Results for "Diederik S. Wiersma"

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Multichannel remote polarization control enabled by nanostructured Liquid Crystalline NetworksJun 08 2019In this article we demonstrate that a grating fabricated through nanoscale volumetric crosslinking of a liquid crystalline polymer enables remote polarization control over the diffracted channels. This functionality is a consequence of the responsivity ... More
Biomimetic Polymer Film with Brilliant Brightness Using a One-Step Water Vapor-Induced Phase Separation MethodJun 11 2019The scales of the white Cyphochilus beetles are endowed with unusual whiteness arising from the exceptional scattering efficiency of their disordered ultrastructure optimized through millions of years of evolution. Here, a simple, one-step method based ... More
Experimental and theoretical investigation of statistical regimes in random laser emissionSep 10 2013We present a theoretical and experimental study aimed at characterizing statistical regimes in a random laser. Both the theoretical simulations and the experimental results show the possibility of three region of fluctuations increasing the pumping energy. ... More
Multiple scattering of light in superdiffusive mediaMar 10 2010Oct 25 2010Light transport in superdiffusive media of finite size is studied theoretically. The intensity Green's function for a slab geometry is found by discretizing the fractional diffusion equation and employing the eigenfunction expansion method. Truncated ... More
Weak* tensor products for von Neumann algebrasJun 04 2015The category of $C^*$-algebras is blessed with many different tensor products. In contrast, virtually the only tensor product ever used in the category of von Neumann algebras is the normal spatial tensor product. We propose a definition of what a generic ... More
Statistical regimes of random laser fluctuationsNov 06 2006Feb 07 2007Statistical fluctuations of the light emitted from amplifying random media are studied theoretically and numerically. The characteristic scales of the diffusive motion of light lead to Gaussian or power-law (Levy) distributed fluctuations depending on ... More
Photon Management in Two-Dimensional Disordered MediaFeb 21 2012Apr 09 2013Elaborating reliable and versatile strategies for efficient light coupling between free space and thin films is of crucial importance for new technologies in energy efficiency. Nanostructured materials have opened unprecedented opportunities for light ... More
Optimized White Reflectance in Photonic Network StructuresMay 28 2019Three-dimensional disordered networks are receiving increasing attention as versatile architectures for highly scattering materials. However, due to their complex morphology, little is still known about the interplay between their structural and optical ... More
Localization in one-dimensional chains with Lévy-type disorderDec 05 2014We study Anderson localization of the classical lattice waves in a chain with mass impurities distributed randomly through a power-law relation $s^{-(1+\alpha)}$ with $ s $ as the distance between two successive impurities and $\alpha>0$. This model of ... More
Spatio-temporal visualization of light transport in complex photonic structuresSep 18 2015Jun 16 2016Spatio-temporal imaging of light propagation is very important in photonics because it provides the most direct tool available to study the interaction between light and its host environment. Sub-ps time resolution is needed to investigate the fine and ... More
Magnetic field generation in relativistic shocks - An early end of the exponential Weibel instability in electron-proton plasmasAug 30 2004We discuss magnetic field generation by the proton Weibel instability in relativistic shocks, a situation that applies to the external shocks in the fireball model for Gamma-ray Bursts, and possibly also to internal shocks. Our analytical estimates show ... More
Activated Transport in the individual Layers that form the $ν_T$=1 Exciton CondensateJul 22 2004We observe the total filling factor $\nu_{T}$=1 quantum Hall state in a bilayer two-dimensional electron system with virtually no tunnelling. We find thermally activated transport in the balanced system with a monotonic increase of the activation energy ... More
Weak localization of light in superdiffusive random systemsOct 07 2011L\'evy flights constitute a broad class of random walks that occur in many fields of research, from animal foraging in biology, to economy to geophysics. The recent advent of L\'evy glasses allows to study L\'evy flights in controlled way using light ... More
CELES: CUDA-accelerated simulation of electromagnetic scattering by large ensembles of spheresJun 06 2017CELES is a freely available MATLAB toolbox to simulate light scattering by many spherical particles. Aiming at high computational performance, CELES leverages block-diagonal preconditioning, a lookup-table approach to evaluate costly functions and massively ... More
