Academic literature on the topic 'Short term flicker'

This study considers a brain-machine interface (BMI) system based on the steady state visually evoked potential (SSVEP) for controlling quadcopters using electroencephalography (EEG) signals. An EEG channel with a single dry electrode, i.e., without conductive gel or paste, was utilized to minimize the load on users. Convolutional neural network (CNN) and long short-term memory (LSTM) models, both of which have received significant research attention, were used to classify the EEG data obtained for flickers from multi-flicker screens at five different frequencies, with each flicker corresponding to a drone movement, viz., takeoff, forward and sideways movements, and landing. The subjects of the experiment were seven healthy men. Results indicate a high accuracy of 97% with the LSTM model for a 2 s segment used as the unit of processing. High accuracy of 93% for 0.5 s segment as a unit of processing can remain in the LSTM classification, consequently decreasing the delay of the system that may be required for safety reasons in real-time applications. A system demonstration was undertaken with 2 out of 7 subjects controlling the quadcopter and monitoring movements such as takeoff, forward motion, and landing, which showed a success rate of 90% on average.

The time series describing the solar activity variations in the diverse solar layers are analyzed in terms of the developed method of the flicker-noise diagnostic which allows one to extract the dynamic characteristics of the process under study. The revealed results allow us to conclude that in all studied solar processes short term variations of the observational variables (with typical time less than ~3 years) reflect the behavior of some global dynamics. The dynamic characteristics turned out to be similar for the processes which are observed at the level of the solar photosphere and gradually changes in the solar atmosphere. That is why all Sun layers can be considered as a single dynamic system. We find that the short term variations of the solar neutrino capture rate are not random but are caused by some dynamic process. The analysis of solar total irradiance time series in terms of the applied method allows us to suggest that the mentioned dynamic processes exists in the solar core.

Voltage quality data has been collected in a single house nanogrid during 48 weeks of islanded operation and 54 weeks of grid-connected operation. The voltage quality data contains the voltage total harmonic distortion (THD), odd harmonics 3 to 11 and 15, even harmonics 4 to 8, voltage unbalance, short-term flicker severity (Pst) and long-term flicker severity (Plt) values, and voltage variations at timescales below 10 min. A comparison between islanded and grid-connected operation values was made, were some of the parameters were compared to relevant grid standard limits. It is shown that some parameters exceed the defined limits in the grid-standards during islanded operation. It was also found that the islanded operation has two modes of operation, one in which higher values of the short circuit impedance, individual harmonic impedance, harmonic voltage distortion and voltage unbalance were reached.

AbstractThe potential effects of zolpidem, a non-benzodiazepine hypnotic, on cognitive and psychomotor functions have been explored in more than 30 placebo controlled studies, and in many cases in comparison with benzodiazepine reference hypnotics (ie flunitrazepam, nitrazepam, triazolam). Daytime impact of drug administration on alertness has been studied with the Multiple Sleep Latency Test, and no significant clinical impairment has been found after zolpidem 5 to 10 mg, unlike benzodiazepines. Evaluation of the effects of zolpidem on attention and psychomotor skills (critical flicker fusion threshold, substitution or copying tests, choice reaction times or driving tests, etc) indicate that zolpidem at recommended doses (5 mg in elderly and 10 mg in adults) is unlikely to produce significant detrimental residual effects on daytime vigilance, concentration and coordination performances on the morning after intake. In accordance with its pharmacokinetic and pharmacodynamic properties, the effects on zolpidem on memory functions were limited to the first hours after administration and no significant difference was observed between zolpidem (5–10 mg) and placebo 6 hours after administration; longer memory impairment was observed with flunitrazepam or triazolam. Various groups of subjects were included in these studies, both young adults and elderly subjects, healthy volunteers and insomniac patients, and duration of treatment varied between one single dose and 28 days of repeated intake. In conclusion, experimental evidence demonstrates a satisfactory safety profile of zolpidem (5–10 mg) on daytime cognitive functions as compared to other hypnotics.

