Evaluation of process parameters of ultrasonic treatment of bacterial suspensions in a pilot scale water disinfection system

In this study, several process parameters that may contribute to the efficiency of ultrasound disinfection are examined on a pilot scale water disinfection system that mimics realistic circumstances as encountered in an industrial environment. The main parameters of sonication are: (i) power; (ii) duration of treatment; (iii) volume of the treated sample. The specific energy (E_s) is an indicator of the intensity of the ultrasound treatment because it incorporates the transferred power, the duration of sonication and the treated volume. In this study, the importance of this parameter for the disinfection efficiency was assessed through changes in volume of treated water, water flow rate and electrical power of the ultrasonic reactor. In addition, the influences of the initial bacterial concentration on the disinfection efficiency were examined. The disinfection efficiency of the ultrasonic technique was scored on a homogenous and on a mixed bacterial culture suspended in water with two different types of ultrasonic reactors (Telsonic and Bandelin). This study demonstrates that specific energy, treatment time of water with ultrasound and number of passages through the ultrasonic reactor are crucial influential parameters of ultrasonic disinfection of contaminated water in a pilot scale water disinfection system. The promising results obtained in this study on a pilot scale water disinfection system indicate the possible application of ultrasound technology to reduce bacterial contamination in recirculating process water to an acceptable low level. However, the energy demand of the ultrasound equipment is rather high and therefore it may be advantageous to apply ultrasound in combination with another treatment.     

The representation of 3D gaussian beams by means of inhomogeneous waves

There are different methods to mathematically represent a bounded beam. Perhaps the most famous method is the classical Fourier method that consists of the superposition of pure homogeneous plane waves all traveling in different directions and having an amplitude that can be found by the Fourier transform of the required profile. This method works perfectly for 2D as well as for 3D bounded beams. However, some researchers prefer the inhomogeneous wave theory to represent a bounded beam because some phenomena, e.g. the Schoch effect, are explained by this method by means of concepts that agree better with intuition. There are several papers dealing with this method for 2D gaussian beams. Until now, it has never been considered possible to represent 3D gaussian beams as well. The present paper shows a method to overcome this shortcoming and presents different sorts of 3D gaussian beams that are built up by means of inhomogeneous plane waves.     

Efficient approximately 2 microm Tm3+ -doped tellurite fiber laser

Laser emission in the range of 1.88-1.99 micrim from a Tm3+ -doped tellurite fiber is demonstrated when pumped with a diode-pumped Er3+/Yb3+-doped silica fiber laser operating at 1.57-1.61 microm. This pump source excites the Tm3+ ions directly into the F43 upper laser level and yields an output power of 280 mW with a slope efficiency of 76% in a 99%-12% laser cavity arrangement and a 32 cm long fiber. This result is very close to the Stokes efficiency limit of approximately 80%. This is, to the authors' knowledge, the first demonstration of high efficiency lasing in a tellurite fiber at wavelengths longer than 1.56 microm.     

Tm(3+)/Ho(3+) codoped tellurite fiber laser

Continuous-wave and Q-switched lasing from a Tm(3+)/Ho(3+) codoped tellurite fiber is reported. An Yb(3+)/Er(3+)-doped silica fiber laser operating at 1.6 microm was used as an in-band pump source, exciting the Tm(3+) ions into the (3)F(4) level. Energy is then nonradiatively transferred to the upper laser level, the (5)I(7) state of Ho(3+). The laser transition is from the (5)I(7) level to the (5)I(8) level, and the resulting emission is at 2.1 microm. For continuous wave operation, the slope efficiency was 62% and the threshold 0.1 W; the maximum output demonstrated was 0.16 W. Mechanical Q switching resulted in a pulse of 0.65 microJ energy and 160 ns duration at a repetition rate of 19.4 kHz.     

