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Relative Degree (relative + degree)
Selected AbstractsRegulation of cerebral blood flow in mammals during chronic hypoxia: a matter of balanceEXPERIMENTAL PHYSIOLOGY, Issue 2 2010Philip N. Ainslie Respiratory-induced changes in the partial pressures of arterial carbon dioxide and oxygen play a major role in cerebral blood flow (CBF) regulation. Elevations in (hypercapnia) lead to vasodilatation and increases in CBF, whereas reductions in (hypocapnia) lead to vasoconstriction and decreases in CBF. A fall in (hypoxia) below a certain threshold (<40,45 mmHg) also produces cerebral vasodilatation. Upon initial exposure to hypoxia, CBF is elevated via a greater relative degree of hypoxia compared with hypocapnia. At this point, hypoxia-induced elevations in blood pressure and loss of cerebral autoregulation, stimulation of neuronal pathways, angiogenesis, release of adenosine, endothelium-derived NO and a variety of autocoids and cytokines are additional factors acting to increase CBF. Following 2,3 days, however, the process of ventilatory acclimatization results in a progressive rise in ventilation, which increases and reduces , collectively acting to attenuate the initial rise in CBF. Other factors acting to lower CBF include elevations in haematocrit, sympathetic nerve activity and local and endothelium-derived vasoconstrictors. Hypoxia-induced alterations of cerebrovascular reactivity, autoregulation and pulmonary vascular tone may also affect CBF. Thus, the extent of change in CBF during exposure to hypoxia is dependent on the balance between the myriad of vasodilators and constrictors derived from the endothelium, neuronal innervations and perfusion pressure. This review examines the extent and mechanisms by which hypoxia regulates CBF. Particular focus will be given to the marked influence of hypoxia associated with exposure to high altitude and chronic lung disease. The associated implications of these hypoxia-induced integrative alterations for the regulation of CBF are discussed, and future avenues for research are proposed. [source] Acheulean artifact accumulation and early hominin land use, Garden Route Casino Road, Pinnacle Point, South AfricaGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 4 2009Erin Thompson An Early Stone Age Acheulean lithic assemblage collected along a 1.5-km transect at the Garden Route Casino near Pinnacle Point, Mossel Bay, South Africa, was examined in order to assess the relative degree to which assemblage variability is impacted by post-occupational processes and/or terrain. It was found that post-occupational variables do vary across the study area, and they affect the positions of artifacts to different degrees. Terrain structure was determined to have minimal effect on artifact movement. Three analysis sections were identified as having artifacts that were likely close to their original positions and compositions. Future interpretations of differential land use can now be tempered with considerations of the post-occupational processes that formed the recovered assemblage. © 2009 Wiley Periodicals, Inc. [source] Adaptive controller design and disturbance attenuation for SISO linear systems with zero relative degree under noisy output measurementsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 4 2010Sheng Zeng Abstract In this paper, we present robust adaptive controller design for SISO linear systems with zero relative degree under noisy output measurements. We formulate the robust adaptive control problem as a nonlinear H, -optimal control problem under imperfect state measurements, and then solve it using game theory. By using the a priori knowledge of the parameter vector, we apply a soft projection algorithm, which guarantees the robustness property of the closed-loop system without any persistency of excitation assumption of the reference signal. Owing to our formulation in state space, we allow the true system to be uncontrollable, as long as the uncontrollable part is stable in the sense of Lyapunov, and the uncontrollable modes on the j,-axis are uncontrollable from the exogenous disturbance input. This assumption allows the adaptive controller to asymptotically cancel out, at the output, the effect of exogenous sinusoidal disturbance inputs with unknown magnitude, phase, and frequency. These strong robustness properties are illustrated by a numerical example. Copyright © 2009 John Wiley & Sons, Ltd. [source] On sliding mode observers for systems with unknown inputsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 8-9 2007T. Floquet Abstract This paper considers the problem of designing an observer for a linear system subject to unknown inputs. This problem has been extensively studied in the literature with respect to both linear and nonlinear (sliding mode) observers. Necessary and sufficient conditions to enable a linear unknown input observer to be designed have been established for many years. One way to express these conditions is that the transfer function