Effect Of Horizontal Distance Research Articles

RADIATION DOSE WITH CIRCULAR EXTERNAL FIXATION: DOES THE SURGEON GET A DOUBLE WHAMMY?

IntroductionThe vast majority of orthopaedic surgeons use C-arm fluoroscopy in the operating theatre when building a circular external fixator. In the absence of previous research in this area, we hypothesised that the surgeon who builds a circular external fixator is exposed to a greater amount of radiation purely as a result of the presence of the metallic fixator in the x-ray beam. The aim of our study therefore was to investigate how the presence of a circular external fixator affects the radiation dose to the surgeon and the surgical assistant.Materials & MethodsA simulated environment was created using a radiolucent operating table, an acrylic lower limb phantom (below knee segment), various configurations of metalic circular external fixation, and a standard size C-arm image intensifier.The variables investigated were 1. the amount of metal in the beam 2. the orientation of the beam (PA vertical vs lateral) 3. the horizonal distance of the person from the beam (surgeon vs assistant) and 4. the vertical distance of the various body parts from the beam (e.g. thyroid, groin).In terms of radiation dose, we recorded two things : 1. the dose produced by the image intensifier 2. the dose rate at standardised positions in the operating theatre. The latter was done using a solid-state survey sensor. These positions represented both where the surgeon and surgical assistant typically stand plus the heights of their various body regions relative to the operating table..ResultsThe effect of the presence of the circular external fixator : all frame constructs tested resulted in a statistically significant greater radiation dose both produced by the image intensifier and received by the surgical team.The effect of the beam orientation : the PA (vertical) orientation resulted in a statistically significant greater radiation dose for the surgeon than did the lateral orientation, but made no difference for the assistant.The effect of horizontal distance from the beam : unsurprisingly, the surgeon (who was closer to the beam) received a statistically significant greater radiation dose than the assistant. The effect of vertical distance from the beam : for the surgeon, the dose received was highest at the level of the phantom leg / frame, whilst for the assistant there was no statistically significant difference for any level.ConclusionsTo our knowledge, this is the first study investigating the radiation dose rate to the orthopaedic surgeon when building a circular external fixator. We found that the surgeon does indeed receive a ‘double whammy’ because the image intensifier puts out a greater amount of radiation plus the metalic frame scatters more of the x-ray beam. Whilst the amounts are relatively small, we think that it's important to quantify doses that orthopaedic surgeons receive to ensure optimal radiation practices.

Cooperative mining technology and strata control of close coal seams and overlying coal pillars

Mining of close coal seams envisages reservation of a large number of section coal pillars of a total width ranging from 30 to 40 m. This results in an enormous waste of coal resources and risks of spontaneous combustion, instability, and damage to the remaining coal pillars. This study attempts to mitigate the above problems via the proposed cooperative mining technical method for close seams and overlying coal pillars. It expounds on the technical principles, the required mining equipment, technology, and the system layout, and analyzes the key influencing factors of strata control. Using the numerical simulation via FLAC3D and PFC2D commercial software packages, the effect of horizontal distance between the lower coal seam roadway and the overlying coal pillar (i.e., spacing) on the surrounding rock control and rational layout of the roadway is studied. The mechanism of the overlying coal pillar width effect on the ground pressure of the stope and coal pillar recovery rate is clarified. The engineering case study shows that when the horizontal spacing was increased from 0 to 15 m, the surrounding rock deformation, surrounding rock stress peak value, and plastic zone area of the roadway decreased significantly. When the coal pillar width in the overlying section was increased from 25 to 40 m, the peak values of lateral and advance bearing stresses in the stope dropped by 21 and 12 MPa, respectively. Besides, the ground pressure driving strength of the stope was significantly reduced, and the recovery rates of the overlying coal pillar and rock between the close coal seams were increased by 7.45 and 4.29%, respectively. Combined with the top coal pillar drawing pattern, optimization concepts and their realization methods were proposed.

