bluuebunny/crossref_metadata_2025 huggingface dataset:
Prevalence and intensity of flea Tunga monositus (Siphonaptera) in an insular population of Peromyscus maniculatus (Rodentia) from Northwest Mexico
Authors: Camargo Issac , Romero-Callejas Evangelina , Cornejo-Latorre Cristian , Rios Evelyn , Álvarez-Castañeda Sergio Ticul
Published: August 2016

We surveyed the status of the endemic deer mouse Peromyscus maniculatus
exiguus from San Martin Island, Baja California, Mexico where the population is numerous. A total of 89 adult rodents of P. m. exiguus were caught, 51 of which were parasitized by the flea Tunga monositus (Siphonaptera: Pulicidae); prevalence was 57% and the mean infection intensity was 1.8 parasites per host. No significant differences in prevalence were found between both sexes and between sites. Our results showed a higher infection percentage than those reported in previous studies for the species.
Schedules for Pneumococcal Vaccination of Preterm Infants: An RCT
Authors: Kent Alison , Ladhani Shamez N. , Andrews Nick J. , Scorrer Tim , Pollard Andrew J. , Clarke Paul , Hughes Stephen M. , Heal Carrie , Menson Esse , Chang John , Satodia Prakash , Collinson Andrew C. , Faust Saul N. , Goldblatt David , Miller Elizabeth , Heath Paul T. ,   on behalf of the PUNS Study Group
Published: August 2016

BACKGROUND AND OBJECTIVE:

Premature infants have a higher risk of invasive pneumococcal disease and are more likely to have lower vaccine responses compared with term infants. Increasingly, immunization schedules are including a reduced, 2-dose, pneumococcal conjugate vaccine priming schedule. Our goal was to assess the immunogenicity of 3 commonly used 13-valent pneumococcal conjugate vaccine (PCV13) priming schedules in premature infants and their response to a 12-month booster dose.

METHODS:

Premature infants (<35 weeks’ gestation) were randomized to receive PCV13 at 2 and 4 months (reduced schedule); 2, 3, and 4 months (accelerated schedule); or 2, 4, and 6 months (extended schedule). All infants received a 12-month PCV13 booster. Serotype-specific pneumococcal immunoglobulin G (IgG) for PCV13 serotypes was measured by using enzyme-linked immunosorbent assay 1 month after the primary and booster vaccinations.

RESULTS:

A total of 210 infants (median birth gestation, 29+6 weeks; range, 23+2–34+6 weeks) were included. After the primary vaccination, 75% (95% confidence interval [CI], 62–85), 88% (95% CI, 76–95), and 97% (95% CI, 87–99) of participants had protective antibody concentrations for at least one-half the PCV13 serotypes for the reduced, accelerated, and extended schedules, respectively. After the booster vaccination, participants receiving the extended schedule had significantly lower (P < .05) geometric mean concentrations compared with reduced (for 9 of 13 serotypes) and accelerated (for 4 of 13 serotypes) schedules, but nearly all participations, regardless of schedule or serotype, had seroprotective IgG concentrations.

CONCLUSIONS:

A reduced priming schedule of PCV13 resulted in higher post-booster IgG concentrations but lower post-primary concentrations. The optimum vaccine schedule for preterm infants will therefore depend on when they are most at risk for invasive pneumococcal disease.
Reasons for Trying E-cigarettes and Risk of Continued Use
Authors: Bold Krysten W. , Kong Grace , Cavallo Dana A. , Camenga Deepa R. , Krishnan-Sarin Suchitra
Published: August 2016

BACKGROUND:

Longitudinal research is needed to identify predictors of continued electronic cigarette (e-cigarette) use among youth. We expected that certain reasons for first trying e-cigarettes would predict continued use over time (eg, good flavors, friends use), whereas other reasons would not predict continued use (eg, curiosity).

METHODS:

Longitudinal surveys from middle and high school students from fall 2013 (wave 1) and spring 2014 (wave 2) were used to examine reasons for trying e-cigarettes as predictors of continued e-cigarette use over time. Ever e-cigarette users (n = 340) at wave 1 were categorized into those using or not using e-cigarettes at wave 2. Among those who continued using e-cigarettes, reasons for trying e-cigarettes were examined as predictors of use frequency, measured as the number of days using e-cigarettes in the past 30 days at wave 2. Covariates included age, sex, race, and smoking of traditional cigarettes.

RESULTS:

Several reasons for first trying e-cigarettes predicted continued use, including low cost, the ability to use e-cigarettes anywhere, and to quit smoking regular cigarettes. Trying e-cigarettes because of low cost also predicted more days of e-cigarette use at wave 2. Being younger or a current smoker of traditional cigarettes also predicted continued use and more frequent use over time.

