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Positive Slope (positive + slope)
Selected AbstractsLifespan is unrelated to investment in reproduction in populations of mammals and birds in captivityECOLOGY LETTERS, Issue 10 2007Robert E. Ricklefs Abstract We examined the relationship between number of offspring produced to a certain age and subsequent longevity in captive zoo populations of 18 species of mammal and 12 species of bird. The age cut-offs in each analysis were set to include 50%, 75% and 90% of the offspring produced in each of the population samples. Only one of 68 regressions was significant, and its slope was positive. In addition, we examined the relationship between age at first reproduction up to a certain age and longevity after that age, generally 5 years (3,8), among 17 species of mammal and 12 species of bird. Only one of these regressions had a significantly positive slope, indicating that early reproduction rarely reduces lifespan. Overall, we found no evidence that producing offspring in a zoo environment influences the age at death. Thus, although trade-offs might apply in natural populations under resource limitation, neither pregnancy, growth of the foetus and lactation in mammals, nor egg production in birds, reduces lifespan in the absence of such stress. If genetically based or other intrinsic antagonistic pleiotropy underlies the evolution of senescence, it was not evident in our analyses. [source] A slowly inactivating sodium current (INa2) in the plateau range in canine cardiac Purkinje single cellsEXPERIMENTAL PHYSIOLOGY, Issue 1 2007Mario Vassalle The action potential of Purkinje fibres is markedly shortened by tetrodotoxin, suggesting the possibility that a slowly inactivating sodium current might flow during the plateau. The aim of the present experiments was to investigate, in canine cardiac Purkinje single cells by means of a whole cell patch clamp technique, whether a sodium current slowly inactivates at less negative potentials and (if so) some of its distinctive characteristics. The results showed that a 500 ms depolarizing step from a holding potential of ,90 mV to ,50 mV induced the fast inward current INa (labelled here INa1). With steps to ,40 mV or less negative values, a slowly decaying component (tentatively labelled here INa2) appeared, which peaked at ,30 to ,20 mV and decayed slowly and incompletely during the 500 ms steps. The INa2 was present also during steps to ,10 mV, but then the transient outward current (Ito) appeared. When the holding potential (Vh) was decreased to ,60 to ,50 mV, INa2 disappeared even if a small INa1 might still be present. Tetrodotoxin (30 ,m), lignocaine (100 ,m) and cadmium (0.2 mm; but not manganese, 1 mm) blocked INa2. During fast depolarizing ramps, the rapid inactivation of INa1 was followed by a negative slope region. During repolarizing ramps, a region of positive slope was present, whereas INa1 was absent. At less negative values of Vh, the amplitude of the negative and positive slopes became gradually smaller. Gradually faster ramps increased the magnitude of the negative slope, and tetrodotoxin (30 ,m) reduced or abolished it. Thus, Purkinje cells have a slowly decaying inward current owing to Na+ entry (INa2) that is different in several ways from the fast INa1 and that appears important for the duration of the plateau. [source] Effect of rheological behavior of epoxy during precuring on foamingJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Osamu Takiguchi Abstract In this study, the effect of rheological behavior of epoxy during precuring on foaming was investigated. Dynamic time sweep test of epoxy/curing agent (100/1, w/w) was conducted. The viscosities as a function of time showed extremely rapid increase from the order of 102,103 to 106Pa · s at a certain time, followed by slow increase of the viscosities. Dynamic frequency sweep test of precured epoxy with curing agent was conducted at 90°C. The critical gelation time was obtained by using rheological criterion proposed by Winter and Chambon. We found that the slopes of G,(,) and G,(,) decreased with increasing precuring time. Correspondingly, tan , showed a change from negative to positive slope at a critical time. By using the results, the critical gelation time was determined as t = 895,935 s. Samples of epoxy/curing agent/blowing agent (100/1/0.5) were precured for 960,1620 s. And then precured samples were foamed at 230°C for 300 s to decompose chemical blowing agent. The formed bubble size distribution becomes sharp with increase of the precuring time. There are roughly two sizes of bubbles when precured for relatively short time (t < 1080 s) before foaming: large bubbles (>100 ,m) and small ones (,30 ,m). On the other hand, foams precured for long time (t > 1200 s) before foaming, large bubbles disappear, and the average diameter of the bubble becomes small while the porosity is low. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Correlation of relative rates of chromyl chloride oxidation and chromic acid oxidation of acyclic alkenes versus alkene IPs and HOMOsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2004Donna J. Nelson Abstract Plots of logarithms of relative reaction rates of chromyl chloride oxidation and of chromic acid oxidation of alkenes (log,krel values) versus alkene ionization potentials (IPs) and versus their highest occupied molecular orbital energy levels (HOMOs) demonstrate excellent correlations. Each plot has a similar appearance and shows a single line with a positive slope. The results indicate that the rate-determining step of each title reaction involves an electrophilic attack on the alkene ,-bond without significant steric effects; this supports a proposed 2,+,3 cycloaddition mechanism and disfavors a proposed stepwise 2,+,2 cycloaddition mechanism. Comparison is