Extended Phases Research Articles

Crystal structures and dynamical properties of dense CO2

Structural polymorphism in dense carbon dioxide (CO2) has attracted significant attention in high-pressure physics and chemistry for the past two decades. Here, we have performed high-pressure experiments and first-principles theoretical calculations to investigate the stability, structure, and dynamical properties of dense CO2 We found evidence that CO2-V with the 4-coordinated extended structure can be quenched to ambient pressure below 200 K-the melting temperature of CO2-I. CO2-V is a fully coordinated structure formed from a molecular solid at high pressure and recovered at ambient pressure. Apart from confirming the metastability of CO2-V (I-42d) at ambient pressure at low temperature, results of ab initio molecular dynamics and metadynamics (MD) simulations provided insights into the transformation processes and structural relationship from the molecular to the extended phases. In addition, the simulation also predicted a phase V'(Pna21) in the stability region of CO2-V with a diffraction pattern similar to that previously assigned to the CO2-V (P212121) structure. Both CO2-V and -V' are predicted to be recoverable and hard with a Vicker hardness of ∼20 GPa. Significantly, MD simulations found that the CO2 in phase IV exhibits large-amplitude bending motions at finite temperatures and high pressures. This finding helps to explain the discrepancy between earlier predicted static structures and experiments. MD simulations clearly indicate temperature effects are critical to understanding the high-pressure behaviors of dense CO2 structures-highlighting the significance of chemical kinetics associated with the transformations.

On thermodynamics of charged AdS black holes in extended phases space via M2-branes background

Motivated by a recent work on asymptotically Ad $$S_4$$ black holes in M-theory, we investigate both thermodynamics and the thermodynamical geometry of Reissner–Nordstrom-AdS black holes from M2-branes. More precisely, we study AdS black holes in $$AdS_{4}\times S^{7}$$ , with the number of M2-branes interpreted as a thermodynamical variable. In this context, we calculate various thermodynamical quantities including the chemical potential, and examine their phase transitions along with the corresponding stability behaviors. In addition, we also evaluate the thermodynamical curvatures of the Weinhold, Ruppeiner, and Quevedo metrics for M2-branes geometry to study the stability of such a black object. We show that the singularities of these scalar curvature’s metrics reproduce similar stability results to those obtained by the phase transition diagram via the heat capacities in different ensembles either when the number of the M2 branes or the charge is held fixed. Also, we note that all results derived in Belhaj et al. (Eur Phys J C 76(2):73, 2016) are recovered in the limit of the vanishing charge.

Brachiopod faunas, facies and biostratigraphy of the Pridolian to lower Eifelian succession in the Rhenish Massif (Rheinisches Schiefergebirge, Germany)

Abstract The succession of Pridolian to lower Eifelian (uppermost Silurian to lowermost Middle Devonian) rhynchonelliformean brachiopod faunas from the Rhenish Massif (Germany) is described and interpreted against the background of sedimentary sequences and facies development. The predominant rhenotypic (‘Rhenish’) facies is redefined as a neritic-siliciclastic facies type of the Devonian. It is subdivided into eurhenotypic, pararhenotypic and allorhenotypic subfacies, based on sedimentary features and specific brachiopod assemblages reflecting different shallow-marine palaeoenvironments under more or less terrigenous influence. The studied sedimentary successions are subdivided biostratigraphically on the basis of brachiopods, correlated on a supraregional scale, and calibrated in terms of the global chronostratigraphy. Stratigraphic intervals with characteristic brachiopod faunas are distinguished. Faunal turnovers between these are attributed to regional events in the context of short or more extended phases of palaeoenvironmental change presumably caused mainly by sea-level fluctuations in combination with varying crustal subsidence and sedimentation rates. These changes resulted in shelf-wide or more regional extinction or emigration of substantial parts of a brachiopod fauna and subsequent replacement by a largely new one. Finally, new taxa of brachiopods are introduced: Sartenaerirhynchus gen. nov., Paraspirifer ( Mosellospirifer ) subgen. nov., Paraspirifer ( Laurentispirifer ) subgen. nov., Iridistrophia ( Flabellistrophia ) subgen. nov. and Iridistrophia ( Flabellistrophia ) musculosa sp. nov.

