Real-time quantitative Schlieren imaging by fast Fourier demodulation of a checkered backdrop

A quantitative synthetic Schlieren imaging (SSI) method based on fast Fourier demodulation is presented. Instead of a random dot pattern (as usually employed in SSI), a 2D periodic pattern (such as a checkerboard) is used as a backdrop to the refractive object of interest. The range of validity and accuracy of this "Fast Checkerboard Demodulation" (FCD) method are assessed using both synthetic data and experimental recordings of patterns optically distorted by small waves on a water surface. It is found that the FCD method is at least as accurate as sophisticated, multi-stage, digital image correlation (DIC) or optical flow (OF) techniques used with random dot patterns, and it is significantly faster. Efficient, fully vectorized, implementations of both the FCD and DIC/OF schemes developed for this study are made available as Matlab scripts.Comment: 21 pages, 7 figures, 1 appendi

The Role of Diet in the Onset of Depression: A Biochemical Connection Between Nutrition and Mental Health

Depression is a major clinical concern, having a complex onset and the presence of multiple, often unidentifiable causes. Depression affects millions of individuals worldwide, with a high prevalence in regions of the world with a Western-style diet as compared to regions with a Mediterranean diet. A Western-style diet consists of foods high in sugar, fat, and processed meats and grains, whereas the Mediterranean diet contains significantly more vegetables, fruits, lean meats, and whole grains. The link between diet and mental health disorders has implications for individuals of all ages who are hesitant to turn to medication. In addition to presenting a closer examination of the biochemical foundation of depression, this review focuses on the effects of factors such as food-related inflammation, nutrition, and probiotics in symptom development

Parental Incarceration, Child Homelessness, and the Invisible Consequences of Mass Imprisonment

Although the share of the homeless population composed of African Americans and children has grown since at least the early 1980s, the causes of these changes remain poorly understood. This article implicates mass imprisonment in at least the second of these shifts by considering the effects of parental incarceration on child homelessness using data from the Fragile Families and Child Wellbeing Study. These are the only data that simultaneously represent a contemporary cohort of the urban children most at risk of homelessness, establish appropriate time-order between parental incarceration and child homelessness, and control for prior housing, which is vital given the imprisonment-homelessness nexus. Results show strong effects of recent but not distal parental incarceration on the risk of child homelessness. They also show that effects are concentrated among African American children. Taken together, results suggest that mass imprisonment exacerbates marginalization among disadvantaged children, thereby contributing to a system of stratification in which the children of the prison boom become virtually invisible.Fragile families, child homelessness, family structure, family stability, imprisonment, African Americans

Can Oslo’s failed aid model be laid to rest?

Overview: Since the signing of the 1993 Oslo Declaration of Principles, the donor community has invested more than $23 billion into “peace and development” in the Occupied Palestinian Territory (OPT), making it one of the highest per capita recipients of non-military aid in the world. However, aid has not brought peace, development, or security for the Palestinian people, let alone justice. Al-Shabaka Guest Author Jeremy Wildeman and Program Director Alaa Tartir examine the origins of the present aid-for-peace model as well as its effects on socio-economic conditions and pull together the many critiques of the Oslo economic model. The authors argue that donors are reinforcing failed past patterns associated with the so-called peace dividends model while making only cosmetic changes to their engagement. Indeed, donors do not appear ready to change an approach dominated by policy “instrumentalists” who ignore and reject outcomes that do not match their pre-determined values instead of upholding international law on Palestinian rights and international development principles that strive to “do no harm.” They underscore the alarming possibility that the Oslo aid model may serve too many interests to be dismantled and conclude with an assessment of what will be needed for change

Dynamics of heavy and buoyant underwater pendulums

The humble pendulum is often invoked as the archetype of a simple, gravity driven, oscillator. Under ideal circumstances, the oscillation frequency of the pendulum is independent of its mass and swing amplitude. However, in most real-world situations, the dynamics of pendulums is not quite so simple, particularly with additional interactions between the pendulum and a surrounding fluid. Here we extend the realm of pendulum studies to include large amplitude oscillations of heavy and buoyant pendulums in a fluid. We performed experiments with massive and hollow cylindrical pendulums in water, and constructed a simple model that takes the buoyancy, added mass, fluid (nonlinear) drag, and bearing friction into account. To first order, the model predicts the oscillation frequencies, peak decelerations and damping rate well. An interesting effect of the nonlinear drag captured well by the model is that for heavy pendulums, the damping time shows a non-monotonic dependence on pendulum mass, reaching a minimum when the pendulum mass density is nearly twice that of the fluid. Small deviations from the model's predictions are seen, particularly in the second and subsequent maxima of oscillations. Using Time- Resolved Particle Image Velocimetry (TR-PIV), we reveal that these deviations likely arise due to the disturbed flow created by the pendulum at earlier times. The mean wake velocity obtained from PIV is used to model an extra drag term due to incoming wake flow. The revised model significantly improves the predictions for the second and subsequent oscillations.Comment: 15 pages, 8 figures, J. Fluid Mech. (in press

Antimicrobial Activity of Modified Oregano Oil-based Compounds

Undergraduate Basi

Classical analogue of the Unruh effect

In the Unruh effect an observer with constant acceleration perceives the quantum vacuum as thermal radiation. The Unruh effect has been believed to be a pure quantum phenomenon, but here we show theoretically how the effect arises from the classical correlation of noise. We demonstrate this idea with a simple experiment on water waves where we see the first indications of a Planck spectrum in the correlation energy

On the spreading of impacting drops

The energy budget and dissipation mechanisms during droplet impact on solid surfaces are studied numerically and theoretically. We find that for high impact velocities and negligible surface friction at the solid surface (i.e. free-slip), about one half of the initial kinetic energy is transformed into surface energy, independent of the impact parameters and the detailed energy loss mechanism(s). We argue that this seemingly universal rule is related to the deformation mode of the droplet and is reminiscent of pipe flow undergoing a sudden expansion, for which the head loss can be calculated by multiplying the kinetic energy of the incoming flow by a geometrical factor. For impacts on a no-slip surface also dissipation in the shear boundary layer at the solid surface is important. In this case the geometric head loss acts as a lower bound on the total dissipation (i.e. the spreading on a no-slip surface approaches that on a free-slip surface when the droplet viscosity is send to zero). This new view on the impact problem allows for simple analytical estimates of the maximum spreading diameter of impacting drops as a function of the impact parameters and the properties of the solid surface. It bridges the gap between previous momentum balance approaches and energy balance approaches, which hitherto did not give consistent predictions in the low viscosity limit. Good agreement is found between our models and experiments, both for impacts on "slippery" or lubricated surfaces (e.g. Leidenfrost droplet impacts and head-on droplet-droplet collisions) and for impacts on no-slip surfaces

In vivo magnetomyograms of skeletal muscle

Magnetomyography (MMG) is a new noninvasive technique inspired by the magnetoneurographic method of J.P. Wikswo (IEEE Trans. Biomed. Eng., Vol.BME-30, p.215-21, 1983). MMG is used to detect action currents in a muscle, which is immersed in a highly conducting fluid. The detection coil is of a toroidal shape, with the muscle passing through the center of the coil. For a long muscle which fits tightly in the toroid, it is to be expected that magnetic fields correspond almost completely to the intracellular longitudinal (axial) currents in active muscle fibers. An experimental setup with specific coils for rat and mouse skeletal muscles was developed. It is sensitive enough to detect currents from single motor units. The technique can be used to record stimulated twitch activity in live muscle as a function of force level, coil position along the muscle, temperature, etc. By simulating the response with a finite-element forward model, it is possible to calculate action currents under various experimental condition