Use of LEU in the aqueous homogeneous medical isotope production reactor
Ball, R.M. [Babock & Wilcox, Lynchburg, VA (United States)
1997-08-01
The Medical Isotope Production Reactor (MIPR) is an aqueous solution of uranyl nitrate in water, contained in an aluminum cylinder immersed in a large pool of water which can provide both shielding and a medium for heat exchange. The control rods are inserted at the top through re-entrant thimbles. Provision is made to remove radiolytic gases and recombine emitted hydrogen and oxygen. Small quantities of the solution can be continuously extracted and replaced after passing through selective ion exchange columns, which are used to extract the desired products (fission products), e.g. molybdenum-99. This reactor type is known for its large negative temperature coefficient, the small amount of fuel required for criticality, and the ease of control. Calculation using TWODANT show that a 20% U-235 enriched system, water reflected can be critical with 73 liters of solution.
AQUEOUS HOMOGENEOUS REACTORTECHNICAL PANEL REPORT
Diamond, D.J.; Bajorek, S.; Bakel, A.; Flanagan, G.; Mubayi, V.; Skarda, R.; Staudenmeier, J.; Taiwo, T.; Tonoike, K.; Tripp, C.; Wei, T.; Yarsky, P.
2010-12-03
Considerable interest has been expressed for developing a stable U.S. production capacity for medical isotopes and particularly for molybdenum- 99 (99Mo). This is motivated by recent re-ductions in production and supply worldwide. Consistent with U.S. nonproliferation objectives, any new production capability should not use highly enriched uranium fuel or targets. Conse-quently, Aqueous Homogeneous Reactors (AHRs) are under consideration for potential 99Mo production using low-enriched uranium. Although the Nuclear Regulatory Commission (NRC) has guidance to facilitate the licensing process for non-power reactors, that guidance is focused on reactors with fixed, solid fuel and hence, not applicable to an AHR. A panel was convened to study the technical issues associated with normal operation and potential transients and accidents of an AHR that might be designed for isotope production. The panel has produced the requisite AHR licensing guidance for three chapters that exist now for non-power reactor licensing: Reac-tor Description, Reactor Coolant Systems, and Accident Analysis. The guidance is in two parts for each chapter: 1) standard format and content a licensee would use and 2) the standard review plan the NRC staff would use. This guidance takes into account the unique features of an AHR such as the fuel being in solution; the fission product barriers being the vessel and attached systems; the production and release of radiolytic and fission product gases and their impact on operations and their control by a gas management system; and the movement of fuel into and out of the reactor vessel.
Perez, Daniel Milian; Lorenzo, Daniel E. Milian; Garcia, Lorena P. Rodriguez; Llanes, Jesus Salomon; Hernandez, Carlos R. Garcia, E-mail: dperez@instec.cu, E-mail: dmilian@instec.cu, E-mail: lorenapilar@instec.cu, E-mail: cgh@instec.cu [Instituto Superior de Tecnologias y Ciencias Aplicadas (InSTEC), La Habana (Cuba); Lira, Carlos A. Brayner de Oliveira, E-mail: cabol@ufpe.br [Universidade Federal de Pernambuco (UFPE), Recife (Brazil); Rodriguez, Manuel Cadavid, E-mail: mcadavid2001@yahoo.com [Tecnologia Nuclear Medica Spa, TNM (Chile)
2015-07-01
{sup 99m}Tc is the most common radioisotope used in nuclear medicine. It is a very useful radioisotope, which is used in about 30-40 million procedures worldwide every year. Medical diagnostic imaging techniques using {sup 99m}Tc represent approximately 80% of all nuclear medicine procedures. Although {sup 99m}Tc can be produced directly on a cyclotron or other type of particle accelerator, currently is almost exclusively produced from the beta-decay of its 66-h parent {sup 99}Mo. {sup 99}Mo production system in an Aqueous Homogeneous Reactor (AHR) is potentially advantageous because of its low cost, small critical mass, inherent passive safety, and simplified fuel handling, processing and purification characteristics. In this paper, an AHR conceptual design using Low Enriched Uranium (LEU) is studied and optimized for the production of {sup 99}Mo. Aspects related with the neutronic behavior such as optimal reflector thickness, critical height, medical isotopes production and the reactivity feedback introduced in the solution by the volumetric expansion of the fuel solution due to thermal expansion of the fuel solution and the void volume generated by radiolytic gas bubbles were evaluated. Thermal-hydraulics studies were carried out in order to show that sufficient cooling capacity exists to prevent fuel overheating. The neutronic and thermal-hydraulics calculations have been performed with the MCNPX computational code and the version 14 of ANSYS CFX respectively. The neutronic calculations demonstrated that the reactor is able to produce 370 six-day curies of {sup 99}Mo in 5 days operation cycles and the CFD simulation demonstrated that the heat removal systems provide sufficient cooling capacity to prevent fuel overheating, the maximum temperature reached by the fuel (89.29 deg C) was smaller to the allowable temperature limit (90 deg C). (author)
Simulator for SUPO, a Benchmark Aqueous Homogeneous Reactor (AHR)
Klein, Steven Karl [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Determan, John C. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-10-14
A simulator has been developed for SUPO (Super Power) an aqueous homogeneous reactor (AHR) that operated at Los Alamos National Laboratory (LANL) from 1951 to 1974. During that period SUPO accumulated approximately 600,000 kWh of operation. It is considered the benchmark for steady-state operation of an AHR. The SUPO simulator was developed using the process that resulted in a simulator for an accelerator-driven subcritical system, which has been previously reported.
Simulator for SUPO, a Benchmark Aqueous Homogeneous Reactor (AHR)
A simulator has been developed for SUPO (Super Power) an aqueous homogeneous reactor (AHR) that operated at Los Alamos National Laboratory (LANL) from 1951 to 1974. During that period SUPO accumulated approximately 600,000 kWh of operation. It is considered the benchmark for steady-state operation of an AHR. The SUPO simulator was developed using the process that resulted in a simulator for an accelerator-driven subcritical system, which has been previously reported.
Development of fuel management code for aqueous homogeneous reactors
Fuel Management Code for Aqueous Homogeneous Reactors (FMCAHR) is developed based on the Monte Carlo transport method. FMCAHR has the ability of doing resonance treatment, searching for critical control rods height, and calculating the thermal hydraulic parameters, bubble volume fraction and burn-up. The main structure and development process of FMCAHR is introduced in this paper, and the verification shows that the computing results of FMCAHR are precise. (authors)
Final report on the aqueous homogeneous suspension reactor project
The most important results of twenty five years of research and development work on circulating aqueous homogeneous suspensions of fissile material are presented. Experiments in the final phase were carried out with a prototype nuclear reactor (KEMA Suspension Test Reactor, KSTR), fuelled with an aqueous suspension of UO2/ThO2 particles. Summarizing the results of the experimental and post-operational research on the KSTR, it can be stated that the suspension reactor has largely fulfilled the expectations of its designers. No operational problems worth mentioning occurred during an experimental period covering several years. From the standpoint of reactor physics the results can be termed wholly favourable, especially at a high power level. The reactor proved to be inherently safe due to the prompt action of the comparatively high negative coefficient of reactivity. The mechanical behaviour of the parts inspected has also satisfied expectations. The problems encountered have been due exclusively to the presence of a flow stabilizer. This was installed in the period following some time of subcritical operation in order to reduce the reactivity fluctuations. A stabilizer closed on all sides might perhaps have prevented the problems mentioned and the applicability of the principle of the suspension reactor would have been demonstrated still more clearly. 19 refs.; 45 figs.; 7 tabs
Technetium-99m (99mTc), the daughter of Molybdenum-99 (99Mo), is the most commonly used medical radioisotope in the world. It accounts for over twenty-five million medical procedures each year worldwide, comprising about 80% of all radiopharmaceutical procedures. 99Mo is mostly prepared by the fission of uranium-235 targets in a nuclear reactor with a fission yield of about 6.1%. Currently over 95% of the fission product 99Mo is obtained using highly enriched uranium (HEU) targets. Smaller scale producers use low enriched uranium (LEU) targets. Small quantities of 99Mo are also produced by neutron activation through the use of the (n, γ) reaction. The concept of a compact homogeneous aqueous reactor fuelled by a uranium salt solution with off-line separation of radioisotopes of interest (99Mo, 131I) from aliquots of irradiated fuel solution has been cited in a few presentations in the series of International Conference on Isotopes (ICI) held in Vancouver (2000), Cape Town (2003) and Brussels (2005) and recently some corporate interest has also been noticeable. Calculations and some experimental research have shown that the use of aqueous homogeneous reactors (AHRs) could be an efficient technology for fission radioisotope production, having some prospective advantages compared with traditional technology based on the use of solid uranium targets irradiated in research reactors. This review of AHR status and prospects by a team of experts engaged in the field of homogeneous reactors and radioisotope producers yields an objective evaluation of the technological challenges and other relevant implications. The meeting to develop this report facilitated the exchange of information on the 'state of the art' of the technology related to homogeneous aqueous solution nuclear reactors, especially in connection with the production of radioisotopes. This publication presents a summary of discussions of a consultants meeting which is followed by the technical presentations
99mTc is a very useful radioisotope in medical diagnostic procedure. 99mTc is produced from 99Mo decay. Currently, most of 99Mo is produced by irradiating 235U in the nuclear reactor. 99Mo mostly results from the fission reaction of 235U targets with a fission yield about 6.1%. A small additional amount is created from 98Mo neutron activation. Actually 99Mo is also created in the reactor fuel, but usually we do not extract it. The fuel will become spent fuel which is a highly radioactive waste. 99Mo production system in the aqueous homogeneous reactor offers a better method, because all of the 99Mo can be extracted from the fuel solution. Fresh reactor fuel solution consists of uranyl nitrate dissolved in water. There is no separation of target and fuel in an aqueous homogeneous reactor where target and fuel become one liquid solution, and there is no spent fuel generated from this reactor. Simulation of the extraction process is performed while reactor in operation (without reactor shutdown). With an extraction flow rate of 3.6 L/h, after 43 hours of reactor operation the production of 99Mo is relatively constant at about 98.6 curie/hour. (author)
A. Isnaeni
2014-04-01
Full Text Available 99mTc is a very useful radioisotope in medical diagnostic procedure. 99mTc is produced from 99Mo decay. Currently, most of 99Mo is produced by irradiating 235U in the nuclear reactor. 99Mo mostly results from the fission reaction of 235U targets with a fission yield about 6.1%. A small additional amount is created from 98Mo neutron activation. Actually 99Mo is also created in the reactor fuel, but usually we do not extract it. The fuel will become spent fuel which is a highly radioactive waste. 99Mo production system in the aqueous homogeneous reactor offers a better method, because all of the 99Mo can be extracted from the fuel solution. Fresh reactor fuel solution consists of uranyl nitrate dissolved in water. There is no separation of target and fuel in an aqueous homogeneous reactor where target and fuel become one liquid solution, and there is no spent fuel generated from this reactor. Simulation of the extraction process is performed while reactor in operation (without reactor shutdown. With an extraction flow rate of 3.6 L/h, after 43 hours of reactor operation the production of 99Mo is relatively constant at about 98.6 curie/hour
Cooling, C.M., E-mail: c.cooling10@imperial.ac.uk [Imperial College of Science, Technology and Medicine (United Kingdom); Williams, M.M.R. [Imperial College of Science, Technology and Medicine (United Kingdom); Nygaard, E.T. [Babcock and Wilcox Technical Services Group (TSG) (United States); Eaton, M.D. [Imperial College of Science, Technology and Medicine (United Kingdom)
2013-09-15
Highlights: • A point kinetics model for the Medical Isotope Production Reactor is formulated. • Reactivity insertions are simulated using this model. • Polynomial chaos is used to simulate uncertainty in reactor parameters. • The computational efficiency of polynomial chaos is compared to that of Monte Carlo. -- Abstract: This paper models a conceptual Medical Isotope Production Reactor (MIPR) using a point kinetics model which is used to explore power excursions in the event of a reactivity insertion. The effect of uncertainty of key parameters is modelled using intrusive polynomial chaos. It is found that the system is stable against reactivity insertions and power excursions are all bounded and tend towards a new equilibrium state due to the negative feedbacks inherent in Aqueous Homogeneous Reactors (AHRs). The Polynomial Chaos Expansion (PCE) method is found to be much more computationally efficient than that of Monte Carlo simulation in this application.
REMOVAL OF REMAZOL ROSSO RB DYE FROM AQUEOUS EFFLUENTS BY HOMOGENOUS FENTON OXIDATION PROCESSES
Carmen Zaharia; Victoria Fedorcea; Adrian Beda; Victor Amarandei; Augustin Muresan
2014-01-01
The paper presents some data from our laboratory-setup experiments of homogenous oxidative processes with hydrogen peroxide (i.e. advanced Fenton oxidation processes) applied for Remazol Rosso RB dye-containing aqueous systems, especially textile effluents. Therefore, some different operating parameters (including pH, concentration of dye, H2O2 and ferrous ions, oxidation time, temperature, stirring regime, among its) were tested for determination of the best performance in effluent decolorat...
Jun Kobayashi
2015-01-01
Full Text Available We propose a robust method to distinguish isolated single gold nanoparticles (AuNP monomers and their dimers under Brownian motion, a key for ultrasensitive homogeneous bioassays, including AuNP sandwich assays. To detect dimers and distinguish them from a larger number of monomers in aqueous solution, single-particle polarization microscopy was performed. For the accurate detection of individual particles, the optical anisotropy and rotational diffusion time are measured because a dimer is much more anisotropic than the nearly spherical monomer and the rotational diffusion time of a dimer is four times that of a monomer. By employing an autocorrelation analysis, we defined a measure of distinguishing that simultaneously enables high detection probability and low error probability. The detection platform offers homogeneous DNA hybridization assays and immunoassays at the subpicomolar level.
REMOVAL OF REMAZOL ROSSO RB DYE FROM AQUEOUS EFFLUENTS BY HOMOGENOUS FENTON OXIDATION PROCESSES
Carmen Zaharia
2014-06-01
Full Text Available The paper presents some data from our laboratory-setup experiments of homogenous oxidative processes with hydrogen peroxide (i.e. advanced Fenton oxidation processes applied for Remazol Rosso RB dye-containing aqueous systems, especially textile effluents. Therefore, some different operating parameters (including pH, concentration of dye, H2O2 and ferrous ions, oxidation time, temperature, stirring regime, among its were tested for determination of the best performance in effluent decoloration and dye removal, meaning the optimal values of each studied parameters for highest decoloration or dye removal.
Zhang, Hairong; Guo, Haijun; Wang, Bo; Shi, Silan; Xiong, Lian; Chen, Xinde
2016-01-20
In this work, bacterial cellulose (BC) was activated by ethylenediamine (EDA) and then dissolved in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) aqueous solutions. The resulting transparent solution was cast on a glass plate to prepare regenerated BC. Then cationic BC was prepared homogeneously by the reaction between regenerated BC and 3-chloro-2-hydroxypropyl-trimethyl ammonium chloride (CHPTAC) in a NaOH/urea aqueous solution. Structure and properties of the BC and its products were characterized by different techniques such as X-ray diffraction (XRD), Fourier transform spectroscopy (FT-IR), scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA). The results showed that there was no significant difference between the structures of BC, activated BC and regenerated BC. The effects of different temperature and molar ratio of CHPTAC to anhydroglucose unit (AGU) on the degree of substitution (DS) value were examined. The DS values of cationic BC ranged between 0.21 and 0.51. PMID:26572343
Soheil Sayyahi; Jafar Saghanezhad
2011-01-01
In this letter, a mild and efficient procedure for synthesis of phenacyl derivatives under homogenous catalysis in the presence of tetrabutylammonium bromide in aqueous media is described. The nucleophilic substitution reactions were performed under ecofriendly conditions and gave the corresponding products in high yields and short reaction times.
Homogeneous liquid-liquid extraction of uranium(VI) from acetate aqueous solution
A selective and very effective concentration method for uranium(VI) was developed by the homogeneous liquid-liquid extraction method based on the ion-pair phase separation of perfluorooctanoate ion (PFOA-) with tetrabutylammonium ion (TBA+). Under the experimental conditions ([PFOA-]T=6.67x10-3 M, [TBA+]T=5.0x10-2 M, [acetate]T=0.17 M, pH 4.0), the extraction % of uranium(VI) was 96%, and the maximum concentration factor was approximately 330-fold (i.e., 90 μl of the sedimented phase was produced from 30 ml of the aqueous phase). The extracted species was estimated by the normal liquid-liquid extraction method in a water/ethyl acetate system to be UO2(CH3COO)-3·TBA+. The proposed homogeneous liquid-liquid extraction method was applied as a preconcentration method for the spectrophotometric determination of uranium(VI) with arsenazo III. The calibration graph was linear over the range 3.3x10-8-2.7x10-6 M. The relative standard deviation for the central value of the calibration graph was 1.4% (10 determinations), and the detection limit (S/N=3) was 6.0x10-10 M. When the proposed method was applied to the separation and determination of uranium(VI) added to sea water, the results were satisfactory. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)
A novel approach to the production of medical radioisotopes: the homogeneous SLOWPOKE reactor
Bonin, H.W., E-mail: bonin-h@rmc.ca [Royal Military College of Canada, Kingston, Ontario (Canada); Hilborn, J.W. [retired, Atomic Energy of Canada Limited, Chalk River, Ontario (Canada); Carlin, G.E. [Ontario Power Generation, Toronto, Ontario (Canada); Gagnon, R.; Busatta, P. [Royal Canadian Navy, Ottawa, Ontario (Canada)
2015-03-15
In 2009, the unexpected 15-month outage of the Canadian NRU nuclear reactor resulted in a sudden 30% world shortage, with higher shortages experienced in North America than in Europe. Commercial radioisotope production is from just eight nuclear reactors, most being aging systems near the end of their service life. This paper proposes a more efficient production and distribution model. Tc-99m unit doses would be distributed to regional hospitals from ten integrated 'industrial radiopharmacies', located at existing licensed nuclear reactor sites in North America. At each site, one or more 20 kW Homogeneous SLOWPOKE nuclear reactors would deliver 15 litres of irradiated aqueous uranyl sulfate fuel solution daily to industrial-scale hot cells, for extraction of Mo-99; and the low-enriched uranium would be recycled. Purified Mo-99 would be incorporated in large Mo-99/Tc-99m generators for extraction of Tc-99m five days a week; and each automated hot-cell facility would be designed to load up to 7,000 Tc-99m syringes daily for road delivery to all of the nuclear medicine hospitals within a 3-hour range. At the current price of $20 per unit dose, the annual gross income from 10 sites would be approximately $360 million. The Homogeneous SLOWPOKE reactor evolved from the inherently safe SLOWPOKE-2 research reactor, with a double goal: replacing the heterogeneous SLOWPOKE-2 reactors at the end-of-core life, enabling them to continue their primary missions of research and education, together with full time commercial radioisotope production. The Homogeneous SLOWPOKE reactor was modelled using both deterministic and probabilistic reactor simulation codes. The homogeneous fuel mixture is a dilute aqueous solution of low-enriched uranyl sulfate containing approximately 1 kg of U-235. The reactor is controlled by mechanical absorber rods in the beryllium reflector. Safety analysis was carried out for both normal operation and transient conditions. The most severe
99mTc is a very useful radioisotope, which is used in nearly 80% of all nuclear medicine procedures. 99mTc is produced from 99Mo decay. Since 2007 the medical community has been plagued by 99Mo shortages due to aging reactors, such as the National Research Universal reactor in Canada and the High Flux Reactor in Petten, The Netherlands. At present, most of the world's supply of 99Mo for medical isotope production involves the neutron fission of 235U in multipurpose research reactors. 99Mo mostly results from the fission reaction of 235U targets with a fission yield about 6.1%. After irradiation in the reactor, the target is digested in acid or alkaline solutions and 99Mo is recovered through a series of extraction (separation) and purification steps. 99Mo production system in an Aqueous Homogeneous Reactor (AHR) offers a better method, because all of the 99Mo can be extracted from the fuel solution. Over 30 AHRs has been built and operated around the world with 149 years of combined experience. In this paper, an AHR conceptual design using LEU (Low Enriched Uranium) is optimized to meet the South American demand for 99Mo for the coming years. Aspect related with the neutronic behavior such as optimal reflector thickness, critical height, medical isotope production and others are evaluated. The neutronic calculations have been performed with the well-known MCNPX computational code. A benchmarking experiments performed at the Russian Research Center 'Kurchatov Institute' in order to validate that the developed models of AHRs with MCNPX code and the available library in XSDIR, ENDF/B VI.2, are adequate for studies of aqueous fuel solutions. (Author)
Conceptual design of a new homogeneous reactor for medical radioisotope Mo-99/Tc-99m production
Liem, Peng Hong [Nippon Advanced Information Service (NAIS Co., Inc.) Scientific Computational Division, 416 Muramatsu, Tokaimura, Ibaraki (Japan); Tran, Hoai Nam [Chalmers University of Technology, Dept. of Applied Physics, Div. of Nuclear Engineering, SE-412 96 Gothenburg (Sweden); Sembiring, Tagor Malem [National Nuclear Energy Agency (BATAN), Center for Reactor Technology and Nuclear Safety, Kawasan Puspiptek, Serpong, Tangerang Selatan, Banten (Indonesia); Arbie, Bakri [PT MOTAB Technology, Kedoya Elok Plaza Blok DA 12, Jl. Panjang, Kebun Jeruk, Jakarta Barat (Indonesia)
2014-09-30
To partly solve the global and regional shortages of Mo-99 supply, a conceptual design of a nitrate-fuel-solution based homogeneous reactor dedicated for Mo-99/Tc-99m medical radioisotope production is proposed. The modified LEU Cintichem process for Mo-99 extraction which has been licensed and demonstrated commercially for decades by BATAN is taken into account as a key design consideration. The design characteristics and main parameters are identified and the advantageous aspects are shown by comparing with the BATAN's existing Mo-99 supply chain which uses a heterogeneous reactor (RSG GAS multipurpose reactor)
Magnetic separation of Dy(III) ions from homogeneous aqueous solutions
The possibility to enrich paramagnetic dysprosium(III) ions in a magnetic field gradient is proved by means of interferometry, which may open the route for a magnetic separation of rare earth ions from aqueous solutions. The separation dynamics are studied for three different concentrations of DyCl3 and compared with those found recently in a sulphate solution of the 3d ion Mn(II). In view of the similar-sized hydration spheres for Dy(III) and Mn(II), the slower separation dynamics in DyCl3 is attributed to both a higher densification coefficient and the strong impact of Brownian motion due to the absence of ion-pair clusters
Tan, Chongxiao; Gajovic-Eichelmann, Nenad; Polzius, Rainer; Hildebrandt, Niko; Bier, Frank F
2010-11-01
The detection of the major active component of cannabis, Δ9-tetrahydrocannabinol (THC), becomes increasingly relevant due to its widespread abuse. For control purposes, some easy-to-use, sensitive and inexpensive test methods are needed. We have developed a fluorescence immunoassay utilising THC-fluorescein conjugate as tracer. Fluorescence spectroscopy of the conjugate revealed an unusual property: The relatively weak fluorescence of a dilute tracer solution was increased by a factor of up to 5 after binding of a THC-specific antibody. Fluorescence lifetime measurements in aqueous solutions suggested two different tracer conformations both associated with quenching of fluorescein fluorescence by the intramolecular THC moiety. After antibody binding, the tracer enters a third conformation in which fluorescence quenching of fluorescein is completely suppressed. Utilising this property, we established a homogeneous competitive immunoassay (homogeneous increasing fluorescence immunoassay) with low detection limits. The test requires only two reagents, the new tracer molecule and an anti-THC antibody. A single test takes only 8 min. The dynamic detection range for THC is 0.5 to 20 ng/mL in buffer, with a limit of detection (LOD) of 0.5 ng/mL. The test also works in diluted saliva samples (1:10 dilution with buffer) with an LOD of 2 ng/mL and a dynamic range of 2-50 ng/mL. PMID:20740278
Peng, Na; Ai, Ziye; Fang, Zehong; Wang, Yanfeng; Xia, Zhiping; Zhong, Zibiao; Fan, Xiaoli; Ye, Qifa
2016-10-01
Water-soluble quaternized chitins (QCs) were homogeneously synthesized by reacting chitin with (3-chloro-2-hydroxypropyl) trimethylammonium chloride (CHPTAC) in 8wt% NaOH/4wt% urea aqueous solutions. The chemical structure and solution properties of the quaternized chitins were characterized by (1)H NMR, FT-IR, elemental analysis, dynamic light scattering (DLS) and zeta potential measurements. The results demonstrated that the water-soluble QCs, with a degree of substitution (DS) values of 0.27-0.54, could be obtained by varying the concentration of chitin, the molar ratio of CHPTAC to chitin unit, and the reaction time at room temperature (25°C). Two QCs (DS=0.36 and 0.54) were selected and studied as gene carriers. Agarose gel retardation assay revealed that both QCs could condense DNA efficiently when N/P ratio>3. The results of particle size and zeta potential indicated that both QCs had a good ability of condensing plasmid DNA into compact nanoparticles with the size of 100-200nm and zeta potential of +18 to +36mV. Compared to polyethylenimine (PEI, 25kDa), the QCs exhibited outstanding low cytotoxicity. Transfection efficiencies of the QCs/DNA complexes were measured using pGL-3 encoding luciferase as the foreign DNA, and the QCs/DNA complexes showed effective transfection efficiencies in 293T cells. These results revealed that the QCs prepared in NaOH/urea aqueous solutions could be used as promising non-viral gene carriers owing to their excellent characteristics. PMID:27312628
Liu, Lingzhi; Dong, Xiaohu; Xiao, Yan; Lian, Wenlong; Liu, Zhihong
2011-05-21
In the present work, a two-photon excited fluorescent chemosensor for Cu(2+) was prepared. The probe was constructed on the basis of internal charge transfer (ICT) principle with macrocyclic dioxotetraamine as the Cu(2+) receptor. The good water-solubility of the molecule enabled recognition and assay of Cu(2+) ions in biological media. The photophysical properties of the chemosensor were investigated in detail, exhibiting favorable fluorescence quantum yield and moderate two-photon absorption cross-section. The studies on binding thermodynamics demonstrated the formation of 1 : 1 complex between the chemosensor and Cu(2+) and an association constant of ca. 1.04 × 10(5) M(-1). Due to the rational design of the molecular structure, the sensor was highly specific to Cu(2+), which ensured high selectivity in Cu(2+) determination. Upon Cu(2+) binding, the intramolecular charge-transfer extent within the chromophore was weakened resulting in a remarkable quenching of fluorescence, based on which quantitative determination of Cu(2+) was performed. Good linearity was obtained between the fluorescence quenching value and Cu(2+) concentration ranging from 0.04 to 2.0 μM in aqueous solution. Benefiting from the merits of two-photon excitation, the chemosensor was free of interference from background luminescence in serum. A homogeneous quantitative determination of Cu(2+) was achieved in the serum medium with a linear range of 0.04 to 2.0 μM. Considering the structural flexibility of the sensor, this work also opens up the possibility to construct other two-photon excited chemosensors for direct homogeneous assay of various molecules/ions in complicated biological sample matrices. PMID:21416097
Thermal-Hydraulics Study of a 75 kWth Aqueous Homogeneous Reactor for 99Mo Production
Daniel Milian Pérez
2015-01-01
Full Text Available Tc99m is a very useful radioisotope, which is used in nearly 80% of all nuclear medicine procedures. Tc99m is produced from 99Mo decay. A potentially advantageous alternative to meeting current and future demand for 99Mo is the use of Aqueous Homogeneous Reactors (AHR. In this paper, a thermal-hydraulics study of the core of a 75 kWth AHR conceptual design based on the ARGUS reactor for 99Mo production is presented. As the ARGUS heat removal systems were designed for working at 20 kWth, the main objective of the thermal-hydraulics study was evaluating the heat removal systems in order to show that sufficient cooling capacity exists to prevent fuel solution overheating. The numerical simulations of an AHR model were carried out using the Computational Fluid Dynamic (CFD code ANSYS CFX 14. Evaluation shows that the ARGUS heat removal systems working at 75 kWth are not able to provide sufficient cooling capacity to prevent fuel solution overheating. To solve this problem, the number of coiled cooling pipes inside the core was increased from one to five. The results of the CFD simulations with this modification in the design show that acceptable temperature distributions can be obtained.
