Simulating the interaction of galaxies and the intergalactic medium

The co-evolution of galaxies and the intergalactic medium as a function of environment is studied using hydrodynamic simulations of the ACDM cosmogony. It is demonstrated with non-radiative calculations that, in the absence of non-gravitational mechanisms, dark matter haloes accrete a near-universal fraction (~ 0.9Ω(_b)/ Ω (_m))of baryons. The absence of a mass or redshift dependence of this fraction augurs well for parameter tests that use X-ray clusters as cosmological probes. Moreover, this result indicates that non- gravitational processes must efficiently regulate the formation of stars in dark matter haloes if the halo mass function is to be reconciled with the observed galaxy luminosity function. Simulations featuring stellar evolution and non-gravitational feedback mechanisms (photo-heating by the ultraviolet background, and thermal and kinetic supemovae feedback) are used to follow the evolution of star formation, and the thermo- and chemo- dynamical evolution of baryons. The observed star formation history of the Universe is reproduced, except at low redshift where it is overestimated by a factor of a few, possibly indicating the need for feedback from active galactic nuclei to quench cooling flows around massive galaxies. The simulations more accurately reproduce the observed abundance of galaxies with late-type morphologies than has been reported elsewhere. The unique initial conditions of these simulations, based on the Millennium Simulation, allow an unprecedented study of the role of large-scale environment to be conducted. The cosmic star formation rate density is found to vary by an order of magnitude across the extremes of environment expected in the local Universe. The mass fraction of baryons in the observationally elusive warm-hot intergalactic medium (WHIM), and the volume filling factor that this gas occupies, is also shown to vary by a factor of a few across such environments. This variation is attributed to differences in the halo mass functions of the environments. Finally, we compare the X-ray properties of haloes from the simulations with the predictions of the White and Frenk (1991) analytic galaxy formation model, and demonstrate that deviations from the analytic prediction arise from the assumptions i) that haloes retain their cosmic share of baryons, and ii) their gas follows an isothermal density profile. The simulations indicate that a significant fraction of gas is ejected from low mass haloes by galactic superwinds, leading to a significant increase in their cooling time profiles and an associated drop in their soft X-ray luminosities, relative to the analytic model. Simulated X-ray luminosities remain greater than present observational upper limits, but it is argued that the observations provide only weak constraints and may suffer from a systematic bias, such that the mass of the halo hosting a given galaxy is overestimated. This bias also follows from the assumption that haloes exhibit isothermal density profiles

Desegregation and Black Achievement: A Review of the Research

Holmen Paper is one of Sweden’s leading manufacturer of paper, with two Swedish production facilities located in Norrköping and Hallstavik. The European continent constitutes the company’s largest customer base which makes the company’s distribution system an integral part of the business. Historically, much of the produced paper has been transported by vessels, as vessels allow large volumes of goods and deliveries to markets which are difficult to reach with other modes of transportation. On the first of January 2015, a new EU directive enters into force which regulates the allowed fuels for vessel transports. This directive leads to an increase in cost for vessel transports due to more expensive fuels needing to be used to comply with the new rules. Therefore, Holmen Paper is interested in evaluating alternatives to the distribution system used today, focusing on the product flow between the Swedish production facilities. Thereof, the purpose of this study is to evaluate four predetermined scenarios regarding the distribution system from a capacity and cost perspective. The first scenario is based on the same distribution system Holmen Paper is using today, which does not include a product flow between the Swedish production facilities. The other three scenarios, in contrast to the first, do include a production flow between Hallstavik and Norrköping. For these scenarios a particular volume of the produced paper in Hallstavik will firstly be transported to Norrköping, then be placed in the warehouse of finished goods and lastly be loaded on new modes of transportation. For the second scenario, the production flow between Hallstavik and Norrköping is based on a combination between rail and road transports. The third scenario is based on only road transports and the last scenario is based on vessel transports between Hallstavik and Norrköping. To perform an evaluation of each scenario, the authors designed a study-specific course of action whose structure is based on four different steps. The first step was a mapping of the operations at the facilities’ warehouses for finished products. The second step was to use the mapping results to calculate the available capacity in the warehouses. The third step was an estimation of the capacity demand which would arise in each scenario, depending on the design of the product flow. The last step of the course of action is to calculate the cost for providing the necessary capacities which was calculated in the previous step. The costs were based on three theoretically chosen logistic costs, called warehousing cost, inventory cost and transportation cost. After a total of 16 days of time measuring at the production facilities, the authors were able to combine the measurement results with the 2015 projected production volumes and for each scenario calculate a capacity need along with the associated costs. The first scenario meant a capacity need below the available capacity and the lowest yearly cost in a comparison with the other scenarios. The calculations for the second scenario also resulted in a capacity need below the available capacity along with the highest yearly cost. The third scenario’s capacity need exceeded the available capacity. This was regarding loading docks and forklift trucks for lorry loading in Hallstavik, as well as personnel in Norrköping. The costs needed to manage this scenario, which meant an increase in personnel in Norrköping, reached the second highest yearly cost. The calculated capacity need for the fourth scenario was below the current available capacity. The cost for this scenario was calculated as the second lowest. To validate the result, the authors performed sensitivity analyzes where the effects of some of the assumptions and simplifications which has been made to produce the result were tested. The sensitivity analyzes showed that some of the assumptions affected the end result but the authors still deem that the relationship regarding capacity need between the scenarios show a representative image of reality

