From Minimal to Realistic Supersymmetric SU(5) Grand Unification

We construct and discuss a "realistic" example of SUSY SU(5) GUT model, with an additional U(1) flavour symmetry, that is not plagued by the need of large fine tunings, like those associated with doublet-triplet splitting in the minimal model, and that leads to an acceptable phenomenology. This includes coupling unification with a value of alpha_s(m_Z) in much better agreement with the data than in the minimal version, an acceptable hierarchical pattern for fermion masses and mixing angles, also including neutrino masses and mixings, and a proton decay rate compatible with present limits (but the discovery of proton decay should be within reach of the next generation of experiments). In the neutrino sector the preferred solution is one with nearly maximal mixing both for atmospheric and solar neutrinos.Comment: 20 pages, LATEX, 2 figures; uses psfig.st

Large Neutrino Mixing from Small Quark and Lepton Mixings

We discuss the special class of models where nearly maximal neutrino mixing is produced through the see-saw mechanism, starting from only nearly diagonal matrices for charged leptons, Dirac neutrinos and Majorana right-handed neutrinos.Comment: 14 pages, LATEX, no figures; added section on the stability under RG

Tuning the Properties of Active Microtubule Networks by Depletion Forces

Suspensions of microtubules and nonadsorbing particles form thick and long bundles due to depletion forces. Such interactions act at the nanometer scale and define the structural and dynamical properties of the resulting networks. In this study, we analyze the depletion forces exerted by two types of nonadsorbing particles, namely, the polymer, poly(ethylene glycol) (PEG), and the block copolymer, Pluronic. We characterize their effects both in passive and active networks by adding motor proteins to the suspensions. By exploiting its bundling effect via entropic forces, we observed that PEG generates a network with thick structures showing a nematic order and larger mesh size. On the other hand, Pluronic builds up a much denser gel-like network without a recognizable mesh structure. This difference is also reflected in the network activity. PEG networks show moderate contraction in lateral directions while Pluronic networks exhibit faster and isotropic contraction. Interestingly, by mixing the two nonadsorbing polymers in different ratios, we observed that the system showed a behavior that exhibited properties of both agents, leading to a robust and fast responsive structure compared to the single-depletant networks. In conclusion, we show how passive osmotic compression modifies the distribution of biopolymers. Its combination with active motors results in a new active material with potential for nanotechnological applications.I.G. acknowledges support from the MaxSynBio Consortium, which is jointly funded by the Federal Ministry of Education and Research of Germany and the Max Planck Society. V.N. and I.G. acknowledge the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie grant agreement MAMI No. 766007. A.V. acknowledges support from the Slovenian Research Agency (grant no. P1-0099

Cellular velocity, electrical persistence and sensing in developed and vegetative cells during electrotaxis

Cells have the ability to detect electric fields and respond to them with directed migratory movement. Investigations identified genes and proteins that play important roles in defining the migration efficiency. Nevertheless, the sensing and transduction mechanisms underlying directed cell migration are still under discussion. We use Dictyostelium discoideum cells as model system for studying eukaryotic cell migration in DC electric fields. We have defined the temporal electric persistence to characterize the memory that cells have in a varying electric field. In addition to imposing a directional bias, we observed that the electric field influences the cellular kinematics by accelerating the movement of cells along their paths. Moreover, the study of vegetative and briefly starved cells provided insight into the electrical sensing of cells. We found evidence that conditioned medium of starved cells was able to trigger the electrical sensing of vegetative cells that would otherwise not orient themselves in the electric field. This observation may be explained by the presence of the conditioned medium factor (CMF), a protein secreted by the cells, when they begin to starve. The results of this study give new insights into understanding the mechanism that triggers the electrical sensing and transduces the external stimulus into directed cell migration. Finally, the observed increased mobility of cells over time in an electric field could offer a novel perspective towards wound healing assays