Wetland plant growth under contrasting water regimes associated with river regulation and drought: implications for environmental water management

An important characteristic of many wetland plants in semi-arid regions is their capacity to withstand fluctuations between extended dry phases and floods. However, anthropogenic river regulation can reduce natural flow variability in riverine wetlands, causing a decline in the frequency and duration of deep flooding as well as extended droughts, and an increase in shallow flooding and soil saturation. Our aim in this paper was to use an experimental approach to examine whether reductions in flooding and drought disadvantage species adapted to both these extremes, and favours those with water requirements that match the new regime of frequent low-level flooding. We compared the growth characteristics and biomass allocation of three native Australian aquatic macrophytes (Pseudoraphis spinescens, Juncus ingens and Typha domingensis), which co-occur at Barmah Forest, south-eastern Australia, under three water treatments: drought, soil saturation and deep flooding. The responses of species to the treatments largely reflected changes in their relative abundance at Barmah Forest since river regulation. Typha domingensis, which has remained uncommon, performed relatively poorly in all treatments, while J. ingens, which has increased its range, exhibited more vigorous growth under soil saturation. Pseudoraphis spinescens, which was once widespread but has declined markedly in its distribution, grew strongly under all water treatments. These findings suggest that a return to more natural, variable river flow regimes can potentially be an important conservation and restoration strategy in ecosystems characterised by species that have adaptations to extreme hydrological growing conditions.

Frustration in the Kondo lattice model: Local versus extended singlet phases

We present a theoretical study of the frustrated Kondo lattice model on a Shastry-Sutherland-type lattice. Using a mean-field decoupling on both the Kondo and intersite exchange interactions, we study three different phases, an antiferromagnetic (AF) phase without Kondo effect, a Kondo (K) phase without magnetic order, and finally a valence bond solid (VBS) phase without magnetic order and Kondo effect. A phase diagram is obtained giving the stability region of the three phases, as a function of the Kondo parameter ${J}_{K}$ and the frustration ratio $J/{J}^{\ensuremath{'}}$ of the two exchange interactions on the Shastry-Sutherland lattice. This phase diagram can account for the change under pressure from a nonmagnetic Kondo phase to an AF phase and to a completely different nonmagnetic VBS phase occurring in some ytterbium compounds such as Yb${}_{2}$Pd${}_{2}$Sn.

Two- and three-dimensional extended solids and metallization of compressed XeF2

The application of pressure, internal or external, transforms molecular solids into extended solids with more itinerant electrons to soften repulsive interatomic interactions in a tight space. Examples include insulator-to-metal transitions in O(2), Xe and I(2), as well as molecular-to-non-molecular transitions in CO(2) and N(2). Here, we present new discoveries of novel two- and three-dimensional extended non-molecular phases of solid XeF(2) and their metallization. At approximately 50 GPa, the transparent linear insulating XeF(2) transforms into a reddish two-dimensional graphite-like hexagonal layered structure of semiconducting XeF(4). Above 70 GPa, it further transforms into a black three-dimensional fluorite-like structure of the first observed metallic XeF(8) polyhedron. These simultaneously occurring molecular-to-non-molecular and insulator-to-metal transitions of XeF(2) arise from the pressure-induced delocalization of non-bonded lone-pair electrons to sp(3)d(2) hybridization in two-dimensional XeF(4) and to p(3)d(5) in three-dimensional XeF(8) through the chemical bonding of all eight valence electrons in Xe and, thereby, fulfilling the octet rule at high pressures.