matrix between the unknown input and the measured output must be minimum phase and relative degree one. Identical conditions must be met in order to design a ,classical' sliding mode observer for the same problem. This paper shows how the relative degree condition can be weakened if a classical sliding mode observer is combined with sliding mode exact differentiators to essentially generate additional independent output signals from the available measurements. A practical example dedicated to actuator fault detection and identification of a winding machine demonstrates the efficacy of the approach. Copyright © 2007 John Wiley & Sons, Ltd. [source] Direct adaptive command following and disturbance rejection for minimum phase systems with unknown relative degreeINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 1 2007Jesse B. Hoagg Abstract This paper considers parameter-monotonic direct adaptive command following and disturbance rejection for single-input single-output minimum-phase linear time-invariant systems with knowledge of the sign of the high-frequency gain (first non-zero Markov parameter) and an upper bound on the magnitude of the high-frequency gain. We assume that the command and disturbance signals are generated by a linear system with known characteristic polynomial. Furthermore, we assume that the command signal is measured, but the disturbance signal is unmeasured. The first part of the paper is devoted to a fixed-gain analysis of a high-gain-stabilizing dynamic compensator for command following and disturbance rejection. The compensator utilizes a Fibonacci series construction to control systems with unknown-but-bounded relative degree. We then introduce a parameter-monotonic adaptive law and guarantee asymptotic command following and disturbance rejection. Copyright © 2006 John Wiley & Sons, Ltd. [source] Model reference adaptive iterative learning control for linear systemsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 9 2006A. Tayebi Abstract In this paper, we propose a model reference adaptive control (MRAC) strategy for continuous-time single-input single-output (SISO) linear time-invariant (LTI) systems with unknown parameters, performing repetitive tasks. This is achieved through the introduction of a discrete-type parametric adaptation law in the ,iteration domain', which is directly obtained from the continuous-time parametric adaptation law used in standard MRAC schemes. In fact, at the first iteration, we apply a standard MRAC to the system under consideration, while for the subsequent iterations, the parameters are appropriately updated along the iteration-axis, in order to enhance the tracking performance from iteration to iteration. This approach is referred to as the model reference adaptive iterative learning control (MRAILC). In the case of systems with relative degree one, we obtain a pointwise convergence of the tracking error to zero, over the whole finite time interval, when the number of iterations tends to infinity. In the general case, i.e. systems with arbitrary relative degree, we show that the tracking error converges to a prescribed small domain around zero, over the whole finite time interval, when the number of iterations tends to infinity. It is worth noting that this approach allows: (1) to extend existing MRAC schemes, in a straightforward manner, to repetitive systems; (2) to avoid the use of the output time derivatives, which are generally required in traditional iterative learning control (ILC) strategies dealing with systems with high relative degree; (3) to handle systems with multiple tracking objectives (i.e. the desired trajectory can be iteration-varying). Finally, simulation results are carried out to support the theoretical development. Copyright © 2006 John Wiley & Sons, Ltd. [source] Closed-loop iterative learning control for non-linear systems with initial shiftsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 7 2002Mingxuan Sun Abstract This paper is concerned with the problem of the iterative learning control with current cycle feedback for a class of non-linear systems with well-defined relative degree. The tracking error caused by a non-zero initial shift is detected as extended D-type learning algorithm is applied. The defect is overcome by adding terms including the output error, its derivatives as well as integrals. Asymptotic tracking of the final output to the desired trajectory is guaranteed. As an alternative approach, an initial rectifying action is introduced in the extended D-type learning algorithm and shown effective to achieve the desired trajectory jointed smoothly with a transitional trajectory from the starting position. Also these algorithms with adjustable tracking interval ensure better robustness performance in the presence of initial shifts. Numerical simulation is conducted to demonstrate the theoretical results. Copyright © 2002 John Wiley & Sons, Ltd. [source] Model reference adaptive control using a low-order controllerINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 