High-pressure Form Research Articles

Hypertensive slit ventricle syndrome: pseudotumor cerebri with a malfunctioning shunt?

Symptomatic shunt malfunction without ventricular enlargement is known as slit ventricle syndrome (SVS). Patients presenting with this syndrome are not a homogeneous group. Of the 5 different types classified by Rekate, Type 1 is caused by CSF overdrainage and is associated with low pressures; Types 2 and 3 are associated with shunt blockage and elevated CSF pressures; Type 4 is cephalocranial disproportion that increases brain parenchymal pressure but not CSF pressure; and Type 5 is headache unrelated to shunt function. The low and normal CSF pressure types are relatively well understood, but the high-pressure forms are more problematic. In the high-pressure forms of SVS it is said that the lack of ventricular dilation is related to a reduction in brain compliance analogous to idiopathic intracranial hypertension or pseudotumor cerebri. Despite this, there is little evidence in the literature to support this conjecture. With this in mind, 3 cases of SVS associated with elevated CSF pressure are presented. The MR venogram findings and hemodynamics of these 3 cases are shown to be identical to those of pseudotumor cerebri. A literature review indicates that an underlying venous impairment may be functioning in the patients who re-present with small ventricles following shunt malfunction.

Sound velocities measurement on MgSiO3 akimotoite at high pressures and high temperatures with simultaneous in situ X-ray diffraction and ultrasonic study

Elastic wave velocities of MgSiO3 akimotoite polycrystalline samples have been measured at pressures up to 25.7GPa and temperatures to 1500K by a combination of in situ X-ray diffraction and ultrasonic interferometry techniques in a large volume Kawai-type multianvil apparatus (KMA). The elastic moduli of akimotoite and their pressure and temperature dependences are determined by a 2D linear fitting analysis of the present data, yielding: KS=219.4(7)GPa, ∂KS/∂P=4.62(3), ∂KS/∂T=−0.0228(4)GPa/K, G0=132.1(7)GPa, ∂G/∂P=1.63(4), ∂G/∂T=−0.0225(4)GPa/K. The bulk and shear moduli at ambient conditions are generally consistent with the result of a previous Brillouin study. However, significant nonlinear behaviors of the elastic moduli were observed at higher temperatures, indicating that the velocities derived from the linear fitting analysis are overestimated for the actual mantle conditions. Using the present new experimental data, we compared the elastic velocities of various high-pressure forms of MgSiO3 under the mantle conditions. The results demonstrate a large velocity difference between akimotoite and perovskite, which may be relevant to the complex seismic structures near the bottom of the mantle transition zone.

Characterization of an MgH2-Ni Alloy Prepared by Mechanical Grinding under Hydrogen

MgH2, rather than Mg, was employed as a starting material in this work. A sample with a composition of 82 wt% MgH2-18 wt% Ni (designated MgH2-18Ni) was prepared by reactive mechanical grinding. Its hydriding and dehydriding properties were then examined. An MgH2-Ni hydrogen-storage alloy that does not require an activation process was developed. The alloy was prepared by grinding for 4 h in a planetary ball mill at a ball disc revolution speed of 250 rpm under a hydrogen pressure of about 12 bar. The sample absorbed 3.51 wt% H for 5 min and 3.96 wt% H for 60 min at 573 K under 12 bar H2, and desorbed 0.90 wt% H for 10 min and 3.24 wt% H for 60 min at 573 K under 1.0 bar H2. MgH2-18Ni after reactive mechanical grinding contained β-MgH2, Ni, γ-MgH2 (a high-pressure form of MgH2), and a very small amount of MgO. The specific surface area and average particle size of MgH2-18Ni after reactive mechanical grinding were analyzed.

