144,817 research outputs found
INDIRECT SAMPLING in the CONTEXT of DUAL FRAME SURVEYS
No full textUnder-coverage is one of the most common problems of sampling frames. To reduce the impact of coverage error on survey estimates several frames can be combined in order to achieve a complete (or nearly complete) coverage of the target population. Multiple frame estimators have been developed to be used in the context of multiple frame surveys. Sampling frames may overlap which is the case when a single unit of the sampling frame is related with more than one element of the target population. Indirect sampling (Lavallée, 1995) is an alternative approach to classical sampling theory in dealing with the overlapping problem of sampling frames on survey estimates. Not infrequently a survey may need more than one sampling frame in order to improve coverage and simultaneously the sampling frame overlap. In this paper a new class of estimators is presented which is the result from merging multiple frames estimators (only the particular case of dual frames will be presented) with indirect sampling estimators in order to bring together in a single estimator the effect of several frames on survey estimates.Indirect Sampling, Generalized Weight Share Method, Dual Frame Surveys
New Stationary Frame Control Scheme for Three Phase PWM Rectifiers Under Unbalanced Voltage Dips Conditions
No full textA new stationary frame control scheme for three-phase pulsewidth-modulation (PWM) rectifiers operating under unbalanced voltage dips conditions is proposed in this paper. The proposed control scheme regulates the instantaneous active power at the converter poles to minimize the harmonics of the input currents and the output voltage ripple. This paper's novelty is the development of a new current-reference generator implemented directly in stationary reference frame. This allows using proportional sinusoidal signal integrator (P-SSI) controllers for simultaneous compensation of both positive and negative current sequence components. No phase-locked loop (PLL) strategies and coordinate transformations are needed for the proposed current-reference generator. Experimental results are presented for a 20-kV A alternative current (ac)/direct current (dc) converter prototype to demonstrate the effectiveness of the proposed control scheme. A comparison with two other existing control techniques is also performed. Fast dynamic performance with small dc-link voltage ripple and input sinusoidal currents are obtained with this control scheme, even under severe voltage dips operating condition
The role of Scene Type and Priming in the processing and selection of a spatial frame of reference
No full textJohannsen K, de Ruiter J. The role of Scene Type and Priming in the processing and selection of a spatial frame of reference. Frontiers in Psychology. 2013;4:182.The selection and processing of a spatial frame of reference (FOR) in interpreting verbal scene descriptions is of great interest to psycholinguistics. In this study, we focus on the choice between the relative and the intrinsic FOR, addressing two questions: (a) does the presence or absence of a background in the scene influence the selection of a FOR, and (b) what is the effect of a previously selected FOR on the subsequent processing of a different FOR. Our results show that if a scene includes a realistic background, this will make the selection of the relative FOR more likely. We attribute this effect to the facilitation of mental simulation, which enhances the relation between the viewer and the objects. With respect to the response accuracy, we found both a higher (with the same FOR) and a lower accuracy (with a different FOR), while for the response latencies, we only found a delay effect with a different FOR
Robust video broadcasting over 802.11a/g in time-correlated fading channels
No full textIn order to deliver video streams efficiently over WiFi to many thousands of consumer handheld devices, broadcast protocols must be employed. In this mode of operation the received video quality can deteriorate rapidly as a result of high application layer packet loss which occurs because MAC frame retransmission cannot be used. In this paper we develop a robust video solution that is used in conjunction with broadcast transmission over 802.11a/g. Using a cross-layer WiFi simulator in combination with an accurate time-correlated fading channel, the received video quality is evaluated for broadcast H.264 video sequences. Application layer cross-packet forward error correction is then used together with error concealment at the video client. The methods developed can be used to successfully broadcast video to many thousands of handheld terminals at large-scale spectator events.In order to deliver video streams efficiently over WiFi to many thousands of consumer handheld devices, broadcast protocols must be employed. In this mode of operation the received video quality can deteriorate rapidly as a result of high application layer packet loss which occurs because MAC frame retransmission cannot be used. In this paper we develop a robust video solution that is used in conjunction with broadcast transmission over 802.11a/g. Using a cross-layer WiFi simulator in combination with an accurate time-correlated fading channel, the received video quality is evaluated for broadcast H.264 video sequences. Application layer cross-packet forward error correction is then used together with error concealment at the video client. The methods developed can be used to successfully broadcast video to many thousands of handheld terminals at large-scale spectator events
Continuous g-Frame in Hilbert C∗-Modules
No full textWe give a generalization of g-frame in Hilbert C∗-modules that was introduced by Khosravies then investigated some properties of it by Xiao and Zeng. This generalization is a natural generalization of continuous and discrete g-frames and frame in Hilbert space too. We characterize continuous g-frame g-Riesz in Hilbert C∗-modules and give some equality and inequality of these frames
Avaliação de desempenho do serviço de voz em redes corporativas Frame Relay
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Ciência da Computação.Um projeto de rede corporativa Frame Relay para serviços de transporte compartilhado de voz em tempo real e dados requer do projetista o ajuste de parâmetros da rede para o melhor desempenho dos serviços. O projetista deve conhecer a arquitetura da rede e o seu comportamento em condições críticas de tráfego, assim como os problemas referentes ao transporte de voz em tempo real em uma rede de comutação de pacotes e os mecanismos de QoS de que pode se beneficiar. Neste trabalho é concebido um modelo real de rede Frame Relay com suporte ao tráfego de voz em tempo real e pacotes IP. É aplicada então uma metodologia de avaliação de desempenho neste modelo, a fim de determinar o melhor ajuste dos parâmetros codec de voz e comprimento do fragmento das PDUs de tráfego IP que compartilham as facilidades de rede. Dois projetos experimentais são realizados, um para determinar o melhor ajuste destes fatores e a influência das características do codec no desempenho do serviço de voz e outro para determinar qual codec de baixa velocidade do ITU-T avaliado apresenta o melhor desempenho em uma situação de níveis elevados de latência de transmissão da rede. No primeiro projeto experimental são aplicados todos os mecanismos de QoS disponíveis do sistema. No segundo é desabilitado o mecanismo de fragmentação para criar condições desfavoráveis de latência da rede. Em ambos é estabelecida uma carga de tráfego limite para o sistema (congestionamento severo dos circuitos de acesso), a fim de avaliar a eficiência dos mecanismos de QoS do Frame Relay no desempenho do serviço de voz
