bluuebunny/crossref_metadata_2025 huggingface dataset:
Detailed Performance Comparison of a Dump and Short Faired Combustor Diffuser System
Authors: Carrotte J. F. , Denman P. A. , Wray A. P. , Fry P.
Published: February 2015

A rectangular model simulating 4 sectors of a combustion chamber was used to compare the performance of a standard dump diffuser, of overall length 180mm, with that of a faired design 25.5mm shorter. The performance of each system was assessed in terms of total pressure loss and static pressure recovery between pre-diffuser inlet and the annuli surrounding the flame tube. Since the program objective was to test design concepts only, no allowance was made for the presence of burner feed arms or flame tube support pins. In addition, tests were performed with relatively low levels of inlet turbulence and no wake mixing effects from upstream compressor blades.

Relative to the dump design, the mass weighted total pressure loss to the outer and inner annuli was reduced by 30% and 40% respectively for the faired diffuser. Measurements around the flame tube head were used to identify regions of high loss within each system and account for the differences in performance. Within a dump diffuser the flow separates at pre-diffuser exit resulting in a free surface diffusion around the flame tube head and a recirculating flow in the dump cavity. This source of loss is eliminated in the faired system where the flow remains attached to the inner casing. Furthermore, the faired system exhibited similar velocity magnitudes and gradients around the combustor head despite its shorter length.
Degradation of a Jet-A Fuel in a Single-Pass Heat Exchanger
Authors: Jones E. Grant , Balster Walter J. , Post Michael E.
Published: February 2015

The formation of bulk and surface insolubles in a Jet-A fuel during a single pass through heated stainless-steel tubes has been studied. Low temperature and low flow rates were utilized to produce near-isothermal conditions. In a second series of experiments, depletion of oxygen in the fuel saturated with respect to room-temperature air was measured under identical isothermal conditions. At a wall/bulk-fuel temperature of 185°C, rates of surface deposition and oxygen depletion were correlated; the maximum in the surface-deposition rate was found to occur after the Jet-A fuel was stressed sufficiently that the dissolved oxygen was totally consumed. Results are discussed in terms of the autoxidation of the Jet-A fuel and the concurrent production of deleterious bulk and surface insolubles.
Mathematical Modelling of an Annular Gas Turbine Combustor
Authors: Sokolov K. Y. , Tumanovskiy A. G. , Gutnik M. N. , Sudarev A. V. , Zakharov Y. I. , Winogradov E. D.
Published: February 2015

Mathematical model for description of axisymmetric swirled flow with diffusion combustion is based on numerical solution of Reynolds equation with k-W modell of turbulence. The results of numerical and experimental investigations of local and general characteristicse of flow, heat and mass transfer, combustion and NOx formation in annular combustor with opposite swirled air jets are presented. Satisfactory agreement between calculations and experiments is obtained. The dependences of combustor characteristics vs geometric and operational parameters are generalized.
The Importance of the Nitrous Oxide Pathway to NOx in Lean-Premixed Combustion
Authors: Nicol David G. , Steele Robert C. , Marinov Nick M. , Malte Philip C.
Published: February 2015

This study addresses the importance of the different chemical pathways responsible for NOx formation in lean-premixed combustion, and especially the role of the nitrous oxide pathway relative to the traditional Zeldovich pathway. NOx formation is modeled and computed over a range of operating conditions for the lean-premixed primary zone of gas turbine engine combustors.

The primary zone, of uniform fuel-air ratio, is modeled as a micro-mixed well-stirred reactor, representing the flame zone, followed by a series of plug flow reactors, representing the post-flame zone. The fuel is methane. The fuel-air equivalence ratio is varied from 0.5 to 0.7. The chemical reactor model permits study of the three pathways by which NOx forms, which are the Zeldovich, nitrous oxide, and prompt pathways. Modeling is also performed for the well-stirred reactor alone. Three recently published, complete chemical kinetic mechanisms for the C1-C2 hydrocarbon oxidation and the NOx formation are applied and compared.

Verification of the model is based on the comparison of its NOx output to experimental results published for atmospheric pressure jet-stirred reactors and for a ten atmosphere porous-plate burner. Good agreement between the modeled results and the measurements is obtained for most of the jet-stirred reactor operating range. For the porous-plate burner, the model shows agreement to the NOx measurements within a factor of two, with close agreement occurring at the leanest and coolest cases examined.

For lean-premixed combustion at gas turbine engine conditions, the nitrous oxide pathway is found to be important, though the Zeldovich pathway cannot be neglected. The prompt pathway, however, contributes small-to-negligible NOx. Whenever the NOx emission is in the 15 to 30ppmv (15% O2, dry) range, the nitrous oxide pathway is predicted to contribute 40 to 45% of the NOx for high pressure engines (30atm), and 20 to 35% of the NOx for intermediate pressure engines (10atm). For conditions producing NOx of less than 10ppmv (15% O2, dry), the nitrous oxide contribution increases steeply and approaches 100%.

For lean-premixed combustion in the atmospheric pressure jet-stirred reactors, different behavior is found. All three pathways contribute; none can be dismissed.

