Results for "Marjolein Dijkstra"

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Crystal nucleation of colloidal hard dumbbellsOct 28 2010Nov 30 2010Using computer simulations we investigate the homogeneous crystal nucleation in suspensions of colloidal hard dumbbells. The free energy barriers are determined by Monte Carlo simulations using the umbrella sampling technique. We calculate the nucleation ... More
Phase behavior and structure of model colloid-polymer mixtures confined between two parallel planar wallsMar 28 2006Using Gibbs ensemble Monte Carlo simulations and density functional theory we investigate the fluid-fluid demixing transition in inhomogeneous colloid-polymer mixtures confined between two parallel plates with separation distances between one and ten ... More
Softness suppresses fivefold symmetry and enhances crystallization of binary Laves phases in nearly hard spheresJun 25 2019Colloidal crystals with a diamond and pyrochlore structure display wide photonic band gaps at low refractive index contrasts. However, these low-coordinated and open structures are notoriously difficult to self-assemble from colloids interacting with ... More
Unsupervised learning for local structure detection in colloidal systemsJul 04 2019We introduce a simple, fast, and easy to implement unsupervised learning algorithm for detecting different local environments on a single-particle level in colloidal systems. In this algorithm, we use a vector of standard bond-orientational order parameters ... More
Pushing the glass transition towards random close packing using self-propelled hard spheresJun 15 2013Oct 25 2013Although the concept of random close packing with an almost universal packing fraction of ~ 0.64 for hard spheres was introduced more than half a century ago, there are still ongoing debates. The main difficulty in searching the densest packing is that ... More
Non-Equilibrium Surface Tension of the Vapour-Liquid Interface of Active Lennard-Jones ParticlesJun 09 2017Aug 28 2017We study a three-dimensional system of self-propelled Brownian particles interacting via the Lennard-Jones potential. Using Brownian Dynamics simulations in an elongated simulation box, we investigate the steady states of vapour-liquid phase coexistence ... More
Ratchet-induced variations in bulk states of an active ideal gasJul 24 2018Nov 12 2018We study the distribution of active, noninteracting particles over two bulk states separated by a ratchet potential. By solving the steady-state Smoluchowski equations in a flux-free setting, we show that the ratchet potential affects the distribution ... More
Inverse design of charged colloidal particle interactions for self assembly into specified crystal structuresMay 27 2019We study the inverse problem of tuning interaction parameters between charged colloidal particles interacting with a hard-core repulsive Yukawa potential, so that they assemble into specified crystal structures. Here, we target the body-centered-cubic ... More
Colloidal Laves phases as precursors of photonic crystalsMar 24 2016A considerable amount of research in the colloidal science community deals with the design and fabrication of crystalline phases to be employed as photonic crystals. Here, we propose a novel route to the fabrication of colloidal Laves phases, which can ... More
Hard competition: stabilizing the elusive biaxial nematic phase in suspensions of colloidal particles with extreme lengthsJan 22 2018Jan 26 2018We use computer simulations to study the existence and stability of a biaxial nematic $N_b$ phase in systems of hard polyhedral cuboids, triangular prisms, and rhombic platelets, characterized by a long ($L$), medium ($M$), and short ($S$) particle axis. ... More
Rational design and dynamics of self-propelled colloidal bead chains: from rotators to flagellaSep 20 2017The quest for designing new self-propelled colloids is fuelled by the demand for simple experimental models to study the collective behaviour of their more complex natural counterparts. Most synthetic self-propelled particles move by converting the input ... More
The role of topological defects in the two-stage melting and elastic behavior of active Brownian particlesJul 10 2019We find that crystalline states of repulsive active Brownian particles at high activity melt into a hexatic state but this transition is not driven by an unbinding of bound dislocation pairs as suggested by the Kosterlitz-Thouless-Halperin-Nelson-Young ... More
