Thermal coatings for titanium-aluminum alloys

Titanium aluminides and titanium alloys are candidate materials for use in hot structure and heat-shield components of hypersonic vehicles because of their good strength-to-weight characteristics at elevated temperature. However, in order to utilize their maximum temperature capability, they must be coated to resist oxidation and to have a high total remittance. Also, surface catalysis for recombination of dissociated species in the aerodynamic boundary layer must be minimized. Very thin chemical vapor deposition (CVD) coatings are attractive candidates for this application because of durability and very light weight. To demonstrate this concept, coatings of boron-silicon and aluminum-boron-silicon compositions were applied to the titanium-aluminides alpha2 (Ti-14Al-21Nb), super-alpha2 (Ti-14Al-23-Nb-2V), and gamma (Ti-33Al-6Nb-1Ta) and to the titanium alloy beta-21S (Ti-15Mo-3Al-3Nb-0.2Si). Coated specimens of each alloy were subjected to a set of simulated hypersonic vehicle environmental tests to determine their properties of oxidation resistance, surface catalysis, radiative emittance, and thermal shock resistance. Surface catalysis results should be viewed as relative performance only of the several coating-alloy combinations tested under the specific environmental conditions of the LaRC Hypersonic Materials Environmental Test System (HYMETS) arc-plasma-heated hypersonic wind tunnel. Tests were also conducted to evaluate the hydrogen transport properties of the coatings and any effects of the coating processing itself on fatigue life of the base alloys. Results are presented for three types of coatings, which are as follows: (1) a single layer boron silicon coating, (2) a single layer aluminum-boron-silicon coating, and (3) a multilayer coating consisting of an aluminum-boron-silicon sublayer with a boron-silicon outer layer

Thermal performance of multilayer insulations Interim report

Heat flux and optical property measurement for multilayer insulatio

Exponential suppression of thermal conductance using coherent transport and heterostructures

We consider coherent thermal conductance through multilayer photonic crystal heterostructures, consisting of a series of cascaded non-identical photonic crystals. We show that thermal conductance can be suppressed exponentially with the number of cascaded crystals, due to the mismatch between photonic bands of all crystals in the heterostructure.Comment: 15 pages, 4 figure

Multipole expansion for H I intensity mapping experiments: simulations and modelling

We present a framework and an open-source python toolkit to analyse the 2-point statistics of 3D fluctuations in the context of HI intensity maps using the multipole expansion formalism. We include simulations of the cosmological HI signal using N-body and log-normal methods, foregrounds and their removal, as well as instrumental effects. Using these simulations and analytical modelling, we investigate the impact of foreground cleaning and the instrumental beam on the power spectrum multipoles as well as on the Fourier space clustering wedges. We find that both the instrumental beam and the foreground removal can produce a quadrupole (and a hexadecapole) signal, and demonstrate the importance of controlling and accurately modelling these effects for precision radio cosmology. We conclude that these effects can be modelled with reasonable accuracy using our multipole expansion technique. We also perform an MCMC analysis to showcase the effect of foreground cleaning on the estimation of the HI abundance and bias parameters. The accompanying python toolkit is available at https://github.com/IntensityTools/MultipoleExpansion, and includes an interactive suite of examples to aid new users.Comment: 21 pages, 14 figure

‘They would rather not have known and me kept my mouth shut’: The role of neutralisation in responding to the disclosure of childhood sexual abuse

There is a well-established literature examining how perpetrators of child sexual abuse (CSA) neutralise the norms and beliefs that ordinarily prohibit such behaviours. However, there has been substantially less focus on how such techniques of neutralisation might also be applied by people and groups who were not directly involved in the abuse, who we might expect to be more supportive. Drawing on a thematic analysis of an open-ended survey (n=140) and semi-structured interviews (n=21) with adults who experienced childhood sexual abuse this paper examines societal responses to disclosure. Identifying three key techniques of neutralisation, it explores how families, professionals and institutions use wider discourses that deny the victim/survivor, deny or minimise harm and silence by appealing to loyalty. The results demonstrate how significant others can constrain, rather than support, the process of disclosure and recovering from CSA

