Littérature scientifique sur le sujet « Crystal cleavage »
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Articles de revues sur le sujet "Crystal cleavage"
1
Vaknin, Uriel, Dov Sherman, and Semën Gorfman. "Geometrical prediction of cleavage planes in crystal structures." IUCrJ 8, no. 5 (2021): 793–804. http://dx.doi.org/10.1107/s2052252521007272.
Texte intégralRésumé :
Cleavage is the ability of single crystals to split easily along specifically oriented planes. This phenomenon is of great interest for materials' scientists. Acquiring the data regarding cleavage is essential for the understanding of brittle fracture, plasticity and strength, as well as for the prevention of catastrophic device failures. Unfortunately, theoretical calculations of cleavage energy are demanding and often unsuitable for high-throughput searches of cleavage planes in arbitrary crystal structures. A simplified geometrical approach (GALOCS = gaps locations in crystal structures) is suggested for predicting the most promising cleavage planes. GALOCS enumerates all the possible reticular lattice planes and calculates the plane-average electron density as a function of the position of the planes in the unit cell. The assessment of the cleavage ability of the planes is based on the width and depth of planar gaps in crystal structures, which appear when observing the planes lengthwise. The method is demonstrated on two-dimensional graphene and three-dimensional silicon, quartz and LiNbO3 structures. A summary of planar gaps in a few more inorganic crystal structures is also presented.
2
Suharso, Suharso. "CHARACTERIZATION OF SURFACE OF THE (010) FACE OF BORAX CRYSTALS USING EX SITU ATOMIC FORCE MICROSCOPY (AFM):." Indonesian Journal of Chemistry 5, no. 3 (2010): 274–77. http://dx.doi.org/10.22146/ijc.21803.
Texte intégralRésumé :
The surface topology of borax crystals grown at a relative supersaturation of 0.21 has been investigated using ex situ atomic force microscopy (AFM). It was found that the cleavage of borax crystals along the (010) face planes has features of the cleavage of layered compounds, exhibiting cleavage steps of low heights. The step heights of the cleavage of the (010) face of borax crystal are from one unit cell to three unit cells of this face. Keywords: AFM, cleavage, borax.
3
Shterenlikht, A., and L. Margetts. "Three-dimensional cellular automata modelling of cleavage propagation across crystal boundaries in polycrystalline microstructures." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 471, no. 2177 (2015): 20150039. http://dx.doi.org/10.1098/rspa.2015.0039.
Texte intégralRésumé :
A three-dimensional cellular automata (CA) with rectilinear layout is used in this work to create and cleave polycrystalline microstructures. Each crystal is defined by a unique randomly generated orientation tensor. Separate states for grains, grain boundaries, crack flanks and crack fronts are created. Algorithms for progressive cleavage propagation through crystals and across grain boundaries are detailed. The mesh independent cleavage criterion includes the critical cleavage stress and the length scale. Resolution of an arbitrary crystallographic plane within a 26-cell Moore neighbourhood is considered. The model is implemented in Fortran 2008 coarrays. The model gives realistic predictions of grain size and mis-orientation distributions, grain boundary topology and crack geometry. Finally, we show how the proposed CA model can be linked to a finite-element model to produce a multi-scale fracture framework.
4
Bury, Charles S., Ian Carmichael, and Elspeth F. Garman. "OH cleavage from tyrosine: debunking a myth." Journal of Synchrotron Radiation 24, no. 1 (2017): 7–18. http://dx.doi.org/10.1107/s1600577516016775.
Texte intégralRésumé :
During macromolecular X-ray crystallography experiments, protein crystals held at 100 K have been widely reported to exhibit reproducible bond scission events at doses on the order of several MGy. With the objective to mitigate the impact of radiation damage events on valid structure determination, it is essential to correctly understand the radiation chemistry mechanisms at play. OH-cleavage from tyrosine residues is regularly cited as amongst the most available damage pathways in protein crystals at 100 K, despite a lack of widespread reports of this phenomenon in protein crystal radiation damage studies. Furthermore, no clear mechanism for phenolic C—O bond cleavage in tyrosine has been reported, with the tyrosyl radical known to be relatively robust and long-lived in both aqueous solutions and the solid state. Here, the initial findings of Tyr –OH group damage in a myrosinase protein crystal have been reviewed. Consistent with that study, at increasing doses, clear electron density loss was detectable local to Tyr –OH groups. A systematic investigation performed on a range of protein crystal damage series deposited in the Protein Data Bank has established that Tyr –OH electron density loss is not generally a dominant damage pathway in protein crystals at 100 K. Full Tyr aromatic ring displacement is here proposed to account for instances of observable Tyr –OH electron density loss, with the original myrosinase data shown to be consistent with such a damage model. Systematic analysis of the effects of other environmental factors, including solvent accessibility and proximity to disulfide bonds or hydrogen bond interactions, is also presented. Residues in known active sites showed enhanced sensitivity to radiation-induced disordering, as has previously been reported.
5
Bramwell, M. G. "Metamorphic differentiation; a mechanism indicated by zoned kyanite crystals in some rocks from the Lukmanier region, Switzerland." Mineralogical Magazine 49, no. 350 (1985): 59–64. http://dx.doi.org/10.1180/minmag.1985.049.350.07.
Texte intégralRésumé :
AbstractTwo samples of garnet-kyanite-staurolite schist from Lukmanier, Switzerland, each contain two chemical varieties of kyanite which occur in texturally distinct areas of the rock. Type 1 form large idiomorphic crystals within an open crenulation cleavage S3. They exhibit a systematic zonation of F2O3, with core values of 0.8% decreasing to 0.3% at the crystal margin. Type 2 form small, much less abundant crystals in areas between S3 cleavage zones, and have a homogeneous distribution of 0.3% Fe2O3 throughout the crystal.It is suggested that the first-nucleated crystals contain the highest core concentration of Fe2O3 and are the largest. A positive correlation between core Fe2O3 values and crystal size is interpreted as a nucleation and growth sequence. This indicates that the first crystals formed preferentially in S3 (Type 1), with Type 2 crystals growing later outside the S3 zones.Concentration of kyanite in S3 zones produces a distinct mineral banding in the rock. A mechanism for the development of metamorphic differentiation by preferred nucleation of kyanite in S3 is proposed.
6
Zhou, Cheng Hong, Yang Bai, and Ming Feng Hu. "Equipment Design for Supercritical Cleavage Technology." Applied Mechanics and Materials 496-500 (January 2014): 939–42. http://dx.doi.org/10.4028/www.scientific.net/amm.496-500.939.
Texte intégralRésumé :
Thin film is a class of materials forming bonds in two dimensional plane, and graphene is the most famous among thin film. Layered crystal is the natural macroscopical collection stacked by thin film and thin film is usually obtained by exfoliating layered crystal. In practice, it is feasible to exfoliate thin film similar to graphene from layered crystal via supercritical cleavage. As supercritical fluid can diffuse into the interlayer space of layered crystal easily, once reduce the pressure of the supercritical system fast, supercritical fluid between layers expands and escapes form interlayer, consequently exfoliating layered crystal into few-layer structure. As the supercritical condition is almost strict for most of supercritical medium, it is meaningful to design a useable reaction kettle that can work in the strict supercritical environment. In this article, the experiment equipment designed is introduced and it works well in the supercritical practical cleavage process.
