervades the universe. While it is invisible to us, we can detect its influence on matter we can see. To illuminate this concept, we have created an interactive javascript program illustrating predictions made by six different models for dark matter distributions in galaxies. Students are able to match the predicted data with actual experimental results, drawn from several astronomy papers discussing dark matter’s impact on galactic rotation curves. Programming each new model requires integration of density equations with parameters determined by nonlinear curve-fitting using MATLAB scripts we developed. Using our javascript simulation, students can determine the most plausible dark matter models as well as the average percentage of dark matter lurking in galaxies, areas where the scientific community is still continuing to research. In that light, we strive to use the most up-to-date and accepted concepts: two of our dark matter models are the pseudo-isothermal halo and Navarro-Frenk-White, and we integrate out to each galaxy’s virial radius. Currently, our simulation includes NGC3198, NGC2403, and our own Milky Way.

Ricci-Gauss-Bonnet holographic dark energy

NASA Astrophysics Data System (ADS)

Saridakis, Emmanuel N.

2018-03-01

We present a model of holographic dark energy in which the infrared cutoff is determined by both the Ricci and the Gauss-Bonnet invariants. Such a construction has the significant advantage that the infrared cutoff, and consequently the holographic dark energy density, does not depend on the future or the past evolution of the universe, but only on its current features, and moreover it is determined by invariants, whose role is fundamental in gravitational theories. We extract analytical solutions for the behavior of the dark energy density and equation-of-state parameters as functions of the redshift. These reveal the usual thermal history of the universe, with the sequence of radiation, matter and dark energy epochs, resulting in the future to a complete dark energy domination. The corresponding dark energy equation-of-state parameter can lie in the quintessence or phantom regime, or experience the phantom-divide crossing during the cosmological evolution, and its asymptotic value can be quintessencelike, phantomlike, or be exactly equal to the cosmological-constant value. Finally, we extract the constraints on the model parameters that arise from big bang nucleosynthesis.

Can tonne-scale direct detection experiments discover nuclear dark matter?

NASA Astrophysics Data System (ADS)

Butcher, Alistair; Kirk, Russell; Monroe, Jocelyn; West, Stephen M.

2017-10-01

Models of nuclear dark matter propose that the dark sector contains large composite states consisting of dark nucleons in analogy to Standard Model nuclei. We examine the direct detection phenomenology of a particular class of nuclear dark matter model at the current generation of tonne-scale liquid noble experiments, in particular DEAP-3600 and XENON1T. In our chosen nuclear dark matter scenario distinctive features arise in the recoil energy spectra due to the non-point-like nature of the composite dark matter state. We calculate the number of events required to distinguish these spectra from those of a standard point-like WIMP state with a decaying exponential recoil spectrum. In the most favourable regions of nuclear dark matter parameter space, we find that a few tens of events are needed to distinguish nuclear dark matter from WIMPs at the 3 σ level in a single experiment. Given the total exposure time of DEAP-3600 and XENON1T we find that at best a 2 σ distinction is possible by these experiments individually, while 3 σ sensitivity is reached for a range of parameters by the combination of the two experiments. We show that future upgrades of these experiments have potential to distinguish a large range of nuclear dark matter models from that of a WIMP at greater than 3 σ.

Can tonne-scale direct detection experiments discover nuclear dark matter?

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

Butcher, Alistair; Kirk, Russell; Monroe, Jocelyn

Models of nuclear dark matter propose that the dark sector contains large composite states consisting of dark nucleons in analogy to Standard Model nuclei. We examine the direct detection phenomenology of a particular class of nuclear dark matter model at the current generation of tonne-scale liquid noble experiments, in particular DEAP-3600 and XENON1T. In our chosen nuclear dark matter scenario distinctive features arise in the recoil energy spectra due to the non-point-like nature of the composite dark matter state. We calculate the number of events required to distinguish these spectra from those of a standard point-like WIMP state with amore » decaying exponential recoil spectrum. In the most favourable regions of nuclear dark matter parameter space, we find that a few tens of events are needed to distinguish nuclear dark matter from WIMPs at the 3 σ level in a single experiment. Given the total exposure time of DEAP-3600 and XENON1T we find that at best a 2 σ distinction is possible by these experiments individually, while 3 σ sensitivity is reached for a range of parameters by the combination of the two experiments. We show that future upgrades of these experiments have potential to distinguish a large range of nuclear dark matter models from that of a WIMP at greater than 3 σ .« less

Organic semiconductor photodiode based on indigo carmine/n-Si for optoelectronic applications

NASA Astrophysics Data System (ADS)

Ganesh, V.; Manthrammel, M. Aslam; Shkir, Mohd.; Yahia, I. S.; Zahran, H. Y.; Yakuphanoglu, F.; AlFaify, S.

2018-06-01

The fabrication of indigo carmine/n-Si photodiode has been done, and a robust dark and photocurrent-voltage ( I- V), capacitance vs. voltage ( C-V) and conductance vs. voltage ( G-V) studies were done over a wide range of applied voltage and frequencies. The surface morphology was assessed by atomic force microscope (AFM), and the grain size was measured to be about 66 nm. The reverse current increased with both increasing illumination intensity and bias potential, whereas the forward current increased exponentially with bias potential. The responsivity value was also calculated. Barrier height and ideality factor of diode were estimated through a log (I) vs log (V) plot, and obtained to be 0.843 and 4.75 eV, respectively. The Vbi values are found between 0.95 and 1.2V for frequencies ranging between 100 kHz and 1 MHz. The value of R s is found to be lower at higher frequencies which may be due to a certain distribution of localized interface states. A strong frequency and voltage dependency were observed for interface states density N ss in the present indigo carmine/n-Si photodiode, and this explained the observed capacitance and resistance variation with frequency. These results suggest that the fabricated diode has the potential to be applied in optoelectronic devices.

Ultrafast traveling wave dominates the electric organ discharge of Apteronotus leptorhynchus: an inverse modelling study.

PubMed

Shifman, Aaron R; Longtin, André; Lewis, John E

2015-10-30

Identifying and understanding the current sources that give rise to bioelectric fields is a fundamental problem in the biological sciences. It is very difficult, for example, to attribute the time-varying features of an electroencephalogram recorded from the head surface to the neural activity of specific brain areas; model systems can provide important insight into such problems. Some species of fish actively generate an oscillating (c. 1000 Hz) quasi-dipole electric field to communicate and sense their environment in the dark. A specialized electric organ comprises neuron-like cells whose collective signal underlies this electric field. As a step towards understanding the detailed biophysics of signal generation in these fish, we use an anatomically-detailed finite-element modelling approach to reverse-engineer the electric organ signal over one oscillation cycle. We find that the spatiotemporal profile of current along the electric organ constitutes a travelling wave that is well-described by two spatial Fourier components varying in time. The conduction velocity of this wave is faster than action potential conduction in any known neuronal axon (>200 m/s), suggesting that the spatiotemporal features of high-frequency electric organ discharges are not constrained by the conduction velocities of spinal neuron pathways.

Ultrafast traveling wave dominates the electric organ discharge of Apteronotus leptorhynchus: an inverse modelling study

PubMed Central

Shifman, Aaron R.; Longtin, André; Lewis, John E.

2015-01-01

Identifying and understanding the current sources that give rise to bioelectric fields is a fundamental problem in the biological sciences. It is very difficult, for example, to attribute the time-varying features of an electroencephalogram recorded from the head surface to the neural activity of specific brain areas; model systems can provide important insight into such problems. Some species of fish actively generate an oscillating (c. 1000 Hz) quasi-dipole electric field to communicate and sense their environment in the dark. A specialized electric organ comprises neuron-like cells whose collective signal underlies this electric field. As a step towards understanding the detailed biophysics of signal generation in these fish, we use an anatomically-detailed finite-element modelling approach to reverse-engineer the electric organ signal over one oscillation cycle. We find that the spatiotemporal profile of current along the electric organ constitutes a travelling wave that is well-described by two spatial Fourier components varying in time. The conduction velocity of this wave is faster than action potential conduction in any known neuronal axon (>200 m/s), suggesting that the spatiotemporal features of high-frequency electric organ discharges are not constrained by the conduction velocities of spinal neuron pathways. PMID:26514932

Thin-Film Quantum Dot Photodiode for Monolithic Infrared Image Sensors †

PubMed Central

Georgitzikis, Epimitheas; Vamvaka, Ioanna; Frazzica, Fortunato; Van Olmen, Jan; De Moor, Piet; Heremans, Paul; Hens, Zeger; Cheyns, David

2017-01-01

Imaging in the infrared wavelength range has been fundamental in scientific, military and surveillance applications. Currently, it is a crucial enabler of new industries such as autonomous mobility (for obstacle detection), augmented reality (for eye tracking) and biometrics. Ubiquitous deployment of infrared cameras (on a scale similar to visible cameras) is however prevented by high manufacturing cost and low resolution related to the need of using image sensors based on flip-chip hybridization. One way to enable monolithic integration is by replacing expensive, small-scale III–V-based detector chips with narrow bandgap thin-films compatible with 8- and 12-inch full-wafer processing. This work describes a CMOS-compatible pixel stack based on lead sulfide quantum dots (PbS QD) with tunable absorption peak. Photodiode with a 150-nm thick absorber in an inverted architecture shows dark current of 10−6 A/cm2 at −2 V reverse bias and EQE above 20% at 1440 nm wavelength. Optical modeling for top illumination architecture can improve the contact transparency to 70%. Additional cooling (193 K) can improve the sensitivity to 60 dB. This stack can be integrated on a CMOS ROIC, enabling order-of-magnitude cost reduction for infrared sensors. PMID:29232871

Constraints on supersymmetric dark matter for heavy scalar superpartners

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

Huang, Peisi; Roglans, Roger A.; Spiegel, Daniel D.

2017-05-01

We study the constraints on neutralino dark matter in minimal low energy supersymmetry models and the case of heavy lepton and quark scalar superpartners. For values of the Higgsino and gaugino mass parameters of the order of the weak scale, direct detection experiments are already putting strong bounds on models in which the dominant interactions between the dark matter candidates and nuclei are governed by Higgs boson exchange processes, particularly for positive values of the Higgsino mass parameter mu. For negative values of mu, there can be destructive interference between the amplitudes associated with the exchange of the standard CP-evenmore » Higgs boson and the exchange of the nonstandard one. This leads to specific regions of parameter space which are consistent with the current experimental constraints and a thermal origin of the observed relic density. In this article, we study the current experimental constraints on these scenarios, as well as the future experimental probes, using a combination of direct and indirect dark matter detection and heavy Higgs and electroweakino searches at hadron colliders« less

Dark energy and equivalence principle constraints from astrophysical tests of the stability of the fine-structure constant

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

Martins, C.J.A.P.; Pinho, A.M.M.; Alves, R.F.C.

2015-08-01

Astrophysical tests of the stability of fundamental couplings, such as the fine-structure constant α, are becoming an increasingly powerful probe of new physics. Here we discuss how these measurements, combined with local atomic clock tests and Type Ia supernova and Hubble parameter data, constrain the simplest class of dynamical dark energy models where the same degree of freedom is assumed to provide both the dark energy and (through a dimensionless coupling, ζ, to the electromagnetic sector) the α variation. Specifically, current data tightly constrains a combination of ζ and the present dark energy equation of state w{sub 0}. Moreover, inmore » these models the new degree of freedom inevitably couples to nucleons (through the α dependence of their masses) and leads to violations of the Weak Equivalence Principle. We obtain indirect bounds on the Eötvös parameter η that are typically stronger than the current direct ones. We discuss the model-dependence of our results and briefly comment on how the forthcoming generation of high-resolution ultra-stable spectrographs will enable significantly tighter constraints.« less

Photoswitchable non-fluorescent thermochromic dye-nanoparticle hybrid probes.

PubMed

Harrington, Walter N; Haji, Mwafaq R; Galanzha, Ekaterina I; Nedosekin, Dmitry A; Nima, Zeid A; Watanabe, Fumiya; Ghosh, Anindya; Biris, Alexandru S; Zharov, Vladimir P

2016-11-08

Photoswitchable fluorescent proteins with controllable light-dark states and spectral shifts in emission in response to light have led to breakthroughs in the study of cell biology. Nevertheless, conventional photoswitching is not applicable for weakly fluorescent proteins and requires UV light with low depth penetration in bio-tissue. Here we introduce a novel concept of photoswitchable hybrid probes consisting of thermochromic dye and absorbing nanoparticles, in which temperature-sensitive light-dark states and spectral shifts in absorption can be switched through controllable photothermal heating of doped nanoparticles. The proof-of-concept is demonstrated through the use of two different types of temperature-sensitive dyes doped with magnetic nanoparticles and reversibly photoswitched by a near-infrared laser. Photoacoustic imaging revealed the high contrast of these probes, which is sufficient for their visualization in cells and deep tissue. Our results suggest that these new photoswitchable multicolour probes can be used for multimodal cellular diagnostics and potentially for magnetic and photothermal therapy.

Indications for chlororespiration in relation to light regime in the marine diatom Thalassiosira weissflogii.

PubMed

Dijkman, Nicole A; Kroon, Bernd M A

2002-04-01

The marine diatom Thalassiosira weissflogii was cultured under a light regime simulating the daily rise and fall of the sun. The light regime caused a daily cycle in non-photochemical quenching. Remarkable were the changes in fluorescence directly after a light-to-dark transition that occurred in addition to the changes induced by non-photochemical quenching. A transient non-photochemical reduction of PQ and of Q(A) was indicated by a transient increase in apparent F(o) and by changes in the shape of the fluorescence induction curve. The observed changes developed approximately the first 100-120 s after a light-to-dark transition and could be reversed by the application of far-red illumination. Chlororespiration is thought to cause the reduction of PQ and, as the PQ-pool is in equilibrium with Q(A), also a reduction of Q(A). The function and ecological relevance of chlororespiration are discussed.

