Validity of functional stability limits as a measure of balance in adults aged 23–73 years

Functional stability limits (FSLs) are the percentage of the base of support that individuals are willing to extend their centre of pressure. The objective of this study was to provide construct validation of FSLs as a measure of balance by comparing FSLs across ages and with clinical balance measures. A total of 52 participants volunteered. FSLs significantly decreased with age (p < 0.004). Correlations between FSLs and age (?0.56 < R < ?0.73), multi-directional reach test (0.35 < R < 0.75) and anteroposterior and mediolateral centre of pressure excursions during static stance (?0.29 < R < ?0.72) were generally moderate to good. Cronbach's alpha (0.75) indicated that these measures were internally consistent, i.e. measuring similar aspects of the balance construct. FSLs appear to be valid indicators of balance ability. They may be used in posture prediction models to determine when a step is required when reaching or lifting objects and in biomechanical models as a means of incorporating stability constraints.     

Investigation of the functional stability limits while squatting

This study investigates the functional stability limits (FSLs) in the squatting positions. Eleven male participants leaned and moved their pelvis horizontally in the clockwise and counter‐clockwise directions while squatting at 11 depth levels. The depth was controlled by changing the hip height from 100% to 0% of the upright position. The FSLs and the center of pressure excursion lengths were calculated from the force‐plate data, and the musculoskeletal loads on the lower limbs were estimated from the joint torques and surface electromyograms. As the hip height reduced, the area of the FSLs narrowed by up to 20% of the base of support (BOS) area at the deepest squatting position. The narrowing was affected by the decreasing FSLs in the forward direction, which also decreased by up to 20% of BOS. These quantitative data accurately evaluate the postural stability, suggesting a considerable fall risk during tasks requiring the squatting position.     

Probabilistic Grammars and Languages

Using an asymptotic characterization of probabilistic finite state languages over a one-letter alphabet we construct a probabilistic language with regular support that cannot be generated by probabilistic CFGs. Since all probability values used in the example are rational, our work is immune to the criticism leveled by Suppes (Synthese 22:95–116, 1970) against the work of Ellis (1969) who first constructed probabilistic FSLs that admit no probabilistic FSGs. Some implications for probabilistic language modeling by HMMs are discussed.     

Control of posture during tasks representing common work-related postures – a reliability study

Assessment of control of posture using a task battery that represents work-related postural conditions is highly recommended for providing a comprehensive understanding of collective postural demands. However, dearth of evidence exists on the reliability of a task battery, thus precluding its use as an outcome measure in field research. This study investigated the intrasession reliability and systematic variation of force plate derived centre of pressure (COP) measures obtained during repeated performance of a task battery (lifting task, limits of stability and bipedal and unipedal stance). COP signals obtained during each task performance were processed to derive various time-domain COP measures. Statistical analyses revealed that 13 of the 19 COP measures displayed excellent relative (ICC_(2,3) ≥ 0.75) and acceptable absolute reliability (SEM%: ≤ 10). Although COP measures displayed systematic variation, the differences were less or equal to the measurement error, except COP measures of unipedal stance and limits of stability. The chosen task battery is reliable and can be used for comprehensive evaluation of control of posture, in both field and laboratory research.

Practitioner Summary: Repeated evaluation of multiple tasks together sequentially could introduce measurement variability. This study investigated intrasession reliability of a task battery representing common work-related postures. The chosen task battery was found to be reliable with acceptable measurement error and can be used in field research settings for evaluation of control of posture.     

Application of decomposition methods in optimization

The problem of optimization of the composition of a production association of diverse enterprises is considered. The participating enterprises in the association model can be represented by relations of the input-output balance. Decomposition methods are used to construct models, describing the operation of such a system in the market environment for various methods of its regulation and to find conditions of asymptotic stability for the equilibrium. It is shown that this equilibrium coincides with the optimal solution to the global problem of the association, depending on the properties of the association balance matrix, the equilibrium can be inflationary rather than economical, when the production volume and income diminish to zero for rather high prices.     

Postural stability when walking: Effect of the frequency and magnitude of lateral oscillatory motion

While walking on an instrumented treadmill, 20 subjects were perturbed by lateral sinusoidal oscillations representative of those encountered in transport: frequencies in the range 0.5–2 Hz and accelerations in the range 0.1–2.0 ms⁻² r.m.s., corresponding to velocities in the range 0.032–0.16 ms⁻¹ r.m.s. Postural stability was assessed from the self-reported probability of losing balance (i.e., perceived risk of falling) and the movements of the centre of pressure beneath the feet. With the same acceleration at all frequencies, the velocities and displacements of the oscillatory perturbations were greater with the lower frequency oscillations, and these caused greater postural instability. With the same velocity at all frequencies, postural instability was almost independent of the frequency of oscillation. Movements of the centre of pressure show that subjects attempted to compensate for the perturbations by increasing their step width and increasing their step rate.     

