KTH Royal Institute of Technology
Recent publications
Working time reduction (WTR) is a policy that could improve quality of life while reducing environmental impacts. However, WTR coupled with a salary reduction may benefit only higher-income earners and increase social inequalities. Against this background, we analyze how the motivations for and the socioecological outcomes from working less vary across different socioeconomic groups. The analysis is based on a survey conducted among municipal employees under full-time contracts who utilized the City of Gothenburg’s “right to part-time” policy. We find that working less improved quality of life not only for higher-income groups but also for lower-income groups through gains in time affluence, energy, health, and time spent on strengthening social ties. However, three negative effects emerged. First, WTR lead to increased work intensification, particularly among higher-income earners. Second, concerns regarding making ends meet and future retirement income were particularly salient issues among lower-income earners. Finally, WTR to cope with unfavorable working conditions was a much more common motive among manual workers with lower salaries. We conclude that WTR can be a viable option across a broader range of socioeconomic groups than previously assumed but that it is nevertheless important to consider the effects on social inequality when designing WTR policies.
The experimental results of Xia and Steen for the contact line dynamics of a drop placed on a vertically oscillating surface are analyzed by numerical phase field simulations. The concept of contact line mobility or friction is discussed, and an angle-dependent model is formulated. The results of numerical simulations based on this model are compared to the detailed experimental results of Xia and Steen with good general agreement. The total energy input in terms of work done by the oscillating support, and the dissipation at the contact line, are calculated from the simulated results. It is found that the contact line dissipation is almost entirely responsible for the dissipation that sets the amplitude of the response. It is argued that angle-dependent line friction may be a fruitful interpretation of the relations between contact line speed and dynamic contact angle that are often used in practical computational fluid dynamics.
Background Age-driven immune signals cause a state of chronic low-grade inflammation and in consequence affect bone healing and cause challenges for clinicians when repairing critical-sized bone defects in elderly patients. Methods Poly( l -lactide-co-ɛ-caprolactone) (PLCA) scaffolds are functionalized with plant-derived nanoparticles from potato, rhamnogalacturonan-I (RG-I), to investigate their ability to modulate inflammation in vitro in neutrophils and macrophages at gene and protein levels. The scaffolds’ early and late host response at gene, protein and histological levels is tested in vivo in a subcutaneous rat model and their potential to promote bone regeneration in an aged rodent was tested in a critical-sized calvaria bone defect. Significant differences were tested using one-way ANOVA, followed by a multiple-comparison Tukey’s test with a p value ≤ 0.05 considered significant. Results Gene expressions revealed PLCA scaffold functionalized with plant-derived RG-I with a relatively higher amount of galactose than arabinose (potato dearabinated (PA)) to reduce the inflammatory state stimulated by bacterial LPS in neutrophils and macrophages in vitro . LPS-stimulated neutrophils show a significantly decreased intracellular accumulation of galectin-3 in the presence of PA functionalization compared to Control (unmodified PLCA scaffolds). The in vivo gene and protein expressions revealed comparable results to in vitro. The host response is modulated towards anti-inflammatory/ healing at early and late time points at gene and protein levels. A reduced foreign body reaction and fibrous capsule formation is observed when PLCA scaffolds functionalized with PA were implanted in vivo subcutaneously . PLCA scaffolds functionalized with PA modulated the cytokine and chemokine expressions in vivo during early and late inflammatory phases. PLCA scaffolds functionalized with PA implanted in calvaria defects of aged rats downregulating pro-inflammatory gene markers while promoting osteogenic markers after 2 weeks in vivo. Conclusion We have shown that PLCA scaffolds functionalized with plant-derived RG-I with a relatively higher amount of galactose play a role in the modulation of inflammatory responses both in vitro and in vivo subcutaneously and promote the initiation of bone formation in a critical-sized bone defect of an aged rodent. Our study addresses the increasing demand in bone tissue engineering for immunomodulatory 3D scaffolds that promote osteogenesis and modulate immune responses.
Deep reinforcement learning (DRL) has proven to be an effective framework for solving various complex control problems. In manufacturing, industrial robots can be trained to learn dexterous manipulation skills from raw pixels with DRL. However, training robots in the real world is a time-consuming, high-cost and of safety concerns process. A frequently adopted approach for easing this is to train robots through simulations first and then deploy algorithms (or policies) on physical robots. How to transfer policies of robot learning from simulation to the real world is a challenging issue. Digital twin that is able to create a dynamic, up-to-date representation of a physical robotic grasping system provides an effective approach for addressing this issue. In this paper, we focus on the scenario of DRL-based assembly-oriented industrial grasping and propose a digital twin-enabled approach for achieving effective transfer of DRL algorithms to a physical robot. Two parallel training systems, i.e., the physical robotic system and corresponding digital twin system, respectively, are established, which take virtual and real images as inputs. The output of the digital twin system is used to correct the real grasping point so that accurate grasping can be achieved. Experimental results verify the effectiveness of the intelligent grasping algorithm and the digital twin-enabled sim-to-real transfer approach and mechanism.
