Computational Screening and Stabilization of Boron-Substituted Type-I and Type-II Carbon Clathrates

Boron substitution represents a promising approach to stabilize carbon clathrate structures, but no thermodynamically stable substitution schemes have been identified for frameworks other than the type-VII (sodalite) structure type. To investigate the possibility for additional tetrahedral carbon-based clathrate networks, more than 5000 unique boron decoration schemes were investigated computationally for type-I and type-II carbon clathrates with a range of guest elements including Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. Density functional theory calculations were performed at 10 and 50 GPa, and the stability and impact of boron substitution were evaluated. The results indicate that the boron-substituted carbon clathrates are stabilized under high-pressure conditions. Full cage occupancies of intermediate-sized guest atoms (e.g., Na, Ca, and Sr) are the most favorable energetically. Clathrate stability is maximized when the boron atoms are substituted within the hexagonal rings of the large [51262]/[51264] cages. Several structures with favorable formation enthalpies <-200 meV/atom were predicted, and type-I Ca8B16C30 is on the convex hull at 50 GPa. This structure represents the first thermodynamically stable type-I clathrate identified and suggests that boron-substituted carbon clathrates may represent a large family of diamond-like framework materials with a range of structure types and guest/framework substitutions.

Identification of western North Atlantic odontocete echolocation click types using machine learning and spatiotemporal correlates

A combination of machine learning and expert analyst review was used to detect odontocete echolocation clicks, identify dominant click types, and classify clicks in 32 years of acoustic data collected at 11 autonomous monitoring sites in the western North Atlantic between 2016 and 2019. Previously-described click types for eight known odontocete species or genera were identified in this data set: Blainville's beaked whales (Mesoplodon densirostris), Cuvier's beaked whales (Ziphius cavirostris), Gervais' beaked whales (Mesoplodon europaeus), Sowerby's beaked whales (Mesoplodon bidens), and True's beaked whales (Mesoplodon mirus), Kogia spp., Risso's dolphin (Grampus griseus), and sperm whales (Physeter macrocephalus). Six novel delphinid echolocation click types were identified and named according to their median peak frequencies. Consideration of the spatiotemporal distribution of these unidentified click types, and comparison to historical sighting data, enabled assignment of the probable species identity to three of the six types, and group identity to a fourth type. UD36, UD26, and UD28 were attributed to Risso's dolphin (G. griseus), short-finned pilot whale (G. macrorhynchus), and short-beaked common dolphin (D. delphis), respectively, based on similar regional distributions and seasonal presence patterns. UD19 was attributed to one or more species in the subfamily Globicephalinae based on spectral content and signal timing. UD47 and UD38 represent distinct types for which no clear spatiotemporal match was apparent. This approach leveraged the power of big acoustic and big visual data to add to the catalog of known species-specific acoustic signals and yield new inferences about odontocete spatiotemporal distribution patterns. The tools and call types described here can be used for efficient analysis of other existing and future passive acoustic data sets from this region.

Measuring the melting curve of iron at super-Earth core conditions

The discovery of more than 4500 extrasolar planets has created a need for modeling their interior structure and dynamics. Given the prominence of iron in planetary interiors, we require accurate and precise physical properties at extreme pressure and temperature. A first-order property of iron is its melting point, which is still debated for the conditions of Earth’s interior. We used high-energy lasers at the National Ignition Facility and in situ x-ray diffraction to determine the melting point of iron up to 1000 gigapascals, three times the pressure of Earth’s inner core. We used this melting curve to determine the length of dynamo action during core solidification to the hexagonal close-packed (hcp) structure. We find that terrestrial exoplanets with four to six times Earth’s mass have the longest dynamos, which provide important shielding against cosmic radiation.

Hydroxychloroquine to Prevent Recurrent Congenital Heart Block in Fetuses of Anti-SSA/Ro-Positive Mothers

BACKGROUND

Experimental and clinical evidence support the role of macrophage Toll-like receptor signaling in maternal anti-SSA/Ro-mediated congenital heart block (CHB).

OBJECTIVES

Hydroxychloroquine (HCQ), an orally administered Toll-like receptor antagonist widely used in lupus including during pregnancy, was evaluated for efficacy in reducing the historical 18% recurrence rate of CHB.

METHODS

This multicenter, open-label, single-arm, 2-stage clinical trial was designed using Simon's optimal approach. Anti-SSA/Ro-positive mothers with a previous pregnancy complicated by CHB were recruited (n = 19 Stage 1; n = 35 Stage 2). Patients received 400 mg daily of HCQ prior to completion of gestational week 10, which was maintained through pregnancy. The primary outcome was 2° or 3° CHB any time during pregnancy, and secondary outcomes included isolated endocardial fibroelastosis, 1° CHB at birth and skin rash.

RESULTS

By intention-to-treat (ITT) analysis, 4 of 54 evaluable pregnancies resulted in a primary outcome (7.4%; 90% confidence interval: 3.4% to 15.9%). Because 9 mothers took potentially confounding medications (fluorinated glucocorticoids and/or intravenous immunoglobulin) after enrollment but prior to a primary outcome, to evaluate HCQ alone, 9 additional mothers were recruited and followed the identical protocol. In the per-protocol analysis restricted to pregnancies exposed to HCQ alone, 4 of 54 (7.4%) fetuses developed a primary outcome as in the ITT. Secondary outcomes included mild endocardial fibroelastosis (n = 1) and cutaneous neonatal lupus (n = 4).

CONCLUSIONS

These prospective data support that HCQ significantly reduces the recurrence of CHB below the historical rate by >50%, suggesting that this drug should be prescribed for secondary prevention of fetal cardiac disease in anti-SSA/Ro-exposed pregnancies. (Preventive Approach to Congenital Heart Block With Hydroxychloroquine [PATCH]; NCT01379573).

