bluuebunny/crossref_metadata_2025 huggingface dataset:
VIP and PACAP in the CNS: Regulators of Glial Energy Metabolism and Modulators of Glutamatergic Signalinga
Authors: MAGISTRETTI P. J. , CARDINAUX J.‐R. , MARTIN J.‐L.
Published: February 2006

Abstract: VIP neurons are a homogeneous population of intracortical bipolar cells. They receive excitatory synapses from afferent circuits to the cortex and exert effects on neurons, astrocytes, and capillaries. Effects on the two latter cell types imply that VIP neurons can translate incoming neuronal signals into local metabolic actions. Indeed, VIP tightly regulates glycogen metabolism in astrocytes. In this cell type VIP regulates the expression of a number of genes related to energy metabolism, such as glycogen synthase. These effects of VIP involve the transcription factor family C/EBP and result in the induction of at least seven new proteins by astrocytes. The actions of VIP on neurons appear to be of a modulatory nature: thus VIP enhances glutamate‐mediated neurotransmission by potentiating the effects of glutamate on arachidonic acid formation and on the induction of c‐fos and on BDNF expression. These effects indicate that VIP can actually increase the strength of glutamate‐mediated neurotransmission.
Glutamate Toxicity in the Lung and Neuronal Cells: Prevention or Attenuation by VIP and PACAP
Authors: SAID S. I. , DICKMAN K. , DEY R. D. , BANDYOPADHYAY A. , DE STEFANIS P. , RAZA S. , PAKBAZ H. , BERISHA H. I.
Published: February 2006

Abstract: VIP, which has been demonstrated to reduce or prevent oxidant injury in the lungs and other organs, is shown here to protect against excitotoxic injury of the lung and excitotoxic death of cortical neuronal cells in primary culture. Glutamate killing of neuron‐like PC‐12 cells, attributable to oxidant stress rather that to excitotoxicity, is also reduced or prevented by VIP and by the closely related peptide PACAP. The exact mechanisms of this protection remain to be determined, but appear to include antioxidant and anti‐apoptotic actions, and suppression of glutamate‐induced upregulation of its own receptor. Both VIP and PACAP offer the promise of novel and nontoxic means of defending against NMDA and glutamate toxicity.
Autoantibody Catalysis: No Longer Hostage to Occam's Razor
Authors: PAUL SUDHIR
Published: February 2006

Abstract: Autoantibody catalysis is now a well‐established phenomenon, but the initial finding of autoantibody‐catalyzed VIP cleavage was suspected to be an artefact by certain practitioners of designer antibody catalysis, mainly because of conceptual complexities not foreseen in our training about the immune system and about the mechanisms of biological catalysis. Confirmation that antibodies can acquire proteolytic activity by entirely natural means has emerged, ironically, in part from the field of designer catalytic antibodies. Recent studies have provided insight into the molecular strategies whereby antibodies can combine antigen binding with chemical catalysis, and the contributions of innate and adaptive immune mechanisms in the proteolytic activity. The history of this field illustrates the dangers of assuming that novel observations must fit into the simple confines of established theories. Scientific theories are changeable entities, dependent on empirical data and interpretations of the data, and their growth is better served by keeping an open mind.
Analogues of VIP, Helodermin, and PACAP Discriminate between Rat and Human VIP1 and VIP2 Receptorsa
Authors: GOURLET P. , VANDERMEERS A. , VAN RAMPELBERGH J. , DE NEEF P. , CNUDDE J. , WAELBROECK M. , ROBBERECHT P.
Published: February 2006

Abstract: Vasoactive intestinal polypeptide (VIP) acts through interaction with two subclasses of seven transmembrane G protein‐coupled receptors named VIP1 and VIP2 receptors. These receptors have been cloned in different species, such as rat and human. Considering the different distribution of both receptor subclasses, there is considerable interest in the development of selective agonists and antagonists. The present study compares the binding properties of VIP, PACAP, GRF, secretin, and helodermin analogues on recombinant rat and human VIP1 and VIP2 receptors. On both rat and human receptors, secretin and GRF had a higher affinity for the VIP1 receptor subtypes. The amino‐shortened VIP, and the carboxy terminal‐shortened VIP and PACAP analogues also presented a higher affinity for the VIP1 receptor. PHI, PHV, helodermin, and helospectin were selective for the human VIP2 receptor subtypes. These results suggest that the helical structure of the carboxy terminal end is necessary for VIP2 recognition. The differences between species were the following: PHI, PHV, helodermin, and helospectin had a higher affinity for the rat VIP1 receptor than for the human VIP1 receptor. On both rat and human receptors, D‐Ala4 VIP and D‐Phe4 VIP had a high affinity for the VIP1 receptor and a low affinity for the VIP2 receptor. Thus, three domains of the ligand involved in VIP1/VIP2 receptor discrimination were identified: the amino acid residue in position 4 ([D‐Ala4], [D‐Phe4]VIP), in positions 8 and 9 (the effects of helodermin and helospectin), and the carboxy terminal end (the effects of the shortened VIP and pituitary adenylate cyclase activating polypeptide analogues).
The PACAP Ligand/Receptor System Regulates Cerebral Cortical Neurogenesisa
Authors: DICICCO‐BLOOM EMANUEL , LU NAIRU , PINTAR JOHN E. , ZHANG JIWEN
Published: February 2006

