bluuebunny/crossref_metadata_2025 huggingface dataset:
ROP Modeling Using Neural Network and Drill String Vibration Data
Authors: Esmaeili Abdolali , Elahifar Behzad , Fruhwirth Rudolf K. , Thonhauser Gerhard
Published: December 2012

Vibrations are caused by bit and drill string interaction with formations under certain drilling conditions. They are affected by different parameters such as weight on bit, rotary speed, mud properties, BHA and bit design as well as by the mechanical properties of the formations. During the actual drilling process the bit interacts with different formation layers whereby each of those layers usually have different mechanical properties. Vibrations are also indirectly affected by the formations since weight on bit and rotary speed are usually optimized against changing formations (drilling optimization process). Therefore it can be concluded that for optimized drilling reduction of vibrations is one of the challenges.

A fully automated laboratory scale drilling rig, the CDC miniRig, has been used to conduct experimental tests. A three component vibration sensor sub attached to drill string records drill string vibrations and an additional sensor system records the drilling parameters. Uniform concrete cubes with different mechanical properties were built. Those cubes as well as a homogeneous sandstone cube were drilled with different ranges of weight on bit and bit rotary speed. The mechanical properties of all cubes were measured prior to the experiments. During all experiments, drilling parameters and the vibration data were recorded. Based on analyses of the data in the time and the frequency domain, linear and non-linear models were built. For this purpose the interrelations of sandstone and concrete mechanical properties, drilling parameters and vibration data were modeled by neural networks. Application of sophisticated attribute selection methods showed that vibration data in both, time- and frequency domain, have a major impact in modeling the rate of penetration.
Automated Real Time ESP Performance Monitoring and Optimization Case Study
Authors: Khalid Al-Deyain , Rachapudi Rama Rao , Al-Mutairi Talal , Haider Bader , Mohammed Al-Yahya
Published: December 2012

Production from Artificially lifted (ESP) well depends on the performance of ESP and reservoir inflow. Realtime monitoring of ESP performance and reservoir productivity is essential for production optimization and this in turn will help in improving the ESP run life. Realtime Workflow was developed to track the ESP performance and well productivity using Realtime ESP sensor data. This workflow was automated by using real time data server and results were made available through Desk top application.

Realtime ESP performance information was used in regular well reviews to identify the problems with ESP performance, to investigate the opportunity for increasing the production. Further ESP real time data combined with well model analysis was used in addressing well problems.

This paper describes about the workflow design, automation and real field case implementation of optimization decisions. Ultimately, this workflow helped in extending the ESP run life and created a well performance monitoring system that eliminated the manual maintenance of the data. In Future, this workflow will be part of full field Digital oil field implementation.
Field Redevelopment Optimization to Unlock Reserves and Enhance Production
Authors: Al-Nabhani Salim , Al-Marhoon Nadhal , Al-Rubaiey Faisal , Al-Kalbani Ammar , Al-Mandhari Badar , Al-Hattali Ahmed , Al-Hashami Ahmed , Hassan Hany
Published: December 2012

A cluster area "H" consists of 4 carbonate gas fields producing dry gas from N-A reservoir in the Northern area of Oman. These fields are producing with different maturity levels since 1968. An FDP study was done in 2006 which proposed drilling of 7 additional vertical wells beside the already existing 5 wells to develop the reserves and enhance gas production from the fields. The FDP well planning was based on a seismic amplitude"QI" study that recommended drilling the areas with high amplitudes as an indication for gas presence, and it ignored the low amplitude areas even if it is structurally high. A follow up study was conducted in 2010 for"H" area fields using the same seismic data and the well data drilled post FDP. The new static and dynamic work revealed the wrong aspect of the 2006 QI study, and proved with evidence from well logs and production data that low seismic amplitudes in high structural areas have sweet spots of good reservoir quality rock. This has led to changing the old appraisal strategy and planning more wells in low amplitude areas with high structure and hence discovering new blocks that increased the reserves of the fields.

Furthermore, water production in these fields started much earlier than FDP expectation. The subsurface team have integrated deeply with the operation team and started a project to find new solutions to handle the water production and enhance the gas rate. The subsurface team also started drilling horizontal wells in the fields to increase the UR, delay the water production and also reduce the wells total CAPEX by drilling less horizontal wells compared to many vertical as they have higher production and recovery. These subsurface and surface activities have successfully helped to stabilize and increase the production of"H" area cluster by developing more reserves and handling the water production.
Mathematical Modeling of Shale Swelling in Water-Based Muds
Authors: Kulkarni Sandeep , Maghrabi Shadaab , Teke Kushabhau , Kulkarni Dhanashree , Jamison Dale
Published: December 2012

Historically, shale instability is a challenging issue when drilling reactive formations using water-based muds (WBM). Shale instability leads to shale sloughing, stuck pipe, and shale disintegration causing an increase in fines that affects the rate of penetration. To characterize shale instability, laboratory tests including Linear Swell Meter (LSM), shale-erosion and slake-durability are conducted in industry. These laboratory tests, under different flow conditions, provide shale-fluid interaction parameters which are indicative of shale instability. The composition of WBM is designed to optimize these interaction parameters, so that when used in the field the fluid helps achieve efficient drilling.