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Yurov, V., and K. Zhangozin. "ABOUT THE MECHANISM OF MICA SPLITTING." Sciences of Europe, no. 133 (January 27, 2024): 97–104. https://doi.org/10.5281/zenodo.10575594.
Texte intégralRésumé :
The article provides an overview of experimental and theoretical methods for splitting mica using muscovite as an example, starting from the 30s of the last century. From a review of these works, it follows that when chopping (splitting) crystals, the structure of its surface layer, which is different from the structure of the main crystal, is not taken into account. In 2018, we proposed an empirical model by which it is theoretically possible to calculate the thickness of the surface layer of solids and its anisotropy. Subsequently, it turned out that the thickness of the surface layer is equal to the length of the nanocrack, which is formed in any solid body, obtained by any method in nature or artificially, and along which the crystal splits. The muscovite splitting model we propose includes: determination of the melting temperature of muscovite mica; determination of adhesion energy using the obtained equations; splitting of muscovite in the cleavage plane due to the creation of frictional forces in the rollers that exceed the adhesion energy.
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Mishnev, Anatoly, and Dmitrijs Stepanovs. "Crystal Structure Explains Crystal Habit for the Antiviral Drug Rimantadine Hydrochloride." Zeitschrift für Naturforschung B 69, no. 7 (2014): 823–28. http://dx.doi.org/10.5560/znb.2014-4075.
Texte intégralRésumé :
The crystal structure of the antiviral drug rimantadine hydrochloride, C12H22N+ Cl−, has been elucidated by a single-crystal X-ray structure analysis. The structure consists of 1-(1- adamantyl)ethanamine (rimantadinium) cations and chloride anions. The Cl− anions link the rimantadinium cations via N-H...Cl hydrogen bonds into infinite rectangular chord-like structural units with charged groups in the inner channel and aliphatic groups on the surface, and oriented along the unit cell c axis. In contrast to strong electrostatic and hydrogen bonding inner interactions the chords in the crystal are held together by weak van der Waals forces only. A two-fold symmetry axis passes through the center of the chord. By indexing of the crystal faces it has been shown that the maximal dimension of the needle-like crystals coincides with the direction of the unit cell c axis. These structural features explain the crystal habit and the anisotropy of the mechanical properties of rimantadine hydrochloride crystals observed upon slicing and cleavage.
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Prieto, Jesús, Pilar Redondo, Nekane Merino, et al. "Structure of the I-SceI nuclease complexed with its dsDNA target and three catalytic metal ions." Acta Crystallographica Section F Structural Biology Communications 72, no. 6 (2016): 473–79. http://dx.doi.org/10.1107/s2053230x16007512.
Texte intégralRésumé :
Homing endonucleases are highly specific DNA-cleaving enzymes that recognize and cleave long stretches of DNA. The engineering of these enzymes provides instruments for genome modification in a wide range of fields, including gene targeting. The homing endonuclease I-SceI from the yeastSaccharomyces cerevisiaehas been purified after overexpression inEscherichia coliand its crystal structure has been determined in complex with its target DNA. In order to evaluate the number of ions that are involved in the cleavage process, thus determining the catalytic mechanism, crystallization experiments were performed in the presence of Mn2+, yielding crystals that were suitable for X-ray diffraction analysis. The crystals belonged to the orthorhombic space groupP212121, with unit-cell parametersa= 80.11,b= 80.57,c= 130.87 Å, α = β = γ = 90°. The self-rotation function and the Matthews coefficient suggested the presence of two protein–DNA complexes in the asymmetric unit. The crystals diffracted to a resolution limit of 2.9 Å using synchrotron radiation. From the anomalous data, it was determined that three cations are involved in catalysis and it was confirmed that I-SceI follows a two-metal-ion DNA-strand cleavage mechanism.
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Schultz, Richard A., Martin C. Jensen, and Richard C. Bradt. "Single crystal cleavage of brittle materials." International Journal of Fracture 65, no. 4 (1994): 291–312. http://dx.doi.org/10.1007/bf00012370.
Texte intégralThèses sur le sujet "Crystal cleavage"
1
Sasmal, Pijus Kumar. "Aspects Of The Chemistry Of Oxovanadiulm(IV) Complexes Showing Photo-Induced Cytotoxicity And DNA Cleavage Activity." Thesis, 2010. https://etd.iisc.ac.in/handle/2005/1266.
Texte intégralRésumé :
The present thesis deals with different aspects of the chemistry of oxovanadium(IV) complexes, their interaction with DNA and protein and photo-induced DNA and protein cleavage activity and photocytotoxicity.
Chapter I presents a general introduction on various modes of interactions of organic compounds and transition metal complexes capable of targeting DNA leading to DNA strand scission, emphasizing particularly the photo-induced DNA cleavage activities for their potential application in PDT. The mechanistic pathways associated with the DNA cleavage are discussed. A comparison has been made on the advantages of photoactive metal complexes over organic conjugates. Objective of the present investigation is also dealt in this Chapter.
Chapter II of the thesis deals with the synthesis, characterization, DNA binding and photo-induced DNA cleavage activity of ternary oxovanadium(IV) complexes of N-salicylidene-S-methyldithiocarbazate (salmdtc) and phenanthroline bases to explore the photo-induced DNA cleavage activity in UV-A light of 365 nm.
Chapter III presents the synthesis, characterization, DNA binding and photo-induced DNA cleavage activity of ternary oxovanadium(IV) complexes containing N-salicylidene-L-methionate (salmet) and N-salicylidene-L-tryptophanate (saltrp) Schiff bases and phenanthroline bases. The objective of this work is to investigate the photo-induced DNA cleavage activity in near-IR light and to see the effect of pendant thiomethyl and indole moieties in the DNA cleavage reactions.
Chapter IV deals with the synthesis, characterization, DNA binding, red-light induced DNA cleavage activity and photocytotoxicity of ternary oxovanadium(IV) complexes having N-salicylidene-L-arginine (sal-argH) and N-salicylidene-L-lysine (sal-lysH) Schiff bases and phenanthroline bases. The important results include the visible light-induced DNA cleavage activity and photocytotoxicity of the complexes in human cervical HeLa cancer cells.
Chapter V describes the synthesis, characterization, DNA binding and photo-induced DNA and protein cleavage activity and photocytotoxicity of oxovanadium(IV) complexes containing bis(2-benzimidazolylmethyl)amine and phenanthroline bases. The significant results include DNA cleavage activity in near-IR light and photocytotoxicity of the dppz complex in non-small cell lung carcinoma/human lung adenocarcinoma A549 cells in visible light. Further, we have studied the protein cleavage activity of the complexes in UV-A light of 365 nm by using bovine serum albumin (BSA) and lysozyme.