Unsteady aerodynamic performance of a tandem flapping–fixed airfoil configuration at low Reynolds number

In nature, insects with their forewings and hindwings undergoing small-gap flapping motion experience strong aerodynamic interaction. Conventional studies mainly focus on the propulsion performance of tandem flapping wings, while the interaction between a flapping wing and a fixed wing in the tandem configuration at low Reynolds numbers (Re) is unclear. In this paper, we numerically studied the aerodynamic performance and vortex structure of this tandem flapping–fixed airfoil configuration. The effects of horizontal distance (LX), vertical distance (LY), and geometric angle of attack (α) of the fixed wing on the thrust and lift performance are investigated. The results show that LX dominates the propulsion performance, while LY and α control the lift performance. The thrust enhancement of the flapping airfoil is effective only within a small range of LX, and the thrust is mainly determined by the changing rate of the impulse of the vortices directly connected to the airfoils. The lift reaches its peak when LY approaches the plunging amplitude. Compared with a fixed airfoil, the flapping–fixed configuration shows a larger lift-to-drag ratio, indicating a lift enhancement led by the interaction with the upstream flapping airfoil. Moreover, increasing LY and α simultaneously can lead to additional advantages in lift generation. Further analysis shows that changes of LY and α both manifest in a variation of the effective angle of attack of the fixed airfoil, thereby manipulating its lift generation. This paper provides an aerodynamic database and guidance for the design of micro air vehicles using tandem flapping–fixed wings.

Study on the interference between parallel pipelines and optimized operation for the cathodic protection systems

Purpose In recent years, the demand for oil and gas pipelines has increased rapidly. Due to the restrictions of the pipeline routing, pipelines are generally laid in parallel or in the same trench, which results in stray-current interference between the independent cathodic protection (CP) systems. The purpose of this paper is to study the interference between the long-distance parallel pipelines and to obtain the optimized operation for the CP systems. Design/methodology/approach In this study, first, the numerical model of parallel pipelines was established using the boundary element analysis software (BEASY). Second, the effects of horizontal distance between parallel pipelines, coating damage rate, soil conductivity and anode output current on the interference of parallel pipelines were studied. Finally, by varying the layout or the output currents of CP stations, an optimized operation scheme osf long-distance parallel pipelines was put forward. Findings Simulation results showed that with a decrease in soil conductivity or coating damage rate, the interference increased. Moreover, the interference decreased with an increase in horizontal distance between two parallel pipelines or a decrease in anode output current. It was found that there are three methods to reduce the interference between long-distance parallel pipelines: to reduce the output currents of CP stations, combined protection and to close part of the CP stations. Among them, to close part of CP stations was the optimized scheme because of the lowest operating and maintenance cost. Originality/value The optimized operation scheme proposed in this study can not only solve the interference between parallel pipelines but also provide guidance for the parallel pipelines to be built in the future. Reasonably arranging the cathodic protection stations using numerical simulation can avoid the interference in the cathodic protection systems, and reduce the construction cost.

Effects of horizontal distance and limb crossing on perceived hand spacing and ownership: Differential sensory processing across hand configurations

We have previously shown that, with the hands apart vertically, passively grasping an artificial finger induces a sense of ownership over the artificial finger and coming-together of the hands. The present study investigated this grasp illusion in the horizontal plane. Thirty healthy participants were tested in two conditions (grasp and no grasp) with their hands at different distances apart, either crossed or uncrossed. After 3 min, participants reported perceived spacing between index fingers, perceived index finger location, and, for the grasp condition, perceived ownership over the artificial finger. On average, there was no ownership at any of the hand configurations. With the hands uncrossed 7.5, 15 or 24 cm apart, there was no difference in perceived spacing between the grasp and no grasp conditions. With the hands crossed and 15 cm apart, perceived spacing between index fingers was 3.2 cm [0.7 to 5.7] (mean [95% CI]) smaller during the grasp condition compared to no grasp. Therefore, compared to when the hands are vertically separated, there is an almost complete lack of a grasp illusion in the horizontal plane which indicates the brain may process sensory inputs from the hands differently based on whether the hands are horizontally or vertically apart.

Effects of horizontal distance between perches on perching behaviors of Lohmann Hens

