Vortex formation and dissolution in sheared sands

Using digital image correlation, we track the displacement fluctuations within a persistent shear band in a dense sand specimen bounded by glass walls undergoing plane strain compression. The data evidences a clear, systematic, temporally recurring pattern of vortex formation, dissolution, and reformation throughout macroscopic softening and critical state regimes. During softening, locally affine deformation zones are observed at various locations along the shear band, which we argue to be kinematic signatures of semi-stable force chains. Force chain collapse then occurs, inducing vortex formation. Local jamming at the conflux of opposing displacements between adjacent vortices arrests the vortices, providing an avenue for potential new force chains to form amidst these jammed regions. The process repeats itself temporally throughout the critical state. The pattern further correlates with fluctuations in macroscopic shear stress. We characterize the nature of the observed vortices, as they are different in our sands comprised of irregular shaped particles, as compared to previous observations from experiments and numerical simulations which involved circular or rounded particles. The results provide an interesting benchmark for behavior of non-circular/non-spherical particles undergoing shear.     

Metal Fabrication by Additive Manufacturing Using Laser and Electron Beam Melting Technologies

Selective laser melting (SLM) and electron beam melting (EBM) are relatively new rapid, additive manufac- turing technologies which can allow for the fabrication of complex, multi-functional metal or alloy monoliths by CAD-directed, selective melting of precursor powder beds. By altering the beam parameters and scan strategies, new and unusual, even non-equilibrium microstructures can be produced; including controlled microstructural architectures which ideally extend the contemporary materials science and engineering paradigm relating structure-properties-processing-performance. In this study, comparative examples for SLM and EBM fabricated components from pre-alloyed, atomized precursor powders are presented. These include Cu, Ti–6Al–4V, alloy 625 (a Ni-base superalloy), a Co-base superalloy, and 17-4 PH stainless steel. These systems are characterized by optical metallography, scanning and transmission electron microscopy, and X-ray diffraction.     

The Influence of Morphology on Photo-catalytic Activity and Optical Properties of Nanocrystalline ZnO Powder

Nano-Micro Letters - ZnO nano-particles were synthesized via an ammonical ammonium carbonate solution by precipitation method in presence of some additives such as urea, oleic and stearic acid. The...     

The impact of a participatory ergonomics intervention: the value of involvement

This article presents the implementation of a participatory ergonomics (PE) approach in a multinational company in the northern side of Italy, aiming to improve ergonomics, well-being and production outcomes. The methodology used is based on the creation of a multi-disciplinary team to provide and discuss ergonomics’ solutions according to the physical problems of the workers involved and better manage the re-introduction of the workers in the line of production. The study consists of a longitudinal analysis before and after the plant redesign and the PE intervention. Some psychosocial variables as job satisfaction, perceived fatigue, perceived usefulness, repetitiveness, occupational safety and company attention to safety have been monitored to verify the impact of the PE intervention. The results show how the PE intervention positively influences the perception of workers regarding the level of fatigue and repetitiveness and increasing job satisfaction, usefulness and occupational safety with a positive impact on productivity.     

Preparation and properties of NiAl(Si)/Al2O3 co-continuous composites obtained by reactive metal penetration

Reactive metal penetration was used to prepare intermetallic–ceramic composites with co-continuous structure, starting from silica glass preforms. Two subsequent metal penetrations were performed: first, the silica was immersed in a liquid Al bath, obtaining an Al(Si)/Al₂O₃ composite, then Ni was put in contact with the composite at high temperature, bringing to the substitution of Al with a Ni–Al intermetallic. The obtained composites present both phases continuous, and the whole process is a near net-shape one. The intermetallic phase is based on the Ni–Al system, with small Si content (lower than 2%) and its composition ranges from Al₃Ni₂ to a mixture of NiAl and Ni₃Al depending on the Ni content during the second penetration step.The composites present high hardness and melting point, low thermal expansion coefficient and good mechanical properties.     

Are cellulose nanocrystals “alien particles” to human experience?

A wide family of cellulose‐based additives are authorized worldwide as fillers and thickening agents in foods, pills, and tablets, and microcrystalline cellulose (MCC) is, among these, the most important one. Since MCC manufacturing is similar to the main production route of cellulose nanocrystals (CNCs), it is reasonable to wonder whether the MCC would contain CNCs as minor components. In this Short Communication, we provide first results about the occurrence of CNCs in MCC, observed by dynamic light scattering and transmission electron microscopy after serial filtrations of MCC suspensions. The incidence of cellulose nanoparticles has been proved in several different trials in our ongoing works on diverse MCC samples, and the nanoparticles isolated showed shape and dimensions similar to those commonly produced by acidic hydrolysis at laboratory level. Therefore, the presence of CNCs in many products is considered as a certainty. The foods and the pharmaceuticals we have been consuming so far do indeed contain traces of CNCs to such an extent that this wide presence in consumed products should be taken into account when considering possible limitations of the use of these nanoparticles in food contact materials manufacture.     

