1,721,029 research outputs found
Identifying on admission patients likely to develop acute kidney injury in hospital
No full textBackgroundThe incidence of Acute Kidney Injury (AKI) continues to increase in the UK, with associated mortality rates remaining significant. Approximately one fifth of hospital admissions are associated with AKI and approximately a third of patients with AKI in hospital develop AKI during their time in hospital. A fifth of these cases are considered avoidable. Early risk detection remains key to decreasing AKI in hospitals, where sub-optimal care was noted for half of patients who developed AKI.MethodsElectronic anonymised data for adults admitted into the Royal Cornwall Hospitals Trust (RCHT) between 18th March and 31st December 2015 was trimmed to that collected within the first 24 h of hospitalisation. These datasets were split according to three separate time periods: data used for training the Takagi-Sugeno Fuzzy Logic Systems (FLS) and the multivariable logistic regression (MLR) models; data used for testing; and data from a later patient spell used for validation.Three fuzzy logic models and three MLR models were developed to link characteristics of patients diagnosed with a maximum stage AKI within 7 days of admission: the first models to identify any AKI Stage (FLS I, MLR I), the second for patterns of AKI Stage 2 or 3 (FLS II, MLR II), and the third to identify AKI Stage 3 (FLS III, MLR III). Model accuracy is expressed by area under the curve (AUC).ResultsAccuracy for each model during internal validation was: FLS I and MLR I (AUC 0.70, 95% CI: 0.64–0.77); FLS II (AUC 0.77, 95% CI: 0.69–0.85) and MLR II (AUC 0.74, 95% CI: 0.65–0.83); FLS III and MLR III (AUC 0.95, 95% CI: 0.92–0.98).ConclusionsFLS II and FLS III (and the respective MLR models) can identify with a high level of accuracy patients at high risk of developing AKI in hospital. These two models cannot be properly assessed against prior studies as this is the first attempt at quantifying the risk of developing specific Stages of AKI for a broad cohort of both medical and surgical inpatients. FLS I and MLR I performance is comparable to other existing models
Divergent demographic strategies of plants in variable environments
Get PDFThis is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this record.One of the best-supported patterns in life history evolution is that organisms cope with environmental fluctuations by
buffering their most important vital rates against them. This demographic buffering hypothesis is evidenced by a tendency
for temporal variation in rates of survival and reproduction to correlate negatively with their contribution to fitness. Here, we show that widespread evidence for demographic buffering can be artefactual, resulting from natural relationships between the mean and variance of vital rates. Following statistical scaling, we find no significant tendency for plant life histories to be buffered demographically. Instead, some species are buffered, whereas others have labile life histories with higher temporal variation in their more important vital rates. We find phylogenetic signal in the strength and direction of variance–importance correlations, suggesting that clades of plants are prone to being either buffered or labile. Species with simple life histories are more likely to be demographically labile. Our results suggest important evolutionary nuances in how species deal with environmental fluctuations.This work was funded by the Natural Environment Research Council (NERC) UK, grant NE/L007770/1, and supported by NERC IOF grant NE/N006798/1. T.H.G.E. is funded by NERC Fellowship NE/J018163/1
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Inferring transient dynamics of human populations from non-normality metrics
No full textIn our increasingly unstable and unpredictable world, population dynamics rarely settle uniformly to long-term behaviour. However, projecting period-by-period through the preceding fluctuations is more data-intensive and analytically involved than evaluating at equilibrium. To efficiently model populations and best inform policy, we require pragmatic suggestions as to when it is necessary to incorporate short-term transient dynamics and their effect on eventual projected population size. To estimate this need for matrix population modelling, we adopt a linear algebraic quantity known as non-normality. Matrix non-normality is distinct from normality in the Gaussian sense, and indicates the amplificatory potential of the population projection matrix given a particular population vector. In this paper, we compare and contrast three well-regarded metrics of non-normality, which were calculated for over 1000 age-structured human population projection matrices from 42 European countries in the period 1960 to 2014. Non-normality increased over time, mirroring