| 1. |
- Löfgren, Joakim, 1989, et al.
(författare)
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Computational assessment of the efficacy of halides as shape-directing agents in nanoparticle growth
- 2020
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Ingår i: Physical Review Materials. - 2475-9953. ; 4:9
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Tidskriftsartikel (refereegranskat)abstract
- We report a comprehensive study of aqueous halide adsorption on nanoparticles of gold and palladium that addresses several limitations hampering the use of atomistic modeling as a tool for understanding and improving wet-chemical synthesis and related applications. A combination of thermodynamic modeling with density functional theory (DFT) calculations and experimental data is used to predict equilibrium shapes of halide-covered nanoparticles as a function of the chemical environment. To ensure realistic and experimentally relevant results, we account for solvent effects and include a large set of vicinal surfaces, several adsorbate coverages, as well as decahedral particles. While the observed stabilization is not significant enough to result in thermodynamic stability of anisotropic shapes such as nanocubes, nonuniformity in the halide coverage indicates the possibility of obtaining such shapes as kinetic products. With regard to technical challenges, we show that inclusion of surface-solvent interactions leads to qualitative changes in the predicted shape. Furthermore, accounting for nonlocal interactions on the functional level yields a more accurate description of surface systems.
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| 2. |
- Adanez-Rubio, Inaki, et al.
(författare)
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Use of a high-entropy oxide as an oxygen carrier for chemical looping
- 2024
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Ingår i: Energy. - 0360-5442 .- 1873-6785. ; 298
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Tidskriftsartikel (refereegranskat)abstract
- One mixed oxide with 5 cations in equimolar proportions in the sublattice, to fulfil high-entropy oxide (HEO) criteria, has been developed and investigated as oxygen carrier for chemical looping combustion processes. As far as we know, nobody has explored this class of material for chemical looping combustion. Material is prepared by direct mixing of five metal oxides (CuO, Mn2O3, Fe2O3, TiO2, MgO), followed by calcination at 1000, 1100 and 1200 °C for 6 h in air. XRD characterization provides strong evidence that the synthesized oxygen carriers possess the hallmark properties of HEO, and SEM-EDX analysis shows an overall homogeneous metal distribution. Materials have one main cubic phase with the empirical formula MnCuMgFeTiO7, dominating under all conditions. One of the key objectives of this study is achieved, reduce chemical stress during redox cycles. Oxygen transfer capability is investigated by thermogravimetric analysis and batch fluidized bed reactor experiments for different fuels and atmospheres. Mass-based oxygen transport capacities for lattice oxygen and oxygen uncoupling are around 5.5 wt% and 1.1 wt%, respectively. This work opens up a new dimension for the future preparation of oxygen carriers for chemical looping processes, since the vast compositional space of HEO provides opportunities to tune both chemical and physical characteristics.
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| 3. |
- Brorsson, Joakim, 1988, et al.
(författare)
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Discovery of Oxygen Carriers by Mining a First-Principle Database
- 2023
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Ingår i: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 127:20, s. 9437-9451
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping is an innovative technique that relies, to a large extent, on the possibility of finding new oxygen carriers. Until now, these materials have primarily been identified via experimental techniques and therefrom derived insights. However, this is both costly and time-consuming. To speed-up this process, we have applied a computational screening approach based on energetic data retrieved from the Open Quantum Materials Database. In particular, we have considered combinations of all mono-, bi-, and trimetallic alloys and mixed oxides with up to three distinctive phases. Here, we specifically focus on a technique referred to as chemical looping oxygen uncoupling, which is especially suitable for solid fuels, e.g., combustion of biomass for negative CO2 emissions. The formation energies obtained for the materials of interest were used to identify phase transitions that are likely to occur under conditions relevant for chemical looping oxygen uncoupling. Given these criteria, the initial list of 300000 materials is reduced by a factor of 20, and after filtering out rare, radioactive, toxic, or harmful elements only 1000 remain. When considering the abundance of elements in the ranking criteria, most of the highest ranking phases include Cu, Mn, and Fe. This adds credibility to the procedure, as many viable oxygen carriers for chemical looping oxygen uncoupling that have been studied experimentally contain these elements. While Cr-based materials have not been widely explored for this application, our study suggests that this might be worthwhile since these occur more frequently than Fe. Other elements that would be interesting as additional components include Ba, K, Na, Al, and Si.
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| 4. |
- Brorsson, Joakim, 1988, et al.
