Reduction In Path Length Research Articles

Improving Light Output of Vertical-Stand-Type InGaN Light-Emitting Diodes Grown on a Free-Standing GaN Substrate With Self-Assembled Conical Arrays

We demonstrated the fabrication and study of vertical-stand-type homoepitaxial light-emitting diodes (VLEDs) on a GaN substrate with conical array structures. The conical arrays were formed on the N-face surface of the GaN substrate using a size-controllable polystyrene nanosphere as etch mask. The 20-mA output power of the VLEDs with flat backside, truncated cone, and cone arrays improved by magnitudes of 16.5%, 66.8%, and 118.5%, respectively, compared with that of conventional planar configuration LEDs. These improvements could be attributed to the increased direct illumination surface and reduction in photon extraction path length. Moreover, small wavelength redshift proved that the VLED on the GaN substrate did not suffer from serious thermal effect.

Visual-Motor Learning Using Haptic Devices: How Best to Train Surgeons?

Laparoscopic surgery has revolutionised medicine but requires surgeons to learn new visual-motor mappings. The optimal method for training surgeons is unknown. For instance, it may be easier to learn planar movements when training is constrained to a plane, since this forces the surgeon to develop an appropriate perceptual-motor map. In contrast, allowing the surgeon to move without constraints could improve performance because this provides greater experience of the control dynamics of the device. In order to test between these alternatives, we created an experimental tool that connected a commercially available robotic arm with specialised software that presents visual stimuli and objectively records kinematics. Participants were given the task of generating a series of aiming movements to move a visual cursor to a series of targets. The actions required movement along a horizontal plane, whereas the visual display was a screen positioned perpendicular to this plane (ie, vertically). One group (n=8) received training where the force field constrained their movement to the correct plane of action, whilst a second group (n=8) trained without constraints. On test trials (after training) the unconstrained group showed better performance, as indexed by reduced movement duration and reduced path length. These results show that participants who explored the entire action space had an advantage, which highlights the importance of experiencing the full dynamics of a control device and the action space when learning a new visual-motor mapping.

Optimizing Communication Overhead while Reducing Path Length in Beaconless Georouting with Guaranteed Delivery for Wireless Sensor Networks

Beaconless or contention-based geographic routing algorithms forward packets toward a geographical destination reactively without the knowledge of the neighborhood. Such algorithms allow greedy forwarding, where only the next hop neighbor responds after a timer-based contention using only three messages (RTS, CTS, and DATA) per forwarding step. However, existing contention-based schemes for recovery from greedy failures do not have this property. In this paper, we show that recovery is possible within this 3-message scheme: the Rotational Sweep (RS) algorithm directly identifies the next hop after timer-based contention and constructs a traversal path that ensures progress after a greedy failure. It uses a traversal scheme (called Sweep Circle) that forwards a message along the $(\alpha)$-shape of the network and provides recovery paths shorter or equal to the prominent face routing with Gabriel graph planarization. An alternative traversal scheme (called Twisting Triangle) provides even shorter routes on average, as shown by simulations. They both also reduce per-node overall network contention delays. We prove that both traversal schemes guarantee delivery in unit disk graphs. Our traversal schemes avoid planarization and are easy to implement, based merely on the evaluation of a function of a neighbor node's relative position. They can also be used for boundary detection and improve path-length in conventional beacon-based routing.

X-ray interaction-induced signal and noise performances of edge-on silicon microstrip detectors for digital mammography

We are developing a silicon microstrip-array detector, which is operated in photon-counting mode, for line-scanned digital mammography. To enhance the x-ray interaction efficiency, the x-ray beam is oriented toward the edge of microstrips, known as the edge-on geometry. To predict the fundamental signal and noise performances induced by x-ray interactions, we performed Monte Carlo simulations. Absorbed energy distribtuions were obtained for various tilting angles (5 to 85 degrees) in the edge-on detector geometry for a wide range of incident energies from 1 to 50 keV. Based on the energy-moments theory with the obtained absorbed energy distributions, we estimated various physical performance parameters such as the quantum absorption efficiency, the average energy deposition per interaction, and the Swank noise factor. In addition, relative accuracy and imprecision in photon-energy measurements were estimated. These analyses were extended to the typical poly-energetic mammography x-ray spectra from various target materials such as molybdenium, rhodium and tungsten. Among performance parameters, the quantum absorption efficiency was gradually decreased as the tilting angle increases because of the reduction in pathlength where x-ray photons travel, while others were almost insensitive to the tilting angle. The best signal and noise performances in the edge-on silicon microstrip detector were obtained for the rhodium spectrum.