made with other d0 transition metal complexes that oxidize alkenes. Copyright © 2004 John Wiley & Sons, Ltd. [source] In situ monitoring of reaction-induced phase separation with modulated temperature DSCMACROMOLECULAR SYMPOSIA, Issue 1 2003Steven Swier Abstract A linearly polymerizing and network forming epoxy-amine system, DGEBA-aniline and DGEBA-MDA, respectively, will be modified with 20 wt% and 50 wt% of a high- Tg thermoplastic poly(ether sulphone) (Tg=223°C), respectively, both showing LCST-type demixing behavior. Reaction-induced phase separation (RIPS) in these modified systems is studied using Modulated Temperature DSC (MTDSC) as an in situ tool. Phase separation in the linear system can be probed by vitrification of the PES-rich phase, occurring at a higher conversion than the actual cloud point from light scattering measurements. The negative slope of the cloud point curve in a temperature-conversion-transformation diagram unambiguously shows the LCST-type demixing behavior of this system, while the relation between the composition/glass transition of the PES-rich phase and the cure temperature is responsible for the positive slope of its vitrification line. Phase separation in the network forming system appears as reactivity increases at the cloud point due to the concentration of reactive groups. Different mixture compositions alter the ratio between the rate of phase separation and the rate of reaction, greatly affecting the morphology. Information about this in situ developed structure can be obtained from the heat capacity evolutions in non-isothermal post-cures. [source] A Safe and Cost-Effective Short Hospital Stay Protocol to Identify Patients at Low Risk for the Development of Significant Hypocalcemia After Total ThyroidectomyTHE LARYNGOSCOPE, Issue 6 2006Zayna S. Nahas BS Abstract Objective: The objective of this retrospective chart review was to determine if serial postoperative serum calcium levels early after total thyroidectomy can be used to develop an algorithm that identifies patients who are unlikely to develop significant hypocalcemia and can be safely discharged within 24 hours after surgery. Methods: Records of 135 consecutive patients who underwent total/completion thyroidectomy and were operated on by the senior author from 2001 to 2005 have been reviewed. For the entire study group, reports of the early postoperative serum calcium levels (6 hours and 12 hours postoperatively), final thyroid pathology, preoperative examination, inpatient course, and postoperative follow up were reviewed. An endocrine medicine consultation was obtained for all patients while in the hospital after surgery. For patients who developed significant hypocalcemia, reports of their management and the need for readmission or permanent medications for hypoparathyroidism were reviewed. According to the change in serum calcium levels between 6 hours and 12 hours postoperatively, patients were divided into two groups: 1) positive slope (increasing) and 2) nonpositive (nonchanging/decreasing). Results: All patients with a positive slope (50/50) did not develop significant hypocalcemia in contrast to only 59 of 85 patients (69.4%) with a nonpositive slope (P < .001, positive predictive value of positive slope in predicting freedom from significant hypocalcemia = 100%, 95% confidence interval = 92.9,100). In the nonpositive slope group, 61 patients had a serum calcium level ,8 mg/dL at 12 hours postoperatively (,0.5 mg/dL below the low end of normal), and 53 (87%) of these patients remained free of significant hypocalcemia in contrast to only 6 (25%) of 24 patients with serum calcium level <8 mg/dL at 12 hours postoperatively (sensitivity = 90%, positive predictive value = 87%). In addition, of the eight patients who developed significant hypocalcemia in the nonpositive slope group with a serum calcium level ,8 mg/dL at 12 hours postoperatively, 7 (88%) patients developed the signs and symptoms during the first 24 hours after total thyroidectomy. Readmission and permanent need for calcium supplementation happened in two patients, respectively, all with serum calcium levels <8 mg/dL at 12 hours after total thyroidectomy. The compressive and/or symptomatic large multinodular goiter as an indication for thyroidectomy was associated with developing significant hypocalcemia (P < .05). There was no statistically significant correlation between the development of significant hypocalcemia and gender, age, thyroid pathology other than goiter, or neck dissection. Conclusion: Patients with a positive serum calcium slope (t = 6 and 12 hours) after total thyroidectomy are safe to discharge within 24 hours after surgery with patient education with or without calcium supplementation. In addition, patients with a nonpositive slope and a serum calcium level ,8 mg/dL at 12 hours postoperatively (,0.5 mg/dL below the low end of normal) are unlikely to develop significant hypocalcemia, especially beyond 24 hours postoperatively, and therefore can be safely discharged within 24 hours after total thyroidectomy with patient education and oral calcium supplementation. Our management algorithm identifies those patients at low risk of developing significant hypocalcemia early in the postoperative course after total thyroidectomy to allow for a short hospital stay and safe discharge. [source] Impact of Cyclosporine Reduction With MMF: A Randomized Trial in Chronic Allograft Dysfunction.AMERICAN JOURNAL OF TRANSPLANTATION, Issue 11 2006Reference' Study Long-term use of calcineurine inhibitors (CNIs) may contribute to the development of chronic allograft dysfunction (CAD). We investigate the impact of the introduction of MMF combined with cyclosporine (CsA) 50% dose reduction. An open, randomized, controlled, multicenter, prospective study was conducted in 103 patients, receiving a CsA-based therapy