Publications

Theoretical Interpretation of Anion Size Effects in Passivity Breakdown

The critical voltage for passivity breakdown on metals and steels in contact with halide-containing solutions is often observed to depend on anion size. In the case of iron and iron-base alloys, and for other metals and alloys (e.g., nickel-base and aluminum alloys), the greatest susceptibility toward passivity breakdown occurs with chloride ion. In this paper, an explanation of anion size effects is offered based upon the Point Defect Model. Briefly, the size effect is attributed to the competing effects of the energy and entropy (Gibbs energy) changes for expansion of a surface oxygen vacancy to a size that can accommodate the halide and the Gibbs energy of halide and possibly vacancy hydration/dehydration. The theory successfully accounts for the effect of anion size on the critical breakdown voltage of Fe-13Cr stainless steel.

Evidence from Type Ia Supernovae for an Accelerating Universe

Tough Ceramic Mimics Mother of Pearl

Quantum revivals and many-body localization

Hierarchical scheduling for diverse datacenter workloads

There has been a recent industrial effort to develop multi-resource hierarchical schedulers. However, the existing implementations have some shortcomings in that they might leave resources unallocated or starve certain jobs. This is because the multi-resource setting introduces new challenges for hierarchical scheduling policies. We provide an algorithm, which we implement in Hadoop, that generalizes the most commonly used multi-resource scheduler, DRF [1], to support hierarchies. Our evaluation shows that our proposed algorithm, H-DRF, avoids the starvation and resource inefficiencies of the existing open-source schedulers and outperforms slot scheduling.

Alterations in Growth, Photosynthesis, and Respiration in a Starchless Mutant of <i>Arabidopsis thaliana</i> (L.) Deficient in Chloroplast Phosphoglucomutase Activity

A mutant of Arabidopsis thaliana (L.) Heynh. which lacks leaf starch was isolated by screening for plants which did not stain with iodine. The starchless phenotype, confirmed by quantitative enzymic analysis, is caused by a single recessive nuclear mutation which results in a deficiency of the chloroplast isozyme of phosphoglucomutase. When grown in a 12-h photoperiod, leaves of the wild-type accumulated substantial amounts of starch but lower levels of soluble sugars. Under these conditions, the mutant accumulated relatively high levels of soluble sugars. Rates of growth and net photosynthesis of the mutant and wild-type were indistinguishable when the plants were grown in constant illumination. However, in a short photoperiod, the growth of the mutant was severely impaired, the rate of photosynthesis was depressed relative to the wild-type, and the rate of dark respiration, which was high following the onset of darkness, exhibited an uncharacteristic decay throughout the dark period. The altered control of respiration by the mutant, which may be related to the relatively high levels of soluble carbohydrate that accumulate in the leaf and stem tissue, is believed to be partially responsible for the low growth rate of the mutant in short days. The depressed photosynthetic capacity of the mutant may also reflect a metabolic adaptation to the accumulation of high levels of soluble carbohydrate which mimics the effects of alterations in source/sink ratio. The activities of sucrose phosphate synthase and acid invertase are significantly higher in the mutant than in the wild-type whereas ADP-glucose pyrophosphorylase activity is lower. This suggests that the activities of these enzymes may be modulated in response to metabolite concentrations or flux through the pathways.

The thermodynamic viability of yttria-stabilized zirconia pH sensors for high temperature aqueous solutions

Pore Chemistry of Metal–Organic Frameworks

Abstract The pores in metal–organic frameworks (MOFs) can be functionalized by placing chemical entities along the backbone and within the backbone. This chemistry is enabled by the architectural, thermal, and chemical robustness of the frameworks and the ability to characterize them by many diffraction and spectroscopic techniques. The pore chemistry of MOFs is articulated in terms of site isolation, coupling, and cooperation and relate that to their functions in guest recognition, catalysis, ion and electron transport, energy transfer, pore‐dynamic modulation, and interface construction. It is envisioned that the ultimate control of pore chemistry requires arranging functionalities into defined sequences and developing techniques for reading and writing such sequences within the pores.

The surface science of heterogeneous catalysis

The authors have concentrated their studies of molecular-scale catalysis on transition metals, which catalyze hydrocarbon conversion reactions, and on the hydrogenation of carbon monoxide. They studied platinum, an excellent catalyst for dehydrocyclization of alkanes to aromatic molecules, and rhodium, which produces oxygenated organic molecules from carbon monoxide and hydrogen selectively. They also investigated iron, that catalyzes the ammonia synthesis from nitrogen and hydrogen as well as the CO-H/sub 2/ reaction. From these studies they identified three necessary ingredients of selective molecular-scale catalysis: atomic surface structure, an active carbonaceous deposit, and the proper oxidation stat of surface atoms.

Conversion of heterogeneous catalysis from art to science: the surface science of heterogeneous catalysis

Commentary: the end of large current account deficits: 1970-2002: are there lessons for the United States?

