Understanding Optical Trapping Phenomena: a Simulation for Undergraduates

Optical trapping is an attractive and multidisciplinary topic that has become the center of attention to a large number of researchers. Moreover, it is a suitable subject for advanced students that requires a knowledge of a wide range of topics. As a result, it has been incorporated into some syllabuses of both undergraduate and graduate programs. In this paper, basic concepts in laser trapping theory are reviewed. To provide a better understanding of the underlying concepts for students, a Java application for simulating the behavior of a dielectric particle trapped in a highly focused beam has been developed. The program illustrates a wide range of theoretical results and features, such as the calculation of the force exerted by a beam in the Mie and Rayleigh regimes or the calibration of the trap stiffness. Some examples that are ready to be used in the classroom or in the computer lab are also supplied

Monitoring groundwater nitrate attenuation in a regional system coupling hydrogeology with multi-isotopic methods: the case of Plana de Vic (Osona, Spain)

This paper describes an integrated application of classical hydrogeological methods and multi-isotopic methods (d15N, d18ONO3, d34S, d18OSO4, d13C) to assess the fate of groundwater nitrate in the Osona area, declared vulnerable to nitrate pollution by the Catalan Government in 1998, where nitrate is derived from intensive pig farming activities. Previous studies, involving a small area, indicated the occurrence of denitrification processes and their relationship with pyrite oxidation [Vitòria, L., Soler, A., Canals, A., Otero, N., 2008. Environmental isotopes (N, S, C, O, D) to determine natural attenuation processes in nitrate contaminated waters: example of Osona (NE Spain). Appl. Geochem. 23, 3597-3611]. For the present study, groundwater samples were collected at 60 production wells at three different periods between April 2005 and May 2006 to confirm that denitrification takes place in a larger area than that studied by Vitòria et al. [Vitòria, L., Soler, A., Canals, A., Otero, N., 2008. Environmental isotopes (N, S, C, O, D) to determine natural attenuation processes in nitrate contaminated waters: example of Osona (NE Spain). Appl. Geochem. 23, 3597-3611]. The aim of the study was to characterize the denitrification processes that control natural attenuation and to study their spatial and temporal variations. Nitrate concentration ranged from 10 to 529 mg/l, with 82% of the wells above the drinking water threshold of 50 mg NO3/l. Nitrate isotopic composition ranged from +5.3% to +35.3% for d15N and from +0.4% to +17.6% for d18ONO3 , and the samples showed a positive correlation between d15N and d18ONO3 , with a eN/eO ratio of 1.8, consistent with denitrification processes. The link between denitrification and pyrite oxidation is demonstrated by coupling chemical data with nitrate and sulfate isotopes. Furthermore, a spatial distribution of samples with significant denitrification was observed, allowing us to determine two main hydrogeological zones where natural attenuation was most effective. In several of the studied points, denitrification processes related to pyrite oxidation predominated and an estimation of the isotopic enrichment factors was performed using the temporal variations of nitrate concentration and the isotopic composition of dissolved nitrate (d15NNO3 and d18ONO3). Finally, using estimated isotopic enrichment factors, an approximation of the degree of natural attenuation of nitrate was performed on those samples showing clear denitrification, and a median value of 30% of contaminant diminution was obtained

Nitrate pollution processes in the Plana de Vic aquifers (Osona, Barcelona)

Nitrate pollution in the Plana de Vic aquifers has presently reached very high levels, which pose enormous limitations to its use. The origin of nitrate is mainly caused by manure application as fer tilizer. In this paper, we present a hydrodynamic scheme of the Plana de Vic aquifer system, based on potentiometric data and nitrate concentrations obtained through a monthly monitoring effort of a 80 well database. The response of those wells to the recharge that ended a severe drought period allows us to depict different hydrogeological behaviours between surface and deep aquifer levels. We conclude that a mixing process occurs in this multilevel leaky-aquifer system facilitated by the uncasing of most of the wells. Therefore, a deficient exploitation of the aquifer is seen as an additional cause for the spreading of nitrat

Estudio multi-isotópico de la atenuación natural de la contaminación por nitratos en un sistema acuífero regional: Plana de Vic (Osona, NE España)

