3,547 research outputs found
Applications of system identification methods to the prediction of helicopter stability, control and handling characteristics
A set of results on rotorcraft system identification is described. Flight measurements collected on an experimental Puma helicopter are reviewed and some notable characteristics highlighted. Following a brief review of previous work in rotorcraft system identification, the results of state estimation and model structure estimation processes applied to the Puma data are presented. The results, which were obtained using NASA developed software, are compared with theoretical predictions of roll, yaw and pitching moment derivatives for a 6 degree of freedom model structure. Anomalies are reported. The theoretical methods used are described. A framework for reduced order modelling is outlined
Electron Transfer Precedes ATP Hydrolysis during Nitrogenase Catalysis
The biological reduction of N2 to NH3 catalyzed by Mo-dependent nitrogenase requires at least eight rounds of a complex cycle of events associated with ATP-driven electron transfer (ET) from the Fe protein to the catalytic MoFe protein, with each ET coupled to the hydrolysis of two ATP molecules. Although steps within this cycle have been studied for decades, the nature of the coupling between ATP hydrolysis and ET, in particular the order of ET and ATP hydrolysis, has been elusive. Here, we have measured first-order rate constants for each key step in the reaction sequence, including direct measurement of the ATP hydrolysis rate constant: kATP = 70 sâ1, 25 °C. Comparison of the rate constants establishes that the reaction sequence involves four sequential steps: (i) conformationally gated ET (kET = 140 sâ1, 25 °C), (ii) ATP hydrolysis (kATP = 70 sâ1, 25 °C), (iii) Phosphate release (kPi = 16 sâ1, 25 °C), and (iv) Fe protein dissociation from the MoFe protein (kdiss = 6 sâ1, 25 °C). These findings allow completion of the thermodynamic cycle undergone by the Fe protein, showing that the energy of ATP binding and proteinâprotein association drive ET, with subsequent ATP hydrolysis and Pi release causing dissociation of the complex between the Feox(ADP)2 protein and the reduced MoFe protein
Non-commuting coordinates, exotic particles, & anomalous anyons in the Hall effect
Our previous ``exotic'' particle, together with the more recent anomalous
anyon model (which has arbitrary gyromagnetic factor ) are reviewed. The
non-relativistic limit of the anyon generalizes the exotic particle which has
to any .When put into planar electric and magnetic fields, the Hall
effect becomes mandatory for all , when the field takes some critical
value.Comment: A new reference added. Talk given by P. Horvathy at the International
Workshop "Nonlinear Physics: Theory and Experiment. III. July'04, Gallipoli
(Lecce, Italy). To be published in Theor. Math. Phys. Latex 9 pages, no
figure
Newton-Hooke spacetimes, Hpp-waves and the cosmological constant
We show explicitly how the Newton-Hooke groups act as symmetries of the
equations of motion of non-relativistic cosmological models with a cosmological
constant. We give the action on the associated non-relativistic spacetimes and
show how these may be obtained from a null reduction of 5-dimensional
homogeneous pp-wave Lorentzian spacetimes. This allows us to realize the
Newton-Hooke groups and their Bargmann type central extensions as subgroups of
the isometry groups of the pp-wave spacetimes. The extended Schrodinger type
conformal group is identified and its action on the equations of motion given.
The non-relativistic conformal symmetries also have applications to
time-dependent harmonic oscillators. Finally we comment on a possible
application to Gao's generalization of the matrix model.Comment: 21 page
Non-commutative mechanics and Exotic Galilean symmetry
In order to derive a large set of Hamiltonian dynamical systems, but with
only first order Lagrangian, we resort to the formulation in terms of
Lagrange-Souriau 2-form formalism. A wide class of systems derived in different
phenomenological contexts are covered. The non-commutativity of the particle
position coordinates are a natural consequence. Some explicit examples are
considered.Comment: 15 pages, Talk given at Nonlinear Physics. Theory and Experiment
VI,Gallipoli (Lecce), Italy, June 23 - July 3, 201
Generalized Massive Gravity and Galilean Conformal Algebra in two dimensions
Galilean conformal algebra (GCA) in two dimensions arises as contraction of
two copies of the centrally extended Virasoro algebra ( with ). The central charges of
GCA can be expressed in term of Virasoro central charges. For finite and
non-zero GCA central charges, the Virasoro central charges must behave as
asymmetric form . We propose that, the bulk
description for 2d GCA with asymmetric central charges is given by general
massive gravity (GMG) in three dimensions. It can be seen that, if the
gravitational Chern-Simons coupling behaves as of order
O() or (), the central charges
of GMG have the above dependence. So, in non-relativistic scaling
limit , we calculated GCA parameters and finite
entropy in term of gravity parameters mass and angular momentum of GMG.Comment: 9 page
Holographic flows to IR Lifshitz spacetimes
Recently we studied `vanishing' horizon limits of `boosted' black D3-brane
geometry \cite{hsnr}. The type IIB solutions obtained by taking these special
double limits were found to describe nonrelativistic Lifshitz spacetimes at
zero temperature. In the present work we study these limits for TsT black-hole
solutions which include -field. The new Galilean solutions describe a
holographic RG flow from Schr\"odinger () spacetime in UV to a Lifshitz
universe () in the IR.Comment: 10 pages; v2: A bad typo in eq.8 corrected; v3: Discussion and
reference on Kaigorodov spaces included, correction in sec-3, to be published
in JHE
Rigorous Physicochemical Framework for Metal Ion Binding by Aqueous Nanoparticulate Humic Substances: Implications for Speciation Modeling by the NICA-Donnan and WHAM Codes
Latest knowledge on the reactivity of charged nanoparticulate complexants toward aqueous metal ions is discussed in mechanistic detail. We present a rigorous generic description of electrostatic and chemical contributions to metal ion binding by nanoparticulate complexants, and their dependence on particle size, particle type (i.e., reactive sites distributed within the particle body or confined to the surface), ionic strength of the aqueous medium, and the nature of the metal ion. For the example case of soft environmental particles such as fulvic and humic acids, practical strategies are delineated for determining intraparticulate metal ion speciation, and for evaluating intrinsic chemical binding affinities and heterogeneity. The results are compared with those obtained by popular codes for equilibrium speciation modeling (namely NICA-Donnan and WHAM). Physicochemical analysis of the discrepancies generated by these codes reveals the a priori hypotheses adopted therein and the inappropriateness of some of their key parameters. The significance of the characteristic time scales governing the formation and dissociation rates of metalânanoparticle complexes in defining the relaxation properties and the complete equilibration of the metalâ nanoparticulate complex dispersion is described. The dynamic features of nanoparticulate complexes are also discussed in the context of predictions of the labilities and bioavailabilities of the metal species
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