Publications

Gotcha! Using electrochemical surface-enhanced Raman spectroscopy, surface-bound hydroxyperoxy (AuOOH) is pinpointed in situ as a reaction intermediate of oxygen evolution on gold catalyst (see picture). Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Proposes a new approach for vision-based longitudinal and lateral vehicle control. The novel feature of this approach is the use of binocular vision. We integrate two modules consisting of a new, domain-specific, efficient binocular stereo algorithm, and a lane marker detection algorithm, and show that the integration results in a improved performance for each of the modules. Longitudinal control is supported by detecting and measuring the distances to leading vehicles using binocular stereo. The knowledge of the camera geometry with respect to the locally planar road is used to map the images of the road plane in the two camera views into alignment. This allows us to separate image features into those lying in the road plane, e.g. lane markers, and those due to other objects which are dynamically integrated into an obstacle map. Therefore, in contrast with the previous work, we can cope with the difficulties arising from occlusion of lane markers by other vehicles. The detection and measurement of the lane markers provides us with the positional parameters and the road curvature which are needed for lateral vehicle control. Moreover, this information is also used to update the camera geometry with respect to the road, therefore allowing us to cope with the problem of vibrations and road inclination to obtain consistent results from binocular stereo.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The BL Lac type object 1ES 2344+51.4 (redshift z = 0.044) was one of the first sources to be included in the extreme high-peaked BL Lac (EHBL) family. EHBLs are characterised by a broadband spectral energy distribution (SED) featuring the synchrotron peak above ∼ 1017 Hz. From previous studies of 1ES 2344+51.4 in the very-high-energy (VHE, >100 GeV) gamma-ray range, its inverse Compton (IC) peak is expected around 200 GeV. 1ES 2344+51.4 was first detected in the VHE range by Whipple in 1995 during a very bright outburst showing around 60% of the flux of the Crab Nebula above 350 GeV. In 1996, during another flare in the X-ray band, observations with Beppo-SAX revealed a large 0.1-10 keV flux variability on timescales of a few hours and an impressive frequency shift of the synchrotron peak to above 1018 Hz. Later on, this extreme behaviour of the source motivated several multiwavelength campaigns, during most of which the source appeared to be in a low state and showing no clear signs of “extremeness”. In August 2016, FACT detected 1ES 2344+51.4 in a high state and triggered multiwavelength observations. The VHE observations show a flux level similar to the historical maximum of 1995. The combination of MAGIC, FACT, and Fermi-LAT spectra provides an unprecedented characterisation of the IC peak. It is the first time that simultaneous HE and VHE data are presented for this object during a flaring episode. We find an atypically hard spectrum in the VHE γ-rays as well as a hard X-ray spectrum, revealing a renewed extreme behaviour.

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Low latency analytics on geographically distributed datasets (across datacenters, edge clusters) is an upcoming and increasingly important challenge. The dominant approach of aggregating all the data to a single datacenter significantly inflates the timeliness of analytics. At the same time, running queries over geo-distributed inputs using the current intra-DC analytics frameworks also leads to high query response times because these frameworks cannot cope with the relatively low and variable capacity of WAN links. We present Iridium, a system for low latency geo-distributed analytics. Iridium achieves low query response times by optimizing placement of both data and tasks of the queries. The joint data and task placement optimization, however, is intractable. Therefore, Iridium uses an online heuristic to redistribute datasets among the sites prior to queries' arrivals, and places the tasks to reduce network bottlenecks during the query's execution. Finally, it also contains a knob to budget WAN usage. Evaluation across eight worldwide EC2 regions using production queries show that Iridium speeds up queries by 3× -- 19× and lowers WAN usage by 15% -- 64% compared to existing baselines.

We address the problem of balancing the traffic load in multi-hop wireless networks. We consider a point-to-point communicating network with a uniform distribution of source-sink pairs. When routing along shortest paths, the nodes that are centrally located forward a disproportionate amount of traffic. This translates into increased congestion and energy consumption. However, the maximum load can be decreased if the packets follow curved paths. We show that the optimum such routing scheme can be expressed in terms of geometric optics and computed by linear programming. We then propose a practical solution, which we call Curveball Routing which achieves results not much worse than the optimum.We evaluate our solution at three levels of fidelity: a Java high-level simulator, the ns2 simulator, and the Intel Mirage Sensor Network Testbed. Simulation results using the high-level simulator show that our solution successfully avoids the crowded center of the network, and reduces the maximum load by up to 40%. At the same time, the increase of the expected path length is minimal, i.e., only 8% on average. Simulation results using the ns2 simulator show that our solution can increase throughput on moderately loaded networks by up to 15%, while testbed results show a reduction in peak energy usage by up to 25%. Our prototype suggests that our solution is easily deployable.

