Determining the Nature of Late Gunn-Peterson Troughs with Galaxy Surveys

Recent observations have discovered long (up to ~110 Mpc/h), opaque Gunn-Peterson troughs in the z ~ 5.5 Lyman-alpha forest, which are challenging to explain with conventional models of the post-reionization intergalactic medium. Here we demonstrate that observations of the galaxy populations in the vicinity of the deepest troughs can distinguish two competing models for these features: deep voids where the ionizing background is weak due to fluctuations in the mean free path of ionizing photons would show a deficit of galaxies, while residual temperature variations from extended, inhomogeneous reionization would show an overdensity of galaxies. We use large (~550 Mpc/h) semi-numerical simulations of these competing explanations to predict the galaxy populations in the largest of the known troughs at z ~ 5.7. We quantify the strong correlation of Lyman-alpha effective optical depth and galaxy surface density in both models and estimate the degree to which realistic surveys can measure such a correlation. While a spectroscopic galaxy survey is ideal, we also show that a relatively inexpensive narrowband survey of Lyman-alpha-emitting galaxies is ~90% likely to distinguish between the competing models.Comment: 12 pages, 16 figures. Submitted to Ap

O-V-S-Z and friends: Non-Gaussianity from inhomogeneous reionization

We calculate the cosmic microwave background (CMB) bispectrum due to inhomogeneous reionization. We calculate all the terms that can contribute to the bispectrum that are products of first order terms on all scales in conformal Newtonian gauge. We also correctly account for the de-correlation between the matter density and initial conditions using perturbation theory up to third order. We find that the bispectrum is of local type as expected. For a reasonable model of reionization, in which the Universe is completely ionized by redshift z_{ri} ~ 8 with optical depth to the last scattering surface \tau_0=0.087 the signal to noise for detection of the CMB temperature bispectrum is S/N ~ 0.1 and confusion in the estimation of primordial non-Gaussianity is f_{NL} ~ -0.1. For an extreme model with z_{ri} ~ 12.5, \tau_0=0.14 we get S/N ~ 0.5 and f_{NL} ~ -0.2.Comment: Published versio

The Effects of Dark Matter Decay and Annihilation on the High-Redshift 21 cm Background

The radiation background produced by the 21 cm spin-flip transition of neutral hydrogen at high redshifts can be a pristine probe of fundamental physics and cosmology. At z~30-300, the intergalactic medium (IGM) is visible in 21 cm absorption against the cosmic microwave background (CMB), with a strength that depends on the thermal (and ionization) history of the IGM. Here we examine the constraints this background can place on dark matter decay and annihilation, which could heat and ionize the IGM through the production of high-energy particles. Using a simple model for dark matter decay, we show that, if the decay energy is immediately injected into the IGM, the 21 cm background can detect energy injection rates >10^{-24} eV cm^{-3} sec^{-1}. If all the dark matter is subject to decay, this allows us to constrain dark matter lifetimes <10^{27} sec. Such energy injection rates are much smaller than those typically probed by the CMB power spectra. The expected brightness temperature fluctuations at z~50 are a fraction of a mK and can vary from the standard calculation by up to an order of magnitude, although the difference can be significantly smaller if some of the decay products free stream to lower redshifts. For self-annihilating dark matter, the fluctuation amplitude can differ by a factor <2 from the standard calculation at z~50. Note also that, in contrast to the CMB, the 21 cm probe is sensitive to both the ionization fraction and the IGM temperature, in principle allowing better constraints on the decay process and heating history. We also show that strong IGM heating and ionization can lead to an enhanced H_2 abundance, which may affect the earliest generations of stars and galaxies.Comment: submitted to Phys Rev D, 14 pages, 8 figure

Experimental analysis of the influence of polymer solutions on performances and cavitation of small size pumps for professional appliances

