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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Efficient Message Passing Decoding Using Vector-based Messages

Grimnell, Mikael, Tjäder, Mats January 2005 (has links)
The family of Low Density Parity Check (LDPC) codes is a strong candidate to be used as Forward Error Correction (FEC) in future communication systems due to its strong error correction capability. Most LDPC decoders use the Message Passing algorithm for decoding, which is an iterative algorithm that passes messages between its variable nodes and check nodes. It is not until recently that computation power has become strong enough to make Message Passing on LDPC codes feasible. Although locally simple, the LDPC codes are usually large, which increases the required computation power. Earlier work on LDPC codes has been concentrated on the binary Galois Field, GF(2), but it has been shown that codes from higher order fields have better error correction capability. However, the most efficient LDPC decoder, the Belief Propagation Decoder, has a squared complexity increase when moving to higher order Galois Fields. Transmission over a channel with M-PSK signalling is a common technique to increase spectral efficiency. The information is transmitted as the phase angle of the signal. The focus in this Master’s Thesis is on simplifying the Message Passing decoding when having inputs from M-PSK signals transmitted over an AWGN channel. Symbols from higher order Galois Fields were mapped to M-PSK signals, since M-PSK is very bandwidth efficient and the information can be found in the angle of the signal. Several simplifications of the Belief Propagation has been developed and tested. The most promising is the Table Vector Decoder, which is a Message Passing Decoder that uses a table lookup technique for check node operations and vector summation as variable node operations. The table lookup is used to approximate the check node operation in a Belief Propagation decoder. Vector summation is used as an equivalent operation to the variable node operation. Monte Carlo simulations have shown that the Table Vector Decoder can achieve a performance close to the Belief Propagation. The capability of the Table Vector Decoder depends on the number of reconstruction points and the placement of them. The main advantage of the Table Vector Decoder is that its complexity is unaffected by the Galois Field used. Instead, there will be a memory space requirement which depends on the desired number of reconstruction points.
32

The EU’s Adoption of IFRS and the Implication for China : In the Perspective of Accounting Quality and Information Comparability

Deng, Shufen January 2013 (has links)
Globalization has led to the growth of international financial markets, as one of the results, the EU adopted IFRS in 2005 to meet the need of accounting globalization and harmonization. This action has triggered a debate about whether the adoption of IFRS is beneficial to accounting quality and information comparability. Meanwhile, China, playing a key role in the global economic development stage, realizes the importance of accounting harmonization and attempts to move towards the IFRS as well. However, to reach the goal that the Chinese companies produce financial statements that are the same as those that apply IFRS, there is still a long way to go. The purpose of this thesis is to examine whether the adoption of IFRS by EU has enhanced the quality of financial reporting and accounting information comparability. Additionally, the thesis further identified the seminal undertakings for the convergence of IFRS in Europe and pointed out the implication for China’s convergence with IFRS. The empirical findings in this thesis were obtained through qualitative interviews. The empirical findings suggest that accounting quality and information comparability has been enhanced with EU’s strong and full enforcement with IFRS. With the confidence in IFRS which is gained from the success of the EU’s adoption of IFRS, a coherent result was found that the convergence towards IFRS would also benefit China in accounting quality and information comparability, and further lead to more international investments. However, when it comes to the question whether China should emulate EU’s example to adopt IFRS directly or keep CAS (Chinese Accounting Standards) which is similar to IFRS, two mixed opinions were obtained basically from Europe side and China side. Through in-depth analysis with these empirical findings, the conclusion is that it is necessary for China to take steps to build intensive programs to enhance its capacity of the adoption of IFRS, so that it could adapt itself to the fact that the IFRS is already making its way around the world as a single set of high quality global accounting standards.
33

