Magnetic and Magneto-Caloric Properties of the Amorphous Fe92−xZr8Bx Ribbons

Magnetic and magnetocaloric properties of the amorphous Fe_92−xZr₈B_x ribbons were studied in this work. Fully amorphous Fe₈₉Zr₈B₃, Fe₈₈Zr₈B₄, and Fe₈₇Zr₈B₅ ribbons were fabricated. The Curie temperature (T_c), saturation magnetization (M_s), and the maximum entropy change with the variation of a magnetic field (−ΔS_m^peak) of the glassy ribbons were significantly improved by the boron addition. The mechanism for the enhanced T_c and −ΔS_m^peak by boron addition was studied.     

Re-Examination of the Microstructural Evolution in Undercooled Co-18.5at.%B Eutectic Alloy

The undercooling (∆T) dependencies of the solidification pathways, microstructural evolution, and recalescence behaviors of undercooled Co-18.5at.%B eutectic alloys were systematically explored. Up to four possible solidification pathways were identified: (1) A lamellar eutectic structure consisting of the FCC–Co and Co₃B phase forms, with extremely low ΔT; (2) The FCC–Co phase primarily forms, followed by the eutectic growth of the FCC–Co and Co₂B phases when ΔT < 100 K; (3) As the ΔT increases further, the FCC–Co phase primarily forms, followed by the metastable Co₂₃B₆ phase with the trace of an FCC–Co and Co₂₃B₆ eutectic; (4) When the ΔT increases to 277 K, the FCC–Co phase primarily forms, followed by an FCC–Co and Co₃B eutectic, which is similar in composition to the microstructure formed with low ΔT. The mechanisms of the microstructural evolution and the phase selection are interpreted on the basis of the composition segregation, the skewed coupled zone, the strain-induced transformation, and the solute trapping. Moreover, the prenucleation of the primary FCC–Co phase was also detected from an analysis of the different recalescence behaviors. The present work not only enriches our knowledge about the phase selection behavior in the undercooled Co–B system, but also provides us with guidance for controlling the microstructures and properties practically.     

Independent photocycles of the spectrally distinct forms of bacteriorhodopsin

Time-resolved, flash-induced difference absorbance spectra (300-700 nm) at pH 10.5 and 5°C for the bacteriorhodopsin photocycle fast and slow decaying forms of the M intermediate (M^f and M^s, respectively) and R intermediate are reported. The main distinguishing features are as follows: For M^f, ΔA_max = 412 nm, a shoulder at 436 nm, no absorbance change at 350 nm; ΔA_min = 565 nm; ΔA₄₁₂/ΔA₅₆₅ = 0.85. For M^s, ΔA_max = 412 nm, a shoulder at 386 nm; ΔA_min = 575 nm; ΔA₄₁₂/ΔA₅₇₅ = 0.6. For R, ΔA_max = 336 and 350 nm (double peak), smaller peaks at 386 and 412 nm; ΔA_min = 585 nm; ΔA₃₅₀/ΔA₅₈₅ = 0.2. The different difference spectra for M^f and M^s provide direct evidence that these species, initially identified by their kinetics, are physically distinct. With fast transient absorption spectroscopy, it was shown that R may form very fast, perhaps faster than the L intermediate decays. On the basis of the different bleaching peaks for M^f and M^s, we propose that M^f and M^s are in independent photocycles formed from slightly different forms of bacteriorhodopsin. R may also be in a different photocycle. The different forms of bacteriorhodopsin are probably in dynamic equilibrium with their ratios, controlled by pH and temperature.     

Structure,Magnetocaloric Effect and Critical Behavior of the Fe60Co12Gd4Mo3B21 Amorphous Ribbons

The aim of the paper was to study the structure, magnetic properties and critical behavior of the Fe₆₀Co₁₂Gd₄Mo₃B₂₁ alloy. The X-ray diffractometry and the Mössbauer spectroscopy studies confirmed amorphous structure. The analysis of temperature evolution of the exponent n (ΔS_M = C·(B_max)ⁿ) and the Arrott plots showed the second order phase transition in investigated material. The analysis of critical behavior was carried out in order to reveal the critical exponents and precise T_C value. The ascertained critical exponents were used to determine the theoretical value of the exponent n, which corresponded well with experimental results.     

