Design of crystal-like aperiodic solids with selective disorder--phonon coupling

Functional materials design normally focuses on structurally-ordered systems because disorder is considered detrimental to many important physical properties. Here we challenge this paradigm by showing that particular types of strongly-correlated disorder can give rise to useful characteristics that are inaccessible to ordered states. A judicious combination of low-symmetry building unit and high-symmetry topological template leads to aperiodic "procrystalline" solids that harbour this type of topological disorder. We identify key classes of procrystalline states together with their characteristic diffraction behaviour, and establish a variety of mappings onto known and target materials. Crucially, the strongly-correlated disorder we consider is associated with specific sets of modulation periodicities distributed throughout the Brillouin zone. Lattice dynamical calculations reveal selective disorder-phonon coupling to lattice vibrations characterised by these same periodicities. The principal effect on the phonon spectrum is to bring about dispersion in energy rather than wave-vector, as in the poorly-understood "waterfall" effect observed in relaxor ferroelectrics. This property of procrystalline solids suggests a mechanism by which strongly-correlated topological disorder might allow new and useful functionalities, including independently-optimised thermal and electronic transport behaviour as required for high-performance thermoelectrics.Comment: 4 figure

Bifurcated polarization rotation in bismuth-based piezoelectrics

ABO3 perovskite-type solid solutions display a large variety of structural and physical properties, which can be tuned by chemical composition or external parameters such as temperature, pressure, strain, electric, or magnetic fields. Some solid solutions show remarkably enhanced physical properties including colossal magnetoresistance or giant piezoelectricity. It has been recognized that structural distortions, competing on the local level, are key to understanding and tuning these remarkable properties, yet, it remains a challenge to experimentally observe such local structural details. Here, from neutron pair-distribution analysis, a temperature-dependent 3D atomic-level model of the lead-free piezoelectric perovskite Na0.5Bi0.5TiO3 (NBT) is reported. The statistical analysis of this model shows how local distortions compete, how this competition develops with temperature, and, in particular, how different polar displacements of Bi3+ cations coexist as a bifurcated polarization, highlighting the interest of Bi-based materials in the search for new lead-free piezoelectrics

Comparison of location, depth, quality and intensity of experimentally induced pain in six low back muscles

Introduction: The pattern of pain originating from experimentally induced low back pain appears diffuse. This may be because sensory information from low back muscles converges, sensory innervation extends over multiple vertebral levels, or people have difficulty accurately representing the painful location on standardized pain maps

The Effect of a High Fat Meal on Cerebral Vascular Function

It is well known that a single high fat meal (HFM) causes a robust and transient elevation in serum triglycerides (TG). This elevation in serum TG is a primary contributor to the post-prandial attenuation of peripheral vascular endothelial function, as assessed by flow-mediated dilation in the brachial artery. Whether a similar impairment in vascular reactivity can be observed in the cerebral circulation remains unknown, and was the focus of this investigation. PURPOSE: To test the hypothesis that cerebral vascular function is impaired following a HFM. METHODS: End-tidal carbon dioxide partial pressure (PETCO2), middle cerebral artery blood velocity (MCAVmean), calculated cerebral vascular conductance index (CVCI; MCAVmean/mean arterial pressure) and cerebral vasodilator response to rebreathing induced hypercapnia (% increase in CVC from baseline at common maximal ΔPETCO2) were assessed in 6 healthy young men (27 ±5 years). Measures were assessed during fasted baseline and again at 2 and 4 h post meal consumption (HFM day) or at a similar time point in the fasted state (TC day). The two visits were separated by 2-7 days and were conducted in a randomized order. Blood lipids were assessed at baseline and at the 2 h time point into each respective condition. RESULTS: As expected, consumption of the HFM significantly elevated serum TG concentrations relative to TC at 2 h (HFM: 101±38 to 169±77mg/dl, TC: 107±32 to 92±31mg/dl, P=0.007). However, the HFM had no effect of cerebral vasodilator capacity during rebreathing induced hypercapnia. The maximal increase in %CVC achieved at the highest common ΔPETCO2 during all conditions within each subject was unchanged during 2hr and 4hr post HFM or TC (condition x time interaction: P=0.96). Similarly, the slope of the change in %CVC per change in ΔPETCO2 was unaffected by HFM across time (P=0.49). CONCLUSION: Contrary to our hypothesis, and unlike the peripheral vasculature, our preliminary data suggest that the cerebral circulation appears to be protected from the acute negative effects of a high fat meal

