Rayleigh scattering, absorption, and birefringence of large-size bulk single-crystal sapphire

While the thermomechanical properties of sapphire make it an excellent candidate of test mass for advanced laser interferometers, its optical quality is not well understood or well controlled. We have studied the results from high-resolution measurements of scattering, absorption, and birefringence in test-mass samples to better understand issues of quality. Samples show large-scale scattering structures clearly linked to the crystal-growth process. Samples characterized by the presence of point defects have significantly lower scattering (except at the point defects). In general on a large scale, high scattering also correlates with higher absorption and higher average birefringence inhomogeneity. However, on a smaller scale there is not a clear point-to-point correlation between scattering and absorption. Often a large-scale scattering structure is spatially displaced by tens of millimeters from a similar absorption structure, indicating that quite separate microscopic mechanisms give rise to scattering and absorption. The spatial displacements indicate that absorption centers and scattering centers are laid down during crystal growth at different distances from the solid-liquid interface. We suggest that absorption may be linked to F centers, while scattering may be linked to impurities such as iron.     

Cobalt‐Catalyzed Cross‐Coupling Reaction between Functionalized Primary and Secondary Alkyl Halides and Aliphatic Grignard Reagents

The coupling of primary and secondary unactivated alkyl bromides with alkyl‐Grignard reagents was performed in good yields under mild conditions by using a new catalytic system: consisting of cobalt chloride and tetramethylethylenediamine (CoCl₂⋅2 LiI, 4 TMEDA). The reaction is very chemoselective since ketone, ester and nitrile functions are tolerated.     

Process algebra with guards: Combining Hoare logic with process algebra

We extend process algebra with guards, comparable to the guards in guarded commands or conditions in common programming constructs such as if — then — else — fi and while — do — od.The extended language is provided with an operational semantics based on transitions between pairs of a process and a (data-)state. The data-states are given by a data environment that also defines in which data-states guards hold and how atomic actions (non-deterministically) transform these states. The operational semantics is studied modulo strong bisimulation equivalence. For basic process algebra (without operators for parallelism) we present a small axiom system that is complete with respect to a general class of data environments. Given a particular data environmentL we add three axioms to this system, which is then again complete, provided weakest preconditions are expressible andL is sufficiently deterministic.Then we study process algebra with parallelism and guards. A two phase-calculus is provided that makes it possible to prove identities between parallel processes. Also this calculus is complete. In the last section we show that partial correctness formulas can easily be expressed in this setting. We use process algebra with guards to prove the soundness of a Hoare logic for linear processes by translating proofs in Hoare logic into proofs in process algebra.Supported by ESPRIT Basic Research Action no. 3006 (CONCUR) and by RACE project no. 1046 (SPECS).Supported by RACE project no. 1046 (SPECS).     

Computation of bases of free modules over the Weyl algebras

A well-known result due to J.T. Stafford asserts that a stably free left module M over the Weyl algebras D=A_n(k) or B_n(k)–where k is a field of characteristic 0–with is free. The purpose of this paper is to present a new constructive proof of this result as well as an effective algorithm for the computation of bases of M. This algorithm, based on the new constructive proofs [Hillebrand, A., Schmale, W., 2001. Towards an effective version of a theorem of Stafford. J. Symbolic Comput. 32, 699–716; Leykin, A., 2004. Algorithmic proofs of two theorems of Stafford. J. Symbolic Comput. 38, 1535–1550] of J.T. Stafford’s result on the number of generators of left ideals of D, performs Gaussian elimination on the formal adjoint of the presentation matrix of M. We show that J.T. Stafford’s result is a particular case of a more general one asserting that a stably free left D-module M with is free, where denotes the stable rank of a ring D. This result is constructive if the stability of unimodular vectors with entries in D can be tested. Finally, an algorithm which computes the left projective dimension of a general left D-module M defined by means of a finite free resolution is presented. It allows us to check whether or not the left D-module M is stably free.     

Salmonella surveillance and control for finisher pigs and pork in Denmark — A case study

Salmonella can either be controlled pre-harvest, post-harvest or by a combination of both approaches. This paper describes the lessons learned in Danish Salmonella surveillance and control programme for finisher pigs and pork. Initially, main focus was on pre-harvest initiatives and correct identification of herds with respect to the risk for Salmonella that they represented. However, an analysis of risk-mitigating actions applied along the chain from stable to table showed that it would be more cost-effective to deal with Salmonella on the abattoirs than in the herds. This knowledge moved focus from pre- to post-harvest without giving up on pre-harvest surveillance. First of all, this meant increased attention on slaughter hygiene and individual interventions in the abattoirs. In brief, we learned that for a programme to be successful it must be based on standardised methods for sampling and testing to be able to evaluate and compare performance of the programme. More specifically, meat-juice samples taken from finisher pigs at the time of slaughter are an effective way of identifying high-risk herds for Salmonella. In addition, a penalty system might act as an incentive for farmers to deal with Salmonella in their herd. Additionally, common targets for all abattoirs allowing for unique control solutions should be adapted. Finally, decontamination techniques like hot water decontamination are a feasible way of dealing with high-risk pigs (Level-3 pigs). The current prevalence in Danish pork is around 1.2%, and a target is set to < 1.0% to be reached by the end of 2013. The experience obtained by use of the Danish programme might be used to develop and implement appropriate types of surveillance programs as well as risk-mitigating measures in other countries.     

Long Range Detection of Defects in Composite Plates Using Lamb Waves Generated and Detected by Ultrasonic Phased Array Probes

This article presents a technique for the generation and detection of Lamb waves guided along large plate-like structures made from various types of materials (metal, polymer, fibre-reinforced composite, etc.). A multi-element matrix ultrasonic probe is driven using the well-known phased array principle, for launching and detecting pure Lamb modes in/from specific directions along the plate, which are arbitrary for isotropic materials and limited to specific directions for anisotropic materials, e.g. principal directions or directions for which both phase and group velocities are collinear. The probe is gel-coupled to the tested specimen and allows quick inspection of large area from its fixed position, even of zones with limited access. The technique, which takes into account the frequency dispersive effects, is different than SHM-like (Structural Health Monitoring) inspection, since all transmitting or receiving elements are grouped together in a localized area defined by the active surface of the probe, and not permanently attached to the tested structure. The use of a multi-element probe, for long range Lamb waves-based inspection, is also distinctive from that usually performed, which consists of very local inspection of a material by steering the ultrasonic beam below and nearby the probe. A prototype is presented, as well as measurements of its performances in terms of modal selectivity and directivity. Finally the detection and localisation of a through-thickness hole in a large aluminium plate, of a delamination-like defect in a carbon epoxy composite plate and of an impact damage on a stiffened composite curved plate are shown.     

Socially Meaningful Vocal Plasticity in Adult Campbell's Monkeys (Cercopithecus campbelli).

Campbell's monkeys (Cercopithecus campbelli) frequently exchange vocalizations, the combined-harmonic calls, with individuals responding to one another's calls. Previous work has shown that these calls can be grouped into several structural variants. Adult females differ in their variant repertoires, which may change during their adult life, particularly after changes in the group composition. Playback of females' currently produced variants triggered vocal responses from other group members, whereas the same females' former, no longer used variants and those of stranger females never did. In contrast, former variants caused long-term cessation of vocal behavior, whereas stranger variants had no effect. Data showed that monkeys were able to distinguish between the different types of variants, indicating that these calls form part of a long-term social memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)