Unbalanced Response Research Articles

Chaos and bifurcation analysis of a flexible rotor supported by short journal bearings with non-linear suspension

The bifurcation and chaos of the unbalanced response of a bearing-rotor system with non-linear suspension are investigated on the basis of the assumption of an incompressible lubricant together with short bearing approximation. Numerical results show that, owing to the non-linear factors, the trajectory of the journal centre demonstrates steady state symmetric motion even when the trajectory of the bearing centre is in a state of disorder. Poincaré maps, bifurcation diagrams and power spectra are used to analyse the behaviour of the bearing centre in the horizontal and vertical directions under different operating conditions. A unidirectional bifurcation phenomenon is detected in the bearing-rotor system in this study. The fractal dimension concept is used to determine whether the system is in a state of chaotic motion. Numerical results show that the dimension of the bearing centre trajectory is fractal and greater than 2 in some operating conditions. This indicates that the bearing centre is in the state of chaotic motion at these operating conditions.

New perspectives in asthma treatment.

The recent advances in the knowledge of the basic mechanisms underlying asthmatic inflammation have significantly contributed to the delineation of new therapeutic perspectives for asthma. There are currently three main approaches to the development of novel antiasthma treatments: 1) improvement in existing classes of drugs 2) identification of new compounds able to interfere with the complex network of proinflammatory mediators, cytokines, chemokines, and adhesion molecules involved in the pathogenesis of asthma 3) utilization of new forms of immunotherapy aimed at blocking the unbalanced Th2 response which characterizes the pathophysiology of asthma. Such a remarkable expansion in available therapeutic options will probably allow us, over the next decade, to treat asthma by more selectively targeting the pathogenetic events responsible for this widespread airway disease.

Sepsis and Septic Shock: Pro-Inflammatory or Anti-Inflammatory State?

A considerable body of evidence indicates that together with an important pro-inflammatory reaction, a anti-inflammatory response contributes to the onset of sepsis and organ failure. At a local site of injury or infection and during the initial appearance of pro- and anti-inflammatory mediators in the circulation, the beneficial effects of these compounds counterbalance their harmful effects. Only when the balance between these two forces is lost may these substances become harmful. The sequelae of an unbalanced systemic inflammatory reaction include derangement of microcirculation, shock, transudation into organs and defects of coagulation. An unbalanced systemic compensatory anti-inflammatory response often results in anergy and immunosuppression. The pro-inflammatory and anti-inflammatory conditions may ultimately reinforce each other, creating a state of destructive immunologic dissonance. In the present report, recent literature on cytokines was reviewed together with the 89 clinical papers published between 1993 and 1997 on the role of cytokines during sepsis and other inflammatory reactions. Cytokines were analyzed in more than 5,000 patients. Sepsis and septic shock were the two groups most represented (2834 individuals and 550 respectively). Only 12% (11) of the studies showed a correlation with the presence of sepsis or septic complications. Overall 27 (39%) studies found a correlation between levels of cytokine and mortality. Fifty (62%) of the 80 studies that investigated this correlation found that the amount of cytokines did not predict death. The rest of the 30 (48%) investigations depicted an unhomogeneous picture: even though 27 studies evidenced higher levels of cytokines in non-survivors, 3 studies found the opposite.

DESIGN OF OPTIMUM SUPPORT PARAMETERS FOR MINIMUM ROTOR RESPONSE AND MAXIMUM STABILITY LIMIT

Viscoelastic polymeric materials provide good support elements to rotor shaft systems by virtue of their efficiency in dissipating vibratory energy. The in-phase stiffness and loss factor for such materials also change with the frequency of excitation they are subjected to. In this paper frequency dependent characteristics of the polymeric supports have been found by simultaneously minimizing the unbalanced response and maximizing the stability limit speed. This process yields better support characteristics than those obtained by minimizing unbalance response alone. Optimum characteristics have been found for the rotor shaft system mounted on (a) rolling element bearings and (b) plain cylindrical journal bearings at the ends having polymeric supports. The effects of viscous internal damping in the shaft, support mass and gyroscopic effect due to non-symmetrical location of the disc have been considered in the analysis. A procedure of controlling the slope of the support characteristics versus frequency of excitation has been used and found to be very suitable for obtaining feasible support characteristics. Examples have been presented to justify the above conclusions.

