243 research outputs found
Effect of nano-scale surface roughness on transverse energy spread from GaAs photocathodes
High quantum yield, low transverse energy spread and prompt response time
make GaAs activated to negative electron affnity, an ideal candidate for a
photocathode in high brightness photoinjectors. Even after decades of
investigation, the exact mechanism of electron emission from GaAs is not well
understood. We show that a nanoscale surface roughness can affect the
transverse electron spread from GaAs by nearly an order of magnitude and
explain the seemingly controversial experimental results obtained so far. This
model can also explain the measured dependence of transverse energy spread on
the wavelength of incident light.Comment: 3pages, 3figure
Sperm penetration assay and its correlation with semen analysis parameters
Background: Aim of current study was to determine whether the Sperm Penetration Assay (SPA) can be used as a test to discriminate the infertile male from fertile one. We have also correlated the SPA with semen analysis.Methods: Sperm characteristics namely Semen analysis and the sperm penetration assay were tested in 44 infertile and 10 fertile men. Sperm penetration assay was determined by using zona free hamster eggs.Results: With decreasing spermatozoa concentration in the semen there was significant decrease in percentage penetration of zona free Hamster eggs (p0.05). Â Conclusions: The Sperm penetration assay could discriminate the infertile group from fertile group significantly (p<0.001). The test appeared to be highly reproducible and probably identifies a truly infertile male.
Comparison of artifacts between paste and collodion method of electrode application in pediatric EEG
© 2019 International Federation of Clinical Neurophysiology Objectives: Children pose challenges to obtain quality EEG data due to excessive artifact. Collodion is used in EEG electrodes due to its water resistance and strong adhesive qualities. This study was done to evaluate differences in artifacts between the collodion and paste method. Methods: 115 subjects (children age \u3e3 years) were randomized into paste and collodion groups and artifacts evaluated at baseline and every hour over 30 s increments. Age, sleep state, and number of electrodes with artifact were also documented. T-test was performed to determine differences in the various parameters between the two groups. Results: 61 subjects were in the paste group and 54 in the collodion group. Mean of total seconds of artifact from 0 to 24 h were 41.8 s in paste group versus 30.3 s in collodion group (P = 0.02). Children \u3e11 years old had less artifact than younger children from 0 to 24 h (24.3 versus 41.2 s, P = 0.03), and from 24 to 48 h (33.1 versus 43.1 s, P = 0.03). There was a significant effect of sleep vs. awake state recordings on artifact from 0 to 24 h (30.3 versus 50.2 s, P = 0.01). Conclusion: Electrode problems are common with both collodion and paste in prolonged AEEG monitoring. However, for studies less than 24 h, collodion may be a better alternative. Significance: Our study provides evidence that in some cases collodion may be a better alternative to paste in terms of decreased artifacts
BICEP3: a 95 GHz refracting telescope for degree-scale CMB polarization
BICEP3 is a 550 mm-aperture refracting telescope for polarimetry of radiation
in the cosmic microwave background at 95 GHz. It adopts the methodology of
BICEP1, BICEP2 and the Keck Array experiments - it possesses sufficient
resolution to search for signatures of the inflation-induced cosmic
gravitational-wave background while utilizing a compact design for ease of
construction and to facilitate the characterization and mitigation of
systematics. However, BICEP3 represents a significant breakthrough in
per-receiver sensitivity, with a focal plane area 5 larger than a
BICEP2/Keck Array receiver and faster optics ( vs. ).
Large-aperture infrared-reflective metal-mesh filters and infrared-absorptive
cold alumina filters and lenses were developed and implemented for its optics.
