Propagation and nanofocusing of infrared surface plasmons on tapered transmission lines: Influence of the substrate

We study the propagation of mid-infrared surface plasmons on non-tapered and tapered two-wire transmission lines on Si and CaF 2 substrates, the two materials representing substrates with large and small refractive index, respectively. A comparative numerical study predicts a larger effective wavelength and an increased propagation length (i.e. weaker damping) for the CaF 2 substrate. By near-field microscopy we image the near-field distribution along the transmission lines and experimentally verify surface plasmon propagation. Amplitude- and phase-resolved near-field images of a non-tapered transmission line on CaF 2 reveal a standing wave pattern caused by back-reflection of the surface plasmons at the open-ended transmission line. Calculated and experimental near-field images of tapered transmission lines on Si and CaF 2 demonstrate that for both substrates the mid-IR surface plasmons are compressed when propagating along the taper. Importantly, the nanofocus at the taper apex yields a stronger local field enhancement for the low-refractive index substrate CaF 2. We assign the more efficient nanofocusing on CaF 2 to the weaker damping of the surface plasmons.Fil: Sarriugarte, P.. No especifíca;Fil: Schnell, M.. No especifíca;Fil: Alonso González, P.. No especifíca;Fil: Arzubiaga, L.. No especifíca;Fil: Golmar, Federico. Instituto Nacional de Tecnología Industrial; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Casanova, F.. No especifíca;Fil: Hueso, L. E.. No especifíca;Fil: Hillenbrand, R.. No especifíca

Experimental demonstration of the microscopic origin of circular dichroism in two-dimensional metamaterials

Optical activity and circular dichroism are fascinating physical phenomena originating from the interaction of light with chiral molecules or other nano objects lacking mirror symmetries in three-dimensional (3D) space. While chiral optical properties are weak in most of naturally occurring materials, they can be engineered and significantly enhanced in synthetic optical media known as chiral metamaterials, where the spatial symmetry of their building blocks is broken on a nanoscale. Although originally discovered in 3D structures, circular dichroism can also emerge in a two-dimensional (2D) metasurface. The origin of the resulting circular dichroism is rather subtle, and is related to non-radiative (Ohmic) dissipation of the constituent metamolecules. Because such dissipation occurs on a nanoscale, this effect has never been experimentally probed and visualized. Using a suite of recently developed nanoscale-measurement tools, we establish that the circular dichroism in a nanostructured metasurface occurs due to handedness-dependent Ohmic heatin

Global overview of the management of acute cholecystitis during the COVID-19 pandemic (CHOLECOVID study)

Background: This study provides a global overview of the management of patients with acute cholecystitis during the initial phase of the COVID-19 pandemic. Methods: CHOLECOVID is an international, multicentre, observational comparative study of patients admitted to hospital with acute cholecystitis during the COVID-19 pandemic. Data on management were collected for a 2-month study interval coincident with the WHO declaration of the SARS-CoV-2 pandemic and compared with an equivalent pre-pandemic time interval. Mediation analysis examined the influence of SARS-COV-2 infection on 30-day mortality. Results: This study collected data on 9783 patients with acute cholecystitis admitted to 247 hospitals across the world. The pandemic was associated with reduced availability of surgical workforce and operating facilities globally, a significant shift to worse severity of disease, and increased use of conservative management. There was a reduction (both absolute and proportionate) in the number of patients undergoing cholecystectomy from 3095 patients (56.2 per cent) pre-pandemic to 1998 patients (46.2 per cent) during the pandemic but there was no difference in 30-day all-cause mortality after cholecystectomy comparing the pre-pandemic interval with the pandemic (13 patients (0.4 per cent) pre-pandemic to 13 patients (0.6 per cent) pandemic; P = 0.355). In mediation analysis, an admission with acute cholecystitis during the pandemic was associated with a non-significant increased risk of death (OR 1.29, 95 per cent c.i. 0.93 to 1.79, P = 0.121). Conclusion: CHOLECOVID provides a unique overview of the treatment of patients with cholecystitis across the globe during the first months of the SARS-CoV-2 pandemic. The study highlights the need for system resilience in retention of elective surgical activity. Cholecystectomy was associated with a low risk of mortality and deferral of treatment results in an increase in avoidable morbidity that represents the non-COVID cost of this pandemic

Real-space mapping of Fano interference in plasmonic metamolecules

An unprecedented control of the spectral response of plasmonic nanoantennas has recently been achieved by designing structures that exhibit Fano resonances. This new insight is paving the way for a variety of applications, such as biochemical sensing and surface-enhanced Raman spectroscopy. Here we use scattering-type near-field optical microscopy to map the spatial field distribution of Fano modes in infrared plasmonic systems. We observe in real space the interference of narrow (dark) and broad (bright) plasmonic resonances, yielding intensity and phase toggling between different portions of the plasmonic metamolecules when either their geometric sizes or the illumination wavelength is varied. © 2011 American Chemical Society.P.A.-G, M.S., P.S., P.A., and R.H. acknowledge support from the European FP7 project “Nanoantenna” (FP7-HEALTH-F5-2009-241818-NANOANTENNA) and the National Project MAT2009-08393 from the Spanish Ministerio de Ciencia e Innovacion. M.S. and P.S. acknowledges financial support from “Programa de Formación de Personal Investigador” promoted by the Department of Education, Universities and Research of the Basque Government. P.N. and H.S. acknowledge support from the Robert A. Welch foundation (C-1222), the US Department of Defense NSEFF program (N00244-09-1-0067), and the Office of Naval Research (N00244-09-1-0989). C.W., N.A., A. K., and G.S. acknowledge support from the Office of Naval Research (N00014-10-1-0929) and the Air Force Research Laboratory.Peer Reviewe