Constant factor approximations for the hotlink assignment problem

The concept of hotlink assignment aims at reducing the navigation effort for the users of a Web directory or similar structure by inserting a limited number of additional hyperlinks called hotlinks . The k -hotlink assignment problem denotes the task of adding at most k outgoing hotlinks to each page of a tree-like site, minimizing the path length , that is, the expected number of “clicks” necessary for the user to reach her destination page. Another common formulation of this problem is to maximize the gain , that is, the path length reduction achieved by the assignment. In this work we analyze the natural greedy strategy, proving that it reaches the optimal gain up to the constant factor of 2. Considering the gain, we also prove the existence of a PTAS. Finally, we give a polynomial-time 2-approximation for the 1-hotlink assignment problem, which constitutes the first constant factor approximation in terms of the path length. The algorithms' performance analyses are made possible by a set of three new basic operations for the transformation of hotlink assignments.

Effects of testosterone on spatial learning and memory in adult male rats

A male advantage over females for spatial tasks has been well documented in both humans and rodents, but it remains unclear how the activational effects of testosterone influence spatial ability in males. In a series of experiments, we tested how injections of testosterone influenced the spatial working and reference memory of castrated male rats. In the eight-arm radial maze, testosterone injections (0.500 mg/rat) reduced the number of working memory errors during the early blocks of testing but had no effect on the number of reference memory errors relative to the castrated control group. In a reference memory version of the Morris water maze, injections of a wide range of testosterone doses (0.0625–1.000 mg/rat) reduced path lengths to the hidden platform, indicative of improved spatial learning. This improved learning was independent of testosterone dose, with all treatment groups showing better performance than the castrated control males. Furthermore, this effect was only observed when rats were given testosterone injections starting 7 days prior to water maze testing and not when injections were given only on the testing days. We also observed that certain doses of testosterone (0.250 and 1.000 mg/rat) increased perseverative behavior in a reversal-learning task. Finally, testosterone did not have a clear effect on spatial working memory in the Morris water maze, although intermediate doses seemed to optimize performance. Overall, the results indicate that testosterone can have positive activational effects on spatial learning and memory, but the duration of testosterone replacement and the nature of the spatial task modify these effects.

Estimation of Path Length Reduction Factor by Using One Year Rain Attenuation Statistics over a Line of Sight Link Operating at 28.75 GHz in Amritsar (INDIA)

The effect of environmental factors in general and rain droplets in particular, on microwave propagation is a very well known fact now. If the rain droplets are present in an inhomogeneous way across the path length of the microwave communication system then, a new concept of path length reduction factor is introduced which accounts for the inhomogeneous nature of the rain droplets along the path length of the microwave signal. The present paper presents results of path length reduction factor using data on attenuation levels obtained on a LOS link operating at 28.75 GHz in Amritsar region and its comparison with Crane’s and ITU-R’s model.

Catalyst light-off behavior of a spark-ignition LPG (liquefied petroleum gas) engine during cold start

The effects of the length of the gas flow path from the exhaust outlet in the cylinder head to the catalyst inlet in the exhaust line, the ignition timing and the engine idle speed on the three-way catalyst light-off behavior in an electronically controlled inlet port LPG (liquefied petroleum gas) injection SI (spark-ignition) engine during cold start were investigated experimentally. The results showed that these factors affect the catalyst light-off behavior significantly during cold start. The reduction of the gas flow path length upstream the catalyst reduces the heat loss from the exhaust gases, increases the temperature of the catalyst, and results in faster catalyst light-off. Retarding the ignition timing from 0 to 15°CA ATDC decreases 22 and 8 s catalyst light-off time for HC and CO respectively. Increasing the engine idle speed from 1400 to 1800 rpm decreases 19 and 15 s the light-off time for HC and CO respectively. ► The evaluation methods of the temperature and conversion efficiency are essential for catalyst light-off. ► We adopt HC and CO emission to explain the catalyst light-off during cold start. ► The reduction of the gas flow path length upstream, retarding the ignition timing and increasing the engine idle speed can reduce the catalyst light-off time during cold start. ► We concluded that improving methods for catalyst light-off are essential for the catalyst light-off behavior during cold start.