the indices of transient dynamics that peaked around the millennium. By standardising the matrices to focus on transient dynamics and not changes in the asymptotic growth rate, we show that the damping ratio is an uninformative predictor of whether a population is prone to transient booms or busts in its size. These analyses suggest that population ecology approaches to inferring transient dynamics have too often relied on suboptimal analytical tools focussed on an initial population vector rather than the capacity of the life cycle to amplify or dampen transient fluctuations. Finally, we introduce the engineering technique of pseudospectra analysis to population ecology, which, like matrix non-normality, provides a more complete description of the transient fluctuations than the damping ratio. Pseudospectra analysis could further support non-normality assessment to enable a greater understanding of when we might expect transient phases to impact eventual population dynamics.<br/
Soft sensor development and process control of anaerobic digestion
No full textThis thesis focuses on soft sensor development based on fuzzy logic used for
real time online monitoring of anaerobic digestion to improve methane output and for
robust fermentation. Important process parameter indicators such as pH, biogas
production, daily difference in pH and daily difference in biogas production were
used to infer alkalinity, a reliable indicator of process stability. Additionally, a fuzzy
logic and a rule-based controller were developed and tested with single stage
anaerobic digesters operating with cow slurry and cellulose. Alkalinity predictions
from the fuzzy logic algorithm were used by both controllers to regulate the organic
loading rate that aimed to optimise the biogas process.
The predictive performance of a software sensor determining alkalinity that
was designed using fuzzy logic and subtractive clustering and was validated against
multiple linear regression models that were developed (Partner N° 2, Rothamsted
Research 2010) for the same purpose. More accurate alkalinity predictions were
achieved by utilizing a fuzzy software sensor designed with less amount of data
compared to a multiple linear regression model whose design was based on a larger
database. Those models were utilised to control the organic loading rate of a twostage,
semi-continuously fed stirred reactor system.
Three 5l reactors without support media and three 5l reactors with different
support media (burst cell reticulated polyurethane foam coarse, burst cell reticulated
polyurethane foam medium and sponge) were operated with cow slurry for a period
of seven weeks and twenty weeks respectively. Reactors with support media were
proven to be more stable than the reactors without support media but did not exhibit
higher gas productivity. Biomass support media were found to influence digester
recovery positively by reducing the recovery period. Optimum process parameter
ranges were identified for reactors with and without support media. Increased biogas
production was found to occur when the loading rates were 3-3.5g VS/l/d and 4-5g
VS/l/d respectively. Optimum pH ranges were identified between 7.1-7.3 and 6.9-7.2
for reactors with and without support media respectively, whereas all reactors
became unstable at ph<6.9. Alkalinity levels for system stability appeared to be
above 3500 mg/l of HCO3
- for reactors without media and 3480 mg/l of HCO3
- for
reactors with support media. Biogas production was maximized when alkalinity was
3
between 3500-4500 mg/l of HCO3
- for reactors without support media and 3480-
4300 mg/l of HCO3
- for reactors with support media. Two fuzzy logic models
predicting alkalinity based on the operation of the three 5l reactors with support
media were developed (FIS I, FIS II). The FIS II design was based on a larger
database than FIS I. FIS II performance when applied to the reactor where sponge
was used as the support media was characterized by quite good MAE and bias
values of 466.53 mg/l of HCO3- and an acceptable value for R2= 0.498. The NMSE
was close to 0 with a value of 0.03 and a slightly higher FB= 0.154 than desired. The
fuzzy system robustness was tested by adding NaHCO3 to the reactor with the burst
cell reticulated polyurethane foam medium and by diluting the reactor where sponge
was used as the support media with water. FIS I and FIS II were able to follow the
system output closely in the first case, but not in the second.
FIS II functionality as an alkalinity predictor was tested through the application
on a 28l cylindrical reactor with sponge as the biomass support media treating cow
manure. If data that was recorded when severe temperature fluctuations occurred
(that highly impact digester performance), are excluded, FIS II performance can be
characterized as good by having R2= 0.54 and MAE=Bias= 587 mg/l of HCO3-.