Vibration Control of a Rotating Shaft: An Analytical Solution

It has been shown that a rotating shaft in the Rayleigh beam model has only a finite number of whirl speeds and vibration modes when the rotating speed is higher than half of the whirl speed. The system’s unbalanced response can therefore be written analytically by the vibration modes and the generalized coordinates. This paper presents an analytical controller design of optimal sensor/actuator location and feedback gain for minimizing the steady-state unbalanced response. Because all of the critical speeds and vibration modes are included in the controller design, there will be no residual mode, hence no spillover. An example is used to illustrate that the controller design in collocated or noncollocated configuration not only guarantees the closed-loop stability but also effectively suppresses the unbalanced response.

INTERLEUKIN 10 PRODUCTION IN PATIENTS UNDERGOING CARDIOPULMONARY BYPASS: EVIDENCE OF INHIBITION OF Th-1-TYPE RESPONSES

The cardiopulmonary bypass (CPB) procedure has long been associated with a generalized immunosuppression. To understand further the cytokine-mediated regulation of the complex physiological and immunological changes induced by CPB, the authors decided to investigate whether CPB affects the release of interleukin (IL)-10, as well as other cytokines, in correlation to the inhibition of T cell responses. Using phytohaemagglutinin (PHA) as mitogen and peripheral blood mononuclear cells (PBMC) isolated from patients undergoing CPB, we investigated whether this procedure has an effect on the secretion of different patterns of cytokines (Th1- and Th2-type) and PBMC proliferation. In all patients, CPB significantly enhances IL-10 and IL-6 production in resting and PHA-stimulated PBMC. On the other hand, IL-2 production, in response to PHA, was significantly diminished. Reduced IL-2 and enhanced IL-10 production were associated with a significant decrease in PBMC proliferation. Immunosuppression was also associated to lymphopenia, while neutrophil counts were significantly enhanced. These results show that after CPB there is a transient but clear unbalanced immune response demonstrated by a differentiated production of Th1- and Th2-type cytokines. The release of different patterns of cytokines observed after CPB may be helpful in understanding and preventing the development of infectious and immune complications in surgical procedure employing CPB.

A program for the weighted linear least-squares regression of unbalanced response arrays

A program is described to establish calibration diagrams by weighted, linear, least-squares regression of unbalanced response arrays. Whatever the confidence level, the number of analysed standard solutions and of their available replicates, the program allows (i) testing for scedasticity, linearity, outliers and normality, (ii) evaluation of slope and intercept of the calibration function and their confidence interval and (iii) evaluation of an unknown concentration and its confidence interval by interpolation/extrapolation. For negative results of the linearity test, the program structure allows a rapid evaluation of data to be discarded to attempt entering the linear range. The program was validated by analysing response arrays obtained by adding a Gaussian noise to known response/concentration functional relationships. The results of validation tests led to the implementation of an empirical but efficient way to correct regression results when certain experimental situations lead to unjustified over-weighting of some responses. The analysis of some real calibration data sets allows the versatility of the software to be evaluated.

Multiloop PI controller tuning for interacting multivariable processes

A trial-and-error method that is a variation of Ziegler–Nichols tuning has been employed in the past for field tuning of PID controllers. This method is now extended for tuning of multiloop PI controllers. The Nyquist array method is refined to determine ultimate gains for multiloop tuning. The proposed method is simple to use and simulation results show that it avoids sluggish responses and unbalanced responses between loops that occur with other tuning methods such as BLT and sequential autotuning.