Two-dimensional disorder for broadband, omnidirectional and polarization-insensitive absorptionNov 27 2012The surface of thin-film solar cells can be tailored with photonic nanostructures to allow light trapping in the absorbing medium. This in turn increases the optical thickness of the film and thus enhances their absorption. Such a coherent light trapping ... More
Light transport and localization in two-dimensional correlated disorderJul 07 2013Feb 03 2014Structural correlations in disordered media are known to affect significantly the propagation of waves. In this article, we theoretically investigate the transport and localization of light in 2D photonic structures with short-range correlated disorder. ... More
Holey Random Walks: Optics of Heterogeneous Turbid CompositesNov 08 2012We present a probabilistic theory of random walks in turbid media with non-scattering regions. It is shown that important characteristics such as diffusion constants, average step lengths, crossing statistics and void spacings can be analytically predicted. ... More
Structured Optical Materials Controlled by LightOct 08 2018Materials of which the optical response is determined by their structure are of much interest both for their fundamental properties and applications. Examples range from simple gratings to photonic crystals. Obtaining control over the optical properties ... More
Path length enhancement in disordered media for increased absorptionJul 13 2015Sep 04 2015We theoretically and numerically investigate the capability of disordered media to enhance the optical path length in dielectric slabs and augment their light absorption efficiency due to scattering. We first perform a series of Monte Carlo simulations ... More
Exploiting breakdown of the similarity relation for diffuse light transport: simultaneous retrieval of scattering anisotropy and diffusion constantNov 28 2012As manifested in the similarity relation of diffuse light transport, it is difficult to assess single scattering characteristics from multiply scattered light. We take advantage of the limited validity of the diffusion approximation of light transport ... More
Walk dimension for light in complex disordered mediaDec 20 2013Aug 21 2014Transport in complex systems is characterized by a fractal dimension -- the walk dimension -- that indicates the diffusive or anomalous nature of the underlying random walk process. Here we report on the experimental retrieval of this key quantity, using ... More
Transport in quenched disorder: light diffusion in strongly heterogeneous turbid mediaOct 23 2013We present a theoretical and experimental study of light transport in disordered media with strongly heterogeneous distribution of scatterers formed via non-scattering regions. Step correlations induced by quenched disorder are found to prevent diffusivity ... More
The dynamics of star-forming regions - which mechanisms set the cluster formation efficiency?Jul 11 2011The fraction of star formation that results in bound stellar clusters (cluster formation efficiency or CFE) is a central quantity in many studies of star formation, star clusters and galaxies. Recent results suggest that contrary to popular assumption, ... More
A Cross-disciplinary Framework for the Description of Contextually Mediated ChangeJun 01 2007We present a mathematical framework (referred to as Context-driven Actualization of Potential, or CAP) for describing how entities change over time under the influence of a context. The approach facilitates comparison of change of state of entities studied ... More
Evolution as context-driven actualization of potential: Toward an interdisciplinary theory of change of stateNov 05 2005It is increasingly evident that there is more to biological evolution than natural selection; moreover, the concept of evolution is not limited to biology. We propose an integrative framework for characterizing how entities evolve, in which evolution ... More
General sGoldstino InflationAug 12 2016We prove that all inflationary models, including those with dark energy after the end of inflation, can be embedded in minimal supergravity with a single chiral superfield. Moreover, the amount of supersymmetry breaking is independently tunable due to ... More
Are globular clusters the natural outcome of regular high-redshift star formation?Sep 09 2015We summarise some of the recent progress in understanding the formation and evolution of globular clusters (GCs) in the context of galaxy formation and evolution. It is discussed that an end-to-end model for GC formation and evolution should capture four ... More
Deducing effective light transport parameters in optically thin systemsSep 14 2015Sep 21 2015We present an extensive Monte Carlo study on light transport in optically thin slabs, addressing both axial and transverse propagation. We completely characterize the so-called ballistic-to-diffusive transition, notably in terms of the spatial variance ... More
