Effect of particle morphology on the mechanical and thermo-mechanical behavior of polymer composites

Fiber reinforced polymer composites have been used in many applications, such as in automobile, aerospace and naval industries, due basically to their high strength-to-weight and modulus-to-weight, among other properties. Even though particles are usually not able to lead to the level of reinforcement of fibers, particle reinforced polymer composites have been proposed for many new applications due to their low cost, easy fabrication and isotropic properties. In this work, polymer composites were prepared by incorporating glass particles of different morphologies on poly(aryl sulfones) matrices. Particles with aspect ratios equal to 1, 2.5 and 10 were used. The prepared composites were characterized using electron microscopy and thermal analysis. Mechanical properties of the composites were evaluated using a four-point bending test. The thermo-mechanical behavior of the obtained composites was also investigated. The results showed that the morphology of the particles alter significantly the mechanical properties of composites. Particles with larger values of aspect ratio led to large elastic modulus but low levels of strain at failure. This result was explained by modeling the thermo-mechanical behavior of the composites using a viscoelastic model. Parameters of the model, obtained from a Cole-Cole type of plot, demonstrated that interactions at the polymer-reinforcing agent interface were higher for composites with large aspect ratio particles. Higher levels of interactions at interfaces can lead to higher degrees of stress transfer and, consequently, to composites with large elastic modulus, as experimentally observed.

Effect of ecological factors on germination of horse purslane (Trianthema portulacastrum)

Trianthema portulacastrum is a very problematic summer crop weed and a complete crop failure has been observed because of this weed at high density. The effect of different ecological factors on germination of T. portulacastrum seeds collected in two different years (2009 and 2005) was studied in laboratory experiments. An increase in temperature from 25 to 35 ºC increased germination percentage of T. portulacastrum from 65 to 85%, after which germination started to decrease, reducing to 71.25% at 45 ºC. Trianthema portulacastrum had maximum germination with distilled water compared with different salt solutions and drought stress levels. Germination was significantly minimum at salinity and drought stress level of 250 mM and -0.8 MPa, respectively. Emergence of T. portulacastrum was maximum (86.25%) at 100% field capacity level but decreased sharply as field capacity decreased thereafter, and minimum emergence (30%) was recorded at field capacity level of 25%. Germination of T. portulacastrum was lowest at pH 5 and any increase in pH resulted in increased germination. A pH range of 8 to 10 had statistically similar germination. Sowing depth of 6 cm reduced the emergence of T. portulacastrum to zero. Reduction in emergence was recorded with depth increase from zero to 5 cm. Maximum emergence was recorded from soil surface (0 cm). An increase in temperature, salinity, drought, sowing depth (up to 4 cm) and a decrease in field capacity increased time to start germination/emergence, time to 50% germination/emergence and mean germination/emergence time but decreased germination/emergence index. Seeds collected during 2009 gave higher germination than old seeds collected in 2005. This information might contribute to development of effective control of T. portulacastrum.

Effect of zone and crops rotation on Ischaemum rugosum and resistance to bispyribac-sodium in Ariari, Colombia

The objectives of this research were to evaluate (1) weed species presented in rice fields in relation to the geographical zone and crop rotation and (2) the resistance level of Ischaemum rugosum to the herbicide bispyribac-sodium. For the first objective, were sampled 79 commercial fields of rice to establish weed density, coverage, and rotation system in the evaluated fields with record of bispyribac-sodium application of at least five years. To reach the second objective, the seeds were collected from plants in commercial fields with different control levels of bispyribac-sodium herbicide. Seeds were germinated in trays under controlled conditions. When plants presented three leaves these were treated with bispyribac-sodium at different doses. Percentages of control and dry weight of plants were evaluated 12 days after treatments (dat). Dominant species in evaluated fields was I. rugosum, with a frequency of 100%, presenting escapes to different chemical commercial treatments. No significant differences were recorded between rotation systems, nevertheless, the most of I. rugosum population was found in the system rice-fallow-rice. The response of applications at different concentrations allows concluding that 65% of samples had resistance at different degrees reported as indexes from 2 to 42 which are related to rotation systems.

