Sequence Of Strokes Research Articles

Characteristics of a rocket‐triggered lightning flash with large stroke number and the associated leader propagation

AbstractA negative lightning flash with 16 leader‐return stroke sequences, triggered in the summer of 2013 using the classical rocket‐and‐wire triggering technique, was examined with simultaneous two‐dimensional (2D) imaging of very high‐frequency (VHF) radiation sources, channel‐base current measurement, broadband electric field waveforms and high‐speed video images. A total of 28.0 C negative charge was transferred to ground during the whole flash, and the charge transferred during the initial stage was 4.9 C, which is the weakest among the triggered lightning flashes at the SHandong Artificially Triggering Lightning Experiment (SHATLE). The peak current of 16 return strokes ranged from 5.8 to 32.5 kA with a geometric mean of 14.1 kA. The progression of upward positive leader and downward negative (dart or dart‐stepped) leaders was reproduced visually by using an improved short‐baseline VHF lightning location system with continuous data recording capability. The upward positive leader was mapped immediately from the tip of the metal wire during the initial stage, developing at a speed of about 104 m/s without branches. The upward positive leader and all the 14 negative leaders captured by the 2D imaging system propagated along the same channel with few branches inside the cloud, which might be the reason for the relatively small charge transfer. The 2D imaging results also show that dart leaders may transform into dart‐stepped leaders after a long time interval between successive strokes.

Lightning channel current persists between strokes

The usual cloud‐to‐ground lightning occurs when a large negative charge contained in a “stepped leader” travels down toward the Earth's surface. It then meets a positive charge that comes up tens of meters from the ground, resulting in a powerful neutralizing explosion that begins the first return stroke of the lightning flash. The entire flash lasts only a few hundred milliseconds, but during that time, multiple subsequent stroke–return stroke sequences usually occur.

MRI-guided selection of patients for treatment of acute ischemic stroke.

To summarize what is known about the use of MRI in acute stroke treatment (predominantly thrombolysis), to examine the assumptions and theories behind the interpretation of magnetic resonance images of acute ischemic stroke and how they are used to select patients for therapies, and to suggest directions for future research. Recent studies have been contradictory about the usefulness of MRI in selecting patients for treatment. New MRI models for selecting patients have emerged that focus not only on the ischemic penumbra but also on the infarct core. Fixed time-window selection parameters are being replaced by timing-based individualized MRI stroke features. New ways to interpret traditional MRI stroke sequences are emerging. Although the efficacy of acute stroke treatment is time dependent, the use of fixed time windows cannot account for individual differences in infarct evolution, which could potentially be detected with MRI. Although MRI shows promise for identifying patients who should be treated, as well as excluding patients who should not be treated, definitive evidence is still lacking. Future research should focus on validating the use of MRI to select patients for intravenous therapies in extended time windows.

Branched dart leaders preceding lightning return strokes

AbstractThis study describes the occurrence of branches in lightning dart leaders, based on data acquired in Florida using a high‐speed video camera and electric field change sensors. More than half (57%) of 72 flashes with analyzable dart leaders show at least one successful branched dart leader (BDL), and nine flashes have two successful BDLs. Overall, 18% of 282 visible successful dart leaders are branched. Most (42 of 50) cases of BDLs occur in the first dart leader after a stepped leader/return stroke sequence, and the data indicate that 55% of first dart leaders are visibly branched. Compared to first dart leaders in the 31 flashes without any branched dart leaders, BDLs tend to follow stepped leader/return strokes with significantly larger average peak currents (−31.3 versus −20.6 kA) and shorter average interstroke intervals (71.94 versus 94.64 ms). Average peak current of BDL strokes is 62% larger (−17.8 versus −11 kA) than that for unbranched first dart leader strokes. Branched dart leaders generally travel in the some of the most recently used lightning channels, but they are not always within the main channel of the prior return stroke. Successful BDLs may dart all the way to ground when in a prior stroke channel, or they may become stepped leaders when they reach the lower end of the prior stroke branch. Electric field change data for all the BDL cases exhibit an erratic pulse character for at least part of the leader duration; in some cases, the erratic character ends when the branches vanish.

