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PubMed1987

Nuclear magnetic resonance spectroscopy of acute and evolving pulmonary hemorrhage. An in vitro study.

The proton NMR relaxation times of lung tissue were determined in a rabbit model of acute and evolving pulmonary hemorrhage (PH). Pure PH was simulated by injecting blood into a single lobe using endobronchial catheterization. In vitro spectroscopic measurements of T1 and T2 were made and total water content was determined on lung samples that were excised at regular intervals. T1 and T2 were markedly longer in lungs with acute PH than in normal lungs (T1: 818 +/- 44 vs. 643 +/- 4 msec; T2 164.0 +/- 16.3 vs. 88.1 +/- 3.4 msec). Within the first 24 hours, evolving PH was characterized by a rapid and progressive decrease in T1 (-50%) and T2 (-57%). Up to seven days after the instillation of blood, the T1 (450 +/- 43 msec) and T2 (69.7 +/- 1.9 msec) of lung with modeled PH remained below values of normal lung. The observed shortening of the relaxation times of lung disease with PH was closely paralleled by a decrease in tissue water content.

Animals↗
PubMedDate not supplied

Changing associate degree nursing curricula to meet evolving healthcare delivery system needs.

Curricular change for evolving healthcare delivery: everyone says to do it, but how, and what do you do? The authors explore the need for curricular change, a process to use in making the changes, essential elements to explore, and what changes one community college made. Included in the curricular revision is the hardest part-what was deleted-as well as what was added, and how nurse educators can continue to evolve.

Curriculum↗
PubMed1985

Massive fatal ventricular septal defect due to nonpenetrating chest trauma in a six-year-old boy: the role of early invasive monitoring in an evolving lesion.

Isolated ventricular septal defects due to nonpenetrating chest trauma are unusual lesions in adults and very rare in children. A review of the literature and of the natural course of traumatic ventricular septal defects is discussed, with emphasis on the evolving course and frequent late appearance of this lesion. Surgical closure is the treatment of choice, most often performed electively following medical treatment. Defects resulting in progressive severe congestive heart failure must be repaired emergently. The key to successful outcome is early suspicion of such a defect in the presence of heart failure following a period of relative cardiovascular stability. Anticipation of evolving myocardial dysfunction in the presence of seemingly minor chest wall injury and nonspecific electrocardiographic changes is emphasized. A case of a fatal traumatic ventricular septal defect is presented. The importance of early invasive monitoring with proper interpretation of hemodynamic data is discussed.

Child↗
PubMed2005

Liver biopsy: evolving role in the new millennium.

Since the origination of the liver biopsy, the technique has evolved into an essential diagnostic tool, with very few complications. In addition to the percutaneous approach, a liver biopsy can also be obtained via transjugular, laparoscopic, or intraoperative approach. While in the early 1960s and 1970s the liver biopsy was used for making a diagnosis in cases of clinically suspected medical liver disease, today it is more often performed to assess disease prognosis and evaluate therapeutic strategies. As a result, indications for the liver biopsy have evolved over the past 2 decades. However with advances in serologic diagnosis of viral/autoimmune hepatitis and laboratory tests for genetic disorders, the role of liver biopsy in certain clinical settings is currently debated. This review discusses the technique, indications, contraindications, and the changing role of liver biopsy in some of the common disorders and the associated controversies.

Biopsy↗
PubMed2006

Mutations of intermediate effect are responsible for adaptation in evolving Pseudomonas fluorescens populations.

The fixation of a beneficial mutation represents the first step in adaptation, and the average effect of such mutations is therefore a fundamental property of evolving populations. It is nevertheless poorly characterized because the rarity of beneficial mutations makes it difficult to obtain reliable estimates of fitness. We obtained 68 genotypes each containing a single fixed beneficial mutation from experimental populations of Pseudomonas fluorescens, evolving in medium with serine as the sole carbon source and estimated the selective advantage of each by competition with the ancestor. The distribution of selection coefficients is modal and closely resembles the Weibull distribution. The average selection coefficient (2.1) and beneficial mutation rate (3.8x10(-8)) are high relative to previous studies, possibly because the ancestral population grows poorly in serine-limited medium. Our experiment suggests that the initial stages of adaptation to stressful environments will involve the substitution of mutations with large effect on fitness.

Adaptation, Physiological↗
PubMed2004

Evasive mimicry: when (if ever) could mimicry based on difficulty of capture evolve?

