Cosmic Microwave Background Polarization and reionization: constraining models with a double reionization

Neutral hydrogen around high-z QSO and an optical depth tau ~ 0.17 can be reconciled if reionization is more complex than a single transition at z ~ 6-8. Tracing its details could shed a new light on the first sources of radiation. Here we discuss how far such details can be inspected through planned experiments on CMB large-scale anisotropy and polarization, by simulating an actual data analysis. By considering a set of double reionization histories of Cen (2003) type, a relevant class of models not yet considered by previous works, we confirm that large angle experiments rival high resolution ones in reconstructing the reionization history. We also confirm that reionization histories, studied with the prior of a single and sharp reionization, yield a biased tau, showing that this bias is generic. We further find a monotonic trend in the bias for the models that we consider, and propose an explanation of the trend, as well as the overall bias. We also show that in long-lived experiments such a trend can be used to discriminate between single and double reionization patterns.Comment: 8 pages, 11 figures. Substantial rewriting, replaced with accepted version. To be published in A&

Risk-Informed design process of the IRIS reactor

Westinghouse is currently conducting the pre-application licensing of the International Reactor Innovative and Secure (IRIS). The design philosophy of the IRIS has been based on the concept of Safety-by-DesignTM and within this framework the PSA is being used as an integral part of the design process. The basis for the PSA contribution to the design phase of the reactor is the close iteration between the PSA team and the design and safety analysis team. In this process the design team is not only involved in the initial phase of providing system information to the PSA team, allowing in this way the identification of the high risk scenarios, but it is also receiving feedback from the PSA team that suggests design modification aimed at reaching risk-related goals. During the first iteration of this process, the design modifications proposed by the PSA team allowed reducing the initial estimate of Core Damage Frequency (CDF) due to internal events from 2E-6/ry to 2E-8/ry. Since the IRIS design is still in a development phase, a number of assumptions have to be confirmed when the design is finalized. Among key assumptions are the success criteria for both the accident sequences analyzed and the systems involved in the mitigation strategies. The PSA team developed the initial accident sequence event trees according to the information from the preliminary analysis and feasibility studies. A recent coupling between the RELAP and GOTHIC codes made possible the actual simulation of all LOCA sequences identified in the first draft of the Event Trees. Working in close coordination, the PSA and the safety analysis teams developed a matrix case of sequences not only with the purpose of testing the assumed success criteria, but also with the perspective of identifying alternative sequences developed mainly by relaxing the extremely conservative assumptions previously made. The results of these simulations, bounded themselves with conservative assumptions on the Core Damage definition, suggested two new versions of the LOCA Event Tree with two possible configurations of the Automatic Depressurization System. The new CDF has been evaluated for both configurations and the design team has been provided with an additional and risk-related perspective that will help choosing the design alternative to be implemented

Modification of the 21-cm power spectrum by X-rays during the epoch of reionisation

We incorporate a contribution to reionization from X-rays within analytic and semi-numerical simulations of the 21-cm signal arising from neutral hydrogen during the epoch of reionization. We explore the impact that X-ray ionizations have on the power spectrum (PS) of 21-cm fluctuations by varying both the average X-ray MFP and the fractional contribution of X-rays to reionization. In general, prior to the epoch when the intergalactic medium is dominated by ionized regions (H {\sevensize II} regions), X-ray-induced ionization enhances fluctuations on spatial scales smaller than the X-ray MFP, provided that X-ray heating does not strongly supress galaxy formation. Conversely, at later times when \H2 regions dominate, small-scale fluctuations in the 21-cm signal are suppressed by X-ray ionization. Our modelling also shows that the modification of the 21-cm signal due to the presence of X-rays is sensitive to the relative scales of the X-ray MFP, and the characteristic size of \H2 regions. We therefore find that X-rays imprint an epoch and scale-dependent signature on the 21-cm PS, whose prominence depends on fractional X-ray contribution. The degree of X-ray heating of the IGM also determines the extent to which these features can be discerned. We show that the MWA will have sufficient sensitivity to detect this modification of the PS, so long as the X-ray photon MFP falls within the range of scales over which the array is most sensitive ($\sim0.1$ Mpc$^{-1}$). In cases in which this MFP takes a much smaller value, an array with larger collecting area would be required.Comment: 15 pages, 6 figures, Accepted for publication in MNRAS X-ray heating contribution now adde