Finally, Chapter VI presents the binary oxovanadium(IV) complexes of phenanthroline bases. We have studied their synthesis, characterization, DNA binding and photo-induced DNA and protein cleavage activity and photocytotoxicity. Photocytotoxicity of dppz complex has been studied in human cervical HeLa cancer cells in visible light. Photo-induced protein cleavage activity of the complexes has been studied in UV-A light of 365 nm by using BSA and lysozyme.
The references have been compiled at the end of each chapter and indicated as superscript numbers in the text. The complexes presented in this thesis are represented by bold-faced numbers. Crystallographic data of the complexes, characterized structurally by single crystal X-ray crystallography, are given in CIF format in the enclosed CD (Appendix-I). Due acknowledgements have been made wherever the work described is based on the findings of other investigators. Any omission that might have happened due to oversight or mistake is regretted.
2
Sasmal, Pijus Kumar. "Aspects Of The Chemistry Of Oxovanadiulm(IV) Complexes Showing Photo-Induced Cytotoxicity And DNA Cleavage Activity." Thesis, 2010. http://etd.iisc.ernet.in/handle/2005/1266.
Texte intégralRésumé :
The present thesis deals with different aspects of the chemistry of oxovanadium(IV) complexes, their interaction with DNA and protein and photo-induced DNA and protein cleavage activity and photocytotoxicity.
Chapter I presents a general introduction on various modes of interactions of organic compounds and transition metal complexes capable of targeting DNA leading to DNA strand scission, emphasizing particularly the photo-induced DNA cleavage activities for their potential application in PDT. The mechanistic pathways associated with the DNA cleavage are discussed. A comparison has been made on the advantages of photoactive metal complexes over organic conjugates. Objective of the present investigation is also dealt in this Chapter.
Chapter II of the thesis deals with the synthesis, characterization, DNA binding and photo-induced DNA cleavage activity of ternary oxovanadium(IV) complexes of N-salicylidene-S-methyldithiocarbazate (salmdtc) and phenanthroline bases to explore the photo-induced DNA cleavage activity in UV-A light of 365 nm.
Chapter III presents the synthesis, characterization, DNA binding and photo-induced DNA cleavage activity of ternary oxovanadium(IV) complexes containing N-salicylidene-L-methionate (salmet) and N-salicylidene-L-tryptophanate (saltrp) Schiff bases and phenanthroline bases. The objective of this work is to investigate the photo-induced DNA cleavage activity in near-IR light and to see the effect of pendant thiomethyl and indole moieties in the DNA cleavage reactions.
Chapter IV deals with the synthesis, characterization, DNA binding, red-light induced DNA cleavage activity and photocytotoxicity of ternary oxovanadium(IV) complexes having N-salicylidene-L-arginine (sal-argH) and N-salicylidene-L-lysine (sal-lysH) Schiff bases and phenanthroline bases. The important results include the visible light-induced DNA cleavage activity and photocytotoxicity of the complexes in human cervical HeLa cancer cells.
Chapter V describes the synthesis, characterization, DNA binding and photo-induced DNA and protein cleavage activity and photocytotoxicity of oxovanadium(IV) complexes containing bis(2-benzimidazolylmethyl)amine and phenanthroline bases. The significant results include DNA cleavage activity in near-IR light and photocytotoxicity of the dppz complex in non-small cell lung carcinoma/human lung adenocarcinoma A549 cells in visible light. Further, we have studied the protein cleavage activity of the complexes in UV-A light of 365 nm by using bovine serum albumin (BSA) and lysozyme.
Finally, Chapter VI presents the binary oxovanadium(IV) complexes of phenanthroline bases. We have studied their synthesis, characterization, DNA binding and photo-induced DNA and protein cleavage activity and photocytotoxicity. Photocytotoxicity of dppz complex has been studied in human cervical HeLa cancer cells in visible light. Photo-induced protein cleavage activity of the complexes has been studied in UV-A light of 365 nm by using BSA and lysozyme.
The references have been compiled at the end of each chapter and indicated as superscript numbers in the text. The complexes presented in this thesis are represented by bold-faced numbers. Crystallographic data of the complexes, characterized structurally by single crystal X-ray crystallography, are given in CIF format in the enclosed CD (Appendix-I). Due acknowledgements have been made wherever the work described is based on the findings of other investigators. Any omission that might have happened due to oversight or mistake is regretted.
3
Bhowmick, Tuhin. "Crystal Structure Of Mycobacterium Tuberculosis Histone Like Protein HU And Structure Based Design Of Molecules To Inhibit MtbHU-DNA Interaction : Leads For A New Target. Structure Aided Computational Analysis Of Metal Coordinated Complexes Containing Amino Acids And Organic Moieties Designed For Photo Induced DNA Cleavage." Thesis, 2012. https://etd.iisc.ac.in/handle/2005/2469.
Texte intégralRésumé :
In bacteria, nucleoid associated proteins (NAPs) represent a prominent group of global regulators that perform the tasks of genome compaction, establishing chromosomal architecture and regulation of various DNA transactions like replication, transcription, recombination and repair. HU, a basic histone like protein, is one of the most important NAPs in Eubacteria. Mycobacterium tuberculosis produces a homodimeric HU (MtbHU), which interacts with DNA non-specifically through minor groove binding. Exploration for essential genes in Mtb (H37Rv) through transposon insertion has identified HU coding gene [Rv2986c, hupB; Gene Id: 15610123; Swiss-Prot ID: P95109)] to be vital for the survival and growth of this pathogen.
MtbHU contains two domains, the N-terminal domain which is considerably conserved among the HU proteins of the prokaryotic world, and a C–terminal domain consisting of Lys-Ala rich multiple repeat degenerate motifs. Sequence analysis carried out by the thesis candidate showed that MtbHU exhibits 86 to 100 percent identity within the N-term region among all the mycobacterium species and some of the members of actinobacteria, including important pathogens like M. tuberculosis, M. leprae, M. ulcerans, M. bovis, Nocardia; while C term repeat region varies relatively more. This strikingly high cross species identity establishes the MtbHU N-terminal domain (MtbHUN) as an important representative structural model for the above mentioned group of pathogens.
The thesis candidate has solved the X-ray crystal structure of MtbHUN, crystallized in two different forms, P2 and P21. The crystal structures in combination with computational analyses elucidate the structural details of MtbHU interaction with DNA. Moreover, the similar mode of self assembly of MtbHUN observed in two different crystal forms reveals that the same DNA binding interface of the protein can also be utilized to form higher order oligomers, that HU is known to form at higher concentrations. Though the bifunctional interface involved in both DNA binding and self assembly is not akin to a typical enzyme active site, the structural analysis identified key interacting residues involved in macromolecular interactions, allowing us to develop a rationale for inhibitor design. Further, the candidate has performed virtual screening against a vast library of compounds, and design of small molecules to target MtbHU and disrupt its binding to DNA. Various biochemical, mutational and biological studies were performed in the laboratory of our collaborator Prof. V. Nagaraja, MCBL, IISc., to investigate these aspects. After a series of iterations including design, synthesis and validation, we have identified novel candidate molecules, which bind to MtbHU, disrupt chromosomal architecture and arrest M. tuberculosis growth. Thus, the study suggests that, these molecules can serve as leads for a new class of DNA-interaction inhibitors and HU as a druggable target, more so because HU is essential to Mtb, but absent in human. Our study proposes that, targeting the nucleoid associated protein HU in Mtb can strategize design of new anti-mycobacterial therapeutics. Perturbation of MtbHU-DNA binding through the identified compounds provides the first instance of medium to small molecular inhibitors of NAP, and augurs well for the development of chemical probe(s) to perturb HU functions, and can be used as a fundamental chemical tool for the system level studies of HU-interactome.
