Batch Fermentation Model of Propionic Acid Production by Propionibacterium acidipropionici in Different Carbon Sources

Propionic acid (PA) is widely used as additive in animal feed and also in the manufacturing of cellulose-based plastics, herbicides, and perfumes. Salts of propionic acid are used as preservative in food. PA is mainly produced by chemical synthesis. Nowadays, PA production by fermentation of low-cost industrial wastes or renewable sources has been an interesting alternative. In the present investigation, PA production by Propionibacterium acidipropionici ATCC 4965 was studied using a basal medium with sugarcane molasses (BMSM), glycerol or lactate (BML) in small batch fermentation at 30 and 36 degrees C. Bacterial growth was carried out under low dissolved oxygen concentration and without pH control. Results indicated that P. acidipropionici produced more biomass in BMSM than in other media at 30 degrees C (7.55 g l(-1)) as well as at 36 degrees C (3.71 g l(-1)). PA and biomass production were higher at 30 degrees C than at 36 degrees C in all cases studied. The best productivity was obtained by using BML (0.113 g l(-1) h(-1)), although the yielding of this metabolite was higher when using glycerol as carbon source (0.724 g g(-1)) because there was no detection of acetic acid. By the way, when using the other two carbon sources, acetic acid emerged as an undesirable by-product for further PA purification.     

Tough and tunable adhesion of hydrogels: experiments and models

As polymer networks infiltrated with water, hydro-gels are major constituents of animal and plant bodies and have diverse engineering applications. While natural hydro-gels can robustly adhere to other biological materials, such as bonding of tendons and cartilage on bones and adhe-sive plaques of mussels, it is challenging to achieve such tough adhesions between synthetic hydrogels and engineer-ing materials. Recent experiments show that chemically anchoring long-chain polymer networks of tough synthetic hydrogels on solid surfaces create adhesions tougher than their natural counterparts, but the underlying mechanism has not been well understood. It is also challenging to tune sys-tematically the adhesion of hydrogels on solids. Here, we provide a quantitative understanding of the mechanism for tough adhesions of hydrogels on solid materials via a com-bination of experiments, theory, and numerical simulations. Using a coupled cohesive-zone and Mullins-effect model val-idated by experiments, we reveal the interplays of intrinsic work of adhesion, interfacial strength, and energy dissipation in bulk hydrogels in order to achieve tough adhesions. We fur-ther show that hydrogel adhesion can be systematically tuned by tailoring the hydrogel geometry and silanization time of solid substrates, corresponding to the control of energy dis-sipation zone and intrinsic work of adhesion, respectively. The current work further provides a theoretical foundation for rational design of future biocompatible and underwater adhesives.     

A reduction in the UHE neutrino flux due to neutrino spin precession

Motivated by the stringent flux limits for UHE neutrinos coming from gamma ray bursts or active galactic nuclei, we explore the possibility that the active neutrinos generated in such astrophysical objects could oscillate to sterile right handed states due to a neutrino magnetic moment _μν${\mu }_{\nu }$. We find that a value as small as _μν≈10⁻¹⁵_μB${\mu }_{\nu }\approx {10}^{-15}{\mu }_B$ could produce such a transition thanks to the intense magnetic fields that are expected in these objects.     

A mixed bonding band structure calculation for GaAs and AlAs using the APW-k · p method

The Augmented Plane Wave (APW) method and the k.p expansion are used to obtain the band structure of GaAs in a mixed covalent and ionic bonding. The energy levels at the Γ point are also obtained for AlAs. The ionicity is introduced as a parameter into the crystalline potential. We explore the dependence of the energy levels and the momentum matrix elements on the values of the ionicity. The value of the ionicity which gave the direct gap Eg = 1.52eV for GaAs (the accepted experimental value) was found to be 0.1, and for AlAs Eg = 2.50 eV was obtained for an ionicity of 0.2.     

A comparative numerical analysis for the guillotine two-dimensional cutting problem

In this work, the behavior of four algorithms in the resolution of the two-dimensional constrained guillotine cutting problem is analyzed. This problem is concerned about the way a set of pieces should be cut from a plate of greater dimensions, considering guillotine cutting and a constrained number of times a piece can be cut from the plate. In this study three combinatorial and two heuristic methods are considered. In the combinatorial methods from the set of pieces, a minimum loss layout is constructively generated based on Wang's algorithm. In addition, an evolutionary and an annealing type approach are considered. All of these models have been implemented on a high performance Silicon Graphics machine. Performance of each algorithm is analyzed both in terms of percentage waste and running time. In order to do that, a set of 1000 instances are classified according to their combinatorial degree and subsequently evaluated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Methoxycarbonylation of olefins catalyzed by palladium(II) complexes containing naphthyl(diphenyl)phosphine ligands

Palladium(II) complexes containing phosphine donor ligands derived from naphthyl(diphenyl)phosphine were synthesized and characterized by NMR and elemental analysis. The complexes were studied as catalyst precursors in the methoxycarbonylation reaction of several aromatic and aliphatic olefins under mild conditions. The catalysts reported high chemoselectivities (over 96%) and regioselectivities between 44% and 93% for different olefins. The best results were obtained over a styrene substrate with 97% of conversion after 6 h of reaction, with high regioselectivity (93%). Kinetic studies permitted the determination of the rate law (v = k [substrate]^1.21±0.02 [catalyst]^0.94±0.11 [acid]^0.52±0.03 [MeOH]^0.53±0.05 [CO]^0.65±0.03) for methoxycarbonylation of styrene. Copyright © 2014 John Wiley & Sons, Ltd.     

Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.     

Oxychlorination–Dehydrochlorination Chemistry on Bifunctional Ceria Catalysts for Intensified Vinyl Chloride Production

Ceria catalyzes the one‐step production of the vinyl chloride monomer (VCM) from ethylene with a high yield because of its bifunctional character: redox centers oxychlorinate ethylene to ethylene dichloride (EDC), which is subsequently dehydrochlorinated to VCM over strong acid sites generated in situ. Nanocrystalline CeO₂ and CeO₂‐ZrO₂ lead to a VCM yield of 25 % in a single pass, outperforming the best reported systems and reaching industrially attractive levels. The use of CeO₂ intensifies the current two‐step process within PVC production encompassing CuCl₂‐catalyzed oxychlorination and thermal cracking. In addition, ceria‐based materials offer stability advantages with respect to the archetypical CuCl₂‐based catalysts.