Channel estimation for OFDM in fast fading channels

Wan, Ping 18 July 2011 (has links)
The increasing demand for high data rate transmission over broadband radio channels has imposed significant challenges in wireless communications. Accurate channel estimation has a major impact on the whole system performance. Specifically, reliable estimate of the channel state information (CSI) is more challenging for orthogonal frequency division multiplexing (OFDM) systems in doubly selective fading channels than for the slower fading channels over which OFDM has been deployed traditionally. With the help of a basis expansion model (BEM), a novel multivariate autoregressive (AR) process is developed to model the time evolution of the fast fading channel. Relying on pilot symbol aided modulation (PSAM), a novel Kalman smoothing algorithm based on a second-order dynamic model is exploited, where the mean square error (MSE) of the channel estimator is near to that of the optimal Wiener filter. To further improve the performance of channel estimation, a novel low-complexity iterative joint channel estimation and symbol detection procedure is developed for fast fading channels with a small number of pilots and low pilot power to achieve the bit error rate (BER) performance close to when the CSI is known perfectly. The new channel estimation symbol detection technique is robust to variations of the radio channel from the design values and applicable to multiple modulation and coding types. By use of the extrinsic information transfer (EXIT) chart, we investigate the convergence behavior of the new algorithm and analyze the modulation, pilot density, and error correction code selection for good system performance for a given power level. The algorithms developed in this thesis improve the performance of the whole system requiring only low ratios of pilot to data for excellent performance in fast fading channels. / Graduate
34

O uso de estratégias na transferência de informação nos vídeos em saúde

Moraes, Alice Ferry de 29 March 2004 (has links)
Made available in DSpace on 2015-10-19T11:49:43Z (GMT). No. of bitstreams: 1 alicemoraes2004.pdf: 1007709 bytes, checksum: 5ec9834050c90c18a35b491b541e4ba9 (MD5) Previous issue date: 2004-03-29 / The feasibility of using strategies in the information transfer process, particularly in health videos for social intervention projects, is born as a research carried out after participation in the panel of judges of the III National Health Video Show promoted by Fundação Oswaldo Cruz -Fiocruz held in Rio de Janeiro in 1998. The diversity of approaches and the plurality of languages and genres arouse our interest and stimulate the study that had its roots in the history of the use of moving images in the health area in Brazil. The focus widens to cover Fiocruz for its performance as a research institution in the field of Communications Policies of the Brazilian Unified Health System (SUS). Informational action in the health area is used in disease prevention and health promotion ratifying the intention of triggering behavior modification in individuals. Questions roused by this subject have their roots in other questions that are part of the essence of Information Science, that is, information transfer and the consequent change of the cognitive structure of its recipient, to which categories of informational strategies presented as facilitating instruments of those processes are added. The use of strategies is an informational intervention based on power, knowledge and ethics. The ethical question stands out, and explanations about it are searched in Sociology and Philosophy authors. Informational strategies categorized as communicational, discursive, cognitive, sociocultural, educational, and power strategies are built on the basis of models and concepts from areas such as Communications, Linguistics, Cognition, Sociology and Education that indicate both the objectives and the intention of the information transferred. And it is based on the technological elements of video equipment that the technical informational strategies are built. Categories of health videos are created based on the observation of videos that are part of the informational day-to-day as well as from the III National Health Video Show. This Show is the main observational field for this thesis, and the data analysis of the finalist videos technical records provides a view of health video production in that period. Identification of the strategies is facilitated by the Discourse Analysis allowing, in some situations exemplified in six videos from the Show, the detection of the simultaneous use of more than one strategy. The production of future videos can also use the same mechanisms according to the objectives to be achieved. By using the strategies, it is possible to facilitate information transfer in the videos and, by extension, their use can be recommended in sites, portals, hypertexts and other informational modalities that particularly use images to transfer information suitable for users and their environment / A viabilidade do uso de estratégias no processo de transferência de informação, particularmente nos vídeos em saúde de projetos de intervenção social, nasce como pesquisa após participação em júri da III Mostra Nacional de Vídeos em Saúde, promovida pela Fundação Oswaldo Cruz (Fiocruz) e ocorrida no Rio de Janeiro, em 1998. A diversidade de abordagens e a pluralidade de linguagens e de gêneros provocam nosso interesse e estimulam o estudo, iniciado pela história do uso de imagens em movimento na área da saúde no Brasil. O foco amplia-se para a Fiocruz por sua atuação como instituição de pesquisa no campo das Políticas de Comunicação do Sistema Único de Saúde (SUS). A área da saúde utiliza a ação informacional na prevenção de doenças e na promoção da saúde, ratificando a intenção de desencadear mudança comportamental nos indivíduos. As questões levantadas por esse tema têm raízes em outras que integram o âmago da Ciência da Informação, ou seja, a transferência da informação e conseqüente mudança da estrutura cognitiva de seu receptor, a qual agregam-se categorias de estratégias informacionais apresentadas como instrumentos facilitadores desses processos. O uso de estratégias é uma intervenção informacional baseada no poder, no saber e na ética. A questão ética destaca-se e esclarecimentos sobre ela são buscados em autores da Sociologia e Filosofia. A partir de modelos e conceitos de áreas como Comunicação, Lingüística, Cognição, Sociologia, Educação, que apontam os objetivos e a intenção da informação transferida, resulta a construção de estratégias informacionais, categorizadas em comunicacionais, discursivas, cognitivas, socioculturais, educacionais e de poder. E com base nos elementos tecnológicos dos equipamentos do vídeo constroem-se as estratégias informacionais técnicas. Categorias de vídeos em saúde são criadas a partir de observações de vídeos que integram o cotidiano informacional e a III Mostra. Esta é descrita como o campo observacional prioritário desta tese e a análise de dados das fichas técnicas dos vídeos finalistas fornecem uma visão da produção de vídeos em saúde nesse período. A identificação das estratégias é facilitada pela Análise do Discurso, percebendo-se, em algumas situações exemplificadas em seis vídeos da Mostra, o uso simultâneo de mais de uma das estratégias. A produção de futuros vídeos também pode dispor desses mesmos mecanismos de acordo com o objetivo que se quer atingir. É possível, por meio da utilização das estratégias, facilitar a transferência de informações nos vídeos e, por extensão, pode-se recomendar esse uso em sites, portais, hipertextos e outras modalidades informacionais que, em especial, usam imagens para transferir informações adequadas aos usuários e seus contextos
35