Photoswitchable non-fluorescent thermochromic dye-nanoparticle hybrid probes

NASA Astrophysics Data System (ADS)

Harrington, Walter N.; Haji, Mwafaq R.; Galanzha, Ekaterina I.; Nedosekin, Dmitry A.; Nima, Zeid A.; Watanabe, Fumiya; Ghosh, Anindya; Biris, Alexandru S.; Zharov, Vladimir P.

2016-11-01

Photoswitchable fluorescent proteins with controllable light-dark states and spectral shifts in emission in response to light have led to breakthroughs in the study of cell biology. Nevertheless, conventional photoswitching is not applicable for weakly fluorescent proteins and requires UV light with low depth penetration in bio-tissue. Here we introduce a novel concept of photoswitchable hybrid probes consisting of thermochromic dye and absorbing nanoparticles, in which temperature-sensitive light-dark states and spectral shifts in absorption can be switched through controllable photothermal heating of doped nanoparticles. The proof-of-concept is demonstrated through the use of two different types of temperature-sensitive dyes doped with magnetic nanoparticles and reversibly photoswitched by a near-infrared laser. Photoacoustic imaging revealed the high contrast of these probes, which is sufficient for their visualization in cells and deep tissue. Our results suggest that these new photoswitchable multicolour probes can be used for multimodal cellular diagnostics and potentially for magnetic and photothermal therapy.

Molecular reorientation in assembled CO structures and contrast inversion in STM

NASA Astrophysics Data System (ADS)

Niemi, Eeva; Nieminen, Jouko

2004-10-01

Recent scanning tunneling microscopy experiments [S. Zöphel, J. Repp, G. Meyer, K.-H. Rieder, Chem. Phys. Lett. 310 (1999) 145; A.J. Heinrich, C.P. Lutz, J.A. Gupta, D.M. Eigler, Science 298 (2002) 1381] for CO on Cu(1 1 1) and Cu(2 1 1) surfaces show CO monomers as dark depressions, whereas dimers and trimers appear as bright patterns. The dark image of a monomer has been shown to result from a destructive interference between two tunneling paths [J. Nieminen, E. Niemi, K.-H. Rieder, Surf. Sci. 552 (2004) L47]. In this Letter, we show how switching between tunneling channels within the through molecule path can be induced by reorientation of a molecule. Hence, a destructive interference between through vacuum and through molecule paths can be reversed into constructive interference by manipulating the adsorbate geometry.

Dark energy from the motions of neutrinos

NASA Astrophysics Data System (ADS)

Simpson, Fergus; Jimenez, Raul; Pena-Garay, Carlos; Verde, Licia

2018-06-01

Ordinarily, a scalar field may only play the role of dark energy if it possesses a potential that is either extraordinarily flat or extremely fine-tuned. Here we demonstrate that these restrictions are lifted when the scalar field undergoes persistent energy exchange with another fluid. In this scenario, the field is prevented from reversing its direction of motion, and instead may come to rest while displaced from the local minimum of its potential. Therefore almost any scalar potential is capable of initiating a prolonged phase of cosmic acceleration. If the rate of energy transfer is modulated via a derivative coupling, the field undergoes a rapid process of freezing, after which the field's equation of state mimicks that of a cosmological constant. We present a physically motivated realisation in the form of a neutrino-majoron coupling, which avoids the dynamical instabilities associated with mass-varying neutrino models. Finally we discuss possible means by which this model could be experimentally verified.

Dark Energy and Dark Matter from Emergent Gravity Picture

NASA Astrophysics Data System (ADS)

Seok Yang, Hyun

2018-01-01

We suggest that dark energy and dark matter may be a cosmic uroboros of quantum gravity due to the coherent vacuum structure of spacetime. We apply the emergent gravity to a large N matrix model by considering the vacuum in the noncommutative (NC) Coulomb branch satisfying the Heisenberg algebra. We observe that UV fluctuations in the NC Coulomb branch are always paired with IR fluctuations and these UV/IR fluctuations can be extended to macroscopic scales. We show that space-like fluctuations give rise to the repulsive gravitational force while time-like fluctuations generate the attractive gravitational force. When considering the fact that the fluctuations are random in nature and we are living in the (3+1)-dimensional spacetime, the ratio of the repulsive and attractive components will end in ¾ : ¼= 75 : 25 and this ratio curiously coincides with the dark composition of our current Universe. If one includes ordinary matters which act as the attractive gravitational force, the emergent gravity may explain the dark sector of our Universe more precisely.

Connecting dark matter annihilation to the vertex functions of Standard Model fermions

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

Kumar, Jason; Light, Christopher, E-mail: jkumar@hawaii.edu, E-mail: lightc@hawaii.edu

We consider scenarios in which dark matter is a Majorana fermion which couples to Standard Model fermions through the exchange of charged mediating particles. The matrix elements for various dark matter annihilation processes are then related to one-loop corrections to the fermion-photon vertex, where dark matter and the charged mediators run in the loop. In particular, in the limit where Standard Model fermion helicity mixing is suppressed, the cross section for dark matter annihilation to various final states is related to corrections to the Standard Model fermion charge form factor. These corrections can be extracted in a gauge-invariant manner frommore » collider cross sections. Although current measurements from colliders are not precise enough to provide useful constraints on dark matter annihilation, improved measurements at future experiments, such as the International Linear Collider, could improve these constraints by several orders of magnitude, allowing them to surpass the limits obtainable by direct observation.« less

Ultra Light Axionic Dark Matter: Galactic Halos and Implications for Observations with Pulsar Timing Arrays

NASA Astrophysics Data System (ADS)

de Martino, Ivan; Broadhurst, Tom; Tye, S.-H. Henry; Chiueh, Tzihong; Shive, Hsi-Yu; Lazkoz, Ruth

2018-01-01

The cold dark matter (CDM) paradigm successfully explains the cosmic structure over an enormous span of redshifts. However, it fails when probing the innermost regions of dark matter halos and the properties of the Milky Way's dwarf galaxy satellites. Moreover, the lack of experimental detection of Weakly Interacting Massive Particle (WIMP) favors alternative candidates such as light axionic dark matter that naturally arise in string theory. Cosmological N-body simulations have shown that axionic dark matter forms a solitonic core of size of ≃ 150 pc in the innermost region of the galactic halos. The oscillating scalar field associated to the axionic dark matter halo produces an oscillating gravitational potential that induces a time dilation of the pulse arrival time of ≃ 400 ns/(m_B/10^{-22} eV) for pulsar within such a solitonic core. Over the whole galaxy, the averaged predicted signal may be detectable with current and forthcoming pulsar timing array telescopes.

Search for domain wall dark matter with atomic clocks on board global positioning system satellites.

PubMed

Roberts, Benjamin M; Blewitt, Geoffrey; Dailey, Conner; Murphy, Mac; Pospelov, Maxim; Rollings, Alex; Sherman, Jeff; Williams, Wyatt; Derevianko, Andrei

2017-10-30

Cosmological observations indicate that dark matter makes up 85% of all matter in the universe yet its microscopic composition remains a mystery. Dark matter could arise from ultralight quantum fields that form macroscopic objects. Here we use the global positioning system as a ~ 50,000 km aperture dark matter detector to search for such objects in the form of domain walls. Global positioning system navigation relies on precision timing signals furnished by atomic clocks. As the Earth moves through the galactic dark matter halo, interactions with domain walls could cause a sequence of atomic clock perturbations that propagate through the satellite constellation at galactic velocities ~ 300 km s -1 . Mining 16 years of archival data, we find no evidence for domain walls at our current sensitivity level. This improves the limits on certain quadratic scalar couplings of domain wall dark matter to standard model particles by several orders of magnitude.

Narrowband ultraviolet photodetector based on MgZnO and NPB heterojunction.

PubMed

Hu, Zuofu; Li, Zhenjun; Zhu, Lu; Liu, Fengjuan; Lv, Yanwu; Zhang, Xiqing; Wang, Yongsheng

2012-08-01

An ultraviolet photodetector was fabricated based on Mg0.07Zn0.93O heterojunction. N, N'-bis (naphthalen-1-y1)-N, N'-bis(pheny) benzidine was selected as the hole transporting layer. I-V characteristic curves of the device were measured in the dark and under the illumination of 340 nm UV light with density of 1.33 mW/cm2. The device showed a low dark current of about 3×10(-10) A and a high photo-dark current ratio of 1×10(5) at -2 V bias. A narrowband photoresponse was observed from 300 to 400 nm and centered at 340 nm with a full width at half-maximum of only 30 nm. The maximum peak response is at 340 nm, which is 0.192 A/W at the bias of -1 V.

Dark Energy from Discrete Spacetime

PubMed Central

Trout, Aaron D.

2013-01-01

Dark energy accounts for most of the matter-energy content of our universe, yet current theories of its origin rely on radical physical assumptions such as the holographic principle or controversial anthropic arguments. We give a better motivated explanation for dark energy, claiming that it arises from a small negative scalar-curvature present even in empty spacetime. The vacuum has this curvature because spacetime is fundamentally discrete and there are more ways for a discrete geometry to have negative curvature than positive. We explicitly compute this effect using a variant of the well known dynamical-triangulations (DT) model for quantum gravity. Our model predicts a time-varying non-zero cosmological constant with a current value, in natural units, in agreement with observation. This calculation is made possible by a novel characterization of the possible DT action values combined with numerical evidence concerning their degeneracies. PMID:24312502

Dim nighttime illumination interacts with parametric effects of bright light to increase the stability of circadian rhythm bifurcation in hamsters.

PubMed

Evans, Jennifer A; Elliott, Jeffrey A; Gorman, Michael R

2011-07-01

The endogenous circadian pacemaker of mammals is synchronized to the environmental day by the ambient cycle of relative light and dark. The present studies assessed the actions of light in a novel circadian entrainment paradigm where activity rhythms are bifurcated following exposure to a 24-h light:dark:light:dark (LDLD) cycle. Bifurcated entrainment under LDLD reflects the temporal dissociation of component oscillators that comprise the circadian system and is facilitated when daily scotophases are dimly lit rather than completely dark. Although bifurcation can be stably maintained in LDLD, it is quickly reversed under constant conditions. Here the authors examine whether dim scotophase illumination acts to maintain bifurcated entrainment under LDLD through potential interactions with the parametric actions of bright light during the two daily photophases. In three experiments, wheel-running rhythms of Syrian hamsters were bifurcated under LDLD with dimly lit scotophases, and after several weeks, dim scotophase illumination was either retained or extinguished. Additionally, "full" and "skeleton" photophases were employed under LDLD cycles with dimly lit or completely dark scotophases to distinguish parametric from nonparametric effects of bright light. Rhythm bifurcation was more stable in full versus skeleton LDLD cycles. Dim light facilitated the maintenance of bifurcated entrainment under full LDLD cycles but did not prevent the loss of rhythm bifurcation in skeleton LDLD cycles. These studies indicate that parametric actions of bright light maintain the bifurcated entrainment state; that dim scotophase illumination increases the stability of the bifurcated state; and that dim light interacts with the parametric effects of bright light to increase the stability of rhythm bifurcation under full LDLD cycles. A further understanding of the novel actions of dim light may lead to new strategies for understanding, preventing, and treating chronobiological disturbances.

Single Particle Damage Events in Candidate Star Camera Sensors

NASA Technical Reports Server (NTRS)

Marshall, Paul; Marshall, Cheryl; Polidan, Elizabeth; Wacyznski, Augustyn; Johnson, Scott

2005-01-01

Si charge coupled devices (CCDs) are currently the preeminent detector in star cameras as well as in the near ultraviolet (uv) to visible wavelength region for astronomical observations in space and in earth-observing space missions. Unfortunately, the performance of CCDs is permanently degraded by total ionizing dose (TID) and displacement damage effects. TID produces threshold voltage shifts on the CCD gates and displacement damage reduces the charge transfer efficiency (CTE), increases the dark current, produces dark current nonuniformities and creates random telegraph noise in individual pixels. In addition to these long term effects, cosmic ray and trapped proton transients also interfere with device operation on orbit. In the present paper, we investigate the dark current behavior of CCDs - in particular the formation and annealing of hot pixels. Such pixels degrade the ability of a CCD to perform science and also can present problems to the performance of star camera functions (especially if their numbers are not correctly anticipated). To date, most dark current radiation studies have been performed by irradiating the CCDs at room temperature but this can result in a significantly optimistic picture of the hot pixel count. We know from the Hubble Space Telescope (HST) that high dark current pixels (so-called hot pixels or hot spikes) accumulate as a function of time on orbit. For example, the HST Advanced Camera for Surveys/Wide Field Camera instrument performs monthly anneals despite the loss of observational time, in order to partially anneal the hot pixels. Note that the fact that significant reduction in hot pixel populations occurs for room temperature anneals is not presently understood since none of the commonly expected defects in Si (e.g. divacancy, E center, and A-center) anneal at such a low temperature. A HST Wide Field Camera 3 (WFC3) CCD manufactured by E2V was irradiated while operating at -83C and the dark current studied as a function of temperature while the CCD was warmed to a sequence of temperatures up to a maximum of +30C. The device was then cooled back down to -83 and re-measured. Hot pixel populations were tracked during the warm-up and cool-down. Hot pixel annealing began below 40C and the anneal process was largely completed before the detector reached +3OC. There was no apparent sharp temperature dependence in the annealing. Although a large fraction of the hot pixels fell below the threshold to be counted as a hot pixel, they nevertheless remained warmer than the remaining population. The details of the mechanism for the formation and annealing of hot pixels is not presently understood, but it appears likely that hot pixels are associated with displacement damage occurring in high electric field regions.

