Relationship between frequency of upside-down posture and space size around upside-down catfish, Synodontis nigriventris.

The catfish Synodontis nigriventris shows a unique habit taking a stable upside-down posture in free water regardless of an above, one-sided illumination. This upside-down posture can be observed when the catfish is apart from objects because the catfish usually orients its ventral side towards the water bottom or objects due to a so-called ventral substrate response. Thus, it is not easy to study the mechanism of the upside-down posture. To resolve this problem, the frequency of the upside-down posture was measured by using various sizes of vessel in which the catfish was kept. Video analysis showed that the frequency of the upside-down posture depended on the space size around the catfish. The smaller the size became, the higher the frequency of the upside-down posture became. Furthermore, the frequency of the upside-down posture depended on the shape of the vessel bottom. Curved-bottom vessels induced the upside-down posture more frequently than flat bottom. These findings suggest that a small, curved-bottom vessel is ideal for researching the upside-down postural control mechanism.     

Disturbance-mediated competition: the interacting roles of inundation regime and mechanical and herbicidal control in determining native and invasive plant abundance

Disturbance is a key component of many successful plant invasions. However, interactions among natural and anthropogenic disturbances and effects of these interacting disturbances on invasive plants and desired vegetation are rarely examined. We investigated the effect of anthropogenic disturbance (herbicidal and mechanical) along a natural inundation gradient (20–282 days) on the biomass and resource allocation of the invasive wetland plant, alligator weed (Alternanthera philoxeroides), and two co-occurring competitor plants, the introduced grass, kikuyu (Pennisetum clandestinum), and the native grass, couch (Cynodon dactylon), over a 2-year period. In the absence of additional disturbance, kikuyu biomass was negatively affected, alligator weed biomass was positively affected, and couch biomass was not affected by inundation disturbance. In addition, kikuyu was not affected by the selective removal of alligator weed, while couch increased in wetter habitats where kikuyu was absent due to inundation stress. This suggests that kikuyu is a superior competitor in drier habitats and inundation facilitates the invasion of alligator weed, while couch is an inferior competitor to both kikuyu and alligator weed and is therefore suppressed across its entire niche by these two introduced species. Mowing alone had no effect on the biomass of the species, suggesting the plants are equally tolerant of shoot removal. Selective herbicide reduced alligator weed biomass by 97.5% and the combination of selective herbicide and mowing reduced the biomass of alligator weed significantly more than herbicide alone, by 98.6% compared with un-manipulated controls. To predict community change and prevent sequential exotic plant invasions after weed removal, it is necessary to consider the interacting effects of disturbance and the niche space of invasive species in the local propagule pool.     

"Necking" behaviour in the giraffe

Previous references to "necking" behaviour, and the main features of the study area are briefly outlined.
"Necking" behaviour in giraffe takes place only in all male herds. When the animals are in a head to head posture the intensity is either high or low, but when animals take up a head to tail posture the actions are always of high intensity and appear to have greater sexual significance.
The significance of "necking" is discussed, and it is suggested that these ritualized actions form an important sexuo-social bonding mechanism whereby a hierarchy is created amongst the males, and movement between strictly bachelor and mixed herds helps to maintain contact between the sexes in this polygamous mammal.     

"Necking" behaviour in the giraffe

Previous references to "necking" behaviour, and the main features of the study area are briefly outlined.
"Necking" behaviour in giraffe takes place only in all male herds. When the animals are in a head to head posture the intensity is either high or low, but when animals take up a head to tail posture the actions are always of high intensity and appear to have greater sexual significance.
The significance of "necking" is discussed, and it is suggested that these ritualized actions form an important sexuo-social bonding mechanism whereby a hierarchy is created amongst the males,and movement between strictly bachelor and mixed herds helps to maintain contact between the sexesin this polygamous mammal.     

Optimal coordination and control of posture and locomotion.