Prediction of an Extended Ferroelectric Clathrate

Using first-principles calculations, we predict a lightweight room-temperature ferroelectric carbon-boron framework in a host-guest clathrate structure. This ferroelectric clathrate, with composition ScB_{3}C_{3}, exhibits high polarization density and low mass density compared with widely used commercial ferroelectrics. Molecular dynamics simulations show spontaneous polarization with a moderate above-room-temperature T_{c} of ∼370  K, which implies large susceptibility and possibly large electrocaloric and piezoelectric constants at room temperature. Our findings open the possibility for a new class of ferroelectric materials with potential across a broad range of applications.

Reconciliation of Experiments and Theory on Transport Properties of Iron and the Geodynamo

We measure the electrical resistivity of hcp iron up to ∼170  GPa and ∼3000  K using a four-probe van der Pauw method coupled with homogeneous flattop laser heating in a DAC, and compute its electrical and thermal conductivity by first-principles molecular dynamics including electron-phonon and electron-electron scattering. We find that the measured resistivity of hcp iron increases almost linearly with temperature, and is consistent with our computations. The results constrain the resistivity and thermal conductivity of hcp iron to ∼80±5  μΩ cm and ∼100±10  W m^{-1} K^{-1}, respectively, at conditions near the core-mantle boundary. Our results indicate an adiabatic heat flow of ∼10±1  TW out of the core, supporting a present-day geodynamo driven by thermal and compositional convection.

Sex Differences in Systemic Lupus Erythematosus: Epidemiology, Clinical Considerations, and Disease Pathogenesis

Systemic lupus erythematosus (SLE) is a chronic, multiorgan, systemic autoimmune disease that is more common in women than men and is typically diagnosed during reproductive age, necessitating sex-specific considerations in care. In women there is no substantive evidence to suggest that SLE reduces fertility, but subfertility may occur as a result of active disease, immunosuppressive drugs, and age-related declines in fertility related to delays in childbearing. Although pregnancy outcomes have improved, SLE still poses risks in pregnancy that contribute to poorer maternal and fetal outcomes. Cyclophosphamide, an important agent for the treatment of severe or life-threatening lupus, may adversely affect fertility, particularly with increases in dose and patient age. Fertility preservation techniques are therefore an important consideration for women and men before cytotoxic treatment. There is mixed evidence as to whether exogenous estrogen in the form of oral contraceptive pills or hormone replacement therapy may increase the risk for the development of SLE, but among women with SLE already diagnosed, combined oral contraceptive pills and hormone replacement therapy do not confer risk for severe flare and remain important in reproductive care. The higher incidence of SLE in women may nonetheless be attributable to effects of endogenous estrogen, as well as failures in X chromosome inactivation, increased Toll-like receptor gene products, and changes in microRNA function. A greater appreciation of the biological underpinnings and consequences of sex differences in SLE may lead to more targeted treatments and improved outcomes for patients with SLE.

Phase Transition Pathway Sampling via Swarm Intelligence and Graph Theory

The prediction of reaction pathways for solid-solid transformations remains a key challenge. Here, we develop a pathway sampling method via swarm intelligence and graph theory and demonstrate that our pallas method is an effective tool to help understand phase transformations in solid-state systems. The method is capable of finding low-energy transition pathways between two minima without having to specify any details of the transition mechanism a priori. We benchmarked our pallas method against known phase transitions in cadmium selenide (CdSe) and silicon (Si). pallas readily identifies previously reported, low-energy phase transition pathways for the wurtzite to rock-salt transition in CdSe and reveals a novel lower-energy pathway that has not yet been observed. In addition, pallas provides detailed information that explains the complex phase transition sequence observed during the decompression of Si from high pressure. Given the efficiency to identify low-barrier-energy reaction pathways, the pallas methodology represents a promising tool for materials by design with valuable insights for novel synthesis.

Polar Metallocenes

Crystalline polar metallocenes are potentially useful active materials as piezoelectrics, ferroelectrics, and multiferroics. Within density functional theory (DFT), we computed structural properties, energy differences for various phases, molecular configurations, and magnetic states, computed polarizations for different polar crystal structures, and computed dipole moments for the constituent molecules with a Wannier function analysis. Of the systems studied, Mn₂(C₉H₉N)₂ is the most promising as a multiferroic material, since the ground state is both polar and ferromagnetic. We found that the predicted crystalline polarizations are 30–40% higher than the values that would be obtained from the dipole moments of the isolated constituent molecules, due to the local effects of the self-consistent internal electric field, indicating high polarizabilities.

Thermal Conductivity and Electrical Resistivity of Solid Iron at Earth's Core Conditions from First Principles

We compute the thermal conductivity and electrical resistivity of solid hcp Fe to pressures and temperatures of Earth's core. We find significant contributions from electron-electron scattering, usually neglected at high temperatures in transition metals. Our calculations show a quasilinear relation between the electrical resistivity and temperature for hcp Fe at extreme high pressures. We obtain thermal and electrical conductivities that are consistent with experiments considering reasonable error. The predicted thermal conductivity is reduced from previous estimates that neglect electron-electron scattering. Our estimated thermal conductivity for the outer core is 77±10  W m^{-1} K^{-1} and is consistent with a geodynamo driven by thermal convection.

Polarization rotation and the electrocaloric effect in barium titanate

We study the electrocaloric effect in the classic ferroelectric BaTiO₃ through a series of phase transitions driven by applied electric field and temperature. We find both negative and positive electrocaloric effects, with the negative electrocaloric effect, where temperature decreases with applied field, in monoclinic phases. Macroscopic polarization rotation is evident through the monoclinic and orthorhombic phases under applied field, and is responsible for the negative electrocaloric effect.

Origin of Negative Longitudinal Piezoelectric Effect

Piezoelectrics with negative longitudinal piezoelectric coefficients will contract in the direction of an applied electric field. Such piezoelectrics are thought to be rare, but there is no fundamental physics preventing the realization of negative longitudinal piezoelectric effect in a single-phase material. Using first-principles calculations, we demonstrate that several hexagonal ABC ferroelectrics possess significant negative longitudinal piezoelectric effects. The data mining of a first-principles-based database of piezoelectrics reveals that this effect is a general phenomenon. The origin of this unusual piezoelectric response relies on the strong ionic bonds associated with small effective charges and rigid potential energy surfaces. Moreover, ferroelectrics with negative longitudinal piezoelectric coefficients show anomalous pressure-enhanced ferroelectricity. Our results offer design principles to aid the search for new piezoelectrics for novel electromechanical device applications.

