bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Properties and Microstructure of Mg∕SiC Nanocomposites Fabricated by Ultrasonic Cavitation Based Nanomanufacturing
Authors: Cao Guoping , Konishi Hiromi , Li Xiaochun
Published: June 2008

Magnesium, the lightest structural metal, is of significance to improve energy efficiency in various applications. Mg∕SiC nanocomposites were successfully fabricated by ultrasonic cavitation based dispersion of SiC nanoparticles in Mg melts. As compared to pure magnesium, the mechanical properties including tensile strength and yield strength of the Mg∕SiC nanocomposites were improved significantly, while the good ductility of pure Mg was retained. The grain size of the pure magnesium was refined significantly when SiC nanoparticles were dispersed in the Mg matrix. In the microstructure of Mg∕SiC nanocomposites, while there were still some SiC microclusters, most of the SiC nanoparticles were dispersed very well. Transmission electron microscopy study of the interface between SiC nanoparticles and magnesium matrix indicates that SiC nanoparticles bond well with Mg without forming an intermediate phase.
An Efficient, Accurate Approach to Representing Cutter-Swept Envelopes and Its Applications to Three-Axis Virtual Milling of Sculptured Surfaces
Authors: Chen Zezhong C. , Cai Wei
Published: June 2008

To address a major technical challenge in simulating geometric models of machined sculptured surfaces in three-axis virtual machining, this paper presents an efficient, accurate approach to representing the 3D envelopes of a cutter sweeping sequentially through cutter locations; these envelopes embody the furrow patches of the machined surfaces. In our research, the basic mechanism of removing stock material in three-axis computer numerically controlled (CNC) milling of sculptured surfaces is investigated, and, consequently, an effective model is proposed to represent the 3D envelopes (or furrow patches). Our main contribution is that a new directrix (or swept profile) of the furrow patches (mathematically, ruled surfaces) is identified as a simple 2D envelope of cutting circles and is formulated with a closed-form equation. Therefore, the 3D cutter-swept envelopes can be represented more accurately and quickly than the existing swept-volume methods. With this innovative approach, a method of accurate prediction of the machining errors along tool paths in three-axis finish machining is provided, which is then applied to the optimization of tool-path discretization in two examples. Their results demonstrate the advantages of our approach and verify that the current machining-error-prediction methods can cause gouging in three-axis sculptured surface milling.
Three Dimensional Analysis of High Frequency Induction Welding of Steel Pipes With Impeder
Authors: Kim Hyun-Jung , Youn Sung-Kie
Published: June 2008

High frequency induction welding is widely employed for longitudinal seam welding of small scale tubes and pipes due to its relatively high processing speed and efficiency. This research is aimed at understanding the variables that affect the quality of the high frequency induction welding. The welding variables include the welding frequency, weld speed, vee angle, and tube thickness. Temperature distribution of the tube is calculated through three dimensional coupled electromagnetic and thermal finite element analysis. The skin and proximity effects are considered in the electromagnetic analysis. The influence of the impeder is also analyzed. The effects of the operating welding variables on the temperature distribution are investigated quantitatively by exhibiting the heat affected zone. The results explain the mechanism of significant enhancement of welding efficiency when the impeder is used. Not only good weld state can be obtained but also overheated edge can be avoided by understating the effect of welding variables. Suggestions are made for the better induction welding conditions.
Estimating Distributions of Surface Parameters for Classification Purposes
Authors: Zhang Min , Levina Elizaveta , Djurdjanovic Dragan , Ni Jun
Published: June 2008

The classification of workpiece surface patterns is an essential element in trying to understand how functional performance is influenced by the surface geometry. Filter banks have been investigated in literature for capturing the multiscale characterization of the engineering surfaces. Conventionally, parametric representations of the filter outputs were used for classification. In this paper, the histogram estimators of the filter bank outputs from engineering surfaces in combination with the nearest neighbor method for classification are investigated to improve the classification accuracy, which are accomplished by utilizing distribution dissimilarity measures to compare histograms. Furthermore, for large and complex surfaces, the histogram estimators of local surface flatness parameters are also proposed for the purpose of simple computation. Two case studies have been conducted to demonstrate the proposed methods. Influence of the histogram bins for histograms and the dissimilarity measures on classification performance is studied in detail. Results from the first case study show that the proposed method is less effective in classifying small surfaces with clear surface patterns, because the filtering is influenced by the quality of the surface data collected from the measurement sensor. In comparison, results from the second case study show that the proposed method performs better in classifying large surfaces with mild surface pattern differences. The classification accuracy using the conventional method drops from 100% to around 50% in the second case study. In general, one can achieve misclassification errors below 5% in both case studies with the histogram representations of surface parameters and the appropriate selection of the number of bins for histogram construction.
Effects of Crystallographic Anistropy on Orthogonal Micromachining of Single-Crystal Aluminum
Authors: Lawson Benjamin L. , Kota Nithyanand , Ozdoganlar O. Burak
Published: June 2008

