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Effect of pressure on heterocyclic compounds: Pyrimidine and s-triazine
We have examined the high-pressure behaviors of six-membered heterocyclic compounds of pyrimidine and s-triazine up to 26 and 26.5 GPa, respectively. Pyrimidine crystallizes in Pna2{sub 1} symmetry (phase I) with the freezing pressure of 0.3 GPa, and transforms to another phase (phase II) at 1.1 GPa. Raman spectra of several compression-decompression cycles demonstrate there is a critical pressure of 15.5 GPa for pyrimidine. Pyrimidine returns back to its original liquid state as long as the highest pressure is below 15.1 GPa. Rupture of the aromatic ring is observed once pressure exceeds 15.5 GPa during a compression-decompression cycle, evidenced by the amorphous characteristics of the recovered sample. As for s-triazine, the phase transition from R-3c to C2/c is well reproduced at 0.6 GPa, in comparison with previous Raman data. Detailed Raman scattering experiments corroborate the critical pressure for s-triazine may locate at 14.5 GPa. That is, the compression is reversible below 14.3 GPa, whereas chemical reaction with ring opening is detected when the final pressure is above 14.5 GPa. During compression, the complete amorphization pressure for pyrimidine and s-triazine is identified as 22.4 and 15.2 GPa, respectively, based on disappearance of Raman lattice modes. Synchrotron X-ray diffraction patterns and Fourier transform infrared spectra of recovered samples indicate the products in two cases comprise of extended nitrogen-rich amorphous hydrogenated carbon (a-C:H:N)
Acoustic travel time gauges for in-situ determination of pressure and temperature in multi-anvil apparatus
In this study, we developed a new method for in-situ pressure determination in multi-anvil, high-pressure apparatus using an acoustic travel time approach within the framework of acoustoelasticity. The ultrasonic travel times of polycrystalline Al{sub 2}O{sub 3} were calibrated against NaCl pressure scale up to 15 GPa and 900 °C in a Kawai-type double-stage multi-anvil apparatus in conjunction with synchrotron X-radiation, thereby providing a convenient and reliable gauge for pressure determination at ambient and high temperatures. The pressures derived from this new travel time method are in excellent agreement with those from the fixed-point methods. Application of this new pressure gauge in an offline experiment revealed a remarkable agreement of the densities of coesite with those from the previous single crystal compression studies under hydrostatic conditions, thus providing strong validation for the current travel time pressure scale. The travel time approach not only can be used for continuous in-situ pressure determination at room temperature, high temperatures, during compression and decompression, but also bears a unique capability that none of the previous scales can deliver, i.e., simultaneous pressure and temperature determination with a high accuracy (±0.16 GPa in pressure and ±17 °C in temperature). Therefore, the new in-situ Al{sub 2}O{sub 3} pressure gauge is expected to enable new and expanded opportunities for offline laboratory studies of solid and liquid materials under high pressure and high temperature in multi-anvil apparatus.
High pressure synthesis of amorphous TiO{sub 2} nanotubes
Amorphous TiO{sub 2} nanotubes with diameters of 8-10 nm and length of several nanometers were synthesized by high pressure treatment of anatase TiO{sub 2} nanotubes. The structural phase transitions of anatase TiO{sub 2} nanotubes were investigated by using in-situ high-pressure synchrotron X-ray diffraction (XRD) method. The starting anatase structure is stable up to ∼20GPa, and transforms into a high-density amorphous (HDA) form at higher pressure. Pressure-modified high- to low-density transition was observed in the amorphous form upon decompression. The pressure-induced amorphization and polyamorphism are in good agreement with the previous results in ultrafine TiO{sub 2} nanoparticles and nanoribbons. The relationship between the LDA form and α-PbO{sub 2} phase was revealed by high-resolution transmission electron microscopy (HRTEM) study. In addition, the bulk modulus (B{sub 0} = 158 GPa) of the anatase TiO{sub 2} nanotubes is smaller than those of the corresponding bulks and nanoparticles (180-240 GPa). We suggest that the unique open-ended nanotube morphology and nanosize play important roles in the high pressure phase transition of TiO{sub 2} nanotubes.