Serviço de informação especializado como elemento de mediação: um estudo a partir da transferência de tecnologias no contexto da agricultura familiar brasileira / -

Daniela Maciel Pinto 01 October 2015 (has links)
Desde os tempos mais remotos, a agricultura se faz presente na história da humanidade. Formalmente, no Brasil, esta atividade teve início durante a colonização por Portugal, no final do século XV, e exerce importante papel no desenvolvimento econômico brasileiro até os dias atuais. Em termos econômicos, em particular neste setor, a Agricultura Familiar destaca-se pela produção de alimentos e geração de empregos. Apesar disto, esta modalidade passou a integrar as políticas públicas agrícolas apenas em meados dos anos 1990, com o Programa Nacional de Fortalecimento da Agricultura Familiar (Pronaf). Com a estruturação deste programa, diversas instituições que desenvolvem pesquisas agrícolas foram estimuladas a criar soluções tecnológicas, objetivando melhorias dos processos produtivos na agricultura de base familiar. Percebe-se, entretanto, dificuldades para que as tecnologias geradas nessas instituições cheguem aos agricultores familiares e possam ser plenamente utilizadas. Conjectura-se que uma das possíveis causas está relacionada à comunicação, em especial, à forma e o conteúdo das informações produzidas e disseminadas pelas instituições de pesquisas. Assim, tendo em vista que os serviços de informação são meios auxiliares do processo de comunicação da informação, na medida em que seu objetivo maior é manter um acervo dos documentos, onde estão registrados os conhecimentos gerados no desenvolvimento de atividades de pesquisa associadas à agricultura, para acesso daqueles a quem esse conhecimento possa interessar e/ou ser necessário, este trabalho teve como objetivo sistematizar um conjunto de elementos necessários à criação e manutenção de um serviço de informação, destinado a viabilizar a transferência/comunicação da informação tecnológica, no contexto da Agricultura Familiar. Trata-se de uma pesquisa de natureza exploratória, onde buscou-se explicação dentro do contexto histórico, com vistas a situar a Agricultura Familiar brasileira. A partir desta explicação e utilizando-se referenciais da Ciência da Informação, estudou-se Informação Tecnológica, Mediação da Informação, Transferência de Tecnologias e Serviços de Informação Especializados. Como resultado, foi proposto um modelo conceitual de Serviço de Informação Tecnológica, que integra todos os atores do processo de Transferência de Tecnologias, situando o serviço como um meio estratégico para a Gestão da Pesquisa Agropecuária. Apresenta, ainda como resultados, a síntese dessa proposta conceitual, a qual é composta por um conjunto de oito elementos para a estruturação do Serviço de Informação Tecnológica. / Since ancient times, agriculture is present in human history. Formally, in Brazil, the activity started during colonization by Portugal in the late fifteenth century, playing an important role in the Brazilian economic development to the present day. In economic terms, particularly in this sector, Family Farming stands out for food production and job creation. Nevertheless, this mode was integrated with agricultural policies only in the mid-1990s, with the National Programme for Strengthening Family Agriculture (Pronaf). With the structure of this program, a number of institutions that develop agricultural research have been encouraged to create technological solutions, aiming improvement of production processes in family-based agriculture. It is clear, however, there are difficulties for technologies generated in these institutions to reach the farmers and be fully used. It is conjectured that one possible cause is related to communication, in particular the form and content of the information produced and disseminated by research institutions. Thus, given that the intelligence services are auxiliary means to the information communication process, to the extent that its main objective is to maintain a collection of documents, which registered the knowledge generated in the development of research activities related to agriculture, access to those whom this knowledge may concern and / or be required, this study aimed to systematize a set of elements necessary to create and maintain an information service designed to facilitate the transfer / communication of technological information within the context of Family Farming. This consists of a research exploratory nature, which sought to explain, within the historical context, and to situate the Brazilian Family Agriculture. From this explanation and by using benchmarks of Information Science, we studied Information Technology, Information Mediation, Technology Transfer and Specialized Information Services. As a result, we proposed a conceptual model of Technological Information Services, which includes all stakeholders in the Technology Transfer process, situating the service as a key vehicle for Agricultural Research Management. It also presents as a result the synthesis of this conceptual proposal, which consists of a set of eight elements for structuring the Technological Information Service.
36

A patente na universidade: contexto e perspectivas de uma política de geração de patentes na Universidade Federal Fluminense