Abstract: The PACAP ligand/type I receptor system is expressed throughout the embryonic nervous system, suggesting roles in regulating neural patterning and neurogenesis. In the forebrain, precursors of the six‐layered cerebral cortex cease dividing in a highly reproducible spatiotemporal sequence. The time of cell cycle exit in fact determines neuron laminar fate. Our studies indicate that PACAP signaling may elicit cortical precursor withdrawal from the cell cycle, antagonizing mitogenic stimulators. PACAP inhibited embryonic day 13.5 rat cortical precursor [3H]thymidine incorporation, decreasing the proportion of mitotic cells. PACAP promoted morphological and biochemical differentiation, indicating that PACAP‐induced cell cycle withdrawal was accompanied by neuronal differentiation.

In vivo, embryonic cortex contains PACAP. In culture, 85% of cells expressed PACAP while 64% exhibited receptor. Co‐localization studies indicated that PACAP ligand and receptor were expressed by the mitotic precursors that divided in response to bFGF, suggesting that precursors integrate mitogenic and anti‐mitogenic signals to determine the timing of cell cycle exit.

The expression of PACAP ligand and receptor in precursors raised the possibility of autocrine function. Indeed, peptide antagonists increased proliferation, suggesting that the PACAP system is expressed to elicit cell cycle exit. During ontogeny, an inhibitory signal, such as PACAP, may be required to counter the stimulatory activity of mitogenic bFGF and IGFI whose expression during cortical neurogenesis is sustained. The dynamic interplay of positive and negative regulators would regulate the timing of cell cycle withdrawal, and thus neuronal phenotype and laminar position.
The Protective Effect of Vasoactive Intestinal Peptide (VIP) on Stress‐Induced Gastric Ulceration in Rats
Authors: TUNÇEL NEŞ'E , ERKASAP N˙ILÜFER , ŞAH˙INTÜRK VAROL , AK D˙ILEK DOĞRUKOL , TUNÇEL MUZAFFER
Published: February 2006

Abstract: The pathogenesis of cold‐restraint stress ulcer involves various factors and is not completely understood. Mast cell degranulation, increased gastric muscular contractility, diminished mucosal blood flow, release of several biogenic amines, activated polymorphonuclear leukocytes, and lipid peroxidation which results from toxic oxygen molecules were suggested to be related to the production of gastric damage by cold‐restraint stress. Recent evidence strongly indicates that VIP has a modulatory effect on tissue injury.

Sprague‐Dawley rats were used in two series of experiments. One set of rats was exposed to cold‐restraint stress with some of the rats pretreated with VIP. The second set of rats was exposed to cold‐restraint stress and then was administered VIP for different durations. Cold‐restraint stress induced gastric lesions and mast cell degranulation and also increased lipid peroxidation in gastric tissue. VIP prevented stress‐induced ulcers and mast cell degranulation and protected gastric tissue from lipid peroxidation. When VIP was used after induction of stress ulcer it was therapeutically beneficial.

Thanks to its antioxidant and anti‐inflammatory activity, VIP can be valuable in the prevention of gastric mucosal damage induced by cold‐restraint stress.
On the Treatment of Diabetes Mellitus with Glucagon‐like Peptide‐1
Authors: HOLST JENS JUUL , DEACON CAROLYN , TOFT‐NIELSEN MAJ‐BRIT , BJERRE‐KNUDSEN LOTTE
Published: February 2006

Abstract: As a therapeutic principle, the insulinotropic peptide, GLP‐1, of the secretin‐glucagon family of peptides, has turned out to possess some remarkably attractive properties, including the capability of normalizing blood glucose concentrations in patients with non‐insulin‐dependant diabetes mellitus and promoting satiety and reducing food intake in healthy volunteers. Because of rapid and extensive metabolization, the peptide is not immediately clinically applicable and, as a therapeutic principle, GLP‐1 is still in its infancy. Some possible avenues for circumventing these difficulties are the development of DPP‐IV‐resistant analogs, the inhibition of DPP‐IV, enhancement of GLP‐1 secretion, GLP delivery systems using continuous subcutaneous infusion or buccal tablets, GLP‐1 absorption, and orally active, stable analogs. It seems likely that one or more of these approaches could result in a clinically useful development program.

In a previous publication, 1 we introduced the new incretin hormone, glucagon‐like peptide‐1 and presented its effects on blood glucose regulation in normal and diabetic subjects. Its role as an incretin hormone, being the most potent insulinotropic hormone known, was emphasized, and it was described how intravenous infusions of GLP‐1 can completely normalize the hyperglycemia of patients with non‐insulin‐dependent diabetes mellitus (NIDDM). It was concluded that GLP‐1 had great potential as a therapeutic agent. The present communication deals with the attempts that have been made to transform this typical peptide hormone of the glucagon‐secretin‐VIP‐PACAP family into a clinically useful therapeutic agent.
Binding Sites for VIP in the Reorganizing Mucosa of the Irradiated Bowela
Authors: HÖCKERFELT U. , HANSSON M. , GULBENKIAN S. , FRANZÉN L. , HENRIKSSON R. , FORSGREN S.
Published: February 2006

