CiteULike: Group: Blog_and_Wiki_Research - library [2910 articles]

A systemic and cognitive view on collaborative knowledge building with wikis

Ulrike Cress — 2008-04-28T00:22:36-00:00

International Journal of Computer-Supported Collaborative Learning, Vol. 3, No. 2. (23 June 2008), pp. 105-122.

Abstract Wikis provide new opportunities for learning and for collaborative knowledge building as well as for understanding these processes. This article presents a theoretical framework for describing how learning and collaborative knowledge building take place. In order to understand these processes, three aspects need to be considered: the social processes facilitated by a wiki, the cognitive processes of the users, and how both processes influence each other mutually. For this purpose, the model presented in this article borrows from the systemic approach of Luhmann as well as from Piaget’s theory of equilibration and combines these approaches. The model analyzes processes which take place in the social system of a wiki as well as in the cognitive systems of the users. The model also describes learning activities as processes of externalization and internalization. Individual learning happens through internal processes of assimilation and accommodation, whereas changes in a wiki are due to activities of external assimilation and accommodation which in turn lead to collaborative knowledge building. This article provides empirical examples for these equilibration activities by analyzing Wikipedia articles. Equilibration activities are described as being caused by subjectively perceived incongruities between an individuals’ knowledge and the information provided by a wiki. Incongruities of medium level cause cognitive conflicts which in turn activate the described processes of equilibration and facilitate individual learning and collaborative knowledge building.

Web 2.0: hypertext by any other name?

David Millard — 2006-11-05T16:34:49-00:00

(2006), pp. 27-30.

Autoencoder, Principal Component Analysis and Support Vector Regression for Data Imputation

Vukosi Marivate — 2007-09-18T20:17:31-00:00

(16 Sep 2007)

ata collection often results in records that have missing values or variables. This investigation compares 3 different data imputation models and identifies their merits by using accuracy measures. Autoencoder Neural Networks, Principal components and Support Vector regression are used for prediction and combined with a genetic algorithm to then impute missing variables. The use of PCA improves the overall performance of the autoencoder network while the use of support vector regression shows promising potential for future investigation. Accuracies of up to 97.4 % on imputation of some of the variables were achieved.

Nonextensive Pythagoras' Theorem

Ambedkar Dukkipati — 2007-09-18T13:21:50-00:00

(12 Sep 2007)

ullback-Leibler relative-entropy, in cases involving distributions resulting from relative-entropy minimization, has a celebrated property reminiscent of squared Euclidean distance: it satisfies an analogue of the Pythagoras' theorem. And hence, this property is referred to as Pythagoras' theorem of relative-entropy minimization or triangle equality and plays a fundamental role in geometrical approaches of statistical estimation theory like information geometry. Equvalent of Pythagoras' theorem in the generalized nonextensive formalism is established in (Dukkipati at el., Physica A, 361 (2006) 124-138). In this paper we give a detailed account of it.

Clinical decision support software for chronic heart failure.

SJ Leslie — 2007-09-15T09:47:49-00:00

Crit Pathw Cardiol, Vol. 6, No. 3. (September 2007), pp. 121-126.

Critical care pathways, protocols, and guidelines have become an everyday feature of clinical practice and represent a distillation of the best available evidence. Chronic heart failure guidelines can be complex, and it is acknowledged that a combination of knowledge and expert advice, in addition to guidelines, is required to optimally treat these patients. This current article describes the potential value of clinical decision support software (CDSS) in the treatment of patients with chronic heart failure and practical aspects of using such a tool. Barriers to implementation of our tool included relatively low computer skills among family physicians and a lack of complexity within CDSS in addressing the wider nonmedical needs of patients. Improving computer skills, integrating CDSS into referral pathways, and requests for investigation may be ways of enhancing the use of this technology.

Glut: Mastering Information Through the Ages

Alex Wright — 2007-08-17T19:39:50-00:00

(01 June 2007)

Pluto: A Monte Carlo Simulation Tool for Hadronic Physics

I Froehlich — 2007-09-03T23:14:34-00:00

(17 Aug 2007)

Pluto is a Monte-Carlo event generator designed for hadronic interactions from Pion production threshold to intermediate energies of a few GeV per nucleon, as well as for studies of heavy ion reactions. This report gives an overview of the design of the package, the included models and the user interface.

Archetypes of Knowledge Communities

Erik Andriessen — 2007-09-03T17:45:24-00:00

(2005), pp. 191-214.

