bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-oriented Sb2Se3 nanoneedle photocathodes for water splitting obtained by a simple spin-coating method
Authors: Kim Jimin , Yang Wooseok , Oh Yunjung , Lee Hyungsoo , Lee Seonhee , Shin Hyunjung , Kim Joosun , Moon Jooho
Published: December 2016

Sb2Se3 nanoneedles for use as a photocathode for water splitting are fabricated by facile spin-coating. After sequential surface modification with n-TiO2 and Pt, a remarkable photocurrent of 2 mA cm−2 at 0 VRHE is realized.
Porous graphdiyne applied for sodium ion storage
Authors: Zhang Shengliang , He Jianjiang , Zheng Jie , Huang Changshui , Lv Qing , Wang Kun , Wang Ning , Lan Zhenggang
Published: December 2016

Porous graphdiyne, a novel carbon-based material, is comprised of sp- and sp2-hybridized carbon atoms and was applied to sodium ion storage.
Imaging of carotid artery inflammatory plaques with superparamagnetic nanoparticles and an external magnet collar
Authors: Shi Yimin , Gao Yongping , Zou Xiang , Chen Liang , Li Yongsheng
Published: December 2016

Stroke is one of the top three fatal diseases in human history.
Numerical‐based frequency domain controller design for stand‐alone brushless doubly fed induction generator power system
Authors: Sun Lei , Chen Yu , Peng Li , Kang Yong
Published: December 2016

Brushless doubly fed induction generator (BDFIG) shows high reliability in either grid‐connected or stand‐alone applications due to its brushless structure. However, the brushless structure results in a complicated electromagnetic feature. The BDFIG controller design is thus challenged. The recent controller design either ignores the usefully model information or requires the complicated feedforward terms. Besides, the bandwidth restriction exists if the dual‐loop control is applied. To overcome these problems, this study proposes a numerical‐based frequency domain design method and applies it to a CW‐current‐oriented stand‐alone BDFIG system with dual‐loop control. The control objects are developed as transfer function forms and derived from the complete BDFIG model. Then the PI controllers for inner current loops and outer voltage loop are designed step by step, and the previous design result is considered in the recent step. In this way, more model and controller information are considered, and the bandwidth limitation can be eliminated. The design steps are presented in this study. The results show that the good steady and dynamic performances of the voltage regulation can be obtained compared with the traditional methods, which is practically important for a stand‐alone BDFIG system.
ZVT high step‐up DC/DC converter with a novel passive snubber cell
Authors: Zhu Binxin , Ren Lulu , Wu Xi , Song Kun
Published: December 2016

A zero voltage turn‐off high step‐up DC/DC converter is presented. The conversion efficiency and power density are improved significantly by using a novel passive snubber cell, which only consists of two diodes and a snubber capacitor. The converter also provides high‐voltage conversion ratio as well as low‐voltage stress on switches and diodes, which make it suitable for some special industrial applications as electric‐vehicle, uninterruptible power supply system or photovoltaic power generation system. The topology, operation principles and performance characteristics are analysed in detail. Moreover, a maximum 800 W experimental prototype has been developed to validate the effectiveness of the theoretical analysis, and 96.2% efficiency has been achieved.
Improved power decoupling control strategy based on virtual synchronous generator
Authors: Li Bin , Zhou Lin , Yu Xirui , Zheng Chen , Liu Jinhong
Published: December 2016

Virtual synchronous generator (VSG) control scheme, which can be regarded as an extension of droop control, has received much attention from researchers as the introduction of rotational inertia to inverters. This study discusses an active and reactive power decoupling technique for VSGs in microgrid, as an important aspect of VSG. The traditional power decoupling mechanism is initially analysed. Subsequently, the properties of the line impedance at different voltage degrees are compared. Results indicate that the traditional power decoupling method is unsuitable for medium‐ and low‐voltage microgrids. Thus, an improved power decoupling method is proposed. By estimating the voltage at the point of common coupling and tracking their reference values, the output active and reactive power of inverters can perform dynamic decoupling. Furthermore, the stability of the new control structure and selection of relevant coefficients are analysed. The simulation and experimental results verify the enhanced decoupling strategy for VSGs.
Very high gain three‐phase indirect matrix converter with two Z‐source networks in its structure
Authors: Hakemi Amir , Monfared Mohammad
Published: December 2016

Nowadays, expansion of new energy sources and the necessity of integrating them with the utility grid require more advanced power electronic converters. Matrix converters (MCs) and indirect matrix converters (IMCs) are recent solutions, which offer direct AC‐to‐AC conversion without the need for bulky capacitors. The main drawback associated to these converters is the limited voltage conversion ratio to 86.6%. Recently, many researchers focused on combination of the conventional IMCs and recently proposed Z‐source (ZS) converters to attain higher voltage conversion ratios. The unique feature of the ZS converter is its ability to change the output voltage amplitude from zero to infinite, theoretically. Based on the previously proposed successful ZS converters, this study proposes a novel combination of two ZS networks with an IMC to achieve a very high voltage gain for practical application of integrating the renewable energy sources to the grid. Simulation results confirm the proper operation of the proposed combined converter topology.
Technical mitigation measures for sharks and rays in fisheries for tuna and tuna-like species: turning possibility into reality
Authors: Poisson François , Crespo Francisco Abascal , Ellis Jim R. , Chavance Pierre , Bach Pascal , Santos Miguel. N. , Séret Bernard , Korta Maria , Coelho Rui , Ariz Javier , Murua Hilario
Published: December 2016

