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1.
Hydrothermal processes for conversion of lignocellulosic biomass to value-added compounds
Tanja Milovanović, 2020, doktorska disertacija

Opis: In this doctorial dissertation subcritical water processes of lignocellulosic biomass to obtain value-added compounds are studied. The doctorial dissertation is divided into four main parts. In the first and second part of dissertation, model compounds (standards of cellulose and sugars and chestnut tannins) were primarly used in order to better understand processes of real biomass material. The degradation of cellulose and different sugars was performed in batch reactor with subcritical water. The different reaction temperatures and times were used. The main phases, such as water-soluble fraction, acetone-soluble fraction and solid residue were separated and analysed. The analysis of water-soluble phase was done by HPLC equipped with UV and RI detector, while acetone-soluble phase of cellulose was analysed by GC-MS. Total sugar content was determined by the phenol-sulphuric acid colorimetric method. The properties of char, obtained using cellulose as a treated material, such as: specific surface area, pore volume and pore diameter were determined by gas adsorption method. A water-soluble phase mainly consists of sugar monomers and monomer degradation products such as 5-hydroxymethylfurfural (5-HMF), furfural, erythrose, sorbitol, 1,6-anhydroglucose, glycolaldehyde, glycerlaldehyde, 1,3-dihydroxyacetone, pyruvaldehyde, formic, levulinic, lactic, oxalic and succinic acids, while acetone-soluble phase, referred to also as bio-oil, consists of furans, phenols, carboxylic acids, aldehydes, ketones and high molecular compounds. The reaction mechanism of cellulose and sugars in subcritical water has been proposed based on the obtained results. Furthermore, the results from cellulose and sugar hydrothermal degradation were utilized in further work to determine which industrially interesting products could be obtained by hydrothermal processing of paper waste in subcritical water. The optimum conditions ( temperature and reaction time), which gave us the highest yield of base chemicals (furfural, 5-HMF, levulinic acid) were determined. Sweet chestnut (Castanea Sativa) bark contains high level of tannins and various phenolic compounds which can be utilized in pharmaceutical, cosmetic, nutritional and medical purposes. The sweet chestnut tannins extract and sweet chestnut bark were used as materials highly rich in bioactive compounds for subcritical water processes which are presented in the second part of doctorial dissertation, respectively. The spectrophotometric methods were used to determine total tannins, phenols and carbohydrates content and antioxidant activity. The identified compounds were ellagic and gallic acid, ellagitannins (vescalagin, castalagin, 1-o-galloyl castalagin, vescalin and castalin), sugars (maltose, glucose, fructose and arabinose) and sugar derivatives (5-HMF, furfural and levulinic acid). The results obtained from hydrothermal hydrolysis were compared to results from acid hydrolysis. Finally, the optimization of reaction parameters of subcritical water processes has been done aiming to obtain the product highly rich in ellagic acid. Subcritical water extraction of horse chestnut (Aesculus hippocastanum) parts such as seeds, seed shell, bark and leaves was described in the third chapter of dissertation. The detected compounds in extracts, such as escins, esculin, fraxin, phenolic compounds (chlorogenic, neochlorogenic and gallic acids) and furfurals (5-hydroxymethyfurfural, furfural, and methylfufrual) are quantified using HPLC. The last part of dissertation proposes extraction of cocoa shell using green technologies (supercritical CO2 and subcritical water extraction) and also conventional methods (Soxhlet extraction with hexane and extraction with 50 % acetone) to obtain bioactive compounds in order to compare the results. The detected compouns were methylxanthines, phenolic compounds, sugars, fatty acids.
Ključne besede: Subcritical water, biomass, biowaste, extraction, hydrothermal degradation, hydrolysis, bioactive compounds.
Objavljeno: 16.10.2020; Ogledov: 367; Prenosov: 61
.pdf Celotno besedilo (6,32 MB)