Entropy-driven formation of prolate and oblate cholesteric phases by computer simulationsNov 30 2015Predicting the macroscopic chiral behaviour of cholesteric liquid crystals from the microscopic chirality of the particles is highly non-trivial, even when the chiral interactions are purely entropic in nature. Here we introduce a novel chiral hard-particle ... More
Random close packing of polydisperse hard spheresMar 24 2009We study jammed configurations of hard spheres as a function of compression speed using an event-driven molecular dynamics algorithm. We find that during the compression, the pressure follows closely the metastable liquid branch until the system gets ... More
Phase behavior and structure of colloidal bowl-shaped particles: simulationsJul 01 2010We study the phase behavior of bowl-shaped particles using computer simulations. These particles were found experimentally to form a meta-stable worm-like fluid phase in which the bowl-shaped particles have a strong tendency to stack on top of each other ... More
Effect of bond length fluctuations on crystal nucleation of hard bead chainsApr 24 2012Jun 26 2012We study the spontaneous nucleation and crystallization of linear and cyclic chains of flexibly connected hard spheres using extensive molecular dynamics simulations. To this end, we present a novel event-driven molecular dynamics simulation method, which ... More
Phase behavior of hard spheres confined between parallel hard plates: Manipulation of colloidal crystal structures by confinementApr 06 2006Jun 11 2006We study the phase behavior of hard spheres confined between two parallel hard plates using extensive computer simulations. We determine the full equilibrium phase diagram for arbitrary densities and plate separations from one to five hard-sphere diameters ... More
Phase Separation and Self-Assembly in a Fluid of Mickey Mouse ParticlesAug 20 2015Recent developments in the synthesis of colloidal particles allow for control over shape and inter-particle interaction. One example, among others, is the so-called "Mickey Mouse" (MM) particle for which the self-assembly properties have been previously ... More
Measuring Colloidal Forces from Particle Position Deviations inside an Optical TrapNov 01 2010Feb 18 2011We measure interaction forces between pairs of charged PMMA colloidal particles suspended in a relatively low-polar medium (5 $\lesssim \epsilon \lesssim$ 8) directly from the deviations of particle positions inside two time-shared optical traps. The ... More
Out-of-equilibrium processes in suspensions of oppositely charged colloids: liquid-to-crystal nucleation and gel formationJul 13 2009We study the kinetics of the liquid-to-crystal transformation and of gel formation in colloidal suspensions of oppositely charged particles. We analyse, by means of both computer simulations and experiments, the evolution of a fluid quenched to a state ... More
Phase behaviour of charged colloidal sphere dispersions with added polymer chainsSep 30 2005We study the stability of mixtures of highly screened repulsive charged spheres and non-adsorbing ideal polymer chains in a common solvent using free volume theory. The effective interaction between charged colloids in an aqueous salt solution is described ... More
Phase Diagrams of Binary Mixtures of Oppositely Charged ColloidsMay 21 2010Phase diagrams of binary mixtures of oppositely charged colloids are calculated theoretically. The proposed mean-field-like formalism interpolates between the limits of a hard-sphere system at high temperatures and the colloidal crystals which minimize ... More
Two-stage melting induced by dislocations and grain boundaries in Monolayers of Hard SpheresJul 04 2013Jan 26 2014Melting in two-dimensional systems has remained controversial as theory, simulations, and experiments show contrasting results. One issue that obscures this discussion is whether or not theoretical predictions on strictly 2D systems describe those of ... More
Gas-liquid phase separation in oppositely charged colloids: stability and interfacial tensionJul 18 2006We study the phase behavior and the interfacial tension of the screened Coulomb (Yukawa) restricted primitive model (YRPM) of oppositely charged hard spheres with diameter s using Monte Carlo simulations. We determine the gas-liquid and gas-solid phase ... More
Effective shape and phase behaviour of short charged rodsDec 18 2008We explicitly calculate the orientation-dependent second virial coefficient of short charged rods in an electrolytic solvent, assuming the rod-rod interactions to be a pairwise sum of hard-core and segmental screened-Coulomb repulsions. From the parallel ... More
