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A study of single grains of lead halide perovskite reveals the presence of both excitons and free charge carriers. The nature of charge carriers in methylammonium lead iodide perovskites (MAPbI 3 ) at room temperature is still a matter of considerable debate 1 , 2 , 3 . Here, we demonstrate that within single grains of MAPbI 3 , strong spatial heterogeneities on the nanometre length scale are present and associated with simultaneous free-carrier and exciton populations. These heterogeneous populations, hidden in ensemble measurements, have a signature of spatially resolved relaxation dynamics for above-bandgap photoexcitation. Using spectrally resolved transient absorption microscopy, we directly observe both red- and blueshifts of the band-edge absorption across individual grains due to a dynamic Stark shift and screening of excitonic transitions by hot carriers. These observations help address a long-standing debate on the identity of the charge carriers, showing that both excitons and free carriers coexist, but are spatially segregated on the length scale of hundreds of nanometres.

We have isolated the gene for a protein designated CCA1. This protein can bind to a region of the promoter of an Arabidopsis light-harvesting chlorophyll a/b protein gene, Lhcb1*3, which is necessary for its regulation by phytochrome. The CCA1 protein interacted with two imperfect repeats in the Lhcb1*3 promoter, AA(A/C)AATCT, a sequence that is conserved in Lhcb genes. A region near the N terminus of CCA1, which has some homology to the repeated sequence found in the DNA binding domain of Myb proteins, is required for binding to the Lhcb1*3 promoter. Lines of transgenic Arabidopsis plants expressing antisense RNA for CCA1 showed reduced phytochrome induction of the endogenous Lhcb1*3 gene, whereas expression of another phytochrome-regulated gene, rbcS-1A, which encodes the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, was not affected. Thus, the CCA1 protein acts as a specific activator of Lhcb1*3 transcription in response to brief red illumination. The expression of CCA1 RNA was itself transiently increased when etiolated seedlings were transferred to light. We conclude that the CCA1 protein is a key element in the functioning of the phytochrome signal transduction pathway leading to increased transcription of this Lhcb gene in Arabidopsis

Achieving control of light-material interactions for photonic device applications at nanoscale dimensions will require structures that guide electromagnetic energy with a lateral mode confinement below the diffraction limit of light. This cannot be achieved by using conventional waveguides 1 or photonic crystals 2 . It has been suggested that electromagnetic energy can be guided below the diffraction limit along chains of closely spaced metal nanoparticles 3 , 4 that convert the optical mode into non-radiating surface plasmons 5 . A variety of methods such as electron beam lithography 6 and self-assembly 7 have been used to construct metal nanoparticle plasmon waveguides. However, all investigations of the optical properties of these waveguides have so far been confined to collective excitations 8 , 9 , 10 , and direct experimental evidence for energy transport along plasmon waveguides has proved elusive. Here we present observations of electromagnetic energy transport from a localized subwavelength source to a localized detector over distances of about 0.5 μm in plasmon waveguides consisting of closely spaced silver rods. The waveguides are excited by the tip of a near-field scanning optical microscope, and energy transport is probed by using fluorescent nanospheres.

The width of valleys and channels affects the hydrology, ecology, and geomorphic functionality of drainage networks. In many studies, the width of valleys and/or channels (W) is estimated as a power-law function of the drainage area (A), W=kcAd. However, in fluvial systems that experience drainage reorganization, abrupt changes in drainage area distribution can result in valley or channel widths that are disproportional to their drainage areas. Such disproportionality may be more distinguished in valleys than in channels due to a longer adjustment timescale for valleys. Therefore, the valley width–area scaling in reorganized drainages is expected to deviate from that of drainages that did not experience reorganization. To explore the effect of reorganization on valley width–drainage area scaling, we studied 12 valley sections in the Negev desert, Israel, categorized into undisturbed, beheaded, and reversed valleys. We found that the values of the drainage area exponents, d, are lower in the beheaded valleys relative to undisturbed valleys but remain positive. Reversed valleys, in contrast, are characterized by negative d exponents, indicating valley narrowing with increasing drainage area. In the reversed category, we also explored the independent effect of channel slope (S) through the equation W=kbAbSc, which yielded negative and overall similar values for b and c. A detailed study in one reversed valley section shows that the valley narrows downstream, whereas the channel widens, suggesting that, as hypothesized, the channel width adjusts faster to post-reorganization drainage area distribution. The adjusted narrow channel dictates the width of formative flows in the reversed valley, which contrasts with the meaningfully wider formative flows of the beheaded valley across the divide. This difference results in a step change in the unit stream power between the reversed and beheaded channels, potentially leading to a “width feedback” that promotes ongoing divide migration and reorganization. Our findings demonstrate that valley width–area scaling is a potential tool for identifying landscapes influenced by drainage reorganization. Accounting for reorganization-specific scaling can improve estimations of erosion rate distributions in reorganized landscapes.