The camera consists of 1280 dual-polarization pixels; each is a pair of
orthogonal antenna arrays coupled to transition-edge sensor bolometers and read
out by multiplexed SQUIDs. Upon deployment at the South Pole during the 2014-15
season, BICEP3 will have survey speed comparable to Keck Array 150 GHz (2013),
and will significantly enhance spectral separation of primordial B-mode power
from that of possible galactic dust contamination in the BICEP2 observation
patch.Comment: 12 pages, 5 figures. Presented at SPIE Astronomical Telescopes and
Instrumentation 2014: Millimeter, Submillimeter, and Far-Infrared Detectors
and Instrumentation for Astronomy VII. To be published in Proceedings of SPIE
Volume 915
The simulation and design of an on-chip superconducting millimetre filter-bank spectrometer
Superconducting on-chip filter banks provide a scalable, space saving solution to create imaging spectrometers at millimetre and submillimetre wavelengths. We present an easy to realise, lithographed superconducting filter design with a high tolerance to fabrication error. Using a capacitively coupled λ/2 microstrip resonator to define a narrow (λ/Δλ=300) spectral pass band, the filtered output of a given spectrometer channel directly connects to a lumped-element kinetic inductance detector. We show the tolerance analysis of our design, demonstrating <11% change in filter quality factor to any one realistic fabrication error and a full filter-bank efficiency forecast to be 50% after accounting for fabrication errors and dielectric loss tangent
The design and characterization of a 300 channel, optimized full-band millimeter filterbank for science with SuperSpec
SuperSpec is an integrated, on-chip spectrometer for millimeter and sub-millimeter astronomy. We report the approach, design optimization, and partial characterization of a 300 channel filterbank covering the 185 to 315 GHz frequency band that targets a resolving power R ~ 310, and fits on a 3.5×5.5 cm chip. SuperSpec uses a lens and broadband antenna to couple radiation into a niobium microstrip that feeds a bank of niobium microstrip half-wave resonators for frequency selectivity. Each half-wave resonator is coupled to the inductor of a titanium nitride lumped-element kinetic inductance detector (LEKID) that detects the incident radiation. The device was designed for use in a demonstration instrument at the Large Millimeter Telescope (LMT)
BICEP2 II: Experiment and Three-Year Data Set
We report on the design and performance of the BICEP2 instrument and on its
three-year data set. BICEP2 was designed to measure the polarization of the
cosmic microwave background (CMB) on angular scales of 1 to 5 degrees
(=40-200), near the expected peak of the B-mode polarization signature of
primordial gravitational waves from cosmic inflation. Measuring B-modes
requires dramatic improvements in sensitivity combined with exquisite control
of systematics. The BICEP2 telescope observed from the South Pole with a 26~cm
aperture and cold, on-axis, refractive optics. BICEP2 also adopted a new
detector design in which beam-defining slot antenna arrays couple to
transition-edge sensor (TES) bolometers, all fabricated on a common substrate.
The antenna-coupled TES detectors supported scalable fabrication and
multiplexed readout that allowed BICEP2 to achieve a high detector count of 500
bolometers at 150 GHz, giving unprecedented sensitivity to B-modes at degree
angular scales. After optimization of detector and readout parameters, BICEP2
achieved an instrument noise-equivalent temperature of 15.8 K sqrt(s). The
full data set reached Stokes Q and U map depths of 87.2 nK in square-degree
pixels (5.2 K arcmin) over an effective area of 384 square degrees within
a 1000 square degree field. These are the deepest CMB polarization maps at
degree angular scales to date. The power spectrum analysis presented in a
companion paper has resulted in a significant detection of B-mode polarization
at degree scales.Comment: 30 pages, 24 figure
Keck array and BICEP3: spectral characterization of 5000+ detectors
The inflationary paradigm of the early universe predicts a stochastic background of gravitational waves which would generate a B-mode polarization pattern in the cosmic microwave background (CMB) at degree angular scales. Precise measurement of B-modes is one of the most compelling observational goals in modern cosmology. Since 2011, the Keck Array has deployed over 2500 transition edge sensor (TES) bolometer detectors at 100 and 150 GHz to the South Pole in pursuit of degree-scale B-modes, and Bicep3 will follow in 2015 with 2500 more at 100 GHz. Characterizing the spectral response of these detectors is important for controlling systematic effects that could lead to leakage from the temperature to polarization signal, and for understanding potential coupling to atmospheric and astrophysical emission lines. We present complete spectral characterization of the Keck Array detectors, made with a Martin-Puplett Fourier Transform Spectrometer at the South Pole, and preliminary spectra of Bicep3 detectors taken in lab. We show band centers and effective bandwidths for both Keck Array bands, and use models of the atmosphere at the South Pole to cross check our absolute calibration. Our procedure for obtaining interferograms in the field with automated 4-axis coupling to the focal plane represents an important step towards efficient and complete spectral characterization of next-generation instruments more than 10000 detectors
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