No universal behavior is found for the pressure dependence of the NOx. It does appear, however, that lean-premixed combustors operated in the vicinity of 10atm have a relatively weak pressure dependence, whereas combustors operated in the vicinity of 30atm have an approximately square root pressure dependence of the NOx.
An Asymptotic Analysis of Mixing Loss
Authors: Fritsch Gerd , Giles Michael B.
Published: February 2015

The objective of this paper is to establish, in a rigorous mathematical manner, a link between the dissipation of unsteadiness in a 2D compressible flow and the resulting mixing loss. A novel asymptotic approach and a control-volume argument are central to the analysis. It represents the first work clearly identifying the separate contributions to the mixing loss from simultaneous linear disturbances, i.e. from unsteady entropy, vorticity, and pressure waves. The results of the analysis have important implications for numerical simulations of turbomachinery flows; the mixing loss at the stator/rotor interface in steady simulations and numerical smoothing are discussed in depth.

For a transonic turbine, the entropy rise through the stage is compared for a steady and an unsteady viscous simulation. The large interface mixing loss in the steady simulation is pointed out and its physical significance is discussed. The asymptotic approach is then applied to the first detailed analysis of interface mixing loss. Contributions from different wave types and wavelengths are quantified and discussed.
Active Stabilization of Rotating Stall in a Three-Stage Axial Compressor
Authors: Haynes Joel M. , Hendricks Gavin J. , Epstein Alan H.
Published: February 2015

A three-stage, low speed axial research compressor has been actively stabilized by damping low amplitude circumferentially travelling waves which can grow into rotating stall. Using a circumferential array of hot wire sensors, and an array of high speed individually positioned control vanes as the actuator, the first and second spatial harmonics of the compressor were stabilized down to a characteristic slope of 0.9, yielding an 8% increase in operating flow range. Stabilization of the third spatial harmonic did not alter the stalling flow coefficient. The actuators were also used open loop to determine the forced response behavior of the compressor. A system identification procedure applied to the forced response data then yielded the compressor transfer function. The Moore-Greitzer, 2-D, stability model was modified as suggested by the measurements to include the effect of blade row time lags on the compressor dynamics. This modified Moore-Greitzer model was then used to predict both the open and closed loop dynamic response of the compressor. The model predictions agreed closely with the experimental results. In particular, the model predicted both the mass flow at stall without control and the design parameters needed by, and the range extension realized from, active control.
A Single Valve Gas Fuel Flow Control for Gas Turbines
Authors: Statler William O.
Published: February 2015

A method of mass flow control of fuel gas to a gas turbine has been developed and applied in control retrofits to existing gas turbines. Unlike other gas flow control systems in use on gas turbines this system actually measures the mass flow going into the turbine combustion system and uses this value as the feedback in a control loop to modulate a single throttling control valve.

The system utilizes a common venturi flow element to develop a differential pressure which, along with inlet pressure and temperature, is used to compute the mass flow. Locating this flow element downstream of the control valve where the pressure is low at low flows reduces the usual problem of the wide range of delta-pressure (proportional to the square of the mass flow) to a workable level. This extends the range of this common type of flow measurement system enough that it becomes practical to apply it to the gas fuel flow control loop of a gas turbine.
Fast-Track Controls Retrofit for a Gas and Steam Turbine Propylene Compressor Drive
Authors: Morton James T. , Drobniak Joseph M.
Published: February 2015

This paper chronicles a control system retrofit for a 38,000 horsepower refrigeration compressor drive at Novacor’s Ethylene #1 Plant, Red Deer, Alberta, Canada (Fig. 1). The changes were designed to meet a 3-year continuous operation requirement. When the plant was constructed in the late 1970’s, annual turnarounds were considered normal operating procedure.

The project replaced original electronic controls on a 23,500 horsepower G. E. Frame 5, Model R gas turbine and a 18,300 horsepower Elliott 2 NV starter/helper steam turbine. Both turbines are connected at opposite ends of a single compressor drive shaft (Fig. 2). Because of the cost associated with any control system malfunction, a programmable triple modular redundant controller was selected as the replacement.

Among the modifications performed to enhance system reliability were wiring dual exhaust thermocouples directly into the system and triplicating critical field devices. Another important aspect of this upgrade was replacing deteriorating underground field instrumentation wiring with cabling in overhead cable trays. The original wiring was over stressed by “frost heaving,” causing several unplanned shutdowns. In April of 1991, the project team initiated a schedule to meet an early August delivery. System specification, checkout, and start-up, as well as its first year of performance are discussed.
A Simplified Gas Turbine Engine Model With Heat Storage/Tip Clearance Effects
Authors: Wong T. H.
Published: February 2015

A simplified turboshaft gas turbine engine model called the direct transient method (DTM) model has been developed. The DTM model consists of table look-up data generated from the actual engine data or the transient engine simulation. The DTM model accounts for heat storage, tip clearance and volume dynamics effects. It can, therefore, better predict engine transient responses and turbine metal temperature than the traditional engine horsepower extraction (HPX) model. This paper presents in detail the DTM methodology for generating accurate simplified engine models of transient performance. Comparisons of engine transient responses between the DTM and HPX models are provided.
Exergy Analysis of Biomass-Fired Cogeneration Plant in a Pulp and Paper Mill
Authors: Näsholm Ann-Sofi E. , Svedberg Gunnar , Westermark Mats O. J.
Published: February 2015

Second Law analysis or exergy analysis is a useful instrument to find ways to improve the efficiency of energy utilization. The method presents the magnitude and locations of true energy losses in an energy system.