Pressure-induced phase transitions of exposed curved surface nano-TiO{sub 2} with high photocatalytic activity
We report a unique phase transition in compressed exposed curved surface nano-TiO{sub 2} with high photocatalytic activity using in situ synchrotron X-ray diffraction and Raman Spectroscopy. High-pressure studies indicate that the anatase phase starts to transform into baddeleyite phase upon compression at 19.4 GPa, and completely transforms into the baddeleyite phase above 24.6 GPa. Upon decompression, the baddeleyite phase was maintained until the pressure was released to 6.4 GPa and then transformed into the α-PbO{sub 2} phase at 2.7 GPa. Together with the results of high-resolution transmission electron microscopy and the pressure-volume relationship, this phase transition's characteristics during the compression-decompression cycle demonstrate that the truncated biconic morphology possessed excellent stability. This study may provide an insight to the mechanisms of stability for high photocatalytic activity of nano-TiO{sub 2}.
Pressure-induced structural transition in chalcopyrite ZnSiP 2
In this paper, the pressure-dependent phase behavior of semiconducting chalcopyrite ZnSiP 2 was studied up to 30 GPa using in situ X-ray diffraction and Raman spectroscopy in a diamond-anvil cell. A structural phase transition to the rock salt type structure was observed between 27 and 30 GPa, which is accompanied by soft phonon mode behavior and simultaneous loss of Raman signal and optical transmission through the sample. The high-pressure rock salt type phase possesses cationic disorder as evident from broad features in the X-ray diffraction patterns. The behavior of the low-frequency Raman modes during compression establishes a two-stage, order-disorder phase transition mechanism. Finally, the phase transition is partially reversible, and the parent chalcopyrite structure coexists with an amorphous phase upon slow decompression to ambient conditions.
Formation of distinctive nanostructured metastable polymorphs mediated by kinetic transition pathways in germanium
High-pressure β -Sn germanium may transform into diverse metastable allotropes with distinctive nanostructures and unique physical properties via multiple pathways under decompression. However, the mechanism and transition kinetics remain poorly understood. Here, we investigate the formation of metastable phases and nanostructures in germanium via controllable transition pathways of β -Sn Ge under rapid decompression at different rates. High-resolution transmission electron microscopy reveals three distinct metastable phases with the distinctive nanostructures: an almost perfect st12 Ge crystal, nanosized bc8/r8 structures with amorphous boundaries, and amorphous Ge with nanosized clusters (0.8–2.5 nm). Fast in situ x-ray diffraction and x-ray absorption measurements indicate that these nanostructured products form in certain pressure regions via distinct kinetic pathways and are strongly correlated with nucleation rates and electronic transitions mediated by compression rate, temperature, and stress. This work provides deep insight into the controllable synthesis of metastable materials with unique crystal symmetries and nanostructures for potential applications.
Multi-phase equation of state of ultrapure hafnium to 120 GPa
Hafnium (Hf) is an industrially important material due to its large neutron absorption cross-section and its high corrosion resistance. When subjected to high pressure, Hf phase transforms from its hexagonal close packed α-Hf phase to the hexagonal ω-Hf phase. Upon further compression, ω-Hf phase transforms to the body centered cubic β-Hf phase. In this study, the high pressure phase transformations of Hf are studied by compressing and decompressing a well-characterized Hf sample in diamond anvil cells up to 120 GPa while collecting x-ray diffraction data. The phase transformations of Hf were compared in both a He pressure transmitting medium (PTM) and no PTM over several experiments. It was found that the α-Hf to ω-Hf phase transition occurs at a higher pressure during compression and lower pressure during decompression with a helium (He) PTM compared to using no PTM. Finally, there was little difference in the ω-Hf to β-Hf phase transition pressure between the He PTM and no PTM. The equation of state was fit for all three phases of Hf and under both PTM and no-PTM.