Improving the Functional Control of Aged Ferroelectrics Using Insights from Atomistic Modeling

We provide a fundamental insight into the microscopic mechanisms of the aging processes. Using large-scale molecular dynamics simulations of the prototypical ferroelectric material PbTiO_{3}, we demonstrate that the experimentally observed aging phenomena can be reproduced from intrinsic interactions of defect dipoles related to dopant-vacancy associates, even in the absence of extrinsic effects. We show that variation of the dopant concentration modifies the material's hysteretic response. We identify a universal method to reduce loss and tune the electromechanical properties of inexpensive ceramics for efficient technologies.

Stable charged antiparallel domain walls in hyperferroelectrics

Charge-neutral 180° domain walls that separate domains of antiparallel polarization directions are common structural topological defects in ferroelectrics. In normal ferroelectrics, charged 180° domain walls running perpendicular to the polarization directions are highly energetically unfavorable because of the depolarization field and are difficult to stabilize. We explore both neutral and charged 180° domain walls in hyperferroelectrics, a class of proper ferroelectrics with persistent polarization in the presence of a depolarization field, using density functional theory. We obtain zero temperature equilibrium structures of head-to-head and tail-to-tail walls in recently discovered ABC-type hexagonal hyperferroelectrics. Charged domain walls can also be stabilized in canonical ferroelectrics represented by LiNbO₃ without any dopants, defects or mechanical clamping. First-principles electronic structure calculations show that charged domain walls can reduce and even close the band gap of host materials and support quasi-two-dimensional electron(hole) gas with enhanced electrical conductivity.

Chemical accuracy from quantum Monte Carlo for the benzene dimer

We report an accurate study of interactions between benzene molecules using variational quantum Monte Carlo (VMC) and diffusion quantum Monte Carlo (DMC) methods. We compare these results with density functional theory using different van der Waals functionals. In our quantum Monte Carlo (QMC) calculations, we use accurate correlated trial wave functions including three-body Jastrow factors and backflow transformations. We consider two benzene molecules in the parallel displaced geometry, and find that by highly optimizing the wave function and introducing more dynamical correlation into the wave function, we compute the weak chemical binding energy between aromatic rings accurately. We find optimal VMC and DMC binding energies of -2.3(4) and -2.7(3) kcal/mol, respectively. The best estimate of the coupled-cluster theory through perturbative triplets/complete basis set limit is -2.65(2) kcal/mol [Miliordos et al., J. Phys. Chem. A 118, 7568 (2014)]. Our results indicate that QMC methods give chemical accuracy for weakly bound van der Waals molecular interactions, comparable to results from the best quantum chemistry methods.

Dew harvesting efficiency of four species of cacti

Four species of cacti were chosen for this study: Copiapoa cinerea var. haseltoniana, Ferocactus wislizenii, Mammillaria columbiana subsp. yucatanensis and Parodia mammulosa. It has been reported that dew condenses on the spines of C. cinerea and that it does not on the spines of F. wislizenii, and our preliminary observations of M. columbiana and P. mammulosa revealed a potential for collecting dew water. This study found all four cacti to harvest dew on their stems and spines (albeit rarely on the spines of F. wislizenii). Dew harvesting experiments were carried out in the UK, recording an increase in cacti mass on dewy nights. By applying a ranking relative to a polymethyl methacrylate (Plexiglas) reference plate located nearby, it was found that C. cinerea collected the most airborne moisture followed by M. columbiana, P. mammulosa and F. wislizenii respectively, with mean efficiency ratio with respect to the Plexiglas reference of 3.48 ± 0.5, 2.44 ± 0.06, 1.81 ± 0.14 and 1.27 ± 0.49 on observed dewy nights. A maximum yield of normalized performance of 0.72 ± 0.006 l/m(-2) on one dewy night was recorded for C. cinerea. Removing the spines from M. columbiana was found to significantly decrease its dew harvesting efficiency. The spines of three of the species were found to be hydrophilic in nature, while F. wislizenii was hydrophobic; the stems of all four species were hydrophilic. The results of this study could be translated into designing a biomimetic water collecting device that utilizes cactus spines and their microstructures.

Industrial-scale spray layer-by-layer assembly for production of biomimetic photonic systems

Layer-by-layer assembly is a powerful and flexible thin film process that has successfully reproduced biomimetic photonic systems such as structural colour. While most of the seminal work has been carried out using slow and ultimately unscalable immersion assembly, recent developments using spray layer-by-layer assembly provide a platform for addressing challenges to scale-up and manufacturability. A series of manufacturing systems has been developed to increase production throughput by orders of magnitude, making commercialized structural colour possible. Inspired by biomimetic photonic structures we developed and demonstrated a heat management system that relies on constructive reflection of near infrared radiation to bring about dramatic reductions in heat content.

Giant electrocaloric effect around Tc

We use molecular dynamics with a first-principles-based shell model potential to study the electrocaloric effect (ECE) in lithium niobate, LiNbO(3), and find a giant electrocaloric effect along a line passing through the ferroelectric transition. With an applied electric field, a line of maximum ECE passes through the zero field ferroelectric transition, continuing along a Widom line at high temperatures with increasing fields, and along the instability that leads to homogeneous ferroelectric switching below T(c) with an applied field antiparallel to the spontaneous polarization. This line is defined as the minimum in the inverse capacitance under an applied electric field. We investigate the effects of pressure, temperature and an applied electric field on the ECE. The behavior we observe in LiNbO(3) should generally apply to ferroelectrics; we therefore suggest that the operating temperature for refrigeration and energy scavenging applications should be above the ferroelectric transition region to obtain a large electrocaloric response. The relationship between T(c), the Widom line, and homogeneous switching should be universal among ferroelectrics, relaxors, multiferroics, and the same behavior should be found under applied magnetic fields in ferromagnets.

