Counts and Sizes of Galaxies in the Hubble Deep Field - South: Implications for the Next Generation Space Telescope

Science objectives for the Next Generation Space Telescope (NGST) include a large component of galaxy surveys, both imaging and spectroscopy. The Hubble Deep Field datasets include the deepest observations ever made in the ultraviolet, optical and near infrared, reaching depths comparable to that expected for NGST spectroscopy. We present the source counts, galaxy sizes and isophotal filling factors of the HDF-South images. The observed integrated galaxy counts reach >500 galaxies per square arcminute at AB<30. We extend these counts to faint levels in the infrared using models. The trend previously seen that fainter galaxies are smaller, continues to AB=29 in the high resolution HDF-S STIS image, where galaxies have a typical half-light radius of 0.1 arcseconds. Extensive Monte Carlo simulations show that the small measured sizes are not due to selection effects until >29mag. Using the HDF-S NICMOS image, we show that galaxies are smaller in the near infrared than they are in the optical. We analyze the isophotal filling factor of the HDF-S STIS image, and show that this image is mostly empty sky even at the limits of galaxy detection, a conclusion we expect to hold true for NGST spectroscopy. At the surface brightness limits expected for NGST imaging, however, about a quarter of the sky is occupied by the outer isophotes of AB<30 galaxies. We discuss the implications of these data on several design concepts of the NGST near-infrared spectrograph. We compare the effects of resolution and the confusion limit of various designs, as well as the multiplexing advantages of either multi-object or full-field spectroscopy. We argue that the optimal choice for NGST spectroscopy of high redshift galaxies is a multi-object spectrograph (MOS) with target selection by a micro electro mechanical system (MEMS) device.Comment: 27 pages including 10 figures, accepted for publication in the Astronomical Journal, June 2000, abridged abstrac

Kinematic Evolution of Simulated Star-Forming Galaxies

Recent observations have shown that star-forming galaxies like our own Milky Way evolve kinematically into ordered thin disks over the last ~8 billion years since z=1.2, undergoing a process of "disk settling." For the first time, we study the kinematic evolution of a suite of four state of the art "zoom in" hydrodynamic simulations of galaxy formation and evolution in a fully cosmological context and compare with these observations. Until now, robust measurements of the internal kinematics of simulated galaxies were lacking as the simulations suffered from low resolution, overproduction of stars, and overly massive bulges. The current generation of simulations has made great progress in overcoming these difficulties and is ready for a kinematic analysis. We show that simulated galaxies follow the same kinematic trends as real galaxies: they progressively decrease in disordered motions (sigma_g) and increase in ordered rotation (Vrot) with time. The slopes of the relations between both sigma_g and Vrot with redshift are consistent between the simulations and the observations. In addition, the morphologies of the simulated galaxies become less disturbed with time, also consistent with observations, and they both have similarly large scatter. This match between the simulated and observed trends is a significant success for the current generation of simulations, and a first step in determining the physical processes behind disk settling.Comment: ApJ accepted; 6 pages; A pdf with full resolution figures can be found at https://db.tt/8y4Vzaff (2.8M

An inventory and condition survey of the Western Australian part of the Nullarbor region

The inventory and condition survey of the Western Australian part of the Nullarbor region, undertaken by the Department of Agriculture and Food, Western Australia (DAFWA) between 2005 and 2007, describes and maps the natural resources of the region. This survey report provides a baseline record of the existence and condition of the area\u27s natural resources, to assist with the planning and implementation of land management practices. The report identified and described the condition of soils, landforms, vegetation, habitat, ecosystems, and declared plants and animals. It also assessed the impact of pastoralism and made land management recommendations. The Nullarbor region has unique, extensive, gently undulating stony plains of limestone karst that form the Bunda Plateau. As well as vast treeless plains through the region\u27s centre, the Bunda Plateau is Australia’s largest karst and the world’s largest arid karst region (~250 000km²). An area of about 118 358km² was covered in the Nullarbor survey. The northern survey limits are defined by pastoral lease boundaries. The southern limits of the survey area are bounded by the Southern Ocean. The western limits of the survey area are defined by the western-most Nullarbor pastoral lease boundaries. The eastern limit of the survey is defined by the Western Australian–South Australian border. Pastoralism is the most extensive land use. Twenty pastoral leases fall wholly within the survey area and collectively occupy about 57 673km² (49% of the area). Eighteen soil groups are identified within the survey area. The most common soil group is calcareous shallow loams, occurring on all but coastal and sub-coastal land systems. In comparison with other biogeographic regions in the State, the flora of the Nullarbor area is not particularly diverse, with 426 vascular species recorded during the survey

