51,925 research outputs found
Spinors, embeddings and gravity
No full textThis thesis is concerned with the theory of spinors, embeddings and everywhere invariance with applications to general relativity. The approach is entirely geometric with particular emphasis on the use of natural structures. A clear indication of the interaction between the above topics is given; this Interaction then sheds light on various aspects of general relativity theory.The main ideas discussed are:- (i) Spinors, conformal structure and the spacetime projective null bundle framework. (ii) Spaces of embeddings. (ill) Embeddings and spin structure. (iv) Null embeddings and the null limit (a technique for obtaining differential equations on null hypersurfaces). (v) Quasi-local momentum. (vi) The space of metrics, natural group actions and generalized conformal structure. (vii) Everywhere invariance and the invariance equation as a method for obtaining spacetime symmetries. Three appendices are also provided:- These give comprehensive summaries of the theories of principal bundles, conformal structure and asymptotic simplicity
Size distortions of tests of the null hypothesis of stationarity: Evidence and implications for applied work
No full textIt is common in applied econometrics to test the null hypothesis of a level-stationary process against the alternative of a unit root process. We show that the use of conventional asymptotic critical values for the stationarity tests of Kwiatkowski et al. (1992) and Leybourne and McCabe (1994) may cause extreme size distortions, if the model under the null hypothesis is highly persistent. The existence of such size distortions has not been recognized in the previous literature. We illustrate the practical importance of these distortions for the problem of testing for long-run purchasing power parity under the recent float. Size distortions of tests of the unit root null hypothesis may be overcome by the use of finite-sample or bootstrap critical values. We show that such corrections are not possible for tests of the null hypothesis of stationarity. Our results suggest that the common practice of viewing tests of stationarity as complementary to tests of the unit root null will tend to result in contradictions or in spurious acceptances of the unit root hypothesis. We conclude that tests of the null hypothesis of stationarity cannot be recommended for applied work unless the sample size is very large. --I(0) null hypothesis,finite-sample critical values,size,Monte Carlo simulation
Performance Evaluation of Distributed-Antenna Communications Systems Using Beam-Hopping
No full textDigital beamforming (DBF) techniques are capable of improving the performance of communications systems significantly. However, if the transmitted signals are conflicted with strong interference, especially, in the direction of the transmitted beams , these directional jamming signals will severely degrade the system performance. In order to efficiently mitigate the interference of the directional jammers, in this contribution a beam-hopping (BH) communications scheme is proposed. In the proposed BH communications scheme, only one pair of the beams is used for transmission and it hops from one to the next according to an assigned BH pattern. In this contribution a range of expressions in terms of the average SINR performance have been derived, when both the uplink and downlink are considered. The average SINR performance of the proposed BH scheme and that of the conventional single-beam (SB) as well as multiple-beam (MB) assisted beam-processing schemes have been investigated. Our analysis and results show that the proposed BH scheme is capable of efficiently combating the directional jamming, with the aid of utilizing the directional gain of the beams generated by both the transmitter and the receiver. Furthermore, the BH scheme is capable of reducing the intercept probability of the communications. Therefore, the proposed BH scheme is suitable for communications, when several distributed antenna arrays are available around a mobile
Triggering the unlearning of null arguments in second language acquisition.