We elucidate the conditions under which an easy-to-catch edible prey species may evolve to resemble another edible species that is much more difficult to capture ('evasive Batesian mimicry'), and the conditions under which two or more edible but hard-to-catch species evolve a common resemblance ('evasive Mullerian mimicry'). Using two complementary mathematical models, we argue that both phenomena are logically possible but that several factors will limit the prevalence of these forms of mimicry in nature. Evasive Batesian mimicry is most likely to arise when it is costly in time or energy for the predator species to pursue evasive prey, when mimics are encountered less frequently than evasive models and where there are abundant alternative prey. Evasive Mullerian mimicry, by contrast, is most likely to arise when evasive prey species differ in abundance, predators are slow to learn to avoid evasive prey and evading capture is costly to the prey. Unequivocal evidence for evasive Batesian or Mullerian mimicry has not yet been demonstrated in the field, and we argue that more empirical work is needed to test whether putative examples are indeed a result of selection to signal difficulty of capture.

Adaptation, Physiological↗
PubMed2005

Contingent movement and cooperation evolve under generalized reciprocity.

How cooperation and altruism among non-relatives can persist in the face of cheating remains a key puzzle in evolutionary biology. Although mechanisms such as direct and indirect reciprocity and limited movement have been put forward to explain such cooperation, they cannot explain cooperation among unfamiliar, highly mobile individuals. Here we show that cooperation may be evolutionarily stable if decisions taken to cooperate and to change group membership are both dependent on anonymous social experience (generalized reciprocity). We find that a win-stay, lose-shift rule (where shifting is either moving away from the group or changing tactics within the group after receiving defection) evolves in evolutionary simulations when group leaving is moderately costly (i.e. the current payoff to being alone is low, but still higher than that in a mutually defecting group, and new groups are rarely encountered). This leads to the establishment of widespread cooperation in the population. If the costs of group leaving are reduced, a similar group-leaving rule evolves in association with cooperation in pairs and exploitation of larger anonymous groups. We emphasize that mechanisms of assortment within populations are often behavioural decisions and should not be considered independently of the evolution of cooperation.

Animals↗
PubMed2003

Evolving spike-timing-dependent plasticity for single-trial learning in robots.

Single-trial learning is studied in an evolved robot model of synaptic spike-timing-dependent plasticity (STDP). Robots must perform positive phototaxis but must learn to perform negative phototaxis in the presence of a short-lived aversive sound stimulus. STDP acts at the millisecond range and depends asymmetrically on the relative timing of pre- and post-synaptic spikes. Although it has been involved in learning models of input prediction, these models require the iterated presentation of the input pattern, and it is hard to see how this mechanism could sustain single-trial learning over a time-scale of tens of seconds. An incremental evolutionary approach is used to answer this question. The evolved robots succeed in learning the appropriate behaviour, but learning does not depend on achieving the right synaptic configuration but rather the right pattern of neural activity. Robot performance during positive phototaxis is quite robust to loss of spike-timing information, but in contrast, this loss is catastrophic for learning negative phototaxis where entrained firing is common. Tests show that the final weight configuration carries no information about whether a robot is performing one behaviour or the other. Fixing weights, however, has the effect of degrading performance, thus demonstrating that plasticity is used to sustain the neural activity corresponding both to the normal phototaxis condition and to the learned behaviour. The implications and limitations of this result are discussed.

Action Potentials↗
PubMed2001

Scaling properties of scale-free evolving networks: continuous approach.

The scaling behavior of scale-free evolving networks, arising in areas such as communications, scientific citations, collaborations, etc., is studied. We derive universal scaling relations describing properties of such networks, and indicate the limits of their validity. We show that the main properties of scale-free evolving networks may be described in the framework of a simple continuous approach. The simplest models of networks, growing according to a mechanism of preferential attachment of links to nodes, are used. We consider different forms of this preference, and demonstrate that the range of preferential attachments producing scale-free networks is wide. We also obtain scaling relations for networks with nonlinear, accelerating growth, and describe the temporal evolution of the arising distributions. Size effects-the cutoffs of these distributions-introduce restrictions for the observation of power-law dependences. Mainly we discuss the so-called degree distribution, i.e., the distribution of the number of connections of nodes. A scaling form of the distribution of links between pairs of individual nodes for a growing network of citations is also studied. We describe the effects of differences between nodes. The "aging" of nodes changes the exponents of the distributions. The appearance of a single node with high fitness changes the degree distribution of a network dramatically. If its fitness exceeds some threshold value, this node captures a finite part of all links of the network. We show that permanent random damage to a growing scale-free network-a permanent deletion of some links-radically changes the values of the scaling exponents. Results of other kinds of permanent damage are described.

Journal Article↗
PubMed2002

Global optimization on an evolving energy landscape.

