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Experimental investigation review of biodiesel usage in bus diesel engine
Breda Kegl, Marko Kegl, 2017, izvirni znanstveni članek

Opis: This paper assembles and analyses extensive experimental research work conducted for several years in relation to biodiesel usage in a MAN bus Diesel engine with M injection system. At first the most important properties of the actually used neat rapeseed biodiesel fuel and its blends with mineral diesel are discussed and compared to that of mineral diesel. Then the injection, fuel spray, and engine characteristics for various considered fuel blends are compared at various ambient conditions, with special emphasis on the influence of low temperature on fueling. Furthermore, for each tested fuel the optimal injection pump timing is determined. The obtained optimal injection pump timings for individual fuels are then used to determine and discuss the most important injection and combustion characteristics, engine performance, as well as the emission, economy, and tribology characteristics of the engine at all modes of emission test cycles test. The results show that for each tested fuel it is possible to find the optimized injection pump timing, which enables acceptable engine characteristics at all modes of the emission test cycles test.
Ključne besede: bus diesel engine, fuel injection, fuel spray, combustion, emission, engine performance, tribology characteristics, optimized injection pump timing
Objavljeno: 07.07.2017; Ogledov: 325; Prenosov: 170
.pdf Celotno besedilo (3,81 MB)
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Examining determinants of leadership style among Montenegrin managers
Anđelko Lojpur, Ana Aleksić, Sanja Vlahović, Mirjana Pejić Bach, Sanja Peković, 2015, izvirni znanstveni članek

Opis: As a leader’s behavior can have a strong impact on different employee work- related outcomes, various approaches have been put forth in an effort to determine the most effective form of leadership and determinants of individuals’ choice of leadership style. This paper analyzed whether one’s choice of leadership style is due more to personal or organizational characteristics. We used survey data to investigate the determinants of leadership style among Montenegrin managers. Our analysis showed that, although demographic characteristics such as gender, age, and education do not influence the choice of leadership style, internal organizational characteristics such as hierarchical level, managerial orientation to tasks/people, and decision-making characteristics such as decision- making style and decision-making environment are positively associated with the choice of democratic leadership style. This contributes to recent research in leadership that shows how some personal characteristics are considered to be less important in developing certain styles and that the choice of style is more dependent and contingent on external influences and situations.
Ključne besede: decision-making characteristics, demographic characteristics, internal organizational characteristics, leadership style, Montenegro
Objavljeno: 03.05.2018; Ogledov: 143; Prenosov: 22
.pdf Celotno besedilo (1,66 MB)
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Investigations to establish the influence of the thermal energy field on soil properties
Srinivas Kadali, Susha Lekshmi, Susmita Sharma, D. N. Singh, 2013, izvirni znanstveni članek

Opis: This paper describes details of a study to investigate and demonstrate the changes undergone by soil when it is exposed to elevated temperatures. Such situations are commonly encountered while designing the foundations for the furnaces, boiler units, forging units, brick kilns, rocket launching pads, buried power-supply cables, air-conditioning ducts, underground explosions, disposal of high-level radioactive and industrial toxic wastes, ground modifications or soil-stabilization techniques, etc. As such, investigations to establish changes undergone by the soil when it is exposed to elevated temperatures assume some importance. With this in view, individual samples of six soils, with entirely different characteristics, were subjected to temperatures up to 300°C (sequentially in steps of 50°C) and after each step of thermal treatment, these samples were characterized for their physical, chemical and mineralogical properties. Based on a critical synthesis of the results, it has been demonstrated that elevated temperatures cause (i) a change in the color, (ii) an increase in the specific gravity, particle size and weight loss, (iii) a reduction in the specific surface area, cation-exchange capacity and zeta-potential, and (iv) a structural transformation of the soil. Though these changes would affect the engineering properties of the soil to a large extent, the scope of this paper is limited to demonstrating the alterations in physical, chemical and mineralogical changes, only, occurring in the soil when it is exposed to elevated temperatures.
Ključne besede: elevated temperatures, soil, characterization, physical characteristics, chemical characteristics, mineralogical characteristics
Objavljeno: 14.06.2018; Ogledov: 194; Prenosov: 12
.pdf Celotno besedilo (1,08 MB)
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Formation of meso- and micro-pores in fly-ash zeolites using a three-step activation
Bhagwanjee Jha, D. N. Singh, 2014, izvirni znanstveni članek