Van't Hoff's Law for Active Suspensions: the Role of the Solvent Chemical PotentialSep 26 2016In equilibrium, the osmotic pressure of a dilute suspension, in osmotic contact with a solvent reservoir via a semipermeable membrane, is given by Van't Hoff's law. We extend Van't Hoff's law to a suspension of active Brownian particles and predict the ... More
Phase diagram and effective shape of semi-flexible colloidal rods and biopolymersJan 11 2011We study suspensions of semi-flexible colloidal rods and biopolymers using an Onsager-type second-virial functional for a segmented-chain model. For suspensions of thin and thick fd virus particles we calculate phase diagrams in quantitative agreement ... More
A Novel Chiral Phase of Achiral Hard Triangles and an Entropy-Driven Demixing of EnantiomersApr 13 2015We investigate the phase behavior of a system of hard equilateral and right-angled triangles in two dimensions using Monte Carlo simulations. Hard equilateral triangles undergo a continuous isotropic-triatic liquid crystal phase transition at packing ... More
Isotropic-Nematic transition of long thin hard spherocylinders confined in a quasi-two-dimensional planar geometryMar 07 2003We present computer simulations of long thin hard spherocylinders in a narrow planar slit. We observe a transition from the isotropic to a nematic phase with quasi-long-range orientational order upon increasing the density. This phase transition is intrinsically ... More
Van't Hoff's law for active suspensions: the role of the solvent chemical potentialSep 26 2016Nov 16 2017We extend Van't Hoff's law for the osmotic pressure to a suspension of active Brownian particles. The propelled particles exert a net reaction force on the solvent, and thereby either drive a measurable solvent flow from the connecting solvent reservoir ... More
Depletion-induced biaxial nematic states of boardlike particlesNov 17 2011Mar 26 2012With the aim of investigating the stability conditions of biaxial nematic liquid crystals, we study the effect of adding a non-adsorbing ideal depletant on the phase behavior of colloidal hard boardlike particles. We take into account the presence of ... More
Non-Gaussian Dynamics in Smectic Liquid Crystals of Parallel Hard RodsOct 14 2009Using computer simulations, we studied the diffusion and structural relaxation in equilibrium smectic liquid crystal bulk phases of parallel hard spherocylinders. These systems exhibit a non-Gaussian layer-to-layer diffusion due to the presence of periodic ... More
Self-Assembly of Patchy Colloidal DumbbellsDec 05 2014We employ Monte Carlo simulations to investigate the self-assembly of patchy colloidal dumbbells interacting via a modified Kern-Frenkel potential by probing the system concentration and dumbbell shape. We consider dumbbells consisting of one attractive ... More
Stabilizing the Hexagonal Close Packed Structure of Hard Spheres with Polymers : Phase diagram, Structure, and DynamicsMay 02 2016We study the phase behaviour of a binary mixture of colloidal hard spheres and freely-jointed chains of beads using Monte Carlo simulations. Recently Panagiotopoulos and coworkers predicted [Nat. Commun. 5, 4472 (2014)] that the hexagonal close packed ... More
Crystallization and gelation in colloidal systems with short-ranged attractive interactionsOct 02 2008We systematically study the relationship between equilibrium and non-equilibrium phase diagrams of a system of short-ranged attractive colloids. Using Monte Carlo and Brownian dynamics simulations we find a window of enhanced crystallization that is limited ... More
Effect of excluded volume interactions on the interfacial properties of colloid-polymer mixturesNov 07 2007We report a numerical study of equilibrium phase-diagrams and interfacial properties of bulk and confined colloid-polymer mixtures using grand canonical Monte Carlo simulations. Colloidal particles are treated as hard spheres, while the polymer chains ... More
Fitting Prediction Rule Ensembles to Psychological Research Data: An Introduction and TutorialJul 11 2019Prediction rule ensembles (PREs) are a relatively new statistical learning method, which aim to strike a balance between predictive accuracy and interpretability. Starting from a decision tree ensemble, like a boosted tree ensemble or a random forest, ... More
