bluuebunny/crossref_metadata_2025_split huggingface dataset:
Individual variability of cerebral autoregulation, posterior cerebral circulation and white matter hyperintensity
Authors: Liu Jie , Tseng Benjamin Y. , Khan Muhammad Ayaz , Tarumi Takashi , Hill Candace , Mirshams Niki , Hodics Timea M. , Hynan Linda S. , Zhang Rong 
Published: January 2016

Key points
Cerebral autoregulation (CA) is a key mechanism to protect brain perfusion in the face of changes in arterial blood pressure, but little is known about individual variability of CA and its relationship to the presence of brain white matter hyperintensity (WMH) in older adults, a type of white matter lesion related to cerebral small vessel disease (SVD).
This study demonstrated the presence of large individual variability of CA in healthy older adults during vasoactive drug‐induced changes in arterial pressure assessed at the internal carotid and vertebral arteries. We also observed, unexpectedly, that it was the ‘over‐’ rather than the ‘less‐reactive’ CA measured at the vertebral artery that was associated with WMH severity.
These findings challenge the traditional concept of CA and suggest that the presence of cerebral SVD, manifested as WMH, is associated with posterior brain hypoperfusion during acute increase in arterial pressure.
AbstractThis study measured the individual variability of static cerebral autoregulation (CA) and determined its associations with brain white matter hyperintensity (WMH) in older adults. Twenty‐seven healthy older adults (13 females, 66 ± 6 years) underwent assessment of CA during steady‐state changes in mean arterial pressure (MAP) induced by intravenous infusion of sodium nitroprusside (SNP) and phenylephrine. Cerebral blood flow (CBF) was measured using colour‐coded duplex ultrasonography at the internal carotid (ICA) and vertebral arteries (VA). CA was quantified by a linear regression slope (CA slope) between percentage changes in cerebrovascular resistance (CVR = MAP/CBF) and MAP relative to baseline values. Periventricular and deep WMH volumes were measured with T2‐weighted magnetic resonance imaging. MAP was reduced by −11 ± 7% during SNP, and increased by 21 ± 8% during phenylephrine infusion. CA demonstrated large individual variability with the CA slopes ranging from 0.37 to 2.20 at the ICA and from 0.17 to 3.18 at the VA; no differences in CA were found between the ICA and VA. CA slopes measured at the VA had positive correlations with the total and periventricular WMH volume (r = 0.55 and 0.59, P < 0.01). Collectively, these findings demonstrated the presence of large individual variability of CA in older adults, and that, when measured in the posterior cerebral circulation, it is the higher rather than lower CA reactivity that is associated with WMH severity.
Simulation and Experimental Investigations of a Hydraulic Stepper Drive
Authors: Gradl Christoph , Kovacic Ivo , Scheidl Rudolf 
Published: January 2016

This paper presents simulation and experimental results of an energy saving hydraulic stepper drive prototype. Different concepts, advantages and the mechanical design of such kind of stepper drive were discussed in a previous publication. The excellent efficiency, the possibility of energy recuperation, and the control by switching and check valves only, may help to open new applications for hydraulic drives. Also the flow rate can be controlled rather directly by adjusting the switching frequency. This characteristic makes the sensorless position and speed control relatively easy.
The drive is realized by a hydraulic cylinder piston unit which displaces a defined fluid quantum by the limited forward stroke of the piston controlled by a fast switching valve. This end to end motion of the piston in its cylinder generates a precise, incremental motion of an additional load cylinder; this enables a sensorless position control. Energy saving is achieved by storing the pressure surplus intermediately in the kinetic energy of the piston to displace a part of the fluid quantum without hydraulic energy from the supply line.
A detailed simulation model of a stepper drive including transmission lines, flow channels, hydraulic accumulators and valve dynamics is applied to analyze the experimental results. This dynamic model in connection with the prototype allows to identify the potential for improvement. The different ways to improve the behavior are reviewed, in particular concerning energy losses: bearing friction, leakages in gaps, pressure losses and backflow through check valves. The measured dynamic characteristics and the energy efficiency are presented and compared to the simulation results.
The preliminary results showed that the energy efficiency can be drastically increased by a better piston sealing and guidance system and faster check valves. Hence, the development of a fast plate type check valve for the hydraulic stepper drive is also proposed in this study.
Development of a Method to Evaluate CNG-Injection Valves
Authors: von Grabe Christian , van Bebber David , Murrenhoff Hubertus 
Published: January 2016