ON THE VIGOR OF MANTLE CONVECTION IN SUPER-EARTHS
Numerical models are presented to clarify how adiabatic compression affects thermal convection in the mantle of super-Earths ten times the Earth's mass. The viscosity strongly depends on temperature, and the Rayleigh number is much higher than that of the Earth's mantle. The strong effect of adiabatic compression reduces the activity of mantle convection; hot plumes ascending from the bottom of the mantle lose their thermal buoyancy in the middle of the mantle owing to adiabatic decompression, and do not reach the surface. A thick lithosphere, as thick as 0.1 times the depth of the mantle, develops along the surface boundary, and the efficiency of convective heat transport measured by the Nusselt number is reduced by a factor of about four compared with the Nusselt number for thermal convection of incompressible fluid. The strong effect of adiabatic decompression is likely to inhibit hot spot volcanism on the surface and is also likely to affect the thermal history of the mantle, and hence, the generation of magnetic field in super-Earths.
Crystallization Stages of the Bishop Tuff Magma Body Recorded in Crystal Textures in Pumice Clasts
The Bishop Tuff is a giant silicic ignimbrite erupted at 0.76 Ma in eastern California, USA. Five pumice clasts from the late-erupted Bishop Tuff (Aeolian Buttes) were studied in an effort to better understand the pre- and syn-eruptive history of the Bishop magma body and place constraints on the timescales of its existence. This study complements and expands on a previous study that focused on early-erupted Bishop Tuff pumice clasts. Bulk densities of pumice clasts were measured using an immersion method, and phenocryst crystal contents were determined using a sieving and winnowing procedure. X-ray tomography was used to obtain qualitative and quantitative textural information, particularly crystal size distributions (CSDs). We have determined CSDs for crystals ranging in size from {approx}10 to {approx}1000 {micro}m for three groups of mineral phases: magnetite ({+-}ilmenite), pyroxene + biotite, quartz + feldspar. Similar to early-erupted pumice, late-erupted pumice bulk density and crystal contents are positively correlated, and comparison of crystal fraction vs size trends suggests that the proportion of large crystals is the primary control on crystallinity. Porosity is negatively correlated with crystal content, which is difficult to reconcile with closed-system crystallization. Magnetite and pyroxene + biotite size distributions are fractal in nature, often attributed to fragmentation; however, crystals are mostly whole and euhedral, such that an alternative mechanism is necessary to explain these distributions. Quartz + feldspar size distributions are kinked, with a shallow-sloped log-linear section describing large crystals (> 140 {micro}m) and a steep-sloped log-linear section describing small crystals (< 140 {micro}m). We interpret these two crystal populations as resulting from a shift in crystallization regime. We suggest that the shallow-sloped section describes a pre-eruptive quartz + feldspar growth-dominated regime, whereas the steep-sloped section represents a population that grew during a nucleation-dominated regime that began as a result of decompression at the onset of eruption. Timescales of quartz growth calculated from the slopes of these two segments of the size distributions indicate that the pre-eruptive crystal population grew on timescales on the order of millennia and may describe the timescale of crystallization of the Bishop magma body. The syn-eruptive population gives timescales of < 1-2 years (but possibly much less) and probably marks the onset of eruptive decompression.
ACDT: Architected Composite Data Types Trading-in Unfettered Data Access for Improved Execution
With Exascale performance and its challenges in mind, one ubiquitous concern among architects is energy efficiency. Petascale systems projected to Exascale systems are unsustainable at current power consumption rates. One major contributor to system-wide power consumption is the number of memory operations leading to data movement and management techniques applied by the runtime system. To address this problem, we present the concept of the Architected Composite Data Types (ACDT) framework. The framework is made aware of data composites, assigning them a specific layout, transformations and operators. Data manipulation overhead is amortized over a larger number of elements and program performance and power efficiency can be significantly improved. We developed the fundamentals of an ACDT framework on a massively multithreaded adaptive runtime system geared towards Exascale clusters. Showcasing the capability of ACDT, we exercised the framework with two representative processing kernels - Matrix Vector Multiply and the Cholesky Decomposition – applied to sparse matrices. As transformation modules, we applied optimized compress/decompress engines and configured invariant operators for maximum energy/performance efficiency. Additionally, we explored two different approaches based on transformation opaqueness in relation to the application. Under the first approach, the application is agnostic to compression and decompression activity. Such approach entails minimal changes to the original application code, but leaves out potential applicationspecific optimizations. The second approach exposes the decompression process to the application, hereby exposing optimization opportunities that can only be exploited with application knowledge. The experimental results show that the two approaches have their strengths in HW and SW respectively, where the SW approach can yield performance and power improvements that are an order of magnitude better than ACDT-oblivious, hand-optimized implementations.We consider the ACDT runtime framework an important component of compute nodes that will lead towards power efficient Exascale clusters.