3 2001Daniel E. Miller Abstract In the model reference adaptive control problem, the goal is to force the error between the plant output and the reference model output asymptotically to zero. The classical assumptions on a single-input,single-output (SISO) plant is that it is minimum phase, and that the plant relative degree, the sign of the high-frequency gain, and an upper bound on the plant order are known. Here we consider a modified problem in which the objective is weakened slightly to that of requiring that the asymptotic value of the error be less than a (arbitrarily small) pre-specified constant. Using recent results on the design of generalized holds for model reference tracking, here we present a new switching adaptive controller of dimension two which achieves this new objective for every minimum phase SISO system; no structural information is required. Copyright © 2001 John Wiley & Sons, Ltd. [source] Tamoxifen and contralateral breast cancer in BRCA1 and BRCA2 carriers: An updateINTERNATIONAL JOURNAL OF CANCER, Issue 9 2006Jacek Gronwald Abstract Women with a mutation in BRCA1 or BRCA2 face a lifetime risk of breast cancer of ,80%, and following the first diagnosis the10-year risk of contralateral breast cancer is ,30%. It has been shown that both tamoxifen and oophorectomy prevent contralateral breast cancer, but it is not clear whether there is a benefit in giving tamoxifen to women who have previously undergone an oophorectomy. Furthermore, the relative degree of protection in BRCA1 and BRCA2 carriers has not been well evaluated. We studied 285 women with bilateral breast cancer and a BRCA1 or BRCA2 mutation, and 751 control women with unilateral breast cancer and a BRCA1 or BRCA2 mutation in a matched case-control study. Control women were of similar age and had a similar age of diagnosis of breast cancer and had been followed for as long as the case for a second primary breast cancer. The history of tamoxifen use for treating the first breast cancer was compared between bilateral and unilateral cases. The multivariate odds ratio for contralateral breast cancer associated with tamoxifen use was 0.50 for carriers of BRCA1 mutations (95% CI, 0.30,0.85) and was 0.42 for carriers of BRCA2 mutations (95% CI, 0.17,1.02). The protective effect of tamoxifen was not seen among women who had undergone an oophorectomy (OR = 0.83; 95%CI, 0.24,2.89) but this subgroup was small. In contrast, a strong protective effect of tamoxifen was apparent among women who were premenopausal or who had undergone natural menopause (OR = 0.44; 95% CI, 0.27,0.65). © 2005 Wiley-Liss, Inc. [source] Relative uncertainty aversion and additively representable set rankingsINTERNATIONAL JOURNAL OF ECONOMIC THEORY, Issue 2 2006Walter Bossert D81 This paper proposes a definition of relative uncertainty aversion for decision models under complete uncertainty. It is shown that, for a large class of decision rules characterized by a set of plausible axioms, the new criterion yields a complete ranking of those rules with respect to the relative degree of uncertainty aversion they represent. In addition, we address a combinatorial question that arises in this context, and we examine conditions for the additive representability of our rules. [source] Antidepressant efficacy and cognitive effects of repetitive transcranial magnetic stimulation in vascular depression: an open trialINTERNATIONAL JOURNAL OF GERIATRIC PSYCHIATRY, Issue 9 2004I. Fabre Abstract Background Beneficial effects of repetitive transcranial magnetic stimulation (rTMS) were demonstrated by many controlled studies in major depression. Moreover, this promising and non invasive therapeutic tool seems to be better tolerated than electroconvulsive therapy. Vascular depression is a subtype of late-life depression, associated with cerebrovascular disease and means a poorer response to antidepressant treatment. We employed rTMS over the left prefrontal cortex in 11 patients with late-onset resistant vascular depression. The primary purpose of this two-week open study was to examine antidepressant efficacy of rTMS in vascular depression. The secondary aim was to evaluate cognitive effects of rTMS in our sample. Methods Clinical status, as measured with the Hamilton Depression Rating Scale (HDRS), and cognitive effects, as evaluated by neuropsychological tests, were assessed at baseline and after two weeks of rTMS. Brain measurements to obtain an index of prefrontal atrophy were performed at both the motor cortex and prefrontal cortex. Results Five out of 11 resistant patients with late-onset vascular depression were responders. They showed a clinically meaningful improvement in HDRS scores, with a decrease of 11, 4 points (p<0.01). Antidepressant response is correlated to the relative degree of prefrontal atrophy (p = 0.05). After two weeks, verbal fluency and visuospatial memory improved. No cognitive performance deteriorated except for verbal memory, as the delayed recall decreased significantly in the responders' group. Conclusions Our preliminary