How confined lubricants diffuse during shear

The translational diffusion of a fluorescent dye embedded at a dilute concentration in a confined fluid was compared at rest and during shear. The fluid, octamethylcyclotetrasiloxane (OMCTS), was confined between step-free muscovite mica to thickness 3-4 layers. Fluorescence correlation spectroscopy showed that the time scales of intensity-intensity autocorrelation functions were essentially the same during shear and at rest, except they were faster during shear by a factor of 2 to 5. This dynamical probe of how liquids order in molecularly thin films fails to support the hypothesis that shear produced a melting transition.open242

Elastic scattering losses in the four-wave mixing of Bose Einstein Condensates

We introduce a classical stochastic field method that accounts for the quantum fluctuations responsible for spontaneous initiation of various atom optics processes. We assume a delta-correlated Gaussian noise in all initially empty modes of atomic field. Its strength is determined by comparison with the analytical results for two colliding condensates in the low loss limit. Our method is applied to the atomic four wave mixing experiment performed at MIT [Vogels {\it et. al.}, Phys. Rev. Lett. {\bf 89}, 020401, (2002)], for the first time reproducing experimental data

Multi-Parameter Entanglement in Femtosecond Parametric Down-Conversion

A theory of spontaneous parametric down-conversion, which gives rise to a quantum state that is entangled in multiple parameters, such as three-dimensional wavevector and polarization, allows us to understand the unusual characteristics of fourth-order quantum interference in many experiments, including ultrafast type-II parametric down-conversion, the specific example illustrated in this paper. The comprehensive approach provided here permits the engineering of quantum states suitable for quantum information schemes and new quantum technologies.Comment: to appear in Physical Review

Multi-parameter Entanglement in Quantum Interferometry

The role of multi-parameter entanglement in quantum interference from collinear type-II spontaneous parametric down-conversion is explored using a variety of aperture shapes and sizes, in regimes of both ultrafast and continuous-wave pumping. We have developed and experimentally verified a theory of down-conversion which considers a quantum state that can be concurrently entangled in frequency, wavevector, and polarization. In particular, we demonstrate deviations from the familiar triangular interference dip, such as asymmetry and peaking. These findings improve our capacity to control the quantum state produced by spontaneous parametric down-conversion, and should prove useful to those pursuing the many proposed applications of down-converted light.Comment: submitted to Physical Review

Entangled-Photon Generation from Parametric Down-Conversion in Media with Inhomogeneous Nonlinearity

We develop and experimentally verify a theory of Type-II spontaneous parametric down-conversion (SPDC) in media with inhomogeneous distributions of second-order nonlinearity. As a special case, we explore interference effects from SPDC generated in a cascade of two bulk crystals separated by an air gap. The polarization quantum-interference pattern is found to vary strongly with the spacing between the two crystals. This is found to be a cooperative effect due to two mechanisms: the chromatic dispersion of the medium separating the crystals and spatiotemporal effects which arise from the inclusion of transverse wave vectors. These effects provide two concomitant avenues for controlling the quantum state generated in SPDC. We expect these results to be of interest for the development of quantum technologies and the generation of SPDC in periodically varying nonlinear materials.Comment: submitted to Physical Review

Dense transcript profiling in single cells by image correlation decoding

Sequential barcoded fluorescent in situ hybridization (seqFISH) allows large numbers of molecular species to be accurately detected in single cells, but multiplexing is limited by the density of barcoded objects. We present correlation FISH (corrFISH), a method to resolve dense temporal barcodes in sequential hybridization experiments. Using corrFISH, we quantified highly expressed ribosomal protein genes in single cultured cells and mouse thymus sections, revealing cell-type-specific gene expression

Melt generation, crystallization, and extraction beneath segmented oceanic transform faults

