Home About us Contact
|
Home About us Contact | ||
|
|
||
Time Estimation (time + estimation)
Selected AbstractsWTCP: an efficient mechanism for improving wireless access to TCP servicesINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 1 2003Karunaharan Ratnam Abstract The transmission control protocol (TCP) has been mainly designed assuming a relatively reliable wireline network. It is known to perform poorly in the presence of wireless links because of its basic assumption that any loss of a data segment is due to congestion and consequently it invokes congestion control measures. However, on wireless access links, a large number of segment losses will occur more often because of wireless link errors or host mobility. For this reason, many proposals have recently appeared to improve TCP performance in such environment. They usually rely on the wireless access points (base stations) to locally retransmit the data in order to hide wireless losses from TCP. In this paper, we present Wireless-TCP (WTCP), a new mechanism for improving wireless access to TCP services. We use extensive simulations to evaluate TCP performance in the presence of congestion and wireless losses when the base station employs WTCP, and the well-known Snoop proposal (A comparison of mechanisms for improving TCP performance in wireless networks. In ACM SIGCOMM Symposium on Communication, Architectures and Protocols, August 1996). Our results show that WTCP significantly improves the throughput of TCP connections due to its unique feature of hiding the time spent by the base station to locally recover from wireless link errors so that TCPs round trip time estimation at the source is not affected. This proved to be critical since otherwise the ability of the source to effectively detect congestion in the fixed wireline network is hindered. Copyright © 2003 John Wiley & Sons, Ltd. [source] Working at the interface of phylogenetics and population genetics: a biogeographical analysis of Triaenops spp. (Chiroptera: Hipposideridae)MOLECULAR ECOLOGY, Issue 4 2007A. L. RUSSELL Abstract New applications of genetic data to questions of historical biogeography have revolutionized our understanding of how organisms have come to occupy their present distributions. Phylogenetic methods in combination with divergence time estimation can reveal biogeographical centres of origin, differentiate between hypotheses of vicariance and dispersal, and reveal the directionality of dispersal events. Despite their power, however, phylogenetic methods can sometimes yield patterns that are compatible with multiple, equally well-supported biogeographical hypotheses. In such cases, additional approaches must be integrated to differentiate among conflicting dispersal hypotheses. Here, we use a synthetic approach that draws upon the analytical strengths of coalescent and population genetic methods to augment phylogenetic analyses in order to assess the biogeographical history of Madagascar's Triaenops bats (Chiroptera: Hipposideridae). Phylogenetic analyses of mitochondrial DNA sequence data for Malagasy and east African Triaenops reveal a pattern that equally supports two competing hypotheses. While the phylogeny cannot determine whether Africa or Madagascar was the centre of origin for the species investigated, it serves as the essential backbone for the application of coalescent and population genetic methods. From the application of these methods, we conclude that a hypothesis of two independent but unidirectional dispersal events from Africa to Madagascar is best supported by the data. [source] ERD as an index of anticipatory attention?PSYCHOPHYSIOLOGY, Issue 1 2002Effects of stimulus degradation Previous research has suggested that the stimulus-preceding negativity (SPN) is largely independent of stimulus modality. In contrast, the scalp topography of the event-related desynchronization (ERD) related to the anticipation of stimuli providing knowledge of results (KR) is modality dependent. These findings, combined with functional SPN research, lead to the hypothesis that anticipatory ERD reflects anticipatory attention, whereas the SPN mainly depends on the affective-motivational properties of the anticipated stimulus. To further investigate the prestimulus ERD, and compare this measure with the SPN, 12 participants performed a time-estimation task, and were informed about the quality of their time estimation by an auditory or a visual stimulus providing KR. The KR stimuli could be either intact or degraded. Auditory degraded KR stimuli were less effective than other KR stimuli in guiding subsequent behavior, and were preceded by a larger SPN. There were no effects of degradation on the