Quadruped robots have the advantages of traversing complex terrains that are difficult for wheeled robots. Most of the reported quadruped robots are built by rigid parts. This paper proposes a new design of quadruped robots using soft actuators driven by tendons as the four legs. Compared to the rigid robots, the proposed soft quadruped robot has inherent safety, less weight and simpler mechanism for fabrication and control, but the corresponding challenge is that the accurate mathematical model applicable to model-based control design of the soft robot is difficult to derive by dynamics. To synthesize the optimal gait controller of the soft-legged robot, the paper makes the following contributions. First, the flexible components of the quadruped robot are modeled with different finite element and lumped parameter methods. The model accuracy and computation efficiency are analyzed. Second, soft actor-critic methods and curriculum learning are applied to learn the optimal gaits for different walking tasks. Third, The learned gaits are implemented in an in-house robot to transport hand tools. Preliminary results show that the robot can walk forward and correct the walking directions.
In cloud manufacturing systems, fault diagnosis is essential for ensuring stable manufacturing processes. The most crucial performance indicators of fault diagnosis models are generalization and accuracy. An urgent problem is the lack and imbalance of fault data. To address this issue, most of existing approaches demand the label of faults as priori knowledge and require extensive target fault data. These approaches may also ignore the heterogeneity of various equipment. We propose a cloud-edge collaborative method for adaptive fault diagnosis with label sampling space enlarging, named LM-CNN, in cloud manufacturing. First, a multi-attribute cooperative representation-based fault label sampling space enlarging approach is proposed to extend the variety of diagnosable faults. Besides, a multi-input multi-output data augmentation method with label-coupling weighted sampling is developed. In addition, a cloud-edge collaborative adaptation approach for fault diagnosis for scene-specific equipment in cloud manufacturing system is proposed. Experiments demonstrate the effectiveness and accuracy of our method.
Background Whether early fluid accumulation is a risk factor for adverse renal outcomes in septic intensive care unit (ICU) patients remains uncertain. We assessed the association between cumulative fluid balance and major adverse kidney events within 30 days (MAKE30), a composite of death, dialysis, or sustained renal dysfunction, in such patients. Methods We performed a multicenter, retrospective observational study in 1834 septic patients admitted to five ICUs in three hospitals in Stockholm, Sweden. We used logistic regression analysis to assess the association between cumulative fluid balance during the first two days in ICU and subsequent risk of MAKE30, adjusted for demographic factors, comorbidities, baseline creatinine, illness severity variables, haemodynamic characteristics, chloride exposure and nephrotoxic drug exposure. We assessed the strength of significant exposure variables using a relative importance analysis. Results Overall, 519 (28.3%) patients developed MAKE30. Median (IQR) cumulative fluid balance was 5.3 (2.8–8.1) l in the MAKE30 group and 4.1 (1.9–6.8) l in the no MAKE30 group, with non-resuscitation fluids contributing to approximately half of total fluid input in each group. The adjusted odds ratio for MAKE30 was 1.05 (95% CI 1.02–1.09) per litre cumulative fluid balance. On relative importance analysis, the strongest factors regarding MAKE30 were, in decreasing order, baseline creatinine, cumulative fluid balance, and age. In the secondary outcome analysis, the adjusted odds ratio for dialysis or sustained renal dysfunction was 1.06 (95% CI 1.01–1.11) per litre cumulative fluid balance. On separate sensitivity analyses, lower urine output and early acute kidney injury, respectively, were independently associated with MAKE30, whereas higher fluid input was not. Conclusions In ICU patients with sepsis, a higher cumulative fluid balance after 2 days in ICU was associated with subsequent development of major adverse kidney events within 30 days, including death, renal replacement requirement, or persistent renal dysfunction.
