Effect of Chain Polydispersity on the Elasticity of Disordered Polymer Networks

Due to their unique structural and mechanical properties, randomly cross-linked polymer networks play an important role in many different fields, ranging from cellular biology to industrial processes. In order to elucidate how these properties are controlled by the physical details of the network (e.g., chain-length and end-to-end distributions), we generate disordered phantom networks with different cross-linker concentrations C and initial densities ρinit and evaluate their elastic properties. We find that the shear modulus computed at the same strand concentration for networks with the same C, which determines the number of chains and the chain-length distribution, depends strongly on the preparation protocol of the network, here controlled by ρinit. We rationalize this dependence by employing a generic stress-strain relation for polymer networks that does not rely on the specific form of the polymer end-to-end distance distribution. We find that the shear modulus of the networks is a nonmonotonic function of the density of elastically active strands, and that this behavior has a purely entropic origin. Our results show that if short chains are abundant, as it is always the case for randomly cross-linked polymer networks, the knowledge of the exact chain conformation distribution is essential for correctly predicting the elastic properties. Finally, we apply our theoretical approach to literature experimental data, qualitatively confirming our interpretations

A novel model for cyanobacteria bloom formation: the critical role of anoxia and ferrous iron

SUMMARY 1. A novel conceptual model linking anoxia, phosphorus (P), nitrogen (N), iron (Fe) and sulphate to the formation of noxious filamentous and colonial cyanobacteria blooms is presented that reconciles seemingly contradictory ideas about the roles of P, N and Fe in bloom formation. 2. The model has several critical concepts: (i) P regulates biomass and productivity in fresh waters until excessive loading renders a system N-limited or light-limited, but it is the availability of ferrous ions (Fe 2+ ) that regulates the ability of cyanobacteria to compete with its eukaryotic competitors; (ii) Fe 2+ diffusing from anoxic sediments is a major Fe source for cyanobacteria, which acquire it by migrating downwards into Fe 2+ -rich anoxic waters from oxygenated waters; and (iii) subsequent cyanobacterial siderophore production provides a supply of Fe 3+ for reduction at cyanobacteria cell membranes that leads to very low Fe 3+ concentrations in the mixing zone. 3. When light and temperature are physiologically suitable for cyanobacteria growth, bloom onset is regulated by the onset of internal Fe 2+ loading which in turn is controlled by anoxia, reducible Fe content of surface sediments and sulphate reduction rate. 4. This conceptual model provides the basis for improving the success of approaches to eutrophication management because of its far-reaching explanatory power over the wide range of conditions where noxious cyanobacteria blooms have been observed

Parametric modeling of wideband piezoelectric polymer sensors:Design for optoacoustic applications

In this work, we present a three-dimensional model for the design of wideband piezoelectric polymer sensors which includes the geometry and the properties of the transducer materials. The model uses FFT and numerical integration techniques in an explicit, semi-analytical approach. To validate the model, we made electrical and mechanical measurements on homemade sensors for optoacoustic applications. Each device was implemented using a polyvinylidene fluoride thin film piezoelectric polymer with a thickness of 25 μm. The sensors had detection areas in the range between 0.5 mm2 and 35 mm2 and were excited by acoustic pressure pulses of 5 ns (FWHM) from a source with a diameter around 10 μm. The experimental data obtained from the measurements agree well with the model results. We discuss the relative importance of the sensor design parameters for optoacoustic applications and we provide guidelines for the optimization of devices.Fil: Fernández Vidal, A.. Universidad de Buenos Aires. Facultad de Ingeniería; ArgentinaFil: Ciocci Brazzano, Ligia. Universidad de Buenos Aires. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Matteo, Claudia Leda. Universidad de Buenos Aires. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sorichetti, Patricio Aníbal. Universidad de Buenos Aires. Facultad de Ingeniería; ArgentinaFil: González, Martín Germán. Universidad de Buenos Aires. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

High frequency of otolaryngology/ENT encounters in Canadian primary care despite low medical undergraduate experiences