Anisotropy of workpiece crystals has a significant effect in micromachining since the uncut chip thickness values used in micromachining are commensurate with characteristic dimensions of crystals in crystalline materials. This paper presents an experimental investigation on orthogonal micromachining of single-crystal aluminum at different crystallographic orientations for varying uncut chip thicknesses and cutting speeds using a diamond tool. Micromachining forces, specific energies, effective coefficient of friction, shear angles, shear stresses, and chip morphology were examined for six crystallographic orientations at uncut chip thicknesses ranging from 5μmto20μm and cutting speeds ranging from 5mm∕sto15mm∕s. Three distinct types of forces were observed, including steady (Type-I), bistable (Type-II), and fluctuating (Type-III) force signatures. The forces were seen to vary by as much as threefold with crystallographic orientation. Although the effect of cutting speed was small, the uncut chip thickness was seen to have a significant orientation-dependent effect on average forces. Chip morphology, analyzed under scanning electron microscopy, showed shear-front lamella, the periodicity of which was seen to vary with crystallographic orientations and uncut chip thicknesses.
An Acoustic Emission-Based Method for Determining Contact Between a Tool and Workpiece at the Microscale
Authors: Bourne Keith A. , Jun Martin B. G. , Kapoor Shiv G. , DeVor Richard E.
Published: June 2008

An acoustic emission-based touch-off detection system has been developed to determine contact between a rotating microtool and a workpiece surface with micron-level accuracy. The system has been implemented on an existing three-axis microscale machine tool. The system has been tested with microendmills as small as 50μm in diameter and microdrills as small as 254μm in diameter. The accuracy of the system has been found to depend on tool geometry and workpiece surface characteristics and is generally on the order of 1μm. An analytical model has been constructed to predict touch-off detection error. The calibrated model has been shown to predict surface overshoot and undershoot trends quite well. Simulations have shown that touch-off error is dominated by part surface roughness.
An Experimental Investigation of the Feasibility of “Self-Sensing” Shape Memory Alloy Based Actuators
Authors: Malukhin K. , Ehmann K. F.
Published: June 2008

Shape memory alloys (SMAs) change their crystallographic structure and shape during heating/cooling and, as a consequence, their electrical resistance also changes. This allows the determination of the location of a SMA-based structure in space without separate sensors by suitably measuring this change. In this paper, this “self-sensing” concept is explored in SMA wire-type actuators. Step responses, expressed in terms of resistance (voltage drop) across the wire, and the corresponding displacement changes during heating/cooling, were measured. It was shown that the relationship between the displacement and the voltage drop can be approximated by a linear regression with a correlation coefficient close to 1. System identification has shown that SMA wire actuator performance can be best approximated by first or by second order system response depending on the thermal insulation condition of the actuator. The resolution and the sensitivity of the self-sensing method were evaluated based on experimental data and it was shown that their minimal values were less than 1.7μm and 0.7μm, respectively, thus supporting the feasibility of the “self-sensing concept.” Both values exponentially increase with the increase in the range of the measured displacements whose magnitudes vary under different working conditions.
Model-Based Pulse Frequency Control for Micro-EDM Milling Using Real-Time Discharge Pulse Monitoring
Authors: Jung Jae Won , Jeong Young Hun , Min Byung-Kwon , Lee Sang Jo
Published: June 2008

Because electrode wear in microelectrical discharge machining significantly deteriorates the machining accuracy, the electrode wear must be compensated in process to improve the geometric accuracy of the product. Therefore, there has been a substantial amount of research on electrode wear and the compensation for EDM processes. In this study, a novel control method for a micro-EDM process using discharge pulse counting is proposed. The method is based on the proportional relationship between the removed workpiece volume and the number of discharge pulses. A model-based control was designed using the relationship between the pulse frequency and gap distance, and implemented in an actual micro-EDM system. Experimental results demonstrated that the developed method makes two- and three-dimensional micro-EDM milling processes fast and accurate without complex path planning to compensate electrode wear.
Microendmill Dynamics Including the Actual Fluted Geometry and Setup Errors—Part I: Model Development and Numerical Solution
Authors: Filiz Sinan , Ozdoganlar O. Burak
Published: June 2008

This paper presents an analytical model for the microendmill dynamics, including the setup errors, the axial force, the sectioned tool geometry, and the actual crosssection of the twisted fluted section. Different tool geometries and tool-grinding errors can also be incorporated in the presented model. To include the shear deformations and rotary inertia effects arising from the stubby nature of the microendmill, the Timoshenko beam equations are used in the derivation. The boundary-value problem is derived for each of the shank, taper, and fluted sections of the microendmill, and a component mode synthesis technique is used to combine the individual sections. A new spectral-Tchebychev technique is utilized to obtain the numerical solution of the boundary-value problem without resorting to the finite-elements technique. As a result, a simple yet accurate description of the microendmill dynamics is obtained. The solution is experimentally validated in Part II of the paper.
Laser Ablation of Metals: A 3D Process Simulation for Industrial Applications
Authors: Tani Giovanni , Orazi Leonardo , Fortunato Alessandro , Cuccolini Gabriele
Published: June 2008

A model for laser milling simulation is presented in this paper. A numerical model able to predict the physical phenomena involved in laser ablation of metals was developed where the heat distribution in the work piece, the prediction of the velocity of the vapor/liquid front, and the physical state of the plasma plume were taken into account. The model is fully 3D and the simulations makes it possible to predict the ablated workpiece volume and the shape of the resulting craters for a single laser pulse or multiple pulses, or for any path of the laser spot. The numerical model was implemented in C++ and an overview of the code capacities is presented.
Development of Spherical Magnetic Abrasive Made by Plasma Spray
Authors: Yamaguchi Hitomi , Hanada Kotaro
Published: June 2008

