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1.	Abbas, Haider, et al. (författare) DUDE: Decryption, Unpacking, Deobfuscation, and Endian Conversion Framework for Embedded Devices Firmware 2023 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1545-5971 .- 1941-0018. Tidskriftsartikel (refereegranskat)abstract Commercial-Off-The-Shelf (COTS) embedded devices rely on vendor-specific firmware to perform essential tasks. These firmware have been under active analysis by researchers to check security features and identify possible vendor backdoors. However, consistently unpacking newly created filesystem formats has been exceptionally challenging. To thwart attempts at unpacking, vendors frequently use encryption and obfuscation methods. On the other hand, when handling encrypted, obfuscated, big endian cramfs, or custom filesystem formats found in firmware under test, the available literature and tools are insufficient. This study introduces DUDE, an automated framework that provides novel functionalities, outperforming cutting-edge tools in the decryption, unpacking, deobfuscation, and endian conversion of firmware. For big endian compressed romfs filesystem formats, DUDE supports endian conversion. It also supports deobfuscating obfuscated signatures for successful unpacking. Moreover, decryption support for encrypted binaries from the D-Link and MOXA series has also been added, allowing for easier analysis and access to the contents of these firmware files. Additionally, the framework offers unpacking assistance by supporting the extraction of special filesystem formats commonly found in firmware samples from various vendors. A remarkable 78% (1424 out of 1814) firmware binaries from different vendors were successfully unpacked using the suggested framework. This performance surpasses the capabilities of commercially available tools combined on a single platform.
2.	Calandriello, G., et al. (författare) On the Performance of Secure Vehicular Communication Systems 2011 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : IEEE. - 1545-5971 .- 1941-0018. Tidskriftsartikel (refereegranskat)
3.	Chatterjee, Santanu, et al. (författare) Secure Biometric-Based Authentication Schemeusing Chebyshev Chaotic Map for Multi-Server Environment 2018 Ingår i: IEEE Transactions on Dependable and Secure Computing. - Piscataway, NJ : IEEE. - 1545-5971 .- 1941-0018. ; 15:5, s. 824-839 Tidskriftsartikel (refereegranskat)abstract Multi-server environment is the most common scenario for a large number of enterprise class applications. In this environment, user registration at each server is not recommended. Using multi-server authentication architecture, user can manage authentication to various servers using single identity and password. We introduce a new authentication scheme for multi-server environments using Chebyshev chaotic map. In our scheme, we use the Chebyshev chaotic map and biometric verification along with password verification for authorization and access to various application servers. The proposed scheme is light-weight compared to other related schemes. We only use the Chebyshev chaotic map, cryptographic hash function and symmetric key encryption-decryption in the proposed scheme. Our scheme provides strong authentication, and also supports biometrics & password change phase by a legitimate user at any time locally, and dynamic server addition phase. We perform the formal security verification using the broadly-accepted AVISPA (Automated Validation of Internet Security Protocols and Applications) tool to show that the presented scheme is secure. In addition, we use the formal security analysis using the Burrows-Abadi-Needham (BAN) logic along with random oracle models and prove that our scheme is secure against different known attacks. High security and significantly low computation and communication costs make our scheme is very suitable for multi-server environments as compared to other existing related schemes.
4.	Cucurull, Jordi, et al. (författare) Surviving Attacks in Challenged Networks 2012 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : IEEE Computer Society. - 1545-5971 .- 1941-0018. ; 9:6, s. 917-929 Tidskriftsartikel (refereegranskat)abstract In the event of a disaster, telecommunication infrastructures can be severely damaged or overloaded. Hastily formed networks can provide communication services in an ad hoc manner. These networks are challenging due to the chaotic context where intermittent connection is the norm and the identity and number of participants cannot be assumed. In such environments malicious actors may try to disrupt the communications to create more chaos for their own benefit. This paper proposes a general security framework for monitoring and reacting to disruptive attacks. It includes a collection of functions to detect anomalies, diagnose them, and perform mitigation. The measures are deployed in each node in a fully distributed fashion, but their collective impact is a significant resilience to attacks, so the actors can disseminate information under adverse conditions. The approach is evaluated in the context of a simulated disaster area network with a many-cast dissemination protocol, Random Walk Gossip, with a store-and-forward mechanism. A challenging threat model where adversaries may 1) try to drain the resources both at node level (battery life) and network level (bandwidth), or 2) reduce message dissemination in their vicinity, without spending much of their own energy, is adopted. The results demonstrate that the approach diminishes the impact of the attacks considerably.
5.	Dimitrakakis, Christos, 1975, et al. (författare) Guest editors' introduction: Special section on learning, games, and security 2012 Ingår i: IEEE Transactions on Dependable and Secure Computing. - 1545-5971 .- 1941-0018. ; 9:4, s. 449-450 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
6.	Etemadi, Khashayar, et al. (författare) Sorald : Automatic Patch Suggestions for SonarQube Static Analysis Violations 2022 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1545-5971 .- 1941-0018. ; , s. 1-1 Tidskriftsartikel (refereegranskat)abstract Previous work has shown that early resolution of issues detected by static code analyzers can prevent major costs later on. However, developers often ignore such issues for two main reasons. First, many issues should be interpreted to determine if they correspond to actual flaws in the program. Second, static analyzers often do not present the issues in a way that is actionable. To address these problems, we present Sorald: a novel system that uses metaprogramming templates to transform the abstract syntax trees of programs and suggests fixes for static analysis warnings. Thus, the burden on the developer is reduced from interpreting and fixing static issues, to inspecting and approving full fledged solutions. Sorald fixes violations of 10 rules from SonarJava, one of the most widely used static analyzers for Java. We evaluate Sorald on a dataset of 161 popular repositories on Github. Our analysis shows the effectiveness of Sorald as it fixes 65% (852/1,307) of the violations that meets the repair preconditions. Overall, our experiments show it is possible to automatically fix notable violations of the static analysis rules produced by the state-of-the-art static analyzer SonarJava.