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): B11102, doi:10.1029/2008JB006100.We examine mantle melting, fractional crystallization, and melt extraction beneath fast slipping, segmented oceanic transform fault systems. Three-dimensional mantle flow and thermal structures are calculated using a temperature-dependent rheology that incorporates a viscoplastic approximation for brittle deformation in the lithosphere. Thermal solutions are combined with the near-fractional, polybaric melting model of Kinzler and Grove (1992a, 1992b, 1993) to determine extents of melting, the shape of the melting regime, and major element melt composition. We investigate the mantle source region of intratransform spreading centers (ITSCs) using the melt migration approach of Sparks and Parmentier (1991) for two end-member pooling models: (1) a wide pooling region that incorporates all of the melt focused to the ITSC and (2) a narrow pooling region that assumes melt will not migrate across a transform fault or fracture zone. Assuming wide melt pooling, our model predictions can explain both the systematic crustal thickness excesses observed at intermediate and fast slipping transform faults as well as the deeper and lower extents of melting observed in the vicinity of several transform systems. Applying these techniques to the Siqueiros transform on the East Pacific Rise we find that both the viscoplastic rheology and wide melt pooling are required to explain the observed variations in gravity inferred crustal thickness. Finally, we show that mantle potential temperature Tp = 1350°C and fractional crystallization at depths of 9–15.5 km fit the majority of the major element geochemical data from the Siqueiros transform fault system.This research was supported by WHOI Academic Programs Office (PMG), NSF grants OCE-0649103 and OCE-0623188 (MDB), and the Charles D. Hollister Endowed Fund for Support of Innovative Research at WHOI (J.L.)

Electromagnetic constraints on a melt region beneath the central Mariana back-arc spreading ridge

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 13 (2012): Q10017, doi:10.1029/2012GC004326.An electrical resistivity profile across the central Mariana subduction system shows high resistivity in the upper mantle beneath the back-arc spreading ridge where melt might be expected to exist. Although seismic data are equivocal on the extent of a possible melt region, the question arises as to why a 2-D magnetotelluric (MT) survey apparently failed to image any melt. We have run forward models and inversions that test possible 3-D melt geometries that are consistent with the MT data and results of other studies from the region, and that we use to place upper bounds on the possible extent of 3-D melt region beneath the spreading center. Our study suggests that the largest melt region that was not directly imaged by the 2-D MT data, but that is compatible with the observations as well as the likely effects of melt focusing, has a 3-D shape on a ridge-segment scale focused toward the spreading center and a resistivity of 100 Ω-m that corresponds to ∼0.1–∼1% interconnected silicate melt embedded in a background resistivity of ∼500 Ω-m. In contrast to the superfast spreading southern East Pacific Rise, the 3-D melt region suggests that buoyant mantle upwelling on a ridge-segment scale is the dominant process beneath the slow-spreading central Mariana back-arc. A final test considers whether the inability to image a 3-D melt region was a result of the 2-D survey geometry. The result reveals that the 2-D transect completed is useful to elucidate a broad range of 3-D melt bodies.TM and NS are supported by the scientific program of “TAIGA” (Trans-crustal Advection and In situ reaction of Global sub-seafloor Aquifer)” sponsored by the MEXT of Japan, and are also supported by the JSPS for Grant-In-Aid for Scientific Research (21244070). Participation in the Marianas experiment by RLE and ADC was supported by NSF grant OCE0405641.2013-04-2

Evaluation of natural and tracer fluorescent emission methods for droplet size measurements in a diesel spray

