The Las Campanas Infra-red Survey. V. Keck Spectroscopy of a large sample of Extremely Red Objects

(Abridged) We present deep Keck spectroscopy, using the DEIMOS and LRIS spectrographs, of a large and representative sample of 67 ``Extremely Red Objects'' (EROs) to H=20.5, with I-H>3.0, in three of the Las Campanas Infrared Survey fields. Spectroscopic redshifts are determined for 44 sources, of which only two are contaminating low mass stars. When allowance is made for incompleteness, the spectroscopic redshift distribution closely matches that predicted earlier on the basis of photometric data. Our spectra are of sufficient quality that we can address the important question of the nature and homogeneity of the z>0.8 ERO population. A dominant old stellar population is inferred for 75% of our spectroscopic sample; a higher fraction than that seen in smaller, less-complete samples with broader photometric selection criteria (e.g. R-K). However, only 28% have spectra with no evidence of recent star formation activity, such as would be expected for a strictly passively-evolving population. More than ~30% of our absorption line spectra are of the `E+A' type with prominent Balmer absorption consistent, on average, with mass growth of 5-15% in the past Gyr. We use our spectroscopic redshifts to improve earlier estimates of the spatial clustering of this population as well as to understand the significant field-to-field variation. Our spectroscopy enables us to pinpoint a filamentary structure at z=1.22 in the Chandra Deep Field South. Overall, our study suggests that the bulk of the ERO population is an established population of clustered massive galaxies undergoing intermittent activity consistent with continued growth over the redshift interval 0.8<z<1.6.Comment: 27 pages, including 14 figures and appendix of spectra (at low resolution). Full resolution paper can be found at http://www.ast.cam.ac.uk/~md . To appear in MNRA

NASA's progress in nuclear electric propulsion technology

The National Aeronautics and Space Administration (NASA) has established a requirement for Nuclear Electric Propulsion (NEP) technology for robotic planetary science mission applications with potential future evolution to systems for piloted Mars vehicles. To advance the readiness of NEP for these challenging missions, a near-term flight demonstration on a meaningful robotic science mission is very desirable. The requirements for both near-term and outer planet science missions are briefly reviewed, and the near-term baseline system established under a recent study jointly conducted by the Lewis Research Center (LeRC) and the Jet Propulsion Laboratory (JPL) is described. Technology issues are identified where work is needed to establish the technology for the baseline system, and technology opportunities which could provide improvement beyond baseline capabilities are discussed. Finally, the plan to develop this promising technology is presented and discussed

