Implications of WMAP Observations On the Population III Star Formation Processes

In an earlier paper (Cen 2003) we pointed out the strong likelihood for the universal reionization to occur twice, giving rise to a larger Thomson optical depth. Here we perform a more focused analysis of the Thomson optical depth in light of the WMAP observations. While the current uncertainties on the observed Thomson optical depth are still relatively large, with tau_e=0.17+-0.04 (68%) (Kogut et al 2003), important implications on Pop III star formation processes at high redshift can already be inferred. We are able to draw four conclusions: (1) in the absence of a top-heavy initial stellar mass function (IMF) for Pop III metal-free stars and without a dramatic upturn in the star formation efficiency and ionizing photon escape fraction at high redshift (z>6), we find tau_e =< 0.09; (2) with a top-heavy IMF for the Pop III metal-free stars and plausible star formation efficiency and ionizing photon escape fraction, it is expected that tau_e =< 0.12; (3) it is possible to reach tau_e = 0.15, if the metal enrichment efficiency of the intergalactic medium by Pop III stars is very low thus Pop III era is prolonged; (4) to reach tau_e >= 0.17 requires either of the following two conditions: the cosmological model power index n is positively tilted to n >= 1.03, Pop III star formation in minihalos with molecular hydrogen cooling has an efficiency c_*(H_2,III)>0.01 (with ionizing photon escape fraction greater than 30%). If the current observed value of Thomson optical depth withstands future data, we will have strong observational evidence that Pop III stars are massive and their formation efficiency may be much higher than current theoretical works suggest. Alternatively, there may be unknown, non-stellar ionizing sources at very high redshift.Comment: a numerical error corrected, conclusions strengthened, submitted to ApJ Letters, 13 page

Hard x-ray emission spectroscopy: a powerful tool for the characterization of magnetic semiconductors

This review aims to introduce the x-ray emission spectroscopy (XES) and resonant inelastic x-ray scattering (RIXS) techniques to the materials scientist working with magnetic semiconductors (e.g. semiconductors doped with 3d transition metals) for applications in the field of spin-electronics. We focus our attention on the hard part of the x-ray spectrum (above 3 keV) in order to demonstrate a powerful element- and orbital-selective characterization tool in the study of bulk electronic structure. XES and RIXS are photon-in/photon-out second order optical processes described by the Kramers-Heisenberg formula. Nowadays, the availability of third generation synchrotron radiation sources permits applying such techniques also to dilute materials, opening the way for a detailed atomic characterization of impurity-driven materials. We present the K{\beta} XES as a tool to study the occupied valence states (directly, via valence-to-core transitions) and to probe the local spin angular momentum (indirectly, via intra-atomic exchange interaction). The spin sensitivity is employed, in turn, to study the spin-polarized unoccupied states. Finally, the combination of RIXS with magnetic circular dichroism (RIXS-MCD) extends the possibilities of standard magnetic characterization tools.Comment: Topical review (17 pages, 13 figures, 188 references). This is an author-created, un-copyedited version of an article accepted for publication in Semiconductor Science and Technology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

Simulation of stellar instabilities with vastly different timescales using domain decomposition

Strange mode instabilities in the envelopes of massive stars lead to shock waves, which can oscillate on a much shorter timescale than that associated with the primary instability. The phenomenon is studied by direct numerical simulation using a, with respect to time, implicit Lagrangian scheme, which allows for the variation by several orders of magnitude of the dependent variables. The timestep for the simulation of the system is reduced appreciably by the shock oscillations and prevents its long term study. A procedure based on domain decomposition is proposed to surmount the difficulty of vastly different timescales in various regions of the stellar envelope and thus to enable the desired long term simulations. Criteria for domain decomposition are derived and the proper treatment of the resulting inner boundaries is discussed. Tests of the approach are presented and its viability is demonstrated by application to a model for the star P Cygni. In this investigation primarily the feasibility of domain decomposition for the problem considered is studied. We intend to use the results as the basis of an extension to two dimensional simulations.Comment: 15 pages, 10 figures, published in MNRA

The digital code driven autonomous synthesis of ibuprofen automated in a 3D-printer-based robot

