Design of high-temperature superconductors at moderate pressures by alloying AlH3 or GaH3

Since the discovery of hydride superconductors,a significant challenge has been to reduce the pressure required for their stabilization.In this context,we propose that alloying could be an effective strategy to achieve this.We focus on a series of alloyed hydrides with the AMH_(6)composition,which can be made via alloying A15 AH_(3)(A=Al or Ga)with M(M=a group IIIB or IVB metal),and study their behavior under pressure.Seven of them are predicted to maintain the A15-type structure,similar to AH_(3)under pressure,providing a platform for studying the effects of alloying on the stability and superconductivity of AH_(3).Among these,the A15-type phases of AlZrH_(6)and AlHfH_(6)are found to be thermodynamically stable in the pressure ranges of 40–150 and 30–181 GPa,respectively.Furthermore,they remain dynamically stable at even lower pressures,as low as 13 GPa for AlZrH_(6)and 6 GPa for AlHfH_(6).These pressures are significantly lower than that required for stabilizing A15 AlH3.Additionally,the introduction of Zr or Hf increases the electronic density of states at the Fermi level compared with AlH3.This enhancement leads to higher critical temperatures(Tc)of 75 and 76 K for AlZrH_(6)and AlHfH_(6)at 20 and 10 GPa,respectively.In the case of GaMH_(6)alloys,where M represents Sc,Ti,Zr,or Hf,these metals reinforce the stability of the A15-type structure and reduce the lowest thermodynamically stable pressure for GaH_(3) from 160 GPa to 116,95,80,and 85 GPa,respectively.Particularly noteworthy are the A15-type GaMH_(6)alloys,which remain dynamically stable at low pressures of 97,28,5,and 6 GPa,simultaneously exhibiting high Tc of 88,39,70,and 49 K at 100,35,10,and 10 GPa,respectively.Overall,these findings enrich the family of A15-type superconductors and provide insights for the future exploration of high-temperature hydride superconductors that can be stabilized at lower pressures.

Pressure-induced evolution of stoichiometries and electronic structures of host-guest Na-B compounds

Superionic and electride behaviors in materials,which induce a variety of exotic physical properties of ions and electrons,are of great importance both in fundamental research and for practical applications.However,their coexistence in hot alkali-metal borides has not been observed.In this work,we apply first-principles structure search calculations to identify eight Na-B compounds with host-guest structures,which exhibit a wide range of building blocks and interesting properties linked to the Na/B composition.Among the known borides,Na-rich Na9B stands out as the composition with the highest alkali-metal content,featuring vertex-and face-sharing BNa16 polyhedra.Notably,it exhibits electride characteristics and transforms into a superionic electride at 200 GPa and 2000 K,displaying unusual Na atomic diffusion behavior attributed to the modulation of the interstitial anion electrons.It demonstrates semiconductor behavior in the solid state,and metallic properties associated with Na 3p/3s states in the superionic and liquid regions.On the other hand,B-rich NaB7,consisting of a unique covalent B framework,is predicted to exhibit low-frequency phonon-mediated superconductivity with a T_(c) of 16.8 K at 55 GPa.Our work advances the understanding of the structures and properties of alkali-metal borides.

Synthesis and Characterization of a Polymeric Material Blended to Bone Forming Elements

A synthetizing material blended with two distinct proteins (collagen and casein) and mineral mixture, was developed in order to evaluate their properties suitable for possible applications in the biomedical such as inducing the regeneration of damaged bone, either due to an accident or illness. Samples were evaluated by 1) Mechanical properties tests under the bending, 2) Scanning electronic microscopy and 3) Infrared spectroscopy were carried out. The results showed that the developed material has breaking strength and structure characteristics associated with the protein used in their composition. This fact suggests that the used protein determines the resistance of the material, in such a way according to the required use, being able to choose appropriate strength and duration either short or long time. The material composition for specific use, in order to find the most suitable mixture for bone replacement, or induce bone recovery, according to the required properties similar to those of damaged living tissue.

