Overview of the Langmuir probe system on the Mega Ampere Spherical Tokamak (MAST) Upgrade.

A detailed description of the Langmuir probe system on Mega Ampere Spherical Tokamak Upgrade is presented. The system features 850 tile-embedded probes and 40 bespoke electronic modules that each have the capability to drive and acquire data from up to 16 probes in a time-multiplexed manner. The system provides spatiotemporal-resolved measurements (1 cm and ∼1 ms, respectively) in the divertor region of ion saturation current, electron temperature, and floating potential. The standard interpretation of current-voltage (IV) characteristics is to apply a four-parameter fit, based on unmagnetized probe theory, which includes a linear model for the ion saturation region. To mitigate the effect of the magnetic field, analysis is restricted to the region of the IV characteristic, which is sensitive to only the tail of the electron energy distribution function.

Controlling spin current polarization through non-collinear antiferromagnetism.

The interconversion of charge and spin currents via spin-Hall effect is essential for spintronics. Energy-efficient and deterministic switching of magnetization can be achieved when spin polarizations of these spin currents are collinear with the magnetization. However, symmetry conditions generally restrict spin polarizations to be orthogonal to both the charge and spin flows. Spin polarizations can deviate from such direction in nonmagnetic materials only when the crystalline symmetry is reduced. Here, we show control of the spin polarization direction by using a non-collinear antiferromagnet Mn3GaN, in which the triangular spin structure creates a low magnetic symmetry while maintaining a high crystalline symmetry. We demonstrate that epitaxial Mn3GaN/permalloy heterostructures can generate unconventional spin-orbit torques at room temperature corresponding to out-of-plane and Dresselhaus-like spin polarizations which are forbidden in any sample with two-fold rotational symmetry. Our results demonstrate an approach based on spin-structure design for controlling spin-orbit torque, enabling high-efficient antiferromagnetic spintronics.

Traumatic brain injury and sleep disturbances in combat-exposed service members and veterans: Where to go next?

OBJECTIVE: To synthesize the current evidence on sleep disturbances in military service members (SMs) and veterans with traumatic brain injury (TBI). METHODS: An electronic literature search first identified abstracts published from 2008-2018 inclusively referencing sleep, TBI, and military personnel from Operation Enduring Freedom, Operation Iraqi Freedom, Operation New Dawn, and Persian Gulf veterans. Selection criteria eliminated studies on non-combat TBI, open or penetrating injuries, and articles where the relationship between sleep and TBI was not directly examined. Articles on all military branches and components, those currently serving and veterans-ranging from medical chart reviews to clinical trials, were included. Forty-one articles were selected for full text-review. RESULTS: Twenty-four papers estimated the prevalence of sleep disturbances in TBI. Eight studies demonstrated the contribution of common co-occurring conditions, most notably posttraumatic stress disorder, to the relationship between disrupted sleep and TBI. Ten studies differentiated sleep profiles between military SMs and veterans with and without acute TBI and detected significant differences in sleep disturbances across the course of injury. Longitudinal studies were scarce but helped to establish the temporal relationship between sleep disturbances and TBI and isolate sleep-related mechanisms influencing TBI prognosis. Only three studies reported on interventions for improving sleep quality and TBI symptoms. Systematic research testing assessments and interventions that target sleep disturbances for improving sleep, TBI symptoms, and long-term functional outcomes were identified as critical knowledge gaps. CONCLUSION: Findings unequivocally establish that sleep disturbances are highly prevalent in SMs and veterans with TBI. However, studies testing the effectiveness of treatments for improving sleep in military groups with TBI have been limited and their results inconsistent. This review highlights a critical opportunity for advancing military medicine through future research aimed at identifying and testing sleep-focused treatments in SMs and veterans with combat-related TBI.

Magnetism in iridate heterostructures leveraged by structural distortions.

