179 research outputs found
Constraints from and the isotope effect for MgB
With the constraint that K, as observed for MgB, we use the
Eliashberg equations to compute possible allowed values of the isotope
coefficient, . We find that while the observed value can
be obtained in principle, it is difficult to reconcile a recently calculated
spectral function with such a low observed value
The Iliad’s big swoon: a case of innovation within the epic tradition
In book 5 of the Iliad Sarpedon suffers so greatly from a wound that his ‘‘ψυχή leaves him’. Rather than dying, however, Sarpedon lives to fight another day. This paper investigates the phrase τὸν δὲ λίπε ψυχή in extant archaic Greek poetry to gain a sense of its traditional referentiality and better assess the meaning of Sarpedon’s swoon. Finding that all other instances of the ψυχή leaving the body signify death, it suggests that the Iliad exploits a traditional unit of utterance to flag up the importance of Sarpedon to this version of the Troy story
Subtraction terms for one-loop amplitudes with one unresolved parton
Fully differential next-to-next-to-leading order calculations require a
method to cancel infrared singularities. In a previous publication, I discussed
the general setup for the subtraction method at NNLO. In this paper I give all
subtraction terms for electron-positron annihilation associated with one-loop
amplitudes with one unresolved parton. These subtraction terms are integrated
within dimensional regularization over the unresolved one-particle phase space.
The results can be used with all variants of dimensional regularization
(conventional dimensional regularization, the 't Hooft-Veltman scheme and the
four-dimensional scheme).Comment: 27 page
Subtraction terms at NNLO
Perturbative calculations at next-to-next-to-leading order for multi-particle
final states require a method to cancel infrared singularities. I discuss the
subtraction method at NNLO. As a concrete example I consider the leading-colour
contributions to e+ e- --> 2 jets. This is the simplest example which exhibits
all essential features. For this example, explicit subtraction terms are given,
which approximate the four-parton and three-parton final states in all double
and single unresolved limits, such that the subtracted matrix elements can be
integrated numerically.Comment: 41 page
Dynamic Scaling and Two-Dimensional High-Tc Superconductors
There has been ongoing debate over the critical behavior of two-dimensional
superconductors; in particular for high Tc superconductors. The conventional
view is that a Kosterlitz-Thouless-Berezinskii transition occurs as long as
finite size effects do not obscure the transition. However, there have been
recent suggestions that a different transition actually occurs which
incorporates aspects of both the dynamic scaling theory of Fisher, Fisher, and
Huse and the Kosterlitz-Thouless-Berezinskii transition. Of general interest is
that this modified transition apparently has a universal dynamic critical
exponent. Some have countered that this apparent universal behavior is rooted
in a newly proposed finite-size scaling theory; one that also incorporates
scaling and conventional two-dimensional theory. To investigate these issues we
study DC voltage versus current data of a 12 angstrom thick YBCO film. We find
that the newly proposed scaling theories have intrinsic flexibility that is
relevant to the analysis of the experiments. In particular, the data scale
according to the modified transition for arbitrarily defined critical
temperatures between 0 K and 19.5 K, and the temperature range of a successful
scaling collapse is related directly to the sensitivity of the measurement.