No full textby Yang Xiaolu.Thesis (M.Phil.)--Chinese University of Hong Kong, 1994.Includes bibliographical references (leaves 134-140).Chapter 1. --- Introduction --- p.1Chapter 1.1 --- Parameter Model of Acquisition --- p.1Chapter 1.2 --- "Positive Evidence, Negative Evidence and the Catapult Hypothesis" --- p.5Chapter 1.3 --- The Focus of the Present Study --- p.7Chapter 1.4 --- The Organization of the Thesis --- p.9Chapter 2. --- Null Arguments: A Theory of Parameters and Language Acquisition --- p.10Chapter 2.1 --- A Theory of Parameters: the Null Argument Parameters --- p.10Chapter 2.2 --- Predicting and Explaining L1 Acquisition --- p.17Chapter 2.2.1 --- A Summary of Research Findings --- p.18Chapter 2.2.2 --- The Initial Setting --- p.21Chapter 2.2.3 --- Identification of Early Null Arguments --- p.22Chapter 2.2.4 --- Triggers in the L1 Acquisition of the Target Parameters --- p.25Chapter 2.3 --- A Review of L2 Acquisition Studies: Related Issues --- p.31Chapter 2.3.1 --- The Null Argument Phenomenon in L2 Acquisition --- p.31Chapter 2.3.2 --- The Initial Setting and the Role of L1 --- p.35Chapter 2.3.3 --- Identification of the Null Arguments in Interlanguages --- p.36Chapter 2.3.4 --- Parameter Resetting and Triggers --- p.37Chapter 3. --- The Formulation of The Present Study --- p.40Chapter 3.1 --- The Status of Null Arguments in Chinese --- p.40Chapter 3.2 --- The Null Argument Parameters in Chinese and English --- p.50Chapter 3.3 --- Resetting the Null Argument Parameters and Unlearning Null Arguments --- p.53Chapter 3.4 --- Suggesting Triggers in the L2 Acquisition of English --- p.54Chapter 3.5 --- "Predictions: Null Arguments, Triggers and ILs" --- p.57Chapter 4. --- The Present Study (I): The Experiment´ؤMethodology --- p.59Chapter 4.1 --- Subjects --- p.59Chapter 4.2 --- The Tasks --- p.61Chapter 4.3 --- Coding and Marking --- p.67Chapter 5. --- The Present Study (II): The Experiment´ؤResults --- p.70Chapter 5.1 --- An Overview of the Written Results --- p.70Chapter 5.1.1 --- Comparing Task Performance --- p.70Chapter 5.1.1.1 --- Comparing Task 1 and Task2 --- p.70Chapter 5.1.1.2 --- Comparing Task 2 and Task3 --- p.72Chapter 5.1.2 --- An Overall View of the Written Results --- p.73Chapter 5.2 --- Null Elements in the Interlanguages of Chinese Learners of English --- p.75Chapter 5.2.1 --- Null Subjects and Null Objects --- p.76Chapter 5.2.2 --- Null Expletives --- p.79Chapter 5.2.3 --- Null Subjects in Matrix Clauses and Tensed Embedded Clauses --- p.81Chapter 5.2.3.1 --- Null Thematic Subjects --- p.82Chapter 5.2.3.2 --- Null Expletive Subjects --- p.86Chapter 5.3 --- Infl and Null Thematic Subjects --- p.89Chapter 5.4 --- Expletives and Null Arguments --- p.92Chapter 5.5 --- Results: Oral Task --- p.94Chapter 6. --- Discussion --- p.97Chapter 6.1 --- The Expletives-as-triggers Hypothesis Reconsidered --- p.97Chapter 6.2 --- "There, Weather it and Raising it: Their Status as the Triggering Experience" --- p.101Chapter 6.3 --- Triggering the Unlearning of Null Arguments --- p.108Chapter 7. --- Conclusion --- p.112Appendix --- p.118References --- p.13
Relating the fossil record to deglaciation in the early Permian of Gondwana : development of a Gondwana-wide biotic deglaciation model
No full textSpecial issue: Process safety in times of a pandemic
No full textGreen Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Safety and Security Scienc
The incidence of liver injury in Uyghur patients treated for TB in Xinjiang Uyghur autonomous region, China, and its association with hepatic enzyme polymorphisms nat2, cyp2e1, gstm1 and gstt1.
