Research study: Space vehicle control systems

From the control point of view, spacecraft are classified into two main groups: those for which the spacecraft is fully defined before the control system is designed; and those for which the control system must be specified before certain interchangeable parts of a multi-purpose spacecraft are selected for future missions. Consideration is given to both classes of problems

Human energetic stress associated with upregulation of spatial cognition

Objectives: Evolutionary life history theory has a unique potential to shed light on human adaptive capabilities. Ultra-endurance challenges are a valuable experimental model allowing the direct testing of phenotypic plasticity via physiological trade-offs in resource allocation. This enhances our understanding of how the body prioritizes different functions when energetically stressed. However, despite the central role played by the brain in both hominin evolution and metabolic budgeting, cognitive plasticity during energetic deficit remains unstudied. Materials: We considered human cognitive plasticity under conditions of energetic deficit by evaluating variability in performance in three key cognitive domains. To achieve this, cognitive performance in a sample of 48 athletes (m = 29, f = 19) was assessed before and after competing in multiday ultramarathons. Results: We demonstrate that under conditions of energetic deficit, performance in tasks of spatial working memory (which assessed ability to store location information, promoting landscape navigation and facilitating resource location and calorie acquisition) increased. In contrast, psychomotor speed (reaction time) remained unchanged and episodic memory performance (ability to recall information about specific events) decreased. Discussion: We propose that prioritization of spatial working memory performance during conditions of negative energy balance represents an adaptive response due to its role in facilitating calorie acquisition. We discuss these results with reference to a human evolutionary trajectory centred around encephalisation. Encephalisation affords great plasticity, facilitating rapid responses tailored to specific environmental conditions, and allowing humans to increase their capabilities as a phenotypically plastic species

In-plane Creep Behavior of Cross-laminated Timber and Mass Plywood Panels: A Methodology to Evaluate the Long-term Performance of Post-Tensioned Mass Timber Walls

Post-tensioned (PT) self-centering shear walls were designed to reduce structural damage from seismic activity. However, these lateral force resistant systems experience post-tension loss negatively affecting the re-centering capability due to delayed deformations experienced by engineered wood products over time. The long-term mechanical response of mass-timber panels to in-plane PT loads is a complex, multi-physics problem involving moisture diffusion, constrained hygroexpansion, and viscoelastic and mechano-sorptive response of the panel to the PT load, which is mitigated by the deformation of the panel. Changes in the relative humidity of the surrounding environment affects the wood moisture content and results in additional creep due to the mechano-sorptive effect. Methodologies developed to accurately measure creep and post-tension loss and improve the visualization of monitoring these phenomena in an existing building to-date proved insufficient. Therefore, a new methodology was developed to measure viscoelastic and mechano-sorptive creep characteristics of small-scale post-tensioned cross-laminated timber (CLT) and mass plywood panel (MPP) wall specimens in two controlled environments. The combined data from these tests will be useful for updating PT loss modeling parameters, or to create a new predictive creep model. Additionally, a full-scale monitoring study of 28 ft tall post-tensioned CLT and MPP walls was proposed to obtain long-term data from a structural system and validate the model. The model will then be used to predict PT losses in a real building based on input data obtained from a structural health monitoring (SHM) system. Furthermore, to streamline SHM, measurands including relative humidity, air and wood temperature, wood moisture content, displacements and deformations of shear walls, and tensile force of post-tensioned rods, were integrated and visualized in a Building Information Model (BIM), as it enables the storage of spatial information, including building geometry and dimensions, and non-spatial attributes, such as material type and sensor readings. The approach intends to simplify the necessary steps required to create a digital model of a structure linked to historical sensor data to improve the visualization of SHM data to assist with maintenance decisions. Specifically, the BIM was proposed to access all the environmental and structural monitored parameters used to describe and predict the long-term response of mass timber post-tensioned shear walls in a building. The east stairwell of the George W. Peavy Forest Science Center (“Peavy Hall”) at Oregon State University was used as a case study to test the proposed approach. Since there was no accurate, as-built BIM available, the BIM of PT CLT shear walls was developed using a Scan-to-BIM approach by converting Light Detection and Ranging (LiDAR) point clouds into a BIM. All sensors included in the BIM were linked to their historical data displayed on the internet and easily accessible through a list that highlights their locations within the digital model. The precise placement of these sensors and the possibility to associate the measured parameters of these entities within a BIM is hypothesized to assist with data management by adding a spatial element to data and analysis results, which could lead to a more streamlined maintenance and service life planning of a building. The creep tests, modeling, full-scale monitoring of post-tensioned systems, and BIM for SHM were developed to assist with the design and maintenance of post-tensioned timber shear walls. The creep tests were designed to capture important data such as load, viscoelastic creep, mechano-sorptive creep, timber moisture content, environmental conditions, and timber shrinkage and swelling, useful for refining material properties to create a predictive model. The creep model currently accounts for the creep of CLT under a constant load, which is a preliminary step towards predicting the post-tension loss of PT shear walls. In future work, the data recorded from the tests should be analyzed to update the creep model to include mechano-sorptive effects and a varying load due to PT loss. Engineers can benefit from a predictive model to design a system that reduces and accounts for expected PT loss, so the building remains seismically resilient. Building managers and occupants of a building can benefit through the improved visualization of SHM data. A future study can incorporate the live sensory data into the BIM and display the data for the public. This would allow occupants to make maintenance requests and be aware of future maintenance tasks that can improve the service life of the building

