143 research outputs found
Casimir interaction at liquid nitrogen temperature: Comparison between experiment and theory
We have measured the normalized gradient of the Casimir force between
Au-coated surfaces of the sphere and the plate and equivalent Casimir pressure
between two parallel Au plates at T=77K. These measurements have been performed
by means of dynamic force microscope adapted for operating at low temperatures
in the frequency shift technique. It was shown that the measurement results at
T=77K are in a very good agreement with those at T=300K and with computations
at T=77K using both theoretical approaches to the thermal Casimir force
proposed in the literature. No thermal effect in the Casimir pressure was
observed in the limit of experimental errors with the increase of temperature
from T=77K to T=300K. Taking this into account, we have discussed the possible
role of patch potentials in the comparison between measured and calculated
Casimir pressures.Comment: 18 pages, 8 figures, to appear in Phys. Rev.
Perturbations on the antidiagonals of Hankel matrices
Given a strongly regular Hankel matrix, and its associated sequence of moments whichdefines a quasi-definite moment linear functional, we study the perturbation of a fixedmoment, i.e., a perturbation of one antidiagonal of the Hankel matrix. We define a linearfunctional whose action results in such a perturbation and establish necessary and sufficientconditions in order to preserve the quasi-definite character. A relation between thecorresponding sequences of orthogonal polynomials is obtained, as well as the asymptoticbehavior of their zeros. We also study the invariance of the Laguerre-Hahn class of linearfunctionals under such perturbation, and determine its relation with the so-called canonicallinear spectral transformations.The research of the first author was supported by Bolsa de Atração de Jovens Talentos CAPES/CNPq/FAPs of
Brazil, Project 370291/2013 1 and Dirección General de Investigación, Ministerio de Economía y Competitividad of Spain,
Grant MTM2012 36732 C03 0
Gradient of the Casimir force between Au surfaces of a sphere and a plate measured using atomic force microscope in a frequency shift technique
We present measurement results for the gradient of the Casimir force between
an Au-coated sphere and an Au-coated plate obtained by means of an atomic force
microscope operated in a frequency shift technique. This experiment was
performed at a pressure of 3x10^{-8} Torr with hollow glass sphere of 41.3 mcm
radius. Special attention is paid to electrostatic calibrations including the
problem of electrostatic patches. All calibration parameters are shown to be
separation-independent after the corrections for mechanical drift are included.
The gradient of the Casimir force was measured in two ways with applied
compensating voltage to the plate and with different applied voltages and
subsequent subtraction of electric forces. The obtained mean gradients are
shown to be in mutual agreement and in agreement with previous experiments
performed using a micromachined oscillator. The obtained data are compared with
theoretical predictions of the Lifshitz theory including corrections beyond the
proximity force approximation. An independent comparison with no fitting
parameters demonstrated that the Drude model approach is excluded by the data
at a 67% confidence level over the separation region from 235 to 420 nm. The
theoretical approach using the generalized plasma-like model is shown to be
consistent with the data over the entire measurement range. Corrections due to
the nonlinearity of oscillator are calculated and the application region of the
linear regime is determined. A conclusion is made that the results of several
performed experiments call for a thorough analysis of the basics of the theory
of dispersion forces.Comment: 35 pages, 14 figures, 1 table; to appear in Phys. Rev.
Experimental procedures for precision measurements of the Casimir force with an Atomic Force Microscope
Experimental methods and procedures required for precision measurements of
the Casimir force are presented. In particular, the best practices for
obtaining stable cantilevers, calibration of the cantilever, correction of
thermal and mechanical drift, measuring the contact separation, sphere radius
and the roughness are discussed.Comment: 14 pages, 7 figure
Cuantificación de antioxidantes en plantas de tomate (Solanum lycopersicon L. Mill) enriquecida con selenio.
