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• 401. Koci, L.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
Ab initio and classical molecular dynamics of neon melting at high pressure2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 21Article in journal (Refereed)

First-principles and classical molecular dynamics calculations have been performed to study the high-pressure melting curve of Ne. In the low temperature region, simulations with solid and liquid in coexistence (two-phase) with a Lennard-Jones interatomic potential well reproduce experimental findings. As anticipated, there is a melting temperature overestimation when heating a crystal (one-phase) compared to the two-phase results. Furthermore, there is a significant discrepancy comparing the one-phase ab initio curve to previously reported classical predictions: at 150 GPa, the calculations in this work show a melting temperature approximately 1000 K above the estimate based on an exponential-6 potential. However, there is a close match between the one-phase ab initio curve and the classical one-phase results in this work. This could also imply an agreement between a two-phase ab initio and classical two-phase melting curve. Therefore, considering the documented accuracy of the coexistence method, the classical two-phase melting in this work could well indicate the most probable melting behavior. In conjunction with recent theoretical results for Xe, no significant melting slope decrease was observed for Ne in this study.

• 402. Koci, L.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
The impact of system restriction in molecular dynamics applied to the melting of Ne at high pressure2008In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 44, no 2, p. 605-610Article in journal (Refereed)

There are two major ways to perform molecular dynamics (MD) calculations, namely classical and ab initio MD. As ab initio techniques require considerably longer calculation times, it is of interest to compare the results of the two methods. Furthermore, when melting is studied with MD, the use of coexistent solid and liquid structures (two-phase) in the calculations, instead of only a solid structure (one-phase), can have a substantial impact on the results obtained. In this work, comparisons have been made between classical and ab initio methods applied to one- and two-phase systems for the melting of Ne at high pressure. The temperatures needed to melt the classical one-phase system are somewhat higher compared to the two-phase temperatures, evaluated at the same pressure. Furthermore, there is a significant discrepancy comparing the one-phase ab initio curve to previously reported classical predictions. At 150 GPa, the calculations in this work show a melting temperature approximately 1000 K above the estimate based on an exponential-6 potential. However, there is a close match between the one-phase ab initio curve and the classical one-phase results in this work. This suggests a possible agreement between a two-phase ab initio and classical two-phase melting curve.

• 403. Koci, L.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
Study of the high-pressure helium phase diagram using molecular dynamics2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 1Article in journal (Refereed)

The rich occurrence of helium and hydrogen in space makes their properties highly interesting. By means of molecular dynamics ( MD), we have examined two interatomic potentials for He-4. Both potentials are demonstrated to reproduce high-pressure solid and liquid equation of state (EOS) data. The EOS, solid - solid transitions and melting at high pressures ( P) were studied using a two-phase method. The Buckingham potential shows a good agreement with theoretical and experimental EOS, but does not reproduce experimental melting data. The Aziz potential shows a perfect match with theoretical melting data. We conclude that there is a stable body-centred-cubic (bcc) phase for He-4 at temperatures ( T) above 340 K and pressures above 22 GPa for the Buckingham potential, whereas no bcc phase is found for the Aziz potential in the applied PT range.

• 404. Koci, L.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
Molecular dynamics calculation of liquid iron properties and adiabatic temperature gradient in the Earth's outer core2007In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 168, no 2, p. 890-894Article in journal (Refereed)

The knowledge of the temperature radial distribution in the Earth's core is important to understand the heat balance and conditions in the Earth's interior. Molecular dynamics (MD) simulations were applied to study the properties of liquid iron under the pressure-temperature conditions of the Earth's outer core. It is shown that the model used for the MD simulations can reproduce recent experimentally determined structure factor calculations to the highest pressure of 58 GPa. Applying this model for higher pressures, the calculated densities and diffusion parameters agree well with the results of first-principles. The MD calculations indicate that a reasonable estimate of the adiabatic temperature profile in the Earth's outer core could be evaluated.