Dialkyl- and diarylammonium ions are able to form complexes with α-cyclodextrin and cucurbit[6]uril. These amines are able to complex two guest molecules simultaneously resulting in the formation of homogeneous or heterogeneous 1:2 (ratio of dialkylammonium to ligand) complexes. The stability constants and reaction enthalpies for the formation of 1:1 complexes have been measured using potentiometric and calorimetric titrations. Differences between the values obtained by these methods can be attributed to solvent composition. Only for the 1:2 complex formation with cucurbit[6]uril, the ligands influenced each other. The polar carbonyl groups at each portal of the cucurbit[6]urils interacted simultaneously with the protonated amino group resulting in an electrostatic repulsion between both molecules. No further interactions between two complexed molecules of α-cyclodextrin or cucurbit[6]uril and α-cyclodextrin were observed. The absence of polar groups in the case of α-cyclodextrin led to unaffected formation of homogeneous and even heterogeneous 1:2 complexes.
Chadwick, John C; Freixa, Zoraida; van Leeuwen, Piet W N M
2011-01-01
This first book to illuminate this important aspect of chemical synthesis improves the lifetime of catalysts, thus reducing material and saving energy, costs and waste.The international panel of expert authors describes the studies that have been conducted concerning the way homogeneous catalysts decompose, and the differences between homogeneous and heterogeneous catalysts. The result is a ready reference for organic, catalytic, polymer and complex chemists, as well as those working in industry and with/on organometallics.
Sanchez, R.; Ragusa, J.; Santandrea, S. [Commissariat a l' Energie Atomique, Direction de l' Energie Nucleaire, Service d' Etudes de Reacteurs et de Modelisation Avancee, CEA de Saclay, DM2S/SERMA 91 191 Gif-sur-Yvette cedex (France)]. e-mail: richard.sanchez@cea.fr
2004-07-01
The problem of the determination of a homogeneous reflector that preserves a set of prescribed albedo is considered. Duality is used for a direct estimation of the derivatives needed in the iterative calculation of the optimal homogeneous cross sections. The calculation is based on the preservation of collapsed multigroup albedo obtained from detailed reference calculations and depends on the low-order operator used for core calculations. In this work we analyze diffusion and transport as low-order operators and argue that the P{sub 0} transfers are the best choice for the unknown cross sections to be adjusted. Numerical results illustrate the new approach for SP{sub N} core calculations. (Author)
Lai, Chien-Han; Wu, Yu-Te
2016-03-01
This study surveyed the characteristics of the indicator for the synchrony of brain activities, regional homogeneity (ReHo), in patients who were diagnosed with major depressive disorder (MDD) without co-morbidities. Forty-four patients with MDD and twenty-seven normal controls were enrolled in our study. The ReHo outputs of patients and controls were compared by a nonparametric permutation-based method with global brain volume, age, and gender as covariates. In addition, the correlations between the clinical variables (such as depression severity, anxiety severity, illness duration) and ReHo values were also estimated in each group and across both groups. The patients with MDD had lower ReHo values than the controls for the cognitive division of right anterior cingulate cortex and the left inferior parietal lobule. In contrast, the patients had higher values of ReHo than controls for the right inferior temporal lobe and the right cerebellum. Additionally, the ReHo values were negatively correlated with the depression severity and with illness duration in the right anterior cingulate cortex. MDD patients had significant alterations in the ReHo of the parieto-cingulate and temporo-cerebellum regions with opposite trends. PMID:25904155
Calviño-Louzao, E.; Hervella, L. M.; Seoane-Bascoy, J.; Vázquez-Lorenzo, R.
2013-01-01
Left-invariant Cotton solitons on homogeneous manifolds are determined. Moreover, algebraic Cotton solitons are studied providing examples of non-invariant Cotton solitons, both in the Riemannian and Lorentzian homogeneous settings.
Homogeneity of Inorganic Glasses
Jensen, Martin; Zhang, L.; Keding, Ralf;
2011-01-01
Homogeneity of glasses is a key factor determining their physical and chemical properties and overall quality. However, quantification of the homogeneity of a variety of glasses is still a challenge for glass scientists and technologists. Here, we show a simple approach by which the homogeneity o...
Passive safety of the Medical Isotope Production Reactor (MIPR)
The Medical Isotope Production Reactor (MIPR) is an aqueous homogeneous reactor designed with the minimum possible waste heat and waste radioactive products, lowest uranium consumption, and enhanced passive safety to produce medical isotopes that are based on short-lived fission products. A major product of the reactor is 99Mo, which decays to a daughter isotope, 99Tc, which can be fixed chemically to pharmaceuticals. Technetium-99 is widely used by the medical community for diagnostic purposes arising form the short half-life and desirable gamma energy of the decay. The only approved method of obtaining 99Mo for use in humans is from a fission product using chemical separation means
Maartens, Roy
2011-12-28
The standard model of cosmology is based on the existence of homogeneous surfaces as the background arena for structure formation. Homogeneity underpins both general relativistic and modified gravity models and is central to the way in which we interpret observations of the cosmic microwave background (CMB) and the galaxy distribution. However, homogeneity cannot be directly observed in the galaxy distribution or CMB, even with perfect observations, since we observe on the past light cone and not on spatial surfaces. We can directly observe and test for isotropy, but to link this to homogeneity we need to assume the Copernican principle (CP). First, we discuss the link between isotropic observations on the past light cone and isotropic space-time geometry: what observations do we need to be isotropic in order to deduce space-time isotropy? Second, we discuss what we can say with the Copernican assumption. The most powerful result is based on the CMB: the vanishing of the dipole, quadrupole and octupole of the CMB is sufficient to impose homogeneity. Real observations lead to near-isotropy on large scales--does this lead to near-homogeneity? There are important partial results, and we discuss why this remains a difficult open question. Thus, we are currently unable to prove homogeneity of the Universe on large scales, even with the CP. However, we can use observations of the cosmic microwave background, galaxies and clusters to test homogeneity itself. PMID:22084298
Benchmarking monthly homogenization algorithms
V. K. C. Venema
2011-08-01
Full Text Available The COST (European Cooperation in Science and Technology Action ES0601: Advances in homogenization methods of climate series: an integrated approach (HOME has executed a blind intercomparison and validation study for monthly homogenization algorithms. Time series of monthly temperature and precipitation were evaluated because of their importance for climate studies and because they represent two important types of statistics (additive and multiplicative. The algorithms were validated against a realistic benchmark dataset. The benchmark contains real inhomogeneous data as well as simulated data with inserted inhomogeneities. Random break-type inhomogeneities were added to the simulated datasets modeled as a Poisson process with normally distributed breakpoint sizes. To approximate real world conditions, breaks were introduced that occur simultaneously in multiple station series within a simulated network of station data. The simulated time series also contained outliers, missing data periods and local station trends. Further, a stochastic nonlinear global (network-wide trend was added.
Participants provided 25 separate homogenized contributions as part of the blind study as well as 22 additional solutions submitted after the details of the imposed inhomogeneities were revealed. These homogenized datasets were assessed by a number of performance metrics including (i the centered root mean square error relative to the true homogeneous value at various averaging scales, (ii the error in linear trend estimates and (iii traditional contingency skill scores. The metrics were computed both using the individual station series as well as the network average regional series. The performance of the contributions depends significantly on the error metric considered. Contingency scores by themselves are not very informative. Although relative homogenization algorithms typically improve the homogeneity of temperature data, only the best ones improve
Homogenization approach in engineering
Homogenization is an approach which studies the macrobehavior of a medium by its microproperties. Problems with a microstructure play an essential role in such fields as mechanics, chemistry, physics, and reactor engineering. Attention is concentrated on a simple specific model problem to illustrate results and problems typical of the homogenization approach. Only the diffusion problem is treated here, but some statements are made about the elasticity of composite materials. The differential equation is solved for linear cases with and without boundaries and for the nonlinear case. 3 figures, 1 table
Dynamics of homogeneous nucleation
Toxværd, Søren
2015-01-01
clusters fluctuates, but the mean temperature remains below the temperature in the supersaturated gas until they reach the critical nucleation size. The critical nuclei have, however, a temperature equal to the supersaturated gas. The kinetics of homogeneous nucleation is not only caused by a grow or......The classical nucleation theory for homogeneous nucleation is formulated as a theory for a density fluctuation in a supersaturated gas at a given temperature. But molecular dynamics simulations reveal that it is small cold clusters which initiates the nucleation. The temperature in the nucleating...
Tignanelli, H. L.; Vazquez, R. A.; Mostaccio, C.; Gordillo, S.; Plastino, A.
1990-11-01
RESUMEN. Presentamos una metodologia de analisis de la homogeneidad a partir de la Teoria de la Informaci6n, aplicable a muestras de datos observacionales. ABSTRACT:Standard concepts that underlie Information Theory are employed in order design a methodology that enables one to analyze the homogeneity of a given data sample. Key : DATA ANALYSIS
Strictly homogeneous laterally complete modules
Chilin, V. I.; Karimov, J. A.
2016-03-01
Let A be a laterally complete commutative regular algebra and X be a laterally complete A-module. In this paper we introduce a notion of homogeneous and strictly homogeneous A-modules. It is proved that any homogeneous A-module is strictly homogeneous A-module, if the Boolean algebra of all idempotents in A is multi-σ-finite.
Synthesis of silica nanosphere from homogeneous and heterogeneous systems
N Venkatathri
2007-12-01
Silica nanosphere was synthesized using homogeneous and heterogeneous systems, respectively. In homogeneous system, silica spheres were synthesized without cetyltrimethylammonium bromide (CTABr), which gave bimodal particle size and lower yield (77%). To improve the yield, CTABr was added and found that the yield was very high (100%). The particle was in nm range, but the particle sizes are bimodal. To avoid it, reaction in heterogeneous system using CTABr was carried out. Nanosized silica sphere with uniform size (yield, 94%) was observed. Homogeneous system contains a mixture of ethanol, water, aqueous ammonia and tetraethylorthosilicate (TEOS). In the case of heterogeneous system, only ethanol was absent.
Homogenous finitary symmetric groups
Otto. H. Kegel
2015-03-01
Full Text Available We characterize strictly diagonal type of embeddings of finitary symmetric groups in terms of cardinality and the characteristic. Namely, we prove the following. Let kappa be an infinite cardinal. If G=underseti=1stackrelinftybigcupG i , where G i =FSym(kappan i , (H=underseti=1stackrelinftybigcupH i , where H i =Alt(kappan i , is a group of strictly diagonal type and xi=(p 1 ,p 2 ,ldots is an infinite sequence of primes, then G is isomorphic to the homogenous finitary symmetric group FSym(kappa(xi (H is isomorphic to the homogenous alternating group Alt(kappa(xi , where n 0 =1,n i =p 1 p 2 ldotsp i .
Homogeneous group, research, institution
Francesca Natascia Vasta
2014-09-01
Full Text Available The work outlines the complex connection among empiric research, therapeutic programs and host institution. It is considered the current research state in Italy. Italian research field is analyzed and critic data are outlined: lack of results regarding both the therapeutic processes and the effectiveness of eating disorders group analytic treatment. The work investigates on an eating disorders homogeneous group, led into an eating disorder outpatient service. First we present the methodological steps the research is based on including the strong connection among theory and clinical tools. Secondly clinical tools are described and the results commented. Finally, our results suggest the necessity of validating some more specifical hypothesis: verifying the relationship between clinical improvement (sense of exclusion and painful emotions reduction and specific group therapeutic processes; verifying the relationship between depressive feelings, relapses and transition trough a more differentiated groupal field.Keywords: Homogeneous group; Eating disorders; Institutional field; Therapeutic outcome
Homogen Mur - et udviklingsprojekt
Dahl, Torben; Beim, Anne; Sørensen, Peter; Nørbak, Charlotte; Nicolaisen, Ole
1997-01-01
Mølletorvet i Slagelse er det første byggeri i Danmark, hvor ydervæggen er udført af homogene bærende og isolerende teglblokke. Byggeriet viser en række af de muligheder, der både med hensyn til konstruktioner, energiforhold og arkitektur ligger i anvendelsen af homogent blokmurværk.......Mølletorvet i Slagelse er det første byggeri i Danmark, hvor ydervæggen er udført af homogene bærende og isolerende teglblokke. Byggeriet viser en række af de muligheder, der både med hensyn til konstruktioner, energiforhold og arkitektur ligger i anvendelsen af homogent blokmurværk....
Blau, Matthias; O'Loughlin, Martin
2002-01-01
Motivated by the search for potentially exactly solvable time-dependent string backgrounds, we determine all homogeneous plane wave (HPW) metrics in any dimension and find one family of HPWs with geodesically complete metrics and another with metrics containing null singularities. The former generalises both the Cahen-Wallach (constant $A_{ij}$) metrics to time-dependent HPWs, $A_{ij}(t)$, and the Ozsvath-Sch\\"ucking anti-Mach metric to arbitrary dimensions. The latter is a generalisation of ...
Homogenization of dislocation dynamics
In this paper we consider the dynamics of dislocations with the same Burgers vector, contained in the same glide plane, and moving in a material with periodic obstacles. We study two cases: i) the particular case of parallel straight dislocations and ii) the general case of curved dislocations. In each case, we perform rigorously the homogenization of the dynamics and predict the corresponding effective macroscopic elasto-visco-plastic flow rule.
Homogenization of dislocation dynamics
El Hajj, Ahmad; Ibrahim, Hassan; Monneau, Regis, E-mail: elhajj@cermics.enpc.fr, E-mail: ibrahim@cermics.enpc.fr, E-mail: monneau@cermics.enpc.fr [CERMICS, ENPC, 6 and 8 avenue Blaise Pascal, Cite Descartes, Champs sur Marne, 77455 Marne-la-Valle Cedex 2 (France)
2009-07-15
In this paper we consider the dynamics of dislocations with the same Burgers vector, contained in the same glide plane, and moving in a material with periodic obstacles. We study two cases: i) the particular case of parallel straight dislocations and ii) the general case of curved dislocations. In each case, we perform rigorously the homogenization of the dynamics and predict the corresponding effective macroscopic elasto-visco-plastic flow rule.
Figueroa-O'Farrill, José
2015-01-01
Motivated by the search for new gravity duals to M2 branes with $N>4$ supersymmetry --- equivalently, M-theory backgrounds with Killing superalgebra $\\mathfrak{osp}(N|4)$ for $N>4$ --- we classify (except for a small gap) homogeneous M-theory backgrounds with symmetry Lie algebra $\\mathfrak{so}(n) \\oplus \\mathfrak{so}(3,2)$ for $n=5,6,7$. We find that there are no new backgrounds with $n=6,7$ but we do find a number of new (to us) backgrounds with $n=5$. All backgrounds are metrically products of the form $\\operatorname{AdS}_4 \\times P^7$, with $P$ riemannian and homogeneous under the action of $\\operatorname{SO}(5)$, or $S^4 \\times Q^7$ with $Q$ lorentzian and homogeneous under the action of $\\operatorname{SO}(3,2)$. At least one of the new backgrounds is supersymmetric (albeit with only $N=2$) and we show that it can be constructed from a supersymmetric Freund--Rubin background via a Wick rotation. Two of the new backgrounds have only been approximated numerically.
Deng, Shaoqiang
2012-01-01
"Homogeneous Finsler Spaces" is the first book to emphasize the relationship between Lie groups and Finsler geometry, and the first to show the validity in using Lie theory for the study of Finsler geometry problems. This book contains a series of new results obtained by the author and collaborators during the last decade. The topic of Finsler geometry has developed rapidly in recent years. One of the main reasons for its surge in development is its use in many scientific fields, such as general relativity, mathematical biology, and phycology (study of algae). This monograph introduc
Blau, Matthias E-mail: mblau@ictp.trieste.it; O' Loughlin, Martin E-mail: loughlin@sissa.it
2003-03-24
Motivated by the search for potentially exactly solvable time-dependent string backgrounds, we determine all homogeneous plane wave (HPW) metrics in any dimension and find one family of HPWs with geodesically complete metrics and another with metrics containing null singularities. The former generalises both the Cahen-Wallach (constant A{sub ij}) metrics to time-dependent HPWs, A{sub ij}(x{sup +}), and the Ozsvath-Schuecking anti-Mach metric to arbitrary dimensions. The latter is a generalisation of the known homogeneous metrics with A{sub ij}{approx}1/(x{sup +}){sup 2} to a more complicated time-dependence. We display these metrics in various coordinate systems, show how to embed them into string theory, and determine the isometry algebra of a general HPW and the associated conserved charges. We review the Lewis-Riesenfeld theory of invariants of time-dependent harmonic oscillators and show how it can be deduced from the geometry of plane waves. We advocate the use of the invariant associated with the extra (timelike) isometry of HPWs for lightcone quantisation, and illustrate the procedure in some examples.
Motivated by the search for potentially exactly solvable time-dependent string backgrounds, we determine all homogeneous plane wave (HPW) metrics in any dimension and find one family of HPWs with geodesically complete metrics and another with metrics containing null singularities. The former generalises both the Cahen-Wallach (constant Aij) metrics to time-dependent HPWs, Aij(x+), and the Ozsvath-Schuecking anti-Mach metric to arbitrary dimensions. The latter is a generalisation of the known homogeneous metrics with Aij∼1/(x+)2 to a more complicated time-dependence. We display these metrics in various coordinate systems, show how to embed them into string theory, and determine the isometry algebra of a general HPW and the associated conserved charges. We review the Lewis-Riesenfeld theory of invariants of time-dependent harmonic oscillators and show how it can be deduced from the geometry of plane waves. We advocate the use of the invariant associated with the extra (timelike) isometry of HPWs for lightcone quantisation, and illustrate the procedure in some examples
Blau, Matthias; Blau, Matthias; Loughlin, Martin O'
2003-01-01
Motivated by the search for potentially exactly solvable time-dependent string backgrounds, we determine all homogeneous plane wave (HPW) metrics in any dimension and find one family of HPWs with geodesically complete metrics and another with metrics with null singularities. The former generalises both the Cahen-Wallach (constant $A_{ij}$) metrics to time-dependent HPWs, $A_{ij}(t)$, and the Ozsvath-Sch\\"ucking anti-Mach metric to arbitrary dimensions. The latter is a generalisation of the known homogeneous metrics with $A_{ij}\\sim 1/t^2$ to a more complicated time-dependence. We display these metrics in various coordinate systems, show how to embed them into string theory, and determine the isometry algebra of a general HPW and the associated conserved charges. We review the Lewis-Riesenfeld theory of invariants of time-dependent harmonic oscillators and show how it can be deduced from the geometry of plane waves. We advocate the use of the invariant associated with the extra (timelike) isometry of HPWs for ...
BWXT Services medical isotope production system status
BWXT Services, Inc. (BWXS) a subsidiary of BWX Technologies, Inc., one of the Babcock and Wilcox companies, has for some years conducted small scale development of its patented uranyl nitrate Medical Isotope Production System (MIPS). This application of an Aqueous Homogeneous Reactor (AHR) for isotope production was invented by BWXT's Dr. Russell M. Ball in 1997. The MIPS approach targets commercial scale production of medical isotopes, primarily 99Mo, used to supply 99mTc for diagnostic imaging purposes, using a Low Enriched Uranium (LEU) salt solution as the fuel/target. Recent heightened emphasis on controlling use of Highly Enriched Uranium (HEU) throughout the world in support of nuclear non-proliferation goals has motivated increased commercial interest in this safe and cost effective technology. Conceptual designs for commercial application have been developed and efforts are under way to establish a partnership with an established pharmaceutical firm familiar with current 99Mo production technology and operating practice. (author)
Homogenization of resonant chiral metamaterials
Andryieuski, Andrei; Menzel, C.; Rockstuhl, Carsten;
2010-01-01
Homogenization of metamaterials is a crucial issue as it allows to describe their optical response in terms of effective wave parameters as, e.g., propagation constants. In this paper we consider the possible homogenization of chiral metamaterials. We show that for meta-atoms of a certain size a...... critical density exists above which increasing coupling between neighboring meta-atoms prevails a reasonable homogenization. On the contrary, a dilution in excess will induce features reminiscent to photonic crystals likewise prevailing a homogenization. Based on Bloch mode dispersion we introduce an...... analytical criterion for performing the homogenization and a tool to predict the homogenization limit. We show that strong coupling between meta-atoms of chiral metamaterials may prevent their homogenization at all....