Knowledge sharing communities can be found in many organizations, but their forms and functions appear to be quite diverse. This implies that questions concerning the functioning of communities, (how do they work) and questions concerning success conditions (how to organize and facilitate them) cannot be answered in a general way. The purpose of this article is to develop the theory in this area by discovering basic dimensions along which communities differ, and by identifying basic types of knowledge communities, underlying the diversity of knowledge sharing groups. Through an analysis of the literature and of a series of communities in large organizations, two basic dimensions and five archetypes of knowledge communities are identified.

TimeSpace: activity-based temporal visualisation of personal information spaces

Aparna Krishnan — 2005-02-11T14:46:03-00:00

Personal Ubiquitous Comput., Vol. 9, No. 1. (January 2005), pp. 46-65.

Blink . The Power of Thinking Without Thinking

Malcolm Gladwell — 2007-09-12T17:25:45-00:00

(02 January 2006)

On Localized

Erasmo Recami — 2007-09-12T16:26:44-00:00

(10 Sep 2007)

In this paper we extend for the case of Maxwell equations the "X-shaped" solutions previously found in the case of scalar (e.g., acoustic) wave equations. Such solutions are localized in theory, i.e., diffraction-free and particle-like (wavelets), in that they maintain their shape as they propagate. In the electromagnetic case they are particularly interesting, since they are expected to be Superluminal. We address also the problem of their practical, approximate production by finite (dynamic) radiators. Finally, we discuss the appearance of the X-shaped solutions from the purely geometric point of view of the Special Relativity theory. [PACS nos.: 03.50.De; 1.20.Jb; 03.30.+p; 03.40.Kf; 14.80.-j. Keywords: X-shaped waves; localized solutions to Maxwell equations; Superluminal waves; Bessel beams; Limited-dispersion beams; electromagnetic wavelets; Special Relativity; Extended Relativity].

Kurt Goedel and His Universe

Ivan Todorov — 2007-09-12T16:19:58-00:00

(10 Sep 2007)

A portrait of Kurt Goedel with emphasis on his work on relativity theory and idealistic philosophy.

Six Degrees: The Science of a Connected Age

Duncan Watts — 2006-05-04T11:33:47-00:00

(25 February 2003)

You may be only six degrees away from Kevin Bacon, but would he let you borrow his car? It depends on the structures within the network that links you. When the power goes out, when we find that a stranger knows someone we know, when dot-com stocks soar in price, networks are evident. In Six Degrees, sociologist Duncan Watts examines networks like these: what they are, how they're being studied, and what we can use them for. To illustrate the often complicated mathematics that describe such structures, Watts uses plenty of examples from life, without which this book would quickly move beyond a general science readership. Small chapters make each thought-provoking conclusion easy to swallow, though some are hard to digest. For instance, in a short bit on "coercive externalities," Watts sums up sociological research showing that: <blockquote>"Conversations concerning politics displayed a consistent pattern .... On election day, the strongest predictor of electoral success was not which party an individual privately supported but which party he or she expected would win."</blockquote> Six Degrees attempts to help readers understand the new and exciting field of networks and complexity. While considerably more demanding than a general book like The Tipping Point, it offers readers a snapshot of a riveting moment in science, when understanding things like disease epidemics and the stock market seems almost within our reach. --Therese Littleton The pioneering young scientist whose work on the structure of small worlds has triggered an avalanche of interest in networks. In this remarkable book, Duncan Watts, one of the principal architects of network theory, sets out to explain the innovative research that he and other scientists are spearheading to create a blueprint of our connected planet. Whether they bind computers, economies, or terrorist organizations, networks are everywhere in the real world, yet only recently have scientists attempted to explain their mysterious workings. From epidemics of disease to outbreaks of market madness, from people searching for information to firms surviving crisis and change, from the structure of personal relationships to the technological and social choices of entire societies, Watts weaves together a network of discoveries across an array of disciplines to tell the story of an explosive new field of knowledge, the people who are building it, and his own peculiar path in forging this new science. 24 b/w illustrations.

