Streak Length Research Articles

Look, over there! A streaker! – Qualitative study examining streaking as a behaviour change technique for habit formation in recreational runners

ABSTRACT Background Running as a form of physical activity is beneficial to overall health and wellbeing. The aim of the study is to examine ‘run streaking’ (i.e. running on consecutive days, for a minimum period of time or distance, typically at least one mile) as a technique for habit formation and behaviour change. Methods Qualitative semi-structured interviews with 21 recreational adult runners (11 female and 10 male). Run streak length ranged from a minimum of 100 days to over 4500 days. Transcripts were analysed using a hybrid deductive–inductive thematic analysis. Results Run streaking was reported to lead to several benefits, health improvements and a sense of accomplishment, although many run streakers reported running through injuries and lack of recovery. Accounts of run streaking showed features of automaticity indicative of habitual behaviour. Other behavioural processes identified included motivation, identity, self-regulation and social support. Behavioural streaking showed the potential to influence change in behaviours other than running. Conclusion Accounts of run streaking demonstrate an interplay between automatic and deliberate processes in the maintenance of running behaviour. Behavioural streaking is a technique that could be used in other behaviour change contexts beyond running to support habit formation.

Investigation of streamwise streak characteristics over a compression ramp at Mach 4

Experiments of shock wave/boundary layer interactions over a nominally two-dimensional compression ramp are conducted in a Mach 4 Ludwieg tube tunnel. Measurements of Schlieren, Rayleigh scattering, and surface pressure are performed to present the relevant flow features. The effects of two parameters, namely the Reynolds number based on the length of the flat plate and the ramp angle, on the flow stabilities are focused on. Four ramp angles of 6°, 8°, 10°, and 12° are tested under a Reynolds number of 7.22 × 105, while two other Reynolds numbers (3.66 × 105 and 9.19 × 105) are investigated with a ramp angle of 10°. Streamwise streaks are observed downstream of the reattachment point. The spanwise wavelength of the streaks remains unchanged with different ramp angles, whereas it slightly decreases as the Reynolds number increases. Power spectral density results show that the flow is transitional in the streak region and becomes turbulent where streaks break down. When increasing the ramp angle or the Reynolds number, the streamwise length of streaks shrinks. Two different patterns are distinguished at the breakdown, resembling the two unstable modes observed in the breakdown of Görtler vortices. To clarify the underlying physics of the formation of streaks, global stability analysis and resolvent analysis are carried out. Two regions of maximum optimal gain are identified, which are associated with Mack's first mode and streaks. The former can serve as an initial seed of Görtler instability via nonlinear interaction, while the latter can be associated with transient growth due to the lift-up mechanism and Görtler instability.

Optic Disc Drusen in Pseudoxanthoma Elasticum Are Associated with the Extent of Bruch's Membrane Calcification.

Background/Objectives: To assess the frequency, extent, localization and potential progression of optic disc drusen (ODD) and the correlation with the angioid streak (AS) length and retinal atrophy in patients with pseudoxanthoma elasticum (PXE). Methods: This retrospective study included patient data from a dedicated PXE clinic at the Department of Ophthalmology, University of Bonn, Germany (observation period from February 2008 to July 2023). Two readers evaluated the presence, localization, and the extent of the ODD on fundus autofluorescence (FAF) imaging at baseline and the follow-up assessments. Additionally, we measured the length of the longest AS visible at baseline and follow-up and the area of atrophy at baseline, both on FAF. Results: A total of 150 eyes of 75 PXE patients (median age at baseline 51.8 years, IRQ 46.3; 57.5 years, 49 female) underwent retrospective analysis. At baseline, 23 of 75 patients exhibited ODD in a minimum of one eye, resulting in an ODD prevalence of 30.7% in our cohort of PXE patients. Among these, 14 patients showed monocular and 9 binocular ODD that were localized predominantly nasally (46.9%). During the observational period (mean 97.5 ± 44.7 months), only one patient developed de novo ODD in one eye and one other patient showed a progression in the size of the existing ODD. The group of patients with ODD had significantly longer ASs (median 7020 µm, IQR 4604; 9183, vs. AS length without ODD: median 4404 µm, IQR 3512; 5965, p < 0.001). No association with the size of the atrophy was found at baseline (p = 0.27). Conclusions: This study demonstrates a prevalence of ODD of 30.7%. ODD presence is associated with longer ASs (an indicator of the severity and extent of ocular Bruch's membrane calcification), suggesting that ODD formation is tightly related to ectopic calcification-possibly secondary to calcification of the lamina cribrosa. Prospective studies investigating the impact of ODD (in conjunction with intraocular pressure) on visual function in PXE warrant consideration.