Synthesis of Cu nanoparticles by chemical reduction method

Cu nanoparticles (CuNPs) have been synthesized through an easy route by chemical reduction at room temperature. The Cu^2+ ions were reduced and stabilized with sodium borohydride and polyvinylpyrrolidone, respectively. The effect of the variation of the reducing agent/precursor-salt (RA/PS) ratio on the size and morphology of the CuNPs was evaluated. The synthesized material was studied by ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The UV-Vis spectra showed a CuNPs plasmon peak at 569 nm and another peak belonging to Cu2O at 485 nm. XRD analysis showed the fcc-Cu phase with a small amount of fcc-Cu2O compound. SEM and TEM studies displayed that small semispherical CuNPs of approximately 7 nm were obtained at the RA/PS ratio of 2.6. The excess of polyvinylpyrrolidone stabilizer played an essential role in preventing CuNPs oxidation. On the other side, Cu2O polyhedral particles with larger sizes up to 150 nm were identified in the RA/PS ratio range of 2.0-1.84. In addition, Cu2O particles having star morphologies with quantum confinement at their tips were obtained at the RA/PS ratio of 1.66.

The Influence of the Precipitation Heat Treatment Temperature on the Metallurgical, Microstructure, Thermal Properties, and Microhardness of an Alpha Brass

Metals obtain optimum conditions of metallurgical and physical properties through a heat treatment. Brass is one of the copper alloys which has many applications in everyday life and in the industry. Brass is one of the copper alloys which has many applications in everyday life and the industry. In this work, the influence of the precipitation heat treatment temperature on the metallurgical microstructure, structure, thermal properties, and microhardness of an alpha brass is analyzed. Samples were heat treated by precipitation for 2 h at 300°C, 400°C, 500°C, 600°C, and 700°C. The best mechanical properties were found at 500°C of precipitation heat treatment temperature. Specimens were characterized by scanning electron microscopy, X-ray diffraction, Vickers microhardness, photothermal radiometry, and photoacoustic to study the thermal diffusivity and conductivity, as well as the heat capacity. The inverse of the full width at the half maximum analysis showed that the crystallinity decreased as the precipitation heat treatment temperature increased. Metallurgical microstructure and microhardness were correlated to the precipitation heat treatment temperatures to determine the effect on the metallurgical and mechanical properties, as well as the effect on the thermal properties of alpha brass.

The Effect of Maize Grain Size on the Physicochemical Properties of Isolated Starch, Crude Maize Flour and Nixtamalized Maize Flours

Usually, the maize cob is formed by grains of medium size. However, the extremes have larger or smaller size grains. The objective of this study was to investigate the influence of grain size from the same hybrid on the physicochemical properties of isolated starch, crude maize flours and nixtamalized maize flours. Two hybrids, one from CIMMyT-Mexico called IMIC-254 and one commercial sample from Monsanto (Puma) were studied. The isolated starch granules from small, medium, and large grains exhibit the same size and distribution. The grain size has influence in the determination of cooking and steeping times;small grains reach these parameters faster than medium and large ones. The hardness of the grain size for both hybrids does not showed statistical differences between them. The starch from small, medium and large grains is mainly composed of amylopectin;this result is confirmed by X-ray diffraction and Megazine analysis. The apparent viscosity of the isolated starches of small grains showed statistically significant higher peak values. According to these results, it is possible to use small, medium, and large grains to obtain products with the same physicochemical properties, by adjusting the cooking and steeping times and Ca2+ content.

Two-proton sequential decay from excited states of ^(18)Ne

Two-proton radioactivity from18Ne is discussed in terms of sequential decay.The branch ratios for oneproton emission from excited states are calculated,which including spectroscopic factors,obtained from a Shellmodel calculation with realistic interactions.The branch ratios show that the two-proton emission from the 1-state of 18Ne at 7.94 MeV is most likely to go through the sequential decay.The same mechanism is discussed for other excited states at higher energy by different interactions.

Effective Interaction Force between an Electric Charge and a Magnetic Dipole and Locality (or Nonlocality) in Quantum Effects of the Aharonov–Bohm Type

Classical electrodynamics foresees that the effective interaction force between a moving charge and a magnetic dipole is modified by the time-varying total momentum of the interaction fields. We derive the equations of motion of the particles from the total stress-energy tensor, assuming the validity of Maxwell’s equations and the total momentum conservation law. Applications to the effects of Aharonov–Bohm type show that the observed phase shift may be due to the relative lag between interfering particles caused by the effective local force.

