bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recent Developments in Aggregation Kinetics
Authors: Asnaghi D. , Carpineti M. , Giglio M. 
Published: August 2016

Colloidal aggregation is a very old field of research. The basic mechanism that controls the stability of colloidal solutions has been described in the celebrated papers of Derjaguin, Landau, Verwey, and Overbeek (DLVO), and indeed the prevention of undesired aggregation is one of the primary concerns in many industrial processes involving colloids. In the last 10 years a resurgence of interest in aggregation rather than in stability has been spurred by a number of fortuitous coincidences. Both through simulations and experiments, it was realized that colloidal aggregates exhibit a fractal nature. More importantly, it was found that there are two universal modes of aggregation, irrespective of the type of colloidal system. The aggregates grown according to these modes have different fractal dimensions, different reaction kinetics, and different mass distributions. The two modes are called diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation (RLCA), according to whether the probability that a bond formed as a consequence of an encounter is equal to, or much smaller than one, respectively. The study of these limiting cases has been the object of extensive studies in the late 1980s, and many of the features of these modes are by now well understood.This article describes some recent results in the area of colloidal aggregation. Although we present mostly static light-scattering data from our laboratory, connections to similar work from other groups are also discussed. For the convenience of the reader, we start by recalling some of the relevant features of both DLCA and RLCA.
Studies of Material Reactions by In Situ High-Resolution Electron Microscopy
Authors: Sinclair Robert 
Published: August 2016

Processing has always been a key component in the development of new materials. Basic scientific understanding of the reactions and transformations that occur has obvious importance in guiding progress. Invaluable insight can be provided by observing the changes during processing, especially at high magnification by in situ microscopy. Now that this can be achieved at the atomic level by using high-resolution electron microscopy (HREM), atomic behavior can be seen directly. Accordingly, many deductions concerning reactions in materials at the atomic scale are possible.The purpose of this article is to illustrate the level reached by in situ HREM. The essential procedure is to form a high-resolution image of a standard transmission electron microscope (TEM) sample and then to alter the structure by some means in a controlled manner, such as by heating. Continual recording on videotape allows subsequent detailed analysis of the behavior, even on a frame-by-frame (1/30 second) basis. The most obvious advantage is to follow the atomic rearrangements directly in real time. However, in addition, by continuous recording no stages in a reaction are missed, which can often occur in a series of conventional ex situ annealed samples because of the limited number of samples that can realistically be examined by HREM. One can be sure that the same reaction, in the same area, is being studied. Furthermore, by changing the temperature systematically, extremely precise kinetic measurements can be made (e.g., for activation energies and kinetic laws) and the whole extent of a material transformation can be investigated in one sample, something that would take months of work if studied conventionally. The information provided by in situ HREM is often unique and so it can become an important technique for fundamental materials investigations.
Perturbed-Angular-Correlation Spectroscopy: Renaissance of a Nuclear Technique
Authors: Catchen Gary L. 
Published: August 2016

During the past decade, perturbed-angular-correlation (PAC) spectroscopy has emerged as an important technique in several areas of materials science. PAC spectroscopy is used to measure the effects of local fields at well-defined lattice sites in a crystal. These measurements can provide unique information about the structures, kinetics, and energetics associated with point defects, the mechanisms of phase transitions, and the strengths and symmetries of chemical bonds of atoms on surfaces and at interfaces. In what follows, I describe the PAC technique in the context of several examples of these applications and I comment on the historical evolution of this spectroscopy.Hyperfine InteractionsThe field of hyperfine interactions encompasses spectroscopic techniques that use the electric and magnetic nuclear moments to measure the specific extranuclear environment of the nuclear moments. Examples of these techniques are nuclear-magnetic-resonance (NMR), nuclear-quadrupole-resonance (NQR), electron-paramagnetic-resonance (EPA), muon-spin-rotation (MSR), Mössbauer-effect (ME), and perturbed-angular-correlation (PAC) spectroscopies. Each of these techniques is well-suited to certain types of measurements but useless for others. For example, NMR spectroscopy can be particularly useful for measuring chemical shifts associated with nuclei of atoms that are major constituents of crystalline solids. However, nuclear electricquadrupole interactions associated with some NMR-active nuclei are not only difficult to measure but they often obscure much of the chemical-shift information by producing spectral-line broadening. PAC spectroscopy can be used to accurately measure the nuclear electric-quadrupole interactions at the sites of nuclei of atoms that are trace dopants in crystals. But the PAC technique is insensitive to the effects of local charge distributions that produce the NMR chemical shifts. ME spectroscopy can be used to measure both of these effects as well as nuclear magnetic-dipole interactions. However, ME measurements are often only practical on crystals that have one of several elements as a major constituent, that is, either Fe or Sn. In addition, the ME sensitivity depends on temperature, and the NMR and EPR sensitivities also depend on temperature. However, the PAC measurement is independent of temperature, which can be a great advantage for studying phenomena such as phase transitions.
Smart, Very Smart, and Intelligent Materials
Authors: Newnham Robert E. 
Published: August 2016