The presence of nitrate in groundwater of the Osona area is derived from the intensive cattle raising. Even though local administration regulates and controls the present use and distribution of manure as fertilizer, according to legal application rates, nitrate pollution in Osona shows the effect of decades of uncontrolled manure application. Vitòria (2004) using stable isotopes determined the presence of denitrification processe (natural attenuation of nitrate pollution) in a small area located in the Osona province. The main goal of this still on-going research (2005-2006) is to determine the extent of denitrification at a regional scale, and the processes that control natural attenuation, using multi-isotopic methods (dD, d18O, T, d34S, d15N,d13C). Results show that denitrification is active in two areas, and that this process is linked to pyrite oxidation. In the studied area, data do not allow to identify the role of organic matter oxidation in denitrification. The observed denitrification processes reveal optional strategies for nitrogen attenuation

Community-acquired pneumonia management in a short-stay unit: analysis of safety and efficacy

Podeu consultar la versió en castellà a: http://hdl.handle.net/2445/119397Background and objective: Community-acquired pneumonia (CAP) is a highly prevalent disease that often requires hospital admission. We aimed to assess the safety and efficacy of treating CAP in a short-stay unit as an alternative to conventional hospitalization. Methods: Retrospective comparison of patients admitted to a tertiary care hospital with a diagnosis of CAP between November 2005 and April 2007. We compared outcomes for cases managed in the 2 locations (short-stay unit vs conventional hospital ward), excluding patients who required intensive care. Variables and outcomes analyzed were age, sex, Charlson index, mean weight in the diagnosis-related group, scores on the CURB-65 criteria and the Pneumonia Severity Index (PSI), findings of microbiology, and readmission and mortality rates. Results: A total of 606 patients were studied; 187 were treated in the short-stay unit and 419 were admitted to the conventional ward. The main significant differences between the 2 groups were mean age (77.3 vs 67.9 years, respectively; P<.0001) and mean stay (3.48 vs 7.89 days; P<.0001). These differences were also reflected in the comparison between severity subgroups (by PSI). Mortality rates did not differ. Conclusions: Our experience with the short-stay unit suggests it offers a safe and effective way to manage CAP and leads to a significantly shorter hospital stay in comparison with conventional hospitalization, without increasing readmission and mortality rates

Análisis de la seguridad y la eficacia de una unidad de corta estancia en el tratamiento de la neumonía adquirida en la comunidad

Podeu consultar la versió en anglès a: http://hdl.handle.net/2445/119414Introducción: La neumonía adquirida en la comunidad (NAC) es una patología de alta prevalencia que a menudo requiere ingreso hospitalario. El objetivo de nuestro estudio es evaluar la eficacia y seguridad en el tratamiento de la NAC de una unidad de corta estancia (UCE) como alternativa a las unidades de hospitalización convencional (UHC). Método: Estudio retrospectivo comparativo de pacientes ingresados en un hospital terciario con diagnóstico al alta de NAC entre noviembre del 2005 y abril del 2007. Se comparan dos grupos: pacientes ingresados en UCE frente a pacientes ingresados en UHC (se excluyen pacientes que requieren terapia intensiva). Variables analizadas: edad y sexo, índice de Charlson, peso según el grupo relacionado de diagnóstico (GRD), CURB 65 y Pneumonia Severity Index (PSI), hallazgos microbiológicos, tasas de readmisión y de mortalidad. Resultados: Un total de 606 pacientes fueron reclutados, 187 ingresados en el UCE (grupo 1) y 419 en UHC (grupo 2 o grupo control). Las diferencias más significativas entre los dos grupos fueron el promedio de edad (77,3 vs 67,9 p < 0,001) y la estancia promedio (3,48 vs 7,89 p < 0,001). Estas diferencias se objetivan en el comparativo general y por subgrupos según la escala de riesgo (PSI). No se observaron diferencias significativas en la tasa de mortalidad ni en la de reingreso entre las dos formas de hospitalización. Conclusiones: La UCE es eficaz y segura en el manejo de los pacientes con NAC, con una estancia media significativamente inferior respecto a las UHC, y sin diferencias en las tasas de mortalidad y reingreso

Cal Sitjo: A new Mesolithic to Neolithic sequence in a chert-rich region (Sant Martí de Tous, NE Iberia)