Corrêa, Fátima Carvalho January 2007 (has links)
Submitted by Maria Dulce (mdulce@ndc.uff.br) on 2014-08-29T19:33:13Z No. of bitstreams: 1 Dissertacao_Fatima_Correa-2007.pdf: 1947335 bytes, checksum: 4e99f62aad6d9f735ef5ef57763c0fdd (MD5) / Approved for entry into archive by Maria Dulce (mdulce@ndc.uff.br) on 2014-08-29T19:33:50Z (GMT) No. of bitstreams: 1 Dissertacao_Fatima_Correa-2007.pdf: 1947335 bytes, checksum: 4e99f62aad6d9f735ef5ef57763c0fdd (MD5) / Made available in DSpace on 2014-08-29T19:33:50Z (GMT). No. of bitstreams: 1 Dissertacao_Fatima_Correa-2007.pdf: 1947335 bytes, checksum: 4e99f62aad6d9f735ef5ef57763c0fdd (MD5) Previous issue date: 2007 / Universidade Federal Fluminense / Este estudo visou traçar um quadro atual sobre a questão da geração de patentes na universidade brasileira, discutindo, especialmente, o tema no âmbito da UFF. Teve como objetivo trazer para a discussão – localizada nos marcos da Ciência da Informação – a perspectiva desta universidade, mediante a visão de alguns de seus atores, membros destacados de sua comunidade acadêmica, sobre o fortalecimento de políticas de patenteamento na UFF. Pretendeu-se colaborar para a ampliação dos estudos na área de Ciência da Informação, tendo a patente como objeto de investigação. Partiu-se dos pressupostos de que a pesquisa desenvolvida na universidade subordina-se a uma lógica acadêmica que se confrontaria com as exigências dos processos tecnológicos e de que o sistema acadêmico valoriza a publicação de artigos considerando esta atividade como critério de excelência. Buscou-se a literatura da área de Ciência da Informação para contemplar o conceito de transferência da informação e, além desta, as de Arquivologia e da História Cultural para cobrir a questão da possível contradição entre sigilo e publicização no ambiente acadêmico, em torno da produção de patentes. Os métodos empregados, de caráter qualitativo, consistiram em levantamento e análise bibliográfica e documental e, na pesquisa empírica, em entrevistas com atores da UFF envolvidos com a questão de patentes. As conclusões do estudo revelam as fragilidades da universidade, por um lado, e a potencialidades dela e da sua comunidade, por outro, apontando a necessidade de que sejam promovidas ações compatíveis com a importância da questão das patentes no ambiente referido. / The main objective of this study is to trace a picture about the question of patent generation at the Brazilian University, in particular the focus of the research is directed to the Universidade Federal Fluminense (UFF). The discussion of the subject is performed within the Information Science context and has the objective of present the view of some prominent members of the University community concerning the strengthen of the patent policies at UFF. The purpose of the work is to enhance the study of the Information Science area, considering the patent as object of investigation. The starting point of the work is that the scientific research developed as the University is subordinated to an academic logic that opposes the logic of technological process and that the academic system gives value to the publication of papers and considers the activity as the main scientific excellence criteria. Therefore, the research seeks, in the literature, the Information Science as well as in the Archive area and Cultural History, the elements to discuss the possible contradiction between the secrecy and the publication of patents in the academic environment. The method employed is founded in bibliographical and document analysis, as well as in an empirical qualitative research. The work results reveal the university weakness, but on the other hand, also reveals all of its potentiality to promotes actions to valorize the generation and development of patents in the University environment.
37

Den perioperativa sjuksköterskans upplevelser av informationsöverföring, pre- och postoperativt : Litteraturstudie med systematiskt tillvägagångssätt / The perioperative nurse experience of information transfer, pre- and postoperative : A systematic literature review

Pettersson, Linnéa, Klintsäter, Sofie January 2020 (has links)
Bakgrund: Informationsöverföring sker kontinuerligt i den perioperativa vården. Det anses vara ett riskmoment när patient och information överförs till ny personal och vårdenhet. Kontinuitet, kvalitet, effektivitet och patientsäkerhet uppnås genom att operationssjuksköterskan initierar och genomför adekvat informationsöverföring i samband med patientens kirurgiska ingrepp. Syfte: Var att belysa den perioperativa sjuksköterskans upplevelser av informationsöverföring, pre- och postoperativt. Metod: En litteraturstudie med systematiskt tillvägagångssätt i enlighet med Bettany-Saltikov och McSherry (2016). Resultatet baseras på analysen av tolv kvalitativa vetenskapliga artiklar. Resultat: Resultatet påvisade att det fanns flertalet brister i den perioperativa informationsöverföringen och att den upplevdes som komplex. Resultatet redovisades i tre huvudkategorier; Utspridd och bristfällig information, Förutsättningar för informationsöverföring samt Människans inverkan på informationsöverföring. Slutsats: Många faktorer påverkar informationsöverföringen pre- och postoperativt utifrån den perioperativa sjuksköterskans upplevelser. Då medlemmar av det kirurgiska teamet inte alltid medverkar vid den postoperativa patientöverlämningen  finns en risk för att kirurgisk information kan gå förlorad. När  informationsöverföringen brister kan det ge upphov till negativa konsekvenser för patienten. / Background: The transfer of information within perioperative care, is a continuous process. When a patient, together with the relevant patient-information is transferred to a new carer and care unit, there is considered to be an element of risk involved. Continuity, quality, efficiency and patient safety will be achieved when the operating theatre nurse initiates and implements an adequate transfer of information, in connection with the patient’s surgical procedure. Aim: To illustrate how perioperative nurses experience the pre and postoperative transfer of information. Method: A systematic literature review in accordance with  Bettany-Saltikov and McSherry (2016).  The result is based on an analysis of twelve qualitative, scientific articles. Results: The study results demonstrate that there are several deficiencies during the transfer of perioperative information, and that it is perceived as complex. The results are presented in three main categories; Scattered and inadequate information, Prerequisites for information transfer and The human influence on information transfer. Conclusion: Based on the experiences of the perioperative nurses, there are many factors which influence the pre and postoperative transfer of information. As members of the surgical team do not always participate in the postoperative patient handover, there is a risk that surgical information may be lost. There can be negative consequences for the patient when the transfer of information is inadequate.
38

