| 1. |
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| 2. |
- Waltersson, Erik, 1979-, et al.
(author)
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Controlled operations in a strongly correlated two-electron quantum ring
- 2009
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 79:11, s. 115318-
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Journal article (peer-reviewed)abstract
- We have analyzed the electronic spectrum and wave-function characteristics of a strongly correlated two-electron quantum ring with model parameters close to those observed in experiments. The analysis is based on an exact diagonalization of the Hamiltonian in a large B-spline basis. We propose a qubit pair for storing quantum information, where one component is stored in the total electron spin and one multivalued “quMbit” is represented by the total angular momentum. In this scheme the controlled-NOT quantum gate is demonstrated with near 100% fidelity for a realistic far-infrared electromagnetic pulse.
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| 3. |
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| 4. |
- Mamontov, Eugen, 1955
(author)
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Ordinary differential equation system for population of individuals and the corresponding probabilistic model
- 2008
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In: Mathl. Computer Modelling. - : Elsevier BV. - 0895-7177.
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Journal article (peer-reviewed)abstract
- The key model for particle populations in statistical mechanics is the Bogolyubov–Born– Green–Kirkwood–Yvon (BBGKY) equation chain. It is derived mainly from the Hamilton ordinary differential equation (ODE) system for the vectors of the particle states in the particle position-momentum phase space. Many problems beyond physics or chemistry, for instance, in the living-matter sciences (biology, medicine, ecology, and scoiology) make it necessary to extend the notion of a particle to an individual, or active particle. This challenge is met by the generalized kinetic theory. It implements the extension by extending the phase space from the space of the position-momentum vectors to more rich spaces formed by the state vectors with the entries which need not be limited to the entries of the position and momentum: they include other scalar variables (e.g., those associated with modelling homeorhesis or other features inherent to the individuals). One can assume that the dynamics of the state vector in the extended space, i.e. the states of the individuals (rather than common particles) is also described by an ODE system. The latter, however, need not be the Hamilton one. The question is how one can derive the analogue of the BBGKY paradigm for the new settings. The present work proposes an answer to this question. It applies a very limited number of carefully selected tools of probability theory and common statistical mechanics. It in particular uses the well-known feature that the maximum number of the individuals which can mutually interact simultaneously is bounded by a fixed value of a few units. The present approach results in the finite system of equations for the reduced many-individual distribution functions thereby eliminating the so-called closure problem inevitable in the BBGKY theory. The thermodynamic-limit assumption is not needed either. The system includes consistently derived terms of all of the basic types known in kinetic theory, in particular, both the “mean-field” and scattering-integral terms, and admits the kinetic equation of the form allowing a direct chemical-reaction reading. The present approach can deal with Hamilton’s equation systems which are nonmonogenic and not treated in statistical mechanics. The proposed modelling suggests the basis of the generalized kinetic theory and may serve as the stochastic mechanics of population of individuals.
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| 5. |
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| 6. |
- Mårtensson-Pendrill, Ann-Marie, 1952
(author)
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The Manhattan Project - a part of physics history
- 2006
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In: Physics Education. - 0031-9120. ; 41:6, s. 493-501
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Journal article (peer-reviewed)abstract
- Current physics textbooks tend to exclude military applications, but it is explained here how a study of the Manhattan project—the devastatingly successful attempt to develop an atomic bomb—can show students how the lives and work of physicists are shaped by events in society. Much of the original source material is available in books and on the internet (and referenced here), which allows students to discover the views of the scientists for themselves.
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| 7. |
- Giangreco Marotta Puletti, Valentina, 1980-
(author)
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On string integrability : A journey through the two-dimensional hidden symmetries in the AdS/CFT dualities
- 2009
-
Doctoral thesis (other academic/artistic)abstract
- One of the main topics in the modern String Theory are the conjectured string/gauge (AdS/CFT) dualities. Proving such conjectures is extremely difficult since the gauge and string theory perturbative regimes do not overlap. In this perspective, the discovery of infinitely many conserved charges, i.e. the integrability, in the planar AdS/CFT has allowed us to reach immense progresses in understanding and confirming the duality.The first part of this thesis is focused on the gravity side of the AdS5/CFT4 duality: we investigate the quantum integrability of the type IIB superstring on AdS5 x S5. In the pure spinor formulation we analyze the operator algebra by computing the operator product expansion of the Maurer-Cartan currents at the leading order in perturbation theory. With the same approach at one loop order, we show the path-independence of the monodromy matrix which implies the charge conservation law, strongly supporting the quantum integrability of the string sigma-model. We also verify that the Lax pair field strength remains well-defined at one-loop order being free from UV divergences. The same string sigma-model is analyzed in the Green-Schwarz formalism in the near-flat-space (NFS) limit. Such a limit remarkably simplifies the string world-sheet action but still leaving interesting physics. We use the NFS truncation to show the factorization of the world-sheet S-matrix at one-loop order. This property defines a two-dimensional field theory as integrable: it is the manifestation of the higher conserved charges. Hence, we have explicitly checked their presence at quantum level. The second part is dedicated to the AdS4/CFT3 duality: in particular the type IIA superstring on AdS4 x CP3. We compute the leading quantum corrections to the string energies for string configurations with a large but yet finite angular momentum on CP3 and show that they match the conjectured all-loop Bethe Ansatz equations.
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| 8. |
- Hollmark, Malin, et al.
(author)
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Analytical model for light ion pencil beam dose distributions: multiple scattering of primary and secondary ions
- 2008
-
In: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 53:13, s. 3477-3491
-
Journal article (peer-reviewed)abstract
- An analytical algorithm based on the generalized Fermi–Eyges theory, amended for multiple Coulomb scattering and energy loss straggling, is used for calculation of the dose distribution of light ion beams in water. Pencil beam energy deposition distributions are derived for light ions by weighting a Monte Carlo (MC) calculated planar integral dose distribution with analytically calculated multiple scattering and range straggling distributions. The planar integral dose distributions are calculated using the MC code SHIELD-HIT07, in which multiple scattering and energy loss straggling processes are excluded. The contribution from nuclear reactions is included in the MC calculations. Multiple scattering processes are calculated separately for primary and secondary ions and parameters of the initial angular and radial spreads, and the covariance of these are derived by a least-square parameterization of the SHIELD-HIT07 data. The results from this analytical algorithm are compared to pencil beam dose distributions obtained from SHIELD-HIT07, where all processes are included, as well as to experimental data. The presented analytical approach allows for the accurate calculation of the spatial energy deposition distributions of ions of atomic numbers Z = 1 − 8.
