The impact of local stellar radiation on the HI column density distribution

It is often assumed that local sources of ionizing radiation have little impact on the distribution of HI in the post-reionization Universe. While this is a good assumption for the IGM, analytic arguments suggest that local sources may typically be more important than the background radiation for high column density absorbers (N_HI > 10^17 /cm^2). We post-process cosmological simulations with accurate radiation transport to investigate the impact of local stellar sources on the HI distribution. We demonstrate that the limited numerical resolution and the simplified treatment of the ISM that are typical of current cosmological simulations provide significant challenges, but that many of the problems can be overcome by taking two steps. First, using ISM particles rather than stellar particles as sources results in a much better sampling of the source distribution. Second, by rescaling the source luminosities so that the amount of radiation escaping into the IGM agrees with that required to produce the observed background, many of the results become insensitive to errors in the predicted fraction of the radiation that escapes the immediate vicinity of the sources. By adopting this strategy and by varying the assumptions about the structure of the unresolved ISM, we conclude that we can robustly estimate the effect of local sources for column densities N_HI << 10^21 /cm^2. However, neither the escape fraction of ionizing radiation nor the effect of local sources on the abundance of N_HI >~ 10^21 systems can be predicted with confidence. We find that local stellar radiation is unimportant for N_HI << 10^17, but that it can affect Lyman Limit and DLA systems. For 10^18 < N_HI < 10^21 the impact of local sources increases with redshift. At z = 5 the abundance of absorbers with N_HI >> 10^17 is substantially reduced, but at z = 0 the reduction only becomes significant for N_HI >~ 10^21 /cm^2.Comment: 19 pages, 12 figures; Accepted for publication in MNRA

The Aurora radiation-hydrodynamical simulations of reionization: calibration and first results

We introduce a new suite of radiation-hydrodynamical simulations of galaxy formation and reionization called Aurora. The Aurora simulations make use of a spatially adaptive radiative transfer technique that lets us accurately capture the small-scale structure in the gas at the resolution of the hydrodynamics, in cosmological volumes. In addition to ionizing radiation, Aurora includes galactic winds driven by star formation and the enrichment of the universe with metals synthesized in the stars. Our reference simulation uses 2x512^3 dark matter and gas particles in a box of size 25 comoving Mpc/h with a force softening scale of at most 0.28 kpc/h. It is accompanied by simulations in larger and smaller boxes and at higher and lower resolution, employing up to 2x1024^3 particles, to investigate numerical convergence. All simulations are calibrated to yield simulated star formation rate (SFR) functions in close agreement with observational constraints at redshift z = 7 and to achieve reionization at z = 8.3, which is consistent with the observed optical depth to reionization. We focus on the design and calibration of the simulations and present some first results. The median stellar metallicities of low-mass galaxies at z = 6 are consistent with the metallicities of dwarf galaxies in the Local Group, which are believed to have formed most of their stars at high redshifts. After reionization, the mean photoionization rate decreases systematically with increasing resolution. This coincides with a systematic increase in the abundance of neutral hydrogen absorbers in the IGM.Comment: 16 pages, 8 figures, accepted for publication in MNRA

Kyrgyz Republic

Presented during the Third international conference on irrigation and drainage held March 30 - April 2, 2005 in San Diego, California. The theme of the conference was "Water district management and governance."Includes bibliographical references.Under the On-Farm Irrigation Project (OIP), the Department of Water Resources (DWR) of the Kyrgyz Republic is to rehabilitate tertiary irrigation infrastructure. Rehabilitation on infrastructure serving 50,000 ha is underway; infrastructure serving 160,000 ha is to be rehabilitated over the six-year life of the project. To replace the role of irrigation brigades on former state farms, the Government has promoted establishment of Water User Associations (WUAs) to take over on-farm irrigation O&M. Initially, WUAs were formed under a Presidential Decree but with project assistance, in 2002 the Republic passed a WUA Law that superseded the decree. Under the law 350 WUAs have been registered. As part of OIP, WUA Support Units at the central (1), provincial (7) and district (26) level have been formed to develop and strengthen WUAs. During the first three years of the project, these units have provided training to almost 11,000 trainees as well as assisting with WUA re-registration under the new law. Although still too low, fees paid by members to cover WUA O&M and administration as well as pay the DWR for water supplied have increased in every province since 2000. A resolution just passed by the Government now gives WUAs legal ownership of their on-farm irrigation infrastructure.Sponsored by USCID; co-sponsored by Association of California Water Agencies and International Network for Participatory Irrigation Management

Institutional Design

Within public administration and policy sciences the concept of policy networks nowadays is well accepted. Not much attention has been paid so far to strategies aimed at institutional design. Therefore, in this article, we develop a conceptual framework to study institutional design more thoroughly. We do this by specifying the nature and variety of institutional rules that guide the behaviour of actors within networks. Given this categorization of rules, we identify possible strategies to change network rules. Next, we focus on the strategic context of attempts to influence the nature of instit

The impact of contract characteristics on the performance of public–private partnerships (PPPs)

Four significant features of public–private partnership (PPP) contracts are analysed to understand their impact on performance. These are whether the contract allows sanctions to be imposed; its complexity; its flexibility; and whether renegotiation is possible. The effects of these characteristics were investigated by surveying participants in all of the PPP projects in The Netherlands. The only feature considered to have any significant impact on perceived performance was the possibility of imposing sanctions. The authors’ findings cast doubt on earlier research into managing PPP performance and suggest that researchers, governments and the private sector need to look beyond contract terms to prop

Governance network theory: Past, present and future

__Abstract__ This article argues that governance network theory (GNT) has developed into a fullyfledged theory that has gained prominence within public administration. The emergence of New Public Governance opens up new challenges, however, and instead of governance networks and network governance replacing the traditional public administration model and New Public Management, hybrid practices will emerge. Addressing this topic, andother new challenges, will require GNT to further develop, and perhaps even reinvent itself. This is not without risks. If GNT evolves into a theory of everything, it will lose its explanatory power