Performance Optimization for Relative-Error-Bounded Lossy Compression on Scientific Data
Scientific simulations in high-performance computing (HPC) environments generate vast volume of data, which may cause a severe I/O bottleneck at runtime and a huge burden on storage space for postanalysis. Unlike traditional data reduction schemes such as deduplication or lossless compression, not only can error-controlled lossy compression significantly reduce the data size but it also holds the promise to satisfy user demand on error control. Pointwise relative error bounds (i.e., compression errors depends on the data values) are widely used by many scientific applications with lossy compression since error control can adapt to the error bound in the dataset automatically. Pointwise relative-error-bounded compression is complicated and time consuming. In this article, we develop efficient precomputation-based mechanisms based on the SZ lossy compression framework. Our mechanisms can avoid costly logarithmic transformation and identify quantization factor values via a fast table lookup, greatly accelerating the relative-error-bounded compression with excellent compression ratios. In addition, we reduce traversing operations for Huffman decoding, significantly accelerating the decompression process in SZ. Experiments with eight well-known real-world scientific simulation datasets show that our solution can improve the compression and decompression rates (i.e., the speed) by about 40 and 80 p, respectively, in most of cases, making our designed lossy compression strategy the best-in-class solution in most cases.
Dynamic Virtual Chunks: On Supporting Efficient Accesses to Compressed Scientific Data
Data compression could ameliorate the I/O pressure of data-intensive scientific applications. Unfortunately, the conventional wisdom of naively applying data compression to the file or block brings the dilemma between efficient random accesses and high compression ratios. File-level compression barely supports efficient random accesses to the compressed data: any retrieval request need trigger the decompression from the beginning of the compressed file. Block-level compression provides flexible random accesses to the compressed blocks, but introduces extra overhead when applying the compressor to each and every block that results in a degraded overall compression ratio. This paper extends our prior work that introduces virtual chunks offering efficient random accesses to the compressed scientific data without sacrificing the compression ratio. Virtual chunks are logical blocks pointed at by appended references without breaking the physical continuity of the file content. These references allow the decompression to start from an arbitrary position (efficient random accesses), while no per-block overhead is introduced because the file’s physical entirety is retained (high compression ratio). One limitation of virtual chunk is it only supports static references. This paper presents the algorithms, analysis, and evaluations of dynamic virtual chunks to deal with the cases where the references are updated dynamically.
In situ Raman spectroscopy of pressure-induced phase transformations in polycrystalline TbPO 4 , DyPO 4 , and Gd x Dy (1– x ) PO 4 [ In situ Raman spectroscopy of pressure-induced phase transformations in DyPO 4 and Gd x Dy (1– x ) PO 4 ]
Xenotime DyPO 4 and Gd x Dy (1–x) PO 4 (x = 0.4, 0.5, 0.6) (tetragonal I41amd zircon structure) have been studied at ambient temperature under high pressures inside a diamond anvil cell with in situ Raman spectroscopy. The typical Raman–active modes of the xenotime structure were observed at low pressures and the appearance of new Raman peaks at higher pressures indicated a phase transformation to a lower symmetry structure—likely monoclinic. Raman mode softening was observed, resulting in a line crossing at approximately 7–8 GPa for each material and preceding the phase transformation. The onset of phase transformation for DyPO 4 occurred at a pressure of 15.3 GPa. DyPO 4 underwent a reversible phase transformation and returned to the xenotime phase after decompression. The transformation pressures of the solid solutions (Gd x Dy (1–x) PO 4 ) were in the range 10–12 GPa. The GdxDy(1–x)PO 4 solid solutions yielded partially reversible phase transformations, retaining some of the high–pressure phase spectrum while reforming xenotime peaks during decompression. The substitution of Gd into DyPO 4 decreased the transformation pressure relative to pure DyPO 4 . In conclusion, the ability to modify the phase transformation pressures of xenotime rare–earth orthophosphates by chemical variations of solid solutions may provide additional methods to improve the performance of ceramic matrix composites.