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| 9. |
- Grönbeck, Henrik, 1966, et al.
(author)
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Ab initio molecular dynamics calculations of H2O on BaO(001)
- 2008
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In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 77:24, s. 245419-
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Journal article (peer-reviewed)abstract
- Density functional theory calculations are used to explore water adsorption on BaO(001). The stable configuration is found to be a novel hydroxide pair. A detailed analysis demonstrates that the electrostatic repulsion between the OH− species is screened by Ba2+ cations and that the net interaction is provided by hydrogen bonding. Ab initio molecular dynamics at low coverage reveals that the pair is stable at elevated temperatures. The large structural flexibility of the hydoxylated surface may, however, lead to pair dissociation at high coverage. Simulations of a mixed (H2O+OH) overlayer uncover proton transfer between H2O and OH groups.
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| 10. |
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| 11. |
- Höök, Mikael, 1982-
(author)
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Depletion and decline curve analysis in crude oil production
- 2009
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Licentiate thesis (other academic/artistic)abstract
- Oil is the black blood that runs through the veins of the modern global energy system. While being the dominant source of energy, oil has also brought wealth and power to the western world. Future supply for oil is unsure or even expected to decrease due to limitations imposed by peak oil. Energy is fundamental to all parts of society. The enormous growth and development of society in the last two-hundred years has been driven by rapid increase in the extraction of fossil fuels. In the foresee-able future, the majority of energy will still come from fossil fuels. Consequently, reliable methods for forecasting their production, especially crude oil, are crucial. Forecasting crude oil production can be done in many different ways, but in order to provide realistic outlooks, one must be mindful of the physical laws that affect extraction of hydrocarbons from a reser-voir. Decline curve analysis is a long established tool for developing future outlooks for oil production from an individual well or an entire oilfield. Depletion has a fundamental role in the extraction of finite resources and is one of the driving mechanisms for oil flows within a reservoir. Depletion rate also can be connected to decline curves. Consequently, depletion analysis is a useful tool for analysis and forecasting crude oil production. Based on comprehensive databases with reserve and production data for hundreds of oil fields, it has been possible to identify typical behaviours and properties. Using a combination of depletion and decline rate analysis gives a better tool for describing future oil production on a field-by-field level. Reliable and reasonable forecasts are essential for planning and nec-essary in order to understand likely future world oil production.
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| 12. |
- Ingerman, Åke, 1973, et al.
(author)
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The learners’ experience of variation : Following students’ threads of learning physics in computer simulation sessions
- 2009
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In: Instructional science. - : Springer Science and Business Media LLC. - 0020-4277 .- 1573-1952. ; 37:3, s. 273-292
-
Journal article (peer-reviewed)abstract
- This article attempts to describe students' process of learning physics using the notion of experiencing variation as the basic mechanism for learning, and thus explores what variation, with respect to a particular object of learning, that students experience in their process of constituting understanding. Theoretically, the analysis relies on analytic tools from the phenomenographic research tradition, and the recent group of studies colloquially known as the variation theory of learning, having the notion of experiencing variation as a key for learning at its core. Empirically, the study relies on video and audio recordings of seven pairs of students interacting in a computer-simulation learning environment featuring Bohr's model of the atom. The data was analysed on a micro-level for the emergence of student-recognised variation, depicted in terms of 'threads of learning'. This was done by linking variation around aspects of the object of learning present in the situation, and attended to by the students, to new ways of seeing-characterised as an expanding anatomy of awareness, and hence as learning. The students' threads of learning are characterised in terms of two stages of learning progress: (1) discerning variation, and (2) constituting meaning from this experience of variation (experienced as holistically relevant in the students' conceptual domain of physics and the Bohr model). Two groups of threads of learning were identified: one where the variation experienced by students was within an aspect of the object of learning, and one where variation was across several aspects.
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| 13. |
- Airey, John, et al.
(author)
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Bilingual Scientific Literacy...
- 2008
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In: Paper presented at Canadian Society for the Study of Education Conference 31 May-3 June 2008, University of British Columbia.
-
Conference paper (peer-reviewed)
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| 14. |
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| 15. |
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| 16. |
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| 17. |
- Baek, Seung Ki, 1979-, et al.
(author)
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Curvature-induced frustration in the XY model on hyperbolic surfaces
- 2009
-
In: Physical Review E - Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755. ; 79:6, s. 060106(R)-
-
Journal article (peer-reviewed)abstract
- We study low-temperature properties of the XY spin model on a negatively curved surface. Geometric curvature of the surface gives rise to frustration in local spin configuration, which results in the formation of high-energy spin clusters scattered over the system. Asymptotic behavior of the spin-glass susceptibility suggests a zero-temperature glass transition, which is attributed to multiple optimal configurations of spin clusters due to nonzero surface curvature of the system. It implies that a constant ferromagnetic spin interaction on a regular lattice can exhibit glasslike behavior without possessing any disorder if the lattice is put on top of a negatively curved space such as a hyperbolic surface.
