Medición de la constante elástica k en un sistema de pinzas ópticas usando el método de densidad espectral de potencia

Optical tweezers are well suited to manipulate micron-sized particles and measure forces in the PicoNewton range. A bead in an optical tweezers is not completely immobile; there are thermal fluctuations that cause the bead to execute Brownian motion while trapped. Here we present an optical tweezers setup combined with quadrant photodiode position detection and we use the power spectral density method to measure the force exerted by an optical trap on a dielectric bead in a fluid. This stiffness is often found by fitting a Lorentzian to the power spectral density curves, obtained from the position detection signal of the bead trapped. The obtained results for the stiffness are around of 2.66 and 3.73 pN/μm for different laser powers (15 a 41 mW). There is a double interest to measure forces involved in Optical Tweezers. The first one concerns the physics of optical traps themselves in the sense of comparing experimental trapping forces with theoretically expected values. The other reason is more practical in the sense that for many applications an exact knowledge of the optical forces applied at the trapped particle is useful.Las pinzas ópticas son una herramienta conveniente para manipular partículas de tamaño micrométrico y medir las fuerzas involucradas en el sistema en picoNewtons. Una partícula en un sistema de pinzas ópticas no esta completamente inmóvil, existen fluctuaciones térmicas que producen que la partícula realice movimiento Browniano mientras es atrapada. En este trabajo presentamos un diseño experimental de pinzas ópticas combinado con un fotodiodo de cuadrante, para la medición de los desplazamientos de la partícula en la trampa óptica. Utilizamos el método de densidad espectral de potencia para medir la rigidez o constante elástica k de una pinza óptica, esta constante se determina ajustando una Lorentziana a las curvas de la densidad espectral de potencia, obtenidas del movimiento Browniano de la partícula. Los resultados obtenidos para la constante elástica estan en el intervalo de 2.66 a 3.73 pN/μm para potencias del láser entre 15 a 41 mW, bajo las condiciones descritas en este trabajo. Conociendo el valor de la constante elástica k y el desplazamiento x de la partícula, podemos conocer la fuerza aplicada por una pinza óptica sobre objetos micrométricos mediante la ley de Hooke. Existe un doble interés por medir la fuerza de atrapamiento; la primera, relaciona la física de la pinza óptica por sí misma, en el sentido de comparación de la fuerza experimental obtenida con el valor esperado teóricamente y la segunda razón es que para muchas aplicaciones se requiere un conocimiento exacto de la fuerza óptica aplicada a la partícula o molécula a estudiar

Thermocavitation: A novel optical cavitation method

Cavitation can be defined as the formation, growth and implosion of vapor bubbles within a liquid. The shock wave produced at the moment of the collapse is responsible for the damage on nearby surfaces, such as ship propellers or hydraulic machinery. This phenomenon has been studied by several scientists due to the potentials applications that it offers in different disciplines. The most common techniques to generate cavitation bubbles under a controlled environment involve the use of pulsed lasers, electrical discharge or ultrasound probes. However, these methods are either too expensive or intrusive. In contrast, cavitation bubbles may also be produced with inexpensive, low-power continuous wave (CW) lasers, so long as they are focused in strongly absorbing liquids, this approach leads to the so called thermocavitation. In the present thesis, I propose to study again some of the physical mechanisms of thermocavitation reported by Rastopov and to explore feasible applications of the shock waves generated by the collapse of thermocavitation bubbles as a method to: • To produce damage in materials as hard as titanium and indium tin oxide thin films. This damage was in the form of micro-holes, which could be used for micrometric light sources or spatial filters. • For tissue ablation; mainly to pierce the stratum corneum and thus enhance transdermal drug delivery. • If the thermocavitation bubble is generated within a highly absorbing droplet, the shock wave that is produced upon the bubble collapse overcomes the droplet surface tension and a long and fast moving liquid jet is expelled through the liquid-air interface. Therefore, thermocavitation induced in absorbing droplets could lead to an alternative jet generator. In general, from an application point of view, this combination of CW laser and absorbing solution is in fact quite convenient because it would reduce the cost relative to other more sophisticated methods

