9,619 research outputs found
Energy efficient engine high-pressure turbine detailed design report
The energy efficient engine high-pressure turbine is a single stage system based on technology advancements in the areas of aerodynamics, structures and materials to achieve high performance, low operating economics and durability commensurate with commercial service requirements. Low loss performance features combined with a low through-flow velocity approach results in a predicted efficiency of 88.8 for a flight propulsion system. Turbine airfoil durability goals are achieved through the use of advanced high-strength and high-temperature capability single crystal materials and effective cooling management. Overall, this design reflects a considerable extension in turbine technology that is applicable to future, energy efficient gas-turbine engines
The roles of the subunits in the function of the calcium channel
Dihydropyridine-sensitive voltage-dependent L-type calcium channels are critical to excitation-secretion and excitation-contraction coupling. The channel molecule is a complex of the main, pore-forming subunit alpha 1 and four additional subunits: alpha 2, delta, beta, and gamma (alpha 2 and delta are encoded by a single messenger RNA). The alpha 1 subunit messenger RNA alone directs expression of functional calcium channels in Xenopus oocytes, and coexpression of the alpha 2/delta and beta subunits enhances the amplitude of the current. The alpha 2, delta, and gamma subunits also have pronounced effects on its macroscopic characteristics, such as kinetics, voltage dependence of activation and inactivation, and enhancement by a dihydropyridine agonist. In some cases, specific modulatory functions can be assigned to individual subunits, whereas in other cases the different subunits appear to act in concert to modulate the properties of the channel
The Algebras of Large N Matrix Mechanics
Extending early work, we formulate the large N matrix mechanics of general
bosonic, fermionic and supersymmetric matrix models, including Matrix theory:
The Hamiltonian framework of large N matrix mechanics provides a natural
setting in which to study the algebras of the large N limit, including
(reduced) Lie algebras, (reduced) supersymmetry algebras and free algebras. We
find in particular a broad array of new free algebras which we call symmetric
Cuntz algebras, interacting symmetric Cuntz algebras, symmetric
Bose/Fermi/Cuntz algebras and symmetric Cuntz superalgebras, and we discuss the
role of these algebras in solving the large N theory. Most important, the
interacting Cuntz algebras are associated to a set of new (hidden) local
quantities which are generically conserved only at large N. A number of other
new large N phenomena are also observed, including the intrinsic nonlocality of
the (reduced) trace class operators of the theory and a closely related large N
field identification phenomenon which is associated to another set (this time
nonlocal) of new conserved quantities at large N.Comment: 70 pages, expanded historical remark
Distributing the burdens of climate change
Global climate change raises many questions for environmental political theorists. This article focuses on the question of identifying the agents that should bear the financial burden of preventing dangerous climate change. Identifying in a fair way the agents that should take the lead in climate mitigation and adaptation, as well as the precise burdens that these parties must bear, will be a key aspect of the next generation of global climate policies. After a critical review of a number of rival approaches to burden sharing, the paper argues that only a principled and philosophically robust reconciliation of three approaches to burden sharing (‘contribution to problem’, ‘ability to pay’ and ‘beneficiary pays’) can generate a satisfactory mix of theoretical coherence and practical application
Magnetic friction due to vortex fluctuation
We use Monte Carlo and molecular dynamics simulation to study a magnetic
tip-sample interaction. Our interest is to understand the mechanism of heat
dissipation when the forces involved in the system are magnetic in essence. We
consider a magnetic crystalline substrate composed of several layers
interacting magnetically with a tip. The set is put thermally in equilibrium at
temperature T by using a numerical Monte Carlo technique. By using that
configuration we study its dynamical evolution by integrating numerically the
equations of motion. Our results suggests that the heat dissipation in this
system is closed related to the appearing of vortices in the sample.Comment: 6 pages, 41 figure
Cosmology, cohomology, and compactification
Ashtekar and Samuel have shown that Bianchi cosmological models with compact
spatial sections must be of Bianchi class A. Motivated by general results on
the symmetry reduction of variational principles, we show how to extend the
Ashtekar-Samuel results to the setting of weakly locally homogeneous spaces as
defined, e.g., by Singer and Thurston. In particular, it is shown that any
m-dimensional homogeneous space G/K admitting a G-invariant volume form will
allow a compact discrete quotient only if the Lie algebra cohomology of G
relative to K is non-vanishing at degree m.Comment: 6 pages, LaTe
Statistical properties of a free-electron laser revealed by the Hanbury Brown and Twiss interferometry
We present a comprehensive experimental analysis of statistical properties of
the self-amplified spontaneous emission (SASE) free-electron laser (FEL) FLASH
at DESY in Hamburg by means of Hanbury Brown and Twiss (HBT) interferometry.
The experiments were performed at the FEL wavelengths of 5.5 nm, 13.4 nm, and
20.8 nm. We determined the 2-nd order intensity correlation function for all
wavelengths and different operation conditions of FLASH. In all experiments a
high degree of spatial coherence (above 50%) was obtained. Our analysis
performed in spatial and spectral domains provided us with the independent
measurements of an average pulse duration of the FEL that were below 60 fs. To
explain complicated behaviour of the 2-nd order intensity correlation function
we developed advanced theoretical model that includes the presence of multiple
beams and external positional jitter of the FEL pulses. By this analysis we
determined that in most experiments several beams were present in radiating
field and in one of the experiments external positional jitter was about 25% of
the beam size. We envision that methods developed in our study will be used
widely for analysis and diagnostics of the FEL radiation.Comment: 29 pages, 14 figures, 3 table
Transport of charged particles by adjusting rf voltage amplitudes
We propose a planar architecture for scalable quantum information processing
(QIP) that includes X-junctions through which particles can move without
micromotion. This is achieved by adjusting radio frequency (rf) amplitudes to
move an rf null along the legs of the junction. We provide a proof-of-principle
by transporting dust particles in three dimensions via adjustable rf potentials
in a 3D trap. For the proposed planar architecture, we use regularization
techniques to obtain amplitude settings that guarantee smooth transport through
the X-junction.Comment: 16 pages, 10 figure
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