(författare)
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Efficient Calculation of the Lattice Thermal Conductivity by Atomistic Simulations with Ab Initio Accuracy
- 2022
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Ingår i: Advanced Theory and Simulations. - : Wiley. - 2513-0390. ; 5:2
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Tidskriftsartikel (refereegranskat)abstract
- High-order force constant expansions can provide accurate representations of the potential energy surface relevant to vibrational motion. They can be efficiently parametrized using quantum mechanical calculations and subsequently sampled at a fraction of the cost of the underlying reference calculations. Here, force constant expansions are combined via the hiphive package with GPU-accelerated molecular dynamics simulations via the GPUMD package to obtain an accurate, transferable, and efficient approach for sampling the dynamical properties of materials. The performance of this methodology is demonstrated by applying it both to materials with very low thermal conductivity (Ba8Ga16Ge30, SnSe) and a material with a relatively high lattice thermal conductivity (monolayer-MoS2). These cases cover both situations with weak (monolayer-MoS2, SnSe) and strong (Ba8Ga16Ge30) pho renormalization. The simulations also enable to access complementary information such as the spectral thermal conductivity, which allows to discriminate the contribution by different phonon modes while accounting for scattering to all orders. The software packages described here are made available to the scientific community as free and open-source software in order to encourage the more widespread use of these techniques as well as their evolution through continuous and collaborative development.
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| 5. |
- Brorsson, Joakim, 1988, et al.
(författare)
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First-Principles Study of Order-Disorder Transitions in Pseudobinary Clathrates
- 2021
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:41, s. 22817-22826
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Tidskriftsartikel (refereegranskat)abstract
- It has been recently demonstrated that the pseudoternary Ba8AlxGayGe46-x-y clathrate undergoes an order-disorder transition with increasing temperature that can be observed via site occupation factors (SOFs) and manifests itself, e.g., in electrical transport properties. Here, we generalize this result and analyze the characteristics of this order-disorder transition in the pseudobinary clathrates Ba8GaxGe46-x, Ba8GaxSi46-x, Ba8AlxGe46-x, and Ba8AlxSi46-x. To this end, we employ atomistic simulations that combine alloy cluster expansions trained against density functional theory calculations with Wang-Landau and ensemble Monte Carlo simulations. The simulations show that all four systems studied here display order-disorder transitions for at least some composition range. Based on an extensive literature survey, we also provide evidence for signatures of the transition in earlier experimental studies that to the best of our knowledge have hitherto not been related to such transitions. The predicted transition temperatures are lower for Ba8GaxGe46-x and Ba8GaxSi46-x than for Ba8AlxGe46-x and Ba8AlxSi46-x, although it appears that the simulations underestimate the transition temperatures for Ga-containing systems compared to the experiment. This nonetheless provides a sensible explanation for why the experimentally determined Al SOFs agree better with the simulated higherature disordered configurations, while the Ga SOFs more closely agree with the simulated ground-state configurations. As a result of stronger interactions, the SOFs vary substantially, especially near the stoichiometric 16:30 composition, providing an indication of why it has proved difficult to synthesize Ba8AlxGe46-x and Ba8AlxSi46-x samples at this ratio. The present study thereby yields detailed atomic-scale insights into the ordering in inorganic clathrates that, given the connection to transport properties established earlier, are not only useful from a fundamental perspective but also relevant for applications.
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| 6. |
- Brorsson, Joakim, et al.
(författare)
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Guarding the Guards: Accountable Authorities in VANETs
- 2019
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Ingår i: 2018 IEEE Vehicular Networking Conference (VNC). - 9781538694282
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Konferensbidrag (refereegranskat)abstract
- In this paper we present an approach to gaining increased anonymity from authorities within a VANET. Standardization organizations and researchers working on VANETs recognize privacy as highly important. However, most research focuses on privacy from other vehicles and external attackers, as opposed to privacy from system-administrating authorities. Our proposed solution forces authorities to resolve identities, i.e. de-anonymize vehicles, in public. It thereby creates a public log of identity resolutions and offers end-users a tool with which they can both validate the authorities' reasons for resolving identities and measure the extent to which such power is exercized.
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| 7. |
- Brorsson, Joakim, et al.
(författare)
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On the Suitability of Using SGX for Secure Key Storage in the Cloud
- 2020
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Ingår i: Lecture Notes in Computer Science. - Cham : Springer International Publishing. - 9783030589851 ; 12395, s. 32-47
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Konferensbidrag (refereegranskat)abstract
- This paper addresses the need for secure storage in virtualized services in the cloud. To this purpose, we evaluate the security properties of Intel's Software Guard Extensions (SGX) technology, which provides hardware protection for general applications, for securing virtual Hardware Security Modules (vHSM). In order for the analysis to be comparable with analyses of physical HSMs, the evaluation proceeds from the FIPS 140--3 standard, the successor to FIPS 140--2, which is commonly used to assess security properties of HSMs.Our contribution is twofold. First, we provide a detailed security evaluation of vHSMs using the FIPS 140–3 standard. Second, after concluding that the standard is designed for stand-alone rather than virtual systems, we propose a supplementary threat model, which considers threats from different actors separately. This model allows for different levels of trust in actors with different capabilities and can thus be used to assess which parts of FIPS 140--3 that should be considered for a specific attacker.Using FIPS 140--3 in combination with the threat model, we find that SGX enclaves provide sufficient protection against a large part of the potential actors in the cloud. Thus, depending on the threat model, SGX can be a helpful tool for providing secure storage for virtualized services.
