Coincident Occurrences of Tropical Individual Cirrus Clouds and Deep Convective Systems Derived from TRMM Observations

Measurements of cloud properties and atmospheric radiation taken between January and August 1998 by the Tropical Rainfall Measuring Mission (TRMM) satellite were used to investigate the effect of spatial and temporal scales on the coincident occurrences of tropical individual cirrus clouds (ICCs) and deep convective systems (DCSs). It is found that there is little or even negative correlation between instantaneous occurrences of ICC and DCS in small areas, in which both types of clouds cannot grow and expand simultaneously. When spatial and temporal domains are increased, ICCs become more dependent on DCSs due to the origination of many ICCs from DCSs and moisture supply from the DCS in the upper troposphere for the ICCs to grow, resulting in significant positive correlation between the two types of tropical high clouds in large spatial and long temporal scales. This result may suggest that the decrease of tropical high clouds with SST from model simulations is likely caused by restricted spatial domains and limited temporal periods. Finally, the radiative feedback due to the change in tropical high cloud area coverage with sea surface temperature appears small and about -0.14 W/sq m per degree Kelvin

D-Brane Potentials from Multi-Trace Deformations in AdS/CFT

It is known that certain AdS boundary conditions allow smooth initial data to evolve into a big crunch. To study this type of cosmological singularity, one can use the dual quantum field theory, where the non-standard boundary conditions are reflected by the presence of a multi-trace potential unbounded below. For specific AdS_4 and AdS_5 models, we provide a D-brane (or M-brane) interpretation of the unbounded potential. Using probe brane computations, we show that the AdS boundary conditions of interest cause spherical branes to be pushed to the boundary of AdS in finite time, and that the corresponding potential agrees with the multi-trace deformation of the dual field theory. Systems with expanding spherical D3-branes are related to big crunch supergravity solutions by a phenomenon similar to geometric transition.Comment: 26 pages, 3 figures, v4: a few typos fixed

Coiling Instability of Multilamellar Membrane Tubes with Anchored Polymers

We study experimentally a coiling instability of cylindrical multilamellar stacks of phospholipid membranes, induced by polymers with hydrophobic anchors grafted along their hydrophilic backbone. Our system is unique in that coils form in the absence of both twist and adhesion. We interpret our experimental results in terms of a model in which local membrane curvature and polymer concentration are coupled. The model predicts the occurrence of maximally tight coils above a threshold polymer occupancy. A proper comparison between the model and experiment involved imaging of projections from simulated coiled tubes with maximal curvature and complicated torsions.Comment: 11 pages + 7 GIF figures + 10 JPEG figure

Assessment of Global Annual Atmospheric Energy Balance from Satellite Observations

Global atmospheric energy balance is one of the fundamental processes for the earth's climate system. This study uses currently available satellite data sets of radiative energy at the top of atmosphere (TOA) and surface and latent and sensible heat over oceans for the year 2000 to assess the global annual energy budget. Over land, surface radiation data are used to constrain assimilated results and to force the radiation, turbulent heat, and heat storage into balance due to a lack of observation-based turbulent heat flux estimations. Global annual means of the TOA net radiation obtained from both direct measurements and calculations are close to zero. The net radiative energy fluxes into the surface and the surface latent heat transported into the atmosphere are about 113 and 86 Watts per square meter, respectively. The estimated atmospheric and surface heat imbalances are about -8 ~ 9 Watts per square meter, values that are within the uncertainties of surface radiation and sea surface turbulent flux estimates and likely systematic biases in the analyzed observations. The potential significant additional absorption of solar radiation within the atmosphere suggested by previous studies does not appear to be required to balance the energy budget the spurious heat imbalances in the current data are much smaller (about half) than those obtained previously and debated at about a decade ago. Progress in surface radiation and oceanic turbulent heat flux estimations from satellite measurements significantly reduces the bias errors in the observed global energy budgets of the climate system

Mid-Infrared Spectroscopy of Two Lensed Star-forming Galaxies

We present low-resolution, rest-frame ~ 5 - 12 micron Spitzer/IRS spectra of two lensed z ~ 2 UV-bright star-forming galaxies, SDSS J120602.09+514229.5 and SDSS J090122.37+181432.3. Using the magnification boost from lensing, we are able to study the physical properties of these objects in greater detail than is possible for unlensed systems. In both targets, we detect strong PAH emission at 6.2, 7.7, and 11.3 microns, indicating the presence of vigorous star formation. For J1206, we find a steeply rising continuum and significant [S IV] emission, suggesting that a moderately hard radiation field is powering continuum emission from small dust grains. The strength of the [S IV] emission also implies a sub-solar metallicity of ~ 0.5 Z_{Sun}, confirming published rest-frame optical measurements. In J0901, the PAH lines have large rest-frame equivalent widths (> 1 micron) and the continuum rises slowly with wavelength, suggesting that any AGN contribution to L_{IR} is insignificant, in contrast to the implications of optical emission-line diagnostics. Using [O III] line flux as a proxy for AGN strength, we estimate that the AGN in J0901 provides only a small fraction of its mid-infrared continuum flux. By combining the detection of [Ar II] with an upper limit on [Ar III] emission, we infer a metallicity of > 1.3 Z_{Sun}. This work highlights the importance of combining rest-frame optical and mid-IR spectroscopy in order to understand the detailed properties of star-forming galaxies at high redshift.Comment: 20 pages, 3 figures, 2 tables. ApJ accepte

