Palo Alto Research Center

Statistical approaches to processing natural language text have become dominant in recent years. This foundational text is the first comprehensive introduction to statistical natural language processing (NLP) to appear. The book contains all the theory and algorithms needed for building NLP tools. It provides broad but rigorous coverage of mathematical and linguistic foundations, as well as detailed discussion of statistical methods, allowing students and researchers to construct their own implementations. The book covers collocation finding, word sense disambiguation, probabilistic parsing, information retrieval, and other applications.

Recent ethnographic studies of workplace practices indicate that the ways people actually work usually differ fundamentally from the ways organizations describe that work in manuals, training programs, organizational charts, and job descriptions. Nevertheless, organizations tend to rely on the latter in their attempts to understand and improve work practice. We examine one such study. We then relate its conclusions to compatible investigations of learning and of innovation to argue that conventional descriptions of jobs mask not only the ways people work, but also significant learning and innovation generated in the informal communities-of-practice in which they work. By reassessing work, learning, and innovation in the context of actual communities and actual practices, we suggest that the connections between these three become apparent. With a unified view of working, learning, and innovating, it should be possible to reconceive of and redesign organizations to improve all three.

Dendritic cells (DCs) are antigen-presenting cells with a unique ability to induce primary immune responses. DCs capture and transfer information from the outside world to the cells of the adaptive immune system. DCs are not only critical for the induction of primary immune responses, but may also be important for the induction of immunological tolerance, as well as for the regulation of the type of T cell-mediated immune response. Although our understanding of DC biology is still in its infancy, we are now beginning to use DC-based immunotherapy protocols to elicit immunity against cancer and infectious diseases.

Preface Acknowledgements 1. Introduction 2. Interactive artefacts 3. Plans 4. Situated actions 5. Communicative resources 6. Case and methods 7. Human-machine communication 8. Conclusion References Indices.

No abstract available.

Tapestry is an experimental mail system developed at the Xerox Palo Alto Research

Network use has evolved to be dominated by content distribution and retrieval, while networking technology still speaks only of connections between hosts. Accessing content and services requires mapping from the what that users care about to the network's where. We present Content-Centric Networking (CCN) which treats content as a primitive - decoupling location from identity, security and access, and retrieving content by name. Using new approaches to routing named content, derived heavily from IP, we can simultaneously achieve scalability, security and performance. We implemented our architecture's basic features and demonstrate resilience and performance with secure file downloads and VoIP calls.

1. Information Visualization 2. Space 3. Interaction 4. Focus + Context 5. Data Mapping: Text 6. Higher-Level Visualization 7. Using Vision to Think 8. Applications and Innovations 9. Conclusion Bibliography Index

Smalltalk-80 is the classic standard Smalltalk language as described in Smalltalk-80: The Language and Its Implementation by Goldberg and Robson. This book is commonly called “the Blue Booki. Squeak implements the dialect of Smalltalk described in this book, but has a different implementation. Overview of the Smalltalk Language Smalltalk is a general purpose, high level programming language. It was the first original “purei object oriented language, but not the first to use the object oriented concept, which is credited to Simula 67. The explosive growth of Object Oriented Programming (OOP) technologies began in the early 1980's, with Smalltalk's introduction. Behind it was the idea that the individual human user should be the most important component of any computing system, and that programming should be a natural extension of thinking, and also a dynamic and evolutionary process consistent with the model of human learning activity. In Smalltalk, these ideas are embodied in a framework for human-computer communication. In a sense, Smalltalk is yet another language like C and Pascal, and programs can be written in Smalltalk that have the look and feel of such conventional languages. The difference lies * in the amount of code that can be reduced, * less cryptic syntax, * and code that is easier to handle for application maintenance and enhancement. But Smalltalk's most powerful feature is easy code reuse. Smalltalk makes reuse of programs, routines, and subroutines (methods) far easier. Though procedural languages allow reuse too, it is harder to do, and much easier to cheat. It is no surprise that Smalltalk is relatively easy to learn, mainly due to its simple syntax and semantics, as well as few concepts. Objects, classes, messages, and methods form the basis of programming in Smalltalk. The general methodology to use Smalltalk The notion of human-computer interface also results in Smalltalk promoting the development of safer systems. Errors in Smalltalk may be viewed as objects telling users that confusion exists as to how to perform a desired function.