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| 8. |
- Brorsson, Joakim, 1988, et al.
(författare)
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Order-Disorder Transition in Inorganic Clathrates Controls Electrical Transport Properties
- 2021
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 33:12, s. 4500-4509
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Tidskriftsartikel (refereegranskat)abstract
- Inorganic clathrates have been extensively investigated owing to their unique and intriguing atomic structure as well as their potential as thermoelectric materials. The connection between the chemical ordering and the physical properties has, however, remained elusive. Here, this relation is uncovered through a combination of first-principles calculations, atomistic simulations, and experimental measurements of thermodynamic as well as electrical transport properties. This approach is, specifically, used to reveal the existence of an order-disorder transition in the quaternary clathrate series Ba8AlxGa16-xGe30. The results, furthermore, demonstrate that this phenomenon is responsible for the discontinuity in the heat capacity that has been observed previously. Moreover, the unusual temperature dependence of both Seebeck coefficient and electrical conductivity can be fully explained by the alterations of the band structure brought about by the phase transformation. It is finally argued that the phenomenology described here is not limited to this particular material but should be present in a wide range of inorganic clathrates and could even be observed in other materials that exhibit chemical ordering on at least one sublattice.
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| 9. |
- Brorsson, Joakim, et al.
(författare)
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PAPR : Publicly Auditable Privacy Revocation for Anonymous Credentials
- 2023
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Ingår i: Topics in Cryptology – CT-RSA 2023 - Cryptographers’ Track at the RSA Conference 2023, Proceedings. - 1611-3349 .- 0302-9743. - 9783031308710 ; 13871 LNCS, s. 163-190
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Konferensbidrag (refereegranskat)abstract
- We study the notion of anonymous credentials with Publicly Auditable Privacy Revocation (PAPR). PAPR credentials simultaneously provide conditional user privacy and auditable privacy revocation. The first property implies that users keep their identity private when authenticating unless and until an appointed authority requests to revoke this privacy, retroactively. The second property enforces that auditors can verify whether or not this authority has revoked privacy from an issued credential (i.e. learned the identity of the user who owns that credential), holding the authority accountable. In other words, the second property enriches conditionally anonymous credential systems with transparency by design, effectively discouraging such systems from being used for mass surveillance. In this work, we introduce the notion of a PAPR anonymous credential scheme, formalize it as an ideal functionality, and present constructions that are provably secure under standard assumptions in the Universal Composability framework. The core tool in our PAPR construction is a mechanism for randomly selecting an anonymous committee which users secret share their identity information towards, while hiding the identities of the committee members from the authority. As a consequence, in order to initiate the revocation process for a given credential, the authority is forced to post a request on a public bulletin board used as a broadcast channel to contact the anonymous committee that holds the keys needed to decrypt the identity connected to the credential. This mechanism makes the user de-anonymization publicly auditable.
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| 10. |
- Brorsson, Joakim, 1988, et al.
(författare)
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Strategic Optimization of the Electronic Transport Properties of Pseudo-Ternary Clathrates
- 2022
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Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X .- 2199-160X. ; 8:3
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Tidskriftsartikel (refereegranskat)abstract
- While alloying is a powerful handle for materials engineering, it is an ongoing challenge to navigate the large and complex parameter space of these materials. This applies in particular for thermoelectrics and even more so clathrates. Here, a combination of density functional theory calculations, alloy cluster expansions, Monte Carlo simulations, and Boltzmann transport theory calculations is used to identify compositions that yield high power factors in the pseudo-ternary clathrates Ba8AlxGayGe46−x−y and Ba8GaxGeySi46−x−y, while accounting for weight and raw material costs. The results show how a cost-efficient performance can be achieved by reducing the number of Al and Ga atoms per unit cell, while compensating the resulting increase in the carrier concentration via an extrinsic dopant. The approach used in this study is transferable and can be a useful tool for mapping the thermodynamic and transport properties of other multinary systems.
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| 11. |
- Brorsson, Joakim, 1988, et al.
