Elastic turbulence in curvilinear flows of polymer solutions

Following our first report (A. Groisman and V. Steinberg, \sl Nature $\bf 405$, 53 (2000)) we present an extended account of experimental observations of elasticity induced turbulence in three different systems: a swirling flow between two plates, a Couette-Taylor (CT) flow between two cylinders, and a flow in a curvilinear channel (Dean flow). All three set-ups had high ratio of width of the region available for flow to radius of curvature of the streamlines. The experiments were carried out with dilute solutions of high molecular weight polyacrylamide in concentrated sugar syrups. High polymer relaxation time and solution viscosity ensured prevalence of non-linear elastic effects over inertial non-linearity, and development of purely elastic instabilities at low Reynolds number (Re) in all three flows. Above the elastic instability threshold, flows in all three systems exhibit features of developed turbulence. Those include: (i)randomly fluctuating fluid motion excited in a broad range of spatial and temporal scales; (ii) significant increase in the rates of momentum and mass transfer (compared to those expected for a steady flow with a smooth velocity profile). Phenomenology, driving mechanisms, and parameter dependence of the elastic turbulence are compared with those of the conventional high Re hydrodynamic turbulence in Newtonian fluids.Comment: 23 pages, 26 figure

Sub-femtosecond determination of transmission delay times for a dielectric mirror (photonic bandgap) as a function of angle of incidence

Using a two-photon interference technique, we measure the delay for single-photon wavepackets to be transmitted through a multilayer dielectric mirror, which functions as a ``photonic bandgap'' medium. By varying the angle of incidence, we are able to confirm the behavior predicted by the group delay (stationary phase approximation), including a variation of the delay time from superluminal to subluminal as the band edge is tuned towards to the wavelength of our photons. The agreement with theory is better than 0.5 femtoseconds (less than one quarter of an optical period) except at large angles of incidence. The source of the remaining discrepancy is not yet fully understood.Comment: 5 pages and 5 figure

Conditional probabilities in quantum theory, and the tunneling time controversy

It is argued that there is a sensible way to define conditional probabilities in quantum mechanics, assuming only Bayes's theorem and standard quantum theory. These probabilities are equivalent to the ``weak measurement'' predictions due to Aharonov {\it et al.}, and hence describe the outcomes of real measurements made on subensembles. In particular, this approach is used to address the question of the history of a particle which has tunnelled across a barrier. A {\it gedankenexperiment} is presented to demonstrate the physically testable implications of the results of these calculations, along with graphs of the time-evolution of the conditional probability distribution for a tunneling particle and for one undergoing allowed transmission. Numerical results are also presented for the effects of loss in a bandgap medium on transmission and on reflection, as a function of the position of the lossy region; such loss should provide a feasible, though indirect, test of the present conclusions. It is argued that the effects of loss on the pulse {\it delay time} are related to the imaginary value of the momentum of a tunneling particle, and it is suggested that this might help explain a small discrepancy in an earlier experiment.Comment: 11 pages, latex, 4 postscript figures separate (one w/ 3 parts

Velocity control propulsion subsystem of the Radio Astronomy Explorer satellite for Goddard Space Flight Center

The Velocity Control Propulsion Subsystem (VCPS) was designed the propulsion required for trajectory and lunar orbit corrections of the spacecraft. A GFE clamp assembly physically attaches the VCPS to the spacecraft and the unit is ejected after completing the required corrections. The VCPS is physically and functionally separated from the spacecraft except for the electrical and telemetry interfaces. A GFE transtage provides the superstructure on which the VCPS is assembled. The subsystem consists of two 5 foot pound rocket engine assemblies, 4 propellant tanks, 2 latching valves, 2 fill and drain valves, a system filter, pressure transducer, gas and propellant manifolds and electrical heaters and thermostats. The RAE-B VCPS program covered the design, manufacture and qualification of one subsystem. This subsystem was to be manufactured, subjected to qualification tests; and refurbished, if necessary, prior to flight. The VCPS design and test program precluded the need for refurbishing the subsystem and the unit was delivered to GSFC at the conclusion of the program