observations prompt to perform a subsequent controlled study to examine if rTMS may constitute an alternative to electroconvulsive therapy. Copyright © 2004 John Wiley & Sons, Ltd. [source] A model reference robust control with unknown high-frequency gain signINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 12 2010Jiang Xu Abstract In this paper, we discuss the model reference robust control (MRRC) for plants with unknown high-frequency gain sign. Based on an appropriate monitoring function, a switching scheme is proposed so that after a finite number of switching, for plants with relative degree one, the tracking error converges to zero exponentially, while for plants with relative degree greater than one, it converges exponentially to a residual set that can be made arbitrarily small by properly choosing some design parameters. Copyright © 2009 John Wiley & Sons, Ltd. [source] On an output-feedback stabilization problem with uncertainty in the relative degreeINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 7 2008Giorgio Bartolini Abstract This paper deals with an output-feedback finite-time control problem for a class of nonlinear uncertain systems whose relative degree is affected by an uncertain system parameter and is therefore unknown at the stage of control design. We show that an existing second-order sliding mode control algorithm can address successfully the control task of a finite-time output-feedback stabilization when the uncertain relative degree is equal to 1 or 2. We derive constructive tuning rules for the control parameters and show its effectiveness by using computer simulations. Copyright © 2007 John Wiley & Sons, Ltd. [source] Boundedness in Lurie system with stiffening nonlinearitiesINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 6 2008Abdallah Ben Abdallah Abstract In this paper, we deal with the problem of boundedness of solutions in single-input single-output Lurie system. We prove the boundedness of solutions from the stability of zero dynamics under a restriction on the nonlinearity. The linear block is supposed to be of relative degree one or two, stabilizable by high-gain output feedback and not necessary minimum phase. The nonlinearity is required to have the stiffening property. Copyright © 2007 John Wiley & Sons, Ltd. [source] New results in robust actuator fault reconstruction for linear uncertain systems using sliding mode observersINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 14 2007Kok Yew Ng Abstract This paper presents a robust actuator fault reconstruction scheme for linear uncertain systems using sliding mode observers. In existing work, fault reconstruction via sliding mode observers is limited to either linear certain systems subject to unknown inputs, relative degree one systems or a specific class of relative degree two systems. This paper presents a new method that is applicable to a wider class of systems with relative degree higher than one, and can also be used for systems with more unknown inputs than outputs. The method uses two sliding mode observers in cascade. Signals from the first observer are processed and used to drive the second observer. Overall, this results in actuator fault reconstruction being feasible for a wider class of systems than using existing methods. A simulation example verifies the claims made in this paper. Copyright © 2007 John Wiley & Sons, Ltd. [source] Discrete output feedback sliding-mode control with integral actionINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 1 2006Nai One Lai Abstract This paper presents a novel approach to the problem of discrete time output feedback sliding-mode control design. The method described applies to uncertain systems (with matched uncertainties) which are not necessarily minimum phase or relative degree one. A new sliding surface is proposed, which is associated with the equivalent control of the output feedback sliding-mode controller. Design freedom is available to select the sliding surface parameters to produce an appropriate reduced-order sliding motion. In order for this to be achieved, a static output feedback condition associated with a certain reduced-order system obtained from the original plant must be solvable. The practicality of the results are demonstrated through the implementation of the controller on a small DC motor test rig. Copyright © 2005 John Wiley & Sons, Ltd. [source] Sampled-data iterative learning control with well-defined relative degreeINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 8 2004Mingxuan Sun Abstract This paper addresses the problem of iterative learning control with well-defined relative degree. The solution is a family of sampled-data learning algorithms using lower-order differentiations of the tracking error with the order less than the relative degree. A unified convergence condition for the family of learning algorithms is derived and is proved to be independent of the highest order of the differentiations. In the presence of initial condition errors, the system output