Aluminum Enclosure Research Articles

Feedback-controlled LED photobioreactor for photophysiological studies of cyanobacteria

A custom photobioreactor was designed to enable automatic light adjustments using computerized feedback control. The system consisted of a 7.5-L cylindrical vessel and an aluminum enclosure housing quantum sensors and light-emitting diode arrays, which provide 630 or 680nm light to preferentially excite the major cyanobacterial pigments, phycocyanin and/or chlorophyll a, respectively. Custom-developed software rapidly measures light transmission and subsequently adjusts the irradiance to maintain a defined light profile to compensate for culture dynamics, biomass accumulation, and pigment adaptations during physiological transitions, thus ensuring appropriate illumination across batch and continuous growth modes. In addition to chemostat cultivation, the photobioreactor may also operate as a turbidostat, continuously adjusting the media dilution to achieve maximal growth at a fixed culture density. The cultivation system doubles as an analytical device, using real-time monitoring to avoid sampling bias (e.g., in-situ light-saturation response), determine conditions for optimal growth, and observe perturbation responses at high time-resolution.

Development of a GPS Herd Activity and Well-Being Kit (GPS HAWK) to Monitor Cattle Behavior and the Effect of Sample Interval on Travel Distance

As an alternative to commercial GPS tracking collars, a low-cost GPS Herd Activity and Well-being Kit (GPS HAWK) was developed to monitor locomotion behavior of cattle at a high sampling frequency (20 s). The operational goal of the GPS HAWK was to collect GPS location data at a user-specified frequency and store the data in a secure format (compact flash media) for retrieval and optimize power consumption to extend the sampling period. The GPS HAWK uses a Garmin 12-channel low-power GPS receiver powered by a sealed-lead acid battery housed in an aluminum enclosure on a shoulder-mounted harness. Data gathered by the GPS HAWKs were used to determine individual daily travel distance (DTD) and the effect of sample interval (SI) on this measurement. Differences (P < 0.0001) were shown in DTD across four days using animals with available data. The Angus cows (Bos Tarus L.) averaged 4.05 0.14 km/d (2.52 0.09 mi/d) during the four days. Sample interval (SI) had an effect on DTD. Differences in DTD were detected for all SIs (P < 0.0001) except between the 60- and 120-s intervals. By changing the SI from 20 s to 20 min, the mean DTD decreased by 1.68 km or 44%. Significant errors in estimates of cattle energetics from GPS monitoring can be introduced by increasing sampling interval. Therefore, researchers must account for increasing error in DTD due to undersampling as SI is increased to save battery power and to increase the interval between animal handling periods. Holding the GPS system in place consistently with a shoulder mounted harness proved to be somewhat challenging.

Designing of an online system for radiocaesium measurements in the marine environment

An online radiocaesium measuring system (ORMS) is designed to determine the environmental radiocaesium contamination of sea water near the Bushehr Nuclear Power Plant (BNPP). The System consists of a 400-liter, spherical stainless steel water tank, including three aluminum (0.5mm) enclosure NaI (TI) detectors, which each are located in 120° phase angle with size (6×3in.) to confirm each other. Responses of detectors to gamma radiations were calculated, using Monte Carlo code MCNP.4C. Moreover, delay time of each response and the dead time of the whole system to be considered due to designing decisions were calculated.

Circuital Modeling and Measurement of Shielding Effectiveness Against Oblique Incident Plane Wave on Apertures in Multiple Sides of Rectangular Enclosure

A simple circuital approach to evaluate the shielding effectiveness (SE) of rectangular enclosures with apertures is proposed, considering oblique incidence and polarization. The scope of the proposed model is extended beyond 1 GHz, including higher order modes of the cavity. Furthermore, apertures are not required to be on the front face of the enclosure. In the proposed model, the SE of the enclosure with apertures on multiple sides can be simply calculated by vector decomposition. The proposed model has been successfully verified by using a conventional full-wave simulation tool. We also measured the SE of a manufactured aluminum enclosure with apertures on multiple sides.