Water Flow Visualization And Velocity Measurement Using Hydrogen Bubble Generation Technique In Low Speed Open Channel

Visualization of water flow around different bluff bodies at different Reynolds number ranging (1505 - 2492) was realized by designing and building a test rig which contains an open channel capable to ensure water velocity range (4-8cm/s) in this channel. Hydrogen bubbles generated from the ionized water using DC power supply are visualized by a light source and photographed by a digital camera. Flow pattern around a circular disk of (3.6cm) diameter and (3mm) thickness, a sphere of (3.8cm) diameter and a cylinder of (3.2cm) diameter and (10cm) length are studied qualitatively. Parameters of the vortex ring generated in the wake region of the disk and the separation angle of water stream lines from the surface of the sphere are plotted versus Reynolds number. Proper empirical formulas are investigated to describe the behavior of vortex ring parameters and separation angle versus Reynolds number. Vortex growth history in the wake region of the cylinder is identified by analyzing the photographs extracted from the digital camera used for photography purposes. Water velocity measurement in the upstream region and near the edge of the disk is conducted at different Reynolds number by measuring the length of Hydrogen bubble pulse streaks generated in the upstream region of the disk using electronic pulse generator circuit. Special electronic circuit is designed and fabricated to cut off the applied DC voltage. The calibration of the designed pulse generator is conducted using the proper oscilloscope device. The pictures extracted from the digital camera are used for analyzing the generated Hydrogen pulses.

AISLAMIENTO, CARACTERIZACIÓN Y PATOGENICIDAD DE HONGOS ASOCIADOS A LA ENFERMEDAD DE PETRI

&lt;p&gt;&lt;strong&gt;Background: &lt;/strong&gt;Peru has become the leading exporter of table grapes focusing its production in the Piura and Ica regions. However, most of the young vineyards (&amp;lt;5 years) in the Piura region have been showing symptoms of Petri's disease. &lt;strong&gt;Objective&lt;/strong&gt;: To isolate, identify and pathogenicity evaluation of fungi associated with Petri disease. &lt;strong&gt;Methodology:&lt;/strong&gt; Isolates were obtained from necrotic streaks in vascular bundles in plants with symptoms of the Petri disease. Identification was performed with the keys proposed by Mostert, by means of macro and microscopic observations. Pathogenicity tests were also performed by measuring the advancement of the length of the necrotic streak (LNE). &lt;strong&gt;Results:&lt;/strong&gt; By their cultural and microscopic characteristics, the following were identified: &lt;em&gt;Phaeoacremonium&lt;/em&gt; spp, &lt;em&gt;P. krajdenii&lt;/em&gt;, &lt;em&gt;P. inflatipes&lt;/em&gt;, &lt;em&gt;P. parasiticum&lt;/em&gt; and &lt;em&gt;Phaeomoniella chlamydospora&lt;/em&gt;. All the selected isolates were pathogenic in pathogenicity tests 75 days post inoculation (DPI), being the &lt;em&gt;Phaeoacremonium&lt;/em&gt; species the ones that presented higher LNE compared to &lt;em&gt;Pa. chlamydospora&lt;/em&gt;, which demonstrates their capacity for colonization of vascular bundles and wood degradation. &lt;strong&gt;Implications:&lt;/strong&gt; The pathogens Phaeoacremonium spp, &lt;em&gt;P. krajdenii&lt;/em&gt;, &lt;em&gt;P. inflatipes&lt;/em&gt;, &lt;em&gt;P. parasiticum&lt;/em&gt; and &lt;em&gt;Phaeomoniella chlamydospora&lt;/em&gt; are related to Petri's disease in the Piura-Peru region. &lt;strong&gt;Conclusion:&lt;/strong&gt; &lt;em&gt;Phaeoacremonium&lt;/em&gt; species showed higher pathogenicity than &lt;em&gt;Pa. chlamydospora&lt;/em&gt; 75 DPI. Also, &lt;em&gt;P. inflatipes&lt;/em&gt; was morphologically identified in the Piura region requiring molecular identification for corroboration.&lt;/p&gt;