The development of combustion engines with direct injection requires a comprehensive knowledge of the in cylinder combustion process as well as the used high pressure injection system. One main characteristic of injection systems is their mass flow over time behavior. For prevalent diesel and gasoline injection valves (injectors) fully developed simulation models as well as test benches are available to analyze the injection process. Besides the established engines a trend towards compressed natural gas (CNG) engines in passenger cars is recognized. Due to the small injection duration of a few milliseconds, the flow rate measurement is particularly challenging and requires highly dynamic measuring. The existing test benches are designed and optimized for liquid fuels and are only partly suitable for the evaluation of gaseous fuels such as CNG. A typical test method is to inject fuel into a long tube in which a pressure wave propagates. Based on the pressure signal the mass flow of the injected fuel is approximated. For gaseous fuels the correlation of mass flow and pressure propagation is only known for specific test cases and therefore the method is not directly applicable to gaseous fuels.
This paper presents a newly designed measurement device to evaluate the mass flow rate as well as the injector needle displacement during an injection process of gaseous fuels. The test bench is designed to operate in a fully equipped injection system including gas lines, common rail and injection valves, to also investigate the interaction of the individual system components.
The design is based on a closed test chamber in which the pressure rises during the injection. To overcome the influence of propagating pressure waves inside the chamber on the measurement, different chamber designs are evaluated. An optimized design, separating the chamber into two volumes which are connected by a damping sleeve, is presented. The injection itself is carried out in a first volume and the measurement is conducted in a second damped volume.
Based on the measured pressure the mass flow rate through the injection valve is approximated, utilizing the equations of thermodynamics.
Compact Fluid-Borne Noise Silencers for Aviation Hydraulic Systems
Authors: Waitschat Arne , Thielecke Frank , Kloft Peter , Nisters Christian , Behr Robert M. , Heise Ulrich 
Published: January 2016

The aviation environment holds challenging application constraints for efficient hydraulic system noise reduction devices. Besides obligatory strong limits on component weight and size, the high safety and reliability standards demand simple and maintenance-free silencer solutions. Hence, basic Helmholtz-Resonators and inline expansion chambers are state-of-the-art aboard commercial aircrafts in service.
Unfortunately, they do not meet today’s noise attenuation performance aims regarding passenger comfort and equipment durability. Furthermore, production and installation costs have to be considered, plus particular aircraft operating conditions. Commercial aircrafts come with relatively high operating pressures of 210/350bar (3000/5000psi) and fluid-borne noise fundamental frequencies up to approximately 1200 Hz for some of the hydraulic pumps.
This conference contribution discusses a new compact approach for an inline expansion chamber, named DiscSilencer that accounts for the mentioned aviation constraints.
The silencer chamber is designed as smooth expansion in only one radial direction relative to the connected piping. The perpendicular radial dimension is kept identical to the piping diameter. This results in a flat rectangular cross area of the flow passageway instead of a circular shape, enabling new options for installation and further incremental development.
In this paper, the modelling and experimental validation of such an unconventional hydraulic silencer are presented.
A Consideration on the Behavior of Hydraulic Pressure Ripples in Relation to Hydraulic Oil Temperature
Authors: Nakagawa Shuichi , Ichiyanagi Takayoshi , Nishiumi Takao 
Published: January 2016

It is well known that hydraulic noise can change as a system warms up. That change can be a factor for misperception of mechanical failure, because noise can play an important role as a signal that indicates abnormal operation. It is therefore important to understand the behavior of hydraulic pressure ripples that are a source of hydraulic noise in operating conditions, and how they change in relation to the temperature of the hydraulic oil.
This study has investigated the ripple behavior that results from temperature change in simple hydraulic systems, using mathematical models that took thermal properties into account. Physical properties of the oil and the speed of sound in the oil have been defined as temperature-related variables in the mathematical models. The physical properties that should be used in the mathematical models have been obtained directly from the oil manufacturer. In contrast, the speed of sound in the oil has to be obtained from the isentropic tangent bulk modulus of the oil in an actual operating condition. That has been determined from the specific volume ratio of entrained air to the oil and the isentropic tangent bulk modulus of the only oil. The thermal properties of the speed of sound in the oil have been determined from the thermal characteristics of these variables, and it has been found that the speed of sound in the oil decreases with a rise in the oil temperature.
The mathematical models of pressure ripples have shown that there were three distinct phenomena resulting from the temperature change of the oil. The first is the change of wavelength. The second is the spatial dependence of the thermal characteristics of the pressure ripples. The third is the difference of the thermal characteristics of the pressure amplitude at the peak in spatial modes. These changes that result from the temperature variation tend to be large at higher frequency.
Novel ICT-Enabled Collaborative Design Processes and Tools for Developing Non-Road Mobile Machinery
Authors: Åman Rafael , Handroos Heikki , Kärkkäinen Hannu , Jussila Jari , Korkealaakso Pasi 
Published: January 2016