3D Ordering at the Liquid–Solid Polar Interface of Nanowires

The nature of the liquid–solid interface determines the characteristics of a variety of physical phenomena, including catalysis, electrochemistry, lubrication, and crystal growth. Most of the established models for crystal growth are based on macroscopic thermodynamics, neglecting the atomistic nature of the liquid–solid interface. Here, experimental observations and molecular dynamics simulations are employed to identify the 3D nature of an atomic-scale ordering of liquid Ga in contact with solid GaAs in a nanowire growth configuration. An interplay between the liquid ordering and the formation of a new bilayer is revealed, which, contrary to the established theories, suggests that the preference for a certain polarity and polytypism is influenced by the atomic structure of the interface. The conclusions of this work open new avenues for the understanding of crystal growth, as well as other processes and systems involving a liquid–solid interface.     

Picogram per liter level determination of estrogens in natural waters and waterworks by a fully automated on-line solid-phase extraction-liquid chromatography-electrospray tandem mass spectrometry method

The present work describes a novel, fully automated method, based on on-line solid-phase extraction-liquid chromatography-electrospray tandem mass spectrometry (SPE-LC-ESI-MS-MS), which allows the unequivocal identification and quantification of the most environmentally relevant estrogens (estradiol, estrone, estriol, estradiol-17-glucuronide, estradiol-17-acetate, estrone-3-sulfate, ethynyl estradiol, diethylstilbestrol) in natural and treated waters at levels well below those of concern (limits of quantification between 0.02 and 1.02 ng/L). The method is highly precise, with relative standard deviations varying between 1.43 and 3.89%, and accurate (recovery percentages >74 %). This method was used to track the presence and fate of the target compounds in a waterworks and to evaluate the removal efficiency of the treatment processes applied. Only estrone and estrone-3-sulfate were detected in the river water used as source (at 0.68 and 0.33 ng/L, respectively). After progressive removal through the various treatment steps, none of them were detected in the finished drinking water. In addition to selectivity, sensitivity, repeatability, and automation (up to 15 samples plus 6 calibration solutions and 1 blank can be analyzed unattended), this technique offers fairly high throughput (analysis time per sample is 60 min), low time and solvent consumption, and ease of use.     

Spectroelectrochemical sensing based on multimode selectivity simultaneously achievable in a single device. 17. Improvement in detection limits using ultrathin perfluorosulfonated ionomer films in conjunction with continuous sample flow

We report herein an attenuated total reflectance (ATR) absorbance-based spectroelectrochemical sensor for tris(2,2'-bipyridyl)ruthenium(II) ion [Ru(bpy)(3)(2+)] that employs ultrathin (24-50 nm) Nafion films as the charge-selective layer. This film serves to sequester and preconcentrate the analyte at the optically transparent electrode surface such that it can be efficiently detected optically via electrochemical modulation. Our studies indicate that use of ultrathin films in tandem with continuous flow of sample solution through the cell compartment leads to a 100-500-fold enhancement in detection limit (10 nM) compared to earlier absorbance-based spectroelectrochemical sensors ( approximately 1-5 microM); markedly shorter analysis times also result. We report the dependence of the measured absorbance on sample flow rate and Nafion film thickness, and also provide calibration curves that illustrate the linear range and detection limits of the sensor using a 24 nm film at a constant sample flow rate of 0.07 mL/min.     

A Comparative Life Cycle Assessment of Disposable and Reusable Packaging for the Distribution of Italian Fruit and Vegetables

Each year in Italy, millions of tons of fruits and vegetables are harvested, packed and transported to national and foreign retail outlets. Packaging is an essential component of this system, but what is its environmental impact? This study takes into consideration the delivery from the field to the retail outlet of 12 types of fruits and vegetables grown and harvested in Italy and sold in Italy and Europe. The study compares two different packaging and distribution systems: one‐way with corrugated boxes and reusable with plastic containers. A number of different scenarios were generated by combining the most diffused packaging sizes with the most important production and selling locations for each type of fruit and vegetable and by considering the specific route required to perform the transportation with each distribution system. The environmental impact of each system in each scenario has then been analysed using the life cycle assessment methodology. Two algorithms and a number of coefficients were derived to simplify data collection and impact analysis for all scenarios. This provides an easy tool to evaluate the potential environmental burden of the two alternative distribution systems in a specific scenario by taking into consideration only a few variables (such as size of packaging and transportation distance). These algorithms and coefficients are presented in the work, along with the process that led to their generation and with considerations about the main critical environmental aspects for both distribution systems. The work aims to suggest possible design solutions that can make each system more sustainable. Copyright © 2011 John Wiley & Sons, Ltd.