Enhancement in Structural and Electroluminescence Properties of Green Light Emission for Semipolar (11–22) InGaN/GaN Based Grown on m-Plane Sapphire via Low Temperature Ammonia Treatment (LTAT)

Research on enhancement green light emitter is important to obtain a perfect red-green-blue (RGB) induced white light source. Unfortunately the present of mixed phase in deposition of InGaN/GaN limited the potential LED efficiency. Therefore, we introduce a new method called as Low Temperature Ammonia Treatment (LTAT) to eliminate the mixed phase and to enhance the structure properties of InGaN/GaN. Two samples have been prepared, with LTAT (LED A) and without LTAT (LED B). Both samples have been characterized using optical microscope (OM), Atomic Force Microscope (AFM), X-ray rocking curve (XRC) and Electroluminescence (EL). On the structural characterization, the OM results show the present 3D island on LED B sample while sample LED A only shows 2D surface. The RMS surface roughness from AFM are 10.3 ± 0.4 nm and 13.5 ± 10.7 nm for LED A and LED B respectively. XRC analysis proved the LED A with LTAT has a homogenous XRD curve while LED B without LTAT has a mixed phase. The BSFs streak length measured as 1.42 nm−1 and 1.61 nm−1 for LED A and LED B respectively shows low crystallographic defect in LED A compared to LED B. For the EL characteristic, LED A shows a single sharp peak near 538.2 nm wavelength, while LED B shows a broad multi-peak profile at 435.7 nm, 480.6 nm and 520.5 nm. The single sharp peak shows enhancement in green light emission when LTAT is applied during deposition. Successful enhancement is structural and electroluminescence properties shows the effectiveness of LTAT proposed in this work for perfect RGB.

Cashless gambling and the pain of paying: effects of monetary format on slot machine gambling

Advances in cashless technologies create a dilemma for gambling regulators. Research indicates that cash purchases entail a ‘pain of paying’ that is attenuated with more abstract forms of payment, yet limited research has directly tested the impact of mode of payment on gambling behavior. Across two experiments, community-recruited gamblers were randomized to use an authentic slot machine in the laboratory, under different conditions of monetary endowment. In Experiment 1 (n = 61), participants were endowed with funds to play the slot machine, in either a cash or voucher format. In Experiment 2 (n = 48), participants acquired the cash endowment as a windfall or from an earning task. In session-level analyses, bet size and bet volume did not vary as a function of monetary condition. In more sensitive trial-level analyses, no interactions involving the monetary manipulations were consistent across the two experiments. Data from both experiments indicated faster spin initiation latencies as a function of losing streak length, and slower spin initiation latencies and larger bet size as a function of the prior win magnitude. These trial-level analyses show systematic influences on gambling behavior in the laboratory environment, supporting the basic sensitivity of our design. Overall, our data provide weak evidence for the hypothesis that monetary factors influence gambling tendencies. Acknowledging the possibility of the null hypothesis, these data also highlight the methodological challenges with manipulating monetary value in gambling research, including the use of endowed funds, and controlling for sources of variability when using authentic slot machines.

Genotype-phenotype correlation in pseudoxanthoma elasticum

Background and aimsPseudoxanthoma elasticum (PXE) is caused by variants in the ABCC6 gene. It results in calcification in the skin, peripheral arteries and the eyes, but has considerable phenotypic variability. We investigated the association between the ABCC6 genotype and calcification and clinical phenotypes in these different organs. MethodsABCC6 sequencing was performed in 289 PXE patients. Genotypes were grouped as two truncating, mixed, or two non-truncating variants. Arterial calcification mass was quantified on whole body, low dose CT scans; and peripheral arterial disease was measured with the ankle brachial index after treadmill test. The presence of pseudoxanthoma in the skin was systematically scored. Ophthalmological phenotypes were the length of angioid streaks as a measure of Bruchs membrane calcification, the presence of choroidal neovascularizations, severity of macular atrophy and visual acuity. Regression models were built to test the age and sex adjusted genotype-phenotype association. Results158 patients (median age 51 years) had two truncating variants, 96 (median age 54 years) a mixed genotype, 18 (median age 47 years) had two non-truncating variants. The mixed genotype was associated with lower peripheral (β: 0.39, 95%CI:-0.62;-0.17) and total (β: 0.28, 95%CI:-0.47;-0.10) arterial calcification mass scores, and lower prevalence of choroidal neovascularizations (OR: 0.41 95%CI:0.20; 0.83) compared to two truncating variants. No association with pseudoxanthomas was found. ConclusionsPXE patients with a mixed genotype have less severe arterial and ophthalmological phenotypes than patients with two truncating variants in the ABCC6 gene. Research into environmental and genetic modifiers might provide further insights into the unexplained phenotypic variability.

