Aalto University
  • Helsinki, Finland
Recent publications
I study how to get by on a planet where people experience interrelated socio-ecological crises beyond one’s location—but I have little answers how to do it myself. There are many studies of academic work, ecological crisis, and one’s agency in either of these—but often they are treated separately. This chapter is an attempt to bring these burning themes together with autoethnography and makes sense of the contemporary practice of being an academic in the era of socio-ecological crisis. When knowing of multiple crises as an academic, how and why to do research as an engaged scholar in hyper-individualistic and competitive research environments? What kinds of possibilities for collective action are there for engaged scholars within or in the outskirts of academia? This chapter draws from practice theorising, tempered radicalism, engaged scholarship, and the role of academics impacting contemporary phenomena. In order to make visible options beyond only playing the game within academia or leaving academia altogether, I explore existing engaged scholarship stemming from my networks.
BACKGROUND Limited data exist on the temporal relationship between new-onset atrial fibrillation (AF) and ischemic stroke and its impact on patients’ clinical characteristics and mortality. METHODS A population-based registry-linkage database includes all patients with new-onset AF in Finland from 2007 to 2018. Ischemic stroke temporally associated with AF (ISTAF) was defined as an ischemic stroke occurring within ±30 days from the first AF diagnosis. Clinical factors associated with ISTAF were studied with logistic regression and 90-day survival with Cox proportional hazards analysis. RESULTS Among 229 565 patients with new-onset AF (mean age, 72.7 years; 50% female), 204 774 (89.2%) experienced no ischemic stroke, 12 209 (5.3%) had past ischemic stroke >30 days before AF, and 12 582 (5.8%) had ISTAF. The annual proportion of ISTAF among patients with AF decreased from 6.0% to 4.8% from 2007 to 2018. Factors associated positively with ISTAF were higher age, lower education level, and alcohol use disorder, whereas vascular disease, heart failure, chronic kidney disease cancer, and psychiatric disorders were less probable with ISTAF. Compared with patients without ischemic stroke and those with past ischemic stroke, ISTAF was associated with ≈3-fold and 1.5-fold risks of death (adjusted hazard ratios, 2.90 [95% CI, 2.76–3.04] and 1.47 [95% CI, 1.39–1.57], respectively). The 90-day survival probability of patients with ISTAF increased from 0.79 (95% CI, 0.76–0.81) in 2007 to 0.89 (95% CI, 0.87–0.91) in 2018. CONCLUSIONS ISTAF depicts the prominent temporal clustering of ischemic strokes surrounding AF diagnosis. Despite having fewer comorbidities, patients with ISTAF had worse, albeit improving, survival than patients with a history of or no ischemic stroke. REGISTRATION URL: https://www.clinicaltrials.gov ; Unique identifier: NCT04645537. URL: https://www.encepp.eu ; Unique identifier: EUPAS29845.
Machine-learned potentials (MLPs) trained against quantum-mechanical reference data have demonstrated remarkable accuracy, surpassing empirical potentials. However, the absence of readily available general-purpose MLPs encompassing a broad spectrum of elements and their alloys hampers the applications of MLPs in materials science. In this study, we present a feasible approach for constructing a unified general-purpose MLP for numerous elements and showcase its capability by developing a model (UNEP-v1) for 16 elemental metals (Ag, Al, Au, Cr, Cu, Mg, Mo, Ni, Pb, Pd, Pt, Ta, Ti, V, W, Zr) and their diverse alloys. To achieve a complete representation of the chemical space, we demonstrate that employing 16 one-component and 120 two-component systems suffices, thereby avoiding the enumeration of all 65535 possible combinations for training data generation. Furthermore, we illustrate that systems with more components can be adequately represented as interpolation points in the descriptor space. Our unified MLP exhibits superior performance across various physical properties as compared to the embedded-atom method potential, while maintaining computational efficiency. It achieves a remarkable computational speed of 1.5 × 10⁸ atom step / second in molecular dynamics simulations using eight 80-gigabyte A100 graphics cards, enabling simulations up to 100 million atoms. We demonstrate the generality and high efficiency of the MLP in studying plasticity and primary radiation damage in the MoTaVW refractory high-entropy alloys, showcasing its potential in unraveling complex materials behavior. This work represents a significant leap towards the construction of a unified general-purpose MLP encompassing the periodic table, with profound implications for materials research and computational science.
