Giant optical gain in a rare-earth-ion-doped waveguide amplifier

For optical amplification, typically rare-earth-ion (RE) doped fiber amplifiers (RDFA) or semiconductor optical amplifiers (SOAs) are selected. Despite the weak transition cross-sections of RE ions and their low doping level in silica fibers, resulting in very low gain per unit length, the extremely long interaction lengths realized in fibers can lead to significant overall gain. SOAs can deliver similarly high overall gain over much shorter distances, which makes them suitable for providing on-chip gain. Very high material gain in the nanometer-wide recombination region of a III-V semiconductor, but small overlap with the usually µm-sized signal beam results in a modal gain of several hundred dB/cm. In contrast, the gain per unit length in RE-doped integrated waveguides has hardly exceeded a few dB/cm. Here we demonstrate an ultra-high modal gain of 950 dB/cm in a RE-doped waveguide amplifier, comparable to the modal gain reported for SOAs. The potassium double tungstates KGd(WO4)2, KY(WO4)2, and KLu(WO4)2 are excellent host materials for RE-doped lasers, partly thanks to the high transition cross-sections of RE ions in these hosts. In 2006, the first planar KY(WO4)2:Yb3+ waveguide laser was demonstrated. Co-doping the layer with Gd3+ and Lu3+ ions offers the possibility for lattice matching with the undoped KY(WO4)2 substrate and a significantly enhanced refractive index contrast, hence improved mode confinement. Microstructuring by Ar+ beam etching resulted in channel waveguides, in which lasing with 418 mW output power at 1023 nm and 71% slope efficiency vs. launched pump power was demonstrated. Replacing Y3+ in the layer completely by Gd3+ and Yb3+ ions results in highly doped channel waveguides with a refractive-index contrast of >2 x 10-2. These novel dielectric micro-structures combine a high dopant concentration, large transition cross-sections, and strong light confinement, all features that are crucial for achieving high optical gain, in a single device. When pumping such a KGd0.447Lu0.078Yb0.475(WO4)2 channel waveguide with a 932-nm Ti:Sapphire laser via a microscope objective, high inversion of the Yb3+ system is obtained. Signal light at the zero-phonon line at 980.6 nm, which is the wavelength of highest absorption and emission cross-section, exhibits a small-signal modal gain of 950 dB/cm, exceeding the gain per unit length previously reported in RE-doped materials by two orders of magnitude, thus paving the way for applications of on-chip integrated RE-doped amplifiers

Discovery of Blue Hook Stars in the Massive Globular Cluster M54

We present BV photometry centered on the globular cluster M54 (NGC 6715). The color-magnitude diagram clearly shows a blue horizontal branch extending anomalously beyond the zero age horizontal branch theoretical models. These kinds of horizontal branch stars (also called ``blue hook'' stars), which go beyond the lower limit of the envelope mass of canonical horizontal branch hot stars, have so far been known to exist in only a few globular clusters: NGC 2808, Omega Centauri (NGC 5139), NGC 6273, and NGC 6388. Those clusters, like M54, are among the most luminous in our Galaxy, indicating a possible correlation between the existence of these types of horizontal branch stars and the total mass of the cluster. A gap in the observed horizontal branch of M54 around T(eff)= 27000 K could be interpreted within the late helium flash theoretical scenario, a possible explanation for the origin of those stars.Comment: 10 pages, 2 figures, accepted for publication in the Astrophysical Journa

Low emittance muon accelerator studies with production from positrons on target

A new scheme to produce very low emittance muon beams using a positron beam of about 45~GeV interacting on electrons on target is presented. One of the innovative topics to be investigated is the behaviour of the positron beam stored in a low emittance ring with a thin target, that is directly inserted in the ring chamber to produce muons. Muons can be immediately collected at the exit of the target and transported to two $\mu^+$ and $\mu^-$ accumulator rings and then accelerated and injected in muon collider rings. We focus in this paper on the simulation of the e$^+$ beam interacting with the target, the effect of the target on the 6-D phase space and the optimization of the e$^+$ ring design to maximize the energy acceptance. We will investigate the performance of this scheme, ring plus target system, comparing different multi-turn simulations. The source is considered for use in a multi-TeV collider in ref.[1]Comment: accepted for publication in Physical Review Accelerators and Beam

Isidella elongata (Cnidaria: Alcyonacea) facies in the western Mediterranean Sea: Visual surveys and descriptions of its ecological role

Isidella elongata is a candelabrum-shaped alcyonacean forming important facies on the bathyal muddy bottoms of the Mediterranean Sea, currently considered a sensitive habitat and heavily impacted by deep-sea fisheries. Until a few decades ago, this facies was a widespread habitat of the deep Mediterranean seabed and I. elongata was a common species in the trawling fishery's bycatch. Despite its current persistence in dense aggregations being very scarce, a dense facies of I. elongata was revealed during several ROV (Remotely Operated Vehicle) surveys carried out from 2010 to 2014 on the muddy bottoms between two seamounts east of Ibiza (Balearic Sea). The facies developed in an area between 480 and 615 m in depth where trawling is forbidden, with an extraordinary density of about 2300–2683 colonies/ha, representing one of the biggest facies of I. elongata currently known for the Mediterranean Sea considering the surface covered and the colonies' density. The associated community was surveyed, with 50 taxa identified. Moreover, a canyon southwest of Formentera characterised by the presence of I. elongata together with a high trawling impact was investigated. The density of the colonies was 53–62 colonies/ha and only 19 taxa of associated fauna were observed. The results of the two areas are compared and discussed in the framework of the protection of such an important habitat

