The 18/30 GHz fixed communications system service demand assessment. Volume 1: Executive summary

The total demand for voice, video, and data communications services, and satellite transmission services at the 4/6 GHz, 12/14 GHz, and 18/30 GHz frequencies is discussed. Major study objectives, overall methodology, results, and general observations about a satellite systems market characteristics and trends are summarized

The 30/20 GHz fixed communications systems service demand assessment. Volume 3: Appendices

The market analysis of voice, video, and data 18/30 GHz communications systems services and satellite transmission services is discussed. Detail calculations, computer displays of traffic, survey questionnaires, and detailed service forecasts are presented

A novel approach to security enhancement of chaotic DSSS systems

In this paper, we propose a novel approach to the enhancement of physical layer security for chaotic direct-sequence spread-spectrum (DSSS) communication systems. The main idea behind our proposal is to vary the symbol period according to the behavior of the chaotic spreading sequence. As a result, the symbol period and the spreading sequence vary chaotically at the same time. This simultaneous variation aims at protecting DSSS-based communication systems from the blind estimation attacks in the detection of the symbol period. Discrete-time models for spreading and despreading schemes are presented and analyzed. Multiple access performance of the proposed technique in the presence of additional white Gaussian noise (AWGN) is determined by computer simulations. The increase in security at the physical layer is also evaluated by numerical results. Obtained results show that our proposed technique can protect the system against attacks based on the detection of the symbol period, even if the intruder has full information on the used chaotic sequence.Peer ReviewedPostprint (author's final draft

Evaluating gaps in knowledge, willingness and heating performance in individual preferences on household energy and climate policy: evidence from the UK

This study investigates the knowledge-willingness, willingness-performance, and knowledge-performance gaps regarding reducing carbon dioxide emissions and emerging technologies of the 2137 British residents. Household's heating sources and heat settings are anticipated as key criteria for evaluating respondents' performances. The study revealed more than 80% of respondents have a good knowledge regarding climate change and carbon issues. The study found a smaller gap in knowledge versus willingness as 59%, 87%, 88% and 85% of respondents want to use bioenergy, afforestation/reforestation, solar and wind for their future energy sources. The Multinomial logit regression (MNLR) investigates that incrementing good and very good knowledge index increases the odds of a high willingness to save energy by 33% and 6%, respectively. The willingness versus performance study identified 96% as claiming to be more likely energy savers, whereas, in reality, 52% of them never or rarely took basic measures like setting their heating system to turn off. Despite having a good and very good knowledge index, the knowledge versus performance appears, 75% of respondents are using gas boilers and gas central heating. Policymakers and the research community need to develop comprehensive plans by taking these wider social issues to meet net-zero targets. Employing smart building principles, lowering the installation costs of the new smart technologies, awarding and encouraging the energy saver, setting individual carbon footprint limits, and training and empowering household representatives to select better energy for houses could popularise the emission reduction technologies in the UK.Fortumin Foundation provided financial support as a grant to TK to visit Cambridge and carry out the research. The grant number was 201800255. The YouGov survey was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) grant EP/P02614/

Detection and imaging of the oxygen deficiency in single crystalline YBa2_{\text{2}}Cu3_{\text{3}}O7−δ_{\text{7}-\delta} thin films using a positron beam

Single crystalline YBa$_{\text{2}}$Cu$_{\text{3}}$O$_{\text{7}-\delta}$ (YBCO) thin films were grown by pulsed laser deposition (PLD) in order to probe the oxygen deficiency $\delta$ using a mono-energetic positron beam. The sample set covered a large range of $\delta$ (0.191<$\delta$<0.791) yielding a variation of the critical temperature $T_{\text{c}}$ between 25 and 90\,K. We found a linear correlation between the Doppler broadening of the positron electron annihilation line and $\delta$ determined by X-ray diffraction (XRD). Both, the origin of the found correlation and the influence of metallic vacancies, were examined with the aid of ab-initio calculations that allowed us (i) to exclude the presence of Y vacancies and (ii) to ensure that positrons still probe $\delta$ despite the potential presence of Ba or Cu vacancies. In addition, by scanning with the positron beam the spatial variation of $\delta$ could be analyzed. It was found to fluctuate with a standard deviation of up to $0.079(5)$ within a single YBCO film

