Surface acoustic waves for acousto-optic modulation in buried silicon nitride waveguides

We theoretically investigate the use of Rayleigh surface acoustic waves (SAWs) for refractive index modulation in optical waveguides consisting of amorphous dielectrics. Considering low-loss Si$_3$N$_4$ waveguides with a standard core cross section of 4.4$\times$0.03 $\mu$m$^2$ size, buried 8 $\mu$m deep in a SiO$_2$ cladding we compare surface acoustic wave generation in various different geometries via a piezo-active, lead zirconate titanate film placed on top of the surface and driven via an interdigitized transducer (IDT). Using numerical solutions of the acoustic and optical wave equations, we determine the strain distribution of the SAW under resonant excitation. From the overlap of the acoustic strain field with the optical mode field we calculate and maximize the attainable amplitude of index modulation in the waveguide. For the example of a near-infrared wavelength of 840 nm, a maximum shift in relative effective refractive index of 0.7x10$^{-3}$ was obtained for TE polarized light, using an IDT period of 30 - 35 $\mu$m, a film thickness of 2.5 - 3.5 $\mu$m, and an IDT voltage of 10 V. For these parameters, the resonant frequency is in the range 70 - 85 MHz. The maximum shift increases to 1.2x10$^{-3}$, with a corresponding resonant frequency of 87 MHz, when the height of the cladding above the core is reduced to 3 $\mu$m. The relative index change is about 300-times higher than in previous work based on non-resonant proximity piezo-actuation, and the modulation frequency is about 200-times higher. Exploiting the maximum relative index change of 1.2$\times$10$^{-3}$ in a low-loss balanced Mach-Zehnder modulator should allow full-contrast modulation in devices as short as 120 $\mu$m (half-wave voltage length product = 0.24 Vcm).Comment: 19 pages, 8 figure

A conduction-cooled, 680-mm-long warm bore, 3-T Nb3Sn solenoid for a Cerenkov free electron laser

A compact, cryocooler cooled Nb3Sn superconducting magnet system for a Cerenkov free electron laser has been designed, fabricated and tested. The magnet is positioned directly behind the electron gun of the laser system. The solenoidal field compresses and guides a tube-shaped 100 A, 500 kV electron beam. A two-stage GM cryocooler, equipped with a first generation ErNi5 regenerator, cools the epoxy impregnated solenoid down to the operating temperature of about 7.5 K. This leaves a conservative operational margin for the MJR type of Nb3Sn conductor of about 350% (I c) at 3T. Current leads with HTS sections between the first and second stage of the cryocooler effectively reduce the conductive heat leak. In the warm bore, 60 mm in diameter and 680 mm long, an operational magnetic field of 2 T has been achieved during laser operation without any quench. The field homogeneity is better than 99.5% over 450 mm axial length. Design details and test results of this magnet system are presented

Controlled Nanoparticle Formation by Diffusion Limited Coalescence

Polymeric nanoparticles (NPs) have a great application potential in science and technology. Their functionality strongly depends on their size. We present a theory for the size of NPs formed by precipitation of polymers into a bad solvent in the presence of a stabilizing surfactant. The analytical theory is based upon diffusion-limited coalescence kinetics of the polymers. Two relevant time scales, a mixing and a coalescence time, are identified and their ratio is shown to determine the final NP diameter. The size is found to scale in a universal manner and is predominantly sensitive to the mixing time and the polymer concentration if the surfactant concentration is sufficiently high. The model predictions are in good agreement with experimental data. Hence the theory provides a solid framework for tailoring nanoparticles with a priori determined size.Comment: 4 pages, 3 figure

One-dimensional conduction in Charge-Density Wave nanowires

We report a systematic study of the transport properties of coupled one-dimensional metallic chains as a function of the number of parallel chains. When the number of parallel chains is less than 2000, the transport properties show power-law behavior on temperature and voltage, characteristic for one-dimensional systems.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let

Robust zero-energy modes in an electronic higher-order topological insulator: the dimerized Kagome lattice