is ensured to converge to the desired trajectory with a specified error bound at each sampling instant. The bound will reduce to zero whenever the bound on initial condition errors tends to zero. Numerical examples are provided to illustrate the tracking performance of the proposed learning algorithms. Copyright © 2004 John Wiley & Sons, Ltd. [source] Effect of caking and stickiness on the retention of spray-dried encapsulated orange peel oilJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2003César I Beristain Abstract Flavour microcapsules containing amorphous carbohydrate as wall material can undergo changes such as crystallisation, clumping, sticking and caking during handling and storage. Such physical changes may lead to the release of entrapped flavours. The objective of this study was to investigate the effect of storage temperature and water activity on caking, stickiness and glass transition temperatures and to evaluate the relative degree of protection provided to orange peel oil entrapped in mesquite (Prosopis juliflora) gum by spray drying. The powders were stored at water activities (aw) ranging from 0.108 to 0.972 at 25 and 35 °C. The surface caking temperature (Tsc) and advance caking temperature (Tac) were determined by the modified ampoule and sealed glass tube methods respectively. The glass transition temperature was determined by differential scanning calorimetry. Changes in the amount of encapsulated oil were determined by Clevenger hydrodistillation. As expected, both Tsc and Tac decreased with increasing storage aw. Above aw 0.628 the powders caked and collapsed during storage at 35 °C. Below aw 0.628 the capsules were not damaged and high retention levels (above 90%) were obtained. Increasing aw in the range 0.743,0.972 caused progressive dissolution of the wall polymer, and the retention level dropped sharply. The volatiles are protected and retained by mesquite gum as long as the capsule structure remains intact. Copyright © 2003 Society of Chemical Industry [source] Incorporating a class of constraints into the dynamics of optimal control problemsOPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 6 2009K. Graichen Abstract A method is proposed to systematically transform a constrained optimal control problem (OCP) into an unconstrained OCP, which can be treated in the standard calculus of variations. The considered class of constraints comprises up to m input constraints and m state constraints with well-defined relative degree, where m denotes the number of inputs of the given nonlinear system. Starting from an equivalent normal form representation, the constraints are incorporated into a new system dynamics by means of saturation functions and differentiation along the normal form cascade. This procedure leads to a new unconstrained OCP, where an additional penalty term is introduced to avoid the unboundedness of the saturation function arguments if the original constraints are touched. The penalty parameter has to be successively reduced to converge to the original optimal solution. The approach is independent of the method used to solve the new unconstrained OCP. In particular, the constraints cannot be violated during the numerical solution and a successive reduction of the constraints is possible, e.g. to start from an unconstrained solution. Two examples in the single and multiple input case illustrate the potential of the approach. For these examples, a collocation method is used to solve the boundary value problems stemming from the optimality conditions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Psychosocial Differences Between High-Risk Acute vs.PAIN PRACTICE, Issue 2 2008Chronic Low Back Pain Patients ,,Abstract: The present study was designed to evaluate the relative degree and type of emotional distress in high-risk acute low back pain (ALBP) subjects (defined as less than 3 months since initial injury) vs. high-risk chronic low back pain (CLBP) subjects (defined as greater than 3 months since initial injury). It is an extension of earlier findings that demonstrated the significant role that such emotional distress may play in the development of CLBP disability if not appropriately treated in the acute phase. This work stems from a conceptual three-stage model, which characterizes the progression from acute to chronic pain. Several psychosocial measures were administered that included information allowing for the classification of subjects as high-risk based upon an earlier developed screening algorithm. The ancova procedure in SPSS was used to compare groups, controlling for gender, ethnicity, and age. Results revealed that CLBP subjects had higher rates of certain measures of emotional distress and depression relative to ALBP subjects. These findings further support the importance of effectively managing emotional distress factors early, when treating musculoskeletal disorders such as low back pain.,, [source] Punctuated Equilibrium, Bureaucratization, and Budgetary Changes in SchoolsPOLICY STUDIES JOURNAL, Issue 1 