Water inrush is one of the most dangerous disasters in coal mining. Due to the large-scale mining and complicated hydrogeological conditions, thousands of deaths and huge economic losses have been caused by water inrush disasters in China. There are two main factors determining the occurrence of water inrush: water source and water-conducting pathway. Research on the formation mechanism of the water-conducting pathway is the main direction to prevent and control the water inrush, and the seepage mechanism of rock mass during the formation of the water-conducting pathway is the key for the research on the water inrush mechanism. This paper provides a state-of-the-art review of seepage mechanisms during water inrush from three aspects, i.e., mechanisms of stress-seepage coupling, flow regime transformation and rock erosion. Through numerical methods and experimental analysis, the evolution law of stress and seepage fields in the process of water inrush is fully studied; the fluid movement characteristics under different flow regimes are clearly summarized; the law of particle initiation and migration in the process of water inrush is explored, and the effect of rock erosion on hydraulic and mechanical properties of the rock media is also studied. Finally, some limitations of current research are analyzed, and the suggestions for future research on water inrush are proposed in this review.
Triboelectric nanogenerators (TENGs) have potential to achieve energy harvesting and condition monitoring of oils, the “lifeblood” of industry. However, oil absorption on the solid surfaces is a great challenge for oil–solid TENG (O-TENG). Here, oleophobic/superamphiphobic O-TENGs are achieved via engineering of solid surface wetting properties. The designed O-TENG can generate an excellent electricity (with a charge density of 9.1 µC m ⁻² and a power density of 1.23 mW m ⁻² ), which is an order of magnitude higher than other O-TENGs made from polytetrafluoroethylene and polyimide. It also has a significant durability (30,000 cycles) and can power a digital thermometer for self-powered sensor applications. Further, a superhigh-sensitivity O-TENG monitoring system is successfully developed for real-time detecting particle/water contaminants in oils. The O-TENG can detect particle contaminants at least down to 0.01 wt% and water contaminants down to 100 ppm, which are much better than previous online monitoring methods (particle > 0.1 wt%; water > 1000 ppm). More interesting, the developed O-TENG can also distinguish water from other contaminants, which means the developed O-TENG has a highly water-selective performance. This work provides an ideal strategy for enhancing the output and durability of TENGs for oil–solid contact and opens new intelligent pathways for oil–solid energy harvesting and oil condition monitoring.
Electrochemical behaviour and passive film characteristics of an ultra-thin 316L foil with a thickness of 20 μm in 3.5 wt.% NaCl solution were investigated using multiple techniques, focusing on the effect of microstructure, the applied potential, and the pH of the solution. The microstructure contains mainly fine grains (∼4 μm) with high-angle boundaries and preferential orientation of (220), and no MnS inclusion was detected. The electrochemical measurements show a significantly higher breakdown potential and lower passive current density for the 316L foil than traditional wrought 316L. The surface analyses using angle-resolved X-ray photoelectron spectroscopy (ARXPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) reveal that, compared to the wrought material, both the inner and out parts of the passive film on the 316L foil are more enriched in Cr- and Mo-oxides. The microstructure favourable for elemental diffusion and the absence of MnS inclusion facilitate the formation of a continuous compact Cr- and Mo-rich passive film, which effectively retards corrosion in NaCl solution and remains stable in acidic solution (pH 2) or at high polarised potential up to 600 mV vs Ag/AgCl.
Capacitive mixing (CapMix) is a renewable method of extracting energy from the salinity difference between seawater and freshwater. In this study, we systematically investigate the system behavior and performance of the CapMix system under four operational modes namely, capacitive energy extraction based on double layer expansion (CDLE), capacitive energy extraction based on the Donnan potential (CDP), and CDP with additional charging of constant voltage (CDP-CV) and constant current (CDP-CC). The results indicate that the application of additional charging in the CDP technique can break the limits of the Donnan potential and significantly improve the system’s performance. Accordingly, in terms of energy production and average power density, CDP-CC and CDP-CV are the two superior operational modes, followed by CDP and CDLE. In addition, our results reveal that CDP-CC is determined by the accumulated charge and applied current. CDLE is dependent on the applied voltage, while CDP-CV is not sensitive to the applied voltage. Increasing the external load can considerably increase the energy production of both CDLE and CDP. In summary, the findings in this study provide practical information for the optimization and application of CapMix technologies.
Potassium and sodium compounds play both positive and negative roles during biomass gasification, but the detailed behavior of alkali metal compounds remain incompletely understood. In this study, alkali release during CO 2 gasification of biochar is characterized online with a surface ionization method in combination with ther-mogravimetric analysis of the char samples undergoing gasification. For wood chars, the alkali release rate follows a slowly decreasing trend as the char conversion proceeds, but increases by up to two orders of magnitude when the conversion approaches completion. In contrast, the alkali release from straw char is 40-50 times higher than observed for wood char and decreases continuously during the whole gasification process. A high temperature and a high CO 2 concentration enhance both alkali release and char reactivity. The char preparation method also influences the alkali release from pine char, while the char reactivity is less affected. Alkali release and char reactivity are linked, but other factors including mineral content, surface area and char structure may play important roles for the observed reactivity. The results provide a basis for understanding of alkali behavior during gasification and may help optimize catalytic effects and reduce detrimental issues in biomass gasification.