CONCLUSIONS:

Regulatory strategies such as increasing cost or prohibiting e-cigarette use in certain places may be important for preventing continued use in youth. In addition, interventions targeting current cigarette smokers and younger students may also be needed.
Native Defects in the Ternary Chalcopyrites
Authors: Giles N.C. , Halliburton L.E.
Published: August 2016

Ternary-chalcopyrite crystals contain a variety of point defects—the most common of which are vacancies, antisite ions, and impurities. Usually these defects are isolated, but they can also appear as complexes involving two or more of the simple defects. Depending on the material, the concentrations of these defects may vary from a few hundred parts per billion to a few hundred parts per million. Many of the point defects in the ternary chalcopyrites have associated optical-absorption bands with significant oscillator strengths. It is these absorption features that become important when the crystals are exposed to intense laser beams during device operation. Even a small amount of absorption will seriously degrade the performance of the device if any of the wavelengths of the various propagating beams happen to overlap an absorption band. This phenomenon can be a problem for both second-harmonic-generator and optical-parametric-oscillator applications. In general the absorption leads to heating of the crystal and results in-thermal lensing (due to temperature dependence of the index of refraction) and dephasing of the beams, and it can ultimately lead to thermal fracturing of the crystal. Thus it is important to develop a fundamental understanding of the defect structure of the ternary-chalcopyrite crystals if they are to serve as the critical component in midinfrared frequency-conversion devices. Once the nature and behavior of the point defects are established, processes can be developed to remove the defects from the crystals either during the growth itself or during post-growth treatments.
Mesoscopically Periodic Photonic-Crystal Materials for Linear and Nonlinear Optics and Chemical Sensing
Authors: Asher Sanford A. , Holtz John , Weissman Jesse , Pan Guisheng
Published: August 2016

Over the past decade, we have been working to develop intelligent photonic-crystal materials with unique properties, which will be useful in a number of technological areas. These photonic-crystal materials utilize mesoscopically periodic arrays of spherical particles as their active optical elements and are easily fabricated chemically by the use of crystalline-colloidal-array (CCA) self-assembly techniques.

Crystalline colloidal arrays are mesoscopically periodic fluid materials, which efficiently diffract light meeting the Bragg condition. These photonic-crystal materials consist of arrays of colloidal particles that self-assemble in solution into either face-centered-cubic (fcc) or body-centered-cubic (bcc) crystalline arrays (Figure 1), with lattice constants in the mesoscale size range (50-500 nm). Just as atomic crystals diffract x-rays that meet the Bragg condition, CCAs diffract ultraviolet, visible, and near-infrared light, depending on the lattice spacing; the diffraction phenomena resemble those of opals, which are close-packed arrays of monodisperse silica spheres.

The CCA however can be prepared as macroscopically ordered arrays of non-close-packed spheres. This self-assembly is the result of electrostatic repulsions between colloidal particles, each of which has numerous charged surface functional groups. We have concentrated on the development of CCAs that diffract light in the visible spectral region and generally utilize colloidal particles of ~100-nm diameter. These particles have thousands of surface charges, which result from the ionization of surface sulfonate groups. The nearest-neighbor distances are often >200 nm.
Material Matters
Authors: Stoll W.
Published: August 2016

The following article is based on a talk for Symposium X presented by Wolfgang Stoll, Chief Scientific Advisor and Consultant in Siemens, Germany, at the 1996 MRS Fall Meeting.

Since 1941 when Glenn Seaborg first isolated plutonium in milligram quantities, the total amount converted through neutron capture in U-238 has increased worldwide to about 1,200 tons and continues to grow about 70 tons/year. What was fissioned in situ in operating nuclear power stations is roughly equivalent to 5 billion tons of black coal, while the fission energy contained in those 1,200 tons unloaded in spent fuel is equivalent to another 2 billion tons of coal. About 260 of these 1,200 tons are ready to release their energy in about 4 kg-portions each in microseconds which is equivalent to 10,000 tons of coal. Most people believe this release of energy poses a major threat of the worldwide arsenal of weapons of mass destruction (WMD). The about 20-fold overkill stored in worldwide WMD is considered superfluous after the crumbling of the Soviet Union. Options are sought to dispose of this surplus in a safe, speedy, and controllable manner. While for highly enriched uranium (HEU) (the other nuclear weapons material) dilution into low-enriched uranium and utilization in current light water reactors (LWR) poses market adaptation problems only, and while the worldwide consensus on the elimination of chemical and biological WMD is still in an initial phase, the decision of both the United States (US) and the former Soviet Union (FSU) to remove most of the plutonium out of weapons looks as if it was a firm political decision.
Education Exchange: Independent-Study Course Examines Materials in Tennis Rackets and Hockey Sticks
Authors: Lenoe Edward Mark
Published: August 2016

For the past seven years I have taught the Engineering Materials course (EM 380) at the United States Military Academy (USMA), Department of Civil and Mechanical Engineering (CME). The course has been modified to introduce modern materials technology to the cadets and to provide the opportunity to fabricate, design, test, and evaluate advanced materials in this course, in capstone design projects, and in independent-study projects. Theoretical and experimental studies of sporting equipment have been a sound and compelling basis to develop student ability in applied mechanics and to gain insight into the importance of materials choice. This article describes the methods and results of several of these projects.
Applications of Silicon-Based Optoelectronics
Authors: Soref Richard
Published: August 2016