Galaxy mergers can initiate quenching by unlocking an AGN-driven transformation of the baryon cycle

We use zoom simulations to show how merger-driven disruption of the gas disc in a galaxy provides its central active galactic nucleus (AGN) with fuel to drive outflows that entrain and expel a significant fraction of the circumgalactic medium (CGM). This in turn suppresses replenishment of the interstellar medium, causing the galaxy to quench up to several Gyr after the merger. We start by performing a zoom simulation of a present-day star-forming disc galaxy with the EAGLE galaxy formation model. Then, we re-simulate the galaxy with controlled changes to its initial conditions, using the genetic modification technique. These modifications either increase or decrease the stellar mass ratio of the galaxy’s last significant merger, which occurs at z ≈ 0.74. The halo reaches the same present-day mass in all cases, but changing the mass ratio of the merger yields markedly different galaxy and CGM properties. We find that a merger can unlock rapid growth of the central supermassive black hole if it disrupts the co-rotational motion of gas in the black hole’s vicinity. Conversely, if a less disruptive merger occurs and gas close to the black hole is not disturbed, the AGN does not strongly affect the CGM, and consequently the galaxy continues to form stars. Our result illustrates how a unified view of AGN feedback, the baryon cycle and the interstellar medium is required to understand how mergers and quenching are connected over long timescales

Shifting the Intertial Navigation Paradigm with the MEMS Technology

"Why don't you use MEMS?" is of the most common questions posed to navigation systems engineers designing inertial navigation solutions in the modern era. The question stems from a general understanding that great strides have been made in terrestrial MEMS accelerometers and attitude rate sensors in terms of accuracy, mass, and power. Yet, when compared on a unit-to-unit basis, MEMS devices do not provide comparable performance (accuracy) to navigation grade sensors in several key metrics. This paper will propose a paradigm shift where the comparison in performance is between multiple MEMS devices and a single navigation grade sensor. The concept is that systematically, a sufficient number of MEMS sensors may mathematically provide comparable performance to a single navigation grade device and be competitive in terms power and mass allocations when viewed on a systems level. The implication is that both inertial navigation system design and fault detection, identification, and recovery could benefit from a system of MEMS devices in the same way that swarm sensing has benefited Earth observation and astronomy. A survey of the state of the art in inertial sensor accuracy scaled by mass and power will be provided to show the scaled error in MEMS and navigation graded devices, a mathematical comparison of multi-unit to single-unit sensor errors will be developed, and preliminary application to an Orion lunar skip atmospheric entry trajectory will be explored