Diffusion of light in semitransparent mediaSep 14 2015Sep 21 2015Light diffusion is usually associated with thick, opaque media. Indeed, multiple scattering is necessary for the onset of the diffusive regime and such condition is generally not met in almost transparent media. Nonetheless, at long enough times, transport ... More
On the fraction of star formation occurring in bound stellar clustersAug 14 2012We present a theoretical framework in which bound stellar clusters arise naturally at the high-density end of the hierarchy of the interstellar medium (ISM). Due to short free-fall times, these high-density regions achieve high local star formation efficiencies, ... More
Collateral Damage: the Implications of Utrecht Star Cluster Astrophysics for Galaxy EvolutionJun 06 2012Until the early 2000s, the research portfolio of the Astronomical Institute in Utrecht (SIU) did not include galaxy evolution. Somewhat serendipitously, this changed with the advent of the star cluster group. In only a few years, a simple framework was ... More
A galactic-scale origin for stellar clusteringAug 31 2012We recently presented a model for the cluster formation efficiency (CFE), i.e. the fraction of star formation occurring in bound stellar clusters. It utilizes the idea that the formation of stars and stellar clusters occurs across a continuous spectrum ... More
Towards a multi-scale understanding of the gas-star formation cycle in the Central Molecular ZoneSep 26 2016The Central Molecular Zone (CMZ, the central 500 pc of the Milky Way) contains the largest reservoir of high-density molecular gas in the Galaxy, but forms stars at a rate 10-100 times below commonly-used star formation relations. We discuss recent efforts ... More
Contextualizing concepts using a mathematical generalization of the quantum formalismOct 29 2013Nov 01 2013We outline the rationale and preliminary results of using the state context property (SCOP) formalism, originally developed as a generalization of quantum mechanics, to describe the contextual manner in which concepts are evoked, used and combined to ... More
A Theory of Concepts and Their Combinations I: The Structure of the Sets of Contexts and PropertiesFeb 26 2004We propose a theory for modeling concepts that uses the state-context-property theory (SCOP), a generalization of the quantum formalism, whose basic notions are states, contexts and properties. This theory enables us to incorporate context into the mathematical ... More
The Effect of Pre-Main Sequence Stars on Star Cluster DynamicsOct 07 2005We investigate the effects of the addition of pre-main sequence evolution to star cluster simulations. We allowed stars to follow pre-main sequence tracks that begin at the deuterium burning birthline and end at the zero age main sequence. We compared ... More
A Case for Applying an Abstracted Quantum Formalism to CognitionApr 11 2004This chapter outlines some of the highlights of efforts undertaken by our group to describe the role of contextuality in the conceptualization of conscious experience using generalized formalisms from quantum mechanics.
The Optical Colors of Giant Elliptical Galaxies and their Metal-Rich Globular Clusters Indicate a Bottom-Heavy Initial Mass FunctionNov 21 2012Jan 02 2013We report a systematic and statistically significant offset between the optical (g-z or B-I) colors of seven massive elliptical galaxies and the mean colors of their associated massive metal-rich globular clusters (GCs) in the sense that the parent galaxies ... More
Intrinsic Contextuality as the Crux of ConsciousnessOct 29 2013A stream of conscious experience is extremely contextual; it is impacted by sensory stimuli, drives and emotions, and the web of associations that link, directly or indirectly, the subject of experience to other elements of the individual's worldview. ... More
An Algebraic Classification of Exceptional EFTs Part II: SupersymmetryMay 14 2019We present a novel approach to classify supersymmetric effective field theories (EFTs) whose scattering amplitudes exhibit enhanced soft limits. These enhancements arise due to non-linearly realised symmetries on the Goldstone modes of such EFTs and we ... More
Power Spectrum of Inflationary AttractorsAug 25 2014Jan 20 2015Inflationary attractors predict the spectral index and tensor-to-scalar ratio to take specific values that are consistent with Planck. An example is the universal attractor for models with a generalised non-minimal coupling, leading to Starobinsky inflation. ... More
Fast and inefficient star formation due to short-lived molecular clouds and rapid feedbackMay 21 2019May 23 2019The physics of star formation and the deposition of mass, momentum, and energy into the interstellar medium by massive stars (`feedback') are the main uncertainties in modern cosmological simulations of galaxy formation and evolution. These processes ... More
