Structural and kinetic studies of spin crossover in an Iron(II) complex with a novel tripodal ligand

Configurational and ligand conformational influences on the kinetics of (1)A(1) reversible arrow T-5(2) spin crossover in the Fe(II) complex with the novel tripodal ligand, 1,1,1-tris((N-(2-pyridylmethyl)-N-methylamino)methyl)ethane (tptMetame), have been explored. Despite having six chelate rings and three chiral nitrogen atoms, only one enantiomeric pair of isomers, Delta, SSS, and Lambda, RRR, of the complex ion is observed. The conformation of the three rings forming the upper ''cap'' of the complex structure can be assigned delta or lambda with respect to the 3-fold molecular axis. X-ray data at 300 and 153 K, above and below the critical temperature for the spin transition, show that the conformation of the ligand ''cap'' is the same as the absolute configuration of the complex, with the same Lambda lambda(CAP)(or Delta delta(CAP)) combination prevailing for both the LS ((1)A(1)) and HS (T-5(2)) isomers. Molecular mechanics calculations further show that the ligand energy remains lowest for this Lambda lambda(CAP) (or Delta delta(CAP)) combination at all Fe-N distances over the range spanning the LS and HS isomers. Measurements of the spin crossover relaxation time have been carried out in solution over the temperature range 293-170 K. The observed monophasic relaxation traces are also consistent with the absolute configuration of the complex remaining unaltered during the spin crossover.

Orientation and navigation in bats: known unknowns or unknown unknowns?

Bats have been extensively studied with regard to their ability to orient, navigate and hunt prey by means of echolocation, but almost nothing is known about how they orient and navigate in situations such as migration and homing outside the range of their echolocation system. As volant animals, bats face many of the same problems and challenges as birds. Migrating bats must relocate summer and winter home ranges over distances as far as 2,000 km. Foraging bats must be able to relocate their home roost if they range beyond a familiar area, and indeed circumstantial evidence suggests that these animals can home from more than 600 km. However, an extensive research program on homing and navigation in bats halted in the early 1970s. The field of bird navigation has advanced greatly since that time and many of the mechanisms that birds are known to use for navigation were not known or widely accepted at this time. In this paper I discuss what is known about orientation and navigation in bats and use bird navigation as a model for future research in bat navigation. Technology is advancing such that previous difficulties in studying orientation in bats in the field can be overcome and so that the mechanisms of navigation in this highly mobile animal can finally be elucidated.

Short distance phase shifts revisited: tracking clock-shifted homing pigeons (Rock Dove Columba livia) close to the loft

Clock-shifted homing pigeons (Rock Dove Columba livia) were tracked from familiar release sites using a direction recorder. At relatively short distances from the home loft (

Larval Transport Modeling of Deep-Sea Invertebrates Can Aid the Search for Undiscovered Populations

Background: Many deep-sea benthic animals occur in patchy distributions separated by thousands of kilometres, yet because deep-sea habitats are remote, little is known about their larval dispersal. Our novel method simulates dispersal by combining data from the Argo array of autonomous oceanographic probes, deep-sea ecological surveys, and comparative invertebrate physiology. The predicted particle tracks allow quantitative, testable predictions about the dispersal of benthic invertebrate larvae in the south-west Pacific. Principal Findings: In a test case presented here, using non-feeding, non-swimming (lecithotrophic trochophore) larvae of polyplacophoran molluscs (chitons), we show that the likely dispersal pathways in a single generation are significantly shorter than the distances between the three known population centres in our study region. The large-scale density of chiton populations throughout our study region is potentially much greater than present survey data suggest, with intermediate ‘stepping stone’ populations yet to be discovered. Conclusions/Significance: We present a new method that is broadly applicable to studies of the dispersal of deep-sea organisms. This test case demonstrates the power and potential applications of our new method, in generating quantitative, testable hypotheses at multiple levels to solve the mismatch between observed and expected distributions: probabilistic predictions of locations of intermediate populations, potential alternative dispersal mechanisms, and expected population genetic structure. The global Argo data have never previously been used to address benthic biology, and our method can be applied to any non-swimming larvae of the deep-sea, giving information upon dispersal corridors and population densities in habitats that remain intrinsically difficult to assess.

