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The first study of the effect of the initial microstructure on its evolution under hydrostatic compression before, during, and after the irreversible α → ω phase transformation and during pressure release in Zr using in situ x-ray diffraction is presented. Two samples were studied: one is plastically pre-deformed Zr with saturated hardness and the other is annealed. Phase transformation α → ω initiates at lower pressure for pre-deformed sample but above volume fraction of ω Zr c = 0.7, larger volume fraction is observed for the annealed sample. This implies that the general theory based on the proportionality between the athermal resistance to the transformation and the yield strength must be essentially advanced. The crystal domain size significantly reduces, and microstrain and dislocation density increase during loading for both α and ω phases in their single-phase regions. For the α phase, domain sizes are much smaller for prestrained Zr, while microstrain and dislocation densities are much higher. For the cold-rolled sample at 5.9 GPa (just before initiation of transformation), domain size in α Zr decreased to ∼ 45 nm and dislocation density increased to 1.1 × 1015 lines/m2 , values similar to those after severe plastic deformation under high pressure. Despite the generally accepted concept that hydrostatic pressure does not cause plastic straining, it does and is estimated. During transformation, the first rule was found: The average domain size, microstrain, and dislocation density in ω Zr for c < 0.8 are functions of the volume fraction of ω Zr only, which are independent of the plastic strain tensor prior to transformation and pressure. The microstructure is not inherited during phase transformation. Surprisingly, for the annealed sample, the final dislocation density and average microstrain after pressure release in the ω phase are larger than for the severely pre-deformed sample. The significant evolution of the microstructure and its effect on phase transformation demonstrates that their postmortem evaluation does not represent the actual conditions during loading. A simple model for the initiation of the phase transformation involving microstrain is suggested. The results suggest that an extended experimental basis is required for the predictive models for the combined pressure-induced phase transformations and microstructure evolutions.more » « lessFree, publicly-accessible full text available February 22, 2025
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Abstract Lightning‐induced volcanic spherules (LIVS) are glasses produced by the rapid melting and solidification of molten volcanic ash grains. High temperatures generated by lightning will alter the physical and chemical properties of minerals exposed to the discharge. Laboratory experiments reveal that LIVS glass composition varies depending on the starting material, exhibiting heterogeneous compositional features common in other glasses created by cloud‐to‐ground lightning, nuclear explosions, and high velocity impact events. This study uses scanning electron microscopy, energy dispersive spectroscopy, and Raman spectroscopy to investigate the structure and Raman signatures of lightning‐induced glass spherules manufactured from five igneous minerals (<32 μm powders of albite, labradorite, augite, hornblende, and magnetite). LIVS were created through high‐current impulse experiments using peak currents of 25 and 40 kA. Analysis of the post‐experimental albite, labradorite, augite, and hornblende LIVS reveal primarily homogeneous silicate or aluminosilicate glasses with limited heterogeneity. Their amorphous Raman spectra are comparable to rhyolitic and mafic natural glasses along with Na2O‐K2O‐Al2O3‐SiO2, CaCO3‐Al2O3‐SiO2,and CaO‐MgO‐SiO2synthetic glass networks. A few of the augite and hornblende LIVS spectra exhibit premelting effects, which occur below the melting point and represent the onset of cation disordering in phases that remain crystalline. Magnetite samples produced crystal‐rich, glass‐poor LIVS characterized by the growth of dendritic microcrystals and crystalline spectra that also contain a few bands alluding to the composition of their silicate–phosphate glass matrix. By understanding these chemical changes induced by lightning, we can extract information from other types of glasses produced during high temperature, short duration events.