A Geometric Formulation of SupersymmetrySep 23 2016The scalar fields of supersymmetric models are coordinates of a geometric space. We propose a formulation of supersymmetry that is covariant with respect to reparametrizations of this target space. Employing chiral multiplets as an example, we introduce ... More
Toward a Formal Model of the Shifting Relationship between Concepts and Contexts during Associative ThoughtOct 29 2013The quantum inspired State Context Property (SCOP) theory of concepts is unique amongst theories of concepts in offering a means of incorporating that for each concept in each different context there are an unlimited number of exemplars, or states, of ... More
Fibre Inflation and $α$-attractorsJul 18 2017Dec 26 2017Fibre inflation is a specific string theory construction based on the Large Volume Scenario that produces an inflationary plateau. We outline its relation to $\alpha$-attractor models for inflation, with the cosmological sector originating from certain ... More
Pole Inflation - Shift Symmetry and Universal CorrectionsJul 08 2015Jan 07 2016An appealing explanation for the Planck data is provided by inflationary models with a singular non-canonical kinetic term: a Laurent expansion of the kinetic function translates into a potential with a nearly shift-symmetric plateau in canonical fields. ... More
Do Spectroscopic Dense Gas Fractions Track Molecular Cloud Surface Densities?Nov 19 2018We use ALMA and IRAM 30-m telescope data to investigate the relationship between the spectroscopically-traced dense gas fraction and the cloud-scale (120 pc) molecular gas surface density in five nearby, star-forming galaxies. We estimate the dense gas ... More
The Star Formation Efficiency per Free Fall Time in Nearby GalaxiesJun 28 2018We estimate the star formation efficiency per gravitational free fall time, $\epsilon_{\rm ff}$, from observations of nearby galaxies with resolution matched to the typical size of a Giant Molecular Cloud. This quantity, $\epsilon_{\rm ff}$, is theoretically ... More
Magnetic field generation in relativistic shocksDec 08 2003We present an analytical estimate for the magnetic field strength generated by the Weibel instability in ultra-relativistic shocks in a hydrogen plasma. We find that the Weibel instability is, by itself, not capable of converting the kinetic energy of ... More
Optimal error estimates for corrected trapezoidal rulesMay 16 2012Corrected trapezoidal rules are proved for $\int_a^b f(x)\,dx$ under the assumption that $f"\in L^p([a,b])$ for some $1\leq p\leq\infty$. Such quadrature rules involve the trapezoidal rule modified by the addition of a term $k[f'(a)-f'(b)]$. The coefficient ... More
A new chiral electro-optic effect: Sum-frequency generation from optically active liquids in the presence of a dc electric fieldJun 24 2003We report the observation of sum-frequency signals that depend linearly on an applied electrostatic field and that change sign with the handedness of an optically active solution. This recently predicted chiral electro-optic effect exists in the electric-dipole ... More
Effect of interactions on the localization of a Bose-Einstein condensate in a quasi-periodic latticeNov 06 2006The transport properties of a Bose-Einstein condensate in a 1D incommensurate bichromatic lattice are investigated both theoretically and experimentally. We observe a blockage of the center of mass motion with low atom number, and a return of motion when ... More
Observations of metals in the intra-cluster mediumJan 07 2008Because of their deep gravitational potential wells, clusters of galaxies retain all the metals produced by the stellar populations of the member galaxies. Most of these metals reside in the hot plasma which dominates the baryon content of clusters. This ... More
Effect of optical disorder and single defects on the expansion of a Bose-Einstein condensate in a one-dimensional waveguideJul 06 2005We investigate the one-dimensional expansion of a Bose-Einstein condensate in an optical guide in the presence of a random potential created with optical speckles. With the speckle the expansion of the condensate is strongly inhibited. A detailed investigation ... More
Photonic Crystals with Controlled DisorderNov 05 2010Photonic crystals are extremely sensitive to structural disorder even to the point of completely losing their functionalities. While on one side this can be detrimental for applications in traditional optical devices, on the other side, it gives also ... More
Observation of coherent backscattering of light by cold atomsApr 20 2000Coherent backscattering (CBS) of light waves by a random medium is a signature of interference effects in multiple scattering. This effect has been studied in many systems ranging from white paint to biological tissues. Recently, we have observed CBS ... More
A fundamental test for stellar feedback recipes in galaxy simulationsMay 23 2019Direct comparisons between galaxy simulations and observations that both reach scales < 100 pc are strong tools to investigate the cloud-scale physics of star formation and feedback in nearby galaxies. Here we carry out such a comparison for hydrodynamical ... More