This paper demonstrates modeling of shale-fluid interaction parameters obtained from the LSM test. In the standard LSM test, a laterally confined cylindrical shale sample is exposed to WBM at a specific temperature and its axial swelling is measured with time. The swelling reaches a plateau which is characterized by a shale-fluid interaction parameter called % final swelling volume (A). A typical LSM test runs for around 48–72 hours and many tests may be needed to optimize fluid composition.

In this work, a method/model is developed to predict final swelling volume (A) as a function of the Cation exchange capacity (CEC) of the shale and salt concentration in the fluid (prominent factors affecting shale swelling). An empirical model in the form of A = f(CEC)*f(salt) which describes the explicit dependence on the influencing variables is developed and validated for 16 different shale samples at various salt concentrations. This model would significantly reduce LSM laboratory trials saving time and money. It could also enable rig personnel to obtain quick measure of shale characteristics so that WBM composition could be adjusted immediately to avoid shale instability issues.
Consideration of Voidage Replacement Ratio in Well Placement Optimization
Authors: Awotunde Abeeb A. , Sibaweihi Najmudeen
Published: December 2012

Determining the optimum location of wells during waterflooding contributes significantly to efficient reservoir management. Often, Voidage Replacement Ratio (VRR) and Net Present Value (NPV) are used as indicators of performance of waterflood projects. In addition, VRR is used by regulatory and environmental agencies as a means of monitoring the impact of field development activities on the environment while NPV is used by investors as a measure of profitability of oil and gas projects. Over the years, well placement optimization has been done mainly to increase the NPV. However, regulatory measures call for operators to maintain a VRR of one (or close to one) during waterflooding.

A multiobjective approach incorporating NPV and VRR is proposed for solving the well placement optimization problem. We present the use of both NPV and VRR as objective functions in the determination of optimal location of wells. The combination of these two in a multiobjective optimization framework proves to be useful in identifying the trade-offs between the quest for high profitability of investment in oil and gas projects and the desire to satisfy regulatory and environmental requirements. We conducted the search for optimum well locations in three phases. In the first phase, only the NPV was used as the objective function. The second phase has the VRR as the sole objective function. In the third phase, the objective function was a weighted sum of the NPV and the VRR. A set of four weights were used in the third phase to describe the relative importance of the NPV and the VRR and a comparison of how these weights affect the optimized NPV and VRR values is provided.

We applied the method to determine the optimum placement of wells using two sample reservoirs: one with a distributed permeability field and the other, a channel reservoir with four facies. Two evolutionary-type algorithms: the covariance matrix adaptation evolutionary strategy (CMA-ES) and differential evolution (DE), were used to solve the optimization problem. Significantly, the method illustrates the trade-off between maximizing the NPV and optimizing the VRR. It calls the attention of both investors and regulatory agencies to the need to consider the financial aspect (NPV) and the environmental aspect (VRR) of waterflooding during secondary oil recovery projects. The multiobjective optimization approach meets the economic needs of investors and the regulatory requirements of government and environmental agencies. This approach gives a realistic NPV estimation for companies operating in jurisdiction with requirement for meeting a VRR of one.
Enhanced Model for Bottomhole Pressure Prediction While Performing Underbalanced Drilling Operations
Authors: Aladwani Faisal A , Gray Kenneth E
Published: December 2012

The success of recent applications in underbalanced drilling (UBD) and managed pressure drilling (MPD) has accelerated the development of technology in order to optimize drilling operations. The increased number of depleted reservoirs and the necessity for reducing formation damage has also increased the need to apply UBD/MPD to such candidate fields. Several methods used the latest mechanistic multiphase flow models in order to predict bottomhole circulation pressure when performing UBD/MPD operations. A new model is developed that utilizes the latest mechanistic multiphase flow models; the developed model calculates the bottomhole circulation pressure as a function of surface injection rates, choke pressure and time.

The developed model can be used in designing and optimizing UBD/MPD operations in terms of determining the correct injection rate and/or choke pressure. In addition, the developed model is used to utilize the reservoir energy to attain correct bottomhole conditions. The developed model in addition to utilizing the latest mechanistic models also reduce the error in calculating the bottom hole pressure by incorporating an algorithm in which the injection rates are calculated in-situ rather than assuming constant injection rates.

The model is validated against data from literature and against a commercial simulator. Results show that the developed algorithm has increased the accuracy in predicting bottomhole pressure by incorporating the changes in new gas and liquid injection rates.
Regional In-Situ Stress in Northern Kuwait- Implications for the oil Industry
Authors: Al-Ammar Nada , Hussain Riyasat , Mulyono Rinaldi , Al-Fares Abdulaziz , Al-Kandary Ahmad , Al-Naeimi Reem , Perumalla Satya
Published: December 2012

Role of geomechanics is becoming increasingly important with maturing of conventional reservoirs due to its implications in drilling, completion and production issues. Exploration and development of unconventional reservoirs involve maximizing the reservoir contact and hydraulic fracturing both of which are heavily dependent on geomechanical architecture of the reservoirs and thus require application of geomechanical concepts from the very beginning.

