检索结果-南通市图书馆

Analytical and numerical method assessing the risk of sinkholes formation in mining areas

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

International Journal of Mining Science and Technology 2015年第1期25卷 85-89页

作者： piotr Strzalkowski Krzysztof Tomiczek Faculty of Mining and Geology Silesian University of Technology

Voids, which have not been liquidated and associated with shallow mining excavations, pose a serious threat of potential formation of sinkholes. This threat is connected with the loss of stability of voids that had been formed as a result of mining operations in the deeper strata. Taking into account the impact of lower coal seams mining on shallow excavations and based on the example of a region that had been intensely exploited, this paper proposes a methodology for analysing the stability of shallow mine voids in the rock mass. Deformations in the excavation region were calculated by using FLAC2D computer pro- gram and assigning the Coulomb-Mohr model to the rock mass. Based on the numerical analysis, this paper evaluated the stability of the void in the event of a roof support fall. The results indicate the like- lihood of void formation. Based on the Budryk-Knotbe theory, the deformations of rock mass and sand- stone strata in the roof of the void, which had been caused by mining exploitation in consecutive years, were calculated. The results of numerical calculations and analyses were compared with the limit defor- mations values of sandstone in tension. It is concluded that the exploitations cause the void to break down. The proposed method can forecast the discontinuous deformations threats in the areas that have undergone shallow undermining exploitation and the areas of underground urban.

关键词： Mining exploitationDiscontinued deformationsSinkholesStabilityRisk of sinkhole formationTensile deformations of rocks

DIRECTIONAL DO-NOTHING CONDITION FOR THE NAVIER-STOKES EQUATIONS

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2014年第5期32卷 507-521页

作者： Malte Braack piotr Boguslaw Mucha Mathematisches Seminar Christian-Albrechts-Universitat zu Kiel Ludewig-Meyn-Str. 4 D-24098 Kiel Germany Institute of Applied Mathematics and Mechanics University of Warsaw ul Banacha 2 02-097 Warszawa Poland

The numerical solution of flow problems usually requires bounded domains although the physical problem may take place in an unbounded or substantially larger domain. In this case, artificial boundaries are necessary. A well established artificial boundary condition for the Navier-Stokes equations diseretized by finite elements is the “do-nothing” condition. The reason for this is the fact that this condition appears automatically in the variational formulation after partial integration of the viscous term and the pressure gradient. This condition is one of the most established outflow conditions for Navier-Stokes but there are very few analytical insight into this boundary condition. We address the question of existence and stability of weak solutions for the Navier-Stokes equations with a “directional do-nothing” condition. In contrast to the usual “do-nothing” condition this boundary condition has enhanced stability properties. In the case of pure outflow, the condition is equivalent to the original one, whereas in the case of inflow a dissipative effect appears. We show existence of weak solutions and illustrate the effect of this boundary condition by computation of steady and non-steady flows.

关键词： Boundary conditions Navier-Stokes Outflow condition Existence.

The influence of environmental factors on the carbon dioxide flux across the water–air interface of reservoirs in south-eastern Poland

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Environmental Sciences 2017年第6期29卷 290-299页

作者： Renata Gruca-Rokosz Lilianna Bartoszek piotr Koszelnik Faculty of Civil and Environmental Engineering and Architecture Rzeszdw University of TechnologyRzeszowPoland

Studies concerning the emission of carbon dioxide （CO2） were carried out in 2009-2012 for six reservoirs located in four provinces of south-eastern Poland. The CO2 flux across the water-air interface was measured using the ＂static chamber＂ method. The measured fluxes of CO2 （FCO2） ranged from -30.64 to 183.78 mmol/m2/day, and the average values varied in the range from -3.52 to 82.11 mmol/m2/day. In most of the cases, emission of CO2 to the atmosphere was observed. The obtained values of CO2 fluxes were comparable to values typical for other temperate reservoirs. Analysis of the influence of selected envi- ronmental factors on the FCO2 showed that it depends on parameters characterizing both the sediments and surface water. The CO2 flux at the water-air interface was positively correlated with parameters of bottom sediments such as porosity, content of organic carbon and total nitrogen; and negatively with pH value and 51℃ of organic carbon. In the case of the parameters characterizing surface water, positive dependences on the concen- trations of nitrate and total nitrogen, and negative relationships with water temperature and chlorophyll a concentrations, were found.

