Antiwindup design for induction motor control in the field weakening domain

Operation of induction machines in the high-speed and/or high-torque range requires field-weakening to comply with voltage and current physical limitations. This paper presents an anti-windup approach to this problem: rather than developing an ad-hoc field weakening strategy in the high-speed region, we equip an unconstrained vector-control design with an anti-windup module that automatically adjusts the current and flux set-points so that voltage and current constraints are satisfied at every operating point. The anti-windup module includes a feedforward modification of the set point aimed at maximizing the available torque in steady-state and a feedback modification of the controller based on an internal model-based antiwindup scheme. This paper includes a complete stability analysis of the proposed solution and presents encouraging experimental results on an industrial drive. © 2012 IEEE.

Introducing carbon diffusion barriers for uniform, high-quality graphene growth from solid sources.

Carbon diffusion barriers are introduced as a general and simple method to prevent premature carbon dissolution and thereby to significantly improve graphene formation from the catalytic transformation of solid carbon sources. A thin Al2O3 barrier inserted into an amorphous-C/Ni bilayer stack is demonstrated to enable growth of uniform monolayer graphene at 600 °C with domain sizes exceeding 50 μm, and an average Raman D/G ratio of <0.07. A detailed growth rationale is established via in situ measurements, relevant to solid-state growth of a wide range of layered materials, as well as layer-by-layer control in these systems.

Twin plane re-entrant mechanism for catalytic nanowire growth.

A twin-plane based nanowire growth mechanism is established using Au catalyzed Ge nanowire growth as a model system. Video-rate lattice-resolved environmental transmission electron microscopy shows a convex, V-shaped liquid catalyst-nanowire growth interface for a ⟨112⟩ growth direction that is composed of two Ge {111} planes that meet at a twin boundary. Unlike bulk crystals, the nanowire geometry allows steady-state growth with a single twin boundary at the nanowire center. We suggest that the nucleation barrier at the twin-plane re-entrant groove is effectively reduced by the line energy, and hence the twin acts as a preferential nucleation site that dictates the lateral step flow cycle which constitutes nanowire growth.

Co-catalytic absorption layers for controlled laser-induced chemical vapor deposition of carbon nanotubes.

The concept of co-catalytic layer structures for controlled laser-induced chemical vapor deposition of carbon nanotubes is established, in which a thin Ta support layer chemically aids the initial Fe catalyst reduction. This enables a significant reduction in laser power, preventing detrimental positive optical feedback and allowing improved growth control. Systematic study of experimental parameters combined with simple thermostatic modeling establishes general guidelines for the effective design of such catalyst/absorption layer combinations. Local growth of vertically aligned carbon nanotube forests directly on flexible polyimide substrates is demonstrated, opening up new routes for nanodevice design and fabrication.

Bioinformatic identification of genes encoding C1q-domain-containing proteins in zebrafish

C1q is the first subcomponent of classical pathway in the complement system and a major link between innate and acquired immunities. The globular (gC1q) domain similar with C1q was also found in many non-complement C1q-domain-containing (C1qDC) proteins which have similar crystal structure to that of the multifunctional tumor necrosis factor (TNF) ligand family, and also have diverse functions. In this study, we identified a total of 52 independent gene sequences encoding C1q-domain-containing proteins through comprehensive searches of zebrafish genome, cDNA and EST databases. In comparison to 31 orthologous genes in human and different numbers in other species, a significant selective pressure was suggested during vertebrate evolution. Domain organization of C1q-domain-containing (C1qDC) proteins mainly includes a leading signal peptide, a collagen-like region of variable length, and a C-terminal C1q domain. There are 11 highly conserved residues within the C1q domain, among which 2 are invariant within the zebrafish gene set. A more extensive database searches also revealed homologous C1qDC proteins in other vertebrates, invertebrates and even bacterium, but no homologous sequences for encoding C1qDC proteins were found in many species that have a more recent evolutionary history with zebrafish. Therefore, further studies on C1q-domain-containing genes among different species will help us understand evolutionary mechanism of innate and acquired immunities.

