The Role of Sulphate-Reducing Bacteria and Unconsolidated Organic Matter in the Formation of Primary Dolomite

Laboratory experiments succeeded in producing primary dolomite at Earth-surface conditions using components collected from Christmas Bay near Brazosport, Texas and the Bahamas. Dolomite and calcite precipitates were observed within an anoxic sludge layer of siliciclastic sediment intermingled with decaying particulate organic vegetable matter, e.g., plant stems and roots. After experimentation lasting from 3 to 5 weeks, dolomite was identified by its elemental spectrum via energy-dispersive x-ray spectroscopy compared to known standards. Communities of sulphate-reducing bacteria in anoxic conditions gathered on the decomposing organic matter within the sludge layer. The bacteria on the decaying organic matter changed the microenvironment around them so that dolomite became supersaturated within their immediate vicinity. Although slight changes were made to the solution included in the experiment to decrease the kinetic barriers of the dolomitization reaction, it is concluded that sulphate-reducing bacteria were primarily responsible for the generation of the dolomite precipitates because (a) dolomite was only observed as being directly associated with the decaying organic matter where sulphate-reducing bacteria are thought to have preferentially accumulated, and (b) controlled changes of the chemistry of the solution appeared to have little effect on the precipitation of dolomite. Bacterial precipitates of dolomite and calcite were only found directly on or embedded within organic matter and were preferentially concentrated on organic matter devoid of siliciclastic detritus. Furthermore, dolomite was only synthesized in the presence of ooids which increased the speed and likelihood of dolomitization by contributing Ca2+ and CO32- ions through aragonite dissolution. It is suggested that the reason why primary dolomite is not found naturally within the Christmas Bay sediments is because the process of primary dolomite precipitation requires the presence of carbonate minerals.Earth and Atmospheric Sciences, Department o

Irradiation treatment of laryngeal cancer in a patient with an implantable cardioverter-defibrillator (ICD)

Background: Due to an aging population the incidence of both cardiac and tumor-related illnesses is increasing. A problem may arise if radiotherapy is necessary in close anatomic proximity to an implantable cardioverter-defibrillator (ICD). These highly precise devices may respond to ionizing radiation with a loss of function or uncontrolled stimulation, with both effects being potentially life threatening. Available guidelines recommend the dose maximum to a pacemaker to be cumulative below 2 Gy. For most patients undergoing radiation therapy of the neck or of the chest this limit is exceeded, thus making a removal of the device and an implantation of an external ICD necessary. Case Report: A patient with severe cardiac problems underwent an implantation of an ICD. However, a recurrence of a laryngeal cancer was diagnosed. The irradiation dose after resection was 60 Gy to the tumor region and 50 Gy to the lymph nodes. Irradiation peakload to the ICD was calculated to be 2.5 Gy. This dose was verified with thermoluminescence measurements. The ICD was externally deactivated during the sessions of irradiation. Device checks demonstrated no malfunction. Conclusion: Even though the dose limits of the ICD of 2 Gy were exceeded, the device demonstrated a regular function during and after radiotherapy

Special Interest Partisanship: The Transformation of American Political Parties

Why have group-party alliances become more common since the mid-twentieth century? This dissertation employs both qualitative and statistical tools to address the puzzle of contemporary special interest partisanship. After tracing partisanship across several measures, I develop a continuum of group-party relationships, running from fluid, unstructured interactions (akin to political pluralism) to highly institutionalized alliances (as we might see in a firm). Drawing on pluralist scholarship and theories of firm formation and evolution, I explore the costs and benefits of different arrangements, and explain why we might expect to see movement along the continuum over time. On the one hand, pluralism offers flexibility to parties and groups, and alliances have little value when parties are too weak to discipline their members in Congress. On the other, institutionalized alliances offer significant efficiency gains, which are especially valuable during periods of growth. I argue that changes in group-party relations stem from the growth of national party organizations over the second half of the twentieth century, which increased the value of group resources and intensified parties' need for efficiency. Until this period, parties were weak on the national level and strong on the state and local levels, and patronage was the primary currency of politics, leaving little room for issues in political competition. The New Deal's historic expansion of federal power disrupted this balance, temporarily strengthening local parties by offering new sources of patronage, while also sparking gradual, interconnected processes that would ultimately undermine machine power--most notably, the growth of groups and the rise of issue politics as a site of electoral competition. Realizing the economies of scale necessary to build strong national parties required movement away from pluralism into more structured, long-term relationships. Moreover, in order for the new site of competition to help Republicans build a coalition to compete with the long-dominant New Deal Democrats, distinct issue positions were necessary. The result of this party-building process is a pattern of group-party alliances quite unlike the bipartisan relations V.O. Key, David Truman, and others observed in the mid-twentieth century

