The physics of optimal decision making: A formal analysis of models of performance in two-alternative forced-choice tasks

In this article, the authors consider optimal decision making in two-alternative forced-choice (TAFC) tasks. They begin by analyzing 6 models of TAFC decision making and show that all but one can be reduced to the drift diffusion model, implementing the statistically optimal algorithm (most accurate for a given speed or fastest for a given accuracy). They prove further that there is always an optimal trade-off between speed and accuracy that maximizes various reward functions, including reward rate (percentage of correct responses per unit time), as well as several other objective functions, including ones weighted for accuracy. They use these findings to address empirical data and make novel predictions about performance under optimality.

Variational free energy and the Laplace approximation

This note derives the variational free energy under the Laplace approximation, with a focus on accounting for additional model complexity induced by increasing the number of model parameters. This is relevant when using the free energy as an approximation to the log-evidence in Bayesian model averaging and selection. By setting restricted maximum likelihood (ReML) in the larger context of variational learning and expectation maximisation (EM), we show how the ReML objective function can be adjusted to provide an approximation to the log-evidence for a particular model. This means ReML can be used for model selection, specifically to select or compare models with different covariance components. This is useful in the context of hierarchical models because it enables a principled selection of priors that, under simple hyperpriors, can be used for automatic model selection and relevance determination (ARD). Deriving the ReML objective function, from basic variational principles, discloses the simple relationships among Variational Bayes, EM and ReML. Furthermore, we show that EM is formally identical to a full variational treatment when the precisions are linear in the hyperparameters. Finally, we also consider, briefly, dynamic models and how these inform the regularisation of free energy ascent schemes, like EM and ReML.

The number of scholarly documents on the public web

The number of scholarly documents available on the web is estimated using capture/recapture methods by studying the coverage of two major academic search engines: Google Scholar and Microsoft Academic Search. Our estimates show that at least 114 million English-language scholarly documents are accessible on the web, of which Google Scholar has nearly 100 million. Of these, we estimate that at least 27 million (24%) are freely available since they do not require a subscription or payment of any kind. In addition, at a finer scale, we also estimate the number of scholarly documents on the web for fifteen fields: Agricultural Science, Arts and Humanities, Biology, Chemistry, Computer Science, Economics and Business, Engineering, Environmental Sciences, Geosciences, Material Science, Mathematics, Medicine, Physics, Social Sciences, and Multidisciplinary, as defined by Microsoft Academic Search. In addition, we show that among these fields the percentage of documents defined as freely available varies significantly, i.e., from 12 to 50%.

Mutation-selection balance: ancestry, load, and maximum principle

We analyze the equilibrium behavior of deterministic haploid mutation-selection models. To this end, both the forward and the time-reversed evolution processes are considered. The stationary state of the latter is called the ancestral distribution, which turns out as a key for the study of mutation-selection balance. We find that the ancestral genotype frequencies determine the sensitivity of the equilibrium mean fitness to changes in the corresponding fitness values and discuss implications for the evolution of mutational robustness. We further show that the difference between the ancestral and the population mean fitness, termed mutational loss, provides a measure for the sensitivity of the equilibrium mean fitness to changes in the mutation rate. The interrelation of the loss and the mutation load is discussed. For a class of models in which the number of mutations in an individual is taken as the trait value, and fitness is a function of the trait, we use the ancestor formulation to derive a simple maximum principle, from which the mean and variance of fitness and the trait may be derived; the results are exact for a number of limiting cases, and otherwise yield approximations which are accurate for a wide range of parameters. These results are applied to threshold phenomena caused by the interplay of selection and mutation (known as error thresholds). They lead to a clarification of concepts, as well as criteria for the existence of error thresholds.

Experimental determination of baseball spin and lift

The aim of this study was to develop a new method for the determination of lift on spinning baseballs. Inertial trajectories of (a) ball surface markers during the first metre of flight and (b) the centre of mass trajectory near home-plate were measured in a pitch using high-speed video. A theoretical model was developed, incorporating aerodynamic Magnus-Robins lift, drag and cross forces, which predicts the centre of mass and marker trajectories. Parameters including initial conditions and aerodynamic coefficients were estimated iteratively by minimizing the error between predicted and measured trajectories. We compare the resulting lift coefficients and spin parameter values with those of previous studies. Lift on four-seam pitches can be as much as three times that of two-seam pitches, although this disparity is reduced for spin parameters greater than 0.4.

