142 research outputs found
Are current-induced forces conservative?
The expression for the force on an ion in the presence of current can be
derived from first principles without any assumption about its conservative
character. However, energy functionals have been constructed that indicate that
this force can be written as the derivative of a potential function. On the
other hand, there exist compelling specific arguments that strongly suggest the
contrary. We propose physical mechanisms that invalidate such arguments and
demonstrate their existence with first-principles calculations. While our
results do not constitute a formal resolution to the fundamental question of
whether current-induced forces are conservative, they represent a substantial
step forward in this direction.Comment: 4 pages, 4 Figures, submitted to PR
Approaching the Ground State of Frustrated A-site Spinels: A Combined Magnetization and Polarized Neutron Scattering Study
We re-investigate the magnetically frustrated, {\it
diamond-lattice-antiferromagnet} spinels FeAlO and MnAlO using
magnetization measurements and diffuse scattering of polarized neutrons. In
FeAlO, macroscopic measurements evidence a "cusp" in zero field-cooled
susceptibility around 13~K. Dynamic magnetic susceptibility and {\it memory
effect} experiments provide results that do not conform with a canonical
spin-glass scenario in this material. Through polarized neutron scattering
studies, absence of long-range magnetic order down to 4~K is confirmed in
FeAlO. By modeling the powder averaged differential magnetic neutron
scattering cross-section, we estimate that the spin-spin correlations in this
compound extend up to the third nearest-neighbour shell. The estimated value of
the Land\'{e} factor points towards orbital contributions from Fe.
This is also supported by a Curie-Weiss analysis of the magnetic
susceptibility. MnAlO, on the contrary, undergoes a magnetic phase
transition into a long-range ordered state below 40~K, which is
confirmed by macroscopic measurements and polarized neutron diffraction.
However, the polarized neutron studies reveal the existence of prominent
spin-fluctuations co-existing with long-range antiferromagnetic order. The
magnetic diffuse intensity suggests a similar short range order as in
FeAlO. Results of the present work supports the importance of spin-spin
correlations in understanding magnetic response of frustrated magnets like
-site spinels which have predominant short-range spin correlations
reminiscent of the "spin liquid" state.Comment: 10 pages, 10 figures, double-column, accepted in Phys. Rev. B, 201
Predicting Diabetic Nephropathy Using a Multifactorial Genetic Model
AIMS: The tendency to develop diabetic nephropathy is, in part, genetically determined, however this genetic risk is largely undefined. In this proof-of-concept study, we tested the hypothesis that combined analysis of multiple genetic variants can improve prediction. METHODS: Based on previous reports, we selected 27 SNPs in 15 genes from metabolic pathways involved in the pathogenesis of diabetic nephropathy and genotyped them in 1274 Ashkenazi or Sephardic Jewish patients with Type 1 or Type 2 diabetes of >10 years duration. A logistic regression model was built using a backward selection algorithm and SNPs nominally associated with nephropathy in our population. The model was validated by using random "training" (75%) and "test" (25%) subgroups of the original population and by applying the model to an independent dataset of 848 Ashkenazi patients. RESULTS: The logistic model based on 5 SNPs in 5 genes (HSPG2, NOS3, ADIPOR2, AGER, and CCL5) and 5 conventional variables (age, sex, ethnicity, diabetes type and duration), and allowing for all possible two-way interactions, predicted nephropathy in our initial population (C-statistic = 0.672) better than a model based on conventional variables only (C = 0.569). In the independent replication dataset, although the C-statistic of the genetic model decreased (0.576), it remained highly associated with diabetic nephropathy (χ(2) = 17.79, p<0.0001). In the replication dataset, the model based on conventional variables only was not associated with nephropathy (χ(2) = 3.2673, p = 0.07). CONCLUSION: In this proof-of-concept study, we developed and validated a genetic model in the Ashkenazi/Sephardic population predicting nephropathy more effectively than a similarly constructed non-genetic model. Further testing is required to determine if this modeling approach, using an optimally selected panel of genetic markers, can provide clinically useful prediction and if generic models can be developed for use across multiple ethnic groups or if population-specific models are required
Common variants in WFS1 confer risk of type 2 diabetes
We studied genes involved in pancreatic beta cell function and survival, identifying associations between SNPs in WFS1 and diabetes risk in UK populations that we replicated in an Ashkenazi population and in additional UK studies. In a pooled analysis comprising 9,533 cases and 11,389 controls, SNPs in WFS1 were strongly associated with diabetes risk. Rare mutations in WFS1 cause Wolfram syndrome; using a gene-centric approach, we show that variation in WFS1 also predisposes to common type 2 diabetes
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