Accommodation System Research Articles

Silicon linkage with novel compliant mechanism for piezoelectric actuation of an intraocular implant

An implantable mechatronic microsystem is a new approach to restore the accommodation ability of the human eye. For change of refractive power a lens shift is performed by an actuator. This paper reports on the first actuator solution for such an implant. It is based on a piezoelectric bender the displacement of which has to be amplified in a very limited design space to sufficiently drive the optics of an Artificial Accommodation System. This challenge is solved by a novel compliant mechanism realized in single-crystal silicon that additionally ensures the tilt-free translational displacement of the lens required for optical imaging quality. The design is free of any surface-friction to achieve high durability. Finite element analysis is conducted to calculate and optimize the performance of three linkage design variants. They were fabricated on a scale of 1.5:1 using deep reactive ion etching. Measurements were carried out to characterize the geometry, elastic behavior, and kinematic performance of the linkage samples. The results are in very good agreement with the calculations and indicate sufficient amplification of the piezoelectric bender's displacement by the linkage to generate the required lens shift.

Comparison of different power supply topologies to improve power efficiency of the Artificial Accommodation System

Comparison of different power supply topologies to improve power efficiency of the Artificial Accommodation System

Gestión de precios en un sistema de Revenue Management hotelero en línea

The computerization of the Revenue Management (RM) systems in the tourism industry has increased in recent years, as well as their uses in tourism companies. Moreover, these systems turned into the on-line management. Although the hotel sector seems to drive a slower speed of implementation of these systems than other sectors like the aerial or the maritime, the applications of RM applied to the hotel sector tend to fulfill three basic premises, 1) not being standard and with a self-made structure, 2) that can applicable to all kind of hotels and even to other systems of accommodation, and 3) that can be used for the on-line price establishment. Due to this the main aim of this paper is based on developing a system of pricing management that fulfils these basic premises.

A Robust Fault Detection Algorithm Using q-LPV Interval Observer Together with an Accommodation System Based on Actuators Reconfiguration

This paper presents robust fault detection based on adaptive thresholds for a satellite described by means of a linear parameter varying (LPV) model. Adaptive threshold is generated using an interval LPV observer that produces a band of predicted outputs considering both bounded parametric modeling errors and measurements noises. This strategy propagates the effect of satellite parameter uncertainties into the alarm limits and so enhances the robustness of fault detection system at the decision making stage. The developed method can minimize the missing alarm rates due to modeling uncertainties; also this approach detects small or incipient faults more effectively than the classical robust fault detection algorithms with constant thresholds. In this paper also an accommodation system based on reconfiguration of available actuators has been designed. Accordingly, after isolation of faulty reaction wheels, they turned off and replaced by suitable magnetic torquers. Therefore, despite occurrences of several failures in the ACS, attitude control error was kept limited. In the presented simulation results, some scenarios are developed to verify the performance of the proposed method.

Clinical importance of spherical and chromatic aberration on the accommodative response in contact lens wear

The aim of this study was to evaluate the accommodation response under both mono- and polychromatic light while varying the amount of spherical aberration. It is thought that chromatic and spherical aberrations are directional cues for the accommodative system and could affect response time, velocity or lag. Spherical aberration is often eliminated in modern contact lenses in order to enhance image quality in the unaccommodated eye. This study was divided into two parts. The first part was done to evaluate the amount of spherical and other Zernike aberrations in the unaccommodated eye when uncorrected and with two types of correction (trial lens and spherical-aberration controlled contact lens) and the second part evaluated the dynamic accommodation responses obtained when wearing each of the corrections under polychromatic and monochromatic conditions. Measurements of accommodation showed no significant differences in time, velocity and lag of accommodation after decreasing the spherical aberration with a contact lens, neither in monochromatic nor polychromatic light. It is unlikely that small to normal changes of spherical aberration in white light or monochromatic mid-spectral light affect directional cues for the accommodative system, not in white light or mid-spectral monochromatic light, since the accommodative response did not show any change.