Locating the global minimum of a complex potential energy surface is facilitated by considering a homotopy, namely, a family of surfaces that interpolate continuously from an arbitrary initial potential to the system under consideration. Different strategies can be used to follow the evolving minima. It is possible to enhance the probability of locating the global minimum through a heuristic choice of interpolation schemes and parameters, and the continuously evolving potential landscape reduces the probability of trapping in local minima. In application to a model problem, finding the ground-state configuration and the energy of rare-gas (Lennard-Jones) atomic clusters, we demonstrate the utility and the efficacy of this method.

Journal Article↗
PubMed2002

Stationary and nonstationary properties of evolving networks with preferential linkage.

Networks evolving by preferential attachment of both external and internal links are investigated. The rate of adding an external link is assumed to depend linearly on the degree of a preexisting node to which a new node is connected. The process of creating an internal link, between a pair of existing vertices, is assumed to be controlled entirely by the vertex that has more links than the other vertex in the pair, and the rate of creation of such a link is assumed to be, in general, nonlinear in the degree of the more strongly connected vertex. It is shown that degree distributions of networks evolving only by creating internal links display for large degrees a nonstationary power-law decay with a time-dependent scaling exponent. Nonstationary power-law behaviors are numerically shown to persist even when the number of nodes is not fixed and both external and internal connections are introduced, provided that the rate of preferential attachment of internal connections is nonlinear. It is argued that nonstationary effects are not unlikely in real networks, although these effects may not be apparent, especially in networks with a slowly varying mean degree.

Journal Article↗
PubMed2005

Transport on randomly evolving trees.

The time process of transport on randomly evolving trees is investigated. By introducing the notions of living and dead nodes, a model of random tree evolution is constructed which describes the spreading in time of objects corresponding to nodes. It is assumed that at t=0 the tree consists of a single living node (root), from which the evolution may begin. At a certain time instant tau> or =0, the root produces v> or =0 living nodes connected by lines to the root which becomes dead at the moment of the offspring production. In the evolution process each of the new living nodes evolves further like a root independently of the others. By using the methods of the age-dependent branching processes we derive the joint distribution function of the numbers of living and dead nodes, and determine the correlation between these node numbers as a function of time. It is proved that the correlation function converges to square root of 3/2 independently of the distributions of v and tau when q1-->1 and t-->infinity. Also analyzed are the stochastic properties of the end nodes; and the correlation between the numbers of living and dead end nodes is shown to change its character suddenly at the very beginning of the evolution process. The survival probability of random trees is investigated and expressions are derived for this probability.

Aging↗
PubMed2001

Weighted evolving networks.

Many biological, ecological, and economic systems are best described by weighted networks, as the nodes interact with each other with varying strength. However, most evolving network models studied so far are binary, the link strength being either 0 or 1. In this paper we introduce and investigate the scaling properties of a class of models which assign weights to the links as the network evolves. The combined numerical and analytical approach indicates that asymptotically the total weight distribution converges to the scaling behavior of the connectivity distribution, but this convergence is hampered by strong logarithmic corrections.

Mathematical Computing↗
PubMed1996

Analysis of the Import of Carboxyl-Terminal Truncations of the 23-Kilodalton Subunit of the Oxygen-Evolving Complex Suggests That Its Structure Is an Important Determinant for Thylakoid Transport.

A series of deletions from the carboxyl terminus of the 23-kD subunit of the photosynthetic oxygen-evolving complex OE23 revealed that these truncations result in various degrees of inhibition of translocation across thylakoid membranes and their subsequent assembly to the oxygen-evolving complex. Import of in vitro translated precursors across the chloroplast envelopes was not inhibited by these truncations. Time-course studies of the import of truncated OE23 precursors into intact chloroplasts revealed that the stromal intermediate was subsequently translocated into the thylakoid lumen, where it was processed to a smaller size and rapidly degraded. In contrast to the full-length OE23 intermediate, the truncated intermediate forms that accumulated in the stroma as a result of de-energization of thylakoid membranes could be found associated with the membrane rather than free in the stroma. Protease digestion experiments revealed that the deletions evidently altered the folded conformation of the protein. These results suggest that the carboxyl-terminal portion of the OE23 precursor is important for the maintenance of an optimal structure for import into thylakoids, implying that the efficient translocation of OE23 requires the protein to be correctly folded. In addition, the rapid degradation of the truncated forms of the processed OE23 within the lumen indicates that a protease (or proteases) active in the lumen can recognize and remove misfolded polypeptides.

Journal Article↗
PubMed1997

Thermal protection of the oxygen-evolving machinery by PsbU, an extrinsic protein of photosystem II, in Synechococcus species PCC 7002.