Orientador: Vital Paulino Costa
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciencias Medicas
Made available in DSpace on 2018-08-06T07:32:57Z (GMT). No. of bitstreams: 1 Bernardi_Luciana_M.pdf: 10999549 bytes, checksum: d383c5723aeda31781676f1567189a65 (MD5) Previous issue date: 2006
Resumo: O objetivo deste estudo foi determinar os valores médios da freqüência crítica de fusão (FCF), a flutuação a curto prazo e a variabilidade inter e intra-individual, analisar a influência da idade e sexo e investigar a ocorrência de efeito aprendizado em indivíduos normais submetidos à perimetria ¿flicker¿. A investigação foi dividida em dois estudos. No estudo 1, 95 indivíduos normais foram submetidos à perimetria ¿flicker¿ com o perímetro Octopus 301 (programa G1, estratégia dinâmica) em um olho. Determinaram-se os seguintes valores da FCF: média global, média dos pontos centrais, média dos pontos periféricos, média foveal e média dos quadrantes. Os valores médios foram comparados entre ambos os sexos e a influência da idade foi avaliada utilizando análise de regressão linear. No estudo 2, 20 indivíduos normais foram submetidos à perimetria ¿flicker¿ cinco vezes. Os três primeiros exames foram realizados em dias diferentes, separados por intervalos que variaram de um a 30 dias, enquanto os três últimos exames foram realizados no mesmo dia com intervalos de pelo menos 15 minutos. Os valores obtidos nos três primeiros exames foram utilizados para investigar o efeito aprendizado. A flutuação a curto prazo foi definida como a média das diferenças obtidas entre o valor da FCF mais alto e o mais baixo para cada ponto testado considerando-se os três últimos exames. Também determinou-se a variabilidade média dos valores de FCF inter e intra-individual. No estudo 1, os valores médios de FCF global, foveal, central e periférica foram, respectivamente, 38,2±4,3Hz, 36,4±3,5Hz, 38,7±3,7Hz e 37,9±5,0Hz. O valor médio de FCF periférica foi significativamente menor do que o valor médio de FCF central (p=0,007). A análise de regressão linear demonstrou que os valores médios FCF global, foveal, central, periférico e por quadrante diminuíram significativamente com a idade, porém com baixo coeficiente de determinação (R2 variando entre 0,074 e 0,163). Não houve diferença estatisticamente significante nos valores médios de FCF entre os indivíduos do sexo masculino e feminino (p>0,05) com exceção da área central e do quadrante nasal inferior, onde os valores foram significativamente menores no sexo feminino (p=0,029 e p=0,008 respectivamente). No estudo 2, a comparação entre os três primeiros exames não mostrou diferença estatisticamente significante em relação à duração do teste, porcentagem de respostas falso-positivas e falso-negativas (p>0,05). Os valores médios de FCF global (p=0,010), central (p=0,13) e periférico (p=0,033) foram significativamente menores no 1º exame em relação ao 2º exame . A média global da flutuação a curto prazo foi 5,06±1,13Hz, a li variabilidade média inter-individual foi 11,2±2,3% e a variabilidade média intra-individual foi 6,4±1,5%. Este estudo sugere que os valores da FCF diminuem com a idade e não são influenciados significativamente pelo sexo. Também sugere que a perimetria ¿flicker¿ está associada a efeito aprendizado e que flutuação a curto prazo e variabilidade inter e intra-individual moderadas são esperadas em indivíduos normais submetidos a este teste
Abstract: The aim of this study was to determine the mean critical fusion frequency (CFF), the short term fluctuation and inter and intraindividual variability, to analyze the influence of age and gender, and to investigate the occurrence of a learning effect in healthy subjects undergoing flicker perimetry. The investigation was divided in two study. In study 1, 95 normal subjects underwent flicker perimetry (Octopus 301, G1 program, dynamic strategy) in one eye. Mean global, central, peripheral, and foveal CFF values were determined, as well as mean CFFs per quadrant. Mean CFF values were compared between the two genders, and the influence of age was evaluated using linear regression analysis. In study 2, 20 normal subjects underwent flicker perimetry 5 times. The first 3 sessions were separated by an interval of 1 to 30 days, whereas the last 3 sessions were performed within the same day, with 15-minute intervals. The analysis of the first 3 sessions was used to investigate the presence of a learning effect. The mean of the differences between the highest and the lowest CFF value for each tested point during the last 3 tests were used to calculate the short term fluctuation (SF). Mean interindividual and intraindividual variabilities were determined. In study 1, mean global, foveal, central, and peripheral CFFs were 38.2±4.3Hz, 36.4±3.5Hz, 38.7±3.7Hz, and 37.9±5.0Hz, respectively. The mean peripheral CFF was significantly lower than the mean central CFF (p=0.007). Linear regression analysis demonstrated that mean global, foveal, central, and CFF per quadrant significantly decreased with age, however with a low correlation coefficient (R2 ranging between 0.074 and 0.163). There were no statistically significant differences in mean CFF values between males and females (p> 0.05), with the exception of the central area and the inferonasal quadrant, where the values were significantly lower in females (p=0.029 and p=0.008, respectively). In study 2, there were no statistically significant differences among the first three sessions regarding test duration, rates of false positive and false negative responses (p>0.05). The mean global (p=0.010), central (p=0.013), and peripheral (p=0.033) CFFs were significantly lower in first session compared to the second session. The mean global SF was 5.06+1.13Hz, the mean interindividual variability was 11.2±2.8%, and the mean intraindividual variability was 6.4+1.5%. This study suggests that CFFs decrease with age, and that CFFs are not significantly influenced by gender. It also suggests that flicker perimetry is associated with a learning effect, and that moderately high short term fluctuation and inter and intraindividual variability were expected in normal subjects undergoing such test
Mestrado
Oftalmologia
Mestre em Ciências Médicas

