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Random Pattern (random + pattern)
Selected AbstractsA measure for spatial heterogeneity of a grassland vegetation based on the beta-binomial distributionJOURNAL OF VEGETATION SCIENCE, Issue 5 2000Masae Shiyomi Abstract. A method is proposed to estimate the frequency and the spatial heterogeneity of occurrence of individual plant species composing the community of a grassland or a plant community with a short height. The measure is based on the beta-binomial distribution. The weighted average heterogeneity of all the species composing a community provides a measure of community-level heterogeneity determining the spatial intricateness of community composition of existing species. As an example to illustrate the method, a sown grassland with grazing cows was analysed, on 102 quadrats of 50 cm × 50 cm, each of which divided into four small quadrats of 25 cm × 25 cm. The frequency of occurrence for all the species was recorded in each small quadrat. Good fits to the beta-binomial series for most species of the community were obtained. These results indicate that (1) each species is distributed heterogeneously with respective spatial patterns, (2) the degree of heterogeneity is different from species to species, and (3) the beta-binomial distribution can be applied for grassland communities. In most of the observed species spatial heterogeneity is often characterized by species-specific propagating traits: seed-propagating plant species exhibited a low heterogeneity/random pattern while clonal species exhibited a high heterogeneity/aggregated pattern. This measure can be applied to field surveys and to the estimation of community parameters for grassland diagnosis. [source] Biogeographic effects of red fire ant invasionECOLOGY LETTERS, Issue 4 2000N.J. Gotelli The red imported fire ant, Solenopsis invicta, was accidentally introduced to North America over 60 years ago and has spread throughout the southeastern United States. We document the biogeographic consequences of this invasion. We censused ground-foraging ant communities on a 2000 km transect from Florida through New York that passed through invaded and intact biotas. Native ant species density peaks at mid-latitudes in the eastern United States, and the location of this peak corresponds to the range limit of S. invicta. In uninvaded sites, ant species co-occur less often than expected by chance. In the presence of S. invicta, community structure converges to a random pattern. Our results suggest that the effects of S. invicta on native ant communities are pervasive: not only does the presence of S. invicta reduce species density at local scales, it alters the co-occurrence patterns of surviving species at a biogeographic scale. [source] Loss of intercellular adhesion activates a transition from low- to high-grade human squamous cell carcinomaINTERNATIONAL JOURNAL OF CANCER, Issue 4 2006Alexander Margulis Abstract The relationship between loss of intercellular adhesion and the biologic properties of human squamous cell carcinoma is not well understood. We investigated how abrogation of E-cadherin-mediated adhesion influenced the behavior and phenotype of squamous cell carcinoma in 3D human tissues. Cell-cell adhesion was disrupted in early-stage epithelial tumor cells (HaCaT-II-4) through expression of a dominant-negative form of E-cadherin (H-2Kd -Ecad). Three-dimensional human tissue constructs harboring either H-2Kd -Ecad-expressing or control II-4 cells (pBabe, H-2Kd -Ecad,C25) were cultured at an air-liquid interface for 8 days and transplanted to nude mice; tumor phenotype was analyzed 2 days and 2 and 4 weeks later. H-2Kd -Ecad-expressing tumors demonstrated a switch to a high-grade aggressive tumor phenotype characterized by poorly differentiated tumor cells that infiltrated throughout the stroma. This high-grade carcinoma revealed elevated cell proliferation in a random pattern, loss of keratin 1 and diffuse deposition of laminin 5 ,2 chain. When II-4 cell variants were seeded into type I collagen gels as an in vitro assay for cell migration, we found that only E-cadherin-deficient cells detached, migrated as single cells and expressed N-cadherin. Function-blocking studies demonstrated that this migration was matrix metalloproteinase-dependent, as GM-6001 and TIMP-2, but not TIMP-1, could block migration. Gene expression profiles revealed that E-cadherin-deficient II-4 cells demonstrated increased expression of proteases and cell-cell and cell-matrix proteins. These findings showed that loss of E-cadherin-mediated adhesion plays a causal role in the transition from low- to high-grade squamous cell carcinomas and that the absence of E-cadherin is an important prognostic marker in the progression of this disease. © 2005 Wiley-Liss, Inc. [source] Modulation of peritendinous adhesion formation by alginate solution in a rabbit flexor tendon modelJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2007Jiro Namba Abstract To examine the antiadhesive effect of an alginate solution following tendon surgery, unilateral subtotal laceration of the flexor digitorum communis tendon was created in one hind limb while the other side was left intact in 32 Japanese white rabbits. The lesion was coated with alginate solution in 16 animals and not coated in the other 16. Degree of adhesion formation was assessed histologically and biomechanically by measuring the flexion angle of the first toe when the flexor digitorum tendon was pulled with a specified force at 4 weeks postoperatively. When compared with the control group, the alginate-treated group demonstrated significantly greater toe flexion, with less scar tissue formation at the repair site. Histologically, complete tendon healing with longitudinal remodeling of collagen fibers was observed in the alginate-treated group, while a random pattern of fibers was observed in the control group. Reduction in adhesion formation using alginate solution represents a novel strategy for the management of tendon injury and repair in the clinical setting. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007 [source] Cover Picture: J. Biophoton.JOURNAL OF BIOPHOTONICS, Issue 4 20094/200 AC Dielectrophoretic separation of 10 ,m non-fluorescent microspheres from 40 nm red fluorescent nanoparticles on a microelectrode array. The leftmost 3 × 3 microelectrodes are activated. The rightmost column of microelectrodes are used as control. (Top Left) Red Fluorescence image before experiment showing a red haze. (Top Right) Red Fluorescence image of the 40 nm nanoparticles concentrating on the electrodes at the conclusion of the experiment. (Bottom Left) Bright Field image of 10 ,m microspheres distributed in a random pattern before the experiment. (Bottom Right) Bright Field image of 10 ,m microspheres concentrating in between the microelectrodes at the conclusion of the experiment (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temporal Patterns of Atrial Arrhythmia Recurrences in Patients with Implantable Defibrillators: Implications for Assessing Antiarrhythmic TherapiesJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 4 2002LINA A. SHEHADEH M.S. Temporal Patterns of Atrial Arrhythmias.Introduction: The statistical measures commonly used to assess therapies for recurrent atrial arrhythmias (such as time to first recurrence) often assume a uniformly random pattern of arrhythmic events over time. However, the true temporal pattern of atrial arrhythmia recurrences is unknown. The aim of this study was to use linear and nonlinear analyses to characterize the temporal pattern of atrial arrhythmia recurrences in patients with implantable cardioverter defibrillators. Methods and Results: The time and date of atrial tachyarrhythmias recorded in 65 patients with combined atrial and ventricular defibrillators were used to construct a probability density function (PDF) and a model of a Poisson distribution of arrhythmic events for each patient. Average patient age was 66 ± 10 years and follow-up was 7.8 ± 4.8 months. A total of 10,759 episodes of atrial tachyarrhythmias were analyzed (range 43 to 618 episodes per patient). The PDF fit a power law distribution for all 65 patients, with an average r2= 0.89 ± 0.08. The PDF distribution differed significantly from the model Poisson distribution in 47 of 65 patients (P = 0.0002). Differences from the Poisson distribution were noted for patients both taking (30/43 patients; P < 0.015) and not taking (17/22 patients; P < 0.017) antiarrhythmic drugs. Median time between atrial arrhythmia detections for all 65 patients was 10.8 minutes. Conclusion: In implantable cardioverter defibrillator patients, the temporal pattern of frequent recurrences of atrial tachyarrhythmias usually is characterized by a power law distribution. The unique statistical properties of this type of distribution should be considered in designing outcome measures for treatment of atrial tachyarrhythmias. [source] Improving food purchasing choices through increased understanding of food labels, using itemized till receipts to measure these changesJOURNAL OF HUMAN NUTRITION & DIETETICS, Issue 4 2008P.M. Rigby Background:, Rising obesity and the associated risks of diabetes and heart disease require changes in diet to bring about healthier eating. To achieve this, people need to understand nutrition and daily requirements but are frequently confused by nutrition information on food labels. The introduction of the Food Standards Agency's ,Traffic Light' and the alternative ,Guideline Daily Amount' systems may help or further confuse the public. A previous study showed that although 63% of study participants read labels, only 25% claimed to understand them, also knowledge of nutrient requirements and functions was low (Rigby, 2004). Ransley et al., (2001) have shown that till receipts can be used to estimate fat and energy intake. The aim of the current study was to investigate whether an intervention designed to improve understanding of nutrition and labels could improve food purchases and whether these changes could be measured from till receipts. Method:, Participants were recruited from the general public (80 female; 23 males) (age <30 years (23), 31,45 years (25), 46,60 years (30), >60 years (22). Subjects were randomly assigned to either the intervention group (n = 78) who were provided with an information booklet and credit card sized nutrition and labelling information to use when shopping, or the control group (n = 25), who received the information after four weeks of normal