Perching is a highly-motivated natural behavior of laying hens that has been considered as one of the essential welfare requirements. The objective of the study was to evaluate perching behaviors of laying hens as affected by horizontal distance (HD) between parallel perches. A total of 48 Lohmann white hens in three groups (16 hens/group) were used, 68 weeks of age at the experiment onset. For each group, hens were housed in an enriched wire-mesh floor pen (120cm L×120cm W×120cm H) equipped with two round galvanized tube perches (120cm long×32mm diameter, an average of 15cm perch space/hen). HD was varied sequentially at 60, 40, 30, 25, 20 and 15cm and then in reverse order. A real-time monitoring system was developed to continuously record hen’s perching behaviors. The number or proportion of perching hens, perching duration, and perching trip and frequency were analyzed using an automated VBA (Visual Basic for Applications) program developed in Microsoft Excel. Heading direction of the perching hens and pattern of the perch occupancy were determined manually by video observation. Results showed that reduction of HD to 25cm did not restrain hens’ perching behaviors, whereas HD of 20 or 15cm restrained perching to some extent. Specifically, at HD of 25cm, hens perched interlacing with one another to maximize use of the perches during the dark period. As a result, the proportion of perching hens and perching duration for HD of 25cm were not reduced as compared to HD of 30–60cm. However, the proportion of perching hens was significantly reduced at HD of 15cm (P=0.001–0.025). HD of 15 and 20cm also significantly reduced daily perching time of the hens. In contrast, perching trip or frequency and heading direction of the perching hens were not influenced by HD (15–40cm) except for HD of 60cm. The results suggest that although 30cm is the recommended minimum HD, 25cm may be considered for situations where additonal perches are necessary to meet all hens’ perching needs.

Effect of Horizontal Distance of Tunnel on the Subsidence Of the Surface Building

Effect of Horizontal Distance of Tunnel on the Subsidence Of the Surface Building

Theoretical basis for general lifting equations based on mechanical work performed during manual lifting

Objective: The objective of this research is to develop and validate general lifting equations based on the concept of mechanical work performed during the manual handling of objects. Background: To the authors’ knowledge, the NIOSH lifting equation was based on an empirical approach. Therefore, there is a need for general lifting equations that are based on the laws of mechanics and physics. Methods: General lifting equations were developed as a function of weight, horizontal distance in the sagittal plane, vertical travel distance, vertical distance from the floor to the origin of lift and angle of twist. The equations were based on the mechanical work required against gravity/friction, supplemented with stress coefficients to account for task difficulty not traditionally embedded in the dot product of gravity/friction forces and distance. Validation of the equations was performed with respect to the NIOSH lifting equation. Results: Results indicate that the general lifting index (GLI) was comparable to the NIOSH lifting index (LI) for different values of horizontal distance, vertical travel distance, twisting angle and vertical height at origin of lift. On the other hand, the GLI is more sensitive (i.e. larger) to individual changes in vertical travel distance or vertical height at origin of lift in comparison to the NIOSH LI. Consequently, the effect of horizontal distance was dampened in the GLI. Conclusion: The empirical approach inherent in human expertise, which was used by NIOSH in the development of their lifting equation, appears to be a good approximation on the basis of physics and mechanics laws. As originally planned by NIOSH, the lifting equation appears to be protective of the general workforce. Furthermore, the lifting equations hold the promise of assisting in the estimation of peak and cumulative lifting stresses in the workplace.

Dispersal of Venturia inaequalis Ascospores and Disease Gradients from a Defined Inoculum Source

AbstractAerial concentration of ascospores of Venturia inaequalis and incidence of apple scab were monitored in an orchard during the ascospore release seasons in 1999, 2000 and 2001 on susceptible (Jonagold) and moderately resistant (Schone van Boskoop) apple cultivars. A 1‐ha orchard was divided into an inoculum source block (approximately 0.34 ha) and an inoculum‐free block (approximately 0.66 ha) where inoculum was excluded by covering the soil surface with polythene sheets. Ascospore numbers and disease incidence were measured within the inoculum‐free block at different distances from the inoculum block. Ascospores were sampled with three Burkard volumetric spore traps located at 0, 21 and 45 m from the border of the inoculum block. To determine the incidence of infection, clusters of leaves were assessed at six distances from the border of the infected source from the time the first symptoms appeared. Each year, the aerial ascospore concentration significantly decreased with distance from the source, as did the incidence of infected clusters. Cultivar susceptibility to apple scab markedly influenced incidence of infected clusters and disease gradients. The effect of horizontal distance from the source was identifiable up to 18 m and 33 m for cv. Schone van Boskoop and cv. Jonagold, respectively, beyond which disease was negligible. The disease gradients for cultivar Jonagold in 1999, 2000 and 2001 were well described by an exponential model with gradient coefficients of −0.036, −0.042 and −0.047, respectively. The number of infected clusters at the source border for this cultivar differed significantly over the 3 years. A single exponential model with a gradient coefficient of −0.035 adequately described the disease gradients for cultivar Schone van Boskoop in each of the 3 years. Further analysis showed highly significant correlations (r > 0.85, P < 0.01) between the annual cumulative spore catches and the annual mean number of infected leaf clusters in each year and for both cultivars. The aerobiological and epidemiological implications of these findings are discussed.