Solving Constraint Satisfaction Problems through Belief Propagation-guided decimation

Andrea Montanari — 2007-09-12T11:49:24-00:00

(11 Sep 2007)

Message passing algorithms have proved surprisingly successful in solving hard constraint satisfaction problems on sparse random graphs. In such applications, variables are fixed sequentially to satisfy the constraints. Message passing is run after each step. Its outcome provides an heuristic to make choices at next step. This approach has been referred to as `decimation,' with reference to analogous procedures in statistical physics. The behavior of decimation procedures is poorly understood. Here we consider a simple randomized decimation algorithm based on belief propagation (BP), and analyze its behavior on random k-satisfiability formulae. In particular, we propose a tree model for its analysis and we conjecture that it provides asymptotically exact predictions in the limit of large instances. This conjecture is confirmed by numerical simulations.

Structure and evolution of online social networks

Ravi Kumar — 2006-12-05T14:42:10-00:00

(2006), pp. 611-617.

Kolmogorov Complexity and Information Theory with an interpretation in terms of questions and answers

Peter Grünwald — 2007-09-11T11:29:30-00:00

We compare the elementary theories of Shannon information and Kolmogorov complexity, the extent to which they have a common purpose, and where they are fundamentally different. We discuss and relate the basic notions of both theories: Shannon entropy, Kolmogorov complexity, Shannon mutual information and Kolmogorov (`algorithmic') mutual information. We explain how universal coding may be viewed as a middle ground between the two theories. We consider Shannon's rate distortion theory, which...

The P versus NP Brief

Mikael Franzen — 2007-09-11T09:08:21-00:00

(8 Sep 2007)

This paper discusses why P and NP are likely to be different. It analyses the essence of the concepts and points out that P and NP might be diverse by sheer definition. It also speculates that P and NP may be unequal due to natural laws.

The Description of Information in 4-Dimensional Pseudo-Euclidean Information Space

OI Shro — 2007-09-10T05:50:50-00:00

(7 Sep 2007)

This article is presented new method of description information systems in abstract 4-dimensional pseudo-Euclidean information space (4-DPIES) with using special relativity (SR) methods. This purpose core postulates of existence 4-DPIES are formulated. The theorem setting existence criteria of the invariant velocity of the information transference is formulated and proved. One more theorem allowed relating discrete parameters of information and continuous space-time treating and also row of supplementary theorems is formulated and proved. For description of dynamics and interaction of information, in article is introduced general parameter of information - generalized information emotion (GIE), reminding simultaneously on properties the mass and the charge. At performing calculation of information observable parameters in the information space is introduced continual integration methods of Feynman. The applying idea about existence of GIE as measures of the information inertness and the interaction carrier, and using continual integration methods of Feynman can be calculated probability of information process in 4-DPIES. In this frame presented approach has allowed considering information systems when interest is presented with information processes, their related with concrete definition without necessity. The relation between 4-DPIES and real systems parameters is set at modelling of matching between observable processes and real phenomena from information interpretation.

On the geometry of metrics embeddable in the real line

Adam Letchford — 2007-09-08T10:31:33-00:00

(6 Sep 2007)

For a fixed finite set ${1,...,n}$, we consider the set of metrics for which the metric space can be isometrically embedded in the real line. The convex hull of those metrics, $Q_n$, and its closure $\closeQ_n$ are the main objects of this paper. We first study structural properties of $Q_n$ showing how the set of metrics is contained in this convex set and characterize all unbounded one-dimensional extreme subsets of $Q_n$ combinatorially. Second, and mainly, we give a combinatorial characterization of the set of unbounded edges of $\closeQ_n$. As a simple by-product, we obtain that $Q_n$ is closed if and only if $n≤ 3$. We note that these convex sets have links to the solution of the so-called Linear Arrangement Problem.

Godel's theorem as a corollary of impossibility of complete axiomatization of geometry

Yuri — 2007-09-08T09:48:18-00:00

(6 Sep 2007)

Not any geometry can be axiomatized. The paradoxical Godel's theorem starts from the supposition that any geometry can be axiomatized and goes to the result, that not any geometry can be axiomatized. One considers example of two close geometries (Riemannian geometry and $σ $-Riemannian one), which are constructed by different methods and distinguish in some details. The Riemannian geometry reminds such a geometry, which is only a part of the full geometry. Such a possibility is covered by the Godel's theorem.

On P vs. NP, Geometric Complexity Theory, and the Flip I: a high level view

Ketan Mulmuley — 2007-09-07T18:46:17-00:00

(5 Sep 2007)

Geometric complexity theory (GCT) is an approach to the $P$ vs. $NP$ and related problems through algebraic geometry and representation theory. This article gives a high-level exposition of the basic plan of GCT based on the principle, called the flip, without assuming any background in algebraic geometry or representation theory.

