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PubMed2002

The cost of fluctuating inbreeding depression.

We present a phenotypic model for the evolution of self-fertilization in an infinite population of annual hermaphrodites for the case in which fitness and inbreeding depression vary among generations (e.g., due to fluctuations in the environment from year to year). Conditions for the evolution of selfing, mixed mating, and outcrossing are derived and are compared with results from numerical calculations that assume a normal distribution of inbreeding depression. In contrast to the situation in which inbreeding depression does not vary, when inbreeding depression fluctuates in a stochastic manner among generations with a mean less than 0.5, selfing is not necessarily selected. Thus, fluctuating inbreeding depression can be viewed as an additional cost of selfing that may stabilize mixed mating systems. These results emphasize the need to take into account fluctuating inbreeding depression in empirical studies aimed at understanding mating system evolution in annuals.

Biological Evolution↗
PubMed1977

Early chemical evolution of nucleic acids: a theoretical model.

Recent experimental work suggests a possible cyclical pathway for early prebiotic oligonucleotide formation that involves (i) dry-state (nontemplate) synthesis of random copolymers with mixed 2',5' and 3',5' bonds, (ii) passage of these oligomers into solution at low temperatures, and (iii) a preferential hydrolysis of the 2',5' bond in any short helices that have formed. This early system could have selected for complementary sequences that were largely 3',5'-linked, but may not have selected efficiently for a single enantiomer of ribose.

Cold Temperature↗
PubMedDate not supplied

Proton relaxation in a multicompartmental system with exchange, simulating human tissue.

The proton magnetic resonance behaviour of human tissue was simulated with a numerical model in which the resonating nuclei were assumed to belong to five different compartments of defined relative sizes and with distinct relaxation properties. Effects of various proton exchange rates between the compartments were included in the model. The time evolution of longitudinal and transverse macroscopic magnetizations was calculated. Applications of this model in magnetic resonance imaging are discussed.

Body Fluid Compartments↗
PubMed2005

Evolution of a mature clinical informationist model.

Achieving evidence-based practice will require new approaches to providing information during health care delivery and to integrating evidence and informatics at the point of care. To support evidence-based practice, Vanderbilt University Medical Center's Eskind Biomedical Library (EBL) introduced the role of clinical informationist, an information specialist with sufficient knowledge and insight to function as a true partner in the health care team. To further disseminate evidence-based knowledge, the Vanderbilt University Medical Center's (VUMC) electronic medical record system and pathway development processes integrate advanced information synthesis capabilities provided by clinical informationists. Combining clinical informationist expertise with informatics tools is an effective strategy for delivering the evidence needed to support patient care decisions.

Academic Medical Centers↗
PubMed2001

The evolution of the Fenway Community Health model.

Fenway Community Health was founded by community activists in 1971 in the Fenway neighborhood of Boston, Mass, and within a decade had rapidly expanded its medical services for gay men in response to the AIDS epidemic. Increased expertise and cultural competence in lesbian, gay, bisexual, and transgender (LGBT) care led to expansion of medical services to address broader community concerns, ranging from substance use to parenting issues to domestic and homophobic violence, as well as specialized programs for lesbians, bisexuals, and transgendered individuals. Fenway began as a grassroots neighborhood clinic. In 1975, the center recorded 5000 patient care visits; in 2000, Fenway's clinical departments recorded 50,850 visits by 8361 individuals, including more than 1100 individuals receiving HIV-associated care. The center now has more than 170 staff people responsible for clinical programs, community education, research, administration, planning, and development. Over the past few years, Fenway's annual budget has exceeded $10 million. Fenway has established standards for improved cultural competence about LGBT health issues for other health providers and has developed programs to educate the general community about specific LGBT health concerns. This health center may provide a model of comprehensive LGBT health services that have a local impact.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Evolution of an ASM2d-like model structure due to operational changes of an SBR process.

To model biological nitrogen and phosphorus removal systems with an affordable complexity, the ASM2d model structure is based on many assumptions. In this study, some of these assumptions, however, were observed to become invalid when the biological behaviour in the system altered in response to changes in the operation of the system, a pilot-scale N and P removing SBR. Particularly, the three applied operational scenarios resulted in three distinctive responses in the SBR, namely pronounced limitation of the hydrolysis of the organic nitrogen, nitrite build-up during aerobic conditions and also nitrite build-up during anoxic conditions. This shows that even for the same system with the same influent wastewater composition, the model structure of the ASM2d does not remain constant but adapts parallel to dynamic changes in the activated sludge community. On the other hand, the three calibrated ASM2d models still lacked the ability to entirely describe the observed dynamics particularly those dealing with the phosphorus dynamics and hydrolysis. Understanding the underlying reasons of this discrepancy is a challenging task, which is expected to improve the modelling of bio-P removing activated sludge systems.