Patienters erfarenheter av information i samband med utskrivning från slutenvården : En litteraturöversikt / Inpatients experiences of information associated with discharge from hospital : a literature review

Boström, Rebecca, Nilsson, Angelica January 2023 (has links)
Bakgrund: Tydlig information vid utskrivning från slutenvården har stor betydelse för patienten. I samband med utskrivning från slutenvården finns behov av tydlig och anpassad information om behandling och vård som givits under vårdtiden. Sjuksköterskan som ger information bör försäkra sig om att patienten har förstått både betydelsen och innehållet i den information som lämnats. En god kommunikation i patientmötet är nödvändig för att öka patientens delaktighet och förbättra patientsäkerheten. Syfte: Syftet med litteraturöversikten var att belysa patienters erfarenheter av information i samband med utskrivning från slutenvården. Metod: En strukturerad litteraturstudie baserad på 18 vetenskapliga artiklar med inslag av den metodologi som används vid systematiska översikter. Databaserna som användes var CINAHL och PubMed, artiklarna som användes var publicerade mellan år 2013 och 2022. Resultat: I resultatet identifierades tre huvudkategorier som påverkade patienters erfarenheter av information i samband med utskrivning från slutenvården: Mötet i samband med utskrivning, brist på information och anpassad information. Slutsats: Litteraturöversikten visar att patienter upplever bristande information vid utskrivning från slutenvård. Att tillgodose patientens behov av information och delaktighet vid utskrivning visar sig vara en utmaning för vårdpersonal. Genom att arbeta personcentrerat och fokusera på den enskilda individens behov samt inkludera och informera, ökar delaktighet på ett patientsäkert sätt. / Background: Clear deliver of information through the discharge process is important for the patient. Iti s also important with adapted and person-centered information about the patient treatment plan and the care provided during the period of time at the hospital. The nurse who is providing the information should ensure that the patient has understood the content of the information and the meaning of it. Good communication is necessary to increase patient participation and improve patient safety. Aim: The aim of this literature review was to highlight inpatients experiences of information associated with discharge from hospital. Method: A structured literature review has been made based on 18 scientific articles with elements of the methodology used in systematic reviews. The databases used were CINAHL and PubMed, the articles used were published between 2013 and 2022. Results: The result identified three categories that affected patients experiences of information associated with discharge from hospital: Meeting associated at discharge, lack of information and customized information. Conclusions: The literature review shows that patients experience lack of information when discharge from hospital. Meeting the patient's need for information and participation at discharge turns out to be a challenge for healthcare professionals. By working personcentered and focusing on the individual's needs as well as including and informing, participation increases in a patient-safe manner.
39

盈餘重編之供應鏈外溢效果 / The Spillover Effects of Earnings Restatements Along the Supply Chain