This paper addresses two unresolved issues about Web caching. The first issue is whether Web requests from a fixed user community are distributed according to Zipf's (1929) law. The second issue relates to a number of studies on the characteristics of Web proxy traces, which have shown that the hit-ratios and temporal locality of the traces exhibit certain asymptotic properties that are uniform across the different sets of the traces. In particular, the question is whether these properties are inherent to Web accesses or whether they are simply an artifact of the traces. An answer to these unresolved issues will facilitate both Web cache resource planning and cache hierarchy design. We show that the answers to the two questions are related. We first investigate the page request distribution seen by Web proxy caches using traces from a variety of sources. We find that the distribution does not follow Zipf's law precisely, but instead follows a Zipf-like distribution with the exponent varying from trace to trace. Furthermore, we find that there is only (i) a weak correlation between the access frequency of a Web page and its size and (ii) a weak correlation between access frequency and its rate of change. We then consider a simple model where the Web accesses are independent and the reference probability of the documents follows a Zipf-like distribution. We find that the model yields asymptotic behaviour that are consistent with the experimental observations, suggesting that the various observed properties of hit-ratios and temporal locality are indeed inherent to Web accesses observed by proxies. Finally, we revisit Web cache replacement algorithms and show that the algorithm that is suggested by this simple model performs best on real trace data. The results indicate that while page requests do indeed reveal short-term correlations and other structures, a simple model for an independent request stream following a Zipf-like distribution is sufficient to capture certain asymptotic properties observed at Web proxies.

While the recent focus on knowledge has undoubtedly benefited organizational studies, the literature still presents a sharply contrasting and even contradictory view of knowledge, which at times is described as “sticky” and at other times “leaky.” This paper is written on the premise that there is more than a problem with metaphors at issue here, and more than accounts of different types of knowledge (such as “tacit” and “explicit”) can readily explain. Rather, these contrary descriptions of knowledge reflect different, partial, and sometimes “balkanized” perspectives from which knowledge and organization are viewed. Taking the community of practice as a unifying unit of analysis for understanding knowledge in the firm, the paper suggests that often too much attention is paid to the idea of community, too little to the implications of practice. Practice, we suggest, creates epistemic differences among the communities within a firm, and the firm's advantage over the market lies in dynamically coordinating the knowledge produced by these communities despite such differences. In making this argument, we argue that analyses of systemic innovation should be extended to embrace all firms in a knowledge economy, not just the classically innovative. This extension will call for a transformation of conventional ideas coordination and of the trade-off between exploration and exploitation.

This paper describes systems that examine and react to an individual's changing context. Such systems can promote and mediate people's interactions with devices, computers, and other people, and they can help navigate unfamiliar places. We believe that a limited amount of information covering a person's proximate environment is most important for this form of computing since the interesting part of the world around us is what we can see, hear, and touch. In this paper we define context-aware computing, and describe four catagories of context-aware applications: proximate selection, automatic contextual reconfiguration, contextual information and commands, and contex-triggered actions. Instances of these application types have been prototyped on the PARCTAB, a wireless, palm-sized computer.