Performance characteristics of the NLDN for return strokes and pulses superimposed on steady currents, based on rocket‐triggered lightning data acquired in Florida in 2004–2012

AbstractWe present a detailed evaluation of performance characteristics of the U.S. National Lightning Detection Network (NLDN) using, as ground truth, Florida rocket‐triggered lightning data acquired in 2004–2012. The overall data set includes 78 flashes containing both the initial stage and leader/return‐stroke sequences and 2 flashes composed of the initial stage only. In these 80 flashes, there are a total of 326 return strokes (directly measured channel‐base currents are available for 290 of them) and 173 kiloampere‐scale (≥1 kA) superimposed pulses, including 58 initial continuous current pulses and 115 M components. All these events transported negative charge to the ground. The NLDN detected 245 return strokes and 9 superimposed pulses. The resultant NLDN flash detection efficiency is 94%, return‐stroke detection efficiency is 75%, and detection efficiency for superimposed pulses is 5% for peak currents ≥1 kA and 32% for peak currents ≥5 kA. For return strokes, the median location error is 334 m and the median value of absolute peak current estimation error is 14%. The percentage of misclassified events is 4%, all of them being return strokes. The median value of absolute event‐time mismatch (the difference in times at which the event is reported to occur by the NLDN and recorded at the lightning triggering facility) for return strokes is 2.8 µs. For two out of the nine superimposed pulses detected by the NLDN, we found optical evidence of a reilluminated branch (recoil leader) coming in contact with the existing grounded channel at an altitude of a few hundred meters above ground.

Rocket‐and‐wire triggered lightning in 2012 tropical storm Debby in the absence of natural lightning

AbstractLightning Mapping Array source locations, channel base currents, and electric field waveforms are presented for a lightning flash triggered in the rainbands of 2012 tropical storm Debby. The National Lightning Detection Network reported no natural cloud‐to‐ground discharges within 60 km of the North Florida triggering site for at least 20 h before and 8 h after the triggered flash. Additionally, local electric field mill and wideband antenna networks show no close cloud or cloud‐to‐ground flashes. The triggering rocket was launched with negative charge overhead producing an electric field at the ground of 5 kV m−1 and in coordination with X‐band, dual‐polarimetric radar observations of streamers of enhanced precipitation descending from the melting level as they approached the site. The Debby flash consisted of an initial stage (IS) followed by eleven leader/return stroke sequences. The flash exhibited all the processes of normal triggered and natural cloud‐to‐ground lightning: leader/return stroke sequences, continuing currents, K events, and M components. Additionally, the flash exhibited several exceptional characteristics: three return stroke peak currents greater than 25 kA, one very long, 352 ms, continuing current that transferred about 35 C of charge to ground, and a relatively short, 202 ms, IS containing no initial continuous current pulses. Following a near‐vertical upward positive leader attaining 2.8 km height, the IS branched and propagated horizontally at 3.5 km altitude. The flash, exhibiting strokes and continuing current, then ascended to and propagated horizontally at 5.5 km, extending about 25 km south and 15 km east. The 0°C level was near 4.5 km above sea level. It follows from the above that clouds that are not producing natural lightning can represent a triggered lightning hazard to launch vehicles and aircraft.

Sketched symbol recognition using Latent-Dynamic Conditional Random Fields and distance-based clustering

In this paper we propose a two-stage method for recognizing sketched symbols that combine the use of a discriminative model, for labeling symbol strokes and a distance-based clustering algorithm, for grouping the labels belonging to the same symbol. In the first stage, we employ Latent-Dynamic Conditional Random Field (LDCRF), a discriminative model able to analyze the features of unsegmented sequences of strokes by taking into account spatio-temporal information, and to classify the symbol parts by considering contextual information. In the second stage, the labels obtained from LDCRF are grouped into symbol labels by using a distance-based clustering algorithm which takes into account the geometric relationships among strokes. The effectiveness of our method has been evaluated on the domain of electric circuit diagrams achieving accuracy values varying between 81.3% and 91.0%.

Characteristics of M‐component in rocket‐triggered lightning and a discussion on its mechanism

The current and electric field pulses associated with M‐component following dart leader‐return stroke sequences in negative rocket‐triggered lightning flashes were analyzed in detail by using the data from Shandong Artificially Triggering Lightning Experiment, conducted from 2005 to 2010. For 63 M‐components with current waveforms superimposed on the relatively steady continuing current, the geometric mean values of the peak current, duration, and charge transfer were 276 A, 1.21 ms, and 101 mC, respectively. The behaviors of the channel base current versus close electric field changes and the observation facts by different authors were carefully examined for investigation on mechanism of the M‐component. A modified model based on Rakov's “two‐wave” theory is proposed and confirms that the evolution of M‐component through the lightning channel involves a downward wave transferring negative charge from the upper to the lower channel and an upward wave draining the charge transported by the downward wave. The upward wave serves to deplete the negative charge by the downward wave at its interface and makes the charge density of the channel beneath the interface layer to be roughly zero. Such modified concept is recognized to be reasonable by the simulated results showing a good agreement between the calculated and the measured E‐field waveforms.