Predicting Patchy Particle Crystals: Variable Box Shape Simulations and Evolutionary AlgorithmsMay 15 2012We consider several patchy particle models that have been proposed in literature and we investigate their candidate crystal structures in a systematic way. We compare two different algorithms for predicting crystal structures: (i) an approach based on ... More
Chemical Potential in Active Systems: Towards predicting Phase Equilibra from bulk equations of state using a Swim PotentialSep 07 2016We derive a microscopic expression for the chemical potential of active Brownian spheres in steady state. We show that the local chemical potential consists of (i) an intrinsic chemical potential similar to passive systems, which depends on density and ... More
Removing grain boundaries from three-dimensional colloidal crystals using active dopantsMar 22 2016Using computer simulations we explore how grain boundaries can be removed from three-dimensional colloidal crystals by doping with a small fraction of active colloids. We show that for sufficient self-propulsion, the system is driven into a crystal-fluid ... More
Frustration of the isotropic-columnar phase transition of colloidal hard platelets by a transient cubatic phaseDec 06 2011Using simulations and theory, we show that the cubatic phase is metastable for three model hard platelets. The locally favored structures of perpendicular particle stacks in the fluid prevent the formation of the columnar phase through geometric frustration ... More
Evidence for out-of-equilibrium crystal nucleation in suspensions of oppositely charged colloidsJul 27 2007We report a numerical study of the rate of crystal nucleation in a binary suspension of oppositely charged colloids. Two different crystal structures compete in the thermodynamic conditions under study. We find that the crystal phase that nucleates is ... More
Efficient shapes for microswimming: from three-body swimmers to helical flagellaMar 08 2016We combine a general formulation of microswimmmer equations of motion with a numerical bead-shell model to calculate the hydrodynamic interactions with the fluid, from which the swimming speed, power and efficiency are extracted. From this framework, ... More
Interparticle torques suppress motility-induced phase separation for rodlike particlesApr 02 2019To study the role of torque in motility-induced phase separation (MIPS), we simulate a system of self-propelled particles whose shape varies smoothly from isotropic (disks/spheres) to weakly elongated (rods). We construct the phase diagrams of 2D active ... More
Vapour-Liquid Coexistence of an Active Lennard-Jones fluidJun 21 2016Sep 22 2016We study a three-dimensional system of self-propelled Lennard-Jones particles using Brownian Dynamics simulations. Using recent theoretical results for active matter, we calculate the pressure and report equations of state for the system. Additionally, ... More
Mechanical and chemical equilibrium in mixtures of active and passive Lennard-Jones particlesSep 13 2016We study the liquid-gas phase coexistence in Brownian dynamics simulations of a binary mixture of active and passive Lennard-Jones particles. We measure the pressure and the composition of the coexisting phases and show that they collapse in the pressure-composition ... More
Vacancy-stabilized crystalline order in hard cubesNov 15 2011Sep 16 2012We examine the effect of vacancies on the phase behavior and structure of systems consisting of hard cubes using event-driven molecular dynamics and Monte Carlo simulations. We find a first-order phase transition between a fluid and a simple cubic crystal ... More
Electrostatic Interactions between Janus ParticlesSep 17 2012In this paper we study the electrostatic properties of `Janus' spheres with unequal charge densities on both hemispheres. We introduce a method to compare primitive-model Monte Carlo simulations of the ionic double layer with predictions of (mean-field) ... More
A Triangular Tessellation Scheme for the Adsorption Free Energy at the Liquid-Liquid Interface: Towards Non-Convex Patterned ColloidsAug 24 2009We introduce a new numerical technique, namely triangular tessellation, to calculate the free energy associated with the adsorption of a colloidal particle at a flat interface. The theory and numerical scheme presented here are sufficiently general to ... More
Dense Regular Packings of Irregular Non-Convex ParticlesJul 04 2011Jul 05 2011We present a new numerical scheme to study systems of non-convex, irregular, and punctured particles in an efficient manner. We employ this method to analyze regular packings of odd-shaped bodies, not only from a nanoparticle but also both from a computational ... More