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| 18. |
- Evaldsson, Martin, 1977-
(author)
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Quantum transport and spin effects in lateral semiconductor nanostructures and graphene
- 2008
-
Doctoral thesis (other academic/artistic)abstract
- This thesis studies electron spin phenomena in lateral semi-conductor quantum dots/anti-dots and electron conductance in graphene nanoribbons by numerical modelling. In paper I we have investigated spin-dependent transport through open quantum dots, i.e., dots strongly coupled to their leads, within the Hubbard model. Results in this model were found consistent with experimental data and suggest that spin-degeneracy is lifted inside the dot – even at zero magnetic field.Similar systems were also studied with electron-electron effects incorporated via Density Functional Theory (DFT) in the Local Spin Density Approximation (LSDA) in paper II and III. In paper II we found a significant spin-polarisation in the dot at low electron densities. As the electron density increases the spin polarisation in the dot gradually diminishes. These findings are consistent with available experimental observations. Notably, the polarisation is qualitatively different from the one found in the Hubbard model.Paper III investigates spin polarisation in a quantum wire with a realistic external potential due to split gates and a random distribution of charged donors. At low electron densities we recover spin polarisation and a metalinsulator transition when electrons are localised to electron lakes due to ragged potential profile from the donors. In paper IV we propose a spin-filter device based on resonant backscattering of edge states against a quantum anti-dot embedded in a quantum wire. A magnetic field is applied and the spin up/spin down states are separated through Zeeman splitting. Their respective resonant states may be tuned so that the device can be used to filter either spin in a controlled way.Paper V analyses the details of low energy electron transport through a magnetic barrier in a quantum wire. At sufficiently large magnetisation of the barrier the conductance is pinched off completely. Furthermore, if the barrier is sharp we find a resonant reflection close to the pinch off point. This feature is due to interference between a propagating edge state and quasibond state inside the magnetic barrier.Paper VI adapts an efficient numerical method for computing the surface Green’s function in photonic crystals to graphene nanoribbons (GNR). The method is used to investigate magnetic barriers in GNR. In contrast to quantum wires, magnetic barriers in GNRs cannot pinch-off the lowest propagating state. The method is further applied to study edge dislocation defects for realistically sized GNRs in paper VII. In this study we conclude that even modest edge dislocations are sufficient to explain both the energy gap in narrow GNRs, and the lack of dependance on the edge structure for electronic properties in the GNRs.
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| 19. |
- Alegret, Joan, 1977
(author)
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Numerical Simulations of Plasmonic Nanostructures
- 2008
-
Doctoral thesis (other academic/artistic)abstract
- This thesis focuses on the study of metallic nanostructures that support plasmons. Special emphasis is devoted to two specific numerical methods that allow us to predict plasmon characteristics: the discrete dipole approximation (DDA) and the Green's tensor (GT) method.DDA is an approximate method that produces fast and accurate results, but it can only be applied to systems in which the nanostructure is situated in a homogeneous background. In this thesis, DDA has been applied to predict the field enhancement and field decay around nano-rings, showing that the structure is well suited for biosensing; to obtain the spectral characteristics of silver trimers, showing that the actual plasmon modes are closely related to symmetry-adapted coordinates derived from group-theory; and to calculate the optical forces between two spherical particles illuminated by a plane wave, showing that the illumination wavelength determines the separation between the particles.The GT method, on the other hand, is an exact method, in the sense that the system can be solved to arbitrary precision depending on the size of the discretization elements. Its major drawback is the long time it takes to perform the calculations. To tis end, this thesis introduces a novel algorithm, called the top-down extended meshing algorithm (TEMA), that speeds up GT calculations by reducing the number of elements in the discretization process. This decreases the total time needed to perform the calculations, while keeping the precision of the result essentially unaltered. The GT method with TEMA meshes has successfully been used to study single holes of different sizes and shapes (circular and ellipsoidal) in the near- and far-field regime, as well as hole pairs as a function of their separation distance. The results compare very well with experiments, demonstration that the GT method is well suited for predicting the behavior of nano-holes.
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| 20. |
- Yu, Yongle, et al.
(author)
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Supershell structure in trapped dilute Fermi gases
- 2005
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 72:5
-
Journal article (peer-reviewed)abstract
- We show that a dilute harmonically trapped two-component gas of fermionic atoms with a weak repulsive interaction has a pronounced super-shell structure: The shell fillings due to the spherical harmonic trapping potential are modulated by a beat mode. This changes the "magic numbers" occurring between the beat nodes by half a period. The length and amplitude of this beating mode depend on the strength of the interaction. We give a simple interpretation of the beat structure in terms of a semiclassical trace formula for the symmetry breaking U(3)→SO(3).
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| 21. |
- Ögren, Magnus, 1977-, et al.
(author)
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Super-shell structure in harmonically trapped fermionic gases and its semi-classical interpretation
- 2006
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In: Physica Scripta. - : Royal Swedish Academy of Sciences. - 0031-8949 .- 1402-4896. ; :T125, s. 37-40
-
Journal article (peer-reviewed)abstract
- It was recently shown in self-consistent Hartree–Fock calculations that a harmonically trapped dilute gas of fermionic atoms with a repulsive two-body interaction exhibits a pronounced super-shell structure: the shell fillings due to the spherical harmonic trapping potential are modulated by a beat mode. This changes the 'magic numbers' occurring between the beat nodes by half a period. The length and amplitude of the beating mode depends on the strength of the interaction. We give a qualitative interpretation of the beat structure in terms of a semi-classical trace formula that uniformly describes the symmetry breaking U(3) → SO(3) in a three-dimensional harmonic oscillator potential perturbed by an anharmonic term ∝ r 4 with arbitrary strength. We show that at low Fermi energies (or particle numbers), the beating gross-shell structure of this system is dominated solely by the twofold degenerate circular and (diametrically) pendulating orbits.
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| 22. |
- Ögren, Magnus, 1977-, et al.
(author)
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Supershell structures and pairing in ultracold trapped Fermi gases
- 2007
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 76:2
-
Journal article (peer-reviewed)abstract
- We calculate level densities and pairing gaps for an ultracold dilute gas of fermionic atoms in harmonic traps under the influence of mean field and anharmonic quartic trap potentials. Supershell nodes, which were found in Hartree-Fock calculations, are calculated analytically within periodic orbit theory as well as from WKB calculations. For attractive interactions, the underlying level densities are crucial for pairing and supershell structures in gaps are predicted.