Stability of the replica symmetric solution for the information conveyed by by a neural network

The information that a pattern of firing in the output layer of a feedforward network of threshold-linear neurons conveys about the network's inputs is considered. A replica-symmetric solution is found to be stable for all but small amounts of noise. The region of instability depends on the contribution of the threshold and the sparseness: for distributed pattern distributions, the unstable region extends to higher noise variances than for very sparse distributions, for which it is almost nonexistant.Comment: 19 pages, LaTeX, 5 figures. Also available at http://www.mrc-bbc.ox.ac.uk/~schultz/papers.html . Submitted to Phys. Rev. E Minor change

Correlations between hidden units in multilayer neural networks and replica symmetry breaking

We consider feed-forward neural networks with one hidden layer, tree architecture and a fixed hidden-to-output Boolean function. Focusing on the saturation limit of the storage problem the influence of replica symmetry breaking on the distribution of local fields at the hidden units is investigated. These field distributions determine the probability for finding a specific activation pattern of the hidden units as well as the corresponding correlation coefficients and therefore quantify the division of labor among the hidden units. We find that although modifying the storage capacity and the distribution of local fields markedly replica symmetry breaking has only a minor effect on the correlation coefficients. Detailed numerical results are provided for the PARITY, COMMITTEE and AND machines with K=3 hidden units and nonoverlapping receptive fields.Comment: 9 pages, 3 figures, RevTex, accepted for publication in Phys. Rev.

First-Digit Law in Nonextensive Statistics

Nonextensive statistics, characterized by a nonextensive parameter $q$, is a promising and practically useful generalization of the Boltzmann statistics to describe power-law behaviors from physical and social observations. We here explore the unevenness of the first digit distribution of nonextensive statistics analytically and numerically. We find that the first-digit distribution follows Benford's law and fluctuates slightly in a periodical manner with respect to the logarithm of the temperature. The fluctuation decreases when $q$ increases, and the result converges to Benford's law exactly as $q$ approaches 2. The relevant regularities between nonextensive statistics and Benford's law are also presented and discussed.Comment: 11 pages, 3 figures, published in Phys. Rev.

Expressiveness and complexity of graph logic

We investigate the complexity and expressive power of the spatial logic for querying graphs introduced by Cardelli, Gardner and Ghelli (ICALP 2002).We show that the model-checking complexity of versions of this logic with and without recursion is PSPACE-complete. In terms of expressive power, the version without recursion is a fragment of the monadic second-order logic of graphs and we show that it can express complete problems at every level of the polynomial hierarchy. We also show that it can define all regular languages, when interpretation is restricted to strings. The expressive power of the logic with recursion is much greater as it can express properties that are PSPACE-complete and therefore unlikely to be definable in second-order logic

Local reasoning about mashups

Web mashups are complex programs that dynamically compose XML data and JavaScript code from many sources. Whereas data is sometimes formally specified by XML schema, code never is. This makes it difficult to construct reliable software. Using local Hoare reasoning, introduced in separation logic to reason about e.g. C programs and extended in context logic to reason about e.g. the DOM library, we are able to reason about mashup programs, proving that they are fault-free and providing specifications for code that are analogous to XML schema for data

Fatty-acid uptake in prostate cancer cells using dynamic microfluidic raman technology

It is known that intake of dietary fatty acid (FA) is strongly correlated with prostate cancer progression but is highly dependent on the type of FAs. High levels of palmitic acid (PA) or arachidonic acid (AA) can stimulate the progression of cancer. In this study, a unique experimental set-up consisting of a Raman microscope, coupled with a commercial shear-flow microfluidic system is used to monitor fatty acid uptake by prostate cancer (PC-3) cells in real-time at the single cell level. Uptake of deuterated PA, deuterated AA, and the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were monitored using this new system, while complementary flow cytometry experiments using Nile red staining, were also conducted for the validation of the cellular lipid uptake. Using this novel experimental system, we show that DHA and EPA have inhibitory effects on the uptake of PA and AA by PC-3 cells