2.
Water crimes and policing
Katja Eman, Saša Kuhar, Gorazd Meško, 2017, pregledni znanstveni članek

Opis: Purpose: Water is a crucial natural resource for the survival of the human and various other species. As a result, water is becoming more and more attractive to various economic and criminal groups. Therefore, the purpose of this paper is to present crimes against water, the types of water crimes, an analysis of the situation in Slovenia and the police measures in the field of water security. Methods: The water crimes phenomenon was analysed by applying a descriptive method, literature review, statistical data analysis and information received from the police. Findings: Water crimes are an emerging global issue. Water crimes include diverse types of crimes ranging from the pilfering of water from pipelines, illegal waste management, water theft, river and marine pollution, manipulation of sampling methods to avoid treatment costs, fraud and illegal trafficking of water, terrorism and cyber-attacks on water management operations, illegal waste discharges from factories, and unauthorised consumption from the water network. Water crimes are hard to detect, investigate, prosecute and study. It is necessary for law enforcement officers to have knowledge related to water crimes – from natural and social sciences to other knowledge such as biology and chemistry. Further, they must have well-organised coordination and cooperation with other formal social control entities like inspectorates, institutes etc. Originality/Value: The paper presents water crime issues and makes an important contribution to the professional and general public with respect to the prevention and formal social control of water crime.
Ključne besede: water, water crime, environmental crime, police, policing
Objavljeno: 15.04.2020; Ogledov: 282; Prenosov: 18
.pdf Celotno besedilo (748,05 KB)
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3.
The dry fraction of unsaturated soils
Julio César Leal Vaca, Gustavo Gallegos Fonseca, Eduardo Rojas González, 2015, izvirni znanstveni članek

Opis: An equation to account for the shear strength of unsaturated soils is proposed in this paper. This equation is defined as the equivalent stress, and is an extension of Murray’s equation. This approach applies to the general case of bi-modal structured soils showing a macrostructure and microstructure. The theoretical development considers the existence of a dry fraction in addition to the saturated and unsaturated fractions of the soil. These different fractions are included in a porous model, which allows an evaluation of the parameters of the equivalent stress equation. Finally, the paper includes a comparison between theoretical and experimental results. The comparison shows that the proposed equation can be used to estimate the shear strength of unsaturated soils.
Ključne besede: unsaturated soil, shear strength, equivalent stress, water retention curve
Objavljeno: 15.06.2018; Ogledov: 688; Prenosov: 39
.pdf Celotno besedilo (183,91 KB)
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4.
A new method for testing the anti-permeability strength of clay failure under a high water pressure
Fu-wei Jiang, Ming-tang Lei, Xiao-zhen Jiang, 2015, izvirni znanstveni članek

Opis: It is difficult to judge the failure of clay seepage under a high water pressure.This paper presents a new method to assess clay failure based on the anti-permeability strength, which is the critical water pressure to destroy the clay. An experiment is designed to test the value that avoids the problem of the time-consuming, traditional method to test clay seepage deformation. The experimental system and the process of testing are introduced in this paper. With a self-designed experimental system and method, 18 groups of sample were tested. The results show that the clay thickness and the seepage paths influence the anti-permeability strength. It also indicates that water infiltrates into the clay under the condition that its pressure exceeds a minimum value (P0).
Ključne besede: clay failure, seepage deformation, anti-permeability strength, high water pressure
Objavljeno: 15.06.2018; Ogledov: 564; Prenosov: 31
.pdf Celotno besedilo (249,24 KB)
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5.
Experimental research on variation of pore water pressure in constant rate of strain consolidation test
Hojjat Ahmadi, Hassan Rahimi, Abbas Soroush, Claes Alén, 2014, izvirni znanstveni članek

Opis: Constant rate of strain (CRS) consolidation is a rapid test method which is used for determination of compressibility of clayey soils. In a CRS test, the appropriate strain rate is selected based on pore water pressure ratio, i.e. the ratio of pore pressure to total stress. In the present study, to investigate the effect of strain rate on variation of pore water pressure ratio, four different clay samples of different plasticity were tested by CRS apparatus. The results of the experiments showed that the trend of variation of pore water pressure is dependent on the drained water flow regime which may be either Darcy or non-Darcy. The results also indicated that the plasticity of clay does not have considerable effect on variation of pore water pressure.
Ključne besede: constant rate of strain, consolidation, pore water pressure ratio, soil plasticity, Darcy and non-Darcy flow
Objavljeno: 14.06.2018; Ogledov: 393; Prenosov: 35
.pdf Celotno besedilo (576,58 KB)
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6.
A laboratory characterization of soils and clay-bearing rocks using the Enslin-Neff water-adsorption test
Ana Petkovšek, Matej Maček, Bojan Majes, 2009, izvirni znanstveni članek