Abstract: Rats were given radiotherapy (total dose 30 Gy) over the abdomen. Seven days later specimens of the duodenum were prepared for in vitro receptor autoradiography using the radioligand [125I]VIP. The autoradiograms were quantitatively analyzed using a computer system. Histological examination revealed that a very marked reorganization of the mucosa had occurred in response to irradiation. Using receptor autoradiography, we found [125I]VIP‐specific binding sites in the reorganizing mucosa, except where denudation had occurred. Such binding sites also occurred in the smooth muscle layer of the duodenal wall. The observations suggest that VIP has profound effects in radiation‐induced enteropathy.
Main Sensory Neuropeptides, but not VIP and NPY, Are Involved in Bone Remodeling during Orthodontic Tooth Movement in the Rata
Authors: NOREVALL L. I. , MATSSON L. , FORSGREN S.
Published: February 2006

Abstract: During orthodontic tooth movement (OTM) a remodeling of the periodontal ligament (PDL) and the alveolar bone occurs. We have recently observed that the expression of CGRP and substance P (SP) increases in the PDL and dental pulp in response to buccally directed OTM of the upper first molar in the rat. We have now examined whether there is also an involvement of VIP and NPY in this type of OTM. A sectional arch wire cemented to the upper incisors exerted an orthodontic force, mediated by a coil on the lingual side of the tooth, for 24 hours. It was observed that the blood vessels in the periodontal ligament were supplied with VIP‐ and NPY‐immunoreactive (IR) nerve fibers, whereas VIP‐IR nerve fibers in contrast to NPY‐IR fibers were only occasionally observed in the dental pulp. No significant changes were observed in response to OTM. The observations suggest that VIP and NPY, in contrast to the main sensory neuropeptides CGRP and SP, are not involved in the tissue processes that occur in the remodeling of PDL and alveolar bone during orthodontic tooth movement.
PACAP27 and Other Neuropeptides in the Inferior Mesenteric Ganglionaa
Authors: ERMILOV LEONID G. , SZURSZEWSKI JOSEPH H.
Published: February 2006

Abstract: The presence and location of PACAP27‐like immunoreactivity (PACAP27‐LI) in the colon‐inferior mesenteric ganglion (IMG) reflex pathway and the effect of exogenously administered PACAP27 on the excitability of IMG are reported. The results provide morphological and electrophysiological support for the hypothesis that PACAP modulates reflex activity between the large intestine and IMG. The intense excitatory effect would be expected to increase the rate of action potential discharge in IMG neurons, increasing sympathetic drive to the colon thereby decreasing of colonic activity.
Orbital Complexity, Short‐Time Lyapunov Exponents, and Phase Space Transport in Time‐Independent Hamiltonian Systemsa
Authors: SIOPIS CHRISTOS , ECKSTEIN BARBARA L. , KANDRUP HENRY E.
Published: February 2006

ABSTRACT: This paper compares two alternative characterizations of chaotic orbit segments, one based on the complexity of their Fourier spectra, as probed by the number of frequencies n(k) required to capture a fixed fraction k of the total power, and the other based on the computed values of short‐time Lyapunov exponentsχ. An analysis of orbit ensembles evolved in several different two‐ and three‐dimensional potentials reveals that there is a strong, roughly linear correlation between these alternative characterizations, and that computed distributions of complexities, N[n(k)], and short‐time χ, N[χ], often assume similar shapes. This corroborates the intuition that chaotic segments which are especially unstable should have Fourier spectra with particularly broad‐band power. It follows that orbital complexities can be used as probes of phase space transport and other related phenomena in the same manner as can short‐time Lyapunov exponents.
Bifurcations of Periodic Orbits in Axisymmetric Scalefree Potentialsa
Authors: HUNTER C. , TERZIĆ BALŠA , BURNS AMY M. , PORCHIA DONALD , ZINK CHRIS
Published: February 2006

ABSTRACT: We study orbits in potentials with central cusps, emphasizing the spheriodal equidensity (SED) potentials generated by mass distributions with spheroidal equidensity surfaces. The most prominent bifurcations are those related to 1:1 and 4:3 resonances between radial motions and motions perpendicular to the central plane. We find that 1:1 resonances can cause the thin tube orbit, as well as the equatorial plane orbit, to become unstable. We concentrate on period‐tripling bifurcations because they appear to be the least understood. We study them via a class of analytic maps. This study suggests that stable period‐three orbits generally arise de novo in stable and unstable pairs via a turning‐point bifurcation, and not through a bifurcation from the thin tube at a 120° rotation angle. The stable period‐three orbits typically have only a short span of existence before becoming unstable to a period‐doubling instability through a supercritical pitchfork bifurcation.
Irregular Period‐Tripling Bifurcations in Axisymmetric Scalefree Potentials
Authors: TERZIĆ BALŜA
Published: February 2006

ABSTRACT: We investigate the phenomenon of irregular bifurcations in axisymmetric scalefree potentials, in which a tube orbit gives rise to a new family of orbits of period 3. A proper understanding of the formation of the this irregular family of orbits is important because the family occupies a fair portion of the phase space in models where it occurs. We show that these bifurcations are related to the transition of the rotation number of the phase‐space torus through 1/3. This type of bifurcation is closely related to the behavior of nontwist maps.
From Jupiter's Great Red Spot to the Structure of Galaxies: Statistical Mechanics of Two‐Dimensional Vortices and Stellar Systems
Authors: CHAVANIS PIERRE‐HENRI
Published: February 2006