Pumps used in professional appliances process a solution of water, soils residues and detergents. These affect vapor tension, viscosity and rheology of the solution, mainly due to the presence of surfactants and polymers. Only a few studies have been found on how these substances can influence pump performances. Therefore, an experimental analysis has been carried out with aqueous solutions of a detergent component, the Polyox WSR 301, in the concentration range of 100\u20137000 ppm, to evaluate their influence on pump performances and cavitation. Some properties of the solutions have been preliminary characterized with a rheometer. Then, each solution has been tested in a dedicated test rig, to compare the performance curves of a centrifugal pump used in professional warewashing machines with those obtained with pure water. A non-intrusive method, based on the investigation of high frequency vibrations and noise signals, has been developed to detect cavitation at its early stage of inception. It was observed that polymer mitigates cavitating pump vibrations, with a reduction of the acceleration to less than one g. The analysis has provided the data necessary for the successive development of a control strategy for pump operation in professional appliances

Adaptive Consensus-based Regulation of Open-Channel Networks

This paper deals with water management over open-channel networks subject to water height imbalance. Specifically, it is devised a fully distributed adaptive consensus-based algorithm within the discrete-time domain capable of (i) providing a suitable tracking reference that stabilizes the water increments over the underlying network at a common level; (ii) coping with general flow constraints related to each channel of the considered system. This iterative procedure is derived by solving a guidance problem that guarantees to steer the regulated network - represented as a closed-loop system - while satisfying requirements (i) and (ii), provided that a suitable design for the local feedback law controlling each channel flow is already available. The proposed solution converges exponentially fast towards the average consensus without violating the imposed constraints over time. In addition, numerical results are reported to support the theoretical findings, and the performance of the developed algorithm is discussed in the context of a realistic scenario.Comment: 13 pages, 5 figures, submitted to IEEE Access (version 1

Cavitation Detection and Prevention in Professional Warewashing Machines

Cavitation is a phenomenon characterised by the presence of vapour bubbles in the fluid led by a local drop in pressure. In literature it is well known the impact on cavitation of pressure and temperature of pure water, but there are only few studies analysing how the presence of certain components of detergents and additives can influence the phenomenon. The impact of detergents and additives could be explained by the modified viscosity and rheology of the solution but also by the variation in the vapour tension. Most of these effects are due to the presence of surfactants and polymers in the solution. Cavitation in dynamic pumps is an important aspect that needs to be monitored and prevented, because it can cause damages affecting pump performances and inducing an increment in the level of vibration and noise. In professional warewashing machines, as for example the models of Electrolux Rack Type, this phenomenon can affect the operating functionalities of the machine. An experimental pump test rig has been realized with the aim of studying and monitoring the influence of these parameters on cavitation inception. This test rig permits measuring the pump performances at various operating conditions, in order to obtain its characteristic curves, and also forcing cavitation to measure its Net Positive Suction Head required (NPSHr) at different flow rates. The pump test rig allows also testing various configurations of the pump at different cavitation conditions, obtained by changing not only the suction pressure and temperature of the fluid but also its properties, adding detergents and additives. Cavitation inception can be detected measuring both the corresponding prevalence decrease and the change of vibration and noise level

Transient model of a Professional Oven

Tackling the climate change by reducing energy consumption is among the biggest, most urgent challenges society is facing and requires a continuous efficiency improvement of thermal systems. Appropriate design strategies, developed a priori and then experimentally validated according to suitable test protocols on a prototype, are needed in order to reach potential energy saving targets. These strategies can successfully be implemented in the food service sector, where cooking appliances, in particular, present many possibilities for improving energy savings. Therefore, a valuable design methodology should take into account not only steady state operating conditions but also the transient behaviours of the device, which must be described by means of specially developed theoretical dynamic models. The operating profile of an oven, for example, consists of a sequence of unsteady phases (cavity heating-up, food introduction and extraction, switching from one cooking mode to another) interspersed with steady cooking phases. The dynamic model presented in this paper defines the energy conservation equations of a professional oven, where a high temperature thermal source positioned inside its cavity produces thermal power radiated and modulated over time, according to a suitable control strategy. In particular, when the temperature in the cooking zone of the cavity has reached a specified set point, this is thermostatically controlled in time, depending on the cooking phase. The resulting equation system is then solved by means of numerical methods. With this code, it is possible to support the design phase of both the structure and the control strategy of the oven. It permits, for example, to get a general understanding of the best possible configurations and combinations of insulation materials for the cavity walls or, with reference to the control strategy, to simulate different cooking procedures, with the aim of optimizing the operating sequence of the oven, reaching the maximum energy saving without reducing the cooking quality. The code, validated by comparison with a set of experimental data obtained with a current production model, will be applied in the design phase of a new line of high efficiency professional ovens