Ustilago and the accidental domestication of maize

Maize is the essential crop of the Americas. Maize appeared suddenly about 8,500 years ago as domesticated teosinte; however, there is no evidence (genetical, archaeological, linguistic or ethnobotanical) able to support a gradual transformation from the teosinte ear into the corn ear. Teosinte has never been cultivated by Americans, nor did they ever attempt to domesticate it. Its grains were not used as food, making unrealistic the assumption that prehispanics created something edible from seeds that were not so. Plant domestication is a slow process in almost every known crop but maize evolution might not be the case. Teosinte has a brittle cob, whereas maize forms solid ones that do not release their seeds 2. The latter are soft, while in teosinte they are enclosed in hard inedible cases. Why would the prehispanic natives even think of modifying those hard seeds, if they were not used as food in the first place?. The switch from teosinte to maize were due to important mutations, occurring in a relatively short period so that natives immediately noticed if they were well aware of the importance of teosinte (or its parasites) and rescued the resultant newborn maize.Teosinte-maize hybrids were highly susceptible to the fungus Ustilago maydis (known in Mexico as huitlacoche) under natural conditions. Consequently, this parasite was found to infect every part of the hybrid plant.Huitlacoche is well known as a food delicacy and it has been important to Mexicans since prehispanic times and it might have been very likely used as food taken from infected teosinte at the same time it was changing into maize. Ustilago maydis probably played a vital role on the domestication process of maize, since the change from teosinte to maize was noticed by humans, who then rescued it from natur

Micro-hole drilling in thin films with cw low power lasers

In this work, we perform drilling of micro-holes and micro-patterning in indium tin oxide (ITO) and titanium thin films. In ITO films the drilling is performed by thermocavitation only; meanwhile in titanium two competing processes are identified: (i) laser-induced sublimation producing high-quality micro-holes comparable to those produced with femtosecond pulses but at a reduced cost and (ii) erosion by thermocavitation which tend to degrade the quality of the micro-holes. The micro-holes can be employed as micrometer light sources for use in point-diffraction interferometers or spatial filters; in addition, micron-sized resolution patterning can be performed

Ultrasound induced by CW laser cavitation bubbles

The generation of ultrasound by a collapsing single cavitation bubble in a strongly absorbing liquid illuminated with a moderate power CW laser is described. The ultrasound shock wave is detected with hydrophone and interferometric device. To obtain a stronger pulse it is necessary to adjust a liquid absorption and a beam diameter. Their influence can be qualitatively understood with a simple model

A Large Multicenter Prospective Study of Community-Onset Healthcare Associated Bacteremic Urinary Tract Infections in the Era of Multidrug Resistance: Even Worse than Hospital Acquired Infections?

Introduction: Healthcare-associated (HCA) infections represent a growing public health problem. The aim of this study was to compare community-onset healthcare associated (CO-HCA) bacteremic urinary tract infections (BUTI) and hospital-acquired (HA)-BUTI with special focus on multidrug resistances (MDR) and outcomes. Methods: ITUBRAS-project is a prospective multicenter cohort study of patients with HCA-BUTI. All consecutive hospitalized adult patients with CO-HCA-BUTI or HA-BUTI episode were included in the study. Exclusion criteria were: patients \ 18 years old, non-hospitalized patients, bacteremia from another source or primary bacteremia, non-healthcare related infections and infections caused by unusual pathogens of the urinary tract. Th main outcome variable was 30-day all-cause mortality with day 1 as the first day of positive blood culture. Logistic regression was used to analyze factors associated with clinical cure at hospital discharge and with receiving inappropriate initial antibiotic treatment. Cox regression was used to evaluate 30-day all-cause mortality. Results: Four hundred forty-three episodes were included, 223 CO-HCA-BUTI. Patients with CO-HCA-BUTI were older (p \ 0.001) and had more underlying diseases (p = 0.029) than those with HA-BUTI. The severity of the acute illness (Pitt score) was also higher in CO-HCABUTI (p = 0.026). Overall, a very high rate of MDR profiles (271/443, 61.2%) was observed, with no statistical differences between groups. In multivariable analysis, inadequate empirical treatment was associated with MDR profile (aOR 3.35; 95% CI 1.77?6.35), Pseudomonas aeruginosa (aOR 2.86; 95% CI 1.27?6.44) and Charlson index (aOR 1.11; 95% CI 1.01?1.23). Mortality was not associated with the site of acquisition of the infection or the presence of MDR profile. However, in the logistic regression analyses patients with CO-HCA-BUTI (aOR 0.61; 95% CI 0.40?0.93) were less likely to present clinical cure. Conclusion: The rate of MDR infections was worryingly high in our study. No differences in MDR rates were found between CO-HCA-BUTI and HA-BUTI, in the probability of receiving inappropriate empirical treatment or in 30-day mortality. However, CO-HCA-BUTIs were associated with worse clinical cure.Funding. This study and the journal’s Rapid Service Fee are sponsored and funded by MSD Spain. The study was also supported by Plan Nacional de I+D+i 2013–2016 and Instituto de Salud Carlos III, Subdirección General de Redes y Centros de Investigación Cooperativa, Ministerio de Economía, Industria y Competitividad, Spanish Network for Research in Infectious Diseases (REIPI RD16/0016/0004, RD16/ 0016/0005, RD16/0016/0007, RD16/0016/0010, RD16/0016/0011 and RD16/0016/0015), co-financed by the European Development Regional Fund ‘A way to achieve Europe’ (ERDF), Operative program Intelligent Growth 2014–2020