Energy efficient and fast reversal of a fixed skyrmion two-terminal memory with spin current assisted by voltage controlled magnetic anisotropy

NASA Astrophysics Data System (ADS)

Bhattacharya, Dhritiman; Mamun Al-Rashid, Md; Atulasimha, Jayasimha

2017-10-01

Recent work (P-H Jang et al 2015 Appl. Phys. Lett. 107 202401, J. Sampaio et al 2016 Appl. Phys. Lett. 108 112403) suggests that ferromagnetic reversal with spin transfer torque (STT) requires more current in a system in the presence of Dzyaloshinskii-Moriya interaction (DMI) than switching a typical ferromagnet of the same dimensions and perpendicular magnetic anisotropy (PMA). However, DMI promotes the stabilization of skyrmions and we report that when perpendicular anisotropy is modulated (reduced) for both the skyrmion and ferromagnet, it takes a much smaller current to reverse the fixed skyrmion than to reverse the ferromagnet in the same amount of time, or the skyrmion reverses much faster than the ferromagnet at similar levels of current. We show with rigorous micromagnetic simulations that skyrmion switching proceeds along a different path at very low PMA, which results in a significant reduction in the spin current or time required for reversal. This can offer potential for memory applications where a relatively simple modification of the standard STT-RAM (to include a heavy metal adjacent to the soft magnetic layer and with appropriate design of the tunnel barrier) can lead to an energy efficient and fast magnetic memory device based on the reversal of fixed skyrmions.

Light-Dark Changes in Cytosolic Nitrate Pools Depend on Nitrate Reductase Activity in Arabidopsis Leaf Cells1[w

PubMed Central

Cookson, Sarah J.; Williams, Lorraine E.; Miller, Anthony J.

2005-01-01

Several different cellular processes determine the size of the metabolically available nitrate pool in the cytoplasm. These processes include not only ion fluxes across the plasma membrane and tonoplast but also assimilation by the activity of nitrate reductase (NR). In roots, the maintenance of cytosolic nitrate activity during periods of nitrate starvation and resupply (M. van der Leij, S.J. Smith, A.J. Miller [1998] Planta 205: 64–72; R.-G. Zhen, H.-W. Koyro, R.A. Leigh, A.D. Tomos, A.J. Miller [1991] Planta 185: 356–361) suggests that this pool is regulated. Under nitrate-replete conditions vacuolar nitrate is a membrane-bound store that can release nitrate to the cytoplasm; after depletion of cytosolic nitrate, tonoplast transporters would serve to restore this pool. To study the role of assimilation, specifically the activity of NR in regulating the size of the cytosolic nitrate pool, we have compared wild-type and mutant plants. In leaf mesophyll cells, light-to-dark transitions increase cytosolic nitrate activity (1.5–2.8 mm), and these changes were reversed by dark-to-light transitions. Such changes were not observed in nia1nia2 NR-deficient plants indicating that this change in cytosolic nitrate activity was dependent on the presence of functional NR. Furthermore, in the dark, the steady-state cytosolic nitrate activities were not statistically different between the two types of plant, indicating that NR has little role in determining resting levels of nitrate. Epidermal cells of both wild type and NR mutants had cytosolic nitrate activities that were not significantly different from mesophyll cells in the dark and were unaltered by dark-to-light transitions. We propose that the NR-dependent changes in cytosolic nitrate provide a cellular mechanism for the diurnal changes in vacuolar nitrate storage, and the results are discussed in terms of the possible signaling role of cytosolic nitrate. PMID:15908593

Day–Night Changes of Energy-rich Compounds in Crassulacean Acid Metabolism (CAM) Species Utilizing Hexose and Starch

PubMed Central

CHEN, LI-SONG; NOSE, AKIHIRO

2004-01-01

• Background and Aims Plants with crassulacean acid metabolism (CAM) can be divided into two groups according to the major carbohydrates used for malic acid synthesis, either polysaccharide (starch) or monosaccharide (hexose). This is related to the mechanism and affects energy metabolism in the two groups. In Kalanchoë pinnata and K. daigremontiana, which utilize starch, ATP-dependent phosphofructokinase (tonoplast inorganic pyrophosphatase) activity is greater than inorganic pyrophosphate-dependent phosphofructokinase (tonoplast adenosine triphosphatase) activity, but the reverse is the case in pineapple (Ananas comosus) utilizing hexose. To test the hypothesis that the energy metabolism of the two groups differs, day-night changes in the contents of ATP, ADP, AMP, inorganic phosphate (Pi), phosphoenolpyruvate (PEP) and inorganic pyrophosphate (PPi) in K. pinnata and K. daigremontiana leaves and in pineapple chlorenchyma were analysed. • Methods The contents of energy-rich compounds were measured spectrophotometrically in extracts of tissue sampled in the light and dark, using potted plants, kept for 15 d before the experiments in a growth chamber. • Key Results In the three species, ATP content and adenylate energy charge (AEC) increased in the dark and decreased in the light, in contrast to ADP and AMP. Changes in ATP and AEC were greater in Kalanchoë leaves than in pineapple chlorenchyma. PPi content in the three species increased in the dark, but on illumination it decreased rapidly and substantially, remaining little changed through the rest of the light period. Pi content of Kalanchoë leaves did not change between dark and light, whereas Pi in pineapple chlorenchyma increased in the dark and decreased in the light, and the changes were far greater than in Kalanchoë leaves. Light-dark changes in PEP content in the three species were similar. • Conclusions These results corroborate our hypothesis that day–night changes in the contents of energy-rich compounds differ between CAM species and are related to the carbohydrate used for malic acid synthesis. PMID:15277250

Mechanisms Affecting Performance of the BaBar Resistive Plate Chambers and Searches for Remediation

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

Lu, Changguo

2003-09-19

The BaBar experiment at PEPII relies on the Instrumentation of the Flux Return (IFR) for both muon identification and KL detection. The active detector is composed of Resistive Plate Chambers (RPC's) operated in streamer mode. Since the start of operation the RPC's have suffered persistent efficiency deterioration and dark current increase problems. The ''autopsy'' of bad BaBar RPC's revealed that in many cases uncured Linseed oil droplets had formed on the inner surface of the Bakelite plates, leading to current paths from oil ''stalagmites'' bridging the 2 mm gap. In this paper a possible model of this ''stalagmite'' formation andmore » its effect on the dark current and efficiency of RPC chambers is presented. Laboratory test results strongly support this model. Based upon this model we are searching for solutions to eliminate the unfavorable effect of the oil stalagmites. The lab tests show that the stalagmite resistivity increases dramatically if exposed to the air, an observation that points to a possible way to remedy the damage and increase the efficiency. We have seen that flowing an oxygen gas mixture into the chamber helps to polymerize the uncured linseed oil. Consequently the resistivity of the bridged oil stalagmites increases, as does that of the oil coating on the frame edges and spacers, significantly reducing the RPC dark currents and low-efficiency regions. We have tested this idea on two chambers removed from BaBar because of their low efficiency and high dark current. These test results are reported in the paper, and two other remediation methods also mentioned. We continue to study this problem, and try to find new treatments with permanent improvement.« less

First experience with x-ray dark-field radiography for human chest imaging (Conference Presentation)

NASA Astrophysics Data System (ADS)

Noel, Peter B.; Willer, Konstantin; Fingerle, Alexander A.; Gromann, Lukas B.; De Marco, Fabio; Scherer, Kai H.; Herzen, Julia; Achterhold, Klaus; Gleich, Bernhard; Münzel, Daniela; Renz, Martin; Renger, Bernhard C.; Fischer, Florian; Braun, Christian; Auweter, Sigrid; Hellbach, Katharina; Reiser, Maximilian F.; Schröter, Tobias; Mohr, Jürgen; Yaroshenko, Andre; Maack, Hanns-Ingo; Pralow, Thomas; van der Heijden, Hendrik; Proksa, Roland; Köhler, Thomas; Wieberneit, Nataly; Rindt, Karsten; Rummeny, Ernst J.; Pfeiffer, Franz

2017-03-01

Purpose: To evaluate the performance of an experimental X-ray dark-field radiography system for chest imaging in humans and to compare with conventional diagnostic imaging. Materials and Methods: The study was institutional review board (IRB) approved. A single human cadaver (52 years, female, height: 173 cm, weight: 84 kg, chest circumference: 97 cm) was imaged within 24 hours post mortem on the experimental x-ray dark-field system. In addition, the cadaver was imaged on a clinical CT system to obtain a reference scan. The grating-based dark-field radiography setup was equipped with a set of three gratings to enable grating-based dark-field contrast x-ray imaging. The prototype operates at an acceleration voltage of up to 70 kVp and with a field-of-view large enough for clinical chest x-ray (>35 x 35 cm2). Results: It was feasible to extract x-ray dark-field signal of the whole human thorax, clearly demonstrating that human x-ray dark-field chest radiography is feasible. Lung tissue produced strong scattering, reflected in a pronounced x-ray dark-field signal. The ribcage and the backbone are less prominent than the lung but are also distinguishable. Finally, the soft tissue is not present in the dark-field radiography. The regions of the lungs affected by edema, as verified by CT, showed less dark-field signal compared to healthy lung tissue. Conclusion: Our results reveal the current status of translating dark-field imaging from a micro (small animal) scale to a macro (patient) scale. The performance of the experimental x-ray dark-field radiography setup offers, for the first time, obtaining multi-contrast chest x-ray images (attenuation and dark-field signal) from a human cadaver.

Colony-Forming Progenitor Cells in the Postnatal Mouse Liver and Pancreas Give Rise to Morphologically Distinct Insulin-Expressing Colonies in 3D Cultures

PubMed Central

Jin, Liang; Feng, Tao; Chai, Jing; Ghazalli, Nadiah; Gao, Dan; Zerda, Ricardo; Li, Zhuo; Hsu, Jasper; Mahdavi, Alborz; Tirrell, David A.; Riggs, Arthur D.; Ku, Hsun Teresa

2014-01-01

In our previous studies, colony-forming progenitor cells isolated from murine embryonic stem cell-derived cultures were differentiated into morphologically distinct insulin-expressing colonies. These colonies were small and not light-reflective when observed by phase-contrast microscopy (therefore termed “Dark” colonies). A single progenitor cell capable of giving rise to a Dark colony was termed a Dark colony-forming unit (CFU-Dark). The goal of the current study was to test whether endogenous pancreas, and its developmentally related liver, harbored CFU-Dark. Here we show that dissociated single cells from liver and pancreas of one-week-old mice give rise to Dark colonies in methylcellulose-based semisolid culture media containing either Matrigel or laminin hydrogel (an artificial extracellular matrix protein). CFU-Dark comprise approximately 0.1% and 0.03% of the postnatal hepatic and pancreatic cells, respectively. Adult liver also contains CFU-Dark, but at a much lower frequency (~0.003%). Microfluidic qRT-PCR, immunostaining, and electron microscopy analyses of individually handpicked colonies reveal the expression of insulin in many, but not all, Dark colonies. Most pancreatic insulin-positive Dark colonies also express glucagon, whereas liver colonies do not. Liver CFU-Dark require Matrigel, but not laminin hydrogel, to become insulin-positive. In contrast, laminin hydrogel is sufficient to support the development of pancreatic Dark colonies that express insulin. Postnatal liver CFU-Dark display a cell surface marker CD133+CD49flowCD107blow phenotype, while pancreatic CFU-Dark are CD133-. Together, these results demonstrate that specific progenitor cells in the postnatal liver and pancreas are capable of developing into insulin-expressing colonies, but they differ in frequency, marker expression, and matrix protein requirements for growth. PMID:25148366

Big Mysteries: Dark Energy

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

Lincoln, Don

2014-04-15

Scientists were shocked in 1998 when the expansion of the universe wasn't slowing down as expected by our best understanding of gravity at the time; the expansion was speeding up! That observation is just mind blowing, and yet it is true. In order to explain the data, physicists had to resurrect an abandoned idea of Einstein's now called dark energy. In this video, Fermilab's Dr. Don Lincoln tells us a little about the observations that led to the hypothesis of dark energy and what is the status of current research on the subject.

Dips in the diffuse supernova neutrino background

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

Farzan, Yasaman; Palomares-Ruiz, Sergio, E-mail: yasaman@theory.ipm.ac.ir, E-mail: Sergio.Palomares.Ruiz@ific.uv.es

2014-06-01

Scalar (fermion) dark matter with mass in the MeV range coupled to ordinary neutrinos and another fermion (scalar) is motivated by scenarios that establish a link between radiatively generated neutrino masses and the dark matter relic density. With such a coupling, cosmic supernova neutrinos, on their way to us, could resonantly interact with the background dark matter particles, giving rise to a dip in their redshift-integrated spectra. Current and future neutrino detectors, such as Super-Kamiokande, LENA and Hyper-Kamiokande, could be able to detect this distortion.

Hunting the Dark Matter with DEAP/CLEAN

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

Giuliani, F.

2010-02-10

The potential of the DEAP/CLEAN program for direct Dark Matter detection to test various dark matter models is illustrated. The scintillation pulse of a noble liquid like Argon or Neon has two well distinguished time constants allowing a very reliable correlation between pulse shape and type of event. This pulse shape discrimination already provides the power of rejecting a background10{sup 8}-10{sup 9} times larger than the signal. MiniCLEAN, a 500 kg LAr detector, is currently under construction, and a 3.6 ton detector, DEAP-3600, under development.

Big Mysteries: Dark Energy

ScienceCinema

Lincoln, Don

2018-01-16

Scientists were shocked in 1998 when the expansion of the universe wasn't slowing down as expected by our best understanding of gravity at the time; the expansion was speeding up! That observation is just mind blowing, and yet it is true. In order to explain the data, physicists had to resurrect an abandoned idea of Einstein's now called dark energy. In this video, Fermilab's Dr. Don Lincoln tells us a little about the observations that led to the hypothesis of dark energy and what is the status of current research on the subject.