Chemical reactions at aqueous interfaces
Vecitis, Chad David
2009-12-01
Interfaces or phase boundaries are a unique chemical environment relative to individual gas, liquid, or solid phases. Interfacial reaction mechanisms and kinetics are often at variance with homogeneous chemistry due to mass transfer, molecular orientation, and catalytic effects. Aqueous interfaces are a common subject of environmental science and engineering research, and three environmentally relevant aqueous interfaces are investigated in this thesis: 1) fluorochemical sonochemistry (bubble-water), 2) aqueous aerosol ozonation (gas-water droplet), and 3) electrolytic hydrogen production and simultaneous organic oxidation (water-metal/semiconductor). Direct interfacial analysis under environmentally relevant conditions is difficult, since most surface-specific techniques require relatively `extreme' conditions. Thus, the experimental investigations here focus on the development of chemical reactors and analytical techniques for the completion of time/concentration-dependent measurements of reactants and their products. Kinetic modeling, estimations, and/or correlations were used to extract information on interfacially relevant processes. We found that interfacial chemistry was determined to be the rate-limiting step to a subsequent series of relatively fast homogeneous reactions, for example: 1) Pyrolytic cleavage of the ionic headgroup of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) adsorbed to cavitating bubble-water interfaces during sonolysis was the rate-determining step in transformation to their inorganic constituents carbon monoxide, carbon dioxide, and fluoride; 2) ozone oxidation of aqueous iodide to hypoiodous acid at the aerosol-gas interface is the rate-determining step in the oxidation of bromide and chloride to dihalogens; 3) Electrolytic oxidation of anodic titanol surface groups is rate-limiting for the overall oxidation of organics by the dichloride radical. We also found chemistry unique to the interface, for example: 1
Homogeneous nucleation of methane hydrates: unrealistic under realistic conditions.
Knott, Brandon C; Molinero, Valeria; Doherty, Michael F; Peters, Baron
2012-12-01
Methane hydrates are ice-like inclusion compounds with importance to the oil and natural gas industry, global climate change, and gas transportation and storage. The molecular mechanism by which these compounds form under conditions relevant to industry and nature remains mysterious. To understand the mechanism of methane hydrate nucleation from supersaturated aqueous solutions, we performed simulations at controlled and realistic supersaturation. We found that critical nuclei are extremely large and that homogeneous nucleation rates are extremely low. Our findings suggest that nucleation of methane hydrates under these realistic conditions cannot occur by a homogeneous mechanism. PMID:23148735
Chae, Bora; Cakiner-Egilmez, Tulay; Desai, Manishi
2013-01-01
Glaucoma is a common eye condition that affects millions of individuals worldwide, making it the second-leading cause of blindness. Because glaucoma is associated with increased IOP level, the primary goal in treatment of glaucoma includes lowering IOP to prevent further progression of the disease. While various surgical interventions exist, medical therapy is currently the first line of treatment. Medical treatment of glaucoma includes topical beta-blockers, alpha-2 agonists, prostaglandins, parasympathomimetics and CAIs. Anti-glaucoma agents help reduce IOP by affecting the production of aqueous humor or increasing the outflow of aqueous through the trabecular or uveoscleral pathway. Choosing an appropriate medical regimen can be challenging and various factors such as efficacy, safety, cost and patient compliance must be considered. First-line treatment is often topical beta-blockers or prostaglandin analogs. However, beta-blocking agents can be associated with systemic side effects and need to be used cautiously in patients with serious concomitant cardiopulmonary disease. Alpha-2 agonists and parasympathomimetics are often considered second- or third-line treatment options but good adjunctive agents. Oral CAIs are often indicated for patients with elevated IOP in an acute setting or for patients resistant to other glaucoma medications and patients who are not good surgical candidates. PMID:23505792
Homogeneous Spaces and Equivariant Embeddings
Timashev, DA
2011-01-01
Homogeneous spaces of linear algebraic groups lie at the crossroads of algebraic geometry, theory of algebraic groups, classical projective and enumerative geometry, harmonic analysis, and representation theory. By standard reasons of algebraic geometry, in order to solve various problems on a homogeneous space it is natural and helpful to compactify it keeping track of the group action, i.e. to consider equivariant completions or, more generally, open embeddings of a given homogeneous space. Such equivariant embeddings are the subject of this book. We focus on classification of equivariant em
Treatment of Pesticides in Wastewater by Heterogeneous and Homogeneous Photocatalysis
Catalina Daniela Stan
2012-01-01
Full Text Available The effect of different heterogeneous and homogeneous photocatalytic systems on the oxidative degradation of mepiquat chloride in aqueous solutions was investigated. In the case of heterogeneous reactions, the influence of five factors was studied: the type of catalyst, photocatalyst concentration, pH, pesticide concentration, and the presence of H2O2 and/or Fe3+. For homogeneous catalysis, other factors were studied: the oxidising agent and the light source. Nearly complete degradation of mepiquat chloride was obtained after about 180 minutes in the presence of an acid medium (pH3 using a UV-A lamp and TiO2P-25 catalyst (0.5 g/L, for an initial pesticide concentration of 10 ppm. Degradation rates corresponding to homogeneous photocatalysis were lower compared to those corresponding to the use of TiO2 as the photocatalyst.
... Facebook Twitter Google Plus Email Print this page Flow of Aqueous Humor Most, but not all, forms ... aqueous humor) produced by the eye's ciliary body flows out freely (follow blue arrow). Aqueous humor flows ...
Perin, Chloé
2010-01-01
We show that any non abelian free group $\\F$ is strongly $\\aleph_0$-homogeneous, i.e. that finite tuples of elements which satisfy the same first-order properties are in the same orbit under $\\Aut(\\F)$. We give a characterization of elements in finitely generated groups which have the same first-order properties as a primitive element of the free group. We deduce as a consequence that most hyperbolic surface groups are not $\\aleph_0$-homogeneous.
Albedo matrices in assembly homogenization
Relations between albedo matrices and a set of diffusion coefficients for a homogeneous medium is considered. The possibility to determine albedo matrices in a homogeneous diffusion medium on the basis of diffusion constants is proved. Relations for the reverse calculation of a set of equivalent diffusion constants using the albedo matrices are obtained. These relations can be used to check the albedo matrices determined by a numerical method. 10 refs.; 2 tabs
Optimization of 200 kW medical isotope production reactor design
One of the primary methods of producing medical isotopes such as 99Mo and 131I is by irradiating uranium targets in heterogeneous reactors. Homogeneous aqueous reactors present a potential alternative to medical isotope production. In response to the global demand for medical isotopes, a concept design of the 200 kW medical isotope production reactor (MIPR) was accomplished by Nuclear Power Institute of China in 2000. Further R and D work was completed in subsequent years, including the optimization of design, reactor thermohydraulic experiments, gas circulation system experiments, etc. Compared with the normal isotope production method such as target irradiation, the MIPR can produce more types of isotope at lower cost and with less radioactive waste generation. (author)
Homogenization of neutronic diffusion models
In order to study and simulate nuclear reactor cores, one needs to access the neutron distribution in the core. In practice, the description of this density of neutrons is given by a system of diffusion equations, coupled by non differential exchange terms. The strong heterogeneity of the medium constitutes a major obstacle to the numerical computation of this models at reasonable cost. Homogenization appears as compulsory. Heuristic methods have been developed since the origin by nuclear physicists, under a periodicity assumption on the coefficients. They consist in doing a fine computation one a single periodicity cell, to solve the system on the whole domain with homogeneous coefficients, and to reconstruct the neutron density by multiplying the solutions of the two computations. The objectives of this work are to provide mathematically rigorous basis to this factorization method, to obtain the exact formulas of the homogenized coefficients, and to start on geometries where two periodical medium are placed side by side. The first result of this thesis concerns eigenvalue problem models which are used to characterize the state of criticality of the reactor, under a symmetry assumption on the coefficients. The convergence of the homogenization process is proved, and formulas of the homogenized coefficients are given. We then show that without symmetry assumptions, a drift phenomenon appears. It is characterized by the mean of a real Bloch wave method, which gives the homogenized limit in the general case. These results for the critical problem are then adapted to the evolution model. Finally, the homogenization of the critical problem in the case of two side by side periodic medium is studied on a one dimensional on equation model. (authors)
Toxicological studies of aqueous extract of Acacia nilotica root
Alli Lukman Adewale
2015-03-01
Full Text Available Acacia nilotica is a widely used plant in traditional medical practice in Northern Nigeria and many African countries. The aim of this study was to determine the toxicological effects of a single dose (acute and of repeated doses (sub-acute administration of aqueous extract of A. nilotica root in rodents, following our earlier study on antiplasmodial activity. In the acute toxicity test, three groups of Swiss albino mice were orally administered aqueous extract of A. nilotica (50, 300 and 2000 mg/kg body weight and signs of toxicity were observed daily for 14 days. In the sub-acute toxicity study, four groups of 12 rats (6 male and 6 female were used. Group 1 received 10 ml/kg b.w distilled water (control, while groups 2, 3 and 4 received 125, 250 and 500 mg/kg b.w of the extract, respectively, for 28 consecutive days by oral gavage. Signs of toxicity/mortality, food and water intake and body weight changes were observed. Biochemical parameters were analysed in both plasma and liver homogenate. In the acute and sub-acute toxicity studies, the extract did not cause mortality. A significant reduction in the activity of lactate dehydrogenase was observed at 250 and 500 mg/kg b.w, while alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase activities were significantly higher than control values at 500 mg/kg b.w. The aqueous extract of A. nilotica was found to be safe in single dose administration in mice but repeated administration of doses higher than 250 mg/kg b.w of the extract for 28 days in rats may cause hepatotoxicity.
Genetic Homogenization of Composite Materials
P. Tobola
2009-04-01
Full Text Available The paper is focused on numerical studies of electromagnetic properties of composite materials used for the construction of small airplanes. Discussions concentrate on the genetic homogenization of composite layers and composite layers with a slot. The homogenization is aimed to reduce CPU-time demands of EMC computational models of electrically large airplanes. First, a methodology of creating a 3-dimensional numerical model of a composite material in CST Microwave Studio is proposed focusing on a sufficient accuracy of the model. Second, a proper implementation of a genetic optimization in Matlab is discussed. Third, an association of the optimization script and a simplified 2-dimensional model of the homogeneous equivalent model in Comsol Multiphysics is proposed considering EMC issues. Results of computations are experimentally verified.
Horn, Anna Frisenfeldt; Barouh, Nathalie; Nielsen, Nina Skall;
2013-01-01
The oxidative stability of 10 % fish oil-in-water emulsions was investigated for emulsions prepared under different homogenization conditions. Homogenization was conducted at two different pressures (5 or 22.5 MPa), and at two different temperatures (22 and 72 °C). Milk proteins were used as the...... decreased the oxidative stability of emulsions with α-lactalbumin and β-lactoglobulin. For both types of emulsions the partitioning of proteins between the interface and the aqueous phase appeared to be important for the oxidative stability. The effect of pre-heating the aqueous phase with the milk proteins...
On $\\delta$-homogeneous Riemannian manifolds
Berestovskii, V. N.; Nikonorov, Yu. G.
2006-01-01
We study in this paper previously defined by V.N. Berestovskii and C.P. Plaut $\\delta$-homogeneous spaces in the case of Riemannian manifolds. Every such manifold has non-negative sectional curvature. The universal covering of any $\\delta$-homogeneous Riemannian manifolds is itself $\\delta$-homogeneous. In turn, every simply connected Riemannian $\\delta$-homogeneous manifold is a direct metric product of an Euclidean space and compact simply connected indecomposable homogeneous manifolds; all...
Mayor, G.; Mesiar, Radko; Torrens, J.
2008-01-01
Roč. 44, č. 6 (2008), s. 745-756. ISSN 0023-5954 R&D Projects: GA ČR GA402/08/0618 Institutional research plan: CEZ:AV0Z10750506 Keywords : copula * diagonal section * quasi-homegeneity Subject RIV: BA - General Mathematics Impact factor: 0.281, year: 2008 http://library.utia.cas.cz/separaty/2008/E/mesiar-on quasi-homogeneous copulas.pdf
Self-consolidating concrete homogeneity
Jarque, J. C.; Parra, C.; Valcuende, M.O.
2007-01-01
Concrete instability may lead to the non-uniform distribution of its properties. The homogeneity of self-consolidating concrete in vertically cast members was therefore explored in this study, analyzing both resistance to segregation and pore structure uniformity. To this end, two series of concretes were prepared, self-consolidating and traditional vibrated materials, with different w/c ratios and types of cement. The results showed that selfconsolidating concretes exhibit high resistance to...
Homogenized Elasticity of Martensitic Microstructures
Seiner, Hanuš; Glatz, Ondřej; Landa, Michal
Freiburg : Fraunhofer Verlag, 2010 - (Gumbsch, P.; van der Giessen, E.), s. 546-549 ISBN 978-3-8396-0166-2. [International Conference on Multiscale Materials Modelling MMM2010 /5./. Freiburrg (DE), 04.10.2010-08.10.2010] R&D Projects: GA ČR GP202/09/P164 Institutional research plan: CEZ:AV0Z20760514 Keywords : martensitic transformations * homogenization procedure * 1st order laminate Subject RIV: BM - Solid Matter Physics ; Magnetism
Homogeneous determination of maximum magnitude
Meletti, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; D'Amico, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; Martinelli, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia
2010-01-01
This deliverable represents the result of the activities performed by a working group at INGV. The main object of the Task 3.5 is defined in the Description of Work. This task will produce a homogeneous assessment (possibly multiple models) of the distribution of the expected Maximum Magnitude for earthquakes expected in various tectonic provinces of Europe, to serve as input for the computation and validation of seismic hazard. This goal will be achieved by combining input from earthqu...
Homogenization in elasto-plasticity
Orlik, J
2008-01-01
The theory of the two-scale convergence was applied to homogenization of elasto-plastic composites with a periodic structure and exponential hardening law. The theory is based on the fact that the elastic as well as the plastic part of the stress field two-scale converges to a limit, which is factorized by parts, depending only on macroscopic characteristics, represented in terms of corresponding part of the homogenised stress tensor and only on stress concentration tensor, related to the mic...
Properties of isometrically homogeneous curves
Donne, Enrico Le
2011-01-01
This paper is devoted to the study of isometrically homogeneous spaces from the view point of metric geometry. Mainly we focus on those spaces that are homeomorphic to lines. We show that one can reduce the study to those distances on $\\R$ that are translation invariant. We study possible values of various metric dimensions of such spaces. One of the main results is the equivalence of two properties: the first one is linear connectedness and the second one is 1-dimensionality, with respect to Nagata dimension. Several concrete pathological examples are provided.
Homogenization scheme for acoustic metamaterials
Yang, Min
2014-02-26
We present a homogenization scheme for acoustic metamaterials that is based on reproducing the lowest orders of scattering amplitudes from a finite volume of metamaterials. This approach is noted to differ significantly from that of coherent potential approximation, which is based on adjusting the effective-medium parameters to minimize scatterings in the long-wavelength limit. With the aid of metamaterials’ eigenstates, the effective parameters, such as mass density and elastic modulus can be obtained by matching the surface responses of a metamaterial\\'s structural unit cell with a piece of homogenized material. From the Green\\'s theorem applied to the exterior domain problem, matching the surface responses is noted to be the same as reproducing the scattering amplitudes. We verify our scheme by applying it to three different examples: a layered lattice, a two-dimensional hexagonal lattice, and a decorated-membrane system. It is shown that the predicted characteristics and wave fields agree almost exactly with numerical simulations and experiments and the scheme\\'s validity is constrained by the number of dominant surface multipoles instead of the usual long-wavelength assumption. In particular, the validity extends to the full band in one dimension and to regimes near the boundaries of the Brillouin zone in two dimensions.
ISOTOPE METHODS IN HOMOGENEOUS CATALYSIS.
BULLOCK,R.M.; BENDER,B.R.
2000-12-01
The use of isotope labels has had a fundamentally important role in the determination of mechanisms of homogeneously catalyzed reactions. Mechanistic data is valuable since it can assist in the design and rational improvement of homogeneous catalysts. There are several ways to use isotopes in mechanistic chemistry. Isotopes can be introduced into controlled experiments and followed where they go or don't go; in this way, Libby, Calvin, Taube and others used isotopes to elucidate mechanistic pathways for very different, yet important chemistries. Another important isotope method is the study of kinetic isotope effects (KIEs) and equilibrium isotope effect (EIEs). Here the mere observation of where a label winds up is no longer enough - what matters is how much slower (or faster) a labeled molecule reacts than the unlabeled material. The most careti studies essentially involve the measurement of isotope fractionation between a reference ground state and the transition state. Thus kinetic isotope effects provide unique data unavailable from other methods, since information about the transition state of a reaction is obtained. Because getting an experimental glimpse of transition states is really tantamount to understanding catalysis, kinetic isotope effects are very powerful.
Significance tests and sample homogeneity loophole
Kupczynski, Marian
2015-01-01
In their recent comment, published in Nature, Jeffrey T.Leek and Roger D.Peng discuss how P-values are widely abused in null hypothesis significance testing . We agree completely with them and in this short comment we discuss the importance of sample homogeneity tests. No matter with how much scrutiny data are gathered if homogeneity tests are not performed the significance tests suffer from sample homogeneity loophole and the results may not be trusted. For example sample homogeneity loophol...
Improving homogeneity by dynamic speed limit systems.
Nes, N. van Brandenberg, S. & Twisk, D.A.M.
2010-01-01
Homogeneity of driving speeds is an important variable in determining road safety; more homogeneous driving speeds increase road safety. This study investigates the effect of introducing dynamic speed limit systems on homogeneity of driving speeds. A total of 46 subjects twice drove a route along 12
The homogeneous geometries of real hyperbolic space
Castrillón López, Marco; Gadea, Pedro Martínez; Swann, Andrew Francis
We describe the holonomy algebras of all canonical connections of homogeneous structures on real hyperbolic spaces in all dimensions. The structural results obtained then lead to a determination of the types, in the sense of Tricerri and Vanhecke, of the corresponding homogeneous tensors. We use...... our analysis to show that the moduli space of homogeneous structures on real hyperbolic space has two connected components....
Projective duality and homogeneous spaces
Tevelev, E A
2006-01-01
Projective duality is a very classical notion naturally arising in various areas of mathematics, such as algebraic and differential geometry, combinatorics, topology, analytical mechanics, and invariant theory, and the results in this field were until now scattered across the literature. Thus the appearance of a book specifically devoted to projective duality is a long-awaited and welcome event. Projective Duality and Homogeneous Spaces covers a vast and diverse range of topics in the field of dual varieties, ranging from differential geometry to Mori theory and from topology to the theory of algebras. It gives a very readable and thorough account and the presentation of the material is clear and convincing. For the most part of the book the only prerequisites are basic algebra and algebraic geometry. This book will be of great interest to graduate and postgraduate students as well as professional mathematicians working in algebra, geometry and analysis.
... womb (uterus). There are different types of medical abortions: Therapeutic medical abortion is done because the woman has ... Therapeutic medical abortion; Elective medical abortion; Induced abortion; Nonsurgical abortion
Polyurethane phantoms with homogeneous and nearly homogeneous optical properties
Keränen, Ville T.; Mäkynen, Anssi J.; Dayton, Amanda L.; Prahl, Scott A.
2010-02-01
Phantoms with controlled optical properties are often used for calibration and standardization. The phantoms are typically prepared by adding absorbers and scatterers to a clear host material. It is usually assumed that the scatterers and absorbers are uniformly dispersed within the medium. To explore the effects of this assumption, we prepared paired sets of polyurethane phantoms (both with identical masses of absorber, India ink and scatterer, titanium dioxide). Polyurethane phantoms were made by mixing two polyurethane parts (a and b) together and letting them cure in a polypropylene container. The mixture was degassed before curing to ensure a sample without bubbles. The optical properties were controlled by mixing titanium dioxide or India ink into polyurethane part (a or b) before blending the parts together. By changing the mixing sequence, we could change the aggregation of the scattering and absorbing particles. Each set had one sample with homogeneously dispersed scatterers and absorbers, and a second sample with slightly aggregated scatterers or absorbers. We found that the measured transmittance could easily vary by a factor of twenty. The estimated optical properties (using the inverse adding-doubling method) indicate that when aggregation is present, the optical properties are no longer proportional to the concentrations of absorbers or scatterers.
Self-thinning and neutralizing thickened aqueous liquid
Lybarger, J.H.; Scheuerman, R.F.
1979-04-17
A thickened aqueous liquid is described for use in well treating processes, such as sand or gravel packing, fracturing, fluid-diverting, selective-plugging, fluid-displacing etc. The thickened aqueous liquid consists of an aqueous solution containing 1) an acid-reactive cellulosic water thickener in an amount ranging from 0.1 to 4% by weight of the solution to provide viscosities which at 80/sup 0/F range from 100 to 51,000 cp; 2) an amount and composition of substantially homogeneously distributed acidifying material sufficient to cause a significant decrease in the viscosity of the solution after a selected time-temperature exposure; and 3) an amount and composition of substantially homogeneously-distributed relatively slowly-reactive pH-increasing material sufficient to subsequently raise the pH of the solution to a selected relatively neutral value after an increased time. 10 claims.
Yoshio Kobayashi; Naomichi Takahashi; Takafumi Maeda; Takehiro Yonezawa; Kazuhiko Yamasaki
2015-01-01
The present work proposes a method to fabricate indium tin oxide (ITO) particles using precursor particles synthesized with a combination of a homogeneous precipitation method and a seeding technique, and it also describes their electronic conductivity properties. Seed nanoparticles were produced using a co-precipitation method with aqueous solutions of indium (III) chloride, tin (IV) chloride aqueous solution and sodium hydroxide. Three types of ITO nanoparticles were fabricated. The first t...
Homogeneous modes of cosmological instantons
We discuss the O(4) invariant perturbation modes of cosmological instantons. These modes are spatially homogeneous in Lorentzian spacetime and thus not relevant to density perturbations. But their properties are important in establishing the meaning of the Euclidean path integral. If negative modes are present, the Euclidean path integral is not well defined, but may nevertheless be useful in an approximate description of the decay of an unstable state. When gravitational dynamics is included, counting negative modes requires a careful treatment of the conformal factor problem. We demonstrate that for an appropriate choice of coordinate on phase space, the second order Euclidean action is bounded below for normalized perturbations and has a finite number of negative modes. We prove that there is a negative mode for many gravitational instantons of the Hawking-Moss or ColemanendashDe Luccia type, and discuss the associated spectral flow. We also investigate Hawking-Turok constrained instantons, which occur in a generic inflationary model. Implementing the regularization and constraint proposed by Kirklin, Turok and Wiseman, we find that those instantons leading to substantial inflation do not possess negative modes. Using an alternate regularization and constraint motivated by reduction from five dimensions, we find a negative mode is present. These investigations shed new light on the suitability of Euclidean quantum gravity as a potential description of our universe
Pharmaceutical Industry Oriented Homogeneous Catalysis
Zhang Xumu
2004-01-01
Chiral therapeutics already makes up over one-third of pharmaceutical drugs currently sold worldwide. This is a growing industry with global chiral drug sales for 2002 increasing by 12%to $160 billion (Technology Catalysts International) of a total drug market of $410bn. The increasing demand to produce enantiomerically pure pharmaceuticals, agrochemicals, flavors, and other fine chemicals has advanced the field of asymmetric catalytic technologies.We aim to become a high value technology provider and partner in the chiral therapeutics industry by offering proprietary catalysts, novel building blocks, and collaborative synthetic solutions. In decade, we have developed a set of novel chiral homogeneous phosphorus ligands such as Binaphane, Me-KetalPhos, TangPhos, f-Binaphane, Me-f-KetalPhos, C4TunePhos and Binapine,which we called Chiral Ligand ToolKit. Complementing the ToolKit, (R, S, S, R)-DIOP*, T-Phos,o-BIPHEP, o-BINAPO and FAP were added recently[1].These ligands can be applied to a broad variety of drug structural features by asymmetric hydrogenation of dehydroamino acid derivatives, enamides, unsatisfied acids and esters, ketones,beta ketoesters, imines and cyclic imines. And ligand FAP had been apllied succefully in allylic alkylation and [3+2] cycloaddition.
