Equivalent Positions Research Articles

New Polymorphic Varieties of Boron Nitride with Diamond-Like TA-Type Phases

In this work, a theoretical study of new polymorphic varieties of boron nitride, which have diamond-like structures with boron and nitrogen atoms in equivalent structural positions, was carried out. The model construction of new phases of boron nitride was performed in the process of crosslinking precursor nanostructures. Single-walled boron nitride nanotubes with chirality indices (3;0), (4;0), and (6;0) were chosen as precursors for the model construction of diamond-like phases. Using the density functional theory method in the generalized gradient approximation, the possibility of stable existence of three new structural varieties of boron nitride with a diamond-like structure was established: BN-TA4, BN-TA5, BN-TA6. The structure of the BN-TA7 diamond-like phase turned out to be unstable and, in the process of geometric optimization, was transformed into the initial structure, a boron nitride nanotube (6;0). As a structural characteristic, the bulk density of the new polymorphs was determined, which is in the range from 2.613 to 3.0836 g/cm3. The sublimation energy of new polymorphic varieties ranges from 17.16 to 17.63 eV/(BN). The value of the band gap near the Fermi energy varies from 5.37 to 5.74 eV.

Dissolution of impurities in sodium gadolinium molybdate NaGd(MoO<sub>4</sub>)<sub>2</sub>

Impurity defects simulation in sodium-gadolinium molybdate NaGd(MoO4)2 was carried out using a method of interatomic potentials. The dissolution energies of tri-, di- and monovalent impurities were estimated. The dependences of the dissolution energy on the ionic radius of the impurity were plotted. For heterovalent substitutions, the most energetically favorable mechanism for charge compensation has been found, both due to intrinsic crystal defects and according to the conjugate isomorphism scheme. The positions of the most probable localization of defects are determined. The effect of disordering of sodium and gadolinium ions at equivalent positions on positional differences in the energy of defects is estimated. A comparison of the solubility of impurities in NaGd(MoO4)2 and its isostructural CaMoO4 indicates that, although isovalent substitutions are energetically more favorable than heterovalent ones, the mechanism of conjugate isomorphism, which ensures electrical neutrality, can equalize these processes.

ELUCIDATING THE DIFFERENTIAL IMPACTS OF EQUIVALENT GATING-CHARGE MUTATIONS IN VOLTAGE-GATED SODIUM CHANNELS.

Voltage-gated sodium (Nav) channels are pivotal for cellular signaling and mutations in Nav channels can lead to excitability disorders in cardiac, muscular, and neural tissues. A major cluster of pathological mutations localizes in the voltage-sensing domains (VSDs), resulting in either gain-of-function (GoF), loss-of-function (LoF) effects, or both. However, the mechanism behind this functional divergence of mutations at equivalent positions remains elusive. Through hotspot analysis, we identified three gating charges (R1, R2, and R3) as major mutational hotspots in VSDs. The same amino-acid substitutions at equivalent gating-charge positions in VSDI and VSDII of the cardiac sodium channel Nav1.5 show differential gating-property impacts in electrophysiology measurements. We conducted 120 μs molecular dynamics (MD) simulations on wild-type and six mutants to elucidate the structural basis of their differential impacts. Our μs-scale MD simulations with applied external electric fields captured VSD state transitions and revealed the differential structural dynamics between equivalent R-to-Q mutants. Notably, we observed transient leaky conformations in some mutants during structural transitions, offering a detailed structural explanation for gating-pore currents. Our salt-bridge network analysis uncovered VSD-specific and state-dependent interactions among gating charges, countercharges, and lipids. This detailed analysis elucidated how mutations disrupt critical electrostatic interactions, thereby altering VSD permeability and modulating gating properties. By demonstrating the crucial importance of considering the specific structural context of each mutation, our study represents a significant leap forward in understanding structure-function relationships in Nav channels. Our work establishes a robust framework for future investigations into the molecular basis of ion channel-related disorders.

