Composition-tuned smeared phase transitions

Phase transitions in random systems are smeared if individual spatial regions can order independently of the bulk system. In this paper, we study such smeared phase transitions (both classical and quantum) in substitutional alloys A$_{1-x}$B$_x$ that can be tuned from an ordered phase at composition $x=0$ to a disordered phase at $x=1$. We show that the ordered phase develops a pronounced tail that extends over all compositions $x<1$. Using optimal fluctuation theory, we derive the composition dependence of the order parameter and other quantities in the tail of the smeared phase transition. We also compare our results to computer simulations of a toy model, and we discuss experiments.Comment: 6 pages, 4 eps figures included, final version as publishe

Disorder promotes ferromagnetism: Rounding of the quantum phase transition in Sr_{1-x}Ca_xRuO_3

The subtle interplay of randomness and quantum fluctuations at low temperatures gives rise to a plethora of unconventional phenomena in systems ranging from quantum magnets and correlated electron materials to ultracold atomic gases. Particularly strong disorder effects have been predicted to occur at zero-temperature quantum phase transitions. Here, we demonstrate that the composition-driven ferromagnetic-to-paramagnetic quantum phase transition in Sr1-xCaxRuO3 is completely destroyed by the disorder introduced via the different ionic radii of the randomly distributed Sr and Ca ions. Using a magneto-optical technique, we map the magnetic phase diagram in the composition-temperature space. We find that the ferromagnetic phase is significantly extended by the disorder and develops a pronounced tail over a broad range of the composition x. These findings are explained by a microscopic model of smeared quantum phase transitions in itinerant magnets. Moreover, our theoretical study implies that correlated disorder is even more powerful in promoting ferromagnetism than random disorder.Comment: 15 pages, 4 figures, submitted to Phys. Rev. Let

Comparing two approaches to Hawking radiation of Schwarzschild-de Sitter black holes

We study two different ways to analyze the Hawking evaporation of a Schwarzschild-de Sitter black hole. The first one uses the standard approach of surface gravity evaluated at the possible horizons. The second method derives its results via the Generalized Uncertainty Principle (GUP) which offers a yet different method to look at the problem. In the case of a Schwarzschild black hole it is known that this methods affirms the existence of a black hole remnant (minimal mass $M_{\rm min}$) of the order of Planck mass $m_{\rm pl}$ and a corresponding maximal temperature $T_{\rm max}$ also of the order of $m_{\rm pl}$. The standard $T(M)$ dispersion relation is, in the GUP formulation, deformed in the vicinity of Planck length $l_{\rm pl}$ which is the smallest value the horizon can take. We generalize the uncertainty principle to Schwarzschild-de Sitter spacetime with the cosmological constant $\varLambda=1/m_\varLambda^2$ and find a dual relation which, compared to $M_{\rm min}$ and $T_{\rm max}$, affirms the existence of a maximal mass $M_{\rm max}$ of the order $(m_{\rm pl}/m_\varLambda)m_{\rm pl}$, minimum temperature $T_{\rm min} \sim m_\varLambda$. As compared to the standard approach we find a deformed dispersion relation $T(M)$ close to $l_{\rm pl}$ and in addition at the maximally possible horizon approximately at $r_\varLambda=1/m_\varLambda$. $T(M)$ agrees with the standard results at $l_{\rm pl} \ll r \ll r_\varLambda$ (or equivalently at $M_{\rm min} \ll M \ll M_{\rm max}$).Comment: new references adde

LIPID, CARDIOVASCULAR AND PHARMACOGENETIC EFFECTS OF A COMMON VARIANT IN THE АВСА1 GENE (rs2230806)

ATP-binding cassette transporters (ABC) are a family of proteins that function as transmembrane carriers of molecules using adenosine triphosphate (ATP) hydrolysis as an energy source. ABCA1 is a protein that functions as a «cholesterol pump» in the removal of lipids from the cell and transfersthe cholesterol and phospholipids from the cell membrane to apolipoproteins for the subsequent formation of nascent high-density lipoproteins (HDL). The most common and one of the most studied is the nonsynonymous allelic variant rs2230806; however, the effects of this genetic polymorphism on atherosclerosis and lipid profile till now remain debatable. The phenotypic effects of this variant are opposite to those observed in the ABCA1 mutationheterozygous carriers, suggesting that this genetic variant is associated with increased ABCA1 function and reverse cholesterol transport. Meta-analyses confirmed the association of rs2230806 polymorphism with higher levels of HDL cholesterol and lower levels of TG and LDL cholesterol in the general population, which could mediate a decrease in the risk of coronary heart disease in allelic carriers. It is known that the relationship of rs2230806 variant with HDL levels and coronary heart disease is more stable and consistent in Asian populations than in European ones. Single pharmacogenetic studies show no effect of rs2230806 ABCA1 on the main lipotropic effect of statins, reduction of LDL-C, but indicate a positive reaction of HDL in one study. In practice, the detection of this genetic polymorphism, along with other ABCA1 allelic variants, can be used for screening of persons at higher risk of coronary heart disease with the early preventive measures in carriers of risk alleles