Geometric Complexity Theory: Introduction

Ketan — 2007-09-07T18:44:18-00:00

(5 Sep 2007)

These are lectures notes for the introductory graduate courses on geometric complexity theory (GCT) in the computer science department, the university of Chicago. Part I consists of the lecture notes for the course given by the first author in the spring quarter, 2007. It gives introduction to the basic structure of GCT. Part II consists of the lecture notes for the course given by the second author in the spring quarter, 2003. It gives introduction to invariant theory with a view towards GCT. No background in algebraic geometry or representation theory is assumed. These lecture notes in conjunction with the article \citeGCTflip1, which describes in detail the basic plan of GCT based on the principle called the flip, should provide a high level picture of GCT assuming familiarity with only basic notions of algebra, such as groups, rings, fields etc.

The World as Evolving Information

Carlos Gershenson — 2007-04-12T00:24:11-00:00

(3 Apr 2007)

This philosophical paper discusses the benefits of describing the world as information, especially in the study of the evolution of life and cognition. Traditional studies encounter difficulties because it is difficult to describe life and cognition in terms of matter and energy, falling into a dualist trap. However, if matter and energy, as well as life and cognition, are described in terms of information, evolution can be described consistently as information becoming more complex. Moreover, information theory is already well established and formalized. The paper presents five tentative laws of information, which are generalizations of Darwinian, cybernetic, thermodynamic, and complexity principles. These are further used to discuss the notions of life and cognition, including their origins and evolution.

Effective Generation of Subjectively Random Binary Sequences

Yasmine Sanderson — 2007-09-04T12:15:29-00:00

(3 Sep 2007)

We present an algorithm for effectively generating binary sequences which would be rated by people as highly likely to have been generated by a random process, such as flipping a fair coin.

Using Data Compressors to Construct Rank Tests

Daniil Ryabko — 2007-09-06T20:20:54-00:00

(5 Sep 2007)

Nonparametric rank tests for homogeneity and component independence are proposed, which are based on data compressors. For homogeneity testing the idea is to compress the binary string obtained by ordering the two joint samples and writing 0 if the element is from the first sample and 1 if it is from the second sample and breaking ties by randomization (extension to the case of multiple samples is straightforward). $H_0$ should be rejected if the string is compressed (to a certain degree) and accepted otherwise. We show that such a test obtained from an ideal data compressor is valid against all alternatives. Component independence is reduced to homogeneity testing by constructing two samples, one of which is the first half of the original and the other is the second half with one of the components randomly permuted.

Simple Algorithmic Principles of Discovery, Subjective Beauty, Selective Attention, Curiosity & Creativity

Juergen Schmidhuber — 2007-09-06T20:16:04-00:00

(5 Sep 2007)

I postulate that human or other intelligent agents function or should function as follows. They store all sensory observations as they come - the data is holy. At any time, given some agent's current coding capabilities, part of the data is compressible by a short and hopefully fast program / description / explanation / world model. In the agent's subjective eyes, such data is more regular and more "beautiful" than other data. It is well-known that knowledge of regularity and repeatability may improve the agent's ability to plan actions leading to external rewards. In absence of such rewards, however, known beauty is boring. Then "interestingness" becomes the first derivative of subjective beauty: as the learning agent improves its compression algorithm, formerly apparently random data parts become subjectively more regular and beautiful. Such progress in compressibility is measured and maximized by the curiosity drive: create action sequences that extend the observation history and yield previously unknown / unpredictable but quickly learnable algorithmic regularity. We discuss how all of the above can be naturally implemented on computers, through an extension of passive unsupervised learning to the case of active data selection: we reward a general reinforcement learner (with access to the adaptive compressor) for actions that improve the subjective compressibility of the growing data. An unusually large breakthrough in compressibility deserves the name "discovery". The "creativity" of artists, dancers, musicians, pure mathematicians can be viewed as a by-product of this principle. Several qualitative examples support this hypothesis.

Euler equations are not exactly controllable by a finite-dimensional external force

Armen Shirikyan — 2007-09-06T19:32:54-00:00

(3 Aug 2007)

We show that the Euler system is not exactly controllable by a finite-dimensional external force. The proof is based on the comparison of the Kolmogorov epsilon-entropy for Holder spaces and for the class of functions that can be obtained by solving the 2D Euler equations with various right-hand sides.

