2,706 research outputs found
Experimental and modelling investigation of monolayer development with clustering
No full textStandard differential equation-based models of collective cell behaviour, such as the logistic growth model, invoke a mean-field assumption which is equivalent to assuming that individuals within the population interact with each other in proportion to the average population density. Implementing such assumptions implies that the dynamics of the system are unaffected by spatial structure, such as the formation of patches or clusters within the population. Recent theoretical developments have introduced a class of models, known as moment dynamics models, which aim to account for the dynamics of individuals, pairs of individuals, triplets of individuals, and so on. Such models enable us to describe the dynamics of populations with clustering, however, little progress has been made with regard to applying moment dynamics models to experimental data. Here, we report new experimental results describing the formation of a monolayer of cells using two different cell types: 3T3 fibroblast cells and MDA MB 231 breast cancer cells. Our analysis indicates that the 3T3 fibroblast cells are relatively motile and we observe that the 3T3 fibroblast monolayer forms without clustering. Alternatively, the MDA MB 231 cells are less motile and we observe that the MDA MB 231 monolayer formation is associated with significant clustering. We calibrate a moment dynamics model and a standard mean-field model to both data sets. Our results indicate that the mean-field and moment dynamics models provide similar descriptions of the 3T3 fibroblast monolayer formation whereas these two models give very different predictions for the MDA MD 231 monolayer formation. These outcomes indicate that standard mean-field models of collective cell behaviour are not always appropriate and that care ought to be exercised when implementing such a model.Matthew J. Simpson, Benjamin J. Binder, Parvathi Haridas, Benjamin K.Wood, Katrina K. Treloar, D.L. Sean McElwain, Ruth E. Bake
Quantifying the roles of cell motility and cell proliferation in a circular barrier assay
No full textMoving fronts of cells are essential features of embryonic development, wound repair and cancer metastasis. This paper describes a set of experiments to investigate the roles of random motility and proliferation in driving the spread of an initially confined cell population. The experiments include an analysis of cell spreading when proliferation was inhibited. Our data have been analysed using two mathematical models: a lattice-based discrete model and a related continuum partial differential equation model. We obtain independent estimates of the random motility parameter, D, and the intrinsic proliferation rate, λ, and we confirm that these estimates lead to accurate modelling predictions of the position of the leading edge of the moving front as well as the evolution of the cell density profiles. Previous work suggests that systems with a high λ/D ratio will be characterized by steep fronts, whereas systems with a low λ/D ratio will lead to shallow diffuse fronts and this is confirmed in the present study. Our results provide evidence that continuum models, based on the Fisher–Kolmogorov equation, are a reliable platform upon which we can interpret and predict such experimental observations.Matthew J. Simpson, Katrina K. Treloar, Benjamin J. Binder, Parvathi Haridas, Kerry J. Manton, David I. Leavesley, D. L. Sean McElwain and Ruth E. Bake
Assessing the role of spatial correlations during collective cell spreading
No full textSpreading cell fronts are essential features of development, repair and disease processes. Many mathematical models used to describe the motion of cell fronts, such as Fisher's equation, invoke a mean-field assumption which implies that there is no spatial structure, such as cell clustering, present. Here, we examine the presence of spatial structure using a combination of in vitro circular barrier assays, discrete random walk simulations and pair correlation functions. In particular, we analyse discrete simulation data using pair correlation functions to show that spatial structure can form in a spreading population of cells either through sufficiently strong cell-to-cell adhesion or sufficiently rapid cell proliferation. We analyse images from a circular barrier assay describing the spreading of a population of MM127 melanoma cells using the same pair correlation functions. Our results indicate that the spreading melanoma cell populations remain very close to spatially uniform, suggesting that the strength of cell-to-cell adhesion and the rate of cell proliferation are both sufficiently small so as not to induce any spatial patterning in the spreading populations.Katrina K. Treloar, Matthew J. Simpson, Benjamin J. Binder, D. L. Sean McElwain, Ruth E. Bake
Comparison of several author indices for gauging academic productivity
No full textBackground
Many author indices exist to gauge academic productivity. Several of these indices are calculated based upon an author's scholarly publication record, but the measurement methodology to calculate each index varies considerably, and the precise function being used, as well as the end result, is often complex and difficult to assess.