Impurity Ions Mn<sup>2+</sup> and Fe<sup>3+</sup> as Paired Spin Labels for the Study of Structural Transformations in Phyllosilicates by the ESR Method

Impurity paramagnetic ions Mn2+ and high spin Fe3+ (S = 5/2) are shown to be very informative “paired spin labels” to investigate structural transformations in natural aluminosilicate clay minerals by ESR spectroscopy. Second derivative ESR (SD ESR) enables to detect minor narrow lines of the ions against the background of intense broad lines of other paramagnetic impurities. Complex SD ESR spectra of the ions are explained by the Jahn-Teller effect and hyperfine interactions with OH-groups. SD ESR spectra before and after heating (620°C and 900°C) proved transformations of octahedral crystal cells accompanied by the loss of the OH-groups, displacement of the ions to equivalent positions.

Magnetization related to late-Variscan extensional collapse in the Lugo Dome (NW Iberian Massif): a metamorphic petrology approach

The Eastern Galicia Magnetic Anomaly (EGMA) is one of the most distinctive and best studied magnetic anomalies in Iberia. It is located in NW Spain and overlaps the Variscan gneissic domes of Lugo and Sanabria. The Lugo Dome, in the north of the EGMA, deforms a large thrust sheet, the Mondoñedo Nappe, allowing the outcropping of its relative autochthon in the Xistral Tectonic Window, where extensional detachments resulting from late-Variscan tectonics crop out. A younger major detachment, the Viveiro Fault, developed on the western limb of the dome. Detailed ground-based magnetic mapping and geological charts show a clear spatial relationship between magnetic maxima and the extensional structures. Magnetic and paleomagnetic studies carried out on samples from this region indicate that rocks in the detachments commonly bear magnetite and hematite carrying induced but also remanent magnetizations and a very well-defined anisotropy of the magnetic susceptibility with directions matching those of the late-Variscan extensional fabrics.Three pairs of metasedimentary samples in equivalent structural positions display variously developed medium-pressure Barrovian parageneses attributed to the early compressional phases of the Variscan orogeny, and low-pressure Buchan-type parageneses associated with the late Variscan extension. Our phase diagram-based petrological study suggests that the non-magnetic samples preserve the Barrovian conditions of 560–640 °C, 5–8.7 kbar. The lithologically and structurally equivalent samples, originally non-magnetic, developed magnetite/hematite-bearing mineral assemblages during decompression and cooling to 500–620 °C, 1.5–6 kbar. This recrystallization was probably assisted by metasomatic oxidizing fluids. The induced component of magnetization is essentially carried by magnetite, while hematite seems the main carrier of remanence. These results support the existing cartographic, geophysical and paleomagnetic findings indicating that the magnetization in the Lugo Dome is related to late-Variscan extension.

A Perspective on Centrohexaindane Chemistry and a Deep‐Sleeping “Cartesian” Seed

AbstractCentrohexaindane (C41H24), a structurally unique polyaromatic hydrocarbon bearing six mutually fused indane wings stretched out along the Cartesian axes of space, may be viewed as a seed for the construction of covalent and supramolecular three‐dimensional frameworks. A kaleidoscope of established and yet‐to‐be‐explored aspects of centrohexaindane chemistry is presented in this article. After addressing some ideas about the naked centrohexacyclic (and topologically nonplanar) C17‐core, which can be considered a “centrohexaquinacyne”, the diversity of known but mostly unknown functionalization patterns at the framework of centrohexaindane is addressed in increasing order of substitution at the twelve equivalent peripheral positions. The variety of centrohexaindanes bearing three identical groups is displayed including a very first access to a centrohexaindane that bears a C3‐symmetrically functionalized tribenzotriquinacene (TBTQ) unit and, thus, a potential for 3D oligocondensation. The diversity of known tetra‐ and hexasubstituted centrohexaindane derivatives is presented and conceivable synthesis strategies are discussed for even more highly functionalized derivatives. Finally, the successful access to centrohexaindanes with exhaustive functionalization and hydrocarbon extension at the twelve peripheral positions completes this overview on what may be a vastly open field, still.

