A radio Search for high redshift HI absorption

Ground based optical observations have yielded considerable information on the statistics of damped-lyman alpha systems. In particular these systems are known to be the dominant repository of the observed neutral gas at high redshift. However, particularly at high redshift, there is the possibility that optical observations could be biased due to the exclusion of damped-lyman alpha systems that contain moderate to significant amounts of dust. Independent observational constraints on the neutral hydrogen content at high redshifts and the amount of dust in high redshift systems can be obtained from a radio search against the bright lobes of distant radio galaxies (which is less affected by the presence of dust in foreground damped-lyman alpha systems). We describe here a pilot radio survey along the line of sight to a small sample of high redshift radio galaxies, and also present some preliminary results. The survey uses a novel observing mode at the WSRT which enables one to make sensitive searches of a large redshift interval in a modest amount of telescope time.Comment: A version with figures is available at http://www.nfra.nl/~chengalu/ To appear in "Cold Gas at High Redshift", Eds. M.Bremer et al. (Kluwer, Dordrecht

Evaluation of Emerging Diagnostic Tools for Commercial HVAC Systems

This paper compares and evaluates the capabilities of six emerging diagnostic tools for commercial HVAC systems. We present a brief description of the diagnostic tools, and then focus on evaluating the features of the tools. We include the following six tools in our analysis: Architectural Energy Corporation's ENFORMA? software, Facility Dynamics Engineering's Performance And Continuous Re-commissioning Analysis Tool (PACRAT), Pacific Northwest National Laboratory's Whole Building Diagnostician (WBD), Pacific Gas and Electric's Universal Translator, UC Berkeley's Fan System Tools, and Silicon Energy's Enterprise Energy Management Suite. The air-side economizer operation is the most common diagnostic across the tools, so this diagnostic function is evaluated in detail. We outline the key strengths and weaknesses of each tool, while keeping in mind the tool intent and current extent of commercialization. Each tool has unique features for data management and analysis, which can be beneficial for different applications and users

Cosmology with redshift surveys of radio sources

We use the K-z relation for radio galaxies to illustrate why it has proved difficult to obtain definitive cosmological results from studies based entirely on catalogues of the brightest radio sources, e.g. 3C. To improve on this situation we have been undertaking redshift surveys of complete samples drawn from the fainter 6C and 7C radio catalogues. We describe these surveys, and illustrate the new studies they are allowing. We also discuss our `filtered' 6C redshift surveys: these have led to the discovery of a radio galaxy at z=4.4, and are sensitive to similar objects at higher redshift provided the space density of these objects is not declining too rapidly with z. There is currently no direct evidence for a sharp decline in the space density of radio galaxies for z > 4, a result only barely consistent with the observed decline of flat-spectrum radio quasars.Comment: 8 pages Latex, To appear in the "Cosmology with the New Radio Surveys" Conference - Tenerife 13-15 January 199

Experimental Investigation on the Operation Performance of a Liquid Desiccant Air-conditioning System

A large share of energy consumption is taken by an air-conditioning system. It worsens the electricity load of the power network. Therefore, more and more scholars are paying attention to research on new types of air-conditioning systems that are energy- saving and environment-friendly. A liquid desiccant air conditioning system is among them, as it has a tremendous ability for power storage and low requirements for heat resources. Heat with low temperatures, such as excess heat, waste heat, and solar power, is suitable for the liquid desiccant air-conditioning system. The feasibility and economical efficiency of the system are studied in this experimental research. The result shows that when the temperature of the regeneration is about 80?, the thermodynamic coefficient of the system is about 0.6, and the supply air temperature of the air-conditioning system remains stable at 21?, the air-conditioning system can meet human comfort levels

The Chemical Evolution of the Milky Way

The field of chemical evolution modeling of the Galaxy is experiencing in the last years a phase of high activity and important achievements. There are, however, several open questions which still need to be answered. In this review I summarize what have been the most important achievements and what are some of the most urgent questions to be answered.Comment: 10 pages including 3 figs, to appear in "The Chemical Evolution of the Milky Way. Stars vs Clusters", Proceedings of the Sept.1999 Vulcano Workshop, F.Giovannelli and F.Matteucci eds (Kluwer, Dordrecht) in pres

A lower limit of dz > 0.06 for the duration of the reionization epoch

Observations of the 21-centimetre line of atomic hydrogen in the early Universe directly probe the history of the reionization of the gas between galaxies. The observations are challenging, though, because of the low expected signal strength (~10 mK), and contamination by strong (>100 K) foreground synchrotron emission in the Milky Way and extragalactic continuum sources2. If reionization happened rapidly, there should be a characteristic signature visible against the smooth foreground in an all-sky spectrum. Here we report an all-sky spectrum between 100 and 200 MHz, corresponding to the redshift range 6 < z < 13 for the 21-centimetre line. The data exclude a rapid reionization timescale of dz < 0.06 at the 95% confidence level.Comment: 8 pages, 2 figures, Published in Nature, Volume 468, Issue 7325, pp. 796-798 (2010