Evolution of cooperation on dynamical graphs

There are two key characteristic of animal and human societies: (1) degree heterogeneity, meaning that not all individual have the same number of associates; and (2) the interaction topology is not static, i.e. either individuals interact with different set of individuals at different times of their life, or at least they have different associations than their parents. Earlier works have shown that population structure is one of the mechanisms promoting cooperation. However, most studies had assumed that the interaction network can be described by a regular graph (homogeneous degree distribution). Recently there are an increasing number of studies employing degree heterogeneous graphs to model interaction topology. But mostly the interaction topology was assumed to be static. Here we investigate the fixation probability of the cooperator strategy in the prisoner’s dilemma, when interaction network is a random regular graph, a random graph or a scale-free graph and the interaction network is allowed to change. We show that the fixation probability of the cooperator strategy is lower when the interaction topology is described by a dynamical graph compared to a static graph. Even a limited network dynamics significantly decreases the fixation probability of cooperation, an effect that is mitigated stronger by degree heterogeneous networks topology than by a degree homogeneous one. We have also found that from the considered graph topologies the decrease of fixation probabilities due to graph dynamics is the lowest on scale-free graphs

The temporal characteristics of the motion bridging effect and a connected illusion: Time-related interactions and dependencies in a two-process-model

The Motion Bridging Effect (MBE) is a visual illusion in which a motion that is not consciously visible, due to high speed, induces an illusory rotation percept in a stationary stimulus (test ring) that is presented before or after the inducing stimulus (inducing ring). This illusionary rotation usually has the same direction as the invisible rotation of the inducing ring. Based on investigations on a related illusion, called the Ring Rotation Illusion (RRI), in which a similar motion illusion is set off through the stationary outline of a circle instead of a rotating inducer, the Two-Process-Model of the MBE was developed. In this model, the first process of the MBE could be characterized as some form of an apparent motion or a visual heuristic, that works at the transition of inducing and test stimulus and could be responsible for the RRI as well. The second process gathers the direction signal from the fast rotation of the inducing stimulus and biases the direction of the illusory motion created by the first process. In the three studies of this dissertation, a method to objectively measure the duration of the illusionary motion percept was established. The Two-ProcessModel could be supported through comparison of temporal dependencies of this duration and the perceived clarity of both illusions with the observable direction congruency of the MBE. Also, the temporal features of the emergence of the MBE were revealed. Those take the form of a constant temporal window for the perception of the illusion and an optimal minimal temporal interval for the transfer of the directional signal from the inducing to the test ring.2025-05-2

Energy Selecting Electron Microscopy

One of the major improvements in transmission electron microscopy over the last years is the addition of the capability of producing images with electrons that have specific narrow energy bands out of the total spectrum of energies they possess after having passed through the specimen. Though the idea is not new, the power of this application is only beginning to be recognized. Most simply, selection of elastically scattered electrons permits increased contrast in high resolution i mages in bright field, dark field, and diffraction. The use of combined elastic and inelastic signals adds entirely new contrast mechanisms, partially independent of thickness, partly Z-related. Finally, selection of element specific inelastic events permits elemental mapping with spatial resolutions of 0.3 -0.5 nm and detection sensitivities of about 30 to 50 atoms. Consideration of resolution, sensitivity, image points of analysis and acquisition time leads to a combined improvement of about 1013 times over X-ray microanalysis

Costly sons do not lead to adaptive sex ratio adjustment in pilot whales, Globicephala melas

Maternal investment in reproduction and parental care is an important determinant of both offspring and maternal fitness. However, optimal investment strategies may differ depending on offspring sex, potentially resulting in a sex-biased distribution of maternal resources or adaptive variation in offspring sex-ratio. We used morphometric and genetic data collected from over 3400 long-finned pilot whales Globicephala melas in 40 pods to investigate whether females experience differential costs of producing sons and daughters and whether they differentially invest in male and female offspring. We found that male calves grow faster than female calves during the first five years of life, suggesting that sons may require greater investment from lactating mothers. This appears to result in mothers experiencing a higher cost to future reproductive opportunities when producing male offspring as the presence of dependent sons (but not daughters) reduced the probability that a female would be pregnant. Despite these costs, we found no evidence that mothers adaptively adjust their investment in sons and daughters according to their body condition or their social and physical environment. These results suggest that mothers may be constrained from biasing investment in the sexes, or that additional benefits may be masking such costs. KEY WORDS: cetacean, Globicephala melas, group size, maternal investment, reproductive costs, reproductive success, sex-rati

Minimally invasive instrument for in vivo measurement of solid organ mechanical impedance

