26,010 research outputs found
Modal analysis and nonlinear characterization of an airborne power ultrasonic transducer with rectangular plate radiator
Some industrial processes like particle agglomeration or food dehydration among others can be enhanced by the use of power ultrasonic technologies. These technologies are based on an airborne power ultrasonic transducer (APUT) constituted by a pre-stressed Langevin-type transducer, a mechanical amplifier and an extensive plate radiator. In order to produce the desired effects in industrial processing, the transducer has to vibrate in an extensional mode driving an extensive radiator in the desired flexural mode with high amplitude displacements. Due to the generation of these high amplitude displacements in the radiator surfaces, non-linear effects like frequency shifts, hysteresis or modal interactions, among others, may be produced in the transducer behavior. When any nonlinear effect appears, when applying power, the stability and efficiency of this ultrasonic technology decreases, and the transducer may be damaged depending on the excitation power level and the nature of the nonlinearity. In this paper, an APUT with flat rectangular radiator is presented, as the active part of an innovative system with stepped reflectors. The nonlinear behavior of the APUT has been characterized numerically and experimentally in case of the modal analysis and experimentally in the case of dynamic analysis. According to the results obtained after the experiments, no modal interactions are expected, nor do other nonlinear effects
Rugged, low-conductance, heat-flow probe
Lightweight, compact probe structure has low thermal conductance to enable accurate measurement of slight temperature gradients. Probe combines ruggedness, high precision, accuracy, and stability. Device can withstand vibration, shock, acceleration, temperature extremes, and high vacuums, and should interest industrial engineers and geologists
Study of thermal insulation for airborne liquid hydrogen fuel tanks
A concept for a fail-safe thermal protection system was developed. From screening tests, approximately 30 foams, adhesives, and reinforcing fibers using 0.3-meter square liquid nitrogen cold plate, CPR 452 and Stafoam AA1602, both reinforced with 10 percent by weight of 1/16 inch milled OCF Style 701 Fiberglas, were selected for further tests. Cyclic tests with these materials in 2-inch thicknesses bonded on a 0.6-meter square cold plate with Crest 7410 adhesive systems, were successful. Zero permeability gas barriers were identified and found to be compatible with the insulating concept
Solar radiation force modeling for TDRS orbit determination
The relative orbit determination accuracies resulting from several TDRS models are evaluated. These models include spherical, single-plate, and restricted two-plate models. The plate models can be adjusted in both area and reflectivity through differential correction. The restricted two-plate model has an Earth-pointing plate and a solar plate; the orientation of the solar plate is restricted to rotation about an axis perpendicular to the satellite's orbital plane
The star formation history of RCW 36
Recent studies of massive-star forming regions indicate that they can contain
multiple generations of young stars. These observations suggest that star
formation in these regions is sequential and/or triggered by a previous
generation of (massive) stars. Here we present new observations of the star
forming region RCW 36 in the Vela Molecular Ridge, hosting a young cluster of
massive stars embedded in a molecular cloud complex. In the periphery of the
cluster several young stellar objects (YSOs) are detected which produce bipolar
jets (HH 1042 and HH 1043) demonstrating that these objects are still actively
accreting. The VLT/X-shooter spectrum of the jet structure of HH 1042 provides
detailed information on the physical conditions and kinematical properties of
the jet plasma. From this information the YSO's accretion history can be
derived. Combining the photometric and spectroscopic observations of RCW 36
gives insight into the formation process of individual stars and the star
formation history of this young massive-star forming region.Comment: 10 pages, 5 figures, to appear in the proceedings of the ESO workshop
"Circumstellar Dynamics at High Resolution", Foz do Iguacu (Br), Feb 2012,
eds. A. Carciofi and T. Riviniu
A Submillimeter HCN Laser in IRC+10216
We report the detection of a strong submillimeter wavelength HCN laser line
at a frequency near 805 GHz toward the carbon star IRC+10216. This line, the
J=9-8 rotational transition within the (04(0)0) vibrationally excited state, is
one of a series of HCN laser lines that were first detected in the laboratory
in the early days of laser spectroscopy. Since its lower energy level is 4200 K
above the ground state, the laser emission must arise from the inner part of
IRC+10216's circumstellar envelope. To better characterize this environment, we
observed other, thermally emitting, vibrationally excited HCN lines and find
that they, like the laser line, arise in a region of temperature approximately
1000 K that is located within the dust formation radius; this conclusion is
supported by the linewidth of the laser. The (04(0)0), J=9-8 laser might be
chemically pumped and may be the only known laser (or maser) that is excited
both in the laboratory and in space by a similar mechanism.Comment: 11 pages, 3 figure
Decision-making for unmanned aerial vehicle operation in icing conditions
With the increased use of unmanned aerial systems
(UAS) for civil and commercial applications, there is
a strong demand for new regulations and technology that
will eventually permit for the integration of UAS in
unsegregated airspace. This requires new technology to
ensure sufficient safety and a smooth integration process.
The absence of a pilot on board a vehicle introduces new
problems that do not arise in manned flight. One challenging
and safety-critical issue is flight in known icing
conditions. Whereas in manned flight, dealing with icing is
left to the pilot and his appraisal of the situation at hand; in
unmanned flight, this is no longer an option and new
solutions are required. To address this, an icing-related
decision-making system (IRDMS) is proposed. The system
quantifies in-flight icing based on changes in aircraft performance
and measurements of environmental properties,
and evaluates what the effects on the aircraft are. Based on
this, it determines whether the aircraft can proceed, and
whether and which available icing protection systems should be activated. In this way, advice on an appropriate
response is given to the operator on the ground, to ensure
safe continuation of the flight and avoid possible accidents
Apparatus for time‐resolved measurements of acoustic birefringence in particle dispersions
An apparatus for time‐resolved measurements of the birefringence induced in a particle suspension by an acoustic wave pulse is described. Efficient acoustic coupling is obtained by operating near the transducer resonant frequency and by matching the acoustic impedances of the cell constituents. An almost‐overdamped acoustic configuration can alternatively be employed whenever a faster response is needed. Careful design of the optical setup and of the detection unit minimize diffraction and stress‐birefringence parasitic effects and yields a good responsivity at fairly low acoustic intensities. A test of the apparatus on a colloidal suspension of PTFE rodlike particles is presented and discussed
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