Extreme Softening Research Articles

Field-induced boson insulating states in a 2D superconducting electron gas with strong spin–orbit scatterings

The phenomenon of field-induced superconductor-to-insulator transitions observed experimentally in electron-doped SrTiO3/LaAlO3 interfaces, analyzed recently by menas of 2D superconducting fluctuations theory, is revisited with new insights associating it with the appearnace at low temperatures of field-induced boson insulating states. Within the framework of the time-dependent Ginzburg–Landau functional approach, we pinpoint the origin of these states in field-induced extreme softening of fluctuation modes over a large region in momentum space, upon diminishing temperature, which drives Cooper-pair fluctuations to condense into mesoscopic puddles in real space. Dynamical quantum tunneling of Cooper-pair fluctuations out of these puddles, introduced within a phenomenological approach, which break into mobile single-electron states, contains the high-field resistance onset predicted by the exclusive boson theory.

Extended anharmonic collapse of phonon dispersions in SnS and SnSe

The lattice dynamics and high-temperature structural transition in SnS and SnSe are investigated via inelastic neutron scattering, high-resolution Raman spectroscopy and anharmonic first-principles simulations. We uncover a spectacular, extreme softening and reconstruction of an entire manifold of low-energy acoustic and optic branches across a structural transition, reflecting strong directionality in bonding strength and anharmonicity. Further, our results solve a prior controversy by revealing the soft-mode mechanism of the phase transition that impacts thermal transport and thermoelectric efficiency. Our simulations of anharmonic phonon renormalization go beyond low-order perturbation theory and capture these striking effects, showing that the large phonon shifts directly affect the thermal conductivity by altering both the phonon scattering phase space and the group velocities. These results provide a detailed microscopic understanding of phase stability and thermal transport in technologically important materials, providing further insights on ways to control phonon propagation in thermoelectrics, photovoltaics, and other materials requiring thermal management.

Multilayer friction stir plug welding: A novel solid-state method to repair cracks and voids in thick aluminum plates

In the present paper, a novel solid-state welding method is introduced and investigated which can be used as a repair method for thick aluminum plates. The process is named “multilayer friction stir plug welding”. This process was proposed to overcome issues regarding friction hydro-pillar processing of aluminum alloys including a high oxidation rate and extreme softening at elevated temperatures. In this process, a hole with a special cross-section is drilled to remove the crack or void. Then, the hole is filled using several plugs with the same composition of the parent material. These plugs are welded to the parent material and each other using a set of non-consumable rotary tools. Heat input is the most important parameter which should be controlled during the process. Therefore, tool rotational speed and dwell time were investigated as the main process parameters that dominate the heat input during the process. Tensile tests and optical microscopy were used to investigate the mechanical properties and microstructure of the welds. The fractographic analysis was also carried out to investigate the failure mode. The results indicate the fabrication of sound welds. Higher tool rotational speed and lower dwell time lead to a stronger joint. The highest achieved strength was 124MPa with rotational speed of 3000rpm and dwell time of 5s. The presence of dimples and micro-voids with some evidence of shear failure in fractographic analysis indicates the ductile failure.

Fast self-healing engineered by UV-curable polyurethane contained Diels-Alder structure

A series of UV-curable polyurethanes were made by copolymerization of isocyanate monomers with various diols (PLA1000/PEG2000/HPDMS). The structure of the resulting polyurethanes with DA-generated bonds was characterized by Fourier transform infrared spectroscopy (FTIR) and 1H NMR. In addition, the UV-curing behavior was studied by FTIR. Diels-Alder (DA) and retro-Diels-Alder (r-DA) reactions within cured films was monitored by differential scanning calorimeter (DSC) and dynamic mechanical analysis (DMA), which indicated that the cured film exhibited excellent thermal reversibility over at least three cycles. The resulting PU resins show different healing effect and PLAPU exhibited the most rapid thermal healing with the defect (a scratch with a width of 100 μm) completely healed within 100 s at 120 ˚C. Furthermore, PLAPU has high tensile strength (3MPa) and robust hardness (H) at the same time which is an advantageous feature for applications in which extreme softening or reverse gelation of a self-healing coating would be unacceptable.

