977 resultados para Fixed-effect estimator
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The synthetic control (SC) method has been recently proposed as an alternative to estimate treatment effects in comparative case studies. The SC relies on the assumption that there is a weighted average of the control units that reconstruct the potential outcome of the treated unit in the absence of treatment. If these weights were known, then one could estimate the counterfactual for the treated unit using this weighted average. With these weights, the SC would provide an unbiased estimator for the treatment effect even if selection into treatment is correlated with the unobserved heterogeneity. In this paper, we revisit the SC method in a linear factor model where the SC weights are considered nuisance parameters that are estimated to construct the SC estimator. We show that, when the number of control units is fixed, the estimated SC weights will generally not converge to the weights that reconstruct the factor loadings of the treated unit, even when the number of pre-intervention periods goes to infinity. As a consequence, the SC estimator will be asymptotically biased if treatment assignment is correlated with the unobserved heterogeneity. The asymptotic bias only vanishes when the variance of the idiosyncratic error goes to zero. We suggest a slight modification in the SC method that guarantees that the SC estimator is asymptotically unbiased and has a lower asymptotic variance than the difference-in-differences (DID) estimator when the DID identification assumption is satisfied. If the DID assumption is not satisfied, then both estimators would be asymptotically biased, and it would not be possible to rank them in terms of their asymptotic bias.
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Mode of access: Internet.
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This study presents a report on pyrolysis of Napier grass stem in a fixed bed reactor. The effects of nitrogen flow (20 to 60 mL/min), and reaction temperature (450 to 650 degrees C) were investigated. Increasing the nitrogen flow from 20 to 30 mL/min increased the bio-oil yield and decreased both bio-char and non-condensable gas. 30 mL/min nitrogen flow resulted in optimum bio-oil yield and was used in the subsequent experiments. Reaction temperatures between 450 and 600 degrees C increased the bio-oil yield, with maximum yield of 32.26 wt% at 600 degrees C and a decrease in the corresponding bio-char and non-condensable gas. At 650 degrees C, reductions in the bio-oil and bio-char yields were recorded while the non-condensable gas increased. Water content of the bio-oil decreased with increasing reaction temperature, while density and viscosity increased. The observed pH and higher heating values were between 2.43 to 2.97, and 25.25 to 28.88 MJ/kg, respectively. GC-MS analysis revealed that the oil was made up of highly oxygenated compounds and requires upgrading. The bio-char and non-condensable gas were characterized, and the effect of reaction temperature on the properties was evaluated. Napier grass represents a good source of renewable energy when all pyrolysis products are efficiently utilized.
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This report mainly deals with the interactive effect of different in-stock probabilities used by every individual in a supply chain. Based on a simulation for 10,000 weeks, the effects of varying in-stock probabilities are observed. Based on these observations, an individual in a supply chain can take counter measures in order to avoid stock out chances hence maintaining profits.
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This study investigated the effect of the incorporation of an iodonium salt in experimental composites, on the bond strength of metallic brackets bonded to bovine teeth. Two hundred and seventy bovine teeth were embedded in self-curing acrylic resin and divided into 18 groups (n=15), according to the experimental composite with an iodonium salt at molar concentrations 0 (control), 0.5, or 1%; the light-activation times (8, 20 and 40 s); and the storage times (10 min or 24 h). Metallic brackets were fixed on the tooth surface using experimental composites. Photoactivation was performed with a quartz-tungsten-halogen light-curing unit curing unit for 8, 20 and 40 s. The specimens were stored in distilled water at 37 °C for 10 min or 24 h and submitted to bond strength test at 0.5 mm/min. The data were subjected to three-way ANOVA and Tukey's test (α=0.05). The Adhesive Remnant Index (ARI) was used to classify the failure modes. The shear bond strengths (MPa) at 10 min for light-activation times of 8, 20 and 40 s were: G1 - 4.6, 6.9 and 7.1; G2 - 8.1, 9.2 and 9.9; G3 - 9.1, 10.4 and 10.7; and at 24 h were: G1 - 10.9, 11.1 and 11.7; G2 - 11.8, 12.7 and 14.2; G3 - 12.1, 14.4 and 15.8. There was a predominance of ARI score 3 for groups with 10 min storage time, and ARI score 2 for groups with 24 h storage time. In conclusion, the addition of iodonium salt (C05 and C1) to the experimental composite may increase the bond strength of brackets to bovine enamel using reduced light exposure times.