Evaluation of colonoscopy technical skill levels by use of an objective kinematic-based system

Colonoscopy requires training and experience to ensure accuracy and safety. Currently, no objective, validated process exists to determine when an endoscopist has attained technical competence. Kinematics data describing movements of laparoscopic instruments have been used in surgical skill assessment to define expert surgical technique. We have developed a novel system to record kinematics data during colonoscopy and quantitatively assess colonoscopist performance. To use kinematic analysis of colonoscopy to quantitatively assess endoscopic technical performance. Prospective cohort study. Tertiary-care academic medical center. This study involved physicians who perform colonoscopy. Application of a kinematics data collection system to colonoscopy evaluation. Kinematics data, validated task load assessment instrument, and technical difficulty visual analog scale. All 13 participants completed the colonoscopy to the terminal ileum on the standard colon model. Attending physicians reached the terminal ileum quicker than fellows (median time, 150.19 seconds vs 299.86 seconds; p<.01) with reduced path lengths for all 4 sensors, decreased flex (1.75 m vs 3.14 m; P=.03), smaller tip angulation, reduced absolute roll, and lower curvature of the endoscope. With performance of attending physicians serving as the expert reference standard, the mean kinematic score increased by 19.89 for each decrease in postgraduate year (P<.01). Overall, fellows experienced greater mental, physical, and temporal demand than did attending physicians. Small cohort size. Kinematic data and score calculation appear useful in the evaluation of colonoscopy technical skill levels. The kinematic score appears to consistently vary by year of training. Because this assessment is nonsubjective, it may be an improvement over current methods for determination of competence. Ongoing studies are establishing benchmarks and characteristic profiles of skill groups based on kinematics data.

The average pathlength map: A diffusion MRI tractography-derived index for studying brain pathology

Magnetic resonance diffusion tractography provides a powerful tool for the assessment of white matter architecture in vivo. Quantitative tractography metrics, such as streamline length, have successfully been used in the study of brain pathology. To date, these studies have relied on a priori knowledge of which tracts are affected by injury or pathology and manual delineation of regions of interest (ROIs) for use as waypoints in tractography. This limits the analyses to specific tracts under investigation and relies on the accurate and consistent placement of ROIs. We present a fully automated technique for the voxel-wise analysis of streamline length within the entire brain, the Average Pathlength Map (APM). We highlight the precision and reproducibility of voxel-wise average streamline length over time, and assess normal variability of pathlength values in a cohort of 43 healthy participants. Additionally, we demonstrate the utility of this approach by performing voxel-wise comparison between pathlength values obtained from a patient with a severe traumatic brain injury (TBI, Glasgow Coma Scale Score=7) and those from control participants. Our analysis shows that voxel-wise average pathlength values are comparable to fractional anisotropy (FA) in terms of reproducibility and variability. For the TBI patient, we observed a significant reduction in streamline pathlength in the genu of the corpus callosum and its projections into the frontal lobe. This study demonstrates that the average pathlength map can be used for voxel-based analysis of a quantitative tractography metric within the whole brain, removing both the dependence on a priori knowledge of affected pathways and time-consuming manual delineation of ROIs.

High-concentration zeta potential measurements using light-scattering techniques.

Zeta potential is the key parameter that controls electrostatic interactions in particle dispersions. Laser Doppler electrophoresis is an accepted method for the measurement of particle electrophoretic mobility and hence zeta potential of dispersions of colloidal size materials. Traditionally, samples measured by this technique have to be optically transparent. Therefore, depending upon the size and optical properties of the particles, many samples will be too concentrated and will require dilution. The ability to measure samples at or close to their neat concentration would be desirable as it would minimize any changes in the zeta potential of the sample owing to dilution. However, the ability to measure turbid samples using light-scattering techniques presents a number of challenges. This paper discusses electrophoretic mobility measurements made on turbid samples at high concentration using a novel cell with reduced path length. Results are presented on two different sample types, titanium dioxide and a polyurethane dispersion, as a function of sample concentration. For both of the sample types studied, the electrophoretic mobility results show a gradual decrease as the sample concentration increases and the possible reasons for these observations are discussed. Further, a comparison of the data against theoretical models is presented and discussed. Conclusions and recommendations are made from the zeta potential values obtained at high concentrations.

Experimental Measurements of Supermodes in Superposition Architectures for Coherent Laser Beam Combining

Measurements of the modal properties of Michelson resonators are compared to theory using a common-path generalized Michelson resonator. Conventional Michelson cavities are shown to exhibit significant loss when path length errors are introduced, often resulting in reduced output power. Accurate measurements of these losses as a function of path length error are provided, along with measurements of the field distribution in the resonator. Proper exploitation of spatial and longitudinal supermodes is shown to reduce the path length sensitivity in coherent beam combining systems. In particular, modifying a conventional Michelson resonator to include an additional mirror reduces path length error losses and increases output power. Measurements of the modal performance of these cavities compare well with theoretical expectations.

