380 research outputs found
The contribution of an educational phase to the stress inoculation of anxiety
All subjects were selected from introductory speech classes at the University of Richmond. A public speaking fear survey was given to all students at the beg inning of the semester. Construct validity of this survey has been established by discriminating anxious from non- anxious people. Students scoring above the median were invited to participate in a workshop on dealing with the stress of public speaking. Subjects who accepted the invitation were assigned to one of four groups: stress inoculation with education (Combination) , stress inoculation without education (Skills only), education without stress inoculation (Education only), or a no treatment control (NTC). The assignments were made according to the subjects\u27 schedules
Superfast photon counting
The news that superconducting nanowire detectors can detect single photons with a timing precision of just a few picoseconds will benefit applications ranging from sensing to quantum communications
Superconducting nanowire single-photon detectors with non-periodic dielectric multilayers
We present superconducting nanowire single-photon detectors (SSPDs) on non-periodic dielectric multilayers, which enable us to design a variety of wavelength dependences of optical absorptance by optimizing the dielectric multilayer. By adopting a robust simulation to optimize the dielectric multilayer, we designed three types of SSPDs with target wavelengths of 500 nm, 800 nm, and telecom range respectively. We fabricated SSPDs based on the optimized designs for 500 and 800 nm, and evaluated the system detection efficiency at various wavelengths. The results obtained confirm that the designed SSPDs with non-periodic dielectric multilayers worked well. This versatile device structure can be effective for multidisciplinary applications in fields such as the life sciences and remote sensing that require high efficiency over a precise spectral range and strong signal rejection at other wavelengths
Optical properties of refractory metal based thin films
There is a growing interest in refractory metal thin films for a range of emerging nanophotonic applications including high temperature plasmonic structures and infrared superconducting single photon detectors. We present a detailed comparison of optical properties for key representative materials in this class (NbN, NbTiN, TiN and MoSi) with texture varying from crystalline to amorphous. NbN, NbTiN and MoSi have been grown in an ultra-high vacuum sputter deposition system. Two different techniques (sputtering and atomic layer deposition) have been employed to deposit TiN. We have carried out variable angle ellipsometric measurements of optical properties from ultraviolet to mid infrared wavelengths. We compare with high resolution transmission electron microscopy analysis of microstructure. Sputter deposited TiN and MoSi have shown the highest optical absorption in the infrared wavelengths relative to NbN, NbTiN or ALD deposited TiN. We have also modelled the performance of a semi-infinite metal air interface as a plasmonic structure with the above mentioned refractory metal based thin films as the plasmonic components. This study has implications in the design of next generation superconducting nanowire single photon detector or plasmonic nanostructure based devices
Analysis of a distributed fiber-optic temperature sensor using single-photon detectors
We demonstrate a high-accuracy distributed fiber-optic temperature sensor using superconducting nanowire single-photon detectors and single-photon counting techniques. Our demonstration uses inexpensive single-mode fiber at standard telecommunications wavelengths as the sensing fiber, which enables extremely low-loss experiments and compatibility with existing fiber networks. We show that the uncertainty of the temperature measurement decreases with longer integration periods, but is ultimately limited by the calibration uncertainty. Temperature uncertainty on the order of 3 K is possible with spatial resolution of the order of 1 cm and integration period as small as 60 seconds. Also, we show that the measurement is subject to systematic uncertainties, such as polarization fading, which can be reduced with a polarization diversity receiver
GHz bandwidth electro-optics of a single self-assembled quantum dot in a charge-tunable device
The response of a single InGaAs quantum dot, embedded in a miniaturized
charge-tunable device, to an applied GHz bandwidth electrical pulse is
investigated via its optical response. Quantum dot response times of 1.0 \pm
0.1 ns are characterized via several different measurement techniques,
demonstrating GHz bandwidth electrical control. Furthermore a novel optical
detection technique based on resonant electron-hole pair generation in the
hybridization region is used to map fully the voltage pulse experienced by the
quantum dot, showing in this case a simple exponential rise.Comment: 7 pages, 4 figure
Investigations of afterpulsing and detection efficiency recovery in superconducting nanowire single-photon detectors
We report on the observation of a non-uniform dark count rate in
Superconducting Nanowire Single Photon Detectors (SNSPDs), specifically
focusing on an afterpulsing effect present when the SNSPD is operated at a high
bias current regime. The afterpulsing exists for real detection events
(triggered by input photons) as well as for dark counts (no laser input). In
our standard set-up, the afterpulsing is most likely to occur at around 180 ns
following a detection event, for both real counts and dark counts. We
characterize the afterpulsing behavior and speculate that it is not due to the
SNSPD itself but rather the amplifiers used to boost the electrical output
signal from the SNSPD. We show that the afterpulsing indeed disappears when we
use a different amplifier with a better low frequency response. We also examine
the short-lived enhancement of detection efficiency during the recovery of the
SNSPD due to temporary perturbation of the bias and grounding conditions
Design and characterisation of titanium nitride sub-arrays of kinetic inductance detectors for passive terahertz imaging
We report on the investigation of titanium nitride (TiN) thin films deposited via atomic layer deposition (ALD) for microwave kinetic inductance detectors (MKID). Using our in-house ALD process, we have grown a sequence of TiN thin films (thickness 15, 30, 60 nm). The films have been characterised in terms of superconducting transition temperature Tc , sheet resistance Rs and microstructure. We have fabricated test resonator structures and characterised them at a temperature of 300 mK. At 350 GHz, we report an optical noise equivalent power NEPopt≈2.3×10−15 W/√Hz , which is promising for passive terahertz imaging applications
Nano-optical observation of cascade switching in a parallel superconducting nanowire single photon detector
The device physics of parallel-wire superconducting nanowire single photon
detectors is based on a cascade process. Using nano-optical techniques and a
parallel wire device with spatially-separate pixels we explicitly demonstrate
the single- and multi-photon triggering regimes. We develop a model for
describing efficiency of a detector operating in the arm-trigger regime. We
investigate the timing response of the detector when illuminating a single
pixel and two pixels. We see a change in the active area of the detector
between the two regimes and find the two-pixel trigger regime to have a faster
timing response than the one-pixel regime.Comment: 11 pages, 2 figure
The complete mitochondrial genome of Achatinella mustelina (Gastropoda: Pulmonata: Stylommatophora)
In this study, we report the complete mitochondrial genome sequence of Achatinella mustelina, an endangered Hawaiian tree snail. The mitogenome is 16 323 bp in length and has a base composition of A (34.7%), T (42.6%), C (12.7%) and G (10.0%). Similar to other Pulmonates, it contains 13 protein-coding genes, 2 rRNA genes and 22 tRNA genes. To our knowledge, this is the first mitochondrial genome sequenced within the Achatinelloidea superfamily, which contains a high number of endangered species. As such, this mitogenome will be useful in conservation genetics studies
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