Low dark current and high speed ZnO metal–semiconductor–metal photodetector on SiO{sub 2}/Si substrate

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

Çalışkan, Deniz, E-mail: dcaliskan@fen.bilkent.edu.tr; Department of Nanotechnology and Nanomedicine, Hacettepe University, 06800 Beytepe, Ankara; Bütün, Bayram

2014-10-20

ZnO thin films are deposited by radio-frequency magnetron sputtering on thermally grown SiO{sub 2} on Si substrates. Pt/Au contacts are fabricated by standard photolithography and lift-off in order to form a metal-semiconductor-metal (MSM) photodetector. The dark current of the photodetector is measured as 1 pA at 100 V bias, corresponding to 100 pA/cm{sup 2} current density. Spectral photoresponse measurement showed the usual spectral behavior and 0.35 A/W responsivity at a 100 V bias. The rise and fall times for the photocurrent are measured as 22 ps and 8 ns, respectively, which are the lowest values to date. Scanning electron microscope image shows high aspect ratio andmore » dense grains indicating high surface area. Low dark current density and high speed response are attributed to high number of recombination centers due to film morphology, deducing from photoluminescence measurements. These results show that as deposited ZnO thin film MSM photodetectors can be used for the applications needed for low light level detection and fast operation.« less

Thermally-restorable optical degradation and the mechanism of current transport in Cu2S-CdS photovoltaic cells

NASA Technical Reports Server (NTRS)

Fahrenbruch, A. L.; Bube, R. H.

1974-01-01

The photovoltaic properties of single-crystal Cu2S-CdS heterojunctions have been investigated as a function of heat treatment by detailed measurements of the dependence of short-circuit current on photon energy, temperature, and the state of optical degradation or enhancement. A coherent picture is formulated for the relationship between enhancement and optical degradation, and their effect on the transport of short-circuit photoexcited current and dark, forward-bias current in the cell. Optical degradation in the Cu2S-CdS cell is shown to be closely identical to optical degradation of lifetime in a homogeneous CdS:Cd:Cu crystal, indicating that the CdS:Cu layer near the junction interface controls carrier transport in the cell. It is proposed that both the photoexcited short-circuit current and the dark, forward-bias current are controlled by a tunneling-recombination process through interface states.

I-V-T analysis of radiation damage in high efficiency Si solar cells

NASA Technical Reports Server (NTRS)

Banerjee, S.; Anderson, W. A.; Rao, B. B.

1985-01-01

A detailed analysis of current-voltage characteristics of N(+)-P/P solar cells indicate that there is a combination of different mechanisms which results in an enhancement in the dark current and in turn deteriorates the photovoltaic performance of the solar cells after 1 MeV e(-) irradiation. The increase in the dark current is due to three effects, i.e., bulk recombination, space charge recombination by deep traps and space charge recombination through shallow traps. It is shown that the increase in bulk recombination current is about 2 to 3 orders of magnitude whereas space charge recombination current due to shallow traps increases only by an order or so and no space charge recombination through deep traps was observed after irradiation. Thus, in order to improve the radiation hardness of these devices, bulk properties should be preserved.

Nonthermal electrons in the thick-target reverse-current model for hard X-ray bremsstrahlung

NASA Astrophysics Data System (ADS)

Litvinenko, Iu. E.; Somov, B. V.

1991-02-01

The behavior of the accelerated electrons escaping from a high-temperature source of primary energy in a solar flare is investigated. The direct current of fast electrons is supposed to be balanced by the reverse current of thermal electrons in the ambient colder plasma inside flare loops. The self-consistent kinetic problem is formulated, and the reverse-current electric field and the fast electron distribution function are found from its solution. The X-ray bremsstrahlung polarization is then calculated from the distribution function. The difference of results from those in the case of thermal runaway electrons (Diakonov and Somov, 1988) is discussed. The solutions with and without an account taken of the effect of a reverse-current electric field are also compared.

Sensitivity of housekeeping genes in the suprachiasmatic nucleus of the mouse brain to diet and the daily light-dark cycle.

PubMed

Cleal, Jane K; Shepherd, James N; Shearer, Jasmine L; Bruce, Kimberley D; Cagampang, Felino R

2014-08-05

The endogenous timing system within the suprachiasmatic nuclei (SCN) of the hypothalamus drives the cyclic expression of the clock molecules across the 24h day-night cycle controlling downstream molecular pathways and physiological processes. The developing fetal clock system is sensitive to the environment and physiology of the pregnant mother and as such disruption of this system could lead to altered physiology in the offspring. Characterizing the gene profiles of the endogenous molecular clock system by quantitative reverse transcription polymerase chain reaction is dependent on normalization by appropriate housekeeping genes (HKGs). However, many HKGs commonly used as internal controls, although stably expressed under control conditions, can vary significantly in their expression under certain experimental conditions. Here we analyzed the expression of 10 classic HKG across the 24h light-dark cycle in the SCN of mouse offspring exposed to normal chow or a high fat diet during early development and in postnatal life. We found that the HKGs glyceraldehyde-3-phosphate dehydrogenase, beta actin and adenosine triphosphate synthase subunit to be the most stably expressed genes in the SCN regardless of diet or time within the 24h light-dark cycle, and are therefore suitable to be used as internal controls. However SCN samples collected during the light and dark periods did show differences in expression and as such the timing of collection should be considered when carrying out gene expression studies. Copyright © 2014 Elsevier B.V. All rights reserved.

Search for Dark Matter in Events with One Jet and Missing Transverse Energy in pp̄ Collisions at √s=1.96 TeV

DOE PAGES

Aaltonen, T.; Álvarez González, B.; Amerio, S.; ...

2012-05-23

We present the results of a search for dark matter production in the monojet signature. We analyze a sample of Tevatron pp̄ collisions at √s=1.96 TeV corresponding to an integrated luminosity of 6.7 fb⁻¹ recorded by the CDF II detector. In events with large missing transverse energy and one energetic jet, we find good agreement between the standard model prediction and the observed data. We set 90% confidence level upper limits on the dark matter production rate. The limits are translated into bounds on nucleon-dark matter scattering rates which are competitive with current direct detection bounds on spin-independent interaction belowmore » a dark matter candidate mass of 5 GeV/c², and on spin-dependent interactions up to masses of 200 GeV/c².« less

Search for dark matter in events with one jet and missing transverse energy in pp¯ collisions at √s=1.96 TeV.

PubMed

Aaltonen, T; Alvarez González, B; Amerio, S; Amidei, D; Anastassov, A; Annovi, A; Antos, J; Apollinari, G; Appel, J A; Arisawa, T; Artikov, A; Asaadi, J; Ashmanskas, W; Auerbach, B; Aurisano, A; Azfar, F; Badgett, W; Bae, T; Bai, Y; Barbaro-Galtieri, A; Barnes, V E; Barnett, B A; Barria, P; Bartos, P; Bauce, M; Bedeschi, F; Behari, S; Bellettini, G; Bellinger, J; Benjamin, D; Beretvas, A; Bhatti, A; Bisello, D; Bizjak, I; Bland, K R; Blumenfeld, B; Bocci, A; Bodek, A; Bortoletto, D; Boudreau, J; Boveia, A; Brigliadori, L; Bromberg, C; Brucken, E; Budagov, J; Budd, H S; Burkett, K; Busetto, G; Bussey, P; Buzatu, A; Calamba, A; Calancha, C; Camarda, S; Campanelli, M; Campbell, M; Canelli, F; Carls, B; Carlsmith, D; Carosi, R; Carrillo, S; Carron, S; Casal, B; Casarsa, M; Castro, A; Catastini, P; Cauz, D; Cavaliere, V; Cavalli-Sforza, M; Cerri, A; Cerrito, L; Chen, Y C; Chertok, M; Chiarelli, G; Chlachidze, G; Chlebana, F; Cho, K; Chokheli, D; Chung, W H; Chung, Y S; Ciocci, M A; Clark, A; Clarke, C; Compostella, G; Convery, M E; Conway, J; Corbo, M; Cordelli, M; Cox, C A; Cox, D J; Crescioli, F; Cuevas, J; Culbertson, R; Dagenhart, D; d'Ascenzo, N; Datta, M; de Barbaro, P; Dell'Orso, M; Demortier, L; Deninno, M; Devoto, F; d'Errico, M; Di Canto, A; Di Ruzza, B; Dittmann, J R; D'Onofrio, M; Donati, S; Dong, P; Dorigo, M; Dorigo, T; Ebina, K; Elagin, A; Eppig, A; Erbacher, R; Errede, S; Ershaidat, N; Eusebi, R; Farrington, S; Feindt, M; Fernandez, J P; Field, R; Flanagan, G; Forrest, R; Fox, P J; Frank, M J; Franklin, M; Freeman, J C; Funakoshi, Y; Furic, I; Gallinaro, M; Garcia, J E; Garfinkel, A F; Garosi, P; Gerberich, H; Gerchtein, E; Giagu, S; Giakoumopoulou, V; Giannetti, P; Gibson, K; Ginsburg, C M; Giokaris, N; Giromini, P; Giurgiu, G; Glagolev, V; Glenzinski, D; Gold, M; Goldin, D; Goldschmidt, N; Golossanov, A; Gomez, G; Gomez-Ceballos, G; Goncharov, M; González, O; Gorelov, I; Goshaw, A T; Goulianos, K; Grinstein, S; Grosso-Pilcher, C; Group, R C; Guimaraes da Costa, J; Hahn, S R; Halkiadakis, E; Hamaguchi, A; Han, J Y; Happacher, F; Hara, K; Hare, D; Hare, M; Harnik, R; Harr, R F; Hatakeyama, K; Hays, C; Heck, M; Heinrich, J; Herndon, M; Hewamanage, S; Hocker, A; Hopkins, W; Horn, D; Hou, S; Hughes, R E; Hurwitz, M; Husemann, U; Hussain, N; Hussein, M; Huston, J; Introzzi, G; Iori, M; Ivanov, A; James, E; Jang, D; Jayatilaka, B; Jeon, E J; Jindariani, S; Jones, M; Joo, K K; Jun, S Y; Junk, T R; Kamon, T; Karchin, P E; Kasmi, A; Kato, Y; Ketchum, W; Keung, J; Khotilovich, V; Kilminster, B; Kim, D H; Kim, H S; Kim, J E; Kim, M J; Kim, S B; Kim, S H; Kim, Y K; Kim, Y J; Kimura, N; Kirby, M; Klimenko, S; Knoepfel, K; Kondo, K; Kong, D J; Konigsberg, J; Kotwal, A V; Kreps, M; Kroll, J; Krop, D; Kruse, M; Krutelyov, V; Kuhr, T; Kurata, M; Kwang, S; Laasanen, A T; Lami, S; Lammel, S; Lancaster, M; Lander, R L; Lannon, K; Lath, A; Latino, G; Lecompte, T; Lee, E; Lee, H S; Lee, J S; Lee, S W; Leo, S; Leone, S; Lewis, J D; Limosani, A; Lin, C-J; Lindgren, M; Lipeles, E; Lister, A; Litvintsev, D O; Liu, C; Liu, H; Liu, Q; Liu, T; Lockwitz, S; Loginov, A; Lucchesi, D; Lueck, J; Lujan, P; Lukens, P; Lungu, G; Lys, J; Lysak, R; Madrak, R; Maeshima, K; Maestro, P; Malik, S; Manca, G; Manousakis-Katsikakis, A; Margaroli, F; Marino, C; Martínez, M; Mastrandrea, P; Matera, K; Mattson, M E; Mazzacane, A; Mazzanti, P; McFarland, K S; McIntyre, P; McNulty, R; Mehta, A; Mehtala, P; Mesropian, C; Miao, T; Mietlicki, D; Mitra, A; Miyake, H; Moed, S; Moggi, N; Mondragon, M N; Moon, C S; Moore, R; Morello, M J; Morlock, J; Movilla Fernandez, P; Mukherjee, A; Muller, Th; Murat, P; Mussini, M; Nachtman, J; Nagai, Y; Naganoma, J; Nakano, I; Napier, A; Nett, J; Neu, C; Neubauer, M S; Nielsen, J; Nodulman, L; Noh, S Y; Norniella, O; Oakes, L; Oh, S H; Oh, Y D; Oksuzian, I; Okusawa, T; Orava, R; Ortolan, L; Pagan Griso, S; Pagliarone, C; Palencia, E; Papadimitriou, V; Paramonov, A A; Patrick, J; Pauletta, G; Paus, C; Pellett, D E; Penzo, A; Phillips, T J; Piacentino, G; Pianori, E; Pilot, J; Pitts, K; Plager, C; Pondrom, L; Poprocki, S; Potamianos, K; Prokoshin, F; Pranko, A; Ptohos, F; Punzi, G; Rahaman, A; Ramakrishnan, V; Ranjan, N; Redondo, I; Renton, P; Rescigno, M; Riddick, T; Rimondi, F; Ristori, L; Robson, A; Rodrigo, T; Rodriguez, T; Rogers, E; Rolli, S; Roser, R; Ruffini, F; Ruiz, A; Russ, J; Rusu, V; Safonov, A; Sakumoto, W K; Sakurai, Y; Santi, L; Sato, K; Saveliev, V; Savoy-Navarro, A; Schlabach, P; Schmidt, A; Schmidt, E E; Schwarz, T; Scodellaro, L; Scribano, A; Scuri, F; Seidel, S; Seiya, Y; Semenov, A; Sforza, F; Shalhout, S Z; Shears, T; Shepard, P F; Shimojima, M; Shochet, M; Shreyber-Tecker, I; Simonenko, A; Sinervo, P; Sliwa, K; Smith, J R; Snider, F D; Soha, A; Sorin, V; Song, H; Squillacioti, P; Stancari, M; St Denis, R; Stelzer, B; Stelzer-Chilton, O; Stentz, D; Strologas, J; Strycker, G L; Sudo, Y; Sukhanov, A; Suslov, I; Takemasa, K; Takeuchi, Y; Tang, J; Tecchio, M; Teng, P K; Thom, J; Thome, J; Thompson, G A; Thomson, E; Toback, D; Tokar, S; Tollefson, K; Tomura, T; Tonelli, D; Torre, S; Torretta, D; Totaro, P; Trovato, M; Ukegawa, F; Uozumi, S; Varganov, A; Vázquez, F; Velev, G; Vellidis, C; Vidal, M; Vila, I; Vilar, R; Vizán, J; Vogel, M; Volpi, G; Wagner, P; Wagner, R L; Wakisaka, T; Wallny, R; Wang, S M; Warburton, A; Waters, D; Wester, W C; Whiteson, D; Wicklund, A B; Wicklund, E; Wilbur, S; Wick, F; Williams, H H; Wilson, J S; Wilson, P; Winer, B L; Wittich, P; Wolbers, S; Wolfe, H; Wright, T; Wu, X; Wu, Z; Yamamoto, K; Yamato, D; Yang, T; Yang, U K; Yang, Y C; Yao, W-M; Yeh, G P; Yi, K; Yoh, J; Yorita, K; Yoshida, T; Yu, G B; Yu, I; Yu, S S; Yun, J C; Zanetti, A; Zeng, Y; Zhou, C; Zucchelli, S

