Polymer degradation rate control of hybrid rocket combustion

Polymer degradation to small fragments is treated as a rate controlling step in hybrid rocket combustion. Both numerical and approximate analytical solutions of the complete energy and polymer chain bond conservation equations for the condensed phase are obtained. Comparison with inert atmosphere data is very good. It is found that the intersect of curves of pyrolysis rate versus interface temperature for hybrid combustors, with the thermal degradation theory, falls at a pyrolysis rate very close to that for which a pressure dependence begins to be observable. Since simple thermal degradation cannot give sufficient depolymerization at higher pyrolysis rates, it is suggested that oxidative catalysis of the process occurs at the surface, giving a first order dependence on reactive species concentration at the wall. Estimates of the ratio of this activation energy and interface temperature are in agreement with best fit procedures for hybrid combustion data. Requisite active species concentrations and flux are shown to be compatible with turbulent transport. Pressure dependence of hybrid rocket fuel regression rate is thus shown to be describable in a consistent manner in terms of reactive species catalysis of polymer degradation

The Influence of High-Temperature Creep on the Ultrasonic Velocity in Alloy 800H

The occurrence of creep damage limits the lifetime of component that are exposed to stresses at temperatures higher than approximately half the melting temperature. Such conditions are generally met by a lot of structural components especially in power plants (pipes, turbines, etc.). According to conventional safety rules critical parts are usually exchanged long before any failure has to be expected. This procedure is based on statistics drawn from material tests by standardized methods rather than on the actual state of the component concerned. During the last years an increasing need can be stated to develop NDE methods for the detection of early damage stages in order to improve the reliability and safety of components. Basically, techniques are required which are sensitive to either small strains or, better, to small concentrations of micropores and microcracks, respectively. With regard to in-field applications, only replica techniques are used successfully for that purpose up to now [1,2]. These metallographic techniques are restricted to surfaces where appropriate spots have to be selected and to be prepared carefully. In this work the influence of creep damage on the ultrasonic velocity has been investigated on a representative high-temperature alloy for tube components, i. e., Alloy 800 H (X10 NiCrAlTi 32 20)

Correlated Information Reduces Accuracy of Pioneering Decision-Makers

Normative models are often used to describe how humans and animals make decisions. These models treat deliberation as the accumulation of uncertain evidence that terminates with a commitment to a choice. When extended to social groups, such models often assume that individuals make independent observations. However, individuals typically gather evidence from common sources, and their observations are rarely independent. Here we ask: For a group of ideal observers who do not exchange information, what is the impact of correlated evidence on decision accuracy? We show that even when agents are identical, correlated evidence causes decision accuracy to depend on temporal decision order. Surprisingly, the first decider is less accurate than a lone observer. Early deciders are less accurate than late deciders. These phenomena occur despite the fact that the rational observers use the same decision criterion, so they are equally confident in their decisions. We analyze discrete and continuum evidence-gathering models to explain why the first decider is less accurate than a lone observer when evidence is correlated. Pooling the decisions of early deciders using a majority rule does not rescue accuracy in the sense that such pooling results in only modest accuracy gain. Although we analyze an idealized model, we believe that our analysis offers insights that do not depend on exactly how groups integrate evidence and form decisions.Comment: 19 pages, 5 figure

Quantum Rotor Engines

This chapter presents autonomous quantum engines that generate work in the form of directed motion for a rotor. We first formulate a prototypical clock-driven model in a time-dependent framework and demonstrate how it can be translated into an autonomous engine with the introduction of a planar rotor degree of freedom. The rotor plays both the roles of internal engine clock and of work repository. Using the example of a single-qubit piston engine, the thermodynamic performance is then reviewed. We evaluate the extractable work in terms of ergotropy, the kinetic energy associated to net directed rotation, as well as the intrinsic work based on the exerted torque under autonomous operation; and we compare them with the actual energy output to an external dissipative load. The chapter closes with a quantum-classical comparison of the engine's dynamics. For the single-qubit piston example, we propose two alternative representations of the qubit in an entirely classical framework: (i) a coin flip model and (ii) a classical magnet moment, showing subtle differences between the quantum and classical descriptions.Comment: Chapter of the upcoming book "Thermodynamics in the Quantum Regime - Recent Progress and Outlook

Principles and Strategies for Monitoring Data Collection Integrity in a Multi-site Randomized Clinical Trial of a Behavioral Intervention

Although treatment fidelity strategies for enhancing the integrity of behavioral interventions have been well described, little has been written about monitoring data collection integrity. This article describes the principles and strategies developed to monitor data collection integrity of the "Stories and Music for Adolescent/Young Adult Resilience During Transplant" study (R01NR008583; U10CA098543; U10CA095861) -- a multi-site Children's Oncology Group randomized clinical trial of a music therapy intervention for adolescents and young adults undergoing stem cell transplant. The principles and strategies outlined in this article provide one model for development and evaluation of a data collection integrity monitoring plan for behavioral interventions that may be adapted by investigators and may be useful to funding agencies and grant application reviewers in evaluating proposals

