Monotonicity in multidimensional Markov decision processes for the batch dispatch problem

Structural properties of stochastic dynamic programs are essential to understanding the nature of the solutions and in deriving appropriate approximation techniques. We concentrate on a class of multidimensional Markov decision processes and derive sufficient conditions for the monotonicity of the value functions. We illustrate our result in the case of the multiproduct batch dispatch (MBD) problem.     

Optimization of separation and detection conditions for comprehensive two-dimensional gas chromatography--time-of-flight mass spectrometry analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans

The 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are among the most toxic compounds known, and several sources of exposure to these chemicals should be monitored to protect human and environmental health. The current predominant method of analysis is too expensive and cumbersome, and comprehensive two-dimensional GC coupled to time-of-flight mass spectrometry (GC x GC--TOF-MS) has the potential to lower the costs and speed analysis of PCDD/Fs. In this study, GC x GC--TOF parameters were evaluated and optimized to yield complete separation of the 17 most important PCDD/F congeners from polychlorinated biphenyls (PCBs) interferences, and to attain the lowest detection limits. The optimization study entailed evaluation of oven temperature programs, column flow rates, ion source temperatures, electron ionization energy, data acquisition rate, and various GC x GC parameters, including modulation period, modulator temperature offset and hot pulse duration. After optimization, all 17 PCDD/Fs were separated in <60 min, and in particular, the critical pair of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and pentachlorobiphenyl congener CB126 did not co-elute chromatographically. Accurate identification and determination of all analytes could be made using their deconvoluted full mass spectra. In GC x GC, the modulation period and start time were the most important factors that affected sensitivity and selectivity for the analysis of the PCDD/Fs. The modulation period should be < or = 4s to preserve separations achieved in one-dimensional GC, and the modulation start time was important to achieve one large slice and two smaller symmetrical slices of TCDD to maximize its detection sensitivity. After optimization, the method could identify 0.25 pg of TCDD with standard injection from its full mass spectrum.     

Composition and enantiomeric analysis of the essential oil of the fruits and the leaves of Pistacia vera from Greece

The essential oils of the fruits and the leaves of pistachio (Pistacia vera L.) were analyzed by GC and GC/MS. Fresh unripe pistachio fruits were richer in essential oil (0.5%, w/w) than the leaves (0.1%, w/w). Twenty one compounds were identified in the essential oil of the fruits and the major components were (+)-alpha-pinene (54.6%) and terpinolene (31.2%). The enantiomeric ratio of the major constituents of the essential oil of the fruits was determined using chiral GC/MS and it was found that the (+)/(-)-alpha-pinene ratio was 99.5:0.5, (+)/(-)-limonene 80:20, (+)/(-)-beta-pinene 96:4, and (+)/(-)-alpha-terpineol 0:100. Thirty three compounds were identified in the essential oil of the leaves and the major components were found to be alpha-pinene (30.0%), terpinolene (17.6%) and bornyl acetate (11.3%).     

Phase system selectivity and two-dimensional separations in liquid column chromatography

Correlations between the separation selectivity in aqueous and non-aqueous reversed-phase systems and in normal-phase LC systems were investigated for samples containing different numbers of two repeat structural elements. Such samples are best separated in "orthogonal" two-dimensional chromatographic systems, showing selectivity for one type of the repeat structural element only in the first dimension and for the other structural element only in the second dimension. The number of resolved compounds improves as the degree of orthogonality of the separation systems increases with decreasing correlation between the selectivities for the sample structural distribution in the two dimensions. Orthogonal systems with non-correlated selectivities for each repeat structural element provide the highest number of separated peaks and regular arrangement of the peaks over the two-dimensional retention space according to the individual structural element distribution and the best use of the available peak capacity. Fully orthogonal systems are difficult to find in practice. Partially orthogonal system with correlated selectivities for one structural type distribution, but with one system non-distinguishing the distribution for the other structural element are still useful for the two-dimensional separations. The correlations between the selectivities for repeat regular structural increments were employed to evaluate the suitability of phase systems for two-dimensional HPLC separations. The selectivity correlation in various reversed-phase and normal-phase systems was evaluated for two sample types: (1) Various RP columns show significantly inversely correlated selectivities for acyl lengths and numbers of double bonds distribution, but the differences in the double bond selectivity can be used for practical separations of triacylglycerols with the same equivalent carbon numbers. (2) Synthetic EO-PO block (co)oligomers with two-dimensional distribution of oxyethylene and oxypropylene monomer units were separated according to the two distribution types using on-line two-dimensional reversed-phase-normal-phase LC with a C18 column in the first dimension and an aminopropyl silica column in the second dimension.     

