Competing interactions in two dimensional Coulomb systems: Surface charge heterogeneities in co-assembled cationic-anionic incompatible mixtures

A binary mixture of oppositely charged components confined to a plane such as cationic and anionic lipid bilayers may exhibit local segregation. The relative strength of the net short range interactions, which favors macroscopic segregation, and the long range electrostatic interactions, which favors mixing, determines the length scale of the finite size or microphase segregation. The free energy of the system can be examined analytically in two separate regimes, when considering small density fluctuations at high temperatures, and when considering the periodic ordering of the system at low temperatures (F. J. Solis and M. Olvera de la Cruz, J. Chem. Phys. 122, 054905 (2000)). A simple Molecular Dynamics simulation of oppositely charged monomers, interacting with a short range Lennard Jones potential and confined to a two dimensional plane, is examined at different strengths of short and long range interactions. The system exhibits well-defined domains that can be characterized by their periodic length-scale as well as the orientational ordering of their interfaces. By adding salt, the ordering of the domains disappears and the mixture macroscopically phase segregates in agreement with analytical predictions.Comment: 8 pages, 5 figures, accepted for publication in J. Chem. Phys, Figure 1 include

Modeling truncated pixel values of faint reflections in MicroED images.

The weak pixel counts surrounding the Bragg spots in a diffraction image are important for establishing a model of the background underneath the peak and estimating the reliability of the integrated intensities. Under certain circumstances, particularly with equipment not optimized for low-intensity measurements, these pixel values may be corrupted by corrections applied to the raw image. This can lead to truncation of low pixel counts, resulting in anomalies in the integrated Bragg intensities, such as systematically higher signal-to-noise ratios. A correction for this effect can be approximated by a three-parameter lognormal distribution fitted to the weakly positive-valued pixels at similar scattering angles. The procedure is validated by the improved refinement of an atomic model against structure factor amplitudes derived from corrected micro-electron diffraction (MicroED) images

Hydrodynamics of thermally-driven chiral propulsion and separation

Considerable effort has been directed towards the characterization of chiral mesoscale structures, as shown in chiral protein assemblies and carbon nanotubes. Here, we establish a thermally-driven hydrodynamic description for the actuation and separation of mesoscale chiral structures in a fluid medium. Cross flow of a Newtonian liquid with a thermal gradient gives rise to chiral structure propulsion and separation according to their handedness. In turn, the chiral suspension alters the liquid flow which thus acquires a transverse (chiral) velocity component. Since observation of the predicted effects requires a low degree of sophistication, our work provides an efficient and inexpensive approach to test and calibrate chiral particle propulsion and separation strategies

New method for non-standard invisible particle searches in tau lepton decays

Motivated by models proposed to explain the Standard Model anomalies, and the unprecedented $\tau^{+}\tau^{-}$ data to be collected by the Belle~II experiment during the next years, we study the kinematics of tau pair decays and propose a new method to search for lepton flavor violating processes in tau lepton decays to invisible beyond Standard Model particles, such as $\tau \to \ell \alpha$, where $\ell$ is either an electron or a muon, and $\alpha$ is a massive particle that escapes undetected. The new method improves by one order of magnitude the expected upper limit on the $\tau \to \ell \alpha$ production in 3x1 prong tau decays and establishes the possibility of performing this search in 1x1 prong tau decays which has not been previously considered.Comment: 6 pages, 7 figure

MicroED data collection and processing.

MicroED, a method at the intersection of X-ray crystallography and electron cryo-microscopy, has rapidly progressed by exploiting advances in both fields and has already been successfully employed to determine the atomic structures of several proteins from sub-micron-sized, three-dimensional crystals. A major limiting factor in X-ray crystallography is the requirement for large and well ordered crystals. By permitting electron diffraction patterns to be collected from much smaller crystals, or even single well ordered domains of large crystals composed of several small mosaic blocks, MicroED has the potential to overcome the limiting size requirement and enable structural studies on difficult-to-crystallize samples. This communication details the steps for sample preparation, data collection and reduction necessary to obtain refined, high-resolution, three-dimensional models by MicroED, and presents some of its unique challenges

What to expect from alternative management strategies to conserve seabirds? Hints from a dynamic modelling framework applied to an endangered population

The worldwide decline of seabird populations due to the combined effects of global and regional changes is creating immense challenges for managers and conservationists. Predicting population responses to proposed management strategies could provide the most effective tools to prevent, halt and reverse ongoing declines. System dynamic modelling frameworks are considered particularly relevant to interrelate biological, ecological and environmental characteristics and to predict population trends. A system dynamics model was designed, compiling diverse information concerning a relict population of the European Shag located in western Iberia, to outline the most effective management options for its conservation. The simulations demonstrate that mortality caused by invasive animals and bycatch mortality were the main reasons for the current population decline. Without management interventions, a decrease of 8% was projected for the next decade, which could be mitigated by specific conservation actions. The results show the usefulness of dynamic modelling frameworks to understand local cause-effect relationships and species responses to ecosystem management under changing environmental conditions. We highlight that the framework proposed, after specific parameterization, could be easily adaptable to other species within similar socio-ecological systems.This study was supported by the International Internship Grant Program of the University of Cadiz (EDUCA), Spain for conducting research in internationally renowned centres and the Centre for the Research and Technology of AgroEnvironmental and Biological Sciences (CITAB) of the Universidad de Tras-os-Montes e Alto Douro (UTAD), Vila Real, Portugal. In addition, the following entities contributed to this work: European Investment Funds by FEDER/COMPETE/POCI Operational Competitiveness and Internationalization Programme, under Project POCI-01-0145-FEDER-006958, National Funds by FCT -Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020 and INTERACT, Integrative Research in Environment, AgroChains and Technology, Project Norte 2020 45/2015/02. R. B. received support from POPH/FSE, funds and by National Funds through FCT Foundation for Science and Technology under the Portuguese Science Foundation through Doctoral grant FCT_SFRH/BD/102428/2014

First order phase transition from the vortex liquid to an amorphous solid

We present a systematic study of the topology of the vortex solid phase in superconducting Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ samples with low doses of columnar defects. A new state of vortex matter imposed by the presence of geometrical contours associated with the random distribution of columns is found. The results show that the first order liquid-solid transition in this vortex matter does not require a structural symmetry change.Comment: 4 pages, 5 figure