Photopatterned Multidomain Gels : Multi-Component Self-Assembled Hydrogels Based on Partially Self-Sorting 1,3:2,4-Dibenzylidene-d-sorbitol Derivatives

We report a multicomponent self-assembling system based on 1,3:2,4-dibenzyldene-d-sorbitol (DBS) derivatives which form gels as the pH is lowered in a controlled way. The two DBS gelators are functionalized with carboxylic acids: the first in the 4-position of the aromatic rings (DBS-CO2H), the second having glycine connected through an amide bond and displaying a terminal carboxylic acid (DBS-Gly). Importantly, these two self-assembling DBS-acids have different pKa values, and as such, their self-assembly is triggered at different pHs. Slowly lowering the pH of a mixture of gelators using glucono-d-lactone (GdL) initially triggers assembly of DBS-CO2H, followed by DBS-Gly; a good degree of kinetic self-sorting is achieved. Gel formation can also be triggered in the presence of diphenyliodonium nitrate (DPIN) as a photoacid under UV irradiation. Two-step acidification of a mixture of gelators using (a) GdL and (b) DPIN assembles the two networks sequentially. By combining this approach with a mask during step b, multidomain gels are formed, in which the network based on DBS-Gly is positively patterned into a pre-existing network based on DBS-CO2H. This innovative approach yields spatially resolved multidomain multicomponent gels based on programmable low-molecular-weight gelators, with one network being positively 'written' into another

Full stress tensor measurement using colour centres in diamond

Stress and strain are important factors in determining the mechanical, electronic, and optical properties of materials, relating to each other by the material's elasticity or stiffness. Both are represented by second rank field tensors with, in general, six independent components. Measurements of these quantities are usually achieved by measuring a property that depends on the translational symmetry and periodicity of the crystal lattice, such as optical phonon energies using Raman spectroscopy, the electronic band gap using cathodoluminescence, photoelasticity via the optical birefringence, or Electron Back Scattering Diffraction (EBSD). A reciprocal relationship therefore exists between the maximum sensitivity of the measurements and the spatial resolution. Furthermore, of these techniques, only EBSD and off-axis Raman spectroscopy allow measurement of all six components of the stress tensor, but neither is able to provide full 3D maps. Here we demonstrate a method for measuring the full stress tensor in diamond, using the spectral and optical polarization properties of the photoluminescence from individual nitrogen vacancy (NV) colour centres. We demonstrate a sensitivity of order 10 MPa, limited by local fluctuations in the stress in the sample, and corresponding to a strain of about 10^-5, comparable with the best sensitivity provided by other techniques. By using the colour centres as built-in local sensors, the technique overcomes the reciprocal relationship between spatial resolution and sensitivity and offers the potential for measuring strains as small as 10^-9 at spatial resolution of order 10 nm. Furthermore it provides a straightforward route to volumetric stress mapping. Aside from its value in understanding strain distributions in diamond, this new approach to stress and strain measurement could be adapted for use in micro or nanoscale sensors.Comment: 12 pages, 5 figures - supplementary informations included in appendi

Expanding the scope of gels - Combining polymers with low-molecular-weight gelators to yield modified self-assembling smart materials with high-tech applications

Combining low molecular weight gelators (LMWGs) with polymers is a broad yet relatively recent field, in a phase of rapid expansion and with huge potential for exploitation. This review provides an overview of the state-of-the-art and reflects on new technologies that might be unlocked. We divide LMWG-polymer systems into five categories: (i) polymerisation of self-assembled LMWG fibres, (ii) capture of LMWG fibres in a polymer matrix, (iii) addition of non-gelling polymer solutions to LMWGs, (iv) systems with directed interactions between polymers and LMWGs, and (v) hybrid gels containing both LMWGs and polymer gels (PGs). Polymers can have significant impacts on the nanoscale morphology and materials performance of LMWGs, and conversely LMWGs can have a major effect on the rheological properties of polymers. By combining different types of gelation system, it is possible to harness the advantages of both LMWGs and PGs, whilst avoiding their drawbacks. Combining LMWG and polymer technologies enhances materials performance which is useful in traditional applications, but it may also yield major steps forward in high-tech areas including environmental remediation, drug delivery, microfluidics and tissue engineering

The Precision Array for Probing the Epoch of Reionization: 8 Station Results

We are developing the Precision Array for Probing the Epoch of Reionization (PAPER) to detect 21cm emission from the early Universe, when the first stars and galaxies were forming. We describe the overall experiment strategy and architecture and summarize two PAPER deployments: a 4-antenna array in the low-RFI environment of Western Australia and an 8-antenna array at our prototyping site in Green Bank, WV. From these activities we report on system performance, including primary beam model verification, dependence of system gain on ambient temperature, measurements of receiver and overall system temperatures, and characterization of the RFI environment at each deployment site. We present an all-sky map synthesized between 139 MHz and 174 MHz using data from both arrays that reaches down to 80 mJy (4.9 K, for a beam size of 2.15e-5 steradians at 154 MHz), with a 10 mJy (620 mK) thermal noise level that indicates what would be achievable with better foreground subtraction. We calculate angular power spectra ($C_\ell$) in a cold patch and determine them to be dominated by point sources, but with contributions from galactic synchrotron emission at lower radio frequencies and angular wavemodes. Although the cosmic variance of foregrounds dominates errors in these power spectra, we measure a thermal noise level of 310 mK at $\ell=100$ for a 1.46-MHz band centered at 164.5 MHz. This sensitivity level is approximately three orders of magnitude in temperature above the level of the fluctuations in 21cm emission associated with reionization.Comment: 13 pages, 14 figures, submitted to AJ. Revision 2 corrects a scaling error in the x axis of Fig. 12 that lowers the calculated power spectrum temperatur

