Results for "Daniel Bienstock"

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Optimal adaptive control of cascading power grid failuresDec 17 2010We present theoretical results and experiments with parallel algorithms for computing an adaptive, online control with the objective of attenuating a power grid cascading failure.
A note on polynomial solvability of the CDT problemJun 25 2014Feb 23 2015We describe a simple polynomial-time algorithm for the CDT problem that relies on a construction of Barvinok.
Variance-Aware Optimal Power FlowNov 02 2017The incorporation of stochastic loads and generation into the operation of power grids gives rise to an exposure to stochastic risk. This risk has been addressed in prior work through a variety of mechanisms, such as scenario generation or chance constraints, ... More
Stochastic defense against complex grid attacksJul 17 2018Oct 16 2018We describe defense mechanisms designed to detect sophisticated grid attacks involving both physical actions (including load modification) and sensor output alteration, with the latter performed in a sparse manner and also so as to take into account grid ... More
The N-K Problem in Power Grids: New Models, Formulations and Numerical Experiments (extended version)Dec 29 2009Dec 31 2009Given a power grid modeled by a network together with equations describing the power flows, power generation and consumption, and the laws of physics, the so-called N-k problem asks whether there exists a set of k or fewer arcs whose removal will cause ... More
LP approximations to mixed-integer polynomial optimization problemsJan 01 2015Oct 19 2016We present a class of linear programming approximations for constrained optimization problems. In the case of mixed-integer polynomial optimization problems, if the intersection graph of the constraints has bounded tree-width our construction yields a ... More
On linear relaxations of OPF problemsNov 05 2014We present lifted linear relaxations of the OPF problem.
Optimizing convex functions over nonconvex setsDec 14 2011In this paper we derive strong linear inequalities for sets of the form {(x, q) \in Rd \times R : q \geq Q(x), x \in Rd - int(P)}, where Q(x) : Rd \rightarrow R is a quadratic function, P \subset Rd and "int" denotes interior. Of particular but not exclusive ... More
Simpler derivation of bounded pitch inequalities for set covering, and minimum knapsack setsJun 19 2018A valid inequality \alpha^Tx \ge \alpha_0 for a set covering problem is said to have pitch <= k ( a positive integer) if the k smallest positive \alpha_j sum to at least alpha_0. This paper presents a new, simple derivation of a relaxation for set covering ... More
Strong NP-hardness of AC power flows feasibilityDec 23 2015Apr 09 2019We present a rigorous proof of strong NP-hardness of the AC-OPF problem.
Robust Control of Cascading Power Grid Failures using Stochastic ApproximationApr 03 2015Jul 18 2015Cascading failure of a power transmission system are initiated by an exogenous event that disable a set of elements (e.g., lines) followed by a sequence of interrelated failures (or more precisely, trips) of overloaded elements caused by the combination ... More
Strong NP-hardness of AC power flows feasibilityDec 23 2015We present a rigorous proof of strong NP-hardness of the AC-OPF problem.
