5,997 research outputs found
Excitations of the nucleon with dynamical fermions
We measure the spectrum of low-lying nucleon resonances using Bayesian
fitting methods. We compare the masses obtained in the quenched approximation
to those obtained with two flavours of dynamical fermions at a matched lattice
spacing. At the pion masses employed in our simulations, we find that the mass
of the first positive-parity nucleon excitation is always greater than that of
the parity partner of the nucleon.Comment: Lattice2002(spectrum) 3 pages, 4 figure
The Influence of Quantum Critical Fluctuations of Circulating Current Order Parameters on the Normal State Properties of Cuprates
We study a model of the quantum critical point of cuprates associated with
the "circulating current" order parameter proposed by Varma. An effective
action of the order parameter in the quantum disordered phase is derived using
functional integral method, and the physical properties of the normal state are
studied based on the action. The results derived within the ladder
approximation indicate that the system is like Fermi liquid near the quantum
critical point and in disordered regime up to minor corrections. This implies
that the suggested marginal Fermi liquid behavior induced by the circulating
current fluctuations will come in from beyond the ladder diagrams.Comment: 7pages, 1 figure included in RevTex file. To appear in Phys. Rev.
Effectiveness of alternative organic solvents in field preservation of whole barnacles for PCR analyses
There are few reports of non-cryogenic preservation methods for marine invertebrates, so potable alcohol and acetone-based nail varnish remover (NVR) are for the first time evaluated against absolute ethanol as short-term preservatives of whole barnacles. Performance of ethanol and NVR-preserved material was comparable, but potable alcohol was significantly worse. These results are of practical importance for fieldwork in remote areas where laboratory chemicals are unattainable but potable alcohol or NVR are locally available. Of these, acetone-based NVR would be the solvent of preference
Longitudinal Momentum Mining of Beam Particles in a Storage Ring
I describe a new scheme for selectively isolating high density low
longitudinal emittance beam particles in a storage ring from the rest of the
beam without emittance dilution. I discuss the general principle of the method,
called longitudinal momentum mining, beam dynamics simulations and results of
beam experiments. Multi-particle beam dynamics simulations applied to the
Fermilab 8 GeV Recycler (a storage ring) convincingly validate the concepts and
feasibility of the method, which I have demonstrated with beam experiments in
the Recycler. The method presented here is the first of its kind.Comment: 11 pages, 3 figure
Comprehensive Solution to the Cosmological Constant, Zero-Point Energy, and Quantum Gravity Problems
We present a solution to the cosmological constant, the zero-point energy,
and the quantum gravity problems within a single comprehensive framework. We
show that in quantum theories of gravity in which the zero-point energy density
of the gravitational field is well-defined, the cosmological constant and
zero-point energy problems solve each other by mutual cancellation between the
cosmological constant and the matter and gravitational field zero-point energy
densities. Because of this cancellation, regulation of the matter field
zero-point energy density is not needed, and thus does not cause any trace
anomaly to arise. We exhibit our results in two theories of gravity that are
well-defined quantum-mechanically. Both of these theories are locally conformal
invariant, quantum Einstein gravity in two dimensions and Weyl-tensor-based
quantum conformal gravity in four dimensions (a fourth-order derivative quantum
theory of the type that Bender and Mannheim have recently shown to be
ghost-free and unitary). Central to our approach is the requirement that any
and all departures of the geometry from Minkowski are to be brought about by
quantum mechanics alone. Consequently, there have to be no fundamental
classical fields, and all mass scales have to be generated by dynamical
condensates. In such a situation the trace of the matter field energy-momentum
tensor is zero, a constraint that obliges its cosmological constant and
zero-point contributions to cancel each other identically, no matter how large
they might be. Quantization of the gravitational field is caused by its
coupling to quantized matter fields, with the gravitational field not needing
any independent quantization of its own. With there being no a priori classical
curvature, one does not have to make it compatible with quantization.Comment: Final version, to appear in General Relativity and Gravitation (the
final publication is available at http://www.springerlink.com). 58 pages,
revtex4, some additions to text and some added reference
An ultrametric state space with a dense discrete overlap distribution: Paperfolding sequences
We compute the Parisi overlap distribution for paperfolding sequences. It
turns out to be discrete, and to live on the dyadic rationals. Hence it is a
pure point measure whose support is the full interval [-1; +1]. The space of
paperfolding sequences has an ultrametric structure. Our example provides an
illustration of some properties which were suggested to occur for pure states
in spin glass models
Inferring meta-covariates in classification
This paper develops an alternative method for gene selection that combines model based clustering and binary classification. By averaging the covariates within the clusters obtained from model based clustering, we define “meta-covariates” and use them to build a probit regression model, thereby selecting clusters of similarly behaving genes, aiding interpretation. This simultaneous learning task is accomplished by an EM algorithm that optimises a single likelihood function which rewards good performance at both classification and clustering. We explore the performance of our methodology on a well known leukaemia dataset and use the Gene Ontology to interpret our results
Magnetization reversal in mesoscopic Ni80Fe20 wires: A magnetic domain launching device
The magnetization reversal process in mesoscopic permalloy (Ni80Fe20) wire structures has been investigated using scanning Kerr microscopy, magnetic force microscopy (MFM) and micromagnetic calculations. We find that the junction offers a site for reversed domain wall nucleation in the narrow part of the wires. As a consequence, the switching field is dominated by the domain nucleation field and the junction region initiates reversal by the wall motion following the nucleation of domains. Our results suggest the possibility of designing structures that can be used to “launch” reverse domains in narrow wires within a controlled field rang
Ferromagnetic/III-V semiconductor heterostructures and magneto-electronic devices
The interface magnetic and electronic properties of two Fe/III-V semiconductor systems, namely Fe/GaAs and Fe/InAs, grown at room temperature have been studied. A "magnetic interface", which is essential for the fabrication of magneto-electronic (ME) devices, was realized in both Fe/GaAs and Fe/InAs systems with suitable substrate processing and growth conditions. Furthermore, Fe/InAs was shown to have favorable interface electronic properties as Fe forms a low resistance ohmic contact on InAs. Two prototypes of ME device based on Fe/InAs are also discussed
Uncertainty quantification for honest regression trees
A new method is developed for quantifying the uncertainties of the estimates and predictions produced by honest random forests. This new method is based on the generalized fiducial methodology, and provides a fiducial density function that measures how likely each single honest tree is the true model. With such a density function, estimates and predictions, as well as their confidence/prediction intervals, can be obtained. The promising empirical properties of the proposed method are demonstrated by numerical comparisons with several state-of-the-art methods, and by applications to a few real data sets. Lastly, the proposed method is theoretically backed up by an asymptotic guarantee
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