Czochralski crystal growth and characterization of large langatate (La3Ga5.5Ta0.5O14, LGT) crystals for SAW applications

1.5 and 2 inch LGT, langatate (La₃Ga_5.5Ta_0.5O₁₄) crystals along the X[100], Y[120] and Z[001]-directions were successfully grown by the Czochralski technique.

Vapor-fed microfluidic hydrogen generator

Water-splitting devices that operate with humid air feeds are an attractive alternative for hydrogen production as the required water input can be obtained directly from ambient air. This article presents a novel proof-of-concept microfluidic platform that makes use of polymeric ion conductor (Nafion®) thin films to absorb water from air and performs the electrochemical water-splitting process. Modelling and experimental tools are used to demonstrate that these microstructured devices can achieve the delicate balance between water, gas, and ionic transport processes required for vapor-fed devices to operate continuously and at steady state, at current densities above 3 mA cm(-2). The results presented here show that factors such as the thickness of the Nafion films covering the electrodes, convection of air streams, and water content of the ionomer can significantly affect the device performance. The insights presented in this work provide important guidelines for the material requirements and device designs that can be used to create practical electrochemical hydrogen generators that work directly under ambient air.

Substrate oxidation during exercise: impact of time interval from the last meal in obese women

OBJECTIVE

To investigate whether time interval between meal and exercise alters the balance of substrate oxidation during an exercise bout.

HYPOTHESIS

Exercise performed 3-h after meal induces a higher rate of lipid oxidation than when performed only 1-h after meal.

RESEARCH METHODS AND PROCEDURES

Eight overweight and obese postmenopausal women (age: 57.4+/-2.4 y; BMI: 31.8+/-2.1 kg m(-2); %FAT: 42.7+/-1.2%, mean+/-s.e.m.) performed two sessions of exercise training at an intensity corresponding to their ' crossover' point of substrate oxidation (COP(ox)). One session was held 1 h after a standardized meal and the other, 3 h after an identical meal on another day. Substrate oxidation was evaluated by indirect calorimetry. Hormonal responses were investigated during exercise.

RESULTS

Respiratory exchange ratio values were lower in the 3-h condition, showing higher lipid oxidation during exercise (average difference+38.9+/-2.7 mg min(-1); P<0.001), while mean energy expenditure did not differ. Basal heart rate was reduced in the 3 h compared with the 1-h condition (78+/-5 vs 87+/-5 bpm; P<0.05). Glycemia, lactatemia and insulinemia were reduced when exercise was performed 3 h after meal (P<0.05).

DISCUSSION

When exercise is performed 3 h after meal at an intensity corresponding to the COP(ox), metabolic and hormonal responses are similar to those targeted during the submaximal exercise test performed at fast that we previously proposed to individualize exercise training in the obese.

Low intensity endurance exercise targeted for lipid oxidation improves body composition and insulin sensitivity in patients with the metabolic syndrome

BACKGROUND

To investigate the effects of individualized training on the metabolic syndrome.

METHODS

Twenty-eight patients, suffering from the metabolic syndrome were studied before and after 2 months of training and compared to eleven patients who did not follow any training. All the patients were overweight. Training was individualized at the point where fat oxidation was maximal (LIPOX(max)) as determined by calorimetry.

RESULTS

The patients exhibited a significant reduction in body weight (- 2.6 +/- 0.7 kg; P=0.002), fat mass (- 1.55 +/- 0.5 kg; P=0.009), waist (- 3.53 +/- 1.3 cm; P<0.05) and hip (- 2.21 +/- 0.9 cm; P<0.05) circumferences, and improved the ability to oxidize lipids at exercise (crossover point: + 31.7 +/- 5.8 W; P<0.0001; LIPOX(max): + 23.5 +/- 5.6 W; P<0.0001; lipid oxidation: + 68.5 +/- 15.4 mg.min(-1); P=0.0001). No clear improvement in either lipid parameters or fibrinogen were observed. The surrogates of insulin sensitivity evidenced a decrease in insulin resistance: HOMA%S (software): + 72.93 +/- 32.64; p<0.05; HOMA-IR (simplified formula): - 2.42 +/- 1.07; P<0.05; QUICKI: + 0.02 +/- 0.004; P<0.01; SI=40/I: + 3.28 +/- 1.5; P<0.05. Significant correlations were found between changes in body weight and HOMA-IR and between changes in LIPOX(max) and QUICKI.