Con el propósito de analizar la capacidad del selenito de sodio para incrementar la concentración de Selenio y modificar la actividad antioxidante en plantas de tomate. Se aplicaron tres tratamientos de selenito de sodio utilizando como vehículo el agua de riego. Se llevaron a cabo tres muestreos 40, 80 y 120 días después del tras plante y cuantificaron la acumulación de selenio en frutos. Se obtuvo una cuantificación del potencial oxido reducción y de la actividad de antioxidante como la catalasa, glutatión peroxidasa, el ácido ascórbico y licopeno. Para cada variable se llevó a cabo un análisis de varianza. Los resultados mostraron un incremento en la acumulación de selenio, hasta un 53.1% con el tratamiento 5 mg L-1en comparación con el testigo. Los valores del potencial oxido-reducción se redujeron desde -41.4 mV para el testigo y hasta -68.0 mV con el mayor tratamiento. La concentración de Se influyó en los parámetros de calidad incluyendo el ácido ascórbico hasta un 50% de aumento y el licopeno (66.9%). La actividad de las enzimas antioxidantes aumentó notablemente en el fruto con el tratamiento 5 mg L-1de selenito encontrándose 60.9% de aumento para CAT, 33.4% para GPX y 26.0% para SOD
Modifying the Casimir force between indium tin oxide film and Au sphere
We present complete results of the experiment on measuring the Casimir force
between an Au-coated sphere and an untreated or, alternatively, UV-treated
indium tin oxide film deposited on a quartz substrate. Measurements were
performed using an atomic force microscope in a high vacuum chamber. The
measurement system was calibrated electrostatically. Special analysis of the
systematic deviations is performed, and respective corrections in the
calibration parameters are introduced. The corrected parameters are free from
anomalies discussed in the literature. The experimental data for the Casimir
force from two measurement sets for both untreated and UV-treated samples are
presented. The experimental errors are determined at a 95% confidence level. It
is demonstrated that the UV treatment of an I TO plate results in a significant
decrease in the magnitude of the Casimir force (from 21% to 35% depending on
separation). However, ellipsometry measurements of the imaginary parts of
dielectric permittivities of the untreated and UV-treated samples did not
reveal any significant differences. The experimental data are compared with
computations in the framework of the Lifshitz theory. It is found that the data
for the untreated sample are in a very good agreement with theoretical results
taking into account the free charge carriers in an ITO film. For the UV-treated
sample the data exclude the theoretical results obtained with account of free
charge carriers. These data are in a very good agreement with computations
disregarding the contribution of free carriers. According to the explanation
provided, this is caused by the phase transition of the ITO film from metallic
to dielectric state caused by the UV treatment. Possible applications of the
discovered phenomenon in nanotechnology are discussed.Comment: 30 pages, 19 figures, 1 tabl
Calidad nutricional del tomate (Solanum lycopersicon L. Mill) enriquecida con selenio.
La biofortificación tiene como finalidad incrementar la concentración de elementos biodisponibles en cultivos hortalizas para elevar la calidad nutricional. El selenio es un elemento traza de gran impacto para el metabolismo antioxidante de las plantasy su acumulación es pobre en especies como el tomate, por lo que adicionarlo en las plantas forma parte de los programas de biofortificación. El propósito de este trabajo fue analizar la capacidad del selenito de sodio para incrementar la concentración de Se y modificar la actividad antioxidante en plantas de tomate. Para ello a l a s plantas se aplicaron tres tratamientos 0, 2 y 5 mg L-1 de selenito de sodio utilizando como vehículo el agua de riego. Se llevaron a cabo tres muestreos 40, 80 y 120 días después del trasplante y cuantificación la acumulación de selenio y macronutrientes en hojas, tallos y frutos asícomo su impacto en la producción de frutos bajo un diseño experimental completamente al azar. Se determinó la altura, diámetro de tallos, firmeza, sólidos solubles de frutos y la materia seca total de los diferentes tejidos. Se obtuvo una cuantificación del potencial oxido reducción y de la actividad de antioxidante específicos como la catalasa, glutatión peroxidasa, superóxido dismutasa, el ácido ascórbico y licopeno. Los resultados se analizaron mediante el ANOVA y posteriormente una prueba de comparación de medias de Tukey. Se observó un incremento en la acumulación de Se, encontrándose hasta un 53.1% de aumento en la concentración en los frutos bajo el tratamiento 5 mg L-1 en comparación con el testigo, sin embargo, este incremento no tuvo un impacto notorio en la producción y el rendimiento del tomate. La concentración de Se influyó positivamente en los parámetros de calidad incluyendo el ácido ascórbico y el licopeno
Experimental approaches to the difference in the Casimir force through the varying optical properties of boundary surface
We propose two novel experiments on the measurement of the Casimir force
acting between a gold coated sphere and semiconductor plates with markedly
different charge carrier densities. In the first of these experiments a