(författare)
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Thermodynamic properties for metal oxides from first-principles
- 2024
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Ingår i: Computational Materials Science. - 0927-0256. ; 233
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Tidskriftsartikel (refereegranskat)abstract
- In this study, an efficient first-principles approach for calculating the thermodynamic properties of mixed metal oxides at high temperatures is demonstrated. More precisely, this procedure combines density functional theory and harmonic phonon calculations with tabulated thermochemical data to predict the heat capacity, formation energy, and entropy of important metal oxides. Alloy cluster expansions are, moreover, employed to represent phases that display chemical ordering as well as to calculate the configurational contribution to the specific heat capacity. The methodology can, therefore, be applied to compounds with vacancies and variable site occupancies. Results are, moreover, presented for a number of systems of high practical relevance: Fe–K–Ti–O, K–Mn–O, and Ca–Mn–O. For the reference materials, the agreement with experimental measurements is exceptional in the case of ilmenite (FeTiO3) and good for CaMnO3. When the generated data is used in multi-phase thermodynamic calculations to represent materials for which experimental data is not available, the predicted phase-diagrams for the K–Mn–O and K–Ti–O systems change dramatically. The demonstrated methodology is highly useful for obtaining approximate values on key thermodynamic properties in cases where experimental data is hard to obtain, inaccurate or missing.
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| 12. |
- Brorsson, Joakim, 1988
(författare)
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Unlocking the potential of a caged star: Thermoelectric quaternary clathrates
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Heat losses are an inevitable consequence of any energy conversion process, dictated by the second law of thermodynamics. This not only leads to an eternal struggle, via the pursuit of maximal efficiency, it also undermines our efforts to solve the two issues that pose the most significant challenges to modern society: climate change and the worlds surging energy need. Thanks to our inherent ingenuity, humankind has, however, been adept at finding ways of harnessing the power of heat; from the fires that lit up the neolithic era to the steam engines of the industrial revolution. Thermoelectrics can, in some sense, be seen as the next step in this endeavour, since they allow the direct conversion of a temperature difference to an electric voltage. This thesis summarises a seven year long journey, which has focused on a fascinating and unique group of thermoelectric materials, namely inorganic clathrates. Though these have been the subject of intense research over the last three decades, many of their properties and attributes have, as of yet, not been fully explored. In particular, this project has addressed three fundamental questions: (i) Why is the lattice thermal conductivity intrinsically low? (ii) What is the impact of chemical ordering on the physical properties? (iii) How can the electronic transport be optimised? Due to the inherent complexity of these materials, computational and experimental methods should ideally be used in tandem, in order to gain further insights. This project has, thus, involved the use of both atomic scale simulations, based on a combination of density functional theory, alloy cluster expansions, and Monte Carlo simulations, as well as advanced measurement and characterisation techniques. Through these efforts, the confusion regarding the origin of the low lattice thermal conductivity has partly been clarified. In addition, it has been shown that chemical ordering in these materials leads to the emergence of an order-disorder transition, which has a direct impact on the physical properties. Last but not least, it is found that the consideration of ternary systems can facilitate the enhancement of the thermoelectric performance by enabling not only independent tuning of doping level and band structure via the composition, but also manipulation of the nano- and microstructure.
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| 13. |
- Brorsson, Torbjörn, et al.
(författare)
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Äldre rödgods från Studentholmen i Uppsala - en undersökning av proveniens genom pXRF- och ICP-analys
- 2024
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Ingår i: META Historiskarkeologisk tidskrift. - 2002-0406. ; 2024, s. 61-78
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Tidskriftsartikel (refereegranskat)abstract
- The assemblage of pottery from Studentholmen, excavated by Knut Stjerna in 1907, contains one of the largest and most varied collections of medieval ledglazed redwares from the medieval town of Uppsala. Previous have pointed to the similarities in form and technology with the larger productions centers in western Europe as well as to the possibilities that some of the less elaborately decorated pitchers and jugs might be locally produced. A study, aimed at establishing the provenance of the material by using handheld XRF for a non-destructive screening of the larger material and following ICP-analysis from identified and selected groups have been conducted in 2023. The study shows that the main centers for production of the vessels in Studentholmen where northern Germany and Netherlands. Further the study shows methodological potential for cost effective analyses of large assemblages of early redwares in the future, thus making more materials in museum collections available for much needed research
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| 14. |
- Faust, Robin, 1992, et al.
