Carbon dioxide hydrogenation over the carbon-terminated niobium carbide (111) surface: a density functional theory study.

Carbon dioxide (CO2) hydrogenation is an energetic process which could be made more efficient through the use of effective catalysts, for example transition metal carbides. Here, we have employed calculations based on the density functional theory (DFT) to evaluate the reaction processes of CO2 hydrogenation to methane (CH4), carbon monoxide (CO), methanol (CH3OH), formaldehyde (CH2O), and formic acid (HCOOH) over the carbon-terminated niobium carbide (111) surface. First, we have studied the adsorption geometries and energies of 25 different surface-adsorbed species, followed by calculations of all of the elementary steps in the CO2 hydrogenation process. The theoretical findings indicate that the NbC (111) surface has higher catalytic activity towards CO2 methanation, releasing 4.902 eV in energy. CO represents the second-most preferred product, followed by CH3OH, CH2O, and HCOOH, all of which have exothermic reaction energies of 4.107, 2.435, 1.090, and 0.163 eV, respectively. Except for the mechanism that goes through HCOOH to produce CH2O, all favourable hydrogenation reactions lead to desired compounds through the creation of the dihydroxycarbene (HOCOH) intermediate. Along these routes, CH3* hydrogenation to CH4* has the highest endothermic reaction energy of 3.105 eV, while CO production from HCO dehydrogenation causes the highest exothermic reaction energy of -3.049 eV. The surface-adsorbed CO2 hydrogenation intermediates have minimal effect on the electronic structure and interact only weakly with the surface. Our results are consistent with experimental observations.

Effect of Si and B on the Electrochemical Behavior of FeCoNiCr-Based High-Entropy Amorphous Alloys.

The ability to produce high-entropy alloys with an amorphous structure, so-called high-entropy metallic glasses (HEMGs), offers the possibility to produce new compositions with good mechanical properties and resistance to corrosion. In this study, corrosion behavior was studied in two HEMGs, FeCoNiCrB and FeCoNiCr(BSi). In both cases, the total amount of metalloid atoms was kept constant at 20 at.%. The electrochemical behavior of these alloys was studied by means of linear polarization resistance (LPR) measurements and electrochemical impedance spectroscopy in a 3 wt.% NaCl solution. The effect of corrosion was characterized by using X-ray photoelectron spectroscopy (XPS) and the surface morphology was checked using a scanning electron microscope (SEM). The results show that samples with B but without Si exhibit better corrosion resistance due to its chemical homogeneity and lack of structural heterogeneity.

A First-Principles Study of CO2 Hydrogenation on a Niobium-Terminated NbC (111) Surface.

As promising materials for the reduction of greenhouse gases, transition-metal carbides, which are highly active in the hydrogenation of CO2 , are mainly considered. In this regard, the reaction mechanism of CO2 hydrogenation to useful products on the Nb-terminated NbC (111) surface is investigated by applying density functional theory calculations. The computational results display that the formation of CH4 , CH3 OH, and CO are more favored than other compounds, where CH4 is the dominant product. In addition, the findings from reaction energies reveal that the preferred mechanism for CO2 hydrogenation is thorough HCOOH* , where the largest exothermic reaction energy releases during the HCOOH* dissociation reaction (2.004 eV). The preferred mechanism of CO2 hydrogenation towards CH4 production is CO2 * →t,c-COOH* →HCOOH* →HCO* →CH2 O* →CH2 OH* →CH2 * →CH3 * →CH4 * , where CO2 * →t,c-COOH* →HCOOH* →HCO* →CH2 O* →CH2 OH* →CH3 OH* and CO2 * →t,c-COOH* →CO* are also found as the favored mechanisms for CH3 OH and CO productions thermodynamically, respectively. During the mentioned mechanisms, the hydrogenation of CH2 O* to CH2 OH* has the largest endothermic reaction energy of 1.344 eV.

Electron transport in polycyclic aromatic hydrocarbons/boron nitride hybrid structures: density functional theory combined with the nonequilibrium Green's function.

We investigate the electronic transport properties of two types of junction based on single polyaromatic hydrocarbons (PAHs) and PAHs embedded in boron nitride (h-BN) nanoribbons, using nonequilibrium Green's functions (NEGF) and density functional theory (DFT). In the PAH junctions, a Fano resonance line shape at the Fermi energy in the transport feature can be clearly seen. In hybrid junctions, structural asymmetries enable interactions between the electronic states, leading to observation of interface-based transport. Our findings reveal that the interface of PAH/h-BN strongly affects the transport properties of the structures.

Yogurt, diet quality and lifestyle factors.

