21,202 research outputs found
Gain Stabilization of a Submillimeter SIS Heterodyne Receiver
We have designed a system to stabilize the gain of a submillimeter heterodyne
receiver against thermal fluctuations of the mixing element. In the most
sensitive heterodyne receivers, the mixer is usually cooled to 4 K using a
closed-cycle cryocooler, which can introduce ~1% fluctuations in the physical
temperature of the receiver components. We compensate for the resulting mixer
conversion gain fluctuations by monitoring the physical temperature of the
mixer and adjusting the gain of the intermediate frequency (IF) amplifier that
immediately follows the mixer. This IF power stabilization scheme, developed
for use at the Submillimeter Array (SMA), a submillimeter interferometer
telescope on Mauna Kea in Hawaii, routinely achieves a receiver gain stability
of 1 part in 6,000 (rms to mean). This is an order of magnitude improvement
over the typical uncorrected stability of 1 part in a few hundred. Our gain
stabilization scheme is a useful addition to SIS heterodyne receivers that are
cooled using closed-cycle cryocoolers in which the 4 K temperature fluctuations
tend to be the leading cause of IF power fluctuations.Comment: 7 pages, 6 figures accepted to IEEE Transactions on Microwave Theory
and Technique
Developing a framework of non-fatal occupational injury surveillance for risk control in palm oil mills
Non-fatal occupational injury (NFOI) and its risk factors have become a current global
concern. The need of research towards the relationship between occupational injury
and its risk factor is essential, to fulfil the purpose and setting the priority of
implementing safety preventive approaches at workplace. This research intended to
develop a framework of NFOI surveillance by using epidemiological data, noise
exposure data and NFOI data among palm oil mills’ workers. A total of 420
respondents who assigned in operation and processing areas (OP) (n=333) and general
or office workers (n=87) had voluntary participated in this research. A questionnaire
session with respondents was held to obtain epidemiological data and NFOI
information via validated questionnaire. Noise hazard monitoring was executed by
using Sound Level Meter (SLM) for environmental noise monitoring and Personal
Sound Dosimeter for personal noise monitoring. Gathered data were analysed in
quantitative method by using statistical software IBM SPSS Statistic version 21 and a
risk matrix table for injury risk rating evaluation. It was discovered that high noise
exposure level (≥ 85 dB[A]) was significantly associated with non-fatal occupational
injury among OP workers (φ=0.123, p<0.05) with OR=1.87 (95% CI, 1.080-3.235,
p<0.05). Risk rating for reported NFOI was at moderate level, with minor cuts and
scratches were the dominant type of injury (42.6%). Analysis of logistic regression
indicated that working in shift, not wearing protective gloves, health problems such as
shortness of breath and ringing in ears, and excessive noise level (≥ 85 dB[A]) were
the risk factors of NFOI in palm oil mills among OP workers. A framework of nonfatal
injury surveillance in palm oil mills was developed based on the findings with
integration of risk management process and injury prevention principles. This
framework is anticipated to help the management in decision making for preventive
actions and early detection of occupational health effects among workers
Design of a Torque Current Generator for Strapdown Gyroscopes
The design, analysis, and experimental evaluation of an optimum performance torque current generator for use with strapdown gyroscopes, is presented. Among the criteria used to evaluate the design were the following: (1) steady-state accuracy; (2) margins of stability against self-oscillation; (3) temperature variations; (4) aging; (5) static errors drift errors, and transient errors, (6) classical frequency and time domain characteristics; and (7) the equivalent noise at the input of the comparater operational amplifier. The DC feedback loop of the torque current generator was approximated as a second-order system. Stability calculations for gain margins are discussed. Circuit diagrams are shown and block diagrams showing the implementation of the torque current generator are discussed
Some aspects of optical feedback with cadmium sulfide and related photoconductors
A primary limitation of many solid state photoconductors used in electro-optical systems is their slow response in converting varying light intensities into electrical signals. An optical feedback technique is presented which can extend the frequency response of systems that use these detectors by orders of magnitude without adversely affecting overall signal-to-noise ratio performance. The technique is analyzed to predict the improvement possible and a system is implemented using cadmium sulfide to demonstrate the effectiveness of the technique and the validity of the analysis
Operational amplifiers for use in nuclear spectroscopy
Operational amplifiers for nuclear spectroscop
Compact Integrated Transconductance Amplifier Circuit for Temporal Differentiation
A compact integrated CMOS circuit for temporal differentiation is presented. It consists of a high-gain inverting amplifier, an active non-linear transconductance and a capacitor and requires only 4 transistors in its minimal configuration.The circuit provides two rectified current outputs that are proportional to the temporal derivative of the input voltage signal. Besides the compactness of its design, the presented circuit is not dependent on the DC-value of the input signal, as compared with known integrated differentiator circuits. Measured chip results show that the circuit operates on a large input frequency range for which it provides nearideal temporal differentiation. The circuit is particularly suited for focal-plane implementations of gradient-based visual motion systems
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