Changes in Accommodative Responses with Multifocal Contact Lenses: A Pilot Study

To evaluate induced changes in pupil and accommodative response for different accommodative stimuli with three different multifocal contact lenses (CLs). Accommodative and pupil responses with three aspheric multifocal CLs of simultaneous focus center near (PureVision Low Add, PureVision High Add and Focus Progressives) for two accommodative stimuli of -2.5 and -4.00 D were recorded in 10 young subjects. Accommodative response, peak velocity, and time constant of accommodation and pupil constriction were assessed. The measurements were evaluated in all the participants with distance-single vision CLs and with the three multifocal CLs. The monocular measurements were performed in a random sequence for each participant. All parameters were measured with a Hartmann-Shack aberrometer (IRX-3; Imagine Eyes, Orsay, France). Differences were not found in accommodation response for both accommodative stimuli studied between the single vision lens and the three different multifocal CLs (p > 0.05 for both stimuli). For the 2.5 D stimulus, significant differences were not found in peak velocity and time constant between the single vision lens and the three different multifocal CLs (p > 0.05 for all situations); in amplitude of pupil constriction, differences were only found for the situation with PureVision High Add, where the value was lower than the single vision lens (p = 0.015). For the 4.00 D stimulus, differences with single vision lens in peak of velocity and time constant were only found with PureVision Low Add, where the peak velocity value was higher and the time constant was lower (p = 0.024 and p = 0.032 for peak of velocity and time constant, respectively); for amplitude of pupil constriction differences were not found (p > 0.05). Data obtained in this pilot study suggest that in young observers, the multifocal CLs studied do not induce large changes in accommodative system compared with the single vision lens.

Accommodation and Adjudication in Student–Administration Conflicts: The Difficult Legacy of the U.S. Supreme Court

In this article, we consider a series of U.S. Supreme Court rulings that place public school students under an expansive shield of constitutional rights while often hampering the ability of administrators to engage in flexible and creative conflict resolution in the context of the school's mission. The court's readiness to adjudicate a large range of student–administration conflicts has weakened schools’ ability to pragmatically accommodate conflicts that, by their nature, do not have principled solutions at the level of the law. We argue that as long as adjudication is the privileged course of action, the court seems locked into a philosophical zigzag, now endowing 8th graders with due process and constitutional rights, now framing them as mere “subjects.” To strengthen schools as educational and moral institutions, school leaders need to be able to construct systems of accommodation that are sensitive to their special educational nature and mission.

THE USAGE OF RELATIONSHIP MARKETING WITHIN ACCOMMODATION INDUSTRY – MERCURE PATRIA IN CZESTOCHOWA EXAMPLE

Many accommodation enterprises perceive the chance for their further development in joining international accommodation systems. The potential of their knowledge and experience as well as funds’ concentration allow them to win predominance in the market. The paper present possibilities of relationship marketing usage in the accommodation sector and advantages of unified marketing programs introduction in the hotel’s networks.

Hotel water consumption at a seasonal mass tourist destination. The case of the island of Mallorca

While it is true that tourism is one of the main driving forces behind economic growth in several world regions, it is also true that tourism can have serious negative environmental impacts, especially with regard to water resources. The tourist water demand can generate big problems of sustainability, mainly in those regions where water is scarce, as occurs in most coastal and small island destinations where a large part of world tourism is concentrated. Given the shortage of literature on the subject, further research into the tourist water demand is required, with particular attention to the hotel sector, since hotels are the most popular option for tourists, displaying higher levels of water consumption. The main purpose of this study is to develop a model to analyse hotel water consumption at a mature sun and sand destination with a strong seasonal pattern and scarcity of water; characteristics shared by some of the world’s main tourist destinations. Our model includes a set of different hotel variables associated with physical, seasonal and management-related factors and it improves on the capacity to explain water consumption at such destinations. Following a hierarchical regression methodology, the model is empirically tested through a survey distributed to managers of a representative sample of hotels on the island of Mallorca. From the obtained results, interesting recommendations can be made for both hotel managers and policy makers. Among these, it should be highlighted that the strategic move contemplated by many mature destinations towards a higher quality, low-season model could have significant negative effects in terms of the sustainability of water resources. Our results also conclude that managerial decisions, like the system of accommodation that is offered (i.e. the proliferation of the “all-inclusive” formula, both at mature and new destinations), could give rise to the same negative effect. Development of water saving initiatives (usually introduced in response to demand-based factors), also reveals significant effects over water consumption. Finally, other key factor in explaining hotel water consumption is the management system under which the hotel is run.