7.	Fu, Zhang, 1982, et al. (författare) Mitigating Distributed Denial of Service Attacks in Multiparty Applications in the Presence of Clock Drifts 2012 Ingår i: IEEE Transactions on Dependable and Secure Computing. - 1545-5971 .- 1941-0018. ; 9:3, s. 401-413 Tidskriftsartikel (refereegranskat)abstract Network-based applications commonly open some known communication port(s), makingthemselves easy targets for (distributed) denial of service attacks. Earlier solutions for this problem are based on port-hopping between pairs of processes which are synchronous or exchange acknowledgments. However, acknowledgments, if lost, can cause a port to be open for longer time and thus be vulnerable, while time servers can become targets to DoS attack themselves.Here we extend port-hopping to support multi-party applications, by proposing the BIGWHEEL algorithm, for each application-server to communicate with multiple clients in a port-hopping manner without the need for group synchronization.Furthermore, we present an adaptive algorithm, HOPERAA, for enabling hopping in the presence of bounded asynchrony, namely when the communicating parties have clocks with clock drifts. The solutions are simple, based on each client interacting with the server independently of the other clients, without the need of acknowledgments or time server(s).Further, they do not rely on the application having a fixed port open in the beginning, neither do they require the clients to get a "first-contact" port from a third party. We show analytically the properties of the algorithms and also study experimentally their success rates, confirm the relation with the analytical bounds.
8.	He, Debiao, et al. (författare) A Provably-Secure Cross-Domain Handshake Scheme with Symptoms-Matching for Mobile Healthcare Social Network 2018 Ingår i: IEEE Transactions on Dependable and Secure Computing. - Piscataway, NJ : Institute of Electrical and Electronics Engineers (IEEE). - 1545-5971 .- 1941-0018. ; 15:4, s. 633-645 Tidskriftsartikel (refereegranskat)abstract With rapid developments of sensor, wireless and mobile communication technologies, Mobile Healthcare Social Networks (MHSNs) have emerged as a popular means of communication in healthcare services. Within MHSNs, patients can use their mobile devices to securely share their experiences, broaden their understanding of the illness or symptoms, form a supportive network, and transmit information (e.g. state of health and new symptoms) between users and other stake holders (e.g. medical center). Despite the benefits afforded by MHSNs, there are underlying security and privacy issues (e.g. due to the transmission of messages via a wireless channel). The handshake scheme is an important cryptographic mechanism, which can provide secure communication in MHSNs (e.g. anonymity and mutual authentication between users, such as patients). In this paper, we present a new framework for the handshake scheme in MHSNs, which is based on hierarchical identity-based cryptography. We then construct an efficient Cross-Domain HandShake (CDHS) scheme that allows symptoms-matching within MHSNs. For example, using the proposed CDHS scheme, two patients registered with different healthcare centers can achieve mutual authentication and generate a session key for future secure communications. We then prove the security of the scheme, and a comparative summary demonstrates that the proposed CDHS scheme requires fewer computation and lower communication costs. We also implement the proposed CDHS scheme and three related schemes in a proof of concept Android app to demonstrate utility of the scheme. Findings from the evaluations demonstrate that the proposed CDHS scheme achieves a reduction of 18.14% and 5.41% in computation cost and communication cost, in comparison to three other related handshake schemes. © 2016 IEEE.
9.	Holm, Hannes (författare) A Large-Scale Study of the Time Required To Compromise a Computer System 2014 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : IEEE Computer Society. - 1545-5971 .- 1941-0018. ; 11:1, s. 6506084- Tidskriftsartikel (refereegranskat)abstract A frequent assumption in the domain of cybersecurity is that cyberintrusions follow the properties of a Poisson process, i.e., that the number of intrusions is well modeled by a Poisson distribution and that the time between intrusions is exponentially distributed. This paper studies this property by analyzing all cyberintrusions that have been detected across more than 260,000 computer systems over a period of almost three years. The results show that the assumption of a Poisson process model might be unoptimalâthe log-normal distribution is a significantly better fit in terms of modeling both the number of detected intrusions and the time between intrusions, and the Pareto distribution is a significantly better fit in terms of modeling the time to first intrusion. The paper also analyzes whether time to compromise (TTC) increase for each successful intrusion of a computer system. The results regarding this property suggest that time to compromise decrease along the number of intrusions of a system.
10.	Holm, Hannes, et al. (författare) Empirical Analysis of System-Level Vulnerability Metrics through Actual Attacks 2012 Ingår i: IEEE Transactions on Dependable and Secure Computing. - 1545-5971 .- 1941-0018. ; 9:6, s. 825-837 Tidskriftsartikel (refereegranskat)abstract The Common Vulnerability Scoring System (CVSS) is a widely used and well-established standard for classifying the severity of security vulnerabilities. For instance, all vulnerabilities in the US National Vulnerability Database (NVD) are scored according to this method. As computer systems typically have multiple vulnerabilities, it is often desirable to aggregate the score of individual vulnerabilities to a system level. Several such metrics have been proposed, but their quality has not been studied. This paper presents a statistical analysis of how 18 security estimation metrics based on CVSS data correlate with the time-to-compromise of 34 successful attacks. The empirical data originates from an international cyber defense exercise involving over 100 participants and were collected by studying network traffic logs, attacker logs, observer logs, and network vulnerabilities. The results suggest that security modeling with CVSS data alone does not accurately portray the time-to-compromise of a system. However, results also show that metrics employing more CVSS data are more correlated with time-to-compromise. As a consequence, models that only use the weakest link (most severe vulnerability) to compose a metric are less promising than those that consider all vulnerabilities.
11.	Holm, Hannes, et al. (författare) P2CySeMoL : Predictive, Probabilistic Cyber Security Modeling Language 2015 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : IEEE Press. - 1545-5971 .- 1941-0018. ; 12:6, s. 626-639 Tidskriftsartikel (refereegranskat)abstract This paper presents the Predictive, Probabilistic Cyber Security Modeling Language ((PCySeMoL)-Cy-2), an attack graph tool that can be used to estimate the cyber security of enterprise architectures. (PCySeMoL)-Cy-2 includes theory on how attacks and defenses relate quantitatively; thus, users must only model their assets and how these are connected in order to enable calculations. The performance of (PCySeMoL)-Cy-2 enables quick calculations of large object models. It has been validated on both a component level and a system level using literature, domain experts, surveys, observations, experiments and case studies.
12.	Johnson, Pontus, et al. (författare) Can the Common Vulnerability Scoring System be Trusted? : A Bayesian Analysis 2018 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : IEEE Press. - 1545-5971 .- 1941-0018. ; 15:6, s. 1002-1015 Tidskriftsartikel (refereegranskat)abstract The Common Vulnerability Scoring System (CVSS) is the state-of-the art system for assessing software vulnerabilities. However, it has been criticized for lack of validity and practitioner relevance. In this paper, the credibility of the CVSS scoring data found in five leading databases – NVD, X-Force, OSVDB, CERT-VN, and Cisco – is assessed. A Bayesian method is used to infer the most probable true values underlying the imperfect assessments of the databases, thus circumventing the problem that ground truth is not known. It is concluded that with the exception of a few dimensions, the CVSS is quite trustworthy. The databases are relatively consistent, but some are better than others. The expected accuracy of each database for a given dimension can be found by marginalizing confusion matrices. By this measure, NVD is the best and OSVDB is the worst of the assessed databases.
