14,520 research outputs found
Lee and Lee's atlas of Porter County, Indiana : illustrated /
No full textIncludes index and advertisements.LC copy imperfect: Front board and t.p. separated from binding. DL
dl-Polyalanine as a PEG-Free Thermogel
No full textThermogelling behavior of aqueous
polymer solutions comes from
the delicate balance between hydrophilic and hydrophobic moieties
of the polymer. Typically, poly(ethylene glycol) (PEG) has been used
as a hydrophilic block in most thermogels reported to date. However,
recent papers have suggested the potential immunogenicity of PEG-conjugated
compounds. Here, we report that aqueous solutions of dl-polyalanine
(DL-PA) with a specific molecular weight can exhibit thermogelling
behavior. In particular, DL-PA with a molecular weight (Mn) of 6690 Da, DL-PA67, exhibited sol-to-gel transition
at the physiologically important temperature range of 30–40
°C. 1H NMR and FTIR data indicated that the mechanism
of thermogelation is related to dehydration and conformational changes
of DL-PA67 from random coil to β-sheet structures. Subcutaneous
injection of an aqueous DL-PA67 solution into rats confirmed the gel
formation and its histocompatibility with mild tissue irritation
High cycle fatigue life prediction of cold forging tools based on workpiece material property
No full textThe present investigation is focused on high cycle fatigue life prediction based on material property of the workpiece. A new approach based on industrial tool life data was introduced for estimation of fatigue properties of the tool material. The effect of the strength coefficient K and strain hardening exponent n of four different workpiece materials was included in the local stress and strain approach to derive a simple relationship between the high cycle fatigue life and material property of the workpiece. According to this relationship, a reasonably reliable high cycle fatigue tool life can be estimated. (C) 2007 Elsevier B.V. All rights reserved.The authors wish to thank for grants from POSCO and
National Research Laboratory Programs of the KOSEF and for
the technical data from Thaeyang Industry. The fellowship from
the Korea Research Foundation was much appreciated for the
Master work of the first author
Two-dimensional finite element approximation of the hexagonal bolt forming process
No full textIn cold forging industry, it is well known that deformation mechanism of the billet and forming tools should be known during forging to properly design the dies and estimate the tool life. Since three-dimensional simulations of forging the geometrically complex forged parts involve with large computation time and effort, two-dimensional (2D) axi-symmetric approximation might be beneficial for an initial die design and selection of the machine capacity and die material. In the present study such an approximation was made for the two-stage hexagonal bolt forming process of two different carbon steels for comparative study. For simulations, in-house rigid-viscoplastic finite element (FE) programs were used for the deformation analysis with 2D and 3D approaches with hexahedral and tetrahedral elements to compare computation time, load requirement, distributions of the effective strain and stress, and interface boundary die force among three cases. The elastic analysis of tools was also carried out for comparison. It was found out that the load values and strain distributions were similar between 2D and 3D simulation results. However, elastic stress distributions in lower dies for 2D and 3D cases showed a relatively reasonable difference incurring the variation of tool life. For 3D simulations hexahedral element was more effective under the present investigation condition. (C) 2007 Elsevier B.V. All rights reserved.This work was supported by the Korea Science and Engineer-
ing Foundation (KOSEF) through the National Research Lab.
Program funded by the Ministry of Science and Technology
(No. R0A-2006-000-10240-0
Tool life prediction for the bolt forming process based on high-cycle fatigue and wear
No full textIn the present investigation an integrated model for predicting tool life in the cold forging process considering the high-cycle fatigue and wear is proposed in terms of mechanical properties of the workpiece. For calculating wear amount during cold forging, Archard's wear model was reformulated as an incremental form and implemented into the finite element code. Following a series of FE simulations, empirical equations for estimating the tool life based on wear and fatigue models were obtained. The present results showed that tool life due to high-cycle fatigue failure decreased significantly as the strength of material increased. Meanwhile tool life caused by wear also decreased as the strength of material decreased but the rate of tool life reduction was relatively small. This implies that tool life should be estimated using the fatigue failure model for cold forging of high strength steels. On the other hand, for cold forging of low strength steels, die life should be evaluated considering wear model as well. (C) 2007 Elsevier B.V. All rights reserved.This work was supported by the Korea Science and Engineer-
ing Foundation (KOSEF) through the National Research Lab.
Program funded by the Ministry of Science and Technology
(No. R0A-2006-000-10240-0
Effect of inclusion of dried distillers’ grains with solubles on the growth performance and immune responses of broilers
No full textSolution behavior of synthetic silk peptides and modified recombinant silk proteins
No full textSpider dragline silk from Nephila clavipes possesses impressive mechanical properties derived in part from repetitive primary sequence containing polyalanine regions that self-assemble into crystalline beta-sheets. In the present study, we have sought to understand more details of redox responses related to conformational transitions of modified silk peptides and a recombinant protein containing encoded methionine triggers. Regardless of the position of the methionine trigger relative to the polyalanine domain, chemical oxidation was rapid and slight increases in the alpha-helical structure and decreases in the beta-sheet and random coil content were observed by CD and FTIR in the assembled silk-like peptides and the recombinant protein. CD results indicated that the decrease in beta-sheet and random coil conformations, coupled with the increase in helical content during oxidation, occurred during the first 30 min of the reaction. No further conformational changes occurred after this time and the response was independent of methionine trigger location relative to the penta-alanine domain. These results were confirmed with fluorescence studies. The design, processing and utility of these modified redox triggered silk-like peptides and proteins suggest a range of potential utility, from biomaterials to engineered surface coatings with chemically alterable secondary structure and, thus, properties.Thanks are provided to Brian Vernaglia
for their input regarding the CD and fluorescence work. This work
was funded through the National Science Foundation-Division of Materials
Research grant
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