1,317 research outputs found
Design and Fabrication of the NASA Decoupler Pylon for the F-16 Aircraft
The NASA Decoupler Pylon is a passive means of suppressing wing-store flutter. The feasibility of demonstrating this concept on the F-16 aircraft was established through model wind tunnel tests and analyses. As a result of these tests and studies a ship set of Decoupler Pylons was designed and fabricated for a flight test demonstration on the F-16 aircraft. Basic design criteria were developed during the analysis study pertaining to pylon pitch stiffness, alignment system requirements, and damping requirements. A design was developed which utilized an electrical motor for the pylon alignment system. The design uses a four pin, two link pivot design which results in a remote pivot located at the center of gravity of the store when the store is in the aligned position. The pitch spring was fabricated from a tapered constant stress cantilevered beam. The pylon has the same external lines as the existing production pylon and is designed to use a MAU-12 ejection rack which is the same as the one used with the production pylon. The detailed design and fabrication was supported with a complete ground test of the pylon prior to shipment to NASA
From Majorana Fermions to Topological Order
We consider a system consisting of a 2D network of links between Majorana
fermions on superconducting islands. We show that the fermionic Hamiltonian
modeling this system is topologically-ordered in a region of parameter space.
In particular we show that Kitaev's toric code emerges in fourth-order
perturbation theory. By using a Jordan-Wigner transformation we can map the
model onto a family of signed 2D Ising models in a transverse field where the
signs (FM or AFM) are determined by additional gauge bits. Our mapping allows
an understanding of the non-perturbative regime and the phase transition to a
non-topological phase. We discuss the physics behind a possible implementation
of this model and argue how it can be used for topological quantum computation
by adiabatic changes in the Hamiltonian.Comment: 4+4 pages, 5 figures. v2 has a new reference and a few new comments.
In v3: yet another new reference and Supplementary Material is renamed
Appendix. In v4: several typos are corrected, to appear in Phys. Rev. Let
Enhanced levels of leukotriene B4 in synovial fluid in Lyme disease
The purpose of this study was to evaluate the potential role of LTB4 and cysteinyl leukotrienes in Lyme disease (LD). Therefore, a total number of 34 patients divided into four groups was studied. The patients were classified as having Lyme arthritis (n = 7) or Lyme meningitis (n = 10), and as control groups patients with a noninflammatory arthropathy (NIA) (n = 7) and healthy subjects (n = 10). LTB4 as well as LTC4 secretion from stimulated polymorphonuclear leukocytes (PMNL) from all groups of patients showed no statistical differences. LTB4 levels in synovial fluid were significantly increased in patients with Lyme arthritis (median 142 ng/ml, range 88–296) when compared to the control subjects with NIA (median 46 ng/ml, range 28–72) (p < 0.05). No statistical difference of urinary LTE4 levels between all the different groups of patients was observed. These results show that cysteinyl leukotrienes do not play an important role in the pathogenesis of LD. In contrast to previous findings in rheumatoid arthritis, LTB4 production from stimulated PMNL was not found to be increased in LD. However, the significantly elevated levels of LTB4 in synovial fluid of patients with Lyme arthritis underline the involvement of LTB4 in the pathogenesis of this disease
Observations Supporting the Role of Magnetoconvection in Energy Supply to the Quiescent Solar Atmosphere
Identifying the two physical mechanisms behind the production and sustenance
of the quiescent solar corona and solar wind poses two of the outstanding
problems in solar physics today. We present analysis of spectroscopic
observations from the Solar and Heliospheric Observatory that are consistent
with a single physical mechanism being responsible for a significant portion of
the heat supplied to the lower solar corona and the initial acceleration of the
solar wind; the ubiquitous action of magnetoconvection-driven reprocessing and
exchange reconnection of the Sun's magnetic field on the supergranular scale.
We deduce that while the net magnetic flux on the scale of a supergranule
controls the injection rate of mass and energy into the transition region
plasma it is the global magnetic topology of the plasma that dictates whether
the released ejecta provides thermal input to the quiet solar corona or becomes
a tributary that feeds the solar wind.Comment: 34 pages, 13 figures - In press Astrophysical Journal (Jan 1 2007
Design and Fabrication of the NASA Decoupler Pylon for the F-16 Aircraft, Addendum 2
The decoupler pylons which were originally designed and assembled with bushings in the pivot joints were retrofitted with roller bearings. This retrofit, the supporting analyses and the fixture tests of the modified pylons are reported in this document. The loads and stress analysis was directed toward the redesigned parts which were the pylon links and pins. The loads and stress analysis indicates that the pylons with the bearing installation have reduced capacity with respect to the bushing design. Fixture tests of the redesigned pylons were conducted in the GD/FW facility. Breakout friction tests and vibration tests were conducted. The tests show that the joint friction is approximately one-half the level with bearings as compared with the bushing installation. The vibration test data was used to tune the pylon mathematical simulation and this revised pylon simulation was used to recompute airplane modes of vibration. These computed modes of vibration were used in complete airplane symmetric and antisymmetric flutter and aeroservoelastic analyses
Earth‐Moon‐Mars Radiation Environment Module framework