Otolaryngology involves the treatment of patients with diseases and disorders of the ear, nose, throat (ENT), and related structures of the head and neck. Many medical students in Canada have limited experiences in ENT and a vast majority of these students go on to pursue a career as primary care physicians. Physicians at a primary care facility classified patient’s visits as either being “ENT” related or not, to assess the amount of ENT related concerns they typically encounter. The data was collected separately in the summer and winter months to assess any seasonal variability. One in eight patient encounters presented with an ENT related concern. The percentage of ENT related symptom presentation visits in the pediatric population for both data collection periods (29%) was more than three times that of the adult population (9%). The rate of ENT symptom presentation in both adult and pediatric populations was not affected by seasonality. Primary care physicians will encounter new patients presenting with ENT related concerns quite frequently. This is especially true in the pediatric patient population. Increased ENT medical education is both necessary and essential for undergraduate medical students, residents, and primary care physicians.L’oto-rhino-laryngologie (ORL) concerne les maladies et les troubles de l’oreille, du nez, de la gorge et des structures connexes de la tête et du cou. De nombreux étudiants au Canada n’ont qu’une expérience limitée de cette spécialité alors que la grande majorité d’entre eux poursuivent une carrière de médecin de soins primaires. Les médecins d’un établissement de soins primaires ont classé les visites des patients afin de déterminer le volume de consultations en lien avec l’ORL. Les données ont été recueillies séparément pendant les mois d’été et d’hiver pour évaluer la variabilité saisonnière. D’après les données, une consultation sur huit était liée à la présence de symptômes ORL. Le pourcentage de consultations chez la population pédiatrique pour les deux périodes de collecte de données (29 %) était plus de trois fois supérieur à celui de la population adulte (9 %). La survenance de symptômes ORL n’était pas affectée par la saisonnalité, ni chez l’une ni chez l’autre. Les médecins de soins primaires voient assez souvent de nouveaux patients présentant des problèmes ORL, particulièrement des enfants. Un renforcement de l’enseignement de la médecine ORL est à la fois nécessaire et essentiel pour les étudiants en médecine de premier cycle, les résidents et les médecins de soins primaires

NEUCAL, an innovative neutron detector for e/h discrimination: testbeam results

An excellent hadron to electron discrimination is a crucial aspect of calorimeter-based experiments in astroparticle physics. Standard discrimination techniques require full shower development and fine granularity but in space detectors severe limitations exist due to constraints on dimensions, weight and power consumption. A possible approach is to exploit the different neutron yield of electromagnetic and hadronic showers. NEUCAL is a light and compact innovative neutron detector, to be used as an auxiliary complement of electromagnetic calorimeters. This new approach to neutron counting relies on scintillation detectors which are sensitive to the moderation phase of the neutron component. The NEUCAL prototype has been placed after a conventional calorimeter and tested with high energy beams of pions and positrons. The comparison of experimental data with a detailed Geant4 simulation and the encouraging results obtained are presented

Kekule Structure Counting of Single-Walled Boron Nitride Nanotube

氮化硼纳米管(BoronNitrideNanotube)、碳纳米管(CarbonNanotube)以及多环芳烃（PolycyclicAromaticHydrocarbon）等巨大共轭分子，是结构化学的重要研究对象。从图论角度来描述这些大分子的共轭分子系统(包括六角系统)的理论和计算，已得到了很大的发展。但随着所研究分子规模（立体或平面）的增大，手工计算无疑已变得十分艰巨甚至不可胜任。随着计算机软硬件技术的发展，可以设计一个辅助软件研究平台，为研究较大规模分子系统提供便利。我们将以图论与结构化学中相关的现有理论研究结果为基础，结合现代软件技术，提出对这些大分子系统的Kekule结构计数问题的计算...Gigantic conjugated molecules, such as Boron Nitride Nanotubes, Carbon Nanotubes, and Polycyclic Aromatic Hydrocarbons, are important research subjects of structural chemistry. Theories and caculations on conjugated molecule system(include hexagonal system), which is used to represent mathematically these gigantic molecules in organic chemistry, are well developed in recent years. When the size of...学位：工学硕士院系专业：计算机与信息工程学院自动化系_控制理论与控制工程学号：20003100

Duns Scoto in Italia. Edizioni, traduzioni, studi

Il volume si articola in tre parti. Nella prima è presentato un bilancio delle edizioni delle opere di Scoto, vengono ripercorsi i criteri delle diverse edizioni critiche, sono esposti i programmi e le prossime uscite. Nella seconda si affronta il delicato tema delle traduzioni in lingua moderna, in particolare in italiano, dei testi scotiani. Nella terza, la più ampia, introdotta da un bilancio storiografico della ricerca su Scoto in Italia, sono presentati contributi su specifici temi della teologia e della filosofia di Scoto, con particolare riferimento alla dottrina della conoscenza, alla metafisica e all’antropologia