Granular size segregation in silos with and without inserts.

The storage of granular materials is a critical process in industry, which has driven research into flow in silos. Varying material properties, such as particle size, can cause segregation of mixtures. This work seeks to elucidate the effects of size differences and determine how using a flow-correcting insert mitigates segregation during silo discharge. A rotating table was used to collect mustard seeds discharged from a three-dimensional (3D)-printed silo. This was loaded with bidisperse mixtures of varying proportions. A 3D-printed biconical insert was suspended near the hopper exit to assess its effect on the flow. Samples were analysed to determine the mass fractions of small particle species. The experiments without the insert resulted in patterns consistent with segregation. Introducing the insert into the silo eliminated the observed segregation during discharge. Discrete element method simulations of silo discharge were performed with and without the insert. These results mirrored the physical experiment and, when complimented with coarse graining analysis, explained the effect of the insert. Most of the segregation occurs at the grain-air free surface and is driven by large velocity gradients. In the silo with an insert, the velocity gradient at the free surface is greatly reduced, hence, so is the degree of segregation.

The dynamics of granular flow from a silo with two symmetric openings.

The dynamics of granular flow in a rectangular silo with two symmetrically placed exit openings is investigated using particle image velocimetry (PIV), flow rate measurements and discrete element modelling (DEM). The flow of mustard seeds in a Perspex silo is recorded using a high-speed camera and the resulting image frames are analysed using PIV to obtain velocity, velocity divergence and shear rate plots. A change in flow structure is observed as the distance L between the two openings is varied. The mass flow rate is shown to be at a maximum at zero opening separation, decreasing as L is increased; it then reaches a minimum before rising to an equilibrium rate close to two times that of an isolated (non-interacting) opening. The flow rate experiment is repeated using amaranth and screened sand and similar behaviour is observed. Although this result is in contrast with some recent DEM and physical experiments in silo systems, this effect has been reported in an analogous system: the evacuation of pedestrians from a room through two doors. Our experimental results are replicated using DEM and we show that inter-particle friction controls the flow rate behaviour and explains the discrepancies in the literature results.

A first look into the influence of triathlon wetsuit on resting blood pressure and heart rate variability.

The purpose of this study was to investigate the effects of wearing a wetsuit on resting cardiovascular measures (blood pressure (BP), heart rate variability (HRV)). The influence of position (upright, prone) and wetsuit size were also explored. Participants (n=12 males, 33.3±12.1 years) had BP and HRV measured during six resting conditions: standing or prone while not wearing a wetsuit (NWS), wearing the smallest (SWS), or largest (LWS) wetsuit (based upon manufacturer guidelines). Heart rate was recorded continuously over 5-mins; BP was measured three times per condition. HRV was represented by the ratio of low (LF) and high (HF) frequency (LF/HF ratio); mean arterial pressure (MAP) was calculated. Each dependent variable was analyzed using a 2 (position) x 3 (wetsuit) repeated measures ANOVA (α=0.05). Neither HRV parameter was influenced by position x wetsuit condition interaction (p>0.05) and MAP was not influenced by position (p=0.717). MAP and LF/HF ratio were both influenced by wetsuit condition (p<0.05) with higher during SWS than NWS (p=0.026) while LF/HF ratio was lower during SWS compared to NWS (p=0.032). LF/HF ratio was influenced by position being greater during standing vs. prone (p=0.001). It was concluded that during resting while on land (i.e., not submerged in water), wearing a small, tight-fitting wetsuit subtlety altered cardiovascular parameters for healthy, normotensive subjects.

[Peripheral nerve injury and the degree of motor involvement in Parkinson's disease: a correlation study]. / Postizení periferního nervového systému a míra motorického postizení u Parkinsonovy nemocí: korelacní studie.

BACKGROUND: The aim of the study was to validate a hypothesis about the presence of a concomitant peripheral nerves injury in patients suffering from neurodegenerative disorders. The study was focused on the correlation between motor involvement in Parkinson's disease and peripheral nerves injury. METHODS AND RESULTS: 23 patients suffering from Parkinson's disease, which was diagnosed in terms of strict UK-PDBB criteria, were examined. There were 14 men (mean age: 57 years, mean age at the disease onset: 51 years, mean disease duration: 7 years, mean duration of dopaminergic treatment: 4 years) and 9 women (mean age: 67 years, mean age at the disease onset: 63 years, mean duration of disease: 4 years, mean duration of dopaminergic treatment: 1 year). Polyneuropathy was clinically present and confirmed using EMG examination in 10 patients (43.5 %), 5 men and 5 women. CONCLUSIONS: Our observation indicates that the neurodegenerative process can be involved not only in the degeneration of central nervous system, but also in the peripheral disorders in this population.