This paper presents a theoretical model of stability and coordination of posture and locomotion, together with algorithms for continuous-time quadratic optimization of motion control. Explicit solutions to the Hamilton-Jacobi equation for optimal control of rigid-body motion are obtained by solving an algebraic matrix equation. The stability is investigated with Lyapunov function theory, and it is shown that global asymptotic stability holds. It is also shown how optimal control and adaptive control may act in concert in the case of unknown or uncertain system parameters. The solution describes motion strategies of minimum effort and variance. The proposed optimal control is formulated to be suitable as a posture and stance model for experimental validation and verification. The combination of adaptive and optimal control makes this algorithm a candidate for coordination and control of functional neuromuscular stimulation as well as of prostheses.     

Optimal coordination and control of posture and movements

This paper presents a theoretical model of stability and coordination of posture and locomotion, together with algorithms for continuous-time quadratic optimization of motion control. Explicit solutions to the Hamilton–Jacobi equation for optimal control of rigid-body motion are obtained by solving an algebraic matrix equation. The stability is investigated with Lyapunov function theory and it is shown that global asymptotic stability holds. It is also shown how optimal control and adaptive control may act in concert in the case of unknown or uncertain system parameters. The solution describes motion strategies of minimum effort and variance. The proposed optimal control is formulated to be suitable as a posture and movement model for experimental validation and verification. The combination of adaptive and optimal control makes this algorithm a candidate for coordination and control of functional neuromuscular stimulation as well as of prostheses. Validation examples with experimental data are provided.     

Agro-ecology of onion couch (Arrhenathemm elatius var. bulbosum (Willd.)).

This study investigates the performance of vegetative propagules of onion couch (Arrhenatherum elatius var. bulbosum) of varying sizes during the crop growth cycle; especially trends in tiller and bulb production and crop yield loss. The results suggest that the earlier the crop canopy closes the more suppression it will exert on the bulb formation stage of onion couch and hence its future reproductive potential. The closed canopy provided by a dense crop cut short the bulb formation phase and forced onion couch to invest more in aerial tillers in order to compete and coexist with the taller tillers of the crop. An additive experimental design used here to predict the crop losses indicated that natural infestation of onion couch caused greater crop yield loss compared to artificially planted plots. It was found that, although the regrowth from large aggregates with densely packed bulb chains is reduced by correlative dominance and density dependent mortality, presence of such large aggregates can affect crop yield by interfering with the establishment of crop. The competitiveness and development pattern of onion couch suggests that the recent spread of the weed and the reported variable results of control measures is due to the recent shift in agricultural practices.     

Studies on spatial orientation and posture control and changes in otolith function due to linear acceleration loading.

Otolith function is directly affected by weightlessness at the time of movement in outer space, and changes occur in the mode of response. It has been known for some time that such changes occur in the posture and gait of astronauts just after they return from a trip into space. It is thought that the cause of these changes is disuse atrophy of the antigravity muscles. However, in the present study, experimental subjects underwent repeated linear acceleration loading over a long period of time, and instability of the head and a decrease in posture control, especially in relation to the gait, were observed for the first time. To date, it has been said that the otolith function has a close relationship with ocular counter rolling. However, when the otolith organ was stimulated, the response was seen to be head instability and an irregular effect on the gait. It is surmised that these findings will facilitate future research into the otolith function under gravity-free conditions.     

Development of head docking device for linac-based radiosurgery with a Neptun 10 PC linac

Stereotactic radiosurgery is a method for focused irradiation of intracranial lesions. Linac-based radiosurgery is currently performed by two techniques: couch mounted and pedestal mounted. In the first technique a device is required to affix the patient's head to the couch and neoreover to translate it accurately. Structure of such a device constructed by the authors plus acceptance test performed for evaluation is described in the article.A head docking device has been designed and constructed according to geometry of linac's couch and also desired functions. The device is cornpletely made from aluminum and consists of four major components: attachment bar, lower structure with four moveing accuracy mechanical stability and isocentric accuracy were assessed in the frame of acceptance test.Translating accuracy, mechanical stability and isocentric accuracy were found to be respectively: 1 mm, 1.64 mm and 3.2 mm with accuracy of 95%.According to AAPM report no. 54, a head docking device should translate head with an accuracy of 1 mm; this recommendation has been met. Moreover, we have demonstrated that the isocentric accuracy and mechanical stability of the device are sufficient that the device on confidently be used in stereotactic treatment.     