To support the unconventional exploration and conventional reservoir development in Kuwait, country-wide in-situ stress mapping exercise has been carried out in nine fields of Northern Kuwait. Stringent customized quality control measures were put in place to evaluate stress orientation. Cretaceous and sub-Gotnia Salt Jurassic rocks exhibit distinct patterns of stress orientations and magnitudes. While the variations in stress orientation in the Cretaceous rocks are within a small range (N40°E-N50°E) and consistent across major fault systems, the Jurassic formations exhibit high variability (N20°E-N90°E) with anomalous patterns across faults as well as in the vicinity of fracture corridors. Moreover, the overall stress magnitudes were found to be much higher in the strong Jurassic section compared with the relatively less strong Cretaceous strata. During the analysis, it was also observed that several natural fractures in Jurassic reservoirs appear to be critically stressed with evidences of rotation of breakouts.

Using geomechanical models from a specific field, the effects of in-situ stress, pore pressure and rock properties on formations were evaluated in inducing wellbore instability during drilling operations in a tight gas reservoir. It was found that the most favorable orientation for directional drilling is parallel to the maximum horizontal stress (SHmax) within that field.

The geomechanical study provided inputs not only for wellbore stability during drilling, but also regarding the response of natural fractures to in-situ stresses to become hydraulically conductive (permeable) to act as flow conduits. The fracture model of the field shows that the dominant fracture corridor trend in the field is NNE coinciding with present day in-situ maximum principal stress direction.
Implementing Artificial Neural Networks and Support Vector Machines in Stuck Pipe Prediction
Authors: Al-Baiyat Islam , Heinze Lloyd
Published: December 2012

Stuck pipe has been recognized as one of the most challenging and costly problems in the oil and gas industry. However, this problem can be treated proactively by predicting it before it occurs.

The purpose of this study is to implement the two most powerful machine learning methods, Artificial Neural Networks (ANNs) and Support Vector Machines (SVMs), to predict stuck pipe occurrences. Two developed models for ANNs and SVMs with different scenarios were implemented for prediction purposes. The models were designed and constructed by the MATLAB language. The MATLAB built-in functions of ANNs and SVMs, and the MATLAB interface from the library of support vector machines were applied to compare the results. Furthermore, one database that included mud properties, directional characteristics, and drilling parameters has been assembled for training and testing processes. The study involved classifying stuck pipe incidents into two groups - stuck and non-stuck - and also into three subgroups: differentially stuck, mechanically stuck, and non-stuck. This research has also gone through an optimization process which is vital in machine learning techniques to construct the most practical models. This study demonstrated that both ANNs and SVMs are able to predict stuck pipe occurrences with reasonable accuracy, over 85%.

The competitive SVM technique is able to generate generally reliable stuck pipe prediction. Besides, it can be found that SVMs are more convenient than ANNs since they need fewer parameters to be optimized. The constructed models generally apply very well in the areas for which they are built, but may not work for other areas. However, they are important especially when it comes to probability measures. Thus, they can be utilized with real-time data and would represent the results on a log viewer.
Evaluation of Micronized Ilmenite as Weighting Material in Water-Based Drilling Fluids for HPHT Applications
Authors: Elkatatny S. M. , Nasr-El-Din H. A. , Al-Bagoury M..
Published: December 2012

Barite is the most common weighting material for drilling fluids, which contain several heavy components including lead, cadmium, mercury, and arsenic. Some of these heavy materials can discharge into the sea, which is not allowed especially in the case of oil-based drilling fluid. The supply of barite is geographically limited, with high transportation costs. To overcome the high cost, shortage, and common problems of barite, an alternative weighting material, ilmenite (5 µm), is introduced which is heavier than barite and more stable at high temperature. Also, the micronized ilmenite was introduced to overcome the ECD challenges in some drilling operations at reasonable cost.

Extensive lab work was done in order to: 1) optimize the rheological properties of the drilling fluid, 2) determine the optimum pH that gives stable dispersion, 3) assess the thermal stability, 4) optimize the filtration parameters (filtrate volume and filter cake thickness), and 5) characterize the ilmenite-based filter cake.

