Superconductivity at 250 K in lanthanum hydride under high pressures.

With the discovery1 of superconductivity at 203 kelvin in H3S, attention returned to conventional superconductors with properties that can be described by the Bardeen-Cooper-Schrieffer and the Migdal-Eliashberg theories. Although these theories predict the possibility of room-temperature superconductivity in metals that have certain favourable properties-such as lattice vibrations at high frequencies-they are not sufficient to guide the design or predict the properties of new superconducting materials. First-principles calculations based on density functional theory have enabled such predictions, and have suggested a new family of superconducting hydrides that possess a clathrate-like structure in which the host atom (calcium, yttrium, lanthanum) is at the centre of a cage formed by hydrogen atoms2-4. For LaH10 and YH10, the onset of superconductivity is predicted to occur at critical temperatures between 240 and 320 kelvin at megabar pressures3-6. Here we report superconductivity with a critical temperature of around 250 kelvin within the [Formula: see text] structure of LaH10 at a pressure of about 170 gigapascals. This is, to our knowledge, the highest critical temperature that has been confirmed so far in a superconducting material. Superconductivity was evidenced by the observation of zero resistance, an isotope effect, and a decrease in critical temperature under an external magnetic field, which suggested an upper critical magnetic field of about 136 tesla at zero temperature. The increase of around 50 kelvin compared with the previous highest critical temperature1 is an encouraging step towards the goal of achieving room-temperature superconductivity in the near future.

Depletions of Multi-MeV Electrons and Their Association to Minima in Phase Space Density.

Fast-localized electron loss, resulting from interactions with electromagnetic ion cyclotron (EMIC) waves, can produce deepening minima in phase space density (PSD) radial profiles. Here, we perform a statistical analysis of local PSD minima to quantify how readily these are associated with radiation belt depletions. The statistics of PSD minima observed over a year are compared to the Versatile Electron Radiation Belts (VERB) simulations, both including and excluding EMIC waves. The observed minima distribution can only be achieved in the simulation including EMIC waves, indicating their importance in the dynamics of the radiation belts. By analyzing electron flux depletions in conjunction with the observed PSD minima, we show that, in the heart of the outer radiation belt (L* < 5), on average, 53% of multi-MeV electron depletions are associated with PSD minima, demonstrating that fast localized loss by interactions with EMIC waves are a common and crucial process for ultra-relativistic electron populations.

Swelling of Thermo-Responsive Gels in Aqueous Solutions of Salts: A Predictive Model.

The equilibrium degree of swelling of thermo-responsive (TR) gels is strongly affected by the presence of ions in an aqueous solution. This phenomenon plays an important role in (i) the synthesis of multi-stimuli-responsive gels for soft robotics, where extraordinary strength and toughness are reached by soaking of a gel in solutions of multivalent ions, and (ii) the preparation of hybrid gels with interpenetrating networks formed by covalently cross-linked synthetic chains and ionically cross-linked biopolymer chains. A model is developed for equilibrium swelling of a TR gel in aqueous solutions of salts at various temperatures T below and above the critical temperature at which collapse of the gel occurs. An advantage of the model is that it involves a a small (compared with conventional relations) number of material constants and allows the critical temperature to be determined explicitly. Its ability (i) to describe equilibrium swelling diagrams on poly(N-isopropylacrylamide) gels in aqueous solutions of mono- and multivalent salts and (ii) to predict the influence of volume fraction of salt on the critical temperature is confirmed by comparison of observations with results of numerical simulation.

Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system.

A superconductor is a material that can conduct electricity without resistance below a superconducting transition temperature, Tc. The highest Tc that has been achieved to date is in the copper oxide system: 133 kelvin at ambient pressure and 164 kelvin at high pressures. As the nature of superconductivity in these materials is still not fully understood (they are not conventional superconductors), the prospects for achieving still higher transition temperatures by this route are not clear. In contrast, the Bardeen-Cooper-Schrieffer theory of conventional superconductivity gives a guide for achieving high Tc with no theoretical upper bound--all that is needed is a favourable combination of high-frequency phonons, strong electron-phonon coupling, and a high density of states. These conditions can in principle be fulfilled for metallic hydrogen and covalent compounds dominated by hydrogen, as hydrogen atoms provide the necessary high-frequency phonon modes as well as the strong electron-phonon coupling. Numerous calculations support this idea and have predicted transition temperatures in the range 50-235 kelvin for many hydrides, but only a moderate Tc of 17 kelvin has been observed experimentally. Here we investigate sulfur hydride, where a Tc of 80 kelvin has been predicted. We find that this system transforms to a metal at a pressure of approximately 90 gigapascals. On cooling, we see signatures of superconductivity: a sharp drop of the resistivity to zero and a decrease of the transition temperature with magnetic field, with magnetic susceptibility measurements confirming a Tc of 203 kelvin. Moreover, a pronounced isotope shift of Tc in sulfur deuteride is suggestive of an electron-phonon mechanism of superconductivity that is consistent with the Bardeen-Cooper-Schrieffer scenario. We argue that the phase responsible for high-Tc superconductivity in this system is likely to be H3S, formed from H2S by decomposition under pressure. These findings raise hope for the prospects for achieving room-temperature superconductivity in other hydrogen-based materials.