Impact of Annealing on Magnetic Properties and Structure of Co40Fe40W20 Thin Films on Si(100) Substrate

Co₄₀Fe₄₀W₂₀ monolayers of different thicknesses were deposited on Si(100) substrates by DC magnetron sputtering, with Co₄₀Fe₄₀W₂₀ thicknesses from 10 to 50 nm. Co₄₀Fe₄₀W₂₀ thin films were annealed at three conditions (as-deposited, 250 °C, and 350 °C) for 1 h. The structural and magnetic properties were then examined by X-ray diffraction (XRD), low-frequency alternative-current magnetic susceptibility (χ_ac), and an alternating-gradient magnetometer (AGM). The XRD results showed that the CoFe (110) peak was located at 2θ = 44.6°, but the metal oxide peaks appeared at 2θ = 38.3, 47.6, 54.5, and 56.3°, corresponding to Fe₂O₃ (320), WO₃ (002), Co₂O₃ (422), and Co₂O₃ (511), respectively. The saturation magnetization (Ms) was calculated from the slope of the magnetization (M) versus the CoFeW thickness. The Ms values calculated in this manner were 648, 876, 874, and 801 emu/cm³ at the as-deposited condition and post-annealing conditions at 250, 350, and 400 °C, respectively. The maximum M_S was about 874 emu/cm³ at a thickness of 50 nm following annealing at 350 °C. It indicated that the M_S and the χ_ac values rose as the CoFeW thin films’ thickness increased. Owing to the thermal disturbance, the M_S and χ_ac values of CoFeW thin films after annealing at 350 °C were comparatively higher than at other annealing temperatures. More importantly, the Co₄₀Fe₄₀W₂₀ films exhibited a good thermal stability. Therefore, replacing the magnetic layer with a CoFeW film improves thermal stability and is beneficial for electrode and strain gauge applications.     

On the attribution and additivity of binding energies

It can be useful to describe the Gibbs free energy changes for the binding to a protein of a molecule, A—B, and of its component parts, A and B, in terms of the “intrinsic binding energies” of A and B, ΔG_Aⁱ and ΔG_Bⁱ, and a “connection Gibbs energy,” ΔG^s that is derived largely from changes in translational and rotational entropy. This empirical approach avoids the difficult or insoluble problem of interpreting observed ΔH and TΔS values for aqueous solutions. The ΔGⁱ and ΔG^s terms can be large for binding to enzymes and other proteins.     

The Effect of Cobalt-Sublattice Disorder on Spin Polarisation in Co2FexMn1?xSi Heusler Alloys

In this work we present a theoretical study of the effect of disorder on spin polarisation at the Fermi level, and the disorder formation energies for Co₂Fe_xMn_1−xSi (CFMS) alloys. The electronic calculations are based on density functional theory with a Hubbard U term. Chemical disorders studied consist of swapping Co with Fe/Mn and Co with Si; in all cases we found these are detrimental for spin polarisation, i.e., the spin polarisation not only decreases in magnitude, but also can change sign depending on the particular disorder. Formation energy calculation shows that Co–Si disorder has higher energies of formation in CFMS compared to Co₂MnSi and Co₂FeSi, with maximum values occurring for x in the range 0.5–0.75. Cross-sectional structural studies of reference Co₂MnSi, Co₂Fe_0.5Mn_0.5Si, and Co₂FeSi by Z-contrast scanning transmission electron microscopy are in qualitative agreement with total energy calculations of the disordered structures.     

The Role of Anisotropy in Distinguishing Domination of Néel or Brownian Relaxation Contribution to Magnetic Inductive Heating: Orientations for Biomedical Applications

Magnetic inductive heating (MIH) has been a topic of great interest because of its potential applications, especially in biomedicine. In this paper, the parameters characteristic for magnetic inductive heating power including maximum specific loss power (SLP_max), optimal nanoparticle diameter (D_c) and its width (ΔD_c) are considered as being dependent on magnetic nanoparticle anisotropy (K). The calculated results suggest 3 different Néel-domination (N), overlapped Néel/Brownian (NB), and Brownian-domination (B) regions. The transition from NB- to B-region changes abruptly around critical anisotropy K_c. For magnetic nanoparticles with low K (K < K_c), the feature of SLP peaks is determined by a high value of D_c and small ΔD_c while those of the high K (K > K_c) are opposite. The decreases of the SLP_max when increasing polydispersity and viscosity are characterized by different rates of d(SLP_max)/dσ and d(SLP_max)/dη depending on each domination region. The critical anisotropy K_c varies with the frequency of an alternating magnetic field. A possibility to improve heating power via increasing anisotropy is analyzed and deduced for Fe₃O₄ magnetic nanoparticles. For MIH application, the monodispersity requirement for magnetic nanoparticles in the B-region is less stringent, while materials in the N- and/or NB-regions are much more favorable in high viscous media. Experimental results on viscosity dependence of SLP for CoFe₂O₄ and MnFe₂O₄ ferrofluids are in good agreement with the calculations. These results indicated that magnetic nanoparticles in the N- and/or NB-regions are in general better for application in elevated viscosity media.     