Unified form language: A domain-specific language for weak formulations of partial differential equations

We present the Unified Form Language (UFL), which is a domain-specific language for representing weak formulations of partial differential equations with a view to numerical approximation. Features of UFL include support for variational forms and functionals, automatic differentiation of forms and expressions, arbitrary function space hierarchies formultifield problems, general differential operators and flexible tensor algebra. With these features, UFL has been used to effortlessly express finite element methods for complex systems of partial differential equations in near-mathematical notation, resulting in compact, intuitive and readable programs. We present in this work the language and its construction. An implementation of UFL is freely available as an open-source software library. The library generates abstract syntax tree representations of variational problems, which are used by other software libraries to generate concrete low-level implementations. Some application examples are presented and libraries that support UFL are highlighted. © 2014 ACM.

High-frequency programmable acoustic wave device realized through ferroelectric domain engineering

Surface acoustic wave devices are extensively used in contemporary wireless communication devices. We used atomic force microscopy to form periodic macroscopic ferroelectric domains in sol-gel deposited lead zirconate titanate, where each ferroelectric domain is composed of many crystallites, each of which contains many microscopic ferroelastic domains. We examined the electro-acoustic characteristics of the apparatus and found a resonator behavior similar to that of an equivalent surface or bulk acoustic wave device. We show that the operational frequency of the device can be tailored by altering the periodicity of the engineered domains and demonstrate high-frequency filter behavior (>8GHz), allowing low-cost programmable high-frequency resonators. © 2014 AIP Publishing LLC.

Sparse recovery of complex phase-encoded velocity images using iterative thresholding

In this paper we propose a new algorithm for reconstructing phase-encoded velocity images of catalytic reactors from undersampled NMR acquisitions. Previous work on this application has employed total variation and nonlinear conjugate gradients which, although promising, yields unsatisfactory, unphysical visual results. Our approach leverages prior knowledge about the piecewise-smoothness of the phase map and physical constraints imposed by the system under study. We show how iteratively regularizing the real and imaginary parts of the acquired complex image separately in a shift-invariant wavelet domain works to produce a piecewise-smooth velocity map, in general. Using appropriately defined metrics we demonstrate higher fidelity to the ground truth and physical system constraints than previous methods for this specific application. © 2013 IEEE.

Molecular cloning and stress-induced expression of paralichthys olivaceus heme-regulated initiation factor 2 alpha kinase

The heme-regulated initiation factor 2 alpha kinase (HRI) is acknowledged to play an important role in translational shutoff in reticulocytes in response to various cellular stresses. In this study, we report its homologous cDNA cloning and characterization from cultured flounder embryonic cells (FEC) after treatment with UV-inactivated grass carp haemorrhagic virus (GCHV). The full-length cDNA of Paralichthys olivaceus HRI homologue (PoHRI) has 2391 bp and encodes a protein of 651 amino acids. The putative PoHRI protein exhibits high identity with all members of eIF2 alpha kinase family. It contains 12 catalytic subdomains located within the C-terminus of all Ser/Thr protein kinases, a unique kinase insertion of 136 amino acids between subdomains IV and V, and a relatively conserved N-terminal domain (NTD). Upon heat shock, virus infection or Poly PC treatment, PoHRI mRNA and protein are significantly upregulated in FEC cells but show different expression patterns in response to different stresses. In healthy flounders, PoHRI displays a wide tissue distribution at both the mRNA and protein levels. These results indicate that PoHRI is a ubiquitous eIF2a kinase and might play an important role in translational control over nonheme producing FEC cells under different stresses. (c) 2006 Elsevier Ltd. All rights reserved.

Identification of a novel C2 domain factor in ovaries of orange-spotted grouper (Epinephelus coioides)

Follicle consists of an oocyte and a lot of surrounding follicular cells, and significant interactions exist between the oocyte and the somatic cells. In this study, a novel cDNA has been screened from a subtractive cDNA library between tail bud embryos and blastula embryos in the protogynous hermaphrodite orange-spotted grouper (Epinephelus coioides). Its full-length cDNA is 821 bp, and has an ORF of 414 by for encoding a peptide of 137 aa, which shows 38%, 37%, 33%, and 33% homology with 4 putative proteins screened from zebrafish (Danio rerio). Conserved domain search in NCBI reveals a single C2 domain existing in the C2 domain superfamily proteins, and has only 7 beta strands in comparison with 8 beta strands of C2 domains in other C2 domain superfamily proteins. Artificial sex reversal, RT-PCR analysis and Western blot detection demonstrated ovary-specific expression of the C2 domain factor, and therefore the novel gene was designated as E. coioides ovary-specific C2 domain factor, EcOC2 factor. Moreover, predominant expression of EcOC2 factor was further revealed in grouper mature ovary, and its strong immunofluorescence signals were located between granulosa cells and oocyte zona radiata in grouper mature follicles. The data indicate that the novel EcOC2 factor might be a main component that associates between granulosa cells and the oocyte during oocyte maturation, and might play significant roles in regulating oocyte maturation and ovulation. Further studies on its developmental behaviour and physiological functions will elucidate the interactions between oocyte and the surrounding somatic cells and the underlying molecular mechanisms. (C) 2005 Elsevier Inc. All rights reserved.