No full textBACKGROUND AND OBJECTIVE: Of three first-line anti-tuberculosis (anti-TB) drugs, isoniazid is most commonly associated with hepatotoxicity. Differences in INH-induced toxicity have been attributed to genetic variability at several loci, NAT2, CYP2E1, GSTM1and GSTT1, that code for drug-metabolizing enzymes. This study evaluated whether the polymorphisms in these enzymes were associated with an increased risk of anti-TB drug-induced hepatitis in patients and could potentially be used to identify patients at risk of liver injury. METHODS AND DESIGN: In a cross-sectional study, 2244 tuberculosis patients were assessed two months after the start of treatment. Anti-TB drug-induced liver injury (ATLI) was defined as an ALT, AST or bilirubin value more than twice the upper limit of normal. NAT2, CYP2E1, GSTM1 and GSTT1 genotypes were determined using the PCR/ligase detection reaction assays. RESULTS: 2244 patients were evaluated, there were 89 cases of ATLI, a prevalence of 4% 9 patients (0.4%) had ALT levels more than 5 times the upper limit of normal. The prevalence of ATLI was greater among men than women, and there was a weak association with NAT2*5 genotypes, with ATLI more common among patients with the NAT2*5*CT genotype. The sensitivity of the CT genotype for identifying patients with ATLI was 42% and the positive predictive value 5.9%. CT ATLI was more common among slow acetylators (prevalence ratio 2.0 (95% CI 0.95,4.20) )compared to rapid acetylators. There was no evidence that ATLI was associated with CYP2E1 RsaIc1/c1genotype, CYP2E1 RsaIc1/c2 or c2/c2 genotypes, or GSTM1/GSTT1 null genotypes. CONCLUSIONS: In Xinjiang Uyghur TB patients, liver injury was associated with the genetic variant NAT2*5, however the genetic markers studied are unlikely to be useful for screening patients due to the low sensitivity and low positive predictive values for identifying persons at risk of liver injury
Distributed human computation framework for linked data co-reference resolution
No full textDistributed Human Computation (DHC) is a technique used to solve computational problems by incorporating the collaborative effort of a large number of humans. It is also a solution to AI-complete problems such as natural language processing. The Semantic Web with its root in AI is envisioned to be a decentralised world-wide information space for sharing machine-readable data with minimal integration costs. There are many research problems in the Semantic Web that are considered as AI-complete problems. An example is co-reference resolution, which involves determining whether different URIs refer to the same entity. This is considered to be a significant hurdle to overcome in the realisation of large-scale Semantic Web applications. In this paper, we propose a framework for building a DHC system on top of the Linked Data Cloud to solve various computational problems. To demonstrate the concept, we are focusing on handling the co-reference resolution in the Semantic Web when integrating distributed datasets. The traditional way to solve this problem is to design machine-learning algorithms. However, they are often computationally expensive, error-prone and do not scale. We designed a DHC system named iamResearcher, which solves the scientific publication author identity co-reference problem when integrating distributed bibliographic datasets. In our system, we aggregated 6 million bibliographic data from various publication repositories. Users can sign up to the system to audit and align their own publications, thus solving the co-reference problem in a distributed manner. The aggregated results are published to the Linked Data Cloud
Lower Permian brachiopods and palynomorphs of the Alborz Mountain (North Iran) and their palaeobiogeographical affinity
No full textIntersystem soft handover for converged DVB-H and UMTS networks
No full textDigital video broadcasting for handhelds (DVB-H) is the standard for broadcasting Internet Protocol (IP) data services to mobile portable devices. To provide interactive services for DVB-H, the Universal Mobile Telecommunications System (UMTS) can be used as a terrestrial interaction channel for the unidirectional DVB-H network. The converged DVB-H and UMTS network can be used to address the congestion problems due to the limited multimedia channel accesses of the UMTS network. In the converged network, intersystem soft handover between DVB-H and UMTS is needed for an optimum radio resource allocation, which reduces network operation cost while providing the required quality of service. This paper deals with the intersystem soft handover between DVB-H and UMTS in such a converged network. The converged network structure is presented. A novel soft handover scheme is proposed and evaluated. After considering the network operation cost, the performance tradeoff between the network quality of service and the network operation cost for the intersystem soft handover in the converged network is modeled using a stochastic tree and analyzed using a numerical simulation. The results show that the proposed algorithm is feasible and has the potential to be used for implementation in the real environment
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