Binding of rhodopsin and rhodopsin analogues to transducin, rhodopsin kinase and arrestin-1

AIM: To investigate the interaction of reconstituted rhodopsin, 9-cis-retinal-rhodopsin and 13-cis-retinal-rhodopsin with transducin, rhodopsin kinase and arrestin-1. METHODS: Rod outer segments(ROS) were isolated from bovine retinas. Following bleaching of ROS membranes with hydroxylamine, rhodopsin and rhodopsin analogues were generated with the different retinal isomers and the concentration of the reconstituted pigments was calculated from their UV/visible absorption spectra. Transducin and arrestin-1 were purified to homogeneity by column chromatography, and an enriched-fraction of rhodopsin kinase was obtainedby extracting freshly prepared ROS in the dark. The guanine nucleotide binding activity of transducin was determined by Millipore filtration using β,γ-imido-(3H)-guanosine 5'-triphosphate. Recognition of the reconstituted pigments by rhodopsin kinase was determined by autoradiography following incubation of ROS membranes containing the various regenerated pigments with partially purified rhodopsin kinase in the presence of(γ-32P) ATP. Binding of arrestin-1 to the various pigments in ROS membranes was determined by a sedimentation assay analyzed by sodium dodecyl sulphatepolyacrylamide gel electrophoresis. RESULTS: Reconstituted rhodopsin and rhodopsin analogues containing 9-cis-retinal and 13-cis-retinal rendered an absorption spectrum showing a maximum peak at 498 nm, 486 nm and about 467 nm, respectively, in the dark; which was shifted to 380 nm, 404 nm and about 425 nm, respectively, after illumination. The percentage of reconstitution of rhodopsin and the rhodopsin analogues containing 9-cis-retinal and 13-cis-retinal was estimated to be 88%, 81% and 24%, respectively. Although only residual activation of transducin was observed in the dark when reconstituted rhodopsin and 9-cis-retinal-rhodopsin was used, the rhodopsin analogue containing the 13-cis isomer of retinal was capable of activating transducin independently of light. Moreover, only a basal amount of the reconstituted rhodopsin and 9-cis-retinal-rhodopsin was phosphorylated by rhodopsin kinase in the dark, whereas the pigment containing the 13-cis-retinal was highly phosphorylated by rhodopsin kinase even in the dark. In addition, arrestin-1 was incubated with rhodopsin, 9-cis-retinal-rhodopsin or 13-cis-retinal-rhodopsin. Experiments were performed using both phosphorylated and non-phosphorylated regenerated pigments. Basal amounts of arrestin-1 interacted with rhodopsin, 9-cis-retinal-rhodopsin and 13-cis-retinal-rhodopsin under dark and light conditions. Residual arrestin-1 was also recognized by the phosphorylated rhodopsin and phosphorylated 9-cis-retinal-rhodopsin in the dark. However, arrestin-1 was recognized by phosphorylated 13-cis-retinal-rhodopsin in the dark. As expected, all reformed pigments were capable of activating transducin and being phosphorylated by rhodopsin kinase in a lightdependent manner. Additionally, all reconstituted photolyzed and phosphorylated pigments were capable of interacting with arrestin-1. CONCLUSION: In the dark, the rhodopsin analogue containing the 13-cis isomer of retinal appears to fold in a pseudo-active conformation that mimics the active photointermediate of rhodopsin.

Agro-Industrial Waste as a Source of Raw Material:Eggshell and Ash of Agave salmiana Useful for the Synthesis of Hydroxyapatite

Agave salmiana ash and poultry eggshell powder as CaO sources were used for obtaining nanostructured hydro-xyapatite(HAP).The synthesis was carried out by the Green Chemistry Hydrothermal Biosynthesis at 180℃ with a pH of 5,by reacting CaO from Agave Salmiana ash and Eggshell powder,with dibasic caldium phosphate(CaH-PO_(4)+2H_(2)O)in an aqueous solution,with Aloe barbadensis extract.The product was characterized by X-ray dif-fraction,Fourier transform infrared spectroscopy(FT-IR),Scanning Electron Microscopy(SEM),and Transmission Electron Microscopy(TEM).The size and shape of the hydroxyapatite particles changed dramati-cally in the presence of Aloe barbadensis.Large crystals of Hydroxyapatite were observed when Eggshell powder and Agave salmiana ash were used as raw materials in the presence of the Aloe barbadensis surfactant.Crystals with shapes of ribbons and plates from 1 micrometers to 8 micrometers were observed when using the eggshell powder in the presence of Aloe bar badensis and,in the case of Agave salmiana ash in the presence of Aloe bar-badensis,crystals with shapes of quadra ngular prisms and hexagonal(polyhedra)with sizes from 2 micrometers to 20 micrometers were observed.Hydroxyapatite was therefore successfully biosynthesized by a green and sus-tainable method that reduces the environmental impact.