Magnetic abrasive used for the internal finishing of capillary tubes, which prevents accumulation of contamination and erratic flow of the conveyed fluid, is a composite particle, consisting of iron and Al2O3 abrasive grains. The irregularity of the magnetic abrasive shape, due to the mechanical crushing process, causes nonuniform depth of cut of the abrasive and restricts the improvement of the finished surface quality. This has resulted in a narrow range of finishing performance. Moreover, the irregularity of the magnetic abrasive shape brings about difficulty in merely introducing it into capillary tubes. To break through these difficulties, this research proposes to develop a spherical iron-based magnetic abrasive, which carries Al2O3 grains on the surface, made by plasma spray. First, this paper examines the feasibility of the plasma spray to make the existing magnetic abrasive more spherical, and suggests the conditions needed to produce the spherical magnetic abrasive. Second, it studies the development of the new spherical magnetic abrasive made of separate particles: iron particles and Al2O3 abrasive grains, which carries the nonferrous abrasive on the outer surface alone. Their finishing performance, evaluated through the experiments using SUS304 stainless steel tubes, shows their applicability to magnetic abrasive finishing.
Microstructure-Level Machining Simulation of Carbon Nanotube Reinforced Polymer Composites—Part I: Model Development and Validation
Authors: Dikshit A. , Samuel J. , DeVor R. E. , Kapoor S. G.
Published: June 2008

A microstructure-level finite element machining model has been developed to simulate the machining of carbon nanotube (CNT) reinforced polymer composites. The model integrates a failure model with a previously developed microstructure-based material model. The competition between ductile and brittle modes of failure in the polymer phase (polycarbonate) is captured by implementing the Gearing and Anand failure model calibrated at different temperatures. The CNT phase is given a simple strain-to-failure criterion. The proposed machining model has been validated at different orthogonal machining conditions for the plain polycarbonate and for composites with two different percentage loadings of CNTs. On an average, the model is seen to successfully predict the cutting forces with an accuracy of 8% and the thrust forces with an accuracy of 13.4% for all the materials. The machining model also predicts the continuous chip morphology and formation of adiabatic shear bands in plain polycarbonate and for composites with lower loadings of CNTs. On an average, the chip thicknesses are predicted within an accuracy of 14% for plain polycarbonate and 10% for the CNT composites.
A Microstructure-Level Material Model for Simulating the Machining of Carbon Nanotube Reinforced Polymer Composites
Authors: Dikshit Ashutosh , Samuel Johnson , DeVor Richard E. , Kapoor Shiv G.
Published: June 2008

A continuum-based microstructure-level material model for simulation of polycarbonate carbon nanotube (CNT) composite machining has been developed wherein polycarbonate and CNT phases are modeled separately. A parametrization scheme is developed to characterize the microstructure of composites having different loadings of carbon nanotubes. The Mulliken and Boyce constitutive model [2006, “Mechanics of the Rate Dependent Elastic Plastic Deformation of Glassy Polymers from Low to High Strair Rates,” Int. J. Solids Struct., 43(5), pp. 1331–1356] for polycarbonate has been modified and implemented to capture thermal effects. The CNT phase is modeled as a linear elastic material. Dynamic mechanical analyzer tests are conducted on the polycarbonate phase to capture the changes in material behavior with temperature and strain rate. Compression tests are performed over a wide range of strain rates for model validation. The model predictions for yield stress are seen to be within 10% of the experimental results for all the materials tested. The model is used to study the effect of weight fraction, length, and orientation of CNTs on the mechanical behavior of the composites.
The Experimental Study on Improved Polishing Method for Terminating Optical Connector
Authors: Lin Samuel I-En
Published: June 2008

The growing demand for a wide variety of data communication and telecomunication service requires interconnection devices, such as fiber optic connectors, cable assemblies, and adapters. The strong demands for high performance and cost reduction of these components are thus arising. To ensure connector performance in actual use, several process parameters related to geometric and optical characteristics of the connector must be thoroughly understood during the manufacturing stage. This paper describes an improved polishing technique, which greatly saves production cost and polishing time. A suggested grinding profile for each step is also presented to extend the lifetime cycle on lapping films. The less the number of polishing process involve, the less the geometric imperfection it can produce. By a proper choice of rubber pad hardness and processing conditions, we are able to obtain fiber connectors with 90% overall yield using two-step process.
Automated Sensor Selection and Fusion for Monitoring and Diagnostics of Plunge Grinding
Authors: Subrahmanya Niranjan , Shin Yung C.
Published: June 2008

This paper deals with the development of an online monitoring system based on feature-level sensor fusion and its application to OD plunge grinding. Different sensors are used to measure acoustic emission, spindle power, and workpiece vibration signals, which are used to monitor three of the most common faults in grinding—workpiece burn, chatter, and wheel wear. Although a number of methods have been reported in recent literature for monitoring these faults, they have not found widespread application in industry as no single method or feature has been shown to be successful for all setups and for all wheel-workpiece combinations. This paper proposes a systematic approach, which allows the development and deployment of process-monitoring systems via automated sensor and feature selection combined with parameter-free model training, both of which are especially crucial for implementation in industry. The proposed algorithm makes use of “sparsity-promoting” penalty terms to encourage sensor and feature selection while the “hyperparameters” of the algorithm are tuned using an approximation of the leave-one-out error. Experimental results obtained for monitoring burn, chatter, and wheel wear from a plunge grinding test bed show the effectiveness of the proposed method.
Density Measurement of Powder Metallurgy Compacts by Means of Small Indentation
Authors: Quadrini Fabrizio , Squeo Erica Anna
Published: June 2008