Euclid: Identification of asteroid streaks in simulated images using StreakDet software

Context.The ESAEuclidspace telescope could observe up to 150 000 asteroids as a side product of its primary cosmological mission. Asteroids appear as trailed sources, that is streaks, in the images. Owing to the survey area of 15 000 square degrees and the number of sources, automated methods have to be used to find them.Euclidis equipped with a visible camera, VIS (VISual imager), and a near-infrared camera, NISP (Near-Infrared Spectrometer and Photometer), with three filters.Aims.We aim to develop a pipeline to detect fast-moving objects inEuclidimages, with both high completeness and high purity.Methods.We tested theStreakDetsoftware to find asteroids from simulatedEuclidimages. We optimized the parameters ofStreakDetto maximize completeness, and developed a post-processing algorithm to improve the purity of the sample of detected sources by removing false-positive detections.Results.StreakDetfinds 96.9% of the synthetic asteroid streaks with apparent magnitudes brighter than 23rd magnitude and streak lengths longer than 15 pixels (10 arcsec h−1), but this comes at the cost of finding a high number of false positives. The number of false positives can be radically reduced with multi-streak analysis, which utilizes all four dithers obtained byEuclid.Conclusions.StreakDetis a good tool for identifying asteroids inEuclidimages, but there is still room for improvement, in particular, for finding short (less than 13 pixels, corresponding to 8 arcsec h−1) and/or faint streaks (fainter than the apparent magnitude of 23).

Effects of sequential winning vs. losing on subsequent gambling behavior: analysis of empirical data from casino baccarat players

ABSTRACT Problem gambling is characterized by intense urges to repeatedly engage in gambling and is highly deleterious to individuals’ financial and social well-being. A fundamental issue in problem gambling is how repeated and risky betting behavior varies as a function of outcome history. We used empirical data on gamblers playing baccarat, one of the most popular casino games, to examine the effects of sequential winning versus losing on subsequent gambling behavior. Specifically, we analyzed data from 7,935,566 games played by 3,986 players at a land-based casino to examine changes in the betting amount and in the rate of betting on hands with different dividend rates according to prior consecutive wins or losses. The results revealed that the bet amount in baccarat gradually increased according to streak length, and this effect was more pronounced after sequential winning than after sequential losing. The proportions of multiple bets, including ‘longshots’ – hands with low winning percentages and high dividend rates – decreased after sequential losing but increased after sequential winning. The present study, as the first attempt to analyze a large dataset on baccarat betting, indicates that gamblers shift their gambling behavior to be more reckless after experiencing consecutive wins more than consecutive losses.

Could Modifying the Bagolini Glasses Improve the Reliability of Responses?

Aims:Bagolini striated lenses are a useful test of binocular vision, but the variations in the striations (frequency and thickness) can impact on the perceived image. Also, responses can be difficult to interpret in young children. Therefore, the aims of this project were to evaluate the impact of striation frequency and the addition of coloured filters on subjective responses.Methods:Three sets of striated lenses were made (small, medium and large striations), each produced in two forms (both lenses clear, or with a red and blue lens). Also, Bagolini glasses (Optiker Ryser) were used, with and without the addition of red and blue filters. Subjects were asked to report what they perceived, with subsequent questions regarding the number and length of lines.Results:Forty-two adult subjects were tested, with uniocular VA ranging from –0.18 to 1.10 logMAR (mean 0.08 ± 0.25). The number of lines seen when varying the line thickness did not vary between coloured and clear lenses (post-hoc analysis following ANOVA, p > 0.1 in all comparisons). Adding red/blue filters to the original Bagolini glasses did not alter the rates of subjects perceiving a cross (Chi-square, p = 0.8). However, the laser-cut lenses produced a significantly shorter light streak than the original lenses (One-way ANOVA, p < 0.001), but the colour of the filters made no difference to the length of streak perceived (Tukey’s Test, p = 0.20).Conclusions:The addition of coloured filters did not impact on the responses given to the original or laser-cut lenses, suggesting this modification may aid responses in children. However, further evaluation is required with finer striations and thinner lenses to improve the visibility of the lines.