Models for managing the impact of an epidemicJul 30 2015In this paper we consider robust models for emergency staff deployment in the event of a flu pandemic. We focus on managing critical staff levels at organizations that must remain operational during such an event, and develop methodologies for managing ... More
Learning from power system data stream: phasor-detective approachNov 17 2018Dec 17 2018Assuming access to synchronized stream of Phasor Measurement Unit (PMU) data over a significant portion of a power system interconnect, say controlled by an Independent System Operator (ISO), what can you extract about past, current and future state of ... More
Non-Stationary Streaming PCAFeb 08 2019We consider the problem of streaming principal component analysis (PCA) when the observations are noisy and generated in a non-stationary environment. Given $T$, $p$-dimensional noisy observations sampled from a non-stationary variant of the spiked covariance ... More
Chance Constrained Optimal Power Flow: Risk-Aware Network Control under UncertaintySep 25 2012Feb 04 2013When uncontrollable resources fluctuate, Optimum Power Flow (OPF), routinely used by the electric power industry to re-dispatch hourly controllable generation (coal, gas and hydro plants) over control areas of transmission networks, can result in grid ... More
Approximation Algorithms for the Incremental Knapsack Problem via Disjunctive ProgrammingNov 18 2013In the incremental knapsack problem ($\IK$), we are given a knapsack whose capacity grows weakly as a function of time. There is a time horizon of $T$ periods and the capacity of the knapsack is $B_t$ in period $t$ for $t = 1, \ldots, T$. We are also ... More
Principled Deep Neural Network Training through Linear ProgrammingOct 07 2018Nov 26 2018Deep Learning has received significant attention due to its impressive performance in many state-of-the-art learning tasks. Unfortunately, while very powerful, Deep Learning is not well understood theoretically and in particular only recently results ... More
Outer-Product-Free Sets for Polynomial Optimization and Oracle-Based CutsOct 14 2016Cutting planes are derived from specific problem structures, such as a single linear constraint from an integer program. This paper introduces cuts that involve minimal structural assumptions, enabling the generation of strong polyhedral relaxations for ... More
Outer-Product-Free Sets for Polynomial Optimization and Oracle-Based CutsOct 14 2016Nov 03 2016Cutting planes are derived from specific problem structures, such as a single linear constraint from an integer program. This paper introduces cuts that involve minimal structural assumptions, enabling the generation of strong polyhedral relaxations for ... More
Synchronization-Aware and Algorithm-Efficient Chance Constrained Optimal Power FlowJun 12 2013One of the most common control decisions faced by power system operators is the question of how to dispatch generation to meet demand for power. This is a complex optimization problem that includes many nonlinear, non convex constraints as well as inherent ... More
Two-sided linear chance constraints and extensionsJul 08 2015Feb 27 2016We examine the convexity and tractability of the two-sided linear chance constraint model under Gaussian uncertainty. We show that these constraints can be applied directly to model a larger class of nonlinear chance constraints as well as provide a reasonable ... More
Non-Stationary Streaming PCAFeb 08 2019Mar 30 2019We consider the problem of streaming principal component analysis (PCA) when the observations are noisy and generated in a non-stationary environment. Given $T$, $p$-dimensional noisy observations sampled from a non-stationary variant of the spiked covariance ... More
Outer-Product-Free Sets for Polynomial Optimization and Oracle-Based CutsOct 14 2016Apr 26 2017Cutting planes are derived from specific problem structures, such as a single linear constraint from an integer program. This paper introduces cuts that involve minimal structural assumptions, enabling the generation of strong polyhedral relaxations for ... More
Robust linear control of nonconvex battery operation in transmission systemsOct 29 2016Nov 06 2016We describe a robust multiperiod transmission plan- ning model including renewables and batteries, where battery output is used to partly offset renewable output deviations from forecast. A central element is a nonconvex battery operation model which ... More
Power Grid Vulnerability to Geographically Correlated Failures - Analysis and Control ImplicationsJun 06 2012We consider power line outages in the transmission system of the power grid, and specifically those caused by a natural disaster or a large scale physical attack. In the transmission system, an outage of a line may lead to overload on other lines, thereby ... More