Opis: Researchers have comprehensively characterized alkali- activated fly-ash (the residue) and ascertained its highly zeolitic nature. In order to evaluate its potential for application as an adsorbent for the decontamination of waste water, the decisive parameters have mostly been the cation-exchange capacity, the mineralogy and the morphology of the residue. However, a study of the pore characteristics (e.g., the size and volume) of such residues is still warranted to anticipate their contaminant transport and the diffusion phenomena as a type of geotechnical engineering material. In this situation, the present study demonstrates the evolution of pores in the fly-ash after alkali activation up to three steps, and simultaneously, its effects` on other characteristics (e.g., the specific gravity, specific surface area and the cation-exchange capacity) of three types of similarly synthesized residues (the first, produced by using a NaOH aqueous solution and the other two residues, the result of alkali activation using a NaOH spent solution, the filtrates). Based on N2 gas absorption isotherms and infrared transmittance spectra, residues obtained from the second and third steps, each involving 24 hours of treatment using filtrates of 1.5-M NaOH, are established to be significantly enriched in the finer meso- and micro-pores, respectively, in comparison with a pure and macro-porous zeolite 4A.
Ključne besede: fly-ash, hydrothermal treatment, three-step activation, pore characteristics
Objavljeno: 14.06.2018; Ogledov: 160; Prenosov: 32
.pdf Celotno besedilo (298,21 KB)
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Relationship between the compressive and tensile strengths of lime-treated clay containing coconut fibres
Vivi Anggraini, Bujang Huat, Afshin Asadi, Haslinda Nahazanan, 2015, izvirni znanstveni članek

Opis: The effects of coconut fibre on the mechanical characteristics of lime-treated clay are investigated in this study. The lime-treated clay specimens were prepared with a variety of coconut-fibre contents, i.e., 0.5%, 1%, 1.5% and 2%, in terms of the weight of dry soil. The stabilized specimens were tested at 7, 28 and 90 days after the treatment in order to observe the evolution of the mechanical resistance with time. The results of the unconfined compressive strength tests were used to determine the relationships between the compressive strengths and the indirect tensile strengths of the stabilized soil. Furthermore, the optimum percentage of coconut fibre mixed in the soil/lime mixtures was 1% of the dry mass and reinforcement at 90 days increases the peak compressive strength and the indirect tensile strength. Coconut-fibre inclusion changes the brittle behaviour of the lime-treated clay soil to give it a more ductile character.
Ključne besede: coconut fibre, lime, compressive strength, indirect tensile strength, clay soil, failure characteristics
Objavljeno: 14.06.2018; Ogledov: 133; Prenosov: 8
.pdf Celotno besedilo (755,61 KB)
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Evaluation of the plastic critical depth in seismic active lateral earth pressure problems using the stress-characteristics method
Amin Keshavarz, 2016, izvirni znanstveni članek

Opis: The plastic critical depth or the conventional tension crack depth has a considerable effect on the active lateral earth pressure in cohesive soils. In this paper the depth for c-ϕ soils has been evaluated in the seismic case using the stress-characteristics or slip-line method. The plastic critical depth was calculated on the basis of the theory of the stress-characteristics method and by considering the horizontal and vertical pseudo-static earthquake coefficients. The proposed solution considers the line of discontinuity in the stress-characteristics network. The earth slope, wall slope, cohesion and friction angle of the soil and the adhesion and the friction angle of the soil-wall interface were considered in the analysis as well. The results show that the plastic critical depths of this study are smaller than those of the other methods and are closer to the modified Mononobe-Okabe method. The effects of the wall and the backfill geometry, the mechanical properties of the soil and the pseudo-static coefficients were studied.
Ključne besede: plastic critical depth, stress characteristics, active lateral earth pressure, seismic
Objavljeno: 15.06.2018; Ogledov: 286; Prenosov: 13
.pdf Celotno besedilo (353,82 KB)
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Assessments of the hydraulic conductivity for predicting the swelling characteristics of compacted expansive soils
Hakan Güneyli, 2017, izvirni znanstveni članek

