Heat Capacity Under Pressure of CeCoIn 5

Among heavy-fermion (HF) superconductors, CeCoIn 5 exhibits a record high value of T c =2.3 K at ambient pressure [1]. CeCoIn 5 belongs to a new class of HF-superconductors that crystallize in the tetragonal HoCoGa 5 -structure. This structure can be regarded as alternating layers of CeIn 3 and CoIn 2 . Bulk CeIn 3 undergoes a transition from an antiferromagnetic (AFM) state at ambient pressure ( T N =10.2 K) to a superconducting state with very low T C =0.15 K at a critical pressure p c =2.8 GPa [2] at which long range magnetic order vanishes. It is, therefore, regarded as a possible candidate for magnetically mediated superconductivity (SC). We report on measurements of the heat capacity of CeCoIn 5 at hydrostatic pressures p h 1.5 GPa. While T c increases with increasing pressure, the effective mass of the quasi-particles m eff decreases, as indicated by the ratio C / T | T c . As a working hypothesis based on theories of a nearly antiferromagnetic Fermi-liquid (NAFFL), this may be interpreted as the stabilization of the superconducting state by an increase of the characteristic spin fluctuation temperature T_{SF} (T_{SF}\propto k_F^2/m_{\rm eff}).     

Multiobjective management of mining under water hazard by game theory

The management of an aquifer is studied under the assumption that the solution of the multiobjective programming model describing the management problem should satisfy a certain set of axioms. It is shown that a certain class of multiobjective problems may be solved by a game-theoretical concept leading to a single objective quasiconvex programming problem. The method is generalization of Nash's cooperative game theoretical model, and may lean on Zeuther's bargaining process. The methodology is applied to the Transdanubian Karstic region in Hungary where three objectives are present: mining costs, water supply and environmental protection. Results are compared with the solution previously obtained by compromise programming with an l₁-norm. It is found that results obtained by the two methods are comparable.     

On some properties of the series ∑k=0 kx and the Stirling numbers of the second kind

We partially characterize the rational numbers x and integers n 0 for which the sum ∑_k=0^∞ kⁿx^k assumes integers. We prove that if ∑_k=0^∞ kⁿx^k is an integer for x = 1 − a/b with a, b> 0 integers and gcd(a,b) = 1, then a = 1 or 2. Partial results and conjectures are given which indicate for which b and n it is an integer if a = 2. The proof is based on lower bounds on the multiplicities of factors of the Stirling number of the second kind, S(n,k). More specifically, we obtain for all integers k, 2 k n, and a 3, provided a is odd or divisible by 4, where v_a(m) denotes the exponent of the highest power of a which divides m, for m and a> 1 integers.

New identities are also derived for the Stirling numbers, e.g., we show that ∑_k=0²ⁿk! S(2n, k) , for all integers n 1.     

Experimental strategy for characterization of essential dynamical variables in oscillatory systems: effect of double-layer capacitance on the stability of electrochemical oscillators

An experimentally accessible algorithm for changing the time scale associated with a dynamical variable is proposed. In general, a differential controller can be applied to (a) identify the essential species in oscillatory systems and (b) explore their role in the feedback loops. Here, we report on classifying electrochemical oscillators by changing the time scale over which the electrode potential varies; the type of different electrochemical oscillators is identified based on whether the controlled modification of pseudo-capacitance induces or suppresses current oscillations.     

Kinetics and mechanism of the oxidation of sulfite by chlorine dioxide in a slightly acidic medium

The sulfite-chlorine dioxide reaction was studied by stopped-flow method at I = 0.5 M and at 25.0 +/- 0.1 degrees C in a slightly acidic medium. The stoichiometry was found to be 2 SO(3)(2-) + 2.ClO(2) + H(2)O --> 2SO(4)(2) (-) + Cl(-) + ClO(3)(-) + 2H(+) in *ClO(2) excess and 6SO(3)(2-) + 2*ClO(2) --> S(2)O(6)(2-) + 4SO(4)(2-) + 2Cl(-) in total sulfite excess ([S(IV)] = [H(2)SO(3)] + [HSO(3)(-)] + [SO(3)(2-)]). A nine-step model with four fitted kinetic parameters is suggested in which the proposed adduct *SO(3)ClO(2)(2-) plays a significant role. The pH-dependence of the kinetic traces indicates that SO(3)(2-) reacts much faster with *ClO(2) than HSO(3)(-) does.     

A concise total synthesis of the lichen macrolide (+)-aspicilin

The total synthesis of the polyhydroxylated macrolide (+)-aspicilin 5 is described using as a key step a highly diastereoselective allylation of aldehyde 6 with the uniquely functionalized allylstannane 1. (+)-Aspicilin is obtained in 18 steps and 10% overall yield. [structure: see text]     

A mass spectrometric line for tritium analysis of water and noble gas measurements from different water amounts in the range of microlitres and millilitres

This paper describes the procedure followed for noble gas measurements for litres, millilitres and microlitres of water samples in our laboratory, including sample preparation, mass spectrometric measurement procedure, and the complete calibrations. The preparation line extracts dissolved gases from water samples of volumes of 0.2 μ l to 3 l and it separates them as noble and other chemically active gases. Our compact system handles the following measurements: (i) determination of tritium concentration of environmental water samples by the ³He ingrowth method; (ii) noble gas measurements from surface water and groundwater; and (iii) noble gas measurements from fluid inclusions of solid geological archives (e.g. speleothems). As a result, the tritium measurements have a detection limit of 0.012 TU, and the expectation value (between 1 and 20 TU) is within 0.2 % of the real concentrations with a standard deviation of 2.4 %. The reproducibility of noble gas measurements for water samples of 20–40 ml allows us to determine solubility temperatures by an uncertainty better than 0.5 °C. Moreover, noble gas measurements for tiny water amounts (in the microlitre range) show that the results of the performed calibration measurements for most noble gas isotopes occur with a deviation of less than 2 %. Theoretically, these precisions for noble gas concentrations obtained from measurements of waters samples of a few microlitres allow us to determine noble gas temperatures by an uncertainty of less than 1 °C. Here, we present the first noble gas measurements of tiny amounts of artificial water samples prepared under laboratory conditions.     

In celebration of 30 years of Structural Chemistry: launching a series of prefatory reviews

Structural Chemistry -