Silicon-based optoelectronics is a diversified technology that has grown steadily but not exponentially over the past decade. Some applications—such as smart-pixel signal processing and chip-to-chip optical interconnects—have enjoyed impressive growth, whereas other applications have remained quiescent. A few important applications such as optical diagnosis of leaky metal-oxide-semiconductor-field-effect-transistor circuits, have appeared suddenly. Over the years, research and development has unveiled some unique and significant aspects of Si-based optoelectronics. The main limitation of this technology is the lack of practical silicon light sources—Si lasers and efficient Si light-emitting devices (LEDs)—though investigators are “getting close” to the LED.

Silicon-based optoelectronics refers to the integration of photonic and electronic components on a Si chip or wafer. The photonics adds value to the electronics, and the electronics offers low-cost mass-production benefits. The electronics includes complementary-metal-oxide semiconductors (CMOS), very large-scale integration (VLSI), bipolar CMOS, SiGe/Si heterojunction bipolar transistors, and heterostructure field-effect transistors. In this discussion, we will use a loose definition of optoelectronics that includes photonic and optoelectronic integrated circuits (PICs and OEICs), Si optical benches, and micro-optoelectromechanical (MOEM) platforms. Optoelectronic chips and platforms are subsystems of computer systems, communication networks, etc. Silicon substrates feature a superior native oxide, in addition to excellent thermal, mechanical, and economic properties. Silicon wafers “shine” as substrates for PICs and OEICs.
Silicon-Based Microphotonics and Integrated Optoelectronics
Authors: Fitzgerald E.A. , Kimerling L.C.
Published: August 2016

The need for integrated optical interconnects in electronic systems is derivedfrom the cost and performance of electronic systems. If we examine the cost of all interconnects, it becomes apparent that there is an exponential growth in cost per interconnect with the length of the interconnect. A remarkable feature of interconnect cost is that the exponential relation holds over all length scales—from the shortest interconnects on a chip to the longest interconnects in global telecommunications networks. Longer interconnects are drastically more expensive, and these costs are ultimately related to the labor cost associated with each interconnect. Given this economic pressure, it is not surprising that there is a driving force to condense more functions locally on the same chip, board, or system. In condensing these functions, the number of long interconnects are decreased and the overall cost of the electronic system decreases dramatically. A specific glaring example of this driving force is Si complementary-metal-oxide-semiconductor (CMOS) technology, especially the case of microprocessors. In the Si microprocessor case, the flood gates to interconnect condensation were opened and the miraculous trend of lower cost for exponentially increasing performance was revealed.
InGaN/GaN/AIGaN-Based Laser Diodes With an Estimated Lifetime of Longer Than 10,000 Hours
Authors: Nakamura Shuji
Published: August 2016

The following article, originally published in Materials Research Society Proceedings Volume 482, is based on the address that Shuji Nakamura, recipient of an MRS Medal Award, presented during Symposium X of the 1997 MRS Fall Meeting. Nakamura was recognized for “the development of lattice-mismatched GaN based heteroepitaxy and its application to the creation of blue and green light-emitting diodes and short wave-length laser diodes.”
Links of Science & Technology
Authors: DeCristofaro Nicholas
Published: August 2016

On April 13, 1982, the Duke Power Company energized an experimental pad-mount distribution transformer in Hickory, North Carolina. The transformer, manufactured by General Electric, provided electric power to a local residence. That same month, the Georgia Power Company installed a similar transformer, made by Westinghouse Electric, atop a utility pole in Athens, Georgia. It supplied electricity for the exterior lights at the Westinghouse Newton Bridge Road plant. These devices shown in Figure 1 were unique among the nearly 40 million distribution transformers in service in the United States because their magnetic cores were made from an Fe–B–Si amorphous-metal alloy. This new material, produced by Allied-Signal (formerly Allied Chemical), was capable of magnetizing more efficiently than any electrical steel. By replacing grain-oriented silicon steel in the transformer cores, the amorphous metal reduced the core losses of the transformers by 75%.

Although distribution transformers are relatively efficient devices, often operating at efficiencies as high as 99% at full load, they lose a significant amount of energy in their use. Because of the number of units in service, coupled with the fact that the core material is continuously magnetized and demagnetized at line frequency, transformers account for the largest portion of the energy losses on electric power distribution systems. It is estimated that over 50 × 109 kWh are dissipated annually in the United States in the form of distribution transformer core losses. At today's average electricity generating cost of $0.035/kWh, that energy is worth over $1,500 million.
Energy Dissipation in Interfacial Friction
Authors: Robbins Mark O. , Krim Jacqueline
Published: August 2016

