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

Two-dimensional simulation of the electron transport in a photomultiplier tube

Photomultiplier tubes are widely used in experimental physics because they convert small light signals into a measurable electric current. Although their working principle is well known, it is very difficult to find simulations of the electron transport in these devices. For this reason, the electron transport in the Hamamatsu R13408-100 photomultiplier tube has been simulated in 2D. The software SUPERFISH is used for calculating the electrostatic fields and the Boris method for the effective electron dynamics. The secondary electron emission in the dynodes is implemented using an effective electron model and the modified Vaughan’s model. Some figures of merit for photomultiplier tubes (e.g. the gain, the electron transit time or the transit time spread) in function of the supply voltage and an external magnetic field have been studied obtaining a good qualitative accordance with the Hamamatsu datasheet. In further studies, we are going to compare our simulations with experimental measurements

Resiliencia de la cubierta vegetal en un área de montaña mediterránea afectada por el fuego: el caso del incendio de Río Verde (provincia de Málaga, sur de España)

The study aim is the comparison of the vegetation cover type before and 22-years after a wildfire in order to evaluate its post-fire resilience as well as the effect of topographic attributes. The study area is that affected by a wildfire in 1991 (Río Verde, Sierra de las Nieves). By means of remote sensing and mapping techniques, the type of vegetation cover was obtained for 1991, just before the wildfire, and for 2013. The comparison of both years indicates 50% of the burned area recovered the pre-fire vegetation cover, while 1/3 presented a major vegetation cover and a type of cover more evolved. Generally speaking, after the wildfire, the most influential topographic features in the vegetal cover evolution were slope gradient, altitude and radiationEl propósito de este estudio es comparar el tipo de cubierta vegetal antes de un incendio y varios años después para evaluar su resiliencia post-incendio, así como la influencia de ciertos atributos topográficos. El área de estudio es el área afectada por el incendio de río Verde, en 1991 (Sierra de las Nieves), con una orografía muy abrupta. Mediante el tratamiento y análisis de imágenes de satélite y posterior procesamiento cartográfico en un SIG, se obtuvieron los tipos de cubierta vegetal en 1991, justo antes del incendio, y en 2013. De la comparación de ambos años, puede decirse que, tras 22 años desde el incendio, la mitad del área quemada ha recuperado la cubierta vegetal previa y 1/3 de la misma presenta actualmente una cubierta vegetal superior, con un tipo de cubierta que evidencia un estado evolutivo más avanzado respecto al determinado antes del incendio. En general, los atributos topográficos que más influyeron en la evolución post-incendio de la cubierta vegetal fueron, en este orden, pendiente, altitud y radiación

Muscle thickness and echogenicity measured by ultrasound could detect local sarcopenia and malnutrition in older patients hospitalized for hip fracture

Background: The aim of this work was to assess whether the muscle thickness and echogenicity were associated with dysphagia, malnutrition, sarcopenia, and functional capacity in acute hospital admission for a hip fracture. Methods: Observational study that assessed nutritional status by Global Leadership Initiative on Malnutrition, risk of dysphagia and sarcopenia by European Working Group on Sarcopenia in Older People and Barthel functional index. We measured muscle thickness and echogenicity of masseter, bicipital, and quadriceps rectus femoris (RF) and vastus intermedius (VI) by ultrasound. Results: One hundred and one patients were included in the study (29.7% sarcopenia and 43.8% malnutrition). Logistic regression models adjusted for age, sex, and body mass index showed an inverse association of the masseter thickness with both sarcopenia (OR: 0.56) and malnutrition (OR: 0.38) and quadriceps with sarcopenia (OR: 0.74). In addition, patients at high risk of dysphagia had lower masseter thickness (p: 0.0001) while patients able to self-feeding had thicker biceps (p: 0.002) and individuals with mobility on level surfaces higher thickness of biceps (p: 0.008) and quadriceps (p: 0.04). Conclusion: Thickness of the masseter was associated with risk of dysphagia, biceps with the ability to self-feed, and that of the quadriceps RF-VI with mobility

Experimental characterization and test-beam results of MACACO III Compton camera

The IRIS group at IFIC-Valencia is developing a Compton camera prototype with the aim of applying it in hadron therapy treatment monitoring. Recently, a third version of the prototype MACACO (Medical Applications CompAct COmpton camera) has been built. The system is composed of three Lanthanum (III) bromide scintillator crystals coupled to silicon photomultipliers. To improve its performance for the final application, several detectors are tested, two different silicon photomultipliers (25 and 50 um) have been chosen as possible candidates. The 25 up photodetector provided better performance in therms of dynamic range, energy resolution (5.2/ FWHM at 511 keV) and stability with temperature variations. MACACO III has also been tested in the CNA cyclotron (Seville) with 18 MeV proton beam to produce 4.439 MeV gamma rays. Data have been acquired with a graphite target in five different positions at 2.5 nA nominal beam intensity. Images with 4.439 MeV photons have been reconstructed, demonstrating the system capability to reconstruct images at energies relevant for hadron therapy. Moreover, the system has been able to distinguish 1mm displacements in the target position

Strong interfacial exchange field in a heavy metal/ferromagnetic insulator system determined by spin Hall magnetoresistance

Spin-dependent transport at heavy metal/magnetic insulator interfaces is at the origin of many phenomena at the forefront of spintronics research. A proper quantification of the different interfacial spin conductances is crucial for many applications. Here, we report the first measurement of the spin Hall magnetoresistance (SMR) of Pt on a purely ferromagnetic insulator (EuS). We perform SMR measurements in a wide range of temperatures and fit the results by using a microscopic model. From this fitting procedure we obtain the temperature dependence of the spin conductances ($G_s$, $G_r$ and $G_i$), disentangling the contribution of field-like torque ($G_i$), damping-like torque ($G_r$), and spin-flip scattering ($G_s$). An interfacial exchange field of the order of 1 meV acting upon the conduction electrons of Pt can be estimated from $G_i$, which is at least three times larger than $G_r$ below the Curie temperature. Our work provides an easy method to quantify this interfacial spin-splitting field, which play a key role in emerging fields such as superconducting spintronics and caloritronics, and topological quantum computation.Comment: 15 pages, 3 figures, Supporting information included at the en

A simple analytical method for heterogeneity corrections in low dose rate prostate brachytherapy

In low energy brachytherapy, the presence of tissue heterogeneities contributes significantly to the discrepancies observed between treatment plan and delivered dose. In this work, we present a simplified analytical dose calculation algorithm for heterogeneous tissue. We compare it with Monte Carlo computations and assess its suitability for integration in clinical treatment planning systems. The algorithm, named as RayStretch, is based on the classic equivalent path length method and TG-43 reference data. Analytical and Monte Carlo dose calculations using Penelope2008 are compared for a benchmark case: a prostate patient with calcifications. The results show a remarkable agreement between simulation and algorithm, the latter having, in addition, a high calculation speed. The proposed analytical model is compatible with clinical real-time treatment planning systems based on TG-43 consensus datasets for improving dose calculation and treatment quality in heterogeneous tissue. Moreover, the algorithm is applicable for any type of heterogeneities