The final publication is available at Springer via http://dx.doi.org/10.1007/s12239-012-0070-zSpray sizing that records fluorescent emission and scattered light has been widely applied to spray diagnostics over the last two decades. Different experimental strategies have been developed, but comparing the different solutions offered has remained of interest to experimentalists. In this work, a comparison of two fluorescence strategies for measuring droplet size in the liquid phase of a last-generation DI diesel spray is conducted. The natural fluorescent emission of a commercial diesel fuel and the fluorescence emitted by a tracer (Rhodamine B) are compared using theoretical and experimental approaches. The LIF/Mie ratio commonly called Planar Droplet Sizing (PDS) technique is applied in two different ways to elucidate the possible advantages of using a fluorescent dopant. The sprays were injected under non-evaporative conditions into a constant pressure vessel that simulates densities present at the moment of injection in currently used passenger car diesel engines. Characterization of the signal properties was performed by measuring the absorption coefficient, fluorescence emission spectrum, quantum yield and lifetime of both configurations. The scattered light and fluorescence intensities were calculated to verify the dependencies of the droplet surface and volume. When applying the two techniques to quantify droplet size in dense diesel sprays, the results show that signal weakness and lack of control over the properties of natural fluorescence produce distortion in the shape of the spray and cause measurements to be unreliable. © 2012 The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg.This research has been funded in the frame of the project PROFUEL reference TRA2011-26293 from Ministerio de Ciencia e Innovacion. The injectors are part of the ECN international project.Pastor Soriano, JV.; Payri, R.; Salavert Fernandez, J.; Manin, J. (2012). Evaluation of natural and tracer fluorescent emission methods for droplet size measurements in a diesel spray. International Journal of Automotive Technology. 13(5):713-724. https://doi.org/10.1007/s12239-012-0070-zS713724135Albrecht, H. E., Damaschke, N., Borys, M. and Tropea, C. (2003). Laser Doppler and Phase Doppler Measurement Techniques. Springer. Berlin.Barnes, M. D., Whitten, W. B. and Ramsey, J. M. (1994). Enhanced fluorescence yields through cavity quantumelectrodynamic effects in microdroplets. J. Optical Society of America B 11,7, 1297–1304.Benajes, J., Molina, S., Novella, R., Amorim, R., Ben Hadj Hamouda, H. and Hardy, J. (2010). Comparison of two injection systems in an HSDI diesel engine using split injection and different injector nozzles. Int. J. Automotive Technology 11,2, 139–146.Charalampous, G. and Hardalupas, Y. (2011). 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Quantitative measurement of planar droplet sauter mean diameter in sprays using planar droplet sizing. 11th Int. Symp. Application of Laser Techniques to Fluid Mechanics, Lisbon, Portugal.Eckbreth, A. C. (1988). Laser Diagnostics for Combustion Species and Temperature. Abacus. Cambridge. Mass.Greenhalgh, D. A. (1999). Planar measurements of fuel vapour, liquid fuel, liquid droplet size and soot. Planar Optical Measurement Methods for Gas Turbine Components, 1–7.Im, K., Lin, K., Lai, M. and Chon, M. (2011). Breakup modeling of a liquid jet in cross flow. Int. J. Automotive Technology 12,4, 489–496.Jermy, M. C. and Greenhalgh, D. A. (2000). Planar dropsizing by elastic and fluorescence scattering in sprays too dense for phase doppler measurement. Appl. Phys. B, 71, 703–710.Kim, Y., Kim, K. and Lee, K. (2011). Effect of a 2-stage injection strategy on the combustion and flame characteristics in a PCCI engine. Int. J. Automotive Technology 12,5, 639–644.Ko, F. H., Weng, L. Y., Ko, C. J. and Chu, T. C. (2006). Characterization of imprinting polymeric temperature variation with fluorescent Rhodamine B molecule. Microelectronic Engineering, 83, 864–868.Lakowicz, J. R. (2006). Principles of Fluorescence Spectroscopy. 3rd Edn. Springer.Lee, S. H., Teong, J., Lee, J. T., Ryou, H. S. and Hong, K. (2005). Investigation on spray characteristics under ultrahigh injection pressure conditions. Int. J. Automotive Technology 6,2, 125–131.Lee, B., Song, J., Chang, Y. and Jeon, C. (2010). Effect of the number of fuel injector holes on characteristics of combustion and emissions in a diesel engine. Int. J. Automotive Technology 11,6, 783–791.LeGal, P., Farrugia, N. and Greenhalgh, D. A. (1999). Laser sheet dropsizing of dense sprays. Optics and Laser Techn., 31, 75–83.Lockett, R. D., Richter, J. and Greenhalgh, D. A. (1998). The characterisation of a diesel spray using combined laser induced fluorescence and laser sheet dropsizing. Conf. 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Thermalisation of a two-dimensional photonic gas in a 'white-wall' photon box

Bose-Einstein condensation, the macroscopic accumulation of bosonic particles in the energetic ground state below a critical temperature, has been demonstrated in several physical systems. The perhaps best known example of a bosonic gas, blackbody radiation, however exhibits no Bose-Einstein condensation at low temperatures. Instead of collectively occupying the lowest energy mode, the photons disappear in the cavity walls when the temperature is lowered - corresponding to a vanishing chemical potential. Here we report on evidence for a thermalised two-dimensional photon gas with freely adjustable chemical potential. Our experiment is based on a dye filled optical microresonator, acting as a 'white-wall' box for photons. Thermalisation is achieved in a photon number-conserving way by photon scattering off the dye-molecules, and the cavity mirrors both provide an effective photon mass and a confining potential - key prerequisites for the Bose-Einstein condensation of photons. As a striking example for the unusual system properties, we demonstrate a yet unobserved light concentration effect into the centre of the confining potential, an effect with prospects for increasing the efficiency of diffuse solar light collection.Comment: 15 pages, 3 figure