The pulp and paper industries have a big potential for increasing the energy efficiencies. An integration of a gas turbine with an existing steam turbine plant is one possible way to increase the energy efficiency and the power production. The cogeneration plant analysed in this paper is a hybrid combined plant in which two types of fuels are used.

The exhaust gas from a combined cycle gas turbine via a waste heat recovery steam generator (HRSG) is used as preheated combustion air in a supplementary fired steam boiler. Saturated steam from the HRSG is assumed to be superheated in a boiler in which sludge, bark and other types of biomass are being used as fuels. To reduce the waste of energy, a flue gas driven fuel dryer is connected to evaporate some of the moisture in these biomass fuels.

The study shows the effect of using a combined cycle instead of a simple steam cycle and the effect of using a fuel dryer.

Among the configurations investigated, a plant with both a gas turbine and a fuel dryer yields the highest exergy efficiency and total efficiency. However, the net power efficiency is higher for a plant without a fuel dryer than for one with a fuel dryer.
Effect of Pressure on Second-Generation Pressurized Fluidized Bed Combustion Plants
Authors: Robertson Archie , Bonk Donald
Published: February 2015

In the search for a more efficient, less costly, and more environmentally responsible method for generating electrical power from coal, research and development has turned to advanced pressurized fluidized bed combustion (PFBC) and coal gasification technologies. A logical extension of this work is the second-generation PFBC plant, which incorporates key components of each of these technologies. In this new type of plant, coal is devolatilized/carbonized before it is injected into the PFB combustor bed, and the low-Btu fuel gas produced by this process is burned in a gas turbine topping combustor. By integrating coal carbonization with PFB coal/char combustion, gas turbine inlet temperatures higher than 1149°C (2100°F) can be achieved. The carbonizer, PFB combustor, and particulate-capturing hot gas cleanup systems operate at 871°C (1600°F), permitting sulfur capture by lime-based sorbents and minimizing the release of coal contaminants to the gases.

This paper presents the performance and economics of this new type of plant and provides a brief overview of the pilot plant test programs being conducted to support its development.
Advancement of Turbine Aerodynamic Design Techniques
Authors: Griffin Lisa W. , Huber Frank W.
Published: February 2015

The Consortium for Computational Fluid Dynamics (CFD) Application in Propulsion Technology has been created at NASA/MSFC. Its purpose is to advance the state-of-the-art of CFD technology, to validate CFD codes and models, and to demonstrate the benefits attainable through the application of CFD in component design. Three teams are currently active within the Consortium: (1) the Turbine Technology Team, (2) the Pump Stage Technology Team, and (3) the Combustion Devices Technology Team. The goals, dynamics, and activities of the Turbine Team are the subjects of this paper.

The Consortium is managed by NASA. The Turbine Team is co-coordinated by a NASA representative from the CFD area and an industry (Pratt & Whitney) representative from the area of turbine aerodynamic design. Membership of the Turbine Team includes experts in design, analysis, and testing from the government, industry, and academia. Each member brings a unique perspective, expertise, and experience to bear on the team’s goals of improving turbine efficiency and robustness while reducing the amount of developmental testing. To this end, an advanced turbine concept has been developed within the team using CFD as an integral part of the design process. This concept employs unconventionally high turning blades and is predicted to provide cost and performance benefits over traditional designs. This concept will be tested in the MSFC Turbine Airflow Facility to verify the design and to provide a unique set of data for CFD code validation. Currently, the team is developing and analyzing methods to reduce secondary and tip losses to further enhance turbine efficiency. The team has also targeted volute development as an area that could benefit from detailed CFD analysis.
Evaluation of Thermal-Sprayed Bronze Abradable Coatings: Effect of Temperature and Time on Coating Microstructure and Performance
Authors: Mutasim Zaher Z. , Hsu Lulu L.
Published: February 2015

Metallurgical evaluation was conducted on thermally-sprayed bronze coatings that are commonly found in gas turbine labyrinth seals. These bronze coatings serve as abradable surfaces for air/air and air/oil seals operating at low temperatures. As-coated and post-oxidation coating microstructures were examined metallographically to establish the coating’s functional life at various operating temperature ranges. Oxidation tests at several temperatures and times were carried out in order to construct a time-temperature map that could be used to predict the useful life of this bronze coating as correlated to gas turbine bronze seals returned from field service. Scanning electron microscopy in conjunction with polarized light microscopy were utilized to identify the presence of red cuprous oxide, a key factor in the determining the extent of internal oxidation.
Integrity Testing of Brush Seal in Shroud Ring of T-700 Engine
Authors: Hendricks Robert C. , Griffin Thomas A. , Bobula George A. , Bill Robert C. , Howe Harold W.
Published: February 2015

