273 Search Results

The rare gas solids exhibit systematic differences in crystal structure, phase transition conditions, bond strength, and other physical properties. The physical properties of heavy rare gas solids krypton and xenon are modified by the martensitic phase transition from face-centered cubic to hexagonal close packed structure over a broad pressure range. Crystal structure, strength, and plastic deformation of krypton and xenon have been investigated at 300 K using compression in the diamond-anvil cell with synchrotron angle-dispersive x-ray diffraction and complementary ruby fluorescence spectroscopy for Xe. Stacking faults indicative of the fcc–hcp phase transition are observed at pressures at and above 1.23 ± 0.05 andmore » 1.9 ± 0.6 GPa in Kr and Xe, respectively. The transition remains incomplete in both solids to pressures greater than 100 GPa. Strength determined from stress measurements in Pt and ruby standards at pressures up to 111 GPa and complemented by observations of strain and texture measurements obtained by x-ray diffraction in the radial geometry to 100 GPa indicates similar or higher strength than Ar at all conditions, with significant stiffening at 15–20 GPa. Radial diffraction data reveal the persistence of broad highly textured fcc diffraction lines to 101 GPa in Xe, suggesting that the axial measurements may underestimate the metastable persistence of the fcc phase due to biased sampling of hcp crystallites resulting from preferred crystallite orientation. Kr and Xe are compared with He, Ne, and Ar for a systematic understanding of physical properties and phase equilibria of rare gas solids.« less

The superconducting and structural properties of elemental strontium metal were investigated under pressures up to 60 GPa while maintaining cryogenic conditions during pressure application. Applying pressure at low temperatures reveals differences in superconducting and structural phases compared to previous reports obtained at room temperatures. Notably, the superconducting critical temperature exhibits a twofold increase under compression after cryogenic cooling within the pressure range of 35–42 GPa, compared to cryogenic cooling after room-temperature compression. Subsequently, the transition width becomes significantly sharper above 42 GPa. Low-temperature x-ray diffraction measurements under pressure reveal that this change corresponds to the Sr-III to Sr-IV transition, withmore » no evidence of any metastable structure. Furthermore, the monoclinic Sr-IV structure was observed to remain stable to much higher pressures—at least up to 60 GPa, without the appearance of the incommensurate Sr-V phase present at room temperature. As a result, this implies that thermal activation energy plays an important role in overcoming the presence of a kinetic barrier to the Sr-V phase at room temperature.« less

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 ≈ 10-16 erg s-1 cm-2. Covariances and cosmological inferences are obtained from a series of mock catalogs built upon high-resolution N-body simulations thatmore » match the footprint, number density, redshift distribution and observed clustering of the sample. We find that both samples have a correlation length of r 0 = 3.0 ± 0.2 h-1 Mpc. Within our fiducial cosmology these correspond to 3D number densities of ≈ 10-3 h3 Mpc-3 and, from our mock catalogs, biases of 1.7 and 2.0 at z = 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.« less

Cluster states in ${}^{13}\mathrm{N}$ are extremely difficult to measure due to the unavailability of ${}^9\mathrm{B}+\alpha$ elastic-scattering data. Using $\beta$ -delayed charged-particle spectroscopy of ${}^{13}\mathrm{O}$ , clustered states in ${}^{13}\mathrm{N}$ can be populated and measured in the $3\alpha +p$ decay channel. One-at-a-time implantation and decay of ${}^{13}\mathrm{O}$ was performedmore » with the Texas Active Target Time Projection Chamber. $149\beta 3\alpha p$ decay events were observed and the excitation function in ${}^{13}\mathrm{N}$ reconstructed. Four previously unknown $\alpha$ -decaying excited states were observed in ${}^{13}\mathrm{N}$ at an excitation energy of 11.3, 12.4, 13.1, and 13.7 MeV decaying via the $3\alpha +p$ channel. These states are seen to have a ${[}^9\mathrm{B}(\mathrm{g}.\mathrm{s})⨂\alpha /p+{}^{12}\mathrm{C}\left(0_2^{+}\right)], {[}^9\mathrm{B}\left({\frac{1}{2}}^{+}\right)⨂\alpha ], {[}^9\mathrm{B}\left({\frac{5}{2}}^{+}\right)⨂\alpha ]$ , and ${[}^9\mathrm{B}\left({\frac{5}{2}}^{+}\right)⨂\alpha ]$ structure, respectively. A previously seen state at 11.8 MeV was also determined to have a $[p+{}^{12}\mathrm{C}(\mathrm{g}.\mathrm{s}.)/p+{}^{12}\mathrm{C}\left(0_2^{+}\right)]$ structure. The overall magnitude of the clustering is not able to be extracted, however, due to the lack of a total width measurement. Clustered states in ${}^{13}\mathrm{N}$ (with unknown magnitude) seem to persist from the addition of a proton to the highly $\alpha$ -clustered ${}^{12}\mathrm{C}$ . Evidence of the ${\frac{1}{2}}^{+}$ state in ${}^9\mathrm{B}$ was also seen to be populated by decays from ${}^{13}\mathrm{N}^{★}$ . Published by the American Physical Society 2024« less