Vulnerability Analysis of Power SystemsMar 09 2015Potential vulnerabilities in a power grid can be exposed by identifying those transmission lines on which attacks (in the form of interference with their transmission capabilities) causes maximum disruption to the grid. In this study, we model the grid ... More
Robust linear control of nonconvex battery operation in transmission systemsOct 29 2016We describe a robust multiperiod transmission plan- ning model including renewables and batteries, where battery output is used to partly offset renewable output deviations from forecast. A central element is a nonconvex battery operation model which ... More
Efficient Synchronization Stability Metrics for Fault ClearingSep 15 2014Direct methods can provide rapid screening of the dynamical security of large numbers fault and contingency scenarios by avoiding extensive time simulation. We introduce a computationally-efficient direct method based on optimization that leverages efficient ... More
Unit Commitment with N-1 Security and Wind UncertaintyJan 30 2016As renewable wind energy penetration rates continue to increase, one of the major challenges facing grid operators is the question of how to control transmission grids in a reliable and a cost-efficient manner. The stochastic nature of wind forces an ... More
Scaling Laws in Self-Gravitating DisksApr 16 1999The interstellar medium (ISM) reveals strongly inhomogeneous structures at every scale. These structures do not seem completely random since they obey certain power laws. Larson's law (\citeyear{Larson81}) $\sigma \propto R^{\delta}$ and the plausible ... More
Supergravity for Effective TheoriesSep 01 2011Higher-derivative operators are central elements of any effective field theory. In supersymmetric theories, these operators include terms with derivatives in the K\"ahler potential. We develop a toolkit for coupling such supersymmetric effective field ... More
Inflating with BaryonsSep 15 2010We present a field theory solution to the eta problem. By making the inflaton field the phase of a baryon of SU(N_c) supersymmetric Yang-Mills theory we show that all operators that usually spoil the flatness of the inflationary potential are absent. ... More
Casimir force in O(n) lattice models with a diffuse interfaceJun 23 2008On the example of the spherical model we study, as a function of the temperature $T$, the behavior of the Casimir force in O(n) systems with a diffuse interface and slab geometry $\infty^{d-1}\times L$, where $2<d<4$ is the dimensionality of the system. ... More
Fragmentation in Kinematically Cold DisksJan 16 2001Gravity is scale free. Thus gravity may form similar structures in self-gravitating systems on different scales. Indeed, observations of the interstellar medium, spiral disks and cosmic structures, reveal similar characteristics. The structures in these ... More
A Field Range Bound for General Single-Field InflationNov 13 2011We explore the consequences of a detection of primordial tensor fluctuations for general single-field models of inflation. Using the effective theory of inflation, we propose a generalization of the Lyth bound. Our bound applies to all single-field models ... More
Unconditionality in tensor products and ideals of polynomials, multilinear forms and operatorsJun 17 2009Feb 08 2010We study tensor norms that destroy unconditionality in the following sense: for every Banach space $E$ with unconditional basis, the $n$-fold tensor product of $E$ (with the corresponding tensor norm) does not have unconditional basis. We establish an ... More
Extending polynomials in maximal and minimal idealsOct 20 2009Feb 08 2010Given an homogeneous polynomial on a Banach space $E$ belonging to some maximal or minimal polynomial ideal, we consider its iterated extension to an ultrapower of $E$ and prove that this extension remains in the ideal and has the same ideal norm. As ... More
Five basic lemmas for symmetric tensor products of normed spacesMay 18 2011We give the symmetric version of five lemmas which are essential for the theory of tensor products (and norms). These are: the approximation, extension, embedding, density and local technique lemmas. Some application of these tools to the metric theory ... More
Long-Range Correlations in Self-Gravitating N-Body SystemsJan 29 2002Observed self-gravitating systems reveal often fragmented non-equilibrium structures that feature characteristic long-range correlations. However, models accounting for non-linear structure growth are not always consistent with observations and a better ... More
Lumpy Structures in Self-Gravitating DisksMay 29 2001Following Toomre & Kalnajs (1991), local models of slightly dissipative self-gravitating disks show how inhomogeneous structures can be maintained over several galaxy rotations. Their basic physical ingredients are self-gravity, dissipation and differential ... More