Silicon Nanocrystals on the Surface of Standard Si Wafers: A Micro-Raman Investigation

The presence of silicon nanocrystals on the surface of standard wafer samples of Si, conserved under “usual” laboratory conditions, has been investigated by micro-Raman analysis, performed for increasing intensity of laser irradiation. The poor thermal connection of such small crystals to the Si wafer bulk allows for the appearance of two well distinct Raman bands in the spectra, with a different evolution for increasing irradiance levels: the first, expected, due to bulk silicon response, the other one assignable to the silicon nanocrystals. A careful analysis of peak position and linewidth has been carried out, both for the Raman contribution from the nanocrystals, reaching high temperatures under irradiation (up to 1400 K), and for the one from the “bulk” Si, which remains practically at room temperature. The analysis of the spectra and the comparison with previous studies on nc-Si suggest that such nanocrystals do not have a very small size, so that the observed changes of spectral parameters are mainly due to laser heating, rather than quantum confinement effects. In any case, we performed also an independent size deter-mination by AFM mapping, confirming a size distribution well peaked be-tween 50 and 100 nm. As a corollary from this analysis, we get the indication that apparent linewidths and positions, at low laser irradiation levels, can be slightly changed in the presence of nc-Si on the surface. It is due to the differ-ent thermal responses of bulk and nanocrystalline components, inducing un-resolved separate components;this hypothesis suggests reanalysing some previous experimental data, in particular for many Raman spectra of Si col-lected at “room temperature”.

Crystallographic Study of the TiO₂Obtained by Different Synthesis Methods

In this work, the crystal structure of titanium dioxide was studied, and the effect of the different synthesis routes on the microstructure and morphology of the nanostructures was analyzed. Samples characterization was carried out by X-ray diffraction by powders (XRD) to determine the different crystalline phases contented in the samples and using scanning electron microscopy (SEM), the morphology and topology of all samples were studied. XRD results were analyzed through Eva provided by Bruker to determine the average crystallite size. The results portrayed here showed that all the synthesis process produced anatase nanostructures with an average crystallite size smaller than 27 nm. Synthesized powders presented similar morphologies in all cases and they were homogeneous in their chemical composition.

Towards a Mathematical Model for Elastic Wave Propagation in Granular Materials

A theoretical model for the propagation of acoustic waves in dry granular media is presented within the framework of the nonlinear granular elasticity. An essential ingredient is the dependence of the elastic moduli on compression. For the purpose of illustration, we analyze the case of a time-harmonic plane wave propagation under isotropic compression. We derive explicit relations for the wave speed dependence with the confining pressure. The present approach provides an accurate description of acoustic wave propagation in granular packings and represents a powerful tool to interpret the results of current experiments.

Quantum Instability of Magnetized Stellar Objects

The equations of state for degenerate electron and neutron gases are studied in the presence of magnetic fields.After including quantum effects in the investigation of the structural properties of these systems,it is found that some hypermagnetized stars can be unstable according to the criterion of stability of pressures.Highly magnetized white dwarfs should collapse producing a supernova type Ia,while superstrong magnetized neutron stars cannot stand their own magnetic field and must implode,too.A comparison of our results with a set of the available observational data of some compact stars is also presented,and the agreement between this theory and observations is verified.

Temporal Evolution of Anodization Current of Porous Silicon Samples

Temporal evolution of the anodization current of porous silicon samples was studied by means of a model of resistances connected in series that represented the temporal changes of the substrate and of the interface between the substrate and the electrolyte during the porous sample formation process. The porous samples were obtained by means of photoelectrochemical etching of (100) n-type silicon wafers with different resistivity values, all in the range of 1 - 25 Wcm. The samples were formed at room temperature in an electrolytic bath composed by a mixture of hydrofluoric acid (48%) and ethanol having a composition ratio of 1:1 in volume under potentiostatic condition (10 V and 20 V) and an etching time of 2 minutes using back illumination provided by a laser beam with a wavelength of 808 nm.