Interlayer interactions are one of the crucial parameters of two‐dimensional (2D) layered materials‐based junctions. Understanding the limits of interlayer coupling and defining the “maximum building block thickness” in artificially stacked 2D layered materials are key tasks that hold significant importance, not only in fundamental physics, but also in practical applications such as electronics, photonics, and optoelectronics. Here, the interlayer coupling limits are optically investigated of a model 2D layered semiconductor, MoS2, revealing the evolution of distinct interaction mechanisms between layers via artificial stacking. As the total thickness increases, a reduction in the stacking angle influence on the properties of the homojunctions is reflected in the photoluminescence and second harmonic generation responses. The results show that the effective coupling limit for vertically stacked 2D metamaterials resides in three‐layer flakes. The findings pave the way to advanced and complex devices of 2D superlattices for photonics and optoelectronics.
Internet of Things is an emerging paradigm based on interconnecting physical and virtual objects with each other and to the Internet. Most connected things fall into the category of constrained devices, with restricted resources (processing power, memory, and energy). These low‐power and lossy networks (LLNs) are known for their instability, high loss rates and low data rates, which makes routing one of the most challenging problems in low‐cost communications. A routing protocol for low‐power and lossy networks (RPL) is a proactive dynamic routing protocol based on IPv6. This protocol defines an objective function (OF) that utilises a set of metrics to select the best possible path to the destination. Minimum rank hysteresis objective function (MRHOF) and objective function zero (OF0) are the most basic OFs, where the first one selects the path to the sink based on the expected transmission count (ETX) metric, and OF0 is based on the hop count (HC). These two metrics prioritise either brute performance (i.e. ETX) or simplicity (i.e. HC). Therefore, using a single metric with an OF can either limit the performance or have an inefficient impact on load management and energy consumption. To overcome these challenges, a routing metric based on MRHOF OF which takes into consideration the link‐based routing metric (i.e. ETX) and node‐based metric (i.e. remaining energy) for route selection is provided. Expected transmission count remaining energy (ETXRE) is evaluated through 36 scenarios with different parameters. Preliminary results show that ETXRE outperforms ETX and RE in terms of end‐to‐end delay by an average of at least 17%, packet delay by 13% and consumes 10% less energy.
Light is a powerful and sustainable resource, but it can be detrimental to the performance and longevity of optical devices. Materials with near-zero light reflectance, i.e. superblack materials, are sought to improve the performance of several light-centered technologies. Here we report a simple top-down strategy, guided by computational methods, to develop robust superblack materials following metal-free wood delignification and carbonization (1500 °C). Subwavelength severed cells evolve under shrinkage stresses, yielding vertically aligned carbon microfiber arrays with a thickness of ~100 µm and light reflectance as low as 0.36% and independent of the incidence angle. The formation of such structures is rationalized based on delignification method, lignin content, carbonization temperature and wood density. Moreover, our measurements indicate a laser beam reflectivity lower than commercial light stoppers in current use. Overall, the wood-based superblack material is introduced as a mechanically robust surrogate for microfabricated carbon nanotube arrays.
We describe herein a poly(N-isopropylacrylamide) (PNIPAAm)-cellulose nanocrystals (CNC) hydrogel as thermoresponsive and biocompatible material. The hydrogel was generated with simple and robust mixing without need for complicated derivatization. The composition of the hydrogel was optimized for good stiffening and its biocompatibility was verified with fibroblast cells. The hydrogel was prepared using an osmotic dehydration method by tuning its water content and porosity without the incorporation of additional cross-linkers. The interaction of PNIPAAm and CNC was supported by the formation of a small endotherm at 30.5-33.5 1C observed with differential scanning calorimetry and a negative value for the enthalpy during the adsorption of both compounds by the isothermal titration calorimeter. The resulting PNIPAAm-CNC hydrogel (0.25 wt%; 0.5 wt%) showed better compatibility with fibroblasts than 0.5 wt% CNC alone. Our preliminary data indicates that it is possible to use the thermoresponsive characteristics of the material to influence cell behavior by temperature changes. PNIPAAm-CNC hydrogel offer a platform for the development of versatile and affordable plant-based materials for controllable 3D cell culture and the thermoresponsive nature of the material may help to develop novel applications for example in 3D-printing.