2012-05-25

We present the results of a search for dark matter production in the monojet signature. We analyze a sample of Tevatron pp[over ¯] collisions at √s=1.96 TeV corresponding to an integrated luminosity of 6.7 fb(-1) recorded by the CDF II detector. In events with large missing transverse energy and one energetic jet, we find good agreement between the standard model prediction and the observed data. We set 90% confidence level upper limits on the dark matter production rate. The limits are translated into bounds on nucleon-dark matter scattering rates which are competitive with current direct detection bounds on spin-independent interaction below a dark matter candidate mass of 5 GeV/c(2), and on spin-dependent interactions up to masses of 200 GeV/c(2).

Updated constraints on the dark matter interpretation of CDMS-II-Si data

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

Witte, Samuel J.; Gelmini, Graciela B., E-mail: switte@physics.ucla.edu, E-mail: gelmini@physics.ucla.edu

2017-05-01

We present an updated halo-dependent and halo-independent analysis of viable light WIMP dark matter candidates which could account for the excess observed in CDMS-II-Si. We include recent constraints from LUX, PandaX-II, and PICO-60, as well as projected sensitivities for XENON1T, SuperCDMS SNOLAB, LZ, DARWIN, DarkSide-20k, and PICO-250, on candidates with spin-independent isospin conserving and isospin-violating interactions, and either elastic or exothermic scattering. We show that there exist dark matter candidates which can explain the CDMS-II-Si data and remain very marginally consistent with the null results of all current experiments, however such models are highly tuned, making a dark matter interpretationmore » of CDMS-II-Si very unlikely. We find that these models can only be ruled out in the future by an experiment comparable to LZ or PICO-250.« less

Dark interactions and cosmological fine-tuning

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

Quartin, Miguel; Calvao, Mauricio O; Joras, Sergio E

2008-05-15

Cosmological models involving an interaction between dark matter and dark energy have been proposed in order to solve the so-called coincidence problem. Different forms of coupling have been studied, but there have been claims that observational data seem to narrow (some of) them down to something annoyingly close to the {Lambda}CDM (CDM: cold dark matter) model, thus greatly reducing their ability to deal with the problem in the first place. The smallness problem of the initial energy density of dark energy has also been a target of cosmological models in recent years. Making use of a moderately general coupling scheme,more » this paper aims to unite these different approaches and shed some light on whether this class of models has any true perspective in suppressing the aforementioned issues that plague our current understanding of the universe, in a quantitative and unambiguous way.« less

Echo of interactions in the dark sector

NASA Astrophysics Data System (ADS)

Kumar, Suresh; Nunes, Rafael C.

2017-11-01

We investigate the observational constraints on an interacting vacuum energy scenario with two different neutrino schemes (with and without a sterile neutrino) using the most recent data from cosmic microwave background (CMB) temperature and polarization anisotropy, baryon acoustic oscillations (BAO), type Ia supernovae from JLA sample and structure growth inferred from cluster counts. We find that inclusion of the galaxy clusters data with the minimal data combination CMB +BAO +JLA suggests an interaction in the dark sector, implying the decay of dark matter particles into dark energy, since the constraints obtained by including the galaxy clusters data yield a non-null and negative coupling parameter between the dark components at 99% confidence level. We deduce that the current tensions on the parameters H0 and σ8 can be alleviated within the framework of the interacting as well as noninteracting vacuum energy models with sterile neutrinos.

Accurate Modeling of Dark-Field Scattering Spectra of Plasmonic Nanostructures.

PubMed

Jiang, Liyong; Yin, Tingting; Dong, Zhaogang; Liao, Mingyi; Tan, Shawn J; Goh, Xiao Ming; Allioux, David; Hu, Hailong; Li, Xiangyin; Yang, Joel K W; Shen, Zexiang

2015-10-27

Dark-field microscopy is a widely used tool for measuring the optical resonance of plasmonic nanostructures. However, current numerical methods for simulating the dark-field scattering spectra were carried out with plane wave illumination either at normal incidence or at an oblique angle from one direction. In actual experiments, light is focused onto the sample through an annular ring within a range of glancing angles. In this paper, we present a theoretical model capable of accurately simulating the dark-field light source with an annular ring. Simulations correctly reproduce a counterintuitive blue shift in the scattering spectra from gold nanodisks with a diameter beyond 140 nm. We believe that our proposed simulation method can be potentially applied as a general tool capable of simulating the dark-field scattering spectra of plasmonic nanostructures as well as other dielectric nanostructures with sizes beyond the quasi-static limit.

Solid State Research.

DTIC Science & Technology

1984-11-15

Coupling to Surface Plasma Waves 20 2.3 Theory of the Effect of Traps on the Spectral Charac- teristics of Diode Lasers 23 3 . MATERIALS RESEARCH 27...Page 1-1(a) Schematic Cross Section of InGaAs PSIN Structure. Gap Spac- ing (d) Is 3 , 5, 10, or 20 pm. 2 1-1(b) Curve Tracer I-V Characteristics of a...20-pim PSIN Device in Dark and Under Illumination 2 1-2 Pulse Response of a 3 -#Am PSIN Device, Under Forward and Reverse Bias. to a Comb-Generator

Detecting ultralight bosonic dark matter via absorption in superconductors

DOE PAGES

Hochberg, Yonit; Lin, Tongyan; Zurek, Kathryn M.

2016-07-18

Superconducting targets have recently been proposed for the direct detection of dark matter as light as a keV, via elastic scattering off conduction electrons in Cooper pairs. Detecting such light dark matter requires sensitivity to energies as small as the superconducting gap of O(meV). Here we show that these same superconducting devices can detect much lighter DM, of meV to eV mass, via dark matter absorption on a conduction electron, followed by emission of an athermal phonon. Lastly, we demonstrate the power of this setup for relic kinetically mixed hidden photons, pseudoscalars, and scalars, showing that the reach can exceedmore » current astrophysical and terrestrial constraints with only a moderate exposure.« less

What We Know About Dark Energy From Supernovae

ScienceCinema

Filippenko, Alex

2018-01-24

The measured distances of type Ia (white dwarf) supernovae as a function of redshift (z) have shown that the expansion of the Universe is currently accelerating, probably due to the presence of dark energy (X) having a negative pressure. Combining all of the data with existing results from large-scale structure surveys, we find a best fit for Omega M and Omega X of 0.28 and 0.72 (respectively), in excellent agreement with the values derived independently from WMAP measurements of the cosmic microwave background radiation. Thus far, the best-fit value for the dark energy equation-of-state parameter is -1, and its first derivative is consistent with zero, suggesting that the dark energy may indeed be Einstein's cosmological constant.

Enlightenment and the "Heart of Darkness": (Neo)Imperialism in the Congo, and Elsewhere

ERIC Educational Resources Information Center

Stronach, Ian

2006-01-01

This article approaches the current state of qualitative inquiry by constructing an allegory of neo-imperialism. It is based substantively on a history and contemporary anthro-politics of the Congo and in particular the city of Kisangani; metaphorically on Conrad's unsettling deployment of that same place as "the heart of darkness"; and…

Reverse current in solar flares

NASA Technical Reports Server (NTRS)

Knight, J. W.; Sturrock, P. A.

1977-01-01

We examine the proposal that impulsive X-ray bursts are produced by high-energy electrons streaming from the corona to the chromosphere. It is known that the currents associated with these streams are so high that either the streams do not exist or their current is neutralized by a reverse current. Analysis of a simple model in which the reverse current is stable indicates that the primary electron stream leads to the development of an electric field in the ambient corona which (a) decelerates the primary beam and (b) produces a neutralizing reverse current. It appears that, in some circumstances, this electric field could prevent the primary beam from reaching the chromosphere. In any case, the electric field acts as an energy exchange mechanism, extracting kinetic energy from the primary beam and using it to heat the ambient plasma. This heating is typically so rapid that it must be expected to have important dynamical consequences.

Two-fluid dynamo relaxation and momentum transport induced by CHI on HIST

NASA Astrophysics Data System (ADS)

Nagata, Masayoshi; Hirono, Hidetoshi; Hanao, Takafumi; Hyobu, Takahiro; Ito, Kengo; Matsumoto, Keisuke; Nakayama, Takashi; Oki, Nobuharu; Kikuchi, Yusuke; Fukumoto, Naoyuki

2013-10-01

Non-inductive current drive by using Multi-pulsing coaxial helicity injection was studied on HIST. In the double-pulsing CHI experiment, we have examined two-fluid effects by reversing polarity of the bias poloidal coil current. In the ST magnetic configurations with the right-handed magnetic field (positive CHI), there are a diamagnetic structure in the open flux column region and a paramagnetic structure in the closed flux region. It is naturally understood that the direction of the poloidal magnetic field (toroidal current) is reversed in reversing the polarity of the bias flux from positive to negative. However, the poloidal current is surprisingly reversed in reversing the magnetic helicity polarity. The direction of the poloidal current is opposite in the each region. The toroidal flow is reversed, but a shear profile of the poloidal flow is not changed significantly. In this configuration, the diamagnetic structure appears in the closed flux region. Thus, not only Jt×Bp but also Jp×Bt force contributes on pressure balance leading to a higher beta. We are studying a more general helicity conservation that constrains the interaction between flows and magnetic fields and momentum transport in the two-fluid framework.

Real space mapping of oxygen vacancy diffusion and electrochemical transformations by hysteretic current reversal curve measurements

DOEpatents

Kalinin, Sergei V.; Balke, Nina; Borisevich, Albina Y.; Jesse, Stephen; Maksymovych, Petro; Kim, Yunseok; Strelcov, Evgheni

2014-06-10

An excitation voltage biases an ionic conducting material sample over a nanoscale grid. The bias sweeps a modulated voltage with increasing maximal amplitudes. A current response is measured at grid locations. Current response reversal curves are mapped over maximal amplitudes of the bias cycles. Reversal curves are averaged over the grid for each bias cycle and mapped over maximal bias amplitudes for each bias cycle. Average reversal curve areas are mapped over maximal amplitudes of the bias cycles. Thresholds are determined for onset and ending of electrochemical activity. A predetermined number of bias sweeps may vary in frequency where each sweep has a constant number of cycles and reversal response curves may indicate ionic diffusion kinetics.

Simplified phenomenology for colored dark sectors

NASA Astrophysics Data System (ADS)

El Hedri, Sonia; Kaminska, Anna; de Vries, Maikel; Zurita, Jose

2017-04-01

We perform a general study of the relic density and LHC constraints on simplified models where the dark matter coannihilates with a strongly interacting particle X. In these models, the dark matter depletion is driven by the self-annihilation of X to pairs of quarks and gluons through the strong interaction. The phenomenology of these scenarios therefore only depends on the dark matter mass and the mass splitting between dark matter and X as well as the quantum numbers of X. In this paper, we consider simplified models where X can be either a scalar, a fermion or a vector, as well as a color triplet, sextet or octet. We compute the dark matter relic density constraints taking into account Sommerfeld corrections and bound state formation. Furthermore, we examine the restrictions from thermal equilibrium, the lifetime of X and the current and future LHC bounds on X pair production. All constraints are comprehensively presented in the mass splitting versus dark matter mass plane. While the relic density constraints can lead to upper bounds on the dark matter mass ranging from 2 TeV to more than 10 TeV across our models, the prospective LHC bounds range from 800 to 1500 GeV. A full coverage of the strongly coannihilating dark matter parameter space would therefore require hadron colliders with significantly higher center-of-mass energies.

Prospects for Dark Matter Measurements with the Advanced Gamma Ray Imaging System (AGIS)

NASA Astrophysics Data System (ADS)

Buckley, James

2009-05-01

AGIS, a concept for a future gamma-ray observatory consisting of an array of 50 atmospheric Cherenkov telescopes, would provide a powerful new tool for determining the nature of dark matter and its role in structure formation in the universe. The advent of more sensitive direct detection experiments, the launch of Fermi and the startup of the LHC make the near future an exciting time for dark matter searches. Indirect measurements of cosmic-ray electrons may already provide a hint of dark matter in our local halo. However, gamma-ray measurements will provide the only means for mapping the dark matter in the halo of our galaxy and other galaxies. In addition, the spectrum of gamma-rays (either direct annihilation to lines or continuum emission from other annihilation channels) will be imprinted with the mass of the dark matter particle, and the particular annihilation channels providing key measurements needed to identify the dark matter particle. While current gamma-ray instruments fall short of the generic sensitivity required to measure the dark matter signal from any sources other than the (confused) region around the Galactic center, we show that the planned AGIS array will have the angular resolution, energy resolution, low threshold energy and large effective area required to detect emission from dark matter annihilation in Galactic substructure or nearby Dwarf spheroidal galaxies.