Dispersion interactions in room-temperature ionic liquids: Results from a non-empirical density functional

The role of dispersion or van de Waals (VDW) interactions in imidazolium-based room-temperature ionic liquids is studied within the framework of density functional theory, using a recently developed non-empirical functional [M. Dion, H. Rydberg, E. Schroder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004)], as efficiently implemented in the SIESTA code [G. Roman-Perez and J. M. Soler, Phys. Rev. Lett. 103, 096102 (2009)]. We present results for the equilibrium structure and lattice parameters of several crystalline phases, finding a general improvement with respect to both the local density (LDA) and the generalized gradient approximations (GGA). Similar to other systems characterized by VDW bonding, such as rare gas and benzene dimers as well as solid argon, equilibrium distances and volumes are consistently overestimated by approximate to 7%, compared to -11% within LDA and 11% within GGA. The intramolecular geometries are retained, while the intermolecular distances and orientations are significantly improved relative to LDA and GGA. The quality is superior to that achieved with tailor-made empirical VDW corrections ad hoc [M. G. Del Popolo, C. Pinilla, and P. Ballone, J. Chem. Phys. 126, 144705 (2007)]. We also analyse the performance of an optimized version of this non-empirical functional, where the screening properties of the exchange have been tuned to reproduce high-level quantum chemical calculations [J. Klimes, D. Bowler, and A. Michaelides, J. Phys.: Condens. Matter 22, 074203 (2010)]. The results for solids are even better with volumes and geometries reproduced within 2% of experimental data. We provide some insight into the issue of polymorphism of [bmim][Cl] crystals, and we present results for the geometry and energetics of [bmim][Tf] and [mmim][Cl] neutral and charged clusters, which validate the use of empirical force fields. (C) 2011 American Institute of Physics. [doi:10.1063/1.3652897]

Increasing the accuracy of Nitrogen Dioxide (NO2) pollution mapping using geographically weighted regression (GWR) and geostatistics.

Nitrogen Dioxide (NO2) is known to act as an environmental trigger for many respiratory illnesses. As a pollutant it is difficult to map accurately, as concentrations can vary greatly over small distances. In this study three geostatistical techniques were compared, producing maps of NO2 concentrations in the United Kingdom (UK). The primary data source for each technique was NO2 point data, generated from background automatic monitoring and background diffusion tubes, which are analysed by different laboratories on behalf of local councils and authorities in the UK. The techniques used were simple kriging (SK), ordinary kriging (OK) and simple kriging with a locally varying mean (SKlm). SK and OK make use of the primary variable only. SKlm differs in that it utilises additional data to inform prediction, and hence potentially reduces uncertainty. The secondary data source was Oxides of Nitrogen (NOx) derived from dispersion modelling outputs, at 1km x 1km resolution for the UK. These data were used to define the locally varying mean in SKlm, using two regression approaches: (i) global regression (GR) and (ii) geographically weighted regression (GWR). Based upon summary statistics and cross-validation prediction errors, SKlm using GWR derived local means produced the most accurate predictions. Therefore, using GWR to inform SKlm was beneficial in this study.

The Type Ia supernova 2004s, a clone of SN 2001el, and the optimal photometric bands for extinction estimation

We present optical (UBVRI) and near-IR (YJHK) photometry of the normal Type Ia supernova (SN) 2004S. We also present eight optical spectra and one near-IR spectrum of SN 2004S. The light curves and spectra are nearly identical to those of SN 2001el. This is the first time we have seen optical and IR light curves of two Type Ia SNe match so closely. Within the one parameter family of light curves for normal Type Ia SNe, that two objects should have such similar light curves implies that they had identical intrinsic colors and produced similar amounts of Ni-56. From the similarities of the light-curve shapes we obtain a set of extinctions as a function of wavelength that allows a simultaneous solution for the distance modulus difference of the two objects, the difference of the host galaxy extinctions, and RV. Since SN 2001el had roughly an order of magnitude more host galaxy extinction than SN 2004S, the value of R-V = 2.15(-0.22)(+0.24) pertains primarily to dust in the host galaxy of SN 2001el. We have also shown via Monte Carlo simulations that adding rest-frame J-band photometry to the complement of BVRI photometry of Type Ia SNe decreases the uncertainty in the distance modulus by a factor of 2.7. A combination of rest-frame optical and near-IR photometry clearly gives more accurate distances than using rest-frame optical photometry alone.

