Dispersion relations of Yukawa fluids at weak and moderate coupling

In this paper we compare different theoretical approaches to describe the dispersion of collective modes in Yukawa fluids when the inter-particle coupling is relatively weak, so that kinetic and potential contributions to the dispersion relation compete. Thorough comparison with the results from molecular dymamics simulation allows us to conclude that in the regime investigated the best description is provided by the sum of the generalized excess bulk modulus and the Bohm-Gross kinetic term.Comment: 9 pages, 7 figure

Self-diffusion in single-component Yukawa fluids

It was suggested in the literature that the self-diffusion coefficient of simple fluids can be approximated as a ratio of the squared thermal velocity of the atoms to the "fluid Einstein frequency," which can thus serve as a rough estimate of the friction (momentum transfer) rate in the dense fluid phase. In this article we test this suggestion using a single-component Yukawa fluid as a reference system. The available simulation data on self-diffusion in Yukawa fluids, complemented with new data for Yukawa melts (Yukawa fluids near the freezing phase transition), are carefully analyzed. It is shown that although not exact, this earlier suggestion nevertheless provides a very sensible way of normalization of the self-diffusion constant. Additionally, we demonstrate that certain quantitative properties of self-diffusion in Yukawa melts are also shared by systems like one-component plasma and liquid metals at freezing, providing support to an emerging dynamical freezing indicator for simple soft matter systems. The obtained results are also briefly discussed in the context of the theory of momentum transfer in complex (dusty) plasmas.Comment: 6 pages, 3 figure

Statistical Quality Control of a Production Process of Invisible Zippers

The present work exhibits the development and implementation of an innovative sta- tistical control plan applied to the production process of invisible zippers, within the context of a project developed by the NOVA School of Science and Technology for a zipper producer. The plan focused on two main axes: reevaluating currently applied sampling plans and iden- tifying critical characteristics in the various stages of the process, with the development of a proposal for control charts for each of the stages and implementation of the respective charts. An important part of the plan was the implementation of a design of experiments to optimize critical processes. Consequently, an integrated approach was implemented to define and solve the prob- lem. At first, a complete definition and description of the process was executed through a visual representation with flowcharts. Then, critical points of the process were identified, which led to a preliminary implementation of control charts, planification of a design of ex- periments, and execution of several hypothesis tests. Even though, as of the redaction of this study, no improvement on the process was achieved, several crucial conclusions were reached over its behavior following the implemen- tation of the statistical tools. Some important conclusions were the out-of-control state of the process on some important characteristics, and strong presence of internal variability in the process. As a result, a design of experiments was considered the best approach for improve- ment, and its full planification has been achieved, as it is currently being performed. As for the sampling plans, a necessity to reduce end-of-line inspections was identified and is expected to be enabled by the improvements arising from the design of experiments. On the other hand, the reception sampling plan was identified as insufficient, and is to be reviewed.O presente trabalho expõe o desenvolvimento e implementação de um plano de con- trolo estatístico inovador aplicado ao processo de produção de fechos invisíveis, no contexto de um projeto desenvolvido pela Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para um produtor de fechos de correr. O plano centrou-se em dois eixos principais: a reavaliação dos planos de amostragem atualmente aplicados e identificação de característi- cas críticas nas várias fases do processo, com o desenvolvimento de uma proposta de cartas de controlo para cada uma das fases e implementação das respetivas cartas. Uma parte im- portante do plano foi a implementação de um desenho de experiências para a otimização de processos críticos. Consequentemente, foi implementada uma abordagem integrada para definir e resolver o problema. No início, foi realizada uma definição e descrição completa do processo através de uma representação visual com fluxogramas. De seguida, foram identificados pontos críti- cos do processo, o que levou à implementação preliminar de cartas de controlo, planificação de um desenho de experiências e execução de vários testes de hipóteses. Apesar de, à data de redação deste estudo, não se ter alcançado uma melhoria do pro- cesso, alcançaram-se várias conclusões cruciais sobre o seu comportamento. Algumas conclu- sões importantes foram o estado fora de controlo do processo em certas características impor- tantes, e a forte presença de variabilidade interna no processo. Como resultado, o desenho de experiências foi considerado a melhor abordagem para a sua melhoria, e a sua planificação completa foi efetuada, sendo que as experiências se encontram de momento a decorrer. Quanto aos planos de amostragem, foi identificada a necessidade de reduzir as inspe- ções de fim de linha. Por outro lado, o plano de amostragem de receção foi identificado como insuficiente, e deverá ser revisto

Nanoparticle formation and dynamics in a complex (dusty) plasma: from the plasma ignition to the afterglow.

