Competitive Incorporation Research Articles

The impact and implications of aragonite-to-calcite transformation on speleothem trace element composition

Trace elements in cave carbonates (both calcite and aragonite) have been considered major proxies in paleo-hydroclimatic research. However, their imprints in authigenic minerals might be altered by neomorphic processes (e.g., aragonite-to-calcite transformation). Therefore, it is crucial to understand the impacts of neomorphism on the trace element compositions of secondary calcite and understand the mechanisms of trace elements redistribution during neomorphic processes. In this study, two aragonite stalagmites (SN3 and SN15) from Shennong Cave, part of which were transformed into calcite, were further inspected and analyzed in terms of petrological observations, trace element geochemistry, and Mg compositional mapping. The results show that (1) the aragonite-to-calcite transformation in SN3 and SN15 occurs by a dissolution-precipitation mechanism and is influenced by several factors, including internal fluid compositions, microstructure (such as porosity and permeability) of the parent material, and crystal defects. (2) The primary aragonite is enriched in Sr but depleted in Mg compared with secondary calcite because of the crystallographic disparity. The non-equilibrium absorption of Mg and slow diffusive element transport may contribute to the extremely high Mg/Ca ratios in secondary calcite near the mineral phase boundary. Incorporation competition among trace elements also plays an important role in affecting the distribution of Sr and Mg in neomorphic calcite. Considering the previous study on the alteration of isotopes (δ18O, δ13C) associated with the aragonite-to-calcite transformation, we propose that intervening fluids play an important role in altering the secondary calcite oxygen isotopic composition and Mg/Ca ratio, while the composition of primary aragonite dictates the secondary calcite carbon isotopic composition and Sr/Ca ratio, provided that the transformation of aragonite to calcite caused by a dissolution–reprecipitation process occurring in trapped pore water. These results highlight the indispensability of petrographic analysis of speleothem specimens before using trace elements and isotopes for paleoclimate research.

Forum-Selection Provisions in Corporate 'Contracts'

We consider the emergent practice of including clauses in corporate certificates of incorporation or bylaws that specify an exclusive legal forum for lawsuits. According to their proponents and most courts that have considered the question, such forum-terms are, and should be, enforceable as contractual choice-of-forum provisions. We argue that treating corporate charter and bylaw forum-terms as a matter of ordinary contact doctrine is neither logical nor justified. Because charters and bylaws involve the state in ways that are at odds with private-ordering principles and because they entail only a limited form of “consent,” an analysis of enforceability must account for the hybrid nature — public and private — of such terms. Specifically, the state’s role should render forum-terms invalid that oust federal courts of diversity jurisdiction. Likewise, because of a lack of any meaningful consent, a forum-term that applies to a claim that neither is derivative nor brought by a shareholder should not be enforced. In other situations, courts should consider, before enforcing a corporate forum-term, whether adjudicating the entire dispute in the designated forum would be efficient (e.g., whether the court has subject matter jurisdiction over all claims) or fair (e.g., whether the procedural rules, including the limitations period, of the designated forum are substantially more advantageous to the defendants than those of the state that supplies the substantive law. On the other hand, several factors may tip the balance towards enforcement in other corporate settings and, in particular, in merger-related representative suits. First, the fact that “consent” by class members to these suits is also limited counter-balances concerns about the limited consent shareholders may have given to the forum-term. Second, a forum-term reduces the ability to avoid the crack-down on “disclosure-only” settlements — that provide broad releases, but entail minimal recovery — that Delaware courts have embarked on. Finally, we consider the implications of corporate forum-terms for interstate competition for incorporation and for corporate litigation. We raise questions whether Delaware in adopting legislation that discriminates against out-of-state courts, sought to centralize corporate litigation in its own courts for the benefit of its local bar rather than enhance its attractiveness as corporate domicile, and thereby have provided grounds for sister states to refuse to enforce forum-terms.

Carotenoid interactions.

Interactions between carotenoids during absorption and during postabsorptive metabolism have been demonstrated or suggested in animal and human feeding or supplementation studies, as well as in in vitro studies of intestinal beta-carotene cleavage. Much of the evidence suggests an interaction between beta-carotene and oxycarotenoids such as canthaxanthin and lutein, and between the hydrocarbon carotenoids beta-carotene and lycopene. The evidence is equivocal, however, with discrepant findings between studies, both in magnitude and in direction of the interactions observed. This review discusses studies of carotenoid interactions and explores the possible underlying mechanisms and implications of these interactions. The most likely explanations for carotenoid interactions appear to be competition for incorporation into micelles, carotenoid exchange between lipoproteins in the postprandial state, and inhibition of provitamin A (beta-carotene) cleavage.

Correlation of the structural and ferromagnetic properties of Ga 1−xMn xN grown by metalorganic chemical vapor deposition

Metalorganic chemical vapor deposition (MOCVD) has been used to grow high-quality epitaxial films of Ga 1− x Mn x N of varying thickness and manganese doping levels. No macroscopic second phases were observed via high resolution X-ray diffraction. Atomic force microscopy revealed MOCVD-like step flow growth patterns with a mean surface roughness as low as 3.78 Å in lightly doped samples, and matched that of the underlying GaN template layers. No change in the growth mechanism and morphology with Mn incorporation is observed. A uniform Mn concentration in the epitaxial layers is confirmed by secondary ion mass spectrometry. SQUID measurements showed an apparent RT ferromagnetic hysteresis with saturation magnetizations as high as 2.4 μ B/Mn at x = 0.008 , which decreases with increasing Mn incorporation or reduced structural quality. Co-doping with either Si or Mg during the resulting growth process resulted in a large decrease in the saturation magnetization values. Competition for incorporation between Mn and Mg during the MOCVD growth process is observed.

