Drop deformation by laser-pulse impact

A free-falling absorbing liquid drop hit by a nanosecond laser-pulse experiences a strong recoil-pressure kick. As a consequence, the drop propels forward and deforms into a thin sheet which eventually fragments. We study how the drop deformation depends on the pulse shape and drop properties. We first derive the velocity field inside the drop on the timescale of the pressure pulse, when the drop is still spherical. This yields the kinetic-energy partition inside the drop, which precisely measures the deformation rate with respect to the propulsion rate, before surface tension comes into play. On the timescale where surface tension is important the drop has evolved into a thin sheet. Its expansion dynamics is described with a slender-slope model, which uses the impulsive energy-partition as an initial condition. Completed with boundary integral simulations, this two-stage model explains the entire drop dynamics and its dependance on the pulse shape: for a given propulsion, a tightly focused pulse results in a thin curved sheet which maximizes the lateral expansion, while a uniform illumination yields a smaller expansion but a flat symmetric sheet, in good agreement with experimental observations.Comment: submitted to J. Fluid Mec

Drop Shaping by Laser-Pulse Impact

We show how the deposition of laser energy induces propulsion and strong deformation of an absorbing liquid body. Combining high speed with stroboscopic imaging, we observe that a millimeter-sized dyed water drop hit by a millijoule nanosecond laser pulse propels forward at several meters per second and deforms until it eventually fragments. The drop motion results from the recoil momentum imparted at the drop surface by water vaporization. We measure the propulsion speed and the time-deformation law of the drop, complemented by boundary-integral simulations. The drop propulsion and shaping are explained in terms of the laser-pulse energy, the drop size, and the liquid properties. These findings are, for instance, crucial for the generation of extreme ultraviolet light in nanolithography machines.Comment: Submitted as research article to Physical Review Applied, 6 pages with 6 figure

A search for fast radio burst-like emission from Fermi gamma-ray bursts

We report the results of the rapid follow-up observations of gamma-ray bursts (GRBs) detected by the Fermi satellite to search for associated fast radio bursts. The observations were conducted with the Australian Square Kilometre Array Pathfinder at frequencies from 1.2-1.4 GHz. A set of 20 bursts, of which four were short GRBs, were followed up with a typical latency of about one minute, for a duration of up to 11 hours after the burst. The data was searched using 4096 dispersion measure trials up to a maximum dispersion measure of 3763 pc cm$^{-3}$, and for pulse widths $w$ over a range of duration from 1.256 to 40.48 ms. No associated pulsed radio emission was observed above $26 {\rm Jy ms} (w/1 {\rm ms})^{-1/2}$ for any of the 20 GRBs.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa

Point-Form Analysis of Elastic Deuteron Form Factors

Point-form relativistic quantum mechanics is applied to elastic electron-deuteron scattering. The deuteron is modeled using relativistic interactions that are scattering-equivalent to the nonrelativistic Argonne $v_{18}$ and Reid '93 interactions. A point-form spectator approximation (PFSA) is introduced to define a conserved covariant current in terms of single-nucleon form factors. The PFSA is shown to provide an accurate description of data up to momentum transfers of 0.5 ${\rm GeV}^2$, but falls below the data at higher momentum transfers. Results are sensitive to the nucleon form factor parameterization chosen, particularly to the neutron electric form factor.Comment: RevTex, 31 pages, 1 table, 13 figure

Poincare' Covariant Current Operator and Elastic Electron-Deuteron Scattering in the Front-form Hamiltonian Dynamics

The deuteron electromagnetic form factors, $A(Q^2)$ and $B(Q^2)$, and the tensor polarization $T_{20}(Q^2)$, are unambiguously calculated within the front-form relativistic Hamiltonian dynamics, by using a novel current, built up from one-body terms, which fulfills Poincar\'e, parity and time reversal covariance, together with Hermiticity and the continuity equation. A simultaneous description of the experimental data for the three deuteron form factors is achieved up to $Q^2 < 0.4 (GeV/c)^2$. At higher momentum transfer, different nucleon-nucleon interactions strongly affect $A(Q^2)$, $B(Q^2)$, and $T_{20}(Q^2)$ and the effects of the interactions can be related to $S$-state kinetic energy in the deuteron. Different nucleon form factor models have huge effects on $A(Q^2)$, smaller effects on $B(Q^2)$ and essentially none on $T_{20}(Q^2)$.Comment: 31 pages + 16 figures. Submitted to Phys. Rev.

