A novel tetra(μ3-phenoxo) bridged copper(II) Schiff base complex containing a Cu4O4 cubane core: Synthesis,structural aspects and magneto-structural correlations

A novel tetranuclear complex, [Cu₄L₄] · Na · ClO₄ (1) has been prepared from an interesting multidentate Schiff base ligand H₂L resulting from the 1:1 condensation of 3-methoxysalicylaldehyde with benzhydrazide. The prepared complex has been characterized by elemental analysis, FT-IR, UV–Vis spectroscopy, electrochemical studies and single crystal X-ray diffraction analysis. The Cu₄O₄ cubane core consists of four μ₃-phenoxo-bridged copper(II) atoms giving an approximately cubic array of alternating copper(II) and oxygen atoms. Magneto-structural correlations have been drawn from cryomagnetic susceptibility measurements over a wide range of temperature (2–300 K) under 0.5 T magnetic field. The measurements reveal both ferromagnetic and antiferromagnetic interactions in a 2J model [J₁₁ = +13.6(4) cm⁻¹ and J₁₂ = −34.9(4) cm⁻¹] which in turn results in an overall antiferromagnetic behaviour of the magnetic system.     

Carbon nanotubes as the sorbent for integrating μ-solid phase extraction within the needle of a syringe

In this research we report the implementation of micro-solid-phase extraction (μ-SPE) in the needle of a syringe for integrating sampling, analyte enrichment and sample introduction into a single device. Both single- and multi-walled carbon nanotubes (CNTs) were explored as high performance sorbents for μ-SPE in packed and self assembled formats. The need for such a sorbent was critical because the needle probe could hold only a small amount of material (around 300 μg). Conventional C-18 and self-assembled CNTs were found to be ineffective with enrichment factors less than one. However, packed beds of CNTs were found to be excellent sorbent phases, where high extraction efficiencies (as high as 27%) as well as enrichment factors (close to 7) could be achieved. The overall method showed excellent linearity, reproducibility, and low method detection limit (0.1–3 ng/mL for MWNTs). The sorption on CNTs followed Freundlich isotherms, and the functionalized CNTs were more effective for enriching the polar compounds.     

Evidence for the charged θ-meson

A K-meson is found to decay at rest into a nearly relativistic secondary particle. The secondary particle produces a nuclear disintegration in flight and is identified as a π-meson of kinetic energy ～ 110 MeV. The event is interpreted as the decay of a θ^±-meson according to the scheme:

$$\theta ^ \pm \to \pi ^ \pm + \pi ^0 + (222 \pm 12 MeV.)$$     

Observation of minority spin character of the new electron doped manganite La0.7Ce0.3MnO3 from tunneling magnetoresistance

We report the magnetotransport characteristics of a trilayer ferromagnetic tunnel junction built of an electron doped manganite (La0.7Ce0.3MnO3) and a hole doped manganite (La0.7Ca0.3MnO3). At low temperatures the junction exhibits a large positive tunneling magnetoresistance (TMR), irrespective of the bias voltage. At intermediate temperatures below T(C) the sign of the TMR is dependent on the bias voltage across the junction. The magnetoresistive characteristics of the junction strongly suggest that La0.7Ce0.3MnO3 is a minority spin carrier ferromagnet with a high degree of spin polarization, i.e., a transport half-metal.     

A microfabricated microconcentrator for sensors and gas chromatography

The key component in trace analysis is the concentration step where the analytes are accumulated before the analysis. This paper presents the development of a micromachined microconcentrator that can be used to enhance the sensitivity of microsensors. Another application demonstrated here is a concentrator-injector for a gas chromatograph. The microconcentrators were fabricated on a 6-in. silicon substrate using standard photolithographic techniques (1 in.= 2.54 cm). The channels were lined with a resistive layer, through which an electric current could be passed to cause ohmic heating. The preconcentration was done on a thin-film polymeric layer deposited above the heater in the channel. Rapid heating of the resistive layer caused the "desorption pulse" to be injected into the sensor, or onto a GC column. Due to their small size, the microconcentrators could be fabricated 20 to 50 (depending upon the size) at a time on a 6-in. silicon wafer. This paper presents the development and characterization of the microconcentrator. It was found that the microconcentrator performed well as a concentrator, and as an injector for GC. A 14-fold enrichment factor was achieved. The microconcentrator exhibited long-term stability in response, with typical relative standard deviation of between 3 and 5%.     

An extension of set partitioning with application to scheduling problems

The well known problems of set covering, set partitioning and set packing are defined and their interrelationship is considered. A natural generalisation called the extended set partitioning model is presented and the three standard models are shown to be special cases of this generalisation. In addition, the extended model includes another type of set problem which can be of greater use in certain applications. The model forms the basis of a computer assisted bus crew scheduling system developed by the authors. The system is in regular use by Dublin City Services in the Republic of Ireland. Finally, the equivalence between a special case of the set partitioning problem and the shortest route problem is considered and it is shown that this equivalence also applies to the extended model.     

A new computational approach for stochastic fluid models of multiplexers with heterogeneous sources

In this paper we derive an efficient computational procedure for the system in which fluid is produced byN ₁ on-off sources of type 1,N ₂ on-off sources of type 2 and transferred to a buffer which is serviced by a channel of constant capacity. This is a canonical model for multiservice ATM multiplexing, which is hard to analyze and also of wide interest. This paper's approach to the computation of the buffer overflow probability,G(x) = Pr{buffer content >x}, departs from all prior approaches in that it transforms the computation ofG(x) for a particularx into a recursive construction of an interpolating polynomial. For the particular case of two source types the interpolating polynomial is in two variables. Our main result is the derivation of recursive algorithms for computing the overflow probabilityG(x) and various other performance measures using their respective relations to two-dimensional interpolating polynomials. To make the computational procedure efficient we first derive a new system of equations for the coefficients in the spectral expansion formula forG(x) and then use specific properties of the new system for efficient recursive construction of the polynomials. We also develop an approximate method with low complexity and analyze its accuracy by numerical studies. We computeG(x) for different values ofx, the mean buffer content and the coefficient of the dominant exponential term in the spectral expansion ofG(x). The accuracy of the approximations is reasonable when the buffer utilization characterized by G(0) is more than 10^–2.