Influence of three-dimensional image viewing on visual function

A three-dimensional (3D) image viewing experiment was performed using a new 3D scenography system. The influence on visual function was investigated both in adults and in children employing both objective and subjective methods. The subjects were 21 healthy adults (mean age ± standard deviation: 42.1 ± 10.0 years) and 21 healthy children (7.8 ± 1.5 years). The 3D image viewing time was set at 90 min for adults and 60 min for children, and the visual function was objectively evaluated using an accommodative microfluctuation analysis system both before and after 3D image viewing. In addition, subjective symptoms were surveyed employing a questionnaire both before and after viewing in the adult group to subjectively evaluate the visual function. No significant difference was noted in accommodative microfluctuation between the before and after viewing in either the adult or child group, nor was there a significant difference in subjective symptoms in the adult group based on the questionnaire. However, accommodative microfluctuation tended to increase after viewing in some subjects. Under the conditions of this study, 3D image viewing did not influence visual function, or only very slightly influenced it, if at all, but there are many unknown problems, requiring further surveys using 3D image viewing.

Accommodative amplitude required for sustained near work

Many practitioners base the prescription of near vision additions on the assertion that only one half or two-thirds of an individual's amplitude of accommodation is sustainable for a prolonged period. To better understand how much eye focus needs to be restored for presbyopic corrections to be adequate, this study investigated the robustness of the pre-presbyopic human accommodative system during a sustained and intensive near vision task. Twenty-one pre-presbyopic volunteers (aged 26.1 ± 4.7 years) participated in the study. Binocular subjective amplitude of accommodation was measured before and after a prolonged reading exercise, using the RAF rule. During the 30 min reading task, the subject's closest comfortable eye-to-text distance and pupil size was monitored. Accommodative accuracy to 0.2, 1.0, 2.0, 3.0 and 4.0 D stimuli was determined objectively using a validated binocular open-view autorefractor immediately before, and after the reading task. Amplitude of accommodation (p=0.09) and accommodative accuracy (p>0.05) were statistically unchanged following the intensive near task. The mean proportion of accommodation exerted throughout the near exercise was 80.6% (range 45.3 ± 3.7 to 96.6 ± 4.3%), which increased as the task progressed (F=2.24, p=0.02). The mean percentage of accommodation utilised increased with subject age (r=0.517, p = 0.016). The pre-presbyopic human accommodative system is robust to fatigue during intense and prolonged near work. A greater proportion of one's amplitude of accommodation may be continuously exerted than previously suggested.

Analisis estratigrafico secuencial de las formaciones Anacleto y Allen (Cretacico Tardio) en el borde nororiental de Cuenca Neuquina, Argentina

En las provincias de Neuquén y Río Negro a partir de un estudio sedimentológico de detalle se realizó un análisis estratigráfico secuencial de los depósitos del Cretácico Superior de la Formación Anacleto y miembro inferior de la Formación Allen para el borde nororiental de Cuenca Neuquina. La asociación de las litofacies permitió interpretar elementos arquitecturales de origen fluvial y elementos con influencia de mareas. Tres sistemas fluviales (sistema entrelazado, sistema anastomosado y sistema meándrico), un sistema estuárico proximal y uno medio fueron identificados para La Formación Anacleto. Para el miembro basal de la Formación Allen, se definió un sistema estuárico distal o boca de estuario. En el análisis de estratigrafía secuencial se identificó una secuencia constituida por: un cortejo de baja acomodación, en ambiente continental limitado por una superficie de inundación fluvial (discontinuidad I) y la discontinuidad II; y un cortejo de alta acomodación y su equivalente cortejo transgresivo en ambiente marino, incluyendo este último las discontinuidades III, IV y V.

