bluuebunny/crossref_metadata_2025 huggingface dataset:
Lipid and Insulin Levels in Obese Children: Changes with Age and Puberty
Authors: Pinhas‐Hamiel Orit , Lerner‐Geva Liat , Copperman Nancy M. , Jacobson Marc S.
Published: July 2008

Objective: The goal was to describe the lipid profile and insulin changes seen in obese children and adolescents at different stages of puberty.

Research Methods and Procedures: A cross‐sectional study was conducted by chart review of 181 obese (BMI > 95th) children and adolescents 5 to 17 years of age, who were referred to the Center for Atherosclerosis Prevention for cardiovascular risk reduction from January 2003 through December 2003.

Results: Eighty (44.2%) subjects were <12 years of age, and 101 (55.8%) were ≥12 years. Severity of obesity as expressed by BMI standard deviation score did not differ between these age groups. A significant difference with lower serum levels of total cholesterol, non‐high‐density lipoprotein cholesterol, low‐density lipoprotein cholesterol, and high‐density lipoprotein cholesterol was seen with older age and with advancing sexual maturity rating. Triglycerides, very‐low‐density lipoprotein cholesterol, and lipoprotein(a) levels remained elevated across age and pubertal stages. Insulin levels and insulin resistance as expressed by homeostasis model assessment were significantly higher with older age. Similar trends were observed both in obese boys and obese girls during puberty.

Discussion: The most striking findings of this study are that in the 5‐ to 17‐year‐old obese population, the combination of elevated triglycerides and very‐low‐density lipoprotein cholesterol and low high‐density lipoprotein cholesterol levels place them at greater cardiovascular risk than their non‐obese peers, even when the changing patterns of lipids and lipoproteins seen during pubertal maturation are accounted for.
Obesity, White Blood Cell Counts, and Platelet Counts among Police Officers
Authors: Charles Luenda E. , Fekedulegn Desta , McCall Terika , Burchfiel Cecil M. , Andrew Michael E. , Violanti John M.
Published: July 2008

Objective: To determine the association between several obesity indices (BMI, waist circumference, waist‐to‐hip and waist‐to‐height ratios, and abdominal height) and hematologic parameters [white blood cell (WBC) and platelet counts] among police officers.

Research Methods and Procedures: The authors conducted this cross‐sectional study among 104 randomly selected officers (41 women and 63 men) from the Buffalo, NY, Police Department. Anthropometric measures were performed by clinic staff, and fasting blood samples were drawn for complete blood counts. Pearson's correlation, Student's t tests, ANOVA, analysis of covariance, and linear regression were used to assess the associations.

Results: Officers ranged in age from 26 to 61 years old and were predominantly white. Among women, current smokers had significantly higher WBC counts (7.4 × 103 cells/µL ± 1.4) than former (5.2 × 103 cells/µL ± 1.4) or never smokers (5.6 × 103 cells/µL ± 1.5) (p = 0.002). Women had similar WBC counts but higher mean platelet counts than men (p = 0.005). Among women, abdominal height was positively associated with platelet count after adjustment for depression (p for trend = 0.039). Among women and men, a non‐significant step‐wise trend was observed between abdominal height and mean WBC counts before and after adjustment for smoking, race, and physical activity. No association was observed between obesity and platelet count among men.

Discussion: Abdominal height was significantly associated with increased platelet counts among female officers. No significant associations were observed between obesity and WBC or platelet counts among male officers.
Effect of Obesity on High‐density Lipoprotein Metabolism
Authors: Rashid Shirya , Genest Jacques
Published: July 2008

Reduced levels of high‐density lipoproteins (HDL) in non‐obese and obese states are associated with increased risk for the development of coronary artery disease. Therefore, it is imperative to determine the mechanisms responsible for reduced HDL in obese states and, conversely, to examine therapies aimed at increasing HDL levels in these individuals. This paper examines the multiple causes for reduced HDL in obese states and the effect of exercise and diet—two non‐pharmacologic therapies—on HDL metabolism in humans. In general, the concentration of HDL‐cholesterol is adversely altered in obesity, with HDL‐cholesterol levels associated with both the degree and distribution of obesity. More specifically, intra‐abdominal visceral fat deposition is an important negative correlate of HDL‐cholesterol. The specific subfractions of HDL that are altered in obese states include the HDL2, apolipoprotein A‐I, and pre‐β1 subfractions. Decreased HDL levels in obesity have been attributed to both an enhancement in the uptake of HDL2 by adipocytes and an increase in the catabolism of apolipoprotein A‐I on HDL particles. In addition, there is a decrease in the conversion of the pre‐β1 subfraction, the initial acceptor of cholesterol from peripheral cells, to pre‐β2 particles. Conversely, as a means of reversing the decrease in HDL levels in obesity, sustained weight loss is an effective method. More specifically, weight loss achieved through exercise is more effective at raising HDL levels than dieting. Exercise mediates positive effects on HDL levels at least partly through changes in enzymes of HDL metabolism. Increased lipid transfer to HDL by lipoprotein lipase and reduced HDL clearance by hepatic triglyceride lipase as a result of endurance training are two important mechanisms for increases in HDL observed from exercise.
Single Nucleotide Polymorphisms of the MCHR1 Gene Do Not Affect Metabolism in Humans
Authors: Rutanen Jarno , Pihlajamäki Jussi , Vänttinen Markku , Salmenniemi Urpu , Ruotsalainen Eija , Kuulasmaa Teemu , Kainulainen Sakari , Kuusisto Johanna , Laakso Markku
Published: July 2008