In order to gain a fundamental understanding of friction, one must understand how the energy associated with work performed to overcome the frictional force is converted into heat at the molecular level. One of the simplest possible geometries in which friction can occur, and thus be studied, is that of a fluid or crystalline layer adsorbed on the surface of an ideal, atomically flat crystal. This system is ideal for studies of “interfacial” friction—that is, friction attributable to atoms and molecules immediately adjacent to the plane along which sliding occurs. Moreover it is directly accessible to experiments with a quartz crystal microbalance (QCM) and to theoretical studies through analytic calculations or molecular-dynamics (MD) simulations. The geometry is vastly simpler than that of contact between macroscopic objects in which the friction necessarily reflects the collective behavior of a multitude of buried contacts. (See the article by T. Baumberger and C. Caroli in this issue.) It is also far simpler than a case in which shear occurs within the bulk of a material rather than being confined to an interface. (See the article by D.A. Rigney and J.E. Hammerberg in this issue.) Nonetheless even in this simple geometry, friction can be far from negligible. A remarkable range of shear stresses, from 10−2 to 1010 N/m2, have been measured by a variety of techniques for wear-free geometries involving contact between crystalline interfaces.
Multicontact Solid Friction: A Macroscopic Probe of Pinning and Dissipation on the Mesoscopic Scale
Authors: Baumberger Tristan , Caroli Christiane
Published: August 2016

In this article, we review the present status of experimental and theoretical work on friction at the interface between extended macroscopic bodies, rough on the micrometer scale. We show that systematic detailed studies of low-velocity friction using dynamical systems analysis, together with their shear response in the static state, provide a tool for investigating the physical processes taking place on the mesoscopic scale of real contacts between rough surfaces. This approach should shed light on the enduring question of the relationship between macroscopic friction and microscopic dissipative mechanisms. This still open issue has come back to the fore during the last decades, following considerable progress due to the development of “molecular tribometers.

Bowden and Tabor pointed out that, because nominally flat surfaces are in general rough on small scales, the real area of contact Ar (Figure 1) is only a small fraction ϕ of apparent contact area A0. On the other hand, they postulated the existence of a stressσs characteristic of the shear strength of the interface between a given couple of solids. Hence the friction force:

In this framework, the Amontons-Coulomb (AC) law F = μFN amounts to stating that Ar is proportional to the normal load FN where μ is the coefficient of friction.

When considering soft metals, Bowden and Tabor noticed that ϕ ≪ 1 entails that the nominal local pressure p on the real contacts—of the order of FN/(ϕA0)–generally overcomes the yield strength Y so that the contacting asperities flow plastically until p = H≈ 3Y, the “hardness” of the (softer) material. So, Ar = FN/H.
Transparent Oxyfluoride Glass Ceramics
Authors: Dejneka Matthew J.
Published: August 2016

Low-phonon energy glasses are desirable hosts for rare-earth (RE) ions because they enable emission from RE energy levels that would otherwise be quenched in high-phonon energy glasses. Such emissions are of interest for fiber amplifiers operating at telecommunications wavelength band s of 1.31, 1.46, and 1.55μm, and for up-conversion lasers and three-dimensional displays.

Phonons are optical-frequency molecular vibrations in a material. If the RE energy level of interest lies only a few phonons in energy above the next lower lying level such as the1G4level of Pr3+, which is only 3,000 cm−1above the3F4, only three Si—O vibrational phonons (1,100 cm−1) are required to bridge the gap as shown in Figure 1. Thus any electrons excited to the1G4level via an external pump source will be deexcited to the3F4on down to the3H4ground state via phonons, and no radiation of usable light will be produced. This is why emission from the1G4level of Pr3+is absent in silicates and why researchers have gone to great lengths to make low-phonon energy glasses.
Spectroscopic Studies on the Structures of Phosphate Sealing Glasses
Authors: Brow Richard K. , Alam Todd M. , Tallant David R. , Kirkpatrick R. James
Published: August 2016

Phosphate glasses generally have lower glass-transition temperatures and greater thermal-expansion coefficients than silicate and borate glasses, and so are candidate materials for specialty glass-metal sealing applications. Phosphate glasses also have desirable optical properties (rare-earth stimulated-emission cross sections, low thermo-optical coefficients, ultraviolet transparency, etc.) and so are used as laser glasses. Recent developments of novel compositions for biomedical applications and as fast-ion conductors have also revived interest in the study of phosphate glass structures.

The structure/property relationships in simple phosphate glasses have not received nearly the attention paid to silicate and borate-based systems. This is partially due to the difficulty in preparing anhydrous compositions with more than 50-mol% P2O5. Ultraphosphate compositions (where the [O]/[P] ratio is less than 3) are highly reactive to ambient water. In addition because P2O5sublimes at about 300°C, ultraphosphate glasses have not been studied to the extent that metaphosphate ([O]/[P] = 3) and polyphosphate ([O]/[P] > 3) compositions have.
Transport in Quantum Dots: Observation of Atomlike Properties
Authors: Tarucha Seigo
Published: August 2016

