131 research outputs found
Comment on Stallinga, P. (2023), Residence Time vs. Adjustment Time of Carbon Dioxide in the Atmosphere
No full textThe goal of Stallinga (2023), to address confusion about CO2 "residence time" and "adjustment time," is laudable. Unfortunately, the author, himself, has confused them. Dr. Stallinga made two key errors, the second following from the first. His first and most important mistake was his claim that, "the adjustment time is never larger than the residence time." That is backward. It is easily shown that the adjustment time is much longer than the residence time, because some of the processes which reduce the residence time do not reduce the adjustment time. He also wrote that neither the residence time nor the adjustment time is "longer than about 5 years." That is correct only for the residence time. It is wrong by a full order of magnitude for the adjustment time. The adjustment time can be determined from measurements, and it is approximately fifty years
Desenvolvimento de uma rede de sensores sem fios para monitorização de peixes
Get PDFDissertação de Mestrado, Engenharia Electrónica e Telecomunicações, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2014Este trabalho teve como principal objetivo desenvolver e implementar uma rede de sensores fios, capaz de monitorizar tanques de aquacultura. Dada a necessidade de um sistema de baixo custo e elevada flexibilidade para monitorização dos tanques de cultivo de esturjão Beluga por parte de empresa Caviar Portugal, foi efetuado um estudo detalhado sobre sensores, rede de sensoressem fios e sobre o protocolo ZigBee, permitido assim desenvolver um módulo de hardware capaz de efetuar o pretendido
Image based aberration retrieval using helical point spread functions
No full textA practical method for determining wavefront aberrations in optical systems based on the acquisition of an extended, unknown object is presented. The approach utilizes a conventional phase diversity approach in combination with a pupil-engineered, helical point spread function (PSF) to discriminate the aberrated PSF from the object features. The analysis of the image’s power cepstrum enables an efficient retrieval of the aberration coefficients by solving a simple linear system of equations. An extensive Monte Carlo simulation is performed to demonstrate that the approach makes it possible to measure low-order Zernike modes including defocus, primary astigmatism, coma, and trefoil. The presented approach is tested experimentally by retrieving the two-dimensional aberration distribution of a test setup by imaging an extended, unknown scene.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ImPhys/Computational ImagingImPhys/Imaging Physic
Development of biosensors for molecular analysis
Get PDFTese dout., Ciências Biotecnológicas, Universidade do Algarve, 2007This thesis deals with the application of piezoelectric sensors, namely quartz crystal
microbalances (QCM), for the study of molecular interactions and for biomedical purposes.
Piezoelectric transduction allows the detection of biorecognition events and its operation
depends on the mechanical vibration of the crystal whose resonance frequency is sensible to
surface mass changes. But in liquid medium these sensors also respond to the properties of
solutions and adsorbed films. Thus, a major aspect explored in this thesis is the expansion of
the physical understanding of the behavior of these sensors in liquid medium and also how
organic or biological layers can affect the results and their interpretation. This was achieved
using impedance analysis where the behavior of the piezoelectric sensor is interpreted with
the help of equivalent electric RLC circuits. The potential electroacoustic interference of
charged species in solution was particularly studied and a new equivalent circuit is proposed
in order to detect and quantify these effects with the assistance of impedance analysis.
The efficiency of the key steps taken for the development of our QCM system, was
experimentally demonstrated with the qualitative and quantitative analysis of the process of
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11-hydroxy-1-undecanothiol SAMs (self-assembled monolayers) formation and the
recognition of streptavidin in aqueous medium using biotin modified sensors.