Una de conejos. Análisis estadístico para la creación de juegos de azar para niños

La literatura estudia desde las primeras edades hasta las edades adultas las intuiciones que tiene una persona sobre el lanzamiento de monedas. Estos trabajos concluyen que cuando a los alumnos se les manda escribir una secuencia o analizar una secuencia dada que pudiera ser aleatoria, consideran que debe haber un número casi igual de caras y cruces. ¿Quién de nosotros no escribiría una secuencia de esta forma? Cuando tienen que manifestarse respecto a otras características como son las rachas, piensan que en longitudes de rachas cortas y por lo tanto en un número de rachas amplio. ¿Sabemos acaso cuáles son el valor mínimo y máximo o al menos más habitual del número de rachas y de las longitudes de rachas? Este trabajo profundiza en estas preguntas desde diferentes perspectivas.

Detection, Location Estimation, and CRLB of a Streaking Target in an FPA With a Poisson Model

This paper deals with measurement extraction, from an optical sensor's Focal Plane Array (FPA), of a streaking target. We use a model that assumes pixels are separated by dead zones and model the streaking target's point spread function (PSF) as a Gaussian PSF that moves during the optical sensor's integration time. We make an assumption that the target has a constant velocity over the sampling interval and parametrize its motion with a starting and ending position. The noise model for a single pixel has variance proportional to its area, consistent with a Poisson model of the number of nontarget originated photons. We develop a maximum likelihood (ML) method of estimating the target motion parameter vector based on the set of pixel measurements from the optical sensor. This paper then derives the Cramer–Rao lower bound (CRLB) on the estimation error of the target motion parameter. We then present a matched filter (MF) based definition of the signal-to-noise ratio (SNR) to use as a basis for comparison of Monte Carlo simulation based location estimates to the calculated CRLB. It is shown that the ML estimator for the starting and ending positions of a streak in the FPA is efficient for MFSNR $\geq 12$ dB. We then provide a test statistic for target detection and propose approximate distributions to set the detection threshold for specific detection ( $P_D$ ) and false alarm probabilities ( $P_{\text{FA}}$ ), which are then verified via simulations. This paper's major contributions are the proposal of an ML/MF method for measurement extraction of streaking targets, confirmation that this method achieves the best accuracy possible for realistic FPA sensors, i.e., it attains the CRLB, the introduction of a statistically supported definition of SNR for these measurements, and an evaluation of the target measurement detection performance. Furthermore, this paper shows that, given our MFSNR definition, the streak length and direction of motion in the FPA have a negligible effect on performance compared to the SNR where we show that with a 4-dB change, the detection performance increases dramatically.

Azimuthal organization of large-scale motions in a turbulent minimal pipe flow

Direct numerical simulation data for turbulent minimal pipe flows with Reτ = 927, 1990, and 2916 are examined to explore the azimuthal (or spanwise) organization of their large-scale structures. We chose a streamwise-minimal unit with a streamwise domain length of Lx+≈1000, which is the characteristic streamwise length of near-wall streaks. The spanwise scales of most of the energetic motions and their contributions to the total energy are comparable with those of the streamwise long-domain simulation. In the azimuthal energy spectra of the streamwise velocity fluctuations (u), the large-scale energy increases with Reτ and three outer peaks (λθ = 0.7–0.8, π/2 and π) become evident when Reτ = 2916. The presence of the outer peaks at λθ = 0.7–0.8 and π/2 is consistent with the results of the long-domain simulation. The peak at λθ = 0.7–0.8 is associated with large-scale motions and the other two peaks are associated with very-large-scale motions (VLSMs). The maximum spanwise wavelength increases linearly with the wall-normal distance from the wall. A kz−1 region is evident in the range 0.3R &amp;lt; λz (=rλθ) &amp;lt; R, which indicates the presence of self-similar motions. The conditional two-point correlation with a cut-off wavelength of λz = 0.9R shows that there is a strong correlation between the enhanced energy in the outer region and the wall-attached structures, which were extracted from the time evolution of the streamwise-averaged u field (u2D). The spanwise sizes (lz) of the attached u2D structures scale with their height (ly) in the log region and their time scales (lt) follow ltuτ/lz = 2, which is consistent with the bursting time scale. Their spanwise sizes lie in the range R &amp;lt; lz &amp;lt; 3R, for which lt increases significantly, which indicates that these structures are associated with VLSMs and make the dominant contributions to the enhanced energy in the outer region. These structures penetrate to the wall region as a manifestation of the footprint and modulate the small-scale energy. The negative-u2D structures induce congregative motions in the near-wall region.