Zeta potential results showed that ilmenite was stable when mixed with water at a pH above 7 and it was dispersed and stable when mixed with the drilling fluid components. Drilling fluids have a density range from 100 to 120 pcf and a plastic viscosity of 28–32 cp. No phase separation was observed after hot rolling for 16 hrs at 300°F. The optimized water-based drilling fluid formula had a small filtrate volume (12 cm3) and thin filter cake (0.2 in.) under dynamic conditions. SEM analysis showed that ilmenite filter cake was heterogeneous and contained ilmenite particles in the layer closer to the rock surface. The layer closer to the drilling surface had a mixture of xanthan gum and modified starch, which were used to optimize the rheological properties at 250°F. This study will provide a complete evaluation of the drilling fluids with ilmenite as a weighting material and will help drilling engineers to better design drilling fluids for HPHT wells.
An Integrated and Effective Method for Well Placement Using a Numerical Simulation Model: A North Kuwait Field Case Study
Authors: Abdy Yaser , Amari Mustafa , Sharifzadeh Ahmad , Al-Anzi Ealian , Al-Ansari Muaath
Published: December 2012

The need to develop new tools that allow reservoir engineers to optimize reservoir performance is becoming more demanding by the day. One of the most challenging and influential problems facing reservoir engineers is well placement optimization.

The North Kuwait field (NKF) consists of six fields containing four naturally fractured carbonate formations. The reservoirs are composed of relatively tight limestone and dolomite embedded with anhydrate and shale. The fields are divided into isolated compartments based on fault zones and supported by a combination of different fluid compositions, initial pressures, and estimated free-water levels. Due to natural complexity, tightness, and high drilling costs of wells in the NKF, it is very important to identify the sweet spots and the optimum well locations.

This paper presents two intelligent methods that use dynamic numerical simulation model results and static reservoir properties to identify zones with a high-production potential: reservoir opportunity index (ROI) and simulation opportunity index (SOI). The Petrel* E&P software platform was chosen as the integrated platform to implement the workflow. The fit-for-purpose time dependent 2D maps generated by the Petrel platform facilitated the decision-making process used for locating new wells in the dominant flow system and provided immense support for field-development plans.

The difference between the two methods is insignificant because of reservoir tightness, limited interference, and natural uncertainty on compartmentalization. At this stage, pressure is not a key parameter. As a result, unlike brown fields, less weight was given to simulated pressure, and SOI was used to select the well locations.

The results of this study show that implementing these workflows and obtaining the resulting maps significantly improve the selection process to identify the most productive areas and layers in a field. Also, the optimum numbers of wells using this method obtained in less time and with fewer resources are compared with results using traditional industry approaches.
Integrated Workflow for Small Scale Reservoir Characterization Using Borehole Image, NMR and Core Data
Authors: Al Bloushi Asmaa Faisal , Joshi Deepak , Al Murakhi Haifa Rashed
Published: December 2012

The Middle Minagish Oolite Formation is 450 to 550 feet thick interval of porous limestone reservoir, composed of peloidal/skeletal grainstones with lesser amount of packstone, oolitic grainstone, wackstone and mudstone in Umm Gudair field, West Kuwait. It is characterized by small scale reservoir heterogeneity, primarily related to the depositional as well as diagenetic features. Capturing reservoir properties in micro scale and its spatial variation needs special attention in this reservoir due to its inherent anisotropy. Reservoir properties will depend on the level that we are analyzing on reservoir (millimeter to meter scale). Here we used Electrical Borehole Image (EBI) and Nuclear Magnetic Resonance (NMR) to capture small scale feature of Umm Gudair carbonate reservoir and compared them with core data In present work, reservoir properties (including texture, facies, porosity and permeability) interpreted by the EBI shows good match with NMR driven properties and core data. Textural changes in image logs also match well with pore size distribution from NMR logs. Further highly porous zones which are considered either due to primary porosity or vugs match with larger pores of NMR logs and these corroborates with also core derived porosity. A good match has been observed between EBI, NMR and cored derived porosity. Permeability calculations have also been made and compared with core data. A detail workflow has been developed here to interpret reservoir properties on un-cored wells, where only low vertical resolution data is available. This technique is quite useful to identify the characters and mode of origin highly porous zones in reservoir section which are generally not identifiable by low resolution standard logs. This workflow will allow us to interpret the heterogeneity at high resolution level in un-cored wells, as results are validated with integration of EBI, NMR and core data.
Unique Process and Tool Provides Better Acid Stimulation and Better Production Results
Authors: Al-Saqabi Mishari , Gazi Naz , Vishwanath Chimmalgi , Al Bahrani Hasan , Turkey Naween , Abdul-Razaq Eman , Al-Zankawi Omran , Bouland Ali , Surjaatmadja Jim B. , Al Hamad Abdulla M. , Brand Shannon
Published: December 2012

There are many ways to stimulate an unlined openhole horizontal well using acid. The simplest way is to just pump acid into the well (i.e., bullhead) without placement control. However, this can often be ineffective. Although still used, such approaches can create massive enlargements at the entry point or high injectivity area, thus causing ineffective treatments and re-entry issues. Wellbore collapse often follows. The use of coiled tubing (CT) as a "pin-point" delivery method is therefore preferred. Using CT allows dispersal of the acid either uniformly or intermittently along the lateral, as desired. CT also allows acid washing to be performed, which is another common process that can improve stimulation without much additional expense to the operator. Using a jetting tool with many jets, acid can be sprayed onto the wellbore wall, and the active agitation caused by the acid-wash process increases the chemical reactivity of the acid at the desired locations.

