On the operation of the chemothermal instability in primordial star-forming clouds

We investigate the operation of the chemothermal instability in primordial star-forming clouds with a suite of three-dimensional, moving-mesh simulations. In line with previous studies, we find that the gas at the centre of high-redshift minihaloes becomes chemothermally unstable as three-body reactions convert the atomic hydrogen into a fully molecular gas. The competition between the increasing rate at which the gas cools and the increasing optical depth to H2 line emission creates a characteristic dip in the cooling time over the free-fall time on a scale of 100 au. As a result, the free-fall time decreases to below the sound-crossing time, and the cloud may become gravitationally unstable and fragment on a scale of a few tens of au during the initial free-fall phase. In three of the nine haloes investigated, secondary clumps condense out of the parent cloud, which will likely collapse in their own right before they are accreted by the primary clump. In the other haloes, fragmentation at such an early stage is less likely. However, given that previous simulations have shown that the infall velocity decreases substantially once the gas becomes rotationally supported, the amount of time available for perturbations to develop may be much greater than is evident from the limited period of time simulated here.Comment: 17 pages, 12 figures, accepted for publication in MNRAS, simulation movie available at http://www.cfa.harvard.edu/~tgrei

The First Galaxies: Assembly under Radiative Feedback from the First Stars

We investigate how radiative feedback from the first stars affects the assembly of the first dwarf galaxies. We perform cosmological zoomed SPH simulations of a dwarf galaxy assembling inside a halo of virial mass 10^9 solar at z = 10. The simulations follow the non-equilibrium chemistry/cooling of primordial gas and the conversion of the gas into metal-free stars. To quantify the radiative feedback, we compare a simulation in which stars emit both molecular hydrogen dissociating and hydrogen/helium ionizing radiation with a simulation in which stars emit only dissociating radiation, and with a simulation in which stars remain dark. Photodissociation and -ionization exert a strong negative feedback on the assembly of the simulated galaxy. Gas condensation is strongly impeded, and star formation is strongly suppressed in comparison with the simulation in which stars remain dark. The feedback on the gas implies a suppression of the central dark matter densities in the minihalo progenitor by factors of up to a few, which is a significant deviation from the singular isothermal density profile characterizing the dark matter distribution in the absence of radiative feedback. The evolution of gas densities, star formation rates, and the distribution of dark matter becomes insensitive to the inclusion of dissociating radiation in the late stages of the minihalo assembly, and it becomes insensitive to the inclusion of ionizing radiation once the minihalo turns into an atomically cooling galaxy. The formation of an extended disk inside the dwarf galaxy is a robust outcome not affected by the inclusion of radiation. We estimate that dwarf galaxies such as simulated here will be among the faintest galaxies the upcoming James Webb Space Telescope will detect. Our conclusions are subject to our neglect of feedback from supernovae and chemical enrichment as well as to cosmic variance. [abridged]Comment: 25 pages (including 5 pages appendix), 13 figures. Accepted for publication in Ap

The impact of the EU ETS on the sectoral innovation system for power generation technologies: findings for Germany

This paper provides an overview of early changes in the sectoral innovation system for power generation technologies which have been triggered by the European Emission Trading Scheme (EU ETS). Based on a broad definition of the sector, our research analyses the impact of the EU ETS on the four building blocks knowledge and technologies, actors and networks, institutions and demand by combining two streams of literature, namely systems of innovation and environmental economics. Our analysis is based on 42 exploratory inter-views with German and European experts in the field of the EU ETS, the power sector and technological innovation. We find that the EU ETS mainly affects the rate and direction of the technological change of power generation technologies within the large-scale, coal-based power generation technological regime to which carbon capture technologies are added as a new technological trajectory. While this impact can be interpreted as defensive behaviour of incumbents, the observed changes should not be underestimated. We argue that the EU ETS' impact on corporate CO2 culture and routines may prepare the ground for the transition to a low carbon sectoral innovation system for power generation tech-nologies. --EU emission trading scheme (EU ETS),innovation system,power sector

Towards the First Galaxies

The formation of the first galaxies at redshifts z~10-15 signaled the transition from the simple initial state of the universe to one of ever increasing complexity. We here review recent progress in understanding their assembly process with numerical simulations, starting with cosmological initial conditions and modelling the detailed physics of star formation. In particular, we study the role of HD cooling in ionized primordial gas, the impact of UV radiation produced by the first stars, and the propagation of the supernova blast waves triggered at the end of their brief lives. We conclude by discussing promising observational diagnostics that will allow us to probe the properties of the first galaxies, such as their contribution to reionization and the chemical abundance pattern observed in extremely low-metallicity stars.Comment: 12 pages, 14 figures, appeared in "First Stars III", eds. B. O'Shea, A. Heger and T. Abel, a high resolution version (highly recommended) can be found at http://www.ita.uni-heidelberg.de/~tgreif/files/gjb07.pd

Radiative Feedback from high mass X-ray binaries on the formation of the first galaxies and early reionization