Maximal air bubble entrainment at liquid drop impact

At impact of a liquid drop on a solid surface an air bubble can be entrapped. Here we show that two competing effects minimize the (relative) size of this entrained air bubble: For large drop impact velocity and large droplets the inertia of the liquid flattens the entrained bubble, whereas for small impact velocity and small droplets capillary forces minimize the entrained bubble. However, we demonstrate experimentally, theoretically, and numerically that in between there is an optimum, leading to maximal air bubble entrapment. Our results have a strong bearing on various applications in printing technology, microelectronics, immersion lithography, diagnostics, or agriculture.Comment: 4 page

Healthy and diseased placental barrier on-a-chip models suitable for standardized studies

Pathologies associated with uteroplacental hypoxia, such as preeclampsia are among the leading causes of maternal and perinatal morbidity in the world. Its fundamental mechanisms are yet poorly understood due to a lack of good experimental models. Here we report an in vitro model of the placental barrier, based on co-culture of trophoblasts and endothelial cells against a collagen extracellular matrix in a microfluidic platform. The model yields a functional syncytium with barrier properties, polarization, secretion of relevant extracellular membrane components, thinning of the materno-fetal space, hormone secretion, and transporter function. The model is exposed to low oxygen conditions and perfusion flow is modulated to induce a pathological environment. This results in reduced barrier function, hormone secretion, and microvilli as well as an increased nuclei count, characteristics of preeclamptic placentas. The model is implemented in a titer plate-based microfluidic platform fully amenable to high-throughput screening. We thus believe this model could aid mechanistic understanding of preeclampsia and other placental pathologies associated with hypoxia/ischemia, as well as support future development of effective therapies through target and compound screening campaigns.Statement of Significance: The human placenta is a unique organ sustaining fetus growth but is also the source of severe pathologies, such as Preeclampsia. Though leading cause of perinatal mortality in the world, preeclampsia remains untreatable due to a lack of relevant in vitro placenta models. To better understand the pathology, we have developed 3D placental barrier models in a microfluidic device. The platform allows parallel culture of 40 perfused physiological miniaturized placental barriers, comprising a differentiated syncytium and endothelium that have been validated for transporter functions. Exposure to a hypoxic and ischemic environment enabled the mimicking of preeclamptic characteristics in high-throughput, which we believe could lead to a better understanding of the pathology as well as support future effective therapies development.</p

Tensor Analyzing Powers for Quasi-Elastic Electron Scattering from Deuterium

We report on a first measurement of tensor analyzing powers in quasi-elastic electron-deuteron scattering at an average three-momentum transfer of 1.7 fm$^{-1}$. Data sensitive to the spin-dependent nucleon density in the deuteron were obtained for missing momenta up to 150 MeV/$c$ with a tensor polarized $^2$H target internal to an electron storage ring. The data are well described by a calculation that includes the effects of final-state interaction, meson-exchange and isobar currents, and leading-order relativistic contributions.Comment: 4 pages, 3 figure

Spin-Momentum Correlations in Quasi-Elastic Electron Scattering from Deuterium

We report on a measurement of spin-momentum correlations in quasi-elastic scattering of longitudinally polarized electrons with an energy of 720 MeV from vector-polarized deuterium. The spin correlation parameter $A^V_{ed}$ was measured for the $^2 \vec{\rm H}(\vec e,e^\prime p)n$ reaction for missing momenta up to 350 MeV/$c$ at a four-momentum transfer squared of 0.21 (GeV/c)$^2$. The data give detailed information about the spin structure of the deuteron, and are in good agreement with the predictions of microscopic calculations based on realistic nucleon-nucleon potentials and including various spin-dependent reaction mechanism effects. The experiment demonstrates in a most direct manner the effects of the D-state in the deuteron ground-state wave function and shows the importance of isobar configurations for this reaction.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Lett. for publicatio