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Local charge distributions, electric dipole moments and local electric fields influence reactivity patterns and guide regioselectivities in α-ketoglutarate-dependent nonheme iron dioxygenases.
No full textNonheme iron dioxygenases catalyze vital processes for human health related to the biosynthesis of essential products and the biodegradation of toxic metabolites. Often the natural product biosynthesis by these nonheme iron dioxygenases is highly regio- and chemoselective, which are commonly assigned to tight substrate binding and positioning. However, recent highlevel computational modeling has shown that substrate binding and positioning is only part of the story and long-range electrostatic interactions can play a major additional role. In this Account, we review and summarize computational viewpoints on the high regioand chemoselectivity of α-ketoglutarate-dependent nonheme iron dioxygenases and how external perturbations affect the catalysis. In particular, studies from our groups have shown that often a regioselectivity in enzymes can be accomplished by external perturbations working on the transition state for the reaction through external charges, electric dipole moments or local electric field effects.Furthermore, bond dissociation energies in molecules are shown to be influenced by an electric field effect; and through targeting a specific bond in an electric field this can lead to an unusual specificity reaction. For instance, in the carbon-induced starvation protein, we studied two substrate-bound conformations and showed that regardless of what C-H bond of the substrate is closest to the iron(IV)-oxo oxidant, the lowest hydrogen atom abstraction barrier is always for the pro-S C²-H abstraction due to an induced dipole moment of the protein that weakens this bond. In another example on the hygromycin biosynthesis enzyme, an oxidative ring-closure reaction in the substrate forms an ortho-δ-ester ring. Calculations on this enzyme show that the selectivity is guided by a protonated lysine residue in the active site that, through its positive charge, triggers a low energy hydrogen atom abstraction barrier. A final set of examples in this Account discuss the viomycin biosynthesis enzyme and the 2-(trimethylammonio)ethylphosphonate dioxygenase (TmpA) enzymes. Both of these enzymes are shown to possess a significant local electric dipole moment and local electric field effect due to charged residues surrounding the substrate and oxidant binding pocket. This dipole moment and local electric field strength changes the C-H bond strengths of the substrate and triggers the regioselectivity of substrate activation. In particular, we show that in the gas-phase and in an enzyme environment C-H bond strengths vary due to local electric dipole moments and electric field strengths. These examples show that enzymes have an intricately designed structure that enables a chemical reaction under ambient conditions through the positioning of positively and negatively charged residues that influence and enhance reaction mechanisms. These computational insights create huge possibilities in bioengineering to apply local electric field and dipoles in proteins to achieve an unusual reaction selectivity and trigger a fit-for-purpose biocatalyst for unique biotransformations
Demand vs supply-side approaches to mitigation: What final energy demand assumptions are made to meet 1.5 and 2°C targets?
No full textToday’s climate policies will shape the future trajectory of emissions. Consumption is the main driver behind recent increases in global greenhouse gas emissions, outpacing savings through improved technologies, and therefore its representation in the evidence base will impact on the success of policy interventions. The IPCC’s Special Report on Global Warming of 1.5°C (SR1.5) summarises global evidence on pathways for meeting below-2°C targets, underpinned by a suite of scenarios from integrated assessment models (IAMs). We explore how final energy demand is framed within these, with the aim to making demand-related assumptions more transparent, and evaluating their significance, feasibility, and use or underutilisation as a mitigation lever. We investigate how the integrated assessment models compensate for higher and lower levels of final energy demand across scenarios, and how this varies when mitigating for 2°C and 1.5°C temperature targets through an analysis of (1) final energy demand projections, (2) energy-economy relationships and (3) differences between energy system decarbonisation and carbon dioxide removal in the highest and lowest energy demand pathways. We look across the full suite of mitigation pathways and assess the consequences of achieving different global carbon budgets. We find that energy demand in 2100 in the highest energy demand scenarios is approximately three to four times higher than the lowest demand pathways, but we do not find strong evidence that 1.5°C-consistent pathways cluster on the lower end of demand levels, particularly when they allow for overshoot. The majority of demand reductions happen pre-2040, which assumes absolute decoupling from economic growth in the near-term; thereafter final energy demand levels generally grow to 2100. Lower energy demand pathway moderately result in lower renewable energy supply and lower energy system investment, but do not necessarily reduce reliance on carbon dioxide removal. In this sense, there is more scope for IAMs to implement energy demand reduction as a longer-term mitigation lever and to reduce reliance on negative emissions technologies. We demonstrate the need for integrated assessments to play closer attention to how final energy demand interacts with, relates to, and can potentially offset supply-side characteristics, alongside a more diverse evidence base