SN 2004A: another type II-P supernova with a red supergiant progenitor

We present a monitoring study of SN 2004A and probable discovery of a progenitor star in pre-explosion Hubble Space Telescope (HST) images. The photometric and spectroscopic monitoring of SN 2004A show that it was a normal Type II-P which was discovered in NGC 6207 about two weeks after explosion. We compare SN 2004A to the similar Type II-P SN 1999em and estimate an explosion epoch of 2004 January 6. We also calculate three new distances to NGC 6207 of 21.0 +/- 4.3, 21.4 +/- 3.5 and 25.1 +/- 1.7 Mpc. The former was calculated using the Standard Candle Method (SCM) for SNe II-P, and the latter two from the brightest supergiants method (BSM). We combine these three distances with existing kinematic distances, to derive a mean value of 20.3 +/- 3.4 Mpc. Using this distance, we estimate that the ejected nickel mass in the explosion is 0.046(-0.017)(+0.031) M-circle dot. The progenitor of SN 2004A is identified in pre-explosion WFPC2 F814W images with a magnitude of m(F814W) = 24.3 +/- 0.3, but is below the detection limit of the F606W images. We show that this was likely a red supergiant (RSG) with a mass of 9(-2)(+3) M-circle dot. The object is detected at 4.7 sigma above the background noise. Even if this detection is spurious, the 5 sigma upper limit would give a robust upper mass limit of 12M(circle dot) for a RSG progenitor. These initial masses are very similar to those of two previously identified RSG progenitors of the Type II-P SNe 2004gd (8(-2)(+4) M circle dot) and 2005cs (9(-2)(+3) M-circle dot).

The chemical composition of two supergiants in the dwarf irregular galaxy WLM

The chemical composition of two stars in WLM has been determined from high-quality Ultraviolet-Visual Echelle Spectrograph (UVES) data obtained at the VLT-UT2. The model atmospheres analysis shows that they have the same metallicity, [Fe/H] = - 0.38 +/- 0.20 (+/- 0.29). Reliable magnesium abundances are determined from several lines of two ionization states in both stars resulting in [Mg/Fe] = - 0.24 +/- 0.16 (+/- 0.28). This result suggests that the [alpha(Mg)/Fe] ratio in WLM may be suppressed relative to solar abundances ( also supported by differential abundances relative to similar stars in NGC 6822 and the Small Magellanic Cloud [SMC]). The absolute Mg abundance, [Mg/H] = -0.62, is high relative to what is expected from the nebulae though, where two independent spectroscopic analyses of the H II regions in WLM yield [O/H] = - 0.89. Intriguingly, the oxygen abundance determined from the O I lambda6158 feature in one WLM star is [O/H] = - 0.21 +/- 0.10 (+/- 0.05), corresponding to 5 times higher than the nebular oxygen abundance. This is the first time that a significant difference between stellar and nebular oxygen abundances has been found, and currently, there is no simple explanation for this difference. The two stars are massive supergiants with distances that clearly place them in WLM. They are young ( less than or equal to 10 Myr) and should have a similar composition to the ISM. Additionally, differential abundances suggest that the O/Fe ratio in the WLM star is consistent with similar stars in NGC 6822 and the SMC, galaxies where the average stellar oxygen abundances are in excellent agreement with the nebular results. If the stellar abundances reflect the true composition of WLM, then this galaxy lies well above the metallicity-luminosity relationship for dwarf irregular galaxies. It also suggests that WLM is more chemically evolved than currently interpreted from its color-magnitude diagram. The similarities between the stars in WLM and NGC 6822 suggest that these two galaxies may have had similar star formation histories.

The chemical composition towards the galactic anti-centre .2. Differential abundance analyses and distance determinations

In a previous paper we have published observational data for 6 early B-type stars having, galactocentric distances of between 10 and 18 kpc. Using LTE line-blanketed model at mosphere techniques we derived their atmospheric parameters, finding that all our targets had similar effective temperatures and surface gravities. In the following study we additionally include two stars which have been presented previously (Rolleston et al. 1993) and found also to have compatible atmospheric parameters to the original programme stars. The homogeneity of this sample allows quantitative line-by-line differential abundance analyses to be carried out which should reliably detect variations in the chemical compositions of the stellar photospheres. We present differential abundances for eight stars, in either young open clusters or the field, with respect to an arbitrarily chosen standard which shows a normal abundance pattern. Our method of calculating distances from the derived atmospheric parameters means that the relative distance scale should be accurate.

The chemical composition towards the galactic anti-centre .1. Observations and model atmosphere analyses

High resolution spectra of six early B-type main-sequence stars having galactocentric distances of between 10 and 18 kpc are presented. We List the equivalent widths for the metal lines and illustrate their hydrogen and helium line profiles. The stars are analysed using LTE line-blanketed model atmosphere techniques to derive atmospheric parameters and surface chemical compositions. All six stars have similar effective temperatures and surface gravities, allowing a reliable comparison of their metal abundances and distances. Significant variations in the photospheric abundances are evident and are discuss the need for a more detailed line-by-line differential analysis to exactly quantify the differences. This will be presented in a companion paper (Smartt et al. 1996).