The $\beta$-delayed proton decay of ${}_{13}\mathrm{O}$ has previously been studied, but the direct observation of $\beta$-delayed $3\alpha p$ decay has not been reported. Rare $3\alpha p$ events from the decay of excited states in ${}_{13}{\mathrm{N}}^{\bullet }$ provide a sensitive probe of cluster configurations in ${}_{13}\mathrm{N}$. To measure the low-energy products following $\beta$-delayed $3\alpha pmore »$ decay, the Texas Active Target (TexAT) time projection chamber was employed using the one-at-a-time $\beta$-delayed charged-particle spectroscopy technique at the Cyclotron Institute, Texas A&M University. A total of $1.9\times {10}^5$ ${}_{13}\mathrm{O}$ implantations were made inside the TexAT time projection chamber. A total of 149 $3\alpha p$ events were observed, yielding a $\beta$-delayed $3\alpha p$ branching ratio of 0.078(6)%. Four previously unknown $\alpha$-decaying excited states were observed in ${}_{13}\mathrm{N}$ at 11.3, 12.4, 13.1, and 13.7 MeV decaying via the $3\alpha +p$ channel.« less

A direct cross-section measurement of the ¹⁴O(α, p)¹⁷F reaction is important to understand the light curves of x ray bursts. Here, the measurement will be performed using the Texas Active Target TPC version 2 (TexAT v2). The TexAT v2 aims at measuring lower energy protons from the reaction than the original TexAT. Newly developed silicon and CsI(Tl) detector arrays are added at the left, right and bottom of a modified field cage to increase its detection efficiency. This paper describes the overall specifications and two commissioning experiments performed at Texas A&M University.

We present a new study of jet interactions in the quark-gluon plasma created in high-energy heavy-ion collisions, using a multistage event generator within the jetscape framework. We focus on medium-induced modifications in the rate of inclusive jets and high transverse momentum (high-p_T) hadrons. Scattering-induced jet energy loss is calculated in two stages: a high virtuality stage based on the matter model, in which scattering of highly virtual partons modifies the vacuum radiation pattern, and a second stage at lower jet virtuality based on the lbt model, in which leading partons gain and lose virtuality by scattering and radiation. Coherence effectsmore » that reduce the medium-induced emission rate in the matter phase are also included. The trento model is used for initial conditions, and the (2 + 1)dimensional vishnu model is used for viscous hydrodynamic evolution. Jet interactions with the medium are modeled via 2-to-2 scattering with Debye screened potentials, in which the recoiling partons are tracked, hadronized, and included in the jet clustering. Holes left in the medium are also tracked and subtracted to conserve transverse momentum. Calculations of the nuclear modification factor (R_AA) for inclusive jets and high-p_T hadrons are compared to experimental measurements at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). Within this framework, we find that with one extra parameter which codifies the transition between stages of jet modification—along with the typical parameters such as the coupling in the medium, the start and stop criteria, etc.—we can describe these data at all energies for central and semicentral collisions without a rescaling of the jet transport coefficient qˆ.« less

AbstractHigh-pressure electrical resistivity measurements reveal that the mechanical deformation of ultra-hard WB2 during compression induces superconductivity above 50 GPa with a maximum superconducting critical temperature, Tcof 17 K at 91 GPa. Upon further compression up to 187 GPa, the Tcgradually 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 MgB2 (hP3, space group 191, prototype AlB2). Synchrotron x-ray diffraction measurements up to 145 GPa show that the ambient pressure hP12 structure (space group 194, prototype WB2) continues to persist to this pressure, consistent with themore » 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.« less

Little is known about the origin of the spectral diversity of asteroids and what it says about conditions in the protoplanetary disk. Here we show that samples returned from Cb­type asteroid Ryugu have Fe isotopic anomalies indistinguishable from Ivuna­type (CI) chondrites, which are distinct from all other carbonaceous chondrites. Iron isotopes, therefore, demonstrate that Ryugu and CI chondrites formed in a reservoir that was different from the source regions of other carbonaceous asteroids. Growth and migration of the giant planets destabilized nearby planetesimals and ejected some inwards to be implanted into the Main Belt. In this framework, most carbonaceous chondritesmore » may have originated from regions around the birthplaces of Jupiter and Saturn, while the distinct isotopic composition of CI chondrites and Ryugu may reflect their formation further away in the disk, owing their presence in the inner Solar System to excitation by Uranus and Neptune« less

The Hayabusa2 spacecraft has returned samples from the Cb-type asteroid (162173) Ryugu to Earth. Previous petrological and chemical analyses support a close link between Ryugu and CI chondrites that are presumed to be chemically the most primitive meteorites with a solar-like composition. However, Ryugu samples are highly enriched in Ca compared to typical CI chondrites. To identify the cause of this discrepancy, here we report stable Ca isotopic data (expressed as δ^44/40Ca_SRM915a) for returned Ryugu samples collected from two sites. We found that samples from both sites have similar δ^44/40Ca_SRM915a (0.58 ± 0.03 ‰ and 0.55 ± 0.08 ‰, 2more » s.d.) that fall within the range defined by CIs. This isotopic similarity suggests that the Ca budget of CIs and Ryugu samples is dominated by carbonates, and the variably higher Ca contents in Ryugu samples are due to the abundant carbonates. Precipitation of carbonates on Ryugu likely coincided with a major episode of aqueous activity dated to have occurred ~5 Myr after Solar System formation. Based on the pristine Ryugu samples, the average δ^44/40Ca_SRM915a of the Solar System is defined to be 0.57 ± 0.04 ‰ (2 s.d.).« less