• 405. Koci, L.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
Molecular dynamics study of liquid iron under high pressure and high temperature2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 22Article in journal (Refereed)

Unlike ab initio calculations, classical potentials in molecular dynamics (MD) allow the treatment of very large atomic systems. However, the quality of the potentials has to be carefully assessed, making the evaluation of the models important. By means of MD simulations, we have studied the properties of liquid iron (Fe) with an embedded-atom method (EAM) under extreme pressure-temperature conditions, to resemble the conditions found in the Earth's outer core. The model used for the MD simulations is demonstrated to reproduce recent experimentally determined structure factor calculations to the highest pressure of 58 GPa. The calculations of densities and diffusion parameters at the various temperatures and pressures agree well with first-principles calculations. The results indicate the model's validity for the physical description of liquid iron at extreme conditions.

• 406. Koci, L.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
Simulation of shock-induced melting of Ni using molecular dynamics coupled to a two-temperature model2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 1Article in journal (Refereed)

Using nonequilibrium molecular dynamics (MD) simulations we study shock-induced melting in Ni with an embedded atom method (EAM). Dynamic melting is probed by the pair correlation function, and we find a melting lattice temperature of T-melt=6400 +/- 300 K for a melting pressure of P-melt=275 +/- 10 GPa. When a combined MD+TTM (two-temperature model) approach is used to include electronic heat conduction and electron-phonon coupling, P-melt and T-melt change. For a given pressure, the temperature behind the shock decreases due to electronic heat diffusion into the cold, unshocked material. This cooling of the material behind the shock slightly increases the melting pressure compared to simulations without electronic heat conduction and electron-phonon coupling. The decrease in the temperature behind the shock front is enhanced if the electron-phonon coupling is artificially made larger. We also explore the feasibility of using x-ray diffraction to detect melting.

• 407.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
Electroweak baryogenesis in the nMSSM2007In: SUSY06: The 14th International Conference on Supersymmetry and the Unification of Fundamental Interactions / [ed] Feng, JL, 2007, Vol. 903, p. 689-692Conference paper (Refereed)

In this talk, electroweak baryogenesis in the nMSSM is discussed following Ref [1]. We focus on differences compared to the MSSM. We conclude that electroweak baryogenesis in the nMSSM is rather generic. Still, sfermions of the first two generations are required to be heavy to evade constraints from electric dipole moments.

• 408.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
Numerical approach to multi-dimensional phase transitions2006In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 6, p. 021-Article in journal (Refereed)

We present an algorithm for numerically analysing the bounce solution for first-order phase transitions. Our approach is well suited to treating phase transitions with several fields. The algorithm consists of two parts. In the first part the bounce solution without damping is determined; in this case energy is conserved. In the second part the continuation to the physically relevant case with damping is performed. The approach presented is numerically stable and easily implemented.

• 409.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
The effective matter potential for highly relativistic neutrinos2006In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 634, no 03-feb, p. 267-271Article in journal (Refereed)

We investigate matter effects on highly relativistic neutrinos. The self-energy of neutrinos is determined in an electron or neutrino background taking into account resonance and finite width effects of the gauge bosons. We find minor changes compared to the formerly used formula for the propagator function and large deviations of the effective width from the decay width of the gauge bosons considering higher moments of the electron or neutrino distribution function.

• 410. Koči, L.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Condensed Matter Theory Group, Physics Department, Uppsala University, Sweden. KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
Ab initio and classical molecular dynamics calculations of the high-pressure melting of Ne2008In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 121Article in journal (Refereed)

Classical molecular dynamics (CMD) calculations are fast but are heavily dependent on the potential feasibility. On the other hand, first-principles (ab initio) molecular dynamics (AIMD) does not use any empirical knowledge, but can be extremely time consuming. As both techniques have been applied to study melting at extreme conditions, a comparison of the methods is motivated. Furthermore, when melting is studied with MD, the use of coexistent solid and liquid structures (two-phase) in the initial simulation configuration, instead of a only a solid structure (one-phase), can have a significant impact. In this work, comparisons have been made between CMD and AIMD methods applied to one- and two-phase systems for the melting of Ne at high pressure.

• 411. Kutzner, C.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC. KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
Scaling of the GROMACS 4.6 molecular dynamics code on SuperMUC2014In: Advances in Parallel Computing, ISSN 0927-5452, E-ISSN 1879-808X, Vol. 25, p. 722-727Article in journal (Refereed)

Here we report on the performance of GROMACS 4.6 on the SuperMUC cluster at the Leibniz Rechenzentrum in Garching. We carried out benchmarks with three biomolecular systems consisting of eighty thousand to twelve million atoms in a strong scaling test each. The twelve million atom simulation system reached a performance of 49 nanoseconds per day on 32,768 cores.

