Cu-rich Regions Research Articles

Unusually Cu-rich magmas associated with giant porphyry copper deposits: Evidence from Bingham, Utah

Mass-balance constraints indicate that formation of giant porphyry copper deposits (PCDs) requires either highly efficient collection of Cu from large volumes of magma or unusually Cu-rich parent magmas. Support for the second of these possibilities has been discovered in the form of mafic enclaves with abundant bornite and chalcopyrite in the Last Chance stock, one of the parent intrusions of the giant Bingham PCD, Utah, United States. Mineral assemblages and compositions indicate that the Last Chance enclaves are autoliths consisting of phases that crystallized from the intrusion, and that the intrusion was unusually enriched in Cu. One possible mechanism for generating Cu-rich magmas is fractional crystallization during pyrrhotite undersaturated conditions. The high fO 2 conditions observed for the Last Chance stock may have allowed such an evolution. Alternatively, if the magma has not undergone significant fractionation, early crystallization of chalcopyrite and bornite from the magma would indicate that the lower-crustal source region for the magma probably contained Cu-Fe sulfides. Possible Cu-rich source regions are a subcrustal mafic intrusion with sulfide cumulates, or a deeply buried metamorphic terrane containing Cu deposits such as those in the Curaca Valley (Brazil) or Okiep (South Africa). Heterogeneous distribution of Cu-Fe sulfides in an Okiep-type source terrane would produce local PCDs such as Bingham, or large accumulations of Cu-Fe sulfides, possibly in the form of cumulates in subcrustal intrusions at convergent margins, could produce giant PCD provinces such as those in Indonesia, Papua New Guinea, and central Chile.

Megaprimer-Based Methodology for Deletion of a Large Fragment Within a Repetitive Polypyrimidine-Rich DNA

Site-directed mutagenesis is often a prerequisite for elucidation of the functional significance of cis- and trans-factors involved in gene regulation. The aim of this study was to delete the primary binding site for heterogeneous nuclear ribonucleoprotein I (hnRNPI) within the inducible nitric oxide synthase (iNOS) 3' untranslated region mRNA. The binding site consists of a 53-nucleotide CU-rich region within a long stretch of polypyrimidines. As a result of primer pair annealing, the repetitive sequence limited the use of several deletion methods based on polymerase chain reaction. Therefore, a megaprimer approach was chosen. The megaprimer was produced by a forward primer outside the polypyrimidine-rich region, and a mutagenic reverse primer annealing to flanking regions of the desired deletion, thereby looping out the target sequence. Subsequently, this megaprimer was used to create the final deletion recombinant. The deletion was verified by sequencing and by ultraviolet cross-linking mouse liver protein extracts with radiolabeled mutant and wild-type RNAs. In conclusion, the megaprimer method offers a solution for generating large internal deletions in repetitive sequences, which facilitates investigations on large repetitive DNA or RNA regions interacting with trans-factors.

Microstructural evolution in the friction stir welded 6061 aluminum alloy (T6-temper condition) to copper

This paper concentrates on the temperature distribution and microstructural evolution of the friction stir welding of 6061 aluminum alloy (T6-temper condition) to copper. The mechanically mixed region in the joining of the dissimilar metals 6061 aluminum alloy and copper weld consists mainly of several intermetallic compounds such as CuAl 2, CuAl, and Cu 9Al 4 together with small amounts of α-Al and the saturated solid solution of Al in Cu. Distributed at the bottom of the weld nugget are numerous deformed copper lamellae with a high solid-solubility of aluminum. An intercalated structure or vertex flow pattern consisting of CuAl 4 and the saturated solid solution of Al in Cu is formed in the Cu-rich regions adjacent to the bottom of the weld by the mechanical integration of aluminum into copper. The measured peak temperature in the weld zone of the 6061 aluminum side reaches 580 °C, which is distinctly higher than the melting points of the Al–Cu eutectic or some of the hypo- and hyper-eutectic alloys. Higher peak temperatures are expected at the near interface regions between the weld metal and the stirred tool pin. The phases present in the welds can be explained from the Al–Cu equilibrium phase diagram with the assumption that a complete phase equilibrium is reached in the liquid state but not during solidification. The primary dendrites of α-Al, CuAl 2, and CuAl, and the eutectic of α-Al/CuAl 2 are formed in the weld nugget during solidification. Distinctly different micro-hardness levels from 136 to 760 HV 0.2 are produced corresponding to various microstructural features in the weld nugget.