Greenspan, Alan; Interest rates; Deficit financing

Biophysical Controls of Ecosystem‐Scale Methane Fluxes From a Subtropical Estuarine Mangrove: Multiscale, Nonlinearity, Asynchrony and Causality

Abstract Mangroves are complex ecosystems subject to periodic and irregular changes in meteorology, tides, water quality and biological factors. Methane dynamics in mangroves and their dependence on biogeochemical controls across scales are poorly characterized using traditional parametric statistics. We measured the ecosystem‐scale methane flux (F CH4 ) using an eddy covariance system in a subtropical estuarine mangrove for two years. A combination of nonparametric statistical approaches, including singular spectrum analysis and information theory, was used to isolate multiscale F CH4 variations and explore their variability and dominant controls at different time scales. F CH4 exhibited the largest variability at the diel scale (57%), followed by seasonal (25%) and multiday (18%) scales. Mutual information metrics suggested that variation in F CH4 was dominantly coupled to plant activities through synchronous processes at the diel scale. Moreover, fluctuations in atmospheric turbulence and soil temperature dominated multiday variation in F CH4 through asynchronous processes. Seasonally, soil temperature and water salinity were dominant variables leading to changes in F CH4 with a time lag of 12 and 17 days, respectively. Weak links between F CH4 and tidal heights were found across all the studied time scales. Transfer entropy metrics indicated that a super typhoon event substantially weakened causal links between biophysical variables and F CH4 by causing severe defoliation and disturbing the soil microbial community. The typhoon also temporarily decoupled the causal link between F CH4 and temperature. These findings call for the inclusion of the properties of scale emergence, nonlinearity, asynchrony and causality for comprehensively understanding and accurately predicting the interactions between mangrove F CH4 and its biophysical controls.

Intermolecular Insertion of Ethylene and Octene into a Palladium−Amide Bond. Spectroscopic Evidence for an Ethylene Amido Intermediate

We report a series of palladium diarylamido complexes containing a cyclometalated phosphine ligand and a coordinated THF that form enamine products from migratory insertion of ethylene and octene into the metal-nitrogen bond. The reactions of these complexes were sensitive to the electronic properties of the diarylamido group. The complex with the more electron-donating amido ligand reacted nearly 2 orders of magnitude faster than the complex with the least electron-donating amido group. The mechanism of the reactions with alkenes involves exchange of olefin for THF, as revealed by the positive order of the reaction in alkene and inverse order in the concentration of THF. A syn-aminopalladation that would result from migratory insertion was revealed by the stereochemistry of the enamine product resulting from reaction with cis-ethylene-d(2). Finally, a three-coordinate THF-free species was isolated from a synthesis of the amido complex in aromatic solvents, and spectroscopic evidence for an ethylene amido species was gained, in part by the addition of H(2)(13)C=(13)CH(2) to the three-coordinate amido complex at -100 degrees C.

On Local Activity and Edge of Chaos in a NaMLab Memristor

Local activity is the capability of a system to amplify infinitesimal fluctuations in energy. Complex phenomena, including the generation of action potentials in neuronal axon membranes, may never emerge in an open system unless some of its constitutive elements operate in a locally active regime. As a result, the recent discovery of solid-state volatile memory devices, which, biased through appropriate DC sources, may enter a local activity domain, and, most importantly, the associated stable yet excitable sub-domain, referred to as edge of chaos, which is where the seed of complexity is actually planted, is of great appeal to the neuromorphic engineering community. This paper applies fundamentals from the theory of local activity to an accurate model of a niobium oxide volatile resistance switching memory to derive the conditions necessary to bias the device in the local activity regime. This allows to partition the entire design parameter space into three domains, where the threshold switch is locally passive (LP), locally active but unstable, and both locally active and stable, respectively. The final part of the article is devoted to point out the extent by which the response of the volatile memristor to quasi-static excitations may differ from its dynamics under DC stress. Reporting experimental measurements, which validate the theoretical predictions, this work clearly demonstrates how invaluable is non-linear system theory for the acquirement of a comprehensive picture of the dynamics of highly non-linear devices, which is an essential prerequisite for a conscious and systematic approach to the design of robust neuromorphic electronics. Given that, as recently proved, the potassium and sodium ion channels in biological axon membranes are locally active memristors, the physical realization of novel artificial neural networks, capable to reproduce the functionalities of the human brain more closely than state-of-the-art purely CMOS hardware architectures, should not leave aside the adoption of resistance switching memories, which, under the appropriate provision of energy, are capable to amplify the small signal, such as the niobium dioxide micro-scale device from NaMLab, chosen as object of theoretical and experimental study in this work.