Another beneficial approach of using CT is the hydrajet assisted acid fracturing (HJAAF) method. With focused jetting of acid at much higher pressures, the process initiates microfractures in the wellbore walls. When etched with acid, this approach effectively bypasses near-wellbore (NWB) damage much deeper than common washes, thus providing much better results. Further modification of the process by exerting high annular pressures offers the capability of delivering medium to large fractures.

This paper discusses two HJAAF processes uniquely combined into one process used in two large horizontal wells. Because of the large dimension of the inner diameter (ID) of the wells combined with the small production tubing the tool must pass through, the implementation had to be further improved by using a unique jetting mechanism, which positioned the jet nozzles closer to the target. Actual results of such stimulations are presented.
Real-Time Estimation of Well Drainage Parameters
Authors: Al-Kadem Mohammad S. , Al-Khelaiwi Faisal T. , Al-Amri Meshal A.
Published: December 2012

The well drainage pressure and radius are key parameters of real-time well and reservoir performance optimization, well test design and new wells' location identification. Currently, the primary method of estimating the well drainage radius is buildup tests and their subsequent well test analysis. Such buildup tests are conducted using wireline-run quartz gauges for an extended well shut-in period resulting in deferred production and risky operations.

A calculation method for predicting well/reservoir drainage pressure and radius is proposed based on single-downhole pressure gauge, flowing well parameters and PVT data. The proposed method uses a simple approach and applies established well testing equations on the flowing pressure and rates of a well to estimate its drainage parameters. This method of estimation is therefore not only desirable, but also necessary to eliminate shutting-in producing wells for extended periods; in addition to avoiding the cost and risk associated with the wireline operations. The results of this calculation method has been confirmed against measured downhole, shut-in pressure using wireline run gauges as well as dual gauge completed wells in addition to estimated well parameters from buildup tests.

This paper covers the procedure of the real-time estimation of the well/reservoir drainage pressure and radius in addition to an error estimation method between the measured and calculated parameters. Furthermore, the paper shows the value, applicability and validity of this technique through multiple examples.
Labour engagement optimization in planning the execution of river regulation works on the Jelasnicka river
Authors: Andrijanic Tijana , Dragovic Nada , Todosijevic Mirjana
Published: December 2012

A project is a task comprising a set of interrelated activities requiring
time and resources for their execution. It is often the case that during the
construction of longitudinal and cross section structures for the regulation
of a torrential catchment the required resources (labour, materials,
mechanization, and finances) are often limited and because of that we face
the problem of their efficient use. This paper deals with the problem of
planning the execution of river regulation works on the Jelasnicka River with
the aim to minimize the time extension due to limited resources. In the
planning phase of project realization labour force is the limited resource.
Heuristic techniques, i.e. the Gray-Kidd algorithm with the use of MS Project
software were applied in the distribution of resources for the purposes of
optimal labour engagement. This method uses the data acquired by the CPM
method of network planning as input elements. Through more iterations, by
moving noncritical and then critical project activities, the minimal
extension of project duration was achieved by engaging more labour force.
Therefore, the proposed heuristic and CPM method performed well in resolving
the resource-constrained project scheduling problem.
Galanthus gracilis celak. (Amaryllidaceae) in the flora of Serbia
Authors: Jovanovic Filip , Obratov-Petkovic Dragica , Zlatkovic Bojan
Published: December 2012

There are only ambiguous data in literature that suggest the presence of
Galanthus gracilis Celak. in the flora of Serbia. Throughout its range G.
gracilis is often confused with closely related species G. elwesii Hook.,
with which it shares several morphological characteristics, and in some cases
the same name is erroneously used for both species (G. graecus Orph.). Only
about a decade ago, the genus was a subject of taxonomic revision by the
English author Aaron P. Davis, whose work eliminated confusion created by the
previous conflicting divisions. Therefore, further studies are required to
determine the exact distribution of this species. In this paper, we
officially report the presence of G. gracilis in Serbia, with a description
of its habitat and estimation of the threatened status.
Velocity and uniformity of air circulation in conventional kilns for sawn timber
Authors: Kolin Branko , Milic Goran , Golic Igor
Published: December 2012

This paper presents the results of a research of velocity of air circulation
in the conventional kiln drying of sawn timber and its influence on the
uniformity of final moisture content. The data showed that the air velocity
(between 0.8 - 1.2 m?s -1) is significantly lower than the one that is
optimal for timber drying of coniferous species (3 - 4 m?s-1). This results
in a reduction in the capacity of installations for drying, increased energy
(thermal and electrical) consumption and thereby increase in the cost of
drying. The correlation between the speed of air circulation and the final MC
of timber due to prolonged drying was not established. Recommendations that
should eliminate the identified deficiencies are also given.
Floristic analysis of perennial species on flowerbeds in Belgrade with special attention on invasiveness of the recorded species
Authors: Popovic Marija , Markovic Marija
Published: December 2012