Supporting intelligent and trustworthy maritime path planning decisions

The risk of maritime collisions and groundings has dramatically increased in the past five years despite technological advancements such as GPS-based navigation tools and electronic charts, which may add to, instead of reduce, workload. We propose that an automated path planning tool for littoral navigation can reduce workload and improve the overall system efficiency, particularly under time pressure. To this end, a maritime automated path planner (MAPP) was developed, incorporating information requirements developed from a cognitive task analysis, with special emphasis on designing for trust. Human-in-the-loop experimental results showed that MAPP was successful in reducing the time required to generate an optimized path, as well as reducing path lengths. The results also showed that while users gave the tool high acceptance ratings, they rated the MAPP as average for trust, which we propose is the appropriate level of trust for such a system.

Advanced process planning for subtractive rapid prototyping

PurposeSubtractive rapid prototyping (SRP) uses layer‐based removal from a plurality of orientations in order to create geometry in a highly automated manner. However, unlike additive means, the method can be inefficient due to redundant cutting operations on previously machined regions. The purpose of this paper is to present process planning methods for SRP, specifically dealing with stock material management in multiple setup operations.Design/methodology/approachAnalysis of remaining stock material was performed by considering slices of respective stereolithography (STL) models. Further, an initial approximation was made of accessibility to enable iterative visibility analysis. The combination of these approaches led to efficient and fast algorithms. After analysis, the slices could be converted back to useful STL models through polyhedral reconstruction.FindingsThis method of approximation yields results similar to exact geometry. Using remaining stock data from this approach leads to a significant reduction in tool path length and processing time in SRP.Originality/valueThis paper presents novel methods of geometric representation and inaccessible volume calculation for four‐axis layer‐based machining and shows a successful implementation in an SRP system.

Degradation of dye wastewater in a thin-film photoelectrocatalytic (PEC) reactor with slant-placed TiO2/Ti anode

Abstract A thin-film photoelectrocatalytic (PEC) reactor with slant-placed TiO 2 /Ti anode was developed and successfully applied to degrade Rhodamine B (RhB) and textile effluent. Using a 5–150 mg L −1 RhB solution as the model system, thin-film PEC removed total color and TOC by 99–28% and 78–15%, respectively, in 1 h, which is much higher than 82–7% and 60% to zero by conventional PEC. The enhanced treatment efficiency achieved by thin-film PEC process was attributed to the significantly reduced path length of irradiation light source. The wastewater was kept circulating during the experiments to timely refresh the aqueous film on the TiO 2 /Ti anode and promote the mass transfer of the target pollutants and the degradation products in the bulk solution. The thin-film PEC reactor can degrade both simulated and real dye wastewater efficiently under UV light irradiation. Results suggested that thin-film PEC was particularly superior for treating a high concentration solution. The thin-film PEC reactor was also applied to treat RhB solution efficiently under solar light irradiation. The recycle experiments demonstrated excellent stability and reliability of the slant-placed TiO 2 /Ti anode. This study proposed a simple and effective method to design PEC reactor applicable for industrial dye wastewater treatment.

Multilayer stacking technique for holographic polymer dispersed liquid crystals

We demonstrate an alternate method of stacking holographic polymer dispersed liquid crystal (HPDLC) reflection gratings on substrates coated with indium tin oxide on both sides allowing independent switching of each grating in the stack. Successive layers of the stack are formed by switching existing layers, while exposing the subsequent layer to an interference pattern. Wavefront analysis based on wavefront propagation through HPDLC with electric field on and off is used to substantiate the improvement in the reflection efficiency of the layers in the stack. Results show an optical path length reduction due to elimination of substrate layers at each grating.

New routing framework base on rumor routing in wireless sensor networks

Rumor routing is a classic routing algorithm based on agents’ random walk. This paper proposes a novel approach based on this routing algorithm. Here, we try to improve the latency and energy consumption of the traditional algorithm using propagation of query and event agents within straight lines, instead of using purely random walk paths. As can be seen in our results, this method improves the delivery ratio of the queries which is a drawback of traditional rumor routing. Due to the reduction of final path length between source and destination, we introduce a second layer geographical routing. Moreover, a method is proposed to reduce the cost of localization equipments by using cheaper equipments like AoA antennas. In order to compare the performance measures with traditional algorithm, a simulation framework is developed and extensive simulations are performed.

