Multi-spin dynamics of the solid-state NMR Free Induction Decay

We present a new experimental investigation of the NMR free induction decay (FID) in a lattice of spin-1/2 nuclei in a strong Zeeman field. Following a pi/2 pulse, evolution under the secular dipolar Hamiltonian preserves coherence number in the Zeeman eigenbasis, but changes the number of correlated spins in the state. The observed signal is seen to decay as single-spin, single-quantum coherences evolve into multiple-spin coherences under the action of the dipolar Hamiltonian. In order to probe the multiple-spin dynamics during the FID, we measured the growth of coherence orders in a basis other than the usual Zeeman eigenbasis. This measurement provides the first direct experimental observation of the growth of coherent multiple-spin correlations during the FID. Experiments were performed with a cubic lattice of spins (19F in calcium fluoride) and a linear spin chain (19F in fluorapatite). It is seen that the geometrical arrangement of the spins plays a significant role in the development of higher order correlations. The results are discussed in light of existing theoretical models.Comment: 7 pages, 6 figure

Enhanced resolution imaging of ultrathin ZnO layers on Ag(111) by multiple hydrogen molecules in a scanning tunneling microscope junction

Molecular hydrogen in a scanning tunneling microscope (STM) junction has been found to enhance the lateral spatial resolution of the STM imaging, referred to as scanning tunneling hydrogen microscopy (STHM). Here we report atomic resolution imaging of 2- and 3-monolayer (ML) thick ZnO layers epitaxially grown on Ag(111) using STHM. The enhanced resolution can be obtained at a relatively large tip to surface distance and resolves a more defective structure exhibiting dislocation defects for 3-ML-thick ZnO than for 2 ML. In order to elucidate the enhanced imaging mechanism, the electric and mechanical properties of the hydrogen molecular junction (HMJ) are investigated by a combination of STM and atomic force microscopy. It is found that the HMJ shows multiple kinklike features in the tip to surface distance dependence of the conductance and frequency shift curves, which are absent in a hydrogen-free junction. Based on a simple modeling, we propose that the junction contains several hydrogen molecules and sequential squeezing of the molecules out of the junction results in the kinklike features in the conductance and frequency shift curves. The model also qualitatively reproduces the enhanced resolution image of the ZnO films

A Novel Use of Light Guides and Wavelength Shifting Plates for the Detection of Scintillation Photons in Large Liquid Argon Detectors

Scintillation light generated as charged particles traverse large liquid argon detectors adds valuable information to studies of weakly-interacting particles. This paper uses both laboratory measurements and cosmic ray data from the Blanche dewar facility at Fermilab to characterize the efficiency of the photon detector technology developed at Indiana University for the single phase far detector of DUNE. The efficiency of this technology was found to be 0.48% at the readout end when the detector components were characterized with laboratory measurements. A second determination of the efficiency using cosmic ray tracks is in reasonable agreement with the laboratory determination. The agreement of these two efficiency determinations supports the result that minimum ionizing muons generate ${\mathcal N}_{phot} = 40,000$ photons/MeV as they cross the LAr volume.Comment: Accepted version (without final editorial corrections

Social Communication Across Reproductive Boundaries: Hormones And The Auditory Periphery Of Songbirds And Frogs

Most animals experience reproductive transitions in their lives; for instance, reaching reproductive maturity or cycling in and out of breeding condition. Some reproductive transitions are abrupt, while others are more gradual. In most cases, changes in communication between the sexes follow the time course of these reproductive transitions and are typically thought to be coordinated by steroid hormones. We know a great deal about hormonal control of communication behaviors in birds and frogs, as well as the central neural control of these behaviors. There has also been significant interest in the effects of steroid hormones on central nervous system structures that control both the production and reception of communication signals associated with reproductive behaviors. However, peripheral sensory structures have typically received less attention, although there has been growing interest in recent years. It is becoming clear that peripheral sensory systems play an important role in reproductive communication, are plastic across reproductive conditions, and, in some cases, this plasticity may be mediated by steroid hormones. In this paper, we discuss recent evidence for the role of peripheral auditory structures in reproductive communication in birds and frogs, the plasticity of the peripheral auditory system, and the role of steroid hormones in mediating the effects of the peripheral auditory system on reproductive communication. We focus on both seasonal and acute reproductive transitions, introduce new data on the role of hormones in modulating seasonal patterns, and make recommendations for future work

Cosmic cookery : making a stereoscopic 3D animated movie.

