12,493 research outputs found
Kerr-microresonator solitons from a chirped background
No full textWe demonstrate protected single-soliton formation and operation in a Kerr microresonator using a phase-modulated pump laser. Phase modulation gives rise to spatially varying effective loss and detuning parameters, which in turn lead to an operation regime in which multi-soliton degeneracy is lifted and a single soliton is the only observable behavior. Direct excitation of single solitons is indicated by observed reversal of the characteristic 'soliton step.' Phase modulation also enables precise control of the soliton pulse train's properties, and measured dynamics agree closely with simulations. We show that the technique can be extended to high repetition-frequency Kerr solitons through subharmonic phase modulation. These results facilitate straightforward generation and control of Kerr-soliton microcombs for integrated photonics systems
Magneto–Optical Kerr Effect Microscopy Investigation on Permalloy Nanostructures
No full textThis thesis focuses on the investigation of magnetic domains in ultrasmall permalloy (Ni80Fe20) structures down to nanometre size. Magnetic domains and domain walls in nano objects are often observed using a very high resolution and high power microscope such as magnetic soft x-ray microscope, magnetic force microscopy imaging and photoemission electron microscopy. A reason for this is because the Kerr signal in nanostructures is very weak. However the results from this thesis demonstrate that magnetic domains in permalloy magnetic nanostructures can still be observed with very good contrast using a Magneto-optical Kerr effect (MOKE) microscope. The constructed Kerr microscope is a home-build wide field microscope and is able to produce magnetic domains image of permalloy nanowire as small as 245 nm, although the resolution limit of the microscope is 505 nm. For the first time, a magnetic domain in nanowire with width of 245 nm is observed using a wide-field microscope. The combination of hysteresis loops and magnetic domains observations for studying a magnetic sample provides a three-dimensional understanding of the magnetic characteristic of the sample. This is crucial in investigating nano samples as the theoretical arguments with the experimental results are always constrained by the experimental part. Three kinds of nanostructure sample were observed using the Kerr microscope; a cross nanowire, zigzag nanowire and a nanowire with notch and a nucleation pad at one end. It was found that a cross nanowire can form magnetic domains upon reversal and the junction forms a magnetisation vortex. Findings from zigzag nanowire demonstrate a complex, multiple magnetic domains formation upon magnetisation reversal. A weak domain wall pinning effect was observed in the nanowire, causing a multiple domains formation in the nanowire upon reversal. It can be confirmed that this effect was caused by the high coercivity of the nucleation pad. For the nanowire with notch, it was demonstrated that the coercivities were different at negative and positive field. But for such case, there is a relationship observed between the percentage notch depth and the coercivity at the junction
Letters between J. C. Hogenson and W. J. Kerr
No full textLetters concerning a position at Utah Agricultural College
Callichimaeridae Luque & Feldmann & Vernygora & Schweitzer & Cameron & Kerr & Vega & Duque & Strange & Palmer & Jaramillo 2019, fam. nov.
