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To study and evaluate the structure–activity relationships in di-aryl bismuth phosphinates on antibacterial activity and cytotoxicity a series of complexes containing ortho-methoxyphenyl, meta-methoxyphenyl, meta-tolyl and para-tolyl aryl groups; [Bi(o-MeOPh)2(O(O)P(H)Ph)]n1, [Bi(o-MeOPh)2(O(O)PPh2)]n2, [Bi(o-MeOPh)2(O(O)P(p-MeOPh)2)]n3, [Bi(m-MeOPh)2(O(O)P(H)Ph)]n4, [Bi(m-MeOPh)2(O(O)PPh2)]n5, [Bi(m-MeOPh)2(O(O)P(p-MeOPh)2)]n6, [Bi(m-tol)2(O(O)P(H)Ph)]n7, [Bi(m-tol)2(O(O)PPh2)]n8, [Bi(m-tol)2(O(O)P(p-MeOPh)2)]n9, [Bi(p-tol)2(O(O)P(H)Ph)]n10, [Bi(p-tol)2(O(O)PPh2)]n11 and [Bi(p-tol)2(O(O)P(p-MeOPh)2)]n12, were synthesised and characterised. Complexes 4, 7, 8, 10 and 11 were structurally authenticated by X-ray crystallography. Evaluation of their antibacterial activity towards methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) showed that the bismuth bound aryl group has a profound influence on activity, with the o-MeOPh complexes 1–3 showing very little activity while the m-MeOPh complexes have the greatest activity towards MRSA and VRE in the range of 0.63 to 1.25 μM. Viability studies with Cos-7 cells showed that the di-aryl bismuth complexes 1–12 are less cytotoxic than their di-phenyl bismuth analogues, with a general trend of toxicity observed as p-tolyl > m-tolyl > m-methoxyphenyl > o-methoxyphenyl. The large difference in Cos-7 viability for complexes 1 (IC50 > 80 μM) and 4 (IC50 14.0 μM) was further investigated through bismuth uptake studies, where there was no obvious difference in Cos-7 bismuth uptake at 5 μM. This suggests that the bismuth-bound aryl group has a significant impact on biological activity, which is then further mediated by other ligands. [ABSTRACT FROM AUTHOR]

* Premise of the study: The molecular mechanisms regulating the expansive growth of the plant cell wall have yet to be fully understood. The recent development of a computational cell wall model allows quantitative examinations of hypothesized cell wall loosening mechanisms. * Methods: Computational cell wall network (CWN) models were generated using cellulose microfibrils (CMFs), hemicelluloses (HCs), and their interactions (CMF-HC). For each component, a range of stiffness values, representing various situations hypothesized as potential cell-wall-loosening mechanisms, were used in the calculation of the overall stiffness of the computational CWN model. Thus, a critical mechanism of the loosening of the primary cell wall was investigated using a computational approach by modeling the molecular structure. * Key results: The increase in the stiffness equivalent of the CMF-HC interaction results in an increase in the Young's modulus of the CWN. In the major growth direction, the CWN stiffness is most sensitive to the CMF-HC interaction (75%). HC stiffness contributes moderately (24%) to the change in the CWN stiffness, whereas the CMF contribution is marginal (1%). Minor growth direction exhibited a similar trend except that the contributions of CMFs and HCs are higher than for the major growth direction. * Conclusions: The stiffness of the CMF-HC interaction is the most critical mechanical component in altering stiffness of the CWN model, which supports the hypothesized mechanism of expansin's role in efficient loosening of the plant cell wall by disrupting HC binding to CMFs. The comparison to experiments suggests additional load-bearing mechanisms in CMF-HC interactions. [ABSTRACT FROM AUTHOR]