The removal of trivalent iron and aluminum was studied from synthetic Li-ion battery leach solution by phosphate and hydroxide precipitation (pH 2.5–4.25, t = 3 h, T = 60 °C). Phosphate precipitation exhibited both crystal nucleation initiation (pH 2 vs. pH 3) as well as complete (~ 99%) Fe and Al removal at lower pH compared to hydroxide precipitation (pH 3 vs. 3.5). The precipitation time of phosphate was shorter (40 min) than that of hydroxide precipitation (80 min). At pH 4 the loss of valuable metals (Li, Ni, Co) in the precipitate was negligible in the phosphate cake, whereas in the hydroxide process the co-precipitation was 4–5% for Li, Ni and Co. The filtration rate of phosphate precipitate was shown to be significantly faster. The presence of fluoride did not have any notable effect on phosphate precipitation, whereas in hydroxide precipitation, it potentially had a negative effect on aluminum extraction.
The COVID-19 pandemic imposed urgent challenges for educational institutions. The sudden shift from on-site teaching to online distance learning offered the possibility to examine new settings of the studio, a core element of planning and architecture education. Although the pandemic is now over, online learning has secured a fixed place in university education, and consequently, educational institutions need to reconsider studio education based on the lessons learned during the pandemic. Through studying four studios taught at Aalto University, Finland, in 2020 and 2021, this article examines student-teacher experiences, and proposes opportunities for evolving studio education. The findings show that distance learning has in general sustained the objectives of studio education. However, challenges remain especially regarding the social aspects of learning. The degree of success of online teaching varied greatly depending on the tasks and the orientation of the studio (design or strategy). Technological aids and devices also had an influence on fulfilling the ped-agogical objectives of learning. Professional socialization was highly affected by the online environment both in design and planning studios and the architectural representation witnessed difficulties specifically in design studios. To evolve the studio setting, the article suggests a mixed modality model supporting the social dimension of studio teaching by combining on-site and online learning activities to enrich the learning process. Such a model can harmonize the intended learning objectives and activities with the teaching methods and modality, thus improving the social dimension of studio teaching.
Optical phase matching involves establishing a proper phase relationship between the fundamental excitation and generated waves to enable efficient optical parametric processes. It is typically achieved through birefringence or periodic polarization. Here, we report that the interlayer twist angle in two-dimensional (2D) materials creates a nonlinear geometric phase that can compensate for the phase mismatch, and the vertical assembly of the 2D layers with a proper twist sequence generates a nontrivial “twist-phase-matching” (twist-PM) regime. The twist-PM model provides superior flexibility in the design of optical crystals, which can be applied for twisted layers with either periodic or random thickness distributions. The designed crystal from the twisted rhombohedral boron nitride films within a thickness of only 3.2 μm is capable of producing a second-harmonic generation with conversion efficiency of ∼8% and facile polarization controllability that is absent in conventional crystals. Our methodology establishes a platform for the rational design and atomic manufacturing of nonlinear optical crystals based on abundant 2D materials.