One of the qualities that distinguishes living systems from inanimate matter is the ability to adapt to changes in the environment. Smart materials have the ability to perform both sensing and actuating functions and are, therefore, capable of imitating this rudimentary aspect of life. Poled piezoelectric ceramics, for instance, are capable of acting as both sensor and actuator. External forces are detected through the direct piezoelectric effect, and a response is elicited through the converse piezoelectric effect, in which a voltage of suitable phase, frequency, and amplitude is applied to the same ceramic.In this special issue, emphasis is placed on actuators, with articles on piezoelectric, electrostrictive, magnetostrictive, and shape memory materials. This is not to say that sensor materials are any less important; it is simply a matter of space. Optical fiber sensors, chemical sensors, thermistors, micromachined semiconductors, and other smart materials deserve special issues of their own.Smart materials can be conveniently subdivided into passively smart materials that respond to external change without assistance, and actively smart materials that utilize a feedback loop enabling them to both recognize the change and initiate an appropriate response through an actuator circuit.Zinc oxide varistors are passively smart materials capable of self-protection against high voltage breakdown. When struck by lightning, the ceramic varistor loses most of its electrical resistance, and the current is bypassed to ground. The resistance change is reversible, and acts as a standby protection phenomenon.
Sensors, Actuators, and Smart Materials
Authors: Trolier-McKinstry S. , Newnham R.E. 
Published: August 2016

The field of electronic ceramics includes components as diverse as Mn-Zn ferrites, lead zirconate titanate transducers, ZnO varistors, and Al2O3 or cordierite-based packages for integrated circuits. An overview of electroceramics is given in Figure 1, which depicts schematically the types of electronic and ionic phenomena of interest. Many of the materials pictured utilize some bulk property of the ceramic, such as the presence of ferroelectric of ferrimagnetic dipoles, electronic or ionic conductivity, or a phase transition to provide a useful function. In other materials, extraordinary responses can be engineered by suitably tailoring the thickness and properties of a grain boundary phase. Varistors, barrier layer capacitors, and PTC thermistors, for example, all rely on the preparation of semiconducting grains and insulating grain boundaries to create properties that cannot be found in single crystals. In a similar way, some of the porous ceramics utilized in humidity sensors rely on surface properties rather than on a bulk response to detect changes in the ambient humidity (Kulwicki, 1992). Finally, in materials for insulators or substrates, all of the otherwise interesting phenomena must be eliminated. With the exception of the last category, all of the phenomena depicted in Figure 1 can be utilized in ceramic sensors. While sensing and actuating materials are currently a fraction of the overall multibillion-dollar electroceramics market, the percentage is expected to grow as more and more devices are made “smart.”As discussed in the introduction to this issue, smart materials are capable of sensing a change in the environment and responding in a useful way.
A Concept of a “Virtual Production Line” Produced by Integrating Databases and Models of Materials
Authors: Iwata Shuichi 
Published: August 2016

One of the requirements for an intelligent system is to construct a virtual reality in the computer. For materials development, the “reality” is a laboratory or a production line used to improve some aspect of a material by changing its composition, processing parameters, service conditions, etc. In the case of information in libraries, the reality is a search that uses a thesaurus and bibliographic (fact) databases. The greatest barrier faced by users of materials information is that of accessing necessary information through both a librarian's view and a scientific/technological expert's view. One of the objectives of a virtual production line is to reduce this barrier through user-friendly interfaces.In designing materials, two typical approaches are combined to solve a given problem. The first is a top-down approach, in which a number of requirements are resolved to a set of possible and practical solutions for satisfying these requirements to a certain level. Almost all alloy development has followed such an approach. The second approach is a bottom-up approach, where different materials properties are described on the basis of underlying theories, preferably using first principles and fundamental data. But the vast number of possible materials makes the bottom-up approach unrealistic on its own. Instead, semi-empirical approaches are needed to bridge the gap between ad hoc data sets for practical applications and results produced by the bottom-up approach using fundamental data and first-principle calculations.
Implications of Amalgam and Ceramic Degradation in the Oral Environment
Authors: Anusavice Kenneth J. , Söderholm Karl-Johan , Grossman David G. 
Published: August 2016