Progressive apraxic agraphia with micrographia presenting as corticobasal syndrome showing extensive Pittsburgh compound B uptake

A 65-year-old woman developed progressive apraxic agraphia, characterized by poorly formed graphemes, a kanji (Japanese morphograms) recall impairment, relatively preserved oral spelling of kanji characters, and incorrect stroke sequences on writing accompanied by micrographia over a 3-year period. She also showed minor degrees of rigidity, limb-kinetic apraxia, and ideomotor apraxia of the left hand. Although asymmetric rigidity and limb-kinetic apraxia strongly suggested corticobasal degeneration, (11)C-Pittsburgh compound B positron emission tomography (PiB-PET) showed the predominantly right-sided accumulation of amyloid β in the cortices and striatum. (18)F-fluoro-deoxy-glucose PET and single photon emission computed tomography with a (99m)Tc-ethylcysteinate dimer (ECD-SPECT) also revealed predominantly right-sided hypometabolism and hypoperfusion in the primary sensorimotor cortex, posterior cingulate gyrus, temporoparietal cortices, frontal cortices, thalamus, and basal ganglia, a pattern characteristic of both corticobasal degeneration and Alzheimer's disease. The findings suggest that progressive apraxic agraphia with micrographia presenting as corticobasal syndrome can show an Alzheimer's disease pathology. It is also suggested that ideomotor apraxia of the left hand can occur without a callosal lesion, and is caused by hypometabolism or hypoperfusion in the right frontal and parietal cortices, as revealed by PET and SPECT.

Development of an Arabic Handwriting Learning Educational System

In today many students produce a wrong and illegible handwriting and teachers need a lot of time to check the handwriting errors. The traditional approach for handwriting teaching needs a long hours of handwriting practice. Unfortunately, this is not advantageous in many cases. In this paper, we develop an automated educational system for Arabic h andwriting learning and detection of errors such as: the stroke production errors, stroke sequence errors, stroke relationship errors and stroke interline errors. Then our system can check the handwriting mistakes andimmediately provide a feedback to the students to correct themselves. In this work, we used an attributed relational graph to locate the handwriting mistakes. The experimental results show that our proposed systemcan treat multiple cases of errors with satisfied accuracy.

Performance of Biopsy Needle With Therapeutic Injection System to Prevent Bleeding Complications

Renal disease is epidemic in the United States with approximately 8 × 106 people having chronic kidney disease. Renal biopsies are widely used to provide essential diagnostic information to physicians. However, the risk of bleeding complications possibly leading to life-threatening situations results in the contra-indication of biopsy in certain patient populations. Safer renal biopsies will allow more accurate diagnosis and better management of this epidemic health problem. We report the preclinical testing of a novel biopsy device called the therapeutic injection system (TIS). The device introduces a third stage to the standard two-stage side-cut percutaneous biopsy process. The third stage is designed to reduce bleeding complications by injecting a hemostatic plug at the time of biopsy. Laboratory evaluation and preliminary in vivo animal testing using an anticoagulated porcine model of the TIS and Bard Monopty® (Bard Medical, Covington, GA) control device were performed. The hemostatic material Gelfoam® (Pfizer, Brussels, Belgium) was selected as the active material comprising the hemostatic plugs. The performance of two composite plugs, one composed of polyvinyl alcohol (PVA) combined in 2:1 and 12:1 ratios with the hemostatic material, and one plug composed of 100[Formula: see text] hemostatic material were tested. Stroke sequence and hemostatic plug deployment were verified by sequential firing of the TIS biopsy needle into clear gelatin and ex vivo bovine kidney specimens. In vivo trials with porcine specimens revealed a significant reduction in blood loss (8.1 [Formula: see text] 3.9 ml, control versus 1.9 [Formula: see text] 1.6 ml, 12:1 PVA/hemostatic, TIS, [Formula: see text] = 0.01, [Formula: see text] = 6). The 100[Formula: see text] hemostatic plug showed a substantial and immediate reduction in blood loss (9.2 ml, control versus 0.0 ml, TIS, [Formula: see text] = 1). The prototype device was shown to work repeatedly and reliably in laboratory trials. Initial results show promise in this approach to control post biopsy bleeding. This solution maintains the simplicity and directness of the percutaneous approach, while not significantly changing the standard percutaneous biopsy procedure.

