3,215 research outputs found
Results from the 4PI Effective Action in 2- and 3-dimensions
We consider a symmetric scalar theory with quartic coupling and solve the
equations of motion from the 4PI effective action in 2- and 3-dimensions using
an iterative numerical lattice method. For coupling less than 10 (in
dimensionless units) good convergence is obtained in less than 10 iterations.
We use lattice size up to 16 in 2-dimensions and 10 in 3-dimensions and
demonstrate the convergence of the results with increasing lattice size. The
self-consistent solutions for the 2-point and 4-point functions agree well with
the perturbative ones when the coupling is small and deviate when the coupling
is large.Comment: 14 pages, 11 figures; v5: added numerical calculations in 3D; version
accepted for publication in EPJ
Spontaneous Symmetry Breaking for Scalar QED with Non-minimal Chern-Simons Coupling
We investigate the two-loop effective potential for both minimally and
non-minimally coupled Maxwell-Chern-Simons theories. The non-minimal gauge
interaction represents the magnetic moment interaction between a charged scalar
and the electromagnetic field. In a previous paper we have shown that the two
loop effective potential for this model is renormalizable with an appropriate
choice of the non-minimal coupling constant. We carry out a detailed analysis
of the spontaneous symmetry breaking induced by radiative corrections. As long
as the renormalization point for all couplings is chosen to be the true minimum
of the effective potential, both models predict the presence of spontaneous
symmetry breaking. Two loop corrections are small compared to the one loop
result, and thus the symmetry breaking is perturbatively stable.Comment: Revtex 25 pages, 9 figure
Temperature dependent anisotropy of the penetration depth and coherence length in MgB$_2
We report measurements of the temperature dependent anisotropies
( and ) of both the London penetration depth
and the upper critical field of MgB. Data for
was obtained from measurements of
and on a single crystal sample using a tunnel diode
oscillator technique. was
deduced from field dependent specific heat measurements on the same sample.
and have opposite temperature dependencies, but
close to tend to a common value (). These results are in good agreement with theories
accounting for the two gap nature of MgBComment: 4 pages with figures (New version
Destruction of chain-superconductivity in YBa_2Cu_4O_8 in a weak magnetic field
We report measurements of the temperature dependent components of the
magnetic penetration depth {\lambda}(T) in single crystal samples of
YBa_2Cu_4O_8 using a radio frequency tunnel diode oscillator technique. We
observe a downturn in {\lambda}(T) at low temperatures for currents flowing
along the b and c axes but not along the a axis. The downturn in {\lambda}_b is
suppressed by a small dc field of ~0.25 T. This and the zero field anisotropy
of {\lambda}(T) likely result from proximity induced superconducting on the CuO
chains, however we also discuss the possibility that a significant part of the
anisotropy might originate from the CuO2 planes.Comment: 5 page
Interpretation of the angular dependence of the de Haas-van Alphen effect in MgB_2
We present detailed results for the amplitude and field dependence of the de
Haas-van Alphen (dHvA) signal arising from the electron-like sheet of
Fermi surface in MgB_2. Our data and analysis show that the dip in dHvA
amplitude when the field is close to the basal plane is caused by a beat
between two very similar dHvA frequencies and not a spin-zero effect as
previously assumed. Our results imply that the Stoner enhancement factors in
MgB_2 are small on both the Sigma and Pi sheets.Comment: 4 pages with figures. Submitted to PR
Reflections on the Interface of Treaties and Rules of Procedure: Time for Federal “Long-Arm” Legislation
Civil justice in the US is a primary means of law enforcement, and those who compete in the US economy ought, except in compelling circumstances, to be subject to the same modes of law enforcement as their US competitors. The five-tiered process for rulemaking regarding special accomodation of foreign interests is examined
Negative Attitudes of Law Students: A Replication of the Alienation and Dissatisfaction Factors
In 1976 we conducted a survey of law students at The University of Michigan. Demographic information; personal goals and values; and attitudes toward the law school, the faculty, and fellow students were surveyed. We factor-analyzed the items relating to attitudes, personal goals, and values. Three major factors were identified and labeled as alienation, dissatisfaction, and sociability. We have recently described the alienation factor extensively and outlined the dissatisfaction and sociability factors. In March 1977, we conducted a second survey designed to replicate the earlier study. Despite the addition of a few new items, the questionnaire was essentially unchanged. The new study group consisted of 165 first-year students and 38 second- or third-year students. We randomly selected the first-year students from the class entering in 1976. The advanced students were enrolled in a course on evidence. We used the same procedure as in the first study to factor-analyze the data. The first two rotated factors-alienation and dissatisfaction-were quite comparable to those in the earlier study. The third factor, sociability, did not replicate, and it seems advisable to discard it as a central construct in studies of the professional socialization of law students
Evidence for nodal superconductivity in LaFePO
In several iron-arsenide superconductors there is strong evidence for a fully
gapped superconducting state consistent with either a conventional s-wave
symmetry or an unusual state where there the gap changes sign between
the electron and hole Fermi surface sheets. Here we report measurements of the
penetration depth in very clean samples of the related
iron-phosphide superconductor, LaFePO, at temperatures down to 100 mK.
We find that varies almost perfectly linearly with strongly
suggesting the presence of gap nodes in this compound. Taken together with
other data, this suggests the gap function may not be generic to all pnictide
superconductors
de Haas-van Alphen effect investigation of the electronic structure of Al substituted MgB_2
We report a de Haas-van Alphen (dHvA) study of the electronic structure of Al
doped crystals of MgB. We have measured crystals with % Al which
have a of 33.6 K, (% lower than pure MgB). dHvA frequencies
for the tube orbits in the doped samples are lower than in pure
MgB, implying a reduction in the number of holes in this sheet of
Fermi surface. The mass of the quasiparticles on the larger orbit is
lighter than the pure case indicating a reduction in electron-phonon coupling
constant . These observations are compared with band structure
calculations, and found to be in excellent agreement.Comment: 4 pages with figure
Perceptions Of School By Two Teenage Boys With Asperger Syndrome And Their Mothers: A Qualitative Study
This qualitative study aimed to develop an understanding of the challenges faced by teenage boys with Asperger syndrome and their mothers. A case study approach was used to collect data from two 13-year-old boys who have Asperger syndrome and their mothers in Queensland, Australia. Data were collected through the use of semi¬structured interviews. The words of the boys and their mothers provide a valuable insight into the personal experiences and feelings of the par¬ticipants. An inductive approach to data analysis identified four themes: (1) developmental differences; (2) problems associated with the general characteristics of Asperger syndrome (i.e. communication and social difficulties, restricted range of interests, a need for routine); (3) stress; and (4) 'masquerading'. The first three themes relate strongly to the current literature, but the emergence of masquerading is of particular interest in developing a fuller understanding of the experiences of individuals with Asperger syndrome at school
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