Stability and Bifurcation of a Rotor-Fluid Film Bearing System With Squeeze Film Damper

The dynamical behaviors of a flexible rotor supported by two plain cylindrical bearings surrounded by squeeze film damper are investigated. In this study, the Hopf bifurcation theory is used to investigate the stability of the equilibrium position of the system, then the unbalanced rotor response is determined by the shooting method and the stability of these solution is examined using the Floquet transition matrix method. It is shown that the quasi-periodic motion and period-doubling motion may be excited by the rotor unbalance.

Immunologic aspects in the pathogenesis and treatment of immune thrombocytopenic purpura in children.

Immune thrombocytopenic purpura (ITP) is either a transient or a chronic bleeding disorder characterized by an unbalanced immune response due to inflammation (ie, infection, autoimmunity). There is new evidence arguing for an immune-mediated mechanism operative in ITP-increased HLA-DR expression, defects in cellular and humoral immunity, and specific autoantibody production. Moreover, different forms of ITP may be associated with specific alterations in the immune response. New immunosupportive modalities emphasize biologic interventions as a therapeutic strategy for autoimmune disorders. Practical guidelines for the diagnosis and treatment of ITP were recently established by the American Society of Hematology. These recommendations will substantially influence patient care and future research.

Immunologic dissonance: a continuing evolution in our understanding of the systemic inflammatory response syndrome (SIRS) and the multiple organ dysfunction syndrome (MODS)

Our current understanding of sepsis and multiple organ dysfunction needs to be revised, as the uniformly negative results of new therapies for these disorders suggest. Previous theories for the pathogenesis of these conditions are incomplete; reasons for this include the following. First, the surrogate models that have been used to study these disorders are not analogous to the clinical situation. Second, patients who have less severe manifestations of these diseases are often overlooked. And third, patients' preexisting conditions have not been taken into account. Considerable new evidence indicates that, in addition to a massive proinflammatory reaction, a compensatory anti-inflammatory response contributes to the onset of these disorders. At a local site of injury or infection and during the initial appearance of pro- and anti-inflammatory mediators in the circulation, the beneficial effects of these mediators outweigh their harmful effects. Only when the balance between these two forces is lost do these mediators become harmful. Sequelae of an unbalanced systemic proinflammatory reaction include shock, transudation into organs, and defects in coagulation. An unbalanced systemic compensatory anti-inflammatory response can result in anergy and immunosuppression. The proinflammatory and anti-inflammatory forces may ultimately reinforce each other, creating a state of increasingly destructive immunologic dissonance.

Parametric Study of the Unbalance Response of an Eccentric Sueeze Film Damper-Mounted Rigid Rotor.

This paper presents a limited parametric study of the unbalanced response of a rigid rotor supported by an eccentric squeeze film damper bearing. The rotor unbalance response is approximated by a trigonometric series whose coefficients are determined by the collocation method. The results indicate that for small static misalignments and unbalances, nonsynchronous components are negligible and the rotor response is an offset ellipse. Nonsynchronous components increase as both the unbalance and the static misalignment are increased. However, the amplitude of the rotor response is independent of the static misalignment direction. There is a tendency for the rotor to self-center in the vicinity of the resonance. This self-centering effect is more pronounced as the unbalance is increased and it is reduced as the static misalignment is increased. For large unbalances and static misalignments, both main resonant jump and secondary resonant jump are predicted at speeds above twice the system critical speed.