A liquid metal layer heated from bottom and cooled from both side and top can be encountered in industrial applications. A special interest is from safety design of advanced pressurized water reactors that adopt the so-called in-vessel melt retention (IVR) to mitigate severe accident risk. Quantification of heat transfer in a stratified melt pool in the lower head of a reactor pressure vessel (RPV) is of great importance to the qualification of the IVR strategy. The upper liquid metal layer of the stratified melt pool is heated by the lower molten oxide layer (with decay heat) underneath, and cooled by water outside the reactor vessel and by radiation or flooded water at the top. This is essentially a problem of natural convection and heat transfer in a liquid metal layer heated from bottom and cooled from both side and top. The present study is conducted to numerically investigate the heat transfer characteristics of such layer with an emphasis on the influence of the aspect ratio (ratio of radius to height; R/H) of the liquid metal layer. Based on the numerical outcomes, three correlations of heat transfer coefficients (for downward, upward and sideward flows) are also developed to account for the impact the aspect ratio. The numerical simulation results show that, under the same Rayleigh number, the bulk temperature and the upward and sideward heat fluxes all increase with R/H, but the downward heat flux decreases with R/H. The Nusselt numbers in all directions decrease with increasing R/H, as a reduced cooling-heating area ratio due to increasing R/H shall suppress the cooling efficiency and the convection. When R/H is larger than a threshold (∼8), the heat transfer characteristics are no longer sensitive to R/H. Each correlation of heat transfer coefficient is developed as the product of two terms: a base correlation of heat transfer coefficient that is Ra dependent only, and an aspect ratio factor that considers the effect of aspect ratio R/H. The developed correlations are compared with the numerical simulation results of cases with different aspect ratios and Rayleigh numbers, and good agreements achieved.
The growing prominence of electric vehicle (EV) aggregators in the modern power system is drawing more attention towards modeling their behavior in the short-term electricity markets. The demand-side flexibility offered by the EVs can be leveraged to reduce their charging costs. In this paper, the participation of an EV aggregator in the intraday and balancing market is modeled as a multistage stochastic programming problem. The computational complexity introduced by the peculiarities of the intraday market is solved by a progressive hedging algorithm (PHA), a scenario-based decomposition technique. A randomized scenario sampling approach is implemented to accelerate the PHA which is further improved with a parallel randomized PHA. Finally, an asynchronous version of the parallel randomized PHA is leveraged to speed up the multistage model of EV aggregator trading. We compare the computation time of the modified versions of the PHA algorithm with the conventional PHA for the proposed EV aggregator model. Furthermore, we also show the value of EV aggregator trading in the intraday and balancing markets by comparing its cost to baseline models.
In this paper we study vector-valued almost minimizers of the energy functional∫D(|∇u|2+2|u|)dx. We establish the regularity for both minimizers and the “regular” part of the free boundary. The analysis of the free boundary is based on Weiss-type monotonicity formula and the epiperimetric inequality for the energy minimizers.
Sensor type (accelerometers only versus inertial measurement units, IMUs) and angular velocity computational method (inclination versus generalized velocity) have been shown to affect the measurements of arm and trunk movements. This study developed models for conversions between accelerometer and IMU measurements of arm and trunk inclination and between accelerometer and IMU measurements of inclination and generalized (arm) velocities. Full-workday recordings from accelerometers and IMUs of arm and trunk postures and movements from 38 warehouse workers were used to develop 4 angular (posture) and 24 angular velocity (movement) conversion models for the distributions of the data. A power function with one coefficient and one exponent was used, and it correlated well (r² > 0.999) in all cases to the average curves comparing one measurement with another. These conversion models facilitate the comparison and merging of measurements of arm and trunk movements collected using the two sensor types and the two computational methods.
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12,273 members
Boualem Djehiche
  • Department of Mathematics (SCI-MAT)
Sanjiv Kumar
  • Department of Chemistry
Thomas Crouzier
  • Division of Glycoscience
Prosun Bhattacharya
  • Department of Sustainable Development, Environmental Sciences and Engineering (SEED)
KTH, Stockholm, Sweden