A split-ring brush seal was fabricated, installed between two labyrinth-honeycomb shroud seals, and tested in the fourth-stage turbine of a T-700 engine. The annealed Haynes 25 bristles rubbed directly against the nonconditioned, irregular René 80 turbine blade shroud surface. A total of 21 hr of cyclic and steady-state data were taken with surface speeds to 335 m/s (1100 ft/s) and shroud temperatures to 620 °C (1150 °F). Wear appeared to be rapid initially, with an orange flash of hot brush fragments during the first engine startup, to minimal after 10 hr of operation. The brush survived the testing but experienced some bristle pullouts and severe bristle wear; some turbine interface wear and possible material transfer was noted. Future design concerns center on tribological behavior at the interface with or without lubricants.
Chemical Vapor Deposition (CVD) Coatings for Protection of Jet Engine Components
Authors: Podob Mark
Published: February 2015

CVD coatings are thin films resulting from the chemical reaction between a gaseous phase and the heated surface of a substrate. Among the industries using CVD coating technology are electronics, tooling, fuel cogeneration, and aerospace. The electronics industry uses CVD to deposit semiconductor materials onto different substrates. For the tooling industry, titanium nitride (TiN), titanium carbide (TiC), or aluminum oxide (Al2O3) is deposited onto cutting or metal forming tools. These hardcoatings act as chemical and thermal barriers between the tool and workpiece.

In the aerospace industry, CVD is used to deposit aluminide or chromide coatings onto jet engine blades and other hot section components. The coatings improve the corrosion and oxidation resistance of the base metal. CVD is replacing older established methods for protecting these same components. While the use of CVD coatings in the aerospace industry is relatively new, it is gaining increasing acceptance. In addition to producing aluminides and chromides, CVD reactions can form coatings containing silicon, yttrium, hafnium and other rare earth elements. Since the coatings are the result of the chemical reaction between high purity gases and solids, coatings can be free of porosity and inclusions.
Expanded SUMED System a Pipeline for the Future
Authors: Haddara Sherif Hassan
Published: February 2015

This paper describes the Design, Engineering, Planning and Implementation activities that led up to an advanced, state of the art, optimum and economical solution for expanding an existing system to handle an increase of crude oil throughput from 80 to 117 mta metric tons per year (2.53 t/s to 3.71 t/s).

The growing demand and reduced net imports of products will increase Western European crude oil requirements to 11 million b/d (barrel per day) equivalent to 20.24 m3/s by year 2000.

SUMED (gulf of SUez - MEDiterranean) the Arab Petroleum Pipelines Company has historically secured about 40% of the market for middle Eastern crude oil movements to Europe.

Given these market shares on incremental volume SUMED should achieve its maximum design throughput of 117 mta by year 2000.

The SUMED pipelines system which is owned and operated by an Arab company having EGYPT, SAUDI ARABIA, KUWAIT, EMIRATES AND QATAR as share holders has been in operation since 1977. An expansion project has started to increase the throughput capacity of the system from 80 to 117 mta. The project completion is expected by mid 1994 with a total expenditure of 120 million dollars.

This paper reviews the evaluation and selection of various electric motor and gas turbines for the main pumping station addition for this pipeline expansion.
The Marshall Space Flight Center Turbine Test Equipment: Description and Performance
Authors: Bordelon Wayne J. , Kauffman William J. , Heaman John P.
Published: February 2015

Performance evaluations of rocket engine turbopump drive turbines are difficult to obtain from turbopump or engine firings due to measurement limitations and operating point restrictions. The Marshall Space Flight Center (MSFC) Turbine Test Equipment (TTE) was developed to provide an accurate, economical method of measuring the performance of full-scale turbopump gas turbines. By expanding air at pressures as high as 435 psia (3.0 MPa) to atmospheric conditions, the TTE provides metered air at nominal conditions of 100 psia (0.69 MPa), 550 °R (350 °K), and 15 lbm/sec (6.8 kg/sec) with run times of 100 seconds or greater. A 600 hp (448 kW) direct current dynamometer and gearbox provide turbine power absorption for speeds up to 14,000 rpm. This paper describes the MSFC TTE and its performance including the performance envelope, turbine inlet flow quality, and measurement uncertainty.
Probabilistic Assessment of Space Nuclear Propulsion System Nozzle
Authors: Shah Ashwin R. , Ball Richard D.
Published: February 2015

Uncertainties associated with the design parameters of the Space Nuclear Propulsion System (SNPS) nozzle such as geometry, boundary conditions, material behavior, thermal and pressure loads, etc. are considered to assess its reliability. Preliminary assessment of the reliability is performed using NESSUS (Numerical Evaluation of Stochastic Structures Under Stress) computer code developed at NASA Lewis Research Center (LeRC). Probabilistic finite element analysis of the nozzle system is conducted and the sensitivity of reliability to the uncertainties in the random variables is quantified. For example the nozzle spatial geometry uncertainties have the most significant effect on the effective stress at low probabilities while the inner wall temperature has the most significant effect at higher probabilities.
An Electromechanical Simulation Method for Active Vibration Control of a Magnetic Bearing Supported Rotor
Authors: Tang Punan , Palazzolo A. B. , Brown Gerald , DiRusso Eliseo , Kascak Albert
Published: February 2015

