The Trouble with Hubble Types in the Virgo Cluster

Quantitative measures of central light concentration and star formation activity are derived from R and Halpha surface photometry of 84 bright S0-Scd Virgo Cluster and isolated spiral galaxies. For isolated spirals, there is a good correlation between these two parameters and assigned Hubble types. In the Virgo Cluster, the correlation between central light concentration and star formation activity is significantly weaker. Virgo Cluster spirals have systematically reduced global star formation with respect to isolated spirals, with severe reduction in the outer disk, but normal or enhanced activity in the inner disk. Assigned Hubble types are thus inadequate to describe the range in morphologies of bright Virgo Cluster spirals. In particular, spirals with reduced global star formation activity are often assigned misleading early-type classifications, irrespective of their central light concentrations. 45+-25% of the galaxies classified as Sa in the Virgo Cluster sample have central light concentrations more characteristic of isolated Sb-Sc galaxies. The misleading classification of low concentration galaxies with low star formation rates as early-type spirals may account for part of the excess of `early-type' spiral galaxies in clusters. Thus the morphology-density relationship is not all due to a systematic increase in the bulge-to-disk ratio with environmental density.Comment: Accepted for publication in ApJ Letters. Latex aaspp4.sty, 9 pages, 2 Postscript (embedded) figures. Also available at http://www.astro.yale.edu/koopmann/preprint.htm

Stabilizing nuclear spins around semiconductor electrons via the interplay of optical coherent population trapping and dynamic nuclear polarization

We experimentally demonstrate how coherent population trapping (CPT) for donor-bound electron spins in GaAs results in autonomous feedback that prepares stabilized states for the spin polarization of nuclei around the electrons. CPT was realized by excitation with two lasers to a bound-exciton state. Transmission studies of the spectral CPT feature on an ensemble of electrons directly reveal the statistical distribution of prepared nuclear spin states. Tuning the laser driving from blue to red detuned drives a transition from one to two stable states. Our results have importance for ongoing research on schemes for dynamic nuclear spin polarization, the central spin problem and control of spin coherence.Comment: 5 pages, 4 figure

Split-gate quantum point contacts with tunable channel length

We report on developing split-gate quantum point contacts (QPCs) that have a tunable length for the transport channel. The QPCs were realized in a GaAs/AlGaAs heterostructure with a two- dimensional electron gas (2DEG) below its surface. The conventional design uses 2 gate fingers on the wafer surface which deplete the 2DEG underneath when a negative gate voltage is applied, and this allows for tuning the width of the QPC channel. Our design has 6 gate fingers and this provides additional control over the form of the electrostatic potential that defines the channel. Our study is based on electrostatic simulations and experiments and the results show that we developed QPCs where the effective channel length can be tuned from about 200 nm to 600 nm. Length-tunable QPCs are important for studies of electron many-body effects because these phenomena show a nanoscale dependence on the dimensions of the QPC channel

Magnetic Properties of Cadmium Manganese Ferrite

The room-temperature saturation magnetization of CdxMn1-xFe2O4 decreased with increasing cadmium concentration. When 0 \u3c x \u3c 0.5, the decrease in saturation magnetization was due to the increase in the amount of non-mgnetic distorted cubic Cd(Mn, Fe) 2O4

Formation and Densification of Cadmium Manganese Ferrite

Formation of Ni-ferrite, Mn-ferrite, NiZn-ferrite, Zn-ferrite and Mg-ferrite have been investigated using X-ray diffraction analysis. Jander\u27s diffusion equation described the data from these investigations over a portion of the temperature ranges studied. However, the reaction mechanisms and sequences involved in the formation of mixed ferrites have not been well defined in the literature. The purposes of this investigation were: ( 1) To further the understanding of the formation of CdMnferrite by studying first the kinetics of the formation of Cd-ferrite and Cd-manganite, which provides a basis for understanding the details of the mixed CdMn-ferrite reaction and to obtain the optimum temperature-time cycle for calcination and sintering, along with the reaction sequence and densification behavior for polycrystalline CdMn-ferrite. (2) To determine the magnetic properties of CdMn-ferrite as a function of composition, bulk density and grain size

Trigeminal nerve morphology in the American alligator : implications for infering sensory potential in extinct species [abstract]

Among the many adaptations of modern crocodilians, one of the most intriguing is their derived sense of face touch, in which numerous trigeminal nerve-innervated dome pressure receptors speckle the face and mandible and sense vibrations and other mechanical stimuli, directing the animal towards, or away from stimuli. However, the morphological features of this system are not well known, and it remains unclear how aspects of the trigeminal system change during ontogeny and how they scale with other cranial and nervous structures

Intelligent multimedia indexing and retrieval through multi-source information extraction and merging

This paper reports work on automated meta-data\ud creation for multimedia content. The approach results\ud in the generation of a conceptual index of\ud the content which may then be searched via semantic\ud categories instead of keywords. The novelty\ud of the work is to exploit multiple sources of\ud information relating to video content (in this case\ud the rich range of sources covering important sports\ud events). News, commentaries and web reports covering\ud international football games in multiple languages\ud and multiple modalities is analysed and the\ud resultant data merged. This merging process leads\ud to increased accuracy relative to individual sources

A Look At Three Different Scenarios for Bulge Formation

In this paper, we present three qualitatively different scenarios for bulge formation: a secular evolution model in which bulges form after disks and undergo several central starbursts, a primordial collapse model in which bulges and disks form simultaneously, and an early bulge formation model in which bulges form prior to disks. We normalize our models to the local z=0 observations of de Jong & van der Kruit (1994) and Peletier & Balcells (1996) and make comparisons with high redshift observations. We consider model predictions relating directly to bulge-to-disk properties. As expected, smaller bulge-to-disk ratios and bluer bulge colors are predicted by the secular evolution model at all redshifts, although uncertainties in the data are currently too large to differentiate strongly between the models.Comment: 19 pages, 6 figures, accepted for publication in the Astrophysical Journa