1,022 research outputs found
A holomorphic representation of the Jacobi algebra
A representation of the Jacobi algebra by first order differential operators with polynomial
coefficients on the manifold is presented. The
Hilbert space of holomorphic functions on which the holomorphic first order
differential operators with polynomials coefficients act is constructed.Comment: 34 pages, corrected typos in accord with the printed version and the
Errata in Rev. Math. Phys. Vol. 24, No. 10 (2012) 1292001 (2 pages) DOI:
10.1142/S0129055X12920018, references update
Force transmission in a packing of pentagonal particles
We perform a detailed analysis of the contact force network in a dense
confined packing of pentagonal particles simulated by means of the contact
dynamics method. The effect of particle shape is evidenced by comparing the
data from pentagon packing and from a packing with identical characteristics
except for the circular shape of the particles. A counterintuitive finding of
this work is that, under steady shearing, the pentagon packing develops a lower
structural anisotropy than the disk packing. We show that this weakness is
compensated by a higher force anisotropy, leading to enhanced shear strength of
the pentagon packing. We revisit "strong" and "weak" force networks in the
pentagon packing, but our simulation data provide also evidence for a large
class of "very weak" forces carried mainly by vertex-to-edge contacts. The
strong force chains are mostly composed of edge-to-edge contacts with a marked
zig-zag aspect and a decreasing exponential probability distribution as in a
disk packing
Invariant Differential Operators for Non-Compact Lie Groups: the Sp(n,R) Case
In the present paper we continue the project of systematic construction of
invariant differential operators on the example of the non-compact algebras
sp(n,R), in detail for n=6. Our choice of these algebras is motivated by the
fact that they belong to a narrow class of algebras, which we call 'conformal
Lie algebras', which have very similar properties to the conformal algebras of
Minkowski space-time. We give the main multiplets and the main reduced
multiplets of indecomposable elementary representations for n=6, including the
necessary data for all relevant invariant differential operators. In fact, this
gives by reduction also the cases for n<6, since the main multiplet for fixed n
coincides with one reduced case for n+1.Comment: Latex2e, 27 pages, 8 figures. arXiv admin note: substantial text
overlap with arXiv:0812.2690, arXiv:0812.265
Two-Dimensional Molecular Patterning by Surface-Enhanced Zn-Porphyrin Coordination
In this contribution, we show how zinc-5,10,15,20-meso-tetradodecylporphyrins (Zn-TDPs) self-assemble into stable organized arrays on the surface of graphite, thus positioning their metal center at regular distances from each other, creating a molecular pattern, while retaining the possibility to coordinate additional ligands. We also demonstrate that Zn-TDPs coordinated to 3-nitropyridine display a higher tendency to be adsorbed at the surface of highly oriented pyrolytic graphite (HOPG) than noncoordinated ones. In order to investigate the two-dimensional (2D) self-assembly of coordinated Zn-TDPs, solutions with different relative concentrations of 3-nitropyridine and Zn-TDP were prepared and deposited on the surface of HOPG. STM measurements at the liquid-solid interface reveal that the ratio of coordinated Zn-TDPs over noncoordinated Zn-TDPs is higher at the n-tetradecane/HOPG interface than in n-tetradecane solution. This enhanced binding of the axial ligand at the liquid/solid interface is likely related to the fact that physisorbed Zn-TDPs are better binding sites for nitropyridines.
Memory of the Unjamming Transition during Cyclic Tiltings of a Granular Pile
Discrete numerical simulations are performed to study the evolution of the
micro-structure and the response of a granular packing during successive
loading-unloading cycles, consisting of quasi-static rotations in the gravity
field between opposite inclination angles. We show that internal variables,
e.g., stress and fabric of the pile, exhibit hysteresis during these cycles due
to the exploration of different metastable configurations. Interestingly, the
hysteretic behaviour of the pile strongly depends on the maximal inclination of
the cycles, giving evidence of the irreversible modifications of the pile state
occurring close to the unjamming transition. More specifically, we show that
for cycles with maximal inclination larger than the repose angle, the weak
contact network carries the memory of the unjamming transition. These results
demonstrate the relevance of a two-phases description -strong and weak contact
networks- for a granular system, as soon as it has approached the unjamming
transition.Comment: 13 pages, 15 figures, soumis \`{a} Phys. Rev.
Chemical Potential Shift in NdCeCuO: Contrasting Behaviors of the Electron- and Hole-Doped Cuprates
We have studied the chemical potential shift in the electron-doped
superconductor NdCeCuO by precise measurements of
core-level photoemission spectra. The result shows that the chemical potential
monotonously increases with electron doping, quite differently from
LaSrCuO, where the shift is suppressed in the underdoped
region.
If the suppression of the shift in LaSrCuO is attributed
to strong stripe fluctuations, the monotonous increase of the chemical
potential is consistent with the absence of stripe fluctuations in
NdCeCuO. The chemical potential jump between
NdCuO and LaCuO is found to be much smaller than the
optical band gaps.Comment: 4 pages, 5 figure
THERMODYNAMICS OF A BROWNIAN BRIDGE POLYMER MODEL IN A RANDOM ENVIRONMENT
We consider a directed random walk making either 0 or moves and a
Brownian bridge, independent of the walk, conditioned to arrive at point on
time . The Hamiltonian is defined as the sum of the square of increments of
the bridge between the moments of jump of the random walk and interpreted as an
energy function over the bridge connfiguration; the random walk acts as the
random environment. This model provides a continuum version of a model with
some relevance to protein conformation. The thermodynamic limit of the specific
free energy is shown to exist and to be self-averaging, i.e. it is equal to a
trivial --- explicitly computed --- random variable. An estimate of the
asymptotic behaviour of the ground state energy is also obtained.Comment: 20 pages, uuencoded postscrip
Analysis of donor criteria for the prediction of outcome in clinical liver transplantation.
The results of 219 orthotopic human liver transplants performed during 1985 at the University of Pittsburgh were reviewed to determine whether donor parameters could be used to predict the quality of early graft function. Multivariate discriminant analysis demonstrated that traditional parameters of donor assessment are unreliable predictors of poor graft function. Furthermore, 56% of the donors considered poor by conservative selection criteria produced livers with good early posttransplant function. Survival of recipients of primary allografts from donors rated poor was no different than survival of recipients of allografts from donors rated good
An Integration Formula for the Moment Maps of Circle Actions
The integration of the exponential of the square of the moment map of the
circle action is studied by a direct stationary phase computation and by
applying the Duistermaat-Heckman formula. Both methods yield two distinct
formulas expressing the integral in terms of contributions from the critical
set of the square of the moment map. The cohomological pairings on the
symplectic quotient, including its volume (which was known to be a piecewise
polynomial), are computed explicitly using the asymptotic behavior of the two
formulas.Comment: LaTeX file, 17 pages (typos corrected, include non-isolated fixed
pts
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