Joint Altitude and Hybrid Beamspace PrecodingOptimization for UAV-enabled Multiuser mmWave MIMO System
No full textThe combination of unmanned aerial vehicles (UAVs) and millimeter wave (mmWave) multiple-input multipleout (MIMO) system is regarded as a key enabling technology for beyond 5G networks, as it provides high data rate aerial links. However, establishing UAV-enabled mmWave MIMO communication is quite challenging due to the high hardware cost in terms of radio frequency (RF) chains. As a cost-effective alternative, a beamspace precoding with discrete lens arrays (DLA) architecture has received considerable attention. However, the underlying optimal design in beamspace precoding has not been fully exploited in UAV-enabled communication scenario. In this paper, the joint design of the UAV’s altitude and hybrid beamspace precoding is proposed for the UAV-enabledmultiuser MIMO system, in which the DLA is exploited to reduce the number of the RF chain. In the proposed scheme, the optimization problem is formulated as a minimum weighted mean squared error (MWMSE) method. Then an efficient algorithm with the penalty dual decomposition (PDD) is proposed that aimsto jointly optimize the altitude of UAV, beam selection and digital precoding matrices. Simulation results confirm the comparable performance of the proposed scheme and perform close to fulldigital beamforming in terms of achievable spectral efficiency.Index Terms—UAV, mmWave communication, MIMO, hybri
Towards personalised treatment for prostate cancer biology improves image-based data mining models
No full textA new class of control structures for heterogeneous reactive distillation processes
No full textThere are only a handful of process control structures applied to the neat operation of both homogeneous and heterogeneous reactive distillation, for two-reactants / two-products one reaction systems. All of these control structures employ inferential temperature control (or concentration analyzers) at some location in the column to balance the reaction stoichiometry. This original study proposes a new class of control structures applicable to heterogeneous reactive distillation. The novel idea, common to all control structures, is based on monitoring the inventory of the reactant involved in the heterogeneous azeotrope. The organic reflux (or the organic reflux / aqueous distillate ratio) is used to detect the excess or deficiency of the reactant, based on which the fresh feed rate is adjusted such that the reaction stoichiometry is balanced. This control philosophy is simple and easy to implement in different ways as illustrated by several case studies. The performance of the proposed control structures depends on the system studied. For some systems, the performance is better, as good or nearly as good as that of the literature control structures. But for other systems, the performance is poor or the structure even fails to control the process, due to the insufficient feedback from inventory measurements. <br/
A Syscall-Level Binary-Compatible Unikernel
No full textUnikernels are minimal single-purpose virtual machines. They are highly popular in the research domain due to the benefits they provide. A barrier to their widespread adoption is the difficulty/impossibility to port existing applications to current unikernels. HermiTux is the first unikernel providing system call-level binary compatibility with Linux applications. It is composed of a hypervisor and a lightweight kernel layer emulating the load- and runtime Linux ABI. HermiTux relieves application developers from the burden of porting software, while providing unikernel benefits such as security through hardware-assisted virtualized isolation, swift boot time, and low disk/memory footprint. Fast system calls and kernel modularity are enabled through binary rewriting and analysis techniques, as well as shared library substitution. HermiTux’s design principles are architecture-independent and we present a prototype on both the x86-64 and ARM aarch64 ISAs, targeting various cloud as well as edge/embedded deployments. We demonstrate HermiTux’s compatibility over a range of native C/C++/Fortran/Python Linux applications. We also show that it offers a similar degree of lightweightness compared to other unikernels, and that it performs similarly to Linux in many cases: its performance overhead averages 3% in memory- and compute-bound scenarios, and its I/O performance is acceptable
How Will Extreme Weather Change Due to Climate Change? (and How to Interpret Media Stories)
No full textDesigning for longevity and neutrality: Investigating how the Swedish children’s clothing industry implements circular economy principles
No full textAs research has well established, the fashion industry has a significant and growing waste problem. In response, experts argue that our clothing needs to have a longer life. However, not all items of clothing can be used for a long period of time. Children’s clothing, for example, can quickly become obsolete, creating a waste issue. To explore this issue further, we examine the Swedish children’s wear market and how designing for the circular economy can address this market segment’s unique sustainability challenges. Rather than centering on a consumer perspective, we investigate the role of design in supporting the transition to a more circular children’s clothing industry. As a key contribution, this article demonstrates that there are more circular design strategies available than prior research has explicitly mentioned. In particular, we show how design for longevity and design for neutrality can help to overcome some of the sustainability challenges facing the industry
