| 1. |
- Abedi, Hamidreza, 1979, et al.
(författare)
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Preliminary Analysis of Compression System Integrated Heat Management Concepts Using LH 2 -Based Parametric Gas Turbine Model
- 2022
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Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- The investigation of the various heat management concepts using LH2 requires the development of a modeling environment coupling the cryogenic hydrogen fuel system with turbofan performance. This paper presents a numerical framework to model hydrogen-fueled gas turbine engines with a dedicated heat-management system, complemented by an introductory analysis of the impact of using LH2 to precool and intercool in the compression system. The propulsion installations comprise Brayton cycle-based turbofans and first assessments are made on how to use the hydrogen as a heat sink integrated into the compression system. Conceptual tubular compact heat exchanger designs are explored to either precool or intercool the compression system and preheat the fuel to improve the installed performance of the propulsion cycles. The precooler and the intercooler show up to 0.3% improved specific fuel consumption for heat exchanger effectiveness in the range 0.5–0.6, but higher effectiveness designs incur disproportionately higher pressure losses that cancel-out the benefits.
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| 2. |
- Almgren, Magnus, 1972, et al.
(författare)
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Mapping Systems Security Research at Chalmers
- 2011
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Ingår i: First SysSec Workshop (SysSec 2011). - 9780769545301 ; , s. 67-70
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Konferensbidrag (refereegranskat)abstract
- The department of Computer Science and Engineering at Chalmers University has a long tradition of research in systems security, including security metrics, attack detection, and mitigation. We focus on security issues arising in four specific environments: (1) backbone links, (2) sensor networks, (3) the connected car, and (4) the smart grid. In this short summary we describe recent results as well as open research questions we are exploring.
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| 3. |
- ANGHOLT, JONAS, et al.
(författare)
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A First Security Analysis of a Secure Intermodal Goods Transport System
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The goods transport business involves a lot of money and is a big part of the infrastructure of any European country. There are often many different actors involved in each transport and the communication network is rather complex due to the point-topoint communication structure. It is easy to understand why there is a high demand for increased simplicity and effectiveness. With this in mind, the e-Freight project which is based on PEPPOL has moved towards a standardized solution by developing a communication system based on access points (APs). These APs act as the interface to the system and makes it easy to establish communication between any two connected actors.With PEPPOL and e-Freight as a foundation, VOLVO leads the SITS project in close cooperation with Stena Line and DSV. The goal is to develop a harmonized communication framework that promotes increased sharing of information between actors and enable new applications to increase effectiveness and security in the chain of transportation. This leads to simplified accessibility for actors to a set of services by being connected to an AP. At the same time service providers benefit from being able to easily set up cloud services available for all actors. In addition to the back-office communication between APs, external devices such as cellphones, in-vehicle computers and check-in terminals can communicate directly with each other over short distances. This type of communication is only partially specified and a mutual standard is yet to be decided upon.In this report we have analyzed the SITS project from an IT-security perspective. The back-end system derived from e-Freight is looked into and communication links, access points, protocols, certificate handling etc., are examined. Another concern in the SITS project is the short-range communication between trucks and terminals. Since RFID is a highly potential candidate for use in this area, we have studied the technology by categorizing a typical RFID system into three distinct layers and researched important security threats with the classic CIA approach. Based on the security issues found, countermeasures such as encryption, authentication and protection against man-in-themiddle attacks are reviewed.
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| 4. |
- Ankel, Martin, 1996, et al.
(författare)
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Bistatic noise radar: Demonstration of correlation noise suppression
- 2023
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Ingår i: IET Radar, Sonar and Navigation. - : Institution of Engineering and Technology (IET). - 1751-8792 .- 1751-8784. ; 17:3, s. 351-361
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Tidskriftsartikel (refereegranskat)abstract
- In this study, spatial separation of the radar transmitter and receiver units is considered, as a means of reducing the masking effect in noise radars. A bistatic radar system is constructed, with emphasis on a lightweight transmitter unit that can be mounted on a commercial Unmanned Aerial Vehicle (UAV). The system uses pseudo-random noise, generated digitally at the receiver and transmitter units. Correlation losses, due to non-linearities in the transmitter and receiver units, are measured to 0.1 dB. This study shows that by separating the transmitter and receiver unit the masking effect is significantly reduced, compared to a monostatic setup. This reduction is enough for the system to detect a slow flying UAV. Thus, bistatic separation should be considered as a practical tool to reduce the masking effect. By processing clutter with an extended CLEAN algorithm, the correlation noise floor is further suppressed.
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| 5. |
- Ankel, Martin, 1996, et al.
(författare)
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Experimental Evaluation of Moving Target Compensation in High Time-Bandwidth Noise Radar
- 2023
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Ingår i: 20th European Radar Conference, EuRAD 2023. ; , s. 213-216
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Konferensbidrag (refereegranskat)abstract
- In this article, the effect a moving target has on the signal-to-interference-plus-noise-ratio (SINR) for high time-bandwidth noise radars is investigated. To compensate for cell migration we apply a computationally efficient stretch processing algorithm that is tailored for batched processing and suitable for implementation onto a real-time radar processor. The performance of the algorithm is studied using experimental data. In the experiment, pseudorandom noise, with a bandwidth of 100 MHz, is generated and transmitted in real-time. An unmanned aerial vehicle (UAV), flown at a speed of 11.5 m/s, is acting as a target. For an integration time of 1 s, the algorithm is shown to yield an increase in SINR of roughly 13 dB, compared to no compensation. It is also shown that coherent integration times of 2.5 s can be achieved.
