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At least 613 records · Page 34Linked to original sources
PubMed2005

Structural comparison of metabolic networks in selected single cell organisms.

BACKGROUND: There has been tremendous interest in the study of biological network structure. An array of measurements has been conceived to assess the topological properties of these networks. In this study, we compared the metabolic network structures of eleven single cell organisms representing the three domains of life using these measurements, hoping to find out whether the intrinsic network design principle(s), reflected by these measurements, are different among species in the three domains of life. RESULTS: Three groups of topological properties were used in this study: network indices, degree distribution measures and motif profile measure. All of which are higher-level topological properties except for the marginal degree distribution. Metabolic networks in Archaeal species are found to be different from those in S. cerevisiae and the six Bacterial species in almost all measured higher-level topological properties. Our findings also indicate that the metabolic network in Archaeal species is similar to the exponential random network. CONCLUSION: If these metabolic network properties of the organisms studied can be extended to other species in their respective domains (which is likely), then the design principle(s) of Archaea are fundamentally different from those of Bacteria and Eukaryote. Furthermore, the functional mechanisms of Archaeal metabolic networks revealed in this study differentiate significantly from those of Bacterial and Eukaryotic organisms, which warrant further investigation.

Algorithms↗
PubMed2006

Using networks to enhance health services delivery: perspectives, paradoxes and propositions.

There is a growing need to better understand and address the consequences of an increasing reliance on networks used to enhance health services delivery. Networks seem to have emerged as the definitive solution for tackling complex healthcare problems together that we have not been able to adequately address separately. Emphasizing the collective and the collaborative, networks are assumed to address healthcare issues in ways that are superior to previous service-delivery models. While this assumption would appear to be sound theoretically, we have little empirical information available to actually understand what networks are, what they do and whether they achieve their stated goals--truly making a difference in the delivery of care and the maintenance of health. With a diversity of networks within Canada focused on health services delivery, this paper offers a multi-dimensional framework for conceptualizing how these complex inter-organizational relationships generate both challenges and opportunities. We identify six paradoxes that the networks create when used to enhance the delivery of health services and posit several propositions concerning the evaluative work that needs to be done to enhance our understanding of and confidence in this inter-organizational form. Unless these paradoxes are adequately recognized and addressed, the value and costs associated with developing and using networks in healthcare contexts will remain unclear at best. Given the broad interest in and use of networks proliferating in health-related arenas, it is time to amass the evidence and than align the perspectives. Are networks here to stay in healthcare because they make a difference or because we got tired of talking about the need for greater collaboration and so gave it a new name and frame? At the very least, it will be important to build on what we have already learned through research into collaboration in healthcare and related fields, and even more critical to be mindful of the pitfalls and possibilities of using networks as the solution of choice as we move forward.

Canada↗
PubMed2006

Networks: better language required.

While networks have proliferated in literature and in our health system, our day-to-day language has not kept up in sophistication. This commentary builds on the work presented by Huerta, Casebeer and VanderPlaat to further explore the language of networks. An expansion of our "network literacy" needs to be reflected in a broader vocabulary for describing particular networks and identifying patterns of relationship that are not appropriately labelled a network. Dimensions along which network managers often understand and place their networks are reported, and the implications of various network images are considered. The distinction between the image of a fishing net and that of a spider's web explores the difference between networks as system substrates and as centres. A moratorium on the term network is called for, to ensure an expanded vocabulary is applied to emerging new relationship patterns between or independent of organizations.

Canada↗
PubMed2006

Re-examining the paradox of structure: a child health network perspective.