High Pressure Semiconductor Physics

The present issue of physica status solidi (b) contains a Special Section of papers (Three Invited Articles and 18 Original Papers) that are based on contributions presented at the 15th High Pressure Semiconductor Physics (HPSP15) International Conference held in Montpellier, France, from July 25th to 27th, 2012. This conference was the fifteenth in a series of biennial meetings held under the general title “International Conference on High Pressure Semiconductor Physics” organized as a satellite of the International Conference on the Physics of Semiconductors (ICPS). During the past thirty years, the HPSP series of conferences has been established as a leading event for the scientific community involved in the application of high pressure and other forms of high stress in the study of semiconductors and their micro/nano-structures. The contents of HPSP evolves together with the scientific challenges associated with the technological uses of semiconductor materials and systems, as well as with the evolution of the technical tools and methods – both experimental and theoretical – utilized in fundamental and applied investigations. In particular, the emergence of novel nano-materials and nano-systems has been an important development in the last twenty years, such that semiconductors at the nanoscale constitute now an important topic of HPSP. On the other hand, the more “traditional” semiconductor systems have to face new challenges due to their progressive miniaturization in microelectronics or to their new technological application which results from the demands of the society in the 21st century. All this calls for a better fundamental understanding of the physics of semiconductors through efficient predictive tools, precise experimental work and novel synthesis processes. Several years ago, the organizers of the conference series made an effort to widen the scope of HPSP by not applying a narrow definition of semiconductor physics, but including new materials and novel experimental approaches. Within the case materials of the HPSP15 conference one can still find group-III nitrides and the discussion of remaining open questions concerning their electronic, vibrational as well as optical properties 1, but also carbon based nanomaterials such as fullerenes, carbon nanotubes and, very recently, graphene, or a new class of materials that behave as insulators in the bulk but conduct electrical current in the surface, so-called topological insulators 2. Probing semiconductors at highly anisotropic strains is difficult due to the inherent limitations of the commonly used static compression methods to generate the hydrostatic pressure or uniaxial stress. The uniaxial strain conditions produced during strong dynamic compression can overcome these limitations and have revealed lately important electronic structure changes 3. From the more technological point of view several papers deal with investigations of laser diodes under high pressure. They arrive not only at a better understanding of the lasing mechanisms at work but also at practical applications, for instance, allowing for the pressure tuning of lasers in the 1 to 1.5 micrometer range 4.

The mechanism of propulsion effect of BLEVE based on discharge

Propellant could reach a high pressure and temperature situation in a very short time by the use of high voltage pulsed discharge. Once sharp depressurization occurs, BLEVE (boiling liquid expanding vapor explosion) happens immediately with a violent phase transition. A two-phase flow with high pressure and speed forms and often causes severe damage. It is also useful in other aspects such as propulsion. The numerical simulation of BLEVE for propulsion shows the pressure has a sharp increasing when phase transition begins. Then a two phase mixture flow moves forward with a high speed and compresses the gas in front.

Structural Characterization of Magnesium-Based Compounds Mg9Si5 and Mg4Si3Al (Superconductor) Synthesized under High Pressure and High Temperature Conditions

Two kinds of magnesium-based compounds Mg9Si5 and Mg4Si3Al have been prepared under high pressure and high temperature (HPHT) conditions of 5 GPa at 900-1100 °C. Single crystal study revealed that Mg9Si5 crystallizes in space group P6(3) (No. 173) with the lattice parameters a = 12.411(1) Å, c = 12.345(1) Å, and Z = 6. The structure can be derived from the high pressure form Mg2Si with the anticotunnite structure; excess Si atoms of Mg9Si5 form Si-Si pairs in the prismatic cotunnite columns running along the c axis. Mg4Si3Al is obtained by a rapid cooling of a ternary mixture Mg:Al:Si = 1:1:1 from ~800 °C to room temperature under a pressure of 5 GPa. The compound crystallizes in space group P4/ncc (No. 130) with the lattice parameters a = 6.7225(5) Å, c = 13.5150(9) Å, and Z = 4. The structure consists of an alternate stacking of [AlSi2] layers having a Cairo pattern and [Mg4Si] antitetragonal prismatic layers. It can be viewed as composed of hexa-Si-capped tetragonal prismatic cages Mg8Si6 with an Al atom at the center of each cage, Al@Mg8Si6. The compound shows superconductivity with a transition temperature Tc = 5.2 K. The formation regions of the two kinds of new magnesium-based compounds have been proposed.