THE LICK AGN MONITORING PROJECT 2011: DYNAMICAL MODELING OF THE BROAD-LINE REGION IN Mrk 50

We present dynamical modeling of the broad line region (BLR) in the Seyfert 1\ngalaxy Mrk 50 using reverberation mapping data taken as part of the Lick AGN\nMonitoring Project (LAMP) 2011. We model the reverberation mapping data\ndirectly, constraining the geometry and kinematics of the BLR, as well as\nderiving a black hole mass estimate that does not depend on a normalizing\nfactor or virial coefficient. We find that the geometry of the BLR in Mrk 50 is\na nearly face-on thick disk, with a mean radius of 9.6(+1.2,-0.9) light days, a\nwidth of the BLR of 6.9(+1.2,-1.1) light days, and a disk opening angle of\n25\\pm10 degrees above the plane. We also constrain the inclination angle to be\n9(+7,-5) degrees, close to face-on. Finally, the black hole mass of Mrk 50 is\ninferred to be log10(M(BH)/Msun) = 7.57(+0.44,-0.27). By comparison to the\nvirial black hole mass estimate from traditional reverberation mapping\nanalysis, we find the normalizing constant (virial coefficient) to be log10(f)\n= 0.78(+0.44,-0.27), consistent with the commonly adopted mean value of 0.74\nbased on aligning the M(BH)-{\\sigma}* relation for AGN and quiescent galaxies.\nWhile our dynamical model includes the possibility of a net inflow or outflow\nin the BLR, we cannot distinguish between these two scenarios.\n

Diffractive Spectral-Splitting Optical Element Designed by Adjoint-Based Electromagnetic Optimization and Fabricated by Femtosecond 3D Direct Laser Writing

The greatest source of loss in conventional single-junction photovoltaic cells is their inefficient utilization of the energy contained in the full spectrum of sunlight. To overcome this deficiency, we propose a multijunction system that laterally splits the solar spectrum onto a planar array of single-junction cells with different band gaps. As a first demonstration, we designed, fabricated, and characterized dispersive diffractive optics that spatially separated the visible (360–760 nm) and near-infrared (760–1100 nm) bands of sunlight in the far field. Inverse electromagnetic design was used to optimize the surface texture of the thin diffractive phase element. An optimized thin film fabricated by femtosecond two-photon absorption 3D direct laser writing shows an average splitting ratio of 69.5% between the visible and near-infrared light over the 380–970 nm range at normal incidence. The splitting efficiency is predicted to be 80.4% assuming a structure without fabrication errors. Spectral-splitting action is observed within an angular range of ±1° from normal incidence. Further design optimization and fabrication improvements can increase the splitting efficiency under direct sunlight, increase the tolerance to angular errors, allow for a more compact geometry, and ultimately incorporate a greater number of photovoltaic band gaps.

Potential-pH Diagrams for Iron and Nickel in High Salinity Geothermal Brine Containing Low Concentrations of Hydrogen Sulfide

Potential-pH diagrams are reported for iron and nickel in sulfide containing high salinity geothermal brine at 25 and 250 C. Metal sulfides, as well as dissolved chloride complexes, were considered in deriving the diagrams, and the potential-pH relationships for those equilibria involving dissolved H2S or its anions are plotted for a constant total dissolved sulfide content of 10 ppm. The diagrams are used to analyze the general features of the thermodynamic behavior of iron and nickel in geothermal systems, and to identify processes that might be expected to occur in high temperature sulfide containing brines.

What Does the Geometry of the Hβ BLR Depend On?

Abstract We combine our dynamical modeling black-hole mass measurements from the Lick AGN Monitoring Project 2016 sample with measured cross-correlation time lags and line widths to recover individual scale factors, f , used in traditional reverberation-mapping analyses. We extend our sample by including prior results from Code for AGN Reverberation and Modeling of Emission Lines ( caramel ) studies that have utilized our methods. Aiming to improve the precision of black-hole mass estimates, as well as uncover any regularities in the behavior of the broad-line region (BLR), we search for correlations between f and other AGN/BLR parameters. We find (i) evidence for a correlation between the virial coefficient <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>mean</mml:mi> <mml:mo>,</mml:mo> <mml:mi>σ</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> and black-hole mass, (ii) marginal evidence for a similar correlation between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>rms</mml:mi> <mml:mo>,</mml:mo> <mml:mi>σ</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> and black-hole mass, (iii) marginal evidence for an anticorrelation of BLR disk thickness with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>mean</mml:mi> <mml:mo>,</mml:mo> <mml:mi>FWHM</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>rms</mml:mi> <mml:mo>,</mml:mo> <mml:mi>FWHM</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> , and (iv) marginal evidence for an anticorrelation of inclination angle with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>mean</mml:mi> <mml:mo>,</mml:mo> <mml:mi>FWHM</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>rms</mml:mi> <mml:mo>,</mml:mo> <mml:mi>σ</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>mean</mml:mi> <mml:mo>,</mml:mo> <mml:mi>σ</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> . Last, we find marginal evidence for a correlation between line-profile shape, when using the root-