Publications

Monolithic columns for capillary electrochromatography have been prepared within the confines of untreated fused-silica capillaries in a single step by a simple copolymerization of mixtures of butyl methacrylate, ethylene dimethacrylate, and 2-acrylamido-2-methyl-1-propane-sulfonic acid (AMPS) in the presence of a porogenic solvent. The use of these novel macroporous monoliths eliminates the need for frits, the difficulties encountered with packed capillaries, and capillary surface functionalization. Since the porous properties of the monolithic materials can be easily tailored through changes in the composition of the ternary porogenic solvent, the effects of both pore size and the percentage of sulfonic acid monomer on the efficiency and the electroosmotic flow velocity of the capillary columns could be studied independently over a broad range. A simple increase in the content of charged functionalities within the monolith leads to an expected acceleration of the flow velocity. However, increasing the pore size leads to a substantial deterioration of the efficiency of the separation. In contrast, monoliths with increasing levels of AMPS in which the pore size remains fixed due to adjustments in the composition of the porogenic solvent show no deterioration in efficiency while maintaining the same increase in flow velocity, thus producing a significant reduction in separation time. Additionally, measurements on monoliths with constant levels of AMPS but different pore sizes suggest that flow velocity may be affected by the flow resistance within the capillary column.

Single-phase body-centered cubic (bcc) refractory medium- or high-entropy alloys can retain compressive strength at elevated temperatures but suffer from extremely low tensile ductility and fracture toughness. We examined the strength and fracture toughness of a bcc refractory alloy, NbTaTiHf, from 77 to 1473 kelvin. This alloy's behavior differed from that of comparable systems by having fracture toughness over 253 MPa·m

Migratory insertion of carbon-based species into transition-metal-carbon bonds is a mechanistic manifold of vast significance: it underlies the Fischer-Tropsch process, Mizoroki-Heck reaction, Ziegler-Natta and analogous late-transition-metal-catalyzed olefin polymerizations, and a number of carbonylative methods for the synthesis of ketones and esters, among others. Although this type of reactivity is well-precedented for most transition metals, gold constitutes a notable exception, with virtually no well-characterized examples known to date. Yet, the complementary reactivity of gold to numerous other transition metals would offer new synthetic opportunities for migratory insertion of carbon-based species into gold-carbon bonds. Here we report the discovery of well-defined Au(III) complexes that participate in rapid migratory insertion of carbenes derived from silyl- or carbonyl-stabilized diazoalkanes into Au-C bonds at temperatures ≥ -40 °C. Through a combined theoretical and experimental approach, key kinetic, thermodynamic, and structural details of this reaction manifold were elucidated. This study paves the way for homogeneous gold-catalyzed processes incorporating carbene migratory insertion steps.

Network middleboxes must offer high availability, with automatic failover when a device fails. Achieving high availability is challenging because failover must correctly restore lost state (e.g., activity logs, port mappings) but must do so quickly (e.g., in less than typical transport timeout values to minimize disruption to applications) and with little overhead to failure-free operation (e.g., additional per-packet latencies of 10-100s of us). No existing middlebox design provides failover that is correct, fast to recover, and imposes little increased latency on failure-free operations. We present a new design for fault-tolerance in middleboxes that achieves these three goals. Our system, FTMB (for Fault-Tolerant MiddleBox), adopts the classical approach of "rollback recovery" in which a system uses information logged during normal operation to correctly reconstruct state after a failure. However, traditional rollback recovery cannot maintain high throughput given the frequent output rate of middleboxes. Hence, we design a novel solution to record middlebox state which relies on two mechanisms: (1) 'ordered logging', which provides lightweight logging of the information needed after recovery, and (2) a `parallel release' algorithm which, when coupled with ordered logging, ensures that recovery is always correct. We implement ordered logging and parallel release in Click and show that for our test applications our design adds only 30$\mu$s of latency to median per packet latencies. Our system introduces moderate throughput overheads (5-30%) and can reconstruct lost state in 40-275ms for practical systems.

