Egg-Clutch Biomechanics Affect Escape-Hatching Behavior and Performance.

Arboreal embryos of phyllomedusine treefrogs hatch prematurely to escape snake predation, cued by vibrations in their egg clutches during attacks. However, escape success varies between species, from ∼77% in Agalychnis callidryas to just ∼9% in A. spurrelli at 1 day premature. Both species begin responding to snake attacks at similar developmental stages, when vestibular mechanosensory function begins, suggesting that sensory ability does not limit the hatching response in A. spurrelli. Agalychnis callidryas clutches are thick and gelatinous, while A. spurrelli clutches are thinner and stiffer. We hypothesized that this structural difference alters the egg motion excited by attacks. Since vibrations excited by snakes must propagate through clutches to reach embryos, we hypothesized that the species difference in attack-induced hatching may reflect effects of clutch biomechanics on the cues available to embryos. Mechanics predicts that thinner, stiffer structures have higher free vibration frequencies, greater spatial attenuation, and faster vibration damping than thicker, more flexible structures. We assessed clutch biomechanics by embedding small accelerometers in clutches of both species and recording vibrations during standardized excitation tests at two distances from the accelerometer. Analyses of recorded vibrations showed that A. spurrelli clutches have higher free vibration frequencies and greater vibration damping than A. callidryas clutches. Higher frequencies elicit less hatching in A. callidryas, and greater damping could reduce the amount of vibration embryos can perceive. To directly test if clutch structure affects escape success in snake attacks, we transplanted A. spurrelli eggs into A. callidryas clutches and compared their escape rates with untransplanted, age-matched conspecific controls. We also performed reciprocal transplantation of eggs between pairs of A. callidryas clutches as a method control. Transplanting A. spurrelli embryos into A. callidryas clutches nearly tripled their escape success (44%) compared to conspecific controls (15%), whereas transplanting A. callidryas embryos into different A. callidryas clutches only increased escape success by 10%. At hatching competence, A. callidryas eggs are no longer jelly-encapsulated, while A. spurrelli eggs retain their jelly coat. Therefore, we compared the hatching response and latency of A. spurrelli in de-jellied eggs and their control, jelly-encapsulated siblings using manual egg-jiggling to simulate predation cues. Embryos in de-jellied eggs were more likely to hatch and hatched faster than control siblings. Together, our results suggest that the properties of parentally produced egg-clutch structures, including their vibration biomechanics, constrain the information available to A. spurrelli embryos and contribute to interspecific differences in hatching responses to predator attacks.

Resumen Los embriones arbóreos de las ranas Phyllomedusinae eclosionan prematuramente para escapar de la depredación de las serpientes, señaladas por las vibraciones en sus posturas durante los ataques. El éxito de escape varía entre especies, desde ∼77% en Agalychnis callidryas hasta sólo ∼9% en A. spurrelli a un día antes de la eclosión espontanea. Ambas especies comienzan a responder a los ataques de serpientes en etapas del desarrollo similares cuando inicia la función mecanosensorial vestibular, lo que sugiere que la capacidad sensorial no limita la respuesta de eclosión en A. spurrelli. Estructuralmente, las posturas de A. callidryas son gruesas y gelatinosas, mientras que las de A. spurrelli son más delgadas y rígidas. Esta diferencia en estructura de la postura podría afectar su movimiento y la propagación de las señales de vibración que perciben los embriones durante los ataques de serpientes. Por lo tanto, investigamos la hipótesis de que las diferencias entre especies en las respuestas de eclosión a los ataques de serpientes se deben a la influencia de la biomecánica de las posturas en las señales disponibles para los embriones. Mecánicamente, las estructuras más delgadas deberían tener frecuencias de resonancia más altas, mayor atenuación espacial y una amortiguación de vibraciones más rápida que las estructuras más gruesas y flexibles. Evaluamos la biomecánica de las posturas mediante la incorporación de acelerómetros pequeños dentro de las posturas de ambas especies, así como la grabación de vibraciones causadas por pruebas de excitación estandarizadas a diferentes distancias del acelerómetro. Los análisis de las vibraciones registradas indican que las posturas de A. spurrelli tienen frecuencias de vibración más altas y una mayor amortiguación de vibraciones que las posturas de A. callidryas. Las frecuencias más altas provocan menos eclosión en A. callidryas, y una mayor amortiguación podría reducir la cantidad de vibración que pueden percibir los embriones. Para probar directamente si la estructura de posturas afecta el éxito de escape en los ataques de serpientes, trasplantamos huevos de A. spurrelli en posturas de A. callidryas y comparamos sus tasas de escape con controles conespecíficos de la misma edad no trasplantados. También realizamos trasplante recíproco en A. callidryas como control de método. El trasplante de embriones de A. spurrelli en posturas de A. callidryas casi triplicó su éxito de escape (44%) en comparación con los controles conespecíficos (15%), mientras que el trasplante de huevos de A. callidryas aumentó el éxito de escape en solo un 10%. Al momento de la eclosión, los huevos de A. callidryas ya no están encapsulados en gelatina, mientras que los huevos de A. spurrelli conservan su cápsula de gelatina. Por lo tanto, comparamos la respuesta de eclosión y la latencia de A. spurrelli en huevos sin gelatina y sus hermanos de control, encapsulados en gelatina, usando movimientos manuales de huevos para simular señales de depredación. Los embriones en huevos sin gelatina tenían más probabilidades de eclosionar y eclosionaron más rápido que los hermanos de control. Nuestros resultados sugieren que las propiedades de las estructuras producidas por padres, como las posturas de huevos, incluida su biomecánica de vibración, restringen la información disponible para los embriones de A. spurrelli y contribuyen a las diferencias interespecíficas en las respuestas de eclosión a los ataques de los depredadores.

