Summary: Bis(phenoxy‐imine) Zr complexes with MAO activation can produce polyethylenes with well‐defined bimodal molecular weight distributions. Polymerization behavior indicates that minor changes in the ligand structures can have a significant effect on the modality of the resulting polyethylenes. Although there is no direct relationship between the bimodal catalytic behavior and the structure of a precatalyst complex in solution, a precatalyst complex having a methyl or methoxy group para to the phenoxy‐oxygen inclined to exhibit bimodal behavior whereas that with a pentafluorophenyl group on the imine‐nitrogen displayed unimodal behavior. Polymerization results suggest that bimodal behavior is linked to the presence of two kinds of cationic active species, which arise from different modes of ligand coordination. A qualitative correlation was found between the calculated amounts of possible cationic active species and the uni‐ and bimodal catalytic behavior. Based on the results obtained, we concluded that the bimodal polyethylenes are produced by two kinds of cationic active species having two available cis‐located sites with cis‐N, trans‐O and cis‐N, cis‐O arrangements. The results introduced herein are rare examples of the production of well‐defined bimodal polyethylenes using a single precatalyst.
Bis(phenoxy imine) Zr complexes can produce well‐defined bimodal polyethylenes. 相似文献
Summary: Fluorinated bis(phenoxy‐imine)Ti complexes 1 – 3 combined with MgCl2/i‐BunAl(OR)3−n (MgCl2‐supported catalysts) were able to polymerize propylene in a living fashion at room temperature to provide slightly to highly syndiotactic poly(propylenes) (PPs) with extremely narrow distributions of molecular weight. These represent the first examples of MAO‐ and borate‐free group 4 metal‐based living catalysts. The supported complexes 2 and 3 formed PPs with higher syndiotacticity and Tm's than the corresponding homogeneous MAO‐activation systems (e.g., 3 : rr 97%, Tm 155 °C; MAO activation: rr 93%, Tm 152 °C). The measured Tm of 155 °C represents the highest known Tm for syndiotactic PPs synthesized at room temperature.
Polymerization of propylene to poly(propylene) with supported Ti‐based catalysts. 相似文献
Responses of lateral medullary neurons to microstimulation of two points in the locomotor strip—rostral and caudal to the obex—were recorded intracellularly in mesencephalic decerebellated uncurarized cats. Excitatory and inhibitory postsynaptic potentials and orthodromic action potentials occurred up to 20 ms after a single stimulus. A number of cells responded to stimulation of a locomotor point by a repetitive discharge, and in some cells synaptic responses were evoked by contralateral stimulation. The responsive neurons were scattered among other cells in the lateral medullary tegmentum. At least one-third of neurons with synaptic responses to stimulation of the rostral locomotor point were antidromically invaded from the caudal one. The characteristic length of these descending axons was between 4 and 9 mm, although there were longer axons too.The lateral medullary cells which give synaptic responses to stimulation of the locomotor strip form the locomotor column located medial to the strip, and a portion of these cells send their axons to the strip. It is suggested that the activity is propagated polysynaptically along the column through axonal collaterals of its neurons. One can assume that when repetitive stimulation achieves a threshold for locomotion such a propagation occurs without decrement. As a result, spinal stepping generators are activated. 相似文献
Male albino Wistar rats were injected bilaterally with 4 micrograms of 6-hydroxydopamine into the dorsal noradrenergic bundle to deplete forebrain noradrenaline to less than 5% of control values. Acquisition learning of a fixed interval schedule or a continuously reinforced schedule was not altered but resistance to extinction was seen after food reinforced training on either schedule but not after water reinforced training. A possible increase in food motivation was tested by the use of preloading with free food prior to a fixed interval session but both control and lesioned rats reacted similarly to this manipulation thus appearing to exclude an increase in food motivation. An attentional explanation is proposed and tested by the demonstration that resistance to extinction does not occur after a partially (variable ratio 4), as opposed to a continuously, reinforced schedule. Further evidence in favour of an attentional mechanism comes from the finding that on both a fixed interval and a continuously reinforced schedule the lesion has to be present during the acquisition phase to result in subsequent resistance to extinction. Intact animals trained on either schedule and subsequently subjected to the lesion failed to show an increased resistance to extinction. 相似文献
