Quantum Monte Carlo Study of High Pressure Solid Molecular Hydrogen

We use the diffusion quantum Monte Carlo (DMC) method to calculate the ground state phase diagram of solid molecular hydrogen and examine the stability of the most important insulating phases relative to metallic crystalline molecular hydrogen. We develop a new method to account for finite-size errors by combining the use of twist-averaged boundary conditions with corrections obtained using the Kwee-Zhang-Krakauer (KZK) functional in density functional theory. To study band-gap closure and find the metallization pressure, we perform accurate quasi-particle many-body calculations using the $GW$ method. In the static approximation, our DMC simulations indicate a transition from the insulating Cmca-12 structure to the metallic Cmca structure at around 375 GPa. The $GW$ band gap of Cmca-12 closes at roughly the same pressure. In the dynamic DMC phase diagram, which includes the effects of zero-point energy, the Cmca-12 structure remains stable up to 430 GPa, well above the pressure at which the $GW$ band gap closes. Our results predict that the semimetallic state observed experimentally at around 360 GPa [Phys. Rev. Lett. {\bf 108}, 146402 (2012)] may correspond to the Cmca-12 structure near the pressure at which the band gap closes. The dynamic DMC phase diagram indicates that the hexagonal close packed $P6_3/m$ structure, which has the largest band gap of the insulating structures considered, is stable up to 220 GPa. This is consistent with recent X-ray data taken at pressures up to 183 GPa [Phys. Rev. B {\bf 82}, 060101(R) (2010)], which also reported a hexagonal close packed arrangement of hydrogen molecules

Deletion of annexin 2 light chain p11 in nociceptors causes deficits in somatosensory coding and pain behavior

The S100 family protein p11 (S100A10, annexin 2 light chain) is involved in the trafficking of the voltage-gated sodium channel Na(V)1.8, TWIK-related acid-sensitive K+ channel (TASK-1), the ligand-gated ion channels acid-sensing ion channel 1a (ASIC1a) and transient receptor potential vanilloid 5/6 (TRPV5/V6), as well as 5-hydroxytryptamine receptor 1B (5-HT1B), a G-protein-coupled receptor. To evaluate the role of p11 in peripheral pain pathways, we generated a loxP-flanked (floxed) p11 mouse and used the Cre-loxP recombinase system to delete p11 exclusively from nociceptive primary sensory neurons in mice. p11-null neurons showed deficits in the expression of NaV1.8, but not of annexin 2. Damage-sensing primary neurons from these animals show a reduced tetrodotoxin-resistant sodium current density, consistent with a loss of membrane-associated NaV1.8. Noxious coding in wide-dynamic-range neurons in the dorsal horn was markedly compromised. Acute pain behavior was attenuated in certain models, but no deficits in inflammatory pain were observed. A significant deficit in neuropathic pain behavior was also apparent in the conditional-null mice. These results confirm an important role for p11 in nociceptor function

The role of p11 (S100A10) in nociception.