First-principles calculations have evolved from mere aids in explaining and supporting experiments to powerful tools for predicting new materials and their properties. In the first part of this review we describe the state-of-the-art computational methodology for calculating the structure and energetics of point defects and impurities in semiconductors. We will pay particular attention to computational aspects which are unique to defects or impurities, such as how to deal with charge states and how to describe and interpret transition levels. In the second part of the review we will illustrate these capabilities with examples for defects and impurities in nitride semiconductors. Point defects have traditionally been considered to play a major role in wide-band-gap semiconductors, and first-principles calculations have been particularly helpful in elucidating the issues. Specifically, calculations have shown that the unintentional n-type conductivity that has often been observed in as-grown GaN cannot be attributed to nitrogen vacancies, but is due to unintentional incorporation of donor impurities. Native point defects may play a role in compensation and in phenomena such as the yellow luminescence, which can be attributed to gallium vacancies. In the section on impurities, specific attention will be focused on dopants. Oxygen, which is commonly present as a contaminant, is a shallow donor in GaN but becomes a deep level in AlGaN due to a DX transition. Magnesium is almost universally used as the p-type dopant, but hole concentrations are still limited. Reasons for this behavior are discussed, and alternative acceptors are examined. Hydrogen plays an important role in p-type GaN, and the mechanisms that underlie its behavior are explained. Incorporating hydrogen along with acceptors is an example of codoping; a critical discussion of codoping is presented. Most of the information available to date for defects and impurities in nitrides has been generated for GaN, but we will also discuss AlN and InN where appropriate. We conclude by summarizing the main points and looking towards the future.

Measurements of the transient photocurrent $I(t)$ in an increasing number of inorganic and organic amorphous materials display anomalous transport properties. The long tail of $I(t)$ indicates a dispersion of carrier transit times. However, the shape invariance of $I(t)$ to electric field and sample thickness (designated as universality for the classes of materials here considered) is incompatible with traditional concepts of statistical spreading, i.e., a Gaussian carrier packet. We have developed a stochastic transport model for $I(t)$ which describes the dynamics of a carrier packet executing a time-dependent random walk in the presence of a field-dependent spatial bias and an absorbing barrier at the sample surface. The time dependence of the random walk is governed by hopping time distribution $\ensuremath{\Psi}(t)$. A packet, generated with a $\ensuremath{\Psi}(t)$ characteristic of hopping in a disordered system [e.g., $\ensuremath{\Psi}(t)\ensuremath{\sim}{t}^{\ensuremath{-}(1+\ensuremath{\alpha})}$, $0<\ensuremath{\alpha}<1$], is shown to propagate with a number of anomalous non-Gaussian properties. The calculated $I(t)$ associated with this packet not only obeys the property of universality but can account quantitatively for a large variety of experiments. The new method of data analysis advanced by the theory allows one to directly extract the transit time even for a featureless current trace. In particular, we shall analyze both an inorganic ($a\ensuremath{-}{\mathrm{As}}_{2}{\mathrm{Se}}_{3}$) and an organic (trinitrofluorenone-polyvinylcarbazole) system. Our function $\ensuremath{\Psi}(t)$ is related to a first-principles calculation. It is to be emphasized that these $\ensuremath{\Psi}(t)$'s characterize a realization of a non-Markoffian transport process. Moreover, the theory shows the limitations of the concept of a mobility in this dispersive type of transport.

A new theory is presented for describing band gaps and electronic structures of transition-metal compounds. A theoretical phase diagram is presented in which both the metallic sulfides and insulating oxides and halides occur in a quite natural manner.