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| 23. |
- Görnerup, Olof, 1977
(author)
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Inference of Hierarchical Structure in Complex Systems
- 2008
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Doctoral thesis (other academic/artistic)abstract
- Hierarchical organization is a central property of complex systems. It is even argued that a system is required to be hierarchical in order to evolve complexity within reasonable time. A hierarchy of a system is defined as the set of self-contained levels at which the system operates and can be described on. Given a dynamical system there are only specific levels that are valid. This thesis mainly concerns the definition and inference of such levels. Paper I describes an algorithm for finding hierarchical levels in stochastic processes. The method systematically explores the set of possible partitions of a process' state space and statistically determines which of the partitions that impose closed dynamics. It is applicable to moderately sized systems. In Paper II an alternative approach that applies to linear dynamical systems is presented. In this case the spectral properties of the matrix that defines a system's dynamics is utilized, which allows for analysis of large systems (with on the order of thousand states). The specification and analysis of an algorithm that is based on the results in Paper II is presented in Paper III. Paper IV applies the spectral method and a complementary agglomeration method to infer aggregated dynamics in a Markov model of codon substitutions in DNA. The standard genetic code is identified as a projection that gives the hierarchical level of amino acid substitutions. Further, higher order amino acid groups that are relatively conserved under substitutions are found to define other levels of dynamics. Paper V and VI relate hierarchical organization to primordial evolution in a conceptual model that is based on the RNA world hypothesis. A well-stirred system of processes that catalyze the production of other processes is shown to successively build higher levels of organization from simple and general-purpose components by autocatalysis.
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| 24. |
- Lindén, Martin, et al.
(author)
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Dwell Time Symmetry in Random Walks and Molecular Motors
- 2007
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In: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 92:11, s. 3804-3816
-
Journal article (peer-reviewed)abstract
- The statistics of steps and dwell times in reversible molecular motors differ from those of cycle completion in enzyme kinetics. The reason is that a step is only one of several transitions in the mechanochemical cycle. As a result, theoretical results for cycle completion in enzyme kinetics do not apply to stepping data. To allow correct parameter estimation, and to guide data analysis and experiment design, a theoretical treatment is needed that takes this observation into account. In this article, we model the distribution of dwell times and number of forward and backward steps using first passage processes, based on the assumption that forward and backward steps correspond to different directions of the same transition. We extend recent results for systems with a single cycle and consider the full dwell time distributions as well as models with multiple pathways, detectable substeps, and detachments. Our main results are a symmetry relation for the dwell time distributions in reversible motors, and a relation between certain relative step frequencies and the free energy per cycle. We demonstrate our results by analyzing recent stepping data for a bacterial flagellar motor, and discuss the implications for the efficiency and reversibility of the force-generating subunits.
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| 25. |
- Tsygankov, Denis, et al.
(author)
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Back-stepping, hidden substeps, and conditional dwell times in molecular motors
- 2007
-
In: Physical Review E. - 1539-3755 .- 1550-2376. ; 75:2, s. 021909-1-021909-16
-
Journal article (peer-reviewed)abstract
- Processive molecular motors take more-or-less uniformly sized steps, along spatially periodic tracks, mostly forwards but increasingly backwards under loads. Experimentally, the major steps can be resolved clearly within the noise but one knows biochemically that one or more mechanochemical substeps remain hidden in each enzymatic cycle. In order to properly interpret experimental data for back-to-forward step ratios, mean conditional step-to-step dwell times, etc., a first-passage analysis has been developed that takes account of hidden substeps in N-state sequential models. The explicit, general results differ significantly from previous treatments that identify the observed steps with complete mechanochemical cycles; e.g., the mean dwell times tau(+) and tau(-) prior to forward and back steps, respectively, are normally unequal although the dwell times tau(++) and tau(- -) between successive forward and back steps are equal. Illustrative (N=2)-state examples display a wide range of behavior. The formulation extends to the case of two or more detectable transitions in a multistate cycle with hidden substeps.
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| 26. |
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| 27. |
- Shiu, Jin-Yu, 1978, et al.
(author)
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DC and microwave performance of AlGaN/GaN HEMTs passivated with sputtered SiNx
- 2007
-
In: Semicronductor Science and Technology. ; 22, s. 717-721
-
Journal article (peer-reviewed)abstract
- The effects of sputtered and room temperature plasma enhanced chemical vapour deposition (RT-PECVD) SiNx passivation on the dc and microwave performance of AlGaN/GaN high electron mobility transistors (HEMTs)are studied. The pulsed I–V characteristics from a class B quiescent bias point and transient measurements indicate that the sputtered SiNx passivation is more efficient in suppressing lag effects in AlGaN/GaN HEMTs. Dispersion-free sputtered SiNx passivated AlGaN/GaN HEMTs were obtained using this technique. Continuous-wave (CW) measurements without active cooling give a maximum output power density of 6.6 W mm−1 at Vgs=−4 V, Vds = 50 V and a maximum power added efficiency of 51.3% at Vgs=−4 V, Vds = 30 V at 3 GHz on 2 × 50 μmAlGaN/GaN HEMTs on the sapphire substrate, with a gate length of 2 μm and without field-plated gates. To the best of our knowledge, this is the highest level power density reported on the sapphire substrate without field-plate design. The extrinsic cut-off frequency ( ft) and maximumoscillation frequency ( fmax) are 51 GHz and 100 GHz, respectively, on 2 × 50 × 0.15 μm HEMTs. To our knowledge, the sputtered SiNx passivation for AlGaN/GaN HEMTs is a unique technique, which has never beenpublished before.
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| 28. |
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| 29. |
- Aleksandrovskii, A. N., et al.
(author)
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Thermal expansion of single-crystal fullerite C60 at helium temperatures
- 2000
-
In: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 26:1, s. 75-80
-
Journal article (peer-reviewed)abstract
- The thermal expansion of single-crystal fullerite C60 has been studied in the range of liquid-helium temperatures (2–10 K). At temperatures below ~4.5 K the thermal expansion of fullerite C60 becomes negative, in agreement with the previous results on polycrystalline materials. A qualitative explanation of the results is proposed.
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| 30. |
- Mizielinski, M. S., et al.
(author)
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Electronic nonadiabatic effects in the adsorption of hydrogen atoms on metals
- 2005
-
In: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 122:8
-
Journal article (peer-reviewed)abstract
- The time-dependent, mean-field Newns-Anderson model for a spin-polarized adsorbate approaching a metallic surface is solved in the wide-band limit. Equations for the time evolution of the occupation of the spin dependent adsorbate states and for the nonadiabatic and nearly adiabatic adsorbate-surface energy transfer rates are derived. Numerical solutions are obtained using characteristic parameters derived from density functional theory calculations for the H/Cu(111) system. The time evolution of the model system is shown to be strongly nonadiabatic in the vicinity of the transition point between spin-polarized and nonpolarized ground states. Away from the spin transition the nonadiabatic energy transfer is in close agreement with the nearly adiabatic limit. Near the transition, nonadiabatic effects are large and the nearly adiabatic approximation fails.