Expression of aromatase and two isozymes of 5α-reductase in the developing green anole forebrain

Neural steroids, as well as the enzymes that produce these hormones, are important for sexual differentiation of the brain during development. Aromatase converts testosterone into oestradiol. 5α-reductase converts testosterone to 5α-dihydrotestosterone and occurs in two isozymes: type 1 (5αR1) and type 2 (5αR2). Each of these enzymes is present in the developing brain in many species, although no work has been carried out examining the expression of all three enzymes in non-avian reptiles with genetic sex determination. In the present study, we evaluated mRNA expression of neural aromatase, 5αR1 and 5αR2, on the day of hatching and at day 50 in one such lizard, the green anole. We describe the distribution of these enzymes throughout the brain and the quantification of mRNA expression in three regions that control adult sexual behaviours: the preoptic area (POA) and ventromedial amygdala (AMY), which are involved in male displays, as well as the ventromedial hypothalamus, which regulates female receptivity. Younger animals had a greater number (POA) and density (AMY) of 5αR1 mRNA expressing cells. We detected no effects of sex or age on aromatase or 5αR2. In comparison with data from adults, the present results support the idea that the green anole forebrain has not completely differentiated by 50 days after hatching and that 5αR1 may play a role in the early development of regions important for masculine function.

Experimental and theoretical evidence for pressure-induced metallization in FeO with rocksalt-type structure

Electrical conductivity of FeO was measured up to 141 GPa and 2480 K in a laser-heated diamond-anvil cell. The results show that rock-salt (B1) type structured FeO metallizes at around 70 GPa and 1900 K without any structural phase transition. We computed fully self-consistently the electronic structure and the electrical conductivity of B1 FeO as a function of pressure and temperature, and found that although insulating as expected at ambient condition, B1 FeO metallizes at high temperatures, consistent with experiments. The observed metallization is related to spin crossover.

First-principles based atomistic modeling of phase stability in PMN-xPT

We have performed molecular dynamics simulations using a shell model potential developed by fitting first-principles results to describe the behavior of the relaxor-ferroelectric (1 - x)PbMg(1/3)Nb(2/3)O(3)-xPbTiO(3) (PMN-xPT) as a function of concentration and temperature, using site occupancies within the random site model. In our simulations, PMN is cubic at all temperatures and behaves as a polar glass. As a small amount of Ti is added, a weak polar state develops, but structural disorder dominates, and the symmetry is rhombohedral. As more Ti is added the ground state is clearly polar and the system is ferroelectric, but with easy rotation of the polarization direction. In the high Ti content region, the solid solution adopts ferroelectric behavior similar to PT, with tetragonal symmetry. The ground state sequence with increasing Ti content is R-M(B)-O-M(C)-T. The high-temperature phase is cubic at all compositions. Our simulations give the slopes of the morphotropic phase boundaries, crucial for high-temperature applications. We find that the phase diagram of PMN-xPT can be understood within the random site model.

Aromatase mRNA in the brain of adult green anole lizards: effects of sex and season

Neural testosterone metabolism, particularly the synthesis of oestradiol (E(2)) via the aromatase enzyme, is important for sexual behaviours in many vertebrates. In green anole lizards, E(2) metabolised from testosterone facilitates female receptivity and increases sexual motivation in males. Testosterone treatment increases aromatase activity in the whole brain homogenates of gonadectomised male, but not female, anoles, which is an effect limited to the breeding season (BS). To investigate the potential for local effects of this enzyme in reproductive behaviour, we used in situ hybridisation for aromatase mRNA to examine expression during the BS and nonbreeding season (NBS) in areas of the brain that control male sexual behaviours [preoptic area (POA) and amygdala (AMY)], as well as one regulating female reproductive behaviours ventromedial hypothalamus (VMH). Males had a greater total number of aromatase-expressing cells in the POA than females, and the density of aromatase-expressing cells (number per unit volume) was greater in the VMH and AMY of females. This density was also higher during the BS than NBS in the POA. Expression of aromatase in the AMY appeared to be lateralised because trends were detected for the left side to have more total cells and more cells per unit volume than the right. These results suggest that, similar to other vertebrates, regional aromatisation of testosterone may be important for the control of sex-specific reproductive behaviours.

First-principles studies of electrical resistivity of iron under pressure

We investigate the temperature and pressure dependences of the electrical resistivity, thermal conductivity and thermal diffusivity for bcc and hcp Fe using the low-order variational approximation and theoretical transport spectral functions calculated from the first-principles linear response linear-muffin-tin-orbital method in the generalized gradient approximation. The calculated values for the electrical resistivity show a strong increase with temperature and decrease with pressure, and are in agreement with high-temperature shock data. We also discuss the behavior of the electrical resistivity for the bcc→hcp phase transition.

Finite-temperature magnetism in bcc Fe under compression

We investigate the contributions of finite-temperature magnetic fluctuations to the thermodynamic properties of bcc Fe as functions of pressure. First, we apply a tight-binding total-energy model parameterized to first-principles linearized augmented plane-wave computations to examine various ferromagnetic, anti-ferromagnetic, and noncollinear spin spiral states at zero temperature. The tight-binding data are fit to a generalized Heisenberg Hamiltonian to describe the magnetic energy functional based on local moments. We then use Monte Carlo simulations to compute the magnetic susceptibility, the Curie temperature, heat capacity, and magnetic free energy. Including the finite-temperature magnetism improves the agreement with experiment for the calculated thermal expansion coefficients.

Fundamental high-pressure calibration from all-electron quantum Monte Carlo calculations

We develop an all-electron quantum Monte Carlo (QMC) method for solids that does not rely on pseudopotentials, and use it to construct a primary ultra-high-pressure calibration based on the equation of state of cubic boron nitride. We compute the static contribution to the free energy with the QMC method and obtain the phonon contribution from density functional theory, yielding a high-accuracy calibration up to 900 GPa usable directly in experiment. We compute the anharmonic Raman frequency shift with QMC simulations as a function of pressure and temperature, allowing optical pressure calibration. In contrast to present experimental approaches, small systematic errors in the theoretical EOS do not increase with pressure, and no extrapolation is needed. This all-electron method is applicable to first-row solids, providing a new reference for ab initio calculations of solids and benchmarks for pseudopotential accuracy.

