Strong-field photodetachment of H- by few-cycle laser pulses

The recent adiabatic saddle-point method of Shearer et al. [ Phys. Rev. A 84 033409 (2011)] is applied to study strong-field photodetachment of H- by few-cycle linearly polarized laser pulses of frequencies near the two-photon detachment threshold. The behavior of the saddle points in the complex-time plane for a range of laser parameters is explored. A detailed analysis of the influence of laser intensities [(2×1011)–(6.5 × 1011) W/cm2], midinfrared laser wavelengths (1800–2700 nm), and various values of the carrier envelope phase (CEP) on (i) three-dimensional probability detachment distributions, (ii) photoangular distributions (PADs), (iii) energy spectra, and (iv) momentum distributions are presented. Examination of the probability distributions and PADs reveal main lobes and jetlike structures. Bifurcation phenomena in the probability distributions and PADs are also observed as the wavelength and intensity increase. Our simulations show that the (i) probability distributions, (ii) PADs, and (iii) energy spectra are extremely sensitive to the CEP and thus measuring such distributions provides a useful tool for determining this phase. The symmetrical properties of the electron momentum distributions are also found to be strongly correlated with the CEP and this provides an additional robust method for measuring the CEP of a laser pulse. Our calculations further show that for a three-cycle pulse inclusion of all eight saddle points is required in the evaluation of the transition amplitude to yield an accurate description of the photodetachment process. This is in contrast to recent results for a five-cycle pulse.

Time-Dependent Density Diagnostics of Solar Flare Plasmas Using SDO/EVE

Temporally resolved electron density measurements of solar flare plasmas are presented using data from the EUV Variability Experiment (EVE) on board the Solar Dynamics Observatory. The EVE spectral range contains emission lines formed between 104 and 107 K, including transitions from highly ionized iron (gsim10 MK). Using three density-sensitive Fe XXI ratios, peak electron densities of 1011.2-1012.1 cm–3 were found during four X-class flares. While previous measurements of densities at such high temperatures were made at only one point during a flaring event, EVE now allows the temporal evolution of these high-temperature densities to be determined at 10 s cadence. A comparison with GOES data revealed that the peak of the density time profiles for each line ratio correlated well with that of the emission measure time profile for each of the events studied.

Genetic characterization of tigecycline resistance in clinical isolates of Enterobacter cloacae and Enterobacter aerogenes

OBJECTIVES:
The intrinsically encoded ramA gene has been linked to tigecycline resistance through the up-regulation of efflux pump AcrAB in Enterobacter cloacae. The molecular basis for increased ramA expression in E. cloacae and Enterobacter aerogenes, as well as the role of AraC regulator rarA, has not yet been shown. To ascertain the intrinsic molecular mechanism(s) involved in tigecycline resistance in Enterobacter spp., we analysed the expression levels of ramA and rarA and corresponding efflux pump genes acrAB and oqxAB in Enterobacter spp. clinical isolates.

METHODS:
The expression levels of ramA, rarA, oqxA and acrA were tested by quantitative real-time RT-PCR. The ramR open reading frames of the ramA-overexpressing strains were sequenced; strains harbouring mutations were transformed with wild-type ramR to study altered ramA expression and tigecycline susceptibility.

RESULTS:
Tigecycline resistance was mediated primarily by increased ramA expression in E. cloacae and E. aerogenes. Only the ramA-overexpressing E. cloacae isolates showed increased rarA and oqxA expression. Upon complementation with wild-type ramR, all Enterobacter spp. containing ramR mutations exhibited decreased ramA and acrA expression and increased tigecycline susceptibility. Exceptions were one E. cloacae strain and one E. aerogenes strain, where a decrease in ramA levels was not accompanied by lower acrA expression.

CONCLUSIONS:
Increased ramA expression due to ramR deregulation is the primary mediator of tigecycline resistance in clinical isolates of E. cloacae and E. aerogenes. However, some ramA-overexpressing isolates do not show changes in ramR, suggesting alternate pathways of ramA regulation; the rarA regulator and the oqxAB efflux pump may also play a role in tigecycline resistance in E. cloacae.