On 15 September 2021, Chandra carried out a 40‐hr (∼4 jovian rotations) observation as part of its longest planetary campaign to study the drivers of jovian X‐ray aurora that may be linked to ultra‐low frequency (ULF) wave activity. During this time, Juno's orbit had taken the spacecraft into Jupiter's dusk magnetosphere. Here is believed to be the most probable location of ULF waves propagating along jovian magnetic field lines that drive the X‐ray auroral emissions. This is the first time that this region has been observed by an orbiter since Galileo >20 years ago, and never before has there been contemporaneous in situ and X‐ray observations. A 1D solar wind propagation model identifies a compression event near the midpoint of the 40‐hr observation window. The influence of a compression is confirmed when comparing the measured magnetic field in the dusk lobes of the magnetotail from Juno MAG data against a baseline lobe field model. Data from the Juno Waves instrument also show activation of broadband kilometric (bKOM) emissions during the arrival of the shock, a feature that has previously been observed during compression events. Therefore this is the first time we can fully analyze the morphological variability during the evolution of a shock. Wavelet transforms and Rayleigh testing are used to search for statistically significant quasi‐periodic pulsations (QPPs) of the X‐ray emissions in the data set, and find significant QPPs with periods of 25–26 min for the northern auroral X‐rays.
Background Periodontitis is an oral disorder triggered by chronic inflammation, and a major cause of human tooth loss. Porphyromonas gingivalis is a prominent component in the etiology of chronic periodontitis which forms a bacterial “red complex” with Tannerella forsythia and Treponema denticola. P. gingivalis can invade the periodontal tissue and lower the host-defense mechanisms by deregulating immune and inflammatory responses. In parallel, Streptococcus sanguinis represents oral commensal bacteria that act as pioneers for bacterial colonization in biofilm formation. A plant of traditional medicine to inhibit bacterial growth is soursop (Annona muricata L.) that contains active chemical compounds, namely alkaloids, phenolics, flavonoids, and tannins. Aim The study aimed to determine the antibacterial effectiveness of soursop leaf extract on P. gingivalis and S. sanguinis, and to compare the effect of the extract to that of the positive control of 0.2% chlorhexidine. Methods Ethanol extract of soursop leaves was prepared at concentrations of 60, 50, 25, 12,5, 6,25, and 3,125 vol%. The antibacterial effectiveness of soursop leaf extract on P. gingivalis dan S. sanguinis is tested for Minimum Inhibitory Concentration and Minimum Bactericidal Concentration. Results The observed MIC values of soursop leaf extract on P. gingivalis and S. sanguinis were 25% and 12,5%, while the MBC values were 50% and 60% (vol), respectively. There were significant differences in the inhibitory concentration of soursop leaf extract and positive control by 0,2% chlorhexidine against both P. gingivalis and S. sanguinis in post-hoc Tukey test (p ≤ 0.05). Conclusion Ethanol extract of soursop leaves can effectively inhibit and kill P. gingivalis and S. sanguinis in vitro.
Caries is the most prevalent disease in the world, and in Indonesia its prevalence is 88.8%. While the causative microbial agent of caries is Streptococcus mutans, Streptococcus sanguinis is a primary colonizer related to the formation of oral biofilms. Due to concerns on cost, access and side effects of the commercial solutions, many people still depend on plant-based medicinal alternatives. Plectranthus amboinicus (Lour.) Spreng is such a medicinal plant containing carvacrol and thymol that are known to have antibacterial effects. Aim: To determine the effectiveness of P. amboinicus extract in inhibiting growth of and killing S. mutans and S. sanguinis. Methods: Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were determined to characterize the antibacterial properties of the ethanol extract of P. amboinicus from extract concentrations of 50%, 25%, 12.5%, 6.25 %, and 3.125% (vol) against the two bacterial species. Results: MIC and MBC levels of the ethanol extract of P. amboinicus against S. mutans were 3.125% and 50%, respectively. The corresponding MIC and MBC levels of the extract against S. sanguinis were respectively 6.25% and 25%l test showed a significant difference between each treatment (p <0.05). Conclusion: Ethanol extract of P. amboinicus can effectively inhibit growth of and kill S. mutans and S. sanguinis.
