Geometric magic numbers of sodium clusters: Interpretation of the melting behaviour

Putative global minima of sodium clusters with up to 380 atoms have been located for two model interatomic potentials. Structures based upon the Mackay icosahedra predominate for both potentials, and the magic numbers for the Murrell-Mottram model show excellent agreement with the sizes at which maxima in the latent heat and entropy change at melting have been found in experiment.Comment: 4 pages, 2 figure

New Challenges Regarding the Intervention of Musculoskeletal Risk in Truck Service Garages

Background: The automotive industry is heavily affected by sick leaves caused by the handling of loads and using postures that produce musculoskeletal disorders. Research is needed to analyse their causes and find possible solutions to eliminate or mitigate these risks. Objective: Our objective was to analyse the level of musculoskeletal risk in the different work tasks performed by truck and bus mechanics. Our intention is also to analyse whether postural training and feedback can help reduce risk. Methods: The rapid entire body assessment (REBA) was used to assess the postures performed by 35 mechanics from eight branches throughout Spain. The participants were subsequently divided randomly into two groups (experimental group and control group). The experimental group (EG) was given training and feedback on their postures and the control group (CG) was not offered any type of intervention. A few months after the initial assessment, their postural load in the usual tasks was re-evaluated. Results: An overall average REBA Score: 10.49 ± 1.33. The main risk was found in the trunk and arms with sustained above-the-head postures. EG’s second results are significantly improved compared to the first (p = 0.026 *). Conclusions: These jobs have a high-risk level of musculoskeletal disorders. The course of action presented with postural training and feedback has shown satisfactory results. Nevertheless, given the size of the sample, further research will be needed to delve deeper into this possibility as a future line of intervention.Depto. de Psicología Social, del Trabajo y DiferencialFac. de PsicologíaTRUEpu

Ground State Entanglement Energetics

We consider the ground state of simple quantum systems coupled to an environment. In general the system is entangled with its environment. As a consequence, even at zero temperature, the energy of the system is not sharp: a projective measurement can find the system in an excited state. We show that energy fluctuation measurements at zero temperature provide entanglement information. For two-state systems which exhibit a persistent current in the ground state, energy fluctuations and persistent current fluctuations are closely related. The harmonic oscillator serves to illustrate energy fluctuations in a system with an infinite number of states. In addition to the energy distribution we discuss the energy-energy time-correlation function in the zero-temperature limit.Comment: 10 pages, 6 figure

On the physical interpretation of fractional diffusion

[EN] Even if the diffusion equation has been widely used in physics and engineering, and its physical content is well understood, some variants of it escape fully physical understanding. In particular, anormal diffusion appears in the so-called fractional diffusion equation, whose main particularity is its non-local behavior, whose physical interpretation represents the main part of the present work.Nadal, E.; Abisset-Chavanne, E.; Cueto, E.; Chinesta Soria, FJ. (2018). On the physical interpretation of fractional diffusion. Comptes Rendus Mécanique. 346(7):581-589. https://doi.org/10.1016/j.crme.2018.04.004S581589346

Crossover between ionic/covalent and pure ionic bonding in magnesium oxyde clusters

An empirical potential with fluctuating charges is proposed for modelling (MgO)_n clusters in both the molecular (small n) and bulk (n->infty) regimes. Vectorial polarization forces are explicitely taken into account in the self-consistent determination of the charges. Our model predicts cuboid cluster structures, in agreement with previous experimental and theoretical results. The effective charge transferred between magnesium and oxygen smoothly increases from 1 to 2, with an estimated crossover size above 300 MgO molecules

Non-Markovian Transmission through Two Quantum Dots Connected by a Continuum

We consider a transport setup containing a double-dot connected by a continuum. Via an exact solution of the time-dependent Schr\"odinger equation, we demonstrate a highly non-Markovian quantum-coherence-mediated transport through this dot-continuum-dot (DCD) system, which is in contrast with the common premise since in typical case a quantum particle does not reenter the system of interest once it irreversibly decayed into a continuum (such as the spontaneous emission of a photon). We also find that this DCD system supports an unusual steady state with unequal source and drain currents, owing to electrons irreversibly entering the continuum and floating there

