25 resultados para progressive mesh

em Aston University Research Archive


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A long-period grating (LPG) was written into a progressive three-layered single-mode fiber that was embedded into a flexible platform as a curvature sensor. The spectral location and profile of the LPGs were unaltered after implantation in the platform. The curvature sensitivity was 3.747 nm m with a resolution of ± 1.1 × 10-2 m-1. The bend sensor is intended to be part of a respiratory monitoring system and was tested on a resuscitation training manikin. © 2003 society of Photo-Optical Instrumentation Engineers.

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OBJECTIVE: To determine the laminar distribution of the pathological changes in the cerebral cortex in progressive supranuclear palsy (PSP). METHOD: The distribution of the abnormally enlarged neurons (EN), surviving neurons, neurofibrillary tangles (NFT), glial inclusions (GI), tufted astrocytes (TA), and neuritic plaques (NP) were studied across the cortex in tau immunolabeled sections of frontal and temporal cortex in 8 cases of PSP. RESULTS: The distribution of the NFT was highly variable with no consistent pattern of laminar distribution. The GI were distributed either in the lower laminae or uniformly across the cortex. Surviving neurons exhibited either a density peak in the upper laminae or a bimodal distribution was present with density peaks in the upper and lower laminae. The EN and glial cell nuclei were distributed primarily in the lower cortical laminae. There were positive correlations between the densities of the EN and glial cell nuclei and negative correlations between the surviving neurons and glial cells. No correlations were present between the densities of the NFT and GI. CONCLUSION: Cortical pathology in PSP predominantly affects the lower laminae but may spread to affect the upper laminae in some cases. The NFT and GI may have different laminar distributions and gliosis occurs concurrently with neuronal enlargement.

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Objective: To quantify the neuronal and glial cell pathology in the hippocampus and the parahippocampal gyrus (PHG) of 8 cases of progressive supranuclear palsy (PSP). Material: tau-immunolabeled sections of the temporal lobe of 8 diagnosed cases of PSP. Method: The densities of lesions were measured in the PHG, CA sectors of the hippocampus and the dentate gyrus (DG) and studied using spatial pattern analysis. Results: Neurofibrillary tangles (NFT) and abnormally enlarged neurons (EN) were most frequent in the PHG and in sector CA1 of the hippocampus, oligodendroglial inclusions (“coiled bodies”) (GI) in the PHG, subiculum, sectors CA1 and CA2, and neuritic plaques (NP) in sectors CA2 and CA4. The DG was the least affected region. Vacuolation and GI were observed in the alveus. No tufted astrocytes (TA) were observed. Pathological changes exhibited clustering, the lesions often exhibiting a regular distribution of the clusters parallel to the tissue boundary. There was a positive correlation between the degree of vacuolation in the alveus and the densities of NFT in CA1 and GI in CA1 and CA2. Conclusion: The pathology most significantly affected the output pathways of the hippocampus, lesions were topographically distributed, and hippocampal pathology may be one factor contributing to cognitive decline in PSP.

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In eight cases of progressive supranuclear palsy (PSP), neurofibrillary tangles (NFT) were numerous in the substantia nigra (SN), red nucleus (RN), locus caeruleus (LC), pontine nuclei (PN), and inferior olivary nucleus (ION) and abnormally enlarged neurons (EN) in the ION, LC and PN. Loss of Purkinje cells was evident in the cerebellum. Tufted astrocytes (TA) were abundant in the striatum, SN and RN and glial inclusions ('coiled bodies') (GI) in the midbrain (SN, RN) and pons (LC). Neuritic plaques were frequent in one case. NFT, GI, and TA densities were uncorrelated in most areas. NFT and EN densities were positively correlated in the midbrain and surviving neurons and disease duration in several areas. These results suggest: 1) predominantly subcortical pathology in PSP with widespread NFT while TA and GI have a more localized distribution, 2) little correlation between neuronal and glial pathologies, and 3) shorter duration cases may be more likely to develop cortical pathology. © 2007 Springer-Verlag.

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Objective: To study the topography of neurofibrillary tangles (NFT) in cortical and subcortical areas in progressive supranuclear palsy (PSP). Methods: Pattern analysis was carried out on tau-positive NFT in eight PSP cases. Results: Of the areas studied, NFT were randomly distributed in 68%, regularly distributed in 3%, and clustered in 29%. A regular distribution of clusters was more frequent in cortical than subcortical areas. Conclusion: NFT topography in subcortical areas was similar to inclusions in the synucleinopathy multiple system atrophy (MSA) but in cortical areas was comparable to other tauopathies. © 2006 Elsevier Ltd. All rights reserved.