Evidence for dark energy from the cosmic microwave background alone using the Atacama Cosmology Telescope lensing measurements

For the first time, measurements of the cosmic microwave background radiation (CMB) alone favor cosmologies with w = -1 dark energy over models without dark energy at a 3.2-sigma level. We demonstrate this by combining the CMB lensing deflection power spectrum from the Atacama Cosmology Telescope with temperature and polarization power spectra from the Wilkinson Microwave Anisotropy Probe. The lensing data break the geometric degeneracy of different cosmological models with similar CMB temperature power spectra. Our CMB-only measurement of the dark energy density Ω(Λ) confirms other measurements from supernovae, galaxy clusters, and baryon acoustic oscillations, and demonstrates the power of CMB lensing as a new cosmological tool.     

Rheological representation of fractional order viscoelastic material models

We develop rheological representations, i.e., discrete spectrum models, for the fractional derivative viscoelastic element (fractional dashpot or springpot). Our representations are generalized Maxwell models or series of Kelvin-Voigt units, which, however, maintain the number of parameters of the corresponding fractional order model. Accordingly, the number of parameters of the rheological representation is independent of the number of rheological units. We prove that the representations converge to the corresponding fractional model in the limit as the number of units tends to infinity. The representations extend to compound fractional derivative models such as the fractional Maxwell model, fractional Kelvin-Voigt model, and fractional standard linear solid. Computational experiments show that the rheological representations are accurate approximations of the fractional order models even for a small number of units.     

Synthesis of Composite Polystyrene/Silica Nanoparticles via Precipitation and Emulsion Polymerization Methods

Polystyrene/silica composite nanoparticles were synthesized via precipitation and emulsion polymerization methods, in the presence of a basic co‐monomer (e.g., 4‐VP and 1‐VID), and a colloidal aqueous silica solution. The effects of key process parameters, that is, solvent type, monomer/co‐monomer volume ratio and total monomers concentration for precipitation polymerization, and reaction temperature, pH value, initial silica‐sol concentration and initial monomer/co‐monomer molar ratio for emulsifier‐free emulsion polymerization on the particle morphology, silica content, and particle size distribution of the composite nanoparticles were experimentally investigated. Stable, spherical, and uniform in size composite nanoparticles were synthesized by both techniques. The average particle diameter varied from 108 to 182 nm for the emulsifier‐free emulsion polymerization and from 400 to 800 nm for the precipitation polymerization, while the silica content was as high as 38.3 wt.‐% for the former method and up to 15.5 wt.‐% for the later. The synthesized composite polymer/silica particles were then electrolytically co‐deposited with zinc on steel plates to improve the corrosion resistance of the metal's surface.

     

Effect of gamma irradiation on antiradical activity of goji berry fruits (Lycium barbarum) evaluated by EPR spectroscopy

Antiradical activity of goji berry (Lycium barbarum) was evaluated by means of electron paramagnetic resonance spectroscopy. The goji berry samples were exposed to gamma-irradiation at doses 0.05, 2 and 10 kGy. The characteristic satellite lines from cellulose radicals can prove irradiation treatment. Their intensity increase after alcohol washing and lyophilization. The fading property of satellite lines show that identification of radiation treatment is possible for 50 days. The effect of irradiation on antiradical properties of goji berry extracts was investigated by radical scavenging activity using the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH). The percentages of scavenged DPPH radicals and IC₅₀ of the extracts of goji berry before and after irradiation were calculated. The antioxidant capacity was presented in Trolox Equivalents as well. It was found out that gamma irradiation of goji berry fruits increases its antiradical activity.