arXiv subjects

George C. Cardoso

Publications and source records attributed to George C. Cardoso.

11 recordsLinked to original sources

arXiv2021

A battery-resistor analogy for further insights on measurement uncertainties

We use analogies to give introductory laboratory students intuition about measurement uncertainties. Using a battery-resistor circuit we discuss uncertainty concepts and derive expressions for uncertainty of the mean and sums of uncertainties. Finally, we draw attention to the fact that the interpretation of standard deviation as uncertainty depends on the statistical distribution of the data, while the interpretation of uncertainty of the mean is largely insensitive to such distribution, especially for large samples. If the resistor in the battery-resistor circuit is a resistive loudspeaker, the uncertainty or noise is literally the acoustic power of the sound produced by such noise. In the sound analogy the statistical distribution of the noise is related to its timbre.

physics.ed-ph↗

arXiv2019

Citation network centrality: a scientific awards predictor?

The $K$-index is an easily computable centrality index in complex networks, such as a scientific citations network. A researcher has a $K$-index equal to $K$ if he or she is cited by $K$ articles that have at least $K$ citations. The $K$-index has several advantages over Hirsh's $h$-index and, in previous studies, has shown better correlation with Nobel prizes than any other index given by the {\em Web of Science}, including the $h$-index. It is plausible that researchers who are the most connected to other scientifically well-connected researchers are the most likely to be doing important work and more likely to be awarded major prizes in a given area. However, the correlation found does not imply causation. Here we perform an experiment using the $K$-index, producing a shortlist of twelve candidates for major scientific prizes, including the Physics Nobel award, in the near future. For example, our top-12 $K$-index list naturally selects the 2019 Nobel laureate, James Peebles. The list can be updated annually and should be compared to laureates of the following years

cs.DL↗

arXiv2018

Skin optical attenuation coefficient modulation with arterial pulsation

Video plethysmographic (vPPG) signals arise from subtle color modulations in reflected light. vPPG signals can be used to monitor vital signs remotely in a noninvasive manner. We have used optical coherence tomography (OCT) imaging to find whether vPPG signals may result from skin optical properties being modulated by arterial transmural pressure propagation. Our results confirm this hypothesis and show that the attenuation coefficient of even the most external, non-vascularized skin, changes at the same frequency as the arterial pulsation.

physics.bio-ph↗

arXiv2017

A simple centrality index for scientific social recognition

We introduce a new centrality index for bipartite network of papers and authors that we call $K$-index. The $K$-index grows with the citation performance of the papers that cite a given researcher and can seen as a measure of scientific social recognition. Indeed, the $K$-index measures the number of hubs, defined in a self-consistent way in the bipartite network, that cites a given author. We show that the $K$-index can be computed by simple inspection of the Web of Science platform and presents several advantages over other centrality indexes, in particular Hirsch $h$-index. The $K$-index is robust to self-citations, is not limited by the total number of papers published by a researcher as occurs for the $h$-index and can distinguish in a consistent way researchers that have the same $h$-index but very different scientific social recognition. The $K$-index easily detects a known case of a researcher with inflated number of papers, citations and $h$-index due to scientific misconduct. Finally, we show that, in a sample of twenty-eight physics Nobel laureates and twenty-eight highly cited non-Nobel-laureate physicists, the $K$-index correlates better to the achievement of the prize than the number of papers, citations, citations per paper, citing articles or the $h$-index. Clustering researchers in a $K$ versus $h$ plot reveals interesting outliers that suggest that these two indexes can present complementary independent information.

cs.DL↗

arXiv2016

Method to study student engagement uniformity in a classroom

We present a method to study engagement level uniformity in a class of students. We validate our method by comparing two semesters taught using different methods in a physics and mathematics course. The first semester used conventional methods while the second semester used graphic spreadsheets-based laboratories and homework before the introduction of formal methods. We found that engagement of the students that were below the median at the beginning of the semester improved by an order of magnitude (by our metric) while the engagement level of students initially above the median did not change.

physics.ed-ph↗

arXiv2016

Blood Pulsation Intensity Video Mapping

In this study, we make non-invasive, remote, passive measurements of the heart beat frequency and determine the map of blood pulsation intensity in a region of interest (ROI) of skin. The ROI used was the forearm of a volunteer. The method employs a regular video camera and visible light, and the video acquisition takes less than 1 minute. The mean cardiac frequency found in our volunteer was within 1 bpm of the ground-truth value simultaneously obtained via earlobe plethysmography. Using the signals extracted from the video images, we have determined an intensity map for the blood pulsation at the surface of the skin. In this paper we present the experimental and data processing details of the work and well as limitations of the technique. ----------------------------------------- Neste estudo medimos a frequência cardíaca de forma não invasiva, remota e passiva e determinamos o mapa da atividade de pulsação sanguínea numa região de interesse (ROI) da pele. A ROI utilizada foi o antebraço de um voluntário. O método utiliza uma câmara de vídeo comum e luz visível como processo de aquisição do vídeo durando menos de 1 minuto. A frequência cardíaca média encontrada tem erro em torno de 1 batimento por minuto em relação a uma medida simultânea usando fotopletismografia de lóbulo de orelha. A partir dos sinais extraídos das imagens de vídeo, determinamos um mapa da intensidade da pulsação sanguínea na superfície da pele. Apresentamos detalhes experimentais e de processamento dos sinais, assim como limitações da técnica.