IL-10 inhibits the ability of macrophage but not B cell APC to stimulate cytokine synthesis by Th1 T cell clones. In this study we have examined the direct effects of IL-10 on both macrophage cell lines and normal peritoneal macrophages. LPS (or LPS and IFN-gamma)-induced production of IL-1, IL-6, and TNF-alpha proteins was significantly inhibited by IL-10 in two macrophage cell lines. Furthermore, IL-10 appears to be a more potent inhibitor of monokine synthesis than IL-4 when added at similar concentrations. LPS or LPS- and IFN-gamma-induced expression of IL-1 alpha, IL-6, or TNF-alpha mRNA was also inhibited by IL-10 as shown by semiquantitative polymerase chain reaction or Northern blot analysis. Inhibition of LPS-induced IL-6 secretion by IL-10 was less marked in FACS-purified peritoneal macrophages than in the macrophage cell lines. However, IL-6 production by peritoneal macrophages was enhanced by addition of anti-IL-10 antibodies, implying the presence in these cultures of endogenous IL-10, which results in an intrinsic reduction of monokine synthesis after LPS activation. Consistent with this proposal, LPS-stimulated peritoneal macrophages were shown to directly produce IL-10 detectable by ELISA. Furthermore, IFN-gamma was found to enhance IL-6 production by LPS-stimulated peritoneal macrophages, and this could be explained by its suppression of IL-10 production by this same population of cells. In addition to its effects on monokine synthesis, IL-10 also induces a significant change in morphology in IFN-gamma-stimulated peritoneal macrophages. The potent action of IL-10 on the macrophage, particularly at the level of monokine production, supports an important role for this cytokine not only in the regulation of T cell responses but also in acute inflammatory responses.

Much current work on organizational knowledge, intellectual capital, knowledge-creating organizations, knowledge work, and the like rests on a single, traditional understanding of the nature of knowledge. We call this understanding the “epistemology of possession,” since it treats knowledge as something people possess. Yet, this epistemology cannot account for the knowing found in individual and group practice. Knowing as action calls for an “epistemology of practice.” Moreover, the epistemology of possession tends to privilege explicit over tacit knowledge, and knowledge possessed by individuals over that possessed by groups. Current work on organizations is limited by this privileging and by the scant attention given to knowing in its own right. Organizations are better understood if explicit, tacit, individual and group knowledge are treated as four distinct and coequal forms of knowledge (each doing work the others cannot), and if knowledge and knowing are seen as mutually enabling (not competing). We hold that knowledge is a tool of knowing, that knowing is an aspect of our interaction with the social and physical world, and that the interplay of knowledge and knowing can generate new knowledge and new ways of knowing. We believe this generative dance between knowledge and knowing is a powerful source of organizational innovation. Harnessing this innovation calls for organizational and technological infrastructures that support the interplay of knowledge and knowing. Ultimately, these concepts make possible a more robust framing of such epistemologically-centered concerns as core competencies, the management of intellectual capital, etc. We explore these views through three brief case studies drawn from recent research.

article Free Access Share on Some computer science issues in ubiquitous computing Author: Mark Weiser Xerox PARC, Palo Alto, CA Xerox PARC, Palo Alto, CAView Profile Authors Info & Claims Communications of the ACMVolume 36Issue 7July 1993 pp 75–84https://doi.org/10.1145/159544.159617Published:01 July 1993Publication History 1,500citation17,779DownloadsMetricsTotal Citations1,500Total Downloads17,779Last 12 Months736Last 6 weeks162 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my Alerts New Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

Use of encryption to achieve authenticated communication in computer networks is discussed. Example protocols are presented for the establishment of authenticated connections, for the management of authenticated mail, and for signature verification and document integrity guarantee. Both conventional and public-key encryption algorithms are considered as the basis for protocols.

An algorithm is presented that searches for the location, “ i l” of the first occurrence of a character string, “ pat ,” in another string, “ string .” During the search operation, the characters of pat are matched starting with the last character of pat . The information gained by starting the match at the end of the pattern often allows the algorithm to proceed in large jumps through the text being searched. Thus the algorithm has the unusual property that, in most cases, not all of the first i characters of string are inspected. The number of characters actually inspected (on the average) decreases as a function of the length of pat . For a random English pattern of length 5, the algorithm will typically inspect i /4 characters of string before finding a match at i . Furthermore, the algorithm has been implemented so that (on the average) fewer than i + patlen machine instructions are executed. These conclusions are supported with empirical evidence and a theoretical analysis of the average behavior of the algorithm. The worst case behavior of the algorithm is linear in i + patlen , assuming the availability of array space for tables linear in patlen plus the size of the alphabet.