The Spin Density Matrix II: Application to a system of two quantum dots

This work is a sequel to our work "The Spin Density Matrix I: General Theory and Exact Master Equations" (eprint arXiv:0708.0644 [cond-mat]). Here we compare pure- and pseudo-spin dynamics using as an example a system of two quantum dots, a pair of localized conduction-band electrons in an n-doped GaAs semiconductor. Pure-spin dynamics is obtained by tracing out the orbital degrees of freedom, whereas pseudo-spin dynamics retains (as is conventional) an implicit coordinate dependence. We show that magnetic field inhomogeneity and spin-orbit interaction result in a non-unitary evolution in pure-spin dynamics, whereas these interactions contribute to the effective pseudo-spin Hamiltonian via terms that are asymmetric in spin permutations, in particular, the Dzyaloshinskii-Moriya (DM) spin-orbit interaction. We numerically investigate the non-unitary effects in the dynamics of the triplet states population, purity, and Lamb energy shift, as a function of interdot distance and magnetic field difference. The spin-orbit interaction is found to produce effects of roughly four orders of magnitude smaller than those due to magnetic field difference in the pure-spin model. We estimate the spin-orbit interaction magnitude in the DM-interaction term. Our estimate gives a smaller value than that recently obtained by Kavokin [Phys. Rev. B 64, 075305 (2001)], who did not include double occupancy effects. We show that a necessary and sufficient condition for obtaining a universal set of quantum logic gates, involving only two spins, in both pure- and pseudo-spin models is that the magnetic field inhomogeneity and the Heisenberg interaction are both non-vanishing. We also briefly analyze pure-spin dynamics in the electron on liquid helium system recently proposed by Lyon [Phys. Rev. A 74, 052338 (2006)].Comment: 16 pages including 12 figures. Sequel to "The Spin Density Matrix I: General Theory and Exact Master Equations", arXiv:0708.064

The probability of identifying the cosmic web environment of galaxies around clusters motivated by the Weave Wide Field Cluster Survey

Upcoming wide-field spectroscopic surveys will observe galaxies in a range of cosmic web environments in and around galaxy clusters. In this paper, we test and quantify how successfully we will be able to identify the environment of individual galaxies in the vicinity of massive galaxy clusters, reaching out to $\sim5R_{200}$ into the clusters' infall region. We focus on the WEAVE Wide Field Cluster Survey (WWFCS), but the methods we develop can be easily generalised to any similar spectroscopic survey. Using numerical simulations of a large sample of massive galaxy clusters from \textsc{TheThreeHundred} project, we produce mock observations that take into account the selection effects and observational constraints imposed by the WWFCS. We then compare the `true' environment of each galaxy derived from the simulations (cluster core, filament, and neither core nor filament, {``NCF''}) with the one derived from the observational data, where only galaxy sky positions and spectroscopic redshifts will be available. We find that, while cluster core galaxy samples can be built with a high level of completeness and moderate contamination, the filament and NCF galaxy samples will be significantly contaminated and incomplete due to projection effects exacerbated by the galaxies' peculiar velocities. We conclude that, in the infall regions surrounding massive galaxy clusters, associating galaxies with the correct cosmic web environment is highly uncertain. However, with large enough spectroscopic samples like the ones the WWFCS will provide (thousands of galaxies per cluster, {out to $5R_{200}$}), and the correct statistical treatment that takes into account the probabilities we provide here, we expect we will be able to extract robust and well-quantified conclusions on the relationship between galaxy properties and their environment.Comment: Accepted for publication in MNRAS (14 pages, 7 figures

Reprint of: High prey-predator size ratios and unselective feeding in copepods: A seasonal comparison of five species with contrasting feeding modes

There has been an upsurge of interest in trait-based approaches to zooplankton, modelling the seasonal changes in the feeding modes of zooplankton in relation to phytoplankton traits such as size or motility. We examined this link at two English Channel plankton monitoring sites south of Plymouth (L4 and E1). At L4 there was a general transition from diatoms in spring to motile microplankton in summer and autumn, but this was not mirrored in the succession of copepod feeding traits; for example the ambushing Oithona similis dominated during the spring diatom bloom. At nearby E1 we measured seasonality of food and grazers, finding strong variation between 2014 and 2015 but overall low mesozooplankton biomass (median 4.5 mg C m−3). We also made a seasonal grazing study of five copepods with contrasting feeding modes (Calanus helgolandicus, Centropages typicus, Acartia clausi, Pseudocalanus elongatus and Oithona similis), counting the larger prey items from the natural seston. All species of copepod fed on all food types and differences between their diets were only subtle; the overriding driver of diet was the composition of the prey field. Even the smaller copepods fed on copepod nauplii at significant rates, supporting previous suggestions of the importance of intra-guild predation. All copepods, including O. similis, were capable of tackling extremely long (>500 µm) diatom chains at clearance rates comparable to those on ciliates. Maximum observed prey:predator length ratios ranged from 0.12 (C. helgolandicus) up to 0.52 (O. similis). Unselective feeding behaviour and the ability to remove highly elongated cells have implications for how copepod feeding is represented in ecological and biogeochemical models