Enhanced dye wastewater degradation efficiency using a flowing aqueous film photoelectrocatalytic reactor

A TiO2/Ti flowing aqueous film photoelectrocatalytic (PEC) reactor was developed and successfully applied to degrade Reactive Brilliant Blue X-BR (RBB) and textile effluent. The high treatment efficiency achieved by flowing aqueous film PEC process was attributed to the enhanced light utilization resulting from the significantly reduced path length (down to average approximately 78 μ m level). The dye wastewater was kept circulating (7.7 L h−1) during the experiments to continuously refresh the aqueous film on the TiO2/Ti photoanode and promote the mass transfer of the target pollutants and the degradation products in the bulk solution. Using a 20–150 mg L−1RBB solution as the model system, flowing aqueous film PEC removed color by 83–44% in one hour, much higher than the 75–12% by conventional PEC. Results also suggested that flowing aqueous film PEC was particularly superior to conventional PEC for treatment of a high concentration solution. The feasibility of the TiO2/Ti flowing aqueous film PEC reactor was investigated by treating industrial textile effluent. A color and total organic carbon (TOC) removal of 75% and 50% respectively, were achieved in two hours. Thus, in the present study, we propose a new concept for the design of a PEC reactor applicable to industrial wastewater treatment.

Reduction of Average Path Length in Binary Decision Diagrams by Spectral Methods

This paper deals with analytic methods for the calculation and reduction of the average path lengths (APLs) in binary decision diagrams (BDDs). Usually, information-theoretic measures and information-theoretic techniques are used to construct BDDs of minimal APLs. Specifically, the mutual information between a Boolean function and its variables and the Shannon-Fano prefix coding are utilized. This paper deals with the problem of the APL reduction by using spectral techniques. Particularly, methods based on the properties of the Walsh spectrum of a Boolean function and its autocorrelation function are discussed. It is shown that the APL is a linear function of the autocorrelation values, that is, the APL depends on the Boolean function's properties in the time domain (autocorrelation) rather on the Boolean function's properties in the frequency domain (Walsh spectrum). In addition, it is shown that information-theoretic criteria like the mutual information or the conditional entropy are equivalent to frequency-domain criteria. Consequently, existing information-theoretic approaches for APL reduction that are based on mutual-information criterion or the Walsh transform coefficients may derive a suboptimal APL. The representation of the APL as a function of the autocorrelation values opens a way to determine the optimal ordering of the input variables analytically. Two procedures for APL reduction by ordering and by using linear combinations of the input variables are presented: (1) minimization by using the autocorrelation values and (2) minimization by using the mutual information between the Boolean function and a linear function of the input variables. The time-domain approach may derive a linearized BDD of a lower APL, whereas the information-theoretic approach has a lower computational complexity with comparable performance. Experimental results show the efficiency of the suggested techniques.

Effects of affective picture viewing on postural control

BackgroundEmotion theory holds that unpleasant events prime withdrawal actions, whereas pleasant events prime approach actions. Recent studies have suggested that passive viewing of emotion eliciting images results in postural adjustments, which become manifest as changes in body center of pressure (COP) trajectories. From those studies it appears that posture is modulated most when viewing pictures with negative valence. The present experiment was conducted to test the hypothesis that pictures with negative valence have a greater impact on postural control than neutral or positive ones. Thirty-four healthy subjects passively viewed a series of emotion eliciting images, while standing either in a bipedal or unipedal stance on a force plate. The images were adopted from the International Affective Picture System (IAPS). We analysed mean and variability of the COP and the length of the associated sway path as a function of emotion.ResultsThe mean position of the COP was unaffected by emotion, but unipedal stance resulted in overall greater body sway than bipedal stance. We found a modest effect of emotion on COP: viewing pictures of mutilation resulted in a smaller sway path, but only in unipedal stance. We obtained valence and arousal ratings of the images with an independent sample of viewers. These subjects rated the unpleasant images as significantly less pleasant than neutral images, and the pleasant images as significantly more pleasant than neutral images. However, the subjects rated the images as overall less pleasant and less arousing than viewers in a closely comparable American study, pointing to unknown differences in viewer characteristics.ConclusionOverall, viewing emotion eliciting images had little effect on body sway. Our finding of a reduction in sway path length when viewing pictures of mutilation was indicative of a freezing strategy, i.e. fear bradycardia. The results are consistent with current knowledge about the neuroanatomical organization of the emotion system and the neural control of behavior.