148 research outputs found
Effective Theory Approach to the Spontaneous Breakdown of Lorentz Invariance
We generalize the coset construction of Callan, Coleman, Wess and Zumino to
theories in which the Lorentz group is spontaneously broken down to one of its
subgroups. This allows us to write down the most general low-energy effective
Lagrangian in which Lorentz invariance is non-linearly realized, and to explore
the consequences of broken Lorentz symmetry without having to make any
assumptions about the mechanism that triggers the breaking. We carry out the
construction both in flat space, in which the Lorentz group is a global
spacetime symmetry, and in a generally covariant theory, in which the Lorentz
group can be treated as a local internal symmetry. As an illustration of this
formalism, we construct the most general effective field theory in which the
rotation group remains unbroken, and show that the latter is just the
Einstein-aether theory.Comment: 45 pages, no figures
A chronometric exploration of high-resolution âsensitive TMS maskingâ effects on subjective and objective measures of vision
Transcranial magnetic stimulation (TMS) can induce masking by interfering with ongoing neural activity in early visual cortex. Previous work has explored the chronometry of occipital involvement in vision by using single pulses of TMS with high temporal resolution. However, conventionally TMS intensities have been high and the only measure used to evaluate masking was objective in nature. Recent studies have begun to incorporate subjective measures of vision, alongside objective ones. The current study goes beyond previous work in two regards. First, we explored both objective vision (an orientation discrimination task) and subjective vision (a stimulus visibility rating on a four-point scale), across a wide range of time windows with high temporal resolution. Second, we used a very sensitive TMS-masking paradigm: stimulation was at relatively low TMS intensities, with a figure-8 coil, and the small stimulus was difficult to discriminate already at baseline level. We hypothesized that this should increase the effective temporal resolution of our paradigm. Perhaps for this reason, we are able to report a rather interesting masking curve. Within the classical-masking time window, previously reported to encompass broad SOAs anywhere between 60 and 120Â ms, we report not one, but at least two dips in objective performance, with no masking in-between. The subjective measure of vision did not mirror this pattern. These preliminary data from our exploratory design suggest that, with sensitive TMS masking, we might be able to reveal visual processes in early visual cortex previously unreported
Thermodynamics of String Field Theory Motivated Nonlocal Models
We investigate the thermodynamic properties of the nonlocal tachyon motivated
by their nonlocal structure in string field theory. We use previously developed
perturbative methods for nonlocal fields to calculate the partition function
and the equation of state in the high temperature limit. We find that in these
models the tachyons undergo a second order phase transition. We compare our
results with those of ordinary scalar field theory. We also calculate the one
loop finite temperature effective potential.Comment: 31 pages, 9 figure
Relationship between plasma sialic acid and fibrinogen concentration and incident micro- and macrovascular complications in type 1 diabetes. The EURODIAB Prospective Complications Study (PCS)
AIMS/HYPOTHESIS: Type 1 diabetes is associated with an increased risk of vascular complications. This increased risk could be explained by sialic acid and/or fibrinogen. It is also not clear what explains the abolition of sex-related differences affecting risk of CHD in the presence of type 1 diabetes. Therefore, we examined whether fibrinogen and sialic acid are related to incident micro- and macrovascular complications in patients with type 1 diabetes. METHODS: A subset (n=2329) of the EURODIAB Prospective Complications Study was analysed. Sialic acid and fibrinogen concentrations were measured at baseline. The main outcomes after 7 years were development of albuminuria, retinopathy, neuropathy and CHD. RESULTS: Univariable and multivariable models using Cox proportional survival analyses showed that an SD unit increase in sialic acid and fibrinogen levels was significantly associated with CHD in men only. Adjusted standardised hazard ratios (sHRs) were 1.50 (95% CI 1.05-2.15) and 1.40 (95% CI 1.06-1.86) for sialic acid and fibrinogen, respectively. Initial associations between (1) sialic acid and incident retinopathy [standardised odds ratio (sOR) men 1.68, 95% CI 1.10-2.57], (2) fibrinogen and retinopathy (sOR women 1.37, 95% CI 1.06-1.78) and (3) sialic acid and neuropathy (sOR men 1.37, 95% CI 1.06-1.77) were shown, but became non-significant in multivariable models. CONCLUSIONS/INTERPRETATION: Sialic acid and fibrinogen are strong predictors of CHD in men with type 1 diabetes, beyond the effect of established risk factors. The associations found with microvascular complications were not independent of other risk factors
Relationship Between Risk Factors and Mortality in Type 1 Diabetic Patients in Europe: The EURODIAB Prospective Complications Study (PCS)
OBJECTIVEâThe purpose of this study was to examine risk factors for mortality in patients with type 1 diabetes
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