A Class of Homogeneous Einstein Manifolds
Yifang KANG; Ke LIANG
2006-01-01
A Riemannian manifold (M,g) is called Einstein manifold if its Ricci tensor satisfies r=c·g for some constant c. General existence results are hard to obtain,e.g., it is as yet unknown whether every compact manifold admits an Einstein metric. A natural approach is to impose additional homogeneous assumptions. M. Y. Wang and W. Ziller have got some results on compact homogeneous space G/H. They investigate standard homogeneous metrics, the metric induced by Killing form on G/H, and get some classification results. In this paper some more general homogeneous metrics on some homogeneous space G/H are studies, and a necessary and sufficient condition for this metric to be Einstein is given. The authors also give some examples of Einstein manifolds with non-standard homogeneous metrics.
Model Misspecification: Finite Mixture or Homogeneous?
Tarpey, Thaddeus; Yun, Dong; Petkova, Eva
2008-01-01
A common problem in statistical modelling is to distinguish between finite mixture distribution and a homogeneous non-mixture distribution. Finite mixture models are widely used in practice and often mixtures of normal densities are indistinguishable from homogenous non-normal densities. This paper illustrates what happens when the EM algorithm for normal mixtures is applied to a distribution that is a homogeneous non-mixture distribution. In particular, a population-based EM algorithm for fi...
A literature review on biotic homogenization
Guangmei Wang; Jingcheng Yang; Chuangdao Jiang; Hongtao Zhao; Zhidong Zhang
2009-01-01
Biotic homogenization is the process whereby the genetic, taxonomic and functional similarity of two or more biotas increases over time. As a new research agenda for conservation biogeography, biotic homogenization has become a rapidly emerging topic of interest in ecology and evolution over the past decade. However, research on this topic is rare in China. Herein, we introduce the development of the concept of biotic homogenization, and then discuss methods to quantify its three components (...
The Homogeneity Scale of the universe
Ntelis, Pierros
2016-01-01
In this study, we probe the cosmic homogeneity with the BOSS CMASS galaxy sample in the redshift region of $0.43 < z < 0.7$. We use the normalised counts-in-spheres estimator $\\mathcal{N}(
Self-consolidating concrete homogeneity
Jarque, J. C.
2007-08-01
Full Text Available Concrete instability may lead to the non-uniform distribution of its properties. The homogeneity of self-consolidating concrete in vertically cast members was therefore explored in this study, analyzing both resistance to segregation and pore structure uniformity. To this end, two series of concretes were prepared, self-consolidating and traditional vibrated materials, with different w/c ratios and types of cement. The results showed that selfconsolidating concretes exhibit high resistance to segregation, albeit slightly lower than found in the traditional mixtures. The pore structure in the former, however, tended to be slightly more uniform, probably as a result of less intense bleeding. Such concretes are also characterized by greater bulk density, lower porosity and smaller mean pore size, which translates into a higher resistance to pressurized water. For pore diameters of over about 0.5 Î¼m, however, the pore size distribution was found to be similar to the distribution in traditional concretes, with similar absorption rates.En este trabajo se estudia la homogeneidad de los hormigones autocompactantes en piezas hormigonadas verticalmente, determinando su resistencia a la segregación y la uniformidad de su estructura porosa, dado que la pérdida de estabilidad de una mezcla puede conducir a una distribución no uniforme de sus propiedades. Para ello se han fabricado dos tipos de hormigones, uno autocompactante y otro tradicional vibrado, con diferentes relaciones a/c y distintos tipos de cemento. Los resultados ponen de manifiesto que los hormigones autocompactantes presentan una buena resistencia a la segregación, aunque algo menor que la registrada en los hormigones tradicionales. A pesar de ello, su estructura porosa tiende a ser ligeramente más uniforme, debido probablemente a un menor sangrado. Asimismo, presentan una mayor densidad aparente, una menor porosidad y un menor tamaño medio de poro, lo que les confiere mejores
Bacterial Acclimation Inside an Aqueous Battery
Dong, Dexian; Chen, Baoling; Chen, P
2015-01-01
Specific environmental stresses may lead to induced genomic instability in bacteria, generating beneficial mutants and potentially accelerating the breeding of industrial microorganisms. The environmental stresses inside the aqueous battery may be derived from such conditions as ion shuttle, pH gradient, free radical reaction and electric field. In most industrial and medical applications, electric fields and direct currents are used to kill bacteria and yeast. However, the present study focu...
Investigations into homogenization of electromagnetic metamaterials
Clausen, Niels Christian Jerichau
This dissertation encompasses homogenization methods, with a special interest into their applications to metamaterial homogenization. The first method studied is the Floquet-Bloch method, that is based on the assumption of a material being infinite periodic. Its field can then be expanded in term...
CLASSIFICATION OF CUBIC PARAMETERIZED HOMOGENEOUS VECTOR FIELDS
Karnal H.Yasir; TANG Yun
2002-01-01
In this paper the cubic homogeneous parameterized vector fields are studied.The classification of the phase portrait near the critical point is presented. This classification is an extension of the result given by Takens to the cubic homogeneous parameterized vector fields with six parameters.
CLASSIFICATION OF CUBIC PARAMETERIZED HOMOGENEOUS VECTOR FIELDS
KamalH.Yasir; TNAGYun
2002-01-01
In this paper the cubic homogeneous parameterized vector fields are studied.The classification of the phase portrait near the critical point is presented.This classification is an extension of the result given by takens to the cubic homogeneous parameterized vector fields with six parameters.
s-Numbers sequences for homogeneous polynomials
Caliskan, Erhan; Rueda, Pilar
2015-01-01
We extend the well known theory of $s$-numbers of linear operators to homogeneous polynomials defined between Banach spaces. Approximation, Kolmogorov and Gelfand numbers of polynomials are introduced and some well-known results of the linear and multilinear settings are obtained for homogeneous polynomials.
DETERMINISTIC HOMOGENIZATION OF QUASILINEAR DAMPED HYPERBOLIC EQUATIONS
Gabriel Nguetseng; Hubert Nnang; Nils Svanstedt
2011-01-01
Deterministic homogenization is studied for quasilinear monotone hyperbolic problems with a linear damping term.It is shown by the sigma-convergence method that the sequence of solutions to a class of multi-scale highly oscillatory hyperbolic problems converges to the solution to a homogenized quasilinear hyperbolic problem.
Multilevel Monte Carlo Approaches for Numerical Homogenization
Efendiev, Yalchin R.
2015-10-01
In this article, we study the application of multilevel Monte Carlo (MLMC) approaches to numerical random homogenization. Our objective is to compute the expectation of some functionals of the homogenized coefficients, or of the homogenized solutions. This is accomplished within MLMC by considering different sizes of representative volumes (RVEs). Many inexpensive computations with the smallest RVE size are combined with fewer expensive computations performed on larger RVEs. Likewise, when it comes to homogenized solutions, different levels of coarse-grid meshes are used to solve the homogenized equation. We show that, by carefully selecting the number of realizations at each level, we can achieve a speed-up in the computations in comparison to a standard Monte Carlo method. Numerical results are presented for both one-dimensional and two-dimensional test-cases that illustrate the efficiency of the approach.
... this page: //medlineplus.gov/ency/patientinstructions/000899.htm Medical marijuana To use the sharing features on this ... have legalized marijuana for medical use. How Does Medical Marijuana Work? Medical marijuana may be: Smoked Vaporized ...
String pair production in non homogeneous backgrounds
Bolognesi, S.; Rabinovici, E.; Tallarita, G.
2016-04-01
We consider string pair production in non homogeneous electric backgrounds. We study several particular configurations which can be addressed with the Euclidean world-sheet instanton technique, the analogue of the world-line instanton for particles. In the first case the string is suspended between two D-branes in flat space-time, in the second case the string lives in AdS and terminates on one D-brane (this realizes the holographic Schwinger effect). In some regions of parameter space the result is well approximated by the known analytical formulas, either the particle pair production in non-homogeneous background or the string pair production in homogeneous background. In other cases we see effects which are intrinsically stringy and related to the non-homogeneity of the background. The pair production is enhanced already for particles in time dependent electric field backgrounds. The string nature enhances this even further. For spacial varying electrical background fields the string pair production is less suppressed than the rate of particle pair production. We discuss in some detail how the critical field is affected by the non-homogeneity, for both time and space dependent electric field backgrouds. We also comment on what could be an interesting new prediction for the small field limit. The third case we consider is pair production in holographic confining backgrounds with homogeneous and non-homogeneous fields.
Benchmarking homogenization algorithms for monthly data
V. K. C. Venema
2012-01-01
Full Text Available The COST (European Cooperation in Science and Technology Action ES0601: advances in homogenization methods of climate series: an integrated approach (HOME has executed a blind intercomparison and validation study for monthly homogenization algorithms. Time series of monthly temperature and precipitation were evaluated because of their importance for climate studies and because they represent two important types of statistics (additive and multiplicative. The algorithms were validated against a realistic benchmark dataset. The benchmark contains real inhomogeneous data as well as simulated data with inserted inhomogeneities. Random independent break-type inhomogeneities with normally distributed breakpoint sizes were added to the simulated datasets. To approximate real world conditions, breaks were introduced that occur simultaneously in multiple station series within a simulated network of station data. The simulated time series also contained outliers, missing data periods and local station trends. Further, a stochastic nonlinear global (network-wide trend was added.
Participants provided 25 separate homogenized contributions as part of the blind study. After the deadline at which details of the imposed inhomogeneities were revealed, 22 additional solutions were submitted. These homogenized datasets were assessed by a number of performance metrics including (i the centered root mean square error relative to the true homogeneous value at various averaging scales, (ii the error in linear trend estimates and (iii traditional contingency skill scores. The metrics were computed both using the individual station series as well as the network average regional series. The performance of the contributions depends significantly on the error metric considered. Contingency scores by themselves are not very informative. Although relative homogenization algorithms typically improve the homogeneity of temperature data, only the best ones improve
Self-thinning and neutralizing thickened aqueous liquid
Lybarger, J.H.; Scheuerman, R.F.
1975-07-01
A method is described for thickening water and then reducing the viscosity at a selected time. The thickened aqueous liquid contains (1) enough dissolved acid-reactive cellulosic water thickener to provide a selected viscosity, (2) an amount and composition of substantially homogeneously distributed acidifying material sufficient to cause a decrease in the viscosity of the solution after a selected time-temperature exposure, and (3) an amount and composition of substantially homogeneously distributed relatively slowly reactive pH-increasing material sufficient to raise the pH of the solution to a selected substantially neutral value after an additional time. (5 claims)
Higher Order Macro Coefficients in Periodic Homogenization
Conca, Carlos; San Martin, Jorge; Smaranda, Loredana; Vanninathan, Muthusamy
2011-09-01
A first set of macro coefficients known as the homogenized coefficients appear in the homogenization of PDE on periodic structures. If energy is increased or scale is decreased, these coefficients do not provide adequate approximation. Using Bloch decomposition, it is first realized that the above coefficients correspond to the lowest energy and the largest scale. This naturally paves the way to introduce other sets of macro coefficients corresponding to higher energies and lower scales which yield better approximation. The next task is to compare their properties with those of the homogenized coefficients. This article reviews these developments along with some new results yet to be published.
Higher Order Macro Coefficients in Periodic Homogenization
Conca, Carlos; San Martin, Jorge [Departamento de IngenierIa Matematica, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile and Centro de Modelamiento Matematico, UMR 2071 CNRS-UChile, Casilla 170/3 - Correo 3, Santiago (Chile); Smaranda, Loredana [Department of Mathematics, Faculty of Mathematics and Computer Science, University of Pitesti, 110040 Pitesti, Str. Targu din Vale Nr.1, Arges (Romania); Vanninathan, Muthusamy, E-mail: cconca@dim.uchile.cl, E-mail: jorge@dim.uchile.cl, E-mail: smaranda@dim.uchile.cl, E-mail: vanni@math.tifrbng.res.in [TIFR-CAM, Post Bag 6503, GKVK Post, Bangalore - 560065 (India)
2011-09-15
A first set of macro coefficients known as the homogenized coefficients appear in the homogenization of PDE on periodic structures. If energy is increased or scale is decreased, these coefficients do not provide adequate approximation. Using Bloch decomposition, it is first realized that the above coefficients correspond to the lowest energy and the largest scale. This naturally paves the way to introduce other sets of macro coefficients corresponding to higher energies and lower scales which yield better approximation. The next task is to compare their properties with those of the homogenized coefficients. This article reviews these developments along with some new results yet to be published.
Homogeneous phosphorus of silicon by neutron transmutation
The manufacture of high-voltage power semiconductors requires a homogeneous phosphorus doping of silicon within extremely narrow limits. It was the aim of the investigations to develop neutron irradiation as a means to homogeneously dope silicon with phosphorus on an industrial scale. Special attention was given to the selection of suitable reactor positions, the annealing of the irradiation damage, and the electrical properties of the devices. The experience with the application of neutron irradiated silicon for a wide spectrum of devices shows that expected homogeneity and aiming accuracy with respect to the doping can be reached with high reliability. (orig.) 891 ORU/orig. 892 MB
Three-dimensional homogeneous generalized Ricci solitons
Calvaruso, Giovanni
2015-01-01
We study three-dimensional generalized Ricci solitons, both in Riemannian and Lorentzian settings. We shall determine their homogeneous models, classifying left-invariant generalized Ricci solitons on three-dimensional Lie groups.
Homogeneous cosmological models in Yang's gravitation theory
Fennelly, A. J.; Pavelle, R.
1979-01-01
We present a dynamic, spatially homogeneous solution of Yang's pure space gravitational field equations which is non-Einsteinian. The predictions of this cosmological model seem to be at variance with observations.
Lie superalgebras with some homogeneous structures
Ayadi, Imen; Benayadi, Saïd
2010-01-01
We generalize to the case of Lie superalgebras the classical symplectic double extension of symplectic Lie algebras introduced in [2]. We use this concept to give an inductive description of nilpotent homogeneous-symplectic Lie superalgebras. Several examples are included to show the existence of homogeneous quadratic symplectic Lie superalgebras other than even-quadratic even-symplectic considered in [6]. We study the structures of even (resp. odd)-quadratic odd (resp. even)-symplectic Lie superalgebras and odd-quadratic odd-symplectic Lie superalgebras and we give its inductive descriptions in terms of quadratic generalized double extensions and odd quadratic generalized double extensions. This study complete the inductive descriptions of homogeneous quadratic symplectic Lie superalgebras started in [6]. Finally, we generalize to the case of homogeneous quadratic symplectic Lie superargebras some relations between even-quadratic even-symplectic Lie superalgebras and Manin superalgebras established in [6].
On homogeneous Einstein (α , β) -metrics
Yan, Zaili; Deng, Shaoqiang
2016-05-01
In this paper, we study homogeneous Einstein (α , β) -metrics. First, we deduce a formula for Ricci curvature of a homogeneous (α , β) -metric. Based on this formula, we obtain a sufficient and necessary condition for a compact homogeneous (α , β) -metric to be Einstein and with vanishing S-curvature. Moreover, we prove that any homogeneous Ricci flat (α , β) space with vanishing S-curvature must be a Minkowski space. Finally, we consider left invariant Einstein (α , β) -metrics on Lie groups with negative Ricci constant. Under some appropriate conditions, we show that the underlying Lie groups must be two step solvable. We also present a more convenient sufficient and necessary condition for the metric to be Einstein in this special case.
Spatial homogenization of diffusion theory parameters
It is common practice in the determination of nuclear reactor criticality and power distributions to introduce two stages of homogenization. This paper will be concerned with the second stage in which group diffusion parameters for homogenized fuel rod cells, explicitly represented control rods, poison lumps and structural materials are further homogenized over fuel assemblies. We first extend some work by Kollas and Henry (1976) dealing with the question of whether ''exact'' equivalent homogenized diffusion theory parameters exist. We prove that, if an assembly composed of heterogeneous slabs can be described by group-diffusion theory, it is possible to define group parameters spatially constant over the entire assembly that reproduce exactly the average reaction rates and leakage rates of that assembly
Homogenization of ordinary and linear transport equations
Peirone, Roberto
1996-01-01
The homogenization of first order ordinary differential equations in $\\mathbb{R}^N$ and associated linear transport equations are studied. We prove the equivalence between $G$-convergence and strong $G$-convergence for the ordinary equations. We give a sufficient condition, which is also necessary in the autonomous case, for the weak homogenization of the linear transport equations. This condition is satisfied when div$_x f=0$.
Layout optimization using the homogenization method
Suzuki, Katsuyuki; Kikuchi, Noboru
A generalized layout problem involving sizing, shape, and topology optimization is solved by using the homogenization method for three-dimensional linearly elastic shell structures in order to seek a possibility of establishment of an integrated design system of automotive car bodies, as an extension of the previous work by Bendsoe and Kikuchi. A formulation of a three-dimensional homogenized shell, a solution algorithm, and several examples of computing the optimum layout are presented in this first part of the two articles.
Bloch Approximation in Homogenization and Applications
Conca Rosende, Carlos; Orive, R.; Vanninathan, Muthusamy
2002-01-01
The classical problem of homogenization of elliptic operators with periodically oscillating coefficients is revisited in this paper. As is well known, the homogenization process in a classical framework is concerned with the study of asymptotic behavior of solutions $u^\\varepsilon$ of boundary value problems associated with such operators when the period $\\varepsilon>0$ of the coefficients is small. In a previous work by C. Conca and M. Vanninathan [SIAM J. Appl. Math., 57 (1997), pp. 1639--1...
Layout optimization using the homogenization method
Suzuki, Katsuyuki; Kikuchi, Noboru
1993-01-01
A generalized layout problem involving sizing, shape, and topology optimization is solved by using the homogenization method for three-dimensional linearly elastic shell structures in order to seek a possibility of establishment of an integrated design system of automotive car bodies, as an extension of the previous work by Bendsoe and Kikuchi. A formulation of a three-dimensional homogenized shell, a solution algorithm, and several examples of computing the optimum layout are presented in this first part of the two articles.
On homogeneous nontransitive binary perfect code
Mogilnykh, I. Yu.; Solov'eva, F. I.
2014-01-01
Studying binary perfect codes we show the existence of homogeneous nontransitive codes. Thus, as far as perfect codes are concerned, the propelinear codes are strictly contained in transitive codes, wheresas homogeneous codes form a strict subclass of transitive codes. In the work we deduce a necessary and sufficient condition for transitivity of perfect binary codes of rank one more than that of Hamming code. The paper is in Russian.
Significance tests and sample homogeneity loophole
Kupczynski, Marian
2015-01-01
In their recent comment, published in Nature, Jeffrey T.Leek and Roger D.Peng discuss how P-values are widely abused in null hypothesis significance testing . We agree completely with them and in this short comment we discuss the importance of sample homogeneity tests. No matter with how much scrutiny data are gathered if homogeneity tests are not performed the significance tests suffer from sample homogeneity loophole and the results may not be trusted. For example sample homogeneity loophole was not closed in the experiment testing local realism in which a significant violation of Eberhard inequality was found. We are not surprised that Bell type inequalities are violated since if the contextual character of quantum observables is properly taken into account these inequalities cannot be proven. However in order to trust the significance of the violation sample homogeneity loophole must be closed. Therefore we repeat after Jeffrey T.Leek and Roger D.Peng that sample homogeneity loophole is probably just the ...
Ototoxic Medications (Medication Effects)
... effects of the medications on your hearing and balance systems. The team will discuss with you how these side effects will affect your quality of life. What are the effects I may notice from ... speech is affected. Balance problems can also occur as a result of ...
Therapeutic medical abortion; Elective medical abortion; Induced abortion; Nonsurgical abortion ... A medical, or nonsurgical, abortion can be done within 7 weeks from the first day of the woman's last ...
Aqueous polyethylene oxide solutions
A number of aspects concerning the reorientation of polymer, water and ion hydration complexes have been studied in aqueous solution of polyethylene oxide (PEO). The polymer dynamics are investigated by 1H-PEO and 13C-PEO nuclear relaxation experiments. 162 refs.; 30 figs.; 19 tabs
Homogeneous and heterogeneous aqueous phase oxidation of phenol with fenton-like processes
Messele, Selamawit Ashagre
2014-01-01
In the last decades, various chemical oxidation techniques have been developed to overcome the inconveniences associated to conventional treatment of industrial wastewaters. Advanced oxidation processes (AOPs) have been reported to be effective for the degradation of soluble organic contaminants from wastewaters containing non-biodegradable organic pollutants, because they can often provide an almost total degradation, under reasonably mild conditions of temperature and pressure. Among them, ...
Ahmad, R.
2016-07-01
This article reports an unbiased analysis for the water based rod shaped alumina nanoparticles by considering both the homogeneous and non-homogeneous nanofluid models over the coupled nanofluid-surface interface. The mechanics of the surface are found for both the homogeneous and non-homogeneous models, which were ignored in previous studies. The viscosity and thermal conductivity data are implemented from the international nanofluid property benchmark exercise. All the simulations are being done by using the experimentally verified results. By considering the homogeneous and non-homogeneous models, the precise movement of the alumina nanoparticles over the surface has been observed by solving the corresponding system of differential equations. For the non-homogeneous model, a uniform temperature and nanofluid volume fraction are assumed at the surface, and the flux of the alumina nanoparticle is taken as zero. The assumption of zero nanoparticle flux at the surface makes the non-homogeneous model physically more realistic. The differences of all profiles for both the homogeneous and nonhomogeneous models are insignificant, and this is due to small deviations in the values of the Brownian motion and thermophoresis parameters.
A new concept of equivalent homogenization method
A new concept of equivalent homogenization is proposed. The concept employs new set of homogenized parameters: homogenized cross sections (XS) and interface matrix (IM), which relates partial currents at the cell interfaces. The idea of interface matrix generalizes the idea of discontinuity factors (DFs), proposed and developed by K. Koebke and K. Smith. The offered concept covers both those of K. Koebke and K. Smith; both of them can be simulated within framework of new concept. Also, the offered concept covers Siemens KWU approach for baffle/reflector simulation, where the equivalent homogenized reflector XS are derived from the conservation of response matrix at the interface in 1D simi-infinite slab geometry. The IM and XS of new concept satisfy the same assumption about response matrix conservation in 1D semi-infinite slab geometry. It is expected that the new concept provides more accurate approximation of heterogeneous cell, especially in case of the steep flux gradients at the cell interfaces. The attractive shapes of new concept are: improved accuracy, simplicity of incorporation in the existing codes, equal numerical expenses in comparison to the K. Smith's approach. The new concept is useful for: (a) explicit reflector/baffle simulation; (b) control blades simulation; (c) mixed UO2/MOX core simulation. The offered model has been incorporated in the finite difference code and in the nodal code PANDOX. The numerical results show good accuracy of core calculations and insensitivity of homogenized parameters with respect to in-core conditions. 9 figs., 7 refs. (Author)
Exploring an approximation for the homogeneous freezing temperature of water droplets
O, Kuan-Ting; Wood, Robert
2016-06-01
In this work, based on the well-known formulae of classical nucleation theory (CNT), the temperature TNc = 1 at which the mean number of critical embryos inside a droplet is unity is derived from the Boltzmann distribution function and explored as an approximation for homogeneous freezing temperature of water droplets. Without including the information of the applied cooling rate γcooling and the number of observed droplets Ntotal_droplets in the calculation, the approximation TNc = 1 is able to reproduce the dependence of homogeneous freezing temperature on drop size V and water activity aw of aqueous drops observed in a wide range of experimental studies for droplet diameter > 10 µm and aw > 0.85, suggesting the effect of γcooling and Ntotal_droplets may be secondary compared to the effect of V and aw on homogeneous freezing temperatures in these size and water activity ranges under realistic atmospheric conditions. We use the TNc = 1 approximation to argue that the distribution of homogeneous freezing temperatures observed in the experiments may be partly explained by the spread in the size distribution of droplets used in the particular experiment. It thus appears that the simplicity of this approximation makes it potentially useful for predicting homogeneous freezing temperatures of water droplets in the atmosphere.
