Role of Galaxy Mergers in Cosmic Star Formation History

We present a morphology study of intermediate-redshift (0.2<z<1.2) luminous infrared galaxies (LIRGs) and general field galaxies in the GOODS fields using a revised asymmetry measurement method optimized for deep fields. By taking careful account of the importance of the underlying sky-background structures, our new method does not suffer from systematic bias and offers small uncertainties. By redshifting local LIRGs and low-redshift GOODS galaxies to different higher redshifts, we have found that the redshift dependence of the galaxy asymmetry due to surface-brightness dimming is a function of the asymmetry itself, with larger corrections for more asymmetric objects. By applying redshift-, IR-luminosity- and optical-brightness-dependent asymmetry corrections, we have found that intermediate-redshift LIRGs generally show highly asymmetric morphologies, with implied merger fractions ~50% up to z=1.2, although they are slightly more symmetric than local LIRGs. For general field galaxies, we find an almost constant relatively high merger fraction (20-30%). The B-band LFs of galaxy mergers are derived at different redshifts up to z=1.2 and confirm the weak evolution of the merger fraction after breaking the luminosity-density degeneracy. The IR luminosity functions (LFs) of galaxy mergers are also derived, indicating a larger merger fraction at higher IR luminosity. The integral of the merger IR LFs indicates a dramatic evolution of the merger-induced IR energy density [(1+z)^(5-6)}], and that galaxy mergers start to dominate the cosmic IR energy density at z>~1.Comment: Accepted for publication in ApJ, 25 pages, 23 figures (2 colors). The high-resolution pdf is at http://cztsy.as.arizona.edu/~yong/Research/SHI_MERGER.pd

Primordial r-process Dispersion in Metal-Poor Globular Clusters

Heavy elements, those produced by neutron-capture reactions, have traditionally shown no star-to-star dispersion in all but a handful of metal-poor globular clusters (GCs). Recent detections of low [Pb/Eu] ratios or upper limits in several metal-poor GCs indicate that the heavy elements in these GCs were produced exclusively by an r-process. Reexamining GC heavy element abundances from the literature, we find unmistakable correlations between the [La/Fe] and [Eu/Fe] ratios in 4 metal-poor GCs (M5, M15, M92, and NGC 3201), only 2 of which were known previously. This indicates that the total r-process abundances vary star-to-star (by factors of 2-6) relative to Fe within each GC. We also identify potential dispersion in two other GCs (M3 and M13). Several GCs (M12, M80, and NGC 6752) show no evidence of r-process dispersion. The r-process dispersion is not correlated with the well-known light element dispersion, indicating it was present in the gas throughout the duration of star formation. The observations available at present suggest that star-to-star r-process dispersion within metal-poor GCs may be a common but not ubiquitous phenomenon that is neither predicted by nor accounted for in current models of GC formation and evolution.Comment: Accepted for publication in the Astrophysical Journal Letters (6 pages, 2 figures). v2: references update

A_4 flavour symmetry breaking scheme for understanding quark and neutrino mixing angles

We propose a spontaneous A_4 flavour symmetry breaking scheme to understand the observed pattern of quark and neutrino mixing. The fermion mass eigenvalues are arbitrary, but the mixing angles are constrained in such a way that the overall patterns are explained while also leaving sufficient freedom to fit the detailed features of the observed values, including CP violating phases. The scheme realises the proposal of Low and Volkas to generate zero quark mixing and tribimaximal neutrino mixing at tree-level, with deviations from both arising from small corrections after spontaneous A_4 breaking. In the neutrino sector, the breaking is A_4 --> Z_2, while in the quark and charged-lepton sectors it is A_4 --> Z_3 = C_3. The full theory has A_4 completely broken, but the two different unbroken subgroups in the two sectors force the dominant mixing patterns to be as stated above. Radiative effects within each sector are shown to deviate neutrino mixing from tribimaximal, while maintaining zero quark mixing. Interactions between the two sectors -- "cross-talk" -- induce nonzero quark mixing, and additional deviation from tribimaximal neutrino mixing. We discuss the vacuum alignment challenge the scenario faces, and suggest three generic ways to approach the problem. We follow up one of those ways by sketching how an explicit model realising the symmetry breaking structure may be constructed.Comment: 14 pages, no figures; v3: Section 5 rewritten to correct an error; new section added to the appendix; added references; v4: minor change to appendix C, version to be published by JHE

Swinging between shine and shadow: Theoretical advances on thermally-activated vibropolaritonic chemistry (a perspective)

