68,302 research outputs found
Multiport VNA Measurements
This article presents some of the most recent multiport VNA measurement methodologies used to characterize these highspeed digital networks for signal integrity. There will be a discussion of the trends and measurement challenges of high-speed digital systems, followed by a presentation of the multiport VNA measurement system details, calibration, and measurement techniques, as well as some examples of interconnect device measurements. The intent here is to present some general concepts and trends for multiport VNA measurements as applied to computer system board-level interconnect structures, and not to promote any particular brand or produc
Combining Magnetic and Electric Sails for Interstellar Deceleration
The main benefit of an interstellar mission is to carry out in-situ
measurements within a target star system. To allow for extended in-situ
measurements, the spacecraft needs to be decelerated. One of the currently most
promising technologies for deceleration is the magnetic sail which uses the
deflection of interstellar matter via a magnetic field to decelerate the
spacecraft. However, while the magnetic sail is very efficient at high
velocities, its performance decreases with lower speeds. This leads to
deceleration durations of several decades depending on the spacecraft mass.
Within the context of Project Dragonfly, initiated by the Initiative of
Interstellar Studies (i4is), this paper proposes a novel concept for
decelerating a spacecraft on an interstellar mission by combining a magnetic
sail with an electric sail. Combining the sails compensates for each
technologys shortcomings: A magnetic sail is more effective at higher
velocities than the electric sail and vice versa. It is demonstrated that using
both sails sequentially outperforms using only the magnetic or electric sail
for various mission scenarios and velocity ranges, at a constant total
spacecraft mass. For example, for decelerating from 5% c, to interplanetary
velocities, a spacecraft with both sails needs about 29 years, whereas the
electric sail alone would take 35 years and the magnetic sail about 40 years
with a total spacecraft mass of 8250 kg. Furthermore, it is assessed how the
combined deceleration system affects the optimal overall mission architecture
for different spacecraft masses and cruising speeds. Future work would
investigate how operating both systems in parallel instead of sequentially
would affect its performance. Moreover, uncertainties in the density of
interstellar matter and sail properties need to be explored
The STAR MAPS-based PiXeL detector
The PiXeL detector (PXL) for the Heavy Flavor Tracker (HFT) of the STAR
experiment at RHIC is the first application of the state-of-the-art thin
Monolithic Active Pixel Sensors (MAPS) technology in a collider environment.
Custom built pixel sensors, their readout electronics and the detector
mechanical structure are described in detail. Selected detector design aspects
and production steps are presented. The detector operations during the three
years of data taking (2014-2016) and the overall performance exceeding the
design specifications are discussed in the conclusive sections of this paper
Broadband passive InP membrane regenerator for silicon-based optical interconnect applications
Improved passive signal regeneration performance based on bonded InP membrane waveguides is demonstrated. A tripling of the ER and receiver sensitivity enhancement of >3.6dB is achieved over the entire C-band at a bitrate of 2.5Gb/
Near-field Testing of the 15-meter Model of the Hoop Column Antenna
The technical results from near-field testing of the 15-meter model of the hoop column antenna at the Martin Marietta Denver Aerospace facility are documented. The antenna consists of a deployable central column and a 15 meter hoop, stiffened by cables into a structure with a high tolerance repeatable surface and offset feed location. The surface has been configured to have four offset parabolic apertures, each about 6 meters in diameter, and is made of gold plated molybdenum wire mesh. Pattern measurements were made with feed systems radiating at frequencies of 7.73, 11.60, 2.27, 2.225, and 4.26 (all in GHz). This report (Volume 1) covers the testing from an overall viewpoint and contains information of generalized interest for testing large antennas. This volume discusses the deployment of the antenna in the Martin Facility and the measurements to determine mechanical stability and trueness of the reflector surface, gives the test program outline, and gives a synopsis of antenna electromagnetic performance. Three techniques for measuring surface mechanical tolerances were used (theodolites, metric cameras, and near-field phase), but only the near-field phase approach is included. The report also includes an error analysis. A detailed listing of the antenna patterns are provided for the 2.225 Ghz feed in Volume 3 of this report, and for all other feeds in Volume 2