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Background: The oocyte ability to undergo successful fertilization, cleavage and embryonic development depends on meiotic maturation and developmental competence acquisition. In vitro maturation (IVM) protocols currently use eCG, hCG or a combination of both, the effect of these gonadotrophins during IVM and subsequent embryonic development is still controversial. Several media have been used for IVM of porcine oocytes: TCM199, Whitten's and NCSU23 have also been shown to support pig oocyte IVM. This study was designed to determine the effect of hormonal supplementation period and maturation media during in vitro maturation of pig oocytes (1) and subsequent embryonic development (2). Materials, Methods & Results: Oocytes with intact cumulus oophurus layers and homogeneous cytoplasm were collected from prebubertal gilts. IVM was subjected in NCSU23, TCM199 or Whitten's media supplemented with 10 IU/mL eCG and 10 IU/mL hCG for the first 24 or 48 h of IVM. In each replicate the oocytes were fixed every 4 h from 32 to 48 h IVM or the past 48 h after IVM, oocytes were fertilized in vitro in mTBM medium for six hours and cultured in NCSU23 medium for nine days. Cleavage, blastocyst and hatching rates were evaluated at 48 h (day 2), 168 h (day 7) and 216 h (day 9), respectively. The addition of eCG and hCG during the first 24 h IVM increased the proportion of oocytes that reached MII stage at 44 h of maturation in NCSU23 medium. This effect was also observed in Whitten medium at 44 and 48 h (P < 0.05). However, it was not observed in the TCM199 medium. No effect of maturation medium on oocyte nuclear maturation (P > 0.05) was observed in oocytes matured in the presence of eCG and hCG during the first 24 h IVM or during 48 h IVM. A progressive increase of maturation indexes was observed on oocytes matured with hormonal supplementation in Whitten media for 24 h. Higher indexes were obtained at 44 and 48 h. When NCSU23 media was used, no difference after 36 h of maturation was observed. The same result was observed in TCM199. A progressive increase of maturation indexes was observed on oocytes matured with hormonal supplementation for 48 h in Whitten media. Higher indexes were obtained in 36 and 40 h. When NCSU23 or TCM199 were used, no difference was observed. No effect of IVM media on the percentage of fertilized oocytes and polyspermic oocytes or number of spermatozoa per fertilized oocytes was observed. Also, no effect of IVM media on cleavage and blastocyst rates was seen. However, the proportion of hatched blastocysts was lower in NCSU23 compared to Whitten or TCM199. Discussion: Similar results were reported by Marques et al. [13], that it no differences between hormonal supplementation for 22 or 44 h were observed. Therefore, more studies are needed to elucidate the role of these hormones in nuclear in vitro maturation in pig oocytes. In conclusion, no effect of maturation media on meiotic progression was observed. However, the proportion of oocytes that reached metaphase II (MII) stage was higher when eCG + hCG were added for 24 h than 48 h mainly at the 44 h of maturation. In addition, no differences were observed in cleavage and blastocyst rates of the cultured embryos. However, embryos cultured in NCSU23 showed lower rates of hatching compared to other media. These results indicated no effect of maturation media on the fertilization and embryonic development even in the presence of cysteine, PFF and EGF, except for hatched embryos that these rates were lower in NCSU23.
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In this study four irons were casted with different chromium and vanadium contents: 2.66% Cr, 5.01% Cr, 2.51% V and 5.19% V. Their microstructure is composed of: ledeburite, graphite and M(3)C carbides (cementite). Pin-abrasion tests were carried out using fixed alumina abrasive grains at different loads: 1, 2, 4.6 and 10 N. The wear surface and the abrasive paper were examined by scanning electron microscopy for identifying the wear micromechanism. The results reveal that the mass loss increased with the load increase, and the effect of the percentage of chromium on mass loss is inverted when the load is increased from 4.6 to 10 N; for 4.6 N the mass loss decreased when the chromium percentage was increased from 2.66% to 5.01%. Nevertheless, for 10 N the mass loss increased when the chromium percentage was increased. The worn surfaces of the materials tested at 1 N show microcutting caused by the abrasive tip that produces continuous microchips. The worn surfaces and the abrasive paper tested at 10 N show continuous microchips and brittle debris. The results show that high pressures produce a brittle wear mechanism and low pressures produce a more ductile wear micromechanism, for this, the applied pressure defines the dependence between the wear resistance and wear micromechanism. (C) 2009 Elsevier B.V. All rights reserved.
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We assess the effect of the choice of spanwise periodic length on simulations of the flow around a fixed circular cylinder. The Reynolds number is set to 400 because, at this value, both lift coefficient and shedding frequency show significant drop due to three-dimensional flow structures. From the analysis of the three-dimensionalities of the wake and of the integral quantities such as Strouhal number, RMS of lift coefficient and energy contained in the three-dimensional portion of the flow we obtain an estimate of the minimum spanwise length to satisfactorily represent the flow. Furthermore, we observe a distinct wake behavior when the spanwise length is approximately the mode B instability wavelength. (C) 2011 Elsevier Ltd. All rights reserved.