• 412. Kutzner, Carsten
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
Best bang for your buck: GPU nodes for GROMACS biomolecular simulations2015In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 36, no 26, p. 1990-2008Article in journal (Refereed)

The molecular dynamics simulation package GROMACS runs efficiently on a wide variety of hardware from commodity workstations to high performance computing clusters. Hardware features are well-exploited with a combination of single instruction multiple data, multithreading, and message passing interface (MPI)-based single program multiple data/multiple program multiple data parallelism while graphics processing units (GPUs) can be used as accelerators to compute interactions off-loaded from the CPU. Here, we evaluate which hardware produces trajectories with GROMACS 4.6 or 5.0 in the most economical way. We have assembled and benchmarked compute nodes with various CPU/GPU combinations to identify optimal compositions in terms of raw trajectory production rate, performance-to-price ratio, energy efficiency, and several other criteria. Although hardware prices are naturally subject to trends and fluctuations, general tendencies are clearly visible. Adding any type of GPU significantly boosts a node's simulation performance. For inexpensive consumer-class GPUs this improvement equally reflects in the performance-to-price ratio. Although memory issues in consumer-class GPUs could pass unnoticed as these cards do not support error checking and correction memory, unreliable GPUs can be sorted out with memory checking tools. Apart from the obvious determinants for cost-efficiency like hardware expenses and raw performance, the energy consumption of a node is a major cost factor. Over the typical hardware lifetime until replacement of a few years, the costs for electrical power and cooling can become larger than the costs of the hardware itself. Taking that into account, nodes with a well-balanced ratio of CPU and consumer-class GPU resources produce the maximum amount of GROMACS trajectory over their lifetime.

• 413.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
The entropy of frustrated Ising systems calculated using Monte Carlo methods.2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
• 414.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
The MIT bag-model: Glueball mass spectrum using the MIT bag-model2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

This thesis studies the MIT bag-model and derives important equations regarding this model. The masses of the hypothetical glueballs are determined using the MIT bag-model. Five different glueball masses are predicted and the lowest glueball mass is determined to be 0.961 GeV. This is in excellent agreement with similar predictions using the MIT bag-model. Lattice QCD and other nucleon models are compared to the MIT bag-model. Many recent studies using lattice QCD have found the lowest glueball mass to be $\sim$1.6 GeV. This result better suits newly discovered glueball candidates, indicating that our calculated mass is to low.

• 415. Lahtinen, V.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
Hierarchy of exactly solvable spin- 1 2 chains with s o (N) 1 critical points2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 1, p. 014409-Article in journal (Refereed)

We construct a hierarchy of exactly solvable spin-1/2 chains with so(N)1 critical points. Our construction is based on the framework of condensate-induced transitions between topological phases. We employ this framework to construct a Hamiltonian term that couples N transverse field Ising chains such that the resulting theory is critical and described by the so(N)1 conformal field theory. By employing spin duality transformations, we then cast these spin chains for arbitrary N into translationally invariant forms that all allow exact solution by the means of a Jordan-Wigner transformation. For odd N our models generalize the phase diagram of the transverse field Ising chain, the simplest model in our hierarchy. For even N the models can be viewed as longer ranger generalizations of the XY chain, the next model in the hierarchy. We also demonstrate that our method of constructing spin chains with given critical points goes beyond exactly solvable models. Applying the same strategy to the Blume-Capel model, a spin-1 generalization of the Ising chain in a generic magnetic field, we construct another critical spin-1 chain with the predicted conformal field theory (CFT) describing the criticality.

• 416.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
Photoluminescense and AFM characterization of silicon nanocrystals prepared by low-temperature plasma enhanced chemical vapour deposition and annealing2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

When studying quantum dots one of the most important properties

is the size of the band gap, and thus also their physical dimensions.

We investigated these properties for silicon quantum dots created

by means of plasma-enhanced chemical vapour deposition and annealing.