Electron energy loss spectroscopy of infrared plasmonic antennas

Resumen del póster presentado al 8th International Workshop on Electron Energy Loss Spectroscopy and Related Techniques, celebrado en Okuma, Okinawa (Japan) del 14 al 19 de mayo de 2017.Spatially-resolved low-loss electron energy loss spectroscopy (EELS) is a wellestablished technique for probing optical excitations in nanostructures and with recent instrumental improvements, it can be utilized even in infrared (IR) spectral region. We explore possibilities of IR-EELS for characterizing metallic nanostructures supporting excitations of localized surface plasmons. We present experimental and theoretical results for different antenna geometries and demonstrate that both spectral and spatial information provided by the electron beam is important for an elaborate analysis of such systems.Peer reviewe

Discipline-Based Educational Research to Improve Active Learning at University

Introductory physics course design is a challenge requiring innovation across many dimensions and responsibilities, all with the goal of improving student competencies. Discipline-based education research contributes to reaching that goal through developing and validating ways to improve active learning. For physics competencies, the main aspects to integrate are conceptual understanding, problem solving and lab work. Each aspect must be taken into account, especially for students who are not pursuing a physics degree. This paper illustrates research carried out in a coordinated way on different aspects, from the same perspective, using the same research approach, and with coherent methods to contribute to innovation in teaching physics at university level

Computational refocusing in phase-resolved confocal microscopy -- Code and Data

Numerical refocusing of phase-resolved confocal microscopy data   This matlab script performs the numerical refocusing as presented in "Computational refocusing in phase-resolved confocal microscopy", M. Schnell et al. Included are the original data from the paper.</p

Real-Space Mapping of the Chiral Near-Field Distributions in Spiral Antennas and Planar Metasurfaces

Chiral antennas and metasurfaces can be designed to react differently to left- and right-handed circularly polarized light, which enables novel optical properties such as giant optical activity and negative refraction. Here, we demonstrate that the underlying chiral near-field distributions can be directly mapped with scattering-type scanning near-field optical microscopy employing circularly polarized illumination. We apply our technique to visualize, for the first time, the circular-polarization selective nanofocusing of infrared light in Archimedean spiral antennas, and explain this chiral optical effect by directional launching of traveling waves in analogy to antenna theory. Moreover, we near-field image single-layer rosette and asymmetric dipole–monopole metasurfaces and find negligible and strong chiral optical near-field contrast, respectively. Our technique paves the way for near-field characterization of optical chirality in metal nanostructures, which will be essential for the future development of chiral antennas and metasurfaces and their applications

Early laparoscopic cholecystectomy in oldest-old patients: a propensity score matched analysis of a nationwide registry

The role of early laparoscopic cholecystectomy (ELC) in “oldest-old” patients with acute calculous cholecystitis (ACC) is still controversial. The aim of this study is to assess the safety of ELC for ACC in ≥ 85-year-old patients. Multicentric retrospective study that analysed data of patients who underwent ELC for ACC between 2013 and 2018. Patients ≥ 85-year-old (oldest-old patients) were compared with younger patients, before and after propensity score matching (PSM). The main outcomes were mortality, post-operative complications, length of stay (LOS), and readmissions. The study included 1670 patients. The unmatched comparison revealed a selection bias towards the oldest-old group, which was associated with higher Charlson Comorbidity Index (5 vs 1, p &lt; 0.001), more ASA III/IV subjects (54.2% vs 19.3%, p &lt; 0.001), class II/III ACC (80.1% vs 69.1%, p = 0.016) and higher Chole-Risk Score (p &gt; 0.001). The oldest-old also required more conversion to open surgery (20% vs 10.3%, p = 0.005). Postoperatively, they had a higher 90-day mortality rate (7.6% vs 1%, p &lt; 0.001), more total complications (40.6% vs 17.7%, p &lt; 0.001), complications ≥ IIIa Clavien–Dindo (14.4% vs 5.8%, p = 0.002), longer LOS (6 vs 5&nbsp;days, p &lt; 0.001), and more readmissions (6.6% vs 2.6%, p &lt; 0.001). After PSM (n = 206), the two groups were comparable in terms of baseline characteristics and intraoperative outcomes. No differences were observed in post-operative complications; bile leak; incisional, intrabdominal, urinary or respiratory tract infections; LOS or readmissions. In the oldest-old, ELC for ACC is still associated with significant morbidity and mortality. However, it seems to be safe in selected patients. Therefore, age itself should not be regarded as a contraindication to ELC for ACC