HermesD: A High-Rate Long-Range Wireless Transmission System for Simultaneous Multichannel Neural Recording Applications

HermesD is a high-rate, low-power wireless transmission system to aid research in neural prosthetic systems for motor disabilities and basic motor neuroscience. It is the third generation of our "Hermes systems" aimed at recording and transmitting neural activity from brain-implanted electrode arrays. This system supports the simultaneous transmission of 32 channels of broadband data sampled at 30 ks/s, 12 b/sample, using frequency-shift keying modulation on a carrier frequency adjustable from 3.7 to 4.1 GHz, with a link range extending over 20 m. The channel rate is 24 Mb/s and the bit stream includes synchronization and error detection mechanisms. The power consumption, approximately 142 mW, is low enough to allow the system to operate continuously for 33 h, using two 3.6-V/1200-mAh Li-SOCl2 batteries. The transmitter was designed using off-the-shelf components and is assembled in a stack of three 28 mm ? 28-mm boards that fit in a 38 mm ? 38 mm ? 51-mm aluminum enclosure, a significant size reduction over the initial version of HermesD. A 7-dBi circularly polarized patch antenna is used as the transmitter antenna, while on the receiver side, a 13-dBi circular horn antenna is employed. The advantages of using circularly polarized waves are analyzed and confirmed by indoor measurements. The receiver is a stand-alone device composed of several submodules and is interfaced to a computer for data acquisition and processing. It is based on the superheterodyne architecture and includes automatic frequency control that keeps it optimally tuned to the transmitter frequency. The HermesD communications performance is shown through bit-error rate measurements and eye-diagram plots. The sensitivity of the receiver is -83 dBm for a bit-error probability of 10(-9). Experimental recordings from a rhesus monkey conducting multiple tasks show a signal quality comparable to commercial acquisition systems, both in the low-frequency (local field potentials) and upper-frequency bands (action potentials) of the neural signals. This system can be easily scaled up in terms of the number of channels and data rate to accommodate future generations of Hermes systems.

Benchmark of Computational Fluid Dynamics Simulations Using Temperatures Measured Within Enclosed Vertical and Horizontal Arrays of Heated Rods

Experiments and computational fluid dynamics/radiation heat transfer simulations of an 8 × 8 array of heated rods within an air-filled aluminum enclosure are performed. This configuration represents a region inside the channel of a boiling water reactor fuel assembly between two consecutive spacer plates. The rods are oriented horizontally or vertically to represent transport or storage conditions. The measured and simulated rod temperatures are compared for three different rod heat generation rates to assess the accuracy of the simulation technique. Simulations show that temperature gradients in the air are much steeper near the enclosure walls than they are near the center of the rod array. The measured temperatures of rods at symmetric locations are not identical, and the difference is larger for rods close to the wall than for those far from it. Small but uncontrolled deviations of the rod positions away from the design locations may cause these differences. The simulations reproduce the measured temperature profiles. For a total rod heat generation rate of 300 W, the maximum rod-to-enclosure temperature difference is 150°C. Linear regression shows that the simulations slightly but systematically overpredict the hotter rod temperatures but underpredict the cooler ones. For all rod locations, heat generation rates, and rod orientations, 95% of the simulated temperatures are within 11°C of the correlation values. For the hottest rods, which reside in the center of the domain where the air temperature gradients are small, 95% of the simulated temperatures are within 4.3°C of the correlation values. These results can be used to assess the accuracy of using simulations to design spent nuclear fuel transport and storage systems.

Multi-channel active control of axial cooling fan noise

A multi-channel active control system has been applied to the reduction of free-field tonal noise from a small axial cooling fan. The experimental apparatus consists of an aluminum enclosure which houses the fan, an infrared detector-emitter pair which serves as a reference sensor, loudspeakers, microphones, and appropriate filters and amplifiers. The research fan and loudspeakers have been modeled theoretically as point sources to derive a mathematical expression for radiated power. The minimization of this power has served to guide the number and location of control sources, as well as to discover potential error microphone locations in the extreme near-field. Experiments with these microphone positions have shown that there are predictable near-field locations which consistently lead to significant reductions in the global mean-squared pressure for the first four harmonics of the blade passage frequency. For example, a four channel configuration with the error microphones placed appropriately results in global mean-squared pressure reductions on the order of 10 dB or more for the targeted frequencies.