Keeping the World in Focus: How Might This Be Achieved?

To see clearly, the eye needs to have a sharply focused image on its retina. For distance vision, the eye should ideally develop toward emmetropia, and for near vision, the accommodation system should produce an appropriate increase in ocular power. The characteristics of the emmetropization and accommodation mechanisms are compared. Following Howland (paper presented at the 13th International Myopia Conference, July 26-29, 2010, Tubingen, Germany), it is suggested that emmetropization may be guided by imagery in the peripheral retina, perhaps making use of oblique astigmatism; however, such a mechanism can only be effective if dioptric stimuli approximate to 0 across the visual field, as is the case in many outdoor environments. In contrast, the accommodation system must be driven mainly by the axial image, because during most close work, dioptric stimuli vary widely across the peripheral field. Thus, the differences between the emmetropization and accommodation mechanisms may reflect the nature of the spatial distribution of object vergence in the outdoor and near environments.

Bem-estar na produção de frango de corte em diferentes sistemas de criação

Esta pesquisa foi conduzida com o objetivo de avaliar diferentes sistemas de criação para frangos de corte, caracterizando o ambiente térmico, os parâmetros fisiológicos e o comportamento animal. O experimento foi realizado no decorrer de um ciclo produtivo de 42 dias, no município de Carpina, Estado de Pernambuco, na Estação Experimental de Pequenos Animais da Universidade Federal Rural de Pernambuco (UFRPE). A pesquisa foi desenvolvida em um módulo de produção dividido em 15 boxes, com 10 aves por Box, e densidade de 10 aves por m², totalizando 150 aves, submetidas a três sistemas de criação: semiconfinado com 3 m² por ave de área de piquete (SC 3), semiconfinado com 6 m² por ave de área de piquete (SC 6) e confinamento total (CONF). O delineamento experimental para análise geral dos dados foi inteiramente casualizado (DIC) em parcelas subdivididas, sendo as semanas alocadas nas parcelas, e os sistemas de criação (SC 3, SC 6, CONF e EXT), nas subparcelas, com as médias comparadas pelo teste de Tukey. As variáveis meteorológicas, índices de conforto e os parâmetros fisiológicos apontam o sistema de criação SC 3 como aquele que permitiu melhor acondicionamento térmico natural às aves, apresentando valores médios da ordem de 25,4 ºC; 69,9 kJ kg-1; 75,7; 65,12 movimentos min-1 e 41,92 ºC para temperatura de bulbo seco, entalpia, índice de temperatura de globo e umidade, frequência respiratória e temperatura cloacal, respectivamente. As aves submetidas ao sistema de criação SC 3 foram as que tiveram melhor oportunidade de expressar seus comportamentos naturais e de explorar o ambiente externo ao módulo de criação, potencializando o bem-estar animal.

The effect of blur adaptation on accommodative response and pupil size during reading

To study the effect of blur adaptation on accommodative variability, accommodative responses and pupil diameters in myopes (n = 22) and emmetropes (n = 19) were continuously measured before, during, and after exposure to defocus blur. Accommodative and pupillary response measurements were made by an autorefractor during a monocular reading exercise. The text was presented on a computer screen at 33 cm viewing distance with a rapid serial visual presentation paradigm. After baseline testing and a 5-min rest, blur was induced by wearing either an optimally refractive lens, or a +1.0 DS or a +3.0 DS defocus lens. Responses were continuously measured during a 5-min period of adaptation. The lens was then removed, and measurements were again made during a 5-min post-adaptation period. After a second 5-min rest, a final post-adaptation period was measured. No significant change of baseline accommodative responses was found after the 5-min period of adaptation to the blurring lenses (p > 0.05). Compared to the pre-adaptation level, both refractive groups had similar and significant increases in accommodative variability right after blur adaptation to both defocus lenses. After the second rest period, the accommodative variability in both groups returned to the pre-adaptation level. The results indicate that blur adaptation has a short-term effect on the accommodative system to elevate instability of the accommodative response. Mechanisms underlying the increase in accommodative variability by blur adaptation and possible influences of the accommodation stability on myopia development were discussed.

