10,000 publications from this institution
The applicability of AC impedance spectroscopy (ACIS) for detecting corrosion on rebar in concrete is explored theoretically. Corroding rebar is simulated as a one-dimensional electrical transmission line of twenty one-meter segments embedded in a uniform concrete matrix, with the corrosion being restricted to one segment. The simulations indicate that corrosion can only be detected at very low frequencies (<1 mHz), but that the impedance and the peak voltage monitored at the concrete surface may be used to locate the site of the corrosive attack.
Aksu Akçaoğlu przebywał w latach 2014-2015 na Wydziale Socjologii Uniwersytetu Kalifornijskiego w Berkeley jako visiting scholar, gdzie wspólnie z Loikiem Wacquantem pracował na swym projektem poświęconym „habitusowi konserwatywnemu”. W poniższej rozmowie prosi Wacquanta o wyjaśnienie filozofii i pedagogiki jego słynnego seminarium prowadzonego w Berkeley, poświęconego Pierre’owi Bourdieu. Stanowi to okazję do przyjrzenia się raz jeszcze kluczowym węzłom konceptualnym w pracach Bourdieu, naświetlenie jego antyteoretycznej postawy, czy też rozwikłania relacji między przestrzenią społeczną, polem i władzą symboliczną oraz ostrzeżenia przed pokusami „bourdieziańskiej mowy”.
Abstract not Available.
Potassium vanadium fluorophosphate (KVPO 4 F) is one of the most promising cathode candidates for K-ion batteries because of its high specific capacity, voltage, and energy density. However, reducing its capacity fade remains an important challenge. This work leverages structure and electrochemical analysis to understand the capacity degradation mechanism of the KVPO 4 F cathode. Interestingly, no structural degradation of the KVPO 4 F cathode is detected after 200 cycles in the wide voltage window of 5.0–2.5 V (vs K/K + ). Instead, the capacity degradation is attributed to electrolyte decomposition at high voltage (>4.5 V vs K/K + ), which causes drying of the electrolyte and the formation of insulating layers on the cathode surface, significantly increasing the polarization. The properties of four KPF 6 - and carbonate-based K electrolytes are compared, and 0.7 M KPF 6 in ethylene carbonate/propylene carbonate exhibits the highest oxidation stability and results in the best cycling stability for the KVPO 4 cathode. These findings suggest that the key to improving the cycling stability of KVPO 4 F is to develop novel K electrolytes with even higher oxidation stability.
Abstract The application of the eddy covariance flux method to measure fluxes of trace gas and energy between ecosystems and the atmosphere has exploded over the past 25 years. This opinion paper provides a perspective on the contributions and future opportunities of the eddy covariance method. First, the paper discusses the pros and cons of this method relative to other methods used to measure the exchange of trace gases between ecosystems and the atmosphere. Second, it discusses how the use of eddy covariance method has grown and evolved. Today, more than 400 flux measurement sites are operating world‐wide and the duration of the time series exceed a decade at dozens of sites. Networks of tower sites now enable scientists to ask scientific questions related to climatic and ecological gradients, disturbance, changes in land use, and management. The paper ends with discussions on where the field of flux measurement is heading. Topics discussed include role of open access data sharing and data mining, in this new era of big data, and opportunities new sensors that measure a variety of trace gases, like volatile organic carbon compounds, methane and nitrous oxide, and aerosols, may yield.
This Perspective presents the fundamental principles, the elementary reactions, the initial catalytic systems, and the contemporary catalysts that have converted C-H bond functionalization from a curiosity to a reality for synthetic chemists. Many classes of elementary reactions involving transition-metal complexes cleave C-H bonds at typically unreactive positions. These reactions, coupled with a separate or simultaneous functionalization process lead to products containing new C-C, C-N, and C-O bonds. Such reactions were initially studied for the conversion of light alkanes to liquid products, but they have been used (and commercialized in some cases) most often for the synthesis of the more complex structures of natural products, medicinally active compounds, and aromatic materials. Such a change in direction of research in C-H bond functionalization is remarkable because the reactions must occur at an unactivated C-H bond over functional groups that are more reactive than the C-H bond toward classical reagents. The scope of reactions that form C-C bonds or install functionality at an unactivated C-H bond will be presented, and the potential future utility of these reactions will be discussed.
