721 research outputs found
The largest white light flare ever observed: 25 April 1984, 0001 UT
The X13/3B flare of 25 April 1984, 0001 UT, was accompanied by intense white light emission that reached a peak power output approx 2x10 to the 29 erg/sec in the optical/near UV continuum; the total energy radiated in the continuum alone reached 10 to the 32 power ergs. This was the most powerful white light flare yet recorded, exceeding the peak output of the largest previously known event by more than one order of magnitude. The flare was a two-ribbon type with intense embedded kernels as observed in both Balmer-alpha line and Balmer continuum, and each of these flare ribbons covered separate umbrae shortly after the maximum of the event. The onset and peak of the white light emission coincided with the onset and peak of the associated E greater than 100 KeV hard X-ray burst, while the 1-8 angstrom soft X-ray emission reached its maximum 4 minutes after the peak in white light
Nonadiabatic transitions in the exit channel of atom-molecule collisions: Fine-structure branching in Na+N[sub 2]
We study Na+Nâcollisions by laser excitation of the collision complex in a differential scattering experiment. The measured relative population of the Na(3p) fine-structure levels reflects the nonadiabatic transitions occuring in the exit channel of the collision.Theoretical results obtained with a classical-path formalism and accurate quantum chemical data for NaNâ are found to be in good agreement. The presence of a conical intersection for the T-shaped geometry has a profound influence on the observed fine-structure branching.Support from the Deutsche Forschungsgemeinschaft is
gratefully acknowledged
mlirSynth: Automatic, Retargetable Program Raising in Multi-Level IR using Program Synthesis
MLIR is an emerging compiler infrastructure for modern hardware, but existing programs cannot take advantage of MLIRâs high-performance compilation if they are described in lower-level general purpose languages. Consequently, to avoid programs needing to be rewritten manually, this has led to efforts to automatically raise lower-level to higher-level dialects in MLIR. However, current methods rely on manually-defined raising rules, which limit their applicability and make them challenging to maintain as MLIR dialects evolve. We present mlirSynth â a novel approach which translates programs from lower-level MLIR dialects to high-level ones without manually defined rules. Instead, it uses available dialect definitions to construct a program space and searches it effectively using type constraints and equivalences. We demonstrate its effectiveness by raising C programs to two distinct high-level MLIR dialects, which enables us to use existing high-level dialect specific compilation flows. On Polybench, we show a greater coverage than previous approaches, resulting in geomean speedups of 2.5x (Intel) and 3.4x (AMD) over state-of-the-art compilation flows. mlirSynth also enables retargetability to domain-specific accelerators, resulting in a geomean speedup of 21.6x on a TPU
mlirSynth: Automatic, Retargetable Program Raising in Multi-Level IR using Program Synthesis
MLIR is an emerging compiler infrastructure for modern hardware, but existing
programs cannot take advantage of MLIR's high-performance compilation if they
are described in lower-level general purpose languages. Consequently, to avoid
programs needing to be rewritten manually, this has led to efforts to
automatically raise lower-level to higher-level dialects in MLIR. However,
current methods rely on manually-defined raising rules, which limit their
applicability and make them challenging to maintain as MLIR dialects evolve.
We present mlirSynth -- a novel approach which translates programs from
lower-level MLIR dialects to high-level ones without manually defined rules.
Instead, it uses available dialect definitions to construct a program space and
searches it effectively using type constraints and equivalences. We demonstrate
its effectiveness \revi{by raising C programs} to two distinct high-level MLIR
dialects, which enables us to use existing high-level dialect specific
compilation flows. On Polybench, we show a greater coverage than previous
approaches, resulting in geomean speedups of 2.5x (Intel) and 3.4x (AMD) over
state-of-the-art compilation flows for the C programming language. mlirSynth
also enables retargetability to domain-specific accelerators, resulting in a
geomean speedup of 21.6x on a TPU
Regularity properties of distributions through sequences of functions
We give necessary and sufficient criteria for a distribution to be smooth or
uniformly H\"{o}lder continuous in terms of approximation sequences by smooth
functions; in particular, in terms of those arising as regularizations
.Comment: 10 page
On the completeness of impulsive gravitational wave space-times
We consider a class of impulsive gravitational wave space-times, which
generalize impulsive pp-waves. They are of the form ,
where is a Riemannian manifold of arbitrary dimension and carries
the line element with the line
element of and the Dirac measure. We prove a completeness result
for such space-times with complete Riemannian part .Comment: 13 pages, minor changes suggested by the referee
On the Geroch-Traschen class of metrics
We compare two approaches to semi-Riemannian metrics of low regularity. The maximally 'reasonable' distributional setting of Geroch and Traschen is shown to be consistently contained in the more general setting of nonlinear distributional geometry in the sense of Colombea
PENCIL: Towards a Platform-Neutral Compute Intermediate Language for DSLs
We motivate the design and implementation of a platform-neutral compute
intermediate language (PENCIL) for productive and performance-portable
accelerator programming
Collision photography: polarization imaging of atom-molecule collisions
We report differential scattering experiments on the laser excitation of Na+Mcollision pairs with M=Nâ, CO, CâHâ, and COâ. The collision event is probed by the laser polarization revealing geometric and electronic properties of the collision pair. The experimental data are compared to the results of a Monte Carlo trajectory simulation using ab initio quantum chemical data.Financial support from the Deutsche Forschungsgemeinschaft
and the Schweizerischer Nationalfond (Project No. 20-
065290.01) is gratefully acknowledged
Isomorphisms of algebras of Colombeau generalized functions
We show that for smooth manifolds X and Y, any isomorphism between the
special algebra of Colombeau generalized functions on X, resp. Y is given by
composition with a unique Colombeau generalized function from Y to X. We also
identify the multiplicative linear functionals from the special algebra of
Colombeau generalized functions on X to the ring of Colombeau generalized
numbers. Up to multiplication with an idempotent generalized number, they are
given by an evaluation map at a compactly supported generalized point on X.Comment: 10 page
- âŠ