Crystal nucleation of hard spheres using molecular dynamics, umbrella sampling and forward flux sampling: A comparison of simulation techniquesJun 15 2010Over the last number of years several simulation methods have been introduced to study rare events such as nucleation. In this paper we examine the crystal nucleation rate of hard spheres using three such numerical techniques: molecular dynamics, forward ... More
A Case Study of Sedimentation of Charged Colloids: The Primitive Model and the Effective One-Component ApproachFeb 16 2007Feb 20 2007Sedimentation-diffusion equilibrium density profiles of suspensions of charge-stabilized colloids are calculated theoretically and by Monte Carlo simulation, both for a one-component model of colloidal particles interacting through pairwise screened-Coulomb ... More
Cholesterics of colloidal helices: Predicting the macroscopic pitch from the particle shape and thermodynamic stateDec 03 2014Building a general theoretical framework to describe the microscopic origin of macroscopic chirality in (colloidal) liquid crystals is a long-standing challenge. Here, we combine classical density functional theory with Monte Carlo calculations of virial-type ... More
Microphase separation in oil-water mixtures containing hydrophilic and hydrophobic ionsSep 01 2017We develop a lattice-based Monte Carlo simulation method for charged mixtures capable of treating dielectric heterogeneities. Using this method, we study oil-water mixtures containing an antagonistic salt, with hydrophilic cations and hydrophobic anions. ... More
Chemical potential in active systems: predicting phase equilibrium from bulk equations of state?Sep 07 2016Jan 16 2018We derive a microscopic expression for a quantity $\mu$ that plays the role of chemical potential of Active Brownian Particles (ABPs) in a steady state in the absence of vortices. We show that $\mu$ consists of (i) an intrinsic chemical potential similar ... More
Efficient shapes for microswimming: from three-body swimmers to helical flagellaMar 08 2016Mar 06 2017We combine a general formulation of microswimmmer equations of motion with a numerical bead-shell model to calculate the hydrodynamic interactions with the fluid, from which the swimming speed, power and efficiency are extracted. From this framework, ... More
Heterogeneous Dynamics in Columnar Liquid Crystals of Parallel Hard RodsSep 02 2010Sep 25 2010In the wake of previous studies on the rattling-and-jumping diffusion in smectic liquid crystal phases of colloidal rods, we analyze here for the first time the heterogeneous dynamics in columnar phases. More specifically, we perform computer simulations ... More
Collective Diffusion of Colloidal Hard Rods in Smectic Liquid Crystals: Effect of Particle AnisotropyApr 16 2010We study the layer-to-layer diffusion in smectic-A liquid crystals of colloidal hard rods with different length-to-diameter ratios using computer simulations. The layered arrangement of the smectic phase yields a hopping-type diffusion due to the presence ... More
Glassy dynamics, spinodal fluctuations, and the kinetic limit of hard-rod nucleationMay 25 2010Jul 15 2010Using simulations we identify three dynamic regimes in supersaturated isotropic fluid states of short hard rods: (i) for moderate supersaturations we observe nucleation of multi-layered crystalline clusters; (ii) at higher supersaturation, we find nucleation ... More
Wall-Fluid and Liquid-Gas Interfaces of Model Colloid-Polymer Mixtures by Simulation and TheoryJan 07 2005May 30 2005We perform a study of the interfacial properties of a model suspension of hard sphere colloids with diameter $\sigma_c$ and non-adsorbing ideal polymer coils with diameter $\sigma_p$. For the mixture in contact with a planar hard wall, we obtain from ... More
Jacobi-Angelesco multiple orthogonal polynomials on an $r$-starApr 20 2018We investigate type I multiple orthogonal polynomials on $r$ intervals which have a common point at the origin and endpoints at the $r$ roots of unity $\omega^j$, $j=0,1,\ldots,r-1$, with $\omega = \exp(2\pi i/r)$. We use the weight function $|x|^\beta ... More
Computer simulations of the restricted primitive model at very low temperature and densitySep 30 2009Jan 13 2010The problem of successfully simulating ionic fluids at low temperature and low density states is well known in the simulation literature: using conventional methods, the system is not able to equilibrate rapidly due to the presence of strongly associated ... More
