Picosecond pulses from a cryogenically cooled, composite amplifier using Yb:YAG and Yb:GSAG

A cryogenic Yb amplifier using two laser materials, Gd3Sc2Al3O12 and Y3Al5O12 (YAG), has been used to obtain 70 W average power at 5 kHz pulse repetition frequency; the output was compressed to 1.6 ps, compared with an input compressible to 1.4 ps. The gain broadening obtained by combining two media enables shorter pulses than using Yb:YAG alone but retains the power-scaling advantages of cryogenic Yb:YAG.     

Effective learning hyper-heuristics for the course timetabling problem

Course timetabling is an important and recurring administrative activity in most educational institutions. This article combines a general modeling methodology with effective learning hyper-heuristics to solve this problem. The proposed hyper-heuristics are based on an iterated local search procedure that autonomously combines a set of move operators. Two types of learning for operator selection are contrasted: a static (offline) approach, with a clear distinction between training and execution phases; and a dynamic approach that learns on the fly. The resulting algorithms are tested over the set of real-world instances collected by the first and second International Timetabling competitions. The dynamic scheme statistically outperforms the static counterpart, and produces competitive results when compared to the state-of-the-art, even producing a new best-known solution. Importantly, our study illustrates that algorithms with increased autonomy and generality can outperform human designed problem-specific algorithms.     

Acrylamide inverse microemulsion polymerization in a paraffinic solvent: Rolling‐M‐245

The inverse microemulsion polymerization of acrylamide in a paraffinic solvent, Rolling‐M‐245, stabilized by a mixture of nonionic surfactants (Emulan‐ELP‐11 and Brij‐92), was studied. Pseudoternary phase diagrams of this system were determined, and a range of hydrophilic‐lipophilic balance (HLB) values, from 8.98 to 9.2, were selected as the most favorable for acrylamide polymerization. The influence of factors such as the initiator composition, HLB, percentage of the aqueous phase, and addition of the monomer by steps on the final conversion and polyacrylamide molar masses were investigated. High conversions and molar masses were generally obtained with the different formulations. The polyacrylamide molar masses were influenced by the HLB and content in the aqueous phase. The addition of the aqueous phase by steps led to a progressive diminution of the molar masses as the number of stages increased. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2495–2503, 2005     

The microscopic investigation of structures of moving flux lines by neutron and muon techniques

We have used a variety of microscopic techniques to reveal the structure and motion of flux line arrangements, when the flux lines in low T _c type II superconductors are caused to move by a transport current. Using small-angle neutron scattering by the flux line lattice (FLL), we are able to demonstrate directly the alignment by motion of the nearest-neighbor FLL direction. This tends to be parallel to the direction of flux line motion, as had been suspected from two-dimensional simulations. We also see the destruction of the ordered FLL by plastic flow and the bending of flux lines. Another technique that our collaboration has employed is the direct measurement of flux line motion, using the ultra-high-resolution spectroscopy of the neutron spin-echo technique to observe the energy change of neutrons diffracted by moving flux lines. The muon spin rotation (μSR) technique gives the distribution of values of magnetic field within the FLL. We have recently succeeded in performing μSR measurements while the FLL is moving. Such measurements give complementary information about the local speed and orientation of the FLL motion. We conclude by discussing the possible application of this technique to thin film superconductors.     

Efficient synthesis of fluorinated α- and β-amino nitriles from fluoroalkylated α,β-unsaturated imines

A simple and efficient synthesis of fluoroalkylated α-amino nitrile (4) derivatives by regioselective 1,2-addition of trimethylsilyl cyanide to fluoroalkylated α,β-unsaturated imines (1) is described. Fluoroalkylated β-amino nitriles (7) are also prepared by regioselective 1,2-addition of α-carbanions derived from acetonitrile to fluoroalkylated α,β-unsaturated imines (1). Fluoroalkylated α-(4) and β-amino nitriles (7) are also prepared through an ‘one pot’ procedure by reaction of enaminophosphonate 2 with BuLi, addition of aldehydes and subsequent addition of either trimethylsilyl cyanide or α-carbanion derived from acetonitrile. Basic hydrolysis of α-(4) and β-amino nitriles (7) gives fluoroalkylated α-(5) and β-amino acids (8).     

Preisach modelling of nonlinear response in electrically biased lead zirconate titanate-based piezoceramics

The alteration of the high-field electrical permittivity (nonlinear response) of PZT-based ceramics when an electrical bias field is applied is reported in this work. Large differences are observed between soft and hard PZT behaviours. While in soft PZT a bias field does not modify the nonlinear behaviour, a notable dependence is verified in hard PZT. The Preisach model is satisfactorily used to describe experimental results. A distribution function containing the first terms of the Maclaurin development series of a function composed by two Gaussian-like functions of different amplitudes is proposed. The model gives a satisfactory explanation for the fact that the permittivity depends not only on the amplitude of the applied electric field, but also on the bias field, both for soft and hard ceramics and for poled or unpoled samples.     

Dynamic-mechanical analysis of the photo-degradation of long glass fibre reinforced polypropylene: Mechanical properties' changes

Polypropylene matrix composites, with different degrees of reinforcement with long glass fibres, are employed in different fields of the industry, such as aeronautics or automotive. Samples of the material were exposed to artificial accelerated photo-ageing in UV chamber (Heraeus Xenotest 150S). Their high content of glass fibres causes a surface degradation that can seriously affect mechanical properties. Therefore, dynamic mechanical and tensile tests were carried out in order to compare the changes of the properties with exposure time. These modifications are accompanied with microscopic changes in the crystallinity as can be seen in the thermal analysis experiments.