14,279 research outputs found
Removal of violations of the Master Ward Identity in perturbative QFT
We study the appearance of anomalies of the Master Ward Identity, which is a
universal renormalization condition in perturbative QFT. The main insight of
the present paper is that any violation of the Master Ward Identity can be
expressed as a LOCAL interacting field; this is a version of the well-known
Quantum Action Principle of Lowenstein and Lam. Proceeding in a proper field
formalism by induction on the order in , this knowledge about the
structure of possible anomalies as well as techniques of algebraic
renormalization are used to remove possible anomalies by finite
renormalizations. As an example the method is applied to prove the Ward
identities of the O(N) scalar field model.Comment: 51 pages. v2: a few formulations improved, one reference added. v3: a
few mistakes corrected and one additional reference. v4: version to be
printed in Reviews in Mathematical Physic
Causal perturbation theory in terms of retarded products, and a proof of the Action Ward Identity
In the framework of perturbative algebraic quantum field theory a local
construction of interacting fields in terms of retarded products is performed,
based on earlier work of Steinmann. In our formalism the entries of the
retarded products are local functionals of the off shell classical fields, and
we prove that the interacting fields depend only on the action and not on terms
in the Lagrangian which are total derivatives, thus providing a proof of
Stora's 'Action Ward Identity'. The theory depends on free parameters which
flow under the renormalization group. This flow can be derived in our local
framework independently of the infrared behavior, as was first established by
Hollands and Wald. We explicitly compute non-trivial examples for the
renormalization of the interaction and the field.Comment: 76 pages, to appear in Rev. Math. Phy
Online unit clustering in higher dimensions
We revisit the online Unit Clustering and Unit Covering problems in higher
dimensions: Given a set of points in a metric space, that arrive one by
one, Unit Clustering asks to partition the points into the minimum number of
clusters (subsets) of diameter at most one; while Unit Covering asks to cover
all points by the minimum number of balls of unit radius. In this paper, we
work in using the norm.
We show that the competitive ratio of any online algorithm (deterministic or
randomized) for Unit Clustering must depend on the dimension . We also give
a randomized online algorithm with competitive ratio for Unit
Clustering}of integer points (i.e., points in , , under norm). We show that the competitive ratio of
any deterministic online algorithm for Unit Covering is at least . This
ratio is the best possible, as it can be attained by a simple deterministic
algorithm that assigns points to a predefined set of unit cubes. We complement
these results with some additional lower bounds for related problems in higher
dimensions.Comment: 15 pages, 4 figures. A preliminary version appeared in the
Proceedings of the 15th Workshop on Approximation and Online Algorithms (WAOA
2017
Thermoelectric Amplification of Phonons in Graphene
Amplification of acoustic phonons due to an external temperature gredient
() in Graphene was studied theoretically. The threshold temperature
gradient at which absorption switches over to amplification
in Graphene was evaluated at various frequencies and temperatures
. For and frequency , . The calculation was done in the regime at . The
dependence of the normalized () on the frequency
and the temperature gradient are evaluated numerically and
presented graphically. The calculated for Graphene is lower
than that obtained for homogeneous semiconductors () , Superlattices , Cylindrical Quantum Wire . This makes Graphene a much better material for thermoelectric
phonon amplifier.Comment: 12 Pages, 6 figure
Thin front propagation in random shear flows
Front propagation in time dependent laminar flows is investigated in the
limit of very fast reaction and very thin fronts, i.e. the so-called
geometrical optics limit. In particular, we consider fronts evolving in time
correlated random shear flows, modeled in terms of Ornstein-Uhlembeck
processes. We show that the ratio between the time correlation of the flow and
an intrinsic time scale of the reaction dynamics (the wrinkling time ) is
crucial in determining both the front propagation speed and the front spatial
patterns. The relevance of time correlation in realistic flows is briefly
discussed in the light of the bending phenomenon, i.e. the decrease of
propagation speed observed at high flow intensities.Comment: 5 Revtex4 pages, 4 figures include
Changing Bases: Multistage Optimization for Matroids and Matchings
This paper is motivated by the fact that many systems need to be maintained
continually while the underlying costs change over time. The challenge is to
continually maintain near-optimal solutions to the underlying optimization
problems, without creating too much churn in the solution itself. We model this
as a multistage combinatorial optimization problem where the input is a
sequence of cost functions (one for each time step); while we can change the
solution from step to step, we incur an additional cost for every such change.
