318 research outputs found
Approximation on partially ordered sets of regular grids
In this paper we analyse the approximation of functions on partially ordered sequences of regular grids. We start with the formulation of minimal requirements for useful grid transfer operators in such a partially ordered context, and we continue with the introduction of hierarchical decompositions and the identification of piecewise constant and piecewise linear approximations as special instances of the tensor product case. In the second part of the paper we derive error estimates for approximation in different norms on more-dimensional dyadic sequences of regular and sparse grids. We give special attention to a convenient notation
An instrument to measure atmospheric pressure fluctuations above surface gravity waves
This paper describes an instrument which has been used successfully at a field site in the Bight of Abaco, Bahamas, to monitor the atmospheric pressure field above surface gravity waves in the frequency range .5 to 5. rad/s. The atmospheric pressure is sampled at fixed elevations with a cone-shaped probe having a pressure coefficient of less than .02 magnitude for angles of attack less than 15°; the probe is mounted on a vane to minimize horizontal angles of attack. The pressure signal is conducted to a subsurface transducer through a mercury-sealed bearing. Overall system noise is estimated to be of order .5 ”bars and is largely wave-incoherent
HOMOâHOMO Electron Transfer : An Elegant Strategy for p-Type Doping of Polymer Semiconductors toward Thermoelectric Applications
Unlike the conventional pâdoping of organic semiconductors (OSCs) using acceptors, here, an efficient doping concept for diketopyrrolopyrroleâbased polymer PDPP[T]âEDOT (OSCâ1) is presented using an oxidized pâtype semiconductor, SpiroâOMeTAD(TFSI) (OSCâ2), exploiting electron transfer from HOMO to HOMO. A shift of work function toward the HOMO upon doping is confirmed by ultraviolet photoelectron spectroscopy (UPS). Detailed Xâray photoelectron spectroscopy (XPS) and UVâvisâNIR absorption studies confirm HOMO to HOMO electron transfer. The reduction products of SpiroâOMeTAD(TFSI) to SpiroâOMeTAD(TFSI) and SpiroâOMeTAD is also confirmed and their relative amounts in doped samples is determined. MottâSchottky analysis shows two orders of magnitude increase in free charge carrier density and one order of magnitude increase in the charge carrier mobility. The conductivity increases considerably by four orders of magnitude to a maximum of 10 S m for a very low doping ratio of 8 mol%. The doped polymer films exhibit high thermal and ambient stability resulting in a maximum power factor of 0.07 ”W m K at a Seebeck coefficient of 140 ”V K for a very low doping ratio of 4 mol%. Also, the concept of HOMO to HOMO electron transfer is a highly efficient, stable and generic way to pâdope other conjugated polymers
Toeplitz operators on symplectic manifolds
We study the Berezin-Toeplitz quantization on symplectic manifolds making use
of the full off-diagonal asymptotic expansion of the Bergman kernel. We give
also a characterization of Toeplitz operators in terms of their asymptotic
expansion. The semi-classical limit properties of the Berezin-Toeplitz
quantization for non-compact manifolds and orbifolds are also established.Comment: 40 page
A variant of the Mukai pairing via deformation quantization
We give a new method to prove a formula computing a variant of Caldararu's
Mukai pairing \cite{Cal1}. Our method is based on some important results in the
area of deformation quantization. In particular, part of the work of Kashiwara
and Schapira in \cite{KS} as well as an algebraic index theorem of Bressler,
Nest and Tsygan in \cite{BNT},\cite{BNT1} and \cite{BNT2} are used. It is hoped
that our method is useful for generalization to settings involving certain
singular varieties.Comment: 8 pages. Comments and suggestions welcom
Gauge Orbit Types for Theories with Classical Compact Gauge Group
We determine the orbit types of the action of the group of local gauge
transformations on the space of connections in a principal bundle with
structure group O(n), SO(n) or over a closed, simply connected manifold
of dimension 4. Complemented with earlier results on U(n) and SU(n) this
completes the classification of the orbit types for all classical compact gauge
groups over such space-time manifolds. On the way we derive the classification
of principal bundles with structure group SO(n) over these manifolds and the
Howe subgroups of SO(n).Comment: 57 page
Structural Transitions and Global Minima of Sodium Chloride Clusters
In recent experiments on sodium chloride clusters structural transitions
between nanocrystals with different cuboidal shapes were detected. Here we
determine reaction pathways between the low energy isomers of one of these
clusters, (NaCl)35Cl-. The key process in these structural transitions is a
highly cooperative rearrangement in which two parts of the nanocrystal slip
past one another on a {110} plane in a direction. In this way the
nanocrystals can plastically deform, in contrast to the brittle behaviour of
bulk sodium chloride crystals at the same temperatures; the nanocrystals have
mechanical properties which are a unique feature of their finite size. We also
report and compare the global potential energy minima for (NaCl)NCl- using two
empirical potentials, and comment on the effect of polarization.Comment: extended version, 13 pages, 8 figures, revte
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The Inverse Ocean Modeling System. Part I: Implementation
The Inverse Ocean Modeling (IOM) system constructs and runs weak-constraint, four-dimensional variational data assimilation (W4DVAR) for any dynamical model and any observing array. The dynamics and the observing algorithms may be nonlinear but must be functionally smooth. The user need only provide the model and the observing algorithms, together with an interpolation scheme that relates the model numerics to the observerâs coordinates. All other model-dependent elements of the Inverse Ocean Modeling assimilation algorithm (see both Chua and Bennett), including adjoint generators and Monte Carlo estimates of posteriors, have been derived and coded as templates in Parametric FORTRAN (Erwig et al.). This language has been developed for the IOM but has wider application in scientific programming. Guided by the Parametric FORTRAN templates, and by model information entered via a graphical user interface (GUI), the IOM generates conventional FORTRAN code for each of the many algorithm elements, customized to the userâs model. The IOM also runs the various W4DVAR assimilations, which are monitored by the GUI. The system is supported by a Web site that includes interactive tutorials for the assimilation algorithm.Keywords: Data assimilation, Ocean models, Variational analysi
Effect of Impurities on Pentacene Thin Film Growth for Field-Effect Transistors
Pentacenequinone (PnQ) impurities have been introduced into a pentacene
source material at number densities from 0.001 to 0.474 to quantify the
relative effects of impurity content and grain boundary structure on transport
in pentacene thin-film transistors. Atomic force microscopy (AFM) and
electrical measurements of top-contact pentacene thin-film transistors have
been employed to directly correlate initial structure and final film
structures, with the device mobility as a function of added impurity content.
The results reveal a factor four decrease in mobility without significant
changes in film morphology for source PnQ number fractions below ~0.008. For
these low concentrations, the impurity thus directly influences transport,
either as homogeneously distributed defects or by concentration at the
otherwise-unchanged grain boundaries. For larger impurity concentrations, the
continuing strong decrease in mobility is correlated with decreasing grain
size, indicating an impurity-induced increase in the nucleation of grains
during early stages of film growth.Comment: 18 pages, 4 Figures, 1 Tabl
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