nucleotides of arbitrary size, complexity and conformational fl exibility in physiological buffers, albeit adsorbed on a fl at substrate. [ 7 ] In some cases, it yielded suffi cient resolution to resolve the helical repeat of B-DNA, [ 7b , 8 ] and recent advances in AFM technology have resulted in the visualization of both strands of the DNA double helix. [ 9 ] To reproducibly visualize oligonucleotide secondary structure, we here minimize the invasiveness of the AFM measurements using both rapid force-distance (PeakForce Tapping) [ 6b ] and amplitude-modulation (tapping) [ 7b ] imaging modes (see the Experimental Section), and apply novel image analysis procedures to extract structural parameters.DNA helical structure can readily be observed in our AFM images as a double-banded corrugation along the molecule ( Figure 1 a), here demonstrated for a supercoiled plasmid of about 1.2 µm length (3486 base pairs) adsorbed on mica in the presence of Ni 2+ ions (see Experimental Section and Supporting Information Figure 1). We fi nd that both the measured corrugation and the overall height of the plasmids critically depend on the force that the AFM tip applies to the sample. This is quantifi ed by force-distance imaging, where continuous and rapid acquisition of force-distance curves facilitates an estimation of the peak forces during the imaging process (Figure 1 b-f). At minimum peak forces, the measured height of the DNA (1.9 ± 0.2 nm) agrees with the diameter of the molecule as estimated from the B-DNA crystal structure (2.0 ± 0.1 nm; RCSB protein data bank, 1BNA). [ 10 ] On increasing the peak force to ≈50 pN, the corrugation becomes marginally clearer, at the expense of few-Ångström vertical compression of the plasmid. At about 70 pN and 20% compression of the molecule, the corrugation is most visible. Beyond 100 pN, the major and minor grooves become less clear and the measured heights reduce to <1.5 nm, similar to most earlier AFM experiments in liquid. [ 7b , 8b ] We typically observe damage to or dislocation of the plasmids on imaging at peak forces exceeding ≈200 pN. For peak forces up to ≈200 pN, the plasmid can be repeatedly compressed and then imaged again at its uncompressed height (Supporting Information Figure 2). The compression of the plasmid is also apparent from its narrower appearance (Figure 1 b-d) and dislocation of a plasmid loop (see white arrow in Figure 1 d) at higher forces. These results demonstrate that the oligonucleotide diameter can be accurately measured as a molecular height by AFM for low tip-sample forces. [ 9 ] For a comparison of the AFM images with the B-DNA crystal structure, we digitally straightened the measured surface topography of a DNA segment, using a coordinate
A hollow bottle-like microresonator (BLMR) with ultra-high quality factor is fabricated from a microcapillary with nearly parabolic profile. At 1.55 µm pumping, degenerate four-wave mixing can be observed for a BLMR of diameter 102 µm. The parabolic profile of the BLMR guarantees a nearly zero waveguide dispersion, which is theoretically discussed in detail. From the simulation, at 1.55 µm wavelength in such a BLMR, the fundamental bottle mode is in the anomalous dispersion regime, whilst the ordinary whispering gallery mode (WGM) confined at the center of the BLMR is in the normal dispersion regime. Experimentally, no degenerate FWM is observed for the WGM selected by positioning the coupling tapered fiber in the same BLMR. Furthermore, dispersion tuning is briefly discussed. As the work predicted, the BLMR shows promise for the implementation of sparsely distributed, widely spanned frequency combs at the telecommunication wavelength.
Internet-based research is increasingly important for conservation science and has wideranging applications and contexts, including culturomics, illegal wildlife trade, and citizen science. However, online research methods pose a range of ethical and legal challenges. Online data may be protected by copyright, database rights, or contract law. Privacy rights may also restrict the use and access of data, as well as ethical requirements from institutions. Online data have real-world meaning, and the ethical treatment of individuals and communities must not be marginalized when conducting internet-based research. As ethics frameworks originally developed for biomedical applications are inadequate for these methods, we propose that research activities involving the analysis of preexisting online data be treated analogous to offline social science methods, in particular, nondeceptive covert observation. By treating internet users and their data with respect and due consideration, conservationists can uphold the public trust needed to effectively address real-world issues. KEYWORDS compliance, copyright, cyberethics, data protection, integrity, intellectual property, internet mediated, privacy PALABRAS CLAVE cibernética, cumplimiento, derechos de autor, integridad, mediado por internet, privacidad, propiedad intelectual, protección de datosThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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