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| 31. |
- Wågberg, Thomas, et al.
(author)
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2D polymerization and doping of fullerenes under pressure
- 2000
-
In: High Pressure Research vol. 18. - : Gordon & Breach. ; 18:1-6, s. 139-143
-
Conference paper (peer-reviewed)abstract
- Tetragonal polymeric C60 has been studied by Raman spectroscopy and other methods. Attempts have been made to transform samples from the tetragonal to the orthorhom-bic phase and vice versa. The results suggest that the transformation is direct with no intermediate stage with free molecules. Tetragonal C60 has also been intercalated by potassium metal.
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| 32. |
- Hellberg, Magnus, et al.
(author)
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In situ scanning probe microscopy studies of morphology and growth kinetics in amyloid-peptide fibrillogenesis with custom designed tapping mode and pulsed force mode systems
- 2004
-
In: Proceedings of 5th Nordic-Baltic Scanning Probe Microscopy Workshop. ; , s. 93-95
-
Conference paper (peer-reviewed)abstract
- We have used a commercial Nanoscope II atomic force microscope (AFM) with a custom designedtapping mode (TM) system to in situ monitor amyloid β-peptide aggregation related to Alzheimer’sdisease (AD). The custom tapping mode setup was successfully used to image the real timeaggregation behaviour of the arctic mutation amyloid β-peptide, Aβ(1-40), in vitro in aphysiologically relevant buffer and compare with the behaviour of the normal wild type of theAlzheimer’s amyloid peptide Aβ(1-40) at the same conditions. The investigation revealed distinctdifferences in fibrillogenesis behaviour for the two peptides. Our results demonstrate a previouslysuggested alternative fibrillogenesis pathway, of highly distinct aggregates with orderedmorphology as on-pathway. Moreover, additional investigations using a pulsed force mode (PFM)are under way.
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| 33. |
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| 34. |
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| 35. |
- Hansen, Klavs, 1958, et al.
(author)
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Stability and dissociation pathways of doped AunX+ clusters (X=Y,Er,Nb)
- 2008
-
In: Faraday Discussion. ; 138
-
Journal article (peer-reviewed)abstract
- Size dependent stabilities, fragmentation pathways and dissociation energies of a series of gas phase cationic doped gold clusters, AunX+ (5 < n < 20; X = Y, Er and Nb), and pure Aun+ clusters were investigated in photofragmentation experiments. Size dependent stability patterns were obtained and the branching between monomer and dimer evaporation was studied. For bare gold, the competing neutral monomer and dimer evaporation channels were found in agreement with earlier studies. For doped clusters, monomer evaporation is the most likely fragmentation channel with the exception of Au18Y+ and Au20Y+ for which gold dimer evaporation is also observed. Relations between the evaporative activation energies and both the experimental abundances and the fragment yield were derived based on unimolecular rate constants. The dissociation energies from this analysis show an odd-even staggering and enhanced stabilities for certain cluster sizes, in agreement with simple electronic shell model predictions.
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| 36. |
- Borck, Øyvind, 1971, et al.
(author)
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Adsorption of Methanol on Aluminum Oxide: A Density Functional Study
- 2003
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In: ATB-Metallurgie. - 0365-7302. ; 43, s. 342-
-
Conference paper (peer-reviewed)abstract
- Theoretical calculations based on density functional theory have made significant contributions to our understanding of metal oxides, their surfaces, and the binding of molecules at these surfaces. In this paper we investigate the binding of methanol at the alpha-Al2O3(0001) surface using first-principles density functional theory. We calculate the molecular adsorption energy of methanol to be E^g_ads=1.03 eV/molecule. Taking the methanol-methanol interaction into account, we obtain the adsorption energy E_ads=1.01 eV/molecule. Our calculations indicate that methanol adsorbs chemically by donating electron charge from the methanol oxygen to the surface aluminum. We find that the surface atomic structure changes upon adsorption, most notably the spacing between the outermost Al and O layers changes from 0.11 Angstrom to 0.33 Angstrom.
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| 37. |
- Johannesson, Henrik, 1953, et al.
(author)
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Conformal field theory approach to the two-channel Anderson model
- 2004
-
In: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 272-276:SUPPL. 1
-
Journal article (peer-reviewed)abstract
- The two-channel Anderson impurity model serves as a prototype for describing heavy-fermion materials with a possible mixed-valent regime with both quadrupolar and magnetic character. We report on the low-energy physics of the model, using a conformal field theory approach with exact Bethe Ansatz results as input.
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| 38. |
- Mamontov, Eugen, 1955
(author)
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Homeorhesis and evolutionary properties of living systems: From ordinary differential equations to the active-particle generalized kinetics theory
- 2006
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In: 10th Evolutionary Biology Meeting at Marseilles, 20-22 September 2006, Marseilles, France.