Epsilon-Near-Zero Al-Doped ZnO for Ultrafast Switching at Telecom Wavelengths: Outpacing the Traditional Amplitude-Bandwidth Trade-Off
Transparent conducting oxides have recently gained great attention as
CMOS-compatible materials for applications in nanophotonics due to their low
optical loss, metal-like behavior, versatile/tailorable optical properties, and
established fabrication procedures. In particular, aluminum doped zinc oxide
(AZO) is very attractive because its dielectric permittivity can be engineered
over a broad range in the near infrared and infrared. However, despite all
these beneficial features, the slow (> 100 ps) electron-hole recombination time
typical of these compounds still represents a fundamental limitation impeding
ultrafast optical modulation. Here we report the first epsilon-near-zero AZO
thin films which simultaneously exhibit ultra-fast carrier dynamics (excitation
and recombination time below 1 ps) and an outstanding reflectance modulation up
to 40% for very low pump fluence levels (< 4 mJ/cm2) at the telecom wavelength
of 1.3 {\mu}m. The unique properties of the demonstrated AZO thin films are the
result of a low temperature fabrication procedure promoting oxygen vacancies
and an ultra-high carrier concentration. As a proof-of-concept, an all-optical
AZO-based plasmonic modulator achieving 3 dB modulation in 7.5 {\mu}m and
operating at THz frequencies is numerically demonstrated. Our results overcome
the traditional "modulation depth vs. speed" trade-off by at least an order of
magnitude, placing AZO among the most promising compounds for
tunable/switchable nanophotonics.Comment: 14 pages, 9 figures, 1 tabl
Avco Lycoming quiet clean general aviation turbofan engine
A fan module was developed using an existing turboshaft engine. The fan was designed using the latest in large engine noise control technology. A mixer was added to reduce the already low exhaust gas velocity. A nacelle incorporating sound treatment was provided for the test engine. A noise prediction model was used through the design process to evaluate the various design alternatives. Acoustic tests were then made to verify the prediction and identify the noise characteristics of the fan, core, jet, and sound treatment. Analysis of the recorded data yielded close agreement with the expected results. Core noise, as was expected, was the predominant source of noise for the quiet clean general aviation turbofan (QCGAT) engine. Flyover noise predictions were made which indicated that the Avco Lycoming QCGAT engine would meet the goals set for the QCGAT program
Low Velocity Granular Drag in Reduced Gravity
We probe the dependence of the low velocity drag force in granular materials
on the effective gravitational acceleration (geff) through studies of spherical
granular materials saturated within fluids of varying density. We vary geff by
a factor of 20, and we find that the granular drag is proportional to geff,
i.e., that the granular drag follows the expected relation Fprobe = {\eta}
{\rho}grain geff dprobe hprobe^2 for the drag force, Fprobe on a vertical
cylinder with depth of insertion, hprobe, diameter dprobe, moving through
grains of density {\rho}grain, and where {\eta} is a dimensionless constant.
This dimensionless constant shows no systematic variation over four orders of
magnitude in effective grain weight, demonstrating that the relation holds over
that entire range to within the precision of our data
Space programs summary no. 37-56, volume 1 for the period 1 January to 28 February 1969. Flight projects
Mariner Mars 1969 Project, Mariner Mars 1971 Project, and Viking Project description
Intraoperative detection of blood vessels with an imaging needle during neurosurgery in humans
Intracranial hemorrhage can be a devastating complication associated with needle biopsies of the brain. Hemorrhage can occur to vessels located adjacent to the biopsy needle as tissue is aspirated into the needle and removed. No intraoperative technology exists to reliably identify blood vessels that are at risk of damage. To address this problem, we developed an “imaging needle” that can visualize nearby blood vessels in real time. The imaging needle contains a miniaturized optical coherence tomography probe that allows differentiation of blood flow and tissue. In 11 patients, we were able to intraoperatively detect blood vessels (diameter, \u3e500 μm) with a sensitivity of 91.2% and a specificity of 97.7%. This is the first reported use of an optical coherence tomography needle probe in human brain in vivo. These results suggest that imaging needles may serve as a valuable tool in a range of neurosurgical needle interventions
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