Crystal Structure and Magnetic Properties of Cu‐Rich Ce—Mn—Cu Intermetallics.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Nucleolin is a second component of the CD154 mRNA stability complex that regulates mRNA turnover in activated T cells.

CD154 (CD40L) mRNA turnover is regulated in part at the posttranscriptional level by a protein complex (termed Complex I) that binds to a highly CU-rich region of the 3'UTR. Polypyrimidine tract-binding protein (PTB) has previously been identified as a major RNA-binding protein in Complex I. Nondenaturing gel filtration of total extract from Jurkat T cells demonstrated that the CD154 mRNA-binding activity migrates as a approximately 200-kDa complex, indicating the presence of multiple complex-associated proteins. We have currently undertaken a biochemical approach to further characterize Complex I and observed that it segregates over DEAE-Sepharose into two subcomplexes (termed I-L and I-U). Furthermore, nucleolin was identified as a component of both subcomplexes and was shown that it is the major RNA-binding protein in I-U. To directly demonstrate the biological significance of Complex I binding to the CD154 transcript, cytoplasm from human Jurkat cells was fractionated over a sucrose gradient and the different cellular fractions subjected to immunoprecipitation with anti-PTB and anti-nucleolin Abs. RT-PCR of the immunoprecipitated products using CD154-specific primers clearly demonstrated that nucleolin and PTB are associated with CD154 mRNA in both the ribonucleoprotein and polysome fractions. These data strongly support a model whereby nucleolin and PTB are integral to the stability of CD154 mRNA and are components of the CD154 ribonucleoprotein particle associated with actively translating ribosomes.

Synthesis of dual phase bronze alloys from elemental nanoparticle constituents

Dual phase (α+β) copper–tin alloys were synthesized from elemental nanoparticle precursors following consolidation, annealing and quenching steps. The precursors were derived from the sequential reduction of tin and copper salts in ethanolic solution. The dual phase microstructure exhibits a duplex character with a mixture of Cu-rich and Sn-rich (α+β) regions.

Crystal structure and magnetic properties of Cu-rich Ce–Mn–Cu intermetallics

A study on the ternary intermetallic phases in the Cu-rich region of Ce–Mn–Cu system has been performed. Three compounds were identified and their transport and magnetic properties determined. The crystal structures were investigated by X-ray diffraction both on powders and single crystals: CeMn0.85Cu5.15, related to the CeCu5Au-type (oP28, Pnma, a=8.246(1)Å, b=5.0870(4)Å, c=10.346(1)Å); CeMn1.3Cu4.7, related to the YbMo2Al4 type (tI14, I4/mmm, a=6.5763(6)Å, c=5.0488(4)Å) and CeMn2.25Cu8.75, related to the CeMn6Ni5 type (tP24, P4/mbm, a=8.394(1)Å, c=4.973(1)Å). In all the three compounds the Mn atoms preferentially occupy sites, available on the non-rare earth atom sublattice, with higher coordination and larger interatomic distances. The Mn ions order ferromagnetically near 50K in the first compound, while the resistivity exhibits Kondo like behaviour. There is no clear evidence of a bulk magnetic phase transition below 300K in the latter two compounds. The heat capacity data indicate a strongly correlated electronic ground state in all the three alloys due to the Ce-4f hybridization with the conduction band states.