Retrieval of magnetic medical microrobots from the bloodstream

Untethered magnetic microrobots hold the potential to penetrate hard-to-reach areas of the human body and to perform therapy in a controlled way. In the past decade, impressive advancements have been made in this field but the clinical adoption of magnetoresponsive microrobots is still hampered by safety issues. A tool appointed for magnetic microrobots retrieval within body fluids could enable a real paradigm change, fostering their clinical translation.By starting from the general problem to retrieve magnetic microrobots injected into the bloodstream, the authors introduce a magnetic capture model that allows to design retrieval tools for magnetic cores of different diameters (down to 10 nm) and in different environmental conditions (fluid speed up to 7 cms-1). The model robustness is demonstrated by the design and testing of a retrieval catheter. In its optimal configuration, the catheter includes 27 magnets and fits a 12 F catheter. The model provides a good prediction of capture efficiency for 250 nm magnetic particles (experimental data: 77.6%, model prediction: 65%) and a very good prediction for 500 nm particles (experimental data: 93.6%, model prediction: 94%). The results support the proposed model-based design approach, which can be extended to retrieve other magnetoresponsive agents from body compartments

Feedback from Galaxy Formation: Production and Photodissociation of Primordial Molecular Hydrogen

We use one-dimensional radiative transfer simulations to study the evolution of H_2 gas-phase (H^- catalyzed) formation and photo-dissociation regions in the primordial universe. We find a new positive feedback mechanism capable of producing shells of H_2 in the intergalactic medium, which are optically thick in some Lyman-Werner bands. While these shells exist, this feedback effect is important in reducing the H_2 dissociating background flux and the size of photo-dissociation spheres around each luminous object. The maximum background opacity of the IGM in the H_2 Lyman-Werner bands is \tau_{H_2} ~ 1-2 for a relic molecular fraction x_{H_2}=2 x 10^{-6}, about 6 times greater than found by Haiman, Abel & Rees. Therefore, the relic molecular hydrogen can decrease the photo-dissociation rate by about an order of magnitude. The problem is relevant to the formation of small primordial galaxies with masses M_{DM} < 10^8 M_\odot, that rely on molecular hydrogen cooling to collapse. Alternatively, the universe may have remained dark for several hundred million years after the birth of the first stars, until galaxies with virial temperature T_{vir} > 10^4 K formed.Comment: Accepted for pubblication on ApJ vol 560, October 2001 with minor changes. 31 pages,including 12 figures and 1 table. Higher quality figures are available at: http://casa.colorado.edu/~ricotti/papers.htm

Gamma-Ray Bursts in Circumstellar Shells: A Possible Explanation for Flares

It is now generally accepted that long-duration gamma ray bursts (GRBs) are due to the collapse of massive rotating stars. The precise collapse process itself, however, is not yet fully understood. Strong winds, outbursts, and intense ionizing UV radiation from single stars or strongly interacting binaries are expected to destroy the molecular cloud cores that give birth to them and create highly complex circumburst environments for the explosion. Such environments might imprint features on GRB light curves that uniquely identify the nature of the progenitor and its collapse. We have performed numerical simulations of realistic environments for a variety of long-duration GRB progenitors with ZEUS-MP, and have developed an analytical method for calculating GRB light curves in these profiles. Though a full, three-dimensional, relativistic magnetohydrodynamical computational model is required to precisely describe the light curve from a GRB in complex environments, our method can provide a qualitative understanding of these phenomena. We find that, in the context of the standard afterglow model, massive shells around GRBs produce strong signatures in their light curves, and that this can distinguish them from those occurring in uniform media or steady winds. These features can constrain the mass of the shell and the properties of the wind before and after the ejection. Moreover, the interaction of the GRB with the circumburst shell is seen to produce features that are consistent with observed X-ray flares that are often attributed to delayed energy injection by the central engine. Our algorithm for computing light curves is also applicable to GRBs in a variety of environments such as those in high-redshift cosmological halos or protogalaxies, both of which will soon be targets of future surveys such as JANUS or Lobster.Comment: 12 pages, 5 figures, Accepted by Ap