Analysis using large-scale ringing data

Birds are highly mobile organisms and there is increasing evidence that studies at large spatial scales are needed if we are to properly understand their population dynamics. While classical metapopulation models have rarely proved useful for birds, more general metapopulation ideas involving collections of populations interacting within spatially structured landscapes are highly relevant (Harrison, 1994). There is increasing interest in understanding patterns of synchrony, or lack of synchrony, between populations and the environmental and dispersal mechanisms that bring about these patterns (Paradis et al., 2000). To investigate these processes we need to measure abundance, demographic rates and dispersal at large spatial scales, in addition to gathering data on relevant environmental variables. There is an increasing realisation that conservation needs to address rapid declines of common and widespread species (they will not remain so if such trends continue) as well as the management of small populations that are at risk of extinction. While the knowledge needed to support the management of small populations can often be obtained from intensive studies in a few restricted areas, conservation of widespread species often requires information on population trends and processes measured at regional, national and continental scales (Baillie, 2001). While management prescriptions for widespread populations may initially be developed from a small number of local studies or experiments, there is an increasing need to understand how such results will scale up when applied across wider areas. There is also a vital role for monitoring at large spatial scales both in identifying such population declines and in assessing population recovery. Gathering data on avian abundance and demography at large spatial scales usually relies on the efforts of large numbers of skilled volunteers. Volunteer studies based on ringing (for example Constant Effort Sites [CES]; Peach et al., 1998; DeSante et al., 2001) are generally co–ordinated by ringing centres such as those that make up the membership of EURING. In some countries volunteer census work (often called Breeding Bird Surveys) is undertaken by the same organizations while in others different bodies may co–ordinate this aspect of the work. This session was concerned with the analysis of such extensive data sets and the approaches that are being developed to address the key theoretical and applied issues outlined above. The papers reflect the development of more spatially explicit approaches to analyses of data gathered at large spatial scales. They show that while the statistical tools that have been developed in recent years can be used to derive useful biological conclusions from such data, there is additional need for further developments. Future work should also consider how to best implement such analytical developments within future study designs. In his plenary paper Andy Royle (Royle, 2004) addresses this theme directly by describing a general framework for modelling spatially replicated abundance data. The approach is based on the idea that a set of spatially referenced local populations constitutes a metapopulation, within which local abundance is determined as a random process. This provides an elegant and general approach in which the metapopulation model as described above is combined with a data–generating model specific to the type of data being analysed to define a simple hierarchical model that can be analysed using conventional methods. It should be noted, however, that further software development will be needed if the approach is to be made readily available to biologists. The approach is well suited to dealing with sparse data and avoids the need for data aggregation prior to analysis. Spatial synchrony has received most attention in studies of species whose populations show cyclic fluctuations, particularly certain game birds and small mammals. However, synchrony is in fact a much more widespread process, with bird populations across wide areas showing similar trends and fluctuations as a result of common climatic and environmental factors (Paradis et al., 2000). Dispersal may also play an important role in such synchrony but its role is less well understood. Nigel Yoccoz and Rolf Ims (Yoccoz & Ims, 2004) show how synchrony can be investigated using data at three spatial scales taken from their field studies of the population dynamics of small mammals in North Norway. Small mammal abundance was estimated from trapping data using closed population models and also from total numbers of individuals captured. They use simulated data to show that synchrony, measured by the correlation coefficients between time series, was biased low by up to 30% when sampling variation was ignored. Appropriate analysis of such data will require simultaneous modelling of process and sampling variation, for example through the use of state–space models (Buckland et al., 2004). This view links back nicely to the approaches proposed by Andy Royle (Royle, 2004). Cycles in the abundance of small mammals have major affects on the demography of their predators, as is shown in the paper by Pertti Saurola and Charles Francis (Saurola & Francis, 2004). They report on the design and results of large–scale, long–term studies of owl populations by a network of amateur bird ringers in Finland. They show that breeding success varies with the stage of the microtine cycle. They also show how their data can be used to estimate dispersal over large spatial scales and illustrate the importance of correcting for uneven spatial variation in sampling effort. Further results from this study are reported in a companion paper within the population dynamics session (Francis & Saurola, 2004). Multi–species analyses of population dynamics are developed further in the paper by Romain Julliard (Julliard, 2004). He combines counts from the French Breeding Bird Survey with survival and recruitment estimates from the French CES scheme to assess the relative contributions of survival and recruitment to overall population changes. He develops a novel approach to modelling survival rates from such multi–site data by using within–year recaptures to provide a covariate of between–year recapture rates. This provided parsimonious models of variation in recapture probabilities between sites and years. The approach provides promising results for the four species investigated and can potentially be extended to similar data from other CES/MAPS schemes. The final paper by Blandine Doligez, David Thomson and Arie van Noordwijk (Doligez et al., 2004) illustrates how large-scale studies of population dynamics can be important for evaluating the effects of conservation measures. Their study is concerned with the reintroduction of White Stork populations to the Netherlands where a re–introduction programme started in 1969 had resulted in a breeding population of 396 pairs by 2000. They demonstrate the need to consider a wide range of models in order to account for potential age, time, cohort and "trap–happiness" effects. As the data are based on resightings such trap–happiness must reflect some form of heterogeneity in resighting probabilities. Perhaps surprisingly, the provision of supplementary food did not influence survival, but it may have had an indirect effect via the alteration of migratory behaviour. Spatially explicit modelling of data gathered at many sites inevitably results in starting models with very large numbers of parameters. The problem is often complicated further by having relatively sparse data at each site, even where the total amount of data gathered is very large. Both Julliard (2004) and Doligez et al. (2004) give explicit examples of problems caused by needing to handle very large numbers of parameters and show how they overcame them for their particular data sets. Such problems involve both the choice of appropriate starting models for sparse data and the speed with which convergence is achieved. Further analytical and software developments are needed in order to make it easier to analyse such data sets