(författare)
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Thermodynamic Modeling and Experimental Investigation of the System Fe-Ti-O-K for Ilmenite Used as Fluidized Bed Oxygen Carrier
- 2024
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 38:15, s. 14569-14576
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Tidskriftsartikel (refereegranskat)abstract
- The capability of ilmenite for potassium uptake in a simulated oxygen carrier-aided combustion environment has been investigated. The maximum uptake of potassium and the effect of potassium inclusion on the Fe-Ti-O system was analyzed. Through laboratory experiments and thermodynamic calculations, it was found that a molar ratio of 1:1 can be formed spontaneously for both the K-Ti-system (where the formation of K2Ti2O5 was found) and the K-Fe-system (where KFeO2 was found). K2Ti2O5 was identified as an unstable phase, undergoing decomposition into K2Ti4O9. The study demonstrates that the maximum K uptake, through forming K2Ti4O9 and KFeO2, reaches 25 wt %─a notably higher value than ilmenite exposed to biomass in a fluidized bed. The research concludes that the lifetime of ilmenite is therefore rather dependent on its mechanical integrity than its maximum potassium uptake.
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| 15. |
- Gunnarsson, Martin, et al.
(författare)
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Evaluating the performance of the OSCORE security protocol in constrained IoT environments
- 2021
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Ingår i: Internet of Things. - : Elsevier BV. - 2542-6605. ; 13
-
Tidskriftsartikel (refereegranskat)abstract
- The Constrained Application Protocol (CoAP) is a standard communication protocol for resource-constrained devices in the Internet of Things (IoT). Many IoT deployments require proxies to support asynchronous communication between edge devices and the back-end. This allows (non-trusted) proxies to access sensitive parts of CoAP messages. Object Security for Constrained RESTful Environments (OSCORE) is a recent standard protocol that provides end-to-end security for CoAP messages at the application layer. Unlike the commonly used standard Datagram Transport Layer Security (DTLS), OSCORE efficiently provides selective integrity protection and encryption on different parts of CoAP messages. Thus, OSCORE enables end-to-end security through intermediary (non-trusted) proxies, while still allowing them to perform their expected services, with considerable security and privacy improvements.To assess whether these security features consume too much of the limited resources available on a constrained device, we have implemented OSCORE (the implementation is available as open-source), and evaluated its efficiency. This paper provides a comprehensive, comparative and experimental performance evaluation of OSCORE on real resource-constrained IoT devices, using the operating system Contiki-NG as IoT software platform. In particular, we experimentally evaluated the efficiency of our OSCORE implementation on resource-constrained devices running Contiki-NG, in comparison with the DTLS implementation TinyDTLS maintained by the Eclipse Foundation. The evaluation results show that our OSCORE implementation displays moderately better performance than TinyDTLS, in terms of per-message network overhead, memory usage, message round-trip time and energy efficiency, thus providing the security improvements of OSCORE with no additional performance penalty.
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| 16. |
- Johnston, Nina, et al.
(författare)
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Effects of interactive patient smartphone support app on drug adherence and lifestyle changes in myocardial infarction patients: A randomized study
- 2016
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Ingår i: American Heart Journal. - : MOSBY-ELSEVIER. - 0002-8703 .- 1097-6744. ; 178, s. 85-94
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Tidskriftsartikel (refereegranskat)abstract
- Background Patients with myocardial infarction (MI) seldom reach recommended targets for secondary prevention. This study evaluated a smartphone application ("app") aimed at improving treatment adherence and cardiovascular lifestyle in MI patients. Design Multicenter, randomized trial. Methods A total of 174 ticagrelor-treated MI patients were randomized to either an interactive patient support tool (active group) or a simplified tool (control group) in addition to usual post-MI care. Primary end point was a composite nonadherence score measuring patient-registered ticagrelor adherence, defined as a combination of adherence failure events (2 missed doses registered in 7-day cycles) and treatment gaps (4 consecutive missed doses). Secondary end points included change in cardiovascular risk factors, quality of life (European Quality of Life-5 Dimensions), and patient device satisfaction (System Usability Scale). Results Patient mean age was 58 years, 81% were men, and 21% were current smokers. At 6 months, greater patient registered drug adherence was achieved in the active vs the control group (nonadherence score: 16.6 vs 22.8 [P = .025]). Numerically, the active group was associated with higher degree of smoking cessation, increased physical activity, and change in quality of life; however, this did not reach statistical significance. Patient satisfaction was significantly higher in the active vs the control group (system usability score: 87.3 vs 78.1 [P = .001]). Conclusions In MI patients, use of an interactive patient support tool improved patient self-reported drug adherence and may be associated with a trend toward improved cardiovascular lifestyle changes and quality of life. Use of a disease-specific interactive patient support tool may be an appreciated, simple, and promising complement to standard secondary prevention.
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| 17. |
- Jung, Christian, et al.