-
Conference paper (peer-reviewed)abstract
- Advanced generalized-kinetic-theory (GKT) models for biological systems are developed for populations of active (or living) particles [1]-[5]. These particles are described with both the stochastic variables common in kinetic theory (such as time, the particle random location and velocity) and the stochastic variables related to the internal states of an active particle. Evolution of these states represents biological, ecological, or social properties of the particle behavior. Paper [6] analyzes a number of the well-known statistical-mechanics approaches and shows that the active-particle GKT (APGKT) is the only treatment capable of modelling living systems. Work [2] summarizes the significance of the notion of an active particle in kinetic models. This notion draws attention to the features distinguishing living matter from nonliving matter. They are discussed by many authors (e.g., [7]-[15], [1]-[3], [6], [16]-[18]). Work [11] considers a lot of differences between living and nonliving matters, and the limitations of the modelling approaches developed for nonliving matter. Work [6] mainly focuses on the comparison of a few theoretical mechanics treatments in terms of the key living-matter properties formulated in [15]. One of the necessary properties of the evolution of living systems is homeorhesis. It is, loosely speaking, a peculiar qualitative and quantitative insensitivity of a living system to the exogenous signals acting on it. The earlier notion, homeostasis, was introduced by W. B. Cannon in 1926 who discussed the phenomenon in detail later [7]. Homeorhesis introduced by C. H. Waddington [8, p. 32] generalizes homeostasis and is well known in biology [8], [9], [12]. It is an inherent part of mathematical models for oncogeny (e.g., [16]-[18], [6, Appendix]). Homeorhesis is also discussed in [3, Section 4] in connection with APGKT. Homeorhesis is documented in ecology (e.g., [11], [13, the left column on p. 675]) where it is one of the key notions of the strong Gaia theory, a version of the Gaia theory (e.g., [14, Chapter 8]). The strong Gaia theory “states that the planet with its life, a single living system, is regulated in certain aspects by that life” [14, p. 124]. The very origin of the name “Gaia” is related to homeorhesis or homeostasis [14, p. 118]. These notions are also used in psychology and sociology. If evolution of a system is not homeorhetic, the system can not be living. Work [6, Appendix] derives a preliminary mathematical formulation of homeorhesis in terms of the simplest dynamical systems, i.e. ordinary differential equations (ODEs). The present work complements, extended, and further specify the approach of [6, Appendix]. The work comprises the two main parts. The first part develops the sufficient conditions for ODE systems to describe homeorhesis, and suggests a fairly general structure of the ODE model. It regards homeorhesis as piecewise homeostasis. The model can be specified in different ways depending on specific systems and specific purposes of the analysis. An example of the specification is also noted (the PhasTraM nonlinear reaction-diffusion model for hyperplastic oncogeny [16]-[18]). The second part of the work discusses implementation of the above homeorhesis ODE model in terms of a special version [3] of APGKT (see above). The key feature of this version is that the components of a living population need not be discrete: the subdivision into the components is described with a general, continuous-discrete probability distribution (see also [6]). This enables certain properties of living matter noted in [15]. Moreover, the corresponding APGKT model presents a system of, firstly, a generalized kinetic equation for the conditional distribution function conditioned by the internal states of the population and, secondly, Ito's stochastic differential equations for these states. This treatement employs the results on nonstationary invariant diffusion stochastic processes [19]. The second part of the work also stresses that APGKT is substantially more important for the living-matter analysis than in the case of nonliving matter. One of the reasons is certain limitations in experimental sampling of the living-system modes presented with stochastic processes. A few directions for future research are suggested as well. REFERENCES: [1] Bellomo, N., Bellouquid, A. and Delitala, M., 2004, Mathematical topics on the modelling complex multicellular systems and tumor immune cells competition, Math. Models Methods Appl. Sci., 14, 1683-1733. [2] Bellomo, N., 2006, New hot Paper Comments, Essential Science Indicators, http://www.esi-topics.com/nhp/2006 /may- 06-NicolaBellomo.html. [3] Willander, M., Mamontov, E. and Chiragwandi, Z., 2004, Modelling living fluids with the subdivision into the components in terms of probability distributions, Math. Models Methods Appl. Sci. 14, 1495-1520. [4] Bellomo, N. and Maini, P.K., 2005, Preface and the Special Issue “Multiscale Cancer Modelling-A New Frontier in Applied Mathematics”, Math. Models Methods Appl. Sci., 15, iii-viii. [5] De Angelis, E. and Delitala, M., 2006, Modelling complex systems in applied sciences: Methods and tools of the mathematical kinetic theory for active particles. Mathl Comput. Modelling, 43, 1310-1328. [6] Mamontov, E., Psiuk-Maksymowicz, K. and Koptioug, A., 2006, Stochastic mechanics in the context of the properties of living systems, Mathl Comput. Modelling, Article in Press, 13 pp. [7] Cannon, W.B., 1932, The Wisdom of the Body (New York: Norton). [8] Waddington, C.H., 1957, The Strategy of the Genes. A Discussion of Some Aspects of Theoretical Biology (London, George Allen and Unwin). [9] Waddington, C.H., 1968, Towards a theoretical biology, Nature, 218, 525-527. [10] Cotnoir, P.-A., 1981, La compétence environnementale: Une affaire d’adaptation. Séminaire en écologie behaviorale, Univeristé du Québec, Montralé. Available online at: http://pac.cam.org/culture.doc . [11] O’Neill, R.V., DeAngelis, D.L., Waide, J.B. and Allen, T.F.H., 1986, A Hierarchical Concept of Ecosystems, Princeton: Princeton Univ. Press). [12] Sauvant, D., 1992, La modélisation systémique en nutrition, Reprod. Nutr. Dev., 32, 217-230. [13] Christensen, N.L., Bartuska, A.M., Brown, J.H., Carpenter, S., D'Antonio, C., Francis, R., Franklin, J.F., MacMahon, J.A., Noss, R.F., Parsons, D.J., Peterson, C.H., Turner, M.G. and Woodmansee, R.G., 1996, The Report of the Ecological Society of America Committee on the Scientific Basis for Ecosystem Management, Ecological Applications, 6, 665-691. Available online at: http://www.esa.org/pao/esaPositions/Papers/ReportOfSBEM.php. [14] Margulis, L., 1998, Symbiotic Planet. A New Look at Evolution (Amherst: Sciencewriters). [15] Hartwell, L.H., Hopfield, J.J., Leibler, S. and Murray, A.W., 1999, From molecular to modular cell biology, Nature, 402, C47-C52. [16] Mamontov, E., Koptioug, A.V. and Psiuk-Maksymowicz, K., 2006, The minimal, phase-transition model for the cell- number maintenance by the hyperplasia-extended homeorhesis, Acta Biotheoretica, 54, 44 pp., (no. 2, May-June, accepted). [17] Psiuk-Maksymowicz, K. and Mamontov, E., 2005, The time-slices method for rapid solving the Cauchy problem for nonlinear reaction-diffusion equations in the competition of homeorhesis with genotoxically activated hyperplasia, In: European Conference on Mathematical and Theoretical Biology - ECMTB05 (July 18-22, 2005) Book of Abstracts, Vol.1 (Dresden: Center for Information Services and High Performance Computing, Dresden Univ. Technol.), p. 429 (http://www.ecmtb05.org/). [18] Psiuk-Maksymowicz, K. and Mamontov, E., 2006, The homeorhesis-based modelling and fast numerical analysis for oncogenic hyperplasia under radiation therapy, submitted. [19] Mamontov, E., 2005, Nonstationary invariant distributions and the hydrodynamic-style generalization of the Kolmogorov-forward/Fokker-Planck equation, Appl. Math. Lett. 18 (9) 976-982.