The dynamical evolution of molecular clouds near the Galactic Centre -- III. Tidally--induced star formation in protocluster cloudsMar 25 2019As part of a series of papers aimed at understanding the evolution of the Milky Way's Central Molecular Zone (CMZ), we present hydrodynamical simulations of turbulent molecular clouds orbiting in an accurate model of the gravitational potential extant ... More
How sustainable are different levels of consciousness?May 12 2017The human brain processes a wide variety of inputs and does so either consciously or subconsciously. According to the Global Workspace theory, conscious processing involves broadcasting of information to several regions of the brain and subconscious processing ... More
Exotic C*-algebras of geometric groupsSep 19 2018We consider a new class of potentially exotic group C*-algebras $C^*_{PF_p^*}(G)$ for a locally compact group $G$, and its connection with the class of potentially exotic group C*-algebras $C^*_{L^p}(G)$ introduced by Brown and Guentner. Surprisingly, ... More
Simple derivation of basic quadrature formulasFeb 01 2012Simple proofs of the midpoint, trapezoidal and Simpson's rules are proved for numerical integration on a compact interval. The integrand is assumed to be twice continuously differentiable for the midpoint and trapezoidal rules, and to be four times continuously ... More
Cosmological simulations of the formation of the stellar haloes around disc galaxiesFeb 12 2011Jul 18 2011We use the Galaxies-Intergalactic Medium Interaction Calculation (GIMIC) suite of cosmological hydrodynamical simulations to study the formation of stellar spheroids of Milky Way-mass disc galaxies. The simulations contain accurate treatments of metal-dependent ... More
Relativity Theory RefoundedNov 27 2015We put forward a new view of relativity theory that makes the existence of a flow of time compatible with the four-dimensional block universe. To this end, we apply the creation-discovery view elaborated for quantum mechanics to relativity theory and ... More
Quantum Theory and Human Perception of the Macro-WorldMar 17 2014May 29 2014We investigate the question of 'why customary macroscopic entities appear to us humans as they do, i.e. as bounded entities occupying space and persisting through time', starting from our knowledge of quantum theory, how it affects the behavior of such ... More
Universality classes of inflationSep 05 2013Dec 23 2013We investigate all single-field, slow-roll inflationary models whose slow-roll parameters scale as 1/N in the limit of a large number of e-folds N. We proof that all such models belong to two universality classes, characterised by a single parameter. ... More
Interpreting Quantum Particles as Conceptual EntitiesApr 15 2010We elaborate an interpretation of quantum physics founded on the hypothesis that quantum particles are conceptual entities playing the role of communication vehicles between material entities composed of ordinary matter which function as memory structures ... More
M-theory and Gauged SupergravitiesAug 23 2004Aug 31 2004We present a pedagogical discussion of the emergence of gauged supergravities from M-theory. First, a review of maximal supergravity and its global symmetries and supersymmetric solutions is given. Next, different procedures of dimensional reduction are ... More
Gaugings at angles from orientifold reductionsFeb 03 2009Jun 10 2009We consider orientifold reductions to N=4 gauged supergravity in four dimensions. A special feature of this theory is that different factors of the gauge group can have relative angles with respect to the electro-magnetic SL(2) symmetry. These are crucial ... More
On exotic group C*-algebrasMay 04 2015Mar 09 2016Let $\Gamma$ be a discrete group. A $C^*$-algebra $A$ is an exotic $C^*$-algebra (associated to $\Gamma$) if there exist proper surjective $C^*$-quotients $C^*(\Gamma)\to A\to C^*_r(\Gamma)$. In this paper, we show that a large class of exotic $C^*$-algebras ... More
A conceptual study on real-time adaptive radiation therapy optimization through ultra-fast beamlet controlNov 08 2018Mar 04 2019A central problem in the field of radiation therapy (RT) is how to optimally deliver dose to a patient in a way that fully accounts for anatomical position changes over time. As current RT is a static process, where beam intensities are calculated before ... More
Spin and Wind Directions: Identifying Entanglement in Nature and CognitionJul 31 2015Aug 20 2015We performed a cognitive experiment in which we asked the participants to pick a pair of directions they considered as the 'preferred good example of two different wind directions'. The results of the experiment reveal that the 'Clauser Horne Shimony ... More
A Contextual Risk Model for the Ellsberg ParadoxMay 09 2011The Allais and Ellsberg paradoxes show that the expected utility hypothesis and Savage's Sure-Thing Principle are violated in real life decisions. The popular explanation in terms of 'ambiguity aversion' is not completely accepted. On the other hand, ... More