Formation of a High Pressure Form of Magnesium Hydride γ-MgH2 by Mechanical Grinding under Low Hydrogen Pressure

In order to investigate the formation of a high pressure form of magnesium hydride, γ-MgH2, X-ray diffraction patterns before and after the hydriding reaction were obtained for samples of MgH2, MgH2 after reactive mechanical grinding (RMG), and 94 wt% MgH2-6 wt% Ni after reactive mechanical grinding. In addition, absorbed hydrogen quantity versus time curves at the first cycle were examined. The MgH2 sample did not contain γ-MgH2. However, the MgH2 after RMG and the 94 wt% MgH2-6 wt% Ni after RMG contained γ-MgH2. All these results prove that after reactive mechanical grinding, γ-MgH2, one of the high pressure forms of MgH2, was formed in the MgH2 and 94 wt% MgH2-6 wt% Ni samples under low hydrogen pressures.

A high-pressure polymorph of chlorpropamide formed on hydrostatic compression of the α-form in saturated ethanol solution

The crystal structure of the high-pressure polymorph (α') of an antidiabetic drug, chlorpropamide [4-chloro-N-(propylaminocarbonyl)benzenesulfonamide, C(10)H(13)ClN(2)O(3)S], which is formed at ~2.8 GPa from the α-polymorph (P2(1)2(1)2(1)) on hydrostatic compression in saturated ethanol solution, has been determined. As a result of the phase transition, the a, c and α parameters change jumpwise, whereas the changes in b parameter are continuous through the phase transition point. The high-pressure form is monoclinic (P2(1)11) and has Z' equal to 2, the two independent molecules differing in their conformations. The hydrogen bonds expand slightly in the high-pressure polymorph after the transition, and this expansion is interrelated with the changes in molecular conformations enabling a denser packing. The transition is reversible, but the crystal quality deteriorates as a result of multiple compression-decompression cycles, and a pseudomerohedral twinning accompanies the transformation.

A high-pressure polymorph of chlorpropamide formed on hydrostatic compression of the α-form in saturated ethanol solution

The crystal structure of the high-pressure polymorph (α′) of an antidiabetic drug, chlorpropamide [4-chloro-N-(propylaminocarbonyl)benzenesulfonamide, C10H13ClN2O3S], which is formed at ∼ 2.8 GPa from the α-polymorph (P212121) on hydrostatic compression in saturated ethanol solution, has been determined. As a result of the phase transition, the a, c and α parameters change jumpwise, whereas the changes in b parameter are continuous through the phase transition point. The high-pressure form is monoclinic (P2111) and has Z′ equal to 2, the two independent molecules differing in their conformations. The hydrogen bonds expand slightly in the high-pressure polymorph after the transition, and this expansion is interrelated with the changes in molecular conformations enabling a denser packing. The transition is reversible, but the crystal quality deteriorates as a result of multiple compression–decompression cycles, and a pseudomerohedral twinning accompanies the transformation.

Thickness dependence of structural and electrical properties of electron-doped Sr1−xLaxCuO2 infinite-layer thin films grown by pulsed laser deposition

As the building blocks for all of the high-Tc cuprate superconductors, infinite layer (IL) compounds have the simplest structures and the highest Tc of electron-doped superconductors. However, IL structure is one of the high-pressure forms, which makes it difficult to synthesize a single crystal. Therefore, it is highly desirable to obtain high-quality epitaxial thin films making use of epitaxial effect. Although there are many reported attempts to grow IL thin films on different substrates, no one has systematically studied the thickness dependence of structural and electrical properties of IL thin films. In this report, electron-doped Sr1−xLaxCuO2 thin films of various thicknesses were deposited on (001) KTaO3 substrate by pulsed laser deposition. It is shown that IL peak shifts to a lower angle with increase of film thickness, indicating the reduction of the tensile strain. With further increase of thickness, there emerges an impurity phase. Transport measurements showed strong influence of the sample thickness on resistivity and Tc. For a certain thickness range we have demonstrated that superconductivity will occur. The resistive superconducting transition with Tc onset = 14.2 K and Tc (ρ =0) = 10 K has been observed. A moderate thickness is required to obtain IL thin films with superconductivity.

