Development of local-scale high-resolution atmospheric dispersion model using large-eddy simulation. Part 3: turbulent flow and plume dispersion in building arrays

We have developed a LOcal-scale High-resolution atmospheric DIspersion Model using Large-Eddy Simulation (LOHDIM-LES) to assess the safety at nuclear facilities and to respond to emergencies against accidental or intentional release of radioactive materials (e.g., a terrorist attack in an urban area). In Part 1, the unsteady behavior of a plume over a flat terrain was successfully simulated. In Part 2, a new scheme to generate a spatially developing turbulent boundary layer flow was proposed. Then, the large-eddy simulation (LES) model for turbulent flow and plume dispersion around an isolated building was validated. In this study, we extend the LES model to turbulent flows and plume dispersion in various building arrays that represent typical urban surface geometries. Concerning the characteristics of flow and dispersion in building arrays, the flow patterns associated with obstacle densities and the distribution patterns of mean and root-mean-square (r.m.s.) concentrations agree well with those of the wind tunnel experiments. It is shown that the LES model successfully simulates the unsteady behaviors of turbulent flows and plume dispersion in urban-type surface geometries.     

Observation of Electrically Tunable van Hove Singularities in Twisted Bilayer Graphene from NanoARPES

The possibility of triggering correlated phenomena by placing a singularity of the density of states near the Fermi energy remains an intriguing avenue toward engineering the properties of quantum materials. Twisted bilayer graphene is a key material in this regard because the superlattice produced by the rotated graphene layers introduces a van Hove singularity and flat bands near the Fermi energy that cause the emergence of numerous correlated phases, including superconductivity. Direct demonstration of electrostatic control of the superlattice bands over a wide energy range has, so far, been critically missing. This work examines the effect of electrical doping on the electronic band structure of twisted bilayer graphene using a back-gated device architecture for angle-resolved photoemission measurements with a nano-focused light spot. A twist angle of 12.2° is selected such that the superlattice Brillouin zone is sufficiently large to enable identification of van Hove singularities and flat band segments in momentum space. The doping dependence of these features is extracted over an energy range of 0.4 eV, expanding the combinations of twist angle and doping where they can be placed at the Fermi energy and thereby induce new correlated electronic phases in twisted bilayer graphene.     

Deep red upconversion photoluminescence in Er3+-doped Yb3Ga5O12 nanocrystalline garnet

The nanocrystalline single-phase Er³⁺-doped Yb₃Ga₅O₁₂ garnets have been prepared by the sol-gel combustion technique with a crystallite size of ≈30 nm. The presence of Yb³⁺ in garnet hosts allows their efficient excitation at the ≈977 nm wavelength. The Er³⁺ doping of Yb₃Ga₅O₁₂ garnet host results in deep red Er³⁺: ⁴F_9/2 → ⁴I_15/2 upconversion photoluminescence (UCPL) emission. The dominance of the red UCPL emission over the green Er³⁺: ⁴F_7/2/²H_11/2/⁴S_3/2 → ⁴I_15/2 component was investigated using the measurement of the steady-state and time-dependent Er³⁺ and Yb³⁺ emission spectra in combination with the power-dependent UCPL emission intensity. The proposed upconversion mechanism is discussed in terms of the Er³⁺ → Yb³⁺ energy back transfer process as well as Yb³⁺(Er³⁺) → Er³⁺ energy transfer and Er³⁺ ↔ Er³⁺ cross-relaxation processes. The studied Er³⁺-doped Yb₃Ga₅O₁₂ garnet may be utilized as a red upconversion emitting phosphor.     

Adaptive versus Reservation-Based Synchronization Protocols—Analysis and Comparison

With the expansion of distributed multimedia applications, such as video-phone, video-conference, and video-on-demand, synchronization among various media (time-dependent, time-independent) becomes an integral part of various protocols, mechanisms and services in the underlying computing and communication systems. The current systems allow and provide two different resource management environments where synchronization will be considered: (1) best effort resource management, and (2) reservation-based resource management with differentiation of service classes. Under these two resource management environments, our goal is to analyze and compare the design, implementation, and performance of synchronization protocols and services. Our approach to accomplish this complex analysis is inductive, because we select a representative protocol from each group, and consider an adaptive synchronization protocol on top of the best effort resource management and a reservation-based synchronization protocol on top of the reservation-based resource management. We believe that both protocols include a rich set of known synchronization algorithms and mechanisms, hence our resulting analysis and comparison show: (1) trade-offs/difference in design complexity of the synchronization protocols (space and time), (2) trade-offs/difference in implementation complexity of the synchronization protocols (space and time), and (3) magnitude of performance changes.     

pest: Fast approximate keyword search in semantic data using eigenvector-based term propagation

