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Melting Experiments (melting + experiment)
Selected AbstractsFloating zone growth of CuO under elevated oxygen pressure and its relevance for the crystal growth of cupratesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1-2 2005G. Behr Abstract CuO single crystals have been grown from the melt by a floating zone method with optical heating at elevated oxygen pressures 3.5 to 5.5 MPa and growth rates as high as 10 mm/h. Melting experiments and recalculated Cu-O phase diagram data show that CuO melts incongruently. The melting temperature increases and the concentration difference between the melt and the CuO phase decreases for rising oxygen partial pressure. Accordingly, increasing the oxygen partial pressure improves the growth process by reducing both the significant oxygen loss during melting as well as the composition difference at the growth interface. The results on CuO provide important information for the crystal growth of more complex cuprates. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Role of Binder Content on Microstructure and Properties of a Cu-base Active Brazing Filler Metal for Diamond and cBNADVANCED ENGINEERING MATERIALS, Issue 5 2005R. Elsener Melting experiments of Cu-Sn-Ti-Zr filler metal powder containing cellulose nitrate and graphite, respectively, resulted in the formation of nanosized TiC particles in both Cu-rich phase and CuSn3Ti5 intermetallic regions of the alloy (see figure). The variation of the binder type and content allows to tailor the properties of the filler metals in terms of erosion resistance, decisive for a new generation of superabrasive tools. [source] SAND FOR ROMAN GLASS PRODUCTION: AN EXPERIMENTAL AND PHILOLOGICAL STUDY ON SOURCE OF SUPPLY*ARCHAEOMETRY, Issue 3 2006A. SILVESTRI This paper reports the results of an experimental study performed on Campanian littoral sand, together with a careful philological analysis of Pliny's text concerning the production of glass using the above sand in order to verify its suitability. Accurate chemical and mineralogical characterization of sand samples and experimental glasses was carried out, proving the unsuitability of sand for glass production in its original state. Taking into account both the results of the philological analysis of Pliny's text and the mineralogical assemblage of the sand, a new hypothesis regarding Roman glass-making technology is proposed and tested here. The technology implies the production of ,quartz-enriched' sand by means of selective grindings according to the different degrees of hardness and cleavage of the mineralogical phases. Melting experiments, carried out on treated sand and in the temperature range compatible with Roman technology, yielded a glass with composition similar to those of typical Roman glasses. Therefore, new perspectives on the sources of supply of raw materials, hitherto debated, are opened up. [source] Synchrotron X-ray and DSC Studies of the Phase Behaviour of Poly(diethylene glycol p,p,-bibenzoate)MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 17 2003Ernesto Pérez Abstract Time-resolved synchrotron X-ray and DSC experiments were applied to investigate the phase behaviour of poly(diethylene glycol p,p,-bibenzoate), PDEB. The DSC results are indicative of the formation of a smectic mesophase, previously identified as a SmCA type, which can be easily quenched down to room temperature. However, the synchrotron results show that the SmCA phase undergoes some kind of ordering or transformation at temperatures below 110,°C. Moreover, the annealing of PDEB at temperatures above Tg for sufficiently long times leads to the formation of a highly ordered structure, although very thin crystals and low crystallinities are obtained. Scattering profiles corresponding to sample PDEB85 in a melting experiment. [source] A novel thermostable hemoglobin from the actinobacterium Thermobifida fuscaFEBS JOURNAL, Issue 16 2005Alessandra Bonamore The gene coding for a hemoglobin-like protein (Tf-trHb) has been identified in the thermophilic actinobacterium Thermobifida fusca and cloned in Escherichia coli for overexpression. The crystal structure of the ferric, acetate-bound derivative, was obtained at 2.48 Å resolution. The three-dimensional structure of Tf-trHb is similar to structures reported for the truncated hemoglobins from Mycobacterium tuberculosis and Bacillus subtilis in its central domain. The complete lack of diffraction patterns relative to the N- and C-terminal segments indicates that these are unstructured polypeptides chains, consistent with their facile cleavage in solution. The absence of internal cavities and the presence of two water molecules between the bound acetate ion and the protein surface suggest that the mode of ligand entry is similar to that of typical hemoglobins. The protein is characterized by higher thermostability than the similar mesophilic truncated hemoglobin from B. subtilis, as demonstrated by far-UV CD melting experiments on the cyano-met derivatives. The ligand-binding properties of Tf-trHb, analyzed in stopped flow experiments, demonstrate that Tf-trHb is capable of efficient O2 binding and release between 55 and 