13.	Khurshid, Anum, et al. (författare) ShieLD : Shielding Cross-zone Communication within Limited-resourced IoT Devices running Vulnerable Software Stack 2023 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : Institute of Electrical and Electronics Engineers Inc.. - 1545-5971 .- 1941-0018. ; 20:2, s. 1031- Tidskriftsartikel (refereegranskat)abstract Securing IoT devices is gaining attention as the security risks associated with these devices increase rapidly. TrustZone-M, a Trusted Execution Environment (TEE) for Cortex-M processors, ensures stronger security within an IoT device by allowing isolated execution of security-critical operations, without trusting the entire software stack. However, TrustZone-M does not guarantee secure cross-world communication between applications in the Normal and Secure worlds. The cryptographic protection of the communication channel is an obvious solution; however, within a low-power IoT device, it incurs high overhead if applied to each cross-world message exchange. We present ShieLD, a framework that enables a secure communication channel between the two TrustZone-M worlds by leveraging the Memory Protection Unit (MPU). ShieLD guarantees confidentiality, integrity and authentication services without requiring any cryptographic operations. We implement and evaluate ShieLD using a Musca-A test chip board with Cortex-M33 that supports TrustZone-M. Our empirical evaluation shows, among other gains, the cross-zone communication protected with ShieLD is 5 times faster than the conventional crypto-based communication.
14.	Khurshid, Anum, et al. (författare) ShieLD : Shielding Cross-Zone Communication Within Limited-Resourced IoT Devices Running Vulnerable Software Stack 2023 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1545-5971 .- 1941-0018 .- 2160-9209. ; 20:2, s. 1031-1047 Tidskriftsartikel (refereegranskat)abstract Securing IoT devices is gaining attention as the security risks associated with these devices increase rapidly. TrustZone-M, a Trusted Execution Environment (TEE) for Cortex-M processors, ensures stronger security within an IoT device by allowing isolated execution of security-critical operations, without trusting the entire software stack. However, TrustZone-M does not guarantee secure cross-world communication between applications in the Normal and Secure worlds. The cryptographic protection of the communication channel is an obvious solution; however, within a low-power IoT device, it incurs high overhead if applied to each cross-world message exchange. We present ShieLD, a framework that enables a secure communication channel between the two TrustZone-M worlds by leveraging the Memory Protection Unit (MPU). ShieLD guarantees confidentiality, integrity and authentication services without requiring any cryptographic operations. We implement and evaluate ShieLD using a Musca-A test chip board with Cortex-M33 that supports TrustZone-M. Our empirical evaluation shows, among other gains, the cross-zone communication protected with ShieLD is 5 times faster than the conventional crypto-based communication.
15.	Phung, Phu, 1979, et al. (författare) Between Worlds: Securing Mixed JavaScript/ActionScript Multi-Party Web Content 2015 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1545-5971 .- 1941-0018. ; 12:4, s. 443-457 Tidskriftsartikel (refereegranskat)abstract Mixed Flash and JavaScript content has become increasingly prevalent; its purveyance of dynamic features unique to each platform has popularized it for myriad web development projects. Although Flash and JavaScript security has been examined extensively, the security of untrusted content that combines both has received considerably less attention. This article considers this fusion in detail, outlining several practical scenarios that threaten the security of web applications. The severity of these attacks warrants the development of new techniques that address the security of Flash-JavaScript content considered as a whole, in contrast to prior solutions that have examined Flash or JavaScript security individually. Toward this end, the article presents FlashJaX, a cross-platform solution that enforces fine-grained, history-based policies that span both Flash and JavaScript. Using in-lined reference monitoring, FlashJaX safely embeds untrusted JavaScript and Flash content in web pages without modifying browser clients or using special plug-ins. The architecture of FlashJaX, its design and implementation, and a detailed security analysis are exposited. Experiments with advertisements from popular ad networks demonstrate that FlashJaX is transparent to policy-compliant advertisement content, yet blocks many common attack vectors that exploit the fusion of these web platforms.
16.	Poturalski, M., et al. (författare) Formal Analysis of Secure Neighbor Discovery in Wireless Networks 2013 Ingår i: IEEE Transactions on Dependable and Secure Computing. - 1545-5971 .- 1941-0018. ; 10:6, s. 355-367 Rapport (refereegranskat)abstract We develop a formal framework for the analysis of security protocols in wireless networks. The framework captures characteristics necessary to reason about neighbor discovery protocols, such as the neighbor relation, device location, and message propagation time. We use this framework to establish general results about the possibility of neighbor discovery. In particular, we show that time-based protocols cannot in general provide secure neighbor discovery. Given this insight, we also use the framework to prove the security of four concrete neighbor discovery protocols, including two novel time-and-location based protocols. We mechanize the model and some proofs in the theorem prover Isabelle.
17.	Rafnsson, Willard Thor, 1982, et al. (författare) Securing Class Initialization in Java-like Languages 2013 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1545-5971 .- 1941-0018. ; 10:1, s. 1-13 Tidskriftsartikel (refereegranskat)abstract Language-based information-flow security is concerned with specifying and enforcing security policies for information flow via language constructs. Although much progress has been made on understanding information flow in object-oriented programs, little attention has been given to the impact of class initialization on information flow. This paper turns the spotlight on security implications of class initialization. We reveal the subtleties of information propagation when classes are initialized, and demonstrate how these flows can be exploited to leak information through error recovery. Our main contribution is a type-and-effect system which tracks these information flows. The type system is parameterized by an arbitrary lattice of security levels. Flows through the class hierarchy and dependencies in field initializers are tracked by typing class initializers wherever they could be executed. The contexts in which each class can be initialized are tracked to prevent insecure flows of out-of-scope contextual information through class initialization statuses and error recovery. We show that the type system enforces termination-insensitive noninterference.