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (p. 161-165).The medical field, and surgeons in particular, are turning to engineers to develop systems that help them learn their craft better. Mannequin-based systems, animal labs and surgery on cadavers each have drawbacks that could be addressed through realistic computer-based surgical simulation systems. To generate a simulation that includes both tactile/haptic and visual feedback, one must know what the material properties of tissue are, so that a finite element or other model can generate the proper predictions for interactions between surgical instruments and tissue. This thesis presents the design, construction, characterization, and use of a mini- mally invasive surgical instrument designed to measure the linear visco-elastic prop- erties of solid organs. The Tissue Material Property Sampling Tool, or TeMPeST 1-D, applies a small amplitude vibration normal to the surface of an organ such as liver or spleen, and records the applied force and displacement. It has a range of motion of up to lmm, and can apply up to 300mN force with a 5mm right circular indenter. The open loop bandwidth of the system is approximately 100Hz, which is greater than the bandwidth of both the human visual and motor control systems. The relationships between indentation force and displacement and material prop- erties such as the elastic modulus of tissue are presented, and models are developed that show the expected response to a standard tissue model. Characterization and calibration tests demonstrate the response of the prototype components. Experi- ments performed on spring and mass elements and on silicone gel samples, which mimic tissue response, show that the TeMPeST 1-D can accurately measure their force-displacement responses.(cont.) The TeMPeST 1-D and its data acquisition system are intended to be portable, to be easily transported to and used in an operating room. The system was used in proof-of-concept experiments performed on live pigs; an example of the measured properties of porcine liver is presented. The TeMPeST 1-D is the first in a series of instruments that will be developed to support the generation of a comprehensive atlas of tissue material properties.by Mark Peter Ottensmeyer.Ph.D

Integrated Design and Prototyping of a Robotic Head for Ocular and Craniofacial Trauma Simulators

Background: Medical simulation is relevant for training medical personnel in the delivery of medical and trauma care, with benefits including quantitative evaluation and increased patient safety through reduced need to train on patients. Methods: This paper presents a prototype medical simulator focusing on ocular and craniofacial trauma (OCF), for training in management of facial and upper airway injuries. It consists of a physical, electromechanical representation of head and neck structures, including the mandible, maxillary region, neck, orbit and peri-orbital regions to replicate different craniofacial traumas. Actuation and hydraulic systems are designed to control animatronic features and flow of simulated blood, tears, and cerebrospinal fluid. Results: Experimentally validated, the OCF simulator achieves structural and functional characteristics as close as possible to those of a human body. Conclusions: The OCF Simulator can be used as a stand-alone active simulator, it can be transported and used to train surgeons in simulated real-life scenarios. Clinical Trial Registration: The authors declare that this statement is not applicable since no clinical tests have been performed

A New Tissue Resonator Indenter Device and Reliability Study

Knowledge of tissue mechanical properties is widely required by medical applications, such as disease diagnostics, surgery operation, simulation, planning, and training. A new portable device, called Tissue Resonator Indenter Device (TRID), has been developed for measurement of regional viscoelastic properties of soft tissues at the Bio-instrument and Biomechanics Lab of the University of Toronto. As a device for soft tissue properties in-vivo measurements, the reliability of TRID is crucial. This paper presents TRID’s working principle and the experimental study of TRID’s reliability with respect to inter-reliability, intra-reliability, and the indenter misalignment effect as well

Palpation Device for the Identification of Kidney and Bladder Cancer: A Pilot Study

PURPOSE: To determine the ability of a novel palpation device to differentiate between benign and malignant tissues of the kidney and bladder by measuring tissue elasticity. MATERIALS AND METHODS: A novel palpation device was developed, mainly composed of a micromotor, a linear position sensor, a force transducer, and a hemisphere tip and cylindrical body probe. Motion calibration as well as performance validation was done. The tissue elasticity of both benign and malignant tissues of the kidney and bladder was measured using this device. A single investigator performed the ex-vivo palpation experiment in twelve kidneys and four bladder specimens. Malignant tissues were made available from partial nephrectomy specimens and radical cystectomy specimens. Palpations for benign renal parenchyma tissue were carried out on nephroureterectomy specimens while non-involved areas in the radical cystectomy specimens were used for benign bladder samples. Elastic modulus (Young's modulus) of tissues was estimated using the Hertz-Sneddon equation from the experimental results. These were then compared using a t-test for independent samples. RESULTS: Renal cell carcinoma tissues appear to be softer than normal kidney tissues, whereas tissues from urothelial carcinoma of the bladder appear to be harder than normal bladder tissues. The results from renal cell carcinoma differed significantly from those of normal kidney tissues (p=0.002), as did urothelial carcinoma of the bladder from normal bladder tissues (p=0.003). CONCLUSION: Our novel palpation device can potentially differentiate between malignant and benign kidney and bladder tissues. Further studies are necessary to verify our results and define its true clinical utility.ope