The Effect of Different Weed Management Strategies on the Growth and Yield of Direct-Seeded Dry Rice (Oryza sativa)

Weed management is a primary concern in direct seeded rice (DSR) cropping because weed growth becomes a major constraint on crop yield. A two year field study was set up to evaluate the effect of various weed control measures on crop growth, grain yield and grain quality of DSR. The experiment involved five different weed control measures: hand weeding, hoeing, inter-row tine cultivation, inter-row spike hoeing and herbicide treatment (Nominee 100 SC). The extent of weed control (compared to a non-weeded control) ranged from 50-95%. The highest crop yield was obtained using hand weeding. Hand weeding, tine cultivation and herbicide treatment raised the number of fertile rice tillers formed per unit area and the thousand grain weight. Tine cultivation provided an effective and economical level of weed control in the DSR crop.

Anhydrobiosis in yeast: activation effect

Intracellular substances released into the medium during rehydration of dry yeast cells can significantly improve the quality of a synthetic medium. Acceleration of yeast growth in this medium and increased yield of biomass are observed simultaneously. The change in the molecular arrangement of intracellular membranes as a result of the strong dehydration of live organisms is a negative phenomenon that reduces the level of cell viability. However, this phenomenon also represents an adaptive mechanism which facilitates the maintenance of population viability as a whole under extreme environmental conditions

Effect of ventilation on systemic blood flow evaluated by echodopplercardiography

Systemic blood flow (Q) was measured by echodopplercardiography in 5 normal young adult males during apnea, eupnea and tachypnea. Measurements were made in a recumbent posture at 3-min intervals. Tachypnea was attained by doubling the respiratory frequency at eupnea at a constant tidal volume. An open glottis was maintained during apnea at the resting respiratory level. The Q values were positively correlated with the respiratory frequency, decreasing from eupnea to apnea and increasing from eupnea to tachypnea (P<0.05). These data demonstrate that echodopplercardiography, a better qualified tool for this purpose, confirms the positive and progressive effects of ventilation on systemic blood flow, as suggested by previous studies based on diverse technical approaches

The effect of methotrexate and azathioprine on the serum levels of IgA-a1-antitrypsin complex in juvenile chronic arthritis

In the present study we investigated the influence of methotrexate (MTX) and azathioprine (AZA) on the serum levels of the IgA-a1-antitrypsin (IgA-AT) complex in patients with the systemic form of juvenile chronic arthritis (JCA). Fifty-six JCA patients (22 treated with MTX, 18 treated with AZA, and 16 not treated with any immunosuppressive agent) were enrolled in the study. MTX dosage ranged from 0.3 to 0.5 mg kg-1 week-1, while AZA was given daily at an average dose of 1 mg/kg. MTX was given for 13 months (SD = 7 months) whereas AZA for 11 months (SD = 6 months). The average value of the complex was higher in JCA patients than in both control groups (0.74 ± 0.73 U vs 0.37 ± 0.13 U (control children), P<0.001 and vs 0.23 ± 0.12 U (control adults), P<0.001). Values exceeding the normal range were found in twenty-two JCA patients (39.4%). Serum IgA-AT level was lowest in the MTX group compared to AZA and non-treated patients (0.56 ± 0.24 U, 0.76 ± 0.43 U, 0.95 ± 0.52 U, respectively, P<0.05). IgA values exceeding normal levels for age were found in 14% of the patients. A correlation between the levels of the IgA-AT complex and C-reactive protein (r = 0.43, P<0.01), a1-acid-glycoprotein (r = 0.45, P<0.01), a1-antichymotrypsin (r = 0.52, P<0.01), a1-antitrypsin (r = 0.40, P<0.01) and IgA (r = 0.56, P<0.01) was established