Comparison of J Integral Assessments for Cracked Plates and Pipes

The purpose of this article is to compare two predictive methods of J integral assessments for center-cracked plates, single-edge cracked plates and double-edge cracked plates produced from X52 and X70 steels, and a longitudinally cracked pipe produced from X70 steel. The two methods examined are: the GSM method and the J_s procedure of the French RCC-MR construction code, designated here as the FC method. The accuracy of J integral predictions by these methods is visualized by comparing the results obtained with the “reference” values calculated by the EPRI method. The main results showed that both methods yielded similar J integral values, although in most cases, the GSM predictions were slightly more conservative than the FC predictions. In comparison with the “reference” values of the J integral, both methods provided conservative results for most crack configurations, although the estimates for cracks of a relative length smaller than 1/8 were not found to be so conservative. The prediction of burst pressures for external longitudinal semielliptical part-through cracks in X70 steel pipe showed that the magnitudes of predicted burst pressures came very close to each other, and were conservative compared to FEM (finite element method) calculations and experimentally determined burst pressures.     

Study on the Magnetocaloric Effect of Room Temperature Magnetic Refrigerant Material La0.5Pr0.5(Fe1−xCox)11.4Si1.6 and the Effect Arising from Co Doping on Its Curie Temperature

The arc-melting method was adopted to prepare the compound La_0.5Pr_0.5(Fe_1−xCo_x)_11.4Si_1.6 (x = 0, 0.02, 0.04, 0.06, 0.08), and the magnetocaloric effect of the compound was investigated. As indicated by the powder X-ray diffraction (XRD) results, after receiving 7-day high temperature annealing at 1373 K, all the compounds formed a single-phase cubic NaZn₁₃ crystal structure. As indicated by the magnetic measurement, the most significant magnetic entropy change |∆S_M(T)| of the sample decreased from 28.92 J/kg·K to 4.22 J/kg·K with the increase of the Co content under the 0–1.5 T magnetic field, while the Curie temperature T_C increased from 185 K to the room temperature 296 K, which indicated that this series of alloys are the room temperature magnetic refrigerant material with practical value. By using the ferromagnetic Curie temperature theory and analyzing the effect of Co doping on the exchange integral of these alloys, the mechanism that the Curie temperature of La_0.5Pr_0.5(Fe_1−xCo_x)_11.4Si_1.6 and La_0.8Ce_0.2(Fe_1−xCo_x)_11.4Si_1.6 increased with the increase in the Co content was reasonably explained. Accordingly, this paper can provide a theoretical reference for subsequent studies.     

Computing protein stabilities from their chain lengths

New amino acid sequences of proteins are being learned at a rapid rate, thanks to modern genomics. The native structures and functions of those proteins can often be inferred using bioinformatics methods. We show here that it is also possible to infer the stabilities and thermal folding properties of proteins, given only simple genomics information: the chain length and the numbers of charged side chains. In particular, our model predicts ΔH(T), ΔS(T), ΔC_p, and ΔF(T) —the folding enthalpy, entropy, heat capacity, and free energy—as functions of temperature T; the denaturant m values in guanidine and urea; the pH-temperature-salt phase diagrams, and the energy of confinement F(s) of the protein inside a cavity of radius s. All combinations of these phase equilibria can also then be computed from that information. As one illustration, we compute the pH and salt conditions that would denature a protein inside a small confined cavity. Because the model is analytical, it is computationally efficient enough that it could be used to automatically annotate whole proteomes with protein stability information.     

Compositional Dependence of Curie Temperature and Magnetic Entropy Change in the Amorphous Tb–Co Ribbons

The Curie temperature (T_c) and magnetic entropy change (−ΔS_m), and their relationship to the alloy composition of Tb–Co metallic glasses, were studied systematically in this paper. It was found that, in contrast to the situation in amorphous Gd–Co ribbons, the dependence of Tc on Tb content and the maximum −ΔS_m vs. T_c -2/3 plots in Tb–Co binary amorphous alloys do not follow a linear relationship, both of which are supposed to be closely related to the non-linear compositional dependence of Tb–Co interaction due to the existence of orbital momentum in Tb.     