Pressure induced phase transitions in PbTiO(3)

Recent theoretical simulations using density functional theory (DFT) and novel low temperature high energy x-ray diffraction experiments clearly show the existence of a high pressure morphotropic phase boundary (MPB) in pure PbTiO(3). The experiments show a richer phase diagram than the simulations, with multiple monoclinic phases (Pm and Cm) in the MPB region. In this paper we examine the MPB region in more detail using high precision DFT calculations within the local-density approximation (LDA) and the Wu-Cohen generalized gradient approximation. Our results support the polarization rotation theory and open up fresh possibilities for applying chemical pressure to engineer novel electromechanical materials. We also explain why the zone-boundary mode is more likely to be stable only at higher pressures above ∼25 GPa and not at moderate pressures of ∼10 GPa, using the LDA.

Absence of magnetism in hcp iron-nickel at 11 K

Synchrotron Mössbauer spectroscopy (SMS) was performed on an hcp-phase alloy of composition Fe92Ni8 at a pressure of 21 GPa and a temperature of 11 K. Density functional theoretical calculations predict antiferromagnetism in both hcp Fe and hcp Fe-Ni. For hcp Fe, these calculations predict no hyperfine magnetic field, consistent with previous experiments. For hcp Fe-Ni, however, substantial hyperfine magnetic fields are predicted, but these were not observed in the SMS spectra. Two possible explanations are suggested. First, small but significant errors in the generalized gradient approximation density functional may lead to an erroneous prediction of magnetic order or of erroneous hyperfine magnetic fields in antiferromagnetic hcp Fe-Ni. Alternately, quantum fluctuations with periods much shorter than the lifetime of the nuclear excited state would prohibit the detection of moments by SMS.

Effects of occlusal load on cervical lesions

Toothbrush abrasion has been considered to cause cervical lesions. However, some investigators have proposed that occlusal loading factors direct tensile stresses at the cervical area, resulting in wedge-shaped abfraction defects. The purpose of this study is to investigate the role of axial and non-axial load on the development of cervical lesions. Matched paired premolars, extracted for orthodontic purposes, were used in a custom-fabricated toothbrushing apparatus. A periodontal sulcus width of 0b1 mm with 1 mm gingival recession was simulated with denture base resin. In phase 1, eight matched premolar pairs were subjected to 80 h (1b4 million strokes) of brushing and 300 g of toothbrush force. Toothpaste slurry was applied continuously through the toothbrush. One specimen in each pair was subjected to 250 h and 45 kg of continuous axial load, while the other unloaded tooth served as a negative control. In phase 2, 10 matched premolar pairs were subjected to the same conditions; however, the experimental teeth were subjected to 250 h and 45 kg of intermittent non-axial load, directed at a 45 degrees angle to the buccal cusp. Rubber impressions were made of the cervical lesions, then trimmed, weighed, and compared to determine the amount of tooth material lost. When teeth were loaded axially, there was significantly less tooth material loss (P < 0b02); however, when teeth were loaded non-axially, there was no significant difference (P =0b80) when compared with controls. Optical and scanning electron microscopy did not reveal any significant differences in the morphology between pairs. Our data suggest that the application of occlusal load may not necessarily play a significant role in the progression of cervical tooth wear commonly referred to as abfraction.

Elasticity of iron at the temperature of the Earth's inner core

Seismological body-wave and free-oscillation studies of the Earth's solid inner core have revealed that compressional waves traverse the inner core faster along near-polar paths than in the equatorial plane. Studies have also documented local deviations from this first-order pattern of anisotropy on length scales ranging from 1 to 1,000 km (refs 3, 4). These observations, together with reports of the differential rotation of the inner core, have generated considerable interest in the physical state and dynamics of the inner core, and in the structure and elasticity of its main constituent, iron, at appropriate conditions of pressure and temperature. Here we report first-principles calculations of the structure and elasticity of dense hexagonal close-packed (h.c.p.) iron at high temperatures. We find that the axial ratio c/a of h.c.p. iron increases substantially with increasing temperature, reaching a value of nearly 1.7 at a temperature of 5,700 K, where aggregate bulk and shear moduli match those of the inner core. As a consequence of the increasing c/a ratio, we have found that the single-crystal longitudinal anisotropy of h.c.p. iron at high temperature has the opposite sense from that at low temperature. By combining our results with a simple model of polycrystalline texture in the inner core, in which basal planes are partially aligned with the rotation axis, we can account for seismological observations of inner-core anisotropy.

Cyclization of polyubiquitin by the E2-25K ubiquitin conjugating enzyme

For most substrates of ubiquitin (Ub)-dependent degradation, recognition by the proteasome is mediated by a covalently attached signal assembled from multiple ubiquitins linked to each other via the C terminus of one Ub and the epsilon-amine of Lys(48) of another Ub. Among Ub-conjugating enzymes, E2-25K is unique in its ability to synthesize in vitro unanchored Lys(48)-linked poly-Ub chains from mono- or poly-Ub, E1, and ATP; thus, E2-25K has distinct binding sites for donor and acceptor (poly)Ub. During studies of chain assembly by E2-25K, we observed that Lys(48)-linked tri-Ub was efficiently converted to a new species that upon SDS-polyacrylamide gel electrophoresis migrated between linear di-Ub and tri-Ub. Analysis of this product by mass spectrometry and tryptic digestion showed that it was a cyclic form of tri-Ub. Cyclization of tri-Ub requires E1, E2-25K, ATP, and that the linear substrate has a free Gly(76) C terminus on the proximal end Ub and a Lys(48) side chain available on the distal end Ub. E2-25K similarly can catalyze the cyclization of longer poly-Ub chains, including tetra- and penta-Ub. Although cyclic tri-Ub resists hydrolysis by the PA700 or isopeptidase T deubiquitinating enzymes, it can be disassembled to Ub monomers by isopeptidase(s) in a red blood cell extract. Thus, if cyclic poly-Ub forms in vivo, it will not accumulate as a dead-end product.