In this study, the density of powder metallurgy compacts was measured by means of small indentation. Zinc (Zn) and aluminum (Al) tablets were fabricated by cold compaction of powders: different tablet densities were obtained by changing the packing pressure. Instrumented indentation tests were carried out by means of flat cylindrical indenters having diameters of 1mm and 2mm. After a calibration procedure, the slope of the indentation curve or the indentation load can be used for the density evaluation.
Dynamics Modeling and Analysis of Thin-Walled Aerospace Structures for Fixture Design in Multiaxis Milling
Authors: Meshreki Mouhab , Kövecses József , Attia Helmi , Tounsi Nejah
Published: June 2008

Milling of thin-walled aerospace structures is a critical process due to the high flexibility of the workpiece. Current practices in the fixture design and the choice of cutting parameters rely solely on conservative guidelines and the designer’s experience. This is a result of the lack of computationally efficient dynamic models to represent the dynamic response of the workpiece during machining, and the interaction between the workpiece, fixture and the cutting forces. This paper presents a novel dynamic formulation of typical thin-walled pockets encountered in aerospace structures. It is based on an analytical description of a five-sided pocket using a plate model. An off-line calibration of the model parameters, using global and local optimization, is performed in order to match the dynamic response of the pocket structure. The developed simplified model is based on Rayleigh’s energy method. Various pocket shapes are examined under different loading conditions and compared to finite element (FE) predictions and experimental results. In both cases, the results obtained by the developed model are in excellent agreement. This proposed approach resulted in one to two orders of magnitude reduction in computational time when compared to FE models, with a prediction error less than 10%.
Mechanism and Prediction of Laser Wet Cleaning of Marble Encrustation
Authors: Zhang Jie , Birnbaum Andrew J. , Yao Y. Lawrence , Xu Fen , Lombardi John R.
Published: June 2008

During the removal of encrustation from marble with 355nm laser pulses, the effects of the thin liquid layer covering the encrustation are experimentally and numerically investigated. The working mechanism of the liquid layer is analyzed. A two-dimensional axial symmetric model is proposed to simulate the changes in the temperature, liquid volumetric fraction, and vapor pressure in the irradiated encrustation. To model the conservation of mass, momentum, and energy, three coupled nonlinear partial differential equations are numerically solved. The measured porosity of the encrustation is incorporated into the model. Marble cleaning with three different liquids having different thermodynamic properties, distilled water, ethanol, and acetone, are compared in terms of the cleaning efficiency at different fluence levels. With the liquid layer, the surface color of cleaned marble is also studied. In addition, surface-enhanced raman spectroscopy and a chromameter are used to identify the chemical constituents and measure the color of the cleaned marble, respectively.
Laser-Assisted Milling of Silicon Nitride Ceramics and Inconel 718
Authors: Tian Yinggang , Wu Benxin , Anderson Mark , Shin Yung C.
Published: June 2008

Laser-assisted machining (LAM) has shown its potential to significantly reduce fabrication costs and improve product quality for advanced materials. While extensive studies have been conducted on laser-assisted turning of various ceramics and high temperature alloys, few attempts have been made to extend LAM to milling operations. In this paper, a transient, three-dimensional thermal model developed for laser-assisted milling (LAML) is presented and its accuracy is verified by surface temperature measurements with an infrared camera. LAML experiments designed by the model are successfully conducted on silicon nitride ceramics using TiAlN coated carbide end mills and Inconel 718 using SiC reinforced alumina cutting tools. The promising experimental results, including good surface roughness and acceptable tool wear, show the validation of applying the thermal model to design LAML processes and the feasibility of employing LAML for difficult-to-machine materials such as advanced ceramics and superalloys.
Micromachining Characteristics of NiTi Based Shape Memory Alloy Using Femtosecond Laser
Authors: Uppal Nitin , Shiakolas Panos S.
Published: June 2008

Femtosecond laser micromachining (FLM) is a relatively new and promising technology for the micromachining of a wide spectrum of engineering materials with micron and submicron size features. The interaction mechanism of femtosecond laser pulses with matter is not the same as that found in traditional lasers. This manuscript presents a detailed study of the ablation characteristics of a nickel-titanium (NiTi) shape memory alloy in air with femtosecond laser pulses. The single- and multishot ablation threshold fluence and the incubation coefficient (predicting the extent to which accumulation could take place in a material) are evaluated. In addition, morphological changes, such as the emergence of a ripple pattern, are discussed along with the identification of gentle and strong ablation phases. This study provides for the understanding and characterization of NiTi micromachining using FLM technology, which could aid in the identification of new applications for smart materials in the macro-, nano-, and microelectromechanical system domains using this technology.
FINITE TYPE INVARIANTS AND MILNOR INVARIANTS FOR BRUNNIAN LINKS
Authors: HABIRO KAZUO , MEILHAN JEAN-BAPTISTE
Published: June 2008