Opis: The application of the Enslin-Neff water-adsorption test for the determination of soil-index properties has been investigated on commercially available reference minerals and on real soils. The Enslin-Neff test is a simple and reliable laboratory method, which can provide important information about the behavior of soils, clay-bearing rocks and aggregate fines that are in contact with water. Although the test has been frequently used for bentonite testing, practically no results have been published about the physical meaning of the Enslin-Neff water-adsorption values for real soils. The results of this study indicate that the Enslin-Neff water-adsorption test can be used to obtain accurate values of some soil-index properties, such as the liquid limit, the plasticity index, the methylene-blue value, and the soil-water characteristic curve.
Ključne besede: water adsorption, soil water characteristic curve, methylene blue value, soil suction
Objavljeno: 06.06.2018; Ogledov: 706; Prenosov: 64
.pdf Celotno besedilo (380,52 KB)
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7.
The development of a “drive-in” filters dewatering system in the Velenje coal mine using finite-element modelling
Goran Vižintin, Miran Veselič, Andrej Bombač, Evgen Dervarič, Jakob Likar, Đorđe Vukelič, 2009, izvirni znanstveni članek

Opis: During the mining operations at the Velenje coal mine, groundwater has been presenting a constant threat to underground works. The hydrogeological setup is so complex that a lot of structural drilling and well-logging operations were needed in the past to clarify it. Above the lignite seam is a Pliocene and Pleisticene multilayer aquifer system, composed mainly of permeable sand layers and impermeable clay layers. In 1981 the Pliocene aquifers were divided into three packages. Based on the water-table data of each aquifer, pumping tests, chemical analyses of the groundwater and the geophysical properties the Pliocene aquifers directly above the seam, together with impermeable layers, were divided into: a) the first water-bearing sands (Pl1), b) the aquifers 2080 m above the coal seam (Pl2) and c) the upper Pliocene aquifers (Pl3). For the mining operations the most important aquifer of saturated sands is Pl1. The hydraulic pressure of the groundwater in these sands directly affects the safety of the mining. These aquifers are mostly affected by the dewatering activities, too. However, the dewatering wells are constructed in such a way as to capture the whole Pl2 and, somewhere, even a part of the Pl3 complex, too. The water pressure in this multilayer aquifer can reach over 35 bars, so a massive program of drawdown activities has been needed and is still in place to decrease the water table in the area related to the mining operations. Special, multilevel observation wells are used to monitor the water level. A number of 3D finite-difference models (FDMs) were used to estimate the regional groundwater drawdown. It was observed that the FDMs performed well when predicting the regional situation, but the model-predicted drawdown was lower than the observed values at observation points in the area where the dewatering operations using “drive-in” filters have taken place in the past. This is a well-known problem of the FDM: the drawdown being rather a function of the cell size than of the flow net. The risk of water inrushes will increase, especially after 2012 and 2017, when a series of surface-drilled wells, connected into the mine’s pumping-line batteries, will be abandoned due to excavation works and mining-subsidence effects. Consequently, the dewatering schemes had to be completely reviewed. The destroyed, first-order dewatering structures will have to be replaced by a series of “drive-in” filters, drilled from the mine roadways in the area of the planned longwall face operations. For the drive-in filter-system design the FDM does not seem to be appropriate. This is especially so if the error in the drawdown and pumping flow prediction is taken into account. That led, in 2007, to the selection of the finite-element method (FEM) for the prediction of the groundwater drawdown and the water pumping rates in the areas were the underground works will encounter the risk of a water inrush. Based on the FEM prediction the sizing and the layout pattern of the “drive-in” filters were made.
Ključne besede: drive-in filters, groundwater, mining water, mining hydrology, geophysical well login, mathematical modelling
Objavljeno: 06.06.2018; Ogledov: 426; Prenosov: 48
.pdf Celotno besedilo (605,68 KB)
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8.
Improvements to the quality of underground water by introducing carbon dioxide
Mojca Poberžnik, Ludvik Trauner, Albrecht Leis, Aleksandra Lobnik, 2008, izvirni znanstveni članek