Recent breakthroughs in materials science and technology have led to improved dental restorative ceramics, metals, and resin-based composites. These breakthroughs have been most important since one of the major controversies during this period has centered on allegations of the physiological risks of mercury released from amalgam restorations. Dental amalgams have been used in the United States since 1832, yet not a single well-documented case of dental patient toxicity to mercury from amalgam restorations has been reported in the scientific literature.A particularly extreme position has been adopted by the Swedish government, which has proposed the progressive elimination of amalgam as a dental restorative material by 1997. Among the materials that have been considered as the most biocompatible alternative to amalgam are dental ceramics. New ceramic products and technologies have gained considerable acceptance in Sweden even though their safety and efficacy have not been fully established.Although dental ceramics constitute a much more costly alternative than some other materials, they offer the advantages of esthetics, inertness, durability, low thermal conductivity, and low diffusivity, as compared with amalgams. Although ceramics are generally considered to be inert in the oral cavity, there are certain phenomena associated with their use that may cause significant surface degradation of these materials and subsequent physiological side effects.
Overview of Cast Multicrystalline Silicon Solar Cells
Authors: Watanabe Hiroyuki 
Published: August 2016

Worldwide environmental problems such as the greenhouse effect and acid rain have been caused by the human race's continuous reliance on the combustion of petroleum for fuel.Solar energy, which is clean and practically unlimited, is expected to be a desirable alternate energy source to conventional power supplies, and demand for the photovoltaic system has increased throughout the world, especially in Europe and the United States.Photovoltaic cells are probably the most effective method for capturing solar energy, since they are easy to use and are the most effective means of directly generating electricity.Many kinds of solar cells have been developed in past years, especially since the first oil crisis in 1973. Among them, solar cells from cast multicrystalline silicon (also refereed to as (cast) polycrystalline silicon or semicrystalline silicon) are considered to be one of the most promising types, capable of achieving both high efficiency and low cost.In 1975, Wacker proposed a new manufacturing method for silicon substrates, using the casting method. Since then, many organizations have been involved in the research and development of multicrystalline ingots and solar cells using multicrystalline silicon substrates.Multicrystalline silicon substrates contain many kinds of defects compared to single-crystal silicon substrates, so the efficiency of multicrystalline silicon solar cells has been inferior to that of single-crystal cells. Recent research on multicrystalline silicon solar cells has resulted in substantial improvements and in the demonstration of high-efficiency cells.
Recent Progress in Amorphous Silicon Solar Cells and Their Technologies
Authors: Hamakawa Y. , Ma W. , Okamoto H. 
Published: August 2016

A big barrier impeding the expansion of large-scale power generation by photovoltaic (PV) systems was the high price of solar cell modules, which was more than $50/Wp (peak watts) by 1974. Therefore, cost reduction of solar cells is of prime importance. To achieve this objective, tremendous R&D efforts have been made over the past ten years in a wide variety of technical fields, from solar cell materials, cell structure, and mass production processes to photovoltaic systems. As a result, more than an order of magnitude in cost reduction has been achieved, and the module cost has come down to less than $5/Wp in a firm bid for the large-scale market. Two phases of technological innovation can be identified. The first innovation in progress is based on low-cost polycrystalline technologies applicable to well-developed single-crystalline silicon solar cell fabrication processes. The second remarkable innovation is a-Si:H (hydrogenated amorphous silicon) technology, which we will discuss.We open our discussion with a brief overview of the present status of a-Si solar cell R&D efforts, with some new insights in device physics. Next, we discuss some new approaches and key technologies for improving solar cell efficiency with stabilized performance using new materials such as a-SiC:H (amorphous silicon carbide), μc-SiC:H (microcrystalline silicon carbide), and a-SiGe:H (amorphous silicon germanium). Also, the progress of conversion efficiency in various types of amorphous silicon solar cells is surveyed and summarized.
Nanocrystalline Thin-Film PV Cells
Authors: Grätzel Michael 
Published: August 2016

In a conventional p-n junction photovoltaic cell, made, for example, from silicon, the semiconductor assumes two roles at the same time: It harvests the incident sunlight and conducts the charge carriers produced under light excitation. In order to function at a good efficiency, the photons have to be absorbed close to the p-n interface. Electron-hole pairs produced away from the junction must diffuse to the p-n contact where the local electrostatic field separates the charges. To avoid charge carrier recombination during the diffusion, the concentration of defects in the solid must be small. This imposes severe requirements on the purity of the semiconductor material, rendering solid-state devices of the conventional type expensive.We have developed a new molecular photovoltaic system for solar light harvesting and conversion to electricity. It is based on the spectral sensitization of a thin ceramic membrane by suitable transition-metal complexes. The film consists of nanometersize colloidal titanium dioxide particles sintered together to allow for charge carrier transport. When derivatized with a suitable chromophore, these membranes yield extraordinary efficiencies for the conversion of incident photons into electric current, exceeding 90% for certain transition metal complexes within the wavelength range of their absorption band. In this article, we discuss the underlying physical principles of these astonishing findings. Exploiting this discovery, we have developed a new type of photovoltaic device whose overall light-to-electric-energy conversion yield is 12–15% in diffuse day-light and 10% under direct (AM1.5) solar irradiation.
Unit Operations for Improving the Bulk Properties of Recycled Fiber
Authors: Silveri Luigi 
Published: August 2016