Tension-compression asymmetry of additively manufactured Maraging steel

Additive Manufacturing (AM) or “3D printing” refers to processes used to synthesize an engineering part, where successive layers of material are formed under computer control to create a three-dimensional object. AM methods allow for production of parts with complex geometries and exceptional properties, which is of particular interest of automotive, aerospace, marine, and defence industries. Most of the parts produced for these applications are non-critical, however applications involving large deformations, such as impact, are of serious interest to industry. Unlike most conventional materials, AM metals do not have the same compressive and tensile behavior. This paper presents a preliminary study of experimental results of the tensile and compressive behaviour of additively manufactured Maraging Steel (MS1) using Digital Image Correlation (DIC) technique. Compression and tension samples in the form of cubes and rods were prepared using Direct Metal Laser Sintering (DMLS) technique through an EOS M290 machine. Compression data was collected using a DIC system to investigate the anisotropy of the strain field in the material. Results showed some material anisotropy due to build direction and dramatic improvement in elongation to failure in compression. Finally, a tension-compression asymmetry analysis of the additively manufactured MS1 revealed that the extreme softening in tension is not a result of void nucleation/growth in the material, but rather geometric softening due to necking.

Overexpression of the class D MADS-box gene Sl-AGL11 impacts fleshy tissue differentiation and structure in tomato fruits.

MADS-box transcription factors are key elements of the genetic networks controlling flower and fruit development. Among these, the class D clade gathers AGAMOUS-like genes which are involved in seed, ovule, and funiculus development. The tomato genome comprises two class D genes, Sl-AGL11 and Sl-MBP3, both displaying high expression levels in seeds and in central tissues of young fruits. The potential effects of Sl-AGL11 on fruit development were addressed through RNAi silencing and ectopic expression strategies. Sl-AGL11-down-regulated tomato lines failed to show obvious phenotypes except a slight reduction in seed size. In contrast, Sl-AGL11 overexpression triggered dramatic modifications of flower and fruit structure that include: the conversion of sepals into fleshy organs undergoing ethylene-dependent ripening, a placenta hypertrophy to the detriment of locular space, starch and sugar accumulation, and an extreme softening that occurs well before the onset of ripening. RNA-Seq transcriptomic profiling highlighted substantial metabolic reprogramming occurring in sepals and fruits, with major impacts on cell wall-related genes. While several Sl-AGL11-related phenotypes are reminiscent of class C MADS-box genes (TAG1 and TAGL1), the modifications observed on the placenta and cell wall and the Sl-AGL11 expression pattern suggest an action of this class D MADS-box factor on early fleshy fruit development.

Effect of Lesion Baseline Severity and Mineral Distribution on Remineralization and Progression of Human and Bovine Dentin Caries Lesions

The aims of this laboratory study were to compare the effects of lesion baseline severity, mineral distribution and substrate on remineralization and progression of caries lesions created in root dentin. Lesions were formed in dentin specimens prepared from human and bovine dentin using three protocols, each utilizing three demineralization periods to create lesions of different mineral distributions (subsurface, moderate softening, extreme softening) and severity within each lesion type. Lesions were then either remineralized or demineralized further and analyzed using transverse microradiography. At lesion baseline, no differences were found between human and bovine dentin for integrated mineral loss (ΔZ). Differences in mineral distribution between lesion types were apparent. Human dentin lesions were more prone to secondary demineralization (ΔΔZ) than bovine dentin lesions, although there were no differences in ΔL. Likewise, smaller lesions were more susceptible to secondary demineralization than larger ones. Subsurface lesions were more acid-resistant than moderately and extremely softened lesions. After remineralization, differences between human and bovine dentin lesions were not apparent for ΔΔZ although bovine dentin lesions showed greater reduction in lesion depth L. For lesion types, responsiveness to remineralization (ΔΔZ) was in the order extremely softened > moderately softened > subsurface. More demineralized lesions exhibited greater remineralization than shallower ones. In summary, some differences exist between human and bovine dentin and their relative responsiveness to de- and remineralization. These differences, however, were overshadowed by the effects of lesion baseline mineral distribution and severity. Thus, bovine dentin appears to be a suitable substitute for human dentin in mechanistic root caries studies.

On the mechanical modeling of the extreme softening/stiffening response of axially loaded tensegrity prisms

We study the geometrically nonlinear behavior of uniformly compressed tensegrity prisms through fully elastic and rigid-elastic models. The given models predict a variety of mechanical behaviors in the regime of large displacements, including an extreme stiffening-type response, already known in the literature, and a newly discovered, extreme softening behavior. The latter may lead to a snap buckling event producing an axial collapse of the structure. The switching from one mechanical regime to another depends on the aspect ratio of the structure, the magnitude of the applied prestress, and the material properties of the constituent elements. We discuss potential mechanical and acoustic applications of such behaviors, which are related to the design and manufacture of tensegrity lattices and innovative metamaterials.