An intelligent e‐learning software for learning to write correct Chinese characters on mobile devices

PurposeLearning Chinese is unquestionably very important and popular worldwide with the fast economic growth of China. To most foreigners and also local students, one of the major challenges in learning Chinese is to write Chinese characters in correct stroke sequences that are considered as significant in the Chinese culture. However, due to the potentially complicated structures of Chinese characters together with their stroke sequences, there are very few character recognition techniques that can effectively tackle the involved training task in an efficient and flexible manner. The purpose of this paper is to propose an intelligent and flexible e‐learning software based on learning objects to facilitate the learning of writing Chinese characters in correct stroke sequences.Design/methodology/approachThe paper adopts an incremental approach in designing the overall system architecture to emphasize on extendibility of the system. The basic features of the system including the evolution and pronunciation of each Chinese character can be embedded as a part of the learning object metadata to enhance students' understanding of Chinese characters. To demonstrate the feasibility of this proposal, a prototype of the proposed e‐learning software was built on smartphones such that students can learn anytime and anywhere.FindingsFrom the empirical evaluation of the e‐learning prototype for learning to write correct Chinese characters on mobile devices, it was found that foreign students can learn and practise the writing more effectively anytime and anywhere on their mobile devices after classes. Some initial positive feedback was collected. Furthermore, a more careful and thorough evaluation is planned to be conducted in relevant courses for foreign students in the upcoming Fall semester.Originality/valueThis proposal represents the first attempt to reduce the complexity while increasing the extendibility of the e‐learning software to learn Chinese through learning objects running on smartphones or mobile devices in general. More importantly, it opens up numerous opportunities for further investigations including possible integrations with other existing Chinese e‐learning systems.

Application of Raman spectroscopy in forensic investigation of questioned documents involving stamp inks

Stamp pad inks from different manufacturers across India have been analyzed to investigate the feasibility of Raman scattering as a tool for forensic analysis of questioned documents involving stamp inks. Nine different stamping inks were analyzed by both Raman spectroscopic and HPTLC methods. The results demonstrate the effectiveness of these methods in classifying the investigated stamping inks based on their spectral pattern and HPTLC chromatogram. Raman scattering tool was able to determine the sequence of heterogeneous intersection strokes involving a blue stamp pad ink and other writing instruments, such as ballpoint pen ink (red and black), pencil and laser printer toner. However, this method was unable to resolve the exact sequencing for the intersection strokes involving investigated stamp ink and blue ballpoint ink or gel pen ink (all colors).

Guided self-management of transient information in animations through pacing and sequencing strategies

Learning with instructional animations may overstretch limited working memory resources due to intense processing demands associated with transient information. The authors investigated whether explicit instructional advice coupled with a task-specific learner control mechanism (such as a timeline scrollbar) could facilitate the successful self-management of transient information. The effectiveness of a timeline scrollbar that allowed self-pacing and self-sequencing of animations was compared with computer-controlled animations. Experiment 1 demonstrated that a timeline scrollbar (with instructional advice on its strategic use) enhanced the retention of stroke sequences in writing Chinese characters. In Experiment 2, a timeline scrollbar was used in an integrated set of narrated animations dealing with complex scientific information. Retention and comprehension post-tests indicated that although a scrollbar accompanied by instructional advice in its use assisted novice learners, no such effect was found with participants who possessed higher levels of prior knowledge. The findings have implications for the formulation of criteria for the effective incorporation of learner control into the design of instructional animations.

Positive lightning: An overview, new observations, and inferences

We examine the various conceptual cloud charge configurations and scenarios leading to production of positive lightning with a view toward an explanation of its observed properties. Data for 52 positive cloud‐to‐ground flashes containing 63 strokes recorded in Gainesville, Florida, in 2007–2008 are presented and discussed. The U.S. National Lightning Detection Network (NLDN) located 51 (96%) of the positive strokes at distances of 7.8 to 157 km from the field‐measuring station. In 42 (81%) of the 52 flashes, the first (or the only) leader‐return stroke sequence was not preceded by in‐cloud discharge activity. The average number of strokes per flash is 1.2. Single‐stroke flashes constitute 81%. In three (38%) of eight two‐stroke flashes, the second stroke likely followed the channel of the first stroke, and in five (62%) flashes it likely created a new termination on ground. Eight (15%) of the 52 positive flashes had detectable preliminary breakdown pulse trains in their electric field records. Electric field waveforms of 14 (27%) first strokes (also of one third stroke) are preceded by pronounced pulses, apparently indicative of leader stepping. NLDN‐reported peak currents for 48 positive strokes in 40 flashes ranged from 20 to 234 kA with a geometric mean value of 75 kA. The median charge transfers in 1, 2, and 40 ms after the beginning of return stroke electric field change for an assumed height of 12 km were estimated to be 13, 18, and 34 C, respectively. Two bipolar lightning discharges are additionally examined.