Tuna fisheries have been identified as one of the major threats to populations of other marine vertebrates, including sea turtles, sharks, seabirds and marine mammals. The development of technical mitigation measures (MM) in fisheries is part of the code of conduct for responsible fisheries. An in-depth analysis of the available literature regarding bycatch mitigation in tuna fisheries with special reference to elasmobranchs was undertaken. Studies highlighting promising MMs were reviewed for four tuna fisheries (longline, purse seine, driftnets and gillnet, and rod and line – including recreational fisheries). The advantages and disadvantages of different MMs are discussed and assessed based on current scientific knowledge. Current management measures for sharks and rays in tuna Regional Fishery Management Organizations (t-RFMOs) are presented. A review of relevant studies examining at-vessel and postrelease mortality of elasmobranch bycatch is provided. This review aims to help fisheries managers identify pragmatic solutions to reduce mortality on pelagic elasmobranchs (and other higher vertebrates) whilst minimizing impacts on catches of target tuna species. Recent research efforts have identified several effective MMs that, if endorsed by t-RFMOs, could reduce elasmobranchs mortality rate in international tropical purse seine tuna fisheries. In the case of longline fisheries, the number of operational effective MMs is very limited. Fisheries deploying driftnets in pelagic ecosystems are suspected to have a high elasmobranchs bycatch and their discard survival is uncertain, but no effective MMs have been field validated for these fisheries. The precautionary bans of such gear by the EU and by some t-RFMOs seem therefore appropriate. Recreational tuna fisheries should be accompanied by science-based support to reduce potential negative impacts on shark populations. Priorities for research and management are identified and discussed.
Sex and breed affect plasma glucose, lactate, cortisol, meat quality but not muscle glycolytic potential of Dorper and Merino lambs
Authors: Stempa T. , Muchenje V. , Abrahams A. M. , Bradley G.
Published: December 2016

Response to pre-slaughter stress differs depending on animal-related factors such as sex and breed. The present study investigated breed and sex effects on plasma stress indicators, muscle glycolytic potential and the quality of meat from 8-month-old lambs of Dorper (n = 52) and Merino (n = 48) breeds. Blood samples were collected at exsanguination for the measurement of glucose, lactate and cortisol levels. Representative meat samples were collected from the Muscularis longissimus thoracis et lumborum for the measurement of glycogen, lactate, glycolytic potential levels, pH and colour coordinates. Results showed that the ewes had higher levels of plasma lactate, cortisol and meat pH than the rams, meaning that the ewes perceived the slaughter process to be more stressful compared with the rams. The Dorper also had higher levels of plasma lactate and lower meat lightness compared with the Merino breed. Significant sex and breed interactions on the meat pH45 min and colour coordinates were observed. Significant correlations were found among plasma cortisol, pH and colour. The results indicate that ewes and Dorper were more stressed than the rams and Merino breed respectively. In this study it can be concluded that the ewes and Dorper breed perceived the slaughter process to be more stressful compared with the rams and Merino breed.
Chiton phylogeny (Mollusca : Polyplacophora) and the placement of the enigmatic species Choriplax grayi (H. Adams & Angas)
Authors: Sigwart Julia D. , Stoeger Isabella , Knebelsberger Thomas , Schwabe Enrico
Published: December 2016

Shallow marine chitons (Mollusca : Polyplacophora : Chitonida) are widespread and well described from established morphoanatomical characters, yet key aspects of polyplacophoran phylogeny have remained unresolved. Several species, including Hemiarthrum setulosum Carpenter in Dall, 1876, and especially the rare and enigmatic Choriplax grayi (Adams & Angas, 1864), defy systematic placement. Choriplax is known from only a handful of specimens and its morphology is a mosaic of key taxonomic features from two different clades. Here, new molecular evidence provides robust support for its correct association with a third different clade: Choriplax is placed in the superfamily Mopalioidea. Hemiarthrum is included in Cryptoplacoidea, as predicted from morphological evidence. Our multigene analysis of standard nuclear and mitochondrial markers demonstrates that the topology of the order Chitonida is divided into four clades, which have also been recovered in previous studies: Mopalioidea is sister to Cryptoplacoidea, forming a clade Acanthochitonina. The family Callochitonidae is sister to Acanthochitonina. Chitonoidea is resolved as the earliest diverging group within Chitonida. Consideration of this unexpected result for Choriplax and our well-supported phylogeny has revealed differing patterns of shell reduction separating the two superfamilies within Acanthochitonina. As in many molluscs, shell reduction as well as the de novo development of key shell features has occurred using different mechanisms, in multiple lineages of chitons.
A distinct phoronid larva: morphological and molecular evidence
Authors: Temereva Elena N. , Neretina Tatiana V.
Published: December 2016