Cosmological simulations of decaying dark matter: implications for small-scale structure of dark matter haloes

NASA Astrophysics Data System (ADS)

Wang, Mei-Yu; Peter, Annika H. G.; Strigari, Louis E.; Zentner, Andrew R.; Arant, Bryan; Garrison-Kimmel, Shea; Rocha, Miguel

2014-11-01

We present a set of N-body simulations of a class of models in which an unstable dark matter particle decays into a stable dark matter particle and a non-interacting light particle with decay lifetime comparable to the Hubble time. We study the effects of the recoil kick velocity (Vk) received by the stable dark matter on the structures of dark matter haloes ranging from galaxy-cluster to Milky Way-mass scales. For Milky Way-mass haloes, we use high-resolution, zoom-in simulations to explore the effects of decays on Galactic substructure. In general, haloes with circular velocities comparable to the magnitude of kick velocity are most strongly affected by decays. We show that models with lifetimes Γ-1 ˜ H_0^{-1} and recoil speeds Vk ˜ 20-40 km s-1 can significantly reduce both the abundance of Galactic subhaloes and their internal densities. We find that decaying dark matter models that do not violate current astrophysical constraints can significantly mitigate both the `missing satellites problem' and the more recent `too big to fail problem'. These decaying models predict significant time evolution of haloes, and this implies that at high redshifts decaying models exhibit the similar sequence of structure formation as cold dark matter. Thus, decaying dark matter models are significantly less constrained by high-redshift phenomena than warm dark matter models. We conclude that models of decaying dark matter make predictions that are relevant for the interpretation of small galaxies observations in the Local Group and can be tested as well as by forthcoming large-scale surveys.

Stellar Velocity Dispersion: Linking Quiescent Galaxies to Their Dark Matter Halos

NASA Astrophysics Data System (ADS)

Zahid, H. Jabran; Sohn, Jubee; Geller, Margaret J.

2018-06-01

We analyze the Illustris-1 hydrodynamical cosmological simulation to explore the stellar velocity dispersion of quiescent galaxies as an observational probe of dark matter halo velocity dispersion and mass. Stellar velocity dispersion is proportional to dark matter halo velocity dispersion for both central and satellite galaxies. The dark matter halos of central galaxies are in virial equilibrium and thus the stellar velocity dispersion is also proportional to dark matter halo mass. This proportionality holds even when a line-of-sight aperture dispersion is calculated in analogy to observations. In contrast, at a given stellar velocity dispersion, the dark matter halo mass of satellite galaxies is smaller than virial equilibrium expectations. This deviation from virial equilibrium probably results from tidal stripping of the outer dark matter halo. Stellar velocity dispersion appears insensitive to tidal effects and thus reflects the correlation between stellar velocity dispersion and dark matter halo mass prior to infall. There is a tight relation (≲0.2 dex scatter) between line-of-sight aperture stellar velocity dispersion and dark matter halo mass suggesting that the dark matter halo mass may be estimated from the measured stellar velocity dispersion for both central and satellite galaxies. We evaluate the impact of treating all objects as central galaxies if the relation we derive is applied to a statistical ensemble. A large fraction (≳2/3) of massive quiescent galaxies are central galaxies and systematic uncertainty in the inferred dark matter halo mass is ≲0.1 dex thus simplifying application of the simulation results to currently available observations.

Simulated Milky Way analogues: implications for dark matter direct searches

NASA Astrophysics Data System (ADS)

Bozorgnia, Nassim; Calore, Francesca; Schaller, Matthieu; Lovell, Mark; Bertone, Gianfranco; Frenk, Carlos S.; Crain, Robert A.; Navarro, Julio F.; Schaye, Joop; Theuns, Tom

2016-05-01

We study the implications of galaxy formation on dark matter direct detection using high resolution hydrodynamic simulations of Milky Way-like galaxies simulated within the EAGLE and APOSTLE projects. We identify Milky Way analogues that satisfy observational constraints on the Milky Way rotation curve and total stellar mass. We then extract the dark matter density and velocity distribution in the Solar neighbourhood for this set of Milky Way analogues, and use them to analyse the results of current direct detection experiments. For most Milky Way analogues, the event rates in direct detection experiments obtained from the best fit Maxwellian distribution (with peak speed of 223-289 km/s) are similar to those obtained directly from the simulations. As a consequence, the allowed regions and exclusion limits set by direct detection experiments in the dark matter mass and spin-independent cross section plane shift by a few GeV compared to the Standard Halo Model, at low dark matter masses. For each dark matter mass, the halo-to-halo variation of the local dark matter density results in an overall shift of the allowed regions and exclusion limits for the cross section. However, the compatibility of the possible hints for a dark matter signal from DAMA and CDMS-Si and null results from LUX and SuperCDMS is not improved.

Current Status of the dark matter experiment DarkSide-50

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

Marini, L.; Pagani, Ioanna; Agnes, P.

2016-07-12

DarkSide-50 is a dark matter direct search experiment at LNGS, searching for rare nuclear recoils possibly induced by WIMPs. It has two nested vetoes and a dual phase liquid argon TPC as dark matter detector. Key features of this experiment are the use of underground argon as radio-pure target and of muon and neutron active vetoes to suppress the background. The first data-taking campaign was running from November 2013 to April 2015 with an atmospheric argon target and a reduced efficiency neutron veto due to internal contamination. However, an upper limit on the WIMP-nucleon cross section of 6.1×10-44 cm2 atmore » 90% CL was obtained for a WIMP mass of 100 GeV/c2 and an exposure of (1422 ± 67) kg·d. At present DarkSide-50 started a 3 years run, intended to be background-free because the neutron veto was successfully recovered and underground argon replaced the atmospheric one. Additionally calibration campaigns for both the TPC and the neutron veto were completed. Thanks to the good performance of the background rejection, the results obtained so far suggest the scalability of DarkSide-50 to a ton-scale detector, which will play a key role into the dark matter search scenario.« less

Current status of the dark matter experiment DarkSide-50

NASA Astrophysics Data System (ADS)

Marini, L.; Pagani, L.; Agnes, P.; Alexander, T.; Alton, A.; Arisaka, K.; Back, H. O.; Baldin, B.; Biery, K.; Bonfini, G.; Bossa, M.; Brigatti, A.; Brodsky, J.; Budano, F.; Cadonati, L.; Calaprice, F.; Canci, N.; Candela, A.; Cao, H.; Cariello, M.; Cavalcante, P.; Chavarria, A.; Chepurnov, A.; Cocco, A. G.; D'Angelo, D.; D'Incecco, M.; Davini, S.; De Deo, M.; Derbin, A.; Devoto, A.; Di Eusanio, F.; Di Pietro, G.; Edkins, E.; Empl, A.; Fan, A.; Fiorillo, G.; Fomenko, K.; Forster, G.; Franco, D.; Gabriele, F.; Galbiati, C.; Goretti, A.; Grandi, L.; Gromov, M.; Guan, M. Y.; Guardincerri, Y.; Hackett, B.; Herner, K.; Humble, P.; Hungerford, E. V.; Ianni, Al.; Ianni, An.; Jollet, C.; Keeter, K.; Kendziora, C.; Kidner, S.; Kobychev, V.; Koh, G.; Korablev, D.; Korga, G.; Kurlej, A.; Li, P. X.; Lombardi, P.; Love, C.; Ludhova, L.; Luitz, S.; Ma, Y. Q.; Machulin, I.; Mandarano, A.; Mari, S.; Maricic, J.; Martoff, C. J.; Meregaglia, A.; Meroni, E.; Meyers, P. D.; Milincic, R.; Montanari, D.; Montuschi, M.; Monzani, M. E.; Mosteiro, P.; Mount, B.; Muratova, V.; Musico, P.; Nelson, A.; Odrowski, S.; Okounkova, M.; Orsini, M.; Ortica, F.; Pallavicini, M.; Pantic, E.; Papp, L.; Parmeggiano, S.; Parsells, R.; Pelczar, K.; Pelliccia, N.; Perasso, S.; Pocar, A.; Pordes, S.; Pugachev, D.; Qian, H.; Randle, K.; Ranucci, G.; Razeto, A.; Reinhold, B.; Renshaw, A.; Romani, A.; Rossi, B.; Rossi, N.; Rountree, S. D.; Sablone, D.; Saggese, P.; Saldanha, R.; Sands, W.; Sangiorgio, S.; Segreto, E.; Semenov, D.; Shields, E.; Skorokhvatov, M.; Smirnov, O.; Sotnikov, A.; Stanford, C.; Suvorov, Y.; Tartaglia, R.; Tatarowicz, J.; Testera, G.; Tonazzo, A.; Unzhakov, E.; Vogelaar, R. B.; Wada, M.; Walker, S.; Wang, H.; Wang, Y.; Watson, A.; Westerdale, S.; Wojcik, M.; Wright, A.; Xiang, X.; Xu, J.; Yang, C. G.; Yoo, J.; Zavatarelli, S.; Zec, A.; Zhu, C.; Zuzel, G.; DarkSide Collaboration

2016-01-01

DarkSide-50 is a dark matter direct search experiment at LNGS, searching for rare nuclear recoils possibly induced by WIMPs. It has two nested vetoes and a dual phase liquid argon TPC as dark matter detector. Key features of this experiment are the use of underground argon as radio-pure target and of muon and neutron active vetoes to suppress the background. The first data-taking campaign was running from November 2013 to April 2015 with an atmospheric argon target and a reduced efficiency neutron veto due to internal contamination. However, an upper limit on the WIMP-nucleon cross section of 6.1×10-44 cm2 at 90% CL was obtained for a WIMP mass of 100 GeV/c2 and an exposure of (1422±67) kg . d . At present DarkSide-50 started a 3 years run, intended to be background-free because the neutron veto was successfully recovered and underground argon replaced the atmospheric one. Additionally calibration campaigns for both the TPC and the neutron veto were completed. Thanks to the good performance of the background rejection, the results obtained so far suggest the scalability of DarkSide-50 to a ton-scale detector, which will play a key role into the dark matter search scenario.

Dark matter direct detection of a fermionic singlet at one loop

NASA Astrophysics Data System (ADS)

Herrero-García, Juan; Molinaro, Emiliano; Schmidt, Michael A.

2018-06-01

The strong direct detection limits could be pointing to dark matter - nucleus scattering at loop level. We study in detail the prototype example of an electroweak singlet (Dirac or Majorana) dark matter fermion coupled to an extended dark sector, which is composed of a new fermion and a new scalar. Given the strong limits on colored particles from direct and indirect searches we assume that the fields of the new dark sector are color singlets. We outline the possible simplified models, including the well-motivated cases in which the extra scalar or fermion is a Standard Model particle, as well as the possible connection to neutrino masses. We compute the contributions to direct detection from the photon, the Z and the Higgs penguins for arbitrary quantum numbers of the dark sector. Furthermore, we derive compact expressions in certain limits, i.e., when all new particles are heavier than the dark matter mass and when the fermion running in the loop is light, like a Standard Model lepton. We study in detail the predicted direct detection rate and how current and future direct detection limits constrain the model parameters. In case dark matter couples directly to Standard Model leptons we find an interesting interplay between lepton flavor violation, direct detection and the observed relic abundance.

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

Choi, K.; Itow, Y.; Rott, C., E-mail: koun@stelab.nagoya-u.ac.jp, E-mail: rott@skku.edu, E-mail: itow@stelab.nagoya-u.ac.jp

Dark matter could be captured in the Sun and self-annihilate, giving rise to an observable neutrino flux. Indirect searches for dark matter looking for this signal with neutrino telescopes have resulted in tight constraints on the interaction cross-section of dark matter with ordinary matter. We investigate how robust limits are against astro-physical uncertainties. We study the effect of the velocity distribution of dark matter in our Galaxy on capture rates in the Sun. We investigate four sources of uncertainties: orbital speed of the Sun, escape velocity of dark matter from the halo, dark matter velocity distribution functions and existence ofmore » a dark disc. We find that even extreme cases currently discussed do not decrease the sensitivity of indirect detection significantly because the capture is achieved over a broad range of the velocity distribution by integration over the velocity distribution. The effect of the uncertainty in the high-velocity tail of dark matter halo is very marginal as the capture process is rather inefficient at this region. The difference in capture rate in the Sun for various scenarios is compared to the expected change in event rates for direct detection. The possibility of co-rotating structure with the Sun can largely boost the signal and hence makes the interpretation of indirect detection conservative compared to direct detection.« less

Microbial Ecology of the Dark Ocean above, at, and below the Seafloor†

PubMed Central

Orcutt, Beth N.; Sylvan, Jason B.; Knab, Nina J.; Edwards, Katrina J.