Forecasting the success of the WEAVE Wide-Field Cluster Survey on the extraction of the cosmic web filaments around galaxy clusters

Next-generation wide-field spectroscopic surveys will observe the infall regions around large numbers of galaxy clusters with high sampling rates for the first time. Here, we assess the feasibility of extracting the large-scale cosmic web around clusters using forthcoming observations, given realistic observational constraints. We use a sample of 324 hydrodynamic zoom-in simulations of massive galaxy clusters from TheThreeHundred project to create a mock-observational catalogue spanning 5R200 around 160 analogue clusters. These analogues are matched in mass to the 16 clusters targetted by the forthcoming WEAVE Wide-Field Cluster Survey (WWFCS). We consider the effects of the fibre allocation algorithm on our sampling completeness and find that we successfully allocate targets to 81.7 ${\rm {per \,cent}}\, \pm$ 1.3 of the members in the cluster outskirts. We next test the robustness of the filament extraction algorithm by using a metric, Dskel, which quantifies the distance to the filament spine. We find that the median positional offset between reference and recovered filament networks is Dskel = 0.13 ± 0.02 Mpc, much smaller than the typical filament radius of ~ 1 Mpc. Cluster connectivity of the recovered network is not substantially affected. Our findings give confidence that the WWFCS will be able to reliably trace cosmic web filaments in the vicinity around massive clusters, forming the basis of environmental studies into the effects of pre-processing on galaxy evolution

Seasonal variation of zooplankton community structure and trophic position in the Celtic Sea: a stable isotope and biovolume spectrum approach

Zooplankton on continental shelves represent an important intermediary in the transfer of energy and matter from phytoplankton to the wider ecosystem. Their taxonomic composition and trophic interactions with phytoplankton vary in space and time, and interpreting the implications of this constantly evolving landscape remains a major challenge. Here we combine plankton taxonomic data with the analysis of biovolume spectra and stable isotopes to provide insights into the trophic interactions that occur in a shelf sea ecosystem (Celtic Sea) across the spring-summer-autumn transition. Biovolume spectra captured the seasonal development of the zooplankton community well, both in terms of total biomass and trophic positioning, and matched trophic positions estimated by stable isotope analysis. In early April, large microplankton (63-200 µm) occupied higher trophic positions than mesozooplankton (>200 µm), likely reflecting the predominance of nanoplankton (2-20 µm) that were not readily available to mesozooplankton grazers. Biomass and number of trophic levels increased during the spring bloom as elevated primary production allowed for a higher abundance of predatory species. During July, the plankton assemblage occupied relatively high trophic positions, indicating important links to the microbial loop and the recycling of organic matter. The strong correlation between biomass and community trophic level across the study suggests that the Celtic Sea is a relatively enclosed and predominantly energy-limited ecosystem. The progression of the zooplankton biomass and community structure within the central shelf region was different to that at the shelf-break, potentially reflecting increased predatory control of copepods by macrozooplankton and pelagic fishes at the shelf break. We suggest that the combination of size spectra and stable isotope techniques are highly complementary and useful for interpreting the seasonal progression of trophic interactions in the plankton

1,3:2,4-Dibenzylidene-d-sorbitol (DBS) and its derivatives-efficient, versatile and industrially-relevant low-molecular-weight gelators with over 100 years of history and a bright future

Dibenzylidene-d-sorbitol (DBS) has been a well-known low-molecular-weight gelator of organic solvents for over 100 years. As such, it constitutes a very early example of a supramolecular gel-a research field which has recently developed into one of intense interest. The ability of DBS to self-assemble into sample-spanning networks in numerous solvents is predicated upon its 'butterfly-like' structure, whereby the benzylidene groups constitute the 'wings' and the sorbitol backbone the 'body'-the two parts representing the molecular recognition motifs underpinning its gelation mechanism, with the nature of solvent playing a key role in controlling the precise assembly mode. This gelator has found widespread applications in areas as diverse as personal care products and polymer nucleation/clarification, and has considerable potential in applications such as dental composites, energy technology and liquid crystalline materials. Some derivatives of DBS have also been reported which offer the potential to expand the scope and range of applications of this family of gelators and endow the nansocale network with additional functionality. This review aims to explain current trends in DBS research, and provide insight into how by combining a long history of application, with modern methods of derivatisation and analysis, the future for this family of gelators is bright, with an increasing number of high-tech applications, from environmental remediation to tissue engineering, being within reach