physics.med-ph↗

arXiv2016

Mobility-limited polyarylamine biscarbonate ester (PABC) /[6,6]-phenyl $C_{61}$ butyric acid methyl ester (PCBM) bulk heterojunction photovoltaic device

Photovoltaic (PV) devices made from blends of a polyarylamine biscarbonate ester (PABC) and [6,6]-phenyl $C_{61}$ butyric acid methyl ester (PCBM) have been fabricated and characterized. PABC is a hole transporting co-polymer prepared from reacting N,N'diphenyl-N,N'bis(3-hydroxyphenyl)1,1;biphenyl(4,4'diamine), diethylene glycol bischloroformate, and triethylemine. By varying the polymer loading in the blend, optimal power conversion efficiency (PCE) of approximately 0.45\% has been achieved for a blend consisting of 25 wt\% PABC, which is an order of magnitude higher than the PCE for a 45 wt\% blend. The optimal ratio is at about 0.44:0.56 molar ratio of the active hole transporting to electron transporting moieties. Results of mobility studies suggest that blends with higher PABC loading have efficiencies limited by 'hole' transport. Also responsible for the lower efficiency at higher PABC concentrations was optical filtering. The efficiency does not appear to be limited by deep charge trapping. Density functional theory calculations conducted pointed toward a strong localization of the frontier orbitals, which might offer an explanation for the low PABC hole mobility. Calculated frontier orbital energy levels found band gap to be consistent with the $V_{OC}$ measured.

physics.chem-ph↗

arXiv2016

Finite symmetries in agent-based epidemic models

We present an algorithm which explores permutation symmetries to describe the time evolution of agent-based epidemic models. The main idea to improve computation times relies on restricting the stochastic process to one sector of the vector space, labeled by a single permutation eigenvalue. In this scheme, the transition matrix reduces to block diagonal form, enhancing computational performance.

q-bio.PE↗

arXiv2016

Fast computation method for comprehensive agent-level epidemic dissemination in networks

Two simple agent based models are often employed in epidemic studies: the susceptible-infected (SI) and the susceptible-infected-susceptible (SIS). Both models describe the time evolution of infectious diseases in networks in which vertices are either susceptible (S) or infected (I) agents. Predicting the effects of disease spreading is one of the major goals in epidemic studies, but often restricted to numerical simulations. Analytical methods using operatorial content are subjected to the asymmetric eigenvalue problem, restraining the usability of standard perturbative techniques, whereas numerical methods are limited to small populations since the vector space increases exponentially with population size $N$. Here, we propose the use of the squared norm of probability vector, $\vert P(t)\vert ^2$, to obtain an algebraic equation which allows the evaluation of stationary states, in time independent Markov processes. The equation requires eigenvalues of symmetrized time generators, which take full advantage of system symmetries, reducing the problem to an $O(N)$ sparse matrix diagonalization. Standard perturbative methods are introduced, creating precise tools to evaluate the effects of health policies.

physics.soc-ph↗

arXiv2004

In-Situ absolute phase detection of a microwave field via incoherent fluorescence

Measuring the amplitude and the absolute phase of a monochromatic microwave field at a specific point of space and time has many potential applications, including precise qubit rotations and wavelength quantum teleportation. Here we show how such a measurement can indeed be made using resonant atomic probes, via detection of incoherent fluorescence induced by a laser beam. This measurement is possible due to self-interference effects between the positive and negative frequency components of the field. In effect, the small cluster of atoms here act as a highly localized pick-up coil, and the fluorescence channel acts as a transmission line.

quant-ph↗

arXiv2004

Effects of the Bloch-Siegert Oscillation on the Precision of Qubit Rotations: Direct Two-Level vs. Off-Resonant Raman Excitation

In a direct two-level qubit system, when the Rabi frequency is comparable to the resonance frequency, the rotating wave approximation is not appropriate. In this case, the Rabi oscillation is accompanied by another oscillation at twice the frequency of the driving field, the so called Bloch-Siegert oscillation (BSO), which depends on the initial phase of the driving field. This oscillation may restrict the precise rotation of a qubit made of direct two-level system. Here, we show that in case of an effectively two-level lambda system, the BSO is inherently negligible, implying a greater precision for rotation of a qubit made of such a lambda system when compared to a direct two-level qubit in a strong driving field.

quant-ph↗