Section I: “Crystal structure of Mycobacterium tuberculosis histone like protein HU and structure based design of molecules to inhibit MtbHU-DNA interaction: Leads for a new target.” of this thesis presents an elaborate elucidation of the above mentioned work.
The candidate has additionally carried out structure based computational and theoretical work to elucidate the interaction of amino acid based metal complexes which efficiently bind to DNA via minor-groove, major-groove or base intercalation interaction and display DNA cleavage activity on photo-irradiation. This understanding is crucial for the design of molecules towards Photodynamic Therapy (PDT). PDT is an emerging method of non-invasive treatment of cancer in which drugs like Photofrin show localized toxicity on photoactivation at the tumor cells leaving the healthy cells unaffected.
The work carried out in our group in close collaboration with Prof. A.R. Chakravarty of Inorganic and Physical Chemistry Department elaborates the structure based design of Amino acid complexes containing single Cu (II), such as [Cu(L-trp)(dpq)(H2O)]+ , [Cu (L-arg) 2](NO3)2 , Amino acid complexes containing oxobridged diiron Fe(III), such as [{Fe(L-his)(bpy)}2(μ-O)](ClO4)2 , [{Fe(L-his)(phen)}2(μ-O)](ClO4)2 , and Complexes containing Binuclear Cu(II) coordinated organic moiety, such as [{(dpq) CuII}2(μ-dtdp)2], which bind to DNA through minor groove/major groove/base intercalation interactions. Docking analysis was performed with the X-ray crystallographic structure of DNA as receptor and the metal complexes as ligands, to study the mode of binding to DNA and to understand the possible mode of DNA cleavage (single/double strand) when activated with laser.
Section II: “Structure based computational and theoretical analysis of metal coordinated complexes containing amino acids and organic moieties designed for photo induced DNA cleavage” of this thesis presents a detailed presentation of the above mentioned work.
4
Bhowmick, Tuhin. "Crystal Structure Of Mycobacterium Tuberculosis Histone Like Protein HU And Structure Based Design Of Molecules To Inhibit MtbHU-DNA Interaction : Leads For A New Target. Structure Aided Computational Analysis Of Metal Coordinated Complexes Containing Amino Acids And Organic Moieties Designed For Photo Induced DNA Cleavage." Thesis, 2012. http://hdl.handle.net/2005/2469.
Texte intégralRésumé :
In bacteria, nucleoid associated proteins (NAPs) represent a prominent group of global regulators that perform the tasks of genome compaction, establishing chromosomal architecture and regulation of various DNA transactions like replication, transcription, recombination and repair. HU, a basic histone like protein, is one of the most important NAPs in Eubacteria. Mycobacterium tuberculosis produces a homodimeric HU (MtbHU), which interacts with DNA non-specifically through minor groove binding. Exploration for essential genes in Mtb (H37Rv) through transposon insertion has identified HU coding gene [Rv2986c, hupB; Gene Id: 15610123; Swiss-Prot ID: P95109)] to be vital for the survival and growth of this pathogen.
MtbHU contains two domains, the N-terminal domain which is considerably conserved among the HU proteins of the prokaryotic world, and a C–terminal domain consisting of Lys-Ala rich multiple repeat degenerate motifs. Sequence analysis carried out by the thesis candidate showed that MtbHU exhibits 86 to 100 percent identity within the N-term region among all the mycobacterium species and some of the members of actinobacteria, including important pathogens like M. tuberculosis, M. leprae, M. ulcerans, M. bovis, Nocardia; while C term repeat region varies relatively more. This strikingly high cross species identity establishes the MtbHU N-terminal domain (MtbHUN) as an important representative structural model for the above mentioned group of pathogens.
The thesis candidate has solved the X-ray crystal structure of MtbHUN, crystallized in two different forms, P2 and P21. The crystal structures in combination with computational analyses elucidate the structural details of MtbHU interaction with DNA. Moreover, the similar mode of self assembly of MtbHUN observed in two different crystal forms reveals that the same DNA binding interface of the protein can also be utilized to form higher order oligomers, that HU is known to form at higher concentrations. Though the bifunctional interface involved in both DNA binding and self assembly is not akin to a typical enzyme active site, the structural analysis identified key interacting residues involved in macromolecular interactions, allowing us to develop a rationale for inhibitor design. Further, the candidate has performed virtual screening against a vast library of compounds, and design of small molecules to target MtbHU and disrupt its binding to DNA. Various biochemical, mutational and biological studies were performed in the laboratory of our collaborator Prof. V. Nagaraja, MCBL, IISc., to investigate these aspects. After a series of iterations including design, synthesis and validation, we have identified novel candidate molecules, which bind to MtbHU, disrupt chromosomal architecture and arrest M. tuberculosis growth. Thus, the study suggests that, these molecules can serve as leads for a new class of DNA-interaction inhibitors and HU as a druggable target, more so because HU is essential to Mtb, but absent in human. Our study proposes that, targeting the nucleoid associated protein HU in Mtb can strategize design of new anti-mycobacterial therapeutics. Perturbation of MtbHU-DNA binding through the identified compounds provides the first instance of medium to small molecular inhibitors of NAP, and augurs well for the development of chemical probe(s) to perturb HU functions, and can be used as a fundamental chemical tool for the system level studies of HU-interactome.
Section I: “Crystal structure of Mycobacterium tuberculosis histone like protein HU and structure based design of molecules to inhibit MtbHU-DNA interaction: Leads for a new target.” of this thesis presents an elaborate elucidation of the above mentioned work.
The candidate has additionally carried out structure based computational and theoretical work to elucidate the interaction of amino acid based metal complexes which efficiently bind to DNA via minor-groove, major-groove or base intercalation interaction and display DNA cleavage activity on photo-irradiation. This understanding is crucial for the design of molecules towards Photodynamic Therapy (PDT). PDT is an emerging method of non-invasive treatment of cancer in which drugs like Photofrin show localized toxicity on photoactivation at the tumor cells leaving the healthy cells unaffected.
The work carried out in our group in close collaboration with Prof. A.R. Chakravarty of Inorganic and Physical Chemistry Department elaborates the structure based design of Amino acid complexes containing single Cu (II), such as [Cu(L-trp)(dpq)(H2O)]+ , [Cu (L-arg) 2](NO3)2 , Amino acid complexes containing oxobridged diiron Fe(III), such as [{Fe(L-his)(bpy)}2(μ-O)](ClO4)2 , [{Fe(L-his)(phen)}2(μ-O)](ClO4)2 , and Complexes containing Binuclear Cu(II) coordinated organic moiety, such as [{(dpq) CuII}2(μ-dtdp)2], which bind to DNA through minor groove/major groove/base intercalation interactions. Docking analysis was performed with the X-ray crystallographic structure of DNA as receptor and the metal complexes as ligands, to study the mode of binding to DNA and to understand the possible mode of DNA cleavage (single/double strand) when activated with laser.