Phoronids can be a major component of benthic and planktonic marine communities. Currently, the phoronid world fauna includes ten recognised species, known from adults; however, at least 32 larval forms have been described or documented. This study examined the morphology and 18S rRNA and 28S rRNA genes of two phoronid larvae abundant in Vostok Bay, Sea of Japan. One type was identified as the larval stage of Phoronopsis harmeri, although some distinctive features of this larva differ from the typical description. The morphological and molecular characteristics of the other larva did not match those of described species. According to our morphological results, this second actinotroch larva belongs to the genus Phoronis, but differs morphologically and molecularly from all the known species in the genus, all of which are represented in GenBank for the markers employed here. Taken together, our data suggest that the second actinotroch larva belongs to an undescribed phoronid species. The adult form of this actinotroch has never been identified, but our data suggest a close relationship with Phoronis pallida. The existence of a putative new phoronid species is also confirmed by presence of competent phoronid larvae, which are found in different aquatic areas, have a unique set of morphological features, and whose belonging is still not established.
More on snails and islands: molecular systematics and taxonomic revision of Setobaudinia Iredale (Gastropoda : Camaenidae) from the Kimberley, Western Australia, with description of new taxa
Authors: Criscione Francesco , Köhler Frank
Published: December 2016

Setobaudinia Iredale, 1933 is a genus of camaenid land snails endemic to the Western Australian Kimberley. It comprises 20 currently recognised species, most of which occur within the north-western high precipitation zone between the Admiralty Gulf and Collier Bay and within less than 60 km distance from the coast. Exceptionally, two species are found on isolated limestone outcrops in the drier interior of the Victoria River District, Northern Territory. By studying the differentiation in shell and genital anatomy as well as in the mitochondrial markers 16S and COI, we revise the taxonomy of Setobaudinia and describe new taxa. The Northern Territory species S. victoriana Solem, 1985 is identified as a member of the genus Trachiopsis, which otherwise comprises species from the York Peninsula, Queensland. The species Damochlora spina Solem, 1985 is shown to be a member of the genus Setobaudinia. A new species from the eastern Kimberley has been identified as the sister group of Setobaudinia. It is placed in the new genus Kymatobaudinia for exhibiting morphological characteristics that differ from those of all other Setobaudinia species. In addition, we describe nine new species from coastal areas and islands off the cost throughout the south-west to north-west Kimberley: S. angustilabiata, sp. nov.; S. colmani, sp. nov.; S. incisa, sp. nov.; S. kessneri, sp. nov.; S. latilabiata, sp. nov.; S. longiflagellata, sp. nov.; S. malbyana, sp. nov.; S. minima, sp. nov.; S. plana, sp. nov. ZooBank Publication code: http://zoobank.org/References/3C953F1A-62E5-4CE5-9D5E-D8D5774B4059
An integrative morphological and molecular approach to identification of three Australian cucurbitaceous invasive weeds: Citrullus colocynthis, C. lanatus and Cucumis myriocarpus
Authors: Shaik Razia S. , Lepschi Brendan J. , Gopurenko David , Urwin Nigel A. R. , Burrows Geoffrey E. , Weston Leslie A.
Published: December 2016

Camel melon (Citrullus lanatus), colocynth (Citrullus colocynthis) and prickly paddy melon (Cucumis myriocarpus) are summer-growing invasive weeds distributed throughout Australia. We used DNA-sequence information from samples collected across Australia and morphological data from glasshouse-grown plants to determine diagnostic features of these species, and to determine the infraspecific identity of Australian Citrullus lanatus and Cucumis myriocarpus. All species possessed distinct genotypes and haplotypes at nuclear G3pdh and chloroplast ycf6–psbM gene regions and could be easily identified on the basis of molecular phylogenetic analysis. A combination of vegetative, floral, fruit and seed characters also allowed for species identification at all developmental stages. On the basis of our morphological and molecular analyses, Australian camel melon and prickly paddy melon populations were identified as Citrullus lanatus var. citroides and Cucumis myriocarpus subsp. myriocarpus respectively.
A ketogenic diet rescues hippocampal memory defects in a mouse model of Kabuki syndrome
Authors: Benjamin Joel S. , Pilarowski Genay O. , Carosso Giovanni A. , Zhang Li , Huso David. L. , Goff Loyal A. , Vernon Hilary J. , Hansen Kasper D. , Bjornsson Hans T.
Published: December 2016

Significance

Intellectual disability is a common clinical entity with few therapeutic options. Kabuki syndrome is a genetically determined cause of intellectual disability resulting from mutations in either of two components of the histone machinery, both of which play a role in chromatin opening. Previously, in a mouse model, we showed that agents that favor chromatin opening, such as the histone deacetylase inhibitors (HDACis), can rescue aspects of the phenotype. Here we demonstrate rescue of hippocampal memory defects and deficiency of adult neurogenesis in a mouse model of Kabuki syndrome by imposing a ketogenic diet, a strategy that raises the level of the ketone beta-hydroxybutyrate, an endogenous HDACi. This work suggests that dietary manipulation may be a feasible treatment for Kabuki syndrome.
Modifications to aLATE MERISTEM IDENTITY1gene are responsible for the major leaf shapes of Upland cotton (Gossypium hirsutumL.)
Authors: Andres Ryan J. , Coneva Viktoriya , Frank Margaret H. , Tuttle John R. , Samayoa Luis Fernando , Han Sang-Won , Kaur Baljinder , Zhu Linglong , Fang Hui , Bowman Daryl T. , Rojas-Pierce Marcela , Haigler Candace H. , Jones Don C. , Holland James B. , Chitwood Daniel H. , Kuraparthy Vasu
Published: December 2016