关键词： Carbon dioxideGreenhouse gasesReservoirSediment

Improving Fault Detection in Modified Code-A Study from the Telecommunication Industry

在线全文

学校读者我要写书评

暂无评论

Journal of Computer Science & Technology 2007年第3期22卷 397-409页

作者： piotr Tomaszewski Lars Lundberg Hkan Grahn School of Engineering Blekinge Institute of Technology SE-372 25 RonnebySweden

Many software systems are developed in a number of consecutive releases. In each release not only new code is added but also existing code is often modified. In this study we show that the modified code can be an important source of faults. Faults are widely recognized as one of the major cost drivers in software projects. Therefore, we look for methods that improve the fault detection in the modified code. We propose and evaluate a number of prediction models that increase the efficiency of fault detection. To build and evaluate our models we use data collected from two large telecommunication systems produced by Ericsson. We evaluate the performance of our models by applying them both to a different release of the system than the one they are built on and to a different system. The performance of our models is compared to the performance of the theoretical best model, a simple model based on size, as well as to analyzing the code in a random order （not using any model）. We find that the use of our models provides a significant improvement over not using any model at all and over using a simple model based on the class size. The gain offered by our models corresponds to 38-57% of the theoretical maximum gain.

关键词： fault prediction metrics testing and debugging

A statistical analysis of geomechanical data and its effect on rock mass numerical modeling:a case study

在线全文

学校读者我要写书评

暂无评论

International Journal of Coal Science & Technology 2021年第3期8卷 312-323页

作者： piotr Malkowski Zbigniew Niedbalski Tafida Balarabe Faculty of Mining and Geoengineering AGH University of Science and Technologyal.Mickiewicza 3030-059 KrakówPoland Revoult Ltd al.Jana PawlaⅡ43a31-864 KrakówPoland

Geomechanical data are never sufficient in quantity or adequately precise and accurate for design purposes in mining and civil *** objective of this paper is to show the variability of rock properties at the sampled point in the roadway's roof,and then,how the statistical processing of the available geomechanical data can affect the results of numerical modelling of the roadway's *** cases were applied in the numerical analysis,using average values(the most common in geomechanical data analysis),average minus standard deviation,median,and average value minus statistical *** study show that different approach to the same geomechanical data set can change the modelling results *** case shows that average minus standard deviation is the most conservative and least *** gives the displacements and yielded elements zone in four times broader range comparing to the average values scenario,which is the least conservative *** two other cases need to be studied *** results obtained from them are placed between most favorable and most adverse *** the average values corrected by statistical error for the numerical analysis seems to be the best ***,the confidence level can be adjusted depending on the object importance and the assumed risk level.

关键词： Statistical analysis Geotechnical data Laboratory tests on rocks Numerical modelling

Architectural Approaches to Network and Service Access Authentication

在线全文

学校读者我要写书评

暂无评论

China Communications 2007年第3期4卷 4-16页

作者： Marcin Dabrowski piotr Pacyna AGH University of Science and Technology Poland AGH University of Science and Technology Poland Universidad Carlos Ⅲ de MadridSpain

Authentication is the first step,of central importance, for access control and for security protection in radio access networks.A general model for authentication was adopted from fixed networks and applied to the wireless ***,the differences in the operational environment between the fixed and the wireless world,heterogeneity of the radio communications systems,new trends in service provisioning, emerging business models and performance requirements raise the need to revisit the original requirements for authentication systems and to come up with schemes that better suit current *** this review paper we discuss authentication in singlehop radio access networks by characterizing the current as well as the emerging authentication schemes.