New EU regulations are currently taking effect, which means there will be stricter requirements on lighting units and more necessity for labs to perform photometric quality control. In the project a flickermeter setup was constructed at the Swedish Energy Agency's lab for performing quality assurance of luminaries by measuring the relevant metrics PST, SVM, and ITHD. By accomplishing this in accordance with the relevant IEC Standards, it creates an example setup which can be reproduced in other labs without the need for expensive nontransparent commercial devices. The project also examines the viability of creating such a setup from scratch without prior expertise, using the IEC Standards as a guide. To ensure the reliability of our setup multiple verifications were performed in accordance with the IEC Standards. Most gave positive results, but some issues were also discovered, mainly in regards to the optical filter needed for the setup. A suitable replacement for the missing optical filter was introduced, with which good results were acquired for both SVM and PST when compared to commercial flickermeters. Good results were also acquired in regards to the effects of dimming and the ITHD measured. Aside from the results, some issues regarding the procedures used for quantifying flicker were raised and discussed, along with discussing inconsistencies and discrepancies in the standards used.

New EU regulations are currently taking effect, which means there will be stricter requirements on lighting units and more necessity for labs to perform photometric quality control. In the project a flickermeter setup was constructed at the Swedish Energy Agency's lab for performing quality assurance of luminaries by measuring the relevant metrics PST, SVM, and ITHD. By accomplishing this in accordance with the relevant IEC Standards, it creates an example setup which can be reproduced in other labs without the need for expensive nontransparent commercial devices. The project also examines the viability of creating such a setup from scratch without prior expertise, using the IEC Standards as a guide. To ensure the reliability of our setup multiple verifications were performed in accordance with the IEC Standards. Most gave positive results, but some issues were also discovered, mainly in regards to the optical filter needed for the setup. A suitable replacement for the missing optical filter was introduced, with which good results were acquired for both SVM and PST when compared to commercial flickermeters. Good results were also acquired in regards to the effects of dimming and the ITHD measured. Aside from the results, some issues regarding the procedures used for quantifying flicker were raised and discussed, along with discussing inconsistencies and discrepancies in the standards used.

This Diploma thesis deals with assessment of the influence of two fundamental types of resistance welders operation on chosen power quality parameters at the point of common coupling (PCC) of the power network. The assessed parameters of power quality are the total harmonic distortion of the supply voltage, asymmetry of the supply voltage and the level of short term flicker at the point of common coupling. The assessment is based on the comparison of the results of computer simulations done in PSCad 4.2.0 with the requirements of technical standards. The outcome of this thesis is the determination of allowable limits for physical and operation parameters for the general arrangement of a power distribution network and a resistance welder that should guarantee the power quality compliance.