Natural symmetric tensor normsFeb 22 2010Dec 14 2010In the spirit of the work of Grothendieck, we introduce and study natural symmetric n-fold tensor norms. We prove that there are exactly six natural symmetric tensor norms for $n\ge 3$, a noteworthy difference with the 2-fold case in which there are four. ... More
Equilateral Non-Gaussianity and New Physics on the HorizonFeb 25 2011Mar 23 2011We examine the effective theory of single-field inflation in the limit where the scalar perturbations propagate with a small speed of sound. In this case the non-linearly realized time-translation symmetry of the Lagrangian implies large interactions, ... More
Formalizing and Checking Thread Refinement for Data-Race-Free Execution Models (Extended Version)Oct 24 2015When optimizing a thread in a concurrent program (either done manually or by the compiler), it must be guaranteed that the resulting thread is a refinement of the original thread. Most theories of valid optimizations are formulated in terms of valid syntactic ... More
The symmetric Radon-Nikodým property for tensor normsMay 15 2010We introduce the symmetric-Radon-Nikod\'ym property (sRN property) for finitely generated s-tensor norms $\beta$ of order $n$ and prove a Lewis type theorem for s-tensor norms with this property. As a consequence, if $\beta$ is a projective s-tensor norm ... More
Desensitizing Inflation from the Planck ScaleApr 21 2010A new mechanism to control Planck-scale corrections to the inflationary eta parameter is proposed. A common approach to the eta problem is to impose a shift symmetry on the inflaton field. However, this symmetry has to remain unbroken by Planck-scale ... More
Signatures of Supersymmetry from the Early UniverseSep 01 2011Oct 11 2011Supersymmetry plays a fundamental role in the radiative stability of many inflationary models. Spontaneous breaking of the symmetry inevitably leads to fields with masses of order the Hubble scale during inflation. When these fields couple to the inflaton ... More
Non-Perturbative Quantum GeometryNov 04 2013The beta-ensemble with cubic potential can be used to study a quantum particle in a double-well potential with symmetry breaking term. The quantum mechanical perturbative energy arises from the ensemble free energy in a novel large N limit. A relation ... More
Dempster-Shafer vs. Probabilistic LogicMar 27 2013The combination of evidence in Dempster-Shafer theory is compared with the combination of evidence in probabilistic logic. Sufficient conditions are stated for these two methods to agree. It is then shown that these conditions are minimal in the sense ... More
Indirect decoherence in optical lattices and cold gasesMay 31 2006The interaction of two--level atoms with a common heat bath leads to an effective interaction between the atoms, such that with time the internal degrees of the atoms become correlated or even entangled. If part of the atoms remain unobserved this creates ... More
Creation of Entanglement by Interaction with a Common Heat BathMay 05 2002Jan 23 2003I show that entanglement between two qubits can be generated if the two qubits interact with a common heat bath in thermal equilibrium, but do not interact directly with each other. In most situations the entanglement is created for a very short time ... More
The Seeds of Cosmic structure as a door to New PhysicsDec 01 2006There is something missing in our understanding of the origin of the seeds of Cosmic Structuture. The fact that the fluctuation spectrum can be extracted from the inflationary scenario through an analysis that involves quantum field theory in curved space-time, ... More
A Classification of Toric, Folded-Symplectic ManifoldsNov 25 2015Given a $G$-toric, folded-symplectic manifold with co-orientable folding hypersurface, we show that its orbit space is naturally a manifold with corners $W$ equipped with a smooth map $\psi: W \to \frak{g}^*$, where $\frak{g}^*$ is the dual of the Lie ... More
A Graph Theoretic Perspective on CPM(Rel)Apr 27 2015Nov 05 2015Mixed states are of interest in quantum mechanics for modelling partial information. More recently categorical approaches to linguistics have also exploited the idea of mixed states to describe ambiguity and hyponym / hypernym relationships. In both these ... More
Simplicity of partial skew group rings of abelian groupsJun 17 2013Let $\A$ be a ring with local units, $\E$ a set of local units for $\A$, $\G$ an abelian group and $\alpha$ a partial action of $\G$ by ideals of $\A$ that contain local units and such that the partial skew group ring $\A\star_{\alpha} \G$ is associative. ... More
A reasonable thing that just might workJul 06 2015In 1964, John Bell proved that quantum mechanics is "unreasonable" (to use Einstein's term): there are nonlocal bipartite quantum correlations. But they are not the most nonlocal bipartite correlations consistent with relativistic causality ("no superluminal ... More
