Visual Acuity Chart

To compare occlusion break surge volumes of UNITY® Vitreoretinal Cataract System (UVCS) with CENTURION® Vision System with Active Sentry™ (CAS). Alcon Research, Ltd., Lake Forest, California, USA. Experimental study. An eye model representing average human eye compliance was used to determine average occlusion break surge volumes. UVCS was tested at target intraocular pressures (IOPs) of 20, 30, 40, 50, 60, and 80 mmHg; vacuum limits of 300, 400, 500, 600, and 650 mmHg; and aspiration flow rates of 20 and 40 cc/min. CAS was tested at target IOPs of 30, 40, 50, 60, and 80 mmHg, and at the same set vacuum limits and aspiration flow rates as UVCS. Additionally, a second order polynomial was fit to the entire data set to compare UVCS and CAS at a target IOP of 20 mmHg. After calculating sample means at each setpoint combination, the largest mean surge volume was 48 µL for UVCS and 75 µL for CAS, corresponding to 19% and 30%, respectively, of the average human phakic anterior chamber volume. For all common setpoint combinations, mean occlusion break surge volumes were 44% lower for UVCS than CAS. At a flow rate of 40 cc/min and IOP setpoint of 20 mmHg, UVCS showed a 46% average decrease across all vacuum limits. UVCS demonstrated lower mean surge volumes following occlusion break than CAS. This may give surgeons greater confidence operating at lower IOPs and may reduce the risk of posterior capsule rupture, especially in complex cases.

In this paper, the characteristics of forces in active control systems connected to adjacent levels of a building are analyzed. The following characteristics are observed: (1) active control can provide significantly superior supplemental damping to a building, but causes a small frequency shift; (2) the linear quadratic regulator (LQR)-based control force is composed of an elastic restoring force component and a damping force component, where the damping force is almost identical to the total control force, however, the elastic restoring force is very small; and (3) the active control forces prevent motion most of the time during the entire control process. These three characteristics imply that active control systems connected to adjacent levels of a building behave like passive damping devices with adjustable parameters, namely damping characteristics in an active control, which is the mechanism used by semi-active control devices to reach similar performance as active control systems. Two indices are defined to quantify the damping characteristics of control forces in active control systems. These two indices can also be used to quantify the capacity of semi-active control to achieve the performance of active control. Based on the above observations, two principles are founded for optimization of parameters of semi-active control devices and passive dampers. The first is that the maximum output force of a semi-active or passive device to be designed is identical to an active device, called “design principle”. The other is the response equivalent principle, which states that the response of a building with semi-active or passive devices is the same as with active devices when the same maximum output force is applied. The design procedure for semi-active control devices and passive dampers is described in detail. Finally, numerical simulations of two benchmark problems is conducted to demonstrate the damping characteristics of active control and investigate the capacity of semi-active control to achieve the same performance as active control.

Target pressure—glaucomatologists’ holey grail

It is generally accepted that active control systems provide better structural performance when compared to their passive counterparts. On the other hand, the design of active control systems based on linear control theory is highly dependent on the structural properties. For this reason, their performance is expected to be affected more severely by variations in structural properties compared to those of passive systems. These variations can occur due to nonlinear structural behavior, or even before that due to uncertainties in the estimation of these properties and in numerical modeling. The present work is an investigation of the dependency of various control systems used for supplemental energy dissipation to the changes in structural properties. For this purpose, the performance degradations of most common control systems are studied for structures entering their nonlinear response range. The considered control systems include active control using linear quadratic regulator algorithm and passive control using viscous fluid dampers and yielding devices. These control systems are optimized separately for linear and nonlinear structures by minimizing performance indices based on inter-story drift and absolute acceleration response. It is shown that among these control systems, viscous dampers are affected the least by the alteration of structural properties, which may further support their utilization contrary to the more costly active control systems. It is also shown that the amount of performance degradation depends on the selected structural performance index, and more importantly, the severity of the earthquake excitation.