Position paper: sonic and ultrasonic scalers in periodontics. Research, Science and Therapy Committee of the American Academy of Periodontology

Ultrasonic and sonic scalers appear to attain similar results as hand instruments for removing plaque, calculus, and endotoxin. Ultrasonic scalers used at medium power seem to produce less root surface damage than hand or sonic scalers. Due to instrument width, furcations may be more accessible using ultrasonic or sonic scalers than manual scalers. It is not clear whether root surface roughness is more or less pronounced following power-driven scalers or manual scalers. It is also unclear if root surface roughness affects long-term wound healing. Periodontal scaling and root planing includes thorough calculus removal, but complete cementum removal should not be a goal of periodontal therapy. Studies have established that endotoxin is weakly adsorbed to the root surface, and can be easily removed with light, overlapping strokes with an ultrasonic scaler. A significant disadvantage of power-driven scalers is the production of contaminated aerosols. Because ultrasonics and sonics produce aerosols, additional care is required to achieve and maintain good infection control when incorporating these instrumentation techniques into dental practice. Preliminary evidence suggests that the addition of certain antimicrobials to the lavage during ultrasonic instrumentation may be of minimal clinical benefit. However, more randomized controlled clinical trials need to be conducted over longer periods of time to better understand the long-term benefits of ultrasonic and sonic debridement.

Chain mobility in the amorphous region of nylon 6 observed under active uniaxial deformation

A specially designed solid-state deuterium nuclear magnetic resonance probe was used to examine the effect of uniaxial elongation on the chain mobility in the amorphous region of semicrystalline nylon 6. In measurements conducted near the glass transition temperature, there was measurable deformation-induced enhancement of the mobility of the amorphous chains up to the yield point. This enhanced mobility decayed once deformation was stopped. Enhanced mobility was not observed in deformation at room temperature. The mechanics of deformation can be explained by the Robertson model for glassy polymers near the glass transition temperature, which states that applied stress induces liquid-like behavior in the polymer chains.

Construct for high-level expression and low misincorporation of lysine for arginine during expression of pET-encoded eukaryotic proteins in Escherichia coli

The arginine codon AGA is rarely used in E. coli but is common in eukaryotic genes. Prior studies have shown that the low level of tRNA(UCUArg) can lead to low expression and misincorporation of lysine for arginine, during expression of genes containing AGA codons in E. coli. The chloramphenicol-selectable plasmid pJY2 is designed to facilitate the expression of such genes cloned into pET vectors: it encodes T7 lysozyme (to depress constitutive expression of the cloned gene) and tRNA(UCUArg) (to suppress lysine misincorporation at AGA codons). Using pJY2, we observed robust and translationally faithful expression of mutant ubiquitin genes in which 14% (11 out of 76) of the total codons were AGA. Competent BL21(DE3)pJY2 cells can be used to suppress lysine misincorporation and achieve high-level expression of pET-encoded target genes without modification of AGA codons in the target gene sequence.

Giant proteases: beyond the proteasome

Proteasomes and related proteases are thought to be the principal machinery responsible for intracellular protein degradation. A new class of giant proteases has been discovered that can augment the catabolic functions of proteasomes and, under some conditions, may even substitute for proteasomes altogether.

Structural basis for the specificity of ubiquitin C-terminal hydrolases

The release of ubiquitin from attachment to other proteins and adducts is critical for ubiquitin biosynthesis, proteasomal degradation and other cellular processes. De-ubiquitination is accomplished in part by members of the UCH (ubiquitin C-terminal hydrolase) family of enzymes. We have determined the 2.25 A resolution crystal structure of the yeast UCH, Yuh1, in a complex with the inhibitor ubiquitin aldehyde (Ubal). The structure mimics the tetrahedral intermediate in the reaction pathway and explains the very high enzyme specificity. Comparison with a related, unliganded UCH structure indicates that ubiquitin binding is coupled to rearrangements which block the active-site cleft in the absence of authentic substrate. Remarkably, a 21-residue loop that becomes ordered upon binding Ubal lies directly over the active site. Efficiently processed substrates apparently pass through this loop, and constraints on the loop conformation probably function to control UCH specificity.

Evaluation of compensation filters in pedal radiographs

Compensation filters allow increased visibility of detail in chest, shoulder, spine, hip, knee, and foot radiographs. This study examines use of an anatomic compensation filter to improve imaging in pedal radiographs. Anteroposterior radiographs were obtained of 25 cadaveric feet at two settings with and without the compensation filter. Densitometer readings were taken at ten forefoot anatomic sites. The compensation filter produced statistically significant reductions in densitometer readings at all anatomic sites and at both radiographic settings. Filtration improved imagery of bony structures, provided excellent soft-tissue visualization, and lowered patient exposure.

Phenotypic characterization of mononuclear cells from gingiva associated with periodontitis and peri-implantitis

The purpose of this study was to compare the phenotypic distribution of resident gingival mononuclear inflammatory cells from tissues associated with peri-implantitis and periodontitis. Inflamed gingiva was obtained from six patients during surgical removal of failed dental implants. Similarly, inflamed gingiva around teeth was obtained from eight patients with moderate to advanced periodontitis. Monoclonal antibodies were used to identify membrane antigens from CD4+ T-lymphocytes, CD4+/CD8(+)-activated T-lymphocytes, tissue macrophages, CD20+ B-lymphocytes, and MHC class II (Ia) antigens. Gingival inflammation associated with both dental implants and natural teeth was characterized by substantial numbers of CD4+ T-lymphocytes, resident macrophages, and B-lymphocytes. In addition, there was an abundance of HLA class II-positive mononuclear cells throughout most specimens. These results suggest that the gingival mononuclear inflammatory response in peri-implantitis and periodontitis is similar and support the hypothesis that similar inflammatory mechanisms are associated with both conditions.

