Diamagnetism Of Graphite

A calculation of the diamagnetism of graphite including the effects of trigonal warping of the Fermi surfaces has been performed using Fukuyama's formulation of the diamagnetism of Bloch electrons. Inclusion of the trigonal warping increases the diamagnetism by about 13% at low temperatures and reduces it by about 1% at high temperatures. A paramagnetic constant is used to represent all effects not associated with the free carriers. The experimental diamagnetism can be fitted quite well using values of the energy band parameters which give agreement with the de Haas-van Alphen effect, optical absorption, and magnetoreflection experiments. © 1974 The American Physical Society.962467247

Are companies using Twitter to greenwash and hide bad environmental performance?

Companies and related consumer behaviours contribute significantly to global carbon emissions. However, consumer behaviour is shifting, with the public now recognising the real and immediate impact of climate change. Many companies are aware and seemingly eager to align to consumer’s increasing environmental consciousness, yet there is a risk that some companies could be presenting themselves as environmentally friendly without implementing environmentally beneficial processes and products (i.e. greenwashing). Here, using longitudinal climate leadership, environmental messaging (Twitter) and stock price data, we explore how climate leadership (a relative climate change mitigation metric) and environmental messaging have changed for hundreds of UK companies. Using the environmental messaging, we also assess whether companies are simply greenwashing their true climate change performance. Finally, we explore how climate leadership and environmental messaging influence companies’ stock prices. We found that companies (on average) have increased their climate leadership (coef: 0.14, CI 0.12–0.16) and environmental messaging (coef: 0.35, CI 0.19–0.50) between 2010 and 2019. We also found an association where companies with more environmental messaging had a higher climate leadership (coef: 0.16, CI 0.07–0.26), suggesting messaging was proportionate to environmental performance, and so there was no clear pattern of using Twitter for greenwashing across UK companies. In fact, some companies may be under-advertising their pro-environmental performance. Finally, we found no evidence that climate leadership, environmental messaging or greenwashing impacts a company’s stock price

Finite element analysis of rectangular reinforced concrete columns wrapped with FRP composites

Fibre reinforced polymer (FRP) wrapping of reinforced concrete (RC) columns has increasingly become the most suitable method used to strengthen and rehabilitate RC columns. It is clear that limited studies have investigated the behaviour of eccentrically loaded RC columns wrapped with FRP composites. In the present study, a three-dimensional finite element (FE) model was developed to simulate the behaviour of rectangular RC columns wrapped with glass fibre-reinforced polymer (GFRP) sheets under concentric and eccentric loading. The FE model was developed in the finite element analysis software ANSYS. The variables within the FE model are the number of GFRP layers and the magnitude of load eccentricity. The FE analysis results showed that GFRP wrapping significantly improved the performance of the strengthened columns by delaying concrete rupture. The presence of load eccentricity reduced the load carrying capacity and performance of the strengthened RC columns. The FE model correlated well with the stress distribution trends observed in the literature

Fully biodegradable and biocompatible emulsion template polymer scaffolds by thiol-acrylate polymerisation of polycaprolactone macropolymers

The emulsion templating process offers a route to highly porous polymers with well-defined morphologies. This study describes the preparation of such porous polymers (polyHIPEs) via the photopolymerization of a multi-functional thiol and polycaprolactone macromonomer. The resulting materials have nominal porosities of 90% and 95%, and are seen to have an interconnected pore morphology, with an average pore diameter of approximately 60 μm. Initial biocompatibility assessments with fibroblast cells (L929) have shown that the polymers are capable of supporting cell growth over 7 days and degradation products are non-toxic to cells up to a concentration of 0.1 mg ml−1

Single-molecule study of redox control involved in establishing the spinach plastocyanin-cytochrome b6f electron transfer complex