ABSTRACT: The statistical mechanics of two‐dimensional ortices and stellar systems both at equilibrium and out of equilibrium are discussed, with emphasis on the analogies (and on the differences) between these two systems. Limitations of statistical theory and problems posed by the long‐range nature of the interactions are described in detail. Special attention is devoted to the problem of “incomplete relaxation” and, in the case of stellar systems, to the “gravothermal catastrophe.” The relaxation toward equilibrium, possibly restricted to a “maximum entropy bubble,” is described with the aid of a maximum entropy production principle (MEPP). The relation with Fokker‐Planck equations is made explicit and the structure of the diffusion current analyzed in terms of a pure diffusion compensated by an appropriate friction or a drift.
On Nonlinear Dynamics of Three‐Dimensional Astrophysical Disksa
Authors: FRIDMAN A. M. , KHORUZHII O. V.
Published: February 2006

ABSTRACT: Nonlinear processes concerned with different aspects of nonlinear dynamics of astrophysical disks‐structures, flows, turbulence‐are re‐viewed. Special attention is paid to the influence of the three dimentionality of disks on their nonlinear behavior.
Chaos in the Centers of Galaxies
Authors: SHLOSMAN ISAAC , HELLER CLAYTON , BERENTZEN INGO
Published: February 2006

ABSTRACT: We compare diverging evolution of a two‐component (gas+stars) galactic disk embedded in a “live” halo with that of an identical pure stellar disk. Our modeling supports the conjecture that the growth of central concentration in galaxies dissolves the main family of regular orbits in the stellar bar and assists in the formation of a galactic bulge.
Global Spiral Patterns in Galaxies: Complexity and Simplicity
Authors: LIN C. C.
Published: February 2006

ABSTRACT: A coherent exposition of the density wave theory of galactic spirals is presented in a recent monograph [3]. It is centered on the working hypothesis of quasi‐stationary spiral structure, a possibility first proposed by Bertil Lindblad [23]. This hypothesis has since been found to be widely applicable in a number of physical contexts, including the explanation of the Hubble classification system and other tegorical classes. Direct empirical support of this hypothesis has been provided especially by the regularity of the infrared images frequently observed in a number of galaxies (e.g., NGC 309), and by the observed amplitude modulation along the spiral arms (e.g., M51, M81, and NGC 1300). The present paper is a brief review of this theory with further clarification of the fundamentals and of certain specific issues raised in the literature.

On the theoretical side, the likelihood for the validity of this hypothesis has been supported by modal studies. Emphasis is placed on the widely observed coexistence of a single regular structure in the Pop II objects and the more complex irregular structures in the Pop I objects, a contrast first discovered by Zwicky many years ago in the main disk of M51. It is pointed out that, in both barred and nonbarred spirals, this basic phenomenon may be understood by noting the fact that the microscale of the collisionless system of Pop II stars‐i.e., the diameter of the epicycle‐is typically on the same order of magnitude as the observed spacing between the spiral arms. The spiral pattern is thus a very compact structure which is unlikely to respond readily to internal and external disturbances of moderate magnitudes. This apparent robustness in structure is suggested by its observed regularity despite the impact from the coexisting Pop I objects with their strong irregular turbulent motions.

This physical picture supports Oort's conjecture [28] of a limited role for tidal interaction in most of the spiral structure of galaxies. It also enables us to place in proper perspective a controversy between two schools of thought, with different emphasis placed on intrinsic mechanisms and on tidal interaction. It is primarily a matter of applicability, or frequency of occurrence of the different scenarios proposed. There is, as yet, little observational evidence presented in the literature that would support the need of an interpretation of the global spiral structure in the galactic disk in terms of a fast evolving structure recently generated from a featureless initial state through tidal interaction. Dynamically, the likelihood for realizing such a scenario is also estimated to be quite low [3, p. 130].

The above discussions are placed in the context of a general point of view much advocated in current scientific literature; namely, the need to analyze alternative mathematical models for diverse physical contexts in the study of “complex” systems and to judge separately the merits of each model on the basis of its empirical confirmation in an appropriate physical context.
Recent Progress in the Study of One‐Dimensional Gravitating Systems
Authors: MILLER BRUCE N. , YAWN KENNETH , YOUNGKINS PAIGE
Published: February 2006

ABSTRACT: We review recent developments in the study of two different interacting gravitational systems: the system of parallel planar mass sheets and the system of concentric spherical mass shells. The approach to equilibrium of a system of parallel planar mass sheets is investigated. Parallels with three‐dimensional systems are described. Mass segregation and kinetic energy equipartition in a two‐component system of planar mass sheets is demonstrated via numerical simulation. The existence of two distinct phases is demonstrated in the system of spherical mass shells. The nature of the transition in the micro‐canonical, canonical, and grand canonical ensembles is studied both theoretically in terms of mean‐field theory and via dynamical simulation.
Modeling the Time Variability of Black Hole Candidates
Authors: KAZANAS DEMOSTHENES , HUA XIN‐MIN
Published: February 2006