Stability Analysis of Inline ZFP Compression for Floating-Point Data in Iterative Methods
Currently, the dominating constraint in many high performance computing applications is data capacity and bandwidth, in both internode communications and even moreso in intranode data motion. A new approach to address this limitation is to make use of data compression in the form of a compressed data array. Storing data in a compressed data array and converting to standard IEEE-754 types as needed during a computation can reduce the pressure on bandwidth and storage. However, repeated conversions (lossy compression and decompression) introduce additional approximation errors, which need to be shown to not significantly affect the simulation results. Here, we extend recent work that analyzed the error of a single use of compression and decompression of the ZFP compressed data array representation to the case of time-stepping and iterative schemes, where an advancement operator is repeatedly applied in addition to the conversions. We show that the accumulated error for iterative methods involving fixed-point and time evolving iterations is bounded under standard constraints. An upper bound is established on the number of additional iterations required for the convergence of stationary fixed-point iterations. An additional analysis of traditional forward and backward error of stationary iterative methods using ZFP compressed arrays is also presented. The results of several 1D, 2D, and 3D test problems are provided to demonstrate the correctness of the theoretical bounds.
Hydrodynamic and Longitudinal Impedance Analysis of Cerebrospinal Fluid Dynamics at the Craniovertebral Junction in Type I Chiari Malformation
Elevated or reduced velocity of cerebrospinal fluid (CSF) at the craniovertebral junction (CVJ) has been associated with type I Chiari malformation (CMI). Thus, quantification of hydrodynamic parameters that describe the CSF dynamics could help assess disease severity and surgical outcome. In this study, we describe the methodology to quantify CSF hydrodynamic parameters near the CVJ and upper cervical spine utilizing subject-specific computational fluid dynamics (CFD) simulations based on in vivo MRI measurements of flow and geometry. Hydrodynamic parameters were computed for a healthy subject and two CMI patients both pre- and post-decompression surgery to determine the differences between cases. For the first time, we present the methods to quantify longitudinal impedance (LI) to CSF motion, a subject-specific hydrodynamic parameter that may have value to help quantify the CSF flow blockage severity in CMI. In addition, the following hydrodynamic parameters were quantified for each case: maximum velocity in systole and diastole, Reynolds and Womersley number, and peak pressure drop during the CSF cardiac flow cycle. The following geometric parameters were quantified: cross-sectional area and hydraulic diameter of the spinal subarachnoid space (SAS). The mean values of the geometric parameters increased post-surgically for the CMI models, but remained smaller than the healthy volunteer. All hydrodynamic parameters, except pressure drop, decreased post-surgically for the CMI patients, but remained greater than in the healthy case. Peak pressure drop alterations were mixed. To our knowledge this study represents the first subject specific CFD simulation of CMI decompression surgery and quantification of LI in the CSF space. Further study in a larger patient and control group is needed to determine if the presented geometric and/or hydrodynamic parameters are helpful for surgical planning.
