| 1. |
- Gorelik, Leonid, 1952, et al.
(författare)
-
Suppression of thermal fluctuations of nanomechanical resonator (ground state cooling) by thermally activated electronic flow
- 2011
-
Ingår i: 21st International Conference on Noise and Fluctuations, ICNF 2011; Toronto, ON; 12 June 2011 through 16 June 2011. - 9781457701924 ; , s. 223-226
-
Konferensbidrag (refereegranskat)abstract
- We consider a doubly clamped suspended metallic carbon nanotube in which extra charge is injected from the tipof a scanning tunneling microscopy (STM). Our analysis shows that the quantum superposition between the different inelastic electronic tunneling paths can be controlled by the bias voltage. In particular, we find that below Coulomb blockade threshold the vibron emission induced by thermally activated electron transportation can be significantly reduced in comparison to the vibron absorption. As a consequence a net suppression of the thermal fluctuations ("cooling") of the vibrational degrees of freedom can be achieved. © 2011 IEEE.
|
|
| 2. |
|
|
| 3. |
- Jonsson, Magnus, 1979, et al.
(författare)
-
Self-organization of irregular nanoelectromechanical vibrations in multimode shuttle structures
- 2008
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 100:18
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate theoretically multimode electromechanical "shuttle" instabilities in dc voltage-biased nanoelectromechanical single-electron tunneling devices. We show that initially irregular (quasiperiodic) oscillations that occur as a result of the simultaneous self-excitation of several mechanical modes with incommensurable frequencies self-organize into periodic oscillations with a frequency corresponding to the eigenfrequency of one of the unstable modes. This effect demonstrates that a local probe can selectively excite global vibrations of extended objects.
|
|
| 4. |
- Larsson Ivanov, Oskar, et al.
(författare)
-
Consideration of uncertainties in LCA for infrastructure using probabilistic methods
- 2019
-
Ingår i: Structure and Infrastructure Engineering. - : Informa UK Limited. - 1573-2479 .- 1744-8980. ; 15:6, s. 711-724
-
Tidskriftsartikel (refereegranskat)abstract
- The construction and usage of transport infrastructure are major causes of greenhouse gas emissions and energy consumption. The effects of resource consumption and pollutant emissions are often quantified through Life Cycle Assessment (LCA) models. All decisions made in infrastructure projects during the whole life cycle are afflicted by uncertainty, e.g. physical properties of materials or amount of pollutants emitted by certain processes. The pervasive role of uncertainty is reflected in LCA models, which therefore should consider uncertainty from various sources and provide a sound quantification of their effects. The aim of the work presented in this paper is to give an overview of different sources of uncertainty in LCA of infrastructure projects and to describe systematic methods to evaluate their influence on the results. The possibility of including uncertainty in a LCA-tool for infrastructure is presented, studying the sensitivity of the model output to the input parameters and two alternative approaches for propagation of uncertainty using two case studies. It is shown that, besides the influence of uncertainty in emission factors, other inputs such as material amounts and service life could contribute significantly to the variability of model output and has to be considered if reliable results are sought.
|
|
| 5. |
- Larsson Ivanov, Oskar, et al.
(författare)
-
Prolca—treatment of uncertainty in infrastructure LCA
- 2019
-
Ingår i: Life-Cycle Analysis and Assessment in Civil Engineering. - : CRC Press/Balkema. - 9781138626331 - 9781351857574 ; , s. 2923-2930
-
Konferensbidrag (refereegranskat)abstract
- The construction, operation and maintenance of transportation infrastructure require energy and materials which impact the environment. Large infrastructure projects thus use resources intensively and leave a significant environmental footprint. To demonstrate and support the sustainability of such large-scale projects, life cycle assessment (LCA) has become a common tool to evaluate environmental impacts in all stages of infrastructure life cycle, from raw material production through end-of-life management. However, the various phases of the assessment are all associated with uncertainties. If decisions are made without consideration of these uncertainties, they might be misleading and suboptimal. In this paper, results are presentedwhere variations associated with different parameters and tools for life cycle assessment have been considered using probabilistic methods. A categorization of common uncertainties in LCA is also included. The most influential parameters can be identified with sensitivity analysis methods, since for LCA with a large number of parameters it may be unreasonable to incorporate all in a probabilistic simulation. For a limited amount of influential variables, Monte Carlo simulation has been used to assess the effects of uncertainties on the results.A bridge has been used as a case study to find important aspects in infrastructure LCA. The results indicate that if the most influential parameters are considered as random variables, it is possible to estimate the uncertainty and increase the validity of the life cycle assessment.