In their lead paper, Huerta, Casebeer and VanderPlaat argue that there are several key forces driving the development of health services delivery (HSD) networks, and propose a series of paradoxes and propositions to initiate this timely and essential dialogue. Ultimately, they submit that networks are likely to remain within the healthcare system to build system capacity and drive integration. Given this, they challenge us to further the dialogue and investigate these networks. While this peer commentary shares many of the lead author's perspectives, the generic nature of the discussion does not bring us to the relative complexities revealed in some HSD network practices. A Canadian child health network lens is used to re-examine the lead paper's conceptualization of network typologies and the proposed paradox of structure. We combine network practice and academic expertise to highlight the structural, governance and leadership tensions between traditional hierarchical public service organizations and the non-hierarchical nature of inter-organizational networks. Child health network leaders and members must examine and work with the challenges associated with importing traditional organizational cultures into an inter-organizationally networked context, while simultaneously maintaining these dual (or duelling) cultures.

Canada↗
PubMed2006

Comparing patients seen in pediatric resident continuity clinics and national ambulatory medical care survey practices: a study from the continuity research network.

OBJECTIVES: The goal was to compare visit data from Continuity Research Network practices with data for a nationally representative sample of pediatric visits in practice settings from the National Ambulatory Medical Care Survey. METHODS: A cross-sectional study comparing data for Continuity Research Network practice visits during a 1-week period in 2002 with data from the 2000 National Ambulatory Medical Care Survey was performed. Continuity Research Network and National Ambulatory Medical Care Survey data were derived from 30 patient visits per practice site for patients < 22 years of age, with the primary care providers being residents and practicing pediatricians, respectively. RESULTS: Eighteen Continuity Research Network practices reported on 540 visits, compared with 32 National Ambulatory Medical Care Survey physicians reporting on 792 visits. Continuity Research Network patients were more likely to be black non-Hispanic or Hispanic/Latino and to have public insurance. The top 5 reasons for visits were the same for Continuity Research Network and National Ambulatory Medical Care Survey visits, although the orders varied slightly. These 5 reasons accounted for 58% of Continuity Research Network visits and 49% of National Ambulatory Medical Care Survey visits. Continuity Research Network visits were more likely to result in patient instructions to return at a specific time (78% vs 52%). CONCLUSIONS: Residents in Continuity Research Network practices provide care to more underserved patients but evaluate problems that are similar to those observed in office practices; the Continuity Research Network practices thus provide important training experiences for residents who will serve both minority and nonminority children.

Adolescent↗
PubMedDate not supplied

Predicting the duration of the first stage of spontaneous labor using a neural network.

To create a neural network that predicts the length of the first stage of term labor. Two hundred patients with gestations > or = 36 weeks, in spontaneous active labor are the study group: 159 for training and 41 for testing; 4 training set patients had second-stage cesarean section for obstructed labor. The network is designed with Brainmaker MacIntosh 1.0 (California Scientific Software). Inputs are uterine activity, estimated fetal weight, position, station, and gestational age; maternal parity, age, height, weight, membrane status, and cervical dilatation. Actual first stages are regressed on those predicted by the network or by a standard partogram set. Differences between actual first stage lengths and those predicted by the neural network or partogram are compared with t-tests; while the proportions of first stages accurately predicted within 1 or 2 h are compared for both methods with chi-square tests. The network trained in 4 h (1388 runs) to a 0.15 tolerance. The network predictions have significantly higher correlation (r = 0.88) than do standard partograms (r = 0.35) with actual first stage durations. Mean differences between predicted and actual first stages are significantly lower for network output than with partograms; these differences increased with first stages exceeding 3 h; 100% of trained network values are within 2 h of actual first stage length. The network performs similarly for a new set of 41 previously unseen labors. This neural network predicts the length of the first stage of spontaneous labor and uses inputs readily available to obstetricians. It outperforms typical partograms for estimating this important feature of normal labor. Future application for intrapartum prognosis could be based on this successful design.

Artificial Intelligence↗
PubMed1994

Identification of low frequency patterns in backpropagation neural networks.