Melanin concentrating hormone receptor‐1 (MCHR1) is a centrally and peripherally expressed receptor that regulates energy expenditure and appetite. Single nucleotide polymorphisms (SNPs) of the MCHR1 gene have been previously associated with obesity, but the results are inconsistent among different populations. This study was performed to determine whether SNPs of MCHR1 affect glucose and energy metabolism. We screened six SNPs of MCHR1 in a cross‐sectional study of 217 middle‐age, non‐diabetic Finnish subjects who were offspring of type 2 diabetic patients. Insulin secretion was evaluated by an intravenous glucose tolerance test and insulin sensitivity and energy metabolism by the hyperinsulinemic euglycemic clamp and indirect calorimetry. SNPs of MCHR1 were not associated with BMI, waist circumference, subcutaneous or intra‐abdominal fat area, glucose tolerance, first‐phase insulin release, insulin sensitivity, or energy metabolism. One SNP, which was in >0.50 linkage disequilibrium with the other five SNPs, was also screened in 1455 unrelated Finnish middle‐age subjects in a population‐based study. No differences in BMI, waist circumference, or glucose or insulin levels in an oral glucose tolerance test among the genotypes were found. In conclusion, SNPs of MCHR1 did not have effects on metabolic variables in humans.
Monocyte Chemoattractant Protein‐1 and Nitric Oxide Promote Adipogenesis in a Model That Mimics Obesity
Authors: Hemmrich Karsten , Thomas Gregory P.L. , Abberton Keren M. , Thompson Erik W. , Rophael John A. , Penington Anthony J. , Morrison Wayne A.
Published: July 2008

Objective: An increasing body of evidence is emerging linking adipogenesis and inflammation. Obesity, alone or as a part of the metabolic syndrome, is characterized by a state of chronic low‐level inflammation as revealed by raised plasma levels of inflammatory cytokines and acute‐phase proteins. If inflammation can, in turn, increase adipose tissue growth, this may be the basis for a positive feedback loop in obesity. We have developed a tissue engineering model for growing adipose tissue in the mouse that allows quantification of increases in adipogenesis. In this study, we evaluated the adipogenic potential of the inflammogens monocyte chemoattractant protein (MCP)‐1 and zymosan‐A (Zy) in a murine tissue engineering model.

Research Methods and Procedures: MCP‐1 and Zy were added to chambers filled with Matrigel and fibroblast growth factor 2. To analyze the role of inducible nitric oxide synthase (iNOS), the iNOS inhibitor aminoguanidine was added to the chamber.

Results: Our results show that MCP‐1 generated proportionally large quantities of new adipose tissue. This neoadipogenesis was accompanied by an ingrowth of macrophages and could be mimicked by Zy. Aminoguanidine significantly inhibited the formation of adipose tissue.

Discussion: Our findings demonstrate that low‐grade inflammation and iNOS expression are important factors in adipogenesis. Because fat neoformation in obesity and the metabolic syndrome is believed to be mediated by macrophage‐derived proinflammatory cytokines, this adipose tissue engineering system provides a model that could potentially be used to further unravel the pathogenesis of these two metabolic disorders.
Effect of Calorie Restriction on Resting Metabolic Rate and Spontaneous Physical Activity
Authors: Martin Corby K. , Heilbronn Leonie K. , de Jonge Lilian , DeLany James P. , Volaufova Julia , Anton Stephen D. , Redman Leanne M. , Smith Steven R. , Ravussin Eric
Published: July 2008

Objective: It is unclear if resting metabolic rate (RMR) and spontaneous physical activity (SPA) decrease in weight‐reduced non‐obese participants. Additionally, it is unknown if changes in SPA, measured in a respiratory chamber, reflect changes in free‐living physical activity level (PAL).