Section II: “Structure based computational and theoretical analysis of metal coordinated complexes containing amino acids and organic moieties designed for photo induced DNA cleavage” of this thesis presents a detailed presentation of the above mentioned work.
5
Paul, Subhadeep. "Studies on BODIPY Appended Ruthenium(II) Complexes for Bioimaging and Photodynamic Therapy Applications." Thesis, 2022. https://etd.iisc.ac.in/handle/2005/5894.
Texte intégralRésumé :
Photodynamic therapy (PDT) is a medical technique that utilizes light, oxygen, and a photosensitizer to treat several medical conditions, including cancer. Because of the limitations and side effects of traditional anticancer therapies like surgery, chemotherapy, and radiation therapy, PDT has been recognized as an adjuvant and, in some cases, a mainstream alternative. Currently, clinical PDT utilizes tetrapyrrolic photosensitizers that possess several drawbacks. Even worldwide approved gold standard photosensitizer Photofrin® requires a high dose for the therapeutic effect that results in undesirable side effects like skin sensitivity and hepatotoxicity. In recent years, transition metal complexes are gaining interest as new photosensitizers with their fine-tuned photophysical and biological properties. This thesis work presents the results from a systematic study on the design and synthesis of new boron-dipyrromethene (BODIPY) appended ruthenium(II)complexes to study their photoinduced reactive oxygen species (ROS) generation ability, light-induced cytotoxicity and cellular imaging ability.
Here, a wide range of ruthenium coordination units are connected to BODIPY chromophore with various linkers, and their effect on photophysical and photobiological properties investigated. New ruthenium(II) complexes with formulations [Ru(L1/2)(L3/4)Cl]Cl where L1, L2 (having biotin) are NN-donor bidentate phenanthroline derivatives and L3, L4 (contain BODIPY) are NNN-donor tridentate dipicolylamine derivative, were synthesized, characterized and their photocytotoxicity evaluated. The complex having both BODIPY and cancer targeting biotin showed cancer cells elective PDT effect giving respective IC50 value of 0.98±0.04 and 3.9±0.4 μM in A549 (lung cancer) and HPL1D (noncancerous) cell lines in visible light of 400-700 nm, while being non-toxic in the dark. Analogous complexes containing di-styryl BODIPY were prepared and their PDT activity with redlight activation was evaluated. The active complex produced a remarkable photocytotoxicity index (PI, ratio of IC50 in dark and with light exposure) of >5000 with red light (600- 720 nm) activation. Next, a series of bichromophoric systems having a heteroleptic [Ru(tpy)2] (tpy = terpyridine) moiety covalently linked to a BODIPY pendant were prepared, characterized and their photophysical and photobiological properties were evaluated. In a following study, a series of biotin-conjugated compounds containing BODIPY or Ru(II)-bis-tpy or both chromophoric units were developed and the difference of multichromophoric Ru-BODIPY conjugates with structurally similar compounds having a single chromophore were investigated highlighting the importance of constructing such bichromophoric systems. These bichromophoric systems produced both superoxide and singlet oxygen via dual type-I/II photosensitization processes and exerted potent apoptotic PDT effect with visible light activation. Finally, two homoleptic complexes with formulation [Ru(tpy-BODIPY)2]Cl2,where the connection between the BODIPY unit and the Ru(II)-bis-tpy scaffold differs by a phenylacetylene spacer, were prepared as PDT agents with simple molecular design and the effect of the spacer was studied in terms of structure-activity relationship. In summary, this thesis work presents systematic developments of Ru(II)-BODIPY conjugates as novel photosensitizers and photodetection agents for phototherapeutic applications.
Livres sur le sujet "Crystal cleavage"
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Chen, Po-Shou. Hydrogen induced fracture characteristics of single crystal nickel-based superalloys: Final report, NAS8-38184, June 19, 1989 - June 18, 1990. George C. Marshall Space Flight Center, 1990.
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C, Wilcox Roy, and United States. National Aeronautics and Space Administration., eds. Determination of cleavage planes and fracture characterization of Ni-based single crystal superalloys: Final progress report. Dept. of Mechanical Engineering, Auburn University, 1992.
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Evaluation of the effect of microalloying on cleavage of monocrystalline NiAl using a miniaturized disk-bend test: Summary of research for the period March 1, 1992 to March 6, 1996; National Aeronautics and Space Administration, grant no. NAG 3-1325. National Aeronautics and Space Administration, 1997.
Trouver le texte intégralChapitres de livres sur le sujet "Crystal cleavage"
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Yamanoi, Yoshinori, Kenichiro Omoto, Toyotaka Nakae, and Masaki Nishio. "Thermosalient Phenomena in Molecular Crystals: A Case Study of Representative Molecules." In The Materials Research Society Series. Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-0260-6_8.
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AbstractMolecular crystals have a regularly packed structure, and their physical properties often depend on intramolecular and intermolecular interactions. Here, we review the crystal jumping phenomena under a thermal stimulus (thermosalient phenomenon). Thermosalient phenomena are characterized by thermal phase transitions and anisotropic lattice expansion/contraction at a microscopic scale and jumping behavior through bending/deformation/rotation/cleavage of crystals at a macroscopic scale. The absence of strong intermolecular interaction in the crystal and the misalignment of the crystal plane associated with the phase transition are explained as factors causing the thermosalient phenomena. In this chapter, various case studies with representative molecular crystals that exhibit the thermosalient phenomenon are explained in detail.
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Kitamura, Takayuki, Kisaragi Yashiro, and Ryuichi Ohtani. "Criteria for Nucleation of a Dislocation and a Cleavage Crack in a Nickel Single Crystal Based on Molecular Dynamics." In Mesoscopic Dynamics of Fracture. Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/978-3-662-35369-1_10.
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Schultz, Richard A., and Richard C. Bradt. "Cleavage of Ceramic and Mineral Single Crystals." In Fracture Mechanics of Ceramics. Springer US, 1992. http://dx.doi.org/10.1007/978-1-4615-3348-1_9.
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Neumann, P., and H. Vehoff. "Discussion: Remark Concerning the Evidence of Cleavage in our Experiments in Single Crystals of Fe2.6%Si." In Chemistry and Physics of Fracture. Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-009-3665-2_6.
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Newnham, Robert E. "Chemical anisotropy." In Properties of Materials. Oxford University Press, 2004. http://dx.doi.org/10.1093/oso/9780198520757.003.0034.
