Comparison of the noise characteristics of two low pressure ratio fans with a high throat Mach number inlet

Acoustics data obtained in experiments with two low pressure ratio 50.8 cm (20 in.) diameter model fans differing in design tip speed were compared. Determination of the average throat Mach number used to compare high Mach inlet noise reduction characteristics was based on a correlation of inlet wall static pressure measurements with a flow field calculation. The largest noise reductions were generally obtained with the higher tip speed fan. At a throat Mach number of 0.79, the difference in noise reduction was about 3.5 db with static test conditions. Although the noise reduction increased for the lower tip speed fan with a simulated flight velocity of 41 m/sec (80 knots), it was still about 2 db less than that of the high tip speed fan which was only tested at the static condition. However, variations in acoustic performance could not be absolutely attributed to the different fan designs because of differences in inlet lip contours which resulted in small variations of peak wall Mach number and axial extend of supersonic and near-sonic flow

Simulated flight effects on noise characteristics of a fan inlet with high throat Mach number

An anechoic wind tunnel experiment was conducted to determine the effects of simulated flight on the noise characteristics of a high throat Mach number fan inlet. Comparisons were made with the performance of a conventional low throat Mach number inlet with the same 50.8 cm fan noise source. Simulated forward velocity of 41 m/sec reduced perceived noise levels for both inlets, the largest effect being more than 3 db for the high throat Mach number inlet. The high throat Mach number inlet was as much as 7.5 db quieter than the low throat Mach number inlet with tunnel airflow and about 6 db quieter without tunnel airflow. Effects of inlet flow angles up to 30 deg were seemingly irregular and difficult to characterize because of the complex flow fields and generally small noise variations. Some modifications of tones and directivity at blade passage harmonics resulting from inlet flow angle variation were noted

Implications of Quasar Black Hole Masses at High Redshifts

We investigated a sample of 15 luminous high-redshift quasars (3.3 < z < 5.1) to measure the mass of their super-massive black holes (SMBH) and compare, for the first time, results based on CIV, MgII, and Hbeta emission lines at high-redshifts. Assuming gravitationally bound orbits as dominant broad-line region gas motion, we determine black hole masses in the range of M_bh = 2 times 10^8 M_sun up to M_bh = 4 times 10^10 M_sun. While the black hole mass estimates based on CIV and Hbeta agree well, MgII typically indicates a factor of $\sim 5 \times$ lower SMBH masses. A flatter slope of the Hbeta radius - luminosity relation, a possibly steeper slope of the MgII radius - luminosity relation, and a slightly larger radius of the MgII BLR than for Hbeta could relax the discrepancy. In spite of these uncertainties, the CIV, MgII, and Hbeta emission lines consistently indicate super-massive black hole masses of several times 10^9 M_sun at redshifts up to z = 5.1. Assuming logarithmic growth by spherical accretion with a mass to energy conversion efficiency of epsilon = 0.1 and an Eddington ratio L_bol / L_edd calculated for each quasar individually, we estimate black hole growth-times of the order of several ~100 Myr which are smaller than the age of the universe at the corresponding redshift. Assuming high-mass seed black holes (M_bh^seed = 10^3 to 10^5 M_sun) the SMBHs in the z = 3.5 quasars began to grow at redshifts z > 4, while for the quasars with z > 4.5 they started at z = 6 to 10. These estimated time scales for forming SMBHs at high redshifts, together with previous studies indicating high quasar metallicities, suggest that the main SMBH growth phase occurs roughly contemporaneously with a period of violent and extensive star formation in proto-galactic nuclei.Comment: 26 pages, 4 figures. ApJ, accepted, Vol.611 (Aug20

Development of an ex vivo model for the study of cerebrovascular function utilizing isolated mouse olfactory artery

