Distribution of lipids in non-lamellar phases of their mixtures

We consider a model of lipids in which a head group, characterized by its volume, is attached to two flexible tails of equal length. The phase diagram of the anhydrous lipid is obtained within self-consistent field theory, and displays, as a function of lipid architecture, a progression of phases: body-centered cubic, hexagonal, gyroid, and lamellar. We then examine mixtures of an inverted hexagonal forming lipid and a lamellar forming lipid. As the volume fractions of the two lipids vary, we find that inverted hexagonal, gyroid, or lamellar phases are formed. We demonstrate that the non-lamellar forming lipid is found preferentially at locations which are difficult for the lipid tails to reach. Variations in the volume fraction of each type of lipid tail are on the order of one to ten per cent within regions dominated by the tails. We also show that the variation in volume fraction is correlated qualitatively with the variation in mean curvature of the head-tail interface.Comment: 10 pages, 12 figures (better figures are available upon request), to appear in J. Chem. Phy

Magnetic and magnetocaloric properties of (MnCo)1-xGe compounds

The crystal structure, magnetic properties, and heat capacity of the (MnCo)1-xGe compounds with x ≤ 0.05 have been studied. It was found that, as the deviation from the MnCoGe stoichiometric composition increases, the temperature of structural transition from the low-temperature phase with the orthorhombic TiNiSi-type structure to the high-temperature phase with the hexagonal Ni2In-type phase decreases rapidly, whereas the magnetic ordering temperature varies slightly. The temperature of structural transition for the composition with x = 0.02 approximately coincides with the Curie temperature of the hexagonal phase, and the transition is accompanied by a significant entropy change, namely, ΔS = 34 J/(kg K). The application of high magnetic field in the transition-temperature range causes an increase in the relative volume of the orthorhombic phase. An analysis of magnetocaloric properties of these compounds, which was performed with the formal application of the Maxwell's relationship near the temperature of first-order structural phase transition, is shown to give overestimated values of the entropy change. © Pleiades Publishing, Ltd., 2013

Field theoretic calculation of the surface tension for a model electrolyte system

We carry out the calculation of the surface tension for a model electrolyte to first order in a cumulant expansion about a free field theory equivalent to the Debye-H\"uckel approximation. In contrast with previous calculations, the surface tension is calculated directly without recourse to integrating thermodynamic relations. The system considered is a monovalent electrolyte with a region at the interface, of width h, from which the ionic species are excluded. In the case where the external dielectric constant epsilon_0 is smaller than the electrolyte solution's dielectric constant epsilon we show that the calculation at this order can be fully regularized. In the case where h is taken to be zero the Onsager-Samaras limiting law for the excess surface tension of dilute electrolyte solutions is recovered, with corrections coming from a non-zero value of epsilon_0/epsilon.Comment: LaTeX, 14 pages, 3 figures, 1 tabl

Continuous selections of multivalued mappings

This survey covers in our opinion the most important results in the theory of continuous selections of multivalued mappings (approximately) from 2002 through 2012. It extends and continues our previous such survey which appeared in Recent Progress in General Topology, II, which was published in 2002. In comparison, our present survey considers more restricted and specific areas of mathematics. Note that we do not consider the theory of selectors (i.e. continuous choices of elements from subsets of topological spaces) since this topics is covered by another survey in this volume

Curvature-Induced Defect Unbinding in Toroidal Geometries

Toroidal templates such as vesicles with hexatic bond orientational order are discussed. The total energy including disclination charges is explicitly computed for hexatic order embedded in a toroidal geometry. Related results apply for tilt or nematic order on the torus in the one Frank constant approximation. Although there is no topological necessity for defects in the ground state, we find that excess disclination defects are nevertheless energetically favored for fat torii or moderate vesicle sizes. Some experimental consequences are discussed.Comment: 12 pages, 15 eps figure

CARDIOVASCULAR RISK FACTORS IN PATIENTS WITH OBSTRUCTIVE SLEEP APNEA SYNDROME

The paper analyzes the cause-and-effect relations of obstructive sleep apnea syndrome (OSAS) and cardiovascular diseases (CVD). In OSAS,there is activation of the sympathetic nervous system and proinflammatory and procoagulant systems, endothelial dysfunction, and accelerated atherosclerosis in response to intermittent hypoxia and sleep fragmentation, which leads to increased risk for CVD. Continuous positive airway pressure therapy reduces the risk of death in patients with OSAS</p

Low-Temperature Polymorphic Phase Transition in a Crystalline Tripeptide L-Ala-L-Pro-Gly·H2O Revealed by Adiabatic Calorimetry

We demonstrate application of precise adiabatic vacuum calorimetry to observation of phase transition in the tripeptide l-alanyl-l-prolyl-glycine monohydrate (APG) from 6 to 320 K and report the standard thermodynamic properties of the tripeptide in the entire range. Thus, the heat capacity of APG was measured by adiabatic vacuum calorimetry in the above temperature range. The tripeptide exhibits a reversible first-order solid-to-solid phase transition characterized by strong thermal hysteresis. We report the standard thermodynamic characteristics of this transition and show that differential scanning calorimetry can reliably characterize the observed phase transition with <5 mg of the sample. Additionally, the standard entropy of formation from the elemental substances and the standard entropy of hypothetical reaction of synthesis from the amino acids at 298.15 K were calculated for the studied tripeptide.National Institute of Biomedical Imaging and Bioengineering (U.S.) (EB-003151)National Institute of Biomedical Imaging and Bioengineering (U.S.) (EB-001960)National Institute of Biomedical Imaging and Bioengineering (U.S.) (EB-002026

Structural State and Magnetic Properties of Nd2Fe14B-Type Rapidly Quenched Alloys

Using the X-ray, elastic neutron diffraction (END) and small angular neutron scattering (SANS) methods (Diffractometers D2 and D3 respectively), transmitting electronic microscopy (JEOL JEM-200CX) and magnetometry technique (vibrating sample magnetometer - VSM) the structure and magnetic properties of the rapidly quenched (RQ) alloys of the following compositions: A) Nd14Fe78B8; B) Y12Fe82B6; C) Nd13.3Co6.6Fe72.6Ge0.9B6.6; D)Nd9Fe85B6; E) Nd9Fe79B12; F) Nd9Fe74Ti4CB12 have been studied. At some quenching conditions or after consequent heat treatments of these alloys the nanoscale state of the main 2-14-1 phase and α-Fe grains can be formed. Their size depends on the sample-preparation conditions and lies in the interval of 10-200 nm. Their influence on magnetic properties of alloys under study is discussed. © 2006 Central Iron and Steel Research Institute.This work was supported by the RF Science and Innovations Agency for Priority, Direction Program "Industry of nanosystems and materials" (Project IN-12.3/00l) and partly by High School Science Potential Development Program (project RNP 2.1.1. 6945)