Development of MgH2-Ni Hydrogen Storage Alloy Requiring No Activation Process via Reactive Mechanical Grinding

MgH2 was employed as a starting material instead of Mg in this work. A sample with a composition of 94 wt% MgH2-6 wt% Ni (called MgH2-6Ni) was prepared by reactive mechanical grinding. The hydriding and dehydriding properties were then examined. An MgH2-Ni hydrogen storage alloy that does not require an activation process was developed. The alloy was prepared in a planetary ball mill by grinding for 4 h at a ball disc revolution speed of 250 rpm under a hydrogen pressure of about 12 bar. The sample absorbed 3.74 wt% H for 5 min, 4.07 wt% H for 10 min, and 4.41 wt% H for 60 min at 573 K under 12 bar H2, and desorbed 0.93 wt% H for 10 min, 1.99 wt% H for 30 min, and 3.16 wt% H for 60 min at 573 K under 1.0 bar H2. MgH2-6Ni after reactive mechanical grinding contained β-MgH2 (a room temperature form of MgH2), Ni, γ-MgH2 (a high pressure form of MgH2), and a very small amount of MgO. Reactive mechanical grinding of Mg with Ni is considered to facilitate nucleation, and to reduce the particle size of Mg. Mg2Ni formed during reactive mechanical grinding also increases the hydriding and dehydriding rates of the sample.

PASCal: a principal axis strain calculator for thermal expansion and compressibility determination

This article describes a web-based tool (PASCal; principal axis strain calculator; http://pascal.chem.ox.ac.uk) designed to simplify the determination of principal coefficients of thermal expansion and compressibilities from variable-temperature and variable-pressure lattice parameter data. In a series of three case studies,PASCalis used to reanalyse previously published lattice parameter data and show that additional scientific insight is obtainable in each case. First, the two-dimensional metal–organic framework [Cu2(OH)(C8H3O7S)(H2O)]·2H2O is found to exhibit the strongest area negative thermal expansion (NTE) effect yet observed; second, the widely used explosive HMX exhibits much stronger mechanical anisotropy than had previously been anticipated, including uniaxial NTE driven by thermal changes in molecular conformation; and third, the high-pressure form of the mineral malayaite is shown to exhibit a strong negative linear compressibility effect that arises from correlated tilting of SnO6and SiO4coordination polyhedra.

Cagelike Diamondoid Nitrogen at High Pressures

Under high pressure, triply bonded molecular nitrogen dissociates into singly bonded polymeric nitrogen, a potential high-energy-density material. The discovery of stable high-pressure forms of polymeric nitrogen is of great interest. We report the striking stabilization of cagelike diamondoid nitrogen at high pressures predicted by first-principles structural searches. The diamondoid structure of polymeric nitrogen has not been seen in any other elements, and it adopts a highly symmetric body-centered cubic structure with lattice sites occupied by diamondoids, each of which consists of ten nitrogen atoms, forming a N(10) tetracyclic cage. Diamondoid nitrogen possesses a wide energy gap and is energetically most stable among all known polymeric structures above 263 GPa, a pressure that is accessible to a high-pressure experiment. Our findings represent a significant step toward the understanding of the behavior of solid nitrogen at extreme conditions.

High-pressure transition to the post-barite phase in BaCrO4hashemite

A recent high-pressure study on barium chromate BaCrO${}_{4}$ reported a phase transition but the structure of the high-pressure phase structure could not be identified. This high-pressure phase was suggested to have a monoclinic structure different from other high-pressure forms of $AB$O${}_{4}$-type compounds. In this work, we have carried out x-ray diffraction measurements up to 46 GPa using He as the quasihydrostatic pressure medium and density-functional theory calculations. Our studies allow us to identify the high-pressure phase as the $P$2${}_{1}$2${}_{1}$2${}_{1}$ post-barite-type phase, recently reported for BaSO${}_{4}$. The equations of state of both, the low- and the high-pressure phases have been determined. Elastic constants of the initial barite-type phase were calculated and the shear and Young moduli, and the Poisson coefficient deduced from them. Finally Raman and infrared-active modes are also calculated, discussed, and compared with experiments when possible. As a first approximation, the vibrations can be separated in internal vibrations of the CrO${}_{4}$ tetrahedra and vibrations where the tetrahedral units behave as rigid units. Pressure coefficients of the different modes are reported being two soft modes found for the high-pressure phase.