Asymmetry of medullary veins on multiphase CT-angiography in patients with acute ischemic stroke.

BACKGROUND: It was previously demonstrated that decreased cortical venous drainage is a predictive factor of poor clinical outcome in patients with an acute ischemic stroke. The aim of this investigation is to test the hypothesis that the decline in blood flow in medullary veins (MV) on CT angiogram (CTA) of patients with acute ischemic stroke (AIS) can also be predictive of clinical outcome. METHODS: We retrospectively reviewed a database of patients with AIS who were evaluated by multiphase CTA and enrolled individuals with AIS and evidence of occlusion of the intracranial internal carotid artery, the M1 or M2 segment of the middle cerebral artery, or combination of two occlusions. To characterize asymmetry of MV we used similar principle that was previously established for MV on SWI MR-images; asymmetry was defined was presence of 5 or more contrast opacified MV in one hemisphere as compared to the contralateral side. Clinical outcomes were evaluated by mRS in 90 days. The Fisher Exact test was used to examine the significance of the MV asymmetry. Odds ratio and interrater variability were calculated. RESULTS: 66 patients with AIS were included. The presence of asymmetry in MV was associated with the higher frequency of poor clinical outcomes (84.6% vs 50.9%); the OR was 5.3. Interrater agreement in assessment on MV was moderate in our study (κ=0.55). CONCLUSION: This study shows that (a) medullary veins can be reliably assessed on multiphase CTA, (b) in patients with AIS, asymmetric appearance of MV is associated with poor clinical outcome.

Molecular Genetic Markers of Intra- and Interspecific Divergence within Starfish and Sea Urchins (Echinodermata).

A fragment of the mitochondrial COI gene from isolates of several echinoderm species was sequenced. The isolates were from three species of starfish from the Asteriidae family (Asterias amurensis and Aphelasterias japonica collected in the Sea of Japan and Asterias rubens collected in the White Sea) and from the sea urchin Echinocardium cordatum (family Loveniidae) collected in the Sea of Japan. Additionally, regions including internal transcribed spacers and 5.8S rRNA (ITS1 - 5.8S rDNA - ITS2) were sequenced for the three studied starfish species. Phylogenetic analysis of the obtained COI sequences together with earlier determined homologous COI sequences from Ast. forbesii, Ast. rubens, and Echinocardium laevigaster from the North Atlantic and E. cordatum from the Yellow and North Seas (GenBank) placed them into strictly conspecific clusters with high bootstrap support (99% in all cases). Only two exceptions - Ast. rubens DQ077915 sequence placed with the Ast. forbesii cluster and Aph. japonica DQ992560 sequence placed with the Ast. amurensis cluster - were likely results of species misidentification. The intraspecific polymorphism for the COI gene within the Asteriidae family varied within a range of 0.2-0.9% as estimated from the genetic distances. The corresponding intrageneric and intergeneric values were 10.4-12.1 and 21.8-29.8%, respectively. The interspecific divergence for the COI gene in the sea urchin of Echinocardium genus (family Loveniidae) was significantly higher (17.1-17.7%) than in the starfish, while intergeneric divergence (14.6-25.7%) was similar to that in asteroids. The interspecific genetic distances for the nuclear transcribed sequences (ITS1 - 5.8S rDNA - ITS2) within the Asteriidae family were lower (3.1-4.5%), and the intergeneric distances were significantly higher (32.8-35.0%), compared to the corresponding distances for the COI gene. These results suggest that the investigated molecular-genetic markers could be used for segregation and identification of echinoderm species.

Modeling the effects of pH and ionic strength on swelling of polyelectrolyte gels.

A model is developed for the elastic response of a polyelectrolyte gel under unconstrained and constrained swelling in a water bath with an arbitrary pH, where a monovalent salt is dissolved. A gel is treated as a three-phase medium consisting of an equivalent polymer network, solvent (water), and solute (mobile ions). Transport of solvent and solute is thought of as their diffusion through the network accelerated by an electric field formed by mobile and fixed ions and accompanied by chemical reactions (self-ionization of water molecules, dissociation of functional groups attached to polymer chains, and formation of ion pairs between bound charges and mobile counter-ions). Constitutive equations are derived by means of the free energy imbalance inequality for an arbitrary three-dimensional deformation with finite strains. Adjustable parameters in the governing relations are found by fitting equilibrium swelling diagrams on several hydrogels. The effects of pH, ionic strength of solution, and constraints on equilibrium water uptake are studied numerically.