A link L in the 3-sphere is called Brunnian if every proper sublink of L is trivial. In a previous paper, Habiro proved that the restriction to Brunnian links of any Goussarov–Vassiliev finite type invariant of (n + 1)-component links of degree < 2n is trivial. The purpose of this paper is to study the first nontrivial case. We show that the restriction of an invariant of degree 2n to (n + 1)-component Brunnian links can be expressed as a quadratic form on the Milnor link-homotopy invariants of length n + 1.
COLLAPSES AND REVIVALS IN M TWO-LEVEL ATOMS INTERACTING WITH A SINGLE MODE COHERENT RADIATION
Authors: PRAKASH RANJANA , SHUKLA PRAMILA
Published: June 2008

We report here results for collapses and revivals phenomenon for a collection of M two-level atoms contained in a volume having dimensions much smaller than the radiation wavelength and existing in the Dicke state |r,m〉. We use a perturbation approach and obtain in the lowest contributing order of perturbation second harmonic, besides the main Rabi frequency. The amplitude of the fundamental depends on m only, but the amplitude of the harmonic has dependence on r as well as m. If the atoms are in superradiant states, only the second harmonic is obtained. Revival time for the second harmonic is one half that for the fundamental. It is interesting to note that the number of atoms M does not matter in Rabi frequency, collapse times, revival times or in amplitudes, and only r and m matter. Values of r and m of atoms in a Dicke state can be determined, in principle, by observing Rabi oscillations and average atomic inversion.
NEW SOLITARY WAVE AND JACOBI PERIODIC WAVE EXCITATIONS IN (2+1)-DIMENSIONAL BOITI–LEON–MANNA–PEMPINELLI SYSTEM
Authors: BAI CHENG-JIE , ZHAO HONG
Published: June 2008

By means of the multilinear variable separation approach, a general variable separation solution of the Boiti–Leon–Manna–Pempinelli equation is derived. Based on the general solution, some new types of localized structures — compacton and Jacobi periodic wave excitations are obtained by introducing appropriate lower-dimensional piecewise smooth functions and Jacobi elliptic functions.
GENERATION OF MULTI-SCROLL CHAOTIC ATTRACTORS VIA THE SAW-TOOTH FUNCTION
Authors: WANG FA-QIANG , LIU CHONG-XIN
Published: June 2008

A new method for generating the multi-scroll chaotic attractors is introduced. It is demonstrated that the multi-scroll chaotic attractors can be generated using the saw-tooth function series and different number of scrolls can be designed easily by modifying the natural number n of the saw-tooth function. Various scroll attractors are illustrated not only by computer simulation, but also by the realization of an electronic circuit experiment on EWB.
SUPPRESSION OF SOLITON TIMING JITTERS BY PERIODIC OPTICAL PHASE CONJUGATIONS AND OPTICAL FILTERS
Authors: CHEN WEICHENG , XU WENCHENG , LUO AIPING , HAN DINGAN , CHEN LIBING
Published: June 2008

We propose a new method for suppressing the timing jitters of soliton pulses by using periodic phase conjugations and optical spectral filters in a high bit-rate transmission system. It is proven that the tolerable transmission distance limited by timing jitters can be increased through modulating frequency shifts by optical phase conjugators and eliminating the interaction between dispersive waves and the central pulses by optical filters. Our results also show that the optical-phase-conjugated soliton with spectral filters is superior to the common soliton in suppressing polarization mode dispersion induced by random birefringence. The physical mechanisms of soliton timing jitters are analyzed.
CLUSTER-VARIATIONAL TREATMENT OF DISORDERED MIXED SPIN ISING MODEL
Authors: GHATAK SOBHENDU K.
Published: June 2008

A disordered alloy ApB1-pwhere both A and B represent magnetic atoms with respective spins SA= 1/2 and SB= 1 and whose magnetic interaction can be described by the Ising Hamiltonian is treated using the cluster-variational method. In this method, it is assumed that the system is built out of a "building block" which is embedded in an effective field. Taking the "building block" as a 4-atom cluster, the approximate free energy of the alloy is then obtained by treating the interactions between spins within the cluster of all possible configurations in an exact manner and the rest of the interaction by an effective variational field. The magnetization M and the transition temperature Tcare then calculated for different concentration and exchange parameters (JAA, JBBand JAB). The magnetization M exhibits different kinds of ferrimagnetic behavior depending on the concentration and the relative strengths of the intra- and inter-sub-network exchange interactions. For antiferromagnetic JAB, the sub-network magnetization saturates and is aligned antiferromagnetically at low temperature. The existence of the compensation temperature, Tcm, where the total magnetization reverses its direction, and depends sensitively on the relative values of JAA/JABand JBB/JABand p. For B (A)-rich alloy with small JAB, the direction of the net magnetization remains unchanged up to Tc, and a maximum in M appears at intermediate T < Tcwhen JBB≫ JAA(JBB≪ JAA). When |JAB| > JAA, JBB, Tcexhibits a maximum with p. The transition temperature is much less than the mean-field value in all cases. The magnetic susceptibility diverges as T tends to Tcand is Curie-Wiess like at T ≫ Tc. The meta-magnetic behavior has been found at high magnetic fields. Some of these results are in tune with the experimental observations in the amorphous rare-earth transition metal alloys.
homalg – A META-PACKAGE FOR HOMOLOGICAL ALGEBRA
Authors: BARAKAT MOHAMED , ROBERTZ DANIEL
Published: June 2008

