The frequency response of temperature and precipitation in a climate model

Dynamic aspects of the climate's response to forcing are typically explored through transient simulations in the time domain. However, because of the large range of time-scales involved, some features are more easily observed in the frequency domain. We compute the frequency-response of the HadCM3L general circulation model (GCM) to sinusoidal perturbations in solar radiative forcing, with periods between 2^(−1/2) and 2^9 (512) years. The global mean temperature response decreases with increasing frequency, and the frequency scaling at time-scales longer than one year is consistent with the behavior of diffusion into a semi-infinite slab. The land-sea contrast and land-averaged precipitation, however, exhibit relatively little dependency on the frequency of the imposed perturbation, with significant response at both short and long periods. Understanding these relative characteristics of different climate variables in the frequency domain is important to understanding the transient response of the climate system to both anthropogenic and natural (e.g., volcanic) forcings; the frequency response is also relevant in understanding the spectrum of natural variability

A study of solvent effects on the reaction between p-nitrobenzyl chloride and hydroxide ion in aqueous dioxane homogeneous media

The kinetics and activation parameters of the reaction between p̲, p̲\u27 - dinitrostilbene quantitatively, have been studied in five aqueous dioxane solvent systems at five different temperatures between 20⁰ and 40⁰C. At any one temperature the second-order rate constants are minimum in the 30% dioxane solvent mixture, reach a maximum in the 50% dioxane systems, and fall off slightly in the 60% and 70% dioxane systems. The Arrhenius activation energies are highest in the 30% dioxane and lowest in the 70% dioxane systems. The free energies of activation change in the same direction but the magnitude of change is much less than that for Ea or ΔH*. The greatest variation is shown in the entropies of activation: 14.4 e.u. in the 30% aqueous dioxane solvent mixture and only 2.5 e.u. in the 70% system. The significance of these results is discussed in terms of specific solute-solvent interactions, dielectric constants, and variations in the activities of hydroxide ion with variations in the solvent composition --Abstract, page vi

Analysing the impact of learning inputs - Application to terrain traversability estimation

Data-driven approaches such as Gaussian Process (GP) regression have been used extensively in recent robotics literature to achieve estimation by learning from experience. To ensure satisfactory performance, in most cases, multiple learning inputs are required. Intuitively, adding new inputs can often contribute to better estimation accuracy, however, it may come at the cost of a new sensor, larger training dataset and/or more complex learning, some- times for limited benefits. Therefore, it is crucial to have a systematic procedure to determine the actual impact each input has on the estimation performance. To address this issue, in this paper we propose to analyse the impact of each input on the estimate using a variance-based sensitivity analysis method. We propose an approach built on Analysis of Variance (ANOVA) decomposition, which can characterise how the prediction changes as one or more of the input changes, and also quantify the prediction uncertainty as attributed from each of the inputs in the framework of dependent inputs. We apply the proposed approach to a terrain-traversability estimation method we proposed in prior work, which is based on multi-task GP regression, and we validate this implementation experimentally using a rover on a Mars-analogue terrain

What is technicality? A Technicality Analysis Model for EAP vocabulary

The identification of technical words for teaching discipline-specific EAP courses remains a problem for materials designers and teachers alike. This study proposes a method that identifies technicality and measures the degree of technicality of a word. The Technicality Analysis Model (TAM) suggests five levels of technicality: least technical, slightly technical, moderately technical, very technical and most technical. In identifying technicality we take four factors into account: 1) both general and specialised senses of a word; (2) the banding of a word in reference word lists; (3) the polysemy of a word; (4) the literal meaning of a word. The set of categorisation criteria is stringent in the sense that even least technical words may have specialised senses in a specific discipline but those senses may be almost the same as the general sense. All words in more technical categories have specialised senses. We trialled the TAM with 837 financial-sector-specific words generated from a 6.7-million-word corpus of financial texts. Results show that with the categorisation criteria in the technicality analysis, every financial-sector-specific word could be categorised into one of the technical word categories. Future research may use the TAM to develop a repertoire of discipline-specific vocabulary for EAP teaching and learning

