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G. Hirt,D. Schafer 한국소성가공학회 2010 기타자료 Vol.2010 No.6
For the process design of incremental forming processes like ring rolling or stretch forging there is need for fast and accurate simulation techniques. For many applications it would be necessary to predict the microstructural evolution during the process. For this reason the FEM-software Larstran/Shape which is used for the plastomechanical simulation can be coupled with the microstructure simulation module Strucsim. This software uses phenomenological equations for the calculation of recrystallization (dynamic and static) and grain size evolution [7]. To accelerate the simulation a multi mesh method has been developed. This method uses an adapted simulation mesh with fine elements only in the locally limited contact and forming zone to achieve a reduction of the number of elements. Due to the relative movement of the tool and workpiece the adapted FE-mesh has to be remeshed regularly according to the position of the tool. To avoid loss of information caused by the use of coarse elements the multi mesh method uses a second storage mesh which represents the entire workpiece and which is discretized using only fine elements. For the update of the storage mesh the displacement vectors and changes of scalar values like temperature can be interpolated. For the application of the multi mesh method to the microstructure simulation the update algorithm for the microstructure values has to be modified. The microstructure and plastomechanical simulation have to be uncoupled and the static recrystallization and grain growth outside the forming zone have to be calculated separately. Using the multi mesh method the simulation of incremental bulk metal forming processes including a microstructural simulation can be accelerated. The acceleration factor of the simulation compared to a simulation without adaptive meshing is dependent on the reduction of elements and nodes.
A lattice Dirac operator for QCD with light dynamical quarks
Cundy, N.,Kennedy, A.D.,Schafer, A. North Holland 2011 Nuclear physics, B Vol.845 No.1
In QCD chiral symmetry is explicitly broken by quark masses, the effect of which can be described reliably by chiral perturbation theory. Effects of explicit chiral symmetry breaking by the lattice regularisation of the Dirac operator, typically parametrised by the residual mass, should be negligible for almost all observables if the residual mass of the Dirac operator is much smaller than the quark mass. However, maintaining a small residual mass becomes increasingly expensive as the quark mass decreases towards the physical value and the continuum limit is approached. We investigate the feasibility of using a new approximately chiral Dirac operator with a small residual mass as an alternative to overlap and domain wall fermions for lattice simulations. Our Dirac operator is constructed from a Zolotarev rational approximation for the matrix sign function that is optimal for bulk modes of the hermitian kernel Dirac operator but not for the low-lying parts of its spectrum. We test our operator on various 32<SUP>3</SUP>x64 lattices, comparing the residual mass and the performance of the Hybrid Monte Carlo algorithm at a similar lattice spacing and pion mass with a hyperbolic tangent operator as used by domain wall fermions. We find that our approximations have a significantly smaller residual mass than domain wall fermions at a similar computational cost, and still admit topological charge change.
Arab, K.,Park, Y.,Lindroth, Anders M.,Schafer, A.,Oakes, C.,Weichenhan, D.,Lukanova, A.,Lundin, E.,Risch, A.,Meister, M.,Dienemann, H.,Dyckhoff, G.,Herold-Mende, C.,Grummt, I.,Niehrs, C.,Plass, C. Cell Press 2014 Molecular cell Vol.55 No.4
DNA methylation is a dynamic and reversible process that governs gene expression during development and disease. Several examples of active DNA demethylation have been documented, involving genome-wide and gene-specific DNA demethylation. How demethylating enzymes are targeted to specific genomic loci remains largely unknown. We show that an antisense lncRNA, termed TARID (for TCF21 antisense RNA inducing demethylation), activates TCF21 expression by inducing promoter demethylation. TARID interacts with both the TCF21 promoter and GADD45A (growth arrest and DNA-damage-inducible, alpha), a regulator of DNA demethylation. GADD45A in turn recruits thymine-DNA glycosylase for base excision repair-mediated demethylation involving oxidation of 5-methylcytosine to 5-hydroxymethylcytosine in the TCF21 promoter by ten-eleven translocation methylcytosine dioxygenase proteins. The results reveal a function of lncRNAs, serving as a genomic address label for GADD45A-mediated demethylation of specific target genes.
Eck, T. F.,Holben, B. N.,Reid, J. S.,Xian, P.,Giles, D. M.,Sinyuk, A.,Smirnov, A.,Schafer, J. S.,Slutsker, I.,Kim, J.,Koo, J.-H.,Choi, M.,Kim, K. C.,Sano, I.,Arola, A.,Sayer, A. M.,Levy, R. C.,Munchak American Geophysical Union 2018 Journal of Geophysical Research: Atmospheres Vol.123 No.10
<P>Analysis of Sun photometer measured and satellite retrieved aerosol optical depth (AOD) data has shown that major aerosol pollution events with very high fine mode AOD (>1.0 in midvisible) in the China/Korea/Japan region are often observed to be associated with significant cloud cover. This makes remote sensing of these events difficult even for high temporal resolution Sun photometer measurements. Possible physical mechanisms for these events that have high AOD include a combination of aerosol humidification, cloud processing, and meteorological covariation with atmospheric stability and convergence. The new development of Aerosol Robotic Network Version 3 Level 2 AOD with improved cloud screening algorithms now allow for unprecedented ability to monitor these extreme fine mode pollution events. Further, the spectral deconvolution algorithm (SDA) applied to Level 1 data (L1; no cloud screening) provides an even more comprehensive assessment of fine mode AOD than L2 in current and previous data versions. Studying the 2012 winter-summer period, comparisons of Aerosol Robotic Network L1 SDA daily average fine mode AOD data showed that Moderate Resolution Imaging Spectroradiometer satellite remote sensing of AOD often did not retrieve and/or identify some of the highest fine mode AOD events in this region. Also, compared to models that include data assimilation of satellite retrieved AOD, the L1 SDA fine mode AOD was significantly higher in magnitude, particularly for the highest AOD events that were often associated with significant cloudiness.</P>
Cohesive zone model을 이용한 접착 power steering cylinder 개발
손영기(Y.K. Son),이찬주(C.J. Lee),이상곤(S.K. Lee),고대철(D.C. Ko),H. Schafer,이종만(J.M. Lee),김병민(B.M. Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Adhesively bonded power steering cylinder with steel tube and aluminum bracket was developed to reduce the weight of steering system. To achieve the joint strength between steel tube and aluminum bracket, the shape aluminum bracket re-designed by using FE-analysis. The fracture behavior of adhesive layer is considered by cohesive zone model(CZM), which is based on two-parameter fracture phenomenon with critical stress and fracture toughness. From the result of FE-analysis with CZM, re-designed power steering cylinder was satisfied desired joint strength for axial and torsion modes. And its joint strength was verified by fracture test for each mode.
이찬주(C.J. Lee),김재영(J.Y. Kim),이상곤(S.K. Lee),고대철(D.C. Ko),H. Schafer,김병민(B.M. Kim) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
The purpose of this study is investigating the joint characteristics of advanced high strength steel DP780 and Al5052 alloy sheet in the clinching process. It is difficult to join the advanced high strength with light-weight materials like aluminum alloy, because of low formability of DP780. The defects of clinching joint such as necking of the upper sheet, cracks of the lower sheet and no interlocking were occurred by different ductility between advanced high strength steel and aluminum alloy. The clinching conditions should be optimized to interlock without andy defects. In this study, the effect of process parameters of clinching process on joinability of advanced high strength steel with Al5052 alloy was investigated by using FE-analysis. From the result of FE-analysis, the clearance between clinching punch and die, die depth and the shape of die cavity mainly affected the joinability of advanced high strength steel with Al5052 alloy.