The S100-family protein p11 (S100A10) is involved in a variety of physiological processes, including channel trafficking and angiogenesis. In this thesis, we used genetic approaches to investigate the functional roles of p11. p11 modulates the plasma membrane trafficking of the sensory neuron-specific voltage-gated Na" channel Nay 1.8 and numerous other proteins. Since Nav1.8 performs a specialised function in the detection of noxious stimuli (nociception), we investigated the role of p11 in peripheral pain pathways. We used the Ctq-IoxP system to delete p11 exclusively from nociceptive neurons, allowing the examination of this aspect of p11 function without confounding effects from roles of p11 in other tissues, p11-null neurons showed deficits in the functional expression of Nav1.8. Noxious coding in wide-dynamic range neurons in the dorsal horn was compromised in p11-null animals. Acute mechanical pain behaviour was attenuated, but no deficits in inflammatory pain were observed. Reduced neuropathic pain behaviour was apparent in nociceptor-specific p11-null mice. While certain effects of p11 deletion can be explained by reduced Nav1.8 trafficking. Nav1.8 is not required for neuropathic pain, p11 therefore acts through both Nay1.8-dependent and alternative mechanisms to control nociceptive thresholds. This suggests it is a potential therapeutic target. Given the importance of p11-dependent modulation of Nav1.8. we investigated the p11-binding site on the Nav1.8 N-terminus. In vitro fluorescence resonance energy transfer (FRET) assays were used to examine this interaction. In contrast to previous studies, we found the interaction to be complex, involving two distinct binding sites and an autoinhibitory domain. The p11-Nav1.8 interaction is therefore not well-suited to small molecule-based inhibition. p11 has been reported to play an important role in processes required for angiogenesis. In assays of angiogenesis-dependent tumour growth, global p11 deletion resulted in increased tumour volume and altered vascular morphology. This may have implications for novel anti-cancer therapies targeting p11

The Einstein-de Haas effect in an Fe_{15} cluster

Classical models of spin-lattice coupling are at present unable to accurately reproduce results for numerous properties of ferromagnetic materials, such as heat transport coefficients or the sudden collapse of the magnetic moment in hcp-Fe under pressure. This failure has been attributed to the absence of a proper treatment of effects that are inherently quantum mechanical in nature, notably spin-orbit coupling. This paper introduces a time-dependent, non-collinear tight binding model, complete with spin-orbit coupling and vector Stoner exchange terms, that is capable of simulating the Einstein-de Haas effect in a ferromagnetic Fe15 cluster. The tight binding model is used to investigate the adiabaticity timescales that determine the response of the orbital and spin angular momenta to a rotating, externally applied Β field, and we show that the qualitative behaviours of our simulations can be extrapolated to realistic timescales by use of the adiabatic theorem. An analysis of the trends in the torque contributions with respect to the field strength demonstrates that SOC is necessary to observe a transfer of angular momentum from the electrons to the nuclei at experimentally realistic Β fields. The simulations presented in this paper demonstrate the Einstein-de Haas effect from first principles using a Fe cluster

On the Growth of Al_2 O_3 Scales

Understanding the growth of Al2O3 scales requires knowledge of the details of the chemical reactions at the scale–gas and scale–metal interfaces, which in turn requires specifying how the creation/annihilation of O and Al vacancies occurs at these interfaces. The availability of the necessary electrons and holes to allow for such creation/annihilation is a crucial aspect of the scaling reaction. The electronic band structure of polycrystalline Al2O3 thus plays a decisive role in scale formation and is considered in detail, including the implications of a density functional theory (DFT) calculation of the band structure of a Σ7 View the MathML source bicrystal boundary, for which the atomic structure of the boundary was known from an independent DFT energy-minimization calculation and comparisons with an atomic-resolution transmission electron micrograph of the same boundary. DFT calculations of the formation energy of O and Al vacancies in bulk Al2O3 in various charge states as a function of the Fermi energy suggested that electronic conduction in Al2O3 scales most likely involves excitation of both electrons and holes, which are localized on singly charged O vacancies, View the MathML source and doubly charged Al vacancies, View the MathML source, respectively. We also consider the variation of the Fermi level across the scale and bending (“tilting”) of the conduction band minimum and valence band maximum due to the electric field developed during the scaling reaction. The band structure calculations suggest a new mechanism for the “reactive element” effect—a consequence of segregation of Y, Hf, etc., to grain boundaries in Al2O3 scales, which results in improved oxidation resistance—namely, that the effect is due to the modification of the near-band edge grain-boundary defect states rather than any blocking of diffusion pathways, as previously postulated. Secondly, Al2O3 scale formation is dominated by grain boundary as opposed to lattice diffusion, and there is unambiguous evidence for both O and Al countercurrent transport in Al2O3 scale-forming alloys. We postulate that such transport is mediated by migration of grain boundary disconnections containing charged jogs, rather than by jumping of isolated point defects in random high-angle grain boundaries