ABSTRACT: We present model light curves for accreting black hole candidates (BHC) based on a recently developed model of these sources. According to this model, the observed light curves and aperiodic variability of BHC are due to a series of soft photon injections at random (Poisson) intervals and the stochastic nature of the Comptonization process in converting these soft photons to the observed high energy radiation. The additional assumption of our model is that the Comptonization process takes place in an extended but non‐uniform hot plasma corona surrounding the compact object. We compute the corresponding power spectral densities (PSD), autocorrelation functions, time skewness of the light curves, and time lags between the light curves of the sources at different photon energies and compare our results to observation. Our model reproduces the observed light curves well, in that it provides good fits to their overall morphology (as manifest by the autocorrelation and time skewness) and also to their PSDs and time lags, by producing most of the variability power at time scales ≲ a few seconds, while at the same time allowing for shots of a few msec in duration, in accordance with observation. We suggest that refinement of this type of model along with spectral and phase lag information can be used to probe the structure of this class of high energy sources.
Stellar Oscillons
Authors: UMURHAN O.M. , TAO L. , SPIEGEL E.A
Published: February 2006

ABSTRACT: We study the weakly nonlinear evolution of acoustic instability of a plane‐parallel polytrope with thermal dissipation in the form of Newton's law of cooling. The most unstable horizontal wavenumbers form a band around zero and this permits the development of a nonlinear pattern theory leading to a complex Ginzburg‐Landau equation (CGLE). Numerical solutions for a subcritical, quintic CGLE produce vertically oscillating, localized structures that resemble the oscillons observed in recent experiments of vibrated granular material.
Chaos in Cosmological Hamiltoniansa
Authors: KANDRUP HENRY E. , DRURY JOHN
Published: February 2006

ABSTRACT: This paper summarizes a numerical investigation which aimed to identify and characterize regular and chaotic behavior in time‐dependent Hamiltonians H(r, p, t) = p2/2 +V(r, t), with V=R(T)V0(r) or V=V0[R(t)r], where V0 is a polynomial in x, y, and/or z and R(t) ∞tp is a time‐dependent scale factor When p is not too negative, one can distinguish between regular and chaotic behavior by determining whether an orbit segment exhibits a sensitive dependence on initial conditions. However, chaotic segments in these potentials differ from chaotic segments in time‐independent potentials in that a small initial perturbation will usually exhibit a sub‐ or superexponential growth in time. Although not periodic, regulat segments typically exhibit simpler shapes, topologies, and Fourier spectra than do chaotic segments. This distinction between regular and chaotic behavior is not absolute since a single orbit segment can seemingly change from regular to chaotic and visa versa. All these observed phenomena can be understood in terms of a simple theoretical model.
Cutter/Workpiece Engagement Feature Extraction from Solid Models for End Milling
Authors: Yip-Hoi Derek , Huang Xuemei
Published: February 2006

Accurate process modeling requires the calculation of cutter/workpiece engagement (CWE) geometry. This is challenging when the geometry of the workpiece is changing unpredictably as is the case for most machined components of moderate complexity. Solid modelers are increasingly being considered as a computational engine for performing these calculations. This is largely due to increased robustness and computing efficiency that is evolving within this technology. The vast majority of reported research using solid modelers focuses on the domain of 212D machining with flat end mills. While significant there remain restrictions in the types of in-process workpiece geometry that can be processed with these approaches. In particular, they assume a constant axial engagement for a connected set of tool paths. This assumption cannot be made when the initial workpiece geometry is nonrectangular prismatic stock, when multiple setups are machined and when tool changes introduce tools of different diameters. In these cases the depth of engagement can vary over a single rotation of the cutter even though there is no axial feed motion. In this paper a solid modeling based solution is presented for calculating CWE geometry when multiple setups and tool changes are considered. Orthogonal setups and flat end mills are assumed so as to preclude cutter engagement on inclined workpiece faces. Intersections between a semi-cylinder representing the cutting tool and the workpiece are performed so as to generate the CWE geometry. Cutter Engagement Features (ceF) are used to characterize this geometry. Several classes of ceFs are defined to support this approach. The process of identifying ceFs is presented as a feature extraction problem. Algorithms for ceF extraction and parametrization are provided in this paper and validated using a test part. This is a new application for features which have traditionally been used to define final part geometry or in-process geometry between material removal steps. The results obtained validate the extraction algorithms presented. This work also extends the capabilities of solid modeling techniques for calculating CWE geometry.
A Geometrical Simulation System of Ball End Finish Milling Process and Its Application for the Prediction of Surface Micro Features
Authors: Liu Xianbing , Soshi Masakazu , Sahasrabudhe Abhijit , Yamazaki Kazuo , Mori Masahiko
Published: February 2006