with a serum creatinine between 1.7,3.4 mg/dL, more than 1 year after transplantation. They were randomized to receive MMF with half dose of CsA (MMF group) or to continue their maintenance CsA dose (control group). A total of 96 weeks after randomization, the evolution of renal function assessed by regression line analysis of 1/SeCr improved in the MMF group (positive slope) vs. the control group (negative slope), 4.2 × 10,4 vs. ,3.0 × 10,4, respectively (p < 0.001). Concurrently, the absolute renal function improved significantly in the MMF group. No episode of biopsy-proven acute rejection occurred. One patient in each group lost his graft because of biopsy-proven chronic allograft nephropathy. There was a significant decrease of triglycerides level in the MMF group. Anemia and diarrhea were statistically more frequent in the MMF group. In CAD, the reduction of CsA in the presence of MMF results in significant improvement in renal function during a 2-year follow-up. [source] Cerebral white matter blood flow and arterial blood pressure in preterm infantsACTA PAEDIATRICA, Issue 10 2010Klaus Børch Abstract It is generally assumed that one reason why white matter injury is common in preterm infants is the relatively poor vascular supply. Aim:, To examine whether blood flow to the white matter is relatively more reduced at low blood pressure than is blood flow to the brain as a whole. Methods:, Thirteen normoxic preterm infants had blood flow imaging on 16 occasions with single-photon emission computed tomography (SPECT) using 99Tc labelled hexa-methylpropylenamide oxime (HMPAO) as the tracer. Gestational age was 26,32 weeks. Transcutaneous carbon dioxide was between 4.7 and 8.5 kPa and mean arterial blood pressure between 22 and 55 mmHg. Results:, There was no statistically significant direct relation between white matter blood flow percentage and any of the variables. Using non-linear regression, however, assuming a plateau over a certain blood pressure threshold and a positive slope below this threshold, the relation to white matter flow percentage was statistically significant (p = 0.02). The threshold was 29 mmHg (95% confidence limits 26,33). Conclusion:, Our analysis supports the concept of periventricular white matter as selectively vulnerable to ischaemia during episodes of low blood pressure. [source] A slowly inactivating sodium current (INa2) in the plateau range in canine cardiac Purkinje single cellsEXPERIMENTAL PHYSIOLOGY, Issue 1 2007Mario Vassalle The action potential of Purkinje fibres is markedly shortened by tetrodotoxin, suggesting the possibility that a slowly inactivating sodium current might flow during the plateau. The aim of the present experiments was to investigate, in canine cardiac Purkinje single cells by means of a whole cell patch clamp technique, whether a sodium current slowly inactivates at less negative potentials and (if so) some of its distinctive characteristics. The results showed that a 500 ms depolarizing step from a holding potential of ,90 mV to ,50 mV induced the fast inward current INa (labelled here INa1). With steps to ,40 mV or less negative values, a slowly decaying component (tentatively labelled here INa2) appeared, which peaked at ,30 to ,20 mV and decayed slowly and incompletely during the 500 ms steps. The INa2 was present also during steps to ,10 mV, but then the transient outward current (Ito) appeared. When the holding potential (Vh) was decreased to ,60 to ,50 mV, INa2 disappeared even if a small INa1 might still be present. Tetrodotoxin (30 ,m), lignocaine (100 ,m) and cadmium (0.2 mm; but not manganese, 1 mm) blocked INa2. During fast depolarizing ramps, the rapid inactivation of INa1 was followed by a negative slope region. During repolarizing ramps, a region of positive slope was present, whereas INa1 was absent. At less negative values of Vh, the amplitude of the negative and positive slopes became gradually smaller. Gradually faster ramps increased the magnitude of the negative slope, and tetrodotoxin (30 ,m) reduced or abolished it. Thus, Purkinje cells have a slowly decaying inward current owing to Na+ entry (INa2) that is different in several ways from the fast INa1 and that appears important for the duration of the plateau. [source] Improvements to resampling measures of group supportCLADISTICS, Issue 4 2003Pablo A Goloboff Several aspects of current resampling methods to assess group support are reviewed. When the characters have different prior weights or some state transformation costs are different, the frequencies under either bootstrapping or jackknifing can be distorted, producing either under- or overestimations of the actual group support. This is avoided by symmetric resampling, where the probability p of increasing the weight of a character equals the probability of decreasing it. Problems with interpreting absolute group frequencies as a measure of the support are discussed; group support does not necessarily vary with the frequency itself, since in some cases groups with positive support may have much lower frequencies than groups with no support at all. Three possible solutions for this problem are suggested. The first is measuring the support as the difference in frequency between the group and its most frequent contradictory group. The second is calculating frequencies for values of p below the threshold under which the frequency ranks the groups in the right order of support (this threshold may vary from data set to data set). The third is estimating the support by using the slope of the frequency as a function of different (low) values of p; when p is low, groups with actual support have negative slopes (closer to 0 when the support is higher), and groups with no support have positive slopes (larger when evidence for and against the group is more abundant). [source] | ||||||||||||||||