Pain Genes

Pain, which afflicts up to 20% of the population at any time, provides both a massive therapeutic challenge and a route to understanding mechanisms in the nervous system. Specialised sensory neurons (nociceptors) signal the existence of tissue damage to the central nervous system (CNS), where pain is represented in a complex matrix involving many CNS structures. Genetic approaches to investigating pain pathways using model organisms have identified the molecular nature of the transducers, regulatory mechanisms involved in changing neuronal activity, as well as the critical role of immune system cells in driving pain pathways. In man, mapping of human pain mutants as well as twin studies and association studies of altered pain behaviour have identified important regulators of the pain system. In turn, new drug targets for chronic pain treatment have been validated in transgenic mouse studies. Thus, genetic studies of pain pathways have complemented the traditional neuroscience approaches of electrophysiology and pharmacology to give us fresh insights into the molecular basis of pain perception

Ferromagnetic and antiferromagnetic spin fluctuations and superconductivity in the hcp-phase of Fe

High purity iron, which transforms into the hcp phase under pressure, has recently been reported to be superconducing in the pressure range 150-300 kBar [shim]. The electronic structure and the electron-phonon coupling ($\lambda_{ph}$) are calculated for hcp iron at different volumes. A parameter-free theory for calculating the coupling constants $\lambda_{sf}$ from ferromagnetic (FM) and antiferromagnetic (AFM) spin fluctuations is developed. The calculated $\lambda_{sf}$ are sufficiently large to explain superconductivity especially from FM fluctuations. The results indicate that superconductivity mediated by spin fluctuations is more likely than from electron-phonon interaction.Comment: (4 pages, 1 figure

A new multi-center approach to the exchange-correlation interactions in ab initio tight-binding methods

A new approximate method to calculate exchange-correlation contributions in the framework of first-principles tight-binding molecular dynamics methods has been developed. In the proposed scheme on-site (off-site) exchange-correlation matrix elements are expressed as a one-center (two-center) term plus a {\it correction} due to the rest of the atoms. The one-center (two-center) term is evaluated directly, while the {\it correction} is calculated using a variation of the Sankey-Niklewski \cite{Sankey89} approach generalized for arbitrary atomic-like basis sets. The proposed scheme for exchange-correlation part permits the accurate and computationally efficient calculation of corresponding tight-binding matrices and atomic forces for complex systems. We calculate bulk properties of selected transition (W,Pd), noble (Au) or simple (Al) metals, a semiconductor (Si) and the transition metal oxide Ti$O_2$ with the new method to demonstrate its flexibility and good accuracy.Comment: 17 pages, 5 figure

'But what is the reason why you know such things?' Question and response patterns in the LADO interview

This study uses the tools of Conversation Analysis (CA) to investigate problems that occur in LADO (Language Analysis for the Determination of Origin) interviews. We analysed five recorded interviews with female asylum seekers, focussing on question and response pairs. Several problems were identified, associated with directives, echo questions, and challenges. The study also looked at how repair is initiated and carried out. Directives were frequently issued as part of multiple questions from the interviewer, alongside additional questions or modifiers. Interviewees typically provided an answer to the most specific and/or most recent question rather than fulfilling the directive itself. Directives were also used to elicit language samples, and it was found that including a clear topic for talk was the most effective way of accomplishing this goal. Echo questions were predominantly used for requesting confirmation, and were occasionally interpreted as performing this function even where there was evidence that interviewers were using echo questions to prompt for more information or to initiate repair. Challenges contributed to a hostile atmosphere in interviews. Similarly, repair prefaced by initial but was found to be potentially hostile in some instances. Various modes of accomplishing repair were also investigated, but their effectiveness was variable. In assessing the set of question and response pairs in the recordings, we make a number of practical recommendations for improving interview practice in LADO