18.	Ron Arteaga, Javier, et al. (författare) Highly Available Blockchain Nodes With N-Version Design 2023 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1545-5971 .- 1941-0018. Tidskriftsartikel (refereegranskat)abstract As all software, blockchain nodes are exposed to faults in their underlying execution stack. Unstable execution environments can disrupt the availability of blockchain nodes' interfaces, resulting in downtime for users. This paper introduces the concept of N-Version Blockchain nodes. This new type of node relies on simultaneous execution of different implementations of the same blockchain protocol, in the line of Avizienis' N-Version programming vision. We design and implement an N-Version blockchain node prototype in the context of Ethereum, called N-ETH. We show that N-ETH is able to mitigate the effects of unstable execution environments and significantly enhance availability under environment faults. To simulate unstable execution environments, we perform fault injection at the system-call level. Our results show that existing Ethereum node implementations behave asymmetrically under identical instability scenarios. N-ETH leverages this asymmetric behavior available in the diverse implementations of Ethereum nodes to provide increased availability, even under our most aggressive fault-injection strategies. We are the first to validate the relevance of N-Version design in the domain of blockchain infrastructure. From an industrial perspective, our results are of utmost importance for businesses operating blockchain nodes, including Google, ConsenSys, and many other major blockchain companies.
19.	Samhi, Jordan, et al. (författare) On the (in)effectiveness of static logic bomb detector for android apps 2022 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : IEEE. - 1545-5971 .- 1941-0018 .- 2160-9209. ; 19:6, s. 3822-3836 Tidskriftsartikel (refereegranskat)abstract Android is present in more than 85% of mobile devices, making it a prime target for malware. Malicious code is becoming increasingly sophisticated and relies on logic bombs to hide itself from dynamic analysis. In this article, we perform a large scale study of TSOpen , our open-source implementation of the state-of-the-art static logic bomb scanner TriggerScope , on more than 500k Android applications. Results indicate that the approach scales. Moreover, we investigate the discrepancies and show that the approach can reach a very low false-positive rate, 0.3%, but at a particular cost, e.g., removing 90% of sensitive methods. Therefore, it might not be realistic to rely on such an approach to automatically detect all logic bombs in large datasets. However, it could be used to speed up the location of malicious code, for instance, while reverse engineering applications. We also present TrigDB a database of 68 Android applications containing trigger-based behavior as a ground-truth to the research community.
20.	Sangchoolie, Behrooz, 1986, et al. (författare) An Empirical Study of the Impact of Single and Multiple Bit-Flip Errors in Programs 2022 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : IEEE. - 1545-5971 .- 1941-0018. ; 19:3, s. 1988-2006 Tidskriftsartikel (refereegranskat)abstract Recent studies have shown that technology and voltage scaling are expected to increase the likelihood that particle-induced soft errors manifest as multiple-bit errors. This raises concerns about the validity of using single bit-flips in fault injection experiments aiming to assess the program-level impact of soft errors. The goal of this paper is to investigate whether multiple-bit errors could cause a higher percentage of silent data corruptions (SDCs) compared to single-bit errors. Based on 2700 fault injection campaigns with 15 benchmark programs, featuring a total of 27 million experiments, our results show that single-bit errors in most cases either yield a higher percentage of SDCs compared to multiple-bit errors or yield SDC results that are very close to the ones obtained for the multiple-bit errors. Further, we find that only around 2% of the multiple-bit campaigns resulted in an SDC percentage that was more than 5 percentage points higher than that obtained for the corresponding single-bit campaigns. For most of these campaigns, the highest percentage of SDCs was obtained by flipping at most 3 bits. Based on our results, we also propose four techniques for error space pruning to avoid injection of multiple-bit errors that are either unlikely or infeasible to cause SDCs.
21.	Shokri, Reza, et al. (författare) Hiding in the Mobile Crowd : Location Privacy through Collaboration 2014 Ingår i: IEEE Transactions on Dependable and Secure Computing. - 1545-5971 .- 1941-0018. ; 11:3, s. 266-279 Tidskriftsartikel (refereegranskat)abstract Location-aware smartphones support various location-based services (LBSs): users query the LBS server and learn on the fly about their surroundings. However, such queries give away private information, enabling the LBS to track users. We address this problem by proposing a user-collaborative privacy-preserving approach for LBSs. Our solution does not require changing the LBS server architecture and does not assume third party servers; yet, it significantly improves users' location privacy. The gain stems from the collaboration of mobile devices: they keep their context information in a buffer and pass it to others seeking such information. Thus, a user remains hidden from the server, unless all the collaborative peers in the vicinity lack the sought information. We evaluate our scheme against the Bayesian localization attacks that allow for strong adversaries who can incorporate prior knowledge in their attacks. We develop a novel epidemic model to capture the, possibly time-dependent, dynamics of information propagation among users. Used in the Bayesian inference framework, this model helps analyze the effects of various parameters, such as users' querying rates and the lifetime of context information, on users' location privacy. The results show that our scheme hides a high fraction of location-based queries, thus significantly enhancing users' location privacy. Our simulations with real mobility traces corroborate our model-based findings. Finally, our implementation on mobile platforms indicates that it is lightweight and the cost of collaboration is negligible.
22.	Sun, Min-Te, et al. (författare) Private and Secure Tag Access for Large-Scale RFID Systems 2016 Ingår i: IEEE Transactions on Dependable and Secure Computing. - 1545-5971 .- 1941-0018. ; 13:6, s. 657-671 Tidskriftsartikel (refereegranskat)abstract The performance of key authentication and the degree of privacy in large-scale RFID systems are considered by manyresearchers as tradeoffs. Based on how keys are managed in the system, the privacy preserving tag authentications proposed in thepast can be categorized into tree-based and group-based approaches. While a tree-based approach achieves high performance in keyauthentication, it suffers from the issue of low privacy should a fraction of tags be compromised. On the contrary, while group-based keyauthentication is relatively invulnerable to compromise attacks, it is not scalable to a large number of tags. In this paper, we propose anew private tag authentication protocol based on skip lists, named randomized skip lists-based authentication (RSLA). Withoutsacrificing the authentication performance, RSLA provides a high privacy preserving mechanism. While RSLA provides the same levelof unpredictability-based-privacy and indistinguishability-based privacy compared with other structured key management approaches,our scheme achieves the highest system anonymity with good performance in key look up and update. In addition, the simulationresults match our analyses closely.