Effect of trolox C on cardiac contracture induced by hydrogen peroxide

Hydrogen peroxide (H2O2) perfused into the aorta of the isolated rat heart induces a positive inotropic effect, with cardiac arrhythmia such as extrasystolic potentiation or cardiac contractures, depending on the dose. The last effect is similar to the "stone heart" observed in reperfusion injury and may be ascribed to lipoperoxidation (LPO) of the membrane lipids, to protein damage, to reduction of the ATP level, to enzymatic alterations and to cardioactive compounds liberated by LPO. These effects may result in calcium overload of the cardiac fibers and contracture ("stone heart"). Hearts from male Wistar rats (300-350 g) were perfused at 31oC with Tyrode, 0.2 mM trolox C, 256 mM H2O2 or trolox C + H2O2. Cardiac contractures (baseline elevation of the myograms obtained) were observed when hearts were perfused with H2O2 (Tyrode: 5.9 ± 3.2; H2O2: 60.5 ± 13.9% of the initial value); perfusion with H2O2 increased the LPO of rat heart homogenates measured by chemiluminescence (Tyrode: 3,199 ± 259; H2O2: 5,304 ± 133 cps mg protein-1 60 min-1), oxygen uptake (Tyrode: 0.44 ± 0.1; H2O2: 3.2 ± 0.8 nmol min-1 mg protein-1) and malonaldehyde (TBARS) formation (Tyrode: 0.12 ± 0; H2O2: 0.37 ± 0.1 nmol/ml). Previous perfusion with 0.2 mM trolox C reduced the LPO (chemiluminescence: 4,098 ± 531), oxygen uptake (0.51 ± 0) and TBARS (0.13 ± 0) but did not prevent the H2O2-induced contractures (33.3 ± 16%). ATP (Tyrode: 2.84 ± 0; H2O2: 0.57 ± 0) and glycogen levels (Tyrode: 0.46 ± 0; H2O2: 0.26 ± 0) were reduced by H2O2. Trolox did not prevent these effects (ATP: 0.84 ± 0 and glycogen: 0.27 ± 0). Trolox C is known to be more effective than a -tocopherol or g -tocopherol in reducing LPO though it lacks the phytol portion of vitamin E to be fixed to the cell membranes. Trolox C, unlike vitamin A, did not prevent the glycogen reduction induced by H2O2. Trolox C induced a positive chronotropic effect that resulted in higher energy consumption. The reduction of energy level seemed to be more important than LPO in the mechanism of H2O2-induced contracture

Effect of metabolic acidosis on renal tubular sodium handling in rats as determined by lithium clearance

Systemic metabolic acidosis is known to cause a decrease in salt and water reabsorption by the kidney. We have used renal lithium clearance to investigate the effect of chronic, NH4Cl-induced metabolic acidosis on the renal handling of Na+ in male Wistar-Hannover rats (200-250 g). Chronic acidosis (pH 7.16 ± 0.13) caused a sustained increase in renal fractional Na+ excretion (267.9 ± 36.4%), accompanied by an increase in fractional proximal (113.3 ± 3.6%) and post-proximal (179.7 ± 20.2%) Na+ and urinary K+ (163.4 ± 5.6%) excretion when compared to control and pair-fed rats. These differences occurred in spite of an unchanged creatinine clearance and Na+ filtered load. A lower final body weight was observed in the acidotic (232 ± 4.6 g) and pair-fed (225 ± 3.6 g) rats compared to the controls (258 ± 3.7 g). In contrast, there was a significant increase in the kidney weights of acidotic rats (1.73 ± 0.05 g) compared to the other experimental groups (control, 1.46 ± 0.05 g; pair-fed, 1.4 ± 0.05 g). We suggest that altered renal Na+ and K+ handling in acidotic rats may result from a reciprocal relationship between the level of metabolism in renal tubules and ion transport.

