Revisiting the Lyman Continuum Escape Crisis: Predictions for z > 6 from Local Galaxies

The intrinsic escape fraction of ionizing Lyman continuum photons ($f_{esc}$) is crucial to understand whether galaxies are capable of reionizing the neutral hydrogen in the early universe at z>6. Unfortunately, it is not possible to access $f_{esc}$ at z>4 with direct observations and the handful of measurements from low redshift galaxies consistently find $f_{esc}$ < 10%, while at least $f_{esc}$ ~ 10% is necessary for galaxies dominate reionization. Here, we present the first empirical prediction of $f_{esc}$ at z>6 by combining the (sparsely populated) relation between [OIII]/[OII] and $f_{esc}$ with the redshift evolution of [OIII]/[OII] as predicted from local high-z analogs selected by their H$\alpha$ equivalent-width. We find $f_{esc}$ = $5.7_{-3.3}^{+8.3}$% at z=6 and $f_{esc}$ = $10.4_{-6.3}^{+15.5}$% at z=9 for galaxies with log(M/M$_{sun}$) ~ 9.0 (errors given as 1$\sigma$). However, there is a negative correlation with stellar mass and we find up to 50% larger $f_{esc}$ per 0.5 dex decrease in stellar mass. The population averaged escape fraction increases according to $f_{esc}$ = $f_{esc,0} ((1+z)/3)^a$, with $f_{esc,0} = 2.3 \pm 0.05$% and $a=1.17 \pm 0.02$ at z > 2 for log(M/M$_{sun}$) ~ 9.0. With our empirical prediction of $f_{esc}$ (thus fixing an important previously unknown variable) and further reasonable assumption on clumping factor and the production efficiency of Lyman continuum photons, we conclude that the average population of galaxies is just capable to reionize the universe by z ~ 6.Comment: 10 pages, 4 figure, 1 table. Accepted by Ap

Two devices for analysis of nystagmus

Electromechanical Slope Computer /ESC/ and Electronic Summation Device /ESD/ facilitates rapid analysis of nystagmus records. The ESC reads out the slope and time of each nystagmus wave form. The ESD provides much faster analysis than the ESC. It provides an immediate analog display and digital display of analyzed nystagmus

Blocking Former Sex Offenders from Online Social Networks: Is this a Due Process Violation?

Extremum seeking control (ESC) is a classical adaptive control method aimed at locating and tracking optimal operating conditions in complex non-linear plants. Early results on ESC were restricted to plants that could bedescribed by Wiener or Hammerstein models. However, recent results haveshown that ESC will possess a stationary solution close to the optimum also for more general dynamical systems, provided the gradient estimation and feedback is sufficiently slow relative to the process dynamics. This thesis addresses the uniqueness of this solution and the achievable rate of convergence.The motivation for the work stems from the need to optimize a complex biofilm reactor, the CANON process, which if operated near a narrow optimum may significantly lower the cost of ammonium removal in wastewater treatment. Simulations of ESC applied to the CANON process reveal that, depending on initial conditions and tuning parameters, the ESC loop may converge to stationary solutions far removed from the optimum and that multiple stationary solutions may exist. Analysis of a general model for the ESC loop shows that the stationary solutions are characterized either by a gain condition or a phase lag condition on the locally linearized system, the latter indicating that the ESC loop can act as a phase-lock loop. The phase lag condition is shown to be satisfied close to the optimum, but can be fulfilled also at operating points with no relation to the optimality criterion whatsoever and this serves to explain the observed solution multiplicity. Bifurcation theory is employed to further analyze the stationary solutions of the ESC loop and conditions for existence of saddle-node bifurcations are derived. A saddle node bifurcation implies a hard loss of stability and the existence of multiple stationary solutions. It is also demonstrated, using examples, that the ESC loop may undergo other types of bifurcations, including period doubling bifurcations into chaos. For the considered example, the resulting chaotic solution is significantly closer to optimum than the underlying nominal limit cycle. Previous results on ESC applied to general dynamic systems have relied on the use of asymptotic methods, such as singular perturbations and averaging. This has resulted in a three time-scale separation of the problem, in which the gradient estimation and control have been forced to be significantly slower than the open-loop process dynamics. For most processes, including the CANON process studied in this thesis, this renders ESC of little practical use and we therefore consider relaxing some of the restrictive assumptions. Inparticular, we allow for any gradient estimation rate and significantly faster gradient feedback as compared to previous studies. Using a linear parameter varying (LPV) description of the plant, quantitative expressions for the convergence rate in terms of the ESC tuning parameters and plant properties are derived.QC 20141106</p

Cell-free Embryonic Stem Cell Extract-mediated Derivation of Multi-potent Stem Cells from NIH3T3 Fibroblasts for Functional and Anatomical Ischemic Tissue Repair

