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Realistic Values (realistic + value)
Selected AbstractsField testing of equilibrium passive samplers to determine freely dissolved native polycyclic aromatic hydrocarbon concentrationsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2008Gerard Cornelissen Abstract Equilibrium passive samplers are promising tools to determine freely dissolved aqueous concentrations (CW,free) of hydrophobic organic compounds. Their use in the field, however, remains a challenge. In the present study on native polycyclic aromatic hydrocarbons (PAHs) in Oslo Harbor, Norway, two different passive sampler materials, polyoxymethylene (POM; thickness, 55 ,m [POM-55] and 500 ,m [POM-500]) and polydimethylsiloxane (PDMS; thickness, 200 ,m), were used to determine in the laboratory CW,free in sediment pore water (CPW,free), and the suitability of five passive samplers for determination of CW,free in overlying surface water was tested under field conditions. For laboratory determinations of CPW,free, both POM-55 and PDMS turned out to be suitable. In the field, the shortest equilibrium times (approximately one month) were observed for POM-55 and PDMS (thickness, 28 ,m) coatings on solid-phase microextraction fibers, with PDMS tubing as a good alternative. Low-density polyethylene (thickness, 100 ,m) and POM-500 did not reach equilibrium within 119 d in the field. Realistic values were obtained for dissolved organic carbon,water partition coefficients in the field (approximately one log unit under log KOW), which strengthened the conclusion that equilibrium was established in field-exposed passive samplers. At all four stations, chemical activity ratios between pore water and overlying water were greater than one for all PAHs, indicating that the sediment was a PAH diffusion source and that sediment remediation may be an appropriate treatment for PAH contamination in Oslo Harbor. [source] Individual-based Computational Modeling of Smallpox Epidemic Control StrategiesACADEMIC EMERGENCY MEDICINE, Issue 11 2006Donald S. Burke MD In response to concerns about possible bioterrorism, the authors developed an individual-based (or "agent-based") computational model of smallpox epidemic transmission and control. The model explicitly represents an "artificial society" of individual human beings, each implemented as a distinct object, or data structure in a computer program. These agents interact locally with one another in code-represented social units such as homes, workplaces, schools, and hospitals. Over many iterations, these microinteractions generate large-scale macroscopic phenomena of fundamental interest such as the course of an epidemic in space and time. Model variables (incubation periods, clinical disease expression, contagiousness, and physical mobility) were assigned following realistic values agreed on by an advisory group of experts on smallpox. Eight response scenarios were evaluated at two epidemic scales, one being an introduction of ten smallpox cases into a 6,000-person town and the other an introduction of 500 smallpox cases into a 50,000-person town. The modeling exercise showed that contact tracing and vaccination of household, workplace, and school contacts, along with prompt reactive vaccination of hospital workers and isolation of diagnosed cases, could contain smallpox at both epidemic scales examined. [source] Dispersal and egg shortfall in Monarch butterflies: what happens when the matrix is cleaned up?ECOLOGICAL ENTOMOLOGY, Issue 1 2010MYRON P. ZALUCKI 1. We use an individual-based model describing the life of a monarch butterfly, which utilises milkweeds both aggregated in patches and scattered across the wider landscape as a substrate for laying eggs. The model simplifies the metapopulation of milkweed habitat patches by representing them as a proportion of the overall landscape, with the rest of the landscape considered matrix, which may contain some low density of milkweed plants. 2. The model simulates the number of eggs laid daily by a butterfly as it searches for hosts. The likelihood of finding hosts is related to the density of plants and the search ability of the butterfly. For an empty matrix, remaining in a habitat patch results in more eggs laid. However individuals that are good searchers have almost equivalent success without remaining in a habitat patch. These individuals are most affected by the presence of hosts in the matrix. 3. Given realistic values of habitat patch availability, our model shows that the presence of plants at a low density in the matrix has a substantial impact on the number of eggs laid; removing these plants can reduce lifetime potential fecundity by ca. 20%. These results have implications for monarch butterflies inhabiting agricultural landscapes, in which genetically modified soybean that is resistant to herbicides has resulted in the decimation of milkweeds over large areas. [source] Validation of roughhead grenadier (Macrourus berglax) otolith readingJOURNAL OF APPLIED ICHTHYOLOGY, Issue 2 2002E. Rodríguez-Marín Roughhead grenadier Macrourus berglax Lacépède 1802, is becoming an important commercial fish in the north-west Atlantic fisheries and reliable age information is needed for its assessment. Macrourus berglax has been aged by counting otolith growth zones assumed to represent anulli. Three validation methods were applied: back-calculation of length-at-age, length,frequency analysis, and analyses of the progression of the length mode of an exceptionally large year class. Results on size-at-age estimated by otolith growth zone counts, length,frequency analysis of pre-anal fin length and modal progression were internally consistent, but estimates by back-calculation were different. This latter method produces unrealistic growth curves for each sex due to the weak relationship between otolith size as measured and pre-anal fin length. Up to age 8,9 the size-at-age were the same for males and females; thereafter males were smaller than females. Male growth rate declined when pre-anal fin length reached 18 cm at around age 9, whereas the growth of females started to decline at about 30 cm at around age 16. The Von Bertalanffy growth model derived from otolith analysis was similar to that obtained by the Multifan length frequency analysis model, and gave realistic values of Linf, close to the maximum anal fin lengths found in catches. The results showed that Macrourus berglax has a prolonged life cycle and differences in growth between males and females. [source] Architectural and growth traits differ in effects on