Reversible insertion of Mg 2+ into metal oxide frameworks stands as a critical factor for facilitating the operation of a Mg-ion battery boasting high energy density, imperative for advancing energy storage technologies. While functional Mg-ion batteries have been achieved in frameworks featuring soft anions like S 2– and Se 2– , they fall short of meeting the energy density benchmarks to rival current rechargeable lithium-ion batteries due to their low insertion potentials. This underscores the need to pinpoint an oxide-based cathode capable of operating at elevated potentials. A leading theory posits that the limited availability of oxide Mg-ion cathodes stems from the sluggish diffusion kinetics of Mg 2+ in oxides, attributed to robust electrostatic interactions between Mg2+ ions and oxide anions within the lattice. Consequently, it is hypothesized that rectifying these kinetic shortcomings could be achieved by tailoring an oxide framework to foster less stable Mg 2+ –O 2– coordination. Drawing upon theoretical computations and preliminary experimental findings, oxide spinels emerge as promising candidates for cathodes, possessing storage capacity, insertion potential, and cation mobility that align with the requisites for a secondary Mg-ion battery. However, spinels featuring a single redox metal, such as MgCr 2 O 4 or MgMn 2 O 4 , failed to exhibit adequately reversible Mg-ion intercalation at high redox potentials when paired with nonaqueous Mg-electrolytes. Consequently, a concerted effort in materials development was launched to conceive, synthesize, and assess a novel class of solid-solution oxide spinels designed to fulfill the requisite properties for a sustainable Mg-ion cathode. These materials were engineered by combining electrochemically active metals boasting stable redox potentials and charged states vis-a-vis the electrolyte, such as Mn 3+ , alongside a structural stabilization component, typically Cr 3+ . Additionally, common spinel structural defects known to compromise performance, such as antisite inversion, were managed to explore the relationship between structures and electrochemical overpotentials, thereby regulating overall hysteresis. Comprehensive structural characterization, encompassing both short- and long-range analyses in both ex-situ and in-situ settings, confirmed the nature of solid-solution and established a correlation between structural modifications and redox activity vis-a-vis electrochemical performance. Encouragingly, consistent and reproducible outcomes were noted, manifesting facile bulk Mg2+-ion activity sans phase transformations, thus bolstering energy storage capacity through reversible Mg 2+ intercalation, facilitated by an understanding of the variables governing the electrochemical performance of spinel oxide. Leveraging these insights, it becomes conceivable to engineer an oxide cathode material boasting many of the desired attributes of a Li-ion intercalation cathode, marking a significant milestone in the pursuit of high energy density Mg-ion batteries. This study delineates strategies for designing and developing novel spinel oxide intercalation materials tailored for high-energy Mg-ion battery cathodes, leveraging a blend of theoretical and experimental methodologies. We discuss the key factors dictating the kinetics of Mg2+ diffusion in spinel oxides, elucidating how material complexity aligns with the electrochemical Mg2+ activity in oxides, bolstered by supplementary characterization. The insights gleaned from fundamental inquiries into cation diffusion in oxide cathodes are poised to benefit chemists and materials scientists engaged in the advancement of rechargeable batteries. Related publication: B. Kwon et al., Accounts of Chemical Research, 2024, 57, 1, 1–9 Figure 1

A series of oligothiophene-perfluoro-9-heterofluorene donor-acceptor (DA) compounds was synthesized via a combination of nucleophilic aromatic substitution (S(N)Ar(F)) and palladium coupling reactions. These compounds are of interest as possible building blocks for materials with useful electron transport properties, since they possess relatively low LUMO energy levels of -3.3 to -3.6 eV (as determined by differential pulse voltammetry). The HOMO-LUMO energy gaps, as determined by UV-vis spectroscopy, range between 2.4 and 2.5 eV, and photoluminescence emission spectra reveal lambda(ems) values in the range of 480-600 nm (corresponding to yellow-orange emission). Dilute solution-state photoluminescence quantum yields were significantly lower than those of the pure acceptor heterofluorenes (0.02-0.38 for the DA compounds vs approximately 1 for the pure acceptors), and notable solvatochromism in the fluorescence suggests emission from a charge-separated state. Theoretical calculations show that HOMO-level electron density is more localized on the thiophene fragment, while the LUMO level electron density is mostly associated with the electron-deficient portion of the molecule. Photovoltaic (PV) devices based on DA/poly-3-hexylthiophene (P3HT) blends exhibit improved performance over P3HT-only devices, suggesting the ability of these DA compounds to transport electrons in the solid state.