Full Azimuth Research Articles

Hover acoustic characteristics of the XV-15 with advanced technology blades

An experiment has been performed to investigate the far-field hover acoustic characteristics of the XV-15 aircraft with advanced technology blades (ATB). An extensive, high-quality, far-field acoustics data base was obtained for a rotor tip speed range of 645-771 ft/s. A 12-microphone, 500-ft radius semicircular array combined with two aircraft headings provided acoustic data over the full 360-deg azimuth about the aircraft with a resolution of 15 deg. Altitude variations provided data from near in-plane to 45 deg below the rotor tip path plane. Acoustic directivity characteristics in the lower hemisphere are explored through pressure time histories, narrow-band spectra, and contour plots. Directivity patterns were found to vary greatly with azimuth angle, especially in the forward quadrants. Sharp positive pressure pulses typical of blade-vortex interactions were found to propagate aft of the aircraft and were most intense at 45 deg below the rotor plane. Modest overall sound pressure levels were measured near in-plane indicating that thickness noise is not a major problem for this aircraft when operating in the hover mode with ATB. Rotor tip speed reductions reduced the average overall sound pressure level (dB (0.0002 dyne/cm(exp 2)) by nearly 8 dB in-plane, and 12.6 deg below the rotor plane.

The ALICE detector at LHC

ALICE (A Large Ion Collider Experiment) is a dedicated detector designed to exploit the unique physics opportunities which will be offered by nucleus-nucleus collisions at the LHC. ALICE has been conceived as a general-purpose detector, in which hadrons, electrons and photons produced in the interaction can be measured and identified. The detector is designed to cope with the highest particle densities anticipated in PbPb interactions at the LHC (8000 per unit of rapidity). An acceptance of about two units of rapidity has been chosen, which has been calculated to be sufficient to define most of the variables sensitive to the onset of a phase transition to a quark-gluon plasma. The baseline design of ALICE consists of a central (| η| ≤ 0.9) detector covering the full azimuth, complemented by a multiplicity detector covering the forward rapidity region (up to η = 4.8) and a zero degree calorimeter. The central detector will be embedded in large magnet with a weak field of 0.2 T, and will consist of a high-resolution inner tracking system, a cylindrical TPC, a particle identification array (time of flight or ring imaging Cherenkov detectors) and a single-arm electromagnetic calorimeter. Possible upgrades to this baseline design are currently under study, including a muon identification system and a large acceptance electromagnetic calorimeter.

The ALICE heavy-ion experiment at the CERN LHC

ALICE (A Large Ion Collider Experiment) is a dedicated heavy-ion detector designed to exploit the physics potential of nucleus-nucleus interactions at the LHC. As a general purpose experiment, it will allow a comprehensive study of hadrons, electrons, and photons produced in the collision of heavy nuclei, up to the highest particle multiplicities anticipated at the LHC. The central part of ALICE, which covers (90 ± 45)° (| η|< 0.9) over the full azimuth, is embedded in a large magnet with a weak solenoidal field. The base-line design consists (from inside out) of a high-resolution inner tracking system, a cylindrical TPC, a particle identification array (TOF or RICH detectors), and a single-arm electromagnetic calorimeter. Possible upgrades under study include large-acceptance electromagnetic calorimeters and a muon identification system. We will trigger on central collisions with a zero degree calorimeter and measure multiplicity distributions over a large fraction of the available phase space.

A high aperture efficiency, wide-angle scanning offset reflector antenna

A unique single offset reflector antenna has been designed which provides as much as +or-30 degrees of scanning in azimuth while maintaining a much higher aperture efficiency than a torus antenna. Like a torus antenna, different portions of the reflector are illuminated for each scanned beam. The reflector profile curve in the plane of scan is found by least squares to minimize the error for the beams with the greatest scan angle, and then polynomial terms of up to sixth order which minimize nonplanar phase errors are added to produce a three-dimensional reflector surface. Numerical simulation indicates very good results for all 0.5 degrees beams in the +or-30 degrees azimuth field of view, with peak gain no more than 0.3 dB below ideal and highest side-lobe levels no worse than 13.3 dB below the peak gain. Additionally, comparable performance can be extended to the elevation plane out to 15 degrees /-30 degrees , although full azimuth performance becomes compromised at extreme elevation scan angles. By using an offset design, there is no blockage of the outgoing beam by the feed array assembly for azimuth scanning. With better feed performance than comparably sized paraboloids, and being more compact than similar torus reflectors, this novel antenna should find numerous uses in spacecraft and terrestrial applications. >