Miniaturized peristaltic rotary pump for non-continuous drug dosing

Micro dosing pumps are the beating heart of infusion systems. Among many technologies to inject micro quantities of fluids, peristaltic pumps show high precision and the possibility to not alter the fluid properties. However, in real drug delivery applications, the continuous release behavior of typical peristaltic pumps is not favorable. In this paper, we investigate the intermittent performance of two prototypes of peristaltic pumps, based on four and five rollers, used to occlude the tube. The pump performances are reported for different rotation speeds and lag times between consecutive infusions. The proposed pumps showed a good volumetric precision (2.88 μL for the five rollers pump and 4.11 μL for the four rollers pump) without any dependency on rotation speed and lag time

The Abundance of New Kind of Dark Matter Structures

A new kind of dark matter structures, ultracompact minihalos (UCMHs) was proposed recently. They would be formed during the radiation dominated epoch if the large density perturbations are existent. Moreover, if the dark matter is made up of weakly interacting massive particles, the UCMHs can have effect on cosmological evolution because of the high density and dark matter annihilation within them. In this paper, one new parameter is introduced to consider the contributions of UCMHs due to the dark matter annihilation to the evolution of cosmology, and we use the current and future CMB observations to obtain the constraint on the new parameter and then the abundance of UCMHs. The final results are applicable for a wider range of dark matter parametersComment: 4 pages, 1 tabl

Radiation Hydrodynamical Instabilities in Cosmological and Galactic Ionization Fronts

Ionization fronts, the sharp radiation fronts behind which H/He ionizing photons from massive stars and galaxies propagate through space, were ubiquitous in the universe from its earliest times. The cosmic dark ages ended with the formation of the first primeval stars and galaxies a few hundred Myr after the Big Bang. Numerical simulations suggest that stars in this era were very massive, 25 - 500 solar masses, with H II regions of up to 30,000 light-years in diameter. We present three-dimensional radiation hydrodynamical calculations that reveal that the I-fronts of the first stars and galaxies were prone to violent instabilities, enhancing the escape of UV photons into the early intergalactic medium (IGM) and forming clumpy media in which supernovae later exploded. The enrichment of such clumps with metals by the first supernovae may have led to the prompt formation of a second generation of low-mass stars, profoundly transforming the nature of the first protogalaxies. Cosmological radiation hydrodynamics is unique because ionizing photons coupled strongly to both gas flows and primordial chemistry at early epochs, introducing a hierarchy of disparate characteristic timescales whose relative magnitudes can vary greatly throughout a given calculation. We describe the adaptive multistep integration scheme we have developed for the self-consistent transport of both cosmological and galactic ionization fronts.Comment: 6 pages, 4 figures, accepted for proceedings of HEDLA2010, Caltech, March 15 - 18, 201

Constraints on ultracompact minihalos from extragalactic {\gamma}-ray background

It has been proposed that ultracompact minihalos (UCMHs) might be formed in earlier epoch. If dark matter consists of Weakly Interacting Massive Particles (WIMPs), UCMHs can be treated as the {\gamma}-ray sources due to dark matter annihilation within them. In this paper, we investigate the contributions of UCMHs formed during three phase transi- tions (i.e., electroweak symmetry breaking, QCD confinement and e+ e- annihilation) to the extragalactic {\gamma}-ray background. Moreover, we use the Fermi-LAT observation data of the extragalactic {\gamma}-ray background to get the constraints on the current abundance of UCMHs produced during these phase transitions. We also compare these results with those obtained from Cosmic Microwave Background (CMB) observations and find that the constraints from the Fermi-LAT are more stringent than those from CMBComment: 13 pages, 4 figures, 1 tabl