Postural stability when walking and exposed to lateral oscillatory motion: benefits from hand supports

While walking on a treadmill, 20 subjects experienced lateral oscillations: frequencies from 0.5 to 2 Hz and velocities from 0.05 to 0.16 m s^? 1 rms. Postural stability was indicated by ratings of ‘discomfort or difficulty in walking’, the movement of the centre of pressure beneath the feet and lateral forces applied to a hand support. Hand support improved postural stability with all frequencies and all velocities of oscillatory motion: the lateral velocity of the centre of pressure reduced by 30–50% when using support throughout motion, by 20–30% when instructed to use the support only when required and by 15% during normal walking without oscillation. Improvements in stability, and the forces applied to the hand support, were independent of support height when used continuously throughout motion. When support was used only when required, subjects preferred to hold it 118–134 cm above the surface supporting the feet.     

Fall risk assessment of construction workers based on biomechanical gait stability parameters using wearable insole pressure system

Falls on the same level are a leading cause of non-fatal injuries in the construction industry, and loss of balance events are the primarily contributory risk factors associated with workers’ fall injuries. Previous studies have indicated that changes in biomechanical gait stability parameters provide substantial safety gait metrics for assessing workers’ fall risks. However, scant research has been conducted on changes in biomechanical gait stability parameters based on foot plantar pressure patterns to assess workers’ fall risks. This research examined the changes in spatial foot regions and loss of balance events associated with biomechanical gait stability parameters based on foot plantar pressure patterns measured by wearable insole pressure system. To test the hypotheses of this study, ten asymptomatic participants conducted laboratory simulated loss of balance events which are often initiated by extrinsic fall risk factors. Our results found: (1) statistically significant differences in biomechanical gait stability parameters between spatial foot regions, especially with the peak pressure parameter; and (2) statistically significant differences in biomechanical gait stability parameters between loss of balance events when compared to normal gait (baseline), especially with the pressure-time integral parameter. Overall, the findings of this study not only provide useful safety gait metrics for early detection of specific spatial foot regions but also allow safety managers to understand the mechanism of loss of balance events in order to implement proactive fall-prevention strategies.     

Calculating adjusted R(2) measures for Poisson regression models

In regression models not only the parameter estimates and significances of explanatory variables are of interest, but also the degree to which variation in the dependent variable can be explained by covariates. In recent publications, an R(2) measure based on deviance was recommended for Poisson regression models, one of the most frequently used modelling tools in epidemiological studies. However, when sample size is small relative to the number of covariates in the model, simple R(2) measures may be seriously inflated and may need to be adjusted according to the number of covariates in the model. We present a SAS-macro that calculates adjustments for the R(2) measures in Poisson regression models based on log-likelihood and on sums of squares. The proposed measures are applied to real data sets and their performance is discussed.     

Object-oriented class maintainability prediction using internal quality attributes

ContextClass maintainability is the likelihood that a class can be easily modified. Before releasing an object-oriented software system, it is impossible to know with certainty when, where, how, and how often a class will be modified. At that stage, this likelihood can be estimated using the internal quality attributes of a class, which include cohesion, coupling, and size. To reduce the future class maintenance efforts and cost, developers are encouraged to carefully test and well document low maintainability classes before releasing the object-oriented system.ObjectiveWe empirically study the relationship between internal class quality attributes (size, cohesion, and coupling) and an external quality attribute (class maintainability). Using statistical techniques, we also construct models based on the selected internal attributes to predict class maintainability.MethodWe consider classes of three open-source systems. For each class, we account for two actual maintainability indicators, the number of revised lines of code and the number of revisions in which the class was involved. Using 19 internal quality measures, we empirically explore the impact of size, cohesion, and coupling on class maintainability. We also empirically investigate the abilities of the measures, considered both individually and combined, to estimate class maintainability. Statistically based prediction models are constructed and validated.ResultsOur results demonstrate that classes with better qualities (i.e., higher cohesion values and lower size and coupling values) have better maintainability (i.e., are more likely to be easily modified) than those of worse qualities. Most of the considered measures are shown to be predictors of the considered maintainability indicators to some degree. The abilities of the considered internal quality measures to predict class maintainability are improved when the measures are combined using optimized multivariate statistical models.ConclusionThe prediction models can help software engineers locate classes with low maintainability. These classes must be carefully tested and well documented.     

