8,254 research outputs found
Variational Principle in the Algebra of Asymptotic Fields
This paper proposes a variational principle for the solutions of quantum
field theories in which the ``trial functions'' are chosen from the algebra of
asymptotic fields, and illustrates this variational principle in simple cases.Comment: 15 pages, Latex, no figure
Reaction of O/1D/ with N2O
Reaction of excited oxygen with nitrous oxide 1 yielding nitrogen and oxyge
An Interval Newton Method
We introduce an interval Newton method for bounding solutions of systems of nonlinear equations. It entails three subalgorithms. The first is a Gauss-Seidel-type step. The second is a real (noninterval) Newton iteration. The third solves the linearized equations by elimination. We explain why each subalgorithm is desirable and how they fit together to provide solutions in as little as one-third or one-quarter the time required by Krawczyk\u27s method [7] in our implementations
Some economic benefits of a synchronous earth observatory satellite
An analysis was made of the economic benefits which might be derived from reduced forecasting errors made possible by data obtained from a synchronous satellite system which can collect earth observation and meteorological data continuously and on demand. User costs directly associated with achieving benefits are included. In the analysis, benefits were evaluated which might be obtained as a result of improved thunderstorm forecasting, frost warning, and grain harvest forecasting capabilities. The anticipated system capabilities were used to arrive at realistic estimates of system performance on which to base the benefit analysis. Emphasis was placed on the benefits which result from system forecasting accuracies. Benefits from improved thunderstorm forecasts are indicated for the construction, air transportation, and agricultural industries. The effects of improved frost warning capability on the citrus crop are determined. The benefits from improved grain forecasting capability are evaluated in terms of both U.S. benefits resulting from domestic grain distribution and U.S. benefits from international grain distribution
Locating regions in a sequence under density constraints
Several biological problems require the identification of regions in a
sequence where some feature occurs within a target density range: examples
including the location of GC-rich regions, identification of CpG islands, and
sequence matching. Mathematically, this corresponds to searching a string of 0s
and 1s for a substring whose relative proportion of 1s lies between given lower
and upper bounds. We consider the algorithmic problem of locating the longest
such substring, as well as other related problems (such as finding the shortest
substring or a maximal set of disjoint substrings). For locating the longest
such substring, we develop an algorithm that runs in O(n) time, improving upon
the previous best-known O(n log n) result. For the related problems we develop
O(n log log n) algorithms, again improving upon the best-known O(n log n)
results. Practical testing verifies that our new algorithms enjoy significantly
smaller time and memory footprints, and can process sequences that are orders
of magnitude longer as a result.Comment: 17 pages, 8 figures; v2: minor revisions, additional explanations; to
appear in SIAM Journal on Computin
A model of ballistic aggregation and fragmentation
A simple model of ballistic aggregation and fragmentation is proposed. The
model is characterized by two energy thresholds, Eagg and Efrag, which
demarcate different types of impacts: If the kinetic energy of the relative
motion of a colliding pair is smaller than Eagg or larger than Efrag, particles
respectively merge or break; otherwise they rebound. We assume that particles
are formed from monomers which cannot split any further and that in a
collision-induced fragmentation the larger particle splits into two fragments.
We start from the Boltzmann equation for the mass-velocity distribution
function and derive Smoluchowski-like equations for concentrations of particles
of different mass. We analyze these equations analytically, solve them
numerically and perform Monte Carlo simulations. When aggregation and
fragmentation energy thresholds do not depend on the masses of the colliding
particles, the model becomes analytically tractable. In this case we show the
emergence of the two types of behavior: the regime of unlimited cluster growth
arises when fragmentation is (relatively) weak and the relaxation towards a
steady state occurs when fragmentation prevails. In a model with mass-dependent
Eagg and Efrag the evolution with a cross-over from one of the regimes to
another has been detected
Multi-Scan Correlation to Separate Radar Tracks from False Alarms
An algorithm and computer software have been developed to filter out clutter in radar displays in order to clarify real tracks. Detections are generally declared valid when found to be part of a reasonable pattern of three or four detections in an eight scan history. The filtering process reduces the number of spurious reports by several orders of magnitude, providing significant improvement in distinguishing ships from waves and other sources of undesired radar reflections. The algorithm is being incorporated into radar system hardware in order to improve tracking of ships as signals are received. The method also shows promise for air tracking
Lorentz-Invariant "Elements of Reality" and the Question of Joint Measurability of Commuting Observables
It is shown that the joint measurements of some physical variables
corresponding to commuting operators performed on pre- and post-selected
quantum systems invariably disturb each other. The significance of this result
for recent proofs of the impossibility of realistic Lorentz invariant
interpretation of quantum theory (without assumption of locality) is discussed.Comment: 15 page
Search for exchange-antisymmetric two-photon states
Atomic two-photon J=0 J'=1 transitions are forbidden for
photons of the same energy. This selection rule is related to the fact that
photons obey Bose-Einstein statistics. We have searched for small violations of
this selection rule by studying transitions in atomic Ba. We set a limit on the
probability that photons are in exchange-antisymmetric states:
.Comment: 5 pages, 4 figures, ReVTeX and .eps. Submitted to Phys. Rev. Lett.
Revised version 9/25/9
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