7,373 research outputs found
High-pressure calorimeter chamber tests for liquid oxygen/kerosene (LOX/RP-1) rocket combustion
An experimental program was conducted to investigate the rocket combustion and heat transfer characteristics of liquid oxygen/kerosene (LOX/RP-1) mixtures at high chamber pressures. Two water-cooled calorimeter chambers of different combustion lengths were tested using 37- and 61-element oxidizer-fuel-oxidizer triplet injectors. The tests were conducted at nominal chamber pressures of 4.1, 8.3, and 13.8 MPa abs (600, 1200, and 2000 psia). Heat flux Q/A data were obtained for the entire calorimeter length for oxygen/fuel mixture ratios of 1.8 to 3.3. Test data at 4.1 MPa abs compared favorably with previous test data from another source. Using an injector with a fuel-rich outer zone reduced the throat heat flux by 47 percent with only a 4.5 percent reduction in the characteristic exhaust velocity efficiency C* sub eff. The throat heat transfer coefficient was reduced approximately 40 percent because of carbon deposits on the chamber wall
Strain-induced gauge and Rashba fields in ferroelectric Rashba lead chalcogenide PbX monolayers (X = S, Se, Te)
One of the exciting features of two-dimensional (2D) materials is their
electronic and optical tunability through strain engineering. Previously, we
found a class of 2D ferroelectric Rashba semiconductors PbX (X = S, Se, Te)
with tunable spin-orbital properties. In this work, based on our previous
tight-binding (TB) results, we derive an effective low-energy Hamiltonian
around the symmetry points that captures the effects of strain on the
electronic properties of PbX. We find that strains induce gauge fields which
shift the Rashba point and modify the Rashba parameter. This effect is
equivalent to the application of in-plane magnetic fields. The out-of-plane
strain, which is proportional to the electric polarization, is also shown to
modify the Rashba parameter. Overall, our theory connects strain and spin
splitting in ferroelectric Rashba materials, which will be important to
understand the strain-induced variations in local Rashba parameters that will
occur in practical applications
Large-scale Advanced Prop-fan (LAP) high speed wind tunnel test report
High Speed Wind Tunnel testing of the SR-7L Large Scale Advanced Prop-Fan (LAP) is reported. The LAP is a 2.74 meter (9.0 ft) diameter, 8-bladed tractor type rated for 4475 KW (6000 SHP) at 1698 rpm. It was designated and built by Hamilton Standard under contract to the NASA Lewis Research Center. The LAP employs thin swept blades to provide efficient propulsion at flight speeds up to Mach .85. Testing was conducted in the ONERA S1-MA Atmospheric Wind Tunnel in Modane, France. The test objectives were to confirm that the LAP is free from high speed classical flutter, determine the structural and aerodynamic response to angular inflow, measure blade surface pressures (static and dynamic) and evaluate the aerodynamic performance at various blade angles, rotational speeds and Mach numbers. The measured structural and aerodynamic performance of the LAP correlated well with analytical predictions thereby providing confidence in the computer prediction codes used for the design. There were no signs of classical flutter throughout all phases of the test up to and including the 0.84 maximum Mach number achieved. Steady and unsteady blade surface pressures were successfully measured for a wide range of Mach numbers, inflow angles, rotational speeds and blade angles. No barriers were discovered that would prevent proceeding with the PTA (Prop-Fan Test Assessment) Flight Test Program scheduled for early 1987
Two-dimensional square buckled Rashba lead chalcogenides
We propose the lead sulphide (PbS) monolayer as a two-dimensional semiconductor with a large Rashba-like spin-orbit effect controlled by the out-of-plane buckling. The buckled PbS conduction band is found to possess Rashba-like dispersion and spin texture at the M and Γ points, with large effective Rashba parameters of λ∼5 eV Å and λ∼1 eV Å, respectively. Using a tight-binding formalism, we show that the Rashba effect originates from the very large spin-orbit interaction and the hopping term that mixes the in-plane and out-of-plane p orbitals of Pb and S atoms. The latter, which depends on the buckling angle, can be controlled by applying strain to vary the spin texture as well as the Rashba parameter at Γ and M. Our density functional theory results together with tight-binding formalism provide a unifying framework for designing Rashba monolayers and for manipulating their spin properties.P.Z.H., H.S.P., and D.K.C. acknowledge the support of the Physics and Mechanical Engineering Department at Boston University. P.Z.H. is grateful for the hospitality of the NUS Centre for Advanced 2D Materials and Graphene Research Centre where this work was initiated. D.K.C. acknowledges the hospitality of the Aspen Center for Physics, which is supported by the US National Science Foundation Grant No. PHY-1607611. A.S.R., A.C.,and A.H.C.N. acknowledge support by the National Research Foundation, Prime Minister Office, Singapore, under its Medium Sized Centre Programme and CRP award "Novel 2D materials with tailored properties: Beyond graphene" (Grant No. R-144-000295-281). (Physics and Mechanical Engineering Department at Boston University; PHY-1607611 - US National Science Foundation; R-144-000295-281 - National Research Foundation, Prime Minister Office, Singapore, under its Medium Sized Centre Programme and CRP award "Novel 2D materials with tailored properties: Beyond graphene")Published versio
Interaction-Induced Strong Localization in Quantum Dots
We argue that Coulomb blockade phenomena are a useful probe of the cross-over
to strong correlation in quantum dots. Through calculations at low density
using variational and diffusion quantum Monte Carlo (up to r_s ~ 55), we find
that the addition energy shows a clear progression from features associated
with shell structure to those caused by commensurability of a Wigner crystal.