Significance

Leaves are the primary source of photoassimilate in crop plants. A precise understanding of the genetic architecture underlying leaf morphology is critical to engineering climate-resilient crop varieties. An ideal cotton cultivar would produce a lower canopy of broad,normalleaves before transitioning to an upper canopy of highly lobed,okraleaves. Here we show that the major leaf shapes of cotton are controlled by theokralocus, which encodes an HD-Zip transcription factorGossypium hirsutumLATE MERISTEM IDENTITY1-D1b(GhLMI1-D1b). Using gene silencing, we temporarily induced normal leaf formation inokra, thus validating the candidate gene and creating the leaf shape ideotype in cotton. This study, identifying a single locus responsible for cotton leaf shape, expands the genetic toolbox for breeders to produce superior cotton varieties.
Arabidopsis
B-BOX32 interacts with CONSTANS-LIKE3 to regulate flowering
Authors: Tripathi Prateek , Carvallo Marcela , Hamilton Elizabeth E. , Preuss Sasha , Kay Steve A.
Published: December 2016

Significance

Clock genes have been shown to be important in regulating many key agronomic traits. Therefore, identifying new players in this interconnected clock network will provide novel strategies toward developing new crop varieties. Our study identifies CONSTANS-LIKE 3 (COL3) as a critical protein-binding partner for B-BOX32 (BBX32) action in
Arabidopsis
. The discovery of the interaction with COL3 provides molecular clues as to how BBX32 exerts its effects on growth and yield. It also implicates COL3 as an integral protein-binding partner that can be used in combination with BBX32 for increased productivity. This regulatory pathway could be applied as an efficient strategy for genetic manipulation in crops for increased agricultural productivity.
Quantifying Elements in Arctic Grayling and Bull Trout in the South Nahanni River Watershed, Northwest Territories, Using Nonlethal Tissue Samples
Authors: Anderson Julie , Scrimgeour Garry , Palace Vince , Suitor Michael , Wilcockson John
Published: December 2016

Monitoring of contaminants in fish generally involves lethal sampling, but public scrutiny and increased pressure on fisheries have driven the need to develop nonlethal sampling methods. We examined the ability of adipose, anal, and caudal fin tissues to serve as nonlethal surrogates for lethal muscle tissue samples in the analysis of metals (elements). First, we evaluated the use of biopsies by examining relationships between concentrations of 39 elements in low-volume dorsal muscle biopsies and high-volume muscle samples from Arctic Grayling Thymallus arcticus and Bull Trout Salvelinus confluentus collected in the South Nahanni River watershed, Northwest Territories, Canada. Low-volume dorsal biopsy samples in this study served to most closely model the concentrations of elements found in high-volume dorsal samples; caudal and anal fins were more representative of high-volume dorsal samples than were adipose fins. Regressions between high- and low-volume dorsal muscle samples were significant for 12 elements/species, with Cs, Rb, and Tl having the strongest relationships in both species. Regression analyses comparing low-volume muscle samples and fin samples revealed variation between Arctic Grayling and Bull Trout, but Co, Hg, and Tl concentrations among samples were strongly related for both species. Addition of fish length or age as a covariate did not greatly improve the predictive power of calculated regressions. For future monitoring, selection of a nonlethal sampling strategy (e.g., use of dorsal biopsy or adipose fin samples) will require consideration of the element of interest, the primary route of exposure, interaction with other elements, and the basic biology and ecology of the fish species. Ideally, nonlethal sampling tools can be further developed for the two species to promote inclusion of community partners; these tools offer sustainable, long-term approaches for monitoring sensitive fish populations in northern Canadian habitats.

Received February 29, 2016; accepted September 9, 2016Published online December 20, 2016
Sexual mimicry
Authors: Johnson Steven D. , Schiestl Florian P.
Published: December 2016

Sexual mimicry involves extensive floral modifications, particularly the evolution of highly specialized volatile signals to attract male insects. The study of sexual mimicry in plants has given new insights into insect reproductive biology and provides some of the best examples of pollinator-mediated plant speciation. This chapter reviews the occurrence of sexual mimics among plants and the most commonly recruited groups of pollinators. It shows which signals are the most important and how they evolve. Next, the evidence is reviewed for pollinator shifts and how they may drive speciation in this highly specific pollination system. It also discusses how the typically low genetic differentiation between species of sexual mimics can be interpreted. Finally, the factors that drive the evolution of sexual mimicry in different plant lineages are considered.
Elastic Behavior of Solids
Authors: Ketterson J. B.
Published: December 2016