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| 6. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 7. |
- Blomquist, Bo, 1958, et al.
(författare)
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Assembly Systems and Work in the Swedish Automotive Industry
- 2013
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Ingår i: Nordic Lights. Work, Management, and Welfare in Scandinavia. - 1 85972 106 0 ; , s. 225-254
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- See web-link given på Chalmers Public Library (CPL). This is an edited chapter in a book (editor was Åke Sandberg from the Swedish Institute for work Life Research Stockholm (Arbetslivsinstitutet in Swedish). This publication enlightens the authors' research and development work regarding alternatives to line assembly. Comprising e.g. explaining of the different (real-life) assembly systems utilized in Sweden all through the passing years. In a more overarching way, it criticizes the way the insights and experiences gained by such (more or less socio-technically advanced assembly system designs practised (a vast of misunderstandings and rumours are obviously at hand today. To some extent is thereby this actually a refined summarization of some of our earlier scientific contributions (see some of the other publications registered in Chalmers Public Library CPL).
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| 8. |
- Brocklehurst, Sarah, et al.
(författare)
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On measurement of operational security
- 1994
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Ingår i: IEEE Aerospace and Electronic Systems Magazine. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8985. ; 9:10, s. 7-16
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Tidskriftsartikel (refereegranskat)abstract
- Ideally, a measure of the security of a system should capture quantitatively the intuitive notion of "the ability of the system to resist attack." That is, it should be operational, reflecting the degree to which the system can be expected to remain free of security breaches under particular conditions of operation (including attack). Instead, current security levels at best merely reflect the extensiveness of safeguards introduced during the design and development of a system. Whilst we might expect a system developed to a higher level than another to exhibit "more secure behavior" in operation, this cannot be guaranteed; more particularly, we cannot infer what the actual security behavior will be from knowledge of such a level. In the paper we discuss similarities between reliability and security with the intention of working toward measures of "operational security" similar to those that we have for reliability of systems. Very informally, these measures could involve expressions such as the rate of occurrence of security breaches, or the probability that a specified "mission" can be accomplished without a security breach. This new approach is based on the analogy between system failure and security breach, but it raises several issues which invite empirical investigation. We briefly describe a pilot experiment that we have conducted to judge the feasibility of collecting data to examine these issues.
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| 9. |
- Capitao Patrao, Alexandre, 1988, et al.
(författare)
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Compact heat exchangers for hydrogen-fueled aero engine intercooling and recuperation
- 2024
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Ingår i: Applied Thermal Engineering. - 1359-4311. ; 243
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the application of compact heat exchangers for the purpose of intercooling and recuperation systems for short-to-medium range aircraft equipped with hydrogen-fueled turbofan engines. The primary objective is to assess the potential effects of engine-integrated compact heat exchangers on fuel consumption and emissions. The paper encompasses the conceptual design of integrated heat exchangers and associated ducts, followed by aerodynamic optimization studies to identify suitable designs that minimize air-side pressure losses and ensure flow uniformity at the inlet of the high-pressure compressor. Pressure drop correlations are then established for selected duct designs and incorporated into a system-level performance model, allowing for a comparison of their impact on specific fuel consumption, NOx emissions, and fuel burn against an uncooled baseline engine. The intercooled-recuperated engine resulted in the most significant improvement in take-off specific fuel consumption, with a reduction of up to 7.7% compared to the baseline uncooled engine, whereas the best intercooled engine resulted in an improvement of about 4%. Furthermore, the best configuration demonstrated a decrease in NOx emissions by up to 37% at take-off and a reduction in mission fuel burn by 5.5%. These enhancements were attributed to reduced compression work, pre-heating of the hydrogen fuel, and lower high-pressure compressor outlet temperatures.
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| 10. |
- Capitao Patrao, Alexandre, 1988, et al.
(författare)
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The heat transfer potential of compressor vanes on a hydrogen fueled turbofan engine
- 2024
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Ingår i: Applied Thermal Engineering. - 1359-4311. ; 236
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen is a promising fuel for future aviation due to its CO2-free combustion. In addition, its excellent cooling properties as it is heated from cryogenic conditions to the appropriate combustion temperatures provides a multitude of opportunities. This paper investigates the heat transfer potential of stator surfaces in a modern high-speed low-pressure compressor by incorporating cooling channels within the stator vane surfaces, where hydrogen is allowed to flow and cool the engine core air. Computational Fluid Dynamics simulations were carried out to assess the aerothermal performance of this cooled compressor and were compared to heat transfer correlations. A core air temperature drop of 9.5 K was observed for this cooling channel design while being relatively insensitive to the thermal conductivity of the vane and cooling channel wall thickness. The thermal resistance was dominated by the air-side convective heat transfer, and more surface area on the air-side would therefore be required in order to increase overall heat flow. While good agreement with established heat transfer correlations was found for both turbulent and transitional flow, the correlation for the transitional case yielded decent accuracy only as long as the flow remains attached, and while transition was dominated by the bypass mode. A system level analysis, indicated a limited but favorable impact at engine performance level, amounting to a specific fuel consumption improvement of up to 0.8 % in cruise and an estimated reduction of 3.6 % in cruise NOx. The results clearly show that, although it is possible to achieve high heat transfer rate per unit area in compressor vanes, the impact on cycle performance is constrained by the limited available wetted area in the low-pressure compressor.
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