This cross-over (which occurs near r_s ~ 20 for spin-polarized electrons) is,
then, a signature of interaction-driven localization. As the addition energy is
directly measurable in Coulomb blockade conductance experiments, this provides
a direct probe of localization in the low density electron gas.Comment: 4 pages, published version, revised discussio
Graphene kirigami as a platform for stretchable and tunable quantum dot arrays
The quantum transport properties of a graphene kirigami similar to those
studied in recent experiments are calculated in the regime of elastic,
reversible deformations. Our results show that, at low electronic densities,
the conductance profile of such structures replicates that of a system of
coupled quantum dots, characterized by a sequence of minibands and stop-gaps.
The conductance and I-V curves have different characteristics in the distinct
stages of elastic deformation that characterize the elongation of these
structures. Notably, the effective coupling between localized states is
strongly reduced in the small elongation stage, whereas in the large elongation
regime the development of strong, localized pseudomagnetic field barriers can
reinforce the coupling and reestablish resonant tunneling across the kirigami.
This provides an interesting example of interplay between geometry and
pseudomagnetic field-induced confinement. The alternating miniband and
stop-gaps in the transmission lead to I-V characteristics with negative
differential conductance in well defined energy/doping ranges. These effects
should be stable in a realistic scenario that includes edge roughness and
Coulomb interactions, as these are expected to further promote localization of
states at low energies in narrow segments of graphene nanostructures.Comment: 10 pages, 10 figure
New Horizons: Long-Range Kuiper Belt Targets Observed by the Hubble Space Telescope
We report on Hubble Space Telescope (HST) observations of three Kuiper Belt
Objects (KBOs), discovered in our dedicated ground-based search campaign, that
are candidates for long-range observations from the New Horizons spacecraft:
2011 JY31, 2011 HZ102, and 2013 LU35. Astrometry with HST enables both current
and future critical accuracy improvements for orbit precision, required for
possible New Horizons observations, beyond what can be obtained from the
ground. Photometric colors of all three objects are red, typical of the Cold
Classical dynamical population within which they reside; they are also the
faintest KBOs to have had their colors measured. None are observed to be binary
with HST above separations of ~0.02 arcsec (~700 km at 44 AU) and {\Delta}m
less than or equal to 0.5.Comment: Pages: 11, Figures: 2, Tables: 3, Icarus, available online May 2014
(http://dx.doi.org/10.1016/j.icarus.2014.04.014
ELECTROKINETIC PHENOMENA : XIII. A COMPARISON OF THE ISOELECTRIC POINTS OF DISSOLVED AND CRYSTALLINE AMINO ACIDS
1. Although the isoelectric points of dissolved cystine, tyrosine, and aspartic acid molecules lie at widely differing pH values, the isoelectric points of the surfaces of these substances in the crystalline state are all near pH 2.3. This was found to be true in solutions of hydrochloric acid and in acetate buffers of approximately constant ionic strength. 2. When suspended in gelatin, tyrosine and cystine crystals adsorb the protein and attain a surface identical in behavior with gelatin-coated quartz or collodion particles. 3. Aluminum ions at low concentrations reduce the electric mobilities of tyrosine crystals to zero in a manner analogous to their effect on other surfaces. 4. Alkyl benzene droplets also have their electric mobility reduced to zero at low pH values but, unlike the amino acids, a change in sign was never noticed. 5. The mobility of tyrosine crystals is independent of crystal length between 2–100µ. Below this size the mobilities are decreased. 6. These results are discussed in connection with the concept of the general definition of the isoelectric point and the behavior of certain insoluble proteins such as wool and silk fibroin
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