Crystal structure and magnetic properties of Cu-rich Ce?Mn?Cu intermetallics

A study on the ternary intermetallic phases in the Cu-rich region of Ce–Mn–Cu system has been performed. Three compounds were identified and their transport and magnetic properties determined. The crystal structures were investigated by X-ray diffraction both on powders and single crystals: CeMn 0.85 Cu 5.15 , related to the CeCu 5 Au-type (oP28, Pnma, a =8.246(1) Å, b =5.0870(4) Å, c =10.346(1) Å); CeMn 1.3 Cu 4.7 , related to the YbMo 2 Al 4 type (tI14, I4/mmm, a =6.5763(6) Å, c =5.0488(4) Å) and CeMn 2.25 Cu 8.75 , related to the CeMn 6 Ni 5 type (tP24, P4/mbm, a =8.394(1) Å, c =4.973(1) Å). In all the three compounds the Mn atoms preferentially occupy sites, available on the non-rare earth atom sublattice, with higher coordination and larger interatomic distances. The Mn ions order ferromagnetically near 50 K in the first compound, while the resistivity exhibits Kondo like behaviour. There is no clear evidence of a bulk magnetic phase transition below 300 K in the latter two compounds. The heat capacity data indicate a strongly correlated electronic ground state in all the three alloys due to the Ce-4f hybridization with the conduction band states.

A complex containing polypyrimidine tract-binding protein is involved in regulating the stability of CD40 ligand (CD154) mRNA.

CD40 ligand (CD154) expression has been shown to be regulated, in part, at the posttranscriptional level by a pathway of "regulated instability" of mRNA decay throughout a time course of T cell activation. This pathway is modulated at late times of activation by the binding of a stability complex (termed complex I) to a CU-rich region in the 3' untranslated region of the CD154 message. We have undertaken experiments to extend these findings and to analyze the cis-acting elements and trans-acting factors involved in this regulation. We have previously shown that the minimal binding sequence for complex I is a 63 nt CU-rich motif. However, our current study shows that when this site was deleted additional complex binding was observed upstream and downstream of the minimal binding region. Only after deletion of an extended region (termed Delta1515) was complex binding completely abolished. Analysis of complex binding using competition experiments revealed that the three adjacent regions bound related but not identical complexes. However, all three sites appeared to have a 55-kDa protein as the RNA-binding protein. Deletion of the Delta1515 region resulted in reduced transcript stability as measured by both in vitro and in vivo decay assays. Finally, using Abs against known RNA-binding proteins, we identified the polypyrimidine tract-binding protein (or heterogeneous nuclear ribonucleoprotein I) as a candidate RNA-binding component of complex I.

Ferromagnetic interaction and superconductivity of CeCu 2Si 2

We have recently reported our finding of a weakly ferromagnetic phase and two superconducting phases in the Cu-deficient and Cu-rich region of the homogeneity range, respectively, for the heavy-electron compound CeCu 2Si 2. We herein report more detailed results of the specific heat, magnetic susceptibility, resistivity ( R), magnetoresistance (Δ R) and thermopower for many different compositions. We confirmed the slightly re-entrant behavior in the H c2( T) curve and a change of regime in the Δ R at about 0.35 K above H c2( T) for the low- T c phase. Above about 0.75 K, the normal state of this phase exhibited no magnetoresistance up to 70 kOe, while that of high- T c phase and the weakly ferromagnetic phase did a slightly positive Δ R. These differences in the three phases may provide an important clue to better understanding of the heavy-electron superconductivity of CeCu 2Si 2.

Microstructure Feature of Bulk Glassy Cu<SUB>60</SUB>Zr<SUB>30</SUB>Ti<SUB>10</SUB> Alloy in As-cast and Annealed States

The microstructures of a bulk glassy Cu 60 Zr 30 Ti 10 alloy in as-cast state and annealed at glass transition temperature (T g ), i.e., 440°C, have been studied using an electron transmission microscope (TEM) and a high-resolution transmission electron microscope (HRTEM). Nanocrystals with a size of 4 nm were observed in the cast rod with a diameter of 4 mm. The nanocrystal was determined to be CuZr, which is primitive cubic structure with a lattice parameter of a = 0.3262 nm by analyzing its nano-beam electron diffraction pattern, suggesting that such nanocrystals have a positive effect on mechanical properties. Obviously distinguished interval dark and bright regions were observed in the glassy Cu 60 Zr 30 Ti 10 alloy annealed for 10 min at T g . Nanocrystalline phase with a size of ∼10 nm was recognized after the annealing treatment. The concentration distribution of Cu, Zr and Ti in the alloy annealed for 10 min at T g was examined with a three-dimensional atom probe field ion microscopy (3DAP-FIM). It was found that the Cu and Zr elements fluctuated along depth direction while the Ti element remained almost unchanged. It is therefore interpreted that the annealing-induced nanocrystalline phase results from nucleation and growth at the sites of the Cu-rich and/or Zr-rich regions as well as from growth of the cast-in nanocrystals.