An integrated methodology to assess the benefits of urban green space.

The interrelated issues of urban sprawl, traffic congestion, noise, and air pollution are major socioeconomic problems faced by most European cities. A methodology is currently being developed for evaluating the role of green space and urban form in alleviating the adverse effects of urbanisation, mainly focusing on the environment but also accounting for socioeconomic aspects. The objectives and structure of the methodology are briefly outlined and illustrated with preliminary results obtained from case studies performed on several European cities.

Characteristics of shock attenuation during fatigued running.

The aim of this study was to examine shock attenuation before and after completing a maximal effort graded exercise test while running on a treadmill. Ten individuals ran before and after a maximal graded exercise test with running speed controlled between conditions. Transfer functions were calculated using surface-mounted accelerometers to represent shock attenuation. An accelerometer was mounted on the distal aspect of the tibia and another on the anterior aspect of the forehead. Ten strides were analysed in each condition for all participants. Paired t-tests were used to compare each dependent variable (shock attenuation, stride length, rate of oxygen consumption) between conditions (running before vs after the exercise test). Oxygen consumption was 16% greater when running after the graded exercise test (47.9 +/- 5.0 ml x kg(-1) x min(-1); mean+/-s) than when running before it (41.1 +/- 2.7 ml x kg(-1) x min(-1)) (P < 0.05). Stride length was similar during running before (2.71 +/- 0.15 m) and after (2.75 +/- 0.17 m) the graded exercise test (P > 0.05). Shock attenuation was, on average, 12% lower during running after (-9.8 +/- 2.6 dB) than before (-11.3 +/- 2.7 dB) the graded exercise test (P < 0.05). We conclude that less shock was attenuated during fatigued than non-fatigued running and that only subtle changes in stride length were made while fatigued.

Effects of injury proneness and task difficulty on joint kinetic variability.

PURPOSE: The purpose was to investigate the effects of lower extremity overuse injury proneness and landing height on the variability of selected joint moment characteristics. METHODS: Ten subjects from each of two groups (healthy and injury prone) performed 10 landings from a platform (heights: 50, 100, and 200% of maximum vertical jump). Force platform (1000 Hz) and video (200 Hz) information were collected and used to compute ankle, knee, and hip joint moment values during impact (0-100 ms post contact). Moment peak, time to peak, and impulse values were used to determine variability across 10 trials for each subject and height. MANOVAs and univariate follow-up tests were used to assess variability differences between groups and among heights. RESULTS: Results revealed ankle moment variability differences (P < or = 0.05; Tukey) between groups for peak and time to peak variables at the 100% and 50% heights, respectively. The injury-prone group exhibited greater variability for the peak variable, whereas the healthy group showed greater variability for the temporal variable. Groups also differed on the impulse variables (P < or = 0.02; MANOVA), but follow-up tests failed to determine specific joints or directions of differences. Both groups exhibited tendencies for greater variability (P < or = 0.05; Tukey) with increases in height up to 100% MVJ and decreases in variability with further height increases. CONCLUSIONS: Results suggest that groups differed in joint moment variability, possibly indicating a relationship between variability and overuse injuries, although the variables and directions of differences were inconsistent. For some variables, variability increased and then decreased with height increases for both groups, suggesting a range of heights within which the neuromuscular system adapted.

Contributions of lower extremity joints to energy dissipation during landings.

PURPOSE: The purpose of the study was to investigate changes in lower extremity joint energy absorption for different landing heights and landing techniques. METHODS: Nine healthy, active male subjects volunteered to perform step-off landings from three different heights (0.32 m, 2.5 m(-s); 0.62 m, 3.5 m(-s); and 1.03 m, 4.5 m(-s)) using three different landing techniques (soft, SFL; normal, NML; and stiff landing, STL). Each subject initially performed five NML trials at 0.62 m to serve as a baseline condition and subsequently executed five trials in each of the nine test conditions (3 heights x 3 techniques). RESULTS: The results demonstrated general increases in peak ground reaction forces, peak joint moments, and powers with increases in landing height and stiffness. The mean eccentric work was 0.52, 0.74, and 0.87 J x kg(-1) by the ankle muscles, and 0.94, 1.31, and 2.15 J x kg(-1) by the hip extensors, at 0.32, 0.62, and 1.03 m, respectively. The average eccentric work performed by the knee extensors was 1.21, 1.63, and 2.26 J x kg(-1) for the same three heights. CONCLUSIONS: The knee joint extensors were consistent contributors to energy dissipation. The ankle plantarflexors contributed more in the STL landings, whereas the hip extensors were greater contributors during the SFL landings. Also a shift from ankle to hip strategy was observed as landing height increased.