Finally the work was focused on the development of a new detection tool for the HIV1 virus
using piezoelectric immunosensors based on recombinant antibodies to detect the Vif
molecule (virion infectivity factor). The developed immunosensors selectively detected Vif in
aqueous solutions and presented specificity and good sensibility when detecting the target
protein in complex samples like mixtures of proteins and cell extracts
Optical trapping at low numerical aperture
Get PDFA theory of optical trapping at low Numerical Aperture (NA) is presented. The theory offers an analytical description of the competition between the stabilizing gradient and destabilizing scattering force. The trade-off can be characterized by a single dimensionless trapping parameter, which increases with bead size to wavelength ratio ?/?, m, NA and refractive index contrast m and decreases with NA. The gradient force dominates for small trapping parameters, the scattering force for large trapping parameters. The potential well depth, maximum forces and trap stiffness as a function of the three parameters (?/?, m, NA ) can be mapped onto universal functions of the trapping parameter. These functions do not depend on any free parameter. The universal well depth and maximum force curves match with numerical results based on the exact multipole expansion of the optical trapping force. The paraxial limit of low NA is relevant for compact optical tweezers based on Optical Pickup Units known from optical data storage.Imaging Science & TechnologyApplied Science
Residence Time vs. Adjustment Time of Carbon Dioxide in the Atmosphere
Get PDFWe study the concepts of residence time vs. adjustment time time for carbon dioxide in the atmosphere. The system is analyzed with a two-box first-order model. Using this model, we reach three important conclusions: (1) The adjustment time is never larger than the residence time and can, thus, not be longer than about 5 years. (2) The idea of the atmosphere being stable at 280 ppm in pre-industrial times is untenable. (3) Nearly 90% of all anthropogenic carbon dioxide has already been removed from the atmosphere
The effect of water related traps on the reliability of organic based transistors
No full textThe electrical stability of metal-insulator semiconductor (MIS) capacitors and field-effect transistor structures based in organic semiconductors were investigated. The device characteristics were studied using steady state measurements AC admittance measurements as well as techniques for addressing trap states. Temperature-dependent measurements show clear evidence that an electrical instability occurs above 200 K and is caused by an electronic trapping process. Experimental results show that water is responsible for the trapping mechanism. (c) 2006 Elsevier B.V. All rights reserved
Single emitter localization analysis in the presence of background
No full textLocalization microscopy for imaging at the nano-scale relies on the quality of fitting the emitter positions from the measured light spots. The type and magnitude of the noise in the detection process, the background light level and the Point Spread Function model that is used in the fit are of paramount importance for the precision and accuracy of the fit. We present several developments on the computational methods and performance limits of single emitter localization, targeting specifically these three aspects.ImPhys/Imaging PhysicsApplied Science
Optimal transfer functions for bandwidth-limited imaging
No full textOne of the fundamental limits of classical optical microscopy is the diffraction limit of optical resolution. It results from the finite bandwidth of the optical transfer function (or OTF) of an optical microscope, which restricts the maximum spatial frequencies that are transmitted by a microscope. However, given the frequency support of the OTF, which is fully determined by the used optical hardware, an open and unsolved question is what is the optimal amplitude and phase distribution of spatial frequencies across this support that delivers the "sharpest"possible image. In this paper, we will answer this question and present a general rule how to find the optimal OTF for any given imaging system. We discuss our result in the context of optical microscopy, by considering in particular the cases of wide-field microscopy, confocal image scanning microscopy (ISM), 4pi microscopy, and structured illumination microscopy (SIM). Our results are important for finding optimal deconvolution algorithms for microscopy images, and we demonstrate this experimentally on the example of ISM. They can also serve as a guideline for designing optical systems that deliver best possible images, and can be easily generalized to nonoptical imaging such as telescopic imaging, ultrasound imaging, or magnetic resonance imaging.ImPhys/Imaging Physic
Nonlinear optical trapping effect with reverse saturable absorption
No full textNonlinear responses of nanoparticles induce enlightening phenomena in optical tweezers. With the gradual increase in optical intensity, effects from saturable absorption (SA) and reverse SA (RSA) arise in sequence and thereby modulate the nonlinear properties of materials. In current nonlinear optical traps, however, the underlying physical mechanism is mainly confined within the SA regime because threshold values required to excite the RSA regime are extremely high. Herein, we demonstrate, both in theory and experiment, nonlinear optical tweezing within the RSA regime, proving that a fascinating composite trapping state is achievable at ultrahigh intensities through an optical force reversal induced through nonlinear absorption. Integrated results help in perfecting the nonlinear optical trapping system, thereby providing beneficial guidance for wider applications of nonlinear optics. ImPhys/Adam groupImPhys/OpticsImPhys/Stallinga grou
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