Effect of a submaxillary gland extract on Ehrlich tumor growth in mice

Ablation of host submaxillary glands modifies Ehrlich tumor growth and tumor-infiltrating leukocytes, possibly by modifications in the serum level of growth factors produced by this gland. To extend this research, 7-month-old male EPM-1 mice (N = 30) were divided into two groups: 1) inoculated with tumor cells previously incubated with submaxillary salivary gland extract (SGE) in PBS for 30 min at 37%; 2) inoculated with tumor cells previously incubated with PBS, under the same conditions. Animals were inoculated into the footpad with 40 µl of a suspension containing 4.5 x 107 tumor cells/ml, and footpad thickness was measured daily for 10 days. Sections and smears of tumor cells were prepared from the tumor mass to determine mitosis frequency, percent of tumor cells immunopositive to nerve (NGF) and epidermal (EGF) growth factors and percent of tumor-infiltrating leukocytes. The incubation of tumor cells with SGE produced a tumor reduction of about 30% in size (P<0.01). This effect was not related to loss of cell viability during incubation, but a 33% increase (P<0.05) in the percentage of dead or dying tumor cells and a 15% increase in the percent of NGF/EGF-positive tumor cells (P<0.01) were observed in vivo at the end of experiment. Tumor-infiltrating lymphocytes and mitosis frequency did not differ between groups. These data suggest a direct effect of factors present in SGE on tumor cells, which induce degeneration of tumor cells.

Effect of chronic oral administration of a low dose of captopril on sodium appetite of hypothyroid rats: Influence of aldosterone treatment

Rats rendered hypothyroid by treatment with methimazole develop an exaggerated sodium appetite. We investigated here the capacity of hypothyroid rats (N = 12 for each group) to respond to a low dose of captopril added to the ration, a paradigm which induces an increase in angiotensin II synthesis in cerebral areas that regulate sodium appetite by increasing the availability of circulating angiotensin I. In addition, we determined the influence of aldosterone in hypothyroid rats during the expression of spontaneous sodium appetite and after captopril treatment. Captopril significantly increased (P<0.05) the daily intake of 1.8% NaCl (in ml/100 g body weight) in hypothyroid rats after 36 days of methimazole administration (day 36: 9.2 ± 0.7 vs day 32: 2.8 ± 0.6 ml, on the 4th day after captopril treatment). After the discontinuation of captopril treatment, daily 1.8% NaCl intake reached values ranging from 10.0 ± 0.9 to 13.9 ± 1.0 ml, 48 to 60 days after treatment with methimazole. Aldosterone treatment significantly reduced (P<0.05) saline intake before (7.3 ± 1.6 vs day 0, 14.4 ± 1.3 ml) and after captopril treatment. Our results demonstrate that, although hypothyroid rats develop a deficiency in the production of all components of the renin-angiotensin-aldosterone system, their capacity to synthesize angiotensin II at the cerebral level is preserved. The partial reversal of daily 1.8% NaCl intake during aldosterone treatment suggests that sodium retention reduces both spontaneous and captopril-induced salt appetite.

Acute and chronic effects of cadmium on blood homeostasis of an estuarine crab, Chasmagnathus granulata, and the modifying effect of salinity

Whole body oxygen consumption and some hemolymph parameters such as pH, partial pressure of gases, level of ions and lactate were measured in the estuarine crab Chasmagnathus granulata after both acute (96 h) and chronic (2 weeks) exposure to cadmium at concentrations ranging from 0.4 to 6.3 mg/l. In all instances, the crabs developed hemolymph acidosis, but no respiratory (increased PCO2) or lactate increases were evident. Hemolymph levels of sodium and calcium were always increased by cadmium exposure. The chronic toxicity of cadmium was enhanced at 12‰ salinity, even causing a significantly higher mortality in comparison with the higher salinity (30‰) used. A general metabolic arrest took place at 12‰ salinity in the crabs chronically exposed to cadmium, as indicated by decreases of oxygen consumption and PCO2, an increase of PO2, along with no changes in lactate levels. These imbalances were associated with severe necrosis and telangiectasia in the respiratory gills, probably leading to respiratory impairment and finally histotoxic hypoxia and death of the animals.