2D transition metal carbides and nitrides (MXenes) suggest an uncommonly broad combination of important functionalities amongst 2D materials. Nevertheless, MXene suffers from facile oxidation and colloidal instability upon conventional water‐based processing, thus limiting applicability. By experiments and theory, It is suggested that for stability and dispersibility, it is critical to select uncommonly high permittivity solvents such as N ‐methylformamide (NMF) and formamide (FA) ( ε r = 171, 109), unlike the classical solvents characterized by high dipole moment and polarity index. They also allow high MXene stacking order within thin films on carbon nanotube (CNT) substrates, showing very high Terahertz (THz) shielding effectiveness (SE) of 40–60 dB at 0.3–1.6 THz in spite of the film thinness < 2 µm. The stacking order and mesoscopic porosity turn relevant for THz‐shielding as characterized by small‐angle X‐ray scattering (SAXS). The mechanistic understanding of stability and structural order allows guidance for generic MXene applications, in particular in telecommunication, and more generally processing of 2D materials.
We consider the distributed channel access problem for a system consisting of multiple control subsystems that close their loop over a shared wireless network with multiple channels subject to Markovian packet dropouts. Provided that an acknowledgement/negative-acknowledgement feedback mechanism is in place, we show that this problem can be formulated as a Markov decision process. We then transform this problem to a form that enables distributed control-aware channel access. More specifically, we show that the control objective can be minimized without requiring information exchange between subsystems as long as the channel parameters are known. The objective is attained by adopting a priority-based deterministic channel access method and the stability of the system under the resulting scheme is analyzed. Next, we consider a practical scenario in which the channel parameters are unknown and adopt a learning method based on Bayesian inference which is compatible with distributed implementation. We propose a heuristic posterior sampling algorithm which is shown to significantly improve performance via simulations.
Large-scale multibeam phased array systems suffer from interbeam interference (IBI) that should be canceled either in the analog or digital domain. In wideband systems such as fifth generation (5G), interference rejection over a wide bandwidth is challenging to achieve, not only due to nonidealities of the receiver chain but also due to the properties of the radio channel. This article presents a scalable IBI cancellation (IBIC) scheme at intermediate frequency (IF) using an IF receiver (IF-RX) chip. The IF-RX provides the flexibility of not just interference rejection between the subarrays but also wideband signal combining over multiple subarrays. It also provides wideband filtering before the analog-to-digital converter (ADC) to support 5G channel bandwidths of up to 800 MHz, high linearity, and low noise figure. A calibration method is proposed to find the cancellation coefficients for the IF-RX in measurements. Furthermore, a simplified over-the-air (OTA) IBIC model for analyzing rejection bandwidth limitations is presented. Interference rejection performance is demonstrated through the OTA measurements using 5G new radio (5G NR) signals. In the OTA measurements, 34–37-dB rejection was achieved for 50–100-MHz signals, while error vector magnitude (EVM) requirements of the 5G standards were met with good margins. Finally, the interference rejection over $4\ttimes 100$ MHz carrier aggregated 5G NR waveform was demonstrated.
We study whether realistic fifth-generation (5G) mm-wave cellular networks would cause harmful out-of-band interference to weather satellites sensing in the 23.8 GHz band. We estimate uplink and downlink interference from a single interferer and a network of interferers in New York City, using real three-dimensional (3D) building data and realistic antenna patterns. We perform detailed ray-tracing propagation simulations, for locations of the MetOp-B weather satellite and its scanning orientations and ground interferer antenna orientations for representative urban cell sites. In addition to the ITU-R threshold of –136 dBm/200 MHz, we propose an alternative set of harmful interference thresholds directly related to the sensitivity of the satellite sensor. Our results show that the 3GPP power leakage limits are sufficient to ensure that interference from a single 5G device is not harmful if considering the ITU-R threshold, but not if the weather prediction software can tolerate only very low interference levels. Importantly, aggregate interference resulting in practice from a 5G network with realistic network densities is often harmful, even considering the least conservative ITU-R threshold. Overall, our comprehensive coexistence study thus strongly suggests that additional engineering and/or regulatory solutions will be necessary to protect weather satellite passive sensing from mm-wave cellular network interference.
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Sari Kujala
  • Department of Computer Science
Kari Tammi
  • Department of Mechanical Engineering
Lasse Leskelä
  • Department of Mathematics and Systems Analysis
Otakaari 5A, 02150, Helsinki, Finland
Head of institution
Prof. Ilkka Niemelä
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