12,555 research outputs found
The EET Horizontal Tails Investigation and the EET Lateral Controls Investigation
In the energy efficient transport (EET) Horizontal Tails Investigation, aerodynamic data were measured for five different horizontal tails on a full span model with a wide body fuselage. Three of the horizontal tails were low tail configurations and two were T tail configurations. All tails were tested in conjunction with two wings, a current wide body wing and a high aspect ratio supercritical wing. Local downwash angles and dynamic pressures in the vicinity of the tails were measured using a yaw head rake. The results provide a comparison of the aerodynamic characteristics of the two wing configurations at trimmed conditions for Mach numbers between 0.60 and 0.90. In the EET Lateral Controls Investigation, the control effectiveness of a conventional set of lateral controls was measured over a Mach number range from 0.60 to 0.90 on a high aspect ratio supercritical wing semispan model. The conventional controls included a high speed aileron, a low speed aileron, and six spoiler segments. The wing was designed so that the last 25% of the chord is removable to facilitate testing of various control systems. The current status and an indication of the data obtained in these investigations are presented
Dynamics of a Quantum Reference Frame
We analyze a quantum mechanical gyroscope which is modeled as a large spin
and used as a reference against which to measure the angular momenta of
spin-1/2 particles. These measurements induce a back-action on the reference
which is the central focus of our study. We begin by deriving explicit
expressions for the quantum channel representing the back-action. Then, we
analyze the dynamics incurred by the reference when it is used to sequentially
measure particles drawn from a fixed ensemble. We prove that the reference
thermalizes with the measured particles and find that generically, the thermal
state is reached in time which scales linearly with the size of the reference.
This contrasts a recent conclusion of Bartlett et al. that this takes a
quadratic amount of time when the particles are completely unpolarized. We now
understand their result in terms of a simple physical principle based on
symmetries and conservation laws. Finally, we initiate the study of the
non-equilibrium dynamics of the reference. Here we find that a reference in a
coherent state will essentially remain in one when measuring polarized
particles, while rotating itself to ultimately align with the polarization of
the particles
Nonnegative subtheories and quasiprobability representations of qubits
Negativity in a quasiprobability representation is typically interpreted as
an indication of nonclassical behavior. However, this does not preclude states
that are non-negative from exhibiting phenomena typically associated with
quantum mechanics - the single qubit stabilizer states have non-negative Wigner
functions and yet play a fundamental role in many quantum information tasks. We
seek to determine what other sets of quantum states and measurements for a
qubit can be non-negative in a quasiprobability representation, and to identify
nontrivial unitary groups that permute the states in such a set. These sets of
states and measurements are analogous to the single qubit stabilizer states. We
show that no quasiprobability representation of a qubit can be non-negative for
more than four bases and that the non-negative bases in any quasiprobability
representation must satisfy certain symmetry constraints. We provide an
exhaustive list of the sets of single qubit bases that are non-negative in some
quasiprobability representation and are also permuted by a nontrivial unitary
group. This list includes two families of three bases that both include the
single qubit stabilizer states as a special case and a family of four bases
whose symmetry group is the Pauli group. For higher dimensions, we prove that
there can be no more than 2^{d^2} states in non-negative bases of a
d-dimensional Hilbert space in any quasiprobability representation.
Furthermore, these bases must satisfy certain symmetry constraints,
corresponding to requiring the bases to be sufficiently complementary to each
other.Comment: 17 pages, 8 figures, comments very welcome; v2 published version.