A reliable electromechanical simulation model is essential for designing rotor systems supported by magnetic bearings. Accurate predictions of forced response, critical speeds and stability are required to assure machinery health and reliability. This paper presents a general methodology which couples a finite element based model of the rotor with state space models of the sensors, control system and actuators. A least squares based algorithm is presented for obtaining the state space representation of the digital (DSP) controller, actuator, and power amplifiers from their measured frequency response functions. This general simulation method is illustrated by application to a cryogenic magnetic bearing test rig at NASA Lewis.
A Fracture Mechanics Approach to Life Prediction of Turbine Blades
Authors: Vyas N. S. , Sidharth  , Rao J. S.
Published: February 2015

Emerging blade technologies are finding it increasingly essential to correlate blade vibrations to blade fatigue in order to asses the residual life of existing blading and for development of newer designs. In this paper an analytical code for Dynamic Stress Analysis and Fatigue Life Prediction of blades is presented. The life prediction algorithm is based on a combination method, which combines the local strain approach to predict the initiation life and fracture mechanics approach to predict the propagation life, to estimate the total fatigue life. The conventional stress based approach involving von Mises theory along with S-N-Mean stress diagram suffer from the drawback that they do not make allowance for the possibility of development of plastic strain zones, especially in cases of low cycle fatigue. In the present paper, strain life concepts are employed to analyse the crack initiation phenomenon. Dynamic and static stresses incurred by the blade form inputs to the life estimation algorithm. The modeling is done for a general tapered, twisted and asymmetric cross section blade mounted on a rotating disc at a stagger angle. Blade damping is nonlinear in nature and a numerical technique is employed for estimation of blade stresses under typical nozzle excitation. Critical cases of resonant conditions of blade operation are considered. Neuber’s rule is applied to the dynamic stresses to obtain the elasto-plastic strains and then the material hysteresis curve is used to iteratively solve for the plastic stress. Static stress effects are accounted for and crack initiation life is estimated by solving the strain life equation. Crack growth formulations are then applied to the initiated crack to analyse the propagation of crack leading to failure. The engineering approximations involved are stated and the algorithm is numerically demonstrated for typical conditions of blade operations.
Load Control–Strain Control Isochronous Stress–Strain Curves for High Temperature Nonlinear Analysis
Authors: Bechtel Gregory S. , Cook Thomas S.
Published: February 2015

Aircraft gas turbine components are subjected to severe operating conditions. High temperatures, large thermal strains, and mechanical loads combine to cause the material to undergo significant nonlinear behavior. In order to assure safe, durable components, it is necessary that analysis methods be available to predict the nonlinear deformation. General purpose finite element codes are available to perform elastic and viscoplastic analyses, but the analyses are expensive. Both large plastic and creep strain analyses can require significant computer resources, but typically a plastic solution is more economical to run than a time stepping creep or viscoplastic model solution. For those applications where the deformation is principally time dependent, it is advantageous to include time dependent creep effects in a “constant time” or “isochronous” analysis. Although this approach has been used in the past to estimate rupture life, this paper will present several significant new techniques for doing an isochronous analysis to analyze time dependent deformation.
Low Emissions Combustor Development for an Industrial Gas Turbine to Utilise LCV Fuel Gas
Authors: Kelsall G. J. , Smith M. A. , Cannon M. F.
Published: February 2015

Advanced coal based power generation systems such as the British Coal Topping Cycle offer the potential for high efficiency electricity generation with minimum environmental impact. An important component of the Topping Cycle programme is the gas turbine, for which development of a combustion system to burn low calorific value coal derived fuel gas, at a turbine inlet temperature of 1260°C (2300 F), with minimum pollutant emissions, is a key R&D issue.

A phased combustor development programme is underway burning low calorific value fuel gas (3.6–4.1 MJ/m3) with low emissions, particularly NOx derived from fuel bound nitrogen.

The first phase of the combustor development programme has now been completed using a generic tubo-annular, prototype combustor design. Tests were carried out at combustor loading and mach numbers considerably greater than the initial design values. Combustor performance at these conditions was encouraging.

The second phase of the programme is currently in progress. This will assess, initially, an improved variant of the prototype combustor operating at conditions selected to represent a particular medium sized industrial gas turbine. This combustor will also be capable of operating using natural gas as an auxiliary fuel, to suit the start-up procedure for the Topping Cycle.

The paper presents the Phase 1 test programme results for the prototype combustor. Design of the modified combustor for Phase 2 of the development programme is discussed, together with preliminary combustion performance results.
Steam-Injected Gas Turbine Analysis: Part II — Steam-Cycle Efficiency
Authors: Rice Ivan G.
Published: February 2015

Part II of this three-part paper focuses on injection Steam-Cycle Efficiency. Part I relates to Steam Rates and Part III analyzes Steam ReGenerated Heat (RGH). The following cycle-efficiency analysis is based on the same approach used for large-utility steam turbines where one pound of throttle steam is passed through the steam turbine, and where enthalpy points are determined along the steam path. Accurate analysis of heat input, partial pressure expansion and heat-rejection steam enthalpy points are computed with steam-table software.
Experimental Investigation of the Steady and Unsteady Relative Flow in a Model Centrifugal Impeller Passage
Authors: Abramian M. , Howard J. H. G.
Published: February 2015

The behaviour of the relative flow in centrifugal turbomachines is extremely complex due to the existence of various fluid dynamic phenomena and their interaction. At design and off-design operating conditions, the relative flow is subject to stationary unsteadiness which includes flow separation and wakes associated with passage pressure gradients, secondary flows, and boundary layer stability. It may also be subject to periodic unsteadiness such as is the rotating stall and cyclic flow phenomena induced by the casing.