(författare)
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A comparison of very old patients admitted to intensive care unit after acute versus elective surgery or intervention
- 2019
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Ingår i: Journal of critical care. - : W B SAUNDERS CO-ELSEVIER INC. - 0883-9441 .- 1557-8615. ; 52, s. 141-148
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Tidskriftsartikel (refereegranskat)abstract
- Background: We aimed to evaluate differences in outcome between patients admitted to intensive care unit (ICU) after elective versus acute surgery in a multinational cohort of very old patients (80 years; VIP). Predictors of mortality, with special emphasis on frailty, were assessed.Methods: In total, 5063 VIPs were induded in this analysis, 922 were admitted after elective surgery or intervention, 4141 acutely, with 402 after acute surgery. Differences were calculated using Mann-Whitney-U test and Wilcoxon test. Univariate and multivariable logistic regression were used to assess associations with mortality.Results: Compared patients admitted after acute surgery, patients admitted after elective surgery suffered less often from frailty as defined as CFS (28% vs 46%; p < 0.001), evidenced lower SOFA scores (4 +/- 5 vs 7 +/- 7; p < 0.001). Presence of frailty (CFS >4) was associated with significantly increased mortality both in elective surgery patients (7% vs 12%; p = 0.01), in acute surgery (7% vs 12%; p = 0.02).Conclusions: VIPs admitted to ICU after elective surgery evidenced favorable outcome over patients after acute surgery even after correction for relevant confounders. Frailty might be used to guide clinicians in risk stratification in both patients admitted after elective and acute surgery.
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| 18. |
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| 19. |
- Lindroth, Daniel, 1978, et al.
(författare)
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Thermal conductivity in intermetallic clathrates: A first-principles perspective
- 2019
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 100:4
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Tidskriftsartikel (refereegranskat)abstract
- Inorganic clathrates such as Ba8GaxGe46-x and Ba8AlxSi46-x commonly exhibit very low thermal conductivities. A quantitative computational description of this important property has proven difficult, in part due to the large unit cell, the role of disorder, and the fact that both electronic carriers and phonons contribute to transport. Here, we conduct a systematic analysis of the temperature and composition dependence of low-frequency modes associated with guest species in Ba8GaxGe46-x and Ba8AlxSi46-x ("rattler modes"), as well as thermal transport in stoichiometric Ba8Ga16Ge30. To this end, we account for phonon-phonon interactions by means of temperature-dependent effective interatomic force constants, which we find to be crucial in order to achieve an accurate description of the lattice part of the thermal conductivity. While the analysis of the thermal conductivity is often largely focused on the rattler modes, here it is shown that at room temperatures modes with ω 10meV account for 50% of lattice heat transport. Finally, the electronic contribution to the thermal conductivity is computed, which shows the Wiedemann-Franz law to be only approximately fulfilled. As a result, it is crucial to employ the correct prefactor when separating electronic and lattice contributions for experimental data.
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| 20. |
- Lundgren, Anders, 1978, et al.
(författare)
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Gold-nanoparticle-assisted self-assembly of chemical gradients with tunable sub-50 nm molecular domains
- 2014
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Ingår i: Particle & particle systems characterization. - : Wiley. - 0934-0866 .- 1521-4117. ; 31:2, s. 209-218
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Tidskriftsartikel (refereegranskat)abstract
- A simple and efficient principle for nanopatterning with wide applicability in the sub-50 nanometer regime is chemisorption of nanoparticles; at homogeneous substrates, particles carrying surface charge may spontaneously self-organize due to the electrostatic repulsion between adjacent particles. Guided by this principle, a method is presented to design, self-assemble, and chemically functionalize gradient nanopatterns where the size of molecular domains can be tuned to match the level corresponding to single protein binding events. To modulate the binding of negatively charged gold nanoparticles both locally (<100 nm) and globally (>100 μm) onto a single modified gold substrate, ion diffusion is used to achieve spatial control of the particles' mutual electrostatic interactions. By subsequent tailoring of different molecules to surface-immobilized particles and the void areas surrounding them, nanopatterns are obtained with variable chemical domains along the gradient surface. Fimbriated Escherichia coli bacteria are bound to gradient nanopatterns with similar molecular composition and macroscopic contact angle, but different sizes of nanoscopic presentation of adhesive (hydrophobic) and repellent poly(ethylene) glycol (PEG) domains. It is shown that small hydrophobic domains, similar in size to the diameter of the bacterial fimbriae, supported firmly attached bacteria resembling catch-bond binding, whereas a high number of loosely adhered bacteria are observed on larger hydrophobic domains. Chemical gradients with the resolution needed to address complex biological binding events at the single protein level are prepared using surface-deposited gold nanoparticles as a versatile template for orthogonal chemical modifications. The effect of hydrophobic domain arrangement on the sub-50 nm scale is shown to influence binding of fimbriae carrying E. coli bacteria. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 21. |
- Mikulskis, Paulius, et al.