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Purpose: The purpose of this paper is to investigate the use of 802.11e MAC to resolve the transmission control protocol (TCP) unfairness. Design/methodology/approach: The paper shows how a TCP sender may adapt its transmission rate using the number of hops and the standard deviation of recently measured round-trip times to address the TCP unfairness. Findings: Simulation results show that the proposed techniques provide even throughput by providing TCP fairness as the number of hops increases over a wireless mesh network (WMN). Research limitations/implications: Future work will examine the performance of TCP over routing protocols, which use different routing metrics. Other future work is scalability over WMNs. Since scalability is a problem with communication in multi-hop, carrier sense multiple access (CSMA) will be compared with time division multiple access (TDMA) and a hybrid of TDMA and code division multiple access (CDMA) will be designed that works with TCP and other traffic. Finally, to further improve network performance and also increase network capacity of TCP for WMNs, the usage of multiple channels instead of only a single fixed channel will be exploited. Practical implications: By allowing the tuning of the 802.11e MAC parameters that have previously been constant in 802.11 MAC, the paper proposes the usage of 802.11e MAC on a per class basis by collecting the TCP ACK into a single class and a novel congestion control method for TCP over a WMN. The key feature of the proposed TCP algorithm is the detection of congestion by measuring the fluctuation of RTT of the TCP ACK samples via the standard deviation, plus the combined the 802.11e AIFS and CWmin allowing the TCP ACK to be prioritised which allows the TCP ACKs will match the volume of the TCP data packets. While 802.11e MAC provides flexibility and flow/congestion control mechanism, the challenge is to take advantage of these features in 802.11e MAC. Originality/value: With 802.11 MAC not having flexibility and flow/congestion control mechanisms implemented with TCP, these contribute to TCP unfairness with competing flows. © Emerald Group Publishing Limited.

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Wireless Mesh Networks (WMNs) have emerged as a key technology for the next generation of wireless networking. Instead ofbeing another type of ad-hoc networking, WMNs diversify the capabilities of ad-hoc networks. There are many kinds of protocols that work over WMNs, such as IEEE 802.11a/b/g, 802.15 and 802.16. To bring about a high throughput under varying conditions, these protocols have to adapt their transmission rate. While transmission rate is a significant part, only a few algorithms such as Auto Rate Fallback (ARF) or Receiver Based Auto Rate (RBAR) have been published. In this paper we will show MAC, packet loss and physical layer conditions play important role for having good channel condition. Also we perform rate adaption along with multiple packet transmission for better throughput. By allowing for dynamically monitored, multiple packet transmission and adaptation to changes in channel quality by adjusting the packet transmission rates according to certain optimization criteria improvements in performance can be obtained. The proposed method is the detection of channel congestion by measuring the fluctuation of signal to the standard deviation of and the detection of packet loss before channel performance diminishes. We will show that the use of such techniques in WMN can significantly improve performance. The effectiveness of the proposed method is presented in an experimental wireless network testbed via packet-level simulation. Our simulation results show that regardless of the channel condition we were to improve the performance in the throughput.

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PURPOSE: To evaluate the relationship between ocular perfusion pressure and color Doppler measurements in patients with glaucoma. MATERIALS AND METHODS: Twenty patients with primary open-angle glaucoma with visual field deterioration in spite of an intraocular pressure lowered below 21 mm Hg, 20 age-matched patients with glaucoma with stable visual fields, and 20 age-matched healthy controls were recruited. After a 20-minute rest in a supine position, intraocular pressure and color Doppler measurements parameters of the ophthalmic artery and the central retinal artery were obtained. Correlations between mean ocular perfusion pressure and color Doppler measurements parameters were determined. RESULTS: Patients with glaucoma showed a higher intraocular pressure (P <.0008) and a lower mean ocular perfusion pressure (P <.0045) compared with healthy subjects. Patients with deteriorating glaucoma showed a lower mean blood pressure (P =.033) and a lower end diastolic velocity in the central retinal artery (P =.0093) compared with normals. Mean ocular perfusion pressure correlated positively with end diastolic velocity in the ophthalmic artery (R = 0.66, P =.002) and central retinal artery (R = 0.74, P <.0001) and negatively with resistivity index in the ophthalmic artery (R = -0.70, P =.001) and central retinal artery (R = -0.62, P =.003) in patients with deteriorating glaucoma. Such correlations did not occur in patients with glaucoma with stable visual fields or in normal subjects. The correlations were statistically significantly different between the study groups (parallelism of regression lines in an analysis of covariance model) for end diastolic velocity (P =.001) and resistivity index (P =.0001) in the ophthalmic artery, as well as for end diastolic velocity (P =.0009) and resistivity index (P =. 001) in the central retinal artery. CONCLUSIONS: The present findings suggest that alterations in ocular blood flow regulation may contribute to the progression in glaucomatous damage.

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A long period fibre grating written in a progressive three-layered optical fibre is shown to exhibit an attenuation band that has a very low bending sensitivity (5.1×10 –2 nm m) compared to normal step-index fibre, and is also insensitive to changes in the refractive index of the surrounding medium. Applications to sensing and telecommunications are discussed.

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A long-period grating (LPG) was written into a progressive three-layered single-mode fiber that was embedded into a flexible platform as a curvature sensor. The spectral location and profile of the LPGs were unaltered after implantation in the platform. The curvature sensitivity was 3.747 nm m with a resolution of ±1.1×10–2 m–1. The bend sensor is intended to be part of a respiratory monitoring system and was tested on a resuscitation training manikin.