23.	Tiloca, Marco, et al. (författare) JAMMY: a Distributed and Dynamic Solution to Selective Jamming Attack in TDMA WSNs 2015. - 10 Ingår i: IEEE Transactions on Dependable and Secure Computing. - 1545-5971 .- 1941-0018. ; 14:4, s. 392-405 Tidskriftsartikel (refereegranskat)abstract Time Division Multiple Access (TDMA) is often used in Wireless Sensor Networks (WSNs), especially for critical applications, as it provides high energy efficiency, guaranteed bandwidth, bounded and predictable latency, and absence of collisions. However, TDMA is vulnerable to selective jamming attacks. In TDMA transmission, slots are typically pre-allocated to sensor nodes, and each slot is used by the same node for a number of consecutive superframes. Hence, an adversary could thwart a victim node’s communication by simply jamming its slot(s). Such attack turns out to be effective, energy efficient, and extremely difficult to detect. In this paper, we present JAMMY, a distributed and dynamic solution to selective jamming in TDMA-based WSNs. Unlike traditional approaches, JAMMY changes the slot utilization pattern at every superframe, thus making it unpredictable to the adversary. JAMMY is decentralized, as sensor nodes determine the next slot utilization pattern in a distributed and autonomous way. Results from performance analysis of the proposed solution show that JAMMY introduces negligible overhead yet allows multiple nodes to join the network, in a limited number of superframes.
24.	Vinel, Alexey, 1983-, et al. (författare) Guest Editors’ Introduction : Special Issue on Reliable and Secure VANETs 2016 Ingår i: IEEE Transactions on Dependable and Secure Computing. - Piscataway, NJ : IEEE Press. - 1545-5971 .- 1941-0018. ; 13:1, s. 2-4 Tidskriftsartikel (refereegranskat)
25.	Wang, H., et al. (författare) Oracle-Supported Dynamic Exploit Generation for Smart Contracts 2020 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1545-5971 .- 1941-0018. Tidskriftsartikel (refereegranskat)abstract Despite the high stakes involved in smart contracts, they are often developed in an undisciplined manner, leaving the security and reliability of blockchain transactions at risk. In this paper, we introduce ContraMaster an oracle-supported dynamic exploit generation framework for smart contracts. Existing approaches mutate only single transactions; ContraMaster exceeds these by mutating the transaction sequences. ContraMaster uses data-flow, control-flow, and the dynamic contract state to guide its mutations. It then monitors the executions of target contract programs, and validates the results against a general-purpose semantic test oracle to discover vulnerabilities. Being a dynamic technique, it guarantees that each discovered vulnerability is a violation of the test oracle and is able to generate the attack script to exploit this vulnerability. In contrast to rule-based approaches, ContraMaster has not shown any false positives, and it easily generalizes to unknown types of vulnerabilities (e.g., logic errors). We evaluate ContraMaster on 218 vulnerable smart contracts. The experimental results confirm its practical applicability and advantages over the state-of-the-art techniques, and also reveal three new types of attacks.
26.	Zhang, Long, et al. (författare) Maximizing Error Injection Realism for Chaos Engineering with System Calls 2021 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1545-5971 .- 1941-0018. Tidskriftsartikel (refereegranskat)abstract In this paper, we present a novel fault injection framework for system call invocation errors, called Phoebe. Phoebe is unique as follows; First, Phoebe enables developers to have full observability of system call invocations. Second, Phoebe generates error models that are realistic in the sense that they mimic errors that naturally happen in production. Third, Phoebe is able to automatically conduct experiments to systematically assess the reliability of applications with respect to system call invocation errors in production. We evaluate the effectiveness and runtime overhead of Phoebe on two real-world applications in a production environment. The results show that Phoebe successfully generates realistic error models and is able to detect important reliability weaknesses with respect to system call invocation errors. To our knowledge, this novel concept of "realistic error injection", which consists of grounding fault injection on production errors, has never been studied before.
27.	Zhou, Fanfu, et al. (författare) D2 FL: Design and Implementation of Distributed Dynamic Fault Localization 2018 Ingår i: IEEE Transactions on Dependable and Secure Computing. - : IEEE. - 1545-5971 .- 1941-0018. ; 15:3, s. 378-392 Tidskriftsartikel (refereegranskat)abstract Compromised or misconfigured routers have been a major concern in large-scale networks. Such routers sabotage packet delivery, and thus hurt network performance. Data-plane fault localization (FL) promises to solve this problem. Regrettably, the path-based FL fails to support dynamic routing, and the neighbor-based FL requires a centralized trusted administrative controller (AC) or global clock synchronization in each router and introduces storage overhead for caching packets. To address these problems, we introduce a dynamic distributed and low-cost model, D2FL. Using random 2-hop neighborhood authentication, D2FL supports volatile path without the AC or global clock synchronization. Besides, D2FL requires only constant tens of KB for caching which is independent of the packet transmission rate. This is much less than the cache size of DynaFL or DFL which consumes several MB. The simulations show that D2FL achieves low false positive and false negative rate with no more than 3% bandwidth overhead. We also implement an open source prototype and evaluate its effect. The result shows that the performance burden in user space is less than 10% with the dynamic sampling algorithm.
28.	Abeywickrama, K. G. Nilanga B., et al. (författare) Determination of complex permeability of silicon steel for use in high-frequency modeling of power transformers 2008 Ingår i: IEEE transactions on magnetics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9464 .- 1941-0069. ; 44:4, s. 438-444 Tidskriftsartikel (refereegranskat)abstract Information about frequency dependence of complex permeability of silicon steel is a vital input parameter in calculations of transformer winding inductance used for modeling. high-frequency behavior (100 Hz-1 MHz). We present two ways of determining small signal complex permeability spectra in frequency domain and compare and discuss the results. The first method is based on an optimization procedure, in which inductance of a winding is measured and calculated by analytical formulas and finite-element modeling. The second method makes use of a single sheet tester. We show that the magnitude of effective permeability of the silicon steel laminations remains significant up to about 100 kHz. We also report on the effect of magnetic viscosity on complex permeability.
29.	Abrahamsson, Johan, 1977-, et al. (författare) A Fully Levitated Cone-Shaped Lorentz-Type Self-Bearing Machine With Skewed Windings 2014 Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 50:9 Tidskriftsartikel (refereegranskat)abstract Brushless dc coreless electric machines with double-rotor and single-stator configuration have very low losses, since the return path of the magnetic flux rotates with the permanent magnets. The eddy-current loss in the stator is additionally very small due to the lack of iron, making it ideal for kinetic energy storage. This paper presents a design for self-bearing rotor suspension, achieved by placing the stator windings skewed on a conical surface. A mathematical analysis of the force from a skewed winding confined to the surface of a cone was found. The parametric analytical expressions of the magnitude and direction of force and torque were verified by finite-element method simulations for one specific geometry. A dynamic model using proportional-integral-differential control was implemented in MATLAB/Simulink, and the currents needed for the self-bearing effect were found by solving an underdetermined system of linear equations. External forces, calculated from acceleration measurements from a bus in urban traffic, were added to simulate the dynamic environment of an electrical vehicle.