Complex (dusty) plasmas are a subject of growing interest. They areionized gases containing charged dust particles. In capacitively-coupled RF discharges, dust growth can occur naturally and two methods can be used to grow dust particles: chemically active plasmas or sputtering. The growth of dust particles in argon discharges by RF sputtering and the effect of dust particles on theplasma have been investigated from the plasma ignition to the afterglow. It was shown that plasma and discharge parameters are greatly affected by the dust particles. Furthermore, plasma instabilities can be triggered by the presence of the dust particles. These instabilities can be due to dust particle growth or they can be instabilities of a well established dust cloud filling the interelectrode space. When the discharge is switched off, the dust particles act like a sink for the charge carrier and consequently affect the plasma losses. It was shown that the dust particles do keep residual chargeswhich values are greatly affected by the diffusion of the charge carriers and especially the transition from ambipolar to free diffusion

Three-dimensional structure of Mach cones in monolayer complex plasma

Structure of Mach cones in a crystalline complex plasma has been studied experimentally using an intensity sensitive imaging, which resolved particle motion in three dimensions. This revealed a previously unknown out-of-plane cone structure, which appeared due to excitation of the vertical wave mode. The complex plasma consisted of micron sized particles forming a monolayer in a plasma sheath of a gas discharge. Fast particles, spontaneously moving under the monolayer, created Mach cones with multiple structures. The in-plane cone structure was due to compressional and shear lattice waves.Comment: Accepted for publication in Physical Review Letter

Analysis of performances of crucifers-legumes cover crop mixtures to provide multiple-ecosystem services

Multi-services cover crops (MSCC) grown during fallow period between two cash crops provide various ecosystem services. Among species used as MSCC, crucifers can efficiently prevent nitrate and sulphate leaching by catching residual soil mineral nitrogen (N) and sulphur (S) afterthe preceding cash crop (N and S catch crop services). Crucifers also have a unique capacity to suppress pathogens due to the biocidal hydrolysis products of endogenous secondary metabolites called glucosinolates (GSL). The aim of our study was to assess the provision of various ecosystem services linked to N, S cycles and biocontrol potential for a wide range of bispecific crucifer-legume mixtures in comparison to sole cover crops of legume and crucifer. We carried out experiments in 2 contrasted sites (Toulouse and Orléans regions, France) during 2 years in order to assess these services and the compatibility of various bi-specific crucifer-legume mixtures. We tested a great diversity of species, such as i) crucifers : rape, white mustard, Indian mustard, Ethiopian mustard, turnip, turnip rape, radish and rocket, and ii) legumes: Egyptian clover, crimson clover, common vetch, purple vetch, hairy vetch, pea, soya bean, faba bean, and white lupin. Our study demonstrated that crucifer-legume mixtures can provide and mutualize various ecosystem services by reaching from 2 thirds (GSL production, S and N green manure) to the same level ofservice (N and S catch crop) than the best sole family of species. GSL profile and concentration did not change in mixtures meaning that crucifer-pests interactions were identical. Through a literature review we also illustrated that biocontrol services of crucifers could be largely maintained in crucifer-legume mixtures for a wide range of pathogens and weeds while reducing potential disservices on beneficials and increasing N related servic

Brownian-like motion of a single dust grain in a radio-frequency plasma discharge comparison of experiments and simulations

Bronwnian-like motion of a single dust-grain in a radio frequency plasma has been studied by different research groups. The rise of the particles temperature above “room temperature” is attributed to e.g. random fluctuations of the particle charge and fluctuations of the electrical field. Additional disturbance might occur due to gas density variations, temporal variation of the particles mass and particle interaction with the illuminating laser light. In addition, a nonoptimal frame rate of the optical diagnostic system and pixel locking can lead to an incorrect estimation of the particle kinetic temperature. Our experiments are conducted in a weakly ionized radio-frequency gas discharge at a low neutral gas pressure and power. A single micron sized spherical particle is trapped in a harmonic-like potential trap in the sheath of the lower driven electrode [1]. Its twodimensional planar motion is recorded with a long-distance microscope and a high-resolution camera. From the measured particle positions we derive the probability density function, the velocity autocorrelation function and the mean squared displacement. We obtain a particle kinetic temperature above 350 K, a neutral gas damping time of about 0.5 sec and a resonance frequency of 1-2 Hz. Anisotropic oscillation of the particle occurs, leading to angle dependent temperatures along the x and y direction in the plane of the recorded images, which can be explained by the presence of an asymmetric horizontal potential trap. Experimental observations are compared with our simulations using md simulations and the Ornstein-Uhlenbeck stochastic process

Characteristics of DNA-binding proteins determine the biological sensitivity to high-linear energy transfer radiation

Non-homologous end-joining (NHEJ) and homologous recombination repair (HRR), contribute to repair ionizing radiation (IR)-induced DNA double-strand breaks (DSBs). Mre11 binding to DNA is the first step for activating HRR and Ku binding to DNA is the first step for initiating NHEJ. High-linear energy transfer (LET) IR (such as high energy charged particles) killing more cells at the same dose as compared with low-LET IR (such as X or γ rays) is due to inefficient NHEJ. However, these phenomena have not been demonstrated at the animal level and the mechanism by which high-LET IR does not affect the efficiency of HRR remains unclear. In this study, we showed that although wild-type and HRR-deficient mice or DT40 cells are more sensitive to high-LET IR than to low-LET IR, NHEJ deficient mice or DT40 cells are equally sensitive to high- and low-LET IR. We also showed that Mre11 and Ku respond differently to shorter DNA fragments in vitro and to the DNA from high-LET irradiated cells in vivo. These findings provide strong evidence that the different DNA DSB binding properties of Mre11 and Ku determine the different efficiencies of HRR and NHEJ to repair high-LET radiation induced DSBs