Finish milling with a ball end mill is a key process in manufacturing high-precision and complex workpieces, such as dies and molds. Because of the complexity of the milling process, it is difficult to evaluate the microcharacteristics of machined surfaces real time, which necessitates the simulation of the process. In this area, the existing related simulation researches mainly focus on scallop height evaluation, but few have presented a whole picture of the microcharacteristics of milled surfaces. This paper develops a comprehensive simulation system based on a Z-map model for predicting surface topographic features and roughness formed in the finish milling process and studies the effect of machining parameters. The adoption of the discretization concept of the tool’s cutting motion makes it possible to dynamically track the cutting tool-workpiece interaction with the tool movement and to describe the cutting edges-workpiece discrete cutting interaction more realistically and, therefore, the microcharacteristics of the machined surfaces more accurately. Also, the effects of the cutting tool run-out and wear are incorporated into the developed model through modifying the tool center motion and the cutting-edge shape, respectively. As a fundamental study, the tool-swept envelope has been simulated. The developed simulation system is applied to thoroughly study the surface features formed by the 2.5-axis finish milling process. The application for general three-axis machining is discussed. Additionally, this paper studies the effect of the tool inclination, which is the most common characteristic in 3+2- or five-axis milling processes, on the machined surface features. Experiments are carried out to study the milling process and to verify the simulation results. The difference between the simulated and experimental results is discussed, and the reason behind the difference is explored.
Determining Setup Orientations From the Visibility of Slice Geometry for Rapid Computer Numerically Controlled Machining
Authors: Frank Matthew C. , Wysk Richard A. , Joshi Sanjay B.
Published: February 2006

A method for rapid computer numerically controlled (CNC) machining is being developed in an effort to automatically create functional prototypes and parts in a wide array of materials. The method uses a plurality of simple two-and-a-half-dimensional (212-D) toolpaths from various orientations about an axis of rotation in order to machine the entire surface of a part without refixturing. It is our goal to automatically create these toolpaths for machining and eliminate the complex planning traditionally associated with CNC machining. In this paper, we consider a problem that arises in automating this process—visibility to the surface of a model that is rotated about a fourth axis. Our approach involves slicing the computer-aided design (CAD) model orthogonal to the axis of rotation. The slice geometry is used to calculate two-dimensional visibility maps for the set of polygons on each slice plane. The visibility data provides critical information for determining the minimum number and orientation of 212-D toolpaths required to machine the entire surface of a part.
Progressive Die Sequence Design for Deep Drawing Round Cups Using Finite Element Analysis
Authors: Altan Taylan , Jain Nitin , Shi Xiaoxiang , Ngaile Gracious , Pax Bryan , Harman Brent , Homan Greg
Published: February 2006

A methodology for progressive die sequence design for forming round cups using finite element method (FEM) based simulations is discussed. The process sequence design developed was applied to forming of an automotive part and was compared with the design obtained from past experience. The methodology proposed in this paper has shown that the integration of design experience and FEM simulations can enhance the robustness of the procedure for die design sequence and reduces the die development cost considerably.
Note on “Effects of Random Defective Rate and Imperfect Rework Process on Economic Production Quantity Model”
Authors: Chiu Yuan-Shyi Peter , Chiu Singa Wang
Published: February 2006

Conventional approaches for deriving optimal production lot size are by using the differential calculus on the production-inventory cost function with the need to prove optimality first. Recent articles proposed the algebraic approach to the solution of classic economic order quantity and economic production quantity (EPQ) model without reference to the use of derivatives. This note extends it to an EPQ model taking the random defective rate and imperfect rework process into consideration. We demonstrate that the optimal lot size can be solved algebraically and the expected inventory cost can be derived immediately as well.
Optimized Upper Bound Analysis of Axisymmetric Extrusion Using Spherical Velocity Field
Authors: Chang Der-Form , Wang Jyhwen
Published: February 2006

This paper presents an upper bound approach to analyze axisymmetric extrusion processes. A cylindrical and a spherical coordinate system are defined to represent the die geometry and the velocity field, respectively. For various curved dies, minimized upper bound results can be obtained by relating these two coordinate systems. Based on this modeling technique, the effects of die geometry, reduction ratio, and friction are investigated. Axisymmetric extrusion through various curved dies can be easily optimized with the proposed methodology.
Digital Panel Assembly Methodologies and Applications for Compliant Sheet Components
Authors: Cai Wayne W. , Hsieh Ching-Chieh , Long Yufeng , Marin Samuel P. , Oh Kong P.
Published: February 2006

This paper presents digital panel assembly (DPA) methodologies and applications for sheet component assembly in automotive body manufacturing processes. Core to DPA is the customized finite element analysis formulas we have developed, which simulates assembly processes and predicts assembly dimensions by taking into consideration the panel compliances. Two key analysis types of the DPA are presented, the deterministic analysis and variation analysis. We present a methodology to utilize the quadratic form of Taylor series expansion to approximate the assembly dimensions efficiently in variation simulation, and discuss its pros and cons versus the traditional Monte Carlo method under different modeling conditions. For either the deterministic or variation analysis, linear models (without contact, efficient but less accurate), and nonlinear models (with contact, less efficient but accurate) can be established. It is shown that the linear models are only valid when panels do not penetrate, and that the nonlinear models should generally be used for accurate assembly dimension prediction. Based on the DPA methodologies, a software tool called Elastic Assembly Variation Simulation (EAVS) is presented, followed by application case studies. The confidence intervals for variation analysis are also discussed.
Optimal Approximated Unfolding of General Curved Shell Plates Based on Deformation Theory
Authors: Ryu Cheolho , Shin Jong Gye
Published: February 2006