No full textCallichimaeridae fam. nov. LSID. urn:lsid:zoobank.org:act: A5D6688D-756B-4FB7-8098- 5EB066C38383 Included genus. Callichimaera gen. nov. Diagnosis. As for type genus and species.Published as part of Luque, J., Feldmann, R. M., Vernygora, O., Schweitzer, C. E., Cameron, C. B., Kerr, K. A., Vega, F. J., Duque, A., Strange, M., Palmer, A. R. & Jaramillo, C., 2019, Exceptional preservation of mid-Cretaceous marine arthropods and the evolution of novel forms via heterochrony, pp. 1-15 in Science Advances 5 (4) on page 3, DOI: 10.1126/sciadv.aav3875, http://zenodo.org/record/590278
Scalar QNM spectra of Kerr and Reissner-Nordström revealed by eigenvalue repulsions in Kerr-Newman
No full textRecent studies of the gravito-electromagnetic frequency spectra of Kerr-Newman (KN) black holes have revealed two families of quasinormal modes (QNMs), namely photon sphere modes and near-horizon modes. However, they can only be unambiguously distinguished in the Reissner-Nordström (RN) limit, due to a phenomenon called eigenvalue repulsion (also known as level repulsion, avoided crossing or the Wigner-Teller effect), whereby the two families can interact strongly near extremality. We find that these features are also present in the QNM spectra of a scalar field in KN, where the perturbation modes are described by ODEs and thus easier to explore. Starting from the RN limit, we study how the scalar QNM spectra of KN dramatically changes as we vary the ratio of charge to angular momentum, all the way until the Kerr limit, while staying at a fixed distance from extremality. This scalar field case clarifies the (so far puzzling) relationship between the QNM spectra of RN and Kerr black holes and the nature of the eigenvalue repulsions in KN, that ultimately settle the fate of the QNM spectra in Kerr. We study not just the slowest-decaying QNMs (both for ℓ=m=0 and ℓ=m=2), but several sub-dominant overtones as well, as these turn out to play a crucial role understanding the KN QNM spectra. We also give a new high-order WKB expansion of KN QNMs that typically describes the photon sphere modes beyond the eikonal limit, and use a matched asymptotic expansion to get a very good approximation of the near-horizon modes near extremality
Isolation of steroidal glycosides from the Caribbean SpongePandaros acanthifolium
No full textFour new steroidal glycosides, acanthifoliosides G-J (1-4), were isolated as minor constituents from the Caribbean marine sponge Pandaros acanthifolium. These metabolites are characterized by a highly oxygenated D ring and the presence of a disaccharide rhamnose-glucose residue and a rhamnose at positions C-3 and C-15, respectively. Their structures were established on the basis of extensive interpretation of 1D and 2D NMR data and HRESIMS analyses. The absolute configurations of the glucose and rhamnose sugars were determined by preparing aldose o-tolylthiocarbamate derivatives and comparison to authentic standards by LC/HRESIMS. Acanthifolioside G (1) exhibited antioxidant and cytoprotective activities
Payment to healthcare professionals for patient recruitment to trials: systematic review and qualitative study
No full textAim/Principal Research Question:The systematic review had three aims:• to synthesise the evidence on the effectiveness of offering monetary incentives to healthcare professionals to recruit patients to clinical trials; • to provide an overview of the ethical issues as debated in the published literature; • to identify current UK guidelines on financial incentives to healthcare professionals to recruit patients to trials.The primary research aimed to: • to identify the attitudes, beliefs and behaviour of healthcare professionals and consumers in relation to financial incentives for recruitment to trials;• to explore how financial incentives are viewed in relation to other barriers and facilitators to healthcare professionals recruiting patients to clinical trials?• to provide an overview of the current UK practice regarding the payment of financial incentives to healthcare professionals for recruitment of patients to trials.Methods:Electronic databases including the Cochrane Library, Medline, Embase, CINAHL, PsycINFO, Science Citation Index/Social Science Citation Index, Current Controlled Trials and the National Research Register were searched from inception to June 2006 for published English language studies of any payment or reimbursement to any healthcare professional recruiting patients to trials with reported recruitment rates. Bibliographies and grey literature were also searched. Inclusion criteria, data extraction and quality assessment were undertaken independently by two investigators using standard systematic review methodology. Quality assessment used the DuRant tool. Synthesis was by narrative review with full tabulation of results from all included studies. The qualitative investigation involved semi-structured interviews with purposive samples of healthcare professionals and healthcare consumers. Sampling of individuals for interview was from the National Research Register, National Coordinating Centre for Health Technology Assessment and through ‘snowballing’. Interviews were transcribed verbatim and entered into NVivo software for analysis and management. A hierarchical coding system was devised centred around themes of ‘motivation’ and ‘incentives’ for