A tomato (Lycopersicon esculentum L.) gene encoding a precursor of polyphenol oxidase (PPO) was transcribed and translated in vitro. The import, targeting, and processing of the [35S]methionine-labeled precursor protein (pPPO) were studied in isolated chloroplasts. The protein was routed to the thylakoid lumen in two steps. The 67-kD precursor was first imported into the stroma in an ATP-dependent step. It was processed to a 62-kD intermediate by a stromal peptidase. Translocation into the lumen was light dependent and involved processing of the 62-kD to the 59-kD mature form. The mature polypeptide was soluble in the lumen and not bound to thylakoids. This two-step targeting pattern was observed in plastids from a variety of plants including pea (Pisum sativum L.), tomato, and maize (Zea mays L.). The ratio between the intermediate and mature forms observed depended on the plant species, leaf age, growth conditions, and illumination regime to which the plants had been subjected. Cu2+ was not required for pPPO import or processing. Furthermore, low concentrations of Cu2+ (1-5 micromolar) markedly inhibited the first import step. Tentoxin specifically inhibited pPPO import, leaving the precursor bound to the envelope membrane. The two-step routing of pPPO into chloroplasts, typical of thylakoid lumen proteins, is consistent with the two-domain structure of the transit peptide and appears to be a feature of all plant PPO genes isolated so far. No evidence was found for unorthodox routing mechanisms, which have been suggested to be involved in the import of plant PPOs. The two-step routing may account for some of the multiplicity of PPO observed in vivo

A HTS magnet system used in a saturated core Fault Current Limiter (FCL) device is described. The superconducting magnet, operating in DC mode, is used in such FCL design for saturating the magnetic core and maintaining low device impedance under nominal conditions. The unique design of the FCL poses constrains on the DC HTS magnet. A model which meets all the necessary special requirements have been realized in a compact magnet design that is optimized for its electrical characteristics while minimizing its mass and volume. The coil, made of Bi-2223 tapes, has 50000 Ampere-turns required to maintain the core in a saturated state at nominal current in the limiting circuit. Unique, nonmagnetic cryostat made of Delrin was used. Cooling of the coil has been realized by two cold heads: one double-stage head that provides a cooling power of 6 W at 20 K and a single-stage head with a cooling capability of 40W at 70 K. This magnetic system has been successfully integrated and tested in a 120 kVA FCL model. The design, characteristics and tests of this magnetic system are described.

Pore structure and connectivity determine how microstructured materials perform in applications such as catalysis, fluid storage and transport, filtering or as reactors. We report a model study on silica aerogel using a time-of-flight magnetic resonance imaging technique to characterize the flow field and explain the effects of heterogeneities in the pore structure on gas flow and dispersion with 129 Xe as the gas-phase sensor. The observed chemical shift allows the separate visualization of unrestricted xenon and xenon confined in the pores of the aerogel. The asymmetrical nature of the dispersion pattern alludes to the existence of a stationary and a flow regime in the aerogel. An exchange time constant is determined to characterize the gas transfer between them. As a general methodology, this technique provides insights into the dynamics of flow in porous media where several phases or chemical species may be present.

Polyphenol oxidase (PPO; EC 1.10.3.2 or EC 1.14.18.1) takes part in the response of tomato plants (Lycopersicon esculentum Mill.) to wounding and herbivore attack, mediated by the octadecanoid wound-signaling pathway. Wounding and methyl jasmonate (MeJA) induce expression of ppo genes and markedly increase the level of the enzyme. We report that pretreatment with MeJA also markedly increased the ability of isolated tomato chloroplasts to import and process PPO precursors (pPPO). Pea (Pisum sativum L.) chloroplasts showed no such response. Wounding or ethylene alone was ineffective but ethylene was synergistic with MeJA. Treatment with MeJA conferred a strong binding of pPPO, or its processing intermediate, to thylakoids and subsequent translocation into the lumen and processing to the mature protein. The effect on PPO import and translocation was evident after 8-16 h exposure to MeJA. Membrane-bound pPPO was cross-linked to a proteinaceous component of the thylakoid translocation apparatus, apparently induced by MeJA. The import and processing of other nuclear-encoded thylakoid proteins were not affected by MeJA in tomato. A 90-kDa protein that co-fractionated with thylakoids was induced along with the increase in competence for PPO import, and was identified as the proteinase-inhibitor multicystatin. It is concluded that the 90-kDa protein observed is part of the MeJA-induced defense response of tomato, not a component of the thylakoid translocation apparatus.

In our ongoing efforts to develop a vaccine against Streptococcus suis infection, we tested the potential of S. suis enolase (SsEno), a recently described S. suis adhesin with fibronectin-binding activity, as a vaccine candidate in a mouse model of S. suis-induced septicemia and meningitis. Here, we show that SsEno is highly recognized by sera from convalescent pigs and is highly immunogenic in mice. Subcutaneous immunization of mice with SsEno elicited strong immunoglobulin G (IgG) antibody responses. All four IgG subclasses were induced, with IgG1, IgG2a and IgG2b representing the highest titers followed by IgG3. However, SsEno-vaccinated and nonvaccinated control groups showed similar mortality rates after challenge infection with the highly virulent S. suis strain 166'. Similar results were obtained upon passive immunization of mice with hyperimmunized rabbit IgG anti-SsEno. We also showed that anti-SsEno antibodies did not increase the ability of mouse phagocytes to kill S. suis in vitro. In conclusion, these data demonstrate that although recombinant SsEno formulated with Quil A triggers a strong antibody response, it does not confer effective protection against infection with S. suis serotype 2 in mice.