The Angular Momentum of Gas in Proto-Galaxies: II -- The Impact of Preheating

We examine the effect of preheating of the intergalactic medium on galaxy formation using cosmological hydrodynamical simulations. By performing simulations both with and without a simple model for preheating, we analyse and compare the angular momentum distributions of the dark matter and the baryons. Preheating unbinds baryons from their dark matter haloes, yielding a baryonic mass fraction that declines with decreasing halo mass. In addition, the spin parameter of the gas is reduced with respect to the case without preheating, while the misalignment between the angular momentum directions of the gas and dark matter increases strongly. The angular momentum distributions of individual haloes reveal that preheating decreases (increases) the mass fraction with low (negative) specific angular momentum. We discuss the implications of these findings for the formation of disk galaxies in a preheated intergalactic medium, and compare our results to the predictions of Maller & Dekel (2002), who propose an alternative interpretation for the origin of the angular momentum of (proto)-galaxies.Comment: 10 pages, 4 figures. Accepted for publication in MNRA

Heads Up! Supporting Maritime Navigation using Augmented Reality

Augmented Reality (AR) is a technology that shows potential for the improvement of maritime safety. Today, the ship bridge suffers from a lack of standardization and integration. Head-Mounted Displays (HMDs) may alleviate these challenges by showing information when relevant and enhancing operator mobility. Microsoft HoloLens 2 (HL2) is such a HMD. Prior research shows the potential of HMDs in the Maritime AR domain (Rowen et al., 2019). Limited research has been conducted however on the design of AR User Interfaces (UIs) for maritime applications leveraging HMDs. As a result, no framework exists to test new UI designs in the real world, which is necessary due to many variables that cannot be accurately modelled in a lab setting. This led to the research questions (RQs) 1. What makes an effective head-mounted AR UI for maritime navigation? (RQ1); and 2. How can HL2 be used as a ship bridge system? (RQ2) A Research through Design (RtD) process is detailed where a UI design and functional prototype was developed in collaboration with end-users. The prototype, named Sjør, implements the aforementioned interface, provides a framework for in-context UI testing and can be viewed as the next step towards standardizing AR UIs for the maritime industry. The design and development process led to three contributions to the Maritime AR domain. Firstly, a framework for the visualization of location-based data about points of interest on predefined canvases co-located in the real world was developed (Technology Readiness Level (TRL) 6), which runs on the HL2. This first contribution is defined in Section 4 and provides an answer to RQ2. Secondly, using this framework, an interface design (including interactions) is developed in collaboration with end-users and proposed as an answer to RQ1. This process is described in Section 5. The third contribution is a research agenda which provides insights into how contemporary and future research can leverage the developed framework. Section 7 discloses this research agenda.Master's Thesis in Interaction and Media DesignMIX350MASV-MI

Counting in Uncountably Categorical Pseudofinite Structures

We show that every definable subset of an uncountably categorical pseudofinite structure has pseudofinite cardinality which is polynomial (over the rationals) in the size of any strongly minimal subset, with the degree of the polynomial equal to the Morley rank of the subset. From this fact, we show that classes of finite structures whose ultraproducts all satisfy the same uncountably categorical theory are polynomial $R$-mecs as well as $N$-dimensional asymptotic classes, where $N$ is the Morley rank of the theory

Observation of the Holstein shift in high TcT_c superconductors with thermal modulation reflectometry

We use the experimental technique of thermal modulation reflectometry to study the relatively small temperature dependence of the optical conductivity of superconductors. Due to a large cancellation of systematic errors, this technique is shown to a be very sensitive probe of small changes in reflectivity. We analyze thermal modulation reflection spectra of single crystals and epitaxially grown thin films of YBa$_2$Cu$_3$O$_{7-\delta}$ and obtain the ${\alpha_tr}^2F(\omega)$ function in the normal state, as well as the superconductivity induced changes in reflectivity. We present detailed model calculations, based on the Eliashberg-Migdal extension of the BCS model, which show good qualitative and quantitative agreement with the experimental spectra. VSGD.93.12.thComment: 6 pages, figures on request. Revtex, version 2, Materials Science Center Internal Report Number VSGD.93.12.t

The H II Region/PDR Connection: Self-Consistent Calculations of Physical Conditions in Star-Forming Regions