Eureka: Enabling Fine-Grained Access and Range Queries on Compressed Scientific Data via Data-Index Co-Compression
Handling large-scale scientific data in high-performance computing (HPC) environments poses significant challenges, including excessive I/O, high storage costs, and slow query performance. Traditional approaches often require full data decompression and scans, making them impractical for real-time or interactive analysis. To address these limitations, we introduce Eureka, a unified data-index co-compression framework that enables fine-grained access and efficient range queries on compressed scientific datasets. Eureka integrates spatial domain decomposition with block-wise error-bounded lossy compression to support selective decompression. It constructs a hierarchical AVL-tree index during compression to capture block-level value ranges, enabling fast pruning during query execution. To reduce metadata overhead, the index itself is also compressed while ensuring recall-preserving results. Experiments on six diverse HPC simulation datasets show that Eureka achieves up to 25x data compression and over 300x index compression, surpassing state-of-the-art compressors such as SZ3 and ZFP in rate-distortion performance. Additionally, Eureka delivers over 30x speedup for low-selectivity range queries, making it a scalable and efficient solution for modern scientific data analysis.
Leakage Risk Assessment of CO{sub 2} Transportation by Pipeline at the Illinois Basin Decatur Project, Decatur, Illinois
The Illinois Basin Decatur Project (IBDP) is designed to confirm the ability of the Mt. Simon Sandstone, a major regional saline-water-bearing formation in the Illinois Basin, to store 1 million tons of carbon dioxide (CO{sub 2}) injected over a period of three years. The CO{sub 2} will be provided by Archer Daniels Midland (ADM) from its Decatur, Illinois, ethanol plant. In order to transport CO{sub 2} from the capture facility to the injection well (also located within the ADM plant boundaries), a high-pressure pipeline of length 3,200 ft (975 m) has been constructed, running above the ground surface within the ADM plant footprint. We have qualitatively evaluated risks associated with possible pipeline failure scenarios that lead to discharge of CO{sub 2} within the real-world environment of the ADM plant in which there are often workers and visitors in the vicinity of the pipeline. There are several aspects of CO{sub 2} that make its transportation and potential leakage somewhat different from other substances, most notable is its non-flammability and propensity to change to solid (dry ice) upon strong decompression. In this study, we present numerical simulations using Computational Fluid Dynamics (CFD) methods of the release and dispersion of CO{sub 2} from individual hypothetical pipeline failures (i.e., leaks). Failure frequency of the various components of a pipeline transportation system over time are taken from prior work on general pipeline safety and leakage modeling and suggest a 4.65% chance of some kind of pipeline failure over the three-years of operation. Following the Precautionary Principle (see below), we accounted for full-bore leakage scenarios, where the temporal evolution of the mass release rate from the high-pressure pipeline leak locations was simulated using a state-of-the-art Pipe model which considers the thermodynamic effects of decompression in the entire pipeline. Failures have been simulated at four representative locations along the pipeline route within the ADM plant. Leakage scenarios at sites along the route of the pipeline, where plant operations (e.g., vehicular and train transportation) seem to present a higher likelihood of accidental failure, for example due to vehicles or equipment crashing into the pipeline and completely severing it, were modeled by allowing them to have a double source consistent with the pipeline releasing high-pressure CO{sub 2} from both ends of the broken pipe after a full-bore offset rupture. Simulation results show that the built environment of the plant plays a significant role in the dispersion of the gas as leaking CO{sub 2} can impinge upon buildings and other infrastructure. In all scenarios simulated, the region of very high-concentration of CO{sub 2} is limited to a small area around the pipeline failure, suggesting the likelihood of widespread harmful CO{sub 2} exposure to plant personnel from pipeline leakage is low. An additional risk is posed by the blast wave that emanates from a high-pressure pipeline when it is breached quickly. We estimate the blast wave risk as low because it occurs only for a short time in the immediate vicinity of the rupture, and requires an instantaneous large-scale rupture to occur. We recommend consideration of signage and guard rails and posts to mitigate the likelihood of vehicles crashing into the pipeline. A standardized emergency response plan applicable to capture plants within industrial sites could be developed based on the IBDP that would be useful for other capture plants. Finally, we recommend carrying out coupled wellbore-reservoir blowout scenario modeling to understand the potential for hazardous conditions arising from an unexpected blowout at the wellhead.