The scanning-beam digital x-ray (SBDX) system has been developed for fluoroscopic imaging using an inverse x-ray imaging geometry. The SBDX system consists of a large-area x-ray source with a multihole collimator and a small detector. The goal of this study was to build a Monte Carlo (MC) model of the SBDX source as a useful tool for optimization of the SBDX imaging system in terms of its hardware components and imaging parameters. The MC model of the source was built in the EGSnrc/BEAMnrc code and validated using the DOSXYZnrc code and Gafchromic film measurements for 80, 100, and 120 kV x-ray source voltages. The MC simulated depth dose curves agreed with measurements to within 5%, and beam profiles at three selected depths generally agreed within 5%. Exposure rates and half-value layers for three voltages were also calculated from the MC simulations. Patient skin-dose per unit detector-dose was quantified as a function of patient size for all three x-ray source voltages. The skin-dose to detector-dose ratio ranged from 5–10 for a 20 cm thick patient to 1 × 103–1 × 105 for a 50 cm patient for the 120 and 80 kV beams, respectively. Simulations of imaging dose for a prostate patient using common imaging parameters revealed that skin-dose per frame was as low as 0.2 mGy. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the possibility of estimating pediatric thyroid doses from CT using surface neck doses. Optically stimulated luminescence dosimeters were used to measure the neck surface dose of 25 children ranging in ages between one and three years old. The neck circumference for each child was measured. The relationship between obtained surface doses and thyroid dose was studied using acrylic phantoms of various sizes and with holes of different depths. The ratios of hole-to-surface doses were used to convert patients' surface dose to thyroid dose. ImPACT software was utilized to calculate thyroid dose after applying the appropriate age correction factors. A paired t-test was performed to compare thyroid doses from our approach and ImPACT. The ratio of thyroid to surface dose was found to be 1.1. Thyroid doses ranged from 20 to 80mGy. Comparison showed no statistical significance (p = 0.18). In addition, the average of surface dose variation along the z-axis in helical scans was studied and found to range between 5% (in 10 cm diameter phantom/24 mm collimation/pitch 1.0) and 8% (in 16 cm diameter phantom/12 mm collimation/pitch 0.7). We conclude that surface dose is an acceptable predictor for pediatric thyroid dose from CT. The uncertainty due to surface dose variability may be reduced if narrower collimation is used with a pitch factor close to 1.0. Also, the results did not show any effect of thyroid depth on the measured dose. [ABSTRACT FROM AUTHOR]

Causality between near-Earth and midtail substorm processes is one of the most controversial issues about the substorm trigger mechanism. The currently most popular model, the outside-in model, assumes that near-Earth reconnection is initiated in the midtail region before substorm onset and that the associated flow burst causes tail current disruption in the near-Earth region. However, there remain some outstanding issues that may serve as critical tests of this model. The present article reviews recent satellite and ground observations addressing three such critical issues with a focus on substorm-related auroral features. First, near-Earth reconnection, even if it reaches the lobe magnetic field, does not necessarily trigger a global substorm, but it is often related to a pseudobreakup. This fact suggests that there is an additional or alternative condition for substorm development. Secondly, although there appears to be one-to-one correspondence between flow bursts in the plasma sheet and equatorward-moving auroral structures (auroral streamers), no such auroral feature that can be associated with the fast plasma flow can be identified prior to auroral breakups. On the other hand, the flow burst is widely regarded as a manifestation of reconnection and therefore, according to the outside-in model, should be created in the near-Earth plasma sheet before substorm onset. Finally, auroral arcs poleward of a breakup arc are not affected until the front of auroral intensification reaches those arcs. The last two points suggest that if substorm is triggered as the outside-in model describes, the ionosphere is electromagnetically detached from the magnetosphere, which, however, has not been addressed theoretically. Thus, it should be crucial for a better understanding of the substorm trigger process to implement the magnetosphere-ionosphere coupling in future modeling efforts and to address those basic issues as a guide for critically evaluating each model. [ABSTRACT FROM AUTHOR]

Magnetospheric substorms represent the basic dynamic process in the coupled solar wind -- magnetosphere -- ionosphere system. Recent satellite missions have considerably advanced our means to monitor this vast environment. These observations are interpreted in the context of a hierarchy of models: Global MHD simulations and various techniques of nonlinear physics are used to characterize the large-scale features, whereas microphysical models are used to study the small-scale processes. Empirical models are described in order to address questions that involve meso-scale or multi-scale phenomena. We discuss some of the recent observations and relate those to new advancements in various modeling techniques. [ABSTRACT FROM AUTHOR]