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Chemical anisotropy concerns the ways in which crystals grow or dissolve in different directions. It is an appropriate subject to end this book because it brings together the oldest and the newest parts of crystal physics. Long, long ago mineralogists described the shapes of natural crystals and noted correlations with cleavage, hardness, and other physical properties. Chemical etching was another favorite topic in classical crystal physics that has undergone a recent revival because of the interest in the micromachining of semiconductor devices. Chemical anisotropy involves the interaction of a crystal with a chemically active environment that promotes dissolution or growth. For this reason it is primarily a surface property, rather than a bulk property of the crystal. This is one of the reasons why chemical anisotropy is not normally included in crystal physics books. The other reason is that rates of growth and dissolution depend on the chemical nature of the environment much more than the bulk properties of crystals do. Nevertheless, this is an important subject in contemporary crystal physics. Surfaces become more and more important as the scale of engineered devices grows smaller. The crystal physics of surface properties is a natural extension of classical crystal physics. It is a topic still in its infancy. Under favorable conditions, crystal growth takes place in such a way that the external surface is bounded by a set of plane faces. The preferred shape of rocksalt family crystals is cube bounded by six symmetry-related {100} faces. For diamond, an octahedral shape with eight {111} faces often appears. Quartz, calcite, and rutile belong to lower symmetry crystal systems with more anisotropic morphologies. Quartz crystals are often elongated along the c-axis with a hexagonal cross-section bounded by six {100} faces while the ends are terminated by six {101} and six {011} faces. Calcite tends to form rhombohedra with six faces shaped like parallelograms. Rutile (TiO2) crystals are often elongated along the c-axis forming slender needles.
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Glusker, Jenny Pickworth, and Kenneth N. Trueblood. "Micro- and noncrystalline materials." In Crystal Structure Analysis. Oxford University Press, 2010. http://dx.doi.org/10.1093/oso/9780199576340.003.0023.
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The crystalline state is characterized by a high degree of internal order. There are two types of order that we will discuss here. One is chemical order, which consists of the connectivity (bond lengths and bond angles) and stoichiometry in organic and many inorganic molecules, or just stoichiometry in minerals, metals, and other such materials. Some degree of chemical ordering exists for any molecule consisting of more than one atom, and the molecular structure of chemically simple gas molecules can be determined by gaseous electron diffraction or by high-resolution infrared spectroscopy. The second type of order to be discussed is geometrical order, which is the regular arrangement of entities in space such as in cubes, cylinders, coiled coils, and many other arrangements. For a compound to be crystalline it is necessary for the geometrical order of the individual entities (which must each have the same overall conformation) to extend indefinitely (that is, apparently infinitely) in three dimensions such that a three-dimensional repeat unit can be defined from diffraction data. Single crystals of quartz, diamond, silicon, or potassium dihydrogen phosphate can be grown to be as large as six or more inches across. Imagine how many atoms or ions must be identically arranged to create such macroscopic perfection! Sometimes, however, this geometrical order does not extend very far, and microarrays of molecules or ions, while themselves ordered, are disordered with respect to each other on a macroscopic scale. In such a case the three-dimensional order does not extend far enough to give a sharp diffraction pattern. The crystal quality is then described as “poor” or the crystal is considered to be microcrystalline, as in the naturally occurring clay minerals. On the other hand, in certain solid materials the spatial extent of geometrical order may be less than three-dimensional, and this reduced order gives rise to interesting properties. For example, the geometrical order may exist only in two dimensions; this is the case for mica and graphite, which consist of planar structures with much weaker forces between the layers so that cleavage and slippage are readily observed.
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Zhu, Lei, Junjie Huang, Qian Wang, Xiao Luo, and Youliang Xu. "High-Temperature Mechanical Behavior of SiCf/SiC Composite Riveted Structure: An Experimental Investigation." In Advances in Transdisciplinary Engineering. IOS Press, 2025. https://doi.org/10.3233/atde250073.
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Advanced composites have been widely used for aero-engine components for the purpose of their excellent properties. This study aims to improve the understanding of the high-temperature mechanical behavior of ceramic matrix composite riveted joint. 2D plain fabric SiCf/SiC riveted joints were tested under compression load at high temperature. Results showed that for 900∼1300 °C, the shear stiffness and shear strength of the SiCf/SiC riveted joint increased with increasing the temperature. But for 1300∼1350 °C, the shear stiffness and shear strength decreased with increasing the temperature. Fiber crystal orientation and crystallinity degree had effects on the mechanical properties of the SiCf/SiC riveted joint. Besides, the SiCf/SiC composites suffered no oxidation under high temperature, and the SiC fibers showed typical cleavage fracture with mirror zone and plumose zone.
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Beard, W. A., and S. H. Wilson. "Reverse transcriptase." In HIV. Oxford University PressOxford, 1995. http://dx.doi.org/10.1093/oso/9780199634996.003.0002.
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Abstract The reverse transcriptase (RT) of human immunodeficiency virus type-1 (HIV-1) converts the single-stranded (+) viral RNA genome into double¬ stranded proviral DNA prior to its integration into the host genomic DNA. The HIV-1 RT has therefore been the target for anti-viral drug design (1). The cloning of the RT in biologically active form has made large quantities of enzyme available for biophysical and kinetic studies. In vivo, the heterodimeric form (p66/p51) of RT is believed to be the result of carboxy-terminal proteolytic cleavage of one subunit of the homodimer (p66/p66) (2). Crystal structures of RT complexed with DNA (3) and a non-nucleoside inhibitor (4) have recently been published. In addition, pre-steady state kinetic studies are now available (5- 7). This detailed structural and kinetic information is pro¬ viding the prerequisite information for rational drug design of specific and potent inhibitors.
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Yang, Wei, and Thomas A. Steitz. "Crystal Structure of the Site-Specific Recombinase γδ Resolvase Complexed with a 34 bp Cleavage Site." In Structural Insights into Gene Expression and Protein Synthesis. WORLD SCIENTIFIC, 2020. http://dx.doi.org/10.1142/9789811215865_0051.
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Gu, Shenyi, Yan Zhang, Hongxing Wang, et al. "Effects of Solution Temperature on Microstructure and Properties of Zn-2Cu-0.8Mg Alloy." In Advances in Transdisciplinary Engineering. IOS Press, 2024. http://dx.doi.org/10.3233/atde240624.
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Zn-2Cu-0.8Mg zinc alloy was prepared by metal mold casting. The effects of solution temperature on the microstructure, corrosion behavior and mechanical properties of zinc alloy were studied. The results show that the microstructure of zinc alloy is mainly composed of η-Zn, Mg2Zn11 and a small amount of CuZn5 compounds. As the solution temperature increases, η-Zn content increases, the grain size increases, from dendrite to equiaxed crystal to coarsening; The tensile strength and elongation of the solid solution alloy are higher than those of the as cast alloy, and decrease with the increase of solution temperature. The alloy after 320°C solution treatment has the maximum values of mechanical properties, which are 396 MPa and 1.18% respectively, 1.3 and 1.8 times of those of as cast alloy; Fracture analysis shows that the fracture mode of zinc alloy is mainly cleavage fracture. The electrochemical test shows that the corrosion resistance of zinc alloy increases with the increase of solution temperature, and the self-corrosion current density of the alloy after 380°C solution treatment is the lowest, 14.965μA.cm-2. The corrosion rate is the lowest, 0.022mm/y.