|
|
| 6. |
- Pettersson, Pär, 1985, et al.
(författare)
-
A proposal for an operating cycle description format for road transport missions
- 2018
-
Ingår i: European Transport Research Review. - : Springer Science and Business Media LLC. - 1867-0717 .- 1866-8887. ; 10:2
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: This article presents a proposal for an operating cycle format for describing transport missions of road vehicles, for example a logging truck fetching its cargo. The primary application is in dynamic simulation models for evaluation of energy consumption and other costs of transportation. When applied to product development, the objective is an ensemble of components and functions optimised for specific tasks and environments. When applied to selection of vehicle configuration, the objective is a vehicle specification tailored for its task. Method: The proposal is presented and its four main parts: road, weather, traffic and mission, are thoroughly explained. Furthermore, we implement the proposal in an example of a dynamic forward simulation model. Results: The example model is used for two case studies: a synthetic example of a complex transport mission (a logging truck fetching its cargo) that shows some advanced format features, and an example from a real vehicle log file (cargo transport) that seeks to compare the resulting simulated speed profile to the measured one. Conclusion: The results show that the proposed format works in practice. It can represent complex transport missions and it can be used to reproduce the main features of a logged speed profile even when combined with simple driver and vehicle models.
|
|
| 7. |
- Prieto Rábade, Miguel, et al.
(författare)
-
Tillstånd- och konsekvensbaserad livslängdsbedömning av betongkonstruktioner för dricksvatten
- 2023
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In Sweden, there are many assets for drinking water such as water towers, water treatment plants and pipes. Many of these structures are made of reinforced concrete and were built between 1950 – 1970. The normal design life of these structures is 50 years meaning that they are reaching their intended design lifespan. In addition, these structures face harsh environments that can lead to degradation. All these leads to the need of repair and renovation of these specifics assets. For that purpose, methodologies and tools for performing inspections, assessing the condition and the time to intervention are needed. Nowadays, in general the procedures for condition assessment are based on the judgement and expertise of engineers performing the inspection. In this project a compilation of best practices for performing the condition assessment for drinking water structures has been performed. This assessment should include an ocular inspection of the object, documentation, tests to ensure certain parameters and an overall analysis of the assessment of the object and finally provide a proposal for measures. The measures must be designed so that both the method and the time aspect are specified. In addition, in this project a methodology and a simplified tool has been developed to accommodate the condition assessment of reinforced concrete drinking water infrastructures and the time to intervention after the assessment. The tool also includes the uncertainty analysis of the condition assessment performed.
|
|
| 8. |
- Santandrea, Fabio, 1981, et al.
(författare)
-
Cooling of Nanomechanical Resonators by Thermally Activated Single-Electron Transport
- 2011
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 106:18
-
Tidskriftsartikel (refereegranskat)abstract
- We show that the vibrations of a nanomechanical resonator can be cooled to near its quantum ground state by tunneling injection of electrons from a scanning tunneling microscope tip. The interplay between two mechanisms for coupling the electronic and mechanical degrees of freedom results in a bias-voltage-dependent difference between the probability amplitudes for vibron emission and absorption during tunneling. For a bias voltage just below the Coulomb blockade threshold, we find that absorption dominates, which leads to cooling corresponding to an average vibron population of the fundamental bending mode of 0.2.