This chapter analyzes the response of solids to stress. The defining property of a solid is its ability to resist shape changes in the presence of external stresses. Stress, defined as force per unit area, can be divided into two classes: compression and shear. The remainder of the chapter derives expressions for the following: stress tensor, strain tensor, Hooke’s law, energy density, elastic module of cubic and hexagonal systems, distortions of a cubic crystal, elastic waves, elastic waves in a cubic crystal, isotropic media, viscosity in solids, and the measurement of elastic constants of materials. Sample problems are also provided at the end of the chapter.
Electric Behavior of Insulators
Authors: Ketterson J. B.
Published: December 2016

Maxwell’s theory of electromagnetism in free space involves two fields: the electric field, E, and the magnetic field, M. When material media are present two more fields are introduced: the electric displacement, D, and the magnetic induction, B, for a total of four, all of which are position dependent in general. E and D are related through a third field, the polarization field, P, according to D = E + 4πP in c.g.s. units. P arises from a distribution of microscopic electric dipoles within the material. This chapter focuses on electric behaviours associated with the two fields. It discusses the potential from a distribution of dipoles; the local electric field; the dielectric constant; orientational polarization; and dielectric relaxation. Sample problems are also provided at the end of the chapter.
Metals and the Drude–Lorentz Model
Authors: Ketterson J. B.
Published: December 2016

In its more modern context, the Drude–Lorentz model views a material as consisting of an array of the following: fixed positive ions and free electrons; or neutral atoms, or balanced positive and negative ions atoms (as in NaCl), with no free electrons. The first case involves a metal while the second involves an insulator. This chapter derives expressions for the following: electrical conductivity and electrical resistivity of metals at room temperature; the Hall effect; frequency-dependent conductivity; dielectric constant of a metal; dielectric constant of an insulator, a metal in a constant magnetic field and an oscillatory electric field; thermal conductivity of a metal; and thermoelectric effect. The chapter also includes some sample problems.
Elementary Theories of the Thermal Properties of Solids
Authors: Ketterson J. B.
Published: December 2016

This chapter discusses the thermal properties of solids. A fundamental thermodynamic property of a body is its heat capacity, C ≡ dQ/dT, where dQ is an increment of heat transferred to the body and dT is the associated temperature change. When measured at constant volume (where no work is done by the sample on its environment), the heat added goes directly into increasing the internal energy, E. The internal energy is computed using the methods of statistical physics; which is briefly summarized. The remainder of the chapter analyzes the equipartition law for free and bound particles; the lattice heat capacity at low temperatures or the Einstein model; and the Debye model. Sample problems are also provided at the end of the chapter.
Elementary Theories of Magnetism
Authors: Ketterson J. B.
Published: December 2016

This chapter discusses the magnetic properties of matter. All materials are either diamagnetic or paramagnetic; hence diamagnetic materials tend to exclude flux while paramagnetic materials tend to gather flux. Superconductors and (soft) ferromagnets are extreme limits of these behaviors. The presence of a non-zero susceptibility depends ultimately on quantum effects — strictly classical systems cannot be magnetic, although a semi-classical theory works well for many situations. The chapter first analyzes the semi-classical theories of diamagnetism (Langevin diamagnetism) and paramagnetism (Langevin paramagnetism). It then covers the quantum theory of magnetism; quantum theory of non-interacting spins; adiabatic demagnetization; chemical bonding, Hund’s rules and magnetic ions; and magnetic moments of 4f and 3d ions. Sample problems are also provided at the end of the chapter.
Elementary Theories of Crystal Bonding
Authors: Ketterson J. B.
Published: December 2016

This chapter discusses several highly simplified models that have been used historically to discuss crystal bonding. It is customary to divide materials into categories according to the qualitative nature of the chemical or physical bonding existing among the atoms. The ‘dividing line’ between these categories is not always sharp. For instance bonding in transition metals, such as tungsten, may be thought of as both metallic and covalent. The remainder of the chapter discusses simple models of the van der Waals bond, ionic bond, covalent bond, and metallic bond. The chapter also includes some sample problems.
X-ray Diffraction
Authors: Ketterson J. B.
Published: December 2016

This chapter analyzes the diffraction of X-rays from crystals. The wavelengths of X-rays can be of the same order as the interatomic spacings in crystals. In optics we are familiar with the fact that a collection of equally spaced lines (a line grating) scatters (or diffracts) light at discrete angles relative to an incoming beam, when the wavelength becomes smaller than the line spacing. This suggests that a similar phenomenon will occur with crystal lattices; i.e., crystal lattices can function as three-dimensional diffraction gratings. The utility of X-ray diffraction is based on the direction and intensity of the scattered waves. We can obtain information about the atomic positions within the unit cell of a crystal and the distribution of the electron charge density. The chapter also discusses Bragg’s law; Laue equations; the reciprocal lattice; the Ewald construction; the Brillouin zone; the geometrical structure factor; the atomic scattering factor; the Debye–Waller factor; sources of X-rays; and experimental methods to study X-ray diffraction. The chapter finishes with some problems.
Electrons in a Periodic Solid
Authors: Ketterson J. B.
Published: December 2016