Highlights: • Electrochemical characterisation of ferroceneboronic acid-diol interactions in non-aqueous solutions. • Elucidation of the signalling process and signalling mechanism of the ferroceneboronic acid upon interaction with diols in aqueous and non-aqueous solutions. • Effect of coordination of boron atom on electrochemistry of ferroceneboronic acid in free and bound forms with diols. - Abstract: Ferroceneboronic acid (FcBA) was employed as a model compound for clarification of binding and signalling properties of molecular probe for saccharides. As the simplest electrochemically active boronic acid, its interactions with diverse diols were studied in homogeneous phase under aqueous and non-aqueous conditions. The FcBA-diol system was examined by cyclic voltammetry resulting in two redox pairs corresponding to free and bound forms of FcBA. Redox potential of the bound form of FcBA was shifted in the cathodic direction in aqueous conditions due to coordination of the hydroxyl group to the boron atom. Oppositely, the anodic shift of the redox potential was observed upon the interaction of FcBA with diols in non-aqueous solvents. The binding properties and signalling mechanism of electrochemically active boronic acids were deduced and the assumptions resulting from the electrochemical behaviour were confirmed by 1H and 11B NMR spectroscopies. The binding constants of the tested diols in aqueous and non-aqueous media were determined and compared
The chemical homogeneity of open clusters
Bovy, Jo
2015-01-01
Determining the level of chemical homogeneity in open clusters is of fundamental importance in the study of the evolution of star-forming clouds and that of the Galactic disk. Yet limiting the initial abundance spread in clusters has been hampered by difficulties in obtaining consistent spectroscopic abundances for different stellar types. Without reference to any specific model of stellar photospheres, a model for a homogeneous cluster is that it forms a one-dimensional sequence, with any differences between members due to variations in stellar mass and observational uncertainties. I present a novel method for investigating the abundance spread in open clusters that tests this one-dimensional hypothesis at the level of observed stellar spectra, rather than constraining homogeneity using derived abundances as traditionally done. Using high-resolution APOGEE spectra for 49 giants in M67, NGC 6819, and NGC 2420 I demonstrate that these spectra form one-dimensional sequences for each cluster. With detailed forwa...
Method of Mapping Anomalies in Homogenous Material
Woodard, Stanley E. (Inventor); Taylor, Bryant D. (Inventor)
2016-01-01
An electrical conductor and antenna are positioned in a fixed relationship to one another. Relative lateral movement is generated between the electrical conductor and a homogenous material while maintaining the electrical conductor at a fixed distance from the homogenous material. The antenna supplies a time-varying magnetic field that causes the electrical conductor to resonate and generate harmonic electric and magnetic field responses. Disruptions in at least one of the electric and magnetic field responses during this lateral movement are indicative of a lateral location of a subsurface anomaly. Next, relative out-of-plane movement is generated between the electrical conductor and the homogenous material in the vicinity of the anomaly's lateral location. Disruptions in at least one of the electric and magnetic field responses during this out-of-plane movement are indicative of a depth location of the subsurface anomaly. A recording of the disruptions provides a mapping of the anomaly.
Homogenization of Periodic Systems with Large Potentials
Allaire, Grégoire; Capdeboscq, Yves; Piatnitski, Andrey; Siess, Vincent; Vanninathan, M.
2004-11-01
We consider the homogenization of a system of second-order equations with a large potential in a periodic medium. Denoting by ɛ the period, the potential is scaled as ɛ-2. Under a generic assumption on the spectral properties of the associated cell problem, we prove that the solution can be approximately factorized as the product of a fast oscillating cell eigenfunction and of a slowly varying solution of a scalar second-order equation. This result applies to various types of equations such as parabolic, hyperbolic or eigenvalue problems, as well as fourth-order plate equation. We also prove that, for well-prepared initial data concentrating at the bottom of a Bloch band, the resulting homogenized tensor depends on the chosen Bloch band. Our method is based on a combination of classical homogenization techniques (two-scale convergence and suitable oscillating test functions) and of Bloch waves decomposition.
Commensurability effects in holographic homogeneous lattices
Andrade, Tomas
2015-01-01
An interesting application of the gauge/gravity duality to condensed matter physics is the description of a lattice via breaking translational invariance on the gravity side. By making use of global symmetries, it is possible to do so without scarifying homogeneity of the pertinent bulk solutions, which we thus term as "homogeneous holographic lattices." Due to their technical simplicity, these configurations have received a great deal of attention in the last few years and have been shown to correctly describe momentum relaxation and hence (finite) DC conductivities. However, it is not clear whether they are able to capture other lattice effects which are of interest in condensed matter. In this paper we investigate this question focusing our attention on the phenomenon of commensurability, which arises when the lattice scale is tuned to be equal to (an integer multiple of) another momentum scale in the system. We do so by studying the formation of spatially modulated phases in various models of homogeneous ...
Microscopic investigations of homogeneous nucleation in charged sphere suspensions.
Wette, Patrick; Schöpe, Hans Joachim; Palberg, Thomas
2005-11-01
We studied the homogeneous nucleation kinetics of an aqueous suspension of charged colloidal spheres under de-ionized conditions. Samples of equilibrium crystalline structure were shear molten and the metastable melt left to solidify after cessation of shear. At low particle number densities n, corresponding to low metastability of the melt, nucleation was monitored directly via video microscopy. We determined the nucleation rates gamma(t) by counting the number of newly appearing crystals in the observation volume per unit time. Using a suitable discrete adaptation of Avrami's [J. Chem. Phys. 7, 1003 (1939); ibid.8, 212 (1940); ibid.9, 177 (1941)] model for solidification via homogeneous nucleation and subsequent growth, we calculate the remaining free volume VF(t) to obtain the rate densities J(t) = gamma(t)/VF(t). We observe J(t) to rise steeply, display a plateau at a maximum rate density Jmax, and to decrease again. With increased n the plateau duration shrinks while Jmax increases. At low to moderate number densities fully solidified samples were analyzed by microscopy to obtain the grain-size distribution and the average crystallite size angle brackets(L). Under the assumption of stationarity, we obtained the nucleation rate density J(Avr), which increased strongly with increasing n. Interestingly, J(Avr) agrees quantitatively to Jmax and to J(Avr) as obtained previously from scattering data taken on the same sample at large n. Thus, by combination of different methods, reliable nucleation rate densities are now available over roughly one order of magnitude in n and eight orders of magnitude in J. PMID:16375564
Statistical methods for assessment of blend homogeneity
Madsen, Camilla
2002-01-01
In this thesis the use of various statistical methods to address some of the problems related to assessment of the homogeneity of powder blends in tablet production is discussed. It is not straight forward to assess the homogeneity of a powder blend. The reason is partly that in bulk materials as...... shown how to set up parametric acceptance criteria for the batch that gives a high confidence that future samples with a probability larger than a specified value will pass the USP threeclass criteria. Properties and robustness of proposed changes to the USP test for content uniformity are investigated...
Homogenization of High-Contrast Brinkman Flows
Brown, Donald L.
2015-04-16
Modeling porous flow in complex media is a challenging problem. Not only is the problem inherently multiscale but, due to high contrast in permeability values, flow velocities may differ greatly throughout the medium. To avoid complicated interface conditions, the Brinkman model is often used for such flows [O. Iliev, R. Lazarov, and J. Willems, Multiscale Model. Simul., 9 (2011), pp. 1350--1372]. Instead of permeability variations and contrast being contained in the geometric media structure, this information is contained in a highly varying and high-contrast coefficient. In this work, we present two main contributions. First, we develop a novel homogenization procedure for the high-contrast Brinkman equations by constructing correctors and carefully estimating the residuals. Understanding the relationship between scales and contrast values is critical to obtaining useful estimates. Therefore, standard convergence-based homogenization techniques [G. A. Chechkin, A. L. Piatniski, and A. S. Shamev, Homogenization: Methods and Applications, Transl. Math. Monogr. 234, American Mathematical Society, Providence, RI, 2007, G. Allaire, SIAM J. Math. Anal., 23 (1992), pp. 1482--1518], although a powerful tool, are not applicable here. Our second point is that the Brinkman equations, in certain scaling regimes, are invariant under homogenization. Unlike in the case of Stokes-to-Darcy homogenization [D. Brown, P. Popov, and Y. Efendiev, GEM Int. J. Geomath., 2 (2011), pp. 281--305, E. Marusic-Paloka and A. Mikelic, Boll. Un. Mat. Ital. A (7), 10 (1996), pp. 661--671], the results presented here under certain velocity regimes yield a Brinkman-to-Brinkman upscaling that allows using a single software platform to compute on both microscales and macroscales. In this paper, we discuss the homogenized Brinkman equations. We derive auxiliary cell problems to build correctors and calculate effective coefficients for certain velocity regimes. Due to the boundary effects, we construct
An eigenelement method and two homogenization conditions
Yufeng Xing; Xingming Wang
2009-01-01
Under inspiration from the structure-preserving property of symplectic difference schemes for Hamiltonian systems, two homogenization conditions for a representa-tive unit cell of the periodical composites are proposed, one condition is the equivalence of strain energy, and the other is the deformation similarity. Based on these two homoge-nization conditions, an eigenelement method is presented, which is characteristic of structure-preserving property. It follows from the frequency comparisons that the eigenel-ement method is more accurate than the stiffness average method and the compliance average method.
Irregular Homogeneity Domains in Ternary Intermetallic Systems
Jean-Marc Joubert; Mohamed Andasmas; Jean-Claude Crivello
2015-01-01
Ternary intermetallic A–B–C systems sometimes have unexpected behaviors. The present paper examines situations in which there is a tendency to simultaneously form the compounds ABx, ACx and BCx with the same crystal structure. This causes irregular shapes of the phase homogeneity domains and, from a structural point of view, a complete reversal of site occupancies for the B atom when crossing the homogeneity domain. This work reviews previous studies done in the systems Fe–Nb–Zr, Hf–Mo–Re, Hf...
Homogeneous oxalate precipitation of Pu(III)
This paper reports on homogeneous oxalate precipitation using diethyl oxalate which was compared to precipitating Pu(III) oxalate with solid oxalic acid. The diethyl oxalate technique at 75 degrees C is better because it gives 50% less plutonium in the filtrate with a reasonable filtering time. Also, the procedure for the homogeneous precipitation is easier to automate because the liquid diethyl oxalate is simpler to introduce into the precipitator than solid oxalic acid. It also provides flexibility because the hydrolysis rate and therefore the precipitation rate can be controlled by varying the temperature
Hyperelastic bodies under homogeneous Cauchy stress induced by non-homogeneous finite deformations
Mihai, L Angela
2016-01-01
We discuss whether homogeneous Cauchy stress implies homogeneous strain in isotropic nonlinear elasticity. While for linear elasticity the positive answer is clear, we exhibit, through detailed calculations, an example with inhomogeneous continuous deformation but constant Cauchy stress. The example is derived from a non rank-one convex elastic energy. Connections to conforming and non-conforming finite element implementations are drawn.
The chemistry of iodine has been examined in aqueous solutions of pH 6 to 10 containing 2500 ppM boron as H3BO3 at temperatures up to 1500C using absorption spectrophotometry to identify and monitor the iodine species present. Kinetic rate constants for the disproportionation of the HOI intermediate, 3HOI= IO3- + 2I- + 3H+, have been measured as a function of pH even though no direct spectral evidence for HOI itself has been observed. An HOI partition coefficient >104 has been estimated; results of ionic strength tests are consistent with HOI being present as an uncharged triatomic species in solution. Redox and radiation effects on the aqueous iodine chemistry have also been described. 11 refs., 2 figs., 3 tabs
Benchmarking homogenization algorithms for monthly data
Venema, V. K. C.; Mestre, O.; Aquilar, E.; Auer, I.; Guijarro, J. A.; Domonkos, P.; Vertačník, G.; Szentimrey, T.; Štěpánek, Petr; Zahradníček, Pavel; Viarre, J.; Mueller-Westermeier, G.; Lakatos, M.; Williams, C. N.; Menne, M. J.; Lindau, R.; Rasol, D.; Rustemeier, E.; Kolokythas, K.; Marinova, T.; Andresen, L.; Acquaotta, F.; Fratianni, S.; Cheval, S.; Klancar, M.; Brunetti, M.; Gruber, C.; Duran, M. P.; Likso, T.; Esteban, P.; Brandsma, T.
2012-01-01
Roč. 8, č. 1 (2012), s. 89-115. ISSN 1814-9324 Institutional support: RVO:67179843 Keywords : climate data * instrumental time-series * greater alpine region * homogeneity test * variability * inhomogeneities Subject RIV: EH - Ecology, Behaviour Impact factor: 3.556, year: 2012
Volume and geometry of homogeneously adequate knots
Bartholomew, Paige; McQuarrie, Shane; Purcell, Jessica S.; Weser, Kai
2014-01-01
We bound the hyperbolic volumes of a large class of knots and links, called homogeneously adequate knots and links, in terms of their diagrams. To do so, we use the decomposition of these links into ideal polyhedra, developed by Futer, Kalfagianni, and Purcell. We identify essential product disks in these polyhedra.
String pair production in non homogeneous backgrounds
Bolognesi, Stefano; Tallarita, Gianni
2016-01-01
We consider string pair production in non homogeneous electric backgrounds. We study several particular configurations which can be addressed with the Euclidean world-sheet instanton technique, the analogue of the world-line instanton for particles. In the first case the string is suspended between two D-branes in flat space-time, in the second case the string lives in AdS and terminates on one D-brane (this realizes the holographic Schwinger effect). In some regions of parameter space the result is well approximated by the known analytical formulas, either the particle pair production in non-homogeneous background or the string pair production in homogeneous background. In other cases we see effects which are intrinsically stringy and related to the non-homogeneity of the background. The pair production is enhanced already for particles in time dependent electric field backgrounds. The string nature enhances this even further. For spacial varying electrical background fields the string pair production is les...
Price Elasticities Implied by Homogeneous Production Functions
Price, J. Michael
1994-01-01
If a production process is characterized by a homogeneous production function, the conditions required for profit maximization imply that the elasticity of demand for each input must be elastic with respect to output price. This restriction limits the usefulness of these functions in empirical analysis.
Quantum Homogeneous Spaces as Quantum Quotient Spaces
Brzezinski, Tomasz
1995-01-01
We show that certain embeddable homogeneous spaces of a quantum group that do not correspond to a quantum subgroup still have the structure of quantum quotient spaces. We propose a construction of quantum fibre bundles on such spaces. The quantum plane and the general quantum two-spheres are discussed in detail.
Inverse acoustic problem of N homogeneous scatterers
Berntsen, Svend
The three-dimensional inverse acoustic medium problem of N homogeneous objects with known geometry and location is considered. It is proven that one scattering experiment is sufficient for the unique determination of the complex wavenumbers of the objects. The mapping from the scattered fields at a...
Hypersurface homogeneous Killing spinor space–times
I present a complete list of hypersurface homogeneous space–times admitting a non-null valence two Killing spinor, including a new class admitting only exceptional Killing tensors. A connection is established with the classification of locally rotationally symmetric or boost symmetric space–times. (paper)
Homogeneity analysis of precipitation series in Iran
Hosseinzadeh Talaee, P.; Kouchakzadeh, Mahdi; Shifteh Some'e, B.
2014-10-01
Assessment of the reliability and quality of historical precipitation data is required in the modeling of hydrology and water resource processes and for climate change studies. The homogeneity of the annual and monthly precipitation data sets throughout Iran was tested using the Bayesian, Cumulative Deviations, and von Neumann tests at a significance level of 0.05. The precipitation records from 41 meteorological stations covering the years between 1966 and 2005 were considered. The annual series of Iranian precipitation were found to be homogeneous by applying the Bayesian and Cumulative Deviations tests, while the von Neumann test detected inhomogeneities at seven stations. Almost all the monthly precipitation data sets are homogeneous and considered as "useful." The outputs of the statistical tests for the homogeneity analysis of the precipitation time series had discrepancies in some cases which are related to different sensitivities of the tests to break in the time series. It was found that the von Neumann test is more sensitive than the Bayesian and Cumulative Deviations tests in the determination of inhomogeneity in the precipitation series.
Locally periodic homogenization of reflected diffusion
Aboubakary Diakhaby
2006-01-01
Full Text Available We study the homogenization of reflected SDEs with locally periodic coefficients and highly oscillating drift. Our method is entirely probabilistic, and builds upon earlier works of Tanaka, Benchérif-Madani and Pardoux, and Bensoussan et al We extend, to Tanaka's theorem locally periodic case.
Homogeneous protein analysis by magnetic core-shell nanorod probes
Schrittwieser, Stefan
2016-03-29
Studying protein interactions is of vital importance both to fundamental biology research and to medical applications. Here, we report on the experimental proof of a universally applicable label-free homogeneous platform for rapid protein analysis. It is based on optically detecting changes in the rotational dynamics of magnetically agitated core-shell nanorods upon their specific interaction with proteins. By adjusting the excitation frequency, we are able to optimize the measurement signal for each analyte protein size. In addition, due to the locking of the optical signal to the magnetic excitation frequency, background signals are suppressed, thus allowing exclusive studies of processes at the nanoprobe surface only. We study target proteins (soluble domain of the human epidermal growth factor receptor 2 - sHER2) specifically binding to antibodies (trastuzumab) immobilized on the surface of our nanoprobes and demonstrate direct deduction of their respective sizes. Additionally, we examine the dependence of our measurement signal on the concentration of the analyte protein, and deduce a minimally detectable sHER2 concentration of 440 pM. For our homogeneous measurement platform, good dispersion stability of the applied nanoprobes under physiological conditions is of vital importance. To that end, we support our measurement data by theoretical modeling of the total particle-particle interaction energies. The successful implementation of our platform offers scope for applications in biomarker-based diagnostics as well as for answering basic biology questions.
Photodegradation of Lincomycin in Aqueous Solution
2006-01-01
Full Text Available Aqueous solutions of lincomycin were irradiated with UV light in homogeneous and heterogeneous systems. Lincomycin disappeared in both systems but the presence of TiO 2 noticeably accelerated the degradation of the antibiotic in comparison with direct photolysis. The rate of decomposition was dependent on the concentration of lincomycin and followed a pseudo-first-order kinetics. Photolysis involved only the oxidation of lincomycin without mineralization. Differently, the treatment with TiO 2 and UV light resulted in a complete mineralization of the antibiotic. The degradation pathways involved S- and N-demethylation and propyldealkylation. The mineralization of the molecule led to the formation of sulfate, ammonium, and nitrate ions.
Aqueous sodium hydroxide seasonal thermal energy storage
Gantenbein, P.; Daguenet-Frick, X.; Frank, E. [Univ. of Applied Sciences Rapperswil (Switzerland). Inst. for Solar Technologies SPF; Weber, R.; Fumey, B. [EMPA Swiss Federal Laboratories for Materials Science and Technology, Duebendorf (Switzerland); Williamson, T. [Kingspan Renewables Ltd, Portadown, Co. Armagh, Northern Ireland (United Kingdom)
2012-07-01
Seasonal storage of sensible thermal energy in materials is a challenge in respect to thermal loss corresponding to low volumetric energy density. In a process involving absorption and desorption lower heat losses and higher energy densities can be reached. The working pair sodium hydroxide (NaOH) and water can be employed to this purpose. A possible application of such a system can be a single family passive energy building that requires a maximum power output of approximately 8 kW. The required absorption/desorption zone can be designed as a falling film tube bundle, using either Hu's or Owens' correlations. To meet the required power the tube bundle can be built of 300 mm long tubes with an outer diameter of 12 mm in a configuration of either 3 rows of 18 tubes or 2 rows of 25 tubes. During desorption one row of 18 tubes or 3 rows of 6 tubes are sufficient. In the absorption or discharging process a mass flow of 2 to 4 kg/h of aqueous NaOH with a concentration of 50 wt% NaOH is required. In the reverse process 18 to 30 kg/h of aqueous NaOH at a concentration of 30 wt% are necessary. The mass transport is performed without recirculation, reducing the parasitic power consumption. Initial experiments conducted with a less reactive substitute liquid showed good homogeneous distribution.
Bacterial Acclimation Inside an Aqueous Battery.
Dexian Dong
Full Text Available Specific environmental stresses may lead to induced genomic instability in bacteria, generating beneficial mutants and potentially accelerating the breeding of industrial microorganisms. The environmental stresses inside the aqueous battery may be derived from such conditions as ion shuttle, pH gradient, free radical reaction and electric field. In most industrial and medical applications, electric fields and direct currents are used to kill bacteria and yeast. However, the present study focused on increasing bacterial survival inside an operating battery. Using a bacterial acclimation strategy, both Escherichia coli and Bacillus subtilis were acclimated for 10 battery operation cycles and survived in the battery for over 3 days. The acclimated bacteria changed in cell shape, growth rate and colony color. Further analysis indicated that electrolyte concentration could be one of the major factors determining bacterial survival inside an aqueous battery. The acclimation process significantly improved the viability of both bacteria E. coli and B. subtilis. The viability of acclimated strains was not affected under battery cycle conditions of 0.18-0.80 mA cm(-2 and 1.4-2.1 V. Bacterial addition within 1.0×10(10 cells mL(-1 did not significantly affect battery performance. Because the environmental stress inside the aqueous battery is specific, the use of this battery acclimation strategy may be of great potential for the breeding of industrial microorganisms.
A unidirectional acoustic cloak for multilayered background media with homogeneous metamaterials
Zhu, Jian; Chen, Tianning; Liang, Qingxuan; Wang, Xiaopeng; Xiong, Jie; Jiang, Ping
2015-08-01
The acoustic cloak, which can make an object hard to detect acoustically in a homogeneous background, has attracted great attention from researchers in recent years. The inhomogeneous background media were considered in this paper. The relative constitutive parameters were derived for acoustic cloaks working in multilayered media. And a unidirectional acoustic cloak for layered background media was proposed, designed and implemented successfully in a wide frequency range. In water and NaCl aqueous solution, the acoustic cloak was designed and realized with homogeneous metamaterials which were composed of steel and porous materials. The effective parameters of the unit cells of the cloak were determined by using the effective medium theory. Numerical results demonstrated excellent cloaking performance and showed that such a device could be physically realized with natural materials which will greatly promote the real applications of an invisibility cloak in inhomogeneous backgrounds.
A unidirectional acoustic cloak for multilayered background media with homogeneous metamaterials
The acoustic cloak, which can make an object hard to detect acoustically in a homogeneous background, has attracted great attention from researchers in recent years. The inhomogeneous background media were considered in this paper. The relative constitutive parameters were derived for acoustic cloaks working in multilayered media. And a unidirectional acoustic cloak for layered background media was proposed, designed and implemented successfully in a wide frequency range. In water and NaCl aqueous solution, the acoustic cloak was designed and realized with homogeneous metamaterials which were composed of steel and porous materials. The effective parameters of the unit cells of the cloak were determined by using the effective medium theory. Numerical results demonstrated excellent cloaking performance and showed that such a device could be physically realized with natural materials which will greatly promote the real applications of an invisibility cloak in inhomogeneous backgrounds. (paper)
Homogeneous and Heterogeneous (Fex, Cr1-x)(OH)3 Precipitation: Implications for Cr Sequestration.
Dai, Chong; Zuo, Xiaobing; Cao, Bo; Hu, Yandi
2016-02-16
The formation of (Fe, Cr)(OH)3 nanoparticles determines the fate of aqueous Cr in many aquatic environments. Using small-angle X-ray scattering, precipitation rates of (Fe, Cr)(OH)3 nanoparticles in solution and on quartz were quantified from 0.1 mM Fe(III) solutions containing 0-0.25 mM Cr(III) at pH = 3.7 ± 0.2. Concentration ratio of aqueous Cr(III)/Fe(III) controlled the chemical composition (x) of (Fex, Cr1-x)(OH)3 precipitates, solutions' supersaturation with respect to precipitates, and the surface charge of quartz. Therefore, the aqueous Cr(III)/Fe(III) ratio affected homogeneous (in solution) and heterogeneous (on quartz) precipitation rates of (Fex, Cr1-x)(OH)3 through different mechanisms. The sequestration mechanisms of Cr(III) in precipitates were also investigated. In solutions with high aqueous Cr(III)/Fe(III) ratios, surface enrichment of Cr(III) on the precipitates occurred, resulting in slower particle growth in solutions. From solutions with 0-0.1 mM Cr(III), the particles on quartz grew from 2 to 4 nm within 1 h. Interestingly, from solution with 0.25 mM Cr(III), particles of two distinct sizes (2 and 6 nm) formed on quartz, and their sizes remained unchanged throughout the reaction. Our study provided new insights on homogeneous and heterogeneous precipitation of (Fex, Cr1-x)(OH)3 nanoparticles, which can help determine the fate of Cr in aquatic environments. PMID:26765070
Homogeneous and Heterogeneous (Fex, Cr1-x)(OH)3 Precipitation: Implications for Cr Sequestration
Dai, Chong; Zuo, Xiaobing; Cao, B; Hu, Yandi
2016-02-16
The formation of (Fe, Cr)(OH)3 nanoparticles determines the fate of aqueous Cr in many aquatic environments. Using small angle X-ray scattering, precipitation rates of (Fe, Cr)(OH)3 nanoparticles in solution and on quartz were quantified from 0.1 mM Fe(III) solutions containing 0 – 0.25 mM Cr(III) at pH = 3.7 ± 0.2. Concentration ratio of aqueous Cr(III)/Fe(III) controlled the chemical composition (x) of (Fex, Cr1-x)(OH)3 precipitates, solutions’ supersaturation with respect to precipitates, and the surface charge of quartz. Therefore, aqueous Cr(III)/Fe(III) ratio affected homogeneous (in solution) and heterogeneous (on quartz) precipitation rates of (Fex, Cr1-x)(OH)3 through different mechanisms. The sequestration mechanisms of Cr(III) in precipitates were also investigated. In solutions with high aqueous Cr(III)/Fe(III) ratios, surface enrichment of Cr(III) on the precipitates occurred, resulting in slower particle growth in solution. From solutions with 0 – 0.1 mM Cr(III), the particles on quartz grew from 2 to 4 nm within 1 h. Interestingly, from solution with 0.25 mM Cr(III), particles of two distinct sizes (2 and 6 nm) formed on quartz, and their sizes remained unchanged throughout the reaction. Our study provided new insights on homogeneous and heterogeneous precipitation of (Fex, Cr1-x)(OH)3 nanoparticles, which can help determine the fate of Cr in aquatic environments.