To determine the band gap size we measured photoluminescence

for ten dierent samples and to determine the physical

dimensions we used an atomic force microscope. The photoluminescence

measurements indicated that the intensity of the emitted

photons varied across the samples, but did not indicate any shift in

peak wavelength between samples nor any time-dependence of the

luminescence. The peak wavelength was in the order of 600 to 620

nm, corresponding to a band gap of 2.0 to 2.1 eV and a physical size

of approximately 3 nm. The AFM scans revealed densely packed

quantum dots, where few single objects could be distinguished. In

order to be able to perform a better statistical analysis, eorts would

have to be taken to separate the quantum dots.

• 417.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
A 2D Luttinger Model2010In: Journal of statistical physics, ISSN 0022-4715, E-ISSN 1572-9613, Vol. 141, no 1, p. 17-52Article in journal (Refereed)

A detailed derivation of a two dimensional (2D) low energy effective model for spinless fermions on a square lattice with local interactions is given. This derivation utilizes a particular continuum limit that is justified by physical arguments. It is shown that the effective model thus obtained can be treated by exact bosonization methods. It is also discussed how this effective model can be used to obtain physical information about the corresponding lattice fermion system.

• 418.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
A Two-Dimensional Analogue of the Luttinger Model2010In: Letters in Mathematical Physics, ISSN 0377-9017, E-ISSN 1573-0530, Vol. 92, no 2, p. 109-124Article in journal (Refereed)

We present a fermion model that is, as we suggest, a natural 2D analogue of the Luttinger model. We derive this model as a partial continuum limit of a 2D spinless lattice fermion system with local interactions and away from half filling. In this derivation, we use certain approximations that we motivate by physical arguments. We also present mathematical results that allow an exact treatment of parts of the degrees of freedom of this model by bosonization, and we propose to treat the remaining degrees of freedom by mean field theory.

• 419.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
An explicit solution of the (quantum) elliptic Calogero-Sutherland model2005In: SPT 2004: SYMMETRY AND PERTURBATION THEORY / [ed] Gaera, G; Prinari, B; RauchWojciechowshi, S, 2005, p. 159-174Conference paper (Refereed)

We present explicit formulas for the eigenvalues and eigenfunctions of the elliptic Calogero-Sutherland (eCS) model as formal power series to all orders in the nome of the elliptic functions, for arbitrary values of the (positive) coupling constant and particle number. Our solution gives explicit formulas for an elliptic deformation of the Jack polynomials.

• 420.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
Conformal field theory and the solution of the (quantum) elliptic Calogero-Sutherland system2005In: Noncommutative Geometry and Representation Theory in Mathematical Physics / [ed] Fuchs, J; Mickelsson, J; Rozenblioum, G; Stolin, A; Westerberg, A, Providence, Rhode Island: American Mathematical Society (AMS), 2005, p. 223-240Conference paper (Refereed)

We review the construction of a conformal field theory model which describes anyons on a circle and at finite temperature, including previously unpublished results. This anyon model is closely related to the quantum elliptic Calogero-Sutherland (eCS) system. We describe this relation and how it has led to an explicit construction of the eigenvalues and eigenfunctions of the eCS system.

• 421.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
Explicit Solution of the (Quantum) Elliptic Calogero-Sutherland Model2014In: Annales de l'Institute Henri Poincare. Physique theorique, ISSN 1424-0637, E-ISSN 1424-0661, Vol. 15, no 4, p. 755-791Article in journal (Refereed)

The elliptic Calogero-Sutherland model is a quantum many body system of identical particles moving on a circle and interacting via two body potentials proportional to the Weierstrass -function. It also provides a natural many-variable generalization of the Lam, equation. Explicit formulas for the eigenfunctions and eigenvalues of this model as infinite series are obtained, to all orders and for arbitrary particle numbers and coupling parameters. These eigenfunctions are an elliptic deformation of the Jack polynomials. The absolute convergence of these series is proved in special cases, including the two-particle (=Lam,) case for non-integer coupling parameters and sufficiently small elliptic deformation.

• 422.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
Gauge theory approach towards an explicit solution of the (classical) elliptic Calogero-Moser system2005In: Journal of Nonlinear Mathematical Physics, ISSN 1402-9251, E-ISSN 1776-0852, Vol. 12, p. 423-439Article in journal (Refereed)

We discuss the relation of the trigonometric Calogero-Moser (CM) system to Yang-Mills gauge theories and its generalization to the elliptic case. This yields a linearization of the time evolution of the elliptic CM system and suggests two promising strategies for finding a fully explicit solution of this model. We also present a large class of integrable spin-particle systems generalizing the elliptic CM system.