shopping. The intervention group provided an initial till receipt pre intervention and was then given the nutrition and labelling material. Further till receipts were returned from successive shopping trips over the following 4 weeks. The nine categories of food used for comparison were: fruit and vegetables, saturated fats, monounsaturated fats, polyunsaturated fats, white cereals, wholegrain cereals, processed foods, full fat and reduced fat items. Ethics approval was obtained from NWW Wales NHS Trust ethics committee. Results:, Each of the nine food categories on till receipts were calculated as a percentage of the total shopping, excluding non-food items. General linear model repeated measures analyses showed differences between study participants' food purchases. For the intervention group, purchases in three of the nine food categories showed significant improvements: increased purchases of fruits and vegetables (P < 0.001); reduction in purchases of saturated fats (P < 0.001); and reduction of white cereal purchases (P < 0.050). The control group showed no differences in any category. Discussion:, Although the intervention group did show improvements in most of the other food categories, they were not statistically significant. Positive changes were found in seven of the nine categories, with only one, wholegrain cereals, showing a decrease in purchases rather than an increase. The control group displayed a random pattern over the four till receipts, with eight categories either showing negative change or no change; only one showed a positive change. The disproportionate group sizes may mean that it is not be possible to draw firm conclusions regarding the effectiveness of the intervention. Conclusions:, This study demonstrates that positive changes in improving food-purchasing choices, as measured by till receipts, can be made by using educational interventions. Further larger studies using routinely collected supermarket data would enable the study to be replicated on a much larger scale. References, Ransley, J.K., Donnelly, J.K., Khara, T.N., Botham, H., Arnott, H., Greenwood, D.C. & Cade, J.E. (1991) The use of supermarket till receipts to determine the fat and energy intake in a UK population. Public Health Nutr. 4, 1279,1286. Rigby, P. (2004) Effecting change. Understanding nutritional information. Can increased knowledge and understanding in relation to nutritional information bring about a change in eating habits? PhD Thesis WA: Bangor University. [source] Do spatial effects play a role in the spatial distribution of desert-dwelling Acacia raddiana?JOURNAL OF VEGETATION SCIENCE, Issue 4 2000Kerstin Wiegand Abstract. We investigated the spatial pattern of A. raddiana in the Negev desert of Israel in order to gain insights into the factors and processes driving the dynamics of this species. Using a scale-dependent measure, the ring statistic, we analysed both patterns observed in the field and time series of spatial tree distributions produced by a simulation model. In the field, random spacing was the predominant pattern observed. However seedlings were clumped on small scales. We ran the model under two contrasting scenarios representing hypotheses that explain the clumping of seedlings and the random distribution of trees. One hypothesis is that there is spatial heterogeneity in seed distribution, germination and seedling mortality, but that these heterogeneities are not correlated with each other in space. The second hypothesis assumes a correlation between these heterogeneities leading to areas suitable for establishment. However, the suitability of the sites is temporally variable. Furthermore, the second hypothesis assumes density-dependent tree mortality due to competition. Both hypotheses lead to spatial distributions that are in qualitative agreement with the patterns observed in the field. Therefore, the classical view that a clumped seedling distribution and a random pattern of older trees is due to clumped regeneration and density-dependent mortality may not hold for Acacia trees in the Negev. [source] Intraspecific variation in movement patterns: modeling individual behaviour in a large marine predatorOIKOS, Issue 1 2004Deborah Austin In large marine predators, foraging entails movement. Quantitative models reveal how behaviours can mediate individual movement, such that deviations from a random pattern may reveal specific search tactics or behaviour. Using locations for 52 grey seals fitted with satellite-linked recorders on Sable Island; we modeled movement as a correlated random walk (CRW) for individual animals, at two temporal scales. Mean move length, turning angle, and net squared displacement (R2n: the rate of change in area over time) at successive moves over 3 to 10 months were calculated. The distribution of move lengths of individual animals was compared to a Lévy distribution to determine if grey seals use a Lévy flight search tactic. Grey seals exhibited three types of movement as determined by CRW model fit: directed movers , animals displaying directed long distance travel that were significantly underpredicted by the CRW (23% of animals); residents , animals remaining in the area surrounding Sable Island that were overpredicted by the model (29% of animals); and correlated