Agro-ecology of onion couch (Arrhenathemm elatius var. bulbosum).

The agro-ecology of onion couch (Arrhenatherum elatius var. bulbosum), a well known weed of arable land is studied. Contribution of seeds from onion couch and a more widespread variety of Arrhenatherum elatius: tall oat-grass, towards future ingress of onion couch in arable fields has indicated that the tall oat-grass variety is not a potential weed of arable land. It appears that vegetative propagules rather than the seeds are the effective means of propagation of the onion couch variety in arable fields. An experiment performed to test any modifying effect of the soil texture indicated that onion couch is restricted to loamy soils and there is a complete absence from heavy clays and sandy soils. This could be due to the moist and protective micro-environment provided by the texture of the soils to partially buried vegetative propagules of onion couch, which are susceptible to drought.     

Assessment of dose error due to nylon mesh of treatment couch

PurposeThis study aims at the assessment of dose error in patients undergoing radiotherapy due to treatment couch of Co-60 teletherapy unit.Materials and methodsIn this study beam attenuation due to treatment couch of Co-60 unit was measured in air for different gantry angles and field sizes. Polymethylmethacrylate (PMMA) phantom was used to estimate the effect of depth on attenuation. Impact of couch on surface dose was also evaluated.ResultsBeam attenuation due to couch was in the range of 0.5–28% for different gantry angles with standard field size of 10 × 10 cm² with optimum position of metallic cranks. Maximum attenuation (29%) was observed with smallest field size i.e. 5 × 5 cm². Beam attenuation has been found higher in phantom as compared to that in air However, no particular trend of attenuation has been noted with varying depth of phantom. A 6% increase in surface dose has also been observed due to couch insertion for normal beam incidence. Maximum error of 80% is also note-worthy for most unfavorable situation of irradiation at 180 degree through the metallic cranks.ConclusionIt has been determined that ignoring the treatment couch and its accessories can result in dose error of 0.5–80%, depending on gantry angle, field size and position of couch accessories. Therefore, consideration of dose error due to couch during treatment planning is recommended.     

Exercise with and without gravitational gradient: evaluation with the new random access mass spectrometer (RAMS)

Gravity adds about 40-50 mmHg perfusion pressure to the arterial supply of the quadriceps muscles in the upright posture. This could have important implications in supply of blood flow during exercise. Recently, we have shown that when subjects exercise in the supine posture the rate of increase in VO2 is considerably slower then when cycling exercise takes place in the upright posture. The most probable explanation for this slower adaptation was the altered perfusion gradient. Indeed, when the perfusion gradient from heart to legs was restored by placing the lower part of the body of supine subjects in a negative pressure chamber, the rate of increase in VO2 returned to upright values. The hypothesis advanced from these studies was that skeletal muscle blood flow was reduced at the onset of supine exercise. Exercise in the microgravity environment of space should be similar to that in the supine posture. The only experiments conducted in space to this date that have addressed the question of cardiorespiratory adaptation to changing work rates were performed on the German D2 mission using the methodology proposed by Stegemann and colleagues. To conduct these experiments, it is necessary to utilize sensitive breath-by-breath technology. Recently, NASA and the Russian space programs have commissioned a new mass spectrometer based system as part of the GASMAP project. It was the purpose of this study to evaluate the new mass spectrometer under conditions in which the gravitational effects on the cardiorespiratory response were being challenged.     