Uniaxial magnetocrystalline anisotropy in CaRuO3{\rm CaRuO_3}

${\rm CaRuO_3}$ is a paramagnetic metal and since its low temperature resistivity is described by $\rho=\rho_0+AT^\gamma$ with $\gamma \sim 1.5$, it is also considered a non-Fermi liquid (NFL) metal. We have performed extensive magnetoresistance and Hall effect measurements of untwinned epitaxial films of ${\rm CaRuO_3}$. These measurements reveal that ${\rm CaRuO_3}$ exhibits uniaxial magnetocrystalline anisotropy. In addition, the low-temperature NFL behavior is most effectively suppressed when a magnetic field is applied along the easy axis, suggesting that critical spin fluctuations, possibly due to proximity of a quantum critical phase transition, are related to the NFL behavior.Comment: 7 figure

SLM Materials Development

The purpose of this project was to create a procedure to efficiently determine a “recipe” of parameter values that create a desired set of mechanical properties. Research was conducted into the laser powder bed fusion process with focus on underdeveloped materials. A design of experiment was used with a set of density correlated parameters to establish a method of producing nearly dense parts. Our methods include SLM printing, metrology, and statistical analysis. An experimental procedure for materials development was designed, but unable to be validated during the scope of this project, due to unforeseen safety issues (exposure to Chromium 6, a toxic substance). Next steps include validation of this procedure using various metal powders in a SLM 125 HL

Refinement of primary Si in hypereutectic Al-Si alloys by intensive melt shearing

Hypereutectic Al-Si based alloys are gaining popularity for applications where a combination of light weight and high wear resistance is required. The high wear resistance arising from the hard primary Si particles comes at the price of extremely poor machine tool life. To minimize machining problems while exploiting outstanding wear resistance, the primary Si particles must be controlled to a uniform small size and uniform spatial distribution. The current industrial means of refining primary Si chemically by the addition of phosphorous suffers from a number of problems. In the present paper an alternative, physical means of refining primary Si by intensive shearing of the melt prior to casting is investigated. Al-15wt%Si alloy has been solidified under varying casting conditions (cooling rate) and the resulting microstructures have been studied using microscopy and quantitative image analysis. Primary Si particles were finer, more compact in shape and more numerous with increasing cooling rate. Intensive melt shearing led to greater refinement and more enhanced nucleation of primary Si than was achieved by adding phosphorous. The mechanism of enhanced nucleation is discussed.EPSRC (grant EP/H026177/1)

Aluminum Foil Anodes for Li-Ion Rechargeable Batteries: the Role of Li Solubility within β-LiAl

Lithium-ion battery electrodes contain a substantial amount of electrochemically inactive materials, including binders, conductive agents, and current collectors. These extra components significantly dilute the specific capacity of whole electrodes and thus have led to efforts to utilize foils, for example, Al, as the sole anode material. Interestingly, the literature has many reports of fast degradation of Al electrodes, where less than a dozen cycles can be achieved. However, in some studies, Al anodes demonstrate stable cycling life with several hundred cycles. In this work, we present a successful pathway for enabling long-term cycling of simple Al foil anodes: the β-LiAl phase grown from Al foil (α-Al) exhibits a cycling life of 500 cycles with a ∼96% capacity retention when paired with a commercial cathode. The excellent performance stems from strategic utilization of the Li solubility range of β-LiAl that can be (de-)lithiated without altering its crystal structure. This solubility range at room temperature is determined to be ∼6 at %. Consequently, this design circumvents the critical issues associated with the α/β/α phase transformations, such as volume change, mechanical strain, and formation of nanopores. Application-wise, the maturity of the aluminum industry, combined with excellent sustainability prospects, makes this anode an important option for future devices

Aluminum Foil Anodes for Li-ion Rechargeable Batteries: The Role of Li Solubility within β-LiAl

Li-ion battery (LIB) electrodes contain a substantial amount of electrochemically inactive materials, including binder, conductive agent, and current collectors. These extra components significantly dilute the specific capacity of whole electrodes, and thus have led to efforts to utilize foils, e.g., Al, as the sole anode material. Interestingly, the literature has many reports of fast degradation of Al electrodes, where less than a dozen cycles can be achieved. However, in some studies, Al anodes demonstrate stable cycling life with several hundred cycles. In this work, we present a successful pathway for enabling long-term cycling of simple Al foil anodes: β-LiAl phase grown from Al foil (α-Al) exhibits a cycling life of 500 cycles with a ~96% capacity retention when paired with a commercial cathode. The excellent performance stems from strategic utilization of the Li solubility range of β-LiAl that can be (de-)lithiated without altering its crystal structure. This solubility range at room temperature is determined to be ~6 at%. Consequently, this design circumvents the critical issues associated with the α/β/α phase transformations, such as volume change, mechanical strain, and nanopore formation. Application-wise, the maturity of aluminum industry, combined with excellent sustainability prospects, makes this anode an important option for future devices