Pattern Matching in Trees and Strings

Philip Bille — 2007-09-03T06:39:10-00:00

(31 Aug 2007)

We study the design of efficient algorithms for combinatorial pattern matching. More concretely, we study algorithms for tree matching, string matching, and string matching in compressed texts.

A cosmotopological relation for a unified field theory

JJ van der Bij — 2007-08-31T23:08:38-00:00

(30 Aug 2007)

I present an argument, based on the topology of the universe, why there are three generations of fermions. The argument implies a preferred unified gauge group of SU(5), but with SO(10) representations of the fermions. The breaking pattern $SU(5) \to SU(3) × SU(2) × U(1)$ is preferred over the pattern $SU(5) \to SU(4) × U(1)$. On the basis of the argument one expects an asymmetry in the microwave data, which might have been detected already.

Physical limits of inference

David Wolpert — 2007-08-25T22:19:13-00:00

(10 Aug 2007)

We show that physical devices that perform observation, prediction, or recollection share a mathematical structure. We call devices with that structure “inference devices”. We present existence and impossibility results for inference devices. These results hold independent of the precise physical laws of our universe. The impossibility results establish that Laplace was wrong to claim that even in a classical, non-chaotic universe the future can be unerringly predicted. Alternatively, they can be viewed as a non-quantum mechanical “uncertainty principle”. The mathematics of inference devices is related to the theory of Turing Machines (TM's), e.g., some impossibility results for inference devices are related to the Halting theorem for TM's. Furthermore, one can define an analog of Universal TM's (UTM's) for inference devices, which we call “strong inference devices”. We use strong inference devices to define the “inference complexity” of an inference task, which is analogous to the Kolmogorov complexity of a string. A task-independent bound is derived on the difference in inference complexity of an inference task performed with two different inference devices. This is analogous to the “encoding” bound on the difference in Kolmogorov complexity of a string between two UTM's. However whereas the Kolmogorov complexity of a string is arbitrary up to specification of the UTM, there is no such arbitrariness in the inference complexity of an inference task. We informally discuss philosophical implications of these results, e.g., for whether the universe “is” a TM. We also derive some graph-theoretic properties governing sets of multiple inference devices. Next we extend the framework to address physical devices used for control, and then to address probabilistic inference.

Black Holes, Entropy, and Information

Gary Horowitz — 2007-08-29T17:52:59-00:00

(27 Aug 2007)

Black holes are a continuing source of mystery. Although their classical properties have been understood since the 1970's, their quantum properties raise some of the deepest questions in theoretical physics. Some of these questions have recently been answered using string theory. I will review these fundamental questions, and the aspects of string theory needed to answer them. I will then explain the recent developments and new insights into black holes that they provide. Some remaining puzzles are mentioned in the conclusion.

Memoirs of an Early String Theorist

Pierre Ramond — 2007-08-28T19:13:01-00:00

(27 Aug 2007)

I worked on String Theory over a period of five years during the First String Era, the most intellectually satisfying years of my scientific life. One of the early prospectors in the String Theory Mine, I was fortunate enough to contribute to the birth of this subject, which retains after these many years, its magical hold on our imaginations and expectations.

On the Machian Origin of Inertia

Marcelo Berman — 2006-09-06T11:45:25-00:00

(3 Sep 2006)

We determine the numerical value of a constant which appears in the Machian inertial force expression devised by Graneau and Graneau[2]. We point out that this formula may be not restricted to Newtonian physics. Keywords: Einstein; Brans-Dicke; Newton; Gravitation; Graneau and Graneau; Mach. PACS: 01.55.+b; 04.20.-q.

The self-fulfilling prophecy in close relationships: rejection sensitivity and rejection by romantic partners.

G Downey — 2007-08-18T20:56:54-00:00

J Pers Soc Psychol, Vol. 75, No. 2. (August 1998), pp. 545-560.

The authors hypothesized a self-fulfilling prophecy wherein rejection expectancies lead people to behave in ways that elicit rejection from their dating partners. The hypothesis was tested in 2 studies of conflict in couples: (a) a longitudinal field study where couples provided daily-diary reports and (b) a lab study involving behavioral observations. Results from the field study showed that high rejection-sensitive (HRS) people's relationships were more likely to break up than those of low rejection-sensitive (LRS) people. Conflict processes that contribute to relationship erosion were revealed for HRS women but not for HRS men. Following naturally occurring relationship conflicts, HRS women's partners were more rejecting than were LRS women's partners. The lab study showed that HRS women's negative behavior during conflictual discussions helped explain their partners' more rejecting postconflict responses.