Accelerate Beginner English Learner’s Writing Skills From Day One

This article addresses the customary practice of delaying teaching of writing for Beginner English Learners (BELs) which often results in slowing writing development. Barriers preventing teachers from earlier writing instruction include a belief BELs cannot produce written English before learned orally first, a lack of teaching writing know-how, and few level-appropriate materials for older BELs. The systematic approach ALL Beginner Learners of English (ABLE) Writing Method is a solution to build both teachers’ confidence and BELs’ phonics, spelling, and writing skills from day one. The basic premise of the ABLE Writing Method is that if one is able to think, one is able to write with effective instruction and practice. The four phases of an assets-based ABLE Writing Method cycle incorporate the principles of the Language Experience Approach, Translanguaging, Scarborough’s Reading Rope, and Sedita’s Writing Rope so teachers can start teaching writing skills from day one

Simulation of the effects of cavitation and anatomy in the shock path of model lithotripters

We report on recent efforts to develop predictive models for the pressure and other flow variables in the focal region of shock wave lithotripters. Baseline simulations of three representative lithotripters (electrohydraulic, electromagnetic, and piezoelectric) compare favorably with in vitro experiments (in a water bath). We proceed to model and investigate how shock focusing is altered by the presence of material interfaces associated with different types of tissue encountered along the shock path, and by the presence of cavitation bubbles that are excited by tensile pressures associated with the focused shock wave. We use human anatomical data, but simplify the description by assuming that the tissue behaves as a fluid, and by assuming cylindrical symmetry along the shock path. Scattering by material interfaces is significant, and regions of high pressure amplitudes (both compressive and tensile) are generated almost 4 cm postfocus. Bubble dynamics generate secondary shocks whose strength depends on the density of bubbles and the pulse repetition frequency (PRF). At sufficiently large densities, the bubbles also attenuate the shock. Together with experimental evidence, the simulations suggest that high PRF may be counterproductive for stone comminution. Finally, we discuss how the lithotripter simulations can be used as input to more detailed physical models that attempt to characterize the mechanisms by which collapsing cavitation models erode stones, and by which shock waves and bubbles may damage tissue

Learning Temporally Extended Skills in Continuous Domains as Symbolic Actions for Planning

Problems which require both long-horizon planning and continuous control capabilities pose significant challenges to existing reinforcement learning agents. In this paper we introduce a novel hierarchical reinforcement learning agent which links temporally extended skills for continuous control with a forward model in a symbolic discrete abstraction of the environment's state for planning. We term our agent SEADS for Symbolic Effect-Aware Diverse Skills. We formulate an objective and corresponding algorithm which leads to unsupervised learning of a diverse set of skills through intrinsic motivation given a known state abstraction. The skills are jointly learned with the symbolic forward model which captures the effect of skill execution in the state abstraction. After training, we can leverage the skills as symbolic actions using the forward model for long-horizon planning and subsequently execute the plan using the learned continuous-action control skills. The proposed algorithm learns skills and forward models that can be used to solve complex tasks which require both continuous control and long-horizon planning capabilities with high success rate. It compares favorably with other flat and hierarchical reinforcement learning baseline agents and is successfully demonstrated with a real robot.Comment: Project website (including video) is available at https://seads.is.tue.mpg.de/. (v2) Accepted for publication at the 6th Conference on Robot Learning (CoRL) 2022, Auckland, New Zealand. (v3) Added details on checkpointing (S.8.1), with references on p.7, p.8, p.21 to clarify number of env. steps of reported result