Mapping fibre orientation in complex-shaped biological systems with micrometre resolution by scanning X-ray microdiffraction

A fully automated procedure to extract and to image local fibre orientation in biological tissues from scanning X-ray diffraction is presented. The preferred chitin fibre orientation in the flow sensing system of crickets is determined with high spatial resolution by applying synchrotron radiation based X-ray microbeam diffraction in conjunction with advanced sample sectioning using a UV micro-laser. The data analysis is based on an automated detection of azimuthal diffraction maxima after 2D convolution filtering (smoothing) of the 2D diffraction patterns. Under the assumption of crystallographic fibre symmetry around the morphological fibre axis, the evaluation method allows mapping the three-dimensional orientation of the fibre axes in space. The resulting two-dimensional maps of the local fibre orientations - together with the complex shape of the flow sensing system - may be useful for a better understanding of the mechanical optimization of such tissues.

A novel method for measuring lag times in division of individual bacterial cells using image analysis

A method is presented for determining the time to first division of individual bacterial cells growing on agar media. Bacteria were inoculated onto agar-coated slides and viewed by phase-contrast microscopy. Digital images of the growing bacteria were captured at intervals and the time to first division estimated by calculating the "box area ratio". This is the area of the smallest rectangle that can be drawn around an object, divided by the area of the object itself. The box area ratios of cells were found to increase suddenly during growth at a time that correlated with cell division as estimated by visual inspection of the digital images. This was caused by a change in the orientation of the two daughter cells that occurred when sufficient flexibility arose at their point of attachment. This method was used successfully to generate lag time distributions for populations of Escherichia coli, Listeria monocytogenes and Pseudomonas aeruginosa, but did not work with the coccoid organism Staphylococcus aureus. This method provides an objective measure of the time to first cell division, whilst automation of the data processing allows a large number of cells to be examined per experiment. (c) 2005 Elsevier B.V. All rights reserved.

Alignment of a model amyloid peptide fragment in bulk and at a solid surface

The alignment of model amyloid peptide YYKLVFFC is investigated in bulk and at a solid surface using a range of spectroscopic methods employing polarized radiation. The peptide is based on a core sequence of the amyloid beta (A beta) peptide, KLVFF. The attached tyrosine and cysteine units are exploited to yield information on alignment and possible formation of disulfide or dityrosine links. Polarized Raman spectroscopy on aligned stalks provides information on tyrosine orientation, which complements data from linear dichroism (LD) on aqueous solutions subjected to shear in a Couette cell. LD provides a detailed picture of alignment of peptide strands and aromatic residues and was also used to probe the kinetics of self-assembly. This suggests initial association of phenylalanine residues, followed by subsequent registry of strands and orientation of tyrosine residues. X-ray diffraction (XRD) data from aligned stalks is used to extract orientational order parameters from the 0.48 nm reflection in the cross-beta pattern, from which an orientational distribution function is obtained. X-ray diffraction on solutions subject to capillary flow confirmed orientation in situ at the level of the cross-beta pattern. The information on fibril and tyrosine orientation from polarized Raman spectroscopy is compared with results from NEXAFS experiments on samples prepared as films on silicon. This indicates fibrils are aligned parallel to the surface, with phenyl ring normals perpendicular to the surface. Possible disulfide bridging leading to peptide dimer formation was excluded by Raman spectroscopy, whereas dityrosine formation was probed by fluorescence experiments and was found not to occur except under alkaline conditions. Congo red binding was found not to influence the cross-beta XRD pattern.

Using an additive to control the electrospinning of fibres of poly(epsilon-caprolactone)

Electrospinning is a route to polymer fibres with diameters considerably smaller than available from most fibre-producing techniques. We explore the use of a low molecular weight compound as an effective control additive during the electrospinning of poly(epsilon-caprolactone). This approach extends the control variables for the electrospinning of nanoscale fibres from the more usual ones such as the polymer molecular weight, solvent and concentration. We show that through the use of dual solvent systems, we can alter the impact of the additive on the electrospinning process so that finer as well as thicker fibres can be prepared under otherwise identical conditions. As well as the size of the fibres and the number of beads, the use of the additive allows us to alter the level of crystallinity as well as the level of preferred orientation of the poly(epsilon-caprolactone) crystals. This approach, involving the use of a dual solvent and a low molar mass compound, offers considerable potential for application to other polymer systems. (C) 2010 Society of Chemical Industry

Theoretical investigation of infrared spectra and pocket dynamics of photodissociated carbonmonoxy myoglobin