关键词： authentication access control wireless networks next-generation Internet

Overview of Identity Management

在线全文

学校读者我要写书评

暂无评论

China Communications 2008年第4期5卷 129-142页

作者： Marcin Dabrowski piotr Pacyna AGH University of Science and Technology

In recent years there has been a fast grow of various electronic *** service requires specif-ic credentials for authenticating and authorizing user ac-cess or specific subset of user's personal information for transactions the service *** a situation causes problems with remembering multiple,service-specific authentication data,with controlling user's personal data spread across different services-problems with managing user's *** paper is an overview on Identity Management(IdM).It introduces basic terms connected with IdM,shows current and emerging appli-cation areas,enumerates the most important IdM activi-ties,describes the most representative identity manage-ment specifications and frameworks and at the end,it points out important problems in identity management which need to be addressed in the near future.

关键词： Identity Digital identity Contextual iden-tity Identity management Identity federation Circle of trust

Effects of small molecules on neurogenesis:Neuronal proliferation and differentiation

在线全文

学校读者我要写书评

暂无评论

Acta Pharmaceutica Sinica B 2024年第1期14卷 20-37页

作者： MichałK Jastrze˛bski piotr Wo´jcik piotr Ste˛pnicki Agnieszka A.Kaczor Department of Synthesis and Chemical Technology of Pharmaceutical Substances with Computer Modeling Laboratory Medical University of LublinFaculty of PharmacyLublin PL-20093Poland School of Pharmacy University of Eastern FinlandKuopio FI-70211Finland

Neurons are believed to be non-proliferating ***,neuronal stem cells are still present in certain areas of the adult brain,although their proliferation diminishes with *** as with other cells,their proliferation and differentiation are modulated by various *** mechanisms are foundational to the strategies developed to induce neuronal proliferation and differentiation,with potential therapeutic applications for neurodegenerative *** most common among these diseases are Parkinson's disease and Alzheimer's disease,associated with the formation ofβ-amyloid(Aβ)aggregates which cause a reduction in the number of *** such as LiCl,4-aminothiazoles,Pregnenolone,ACEA,harmine,D2AAK1,methyl 3,4-dihydroxybenzoate,and shikonin may induce neuronal proliferation/differentiation through the activation of pathways:MAPK ERK,PI3K/AKT,NFκB,Wnt,BDNF,and ***,combinations of these compounds can potentially transform somatic cells into *** transformation process involves the activation of neuron-specific transcription factors such as NEUROD1,NGN2,ASCL1,and SOX2,which subsequently leads to the transcription of downstream genes,culminating in the transformation of somatic cells into *** diseases are not the only conditions where inducing neuronal proliferation could be ***,the impact of pro-proliferative compounds on neurons has also been researched in mouse models of Alzheimer's disease.

关键词： Neurogenesis Proliferation Differentiation Maturation Small-molecules Drug coctail Alzheimer’s disease Parkinson’s disease

Wear of the working parts of agricultural tools in the context of the mass of chemical elements introduced into soil during its cultivation

在线全文

学校读者我要写书评

暂无评论

International Soil and Water Conservation Research 2021年第2期9卷 229-240页

作者： piotr Kostencki Tomasz Stawicki Aleksandra Krolicka Department of Renewable Energy Engineering Faculty of Environmental Management and AgricultureWest Pomeranian University of Technology in SzczecinPapie_za Pawła VI Street 171-459SzczecinPoland Faculty of Mechanical Engineering Wrocław University of Science and TechnologySmoluchowskiego Street 2550-370WroclawPoland

For the manufacture of working parts of agricultural tools operating in soil,various structural materials are used:alloy and low-alloy steels,weld materials for hardfacing,and plates made from *** design new construction solutions to obtain components that are resistant to abrasive wear and *** components are subject to wear during soil cultivation,due to which wear products remain in the *** this work,the mass of chemical elements remaining in soil from materials used in selected working parts of agricultural tools intended for soil cultivation was *** the operation of the tested parts,it was found that the following elements were introduced into the soil:Al,B,C,Co,Cr,Cu,Fe,Mo,Nb,Ni,P,Pb,S,Si,Ti,V,Wand *** was introduced into the soil in the highest amount(15.907e222.004 g∙ha-1).Among the chemical elements reaching the soil,there were also elements that may pose a toxicological *** was found that the mass of chemical elements introduced into the soil depends on their content in the used structural materials and also on the conditions of cultivation,which determine the wear intensity of the parts.

关键词： Soil cultivation Working parts Potentially toxic elements Soil contamination Cemented-carbide Low-alloy steel