基于需求敏感指数的供应链延保服务模式分析

从供应链管理的视角,应用博弈论对产品延保服务的4种模式建模,并引入了服务需求敏感指数进行分析。分析表明：不论需求敏感指数的大小,制造商始终愿意选择由零售商销售和提供的R模式;而零售商则需权衡各模式中需求敏感指数的大小关系,从中选择合适的模式;当各模式需求敏感指数相等但不大时,供应链系统以P3-M模式能赢得更多的市场需求和利润,而当需求指数较大时, R模式是供应链系统的最优选择。     

Impact of military type footwear and load carrying workload on postural stability

Postural stability has been shown to be impacted by footwear and task performed. This study analysed the impact of two military footwear, standard boot (STB) and minimalist boot (MTB) on postural stability, before (PRE) and after (POST) a load carriage task. Sixteen participants were tested for postural stability using sensory organisation and motor control tests on Neurocom Equitest?. Postural sway, equilibrium scores and postural latencies were analysed using a two-factor repeated measures ANOVA: boot type (STB-MTB)?×?time (PRE-POST) load carriage task. Significantly greater postural sway variables, lower balance scores and slower postural latencies were seen in STB and POST load carriage conditions (p?<?.05). The results suggest that MTB exhibited greater balance compared to STB in balance conditions that rely on somatosensory feedback and that balance is lowered after a load carriage task. Decrements in postural stability could be attributed to boot design characteristics and muscular exertion due to the load carriage task.

Practitioner Summary: Maintaining optimal postural stability is crucial in military. Impact of military footwear types and load carriage task on postural stability are addressed. Findings provide footwear design and physical exertion implications on postural stability leading to potential interventions that reduce postural stability decrements; thereby, reducing potential falls and fall related injuries.     

Measurement and prediction of single and multi-digit finger strength

Hand and finger strength has direct application in the design of human-machine interfaces involving the whole hand or single digits. Limited finger strength data is available, however, particularly for practical situations such as pinching and poking. A study was conducted in which strength in a variety of couplings was collected from 100 participants, in order to enhance and supplement the existing literature. Differences between couplings, gender, and age groups were evaluated. Strength was significantly higher for multi-digit couplings as compared with single digit couplings (p < 0.05). In addition, female strength was approximately 70% of male strength across all couplings. No significant differences were found between three age groups ranging from 18 to 40 + years old. Multiple regression models were used to determine whether finger strength could be predicted from other strength measures and anthropometry. Regression results suggest that finger strength can be predicted with only moderate accuracy using these variables (R2-adj: 0.45 - 0.64; standard error: 12 - 19 N). Such models are easy to implement, however, and begin to overcome the limitations of direct finger strength measurements.     

200MW燃煤机组协调控制系统的改进和应用

电网对电厂机组协调控制系统（CCS）有更高的要求,提出了CCS的改进措施：在锅炉主蒸汽压力控制回路上增加负荷指令的微分前馈信号,主汽压力变化较大时,通过改变负荷指令平衡压力等。这些措施的实施,改善了协调控制系统的调节品质,提高了系统对外界负荷适应能力,抑制了主蒸汽压力的超调。     

Physical load handling and listening comprehension effects on balance control

The purpose of this study was to determine the physical load handling and listening comprehension effects on balance control. A total of 16 young and 16 elderly participants were recruited in this study. The physical load handling task required holding a 5-kg load in each hand with arms at sides. The listening comprehension task involved attentive listening to a short conversation. Three short questions were asked regarding the conversation right after the testing trial to test the participants' attentiveness during the experiment. Balance control was assessed by centre of pressure-based measures, which were calculated from the force platform data when the participants were quietly standing upright on a force platform. Results from this study showed that both physical load handling and listening comprehension adversely affected balance control. Physical load handling had a more deleterious effect on balance control under the listening comprehension condition vs. no-listening comprehension condition. Based on the findings from this study, interventions for the improvement of balance could be focused on avoiding exposures to physically demanding tasks and cognitively demanding tasks simultaneously.

Statement of Relevance:Findings from this study can aid in better understanding how humans maintain balance, especially when physical and cognitive loads are applied. Such information is useful for developing interventions to prevent fall incidents and injuries in occupational settings and daily activities.     

