4,518 research outputs found
Vacuum Nodes and Anomalies in Quantum Theories
We show that nodal points of ground states of some quantum systems with
magnetic interactions can be identified in simple geometric terms. We analyse
in detail two different archetypical systems: i) a planar rotor with a
non-trivial magnetic flux , ii) Hall effect on a torus. In the case of
the planar rotor we show that the level repulsion generated by any reflection
invariant potential is encoded in the nodal structure of the unique vacuum
for . In the second case we prove that the nodes of the first
Landau level for unit magnetic charge appear at the crossing of the two
non-contractible circles , with holonomies
for any reflection invariant potential
. This property illustrates the geometric origin of the quantum translation
anomaly.Comment: 14 pages, 2 ps-figures, to appear in Commun. Math. Phy
Origin of the anomalies: the modified Heisenberg equation
The origin of the anomalies is analyzed. It is shown that they are due to the
fact that the generators of the symmetry do not leave invariant the domain of
definition of the Hamiltonian and then a term, normally forgotten in the
Heisenberg equation, gives an extra contribution responsible for the non
conservation of the charges. This explanation is equivalent to that of the
Fujikawa in the path integral formalism. Finally, this approach is applied to
the conformal symmetry breaking in two-dimensional quantum mechanics.Comment: 7 pages, LaTe
Influence of Magnetic Field on Effective Electron-Electron Interactions in a Copper Wire
We have measured in a copper wire the energy exchange rate between
quasiparticles as a function of the applied magnetic field. We find that the
effective electron-electron interaction is strongly modified by the magnetic
field, suggesting that magnetic impurities play a role on the interaction
processes.Comment: latex anthore.tex, 8 files, 6 figures, 7 pages in: Proceedings of the
XXXVIth Rencontres de Moriond `Electronic Correlations: From Meso- to
Nano-physics' Les Arcs, France January 20-27, 2001 [SPEC-S01/027
Reciprocal peer tutoring and treatment integrity of elementary school students
Academic concerns are the most common reason students are referred for special services in schools. This obviously leads to the necessity for schools to have secondary prevention services in place to address the needs of students who are struggling. Peer tutoring, in its various forms, has been well documented as an effective and inexpensive intervention for all academic areas. Despite the promise of peer tutoring, research evidence suggests that teachers may not consistently carry out their roles in the peer tutoring process with sufficient accuracy to ensure positive outcomes. One possible solution to this problem is to have a consultant directly monitor the intervention. The purpose of this study was to use the well established procedures of Reciprocal Peer Tutoring and Classwide Peer Tutoring to develop an effective peer tutoring process that can be implemented with an absolute minimum of teacher involvement. Students were responsible for initiating the tutoring sessions, collecting data, evaluating their performances, and administering rewards. Students\u27 work was evaluated and monitored by the consultant rather than the teacher. The results demonstrated that the students implemented the reciprocal peer tutoring procedures with high accuracy and integrity. As a result, the students showed increases in their sight word acquisition. Limitations and future directions are discussed
An Innovative Project to Strengthen and Improve the Knowledge Acquisition in the Degree in Chemistry Using e-Learning Tools
Comunicació presentada a EDULEARN2018, 10th International Conference on Education and New Learning Technologies (July 2-4, 2018, Palma, Mallorca, Spain).The subject "Chemistry II (QU910)" is taught at first academic year (second semester) of the Degree in Chemistry at the University Jaume I. Some of its specific and general competencies are selflearning and writing and oral communication, regarding the main chemical concepts: chemical reactions, elements of the periodic table and calculations of the concentrations of the formed products and the remaining reagents in acid/base, complex, precipitation and redox reactions. We have noticed that 65% of the students have not studied any chemistry subjects (or only one) in High School or Professional Training before undertaking the Degree in Chemistry. The present project aims firstly to help these students to overcome their lack of background, secondly to compare the academic results of the students with and without previous contact with chemistry and finally, to establish actions to solve this prejudicial situation. This objective was reached by the implementation of a zero course, a course including the basic content of chemistry taught in the last years of High School, the month before the beginning of the first academic year. After the first year, students having attended chemistry before university obtained only 0.75/10 points more than the others. The Virtual Classroom, the emails and tutorial played an important role in the achievement of this zero-course
Theory of microwave spectroscopy of Andreev bound states with a Josephson junction
We present a microscopic theory for the current through a tunnel Josephson
junction coupled to a non-linear environment, which consists of an Andreev
two-level system coupled to a harmonic oscillator. It models a recent
experiment [Bretheau, Girit, Pothier, Esteve, and Urbina, Nature (London) 499,
312 (2013)] on photon spectroscopy of Andreev bound states in a superconducting
atomic-size contact. We find the eigenenergies and eigenstates of the
environment and derive the current through the junction due to inelastic Cooper
pair tunneling. The current-voltage characteristic reveals the transitions
between the Andreev bound states, the excitation of the harmonic mode that
hybridizes with the Andreev bound states, as well as multi-photon processes.
The calculated spectra are in fair agreement with the experimental data.Comment: 8 pages, 6 figure
- …