• 423.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
Non-commutative geometry and exactly solvable systems2008In: INTERNATIONAL CONFERENCE ON NONCOMMUTATIVE GEOMETRY AND PHYSICS ﻿ / [ed] Wallet, J.C., 2008, Vol. 103Conference paper (Refereed)

I present the exact energy eigenstates and eigenvalues of a quantum many-body system of bosons on non-commutative space and in a harmonic oszillator confining potential at the selfdual point. I also argue that this exactly solvable system is a prototype model which provides a generalization of mean field theory taking into account non-trivial correlations which are peculiar to boson systems in two space dimensions and relevant in condensed matter physics. The prologue and epilogue contain a few remarks to relate my main story to recent developments in non-commutative quantum field theory and an addendum to our previous work together with Szabo and Zarembo on this latter subject.

• 424.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
Remarkable identities related to the (quantum) elliptic Calogero-Sutherland model2006In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 47, no 2Article in journal (Refereed)

We present remarkable functional identities related to the elliptic Calogero-Sutherland (eCS) system. We derive them from a second quantization of the eCS model within a quantum field theory model of anyons on a circle and at finite temperature. The identities involve two eCS Hamiltonians with arbitrary and, in general, different particle numbers N and M, and a particular function of N+M variables arising as anyon correlation function of N particles and M antiparticles. In addition to identities obtained from anyons with the same statistics parameter lambda, we also obtain dual relations involving mixed correlation functions of anyons with two different statistics parameters lambda and 1/lambda. We also give alternative, elementary proofs of these identities by direct computations.

• 425.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
Singular Eigenfunctions of Calogero-Sutherland Type Systems and How to Transform Them into Regular Ones2007In: SIGMA. Symmetry, Integrability and Geometry, ISSN 1815-0659, E-ISSN 1815-0659, Vol. 3, p. 031-Article in journal (Refereed)

There exists a large class of quantum many-body systems of Calogero-Sutherland type where all particles can have different masses and coupling constants and which nevertheless are such that one can construct a complete (in a certain sense) set of exact eigenfunctions and corresponding eigenvalues, explicitly. Of course there is a catch to this result: if one insists on these eigenfunctions to be square integrable then the corresponding Hamiltonian is necessarily non-hermitean (and thus provides an example of an exactly solvable PT-symmetric quantum-many body system), and if one insists on the Hamiltonian to be hermitean then the eigenfunctions are singular and thus not acceptable as quantum mechanical eigenfunctions. The standard Calogero-Sutherland Hamiltonian is special due to the existence of an integral operator which allows to transform these singular eigenfunctions into regular ones.

• 426.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
Source Identity and Kernel Functions for Elliptic Calogero-Sutherland Type Systems2010In: Letters in Mathematical Physics, ISSN 0377-9017, E-ISSN 1573-0530, Vol. 94, no 1, p. 63-75Article in journal (Refereed)

Kernel functions related to quantum many-body systems of Calogero-Sutherland type are discussed, in particular for the elliptic case. The main result is an elliptic generalization of an identity due to Sen that is a source for many such kernel functions. Applications are given, including simple exact eigenfunctions and corresponding eigenvalues of Chalykh-Feigin-Veselov-Sergeev-type deformations of the elliptic Calogero-Sutherland model for special parameter values.

• 427.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.).
Singular factorizations, self-adjoint extensions and applications to quantum many-body physics2006In: Journal of Physics A: Mathematical and General, ISSN 0305-4470, E-ISSN 1361-6447, Vol. 39, no 5, p. 1057-1071Article in journal (Refereed)

We study self-adjoint operators defined by factorizing second-order differential operators in first-order ones. We discuss examples where such factorizations introduce singular interactions into simple quantum-mechanical models such as the harmonic oscillator or the free particle on the circle. The generalization of these examples to the many-body case yields quantum models of distinguishable and interacting particles in one dimensions which can be solved explicitly and by simple means. Our considerations lead us to a simple method to construct exactly solvable quantum many-body systems of Calogero-Sutherland type.