random walkers , those (48% of animals) in which movement was predicted by the CRW model. Kernel home range size differed significantly among all three movement types, as did travel speed, mean move length, mean R2n and total distance traveled. Sex and season of deployment were significant predictors of movement type, with directed movers more likely to be male and residents more likely to be female. Only 30% of grey seals fit a Lévy distribution, which suggests that food patches used by the majority of seals are not randomly distributed. Intraspecific variation in movement behaviour is an important characteristic in grey seal foraging ecology, underscoring the need to account for such variability in developing models of habitat use and predation. [source] An interim analysis of a cohort study on the preoperative anxiety and postoperative behavioural changes in children having repeat anaestheticsPEDIATRIC ANESTHESIA, Issue 9 2002A. Watson Introduction Anxiety in the preoperative period and at induction of anaesthesia in children is associated with disturbances in postoperative behaviour (1,4). There is little work looking at the effects of repeat anaesthetic procedures on anxiety and subsequent postoperative behaviour disturbances. The aim of this study was to see if the effect of repeat anaesthetics was cumulative on postoperative behavioural problems and whether repeated anaesthetics provoke increasing anxiety. We investigated factors that may identify children who are susceptible to behavioural changes following repeat anaesthetics. We present an interim analysis of data on 8 patients as part of a long-term cohort study on 40 children with retinoblastoma who have required repeat anaesthetics for assessment and treatment of their condition. Method Approval for this study was granted by the East London and City Health Authority ethics committee. 40 patients are being recruited and being followed over a two year period. All children have retinoblastoma and are between the ages of 18 months to 4 years. The anaesthetic technique was not standardised but details of it were collected. Data collected were demographic details of child (age, sex, weight, ASA grade, siblings, stressful events in the last 3 months, recent immunisations, number of previous anaesthetics, problems with previous general anaesthetics, medical history of children, temperament of child using the EASI scoring system (4); demographic data of parents (age, parental education, family members affected, baseline measure of parental anxiety using State trait anxiety inventory (STAI). Anxiety on entry into the anaesthetic room and at induction was measured by the modified Yale preoperative anxiety scale (mYPAS), cooperation of the child at induction was measured by the Induction compliance checklist (ICC). Anxiety of the parent after induction was measured by the STAI score. Behaviour was measured at 1 day, 1 week, 1 month and 4 months after each procedure by means of the post hospital behaviour score (PHBQ) (5). A comparison with preoperative behaviour was made and data is presented of the percentage of children with new negative behavioural problems. A detailed analysis of the types of behaviour change was noted. anova for repeat measures with multiple dependent measures was used to analyse data on child anxiety and postoperative behavioural problems. Results Eight patients have had 3 separate anaesthetics over one and a half years. These have been at 4 monthly intervals. There was no significant increase in anxiety levels with repeat anaesthetics. The median mYPAS score at induction were 100 for all 3 anaesthetics. (P = 0.41). The type of behavioural change was variable and demonstrated no trend. No patient was identified as being prone to behavioural changes after every anaesthetic. Patients who displayed new negative behavioural problems would have them after any anaesthetic with no obvious cumulative effect with each repeat anaesthetic. Conclusions Our patients had maximum anxiety scores at induction, so the mYPAS scoring system is not sensitive enough to show that repeat anaesthetics provoke increasing anxiety. There is a very random pattern to behavioural disturbances after repeat anaesthetics with no evidence that negative behavioural changes are compounded with repeated anaesthetics. Collection of complete data from the remaining 32 patients may yield some trends regarding behavioural disturbances but our use of the mYPAS to measure anxiety in this very anxious population is unlikely to be helpful. [source] Ab initio study of spinodal decomposition in (Zn, Cr)TePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006T. Fukushima Abstract The spinodal decomposition in (Zn, Cr)Te is simulated by using first principles calculations and Monte Carlo simulation. It is found that the chemical pair interaction between Cr atoms in (Zn, Cr)Te is attractive interaction and leads to spinodal decomposition. Curie temperatures in decomposed situation are estimated by the random phase approximation with taking the magnetic percolation effect into account. This decomposed phase makes the random pattern of high concentration regions which connect each other and have possibility to realize high Curie temperature. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||