The Pacific Drought Knowledge Exchange: A Co-Production Approach to Deliver Climate Resources to User Groups

Drought is a growing threat to hydrological, ecological, agricultural, and socio-cultural systems of the tropics, especially tropical islands of the Pacific where severe droughts can compromise food and water security. Overcoming barriers to knowledge sharing between land managers and researchers is a critical cross-sector strategy for engaging and mitigating or adapting to drought. Here we describe the establishment and functioning of the Pacific Drought Knowledge Exchange (PDKE), which provides users with easier access to: (1) sector- and geography-specific climate information; (2) better and more comprehensive information; (3) improved technical assistance; and (4) a more collaborative information-transfer environment through participation in knowledge co-production. We focus on our collaborative work with managers of important tropical dryland ecosystems from three distinct geographies to pilot the collaborative development of climate change, climate variability, and drought “portfolios” featuring site-specific historical and forecasted future information. This information was then used to collaboratively produce factsheets that partners used to: (i) better understand past and projected climate for specific management units; (ii) integrate new climate knowledge into management planning; and (iii) support climate-focused educational and outreach efforts. This pilot effort demonstrates the successful application of climate-focused co-production in dry tropical landscapes

Semiclassical Quantization by Pade Approximant to Periodic Orbit Sums

Periodic orbit quantization requires an analytic continuation of non-convergent semiclassical trace formulae. We propose a method for semiclassical quantization based upon the Pade approximant to the periodic orbit sums. The Pade approximant allows the re-summation of the typically exponentially divergent periodic orbit terms. The technique does not depend on the existence of a symbolic dynamics and can be applied to both bound and open systems. Numerical results are presented for two different systems with chaotic and regular classical dynamics, viz. the three-disk scattering system and the circle billiard.Comment: 7 pages, 3 figures, submitted to Europhys. Let

Switching from premixed insulin to glargine-based insulin regimen improves glycaemic control in patients with type 1 or type 2 diabetes: a retrospective primary care-based analysis