A highly-segmented ΔE-time-of-flight wall as forward detector of the 4π-system for charged particles at the SIS/ESR accelerator

At the SIS/ESR accelerator facility at GSI in Darmstadt the 4π-detector system FOPI is under construction at present. It is designed for the investigation of central collisions of heavy ions in the energy range up to 2 A GeV. As phase I of this detector a forward wall has been built and used in various experiments. It comprizes a total number of 764 scintillators with an additional shell of 188 thin ΔE-detectors in front of it and covers the full azimuth of the polar angles from 1° to 30°. The velocity and the nuclear charge of the fragments are determined by a combined time-of-flight and ΔE measurement.

A large-acceptance imaging gas cherenkov detector system

A threshold gas Cherenkov detector for electrons was developed which combines large solid-angle acceptance with high detection efficiency, excellent imaging performance, and effective discrimination against other particles and electrons below β = 0.9997. Operating with air at atmospheric pressure, the counting system consists of an array of 12 ellipsoidal mirrors which focus the Cherenkov photons seen in target direction onto photomultipliers. The mirrors cover the full azimuth for polar angles 115° ≤ ϑ ≤ 145°, thus covering 20% of 4 π. In its use as a nonmagnetic spectrometer for electrons in the medium-energy region, the detector was designed to cut the main part of the scattering spectrum below E = 50 MeV, whereas the detection efficiency surpasses 90% at E = 100 MeV. The detector was used for measuring a 10 −6 asymmetry in the quasielastic scattering of longitudinally polarized electrons which is caused by weak neutral currents.

Comparison of CW-Lidar-Measured Wind Values Obtained by Full Conical Scan, Conical Sector Scan and Two-Point Techniques

Continuous-wave (CW) Doppler lidar measurements of wind magnitude and direction that are based on radial velocity data on only a part of a full azimuth circle compare favorably with measurements based on a full circle. Winds were measured over an altitude range of 750 m. For example, the rms difference between 76 wind data pairs at various altitudes, taken from a full circle and from a ¼-circle sector is 0.43 m s−1 in magnitude (correlation coefficient 0.98) and 4.2° in direction, even when only 12 s of measurement time is used for the ¼-circle sector. Increased integration time leads to an even closer comparison. Useful velocity estimates can be obtained from sector scans as small as ⅙ of a circle when a weighted least-squares fitting program is used to analyze the radial velocity versus azimuth data. Results from a two-point scan technique compare less favorably with the full-scan results than do results from a sector-scan technique. A scan employing a π/2, two-point azimuth difference results in an rms difference of 0.78 m s−1 (correlation coefficient 0.95) for 2 s of measurement time when compared with a full circle scan. We conclude that even if data are available or of interest over only part of an azimuth circle, good wind estimates are still possible.

Azimuth effects on the Kemar Mannequin

The effect of head shadow and diffraction by the Kemar mannequin was explored with both pure‐tone and pink‐noise sound fields in an anechoic chamber. Polar recordings of 360° rotation of the mannequin were made for each 13 octave from 0.25 to 12.5 kHz with the point source on the same horizontal plane as the Zwislocki coupler in the mannequin's ear. Simultaneous magnetic tape recordings were transferred digitally to a computer programmed to compare the data with published human data. Comparisons were made for the full azimuth range for each frequency and for the full frequency range at each 15° of azimuth. Results shown that pink‐noise data agrees closely with averaged human results [E.A.G. Shaw, J. Acoust. Soc. Am. 56, 1848–1861 (1974)]. Pure tone results show good correspondence with the same averaged human data at low and middle frequencies but show deviant peaks at higher frequencies. At least some of these variations appear to be related to detailed pinna geometry.