Recent advances in nanofabrication technologies have enabled us to fabricate semiconductor quantum dots in which electrons are three-dimensionally confined. These quantum dots are often referred to as artificial atoms since their electronic properties—for example the ionization energy and discrete excitation spectrum—resemble those of real atoms. Electrons bound to a nucleus potential encounter sufficiently strong effects of quantum-mechanical confinement and mutual Coulomb interactions that they are well arranged in ordered states, and this leads to the arrangement of atoms in the periodic table. It is well known in atom physics that the threedimensional spherically symmetric potential around atoms gives rise to the shell structure 1s, 2s, 2p, 3s, 3p,…. The ionization energy has a large maximum for atomic numbers 2, 10, 18,…. Up to atomic number 23, these shells are filled sequentially. Hund's rule determines whether a spin-down or a spin-up electron is added. This article describes how closely we can approach the electronic properties of real atoms through the use of semiconductor quantum dots.

Both the effects of quantum confinement and Coulomb interaction become strong in quantum dots when the dot size is comparable to the electron wavelength and contains just a few electrons. The consequence of these factors on transport have only recently been studied in vertical-dot devices, which contain a dot located between source and drain contacts by means of heterostructure tunnel barriers because the few-electron regime is only accessible in the vertical-dot device. Studies include transport measurements through submicron resonant tunneling devices and submicron gated resonant-tunneling devices, and capacitance measurements on submicron double-barrier structures. However quantum-dot devices usually contain some disorder—for instance because of impurities or when the shape of the dot is irregular—which readily causes sample specific inhomogeneity in the electronic properties. Clean quantum dots, in the form of regular disks, have only recently been fabricated in a semiconductor heterostructure (Figure 1), and have been used to study the atomlike properties of artificial atoms.
Tissue Engineering of Bone by Osteoinductive Biomaterials
Authors: Ripamonti Ugo , Duneas Nicolaas
Published: August 2016

Recent advances in materials science and biotechnology have given birth to the new and exciting field of tissue engineering, in which the two normally disparate fields are merging into a profitable matrimony. In particular the use of biomaterials capable of initiating new bone formation via a process called osteoinduction is leading to quantum leaps for the tissue engineering of bone.

The classic work of Marshall R. Urist and A. Hari Reddi opened the field of osteoinductive biomaterials. Urist discovered that, upon implantation of devitalized, demineralized bone matrix in the muscle of experimental animals, new bone formation occurs within two weeks, a phenomenon he described as bone formation by induction. The tissue response elicited by implantation of demineralized bone matrix in muscle or under the skin includes activation and migration of undifferentiated mesenchymal cells by chemotaxis, anchoragedependent cell attachment to the matrix, mitosis and proliferation of mesenchymal cells, differentiation of cartilage, mineralization of the cartilage, vascular invasion of the cartilage, differentiation of osteoblasts and deposition of bone matrix, and finally mineralization of bone and differentiation of marrow in the newly developed ossicle.

The osteoinductive ability of the extracellular matrix of bone is abolished by the dissociative extraction of the demineralized matrix, but is recovered when the extracted component, itself inactive, is reconstituted with the inactive residue—mainly insoluble collagenous bone matrix. This important experiment showed that the osteoinductive signal resides in the solubilized component but needs to be reconstituted with an appropriate carrier to restore the osteoinductive activity. In this case, the carrier is the insoluble collagenous bone matrix—mainly crosslinked type I collagen.
Soft-Tissue Analogue Design and Tissue Engineering of Liver
Authors: Moghe Prabhas V.
Published: August 2016

Tissue engineering involves the application of physical and life sciences to develop functional substitutes for dysfunctional organs or tissue structures. From an engineering standpoint, tissues contain two basic components—the cells that are organized into proper units, and the material surrounding the cells, called the extracellular matrix (ECM). A third, frequently overlooked feature essential to the maintenance of the activity of the engineered tissue is the three-dimensional architecture of the cell-matrix composite.

A comprehensive review of the scope and impact of tissue engineering has previously appeared. Tissue-engineered devices have the potential to reduce the annual health-care cost related to tissue loss and end-stage organ failure to the order of $400 billion, eight million invasive surgical procedures, and 65 million hospital days. A common approach to engineer a functional tissue is to place cells derived from a healthy organ or tissue type (identical or similar to the dysfunctional tissue/organ) on or within matrices analogous to host-tissue ECM. These systems can then be enclosed in appropriate membranes that isolate cells from immune rejection following implantation or can be transplanted directly with the administration of drugs that prevent the immune rejection. Another application of these systems is for extracorporeal (outside the patient's body) device support of a dysfunctional organ. In either instance, the success of the engineered tissue depends critically on the interactions of cells with the tissue analogues. The objective of this article is to outline the simplest matrix-design parameters to control these interactions. While organs are comprised of very different tissue types, for the sake of simplicity, this article is primarily pertinent to the tissue engineering of one major organ, the liver. The choice of this tissue type is intended to serve as a comprehensive generalization of many different cell types since in the diversity and complexity of its activities, the liver has few parallels. The development of an artificial liver is also critically awaited, as in the United States alone, 35,000 people, including the many wait listed for the exorbitant liver organ transplants ($300,000), die each year of chronic liver disorders. In many other countries, liver disease is the second leading cause of death.
Growth-Factor Delivery in Tissue Engineering
Authors: Saltzman W. Mark
Published: August 2016