Experimental optimization of pivot point height for swing-arm type rear suspensions in off-road bicycles

Towards the ultimate goal of designing dual suspension off-road bicycles which decouple the suspension motion from the pedaling action, this study focused on determining experimentally the optimum pivot point height for a swing-arm type rear suspension such that the suspension motion was minimized. Specific objectives were (1) to determine the effect of interaction between the front and rear suspensions on the optimal pivot point height, (2) to investigate the sensitivity of the optimal height to the pedaling mechanics of the rider in both the seated and standing postures, (3) to determine the dependence of the optimal height on the rider posture. Eleven experienced subjects rode a custom-built adjustable dual suspension off-road bicycle, [Needle, S., and Hull, M. L., 1997, "An Off-Road Bicycle With Adjustable Suspension Kinematics," Journal of Mechanical Design 119, pp. 370-375], on an inclined treadmill. The treadmill was set to a constant 6 percent grade at a constant velocity of 24.8 km/hr. With the bicycle in a fixed gear combination of 38 x 14, the corresponding cadence was 84 rpm. For each subject, the pivot point height was varied randomly while the motions across both the front and rear suspension elements were measured. Subjects rode in both the seated and standing postures and with the front suspension active and inactive. It was found that the power loss from the rear suspension at the optimal pivot point height was not significantly dependent on the interaction between the front and rear suspensions. In the seated posture, the optimal pivot point height was 9.8 cm on average and had a range of 8.0-12.3 cm. The average optimal pivot point height for the seated posture corresponded to an average power loss for the rear suspension that was within 10 percent of the minimum power loss for each subject for 8 of the 11 subjects. In the standing posture, the average height was 5.9 cm and ranged from 5.1-7.2 cm. The average heightfor the standing posture was within 10 percent of the minimum power loss for each subject for 9 of the 11 subjects. While the optimum height was relatively insensitive to pedaling mechanics in both the seated and standing postures, the choice of the optimal pivot point height in production bicycles necessitates some compromise in performance given the disparity in the averages between the seated and standing postures.     

Absorption ratio of treatment couch and effect on surface and build-up region doses

Aim

In this study, at different fields, energies and gantry angles, treatment couch and rails dose absorption ratio and treatment couch effect on surface and build-up region doses were examined.

Crossing the Hands Increases Illusory Self-Touch

Manipulation of hand posture, such as crossing the hands, has been frequently used to study how the body and its immediately surrounding space are represented in the brain. Abundant data show that crossed arms posture impairs remapping of tactile stimuli from somatotopic to external space reference frame and deteriorates performance on several tactile processing tasks. Here we investigated how impaired tactile remapping affects the illusory self-touch, induced by the non-visual variant of the rubber hand illusion (RHI) paradigm. In this paradigm blindfolded participants (Experiment 1) had their hands either uncrossed or crossed over the body midline. The strength of illusory self-touch was measured with questionnaire ratings and proprioceptive drift. Our results showed that, during synchronous tactile stimulation, the strength of illusory self-touch increased when hands were crossed compared to the uncrossed posture. Follow-up experiments showed that the increase in illusion strength was not related to unfamiliar hand position (Experiment 2) and that it was equally strengthened regardless of where in the peripersonal space the hands were crossed (Experiment 3). However, while the boosting effect of crossing the hands was evident from subjective ratings, the proprioceptive drift was not modulated by crossed posture. Finally, in contrast to the illusion increase in the non-visual RHI, the crossed hand postures did not alter illusory ownership or proprioceptive drift in the classical, visuo-tactile version of RHI (Experiment 4). We argue that the increase in illusory self-touch is related to misalignment of somatotopic and external reference frames and consequently inadequate tactile-proprioceptive integration, leading to re-weighting of the tactile and proprioceptive signals.The present study not only shows that illusory self-touch can be induced by crossing the hands, but importantly, that this posture is associated with a stronger illusion.     