This paper describes detailed measurements of the relative velocity field in a very low specific speed centrifugal pump impeller (Ns=515). Measurements were conducted by means of a recently developed rotating laser-Doppler anemometry system. Detailed quantitative description of the mean and fluctuating components of the primary and secondary velocity fields are presented for an impeller without volute at design, 50% design and shut-off conditions. The flow pattern in this low specific speed impeller with high blade loading is dominated by the relative eddy (a phenomenon also present in potential flow) which has suppressed suction side separation. When the impeller was fitted with a volute, the cyclic variation of the impeller exit flow, induced by the volute at low flow rates, is also presented.
FINITE AUTOMATA WITH ADVICE TAPES
Authors: KÜÇÜK UĞUR , SAY A. C. CEM , YAKARYILMAZ ABUZER
Published: February 2015

We define a model of advised computation by finite automata where the advice is provided on a separate tape. We consider several variants of the model where the advice is deterministic or randomized, the input tape head is allowed real-time, one-way, or two-way access, and the automaton is classical or quantum. We prove several separation results among these variants, demonstrate an infinite hierarchy of language classes recognized by automata with increasing advice lengths, and establish the relationships between this and the previously studied ways of providing advice to finite automata.
OPERATIONAL CHARACTERIZATION OF SCATTERED MCFLs
Authors: ÉSIK ZOLTÁN , IVÁN SZABOLCS
Published: February 2015

We give a Kleene-type operational characterization of Muller context-free languages (MCFLs) of well-ordered and scattered words.
FACTORIZATIONS AND UNIVERSAL AUTOMATON OF OMEGA LANGUAGES
Authors: CARNINO VINCENT , LOMBARDY SYLVAIN
Published: February 2015

We extend the concept of factorization on finite words to ω-rational languages and show how to compute them. We define a normal form for Büchi automata and introduce a universal automaton for Büchi automata in normal form. We prove that, for every ω-rational language, this Büchi automaton, based on factorization, is canonical and that it is the smallest automaton that contains the morphic image of every equivalent Büchi automaton in normal form.
Metric dimensions of minor excluded graphs and minor exclusion in groups
Authors: Ostrovskii Mikhail I. , Rosenthal David
Published: February 2015

An infinite graph Γ is minor excluded if there is a finite graph that is not a minor of Γ. We prove that minor excluded graphs have finite Assouad–Nagata dimension and study minor exclusion for Cayley graphs of finitely generated groups. Our main results and observations are: (1) minor exclusion is not a group property: it depends on the choice of generating set; (2) a group with one end has a generating set for which the Cayley graph is not minor excluded; (3) there are groups that are not minor excluded for any set of generators, like ℤ3; (4) minor exclusion is preserved under free products; and (5) virtually free groups are minor excluded for any choice of finite generating set.
Growth rates of algebras, II: Wiegold dichotomy
Authors: Kearnes Keith A. , Kiss Emil W. , Szendrei Ágnes
Published: February 2015

We investigate the function dA(n), which gives the size of a least size generating set for An, in the case where A has a cube term. We show that if A has a k-cube term and Ak is finitely generated, then dA(n) ∈ O( log (n)) if A is perfect and dA(n) ∈ O(n) if A is imperfect. When A is finite, then one may replace "Big O" with "Big Theta" in these estimates.
Multi-Oriented Text Extraction in Stylistic Documents
Authors: Mohan Singh Brij , Sharma Rahul , Ghosh Debashis , Mittal Ankush
Published: February 2015

In many documents such as maps, engineering drawings and artistic documents, etc. there exist many printed as well as handwritten materials where text regions and text-lines are not parallel to each other, curved in nature, and having various types of text such as different font size, text and non-text areas lying close to each other and non-straight, skewed and warped text-lines. Optical character recognition (OCR) systems available commercially such as ABYY fine reader and Free OCR, are not capable of handling different ranges of stylistic document images containing curved, multi-oriented, and stylish font text-lines. Extraction of individual text-lines and words from these documents is generally not straight forward. Most of the segmentation works reported is on simple documents but still it remains a highly challenging task to implement an OCR that works under all possible conditions and gives highly accurate results, especially in the case of stylistic documents. This paper presents dilation and flood fill morphological operations based approach that extracts multi-oriented text-lines and words from the complex layout or stylistic document images in the subsequent stages. The segmentation results obtained from our method proves to be superior over the standard profiling-based method.
The fractional Hankel wavelet transformation
Authors: Prasad Akhilesh , Mahato K. L.
Published: February 2015

