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Binary operations for homotopy groups with coefficients

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Science China Mathematics 2018年第9期61卷 1543-1552页

作者： martin Arkowitz Department of Mathematics Dartmouth College

We define and study binary operations for homotopy groups with coefficients, and give conditions to prove that certain binary operations are the homomorphic image of the generalized Whitehead product. This allows carrying over properties of the generalized Whitehead product to these operations. We discuss two classes of binary operations, i.e., the Whitehead products and the torsion products. We also introduce a new class of operations called Ext operations and determine some of its properties. Then we compare the torsion product with the Whitehead product in a special case, and prove that the smash product of two Moore spaces has the homotopy type of a wedge of two Moore spaces.

关键词： homotopy groups with coefficients binary operations the generalized Whitehead product Whitehead products torsion products

Applicability of high-temperature cooling systems in different European countries from the view of the condensation risk

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Building Simulation 2021年第5期14卷 1453-1466页

作者： Vladimir Zmrhal martin Bartak Czech Technical University in Prague Faculty of Mechanical EngineeringDepartment of Environmental Engineering Technicka 416000 Prague 6Czech Republic

Due to the different approaches in determining the ventilation airflow rate per person for workspaces,where high-temperature air conditioning systems are used for air conditioning,problems with the condensation of water vapour on the cold surfaces of the system can *** article analyses the risk of condensation in various European cities using the available climatic *** with cooling ceilings and cooling beams with a ventilation device operating in parallel are taken into *** ventilation airflow rates per person were *** the example of a room equipped with high-temperature cooling,an energy simulation calculation is performed,which includes a ventilation and air-conditioning system with the possibility of capacity *** is clear from the results that the condensation of water vapour can be prevented by technical measures at the cost of reducing the cooling capacity,which can affect the achievement of the thermal comfort of those *** the end,suitable solutions are discussed,which should already be adopted at the time the device is designed so that the risk of condensation is not a major obstacle in the operation of these energy-efficient *** irreplaceable role in the operation of high-temperature cooling systems is played by a measurement and control system with a suitable algorithm to prevent condensation.

关键词： ventilation air-conditioning cooled ceilings chilled beams low energy cooling risk of condensation

Experimental and Numerical Investigation of Centrifugal Pumps with Asymmetric Inflow Conditions

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Journal of Thermal Science 2015年第6期24卷 516-525页

作者： Sten Mittag martin Gabi Institute of Fluid Machinery Karlsruhe Institute of Technology KIT

Most of the times pumps operate off best point *** are changes of operating conditions,modifications,pollution and wearout or *** consequences non-rotational symmetric flows,transient operational conditions,increased risk of cavitation,decrease of efficiency and unpredictable wearout can *** construction components of centrifugal pumps,in particular intake elbows,contribute to this *** elbows causes additional losses and secondary flows,hence non-rotational velocity distributions as intake profile to the centrifugal *** a result the impeller vanes experience permanent changes of the intake flow angle and with it transient flow conditions in the blade *** paper presents the first results of a project,experimentally and numerically investigating the consequences of non-rotational inflow to leading edge flow conditions of a centrifugal *** two pumpintake-elbow systems are compared,by only altering the intake elbow geometry:a common single bended 90°elbow and a numerically optimized elbow(improved regarding rotational symmetric inflow conditions and friction coefficient).The experiments are carried out,using time resolved stereoscopic PIV on a full acrylic pump with refractions index matched(RIM)working *** allows transient investigations of the flow field simultaneously for all blade leading *** CFD results are validated and used to further support the investigation *** comparing an analog pump system with ideal inflow conditions.

关键词： non-rotational symmetric inflow centrifugal pump intake elbow PIV RIM CFD

CFD-DEM simulation of turbulence modulation in horizontal pneumatic conveying

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Particuology 2017年第2期15卷 15-24页

作者： Mohammadreza Ebrahimi martin Crapper Institute for Infrastructure and Environment School of Engineering The University of Edinburgh The King's Buildings Edinburgh EH9 3JL UK Department of Mechanical and Construction Engineering Northumbria University Ellison Place Newcastle-upon-Tyne NE1 8ST UK

A study is presented to evaluate the capabilities of the standard k–ε turbulence model and the k–ε turbulence model with added source terms in predicting the experimentally measured turbulence modulation due to the presence of particles in horizontal pneumatic conveying, in the context of a CFD–DEM Eulerian–Lagrangian simulation. Experiments were performed using a 6.5-m long, 0.075-m diameter horizontal pipe in conjunction with a laser Doppler anemometry （LDA） system. Spherical glass beads with two sizes, 1.5 and 2 mm, were used. Simulations were performed using the commercial discrete element method software EDEM, coupled with the computational fluid dynamics package FLUENT. Hybrid source terms were added to the conventional k–ε turbulence model to take into account the influence of the dispersed phase on the carrier phase turbulence intensity. The simulation results showed that the turbulence modulation depends strongly on the model parameter Cε3. Both the standard k–ε turbulence model and the k–ε turbulence model with the hybrid source terms could predict the gas phase turbulence intensity trend only generally. A noticeable discrepancy in all cases between simulation and experimental results was observed, particularly for the regions close to the pipe wall. It was also observed that in some cases the addition of the source terms to the k–ε turbulence model did not improve the simulation results when compared with those of the standard k–ε turbulence model. Nonetheless, in the lower part of the pipe where particle loading was greater due to gravitational effects, the model with added source terms performed somewhat better.