This paper describes our experience making a short stereoscopic movie visualizing the development of structure in the universe during the 13.7 billion years from the Big Bang to the present day. Aimed at a general audience for the Royal Society's 2005 Summer Science Exhibition, the movie illustrates how the latest cosmological theories based on dark matter and dark energy are capable of producing structures as complex as spiral galaxies and allows the viewer to directly compare observations from the real universe with theoretical results. 3D is an inherent feature of the cosmology data sets and stereoscopic visualization provides a natural way to present the images to the viewer, in addition to allowing researchers to visualize these vast, complex data sets. The presentation of the movie used passive, linearly polarized projection onto a 2m wide screen but it was also required to playback on a Sharp RD3D display and in anaglyph projection at venues without dedicated stereoscopic display equipment. Additionally lenticular prints were made from key images in the movie. We discuss the following technical challenges during the stereoscopic production process; 1) Controlling the depth presentation, 2) Editing the stereoscopic sequences, 3) Generating compressed movies in display speci¯c formats. We conclude that the generation of high quality stereoscopic movie content using desktop tools and equipment is feasible. This does require careful quality control and manual intervention but we believe these overheads are worthwhile when presenting inherently 3D data as the result is signi¯cantly increased impact and better understanding of complex 3D scenes

Quasar Clustering and the Lifetime of Quasars

Although the population of luminous quasars rises and falls over a period of 10^9 years, the typical lifetime of individual quasars is uncertain by several orders of magnitude. We show that quasar clustering measurements can substantially narrow the range of possible lifetimes with the assumption that luminous quasars reside in the most massive host halos. If quasars are long-lived, then they are rare phenomena that are highly biased with respect to the underlying dark matter, while if they are short-lived they reside in more typical halos that are less strongly clustered. For a given quasar lifetime, we calculate the minimum host halo mass by matching the observed space density of quasars, using the Press-Schechter approximation. We use the results of Mo & White to calculate the clustering of these halos, and hence of the quasars they contain, as a function of quasar lifetime. A lifetime of t_Q = 4 x 10^7 years, the e-folding timescale of an Eddington luminosity black hole with accretion efficiency eps=0.1, corresponds to a quasar correlation length r_0 ~ 10 Mpc/h in low-density cosmological models at z=2-3; this value is consistent with current clustering measurements, but these have large uncertainties. High-precision clustering measurements from the 2dF and Sloan quasar surveys will test our key assumption of a tight correlation between quasar luminosity and host halo mass, and if this assumption holds then they should determine t_Q to a factor of three or better. An accurate determination of the quasar lifetime will show whether supermassive black holes acquire most of their mass during high-luminosity accretion, and it will show whether the black holes in the nuclei of typical nearby galaxies were once the central engines of high-luminosity quasars.Comment: ApJ Accepted (Feb 2001). 30 pages, 8 embedded ps figures, AASTEX5. Added discussion of quasar luminosity evolution. Also available at http://www.ociw.edu/~martini/pubs

The Bulge-Disk Orthogonal Decoupling in Galaxies: NGC 4698

The R-band isophotal map of the Sa galaxy NGC 4698 shows that the inner region of the bulge structure is elongated perpendicularly to the major axis of the disk, this is also true for the outer parts of the bulge if a parametric photometric decomposition is adopted. At the same time the stellar component is characterized by an inner velocity gradient and a central zero-velocity plateau along the minor and major axis of the disk respectively. This remarkable geometric and kinematic decoupling suggests that a second event occurred in the formation history of this galaxy.Comment: 12 pages, LaTex, with 4 PostScript figures. Accepted for publication in The Astrophysical Journal Letter

First Measurement of the Clustering Evolution of Photometrically-Classified Quasars

