An Elementary Proof of the Fundamental Property of a Perfect Gas

A sharpened version of an important property of perfect gases proved by Monleón Pradas & Pedregal[1] is proved here by exploiting fully the fact that every perfect gas has an entropy function. In this manner, the more advanced machinery of weak convergence employed in the earlier version is avoided, and a more elementary and accessible proof emerges. (Accepted March 10, 1997)     

An outline of linear programming

Linear programming deals with the maximization or minimization of linear functions subject to linear inequality constraints. Definitions and practical examples are given in Section 2. Section 3 gives a geometric interpretation of the simplex algorithm. Section 4 develops the mathematical theory of duality and gives heuristic interpretations in terms of shadow prices. Section 5 studies those linear programs for which integer solutions are normally required and discusses those cases in which integer solutions arise naturally and those in which special techniques must be used.The preparation of this paper was supported in part by the Army Research Office under Contract No. DA-ARO-D-31-124-70-G42.     

Improved SFE recovery of trace analytes from liver using an integral micrometering valve–SPE column holder assembly

A novel integral restrictor–collector has been designed for use with a conventional supercritical fluid extraction (SFE) apparatus. The assembly reduces the path length between a micrometering valve and collector (a solid phase extraction (SPE) column), obviating the need for the complicated tubing and connectors usually associated with such devices. Also described is a heating-block assembly which encases the micrometering valve and provides uniform heating of the valve during extraction. The valve–SPE column assembly was part of a system used to perform the first reported SFE multi-residue drug recovery from fortified liver. Extractions used carbon dioxide pressurized to 690 bar as the supercritical fluid. Flow rates of expanded gas through the SPE columns were 3–4 L/min with concomitant quantitative trapping of the analytes on the sorbent bed. After SFE the three nitrobenzamide antimicrobial drug residues from the liver were eluted from the SPE columns by off-line analysis. The results demonstrated that losses of trace level analytes in tissue may be significantly reduced by including an integral metering valve-collector assembly as part of the SFE apparatus.     

Linear free energy relationships between dissolution rates and molecular modeling energies of rhombohedral carbonates

Bulk and surface energies are calculated for endmembers of the isostructural rhombohedral carbonate mineral family, including Ca, Cd, Co, Fe, Mg, Mn, Ni, and Zn compositions. The calculations for the bulk agree with the densities, bond distances, bond angles, and lattice enthalpies reported in the literature. The calculated energies also correlate with measured dissolution rates: the lattice energies show a log-linear relationship to the macroscopic dissolution rates at circumneutral pH. Moreover, the energies of ion pairs translated along surface steps are calculated and found to predict experimentally observed microscopic step retreat velocities. Finally, pit formation excess energies decrease with increasing pit size, which is consistent with the nonlinear dissolution kinetics hypothesized for the initial stages of pit formation.     

Bumps, breathers, and waves in a neural network with spike frequency adaptation

We introduce a continuum model of neural tissue that includes the effects of spike frequency adaptation (SFA). The basic model is an integral equation for synaptic activity that depends upon nonlocal network connectivity, synaptic response, and the firing rate of a single neuron. We consider a phenomenological model of SFA via a simple state-dependent threshold firing rate function. As without SFA, Mexican-hat connectivity allows for the existence of spatially localized states (bumps). Importantly recent Evans function techniques are used to show that bumps may destabilize leading to the emergence of breathers and traveling waves. Moreover, a similar analysis for traveling pulses leads to the conditions necessary to observe a stable traveling breather. Simulations confirm our theoretical predictions and illustrate the rich behavior of this model.     

Automated coupling of capillary-HPLC to matrix-assisted laser desorption/ionization mass spectrometry for the analysis of small molecules utilizing a reactive matrix

This study describes the application of a novel, reactive matrix for the mass spectral analysis of steroids by capillary-high performance liquid chromatography (capillary-HPLC) coupled to matrix-assisted laser desorption/ionization (MALDI). The mass spectral analysis of steroids was accomplished after fully automated peak deposition of chromatographic peaks onto MALDI targets. The seven corticosteroids used as test compounds were: triamcinolone, prednisone, cortisone, fludrocortisone, dexamethasone, deoxycorticosterone, and budesonide. They were separated using a PepMap C₁₈ (3 m particle size, 100 Å pore width) column at five different concentration levels of 25, 15, 7.5, 2.5 and 1 ng/L, and the peaks were detected at a wavelength of 237 nm. The column effluent was mixed with 2,4-dinitrophenylhydrazine (DNPH) directly following the UV detector. The chromatographic peaks were then deposited onto the MALDI target with a robotic micro-fraction collector triggered by the UV detector signals. A special hydrophobic surface coating allowed the deposition of up to 4 L (up to 90 % of the chromatographic peak volume) onto one sample spot. The compounds were then identified by MALDI mass spectrometry. Depending on the nature of the analyte, radical cations ([M]^+.) and sodium adduct ions ([M+Na]⁺) of the steroids as well as protonated steroid-dinitrophenylhydrazone derivatives ([M_D+H]⁺) were detected in positive ion mode. The detection limits were between 0.5 and 15 ng injected with capillary-HPLC-MALDI-TOF-MS and between 0.3 and 3 ng on target with MALDI-TOF when deposited manually.     

Model compounds for galactose oxidase: The crystal and molecular structure of dimeric (4-methylpyridine-N) (N-salicylidene-tyrosinato-O, N, O′)copper(II)

Galactose oxidase is a type II copper protein that contains a square–pyramidal five-coordinate copper center and catalyzes the oxidation of primary alcohols to aldehydes with a concomitant reduction of molecular oxygen. Dimeric (4-methylpyridine-N)(N-salicylidene-tyrosinato-O, N, O)copper(II), which contains two square–pyramidal five-coordinate copper centers and thus serves as a model for galactose oxidase, crystallizes in the monoclinic space group P2 ₁/c with a = 8.914(1) Å, b = 18.415(2) Å, c = 12.802(2) Å, = 107.70(1)°. The dinuclear unit comprises two four-coordinate units each consisting of the tridentate Schiff base and 4-methylpyridine with a weaker out-of-plane link to the phenolic oxygen atom from the adjoining unit in a typical 4 + 1 distorted square–pyramidal geometry.     

Scanning electron microscopy of oriented high density polyethylene

Summary The microfibrillar and lamellar morphologies in cold-drawn and cold-drawn/annealed high-density polyethylene sheets were observed by means of scanning electron microscopy. Differences in contrast on fracture surfaces for cold-drawn sheet are interpreted in terms of a preferential orientation of inter-microfibrillar tie molecules in the plane of the sheet brought about by the drawing mechanism. In annealed, cold-drawn sheet, stacks of lamellae were observed which showed twinned orientations of inclined lamellae. This roof-top structure is interpreted in terms of shear within the individual microfibrils during micronecking, and corresponds to the well-known 4-point small-angle X-ray pattern for this type of specimen. Light etching with fuming nitric acid was necessary in order to resolve the individual lamellar texture.With 9 figures