CONCLUSIONS

Individualized aerobic training improves lipid oxidation, body composition and insulin resistance.

Regular exercise (3x45 min/wk) decreases plasma viscosity in sedentary obese, insulin resistant patients parallel to an improvement in fitness and a shift in substrate oxidation balance

Exercise training decreases blood viscosity in athletes parallel with metabolic improvements mostly characterized by an increase in insulin sensitivity. Patients with low insulin sensitivity exhibit a host of metabolic disorders that may also benefit from regular training. However, the hemorheologic aspects of training in such subjects are not known and we aimed at characterizing them.

SUBJECTS

Thirty-two obese insulin resistant subjects were tested before and after 2 months. Twenty-one of them were trained (3x45 min/wk) at a level defined by exercise calorimetry and corresponding to the power at which lipid oxidation reaches a maximum (LIPOX(max )) and eleven served as controls. The two groups were matched for age and body mass index. There was no weight change in controls while the 2 months training period decreased weight by 2.5 kg (p<0.02). This change was totally explained by a loss in fat mass (-2.7 kg, p<0.02) while fat free mass remained unchanged. Blood rheology was unchanged in the control group while training improved plasma viscosity eta(pl) (before: 1.43+/-0.03 mPa.s; after: 1.35+/-0.03 mPa.s, p<0.02). There was no change in either hematocrit, red cell rigidity or red cell aggregation. The balance of substrates oxidation shifted towards a higher use of lipids (point of crossover where subjects oxidize 70% carbohydrates 30% lipids: before 39.3+/-6.9 watts; after 70.8+/-6 watts, p<0.001; point where lipid oxidation is maximal (LIPOX(max )) before: 16.5+/-1.4 watts; after: 21.4+/-1.3 watts, p<0.001) and V(O(2max )) increased by 74% (p<0.01). Consistent with observations in athletes, the metabolic and ergometric improvements induced by training reduces eta(pl) in sedentary, insulin resistant patients, but at those low levels training does not appear to induce "autohemodilution" (as reflected by hematocrit) neither it improves red cell deformability or aggregation. The reliability of eta(pl) as simple and unexpensive marker of efficiency of training in insulin resistant patients should be further evaluated.

Effects of a two-month rehabilitation program on substrate utilization during exercise in obese adolescents

BACKGROUND

We assessed the impact of an exercise and diet program for two weeks in a specialized institute and six weeks at home on body composition and exercise metabolism in obese adolescents.

METHODS

Fourteen obese adolescents took part in the two-week training course and seven continued exercise and diet at home. The substrate crossover point and the maximal fat oxidation point (Lipox max) were determined before and after the program, using indirect calorimetry. Individualized exercise training at Lipox max was programmed over the two months.

RESULTS

At the end of the two-week program, all adolescents showed a decrease in weight (p<0.001). Only the seven subjects who continued exercise training at home showed improved exercise fat use (increased crossover point of 17% +/- 3 (p<0.005) and Lipox max of 12.5% +/- 1.5 (p<0.005)).

CONCLUSION

The teenagers who had performed this targeted regular training for two months exhibit an increase in their ability to oxidize lipids at exercise. This increase is no longer found in those treated by diet alone. The efficiency of this targeted training protocol based on calorimetry for the treatment of teenager obesity will require longer studies on greater samples of subjects.

Multivariate analysis of relationships between insulin sensitivity and blood rheology: is plasma viscosity a marker of insulin resistance?

