Host Specialization and Dispersal in Avian Haemosporidians

In order to be able to understand the ecological and evolutionary processes involved in the emergence of infectious diseases, one needs to comprehend how parasites arrive at new geographical areas and how they manage to maintain viable populations and even expand their ranges. We discuss host specificity in avian haemosporidians and how encounter and compatibility filters affect the dispersal of avian haemosporidians, and how these filters affect avian haemosporidian assemblages at different spatial and evolutionary scales. There are at least three important barriers to the dispersal of avian haemosporidians: (i) geographic barriers, (ii) environmental barriers, and (iii) interspecies barriers. In this chapter, we discuss the factors involved in these barriers and their effects on the structure of avian haemosporidian assemblages. Host specificity plays an important role in parasite dispersal, and in the case of avian haemosporidians that are vector-borne parasites, it needs to be evaluated both at the vector and bird host levels. Understanding the effects of these factors on host–vector–parasite dynamics is important to unravel the dispersal and diversification mechanisms of avian haemosporidians. We end this chapter reviewing host specialization in avian haemosporidians of tropical regions, discussing the mechanisms involved in the dispersal and specialization of these parasites and point out important research gaps that need attention

Effects of exercise on visual evoked potentials

PubMedID: 16051549The aim of this study was to investigate the effects of acute or habitual exercise on visual evoked potentials (VEP). The study group consisted of 9 female and 7 male volleyball players and the control group contained 9 female and 7 male students who were not involved in any sportive activity. The N75, P100, and N145 latency and amplitudes were measured before and after exercise. Intragroup comparison was made to evaluate the acute effects and intergroup comparison for the chronic effects of exercise. Significant differences were noted between athletes and the sedentary subjects in terms of pre-exercise left-N145 latencies and amplitudes and left -P100 amplitudes. Right-eye N145 latencies of inactive female subjects obtained before and after exercise were also statistically different. The results suggest that acute and habitual exercise affects the VEP responses independent from the body temperature and other physiological parameters. Small sized pre-exercise P100 amplitudes in the athletes can be attributed to the effect of rapid visual-activity-demanding sports on the central nervous system. Visual evoked potentials maybe used as neurophysiological criteria in defining the performance of an athlete. Copyright © 2005 Taylor & Francis Inc

Static And Dynamic Testing Of A Concrete T-Beam Bridge Before And After Carbon Fiber-Reinforced Polymer Retrofit

This paper summarizes the design and execution of field studies to improve the performance of a deteriorated bridge through the use of carbon fiber-reinforced polymer (CFRP) material. The objective of the CFRP retrofit was to extend the life of Bridge 2028 in Cayey, Puerto Rico, by increasing its load rating. Field testing before and after the retrofit was performed to evaluate objectively improvement in load capacity and stiffness. The field testing program included both static load tests and dynamic tests. The first set of field tests was conducted in November 2002 to capture baseline bridge performance characteristics before the retrofit The CFRP retrofit was installed in October 2003, and a second set of nearly identical field tests was performed in August 2004. The test results indicated that the retrofit increased the bending stiffness of the bridge by 15% and decreased the tensile strains in the bottom rebars of the concrete T-beams by about 13%. Furthermore, the maximum rebar strains under a heavy truck load case were only 10% of the yield strength after the retrofit The change in stiffness determined from static deflection measurements was well correlated with the stiffness change determined from the dynamic tests. The field testing program showed that the CFRP retrofit was successful in improving the mechanical behavior of the bridge. The long-term performance and durability of the CFRP retrofit could be affected by a number of parameters such as local environmental conditions. The field testing program is to be periodically repeated; alternatively, a continuous monitoring program could be implemented to evaluate objectively the long-term performance and durability of the CFRP retrofit

Limitations In Structural Identification Of Large Constructed Structures

The objective of this paper is to discuss the limitations in structural identification of large constructed structures. These limitations arise due to the geometric complexity, uncertain boundary and continuity conditions, loading environment, and the imperfect knowledge and errors in modeling such large constructed facilities. In this paper, the writers present their studies on developing a mixed microscopic-structural element level three-dimensional finite-element (FE) modeling of a long-span bridge structure and its structural system identification by integrating various experimental techniques. It is shown that a reasonable level of confidence (50-90%) can be achieved with a model that is calibrated using global and local structural monitoring data with a sufficiently high spatial resolution. The reliability of the global attributes, such as boundary and continuity conditions that may be identified and simulated by means of field-calibrated models using only dynamic test results (globally calibrated models), may appear to be high (as much as 90%). However, the reliability that should be expected for local stress fields is shown to be an entirely different matter, and a calibration based on just dynamic testing would be unable to reveal the confidence in simulated local responses. This is especially true for long-span bridges, because the resolutions of the dynamic test grids are often quite sparse due to the large size of the structures. In this paper, the writers illustrate that the density, modality, and bandwidth of experimental data should be carefully evaluated and matched to the size and complexity of a constructed system before claiming that a FE model is validated. It is also shown that even more than three dozen acceleration measurement points, two dozen strain measurements, and a continuous surveillance of wind and temperature were barely sufficient for a credible structural identification of a long-span bridge. © 2007 ASCE

Angiotensin-converting enzyme gene polymorphism, left ventricular remodeling, and exercise capacity in strength-trained athletes

The mechanisms that regulate the development of human physiological cardiac hypertrophy remain poorly understood. The renin-angiotensin system, which is modulated by genetic polymorphism, plays an important role in the regulation of vascular tone and myocardial hypertrophy. Although a few studies have analyzed the association of angiotensin-converting enzyme (ACE) polymorphism and left ventricular (LV) hypertrophy in isotonic exercise-trained subjects who developed eccentric cardiac hypertrophy, there has been no research done in power athletes who developed concentric cardiac hypertrophy. We have hypothesized that ACE genotypic modulation characteristics may affect LV mass in power athletes. This study included 29 elite Caucasian wrestlers ( mean age, 22.6 years) and 51 age-matched sedentary subjects. According to the absence or presence of the insertion segment in the polymerase chain reaction (PCR) product, the subjects were classified as homozygous deletion-deletion (DD), insertion-insertion (II), or heterozygous insertion-deletion ( ID). The association of LV hypertrophy with ACE gene insertion/deletion (I/D) polymorphism was analyzed. Left ventricular mass and index were determined by echocardiography. Angiotensin-converting enzyme genotyping was performed on peripheral leukocytes using the polymerase chain reaction technique. The study and control group subjects were similar in height and weight. Left ventricular hypertrophy in the athletes was more apparent than in the controls. Angiotensin-converting enzyme genotype II frequency was 17.2% (5) in the athletes, 17.6% (9) in the controls; ID frequency was 51.7% (15) in the athletes, 56.8% (29) in the controls; and the DD frequency was 31% ( 9) in the athletes and 25.4% ( 13) in the controls. Left ventricular mass and mass index were found to be higher in genotype DD (126.2 +/- 2.9 g/m(2)) than genotype II (85.5 +/- 4.0 g/m(2)) or genotype ID (110.1 +/- 2.3 g/m(2)) in the athletes ( P < 0.001). Furthermore, maximal oxygen consumption in genotype DD was found to be higher than in II and ID. An association was found between ACE gene I/D polymorphism and LV hypertrophy in strength-trained athletes