Clinical evaluation of the effect of a hydrogen peroxide mouth rinse, sodium bicarbonate dentifrice, and mouth moisturizer on oral health

The objective of this 60-day single-blind, parallel trial, using 150 subjects, was to evaluate the effect of a 20% sodium bicarbonate dentifrice, a 1.5% hydrogen peroxide solution and a mouth moisturizer on oral tissues and microflora. Subjects were randomly assigned to one of five groups. The treatments were: 1) Sage dentifrice (sodium bicarbonate). Toothette Plus containing baking soda saturated with the hydrogen peroxide solution and use of a mouth moisturizer, 2) Crest dentifrice, Toothette Plus containing baking soda saturated with the hydrogen peroxide solution and use of a mouth moisturizer, 3) Crest dentifrice, Toothette Plus containing baking soda with a control solution and no mouth moisturizer, 4) Crest dentifrice, Toothette (without baking soda), saturated with a control solution and no mouth moisturizer, and 5) Crest dentifrice, Toothette saturated with 1.5% flavored H2O2 and no mouth moisturizer. From a subgroup of 35 patients (seven from each group) buccal smears for exfoliative cytology were taken as were supragingival microbiological samples from the mesial aspect of first molars (pooled). Buccal smears were evaluated for signs of histopathological changes. Microbiological samples from supra- and subgingival plaque for P. gingivalis, P. intermedia, A. actinomycetemcomitans. A viscosus, F. nucleatum, F. sanguis and C. albicans were evaluated. Clinical parameters measured were a stain index (SI), the modified gingival index (MGI), and a plaque index (PI). There were no adverse changes in the oral microflora and no anaplastic or other pathological changes in any subjects. Clinical parameters showed a statistically significant reduction in the MGI ranging from 26.7-29.9% with no significant differences among the groups (p > 0.05). The PI showed small reductions in all groups except group 2, but the differences were not statistically significant from each other or baseline (p > 0.05). The SI revealed slight increases in all groups and no differences among the groups. It can be concluded that use of Sage dentifrice, Toothette Plus saturated with Perox-A-Mint and Sage Mouth Moisturizer are safe to oral tissues. Using these components did not result in clinically noticeable stain formation, promote plaque formation, or produce any significant adverse changes in the oral microflora.

Specificity of the ubiquitin isopeptidase in the PA700 regulatory complex of 26 S proteasomes

The specificity of the ubiquitin (Ub) isopeptidase in the PA700 regulatory complex of the bovine 26 S proteasome was investigated. Disassembly of poly-Ub by this enzyme is restricted to the distal-end Ub of the substrate, i.e. the Ub farthest from the site of protein attachment in poly-Ub-protein conjugates. The determinants recognized by the isopeptidase were probed by the use of mutant ubiquitins incorporated into Lys48-linked poly-Ub substrates. PA700 could not disassemble poly-Ub chains that contained a distal Ub(L8A,I44A). This suggested either that the enzyme interacts directly with Leu8 or Ile44 or that it recognizes a higher order structure that caps the distal end of a poly-Ub substrate and is destabilized by Ub(L8A,I44A). The previously determined di-Ub crystal structure (Cook, W. J., Jeffrey, L. C., Carson, M., Chen, Z., and Pickart, C. M. (1992) J. Biol. Chem. 267, 16467-16471) offered a candidate for such a "cap." In solution, however, this structure was not observed by 1H NMR spectroscopy. This and the finding that di-Ub with a single proximal Ub(L8A,I44A) is cleaved efficiently suggest that Leu8 and Ile44 in the distal-end Ub contact the isopeptidase directly. In addition to Lys48-linked chains, PA700 also could disassemble Lys6- and Lys-11-linked poly-Ub, but, surprisingly, not alpha-linked di-Ub. Results with these and other substrates suggest that specificity determinants for the PA700 isopeptidase include Leu8, Ile44, and Lys48 on the distal Ub and, for poly-Ub, some features of the Ub-Ub linkage itself.

Development of methods for quantitative characterization of network morphology in pharmaceutical hydrogels

We have employed a variety of methods which satisfactorily characterize the structure of polymeric hydrogels beyond the level of information provided by a single swelling test. We applied these techniques to gels which have potential for use as pharmaceuticals for the control of elevated phosphorous levels in patients suffering from chronic kidney failure. These 'fingerprinting' techniques help us understand the effects of various processing parameters on the gel morphology. Wide-angle X-ray diffraction experiments verified the structure and reproducibility across synthesized hydrogel batches. Measurements of the temperature- and frequency-dependent dielectric relaxation provided information on the network topology. Real-time diffusion experiments were performed using inductively coupled plasma atomic emission spectroscopy. Spherical gel particles (510 microns diameter) were used to measure equilibrium phosphate loadings of 4.5 mmoles g-1 from direct measurement of the decrease in phosphate ion concentration in aqueous solutions.

Inhibition of the 26 S proteasome by polyubiquitin chains synthesized to have defined lengths

Ubiquitin is a covalent signal that targets cellular proteins to the 26 S proteasome. Multiple ubiquitins can be ligated together through the formation of isopeptide bonds between Lys48 and Gly76 of successive ubiquitins. Such a polyubiquitin chain constitutes a highly effective proteolytic targeting signal, but its mode of interaction with the proteasome is not well understood. Experiments to address this issue have been limited by difficulties in preparing useful quantities of polyubiquitin chains of uniform length. We report a simple method for large scale synthesis of Lys48-linked polyubiquitin chains of defined length. In the first round of synthesis, two ubiquitin derivatives (K48C-ubiquitin and Asp77-ubiquitin) were used as substrates for the well characterized ubiquitin-conjugating enzyme E2-25K. Diubiquitin blocked at the nascent proximal and distal chain termini was obtained in quantitative yield. Appropriately deblocked chains were then combined to synthesize higher order chains (tetramer and octamer in the present study). Deblocking was achieved either enzymatically (proximal terminus) or by chemical alkylation (distal terminus). Chains synthesized by this method were used to obtain the first quantitative information concerning the influence of polyubiquitin chain length on binding to the 26 S proteasome; this was done through comparison of different length (unanchored) polyubiquitin chains as inhibitors of ubiquitin-conjugate degradation. K0.5 was found to decrease approximately 90-fold, from 430 to 4.8 microM, as the chain was lengthened from two to eight ubiquitins. The implications of these results for the molecular basis of chain recognition are discussed.