Actes de conférences sur le sujet "Crystal cleavage"
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Lichter, Barry D., William F. Flanagan, Joung-Soo Kim, Johan Elkenbracht, and M. van Hunen. "Mechanistic Studies of Transgranular Stress-Corrosion Cracking: Application of the Corrosion-Assisted Cleavage Model to Results Employing Oriented Single Crystals." In CORROSION 1995. NACE International, 1995. https://doi.org/10.5006/c1995-95173.
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Abstract Results are described for stress-corrosion experiments carried out on oriented single crystals of copper-gold and copper-zinc (α-brass) using constant load and slow strain-rate loading modes under various chemical conditions in which passive oxides or dealloying in the absence of films are present at the surface. Evidence is presented to support the role of localized dissolution at slip traces in crack-initiation at a free surface, as well as in the re-nucleation of arrested cracks. The orientations of fracture surfaces are predominantly {110} independent of the tensile axis orientation, with the occasional appearance of {111} fracture planes in α-brass. Common fractographic features are seen in all systems studied, including the presence of crack-arrest markings. Dissolution of α-brass in cupric-ammonia solutions produces faceted pits with characteristic morphologies reflecting the symmetry of the exposed surfaces; whereas, dissolution in a cuprous-ammonia solution in equilibrium with copper produces minimal attack and no pitting. None of these morphologies for specimens corroded in the non-equilibrium or equilibrium solutions, with or without static or dynamic loading were observed to be associated with the characteristic surface morphology of T-SCC surfaces. These results are discussed in terms of the applicability of the Corrosion-Assisted Cleavage (CAC) model.
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Zhao, Xinglong, Joa˜o Quinta da Fonseca, Andrew Sherry, and David Lidbury. "Grain-Scale Heterogeneity Effect on Mechanistic Modelling of Cleavage Fracture of a Ferritic RPV Steel Forging Material." In ASME 2008 Pressure Vessels and Piping Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/pvp2008-61569.
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Improving brittle fracture prediction is crucial for structural integrity assessment. In current safety assessments, fracture mechanics treats polycrystalline steels as homogeneous continua. In reality, deformation of structural steels is heterogeneous. Part of this heterogeneity is due to the elastic and plastic anisotropy of their constituent (often randomly orientated) grains. This paper will compare the predicted failure stresses from tensile tests performed on a ferritic pressure vessel steel using the crystal plasticity finite element approach alongside measured carbide distribution and classical Beremin cleavage model. Available tensile data of 22NiMoCr37 steel at low temperature (−91°C and −154°C) were analysed using Bridgman solutions to account for the necking effect on the stress state at the centre of necking where brittle cracking initiates. This stress state imposed on representative volume element (RVE) made up of 10×10×10 randomly orientated grains, whose deformation is simulated using crystal plasticity finite element modelling (CPFEM). Randomly distributed carbides were produced based on the measured carbide size distribution and density for this steel. By assuming carbides as Griffith microcracks, the cleavage fracture stress in each grain can be assessed based the maximum principal stress on the cleavage crystal plane and an assumed surface energy. By repeating the random carbide distribution 1,000 times, brittle fracture probability can be calculated. Detailed examination shows that the above approach is actually a verification of the BEREMIN local approach model for cleavage fracture. The modelling results were compared with the available ductility data at −91°C and the interpolated ductility data at −154°C at the centre of necking. It is foreseen that this approach will lead to improvements in brittle fracture modelling in heterogeneous ferritic steels by introducing realistic surface energies and real defect distributions in specific materials, when used alongside the CPFEM submodelling approach.
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Banerjee, Amit, Yoshikazu Hirai, Toshiyuki Tsuchiya, and Osamu Tabata. "Vacuum emission in large-area nanogap fabricated by MEMS-controlled cleavage of single crystal silicon." In 2018 31st International Vacuum Nanoelectronics Conference (IVNC). IEEE, 2018. http://dx.doi.org/10.1109/ivnc.2018.8520283.
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Arakere, Nagaraj K., Shadab Siddiqui, Shannon Magnan, Fereshteh Ebrahimi, and Luis E. Forero. "Investigation of Three-Dimensional Stress Fields and Slip Systems for FCC Single Crystal Superalloy Notched Specimens." In ASME Turbo Expo 2004: Power for Land, Sea, and Air. ASMEDC, 2004. http://dx.doi.org/10.1115/gt2004-53938.
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Metals and their alloys, except for a few intermetallics, are inherently ductile, i.e. plastic deformation precedes fracture in these materials. Therefore, resistance to fracture is directly related to the development of the plastic zone at the crack tip. Recent studies indicate that the fracture toughness of single crystals depends on the crystallographic orientation of the notch as well as the loading direction. In general, the dependence of crack propagation resistance on crystallographic orientation arises from the anisotropy of (i) elastic constants, (ii) plastic deformation (or slip), and (iii) the weakest fracture planes (e.g. cleavage planes). Because of the triaxial stress state at the notch tips, many slip systems that otherwise would not be activated during uniaxial testing, become operational. The plastic zone formation in single crystals has been tackled theoretically by Rice and his co-workers [10–14] and only limited experimental work has been conducted in this area. The study of the stresses and strains in the vicinity of a FCC single crystal notch tip is of relatively recent origin. We present experimental and numerical investigation of 3D stress fields and evolution of slip sector boundaries near notches in FCC single crystal PWA1480 tension test specimens, and demonstrate that a 3D linear elastic finite element model that includes the effect of material anisotropy is shown to predict active slip planes and sectors accurately. The slip sector boundaries are shown to have complex curved shapes with several slip systems active simultaneously near the notch. Results are presented for surface and mid-plane of the specimens. The results demonstrate that accounting for 3D elastic anisotropy is very important for accurate prediction of slip activation near FCC single crystal notches loaded in tension. Results from the study will help establish guidelines for fatigue damage near single crystal notches.
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Lin, Enqiang, and Yongming Liu. "Atomistic Simulations of Fatigue Crack Growth in Single Crystal Aluminum." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-66084.
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The behaviors of model-I fatigue crack propagation behaviors under different strain cycles in single crystal aluminum have been systematically investigated by molecular dynamic and quasicontinuum method with embedded atom potential. Four different crack orientations: (010)[001], (111)[11-2], (110)[001] and (101)[10-1] are investigated by using the edge-crack model. Different fatigue crack growth mechanisms such as cleavage crack propagation, twinning and dislocation emission are observed. Premature crack surface contact during the unloading path is also observed for the (010)[001] crack, which is consistent with the crack closure hypothesis in the classical fatigue theory. The relationship between local deformation and crack growth kinetics are identified by using crack tip increments and crack tip opening displacement (CTOD) profiles at the selected stress cycle. The results show that crack only grows during part of the loading path and no crack growth during the unloading path, which are well in agreement with our previous in-situ SEM observations.
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Lin, Pandong, Junfeng Nie, and Meidan Liu. "Modelling the Brittle-Ductile Transition Temperature of Irradiated A508-3 Steel With CPFEM." In 2022 29th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/icone29-90986.
