Experimental Permeability Measurements on a Strut-Supported Transpiration-Cooled Turbine Blade with Stainless-Steel Shell made by the Federal-Mogul Corporation under Bureau of Aeronautics Contract N0as 51613-C

A turbine blade with a porous stainless-steel shell sintered to a supporting steel strut has been fabricated for tests at the NACA by Federal-Mogul Corporation under contract from the Bureau of Aeronautics, Department of the Navy. The apparent permeability of this blade, on the average, more nearly approaches the values specified by the NAGA than did two strut-supported bronze blades in a previous investigation. Random variations of permeability in the present blade are substantialy greater than those of the bronze blades, but projected improvements in certain phases of the fabrication process are expected to reduce these variations

Evaluation of Transpiration-Cooled Turbine Blades with Shells of "Poroloy" Wire Cloth

An experimental investigation was made to evaluate the durability and permeability of a group of transpiration-cooled, strut-supported turbine blades. The porous shells were formed from a woven-wire material. The blades were fabricated by a contractor for the Bureau of Aeronautics. The results of permeability tests indicated that the shell material exhibited large random variations in local permeability, which result in excessive coolant flows and very nonuniform cooling. For this reason no heat-transfer evaluations were made because any results would have been inconclusive. Four blades were investigated for structural soundness in a turbo-jet engine operating at a turbine-inlet temperature of approximately 1670 deg F and a turbine tip speed of approximately 1305 feet per second. The maximum temperature of the porous-shell material was approximately 1050 deg F. Inspection of the first two blades after 10 minutes of engine operation revealed that the tips of both of the blades had failed. For the second pair of blades, an improved tip cap was provided by the use of built-up weld extending from strut tip to shell. One of these blades was then operated for 33 hours without failure, and was found to be in good condition at the end of this time. The second blade of this second pair failed within the first 10 minutes of operation because of a poor bond between shell and strut lands

Permeability and Strength Measurements on Sintered, Porous, Hollow Turbine Blades Made by the American Electro Metal Corporation under Office of Naval Research Contract N-ONR-295 (01)

An experimental investigation was made to determine the permeability and strength characteristics of a number of sintered, porous, hollow turbine rotor blades and to determine the effectiveness of the blade fabrication method on permeability control. The test blades were fabricated by the American Electro Metal Corporation under a contract with the Office of Naval Research, Department of the Navy, and were submitted to the NACA for testing. Of the 22 test blades submitted, ten were sintered but not coined, five were sintered and coined, and seven were sintered and not coined but contained perforated reinforcements integral with the blade shells. Representative samples of each group of blades were tested. Large variations in permeability in both chordwise and spanwise directions were found. Local deviations as large as 155 to -85 percent from prescribed values were found in chordwise permeability. Only one blade, an uncoined one, had a chordwise permeability variations which reasonably approached that specified. Even for this blade, local deviations exceeded 10 percent. Spanwise permeability, specified to be held constant, varied as much as 50 percent from root to tip for both an uncoined and a coined blade. Previous NACA analyses have shown that in order to maintain proper control of blade wall temperatures, permeability variations must not exceed plus or minus 10 percent. Satisfactory control of permeability in either the chordwise or the spanwise direction was not achieved in the blades tested. Spin tests made at room temperature for six blades revealed the highest material rupture strength to be 8926 pounds per square inch. This value is about one third the strength required for rotor blades in present-day turbojet engines. The lowest value of blade strength was 1436 pounds per square inch

Pulmonary artery location during microgravity activity: Potential impact for chest-mounted Doppler during space travel

Doppler, or ultrasonic, monitoring for pain manifestations of decompression sickness (the bends) is accomplished by placing a sensor on the chest over the pulmonary artery and listening for bubbles. Difficulties have arisen because the technician notes that the pulmonary artery seems to move with subject movement in a one-g field and because the sensor output is influenced by only slight degrees of sensor movement. This study used two subjects and mapped the position of the pulmonary artery in one-g, microgravity, and two-g environments using ultrasound. The results showed that the pulmonary artery is fixed in location in microgravity and not affected by subject position change. The optimal position corresponded to where the Doppler signal is best heard with the subject in a supine position in a one-g environment. The impact of this result is that a proposed multiple sensor array on the chest proposed for microgravity use may not be necessary to monitor an astronaut during extravehicular activities. Instead, a single sensor of approximately 1 inch diameter and mounted in the position described above may suffice

Endurance Evaluation of Sintered, Porous, Strut-Supported Turbine Blades made by Federal-Mogul-Bower-Bearings, Incorporated, under Bureau of Aeronautics Contract NOas 55-124-C