維基百科知識分享現象之研究

黃俊宇 — 2007-08-18T11:18:44-00:00

(2007)

維基百科是一網路百科全書，提供廣泛的知識給使用者，其內容是由所有使用者共同編輯而得，並非由專家學者制定。維基百科出現之後，以很快的速度成長，幾年之間已有超過250個語言版本，內容更是包羅萬象。相較於其他提供知識的網站，維基百科提供更多且更正式的內容。而編輯維基百科需要耗費個人時間精力，奉獻個人所知，沒有金錢作回報，卻有越來越多人加入編寫行列，本研究針對這一群在維基百科上分享知識的人，以及其他使用維基百科的人為研究對象，以計畫行為理論、社會認同理論以及交換行為理論等，探討其知識分享的影響因素。本研究以維基百科使用者為樣本，發放網路問卷，共回收181份問卷，有效問卷156份。經過分析後發現，聲譽和利他主義對知識分享態度有正向顯著的影響，而期望報酬對知識分享態度是負向顯著的；而知識分享態度對知識分享行為的影響是不顯著的。結果顯示對維基百科的使用者而言，聲譽和利他主義會影響其知識分享態度，但是知識分享態度卻不必然影響其知識分享行為，維基百科的使用者認為分享知識是好的，可能存在其他因素導致使用者無法進行分享的行為。本研究提出外部控制和社群認同為調節變數，發現外部控制和社群認同對於知識分享態度和知識分享行為之關係具有調節效果。

Time in the mind: Using space to think about time

Daniel Casasanto — 2007-05-21T17:37:44-00:00

Cognition, Vol. In Press, Corrected Proof

How do we construct abstract ideas like justice, mathematics, or time-travel? In this paper we investigate whether mental representations that result from physical experience underlie people's more abstract mental representations, using the domains of space and time as a testbed. People often talk about time using spatial language (e.g., a long vacation, a short concert). Do people also think about time using spatial representations, even when they are not using language? Results of six psychophysical experiments revealed that people are unable to ignore irrelevant spatial information when making judgments about duration, but not the converse. This pattern, which is predicted by the asymmetry between space and time in linguistic metaphors, was demonstrated here in tasks that do not involve any linguistic stimuli or responses. These findings provide evidence that the metaphorical relationship between space and time observed in language also exists in our more basic representations of distance and duration. Results suggest that our mental representations of things we can never see or touch may be built, in part, out of representations of physical experiences in perception and motor action.

On the quantification of entanglement in infinite-dimensional quantum systems

Jens Eisert — 2007-04-25T02:12:48-00:00

Journal of Physics A: Mathematical and General, Vol. 35, No. 17. (2002), pp. 3911-3923.

We investigate entanglement measures in the infinite-dimensional regime. First, we discuss the peculiarities that may occur if the Hilbert space of a bi-partite system is infinite dimensional, most notably the fact that the set of states with infinite entropy of entanglement is trace-norm dense in state space, implying that in any neighbourhood of every product state lies an arbitrarily strongly entangled state. The starting point for a clarification of this counterintuitive property is the observation that if one imposes the natural and physically reasonable constraint that the mean energy is bounded from above, then the entropy of entanglement becomes a trace-norm continuous functional. The considerations will then be extended to the asymptotic limit, and we will prove some asymptotic continuity properties. We proceed by investigating the entanglement of formation and the relative entropy of entanglement in the infinite-dimensional setting. Finally, we show that the set of entangled states is still trace-norm dense in state space, even under the constraint of a finite mean energy.

The development of innovation systems and the art of innovation management-strategy, control and the culture of innovation

Markus Pohlmann — 2007-08-18T10:49:15-00:00

pp. 1-7.

The success of strategies of changing or establishing innovation systems is indicated by scientific and technological innovations, the number of new products and patents, the prosperity of regions and firms and the creation of new jobs. However, there is also a less visible outcome of the innovation process in regard to knowledge creation, redesign of cultural software of what is understood as innovation and in new management concepts to maintain and generate organizational innovativeness. The papers in this issue contribute to the identification of blockages to innovation and means of overcoming them related to the latter issue. The first blockage to innovation is the human capital dilemma of insufficient trained persons in innovation management; a second is the paucity of effective organizational mechanisms to realize the full potential of innovations that have been achieved in one environment to transfer them to where they are needed in another. The capacity to integrate innovation mechanisms and carry out technological and organizational transfer is the issue here. With a focus on the less invisible indicators of innovation a new understanding of the management of innovation is possible.