We have performed a series of calculations designed to reproduce infrared diagnostics used to determine physical conditions in star forming regions. We self-consistently calculate the thermal and chemical structure of an H II region and photodissociation region (PDR) that are in pressure equilibrium. This differs from previous work, which used separate calculations for each gas phase. Our calculations span a wide range of stellar temperatures, gas densities, and ionization parameters. We describe improvements made to the spectral synthesis code Cloudy that made these calculations possible. These include the addition of a molecular network with ~1000 reactions involving 68 molecular species and improved treatment of the grain physics. Data from the Spitzer First Look Survey, along with other archives, are used to derive important physical characteristics of the H II region and PDR. These include stellar temperatures, electron densities, ionization parameters, UV radiation flux, and PDR density. Finally, we calculate the contribution of the H II region to PDR emission line diagnostics, which allows for a more accurate determination of physical conditions in the PDR.Comment: 60 pages, 35 figures, to be published in the Astrophysical Journal. Version with full resolution is available at http://www.pa.uky.edu/~nicholas/hii_pdr_high_res.pd

Dust-Bounded ULIRGs? Model Predictions for Infrared Spectroscopic Surveys

The observed faintness of infrared fine-structure line emission along with the warm far-infrared (FIR) colors of ultraluminous infrared galaxies (ULIRGs) is a long-standing problem. In this work, we calculate the line and continuum properties of a cloud exposed to an Active Galactic Nucleus (AGN) and starburst spectral energy distribution (SED). We use an integrated modeling approach, predicting the spectrum of ionized, atomic, and molecular environments in pressure equilibrium. We find that the effects of high ratios of impinging ionizing radiation density to particle density (i.e. high ionization parameters, or U) can reproduce many ULIRG observational characteristics. Physically, as U increases, the fraction of UV photons absorbed by dust increases, corresponding to fewer photons available to photoionize and heat the gas, producing what is known as a "dust-bounded" nebula. We show that high U effects can explain the "[C II] deficit", the ~1 dex drop in the [C II] 158 micron /FIR ratio seen in ULIRGs when compared to starburst or normal galaxies. Additionally, by increasing U through increasing the ionizing photon flux, warmer dust and thus higher IRAS F(60)/F(100) ratios result. High U effects also predict an increase in [O I]63 micron /[C II] 158 micron and a gradual decline in [O III] 88 micron /FIR, similar to the magnitude of the trends observed, and yield a reasonable fit to [Ne V]14 micron /FIR ratio AGN observations.Comment: 34 pages, 13 figures, accepted for publication in the Astrophysical Journa

Rotationally Warm Molecular Hydrogen in the Orion Bar

The Orion Bar is one of the nearest and best-studied photodissociation or photon-dominated regions (PDRs). Observations reveal the presence of H2 lines from vibrationally or rotationally excited upper levels that suggest warm gas temperatures (400 to 700 K). However, standard models of PDRs are unable to reproduce such warm rotational temperatures. In this paper we attempt to explain these observations with new comprehensive models which extend from the H+ region through the Bar and include the magnetic field in the equation of state. We adopt the model parameters from our previous paper which successfully reproduced a wide variety of spectral observations across the Bar. In this model the local cosmic-ray density is enhanced above the galactic background, as is the magnetic field, and which increases the cosmic-ray heating elevating the temperature in the molecular region. The pressure is further enhanced above the gas pressure in the H+ region by the momentum transferred from the absorbed starlight. Here we investigate whether the observed H2 lines can be reproduced with standard assumptions concerning the grain photoelectric emission. We also explore the effects due to the inclusion of recently computed H2 + H2, H2 + H and H2 + He collisional rate coefficients.Comment: Accepted for publication in ApJ (34 pages, including 16 figures

A Study For Efficiently Solving Optimisation Problems With An Increasing Number Of Design Variables

Coupling optimisation algorithms to Finite Element Methods (FEM) is a very promising way to achieve optimal metal forming processes. However, many optimisation algorithms exist and it is not clear which of these algorithms to use. This paper investigates the sensitivity of a Sequential Approximate Optimisation algorithm (SAO) proposed in [1-4] to an increasing number of design variables and compares it with two other algorithms: an Evolutionary Strategy (ES) and an Evolutionary version of the SAO (ESAO). In addition, it observes the influence of different Designs Of Experiments used with the SAO. It is concluded that the SAO is very capable and efficient and its combination with an ES is not beneficial. Moreover, the use of SAO with Fractional Factorial Design is the most efficient method, rather than Full Factorial Design as proposed in [1-4]

Focus Issue: Neck Dissection for Oropharyngeal Squamous Cell Carcinoma

The staging and prognosis of oropharyngeal squamous cell carcinoma is intimately tied to the status of the cervical lymph nodes. Due to the high risk for occult nodal disease, most clinicians recommend treating the neck for these primary tumors. While there are many modalities available, surgical resection of nodal disease offers both a therapeutic and a diagnostic intervention. We review the relevant anatomy, nodal drainage patterns, clinical workup, surgical management and common complications associated with neck dissection for oropharyngeal squamous cell carcinoma