We present pest, a novel approach to the approximate querying of graph-structured data such as RDF that exploits the data's structure to propagate term weights between related data items. We focus on data where meaningful answers are given through the application semantics, e.g., pages in wikis, persons in social networks, or papers in a research network such as Mendeley. The pest matrix generalizes the Google Matrix used in PageRank with a term-weight dependent leap and accommodates different levels of (semantic) closeness for different relations in the data, e.g., friend vs. co-worker in a social network. Its eigenvectors represent the distribution of a term after propagation. The eigenvectors for all terms together form a (vector space) index that takes the structure of the data into account and can be used with standard document retrieval techniques. In extensive experiments including a user study on a real life wiki, we show how pest improves the quality of the ranking over a range of existing ranking approaches, yet achieves a query performance comparable to a plain vector space index.     

Quantitative and qualitative analysis of high molecular compounds in vegetable oils formed under high temperatures in the absence of oxygen

Conditions of deodorization/physical refining of sunflower oil were simulated by high temperature heating in laboratory at 240, 250, and 260 °C. Oxygen atmosphere was excluded by argon atmosphere. Influence of temperature, initial oxidation of incoming oil (peroxide value 2–30 mmol ½ O₂/kg) on geometrical, positional isomerization, and polymerization was measured. The level of initial oxidation of the oil has a significant influence on rate of isomerization, polymerization, and duration of induction period of polymerization reactions. Induction period of polymerization is dependent linearly on temperature at constant hydroperoxide content and is extended with decreasing temperature and lower peroxide value of oil. Significant conjugation took place with geometrical isomerization and resulted in all-trans diene formation. All-trans dienes are incoming reactants for polymerization according to the Diels–Alder mechanism. Suggested “propagation” phase of polymerization took place later. Induction period was observed only in the case of polymerization reactions of triacylglycerols. This is the confirmation of the hypothesis that the cis/trans isomerization, positional isomerization, and polymerization are consecutive reactions in ascending order. Identification of molecular peaks and confirmation of fragments were possible by connecting HPSEC with APCI-MS. Dimers of triacylglycerols (TAG) dominated in studied system. Remaining compounds may have been formed from di-, monoacylglycerols, and other minor constituents of sunflower oil.     

Polychlorinated dibenzo-p-dioxin and dibenzofuran concentration profiles in sediments and flood-plain soils of the Tittabawassee River,Michigan

Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in sediments and flood-plain soils collected along the Tittabawassee River in Michigan ranged from 102 to 53,600 pg/g, dry wt. Mean PCDD/PCDF concentrations in downstream sediment and soil were from 10- to 20-fold greater than those found at locations upstream of Midland, Michigan. Concentrations of PCDD/PCDF in sediments and flood-plain soils from the Tittabawassee watershed were comparable to those found in industrialized areas such as the Housatonic and lower Passaic Rivers in the U.S. Concentrations of PCDDs/PCDFs in soil and sediment were not correlated with total organic carbon (TOC) in sediments or soils. OCDD and 2,3,7,8-TeCDF were the predominant congeners in sediment/soil collected from locations downstream of Midland, Michigan. Principal component analysis of the PCDD/PCDF congener profile suggested the presence of sources originating from a mixture of chlorophenol and other chlorinated compound production. Mass balance analysis of TCDD equivalents (TCDD-EQs) derived from H4IIE-luc bioassay of sediment extracts and 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) estimated from instrumental analysis suggested that PCDDs/PCDFs were the major dioxin-like compounds present in sediments. A significant correlation existed between bioassay-derived TCDD-EQs and instrumentally measured TEQs (r2 = 0.94).     

New Process for Recovery of Zinc Sulfate and Sulfuric Acid from Zinc Electrowinning Bleed Solutions

Acid-base couple extractants extract sulfuric acid and zinc sulfate efficiently, selectively and reversibly. Their properties allowed development of a new, solvent extraction process for treating zinc electrowinning waste streams. In this process, about 95% of the sulfuric acid and 95% of the zinc can be recovered at concentrations high enough to be directly recycled to zinc production. Lime consumption and gypsum formation are substantially reduced. Only one extractant is used in the process, and zinc is recovered as zinc sulfate.     

Binarization, character extraction, and writer identification of historical Hebrew calligraphy documents

We present our work on the paleographic analysis and recognition system intended for processing of historical Hebrew calligraphy documents. The main goal is to analyze documents of different writing styles in order to identify the locations, dates, and writers of test documents. Using interactive software tools, a data base of extracted characters has been established. It now contains about 20,000 characters of 34 different writers, and will be distinctly expanded in the near future. Preliminary results of automatic extraction of pre-specified letters using the erosion operator are presented. We further propose and test topological features for handwriting style classification based on a selected subset of the Hebrew alphabet. A writer identification experiment using 34 writers yielded 100% correct classification.