(författare)
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Free-energy perturbation and quantum mechanical study of SAMPL4 octa-acid host-guest binding energies.
- 2014
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Ingår i: Journal of Computer-Aided Molecular Design. - : Springer Science and Business Media LLC. - 1573-4951 .- 0920-654X. ; 28:4, s. 375-400
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Tidskriftsartikel (refereegranskat)abstract
- We have estimated free energies for the binding of nine cyclic carboxylate guest molecules to the octa-acid host in the SAMPL4 blind-test challenge with four different approaches. First, we used standard free-energy perturbation calculations of relative binding affinities, performed at the molecular-mechanics (MM) level with TIP3P waters, the GAFF force field, and two different sets of charges for the host and the guest, obtained either with the restrained electrostatic potential or AM1-BCC methods. Both charge sets give good and nearly identical results, with a mean absolute deviation (MAD) of 4 kJ/mol and a correlation coefficient (R (2)) of 0.8 compared to experimental results. Second, we tried to improve these predictions with 28,800 density-functional theory (DFT) calculations for selected snapshots and the non-Boltzmann Bennett acceptance-ratio method, but this led to much worse results, probably because of a too large difference between the MM and DFT potential-energy functions. Third, we tried to calculate absolute affinities using minimised DFT structures. This gave intermediate-quality results with MADs of 5-9 kJ/mol and R (2) = 0.6-0.8, depending on how the structures were obtained. Finally, we tried to improve these results using local coupled-cluster calculations with single and double excitations, and non-iterative perturbative treatment of triple excitations (LCCSD(T0)), employing the polarisable multipole interactions with supermolecular pairs approach. Unfortunately, this only degraded the predictions, probably because of a mismatch between the solvation energies obtained at the DFT and LCCSD(T0) levels.
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| 22. |
- Nilsson, Alexander, et al.
(författare)
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A Survey of Published Attacks on Intel SGX
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Intel Software Guard Extensions (SGX) provides a trusted execution environment (TEE) to run code and operate sensitive data.SGX provides runtime hardware protection where both code and data are protected even if other code components are malicious.However, recently many attacks targeting SGX have been identified and introduced that can thwart the hardware defence provided by SGX.In this paper we present a survey of all attacks specifically targeting Intel SGX that are known to the authors, to date.We categorized the attacks based on their implementation details into 7 different categories.We also look into the available defence mechanisms against identified attacks and categorize the available types of mitigations for each presented attack.
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| 23. |
- Stanicic, Ivana, 1994, et al.
(författare)
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Thermodynamic Analysis on the Fate of Ash Elements in Chemical Looping Combustion of Solid Fuels Iron-Based Oxygen Carriers
- 2022
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 36:17, s. 9648-9659
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping combustion (CLC) enables efficient combustion of hydrocarbon fuels while also producing a gas stream with high CO2 concentrations, suitable for carbon capture and storage (CCS). CLC of biomass in combination with CCS results in efficient removal of carbon dioxide from the atmosphere, i.e., negative emissions. However, biomass and waste-derived fuels can contain significant fractions of aggressive ash precursors, which can affect the operability and functionality of oxygen carriers. In this paper, the fate of common ash elements will be investigated thermodynamically in a system utilizing iron-based oxygen carriers: ilmenite and iron oxide. Multiphase, multicomponent equilibrium calculations were performed using databases from FACT and a user-defined database, with a specific focus on alkali (K and Na) and heavy metals (Cu, Zn, and Pb). A detailed and comprehensive comparison with available literature data from experimental investigations was performed, and compounds not available in the databases were identified. Due to a lack of thermodynamic data in the literature, thermodynamic properties for four compounds, K0.85Fe0.85Ti0.15O2, K0.4Fe0.4Ti0.6O2, KTi8O16, and KTi8O16.5, were obtained from first-principles calculations. The fate of ash elements is studied for CLC of three biomass and waste-derived solid fuels under relevant CLC conditions: 950 °C in the fuel reactor and 1050 °C in the air reactor. Results show that the choice of the oxygen carriers largely influences the behavior of the ash elements. Compared to CLC with iron oxide, ilmenite is more beneficial with respect to high-temperature corrosion since less potassium is released into the gas phase since the titanium content in ilmenite immobilizes both potassium and calcium. For both oxygen carriers, the most corrosive compounds are expected to leave with the gas in the fuel reactor, keeping the air reactor free from chlorides. It was found that the compound KTi8O16 is stable in reducing conditions and low potassium concentrations. This is in conformity with previous experimental data, where this phase has been identified in the interior of ilmenite particles used in oxygen carrier aided combustion of wood chips.
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| 24. |
- Stanicic, Ivana, 1994, et al.
