162 research outputs found
Hypersonic airbreathing propulsion/airframe integration
Recent interest in airbreathing hypersonic flight has centered around the need to develop advanced space launch systems which can reduce the cost of inserting payloads in orbit and make space more accessible. An effect of the thermal environment is to require the vehicle to operate at high altitudes, in very thin air, to maintain aircraft structural load limits. The high altitudes at which the hypersonic vehicle must operate give rise to the concept of an airframe integrated propulsion system to provide a much larger inlet and nozzle to process the required volume of air at low density, atmospheric conditions. In the integrated system, the forward portion of the vehicle compresses the air flow and serves as the external portion of the inlet; the aftbody completes the expansion process for the nozzle. In addition, the engine, which is contained between the body and the forebody shock wave, lends itself to a modular integration of a number of separate engines. In this manner, a relatively small engine can be defined to allow engine development in existing ground facilities
A Pre-Mixed Shock-Induced-Combustion Approach to Inlet and Combustor Design for Hypersonic Applications
The need for efficient access to space has created interest in airbreathing propulsion as a means of achieving that goal. The NASP program explored a single-stage-to-orbit approach which could require scramjet airbreathing propulsion out to Mach 16 to 20. Recent interest in global access could require hypersonic cruise engines operating efficiently in the Mach 10 to 12 speed range. A common requirement of both these types of propulsion systems is that they would have to be fully integrated with the aero configuration so that the forebody becomes a part of the external compression inlet and the nozzle expansion is completed on the vehicle aftbody
Effect of Water on the Electrochemical Oxidation of Gas-Phase SO2 in a PEM Electrolyzer for H2 Production
Water plays a critical role in producing hydrogen from the electrochemical oxidation of SO2 in a proton exchange membrane (PEM) electrolyzer. Not only is water needed to keep the membrane hydrated, but it is also a reactant. One way to supply water is to dissolve SO2 in sulfuric acid and feed that liquid to the anode, but this process results in significant diffusion resistance for the SO2. Alternatively, we have developed a process where SO2 is fed as a gas to the anode compartment and reacts with water crossing the membrane to produce sulfuric acid. There was concern that the diffusion resistance of water through the membrane is as significant as SO2 diffusion through water, thus limiting the benefit of a gas-phase anode feed. We show here that water diffusion through the membrane is not as limiting as liquid-phase SO2 diffusion. Therefore, we can control the cell voltage, the limiting current, and the sulfuric acid concentration by varying the diffusion resistance of the membrane via thickness or temperature. Catalyst loading, however, has a negligible effect on cell performance
Theoretical Analysis for Obtaining Physical Properties of Composite Electrodes
A theoretical analysis is presented that allows in situ measurements of the physical properties of a composite electrode, namely, the electronic conductivity, the ionic conductivity, the exchange-current density, and the double-layer capacitance. Use is made of the current-voltage responses of the composite electrode to dc and ac polarizations under three different experimental configurations. This analysis allows the physical properties to be obtained even when the various resistances in the composite (e.g., ionic, electronic, and charge-transfer) are of comparable values
The Effect of Current and Nickel Nitrate Concentration on the Deposition of Nickel Hydroxide Films
An electrochemical quartz crystal nanobalance (EQCN) has been utilized to measure the mass of Ni(OH)2 films electrochemically deposited from Ni(NO3)2 solutions. The objective of this work was to quantify electrochemical deposition as a function of deposition conditions. The changing mass recorded on the EQCN was demonstrated to be the result of Ni(OH)2 deposition. Deposited mass was observed to increase proportionally with applied charge as suggested by previous investigators. Most significantly, the rate of deposition was found to decrease more than an order of magnitude as the Ni(NO3)2 concentration increased from 0.2 to 2.0M. The effect of concentration is shown to be related to Ni(II) concentration as opposed to solution pH or NO concentration. An empirical correlation is given to predict deposition rates in solutions ranging from 0.1 to 3.0M Ni(NO3)2 and at current densities ranging from 0.5 to 5.0 mA/cm2. The decreased deposition rates in concentrated Ni(NO3)2 are attributed to the formation of intermediate species [e.g., NiOH+ or Ni4(OH)] which diffuse away from the reaction interface before deposition can occur
On the normalisation of the cosmic star formation history
Strong constraints on the cosmic star formation history (SFH) have recently
been established using ultraviolet and far-infrared measurements, refining the
results of numerous measurements over the past decade. Taken together, the most
recent and robust data indicate a compellingly consistent picture of the SFH
out to redshift z~6, with especially tight constraints for z<~1. We fit these
data with simple analytical forms, and derive conservative bands to indicate
possible variations from the best fits. Since the z<~1 SFH data are quite
precise, we investigate the sequence of assumptions and corrections that
together affect the SFH normalisation, to test their accuracy, both in this
redshift range and beyond. As lower limits on this normalisation, we consider