The improvement of the energy efficiency is an important topic for non-road mobile machinery developers and manufacturers. These machines normally use fluid power transmission in drivelines and working actuators. New energy efficient technologies, e.g. a hybrid power transmission with an energy recovery feature, have been introduced. Currently most of the manufacturers are still using conventional technologies in their product development process. Human operators have an effect on the overall efficiency of the machines. Taking into account the human effects is difficult and expensive using the conventional design processes and tools.
The objective of this study is to provide international machine manufacturers instrumental, yet novel, community and simulation-based (ICT-enabled) tools/methods for the strategic and cost effective development of their product practices and design processes. The development of models and methods will allow for rapid real-time virtual prototyping of complex machines and machine fleets that operate within a number of worksites or geographical conditions. The introduction of this state-of-the art (and going beyond) advancement in real-time virtual technology, simulation, internet based design technologies and software, cyber-physical and big data processing systems, will present a holistic approach to improve the entire product life. Targeted user groups are manufacturers of non-road mobile machinery (i.e. excavators, wheel loaders, etc.). These machines and production systems share the following key features: 1) They are complex mechatronic systems with several interconnections between hydraulic drives; mechanics, electronics, software and 2) they include autonomous, semiautonomous and human driven operated systems. Methods developed will enable machine manufacturers’ access to technologies that will lead to a more cost effective consumer ordinated, life cycle optimization process.
This paper will introduce the method of developing customized products in a fast, agile and networked way that will lead to significantly reduced life-cycle costs.
Combustion Characteristics of a 2-Stroke Large Bore Natural Gas Spark-Ignited Engine
Authors: Griffin Aaron A. , Jacobs Timothy J. 
Published: January 2016

Naturally, there are complex interactions among internal combustion engine parameters such as in-cylinder pressure, emissions, speed, and load. These basic relationships are studied in a naturally aspirated, spark-ignited, two-stroke large bore natural gas engine. The typical application for such an engine is in the oil and gas industry, operating heavy machinery such as large compressors and oil field pump jacks.
Cylinder pressure measurements averaged over 300 cycles are captured for speeds of 350 and 525 RPM and load ratings of 50%, 75%, and 100% of rated torque at each respective speed. Non-sequential individual cycle pressure curves are also captured to depict cycle-to-cycle variation within the engine at each operating point. Emissions data are captured and presented for each operating point. At another 8 test conditions, pressure measurements averaged from 100 cycles are taken to specifically investigate disagreement among compression pressure curves; these conditions include 350, 400, 440, and 470 RPM at 50% and 85% of the rated load.
It is found that low load cycle-to-cycle variation is extreme, having COV of IMEP values over 30%. Such engines are not designed to operate at low-load conditions. Cyclic variation is shown to decrease with increasing load and decreasing speed. As expected, peak pressures increase with increasing load and decrease with increasing speed. Emissions of THC and CO decrease with increasing load, while emissions of NO are highest at low speed and high load. It is also shown that compression pressure behavior after exhaust port closure but before ignition is different among different speeds and loads. This may be characteristic of scavenging and heat transfer behavior.
Waste Heat Recovery for Locomotive Engines Using the Organic Rankine Cycle
Authors: Jeihouni Yousef , Franke Michael , Lierz Klaus , Tomazic Dean , Heuser Peter 
Published: January 2016

Locomotive engines are emitting high levels of exhaust gas emissions and substantial amount of particulates which is thought to have significant global warming potential. In the past years locomotive regulations have been implemented in the United States to control the emission in this application. Also it can be observed that engine emitted carbon dioxides (CO2) will be limited soon for all on-road engine categories to meet the Green House Gases (GHG) norms.
Tier 4 standards apply to locomotives since the beginning of 2015 for newly built or remanufactured engines. NOx and particulate limits have been reduced by around 70% compared to the Tier 3 standards requiring significant advancements in engine technology and / or exhaust aftertreatment solutions. EGR technology is an option to reduce NOx emissions to Tier 4 locomotive standards indeed of its impact on engine fuel consumption as well as the emitted CO2 gas, which may be controlled either by future CO2 or fuel consumption standards.
To cope with this challenge, new engine technology concepts need to be developed. A waste heat recovery system is a beneficial solution to recover the wasted energies from different heat sources in the engine. Especially the considerable amount of exergy in the exhaust gas (EGR and tailpipe), which results from its high temperature and mass flow, has significant recovery potential. By utilizing a waste heat recovery system a portion of this exergy can be converted into a usable form of power, which then will increase the effective power output of the engine system. A major challenge is to recover the wasted exhaust energy with the maximum possible system efficiency. In a Tier 4 locomotive engine, heat from the EGR system as well as the tailpipe waste heat can be recovered by using an Organic Rankine Cycle (ORC) waste heat recovery system.
This paper will discuss the results of a waste heat recovery (ORC) system evaluation for locomotive applications. With the help of thermodynamic calculations the incremental power from ORC system as well as the fuel economy benefit will be evaluated and discussed. Additionally, a reasonable working fluid and the system layout, which are considered for thermodynamic calculations, will be reviewed.
Combustion Trajectory Visualization Model for Study of Conventional and Advanced Direct Injection Combustion Modes
Authors: Bittle Joshua A. , Jacobs Timothy J. 
Published: January 2016