A study of DNA fragmentation patterns in cells irradiated with charged particles: evidence for non-random distributions

Many studies have shown that the effectiveness of radiations of varying LET is similar when yields of dsb have been measured, despite large differences in biological response. Recent evidence has suggested however, that current techniques underestimate the yields of dsb. By monitoring the fragmentation of DNA over a wide range of fragment sizes ( 6 Mbp) by pulsed field electrophoresis, RBE values greater than 1.0 for radiations of around 100 keV/mm have been determined. The data provide evidence for the production of correlated breaks produced within cells as particle tracks traverse the nucleus. The highly ordered structure of DNA within mammalian cells may lead to clustering of breaks over distances related to the repeating unit structures of the chromatin. As well as these regionally damaged sites, a major contributor to radiation effectiveness will be the localised clustering of damage in the 1 - 20 bp region. A major effort is required to elucidate the relative importance of these levels of clustering and their importance in biological response.

Identification of essential operons with a rhamnose-inducible promoter in Burkholderia cenocepacia

Scanning of bacterial genomes to identify essential genes is of biological interest, for understanding the basic functions required for life, and of practical interest, for the identification of novel targets for new antimicrobial therapies. In particular, the lack of efficacious antimicrobial treatments for infections caused by the Burkholderia cepacia complex is causing high morbidity and mortality of cystic fibrosis patients and of patients with nosocomial infections. Here, we present a method based on delivery of the tightly regulated rhamnose-inducible promoter P(rhaB) for identifying essential genes and operons in Burkholderia cenocepacia. We demonstrate that different levels of gene expression can be achieved by using two vectors that deliver P(rhaB) at two different distances from the site of insertion. One of these vectors places P(rhaB) at the site of transposon insertion, while the other incorporates the enhanced green fluorescent protein gene (e-gfp) downstream from P(rhaB). This system allows us to identify essential genes and operons in B. cenocepacia and provides a new tool for systematically identifying and functionally characterizing essential genes at the genomic level.

The removal of patients who live outside the practice boundary:a study of outside-area removals in Northern Ireland in 2001-2002

It has been suggested that there are significant overlaps between removals due to deregistration and removals arising because patients live outside the practice area. If this is true, it would mean that the current estimates of deregistration would need to be revised upwards. All outside-area removals for the calendar years 2001 and 2002 were reviewed and characterised by age, sex and Jarman score of the enumeration district of the patients' residence and distance from the practice. The average outside-area removal rate was just over one removal per practice per year. Removal rates were highest between the ages of 18 and 44 years; there were no significant differences between the sexes. Rates of removal increased exponentially with distance, although even at marked distances from the practice there were about 10 patients remaining on the list for each one removed. Residents in deprived areas were more likely to be removed, although because areas most distal to the practice tend to be affluent, overall there was a predominance of affluent patients among those who are removed. In Northern Ireland rates of outside-area removal are only slightly higher than those of deregistration. It is evident that GPs are exercising some discretion as to which of the outside-area patients they retain on their list. This has the potential to cause some misunderstanding and resentment among patients, as has been reported previously.

Clara Bog: An ombotrophic groundwater dependant terrestrial ecosystem (Submitted)

Comparison of flow duration curves for a weir draining an undrained raised peat with those generated 20 years previously reveal that more recent curves reflect to be flatter with a lower Q95/Q5 ratio. Comparison of the bog topography for the same period revealed that although marginal drainage/peat reclamation had resulted in desiccation of peat around the bog margin and more frequent intense runoff, the central part of the bog had subsided to form an enclosed basin ,resulting in the creation of newly formed lakes that gave the central part of the bog an improved capacity to store, and more slowly discharge, water. Interrogation of groundwater monitoring data revealed a net decline in groundwater levels of up to three metres in the glacial tills underlying the bog associated with deepening and expansion of a marginal drain network which penetrated the base of the peat. Comparing organic carbon levels in peat the central part of the bog over a ten year period revealed an overall increase, with changes being most marked in deeper fen peat layers. These findings suggest that the decline in groundwater levels in the peat substrate resulted in an increase in effective stress in the peat causing greater subsidence in the central part of the bog due to greater overall thickness. Study results highlight how the hydrology of apparently isolated obotrophic raised bog ecosystems may be influenced by groundwater pressures in deeper deposits, and how marginal drains may have the capacity to impact areas at significant distances.