5 research outputs found
Order Parameter Description of the Anderson-Mott Transition
An order parameter description of the Anderson-Mott transition (AMT) is
given. We first derive an order parameter field theory for the AMT, and then
present a mean-field solution. It is shown that the mean-field critical
exponents are exact above the upper critical dimension. Renormalization group
methods are then used to show that a random-field like term is generated under
renormalization. This leads to similarities between the AMT and random-field
magnets, and to an upper critical dimension for the AMT. For
, an expansion is used to calculate the critical
exponents. To first order in they are found to coincide with the
exponents for the random-field Ising model. We then discuss a general scaling
theory for the AMT. Some well established scaling relations, such as Wegner's
scaling law, are found to be modified due to random-field effects. New
experiments are proposed to test for random-field aspects of the AMT.Comment: 28pp., REVTeX, no figure
Phase transitions in BaTiO from first principles
We develop a first-principles scheme to study ferroelectric phase transitions
for perovskite compounds. We obtain an effective Hamiltonian which is fully
specified by first-principles ultra-soft pseudopotential calculations. This
approach is applied to BaTiO, and the resulting Hamiltonian is studied
using Monte Carlo simulations. The calculated phase sequence, transition
temperatures, latent heats, and spontaneous polarizations are all in good
agreement with experiment. The order-disorder vs.\ displacive character of the
transitions and the roles played by different interactions are discussed.Comment: 13 page
Disease-modifying effects of an SCAF4 structural variant in a predominantly SOD1 ALS cohort
Objective To test the hypothesis that rs573116164 will have disease-modifying effects in patients with superoxide dismutase 1 (SOD1) familial amyotrophic lateral sclerosis (fALS), we characterized rs573116164 within a cohort of 190 patients with fALS and 560 healthy age-matched controls to assess the variant for association with various measures of disease.
Methods Using a previously described bioinformatics evaluation algorithm, a polymorphic short structural variant associated with SOD1 was identified according to its theoretical effect on gene expression. An 12–18 poly-T repeat (rs573116164) within the 3′ untranslated region of serine and arginine rich proteins-related carboxy terminal domain associated factor 4 (SCAF4), a gene that is adjacent to SOD1, was assessed for disease association and influence on survival and age at onset in an fALS cohort using PCR, Sanger sequencing, and capillary separation techniques for allele detection.
Results In a North American cohort of predominantly SOD1 fALS patients (n =190) and age-matched healthy controls (n = 560), we showed that carriage of an 18T SCAF4 allele was associated with disease within this cohort (odds ratio [OR] 6.6; 95% confidence interval [CI] 3.9–11.2; p = 4.0e-11), but also within non-SOD1 cases (n = 27; OR 5.3; 95% CI 1.9–14.5; p = 0.0014). This finding suggests genetically SOD1-independent effects of SCAF4 on fALS susceptibility. Furthermore, carriage of an 18T allele was associated with a 26-month reduction in survival time (95% CI 6.6–40.8; p = 0.014), but did not affect age at onset of disease.
Conclusions The findings in this fALS cohort suggest that rs573116164 could have SOD1-independent and broader relevance in ALS, warranting further investigation in other fALS and sporadic ALS cohorts, as well as studies of functional effects of the 18T variant on gene expression