Small diffusible redox proteins play a ubiquitous role in bioenergetic systems, facilitating electron transfer (ET) between membrane bound complexes. Sustaining high ET turnover rates requires that the association between extrinsic and membrane-bound partners is highly specific, yet also sufficiently weak to promote rapid post-ET separation. In oxygenic photosynthesis the small soluble electron carrier protein plastocyanin (Pc) shuttles electrons between the membrane integral cytochrome b6f (cytb6f) and photosystem I (PSI) complexes. Here we use peak-force quantitative nanomechanical mapping (PF-QNM) atomic force microscopy (AFM) to quantify the dynamic forces involved in transient interactions between cognate ET partners. An AFM probe functionalised with Pc molecules is brought into contact with cytb6f complexes, immobilised on a planar silicon surface. PF-QNM interrogates the unbinding force of the cytb6f-Pc interactions at the single molecule level with picoNewton force resolution and on a time scale comparable to the ET time in vivo (ca. 120 μs). Using this approach, we show that although the unbinding force remains unchanged the interaction frequency increases over five-fold when Pc and cytb6f are in opposite redox states, so complementary charges on the cytb6f and Pc cofactors likely contribute to the electrostatic forces that initiate formation of the ET complex. These results suggest that formation of the docking interface is under redox state control, which lowers the probability of unproductive encounters between Pc and cytb6f molecules in the same redox state, ensuring the efficiency and directionality of this central reaction in the ‘Z-scheme’ of photosynthetic ET

Paradoxical effects of the cannabinoid CB2 receptor agonist GW405833 on rat osteoarthritic knee joint pain

SummaryObjectiveThe present study examined whether local administration of the cannabinoid-2 (CB2) receptor agonist GW405833 could modulate joint nociception in control rat knee joints and in an animal model of osteoarthritis (OA).MethodOA was induced in male Wistar rats by intra-articular injection of sodium monoiodo-acetate with a recovery period of 14 days. Immunohistochemistry was used to evaluate the expression of CB2 and transient receptor potential vanilloid channel-1 (TRPV1) receptors in the dorsal root ganglion (DRG) and synovial membrane of sham- and sodium mono-iodoacetate (MIA)-treated animals. Electrophysiological recordings were made from knee joint primary afferents in response to rotation of the joint both before and following close intra-arterial injection of different doses of GW405833. The effect of intra-articular GW405833 on joint pain perception was determined by hindlimb incapacitance. An in vitro neuronal release assay was used to see if GW405833 caused release of an inflammatory neuropeptide (calcitonin gene-related peptide – CGRP).ResultsCB2 and TRPV1 receptors were co-localized in DRG neurons and synoviocytes in both sham- and MIA-treated animals. Local application of the GW405833 significantly reduced joint afferent firing rate by up to 31% in control knees. In OA knee joints, however, GW405833 had a pronounced sensitising effect on joint mechanoreceptors. Co-administration of GW405833 with the CB2 receptor antagonist AM630 or pre-administration of the TRPV1 ion channel antagonist SB366791 attenuated the sensitising effect of GW405833. In the pain studies, intra-articular injection of GW405833 into OA knees augmented hindlimb incapacitance, but had no effect on pain behaviour in saline-injected control joints. GW405833 evoked increased CGRP release via a TRPV1 channel-dependent mechanism.ConclusionThese data indicate that GW405833 reduces the mechanosensitivity of afferent nerve fibres in control joints but causes nociceptive responses in OA joints. The observed pro-nociceptive effect of GW405833 appears to involve TRPV1 receptors

Interference lithographic nanopatterning of plant and bacterial light-harvesting complexes on gold substrates