We study the multistage matroid maintenance problem, where we need to maintain
a base of a matroid in each time step under the changing cost functions and
acquisition costs for adding new elements. The online version of this problem
generalizes online paging. E.g., given a graph, we need to maintain a spanning
tree at each step: we pay for the cost of the tree at time
, and also for the number of edges changed at
this step. Our main result is an -approximation, where is
the number of elements/edges and is the rank of the matroid. We also give
an approximation for the offline version of the problem. These
bounds hold when the acquisition costs are non-uniform, in which caseboth these
results are the best possible unless P=NP.
We also study the perfect matching version of the problem, where we must
maintain a perfect matching at each step under changing cost functions and
costs for adding new elements. Surprisingly, the hardness drastically
increases: for any constant , there is no
-approximation to the multistage matching maintenance
problem, even in the offline case
Clinical Molecular Marker Testing Data Capture to Promote Precision Medicine Research Within the Cancer Research Network
PURPOSE: To evaluate health care systems for the availability of population-level data on the frequency of use and results of clinical molecular marker tests to inform precision cancer care.
METHODS: We assessed cancer-related molecular marker test data availability across 12 US health care systems in the Cancer Research Network. Overall, these systems provide care to a diverse population of more than 12 million people in the United States. We performed qualitative analyses of test data availability for five blood-based protein, nine germline, and 14 tissue-based tumor marker tests in each health care system\u27s electronic health record and tumor registry using key informants, test code lists, and manual review of data types and output. We then performed quantitative analyses to estimate the proportion of patients with cancer with test utilization data and results for specific molecular marker tests.
RESULTS: Health systems were able to systematically capture population-level data on all five blood protein markers, six of 14 tissue-based tumor markers, and none of the nine germline markers. Successful, systematic data capture was achievable for tests with electronic data feeds for test results (blood protein markers) or through prior manual abstraction by tumor registrars (select tumor-based markers). For test results stored in scanned image files (particularly germline and tumor marker tests), information on which test was performed and test results was not readily accessible in an electronic format.
CONCLUSION: Even in health care systems with sophisticated electronic health records, there were few codified data elements available for evaluating precision cancer medicine test use and results at the population level. Health care organizations should establish standards for electronic reporting of precision medicine tests to expedite cancer research and facilitate the implementation of precision medicine approaches
Non-pharmacological approaches for treating children with ADHD inattentive type
The behavioral difficulties of children with attention-deficit/hyperactivity disorder (ADHD) inattentive type differ from those of children with ADHD combined or hyperactive/impulsive type. Existing evidence-based interventions primarily target the disruptive and impulsive behaviors exhibited by children with ADHD combined and hyperactive/impulsive type. A number of recent advances have been made in the non-pharmacological treatment of behavioral difficulties associated with ADHD inattentive type. Additional research using randomized controlled research designs and long-term follow-up evaluation is necessary before these interventions may be considered established evidence-based interventions for patients with ADHD inattentive type
Vacuum polarization around stars: nonlocal approximation
We compute the vacuum polarization associated with quantum massless fields
around stars with spherical symmetry. The nonlocal contribution to the vacuum
polarization is dominant in the weak field limit, and induces quantum
corrections to the exterior metric that depend on the inner structure of the
star. It also violates the null energy conditions. We argue that similar
results also hold in the low energy limit of quantum gravity. Previous
calculations of the vacuum polarization in spherically symmetric spacetimes,
based on local approximations, are not adequate for newtonian stars.Comment: 8 pages, no figure
Negative Energy Density States for the Dirac Field in Flat Spacetime
Negative energy densities in the Dirac field produced by state vectors that
are the superposition of two single particle electron states are examined. I
show that for such states the energy density of the field is not bounded from
below and that the quantum inequalities derived for scalar fields are
satisfied. I also show that it is not possible to produce negative energy
densities in a scalar field using state vectors that are arbitrary
superpositions of single particle states.Comment: 11 pages, LaTe
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