Mixing by polymers: experimental test of decay regime of mixing

By using high molecular weight fluorescent passive tracers with different diffusion coefficients and by changing the fluid velocity we study dependence of a characteristic mixing length on the Peclet number, $Pe$, which controls the mixing efficiency. The mixing length is found to be related to $Pe$ by a power law, $L_{mix}\propto Pe^{0.26\pm 0.01}$, and increases faster than expected for an unbounded chaotic flow. Role of the boundaries in the mixing length abnormal growth is clarified. The experimental findings are in a good quantitative agreement with the recent theoretical predictions.Comment: 4 pages,5 figures. accepted for publication in PR

Studying the “New” Civil Judges

We know very little about the people and institutions that make up the bulk of the United States civil justice system: state judges and state courts. Our understanding of civil justice is based primarily on federal litigation and the decisions of appellate judges. Staggeringly little legal scholarship focuses on state courts and judges. We simply do not know what most judges are doing in their day-to-day courtroom roles or in their roles as institutional actors and managers of civil justice infrastructure. We know little about the factors that shape and influence judicial practices, let alone the consequences of those practices for courts, litigants, and the public. From top to bottom, we can describe and theorize about our existing civil justice system in only piecemeal ways. Given legal scholarship\u27s near-complete focus on federal civil courts, the stories we tell about the civil justice system may be based on assumptions and models that only apply in the rarefied world of federal court. Meanwhile, state judges and courts--which handle ninety-nine percent of all civil cases--are ripe for theoretical and empirical exploration.In response, we call for more research aimed at increasing our understanding of state civil courts and judges and offer a theoretical framework to support this work, one that reflects how state courts differ from federal courts. This framework is grounded in a core fact of American civil justice, one both easily observed and largely overlooked: the majority of parties in state civil courts are unrepresented. Given this new pro se reality, our theoretical framework identifies four novel assumptions to guide future research: (1) the adversary process is disappearing; (2) most state court business is still conducted through in-person interactions between judges and parties; (3) the judicial role is ethically ambiguous in pro se cases; and (4) a largely static body of written law has not kept pace with the evolving and dynamic issues facing state courts. Building on the growth of empiricism and empirically grounded theory in traditional legal scholarship and access to justice research, we call on scholars to develop theory and gather data to map the new reality of civil justice and judging in America, and suggest questions to guide future research

A Research-Based Curriculum for Teaching the Photoelectric Effect

Physics faculty consider the photoelectric effect important, but many erroneously believe it is easy for students to understand. We have developed curriculum on this topic including an interactive computer simulation, interactive lectures with peer instruction, and conceptual and mathematical homework problems. Our curriculum addresses established student difficulties and is designed to achieve two learning goals, for students to be able to (1) correctly predict the results of photoelectric effect experiments, and (2) describe how these results lead to the photon model of light. We designed two exam questions to test these learning goals. Our instruction leads to better student mastery of the first goal than either traditional instruction or previous reformed instruction, with approximately 85% of students correctly predicting the results of changes to the experimental conditions. On the question designed to test the second goal, most students are able to correctly state both the observations made in the photoelectric effect experiment and the inferences that can be made from these observations, but are less successful in drawing a clear logical connection between the observations and inferences. This is likely a symptom of a more general lack of the reasoning skills to logically draw inferences from observations.Comment: submitted to American Journal of Physic

Effects and metabolism of the phenylurea herbicide isoproturon in the submerged macrophyte Ceratophyllum demersum L.

Phenylurea herbicides such as isoproturon (IPU) restrain photosynthesis by connection to the D1 protein in the photosynthetic apparatus in target plants such as weeds in crop fields. Direct effects of herbicides on organisms, which are not a target of the pesticide, have been examined seldom. Since a many of agriculturally used pesticides are found in surface waters in agricultural areas, we determined the effects on the photosynthetic oxygen production of the submerged macrophyte Ceratophyllum demersum using concentrations of IPU ranging from 0.2 μg/L to 200 μg/L IPU. At environmental relevant concentrations of IPU, the photosynthetic oxygen release was impaired. A reduction of the photosynthetic oxygen release showed a time dependency with the assigned herbicide concentrations. Furthermore, this study presents the first indications for metabolism of IPU in the aquatic plant C. demersum