Quantum-Chemical Consideration of Al2M2 Tetranuclear Metal Clusters (M–3d-Element): Molecular/Electronic Structures and Thermodynamics

Quantum-chemical calculation of most important parameters of molecular and electronic structures of tetra-nuclear (pd) metal clusters having Al₂M₂ composition, where M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn (bond lengths, bond and torsion angles), and HOMO and LUMO of these compounds by means of DFT OPBE/QZVP method, have been carried out. It has been found that, for each of these metal clusters, an existence of rather large amount of structural isomers different substantially in their total energy, occurs. It has been noticed that molecular structures of metal clusters of the given type differ significantly between them in terms of geometric parameters, as well as in geometric form, wherein the most stable modifications of metal clusters considered are similar between themselves in geometric form. In addition, the standard thermodynamic parameters of formation of metal clusters considered here, and namely standard enthalpy Δ_fH⁰(298 K), entropy S_f⁰(298 K), and Gibbs’ energy Δ_fG⁰(298 K) of formation for these metal clusters, were calculated.     

A First-Principles Study of the Cu-Containing β″ Precipitates in Al-Mg-Si-Cu Alloy

The nanostructured β″ precipitates are critical for the strength of Al-Mg-Si-(Cu) aluminum alloys. However, there are still controversial reports about the composition of Cu-containing β″ phases. In this work, first-principles calculations based on density functional theory were used to investigate the composition, mechanical properties, and electronic structure of Cu-containing β″ phases. The results predict that the Cu-containing β″ precipitates with a stoichiometry of Mg_4+xAl_2−xCuSi₄ (x = 0, 1) are energetically favorable. As the concentration of Cu atoms increases, Cu-containing β″ phases with different compositions will appear, such as Mg₄AlCu₂Si₄ and Mg₄Cu₃Si₄. The replacement order of Cu atoms in β″ phases can be summarized as one Si3/Al site → two Si3/Al sites → two Si3/Al sites and one Mg1 site. The calculated elastic constants of the considered β″ phases suggest that they are all mechanically stable, and all β″ phases are ductile. When Cu atoms replace Al atoms at Si3/Al sites in β″ phases, the values of bulk modulus (B), shear modulus (G), and Young’s modulus (E) all increase. The calculation of the phonon spectrum shows that Mg_4+xAl_2−xCuSi₄ (x = 0, 1) are also dynamically stable. The electronic structure analysis shows that the bond between the Si atom and the Cu atom has a covalent like property. The incorporation of the Cu atom enhances the electron interaction between the Mg2 and the Si3 atom so that the Mg2 atom also joins the Si network, which may be one of the reasons why Cu atoms increase the structure stability of the β″ phases.     

Dissection of the high rate constant for the binding of a ribotoxin to the ribosome

Restrictocin belongs to a family of site-specific ribonucleases that kill cells by inactivating the ribosome. The restrictocin–ribosome binding rate constant was observed to exceed 10¹⁰ M⁻¹ s⁻¹. We have developed a transient-complex theory to model the binding rates of protein–protein and protein–RNA complexes. The theory predicts the rate constant as k_a = k_a0 exp(−ΔG_el*/k_BT), where k_a0 is the basal rate constant for reaching the transient complex, located at the outer boundary of the bound state, by random diffusion, and ΔG_el* is the average electrostatic interaction free energy of the transient complex. Here, we applied the transient-complex theory to dissect the high restrictocin–ribosome binding rate constant. We found that the binding rate of restrictocin to the isolated sarcin/ricin loop is electrostatically enhanced by ≈300-fold, similar to results found in other protein–protein and protein–RNA complexes. The ribosome provides an additional 10,000-fold rate enhancement because of two synergistic mechanisms afforded by the distal regions of the ribosome. First, they provide additional electrostatic attraction with restrictocin. Second, they reposition the transient complex into a region where local electrostatic interactions of restrictocin with the sarcin/ricin loop are particularly favorable. Our calculations rationalize a host of experimental observations and identify a strategy for designing proteins that bind their targets with high speed.     

Investigation of the composition and formation constant of molecular complexes

It has been the purpose of the present paper to investigate and explore the conditions under which the linear relation between Δ/C_D⁰ and Δ in the Hanna-Ashbaugh-Foster-Fyfe equation for the evaluation of equilibrium constants holds, (C_D⁰ is initial concentration of a donor and Δ is the observed chemical shift relative to the chemical shift of the acceptor) to obtain the equation representing the exact linear relation between Δ/C_D⁰ and Δ, when the linear relation between Δ/C_D⁰ and Δ holds, and to discuss how to use the Job method in nuclear magnetic resonance measurements to determine the stoichiometry of molecular complexes. We have found that the conventional belief that C_D⁰ should always be chosen to be much greater than C_A⁰ (initial concentration of acceptor) is not necessarily always true and the exact linear relation between Δ/C_D⁰ and Δ is represented by the equation Δ/C_D⁰ = K₁Δ₀/(1 + K₁C_A⁰) - K₁Δ/(1 + K₁C_A⁰)², where K₁ is the formation constant of the complex. It is shown that in the Job method of nuclear magnetic resonance measurements one has to plot ΔC_A⁰ against the mole fraction, and the mole fraction at the maximum should give us the composition of the complex. Theoretical results have been verified experimentally on the weak interaction between naphthalene and methyl iodide.     