Shape optimization in biomimetics by homogenization modelling
Optimal shape design of microstructured materials has recently attracted a great deal of attention in material science. The shape and the topology of the microstructure have a significant impact on the macroscopic properties. The present work is devoted to the shape optimization of new biomorphic microcellular ceramics produced from natural wood by biotemplating. We are interested in finding the best material-and-shape combination in order to achieve the optimal prespecified performance of the composite material. The computation of the effective material properties is carried out using the homogenization method. Adaptive mesh-refinement technique based on the computation of recovered stresses is applied in the microstructure to find the homogenized elasticity coefficients. Numerical results show the reliability of the implemented a posteriori error estimator. (author)
Is the Universe Homogeneous? (On Large Scales)
Guzzo, L
1997-01-01
I critically discuss in a pedagogical and phenomenological way a few crucial tests challenging the claims by Pietronero and collaborators that there is no evidence from available galaxy catalogues that the Universe is actually homogeneous above a certain scale. In a series of papers, these authors assert that observations are consistent with a fractal distribution of objects extending to the limit of the present data. I show that while galaxies are indeed clustered in a scale-free way on small and intermediate scales, this behaviour does not continue indefinitely. Although the specific wavelength at which the galaxy distribution apparently turns to homogeneity is dangerously close to the size of the largest samples presently available, there are serious hints suggesting that this turnover is real and that its effects are detected in the behaviour of statistical estimators. The most recent claims of a continuing fractal hierarchy up to scales of several hundreds Mpc seem to be abscribable to the use of incompl...
Searching for the scale of homogeneity
Martínez, V J; Moyeed, R A; Graham, M J; Martinez, Vicent J.; Pons-Borderia, Maria-Jesus; Moyeed, Rana A.; Graham, Matthew J.
1998-01-01
We introduce a statistical quantity, known as the $K$ function, related to the integral of the two--point correlation function. It gives us straightforward information about the scale where clustering dominates and the scale at which homogeneity is reached. We evaluate the correlation dimension, $D_2$, as the local slope of the log--log plot of the $K$ function. We apply this statistic to several stochastic point fields, to three numerical simulations describing the distribution of clusters and finally to real galaxy redshift surveys. Four different galaxy catalogues have been analysed using this technique: the Center for Astrophysics I, the Perseus--Pisces redshift surveys (these two lying in our local neighbourhood), the Stromlo--APM and the 1.2 Jy {\\it IRAS} redshift surveys (these two encompassing a larger volume). In all cases, this cumulant quantity shows the fingerprint of the transition to homogeneity. The reliability of the estimates is clearly demonstrated by the results from controllable point sets...
Quantum memory with a controlled homogeneous splitting
We propose a quantum memory protocol where an input light field can be stored onto and released from a single ground state atomic ensemble by controlling dynamically the strength of an external static and homogeneous field. The technique relies on the adiabatic following of a polaritonic excitation onto a state for which the forward collective radiative emission is forbidden. The resemblance with the archetypal electromagnetically induced transparency is only formal because no ground state coherence-based slow-light propagation is considered here. As compared to the other grand category of protocols derived from the photon-echo technique, our approach only involves a homogeneous static field. We discuss two physical situations where the effect can be observed, and show that in the limit where the excited state lifetime is longer than the storage time; the protocols are perfectly efficient and noise free. We compare the technique with other quantum memories, and propose atomic systems where the experiment can be realized. (paper)
Smooth homogeneous structures in operator theory
Beltita, Daniel
2005-01-01
Geometric ideas and techniques play an important role in operator theory and the theory of operator algebras. Smooth Homogeneous Structures in Operator Theory builds the background needed to understand this circle of ideas and reports on recent developments in this fruitful field of research. Requiring only a moderate familiarity with functional analysis and general topology, the author begins with an introduction to infinite dimensional Lie theory with emphasis on the relationship between Lie groups and Lie algebras. A detailed examination of smooth homogeneous spaces follows. This study is illustrated by familiar examples from operator theory and develops methods that allow endowing such spaces with structures of complex manifolds. The final section of the book explores equivariant monotone operators and Kähler structures. It examines certain symmetry properties of abstract reproducing kernels and arrives at a very general version of the construction of restricted Grassmann manifolds from the theory of loo...
Beyond relationships between homogeneous and heterogeneous catalysis
Dixon, David A. [Univ. of Alabama, Tuscaloosa, AL (United States); Katz, Alexander [Univ. of California, Berkeley, CA (United States); Arslan, Ilke [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Gates, Bruce C. [Univ. of California, Davis, CA (United States)
2014-08-13
Scientists who regard catalysis as a coherent field have been striving for decades to articulate the fundamental unifying principles. But because these principles seem to be broader than chemistry, chemical engineering, and materials science combined, catalytic scientists commonly interact within the sub-domains of homogeneous, heterogeneous, and bio-catalysis, and increasingly within even narrower domains such as organocatalysis, phase-transfer catalysis, acid-base catalysis, zeolite catalysis, etc. Attempts to unify catalysis have motivated researchers to find relationships between homogeneous and heterogeneous catalysis and to mimic enzymes. These themes have inspired vibrant international meetings and workshops, and we have benefited from the idea exchanges and have some thoughts about a path forward.
Broken Ergodicity in Ideal, Homogeneous, Incompressible Turbulence
Morin, Lee; Shebalin, John; Fu, Terry; Nguyen, Phu; Shum, Victor
2010-01-01
We discuss the statistical mechanics of numerical models of ideal homogeneous, incompressible turbulence and their relevance for dissipative fluids and magnetofluids. These numerical models are based on Fourier series and the relevant statistical theory predicts that Fourier coefficients of fluid velocity and magnetic fields (if present) are zero-mean random variables. However, numerical simulations clearly show that certain coefficients have a non-zero mean value that can be very large compared to the associated standard deviation. We explain this phenomena in terms of broken ergodicity', which is defined to occur when dynamical behavior does not match ensemble predictions on very long time-scales. We review the theoretical basis of broken ergodicity, apply it to 2-D and 3-D fluid and magnetohydrodynamic simulations of homogeneous turbulence, and show new results from simulations using GPU (graphical processing unit) computers.
Kinematical uniqueness of homogeneous isotropic LQC
Engle, Jonathan
2016-01-01
In a paper by Ashtekar and Campiglia, invariance under volume preserving residual diffeomorphisms has been used to single out the standard representation of the reduced holonomy-flux algebra in homogeneous loop quantum cosmology (LQC). In this paper, we use invariance under all residual diffeomorphisms to single out the standard kinematical Hilbert space of homogeneous isotropic LQC for both the standard configuration space $\\mathbb{R}_{\\mathrm{Bohr}}$, as well as for the Fleischhack one $\\mathbb{R} \\sqcup \\mathbb{R}_{\\mathrm{Bohr}}$. We first determine the scale invariant Radon measures on these spaces, and then show that the Haar measure on $\\mathbb{R}_{\\mathrm{Bohr}}$ is the only such measure for which the momentum operator is hermitian w.r.t. the corresponding inner product. In particular, the measure is forced to be identically zero on $\\mathbb{R}$ in the Fleischhack case, so that for both approaches, the standard kinematical LQC-Hilbert space is singled out.
Resonant ultrasound spectroscopy and homogeneity in polycrystals.
Kaplan, Gunes; Darling, T W; McCall, K R
2009-01-01
Resonant ultrasound spectroscopy (RUS) is capable of determining the bulk elastic properties of a solid from its characteristic vibration frequencies, given the dimensions, density and shape of the sample. The model used for extracting values of the elastic constants assumes perfect homogeneity, which can be approximated by average-isotropic polycrystals. This approximation is excellent in the small grain regime assumed for most averaging procedures, but for real samples with indeterminate grain size distributions, it is not clear where the approximation breaks down. RUS measurements were made on pure copper samples where the grain size distribution was changed by progressive heat treatments in order to find a quantitative limit for the loss of homogeneity. It is found that when a measure of the largest grains is 15% of the sample's smallest dimension, the deviation in RUS fits indicates elastic inhomogeneity. PMID:18804831
Homogenization of biomechanical models for plant tissues
Piatnitski, Andrey; Ptashnyk, Mariya
2015-01-01
In this paper homogenization of a mathematical model for plant tissue biomechanics is presented. The microscopic model constitutes a strongly coupled system of reaction-diffusion-convection equations for chemical processes in plant cells, the equations of poroelasticity for elastic deformations of plant cell walls and middle lamella, and Stokes equations for fluid flow inside the cells. The chemical process in cells and the elastic properties of cell walls and middle lamella are coupled becau...
Explaining Price Dispersion for Homogeneous Grocery Products
Aalto-Setälä Ville
2003-01-01
This study examines the dispersion in prices for homogeneous grocery products, and studies the effect of product characteristics, demographic characteristics of consumers, and market structure on search costs and price dispersion. The findings show that price dispersion is affected by search costs. The variables that increased relative price dispersion the most were low budget share and low price of the product. Demographic characteristics affected price dispersion as well: a high proportion ...
Higher dimensional homogeneous cosmology in Lyra geometry
F Rahaman; S Das; N Begum; M Hossain
2003-07-01
Assuming a homogeneous perfect ﬂuid with ρ = ρ() and = (), we have obtained exact solutions for cosmological models in higher-dimension based on Lyra geometry. Depending on the form of metric chosen, the model is similar to FRW type. The explicit solutions of the scale factor are found via the assumption of an equation of state = ρ, where is a constant. Some astrophysical parameters are also calculated.
Algebraic density property of homogeneous spaces
Donzelli, Fabrizio; Dvorsky, Alexander; Kaliman, Shulim
2008-01-01
Let $X$ be an affine algebraic variety with a transitive action of the algebraic automorphism group. Suppose that $X$ is equipped with several non-degenerate fixed point free $SL_2$-actions satisfying some mild additional assumption. Then we show that the Lie algebra generated by completely integrable algebraic vector fields on $X$ coincides with the set of all algebraic vector fields. In particular, we show that apart from a few exceptions this fact is true for any homogeneous space of form ...
Spherical cloaking with homogeneous isotropic multilayered structures.
Qiu, Cheng-Wei; Hu, Li; Xu, Xiaofei; Feng, Yijun
2009-04-01
We propose a practical realization of electromagnetic spherical cloaking by layered structure of homogeneous isotropic materials. By mimicking the classic anisotropic cloak by many alternating thin layers of isotropic dielectrics, the permittivity and permeability in each isotropic layer can be properly determined by effective medium theory in order to achieve invisibility. The model greatly facilitates modeling by Mie theory and realization by multilayer coating of dielectrics. Eigenmode analysis is also presented to provide insights of the discretization in multilayers. PMID:19518392
Homogenization of eigenvalue problems in perforated domains
Vanninathan, M.
1981-01-01
In this paper, we treat some eigenvalue problems in periodically perforated domains and study the asymptotic behaviour of the eigenvalues and the eigenvectors when the number of holes in the domain increases to infinity Using the method of asymptotic expansion, we give explicit formula for the homogenized coefficients and expansion for eigenvalues and eigenvectors. If we denote by ε the size of each hole in the domain, then we obtain the following aysmptotic expansion for the eigenvalues: Dir...
A Statistical Theory of Homogeneous Isotropic Turbulence
de Divitiis, Nicola
2009-01-01
The present work proposes a theory of isotropic and homogeneous turbulence for incompressible fluids, which assumes that the turbulence is due to the bifurcations associated to the velocity field. The theory is formulated using a representation of the fluid motion which is more general than the classical Navier-Stokes equations, where the fluid state variables are expressed in terms of the referential coordinates. The theory is developed according to the following four items: 1) Study of the ...
Emergence of Leadership within a Homogeneous Group
Eskridge, Brent E.; Valle, Elizabeth; Schlupp, Ingo
2015-01-01
Large scale coordination without dominant, consistent leadership is frequent in nature. How individuals emerge from within the group as leaders, however transitory this position may be, has become an increasingly common question asked. This question is further complicated by the fact that in many of these aggregations, differences between individuals are minor and the group is largely considered to be homogeneous. In the simulations presented here, we investigate the emergence of leadership i...
Spin precession in a homogeneous gravitational field
First a geometrical approach for the homogeneous gravitational field is given, emphasizing its main physical features, and in accordance with relativity in which this field is interpreted as the field apparently experienced by a uniformly accelerated observer (Born-Motion). A stationary beam of particles is then studied in both the particle and the wave pictures. In the particle picture, we first study the beam in the non-relativistic approximation, and then the relativistic beam. The velocity fields, and orbit equations, as well as the connection of the relativistic beam to the non-relativistic beam, as c→ infinity, are given. Our main result is then established by calculating the so-called Quasi-Thomas precession of the spin of the particle in a homogeneous gravitational field. The differences with the regular Thomas precession are discussed and illustrated with space-time diagrams. Some numerical estimates are given. The beam is then studied in the wave picture for Dirac particles. First the Dirac equation is established in the homogeneous gravitational field by the appropriate coordinate, and Lorentz transformation, on the Dirac 4-component spinor wave function in the freely falling frame. Then working to first order in the coupling constant g, an approximate plane wave function is given as a solution for the stationary beam. The precession of the spin is then obtained, and it agrees with the result given by the particle picture. The translationary motion is also discussed briefly. The similar problem of a homogeneous electric field is discussed, via the principle of equivalence, and some formal analogies are found. Finally, a brief discussion of future research, in connection with recently available experiments to test the principle of equilavence at the quantum level, and in the context of this thesis, is given
General description of homogeneous isotropic disordered systems
Averbuch, Pierre
1993-01-01
As all the physical quantities describing such a system are spherical tensors, it is shown that homogeneity and isotropy imply for the cross-correlation functions such conditions that they can be written with only standard spherical functions and a few scalar functions in which the whole physical information is included. The two limiting cases of a system with many independent defects and of a polycrystal, Gauss and Poisson limits, are discussed.
'Parodie', a large homogeneous stationary plasma
A low pressure discharge plasma with magnetic multipolar confinement has been constructed to experimentally investigate turbulence phenomena. Its main characteristics are described: the technology (cylindrical machine 1 m in diameter and 1 m long, sliding vacuum rule section, permanent magnets...); and the plasma parameters (108-1010 cm-3 electron density; homogeneous within 1% in a volume of 0.3 m3, fluctuations at thermal level)
Correlated equilibria in homogenous good Bertrand competition
Jann, Ole; Schottmüller, Christoph
2015-01-01
We show that there is a unique correlated equilibrium, identical to the unique Nash equilibrium, in the classic Bertrand oligopoly model with homogenous goods and identical marginal costs. This provides a theoretical underpinning for the so-called "Bertrand paradox'' as well as its most general f...... formulation to date. Our proof generalizes to asymmetric marginal costs and arbitrarily many players in the following way: The market price cannot be higher than the second lowest marginal cost in any correlated equilibrium....
Diffusion homogenization in multicomponent dispersed heterogeneous systems
The processes of diffusion homogenizing in multicomponent powders within the temperature range of solid solutions are under study. The physical model is suggested and the mathematical algorithm is developed to calculate the statistical distribution function in the concentration space as well as other integral values describing the degree of system heterogeneity. Numerical solution is made for ternary metal system (W-Mo-Re) in the form of computer program. Calculation results are presented
... and authentic illustrations used in the publication of medical books, journals, films, videotapes, exhibits, posters, wall charts, and computer programs. A medical illustrator may also work as a member of ...
Musaeus, Peter
2015-01-01
Purpose: To examine philosophical stances underpinning medical identity and assess the conceptual relationship between physician, medical practice and culture. Argument: Medical identity is about the ideals and moral positions that physicians take when justifying themselves. Medical identity is the...... hedonistic versus sentimentalist approaches to medical identity. The sociocultural philosophical analysis of medical identity can shed light on what it means conceptually for a physician to harbor beliefs associated with him/her being taken to be an autonomous professional. It is important because it touches...... on the meaning of being a compassionate, good and skilled physician, making its relevance to person-centered medicine self-evident. Conclusion: Medical identity should be analyzed with reference to literature, philosophy and medical practice in order for the physician to exercise a reflective...
... email share facebook twitter google plus linkedin Medical Management Although there’s no cure for CMT, there are ... individualized physical therapy program. For more on medical management of CMT, see Surgery Sometimes, Bracing Often, Caution ...
Equilibrium states of homogeneous sheared compressible turbulence
M. Riahi
2011-06-01
Full Text Available Equilibrium states of homogeneous compressible turbulence subjected to rapid shear is studied using rapid distortion theory (RDT. The purpose of this study is to determine the numerical solutions of unsteady linearized equations governing double correlations spectra evolution. In this work, RDT code developed by authors solves these equations for compressible homogeneous shear flows. Numerical integration of these equations is carried out using a second-order simple and accurate scheme. The two Mach numbers relevant to homogeneous shear flow are the turbulent Mach number Mt, given by the root mean square turbulent velocity fluctuations divided by the speed of sound, and the gradient Mach number Mg which is the mean shear rate times the transverse integral scale of the turbulence divided by the speed of sound. Validation of this code is performed by comparing RDT results with direct numerical simulation (DNS of [A. Simone, G.N. Coleman, and C. Cambon, Fluid Mech. 330, 307 (1997] and [S. Sarkar, J. Fluid Mech. 282, 163 (1995] for various values of initial gradient Mach number Mg0. It was found that RDT is valid for small values of the non-dimensional times St (St 10 in particular for large values of Mg0. This essential feature justifies the resort to RDT in order to determine equilibrium states in the compressible regime.
Homogeneous Biosensing Based on Magnetic Particle Labels
Schrittwieser, Stefan
2016-06-06
The growing availability of biomarker panels for molecular diagnostics is leading to an increasing need for fast and sensitive biosensing technologies that are applicable to point-of-care testing. In that regard, homogeneous measurement principles are especially relevant as they usually do not require extensive sample preparation procedures, thus reducing the total analysis time and maximizing ease-of-use. In this review, we focus on homogeneous biosensors for the in vitro detection of biomarkers. Within this broad range of biosensors, we concentrate on methods that apply magnetic particle labels. The advantage of such methods lies in the added possibility to manipulate the particle labels by applied magnetic fields, which can be exploited, for example, to decrease incubation times or to enhance the signal-to-noise-ratio of the measurement signal by applying frequency-selective detection. In our review, we discriminate the corresponding methods based on the nature of the acquired measurement signal, which can either be based on magnetic or optical detection. The underlying measurement principles of the different techniques are discussed, and biosensing examples for all techniques are reported, thereby demonstrating the broad applicability of homogeneous in vitro biosensing based on magnetic particle label actuation.
Tits Satake projections of homogeneous special geometries
Fré, Pietro; Gargiulo, Floriana; Rosseel, Jan; Rulik, Ksenya; Trigiante, Mario; Van Proeyen, Antoine
2007-01-01
We organize the homogeneous special geometries, describing as well the couplings of D = 6, 5, 4 and 3 supergravities with eight supercharges, in a small number of universality classes. This relates manifolds on which similar types of dynamical solutions can exist. The mathematical ingredient is the Tits Satake projection of real simple Lie algebras, which we extend to all solvable Lie algebras occurring in these homogeneous special geometries. Apart from some exotic cases all the other, 'very special', homogeneous manifolds can be grouped into seven universality classes. The organization of these classes, which capture the essential features of their basic dynamics, commutes with the r- and c-map. Different members are distinguished by different choices of the paint group, a notion discovered in the context of cosmic billiard dynamics of non-maximally supersymmetric supergravities. We comment on the usefulness of this organization in universality class both in relation with cosmic billiard dynamics and with configurations of branes and orbifolds defining special geometry backgrounds.
Anarjan, Navideh; Jafarizadeh-Malmiri, Hoda; Nehdi, Imededdine Arbi; Sbihi, Hassen Mohamed; Al-Resayes, Saud Ibrahim; Tan, Chin Ping
2015-01-01
Nanodispersion systems allow incorporation of lipophilic bioactives, such as astaxanthin (a fat soluble carotenoid) into aqueous systems, which can improve their solubility, bioavailability, and stability, and widen their uses in water-based pharmaceutical and food products. In this study, response surface methodology was used to investigate the influences of homogenization time (0.5–20 minutes) and speed (1,000–9,000 rpm) in the formation of astaxanthin nanodispersions via the solvent-diffus...
Towards a methanol economy based on homogeneous catalysis: methanol to H_{2} and CO_{2} to methanol
Alberico, E.; Nielsen, Martin
2015-01-01
The possibility to implement both the exhaustive dehydrogenation of aqueous methanol to hydrogen and CO2 and the reverse reaction, the hydrogenation of CO2 to methanol and water, may pave the way to a methanol based economy as part of a promising renewable energy system. Recently, homogeneous...
Antinociceptive activity of Mentha piperita leaf aqueous extract in mice
Taher, Yousef A.
2012-01-01
Background: Mentha piperita L. (Labiatae) is an herbaceous plant, used in folk medicine for the treatment of several medical disorders. Methods and Results: In the present study, the aqueous extract of Mentha piperita leaf, at the i.p doses 200 and 400 mg/kg, showed significant analgesic effects against both acetic acid-induced writhing and hot plateinduced thermal stimulation in mice, with protection values of 51.79% and 20.21% respectively. On the contrary, the Mentha piperita leaf aqueous ...
Synthesis of carboxymethyl chitin in aqueous solution and its thermo- and pH-sensitive behaviors.
Liu, Hui; Yang, Qizhi; Zhang, Lina; Zhuo, Renxi; Jiang, Xulin
2016-02-10
Homogenous modification of natural chitin offers the advantage of fair structure control. In this work, novel carboxymethyl chitins (CMCHs) with broad range of degree of substitution (DS: 0.035 to 0.74), high degree of acetylation (DA) and little de-polymerization were synthesized homogeneously in aqueous NaOH/urea solution. The simultaneous determination of DA, DS and carboxymethylation fraction at C3 and C6 for these CMCHs was achieved by proton NMR in acidic deuterated aqueous solution for the first time. Due to the good homogeneity, the prepared CMCH-4 with lower DS of carboxymethylation exhibited, for the first time to our knowledge, dual thermo- and pH-sensitive properties. The nontoxic thermo-sensitive polymer systems gel at body temperature (37 °C) in physiological condition, which is very useful as injectable hydrogels for drug delivery and tissue engineering. PMID:26686169
Sulfur isotope homogeneity of lunar mare basalts
Wing, Boswell A.; Farquhar, James
2015-12-01
We present a new set of high precision measurements of relative 33S/32S, 34S/32S, and 36S/32S values in lunar mare basalts. The measurements are referenced to the Vienna-Canyon Diablo Troilite (V-CDT) scale, on which the international reference material, IAEA-S-1, is characterized by δ33S = -0.061‰, δ34S ≡ -0.3‰ and δ36S = -1.27‰. The present dataset confirms that lunar mare basalts are characterized by a remarkable degree of sulfur isotopic homogeneity, with most new and published SF6-based sulfur isotope measurements consistent with a single mass-dependent mean isotopic composition of δ34S = 0.58 ± 0.05‰, Δ33S = 0.008 ± 0.006‰, and Δ36S = 0.2 ± 0.2‰, relative to V-CDT, where the uncertainties are quoted as 99% confidence intervals on the mean. This homogeneity allows identification of a single sample (12022, 281) with an apparent 33S enrichment, possibly reflecting cosmic-ray-induced spallation reactions. It also reveals that some mare basalts have slightly lower δ34S values than the population mean, which is consistent with sulfur loss from a reduced basaltic melt prior to eruption at the lunar surface. Both the sulfur isotope homogeneity of the lunar mare basalts and the predicted sensitivity of sulfur isotopes to vaporization-driven fractionation suggest that less than ≈1-10% of lunar sulfur was lost after a potential moon-forming impact event.