Some exact infrared properties of gluon and ghost propagators and long-range force in QCDApr 15 2009We derive some exact relations in Landau gauge that follow from a cut-off at the Gribov horizon which is then implemented by a local, renormalizable action involving auxiliary bose and fermi ghosts. The fermi ghost propagator is more singular than $1/k^2$ ... More
Analytic calculation of color-Coulomb potential and color confinementDec 18 2003We develop a calculational scheme in Coulomb and temporal gauge that respects gauge invariance and is most easily applied to the infrared asymptotic region of QCD. It resembles the Dyson-Schwinger equations of Euclidean quantum field theory in Landau ... More
Non-perturbative Faddeev-Popov formula and infrared limit of QCDMar 04 2003Apr 19 2003We show that an exact non-perturbative quantization of continuum gauge theory is provided by the Faddeev-Popov formula in Landau gauge, $\d(\p \cdot A) \det[-\p \cdot D(A)] \exp[-S_{\rm YM}(A)]$, restricted to the region where the Faddeev-Popov operator ... More
Exact bounds on the free energy in QCDFeb 06 2012We consider the free energy $W[J] = W_k(H)$ of QCD coupled to an external source $J_\mu^b(x) = H_\mu^b \cos(k \cdot x)$, where $H_\mu^b$ is, by analogy with spin models, an external "magnetic" field with a color index that is modulated by a plane wave. ... More
An improved model of color confinementMar 06 2011We consider the free energy $W[J] = W_k(H)$ of QCD coupled to an external source $J_\mu^b(x) = H_\mu^b \cos(k \cdot x)$, where $H_\mu^b$ is, by analogy with spin models, an external "magnetic" field with a color index that is modulated by a plane wave. ... More
A model of color confinementDec 13 2010A simple model is presented that describes the free energy $W(J)$ of QCD coupled to an external current that is a single plane wave, $J(x) = H \cos(k \cdot x)$. The model satisfies a bound obtained previously on $W(J)$ that comes from the Gribov horizon. ... More
Tachyons in Classical de Sitter VacuaMar 29 2016We revisit the possibility of de Sitter vacua and slow-roll inflation in type II string theory at the level of the classical two-derivative supergravity approximation. Previous attempts at explicit constructions were plagued by ubiquitous tachyons with ... More
Precision Stellar Astrophysics in the Kepler EraApr 25 2016The study of fundamental properties (such as temperatures, radii, masses, and ages) and interior processes (such as convection and angular momentum transport) of stars has implications on various topics in astrophysics, ranging from the evolution of galaxies ... More
N-Body Simulations of Open, Self-Gravitating SystemsJan 16 2001Astrophysical systems differ often in two points from classical thermodynamical systems: 1.) They are open and 2.) gravity is a dominant factor. Both modifies the homogeneous equilibrium structure, known from classical thermodynamics. In order to study ... More
Null Polarities as Generators of the Projective GroupJun 02 2014It is well-known that the group of regular projective transformations of $\mathbb{P}^3(\mathbb{R})$ is isomorphic to the group of projective automorphisms of Klein's quadric $M_2^4\subset\mathbb{P}^5(\mathbb{R})$. We introduce the Clifford algebra $\mathcal{C}\ell_{(3,3)}$ ... More
A Criticism of "Gas Mode" Reinterpretations of the Michelson-Morley and Similar ExperimentsApr 24 2014It has been argued by R. T. Cahill and others that a Michelson interferometer in "gas mode" - in which the light paths are through an included gaseous medium - are able to detect and have detected an absolute frame of reference. It is shown here that ... More
A Case for Lorentzian RelativityJan 18 2014Mar 06 2015The Lorentz transformation (LT) is explained by changes occurring in the wave characteristics of matter as it changes inertial frame. This explanation is akin to that favoured by Lorentz, but informed by later insights, due primarily to de Broglie, regarding ... More
Syntagma Lexical DatabaseMar 19 2015This paper discusses the structure of Syntagma's Lexical Database (focused on Italian). The basic database consists in four tables. Table Forms contains word inflections, used by the POS-tagger for the identification of input-words. Forms is related to ... More
What is dimensional reduction really telling us?Sep 25 2015Oct 12 2015Numerous approaches to quantum gravity report a reduction in the number of spacetime dimensions at the Planck scale. However, accepting the reality of dimensional reduction also means accepting its consequences, including a variable speed of light. We ... More
Generalized amalgamation and homogeneityMar 31 2016May 05 2016In this paper we shall prove that any $2$-transitive finitely homogeneous structure with a supersimple theory satisfying a generalized amalgamation property is a random structure. In particular, this adapts a result of Koponen for binary homogeneous structures ... More