Although neural networks have been widely applied to medical problems in recent years, their applicability has been limited for a variety of reasons. One of these barriers has been the inability to discriminate rare classes of solutions (i.e., the identification of categories that are infrequent). In this article, I demonstrate that a system of hierarchical neural networks (HNN) can overcome the problem of recognizing low frequency patterns, and therefore can improve the prediction power of neural-network systems. HNN are designed according to a divide-and-conquer approach: Triage networks are able to discriminate supersets that contain the infrequent pattern, and these supersets are then used by Specialized networks, which discriminate the infrequent pattern from the other ones in the superset. The supersets that are discriminated by the Triage networks are based on pattern similarity. The application of multilayered neural networks in more than one step allows the prior probability of a given pattern to increase at each step, provided that the predictive power of the network at the previous level is high. The method has been applied to one artificial set and one real set of data. In the artificial set, the distribution of the patterns was known and no noise was present. In this experiment, the HNN provided better discrimination than a standard neural network for all classes. In a real data set of nine thousand patients who were suspected of having thyroid disorders, the HNN also provided higher sensitivity than its corresponding standard neural network (without a corresponding decay in specificity) given the same time constraints.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1993

Planning and implementing a microcomputer local-area network.

Factors to be considered in planning and implementing a microcomputer local-area network (LAN) in a pharmacy department are discussed. Reasons for implementing a LAN include the ability to share data, programs, and peripheral devices among multiple users. The network operating system may be full featured or a peer-to-peer system. Full-featured networks require a dedicated file server but are more powerful and versatile. The file server, if used, is the most important piece of equipment. Factors that affect the choice of a file server are the processor, the bus, memory and speed, the supplier, and the power supply. It is necessary to select network adapters and wiring and to decide whether any of the department's current computer equipment will be used in the network. Decisions must also be made about software. The equipment should be set up by the computer services department or a vendor. Two or more pharmacists must be appointed and trained as supervisors to manage the network, diagnose and correct problems, perform network backup, and guard against computer viruses. Security is a major concern because of the need for confidentiality, the licensure of software for only a limited number of users, and the risk of inadvertent alteration or erasure of data. Network users must be trained to use the system properly. Department managers should consider the need to access the LAN from computers outside the department and the possible incorporation of the LAN into a wide-area network. A microcomputer LAN can provide valuable information services, but careful planning is necessary to avoid pitfalls and to ensure that the network meets current and future needs.

Clinical Pharmacy Information Systems↗
PubMed1996

Developing community networks to deliver HIV prevention interventions.

Outreach has a long history in health and social service programs as an important method for reaching at-risk persons within their communities. One method of "outreach" is based on the recruitment of networks of community members (or "networkers") to deliver HIV prevention messages and materials in the context of their social networks and everyday lives. This paper documents the experiences of the AIDS Community Demonstration Projects in recruiting networkers to deliver HIV prevention interventions to high-risk populations, including injecting drug users not in treatment; female sex partners of injecting drug users; female sex traders; men who have sex with men but do not self-identify as gay; and youth in high-risk situations. The authors interviewed project staff and reviewed project records of the implementation of community networks in five cities. Across cities, the projects successfully recruited persons into one or more community networks to distribute small media materials, condoms, and bleach kits, and encourage risk-reduction behaviors among community members. Networkers' continuing participation was enlisted through a variety of monetary and nonmonetary incentives. While continuous recruitment of networkers was necessary due to attrition, most interventions reported maintaining a core group of networkers. In addition, the projects appeared to serve as a starting point for some networkers to become more active in other community events and issues.

Acquired Immunodeficiency Syndrome↗
PubMed2002

Glass micromodel study of bacterial dispersion in spatially periodic porous networks.