Re-entrant melting and freezing in a model system of charged colloidsDec 27 2005We studied the phase behavior of charged and sterically stabilized colloids using confocal microscopy in a less polar solvent (dielectric constant 5.4). Upon increasing the colloid volume fraction we found a transition from a fluid to a body centered ... More
Ion association in low-polarity solvents: comparisons between theory, simulation, and experimentSep 22 2011The association of ions in electrolyte solutions at very low concentration and low temperature is studied using computer simulations and quasi-chemical ion-pairing theory. The specific case of the restricted primitive model (charged hard spheres) is considered. ... More
Phase diagrams of charged colloidal rods: can a uniaxial charge distribution break chiral symmetry?Dec 15 2015Feb 15 2016We construct phase diagrams for charged rodlike colloids within the second-virial approximation as a function of rod concentration, salt concentration, and colloidal charge. Besides the expected isotropic-nematic transition, we also find parameter regimes ... More
Phase Behavior of a Family of Truncated Hard CubesDec 08 2014In continuation of our work in [A.P. Gantapara et al., Phys. Rev. Lett. 111, 015501 (2013)], we investigate here the thermodynamic phase behavior of a family of truncated hard cubes, for which the shape evolves smoothly from a cube via a cuboctahedron ... More
Critical Casimir Forces and Colloidal Phase Transitions in a Near-Critical Solvent : A Simple Model Reveals a Rich Phase DiagramMar 19 2014Dec 17 2014From experimental studies it is well-known that colloidal particles suspended in a near-critical binary solvent exhibit interesting aggregation phenomena, often associated with colloidal phase transitions, and assumed to be driven by long-ranged solvent ... More
Phase diagram of colloidal hard superballs: from cubes via spheres to octahedraNov 18 2011Jan 13 2012The phase diagram of colloidal hard superballs, of which the shape interpolates between cubes and octahedra via spheres, is determined by free-energy calculations in Monte Carlo simulations. We discover not only a stable face-centered cubic (fcc) plastic ... More
Experimental observation of structural crossover in binary mixtures of colloidal hard spheresApr 03 2007Oct 04 2007Using confocal-microscopy we investigate the structure of binary mixtures of colloidal hard spheres with size ratio q=0.61. As a function of the packing fraction of the two particle species, we observe a marked change of the dominant wavelength in the ... More
Self diffusion of particles in complex fluids: temporary cages and permanent barriersJul 25 2008Oct 07 2008We study the self diffusion of individual particles in dense (non-)uniform complex fluids within dynamic density functional theory and explicitly account for their coupling to the temporally fluctuating background particles. Applying the formalism to ... More
Phase diagrams of colloidal spheres with a constant zeta-potentialSep 30 2010We study suspensions of colloidal spheres with a constant zeta-potential within Poisson-Boltzmann theory, quantifying the discharging of the spheres with increasing colloid density and decreasing salt concentration. We use the calculated renormalized ... More
Connectedness percolation of hard deformed rodsSep 25 2017Nov 28 2017Nanofiller particles, such as carbon nanotubes or metal wires, are used in functional polymer composites to make them conduct electricity. They are often not perfectly straight cylinders, but may be tortuous or exhibit kinks. Therefore we investigate ... More
Crystallizing hard-sphere glasses by doping with active particlesOct 28 2013Aug 25 2014Crystallization and vitrification are two different routes to form a solid. Normally these two processes suppress each other, with the glass transition preventing crystallization at high density (or low temperature). This is even true for systems of colloidal ... More
Lyman Alpha Emitting Galaxies as a Probe of ReionizationJun 27 2014Aug 05 2014The Epoch of Reionization (EoR) represents a milestone in the evolution of our Universe. Star-forming galaxies that existed during the EoR likely emitted a significant fraction (~5-40%) of their bolometric luminosity as Lyman Alpha (Lya) line emission. ... More
Prospects for Detecting the First Black Holes with the Next Generation of TelescopesJul 17 2018This chapter describes the prospects for detecting the first black holes in our Universe, with a specific focus on instruments/telescopes that will come online within the next decade, including e.g. the SKA, WFIRST, EUCLID, JWST, and large ground-based ... More