Estimation of structural wave numbers from spatially sparse response measurements.

A method is presented for estimating the complex wave numbers and amplitudes of waves that propagate in damped structures, such as beams, plates, and shells. The analytical basis of the method is a wave field that approximates response measurements in an aperture where no excitations are applied. At each frequency, the method iteratively adjusts wave numbers to best approximate response measurements, using wave numbers at neighboring frequencies as initial estimates in the search. In comparison to existing methods, the method generally requires far fewer measurement locations and does not require evenly spaced locations. The number of locations required by the method scales with the number of waves that propagate in the structure, whereas the number of locations required by existing methods scales with the minimum wavelength. In addition, the method allows convenient inclusion of the analytic relationships between wave numbers that exist for flexural vibrations of beams and plates. Advantages of the method are illustrated by an example in which a beam is excited by a transverse force at one end. Using analytic data and experimental measurements, the method produces a wave field that matches response measurements to within 1 percent. One interesting feature of the new method is that, when applied to analytic data, it supplies more robust wave number estimates using responses at unevenly spaced locations.

Applications of the causality condition to one-dimensional acoustic reflection problems.

The causality condition is examined as a means of determining frequency-domain information about a submerged object from a partial knowledge of its acoustic reflection characteristics. A one-dimensional problem is considered in which an acoustic wave reflects from an object that is described by the impedance it presents to the fluid. Two new applications of the causality condition to the frequency-domain analysis of this problem are investigated and illustrated by numerical examples. In each application, the causality condition is used to find the object's complex impedance from a knowledge of the reflected wave's magnitude. The first application is to experimental studies where one desires a knowledge of an object's complex impedance but practical limitations only allow a measurement of the reflected wave amplitude. Analysis shows that the causality condition may be used to determine the phase of the reflected wave, and hence the object's impedance, if the reflection coefficient is minimum phase. When this is true, examples suggest that the phase of the reflection coefficient may be accurately determined from the causality condition even in the presence of noise and band-limited data. The second application is to design situations, where one wishes to create an object that reflects sound with a specified frequency-dependent magnitude. The causality condition may aid the designer by providing a knowledge of all causal object impedances that produce the same reflection coefficient magnitude. A numerical example is presented in which a variety of causal object impedances produce the same reflection coefficient magnitude over an infinite frequency range.

Adoption of security and confidentiality features in an operational community health information network: the Comox Valley experience--case example.