Study of fuel systems for LH2-fueled subsonic transport aircraft, volume 1

Several engine concepts examined to determine a preferred design which most effectively exploits the characteristics of hydrogen fuel in aircraft tanks received major emphasis. Many candidate designs of tank structure and cryogenic insulation systems were evaluated. Designs of all major elements of the aircraft fuel system including pumps, lines, valves, regulators, and heat exchangers received attention. Selected designs of boost pumps to be mounted in the LH2 tanks, and of a high pressure pump to be mounted on the engine were defined. A final design of LH2-fueled transport aircraft was established which incorporates a preferred design of fuel system. That aircraft was then compared with a conventionally fueled counterpart designed to equivalent technology standards

Study of fuel systems for LH2-fueled subsonic transport aircraft, volume 2

For abstract, see N78-31085

Thermal performance of multilayer insulations

Experimental and analytical studies were conducted in order to extend previous knowledge of the thermal performance and gas evacuation characteristics of three selected multilayer insulation (MLI) composites. Flat plate calorimeter heat flux measurements were obtained for 20- and 80- shield specimens using three representative layer densities over boundary temperatures ranging from 39 K (70 R) to 389 K (700 R). Laboratory gas evacuation tests were performed on representative specimens of each MLI composite after initially purging them with helium, nitrogen, or argon gases. In these tests, the specimens were maintained at temperatures between 128 K (230 R) and 300 K (540 R). Based on the results of the laboratory-scale tests, a composite MLI system consisting of 112 unperforated, double-aluminized Mylar reflective shields and 113 water preconditioned silk net spacer pairs was fabricated and installed on a 1.22-m-(4-ft-) diameter calorimeter tank

Review of UK malaria treatment guidelines 2016 (Public Health England Advisory Committee on Malaria Prevention)

This guideline covers the diagnosis and management of malaria, and was published in the Journal of Infection in June 2016.1 It was written by the Public Health England Advisory Committee on Malaria Prevention (PHE ACMP) based on review of available evidence and expert consultation (using a modified Grading of Recommendations Assessment, Development and Evaluation criteria for assessment of evidence and strength of recommendation), to be in line with WHO guidelines on management of malaria.2 It relates to malaria in both adults and children in the UK although here we focus on the diagnosis and management of children returning to the UK with suspected malaria. Malaria is the most common imported tropical pathogen in the UK, and children comprise about 10% of the 1300–1800 UK cases per annum. Plasmodium falciparum is by far the most common (around 75% of cases) and is associated with more severe disease

Cognitive control mechanisms revealed by ERP and fMRI: Evidence from repeated task-switching

We investigated the extent to which a common neural mechanism is involved in task set-switching and response withholding, factors that are frequently confounded in task-switching and go/no-go paradigms. Subjects' brain activity was measured using event-related electrical potentials (ERPs) and event-related functional MRI (fMRI) neuroimaging in separate studies using the same cognitive paradigm. Subjects made compatible left/right keypress responses to left/right arrow stimuli of 1000 msec duration; they switched every two trials between responding at stimulus onset (GO task-green arrows) and stimulus offset (WAIT task-red arrows). Withholding an immediate response (WAIT vs. GO) elicited an enhancement of the frontal N2 ERP and lateral PFC activation of the right hemisphere, both previously associated with the "no-go" response, but only on switch trials. Task-switching (switch vs. nonswitch) was associated with frontal N2 amplification and right hemisphere ventrolateral PFC activation, but only for the WAIT task. The anterior cingulate cortex (ACC) was the only brain region to be activated for both types of task switch, but this activation was located more rostrally for the WAIT than for the GO switch trials. We conclude that the frontal N2 ERP and lateral PFC activation are not markers for withholding an immediate response or switching tasks per se, hut are associated with switching into a response-suppression mode. Different regions within the ACC may be involved in two processes integral to task-switching: processing response conflict (rostral ACC) and overcoming prior response suppression (caudal ACC)