The quantum physics of chronology protection

Matt Visser — 2007-08-18T09:01:54-00:00

(17 Apr 2002)

This is a brief survey of the current status of Stephen Hawking's “chronology protection conjecture”. That is: “Why does nature abhor a time machine?” I'll discuss a few examples of spacetimes containing “time machines” (closed causal curves), the sorts of peculiarities that arise, and the reactions of the physics community. While pointing out other possibilities, this article concentrates on the possibility of “chronology protection”. As Stephen puts it: “It seems that there is a Chronology Protection Agency which prevents the appearance of closed timelike curves and so makes the universe safe for historians.”

A new time-machine model with compact vacuum core

Amos Ori — 2007-08-18T08:56:47-00:00

(17 Mar 2005)

We present a class of curved-spacetime vacuum solutions which develope closed timelike curves at some particular moment. We then use these vacuum solutions to construct a time-machine model. The causality violation occurs inside an empty torus, which constitutes the time-machine core. The matter field surrounding this empty torus satisfies the weak, dominant, and strong energy conditions. The model is regular, asymptotically-flat, and topologically-trivial. Stability remains the main open question.

Collective tests for quantum nonlocality

Asher Peres — 2007-08-17T21:40:22-00:00

(18 Oct 1998)

Pairs of spin-1/2 particles are prepared in a Werner state (namely, a mixture of singlet and random components). If the random component is large enough, the statistical results of spin measurements that may be performed on each pair separately can be reproduced by an algorithm involving local “hidden” variables. However, if several such pairs are tested simultaneously, a violation of the Clauser-Horne-Shimony-Holt inequality may occur, and no local hidden variable model is compatible with the results.

Separability Criterion for Density Matrices

Asher Peres — 2007-08-17T21:34:32-00:00

(17 Jun 1996)

A quantum system consisting of two subsystems is separable if its density matrix can be written as $ρ=∑_A w_A\,ρ_A'⊗ρ_A”$, where $ρ_A'$ and $ρ_A”$ are density matrices for the two subsytems. In this Letter, it is shown that a necessary condition for separability is that a matrix, obtained by partial transposition of $ρ$, has only non-negative eigenvalues. This criterion is stronger than Bell's inequality.

Mixed State Entanglement and Quantum Error Correction

Charles Bennett — 2006-07-19T03:59:34-00:00

(8 Aug 1996)

Entanglement purification protocols (EPP) and quantum error-correcting codes (QECC) provide two ways of protecting quantum states from interaction with the environment. In an EPP, perfectly entangled pure states are extracted, with some yield D, from a mixed state M shared by two parties; with a QECC, an arbi- trary quantum state $|ξ\rangle$ can be transmitted at some rate Q through a noisy channel $χ$ without degradation. We prove that an EPP involving one- way classical communication and acting on mixed state $M(χ)$ (obtained by sharing halves of EPR pairs through a channel $χ$) yields a QECC on $χ$ with rate $Q=D$, and vice versa. We compare the amount of entanglement E(M) required to prepare a mixed state M by local actions with the amounts $D_1(M)$ and $D_2(M)$ that can be locally distilled from it by EPPs using one- and two-way classical communication respectively, and give an exact expression for $E(M)$ when $M$ is Bell-diagonal. While EPPs require classical communica- tion, QECCs do not, and we prove Q is not increased by adding one-way classical communication. However, both D and Q can be increased by adding two-way com- munication. We show that certain noisy quantum channels, for example a 50% depolarizing channel, can be used for reliable transmission of quantum states if two-way communication is available, but cannot be used if only one-way com- munication is available. We exhibit a family of codes based on universal hash- ing able toachieve an asymptotic $Q$ (or $D$) of 1-S for simple noise models, where S is the error entropy. We also obtain a specific, simple 5-bit single- error-correcting quantum block code. We prove that iff a QECC results in high fidelity for the case of no error the QECC can be recast into a form where the encoder is the matrix inverse of the decoder.

A Time for Change?

John Fisher — 2005-06-04T04:56:16-00:00

Human Resource Development International, Vol. 8, No. 2. (June 2005), pp. 257-263.