GLGM‐3: A degree‐150 lunar gravity model from the historical tracking data of NASA Moon orbiters

In preparation for the radio science experiment of the Lunar Reconnaissance Orbiter (LRO) mission, we analyzed the available radio tracking data of previous NASA lunar orbiters. Our goal was to use these historical observations in combination with the new low‐altitude data to be obtained by LRO. We performed Precision Orbit Determination on trajectory arcs from Lunar Orbiter 1 in 1966 to Lunar Prospector in 1998, using the GEODYN II program developed at NASA Goddard Space Flight Center. We then created a set of normal equations and solved for the coefficients of a spherical harmonics expansion of the lunar gravity potential up to degree and order 150. The GLGM‐3 solution obtained with a global Kaula constraint (2.5 × 10−4l−2) shows good agreement with model LP150Q from the Jet Propulsion Laboratory, especially over the nearside. The levels of data fit with both gravity models are very similar (Doppler RMS of ∼0.2 and ∼1–2 mm/s in the nominal and extended phases, respectively). Orbit overlaps and uncertainties estimated from the covariance matrix also agree well. GLGM‐3 shows better correlation with lunar topography and admittance over the nearside at high degrees of expansion (l> 100), particularly near the poles. We also present three companion solutions, obtained with the same data set but using alternate inversion strategies that modify the power law constraint and expectation of the individual spherical harmonics coefficients. We give a detailed discussion of the performance of this family of gravity field solutions in terms of observation fit, orbit quality, and geophysical consistency.

Immigration history of amphidromous species on a Greater Antillean island

AbstractAim To use molecular data to test for dispersal structuring in the immigration history of an amphidromous community on an island.Location The Caribbean island of Puerto Rico.Methods Mitochondrial DNA sequences were obtained from 11 amphidromous species, including shrimps, fish and a gastropod, sampled from throughout the island. The timing of population expansion (TE) in each species was calculated using nucleotide variation and molecular clock dating methods. The order of species accumulation was then reconstructed (oldest to most recent estimate for TE), and groups of species with non‐overlapping estimates for TE were identified. The temporal span and average immigration rate for each group were calculated and compared with expectations of two previously published models of island immigration [the ‘dispersal‐structured model of island recolonization’ (Whittaker & Jones, Oikos, 1994, 69, 524–529), which predicts short phases of rapid immigration followed by extended phases with relatively slow immigration rates; and the ‘colonization window hypothesis’ (Carine, Taxon, 2005, 54, 895–903), which suggests that opportunities for island colonization are temporally constrained to discrete waves of colonization].Results The molecular data indicated the immigration history of Puerto Rican amphidromous fauna from the late Pleistocene through the Holocene and identified two groups of species with non‐overlapping estimates for TE and one group that overlapped with the other two groups. The temporal span, average immigration rate and lack of discreteness between all three groups indicated a continuum of immigration rather than distinct phases of species arrivals.Main conclusions This study did not support the expectations of the immigration models and suggested that amphidromous species from Puerto Rico comprise a single class of marine‐based dispersers. The immigration sequence we report probably reflects a recolonization chronology in this community, in keeping with the notion of species turnover through time. Four areas of future research into the immigration history of amphidromous species on islands are identified, and indicated the possibility that equilibrium processes govern long‐term community change in amphidromous biota on islands.

Raman studies of molecular-to-nonmolecular transitions in carbon dioxide at high pressures and temperatures

We have studied the molecular-to-nonmolecular phase transformations of carbon dioxide $({\text{CO}}_{2})$ in laser-heated diamond-anvil cells by confocal micro-Raman spectroscopy. Our spatially resolved Raman data across the laser-heated area suggest that two distinct forms of extended phases, phase VIII and disordered phase, coexist with tetrahedrally coordinated phase V above 50 GPa but at somewhat lower temperatures. The existence of these phases are most evident from their characteristic Raman features, which include a strong mode at $1200\text{ }{\text{cm}}^{\ensuremath{-}1}$ for phase VIII and a broad peak at $900\text{ }{\text{cm}}^{\ensuremath{-}1}$ for disordered phase, both of which appear at substantially higher wave numbers than the ${\ensuremath{\nu}}_{\text{b}}(\text{C-O-C})$ mode of phase V at $\ensuremath{\sim}800\text{ }{\text{cm}}^{\ensuremath{-}1}$, around 50 GPa. Our Raman data further suggest that phase III is stable to at least 65 GPa at ambient temperatures and thus, emphasize that the stability field of $a$-carbonia, an amorphous extended phase, is only at elevated temperatures at pressures around 50 GPa or at room temperature above 65 GPa. This apparent extended stability of phase III may be due to strong kinetics associated with the molecular-to-nonmolecular transitions.