Surfaces of many engineering structures, especially those of ships and airplanes, are commonly fabricated as either single- or double-curved surfaces to meet functional requirements. The first step in the fabrication process of a three-dimensional design surface is unfolding or flattening the surface, otherwise known as planar development, so that manufacturers can determine the initial shape of the flat plate. Also a good planar development enables the manufacturer to estimate the strain distribution required to form the design shape. In this paper, an algorithm for optimal approximated development of a general curved surface, including both single- and double-curved surfaces, is established by minimizing the strain energy of deformation from its planar development to the design surface. The unfolding process is formulated into a constrained nonlinear programming problem, based on the deformation theory and finite element. Constraints are subjected to the characteristics of the fabrication method. Some typical surfaces, such as convex-, saddle-, and cylinder-type ones, as well as the surfaces of practical ships are unfolded using the proposed algorithm and the results show the effectiveness of this algorithm.
Statistical Process Control Based Supervisory Generalized Predictive Control of Thin Film Deposition Processes
Authors: Jin Jionghua , Guo Huairui , Zhou Shiyu
Published: February 2006

This paper presents a supervisory generalized predictive control (GPC) by combining GPC with statistical process control (SPC) for the control of the thin film deposition process. In the supervised GPC, the deposition process is described as an ARMAX model for each production run and GPC is applied to the in situ thickness-sensing data for thickness control. Supervisory strategies, developed from SPC techniques, are used to monitor process changes and estimate the disturbance magnitudes during production. Based on the SPC monitoring results, different supervisory strategies are used to revise the disturbance models and the control law in the GPC to achieve a satisfactory control performance. A case study is provided to demonstrate the developed methodology.
Modeling Machining Geometric Variation in a N-2-1 Fixturing Scheme
Authors: Zhong Weiping , Hu S. Jack
Published: February 2006

Fixtures are used to locate and constrain workpieces in machining. Fixture properties, such as accuracy and locator layout schemes, directly affect the resultant geometric variation on the machined workpiece surfaces. N-2-1 fixturing schemes (N>3) are often used for large or compliant workpieces in machining. However, the impact of N-2-1 fixturing on product geometric variation is not well understood because of the uncertainty of contact under the overconstraint condition. This paper presents a modeling methodology to study the machining geometric variation in a 4-2-1 fixturing scheme. The model integrates the fixture-workpiece interactions resulted from the rigid-body variation in fixtures, workpieces, and machine tools, and the static deformation under external forces. The uncertainty of the fixture-workpiece contact condition due to the 4-2-1 constraint condition is modeled using the minimum potential energy theory. A numerical example of face milling is presented to demonstrate the methodology.
Finite Element Modeling for Tap Design Improvement in Form Tapping
Authors: Warrington Curtis , Kapoor Shiv , DeVor Richard
Published: February 2006

The form tapping process typically yields unfinished threads known as split crests. Thread quality can be greatly improved by reducing the size and severity of split crest formation. This paper develops a finite element model to simulate form tapping with an eye towards the reduction of split crests. The model is validated against linear scratch experiments, and simulations are compared to actual tapping. The effects of various tap design parameters and tapping process conditions on the formation of split crests are investigated to strive toward an optimal tap design.
Development of NiCr∕NiSi Thin-Film Thermocouple Sensor for Workpiece Temperature Measurement in Chemical Explosive Material Machining
Authors: Zeng Qiyong , Sun Baoyuan , Xu Jing , Deng Xinlu , Xu Jun , Jia Ying
Published: February 2006

Temperature plays a vital role in the machining industry today. With increasing cutting speeds being used in machining operations, the thermal aspects of cutting have become more important. A nickel-chrome versus nickel-silicon thin-film thermocouple system has been established for measuring instantaneous workpiece temperature in chemical explosive material machining. The thin-film thermocouples have been directly deposited inside high-speed steel cutters by means of multiple arc ion plating and the thickness of the thermocouple junction is only a few micrometers. The research effort has been concentrated on developing solutions to the insulating problem between the thin-film thermocouples and the high-speed steel cutters. SiO2 insulating films have been deposited on the high-speed steel substrates by microwave electron cyclotron resonance plasma source enhanced radiofrequency (rf) reactive magnetron sputtering. Static and dynamic calibrations of the NiCr∕NiSi thin-film thermocouples are presented. The results of the testing indicate that the thin-film thermocouples have good linearity, little response time, and perform excellently when machining in situ.
Nanometer-Level Comparison of Three Spindle Error Motion Separation Techniques
Authors: Marsh Eric , Couey Jeremiah , Vallance Ryan
Published: February 2006

This work demonstrates the state of the art capabilities of three error separation techniques for nanometer-level measurement of precision spindles and rotationally-symmetric artifacts. Donaldson reversal is compared to a multi-probe and a multi-step technique using a series of measurements carried out on a precision aerostatic spindle with a lapped spherical artifact. The results indicate that subnanometer features in both spindle error motion and artifact form are reliably resolved by all three techniques. Furthermore, the numerical error values agree to better than one nanometer. The paper discusses several issues that must be considered when planning spindle or artifact measurements at the nanometer level.
A Methodology to Determine Work Material Flow Stress and Tool-Chip Interfacial Friction Properties by Using Analysis of Machining
Authors: Özel Tuğrul , Zeren Erol
Published: February 2006