Unexpected high pressure effects on the structural properties of condensed whey protein systems

We show that application of high hydrostatic pressure (600 MPa for 15 min) on condensed whey protein (WP) systems (e.g., 80% w/w solids content) results in unexpected structure-function behavior when compared with conventional thermal treatment. Unraveling the relaxation properties in first-order thermodynamic transitions, the manifestation of glass transition phenomena and the preservation of native conformation in condensed preparations were recorded using small-deformation dynamic oscillation in shear, modulated differential scanning calorimetry, and infrared spectroscopy. Informed temperature application results in the formation of continuous networks at the denaturation temperature, which undergo vitrification at subzero temperatures. In contrast, high-pressure-treated WPs resist physicochemical denaturation, hence preserving the native conformation of secondary and tertiary structures. This was rationalized on the basis of a critical concentration threshold where transfer of water molecules to nonpolar residues in the protein interior is minimized because of low moisture content and restricted molecular mobility. The physical state and morphology of these high-solid preparations were further examined by the combined framework of reduced variables and Williams, Landel, and Ferry equation/free volume theory. Theoretical treatment of experimental observations unveils the dynamic range of the mechanical manifestation of the glass transition region in samples subjected to heat or pressure. In addition to preserving native conformation, WPs subjected to high pressure form glassy systems at parity with the structural functionality of the thermally treated counterparts.

Negative linear compressibility and complex high-Pstructure in Zn[Au(CN)2]2

The structure of the framework material zinc dicyanoaurate is built up of tetrahedrally-coordinated Zn cations linked by linear [NC-Au-CN]- complex anions, which form a six-fold interpenetrated -quartz-type network. This material exhibits strong negative linear thermal expansion along the c direction due to framework flexibility [1]. In situ, single-crystal and powder x-ray diffraction under high pressure in diamond anvil cells indicate that the c lattice parameter increases by 8% from ambient pressure up to 1.8 GPa, which is the highest negative linear compressibility (NLC) known for any material. Structural data obtained from single crystal x-ray diffraction indicate that the NLC mechanism is linked to the closing of N-Zn-N angles and the bending of Au-C-N-Zn linkages. A large number of superlattice reflections are observed above 2 GPa, indicating that the unit cell is doubled in all three directions. This phase transition is accompanied by a strong decrease in NLC. Systematic absences indicate that the space group changes from P6222 to P6422 or vice versa depending on the absolute configuration of the initial crystal corresponding to an instability at one of the L points in the Brillouin zone. The resulting unit cell has the following lattice parameters at 3.6 GPa: a=14.485(2)A, c=45.796(6)A with 528 atoms per unit cell. The ZnAu2 sublattice of the new, high-pressure form was solved by direct methods and followed by the use of difference Fourier maps to locate the C and N atoms. A significant change occurs in the Au sublattice with the Au-Au interatomic vector becoming canted with respect to c. This provides an additional compression mechanism, which reduces the need for the structure to expand along c. These results provide a detailed structural mechanism for the exceptional and unusual mechanical properties of this material. [1] Goodwin, A. L., Kennedy, B. J.. & Kepert, C. J. (2009). J. Am. Chem. Soc. 131, 6334-6335. Keywords: structural phase transitions; high-pressure structure determination; mechanical properties of crystals

Numerical Simulation of Outburst Prevention Effect of High-Pressure Mini-Jet Fracturing Coal

Through ANSYS/LS-DYNA simulates mini-jet fracturing coal effect, this paper verifies that high-pressure mini-jet forms ahead hole on working face coal, which increases coal exposing area and relieves pressure inside the coal bed to creative conditions for gas relieving and flowing. Additionally underground stress, the coal around hole shifts to the hole space and enlarges the hole relieving pressure and gas exhausting scope further, which removes the coal outburst potential within the control scope and provides theoretical basis for studing the equipment of high-pressure mini-jet cutting hole against outburst.