Urban areas are among the most important centres of invasive plant species
distribution due to their richness in alien species. Because of that, a
detailed floristic analysis of perennial flowerbeds was conducted in the
central parks of Belgrade. A total of 53 perennial species were found, of
which 55% were the alien species planted on 75% of the research area. Among
them, two species (Aster novi belgii and Solidago canadensis) are invasive
and six species are potentially invasive in Serbia. These are planted on 5%
and 20% of the flowerbeds, respectively. We can conclude that both the
experts and institutions should be informed about the invasive species and
potential damages. In the meantime, planting of native decorative species
should be encouraged, since they will not pose a threat to natural habitats.
Also, detailed research should be conducted in order to eradicate invasive
and potentially invasive species from the surfaces around the research area.
Trends of forest area and population and the impact of population on forest area per hectare in Serbia without APS
Authors: Rankovic Nenad
Published: December 2012

Socio-economic changes throughout history have shaped the attitude towards
the forest and most significant ones are changes in terms of population. Over
the centuries population and population density have had a significant impact
on deforestation and the reduction of forest areas. Therefore, it is
important to check what kind of trends are concerned and how population
growth affects forest areas, forest cover and forest area per capita. These
elements are important for assessing the direction, intensity of activity and
the degree of success in the implementation of all forest policy measures in
Serbia.
Ecotypical characterization of genetic variation of beech provenances from south-eastern Europe based on the morphometric characteristics of leaves
Authors: Sijacic-Nikolic Mirjana , Milovanovic Jelena , Nonic Marina , Knezevic Radmila , Babic Violeta
Published: December 2012

The research was conducted on a provenance test of beech established in the
Educational-research centre ?Majdanpecka domena? - Faculty of Forestry,
University of Belgrade. This paper presents the results of an analysis of the
morphometric characteristics of leaves, at the level of 10 provenances in the
juvenile developmental stage, originating from South-Eastern Europe. Herbaria
material was used to measure the following parameters: leaf length, leaf
width, petiole length, leaf base width at 1 cm (from petiole base), the
number of veins -on the left, the number of veins - on the right, and
distance between the 3rd and 4th vein - on the left. Based on research
results, it can be concluded that the obtained differences between the mean
values of all measured foliar characteristics of the analyzed provenances are
statistically significant, and that there is significant correlation between
the length and width of leaves and the Ellenberg?s quotient (EQ). The
relationship between the adaptive traits of beech from different provenances
and ecological parameters of their seed source stands indicates genetic
differentiation of beech, as a consequence of the population adaptation to
local environmental conditions. Therefore, in the future, ecological criteria
must be a priority in the selection of seed sources and planting materials,
with special consideration of the global climate change.
Ameliorating effects of antioxidative compounds from four plant extracts in experimental models of diabetes
Authors: Dinic Svetlana , Uskokovic Aleksandra , Mihailovic Mirjana , Grdovic Nevena , Arambasic Jelena , Markovic Jelena , Poznanovic Goran , Vidakovic Melita
Published: December 2012

Given that oxidative stress plays a major role in pancreatic ?-cell
dysfunction and ultimate destruction, as well as in different complications
of diabetes, therapy with antioxidants has assumed an important place in
diabetes management. The relatively limited effects of established
antioxidant compounds have stimulated efforts to develop new therapeutic
strategies, e.g. to increase the endogenous antioxidant defenses through
pharmacological modulation of key antioxidant enzymes. Plant extracts are
gaining popularity in treating diabetes because many substances synthesized
by higher plants and fungi possess antioxidant activities and can prevent or
protect tissues against the damaging effects of free radicals. This review
summarizes experimental models of diabetes and possible mechanisms that lie
behind the antioxidative effects of ?-lipoic acid (LA), a powerful
antioxidant and compound that stimulates cellular glucose uptake, as well as
of plant extracts from sweet chestnut (Castanea sativa), edible mushroom
(Lactarius deterrimus) and natural products containing ?-glucans in the
treatment of diabetes. Their roles in preventing pancreatic ?-cell death and
in ameliorating the effects of severe diabetic complications are discussed.
Correlation between grain deviation angles and the partial ordering transformation of grain line in Bi4Si3O12 microcrystals
Authors: Zhang Z.G. , Jiang Z.Y. , Wang X.F. , Tian Q.Q.
Published: December 2012

Bismuth silicate micro-crystals with grain line structure were prepared by
sintering method under atmosphere pressure. The samples were characterized
for structural and surface morphological properties by X-ray diffraction
(XRD) and Environmental scanning electron microscopy (ESEM). The result shows
that Bi4Si3O12 grains are always distributed in pairs on both sides of a
complete grain line. There is highly positive correlation between grain
deviation angles on both sides of a stable complete line. Although the grains
distribute in pairs, there is zero correlation between grain angles on both
sides of an unstable complete line. By the reduction of grain angle on one
side, grain sizes on the side gradually decrease. After adjustment, grain
angles have highly positive correlation and the line turns stable. If there
is disordered structure on one side of a line and ordered structure on the
other side, the disordered structure may turn to highly ordered structure.
The partial ordering transformation on the disordered side has no effect on
the structure on the other side. While the growth directions of the grains on
one side of a line face to a disordered grain distribution zone, the line
loses the characteristic of grain growth in pairs.
The influence of mechanical activation on sintering process of BaCO3-SrCO3-TiO2 system
Authors: Kosanovic Darko , Obradovic N. , Zivojinovic J. , Maricic A. , Pavlovic V.P. , Pavlovic V.B. , Ristic M.M.
Published: December 2012