Phonon-driven electron localization in delta-plutonium

Three remarkable properties of delta-Pu, accurately measured, lead to exceptionally strong constraints on ab-initio electronic structure models and suggest a new route must be taken to understand the localization of electronic states. The three properties that lead to this are the thermal expansion coefficient, the temperature dependence of the elastic moduli, and the absolute values of the elastic moduli. Both neutron diffraction and dilatometer measurements of the thermal expansion reveal a broad temperature range where thermal expansion is zero, and where small changes in Ga concentration can make thermal expansion vary from small and positive to small and negative. Measurements of the bulk modulus of these alloys over the same temperature range reveal extreme softening on warming. How can the bulk modulus, which is the curvature of the energy with respect to volume, change when volume does not? This is the central property that is not encompassed by present electronic structure models. We discuss theory and RUS measurements to understand better what must be true.

Extreme Phonon Softening in Laser-excited Bismuth – Towards an Inverse Peierls-transition

AbstractLarge amplitude coherent optical phonons have been investigated in laser-excited Bismuth by means of femtosecond time-resolved X-ray diffraction. For absorbed laser fluences above 2 mJ/cm2, the experimental data reveal an extreme softening of the excited A1g-mode down to frequencies of about 1 THz, only 1/3 of the unperturbed A1g-frequency. At even stronger excitation the measured diffraction signals no longer exhibit an oscillatory behavior presenting strong indication that upon intense laser-excitation the Peierls-distortion, which defines the equilibrium structure of Bismuth, can be transiently reversed.

High-temperature strength and toughness behaviors for reaction-bonded SiC ceramics below 1400 °C

High-temperature strength and toughness behaviors of reaction-bonded SiC ceramics with 12 and 26 vol.% of free Si were investigated. The flexural strength and fracture toughness started to increase at 1000 °C and reached a maximum at 1300° and 1330 °C before a sharp drop, respectively. The transition from transgranular to intergranular fracture is considered to lead to the slight increase of strength and toughness from room temperature to 1000 °C, while the plastic deformation of free Si contributes to the great increase above 1000 °C. However, too high a temperature will result in the extreme softening of free Si and therefore decrease strength and toughness.

Extreme softening of Vanderbilt pseudopotentials: General rules and case studies of first-row andd-electron elements

We demonstrate the general ability of an extreme softening of non-normconserving Vanderbilt pseudopotentials. We discuss the important case of first-row elements and elements containing core d electrons. Explicitly, such extremely soft pseudopotentials are constructed for carbon, hydrogen, nitrogen, and gallium, the d electrons of which have to be treated as valence electrons. Using a plane-wave basis with cutoff energies between 13 and 16 Ry we observe no loss of accuracy compared to very hard and accurate pseudopotentials working at cutoff energies between 60 and 110 Ry.

Neutron Star Structure and the Equation of State

The structure of neutron stars is considered from theoretical and observational perspectives. We demonstrate an important aspect of neutron star structure: the neutron star radius is primarily determined by the behavior of the pressure of matter in the vicinity of nuclear matter equilibrium density. In the event that extreme softening does not occur at these densities, the radius is virtually independent of the mass and is determined by the magnitude of the pressure. For equations of state with extreme softening or those that are self-bound, the radius is more sensitive to the mass. Our results show that in the absence of extreme softening, a measurement of the radius of a neutron star more accurate than about 1 km will usefully constrain the equation of state. We also show that the pressure near nuclear matter density is primarily a function of the density dependence of the nuclear symmetry energy, while the nuclear incompressibility and skewness parameters play secondary roles. In addition, we show that the moment of inertia and the binding energy of neutron stars, for a large class of equations of state, are nearly universal functions of the star's compactness. These features can be understood by considering two analytic, yet realistic, solutions of Einstein's equations, by, respectively, Buchdahl and Tolman. We deduce useful approximations for the fraction of the moment of inertia residing in the crust, which is a function of the stellar compactness and, in addition, the pressure at the core-crust interface.

Quantum phases of electron double layers: soft collective modes and finite-temperature phase transitions

The extreme softening of spin excitations in electron double layers is studied by resonant inelastic light scattering. At even-integer quantum Hall states we find evidence of three distinct configurations of spin. Transformations among these spin states appear as quantum phase transitions tuned by interlayer interactions and Zeeman energies. A broken-symmetry phase emerges when a long-wavelength spin excitation across the tunneling gap goes soft. Spectra measured in this phase offer remarkable evidence of finite-temperature phase transitions. Critical temperatures determined from spectra display significant dependence on magnetic field.