We describe a facile approach for nanopatterning of photosynthetic light-harvesting complexes over macroscopic areas, and use optical spectroscopy to demonstrate retention of native properties by both site-specifically and non-specifically attached photosynthetic membrane proteins. A Lloyd's mirror dual-beam interferometer was used to expose self-assembled monolayers of amine-terminated alkylthiolates on gold to laser irradiation. Following exposure, photo-oxidized adsorbates were replaced by oligo(ethylene glycol) terminated thiols, and the remaining intact amine-functionalized regions were used for attachment of the major light-harvesting chlorophyll–protein complex from plants, LHCII. These amine patterns could be derivatized with nitrilotriacetic acid (NTA), so that polyhistidine-tagged bacteriochlorophyll–protein complexes from phototrophic bacteria could be attached with a defined surface orientation. By varying parameters such as the angle between the interfering beams and the laser irradiation dose, it was possible to vary the period and widths of NTA and amine-functionalized lines on the surfaces; periods varied from 1200 to 240 nm and linewidths as small as 60 nm (λ/4) were achieved. This level of control over the surface chemistry was reflected in the surface topology of the protein nanostructures imaged by atomic force microscopy; fluorescence imaging and spectral measurements demonstrated that the surface-attached proteins had retained their native functionality

Nanodomains of Cytochrome b(6)f and Photosystem II Complexes in Spinach Grana Thylakoid Membranes

The cytochrome b6f (cytb6f) complex plays a central role in photosynthesis, coupling electron transport between photosystem II (PSII) and photosystem I to the generation of a transmembrane proton gradient used for the biosynthesis of ATP. Photosynthesis relies on rapid shuttling of electrons by plastoquinone (PQ) molecules between PSII and cytb6f complexes in the lipid phase of the thylakoid membrane. Thus, the relative membrane location of these complexes is crucial, yet remains unknown. Here, we exploit the selective binding of the electron transfer protein plastocyanin (Pc) to the lumenal membrane surface of the cytb6f complex using a Pc-functionalized atomic force microscope (AFM) probe to identify the position of cytb6f complexes in grana thylakoid membranes from spinach (Spinacia oleracea). This affinity-mapping AFM method directly correlates membrane surface topography with Pc-cytb6f interactions, allowing us to construct a map of the grana thylakoid membrane that reveals nanodomains of colocalized PSII and cytb6f complexes. We suggest that the close proximity between PSII and cytb6f complexes integrates solar energy conversion and electron transfer by fostering short-range diffusion of PQ in the protein-crowded thylakoid membrane, thereby optimizing photosynthetic efficiency

Correlated fluorescence quenching and topographic mapping of Light-Harvesting Complex II within surface-assembled aggregates and lipid bilayers

Light-Harvesting Complex II (LHCII) is a chlorophyll-protein antenna complex that efficiently absorbs solar energy and transfers electronic excited states to photosystems I and II. Under excess light intensity LHCII can adopt a photoprotective state in which excitation energy is safely dissipated as heat, a process known as Non-Photochemical Quenching (NPQ). In vivo NPQ is triggered by combinatorial factors including transmembrane ΔpH, PsbS protein and LHCII-bound zeaxanthin, leading to dramatically shortened LHCII fluorescence lifetimes. In vitro, LHCII in detergent solution or in proteoliposomes can reversibly adopt an NPQ-like state, via manipulation of detergent/protein ratio, lipid/protein ratio, pH or pressure. Previous spectroscopic investigations revealed changes in exciton dynamics and protein conformation that accompany quenching, however, LHCII-LHCII interactions have not been extensively studied. Here, we correlated fluorescence lifetime imaging microscopy (FLIM) and atomic force microscopy (AFM) of trimeric LHCII adsorbed to mica substrates and manipulated the environment to cause varying degrees of quenching. AFM showed that LHCII self-assembled onto mica forming 2D-aggregates (25–150 nm width). FLIM determined that LHCII in these aggregates were in a quenched state, with much lower fluorescence lifetimes (~0.25 ns) compared to free LHCII in solution (2.2–3.9 ns). LHCII-LHCII interactions were disrupted by thylakoid lipids or phospholipids, leading to intermediate fluorescent lifetimes (0.6–0.9 ns). To our knowledge, this is the first in vitro correlation of nanoscale membrane imaging with LHCII quenching. Our findings suggest that lipids could play a key role in modulating the extent of LHCII-LHCII interactions within the thylakoid membrane and so the propensity for NPQ activation