Four strut-supported, transpiration-cooled turbine blades were investigated experimentally in a turbojet engine. The blade shells were fabricated by the mold-sintering method with spherical stainless-steel powder. Two blades were investigated in order to evolve suitable capping methods for the blade tip. Two other blades were used to evaluate the durability of the porous-shell material. The blades were investigated at a turbine-tip speed of 1305 feet per second, an average turbine-inlet temperature of about 1670 F, and at a porous-shell temperature limited to a maximum of approximately 1040 F

Multi-level, multi-party singlets as ground states and their role in entanglement distribution

We show that a singlet of many multi-level quantum systems arises naturally as the ground state of a physically-motivated Hamiltonian. The Hamiltonian simply exchanges the states of nearest-neighbours in some network of qudits (d-level systems); the results are independent of the strength of the couplings or the network's topology. We show that local measurements on some of these qudits project the unmeasured qudits onto a smaller singlet, regardless of the choice of measurement basis at each measurement. It follows that the entanglement is highly persistent, and that through local measurements, a large amount of entanglement may be established between spatially-separated parties for subsequent use in distributed quantum computation.Comment: Corrected method for physical preparatio

The effect of exercise on venous gas emboli and decompression sickness in human subjects at 4.3 psia

The contribution of upper body exercise to altitude decompression sickness while at 4.3 psia after 3.5 or 4.0 hours of 100% oxygen prebreathing at 14.7 psia was determined by comparing the incidence and patterns of venous gas emboli (VGE), and the incidence of Type 1 decompression sickness (DCS) in 43 exercising male subjects and 9 less active male Doppler Technicians (DT's). Each subject exercised for 4 minutes at each of 3 exercise stations while at 4.3 psia. An additional 4 minutes were spent monitoring for VGE by the DT while the subject was supine on an examination cot. In the combined 3.5 and 4.0 hour oxygen prebreathe data, 13 subjects complained of Type 1 DCS compared to 9 complaints from DT's. VGE were detected in 28 subjects compared to 14 detections from DT's. A chi-square analysis of proportions showed no statistically significantly difference in the incidence of Type 1 DCS or VGE between the two groups; however, the average time to detect VGE and to report Tyep 1 DCS symptoms were statistically different. It was concluded that 4 to 6 hours of upper body exercise at metabolic rates simulating EVA metabolic rates hastens the initial detection of VGE and the time to report Type 1 DCS symptoms as compared to DT's

Verification of an altitude decompression sickness prevention protocol for Shuttle operations utilizing a 10.s psi pressure stage

Three test series involving 173-man tess were conducted to define and verify a pre-extravehicular activity (EVA) denitrogenation procedure that would provide acceptable protection against altitude decompression sickness while minimizing the required duration of oxygen (O2) prebreathe in the suit prior to EVA. The tests also addressed the safety, in terms of incidence of decompression sickness, of conducting EVA's on consecutive days rather than on alternate days. The tests were conducted in an altitude chamber, subjects were selected as representative of the astronaut population, and EVA periods were simulated by reducing the chamber pressure to suit pressure while the subjects breathed O2 with masks and worked at EVA representative work rates. A higher than anticipated incidence of both venous bubbles (55%) and symptoms (26%) was measured following all denitrogenation protocols in this test. For the most part, symptoms were very minor and stabilized, diminished, or disappeared in the six-hour tests. Instances of clear, possible, or potential systemic symptoms were encountered only after use of the unmodified 10.2 psi protocol and not after the modified 10.2 psi protocol, the 3.5-hour O2 prebreathed protocol, or the 4.0-hour O2 prebreathe protocol. The high incidence of symptoms is ascribed to the type and duration of exercise and the sensitivity of the reporting technique to minor symptoms. Repeated EVA exposures after only 17 hours did not increase symptom or bubble incidence

Electrically detected magnetic resonance of carbon dangling bonds at the Si-face 4H-SiC/SiO2_2 interface

SiC based metal-oxide-semiconductor field-effect transistors (MOSFETs) have gained a significant importance in power electronics applications. However, electrically active defects at the SiC/SiO$_2$ interface degrade the ideal behavior of the devices. The relevant microscopic defects can be identified by electron paramagnetic resonance (EPR) or electrically detected magnetic resonance (EDMR). This helps to decide which changes to the fabrication process will likely lead to further increases of device performance and reliability. EDMR measurements have shown very similar dominant hyperfine (HF) spectra in differently processed MOSFETs although some discrepancies were observed in the measured $g$-factors. Here, the HF spectra measured of different SiC MOSFETs are compared and it is argued that the same dominant defect is present in all devices. A comparison of the data with simulated spectra of the C dangling bond (P$_\textrm{bC}$) center and the silicon vacancy (V$_\textrm{Si}$) demonstrates that the P$_\textrm{bC}$ center is a more suitable candidate to explain the observed HF spectra.Comment: Accepted for publication in the Journal of Applied Physic