Regular relations of the composition, structure and properties of crystals of hydrogen-containing compounds

Research subject. Crystals of hydrogen-containing compounds belonging to the superprotonic family. Aim. To obtain knowledge about regular relations between composition, atomic structure, real structure and physical properties of materials, with the purpose of elucidating processes occurring in condensed state and forming the basis for modification of known or obtaining new compounds. Materials and methods. Experimental data were obtained using a set of complementary physical methods, including structural analysis using X-rays, synchrotron radiation and neutrons, optical microscopy, and atomic force microscopy. Results. Experimental data on the atomic structure, real structure, and physical properties of superprotonic crystals, including systems of hydrogen bonds and their changes, were obtained. Conclusions. The physical properties of superprotonic crystals are significantly affected by hydrogen bonding systems and their changes, primarily by the formation of dynamically disordered hydrogen bonds with energetically equivalent positions of hydrogen atoms. When carrying out diagnostics of crystalline samples, account should be taken of their real structure, including the structure of surface layers and the presence of crystallization water. These factors may affect the measured physical parameters, the boundaries of existence of phases, the formation of a multiphase state under variations in temperature.

Numerical representations of AB-type copolymer complexes: analysis of 1H NMR chemical shift patterns in terms of a Smith–Cantor set

When considering the possibility of storing information in the sequence of monomer residues within an AB-type copolymer chain, it is constructive to model that sequence as a string of ones and zeros. The intramolecular environment around any given digit (say a “1”) can then be represented by another string of integers—a code—obtained by summing pairs of digits at equivalent positions, in both directions, from that digit. The code can include only integers 0, 1 and 2, and can represent a number in any base b higher than 2. In base b = 3 the resulting set of codes includes all numbers (because only digits 0, 1 and 2 occur in ternary expansions), but in any base b > 3 the codes define a limited set of numbers comprising a fractal we term a Smith–Cantor set. The 1H NMR spectrum of a random, AB-type co(polyester-imide) shows, on complexation with pyrene, a pattern of complexation shifts approximating very closely to the Smith–Cantor set for which b = 4. Other co(polyimide) complexes show a 1H NMR pattern corresponding to a specific sub-set of this fractal. The sub-set arises from a “stop-at-zero” limitation, whereby digits in the initial string are set to zero for code-generating purposes if they occur beyond a zero, as viewed from the central “1”. The limitation arises in copolymers where pyrene binds by intercalation between pairs of adjacent diimide residues. This numerical approach provides a complete, unifying theory to account for the emergence of fractal character in the 1H NMR spectra of AB-type copolymer complexes.

Using the pan-genomic framework for the discovery of genomic islands in the haloarchaeon Halorubrum ezzemoulense.

In this study, we use pan-genomics to characterize the genomic variability of the widely dispersed halophilic archaeal species Halorubrum ezzemoulense (Hez). We include a multi-regional sampling of newly sequenced, high-quality draft genomes. The pan-genome graph of the species reveals 50 genomic islands that represent rare accessory genetic capabilities available to members. Most notably, we observe rearrangements that have led to the insertion/recombination/replacement of mutually exclusive genomic islands in equivalent genome positions ("homeocassettes"). These conflicting islands encode for similar functions, but homologs from islands located between the same core genes exhibit high divergence on the amino acid level, while the neighboring core genes are nearly identical. Both islands of a homeocassette often coexist in the same geographic location, suggesting that either island may be beyond the reach of selective sweeps and that these loci of divergence between Hez members are maintained and persist long term. This implies that subsections of the population have different niche preferences and rare metabolic capabilities. After an evaluation of the gene content in the homeocassettes, we speculate that these islands may play a role in the speciation, niche adaptability, and group selection dynamics in Hez. Though homeocassettes are first described in this study, similar replacements and divergence of genes on genomic islands have been previously reported in other Haloarchaea and distantly related Archaea, suggesting that homeocassettes may be a feature in a wide range of organisms outside of Hez.IMPORTANCEThis study catalogs the rare genes discovered in strains of the species Halorubrum ezzemoulense (Hez), an obligate halophilic archaeon, through the perspective of its pan-genome. These rare genes are often found to be arranged on islands that confer metabolic and transport functions and contain genes that have eluded previous studies. The discovery of divergent, but homologous islands occupying equivalent genome positions ("homeocassettes") in different genomes, reveals significant new information on genome evolution in Hez. Homeocassette pairs encode for similar functions, but their dissimilarity and distribution imply high rates of recombination, different specializations, and niche preferences in Hez. The coexistence of both islands of a homeocassette pair in multiple environments demonstrates that both islands are beyond the reach of selective sweeps and that these genome content differences between strains persist long term. The switch between islands through recombination under different environmental conditions may lead to a greater range of niche adaptability in Hez.