Contextual Risk and Its Relevance in EconomicsMay 09 2011Uncertainty in economics still poses some fundamental problems illustrated, e.g., by the Allais and Ellsberg paradoxes. To overcome these difficulties, economists have introduced an interesting distinction between 'risk' and 'ambiguity' depending on the ... More
Adam: A Method for Stochastic OptimizationDec 22 2014Jul 23 2015We introduce Adam, an algorithm for first-order gradient-based optimization of stochastic objective functions, based on adaptive estimates of lower-order moments. The method is straightforward to implement, is computationally efficient, has little memory ... More
Universality Classes of Scale Invariant InflationJul 13 2015We investigate the inflationary implications of extensions of Poincare symmetry. The simplest constructions with local scale invariance lead to universal predictions: the spectral index is $n_s = 1-2/N$, in excellent agreement with Planck data, while ... More
Cosmological Attractors from $α$-Scale SupergravityMar 26 2015Sep 16 2015The Planck value of the spectral index can be interpreted as $n_s = 1 - 2/N$ in terms of the number of e-foldings $N$. An appealing explanation for this phenomenological observation is provided by $\alpha$-attractors: the inflationary predictions of these ... More
Quantum Model Theory (QMod): Modeling Contextual Emergent Entangled Interfering EntitiesApr 21 2012Aug 11 2012In this paper we present 'Quantum Model Theory' (QMod), a theory we developed to model entities that entail the typical quantum effects of 'contextuality', 'superposition', 'interference', 'entanglement' and 'emergence'. The aim of QMod is to put forward ... More
Fast Gradient-Based Inference with Continuous Latent Variable Models in Auxiliary FormJun 04 2013We propose a technique for increasing the efficiency of gradient-based inference and learning in Bayesian networks with multiple layers of continuous latent vari- ables. We show that, in many cases, it is possible to express such models in an auxiliary ... More
De Sitter in Extended SupergravityDec 22 2009We show that known de Sitter solutions in extended gauged supergravity theories are interrelated via a web of supersymmetry-breaking truncations. In particular, all N=8 models reduce to a subset of the N=4 possibilities. Furthermore, a different subset ... More
Globular clusters as the relics of regular star formation in 'normal' high-redshift galaxiesSep 07 2015We present an end-to-end, two-phase model for the origin of globular clusters (GCs). In the model, populations of stellar clusters form in the high-pressure discs of high-redshift ($z>2$) galaxies (a rapid-disruption phase due to tidal perturbations from ... More
The evolution of the stellar mass function in star clustersOct 24 2009(Abridged) The dynamical ejection of stars from star clusters affects the shape of the stellar mass function (MF) in these clusters, because the escape probability of a star depends on its mass. The objective of this paper is to provide and to apply a ... More
Distilling the Essence of an Evolutionary Process and Implications for a Formal Description of CultureSep 18 2013It has been proposed that, since the origin of life and the ensuing evolution of biological species, a second evolutionary process has appeared on our planet. It is the evolution of culture-e.g., ideas, beliefs, and artifacts. Does culture evolve in the ... More
Contextualizing Concepts using a Mathematical Generalization of the Quantum FormalismMay 26 2002Aug 06 2004We outline the rationale and preliminary results of using the State Context Property (SCOP) formalism, originally developed as a generalization of quantum mechanics, to describe the contextual manner in which concepts are evoked, used, and combined to ... More
A model of the emergence and evolution of integrated worldviewsJan 09 2010It is proposed that the ability of humans to flourish in diverse environments and evolve complex cultures reflects the following two underlying cognitive transitions. The transition from the coarse-grained associative memory of Homo habilis to the fine-grained ... More
State Property Systems and Closure Spaces: Extracting the Classical and Nonclassical PartsApr 12 2004We introduce classical properties using the concept of super selection rule, i.e. two properties are separated by a superselection rule iff there do not exist 'superposition states' related to these two properties. Then we show that the classical properties ... More
Twin SupergravitiesApr 08 2009Jul 13 2009We study the phenomenon that pairs of supergravities can have identical bosonic field content but different fermionic extensions. Such twin theories are classified and shown to originate as truncations of a common theory with more supersymmetry. Moreover, ... More