Quantum simulators are an essential tool for understanding complex quantum materials. Platforms based on ultracold atoms in optical lattices and photonic devices led the field so far, but electronic quantum simulators are proving to be equally relevant. Simulating topological states of matter is one of the holy grails in the field. Here, we experimentally realize a higher-order electronic topological insulator (HOTI). Specifically, we create a dimerized Kagome lattice by manipulating carbon-monoxide (CO) molecules on a Cu(111) surface using a scanning tunneling microscope (STM). We engineer alternating weak and strong bonds to show that a topological state emerges at the corner of the non-trivial configuration, while it is absent in the trivial one. Contrarily to conventional topological insulators (TIs), the topological state has two dimensions less than the bulk, denoting a HOTI. The corner mode is protected by a generalized chiral symmetry, which leads to a particular robustness against perturbations. Our versatile approach to quantum simulation with artificial lattices holds promises of revealing unexpected quantum phases of matter

Horizontal Transfer and Death of a Fungal Secondary Metabolic Gene Cluster

A cluster composed of four structural and two regulatory genes found in several species of the fungal genus Fusarium (class Sordariomycetes) is responsible for the production of the red pigment bikaverin. We discovered that the unrelated fungus Botrytis cinerea (class Leotiomycetes) contains a cluster of five genes that is highly similar in sequence and gene order to the Fusarium bikaverin cluster. Synteny conservation, nucleotide composition, and phylogenetic analyses of the cluster genes indicate that the B. cinerea cluster was acquired via horizontal transfer from a Fusarium donor. Upon or subsequent to the transfer, the B. cinerea gene cluster became inactivated; one of the four structural genes is missing, two others are pseudogenes, and the fourth structural gene shows an accelerated rate of nonsynonymous substitutions along the B. cinerea lineage, consistent with relaxation of selective constraints. Interestingly, the bik4 regulatory gene is still intact and presumably functional, whereas bik5, which is a pathway-specific regulator, also shows a mild but significant acceleration of evolutionary rate along the B. cinerea lineage. This selective preservation of the bik4 regulator suggests that its conservation is due to its likely involvement in other non–bikaverin-related biological processes in B. cinerea. Thus, in addition to novel metabolism, horizontal transfer of wholesale metabolic gene clusters might also be contributing novel regulation

Generation of three iPSC lines from two patients with heterozygous FOXF1 mutations associated to Alveolar Capillary Dysplasia with Misalignment of the Pulmonary Veins

Diagnosing Alveolar Capillary Dysplasia with Misalignment of the Pulmonary Veins (ACD/MPV) based on a genetic alteration in the FOXF1 gene, is complicated by the poor understanding of the causal relation between FOXF1 variants and the ACD/MPV phenotype. Here, we report the generation of human iPSC lines from two ACD/MPV patients, each carrying a different heterozygous FOXF1 mutation, which enables disease modeling for further research on the effect of FOXF1 variants in vitro. The iPSC lines were generated from skin fibroblasts using the non-integrating Sendai virus. The lines expressed pluripotency genes, retained the heterozygous mutation and were capable of trilineage differentiation

The Monitoring Efficacy of Neurogenic Bowel Dysfunction Treatment on Response (MENTOR) in a Non-Hospital Setting

BACKGROUND: Most patients with a spinal cord injury (SCI) suffer from neurogenic bowel dysfunction (NBD). In spite of well-established treatment algorithms, NBD is often insufficiently managed. The Monitoring Efficacy of Neurogenic bowel dysfunction Treatment On Response (MENTOR) has been validated in a hospital setting as a tool to support clinical decision making in individual patients. The objective of the present study was to describe clinical decisions recommended by the MENTOR (either "monitor", "discuss" or "act") and the use of the tool to monitor NBD in a non-hospital setting. METHODS: A questionnaire describing background data, the MENTOR, ability to work and participation in various social activities was sent by mail to all members of The Danish Paraplegic Association. RESULTS: Among 1316 members, 716 (54%) responded, 429 men (61%) and 278 women (39%), aged 18 to 92 (median 61) years. Based on MENTOR, the recommended clinical decision is to monitor treatment of NBD in 281 (44%), discuss change in treatment in 175 (27%) and act/change treatment in 181 (28%). A recommendation to discuss or change treatment was associated with increasing age of the respondent (p = 0.016) and with impaired ability to work or participate in social activities (p < 0.0001). CONCLUSION: A surprisingly high proportion of persons with SCI have an unmet need for improved bowel care. The MENTOR holds promise as a tool for evaluation of treatment of NBD in a non-hospital setting