Baseball

In this study, we aimed to determine the direction of the spin axis and the spin rate of pitched baseballs and to estimate the associated aerodynamic forces. In addition, the effects of the spin axis direction and spin rate on the trajectory of a pitched baseball were evaluated. The trajectories of baseballs pitched by both a pitcher and a pitching machine were recorded using four synchronized video cameras (60 Hz) and were analyzed using direct linear transform (DLT) procedures. A polynomial function using the least squares method was used to derive the time-displacement relationship of the ball coordinates during flight for each pitch. The baseball was filmed immediately after ball release using a high-speed video camera (250 Hz), and the direction of the spin axis and the spin rate (omega) were calculated based on the positional changes of the marks on the ball. The lift coefficient was correlated closely with omegasinalpha (r = 0.860), where alpha is the angle between the spin axis and the pitching direction. The term omegasinalpha represents the vertical component of the velocity vector. The lift force, which is a result of the Magnus effect occurring because of the rotation of the ball, acts perpendicularly to the axis of rotation. The Magnus effect was found to be greatest when the angular and translational velocity vectors were perpendicular to each other, and the break of the pitched baseball became smaller as the angle between these vectors approached 0 degrees. Balls delivered from a pitching machine broke more than actual pitcher's balls. It is necessary to consider the differences when we use pitching machines in batting practice.

Source separation in astrophysical maps using independent factor analysis

A microwave sky map results from a combination of signals from various astrophysical sources, such as cosmic microwave background radiation, synchrotron radiation and galactic dust radiation. To derive information about these sources, one needs to separate them from the measured maps on different frequency channels. Our insufficient knowledge of the weights to be given to the individual signals at different frequencies makes this a difficult task. Recent work on the problem led to only limited success due to ignoring the noise and to the lack of a suitable statistical model for the sources. In this paper, we derive the statistical distribution of some source realizations, and check the appropriateness of a Gaussian mixture model for them. A source separation technique, namely, independent factor analysis, has been suggested recently in the literature for Gaussian mixture sources in the presence of noise. This technique employs a three layered neural network architecture which allows a simple, hierarchical treatment of the problem. We modify the algorithm proposed in the literature to accommodate for space-varying noise and test its performance on simulated astrophysical maps. We also compare the performances of an expectation-maximization and a simulated annealing learning algorithm in estimating the mixture matrix and the source model parameters. The problem with expectation-maximization is that it does not ensure global optimization, and thus the choice of the starting point is a critical task. Indeed, we did not succeed to reach good solutions for random initializations of the algorithm. Conversely, our experiments with simulated annealing yielded initialization-independent results. The mixing matrix and the means and coefficients in the source model were estimated with a good accuracy while some of the variances of the components in the mixture model were not estimated satisfactorily.

Female medical physicists: The results of a survey carried out by the International Organization for Medical Physics

INTRODUCTION

The gender composition of the existing medical physicist (MP) workforce around the world is basically unknown. The International Organization for Medical Physics (IOMP) performed a survey in order to investigate the number of MPs in countries around the world and the percentage of women MPs compared to total number of MPs.

MATERIALS AND METHODS

A simple online questionnaire prepared as a Google Forms survey asking the country, the total number of MPs, the number of female MPs and finally the gender of the person providing the data was sent in mid-March 2013 to six regional member organizations of IOMP, as well as contact points in many member countries.

RESULTS

Sixty-six countries responded to the survey by mid-July 2013. Fifty two percent of those who filled the form were females, the rest males. The total number of MPs was 17,024, of which 28% were female (4807). The median values of percentages of females were 21% in the USA, 47% in Europe, 35% in Asia, 33% in Africa and 24% in Latin America.

CONCLUSION

This is the first international survey that investigates the number and percentage of female MPs around the world. There are European countries that are far away from the target set by European Commission (40%) whereas in countries in the Middle East and Asia, female MPs actually outnumber males. This study is the first step in a more in-depth study that needs to be taken in near future.