The model of a metal (Chapter 6), in which the mutual interaction between the conduction electrons and their interactions with atomic core electrons and the nucleus was neglected, provided an understanding of some properties associated with the Pauli principle and quantum degeneracy. However, a host of other solid-state properties cannot be understood with such a simple model. For example, such a model tells us nothing about the origin of the differences between metals and insulators or the cohesive energy (which is responsible for binding the atoms into a solid in the first place). The free electron model of solids can be improved by assuming that the interaction of the conduction electrons of the material with other conduction electrons and the atomic cores together with the nuclei can be ‘averaged over’ and approximated by a so-called one-body or one-electron potential energy, V(r). In doing this, direct electron–electron interactions, as well as the effects of the quantum mechanical exchange among electrons is replaced with an approximate, model-dependent interaction. This chapter begins with an analysis of V(r). It then discusses the general form of the eigenfunctions of an electron in a periodic solid; important properties that are associated with the Bloch periodicity condition and the resulting form of the crystal wave functions; dispersion near a band edge; electrons and holes; Brillouin zones; Wannier functions; and the Kronig–Penny model. Sample problems are also provided at the end of the chapter.
The Nearly Free Electron, OPW, Pseudopotential, and Tight Binding Methods
Authors: Ketterson J. B.
Published: December 2016

This chapter discusses the techniques used to calculate the wave functions and energy levels of Bloch electrons propagating in periodic solids, starting with the nearly-free electron (NFE) approximation. It assumes that the periodic potential is rapidly convergent and then truncates the expansion after a few terms. It also assumes that the coefficients retained are small relative to characteristic energies of interest. This nearly-free electron model is rather successful in describing properties of the so-called simple metals, those in which the valence states of the atoms involve only s and p electrons such as Mg or Al. The remainder of the chapter deals with the more powerful orthogonalized plane wave (OPW) method, the pseudo-potential method, and the tight binding or linear combination of atomic orbital (LCAO) method. Sample problems are also provided at the end of the chapter.
The Self-consistent Dielectric Function
Authors: Ketterson J. B.
Published: December 2016

This chapter develops an approach that includes electron–electron interaction, which is analogous to what one does in electromagnetic theory where the effects of the environment are incorporated through a dielectric function (or in the homogeneous static limit, a dielectric constant). It discusses the model of an interacting electron liquid. In order to preserve charge neutrality it is assumed that there is a compensating, uniform, non-deformable, positive background. The first deals with the self-consistent potential method for a uniform electron system. The second section presents applications of the dielectric function formalism, covering static screening, plasma oscillations, zero sound, and the Kohn effect. An appendix extends the periodicity associated with a crystalline solid to cover the periodic case. Sample problems are also provided at the end of the chapter.
Hartree–Fock and Density Functional Theory
Authors: Ketterson J. B.
Published: December 2016

This chapter continues the analysis initiated in Chapter 14 of the effects resulting from the mutual Coulomb repulsion between electrons, by discussing the Hartree and the Hartree–Fock theories. It has been noted previously that the true wave function of electron systems must depend on the coordinates of all the electrons. In the self-consistent field model we can approximate the many-electron wave function as a product of single-particle wave functions, each depending on the coordinate of a single electron, as pioneered by Hartree for atoms; such one-particle states are called orbitals. The exclusion principle is then incorporated by allowing a maximum of one electron per orbital. The effects of the other electrons are incorporated in this model through an effective potential formed by averaging over their positions. In an atom or molecule we can further demand that the total wave function be formed from combinations of products of one-electron orbitals in such a way that it is antisymmetric when interchanging any two electrons, as is done in the Hartree–Fock theory. The chapter concludes with some questions.
Harmonic Lattice Dynamics: Classical and Quantum
Authors: Ketterson J. B.
Published: December 2016

Chapter 4 presented some simple and historically important models of the vibrational response of atoms in solids from which thermal properties of the lattice could be approximately calculated. This chapter presents some more rigorous treatments. It starts with the traditional approach, which assumes the existence of a potential energy function that depends on the displacements of all the nuclei from their equilibrium positions within the unit cells. With the availability of this function, the force acting on individual atoms can be calculated, from which the response of the lattice can be calculated using Newton’s law. The chapter analyses the following: the 1d lattice; the 1d lattice with more than one atom per unit cell; representing the lattice potential in 3d; classical theory of the harmonic lattice in 3d; the quantization of lattice vibrations; inelastic neutron scattering; Raman scattering; and phonon dispersion relations from supercell total energy calculations. Sample problems are also provided at the end of the chapter.
Thermal Expansion, Phonon–Phonon Interactions, and Heat Transport
Authors: Ketterson J. B.
Published: December 2016

The discussion of Chapter 16, although presenting a general strategy for treating lattice dynamics, was limited in its application to the harmonic approximation. This chapter treats a number of applications where the effects of anharmonicity enter. In the same way that collisions among molecules are essential for establishing thermal equilibrium in a gas, so interactions among lattice vibrations are required to equilibrate the mechanical excitations in solids; these interactions arise from the anharmonic terms in the expansion of the lattice potential. In addition to driving the system toward equilibrium, anharmonicity also results in thermal expansion, a linear term in the high-temperature specific heat, and finite thermal conductivity. It is shown here that both the cubic and quartic terms must be included in discussing some of these phenomena. The treatment here is limited to insulators.
Motion of Electrons and Holes in External Electric and Magnetic Fields
Authors: Ketterson J. B.
Published: December 2016