Graduate Medical Education Financing in the US Department of Veterans Affairs.

The US Department of Veterans Affairs (VA) partners with 250 sponsors of graduate medical education (GME), annually providing $850 million for 11,000 full-time equivalent resident positions that support veteran patient care and provide educational opportunities for trainees from affiliated academic programs. Knowledge of VA GME financing is vital to maintain these partnerships. In response to increased scrutiny from several federal oversight bodies, the VA revised its GME reimbursement policy and procedures, including implementing new resident tracking and auditing mechanisms. This article describes the VA GME reimbursement policies and procedures and, to facilitate understanding, compares GME financing policies of the VA and Centers for Medicare and Medicaid Services. Similarities include counting full-time equivalent positions for reimbursable resident activities (eg, patient care and didactics) and ensuring reimbursement is limited to 1 payment per resident. Differences include funding of resident salaries and benefits, indirect funding to support education, and the calculations to determine reimbursement. The VA continues to refine its GME financing policies and procedures to maintain compliance with laws and regulations, and to provide accurate reimbursement to academic affiliates. This endeavor is essential to support the vital GME partnerships between the VA and its affiliate institutions.

Abstract 2343: Adapting gene set enrichment analysis to single cell data

Abstract Gene Set Enrichment Analysis (GSEA) is a method for quantifying the activation of pathways and processes in gene expression data. GSEA works by ranking genes and testing if genes in annotated gene sets representing molecular pathways are overrepresented at the top or bottom of the ranked list. Standard GSEA assumes a gene-by-sample matrix with samples falling in two phenotype class labels and ranks genes based on correlation of expression and sample class labels. Single sample (ssGSEA) uses a similar approach to enrichment scoring but ranks genes in a single sample based on their expression. There has been recent interest in using the ssGSEA modality to measure pathway activity in individual cells from single cell RNA-sequencing (scRNA-seq) data. However, we have observed that ssGSEA scores in scRNA-seq cells are prone to uncertainty due to the characteristic sparsity of scRNA-seq data. This is because sparse data leads to large groups of tied genes, that is, genes with equal expression and subsequently equivalent positions in the ranked list. Because ssGSEA, which was designed for bulk gene expression technologies which yield much less sparse data, breaks ties arbitrarily, these ties can lead to variability in enrichment scores that is purely algorithmic and not a result of the underlying biology. To address this issue, we performed benchmarking to characterize the stability of scores using different enrichment scoring statistics, normalization methods, and aggregation of similar single cells. We have implemented the best practices identified using this analysis as Single Cell GSEA (scGSEA), a software tool which we will make freely available to researchers as open-source software to enable robust gene set enrichment scoring in scRNA-seq data. Citation Format: Alexander T. Wenzel, John Jun, Jill P. Mesirov. Adapting gene set enrichment analysis to single cell data [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2343.