Simulations of large acoustic scintillations in the straits of Florida

Using a full-wave acoustic model, Monte Carlo numerical studies of intensity fluctuations in a realistic shallow water environment that simulates the Straits of Florida, including internal wave fluctuations and bottom roughness, have been performed. Results show that the sound intensity at distant receivers scintillates dramatically. The acoustic scintillation index SI increases rapidly with propagation range and is significantly greater than unity at ranges beyond about 10 km. This result supports a theoretical prediction by one of the authors. Statistical analyses show that the distribution of intensity of the random wave field saturates to the expected Rayleigh distribution with SI= 1 at short range due to multipath interference effects, and then SI continues to increase to large values. This effect, which is denoted supersaturation, is universal at long ranges in waveguides having lossy boundaries (where there is differential mode attenuation). The intensity distribution approaches a log-normal distribution to an excellent approximation; it may not be a universal distribution and comparison is also made to a K distribution. The long tails of the log-normal distribution cause "acoustic intermittency" in which very high, but rare, intensities occur.

Study of the comparison of the methods of equivalent sources and boundary element methods for near-field acoustic holography

Boundary element methods (BEM) based near-field acoustic holography (NAH) has been used successfully in order to reconstruct the normal velocity on an arbitrarily shaped structure surface from measurements of the pressure field on a nearby conformal surface. An alternative approach for this reconstruction on a general structure utilizes the equivalent sources method (ESM). In ESM the acoustic field is represented by a set of point sources located over a surface that is close to the structure surface. This approach is attractive mainly for its simplicity of implementation and speed. In this work ESM as an approximation of BEM based NAH is studied and the necessary conditions for the successful application of this approach in NAH is discussed. A cylindrical fuselage surface excited by a point force as an example to validate the results is used.

Phased array focusing with guided waves in a viscoelastic coated hollow cylinder

Guided wave phased array focusing has shown many advantages in long-range pipeline inspection, such as, longer inspection distance, greater wave penetration power and higher detection resolution. Viscoelastic coatings applied to a large percentage of pipes for protection purposes created some challenges in terms of focusing feasibility and inspection ability. Previous studies were all based on bare pipe models. In this work, guided wave phased array focusing in viscoelastic coated pipes is studied for the first time. Work was carried out with both numerical and experimental methods. A three-dimensional finite element model was developed for quantitatively and systematically modeling guided waves in pipes with different viscoelastic materials. A method of transforming measured coating properties to finite element method inputs was created in order to create a physically based model of guided waves in coated pipes. Guided wave focusing possibilities in viscoelastic coated pipes and the effects from coatings were comprehensively studied afterwards. A comparison of focusing and nonfocusing inspections was also studied quantitatively in coated pipe showing that focusing increased the wave energy and consequently the inspection ability tremendously. This study provides an important base line and guidance for guided wave propagation and focusing in a real field pipeline under various coating and environmental conditions.

Circaseptennian (about 7-year) periodicity in the distribution of birth years of Nobel laureates for physics

The distribution of birth years for Nobel physicists shows a circaseptennian (about 7-year) periodicity. This observation extends an earlier observation of a circaseptennian pattern in the distribution of birth years for early quantum physicists. In both categories, birth rate tends to maximize in years belonging to the (7n + 4) phase.

Modal decomposition method for acoustic impedance testing in square ducts

Accurate duct acoustic propagation models are required to predict and reduce aircraft engine noise. These models ultimately rely on measurements of the acoustic impedance to characterize candidate engine nacelle liners. This research effort increases the frequency range of normal-incidence acoustic impedance testing in square ducts by extending the standard two-microphone method (TMM), which is limited to plane wave propagation, to include higher-order modes. The modal decomposition method (MDM) presented includes four normal modes in the model of the sound field, thus increasing the bandwidth from 6.7 to 13.5 kHz for a 25.4 mm square waveguide. The MDM characterizes the test specimen for normal- and oblique-incident acoustic impedance and mode scattering coefficients. The MDM is first formulated and then applied to the measurement of the reflection coefficient matrix for a ceramic tubular specimen. The experimental results are consistent with results from the TMM for the same specimen to within the 95% confidence intervals for the TMM. The MDM results show a series of resonances for the ceramic tubular material exhibiting a monotonic decrease in the resonant peaks of the acoustic resistance with increasing frequency, resembling a rigidly-terminated viscous tube, and also evidence of mode scattering is visible at the higher frequencies.