Many of the approaches to diagnostics of in-cylinder spatially resolved quantities (such as equivalence ratio, temperature, speciation, etc.) require either optical engines or computational fluid dynamics. These approaches are expensive (time or money) and will likely never be practical for on-board use in the future. The market trend towards real-time control and consumer grade in-cylinder pressure transducers suggest that relatively simple modeling techniques based on cylinder pressure and other standard engine sensors are well situated to be a part of the future engine control schemes. This work expands previous efforts to calculate combustion trajectories (path through equivalence ratio vs. temperature plane) based on cylinder pressure measurements in near real-time.
This work incorporates the current state-of-the-art diesel fuel spray mixing models (Kattke and Musculus entrainment waves) and adds features to accounting for changing cylinder pressure, adaptive time step based on sampling rate of cylinder pressure, and optimizing spray axial resolution for reduced calculation time. Based on the predicted local fuel concentration, flame temperature and relating calculated heat release rates to the amount of fuel burned in each portion of the spray the combustion processes can be tracked to give a cumulative history of the ignition, subsequent mixing and heating/cooling that gives a picture of what combustion looks like on the equivalence ratio vs. temperature plane.
Various engine operating conditions are explored including conventional diesel operation with and without EGR as well as highly dilute late injection low temperature combustion at different injection pressures. The results obtained in this work give encouragement that this type of approach may enable future engine control using these detailed yet computationally simple approaches.
Experimental Analysis of Sudden Pressure Increase Phenomenon by Real-Time Internal Observation of Diesel Particulate Filter
Authors: Fukui Rui , Okamoto Yuki , Nakao Masayuki 
Published: January 2016

As a way of reducing the amount of Particulate Matter (PM) contained in the exhaust gas, Diesel Particulate Filter (DPF) is widely used. To keep the condition of DPF normal and effective, estimation of the amount of PM deposits in the DPF is important. The estimation is mainly conducted based on the value of pressure drop across the DPF. Occasionally, the value of the pressure drop rises suddenly and it leads to overestimation of the amount of PM deposits.
In order to elucidate the cause of the sudden pressure drop increase phenomenon, this paper firstly reveals the engine operating conditions which invoke this phenomenon. The authors also have developed a visualization method to realize the wide-perspective internal observation of the DPF. The observation experiment has been conducted with a commercial engine and DPF under the revealed conditions. Experimental results make clear that the phenomenon is caused by PM deposit layer collapse and channel plugging.
Factors Determining Anti-Knocking Properties of Gaseous Fuels in Spark Ignition Gas Engines
Authors: Tanaka Hiroki , Kobayashi Kazunobu , Sako Takahiro , Kuwahara Kazunari , Kawanabe Hiroshi , Ishiyama Takuji 
Published: January 2016

The factors affecting knock resistance of fuels, including hydrogen (H2), ethane (C2H6), propane (C3H8), normal butane (n-C4H10), and iso-butane (i-C4H10), were determined using modeling and engine operation tests with spark-ignition gas engines. The results of zero-dimensional detailed chemical kinetic computations indicated that H2 had the longest ignition delay time of these gaseous fuels. Thus, H2 possessed the lowest ignitability. Results of engine operation tests indicated that H2 was the fuel most likely to result in knocking. The use of H2 as the fuel produced a temperature profile of the unburned gas compressed by the piston and flame front that was higher than that of the other fuels due to the high specific heat ratio and burning velocity of H2.
The relation between knock resistance and secondary fuel ratio in methane-based fuel blends also was investigated using methane (CH4) as the primary component, and H2, C2H6, C3H8, n-C4H10, or i-C4H10 as the secondary components. When the secondary fuel ratio was small, the CH4/H2 blend possessed the lowest knocking tendency. But as the secondary fuel ratio increased, the CH4/H2 mixture possessed a greater tendency to knock than did CH4/C2H6 due to the high specific heat ratio and burning velocity of H2. These results indicate that the knocking that can occur with gaseous fuels is not only dependent on the ignitability of the fuel, but it also the specific heat ratio and burning velocity.