Molecular dynamics simulations of the photodissociated state of carbonmonoxy myoglobin (MbCO) are presented using a fluctuating charge model for CO. A new three-point charge model is fitted to high-level ab initio calculations of the dipole and quadrupole moment functions taken from the literature. The infrared spectrum of the CO molecule in the heme pocket is calculated using the dipole moment time autocorrelation function and shows good agreement with experiment. In particular, the new model reproduces the experimentally observed splitting of the CO absorption spectrum. The splitting of 3–7 cm−1 (compared to the experimental value of 10 cm−1) can be directly attributed to the two possible orientations of CO within the docking site at the edge of the distal heme pocket (the B states), as previously suggested on the basis of experimental femtosecond time-resolved infrared studies. Further information on the time evolution of the position and orientation of the CO molecule is obtained and analyzed. The calculated difference in the free energy between the two possible orientations (Fe···CO and Fe···OC) is 0.3 kcal mol−1 and agrees well with the experimentally estimated value of 0.29 kcal mol−1. A comparison of the new fluctuating charge model with an established fixed charge model reveals some differences that may be critical for the correct prediction of the infrared spectrum and energy barriers. The photodissociation of CO from the myoglobin mutant L29F using the new model shows rapid escape of CO from the distal heme pocket, in good agreement with recent experimental data. The effect of the protein environment on the multipole moments of the CO ligand is investigated and taken into account in a refined model. Molecular dynamics simulations with this refined model are in agreement with the calculations based on the gas-phase model. However, it is demonstrated that even small changes in the electrostatics of CO alter the details of the dynamics.

Origin of the Parry arc

Laboratory experiments to determine the preferred orientation of free-falling hexagonal prisms were performed at Reynolds numbers appropriate to falling ice crystals in the atmosphere. Hexagonal plates orient with their c axis vertical for aspect ratios < 0.9, whilst hexagonal columns fall with their c axis horizontal. A secondary alignment is also observed: regular hexagonal columns fall preferentially with two prism facets aligned vertically and not horizontally – the latter scenario was previously assumed to be responsible for the rare Parry arc. However, if the column is made scalene in its cross-section, it can orient such that a pair of prism facets is horizontal. This finding indicates that the development of scalene crystals may be key to the production of certain ice-crystal optical phenomena

Configurational preferences of two 1,2-diamine adducts of bis(1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedionato)cobalt(II)

The preparation, the IR and ligand field spectra and the structures of the mixed-ligand addition compounds [(N,N-dimethyl-1,2-diaminoethane)bis(1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedionato)cobalt(II)], [Co(thtf)2me2en], and [(N,N,N′,N′-tetramethyl-1,2-diaminoethane)bis(1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedionato)cobalt(II)], [Co(thtf)2me4en], are reported. The structures were determined by single crystal X-ray diffraction analysis (monoclinic, space group P21/c, Z=4 with a=10.708(6), b=19.531(6), c=13.352(6) Å, β=111.64(10)°, R1=0.0642 and wR2=0.1719 for [Co(thtf)2(me2en)] and a=12.033(6), b=15.565(6), c=15.339(6) Å, β=92.57(6)°, R1=0.0612 and wR2=0.1504 for [Co(thtf)2me4en]). The structures are distorted octahedral and the shortest cobalt–cobalt separation distances are 5.388(2) Å in [Co(thtf)2me2en] and 8.675(3) Å in [Co(thtf)2me4en]. In both compounds the diamine molecules attain the gauche conformation. The U(Z,Z) conformation of the β-dione leads to a semi-chair conformation of the β-dionato chelate rings. The relative orientation of the groups attached to the β-dionato moiety depends on the extent of stereoelectronic effects the N-substitution of the diamine entails. In [Co(thtf)2me2en] the intraligand distance separating the trifluoromethyl carbon atoms is 5.281(18) Å while in [Co(thtf)2me2en] it increases to 8.338(9) Å. The cobalt–cobalt separation distance, the orientation of the chelate rings and the extent of N-substitution seem to affect hydrogen bonding. While in [Co(thtf)2me2en] inter- and intraligand hydrogen bonding is implicated, it is totally absent in [Co(thtf)2me4en].

A qualified defense of American drone attacks in northwest Pakistan under international humanitarian law

Since the terrorist attacks of September 11, 2001, international law has had to grapple with the fundamental challenges that large-scale violence carried out by non-State actors poses to the traditional inter- State orientation of international law. Questions related to the “adequacy” and “effectiveness” of international humanitarian law, international human rights law and the law related to the use of force have been particularly pronounced. This paper focuses on the international humanitarian law implications of American drone attacks in northwest Pakistan. A highly-advanced modality of modern warfare, armed drones highlight the possibilities, problems, prospects and pitfalls of high-tech warfare. How is the battlefield to be defined and delineated geographically and temporally? Who can be targeted, and by whom? Ultimately, this paper concludes that American drone attacks in northwest Pakistan are not unlawful as such under international humanitarian law, though, like any tactical decision in the context of asymmetric warfare, they should be continuously and closely monitored according to the dictates of law with sensitivity to facts on the ground.