The main objective of this paper is to investigate the fractional Hankel wavelet transformation and to study some basic properties. An inversion formula for this fractional Hankel wavelet transformation is also obtained. Some examples of fractional Hankel wavelet transformation are given.
On special subalgebras of derivations of Lie algebras
Authors: Sheikh-Mohseni S. , Saeedi F. , Badrkhani Asl M.
Published: February 2015

Let L be a Lie algebra, and Der (L) and IDer (L) be the set of all derivations and inner derivations of L, respectively. Also, let Der c(L) denote the set of all derivations α ∈ Der (L) for which α(x) ∈ Imad x for all x ∈ L. We give necessary and sufficient conditions under which Der c(L) = Der z(L), where Der z(L) is the set of all derivations of L whose images lie in the center of L. Moreover, it is shown that any two isoclinic Lie algebras L1 and L2 satisfy Der c(L1) ≅ Der c(L2).
High Frequency Non-Invasive Stimulation Over the Spine: Effects on Mood and Mechanical Pain Tolerance in Normal Subjects
Authors: Towell A. D. , Williams D. , Boyd S. G.
Published: February 2015

We investigated the effects of non-invasive high frequency (625Hz) stimulation over the spine on mechanical pain tolerance and subjective mood. Sixty healthy subjects were divided equally into three groups receiving either high intensity (250 V), low intensity (3–4 V) or sham electrical stimulation directly over the spinal cord for 30 minutes. Following high intensity stimulation, subjects felt significantly more elated, leisurely and less tense and, contrary to reports on patients with clinical pain, had lower mechanical pain tolerances. There were no correlations between changes in mood and changes in mechanical pain tolerances. These findings contrasted with the lack of any significant differences in mood or mechanical pain tolerances in a second study where 20 subjects received either high intensity or sham stimulation across the left shoulder joint. The results indicate that decreases in mechanical pain tolerance are independent of changes in mood following non-invasive high frequency, high intensity cutaneous stimulation but that both effects are dependent on that stimulation being applied over the spine.
Superior Vena Cava Syndrome and Colon Carcinoma: A Report of a Multifactorial Association
Authors: Espírito Santo Joana , Coutinho Inês , Pimentel Ana , Garcia Rui , Marques dos Santos Rui
Published: February 2015

Introduction. Superior vena cava (SVC) syndrome results from the obstruction of blood flow through the SVC, having distinct pathophysiological underlying mechanisms. Cancer is associated with an increased risk of thromboembolism that varies according to patient-, tumor-, and treatment-related factors. An individualized clinical approach is important to pursue the accurate diagnosis of the underlying pathology causing thromboembolism in cancer patients.Case Presentation. The authors present a case of a 58-year-old male with an infrequent presentation of an unknown colon carcinoma, who has never had any symptom until he was hospitalized with the diagnosis of superior vena cava syndrome and pulmonary thromboembolism. The patient had an advanced disease by the time of diagnosis and molecular alterations contributing to abnormal hemostasis. He presented venous and arterial thromboembolism and developed disseminated intravascular coagulopathy after surgery, anticoagulant and transfusion therapy, dying 40 days after the hospitalization.Conclusion. The authors discuss thromboembolic disease and tumor metastasis roles in a cancer patient with SVC syndrome. Thromboembolism in a malignancy context is a challenging clinical entity. A multifactorial perspective of the thrombotic disease is warranted to approach thromboembolism risk and stratify patients suitable to receive adequate anticoagulant prophylaxis and targeted therapies, aiming to improve clinical prognosis.
ProGeRF: Proteome and Genome Repeat Finder Utilizing a Fast Parallel Hash Function
Authors: Lopes Robson da Silva , Moraes Walas Jhony Lopes , Rodrigues Thiago de Souza , Bartholomeu Daniella Castanheira
Published: February 2015

Repetitive element sequences are adjacent, repeating patterns, also called motifs, and can be of different lengths; repetitions can involve their exact or approximate copies. They have been widely used as molecular markers in population biology. Given the sizes of sequenced genomes, various bioinformatics tools have been developed for the extraction of repetitive elements from DNA sequences. However, currently available tools do not provide options for identifying repetitive elements in the genome or proteome, displaying a user-friendly web interface, and performing-exhaustive searches. ProGeRF is a web site for extracting repetitive regions from genome and proteome sequences. It was designed to be efficient, fast, and accurate and primarily user-friendly web tool allowing many ways to view and analyse the results. ProGeRF (Proteome and Genome Repeat Finder) is freely available as a stand-alone program, from which the users can download the source code, and as a web tool. It was developed using the hash table approach to extract perfect and imperfect repetitive regions in a (multi)FASTA file, while allowing a linear time complexity.
PAMAM Dendrimers as Potential Carriers of Gadolinium Complexes of Iminodiacetic Acid Derivatives for Magnetic Resonance Imaging
Authors: Markowicz-Piasecka Magdalena , Sikora Joanna , Szymański Paweł , Kozak Oliwia , Studniarek Michał , Mikiciuk-Olasik Elżbieta
Published: February 2015