Peer tutoring in reading: The effects of role and organization on two dimensions of self-esteem

Background. Paired reading (PR) is an application of peer tutoring. It has been extensively researched, and its efficacy across a range of outcomes has been established. Benefits include improvements in key reading skills, and also in affective aspects of learning. Several studies have shown gains in self-esteem, although measurement methods have varied, and the model of self-esteem has rarely been clearly articulated.
Aims. To investigate the changes in self-esteem of children participating in a randomized trial of PR over a 15-week treatment period. To investigate the relative contribution of self-worth and self-competence to any gains in self-esteem. To investigate whether the pattern of change differs in children who take on different roles in the PR process.
Participants. The participants comprised a subset of a large-scale randomized trial of peer learning (The Fife Peer Learning Project). Four schools were randomly selected from schools allocated to the same-age PR condition, and four schools from those allocated to the cross-age PR condition. The same-age group consisted of 87 primary 6 children (10–11 years old). The cross-age group consisted of 81 primary 6 children. The controls, from schools randomly selected from a neighbouring authority, consisted of 92 primary 6 children.
Method. A pre–post design employing self-report measures of self-esteem. Rosenberg’s Self-Esteem Scale was used, with scores analysed for worth and competence. The treatment period was 15 weeks, with the participants following a prescribed PR process.
Results. Significant pre–post gains were noted in self-esteem, driven predominantly by improved beliefs about competence, in both same-age and cross-age conditions, but not for controls. Gains were also seen in self-worth in the cross-age condition. Further analyses of the influence of organizational condition (same-age or cross-age) and role played (tutor vs. tutee) showed significant differences between same-age tutors and cross-age tutors in relation to self-worth. Effect sizes were generally small or moderate.
Conclusions. The findings provide further support for the belief that PR can enhance self-esteem. Importantly, the use of a two-dimensional model provides extra information about self-perceptions in PR contexts: first, the central role of self- competence; and second, the gains in self-worth which are associated with tutoring younger children (but not same-age peers). This new information has educational significance for schools considering the potential of peer tutoring and the benefits of different organizational conditions.

Reflection and Transmission at a Phase Discontinuous Interface

In this paper we extend the derivation of the modified form Snells's law that occurs when an additional phase profile is introduced at the material interface. We show that this permits electromagnetic (EM) beam steering, negative refraction and retrodirective action opportunities for such engineered surfaces even if they are immersed in a uniform dielectric. Simple expressions for the retrodirected and negatively refracted beams are derived along with the propagation conditions that occur at the boundary interface inside the critical angle range. It is also demonstrated how the transmission and reflected power levels are affected by the additional phase taper introduced at the surface.

Electrochemical versus gas-phase oxidation of ru single-crystal surfaces

The electrochemical uptake of oxygen on a Ru(0001) electrode was investigated by electron diffraction, Auger spectroscopy, and cyclic voltammetry. An ordered (2 × 2)-O overlayer forms at a potential close to the hydrogen region. At +0.42 and +1.12 V vs Ag/AgCl, a (3 × 1) phase and a (1 × 1)-O phase, respectively, emerge. When the Ru electrode potential is maintained at +1.12 V for 2 min, RuO2 grows epitaxially with its (100) plane parallel to the Ru(0001) surface. In contrast to the RuO domains, the non-oxidized regions of the Ru electrode surface are flat. If, however, the electrode potential is increased to +1.98 V for 2 min, the remaining non-oxidized Ru area also becomes rough. These findings are compared with O overlayers and oxides on the Ru(0001) and Ru(101¯1) surfaces created by exposure to gaseous O under UHV conditions. On the other hand, gas-phase oxidation of the Ru(101¯0) surface leads to the formation of RuO with a (100) orientation. It is concluded that the difference in surface energy between RuO(110) and RuO(100) is quite small. RuO again grows epitaxially on Ru(0001), but with the (110) face oriented parallel to the Ru(0001) surface. The electrochemical oxidation of the Ru(0001) electrode surface proceeds via a 3-dimensional growth mechanism with a mean cluster size of 1.6 nm, whereas under UHV conditions, a 2-dimensional oxide film (1-2 nm thick) is epitaxially formed with an average domain size of 20 µm. © 2000 American Chemical Society.