Homogeneous almost quaternion-Hermitian manifolds
Moroianu, Andrei; Pilca, Mihaela; Semmelmann, Uwe
2012-01-01
An almost quaternion-Hermitian structure on a Riemannian manifold $(M^{4n},g)$ is a reduction of the structure group of $M$ to $\\mathrm{Sp}(n)\\mathrm{Sp}(1)\\subset \\mathrm{SO}(4n)$. In this paper we show that a compact simply connected homogeneous almost quaternion-Hermitian manifold of non-vanishing Euler characteristic is either a Wolf space, or $\\mathbb{S}^2\\times \\mathbb{S}^2$, or the complex quadric $\\mathrm{SO}(7)/\\mathrm{U}(3)$.
Nonlinear partial differential equations on homogeneous spaces
The work of A.K.N.S. which is based on the s1(2,R) valued soliton connection is extended to obtain new integrable coupled nonlinear partial differential equations. This is achieved by assuming the soliton connection having values in a semisimple Lie, Kac-Moody, Lie super algebras. Extensions of some of the integrable nonlinear p.d.e's are given explicitly. In particular the coupled NLS equations on various homogeneous spaces and the coupled modified KdV equations are obtained on symmetric spaces. (author). 20 refs
Mechanisms in homogeneous and heterogeneous epoxidation catalysis
Oyama, S Ted
2011-01-01
The catalytic epoxidation of olefins plays an important role in the industrial production of several commodity compounds, as well as in the synthesis of many intermediates, fine chemicals, and pharmaceuticals. The scale of production ranges from millions of tons per year to a few grams per year. The diversity of catalysts is large and encompasses all the known categories of catalyst type: homogeneous, heterogeneous, and biological. This book summarizes the current status in these fields concentrating on rates, kinetics, and reaction mechanisms, but also covers broad topics including modeli
REITERATED HOMOGENIZATION OF DEGENERATE NONLINEAR ELLIPTIC EQUATIONS
无
2002-01-01
The authors study homogenization of some nonlinear partial differential equations of the form -div (a (hx,h2x,Duh)) = f,where a is periodic in the first two arguments and monotone in the third.In particular the case where a satisfies degenerated structure conditions is studied.It is proved that uh converges weakly in Wo1.1 (Ω) to the unique solution of a limit problem as h →∞.Moreover,explicit expressions for the limit problem are obtained.
Spin dynamics through homogeneous magnetic superlattices
We develop a theory to study the spin dynamics of a 2DEG moving across a magnetic superlattice, where the external, tilted and sectionally homogeneous magnetic fields, induce spin transitions between the two spin components, along the superlattice. Using the transfer matrix approach, we provide a joint description of the spatial evolution of the spin-1/2 wave functions: amplitude and phase, in terms of the tilting angle, the Fermi energy and the magnetic field strengths. Clear signatures of coherent spin mixing and coherent spin flipping processes are also obtained. (author)
Homogenizing the dose for adjacent fields
Difficulties are found in radiotherapy in the determination of the gap which should be left among adjacent fields on the skin. In order to homogenize the dose at a given depth, measurements are done with a wood phantom using films, thermoluminescent dosemeters and ionization chambers. Field match is checked according to tables related in the literature and experimental data. Two tables of field separation are built at various depths, one for simultaneous adjacent fields and the other for non-simultaneous adjacent fields. Tables must be checked and the additional distances corrected for each field
'Proserpine'. Homogeneous critical experiment with plutonium
Proserpine is a homogeneous critical experiment in which plutonium is used as a fissile material. This experiment has been designed to investigate static and kinetic parameters of a thermal neutron reactor in which fissile material is highly concentrated. This report proposes a brief description of the installation (core, solution circuits, measurement and level adjustment, reflector, adjustment mechanism and safety, thermostatically-controlled booth and temperature control, installation safety), and presents the experimental program (critical mass, characteristics of the fissile solution, temperature coefficient) and the first results obtained in a zircaloy vessel. This experiment had two main objectives: a minimum critical mass, and an operating safety with respect to contamination risks
Homogeneous viscous universes with magnetic field
In this thesis homogeneous universes are studied containing a large scale magnetic field. In the evolution three different phases are distinguished: the lepton, the plasma and the matter dominated eras. During the lepton and plasma eras, which form the radiation dominated phase, the material contents of the universe are taken to consist of a viscous fluid. The transport properties taking place during this radiation dominated period are described with the help of relativistic kinetic theory, thereby taking into account the effect of the magnetic field on the shear viscosity. In the matter dominated phase the contents of the universe mainly consists of dust and, therefore, viscosity is absent during this period. (Auth.)
Paredes, Alejandro Javier; Llabot, Juan Manuel; Sánchez Bruni, Sergio; Allemandi, Daniel; Palma, Santiago Daniel
2016-10-01
Albendazole (ABZ) is a broad-spectrum antiparasitic drug used in the treatment of human or animal infections. Although ABZ has shown a high efficacy for repeated doses in monogastric mammals, its low aqueous solubility leads to erratic bioavailability. The aim of this work was to optimize a procedure in order to obtain ABZ self-dispersible nanocrystals (SDNC) by combining high pressure homogenization (HPH) and spray-drying (SD). The material thus obtained was characterized and the variables affecting both the HPH and SD processes were studied. As expected, the homogenizing pressure and number of cycles influenced the final particle size, while the stabilizer concentration had a strong impact on SD output and redispersion of powders upon contact with water. ABZ SDNC were successfully obtained with high process yield and redispersibility. The characteristic peaks of ABZ were clearly identified in the X-ray patterns of the processed samples. A noticeable increase in the dissolution rate was observed in the aqueous environment. PMID:26856301
On Shearing Fluids with Homogeneous Densities
Srivastava, D C; Kumar, Rajesh
2016-01-01
In this paper, we study shearing spherically symmetric homogeneous density fluids in comoving coordinates. It is found that the expansion of the four-velocity of a perfect fluid is homogeneous, whereas its shear is generated by an arbitrary function of time M(t), related to the mass function of the distribution. This function is found to bear a functional relationship with density. The field equations are reduced to two coupled first order ordinary differential equations for the metric coefficients, g 11 and g 22. We have explored a class of solutions assuming that M is a linear function of the density. This class embodies, as a subcase, the complete class of shear-free solutions. We have discussed the off quoted work of Kustaanheimo (1947) and have noted that it deals with shear-free fluids having anisotropic pressure. It is shown that the anisotropy of the fluid is characterized by an arbitrary function of time. We have discussed some issues of historical priorities and credentials related to shear-free sol...
Homogeneous cooling of mixtures of particle shapes
Hidalgo, R. C.; Serero, D.; Pöschel, T.
2016-07-01
In this work, we examine theoretically the cooling dynamics of binary mixtures of spheres and rods. To this end, we introduce a generalized mean field analytical theory, which describes the free cooling behavior of the mixture. The relevant characteristic time scale for the cooling process is derived, depending on the mixture composition and the aspect ratio of the rods. We simulate mixtures of spherocylinders and spheres using a molecular dynamics algorithm implemented on graphics processing unit (GPU) architecture. We systematically study mixtures composed of spheres and rods with several aspect ratios and varying the mixture composition. A homogeneous cooling state, where the time dependence of the system's intensive variables occurs only through a global granular temperature, is identified. We find cooling dynamics in excellent agreement with Haff's law, when using an adequate time scale. Using the scaling properties of the homogeneous cooling dynamics, we estimated numerically the efficiency of the energy interchange between rotational and translational degrees of freedom for collisions between spheres and rods.
Photo-electret effects in homogenous semiconductors
In the given work is shown the opportunity and created the theory of photo-electret condition in semiconductors with Dember mechanism of photo-voltage generation. Photo-electret of such type can be created, instead of traditional and without an external field as a result of only one illumination. Polar factor, in this case, is the distinction of electrons and holes mobility. Considered the multilayered structure with homogeneous photoactive micro areas shared by the layers, which are interfering to alignment of carriers concentration. We consider, that the homogeneous photoactive areas contain deep levels of stick. Because of addition of elementary photo voltage in separate micro photo cells it is formed the abnormal-large photo voltage (APV-effect). Let's notice, that Dember photo-voltage in a separate micro photo-cell ≤kT/q. From the received expressions, in practically important, special case, when quasi- balance between valent zone and stick levels established in much more smaller time, than free hole lifetime, and we received, that photo-voltage is relaxing. Comparing of the received expressions with the laws of photo voltage attenuation in p-n- junction structures shows their identity; the difference is only in absolute meanings of photo voltage. During the illumination in the semiconductor are created the superfluous concentration of charge carriers and part from them stays at deep levels. At de-energizing light there is a gradual generation of carriers located at these levels
Irregular Homogeneity Domains in Ternary Intermetallic Systems
Jean-Marc Joubert
2015-12-01
Full Text Available Ternary intermetallic A–B–C systems sometimes have unexpected behaviors. The present paper examines situations in which there is a tendency to simultaneously form the compounds ABx, ACx and BCx with the same crystal structure. This causes irregular shapes of the phase homogeneity domains and, from a structural point of view, a complete reversal of site occupancies for the B atom when crossing the homogeneity domain. This work reviews previous studies done in the systems Fe–Nb–Zr, Hf–Mo–Re, Hf–Re–W, Mo–Re–Zr, Re–W–Zr, Cr–Mn–Si, Cr–Mo–Re, and Mo–Ni–Re, and involving the topologically close-packed Laves, χ and σ phases. These systems have been studied using ternary isothermal section determination, DFT calculations, site occupancy measurement using joint X-ray, and neutron diffraction Rietveld refinement. Conclusions are drawn concerning this phenomenon. The paper also reports new experimental or calculated data on Co–Cr–Re and Fe–Nb–Zr systems.
Homogenization in micro-magneto-mechanics
Sridhar, A.; Keip, M.-A.; Miehe, C.
2016-07-01
Ferromagnetic materials are characterized by a heterogeneous micro-structure that can be altered by external magnetic and mechanical stimuli. The understanding and the description of the micro-structure evolution is of particular importance for the design and the analysis of smart materials with magneto-mechanical coupling. The macroscopic response of the material results from complex magneto-mechanical interactions occurring on smaller length scales, which are driven by magnetization reorientation and associated magnetic domain wall motions. The aim of this work is to directly base the description of the macroscopic magneto-mechanical material behavior on the micro-magnetic domain evolution. This will be realized by the incorporation of a ferromagnetic phase-field formulation into a macroscopic Boltzmann continuum by the use of computational homogenization. The transition conditions between the two scales are obtained via rigorous exploitation of rate-type and incremental variational principles, which incorporate an extended version of the classical Hill-Mandel macro-homogeneity condition covering the phase field on the micro-scale. An efficient two-scale computational scenario is developed based on an operator splitting scheme that includes a predictor for the magnetization on the micro-scale. Two- and three-dimensional numerical simulations demonstrate the performance of the method. They investigate micro-magnetic domain evolution driven by macroscopic fields as well as the associated overall hysteretic response of ferromagnetic solids.
Marmor, J B
1998-01-01
Although many clinical studies suggest the medical utility of marijuana for some conditions, the scientific evidence is weak. Many patients in California are self-medicating with marijuana, and physicians need data to assess the risks and benefits. The only reasonable solution to this problem is to encourage research on the medical effects of marijuana. The current regulatory system should be modified to remove barriers to clinical research with marijuana. The NIH panel has identified several...
Radiolysis of berberine or palmatine in aqueous solution
Marszalek, Milena; Wolszczak, Marian
2011-01-01
The reactions of hydrated electron (eaq-), hydrogen atom (H rad ) (reducing species) and Cl2•-, Br2•-, N,O•H radicals (oxidizing species) with berberine or palmatine in aqueous solution have been studied by steady-state and pulse radiolysis. The spectra of transient intermediates, leading to the final products, are presented. The rate constants of the reaction of eaq- and rad OH radical with both alkaloids in the homogenous solution and in the presence of DNA are reported. It is demonstrated that the primary products of the reaction of berberine and palmatine with eaq- and radicals generated during radiolysis are unstable and undergo further reactions.
Polymerization of beta-amino acids in aqueous solution
Liu, R.; Orgel, L. E.; Bada, J. L. (Principal Investigator)
1998-01-01
We have compared carbonyl diimidazole (CDI) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDAC) as activating agents for the oligomerization of negatively-charged alpha- and beta-amino acids in homogeneous aqueous solution. alpha-Amino acids can be oligomerized efficiently using CDI, but not by EDAC. beta-Amino acids can be oligomerized efficiently using EDAC, but not by CDI. Aspartic acid, an alpha- and beta-dicarboxylic acid is oligomerized efficiently by both reagents. These results are explained in terms of the mechanisms of the reactions, and their relevance to prebiotic chemistry is discussed.
Li, Feifei
2013-05-21
Lanthanide-doped core-shell upconversion nanocrystals (UCNCs) have tremendous potential for applications in many fields, especially in bio-imaging and medical therapy. As core-shell UCNCs are mostly synthesized in organic solvents, tedious organic-aqueous phase transfer processes are usually needed for their use in bio-applications. Herein, we demonstrate the first example of one-step synthesis of highly luminescent core-shell UCNCs in the "aqueous" phase under mild conditions using innocuous reagents. A microwave-assisted approach allowed for layer-by-layer epitaxial growth of a hydrophilic NaGdF4 shell on NaYF4:Yb, Er cores. During this process, surface defects of the nanocrystals could be gradually passivated by the homogeneous shell deposition, resulting in obvious enhancement in the overall upconversion emission efficiency. In addition, the up-down conversion dual-mode luminescent NaYF4:Yb, Er@NaGdF4:Ce, Ln (Eu, Tb, Sm, Dy) nanocrystals were also synthesized to further validate the successful formation of the core-shell structure. More significantly, based on their superior solubility and stability in water solution, high upconversion efficiency and Gd-doped predominant X-ray absorption, the as-prepared NaYF4:Yb, Er@NaGdF4 core-shell UCNCs exhibited high contrast in in vitro cell imaging and in vivo X-ray computed tomography (CT) imaging, demonstrating great potential as multiplexed luminescent biolabels and CT contrast agents.
Four-dimensional pseudo-Riemannian homogeneous Ricci solitons
Calvaruso, Giovanni; Fino, Anna
2011-01-01
We consider four-dimensional homogeneous pseudo-Riemannian manifolds with non-trivial isotropy and completely classify the cases giving rise to non-trivial homogeneous Ricci solitons. In particular, we show the existence of non-compact homogeneous (and also invariant) pseudo-Riemannian Ricci solitons which are not isometric to solvmanifolds, and of conformally flat homogeneous pseudo-Riemannian Ricci solitons which are not symmetric.
MULTISCALE HOMOGENIZATION OF NONLINEAR HYPERBOLIC EQUATIONS WITH SEVERAL TIME SCALES
Jean Louis Woukeng; David Dongo
2011-01-01
We study the multiscale homogenization of a nonlinear hyperbolic equation in a periodic setting. We obtain an accurate homogenization result. We also show that as the nonlinear term depends on the microscopic time variable, the global homogenized problem thus obtained is a system consisting of two hyperbolic equations. It is also shown that in spite of the presence of several time scales, the global homogenized problem is not a reiterated one.
Homogenization of a stationary flow of a generalized Newtonian fluid
Bulíček, Miroslav; Kalousek, Martin; Kaplický, Petr
2016-01-01
We perform the homogenization process avoiding the necessity of testing the weak formulation of the initial and homogenized systems by corresponding weak solutions. We show that the stress tensor for homogenized problem depends on the gradient involving the limit of a sequence selected from a family of solutions of initial problems.
THE ANALYTICAL PROPERTIES FOR HOMOGENEOUS RANDOM TRANSITION FUNCTIONS
无
2007-01-01
The concepts of Markov process in random environment and homogeneous random transition functions are introduced. The necessary and sufficient conditions for homogeneous random transition function are given. The main results in this article are the analytical properties, such as continuity, differentiability, random Kolmogorov backward equation and random Kolmogorov forward equation of homogeneous random transition functions.
Kumaraswamy, Mohan
2002-01-01
One element of the CIVCAL project Web-based resources containing images, tables, texts and associated data on the construction of the Medical Complex. This project covers the construction of a new Hong Kong University Medical Complex on Sassoon Road, Pokfulam. The complex will comprise two buildings, one will house laboratories and a car park, while the other will contain lecture halls
Magnetism and homogenization of micro-resonators
Kohn, Robert V
2007-01-01
Arrays of cylindrical metal micro-resonators embedded in a dielectric matrix were proposed by Pendry, et. al., in 1999 as a means of creating a microscopic structure that exhibits strong bulk magnetic behavior at frequencies not realized in nature. This behavior arises for H-polarized fields in the quasi-static regime, in which the scale of the micro-structure is much smaller than the free-space wavelength of the fields. We carry out both formal and rigorous two-scale homogenization analyses, paying special attention to the appropriate method of averaging, which does not involve the usual cell averages. We show that the effective magnetic and dielectric coefficients obtained by means of such averaging characterize a bulk medium that, to leading order, produces the same scattering data as the micro-structured composite.
The homogeneous and isotropic Weyssenhoff fluid
Boehmer, C G; Boehmer, Christian G.; Bronowski, Piotr
2006-01-01
We consider a Weyssenhoff fluid assuming that the spacetime is homogeneous and isotropic, therefore being relevant for cosmological considerations of gravity theories with torsion. In this paper, it is explicitely shown that the Weyssenhoff fluids obeying the Frenkel condition or the Papapetrou-Corinaldesi condition are incompatible with the cosmological principle, which restricts the torsion tensor to have only a vector and an axial vector component. Moreover it turns out that the Weyssenhoff fluid obeying the Tulczyjew condition is also incompatible with the cosmological principle. Based on this result we propose to reconsider a number of previous works that analysed cosmological solutions of Einstein-Cartan theory, since their spin fluids usually did not obey the cosmological principle.
The structure and homogeneity of Psalm 32
J. Henk Potgieter
2014-02-01
Full Text Available Psalm 32 is widely regarded as a psalm of thanksgiving with elements of wisdom poetry intermingled into it. The wisdom elements are variously explained as having been present from the beginning, or as having been added to a foundational composition. Such views of the Gattung have had a decisive influence on the interpretation of the psalm. This article argues, on the basis of a structural analysis, that Psalm 32 should be understood as a homogeneous wisdom composition. The parallel and inverse structure of its two stanzas demonstrate that the aim of its author was to encourage the upright to foster an open, intimate relationship with Yahweh in which transgressions are confessed and Yahweh’s benevolent guidance on the way of life is wisely accepted.
Homogeneous spacelike singularities inside spherical black holes
Burko, L M
1997-01-01
Recent numerical simulations have found that the Cauchy horizon inside spherical charged black holes, when perturbed nonlinearly by a self-gravitating, minimally-coupled, massless, spherically-symmetric scalar field, turns into a null weak singularity which focuses monotonically to $r=0$ at late times, where the singularity becomes spacelike. Our main objective is to study this spacelike singularity. We study analytically the spherically-symmetric Einstein-Maxwell-scalar equations asymptotically near the singularity. We obtain a series-expansion solution for the metric functions and for the scalar field near $r=0$ under the simplifying assumption of homogeneity. Namely, we neglect spatial derivatives and keep only temporal derivatives. We find that there indeed exists a generic spacelike singularity solution for these equations (in the sense that the solution depends on enough free parameters), with similar properties to those found in the numerical simulations. This singularity is strong in the Tipler sense,...
Homogeneously dispersed multimetal oxygen-evolving catalysts.
Zhang, Bo; Zheng, Xueli; Voznyy, Oleksandr; Comin, Riccardo; Bajdich, Michal; García-Melchor, Max; Han, Lili; Xu, Jixian; Liu, Min; Zheng, Lirong; García de Arquer, F Pelayo; Dinh, Cao Thang; Fan, Fengjia; Yuan, Mingjian; Yassitepe, Emre; Chen, Ning; Regier, Tom; Liu, Pengfei; Li, Yuhang; De Luna, Phil; Janmohamed, Alyf; Xin, Huolin L; Yang, Huagui; Vojvodic, Aleksandra; Sargent, Edward H
2016-04-15
Earth-abundant first-row (3d) transition metal-based catalysts have been developed for the oxygen-evolution reaction (OER); however, they operate at overpotentials substantially above thermodynamic requirements. Density functional theory suggested that non-3d high-valency metals such as tungsten can modulate 3d metal oxides, providing near-optimal adsorption energies for OER intermediates. We developed a room-temperature synthesis to produce gelled oxyhydroxides materials with an atomically homogeneous metal distribution. These gelled FeCoW oxyhydroxides exhibit the lowest overpotential (191 millivolts) reported at 10 milliamperes per square centimeter in alkaline electrolyte. The catalyst shows no evidence of degradation after more than 500 hours of operation. X-ray absorption and computational studies reveal a synergistic interplay between tungsten, iron, and cobalt in producing a favorable local coordination environment and electronic structure that enhance the energetics for OER. PMID:27013427
Homogeneous cosmology with aggressively expanding civilizations
Olson, S Jay
2014-01-01
In the context of a homogeneous universe, we note that the appearance of aggressively expanding advanced life is geometrically similar to the process of nucleation and bubble growth in a first-order cosmological phase transition. We exploit this similarity to describe the dynamics of life saturating the universe on a cosmic scale, adapting the phase transition model to incorporate probability distributions of expansion and resource consumption strategies. Through a series of numerical solutions covering several orders of magnitude in the input assumption parameters, the resulting cosmological model is used to address basic questions related to the intergalactic spreading of life, dealing with issues such as timescales, observability, competition between strategies, and first-mover advantage. Finally, we examine physical effects on the universe itself, such as reheating and the backreaction on the evolution of the scale factor, if such life is able to control and convert a significant fraction of the available...
Lyapunov Analysis of Homogeneous Isotropic Turbulence
de Divitiis, Nicola
2009-01-01
The present work studies the isotropic and homogeneous turbulence for incompressible fluids, through an opportune Lyapunov analysis, assuming that the turbulence is due to the bifurcations associated to the velocity field. A particular representation of the fluid motion is adopted, where the fluid state variables are expressed in terms of the referential coordinates. The analysis is based on the Taylor and Kolmogorov scales and is developed according to the following four items: 1) Qualitative description of the route toward the turbulence through the bifurcations of the velocity field. 2) Referential description of the motion and calculation of the velocity fluctuation using the Lyapunov analysis of the local deformation. 3) Study of the mechanism of the energy cascade from large to small scales through the Lyapunov analysis of the relative kinematics equations of motion. 4) Determination of the statistics of the velocity difference with the Fourier analysis. %Each item contributes to the formulation of the ...
A Statistical Theory of Homogeneous Isotropic Turbulence
de Divitiis, Nicola
2009-01-01
The present work proposes a theory of isotropic and homogeneous turbulence for incompressible fluids, which assumes that the turbulence is due to the bifurcations associated to the velocity field. The theory is formulated using a representation of the fluid motion which is more general than the classical Navier-Stokes equations, where the fluid state variables are expressed in terms of the referential coordinates. The theory is developed according to the following four items: 1) Study of the route toward the turbulence through the bifurcations analysis of the kinematic equations. 2) Referential description of the motion and calculation of the velocity fluctuation using the Lyapunov analysis of the local deformation. 3) Study of the mechanism of the energy cascade from large to small scales through the Lyapunov analysis of the relative kinematics equations of motion. 4) Determination of the statistics of the velocity difference with the Fourier analysis. Each item contributes to the formulation of the theory. ...