The central notion of this work is that of a functor between categories of finitely presented modules over so-called computable rings, i.e. rings R where one can algorithmically solve inhomogeneous linear equations with coefficients in R. The paper describes a way allowing one to realize such functors, e.g. HomR, ⊗R, [Formula: see text], [Formula: see text], as a mathematical object in a computer algebra system. Once this is achieved, one can compose and derive functors and even iterate this process without the need of any specific knowledge of these functors. These ideas are realized in the ring independent package homalg. It is designed to extend any computer algebra software implementing the arithmetics of a computable ring R, as soon as the latter contains algorithms to solve inhomogeneous linear equations with coefficients in R. Beside explaining how this suffices, the paper describes the nature of the extensions provided by homalg.
ON THE GRASSMANN T-SPACE
Authors: BEKH-OCHIR CHULUUNDORJ , RILEY DAVID
Published: June 2008

We study the Grassmann T-space, S3, generated by the commutator [x1,x2,x3] in the free unital associative algebra K 〈x1,x2,… 〉 over a field of characteristic zero. We prove that S3 = S2 ∩ T3, where S2 is the commutator T-space generated by [x1,x2] and T3 is the Grassmann T-ideal generated by S3. We also construct an explicit basis for each vector space S3 ∩ Pn, where Pn represents the space of all multilinear polynomials of degree n in x1,…,xn, and deduce the recursive vector space decomposition T3 ∩ Pn = (S3 ∩ Pn) ⊕ (T3 ∩ Pn-1)xn.
CLASSIFICATION OF FINITE CONGRUENCE-SIMPLE SEMIRINGS WITH ZERO
Authors: ZUMBRÄGEL JENS
Published: June 2008

Our main result states that a finite semiring of order > 2 with zero which is not a ring is congruence-simple if and only if it is isomorphic to a "dense" subsemiring of the endomorphism semiring of a finite idempotent commutative monoid.

We also investigate those subsemirings further, addressing e.g. the question of isomorphy.
CLOSE NEIGHBORS IN THE QUIVER OF TILTING MODULES
Authors: HAPPEL DIETER
Published: June 2008

For a finite dimensional hereditary algebra Λ local properties of the quiver [Formula: see text] of tilting modules are investigated. The existence of special neighbors of a given tilting module is shown. If Λ has more than 3 simple modules it is shown as an application that Λ is of wild representation type if and only if [Formula: see text] is a subquiver of [Formula: see text].
WARFIELD INVARIANTS IN COMMUTATIVE GROUP ALGEBRAS
Authors: DANCHEV PETER V.
Published: June 2008

Let F be a field and G an Abelian group. For every prime number q and every ordinal number α we compute only in terms of F and G the Warfield q-invariants Wα, q(VF[G]) of the group VF[G] of all normed units in the group algebra F[G] under some minimal restrictions on F and G.

This expands own recent results from (Extracta Mathematicae, 2005) and (Collectanea Mathematicae, 2008).
Role of glucose in cloned mouse embryo development
Authors: Han Zhiming , Vassena Rita , Chi Maggie M. Y. , Potireddy Santhi , Sutovsky Miriam , Moley Kelle H. , Sutovsky Peter , Latham Keith E.
Published: June 2008

Cloned mouse embryos display a marked preference for glucose-containing culture medium, with enhanced development to the blastocyst stage in glucose-containing medium attributable mainly to an early beneficial effect during the first cell cycle. This early beneficial effect of glucose is not displayed by parthenogenetic, fertilized, or tetraploid nuclear transfer control embryos, indicating that it is specific to diploid clones. Precocious localization of the glucose transporter SLC2A1 to the cell surface, as well as increased expression of glucose transporters and increased uptake of glucose at the one- and two-cell stages, is also seen in cloned embryos. To examine the role of glucose in early cloned embryo development, we examined glucose metabolism and associated metabolites, as well as mitochondrial ultrastructure, distribution, and number. Clones prepared with cumulus cell nuclei displayed significantly enhanced glucose metabolism at the two-cell stage relative to parthenogenetic controls. Despite the increase in metabolism, ATP content was reduced in clones relative to parthenotes and fertilized controls. Clones at both stages displayed elevated concentrations of glycogen compared with parthenogenetic controls. There was no difference in the number of mitochondria, but clone mitochondria displayed ultrastructural alterations. Interestingly, glucose availability positively affected mitochondrial structure and localization. We conclude that cloned embryos may be severely compromised in terms of ATP-dependent processes during the first two cell cycles and that glucose may exert its early beneficial effects via positive effects on the mitochondria.
Amplification of pulsatile glucagon counterregulation by switch-off of α-cell-suppressing signals in streptozotocin-treated rats
Authors: Farhy Leon S. , Du Zhongmin , Zeng Qiang , Veldhuis Paula P. , Johnson Michael L. , Brayman Kenneth L. , McCall Anthony L.
Published: June 2008