Successful implementation of bioremediation clean-up strategies depends on accurate predictions of the transport of bacteria within the subsurface. In this study, etched flat-plate glass micromodels were used to examine bacterial transport in a homogenous network. These networks were created by acid-etching interconnected channels into a glass plate and then fusing it to an unetched plate forming semi-cylindrical pores. The transparent nature of the micromodel allows for both qualitative observations of the bacteria within the pores and quantitative measurements of their concentration. The micromodels are designed to allow establishment of a well-characterized step change in bacterial concentration (Escherichia coli NR50) within the network. During the experiments, bacteria are dispersed through the network by flow. Light scattering is used to detect the change in turbidity within the pores as the bacteria travel through the network. The change in turbidity is used to construct breakthrough curves and spatial concentration profiles of bacteria within the network. The breakthrough curves are fit to the one-dimensional advection/dispersion equation to determine dispersion coefficients at different interstitial fluid velocities. From the breakthrough curves, dispersion coefficients were reproducible for replicate experiments over a range of velocities in the advection-dominated regime. The dispersivity values for two network designs resembling an interconnecting capillary network and a spatially periodic network of cylinders were 0.28 and 0.33 cm respectively, which are slightly greater than the literature values found for other pore networks. Experiments were also conducted within the diffusion-dominated regime to examine the effects of bacterial motility on dispersion. The accumulation of bacteria on the pore walls became significant at the low flow rates and extended experimental times thereby rendering the use of light scattering to determine concentrations ineffective. Bacterial chemotaxis, created by a self-imposed oxygen gradient, was also observed in the micromodel under stagnant fluid conditions.

Biofilms↗
PubMed1976

A critical evaluation of the relationship between the presynaptic network, synaptic vesicles and dense projections in central synapses.

Synapses of the oculomotor nucleus of Echidna have been examined ultrastructurally with the aim of integrating data obtained from osmicated and nonosmicated PTA stained material. Particular emphasis has been laid on the relationship between the synaptic vesicles of the osmicated material and the presynaptic network and vesicular grid of the PTA material. This relationship has been explored qualitatively by examining osmicated material of varying qualities of fixation. Such material contains dense projections in addition to synaptic vesicles, and various vesicular network appearances. A variety of measurement techniques have shown that the PTA network is characterised by reticular strands, spaces, and regular hexagonal units smaller than vesicles, these observations prompting the formulation of a "vesicle-network coincidence" model of the presynaptic terminal. This model has been tested by tracing the profiles of vesicles within the PTA network and comparing their size and shape frequency distributions with those of osmicated synaptic vesicles. The distributions have been found to be essentially similar, suggesting that vesicles can be located within the network, and that the hexagonal network units are formed only in the presence of an underlying vesicular matrix. Additionally, the following points have emerged: 1) the dense projections in the two types of material appear to be quivalent; 2) a loose correlation exists between dense projections and vesicles in osmicated terminals, increase in the area of the dense projections being associated with a decrease in the area of the vesicles; 3) network and dense projection units are similar. In view of the similarity between network and dense projection units, the demonstrated vesicular basis of the network raises the question of whether dense projections are entirely independent structures, or whether they depend in part for their existence on the nearby presence of synaptic vesicles.

Animals↗
PubMed1987

Influence of noise on the function of a "physiological" neural network.

A model neural network with stochastic elements in its millisecond dynamics is investigated. The network consists of neuronal units which are modelled in close analogy to physiological neurons. Dynamical variables of the network are the cellular potentials, axonic currents and synaptic efficacies. The dynamics of the synapses obeys a modified Hebbian rule and, as proposed by v. d. Malsburg (1981, 1985), develop on a time scale of a tenth of a second. In a previous publication (Buhmann and Schulten 1986) we have confirmed that the resulting noiseless auto-associative network is capable of the well-known computational tasks of formal associative networks (Cooper 1973; Kohonen et al. 1984, 1981; Hopfield 1982). In the present paper we demonstrate that random fluctuations of the membrane potential improve the performance of the network. In comparison to a deterministic network a noisy neural network can learn at lower input frequencies and with lower average neural firing rates. The electrical activity of a noisy network is very reminiscent of that observed by physiological recordings. We demonstrate furthermore that associative storage reduces the effective dimension of the phase space in which the electrical activity of the network develops.

Animals↗
PubMed1979

Spatial firing patterns of auditory neuron network modelling by computer simulation.