Yogurt consumption has been associated with healthy dietary patterns and lifestyles, better diet quality and healthier metabolic profiles. Studies have shown that frequent yogurt consumers do not only have higher nutrient intakes, but also an improved diet quality, which includes higher consumption of fruits and vegetables, whole grains, and dairy compared with low or non-consumers indicating better compliance with dietary guidelines. Recent epidemiological and clinical evidence suggests that yogurt contributes to better metabolic health because of its effects on the control of body weight, energy homeostasis and glycemic control. Furthermore, yogurt consumers have been shown to be more physically active (⩾ 2 h/week), smoke less, have higher education and knowledge of nutrition compared with non-consumers. Thus, yogurt consumption may be considered a signature of a healthy diet through its nutritional content, impact on metabolic health including the control of energy balance, body weight and glycemia and its relationships with healthier behaviors and lifestyle factors.

Capsaicinoids: a spicy solution to the management of obesity?

Capsaicin is the molecule that is responsible for the pungency of hot peppers. It stimulates the sympathoadrenal system that mediates the thermogenic and anorexigenic effects of capsaicinoids. Capsaicinoids have been found to accentuate the impact of caloric restriction on body weight loss. Some studies have also shown that capsinoids, the non-pungent analogs of capsaicinoids, increase energy expenditure. Capsaicin supplementation attenuates or even prevents the increase in hunger and decrease in fullness as well as the decrease in energy expenditure and fat oxidation, which normally result from energy restriction. These effects may postpone the occurrence of resistance to lose fat during a weight loss program and facilitate the maintenance of body weight in a postobese state. Evidence also highlights the plausibility of an indirect effect of capsaicin on energy balance via its analgesic effects, which may improve sleep and ultimately facilitate the regulation of energy balance. Although capsaicin intake appears to be a safe practice, further studies will be needed to ascertain the safety of regular long-term consumption. Taken together, these observations reinforce the idea that consumption of capsaicinoids and capsinoids may be helpful to facilitate obesity management.

Adaptations to a diet-based weight-reducing programme in obese women resistant to weight loss.

The aim of this study was to assess energy intake, resting metabolic rate (RMR), appetite sensations, eating behaviours and sleep duration and quality in obese women resistant to body weight loss when subjected to a diet-based weight-reducing programme. A pooled cohort of obese women (n = 75; aged 39 ± 8 years; body mass index: 33 ± 4 kg m(-2)) participated in a 12-16-week diet-based weight loss programme targeting a daily energy deficit of 500-700 kcal d(-1). Women were classified in tertiles a posteriori based on the response of their body weight to dietary supervision (high, moderate and low responders). Post-intervention, mean weight loss was 3.3 ± 2.8 kg and explained by the 2.9 ± 2.6 kg reduction in fat mass. Mean weight loss was 6.2 ± 1.6, 3.4 ± 0.6 and 0.2 ± 1.4 kg in participants classified in the high, middle and low tertiles, respectively. Women in the low tertile reduced their daily energy intake and susceptibility to hunger during the programme to a lesser extent than those in the high tertile and had higher fasting hunger in response to the dietary intervention. Women in the high tertile maintained their RMR, which was in contrast to the significant decrease predicted by their weight loss. They also reported a significant improvement in sleep quality and an increase in sleep duration compared with other tertiles. The differences in the response of body weight to dietary supervision may be explained, in part, by variations in energy intake, eating behaviours, appetite sensations and sleep duration and quality.

Prevalence and associated factors of T-score discordance between different sites in Iranian patients with spinal cord injury.

OBJECTIVES: The present study was conducted to determine the prevalence of T-score discordance and its risk factors in a group of patients with spinal cord injury in a university teaching hospital in the Iranian capital of Tehran. METHODS: This cross-sectional study was conducted on paraplegic men undergoing bone density testing in an outpatient clinic at a hospital in the Iranian capital, Tehran, between March 2011 and 2012. A questionnaire on demographic and anthropometric characteristics, including age, height, weight, engagement in physical activity and personal smoking habits, was filled out for each subject. All the subjects underwent bone mineral density measurement and blood samples were sent for laboratory testing. RESULTS: Major T-score discordance between two sites was noted in 54 (41.22%) patients. Multivariate logistic regression revealed that every unit increase in serum calcium levels, as the only factor influencing T-score discordance, was associated with a 2.49-fold increased risk in T-score discordance in the area. As for the spine and radius, BMI was the only influencing factor as every unit increase in BMI was associated with a 14% lower risk for T-score discordance in these regions. Body mass index was the only factor, based on the multivariate model, affecting the risk of developing T-score discordance between two sites. CONCLUSION: Our study revealed the high prevalence of T-score discordance in patients with spinal cord injury. Physicians should therefore be encouraged to perform BMD at three sites when visiting patients with such injuries.

Electromechanical resonator based on electrostatically actuated graphene-doped PVP nanofibers.