Finite-difference time-domain (FDTD) analysis of magnetic diffusion

Problems with very slow waveforms or very long diffusion times may be difficult to treat using finite-difference time-domain techniques because of the Courant stability condition. Problems of this class, however, often prove to have a response which does not depend on the speed of light. The examples presented here show cases where internal fields do not change if c is reduced by as much as five orders of magnitude. This permits /spl Delta/t to be proportionally increased. For simplicity much of this paper is restricted to one dimension, although generalization to three dimensions is also presented. The author considers an aluminum enclosure. Initially, the transient field will induce eddy currents on the enclosure which exactly cancel the external field and exclude it from the enclosure interior. This scheme has been, in fact, proposed to shield large systems which contain magnetic memories. >

Shielding effectiveness before and after the effects of environmental stress on metalized plastics

Empirical shielding effectiveness data are discussed. Measurements were made on a number of 2-ft-square metalized plastic test samples before and after exposure to environmental stress. It is concluded that metalized plastic enclosures can never provide the shielding effectiveness of a solid aluminium enclosure. However, if a plastic material is to be used, conductive coatings can provide a limited degree of shielding. If the cost can be justified, zinc arc coating provides the greatest degree of shielding.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Erratum: Short-circuit electromagnetic forces in three-phase gas insulated systems with aluminium enclosure

Erratum: Short-circuit electromagnetic forces in three-phase gas insulated systems with aluminium enclosure

Short-circuit electromagnetic forces in three-phase gas insulated systems with aluminium enclosure

In the paper, the short-circuit forces acting on three tubular conductors arranged in an equilateral triangle and constituting a 3-phase system enclosed by a cylindrical aluminium enclosure are examined. The relations for the time functions of the short-circuit forces are developed taking into account the transverse dimensions (diameter) of the conductors. The forces acting on such structures are compared with the forces on structures with filamentary conductors; it results that for usual structures the assumption of filamentary conductors causes a small error in the values of forces; for practical computations the simpler relations that concern forces on filamentary conductors can be used.

Dielectric Design and Test of 1200 kV Semi-Flexible SF6 Insulated Transmission Line

An SF6 insilated semi-flexible transmiission line is described which uses a corrugated aluminum enclosure to reduce cost and provide flexibility. Dielectric characteristics of a compact 1200 kV design (711mm (28 in) internal diameter enclosure) with SF6 at 440 kPa (50 psig) are established through detailed field plotting and scale model tests. High voltage tests on 550 kV and 1200 kV prototypes then verified that a design using a smooth conductor wiith discrete flexible elements meets the performance and cost objectives. The development was jointly funded by the U. S. Department of Energy and Westinghouse.

Modular SCR Assemblies in VSCF Systems

The success of the cycloconverter based VSCF electrical system has clearly been dependent upon the development of the silicon-controlled rectifier (SCR) as a high power electrical switch. The purpose of this paper is to describe the innovative work in process to improve the thermal characteristics of the SCR; and, thereby, improve the cycloconverter power quality and efficiency. The key parameter to improvements in the SCR performance is to reduce the thermal impedance from the semi-conductor junction to case. By improving this characteristic, lower junction temperature or smaller devices may be used in a given application. Significant improvements in this area, for 18 mm SCR pellets and larger, have been severely limited by the necessity for dry interfaces. Up to now, the thermal stresses developed at the silicon-copper interface during low temperature excursion preclude solder or other direct bonding techniques. The unique approach described in this paper eliminates the dry interface, incorporates built-in electrical isolation, and features structured copper, solder bonding, direct bond copper on beryllia, and a hermetic-sealed aluminum enclosure.