This communication examines, in digital computer simulated network, input signals and response patterns established at excitatory neurons' level i.e. the membrane potential of neuron soma. It is restricted to spatial patterns of the auditory neuron networks and time factor for nervous conduction and transmission is neglected compared with long maintained membrane potentials of neuron somas. The model analyzes the change in the spatial patterns of the membrane potential in the two dimensional networks of the auditory system. In order to evaluate the contribution of the various parameters, it is started that the simplest model has only one parameter, lateral inhibition. The other parameters are then added, one at a time, to successive models. The lateral inhibition is a necessary condition in the auditory nervous system if any sharpening of the response areas in the single neurons is to occur. A necessary condition for the validity of the model is that is should be applicable to the other senses such as vision and chemical patterns, taste. The threshold feature of auditory neurons aids in producing a sharpening in the neuron of the auditory relay nuclei. It does this clipping the spatial response patterns in one dimensional arrays of excitatory neurons. Recurrent inhibition seems a necessary condition in the sensory nervous system that any kinds of input signals are to be preserved over a wide range of stimulus intensity. In other words, this network has a wide dynamic range against any kinds of input signals. A simple self-recurrent negative feedback does not contribute to the sharpening, but more complex socalled averaged type does. A neuron network is capable of responding stably to stimuli with a wide range of intensity and with any kind of spatial patterns if there is a simple negative feedback mechanism. When there is no negative feedback, input signals soon disappear or saturate in the neuron network. Therefore, recurrent inhibition is the most important mechanism. Spontaneous activity appears to aid in the sharpening by providing a kind of contrast, that is by reducting the amount of activity in neurons adjacent to the excitatory area. Moreover, the effect of spontaneous activity in the model seems to make repples around the excitatory area and suggests that an introduction of activity at any stage of the networks, from whatever source for example reticulum formation and thalamus, might appreciably alter the response patterns at subsequent neuron network. This suggests that the mechanism of the consciousness that might be controlled by the thalamus and or reticular formation. These two dimensional neuron networks may be expanded to three dimensional neuron networks. The former might simulate the auditory nervous system while the latter might simulate the visual system.

Animals↗
PubMed1995

Barriers to social network interventions with persons with severe and persistent mental illness: a survey of mental health case managers.

In order to empirically assess the existence, strength, and relative influence of barriers to social network interventions for persons with severe mental disability which have been cited in the literature, a survey of the knowledge and attitudes of social networks and social network interventions of eighty mental health case managers and case management supervisors was conducted. Findings indicate gaps in case managers' level of knowledge of social networks, with items based on empirical knowledge about social networks and severe mental disability least likely to be answered correctly. Case managers both perceive, and have experienced, a significant number of obstacles that affect their ability to develop social network interventions-system barriers (paperwork, caseload size, lack of case manager time, etc.), community barriers (stigma and lack of resources), and client/family barriers (lack of interest in social networks, clients having a "burnt out" network, clients not wanting to identify social network needs, etc.). Case managers cited few major barriers pertaining to their own level of knowledge, skills, or interest in, social network interventions. Strategies to address identified barriers are presented.

Adult↗
PubMed2002

A versatile ODE approximation to a network model for the spread of sexually transmitted diseases.

We develop a moment closure approximation (MCA) to a network model of sexually transmitted disease (STD) spread through a steady/casual partnership network. MCA has been used previously to approximate static, regular lattices, whereas application to dynamic, irregular networks is a new endeavour, and application to sociologically-motivated network models has not been attempted. Our goals are 1). to investigate issues relating to the application of moment closure approximations to dynamic and irregular networks, and 2). to understand the impact of concurrent casual partnerships on STD transmission through a population of predominantly steady monogamous partnerships. We are able to derive a moment closure approximation for a dynamic irregular network representing sexual partnership dynamics, however, we are forced to use a triple approximation due to the large error of the standard pair approximation. This example underscores the importance of doing error analysis for moment closure approximations. We also find that a small number of casual partnerships drastically increases the prevalence and rate of spread of the epidemic. Finally, although the approximation is derived for a specific network model, we can recover approximations to a broad range of network models simply by varying model parameters which control the structure of the dynamic network. Thus our moment closure approximation is very flexible in the kinds of network models it can approximate.