Fundamental control of magnetic coupling through heterostructure morphology is a prerequisite for rational engineering of magnetic ground states. We report the tuning of magnetic interactions in superlattices composed of single and bilayers of SrIrO3 inter-spaced with SrTiO3 in analogy to the Ruddlesden-Popper series iridates. Magnetic scattering shows predominately c-axis antiferromagnetic orientation of the magnetic moments for the bilayer, as in Sr3Ir2O7. However, the magnetic excitation gap, measured by resonant inelastic x-ray scattering, is quite different between the two structures, evidencing a significant change in the stability of the competing magnetic phases. In contrast, the single layer iridate hosts a more bulk-like gap. We find these changes are driven by bending of the c-axis Ir-O-Ir bond, which is much weaker in the single layer, and subsequent local environment changes, evidenced through x-ray diffraction and magnetic excitation modeling. Our findings demonstrate how large changes in the magnetic interactions can be tailored and probed in spin-orbit coupled heterostructures by engineering subtle structural modulations.

Isostructural metal-insulator transition in VO2.

The metal-insulator transition in correlated materials is usually coupled to a symmetry-lowering structural phase transition. This coupling not only complicates the understanding of the basic mechanism of this phenomenon but also limits the speed and endurance of prospective electronic devices. We demonstrate an isostructural, purely electronically driven metal-insulator transition in epitaxial heterostructures of an archetypal correlated material, vanadium dioxide. A combination of thin-film synthesis, structural and electrical characterizations, and theoretical modeling reveals that an interface interaction suppresses the electronic correlations without changing the crystal structure in this otherwise correlated insulator. This interaction stabilizes a nonequilibrium metallic phase and leads to an isostructural metal-insulator transition. This discovery will provide insights into phase transitions of correlated materials and may aid the design of device functionalities.

Disentangled Cooperative Orderings in Artificial Rare-Earth Nickelates.

Coupled transitions between distinct ordered phases are important aspects behind the rich phase complexity of correlated oxides that hinder our understanding of the underlying phenomena. For this reason, fundamental control over complex transitions has become a leading motivation of the designer approach to materials. We have devised a series of new superlattices by combining a Mott insulator and a correlated metal to form ultrashort period superlattices, which allow one to disentangle the simultaneous orderings in RENiO_{3}. Tailoring an incommensurate heterostructure period relative to the bulk charge ordering pattern suppresses the charge order transition while preserving metal-insulator and antiferromagnetic transitions. Such selective decoupling of the entangled phases resolves the long-standing puzzle about the driving force behind the metal-insulator transition and points to the site-selective Mott transition as the operative mechanism. This designer approach emphasizes the potential of heterointerfaces for selective control of simultaneous transitions in complex materials with entwined broken symmetries.

Ferromagnetism and Charge Order from a Frozen Electron Configuration in Strained Epitaxial LaCoO_{3}.

We report ordering of the cobalt electron configuration in ferromagnetic strained epitaxial LaCoO_{3}. Specifically, the presence of charge order is demonstrated from distinct features of the resonant cobalt contribution to superstructure reflections. Density functional theory calculations show that the observed order is consistent with the spin-state periodicity predicted to give rise to ferromagnetism in LaCoO_{3}. Through the modification of symmetry by strain, concurrent frozen charge and spin-state order are stabilized, giving rise to long-range magnetic order.

Artificial two-dimensional polar metal at room temperature.

Polar metals, commonly defined by the coexistence of polar crystal structure and metallicity, are thought to be scarce because the long-range electrostatic fields favoring the polar structure are expected to be fully screened by the conduction electrons of a metal. Moreover, reducing from three to two dimensions, it remains an open question whether a polar metal can exist. Here we report on the realization of a room temperature two-dimensional polar metal of the B-site type in tri-color (tri-layer) superlattices BaTiO3/SrTiO3/LaTiO3. A combination of atomic resolution scanning transmission electron microscopy with electron energy-loss spectroscopy, optical second harmonic generation, electrical transport, and first-principles calculations have revealed the microscopic mechanisms of periodic electric polarization, charge distribution, and orbital symmetry. Our results provide a route to creating all-oxide artificial non-centrosymmetric quasi-two-dimensional metals with exotic quantum states including coexisting ferroelectric, ferromagnetic, and superconducting phases.

Effects of Sleep Loss on Subjective Complaints and Objective Neurocognitive Performance as Measured by the Immediate Post-Concussion Assessment and Cognitive Testing.