Time course of incorporation of n-3 PUFA from linseed in pigs and effects on D9-desaturase activity and pork odours

The n-3 polyunsaturated fatty acids (PUFA) are healthy nutrients which can be increased in pork by feeding sources such as linseed to the growing animal. The levels achieved depend on many factors such as the concentrations of lipid classes in tissues (eg phospholipids containing high PUFA levels are more abundant in muscle than adipose tissue) competition for incorporation with n-6 PUFA and possible inhibitory effects of PUFA on synthesis of saturated and monounsaturated fatty acids. This study examined the time course of the incorporation of n-3 PUFA into tissue lipids and the effects on the major synthetic enzyme D9-desaturase. The effects on pork odour were also studied.

Purine metabolism by intracellular Chlamydia psittaci.

Purine metabolism was studied in the obligate intracellular bacterium Chlamydia psittaci AA Mp in the wild type and a variety of mutant host cell lines with well-defined deficiencies in purine metabolism. C. psittaci AA Mp cannot synthesize purines de novo, as assessed by its inability to incorporate exogenous glycine into nucleic acid purines. C. psittaci AA Mp can take ATP and GTP, but not dATP or dGTP, directly from the host cell. Exogenous hypoxanthine and inosine were not utilized by the parasite. In contrast, exogenous adenine, adenosine, and guanine were directly salvaged by C. psittaci AA Mp. Crude extract prepared from highly purified C. psittaci AA Mp reticulate bodies contained adenine and guanine but no hypoxanthine phosphoribosyltransferase activity. Adenosine kinase activity was detected, but guanosine kinase activity was not. There was no competition for incorporation into nucleic acid between adenine and guanine, and high-performance liquid chromatography profiles of radiolabelled nucleic acid nucleobases indicated that adenine, adenosine, and deoxyadenosine were incorporated only into adenine and that guanine, guanosine, and deoxyguanosine were incorporated only into guanine. Thus, there is no interconversion of nucleotides. Deoxyadenosine and deoxyguanosine were cleaved to adenine and guanine before being utilized, and purine (deoxy)nucleoside phosphorylase activity was present in reticulate body extract.

Structural characterization of GaAs/GaP superlattices

Powder and double-crystal X-ray diffraction were used to study the structural properties of highly strained (GaAs)N/(GaP)M short-period superlattices grown on GaAs (001) substrates. In spite of the large lattice mismatch (f=3.6%) between GaAs and GaP and the competition for incorporation between As and P, high-quality short-period superlattices of GaAs/GaP have been grown by a development of conventional molecular beam epitaxy named atomic layer molecular beam epitaxy. The in-plane lattice parameter (a/sub ///) of the different superlattices was measured and studied as a function of the GaP content. The authors found that, for a given total superlattice thickness of 4000 AA, the critical lattice mismatch is fc approximately=0.5% (corresponding to an average GaP content of 13.6% in the superlattice). This means that for an average misfit or lattice mismatch above fc the superlattice starts to relax. This experimental result is compared with predictions of critical thickness theories based on energy criteria. A clear relation of the degree of relaxation with peak width of the superlattice zeroth-order diffraction peak is found. High-resolution transmission electron microscopy has been performed to analyse the type of dislocations that relax the mismatched layers.

Growth and characterization of ultrathin GaP layer in a GaAs matrix by X-ray interference effect

An ultrathin two monolayers thick layer of GaP sandwiched within a GaAs matrix was grown by atomic layer molecular beam epitaxy (ALMBE). The X-ray interference effect (Pendellosung) was used to determine the structural parameters such as thickness, lattice parameter, chemical composition, and strain. Excellent agreement between the experimental rocking curve and the simulation using the dynamical theory of X-ray diffraction was found indicating the high quality of the sample. Analysis of the scans in symmetrical (004) and asymmetrical (224) reflections, sensitive to both perpendicular and parallel strain, shows that the GaP layer is coherent with the substrate, i.e., it is below the critical thickness in agreement with critical thickness theories. Despite the competition for incorporation between arsenic and phosphorus the experimental GaP thickness is found to be identical to the nominal growth value, demonstrating full incorporation of phosphorus when growing by ALMBE. No significant out-diffusion or segregation of P is observed.

Sequential high-dose cytosine arabinoside and asparaginase in refractory acute leukemia.

The development of resistance to Ara-C by leukemia cells may be a multifactorial process. These include diminished rates of anabolism or increased rate of catabolism to Ara-C, competition for incorporation into DNA by higher pool size of the competing normal metabolite, dCTP and perhaps other mechanisms. Laboratory investigations have shown that cellular resistance to lower doses of Ara-C (LoDAC) may be overcome by a substantial increase in the extracellular concentration (dose-effect). Clinical extrapolation of these observations have shown that high dose Ara-C (HiDAC) is effective in re-inducing remission in patients with acute leukemia who have either failed to enter remission or who relapsed while being treated with LoDAC. Other laboratory investigations indicate significant schedule-dependent synergy between sequential HiDAC and asparaginase. Application of these observations to clinical trial has resulted in a 64% complete remission rate in patients with non-lymphocytic leukemia, including those who were previously treated with LoDAC or who had had an antecedent hematologic disorder. Toxicity from this regimen was not significantly different from those employing LoDAC. These preliminary data in patients with high risk disease would suggest that HiDAC/asparaginase might have significant utility in patients with previously untreated acute non-lymphocytic leukemia.