Pressure induced structural transitions in KH, RbH, and CsH

The heavier alkali metal hydrides MH (M = K, Rb, Cs) undergo a series of pressure induced structural phase transitions: B1 (NaCl) → B2 (CsCl) → CrB. Experiments reveal that the latter occurs at 85 and 17.5 GPa for RbH and CsH, but it has not yet been observed for KH. Herein, evolutionary algorithms coupled with density functional theory calculations are employed to explore the potential energy surface of the aforementioned hydrides up to pressures of 300 GPa. The computations support previous theoretical work which predicts that KH will adopt the CrB structure when compressed. In addition, for KH and RbH we find configurations with Pnma and I41/amd symmetry that are thermodynamically competitive with the CrB structure at 300 GPa. Between 100–150 GPa, a Pnma structure which is analogous to a high-pressure form of CsI is found to be the most stable phase for the heaviest alkali hydride considered. At higher pressures a hitherto unknown CsH–P63/mmc arrangement becomes thermodynamically preferred up to at least 400 GPa. A detailed analysis of the geometric and electronic structures of the various phases is provided.

The structure of MgO–SiO2 glasses at elevated pressure

The magnesium silicate system is an important geophysical analogue and neutron diffraction data from glasses formed in this system may also provide an initial framework for understanding the structure-dependent properties of related liquids that are important during planetary formation. Neutron diffraction data collected in situ for a single composition (38 mol% SiO2) magnesium silicate glass sample shows local changes in structure as pressure is increased from ambient conditions to 8.6 GPa at ambient temperature. A method for obtaining the fully corrected, total structure factor, S(Q), has been developed that allows accurate structural characterization as this weakly scattering glass sample is compressed. The measured S(Q) data indicate changes in chemical ordering with pressure and the real-space transforms show an increase in Mg–O coordination number and a distortion of the local environment around magnesium ions. We have used reverse Monte Carlo methods to compare the high pressure and ambient pressure structures and also compare the high pressure form with a more silica-poor glass (Mg2SiO4) that represents the approach to a more dense, void-free and topologically ordered structure. The Mg–O coordination number increases with pressure and we also find that the degree of continuous connectivity of Si–O bonds increases via a collapse of interstices.

A mantle-derived dolomite silicocarbonatite from the southwest coast of Ireland

AbstractThe magma source and evolution of a zoned breccia pipe on the southern Beara Peninsula in southwest Ireland are investigated using the geochemistry of the host mineral assemblages. The clast-poor inner zone of the pipe has a magnesium-rich silicocarbonatite whole-rock composition (14.30 wt.% MgO; 31.80 wt.% SiO2). The silicocarbonatite has retained an ultimate mantle source 13C isotopic composition after metamorphism, consistent with the presence of mantle debris. The silicocarbonatite is Cr-, Ni- and Co-rich (847 ppm, 611 ppm and 60 ppm, respectively) but REE depleted compared with volcanic dolomite carbonatites worldwide. The mineral assemblage consists of Sr-rich (0.55 wt.% SrO) ferroan dolomite, magnesite and pseudomorphs of chlorite after phlogopite, consistent with derivation from a carbonated and hydrated mantle. However, chrome spinel crystals (≤4 40.14 wt.% Cr2O3) are compositionally indistinguishable from unmetasomatized spinel macrocrysts in kimberlites. The silicocarbonatite is inferred to represent a magma produced by partial melting of metasomatized mantle at physical conditions between those in which primary dolomite carbonatite and ultramafic magmas of high-pressure origin form. The primary silicocarbonatite magma ascended and sampled mantle material in a manner similar to kimberlite, and subsequently lost volatile components due to release of metasomatic fluids and later metamorphism.