Site dependent strategy for B/C/N homo and heteroatom co-doping in governing the optoelectronic behavior of MgO monolayers

Density functional theory calculations are carried out to investigate the effects of homo- and hetero-type co-doping of B, C and N on structural and electronic properties of MgO monolayers (MLs). The co-doping sites considered here are the possible equivalent and non-equivalent positions of a hexagon in a pristine MgO ML. The planarity of the monolayers is found to be governed by the site selectivity of the dopant atoms as well as the positions of doping. Planar monolayers have a higher likelihood of formation than the non-planar monolayers. In case of non-equivalent doping, the doping atoms always prefer positions that are closer. Stepwise substitution is more likely to occur than simultaneous substitution in formation of the co-doped monolayers. Most of the co-doping combinations introduce magnetism to the pristine MgO ML. Hetero-type monolayers prefer to be in magnetic states and even exhibit higher magnetic moments than homo-type MLs, with a maximum value of 4 μB for B–N co-doping. Almost all the monolayers are semiconducting with significantly reduced band gaps, while few hetero-type monolayers are metallic in nature. The electronic energy band gaps of the monolayers are compatible with the IR and visible regions of the electromagnetic spectrum. The overall tuning of the electronic properties renders the co-doped MgO monolayers effective for applications in spintronics and optoelectronics.

Site-selective time resolved laser spectroscopy and DFT studies of Nd3+ optical centers in BaF2 doped crystals

Site-selective time-resolved laser spectroscopy techniques, which provide high spectral resolution at low temperatures (4.2 K and 6.5 K), were used to clarify the formation mechanism, spectral and kinetic properties of the Nd3+ ion single-site optical centers formed in the fluorite-type BaF2 single crystals doped with Nd3+. This formation occurs by heterovalent substitution of Ba2+ host cations with additional charge compensation by F− anions. To determine the lifetimes of the Stark 4F3/2(1) levels of the Nd3+ impurity centers, the fluorescence decay kinetics was measured using the gated photon counting technique. The data from spectroscopic experiments were combined with density functional theory (DFT) calculations to identify and analyze the local structure of Nd3+ cations in the Nd3+ ions doped BaF2 crystal. Our studies have shown that several types of single-site Nd3+ optical centers can be distinguished in BaF2:Nd3+. We confirmed the existence of an optical center with high C4v site symmetry and a long radiative lifetime of the 4F3/2(1) state τ = 14.3 ms. We also describe two other configurations of centers with local structure characterized by low site symmetry of Cs, which were identified and described for the first time. The decrease in the tetragonal site symmetry from C4v to Cs was explained by the fact that the Nd3+ dopants, distributed over the equivalent cationic positions of the fluorite-type crystal lattice, coordinate to anionic motifs that essentially differ in the position of the additional charge compensator F−. This structural variability induced in the local coordination environment of the optical center affects its spectroscopic properties through a shift in the energy of the 4F3/2(1) Stark level of the Nd3+ ion and results in a different radiative lifetime τ.

Phosphate-related genomic islands as drivers of environmental adaptation in the streamlined marine alphaproteobacterial HIMB59.

These results shed light on the evolutionary strategies of microbes with streamlined genomes to adapt and survive in the oligotrophic conditions that dominate the surface waters of the global ocean. At the individual level, these microbes have been subjected to evolutionary constraints that have led to a more efficient use of nutrients, removing non-essential genes named as "streamlining theory." However, at the population level, they conserve a highly diverse gene pool in flexible genomic islands resulting in polyclonal populations on the same genomic background as an evolutionary response to environmental pressures. Localization of these islands at equivalent positions in the genome facilitates horizontal transfer between clonal lineages. This high level of environmental genomic heterogeneity could explain their cosmopolitan distribution. In the case of the order HIMB59 within the class Alphaproteobacteria, two factors exert evolutionary pressure and determine this intraspecific diversity: phages and the concentration of P in the environment.

The Structure of 2,6-Di-tert-butylphenol-Argon by Rotational Spectroscopy.