Bioreactors↗
PubMedDate not supplied

The evolution of the clinician-scientist model of neurological rehabilitation.

Over the past three or four decades two treatment technologies have been evolving in parallel, recently to some extent merging. The first of these technologies is behaviour analysis, with its emphasis on identification and manipulation of variables external to the individual as controlling agents. The second is neurological rehabilitation, with a characteristic focus of resources on recovery of function following neurological damage. The histories of both of these technologies are similar in that they emerged from basic laboratory research with non-human subjects, followed by extension of findings to research with humans, culminating in widespread formal application of results. The past 5 years have seen a convergence of behaviour analytic and neurological rehabilitation techniques resulting in major shifts in treatment service delivery systems. We briefly chronicle the emergence of these two technologies from their basic underpinnings through world-wide use. Further, discussion is provided describing our and others' experience with the combining of behaviour and neurological rehabilitation. Finally, we give an account of an innovative neurological rehabilitation service delivery system designed to deliver effective cost-efficient treatment in the patient's natural environment. Implicit in the design and implementation of this real-world model of rehabilitation is the combination of behavioural technology and neurological rehabilitation towards the achievement of functional outcomes which endure. Our purpose in the above is to provide an introduction to present use and future potential of behaviour analytic methodologies and technologies in rehabilitation.

Ambulatory Care↗
PubMed1996

Mathematical models of prevascular spheroid development and catastrophe-theoretic description of rapid metastatic growth/tumor remission.

A brief survey is provided of deterministic models of tumor growth and development over the last three decades. The evolution of these models has proceeded from basic phenomenological and empirical descriptions, through both time-dependent and time-independent diffusion models (largely within the diffusive equilibrium approximation). This includes a study of the diffusion of growth inhibitors. The stability of spheroid models to small perturbations is discussed, and also recent applications of nonlinear elasticity theory and differential geometry to possible staging and grading of cancers. Finally, an excursion is made into catastrophe theory, wherein it is suggested that the cusp catastrophe (in particular) may provide a qualitative description of rapid, almost spontaneous (i) growth of metastases, or (ii) tumor remission (both occurring under certain restrictive conditions).

Animals↗
PubMed2001

Absence of regional affinities of Neandertal DNA with living humans does not reject multiregional evolution.

The recent extraction of mitochondrial DNA sequences from three European Neandertal fossils has led many to the conclusion that ancient DNA analysis supports the African replacement model of modern human origins and rejects models of multiregional evolution that propose some Neandertal ancestry in living humans. This conclusion is based, in part, on the lack of regional affinity of Neandertal DNA to that from living Europeans. Consideration of migration matrix models shows that this conclusion is premature, since under a model of interregional gene flow we expect to see similar levels of Neandertal ancestry in all contemporary regions, and living Europeans should not necessarily show closer affinity. The absence of regional affinity in Neandertal DNA does not distinguish between replacement and multiregional models.

Africa↗
PubMed2006

Self-imposed silence: parental antagonism and the evolution of X-chromosome inactivation.

A model is proposed for the evolution of X-chromosome inactivation (XCI) in which natural selection initially favors the silencing of paternally derived alleles of X-linked demand inhibitors. The compensatory upregulation of maternally derived alleles establishes a requirement for monoallelic expression in females. For this reason, XCI is self-reinforcing once established. However, inactivation of a particular X chromosome is not. Random XCI (rXCI) is favored over paternal XCI because rXCI reduces the costs of functional hemizygosity in females. Once present, rXCI favors the evolution of locus-by-locus imprinting of X-linked loci, which creates an evolutionary dynamic in which different chromosomes compete to remain active.

Animals↗
PubMed2003

A "Long Indel" model for evolutionary sequence alignment.

We present a new probabilistic model of sequence evolution, allowing indels of arbitrary length, and give sequence alignment algorithms for our model. Previously implemented evolutionary models have allowed (at most) single-residue indels or have introduced artifacts such as the existence of indivisible "fragments." We compare our algorithm to these previous methods by applying it to the structural homology dataset HOMSTRAD, evaluating the accuracy of (1) alignments and (2) evolutionary time estimates. With our method, it is possible (for the first time) to integrate probabilistic sequence alignment, with reliability indicators and arbitrary gap penalties, in the same framework as phylogenetic reconstruction. Our alignment algorithm requires that we evaluate the likelihood of any specific path of mutation events in a continuous-time Markov model, with the event times integrated out. To this effect, we introduce a "trajectory likelihood" algorithm (Appendix A). We anticipate that this algorithm will be useful in more general contexts, such as Markov Chain Monte Carlo simulations.

Algorithms↗

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