Product from solutions for multiserver centres with concurrent classes of customers

The MultiServer centre with Concurrent Classes of Customers (MSCCC) is a service centre consisting of B parallel identical exponential servers. The customers requesting service at the MSCCC centre belong to K groups. Customers arriving at the MSCCC centre are queued in the order of their arrival. A customer from group k will go into service at the MSCCC centre provided that one or more of the B servers is free and that at most n − 1 other group k customers are in service at the MSCCC centre.

The MSCCC centre can be applied to model systems where customers simultaneously occupy two resources. The system resources are partitioned into K primary and B secondary resources. A customer of group k can access primary resource k if it already is in possession of a secondary resource and if at most n − 1 other group k customers are using primary resource k.

This paper defines the MSCCC centre and presents several examples of computer (sub)systems that can be modelled using the MSCCC centre. The MSCCC centre is shown to satisfy local balance: therefore a multiclass queuing network consisting of BCMP and MSCCC centres has a product form solution. The joint probability distribution (JPD) for a queuing network consisting of several BCMP centres and one MSCCC centre is derived. Aggregation techniques are next used to reduce the JPD to a computationally tractable form. A Mean Value Analysis algorithm is presented for calculating the closed and open chain performance measures at the MSCCC centre.     

The effect of sustained spinal load on intra-abdominal pressure and EMG characteristics of trunk muscles

Fourteen young male students (mean age 21 years, mean weight 69-4 kg, and mean height 175-4 cm) and 12 young female students (mean age 22-2 years, mean weight 60-6 kg, and mean height 169-3 cm) held 9-07 kg and 6-8 kg, respectively, at their three-quarters horizontal reach distance in upright and stooping postures for a period of 5 min. During these periods the external torque on the lumbosacral disc, intra-abdominal pressure, and electromyographic signals from erectores spinae at T₁₂ and L₃ levels, latissimus dorsi and external obliques were recorded at 1 kHz for 2-1 s every 15 s for a period of 5 min. The EMGs were processed in magnitude and time domains to determine muscle fatigue. Through the data obtained it was seen that the intra-abdominal pressure did not follow or reflect either the spinal load or the muscle activity. Based on the arguments presented, it was concluded that the intra-abdominal pressure does not appear to have a role of relieving the spine of some of its load. Instead, it is suggested that it is a dependent variable manifesting itself when mechanisms for spinal stability are evoked to overcome large voluntary and inertial loads.     

An instability theorem in the large

It is often difficult to construct a definite V(X) function which has a definite time-derivative. Also in practice it is often found that a simple, definite Liapunov function V(X), defined over some region It of state-space containing the equilibrium point, produces a time-derivative, V(X), which is either semi-definite over R or definite over a very restricted part of R. Thus neither asymptotic stability nor instability can be deduced throughout R. If a decreasing, definite V(X) functional is chosen, then this theorem enables instability to be determined if V(X) is semi-definite.     

A generalisation of Norton's theorem for multiclass queueing networks

Consider an arbitrary subset σ of service centres in a locally balanced multiclass queueing network for which a parametric analysis is to be undertaken. It is shown that the complete network only has to be solved once using the convolution algorithm, after which statistical measures for σ can be calculated repeatedly without re-evaluating the rest of the network. It has also been proved that the concept of replacing a subnetwork in a closed multiclass queueng network with a single composite service centre with a state dependent service rate (also called Norton's Theorem for queuing networks) is a very special case of the more general result mentioned above. An example is given in which the theoretical results are applied when σ is a subnetwork of a closed multiclass queueing network satisfying local balance.     

The stability of electric energy markets

Power system markets represented by dynamic equations provide insights into the market behavior which are not available from static models. In particular: (1) markets that are required to balance supply and demand precisely at all times may be unstable if one supplier exhibits economies of scale and will be unstable if two suppliers exhibit this behavior. The instability is characterized by one or more positive eigenvalues. (2) Markets where some energy imbalance is allowed to accumulate can exhibit an instability, depending on the exact values of time constants and delays in the system. (3) Congestion can be helpful from the perspective of stability: a market can become unstable in the eigenvalue sense if congestion is removed. (4) A power system (with stable electromechanical dynamic behavior when considered by itself) and market (by itself stable) can, when analyzed jointly, exhibit unstable behavior. Some of the instabilities alluded here are nothing more than fluctuations in demands and prices. However, fluctuations are likely to require larger security margins, thus greater costs to operate the system.