The Lightweight Design of a Dump Truck Frame based on Dynamic Responses
No full textThis paper develops a new scheme for the
lightweight design of heavy dump truck frames based on the
characteristics of dynamic responses. The dynamic response
is predicted using a finite element (FE) model which is
verified by an experimental mode analysis. The FE model is
then used to investigate the characteristics of dynamic
responses and frame weight changes with respect to the
mass changes of each frame component for selecting
significant components. An optimization is finally developed
for the lightweight design under constrains that maintain
required dynamic responses and static strength. The
optimization results show that the weight of frame can be
reduced by 8%, showing that the scheme is an effective way
to achieve automotive lightweight design
Hysteretic Characteristics of Wood-Frame Structures Under Seismic Motions
No full textIn order to develop seismic codes that can effectively mitigate damage to wood-frame construction under seismic activity, the dynamic characteristics of wood-frame buildings must be well understood. Funding of full-scale structure experimental tests can be costly and may not be a true replica of real life scenarios. Therefore, data interpretation projects focusing on dynamic behavior of low-rise wooden shearwall buildings under large seismic motions have become increasingly important. Procedures include determining the modal parameters and extracting hysteretic characteristics from the available records. The results help extend the understanding of wood-frame structures and update building codes. Furthermore, the amount of information extracted can help evaluate the effectiveness of the current instrumentation program.
This work focuses on the seismic records from wood-frame structures during the 2004 Parkfield Earthquake. Studies involve verifying the amplitude dependence of modal parameters and retrieving pinching hysteresis curves that are common in wood-frame structures. Modal parameters are identified with a robust routine called MODE-ID. Equivalent viscous damping estimates in wood-frame buildings can range from 5% - 10% in largely linear behavior and 10% - 20% in significant nonlinear behavior. The discrepancies of damping estimates reported in the past are a result of inappropriate comparisons without understanding 1) the degree of nonlinear response and 2) the system identification methods used for the studies. By studying the hysteretic curves, insights can be obtained to reveal and to resolve the damping estimate discrepancies. Since displacement time histories of structures are not typically measured, the hysteretic curves are extracted from acceleration time histories. The proposed process accounts for inherent double integration errors and phase delay through filtering. It is still being debated that if the double integration can provide meaningful structural relative displacement time histories. In a laboratory setting with unilateral ground motion, the extraction process provides accurate hysteretic curves. However, this dissertation demonstrates that if the building experiences bi-directional ground motions, the nonlinear behavior of the diaphragm tampers with this process.
The results from modal identification and hysteresis curves serve as a basis for creating numerical models. Direct and gradient search methods were used for model updating. Bayesian updating and model selection provided the best results for dealing with hysteretic structural models. This probabilistic framework demonstrates potential benefits in a seamless integration with a seismic database. The selected hysteretic model showed great resemblance to the measured responses and had evidence of pinching hysteresis. Insights on the structure’s deformations and dissipation of energy can be inferred from the model.</p
GRACE validation and combination in the frame of COST-G
No full textTime-series of monthly gravity fields derived from GRACE observations (2002-2017) and continued by GRACE-FO (science phase starting in January 2019) are a major source for studies on large scale mass transport in the system Earth and for quantification of the effects of climate change. But up to date there is not one correct, agreed upon way of processing the satellite gravimetric observables, but a number of approaches that result in an equal number of time-series. We present a comparison, validation and combination of the latest of these time-series, based on the recent RL03 of the GRACE-L1B observation data. A focus will be laid on the effect of different background modeling strategies on the resulting gravity field models. The validation and combination are performed in the frame of the Combination Service for Time-variable Gravity models (COST-G), a new product center of the International Association of Geodesy (IAG)
Evolution of the G+C content frontier in the rat cytomegalovirus genome
No full textWithin the 230138 bp of the rat cytomegalovirus (RCMV) genome, the G+C content changes abruptly at position 142644, constituting a G+C content frontier. To the left of this point, overall G+C content is 69.2%, and to the right it is only 47.6%. A region of extremely low G+C content (33.8%) is found in the 5 kb immediately to the right of the frontier, in which there are no predicted coding sequences. To the right of position 147501, the G+C content rises and predicted coding sequences reappear. However, these genes are much shorter (average 848bp, 50% G+C) than those in the left two-thirds of the genome (average 1462bp, 70% G+C). Whole genome alignment of several viruses indicates that the initial ultra-low G+C region appeared in the common ancestor of the genera Cytomegalovirus and Muromegalovirus, and that the lowering of G+C in the right third has been a subsequent process in the lineage leading to RCMV. The left two-thirds of RCMV has stop codon occurrences at 67.5% of their expected level, based on a modified Markov chain model of stop codon distribution, and the corresponding figure for the right third is 78%. Therefore, despite heavy mutation pressure, selective constraint has operated in the right third of the RCMV genome to maintain a degree of gene length unusual for such low G+C sequences
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