Structure of cellulose microfibrils in primary cell-walls from collenchyma

In the primary walls of growing plant cells, the glucose polymer cellulose is assembled into long microfibrils a few nanometers in diameter. The rigidity and orientation of these microfibrils control cell expansion; therefore, cellulose synthesis is a key factor in the growth and morphogenesis of plants. Celery (Apium graveolens) collenchyma is a useful model system for the study of primary wall microfibril structure because its microfibrils are oriented with unusual uniformity, facilitating spectroscopic and diffraction experiments. Using a combination of x-ray and neutron scattering methods with vibrational and nuclear magnetic resonance spectroscopy, we show that celery collenchyma microfibrils were 2.9 to 3.0 nm in mean diameter, with a most probable structure containing 24 chains in cross section, arranged in eight hydrogen-bonded sheets of three chains, with extensive disorder in lateral packing, conformation, and hydrogen bonding. A similar 18-chain structure, and 24-chain structures of different shape, fitted the data less well. Conformational disorder was largely restricted to the surface chains, but disorder in chain packing was not. That is, in position and orientation, the surface chains conformed to the disordered lattice constituting the core of each microfibril. There was evidence that adjacent microfibrils were noncovalently aggregated together over part of their length, suggesting that the need to disrupt these aggregates might be a constraining factor in growth and in the hydrolysis of cellulose for biofuel production

First measurement of the total gravitational quadrupole moment of a black widow companion

We present the first measurement of the gravitational quadrupole moment of the companion star of a spider pulsar, namely the black widow PSR J2051–0827. To this end, we have re-analysed radio timing data using a new model that is able to account for periastron precession caused by tidal and centrifugal deformations of the star as well as by general relativity. The model allows for a time-varying component of the quadrupole moment, thus self-consistently accounting for the ill-understood orbital period variations observed in these systems. Our analysis results in the first detection of orbital precession in a spider system at ω˙=−68∘.6+0∘.9−0∘.5 yr−1 and the most accurate determination of orbital eccentricity for PSR J2051–0827 with e = (4.2 ± 0.1) × 10−5. We show that the variable quadrupole component is about 100 times smaller than the average quadrupole moment Q¯=−2.2+0.6−1×1041 kgm2⁠. We discuss how accurate modelling of high-precision optical light curves of the companion star will allow its apsidal motion constant to be derived from our results

Optical, X-ray, and γ-ray observations of the candidate transitional millisecond pulsar 4FGL J0427.8-6704

We present an optical, X-ray, and γ-ray study of 1SXPS J042749.2-670434, an eclipsing X-ray binary that has an associated γ-ray counterpart, 4FGL J0427.8-6704. This association has led to the source being classified as a transitional millisecond pulsar (tMSP) in an accreting state. We analyse 10.5 yr of Fermi LAT data and detect a γ-ray eclipse at the same phase as optical and X-ray eclipses at the >5 σ level, a significant improvement on the 2.8 σ level of the previous detection. The confirmation of this eclipse solidifies the association between the X-ray source and the γ-ray source, strengthening the tMSP classification. However, analysis of several optical data sets and an X-ray observation do not reveal a change in the source’s median brightness over long time-scales or a bi-modality on short time-scales. Instead, the light curve is dominated by flickering, which has a correlation time of 2.6 min alongside a potential quasi-periodic oscillation at ∼21 min. The mass of the primary and secondary stars is constrained to be M1=1.43+0.33−0.19 M⊙ and M2=0.3+0.17−0.12 M⊙ through modelling of the optical light curve. While this is still consistent with a white dwarf primary, we favour the tMSP in a low accretion state classification due to the significance of the γ-ray eclipse detection

The Intentional Use of Service Recovery Strategies to Influence Consumer Emotion, Cognition and Behaviour

Service recovery strategies have been identified as a critical factor in the success of. service organizations. This study develops a conceptual frame work to investigate how specific service recovery strategies influence the emotional, cognitive and negative behavioural responses of . consumers., as well as how emotion and cognition influence negative behavior. Understanding the impact of specific service recovery strategies will allow service providers' to more deliberately and intentionally engage in strategies that result in positive organizational outcomes. This study was conducted using a 2 x 2 between-subjects quasi-experimental design. The results suggest that service recovery has a significant impact on emotion, cognition and negative behavior. Similarly, satisfaction, negative emotion and positive emotion all influence negative behavior but distributive justice has no effect

Aerostructural design optimization of a 100-passenger regional jet with surrogate-based mission analysis

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106481/1/AIAA2013-4372.pd

A rapid optical and X-ray timing study of the neutron star X-ray binary Swift J1858.6–0814