Tactical management of pasture fallows in Western Australian cropping systems

Agricultural systems in the Western Australian wheatbelt are increasingly moving towards specialist crop production due to elevated cereal prices, depressed markets for livestock products, and ongoing labour scarcity. However, the profitability of crop-only farms is threatened by increasing levels of herbicide resistance and declining soil fertility. This study determines the value of ungrazed pasture fallows grown tactically between crop phases to address these agronomic constraints. A novel metaheuristic optimisation technique, compressed annealing, is used to determine profitable flexible land-use sequences in a complex simulation model. Tactical use of single-year, ungrazed pasture phases is found to be more valuable than the use of break crops in crop-only systems. In contrast to previous analysis, it is identified that rotation of short periods of crop and pasture is more profitable than extended phases of both. Effective weed control without dependence on selective herbicides is the key agronomic characteristic determining the value of intermittent pasture phases. Accordingly, the number of single-year pasture phases employed in a sequence should increase with the severity of herbicide resistance. Compressed annealing is shown to be a practical method of identifying profitable land-use sequences that respond to information that unfolds dynamically.

Trigonal-Bipyramidal Metal Cyanide Complexes: A Versatile Platform for the Systematic Assessment of the Magnetic Properties of Prussian Blue Materials

Pentanuclear cyanide-bridged clusters of the general formula {[M(tmphen)(2)](3)[M'(CN)(6)](2)} (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) have been under investigation in our laboratories for a number of years. These related molecules are conveniently prepared by a building block approach that involves the reaction of mononuclear {M(tmphen)(2)X(2)}(0/2+) species (M = Cr, Mn, Fe, Co, Ni, Zn; X = anion, solvent) with [M'(CN)(6)](3-) anions (M' = Cr, Mn, Fe, Co, Os). The resulting trigonal-bipyramidal (TBP) clusters, consisting of M and M' centers in the equatorial and axial positions, respectively, exhibit diverse properties including those that had previously been observed only for Prussian blue extended phases; these properties include single-molecule magnetism, spin crossover, charge-transfer-induced spin transitions, cyanide linkage isomerism, and magnetic coupling through diamagnetic metal ions. Given that a series of clusters with identical axial cyanometallate units can be prepared, we have been able to establish trends in magnetic coupling for families of clusters with different equatorial metal ions. The crystal packing of the clusters, which involves supramolecular pi-stacking interactions, reveals the origin of the observed differences in the coordination environments and, in several cases, the physical properties of the metal ions in the equatorial sites. Recent work has focused on the use of these molecules as building blocks for magnetic chains and the incorporation of highly anisotropic 5d metal ions such as Os(III) into the TBP core. Such comprehensive studies of small clusters are valuable for understanding and modeling the magnetic behavior of more complicated cyanide materials.

Entanglement and the Kondo effect in serially coupled double quantum dots

We investigate entanglement between electrons in serially coupled double quantum dots attached to non interacting leads. In addition to local repulsion we consider the influence of capacitive inter-dot interaction. We show how the competition between extended Kondo and local singlet phases determines the ground state and thereby the entanglement.

Hydriding characteristics of [formula omitted] prepared by mechanical milling of the product of hydriding combustion synthesis

Hydriding combustion synthesis (HCS) and mechanical milling (MM) are both well-known methods for production of magnesium-based hydrogen storage alloys. The former can produce high active hydride by a simple process, and the latter can synthesis various metastable hydrogen storage materials such as nanocrystalline, amorphous and extended solid solutions phases with excellent hydrogen sorption properties. In the present study, HCS and MM were combined, aiming to decrease sorption temperature for Mg 2 Ni . The high active Mg 2 NiH 4 , synthesized by HCS, was mechanically milled for 0.5, 6, 40 and 80 h with 5 wt% of graphite under argon atmosphere. The effect of the milling process on the morphology and crystal structural of Mg 2 NiH 4 were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The hydrogen storage properties were examined by a Sieverts type apparatus. The nanocrystalline Mg 2 NiH 4 milled for 40 h has the best sorption kinetics, which can absorb 2.4 wt% hydrogen at 303 K within 100 s in the first cycle. Several reasons are considered to explain the improvement in hydriding kinetics.