We present new measurements of the quasar autocorrelation from a sample of \~80,000 photometrically-classified quasars taken from SDSS DR1. We find a best-fit model of $\omega(\theta) = (0.066\pm^{0.026}_{0.024})\theta^{-(0.98\pm0.15)}$ for the angular autocorrelation, consistent with estimates from spectroscopic quasar surveys. We show that only models with little or no evolution in the clustering of quasars in comoving coordinates since z~1.4 can recover a scale-length consistent with local galaxies and Active Galactic Nuclei (AGNs). A model with little evolution of quasar clustering in comoving coordinates is best explained in the current cosmological paradigm by rapid evolution in quasar bias. We show that quasar biasing must have changed from b_Q~3 at a (photometric) redshift of z=2.2 to b_Q~1.2-1.3 by z=0.75. Such a rapid increase with redshift in biasing implies that quasars at z~2 cannot be the progenitors of modern L* objects, rather they must now reside in dense environments, such as clusters. Similarly, the duration of the UVX quasar phase must be short enough to explain why local UVX quasars reside in essentially unbiased structures. Our estimates of b_Q are in good agreement with recent spectroscopic results, which demonstrate the implied evolution in b_Q is consistent with quasars inhabiting halos of similar mass at every redshift. Treating quasar clustering as a function of both redshift and luminosity, we find no evidence for luminosity dependence in quasar clustering, and that redshift evolution thus affects quasar clustering more than changes in quasars' luminosity. We provide a new method for quantifying stellar contamination in photometrically-classified quasar catalogs via the correlation function.Comment: 34 pages, 10 figures, 1 table, Accepted to ApJ after: (i) Minor textual changes; (ii) extra points added to Fig.

The Canada-UK Deep Submillimeter Survey VI: The 3-Hour Field

We present the complete submillimeter data for the Canada-UK Deep Submillimeter Survey (CUDSS) 3-hour field. The obeservations were taken with the Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope on Mauna Kea. The 3-hour field is one of two main fields in our survey and covers 60 square arcminutes to a 3-sigma depth of 3 mJy. In this field we have detected 27 sources above 3-sigma and 15 above 3.5-sigma. We assume the source counts follow the form $N(S) {\propto} S^{-\alpha}$ and measure $\alpha$ = 3.3$^{+1.4}_{-1.0}$. This is in good agreement with previous studies and further supports our claim (Eales et al., 2000) that SCUBA sources brighter than 3 mJy produce ~20% of the 850$\mu$m background energy. Using preliminary ISO 15 $\mu$m maps and VLA 1.4 GHz data we have identified counterparts for six objects and have marginal detections at 450$\mu$m for two additional sources. With this information we estimate a median redshift for the sample of 2.0$\pm$0.5, with $\sim$10% lying at $z<$ 1. We have measured the angular clustering of S850 > 3 mJy sources using the source catalogues from the CUDSS two main fields, the 3-hour and 14-hour fields, and find a marginal detection of clustering, primarily from the 14-hour field, of $\omega(\theta)=4.4\pm2.9 \theta^{-0.8}$. This is consistent with clustering at least as strong as that seen for the Lyman-break galaxy population and the Extremely Red Objects. Since SCUBA sources are selected over a broader range in redshifts than these two populations the strength of the true spatial clustering is expected to be correspondingly stronger.Comment: 17 pages, 8 figures, submitted to Ap

The Lx-T Relation and Temperature Function for Nearby Clusters Revisited

The X-ray luminosity-temperature relation for nearby T=3.5-10 keV clusters is rederived using new ASCA temperatures and ROSAT luminosities. Both quantities are derived by directly excluding the cooling flow regions. This correction results in a greatly reduced scatter in the Lx-T relation; cooling flow clusters are similar to others outside the small cooling flow regions. For a fit of the form L_bol ~ T^alpha, we obtain alpha=2.64+-0.27 (90%) and a residual rms scatter in log L_bol of 0.10. The derived relation can be directly compared to theoretical predictions that do not include radiative cooling. It also provides an accurate reference point for future evolution searches and comparison to cooler clusters. The new temperatures together with a newly selected cluster sample are used to update the temperature function at z~0.05. The resulting function is generally higher and flatter than the previous estimates by Edge et al (1990) and Henry & Arnaud (1991, corrected). For a qualitative estimate of constraints that the new data place on the density fluctuation spectrum, we apply the Press-Schechter formalism for Omega=1 and 0.3. For Omega=1, assuming cluster isothermality, the temperature function implies sigma_8=0.55+-0.03, while taking into account the observed cluster temperature profiles, sigma_8=0.51+-0.03, consistent with the previously derived range. The dependence of sigma_8 on Omega differs from earlier findings, because of our treatment of n as a free parameter. We find n=-(2.0-2.3)+-0.3, somewhat steeper than derived from the earlier temperature function data, in agreement with the local slope of the galaxy fluctuation spectrum from the APM survey, and significantly steeper than the standard CDM prediction.Comment: Accepted for ApJ. Significand additions: Omega=0.3 model for the TF; a discussion of the TF derivation method; a comparison with recent Allen & Fabian L-T results. Latex, 8 pages, uses emulateapj.st