2004Scott E. Robinson For half of a century, models of nonrational behavior have grown in popularity for explaining the behavior of administrative organizations. However, models of nonrational behavior are notoriously difficult to test because nonrational behavior is often difficult to separate from fully rational behavior. Recent research has suggested that particular types of nonrational processes should produce "punctuated" equilibria rather than "instantaneous" equilibria. In these nonrational processes, a decision maker underresponds to changes for a long period of time. Once pressure for change becomes overwhelming, the decision maker adopts a radical change. This is called "punctuation." The key to identifying this type of nonrationality of a process's rationality is the comparative success of fitting the observed behavior to "punctuated" rather than "instantaneous" equilibria. True, Jones, and Baumgartner (1999) developed a method for comparing the distribution of decision outputs as a strategy for assessing the relative degree of "punctuation" in the decision processes. By assessing the kurtosis (or "peakedness") of the distribution of decision outputs, one can get a sense of the excess (compared with a standard, normal distribution) of low and high rates of change,a sign of punctuated equilibrium. This article extends these recent developments by adapting the method to a comparative kurtosis framework. The results suggest that bureaucracy in K,12 schools serves to reduce (rather than amplify) the punctuations in budgeting processes. The article concludes with a discussion of the potential extension of the empirical results and modifications to the testing procedure. [source] Influence of the cooling conditions on the temperature and crystallinity profiles generated in a sisal fiber reinforced-polycaprolactone/starch molded partPOLYMER COMPOSITES, Issue 5 2004V. P. Cyras In this work, we performed the simulation of the temperature and relative degree of crystallinity developed across the thickness of a sisal fiber reinforced-polycaprolactone/starch (30%SF-PCL/S) molded part under different cooling conditions. The non-isothermal kinetic model of Kamal and Chu (13) was used to predict the degree of crystallinity profiles. In order to obtain the temperature profiles, the energy equation was solved by treating the composite as a continuum using mass averaged physical properties. The results indicated that for cooling at a constant wall temperature, gradient-less crystallinity profiles for a wall temperature of 283 K and thicknesses lower than 10 mm are obtained. On the other hand, when cooling at a constant cooling rate, paired degree of crystallinity pieces can be obtained only for thicknesses lower than 2 mm. The continuum numerical approach used herein has the ability of predicting the optimal cooling cycle for manufacturing thick and crystallinity gradient-less SF-PCL/S parts. Polym. Compos. 25:461,469, 2004. © 2004 Society of Plastics Engineers. [source] Diversity, abundance, and size structure of bivalve assemblages in the Sipsey River, Alabama,AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2010Wendell R. Haag Abstract 1.Patterns of mussel diversity and assemblage structure in the Sipsey River, Alabama, are described. Qualitative data were used to describe river-wide patterns of diversity. Quantitative data were used to describe the structure of mussel assemblages at several sites based on whole-substrate sampling that ensured all size classes were detected. 2.Major human impacts to the stream are limited to apparent effects of coal mining in the headwaters and the impoundment of the lower 9,km of the river by a dam on the Tombigbee River. These impacts resulted in a sharp decline in mussel diversity in the headwaters, and extirpation or decline of populations of several large-river species in the lower river that were probably dependent on colonization from the Tombigbee River. 3.Despite localized impacts, mussel assemblages throughout much of the river appear to be mostly intact and self-sustaining. These assemblages have several attributes that differ substantially from those in more degraded streams: (1) high retention of historical species richness; (2) gradual, longitudinal increase in species richness from upstream to downstream, resulting in distinctive headwater and downstream assemblages; (3) ubiquity of most species within particular river segments; (4) low dominance and high evenness with large populations of many species; and (5) frequent recruitment for most species resulting in occurrence of individuals in many size classes. 