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A hydraulic jump is characterized by strong energy dissipation and mixing, large-scale turbulence, air entrainment, waves and spray. Despite recent pertinent studies, the interaction between air bubbles diffusion and momentum transfer is not completely understood. The objective of this paper is to present experimental results from new measurements performed in rectangular horizontal flume with partially-developed inflow conditions. The vertical distributions of void fraction and air bubbles count rate were recorded for inflow Froude number Fr1 in the range from 5.2 to 14.3. Rapid detrainment process was observed near the jump toe, whereas the structure of the air diffusion layer was clearly observed over longer distances. These new data were compared with previous data generally collected at lower Froude numbers. The comparison demonstrated that, at a fixed distance from the jump toe, the maximum void fraction Cmax increases with the increasing Fr1. The vertical locations of the maximum void fraction and bubble count rate were consistent with previous studies. Finally, an empirical correlation between the upper boundary of the air diffusion layer and the distance from the impingement point was provided.
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Variation in larval size has been shown to be an important factor for the post-metamorphic performance of marine invertebrates but, despite its importance, few sources of this variation have been identified. For a range of taxa, offspring size is positively correlated with maternal size but the reasons for this correlation remain unclear. We halved the size of colonies in the bryozoan Bugula neritina 1 wk prior to reproduction (but during embryogenesis) to determine if larval size is a fixed or plastic trait. We manipulated colonies in such a way that the ratio of feeding zooids to reproductive zooids was constant between treatment and control colonies. We found that manipulating colony size strongly affects larval size; halved colonies produced larvae that were similar to13% smaller than those produced by intact colonies. We entered these data into a simple model based on previous work to estimate the likely post-metamorphic consequences of this reduction in larval size. The model predicted that larvae that came from manipulated colonies would suffer similar to300% higher post-metamorphic mortality and similar to50% lower fecundity as adults. Colonies that are faced with a stress appear to be trading off current offspring fitness to maximize their own long-term fitness and this may explain previous observations of compensatory growth in colonial organisms. This study demonstrates that larval size is a surprisingly dynamic trait and strong links exist between the maternal phenotype and the fitness of the offspring. The performance of settling larvae may be determined not only by their larval experience but also by the experience of their mothers.
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Background: Over-ventilation causing low arterial carbon dioxide levels (PaCO2) has been associated with the development of neonatal chronic lung disease and adverse outcomes. This may occur very soon after birth. Aim: To investigate the effect on PaCO2 and oxygenation of very premature lambs resuscitated with different tidal volumes and PEEP. Methods: Anaesthetised lambs delivered at 126 days gestation were randomised to 15 min resuscitation with 3 regimes: (1) Laerdal resuscitation bag (B) with 100% oxygen and no PEEP, (2) fixed tidal volume (VT) of 5 mL/kg, or (3) VT of 10 mL/kg, both delivered with a Babylog 8000 ventilator in volume guarantee mode with 8 cm H2O PEEP and variable FiO2. Frequent blood gases were measured and VT, mean airway pressure (Paw), minute volume (MV), ventilation rate (VR), respiratory system compliance (Crs) and alveolar/arterial oxygen difference (AaDO2) were recorded. Results: Twenty lambs were studied. B (1) was associated with more variable VT and peak inspiratory pressures (PIP) compared to fixed tidal volumes (2 and 3). The lambs ventilated with 10 mL/kg were over-ventilated, those ventilated with 5 mL/kg were slightly under-ventilated. Those ventilated with the Laerdal bag had a mean VT of 7.5 mL/kg and were normocarbic. The different tidal volumes had little effect on oxygenation. PEEP improved oxygenation. The table shows the values at 15 minutes expressed as mean and SEM. TABLE. No caption av... TABLE. No caption av... Image Tools Conclusion: Very premature lambs can be effectively resuscitated from birth using volume guarantee ventilation. Within minutes of birth different tidal volumes had a large effect on PaCO2 and no effect on oxygenation. Studies are needed to determine the appropriate tidal volume for resuscitating very premature infants to maintain acceptable levels of PaCO2. © International Pediatrics Research Foundation, Inc. 2004. All Rights Reserved.