Soluble signaling proteins called growth factors execute critical functions during the formation of specialized tissues throughout the developing embryo. When growth factors are provided to adult animals, they often encourage regeneration or repair of organs damaged by disease or trauma: Basic fibroblast growth factor (bFGF) and transforming growth factor ß1 (TGF-ß1) encourage wound healing hematopoetic growth factors stimulate the production of blood cells, bone morphogenetic proteins (BMPs) induce bone formation, nerve growth factor (NGF) enhances the survival of degenerating cholinergic neurons, and angiogenic growth factors activate new blood-vessel growth. Our understanding of the role of growth factors in development and regeneration should continue to expand dramatically over the next decade, inasmuch as new molecules (and new activities for known molecules) are appearing at a rapid rate.

Protein growth factors may be useful in augmenting the new approaches for tissue engineering. Modern biotechnology permits the large-scale manufacture of highly purified proteins so that large quantities can be produced for use in humans. However proteins are often exceedingly difficult to administer, particularly if sustained levels are required. Most protein growth factors have short half-lives after intravenous injection, with their biological activity lasting only a few minutes in the circulation, so that injection must be repeated frequently to obtain sustained blood levels (Table I). Since these molecules are large, they penetrate tissue barriers, such as the capillary wall, very slowly. In addition, growth factors are extremely potent, often possessing biological activity at a number of tissue sites throughout the body. Therefore systemic administration can lead to toxicity. In view of these difficulties, new methods for growth-factor delivery are needed. The most promising new methods involve polymers, which can be engineered to provide precisely controlled, prolonged growth-factor delivery at a localized site.
Fresco to Oils
Authors: Taft W. Stanley
Published: August 2016

What we see when we look at a painting—the image and our belief in it—is the result of choices in painting media, physical components, and methods made by the painter prior to and during the painting process. To a great extent, the number of choices, the way they are made, and the sequence in which they are used are influenced by the environment of the artist. Availability of materials, training, common practice, the demand of imagery, scale, and placement of the completed painting all influence these choices. We certainly cannot discount skill and invention as contributing factors in the making of the object for they guide the use of materials, and when the artist is truly inspired, allow us to be transported into the life of the painting.
Cave Paintings: Structure and Analysis
Authors: Menu Michel
Published: August 2016

Prehistoric art is the oldest manifestation of the human desire to record the religion, myths, and spirituality of prehistoric people. The purpose of this article is by no means to propose an interpretation of this artistic expression but to carry out, within a multidisciplinary approach, research aimed at rediscovering the technical system by which the walls of the prehistoric caves were decorated.
Theory and Simulation of Polymers at Interfaces
Authors: Balazs Anna C.
Published: August 2016

The articles in this issue illustrate how various theoretical and computer models have been used to probe behavior of polymers at penetrable and impenetrable interfaces. Interest in polymer interfaces stems from the control interfaces commonly have over macroscopic properties—such as the strength or biocompatibility of the material. Consider the “alloying” or blending of existing polymers. This technique provides an inexpensive means of fabricating new materials that can display the desirable properties of the individual components. Most polymer pairs however are immiscible, and the mixture segregates into macroscopic domains separated by relatively weak interfaces. To enhance the structural integrity of the blend, copolymer “compatibilizers” are added to the mixture. These chains localize at the interface between the immiscible polymers, enhance the adhesion between the phase-separated regions, and thereby improve the mechanical properties of the blend.

On an impenetrable interface, polymer films or coatings are commonly used to modify the properties of the underlying substrate. For example the polymer layer can be utilized to tailor biocompatibility, wettability, or roughness of the surface. Polymers anchored to solid surfaces can also be used to control the interaction between these surfaces. Thus the tethered layer can promote the adhesion between dissimilar solids or prevent the aggregation of colloidal particles.
Adhesion and Friction of Thin Films
Authors: Baljon Arlette R.C. , Robbins Mark O.
Published: August 2016

Polymers are routinely placed between solid walls to provide lubrication or adhesion. Their function in these roles depends critically on the degree of dissipation within the polymer film and at the film/wall interface as the film shears or ruptures. Good lubrication is achieved by minimizing frictional dissipation while dissipation increases the strength of adhesive bonds.