30.	Albertsson, Dagur Ingi, 1993-, et al. (författare) Compact Macrospin-Based Model of Three-Terminal Spin-Hall Nano Oscillators 2019 Ingår i: IEEE transactions on magnetics. - : IEEE Press. - 0018-9464 .- 1941-0069. ; 55:10 Tidskriftsartikel (refereegranskat)abstract Emerging spin-torque nano oscillators (STNOs) and spin-Hall nano oscillators (SHNOs) are potential candidates for microwave applications. Recent advances in three-terminal magnetic tunnel junction (MTJ)-based SHNOs opened the possibility to develop more reliable and well-controlled oscillators, thanks to individual spin Hall-driven precession excitation and read-out paths. To develop hybrid systems by integrating three-terminal SHNOs and CMOS circuits, an electrical model able to capture the analog characteristics of three-terminal SHNOs is needed. This model needs to be compatible with current electric design automation (EDA) tools. This work presents a comprehensive macrospin-based model of three-terminal SHNOs able to describe the dc operating point, frequency modulation, phase noise, and output power. Moreover, the effect of voltage-controlled magnetic anisotropy (VCMA) is included. The model shows good agreement with experimental measurements and could be used in developing hybrid three-terminal SHNO/CMOS systems.
31.	Albertsson, D. I., et al. (författare) Compact Macrospin-Based Model of Three-Terminal Spin-Hall Nano Oscillators 2019 Ingår i: Ieee Transactions on Magnetics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9464 .- 1941-0069. ; 55:10 Tidskriftsartikel (refereegranskat)abstract Emerging spin-torque nano oscillators (STNOs) and spin-Hall nano oscillators (SHNOs) are potential candidates for microwave applications. Recent advances in three-terminal magnetic tunnel junction (MTJ)-based SHNOs opened the possibility to develop more reliable and well-controlled oscillators, thanks to individual spin Hall-driven precession excitation and read-out paths. To develop hybrid systems by integrating three-terminal SHNOs and CMOS circuits, an electrical model able to capture the analog characteristics of three-terminal SHNOs is needed. This model needs to be compatible with current electric design automation (EDA) tools. This work presents a comprehensive macrospin-based model of three-terminal SHNOs able to describe the dc operating point, frequency modulation, phase noise, and output power. Moreover, the effect of voltage-controlled magnetic anisotropy (VCMA) is included. The model shows good agreement with experimental measurements and could be used in developing hybrid three-terminal SHNO/CMOS systems.
32.	Andersson, Sebastian, et al. (författare) Thermoelectrically Controlled Spin-Switch 2010 Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 46:6, s. 2140-2143 Tidskriftsartikel (refereegranskat)abstract The search for novel spintronic devices brings about new ways to control switching in magnetic thin-films. In this work we experimentally demonstrate a device based on thermoelectrically controlled exchange coupling. The read out signal from a giant magnetoresistance element is controlled by exchange coupling through a weakly ferromagnetic Ni-Cu alloy. This exchange coupling is shown to vary strongly with changes in temperature, and both internal Joule heating and external heating is used to demonstrate magnetic switching. The device shows no degradation upon thermal cycling. Ways to further optimize the device performance are discussed. Our experimental results show a new way to thermoelectrically control magnetic switching in multilayers.
33.	Benbouzid, M. E. H., et al. (författare) Dynamic modelling of giant magnetostriction in Terfenol-D rods by the finite element method 1995 Ingår i: IEEE transactions on magnetics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9464 .- 1941-0069. ; 31, s. 1821-1824 Tidskriftsartikel (refereegranskat)abstract As a contribution to the development of methods for the design and the analysis of devices based on giant magnetostrictive materials, a model for the simulation of the dynamic behaviour of the nonlinear magnetoelastic medium is presented. The coupled magnetic, magnetoelastic and mechanical equations that describe the magnetostrictive problem are solved by means of the finite element method. The thin sheets bending principle (surface splines) is used to introduce in the simulation the nonlinear properties of giant magnetostrictive materials, obtained by static characterizations
34.	Bergqvist, A., et al. (författare) A stress-dependent magnetic Preisach hysteresis model 1991 Ingår i: IEEE transactions on magnetics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9464 .- 1941-0069. ; 27, s. 4796-4798 Tidskriftsartikel (refereegranskat)abstract The authors present a generalization of the classical Preisach model which handles coupled magnetic and mechanical hysteresis. Magnetostrictive materials are known to have hysteresis with respect to both magnetic field H and mechanical stress lambda;. To test the validity of the model, experiments where the two components H and lambda; have been verified in many different ways have been performed on Terfenol-D and compared to results computed from the model. Some of these results are presented. This stress-dependent model is found to have an accuracy comparable to that of the classical Preisach model
35.	Bergqvist, A., et al. (författare) A thermodynamic representation of pseudoparticles with hysteresis 1995 Ingår i: IEEE transactions on magnetics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9464 .- 1941-0069. ; 31, s. 3539-3541 Tidskriftsartikel (refereegranskat)abstract A method of expressing pseudoparticles with hysteresis within a context of irreversible thermodynamics is investigated. The state of a pseudoparticle is uniquely determined by its magnetization and its evolution is governed by entropy maximization. Hysteresis appears if the free energy is a nonconvex function of magnetization. The vectorial nature of magnetization and dependence on rate are accounted for in a systematic manner. Some basic properties are derived for quasistatic processes. In particular, it is found that in the scalar case, the magnetization is a monotonically increasing functional with respect to field and that for quasistatic processes, this implies the wiping-out property
36.	Bergqvist, A. J., et al. (författare) A homogenization procedure of field quantities in laminated electric steel 2001 Ingår i: IEEE transactions on magnetics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9464 .- 1941-0069. ; 37:5, s. 3329-3331 Tidskriftsartikel (refereegranskat)abstract A method for representing structures of laminated electric steel is investigated. The average behavior of laminates, including eddy current effects, is approximately represented using a rate-dependent constitutive law. The accuracy of the method is studied by comparing the homogenized description with finite difference calculations.
37.	Bissal, Ara, 1986-, et al. (författare) Comparison of two Ultra-fast actuator concepts 2012 Ingår i: IEEE transactions on magnetics. - : IEEE Press. - 0018-9464 .- 1941-0069. ; 48:11, s. 3315-3318 Tidskriftsartikel (refereegranskat)abstract In this paper, two different types of ultra-fast electromechanical actuators are compared using a multi-physical finite element simulation model that has been experimentally validated. They are equipped with a single-sided Thomson coil (TC) and a double-sided drive coil (DSC), respectively. The former consists of a spirally-wound flat coil with a copper armature on top, while the latter consists of two mirrored spiral coils that are connected in series. Initially, the geometry and construction of each of the actuating schemes are discussed. Subsequently, the theory behind the two force generation principles are described. Furthermore, the current, magnetic flux densities, accelerations, and induced stresses are analyzed. Moreover, mechanical loadability simulations are performed to study the impact on the requirements of the charging unit, the sensitivity of the parameters, and evaluate the degree of influence on the performance of both drives. Finally, it is confirmed that although the DSC is mechanically more complex, it has a greater efficiency than that of the TC.