Fuzzy Fault Diagnosis and Accommodation System for Hybrid Fuel-Cell/Gas-Turbine Power Plant

The concept of hybrid fuel-cell power plants has shown its potential for applications and is already under commercialization. In a hybrid fuel-cell and turbine power plant, the control system is an essential component that guarantees reliable and efficient operations. However, due to the limited information possessed by particular local controllers, the plant may become degraded or unstable during system failures. To regulate the power plants under such abnormal situations, a fault diagnosis and accommodation (FDA) system based on fuzzy logic has been developed as an effective complement for the local control scheme. Being a quantitative approach, the fuzzy FDA system can be implemented with considerably lower complexities than an analytical fault regulator. The system structures and design methods are discussed in this paper. Three types of controllers are implemented and investigated. Simulation results are presented to verify the performance of the overall system.

Energie- und speichereffiziente Berechnung des Akkommodationsbedarfs im Künstlichen Akkommodationssystem

Presbyopia and cataract are gaining more and more importance in the ageing society. Both age-related complaints are accompanied with a loss of the eye's ability to accommodate. A new approach to restore accommodation is the Artificial Accommodation System, an autonomous micro system, which will be implanted into the capsular bag instead of a rigid intraocular lens. The Artificial Accommodation System will, depending on the actual demand for accommodation, autonomously adapt the refractive power of its integrated optical element. One possibility to measure the demand for accommodation non-intrusively is to analyse eye movements. We present an efficient algorithm, based on the CORDIC technique, to calculate the demand for accommodation from magnetic field sensor data. It can be shown that specialised algorithms significantly shorten calculation time without violating precision requirements. Additionally, a communication strategy for the wireless exchange of sensor data between the implants of the left and right eye is introduced. The strategy allows for a one-sided calculation of the demand for accommodation, resulting in an overall reduction of calculation time by 50 %. The presented methods enable autonomous microsystems, such as the Artificial Accommodation System, to save significant amounts of energy, leading to extended autonomous run-times.

Internal and Locational Factors Affecting Hotel Industry Efficiency: Evidence from Italian Business Corporations

This paper investigates whether and how the competitive delay of the Italian hotel industry is influenced by the level of business corporation efficiency. A stochastic frontier production approach is proposed in which technical inefficiency is specified as a function of the internal and locational factors in a firm. The model is estimated on a balanced panel of tourism business corporations observed during 1998–2005. Estimates show that the competitive gap in the Italian accommodation system is not a result of poor business corporation performance, and the importance of location, human and immaterial capital is assessed as (in)efficiency determinants. The authors then suggest policies to improve the Italian tourist industry's competitiveness.

Ein neues mechatronisches System zur Wiederherstellung der Akkommodationsfähigkeit des menschlichen Auges

In this paper a new approach for restoring human accommodation is presented. It is an artificial accommodation system based on the latest results of microtechnology, electronics and automatic control. The concept of the overall system is described and the results obtained for the different subsystems are discussed.

Kapselung eines mechatronischen Systems zur Wiederherstellung der Akkommodationsfähigkeit

In order to restore the ability of accommodation of the human eye, a lens implant manufactured by micro system technology can be used. This highly integrated Artificial Accommodation System contains sensitive electronics as well as moving components in order to adapt its refractive power. One challenge of the production of this system is the encapsulation. It has to be a biocompatible and long-term reliable package. In this paper the advantages of a hermetic glass package over other approaches of encapsulation are introduced. Concepts of production for a glass package are presented. The package is thereby optimised to be placed in the optical path of the eye, but it can also be used for the encapsulation of other implants.