Downscaling probability of long heatwaves based on seasonal mean daily maximum temperatures

Abstract. A methodology for estimating and downscaling the probability associated with the duration of heatwaves is presented and applied as a case study for Indian wheat crops. These probability estimates make use of empirical-statistical downscaling and statistical modelling of probability of occurrence and streak length statistics, and we present projections based on large multi-model ensembles of global climate models from the Coupled Model Intercomparison Project Phase 5 and three different emissions scenarios: Representative Concentration Pathways (RCPs) 2.6, 4.5, and 8.5. Our objective was to estimate the probabilities for heatwaves with more than 5 consecutive days with daily maximum temperature above 35 ∘C, which represent a condition that limits wheat yields. Such heatwaves are already quite frequent under current climate conditions, and downscaled estimates of the probability of occurrence in 2010 is in the range of 20 %–84 % depending on the location. For the year 2100, the high-emission scenario RCP8.5 suggests more frequent occurrences, with a probability in the range of 36 %–88 %. Our results also point to increased probabilities for a hot day to turn into a heatwave lasting more than 5 days, from roughly 8 %–20 % at present to 9 %–23 % in 2100 assuming future emissions according to the RCP8.5 scenario; however, these estimates were to a greater extent subject to systematic biases. We also demonstrate a downscaling methodology based on principal component analysis that can produce reasonable results even when the data are sparse with variable quality.

Surprised by the Hot Hand Fallacy? A Truth in the Law of Small Numbers

We prove that a subtle but substantial bias exists in a common measure of the conditional dependence of present outcomes on streaks of past outcomes in sequential data. The magnitude of this streak selection bias generally decreases as the sequence gets longer, but increases in streak length, and remains substantial for a range of sequence lengths often used in empirical work. We observe that the canonical study in the influential hot hand fallacy literature, along with replications, are vulnerable to the bias. Upon correcting for the bias we find that the long-standing conclusions of the canonical study are reversed.

A high precision scheme for micro‐channel processing in quartz glass using femtosecond laser

AbstractUltra‐short pulse laser with unique advantages in micromachining, especially on the hard brittle material becomes the focus of study on micro‐structure processing. Theoretical and experimental researches are taken from the ablation properties of micro‐channel in the quartz glass by femtosecond laser. As the ablation depth of quartz glass has not relationship obviously with defocusing distance within LAV effective range, a new way to control precisely the ablation depth of quartz glass is present in the study. With fixed laser power, the ablation depth could be known easily by the length of the ablation streak while moving the femtosecond laser focus along the straight line with a 45‐degree angle from the quartz glass surface within the LAV range. Research is carried out to study laser pulse power, scanning velocity and step distance to do something with micro‐channel ablation quality. According to the parameters of test, the micro‐channel with rectangle cross section of the quartz glass is processed, and then we analyze the ablation morphology and processing efficiency. The results provided a important suggestion to process micro‐structure precisely for quartz glass by femtosecond laser.