Description of the ERA-CLIM historical upper-air data

Historical, i.e. pre-1957, upper-air data are a valuable source of information on the state of the atmosphere, in some parts of the world dating back to the early 20th century. However, to date, reanalyses have only partially made use of these data, and only of observations made after 1948. Even for the period between 1948 (the starting year of the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis) and the International Geophysical Year in 1957 (the starting year of the ERA-40 reanalysis), when the global upper-air coverage reached more or less its current status, many observations have not yet been digitised. The Comprehensive Historical Upper-Air Network (CHUAN) already compiled a large collection of pre-1957 upper-air data. In the framework of the European project ERA-CLIM (European Reanalysis of Global Climate Observations), significant amounts of additional upper-air data have been catalogued (> 1.3 million station days), imaged (> 200 000 images) and digitised (> 700 000 station days) in order to prepare a new input data set for upcoming reanalyses. The records cover large parts of the globe, focussing on, so far, less well covered regions such as the tropics, the polar regions and the oceans, and on very early upper-air data from Europe and the US. The total number of digitised/inventoried records is 61/101 for moving upper-air data, i.e. data from ships, etc., and 735/1783 for fixed upper-air stations. Here, we give a detailed description of the resulting data set including the metadata and the quality checking procedures applied. The data will be included in the next version of CHUAN. The data are available at <a href="http://dx.doi.org/10.1594/PANGAEA.821222"target="_blank">doi:10.1594/PANGAEA.821222</a>

Recruitment strategies and rates of a multi-site behavioral intervention for adolescents and young adults with cancer

INTRODUCTION: To provide an overview of factors related to recruitment of adolescents and young adults (AYA) into research and recruitment rates and reasons for refusal from a multicenter study entitled "Stories and Music for Adolescent/Young Adult Resilience during Transplant" (SMART). METHODS: A randomized clinical trial study design was used. The settings included 9 hospitals. The sample included AYAs (aged 11-24 years) who were undergoing a stem cell transplant. Several instruments were used to measure symptom distress, coping, resilience, and quality of life in AYA with cancer. RESULTS: A total of 113 AYA were recruited (50%) for this study. Strategies were refined as the study continued to address challenges related to recruitment. We provide a description of recruitment strategies and an evaluation of our planning, implementing, and monitoring of recruitment rates for the SMART study. DISCUSSION: When designing a study, careful consideration must be given to factors influencing recruitment as well as special considerations for unique populations. Dissemination of strategies specific to unique populations will be helpful to the design of future research studies

Chemistry, transport and dry deposition of trace gases in the boundary layer over the tropical Atlantic Ocean and the Guyanas during the GABRIEL field campaign

We present a comparison of different Lagrangian and chemical box model calculations with measurement data obtained during the GABRIEL campaign over the tropical Atlantic Ocean and the Amazon rainforest in the Guyanas, October 2005. Lagrangian modelling of boundary layer (BL) air constrained by measurements is used to derive a horizontal gradient (&amp;asymp;5.6 pmol/mol km&lt;sup&gt;&amp;minus;1&lt;/sup&gt;) of CO from the ocean to the rainforest (east to west). This is significantly smaller than that derived from the measurements (16&amp;ndash;48 pmol/mol km&lt;sup&gt;&amp;minus;1&lt;/sup&gt;), indicating that photochemical production from organic precursors alone cannot explain the observed strong gradient. It appears that HCHO is overestimated by the Lagrangian and chemical box models, which include dry deposition but not exchange with the free troposphere (FT). The relatively short lifetime of HCHO implies substantial BL-FT exchange. The mixing-in of FT air affected by African and South American biomass burning at an estimated rate of 0.12 h&lt;sup&gt;&amp;minus;1&lt;/sup&gt; increases the CO and decreases the HCHO mixing ratios, improving agreement with measurements. A mean deposition velocity of 1.35 cm/s for H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; over the ocean as well as over the rainforest is deduced assuming BL-FT exchange adequate to the results for CO. The measured increase of the organic peroxides from the ocean to the rainforest (&amp;asymp;0.66 nmol/mol d&lt;sup&gt;&amp;minus;1&lt;/sup&gt;) is significantly overestimated by the Lagrangian model, even when using high values for the deposition velocity and the entrainment rate. Our results point at either heterogeneous loss of organic peroxides and/or their radical precursors, underestimated photodissociation or missing reaction paths of peroxy radicals not forming peroxides in isoprene chemistry. We calculate a mean integrated daytime net ozone production (NOP) in the BL of (0.2&amp;plusmn;5.9) nmol/mol (ocean) and (2.4&amp;plusmn;2.1) nmol/mol (rainforest). The NOP strongly correlates with NO and has a positive tendency in the boundary layer over the rainforest

Training teachers for the multimedia age: developing teacher expertise to enhance online learner interaction and collaboration

This article considers the skills that enable teachers to foster interaction and collaboration in online language learning. Drawing on Hampel and Stickler’s (2005) skills pyramid for online language learning and teaching, it presents the pre-service and in-service training programme that associate lecturers in the Department of Languages at the Open University undergo in the context of teaching languages with the help of online communication tools. Two projects are presented that shed more light on the expertise required to teach languages in virtual learning environments. The first project highlights the skills that are needed to teach in a complex online environment; the second one, a teacher training study, aimed to examine distance teachers’ experience of facilitating online group work, identify development needs, try out the potential of specific asynchronous and synchronous tools to support collaborative learning and trial possible development activities. The paper concludes by describing the kind of training programme that tutors require in order to acquire the skills identified