In this article the influence of mechanical activation on sintering process
of bariumstrontium-titanate ceramics has been investigated. Both
non-activated and mixtures treated in a planetary ball mill for 5, 10, 20,
40, 80 and 120 minutes were sintered at 1100-1400?C for 2 hours in presence
of air atmosphere. The influence of mechanical activation on phase
composition and crystal structure has been analyzed by XRD, while the effect
of activation and sintering process on microstructure was investigated by
scanning electron microscopy. It has been established that temperature of
1100?C was too low to induce final sintering stage for this system.
Electrical measurements have been conducted for the densest ceramics sintered
at 1400?C for 2 hours.
Soft magnetic properties of MnZn ferrites prepared by powder injection moulding
Authors: Mitrovic N.S. , Zlatkov B.S. , Nikolic M.V. , Maricic A.M. , Aleksic O.S. , Djukic S.R. , Danninger H.
Published: December 2012

In this study, properties of soft-magnetic manganese zinc ferrite
manufactured by powder injection moulding - PIM technology were presented. A
powder consisting of Mn1- xZnxFe2O4 with small addition of hematite ?-Fe2O3
was mixed with an organic binder (wax and thermoplastic) to form ferrite
feedstock. The ferrite feedstock was injected in a mould with a cavity shaped
like a small cylinder with a hole on the main axis. Injection moulded samples
were then solvent, thermally debinded and sintered in air atmosphere.
Structure of sintered sample was characterized using X-ray diffractometry,
scanning electron microscopy and thermomagnetic measurements. Magnetic
properties were measured by hysteresis graph at different frequencies up to 1
kHz. Sintered sample contains a mixture of two phases Mn0.6Zn0.4Fe2O4 (68 wt.
%) and ?-Fe2O3 (32 wt. %). The Curie temperature is TC ? 220?C for the green
sample but after the heating up to 470?C, TC increase up to about 300?C. The
high increase of normalized magnetic permeability of about 800 % was observed
due to melting and burning of binder. The hysteresis loop of sintered MnZn
ferrite toroidal cores has an R-shape with saturation of 0.44 T and remanence
ratio of 0.49. The low value of coercivity (only 47 A/m) was related to the
presence of ?-Fe2O3 crystalline phase and attained already optimum density (?
? 4.8 g/cm?) i.e. observed low level of porosity. Attained relative magnetic
permeability ?r ? 2000 as well as power losses Ps ? 21 W/kg for sintered
sample (at 1 kHz; 0.39 T) is in agreement with the MnZn ferrite commercial
samples.
Effect of binder molecular weight on morphology of TiO2 films prepared by tape casting and their photovoltaic performance
Authors: Tasic N. , Brankovic Z. , Marinkovic-Stanojevic Z. , Brankovic G.
Published: December 2012

Titanium(IV) oxide in the form of anatase has proven to be the best choice
for photoanodic material in dye-sensitized solar cells (DSCs). The aim of the
work was to study the influence of binder molecular weight on the morphology
of deposited films, and consequently, DSC parameters. For this study, five
different TiO2 tape casting slips were prepared from commercially available
nanoanatase powder and polyethylene glycol (PEG) as a binder. The process of
drying and sintering was carefully designed, so that the organic template was
slowly decomposed, leaving favorable crack-free, porous structure. It was
found that there is an optimal region of binder molecular weight for
obtaining homogeneous, nonagglomerated and porous microstructure which is a
necessary condition for application of TiO2 films in DSCs.
Research on Auditor Professional Skepticism: Literature Synthesis and Opportunities for Future Research
Authors: Hurtt R. Kathy , Brown-Liburd Helen , Earley Christine E. , Krishnamoorthy Ganesh
Published: December 2012

Both researchers (e.g., Nelson 2009) and regulators (e.g., the PCAOB) have emphasized the importance of exercising the appropriate level of professional skepticism when conducting an audit. However, professional skepticism remains a hard concept to define and measure. In addition, it is often difficult to determine if a lack of skepticism is the primary cause of audit deficiencies and if so, what factors led to the lack of skepticism. The purpose of this paper is threefold: (1) extend the work of Nelson (2009) by synthesizing research related to auditors' professional skepticism to identify antecedents to both skeptical judgment and skeptical action, (2) identify areas where research is lacking on a particular dimension and suggest avenues for future research, and (3) discuss the implications of research findings for regulators and auditing professionals. We adopt two foundational aspects of the framework introduced in the seminal paper by Nelson (2009), which proposes that lack of skepticism can either be the result of a failure in problem recognition (lack of skeptical judgment) or a failure to act on a problem recognized (lack of skeptical action). We organize research studies into four categories of antecedents: studies relating to auditor characteristics, evidence characteristics, client characteristics, and environmental characteristics. We find that while research studies provide insights into both the antecedents to skeptical judgments and actions, the majority of research efforts to date have focused on the antecedents to skeptical judgments and on auditor characteristics in particular. Research findings have implications for practice, but in order to understand how skeptical judgment translates into skeptical action, additional research on skeptical action will need to be conducted.
Effects of insertion angle and implant thread type on the fracture properties of orthodontic mini-implants during insertion
Authors: Cho Il-Sik , Kim Tae-Woo , Ahn Sug-Joon , Yang Il-Hyung , Baek Seung-Hak
Published: December 2012