Stability and Bifurcation of Unbalanced Response of a Squeeze Film Damped Flexible Rotor

The stability and bifurcation of the unbalance response of a squeeze film damper-mounted flexible rotor are investigated based on the assumption of an incompressible lubricant together with the short bearing approximation and the “π” film cavitation model. The unbalanced rotor response is determined by the trigonometric collocation method and the stability of these solutions is then investigated using the Floquet transition matrix method. Numerical examples are given for both concentric and eccentric damper operations. Jump phenomenon, subharmonic, and quasi-periodic vibrations are predicted for a range of bearing and unbalance parameters. The predicted jump phenomenon, subharmonic and quasi-periodic vibrations are further examined by using a numerical integration scheme to predict damper trajectories, calculate Poincare´ maps and power spectra. It is concluded that the introduction of unpressurized squeeze film dampers may promote undesirable nonsynchronous vibrations.

Dynamic simulation of non-linear models of hydroelectric machinery

This work describes the development of a non-linear model of the hydro-units at the power plant in Ilha-Solteira (Brazil). A computer program is presented that permits the calculation of the bending vibrations of vertical rotor systems. The program takes into account magnetic interactions, seals, journal bearings, as well as unbalanced, constant, harmonic and stochastic excitation forces. The shaft is modelled with the finite-element method including the gyroscopic effect for the discs. Some simulation results are presented. At the same time a linear model is established to compare with the results of the non-linear model, e.g. for the unbalanced response and the characteristic frequencies. This work has been carried out as part of a research programme Diagnosis of Vertical Machines.

The relationship of journal bearing loads and alinment conditions of multispan rotors.

This paper presents a method to calculate the static bearing loads of multispan rotors by considering the nonlinear characteristics of oil film bearings. The initial alignment to be installed in the rotor is determined by minimizing the difference of the bearing load from the designed value and the stress of rigid couplings. To investigate the effects of the journal center displacement varying with rotating speeds, an actual turbogenerator system with four couplings and eight bearings is numerically investigated under initial and misaligned conditions. It is shown that the amount and direction of bearing loads strongly depend on rotating speeds under the misaligned conditions, but are negligibly small under the initial condition. To clarify the fundamental properties induced by the misalignment of the rotor system, the load direction effects on the journal center, unbalanced response and stability are investigated for a partial arc bearing.

Theoretical and experimental investigations of a variable- impedance hydrodynamic bearing

The aim of the work described in this paper is to develop a hydrodynamic bearing whose oil film dynamic stiffness and damping coefficients could be tuned to take on low values, without upsetting the bearing steady load carrying capacity, in order to obtain an improved dynamic response for machines running in such bearings. It was required that this tuning of the bearing dynamic characteristics could be carried out after assembly of the machine in question, and if necessary while the machine was in operation. A theoretical analysis of the new design of bearing was carried out, based on a finite-difference model of the bearing oil film. This analysis enabled the steady-state load carrying capacity of the bearing to be calculated for any particular running conditions. The oil film stiffness and damping characteristics were then calculated using the finite-displacement technique; these were then used to calculate the unbalance response of a flexible rotor running in such bearings. Experimental measurements of the unbalance response of a model rotor running in the new bearing design were also recorded, and compared with similar measurements obtained when conventional bearings were used. Both theoretical and experimental results show that the proposed new bearing design has a similar steady load carrying capacity to that of conventional hydrodynamic bearings, but that the unbalanced response and force transmissibility of machines running in the new design of bearing are substantially superior to that obtained with conventional bearings.

Formalin-inactivated respiratory syncytial virus vaccine induces antibodies to the fusion glycoprotein that are deficient in fusion-inhibiting activity

The fusion (F) glycoprotein of respiratory syncytial virus (RSV) induces neutralizing antibodies and antibodies that inhibit fusion of infected cells (FI antibody). It was previously shown that infants and children immunized with Formalin-inactivated RSV 20 years ago developed antibodies that bound to the F glycoprotein but were deficient in neutralizing activity. A reexamination of these sera indicated that they were also deficient in FI activity. Thus, Formalin-inactivated RSV vaccine stimulated an unbalanced immune response in which an unusually large proportion of the induced antibodies were directed against nonprotective epitopes rather than against the epitopes that induce functional antibodies, i.e., neutralizing and FI antibodies. This deficiency in stimulation of functional antibodies probably decreased the protective efficacy of the vaccine and could have contributed to potentiation of disease in the vaccines during subsequent RSV infection.

