748 research outputs found
On the geometry of lambda-symmetries, and PDEs reduction
We give a geometrical characterization of -prolongations of vector
fields, and hence of -symmetries of ODEs. This allows an extension to
the case of PDEs and systems of PDEs; in this context the central object is a
horizontal one-form , and we speak of -prolongations of vector fields
and -symmetries of PDEs. We show that these are as good as standard
symmetries in providing symmetry reduction of PDEs and systems, and explicit
invariant solutions
Coherent resonant interactions and slow light with molecules confined in photonic band-gap fibers
We investigate resonant nonlinear optical interactions and demonstrate
induced transparency in acetylene molecules in a hollow-core photonic band-gap
fiber at 1.5m. The induced spectral transmission window is used to
demonstrate slow-light effects, and we show that the observed broadening of the
spectral features is due to collisions of the molecules with the inner walls of
the fiber core. Our results illustrate that such fibers can be used to
facilitate strong coherent light-matter interactions even when the optical
response of the individual molecules is weak.Comment: 5 pages, 4 figure
Local and nonlocal solvable structures in ODEs reduction
Solvable structures, likewise solvable algebras of local symmetries, can be
used to integrate scalar ODEs by quadratures. Solvable structures, however, are
particularly suitable for the integration of ODEs with a lack of local
symmetries. In fact, under regularity assumptions, any given ODE always admits
solvable structures even though finding them in general could be a very
difficult task. In practice a noteworthy simplification may come by computing
solvable structures which are adapted to some admitted symmetry algebra. In
this paper we consider solvable structures adapted to local and nonlocal
symmetry algebras of any order (i.e., classical and higher). In particular we
introduce the notion of nonlocal solvable structure
The Modern Irrationalities of American Criminal Codes: An Empirical Study of Offense Grading
The Model Penal Code made great advances in clarity and legality, moving most of the states from a mix of common law and ad hoc statutes to the modern American form of a comprehensive, succinct code that has served as a model around the world. Yet the decades since the wave of Model Code-based codifications have seen a steady degradation of American codes brought on by a relentless and accelerating rate of criminal law amendments that ignore the style, format, and content of the existing codes. The most damaging aspect of this trend is the exponentially increasing number of offense grading irrationalities found in most modern American codes. This Article documents the practical and prudential importance of getting offense grading right – that is, having the grade of each offense or suboffense reflect its relative seriousness in relation to all other offenses – then illustrates just how wrong things have gone, using a case study of offense grading in Pennsylvania, one of the better modern American codes. The critique of Pennsylvania, and its conclusions, does not rely upon the value judgments of the authors but rather upon an empirical study of the judgments of Pennsylvania residents regarding the relative seriousness of more than a hundred existing Pennsylvania offenses. The results suggest a startling conflict between the law\u27s grading judgments and those of the community it governs, as well as a variety of kinds of logical irrationalities and internal inconsistencies. The process by which these grading irrationalities have been and continue to be created is examined, and solutions for fixing and, perhaps, avoiding these problems in the future, are explored
On asymptotic nonlocal symmetry of nonlinear Schr\"odinger equations
A concept of asymptotic symmetry is introduced which is based on a definition
of symmetry as a reducibility property relative to a corresponding invariant
ansatz. It is shown that the nonlocal Lorentz invariance of the free-particle
Schr\"odinger equation, discovered by Fushchych and Segeda in 1977, can be
extended to Galilei-invariant equations for free particles with arbitrary spin
and, with our definition of asymptotic symmetry, to many nonlinear
Schr\"odinger equations. An important class of solutions of the free
Schr\"odinger equation with improved smoothing properties is obtained
Few cycle pulse propagation
We present a comprehensive framework for treating the nonlinear interaction
of few-cycle pulses using an envelope description that goes beyond the
traditional SVEA method. This is applied to a range of simulations that
demonstrate how the effect of a nonlinearity differs between the
many-cycle and few-cycle cases. Our approach, which includes diffraction,
dispersion, multiple fields, and a wide range of nonlinearities, builds upon
the work of Brabec and Krausz[1] and Porras[2]. No approximations are made
until the final stage when a particular problem is considered.
The original version (v1) of this arXiv paper is close to the published
Phys.Rev.A. version, and much smaller in size.Comment: 9 pages, 14 figure
Gravitational Waves: Just Plane Symmetry
We present some remarkable properties of the symmetry group for gravitational
plane waves. Our main observation is that metrics with plane wave symmetry
satisfy every system of generally covariant vacuum field equations except the
Einstein equations. The proof uses the homothety admitted by metrics with plane
wave symmetry and the scaling behavior of generally covariant field equations.
We also discuss a mini-superspace description of spacetimes with plane wave
symmetry.Comment: 10 pages, TeX, uses IOP style file
On the relation between standard and -symmetries for PDEs
We give a geometrical interpretation of the notion of -prolongations of
vector fields and of the related concept of -symmetry for partial
differential equations (extending to PDEs the notion of -symmetry for
ODEs). We give in particular a result concerning the relationship between
-symmetries and standard exact symmetries. The notion is also extended to
the case of conditional and partial symmetries, and we analyze the relation
between local -symmetries and nonlocal standard symmetries.Comment: 25 pages, no figures, latex. to be published in J. Phys.
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