the evolution in stellar mass density, metal mass density, and supernova rate
density, finding it unlikely that the SFH normalisation is much lower than
indicated by our direct fit. Additionally, predictions from the SFH for
supernova type Ia rate densities tentatively suggests delay times of ~3 Gyr. As
a corresponding upper limit on the SFH normalisation, we consider the
Super-Kamiokande (SK) limit on the electron antineutrino flux from past
core-collapse supernovae, which applies primarily to z<~1. We find consistency
with the SFH only if the neutrino temperatures from SN events are relatively
modest. Constraints on the assumed initial mass function (IMF) also become
apparent. The traditional Salpeter IMF, assumed for convenience by many
authors, is known to be a poor representation at low stellar masses (<~ 1 solar
mass), and we show that recently favoured IMFs are also constrained. In
particular, somewhat shallow, or top-heavy, IMFs may be preferred, although
they cannot be too top-heavy. (Abridged)Comment: 15 pages, 8 figures, accepted for publication in ApJ, major revisions
following referee's comment
Upper limits on the strength of periodic gravitational waves from PSR J1939+2134
The first science run of the LIGO and GEO gravitational wave detectors
presented the opportunity to test methods of searching for gravitational waves
from known pulsars. Here we present new direct upper limits on the strength of
waves from the pulsar PSR J1939+2134 using two independent analysis methods,
one in the frequency domain using frequentist statistics and one in the time
domain using Bayesian inference. Both methods show that the strain amplitude at
Earth from this pulsar is less than a few times .Comment: 7 pages, 1 figure, to appear in the Proceedings of the 5th Edoardo
Amaldi Conference on Gravitational Waves, Tirrenia, Pisa, Italy, 6-11 July
200
Improving the sensitivity to gravitational-wave sources by modifying the input-output optics of advanced interferometers
We study frequency dependent (FD) input-output schemes for signal-recycling
interferometers, the baseline design of Advanced LIGO and the current
configuration of GEO 600. Complementary to a recent proposal by Harms et al. to
use FD input squeezing and ordinary homodyne detection, we explore a scheme
which uses ordinary squeezed vacuum, but FD readout. Both schemes, which are
sub-optimal among all possible input-output schemes, provide a global noise
suppression by the power squeeze factor, while being realizable by using
detuned Fabry-Perot cavities as input/output filters. At high frequencies, the
two schemes are shown to be equivalent, while at low frequencies our scheme
gives better performance than that of Harms et al., and is nearly fully
optimal. We then study the sensitivity improvement achievable by these schemes
in Advanced LIGO era (with 30-m filter cavities and current estimates of
filter-mirror losses and thermal noise), for neutron star binary inspirals, and
for narrowband GW sources such as low-mass X-ray binaries and known radio
pulsars. Optical losses are shown to be a major obstacle for the actual
implementation of these techniques in Advanced LIGO. On time scales of
third-generation interferometers, like EURO/LIGO-III (~2012), with
kilometer-scale filter cavities, a signal-recycling interferometer with the FD
readout scheme explored in this paper can have performances comparable to
existing proposals. [abridged]Comment: Figs. 9 and 12 corrected; Appendix added for narrowband data analysi
Surface waves and crustal structure on Mars
We detected surface waves from two meteorite impacts on Mars. By measuring group velocity dispersion along the impact-lander path, we obtained a direct constraint on crustal structure away from the InSight lander. The crust north of the equatorial dichotomy had a shear wave velocity of approximately 3.2 kilometers per second in the 5- to 30-kilometer depth range, with little depth variation. This implies a higher crustal density than inferred beneath the lander, suggesting either compositional differences or reduced porosity in the volcanic areas traversed by the surface waves. The lower velocities and the crustal layering observed beneath the landing site down to a 10-kilometer depth are not a global feature. Structural variations revealed by surface waves hold implications for models of the formation and thickness of the martian crust.D.K., S.C., D.G., J.C., C.D., A. K., S.C.S., N.D., and G.Z. were supported by the ETH+ funding scheme (ETH+02 19-1: âPlanet Marsâ). Marsquake Service operations at ETH ZĂŒrich were supported by ETH Research grant ETH-06 17-02. N.C.S. and V.L. were supported by NASA PSP grant no. 80NSSC18K1628. Q.H. and E.B. are funded by NASA
grant 80NSSC18K1680. C.B. and J.L. were supported by NASA InSight PSP grant no. 80NSSC18K1679. S.D.K. was supported by NASA InSight PSP grant no. 80NSSC18K1623. P.L., E.B., M.D., H.S., E.S., M.W., Z.X., T.W., M.P., R.F.G. were supported by CNES and the Agence Nationale de la Recherche (ANR-19-CE31-0008-08 MAGIS) for SEIS operation and SEIS Science analysis. A.H., C.C. and W.T.P. were supported by the UKSA under grant nos. ST/R002096/1, ST/ W002523/1 and ST/V00638X/1. Numerical computations of McMC Approach 2 were performed on the S-CAPAD/DANTE platform (IPGP, France) and using the HPC resources of IDRIS under the allocation A0110413017 made by GENCI. A.H. was supported by the UKSA under grant nos. ST/R002096/1 and ST/W002523/1. F.N. was supported by InSight PSP 80NSSC18K1627. I.J.D. was supported by NASA InSight PSP grant no. 80NSSC20K0971. L.V.P. was funded by NASANNN12AA01C with subcontract JPL-1515835. The research was carried out in part by W.B.B., M.G. and M.P.P. at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004)Peer reviewe
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