Method
Two straightforward methods to weigh author productivity from the publication and citation record were evaluated as possible means for providing a clearer assessment of scholarly activity. The author characteristic index (termed c-index) assigns author rank for each publication based upon author position. The characteristic prime (c') -index normalizes author rank from author position, so that the total weight per publication is unity. The top 10 scholars with keyword 'celiac disease' in the Google Scholar database were then assessed using these metrics. Rankings according to total number of publications, h-index, and c- and c'-indices were compared, then tabulated along with total papers included for assessment, and mean values per paper for author position, number of authors, citations, and year of publication.
Results
The order of the top ten authors with keyword 'celiac disease' varied substantially depending upon whether the h-index, c-index, or c'-index was used as a gauge. The characteristic indices assign credit to authors according to their position in an author list. The affiliated metrics provided a more complete picture of scholarly activity.
Conclusions
Academic achievement by scholars, based upon quantitative publication characteristics, has recently become of interest for evaluating job candidates, for determining work performance, and for bestowing awards and honors. The characteristic indices as described herein are readily calculated and interpreted, and may improve the assessment of scholarly activity
Large water-hammer pressure for column separation in pipelines
No full textWater-hammer pressures in a pipeline due to the collapse of a vapor cavity adjacent to a valve are investigated. A water-hammer event is initiated by the closure of a valve in a simple reservoir-pipeline-valve system. The sequence of events following an instantaneous valve closure leading to the formation and collapse of a vapor cavity and the resultant occurrence of a short-duration pressure pulse are described. Short-duration pressure pulses result from the superposition of the valve-closure water-hammer wave and the wave generated by the collapse of the vapor cavity. The resulting maximum pressure may exceed the Joukowsky pressure generated from the initial valve closure. A series of numerical model analyses exhibiting short-duration pressure pulses are presented. In addition, experimental results supporting the findings of the numerical studies are also presented. Experimental plots of hydraulic grade line versus time exhibit short-duration pressure pulses of different shape and characteristics.Angus R. Simpson and E. Benjamin Wyli
Groups unaware of food recall: policy implications
No full textOn September 14, 2006, the U.S. Food and Drug Administration (FDA) issued an advisory warning against the consumption of fresh spinach because of suspected contamination with E. coli O157:H71. Following the advisory, a series of voluntary recalls were initiated nationwide, beginning with products from Natural Selection Foods, LLC, of San Juan Bautista, California, which produced bagged fresh spinach under 30 brand names. Fresh spinach was quickly removed from store shelves and restaurant menus.
Because of the serious nature of the risk posed by exposure to E. coli O157:H7, both the FDA and the produce industry carried out aggressive information campaigns to alert the public that they should not eat fresh spinach. In response, the recall received substantial media attention, resulting in extensive coverage in both newspapers and on television news broadcasts.
The objective of this study was to examine which groups of people were most likely to be unaware of the fresh spinach recall and therefore at risk for consuming contaminated spinach.
The study used a nationally representative telephone survey of 1,200 Americans, conducted from November 8-29, 2006.
The results indicated that the majority (87%) of Americans were aware of the spinach recall. However, awareness was not uniformly distributed across the population. While only 13% of Americans were unaware of the recall overall, 22% of African Americans, 23% of the Hispanic population, 21% of Americans age 18-34 and 16% of males reported that they hadn’t heard or read about the spinach recall.
As consuming spinach prior to the recall was associated with awareness of the recall, this variable was controlled for in regression analyses. However, even after controlling for prior spinach consumption, non-Whites, people of Hispanic origin, young adults (18-34 years old) and males were significantly more likely to be unaware of the spinach recall (Table 1).
A second logistic regression model found that those age 55 and older were no more or less likely to know about the recall than those younger than 55.Poster presented August 6, 2008 to the 95th annual meeting of the International Association for Food Protection, Columbus, OhioPeer reviewe
Understanding Consumer Interest in Organics: Production Values vs. Purchasing Behavior
No full textExtensive research exists on who does or might purchase organic food products, however little research has addressed either who values organic production methods when deciding what to eat, and correspondingly, who does not purchase organics regularly. This paper reports that values about organic farming often do not translate into corresponding stated preferences about organic food consumption behavior. The paradox is examined within the context of the consumers’ sociodemographic characteristics as well as through opinions and preferences related to food in their lives.
Results show that consumer claims of buying organics and placing importance on organic production systems when deciding what to eat are highly correlated (.472 at 1% significance level; p<. 001). Organic consumers, however, comprise only slightly more than one quarter (27%) of the highly enthusiastic proponents of organic production methods. Our results corroborate existing research that well-educated persons and those who are primary household shoppers purchase organics most frequently. Additionally, women and those who are older, have higher incomes, and are more liberal, as well as respondents who claim food production knowledge also tend to buy organic food regularly.