Trypan blue staining for capsulorhexis: Ultrastructural effect on lens epithelial cells and capsules
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PURPOSE: To evaluate the ultrastructural effect of trypan blue 0.1% staining for capsulorhexis on lens epithelial cells (LECs) and capsules SETTING: Division of Ophthalmology. University of Sao Paulo, Sao Paulo, Brazil METHODS: Before capsulorhexis, patients were randomly assigned to 1 of 2 groups Trypan blue 0 1% staining was performed in the treatment group No trypan blue was used in the control group Samples of capsules with LECs were fixed and analyzed with routine optical microscopy techniques. immunohistochemistry for beclin-1 expression (a marker of autophagy), terminal deoxynucleotidyl transf erase-mediated dUTP-biotin nick-end labeling to detect apoptosis, and transmission electron microscopy (TEM) Morphometric analyses were performed. and the 2 sets of data were compared. RESULTS: Each group comprised 15 patients Cell death by autophagy and apoptosis was observed in the treatment group but not in the control group The TEM images of subcapsular epithelium cells showed mitochondria` rupture, dilation of the cisterns of the endoplasmic reticulum, increased cytoplasmic and nuclear electron density, and abnormalities in the nuclear profile of trypan blue-stained cells. Morphometric analysis showed statistically significant differences between the 2 groups in the longest nuclear axes and the ratio between the total nuclear perimeter and the cell area (P = .03) The difference in capsule thickness between groups was not significant. CONCLUSION: Trypan blue caused LEC death, which supports the hypothesis that staining with trypan blue 0 1% can help reduce the incidence of posterior capsule pacification after cataract surgery
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Little is known about the physiological mechanisms related to low-intensity laser therapy (LILT), particularly in acute inflammation and subsequent wound healing. The objective of this study was to verify the effect of LILT on mast cell degranulation. Epulis fissuratum tissues from eight patients were used. One part of the lesion was irradiated with an AsGaAl laser (lambda = 670 nm, 8.0 J/cm(2), 5 mW, 4 min). The other part was not irradiated. Then, the specimens were immediately removed, fixed and examined by light microscopy. The number of mast cells was similar in laser-treated samples when compared with non-irradiated specimens. The degranulation indexes of the mast cells observed in the irradiated samples were significantly higher than those of controls (P < 0.05). LILT with the parameters used increased the number of degranulated mast cells in oral mucosa.
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Objectives. To evaluate the effect of the microstructure on the Weibull and slow crack growth (SCG) parameters and on the lifetime of three ceramics used as framework materials for fixed partial dentures (FPDs) (YZ - Vita In-Ceram YZ; IZ - Vita In-Ceram Zirconia; AL - Vita In-Ceram AL) and of two veneering porcelains (VM7 and VM9). Methods. Bar-shaped specimens were fabricated according to the manufacturer`s instructions. Specimens were tested in three-point flexure in 37 degrees C artificial saliva. Weibull analysis (n = 30) and a constant stress-rate test (n = 10) were used to determine the Weibull modulus (m) and SCG coefficient (n), respectively. Microstructural and fractographic analyzes were performed using SEM. ANOVA and Tukey`s test (alpha = 0.05) were used to statistically analyze data obtained with both microstructural and fractographic analyzes. Results. YZ and AL presented high crystalline content and low porosity (0.1-0.2%). YZ had the highest characteristic strength (sigma(0)) value (911 MPa) followed by AL (488 MPa) and IZ (423 MPa). Lower sigma(0) values were observed for the porcelains (68-75 MPa). Except for IZ and VM7, m values were similar among the ceramic materials. Higher n values were found for YZ (76) and AL (72), followed by IZ (54) and the veneering materials (36-44). Lifetime predictions showed that YZ was the material with the best mechanical performance. The size of the critical flaw was similar among the framework materials (34-48 mu m) and among the porcelains (75-86 mu m). Significance. The microstructure influenced the mechanical and SCG behavior of the studied materials and, consequently, the lifetime predictions. (C) 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
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To evaluate the effect of oral rehabilitation with immediately loaded fixed implant-supported mandibular prostheses on chewing and swallowing in elderly individuals. Materials and Methods: Fifteen completely edentulous patients aged more than 60 years (10 women and five men), wearing removable dentures in both arches, had a mandibular denture replaced by an implant-supported prosthesis. All individuals were evaluated before surgery and again 3, 6, and 18 months later with regard to mastication and swallowing conditions. Examinations entailed an interview, evaluation of tactile sensitivity of the face, and observation of food intake, masticatory type, formations of bolus, and pain during mastication. The swallowing evaluation comprised observation of clinical signs related to the oral and pharyngeal stages of swallowing, as well as the presence of oral residue. The findings of different evaluations before and 3, 6, and 18 months after the surgical-prosthetic procedure were statistically compared by analysis of variance for repeated measurements at a significance level of 5%. Results: The questionnaire revealed a reduction in complaints of masticatory and swallowing disturbances, a decreased need for liquid ingestion, and reduced choking and coughing. Clinical evaluations showed improved oral function and bolus propulsion for both solid and paste-consistency foods; pain during mastication was also resolved. Conclusion: Treatment with mandibular implant-supported dentures had positive effects on the clinical aspects of mastication and swallowing in elderly individuals. INT J ORAL MAXILLOFAC IMPLANTS 2009; 24:110-117