OBJECTIVE: This study examined the effects of total and partial sleep deprivation on subjective symptoms and objective neurocognitive performance, as measured by the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) in a sample of healthy adults. METHOD: One-hundred and two, right-handed, healthy participants (between ages 18 and 30 years old) completed three consecutive nights in the sleep laboratory with concurrent continuous polysomnography monitoring. Night 1 served as a baseline night. Prior to Night 2, they were randomly assigned to one of three sleep conditions: undisrupted normal sleep (N = 34), sleep restriction (50% of habitual sleep, N = 37), or total sleep deprivation (N = 31). Participants slept undisturbed on Night 3. ImPACT was administered on three separate occasions. RESULTS: Sleep loss was associated with increased severity of subjectively reported affective, cognitive, physical, and sleep symptoms. Although objective neurocognitive task scores derived from the ImPACT battery did not corroborate subjective complaints, sleep loss was associated with significant differences on tasks of visual memory, reaction time, and visual motor speed over time. CONCLUSIONS: While self-report measures suggested marked impairments following sleep loss, deficits in neurocognitive performance were observed only on three domains measured with ImPACT. ImPACT may capture subtle changes in neurocognitive performance following sleep loss; however, independent and larger validation studies are needed to determine its sensitivity to acute sleep loss and recovery sleep. Neurocognitive screening batteries may be useful for detecting the effects of more severe or chronic sleep loss under high-stress conditions that mimic high-risk occupations.

Pure electronic metal-insulator transition at the interface of complex oxides.

In complex materials observed electronic phases and transitions between them often involve coupling between many degrees of freedom whose entanglement convolutes understanding of the instigating mechanism. Metal-insulator transitions are one such problem where coupling to the structural, orbital, charge, and magnetic order parameters frequently obscures the underlying physics. Here, we demonstrate a way to unravel this conundrum by heterostructuring a prototypical multi-ordered complex oxide NdNiO3 in ultra thin geometry, which preserves the metal-to-insulator transition and bulk-like magnetic order parameter, but entirely suppresses the symmetry lowering and long-range charge order parameter. These findings illustrate the utility of heterointerfaces as a powerful method for removing competing order parameters to gain greater insight into the nature of the transition, here revealing that the magnetic order generates the transition independently, leading to an exceptionally rare purely electronic metal-insulator transition with no symmetry change.

Polar metals by geometric design.

Gauss's law dictates that the net electric field inside a conductor in electrostatic equilibrium is zero by effective charge screening; free carriers within a metal eliminate internal dipoles that may arise owing to asymmetric charge distributions. Quantum physics supports this view, demonstrating that delocalized electrons make a static macroscopic polarization, an ill-defined quantity in metals--it is exceedingly unusual to find a polar metal that exhibits long-range ordered dipoles owing to cooperative atomic displacements aligned from dipolar interactions as in insulating phases. Here we describe the quantum mechanical design and experimental realization of room-temperature polar metals in thin-film ANiO3 perovskite nickelates using a strategy based on atomic-scale control of inversion-preserving (centric) displacements. We predict with ab initio calculations that cooperative polar A cation displacements are geometrically stabilized with a non-equilibrium amplitude and tilt pattern of the corner-connected NiO6 octahedral--the structural signatures of perovskites--owing to geometric constraints imposed by the underlying substrate. Heteroepitaxial thin-films grown on LaAlO3 (111) substrates fulfil the design principles. We achieve both a conducting polar monoclinic oxide that is inaccessible in compositionally identical films grown on (001) substrates, and observe a hidden, previously unreported, non-equilibrium structure in thin-film geometries. We expect that the geometric stabilization approach will provide novel avenues for realizing new multifunctional materials with unusual coexisting properties.

Mott Electrons in an Artificial Graphenelike Crystal of Rare-Earth Nickelate.

Deterministic control over the periodic geometrical arrangement of the constituent atoms is the backbone of the material properties, which, along with the interactions, define the electronic and magnetic ground state. Following this notion, a bilayer of a prototypical rare-earth nickelate, NdNiO_{3}, combined with a dielectric spacer, LaAlO_{3}, has been layered along the pseudocubic [111] direction. The resulting artificial graphenelike Mott crystal with magnetic 3d electrons has antiferromagnetic correlations. In addition, a combination of resonant X-ray linear dichroism measurements and ab initio calculations reveal the presence of an ordered orbital pattern, which is unattainable in either bulk nickelates or nickelate based heterostructures grown along the [001] direction. These findings highlight another promising venue towards designing new quantum many-body states by virtue of geometrical engineering.