In this paper, we develop a methodology to determine flow stress at the machining regimes and friction characteristics at the tool-chip interface from the results of orthogonal cutting tests. We utilize metal cutting analysis originally developed by late Oxley and present some improvements. We also evaluate several temperature models in calculating the average temperatures at primary and secondary deformation zones and present comparisons with the experimental data obtained for AISI 1045 steel through assessment of machining models (AMM) activity. The proposed methodology utilizes measured forces and chip thickness obtained through a basic orthogonal cutting test. We conveniently determine work material flow stress at the primary deformation zone and the interfacial friction characteristics along the tool rake face. Calculated friction characteristics include parameters of the normal and frictional stress distributions on the rake face that are maximum normal stress σNmax, power exponent for the normal stress distribution, a, length of the plastic contact, lp, length of the tool-chip contact, lc, the average shear flow stress at tool-chip interface, kchip, and an average coefficient of friction, μe, in the sliding region of the tool-chip interface. Determined flow stress data from orthogonal cutting tests is combined with the flow stress measured through split-hopkinson pressure bar (SHPB) tests and the Johnson-Cook work material model is obtained. Therefore, with this methodology, we extend the applicability of a Johnson-Cook work material model to machining regimes.
Algorithm for Spatial Straightness Evaluation Using Theories of Linear Complex Chebyshev Approximation and Semi-infinite Linear Programming
Authors: Zhu LiMin , Ding Ye , Ding Han
Published: February 2006

This paper presents a novel methodology for evaluating spatial straightness error based on the minimum zone criterion. Spatial straightness evaluation is formulated as a linear complex Chebyshev approximation problem, and then reformulated as a semi-infinite linear programming problem. Both models for the primal and dual programs are developed. An efficient simplex-based algorithm is employed to solve the dual linear program to yield the straightness value. Also a general algebraic criterion for checking the optimality of the solution is proposed. Numerical experiments are given to verify the effectiveness and efficiency of the presented algorithm.
Dynamic Modeling of Powder Delivery Systems in Gravity-Fed Powder Feeders
Authors: Pan Heng , Landers Robert G. , Liou Frank
Published: February 2006

This paper presents an approach for modeling powder delivery system dynamics in low flow rate applications. Discrete particle modeling (DPM) is utilized to analyze the motion of individual powder particles. In DPM, an irregular bouncing model is employed to represent the powder dispersion in the powder delivery system induced by non-spherical particle-wall collisions. A three-dimensional friction collision model is utilized to simulate the interactions between particles and the powder delivery system walls. The modeling approach is experimentally verified and simulation studies are conducted to explore the effect of powder delivery system mechanical design parameters (i.e., tube length, diameter, and angle, number of tubes and meshes, and mesh orientation and size) on the powder flow dynamics. The simulation studies demonstrate that the powder delivery system dynamics can be modeled by a pure transport delay coupled with a first order system.
Three-Dimensional Modeling of Selective Laser Sintering of Two-Component Metal Powder Layers
Authors: Chen Tiebing , Zhang Yuwen
Published: February 2006

Laser sintering of a metal powder mixture that contains two kinds of metal powders with significantly different melting points under a moving Gaussian laser beam is investigated numerically. The continuous-wave laser-induced melting accompanied by shrinkage and resolidification of the metal powder layer are modeled using a temperature-transforming model. The liquid flow of the melted low-melting-point metal driven by capillary and gravity forces is also included in the physical model. The numerical results are validated by experimental results, and a detailed parametric study is performed. The effects of the moving heat source intensity, the scanning velocity, and the thickness of the powder layer on the sintering depth, the configuration of the heat affected zone, and the temperature distribution are discussed.
Dynamic Analysis of a Mesoscale Machine Tool
Authors: Lee Sang Won , Mayor Rhett , Ni Jun
Published: February 2006

Miniaturized machine tools, referred to as mesoscale machine tools (mMTs) henceforth, have been proposed as a way to manufacture micro/mesoscale mechanical components. A thorough study of the dynamic behavior of the mMT is required for the successful development of its machine structure. This paper demonstrates the development of an mMT, the performance evaluation of its mesoscale milling process, and the characterization of its dynamic behavior. The mMT is developed by using an air turbine spindle and three piezoelectric linear stages, and its volumetric size is 150×70×140mm. A series of micro/mesoscale milling experiments are conducted, and the performances in the developed mMT testbed are evaluated. The dynamic characteristics of the mMT can be different from those of conventional machine tools because the mMT is a miniaturized structure and comprises different machine components. Therefore, the effect of the miniaturization of a structure on the change of its dynamic behavior, called scaling law of the structural dynamics, is studied numerically and experimentally. The dynamic characteristics of the developed mMT that are estimated from the scaling law of the structural dynamics are much different from those obtained from an experimental modal analysis, and the flexible joints of the developed mMT are mainly responsible for this significant difference. Therefore, the joint dynamics of the mMT are studied by introducing an equivalent lumped parameter model, thus enabling simple identification of the joint dynamics and the effective modification of its critical joints to enhance a machining performance.