Mechanical Design and Test of 1200 KV Semi-Flexible SF6 Insulated Transmission Line

An SF6 insulated Semi-Flexible transmission line is described which uses a corrugated aluminum enclosure to reduce cost and provide flexibility. Mechanical behavior was evaluated using finite element computer analysis, bending, hydrostatic, thermal, vacuum and fatigue tests. A 711 mm (28 in) internal diameter, 4 mm (0.16 in) wall, 3004 aluminum enclosure with 19 mm (0.75 in) deep corrugations at a pitch of 70 mm (2.75 in) was shown adequate for internal and external pressure. A field installation centerline bending radius of 15 m (50 ft) was demonstrated. Electrical and mechanical parameters of the 1200 kV and a 550 kV design are reported. These meet the performance and cost objectives of a development program for semi-flexible SF6 insulated transmission lines jointly funded by the U. S. Department of Energy and Westinghouse.

The EL2 Electret Transmitter: Analytical Modeling, Optimization, and Design

We describe here the development of an el2 Electret Transmitter that provides desirable attributes for use in hands-free-answer telephony and future electronic and special-purpose sets. The el2 has lower sensitivity to spurious electromagnetic and mechanical signals than do existing magnetic transmitters. It offers lower dc power consumption, smaller size, and lower intrinsic noise and distortion than the carbon microphone. Formulation of an electro-mechano-acoustic electret model allows parameter optimization, in which side conditions on electrostatic stability and a prescribed transmit frequency response are adhered to. We show that higher sensitivities are possible with larger air film thickness, until the decreasing source capacitance becomes a limiting factor. Multiple diaphragm supports allow decreased film stress with no change in the stable electret charge or sensitivity. We describe theoretically a thermal stabilization procedure that minimizes long-range stress relaxation effects by accelerating viscoelastic changes. Based on film data, we project nominal sensitivity variations within ±1 dB over 20 years of service. In the design, metallized poly(tetrafluoroethylene) electret film is tensioned, supported, and clamped above a selectively metallized stationary electrode forming three cells acoustically and electrically in parallel. A preamplifier completes the subassembly, which is housed in a rectangular aluminum enclosure shielding the transducer. Typical EL2 parameters are −32 dBV/N/m2 sensitivity at 1 kHz, 1 KΩ output impedance, 3.2 kHz response resonance frequency, and 2 to 16 V required dc supply.

SQUID instruments and shielding for low-level magnetic measurements

We have used a thick-walled aluminum enclosure to provide low-frequency shielding for biomagnetic studies with SQUID magnetic gradiometers. The shield provides an attenuation proportional to frequency above 1/3 Hz. A 24-hole fractional-turn SQUID gradiometer has been used in the enclosure to carry out studies of magnetoencephalography on humans. An ’’asymmetric’’ configuration for a second-derivative gradiometer has been developed which provides a significant increase in sensitivity and resolution over more conventional symmetric arrays.

Reduction of acoustic and infrared emissions from a mil. std. 1.5-kW engine-generator set

This is a report of a program conducted jointly by Bolt Beranek and Newman and the U.S. Army Mobility Equipment Research and Development Center. The program was to reduce the acoustic and infrared emissions from a MIL. Std. 1.5 kW gasoline engine-generator. A goal for inaudibility at 100 m in a jungle environment is derived and a feasibility study conducted into ways of achieving it. Of equal importance is the provision of adequate cooling for the engine generator so that it can operate over the temperature range −50°F to +125°F. A new exhaust muffler was designed for the engine, an aluminum enclosure was employed, based upon a standard transit case lined with fiberglass and perforated metal, and new vibration mounts were used. Separate lined inlet and exhaust ducts were employed for the cooling air and inadvertent internal recirculation of the air was prevented. Adequate cooling was then obtained over the whole temperature range. A total noise reduction of 23 dBA was achieved for a unit with a final weight of 217 lb and a volume of 9.5 ft3.