Biaxial optical properties of thermotropic random copolyesters

The optical microstructures of thin sections of two liquid crystalline polymers are examined in the polarizing microscope. The polymers are random copolyesters based on hydroxybenzoic and hydroxynaphthoic acids (B-N), and hydroxybenzoic acid and ethylene terephthalate (B-ET). Sections cut from oriented samples, so as to include the extrusion direction, show microstructures in which there is no apparent preferred orientation of the axes describing the local optical anisotropy. The absence of preferred orientation in the microstructure, despite marked axial alignment of molecular chain segments as demonstrated by X-Ray diffraction, is interpreted in terms of the polymer having biaxial optical properties. The implication of optical biaxiality is that, although the mesophases are nematic, the orientation of the molecules is correlated about three (orthogonal) axes over distances greater than a micron. The structure is classified as a multiaxial nematic.

Effect of shear rupture on aggregate scale formation in sea ice

A discrete element model is used to study shear rupture of sea ice under convergent wind stresses. The model includes compressive, tensile, and shear rupture of viscous elastic joints connecting floes that move under the action of the wind stresses. The adopted shear rupture is governed by Coulomb’s criterion. The ice pack is a 400 km long square domain consisting of 4 km size floes. In the standard case with tensile strength 10 times smaller than the compressive strength, under uniaxial compression the failure regime is mainly shear rupture with the most probable scenario corresponding to that with the minimum failure work. The orientation of cracks delineating formed aggregates is bimodal with the peaks around the angles given by the wing crack theory determining diamond-shaped blocks. The ice block (floe aggregate) size decreases as the wind stress gradient increases since the elastic strain energy grows faster leading to a higher speed of crack propagation. As the tensile strength grows, shear rupture becomes harder to attain and compressive failure becomes equally important leading to elongation of blocks perpendicular to the compression direction and the blocks grow larger. In the standard case, as the wind stress confinement ratio increases the failure mode changes at a confinement ratio within 0.2–0.4, which corresponds to the analytical critical confinement ratio of 0.32. Below this value, the cracks are bimodal delineating diamond shape aggregates, while above this value failure becomes isotropic and is determined by small-scale stress anomalies due to irregularities in floe shape.

Unprecedented coordination of dithiocarbimate in multinuclear and heteroleptic complexes

An uncommon coordination protocol induced by the p-tolylsulfonyl dithiocarbimate ligand (L) [L = p-CH(3)C(6)H(4)SO(2)N CS(2)(2-)] in conjunction with PPh(3) allowed the formation of novel homodimetallic, Cu(2)(PPh(3))(4)L (1), trinuclear heterometallic Cu(2)Ni(L)(2)(PPh(3))(4) (2) and heteroleptic complexes of general formula cis-[M(PPh(3))(2)L] [M = Pd(II) (3), Pt(II) (4)]. The complexes have been characterized by microanalysis, mass spectrometry, IR, (1)H, (13)C and (31)P NMR and electronic absorption spectra and single-crystal X-ray crystallography. 2 uniquely consists of square planar, trigonal planar and tetrahedral coordination spheres within the same molecule. In both heteroleptic complexes 3 and 4 the orientation of aromatic protons of PPh(3) ligand towards the Pd(II) and Pt(II) center reveals C-H center dot center dot center dot Pd and C-H center dot center dot center dot Pt rare intramolecular anagostic or preagostic interactions. These complexes exhibit photoluminescent properties in solution at room temperature arising mainly from intraligand charge transfer (ILCT) transitions. The assignment of electronic absorption bands has been corroborated by time dependent density functional theory (TD-DFT) calculations. Complexes 1 and 2 with sigma(rt) values similar to 10(-6) S cm(-1) show semi-conductor properties in the temperature range 313-403 K whereas 3 and 4 exhibit insulating behaviour.