ABSTRACT Surfaces made of copper or its alloys have strong antimicrobial properties against a wide variety of microorganisms. However, the molecular mode of action responsible for the antimicrobial efficacy of metallic copper is not known. Here, we show that dry copper surfaces inactivate Candida albicans and Saccharomyces cerevisiae within minutes in a process called contact-mediated killing. Cellular copper ion homeostasis systems influenced the kinetics of contact-mediated killing in both organisms. Deregulated copper ion uptake through a hyperactive S. cerevisiae Ctr1p (ScCtr1p) copper uptake transporter in Saccharomyces resulted in faster inactivation of mutant cells than of wild-type cells. Similarly, lack of the C. albicans Crp1p (CaCrp1p) copper-efflux P-type ATPase or the metallothionein CaCup1p caused more-rapid killing of Candida mutant cells than of wild-type cells. Candida and Saccharomyces took up large quantities of copper ions as soon as they were in contact with copper surfaces, as indicated by inductively coupled plasma mass spectroscopy (ICP-MS) analysis and by the intracellular copper ion-reporting dye coppersensor-1. Exposure to metallic copper did not cause lethality through genotoxicity, deleterious action on a cell's genetic material, as indicated by a mutation assay with Saccharomyces . Instead, toxicity mediated by metallic copper surfaces targeted membranes in both yeast species. With the use of Live/Dead staining, onset of rapid and extensive cytoplasmic membrane damage was observed in cells from copper surfaces. Fluorescence microscopy using the indicator dye DiSBaC 2 (3) indicated that cell membranes were depolarized. Also, during contact-mediated killing, vacuoles first became enlarged and then disappeared from the cells. Lastly, in metallic copper-stressed yeasts, oxidative stress in the cytoplasm and in mitochondria was elevated.

An ion exchange reaction that can stabilize potassium transition metal oxides was proposed as a new approach to develop cathode materials for K-ion batteries (KIBs). 1-4 Such ion exchange method indeed has frequently used for the development of novel Li-layered oxides to attain structural features of Na layered oxides. 5-7 Although the ion exchange reaction has the potential to discover novel layered cathode materials by accessing the metastable states that cannot be achieved by conventional high-temperature solid-state reaction, the solid-state ion-exchange mechanism and the resulting phase evolution are barely understood. In this study, we systematically investigate electrochemical Na + /K + ion exchange in layered oxides. 8 Here, O3-type Na 3 Ni 2 SbO cathode is used as a model system. 8 We found intriguing phase evolutions according to the relative Na/K content upon K intercalation by in-situ X-ray diffraction study. First, we observe that K-rich and Na-rich phases coexist during charging and discharging. Second, Na-rich phase goes through phase transformation upon K intercalation. Strong electrostatic repulsion between Na and K ions that have radically different bond lengths to coordinating oxygen ions can result in this complex phase evolutions. We uncovered that the intercalating K ions pushes away Na ions remaining in the desodiated Na x Ni 2 SbO 6 phase, thereby separating Na-rich and K-rich phases in a particle. Interestingly, this phenomenon creates complex, three-phase equilibrium during the desodiation and potassiation processes in Na x K y Ni 2 SbO 6 : phase equilibrium between one K-rich and two Na-rich phases or two K-rich and one Na-rich phase is observed, as dictated by the Gibbs phase rule. Our computational study further demonstrated that this phase separation originates from the large lattice mismatch along the c -axis between the K-rich and Na-rich phases. Our observations and interpretations demonstrate that “ion-exchanged” systems may be more complex to interpret than the previously understood. Our analysis should be applicable to other ion-exchange systems where the exchanged ions are not well miscible in the host structure. References [1] S. Baskar et al. ECS Transactions 2017, 80, 357. [2] N. Naveen et al. Chem. Mater. 2018, 30, 2049. [3] J. Y. Hwang et al. Energy Environ. Sci. 2018, 11, 2821. [4] H. Zhang et al. Chem. Commun. 2019, 55, 7910. [5] C, Delmas et al. Mater. Res. Bull. 1982, 17, 117. [6] A. R. Armstrong et al. Nature 1996, 381, 499. [7] F. Capitaine et al. Solid State Ionc. 1996, 89, 197. [8] H. Kim et al. Chem. Mater. 2020 , 32, 4312.

As the distribution of the video over the Internet becomes main- stream and its consumption moves from the computer to the TV screen, user expectation for high quality is constantly increasing. In this context, it is crucial for content providers to understand if and how video quality affects user engagement and how to best invest their resources to optimize video quality. This paper is a first step towards addressing these questions. We use a unique dataset that spans different content types, including short video on demand (VoD), long VoD, and live content from popular video con- tent providers. Using client-side instrumentation, we measure quality metrics such as the join time, buffering ratio, average bitrate, rendering quality, and rate of buffering events. We quantify user engagement both at a per-video (or view) level and a per-user (or viewer) level. In particular, we find that the percentage of time spent in buffering (buffering ratio) has the largest impact on the user engagement across all types of content. However, the magnitude of this impact depends on the content type, with live content being the most impacted. For example, a 1% increase in buffering ratio can reduce user engagement by more than three minutes for a 90-minute live video event. We also see that the average bitrate plays a significantly more important role in the case of live content than VoD content.