賴淑妙, Lai, Shu-Miao Unknown Date (has links)
本研究主要探討盈餘重編宣告如何影響重編公司之供應商的股價評價與實質投資決策。首先,本研究假設並發現,盈餘重編宣告除了導致重編公司的股價顯著下跌外,亦誘發其上游供應商的股價顯著下跌。實證進一步發現,供應商的股價依盈餘重編之資訊內涵而調整,促使投資人關注重編事件對上游供應商的預期盈餘之影響,也提醒投資人去關心上游供應商的財務報表品質。其次,本研究假設,盈餘重編宣告傳遞有關重編公司未來前景不佳及財務報表不實的資訊,將影響其供應商對投入特定關係資產所能獲得收益之預期,進而影響其對重編公司所投入的特定關係資產投資決策。實證結果支持前述假說,重編公司之供應商於重編宣告年度後將減少其研究發展支出,且此研究發展支出之變動與重編宣告所引起的股價變動具顯著關聯性。最後本文假設,重編公司扭曲其實際盈餘數字將影響供應商的投資決策,進而影響供應商的投資效率性。研究發現,供應商在重編公司財務報表誤述期間有顯著超額投資之現象。然而,此供應商之超額投資現象在盈餘重編宣告年度後不再顯著。 / This dissertation extends prior research on earnings restatements by examining the effects of earnings restatements on valuation and investment decisions of restating firms’ suppliers. First, this paper hypothesizes and finds that earnings restatements that adversely affect stock price of the restating firms also induce their suppliers’ stock price declines. These stock price declines are related to changes in analysts’ earnings forecasts and seem to reflect investors’ financial reporting quality concerns. Second, I hypothesize that earnings restatements contain information about the value of relationship-specific investments by suppliers. This information causes suppliers to revise their belief about the value of relationship-specific investments, and therefore affects their subsequent relationship-specific investment decisions. Consistent with my prediction, I find that changes in suppliers’ relationship-specific investments after restatement announcements are related to information in the restatements. Finally, I predict and find that a restating firm misreporting financial results induces its suppliers to make excess investments during the misreporting period, while excess investment is no longer positive after the restatement announcement.
40