OBJECTIVE: Cerebral vessels, such as intracerebral perforating arterioles isolated from rat brain, have been widely used as an ex vivo model to study the cerebrovascular function associated with cerebrovascular disorders and the therapeutic effects of various pharmacological agents. These perforating arterioles, however, have demonstrated differences in the vascular architecture and reactivity compared with a larger leptomeningeal artery which has been commonly implicated in cerebrovascular disease. In this study, therefore, we developed the method for studying cerebrovascular function utilizing the olfactory artery isolated from the mouse brain. METHODS: The olfactory artery (OA) was isolated from the C57/BL6 wild-type mouse brain. After removing connective tissues, one side of the isolated vessel segment (approximately -500 µm in length) was cannulated and the opposite end of the vessel was completely sealed while being viewed with an inverted microscope. After verifying the absence of pressure leakage, we examined the vascular reactivity to various vasoactive agents under the fixed intravascular pressure (60 mm Hg). RESULTS: We found that the isolated mouse OAs were able to constrict in response to vasoconstrictors, including KCl, phenylephrine, endothelin-1, and prostaglandin PGH(2). Moreover, this isolated vessel demonstrated vasodilation in a dose-dependent manner when vasodilatory agents, acetylcholine and bradykinin, were applied. CONCLUSION: Our findings suggest that the isolated olfactory artery would provide as a useful ex vivo model to study the molecular and cellular mechanisms of vascular function underlying cerebrovascular disorders and the direct effects of such disease-modifying pathways on cerebrovascular function utilizing pharmacological agents and genetically modified mouse models

GaBoDS: The Garching-Bonn Deep Survey VIII. Lyman-break galaxies in the ESO Deep Public Survey

Aims. The clustering properties of a large sample of U-dropouts are investigated and compared to very precise results for B-dropouts from other studies to identify a possible evolution from z=4 to z=3. Methods. A population of ~8800 candidates for star-forming galaxies at z=3 is selected via the well-known Lyman-break technique from a large optical multicolour survey (the ESO Deep Public Survey). The selection efficiency, contamination rate, and redshift distribution of this population are investigated by means of extensive simulations. Photometric redshifts are estimated for every Lyman-break galaxy (LBG) candidate from its UBVRI photometry yielding an empirical redshift distribution. The measured angular correlation function is deprojected and the resulting spatial correlation lengths and slopes of the correlation function of different subsamples are compared to previous studies. Results. By fitting a simple power law to the correlation function we do not see an evolution in the correlation length and the slope from other studies at z=4 to our study at z=3. In particular, the dependence of the slope on UV-luminosity similar to that recently detected for a sample of B-dropouts is confirmed also for our U-dropouts. For the first time number statistics for U-dropouts are sufficient to clearly detect a departure from a pure power law on small scales down to ~2" reported by other groups for B-dropouts.Comment: 10 pages, 11 figures, accepted by A&A, full resolution version available at http://www.astro.uni-bonn.de/~hendrik/5880.pd

Ohmic contacts to GaAs for high-temperature device applications

Ohmic contacts to n-type GaAs were developed for high temperature device applications up to 300 C. Refractory metallizations were used with epitaxial Ge layers to form the contacts: TiW/Ge/GaAs, Ta/Ge/GaAs, Mo/Ge/GaAs, and Ni/Ge/GaAs. Contacts with high dose Si or Se ion implantation of the Ge/GaAs interface were also investigated. The contacts were fabricated on epitaxial GaAs layer grown on N+ or semi-insulating GaAs substrates. Ohmic contact was formed by both thermal annealing (at temperatures up to 700 C) and laser annealing (pulsed Ruby). Examination of the Ge/GaAs interface revealed Ge migration into GaAs to form an N+ doping layer. The specific contact resistances of specimens annealed by both methods are given

Force indeterminacy in the jammed state of hard disks

Granular packings of hard discs are investigated by means of contact dynamics which is an appropriate technique to explore the allowed force-realizations in the space of contact forces. Configurations are generated for given values of the friction coefficient, and then an ensemble of equilibrium forces is found for fixed contacts. We study the force fluctuations within this ensemble. In the limit of zero friction the fluctuations vanish in accordance with the isostaticity of the packing. The magnitude of the fluctuations has a non-monotonous friction dependence. The increase for small friction can be attributed to the opening of the angle of the Coulomb cone, while the decrease as friction increases is due to the reduction of connectivity of the contact-network, leading to local, independent clusters of indeterminacy. We discuss the relevance of indeterminacy to packings of deformable particles and to the mechanical response properties.Comment: 4 pages, 3 figures. Minor changes, journal reference adde