Towards a Theory of Affect and Software Developers' PerformanceJan 12 2016Jan 23 2016For more than thirty years, it has been claimed that a way to improve software developers' productivity and software quality is to focus on people. The underlying assumption seems to be that "happy and satisfied software developers perform better". More ... More
Logic and linear algebra: an introductionJul 09 2014Aug 24 2015We give an introduction to logic tailored for algebraists, explaining how proofs in linear logic can be viewed as algorithms for constructing morphisms in symmetric closed monoidal categories with additional structure. This is made explicit by showing ... More
Green open access in computer science - an exploratory study on author-based self-archiving awareness, practice, and inhibitorsMay 05 2015Access to the work of others is something that is too often taken for granted, yet problematic and difficult to be obtained unless someone pays for it. Green and gold open access are claimed to be a solution to this problem. While open access is gaining ... More
Meromorphic quotients for some holomorphic G-actionsMay 26 2015Using mainly tools from [B.13] and [B.15] we give a necessary and sufficient condition in order that a holomorphic action of a connected complex Lie group $G$ on a reduced complex space $X$ admits a strongly quasi-proper meromorphic quotient. We apply ... More
Some examples due to H. HironakaJan 06 2015Mar 26 2015The aim of this paper is to explain the construction by H. Hironaka [H.61] of a holomorphic (in fact "algebraic") family of compact complex manifolds parametrized by $\C$ such for all $s \in \C\setminus \{0\}$ the fiber is projective, but such that the ... More
Asymptotics of a vanishing period : characterization of semi-simplicityJan 31 2013In this paper we introduce the word {\em fresco} to denote a monogenic geometric (a,b)-module. This "basic object" (generalized Brieskorn module with one generator) corresponds to the formal germ of the minimal filtered (regular) differential equation. ... More
The theme of a vanishing periodOct 06 2011Let \ $\lambda \in \mathbb{Q}^{*+}$ \ and consider a multivalued formal function of the type $$ \phi(s) : = \sum_{j=0}^k \ c_j(s).s^{\lambda + m_j}.(Log\, s)^j $$ where \ $c_j \in \C[[s]], m_j \in \mathbb{N}$ \ for \ $j \in [0,k-1]$. The {\bf theme} associated ... More
Holomorphic families of $[λ]-$primitive themesAug 12 2015This article is the continuation of [B. 13-b] where we show how the isomorphism class of a $[\lambda]-$primitive theme with a given Bernstein polynomial may be characterized by a (small) finite number of complex parameters. We construct here a corresponding ... More
Algebraic differential equations associated to some polynomialsMay 29 2013Mar 01 2014We compute the Gauss-Manin differential equation for any period of a polynomial in \ $\C[x_{0},\dots, x_{n}]$ \ with \ $(n+2)$ \ monomials. We give two general factorizations theorem in the algebra \ $\C< z, (\frac{\partial}{\partial z})^{-1}>$ \ for ... More
Changements de variable pour un th`eme.Mar 26 2010We study the behaviour of the notion of "thema", introduced in our previous article [B.09b], by a change of variable. We show not only that the fundamental invariants of such a thema, corresponding to the Bernstein polynomial, are stable by a change of ... More
Tau lepton reconstruction at collider experiments using impact parametersJul 07 2015Nov 06 2015We present a novel method for the reconstruction of events containing pairs of hadronically decaying tau leptons at collider experiments. This method relies on accurate knowledge of the tau production vertex and precise measurement of its charged decay ... More
Quantum Error Correction and Fault-ToleranceJul 18 2005I give an overview of the basic concepts behind quantum error correction and quantum fault tolerance. This includes the quantum error correction conditions, stabilizer codes, CSS codes, transversal gates, fault-tolerant error correction, and the threshold ... More
The Heisenberg Representation of Quantum ComputersJul 01 1998Since Shor's discovery of an algorithm to factor numbers on a quantum computer in polynomial time, quantum computation has become a subject of immense interest. Unfortunately, one of the key features of quantum computers - the difficulty of describing ... More
A Theory of Fault-Tolerant Quantum ComputationFeb 12 1997Feb 18 1997In order to use quantum error-correcting codes to actually improve the performance of a quantum computer, it is necessary to be able to perform operations fault-tolerantly on encoded states. I present a general theory of fault-tolerant operations based ... More