Gent and Schultz suggested a direct link between frictional losses and the adhesive performance of polymers. This correspondence has been supported by recent experiments and by some of the molecular-dynamics simulations to be described. However we find that the correspondence breaks down when the molecular motion producing dissipation occurs at different locations during shear and rupture. In the following sections, we discuss the types of rate-dependent dissipation observed in thin films and the different factors that control whether dissipation occurs within the polymer or at the wall/film interface. The results suggest an origin for interesting memory effects observed in surface-force-apparatus (SFA) experiments on thin films and expose the atomic-scale processes that produce dissipation during internal rupture of a thin film.
How Do Copolymer Compatibilizers Really Work?
Authors: Milner Scott T.
Published: August 2016

Most pairs of chemically different homopolymers of any useful molecular weight are thermodynamically immiscible. This is because any tiny repulsive interaction per monomer, multiplied by the large number of monomers in a typical polymer, overwhelms entropy of mixing (of the order of kBT per molecule where kB is the Boltzmann constant and T the temperature). Nonetheless blends of immiscible pairs of homopolymers are industrially ubiquitous. Two broad categories of such materials are rubber-toughened plastics and stiffened elastomers. Both are fine dispersions of one polymer in another, with the desirable properties of the resulting material (e.g., stiffness-toughness balance) depending crucially on its composite structure and the mechanical contrast between the two components (e.g., difference in moduli).

Typically a fine dispersion, consisting of submicron particles, is necessary for good final properties. Also necessary is a strong interfacial bond between the particles and the matrix so that the resulting material does not fail at these interfaces. A typical volume fraction of the suspended component is perhaps 20–30%. Such polymer blends are prepared by two time-honored techniques (ancient, really, if one considers their antecedents in cookery): stirring and the use of polymeric surfactants—copolymers. The copolymers can be synthesized beforehand and added to a mixer where the components are stirred, but more often they are produced from the homopolymers during stirring by a grafting reaction, which somehow joins the two dissimilar homopolymers to form some sort of block copolymer.
Tailored Polymer Surfaces
Authors: Mayes Anne M. , Kumar Sanat K.
Published: August 2016

The control of surface chemistry and topography has great technological relevance for numerous applications of polymers in textiles, adhesives, coatings, packaging, membranes, and biomedical implants. Conventionally, chemical modification of polymer surfaces has been achieved through kinetically governed practices that allow little control over the final surface composition or morphology. These chemically generated surfaces are also prone to reconstruction. Hence the development of inexpensive, scaleable routes to impart stable and more complex chemical functionality to polymer surfaces continues to be an active area of research. Apart from surface chemistry, the topography of a polymer surface often plays a determinant role in the adhesive, optical, and wetting characteristics of the surface. Consequently methods to produce surfaces of controlled texture are also of interest. Toward these goals, new, statistical, mechanics-based theoretical approaches, coupled with increased computing power, can now facilitate the first-principles design of polymer surfaces that are chemically and structurally “tailored” for a given application. In this article, we review some of the recent, significant developments in this area.
Implantation and Dry Etching of Group-III-Nitride Semiconductors
Authors: Zolper J.C. , Shul R.J.
Published: August 2016

The recent advances in the material quality of the group-III-nitride semiconductors (GaN, A1N, and InN) have led to the demonstration of high-brightness light-emitting diodes, blue laser diodes, and high-frequency transistors, much of which is documented in this issue of MRS Bulletin. While further improvements in the material properties can be expected to enhance device operation, further device advances will also require improved processing technology. In this article, we review developments in two critical processing technologies for photonic and electronic devices: ion implantation and plasma etching. Ion implantation is a technology whereby impurity atoms are introduced into the semiconductor with precise control of concentration and profile. It is widely used in mature semiconductor materials systems such as silicon or gallium arsenide for selective area doping or isolation. Plasma etching is employed to define device features in the semiconductor material with controlled profiles and etch depths. Plasma etching is particularly necessary in the III-nitride materials systems due to the lack of suitable wet-etch chemistries, as will be discussed later.

Figure 1 shows a laser-diode structure (after Nakamura) where plasma etching is required to form the laser facets that ideally should be vertical with smooth surfaces. The first III-nitride-based laser diode was fabricated using reactive ion etching (RIE) to form the laser facets but suffered from rough mirror facet surfaces that contributed to scattering loss and a high lasing threshold. This is a prime example of how improved material quality alone will not yield optimum device performance.
GaN/AIGaN Heterostructure Devices: Photodetectors and Field-Effect Transistors
Authors: Shur Michael S. , Khan M. Asif
Published: August 2016

In this article, we review recent progress in GaN-based photodetectors and field-effect transistors (FETs), including optoelectronic FETs, and discuss materials parameters and fabrication technologies that determine the device characteristics of these two device families. Many types of visible-blind photodetectors and nearly all types of FETs have been demonstrated in GaN-based materials systems. However many challenges remain, both in improving the existing devices—the performance of which is still quite far from reaching its full potential—and in developing entirely new devices, which use unique properties of this wide-bandgap materials system.
Fundamentals of SiC-Based Device Processing
Authors: Melloch M.R. , Cooper J.A. , Larkin D.J.
Published: August 2016

Since the commercial availability of SiC substrates in 1990, SiC processing technology has advanced rapidly. There have been demonstrations of monolithic digital and analogue integrated circuits, complementary metal-oxide-semiconductor (CMOS) analog integrated circuits, nonvolatile random-access memories, self-aligned polysilicon-gate metal-oxide-semiconductor field-effect transistors (MOSFETs), and buried-channel polysilicon-gate charge-coupled devices (CCDs). In this article, we review processing technologies for SiC.