Hybrid Passive/Active Control Performance in Buildings Using Robust Control Design Approaches

The core of the High Frequency Instrument (HFI) on-board the Planck satellite consists of 52 bolometric detectors cooled at 0.1 Kelvin. In order to achieve such a low temperature, the HFI cryogenic architecture consists in several stages cooled using different active coolers. These generate weak thermal fluctuations on the HFI thermal stages. Without a dedicated thermal control system these fluctuations could produce unwanted systematic effects, altering the scientific data. The HFI thermal architecture allows to minimise these systematic effects, thanks to passive and active control systems described in this paper. The passive and active systems are used to damp the high and low frequency fluctuations respectively. The results of the simulation of these active and passive control systems are presented here. These simulations based on the use of thermal transfer functions for the thermal modelling can then be used for finding the optimal working point of the HFI PID active thermal control system.

An investigation is made of the possible application of an active mass damper control system to tall buildings excited by strong wind turbulence. The effectiveness of active control system, as measured by the reduction of the coupled lateral‐torsional motions of tall buildings is studied. The wind turbulence is modeled as a stochastic process that is stationary in time but non‐homogeneous in space. The problem is formulated using the transfer matrices approach, and a closed‐loop control law. The random vibration analysis is carried out to determine the statistics of the building responses, the required active control forces, and mass damper displacements. The method of Monte‐Carlo simulation is also employed to demonstrate the building response behavior with or without an active control system. A numerical example of a forty‐story building under strong wind excitations is given to illustrate the significant reduction of the building acceleration response by use of an active mass damper control system.

Active control of sound through full-sized open windows

Shutting the window is usually the last resort in mitigating environmental noise, at the expense of natural ventilation. We describe an active sound control system fitted onto the opening of the domestic window that attenuates the incident sound, achieving a global reduction in the room interior while maintaining natural ventilation. The incident sound is actively attenuated by an array of control modules (a small loudspeaker) distributed optimally across the aperture. A single reference microphone provides advance information for the controller to compute the anti-noise signal input to the loudspeakers in real-time. A numerical analysis revealed that the maximum active attenuation potential outperforms the perfect acoustic insulation provided by a fully shut single-glazed window in ideal conditions. To determine the real-world performance of such an active control system, an experimental system is realized in the aperture of a full-sized window installed on a mockup room. Up to 10-dB reduction in energy-averaged sound pressure level was achieved by the active control system in the presence of a recorded real-world broadband noise. However, attenuation in the low-frequency range and its maximum power output is limited by the size of the loudspeakers.

Structural engineers are always struggling with the unpredictable complexities of the extreme vibration due to natural or human induced loads. It is not possible to eliminate the vibration from structures entirely what so ever. Therefore, in order to keep the structures safe and healthy, the vibration needs to be mitigated and that can be done by adopting passive, active or semi-active type control systems. Those aforementioned technologies come with a price, hence, it is not so straightforward to decide which technology should be adopted. The passive vibration systems (e.g. tuned mass damper, base-isolator) can be found both in many old and new structures due to their feasibility and simplicity. On the other hand, many modern structures are adopting active and semi-active control systems (e.g. dampers) as an alternative to achieve better control on structure. Both the active and semi-active control systems are more expensive than passive control systems but they offer better control on structures. In order to understand the discussed issue, herein, a comparative study has been performed to evaluated their performances. A detail comparison among passive, active and semi-active control alternatives have been conducted. The outcome shows that the passive control systems can be suitable where deformations are and the other alternatives would be beneficial where large deformations are expected.

Macro fiber composite (MFC) has been widely investigated in the active vibration control. Yet, the actuation performance of MFC is a function of temperature. For the active vibration control system using MFC based on the linear piezoelectric equation, if the actuation parameters of MFC are variable, it is easy to cause insufficient control force or control spillover, which degrades the performance of control system. Therefore, an adaptive gain adjustment approach for the active vibration control system is developed, which ensures that the active control system can maintain the expected performance of vibration suppression under the time-varying ambient temperatures. The variation of actuation performance of MFC with temperature is measured by the experiment. The polynomial fitting method is utilized to obtain the functional relationship between the regulator parameters and ambient temperature. The performance of the proposed adaptive gain regulator is verified by the experiment in the temperature environment chamber. In the experiment, a scaled vertical tail model attaching the MFC actuator is as an example, and the fractional order positive position feedback control system is as a representative of the control system without temperature adaptability. When the temperature is −60°C, compared with the control system without regulator, the reduction ratio of response RMS of the control system with adaptive gain regulator is increased by 17.26%.The results indicate that the proposed adaptive gain regulator can avoid the adverse influence of the time.varying ambient temperature on the performance of the control system.