4.Few detailed and demographically unbiased descriptions of relatively intact mussel assemblages exist. We propose that characteristics described in the Sipsey River can be used as a baseline comparison for assessing relative degree of assemblage alteration in other streams and can serve as goals for restoration efforts. Published in 2010 by John Wiley and Sons, Ltd. [source] Decentralized Control for Multivariable Processes with Actuator NonlinearitiesASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1-2 2006S. W. Su Decentralized control is the most widely used control strategy in the process industries because of the simplicity to design and implement the controller, and the potential to achieve failure tolerant control. Actuator nonlinearities are often encountered in many chemical processes. This paper presents a decentralized control method for processes which have static actuator nonlinearities, such as saturation and dead zone. The proposed decentralized integral controller is designed based on feedforward passivation, which can be applied to nonminimum phase processes and/or processes of high relative degree. The concept of marginally stable positive real systems is used to analyse the stability of a closedloop system. The feedforward system is constructed to attain dynamic performance on the basis of frequency based passivity analysis. The effectiveness of the proposed approach is demonstrated using an example of a quadruple tank control problem. [source] Variability and size in mammals and birdsBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2000BENEDIKT HALLGRÍMSSON Body size, its variability, and their ecological correlates have long been important topics in evolutionary biology. Yet, the question of whether there is a general relationship between size and size-relative variability has not previously been addressed. Through an analysis of body-mass and length measurements from 65 074 individuals from 351 mammalian species, we show that size-relative variability increases significantly with mean species body size. Analysis of mean body mass and standard deviations for 237 species of birds revealed the same pattern. We present three plausible alternatives explanations and eliminate several others. Of these, the hypothesis that the increase in size-relative variability with mean body mass is related to the scaling of body mass components is most strongly supported. In effect, larger mammals and birds are more variable because their body mass is composed to greater relative degree of components with higher intrinsic variability (bone, fat, and muscle). In contrast, smaller mammals and birds have lower body mass variability because they are composed to a greater relative extent of components (viscera and nervous system) in which size variation is more highly constrained by energetic and functional factors. [source] Construction of the Femoral Neck During Growth Determines Its Strength in Old Age,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 7 2007Roger M D Zebaze Abstract Study of the design of the FN in vivo in 697 women and in vitro in 200 cross-sections of different sizes and shapes along each of 13 FN specimens revealed that strength in old age was largely achieved during growth by differences in the distribution rather than the amount of bone material in a given FN cross-section from individual to individual. Introduction: We studied the design of the femoral neck (FN) to gain insight into the structural basis of FN strength in adulthood and FN fragility in old age. Materials and Methods: Studies in vivo were performed using densitometry in 697 women and in vitro using high-resolution ,CT and direct measurements in 13 pairs of postmortem specimens. Results: The contradictory needs of strength for loading yet lightness for mobility were met by varying FN size, shape, spatial distribution, and proportions of its trabecular and cortical bone in a cross-section, not its mass. Wider and narrower FNs were constructed with similar amounts of bone material. Wider FNs were relatively lighter: a 1 SD higher FN volume had a 0.67 (95% CI, 0.61,0.72) SD lower volumetric BMD (vBMD). A 1 SD increment in height was achieved by increasing FN volume by 0.32 (95% CI, 0.25,0.39) SD with only 0.15 (95% CI, 0.08,0.22) SD more bone, so taller individuals had a relatively lighter FN (vBMD was 0.13 [95% CI, 0.05,0.20 SD] SD lower). Greater periosteal apposition constructing a wider FN was offset by even greater endocortical resorption so that the same net amount of bone was distributed as a thinner cortex further from the neutral axis, increasing resistance to bending and lowering vBMD. This was recapitulated at each point along the FN; varying absolute and relative degrees of periosteal apposition and endocortical resorption focally used the same amount of material to fashion an elliptical FN of mainly cortical bone near the femoral shaft to offset bending but a more circular FN of proportionally more trabecular and less cortical bone to accommodate compressive loads adjacent to the pelvis. This structural heterogeneity was largely achieved by adaptive modeling and remodeling during growth,most of the variance in FN volume, BMC, and vBMD was growth related. Conclusions: Altering structural design while minimizing mass achieves FN strength and lightness. Bone fragility may be the result of failure to adapt bone's architecture to loading, not just low bone mass. [source] | ||||||||||||||||||||||