Nanodosimetric track structure in homogeneous extended beams
Physical aspects of particle track structure are important in determining the induction of clustered damage in relevant subcellular structures like the DNA and higher-order genomic structures. The direct measurement of track-structure properties of ionising radiation is feasible today by counting the number of ionizations produced inside a small gas volume. In particular, the so-called track-nano-dosimeter, installed at the TANDEM-ALPI accelerator complex of LNL, measures ionisation cluster-size distributions in a simulated subcellular structure of dimensions 20 nm, corresponding approximately to the diameter of the chromatin fibre. The target volume is irradiated by pencil beams of primary particles passing at specified impact parameter. To directly relate these measured track-structure data to radiobiological measurements performed in broad homogeneous particle beams, these data can be integrated over the impact parameter. This procedure was successfully applied to 240 MeV carbon ions and compared with Monte Carlo simulations for extended fields. (authors)
Conformally compactified homogeneous spaces (Possible Observable Consequences)
Some arguments based on the possible spontaneous violation of the Cosmological Principles (represented by the observed large-scale structures of galaxies), the Cartan-geometry of simple spinors and on the Fock-formulation of hydrogen-atom wave-equation in momentum-space, are presented in favour of the hypothesis that space-time and momentum-space should be both conformally compactified and represented by the two four-dimensional homogeneous spaces of the conformal group, both isomorphic to (S3 X S1)/Z2 and correlated by conformal inversion. Within this framework, the possible common origin for the S0(4) symmetry underlying the geometrical structure of the Universe, of Kepler orbits and of the H-atom is discussed. On of the consequences of the proposed hypothesis could be that any quantum field theory should be naturally free from both infrared and ultraviolet divergences. But then physical spaces defined as those where physical phenomena may be best described, could be different from those homogeneous spaces. A simple, exactly soluble, toy model, valid for a two-dimensional space-time is presented where the conjecture conformally compactified space-time and momentum-space are both isomorphic to (S1 X S1)/Z2, while the physical spaces are two finite lattice which are dual since Fourier transforms, represented by finite, discrete, sums may be well defined on them. Furthermore, a q-deformed SUq(1,1) may be represented on them if q is a root of unity. (author). 22 refs, 3 figs
NMR studies of thermoresponsive polymers in aqueous solutions and hydrogels
Spěváček, Jiří
Poznań : Department of Macromolecular Physics, Faculty of Physics and NanoBioMedical Centre, Adam Mickiewicz University in Poznań, The Centre for European Integration, 2014 - (Jurga, S.). s. 27 [Ampere NMR School. 22.06.2014-28.06.2014, Zakopane] R&D Projects: GA ČR(CZ) GA13-23392S Institutional support: RVO:61389013 Keywords : NMR * thermoresponsive polymer * aqueous solution Subject RIV: CD - Macromolecular Chemistry
Dissolution test for homogeneity of mixed oxide fuel pellets
Experiments were performed to determine the relationship between fuel pellet homogeneity and pellet dissolubility. Although, in general, the amount of pellet residue decreased with increased homogeneity, as measured by the pellet figure of merit, the relationship was not absolute. Thus, all pellets with high figure of merit (excellent homogeneity) do not necessarily dissolve completely and all samples that dissolve completely do not necessarily have excellent homogeneity. It was therefore concluded that pellet dissolubility measurements could not be substituted for figure of merit determinations as a measurement of pellet homogeneity. 8 figures, 3 tables
Homogeneity study of candidate reference material in fish matrix
A material is perfectly homogeneous with respect to a given characteristic, or composition, if there is no difference between the values obtained from one part to another. Homogeneity is usually evaluated using analysis of variance (ANOVA). However, the requirement that populations of data to be processed must have a normal distribution and equal variances greatly limits the use of this statistical tool. A more suitable test for assessing the homogeneity of RMs, known as sufficient homogeneity, was proposed by Fearn and Thompson. In this work, we evaluate the performance of the two statistical treatments for assessing homogeneity of methylmercury (MeHg) in candidate reference material of fish tissue
Is it possible to homogenize resonant chiral metamaterials ?
Andryieuski, Andrei; Menzel, Christoph; Rockstuhl, Carsten;
2010-01-01
Homogenization of metamaterials is very important as it makes possible description in terms of effective parameters. In this contribution we consider the homogenization of chiral metamaterials. We show that for some metamaterials there is an optimal meta-atom size which depends on the coupling...... between meta-atoms. We introduce numerical criterion of homogeneity on the basis of the Bloch modes dispersion diagram calculation and a tool to predict the homogeneity limit. We show that some metamaterials with strong coupling between meta-atoms cannot be considered as homogeneous at all...
Mars Aqueous Processing System Project
National Aeronautics and Space Administration — Mars Aqueous Processing System (MAPS) is an innovative method to produce useful building materials from Martian regolith. Acids and bases produced from the regolith...
Mars Aqueous Processing System Project
National Aeronautics and Space Administration — The Mars Aqueous Processing System (MAPS) is a novel technology for recovering oxygen, iron, and other constituents from lunar and Mars soils. The closed-loop...
Antidepressant medications and osteoporosis
Rizzoli, R; Cooper, C; Reginster, J-Y;
2012-01-01
types of bone cell (osteoblasts, osteocytes, and osteoclasts), indicating an important role of the neuroendocrine system in bone. Observational studies indicate a complex relationship between depression, antidepressants, and fracture. First, the presence of depression itself increases fracture risk......, in relation with decreased BMD and an increase in falls. A range of aspects of depression may operate, including behavioral factors (e.g., smoking and nutrition), biological changes, and confounders (e.g., comorbidities and concomitant medications). A substantial proportion of depressed patients receive...... for potential confounders. While there is a dose-response relationship for SSRIs, the effect does not appear to be homogeneous across the whole class of drugs and may be linked to affinity for the serotonin transporter system. The increase in risk is the greatest in the early stages of treatment...
... for Medication For the treatment of heart failure Beta Blockers (Also known as Beta-Adrenergic Blocking Agents) Commonly ... have had a heart attack. Combined alpha and beta-blockers Combined alpha and beta-blockers are used as ...
... behavior, such as to reduce self-injury or aggression. Once a symptom is no longer a problem, ... of repetitive behaviors; decrease anxiety, irritability, tantrums, and aggressive behavior; and improve eye contact. Tricyclics These medications are ...
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... Size Small Text Medium Text Large Text Contrast Dark on Light Light on Dark Donate Search Menu Donate What is Glaucoma? Care ... Low Vision Resources Medication Guide Resources on the Web » See All Articles Help the Cause Glaucoma affects ...
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This didactical book presents the medical imaging techniques: radiography, scanner, nuclear magnetic resonance (NMR). Examples are given for the most common pathologies in all domains of medicine. (J.S.)
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This leaflet in the At-a-Glance Series describes the medical use of X-rays, how X-rays help in diagnosis, radiation protection of the patient, staff protection, how radioactive materials in nuclear medicine examinations help in diagnosis and the use of radiation in radiotherapy. Magnetic resonance imaging, a diagnostic technique involving no ionizing radiation, is also briefly examined. The role of the NRPB in the medical use of radiation is outlined. (UK)
Abbas Ghanbari; Khadijeh Zirak Moradlu; Morteza Ramazani
2014-01-01
Medical tourism is considered as one of the tourism dimensions and it can contribute to the stabilized and dynamic development of a country's economy. Since it is cost-effective industry, most developing countries have focused on this industry and they are planning to develop this industry. Not only does Zanjan province, as the central region in medicine services, enjoy different kinds of variety and acceptable medical specialties but also it has historical, natural, and religious tourism pot...
Compositional Homogeneity of CM Parent Bodies
Vernazza, P.; Marsset, M.; Beck, P.; Binzel, R. P.; Birlan, M.; Cloutis, E. A.; DeMeo, F. E.; Dumas, C.; Hiroi, T.
2016-09-01
CM chondrites are the most common type of hydrated meteorites, making up ˜1.5% of all falls. Whereas most CM chondrites experienced only low-temperature (˜0°C–120°C) aqueous alteration, the existence of a small fraction of CM chondrites that suffered both hydration and heating complicates our understanding of the early thermal evolution of the CM parent body(ies). Here, we provide new constraints on the collisional and thermal history of CM-like bodies from a comparison between newly acquired spectral measurements of main-belt Ch/Cgh-type asteroids (70 objects) and existing laboratory spectral measurements of CM chondrites. It first appears that the spectral variation observed among CM-like bodies is essentially due to variations in the average regolith grain size. Second, the spectral properties of the vast majority (unheated) of CM chondrites resemble both the surfaces and the interiors of CM-like bodies, implying a “low” temperature (origin is the likely explanation for the existence of heated CM chondrites. Finally, similarly to S-type asteroids and (2) Pallas, the surfaces of large (D > 100 km)—supposedly primordial—Ch/Cgh-type main-belt asteroids likely expose the interiors of the primordial CM parent bodies, a possible consequence of impacts by small asteroids (D solar system.
Compositional Homogeneity of CM Parent Bodies
Vernazza, P.; Marsset, M.; Beck, P.; Binzel, R. P.; Birlan, M.; Cloutis, E. A.; DeMeo, F. E.; Dumas, C.; Hiroi, T.
2016-09-01
CM chondrites are the most common type of hydrated meteorites, making up ˜1.5% of all falls. Whereas most CM chondrites experienced only low-temperature (˜0°C–120°C) aqueous alteration, the existence of a small fraction of CM chondrites that suffered both hydration and heating complicates our understanding of the early thermal evolution of the CM parent body(ies). Here, we provide new constraints on the collisional and thermal history of CM-like bodies from a comparison between newly acquired spectral measurements of main-belt Ch/Cgh-type asteroids (70 objects) and existing laboratory spectral measurements of CM chondrites. It first appears that the spectral variation observed among CM-like bodies is essentially due to variations in the average regolith grain size. Second, the spectral properties of the vast majority (unheated) of CM chondrites resemble both the surfaces and the interiors of CM-like bodies, implying a “low” temperature (body(ies). It follows that an impact origin is the likely explanation for the existence of heated CM chondrites. Finally, similarly to S-type asteroids and (2) Pallas, the surfaces of large (D > 100 km)—supposedly primordial—Ch/Cgh-type main-belt asteroids likely expose the interiors of the primordial CM parent bodies, a possible consequence of impacts by small asteroids (D < 10 km) in the early solar system.
Persymmetric Adaptive Detectors of Subspace Signals in Homogeneous and Partially Homogeneous Clutter
Ding Hao
2015-08-01
Full Text Available In the field of adaptive radar detection, an effective strategy to improve the detection performance is to exploit the structural information of the covariance matrix, especially in the case of insufficient reference cells. Thus, in this study, the problem of detecting multidimensional subspace signals is discussed by considering the persymmetric structure of the clutter covariance matrix, which implies that the covariance matrix is persymmetric about its cross diagonal. Persymmetric adaptive detectors are derived on the basis of the one-step principle as well as the two-step Generalized Likelihood Ratio Test (GLRT in homogeneous and partially homogeneous clutter. The proposed detectors consider the structural information of the covariance matrix at the design stage. Simulation results suggest performance improvement compared with existing detectors when reference cells are insufficient. Moreover, the detection performance is assessed with respect to the effects of the covariance matrix, signal subspace dimension, and mismatched performance of signal subspace as well as signal fluctuations.
Escher, A; Boulouchos, K.
2006-12-15
This annual report for the Swiss Federal Office of Energy (SFOE) reports on work done in 2006 at the Laboratory for Aero-thermochemistry and Combustion Systems at the Swiss Federal Institute of Technology ETH in Zurich, Switzerland, on the simulation of homogeneous self-igniting combustion. It also presents the results of experimental work on the ignition of n-butane and n-heptane in the institute's one-stroke test engine. Two simulation methods are discussed, both of which corresponded well with the results of experiments carried out. The authors note that the results provide a deeper insight into the mechanisms of self-ignition in homogeneous mixtures.
Nearsightedness of Finite Homogeneous Model Systems
Mitsuta, Yuki; Yamanaka, Shusuke; Kawakami, Takashi; Okumura, Mitsutaka; Yamaguchi, Kizashi; Nakamura, Haruki
On the basis of linear response function (LRF) analysis, nearsightedness of finite systems is examined for nearly homogeneous molecular systems. We first treated with Hn (n = 2-100) to inspect the local or nonlocal responses of these systems, which are, in other words, the magnitudes of nearsightedness of the finite systems. Further, the LRFs of H100n+ (n = 0-98) have been examined in order to clarify whether the magnitude of nearsightedness depends either the size of systems or the number of electrons in systems. From our calculations, we conjectured that the number of electrons are essential for nearsightedness of electronic matter (NEM) of this type of systems. This conjecture has been confirmed from the fact that the LRFs of H100n+ (n = 0-98) are similar to those of N electrons (N = 2-100) in a square well potential, showing that attractive potentials of H100n+ (n = 0-98) do not change significantly the dependence of the magnitudes of NEM on the number of electrons.
Numerical Computation of Homogeneous Slope Stability
Shuangshuang Xiao
2015-01-01
Full Text Available To simplify the computational process of homogeneous slope stability, improve computational accuracy, and find multiple potential slip surfaces of a complex geometric slope, this study utilized the limit equilibrium method to derive expression equations of overall and partial factors of safety. This study transformed the solution of the minimum factor of safety (FOS to solving of a constrained nonlinear programming problem and applied an exhaustive method (EM and particle swarm optimization algorithm (PSO to this problem. In simple slope examples, the computational results using an EM and PSO were close to those obtained using other methods. Compared to the EM, the PSO had a small computation error and a significantly shorter computation time. As a result, the PSO could precisely calculate the slope FOS with high efficiency. The example of the multistage slope analysis indicated that this slope had two potential slip surfaces. The factors of safety were 1.1182 and 1.1560, respectively. The differences between these and the minimum FOS (1.0759 were small, but the positions of the slip surfaces were completely different than the critical slip surface (CSS.
Redatuming Operators Analysis in Homogeneous Media
Oliveira, Fransisco de Souza; Figueiredo, Jose J. S. de; Freitas, Lucas
2015-04-01
A redatuming operation is used to simulate the acquisition of data in new levels, avoiding distortions produced by near-surface irregularities related to either geometric or material property heterogeneities. In this work, the application of the true-amplitude Kirchhoff redatuming (TAKR) operator on homogeneous media is compared with conventional Kirchhoff redatuming (KR) operator restricted to the zero-offset case. The TAKR and the KR operators are analytically and numerically compared in order to verify their impacts on the data at a new level. Analyses of amplitude and velocity sensitivity of the TAKR and KR were performed: one concerning the difference between the weight functions and the other related to the velocity variation. The comparisons between operators were performed using numerical examples. The feasibility of the KR and TAKR operators was demonstrated not only kinematically but also dynamically for their purposes. In other words, one preserves amplitude (KR), and the other corrects the amplitude (TAKR). In the end, we applied the operators to a GPR data set.
Pair reversal in homogeneous isotropic turbulence
We show that the separation of particle pairs in the inertial subrange of homogeneous isotropic turbulence is strongly influenced by the pairs that separate quasi-diffusively. We quantify the influence of the diffusive separators by considering the probability that a pair will 'reverse' direction across a given separation i.e. its separation will decrease (before eventually increasing) and derive an analytical expression for the expected number of reversals across this separation for a quasi-one-dimensional model of relative dispersion in the inertial subrange with Gaussian turbulence. We compare this theoretical result with three different Lagrangian stochastic models in which the influence of the diffusive and ballistic separators (the latter dominated by velocity memory) can be varied by means of the value of C0, the constant of proportionality in the Lagrangian velocity structure function, which appears explicitly in Lagrangian stochastic models. We also compare these results with data from a direct numerical simulation of turbulence. The results indicate the importance of the transverse relative velocity component (i.e. the ability of pairs to rotate), which is absent in Q1D models, in determining the correct quantitative relative dispersion statistics.
Forming homogeneous clusters for differential risk information
Latent risk situations are always present in society. General information on these risk situations is supposed to be received differently by different groups of people in the population. In the aftermath of specific accidents different groups presumably have need of specific information about how to act to survive, to avoid injuries, to find more information, to obtain facts about the accidents etc. As targets for information these different groups could be defined in different ways. The conventional way is to divide the population according to demographic variables, such as age, sex, occupation etc. Another way would be to structure the population according to dependent variables measured in different studies. They may concern risk perception, emotional reactions, specific technical knowledge of the accidents, and belief in the information sources. One procedure for forming such groupings of people into homogeneous clusters would be by statistical clustering methods on dependent variables. Examples of such clustering procedures are presented and discussed. Data are from a Norwegian study on the perception of radiation from nuclear accidents and other radiation sources. Speculations are made on different risk information strategies. Elements of a research programme are proposed. (author)
Homogeneous screening assay for human tankyrase.
Narwal, Mohit; Fallarero, Adyary; Vuorela, Pia; Lehtiö, Lari
2012-06-01
Tankyrase, a member of human PARP protein superfamily, catalyzes a covalent post-translational modification of substrate proteins. This modification, poly(ADP-ribos)ylation, leads to changes in protein interactions and modifies downstream signaling events. Tankyrase 1 is a potential drug target due to its functions in telomere homeostasis and in Wnt signaling. We describe here optimization and application of an activity-based homogenous assay for tankyrase inhibitors in a high-throughput screening format. The method measures the consumption of substrate by the chemical conversion of the remaining NAD(+) into a stable fluorescent condensation product. Conditions were optimized to measure the enzymatic auto-modification of a recombinant catalytic fragment of tankyrase 1. The fluorescence assay is inexpensive, operationally easy and performs well according to the statistical analysis (Z'= 0.7). A validatory screen with a natural product library confirmed suitability of the assay for finding new tankyrase inhibitors. Flavone was the most potent (IC(50)=325 nM) hit from the natural compounds. A flavone derivative, apigenin, and isopropyl gallate showed potency on the micromolar range, but displayed over 30-fold selectivity for tankyrase over the studied isoenzymes PARP1 and PARP2. The assay is robust and will be useful for screening new tankyrase inhibitors. PMID:22357873
Development of a mechanical homogenizer coffee
Raphael Magalhães Gomes Moreira
2013-12-01
Full Text Available The crop Coffee demands investments to the machines development, which it enables the processes ofpost-harvesting, becoming them faster, meanwhile improving the working. The use of stationary layer dryers are responsible for good results at drying and product quality, but it requires a constant revolving, in order to homogenize the grain mass and improve the air distribution inside the drying chamber. The shortage of workmanship, associated to the need of constant revolving and the heavy working conditions, it becomes it indispensable to mechanize, in some way, this step. The agricultural machine design is considered of great complexity, regarding it must be concerned with the interactions among the operator, machine and environment. When designing a machine, the experience and the dominion of several standpoints have to be interpreted clearly. With the increasing competitiveness on the consumer market and agricultural machines, several companies have joined the research centers, because in general, do not make use of systematic procedures during the project, which can result in failures during operation. This article aimed to design and build a semi-mechanized revolving prototype used to mix the coffee beans. The revolving prototype with the helical screw principles proved to be able to performing the grains transport efficiently.
Theoretical studies of homogeneous catalysts mimicking nitrogenase.
Sgrignani, Jacopo; Franco, Duvan; Magistrato, Alessandra
2011-01-01
The conversion of molecular nitrogen to ammonia is a key biological and chemical process and represents one of the most challenging topics in chemistry and biology. In Nature the Mo-containing nitrogenase enzymes perform nitrogen 'fixation' via an iron molybdenum cofactor (FeMo-co) under ambient conditions. In contrast, industrially, the Haber-Bosch process reduces molecular nitrogen and hydrogen to ammonia with a heterogeneous iron catalyst under drastic conditions of temperature and pressure. This process accounts for the production of millions of tons of nitrogen compounds used for agricultural and industrial purposes, but the high temperature and pressure required result in a large energy loss, leading to several economic and environmental issues. During the last 40 years many attempts have been made to synthesize simple homogeneous catalysts that can activate dinitrogen under the same mild conditions of the nitrogenase enzymes. Several compounds, almost all containing transition metals, have been shown to bind and activate N₂ to various degrees. However, to date Mo(N₂)(HIPTN)₃N with (HIPTN)₃N= hexaisopropyl-terphenyl-triamidoamine is the only compound performing this process catalytically. In this review we describe how Density Functional Theory calculations have been of help in elucidating the reaction mechanisms of the inorganic compounds that activate or fix N₂. These studies provided important insights that rationalize and complement the experimental findings about the reaction mechanisms of known catalysts, predicting the reactivity of new potential catalysts and helping in tailoring new efficient catalytic compounds. PMID:21221062
Theoretical Studies of Homogeneous Catalysts Mimicking Nitrogenase
Alessandra Magistrato
2011-01-01
Full Text Available The conversion of molecular nitrogen to ammonia is a key biological and chemical process and represents one of the most challenging topics in chemistry and biology. In Nature the Mo-containing nitrogenase enzymes perform nitrogen ‘fixation’ via an iron molybdenum cofactor (FeMo-co under ambient conditions. In contrast, industrially, the Haber-Bosch process reduces molecular nitrogen and hydrogen to ammonia with a heterogeneous iron catalyst under drastic conditions of temperature and pressure. This process accounts for the production of millions of tons of nitrogen compounds used for agricultural and industrial purposes, but the high temperature and pressure required result in a large energy loss, leading to several economic and environmental issues. During the last 40 years many attempts have been made to synthesize simple homogeneous catalysts that can activate dinitrogen under the same mild conditions of the nitrogenase enzymes. Several compounds, almost all containing transition metals, have been shown to bind and activate N2 to various degrees. However, to date Mo(N2(HIPTN3N with (HIPTN3N= hexaisopropyl-terphenyl-triamidoamine is the only compound performing this process catalytically. In this review we describe how Density Functional Theory calculations have been of help in elucidating the reaction mechanisms of the inorganic compounds that activate or fix N2. These studies provided important insights that rationalize and complement the experimental findings about the reaction mechanisms of known catalysts, predicting the reactivity of new potential catalysts and helping in tailoring new efficient catalytic compounds.
Inhomogeneous radiative forcing of homogeneous greenhouse gases
Huang, Yi; Tan, Xiaoxiao; Xia, Yan
2016-03-01
Radiative forcing of a homogeneous greenhouse gas (HGG) can be very inhomogeneous because the forcing is dependent on other atmospheric and surface variables. In the case of doubling CO2, the monthly mean instantaneous forcing at the top of the atmosphere is found to vary geographically and temporally from positive to negative values, with the range (-2.5-5.1 W m-2) being more than 3 times the magnitude of the global mean value (2.3 W m-2). The vertical temperature change across the atmospheric column (temperature lapse rate) is found to be the best single predictor for explaining forcing variation. In addition, the masking effects of clouds and water vapor also contribute to forcing inhomogeneity. A regression model that predicts forcing from geophysical variables is constructed. This model can explain more than 90% of the variance of the forcing. Applying this model to analyzing the forcing variation in the Climate Model Intercomparison Project Phase 5 models, we find that intermodel discrepancy in CO2 forcing caused by model climatology leads to considerable discrepancy in their projected change in poleward energy transport.
Homogeneous cosmology with aggressively expanding civilizations
Olson, S. Jay
2015-11-01
In the context of a homogeneous Universe, we note that the appearance of aggressively expanding advanced life is geometrically similar to the process of nucleation and bubble growth in a first-order cosmological phase transition. We exploit this similarity to describe the dynamics of life saturating the Universe on a cosmic scale, adapting the phase transition model to incorporate probability distributions of expansion and resource consumption strategies. Through a series of numerical solutions spanning several orders of magnitude in the input assumption parameters, the resulting cosmological model is used to address basic questions related to the intergalactic spreading of life, dealing with issues such as timescales, observability, competition between strategies, and first-mover advantage. Finally, we examine physical effects on the Universe itself, such as reheating and the backreaction on the evolution of the scale factor, if such life is able to control and convert a significant fraction of the available pressureless matter into radiation. We conclude that the existence of life, if certain advanced technologies are practical, could have a significant influence on the future large-scale evolution of the Universe.
Variation principle of piezothermoelastic bodies, canonical equation and homogeneous equation
LIU Yan-hong; ZHANG Hui-ming
2007-01-01
Combining the symplectic variations theory, the homogeneous control equation and isoparametric element homogeneous formulations for piezothermoelastic hybrid laminates problems were deduced. Firstly, based on the generalized Hamilton variation principle, the non-homogeneous Hamilton canonical equation for piezothermoelastic bodies was derived. Then the symplectic relationship of variations in the thermal equilibrium formulations and gradient equations was considered, and the non-homogeneous canonical equation was transformed to homogeneous control equation for solving independently the coupling problem of piezothermoelastic bodies by the incensement of dimensions of the canonical equation. For the convenience of deriving Hamilton isoparametric element formulations with four nodes, one can consider the temperature gradient equation as constitutive relation and reconstruct new variation principle. The homogeneous equation simplifies greatly the solution programs which are often performed to solve nonhomogeneous equation and second order differential equation on the thermal equilibrium and gradient relationship.