Microlensing of the broad-line region in the quadruply imaged quasar HE0435-1223

Using infrared spectra of the z = 1.693 quadruply lensed quasar HE0435-1223 acquired in 2009 with the spectrograph SINFONI at the ESO Very Large Telescope, we have detected a clear microlensing effect in images A and D. While microlensing affects the blue and red wings of the H{\alpha} line profile in image D very differently, it de-magnifies the line core in image A. The combination of these different effects sets constraints on the line-emitting region; these constraints suggest that a rotating ring is at the origin of the H{\alpha} line. Visible spectra obtained in 2004 and 2012 indicate that the MgII line profile is microlensed in the same way as the H{\alpha} line. Our results therefore favour flattened geometries for the low-ionization line-emitting region, for example, a Keplerian disk. Biconical models cannot be ruled out but require more fine-tuning. Flux ratios between the different images are also derived and confirm flux anomalies with respect to estimates from lens models with smooth mass distributions.Comment: 6 pages, 4 figures, 3 tables, accepted by A&A on 10 April 201

Micromagnetism in (001) magnetite by spin-polarized low-energy electron microscopy

Spin-polarized low-energy electron microscopy was used to image a magnetite crystal with (100) surface orientation. Sets of spin-dependent images of magnetic domain patterns observed in this surface were used to map the direction of the magnetization vector with high spatial and angular resolution. We find that domains are magnetized along the surface [110] directions, and domain wall structures include 90{\deg} and 180{\deg} walls. A type of unusually curved domain walls are interpreted as N\'eel-capped surface terminations of 180{\deg} Bloch walls.Comment: 17 pages, 4 figures. Presented at the LEEM-PEEM 8 conferenc

Light-addressable liquid crystal polymer dispersed liquid crystal

Scattering-free liquid crystal polymer-dispersed liquid crystal polymer (LCPDLC) films are fabricated by combining a room temperature polymerizable liquid crystal (LC) monomer with a mesogenic photosensitive LC. The morphological and photosensitive properties of the system are analysed with polarized optical microscopy and high resolution scanning and transmission electron microscopy. A two-phase morphology comprised of oriented fibril-like polymeric structures interwoven with nanoscale domains of phase separated LC exists. The nanoscale of the structures enables an absence of scattering which allows imaging through the LCPDLC sample without optical distortion. The use of a mesogenic monomer enables much smaller phase separated domains as compared to nonmesogenic systems. All-optical experiments show that the transmitted intensity, measured through parallel polarizers, can be modulated by the low power density radiation (31 mW/cm2) of a suitable wavelength (532 nm). The reversible and repeatable transmission change is due to the photoinduced trans-cis photoisomerization process. The birefringence variation (0.01) obtained by optically pumping the LCPDLC films allow their use as an alloptical phase modulato

Optically probing symmetry breaking in the chiral magnet Cu2OSeO3

We report on the linear optical properties of the chiral magnet Cu2OSeO3, specifically associated with the absence of inversion symmetry, the chiral crystallographic structure, and magnetic order. Through spectroscopic ellipsometry, we observe local crystal-field excitations below the charge-transfer gap. These crystal-field excitations are optically allowed due to the lack of inversion symmetry at the Cu sites. Optical polarization rotation measurements were used to study the structural chirality and magnetic order. The temperature dependence of the natural optical rotation, originating in the chiral crystal structure, provides evidence for a finite magneto-electric effect in the helimagnetic phase. We find a large magneto-optical susceptibility on the order of V(540nm)~10^4 rad/(T*m) in the helimagnetic phase and a maximum Faraday rotation of ~165deg/mm in the ferrimagnetic phase. The large value of V can be explained by considering spin cluster formation and the relative ease of domain reorientation in this metamagnetic material. The magneto-optical activity allows us to map the magnetic phase diagram, including the skyrmion lattice phase. In addition to this, we probe and discuss the nature of the various magnetic phase transitions in Cu2OSeO3.Comment: 9 pages, 10 figure

Antimicrobial susceptibility of environmental Staphylococcus aureus strains isolated from a pigeon slaughterhouse in Italy