Cosmological Parameter Estimation Using 21 cm Radiation from the Epoch of Reionization

A number of radio interferometers are currently being planned or constructed to observe 21 cm emission from reionization. Not only will such measurements provide a detailed view of that epoch, but, since the 21 cm emission also traces the distribution of matter in the Universe, this signal can be used to constrain cosmological parameters at 6 < z < 20. The sensitivity of an interferometer to the cosmological information in the signal may depend on how precisely the angular dependence of the 21 cm 3-D power spectrum can be measured. Utilizing an analytic model for reionization, we quantify all the effects that break the spherical symmetry of the 3-D 21 cm power spectrum and produce physically motivated predictions for this power spectrum. We find that upcoming observatories will be sensitive to the 21 cm signal over a wide range of scales, from larger than 100 to as small as 1 comoving Mpc. We consider three methods to measure cosmological parameters from the signal: (1) direct fitting of the density power spectrum to the signal, (2) using only the velocity field fluctuations in the signal, (3) looking at the signal at large enough scales such that all fluctuations trace the density field. With the foremost method, the first generation of 21 cm observations should moderately improve existing constraints on cosmological parameters for certain low-redshift reionization scenarios, and a two year observation with the second generation interferometer MWA5000 can improve constraints on Omega_w, Omega_m h^2, Omega_b h^2, Omega_nu, n_s, and alpha_s. If the Universe is substantially ionized by z = 12 or if spin temperature fluctuations are important, we show that it will be difficult to place competitive constraints on cosmological parameters with any of the considered methods.Comment: 20 pages, 12 figures, accepted by Ap

Reionization and the large-scale 21 cm-cosmic microwave background cross correlation

Of the many probes of reionization, the 21 cm line and the cosmic microwave background (CMB) are among the most effective. We examine how the cross-correlation of the 21 cm brightness and the CMB Doppler fluctuations on large angular scales can be used to study this epoch. We employ a new model of the growth of large scale fluctuations of the ionized fraction as reionization proceeds. We take into account the peculiar velocity field of baryons and show that its effect on the cross correlation can be interpreted as a mixing of Fourier modes. We find that the cross-correlation signal is strongly peaked toward the end of reionization and that the sign of the correlation should be positive because of the inhomogeneity inherent to reionization. The signal peaks at degree scales (l~100) and comes almost entirely from large physical scales (k~0.01 Mpc). Since many of the foregrounds and noise that plague low frequency radio observations will not correlate with CMB measurements, the cross correlation might appear to provide a robust diagnostic of the cosmological origin of the 21 cm radiation around the epoch of reionization. Unfortunately, we show that these signals are actually only weakly correlated and that cosmic variance dominates the error budget of any attempted detection. We conclude that the detection of a cross-correlation peak at degree-size angular scales is unlikely even with ideal experiments.Comment: 15 pages, 4 figures, submitted to MNRA

Redshifted 21 Centimeter Emission from Minihalos Before Reionization

Before reionization, the intergalactic medium (IGM) may have been sufficiently cold for low-mass "minihalos" to condense out of the gas and subsequently affect reionization. Previous work has shown that minihalos generate reasonably large 21 cm fluctuations. Here we consider this signal in its proper cosmological context and show that isolating minihalos from the rest of the IGM is extremely difficult. Using the well-known halo model, we compute the power spectrum of 21 cm fluctuations from minihalos and show that the signal decreases rapidly as feedback increases the Jeans mass. We then show that even a small Lyman-alpha background increases the 21 cm fluctuations of the diffuse IGM well beyond those of the minihalos; because the mass fraction in the IGM is much larger, minihalos will lie buried within the IGM signal. The distinctive signatures of non-linear bias and minihalo structure emerge only at much smaller scales, well beyond the resolution of any upcoming instruments. Using simple, but representative, reionization histories, we then show that the required Lyman-alpha background level is most likely achieved at z>15, while minihalos are still rare, so that they are almost always degenerate with the diffuse IGM.Comment: 8 pages, 6 figures, submitted to Ap