Glucagon counterregulation (GCR) is a key protection against hypoglycemia that is compromised in diabetes via an unknown mechanism. To test the hypothesis that α-cell-inhibiting signals that are switched off during hypoglycemia amplify GCR, we studied streptozotocin (STZ)-treated male Wistar rats and estimated the effect on GCR of intrapancreatic infusion and termination during hypoglycemia of saline, insulin, and somatostatin. Times 10 min before and 45 min after the switch-off were analyzed. Insulin and somatostatin, but not saline, switch-off significantly increased the glucagon levels ( P = 0.03), and the fold increases relative to baseline were significantly higher ( P < 0.05) in the insulin and somatostatin groups vs. the saline group. The peak concentrations were also higher in the insulin (368 pg/ml) and somatostatin (228 pg/ml) groups vs. the saline (114 pg/ml) group ( P < 0.05). GCR was pulsatile in most animals, indicating a feedback regulation. After the switch-off, the number of secretory events and the total pulsatile production were lower in the saline group vs. the insulin and somatostatin groups ( P < 0.05), indicating enhancement of glucagon pulsatile activity by insulin and somatostatin compared with saline. Network modeling analysis demonstrates that reciprocal interactions between α- and δ-cells can explain the amplification by interpreting the GCR as a rebound response to the switch-off. The model justifies experimental designs to further study the intrapancreatic network in relation to the switch-off phenomenon. The results of this proof-of-concept interdisciplinary study support the hypothesis that GCR develops as a rebound pulsatile response of the intrapancreatic endocrine feedback network to switch-off of α-cell-inhibiting islet signals.
The facilitative glucose transporter GLUT3: 20 years of distinction
Authors: Simpson Ian A. , Dwyer Donard , Malide Daniela , Moley Kelle H. , Travis Alexander , Vannucci Susan J.
Published: June 2008

Glucose metabolism is vital to most mammalian cells, and the passage of glucose across cell membranes is facilitated by a family of integral membrane transporter proteins, the GLUTs. There are currently 14 members of the SLC2 family of GLUTs, several of which have been the focus of this series of reviews. The subject of the present review is GLUT3, which, as implied by its name, was the third glucose transporter to be cloned (Kayano T, Fukumoto H, Eddy RL, Fan YS, Byers MG, Shows TB, Bell GI. J Biol Chem 263: 15245–15248, 1988) and was originally designated as the neuronal GLUT. The overriding question that drove the early work on GLUT3 was why would neurons need a separate glucose transporter isoform? What is it about GLUT3 that specifically suits the needs of the highly metabolic and oxidative neuron with its high glucose demand? More recently, GLUT3 has been studied in other cell types with quite specific requirements for glucose, including sperm, preimplantation embryos, circulating white blood cells, and an array of carcinoma cell lines. The last are sufficiently varied and numerous to warrant a review of their own and will not be discussed here. However, for each of these cases, the same questions apply. Thus, the objective of this review is to discuss the properties and tissue and cellular localization of GLUT3 as well as the features of expression, function, and regulation that distinguish it from the rest of its family and make it uniquely suited as the mediator of glucose delivery to these specific cells.
Role of wild-type estrogen receptor-β in mitochondrial cytoprotection of cultured normal male and female human lens epithelial cells
Authors: Flynn J. M. , Dimitrijevich S. D. , Younes M. , Skliris G. , Murphy L. C. , Cammarata P. R.
Published: June 2008

The influence of sexual category as a modifier of cellular function is underinvestigated. Whether sex differences affect estrogen-mediated mitochondrial cytoprotection was determined using cell cultures of normal human lens epithelia (nHLE) from postmortem male and female donors. Experimental indicators assessed included differences in estrogen receptor-β (ERβ) isoform expression, receptor localization in mitochondria, and estrogen-mediated prevention of loss of mitochondrial membrane potential using the potentiometric fluorescent compound JC-1 after nHLE were exposed to peroxide. The impact of wild-type ERβ (wtERβ1) was also assessed using wtERβ1 siRNA to suppress expression. A triple-primer PCR assay was employed to determine the proportional distribution of the receptor isoforms (wtERβ1, -β2, and -β5) from the total ERβ message pool in male and female cell cultures. Irrespective of sex, nHLE express wtERβ1 and the ERβ2 and ERβ5 splice variants in similar ratios. Confocal microscopy and immunofluorescence revealed localization of the wild-type receptor in peripheral mitochondrial arrays and perinuclear mitochondria as well as nuclear staining in both cell populations. The ERβ2 and ERβ5 isoforms were distributed primarily in the nucleus and cytosol, respectively; no association with the mitochondria was detected. Both male and female nHLE treated with E2 (1 μM) displayed similar levels of protection against peroxide-induced oxidative stress. In conjunction with acute oxidative insult, RNA suppression of wtERβ1 elicited the collapse of mitochondrial membrane potential and markedly diminished the otherwise protective effects of E2. Thus, whereas the estrogen-mediated prevention of mitochondrial membrane permeability transition is sex independent, the mechanism of estrogen-induced mitochondrial cytoprotection is wtERβ1 dependent.
Cloning and characterization of novel humanSLC4A8gene products encoding Na+-driven Cl−/HCO3−exchanger variants NDCBE-A, -C, and -D
Authors: Parker Mark D. , Bouyer Patrice , Daly Christopher M. , Boron Walter F.
Published: June 2008