2011-01-01

Summary: The majority of life on Earth—notably, microbial life—occurs in places that do not receive sunlight, with the habitats of the oceans being the largest of these reservoirs. Sunlight penetrates only a few tens to hundreds of meters into the ocean, resulting in large-scale microbial ecosystems that function in the dark. Our knowledge of microbial processes in the dark ocean—the aphotic pelagic ocean, sediments, oceanic crust, hydrothermal vents, etc.—has increased substantially in recent decades. Studies that try to decipher the activity of microorganisms in the dark ocean, where we cannot easily observe them, are yielding paradigm-shifting discoveries that are fundamentally changing our understanding of the role of the dark ocean in the global Earth system and its biogeochemical cycles. New generations of researchers and experimental tools have emerged, in the last decade in particular, owing to dedicated research programs to explore the dark ocean biosphere. This review focuses on our current understanding of microbiology in the dark ocean, outlining salient features of various habitats and discussing known and still unexplored types of microbial metabolism and their consequences in global biogeochemical cycling. We also focus on patterns of microbial diversity in the dark ocean and on processes and communities that are characteristic of the different habitats. PMID:21646433

Fully Integrated Linear Single Photon Avalanche Diode (SPAD) Array with Parallel Readout Circuit in a Standard 180 nm CMOS Process

NASA Astrophysics Data System (ADS)

Isaak, S.; Bull, S.; Pitter, M. C.; Harrison, Ian.

2011-05-01

This paper reports on the development of a SPAD device and its subsequent use in an actively quenched single photon counting imaging system, and was fabricated in a UMC 0.18 μm CMOS process. A low-doped p- guard ring (t-well layer) encircling the active area to prevent the premature reverse breakdown. The array is a 16×1 parallel output SPAD array, which comprises of an active quenched SPAD circuit in each pixel with the current value being set by an external resistor RRef = 300 kΩ. The SPAD I-V response, ID was found to slowly increase until VBD was reached at excess bias voltage, Ve = 11.03 V, and then rapidly increase due to avalanche multiplication. Digital circuitry to control the SPAD array and perform the necessary data processing was designed in VHDL and implemented on a FPGA chip. At room temperature, the dark count was found to be approximately 13 KHz for most of the 16 SPAD pixels and the dead time was estimated to be 40 ns.

Quantum optics with nanowires (Conference Presentation)

NASA Astrophysics Data System (ADS)

Zwiller, Val

2017-02-01

Nanowires offer new opportunities for nanoscale quantum optics; the quantum dot geometry in semiconducting nanowires as well as the material composition and environment can be engineered with unprecedented freedom to improve the light extraction efficiency. Quantum dots in nanowires are shown to be efficient single photon sources, in addition because of the very small fine structure splitting, we demonstrate the generation of entangled pairs of photons from a nanowire. By doping a nanowire and making ohmic contacts on both sides, a nanowire light emitting diode can be obtained with a single quantum dot as the active region. Under forward bias, this will act as an electrically pumped source of single photons. Under reverse bias, an avalanche effect can multiply photocurrent and enables the detection of single photons. Another type of nanowire under study in our group is superconducting nanowires for single photon detection, reaching efficiencies, time resolution and dark counts beyond currently available detectors. We will discuss our first attempts at combining semiconducting nanowire based single photon emitters and superconducting nanowire single photon detectors on a chip to realize integrated quantum circuits.

A 0.18 μm CMOS fluorescent detector system for bio-sensing application

NASA Astrophysics Data System (ADS)

Nan, Liu; Guoping, Chen; Zhiliang, Hong

2009-01-01

A CMOS fluorescent detector system for biological experiment is presented. This system integrates a CMOS compatible photodiode, a capacitive trans-impedance amplifier (CTIA), and a 12 bit pipelined analog-to-digital converter (ADC), and is implemented in a 0.18 μm standard CMOS process. Some special techniques, such as a 'contact imaging' detecting method, pseudo-differential architecture, dummy photodiodes, and a T-type reset switch, are adopted to achieve low-level sensing application. Experiment results show that the Nwell/Psub photodiode with CTIA pixel achieves a sensitivity of 0.1 A/W at 515 nm and a dark current of 300 fA with 300 mV reverse biased voltage. The maximum differential and integral nonlinearity of the designed ADC are 0.8 LSB and 3 LSB, respectively. With an integrating time of 50 ms, this system is sensitive to the fluorescence emitted by the fluorescein solution with concentration as low as 20 ng/mL and can generate 7 fA photocurrent. This chip occupies 3 mm2 and consumes 37 mW.

Light-induced new memory states in electronic resistive switching of NiO/NSTO junction

NASA Astrophysics Data System (ADS)

Wei, Ling; Li, G. Q.; Zhang, W. F.

2016-02-01

n-type and p-type NiO films were prepared on SrTiO3:Nb (NSTO) by controlling oxygen pressures during the process of pulsed laser deposition. The results of current-voltage (I-V) characteristics and photocurrent investigation indicate that the junction shows a typical electronic bipolar resistive switching (RS) behavior and the optical injection can add new resistance states. Photocurrents can obviously be modulated by different resistance states of NiO/NSTO junction. The linear fitting results of I-V curves reveal that the low resistance state follows Ohmic behavior and the high resistance state follows Schottky-emission mechanism. The depletion widths under forward and reverse bias in the dark and with the illumination were estimated respectively. Combined with the energy band structure, the mechanism of RS and photoresponse in the NiO/NSTO junction can be attributed to the variance of interfacial barrier during electrical and optical injection. These results pave the way for the application of the NiO/NSTO junction in the multilevel storage of optical-electrical devices.

Design and characterization of GaN p-i-n diodes for betavoltaic devices

NASA Astrophysics Data System (ADS)

Khan, Muhammad R.; Smith, Joshua R.; Tompkins, Randy P.; Kelley, Stephen; Litz, Marc; Russo, John; Leathersich, Jeff; Shahedipour-Sandvik, Fatemeh (Shadi); Jones, Kenneth A.; Iliadis, Agis

2017-10-01

The performance of gallium nitride (GaN) p-i-n diodes were investigated for use as a betavoltaic device. Dark IV measurements showed a turn on-voltage of approximately 3.2 V, specific-on-resistance of 15.1 mΩ cm2 and a reverse leakage current of -0.14 mA/cm2 at -10 V. A clear photo-response was observed when IV curves were measured under a light source at a wavelength of 310 nm (4.0 eV). In addition, GaN p-i-n diodes were tested under an electron-beam in order to simulate common beta radiation sources ranging from that of 3H (5.6 keV average) to 63Ni (17 keV average). From this data, we estimated output powers of 53 nW and 750 nW with overall efficiencies of 0.96% and 4.4% for our device at incident electron energies of 5.6 keV and 17 keV corresponding to 3H and 63Ni beta sources respectively.

Geiger mode avalanche photodiodes for microarray systems

NASA Astrophysics Data System (ADS)

Phelan, Don; Jackson, Carl; Redfern, R. Michael; Morrison, Alan P.; Mathewson, Alan

2002-06-01

New Geiger Mode Avalanche Photodiodes (GM-APD) have been designed and characterized specifically for use in microarray systems. Critical parameters such as excess reverse bias voltage, hold-off time and optimum operating temperature have been experimentally determined for these photon-counting devices. The photon detection probability, dark count rate and afterpulsing probability have been measured under different operating conditions. An active- quench circuit (AQC) is presented for operating these GM- APDs. This circuit is relatively simple, robust and has such benefits as reducing average power dissipation and afterpulsing. Arrays of these GM-APDs have already been designed and together with AQCs open up the possibility of having a solid-state microarray detector that enables parallel analysis on a single chip. Another advantage of these GM-APDs over current technology is their low voltage CMOS compatibility which could allow for the fabrication of an AQC on the same device. Small are detectors have already been employed in the time-resolved detection of fluorescence from labeled proteins. It is envisaged that operating these new GM-APDs with this active-quench circuit will have numerous applications for the detection of fluorescence in microarray systems.

Interacting dark sector and precision cosmology

NASA Astrophysics Data System (ADS)

Buen-Abad, Manuel A.; Schmaltz, Martin; Lesgourgues, Julien; Brinckmann, Thejs

2018-01-01

We consider a recently proposed model in which dark matter interacts with a thermal background of dark radiation. Dark radiation consists of relativistic degrees of freedom which allow larger values of the expansion rate of the universe today to be consistent with CMB data (H0-problem). Scattering between dark matter and radiation suppresses the matter power spectrum at small scales and can explain the apparent discrepancies between ΛCDM predictions of the matter power spectrum and direct measurements of Large Scale Structure LSS (σ8-problem). We go beyond previous work in two ways: 1. we enlarge the parameter space of our previous model and allow for an arbitrary fraction of the dark matter to be interacting and 2. we update the data sets used in our fits, most importantly we include LSS data with full k-dependence to explore the sensitivity of current data to the shape of the matter power spectrum. We find that LSS data prefer models with overall suppressed matter clustering due to dark matter - dark radiation interactions over ΛCDM at 3–4 σ. However recent weak lensing measurements of the power spectrum are not yet precise enough to clearly distinguish two limits of the model with different predicted shapes for the linear matter power spectrum. In two appendices we give a derivation of the coupled dark matter and dark radiation perturbation equations from the Boltzmann equation in order to clarify a confusion in the recent literature, and we derive analytic approximations to the solutions of the perturbation equations in the two physically interesting limits of all dark matter weakly interacting or a small fraction of dark matter strongly interacting.

Uncorrelated measurements of the cosmic expansion history and dark energy from supernovae

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

Wang Yun; Tegmark, Max; Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104

We present a method for measuring the cosmic expansion history H(z) in uncorrelated redshift bins, and apply it to current and simulated type Ia supernova data assuming spatial flatness. If the matter density parameter {omega}{sub m} can be accurately measured from other data, then the dark-energy density history X(z)={rho}{sub X}(z)/{rho}{sub X}(0) can trivially be derived from this expansion history H(z). In contrast to customary 'black box' parameter fitting, our method is transparent and easy to interpret: the measurement of H(z){sup -1} in a redshift bin is simply a linear combination of the measured comoving distances for supernovae in that bin,more » making it obvious how systematic errors propagate from input to output. We find the Riess et al. (2004) gold sample to be consistent with the vanilla concordance model where the dark energy is a cosmological constant. We compare two mission concepts for the NASA/DOE Joint Dark-Energy Mission (JDEM), the Joint Efficient Dark-energy Investigation (JEDI), and the Supernova Accelaration Probe (SNAP), using simulated data including the effect of weak lensing (based on numerical simulations) and a systematic bias from K corrections. Estimating H(z) in seven uncorrelated redshift bins, we find that both provide dramatic improvements over current data: JEDI can measure H(z) to about 10% accuracy and SNAP to 30%-40% accuracy.« less

Solution-Processed Flexible Organic Ferroelectric Phototransistor.

PubMed

Zhao, Qiang; Wang, Hanlin; Jiang, Lang; Zhen, Yonggang; Dong, Huanli; Hu, Wenping

2017-12-20

In this article, we demonstrate ferroelectric insulator, P(VDF-TrFE), can be integrated with red light sensitive polymeric semiconductor, P(DPP-TzBT), toward ferroelectric organic phototransistors (OPTs). This ferroelectricity-modulated phototransistor possesses different nonvolatile and tunable dark current states due to P(VDF-TrFE)'s remnant polarization. As a result, the OPT is endowed with a tunable dark current level ranging from 1 nA to 100 nA. Once the OPT is programmed or electrically polarized, its photo-to-dark (signal-to-noise) ratio can be "flexible" during photodetection process, without gate bias application. This kind of organic ferroelectric phototransistor has great potential in detecting wide ranges of light signals with good linearity. Moreover, its tuning mechanism discussed in this work can be helpful to understand the operation mechanism of organic phototransistor (OPT). It can be promising for novel photodetection application in plastic electronic devices.

Examining the evidence for dynamical dark energy.

PubMed

Zhao, Gong-Bo; Crittenden, Robert G; Pogosian, Levon; Zhang, Xinmin

2012-10-26

We apply a new nonparametric Bayesian method for reconstructing the evolution history of the equation of state w of dark energy, based on applying a correlated prior for w(z), to a collection of cosmological data. We combine the latest supernova (SNLS 3 year or Union 2.1), cosmic microwave background, redshift space distortion, and the baryonic acoustic oscillation measurements (including BOSS, WiggleZ, and 6dF) and find that the cosmological constant appears consistent with current data, but that a dynamical dark energy model which evolves from w<-1 at z~0.25 to w>-1 at higher redshift is mildly favored. Estimates of the Bayesian evidence show little preference between the cosmological constant model and the dynamical model for a range of correlated prior choices. Looking towards future data, we find that the best fit models for current data could be well distinguished from the ΛCDM model by observations such as Planck and Euclid-like surveys.

Waveguide integrated superconducting single-photon detectors with high internal quantum efficiency at telecom wavelengths

PubMed Central

Kahl, Oliver; Ferrari, Simone; Kovalyuk, Vadim; Goltsman, Gregory N.; Korneev, Alexander; Pernice, Wolfram H. P.

2015-01-01

Superconducting nanowire single-photon detectors (SNSPDs) provide high efficiency for detecting individual photons while keeping dark counts and timing jitter minimal. Besides superior detection performance over a broad optical bandwidth, compatibility with an integrated optical platform is a crucial requirement for applications in emerging quantum photonic technologies. Here we present SNSPDs embedded in nanophotonic integrated circuits which achieve internal quantum efficiencies close to unity at 1550 nm wavelength. This allows for the SNSPDs to be operated at bias currents far below the critical current where unwanted dark count events reach milli-Hz levels while on-chip detection efficiencies above 70% are maintained. The measured dark count rates correspond to noise-equivalent powers in the 10−19 W/Hz−1/2 range and the timing jitter is as low as 35 ps. Our detectors are fully scalable and interface directly with waveguide-based optical platforms. PMID:26061283

Constraints on the dark matter neutralinos from the radio emissions of galaxy clusters

NASA Astrophysics Data System (ADS)

Kiew, Ching-Yee; Hwang, Chorng-Yuan; Zainal Abibin, Zamri

2017-05-01

By assuming the dark matter to be composed of neutralinos, we used the detection of upper limit on diffuse radio emission in a sample of galaxy clusters to put constraint on the properties of neutralinos. We showed the upper limit constraint on <σv>-mχ space with neutralino annihilation through b\\bar{b} and μ+μ- channels. The best constraint is from the galaxy clusters A2199 and A1367. We showed the uncertainty due to the density profile and cluster magnetic field. The largest uncertainty comes from the uncertainty in dark matter spatial distribution. We also investigated the constraints on minimal Supergravity (mSUGRA) and minimal supersymmetric standard model (MSSM) parameter space by scanning the parameters using the darksusy package. By using the current radio observation, we managed to exclude 40 combinations of mSUGRA parameters. On the other hand, 573 combinations of MSSM parameters can be excluded by current observation.