[Analysis of the dynamics of bioluminescence intensity of luminous bacteria Photobacterium phosphoreum].

This contribution presents the results of analysis of the dynamics of the bioluminescence of luminous bacteria Photobacterium phosphoreum IMV B-7071 under optimal conditions of their growth. A quasi-harmonic nature of the bacterial bioluminescence dynamics was detected. The observed periods of these changes have similar values compared with those in the earlier defined periods of changes in physicochemical properties of water. The relationship between biorhythms and a quasi-harmonic nature of changes in physicochemical properties of water is discussed.

Swelling of thermo-responsive hydrogels.

A model is developed for the elastic response and solvent diffusion through a thermo-responsive gel under an arbitrary deformation with finite strains. The constitutive equations involve the stress-strain relation, the nonlinear diffusion equation for solvent molecules, the heat conduction equation, and the Allen-Cahn equation for an order parameter (proportional to the concentration of hydrophilic segments in polymer chains). Material constants are found by fitting swelling diagrams for PNIPA gels under uniaxial tension. Numerical analysis demonstrates good agreement between predictions of the model and observations in tests with stress- and strain-controlled programs.

[Quasi-periodic behavior of intermolecular interactions in water].

We investigated the dynamics of physical characteristics of water by applying various methods of molecular structural analysis: IR spectroscopy, Raman spectroscopy, microwave radiometry and NMR. It was established that the changes in the physical characteristics of water are subject to certain laws. In all experiments, the periods of oscillations of the measured values showed good similarity and reproducibility, regardless of the method of analysis. The values of these periods are as follows: 1-3, 5-9, 10-13, 14-18, 21-29, 30-39, 41-55 and ~60 minutes. The amplitudes of these oscillations vary up to 10%. Based on the two-structure water model the observed quasi-periodic intermolecular interactions can be associated with the dynamics of mutual transitions between local structural inhomogeneities of water. The observed periodic character of intermolecular interactions can presumably be linked to the change in the ratio between the spin isomers of water molecules. The article discusses the connections between variations of the physical properties of water and biorhythms.

Lifetime Predictions for High-Density Polyethylene under Creep: Experiments and Modeling.

Observations are reported in uniaxial tensile tests with various strain rates, tensile relaxation tests with various strains, and tensile creep tests with various stresses on high-density polyethylene (HDPE) at room temperature. Constitutive equations are developed for the viscoelastoplastic response of semicrystalline polymers. The model involves seven material parameters. Four of them are found by fitting observations in relaxation tests, while the others are determined by matching experimental creep curves. The predictive ability of the model is confirmed by comparing observations in independent short- and medium-term creep tests (with the duration up to several days) with the results of numerical analysis. The governing relations are applied to evaluate the lifetime of HDPE under creep conditions. An advantage of the proposed approach is that it predicts the stress-time-to-failure diagrams with account for the creep endurance limit.

Universal diamond edge Raman scale to 0.5 terapascal and implications for the metallization of hydrogen.

The recent progress in generating static pressures up to terapascal values opens opportunities for studying novel materials with unusual properties, such as metallization of hydrogen and high-temperature superconductivity. However, an evaluation of pressure above ~0.3 terapascal is a challenge. We report a universal high-pressure scale up to ~0.5 terapascal, which is based on the shift of the Raman edge of stressed diamond anvils correlated with the equation of state of Au and does not require an additional pressure sensor. According to the new scale, the pressure values are substantially lower by 20% at ~0.5 terapascal compared to the extrapolation of the existing scales. We compare the available data of H2 at the highest static pressures. We show that the onset of the proposed metallization of molecular hydrogen reported by different groups is consistent when corrected with the new scale and can be compared with various theoretical predictions.

Modification of fullerene nanocolumn structure by accelerated C60 ions.

Crystalline C60 and amorphous graphite-like films of nanocolumn arrays fabricated by glancing angle deposition of C60 fullerene at substrate temperatures of -425 K were studied by transmission electron microscopy (TEM) and atomic-force microscopy (AFM). Characteristic dimension of columns is 200-400 nm. We used co-deposition of C60 molecules and accelerated C60 ions to modify the structure and properties of nanocolumn arrays. Influence of incidence angle for C60 ions on formation of film morphology was revealed. Raman spectrum analysis showed that amorphous carbon nanocolumns consist of nanographite areas with average size of -1.5 nm. The films have high conductivity (close to graphite) and have no mechanical stresses. The carbon films were applied in all-solid-state rechargeable thin-film battery as an anode layer. The nanocolumn amorphous carbon film as anode electrode showed the discharge capacity of about 50 microAh cm(-2)microm(-1) and good cycling ability over 100 times in full cell system.