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Severe plastic deformations under high pressure are used to produce nanostructured materials but were studied ex-situ. We introduce rough diamond anvils to reach maximum friction equal to yield strength in shear and perform the first in-situ study of the evolution of the pressure-dependent yield strength and nanostructural parameters for severely pre-deformed Zr. ω-Zr behaves like perfectly plastic, isotropic, and strain-path-independent. This is related to reaching steady values of the crystallite size and dislocation density, which are pressure-, strain- and strain-path-independent. However, steady states for α-Zr obtained with smooth and rough anvils are different, which causes major challenge in plasticity theory.more » « less
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Abstract We measure the clustering of Lyman Alpha Emitting galaxies (LAEs) selected from the One-hundred-square-degree DECam Imaging in Narrowbands (ODIN) survey, with spectroscopic follow-up from Dark Energy Spectroscopic Instrument (DESI). We use DESI spectroscopy to optimize our selection and to constrain the interloper fraction and redshift distribution of our narrow-band selected sources. We select samples of 4000 LAEs at
z = 2.45 and 3.1 in 9 sq.deg. centered on the COSMOS field with median Lyα fluxes of ≈ 10-16erg s-1cm-2. Covariances and cosmological inferences are obtained from a series of mock catalogs built upon high-resolution N-body simulations that match the footprint, number density, redshift distribution and observed clustering of the sample. We find that both samples have a correlation length ofr 0= 3.0 ± 0.2 h-1Mpc. Within our fiducial cosmology these correspond to 3D number densities of ≈ 10-3h3Mpc-3and, from our mock catalogs, biases of 1.7 and 2.0 atz = 2.45 and 3.1, respectively. We discuss the implications of these measurements for the use of LAEs as large-scale structure tracers for high-redshift cosmology.Free, publicly-accessible full text available August 1, 2025 -
Abstract On seasonal time scales, vapor pressure deficit (VPD) is a known predictor of burned area in the southwestern United States (“the Southwest”). VPD increases with atmospheric warming due to the exponential relationship between temperature and saturation vapor pressure. Another control on VPD is specific humidity, such that increases in specific humidity can counteract temperature-driven increases in VPD. Unexpectedly, despite the increased capacity of a warmer atmosphere to hold water vapor, near-surface specific humidity decreased from 1970 to 2019 in much of the Southwest, particularly in spring, summer, and fall. Here, we identify declining near-surface humidity from 1970 to 2019 in the southwestern United States with both reanalysis and in situ station data. Focusing on the interior Southwest in the months preceding the summer forest fire season, we explain the decline in terms of changes in atmospheric circulation and moisture fluxes between the surface and the atmosphere. We find that an early spring decline in precipitation in the interior region induced a decline in soil moisture and evapotranspiration, drying the lower troposphere in summer. This prior season precipitation decline is in turn related to a trend toward a Northern Hemisphere stationary wave pattern. Finally, using fixed humidity scenarios and the observed exponential relationship between VPD and burned forest area, we estimate that with no increase in temperature at all, the humidity decline alone would still lead to nearly one-quarter of the observed VPD-induced increase in burned area over 1984–2019.
Significance Statement Burned forest area has increased significantly in the southwestern United States in recent decades, driven in part by an increase in atmospheric aridity [vapor pressure deficit (VPD)]. Increases in VPD can be caused by a combination of increasing temperature and decreasing specific humidity. As the atmosphere warms with climate change, its capacity to hold moisture increases. Despite this, there is a decrease in near-surface air humidity in the interior southwestern United States over 1970–2019, which during the summer is likely caused by a decline in early spring precipitation leading to limited soil moisture and evaporation in spring and summer. We estimate that this declining humidity alone, without an increase in temperature, would cause about one-quarter of the VPD-induced increase in burned forest area in this region over 1984–2019.
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Abstract High-pressure electrical resistivity measurements reveal that the mechanical deformation of ultra-hard WB 2 during compression induces superconductivity above 50 GPa with a maximum superconducting critical temperature, T c of 17 K at 91 GPa. Upon further compression up to 187 GPa, the T c gradually decreases. Theoretical calculations show that electron-phonon mediated superconductivity originates from the formation of metastable stacking faults and twin boundaries that exhibit a local structure resembling MgB 2 (hP3, space group 191, prototype AlB 2 ). Synchrotron x-ray diffraction measurements up to 145 GPa show that the ambient pressure hP12 structure (space group 194, prototype WB 2 ) continues to persist to this pressure, consistent with the formation of the planar defects above 50 GPa. The abrupt appearance of superconductivity under pressure does not coincide with a structural transition but instead with the formation and percolation of mechanically-induced stacking faults and twin boundaries. The results identify an alternate route for designing superconducting materials.more » « less
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Abstract The physical properties of minerals are modified by the high temperatures of volcanic lightning during explosive eruptions. Alteration involves rapid heating and volatilization, melting, and fusion of ash grains within the discharge channel, followed by rapid quenching into new glassy textures. High current impulse experiments reveal that lightning alters not only the morphology and mineralogy of volcanic ash but also its magnetic properties. We investigate lightning‐induced magnetic changes in five igneous minerals (<32 μm powders of albite, labradorite, augite, hornblende, and magnetite) by comparing hysteresis parameters before and after impulse experiments conducted at peak currents of 25 and 40 kA. Both the paramagnetic and ferrimagnetic behaviors of the samples were altered, which we interpret as a superposition of two processes. (a) Rapid melting allows iron contained within inclusions of Fe‐oxides and Fe‐bearing silicates to diffuse into the newly formed melt, thereby increasing the paramagnetism of the resulting glass. (b) Nucleation and growth of magnetite from the newly formed melt increases the ferrimagnetic behavior of the post‐experimental samples. Nominally non‐Fe‐bearing silicates like albite and labradorite have significantly increased paramagnetism and ferrimagnetism. Fe‐bearing silicates like augite and hornblende contain higher concentrations of ferrimagnetic inclusions, from which Fe diffuses into the newly formed melt, thereby increasing paramagnetism while decreasing ferrimagnetism. Experiments conducted on magnetite produced new magnetite crystals with dendritic habits. Although specific to volcanic ash, these results provide important insights into the magnetism of other materials affected by lightning on Earth, the Moon, and throughout the solar system.