3,268 research outputs found
One-Nucleon Effective Generators of the Poincare Group derived from a Field Theory: Mass Renormalization
We start from a Lagrangian describing scalar "nucleons" and mesons which
interact through a simple vertex. Okubo's method of unitary transformation is
used to describe a single nucleon dressed by its meson cloud. We find an
expression for the physical mass of the nucleon being correct up to second
order in the coupling constant. It is then verified that this result is the
same as the corresponding expression found by Feynman techniques. Finally we
also express the three boost operators in terms of the physical nucleon mass.
Doing so we find expressions for all the ten generators of Poincar\'e
transformations for the system of one single dressed nucleon.Comment: 19 pages, no figure
The s-wave pion-nucleus optical potential
We calculate the s-wave part of the pion-nucleus optical potential using a
unitarized chiral approach that has been previously used to simultaneously
describe pionic hydrogen and deuterium data as well as low energy pi N
scattering in the vacuum. This energy dependent model allows for additional
isoscalar parts in the potential from multiple rescattering. We consider Pauli
blocking and pion polarization in an asymmetric nuclear matter environment.
Also, higher order corrections of the pi N amplitude are included. The model
can accommodate the repulsion required by phenomenological fits, though the
theoretical uncertainties are bigger than previously thought. At the same time,
we also find an enhancement of the isovector part compatible with empirical
determinations.Comment: 31 pages, 27 figure
Entanglement in bosonic systems
We present a technique to resolve a Gaussian density matrix and its time
evolution through known expectation values in position and momentum. Further we
find the full spectrum of this density matrix and apply the technique to a
chain of harmonic oscillators to find agreement with conformal field theory in
this domain. We also observe that a non-conformal state has a divergent
entanglement entropy.Comment: 7 pages, 6 figure
Scattering of neutrinos on a polarized electron target as a test for new physics beyond the Standard Model
In this paper, we analyze the scattering of the neutrino beam on the
polarized electron target, and predict the effects of two theoretically
possible scenarios beyond the Standard Model. In both scenarios, Dirac
neutrinos are assumed to be massive.
First, we consider how the existence of CP violation phase between the
complex vector V and axial A couplings of the Left-handed neutrinos affects the
azimuthal dependence of the differential cross section. The future superbeam
and neutrino factory experiments will provide the unique opportunity for the
leptonic CP violation studies, if the large magnetized sampling calorimeters
with good event reconstruction capabilities are build.
Next, we take into account a scenario with the participation of the exotic
scalar S coupling of the Right-handed neutrinos in addition to the standard
vector V and axial A couplings of the Left-handed neutrinos. The main goal is
to show how the presence of the R-handed neutrinos, in the above process
changes the spectrum of recoil electrons in relation to the expected Standard
Model prediction, using the current limits on the non-standard couplings. The
interference terms between the standard and exotic couplings in the
differential cross section depend on the angle between the transverse
incoming neutrino polarization and the transverse electron polarization of the
target, and do not vanish in the limit of massless neutrino. The detection of
the dependence on this angle in the energy spectrum of recoil electrons would
be a signature of the presence of the R-handed neutrinos in the
neutrino-electron scattering. To make this test feasible, the polarized
artificial neutrino source needs to be identified.Comment: 11 pages, 3 eps figures, revtex, submitted to publicatio
Non-Markovian entanglement dynamics of quantum continuous variable systems in thermal environments
We study two continuous variable systems (or two harmonic oscillators) and
investigate their entanglement evolution under the influence of non-Markovian
thermal environments. The continuous variable systems could be two modes of
electromagnetic fields or two nanomechanical oscillators in the quantum domain.
We use quantum open system method to derive the non-Markovian master equations
of the reduced density matrix for two different but related models of the
continuous variable systems. The two models both consist of two interacting
harmonic oscillators. In model A, each of the two oscillators is coupled to its
own independent thermal reservoir, while in model B the two oscillators are
coupled to a common reservoir. To quantify the degrees of entanglement for the
bipartite continuous variable systems in Gaussian states, logarithmic
negativity is used. We find that the dynamics of the quantum entanglement is
sensitive to the initial states, the oscillator-oscillator interaction, the
oscillator-environment interaction and the coupling to a common bath or to
different, independent baths.Comment: 10 two-column pages, 8 figures, to appear in Phys. Rev.