Generalization of an Upper Bound on the Number of Nodes Needed to Achieve Linear SeparabilityFeb 10 2018An important issue in neural network research is how to choose the number of nodes and layers such as to solve a classification problem. We provide new intuitions based on earlier results by An et al. (2015) by deriving an upper bound on the number of ... More
Orientational order of carbon nanotube guests in a nematic host suspension of colloidal viral rodsJun 23 2013In order to investigate the coupling between the degrees of alignment of elongated particles in binary nematic dispersions, surfactant stabilized single-wall carbon nanotubes (CNTs) have been added to nematic suspensions of colloidal rodlike viruses in ... More
Self-assembly of "Mickey Mouse" shaped colloids into tube-like structures: experiments and simulationsDec 10 2014The self-assembly of anisotropic patchy particles with triangular shape was studied by experiments and computer simulations. The colloidal particles were synthesized in a two-step seeded emulsion polymerization process, and consist of a central smooth ... More
The Polarization of Scattered Lyman Alpha Radiation Around High-Redshift GalaxiesNov 15 2007Jul 16 2008The high-redshift Universe contains luminous Lyman Alpha (hereafter Lya) emitting sources such as galaxies and quasars. The emitted Lya radiation is often scattered by surrounding neutral hydrogen atoms. We show that the scattered Lya radiation obtains ... More
A new model framework for circumgalactic Ly$α$ radiative transfer constrained by galaxy-Ly$α$ forest clusteringOct 27 2017Aug 12 2018We present a new perturbative approach to "constrained Ly$\alpha$ radiative transfer'" (RT) through the circum- and inter-galactic medium (CGM and IGM). We constrain the HI content and kinematics of the CGM and IGM in a physically motivated model, using ... More
Shaping bipolar Planetary Nebulae : How mass loss leads to waistline developmentJul 15 2006Asymptotic Giant Branch (AGB) stars generally have spherically symmetric envelopes, whereas most post-AGB stars and Planetary Nebulae (PNe) show axisymmetric circumstellar envelopes. While various mechanisms for axisymmetric circumstellar structures may ... More
Very Massive Stars in High-Redshift GalaxiesApr 12 2007Jun 27 2007A significant fraction of Lyman Alpha (Lya) emitting galaxies (LAEs) at z> 5.7 have rest-frame equivalent widths (EW) greater than ~100 Angstrom. However only a small fraction of the Lya flux produced by a galaxy is transmitted through the IGM, which ... More
Ly$α$ Spectra from Multiphase Outflows, and their Connection to Shell ModelsApr 22 2016We perform Lyman-$\alpha$ (Ly$\alpha$) Monte-Carlo radiative transfer calculations on a suite of $2500$ models of multiphase, outflowing media, which are characterized by $14$ parameters. We focus on the Ly$\alpha$ spectra emerging from these media, and ... More
Lyman Alpha Driven Outflows Around Star Forming GalaxiesJul 16 2008Sep 11 2008We present accurate Monte-Carlo calculations of Lyman Alpha (hereafter Lya) radiation pressure in a range of models which represent galaxies during various epochs of our Universe. We show that the radiation force that Lya photons exert on hydrogen gas ... More
Star Formation Indicators and Line Equivalent Width in Lyman Alpha GalaxiesNov 06 2009The equivalent width (EW) of the Lyman Alpha (Lya) line is directly related to the ratio of star formation rates determined from Lya flux and UV flux density [SFR(Lya)/SFR(UV)]. We use published data --in the literature EW and SFR(Lya)/SFR(UV) are treated ... More
Naturalness as a reasonable scientific principle in fundamental physicsApr 19 2019I aim to clarify the physical content and significance of naturalness. Physicists' earliest understanding of naturalness, as an autonomy of scales (AoS) requirement provides the most cogent definition of naturalness and I will assert that i) this provides ... More
Acceleration of Galactic Supershells by Lyman Alpha RadiationSep 11 2008Feb 25 2009Scattering of Lyman Alpha (hereafter Lya) photons by neutral hydrogen gas in a single outflowing 'supershell' around star forming regions often explains the shape and offset of the observed Lya emission line from galaxies. We compute the radiation pressure ... More