An automated synthesis robot was constructed by modifying an open source 3D printing platform. The resulting automated system was used to 3D print reaction vessels (reactionware) of differing internal volumes using polypropylene feedstock via a fused deposition modeling 3D printing approach and subsequently make use of these fabricated vessels to synthesize the nonsteroidal anti-inflammatory drug ibuprofen via a consecutive one-pot three-step approach. The synthesis of ibuprofen could be achieved on different scales simply by adjusting the parameters in the robot control software. The software for controlling the synthesis robot was written in the python programming language and hard-coded for the synthesis of ibuprofen by the method described, opening possibilities for the sharing of validated synthetic ‘programs’ which can run on similar low cost, user-constructed robotic platforms towards an ‘open-source’ regime in the area of chemical synthesis

Resonant X-ray emission spectroscopy reveals d–d ligand-field states involved in the self-assembly of a square-planar platinum complex

Resonant X-ray Emission Spectroscopy (RXES) is used to characterize the ligand field states of the prototypic self-assembled square-planar complex, [Pt(tpy)Cl]Cl (tpy=2,2′:6′,2′′-terpyridine), and determine the effect of weak metal-metal and π-π interactions on their energy. © 2012 the Owner Societies

Shrink wrapping redox-active crystals of polyoxometalate open frameworks with organic polymers via crystal induced polymerisation

We report examples of crystal surface modification of polyoxometalate open frameworks whereby the use of pyrrole or aniline as monomers leads to the formation of the corresponding polymers via an oxidative polymerization process initiated by the redox active POM scaffolds. Guest-exchange experiments demonstrate that the polymers can finely tune the guest exchange rate and their structural integrity is retained after the surface modifications. In addition, the formation of polyoxometalate-based self-fabricating tubes by the dissolution of Keggin-based network crystals were also modulated by the polymers, allowing a new type of hybrid inorganic polymer with an organic coating to be fabricated

Private sector responses to water scarcity in the Hashemite Kingdom of Jordan

Until recently climate change adaptation was not on the agenda of international climate negotiations. Only at the 7th Conference of the Parties in 2001 in Marrakech, the particular vulnerability of developing countries to climate change and the need for adaptation was recognised. At the COP 15 in 2009 in Copenhagen the importance of the private sector in funding adaptation projects was emphasised amid the global economic crisis and the public sector’s inability to finance adaptation projects alone. In the Middle East water scarcity presents one of the largest challenges of the future, worsened by climate change. This thesis highlights the importance of adaptation to climate change, with particular focus on the water sector in the Hashemite Kingdom of Jordan, a country which has been identified as a prime example of an emerging economy and Middle Income Country with one of the lowest freshwater availabilities per capita in the world. Despite water scarcity, water usage and management is inefficient, levels of unaccounted-for-water are high and agriculture consumes around two thirds of water resources on extremely low tariffs. At the same time, Jordan’s economy has suffered considerably under the economic crisis, and as an emerging economy is not able to independently finance projects to improve water management and access to safe drinking water over the long term. Jordan will therefore be heavily dependent on foreign development aid as well as private sector investments. Consequently, Jordan was chosen by the author as it makes a good case study for analysis. The thesis aims to identify the drivers and barriers to private sector responses to water scarcity in Jordan and will produce a set of policy recommendations for attracting private sector capital to invest in, what has been identified as, adaptation technologies in a resource poor country. These guidelines will be useful to policymakers and private companies alike. The recommendations given herein provide a basis for enhancing private sector investments in the water sector in Jordan. Though they are specific to Jordan, these recommendations are valid and can be translated to other scenarios under which a Middle Income Country government aims to attract private sector finance for climate change adaptation projects provided that similar political, economic, cultural and environmental conditions prevail: 1. Eliminate corruption 2. Create long-term prospects for investors (especially under uncertainty about climate change and its effects) 3. Build confidence for investors 4. Develop a solid legislative framework and risk-sharing scheme 5. Adaptation makes business sense: open adaptation to climate change as a new market for innovation and investments 6. Achieve high levels of transparency in the award of projects and contracts 7. Develop a regulatory framework that defines the water consumption for agriculture (proportionate to GDP and available water resources) 8. Ensure consistency and coherence in policy-making. Avoid an implementation deficit 9. Frame a trend in climate that requires an adaptation strategy in the context of climate changeOpen Acces