Extended Symmetries in Supergravity: the Semi-simple CaseMay 16 2008Jul 04 2008The bosonic sector of various supergravity theories reduces to a homogeneous space G/H in three dimensions. The corresponding algebras g are simple for (half-)maximal supergravity, but can be semi-simple for other theories. We extend the existing literature ... More
The minimum metallicity of globular clusters and its physical origin -- implications for the galaxy mass-metallicity relation and observations of proto-globular clusters at high redshiftApr 22 2019In the local Universe, globular clusters (GCs) with metallicities $[{\rm Fe}/{\rm H}]<-2.5$ are extremely rare. In this Letter, the close connection between GC formation and galaxy evolution is used to show that this GC metallicity `floor' results from ... More
General sGoldstino InflationAug 12 2016Oct 25 2016We prove that all inflationary models, including those with dark energy after the end of inflation, can be embedded in minimal supergravity with a single chiral superfield. Moreover, the amount of supersymmetry breaking is independently tunable due to ... More
An uncertainty principle for star formation - II. A new method for characterising the cloud-scale physics of star formation and feedback across cosmic historyApr 30 2018Sep 04 2018The cloud-scale physics of star formation and feedback represent the main uncertainty in galaxy formation studies. Progress is hampered by the limited empirical constraints outside the restricted environment of the Local Group. In particular, the poorly-quantified ... More
Metastable supersymmetry breaking in extended supergravityDec 16 2010Jul 28 2011We consider the stability of non-supersymmetric critical points of general N=4 supergravities. A powerful method to analyse this issue based on the sGoldstino direction has been developed for minimal supergravity. We adapt this to the present case, and ... More
Entanglement of Conceptual Entities in Quantum Model Theory (QMod)Apr 22 2012We have recently elaborated 'Quantum Model Theory' (QMod) to model situations where the quantum effects of contextuality, interference, superposition, entanglement and emergence, appear without the entities giving rise to these situations having necessarily ... More
Emulation of CPU-demanding reactive transport models: comparison of Gaussian processes, polynomial chaos expansion and deep neural networksSep 19 2018This paper presents a detailed comparison between 3 methods for emulating CPU-intensive reactive transport models (RTMs): Gaussian processes (GP), polynomial chaos expansion (PCE) and deep neural networks (DNNs). Besides direct emulation of the simulated ... More
An uncertainty principle for star formation - IV. On the nature and filtering of diffuse emissionOct 26 2018Diffuse emission is observed in galaxies in many tracers across the electromagnetic spectrum, including tracers of star formation, such as H$\alpha$ and ultraviolet (UV), and tracers of gas mass, such as carbon monoxide (CO) transition lines and the 21-cm ... More
A quick guide for student-driven community genome annotationMay 09 2018Oct 16 2018High quality gene models are necessary to expand the molecular and genetic tools available for a target organism, but these are available for only a handful of model organisms that have undergone extensive curation and experimental validation over the ... More
Exorcising the Ostrogradsky ghost in coupled systemsApr 06 2016Sep 15 2016The Ostrogradsky theorem implies that higher-derivative terms of a single mechanical variable are either trivial or lead to additional, ghost-like degrees of freedom. In this letter we systematically investigate how the introduction of additional variables ... More
What is Quantum? Unifying Its Micro-Physical and Structural AppearanceMay 29 2014We can recognize two modes in which 'quantum appears' in macro domains: (i) a 'micro-physical appearance', where quantum laws are assumed to be universal and they are transferred from the micro to the macro level if suitable 'quantum coherence' conditions ... More
Globular cluster formation in the context of galaxy formation and evolutionJul 10 2014Sep 09 2015The formation of globular clusters (GCs) remains one of the main unsolved problems in star and galaxy formation. The past decades have seen important progress in constraining the physics of GC formation from a variety of directions. In this review, we ... More
The Current State of Cluster Formation SimulationsApr 16 2013Numerical simulations of star cluster formation have advanced greatly during the past decade, covering increasingly massive gas clouds while accounting for more and more complex physics. In this review, I discuss the present state of the field, paying ... More
Explaining the mass-to-light ratios of globular clustersJun 04 2008Jun 23 2008The majority of observed mass-to-light ratios of globular clusters are too low to be explained by `canonical' cluster models, in which dynamical effects are not accounted for. Moreover, these models do not reproduce a recently reported trend of increasing ... More