performance of clonal plants: an analysis using a field-parameterized simulation modelOIKOS, Issue 5 2007Radka Wildová Individual traits are often assumed to be linked in a straightforward manner to plant performance and processes such as population growth, competition and community dynamics. However, because no trait functions in isolation in an organism, the effect of any one trait is likely to be at least somewhat contingent on other trait values. Thus, to the extent that the suite of trait values differs among species, the magnitude and even direction of correlation between values of any particular trait and performance is likely to differ among species. Working with a group of clonal plant species, we assessed the degree of this contingency and therefore the extent to which the assumption of simple and general linkages between traits and performance is valid. To do this, we parameterized a highly calibrated, spatially explicit, individual-based model of clonal plant population dynamics and then manipulated one trait at a time in the context of realistic values of other traits for each species. The model includes traits describing growth, resource allocation, response to competition, as well as architectural traits that determine spatial spread. The model was parameterized from a short-term (3 month) experiment and then validated with a separate, longer term (two year) experiment for six clonal wetland sedges, Carex lasiocarpa, Carex sterilis, Carex stricta, Cladium mariscoides, Scirpus acutus and Scirpus americanus. These plants all co-occur in fens in southeastern Michigan and represent a spectrum of clonal growth forms from strong clumpers to runners with long rhizomes. Varying growth, allocation and competition traits produced the largest and most uniform responses in population growth among species, while variation in architectural traits produced responses that were smaller and more variable among species. This is likely due to the fact that growth and competition traits directly affect mean ramet size and number of ramets, which are direct components of population biomass. In contrast, architectural and allocation traits determine spatial distribution of biomass; in the long run, this also affects population size, but its net effect is more likely to be mediated by other traits. Such differences in how traits affect plant performance are likely to have implications for interspecific interactions and community structure, as well as on the interpretation and usefulness of single trait optimality models. [source] Acoustic phonons in InSb probed by time-resolved X-ray diffractionPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2006A. Morak Abstract Acoustical phonons in InSb were induced with femtosecond light pulses and probed by diffraction of ultrashort X-ray pulses in the crystal lattice. The time dependent transient X-ray diffraction signal due to elastic lattice deformation was measured with subpicosecond resolution. The elastic lattice deformation depends on the temporal evolution of the energy transfer from excited electrons in the semiconductor into the lattice. As already shown in previous investigation a conventional thermoelastic model is not sufficient to describe this coupling process. Here a complex simulation including a two temperature model of the electron and lattice as well as the microscopic behavior of the electron plasma is applied to explain important effects like thermal carrier diffusion and band gap deformation found in the lattice deformation experiments. When this model is used, with realistic values for both pump laser fluences and bulk material constants, excellent agreement between the experimentally observed time dependent lattice deformation and calculated values is obtained throughout the observation period. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Reporting of minimum clinically important differences in surgical trialsANZ JOURNAL OF SURGERY, Issue 4 2009Irwin Kashani Background:, The minimum clinically important difference (MCID) is the smallest difference in outcome between the groups that would be of clinical interest. It influences the estimates that are made to determine the required sample side. The aim of this study was to explore the reporting of the MCID in surgical trials. Method:, Surgical trials that were published between January 1981 and December 2006 in five prestigious surgical journals were evaluated. Selected for study were trials that studied two groups and reported the main outcome event as a proportion. Results:, Only 21% (100/486) of the admissible surgical trials mentioned a value for the MCID when estimating the sample size. There was a trend, however, for compliance with these factors to increase during the study period. The present post-hoc calculations of the required sample size, which were based on the observed differences between the groups at the end of the study, suggested that one-third of the trials should have accrued at least fivefold the number of patients. Although reporting an estimate of the sample size was associated with the study of more patients (median sample size 145 vs 100), it was not associated with the reporting of more positive results, that is, 61% (95/155) versus 65% (214/331). Conclusion:, There has been an improvement in the proportion of surgical trials reporting formal estimates of sample size during the last three decades. But the construct of these estimates is often suspect because of a failure to provide realistic values for the MCID. [source] The problem of phase mixed shear Alfvén waves in the solar corona revisitedASTRONOMISCHE NACHRICHTEN, Issue 8 2008G. Mocanu Abstract The problem of phase mixing of shear Alfvén waves is revisited taking into account dissipative phenomena specific for the solar corona. In regions of space plasmas where the dynamics is controlled by the magnetic field, transport coefficients become anisotropic with transport mechanism having different behavior and magnitude depending on the orientation with respect to the ambient magnetic field. Taking into account realistic values for dissipative coefficients we obtain that the previous results derived in context of torsional Alfvén wave phase mixing are actually heavily underestimated so phase mixing cannot be used to explain the damping of torsional Alfvén waves and heating of open coronal structures. The presented results indicate that in order for phase mixing to still be a viable mechanism to explain heating or wave damping unrealistic assumptions have to be made. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||