We present a rapid timing analysis of optical (HiPERCAM and ULTRACAM) and X-ray (NICER) observations of the X-ray transient Swift J1858.6−0814 during 2018 and 2019. The optical light curves show relatively slow, large amplitude (∼1 mag in gs) ‘blue’ flares (i.e. stronger at shorter wavelengths) on time-scales of ∼minutes as well as fast, small amplitude (∼0.1 mag in gs) ‘red’ flares (i.e. stronger at longer wavelengths) on time-scales of ∼seconds. The ‘blue’ and ‘red’ flares are consistent with X-ray reprocessing and optically thin synchrotron emission, respectively, similar to what is observed in other X-ray binaries. The simultaneous optical versus soft- and hard-band X-ray light curves show time- and energy-dependent correlations. The 2019 March 4 and parts of the June data show a nearly symmetric positive cross-correlations (CCFs) at positive lags consistent with simple X-ray disc reprocessing. The soft- and hard-band CCFs are similar and can be reproduced if disc reprocessing dominates in the optical and one component (disc or synchrotron Comptonization) dominates both the soft and hard X-rays. A part of the 2019 June data shows a very different CCFs. The observed positive correlation at negative lag in the soft band can be reproduced if the optical synchrotron emission is correlated with the hot flow X-ray emission. The observed timing properties are in qualitative agreement with the hybrid inner hot accretion flow model, where the relative role of the different X-ray and optical components that vary during the course of the outburst, as well as on shorter time-scales, govern the shape of the optical/X-ray CCFs

Two-loop representations of low-energy pion form factors and pi-pi scattering phases in the presence of isospin breaking

Dispersive representations of the pi-pi scattering amplitudes and pion form factors, valid at two-loop accuracy in the low-energy expansion, are constructed in the presence of isospin-breaking effects induced by the difference between the charged and neutral pion masses. Analytical expressions for the corresponding phases of the scalar and vector pion form factors are computed. It is shown that each of these phases consists of the sum of a "universal" part and a form-factor dependent contribution. The first one is entirely determined in terms of the pi-pi scattering amplitudes alone, and reduces to the phase satisfying Watson's theorem in the isospin limit. The second one can be sizeable, although it vanishes in the same limit. The dependence of these isospin corrections with respect to the parameters of the subthreshold expansion of the pi-pi amplitude is studied, and an equivalent representation in terms of the S-wave scattering lengths is also briefly presented and discussed. In addition, partially analytical expressions for the two-loop form factors and pi-pi scattering amplitudes in the presence of isospin breaking are provided.Comment: 57 pages, 12 figure

Measuring the mass of the black widow PSR J1555-2908

Accurate measurements of the masses of neutron stars are necessary to test binary evolution models, and to constrain the neutron star equation of state. In pulsar binaries with no measurable post-Keplerian parameters, this requires an accurate estimate of the binary system's inclination and the radial velocity of the companion star by other means than pulsar timing. In this paper, we present the results of a new method for measuring this radial velocity using the binary synthesis code Icarus. This method relies on constructing a model spectrum of a tidally distorted, irradiated star as viewed for a given binary configuration. This method is applied to optical spectra of the newly discovered black widow PSR J1555-2908. By modelling the optical spectroscopy alongside optical photometry, we find that the radial velocity of the companion star is $397\pm4$ km s$^{-1}$ (errors quoted at 95\% confidence interval), as well as a binary inclination of $>75^{\rm o}$. Combined with $\gamma$-ray pulsation timing information, this gives a neutron star mass of 1.67$^{+0.15}_{-0.09}$ M$_\odot$ and a companion mass of 0.060$^{+0.005}_{-0.003}$ M$_\odot$, placing PSR J1555-2908 at the observed upper limit of what is considered a black widow system.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society. 15 pages, 7 Figures. Underlying data available at https://zenodo.org/record/565306

Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares

The extreme ultraviolet portion of the solar spectrum contains a wealth of diagnostic tools for probing the lower solar atmosphere in response to an injection of energy, particularly during the impulsive phase of solar flares. These include temperature and density sensitive line ratios, Doppler shifted emission lines and nonthermal broadening, abundance measurements, differential emission measure profiles, and continuum temperatures and energetics, among others. In this paper I shall review some of the advances made in recent years using these techniques, focusing primarily on studies that have utilized data from Hinode/EIS and SDO/EVE, while also providing some historical background and a summary of future spectroscopic instrumentation.Comment: 34 pages, 8 figures. Submitted to Solar Physics as part of the Topical Issue on Solar and Stellar Flare