Folding Very Short Peptides Using Molecular Dynamics

Peptides often have conformational preferences. We simulated 133 peptide 8-mer fragments from six different proteins, sampled by replica-exchange molecular dynamics using Amber7 with a GB/SA (generalized-Born/solvent-accessible electrostatic approximation to water) implicit solvent. We found that 85 of the peptides have no preferred structure, while 48 of them converge to a preferred structure. In 85% of the converged cases (41 peptides), the structures found by the simulations bear some resemblance to their native structures, based on a coarse-grained backbone description. In particular, all seven of the β hairpins in the native structures contain a fragment in the turn that is highly structured. In the eight cases where the bioinformatics-based I-sites library picks out native-like structures, the present simulations are largely in agreement. Such physics-based modeling may be useful for identifying early nuclei in folding kinetics and for assisting in protein-structure prediction methods that utilize the assembly of peptide fragments

Can we test geoengineering?

Solar radiation management (SRM), a form of geoengineering, might be used to offset some fraction of the anthropogenic radiative forcing of climate as a means to reduce climate change, but the risks and effectiveness of SRM are uncertain. We examine the possibility of testing SRM through sub-scale deployment as a means to test models of climate response to SRM and explore risks prior to full-scale implementation. Contrary to some claims, this could provide meaningful tests of the climate’s response to SRM within a decade. We use idealized simulations with the HadCM3L general circulation model (GCM) to estimate the response to SRM and signal-to-noise ratio for global-scale SRM forcing tests, and quantify the trade-offs between duration and intensity of the test and it’s ability to make quantitative measurements of the climate’s response to SRM forcing. The response at long time-scales would need to be extrapolated from results measured by a short-term test; this can help reduce the uncertainty associated with relatively rapid climate feedbacks, but uncertainties that only manifest at long time-scales can never be resolved by such a test. With this important caveat, the transient climate response may be bounded with 90% confidence to be no more than $1.5^{\circ} C$ higher than it’s estimated value, in a single decade test that used roughly 1/10th the radiative forcing perturbation of a $CO_2$-doubling. However, tests could require several decades or longer to obtain accurate response estimates, particularly to understand the response of regional hydrological fields which are critical uncertainties. Some fields, like precipitation over land, have as large a response to short period forcing as to slowly- varying changes. This implies that the ratio of the hydrological to the temperature response that results from a sustained SRM deployment will differ from that of either a short-duration test or that which has been observed to result from large volcanic eruptions.Engineering and Applied Science

Experimental Evaluation of Air-to-Ground VHF Band Communication for UAV Relays

Unmanned Aerial Vehicles (UAVs) are a disruptive technology that is transforming a range of industries. Because they operate in the sky, UAVs are able to take advantage of strong Line-of-Sight (LoS) channels for radio propagation, allowing them to communicate over much larger distances than equivalent hardware located at ground level. This has attracted the attention of organisations such as the Irish Defence Forces (DF), with whom we are developing a UAV-based radio relay system as part of the MISTRAL project. This relay system will support digital Very High Frequency (VHF) band communication between ground personnel, while they are deployed on missions. In this paper we report on the initial set of experimental measurements which were carried out to verify the feasibility of VHF signal relaying via UAV. In our experiments, a UAV carrying a lightweight Software-Defined Radio (SDR) receiver is positioned at a height of 500 meters above ground, while two 5W transmitters travel in vehicles on the ground. The SDR receiver measures the received signal power, while the Global Positioning System (GPS) coordinates of the vehicles are logged. This is combined to measure the signal pathloss over distance. Our results show that the signal is received successfully at distances of over 50 kilometers away. While the signals still appear to suffer from a degree of obstacle blockage and multipath effects, these communication ranges are a substantial improvement over the ground communication baseline, and validate the use of UAVs to support wide area emergency communication.Comment: Pre-print of paper presented at the Workshop on Integrating UAVs into 5G and Beyond at IEEE International Conference on Communications 202