Elie Cartan's geometrical vision or how to avoid expression swell

S Neut — 2007-08-11T23:19:22-00:00

(9 Aug 2007)

The aim of the paper is to demonstrate the superiority of Cartan's method over direct methods based on differential elimination for handling otherwise intractable equivalence problems. In this sens, using our implementation of Cartan's method, we establish two new equivalence results. Weestablish when a system of second order ODE's is equivalent to flat system (second derivations are zero), and when a system of holomorphic PDE's with two independent variables and one dependent variables is flat. We consider the problem of finding transformation that brings a given equation to the target one. We shall see that this problem becomes algebraic when the symmetry pseudogroup of the target equation is zerodimensional. We avoid the swelling of the expressions, by using non-commutative derivations adapted to the problem.

Behavioral changes induced by Toxoplasma infection of rodents are highly specific to aversion of cat odors.

A Vyas — 2007-08-12T01:53:36-00:00

Proc Natl Acad Sci U S A, Vol. 104, No. 15. (10 April 2007), pp. 6442-6447.

The protozoan parasite Toxoplasma gondii blocks the innate aversion of rats for cat urine, instead producing an attraction to the pheromone; this may increase the likelihood of a cat predating a rat. This is thought to reflect adaptive, behavioral manipulation by Toxoplasma in that the parasite, although capable of infecting rats, reproduces sexually only in the gut of the cat. The "behavioral manipulation" hypothesis postulates that a parasite will specifically manipulate host behaviors essential for enhancing its own transmission. However, the neural circuits implicated in innate fear, anxiety, and learned fear all overlap considerably, raising the possibility that Toxoplasma may disrupt all of these nonspecifically. We investigated these conflicting predictions. In mice and rats, latent Toxoplasma infection converted the aversion to feline odors into attraction. Such loss of fear is remarkably specific, because infection did not diminish learned fear, anxiety-like behavior, olfaction, or nonaversive learning. These effects are associated with a tendency for parasite cysts to be more abundant in amygdalar structures than those found in other regions of the brain. By closely examining other types of behavioral patterns that were predicted to be altered we show that the behavioral effect of chronic Toxoplasma infection is highly specific. Overall, this study provides a strong argument in support of the behavioral manipulation hypothesis. Proximate mechanisms of such behavioral manipulations remain unknown, although a subtle tropism on part of the parasite remains a potent possibility.

Quantum field theory in curved spacetime

Bernard Kay — 2007-08-11T14:20:39-00:00

(9 Aug 2007)

An encyclopedia article on mathematical aspects of quantum field theory in curved spacetime. Section titles are: Introduction and preliminaries; Construction of *-algebra for a real linear scalar field on globally hyperbolic spacetimes and some general theorems; Particle creation and the limitations of the particle concept; Theory of the stress-energy tensor; Hawking and Unruh effects; Non-globally hyperbolic spacetimes and the time-machine question; Other related topics and some warnings.

Increased serine protease activity and cathelicidin promotes skin inflammation in rosacea

Kenshi Yamasaki — 2007-08-07T12:38:20-00:00

Nature Medicine, Vol. 13, No. 8. (05 August 2007), pp. 975-980.

The effect of ancient population bottlenecks on human phenotypic variation

Andrea Manica — 2007-07-18T23:12:57-00:00

Nature, Vol. 448, No. 7151., pp. 346-348.

Learning Visual Similarity Measures for Comparing Never Seen Objects

Eric Nowak — 2007-08-05T08:24:59-00:00

Computer Vision and Pattern Recognition, 2007. CVPR '07. IEEE Conference on (2007), pp. 1-8.

In this paper we propose and evaluate an algorithm that learns a similarity measure for comparing never seen objects. The measure is learned from pairs of training images labeled "same" or "different". This is far less informative than the commonly used individual image labels (e.g. "car model X"), but it is cheaper to obtain. The proposed algorithm learns the characteristic differences between local descriptors sampled from pairs of "same" and "different" images. These differences are vector quantized by an ensemble of extremely randomized binary trees, and the similarity measure is computed from the quantized differences. The extremely randomized trees are fast to learn, robust due to the redundant information they carry and they have been proved to be very good clusterers. Furthermore, the trees ef ciently combine different feature types (SIFT and geometry). We evaluate our innovative similarity measure on four very different datasets and consistantly outperform the state-of-the-art competitive approaches.