This is the first study describing the utilization of PAMAM dendrimers as delivery vehicles of novel magnetic resonance imaging (MRI) contrast agents. The purpose of this paper was to establish the potential of G4 PAMAM dendrimers as carriers of gadolinium complexes of iminodiacetic acid derivatives and determine imaging properties of synthesized compounds in in vivo studies. Furthermore, we examined the influence of four synthesized complexes on the process of clot formation, stabilization, and lysis and on amidolytic activity of thrombin. Biodistribution studies have shown that the compounds composed of PAMAM G4 dendrimers and gadolinium complexes of iminodiacetic acid derivatives increase signal intensity preferably in liver in range of 59–116% in MRI studies which corresponds with the greatest accumulation of gadolinium after administration of the compounds. Synthesized compounds affect kinetic parameters of the proces of clot formation, its stabilization, and lysis. However, only one synthesized compound at concentration 10‐fold higher than potential plasma concentrations contributed to the increase of general parameters such as the overall potential of clot formation and lysis (↑CLAUC) and total time of the process (↑T). Results of described studies provide additional insight into delivery properties of PAMAM dendrimers but simultaneously underscore the necessity for further research.
A Comparison of the Stability Performance of Blends of Paraffinic Diesel and Petroleum-Derived Diesel, with RME Biodiesel Using Laboratory Stability Measurement Techniques
Authors: de Goede S. , Wilken C. , Ajam M. , Roets P. , Engelbrecht P. , Woolard C.
Published: February 2015

In 2012, a new specification for synthetic fuels containing up to 7% biodiesel (FAME) was approved (CEN TS 15940). This specification allows the sale of neat paraffinic diesel, such as Gas-to-Liquids (GTL) diesel, to captive fleets in Europe. Several aspects are important in the final end-use application, including the stability of the fuel. The current study evaluated the stability of neat GTL diesel and FAME/paraffinic fuel blends via standard laboratory stability tests commonly used to study petroleum-derived fuels. The stability of GTL diesel, containing biodiesel, was evaluated using the Rancimat, PetroOxy, and ASTMD2274 tests. Selected samples were also evaluated using ASTM D5304. The Rancimat results indicated that FAME/GTL diesel blends performed similar to the FAME/petroleum derived fuel blends. In the PetroOxy test, the addition of more than 2 v/v% of a highly stable FAME resulted in an unexpected boost in the stability of the FAME/GTL diesel blend. The ASTM D2274 results were generally insensitive to the addition of FAME. The correlation between the PetroOxy and Rancimant tests was evaluated and found to be base fuel dependent. From this study it was concluded that GTL diesel (in blends with FAME) performed similar to petroleum-derived reference fuels in standard laboratory stability.
Two-Dimensional Metallicity with a Large Spin-Orbit Splitting: DFT Calculations of the Atomic, Electronic, and Spin Structures of the Au/Ge(111)-(3×3)R30°Surface
Authors: Fleszar Andrzej , Hanke Werner
Published: February 2015

Density functional theory (DFT) is applied to study the atomic, electronic, and spin structures of the Au monolayer at the Ge(111) surface. It is found that the theoretically determined most stable atomic geometry is described by the conjugated honeycomb-chained-trimer (CHCT) model, in a very good agreement with experimental data. The calculated electronic structure of the system, being in qualitatively good agreement with the photoemission measurements, shows fingerprints of the many-body effects (self-interaction corrections) beyond the LDA or GGA approximations. The most interesting property of this surface system is the large spin splitting of its metallic surface bands and the undulating spin texture along the hexagonal Fermi contours, which highly resembles the spin texture at the Dirac state of the topological insulator Bi2Te3. These properties make this system particularly interesting from both fundamental and technological points of view.
Investigating the Pretreatment miRNA Expression Patterns of Advanced Hepatocellular Carcinoma Patients in Association with Response to TACE Treatment
Authors: El-Halawany Medhat S. , Ismail Heba M. , Zeeneldin Ahmed A. , Elfiky Ammar , Tantawy Marwa , Kobaisi Mohamed H. , Hamed Ikram , Abdel Wahab Abdel Hady A.
Published: February 2015

Hepatocellular carcinoma (HCC) is a lethal malignancy with poor prognosis and limited treatment options. Transarterial chemoembolization (TACE) using chemotherapy agents—doxorubicin and cisplatin—is an accepted treatment option for locally advanced hepatocellular carcinoma. In the current study, we analyzed the expression pattern of a selected panel of 94 miRNAs in archival samples that were collected prior to treatment from 15 Egyptian patients diagnosed with advanced hepatocelleular carcinoma. We observed an overall increase in miRNA expression in HCC samples compared with normal subjects. Out of 94 examined miRNAs, 53 were significantly upregulated while 3 miRNAs were downregulated in HCC samples compared to normal liver samples. Comparing the pretreatment miRNA expression profiles in HCC patients and the patients response to TACE treatment resulted in the identification of a set of 12 miRNAs that are significantly upregulated in nonresponders group. This miRNA panel includes miR-10a-1, miR-23a-1, miR-24, miR-26a, miR-27a, miR-30c, miR-30e, miR-106b, miR-133b, miR-199a, miR-199-3p, and miR-200b. Furthermore, we observed that a panel of 10 miRNAs was significantly associated with patients’ survival status at 1 year. These results highlight the potential implications of pretreatment miRNAs expression profiling in prediction of the patients’ response to TACE treatment in liver cancer.