The thermodynamic characteristics of formation of ternary sulfides MeLn2S4 and solid solutions based on them

The thermodynamic characteristics of formation of ternary sulfides CaGd2S4 and BaTm2S4 from Ca(Ba)S and Gd2(Tm2)S3 binary sulfides were determined using various modifications of the electromotive force method. Activity and cationic and anionic transfer numbers in extended phases based on MeLn2S4 were studied simultaneously. CaGd2S4 and BaTm2S4 were found to be stable over the electrolytic temperature range 653–723 K. The stability boundaries of phases based on CaY2S4. BaTm2S4, CaPr2S4, and CaSm2S4 were determined. A vacancy mechanism of defect formation with predominantly sulfide ion transfer was suggested for sequential doping of ternary with binary sulfides.

Silicon–metal clusters: Nano-templates for cluster assembled materials

The structure, cohesive energy and electronic properties of MSi n clusters were studied by first-principles calculations as a function of size ( n) and species (M). We investigated 168 different clusters, containing from 1 to 14 Si atoms together with one transition metal atom among 12 different elements: Ti, Zr, Hf, V, Nb, Ta, Ni, Pd, Pt, Cu, Ag, Au. Clusters with n = 7, 10, 12 appear as local maxima in cohesive energy, independently of the metal involved. This, together with our previous findings for MSi n (containing 12 other transition metal elements), establishes a systematic behavior. For most metals, MSi 12 and MSi 10 (the smallest endohedral species) are highly symmetric and exhibit local (with respect to their neighbors in size) stability. Thus, besides practically all MSi 12 clusters (exceptions being HfSi 12, ZrSi 12), also some MSi 10 such as VSi 10, NiSi 10, PdSi 10, NbSi 10 and AgSi 10, are promising candidates as building blocks for cluster assembled materials. Electronic properties of structurally equivalent clusters depend markedly on the transition metal involved, providing the means to tailor pre-defined properties when designing extended phases.

Effects of initial and extended exposure to an endophyte-infected tall fescue seed diet on faecal and urinary excretion of ergovaline and lysergic acid in mature geldings

AIM: To determine the amount of ergovaline and lysergic acid retained or excreted by geldings fed endophyte-infected seed containing known concentrations of these alkaloids, and the effects of exposure time on clinical expression of toxicosis. METHODS: Mature geldings (n=10) received diets containing either endophyte-free (E-) or endophyte-infected (E+) tall fescue seed during three experimental phases. The first phase (Days −14 to −1) was an adaptation phase, to allow all horses to adapt to a diet containing E- tall fescue seed. The second (Days 0 to 3) was the initial exposure phase to E+ tall fescue seed, used for the delivery of ergovaline and lysergic acid at 0.5 and 0.3 mg/kg of diet, respectively, to test the initial effects of exposure on routes and amounts of elimination of alkaloid. During this phase, half the geldings were exposed to an E+ diet while the rest served as controls by remaining on the E- diet. Once assigned to treatments, geldings remained on the same diet through the third phase (Days 4 to 21), which served as the extended exposure phase. Total outputs of faeces and urine were collected within each phase, to determine retention of ergovaline and lysergic acid and nutrient digestibility. Serum was collected weekly and analysed for activities of enzymes and concentrations of prolactin. Bodyweights (BW) and rectal temperatures were recorded weekly. RESULTS: BW, rectal temperature, enzyme activities and concentrations of prolactin in serum, and nutrient digestibility were not affected by treatment. Total intake of ergovaline by geldings on the E+ diet was 3.5 and 3.6 (SE 0.20) mg/day, and 2.1 and 2.3 (SE 0.11) mg/day were not accounted for in initial and extended phases, respectively. Lysergic acid was excreted in the urine (4.0 and 4.9 (SE 0.97) mg/day) and faeces (2.5 and 2.7 (SE 0.35) mg/day) at greater amounts than that consumed (2.0 and 1.9 (SE 0.09) mg/day) during the initial and extended exposure phases, respectively. Animals exposed to E+ seed for a period of 20 days appeared to excrete more (1.5 vs 1.2 mg/day; SE 0.08; p=0.03) ergovaline in the faeces than those exposed for only 4 days. CONCLUSIONS: Exposure time to the ergot alkaloids had a limited effect on the route of elimination or the amounts of ergovaline or lysergic acid excreted by horses. The primary alkaloid excreted was lysergic acid, and urine was the major route of elimination. These data will aid future research to improve animals′ tolerance to toxic endophyte-infected tall fescue.