Pasting Quantum CodesJul 31 1996I describe a method for pasting together certain quantum error-correcting codes that correct one error to make a single larger one-error quantum code. I show how to construct codes encoding 7 qubits in 13 qubits using the method, as well as 15 qubits ... More
Transverse polarization distribution and fragmentation functionsDec 11 1999Apr 27 2000We discuss transverse polarization distribution and fragmentation functions, in particular, T-odd functions with transverse momentum dependence, which might be relevant for the description of single transverse spin asymmetries. The role of intrinsic tranverse ... More
Transverse Lambda Polarization at LHCJul 09 2009Transverse polarization of Lambda hyperons produced in p p and p Pb collisions is discussed. A factorized description in the intermediate to high p_T region is considered that involves transverse momentum and spin dependence in the fragmentation process. ... More
Gluon saturation effects on single spin asymmetriesNov 29 2006We consider forward pion production in p p collisions at RHIC energies,which probes the so-called Extended Geometric Scaling region. Upon inclusion of small-x effects via an anomalous dimension within the Color Glass Condensate formalism at leading order ... More
Hadron structure from gamma^* p scattering: interpreting hadronic matrix elementsSep 30 2004Oct 05 2004Hadron structure from high-Q^2 gamma^* p scattering processes is often expressed in terms of hadronic matrix elements of nonlocal operators. Properly defining and interpreting these quantities is very important in light of experiments aiming to extract ... More
Transversely polarized Lambda productionJul 05 2000Transversely polarized Lambda production in hard scattering processes is discussed in terms of a leading twist T-odd fragmentation function which describes the fragmentation of an unpolarized quark into a transversely polarized Lambda. We focus on the ... More
The K3 category of a cubic fourfoldMay 07 2015Sep 12 2016Smooth cubic fourfolds are linked to K3 surfaces via their Hodge structures, due to work of Hassett, and via Kuznetsov's K3 category A. The relation between these two viewpoints has recently been elucidated by Addington and Thomas. In this paper, both ... More
Introduction to stability conditionsNov 07 2011Oct 25 2012These are notes of a course given at the 'school on moduli spaces' at the Newton Institute in January 2011. The abstract theory of stability conditions (due to Bridgeland and Douglas) on abelian and triangulated categories is developed via tilting and ... More
Derived and abelian equivalence of K3 surfacesApr 06 2006Tom Bridgeland constructed explicit stability conditions on K3 surfaces. This paper attempts to shed more light on these particular examples, especially on the hearts of the underlying t-structures. We prove that two K3 surfaces X and X' are derived equivalent ... More
The Kaehler cone of a compact hyperkaehler manifoldSep 19 1999Jun 03 2001This is an attempt towards the understanding of the (birational) Kaehler cone of a compact hyperkaehler manifold in terms of the Beauville-Bogomolov form on its second cohomology. We discuss birational correspondences between hyperkaehler manifolds and ... More
Birational symplectic manifolds and their deformationsJan 17 1996Jan 17 1996The known counterexamples to the global Torelli theorem for higher-dimensional hyperkahler manifolds are provided by birational manifolds. We address the question whether two birational hyperkahler manifolds (i.e. irreducible symplectic) manifolds always ... More
Dynamics of Accretion Flows Irradiated by a QuasarFeb 21 2007We present the results from axisymmetric time-dependent HD calculations of gas flows which are under the influence of gravity of a black hole in quasars. We assume that the flows are non-rotating and exposed to quasar radiation. We take into account X-ray ... More
Theory of winds in AGNsJan 04 2007I present a brief review of theory of winds in active galactic nuclei (AGN). Magnetic, radiation, and thermal driving likely operate in AGN. In many cases, it is difficult to distinguish, both from observational and theoretical point of view, which of ... More
Virial statistical description of non-extensive hierarchical systemsMay 26 2006In a first part the scope of classical thermodynamics and statistical mechanics is discussed in the broader context of formal dynamical systems, including computer programmes. In this context classical thermodynamics appears as a particular theory suited ... More
Novel type of orbital ordering: complex orbitals in doped Mott insulatorsApr 04 2000Apr 05 2000An orbital ordering, often observed in Mott insulators with orbital degeneracy, is usually supposed to disappear with doping, e.g. in the ferromagnetic metallic phase of manganites. We propose that the orbital ordering of a novel type may exist in such ... More