关键词： Turbulence modulation Pneumatic conveying Eulerian-Lagrangian approach Laser Doppler anemometry

A force-compensated compliant MEMS-amplifier with electrostatic anti-springs

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Microsystems & Nanoengineering 2023年第3期9卷 235-244页

作者： Philip Schmitt martin Hoffmann Microsystems Technology Ruhr-Universität BochumUniversitätsstr.15044801 BochumGermany

In this paper,an electrostatic compliant mechanical amplifier intended for force-compensated displacement amplification in MEMS sensor applications is ***,mechanical transformers that enhance a small input displacement into a large output displacement generate large forces at the input of the *** microsystem proposed here allows for the reduction and compensation of the input stiffness of the amplifier and any mechanical components connected to it while providing a constant amplification ratio at the same *** amplifying mechanism features bidirectional electrostatic anti-springs enabling the control of the stiffness by applying a constant DC *** electrode design of the anti-springs and its influence on the force-displacement characteristic,the side instability and the maximal displacement are studied through analytical approaches and supported by FEA and by *** on the derived models,a compliant electromechanical amplifier is developed,featuring an amplification ratio of *** this amplifier the initial input stiffness of 422 N/m could be reduced to 6.8 N/m by applying a voltage of 100 *** an additional application,we show how the amplifier can be used as a mechanical force sensor with tuneable sensitivity,where the forces at the input are transformed into large output *** experiments,we show how the sensitivity can be adjusted and increased by a factor of 25 by applying a voltage at the anti-springs.

关键词： amplifier electrostatic spring

Froth flotation of scheelite – A review

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International Journal of Mining Science and Technology 2018年第3期28卷 373-384页

作者： Nathalie Kupka martin Rudolph Helmholtz Zentrum Dresden Rossendorf (HZDR) Helmholtz Institute Freiberg for Resource Technology (HIF)

Froth flotation of scheelite has regained new focus since the 2010s and research regarding floatability and reagents has made great progress over the years. The main objective was and remains the selective flotation of scheelite from other calcium-bearing minerals, in particular calcite, fluorite and apatite. Due to similar properties, most attempts have limited success or only specific application(linked to a type of ore or a location). This article aims at reviewing all general physical-chemical information on froth flotation of scheelite, including electrokinetic properties, influence of p H and already existing reagents as well as ones still under examination. It appears that chelating or mixed collectors and modified versions of sodium silicate and quebracho hold great promise for scheelite flotation, while the use of said depressants and/or promoters seems inevitable.

关键词： Scheelite Froth flotation Calcium-bearing minerals Selectivity challenges Promising reagents

MODELING SOCCER BY MEANS OF RELATIVE PHASE

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Journal of Systems Science & Complexity 2013年第1期26卷 14-20页

作者： SIEGLE Malte LAMES martin TU Munchen Department for Training and Computer Science in Sports

Soccer is a complex ***,appropriate(nontrivial) models have to be applied to be able to analyze the behavior of the teams on the *** study analyzed the World Cup Final 2006 between France and Italy by means of relative *** longitudinal and lateral positions of all 20 outfield players were used to calculate relative phase by Hilbert *** team-,group-,and attacker-fullbacks couplings showed that soccer is clearly an in-phase *** of the relative phase structure helped to identify scoring opportunities of the attacking ***,analyses of the relative phase structure can help to understand the complexity of soccer.

关键词： Perturbations relative phase soccer.

Enhanced nitric oxide production is a universal response to hypoxic stress

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National Science Review 2018年第4期5卷 532-533页

作者： martin Feelisch Clinical & Experimental Sciences and Integrative Physiology and Critical Illness Group Faculty of Medicine Southampton General Hospital and Institute for Life Sciences University of Southampton NSR

Life at high altitude poses a formidable challenge to human physiology because every breath of thin air inhaled contains less oxygen(O2)per volume than air at sea level,causing the resultant drop in O2 pressure in blood to limit performance and threaten *** short-term adjustments to hypoxia(acclimatization)including increased erythropoiesis ensure total

关键词： Enhanced nitric oxide production is a universal response to hypoxic stress

Using the DEM-CFD method to predict Brownian particle deposition in a constricted tube

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Particuology 2014年第4期12卷 94-106页

作者： Florian Chaumeil martin Crapper School of Engineering The University of EdinburghEdinburgh EH9 3JLUnited Kingdom

Modelling of the agglomeration and deposition on a constricted tube collector of colloidal size particles immersed in a liquid is investigated using the discrete element method （DEM）. The ability of this method to represent surface interactions allows the simulation of agglomeration and deposition at the particle scale. The numerical model adopts a mechanistic approach to represent the forces involved in colloidal suspensions by including near-wall drag retardation, surface interaction and Brownian forces. The model is implemented using the commercially available DEM package EDEM 2.3~, so that results can be repli- cated in a standard and user-friendly framework. The effects of various particle-to-collector size ratios, inlet fluid flow-rates and particle concentrations are examined and it is found that deposition efficiency is strongly dependent on the inter-relation of these parameters. Particle deposition and re-suspension mechanisms have been identified and analyzed thanks to EDEM＇s post processing capability. One-way coupling with computational fluid dynamics （CFD） is considered and results are compared with a two- way coupling between EDEM 2.3 and FLUENT 12.1. It is found that two-way coupling requires circa 500% more time than one-way coupling for similar results.

关键词： Discrete element method DEM Colloids Agglomeration Deposition Simulation