Increasing information transfer rates for brain-computer interfacing

Dornhege, Guido January 2006 (has links)
The goal of a Brain-Computer Interface (BCI) consists of the development of a unidirectional interface between a human and a computer to allow control of a device only via brain signals. While the BCI systems of almost all other groups require the user to be trained over several weeks or even months, the group of Prof. Dr. Klaus-Robert Müller in Berlin and Potsdam, which I belong to, was one of the first research groups in this field which used machine learning techniques on a large scale. The adaptivity of the processing system to the individual brain patterns of the subject confers huge advantages for the user. Thus BCI research is considered a hot topic in machine learning and computer science. It requires interdisciplinary cooperation between disparate fields such as neuroscience, since only by combining machine learning and signal processing techniques based on neurophysiological knowledge will the largest progress be made.<br><br> In this work I particularly deal with my part of this project, which lies mainly in the area of computer science. I have considered the following three main points:<br><br> <b>Establishing a performance measure based on information theory:</b> I have critically illuminated the assumptions of Shannon's information transfer rate for application in a BCI context. By establishing suitable coding strategies I was able to show that this theoretical measure approximates quite well to what is practically achieveable.<br> <b>Transfer and development of suitable signal processing and machine learning techniques:</b> One substantial component of my work was to develop several machine learning and signal processing algorithms to improve the efficiency of a BCI. Based on the neurophysiological knowledge that several independent EEG features can be observed for some mental states, I have developed a method for combining different and maybe independent features which improved performance. In some cases the performance of the combination algorithm outperforms the best single performance by more than 50 %. Furthermore, I have theoretically and practically addressed via the development of suitable algorithms the question of the optimal number of classes which should be used for a BCI. It transpired that with BCI performances reported so far, three or four different mental states are optimal. For another extension I have combined ideas from signal processing with those of machine learning since a high gain can be achieved if the temporal filtering, i.e., the choice of frequency bands, is automatically adapted to each subject individually.<br> <b>Implementation of the Berlin brain computer interface and realization of suitable experiments:</b> Finally a further substantial component of my work was to realize an online BCI system which includes the developed methods, but is also flexible enough to allow the simple realization of new algorithms and ideas. So far, bitrates of up to 40 bits per minute have been achieved with this system by absolutely untrained users which, compared to results of other groups, is highly successful. / Ein Brain-Computer Interface (BCI) ist eine unidirektionale Schnittstelle zwischen Mensch und Computer, bei der ein Mensch in der Lage ist, ein Gerät einzig und allein Kraft seiner Gehirnsignale zu steuern. In den BCI Systemen fast aller Forschergruppen wird der Mensch in Experimenten über Wochen oder sogar Monaten trainiert, geeignete Signale zu produzieren, die vordefinierten