Bulk and surface properties of liquid In–Cu alloys

In–Cu is a weak interacting system (the excess free energy of mixing G M xs≈−0.2 RT at equiatomic composition) but the composition dependence of the thermodynamic properties exhibit interesting features. G M xs is negative in the Cu-rich region and positive for the In-rich end. Similarly other thermodynamic properties are asymmetric about the equiatomic composition. Such an interesting feature is explained here on the basis that a complex of the form Cu 4In exists in the bulk phase. Its energetics are used to study the surface composition of the In–Cu liquid alloys. Our study indicates that the surface is enormously rich with indium concentrations throughout the composition of the alloys.

Weak antiferromagnetism and superconductivity in pseudo-binaryspinel compounds (Cu,Co)Co2S4 investigated by 59Co and63Cu magnetic resonance

We have carried out a nuclear magnetic resonance study onpseudo-binary spinel compounds (CuxCo1-x)Co2S4 withx = 0-1.0 to deduce the varied impact of variations in theantiferromagnetic (AF) spin correlation and density of states (DOS) that can clearly define the combination of magnetism andsuperconductivity in the system. The Curie-Weiss-type behaviour ofthe Knight shift K for both 59Co and 63Cu on thetetrahedral A site and the temperature-independent K for 59Coon the octahedral B site indicate that the magnetism of the systemoriginates from 3d bands associated with the transition-metalelements on the A site. With the Cu substitution x for Co on the Asite, the negative Weiss temperature θ deduced from the Kdata initially decreases, takes a deep minimum around x = 0.7followed by a rapid increase for x→1. For the compoundswith x⩽0.3 and x>0.8, the nuclear spin-lattice relaxationrate T1-1 for the nuclei on both A and B sites has a T1/2dependence at high temperatures, which is characteristic ofthree-dimensional itinerant weak antiferromagnets. In theCu-rich region (x>0.7) the compounds transform into asuperconducting state below TS with no long-range magneticordering. From a T1-1 data analysis, we find that the increaseof TS correlates not only with the development of the AFspin correlation but also with the significant increase in the DOS atthe Fermi level of the 3d bands Nd(EF) associated withCo on the B site. T1-1 in the superconducting state ofCuCo2S4 (TS = 4.4 K), measured for 59Co on the Bsite utilizing the pure quadrupole resonance spectrum, has acoherence peak followed by an exponential decrease, indicating thatCuCo2S4 is an s-wave superconductor with an energy gap of2Δ = 4.14kBTS. We conclude that the appearance ofsuperconductivity for the compounds in the Cu-rich region originatesfrom the large increase in Nd(EF) associated with Coon the B site, and the development of the AF spin correlationoriginates from the increase in Nd(EF) associated withCu on the A site.

Structural transitions of mechanically alloyed Fe 100− xCu x systems studied by X-ray absorption fine structure

The local structures of the immiscible Fe 100− x Cu x alloys ( x=0, 10, 20, 40, 60, 80 and 100) produced by mechanical alloying have been investigated by X-ray absorption fine structure technique. For the Fe 100− x Cu x solid solutions with x⩾40, the local environment around the Fe atoms changes from bcc to fcc structure and the Cu atoms maintain the original coordination geometry after milling for 160 h. In contrast, the local structures around the Cu atoms in both Fe 80Cu 20 and Fe 90Cu 10 alloys exhibit a transition from fcc to bcc structure. Furthermore, we found that the coordination numbers N in the first shell of the Fe and Cu atoms were largely deviated from the stoichiometric composition for the Fe 100− x Cu x solid solutions with x⩾40. The Debye–waller factor σ of the fcc Fe–Cu phase is larger than that of the bcc Fe–Cu phase, and the σ (0.099 Å) around Fe atoms is larger than that around Cu atoms (0.089 Å) in the Fe 100− x Cu x solid solutions with x⩾40. This indicates that the mechanically alloyed Fe 100− x Cu x supersaturated solid solutions with x⩾40 is not a homogeneous alloy, but consists of fcc Fe-rich and fcc Cu-rich regions. However, In Fe 100− x Cu x solid solutions with x⩽20, the Cu atoms were almost homogeneously solved into the bcc Fe–Cu phase. A possible mechanism for bcc-to-fcc and fcc-to-bcc changes in Fe 100− x Cu x solid solutions is discussed in relation to the interdiffusion and the transition induced by the ball milling.