Computer Simulation↗
PubMed2004

Phylogenetic, ontogenetic and adult adaptive plasticity of rhythmic neural networks: a common neuromodulatory mechanism?

Neuromodulatory inputs are known to play a major role in the adaptive plasticity of rhythmic neural networks in adult animals. Using the crustacean stomatogastric nervous system, we have investigated the role of modulatory inputs in the development of rhythmic neural networks. We found that the same neuronal population is organised into a single network in the embryo, as opposed to the two networks present in the adult. However, these adult networks pre-exist in the embryo and can be unmasked by specific alterations of the neuromodulatory environment. Similarly, adult networks may switch back to the embryonic phenotype by manipulating neuromodulatory inputs. During development, we found that the early established neuromodulatory population display alteration in expressed neurotransmitter phenotypes, and that although the population of modulatory neurones is established early, with morphology and projection pattern similar to adult ones, their neurotransmitter phenotype may appear gradually. Therefore the abrupt switch from embryonic to adult network expression occurring at metamorphosis may be due to network reconfiguration in response to changes in modulatory input, as found in adult adaptive plasticity. Strikingly, related crustacean species express different motor outputs using the same basic network circuitry, due to species-specific alteration in neuromodulatory substances within homologous projecting neurones. Therefore we propose that alterations within neuromodulatory systems to a given rhythmic neural network displaying the same basic circuitry may account for the generation of different motor outputs throughout development (ontogenetic plasticity), adulthood (adaptive plasticity) and evolution (phylogenetic plasticity).

Animals↗
PubMed1991

Studies on fibrin network structure: the effect of some plasma proteins.

Significant differences were found between characteristics of networks developed in plasma and those developed in pure fibrinogen solution. Networks in plasma have thicker fibres, are more permeable and have lower tensile strength. In this investigation determinants of network structure under physiological conditions of clotting have been examined in an attempt to account for the differences in network structure in plasma and fibrinogen solution. Effect of antithrombin III and of physiological concentrations of fibronectin, albumin and gamma-globulin on fibrin network structure was examined using mass-length ratio (microT) from turbidity, bulk permeability of networks (tau) and kinetics of network development. At physiological concentrations effect of ATIII was too pronounced to allow this method to quantify changes in network characteristics. Whilst fibronectin and gamma-globulins increased fibrin fibre thickness and network permeability, albumin caused opposite effects. It is concluded that the final network structure is determined by kinetics of fibrin fibre growth and is highly responsive to the presence of plasma proteins.

Antithrombin III↗
PubMed1996

Erythrocyte aggregation and erythrocyte deformability modify the permeability of erythrocyte enriched fibrin network.

Intravascular thrombus formed under low shear conditions consists of red cells enmeshed within a fibrin network. Since red cells reduce the permeability of fibrin network by surface drag and by volume occupancy the significance of red cell aggregability and deformability in network permeability needs examination. In this study networks were developed by the addition of thrombin to washed red cells suspended in platelet free plasma. The effects of the polymers polyvinylpyrrolidone (PVP) and poloxamer 188 on network permeability were compared to gauge the influence of red cell aggregation. Both polymers increase network permeability by an action on fibrin polymerisation but PVP alone enhances red cell aggregation. PVP was found to increase network permeability significantly both by increasing the permeability of the fibrin component of the network and by increasing red cell aggregation and thus reducing red cell surface drag. In separate experiments red cells were pre-treated with heat, glutaraldehyde, or diamide to reduce cell deformability. Decreased cell deformability caused significant reductions in network permeability. This was ascribed to the reduced aggregability of hardened red cells. Red cell aggregation during coagulation enhances molecular transport through modifying the network. This may have implications for the penetration of fibrinolytic agents.

Blood Coagulation↗