Over the past few years, recycling within the pulp and paper industry has been brought sharply into focus. The primary motivating factors for this have been the crisis in the landfills, of which paper is the largest component, the ensuing legislation, greater public awareness of recycling as an issue, and a desire to recycle more.In reality, recycling has always been a significant part of papermaking. On a worldwide basis, about one third of the fiber supply is recycled fiber (Table I). A further significant portion of the fiber supply comes from the use of residues from sawmills and other woodworking operations; thus, in the strictest sense, the recycled content is even higher.The amount of recycled paper that is used varies from 45–50% for Japan and Continental Europe, which have limited forest resources, to about 10% for Canada and Scandinavia, which are rich in forest resources.In the United States, the recycle rate is about 26% and increasing. Estimates of future usage vary, but the industry as a whole is moving toward a recycle rate close to about 40% or higher by the end of the decade.It is important to understand the effect that recycling has on fiber properties and also the effect that adding recycled pulp can have on the final sheet properties. To arrive at this, it is worthwhile to review the main aspects of the recycling process and how the process affects pulp properties.
Chemical Products from Lignocellulosics
Authors: Glasser Wolfgang G. 
Published: August 2016

Lignocellulosics represent that mass of organic matter produced by land-growing plants in the form of trees, shrubs, and agricultural crops. Lignocellulosics are renewable, and they sustain living conditions on our planet by recycling carbon dioxide to oxygen. Lignocellulosics serve the planet as a carbon sink. Chlorophyll is the essential catalyst and sunlight the necessary energy source that drive this carbon dioxide reduction to an organic mass that varies little from the carbon-to-oxygen ratio of carbon monoxide.There is, however, no distinct “lignocellulose” molecule. Instead, nature has found it necessary to formulate a multiphase material consisting of cellulose, hemicelluloses, and lignin. The composition of this multiphase material can be likened to a fiber-reinforced organic glass where cellulose serves as lightweight fiber, lignin serves as a continuous (glassy) matrix, and hemicelluloses serve as coupling agents. The overall composition suggests that there is 35–45% cellulose, 25–35% hemicelluloses, 20–25% lignin, and various minor constituents.In chemical terms, cellulose is a linear homopolysaccharide with a high degree of crystallinity. It consists of 1,4-β-linked D-glucopyranose units connected in syndiotactic fashion (on alternating sides of the main chain). Cellulose molecules in nature occur with molecular weights exceeding 2 million. Hemicelluloses, by contrast, are branched heterosaccharides of lesser molecular weight. They rarely exceed 20,000 daltons. Hemicelluloses are either rich in glucomannan chains (softwoods), or they consist primarily of branched xylans (hardwoods and annual crops). The chemical composition of hemicelluloses is extraordinarily similar to cellulose (i.e., polyanhydro-pyranoside), but their morphological structure is vastly different.
Bandgap and Defect Engineering for Semiconductor Holographic Materials: Photorefractive Quantum Wells and Thin Films
Authors: Nolte David , Melloch Michael 
Published: August 2016

Bandgap engineering of thin semiconductor layers and defect engineering combine to form photorefractive (PR) quantum well structures. PR quantum wells are semi-insulating thin films useful for dynamic holography and other coherent and incoherent optical applications. As materials for thin-film dynamic holography, they have high nonlinear-optical sensitivity and high speed.The PR effect translates a spatially varying irradiance, from the interference of two or more coherent light beams, into a refractive index grating. The multiple-step PR process begins with photoexcitation of charge carriers, followed by transport and trapping of charge at deep defects. The trapped space-charge generates electric fields that alter the refractive index of the material through the electrooptic effect. The same laser beams that generate the gratings diffract from the gratings, leading to a rich variety of multiple-beam effects, such as two-wave and four-wave mixing.Because the PR process involves several distinct physical parameters, such as carrier mobility and electrooptic coefficients, optimized performance requires a coincidence of favorable properties in a single material. Rather than relying on coincidence, bandgap engineering of multiple layers of semiconductors provides a way to individually tune the separate material pa rameters. Likewise, defect engineering in semiconductors provides flexibility in the choice of defects, their concentrations, and degree of compensation. Bandgap and defect engineering combined make custom designed PR materials possible.