The molecular structure of a van der Waals-bonded complex involving 2,6-di-tert-butylphenol and a single argon atom has been determined through rotational spectroscopy. The experimentally derived structural parameters were compared to the outcomes of quantum chemical calculations that can accurately account for dispersive interactions in the cluster. The findings revealed a π-bound configuration for the complex, with the argon atom engaging the aromatic ring. The microwave spectrum reveals both fine and hyperfine tunneling components. The main spectral doubling is evident as two distinct clusters of lines, with an approximate separation of 179 MHz, attributed to the torsional motion associated with the hydroxyl group. Additionally, each component of this doublet further splits into three components, each with separations measuring less than 1 MHz. Investigation into intramolecular dynamics using a one-dimensional flexible model suggests that the main tunneling phenomenon originates from equivalent positions of the hydroxyl group. A double-minimum potential function with a barrier of 1000 (100) cm-1 effectively describes this extensive amplitude motion. However, the three-fold fine structure, potentially linked to internal motions within the tert-butyl group, requires additional scrutiny for a comprehensive understanding.

Evaluating the use of paralogous protein domains to increase data availability for missense variant classification

BackgroundClassification of rare missense variants remains an ongoing challenge in genomic medicine. Evidence of pathogenicity is often sparse, and decisions about how to weigh different evidence classes may be subjective. We used a Bayesian variant classification framework to investigate the performance of variant co-localisation, missense constraint, and aggregating data across paralogous protein domains (“meta-domains”).MethodsWe constructed a database of all possible coding single nucleotide variants in the human genome and used PFam predictions to annotate structurally-equivalent positions across protein domains. We counted the number of pathogenic and benign missense variants at these equivalent positions in the ClinVar database, calculated a regional constraint score for each meta-domain, and assessed this approach versus existing missense constraint metrics for classifying variant pathogenicity and benignity.ResultsAlternative pathogenic missense variants at the same amino acid position in the same protein provide strong evidence of pathogenicity (positive likelihood ratio, LR+ = 85). Additionally, clinically annotated pathogenic or benign missense variants at equivalent positions in different proteins can provide moderate evidence of pathogenicity (LR+ = 7) or benignity (LR+ = 5), respectively. Applying these approaches sequentially (through PM5) increases sensitivity for classifying pathogenic missense variants from 27 to 41%. Missense constraint can also provide strong evidence of pathogenicity for some variants, but its absence provides no evidence of benignity.ConclusionsWe propose using structurally equivalent positions across related protein domains from different genes to augment evidence for variant co-localisation when classifying novel missense variants. Additionally, we advocate adopting a numerical evidence-based approach to integrating diverse data in variant interpretation.

Kinks on elliptical convergent shock waves in hypersonic flow

Kinks commonly appear on the convergent shock surface when an internal conical flow deviates from the axisymmetric state. In this paper, the formation mechanisms of kinks on internal conical shocks (ICSs) generated by elliptical ring wedges with typical entry aspect ratios ( $AR{\rm s}$ ) in a Mach 6 flow are revealed using a theoretical method, in which the spatial evolution of the three-dimensional elliptical ICS is converted into a temporal evolution of a two-dimensional elliptical moving shock (EMS) using the hypersonic equivalence principle. To simultaneously track the shock front of the EMS and the disturbances propagating along it, a front-disturbance tracking method (FDTM) based on geometrical shock dynamics is proposed. It is found that the shock–compression disturbances from the same family initially near the major axis catch up with the disturbance initially emitted from the major axis to form kinks on the EMS. The equivalent kink formation positions predicted by the FDTM always lag behind the real kink formation positions on the elliptical ICS because the applicability of the hypersonic equivalence principle decays as the shock strengthens along the incoming flow direction. The accuracy of the equivalent kink formation positions predicted by the FDTM gradually declines with the reduction in $AR$ , but it can be significantly improved for all $AR{\rm s}$ after a modification of the equivalent relationship using the shock angle in the major plane of the elliptical ICS, which provides a new way to solve the kinks on the elliptical ICS.