Abstract No information is available concerning the antimicrobial susceptibility of Staphylococcus aureus isolated from pigeon slaughterhouses. In the present study, 59 staphylococcal strains isolated from a pigeon slaughterhouse in central Italy were compared according to their antibiotic resistance. On the basis of cultural and biochemical properties, all isolates could be identified as S. aureus. The strains were checked for the productions of enterotoxins A, B, C, D by reversed passive latex agglutination. Resistance to 26 antibiotics was also determined paying particular attention to resistance to those antimicrobial agents frequently used in human medicine and in poultry breeding. Only one strain was positive for the production of enterotoxins type C and D. It was isolated from the evisceration tube after slaughtering. Enterotoxin B was produced by 2 strains isolated from the eyebrows and conjunctivas of the worker operating the crop rinsing tube. As to the susceptibility to antibiotics, all strains were sensitive to amoxicillin/clavulanic acid, bacitracin, cephalothin, fusidic acid, gentamicin, kanamycin, linezolid, oxacillin, quinupristin/dalfopristin, rifampicin, tobramycin, trimethoprim-sulfamethoxazole, vancomycin. Some (15.2%) of the strains were resistant to ampicillin and to penicillin G; 6.8% were resistant to chloramphenicol, 20.3% to enrofloxacin, 16.9% to erythromycin and to ciprofloxacin, 8.5% to clindamycin, and 11.9% to lincomycin. The highest percentages of strains were resistant to tetracycline and oleandomicin (37.3 and 25.4% respectively). Methicillin-resistant staphylococci were also found (3.4%). Only one strain had a multiple antibiotic resistance index > 0.30. The results were statistically analyzed and clustered in 6 groups. This work provides the antibiotic resistance pattern of S. aureus strains isolated from a pigeon slaughtering plant and represents a study on a quite unknown field in meat production

Reality conditions for Ashtekar variables as Dirac constraints

We show that the reality conditions to be imposed on Ashtekar variables to recover real gravity can be implemented as second class constraints a la Dirac. Thus, counting gravitational degrees of freedom follows accordingly. Some constraints of the real theory turn out to be non-polynomial, regardless of the form, polynomial or non-polynomial, taken for the reality conditions. We comment upon the compatibility of our approach with the recently proposed Wick transform point of view, as well as on some alternatives for dealing with such second class constraints.Comment: 16 pages, plain LaTeX, submitted to Class. Quant. Grav. E-mail: [email protected]

Semantic-based policy engineering for autonomic systems

This paper presents some important directions in the use of ontology-based semantics in achieving the vision of Autonomic Communications. We examine the requirements of Autonomic Communication with a focus on the demanding needs of ubiquitous computing environments, with an emphasis on the requirements shared with Autonomic Computing. We observe that ontologies provide a strong mechanism for addressing the heterogeneity in user task requirements, managed resources, services and context. We then present two complimentary approaches that exploit ontology-based knowledge in support of autonomic communications: service-oriented models for policy engineering and dynamic semantic queries using content-based networks. The paper concludes with a discussion of the major research challenges such approaches raise

Feature selection for chemical sensor arrays using mutual information

We address the problem of feature selection for classifying a diverse set of chemicals using an array of metal oxide sensors. Our aim is to evaluate a filter approach to feature selection with reference to previous work, which used a wrapper approach on the same data set, and established best features and upper bounds on classification performance. We selected feature sets that exhibit the maximal mutual information with the identity of the chemicals. The selected features closely match those found to perform well in the previous study using a wrapper approach to conduct an exhaustive search of all permitted feature combinations. By comparing the classification performance of support vector machines (using features selected by mutual information) with the performance observed in the previous study, we found that while our approach does not always give the maximum possible classification performance, it always selects features that achieve classification performance approaching the optimum obtained by exhaustive search. We performed further classification using the selected feature set with some common classifiers and found that, for the selected features, Bayesian Networks gave the best performance. Finally, we compared the observed classification performances with the performance of classifiers using randomly selected features. We found that the selected features consistently outperformed randomly selected features for all tested classifiers. The mutual information filter approach is therefore a computationally efficient method for selecting near optimal features for chemical sensor arrays

Topological field theories in n-dimensional spacetimes and Cartan's equations

Action principles of the BF type for diffeomorphism invariant topological field theories living in n-dimensional spacetime manifolds are presented. Their construction is inspired by Cuesta and Montesinos' recent paper where Cartan's first and second structure equations together with first and second Bianchi identities are treated as the equations of motion for a field theory. In opposition to that paper, the current approach involves also auxiliary fields and holds for arbitrary n-dimensional spacetimes. Dirac's canonical analysis for the actions is detailedly carried out in the generic case and it is shown that these action principles define topological field theories, as mentioned. The current formalism is a generic framework to construct geometric theories with local degrees of freedom by introducing additional constraints on the various fields involved that destroy the topological character of the original theory. The latter idea is implemented in two-dimensional spacetimes where gravity coupled to matter fields is constructed out, which has indeed local excitations.Comment: LaTeX file, no figure