Non-Gravitational Contributions to the Clustering of Ly-alpha Selected Galaxies: Implications for Cosmological SurveysApr 04 2011We show that the dependence of Ly-alpha absorption on environment leads to significant non-gravitational features in the redshift space power-spectrum of Ly-alpha selected galaxies. We derive a physically motivated fitting formula that can be included ... More
Lyman Alpha Constraints on Very Low Luminosity AGNJun 14 2006Sep 21 2006Recent surveys have detected Lya emission from z=4.5-6.5 at luminosities as low as 10^41 erg/s. There is good evidence that low numbers of AGN are among observed faint Lya emitters. Combining these observations with an empirical relation between the intrinsic ... More
UV Radiative Feedback During the Advanced Stages of ReionizationJun 19 2008The ionizing ultraviolet background (UVB) during reionization can suppress the gas content of low-mass galaxies, even those capable of efficient atomic cooling, and thus lead to an extended reionization epoch. In this work, we explore the importance of ... More
An Empirical Study of the Relationship between Lyα and UV selected Galaxies: Do Theorists and Observers `Select' the Same Objects?Aug 18 2011Nov 30 2011Lyman Alpha Emitters (LAEs) are galaxies that have been selected on the basis of a strong Ly{\alpha} emission line in their spectra. Observational campaigns have dramatically increased the sample of known LAEs, which now extends out to z=7. These discoveries ... More
Seeing Through the Trough: Outflows and the Detectability of Lyman Alpha Emission from the First GalaxiesApr 14 2010The next generation of telescopes aim to directly observe the first generation of galaxies that initiated the reionization process in our Universe. The Lyman Alpha (Lya) emission line is robustly predicted to be the most prominent intrinsic spectral feature ... More
Directional Lya equivalent boosting I. Spherically symmetric distributions of clumpsJun 25 2014Aug 29 2014We quantify the directional dependence of the escape fraction of Lyman-$\alpha$ (Ly$\alpha$) and non-ionising UV-continuum photons from a multiphase medium, and investigate whether there exist directional enhancements in the Ly$\alpha$ equivalent width ... More
Lyman Alpha Blobs as an Observational Signature of Cold Accretion Streams into GalaxiesFeb 17 2009Oct 15 2009Recent hydrodynamic simulations of galaxy formation reveal streams of cold (T ~ 1e4 K) gas flowing into the centers of dark matter halos as massive as 1e12-1e13.5 M_sun at redshifts z~1-3. In this paper we show that if > 20% of the gravitational binding ... More
Requirements for Cosmological 21-cm MasersAug 08 2006Nov 13 2007We perform Monte-Carlo calculations of the radiative transfer of Lyman Alpha (hereafter Lya) photons emitted by a source embedded in a neutral collapsing gas cloud. This represents a young galaxy or quasar during the early stages of the epoch of reionisation ... More
Local and Nonlocal Thermal Field TheoryApr 19 2019Firstly, nonlocal field theories will be motivated, primarily in the gravity sector. We discuss how nonlocal theories of gravity can circumvent typical problems of finitely-many higher derivative theories and can, among other things, be either ghostfree ... More
Binary icosahedral quasicrystals of hard spheres in spherical confinementJun 24 2019The influence of geometry on the local and global packing of particles is important to many fundamental and applied research themes such as the structure and stability of liquids, crystals and glasses. Here, we show by experiments and simulations that ... More
Linear, third- and fifth-order nonlinear spectroscopy of a charge transfer system coupled to an underdamped vibrationFeb 23 2015We study hole, electron and exciton transport in a charge transfer system in the presence of underdamped vibrational motion. We analyze the signature of these processes in the linear and third-, and fifth-order nonlinear electronic spectra. Calculations ... More
Controlling a Quantum System via its Boundary ConditionsOct 01 2018We numerically study a particle in a box with moving walls. In the case where the walls are oscillating sinusoidally with small amplitude, we show that states up to the fourth state can be populated with more than 80 percent population, while higher-lying ... More
Empirical Constraints on the Star Formation & Redshift Dependence of the Lyman Alpha `Effective' Escape FractionMay 15 2013Aug 13 2013We derive empirical constraints on the volume averaged `effective' escape fraction of Lyman Alpha (Lya) photons from star forming galaxies as a function of redshift, by comparing star formation functions inferred directly from observations, to observed ... More