Analysis of several subcycling schemes in partitioned simulations of a strongly coupled fluid-structure interaction

Fluid-structure interaction (FSI) simulations are used extensively to calculate the vibration of structures subjected to an internal or external flow. In the case of partitioned FSI simulations, separate flow and structure solvers are used, which requires some kind of coupling between both. The time step in both solvers is typically taken the same, but this unnecessarily leads to long calculation times when the time step is small due to stability reasons in one of the two solvers. Subcycling, the procedure where the time step of one solver is chosen smaller than the time step used in the other solver, may reduce the computational cost of the FSI simulation. The subcycling procedure can be either explicit or implicit, the latter implying the use of coupling iterations in each time step. Contrary to explicit subcycling, no stability analyses of implicit subcycling schemes are found in the literature. In this paper, the temporal stability of the implicit subcycling procedure is investigated. The one-dimensional flow in an elastic cylindrical tube is studied analytically. The results of this analysis are subsequently compared to a partitioned two-dimensional axisymmetric FSI calculation with implicit coupling between the flow and structure solvers.     

On the nonexistence of certain Hughes generalized quadrangles

In this paper, we prove that the Hermitian quadrangle is the unique generalized quadrangle Γ of order (q ², q ³) containing some subquadrangle of order (q ², q) isomorphic to such that every central elation of the subquadrangle is induced by a collineation of Γ. Dedicated to Dan Hughes on the occasion of his 80th birthday.     

On the optimization of two-class work-conserving parameterized scheduling policies

Numerous scheduling policies are designed to differentiate quality of service for different applications. Service differentiation can in fact be formulated as a generalized resource allocation optimization towards the minimization of some important system characteristics. For complex scheduling policies, however, optimization can be a demanding task, due to the difficult analytical analysis of the system at hand. In this paper, we study the optimization problem in a queueing system with two traffic classes, a work-conserving parameterized scheduling policy, and an objective function that is a convex combination of either linear, convex or concave increasing functions of given performance measures of both classes. In case of linear and concave functions, we show that the optimum is always in an extreme value of the parameter. Furthermore, we prove that this is not necessarily the case for convex functions; in this case, a unique local minimum exists. This information greatly simplifies the optimization problem. We apply the framework to some interesting scheduling policies, such as Generalized Processor Sharing and semi-preemptive priority scheduling. We also show that the well-documented \(c\mu \)-rule is a special case of our framework.     

Enantioselective Artificial Metalloenzymes Based on a Bovine Pancreatic Polypeptide Scaffold

Site creation : Enantioselective artificial metalloenzymes have been created by grafting a new active site onto bovine pancreatic polypeptide through the introduction of an amino acid capable of coordinating a copper(II) ion. This hybrid catalyst gave good enantioselectivities in the Diels–Alder and Michael addition reactions in water (see scheme) and displayed a very high substrate selectivity.

     

Bacillus licheniformis peptidoglycan characterization by CZE–MS: Assessment with the benchmark RP‐HPLC‐MS method

Peptidoglycan or murein is an essential polymer found in bacterial cell wall. It is a dynamic structure that is continuously remodeled or modified during bacterial cell growth or in presence of cell wall stresses. These modifications are still poorly understood mainly due to the peptidoglycan, which is rather non‐soluble, and the difficulties to separate the hydrophilic glycopeptides (muropeptides) by reversed phase liquid chromatography, generated by the enzymatic digestion using mutanolysin, an N‐acetyl‐muramidase, cleaving the β_1→4 bound between N‐acetylglucosamine and N‐acetylmuramic acid. Here, we report the use of CZE–MS for an easy and fast screening of muropeptides generated by the action of muramidase on the Bacillus licheniformis cell wall. Electron transfer and CID–MS were also used to unambiguously identify and localize the presence or the absence of amidation and acetylation moieties on muropeptide variants. The reference method to analyse muropeptides by reversed phase chromatography was also tested and the advantages and disadvantages of both methods were evaluated.     

En route to coordination chemistry under confined conditions in a porous capsule: Pr3+ with different coordination shells

The highly charged nanocontainer capsule of the type [pentagon]12[linker]30 identical with [(Mo)Mo5O21(H2O)6]12[Mo2O4(SO4)]30 with 20 nanosized pores and channels allows the entrance of cations like Pr3+: the latter are positioned at two different sites and have two different coordination shells, corresponding to a coordination chemistry under confined conditions; a fascinating aspect is that capsule encapsulated water shells fixed by hydrogen bonds act formally as polydentate ligands.