Lateralization of the P22/N30 precentral cortical component of the median nerve somatosensory evoked potentials is different in patients with a tonic or tremulous form of cervical dystonia.

Somatosensory evoked potentials (SEPs) of the median nerve were recorded in 40 patients with the tonic and tremulous form of torticollis and in 40 healthy volunteers. Polymyographic recordings of the activity of cervical muscles were performed in all patients with cervical dystonia to determine the dystonic and antagonistic muscles. Patient SEPs were recorded during abnormal head movement. SEPs in 20 healthy volunteers were recorded with the head in the middle position. SEPs in another 20 healthy volunteers were recorded with the head rotated 60 degrees to the right. The mean peak-to-peak amplitude values of the precentral P22/N30 and the postcentral N20/P25 complexes and their mean side-to-side ratios were calculated in the F3 (F4), C3' (C4'), and C3+ (C4+) electrode positions in all four groups. In patients with the tonic form of torticollis (group I), an apparent mean P22/N30 amplitude increase was found above the hemisphere contralateral to the direction of head deviation in both precentral electrode positions, F3(4) and C3(4)'. A statistically significant difference was observed between group I and other patient and control groups. In patients with the tremulous form of torticollis (group II), an increase in the mean P22/N30 amplitude was found above both hemispheres in both precentral electrode positions F3(4) and C3(4)'; a significant difference was found between group II and both control groups. Lateralization of the P22/N30 component was found only in patients with the tonic form of torticollis. The mean side-to-side ratio of the precentral P22/N30 component amplitude was significantly different when group I was compared with either group II or control groups. No significant difference between group II and either control group was found. No significant abnormalities in the postcentral N20/P25 component were found in either the dystonic patients or in healthy control subjects. These results might indicate a different pattern of cortex excitability in patients with tonic versus tremulous forms of torticollis and therefore may implicate different underlying pathophysiological mechanisms in these two forms of disorder.

Change in lateralization of the P22/N30 cortical component of median nerve somatosensory evoked potentials in patients with cervical dystonia after successful treatment with botulinum toxin A.

The precentral P22/N30 cortical component of the median nerve somatosensory evoked potentials (SEPs) was recorded in 16 patients (11 women and five men) suffering from cervical dystonia before and after botulinum toxin therapy. Cervical dystonia was diagnosed as idiopathic in all patients: 13 patients suffered from right-sided torticollis, and three suffered from left-sided torticollis. The amplitude of the P22/N30 component and the side-to-side ratio of amplitude values were measured. Normal values were obtained by acquiring measurements in two groups of healthy volunteers (n1 = 20 and n2 = 20). The recordings in the first control group were done with the patient's head in a normal position, whereas, in the second control group, the patient kept the head intentionally rotated 60 degrees to the right. Patients were treated with local injections of botulinum toxin A (BTX-A). The mean duration of treatment was 8.3 months, and the mean total amount of BTX injected was 295 U. The P22/N30 precentral component was repeatedly recorded in patients after head posture had been corrected to the normal plane by BTX-A treatment. The recordings showed that the amplitude of the P22/N30 precentral component recorded contralaterally to the direction of head deviation was significantly higher in patients before treatment than after treatment. Contralateral pretreatment amplitudes were also significantly higher (p < 0.01 and p < 0.05, respectively) than amplitudes in both groups of healthy volunteers. The mean side-to-side ratio of precentral P22/N30 component amplitudes was significantly higher in patients before treatment compared with after treatment and also compared with both control groups. These changes in dystonic patients probably reflect the direction of head rotation, the muscle pattern of torticollis, and the change in force of dystonic contraction after the treatment. The changes presumably could be the result of higher excitability of the precentral cortex contralateral to head rotation in patients with cervical dystonia and its change after successful BTX-A treatment.

Lateralization of the P22/N30 component of somatosensory evoked potentials of the median nerve in patients with cervical dystonia.