• 428.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
Departments of Mathematics and Physics, Rutgers University. Dipartimento di Matematica, Università degli Studi di Milano. KTH, School of Engineering Sciences (SCI), Theoretical Physics.
Steady states and universal conductance in a quenched Luttinger model2016In: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, p. 1-32Article in journal (Refereed)

We obtain exact analytical results for the evolution of a 1+1-dimensional Luttinger model prepared in a domain wall initial state, i.e., a state with different densities on its left and right sides. Such an initial state is modeled as the ground state of a translation invariant Luttinger Hamiltonian (Formula presented.) with short range non-local interaction and different chemical potentials to the left and right of the origin. The system evolves for time t > 0 via a Hamiltonian (Formula presented.) which differs from (Formula presented.) by the strength of the interaction. Asymptotically in time, as (Formula presented.), after taking the thermodynamic limit, the system approaches a translation invariant steady state. This final steady state carries a current I and has an effective chemical potential difference (Formula presented.) between right- (+) and left- (−) moving fermions obtained from the two-point correlation function. Both I and (Formula presented.) depend on (Formula presented.) and (Formula presented.). Only for the case (Formula presented.) does (Formula presented.) equal the difference in the initial left and right chemical potentials. Nevertheless, the Landauer conductance for the final state, (Formula presented.), has a universal value equal to the conductance quantum (Formula presented.) for the spinless case.

• 429.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
Fermi's Golden Rule and Exponential Decay as a RG Fixed Point2009In: Journal of statistical physics, ISSN 0022-4715, E-ISSN 1572-9613, Vol. 134, no 4, p. 749-768Article in journal (Refereed)

We discuss the decay of unstable states into a quasicontinuum using Hamiltonian models. We show that exponential decay and the golden rule are exact in a suitable scaling limit, and that there is an associated renormalization group (RG) with these properties as a fixed point. The method is inspired by a limit theorem for infinitely divisible distributions in probability theory, where there is a RG with a Cauchy distribution, i.e. a Lorentz line shape, as a fixed point. Our method of solving for the spectrum is well known; it does not involve a perturbation expansion in the interaction, and needs no assumption of a weak interaction. Using random matrices for the interaction we show that the ensemble fluctuations vanish in the scaling limit. For non-random models we can use uniformity assumptions on the density of states and the interaction matrix elements to estimate the deviations from the decay rate defined by the golden rule.

• 430.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
Construction by bosonization of a fermion-phonon model2015In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 56, no 9, article id 091902Article in journal (Refereed)

We discuss an extension of the (massless) Thirring model describing interacting fermions in one dimension which are coupled to phonons and where all interactions are local. This fermion-phonon model can be solved exactly by bosonization.We present a construction and solution of this model which is mathematically rigorous by treating it as a continuum limit of a Luttinger-phonon model. A self-contained account of the mathematical results underlying bosonization is included, together with complete proofs.

• 431.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
Extrinsic curvature effects in brane-world scenariosArticle in journal (Other academic)
• 432.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
Source identity and kernel functions for Inozemtsev-type systems2012In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 53, no 8, p. 082105-Article in journal (Refereed)

The Inozemtsev Hamiltonian is an elliptic generalization of the differential operator defining the BCN trigonometric quantum Calogero-Sutherland model, and its eigenvalue equation is a natural many-variable generalization of the Heun differential equation. We present kernel functions for Inozemtsev Hamiltonians and Chalykh-Feigin-Veselov-Sergeev-type deformations thereof. Our main result is a solution of a heat-type equation for a generalized Inozemtsev Hamiltonian which is the source of all these kernel functions. Applications are given, including a derivation of simple exact eigenfunctions and eigenvalues of the Inozemtsev Hamiltonian.

• 433.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
Mean field magnetic phase diagrams for the two dimensional t-t '-U Hubbard model2007In: Journal of statistical physics, ISSN 0022-4715, E-ISSN 1572-9613, Vol. 127, no 4, p. 825-840Article in journal (Refereed)

We study the ground state phase diagram of the two dimensional t - t' - U Hubbard model concentrating on the competition between antiferro-, ferro-, and paramagnetism. It is known that unrestricted Hartree-Fock- and quantum Monte Carlo calculations for this model predict inhomogeneous states in large regions of the parameter space. Standard mean field theory, i.e., Hartree-Fock theory restricted to homogeneous states, fails to produce such inhomogeneous phases. We show that a generalization of the mean field method to the grand canonical ensemble circumvents this problem and predicts inhomogeneous states, represented by mixtures of homogeneous states, in large regions of the parameter space. We present phase diagrams which differ considerably from previous mean field results but are consistent with, and extend, results obtained with more sophisticated methods.