Síntesis y análisis estructural de la ludwigita Co<sub>2</sub>InBO<sub>5</sub>

We report the study on the synthesis of indium-doped cobalt ludwigite (Co2InBO5). The Match program, applied to the XRD powder standard, determined that the compound consists of two phases: phase I, ludwigite Co2InBO5 and phase II, the indium oxide In2O3 impurity. The Rietveld refinement applied to the XRD powder standard determined that the percentage by weight of phase I was 98.18% and the percentage by weight of phase II was 1.82%. The atomic ratio between Co and in corresponded to Co/In=2/1, for a goodness of fit s = 1.64 and Chi2 ≅ 2.70. With these adjustment values, the chemical content of the experimental compound was adjusted to its theoretical chemical stoichiometric content. In the unit cell, the different types of atoms occupied the Wyckoff positions 2b, 2c, 4g, and 4h. Atoms of the same or different types can occupy the same Wyckoff position, but a group of them occupy equivalent positions forming a crystallographic orbit. The refined position of each of the different types of atoms, in the unit cell, showed that the B ions, Co and In, form bonds with oxygen generating structural units in the form of triangles (BO3) and in the form of octahedrons (CoO6, InO6). These structural units form low- dimensional substructures such as three-legged ladders 313, 424 and zigzag-shaped planes. Both, the three-legged ladders and the zigzag-shaped planes are formed by the (Co/In)O6 octahedrons, and extend along the crystallographic axis c. These substructures are responsible for their extraordinary physical properties.

Simulating auditory nerve fiber response following micro-electrode stimulation

Abstract The cochlear implant was the first effective and is still the most common neuroprosthetic device which is employed for people with severe to profound hearing loss. To restore auditory perception, an array of micro-electrodes that deliver electrical pulses to the auditory nerve is surgically implanted into the lower cochlea duct, the scala tympani (ST). However, implantation into the upper cavity, the scala vestibuli (SV) has been tested due to severe anatomical obstruction or ossification of the ST. Clinical results revealed similar performance and thresholds for SV and ST cochlear implant users. We present a simulation study of auditory nerve fibre response to monophasic stimulation of both polarities. Excitation profiles are compared for microelectrodes placed in the SV and equivalent positions in the ST. In total, 7 different electrode positions for 4 different fibres have been investigated in a homogenous 2D model. Results for the intact fibres predict generally higher anodic thresholds in comparison to cathodic stimulation at the same electrode position and mostly lower thresholds for the SV electrodes in comparison to their ST counterparts. In contrast, anodic thresholds are mostly lower than cathodic thresholds for the degenerated fibres. Furthermore, due to the increased electrode-fibre distance for degenerate fibres which have completely lost the dendrite, SV stimulation is less beneficial. However, for basal fibres and the clinically relevant mid scala placement of the electrode the typically high thresholds remain similar for ST and SV positions.

Molecular structure and internal dynamics of the antioxidant 2,6-di-tert-butylphenol

Antioxidants are a class of chemical compounds with particular chemico-physical properties that make them suitable for reducing oxidative stress. In this work we report the rotational spectroscopy analysis of the antioxidant 2,6-di-tert-butylphenol in a jet expansion. The rotational spectrum reveals both fine and hyperfine tunnelling components. The largest spectral doubling consists of two distinct groups of lines separated by ∼190 MHz, and is due to the torsional motion associated with the hydroxyl group. Each component of the doublet is further split into three fine components, with separations below 1 MHz. The spectrum was reproduced with a two-state torsion-rotation semirigid Hamiltonian for each pair of torsional states. Additional observation of all the singly-substituted 13C isotopologues allowed to determine the substitution structure by means of the Kraitchman equations. The comparison with the equilibrium structure obtained by computational calculations at B3LYP-D3BJ/def2-TZVP level validate the accurate determination of the carbon skeleton and tert‑butyl group positions. The investigation of intramolecular dynamics with a monodimensional flexible model demonstrates that the tunnelling phenomenon arises from the hydroxyl group's equivalent positions, with a double-minimum potential separated by a barrier of 1000(100) cm−1 allowing for this large amplitude motion. However, the three-fold fine structurte, while plausibly associated to internal motions within the tert‑butyl group, will require further exploration.