Modeling of couch transmission in the RayStation treatment planning system

PurposeTo present our methods and results regarding the modeling of a carbon fiber couch (Varian Exact IGRT) in the RayStation treatment planning system (TPS).MethodsThree geometrical-models (GMs) were implemented in the TPS to represent the three different regions of the couch (thick, medium and thin). The materials and densities of each GM component were tuned to maximize the agreement between measured and calculated attenuations. Moreover, a couch computed-tomography (CT) scan was acquired and dosimetrically compared with the GMs. For validation, plan-specific quality assurance (QA) of VMAT plans (TG-119 cases, 5 prostate and 5 H&N clinical cases) was performed by comparing measured dose distributions with doses computed with and without including the GMs in the TPS.ResultsCouch attenuations up to 4.3% were measured (energy: 6MV). Compared to couch CT, GMs could be modified to optimize the agreement with measurements and reduce dependence on the dose grid resolution. For both couch CT and GM, absolute deviations between measured and calculated attenuations were within 1.0%. When including the GMs in plan-specific QA, global 2%/2 mm γ-pass rates showed an average improvement of 4.8% (p-value < 0.001, max +18.6%). The couch reduced the mean dose to targets by up to 2.4% of the prescribed dose for prostate cases and up to 1.4% for H&N cases.ConclusionsRayStation accurately considers the implemented couch GMs replicating measured attenuations within an uncertainty of 1.0%. Materials and densities are proposed for the Varian Exact IGRT couch. The results obtained justify introducing couch GMs in clinical routine.     

Mechanical quality assurance using light field for linear accelerators with camera calibration

Mechanical Quality Assurance (QA) is important to assure spatially precise delivery of external-beam radiation therapy. As an alternative to the conventional-film based method, we have developed a new tool for mechanical QA of LINACs which uses a light field rather than radiation. When light passes through the collimator, a shadow is projected onto a piece of translucent paper and the resulting image is captured by a digital camera via a mirror. With this method, we evaluated the position of the LINAC isocenter and the accuracy of the gantry, collimator, and couch rotation. We also evaluated the accuracy of the digital readouts of the gantry, collimator, and couch rotation. In addition, the treatment couch position indicator was tested. We performed camera calibration as an essential pre-requisite for quantitative measurements of the position of isocenter, the linear motion of the couch, and the rotation angles of the gantry and collimator. Camera calibration reduced the measurement error to submillimeter based on uncertainty in pixel size of the image, while, without calibration, the measurement error of up to 2 mm could occur for an object with a length of 5 cm.     

The optimum finger spacing in human swimming

Competitive swimmers spread fingers during the propulsive stroke. Due to the inherent inefficiency of human swimming, the question is: does this strategy enhance performance or is it just a more comfortable hand posture? Here we show, through computational fluid dynamics (CFD) of a 3D model of the hand, that an optimal finger spacing (12°, roughly corresponding to the resting hand posture) increases the drag coefficient (+8.8%), which is ‘functionally equivalent’ to a greater hand palm area, thus a lower stroke frequency can produce the same thrust, with benefits to muscle, hydraulic and propulsive efficiencies. CFD, through flow visualization, provides an explanation for the increased drag associated with the optimum finger spacing.     

Validation and practical implementation of seated position radiotherapy in a commercial TPS for proton therapy

PurposeThis work aims to validate new 6D couch features and their implementation for seated radiotherapy in RayStation (RS) treatment planning system (TPS).Materials and methodsIn RS TPS, new 6D couch features are (i) chair support device, (ii) patient treatment option of “Sitting: face towards the front of the chair”, and (iii) patient support pitch and roll capabilities. The validation of pitch and roll was performed by comparing TPS generated DRRs with planar x-rays. Dosimetric tests through measurement by 2D ion chamber array were performed for beams created with varied scanning and treatment orientation and 6D couch rotations. For the implementation of 6D couch features for treatments in a seated position, the TPS and oncology information system (Mosaiq) settings are described for a commercial chair. An end-to-end test using an anthropomorphic phantom was performed to test the complete workflow from simulation to treatment delivery.ResultsThe 6D couch features were found to have a consistent implementation that met IEC 61712 standard. The DRRs were found to have an acceptable agreement with planar x-rays based on visual inspection. For dose map comparison between measured and calculated, the gamma index analysis for all the beams was >95% at a 3% dose-difference and 3 mm distance-to-agreement tolerances. For an end-to end-testing, the phantom was successfully set up at isocenter in the seated position and treatment was delivered.ConclusionsChair-based treatments in a seated position can be implemented in RayStation through the use of newly released 6D couch features.