Engineered Mott ground state in a LaTiO(3+δ)/LaNiO3 heterostructure.

In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO3 have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO3 and a doped Mott insulator LaTiO(3+δ), and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibits interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and e(g) orbital band splitting. Our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states.

Effects of Blast Exposure on Subjective and Objective Sleep Measures in Combat Veterans with and without PTSD.

STUDY OBJECTIVES: This study examined the extent to which self-reported exposure to blast during deployment to Iraq and Afghanistan affects subjective and objective sleep measures in service members and veterans with and without posttraumatic stress disorder (PTSD). METHODS: Seventy-one medication-free service members and veterans (mean age = 29.47 ± 5.76 years old; 85% men) completed self-report sleep measures and overnight polysomnographic studies. Four multivariate analyses of variance (MANOVAs) were conducted to examine the impact of blast exposure and PTSD on subjective sleep measures, measures of sleep continuity, non-rapid eye movement (NREM) sleep parameters, and rapid eye movement (REM) sleep parameters. RESULTS: There was no significant Blast × PTSD interaction on subjective sleep measures. Rather, PTSD had a main effect on insomnia severity, sleep quality, and disruptive nocturnal behaviors. There was no significant Blast × PTSD interaction, nor were there main effects of PTSD or Blast on measures of sleep continuity and NREM sleep. A significant PTSD × Blast interaction effect was found for REM fragmentation. CONCLUSIONS: The results suggest that, although persistent concussive symptoms following blast exposure are associated with sleep disturbances, self-reported blast exposure without concurrent symptoms does not appear to contribute to poor sleep quality, insomnia, and disruptive nocturnal disturbances beyond the effects of PTSD. Reduced REM sleep fragmentation may be a sensitive index of the synergetic effects of both psychological and physical insults.

Combat-related blast exposure and traumatic brain injury influence brain glucose metabolism during REM sleep in military veterans.

Traumatic brain injury (TBI), a signature wound of Operations Enduring and Iraqi Freedom, can result from blunt head trauma or exposure to a blast/explosion. While TBI affects sleep, the neurobiological underpinnings between TBI and sleep are largely unknown. To examine the neurobiological underpinnings of this relationship in military veterans, [(18)F]-fluorodeoxyglucose positron emission tomography (FDG PET) was used to compare mTBI-related changes in relative cerebral metabolic rate of glucose (rCMRglc) during wakefulness, Rapid Eye Movement (REM) sleep, and non-REM (NREM) sleep, after adjusting for the effects of posttraumatic stress (PTS). Fourteen veterans with a history of blast exposure and/or mTBI (B/mTBI) (age 27.5±3.9) and eleven veterans with no history (No B/mTBI) (age 28.1±4.3) completed FDG PET studies during wakefulness, REM sleep, and NREM sleep. Whole-brain analyses were conducted using Statistical Parametric Mapping (SPM8). Between group comparisons revealed that B/mTBI was associated with significantly lower rCMRglc during wakefulness and REM sleep in the amygdala, hippocampus, parahippocampal gyrus, thalamus, insula, uncus, culmen, visual association cortices, and midline medial frontal cortices. These results suggest that alterations in neurobiological networks during wakefulness and REM sleep subsequent to B/mTBI exposure may contribute to chronic sleep disturbances and differ in individuals with acute symptoms.

Relaxin-3 mRNA levels in nucleus incertus correlate with alcohol and sucrose intake in rats.

BACKGROUND: Chronic alcohol intake produces multiple neuroadaptive changes, including up- and down-regulation of neuropeptides and receptors. There are widespread projections of relaxin-3 containing neurons to, and abundant relaxin family peptide 3 receptor (RXFP3) expression within, brain regions involved in modulating alcohol intake. Recently we demonstrated the involvement of relaxin-3/RXFP3 signalling in alcohol-seeking in rats; therefore in this study we examined whether relaxin-3 and/or RXFP3 expression were altered by chronic alcohol intake in alcohol-preferring iP rats. METHODS: Expression of relaxin-3 mRNA in the hindbrain nucleus incertus and RXFP3 radioligand binding levels in discrete forebrain regions were investigated following voluntary intake of alcohol or sucrose for 12 weeks, with a 2 day washout, using quantitative in situ hybridisation histochemistry and in vitro receptor autoradiography, respectively, in cohorts of adult, male iP rats. RESULTS: Levels of relaxin-3 mRNA in the hindbrain nucleus incertus were positively correlated with the level of intake of both alcohol (r(12)=0.59, p=0.03) and sucrose (r(7)=0.70, p=0.04) in iP rats. Dense binding of the RXFP3-selective radioligand, [(125)]-R3/I5, was detected in hypothalamic and extrahypothalamic sites, but no significant changes in the density of RXFP3 were observed in the brain regions quantified following chronic sucrose or ethanol intake. CONCLUSIONS: Our findings suggest high endogenous relaxin-3 expression may be associated with higher intake of rewarding substances, rather than its expression being regulated in response to their intake, consistent with an active role for the relaxin-3/RXFP3 system in modulating ingestive and alcohol-related behaviours.