Influence of Cu additions on the morphology of GeSi precipitates in an Al-Ge-Si alloy

Combined additions of Ge and Si to Al are known to produce higher precipitation hardening than that which occurs in the constituent binaries, when the total amounts of alloying atoms are the same for all the alloys investigated. In the resultant Al-Ge-Si alloys, the diamond cubic precipitates contain both Ge and Si and are designated as GeSi. During artificial aging at 160 °C, the GeSi precipitates are commonly present in three forms, i.e., equiaxed, 〈100〉Al lath, and triangular plate. The equiaxed form is the dominant one of the three. This article examines the influence of varying amounts (i.e., 2 to 4 wt pct) of Cu additions on the morphology of GeSi precipitates formed in an Al-2.6 wt pct Ge-1.04 wt pct Si alloy during artificial aging at 160 °C. It is shown that Cu additions have the remarkable effect of maximizing the nucleation frequency of the 〈100〉Al lath form and simultaneously suppressing the nucleation of the equiaxed and the plate forms of the GeSi precipitates. Increasing Cu additions also increase the homogeneity and cause refinement of the 〈100〉Al laths. These results are discussed in light of (1) the critical requirement of vacancies for the nucleation and growth of GeSi precipitates having an atomic volume larger than Al and (2) the crystallographic nature of the negative dilation strains that develop locally in the Cu-rich regions of the Al matrix. It is further shown that, in the alloys containing increased levels (i.e., exceeding about 2.5 wt pct) of Cu, the precipitation of ϑ′ (metastable ϑ-Al2Cu) phase occurs, and that the nucleation of Cu-rich ϑ′ precipitates occurs upon the 〈100〉Al laths of GeSi. The latter effect is discussed in terms of the attainment of both the nucleation site and the necessary solute supersaturation at the 〈100〉Al GeSi/α-Al interfaces.

Local structures of mechanically alloyed Fe100−x Cu x solid solutions studied by X-ray absorption fine structure

The local structures of the immiscible Fe(100-x)Cu(x) alloys (x= 0, 10, 20, 40, 60, 80 and 100) produced by mechanical alloying have been investigated by XAFS. For the Fe(100-x)Cu(x) (x > or = 40) solid solutions, the local structures around Fe atoms change from bcc structure to fcc one and the Cu atoms maintain the original coordination geometry after milling for 160 hours. On the contrary, the local structures around Cu atoms in both of Fe80Cu20 and Fe90Cu10 alloys appear a transition from fcc to bcc structure. We found that the Debye-waller factor sigma of fcc Fe-Cu phase is larger than that of bcc Fe-Cu phase, and the sigma (0.099 A) around Fe atoms is larger than that (0.089 A) of Cu in the Fe(100-x)Cu(x) (x > or = 40) solid solutions. This suggests that the mechanically alloyed Fe(100-x)Cu(x) supersaturated solid solution is not a homogeneous alloy, and consists of Fe-rich and Cu-rich regions for various compositions. A possible mechanism for bcc-to-fcc and fcc-to-bcc changes in Fe(100-x)Cu(x) solid solutions is discussed in relation to the interdiffusion and transition induced by the ball milling.