Atom chip based generation of entanglement for quantum metrology

Atom chips provide a versatile `quantum laboratory on a microchip' for experiments with ultracold atomic gases. They have been used in experiments on diverse topics such as low-dimensional quantum gases, cavity quantum electrodynamics, atom-surface interactions, and chip-based atomic clocks and interferometers. A severe limitation of atom chips, however, is that techniques to control atomic interactions and to generate entanglement have not been experimentally available so far. Such techniques enable chip-based studies of entangled many-body systems and are a key prerequisite for atom chip applications in quantum simulations, quantum information processing, and quantum metrology. Here we report experiments where we generate multi-particle entanglement on an atom chip by controlling elastic collisional interactions with a state-dependent potential. We employ this technique to generate spin-squeezed states of a two-component Bose-Einstein condensate and show that they are useful for quantum metrology. The observed 3.7 dB reduction in spin noise combined with the spin coherence imply four-partite entanglement between the condensate atoms and could be used to improve an interferometric measurement by 2.5 dB over the standard quantum limit. Our data show good agreement with a dynamical multi-mode simulation and allow us to reconstruct the Wigner function of the spin-squeezed condensate. The techniques demonstrated here could be directly applied in chip-based atomic clocks which are currently being set up

Rest-Frame Optical Spectra of Three Strongly Lensed Galaxies at z~2

We present Keck II NIRSPEC rest-frame optical spectra for three recently discovered lensed galaxies: the Cosmic Horseshoe (z = 2.38), the Clone (z = 2.00), and SDSS J090122.37+181432.3 (z = 2.26). The boost in signal-to-noise ratio (S/N) from gravitational lensing provides an unusually detailed view of the physical conditions in these objects. A full complement of high S/N rest-frame optical emission lines is measured, spanning from rest-frame 3600 to 6800AA, including robust detections of fainter lines such as H-gamma, [SII]6717,6732, and in one instance [NeII]3869. SDSS J090122.37+181432.3 shows evidence for AGN activity, and therefore we focus our analysis on star-forming regions in the Cosmic Horseshoe and the Clone. For these two objects, we estimate a wide range of physical properties, including star-formation rate (SFR), metallicity, dynamical mass, and dust extinction. In all respects, the lensed objects appear fairly typical of UV-selected star-forming galaxies at z~2. The Clone occupies a position on the emission-line diagnostic diagram of [OIII]/H-beta vs. [NII]/H-alpha that is offset from the locations of z~0 galaxies. Our new NIRSPEC measurements may provide quantitative insights into why high-redshift objects display such properties. From the [SII] line ratio, high electron densities (~1000 cm^(-3)) are inferred compared to local galaxies, and [OIII]/[OII] line ratios indicate higher ionization parameters compared to the local population. Building on previous similar results at z~2, these measurements provide further evidence (at high S/N) that star-forming regions are significantly different in high-redshift galaxies, compared to their local counterparts (abridged).Comment: 16 pages, 8 figures. Accepted for publication in the Astrophysical Journa

Planetary Construction Zones in Occultation: Discovery of an Extrasolar Ring System Transiting a Young Sun-like Star and Future Prospects for Detecting Eclipses by Circumsecondary and Circumplanetary Disks

The large relative sizes of circumstellar and circumplanetary disks imply that they might be seen in eclipse in stellar light curves. We estimate that a survey of ~10^4 young (~10 Myr old) post-accretion pre-MS stars monitored for ~10 years should yield at least a few deep eclipses from circumplanetary disks and disks surrounding low mass companion stars. We present photometric and spectroscopic data for a pre-MS K5 star (1SWASP J140747.93-394542.6), a newly discovered ~0.9 Msun member of the ~16 Myr-old Upper Cen-Lup subgroup of Sco-Cen at a kinematic distance of 128 pc. SuperWASP and ASAS light curves for this star show a remarkably long, deep, and complex eclipse event centered on 29 April 2007. At least 5 multi-day dimming events of >0.5 mag are identified, with a >3.3 mag deep eclipse bracketed by two pairs of ~1 mag eclipses symmetrically occurring +-12 days and +-26 days before and after. Hence, significant dimming of the star was taking place on and off over at least a ~54 day period in 2007, and a strong >1 mag dimming event occurred over a ~12 day span. We place a firm lower limit on the period of 850 days (i.e. the orbital radius of the eclipser must be >1.7 AU and orbital velocity must be <22 km/s). The shape of the light curve is similar to the lop-sided eclipses of the Be star EE Cep. We suspect that this new star is being eclipsed by a low-mass object orbited by a dense inner disk, girded by at least 3 dusty rings of lower optical depth. Between these rings are at least two annuli of near-zero optical depth (i.e. gaps), possibly cleared out by planets or moons, depending on the nature of the secondary. For possible periods in the range 2.33-200 yr, the estimated total ring mass is ~8-0.4 Mmoon (if the rings have optical opacity similar to Saturn's rings), and the edge of the outermost detected ring has orbital radius ~0.4-0.09 AU.Comment: Astronomical Journal, in press, 13 figure