Objective:

To determine the effects of insertion angle (IA) and thread type on the fracture properties of orthodontic mini-implants (OMIs) during insertion.

Materials and Methods:

A total of 100 OMIs (self-drilling cylindrical; 11 mm in length) were allocated into 10 groups according to thread type (dual or single) and IA (0°, 8°, 13°, 18°, and 23°) (n  =  10 per group). The OMIs were placed into artificial materials simulating human tissues: two-layer bone blocks (Sawbones), root (polymethylmethacrylate stick), and periodontal ligament (Imprint-II Garant light-body). Maximum insertion torque (MIT), total insertion energy (TIE), and peak time (PT) were measured and analyzed statistically.

Results:

There were significant differences in MIT, TIE, and PT among the different IAs and threads (all P < .001). When IA increased, MIT increased in both thread groups. However, TIE and PT did not show significant differences among 0°, 8°, and 13° IAs in the dual-thread group or 8°, 13°, and 18° IAs in the single-thread group. The dual-thread groups showed higher MIT at all IAs, higher TIE at 0° and 23° IAs, and longer PT at a 23° IA than the single-thread groups. In the 0°, 8°, and 13° IA groups, none of the OMIs fractured or became deformed. However, in the 18° IA group, all the OMIs were fractured or deformed. Dual-thread OMIs showed more fracturing than deformation compared to single-thread OMIs (P < .01). In the 23° IA group, all OMIs penetrated the artificial root without fracturing and deformation.

Conclusions:

When OMIs contact artificial root at a critical contact angle, the deformation or fracture of OMIs can occur at lower MIT values than those of penetration.
Study of lattice dynamics of silicon
Authors: Thapa SRB
Published: December 2012

Lattice dynamics of Si has been investigated by using a Urey-Bradley Valence Force Field (UVFF) model which is a phenomenological model. In this model following interactions are taken into account: (i) the central force due to bond-stretching (ii) the angular force due to bond bending (iii) central force between non-bonded atoms (iv) the force due to interaction of one internal co-ordinate to adjacent internal coordinate. Calculated results of phonon dispersion curves, Debye Characteristic temperature, microscopic elastic constants and Bulk modulus of Si are compared with experimental results giving fairly good agreement. DOI: http://dx.doi.org/10.3126/bibechana.v9i0.7145BIBECHANA 9 (2013) 13-17
Compressibility and Moelwyn-Hughes Parameter of NaI crystals under high pressure, as the function of thermal properties
Authors: Khan Arun Kumar
Published: December 2012

The credit for the commencement of inter ionic potential function goes to Born and Lande, one of whose milestone has been their expression into inverse function. Similarly, Born and Mayer also proposed the exponential function of the potential for the repulsive component. However none of them could get the desired success. Subsequently, many more prominent scientists devoted their effort towards these thermal properties of the crystals, among which the endeavour of Jha and Thakur cannot be overlooked, who proposed a new interionic function to observe the properties of ionic crystal under high pressure. During its formulation they included both an inverse power function due to Born and Lande and an exponential function due to to Born and Mayer. Appreciably, Jha and Khan used it for studying the hyped thermal properties of NAI and CsI crystal under high pressure up to 100 Kilo bar. DOI: http://dx.doi.org/10.3126/bibechana.v9i0.7180 BIBECHANA 9 (2013) 88-91
Electrical conductivity and Knight shift of liquid alkali metals
Authors: Chakrabarti SK , Jha IS , Yadav RN , Singh BP
Published: December 2012

In the present work we have considered two alkali metals - sodium and potassium - at their molten stage near the melting point. For the purpose of this theoretical investigation we have used Harrison’s first principle (HFP) pseudopotential technique which is basically an orthogonalised plane wave method. The electrical resistivity has been computed through Ziman’s formula. Then the electrical conductivity of the present metals is found out just by taking the reciprocal of the values so obtained. Our computed results have been compared with the experimental data and a good agreement is obtained. A study of the existing literature reveals that the work with the magnetic property like Knight shift of metals is scarce. This has encouraged us to apply the said HFP technique to study the Knight shift of the present alkali metals. For this purpose we have used Knight’s formula. Our computed values of Knight shift are in reasonable agreement for the metals under investigation. DOI: http://dx.doi.org/10.3126/bibechana.v9i0.7181BIBECHANA 9 (2013) 92-95