Regression and factor analysis show that those who value organic production systems when deciding what to eat may be ranked in the following order: the religiously observant, older and female respondents, persons of color, and those who claim food production knowledge. Results show that many of these organic system proponents are under-represented as buyers, in particular: the religiously observant, those for whom food plays an integral role in their lives, the less educated, and lower income and older respondents. More attention should be directed to people who value organic production systems yet do not purchase organics. This will enhance understanding of the transaction barriers that impede consumer participation in the organic market. How this population values organic production systems also has implications for the development of public policy related to sustainable and organic agriculture.Peer reviewe
Methods Used by Dr. R. K. Benjamin, and Other Mycologists, to Isolate Zygomycetes
No full textThe methods that Dr. Richard K. Benjamin used to isolate Zygomycetes are discussed. These processes involved the following five steps: (1) collection, (2) plating, (3) isolation, (4) culture, and (5) maintenance. Additional methods, materials, and modifications used to isolate Zygomycetes are summarized. The author considers the flattening of the aerial hyphae onto the substrate of the faster- and higher-growing Mucorales for several consecutive days to be the critical step in isolating species of Coemansia, Piptocephalis, Syncephalis, and Dimargaritales. The methods used by other scholars to isolate, culture, and study many taxa in Zygomycetes also are discussed
Prognostic value of the Simpson grading scale in modern meningioma surgery: Barrow Neurological Institute experience
No full textOBJECTIVE: Recently, the prognostic value of the Simpson resection grading scale has been called into question for modern meningioma surgery. In this study, the authors analyzed the relationship between Simpson resection grade and meningioma recurrence in their institutional experience. METHODS: This study is a retrospective review of all patients who underwent resection of a WHO grade I intracranial meningioma at the authors\u27 institution from 2007 to 2017. Binary logistic regression analysis was used to assess for predictors of Simpson grade IV resection and postoperative neurological morbidity. Cox multivariate analysis was used to assess for predictors of tumor recurrence. Kaplan-Meier analysis and log-rank tests were used to assess and compare recurrence-free survival (RFS) of Simpson resection grades, respectively. RESULTS: A total of 492 patients with evaluable data were included for analysis, including 394 women (80.1%) and 98 men (19.9%) with a mean (SD) age of 58.7 (12.8) years. The tumors were most commonly located at the skull base (n = 302; 61.4%) or the convexity/parasagittal region (n = 139; 28.3%). The median (IQR) tumor volume was 6.8 (14.3) cm3. Simpson grade I, II, III, or IV resection was achieved in 105 (21.3%), 155 (31.5%), 52 (10.6%), and 180 (36.6%) patients, respectively. Sixty-three of 180 patients (35.0%) with Simpson grade IV resection were treated with adjuvant radiosurgery. In the multivariate analysis, increasing largest tumor dimension (p \u3c 0.01) and sinus invasion (p \u3c 0.01) predicted Simpson grade IV resection, whereas skull base location predicted neurological morbidity (p = 0.02). Tumor recurrence occurred in 63 patients (12.8%) at a median (IQR) of 36 (40.3) months from surgery. Simpson grade I resection resulted in superior RFS compared with Simpson grade II resection (p = 0.02), Simpson grade III resection (p = 0.01), and Simpson grade IV resection with adjuvant radiosurgery (p = 0.01) or without adjuvant radiosurgery (p \u3c 0.01). In the multivariate analysis, Simpson grade I resection was independently associated with no tumor recurrence (p = 0.04). Simpson grade II and III resections resulted in superior RFS compared with Simpson grade IV resection without adjuvant radiosurgery (p \u3c 0.01) but similar RFS compared with Simpson grade IV resection with adjuvant radiosurgery (p = 0.82). Simpson grade IV resection with adjuvant radiosurgery resulted in superior RFS compared with Simpson grade IV resection without adjuvant radiosurgery (p \u3c 0.01). CONCLUSIONS: The Simpson resection grading scale continues to hold substantial prognostic value in the modern neurosurgical era. When feasible, Simpson grade I resection should remain the goal of intracranial meningioma surgery. Simpson grade IV resection with adjuvant radiosurgery resulted in similar RFS compared with Simpson grade II and III resections
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