We previously reported in populations exhibiting all the spectrum of insulin sensitivity (SI) values correlations between SI and blood viscosity eta suggesting that high eta is an additional symptom of the insulin resistance syndrome. However, due to the elevation of insulinemia (I) which is usually associated with insulin resistance it remained to determine whether this relationship was explained by SI or I. We analyzed SI with the minimal model procedure in 108 nondiabetic subjects and analyzed correlations of SI with blood rheology (eta, RBC aggregation and rigidity). Across quartiles of SI (defined after log transformation since distribution of SI was not normal), hematocrit and red cell rigidity remained stable, while aggregability and plasma viscosity (etap) increased in the lowest quartile. SI was correlated to only two rheological parameters: etap (r= -0.280, p=0.005) and Myrenne index M1 (r= -0.219, p=0.044). Among SI, I, age and BMI multivariate analysis selected only BMI as a determinant of either whole blood viscosity (etawb: r= -0.301, p=0.004) and RBC disaggregation threshold (gammaD: r= -0.331, p=0.013), only I as determinant of M1 (r=0.254, p=0.03), and a combination of BMI (p=0.009) and SI (p=0.007) for etap. Although age and obesity are factors of hyperviscosity, the hemorheological disturbances found in insulin resistance are not fully statistically "explained" by those two factors. While hyperaggregability (measured with M1) is rather related to hyperinsulinism, etap is influenced by SI and should be further investigated as a simple marker for the follow up of insulin-resistant states.

Balance of substrate oxidation during submaximal exercise in lean and obese people

OBJECTIVES

To compare fat and carbohydrate oxidation at different exercise intensities between overweight and normal-weight subjects, in order to analyze the influence of muscular metabolic abnormalities in obese people on substrate utilization during exercise.

MATERIAL AND METHODS

32 healthy sedentary overweight subjects (Body Mass Index (BMI): 30.8 +/- 0.8 kg/m(2); body fat: 37.4 +/- 1.1%; mean +/- SEM) and 26 controls (BMI: 23 +/- 0.4 kg/m(2); body fat: 22.7 +/- 1.1%) matched for age and sex were examined. The test consisted in four six-min. submaximal steady-state workloads with calculation of substrate oxidation rates and derived quantitative parameters, i.e., crossover point (defined as the power at which carbohydrate-derived energy becomes predominant) and maximal fat oxidation rate point. In addition, the accuracy of the test was analyzed and was found to be satisfactory.

RESULTS

While exercise intensities were similar in both group, fat oxidation rates were significantly lower in overweight group (p<0.05). The crossover and the maximal fat oxidation rate points were significantly lower in overweight subjects than in controls: 33.3 +/- 2 vs 50.1 +/- 3.4% and 30.5 +/- 2.3 vs 44.6 +/- 3.3% of maximal aerobic power, respectively (p<0.001).

CONCLUSION

Sedentary overweight subjects, compared to controls at the same exercise intensities, exhibited an alteration of the balance of substrate oxidation, reflected by lower rates of fat oxidation and a shift of quantitative parameters to lower intensities. The test appeared to be reliable and could be of interest to advise an individualized exercise prescription in obese people.

Exercise hypoglycemia in nondiabetic subjects

Hypoglycemia during exercise is a common event due to an unbalance between training volume, nutrition, and external influences such as chronobiology, temperature or altitude, in subjects characterized by an acute and chronic increase in glucose effectiveness and insulin sensitivity. While it is preventable by adequate pre-exercise feeding with carbohydrates, it can also be induced by a prior carbohydrate meal with high glycemic index. Adequate training induces resistance to hypoglycemia via a shift in the balance of oxidized substrates and marked hormonal adaptations, but overtraining, by partially reversing this adaptation, favorizes hypoglycemia. Exercise hypoglycemia is a cause of fatigue or exercise cessation, but also impairs thermoregulatory adaptation and is assumed to fragilize muscles and tendons for traumatic events.