Since 1993, a budding community health information network (CHIN) has been in operation in the Comox Valley in Canada. A general hospital and three multi-doctor clinics are linked electronically. The clinics operate without paper charts using a comprehensive clinic information system. The link is provided by RSALink, a commercial message exchange service, based on Health Link, a system developed at the University of Victoria (McDaniel et al., Can. Med. Inform. 1 (1994) 40-41; McDaniel, Dissertation, University of Victoria, Canada, 1994). Health Link is a highly adaptable message exchange service with rich functionality. Despite this, the system is used exclusively to receive laboratory results transmitted by the hospital's laboratory system (RSAStat). The results are deposited in the patient data base of a commercial clinic information system (CliniCare). This case is instructive because the users' selection of services available through Health Link allows us to observe the preferences in this informational sophisticated environment. Laboratory data transmission is appreciated as highly beneficial. The reliability, security and ample privacy protection and authentication features of Health Link, in contrast, are used in a black box mode and are not consciously exploited. This is consistent with our experience of the use of other systems which have operated for a substantial time, essentially without serious protection features. Our experience suggests that security and confidentiality features are exploited only to the extent that they do not require additional effort or conscientious intervention. This puts the system provider in the difficult position of either offering interactive systems that nobody will use, or providing automated features that nobody is aware of and that are therefore not used to full advantage--if at all.

Discrete-event simulation of a wide-area health care network.

OBJECTIVE: Predict the behavior and estimate the telecommunication cost of a wide-area message store-and-forward network for health care providers that uses the telephone system. DESIGN: A tool with which to perform large-scale discrete-event simulations was developed. Network models for star and mesh topologies were constructed to analyze the differences in performances and telecommunication costs. The distribution of nodes in the network models approximates the distribution of physicians, hospitals, medical labs, and insurers in the Province of Saskatchewan, Canada. Modeling parameters were based on measurements taken from a prototype telephone network and a survey conducted at two medical clinics. Simulation studies were conducted for both topologies. RESULTS: For either topology, the telecommunication cost of a network in Saskatchewan is projected to be less than $100 (Canadian) per month per node. The estimated telecommunication cost of the star topology is approximately half that of the mesh. Simulations predict that a mean end-to-end message delivery time of two hours or less is achievable at this cost. A doubling of the data volume results in an increase of less than 50% in the mean end-to-end message transfer time. CONCLUSION: The simulation models provided an estimate of network performance and telecommunication cost in a specific Canadian province. At the expected operating point, network performance appeared to be relatively insensitive to increases in data volume. Similar results might be anticipated in other rural states and provinces in North America where a telephone-based network is desired.

Impediments to developing wide area networks in health care.

The availability and prominence of telecommunication technology has spurred research into generic wide area health care networks. Electronic exchange of patient data supposedly results in cost efficiencies, increased accessibility to health care resources, and improved delivery of health care services. Although a number of pilot networks have been built, none yet have a broad, heterogeneous base of users and applications. Properties of the health care process and delivery system delay the acceptance of generic wide area networks and end-user computer applications. As the technical problems seem well understood, it seems advisable to investigate these factors in telemedical research.

Simulation studies of a wide area health care network.

There is an increasing number of efforts to install wide area health care networks. Some of these networks are being built to support several applications over a wide user base consisting primarily of medical practices, hospitals, pharmacies, medical laboratories, payors, and suppliers. Although on-line, multi-media telecommunication is desirable for some purposes such as cardiac monitoring, store-and-forward messaging is adequate for many common, high-volume applications. Laboratory test results and payment claims, for example, can be distributed using electronic messaging networks. Several network prototypes have been constructed to determine the technical problems and to assess the effectiveness of electronic messaging in wide area health care networks. Our project, Health Link, developed prototype software that was able to use the public switched telephone network to exchange messages automatically, reliably and securely. The network could be configured to accommodate the many different traffic patterns and cost constraints of its users. Discrete event simulations were performed on several network models. Canonical star and mesh networks, that were composed of nodes operating at steady state under equal loads, were modeled. Both topologies were found to support the throughput of a generic wide area health care network. The mean message delivery time of the mesh network was found to be less than that of the star network. Further simulations were conducted for a realistic large-scale health care network consisting of 1,553 doctors, 26 hospitals, four medical labs, one provincial lab and one insurer. Two network topologies were investigated: one using predominantly peer-to-peer communication, the other using client-server communication.(ABSTRACT TRUNCATED AT 250 WORDS)