Somatosensory evoked potentials (SEPs) of the median nerve were recorded in 40 patients suffering from cervical dystonia and in 40 healthy volunteers as a control. Before recording the median nerve SEPs, polymyographic recordings were performed in all patients with cervical dystonia. The activity of cervical muscles was recorded, and the leading muscle of cervical dystonia was determined. Patients were divided into two groups according to the results of polymyography. The leading muscle was sternocleidomastoid in the first group and the splenius capitis in the second group. Patient SEPs were recorded during abnormal head rotation. SEPs in 20 healthy volunteers were recorded with the head in the middle position. SEPs of another 20 healthy volunteers were recorded with the head rotated 60 degrees to the right. The mean peak-to-peak amplitude values of the precentral P22/N30 complex and the mean ratio of the P22/N30 amplitudes between both hemispheres were calculated in the F3 (F4) and C3' (C4') electrode positions in all four groups. No significant lateralization of the precentral P22/ N30 component was found in either group of healthy volunteers. In dystonic patients in whom the sternocleidomastoid was determined as the leading muscle of dystonia, a statistically significant lateralization of the P22/N30 component toward the ipsilateral side of the leading muscle was found. In the group with the splenius capitis determined as the leading muscle of dystonia, a statistically significant lateralization of the P22/N30 component toward the contralateral side of the leading muscle was found. The possibility that the precentral cortex is activated differently in cervical dystonia patients who have different muscle patterns of dystonia is discussed.

Change in the pattern of cervical dystonia might be the cause of benefit loss during botulinum toxin treatment.

The muscular patterns of cervical dystonia were identified by polymyographic recordings in 76 patients before botulinum toxin treatment. The leading muscles were considered to be those which started dystonic movement and which showed constant and maximal activity during all dystonic movements. The dystonic muscles were repeatedly treated by local Injections of botulinum toxin. Sixteen patients showed (after repeated injections) loss of the benefit of local applications of botulinum toxin after various periods of time. Repeated polymyographic recordings were performed in these patients during the loss of the benefit of injected botulinum toxin. In four patients repeated polymyographic recordings showed an Identical pattern of cervical dystonia, but the activity of previously injected muscles was apparently decreased. In 12 patients only minimum or no activity was recorded in muscles which had previously been treated with botulinum toxin, but the pattern of cervical dystonia was changed. Different patterns of cervical dystonia with different leading muscles, but with identical directions of head deviation, were observed in six patients. In another six patients, the head deviation direction was to the opposite side and was accompanied by a change of the leading muscle and a change of the muscular pattern of dystonia. These results suggest either that dystonic activity from the cerebral generator changes to new effectors during the peripheral blockade of primary dystonic muscles, or that a change of generators at different levels of the CNS occurs. It may be neccessary to carry out repeated polymyographic recordings throughout the period of loss of benefit of previously successful local botulinum toxin injections.

Rapid susceptibility testing for nontuberculosis mycobacteria using flow cytometry.

We demonstrated previously that susceptibility testing of Mycobacterium tuberculosis could be accomplished within 24 h after the organisms were incubated with antituberculosis agents by using fluorescein diacetate (FDA) staining and flow cytometry. Continued studies have now shown that assay suspensions containing M. avium, M. fortuitum, M. gordonae, or M. marinum incubated with various concentrations of ciprofloxacin, clarithromycin, erythromycin, kanamycin, rifampin, tobramycin hydrolyzed less FDA than drug-free controls. Suspensions of treated and nontreated mycobacteria could be easily differentiated at 6 and 24 h after the initiation of the susceptibility assays by using FDA staining and flow cytometry. In addition, multiplication of the mycobacteria was not required to discern differences between drug-free suspensions of mycobacteria and those treated with antimycobacterial agents. The flow cytometric assay is simple, reproducible, and rapid.

The effects of sample size and variability on the correlation coefficient.

The purpose of the study was to investigate the effects of variability as a function of sample size on the Pearson product-moment correlation coefficient (PCC) under the assumption of a perfect relationship between two variables. The effects of sample size (subjects/trials) and variability on the PCC were demonstrated using a computer model. The model was also used to evaluate selected examples taken from the literature. The results indicated that variability in excess of 10% of the range for each variable resulted in a mean reduction of the shared variance by 50% or greater. Although sample size did not affect the mean PCC, it did have a dramatic effect on extreme percentile values producing unreliable results. These results indicate that a small PCC value can be an artifact of variability. It is suggested, therefore, that one should be cautious when stating conclusions regarding the relationship between two variables without having knowledge of the associated variabilities.

Landing models for volleyball players: a longitudinal evaluation.

The purpose of the study was to longitudinally evaluate lower extremity landing performance of elite volleyball players. Seven female members of a Division 1 NCAA volleyball team completed three data collection sessions (pre-, post-, off-season) during which they performed block-jumps on a dual force platform system (1000 Hz) while being simultaneously videotaped from the right sagittal view (200 Hz). Selected kinetic and lower extremity kinematic variables were calculated. Three dependent variables representing landing impact were identified: first (F 1) and second (F 2) maximum vertical force and knee joint range of motion (K(ROM)). A non-landing performance measure, jump height was also evaluated. Results of repeated measures univariate ANOVAs identified a significant (p < 0.05) difference for test session for K(ROM) suggesting a kinematic change in landing performance across the season. Multiple regression models to predict landing impact identified 88.1 and 98.3% explained variance for F1 and F2 with no significant K(ROM) model identified. F1 was predicted by ankle joint angular velocity during the jump while F2 was best predicted by jump phase braking impulse. Application of the group prediction equations to individual athletes produced differential results across subjects, suggesting the need to tailor the model to the athlete. The results further suggest training/practice-related kinematic differences and have implications for training and assessment of individuals who perform dynamic landing activities.