Cell wall properties of kiwifruit affected by low temperature breakdown

Low temperature breakdown (LTB) is a physiological disorder that can affect kiwifruit (Actinidia deliciosa cv Hayward) and some selections of Actinidia chinensis fruit after several months of cold storage. One of its symptoms manifests as the ‘grainy’ appearance of the outer pericarp, followed by water-soaking associated with extreme softening of the fruit. Observation by light microscopy and SEM suggested that the ‘grainy’ appearance of LTB-affected kiwifruit was associated with the presence of gas bubbles, occurring in some cells. Bulk porosity of the cell wall, determined using polyethylene glycol (PEG) of different molecular mass, decreased with increasing severity of the symptoms. Cell wall analysis revealed that the amount of cell wall material (CWM) was 30% higher in ‘grainy’ tissue than in unaffected tissue, and that galactosyl content in the CWM of outer pericarp tissue was 70% higher in affected compared to unaffected tissue. The same trends in LTB-affected tissue were observed in two selections of Actinidia chinensis. Since tissues were excised from fruit of the same firmness, differences reported here are related to the development of LTB.

The Ultrastructure of Wood from a Solubility Parameter Point of View

In later years scientists have taken increased interest in understanding wood ultrastructure, but with limited emphasis on close molecular relationships of its polymers This aspect is examined from the Hansen solubility parameter concept and from the requirement that contacts between wood polymers strive to reduce the free energy. Polymer segments with matching solubility parameters tend to locate e near each other. Wood polymers have larger solubility parameters than the test solvents used to characterize them, but the use of model compounds and group contribution methods yields consistent solubility parameters for the key wood components. Lignin and cellulose are not compatible. Cellulose regions and backbones of hemicelluloses are compatible to a degree, Some hemicellulose segments with hydroxylated side groups are expected to orient themselves towards cellulosic regions, whereas segments, e.g. with acetylated side groups. orient themselves towards lignin regions, in both cases by virtue of similarity of their local solubility parameters The diverse nature of the side groups is expected to determine the movements of water and monomer species through regions of similar solubility parameters in the fibre wall, Hemicellulose molecules may possibly he contained within cellulose regions with the backbones and hydroxylated side groups towards the cellulose and the acetylated side groups inwardly Hemicelluloses are generally likely to act as surfactants, binding the high energy cellulose regions to the lower energy lignin regions. Though wood cannot be dissolved, some strong' solvents may alter its ultrastructure. while others do not affect the structure in spite of extreme softening. Short introductory recapitulations are given of the general knowledge of ultrastructure and of the Hansen solubility parameter concept.

The wüstite enigma

High-pressure energy dispersive X-ray diffraction of wüstite has been obtained with three types of diamond cells; each one is designed to optimize a type of in situ study, namely single-crystal X-ray diffraction, deviatoric strain measurement, or simultaneous high- P-T experimentation. The results demonstrate that above 17 GPa at 300 K wüstite undergoes a displacive transition from B1 to a rhombohedral structure, and above 90 GPa at 600 K, a second transition to the NiAs structure. Many of the earlier inconsistencies concerning the structure and properties of wüstite at high pressures can be attributed to the extreme softening of the C 44 elastic modulus at pressures above 10 GPa.

Dynamics of 2-D alkali domains in graphite intercalation compounds

The two-dimensional diffusion of alkali atoms, the in-plane alkali-modes, and the critical softening of the layer shear elastic constant C 44 in stage 2 MC 24 (M=K, Rb, Cs) compounds can be understood in a unified manner within the frame of a structural model based on alkali-domains separated by discommensuration walls. New data yield evidence that with increasing temperature the diffusion of atoms close to the domain walls coexists with phonon-like excitations within the individual domains. As the domain walls become soft at higher temperatures the alkali-modes exhibit increased anharmonicity and a diffusivity which extends throughout the domains. In this model, the extreme softening of C 44 is due to the unlocking of domain walls above the critical temperature for discommensuration-domain formation.

Simulation of the cubic to orthorhombic phase transition in potassium cyanide

Constant pressure (NPH) ensemble molecular dynamics calculations have been used to study the cubic to orthorhombic phase transition that occurs upon cooling potassium cyanide at low pressures. A rigid ion model consisting of interionic electrostatic terms plus nonbonded atom–atom interactions has been found to yield an almost quantitative account of the transition. In particular, the extreme softening of the shear elastic constant C44 and the anomalous dispersion of the transverse acoustic phonons propagating along the crystal [100] direction in the cubic phase are well reproduced.

Approach to Melting in Ammonia as a Critical Transition

The molar volumes of ammonia solid I and solid II were measured from 0.5 to 14.0 kbar and 185 to 320 K. Over regions that extend 3 kbar and 20 K into the solid phases, variations in compressibility and thermal expansion can be described by power laws with exponents similar to those usually associated with critical transitions. It is suggested that breaking of hydrogen bonds may account for the extreme softening of solid ammonia.