The effect of CagA status on response to Helicobacter pylori eradication therapy in Western Turkey

If cytotoxin-associated gene A (CagA) status affects the response rates of therapy, then it may be possible to predict Helicobacter pylori eradication rates. We aimed to evaluate the response to eradication treatment of H. pylori infection in CagA-positive and CagA-negative patients. A total of 184 patients (93 males, 91 females, mean age 42.6 ± 12.8 years) with H. pylori-positive chronic gastritis were studied. Subjects underwent a gastroscopy and biopsy specimens were taken from the gastric antrum, body, and fundus. Before the eradication therapy was given all patients were tested for CagA, TNF-alpha and gastrin levels. They were then prescribed lansoprazole (30 mg bid), clarithromycin (500 mg bid), and amoxicillin (1.0 mg bid) for one week. On the 8th week a second endoscopy was performed and further biopsy specimens were obtained from the same sites as in the initial endoscopy. One hundred and twenty-seven patients (69.1%) were found to be CagA positive and 57 patients (30.9%) were CagA negative. The total eradication rate was 82.6%. In the CagA-positive group this rate was 87.4%, and in the CagA-negative group it was 71.9% (P = 0.019). TNF-alpha levels were higher in the CagA-positive than in the CagA-negative group (P = 0.001). However, gastrin levels were not different between groups (P = 0.421). Our findings revealed that CagA-negative status might be a risk factor for failure of H. pylori triple therapies. The CagA pathogenicity island gives a growth advantage to H. pylori strains and has been associated with an increase in the inflammatory response at the gastric mucosal level. These properties could make CagA-positive H. pylori strains more susceptible to antibiotics.

Effect of asthma severity on symptom perception in childhood asthma

Individual ability to perceive airway obstruction varies substantially. The factors influencing the perception of asthma are probably numerous and not well established in children. The present study was designed to examine the influence of asthma severity, use of preventive medication, age and gender on the association between respiratory symptoms (RS) and peak expiratory flow (PEF) rates in asthmatic children. We followed 92 asthmatic children, aged 6 to 16 years, for five months. Symptom scores were recorded daily and PEF was measured twice a day. The correlations among variables at the within-person level over time were analyzed for each child and for the pooled data by multivariate analysis. After pooling the data, there was a significant (P<0.05) correlation between each symptom and PEF; 60% of the children were accurate perceivers (defined by a statistically significant correlation between symptoms and PEF across time) for diurnal symptoms and 37% for nocturnal symptoms. The accuracy of perception was independent of asthma severity, age, gender or the use of preventive medication. Symptom perception is inaccurate in a substantial number of asthmatic children, independently of clinical severity, age, gender or use of preventive medication. It is not clear why some asthmatic patients are capable of accurately perceiving the severity of airway obstruction while others are not.

Effect of perimuscular injection of Bothrops jararacussu venom on plasma creatine kinase levels in mice: influence of dose and volume

The effect of dose and volume of a perimuscular injection of Bothrops jararacussu venom on myonecrosis of skeletal muscle was studied in mice. An increase of the venom dose (0.25 to 2.0 µg/g) at a given volume (50 µl) resulted in an increase in plasma creatine kinase (CK) levels 2 h after injection. Plasma CK activity increased from the basal level of 129.27 ± 11.83 (N = 20) to 2392.80 ± 709.43 IU/l (N = 4) for the 1.0 µg/g dose. Histological analysis of extensor digitorum longus muscle 4 h after injection showed lesion of peripheral muscle fibers, disorganization of the bundles or the complete degeneration of muscle fibers. These lesions were more extensive when higher doses were injected. Furthermore, an increase in volume (12.5 to 100 µl) by dilution of a given dose (0.5 µg/g) also increased plasma CK levels from 482.31 ± 122.79 to 919.07 ± 133.33 IU/l (N = 4), respectively. These results indicate that care should be taken to standardize volumes and sites of venom injections.