The oocyte-independent generation of multipotent stem cells is one of the goals in regenerative medicine. We report that upon exposure to mouse ES cell (ESC) extracts, reversibly permeabilized NIH3T3 cells undergo de-differentiation followed by stimulus-induced re-differentiation into multiple lineage cell types. Genome-wide expression profiling revealed significant differences between NIH3T3 and ESC-extract treated NIH3T3 cells including re-activation of ESC specific transcripts. Epigenetically, ESC extracts induced CpG de-methylation of Oct4 promoter, hyper-acetylation of histones 3 and 4 and decreased lysine 9 (K-9) dimethylation of histone 3. In mouse models of surgically-induced hind limb ischemia (HLI) or acute myocardial infarction (AMI) transplantation of reprogrammed NIH3T3 cells significantly improved post-injury physiological functions and showed antomical evidence of engraftment and trans-differentiation into skeletal muscle, endothelial cell and cardiomyocytes. These data provide evidence for the generation of functional multi-potent stem like cells from terminally differentiated somatic cells without the introduction of trans-genes or ESC fusion

On the Low Energy Decrease in Galactic Cosmic Ray Secondary/Primary Ratios

Galactic cosmic ray (GCR) secondary/primary ratios such as B/C and (Sc+Ti+V)/Fe are commonly used to determine the mean amount of interstellar material through which cosmic rays travel before escaping from the Galaxy (Λ_(esc)). These ratios are observed to be energy-dependent, with a relative maximum at ~1 GeV/nucleon, implying a corresponding peak in Λ_(esc). The decrease in Λ_(esc) at energies above 1 GeV/nucleon is commonly taken to indicate that higher energy cosmic rays escape more easily from the Galaxy. The decrease in Λ_(esc) at energies <1 GeV/nuc is more controversial; suggested possibilities include the effects of a galactic wind or the effects of distributed acceleration of cosmic rays as they pass through the interstellar medium. We consider two possible explanations for the low energy decrease in Λ_(esc) and attempt to fit the combined, high-resolution measurements of secondary/primary ratios from ~0.1 to 35 GeV/nuc made with the CRIS instrument on ACE and the C2 experiment on HEAO-3. The first possibility, which hypothesizes an additional, local component of low-energy cosmic rays that has passed through very little material, is found to have difficulty simultaneously accounting for the abundance of both B and the Fe-secondaries. The second possibility, suggested by Soutoul and Ptuskin, involves a new form for Λ_(esc) motivated by their diffusion-convection model of cosmic rays in the Galaxy. Their suggested form for Λ_(esc)(E) is found to provide an excellent fit to the combined ACE and HEAO data sets

Analysis of close encounters with Ganymede and Callisto using a genetic n-body algorithm

In this work we describe a genetic algorithm which is used in order to study orbits of minor bodies in the frames of close encounters. We find that the algorithm in combination with standard orbital numerical integrators can be used as a good proxy for finding typical orbits of minor bodies in close encounters with planets and even their moons, saving a lot of computational time compared to long-term orbital numerical integrations. Here, we study close encounters of Centaurs with Callisto and Ganymede in particular. We also perform n-body numerical simulations for comparison. We find typical impact velocities to be between $v_{rel}=20[v_{esc}]$ and $v_{rel}=30[v_{esc}]$ for Ganymede and between $v_{rel}=25[v_{esc}]$ and $v_{rel}=35[v_{esc}]$ for Callisto.Comment: 18 pages, 3 figure

Novel triblock co-polymer nanofibre system as an alternative support for embryonic stem cells growth and pluripotency

Conventionally, embryonic stem cells (ESCs) are cultured on gelatin or over a mitotically inactivated monolayer of mouse embryonic fibroblasts (MEFsi). Considering the lack of versatile, non-animal-derived and inexpensive materials for that purpose, we aimed to find a biomaterial able to support ESC growth in a pluripotent state that avoids the need for laborious and time-consuming MEFsi culture in parallel with mouse ESC (mESC) culture. Undifferentiated mESCs were cultured in a new nanofibre material designed for ESC culture, which is based on the self-assembly of a triblock co-polymer, poly(ethyleneglycol-β-trimethylsilyl methacrylate-β-methacrylic acid), conjugated with the peptide glycine-arginine-glycine-aspartate-serine, to evaluate its potential application in ESC research. The morphology, proliferation, viability, pluripotency and differentiation potential of mESCs were assessed. Compared to conventional stem cell culture methodologies, the nanofibres promoted a higher increase in mESCs number, enhanced pluripotency and were able to support differentiation after long-term culture. This newly developed synthetic system allows the elimination of animal-derived matrices and provides an economic method of ESC culture, made of a complex network of nanofibres in a scale similar to native extracellular matrices, where the functional properties of the cells can be observed and manipulated

Rare events in population genetics: Stochastic tunneling in a two-locus model with recombination

We study the evolution of a population in a two-locus genotype space, in which the negative effects of two single mutations are overcompensated in a high fitness double mutant. We discuss how the interplay of finite population size, $N$, and sexual recombination at rate $r$ affects the escape times $t_\mathrm{esc}$ to the double mutant. For small populations demographic noise generates massive fluctuations in $t_\mathrm{esc}$. The mean escape time varies non-monotonically with $r$, and grows exponentially as $\ln t_{\mathrm{esc}} \sim N(r - r^\ast)^{3/2}$ beyond a critical value $r^\ast$.Comment: 4 pages, 3 figure