SPN in the visual modality. Preceding auditory KR stimuli no ERD was present, whereas preceding visual stimuli an occipital ERD was found. However, contrary to expectation, the latter was larger preceding intact than preceding degraded stimuli. It is concluded that the data largely agree with an interpretation of the pre-KR SPN as a reflection of the anticipation of the affective-motivational value of KR stimuli, and of the prestimulus ERD as a perceptual anticipatory attention process. [source] The effects of ongoing activity on time estimation in prospective rememberingAPPLIED COGNITIVE PSYCHOLOGY, Issue 6 2010Miranda Occhionero Two experiments examined whether time-based prospective memory performance is influenced by the continuous or discontinuous nature of an ongoing activity. The first experiment demonstrated that prospective memory performance was not influenced by the engagement in continuous or discontinuous ongoing activity. The second experiment demonstrated that a discontinuous ongoing activity negatively affected prospective memory performance when participants had to execute two time-based tasks for which the retention intervals partially overlapped. The results suggest that when individuals are engaged in multiple time-based tasks, a general timing disruption occurs, with a proactive interference effect resulting in costs that are detrimental to prospective timing. Copyright © 2009 John Wiley & Sons, Ltd. [source] Reconstructing the origins of praying mantises (Dictyoptera, Mantodea): the roles of Gondwanan vicariance and morphological convergenceCLADISTICS, Issue 5 2009Gavin J. Svenson A comprehensive taxonomic sampling of Mantodea (praying mantises), covering virtually all higher-level groups, was assembled to reconstruct the phylogeny of the order. Sequence data were generated from five mitochondrial and four nuclear loci (12S rRNA, 16S rRNA, 18S rRNA, 28S rRNA, Histone III, Cytochrome Oxidase I & II, NADH dehydrogenase subunit 4, and Wingless) for 329 mantis exemplars along with seven cockroach and eight termite species. Only seven of 14 families, 14 of 33 subfamilies, and seven of 14 tribes were recovered as monophyletic, indicating that phylogeny is largely incongruent with classification. Mapping biogeographical regions on the phylogeny demonstrated that our results adhere closer to biogeographical distributions than to classification. Specific patterns in distribution suggest that major morphological convergences have confounded taxonomists' ability to reconstruct natural groups. A major revision of higher-level relationships is in order through a comprehensive investigation of morphology and molecular data. We found that major mantis lineages diverged prior to and during the isolation of geographical regions and subsequent ecomorphic specializations within these regions may have led to convergences in morphology. Divergence time estimation places the origin of Mantodea at the beginning of the Jurassic with most modern mantises originating on Gondwana in the Cretaceous. The first major divergence among modern mantises occurred as a result of the north,south splitting of South America and Africa. Subsequent divergences resulted from the breakup of Gondwana. The position of the Indian subcontinent appears to be central to the diversification of Afrotropical and Indomalayan mantises while Antarctica may have served as the conduit for the mantis invasions into South America and Australasia. When India separated from Antarctica and drifted north it distributed mantis lineages back into the Afrotropics and carried a diverse taxonomic assemblage to Asia. [source] Effect of positive and negative emotion on stimulus-preceding negativity prior to feedback stimuliPSYCHOPHYSIOLOGY, Issue 6 2001Yasunori Kotani Stimulus-preceding negativity (SPN) was recorded to investigate the effect of positive and negative emotion on the SPN preceding feedback stimuli. In the time-estimation task in which an acoustic stimulus was presented 3 s after a voluntary movement, (1) the negative valence (aversive band noise and pure tone) and (2) the positive valence (reward and no-reward) of feedback stimuli were manipulated. During noise conditions, participants received the band noise as a feedback stimulus except when their time estimations were accurate. They received a monetary reward for accurate time estimations under the reward conditions. The prefeedback SPN was larger under reward than no-reward conditions. In addition, the prefeedback SPN in the noise condition was larger compared with the pure tone condition. Our results appear to suggest that emotional anticipation is important in eliciting the prefeedback SPN. [source] | |||||||||||||