HCN1 channels reduce the rate of exocytosis from a subset of cortical synaptic terminals

The hyperpolarization-activated cyclic nucleotide-gated (HCN1) channels are predominantly located in pyramidal cell dendrites within the cortex. Recent evidence suggests these channels also exist presynaptically in a subset of synaptic terminals within the mature entorhinal cortex (EC). Inhibition of presynaptic HCN channels enhances miniature excitatory post-synaptic currents (mEPSCs) onto EC layer III pyramidal neurons, suggesting that these channels decrease the release of the neurotransmitter, glutamate. Thus, do pre-synaptic HCN channels alter the rate of synaptic vesicle exocytosis and thereby enhance neurotransmitter release? To address this, we imaged the release of FM1-43, a dye that is incorporated into synaptic vesicles, from EC synaptic terminals using two photon microscopy in slices obtained from forebrain specific HCN1 deficient mice, global HCN1 knockouts and their wildtype littermates. This coupled with electrophysiology and pharmacology showed that HCN1 channels restrict the rate of exocytosis from a subset of cortical synaptic terminals within the EC and in this way, constrain non-action potential-dependent and action potential-dependent spontaneous release as well as synchronous, evoked release. Since HCN1 channels also affect post-synaptic potential kinetics and integration, our results indicate that there are diverse ways by which HCN1 channels influence synaptic strength and plasticity

Temperature dependence of current self-oscillations and electric field domains in sequential tunneling doped superlattices

We examine how the current--voltage characteristics of a doped weakly coupled superlattice depends on temperature. The drift velocity of a discrete drift model of sequential tunneling in a doped GaAs/AlAs superlattice is calculated as a function of temperature. Numerical simulations and theoretical arguments show that increasing temperature favors the appearance of current self-oscillations at the expense of static electric field domain formation. Our findings agree with available experimental evidence.Comment: 7 pages, 5 figure

Assessment and modelling of the effect of precipitated ferric chloride addition on the activated sludge settling properties

[EN] This research studies the effect of the widely used coagulant ferric chloride on the activated sludge sedimentability through a vast array of hindered settling tests considering different application modes and a wide range of reagent doses. Direct application of ferric chloride improved the hindered settling velocity (up to twice the settling velocity of the activated sludge with no coagulant addition), but sharply decreased the pH to levels where the biological process was unfeasible (pH < 4). When the pH was adjusted during coagulation to avoid biological inhibition, the impact on the settling velocity depended on the adjusted pH value. When the added coagulant was previously precipitated and neutralized, no pH inhibition occurred and the hindered settling velocity increased linearly with the dose (up to 8 times). This velocity improvement was caused by the increase in flocs density due to the capture within the flocs of the formed precipitates. Based on these experimental results, the usefulness and reliability of the standard hindered settling velocity mathematical models used for the secondary settler design and optimization (Richardson & Zaki model and the Vesilind's exponential model), was expanded to situations in which precipitated ferric chloride is used in wastewater treatment plants. Two empirical equations were proposed and fitted to relate these mathematical models¿ parameters with the dose of coagulant.Asensi Dasí, EJ.; Alemany Martínez, E.; Duque-Sarango, P.; Aguado García, D. (2019). Assessment and modelling of the effect of precipitated ferric chloride addition on the activated sludge settling properties. Chemical Engineering Research and Design. 150:14-25. https://doi.org/10.1016/j.cherd.2019.07.018S142515

Shot noise in non-adiabatically driven nanoscale conductors

We investigate the noise properties of pump currents through molecular wires and coupled quantum dots. As a model we employ a two level system that is connected to electron reservoirs and is non-adiabatically driven. Concerning the electron-electron interaction, we focus on two limits: non-interacting electrons and strong Coulomb repulsion. While the former case is treated within a Floquet scattering formalism, we derive for the latter case a master equation formalism for the computation of the current and the zero-frequency noise. For a pump operated close to internal resonances, the differences between the non-interacting and the strongly interacting limit turn out to be surprisingly small.Comment: 17 pages, 2 figure