The effect of trial size and variability on statistical power.

A computer model was developed, validated, and used in conjunction with Monte Carlo procedures to study the effects of sample size (subjects and trials), mean differences, and subject variability on statistical power. Also examined were the differences between single subject (SS) and group results. Mean differences were varied from 1/4 to 4 times the distribution SD resulting in improved power values. Mean group F results ranged from 63.6% to 100% while SS results were poorer, especially for the smaller mean differences (16.8%-100%). Subject variability was examined for a Simple model and two Complex (MOD1 and MOD4) models. MOD1 produced group results similar to the corresponding Simple model with an overall mean of 78.2% and a Complex/Simple (C/S) ratio of 0.99. The more variable model (MOD4) produced fewer significant results (52.9%) and a lesser C/S ratio (0.82). The SS results were more dramatic. The percentages of significant values were less (38.1% and 33.9%) and the C/S ratios favored the Complex models (1.48 and 3.17). Both sample size and trial size had a major impact on the results. In summary, these results provide additional insight into the interactive effects and importance of the factors investigated, especially in the area of SS experiments.

Bilateral performance symmetry during drop landing: a kinetic analysis.

The assumption that lower extremity function is bilaterally symmetrical is prevalent throughout the biomechanics literature. The unilateral development of many overuse and acute injuries may suggest that this assumption is inaccurate. Analyses of bilateral function report conflicting results and may be partially attributable to the types of movement activities utilized and to research methodology. The purpose of this study was to evaluate the concurrent bilateral performance of the lower extremities during an apparently symmetrical movement task. Concurrent left/right side vertical ground reaction forces (VGRF) and lower extremity joint moments (JM) were obtained for 10 subjects performing 25 voluntary hanging drop landings (60 cm) on each of 3 consecutive days. Bilateral variability (BV) and systematic bilateral asymmetry (BA) were calculated for each trial. Bilateral variability was less for VGRF variables (12.8%) than JM variables (25.3%). Bilateral asymmetry was identified more often among VGRF variables (52.5%) than JM variables (16.7%). The magnitude of identified BA was greater than either the group BV (25%) or BA (110%) and indicates that bilateral differences are biomechanically meaningful.

Evaluation of time-series data sets using the Pearson product-moment correlation coefficient.

The Pearson product-moment correlation has been used by researchers to compare time series data sets to assess the temporal similarities. Computer generated data, vertical ground reaction force (VGRF) data and hybrid data (constructed by combining features of computer generated and VGRF data) were used to investigate the influence of timing and amplitude differences on the effectiveness of this technique. Under a specific set of conditions the correlation coefficient is a valid and reliable indicator of temporal similarity. Deviations from these conditions, however, result in interactive effects between timing and amplitude components with subsequent reductions in the value of the coefficient. Although GRF data were evaluated, the results apply equally to other types of curves as well. The correlation coefficient is easy to use and can be used to evaluate the entire curve as opposed to discrete data points. Its usefulness is jeopardized, however, since it can be influenced by timing and amplitude differences as well as the characteristics of the curves being analyzed. A high coefficient is always indicative of temporal similarity but a lesser value does not guarantee a lack of temporal similarity.

The effect of trial size on statistical power.

Many research studies produce results that falsely support a null hypothesis due to a lack of statistical power. The purpose of this research was to demonstrate selected relationships between single subject (SS) and group analyses and the importance of data reliability (trial size) on results. A computer model was developed and used in conjunction with Monte Carlo procedures to study the effects of sample size (subjects and trials), within- and between-subject variability, and subject performance strategies on selected statistical evaluation procedures. The inherent advantages of the approach are control and replication. Selected results are presented in this paper. Group analyses on subjects using similar performance strategies identified 10, 5, and 3 trials for sample sizes of 5, 10, and 20, respectively, as necessary to achieve statistical power values greater than 90% for effect sizes equal to one standard deviation of the condition distribution. SS analyses produced results exhibiting considerably less power than the group results for corresponding trial sizes, indicating how much more difficult it is to detect significant differences using a SS design. These results should be of concern to all investigators especially when interpreting nonsignificant findings.