Comparing two methods of informing operators about what might happen next

Operator performance is dependent upon the level of certainty of what will happen next. Knowledge about this certainty can be given by long-term experience of the occurrence of events or by secondary information given immediately before the event. We define these methods as, respectively, memory-dependent and display-dependent. In this experiment nine groups of twelve subjects performed four-choice finger-pressing tasks in response to visual signals. The tasks were based upon the unbalanced frequencies and response priming paradigms of experimental psychology corresponding to the two methods of providing information thus defined. The tasks varied in mean certainty as well as in source of knowledge about the certainty. Mean reaction times varied, to a statistically significant degree, with level of certainty and, for events of low certainty, with the method of presenting information about certainty. Error rates varied inversely with the same factors but not all differences in this respect were statisticall...

Linear Dynamic Coupling in Geared Rotor Systems

The ability to analyze accurately the torsional-axial-lateral coupled response of geared systems is the key to the prediction of dynamic gear forces, shaft moments and torques, dynamic reaction forces, and moments at all bearing points. These predictions can, in turn, be used to estimate gear-tooth lives, shaft lives, housing vibrational response, and noise generation. Typical applications would be the design and analysis of gear drives in heavy-lift helicopters, industrial speed reducers, Naval propulsion systems, and heavy, off-road equipment. In this paper, the importance of certain linear dynamic coupling terms on the predicted response of geared rotor systems is addressed. The coupling terms investigated are associated with those components of a geared system that can be modeled as rigid disks. First, the coupled, nonlinear equations of motion for a disk attached to a rotating shaft are presented. The conventional argument for ignoring these dynamic coupling terms is presented and the error in this argument is revealed. It is shown that in a geared system containing gears with more than about 50 teeth, the magnitude of some of the dynamic-coupling terms is potentially as large as the magnitude of the linear terms that are included in most rotor analyses. In addition, it is shown that the dynamic coupling terms produce the multi-frequency responses seen in geared systems. To quantitatively determine the effects of the linear dynamic-coupling terms on the predicted response of geared rotor systems, a trial problem is formulated in which these effects are included. The results of this trial problem shows that the inclusion of the linear dynamic-coupling terms changed the predicted response up to eight orders of magnitude, depending on the response frequency. In addition, these terms are shown to produce sideband responses greater than the unbalanced response of the system.

Determination of phospholipid ester-linked fatty acids and poly β-hydroxybutyrate for the estimation of bacterial biomass and activity in the rhizosphere of the rape plant Brassica napus (L.)

Examination of seven strains of gram-negative bacteria isolated from the rhizosphere of the rape plant showed profiles of fatty acids, ester-linked to their phospholipids that were distinctly different from sterile roots. The bacteria were enriched in short and branched saturated, cyclopropane and monoenoic fatty acids in which the unsaturation was formed by the anerobic desaturase pathway when growth was on a medium simulating root exudates. This suite of fatty acids was significantly increased in sand and in roots of rape plants grown from seeds in sands inoculated with these organisms at the start of the experiments. Some of the bacteria formed the endogenous storage polymer poly β-hydroxybutyrate in monocultures. Poly β-hydroxybutyrate was formed by the bacteria in the inoculated sand in large amounts but not by the bacteria that were recovered from the roots. This suggests that bacteria associated with the roots were in balanced growth, whereas the bacteria in the sand were lacking essential nutrients and showed an unbalanced growth response. These chemical analyses provided estimates of the bacterial biomass (from the sum of bacterial ester-linked phospholipid fatty acids) and the metabolic status (poly β-hydroxybutyrate to phospholipid fatty acid ratio) in this experiment. With further definition of lipid biomarkers of soil microorganisms these experimental techniques may be extended to the rhizosphere.