allgemeinen Gehirnmustern entsprechen. Die BCI Gruppe in Berlin und Potsdam, der ich angehöre, war in diesem Feld eine der ersten, die erkannt hat, dass eine Anpassung des Verarbeitungssystems an den Menschen mit Hilfe der Techniken des Maschinellen Lernens große Vorteile mit sich bringt. In unserer Gruppe und mittlerweile auch in vielen anderen Gruppen wird BCI somit als aktuelles Forschungsthema im Maschinellen Lernen und folglich in der Informatik mit interdisziplinärer Natur in Neurowissenschaften und anderen Feldern verstanden, da durch die geeignete Kombination von Techniken des Maschinellen Lernens und der Signalverarbeitung basierend auf neurophysiologischem Wissen der größte Erfolg erzielt werden konnte.<br><br> In dieser Arbeit gehe ich auf meinem Anteil an diesem Projekt ein, der vor allem im Informatikbereich der BCI Forschung liegt. Im Detail beschäftige ich mich mit den folgenden drei Punkten:<br><br> <b>Diskussion eines informationstheoretischen Maßes für die Güte eines BCI's:</b> Ich habe kritisch die Annahmen von Shannon's Informationsübertragungsrate für die Anwendung im BCI Kontext beleuchtet. Durch Ermittlung von geeigneten Kodierungsstrategien konnte ich zeigen, dass dieses theoretische Maß den praktisch erreichbaren Wert ziemlich gut annähert.<br> <b>Transfer und Entwicklung von geeigneten Techniken aus dem Bereich der Signalverarbeitung und des Maschinellen Lernens:</b> Eine substantielle Komponente meiner Arbeit war die Entwicklung von Techniken des Machinellen Lernens und der Signalverarbeitung, um die Effizienz eines BCI's zu erhöhen. Basierend auf dem neurophysiologischem Wissen, dass verschiedene unabhängige Merkmale in Gehirnsignalen für verschiedene mentale Zustände beobachtbar sind, habe ich eine Methode zur Kombination von verschiedenen und unter Umständen unabhängigen Merkmalen entwickelt, die sehr erfolgreich die Fähigkeiten eines BCI's verbessert. Besonders in einigen Fällen übertraf die Leistung des entwickelten Kombinationsalgorithmus die beste Leistung auf den einzelnen Merkmalen mit mehr als 50 %. Weiterhin habe ich theoretisch und praktisch durch Einführung geeigneter Algorithmen die Frage untersucht, wie viele Klassen man für ein BCI nutzen kann und sollte. Auch hier wurde ein relevantes Resultat erzielt, nämlich dass für BCI Güten, die bis heute berichtet sind, die Benutzung von 3 oder 4 verschiedenen mentalen Zuständen in der Regel optimal im Sinne von erreichbarer Leistung sind. Für eine andere Erweiterung wurden Ideen aus der Signalverarbeitung mit denen des Maschinellen Lernens kombiniert, da ein hoher Erfolg erzielt werden kann, wenn der temporale Filter, d.h. die Wahl des benutzten Frequenzbandes, automatisch und individuell für jeden Menschen angepasst wird.<br> <b>Implementation des Berlin Brain-Computer Interfaces und Realisierung von geeigneten Experimenten:</b> Eine weitere wichtige Komponente meiner Arbeit war eine Realisierung eines online BCI Systems, welches die entwickelten Methoden umfasst, aber auch so flexibel ist, dass neue Algorithmen und Ideen einfach zu verwirklichen sind. Bis jetzt wurden mit diesem System Bitraten von bis zu 40 Bits pro Minute von absolut untrainierten Personen in ihren ersten BCI Experimenten erzielt. Dieses Resultat übertrifft die bisher berichteten Ergebnisse aller anderer BCI Gruppen deutlich. <br> <hr> Bemerkung:<br> Der Autor wurde mit dem <i>Michelson-Preis</i> 2005/2006 für die beste Promotion des Jahrgangs der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Potsdam ausgezeichnet.

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