Roles of multiple flagellins in flagellar formation and flagellar growth post bdelloplast lysis in Bdellovibrio bacteriovorus

Bdellovibrio bacteriovorus cells have a single polar flagellum whose helical pitch and diameter characteristically change near the midpoint, resulting in a tapered wave. There are six flagellin genes in the genome: fliC1 to fliC6. Accordingly, the flagellar filament is composed of several similar flagellin species. We have used knockout mutants of each gene and analyzed the mutational effects on the filament length and on the composition and localization of each flagellin species in the filament by electron microscopy and one- and two-dimensional polyacrylamide gel electrophoresis. The location and amounts of flagellins in a filament were determined to be as follows: a small amount of FliC3 at the proximal end, followed by a large amount of FliC5, a large amount of FliC1, a small amount of FliC2 in this order, and a large amount of FliC6 at the distal end. FliC4 was present at a low level, but the location was not determined. Filament lengths of newly born progeny cells increased during prolonged incubation in nutrient-deficient buffer. The newly formed part of the elongated filament was composed of mainly FliC6. Reverse transcription PCR analysis of flagellar gene expression over 5 days in buffer showed that fliC gene expression tailed off over 5 days in the wild-type cells, but in the fliC5 mutant, expression of the fliC2, fliC4, and fliC6 genes was elevated on day 5, suggesting that they may be expressed to compensate for the absence of a major component, FliC5.

Design of a Dissolving Microneedle Platform for Transdermal Delivery of a Fixed-Dose Combination of Cardiovascular Drugs

Microneedles (MNs) are a minimally invasive drug delivery platform, designed to enhance transdermal drug delivery by breaching the stratum corneum. For the first time, this study describes the simultaneous delivery of a combination of three drugs using a dissolving polymeric MN system. In the present study, aspirin, lisinopril dihydrate, and atorvastatin calcium trihydrate were used as exemplar cardiovascular drugs and formulated into MN arrays using two biocompatible polymers, poly(vinylpyrrollidone) and poly(methylvinylether/maleic acid). Following fabrication, dissolution, mechanical testing, and determination of drug recovery from the MN arrays, in vitro drug delivery studies were undertaken, followed by HPLC analysis. All three drugs were successfully delivered in vitro across neonatal porcine skin, with similar permeation profiles achieved from both polymer formulations. An average of 126.3 ± 18.1 μg of atorvastatin calcium trihydrate was delivered, notably lower than the 687.9 ± 101.3 μg of lisinopril and 3924 ± 1011 μg of aspirin, because of the hydrophobic nature of the atorvastatin molecule and hence poor dissolution from the array. Polymer deposition into the skin may be an issue with repeat application of such a MN array, hence future work will consider more appropriate MN systems for continuous use, alongside tailoring delivery to less hydrophilic compounds.

The high-energy environment in the super-Earth system CoRoT-7

High-energy irradiation of exoplanets has been identified to be a key influence on the stability of these planets' atmospheres. So far, irradiation-driven mass-loss has been observed only in two Hot Jupiters, and the observational data remain even more sparse in the super-Earth regime. We present an investigation of the high-energy emission in the CoRoT-7 system, which hosts the first known transiting super-Earth. To characterize the high-energy XUV radiation field into which the rocky planets CoRoT-7b and CoRoT-7c are immersed, we analyzed a 25 ks XMM-Newton observation of the host star. Our analysis yields the first clear (3.5σ) X-ray detection of CoRoT-7. We determine a coronal temperature of ≈ 3 MK and an X-ray luminosity of 3 × 1028 erg s-1. The level of XUV irradiation on CoRoT-7b amounts to ≈37 000 erg cm-2 s-1. Current theories for planetary evaporation can only provide an order-of-magnitude estimate for the planetary mass loss; assuming that CoRoT-7b has formed as a rocky planet, we estimate that CoRoT-7b evaporates at a rate of about 1.3 × 1011 g s-1 and has lost ≈4-10 earth masses in total.