Early Tracheostomy for Managing ICU Capacity During the COVID-19 Outbreak: A Propensity-Matched Cohort Study

10 p.Background: During the first wave of the COVID-19 pandemic, shortages of ventilators and ICU beds overwhelmed health care systems. Whether early tracheostomy reduces the duration of mechanical ventilation and ICU stay is controversial. Research question: Can failure-free day outcomes focused on ICU resources help to decide the optimal timing of tracheostomy in overburdened health care systems during viral epidemics? Study design and methods: This retrospective cohort study included consecutive patients with COVID-19 pneumonia who had undergone tracheostomy in 15 Spanish ICUs during the surge, when ICU occupancy modified clinician criteria to perform tracheostomy in Patients with COVID-19. We compared ventilator-free days at 28 and 60 days and ICU- and hospital bed-free days at 28 and 60 days in propensity score-matched cohorts who underwent tracheostomy at different timings (≤ 7 days, 8-10 days, and 11-14 days after intubation). Results: Of 1,939 patients admitted with COVID-19 pneumonia, 682 (35.2%) underwent tracheostomy, 382 (56%) within 14 days. Earlier tracheostomy was associated with more ventilator-free days at 28 days (≤ 7 days vs > 7 days [116 patients included in the analysis]: median, 9 days [interquartile range (IQR), 0-15 days] vs 3 days [IQR, 0-7 days]; difference between groups, 4.5 days; 95% CI, 2.3-6.7 days; 8-10 days vs > 10 days [222 patients analyzed]: 6 days [IQR, 0-10 days] vs 0 days [IQR, 0-6 days]; difference, 3.1 days; 95% CI, 1.7-4.5 days; 11-14 days vs > 14 days [318 patients analyzed]: 4 days [IQR, 0-9 days] vs 0 days [IQR, 0-2 days]; difference, 3 days; 95% CI, 2.1-3.9 days). Except hospital bed-free days at 28 days, all other end points were better with early tracheostomy. Interpretation: Optimal timing of tracheostomy may improve patient outcomes and may alleviate ICU capacity strain during the COVID-19 pandemic without increasing mortality. Tracheostomy within the first work on a ventilator in particular may improve ICU availability

Clinical and structural brain correlates of hypomimia in early-stage Parkinson's disease

Altres ajuts: acord transformatiu CRUE-CSICBackground and purpose: Reduced facial expression of emotions is a very frequent symptom of Parkinson's disease (PD) and has been considered part of the motor features of the disease. However, the neural correlates of hypomimia and the relationship between hypomimia and other non-motor symptoms of PD are poorly understood. Methods: The clinical and structural brain correlates of hypomimia were studied. For this purpose, cross-sectional data from the COPPADIS study database were used. Age, disease duration, levodopa equivalent daily dose, Unified Parkinson's Disease Rating Scale part III (UPDRS-III), severity of apathy and depression and global cognitive status were collected. At the imaging level, analyses based on gray matter volume and cortical thickness were used. Results: After controlling for multiple confounding variables such as age or disease duration, the severity of hypomimia was shown to be indissociable from the UPDRS-III speech and bradykinesia items and was significantly related to the severity of apathy (β = 0.595; p < 0.0001). At the level of neural correlates, hypomimia was related to motor regions brodmann area 8 (BA 8) and to multiple fronto-temporo-parietal regions involved in the decoding, recognition and production of facial expression of emotions. Conclusion: Reduced facial expressivity in PD is related to the severity of symptoms of apathy and is mediated by the dysfunction of brain systems involved in motor control and in the recognition, integration and expression of emotions. Therefore, hypomimia in PD may be conceptualized not exclusively as a motor symptom but as a consequence of a multidimensional deficit leading to a symptom where motor and non-motor aspects converge