Increasing Access to Natural Areas: Connecting Physical and Social Dimensions

Report of the 2015 Berkley Workshop Held at the Asticou Inn, Northeast Harbor, Maine - July 201

A Bright Submillimeter Source in the Bullet Cluster (1E0657--56) Field Detected with BLAST

We present the 250, 350, and 500 micron detection of bright submillimeter emission in the direction of the Bullet Cluster measured by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST). The 500 micron centroid is coincident with an AzTEC 1.1 mm point-source detection at a position close to the peak lensing magnification produced by the cluster. However, the 250 micron and 350 micron centroids are elongated and shifted toward the south with a differential shift between bands that cannot be explained by pointing uncertainties. We therefore conclude that the BLAST detection is likely contaminated by emission from foreground galaxies associated with the Bullet Cluster. The submillimeter redshift estimate based on 250-1100 micron photometry at the position of the AzTEC source is z_phot = 2.9 (+0.6 -0.3), consistent with the infrared color redshift estimation of the most likely IRAC counterpart. These flux densities indicate an apparent far-infrared luminosity of L_FIR = 2E13 Lsun. When the amplification due to the gravitational lensing of the cluster is removed, the intrinsic far-infrared luminosity of the source is found to be L_FIR <= 10^12 Lsun, consistent with typical luminous infrared galaxies.Comment: Accepted for publication in the Astrophysical Journal. Maps are available at http://blastexperiment.info

The transcriptional repressor protein NsrR senses nitric oxide directly via a [2Fe-2S] cluster

The regulatory protein NsrR, a member of the Rrf2 family of transcription repressors, is specifically dedicated to sensing nitric oxide (NO) in a variety of pathogenic and non-pathogenic bacteria. It has been proposed that NO directly modulates NsrR activity by interacting with a predicted [Fe-S] cluster in the NsrR protein, but no experimental evidence has been published to support this hypothesis. Here we report the purification of NsrR from the obligate aerobe Streptomyces coelicolor. We demonstrate using UV-visible, near UV CD and EPR spectroscopy that the protein contains an NO-sensitive [2Fe-2S] cluster when purified from E. coli. Upon exposure of NsrR to NO, the cluster is nitrosylated, which results in the loss of DNA binding activity as detected by bandshift assays. Removal of the [2Fe-2S] cluster to generate apo-NsrR also resulted in loss of DNA binding activity. This is the first demonstration that NsrR contains an NO-sensitive [2Fe-2S] cluster that is required for DNA binding activity

Dissecting the role of MADS-box genes in monocot floral development and diversity

Many monocot plants have high social and economic value. These include grasses such as rice (Oryza sativa), wheat (Triticum aestivum) and barley (Hordeum vulgare), which produce soft commodities for many food and beverage industries, and ornamental flowers like lily (Lilium longiflorum) and orchid (Oncidium Gower Ramsey), which represent an important component of international flower markets. There is constant pressure to improve the development and diversity of these species with a significant emphasis on flower development, and this is particularly relevant considering the impact of changing environments on reproduction and thus yield. MADS-box proteins are a family of transcription factors that contain a conserved 56 amino acid MADS-box motif. In plants, attention has been devoted to characterisation of this family due to their roles in inflorescence and flower development, which holds promise for the modification of floral architecture for plant breeding. This has been explored in diverse angiosperms, but particularly the dicot model Arabidopsis thaliana. The focus of this review is on the less-well characterised roles of the MADS-box proteins in monocot flower development and how changes in MADS-box proteins throughout evolution may have contributed to creating a diverse range of flowers. Examining these changes within the monocots can identify the importance of certain genes and pinpoint those which might be useful in future crop improvement and breeding strategies