Kondo effect in double quantum dots with interdot repulsion

We investigate a symmetrical double quantum dot system serially attached to the leads. The emphasis is on the numerical analysis of finite inter-dot tunneling in the presence of inter-dot repulsive capacitive coupling. The results reveal the competition between extended Kondo phases and local singlet phases in spin and charge degrees of freedom. The corresponding phase diagram is determined quantitatively.

Quantum coherence of hard-core bosons: Extended, glassy, and Mott phases

Quantum phases of hard core bosons (HCBs) confined in a one-dimensional quasiperiodic (QP) potential are studied within the theoretical framework of Hanbury-Brown-Twiss interferometry. The QP potential induces a cascade of Mott-like band-insulator phases in the extended regime, in addition to the Mott insulator, Bose glass, and superfluid phases. The new phases are incompressible and have zero superfluid fraction. At critical filling factors, the appearance of these insulating phases is heralded by a peak to dip transition in the interferogram, which reflects the fermionic aspect of HCBs. In the localized phase, the interference pattern exhibits an hierarchy of peaks at the reciprocal lattice vectors of the system. Our study demonstrates that in contrast to the momentum distribution, HBTI provides an effective method to distinguish Mott and glassy phases.

High-energy-density extended CO solid

Covalently bonded extended phases of molecular solids made of first- and second-row elements at high pressures are a new class of materials with advanced optical, mechanical and energetic properties. The existence of such extended solids has recently been demonstrated using diamond anvil cells in several systems, including nitrogen, carbon dioxide and carbon monoxide. However, the microscopic quantities produced at the formidable high-pressure/temperature conditions have limited the characterization of their predicted novel properties, including high-energy content. In this paper, we present experimental evidence that these extended low-Z solids are indeed high-energy-density materials, by milligram-scale high-pressure synthesis, recovery and characterization of polymeric CO (p-CO). Our spectroscopic data reveal that p-CO is a random polymer made of lactonic entities and conjugated C=C with an energy content rivalling or exceeding that of HMX (cyclo-tetramethylene tetranitramine, a commonly used conventional high explosive). Solid p-CO explosively decomposes to CO(2) and glassy carbon, and thus might be used as an advanced energetic material.

Geriatrische Probleme im perioperativ-chirurgischen Management

Improved healthcare and longer life expectancy have led to more and overall, healthier older patients. As a consequence, we now see more surgical complications attributable to an ever-increasing spectrum of the physiologic changes of aging. These include functional decline, psychiatric as well as medical co-morbidities, medication effects and peri-operative environmental changes. To maintain high patient care standards in geriatric operative patients, surgeons face challenges in peri-operative care (co-morbidities), anesthesia (intra-operative circulatory depression, cardiac insufficiency and limited organ reserve), and intensive care (cardiopulmonary surveillance and delirium). In contrast to the normally temporary surgical period, interdisciplinary approaches are essential during extended peri-operative, convalescent, rehabilitation and follow-up phases of care in the geriatric patient. This will require competency in the realm of geriatrics, on behalf of the treating surgeon who, as a result, will become increasingly more specialized in the future. This article addresses current epidemiology and symptomatology of particular diseases, and as well, offers treatment suggestions with explanations of geriatric pathophysiology and functional decline from a clinically relevant perspective. This review highlights the increased difficulty in treatment of multiple disease processes in the elderly as a result of natural decline in function of all organ systems.