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

Mantle thermal pulses below the Mid-Atlantic Ridge and temporal variations in the formation of oceanic lithosphere

A 20-Myr record of creation of oceanic lithosphere is exposed along a segment of the central Mid-Atlantic Ridge on an uplifted sliver of lithosphere. The degree of melting of the mantle that is upwelling below the ridge, estimated from the chemistry of the exposed mantle rocks, as well as crustal thickness inferred from gravity measurements, show oscillations of 3–4 Myr superimposed on a longer-term steady increase with time. The time lag between oscillations of mantle melting and crustal thickness indicates that the mantle is upwelling at an average rate of 25 mm yr-1, but this appears to vary through time. Slow-spreading lithosphere seems to form through dynamic pulses of mantle upwelling and melting, leading not only to along-axis segmentation but also to across-axis structural variability. Also, the central Mid-Atlantic Ridge appears to have become steadily hotter over the past 20 Myr, possibly owing to north–south mantle flow

Compositional variation and 226Ra-230Th model ages of axial lavas from the southern Mid-Atlantic Ridge, 8°48′S

We present geological observations and geochemical data for the youngest volcanic features on the slow-spreading Mid-Atlantic Ridge at 8°48'S that shows seismic evidence for a thickened crust and excess magma formation. Young lava flows with high sonar reflectivity cover about 14 km2 in the axial rift and were probably erupted from two axial volcanic ridges each of about 3 km in length. Three different lava units occur along an about 11 km long portion of the ridge, and lavas from the northern axial volcanic ridge differ from those of the southern axial volcanic ridge and surrounding lava flows. Basalts from the axial rift flanks and from a pillow mound within the young flows are more incompatible element depleted than those from the young volcanic field. Lavas from this volcanic area have 226Ra-230Th disequilibria model ages of 1,000 and 4,000 years whereas the older lavas from the rift flank and the pillow mound, but also some of the lava field, are older than 8,000 years. Glasses from the northern and southern ends of the southern lava unit indicate up to 100°C cooler magma temperatures than in the center and increased assimilation of hydrothermally altered material. The compositional heterogeneity on a scale of 3 km suggests small magma batches rising vertically from the mantle to the surface without significant lateral flow and mixing. The observations on the 8°48'S lava field support the model of low frequency eruptions from single ascending magma batches that has been developed for slow-spreading ridges

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