Note that the statement and proof of Theorem III.2 in the published version
are incorrect (an erratum has been submitted), and this arXiv version (v2)
presents the corrected theorem and proof. The conclusions of the paper are
unaffected by this correctio
The adult mouse hippocampal progenitor is neurogenic but not a stem cell
The aim of this investigation was to characterize the proliferative precursor cells in the adult mouse hippocampal region. Given that a very large number of new hippocampal cells are generated over the lifetime of an animal, it is predicted that a neural stem cell is ultimately responsible for maintaining this genesis. Although it is generally accepted that a proliferative precursor resides within the hippocampus, contradictory reports exist regarding the classification of this cell. Is it a true stem cell or a more limited progenitor? Using a strict functional definition of a neural stem cell and a number of in vitro assays, we report that the resident hippocampal precursor is a progenitor capable of proliferation and multipotential differentiation but is unable to self-renew and thus proliferate indefinitely. Furthermore, the mitogen FGF-2 stimulates proliferation of these cells to a greater extent than epidermal growth factor ( EGF). In addition, we found that BDNF was essential for the production of neurons from the hippocampal progenitor cells, being required during proliferation to trigger neuronal fate. In contrast, a bona fide neural stem cell was identified in the lateral wall of the lateral ventricle surrounding the hippocampus. Interestingly, EGF proved to be the stronger mitogenic factor for this cell, which was clearly a different precursor from the resident hippocampal progenitor. These results suggest that the stem cell ultimately responsible for adult hippocampal neurogenesis resides outside the hippocampus, producing progenitor cells that migrate into the neurogenic zones and proliferate to produce new neurons and glia
Airloads research study. Volume 2: Airload coefficients derived from wind tunnel data
The development of B-1 aircraft rigid wind tunnel data for use in subsequent tasks of the Airloads Research Study is described. Data from the Rockwell International external structural loads data bank were used to generate coefficients of rigid airload shear, bending moment, and torsion at specific component reference stations or both symmetric and asymmetric loadings. Component stations include the movable wing, horizontal and vertical stabilizers, and forward and aft fuselages. The coefficient data cover a Mach number range from 0.7 to 2.2 for a wing sweep position of 67.5 degree
Airloads research study. Volume 1: Flight test loads acquisition
The acquisition of B-1 aircraft flight loads data for use in subsequent tasks of the Airloads Research Study is described. The basic intent is to utilize data acquired during B-1 aircraft tests, analyze these data beyond the scope of Air Force requirements, and prepare research reports that will add to the technology base for future large flexible aircraft. Flight test data obtained during the airloads survey program included condition-describing parameters, surface pressures, strain gage outputs, and loads derived from pressure and strain gauges. Descriptions of the instrumentation, data processing, and flight load survey program are included. Data from windup-turn and steady yaw maneuvers cover a Mach number range from 0.7 to 2.0 for a wing sweep position of 67.5 deg
^{63}Cu, ^{35}Cl, and ^{1}H NMR in the S=1/2 Kagom\'e Lattice ZnCu_{3}(OH)_{6}Cl_{2}
ZnCu(OH)Cl () is a promising new candidate for an
ideal Kagom\'e Heisenberg antiferromagnet, because there is no magnetic phase
transition down to 50 mK. We investigated its local magnetic and lattice
environments with NMR techniques. We demonstrate that the intrinsic local spin
susceptibility {\it decreases} toward T=0, but that slow freezing of the
lattice near 50 K, presumably associated with OH bonds, contributes to a
large increase of local spin susceptibility and its distribution. Spin dynamics
near T=0 obey a power-law behavior in high magnetic fields.Comment: Phys. Rev. Lett. (in press
Convergence improvement for coupled cluster calculations
Convergence problems in coupled-cluster iterations are discussed, and a new
iteration scheme is proposed. Whereas the Jacobi method inverts only the
diagonal part of the large matrix of equation coefficients, we invert a matrix
which also includes a relatively small number of off-diagonal coefficients,
selected according to the excitation amplitudes undergoing the largest change
in the coupled cluster iteration. A test case shows that the new IPM (inversion
of partial matrix) method gives much better convergence than the
straightforward Jacobi-type scheme or such well-known convergence aids as the
reduced linear equations or direct inversion in iterative subspace methods.Comment: 7 pages, IOPP styl
MACiE: a database of enzyme reaction mechanisms.
SUMMARY: MACiE (mechanism, annotation and classification in enzymes) is a publicly available web-based database, held in CMLReact (an XML application), that aims to help our understanding of the evolution of enzyme catalytic mechanisms and also to create a classification system which reflects the actual chemical mechanism (catalytic steps) of an enzyme reaction, not only the overall reaction. AVAILABILITY: http://www-mitchell.ch.cam.ac.uk/macie/.EPSRC (G.L.H. and J.B.O.M.), the BBSRC (G.J.B. and J.M.T.—CASE studentship in association with Roche Products Ltd; N.M.O.B. and J.B.O.M.—grant BB/C51320X/1), the Chilean Government’s Ministerio de Planificacio´n y Cooperacio´n and
Cambridge Overseas Trust (D.E.A.) for funding and Unilever for supporting the Centre for Molecular Science Informatics.application note restricted to 2 printed pages web site: http://www-mitchell.ch.cam.ac.uk/macie
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