The evolution of oxygen is the reaction that is the most susceptible to heat in photosynthesis. We showed previously that, in the cyanobacterium Synechococcus sp. PCC 7002, some protein factors located on the thylakoid membranes are involved in the stabilization of this reaction against heat-induced inactivation, and we identified cytochrome C550 as one such factor (Y. Nishiyama, H. Hayashi, T. Watanabe, N. Murata [1994] Plant Physiol 105: 1313-1319). In the present study we purified another protein that appears to be essential for the stabilization of the oxygen-evolving machinery. The purified protein had an apparent molecular mass of 13 kD, and the gene encoding the 13-kD protein was cloned from Synechococcus sp. PCC 7002 and sequenced. The deduced amino acid sequence revealed that the protein was homologous to PsbU, an extrinsic protein of the photosystem II complex, which has been found in thermophilic species of cyanobacteria. Western analysis showed that the level of PsbU in thylakoid membranes was constant, regardless of the growth temperature. Our studies indicate that PsbU, a constituent of the photosystem II complex, protects the oxygen-evolving machinery against heat-induced inactivation.

Amino Acid Sequence↗
PubMed1997

Assembly of Newly Imported Oxygen-Evolving Complex Subunits in Isolated Chloroplasts: Sites of Assembly and Mechanism of Binding.

We have examined the assembly of the nuclear-encoded subunits of the oxygen-evolving complex (OEC) after their import into isolated intact chloroplasts. We showed that all three subunits examined (OE33, OE23, and OE17) partition between the thylakoid lumen and a site on the inner surface of the thylakoid membrane after import in a homologous system (e.g., pea or spinach subunits into pea or spinach chloroplasts, respectively). Although some interspecies protein import experiments resulted in OEC subunit binding, maize OE17 did not bind thylakoid membranes in chloroplasts isolated from peas. Newly imported OE33 and OE23 were washed from the membranes at the same concentrations of urea and NaCl as the native, indigenous proteins; this observation suggests that the former subunits are bound productively within the OEC. Inhibition of neither chloroplast protein synthesis nor light- or ATP-dependent energization of the thylakoid membrane significantly affected these assembly reactions, and we present evidence suggesting that incoming subunits actively displace those already bound to the thylakoid membrane. Transport of OE33 took place primarily in the stromal-exposed membranes and proceeded through a protease-sensitive, mature intermediate. Initial binding of OE33 to the thylakoid membrane occurred primarily in the stromal-exposed membranes, from where it migrated with measurable kinetics to the granal region. In contrast, OE23 assembly occurred in the granal membrane regions. This information is incorporated into a model of the stepwise assembly of oxygen-evolving photosystem II.

Journal Article↗
PubMed1997

Administration to innovation: the evolving management challenge in primary care.

The concept of the primary health-care team involving an increasingly diverse range of health care professionals is widely recognized as central to the pursuit of a primary care-led health service in the UK. Although GPs are formally recognized as the team leaders, there is little by way of policy prescription as to how team roles and relationships should be developed, or evidence as to how their roles have in fact evolved. Thus the notion of the primary health-care team while commonly employed, is in reality lacking definition with the current contribution of practice managers to the operation of this team being poorly understood. Focusing on the career backgrounds of practice managers, their range of responsibilities, and their involvement in innovation in general practice, presents a preliminary account of a chief scientist office-funded project examining the role being played by practice managers in primary health-care innovation. More specifically, utilizing data gained from the ongoing study, contextualizes the role played by practice managers in the primary health-care team. By exploring the business environment surrounding the NHS general practice, the research seeks to understand the evolving world of the practice manager. Drawing on questionnaire data, reinforced by qualitative data from the current interview phase, describes the role played by practice managers in differing practice contexts. This facilitates a discussion of a set of ideal type general practice organizational and managerial structures. Discusses the relationships and skills required by practice managers in each of these organizational types with reference to data gathered to date in the research.

Community Health Services↗
PubMed2001

Female choice via indicator traits easily evolves in the face of recombination and migration.

Species that exist in heterogeneous environments experience selection for specialization that is opposed by the homogenizing forces of migration and recombination. Migration tends to reduce associations between alleles and habitats, whereas recombination tends to break down associations among loci. The idea that heterogeneity should favor the evolution of isolating mechanisms has motivated evolutionary studies of reduced migration, habitat preference, and assortative mating. However, costly female choice of high-quality males can also evolve in heterogeneous populations and is not hindered by either recombination or migration. When information on male fitness is available through indicator traits, female choice based on these traits increases associations between female choice alleles and locally adapted alleles. Not only does female choice evolve in a heterogeneous environment, it acts to enhance the level of genetic variation and is thus self-reinforcing. The amount of female choice at equilibrium depends on how well mixed the habitats are, how much information on male genotype is available, and how different the habitats are. Female choice reaches the highest levels for intermediate levels of heterogeneity, because at such levels of heterogeneity there is both a high risk and high cost of mismating.

Alleles↗