healthcare professionals, and ‘patient experiences’ and ‘incentives’ for consumers. Data is presented as representative quotations. Sample groups:Healthcare professionals and consumers, and research managers from pharmaceutical companies. Outcome measures:The primary outcome measure of the systematic review was level of patient recruitment. Secondary outcomes included other measurements of recruitment such as achievement of sample size, proportion of patients with full follow-up, qualitative measures of professional attitudes and of effects on participants. Motivating and facilitating factors and barriers to participating in research for healthcare professionals were the outcomes of the qualitative study, along with attitudes of consumers and industry research managers to incentives. Findings:Three cross-sectional surveys were identified which met the inclusion criteria. These considered recruitment rates and the attitudes and characteristics of clinicians in relation to some financial incentive or reimbursement. One primary care study reported that successful patient recruitment is determined more by motivation driven by the research group than by financial incentives, the research topic or research experience. The other primary care study concluded that patient recruitment by GPs may be aided by the use of a range of strategies including financial reimbursement, which might be enhanced by closer collaboration between GPs and researchers.The hospital based study found that reimbursement to the participating clinics was of only minor importance for both participation in trials and for recruiting patients. The scientific aims of the study were considered to be the most important factor with ethical considerations and communication between participants and researchers also of importance.In existing UK guidelines, the issues around payments to clinicians or patients are implied rather than stated, usually linked to discussion of conflict of interest and disclosure of any such conflicts. Interviews with NHS health professionals, mainly research active clinicians, indicated concerns over the likely effects of payment. While reimbursement of expenses incurred to do research was strongly supported, payment to incentivise recruitment was not. Direct payment to clinicians linked to recruitment or to research involvement was rare in publicly funded trials. A code of practice for any such payments was suggested, closely linked to the principles of Good Clinical Practice in research. Other factors such as interest in the topic, scope for patient benefit and good communication were considered more important motivations for research involvement. Interviews with the public indicated low levels of awareness of payments to clinicians linked to patient involvement in trials, and unanimous support for full disclosure of any such payments. Interviews with research managers in the pharmaceutical industry showed greater familiarity with payments for research involvement, which had in recent years shifted to payment to institutions rather than individual clinicians. GPs were the only group to whom scope existed for individual payments. Concerns were expressed by the pharmaceutical company interviewees at the rising cost of research and unnecessary bureaucracy. Conclusions:The available evidence on the effectiveness of payment to healthcare professionals for patient recruitment to trials is very limited in quality and quantity and is inconclusive. The ethical stance outlined in Good Clinical Practice in research, despite lack of scientific support, was widely endorsed. These preclude payment to patients and allow reasonable payments to clinicians, subject to disclosure of any possible conflicts of interest. Within these principles, considerable scope exists for compiling data on the factors that help and hinder the progress of clinical trials and also for experimenting with different incentives to encourage involvement in clinical research.Implications for further research:The authors recommend research on:1. Improved reporting of those organisational aspects of trials that are known to affect recruitment, including the type and extent of payments.2. Retrospective analysis of the factors associated with different levels of recruitment to RCTs, including payment of expenses to patients.3. Prospective comparative research on trial recruitment including between commercial and publicly funded trials within the NHS research networks and also between the roles of investigators and collaborators.4. Qualitative research on participants’ experiences of being involved in different kinds of trials, and also to do with the appropriateness the guidelines on payment for participation.5. Consideration by funders of clinical trails of proposals to include within trials experiments with payments methods, comparing different levels of disclosure and of payment
Comment on “Greybody radiation and quasinormal modes of Kerr-like black hole in Bumblebee gravity model”
No full textIt is shown that the paper “Greybody radiation and quasinormal modes of Kerr-like black hole in Bumblebee gravity model” (Kanzi and Sakallı in Eur Phys J C 81:501, 2021) recently published in this journal is based on an incorrect result obtained by Ding et al. (Eur Phys J C 80:178, 2020) for a Kerr-like black hole solution
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