Recent work suggests that the first generation of stars, the so-called Population III (Pop III), could have formed primarily in binaries or as members of small multiple systems. Here we investigate the impact of X-ray feedback from High-Mass X-ray Binaries (HMXBs) left behind in stellar binary systems after the primary forms a black hole (BH), accreting gas at a high rate from the companion, a process that is thought to be favored at the low metallicities characteristic of high-redshift gas. Thanks to their large mean free path, X-rays are capable of preionizing and preheating the gas in the intergalactic medium (IGM) and in haloes long before the reionization of the Universe is complete, and thus could have strongly affected the formation of subsequent generations of stars as well as reionization. We have carried out zoomed hydrodynamical cosmological simulations of minihaloes, accounting for the formation of Pop III stars and their collapse into BHs and HMXBs, and the associated radiation-hydrodynamic feedback from UV and X-ray photons. We find no strong net feedback from HMXBs on the simulated star formation history. On the other hand, the preheating of the IGM by HMXBs leads to a strong suppression of small-scale structures and significantly lowers the recombination rate in the IGM, thus yielding a net positive feedback on reionization. We further show that X-ray feedback from HMXBs can augment the ionizing feedback from the Pop III progenitor stars to suppress gas accretion onto the first BHs, limiting their growth into supermassive BHs. Finally, we show that X-ray ionization by HMXBs leaves distinct signatures in the properties of the high-redshift hydrogen that may be probed in upcoming observations of the redshifted 21cm spin-flip line.Comment: 20 pages, 12 figures. Accepted for publication in MNRA

Corporate Responses to Climate Change and Financial Performance: The Impact of Climate Policy

This paper examines the relationship between corporate activities to address climate change and stock performance. By separately analyzing the US and European stock markets for different sub-periods, we highlight the impact of the underlying climate policy regime. Methodologically, we compare risk-adjusted returns of stock portfolios comprising corporations that differ in their responses to climate change. In this respect, we apply the flexible Carhart fourfactor model besides the restricted one-factor model based on the Capital Asset Pricing Model (CAPM). While our portfolio analysis shows negative relationships over the entire observation period from 2001 to 2006, we find that a trading strategy, which bought stocks of corporations with a higher level of responses to climate change and sold stocks of corporations with a lower level, led to negative abnormal returns in regions and periods with less ambitious climate policy, but to positive abnormal returns in regions and periods with stringent climate policy.Climate change, Climate policy, Corporate environmental performance, Financial performance, Portfolio analysis, Asset pricing models

Re-evaluation of HER2 status in metastatic breast cancer and tumor-marker guided therapy with vinorelbine and trastuzumab

Background: HER2 is overexpressed in 20 - 30% of breast cancers. Compared to chemotherapy alone, chemotherapy with trastuzumab improves clinical outcome in patients with HER2- positive metastatic breast cancer ( MBC). In general, HER2 status in a primary lesion predicts the status of metastases, so that biopsy of metastatic lesions appears unnecessary. Case Report: A 39- year old woman was diagnosed with primary breast cancer in November 2000. Using the method and scoring system of the DAKO Hercep Test, the tumor has shown low HER2 expression ( DAKO score 1+). After failure of several chemotherapy regimens for metastatic disease ( liver, skeletal), the patient underwent CT- guided needle biopsy of the liver which showed HER2 positive adenocarcinoma ( DAKO score 3+). In consequence, the patient was treated with vinorelbine ( 30 mg/ m(2) d1,8,15 q4w) and trastuzumab ( 4 mg/ kg loading dose, 2 mg/ kg weekly). During a treatment period of 4 months imaging results as well as tumor marker kinetics indicated an excellent response with sustained decrease of tumor markers. A retrospective analysis of the HER2 shed antigen in metastatic stage revealed excessively increased serum levels and supports HER2 overexpression observed in liver metastasis. The kinetics of the HER2 shed antigen during therapy for metastatic disease were found to be in phase with the kinetics of CEA and CA15- 3. Conclusion: This case report demonstrates that re- evaluation of the HER2 status may be helpful in single patients not sufficiently responding to treatment of metastatic disease. Determination of HER2 overexpression may be facilitated by a determination of the HER2 shed antigen level in peripheral blood

The Mutual Interaction Between Population III Stars and Self-Annihilating Dark Matter

We use cosmological simulations of high-redshift minihalos to investigate the effect of dark matter annihilation (DMA) on the collapse of primordial gas. We numerically investigate the evolution of the gas as it assembles in a Population III stellar disk. We find that when DMA effects are neglected, the disk undergoes multiple fragmentation events beginning at ~ 500 yr after the appearance of the first protostar. On the other hand, DMA heating and ionization of the gas speeds the initial collapse of gas to protostellar densities and also affects the stability of the developing disk against fragmentation, depending on the DM distribution. We compare the evolution when we model the DM density with an analytical DM profile which remains centrally peaked, and when we simulate the DM profile using N-body particles (the 'live' DM halo). When utilizing the analytical DM profile, DMA suppresses disk fragmentation for ~ 3500 yr after the first protostar forms, in agreement with earlier work. However, when using a 'live' DM halo, the central DM density peak is gradually flattened due to the mutual interaction between the DM and the rotating gaseous disk, reducing the effects of DMA on the gas, and enabling secondary protostars of mass ~ 1 M_sol to be formed within ~ 900 yr. These simulations demonstrate that DMA is ineffective in suppressing gas collapse and subsequent fragmentation, rendering the formation of long-lived dark stars unlikely. However, DMA effects may still be significant in the early collapse and disk formation phase of primordial gas evolution.Comment: 17 pages, 11 figures, to appear in MNRA