Challenges to evaluation of multilingual geographic information retrieval in GeoCLEF
This is the third year of the evaluation of
geographic information retrieval (GeoCLEF)
within the Cross-Language Evaluation Forum
(CLEF). GeoCLEF 2006 presented topics and
documents in four languages (English,
German, Portuguese and Spanish). After two
years of evaluation we are beginning to
understand the challenges to both Geographic
Information Retrieval from text and of
evaluation of the results of geographic
information retrieval. This poster enumerates
some of these challenges to evaluation and
comments on the limitations encountered in the
first two evaluations
Recommended from our members
Production and purification of L-lactic acid in lab and pilot scales using sweet sorghum juice
Sweet sorghum juice (SSJ) was evaluated as fermentation substrate for the production of l-lactic acid. A thermophilic Bacillus coagulans isolate was selected for batch fermentations without the use of additional nutrients. The first batch of SSJ (Batch A) resulted on higher lactic acid concentration, yield and productivity with values of 78.75 g·L−1, 0.78 g·g−1 and 1.77 g·L−1 h−1, respectively. Similar results were obtained when the process was transferred into the pilot scale (50 L), with corresponding values of 73 g·L−1, 0.70 g·g−1 and 1.47 g·L−1 h−1. A complete downstream process scheme was developed in order to separate lactic acid from the fermentation components. Coarse and ultra-filtration were employed as preliminary separation steps. Mono- and bipolar electrodialysis, followed by chromatography and vacuum evaporation were subsequently carried out leading to a solution containing 905.8 g·L−1 lactic acid, with an optical purity of 98.9%. The results of this study highlight the importance of the downstream process with respect to using SSJ for lactic acid production. The proposed downstream process constitutes a more environmentally benign approach to conventional precipitation methods
Compton and double Compton scattering processes at colliding electron-photon beams
Radiative corrections (RC) to the Compton scattering cross section are
calculated in the leading and next-to leading logarithmic approximation to the
case of colliding high energy photon-electron beams.
RC to the double Compton scattering cross section in the same experimental
set-up are calculated in the leading logarithmic approximation.
We consider the case when no pairs are created in the final state. We show
that the differential cross section can be written in the form of the Drell-Yan
process cross-section.
Numerical values of the -factor and the leading order distribution on the
scattered electron energy fraction and scattering angle are presented
Designing Contextualized Learning
Specht, M. (2008). Designing Contextualized Learning. In H. H. Adelsberger, Kinshuk, J. M. Pawlowski & D. Sampson (Eds.), Handbook on Information Technologies for Education and Training (2th ed., pp. 101-111). Springer, Berlin Heidelberg 2008: International Handbook on Information Systems Series.Contextualized and ubiquitous learning are relatively new research areas
that combine the latest developments in ubiquitous and context aware
computing with pedagogical approaches relevant to structure more situated
and context aware learning support. Searching for different backgrounds of
mobile and contextualized learning authors have identified the relations
between existing educational paradigms and new classes of mobile appli-
cations for education (Naismith, Lonsdale, Vavoula, & Sharples, 2004).
Furthermore best practices of mobile learning applications have been iden-
tified and discussed in focused workshops (Stone, Alsop, Briggs, & Tomp-
sett, 2002; Tatar, Roschelle, Vahey, & Peunel, 2002). Especially in the
area of educational field trips (Equator Project, 2003; RAFT, 2003) in the
last years innovative approaches for intuitive usage of contextualized mo-
bile interfaces have been developed. The following paper describes the motivation and background for con-
textualizing learning and illustrates the implementation of a service based
and flexible learning toolkit developed in the RAFT project for supporting
contextualized collaborative learning support
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