Soil compaction is an important procedure of precision seeding operation. In this paper, a precise downforce control system based on fuzzy PID was proposed in order to improve the quality of the soil compaction and the accuracy of setting working parameters. The conventional mechanism of seeders for soil compaction was optimised. The compressing spring of the compaction mechanism was replaced by a linear motor, which is actively controlled to adjust downforce in real time. A force sensor was connected in series with the linear motor to detect the actual downforce from a press wheel acting on soil. The detected downforce was employed as feedback for the fuzzy PID model. A slave real-time control system was constructed by using an STM32 microcontroller. A user interface was designed for the portable master computer system based on the ForLinx embedded platform to facilitate the setting of target downforce and display the actual downforce in real time. Meanwhile, it was able to adjust the system for different operating requirements, such as soil stiffness, moisture, and crop species. Experiments were conducted on a soil bin, and the results indicated that the active control system has better performance than the conventional passive system in downforce control. The downforce was stable with a variance less than 2.6% under different conditions, and it was 8.11% less than the conventional passive system.

To compare intraocular pressure (IOP) control in eyes with or without clear corneal phacoemulsification following trabeculectomy. The study group included 30 eyes that underwent uneventful clear corneal phacoemulsification and foldable intraocular lens implantation following trabeculectomy without antimetabolites. Thirty eyes that had undergone filtering surgery without cataract extraction were selected as controls. Case and control groups were matched with respect to age, gender, IOP, number of glaucoma medications, glaucoma type (primary open-angle glaucoma/pseudoexfoliative glaucoma), trabeculectomy time and follow-up. Comparisons between the study and control groups (intergroup) and within the same group at different time-points (intragroup) were performed for IOP, glaucoma medications and bleb morphology. Success rates were investigated by Kaplan-Meier survival analysis and the factors influencing final success by logistic regression. Intraocular pressure (p = 0.04) and glaucoma medications (p = 0.001) increased during an average follow-up of 26.1 +/- 9.9 months in both groups. Intragroup differences became statistically significant after the 6-month visit, but intergroup differences remained insignificant. Bleb height decreased significantly following phacoemulsification in the study group (p = 0.017). Success rates decreased with time in both groups, with no intergroup difference (p = 0.46). The final success rate was negatively correlated with IOP and number of glaucoma medications used at the study entry, while there was a positive correlation between the baseline and final success rates. Trabeculectomy success decreased in a time-dependent manner in eyes with and without subsequent phacoemulsification. Uncomplicated clear corneal phacoemulsification was not found to have any additional unfavorable influence on IOP control in eyes with filtering blebs.

A method of optimal open-loop critical-mode control has been applied to building structures excited by earthquake that is modeled as a nonstationary random process. The time dependent statistics of building response quantities and required active control forces have been presented. Monte Carlo simulations for building response quantities with or without active control systems have been performed to demonstrate the behavior of buildings subject to earthquake excitations. It is shown that a significant reduction for the building response can be achieved by use of active control systems. Furthermore, the required active control forces computed based on the stationary earthquake model are too conservative. A sensitivity study has been carried out to determine the effect of uncertainties involved in estimating structural properties on the results of optimal control. The active tendon control system is not sensitive to the estimation uncertainties for the damping and stiffness of the building. Although the active mass damper system is not sensitive to errors in damping estimation, it is moderately sensitive to the stiffness uncertainty of the building.

This work describes a range of issues relating to the implementation of active control for noise and vibration problems. It is important in the commercialization of this technology to consider these and many other factors relating to design of these systems. Many of the concepts required for efficient implementation have not been considered and it is important to begin giving design consideration to these aspects. A design technique based upon the eigenbehavior of feedforward controlled systems is developed and applied to control radiation from structures. Integration of the control system with the physical system dynamics allows the eigenproperties to be defined to meet a prescribed design criteria. Here the technique is demonstrated to implement a structural system that inefficiently couples vibration energy to acoustic energy. In addition, an approach to integrate “knowledge” about actuator configurations into an active control system that reduces spillover effects into structural vibrations is demonstrated. This approach has the advantages that no additional hardware is required while also reducing the order of the control system in terms of degrees of freedom. Finally, some design trade-offs between the passive material properties of an active trim panel and control system performance are examined. Improved performance can be attained but at the cost of additional weight.