Background: Insulin glargine (glargine) and premixed insulins (premix) are alternative insulin treatments. This analysis evaluated glycaemic control in 528 patients with type 1 (n = 183) or type 2 (n = 345) diabetes, after switching from premix to a glargine-based regimen, using unselected general practice (GP) data. Methods: Data for this retrospective observational analysis were extracted from a UK GP database (The Health Improvement Network). Patients were required to have at least 12 months of available data, before and after, switching from premix to a glargine-based regimen. The principal analysis was the change in HbA1c after 12 months of treatment with glargine; secondary analyses included change in weight, bolus usage and total daily insulin dose. Inconsistent reporting of hypoglycemic episodes precludes reliable assessment of this outcome. Multivariate analyses were used to adjust for baseline characteristics and confounding variables. Results: Both cohorts showed significant reduction in mean HbA1c 12 months after the switch: by -0.67% (p < 0.001) in the type 1 cohort and by -0.53% (p < 0.001) in the type 2 cohort (adjusted data). The size of HbA1c improvement was positively correlated with baseline HbA1c; patients with a baseline HbA1c ≥ 10% had the greatest mean reduction in HbA1c, by -1.7% (p < 0.001) and -1.2% (p < 0.001), respectively. The proportion of patients receiving co-bolus prescriptions increased in the type 1 (mean 24.6% to 95.1%, p < 0.001) and type 2 (mean 16.2% to 73.9%, p < 0.001) cohorts. There was no significant change in weight in either cohort. Total mean insulin use increased in type 2 diabetes patients (from 0.67 ± 1.35 U/Kg to 0.88 ± 1.33 U/Kg, p < 0.001) with a slight decrease in type 1 diabetes patients (from 1.04 ± 2.51 U/Kg to 0.98 ± 2.58 U/Kg, p < 0.001). Conclusion: In everyday practice, patients with type 1 or type 2 diabetes inadequately controlled by premix insulins experienced significant improvement in glycaemic control over 12 months after switching to a glargine-based insulin regimen. These findings support the use of a basal-bolus glargine-based regimen in patients poorly controlled on premix.Peter Sharplin, Jason Gordon, John R Peters, Anthony P Tetlow, Andrea J Longman and Philip McEwa

Collisionless shock acceleration of narrow energy spread ion beams from mixed species plasmas using 1 μ\mum lasers

Collisionless shock acceleration of protons and C$^{6+}$ ions has been achieved by the interaction of a 10$^{20}$ W/cm$^2$, 1 $\mu$m laser with a near-critical density plasma. Ablation of the initially solid density target by a secondary laser allowed for systematic control of the plasma profile. This enabled the production of beams with peaked spectra with energies of 10-18 MeV/a.m.u. and energy spreads of 10-20$\%$ with up to 3x10$^9$ particles within these narrow spectral features. The narrow energy spread and similar velocity of ion species with different charge-to-mass ratio are consistent with acceleration by the moving potential of a shock wave. Particle-in-cell simulations show shock accelerated beams of protons and C$^{6+}$ ions with energy distributions consistent with the experiments. Simulations further indicate the plasma profile determines the trade-off between the beam charge and energy and that with additional target optimization narrow energy spread beams exceeding 100 MeV/a.m.u. can be produced using the same laser conditions.Comment: Accepted for publication in Physical Review Accelerators and Beam

Study of Foaming Properties and Effect of the Isomeric Distribution of Some Anionic Surfactants

Using different reaction conditions of photosulfochlorination of n-dodecane, two samples of anionic surfactants of sulfonate type are obtained. Their micellar behavior has been already reported and the relationship between their isomeric distribution and their chemical structures and micellar behaviors have been more thoroughly explored. In this investigation, we screened the foaming properties (foaming power and foam stability) by a standardized method very similar to the Ross–Miles foaming tests to identify which surfactants are suitable for applications requiring high foaming, or, alternatively, low foaming. The results obtained for the synthesized surfactants are compared to those obtained for an industrial sample of secondary alkanesulfonate (Hostapur 60) and to those of a commercial sample of sodium dodecylsulfate used as reference for anionic surfactants. The foam formation and foam stability of aqueous solutions of the two samples of dodecanesulfonate are compared as a function of their isomeric distribution. These compounds show good foaming power characterized in most cases by metastable or dry foams. The highest foaming power is obtained for the sample rich in primary isomers which also produces foam with a relatively high stability. For the sample rich in secondary isomers we observe under fixed conditions a comparable initial foam height but the foam stability turns out to be low. This property is interesting for applications requiring low foaming properties such as dishwashing liquid for machines. The best results are observed near and above the critical micellar concentrations and at 25 C for both the samples