KTH, School of Engineering Sciences (SCI), Theoretical Physics.
On some almost quadratic algebras coming from twisted derivations2006In: Journal of Nonlinear Mathematical Physics, ISSN 1402-9251, E-ISSN 1776-0852, Vol. 13, p. 76-86Article in journal (Refereed)

This paper explores the quasi-deformation scheme devised in [1, 3] as applied to the simple Lie algebra sl(2)(F) for specific choices of the involved parameters and underlying algebras. One of the main points of this method is that the quasi-deformed algebra comes endowed with a canonical twisted Jacobi identity. We show in the present article that when the quasi-deformation method is applied to sl(2)(F) one obtains multiparameter families of almost quadratic algebras, and by choosing parameters suitably, sl(2)(F) is quasi-deformed into three-dimensional and four-dimensional Lie algebras and algebras closely resembling Lie superalgebras and colour Lie algebras, this being in stark contrast to the classical deformation schemes where sl(2)(F) is rigid.

KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
From Side Chains Rattling on Picoseconds to Ensemble Simulations of Protein Folding2014In: Israel Journal of Chemistry, ISSN 0021-2148, Vol. 54, no 8-9, p. 1274-1285Article, review/survey (Refereed)

Simulations of biological macromolecules have evolved tremendously since the discoveries of the 1970s. The field has moved from simple simulations in vacuo on picosecond scales to milliseconds of accurate sampling of large proteins, and it has become a standard tool in biochemistry and biophysics, rather than a dedicated theoretical one. This is partly due to increasing computational power, but it would not have been possible without huge research efforts invested in new algorithms and software. Here, we illustrate some of this development, both past and future challenges, and in particular, discuss how the recent introduction of modern ensemble methods is breaking the trend of ever-longer simulations to instead focus on throughput and sampling. This has not only helped simulations become much more accurate, but it provides statistical error estimates, which are critical, as simulations are increasingly used to predict properties that have not yet been measured experimentally.

• 436. Lashley, Jason
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
A tribute to James L. Smith Foreword2009In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 89, no 22-24, p. 1751-1756Article in journal (Refereed)
• 437. Laurent, Benoist
KTH. KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
Study of the Interaction between General Anesthetics and a Bacterial Homologue to the Human Nicotinic Receptor2013In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 104, no 2, p. 623A-623AArticle in journal (Other academic)
• 438.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
Comment on "Critical Dynamics of a Vortex-Loop Model for the Superconducting Transition"2002In: Physical Review Letters, Vol. 89, no 10Article in journal (Refereed)
• 439.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
Improving the efficiency of extended ensemble simulations: The accelerated weight histogram method2012In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 85, no 5, p. 056708-Article in journal (Refereed)

We propose a method for efficient simulations in extended ensembles, useful, e. g., for the study of problems with complex energy landscapes and for free energy calculations. The main difficulty in such simulations is the estimation of the a priori unknown weight parameters needed to produce flat histograms. The method combines several complementary techniques, namely, a Gibbs sampler for the parameter moves, a reweighting procedure to optimize data use, and a Bayesian update allowing for systematic refinement of the free energy estimate. In a certain limit the scheme reduces to the 1/t algorithm of B. E. Belardinelli and V. D. Pereyra [Phys. Rev. E 75, 046701 (2007)]. The performance of the method is studied on the two-dimensional Ising model, where comparison with the exact free energy is possible, and on an Ising spin glass.

• 440.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
Critical properties of Bose-glass superconductors1999In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 47, no 4Article in journal (Refereed)

We study vortex lines in high-temperature superconductors with columnar defects produced by heavy-ion irradiation. We reconsider scaling theory for the Bose-glass transition with tilted magnetic fields, and propose, e.g. , a new scaling form for the shape of the Bose glass phase boundary, which is relevant for experiments. We also consider Monte Carlo simulations for a vortex model with a screened interaction. Critical exponents are determined from scaling analysis of Monte Carlo data for current-voltage characteristics and other quantities. The dynamic critical exponent is found to be z = 4.6 ± 0.3.