Evolution of Lagrangian coherent structures in a cylinder-wake disturbed flat plate boundary layer

Evolution of Lagrangian coherent structures (LCS) in a flat plate boundary layer transition induced by the wake of a circular cylinder is investigated. Both hydrogen bubble visualization and particle image velocimetry (PIV) techniques are used. It is found that downstream of the cylinder, the disturbance in the boundary layer experiences a fast growth followed by a slow decay in the transition. Lagrangian coherent structures are revealed by qualitative hydrogen bubble visualizations and quantitative finite-time Lyapunov exponents (FTLE) fields derived from the PIV data. The evolution of the LCS is considered from the very beginning of the transition up to when the boundary layer becomes fully developed turbulent flow. The mean convection velocity and average inclination angle of the LCS are first extracted from the FTLE fields. The streamwise length of the low-speed streaks seems to increase, while their spanwise distance decreases in the boundary layer transition. Proper orthogonal decomposition (POD) of the PIV data shows that low-speed streaks associated with the hairpin vortices and hairpin packets are the dominant coherent structures close to the wall in the transitional and turbulent boundary layer. The POD modes also reveal a variety of scales in the turbulent boundary layer. Moreover, it is found that large-scale coherent structures can modulate the amplitude of the small-scale ones.

Investigation into the design and diffraction efficiency of shifted dual transmission grating

In inertial confined fusion (ICF) experiments, the temporal evolution of X-ray spectrum can provide important diagnostic information such as electron temperature and density on laser-plasma interaction. Accurate diagnostic requires a wide range of X-ray spectrum from several hundred eV to kilo eV to be measured with high temporal resolution. For traditional single grating spectrometer coupled with streak cameras, the limited recording length of streak cameras severely restricts measured X-ray spectral range in one laser shot. Here we design a shifted dual transmission grating (SDTG) spectrometer for laser-produced plasma X-ray diagnostics in ICF experiments which can provide wide-range X-ray spectrum measurement from 100 eV to 5 keV with high temporal and spectral resolution. This SDTG spectrometer comprises two X-ray gratings: one with high line density and the other with low line density. The high line density grating is used to measure X-ray spectrum from 1000 eV to 5000 eV and the low line density grating measures X-ray spectrum from 100 eV to 1000 eV respectively. These two kinds of X-ray gratings are arranged in a plane with their centers shifted by a certain distance. A shifted double slit component is designed according to the spatial positions of the two gratings and set in front of the photocathode in the streak camera to ensure that two sets of X-ray spectra by two shifted gratings are projected on the photocathode without overlapping. This novel SDTG-based X-ray spectrometer can take the most of recording panel space, offering a path to realize a high resolution and broad spectral ranges in diagnosing soft X-rays. In this paper, the design method and the technical data of the SDTG-based X-ray spectrometer are given. The SDTG-based X-ray spectrometer is integrated, debugged and used to measure X-ray pulse at SG-III prototype facility located in Laser Fusion Research Center of Chinese Academy of Engineering Physics. The time integral results are captured by the SDTG spectrometer in the ICF fluid RT experiments and time-resolved spectra are recorded in indirect drive implosion experiment. Experimental results show the SDTG-based X-ray spectrometer can capture X-ray spectrum ranging from 0.1 keV to 5 keV, with a spectral resolution of 0.04 nm and a temporal resolution of better than 30 ps. By fully utilizing limited recording length, the SDTG-based X-ray spectrometer can realize a wide range temporal X-ray spectrum measurement with enough spectral resolution and temporal resolution. This SDTG spectrometer is a good temporal X-ray diagnostic tool for ICF experiments and other high energy density physics experiments.

Detection of bird nests in overhead catenary system images for high-speed rail

The high-speed rail system provides a fast, reliable and comfortable means to transport large number of travelers over long distances. The existence of bird nests in overhead catenary system (OCS) can hazard to the safety of the high-speed rails, which will potentially result in long time delays and expensive damages. A vision-based intelligent inspection system capable of automatic detection of bird nests built on overhead catenary would avoid the damages and increase the reliability and punctuality, and therefore is attractive for a high-speed railway system. However, OCS images exhibit great variations with lighting changes, illumination conditions and complex backgrounds, which pose great difficulty for automatic recognition. This paper addresses the problem of automatic recognition of bird nests for OCS images. Based on the unique properties of bird nests, we propose a novel framework, which is composed of five steps: adaptive binarization, trunk/branch detection, hovering point detection, streak extraction and pattern learning, for bird nest detection. Two histograms, Histogram of Orientation of Streaks (HOS) and Histogram of Length of Streaks (HLS), are novelly proposed to capture the distributions of orientations and lengths of detected twig streaks, respectively. They are modeled with Support Vector Machine to learn the patterns of bird nests. Experiments on different high-speed train lines demonstrate the effectiveness and efficiency of the proposed work.