patterned Si plate is used which consists of two sections of different dopant
densities and oscillates in the horizontal direction below a sphere. The
measurement scheme in this experiment is differential, i.e., allows the direct
high-precision measurement of the difference of the Casimir forces between the
sphere and sections of the patterned plate or the difference of the equivalent
pressures between Au and patterned parallel plates with static and dynamic
techniques, respectively. The second experiment proposes to measure the Casimir
force between the same sphere and a VO film which undergoes the
insulator-metal phase transition with the increase of temperature. We report
the present status of the interferometer based variable temperature apparatus
developed to perform both experiments and present the first results on the
calibration and sensitivity. The magnitudes of the Casimir forces and pressures
in the experimental configurations are calculated using different theoretical
approaches to the description of optical and conductivity properties of
semiconductors at low frequencies proposed in the literature. It is shown that
the suggested experiments will aid in the resolution of theoretical problems
arising in the application of the Lifshitz theory at nonzero temperature to
real materials. They will also open new opportunities in nanotechnology.Comment: 23 pages of the text, 2 tables, and captions of 12 figures (to appear
in Phys. Rev. A
Brain metastasis development and poor survival associated with carcinoembryonic antigen (CEA) level in advanced non-small cell lung cancer: a prospective analysis
<p>Abstract</p> <p>Background</p> <p>Central nervous system is a common site of metastasis in NSCLC and confers worse prognosis and quality of life. The aim of this prospective study was to evaluate the prognostic significance of clinical-pathological factors (CPF), serum CEA levels, and EGFR and HER2 tissue-expression in brain metastasis (BM) and overall survival (OS) in patients with advanced NSCLC.</p> <p>Methods</p> <p>In a prospective manner, we studied 293 patients with NSCLC in IIIB-IV clinical stage. They received standard chemotherapy. CEA was measured prior to treatment; EGFR and HER2 were evaluated by immunohistochemistry. BM development was confirmed by MRI in symptomatic patients.</p> <p>Results</p> <p>BM developed in 27, and 32% of patients at 1 and 2 years of diagnosis with adenocarcinoma (RR 5.2; 95% CI, 1.002–29; p = 0.05) and CEA ≥ 40 ng/mL (RR 11.4; 95% CI, 1.7–74; <it>p </it>< 0.01) as independent associated factors. EGFR and HER2 were not statistically significant. Masculine gender (RR 1.4; 95% CI, 1.002–1.9; <it>p </it>= 0.048), poor performance status (RR 1.8; 95% CI, 1.5–2.3; <it>p </it>= 0.002), advanced clinical stage (RR 1.44; 95% CI, 1.02–2; <it>p </it>= 0.04), CEA ≥ 40 ng/mL (RR 1.5; 95% CI, 1.09–2.2; <it>p </it>= 0.014) and EGFR expression (RR 1.6; 95% CI, 1.4–1.9; <it>p </it>= 0.012) were independent associated factors to worse OS.</p> <p>Conclusion</p> <p>High CEA serum level is a risk factor for BM development and is associated with poor prognosis in patients with advanced NSCLC. Surface expression of CEA in tumor cells could be the physiopathological mechanism for invasion to CNS.</p
Documenting the Recovery of Vascular Services in European Centres Following the Initial COVID-19 Pandemic Peak: Results from a Multicentre Collaborative Study
Objective: To document the recovery of vascular services in Europe following the first COVID-19 pandemic peak. Methods: An online structured vascular service survey with repeated data entry between 23 March and 9 August 2020 was carried out. Unit level data were collected using repeated questionnaires addressing modifications to vascular services during the first peak (March – May 2020, “period 1”), and then again between May and June (“period 2”) and June and July 2020 (“period 3”). The duration of each period was similar. From 2 June, as reductions in cases began to be reported, centres were first asked if they were in a region still affected by rising cases, or if they had passed the peak of the first wave. These centres were asked additional questions about adaptations made to their standard pathways to permit elective surgery to resume. Results: The impact of the pandemic continued to be felt well after countries’ first peak was thought to have passed in 2020. Aneurysm screening had not returned to normal in 21.7% of centres. Carotid surgery was still offered on a case by case basis in 33.8% of centres, and only 52.9% of centres had returned to their normal aneurysm threshold for surgery. Half of centres (49.4%) believed their management of lower limb ischaemia continued to be negatively affected by the pandemic. Reduced operating theatre capacity continued in 45.5% of centres. Twenty per cent of responding centres documented a backlog of at least 20 aortic repairs. At least one negative swab and 14 days of isolation were the most common strategies used for permitting safe elective surgery to recommence. Conclusion: Centres reported a broad return of services approaching pre-pandemic “normal” by July 2020. Many introduced protocols to manage peri-operative COVID-19 risk. Backlogs in cases were reported for all major vascular surgeries
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