Effect of High Latitude Ionospheric Convection on Sun-Aligned Polar Caps

A coupled magnetospheric-ionospheric (M-I) MHD model has been used to simulate the formation of Sun-aligned polar cap arcs for a variety of interplanetary magnetic field (IMF) dependent polar cap convection fields. The formation process involves launching an Alfvén shear wave from the magnetosphere to the ionosphere where the ionospheric conductance can react self-consistently to changes in the upward currents. We assume that the initial Alfvén shear wave is the result of solar wind-magnetosphere interactions. The simulations show how the E region density is affected by the changes in the electron precipitation that are associated with the upward currents. These changes in conductance lead to both a modified Alfvén wave reflection at the ionosphere and the generation of secondary Alfvén waves in the ionosphere. The ensuing bouncing of the Alfvén waves between the ionosphere and magnetosphere is followed until an asymptotic solution is obtained. At the magnetosphere the Alfvén waves reflect at a fixed boundary. The coupled M-I Sun-aligned polar cap arc model of Zhu et al. (1993a) is used to carry out the simulations. This study focuses on the dependence of the polar cap arc formation on the background (global) convection pattern. Since the polar cap arcs occur for northward and strong By IMF conditions, a variety of background convection patterns can exist when the arcs are present. The study shows that polar cap arcs can be formed for all these convection patterns; however, the arc features are dramatically different for the different patterns. For weak sunward convection a relatively confined single pair of current sheets is associated with the imposed Alfvén shear wave structure. However, when the electric field exceeds a threshold, the arc structure intensifies, and the conductance increases as does the local Joule heating rate. These increases are faster than a linear dependence on the background electric field strength. Furthermore, above the threshold, the single current sheet pair splits into multiple current sheet pairs. For the fixed initial ionospheric and magnetospheric conditions used in this study, the separation distance between the current pairs was found to be almost independent of the background electric field strength. For either three-cell or distorted two-cell background convection patterns the arc formation favored the positive By case in the northern hemisphere

Dynamical Effects of Ionospheric Conductivity on the Formation of Polar Cap Arcs

By using a magnetosphere-ionosphere (M-I) coupling model of polar cap arcs [Zhu et al., 1993], a systematic model study of the effects of ionospheric background conductivity on the formation of polar cap arcs has been conducted. The variations of the ionospheric background conductivity in the model study cover typical ionospheric conditions, including solar minimum, solar maximum, winter, and summer. The simulation results clearly indicate that the ionospheric background conductivity can dynamically affect the mesoscale features of polar cap arcs through a nonlinear M-I coupling process associated with the arcs

On the Computation of the Cross-section Properties of Arbitrary Thin-walled Structures

In this paper, a generalized computational algorithm based on the line chain and tree models is developed for the cross section properties of arbitrarily configuration struts without closed loops. The two C++ programs for such models are developed. However, the two models cannot apply to struts with any cross-section possessing closed loops. Therefore, the further investigation should be completed

Selective Plasma Deposition of Fluorocarbon Films on SAMs

A dry plasma process has been demonstrated to be useful for the selective modification of self-assembled monolayers (SAMs) of alkanethiolates. These SAMs are used, during the fabrication of semiconductor electronic devices, as etch masks on gold layers that are destined to be patterned and incorporated into the devices. The selective modification involves the formation of fluorocarbon films that render the SAMs more effective in protecting the masked areas of the gold against etching by a potassium iodide (KI) solution. This modification can be utilized, not only in the fabrication of single electronic devices but also in the fabrication of integrated circuits, microelectromechanical systems, and circuit boards. In the steps that precede the dry plasma process, a silicon mold in the desired pattern is fabricated by standard photolithographic techniques. A stamp is then made by casting polydimethylsiloxane (commonly known as silicone rubber) in the mold. The stamp is coated with an alkanethiol solution, then the stamp is pressed on the gold layer of a device to be fabricated in order to deposit the alkanethiol to form an alkanethiolate SAM in the desired pattern (see figure). Next, the workpiece is exposed to a radio-frequency plasma generated from a mixture of CF4 and H2 gases. After this plasma treatment, the SAM is found to be modified, while the exposed areas of gold remain unchanged. This dry plasma process offers the potential for forming masks superior to those formed in a prior wet etching process. Among the advantages over the wet etching process are greater selectivity, fewer pin holes in the masks, and less nonuniformity of the masks. The fluorocarbon films formed in this way may also be useful as intermediate layers for subsequent fabrication steps and as dielectric layers to be incorporated into finished products