This chapter discusses the dynamics of electrons and holes in conducting solids in the presence of electric and magnetic fields. Topics covered include incorporating external electromagnetic fields; the effect of external magnetic and electric fields on Bloch functions; quasiclassical equation of motion; orbits in a magnetic field; orbit-quantization in a magnetic field; and magnetic breakdown. The chapter concludes with a detailed treatment of Zener breakdown. In treating electrical transport properties we usually assume that in the presence of an electric field, E, scattering from impurities constrains the electron distribution function to deviate only slightly from its equilibrium form, i.e., the electron wave vectors obey a Boltzmann distribution in a semiconductor and lie close to the Fermi surface in a metal. However, in very strong fields electrons can be very far from equilibrium and even tunnel between adjacent energy bands, particularly when there is another state nearby in k-space which is separated by only a small energy barrier. This latter effect is called Zener breakdown. Sample problems are also provided at the end of the chapter.
Electronic Transport Properties Governed by Static Scattering Centers
Authors: Ketterson J. B.
Published: December 2016

There are several mechanisms by which electrons in a crystal lattice may be scattered from one Bloch state to another. Among these are electron–impurity, electron–phonon, and electron–electron scattering. This chapter focuses on electron–impurity scattering. It deals with point defects which are rigidly bound to the rest of the lattice and which have no internal electronic modes that can be excited at low temperatures. In this case the scattering of a conduction electron will be elastic, i.e., there will be no energy exchange between a scattered conduction electron and the scattering centre, only a change in its wave vector, k (the magnitude of which can change if the Fermi surface is anisotropic). Topics discussed include the semi-classical description of the transport of electrical and thermal currents in metals; the Boltzmann equation; electrical conductivity; transport in the presence of electric fields and temperature gradients; thermal conductivity; thermoelectric effects; calculating thermoelectric coefficients; magnetoresistance and the Hall effect; a two-band model to obtain a finite magnetoresistance; calculation of the relaxation time; a technique for solving the Boltzmann equation in the presence of time-dependent external fields; and collective excitations. Sample problems are also provided at the end of the chapter.
The Interacting System of Metallic Electrons and Phonons
Authors: Ketterson J. B.
Published: December 2016

The previous chapters considered the electronic excitations and the lattice vibrations (phonons) of a solid as arising separately. This chapter discusses their mutual interaction. Lattice vibrations arise from the combined effects of electron–electron, ion–ion, and electron–ion Coulomb interactions. Using a simple model, based on a dielectric function approach that treats the positive ions classically, two collective oscillations emerge: longitudinal phonons and electron plasma oscillations. The model can be used to construct a quantum mechanical form for electron–phonon interaction. One result of this interaction is that zero–point phonons have an important effect on the energy and lifetime of electrons near the Fermi surface. The chapter concludes with a more formal quantum mechanical discussion, of the electron–phonon interaction, including the effect of thermally excited phonons on the electrical resistance. Sample problems are also provided at the end of the chapter.
Ferromagnetism and Antiferromagnetism
Authors: Ketterson J. B.
Published: December 2016

The vast majority of materials are either paramagnetic or diamagnetic, and have no magnetic moment in the absence of an external magnetic field. However, a small set of materials can have a spontaneous magnetic structure (i.e., in the absence of an external magnetic field). The two most well known magnetic states pertain to ferromagnets and antiferromagnets, which are the focus of this chapter. It begins with a survey of magnetic properties. The discussions then turn to the density functional theory of band magnetism; the gradient energy; surface tension of a domain wall; ferromagnetic domains; total magnetic free energy of a body; single domain particles; the magnetization curve of an easy-axis uniaxial ferromagnet; and measuring the magnetization. Sample problems are also provided at the end of the chapter.
Dynamic Properties of Magnetic Materials
Authors: Ketterson J. B.
Published: December 2016

Chapter 26 focused on the static and thermodynamic properties of magnetic materials. This chapter extends the discussion to include dynamic, finite frequency, responses generated by external microwave fields. It also treats the Bose spin wave excitations which are excited thermally and contribute to the heat capacity. It begins by examining the Landau–Lifshitz equation, which governs the dynamics of spontaneously magnetized materials at the macroscopic level. The remainder of the chapter derives equations for the following: ferromagnetic resonance, magnetic relaxation, spin wave resonance, antiferromagnetic resonance, thermodynamic properties, the microscopic theory of magnons, and micromagnetics. Sample problems are also provided at the end of the chapter.
Magnetic Resonance28
Authors: Ketterson J. B.
Published: December 2016