|
|
| 9. |
- Santandrea, Fabio, 1981
(författare)
-
Electromechanical Instability in Suspended Nanowire-Based NEMS
- 2009
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- "Nanoelectromechanical systems'' (NEMS) are a class of nanometer-sized mechanical structures coupled to electronic device of comparable dimensions. Their peculiar features make them interesting both from the technological and fundamental research viewpoints. The dynamics of the movable part of these devices is affected on the conditions at which electric charge is transferred across them and vice versa, therefore NEMS offer the ideal playground to investigate the physical effects which originate from coupling mechanical and electronic degrees of freedom at the nanoscale. In this thesis I describe the properties of one of such effects, i.e. the electromechanical instability that can take place in a DC-biased suspended doubly clamped carbon nanotube in which extra charge is locally injected through the tip of a scanning tunneling microscope (STM). The sequence of tunneling events makes the charge state of the nanotube vary in time and accordingly the force exerted on it by the electrostatic field (which is created by the bias voltage) changes in time and can induce mechanical vibrations in the nanotube. Furthermore, the probability of electron tunneling between the tip of the STM and the nanotube depends on the distance between them, hence a coupling between the mechanical and electronic degrees of freedom of the system is established. The analysis described in this thesis indicates that if the energy pumped into the nanotube by the electrostatic field is sufficient to overcome the energy lost because of dissipative processes, the static equilibrium configuration of the nanotube becomes unstable. The onset of the electromechanical instability implies that initially quasi-periodic oscillations (to which all the unstable modes contribute) self-organize into periodic oscillations with a frequency corresponding to the eigenfrequency of one of the unstable modes. Furthermore, the results presented here suggests the possibility to selectively excite the transverse vibrational modes of the nanotube by optimizing their coupling to the electrostatic field through the positioning of the STM tip. This effect could provide the basic physical mechanism for a feasible procedure to control the dynamics of NEMS.
|
|
| 10. |
- Santandrea, Fabio, 1981
(författare)
-
Electronic Control of Flexural Nanowire Vibrations
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- “Nanoelectromechanical systems” (NEMS) are nanometer-sized mechanical structures coupled to electronic devices of comparable size. The coupling between mechanical and electronic degrees of freedom, combined with their mesoscopic size, provide these systemswith some unique properties that make them interesting from both the fundamental and technological point of view. In this thesis, we present theoretical work about a specific kind of NEMS, that is a suspended doubly clamped carbon nanotube in which extra charge is locally injected through the DC voltage-biased tip of a scanning tunneling microscope (STM). The analysis presented here indicates that, in the classical regime, under the conditions of weak dissipation or sufficiently strong electromechanical coupling, the equilibrium configuration of the suspended nanotube becomes unstable and the system evolves towards a state of self-sustained periodic oscillations that is reminescent of the single-electron “shuttle” regime in Coulomb blockade nanostructures. Furthermore, combining the conditions for the onset of the electromechanical instability with the local character of the charge injection provided by the STM, it seems possible to generate a selective excitation of the bending vibrational modes of the nanotube. Instead of pumping energy into the suspended nanotube, the electromechanical coupling can be also exploited to remove energy from it. Even though the tunneling electrons represent a strongly nonequilibrium environment interacting with the mechanical subsystem, the analysis presented in this thesis shows that the dynamics of the nanotube in the regime ofweak coupling is formally equivalent to that one of a quantum harmonic oscillator coupled to an equilibrium thermal bath characterized by an effective temperature that can be much lower than the environmental (i.e. thermodynamic) temperature. This nonequilibrium cooling effect studied here has an intrinsic quantum mechanical nature, since it is based on the (bias voltage controlled-) destructive interference between the probability amplitudes associated to those inelastic tunneling processes characterized by the emission of quantized vibrational excitations. When the transport of charge is thermally activated, this mechanism provides a simple procedure to drive the oscillating nanotube to nearly its quantum ground state.
|
|