Reversible control of magnetic interactions by electric field in a single-phase material.

Intrinsic magnetoelectric coupling describes the interaction between magnetic and electric polarization through an inherent microscopic mechanism in a single-phase material. This phenomenon has the potential to control the magnetic state of a material with an electric field, an enticing prospect for device engineering. Here, we demonstrate 'giant' magnetoelectric cross-field control in a tetravalent titanate film. In bulk form, EuTiO(3), is antiferromagnetic. However, both anti and ferromagnetic interactions coexist between different nearest europium neighbours. In thin epitaxial films, strain was used to alter the relative strength of the magnetic exchange constants. We not only show that moderate biaxial compression precipitates local magnetic competition, but also demonstrate that the application of an electric field at this strain condition switches the magnetic ground state. Using first-principles density functional theory, we resolve the underlying microscopic mechanism resulting in G-type magnetic order and illustrate how it is responsible for the 'giant' magnetoelectric effect.

Peritraumatic dissociation and peritraumatic emotional predictors of PTSD in Latino youth: results from the Hispanic family study.

This is the 1st study to examine peritraumatic dissociation and peritraumatic emotions as they predict symptoms and diagnosis of posttraumatic stress disorder (PTSD) in Latino youth. Our aim was to test the hypothesis that the degree of peritraumatic dissociation would predict the number of PTSD symptoms and PTSD clinical diagnosis when the influences of other salient factors were statistically controlled. We also explored the possible contributions of peritraumatic emotional responses to PTSD symptomatology and PTSD diagnosis. We expected that peritraumatic dissociation would emerge as a significant predictor of PTSD. A total of 204 Latino youth (mean age = 12.37 years) completed semistructured individual clinical interviews with bilingual research assistants. These interviews assessed trauma exposure, peritraumatic responses, and current psychopathology. A linear regression analysis demonstrated significant relationships between lifetime number of traumatic events, peritraumatic dissociation, shame, and number of PTSD symptoms endorsed. Significant inverse (protective) relationships were demonstrated between anger and guilt and current PTSD symptomatology. Logistic regression analysis demonstrated significant relationships between peritraumatic dissociation, shame, lifetime number of traumatic events experienced, and PTSD diagnosis. The analyses examined both the number of PTSD symptoms as well as diagnosis of PTSD while simultaneously controlling for age, lifetime exposure to traumatic events, time residing in the United States, and gender. These results support an increasingly robust body of empirical literature suggesting that the peritraumatic dissociative and emotional responses to trauma are important predictors of future PTSD diagnosis. Possible cultural factors contributing to the dissociative responses in Latino youth and clinical implications are discussed.

Structure of SrTiO3 films on Si.

The epitaxial deposition of oxides on silicon opens the possibility of incorporating their diverse properties into silicon-device technology. Deposition of SrTiO(3) on silicon was first reported over a decade ago, but growing the coherent, lattice-matched films that are critical for many applications has been difficult for thicknesses beyond 5 unit cells. Using a combination of density functional calculations and x-ray diffraction measurements, we determine the atomic structure of coherent SrTiO(3) films on silicon, finding that the Sr concentration at the interface varies with the film thickness. The structures with the lowest computed energies best match the x-ray diffraction. During growth, Sr diffuses from the interface to the surface of the film; the increasing difficulty of Sr diffusion with film thickness may cause the disorder seen in thicker films. The identification of this unique thickness-dependent interfacial structure opens the possibility of modifying the interface to improve the thickness and quality of metal oxide films on silicon.