60 °C, the optimal growth temperature for Thermobifida fusca. [source] Density Fluctuations during the Early Stages of Polymer Crystallization: An OverviewMACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2008Jimmy Baert Abstract The present work provides a critical review of polymer crystallization studies using SALS; experimental methods, analysis techniques, observations and their relations with respect to other techniques are discussed. Furthermore, the fact that nucleation might be accompanied by large scale density fluctuations has been investigated for the flow-induced crystallization of iPB. SALS was applied to measure density and orientation fluctuations, whereas complementary results were obtained from optical microscopy. The observations from both crystallization and melting experiments seem to indicate that the detected density fluctuations result from the presence of weakly anisotropic structures, rather than being an indication of densification before the onset of crystallization. [source] Disequilibrium partial melting experiments on the Leedey L6 chondrite: Textural controls on melting processesMETEORITICS & PLANETARY SCIENCE, Issue 11 2001S. N. Feldstein Chips of the L6 chondrite, Leedey, were heated at 1200 °C and log ,O2 = IW-1 for durations of 1 h to 21 days. We observed a progression of kinetically-controlled textural changes in melt and restite minerals and changes in the liquidus mineralogy in response to factors such as volatile loss. During the course of the experiments, both olivine and orthopyroxene recrystallized at different times. Rare relic chondrules could still be identified after 21 days. The silicate melts that form are very heterogeneous, in terms of both major and trace element chemistry, reflecting heterogeneity of the localized mineral assemblage, particularly with respect to phosphates and clinopyroxene. Metal-sulfide melts formed in short-duration runs are also heterogeneous. The experimental data are relevant to aspects of the genesis of primitive achondrites such as the acapulcoites. The observed textures are consistent with a model for acapulcoite petrogenesis in which silicate melting was limited to only a few volume percent of the chondritic source rock. The experiments are also relevant to the behavior of chondritic material that has been partially melted in an impact environment. [source] Optimization of Triple-Helix-Directed DNA Cleavage by Benzoquinoquinoxaline,Ethylenediaminetetraacetic Acid ConjugatesCHEMBIOCHEM, Issue 9 2003Rula Zain Dr. Abstract The formation of triple-helical structures of DNA is based on sequence-specific recognition of oligopyrimidine,oligopurine stretches of double-helical DNA. Triple-helical structures can be stabilized by DNA-binding ligands. Benzoquinoquinoxaline (BQQ) derivatives are among the most potent intercalating-type agents known to stabilize DNA triple-helical structures. We previously reported the conversion of BQQ into a triplex-directed DNA cleaving agent, namely BQQ,ethylenediaminetetraacetic acid (EDTA), by coupling of 6-(3-aminopropylamino)BQQ to a suitable ethylenediaminetetraacetic acid derivative, and we demonstrated the ability of this conjugate to cause double-stranded cleavage of DNA at the triplex site. However, this prototype derivative BQQ,EDTA conjugate showed lower affinity towards triplex DNA than BQQ itself. In the light of this observation, and guided by molecular modeling studies, we synthesized a second generation of BQQ,EDTA conjugates based on 6-[bis(2-aminoethyl)amino]- and 6-(3,3,-diamino- N -methyldipropylamino),BQQ derivatives. We confirmed by DNA melting experiments that the new conjugates displayed an increased specific affinity towards triple helices when compared to the previously synthesized BQQ,EDTA. In addition, the efficiency of these new agents in triplex-specific binding and cleavage was demonstrated by triplex-directed double-stranded cleavage of plasmid DNA. [source] Synthesis and Hybridization Properties of Modified Oligodeoxynucleotides Carrying Non-Natural BasesCHEMISTRY & BIODIVERSITY, Issue 2 2009Anna Aviñó Abstract The impact of the presence of nonnatural bases on the properties of oligodeoxynucleotides has been studied. First, oligodeoxynucleotides carrying 2,-deoxyzebularine were prepared, and the stability of duplexes carrying this analogue was determined by DNA melting experiments. Melting temperatures and thermodynamic data indicated the preference of 2,-deoxyzebularine for 2,-deoxyguanosine, which behaves as a 2,-deoxycytidine analogue, forming a less stable base pair due to the absence of the amino group at position 4. Moreover, the duplex,hairpin equilibrium of a self-complementary oligodeoxynucleotide carrying several natural and nonnatural bases including 2,-deoxyzebularine as a central mispair, was studied. Depending on the base present in the middle of the sequence, it is possible to affect the stability of the bimolecular duplex modulating the duplex,hairpin equilibrium. Magnesium ions were shown to stabilize preferentially the bimolecular duplex form. The results indicate the importance of the modifications and the role of cations in shifting the structural equilibrium. [source] | ||||||||||||||||