Dilemmi etici ed empatia ai tempi del Covid-19

Con la recente diffusione del virus Covid-19 molte domande sono disponibili, sia da un punto di vista sanitario ed economico, sia da un punto di vista umano. La rapida diffusione del virus e il tasso di contagio hanno costretto gli operatori sanitari a compiere scelte etiche e morali. Abbiamo cercato di vedere quali scelte farebbe un campione rappresentativo della popolazione italiana, inclusi gli operatori sanitari , se confrontato con un dilemma etico riguardo a questa crisi e quali conseguenze emotive potrebbero derivarne. Dai risultati oltre l'80% del campione ha scelto per scelte utilitaristiche e impersonali, mosso quindi dalla razionalità per risolvere il problema. Nonostante l'apparente distacco nella scelta, queste decisioni hanno comunque avuto un impatto emotivo, indicando che anche le scelte più razionali non sono esenti dall'empatia.Con la recente diffusione del virus Covid-19 molte domande sono sorte, sia di carattere sanitario ed economico, sia da unpunto di vista più umano. La rapida diffusione del virus e l’alto tasso di contagio ha costretto gli operatori sanitari a dovercompiere delle scelte etiche e morali. Ci si è dunque domandati quali scelte un campione rappresentativo della popolazioneitaliana, tra cui anche operatori sanitari, avrebbe compiuto se messo di fronte a dilemmi etici riguardanti questa crisi e qualiconseguenze emotive ne sarebbero scaturite. Dai risultati emerge come più dell’80% del campione abbia optato per scelteutilitaristiche e impersonali, quindi mossi da razionalità per la risoluzione del problema. Nonostante l’apparente distacconella scelta, tali decisioni hanno comunque avuto un impatto emotivo, indice del fatto che anche le scelte più razionali nonsono esenti da empatia

Flagella-like beating of a single microtubule

Kinesin motors can induce a buckling instability in a microtubule with a fixed minus end. Here we show that by modifying the surface with a protein-repellent functionalization and using clusters of kinesin motors, the microtubule can exhibit persistent oscillatory motion, resembling the beating of sperm flagella. The observed period is of the order of 1 min. From the experimental images we theoretically determine a distribution of motor forces that explains the observed shapes using a maximum likelihood approach. A good agreement is achieved with a small number of motor clusters acting simultaneously on a microtubule. The tangential forces exerted by a cluster are mostly in the range 0 - 8 pN towards the microtubule minus end, indicating the action of 1 or 2 kinesin motors. The lateral forces are distributed symmetrically and mainly below 10 pN, while the lateral velocity has a strong peak around zero. Unlike well-known models for flapping filaments, kinesins are found to have a strong "pinning" effect on the beating filaments. Our results suggest new strategies to utilize molecular motors in dynamic roles that depend sensitively on the stress built-up in the system

A probabilistic particle tracking framework for guided and Brownian motion systems with high particle densities

This paper presents a new framework for particle tracking based on a Gaussian Mixture Model (GMM). It is an extension of the state-of-the-art iterative reconstruction of individual particles by a continuous modeling of the particle trajectories considering the position and velocity as coupled quantities. The proposed approach includes an initialization and a processing step. In the first step, the velocities at the initial points are determined after iterative reconstruction of individual particles of the first four images to be able to generate the tracks between these initial points. From there on, the tracks are extended in the processing step by searching for and including new points obtained from consecutive images based on continuous modeling of the particle trajectories with a Gaussian Mixture Model. The presented tracking procedure allows to extend existing trajectories interactively with low computing effort and to store them in a compact representation using little memory space. To demonstrate the performance and the functionality of this new particle tracking approach, it is successfully applied to a synthetic turbulent pipe flow, to the problem of observing particles corresponding to a Brownian motion (e.g., motion of cells), as well as to problems where the motion is guided by boundary forces, e.g., in the case of particle tracking velocimetry of turbulent Rayleigh-Bénard convection

Is obedience still a virtue? An Italian research during COVID-19 pandemic

The authors examine some criminological theories that explain adherence to the rules, and in particular those that have been used to account for whether or not the rules imposed or proposed to contain the contagion from COVID-19 are considered. Then, they show the results of their own research, carried out by interviewing a sample of 1,004 Italians using an online questionnaire. The aim of this research: understand who complied with the anti COVID-19 measures and, if so, for what reasons. If the given answer was no, the authors asked the respondents the reasons why them didn’t. After showing the results, the authors discussed them comparing theme with other similarresearches made abroad, underlying also the emerged limits. In conclusion, the authors propose their own thoughts on the subject

Hybrid sideways/longitudinal swimming in the monoflagellate Shewanella oneidensis: from aerotactic band to biofilm

Shewanella oneidensis MR-1 are facultative aerobic electroactive bacteria, with an appealing potential for sustainable energy production and bioremediation. They gather around air sources, forming aerotactic bands and biofilms. Though accumulation is crucial to technological exploitation, their collective behaviour remains poorly reported. Here we establish a comprehensive framework for the study of aerotaxis, unveiling a novel hybrid locomotion pattern. Despite having only one flagellum, MR-1 combine motility features of mono- and multiflagellate bacteria, alternating longitudinal fast and sideways slow swimming. The adaptive tuning of the resulting bimodal velocity distributions fulfils different biological functions, such as aerotaxis and confinement. Overall, we reveal the mechanisms underlying the aerotactic collective behaviour of MR-1, in the process leading from accumulation to biofilm formatio