38.	Bissal, Ara, et al. (författare) On the Design of a Linear Composite Magnetic Damper 2015 Ingår i: IEEE transactions on magnetics. - : IEEE Press. - 0018-9464 .- 1941-0069. ; 51:11 Tidskriftsartikel (refereegranskat)abstract High-voltage direct current (HVdc) breakers are the key components in the realization of multiterminal HVdc grids. In the presence of fault current, these breakers should be able to deliver impulsive forces to swiftly open the metallic contacts. After the acceleration phase, the moving armature should be decelerated using controllable forces to avoid plastically deforming fragile components integrated in the system. In this paper, finite-element method-based simulation models, complimented with small-scale and large-scale experimental prototypes, were utilized to benchmark different damping topologies. It was found that a Halbach-based configuration can deliver a damping force that is almost two and a half times larger than its sequel. Its sequel, composed of vertically stacked oppositely oriented magnets, is easier to assemble and is also capable of generating a considerable damping force. Finally, it has been shown that both these schemes, inserted in a composite tube, have a potential to be used as dampers in HVdc breakers.
39.	Bjurman, U., et al. (författare) Separation of high and low frequency behavior in non-linear circuit simulation, excited with modulated signals 2000 Ingår i: IEEE transactions on magnetics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9464 .- 1941-0069. ; 36:4, s. 968-970 Tidskriftsartikel (refereegranskat)abstract Exciting nonlinear circuits with modulated signals will generate crossmodulation frequencies. In ordinary simulation techniques this makes time stepping methods a necessity, In the case of EMC-testing where the carrier frequency is as high as 2 GHz and the modulating frequency only 1 kHz, the simulation time will be extremely long. This paper presents Time Domain Frequency Separation (TDFS), a method,where the high and low frequency behavior is calculated separately to decrease the computation time. In a simulation made with Saber the calculation took approximately fourteen hours, and with TDFS in Matlab two minutes.
40.	Bormann, Dierk, et al. (författare) Reluctance Network Method for Calculating the Series Impedance Matrix of Multi-Conductor Transmission Lines 2013 Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 49:10, s. 5270-5279 Tidskriftsartikel (refereegranskat)abstract The theoretical foundation of a recently proposed reluctance network method for computing the complex series impedance matrix of multi-conductor transmission lines is presented in detail, and the method is extended to more general cross section geometries with gaps of non-constant width between the conductors. It is argued that the method becomes exact in the limit of high frequencies and narrow gaps between the conductors. This limit usually is the most difficult one in alternative approaches, especially when the proximity effect is concerned. The method is verified by comparison with the exact solution of a stacked-slabs geometry, and with finite-element field calculations on a geometry consisting of tightly packed, round wires, surrounded by a shield.
41.	Bormann, Dierk, et al. (författare) Reluctance Network Treatment of Skin and Proximity Effects in Multi-Conductor Transmission Lines 2012 Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 48:2, s. 735-738 Tidskriftsartikel (refereegranskat)abstract A novel method is developed to easily compute the complex series impedance matrix of amulti-conductor transmissionline in a wide frequency range. It is based on a network of complex reluctances describing ﬂux paths around the conductors. The network parameters are derived from the geometry of the conductor-insulator arrangement and from its material parameters. The method is best suited for situations where the typical gap width between conductors is much smaller than their thicknesses, where it provides an accurate treatment of both skin and proximity effects. Especially the proximity effect is hard to treat by other means in that limit. The method is demonstrated for an idealized example geometry, where its accuracy is veriﬁed with harmonic FEM ﬁeld calculations.
42.	Cherepov, Sergiy, et al. (författare) Micromagnetics of Spin-Flop Bilayers : S, C, and Vortex Spin States 2010 Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 46:6, s. 2124-2127 Tidskriftsartikel (refereegranskat)abstract Spin-flop tunnel junctions subjected to strong gigahertz excitations are found to exhibit highly stable resistance states, intermediate between the two spin-uniform ground states of high and low resistance. The associated spin distributions are necessarily nonuniform and differ significantly from the ground-state anti-parallel spin configuration in their static and dynamic properties. Detailed micromagnetic modeling reveals that inplane spin vortices in dipole-coupled thin-film bilayers are stable spin configurations, where the orientation of the vortex cores and the vortex chirality play an important role in the response of the system to external magnetic fields.
43.	Cherepov, Sergiy, 1981-, et al. (författare) Resonant Switching of Two Dipole-Coupled Nanomagnets 2010 Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 46:6, s. 2112-2115 Tidskriftsartikel (refereegranskat)abstract The storage layer of recently developed spin-flop magnetic random-access memory consists of two closely spaced dipole-coupled nanomagnets and is highly stable in the ground state as well as in quasistatic fields applied off the easy axis. We show experimentally and confirm by using micromagnetic simulations that these spin-flop bilayers can be switched relatively easily by dynamic fields, applied at the frequency of the optical spin resonance of the bilayer. The field amplitude sufficient for this resonant switching can be an order of magnitude lower than the fields necessary for quasistatic reversal. Our data and micromagnetic analysis suggest that thermal agitation can play a role in the observed resonant switching behavior.
44.	Danielsson, Oskar, et al. (författare) Flux Distribution in Linear Permanent-Magnet Synchronous Machines Including Longitudinal End Effects 2007 Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 43:7, s. 3197-3201 Tidskriftsartikel (refereegranskat)abstract We investigated the longitudinal ends' influence on the flux distribution in a permanent-magnet linear synchronous machine with an analytic model and with numeric finite-element methods. We derived a general analytic expression, on closed form, from a linear reluctance model. The model reveals that the flux in a linear machine differs from that in a rotating machine in several aspects. The longitudinal ends introduce a pairwise coupled flux pattern, which will behave differently in circuits with odd or even numbers of magnets. In linear machines with an even number of magnets the pairwise coupled flux will spread throughout the whole machine, whereas in linear machines with an odd number of magnets it will be transformed into an equally distributed flux in the middle. The latter case will give rise to a nonsymmetric air gap flux distribution, where every second pole has larger flux. We confirmed the pairwise coupled flux and the nonsymmetric air gap distribution predicted by the analytic model by finite-element simulations. We noted additional effects when nonlinear behavior of the steel is taken into account. We conclude that saturation counteracts the pairwise coupled flux pattern at the longitudinal ends. Again, a nonsymmetric air gap flux distribution occurs as the pairwise coupled flux is transformed into an equally coupled flux. The pairwise coupling of the flux and the nonsymmetric air gap flux distribution give rise to a number of secondary effects, which we discuss.