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| 39. |
- Mamontov, Eugen, 1955, et al.
(author)
-
What stochastic mechanics are relevant to the study of living systems?
- 2005
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In: Proceedings of the Latvian Academy of Sciences. Section B: Natural, Exact and Applied Sciences. - Riga, Latvia : Latvian Academy of Sciences. - 1407-009X. ; 59:6, s. 255-262
-
Journal article (peer-reviewed)abstract
- Biologists have identified many features of living systems which cannot be studied by application of fundamental statistical mechanics (FSM). The present work focuses on some of these features. By discussing all the basic approaches of FSM, the work formulates the extension of the kinetic-theory paradigm (based on the reduced one-particle distribution function) that possesses all the considered properties of the living systems. This extension appears to be a model within the generalized-kinetic theory developed by N. Bellomo and his co-authors. In connection with this model, the work also stresses some other features necessary for making the model relevant to living systems. An example is discussed, which is a generalized kinetic equation coupled with the probability-density equation which represents the varying component content of a living system. The work also suggests directions for future research.
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| 40. |
- Chen, Si, 1985, et al.
(author)
-
Ultrahigh sensitivity made simple : nanoplasmonic label-free biosensing with an extremely low limit-of-detection for bacterial and cancer diagnostics.
- 2009
-
In: Nanotechnology. - : Institute of Physics (IOP). - 0957-4484 .- 1361-6528. ; 20:43
-
Journal article (peer-reviewed)abstract
- We present a simple and robust scheme for biosensing with an ultralow limit-of-detection down to several pg cm(-2) (or several tens of attomoles cm(-2)) based on optical label-free biodetection with localized surface plasmon resonances. The scheme utilizes cost-effective optical components and comprises a white light source, a properly functionalized sensor surface enclosed in a simple fluidics chip, and a spectral analyzer. The sensor surface is produced by a bottom-up nanofabrication technique with hole mask colloidal lithography. Despite its simplicity, the method is able to reliably detect protein-protein binding events at low picomolar and femtomolar concentrations, which is exemplified by the label-free detection of the extracellular adherence protein (EAP) found on the outer surface of the bacterium Staphylococcus aureus and of prostate-specific antigen (PSA), which is believed to be a prostate cancer marker. These experiments pave the way towards an ultra-sensitive yet compact biodetection platform for point-of-care diagnostics applications.
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| 41. |
- Demoucron, Matthias, 1980-
(author)
-
On the control of virtual violins : Physical modelling and control of bowed string instruments
- 2008
-
Doctoral thesis (other academic/artistic)abstract
- This thesis treats the control of sound synthesis of bowed string instruments based on physical modelling. The work followed two approaches: (a) a systematic exploration of the influence of control parameters (bow force, bow velocity, and bow-bridge distance) on the output of a physical model of the violin, and (b) measurements and analyses of the bowing parameters in real violin playing in order to model and parameterize basic classes of bowing patterns for synthesis control.First a bowed-string model based on modal solutions of the string equation is described and implemented for synthesis of violin sounds. The behaviour of the model is examined through simulations focusing on playability, i.e. the control parameter space in which a periodic Helmholtz motion is obtained, and the variations of the properties of the simulated sound (sound level and spectral centroid) within this parameter space. The response of the model corresponded well with theoretical predictions and empirical expectations based on observations of real performances. The exploration of the model allowed to define optimal parameter regions for the synthesis, and to map sound properties on the control parameters.A second part covers the development of a sensor for measuring the bow force in real violin performance. The force sensor was later combined with an optical motion capture system for measurement of complete sets of bowing parameters in violin performance.In a last part, measurements of the control parameters for basic classes of bowing patterns (sautillé, spiccato, martelé, tremolo) are analyzed in order to propose a realistic control of the sound synthesis. The time evolution of the bowing parameters were modelled by analytical functions, which allowed to describe and control simulated bowing patterns by a limited set of control parameters. For sustained bowing patterns such as détaché, control strategies for basic elements in playing (variations in dynamic level, bow changes) were extracted from exemplary measurements, and simple rules deduced, which allowed extrapolation of parameters to modified bow strokes with other durations and at different dynamic levels.
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| 42. |
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| 43. |
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| 44. |
- Liljequist, David, 1946-
(author)
-
Limits of validity of trajectory simulation: correlation of the error with density of scatterers and particle wavelength
- 2009
-
In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier. - 0168-583X .- 1872-9584. ; 267, s. 3409-3419
-
Journal article (peer-reviewed)abstract
- To a first approximation, the elastic scattering of long wavelength particles in amorphous matter may be modelled as scattering in a volume filled with a density n of N point scatterers in random positions. For not too large N (up to about 2×103), the error in trajectory simulation (classical transport theory) due to the neglect of interference effects can then be determined in detail by means of a comparison with an exact quantum calculation of the plural or multiple scattering process. A relative error RE is defined and calculated for the scattering in different directions as well as for the distribution of scattering events inside the volume. A very strong correlation is found between the relative error and the ratio λ/dnn, where λ is the wavelength of the incident particle and dnn=n-1/3 is an average distance between nearest neighbour scatterers. For scattering in a volume of dimensions large compared to the particle wavelength, present calculations suggest that the correlation can be described as RE≈a·(λ/dnn)b, where the parameters a<0.05 and b∼2 depend on the s-wave phaseshift δ0 in the scattering process. The condition for validity of trajectory simulation, defined in terms of a limit of validity L (maximum acceptable relative error), may thus be written λ/dnn<ξ, where ξ=(L/a)1/b∼1. For λ/dnn<1, the relative error is generally less than 5%, and trajectory simulation may be regarded as valid with at least 95% accuracy. In the exact quantum calculation, two features of pronounced quantum character are observed in the distribution of scattering events: oscillations due to quantum interference in finite volumes, and, for small negative δ0, randomly localized peaks due to proximity resonance.
