15 research outputs found
Tropical degenerations and stable rationality
No full textWe use the motivic obstruction to stable rationality introduced by Shinder
and the first-named author to establish several new classes of stably
irrational hypersurfaces and complete intersections. In particular, we show
that very general quartic fivefolds and complete intersections of a quadric and a cubic in are stably irrational. An important new ingredient is the use of tropical degeneration techniques
Derived categories and K-groups of singular varieties
No full textThis thesis consists of three parts and is a collection of papers written by the author of this text during his postgraduate studies, together with an Appendix chapter.
The first chapter is based on [98] and is in collaboration with Evgeny Shinder. It discusses the K-groups K_1, K_0 and K_{−n} of the singularity category of isolated quotient singularities. The second chapter is based on [73] and is joint with Martin Kalck and Evgeny Shinder. It introduces Kawamata type semiorthogonal decompositions for singular varieties and obstructions for such decompositions are studied, mainly for the case of nodal threefolds. Each of these two chapters can be read independently. The third chapter is an Appendix to the first chapter and explains in more detail how the main technical result in chapter one is proven, on which the main theorems rely on
Variation of stable birational types of hypersurfaces
No full textWe introduce and study the question how can stable birational types vary in a smooth proper family. Our starting point is the specialization for stable birational types of Nicaise and the author and our emphasis is on stable birational types of hypersurfaces. Building up on the work of Totaro and Schreieder on stable irrationality of hypersurfaces of high degree, we show that smooth Fano hypersurfaces of large degree over a field of characteristic zero are in general not stably birational to each other. In the appendix Claire Voisin proves a similar result in a different setting using the Chow decomposition of diagonal and unramified cohomology
Derived categories of Fano threefolds and degenerations
No full textUsing the technique of categorical absorption of singularities we prove that the nontrivial components of the derived categories of del Pezzo threefolds of degree and crepant categorical resolutions of the nontrivial components of the derived categories of nodal del Pezzo threefolds of degree can be smoothly deformed to the nontrivial components of the derived categories of prime Fano threefolds of genus . This corrects and proves the Fano threefolds conjecture of the first author from [Kuz09], and opens a way to interesting geometric applications, including a relation between the intermediate Jacobians and Hilbert schemes of curves of the above threefolds. We also describe a compactification of the moduli stack of prime Fano threefolds endowed with an appropriate exceptional bundle and its boundary component that corresponds to degenerations associated with del Pezzo threefolds.39 pages; v4: final versio
Derived categories of Fano threefolds and degenerations
No full textUsing the technique of categorical absorption of singularities we prove that the nontrivial components of the derived categories of del Pezzo threefolds of degree d∈{2,3,4,5} and crepant categorical resolutions of the nontrivial components of the derived categories of nodal del Pezzo threefolds of degree d=1 can be smoothly deformed to the nontrivial components of the derived categories of prime Fano threefolds of genus g=2d+2∈{4,6,8,10,12}. This corrects and proves the Fano threefolds conjecture of the first author from (Kuznetsov in Tr. Mat. Inst. Steklova 264:116–128, 2009), and opens a way to interesting geometric applications, including a relation between the intermediate Jacobians and Hilbert schemes of curves of the above threefolds. We also describe a compactification of the moduli stack of prime Fano threefolds endowed with an appropriate exceptional bundle and its boundary component that corresponds to degenerations associated with del Pezzo threefolds
Nucleolin-Mediated RNA Localization Regulates Neuron Growth and Cycling Cell Size
No full textSummaryHow can cells sense their own size to coordinate biosynthesis and metabolism with their growth needs? We recently proposed a motor-dependent bidirectional transport mechanism for axon length and cell size sensing, but the nature of the motor-transported size signals remained elusive. Here, we show that motor-dependent mRNA localization regulates neuronal growth and cycling cell size. We found that the RNA-binding protein nucleolin is associated with importin β1 mRNA in axons. Perturbation of nucleolin association with kinesins reduces its levels in axons, with a concomitant reduction in axonal importin β1 mRNA and protein levels. Strikingly, subcellular sequestration of nucleolin or importin β1 enhances axonal growth and causes a subcellular shift in protein synthesis. Similar findings were obtained in fibroblasts. Thus, subcellular mRNA localization regulates size and growth in both neurons and cycling cells