Waveguide integrated superconducting single-photon detectors with high internal quantum efficiency at telecom wavelengths.

PubMed

Kahl, Oliver; Ferrari, Simone; Kovalyuk, Vadim; Goltsman, Gregory N; Korneev, Alexander; Pernice, Wolfram H P

2015-06-10

Superconducting nanowire single-photon detectors (SNSPDs) provide high efficiency for detecting individual photons while keeping dark counts and timing jitter minimal. Besides superior detection performance over a broad optical bandwidth, compatibility with an integrated optical platform is a crucial requirement for applications in emerging quantum photonic technologies. Here we present SNSPDs embedded in nanophotonic integrated circuits which achieve internal quantum efficiencies close to unity at 1550 nm wavelength. This allows for the SNSPDs to be operated at bias currents far below the critical current where unwanted dark count events reach milli-Hz levels while on-chip detection efficiencies above 70% are maintained. The measured dark count rates correspond to noise-equivalent powers in the 10(-19) W/Hz(-1/2) range and the timing jitter is as low as 35 ps. Our detectors are fully scalable and interface directly with waveguide-based optical platforms.

Constraining viscous dark energy models with the latest cosmological data

NASA Astrophysics Data System (ADS)

Wang, Deng; Yan, Yang-Jie; Meng, Xin-He

2017-10-01

Based on the assumption that the dark energy possessing bulk viscosity is homogeneously and isotropically permeated in the universe, we propose three new viscous dark energy (VDE) models to characterize the accelerating universe. By constraining these three models with the latest cosmological observations, we find that they just deviate very slightly from the standard cosmological model and can alleviate effectively the current H_0 tension between the local observation by the Hubble Space Telescope and the global measurement by the Planck Satellite. Interestingly, we conclude that a spatially flat universe in our VDE model with cosmic curvature is still supported by current data, and the scale invariant primordial power spectrum is strongly excluded at least at the 5.5σ confidence level in the three VDE models as the Planck result. We also give the 95% upper limits of the typical bulk viscosity parameter η in the three VDE scenarios.

Dark energy from discrete spacetime.

PubMed

Trout, Aaron D

2013-01-01

Dark energy accounts for most of the matter-energy content of our universe, yet current theories of its origin rely on radical physical assumptions such as the holographic principle or controversial anthropic arguments. We give a better motivated explanation for dark energy, claiming that it arises from a small negative scalar-curvature present even in empty spacetime. The vacuum has this curvature because spacetime is fundamentally discrete and there are more ways for a discrete geometry to have negative curvature than positive. We explicitly compute this effect using a variant of the well known dynamical-triangulations (DT) model for quantum gravity. Our model predicts a time-varying non-zero cosmological constant with a current value, [Formula: see text] in natural units, in agreement with observation. This calculation is made possible by a novel characterization of the possible DT action values combined with numerical evidence concerning their degeneracies.

SuperCDMS Underground Detector Fabrication Facility

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

Platt, M.; Mahapatra, R.; Bunker, Raymond A.

The SuperCDMS SNOLAB dark matter experiment processes Ge and Si crystals into fully tested phonon and ionization detectors at surface fabrication and test facilities. If not mitigated, it is anticipated that trace-level production of radioisotopes in the crystals due to exposure to cosmic rays at (or above) sea level will result in the dominant source of background events in future dark matter searches using the current SuperCDMS detector technology. Fabrication and testing of detectors in underground facilities shielded from cosmic radiation is one way to directly reduce production of trace levels of radioisotopes, thereby improving experimental sensitivity for the discoverymore » of dark matter beyond the level of the current experiment. In this report, we investigate the cost and feasibility to establish a complete detector fabrication processing chain in an underground location to mitigate cosmogenic activation of the Ge and Si detector substrates. For a specific and concrete evaluation, we explore options for such a facility located at SNOLAB, an underground laboratory in Sudbury, Canada hosting the current and future experimental phases of SuperCDMS.« less

Boosted dark matter signals uplifted with self-interaction

DOE PAGES

Kong, Kyoungchul; Mohlabeng, Gopolang; Park, Jong -Chul

2015-04-01

We explore detection prospects of a non-standard dark sector in the context of boosted dark matter. We focus on a scenario with two dark matter particles of a large mass difference, where the heavier candidate is secluded and interacts with the standard model particles only at loops, escaping existing direct and indirect detection bounds. Yet its pair annihilation in the galactic center or in the Sun may produce boosted stable particles, which could be detected as visible Cherenkov light in large volume neutrino detectors. In such models with multiple candidates, self-interaction of dark matter particles is naturally utilized in themore » assisted freeze-out mechanism and is corroborated by various cosmological studies such as N-body simulations of structure formation, observations of dwarf galaxies, and the small scale problem. We show that self-interaction of the secluded (heavier) dark matter greatly enhances the capture rate in the Sun and results in promising signals at current and future experiments. We perform a detailed analysis of the boosted dark matter events for Super-Kamiokande, Hyper-Kamiokande and PINGU, including notable effects such as evaporation due to self-interaction and energy loss in the Sun.« less

Boosted dark matter signals uplifted with self-interaction

NASA Astrophysics Data System (ADS)

Kong, Kyoungchul; Mohlabeng, Gopolang; Park, Jong-Chul

2015-04-01

We explore detection prospects of a non-standard dark sector in the context of boosted dark matter. We focus on a scenario with two dark matter particles of a large mass difference, where the heavier candidate is secluded and interacts with the standard model particles only at loops, escaping existing direct and indirect detection bounds. Yet its pair annihilation in the galactic center or in the Sun may produce boosted stable particles, which could be detected as visible Cherenkov light in large volume neutrino detectors. In such models with multiple candidates, self-interaction of dark matter particles is naturally utilized in the assisted freeze-out mechanism and is corroborated by various cosmological studies such as N-body simulations of structure formation, observations of dwarf galaxies, and the small scale problem. We show that self-interaction of the secluded (heavier) dark matter greatly enhances the capture rate in the Sun and results in promising signals at current and future experiments. We perform a detailed analysis of the boosted dark matter events for Super-Kamiokande, Hyper-Kamiokande and PINGU, including notable effects such as evaporation due to self-interaction and energy loss in the Sun.

Dark energy constraints in light of Pantheon SNe Ia, BAO, cosmic chronometers and CMB polarization and lensing data

NASA Astrophysics Data System (ADS)

Wang, Deng

2018-06-01

To explore whether there is new physics going beyond the standard cosmological model or not, we constrain seven cosmological models by combining the latest and largest Pantheon Type Ia supernovae sample with the data combination of baryonic acoustic oscillations, cosmic microwave background radiation, Planck lensing and cosmic chronometers. We find that a spatially flat universe is preferred in the framework of Λ CDM cosmology, that the constrained equation of state of dark energy is very consistent with the cosmological constant hypothesis in the ω CDM model, that there is no evidence of dynamical dark energy in the dark energy density-parametrization model, that there is no hint of interaction between dark matter and dark energy in the dark sector of the universe in the decaying vacuum model, and that there does not exist the sterile neutrino in the neutrino sector of the universe in the Λ CDM model. We also give the 95% upper limit of the total mass of three active neutrinos Σ mν<0.178 eV under the assumption of Λ CDM scenario. It is clear that there is no any departure from the standard cosmological model based on current observational datasets.

Factors controlling charge recombination under dark and light conditions in dye sensitised solar cells.

PubMed

Barnes, Piers R F; Anderson, Assaf Y; Juozapavicius, Mindaugas; Liu, Lingxuan; Li, Xiaoe; Palomares, Emilio; Forneli, Amparo; O'Regan, Brian C

2011-02-28

A simple and powerful approach for assessing the recombination losses in dye sensitised solar cells (DSSCs) across the current voltage curve (j-V) as a function of TiO(2) electron concentration (n) is demonstrated. The total flux of electrons recombining with iodine species in the electrolyte and oxidised dye molecules can be thought of as a recombination current density, defined as j(rec) = j(inj)-j where j(inj) is the current of electrons injected from optically excited dye states and j is the current density collected at cell voltage (V). The electron concentration at any given operating conditions is determined by charge extraction. This allows comparison of factors influencing electron recombination rates at matched n. We show that j(rec) is typically 2-3 times higher under 1 sun equivalent illumination (j(inj) > 0) relative to dark (j(inj) = 0) conditions. This difference was increased by increasing light intensity, electrolyte iodine concentration and electrolyte solvent viscosity. The difference was reduced by increasing the electrolyte iodide concentration and increasing the temperature. These results allowed us to verify a numerical model of complete operational cells (Barnes et al., Phys. Chem. Chem. Phys., DOI: 10.1039/c0cp01554g) and to relate the differences in j(rec) to physical processes in the devices. The difference between j(rec) in the light and dark can be explained by two factors: (1) an increase in the concentration of electron acceptor species (I(3)(-) and/or I(2)) when current is flowing under illumination relative to dark conditions where the current is flowing in the opposite direction, and (2) a non-trivial contribution from electron recombination to oxidised dye molecules under light conditions. More generally, the technique helps to assign the observed relationship between the components, processing and performance of DSSCs to more fundamental physical processes.

Ion Fluxes and Short-Circuit Current in Internally Perfused Cells of Valonia ventricosa

PubMed Central

Gutknecht, John

1967-01-01

Ion transport in the giant celled marine alga, Valonia ventricosa, was studied during internal perfusion and short-circuiting of the vacuole potential. The perfusing and bathing solutions were similar to natural Valonia sap and contained the following concentrations of major ions: Na 51, K 618, and Cl 652 mM. The average short-circuit current (I sc) was 97 pEq/cm2 sec (inward positive current), and the average open-circuit potential difference (PD) was 74 mv (vacuole positive to external solution). Perfused and short-circuited cells showed a small net influx of Na (2.0 pEq/cm2 sec) and large net influxes of K (80 pEq/cm2 sec) and Cl (50 pEq/cm2 sec). Unidirectional K influx was proportional to I sc, but more than one-half of the I sc remained unaccounted for. Both the I sc and PD were partly light-dependent, declining rapidly during the first 1–2 min of darkness. Ouabain (5 x 10-4 M) had little effect on the influx of Na or K and had no effect on I inf or PD. Fluid was absorbed at a rate of about 93 pliter/cm2 sec. Reversing the direction of fluid movement by adding mannitol to the outside solution had little effect on ion movements. The ionic and electrical properties of normal and perfused cells of Valonia are compared. PMID:6050968

Changes in seasonal climate patterns from 34-4 ka in a Soreq Cave (Israel) speleothem: Sub-annual resolution by ion microprobe and CLFM

NASA Astrophysics Data System (ADS)

Orland, I. J.; Bar-Matthews, M.; Kita, N.; Ayalon, A.; Valley, J. W.

2009-12-01

Speleothems provide an important proxy-record of paleoclimate. Isotopic data from calcite-dominated cave formations have been used to identify changes in annual rainfall, monsoon strength, telecommunication of Northern Hemisphere climate aberrations, changes in vegetation cover, and other region-specific paleoclimate time-series over annual to millennial timescales. As more research is devoted to understanding abrupt climate change events, there is a need to develop high-temporal-resolution records from continental regions. However, in most isotopic studies, seasonality information is lost due to technical limitations. This study focuses on a speleothem from the semi-arid Eastern Mediterranean region (Soreq Cave, Israel) where prior research shows that conventional drill-sampling methods permit a temporal resolution of ~10-50 years in speleothem paleoclimate records. The WiscSIMS lab has developed analytical protocols for ion microprobe analysis that yield a precision of ~0.3‰ (2 s.d.) in δ18O from 10 μm-diameter spots, which permit multiple analyses/year in many speleothems. Orland et al. (2009, Quat. Res.) establish the methodology for the current study by identifying seasonal variability using a combination of confocal laser fluorescent microscopy (CLFM) and ion microprobe analysis in a younger (~2-1 ka) Soreq speleothem that has a consistent bright-grading-to-dark fluorescence pattern within each annual band. Further, Orland et al. define a quantitative measure of seasonality, Δ18O, that measures the difference in δ18O between bright and dark fluorescent portions of individual annual growth bands [Δ18O = δ18Odark - δ18Obright]. Smaller values of Δ18O are interpreted to be caused by dry years. The current study employs the aforementioned methods to examine seasonality trends in a sample that covers a much longer time period. We report δ18O from >1000 spots across a radial traverse of Soreq Cave sample 2N matched to imaging of annual growth bands by CLFM. This record, which extends from 34-4 ka, based on 27 new U-Th dates from the Geological Survey of Israel, preserves a time-series of δ18O across multiple significant climate changes including the last glacial termination, the onset/termination of the YD, and multiple abrupt regional events. As in the younger sample from Soreq, CLFM of the Holocene portion of sample 2N reveals concentric, annual growth bands in bright-grading-to-dark fluorescent couplets. In the pre-Holocene portion of 2N, however, the pattern of fluorescence banding is consistently reversed (i.e. dark-grading-to-bright). Furthermore, the magnitude of Δ18O changes through time. The prominent change in the CLFM and Δ18O record for sample 2N suggests a shift in seasonality in the Eastern Mediterranean before the termination of the YD; variation in seasonal rainfall and/or surface vegetation may have contributed to the observed change.