On the suppression of the diffusion and the quantum nature of a cavity mode. Optical bistability; forces and friction in driven cavities

A new analytical method is presented here, offering a physical view of driven cavities where the external field cannot be neglected. We introduce a new dimensionless complex parameter, intrinsically linked to the cooperativity parameter of optical bistability, and analogous to the scaled Rabbi frequency for driven systems where the field is classical. Classes of steady states are iteratively constructed and expressions for the diffusion and friction coefficients at lowest order also derived. They have in most cases the same mathematical form as their free-space analog. The method offers a semiclassical explanation for two recent experiments of one atom trapping in a high Q cavity where the excited state is significantly saturated. Our results refute both claims of atom trapping by a quantized cavity mode, single or not. Finally, it is argued that the parameter newly constructed, as well as the groundwork of this method, are at least companions of the cooperativity parameter and its mother theory. In particular, we lay the stress on the apparently more fundamental role of our structure parameter.Comment: 24 pages, 7 figures. Submitted to J. Phys. B: At. Mol. Opt. Phy

Semiclassical theory of cavity-assisted atom cooling

We present a systematic semiclassical model for the simulation of the dynamics of a single two-level atom strongly coupled to a driven high-finesse optical cavity. From the Fokker-Planck equation of the combined atom-field Wigner function we derive stochastic differential equations for the atomic motion and the cavity field. The corresponding noise sources exhibit strong correlations between the atomic momentum fluctuations and the noise in the phase quadrature of the cavity field. The model provides an effective tool to investigate localisation effects as well as cooling and trapping times. In addition, we can continuously study the transition from a few photon quantum field to the classical limit of a large coherent field amplitude.Comment: 10 pages, 8 figure

Quantum Heating of a nonlinear resonator probed by a superconducting qubit

We measure the quantum fluctuations of a pumped nonlinear resonator, using a superconducting artificial atom as an in-situ probe. The qubit excitation spectrum gives access to the frequency and temperature of the intracavity field fluctuations. These are found to be in agreement with theoretical predictions; in particular we experimentally observe the phenomenon of quantum heating

What are the limits to time series based recognition of semantic concepts?

Most concept recognition in visual multimedia is based on relatively simple concepts, things which are present in the image or video. These usually correspond to objects which can be identified in images or individual frames. Yet there is also a need to recognise semantic con- cepts which have a temporal aspect corresponding to activities or com- plex events. These require some form of time series for recognition and also require some individual concepts to be detected so as to utilise their time-varying features, such as co-occurrence and re-occurrence patterns. While results are reported in the literature of using concept detections which are relatively specific and static, there are research questions which remain unanswered. What concept detection accuracies are satisfactory for time series recognition? Can recognition methods perform equally well across various concept detection performances? What affecting factors need to be taken into account when building concept-based high-level event/activity recognitions? In this paper, we conducted experiments to investigate these questions. Results show that though improving concept detection accuracies can enhance the recognition of time series based concepts, they do not need to be very accurate in order to characterize the dynamic evolution of time series if appropriate methods are used. Experimental results also point out the importance of concept selec- tion for time series recognition, which is usually ignored in the current literature

The kinetics of the reaction of superoxide radical with Fe(III) complexes of EDTA, DETAPAC and HEDTA

AbstractTo gain an understanding of the mechanism by which the hydroxyl free radical can arise in superoxide generating systems and learn how different chelaters of iron can inhibit this reaction, a pulse radiolysis kinetic study of the reaction of O−2 with Fe(III)EDTA, Fe(III)HEDTA and Fe(III)DETAPAC (or DTPA) was undertaken. Superoxide reacts readily with Fe(III)EDTA and Fe(III)HEDTA with a pH-dependent second-order rate constant having values of 1.9 × 106 M−1.s−1 and 7.6 × 105 M−1.s−1 at pH 7, respectively. However, the rate constant for the reaction of O−2 with Fe(III)DETAPAC was found to be much slower, the upper limit for the rate constant being 104 M−1.s−1. These results in conjunction with spin-trapping experiments with Fe(II)EDTA, Fe(II)HEDTA, Fe(II)DETAPAC and H2O2 suggests that DETAPAC inhibits the formation of OH by slowing the reduction of Fe(III) to Fe(II) and not by inhibiting the Fenton reaction