Staging Parkinson’s Disease According to the MNCD (Motor/Non-motor/Cognition/Dependency) Classification Correlates with Disease Severity and Quality of Life

Background: Recently, a novel simple classification called MNCD, based on 4 axes (Motor; Non-motor; Cognition; Dependency) and 5 stages, has been proposed to classify Parkinson's disease (PD). Objective: Our aim was to apply the MNCD classification in a cohort of PD patients for the first time and also to analyze the correlation with quality of life (QoL) and disease severity. Methods: Data from the baseline visit of PD patients recruited from 35 centers in Spain from the COPPADIS cohort from January 2016 to November 2017 were used to apply the MNCD classification. Three instruments were used to assess QoL: 1) the 39-item Parkinson's disease Questionnaire [PDQ-39]); PQ-10; the EUROHIS-QOL 8-item index (EUROHIS-QOL8). Results: Four hundred and thirty-nine PD patients (62.05 +/- 7.84 years old; 59% males) were included. MNCD stage was: stage 1, 8.4% (N = 37); stage 2, 62% (N = 272); stage 3, 28.2% (N = 124); stage 4-5, 1.4% (N = 6). A more advanced MNCD stage was associated with a higher score on the PDQ39SI (p < 0.0001) and a lower score on the PQ-10 (p < 0.0001) and EUROHIS-QOL8 (p < 0.0001). In many other aspects of the disease, such as disease duration, levodopa equivalent daily dose, motor symptoms, non-motor symptoms, and autonomy for activities of daily living, an association between the stage and severity was observed, with data indicating a progressive worsening related to disease progression throughout the proposed stages. Conclusion: Staging PD according to the MNCD classification correlated with QoL and disease severity. The MNCD could be a proper tool to monitor the progression of PD

Staging Parkinson's Disease Combining Motor and Nonmotor Symptoms Correlates with Disability and Quality of Life.

Introduction: In a degenerative disorder such as Parkinson's disease (PD), it is important to establish clinical stages that allow to know the course of the disease. Our aim was to analyze whether a scale combining Hoehn and Yahr's motor stage (H&Y) and the nonmotor symptoms burden (NMSB) (assessed by the nonmotor symptoms scale (NMSS)) provides information about the disability and the patient's quality of life (QoL) with regard to a defined clinical stage. Materials and methods: Cross-sectional study in which 603 PD patients from the COPPADIS cohort were classified according to H&Y (1, stage I; 2, stage II; 3, stage III; 4, stage IV/V) and NMSB (A: NMSS = 0-20; B: NMSS = 21-40; C: NMSS = 41-70; D: NMSS ≥ 71) in 16 stages (HY.NMSB, from 1A to 4D). QoL was assessed with the PDQ-39SI, PQ-10, and EUROHIS-QOL8 and disability with the Schwab&England ADL (Activities of Daily Living) scale. Results: A worse QoL and greater disability were observed at a higher stage of H&Y and NMSB (p < 0.0001). Combining both (HY.NMSB), patients in stages 1C and 1D and 2C and 2D had significantly worse QoL and/or less autonomy for ADL than those in stages 2A and 2B and 3A and 3B, respectively (p < 0.005; e.g., PDQ-39SI in 1D [n = 15] vs 2A [n = 101]: 28.6 ± 17.1 vs 7.9 ± 5.8; p < 0.0001). Conclusion: The HY.NMSB scale is simple and reflects the degree of patient involvement more accurately than the HΨ Patients with a lower H&Y stage may be more affected if they have a greater NMS burden