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Abstract Crystal Plasticity Finite Element Model (CPFEM) is the powerful tool to bridge the meso-scale and marco-scale and study the mechanical properties of metals systematically. In this paper, crystal plasticity theory coupling with irradiation effect is proposed. Note that it is based on density of dislocation and irradiation-induced full-absorption and partial-absorption dislocation loop and their interaction between each other. Then the model is numerically implemented in UMAT on ABAQUS platform. Secondly, A508-3 steel, the typical BCC crystal material, has specific brittle-ductile transition. The cleavage failure probability theory model (CFPTM) which assumes that the failure probability of specimen depends on its Cauthy stress filed is presented. The tensile tests for A508-3 steel are simulated by CPFEM in a combination of CFPTM to obtain the brittle-ductile transition temperature (BDTT). Results show that failure probability for specimen increases with increasing strain and decreasing temperature. In terms of BDTT, the numerical and experimental result are in close agreement whether there is under irradiation condition or not. Furthermore, the obvious irradiation embrittlement phenomenon is observed.
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Wu, Qun, and Dezhong Shen. "Generation of tunable blue light by frequency doubling of an external cavity diode laser." In OSA Annual Meeting. Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.thjj5.
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The performance of a diode laser can be improved by using an external cavity, which include tuning the laser wavelength, narrow spectral linewidth, and increasing the output power. These advantages are useful to generate SHG of a diode laser. By putting a KNbO3 crystal into an external cavity GaAlAs diode laser, we obtained 135 µW of blue radiation with a linewidth of 1.2 MHz and a tunable wavelength range 426.2–428.6 nm. An unpacked GaAlAs diode laser with AR coating at laser wavelength on the output cleavage plane was placed on a thermoelectric cooler so that the temperature could be stabilized. Diode laser radiation of 20 mW was focused into a KNbO3 crystal (3×3×8 mm3 with dielectric coating on the ends) by a GRIN rod lens. The light transmitted through the crystal was collimated to a grating with a focal lens. The grating was used to feed back infrared radiation and separate the blue output by its dispersion. A piezoelectric translator (PZT) attached to the grating provided fine tuning of the laser wavelength. The KNbO3 crystal was mounted in a thermoelectrically temperature-controlled enclosure. To achieve phase matched SHG in the tunable wavelength range, the temperature of the crystal was changed to track the voltage applied to the PZT by an automatically controlled setup.
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Neite, Maximilian, Michael Dölz, Markus Könemann, and Sebastian Münstermann. "Microstructure-Sensitive Description of the Residual Stressability of Components With the Aid of Virtual Experiments." In ASME 2023 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/pvp2023-102278.
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Abstract The application of macroscopic damage models is often made difficult by the fact that the calibration of the model parameters is associated with great experimental effort. Therefore, a methodological, simulative approach is presented to determine the damage model parameters with significantly less material input for the actual, local material state. Virtual experiments were performed on three-dimensional, statistically Representative Volume Elements (3D-RVE) of the microstructure to incorporate microstructure-based influences. For the generation of 3D-RVE, the in-house software DRAGen was used, which generated a geometric model based on input data gathered from EBSD analyses on the ferritic-bainitic reactor pressure vessel steel 22NiMoCr3-7. Mechanical properties were assigned to the constituents of the microstructure model by utilizing a phenomenological crystal plasticity model, which was inversely calibrated on the experimental flow curve. In addition, damage criteria on the microscale following the macroscopic material behavior are needed for cleavage and ductile fracture mechanism. Finally, the macroscopic damage model can be calibrated locally by micromechanical simulations. The virtual experiments were conducted with prescribed deformation boundary conditions, and different stress states were simulated by varying them.
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Mallampati, Sandeep, Liang Yin, David Shaddock, Harry Schoeller, and Junghyun Cho. "Lead-Free Alternatives for Interconnects in High-Temperature Electronics." In ASME 2017 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems collocated with the ASME 2017 Conference on Information Storage and Processing Systems. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/ipack2017-74169.
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Predominant high melting point solders for high temperature and harsh environment electronics (operating temperatures from 200 to 250°C) are Pb-based systems, which are being subjected to RoHS regulations because of their toxic nature. In this study, high bismuth (Bi) alloy compositions with Bi-XSb-10Cu (X from 10 wt.% to 20 wt.%) were designed and developed to evaluate their potential as high-temperature, Pb-free replacements. Reflow processes were developed to make die-attach samples made out of the cast Bi alloys. In particular, die-attach joints made out of Bi-15Sb-10Cu alloy exhibited an average shear strength of 24 MPa, which is comparable to that of commercially available high Pb solders. These alloy compositions also retained original shear strength even after thermal shock between −55°C and +200°C and high temperature storage at 200°C. Brittle interfacial fracture sometimes occurred along the interfacial NiSb layer formed between Bi(Sb) matrix and Ni metallized surface. In addition, heat dissipation capabilities, using flash diffusivity, were measured on the die-attach assembly, compared to the corresponding bulk alloys. The thermal conductivity of all the Bi-Sb alloys was higher than that of pure Bi. By creating high volume fraction of precipitates in a die-attach joint microstructure, it was feasible to further increase thermal conductivity of this joint to 24 W/m·K, which is three times higher than that of pure Bi (8 W/m·K). Bi-15Sb-10Cu alloy has so far shown the most promising performance as a die-attach material for high temperature applications (operated over 200°C). Hence, this alloy was further studied to evaluate its potential for plastic deformation. Bi-15Sb-10Cu alloy has shown limited plastic deformation in room temperature tensile testing, in which premature fracture occurred via the cracks propagated on the (111) cleavage planes of rhombohedral crystal structure of the Bi(Sb) matrix. The same alloy has, however, shown up to 7% plastic strain under tension when tested at 175°C. The cleavage planes, which became oriented at smaller angles to the tensile stress, contributed to improved plasticity in the high temperature test.
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Purohit, Yojna, and Ram Mohan. "Molecular Dynamics of Crack Growth in Nickel and Nickel-Aluminum Bi-Metallic Interface System Under Cyclic Loading." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-65150.
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Molecular dynamics simulations using embedded atom method inter-atomic potential were used to study crack propagation under cyclic loading in a Ni single crystal and a Ni-Al bi-metallic system. The crack in Ni-Al initiates and propagates from Ni towards the Ni-Al interface. The cyclic loading was applied in a strain controlled manner with constant amplitude of maximum strains (emax) applied to the two systems. The crack growth and propagation mechanism of a crack propagating in Ni were compared with the crack growth and propagation of a surface crack in Ni-Al at two different values of emax. Our results suggest that depending on the maximum value of the applied strain (emax), the crack propagates either by fatigue cleavage of the atomic bonds in the crack plane or by void nucleation in the regions near the crack tip. The creation of voids slows down crack growth in both the Ni and Ni-Al at higher value of emax. A comparison of crack growth under tensile and cyclic loading (emax, 0.046) suggest that plastic deformation around crack tip dominate crack propagation during tensile loading that result in slower crack growth (due to early nucleation of dislocations at the crack tip), when compared to crack growth under cyclic loading.