Theoretical pressure balance arguments have implied that steady convection is hardly possible in the terrestrial magnetotail and that steady energy input necessarily generates a cyclic loading-unloading sequence, i.e., repetitive substorms. However, observations have revealed that enhanced solar wind energy input to the magnetospheric system may either lead to substorm activity or enhanced but steady convection. This topic is reviewed with emphasis on several recent case studies of the Steady Magnetospheric Convection (SMC) events. In these cases extensive data sets from both satellite and ground-based instruments from various magnetospheric and ionospheric regions were available. Accurate distinction of the spatial and temporal scales of the magnetospheric processes is vital for correct interpretation of the observations during SMC periods. We show that on the large scale, the magnetospheric configuration and plasma convection are stable during SMC events, but that both reveal considerable differences from their quiet-time assemblies. On a shorter time scale, there are numerous transient activations which are similar to those found during substorms, but which presumably originate from a more distant tail reconnection process, and map to the poleward boundary of the auroral oval. The available observations and the unresolved questions are summarized here. The tail magnetic field during SMC events resembles both substorm growth and recovery phases in the neartail and midtail, respectively, but this configuration may remain stable for up to ten hours. Based on observations and model results we discuss how the magnetospheric system avoids pressure balance problems when the plasma convects earthward. Finally, the importance of further coordinated studies of SMC events is emphasized. Such studies may shed more light on the substorm dynamics and help to verify quantitatively the theoretical models of the convecting magnetosphere. [ABSTRACT FROM AUTHOR]

The Visible Imaging System (VIS) is a set of three low-light-level cameras to be flown on the POLAR spacecraft of the Global Geospace Science (GGS) program which is an element of the International Solar-Terrestrial Physics (ISTP) campaign. Two of these cameras share primary and some secondary optics and are designed to provide images of the nighttime auroral oval at visible wavelengths. A third camera is used to monitor the directions of the fields-of-view of these sensitive auroral cameras with respect to sunlit Earth. The auroral emissions of interest include those from N at 391.4 nm, O i at 557.7 and 630.0 nm, H i at 656.3 nm, and O ii at 732.0 nm. The two auroral cameras have different spatial resolutions. These resolutions are about 10 and 20 km from a spacecraft altitude of 8 R. The time to acquire and telemeter a 256×256-pixel image is about 12 s. The primary scientific objectives of this imaging instrumentation, together with the in-situ observations from the ensemble of ISTP spacecraft, are (1) quantitative assessment of the dissipation of magnetospheric energy into the auroral ionosphere, (2) an instantaneous reference system for the in-situ measurements, (3) development of a substantial model for energy flow within the magnetosphere, (4) investigation of the topology of the magnetosphere, and (5) delineation of the responses of the magnetosphere to substorms and variable solar wind conditions. [ABSTRACT FROM AUTHOR]

On montre l'intérêt d'étudier les antennes logpériodiques comprimées, c'està-dire à grand angle au sommet. Un programme mis au point précédemment, permet de calculer les caractéristiques de l'antenne. Après un rappel sur les antennes log-périodiques on étudie théoriquement l'influence, sur les caractéristiques de rayonnement, des différents paramètres de l'antenne: finesse des doublets, impédance caractéristique de la ligne d'alimentation et rapport de similitude. Ensuite on vérifie par l'expérience les résultats théoriques en particulier sur une antenne qui fonctionne entre 0,6 et 2,6 GHz avec seulement 9 doublets rayonnants et dont la longueur est seulement de 0,22 λm, où λm désigne la longueur d'onde maximale de la bande passante. The study of compressed log-periodic antennas, i.e. log-periodic antenna arrays having a wide angle at the summet, is shown to be worthwhile. A previously developed programme permits the computation of the electrical characteristics of the antenna. The concept of log-periodic antenna arrays is recalled to mind, and the theoretic effects of the various parameters, such as fineness of dipole antennas, characteristic impedance of feeders and ratio of similarity, upon the radiation characteristics are looked into. Then, theoretic results are checked experimentally, more especially on an antenna operated between 0,6 and 2,6 MHz with but 9 dipole radiators, whose length is only 0,22 λm, where λm is the maximum wavelength of the pass band. [ABSTRACT FROM AUTHOR]