Molecular mechanism of Gαi activation by non-GPCR proteins with a Gα-Binding and Activating motif

Heterotrimeric G proteins are quintessential signalling switches activated by nucleotide exchange on Gα. Although activation is predominantly carried out by G-protein-coupled receptors (GPCRs), non-receptor guanine-nucleotide exchange factors (GEFs) have emerged as critical signalling molecules and therapeutic targets. Here we characterize the molecular mechanism of G-protein activation by a family of non-receptor GEFs containing a Gα-binding and -activating (GBA) motif. We combine NMR spectroscopy, computational modelling and biochemistry to map changes in Gα caused by binding of GBA proteins with residue-level resolution. We find that the GBA motif binds to the SwitchII/α3 cleft of Gα and induces changes in the G-1/P-loop and G-2 boxes (involved in phosphate binding), but not in the G-4/G-5 boxes (guanine binding). Our findings reveal that G-protein-binding and activation mechanisms are fundamentally different between GBA proteins and GPCRs, and that GEF-mediated perturbation of nucleotide phosphate binding is sufficient for Gα activation

Topical application of acyclovir-loaded microparticles: quantification of the drug in porcine skin layers.

The goal of this work was to increase the amount of acyclovir (ACV) in the basal epidermis, site of Herpes virus simplex infections, using microparticles as carriers. Poly(d,l-lactic–co-glycolic acid) microparticles loaded with ACV were prepared using a solvent evaporation technique. ACV distribution into porcine skin after topical application of microparticles for 6, 24 and 88 h, was determined by horizontal slicing of the skin. An ACV suspension served for comparison. The results showed that, at 6 and 24 h, the quantity of the drug in the basal epidermis with the microparticles, is similar to that obtained with the ACV suspension. However, after 88 h, the ACV reservoir in the basal epidermis was higher with the microparticles compared with the control suspension. This could be explained by the controlled drug release produced by the vector in the basal epidermis. Besides, at 88 h the amount of ACV detected in the receptor chamber of the diffusion cells was much lower with the microparticles than with the suspension. This type of carrier can improve acyclovir topical therapy since it increases drug retention in the basal epidermis and consequently increases the time intervals between doses

Molecular Characteristics of Extraintestinal Pathogenic E. coli (ExPEC), Uropathogenic E. coli (UPEC), and Multidrug Resistant E. coli Isolated from Healthy Dogs in Spain. Whole Genome Sequencing of Canine ST372 Isolates and Comparison with Human Isolates Causing Extraintestinal Infections

Under a one health perspective and the worldwide antimicrobial resistance concern, we investigated extraintestinal pathogenic Escherichia coli (ExPEC), uropathogenic E. coli (UPEC), and multidrug resistant (MDR) E. coli from 197 isolates recovered from healthy dogs in Spain between 2013 and 2017. A total of 91 (46.2%) isolates were molecularly classified as ExPEC and/or UPEC, including 50 clones, among which (i) four clones were dominant (B2-CH14-180-ST127, B2-CH52-14-ST141, B2-CH103-9-ST372 and F-CH4-58-ST648) and (ii) 15 had been identified among isolates causing extraintestinal infections in Spanish and French humans in 2015 and 2016. A total of 28 (14.2%) isolates were classified as MDR, associated with B1, D, and E phylogroups, and included 24 clones, of which eight had also been identified among the human clinical isolates. We selected 23 ST372 strains, 21 from healthy dogs, and two from human clinical isolates for whole genome sequencing and built an SNP-tree with these 23 genomes and 174 genomes (128 from canine strains and 46 from human strains) obtained from public databases. These 197 genomes were segregated into six clusters. Cluster 1 comprised 74.6% of the strain genomes, mostly composed of canine strain genomes (p < 0.00001). Clusters 4 and 6 also included canine strain genomes, while clusters 2, 3, and 5 were significantly associated with human strain genomes. Finding several common clones and clone-related serotypes in dogs and humans suggests a potentially bidirectional clone transfer that argues for the one health perspective

High index contrast photonic platforms for on-chip Raman spectroscopy

Nanophotonic waveguide enhanced Raman spectroscopy (NWERS) is a sensing technique that uses a highly confined waveguide mode to excite and collect the Raman scattered signal from molecules in close vicinity of the waveguide. The most important parameters defining the figure of merit of an NWERS sensor include its ability to collect the Raman signal from an analyte, i.e. "the Raman conversion efficiency" and the amount of "Raman background" generated from the guiding material. Here, we compare different photonic integrated circuit (PIC) platforms capable of on-chip Raman sensing in terms of the aforementioned parameters. Among the four photonic platforms under study, tantalum oxide and silicon nitride waveguides exhibit high signal collection efficiency and low Raman background. In contrast, the performance of titania and alumina waveguides suffers from a strong Raman background and a weak signal collection efficiency, respectively