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| 45. |
- Lindén, Martin
(author)
-
Decay times in turnover statistics of single enzymes
- 2008
-
In: Physical review E. - 1539-3755 .- 1550-2376. ; 78:1, s. 010901-1-010901-4
-
Journal article (peer-reviewed)abstract
- The first passage times for enzymatic turnovers in nonequilibrium steady state display a statistical symmetry property related to nonequilibrium fluctuation theorems, which makes it possible to extract the chemical driving force from single molecule trajectories in nonequilibrium steady state. Below, we show that the number of decay constants needed to describe the first passage time distribution of this system is not equal to the number of states in the first passage problem, as one would generally expect. Instead, the structure of the kinetic mechanism makes half of the decay times vanish identically from the turnover time distribution. The terms that cancel out correspond to the eigenvalues of a certain submatrix of the master equation matrix for the first exit time problem. We discuss how these results make modeling and data analysis easier for such systems, and how the turnovers can be measured.
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| 46. |
- Malysheva, Lyuba, et al.
(author)
-
Molecular Orientation in Helical and All-Trans Oligo(ethylene glycol)-Terminated Assemblies on Gold: Results of ab Initio Modeling
- 2005
-
In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215 .- 1520-6106 .- 1520-5207. ; 109:34, s. 7788-7796
-
Journal article (peer-reviewed)abstract
- The structural properties of self-assembled monolayers (SAMs) of oligo(ethylene glycol) (OEG)-terminated and amide-containing alkanethiols (HS(CH2)15CONH(CH2CH2O)6H and related molecules with shorter alkyl or OEG portions) on gold are addressed. Optimized geometry of the molecular constituents, characteristic vibration frequencies, and transition dipole moments are obtained using density-functional theory methods with gradient corrections. These data are used to simulate IR reflection-absorption (RA) spectra associated with different OEG conformations. It is shown that the positions and relative intensities of all characteristic peaks in the fingerprint region are accurately reproduced by the model spectra within a narrow range of the tilt and rotation angles of the alkyl plane, which turns out to be nearly the same for the helical and all-trans OEG conformations. In contrast, the tilt of the OEG axis changes considerably under conformational transition from helical to all-trans OEG. By means of ab initio modeling, we also clarify other details of the molecular structure and orientation, including lateral hydrogen bonding, the latter of which is readily possessed by the SAMs in focus. These results are crucial for understanding phase and folding characteristics of OEG SAMs and other complex molecular assemblies. They are also expected to contribute to an improved understanding of the interaction with water, ions, and ultimately biological macromolecules.
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| 47. |
- Marklund, Mattias, 1970-, et al.
(author)
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Quantum vacuum experiments using high intensity lasers
- 2009
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In: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 55, s. 319-326
-
Journal article (peer-reviewed)abstract
- The quantum vacuum constitutes a fascinating medium of study, in particular since near-future laser facilities will be able to probe the nonlinear nature of this vacuum. There has been a large number of proposed tests of the low-energy, high intensity regime of quantum electrodynamics (QED) where the nonlinear aspects of the electromagnetic vacuum come into play, and we will here give a short description of some of these. Such studies can shed light, not only on the validity of QED, but also on certain aspects of nonperturbative effects, and thus also give insights for quantum field theories in general.
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| 48. |
- Rocha, Luis E C, 1981-
(author)
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Structural evolution of the Brazilian airport network
- 2009
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In: Journal of Statistical Mechanics. - Bristol : Institute of Physics. - 1742-5468. ; , s. 04020-
-
Journal article (peer-reviewed)abstract
- The aviation sector is profitable, but sensitive to economic fluctuations, geopolitical constraints and governmental regulations. As for other means of transportation, the relation between origin and destination results in a complex map of routes, which can be complemented with information associated with the routes themselves, for instance, frequency, traffic load and distance. The theory of networks provides a natural framework for investigating the dynamics on the resulting structure. Here, we investigate the structure and evolution of the Brazilian airport network (BAN) as regards several quantities: routes, connections, passengers and cargo. Some structural features are in accordance with previous results for other airport networks. The analysis of the evolution of the BAN shows that its structure is dynamic, with changes in the relative relevance of some airports and routes. The results indicate that the connections converge to specific routes. The network shrinks at the route level but grows in number of passengers and amount of cargo, which more than doubled during the period studied.
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| 49. |
- Ronchi, Emanuele, 1978-
(author)
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Neural Networks Applications and Electronics Development for Nuclear Fusion Neutron Diagnostics
- 2009
-
Doctoral thesis (other academic/artistic)abstract
- This thesis describes the development of electronic modules for fusion neutron spectroscopy as well as several implementations of artificial neural networks (NN) for neutron diagnostics for the Joint European Torus (JET) experimental reactor in England.The electronics projects include the development of two fast light pulser modules based on Light Emitting Diodes (LEDs) for the calibration and stability monitoring of two neutron spectrometers (MPRu and TOFOR) at JET. The particular electronic implementation of the pulsers allowed for operation of the LEDs in the nanosecond time scale, which is typically not well accessible with simpler circuits. Another electronic project consisted of the the development and implementation at JET of 32 high frequency analog signal amplifiers for MPRu. The circuit board layout adopted and the choice of components permitted to achieve bandwidth above 0.5 GHz and low distortion for a wide range of input signals. The successful and continued use of all electronic modules since 2005 until the present day is an indication of their good performance and reliability.The NN applications include pulse shape discrimination (PSD), deconvolution of experimental data and tomographic reconstruction of neutron emissivity profiles for JET. The first study showed that NN can perform neutron/gamma PSD in liquid scintillators significantly better than other conventional techniques, especially for low deposited energy in the detector. The second study demonstrated that NN can be used for statistically efficient deconvolution of neutron energy spectra, with and without parametric neutron spectroscopic models, especially in the region of low counts in the data. The work on tomography provided a simple but effective parametric model for describing neutron emissivity at JET. This was then successfully implemented with NN for fast and automatic tomographic reconstruction of the JET camera data.The fast execution time of NN, i.e. usually in the microsecond time scale, makes the NN applications presented here suitable for real-time data analysis and typically orders of magnitudes faster than other commonly used codes. The results and numerical methods described in this thesis can be applied to other diagnostic instruments and are of relevance for future fusion reactors such as ITER, currently under construction in Cadarache, France.
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| 50. |
- Österlund, Michael, et al.
(author)
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Projectile Motion in Real Life
- 2000
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In: Proc. Physics Teaching in Engineering Education (PTEE 2000).
-
Conference paper (other academic/artistic)
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