Simulations of optoacoustic wave propagation in light-absorbing media using a finite-difference time-domain method

Optoacoustic (OA) imaging is an emerging technology that combines the high optical contrast of tissues with the high spatial resolution of ultrasound. Taking full advantage of OA imaging requires a better understanding of OA wave propagation in light-absorbing media. Current simulation methods are mainly based on simplified conditions such as thermal confinement, negligible viscosity, and homogeneous acoustic properties throughout the image object. In this study a new numerical approach is proposed based on a finite-difference time-domain (FDTD) method to solve the general OA equations, comprising the continuity, Navier-Stokes, and heat-conduction equations. The FDTD code was validated using a benchmark problem that has an approximate analytical solution. OA experiments were also conducted and data were in good agreement with those predicted by the FDTD method. Characteristics of simulated OA waveforms and OA images were discussed. The simulator was also employed to study wavefront distortion in OA breast imaging.

Bibliometric analysis of the 100 most cited articles on cervical cancer radiotherapy

PURPOSE

To identify the 100 most cited research articles on cervical cancer radiotherapy.

METHODS

The Web of Science and Scopus databases were searched to identify the 100 most cited articles on cervical cancer radiotherapy as of September 29, 2019. Articles were ranked based on the total citations received from 2 databases. One hundred articles about radiotherapy for cervical cancer were identified. The following important information was extracted: author, journal, year and month of publication, country or region, and radiotherapy technologies.

RESULTS

The 100 most cited articles on cervical cancer radiotherapy were published between 1964 and 2016, and the total citations from 2 databases ranged from 3478 to 211, including a total of 49,262 citations as of September 29, 2019. The index of citations per year ranged from 170.4 to 13.1. These articles were from 16 countries or regions, with most publications being from the United States (n = 38), followed by Austria (n = 15), Canada (n = 8), France (n = 8) and the United Kingdom (n = 7). The International Journal of Radiation Oncology, Biology, Physics produced the most articles (n = 42), followed by Radiotherapy and Oncology (n = 13), Cancer (n = 8) and Journal of Clinical Oncology (n = 7). These articles were categorized as original studies (n = 86), recommendations (n = 5), guidelines (n = 5) and reviews (n = 4). Of the 100 most cited articles, intracavitary brachytherapy (n = 50) and 3-dimensional conformal radiotherapy (n = 34) were the most commonly used treatment techniques.

CONCLUSION

To the best of our knowledge, this is the first report and analysis of the most cited articles on cervical cancer radiotherapy. This bibliographic study presents the history of technological development in external radiation therapy and brachytherapy. Brachytherapy is an indispensable part of radiotherapy for cervical cancer. The International Journal of Radiation Oncology Biology Physics is the journal with the most publications related to cervical cancer radiotherapy.

A robust noniterative method for obtaining scattering strengths of multiply scattering point targets

A noniterative method based on the least squares technique is presented in this letter to obtain the scattering strengths of multiply scattering point targets. Benefiting from the least squares' optimization property, this new method achieves a good estimation of the scattering strengths. Compared with the noniterative method proposed in a recent paper [E. A. Marengo and F. K. Gruber "Noniterative analytical formula for inverse scattering of multiply scattering point targets," J. Acoust. Soc. Am. 120, 3782-3788 (2006)], the new method produces more accurate results in the presence of noise.

Assessing Pharmacy Students' Scientific Reasoning After Completing a Physics Course Taught Using Active-Learning Methods

Objective. To assess the degree of change in the level of scientific reasoning in first-year pharmacy students by applying active-learning methods during a physics course. Methods. The efficiency of the active-learning methods of experimentation and discussion in the development of scientific reasoning in 90 pharmacy students was determined by comparing it to the efficiency of using traditional learning methods (eg, lecture) with 60 students. The Lawson Classroom Test of Scientific Reasoning was used to measure change. Results. The data from this five-year study showed that of all pharmacy students in the active-learning group who were functioning on a stable or transitional level of thinking at the time of the pretest, 28.6% achieved a shift towards a higher level of scientific thinking. The active-learning group also achieved better overall results in the course. Conclusion. Using active-learning methods (experimentation and discussion) in a physics course enabled pharmacy students to better master the content. By elevating students' level of scientific reasoning, a foundation for using evidence-based medicine was established.