Polariton chemistry has emerged as an appealing branch of synthetic chemistry that promises mode selectivity and a cleaner approach to kinetic control. Of particular interest are the numerous experiments in which reactivity has been modified by virtue of performing the reaction inside infrared optical microcavities in the absence of optical pumping; this effort is known as "vibropolaritonic chemistry." The optimal conditions for these observations are (1) resonance between cavity and reactive modes at normal incidence ($k=0$), and (2) monotonic increase of the effect with the concentration of emitters in the sample. Importantly, vibropolaritonic chemistry has only been experimentally demonstrated in the so-called "collective" strong coupling regime, where there is a macroscopic number of molecules (rather than a single molecule) coupled to each photon mode of the microcavity. Strikingly, efforts to understand this phenomenon from a conceptual standpoint have encountered several roadblocks and no single, unifying theory has surfaced thus far. This perspective documents the most relevant approaches taken by theorists, laying out the contributions and unresolved challenges from each work. We expect this manuscript to not only serve as a primer for experimentalists and theorists alike, but also inform future endeavors in the quest for the ultimate formalism of vibropolaritonic chemical kinetics.Comment: 18 pages, 5 figure

Influence of Coalescence on the Anisotropic Mechanical and Electrical Properties of Nickel Powder/Polydimethylsiloxane Composites.

Multifunctional polymer-based composites have been widely used in various research and industrial applications, such as flexible and stretchable electronics and sensors and sensor-integrated smart structures. This study investigates the influence of particle coalescence on the mechanical and electrical properties of spherical nickel powder (SNP)/polydimethylsiloxane (PDMS) composites in which SNP was aligned using an external magnetic field. With the increase of the volume fraction of the SNP, the aligned SNP/PDMS composites exhibited a higher tensile strength and a lower ultimate strain. In addition, the composites with aligned SNP showed a lower percolation threshold and a higher electrical conductivity compared with those with randomly dispersed SNP. However, when the concentration of the SNP reached a certain level (40 vol. %), the anisotropy of the effective material property became less noticeable than that of the lower concentration (20 vol. %) composites due to the change of the microstructure of the particles caused by the coalescence of the particles at a high concentration. This work may provide rational methods for the fabrication of aligned composites

The Wide-Field X and Gamma-Ray Telescope ECLAIRs aboard the Gamma-Ray Burst Multi-Wavelength Space Mission SVOM

The X and Gamma-ray telescope ECLAIRs is foreseen to be launched on a low Earth orbit (h=630 km, i=30 degrees) aboard the SVOM satellite (Space-based multi-band astronomical Variable Objects Monitor), a French-Chinese mission with Italian contribution. Observations are expected to start in 2013. It has been designed to detect and localize Gamma-Ray Bursts (GRBs) or persistent sources of the sky, thanks to its wide field of view (about 2 sr) and its remarkable sensitivity in the 4-250 keV energy range, with enhanced imaging sensitivity in the 4-70 keV energy band. These characteristics are well suited to detect highly redshifted GRBs, and consequently to provide fast and accurate triggers to other onboard or ground-based instruments able to follow-up the detected events in a very short time from the optical wavelength bands up to the few MeV Gamma-Ray domain.Comment: Proccedings of the "2008 Nanjing GRB Conference", June 23-27 2008, Nanjing, Chin

GABAergic synaptic scaling is triggered by changes in spiking activity rather than transmitter receptor activation

Homeostatic plasticity represents a set of mechanisms that are thought to recover some aspect of neural function. One such mechanism called AMPAergic scaling was thought to be a likely candidate to homeostatically control spiking activity. However, recent findings have forced us to reconsider this idea as several studies suggest AMPAergic scaling is not directly triggered by changes in spiking. Moreover, studies examining homeostatic perturbations in vivo have suggested that GABAergic synapses may be more critical in terms of spiking homeostasis. Here we show results that GABAergic scaling can act to homeostatically control spiking levels. We find that increased or decreased spiking in cortical cultures triggers multiplicative GABAergic upscaling and downscaling, respectively. In contrast, we find that changes in AMPAR or GABAR transmission only influence GABAergic scaling through their indirect effect on spiking. We propose that GABAergic scaling, rather than glutamatergic scaling, is a key player in spike rate homeostasis

Broad-bandwidth Brillouin slow light in optical fibers

We experimentally demonstrate that Brillouin slow light with an arbitrary large bandwidth can be readily obtained in conventional optical fibers using a simple and inexpensive pump spectral broadening techniqu