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Progressive supranuclear palsy (PSP) is a rare, degenerative disorder of the brain believed to affect between 1.39 and 6.6 individuals per 100,000 of the population. The disorder is likely to be more common than suggested by these data due to difficulties in diagnosis and especially in distinguishing PSP from other conditions with similar symptoms such as multiple system atrophy (MSA), corticobasal degeneration (CBD), and Parkinson’s disease (PD). PSP was first described in 1964 by Steele, Richardson and Olszewski and originally called Steele-Richardson-Olszewski syndrome. The disorder is the second commonest syndrome in which the patient exhibits ‘parkinsonism’, viz., a range of problems involving movement most typically manifest in PD itself but also seen in PSP, MSA and CBD. Although primarily a brain disorder, patients with PSP exhibit a range of visual clinical signs and symptoms that may be useful in differential diagnosis. Hence, the present article describes the general clinical and pathological features of PSP, its specific visual signs and symptoms, discusses the usefulness of these signs in differential diagnosis, and considers the various treatment options.

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Progressive supranuclear palsy is a rare, degenerative brain disorder and the second most common syndrome in which the patient exhibits 'parkinsonism', that is, a variety of symptoms involving problems with movement. General symptoms include difficulties with gait and balance; the patient walking clumsily and often falling backwards. The syndrome can be difficult to diagnose and visual signs and symptoms can help to separate it from closely related movement disorders such as Parkinson's disease, multiple system atrophy, dementia with Lewy bodies and corticobasal degeneration. A combination of the presence of vertical supranuclear gaze palsy, fixation instability, lid retraction, blepharospasm and apraxia of eyelid opening and closing may be useful visual signs in the identification of progressive supranuclear palsy. As primary eye-care practitioners, optometrists should be able to identify the visual problems of patients with this disorder and be expected to work with patients and their carers to manage their visual welfare.

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Progressive addition spectacle lenses (PALs) have now become the method of choice for many presbyopic individuals to alleviate the visual problems of middle-age. Such lenses are difficult to assess and characterise because of their lack of discrete geographical locators of their key features. A review of the literature (mostly patents) describing the different designs of these lenses indicates the range of approaches to solving the visual problem of presbyopia. However, very little is published about the comparative optical performance of these lenses. A method is described here based on interferometry for the assessment of PALs, with a comparison of measurements made on an automatic focimeter. The relative merits of these techniques are discussed. Although the measurements are comparable, it is considered that the interferometry method is more readily automated, and would be ultimately capable of producing a more rapid result.

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The extent to which the surface parameters of Progressive Addition Lenses (PALs) affect successful patient tolerance was investigated. Several optico-physical evaluation techniques were employed, including a newly constructed surface reflection device which was shown to be of value for assessing semi-finished PAL blanks. Detailed physical analysis was undertaken using a computer-controlled focimeter and from these data, iso-cylindrical and mean spherical plots were produced for each PAL studied. Base curve power was shown to have little impact upon the distribution of PAL astigmatism. A power increase in reading addition primarily caused a lengthening and narrowing of the lens progression channel. Empirical measurements also indicated a marginal steepening of the progression power gradient with an increase in reading addition power. A sample of the PAL wearing population were studied using patient records and questionnaire analysis (90% were returned). This subjective analysis revealed the reading portion to be the most troublesome lens zone and showed that patients with high astigmatism (> 2.00D) adapt more readily to PALs than those with spherical or low cylindrical (2.00D) corrections. The psychophysical features of PALs were then investigated. Both grafting visual acuity (VA) and contrast sensitivity (CS) were shown to be reduced with an increase in eccentricity from the central umbilical line. Two sample populations (N= 20) of successful and unsuccessful PAL wearers were assessed for differences in their visual performance and their adaptation to optically induced distortion. The possibility of dispensing errors being the cause of poor patient tolerance amongst the unsuccessful wearer group was investigated and discounted. The contrast sensitivity of the successful group was significantly greater than that of the unsuccessful group. No differences in adaptation to or detection of curvature distortion were evinced between these presbyopic groups.

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Wireless Mesh Networks (WMNs) have emerged as a key technology for the next generation of wireless networking. Instead of being another type of ad-hoc networking, WMNs diversify the capabilities of ad-hoc networks. Several protocols that work over WMNs include IEEE 802.11a/b/g, 802.15, 802.16 and LTE-Advanced. To bring about a high throughput under varying conditions, these protocols have to adapt their transmission rate. In this paper, we have proposed a scheme to improve channel conditions by performing rate adaptation along with multiple packet transmission using packet loss and physical layer condition. Dynamic monitoring, multiple packet transmission and adaptation to changes in channel quality by adjusting the packet transmission rates according to certain optimization criteria provided greater throughput. The key feature of the proposed method is the combination of the following two factors: 1) detection of intrinsic channel conditions by measuring the fluctuation of noise to signal ratio via the standard deviation, and 2) the detection of packet loss induced through congestion. We have shown that the use of such techniques in a WMN can significantly improve performance in terms of the packet sending rate. The effectiveness of the proposed method was demonstrated in a simulated wireless network testbed via packet-level simulation.