Writer recognition enhancement by means of synthetically generated handwritten text

This paper presents a new method to generate synthetic executions of on-line words from real samples. The proposed generation method takes advantage of the characteristics of a writer recognition system developed by the authors and can be seamlessly integrated into it. Both the generation method and the recognition system consider strokes as the structural units of handwriting with words being regarded as two sequences, one of pen-up and one of pen-down strokes. Given two samples from the same word and writer, a new sample is produced by aligning their sequences of strokes and then averaging the matching pairs. Thanks to a self-organising map used to categorise strokes, the alignment and comparison of sequences of strokes are performed in a straightforward and computationally efficient way.The synthetically generated words not only retain much of the discriminative power (i.e. the capability to discriminate among writers) of the words from which they are generated, but in some cases exhibit an increased recognition performance. Also, the newly generated words allow enlarging the number of available samples in the enrolment sets that are used to build writers' models. In most cases, this enlargement has the effect to improve the performance of the recognition system. Experimenting with 320 writers and enrolment sets containing 3 real samples and 6 synthetically generated ones, verification is improved for 15 of the 16 words in the BiosecurID database, with the minimum of the detection cost function being reduced by up to a 26.5%.

Similarity and Degree of Perplexity Analysis of Chinese Characters

The study of Chinese scripts has always been a topic drawing continuous scholarly attention from various perspectives. Facilitated with the development of computing technology, recent years saw an increasing interest in the graphic pattern of Chinese characters. This paper focuses on the likelihood of orthographical confusions among any given set of Chinese characters. By defining a normalized metric based on character stroke sequences, we introduce the similarity between two Chinese characters, a unique numerical value which falls within the interval [0, 1], measuring to what extent one character is prone to be confused with another. For a set consisting of a large quantity of characters, we introduce the concept of degree of perplexity (DP), measuring the number of strokes weighted average similarities between a given character and the rest of the characters in the set. An efficient and easy-to-implement algorithm is designed to compute the similarity and degree of perplexity. Our formulas are calibrated with numerical experiments simulated with the most frequently used 200 characters. Based on the numerical simulations, an exponential functional relationship between the degree of perplexity and the number of strokes is proposed and is calibrated with least square regression. Finally, possible applications of the measures introduced are discussed.

중국 어린이들에게 있어 필순과 기억이 중국어 읽기 능력에 미치는 영향에 관한 연구

중국 어린이들에게 있어 필순과 기억이 중국어 읽기 능력에 미치는 영향에 관한 연구

Physical processes during development of upward leaders from tall structures

The objective of our study was to identify and interpret the various processes during development of upward positive leaders from tall structures. We provide a physical interpretation for the varying luminosity of the leader channel during its initial ascent and the pulsing luminosity during much later stages of the established leader. Our analysis confirms that pulsed luminosity is a result of recoil leaders intercepting the current-carrying channel connected to ground. This interception produces an M-component. Applying the bidirectional leader concept and a simplified electrostatic approximation, we introduce physical models of the dart leader-return stroke sequence and the M-component.

Evaluation of U.S. National Lightning Detection Network performance characteristics using rocket-triggered lightning data acquired in 2004–2009

[1] We evaluated performance characteristics of the U.S. National Lightning Detection Network (NLDN) using rocket-triggered lightning data acquired in 2004-2009 at Camp Blanding, Florida. A total of 37 negative flashes that contained leader/return stroke sequences (a total of 139) were triggered during these years. For all the return strokes, locations of channel terminations on the ground were known exactly, and for 122 of them currents were measured directly using noninductive shunts. The NLDN recorded 105 Camp Blanding strokes in 34 flashes. The resultant flash and stroke detection efficiencies were 92% and 76%, respectively. The median absolute location error was 308 m. The median NLDN-estimated peak current error was -6.1%, while the median absolute value of current estimation error was 13%. Strokes in classical triggered flashes are similar to regular subsequent strokes (following previously formed channels) in natural lightning, and hence the results presented here are applicable only to regular negative subsequent strokes in natural lightning. The flash detection efficiency reported here is expected to be an underestimate of the true value for natural negative lightning flashes, since first strokes typically have larger peak currents than subsequent ones.