Non-Linear Effects in Optical Systems by Lie Algebra and Symplectic Mapping

The use of signals of different frequencies determines the geometrical deviation with respect to the optical axes of a given beam. This angle can be determined by Sympletic Map (SM), a powerful and simple mathematical tool for the characterization and construction of images in Geometrical Optics. The Sympletic Map constitutes a Lie Group, with an algebra associated: the Lie Algebra. In general, the SM can be expressed as an infinite series, where each term corresponds to different contributions produced by the optical devices that constitute the optical system (lenses, apertures, bandwidth cutoff, etc.). The level of correction to be performed on the image to recover the original object is clear and controllable by SM. This formalism can be extended easily to physical optics to describe diffraction and interference phenomena.

Conditions for Singularity of Twist Grain Boundaries between Arbitrary 2-D Lattices

We have shown that the expression =2tan-1/ derived by Ranganathan to calculate the angles at which there exists a CSL for rotational interfaces in the cubic system can also be applied to general (oblique) two-dimensional lattices provided that the quantities 2 and /cos() are rational numbers, with =|b|/|a| and is the angle between the basis vectors a and b. In contrast with Ranganathan’s results, N;given by N=tan2() needs no longer be an integer. Specifically, vectors a and b must have the form a=(1,0);b=(r,tan) where r is an arbitrary rational number. We have also shown that the interfacial classification of cubic twist interfaces based on the recurrence properties of the O-lattice remains valid for arbitrary two-dimensional interfaces provided the above requirements on the lattice are met.

Bacterial microcosms obey Taylor’s law:effects of abiotic and biotic stress and genetics on mean and variance of population density

Introduction:According to the empirical regularity called Taylor’s law,the variance of population density in samples of populations is a power of the mean population density.The exponent is often between 1 and 2.Our experiments investigated how genetics,evolution,and environment shape Taylor’s law.Methods:Genetically different strains(wild type and hypermutator)of the bacterium Pseudomonas fluorescens evolved and were assayed under different environmental conditions(with and without antibiotic rifampicin and bacteriophage SBW25
2,separately and in combination).Results:Experimental treatments altered the exponent b,but not the power law form,of the relation between variance and mean population density.Bacterial populations treated only with rifampicin had a narrow range of mean population densities and exponent b=5.43.Populations exposed to rifampicin plus phage had b=1.51.In ancestral,control,and phage-exposed populations,mean abundance varied widely and b was not significantly different from 2.Evolutionary factors(mutation rate,selection)and ecological factors(abiotic,biotic)jointly influenced b.Conclusions:Taylor’s power law relationship accurately and robustly described variance as a function of mean population density,with overall exponent b=1.89.These and other experiments with different factors acting on bacterial population size support the relevance of models that predict‘universal’patterns of fluctuation scaling.

Infrared phononic nanoantennas:Localized surface phonon polaritons in SiC disks

The electromagnetic interaction of light with polar materials shows a sharp and well defined electromagnetic response in the infrared(IR)region that consists mainly of excitation of optical phonons.Similar to surface plasmons in the visible region,surface phonons can couple efficiently to infrared light in micron-sized antennas made of polar materials.We applied the boundary element method to calculating the infrared electromagnetic response of single SiC disks acting as effective infrared antennas as a function of different parameters such as disk size and thickness.We also analyzed the effect of locating a probing metallic tip near the SiC disk to scatter light in the proximity of the SiC disk,thereby obtaining new spectral peaks connected with localized modes between the tip and the SiC disk.We then further investigated their application in IR scanning probe microscopy.A near-field map of the phononic resonances enhances the understanding of the nature of the IR extinction peaks.

Dynamically generated N* resonances from the interaction of two mesons and a baryon

We have studied the ππN system and coupled channels by using of the Faddeev equations and two N＊ and one A states, all of them with jR =1/2＋, have been found in the formalism as dynamically generated states. In addition, signatures for a new N＊ resonance with JR = 1/2＋ are found around an energy of 1920 MeV in the three-body center of mass system.