STUDY OBJECTIVES: Cystic fibrosis (CF) patients may be predisposed to poor sleep quality due to upper and lower airway abnormalities and impaired gas exchange. Previous sleep investigations of CF patients using single-night polysomnography have reported conflicting results. We hypothesized that sampling sleep for a prolonged period in a patient's normal environment may give a more representative assessment of sleep quality than a single-night polysomnogram, and that impaired sleep quality would correlate with pulmonary disease severity and self-assessed sleep quality. DESIGN: Using wrist actigraphy, we measured sleep quality in clinically stable CF patients and age-matched control subjects. In addition, each CF patient and control subject completed the following three questionnaires: the Epworth sleepiness scale; the Pittsburgh sleep quality index (PSQI); and the Medical Outcomes Study 36-item short form. RESULTS: Twenty CF patients and control subjects were enrolled in the study, and were well-matched for age, sex, and body mass index. The mean (+/- SD) FEV(1) for CF patients was 61.0 +/- 20.1% predicted. CF patients and control subjects had similar sleep duration, sleep latency, and sleep efficiency. However, CF patients had higher PSQI scores (6.45 vs 4.55, respectively; p = .04), a higher fragmentation index (FI) [31.72 vs 18.02, respectively; p < 0.001], and less immobile time (88.87 vs 91.89, respectively; p = 0.02). There was a significant correlation of FI with FEV(1) and PSQI scores. CONCLUSIONS: Stable CF patients have disrupted sleep, and sleep disruption may in part be related to the severity of pulmonary disease. In addition, the PSQI may be useful in detecting CF patients with poor sleep quality. 相似文献
BackgroundOngoing assessment of influenza vaccine effectiveness (VE) is critical to inform public health policy. This study aimed to determine the VE of trivalent influenza vaccine (TIV) for preventing influenza-related hospitalizations and other serious outcomes over three consecutive influenza seasons.MethodsThe Serious Outcomes Surveillance (SOS) Network of the Canadian Immunization Research Network (CIRN) conducted active surveillance for influenza in adults ≥16 years (y) of age during the 2011/2012, 2012/2013 and 2013/2014 seasons in hospitals across Canada. A test-negative design was employed: cases were polymerase chain reaction (PCR)-positive for influenza; controls were PCR-negative for influenza and were matched to cases by date, admission site, and age (≥65 y or <65 y). All cases and controls had demographic and clinical characteristics (including influenza immunization status) obtained from the medical record. VE was estimated as 1-OR (odds ratio) in vaccinated vs. unvaccinated patients × 100%. The primary outcome was VE of TIV for preventing laboratory-confirmed influenza-related hospitalization; secondary outcomes included VE of TIV for preventing influenza-related intensive care unit (ICU) admission/mechanical ventilation, and influenza-related death.ResultsOverall, 3394 cases and 4560 controls were enrolled; 2078 (61.2%) cases and 2939 (64.5%) controls were ≥65 y. Overall matched, adjusted VE was 41.7% (95% Confidence Interval (CI): 34.4–48.3%); corresponding VE in adults ≥65 y was 39.3% (95% CI: 29.4–47.8%) and 48.0% (95% CI: 37.5–56.7%) in adults <65 y, respectively. VE for preventing influenza-related ICU admission/mechanical ventilation in all ages was 54.1% (95% CI: 39.8–65.0%); in adults ≥65 y, VE for preventing influenza-related death was 74.5% (95% CI: 44.0–88.4%).ConclusionsWhile effectiveness of TIV to prevent serious outcomes varies year to year, we demonstrate a statistically significant and clinically important TIV VE for preventing hospitalization and other serious outcomes over three seasons. Public health messaging should highlight the overall benefit of influenza vaccines over time while acknowledging year to year variability.ClinicalTrials.gov Identifier: NCT01517191. 相似文献
Regular physical exercise within structured lifestyle programs may improve weight status and minimize metabolic risk factors in childhood obesity. The aim of this study was to evaluate the effect of the one-year combined physical exercise/lifestyle program KLAKS on anthropometric and metabolic parameters and glycemic control in childhood obesity.
Materials and Methods
142 overweight/obese (BMI > 90th percentile) candidates (7–18 years) were enrolled, 115 participants completed the program. Anthropometrics and biochemical parameters were obtained at beginning and completion. An oral glucose tolerance test (OGTT) was performed in a subgroup of participants. Course of glucose and insulin levels within OGTT was correlated with several parameters and is reported here for those who completed the program.
Results
The mean standard deviation scores (SDS) decreased significantly for BMI, waist circumference, waist-to-height ratio (WHtR) and percentage body fat (all p ≤ 0.01). Improved metabolic risk markers included mean glucose levels within an OGTT at follow-up compared to baseline (p < 0.0001) and HbA1c (p = 0.05) as well as indications of improvement for gamma-glutamyl-transferase and free fatty acids.
Conclusions
The one-year combined exercise/lifestyle program KLAKS significantly improves markers of obesity and glycemic control. Impaired cardiometabolic risk markers, even subclinical, are also favorably influenced by program participation. 相似文献
Shiga toxin 2 (Stx2) is believed to be a major virulence factor of enterohemorrhagic Escherichia coli (EHEC) contributing to hemolytic uremic syndrome (HUS). The complement system has recently been found to be involved in the pathogenesis of EHEC-associated HUS. Stx2 was shown to activate complement via the alternative pathway, to bind factor H (FH) at short consensus repeats (SCRs) 6–8 and 18–20 and to delay and reduce FH cofactor activity on the cell surface. 相似文献