Oxidation

A beneficial feature of SiC processing technology is that SiC can be thermally oxidized to form SiO2. When a thermal oxide of thickness x is grown, 0.5x of the SiC surface is consumed, and the excess carbon leaves the sample as CO. Shown in Figure 1 are the oxide thicknesses as a function of time for the Si-face and the C-face of 6H-SiC, and for Si. The oxidation rates are considerably lower for SiC than for Si. The oxidation rate of the C-face of 6H-SiC is considerably greater than that of the Si-face. Hornetz et al. have shown that the reason for the slower oxidation rate of the Si-face is due to a 1-nm Si4C4−xO2 (x < 2) layer that forms between the SiC and the SiO2 during oxidation of the Si-face. When oxidizing the Si-face, the Si atoms oxidize first, which inhibits the oxidation of the underlying C atoms that are 0.063 nm below the Si atoms. When oxidizing the C-face, the C atoms readily oxidize first to form CO, with no formation of the Si4C4−xO2 layer for temperatures above 1000°C.
Links of science & Technology
Authors: Leamy Harry J. , Wernick Jack H.
Published: August 2016

We humans have employed and improved materials for millennia, but it required the Industrial Revolution of the last century to birth the systematic, science-based development of materials. During this time, effort expended in understanding the process-microstructure-properties relationships of materials conferred great economic and military advantage upon the successful. The introduction of machine power in this era created great leverage for improvements in the strength, ductility, corrosion resistance, formability, and similar properties of materials. Response to this opportunity led to the emergence of the materials profession. Stimulated by opportunity, materials scientists and engineers of the day met many of the challenges by first understanding and then controlling the composition and microstructure of materials. In the process, they defined the materials-engineering profession and left their names as a part of its vocabulary: Martens(ite), Bain(ite), Austen(ite), Schmid, Bessemer, Charpy, and Jomminy, to name a few. In fact the understanding and control of microstructure is the hallmark of materials science and engineering. Of course the ancient art of finding, mining, concentrating, and refining materials from the earth's crust does not apply to this definition since we wish to focus on the engineeringofmaterials.

Five decades ago, a new chapter in the evolution of this profession began by the invention of the transistor. This invention and the development of integrated circuitry that followed from it spawned a new era of materials achievement, again stimulated by the enormous economic and performance gains available. In this arena however, the object of the game was to completely eliminate microstructure while doing away with impurities, save for a desired few, to levels previously unimagined. Today a material thus prepared is a blank slate upon which we can write the microstructure of an integrated circuit.
Spontaneous Lateral Composition Modulation in III-V Semiconductor Alloys
Authors: Millunchick J. Mirecki , Twesten R.D. , Lee S.R. , Follstaedt D.M. , Jones E.D. , Ahrenkiel S.P. , Zhang Y. , Cheong H.M. , Mascarenhas A.
Published: August 2016

The application of III-V semiconductor alloys in device structures is of importance for high-speed microelectronics and optoelectronics. These alloys have allowed the device engineer to tailor material parameters such as the bandgap and carrier mobility to the need of the device by altering the alloy composition. When using ternary or quaternary materials, the device designer presumes that the alloy is completely disordered, without any correlation between the atoms on the cation (anion) sublattice. However the thermodynamics of the alloy system often produce material that has some degree of macroscopic or microscopic ordering. Short-range ordering occurs when atoms adopt correlated neighboring positions over distances of the order of a few lattice spacings. This can be manifested as the preferential association of like atoms, as in clustering, or of unlike atoms, as in chemical ordering (e.g., CuPt ordering). Long-range ordering occurs over many tens of lattice spacings, as in the case of phase separation. In either short-range or long-range ordering, the band structure and the crystal symmetry are greatly altered. Therefore it is absolutely critical that the mechanisms be fully understood to prevent ordering when necessary or to exploit it when possible.
Sputter-Deposited Low-Emissivity Coatings on Glass
Authors: Arbab Mehran
Published: August 2016

Low-emissivity (low-E) and solarcontrol coatings increase the energy efficiency of clear float soda-lime-silicate glass for architectural and automotive window applications. At the same time, coated glass largely maintains its neutral color and high visible transmittance. Two major classes of coated products are currently available for the architectural market: The more durable chemicalvapor- deposition (CVD) coatings are deposited on float glass as it is formed. The vacuum deposited low-E coatings, which are the subject of this article, have superior spectral performance and are deposited off-line by the sputter-deposition process. Many elements of this subjecthave been discussed in the literature, covering energy efficiency for windows, specific examples of low-E coating, a J2 6 brief outline of the deposition techniques, and a more detailed account of optical design considerations for low-E thin-film coatings, particularly for single metal-layer systems. This article briefly discusses aspects of these coatings that relate to their design, performance, and preparation. More attention is given to the materials that constitute the different layers of these coatings and to their specific properties and function.