Predicted alkalinity values followed observed alkalinity values closely during the days
that followed NaHCO3 addition and water dilution. In a second experiment a rulebased
and a Mamdani fuzzy logic controller were developed to regulate the organic
loading rate based on alkalinity predictions from FIS II. They were tested through the
operation of five 6.5l reactors with biomass support media treating cellulose. The
performance indices of MAE=763.57 mg/l of HCO3-, Bias= 398.39 mg/l of HCO3-,
R2= 0.38 and IA= 0.73 indicate a pretty good correlation between predicted and
observed values. However, although both controllers managed to keep alkalinity
within the desired levels suggested for stability (>3480 mg/l of HCO3-), the reactors
did not reach a stable state suggesting that different loading rates should be applied
for biogas systems treating cellulose.New Generation Biogas (NGB
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Using Transfer Function Analysis in Modelling Biological Invasions
No full textThis thesis is made up of seven chapters and two appendices. Chapter 1
provides an introduction whilst Chapter 7 o ers a conclusion. In Chapter 2 we
provide preliminaries on population projection models and robustness analysis.
In Chapter 3 we introduce a stage-structured model in a context of biological
invasions. Using a Transfer Function Approach, we provide a detailed analysis
of the invasion model where the existence and local stability of all possible
equilibria are characterised in terms of the underlying parameters of the model.
In Chapter 4, a Lyapunov function approach is used to estimate the basin of
attraction for each equilibrium. In Chapter 5, harvesting is incorporated into
the model and we speci cally examine the e ect of harvesting on whether
one or both of the species are eliminated. In Chapter 6 we introduce a novel
technique to measure the possibility of invasion in non-normal systems where
the traditional invasion exponent technique is unreliable.Libyan Governmen
Integral Projection Models and analysis of patch dynamics of the reef building coral Monstastraea annularis.
Get PDFOver the past 40 years, coral cover has reduced by as much as 80%. At the same time,
Coral Reefs are coming under increasing threat from hurricanes, as climate change is
expected to increase the intensity of hurricanes. Therefore, it has become increasingly
important to understand the effect of hurricanes on a coral population.
This Thesis focuses on the reef-building coral Montastraea annularis. This species
once dominated Caribbean Coral Reefs, but is fast being replaced by faster growing
more opportunistic species. It is important that the underlying dynamics of the decline
is understood, if managers stand any chance of reversing this decline.
The aim of this Thesis is to investigate the effect of hurricane activity on the dynamics
of the reef-building coral Montastraea annularis. To achieve this the Integral Projection
Model (IPM) method was adopted and the results compared to those produced using the
more traditional method of Population Projection Matrix (PPM) method.
The models were fitted using census data from June 1998 to January 2003, which
described the area of individual coral patches on a sample of ramets on Glovers Reef,
Belize. Glovers Reef is a marine reserve that lies 30km off the coast of Belize and 15km
east of the main barrier reef. Three hurricanes struck Glovers Reef during the study:
Hurricane Mitch (October 1998), Hurricane Keith (September 2000) and Hurricane Iris
(October 2001).
The data have been divided by two different methods in order to test two research
questions, firstly if the initial trauma following a hurricane affects the long term dynamics
of a population and, secondly, if the dynamics exhibited during a hurricane varied with
hurricane strength.
In this Thesis five main results are shown:
1. All models for all divisions of data are in long term decline.
2. As initial trauma increased, the long term growth rates decreased, conversely the
short term extremes increased.
3. Fragmentation is more likely as patch size increased and more likely under stronger
hurricanes.
4. Integral Projection Modelling painted a similar picture to Population Projection
Matrix models and should be a preferred method of analysis.5. Interaction of the IPMs can be used to model the changing occurrence of hurricanes
under climate change. It is shown that with increased intensity, the population
could become extinct 6.3 years sooner.
This research is the first step in modelling coral patch populations by the IPM
method. It suggests possible functional forms and compares the results with the PPM
method. Further research is required into the biological functions which drive fragmentation,
the method by which large patches divide into groups of smaller patches. The
conclusions from this Thesis add to the growing body of knowledge concerning the response
of coral species to hurricanes, focusing on the importance of understanding patch
dynamics, in order to understand colonial dynamics.Exeter University Foundatio
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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