Phenotypic characterization of mononuclear inflammatory cells in salivary glands of bio-breeding rats

The purpose of this study was to assess whether mononuclear cell abnormalities exist in salivary glands from autoimmune Bio-Breeding (BB) rats. Frozen sections of gland tissues were prepared from five diabetes-resistant BB rats (BB-DR), from five BB rats with diabetes (BB-DP) and from five Wistar rats. A panel of six monoclonal antibodies was used to identify membrane antigens associated primarily with monocytes (ED1), mature tissue macrophages (ED2), lymphoid macrophages (ED3), MHC class II (Ia) antigen (OX6), CD5+ T lymphocytes (OX19), and rat B lymphocytes (OX33). Normal submandibular, sublingual and parotid glands contained few ED1-positive cells, usually two or fewer per field. Tissue macrophages identified by clone ED2 comprised a major mononuclear cell subset in both Wistar and BB rats. However, the number of ED2-positive mononuclear cells was significantly depressed in the submandibular and parotid glands from BB-DR and BB-DP animals, being present in quantities 25-50% of those observed in glands from normal Wistar rats (p < 0.001). In contrast, 25- to 30-fold greater numbers of ED3-positive macrophages were observed in submandibular glands from BB rats (p < 0.001). MHC class II (Ia) antigen expression also was 4- to 6-fold greater in BB rat submandibular glands, compared to Wistar rats (p < 0.001). CD5+ T-lymphocytes were rare or entirely absent in BB sublingual glands (0 to 1 cell per 0.87 mm2 field), compared to 47 cells per field from Wistar sublingual glands. No B lymphocytes were identified with antibody OX33 in any of the rat strains. These findings indicate that BB rat salivary glands differ significantly from Wistar salivary glands. In BB rats there is a rich population of ED3-positive macrophages and T lymphocytes in submandibular gland, low quantities of T lymphocytes in sublingual gland, and fewer ED2-positive macrophages in all three major salivary glands. These differences in mononuclear cell subpopulations may also influence salivary gland function in mucosal immunity.

Ubiquitin aldehyde increases adenosine triphosphate-dependent proteolysis of hemoglobin alpha-subunits in beta-thalassemic hemolysates

Two major causes of the anemia in beta-thalassemia are a deficiency in hemoglobin (Hb) beta-subunit (and consequently HbA) synthesis and, due to the resulting excess of Hb alpha-subunits, erythroid cell hemolysis. The hemolytic component might be ameliorated by increasing the intracellular proteolysis of the excess alpha-subunits. Isolated 3H-labeled alpha-chains are known to be degraded primarily by the adenosine triphosphate (ATP)- and ubiquitin (Ub)-dependent proteolysis pathway in unfractionated beta-thalassemic hemolysates. Our objective was to increase this degradation by targeted intervention. Ub aldehyde (Ubal), a synthetic inhibitor of isopeptidases (proteases that hydrolyze the bond between the Ub polypeptide and its protein adduct), was added to reaction mixtures containing a hemolysate from the blood cells of one of four beta-thalassemic donors and 3H-alpha-chains or 3H-alpha-globin as a substrate. Optimum enhancement of ATP-dependent degradation occurred at 0.4 to 1.5 micromol/L Ubal and ranged from 29% to 115% for 3H-alpha-chains and 47% to 96% for 3H-alpha-globin among the four hemolysates. We suggest that Ubal stimulates 3H-alpha-subunit proteolysis by inhibition of an isopeptidase(s) that deubiquitinates, or "edits," Ub-3H-alpha-subunit conjugates, intermediates in the degradative pathway. In control studies, similarly low Ubal concentrations did not enhance the degradation of 3H-alpha2beta2 (HbA) tetramers or inhibit the activities of methemoglobin reductase and four selected glycolysis pathway enzymes. These and other results may be the basis for a therapeutic approach to beta-thalassemia.

Local inflammatory effects of composite resins

Composite resins have been widely used as an anterior restorative material and often have been used to restore posterior teeth. However, composites occasionally can become embedded in oral soft tissues during finishing or shaping procedures, which can lead to persistent chronic inflammation. Limited evaluation in animal model systems has shown that this entrapment in soft tissues can sometimes lead to local inflammation in adjacent soft tissues. Consequently, finishing and polishing procedures should be performed, where practical.

Editing of ubiquitin conjugates by an isopeptidase in the 26S proteasome

In eukaryotes, ubiquitin (Ub)-dependent proteolysis is essential for bulk protein turnover as well as diverse processes including cell-cycle control, differentiation, antigen presentation, and the stress response. Generally, multiple ubiquitins are added onto a substrate to form an isopeptide-linked 'polyubiquitin' chain, which targets substrates for degradation by the 26S proteasome. The specificity of Ub-dependent degradation was thought to depend primarily on the selection of targets for ubiquitination, but recently we have reported evidence for a second level of specificity in which (poly)Ub-protein conjugates are partitioned among two fates: degradation of the protein substrate by the 26S proteasome; and disassembly by Ub isopeptidase(s) to regenerate the protein substrate. Potentially, an isopeptidase could influence degradation by 'editing' (poly)Ub-protein conjugates according to the extent of ubiquitination rather than the structure of the ubiquitination target itself. Here we describe a bovine isopeptidase that is well suited to such an editing function because of its unique localization and specificity. This enzyme is an intrinsic subunit of PA700, the 19S regulatory complex of the 26S proteasome. By disassembling the degradation signal from only the distal end of (poly)Ub chains, this isopeptidase can selectively rescue poorly ubiquitinated or slowly degraded Ub-protein conjugates from proteolysis.