Opis: The presented research work is focused on the development of an innovative way of economically improving the quality of underground water by the application of carbon dioxide. The basic pilot plant was developed with the idea of applying carbon dioxide in order to maintain the carbonate equilibria in water, pumped from under the ground. The optimal content of this natural component in underground water, used in urban areas for different purposes (e.g. drinking water, heating systems etc), simultaneously prevents corrosion and precipitated mineral deposits. The adaptation of an existing pilot plant started with operational testing and preliminary measurements. An appropriate sensor system for the online monitoring of the tap waterćs heating process measuring parameters such as the temperature, the concentration of dissolved carbon dioxide, the conductivity and the pH value was built in. Different amounts of carbon dioxide were applied during the two experimental stages. The composition of the water was regularly analysed using automatic titration and ionic chromatography. The gas-dosing control in the first phase was volumetric. Due to an observed inaccuracy in the gasdosing system, the volumetric dosing control was replaced with a system for the mass control of the introduced gas. Closing the system was considered to be suitable, as the water composition remained almost constant during the entire experiment. Improvements to the gas-dosing control and the closing of the system were carried out in the final phase of the pilot plant's adaptation. Further measurements were made in different seasons to test the seasonal influences on underground water's composition and the efficiency of the carbon dioxide supply.
Ključne besede: underground water, drinking water quality, pilot plant, carbonate equilibria, carbon dioxide, precipitation, scale
Objavljeno: 05.06.2018; Ogledov: 570; Prenosov: 41
.pdf Celotno besedilo (661,89 KB)
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9.
Analyses of the suspended-load sedimentation process and its dynamics in reservoirs with high daily oscillations
Helena Vrecl-Kojc, Bojana Dolinar, Roman Klasinc, Ludvik Trauner, 2008, izvirni znanstveni članek

Opis: The river water pumped into reservoirs with high daily oscillations, e.g. at pumping hydroelectric power plants, contains different amounts of suspended load depending on the time period and the riverćs discharge. This paper presents an analysis of the suspended-load sedimentation process that is based on the interaction between the sedimentation, i.e., the settling, velocity and the motion of the water. The settling velocity of spherical particles in the presence of a buoyancy force is a function of the particle size. Laboratory investigations of the suspended material from the river-watersamples have determined the ratio between the particle size and the concentration of suspended material with respect to the river discharge, the ratio between the concentration of suspended material in the water and the discharge, and the relationship between the concentration of suspended material and the discharge of water, which is for the first time expressed as an exponential function. The motion of the water in the reservoirs with high daily oscillations is solved by the three-dimensional modeling of the liquid streams. The evaluation of the results is presented for the case of the planned Kozjak pumping hydroelectric power plant on the River Drava.
Ključne besede: suspended load, water motion, sedimentation, sedimentation transport, pumped hydroelectric power plant, reservoir
Objavljeno: 05.06.2018; Ogledov: 1186; Prenosov: 40
.pdf Celotno besedilo (348,17 KB)
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10.
Analysis of concentration and sedimentation of suspended load in the reservoirs
Helena Vrecl-Kojc, Bojana Dolinar, Roman Klasinc, Ludvik Trauner, 2008, izvirni znanstveni članek

Opis: This paper deals with the sedimentation of suspended load in the reservoirs. As an example the reservoir of the hydroelectric power plant Boštanj on the Sava River is shown. The objective of the described studies was to determine the quantity and type of deposited material in the reservoir during the selected time period. For this purpose, the mineral and chemical composition, and the concentration and the particle size of the suspended load at the intake of the water into the reservoir and at its outflow were examined. In order to determine the concentration of the suspended load, 24 water samples from the area of the intake and outflow from the reservoir were taken. At the same time the discharge of the Sava River was measured. Solid particles were removed from the water with the help of sedimentation and in the final stage of water evaporation. The results of the studies showed that the concentration of the suspended material was changing in relation to the location and the flow rate of the water. This ratio can be described with an exponential function. In suspended load composition carbonates, muscovite/illite and quartz dominate; however, chlorite was also found, as well as small quantities of plagioclase and organic detritus. With regard to the size of the particles the examined samples are classified as silt. It was determined that the concentration of the suspended load, at the same flow rate of water, at the intake into the reservoir is larger than at the outflow. The difference is represented by the material that was sedimented in the reservoir due to the decreased speed of the water as a result of the river's impoundment. A comparison of the composition of the samples from both collection sites showed that at the outflow site of the water from the reservoir there is a somewhat smaller share of carbonate grains and heavy minerals than at the intake site, and a higher content of organic detritus and clay particles can also be observed. Considering the actual discharge of water in the period between July 2006 and July 2007 and the examined ratio between the flow rate of the water and the quantity of suspended and deposited material, the total quantity of sedimented material in this period was estimated.
Ključne besede: suspended load, sedimentation, sediment transport, water storage reservoir
Objavljeno: 05.06.2018; Ogledov: 1271; Prenosov: 45
.pdf Celotno besedilo (348,17 KB)
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