Preparation of films of a highly aligned lipid cubic phase

We demonstrate a method by which we can produce an oriented film of an inverse bicontinuous cubic phase (QII D) formed by the lipid monoolein (MO). By starting with the lipid as a disordered precursor (the L3 phase) in the presence of butanediol, we can obtain a film of the QII D phase showing a high degree of in-plane orientation by controlled dilution of the sample under shear within a linear flow cell. We demonstrate that the direction of orientation of the film is different from that found in the oriented bulk material that we have reported previously; therefore, we can now reproducibly form QII D samples oriented with either the [110] or the [100] axis aligned in the flow direction depending on the method of preparation. The deposition of MO as a film, via a moving fluid− air interface that leaves a coating of MO in the L3 phase on the capillary wall, leads to a sample in the [110] orientation. This contrasts with the bulk material that we have previously demonstrated to be oriented in the [100] direction, arising from flow producing an oriented bulk slug of material within the capillary tube. The bulk sample contains significant amounts of residual butanediol, which can be estimated from the lattice parameter of the QII D phase obtained. The sample orientation and lattice parameters are determined from synchrotron small-angle X-ray scattering patterns and confirmed by simulations. This has potential applications in the production of template materials and the growth of protein crystals for crystallography as well as deepening our understanding of the mechanisms underlying the behavior of lyotropic liquid-crystal phases.

Kinematical analysis of redundant drive wire mechanisms with velocity constraint

In this paper, we propose a new velocity constraint type for Redundant Drive Wire Mechanisms. The purpose of this paper is to demonstrate that the proposed velocity constraint module can fix the orientation of the movable part and to use the kinematical analysis method to obtain the moving direction of the movable part. First, we discuss the necessity of using this velocity constraint type and the possible applications of the proposed mechanism. Second, we derive the basic equations of a wire mechanism with this constraint type. Next, we present a method of motion analysis on active and passive constraint spaces, which is used to find the moving direction of a movable part. Finally, we apply the above analysis method on a wire mechanism with a velocity constraint module and on a wire mechanism with four double actuator modules. By evaluating the results, we prove the validity of the proposed constraint type.

Solar origin of heliospheric magnetic field inversions: evidence for coronal loop opening within pseudostreamers

The orientation of the heliospheric magnetic field (HMF) in near‒Earth space is generally a good indicator of the polarity of HMF foot points at the photosphere. There are times, however, when the HMF folds back on itself (is inverted), as indicated by suprathermal electrons locally moving sunward, even though they must ultimately be carrying the heat flux away from the Sun. Analysis of the near‒Earth solar wind during the period 1998–2011 reveals that inverted HMF is present approximately 5.5% of the time and is generally associated with slow, dense solar wind and relatively weak HMF intensity. Inverted HMF is mapped to the coronal source surface, where a new method is used to estimate coronal structure from the potential‒field source‒surface model. We find a strong association with bipolar streamers containing the heliospheric current sheet, as expected, but also with unipolar or pseudostreamers, which contain no current sheet. Because large‒scale inverted HMF is a widely accepted signature of interchange reconnection at the Sun, this finding provides strong evidence for models of the slow solar wind which involve coronal loop opening by reconnection within pseudostreamer belts as well as the bipolar streamer belt. Occurrence rates of bipolar‒ and pseudostreamers suggest that they are equally likely to result in inverted HMF and, therefore, presumably undergo interchange reconnection at approximately the same rate. Given the different magnetic topologies involved, this suggests the rate of reconnection is set externally, possibly by the differential rotation rate which governs the circulation of open solar flux.

Factors contributing to the development of extreme North Atlantic cyclones and their relationship with the NAO

The occurrence of extreme cyclones is analysed in terms of their relationship to the NAO phase and the dominating environmental variables controlling their intensification. These are latent energy (equivalent potential temperature 850 hPa is used as an indicator), upper-air baroclinicity, horizontal divergence and jet stream strength. Cyclones over the North Atlantic are identified and tracked using a numerical algorithm, permitting a detailed analysis of their life cycles. Extreme cyclones are selected as the 10% most severe in terms of intensity. Investigations focus on the main strengthening phase of each cyclone. The environmental factors are related to the NAO, which affects the location and orientation of the cyclone tracks, thus explaining why extreme cyclones occur more (less) frequently during strong positive (negative) NAO phases. The enhanced number of extreme cyclones in positive NAO phases can be explained by the larger area with suitable growth conditions, which is better aligned with the cyclone tracks and is associated with increased cyclone life time and intensity. Moreover, strong intensification of cyclones is frequently linked to the occurrence of extreme values of growth factors in the immediate vicinity of the cyclone centre. Similar results are found for ECHAM5/OM1 for present day conditions, demonstrating that relationships between the environment factors and cyclones are also valid in the GCM. For future climate conditions (following the SRES A1B scenario), the results are similar, but a small increase of the frequency of extreme values is detected near the cyclone cores. On the other hand, total cyclone numbers decrease by 10% over the North Atlantic. An exception is the region near the British Isles, which features increased track density and intensity of extreme cyclones irrespective of the NAO phase. These changes are associated with an intensified jet stream close to Europe. Moreover, an enhanced frequency of explosive developments over the British Isles is found, leading to more frequent windstorms affecting Europe.