The reported sequences of the human and mouse Na+-driven Cl−/HCO3−exchangers (NDCBEs) differ greatly in their extreme cytosolic COOH termini (Ct). In human NDCBE (NDCBE-B), a 17-amino acid (aa) sequence replaces 66 aa at the equivalent position in mouse NDCBE (NDCBE-A). We performed 5′- and 3′-rapid amplification of cDNA ends (RACE) on human brain cDNA, followed by PCR of full-length cDNAs to determine whether the human SLC4A8 gene was capable of producing the mouselike Ct sequence. Our study confirmed the presence in human cDNA of mouse NDCBE-like transcripts (human NDCBE-A) and also disclosed the existence of three further novel NDCBE transcripts that we have called NDCBE-C, NDCBE-D, and NDCBE-D′. The novel NDCBE-C/D/D′ transcripts initiate at a novel “exon 0” positioned ∼35 kb upstream of the first exon of NDCBE-A/B. NDCBE-C/D/D′ protein products are predicted to be truncated by 54 aa in the cytosolic NH2terminus (Nt) compared with NDCBE-A/B. Our data, combined with a new in silico analysis of partial transcripts reported by others in the region of the human SLC4A8 gene, increase the known extent of the SLC4A8 gene by 49 kb, to 124 kb. A functional comparison of NDCBE-A/B/C/D expressed in Xenopus oocytes demonstrates that the Nt variation does not affect the basal functional expression of NDCBE, but those with the shorter Ct have a 25–50% reduced functional expression compared with those with the longer Ct. By comparison with an artificially truncated NDCBE that contains neither 17-aa nor 66-aa Ct cassette, we determined that the functional difference is unrelated to the 66-aa cassette of NDCBE-A/C, but is instead due to an inhibitory effect of the 17-aa cassette of NDCBE-B/D.
Neuromagnetic Response to Body Motion and Brain Connectivity
Authors: Pavlova Marina , Bidet-Ildei Christel , Sokolov Alexander N. , Braun Christoph , Krägeloh-Mann Ingeborg
Published: June 2008

Visual detection of body motion is of immense importance for daily-life activities and social nonverbal interaction. Although neurobiological mechanisms underlying visual processing of human locomotion are being explored extensively by brain imaging, the role of structural brain connectivity is not well understood. Here we investigate cortical evoked neuromagnetic response to point-light body motion in healthy adolescents and in patients with early periventricular lesions, periventricular leukomalacia (PVL), that disrupt brain connectivity. In a simultaneous masking paradigm, participants detected the presence of a point-light walker embedded in a few sets of spatially scrambled dots on the joints of a walker. The visual sensitivity to camouflaged human locomotion was lower in PVL patients. In accord with behavioral data, root-mean-square (RMS) amplitude of neuromagnetic trace in response to human locomotion was lower in PVL patients at latencies of 180–244 msec over the right temporal cortex. In this time window, the visual sensitivity to body motion in controls, but not in PVL patients, was inversely linked to the right temporal activation. At later latencies of 276–340 msec, we found reduction in RMS amplitude in PVL patients for body motion stimuli over the right frontal cortex. The findings indicate that disturbances in brain connectivity with the right temporal cortex, a key node of the social brain, and with the right frontal cortex lead to disintegration of the neural network engaged in visual processing of body motion. We suspect that reduced cortical response to body motion over the right temporal and frontal cortices might underlie deficits in visual social cognition.
The Angry Brain: Neural Correlates of Anger, Angry Rumination, and Aggressive Personality
Authors: Denson Thomas F. , Pedersen William C. , Ronquillo Jaclyn , Nandy Anirvan S.
Published: June 2008

Very little is known about the neural circuitry guiding anger, angry rumination, and aggressive personality. In the present fMRI experiment, participants were insulted and induced to ruminate. Activity in the dorsal anterior cingulate cortex was positively related to self-reported feelings of anger and individual differences in general aggression. Activity in the medial prefrontal cortex was related to self-reported rumination and individual differences in displaced aggression. Increased activation in the hippocampus, insula, and cingulate cortex following the provocation predicted subsequent self-reported rumination. These findings increase our understanding of the neural processes associated with the risk for aggressive behavior by specifying neural regions that mediate the subjective experience of anger and angry rumination as well as the neural pathways linked to different types of aggressive behavior.
Dominance and Submission: The Ventrolateral Prefrontal Cortex and Responses to Status Cues
Authors: Marsh Abigail A. , Blair Karina S. , Jones Matthew M. , Soliman Niveen , Blair R. J. R.
Published: June 2008

Status hierarchies constitute a fundamental organizing principle of human society. However, little is known about the neural systems that process nonverbal cues that indicate status. Preliminary neuropsychological work has suggested a role for the ventrolateral and ventromedial prefrontal cortex (VLPFC/VMPFC) and the superior temporal cortex (STC). We used functional magnetic resonance imaging to delineate the nature of these roles. Analyses revealed signal changes in the right VLPFC in connection with two primary functions attributed to status cues. Status cues moderate behavior and the right VLPFC showed increased signal for high-status relative to neutral and low-status cues. The VLPFC also showed increased signal for high-status cues displayed by individuals of the opposite gender to the perceiver; this may be relevant to the role status cues play in moderating mate choice behavior. Connectivity results indicated significant positive connectivity between the VLPFC and both the VMPFC and the STC. We suggest that the VLPFC retrieves information from these regions when processing hierarchy cues to facilitate socially adaptive behavior.