(författare)
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Thermodynamic analysis on the fate of ash elements in chemical looping combustion of solid fuels – Manganese-Based oxygen carriers
- 2024
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Ingår i: Fuel. - 0016-2361. ; 369
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping combustion (CLC) is an innovative technology suitable for converting waste-derived fuels into heat and power. The process inherently produces pure CO2, which is highly favorable for carbon capture and storage and could be instrumental for achieving negative emissions. CLC operates by utilizing solid oxygen carriers (OCs) to transfer heat and oxygen between two reactors. The OC play a crucial role in achieving an efficient combustion. Manganese-based OCs are particularly interesting, due to their ability to release gaseous oxygen. However, ash components from solid fuels could alter their oxygen transfer capacity, and cause problems related to corrosion and agglomeration. The objective of this work is to obtain in-depth insights about Mn-based OCs for CLC of waste-derived fuels. This is achieved by investigating phase transitions during CLC of solid fuels when utilizing two manganese-based OCs: manganese oxide and a representative manganese ore. For this purpose, thermodynamic modeling is employed, and a specific focus is given to K, Na, Cu, Zn, and Pb, due to their important role in corrosion and/or agglomeration. Thermodynamic databases are expanded by calculating properties from first-principles. It is shown that Mn-based OCs are suitable for effectively converting waste-derived fuels while limiting corrosion. Furthermore, the iron in manganese ores is found to have positive implications for oxygen-transfer reactions. In terms of alkali release to the gas phase, manganese ore seems to be a more promising material compared to manganese oxide. The pathways for the heavy metals Zn, Cu, and Pb were, meanwhile, independent of the OC type.
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| 25. |
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| 26. |
- Zhang, Yifei, 1992, et al.
(författare)
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Enhanced Thermoelectric Performance of Ba8Ga16Ge30 Clathrate by Modulation Doping and Improved Carrier Mobility
- 2021
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Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X .- 2199-160X. ; 7:2
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Tidskriftsartikel (refereegranskat)abstract
- Type-I inorganic clathrates are promising high temperature thermoelectric materials. They are known for their intrinsic low thermal conductivity, but a moderate power factor leaves room for further improvement. In this paper, a new route for improving the power factor by enhanced carrier mobility achieved via modulation doping is reported. A series of clathrates with composition Ba-8(AlxGa1-x)(16)Ge-30 are synthesized through ball milling and spark plasma sintering of mixtures of Ba8Al16Ge30 and Ba8Ga16Ge30. Among the materials with x = 0.20, 0.23, and 0.25, it is found that the electrical conductivity is significantly enhanced with increasing x, while the Seebeck coefficient decreases slightly. It is further revealed that the carrier mobility of the sintered sample x = 0.25 is greatly increased, reaching a value that exceeds that for a single crystal. Electron microscopy analysis reveals that the material consists of a heterostructure and is composed of a Ga-rich clathrate matrix phase and Al particles, suggesting that the power factor enhancement is due to modulation doping. As a result, the highest power factor is achieved for Ba-8(Al0.25Ga0.75)(16)Ge-30, with a value of 1.89 mW m(-1) K-2 at 800 degrees C. Consequently, the maximum zT of sample x = 0.25 reaches 0.93 at 800 degrees C.
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| 27. |
- Zhang, Yifei, 1992, et al.
(författare)
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Investigating the Chemical Ordering in Quaternary Clathrate Ba₈AlₓGa₁₆₋ₓGe₃₀
- 2021
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:22, s. 16977-16985
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Tidskriftsartikel (refereegranskat)abstract
- Recently, there has been an increased interest in quaternary clathrate systems as promising thermoelectric materials. Because of their increased complexity, however, the chemical ordering in the host framework of quaternary clathrates has not yet been comprehensively analyzed. Here, we have synthesized a prototypical quaternary type-I clathrate Ba8AlxGa16-xGe30 by Czochralski and flux methods, and we employed a combination of X-ray and neutron diffraction along with atomic scale simulations to investigate chemical ordering in this material. We show that the site occupancy factors of trivalent elements at the 6c site differ, depending on the synthesis method, which can be attributed to the level of equilibration. The flux-grown samples are consistent with the simulated high-temperature disordered configuration, while the degree of ordering for the Czochralski sample lies between the ground state and the high-temperature state. Moreover, we demonstrate that the atomic displacement parameters of the Ba atoms in the larger tetrakaidecahedral cages are related to chemical ordering. Specifically, Ba atoms are either displaced toward the periphery or localized at the cage centers. Consequently, this study reveals key relationships between the chemical ordering in the quaternary clathrates Ba8AlxGa16-xGe30 and the structural properties, thereby offering new perspectives on designing these materials and optimizing their thermoelectric properties.
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