Cal Sitjo is a new archaeological sequence located in a chert-rich region of the NE Iberian Peninsula, in the town of Sant Martí de Tous (Anoia, Barcelona). The area has undergone significant anthropisation and several archaeological sites (e.g., Vilars de Tous), quarries and workshops for the exploitation of chert (e.g., La Guinardera) have been documented, corresponding to different periods. The abundance of chert made this region an almost obligatory passageway for hunter-gatherer communities such as those occupying the nearby cliffs of Cinglera del Capelló (Capellades), located at a direct distance of 15 km, as well as an ideal settlement for later farming communities. Discovered in 2019, the first excavation campaign was carried out in the fall of 2020. Dates have been obtained from a known sequence of around 8 m, providing a chronological framework that ranges from the Mesolithic to the Middle Neolithic. The preliminary results of this excavation have brought to light lithics, ceramics and charcoals from the Neolithic levels (Levels 3 and 4), and faunal, lithic and charcoal remains from the Mesolithic levels (cleaning section). Our preliminary results confirm that this sequence is an ideal location for a diachronic study of the evolution from the last hunter-gatherers to the first farmers, from a paleoenvironmental and technological perspective, as well as in terms of chert management and distribution in a territory with a great abundance of this raw material

Investigation on force detection methods for optical trapping and sensing inside living cells

[eng] Optical Tweezers (OT) are a light-based non-invasive tool that has played an important role during the last decades in the field of biophotonics, together with the advances in optical microscopy techniques. Optical trapping and micromanipulation of microscopic objects is nowadays possible with tightly focused laser beams, with the capability of measuring forces acting on the trapped particle in the order of piconewtons. OT have found numerous applications in the field of biophysics, and more specifically in molecular motor studies. One of the open challenges in the field is measuring molecular motor forces in their natural (in vivo) environment: the interior of living cells. Due to the complex mechanical properties of the cell cytoplasm, standard trap force calibration methods do not apply in this environment. In this thesis we investigate two recent optical force calibration methods: active-passive calibration in viscoelastic media, and direct force measurements via light momentum changes. The two methods are tested and cross-validated inside living cells, and an application involving intracellular molecular motor stall force measurements is demonstrated. The obtained results prove the possibility of measuring forces inside the cell cytoplasm with holographic tweezers, even with an object-independent trap force calibration when the conditions for the momentum-based technique are fulfilled. We also present an algorithm for manipulating groups of optical traps with minimal computational cost, using random mask multiplexing combined with iterative computer-generated holograms for dynamic holographic optical tweezers.[cat] Les pinces òptiques són una tècnica no invasiva, basada en llum, que ha tingut un paper important en les últimes dècades en el camp de la biofotònica, en combinació amb les noves tècniques de microscòpia. L’atrapament i manipulació d’objectes microscòpics per mitjans òptics és avui en dia una possibilitat real, que permet no només desplaçar objectes, sinó també mesurar les forces que actuen sobre aquests. És per això que les trampes òptiques han trobat nombroses aplicacions en el camp de la biofísica, i més concretament, en l’estudi de motors moleculars. Un dels reptes pendents en aquest sentit és la mesura de força de motors moleculars en el seu entorn natural: l’interior de cèl·lules vives. Degut a la complexitat mecànica del citoplasma, els mètodes estàndard de calibratge de pinces òptiques no són vàlids en aquest entorn. En aquesta tesi s’investiguen dos mètodes recents de mesura de força que tenen el potencial de ser utilitzats a l’interior cel·lular: la calibració activa-passiva de pinces òptiques en medis viscoelàstics, i la mesura força directa a través de canvis en el moment del feix de llum. Es demostra que els dos mètodes, basats en principis teòrics totalment diferents, donen resultats compatibles dins de cèl·lules, validant així la possibilitat de mesurar forces pinces òptiques a l’interior cel·lular de forma fiable. La utilitat pràctica del mètode de força directa, la constant de calibració del qual és independent de l’objecte atrapat, es demostra amb una aplicació concreta: la mesura de força de motors moleculars involucrats en el transport de vesícules en cèl·lules animals. També presentem un algoritme per a la manipulació dinàmica de grups de trampes òptiques utilitzant holografia digital, amb un cost computacional mínim. S’utilitza el multiplexat espacial de màscares aleatòries, partint d’hologrames pre-generats amb mètodes iteratius, per experiments de manipulació a temps real