A genealogical approach to academic success

We analyse academic success using a genealogical approach to the careers of over 95,000 scientists in mathematics and associated fields in physics and chemistry. We look at the effect of Ph.D. supervisors (one's mentors) on the number of Ph.D. students that one supervises later on (one's mentees) as a measure of academic success. Supervisors generally provide important inputs in Ph.D. projects, which can have long-lasting effects on academic careers. Moreover, having multiple supervisors exposes one to a diversity of inputs. We show that Ph.D. students benefit from having multiple supervisors instead of a single one. The cognitive diversity of mentors has a subtler effect in that it increases both the likelihood of success (having many mentees later on) and failure (having no mentees at all later on). We understand the effect of diverse mentorship as a high-risk, high-gain strategy: the recombination of unrelated expertise often fails, but sometimes leads to true novelty.

Computation of the homogeneous and forced solutions of a finite length, line-driven, submerged plate

A formulation is developed to predict the vibration response of a finite length, submerged plate due to a line drive. The formulation starts by describing the fluid in terms of elliptic cylinder coordinates, which allows the fluid loading term to be expressed in terms of Mathieu functions. By moving the fluid loading term to the right-hand side of the equation, it is considered to be a force. The operator that remains on the left-hand side is the same as that of the in vacuo plate: a fourth-order, constant coefficient, ordinary differential equation. Therefore, the problem appears to be an inhomogeneous ordinary differential equation. The solution that results has the same form as that of the in vacuo plate: the sum of a forced solution, and four homogeneous solutions, each of which is multiplied by an arbitrary constant. These constants are then chosen to satisfy the structural boundary conditions on the two ends of the plate. Results for the finite plate are compared to the infinite plate in both the wave number and spatial domains. The theoretical predictions of the plate velocity response are also compared to results from finite element analysis and show reasonable agreement over a large frequency range.

Louisiana: a model for advancing regional e-Research through cyberinfrastructure

Louisiana researchers and universities are leading a concentrated, collaborative effort to advance statewide e-Research through a new cyberinfrastructure: computing systems, data storage systems, advanced instruments and data repositories, visualization environments and people, all linked together by software programs and high-performance networks. This effort has led to a set of interlinked projects that have started making a significant difference in the state, and has created an environment that encourages increased collaboration, leading to new e-Research. This paper describes the overall effort, the new projects and environment and the results to date.

Impact of perforation impedance on the transmission loss of reactive and dissipative silencers

The effect of perforation impedance on the acoustic behavior of reactive and dissipative silencers is investigated using experimental and computational approaches. The boundary element method (BEM) is applied for the prediction of transmission loss of silencers with different perforation geometries. The variations are considered in the porosity (8.4 and 25.7%) and hole diameter (0.249 and 0.498 cm) of perforations for both reactive and dissipative silencers, as well as the fiber filling density (100 and 200 kg/m3) for the latter. The acoustic impedance for a number of perforations in contact with air alone and fibrous material has been incorporated into the predictions, which are then compared with the measured transmission loss using an impedance tube setup. The results demonstrate the significance of the accuracy of the perforation impedance in the predictions for both reactive and dissipative silencers.

Noniterative analytical formula for inverse scattering of multiply scattering point targets

This paper derives, in the exact framework of multiple scattering theory for point targets, a noniterative analytical formula for the nonlinear inversion of the target scattering strengths from the scattering or response matrix that can be applied after the target positions have been estimated in a previous step via, e.g., time-reversal multiple signal classification or another approach. The new formula provides a noniterative analytical alternative to the iterative numerical solution approach for the same problem presented in a recent paper [A. J. Devaney, E. A. Marengo, and F. K. Gruber, "Time-reversal-based imaging and inverse scattering of multiply scattering point targets," J. Acoust. Soc. Am. 118, 3129-3138 (2005)]. The two methods (noniterative versus iterative) are comparatively investigated with two numerical examples.

Building a scientific data grid with DiGS

We provide an insight into the challenge of building and supporting a scientific data infrastructure with reference to our experience working with scientists from computational particle physics and molecular biology. We illustrate how, with modern high-performance computing resources, even small scientific groups can generate huge volumes (petabytes) of valuable scientific data and explain how grid technology can be used to manage, publish, share and curate these data. We describe the DiGS software application, which we have developed to meet the needs of smaller communities and we have highlighted the key elements of its functionality.