• 441.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
Superconducting coherence and the helicity modulus in vortex line models1999In: Physical Review B, Vol. 59, no 13, p. 8451-8454Article in journal (Refereed)
• 442.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
Dynamical universality classes of the superconducting phase transition1998In: Physical Review B, Vol. 58, no 5, p. 2827-2833Article in journal (Refereed)
• 443.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Biological Physics.
Solvent diffusion outside macromolecular surfaces1998In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 57, p. 791-796Article in journal (Refereed)

The effect of the inhomogeneous environment upon solvent molecules close to a macromolecular surface is evaluated from a molecular-dynamics simulation of a protein, myoglobin, in water solution. The simulation is analyzed in terms of a mean-field potential from the protein upon the water molecules and spatially varying translational diffusion coefficients for solvent molecules in directions parallel and perpendicular to the protein surface. The diffusion coefficients can be obtained from the slope of the average-square displacements vs time, as well as from the integral of the velocity autocorrelation functions. It is shown that the former procedure gives a lot of ambiguities due to the variation of the slope of the curve with time. The latter, however, after analytic correction for the contribution from algebraic long-time tails, furnish a much more reliable alternative.

• 444.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH.
The Molecular Mechanism For The Dual Alcohol Modulation Of Cys-Loop Receptors2012In: Alcoholism: Clinical and Experimental Research, ISSN 0145-6008, E-ISSN 1530-0277, Vol. 36, p. 74A-74AArticle in journal (Other academic)
• 445.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, School of Biotechnology (BIO).
The Molecular Mechanism for the Dual Alcohol Modulation of Cys-Loop Receptors2012In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 102, no 3, p. 112A-112AArticle in journal (Other academic)
• 446.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics. KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
Accelerated weight histogram method for exploring free energy landscapes2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 141, no 4, p. 044110-Article in journal (Refereed)

Calculating free energies is an important and notoriously difficult task for molecular simulations. The rapid increase in computational power has made it possible to probe increasingly complex systems, yet extracting accurate free energies from these simulations remains a major challenge. Fully exploring the free energy landscape of, say, a biological macromolecule typically requires sampling large conformational changes and slow transitions. Often, the only feasible way to study such a system is to simulate it using an enhanced sampling method. The accelerated weight histogram (AWH) method is a new, efficient extended ensemble sampling technique which adaptively biases the simulation to promote exploration of the free energy landscape. The AWH method uses a probability weight histogram which allows for efficient free energy updates and results in an easy discretization procedure. A major advantage of the method is its general formulation, making it a powerful platform for developing further extensions and analyzing its relation to already existing methods. Here, we demonstrate its efficiency and general applicability by calculating the potential of mean force along a reaction coordinate for both a single dimension and multiple dimensions. We make use of a non-uniform, free energy dependent target distribution in reaction coordinate space so that computational efforts are not wasted on physically irrelevant regions. We present numerical results for molecular dynamics simulations of lithium acetate in solution and chignolin, a 10-residue long peptide that folds into a beta-hairpin. We further present practical guidelines for setting up and running an AWH simulation.

• 447.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
Sampling rare biomolecular events with adaptive pulling simulations2015In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 44, p. S144-S144Article in journal (Other academic)
• 448.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
Dark Matter Galactic Halos as Bose-Einstein Condensates2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
• 449.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
Foundations of quantum mechanics?2011In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 84, no 1Article in journal (Refereed)

Does quantum mechanics have unsolved foundational problems? Is there a dividing line between the quantum and classical descriptions of the world? In this paper, I give an elementary introduction to the mathematical aspects of quantum and classical models which have prompted such questions.

• 450.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
The Behaviour of Test Particles in the Vicinity of a Stationary Black Hole2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

Studying general relativity, with spacetime as a curved four-dimensional pseudo-Riemannian

space, much of ones physical intuition is lost. Furthermore, there no longer exists

any canonical way to visualise this space, in which all other physics take place. In this

paper, different representations of the Schwarzschild solution are studied, in an attempt

to build up an intuitive understanding of the behaviour of test particles in the vicinity

of a spherically symmetric and stationary source of gravity, such as a black hole. Three

representations of the Schwarzschild solution will be studied; the original Schwarzschild

representation, as well as the Fronsdal embedding and Kruskal-Szekeres transform.

6789101112 401 - 450 of 764
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