Structural Stability,Electronic, Mechanical,Phonon, and Thermodynamic Properties of the M2GaC (M = Zr,Hf) MAX Phase: An ab Initio Calculation

The novel ternary carbides and nitrides, known as MAX phase materials with remarkable combined metallic and ceramic properties, offer various engineering and technological applications. Using ab initio calculations based on generalized gradient approximation (GGA), local density approximation (LDA), and the quasiharmonic Debye model; the electronic, structural, elastic, mechanical, and thermodynamic properties of the M₂GaC (M = Zr, Hf) MAX phase were investigated. The optimized lattice parameters give the first reference to the upcoming theocratical and experimental studies, while the calculated elastic constants are in excellent agreement with the available data. Moreover, obtained elastic constants revealed that both the Zr₂GaC and Hf₂GaC MAX phases are brittle. The band structure and density of states analysis showed that these MAX phases are electrical conductors, having strong directional bonding between M-C (M = Zr, Hf) atoms due to M-d and C-p hybridization. Formation and cohesive energies, and phonon calculations showed that Zr₂GaC and Hf₂GaC MAX phases’ compounds are thermodynamically and dynamically stable and can be synthesized experimentally. Finally, the effect of temperature and pressure on volume, heat capacity, Debye temperature, Grüneisen parameter, and thermal expansion coefficient of M₂GaC (M = Zr, Hf) are evaluated using the quasiharmonic Debye model from the nonequilibrium Gibbs function in the temperature and pressure range 0–1600 K and 0–50 GPa respectively.     

Postperovskite phase equilibria in the MgSiO3–Al2O3 system

We investigate high-P,T phase equilibria of the MgSiO₃–Al₂O₃ system by means of the density functional ab initio computation methods with multiconfiguration sampling. Being different from earlier studies based on the static substitution properties with no consideration of Rh₂O₃(II) phase, present calculations demonstrate that (i) dissolving Al₂O₃ tends to decrease the postperovskite transition pressure of MgSiO₃ but the effect is not significant (≈-0.2 GPa/mol% Al₂O₃); (ii) Al₂O₃ produces the narrow perovskite+postperovskite coexisting P,T area (≈1 GPa) for the pyrolitic concentration (x_Al2O3 ≈6 mol%), which is sufficiently responsible to the deep-mantle D″ seismic discontinuity; (iii) the transition would be smeared (≈4 GPa) for the basaltic Al-rich composition (x_Al2O3 ≈20 mol%), which is still seismically visible unless iron has significant effects; and last (iv) the perovskite structure spontaneously changes to the Rh₂O₃(II) with increasing the Al concentration involving small displacements of the Mg-site cations.     

Reinforcing Increase of ΔTc in MgB2 Smart Meta-Superconductors by Adjusting the Concentration of Inhomogeneous Phases

Incorporating with inhomogeneous phases with high electroluminescence (EL) intensity to prepare smart meta-superconductors (SMSCs) is an effective method for increasing the superconducting transition temperature (T_c) and has been confirmed in both MgB₂ and Bi(Pb)SrCaCuO systems. However, the increase of ΔT_c (ΔT_c = T_c ‒ T_cpure) has been quite small because of the low optimal concentrations of inhomogeneous phases. In this work, three kinds of MgB₂ raw materials, namely, ^aMgB₂, ^bMgB₂, and ^cMgB₂, were prepared with particle sizes decreasing in order. Inhomogeneous phases, Y₂O₃:Eu³⁺ and Y₂O₃:Eu³⁺/Ag, were also prepared and doped into MgB₂ to study the influence of doping concentration on the ΔT_c of MgB₂ with different particle sizes. Results show that reducing the MgB₂ particle size increases the optimal doping concentration of inhomogeneous phases, thereby increasing ΔT_c. The optimal doping concentrations for ^aMgB₂, ^bMgB₂, and ^cMgB₂ are 0.5%, 0.8%, and 1.2%, respectively. The corresponding ΔT_c values are 0.4, 0.9, and 1.2 K, respectively. This work open a new approach to reinforcing increase of ΔT_c in MgB₂ SMSCs.