Zebraflsh z-otu, a novel Otu and Tudor domain-containing gene, is expressed in early stages of oogenesis and embryogenesis

Several studies have suggested that Otu domain had de-ubiquitinating activity and Tudor domain was important for the formation of germ cells. Here, we reported a novel zebrafish ovary-specific gene containing Otu and Tudor domain, z-otu, which was expressed at stages I-III oocytes and embryonic stages from zygotes to early blastula during embryonic cells maintained their totipotency. Therefore, z-otu might link the ubiquitin signaling pathway to early oogenesis and maintaining the totipotency of embryonic cell. (c) 2005 Elsevier B.V. All rights reserved.

Wavelength Coded Optical Time-Domain Reflectometry

This paper presents a wavelength coded optical timedomain reflectometry based on optical heterodyne technique. In this scheme, the probe and reference optical pulses have different wavelengths. This enables optical heterodyne detection to be used to improve the system performances significantly. We demonstrate a spatial resolution of 2.5 m within a range of 60 km in weak-reflection signal detection and direct observation of Brillouin scattering over a long optical fiber, suggesting online fiber sensing possible. The principle of wavelength coding is applicable to other systems like lidar and radar to increase receiver sensitivity and simplify system structure.

Domain wall resistance in perpendicular (Ga,Mn) As: Dependence on pinning

We have investigated the domain wall resistance for two types of domain walls in a (Ga,Mn)As Hall bar with perpendicular magnetization. A sizeable positive intrinsic DWR is inferred for domain walls that are pinned at an etching step, which is quite consistent with earlier observations. However, much lower intrinsic domain wall resistance is obtained when domain walls are formed by pinning lines in unetched material. This indicates that the spin transport across a domain wall is strongly influenced by the nature of the pinning.

Parameters determining crystallinity in beta-SiC thin films prepared by catalytic chemical vapor deposition

The effects of deposition gas pressure and H-2 dilution ratio (H-2/SiH4+CH4+H-2), generally considered two of dominant parameters determining crystallinity in beta-SiC thin films prepared by catalytic chemical vapor deposition (Cat-CVD), often called hot-wire CVD method, on the films properties have been systematically studied. As deposition gas pressure increase from 40 to 1000 Pa, the crystallinity of the films is improved. From the study of H-2 dilution ratio, it is considered that H-2 plays a role as etching gas and modulating the phases in beta-SiC thin films. On the basis of the study on the parameters, nanocrystalline beta-SiC films were successfully synthesized on Si substrate at a low temperature of 300degreesC. The Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) spectra show formation of beta-SiC. Moreover, according to Sherrer equation, the average grain size of the films estimated is in nanometer-size. (C) 2003 Elsevier B.V. All rights reserved.

Analysis of modes in a freestanding microsquare resonator by 3-D finite-difference time-domain

Modes in a microsquare resonator slab with strong vertical waveguide consisting of air/semiconductor/air are analyzed by three-dimensional (3-D) finite-difference time-domain simulation, and compared with that of two-dimensional (2-D) simulation under effective index approximation. Mode frequencies and field distributions inside the resonator obtained by the 3-D simulation are in good agreement with those of the 2-D approximation. However, field distributions at the boundary of the resonator obtained by 3-D simulation are different from that of the 2-D simulation, especially the vertical field distribution near the boundary is great different from that of the slab waveguide, which is used in the effective index approximation. Furthermore the quality factors obtained by 3-D simulation are much larger. than that by 2-D simulation for the square resonator slab with the strong vertical waveguide.