Magnetic resonance experiments involving both electrons and nuclei play a major role in solid-state physics. Electrons from uncompensated spins, particularly those involving d and f electrons, provide a powerful probe of local fields within a crystal. Atomic nuclei play a similar role. In metals they probe the overlap of the conduction electron wave function on the nuclei and in superconductors they can be used as a probe of the energy gap. This chapter begins with a discussion of electron spin resonance (ESR) and nuclear magnetic resonance (NMR). It then analyzes relaxation effects, spin echoes, quadrupole resonance, the quantum mechanical expression for energy dissipation, and chemical and Knight shifts, dipolar broadening, and a microscopic theory of spin–lattice relaxation.
A Phenomenological Theory of Superconductivity: The London Equations
Authors: Ketterson J. B.
Published: December 2016

This chapter focuses on superconductors. Many metals, alloys, and intermetallic compounds undergo a phase transition at some (generally low) temperature to a state having zero electrical resistance, a phenomenon which is called superconductivity. Another fundamental characteristic associated with a superconductor is the exclusion of magnetic flux. The combination of zero resistance and perfect diamagnetism results in a clear distinction between a superconductor (in a thermodynamic state) and a hypothetical perfect conductor (which has the unique transport property of zero resistance). The chapter then presents two derivations of equations which are useful in describing many of the magnetic properties of superconductors. This is followed by discussions of the thermodynamics of a type I superconductor, surface energy between a normal and a superconducting metal, quantized vorticity, type II superconductivity, and superconducting magnets.
The Microscopic Theory of Superconductivity: Cooper Pairing and the Bardeen–Cooper–Schrieffer Theory
Authors: Ketterson J. B.
Published: December 2016

One of the important steps leading to the successful formulation of the microscopic theory of superconductivity was the model calculation performed by Cooper (1956) which showed that two electrons, interacting above a filled Fermi sea, had a bound state in the presence of an arbitrarily weak attractive interaction. This chapter first examines Cooper’s calculation. The success of the Cooper model calculation in producing a bound state, with its implication that a proper many-body theory would contain a gap in the excitation spectrum, strongly suggests that the ground state wave function should be constructed from pairs of electrons. However, it is difficult to perform calculations using the many-body pair wave function from Cooper’s model. The chapter then introduces the wave function proposed by Bardeen, Cooper, and Schrieffer (BCS) as an alternative.
Elementary Excitations and the Thermodynamic Properties of Superconductors
Authors: Ketterson J. B.
Published: December 2016

To treat the properties of a superconductor at finite temperatures we need to develop techniques to describe excitations from the Bardeen, Cooper, and Schrieffer (BCS) ground state. The most powerful approach is through a transformation of the creation and destruction operators that were introduced independently by Bogoliubov and Valatin. This chapter first discusses the Bogoliubov–Valatin transformation. It then rewrites the reduced Hamiltonian of the system in terms of the Bogoliubov quasiparticle operators. In doing so, it generates two types of terms: those containing products of an equal number of creation and destruction operators and those containing an unequal number. The chapter also defines a quantity called the anomalous pair amplitude as the expectation value of the operator.
Landau’s Theory of a Fermi Liquid
Authors: Ketterson J. B.
Published: December 2016

This chapter analyses Landau’s Fermi liquid theory. A fundamental postulate of Landau’s Fermi liquid theory is that quasiparticle energies are a function of the momentum, p, and that the momentum, pF, corresponding to the Fermi energy continues to be given by a free particle expression. Thus, the quasiparticle states are in one-to-one correspondence with those of an ideal Fermi gas and each quasiparticle has a spin quantum number, σ ± 1/2. The remainder of the chapter deals with the quasiparticle interaction function; sum rules; and collisionless collective modes, which are defined as a collective mode as a time- (or frequency) and space- (or wave vector) dependent oscillation of the fluid involving a coordinated motion of its constituent particles. Sample problems are also provided at the end of the chapter.
Superfluid3He
Authors: Ketterson J. B.
Published: December 2016

Since liquid 3He (liquid helium isotope) is a Fermi liquid, it is natural to expect that at some temperature it might become a superfluid. As first observed by Osheroff, Richardson, and Lee, this indeed happens at temperatures between approximately 1 × 10−3 K and 3 × 10−3 K, depending on the pressure. The phase diagram in the P–T plane shows that at zero magnetic field there are two different superfluid phases, referred to as the A phase and B phase. The first of these occurs in a narrow wedge in P–T space at higher temperatures and near the melting curve; the latter exists over a broader region. This chapter begins by discussing the generalized order parameter of an isotropic superfluid. It then covers the rotation properties of the order parameter; the phenomenological theory of the superfluid transition in 3He; and the anisotropy of the energy gap.
Alloys
Authors: Ketterson J. B.
Published: December 2016

Metallurgy is basically about mixtures involving at least one metal and, through composition and processing, strategies to achieve better properties for various applications. Forming mixtures of two or more elements can enhance the advantageous properties of solids. Such a mixture is termed an alloy. Such properties include improved hardness or ductility, which involve suppressing or enhancing permanent deformations under the influence of external stresses. This chapter begins by discussing phase equilibrium, covering the Gibbs phase rule, binary mixtures, the chemical potential of a dilute alloy, characteristic binary phase diagrams, and examples of phase diagrams. The discussions then turn to order–disorder transitions, the isolated charged impurity, and the electronic structure of alloys. A sample problem is also provided at the end of the chapter.