Peer-assisted carrying authentication (PACA)
No full textIn this paper we present a method for password recovery through the employment of multiple Web servers, and which we name Peer-Assisted Carrying Authentication (PACA). The paper starts by highlighting the vulnerabilities of the commonly used techniques for password recovery, namely the question-answer approach. It then proceeds to providing a general coverage of the proposed approach and discusses the details and offered solutions to issues that relate to implementation and security. We present a software application that we developed for proof-of-concept and as a tool for class-based experiments. These were conducted to show the ability of users to hack accounts of other users with whom they have or had some kind of relationship and test the effectiveness of piecewise password recovery. The results indicate that people who are close to others can often guess some of their passwords correctly and therefore, are able to hack their computer accounts. It is shown that PACA makes the hacker's job very difficult through the multiple peer authentication mechanism. In this regard, the findings could be used to set a lower bound on the number of peer sites for authenticating users. © 2004 Elsevier Ltd. All rights reserved.[Anonymous], 2616 RFC; Appel AW, 1999, P 6 ACM C COMP COMM, P52, DOI 10.1145-319709.319718; BENSINGER D, 1998, HUMAN MEMORY GRAPHIC; CHIN P, 2003, MUMS WORD EFFECTIVE; Frykholm N., 2001, P ACM C COMP COMM SE, P1; HELD G, 1998, INT J NETWORK MANAGE, V8, P368; KHUSMITH V, 2002, RHULMA20023 U LOND D; Krishnamurthy B., 2001, WEB PROTOCOLS PRACTI; MILLER GA, 1956, IRE T INFORM THEOR, V2, P129, DOI 10.1109-TIT.1956.1056815; Nakata K, 1999, NEW GENERAT COMPUT, V17, P395; Necula GC, 1997, P 24 ACM SIGPLAN SIG, P106, DOI 10.1145-263699.263712; Reed S. K., 1982, COGNITION THEORY APP; SHIMONSKI R, 2002, CREATE EFFECTIVE PAS; SHINDER D, 2002, SCENE CYBERCRIME, pCH7; Smith M, 2000, COMPUT SECUR, V19, P21, DOI 10.1016-S0167-4048(00)86358-0; WAUGH NC, 1965, PSYCHOL REV, V72, P89, DOI 10.1037-h00217970
Poetic Machines: an investigation into the impact of the characteristics of the digital apparatus on poetic expression
No full textThis thesis aims to investigate digital methods of signification in order to examine the impact of the apparatus on poetic expression. This is done through a critical analysis of the translation process from analogue to digital, in the sense that even as we read a page we are in fact translating sight into sound. The resulting effects of this change in form are explored in order to understand their impact on meaning-making in the digital realm. Through this interrogation the comprehension and definition of ePoetry (electronic poetry or digital poetry) is extended, by exposing the unique affordances
and specificities of digital expression.
Digital poetry theorists such as Loss Pequeño Glazier posit that the emerging field of electronic literature is composed of interweaving strands from the areas of computer
science, sociology, and literary studies. This is reflected in the interdisciplinary nature of this thesis, which necessitates an engagement with the broad areas of translation, literature, and digital media studies. Currently the pervasiveness of digital technology
and access to the Internet means that the creation and consumption of online content such as ePoetry is becoming seamless and apparently effortless. Whilst recent studies
have explored electronic literature as a field, there is a noticeable deficit of research that specifically focuses on ePoetry, a deficit that this thesis seeks to rectify.
Within this work cybernetic and technosocial theories of communication are drawn on which provide as much emphasis on the apparatus, as is afforded to the author and
reader. Traditional poetry criticism is problematised with reference to its suitability for application to online works in order to develop a comprehensive ePoetry rhetoric
that explores not only what is being said, but also crucially how it is being said. Theories of translation are also used as a context in which to analyse the transposition
of poetry from analogue to digital. This framework then forms the basis for a study that explores the move from print to pixel by analysing qualitative ePoet interviews as
well as their corresponding ePoems