[1] We are preparing to return humans to the Moon and setting the stage for exploration to Mars and beyond. However, it is unclear if long missions outside of low-Earth orbit can be accomplished with acceptable risk. The central objective of a new modeling project, the Earth-Moon-Mars Radiation Exposure Module (EMMREM), is to develop and validate a numerical module for characterizing time-dependent radiation exposure in the Earth-Moon-Mars and interplanetary space environments. EMMREM is being designed for broad use by researchers to predict radiation exposure by integrating over almost any incident particle distribution from interplanetary space. We detail here the overall structure of the EMMREM module and study the dose histories of the 2003 Halloween storm event and a June 2004 event. We show both the event histories measured at 1 AU and the evolution of these events at observer locations beyond 1 AU. The results are compared to observations at Ulysses. The model allows us to predict how the radiation environment evolves with radial distance from the Sun. The model comparison also suggests areas in which our understanding of the physics of particle propagation and energization needs to be improved to better forecast the radiation environment. Thus, we introduce the suite of EMMREM tools, which will be used to improve risk assessment models so that future human exploration missions can be adequately planned for
Top-transmon: hybrid superconducting qubit for parity-protected quantum computation
Qubits constructed from uncoupled Majorana fermions are protected from
decoherence, but to perform a quantum computation this topological protection
needs to be broken. Parity-protected quantum computation breaks the protection
in a minimally invasive way, by coupling directly to the fermion parity of the
system --- irrespective of any quasiparticle excitations. Here we propose to
use a superconducting charge qubit in a transmission line resonator (a socalled
transmon) to perform parity-protected rotations and read-out of a topological
(top) qubit. The advantage over an earlier proposal using a flux qubit is that
the coupling can be switched on and off with exponential accuracy, promising a
reduced sensitivity to charge noise.Comment: 7 pages, 5 figure
Observation of the spin-orbit gap in bilayer graphene by one-dimensional ballistic transport
We report on measurements of quantized conductance in gate-defined quantum
point contacts in bilayer graphene that allow the observation of subband
splittings due to spin-orbit coupling. The size of this splitting can be tuned
from 40 to 80 eV by the displacement field. We assign this gate-tunable
subband-splitting to a gap induced by spin-orbit coupling of Kane-Mele type,
enhanced by proximity effects due to the substrate. We show that this
spin-orbit coupling gives rise to a complex pattern in low perpendicular
magnetic fields, increasing the Zeeman splitting in one valley and suppressing
it in the other one. In addition, we observe the existence of a spin-polarized
channel of 6 e/h at high in-plane magnetic field and of signatures of
interaction effects at the crossings of spin-split subbands of opposite spins
at finite magnetic field.Comment: 5 pages, 4 figures, Supplement 6 figure
Iron biogeochemistry across marine systems progress from the past decade
Based on an international workshop (Gothenburg, 14–16 May 2008), this review article aims to combine interdisciplinary knowledge from coastal and open ocean research on iron biogeochemistry. The major scientific findings of the past decade are structured into sections on natural and artificial iron fertilization, iron inputs into coastal and estuarine systems, colloidal iron and organic matter, and biological processes. Potential effects of global climate change, particularly ocean acidification, on iron biogeochemistry are discussed. The findings are synthesized into recommendations for future research areas
Soil nitrogen oxide fluxes from lowland forests converted to smallholder rubber and oil palm plantations in Sumatra, Indonesia
Oil palm (Elaeis guineensis) and rubber
(Hevea brasiliensis) plantations cover large areas of former
rainforest in Sumatra, Indonesia, supplying the global demand for these
crops. Although forest conversion is known to influence soil nitrous oxide
(N2O) and nitric oxide (NO) fluxes, measurements from oil palm and
rubber plantations are scarce (for N2O) or nonexistent (for NO). Our
study aimed to (1) quantify changes in soil–atmosphere fluxes of
N oxides with forest
conversion to rubber and oil palm plantations and (2) determine their
controlling factors. In Jambi, Sumatra, we selected two landscapes that
mainly differed in texture but were both on heavily weathered soils: loam and
clay Acrisol soils. Within each landscape, we investigated lowland forests,
rubber trees interspersed in secondary forest (termed as jungle rubber),
both as reference land uses and smallholder rubber and oil palm plantations
as converted land uses. In the loam Acrisol landscape, we conducted a
follow-on study in a large-scale oil palm plantation (called PTPN VI) for
comparison of soil N2O fluxes with smallholder oil palm plantations.
Land-use conversion to smallholder plantations had no effect on soil N-oxide
fluxes (P = 0. 58 to 0.76) due to the generally low soil N availability in
the reference land uses that further decreased with land-use conversion. Soil
N2O fluxes from the large-scale oil palm plantation did not differ with
those from smallholder plantations (P = 0. 15). Over 1-year measurements,
the temporal patterns of soil N-oxide fluxes were influenced by soil mineral
N and water contents. Across landscapes, annual soil N2O emissions were
controlled by gross nitrification and sand content, which also suggest the
influence of soil N and water availability. Soil N2O fluxes
(µg N m−2 h−1) were 7 ± 2 to 14 ± 7
(reference land uses), 6 ± 3 to 9 ± 2 (rubber), 12 ± 3 to
12 ± 6 (smallholder oil palm) and 42 ± 24 (large-scale oil palm).
Soil NO fluxes (µg N m−2 h−1) were −0.6 ± 0.7
to 5.7 ± 5.8 (reference land uses), −1.2 ± 0.5 to
−1.0 ± 0.2 (rubber) and −0.2 ± 1.2 to 0.7 ± 0.7
(smallholder oil palm). To improve the estimate of soil N-oxide fluxes from
oil palm plantations in this region, studies should focus on large-scale
plantations (which usually have 2 to 4 times higher N fertilization rates
than smallholders) with frequent measurements following fertilizer
application
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