Opis: The swelling behaviour of expansive soils is significant in geotechnical engineering since it causes severe damage to civil structures. The swelling characteristics need to be well known for satisfactorily safe and economic engineering designs. A direct determination of the swelling characteristics requires considerable time and money, involving serious experimental effort. Alternatively, several indirect estimation techniques developed using empirical regression models available in literature are widely used in practice. These empirical estimation techniques have generally been assessed as a function of the soil properties, i.e., consistency limits, density, moisture content, clay fraction and type, and cation-exchange capacity. This paper describes the dependence of the percentage swell (S%) and the swell pressure (σsp) obtained from a free-swell (FS) test and a constant-volume swell (CVS) test, and the primary swell time (PST), in which almost 90% of the swelling occurs as strain, which is considered as a new swelling characteristic in this study, on the hydraulic conductivity (k) controlled by a change in the gradation of compacted expansive soils. In addition, the rate of primary swelling (Cps), which is the primary swelling phase’s slope of the curve of percentage swell vs. log time, and the ratio of (Cps/k) were used to analyse their relationships with the swelling characteristics. This study provides the empirical methods that can be utilized to obtain indirect estimations of the percentage swell (S%), swell pressure (σsp) and primary swell time (PST) depending on k, Cps and Cps/k, in addition to, or with, the conventional parameters. The correlation coefficients of the regression analysis, having high performance, and indicating strong relationships between the swelling characteristics and the indices proposed in this study, state that these empirical prediction equations can be used safely in engineering practice.
Ključne besede: swelling characteristics, gradation, hydraulic conductivity, rate of primary swelling
Objavljeno: 18.06.2018; Ogledov: 137; Prenosov: 15
.pdf Celotno besedilo (2,21 MB)
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Prediction of California Bearing Ratio (CBR) and Compaction Characteristics of granular soil
Attique ul Rehman, Khalid Farooq, Hassan Mujtaba, 2017, izvirni znanstveni članek

Opis: This research is an effort to correlate the index properties of granular soils with the California Bearing Ratio (CBR) and the compaction characteristics. Soil classification, modified proctor and CBR tests conforming to the relevant ASTM methods were performed on natural as well as composite sand samples. The laboratory test results indicated that samples used in this research lie in SW, SP and SP-SM categories based on Unified Soil Classification System and in groups A-1-b and A-3 based on the AASHTO classification system. Multiple linear regression analysis was performed on experimental data and correlations were developed to predict the CBR, maximum dry density (MDD) and optimum moisture content (OMC) in terms of the index properties of the samples. Among the various parameters, the coefficient of uniformity (Cu), the grain size corresponding to 30% passing (D30) and the mean grain size (D50) were found to be the most effective predictors. The proposed prediction models were duly validated using an independent dataset of CBR tests on sandy soils. The comparative results showed that the variation between the experimental and predicted results for CBR falls within ±4% confidence interval and that of the maximum dry density and the optimum moisture content are within ±2%. Based on the correlations developed for CBR, MDD and OMC, predictive curves are proposed for a quick estimation based on Cu , D30 and D50. The proposed models and the predictive curves for the estimation of the CBR value and the compaction characteristics would be very useful in geotechnical & pavement engineering without performing the laboratory compaction and CBR tests.
Ključne besede: CBR, regression, model, prediction, compaction characteristics
Objavljeno: 18.06.2018; Ogledov: 181; Prenosov: 88
.pdf Celotno besedilo (830,76 KB)
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