In this paper we present experimental results describing electrical readout of the mechanical vibratory response of graphene-doped fibers by employing electrical actuation. For a fiber resonator with an approximate radius of 850 nm and length of 100 µm, we observed a resonance frequency around 580 kHz with a quality factor (Q) of about 2511 in air at ambient conditions. Through the use of finite element simulations, we show that the reported frequency of resonance is relevant. We also show that the resonance frequency of the fiber resonators decreases as the bias potential is increased due to the electrostatic spring-softening effect.

Regular consumption of pulses for 8 weeks reduces metabolic syndrome risk factors in overweight and obese adults.

Pulses are low in energy density, supporting their inclusion in the diet for the management of risk factors of the metabolic syndrome (MetSyn). The aim of the present study was to describe the effects of frequent consumption (five cups/week over 8 weeks) of pulses (yellow peas, chickpeas, navy beans and lentils), compared with counselling to reduce energy intake by 2093 kJ/d (500 kcal/d), on risk factors of the MetSyn in two groups (nineteen and twenty-one subjects, respectively) of overweight or obese (mean BMI 32·8 kg/m2) adults. Body weight, waist circumference, blood pressure, fasting blood parameters and 24 h food intakes were measured at weeks 1, 4 and 8. Blood glucose, insulin, C-peptide, glucagon-like peptide-1 (GLP-1) and ghrelin were measured after a 75 g oral glucose load at weeks 1 and 8. At week 8, both groups reported reductions in energy intake, waist circumference, systolic blood pressure, glycosylated Hb (HbA1c) and glucose AUC and homeostasis model of insulin resistance (HOMA-IR) following the glucose load (P < 0·05). However, HDL, fasting C-peptide and insulin AUC responses were dependent on diet (P < 0·05). HDL and C-peptide increased by 4·5 and 12·3 %, respectively, in the pulse group, but decreased by 0·8 and 7·6 %, respectively, in the energy-restricted group. Insulin AUC decreased in both females and males on the energy-restricted diet by 24·2 and 4·8 %, respectively, but on the pulse diet it decreased by 13·9 % in females and increased by 27·3 % in males (P < 0·05). In conclusion, frequent consumption of pulses in an ad libitum diet reduced risk factors of the MetSyn and these effects were equivalent, and in some instances stronger, than counselling for dietary energy reduction.

Viscosity of fiber preloads affects food intake in adolescents.

BACKGROUND AND AIMS: Dietary fiber that develops viscosity in the gastrointestinal tract is capable of addressing various aspects of food intake control. The aim of this study was to assess subsequent food intake and appetite in relation to the level of viscosity following three liquid preloads each containing 5 g of either a high (novel viscous polysaccharide; NVP), medium (glucomannan; GLM), or low (cellulose; CE) viscosity fiber. METHODS AND RESULTS: In this double-blind, randomized, controlled and crossover trial, 31 healthy weight adolescents (25 F:6 M; age 16.1+/-0.6 years; BMI 22.2+/-3.7 kg/m(2)) consumed one of the three preloads 90 min prior to an ad libitum pizza meal. Preloads were identical in taste, appearance, nutrient content and quantity of fiber, but different in their viscosities (10, 410, and 700 poise for CE, GLM, and NVP, respectively). Pizza intake was significantly lower (p=0.008) after consumption of the high-viscosity NVP (278+/-111 g) compared to the medium-viscosity GLM (313+/-123 g) and low-viscosity CE (316+/-138 g) preloads, with no difference between the GLM and CE preloads. Appetite scores, physical symptoms and 24-h intake did not differ among treatment groups. CONCLUSION: A highly viscous NVP preload leads to reduced subsequent food intake, in terms of both gram weight and calories, in healthy weight adolescents. This study provides preliminary evidence of an independent contribution of viscosity on food intake and may form a basis for further studies on factors influencing food intake in adolescents.

Femoral neck geometry and hip fracture risk: the Geelong osteoporosis study.