This implies that the apparent universal exponent is due to the intrinsic
flexibility rather than some real physical property. To address this intrinsic
flexibility, we propose a criterion which would give conclusive evidence for
phase transitions in two-dimensional superconductors. We conclude by reviewing
results to see if our criterion is satisfied.Comment: 14 page
Critical behavior of Josephson-junction arrays at f=1/2
The critical behavior of frustrated Josephson-junction arrays at flux
quantum per plaquette is considered. Results from Monte Carlo simulations and
transfer matrix computations support the identification of the critical
behavior of the square and triangular classical arrays and the one-dimensional
quantum ladder with the universality class of the XY-Ising model. In the
quantum ladder, the transition can happen either as a simultaneous ordering of
the and order parameters or in two separate stages, depending on
the ratio between interchain and intrachain Josephson couplings. For the
classical arrays, weak random plaquette disorder acts like a random field and
positional disorder as random bonds on the variables. Increasing
positional disorder decouples the and variables leading to the
same critical behavior as for integer .Comment: 9 pages, Latex, workshop on JJA, to appear in Physica
On the nature of the finite-temperature transition in QCD
We discuss the nature of the finite-temperature transition in QCD with N_f
massless flavors. Universality arguments show that a continuous (second-order)
transition must be related to a 3-D universality class characterized by a
complex N_f X N_f matrix order parameter and by the symmetry-breaking pattern
[SU(N_f)_L X SU(N_f)_R]/Z(N_f)_V -> SU(N_f)_V/Z(N_f)_V, or [U(N_f)_L X
U(N_f)_R]/U(1)_V -> U(N_f)_V/U(1)_V if the U(1)_A symmetry is effectively
restored at T_c. The existence of any of these universality classes requires
the presence of a stable fixed point in the corresponding 3-D Phi^4 theory with
the expected symmetry-breaking pattern. Otherwise, the transition is of first
order. In order to search for stable fixed points in these Phi^4 theories, we
exploit a 3-D perturbative approach in which physical quantities are expanded
in powers of appropriate renormalized quartic couplings. We compute the
corresponding Callan-Symanzik beta-functions to six loops. We also determine
the large-order behavior to further constrain the analysis. No stable fixed
point is found, except for N_f=2, corresponding to the symmetry-breaking
pattern [SU(2)_L X SU(2)_R]/Z(2)_V -> SU(2)_V/Z(2)_V equivalent to O(4) ->
O(3). Our results confirm and put on a firmer ground earlier analyses performed
close to four dimensions, based on first-order calculations in the framework of
the epsilon=4-d expansion. These results indicate that the finite-temperature
phase transition in QCD is of first order for N_f>2. A continuous transition is
allowed only for N_f=2. But, since the theory with symmetry-breaking pattern
[U(2)_L X U(2)_R]/U(1)_V -> U(2)_V/U(1)_V does not have stable fixed points,
the transition can be continuous only if the effective breaking of the U(1)_A
symmetry is sufficiently large.Comment: 30 pages, 3 figs, minor correction
A tale of two capitalisms: preliminary spatial and historical comparisons of homicide rates in Western Europe and the USA
This article examines comparative homicide rates in the United States and Western Europe in an era of increasingly globalized neoliberal economics. The main finding of this preliminary analysis is that historical and spatial correlations between distinct forms of political economy and homicide rates are consistent enough to suggest that social democratic regimes are more successful at fostering the socio-cultural conditions necessary for reduced homicide rates. Thus Western Europe and all continents and nations should approach the importation of American neo-liberal economic policies with extreme caution. The article concludes by suggesting that the indirect but crucial causal connection between political economy and homicide rates, prematurely pushed into the background of criminological thought during the ‘cultural turn’, should be returned to the foreground
International variation in distribution of ASA class in patients undergoing total hip arthroplasty and its influence on mortality: data from an international consortium of arthroplasty registries
Background and purpose — A challenge comparing outcomes from total hip arthroplasty between countries is variation in preoperative characteristics, particularly comorbidity. Therefore, we investigated between-country variation in comorbidity in patients based on ASA class distribution, and determined any variation of ASA class to mortality risk between countries.
Patients and methods — All arthroplasty registries collecting ASA class and mortality data in patients with elective primary THAs performed 2012–2016 were identified. Survival analyses of the influence of ASA class on 1-year mortality were performed by individual registries, followed by meta-analysis of aggregated data.
Results — 6 national registries and 1 US healthcare organization registry with 418,916 THAs were included. There was substantial variation in the proportion of ASA class III/IV, ranging from 14% in the Netherlands to 39% in Finland. Overall, 1-year mortality was 0.93% (95% CI 0.87–1.01) and increased from 0.2% in ASA class I to 8.9% in class IV. The association between ASA class and mortality measured by hazard ratios (HR) was strong in all registries even after adjustment for age and sex, which reduced them by half in all registries. Combined adjusted HRs were 2.0, 6.1, and 22 for ASA class II–IV vs. I, respectively. Associations were moderately heterogeneous across registries.
Interpretation — We observed large variation in ASA class distribution between registries, possibly explained by differences in background morbidity and/or international variation in access to surgery. The similar, strong mortality trends by ASA class between countries enhance the relevance of its use as an indicator of comorbidity in international registry studies
- …