Photoluminescence spectra of CuGaSe 2 crystals

CuGaSe 2 (CGS) crystals (Cu/Ga=0.9–1.4) which have been expected as photovoltaic applications were successfully grown by a vertical gradient freezing method. All samples were of the chalcopyrite structures, nearly stoichiometric and showed p-type conductivities. The samples became poor crystallinity with increasing enclosed Cu/Ga ratios in the Cu-rich region because the values of full-width at half-maximum at (1 1 2) diffraction lines increased with increasing enclosed Cu/Ga ratios. Lattice constants of a and c axes in the Cu-rich regions were larger than those in the Cu-poor regions, indicating that Cu atoms played an important role with the lattice constants. The grown stoichiometric CGS sample was of high quality since the free-exciton emission line was clearly observed in photoluminescence (PL) spectrum at 77 K. The CGS samples turned out to have many donor- and acceptor-type defects because the donor–acceptor pair emission bands had considerable intensities in the PL spectra.

LOCAL STRUCTURES OF MECHANICALLY ALLOYED Fe100-xCux SOLID SOLUTIONS STUDIED BY X-RAY ABSORPTION FINE STRUCTURE

The local structures of the immiscible Fe100-xCux alloys (x=0,10,20,40,60,80 and 100)produced by mechanical alloying have been investigated by XAFS.For the Fe100-xCux(x≥40) alloys,the local structures around Fe atoms change from bcc structure to fcc one,and the Cu atoms maintain the original coordination geometry after milling for 160 h. On the contrary, the local structures around Cu atoms in both Fe80 Cu20and Fe90 Cu10 alloys appears a transition from fcc to bcc structure.We found that the disorder factor σ(0.0099nm)of fcc Fe—Cu phase is larger than that (0.0081nm) of bcc Fe—Cu phase,and the σ(0.0099nm) around Fe atoms is larger than that (0.0089nm) of Cu in the Fe100-xCux(x≥40) alloys. This suggests that the mechanically alloyed Fe100-xCux alloys is not a homogeneous supersaturated solid solution,but consists of Fe-rich and Cu-rich regions for various compositions.A possible mechanism for bcc-to-fcc and fcc-to-bcc changes in Fe100-xCux alloys is discussed in relation to the interdiffusion and transition induced by the ball milling.

Identification of a complex that binds to the CD154 3' untranslated region: implications for a role in message stability during T cell activation.

CD154 expression is regulated throughout a time course of CD3-dependent T cell activation by differential mRNA decay. To understand the molecular basis of the "stability" phase of this pathway, experiments were conducted to identify sequences and specific complexes important in this regulation. Gel retardation assays using extracts from both Jurkat T cells and CD3-activated CD4(+) T cells revealed a major complex (complex I) that bound a 65-bp highly CU-rich region of the CD154 3' untranslated region. The specificity of the CU-rich element for complex-I formation was confirmed by disruption of this complex by oligo(dCT) competition. Formation of complex I strongly correlated with CD154 mRNA stability across a time course of T cell activation. UV cross-linking identified a major oligo(dCT)-sensitive species at approximately 90 kDa that showed induced and increased expression in extracts from 24- and 48-hr anti-CD3-activated T cells, respectively. This protein was absent in equivalent extracts from resting or 2-h-activated T cells. Using an in vitro decay assay, we found that a CD154-specific transcript was more rapidly degraded in 2-h-activated extract and stabilized in the 24- and 48-h extracts compared to extracts from resting T cells. Disruption of complex I resulted in the rapid decay of a CD154-specific transcript demonstrating a functional role for complex I in mRNA stabilization in vitro. These studies support a model of posttranscriptional regulation of CD154 expression being controlled in part by the interaction of a poly(CU)-binding complex with a specific sequence in the 3' untranslated region.

Depth profile analysis of CuInSe 2 (CIS) thin films grown by the electrodeposition technique

In this study, we report the results obtained from the auger electron spectroscopy (AES) depth profiling of CIS thin films grown by the electrodeposition technique. This result enables one to do a comparison between the bulk and superficial elemental compositions. The AES result is also compared with that obtained by the inductively coupled plasma (ICP) spectroscopy. These results support our proposition that the electrodeposited CIS film has a Cu-rich bulk region and an In rich surface, which leads to the formation of an n-layer (CuIn 2Se 3.5) on the top of the p-type CIS (CuInSe 2) phase