45.	Dave, Renu W., et al. (författare) MgO-based tunnel junction material for high-speed toggle magnetic random access memory 2006 Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 42:8, s. 1935-1939 Tidskriftsartikel (refereegranskat)abstract We report the first demonstration of a magnetoresistive random access memory (MRAM) circuit incorporating MgO-based magnetic tunnel junction (MTJ) material for higher performance. We compare our results to those of AlOx-based devices, and we discuss the MTJ process optimization and material changes that made the demonstration possible. We present data on key MTJ material attributes for different oxidation processes and free-layer alloys, including resistance distributions, bias dependence, free-layer magnetic properties, interlayer coupling, breakdown voltage, and thermal endurance. A tunneling magnetoresistance (TMR) greater than 230% was achieved with CoFeB free layers and greater than 85% with NiFe free layers. Although the TMR with NiFe is at the low end of our MgO comparison, even this MTJ material enables faster access times, since its TMR is almost double that of a similar structure with an AlOx barrier. Bit-to-bit resistance distributions are somewhat wider for MgO barriers, with sigma about 1.5% compared to about 0.9% for AlOx. The read access time of our 4 Mb toggle MRAM circuit was reduced from 21 ns with AlOx to a circuit-limited 17 ns with MgO.
46.	Dumas, Randy K., et al. (författare) Graded Anisotropy FePtCu Films 2011 Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 47:6, s. 1580-1586 Tidskriftsartikel (refereegranskat)abstract The fabrication and subsequent analysis of continuously graded anisotropy films are discussed. During deposition, a compositional gradient is first achieved by varying the Cu concentration from Cu-rich (Fe53Pt47)(70)Cu-30 to Cu-free Fe53Pt47. The anisotropy gradient is then realized after thermal post-annealing, and by utilizing the strong composition dependence of the low-anisotropy (A1) to high-anisotropy (L1(0)) ordering temperature. The magnetic properties are investigated by surface sensitive magneto-optical Kerr effect and alternating gradient magnetometer (AGM) measurements. AGM first-order reversal curve (FORC) measurements are employed in order to provide a detailed analysis of the reversal mechanisms, and therefore the induced anisotropy gradient. At low annealing temperatures, the FORC measurements clearly indicate the highly coupled reversal of soft and hard phases. However, significant interdiffusion results in virtually uniform films at elevated annealing temperatures. Additionally, the A1 to L1(0) ordering process is found to depend on the film thickness.
47.	Dumas, Randy K., et al. (författare) Recent Advances in Nanocontact Spin-Torque Oscillators 2014 Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 50:6, s. 4100107- Tidskriftsartikel (refereegranskat)abstract We present a comprehensive review of the most recent advances in nanocontact spin torque oscillators (NC-STOs). NC-STOs are highly tunable, with both applied magnetic field and dc, broadband microwave signal generators. As opposed to the nanopillar geometry, where the lateral cross section of the entire device has been confined to a typically <100 nm diameter, in NC-STOs, it is only the current injection site that has been laterally confined on top of an extended magnetic film stack. Three distinct material combinations will be discussed: 1) a Co/Cu/NiFe pseudospin valve (PSV) where both the Co and NiFe have a dominant in-plane anisotropy; 2) a Co/Cu/[Co/Ni](4) orthogonal PSV where the Co/Ni multilayer has a strong perpendicular anisotropy; and 3) a single NiFe layer with asymmetric non-magnetic Cu leads. We explore the rich and diverse magnetodynamic modes that can be generated in these three distinct sample geometries.
48.	Dumas, Randy K., et al. (författare) Recent Advances in Nanocontact Spin-Torque Oscillators 2014 Ingår i: Ieee Transactions on Magnetics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9464 .- 1941-0069. ; 50:6 Tidskriftsartikel (refereegranskat)abstract We present a comprehensive review of the most recent advances in nanocontact spin torque oscillators (NC-STOs). NC-STOs are highly tunable, with both applied magnetic field and dc, broadband microwave signal generators. As opposed to the nanopillar geometry, where the lateral cross section of the entire device has been confined to a typically <100 nm diameter, in NC-STOs, it is only the current injection site that has been laterally confined on top of an extended magnetic film stack. Three distinct material combinations will be discussed: 1) a Co/Cu/NiFe pseudospin valve (PSV) where both the Co and NiFe have a dominant in-plane anisotropy; 2) a Co/Cu/[Co/Ni](4) orthogonal PSV where the Co/Ni multilayer has a strong perpendicular anisotropy; and 3) a single NiFe layer with asymmetric non-magnetic Cu leads. We explore the rich and diverse magnetodynamic modes that can be generated in these three distinct sample geometries.
49.	Durr, Hermann A., et al. (författare) A Closer Look Into Magnetism : Opportunities With Synchrotron Radiation 2009 Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 45:1, s. 15-57 Forskningsöversikt (refereegranskat)abstract The unique properties of synchrotron radiation, such as broad energy spectrum, variable light polarization, and flexible time structure, have made it an enormously powerful tool in the study of magnetic phenomena and materials. The refinement of experimental techniques has led to many new research opportunities, keeping up with the challenges put up by modern magnetism research. In this contribution, we review some of the recent developments in the application of synchrotron radiation and particularly soft X-rays to current problems in magnetism, and we discuss future perspectives.
50.	Dzhezherya, Yu., et al. (författare) Ultrafast Inertia-Free Switching of Double Magnetic Tunnel Junctions 2024 Ingår i: IEEE Transactions on Magnetics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9464 .- 1941-0069. ; 60:5 Tidskriftsartikel (refereegranskat)abstract We investigate the switching of a magnetic nanoparticle comprising the middle free layer of a memory cell based on a double magnetic tunnel junction under the combined effect of spin-polarized current and weak on-chip magnetic field. We obtain the timing and amplitude parameters for the current and field pulses needed to achieve 100 ps range inertia-free switching under least-power dissipation. The considered method does not rely on the stochastics of thermal agitation of the magnetic nanoparticle typically accompanying spin-torque switching. The regime of ultimate switching speed efficiency found in this work is promising for applications in high-performance nonvolatile memory.

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