Thermo-Mechanical Behavior of Poly(ether ether ketone): Experiments and Modeling.

Observations are reported on poly(ether ether ketone) (PEEK) in uniaxial tensile tests, relaxation tests and creep tests with various stresses in a wide interval of temperatures ranging from room temperature to 180 °C. Constitutive equations are developed for the thermo-mechanical behavior of PEEK under uniaxial deformation. Adjustable parameters in the governing equations are found by matching the experimental data. Good agreement is demonstrated between the observations and results of numerical simulation. It is shown that the activation energies for the elastoplastic, viscoelastic and viscoelastoplastic responses adopt similar values at temperatures above the glass transition point.

Modulation of the volume phase transition temperature of thermo-responsive gels.

Thermo-responsive (TR) gels swell substantially below their volume phase transition temperature Tc and shrink above this temperature. Applications of TR gels in controlled drug delivery and their use as biosensors and temperature-triggered soft actuators require fine tuning of Tc. As the critical temperature is independent of the preparation conditions and molar fractions of monomers and cross-linkers, it is modulated by incorporation of (neutral or ionic) monomers and polymer chains into pre-gel solutions for TR gels. A model is developed for the mechanical response and equilibrium swelling of TR gels. Analytical formulas are derived for the effect of molar fraction of comonomers on the volume phase transition temperature Tc in copolymer gels and gels with semi-interpenetrating networks. Adjustable parameters are found by fitting equilibrium swelling diagrams on poly(N,N-diethylacrylamide) gels. Good agreement is demonstrated between predictions of the model and experimental data.

[Quantum mechanical aspects of effects of weak magnetic fields upon biological objects].

Possible mechanisms of action of weak combined magnetic fields on biological systems have been discussed in terms of quantum mechanics. The approaches proposed make it possible to solve the problem of the failure to compare the energy of active factors with the energy of thermal motion (kT problem). A mechanism of action of combined magnetic fields on biosystems has been proposed.

[Morphology of gametes in sea urchins from Peter the Great Bay, Sea of Japan].

The fine structure of the gametes in six sea urchin species of the Sea of Japan was studied. The spermatozoons in Strongylocentrotus nudus, S. intermedius, Echinocardium cordatum, Scaphechinus mirabilis, Sc. grizeus and Echinarachnius parma are species-specific. The conical head and symmetrically disposed ring-shape mitochondrion are common to regular sea urchin sperm cells. S. nudus is characterized by the bulb-shaped head of the zoosperm; S. intermedius, by a bullet-shaped one. The zoosperm spearhead and small amount of postacrosome material are common to irregular sea urchins; the sperm width: length ratio varies for different species, with the highest for Sc. mirabilis. The zoosperm of Sc. griseus is characterized by two lipid drops in the cell center. Asymmetrical mitochondrion disposal is usual for E. parma. Actin filaments are found in the postacrosome material in the zoosperm of cordiform sea urchins. The differences in the fine structure of zoosperm in eurybiont species Ech. cordatum inhabiting the Sea of Japan and coastal areas of the Northeast Atlantic may bear record to the complex existence of species Ech. cordatum. The fine structure of zoosperm is unique for each of the studied families, Strongylocentrotidae, Scutellidae, and Loveniidae. The eggs of all the species are characterized by vitelline and tremelloid membranes. The vitelline membrane is formed by cytoplasm protrusions; the area between them is filled with fubrillary material. The tremelloid membrane is formed by fubrillary material associated with apical parts of microvilli of the vitelline membrane. The irregular sea urchins Sc. griseus, Sc. mirabilis and E. parma are characterized by chromatophores situated in the tremelloid membrane, with the highest abundance in Sc. mirabilis.

Tension-compression asymmetry in the mechanical response of hydrogels.

Two factors play the key role in application of hydrogels as biomedical implants (for example, for replacement of damaged intervertebral discs and repair of spinal cord injuries): their stiffness and strength (measured in tensile tests) and mechanical integrity (estimated under uniaxial compression). Observations show a pronounced difference between the responses of hydrogels under tension and compression (the Young's moduli can differ by two orders of magnitude), which is conventionally referred to as the tension-compression asymmetry (TCA). A constitutive model is developed for the mechanical behavior of hydrogels, where TCA is described within the viscoplasticity theory (plastic flow is treated as sliding of junctions between chains with respect to their reference positions). The governing equations involve five material constants with transparent physical meaning. These quantities are found by fitting stress-strain diagrams under tension and compression on a number of pristine and nanocomposite hydrogels with various kinds of chemical and physical bonds between chains. Good agreement is demonstrated between the experimental data and results of simulation. The influence of volume fraction of nanoparticles, concentration of cross-links, and topology of a polymer network on material parameters is analyzed numerically.