To determine the relationship between femoral neck geometry and the risk of hip fracture in post-menopausal Caucasian women, we conducted a retrospective study comparing the femoral neck dimensions of 62 hip fracture cases to those of 608 randomly selected controls. Measurements were made from dual-energy X-ray absorptiometry scans (Lunar DPX-L), using the manufacturer's ruler function, and included: hip axis length (HAL), femoral neck axis length (FNAL), femoral neck width (FNW), femoral shaft width (FSW), medial femoral shaft cortical thickness (FSCT(med)), and lateral femoral shaft cortical thickness (FSCT(lat)). The fracture group was older (median age 78.3 years vs 73.8 years), lighter (median weight 59.9 kg vs 64.5 kg), and, after adjustment for age, taller (mean height 158.7+/-0.8 cm vs 156.7+/-0.2 cm) than the controls. Furthermore, bone mineral density was lower in this group (0.682+/-0.016 g/cm(2) vs 0.791+/-0.006 g/cm(2)). After adjustment for age, bone mineral content (BMC) or height, hip fracture patients had greater FNW (up to 6.6%) and FSW (up to 6.3%) than did the controls. Each standard deviation increase in FNW and FSW was associated with a 1.7-fold (95% CI 1.3-2.3) and a 2.4-fold (95% CI 1.8-3.2) increase in the fracture risk, respectively. BMC-adjusted FNAL was greater in the fracture group (+2.1%) than in the controls, while the age-adjusted FSCT(med) was reduced (-7.2%). There was a trend towards longer HAL (up to 2.1%) after adjustment for age or BMC, and thinner age-adjusted FSCT(lat) (-1.7%) in fracture patients that did not reach statistical significance. In multivariate analysis, the risk of hip fracture was predicted by the combination of age, FNW, FSW, BMC and FSCT(med). HAL was not analyzed because of the small number of HAL measurements among fracture cases. We conclude that post-menopausal women with hip fractures have wider femoral necks and shafts, thinner femoral cortices and longer femoral neck axis lengths than do women with no fractures. Alteration in hip geometry is associated with the risk of hip fracture.

Oral contraceptives and bone mineral density: A population-based study.

OBJECTIVE: We sought to test the hypothesis that exposure to oral contraceptives protects the skeleton. STUDY DESIGN: Multiple regression techniques were used to analyze data for a random sample of 710 Australian women (age range, 20-69 years). Bone mineral density was measured at the lumbar spine, proximal femur, whole body, and distal forearm. Oral contraceptive exposure was assessed by a questionnaire. RESULTS: Women exposed to oral contraceptives had a 3.3% greater mean bone mineral density adjusted for body mass index and age at the lumbar spine (partial r (2) = 0.009; P =.014). Adjusted mean vertebral bone mineral density was 3.3% greater for premenopausal women (partial r (2) = 0.008; P <.05), but the effect did not reach significance among postmenopausal women. Higher bone mineral density was associated with increased duration of exposure, with a mean increase of 3.2% associated with the first 5 years and a further 0.2% with >/=5 years of exposure. No association was detected at other sites. CONCLUSION: Exposure to oral contraceptives may be associated with higher lumbar spine bone mineral density.

Femoral neck dimensions are unlikely to be associated with age at menarche.

Hip axis length (HAL) has been reported as an independent risk factor for hip fracture. Later puberty may increase bone size because of delayed epiphyseal fusion. We sought to identify associations between bone size at the proximal femur with age at menarche and other indices of growth such as stature. Femoral neck dimensions were measured from dual-energy X-ray absorptiometry scans of the proximal femur in a random sample of 203 premenopausal Caucasian women (age 20-30 years). There were no associations between age at menarche and HAL, femoral axis length (FAL) or femoral neck width (FNW). Age at menarche was associated with height (r = 0.2, p = 0.02). Variations in HAL, FAL and FNW do not appear to be related to age at menarche.

The exclusion of high trauma fractures may underestimate the prevalence of bone fragility fractures in the community: the Geelong Osteoporosis Study.

Fractures associated with severe trauma are generally excluded from estimates of the prevalence of osteoporotic fractures in the community. Because the degree of trauma is difficult to quantitate, low bone mass may contribute to fractures following severe trauma. We ascertained all fractures in a defined population and compared the bone mineral density (BMD) of women who sustained fractures in either "low" or "high" trauma events with the BMD of a random sample of women from the same population. BMD was measured by dual-energy X-ray absorptiometry and expressed as a standardized deviation (Z score) adjusted for age. The BMD Z scores (mean +/- SEM) were reduced in both the low and high trauma groups, respectively: spine-posterior-anterior (-0.50 +/- 0.05 and -0.21 +/- 0.08), spine-lateral (-0.28 +/- 0.06 and -0.19 +/- 0.10), femoral neck (-0.42 +/- 0.04 and -0.26 +/- 0.09), Ward's triangle (-0.44 +/- 0.04 and -0.28 +/- 0.08), trochanter (-0.44 +/- 0.05 and -0.32 +/- 0.08), total body (-0.46 +/- 0.06 and -0.32 +/- 0.08), ultradistal radius (-0.47 +/- 0.05 and -0.42 +/- 0.07), and midradius (-0.52 +/- 0.06 and -0.33 +/- 0.09). Except at the PA spine, the deficits were no smaller in the high trauma group. Compared with the population, the age-adjusted odds ratio for osteoporosis (t-score < -2.5) at one or more scanning sites was 3.1 (95% confidence interval 1.9, 5.0) in the high trauma group and 2.7 (1.9, 3.8) in the low trauma group. The data suggest that the exclusion of high trauma fractures in women over 50 years of age may result in underestimation of the contribution of osteoporosis to fractures in the community. Bone density measurement of women over 50 years of age who sustain fractures may be warranted irrespective of the classification of trauma.