Research Methods and Procedures: Participants (N = 48) were randomized into 4 groups for 6 months: calorie restriction (CR, 25% restriction), CR plus structured exercise (CR+EX, 12.5% restriction plus 12.5% increased energy expenditure via exercise), low‐calorie diet (LCD, 890 kcal/d supplement diet until 15% weight loss, then weight maintenance), and control (weight maintenance). Measurements were collected at baseline, Month 3, and Month 6. Body composition and RMR were measured by DXA and indirect calorimetry, respectively. Two measures of SPA were collected in a respiratory chamber (percent of time active and kcal/d). Free‐living PAL (PAL = total daily energy expenditure by doubly labeled water/RMR) was also measured. Regression equations at baseline were used to adjust RMR for fat‐free mass and SPA (kcal/d) for body weight.

Results: Adjusted RMR decreased at Month 3 in the CR group and at Month 6 in the CR+EX and LCD groups. Neither measure of SPA decreased significantly in any group. PAL decreased at Month 3 in the CR and LCD groups, but not in the CR+EX group, who engaged in structured exercise. Changes in SPA in the chamber and free‐living PAL were not related.

Discussion: Body weight is defended in non‐obese participants during modest caloric restriction, evidenced by metabolic adaptation of RMR and reduced energy expenditure through physical activity.
Influence of BMI and Gender on Postprandial Hormone Responses
Authors: Carroll Joan F. , Kaiser Kathryn A. , Franks Susan F. , Deere Curtistine , Caffrey James L.
Published: July 2008

Objective: Influences of gender and body weight on the hormonal response to eating are not well understood. This study was conducted to determine a convenient time‐point to evaluate peak postprandial hormone responses and to test the hypothesis that gender and BMI interact to produce differences in postprandial secretion of selected humoral markers implicated in hunger and satiety.

Research Methods and Procedures: Fasting blood glucose, insulin, leptin, ghrelin, glucagon‐like peptide‐1, and glucagon were measured in normal‐weight (20 ≤ BMI < 25 kg/m2) men (n = 10) and women (n = 9) and obese (BMI ≥ 30 kg/m2) men (n = 9) and women (n = 11). A standard liquid meal was consumed, and humoral measurements were repeated every 10 minutes for 1 hour. Data were analyzed using repeated measures ANOVA with BMI and gender as main effects.

Results: Obese subjects had delayed peak insulin responses (p = 0.004), whereas obese men had a delayed nadir ghrelin response (p = 0.05). Obese subjects had higher and more sustained postprandial glucose (p = 0.02), and greater fasting (p = 0.0004) and postprandial insulin (p = 0.0001). Ghrelin decreased after the meal (p = 0.003); the percent change from fasting tended to be reduced in obese subjects (p = 0.07). Men had greater fasting (p = 0.02) and postprandial (p = 0.03) glucagon and a subtle postprandial decline in plasma leptin (p = 0.01).

Discussion: Peak hormone responses occurred 20 to 40 minutes after eating. Measurements made during this interval may be useful in evaluating postprandial response magnitude. Peak/nadir responses and time courses of postprandial responses are influenced by gender and BMI. Nutritional studies need to account for variability introduced by these factors.
Cardiorespiratory Fitness Influences the Blood Pressure Response to Experimental Weight Gain
Authors: Gentile Christopher L. , Orr Jeb S. , Davy Brenda M. , Davy Kevin P.
Published: July 2008

Objective: We tested the hypothesis that with similar weight gain the increase in blood pressure (BP) would be smaller in men with higher cardiorespiratory fitness (HCRF) than in men with lower cardiorespiratory fitness (LCRF).

Research Methods and Procedures: Thirteen men (age = 23 ± 1, BMI = 24 ± 1) were overfed by ∼1000 kcal/d over ∼8 weeks to achieve a 5‐kg weight gain. Resting BP and 24‐hour ambulatory BP, body composition, and fat distribution were measured.

Results: Cardiorespiratory fitness (CRF) was higher in the HCRF group compared with the LCRF group (49.9 ± 1.2 vs. 38.1 ± 1.4 mL/kg per minute, p < 0.001). At baseline, body weight was similar in the HCRF and LCRF groups, whereas the HCRF group displayed lower levels of total body fat (13.0 ± 1.7 vs. 16.9 ± 1.3 kg, p = 0.049) and abdominal visceral fat (49 ± 6 vs. 80 ± 14 cm2, p = 0.032). Resting BP and 24‐hour ambulatory BP were similar in the two groups at baseline. After weight gain, body weight increased ∼5 kg (p < 0.05) in both groups; the changes in body composition and regional fat distribution were similar. As hypothesized, the increases in resting systolic (1 ± 2 vs. 7 ± 2 mm Hg; p = 0.008) and diastolic (−1 ± 4 vs. 5 ± 1 mm Hg; p = 0.005) BP were smaller in the HCRF group. CRF was correlated with the increases in resting systolic (r = −0.64; p = 0.009) and diastolic BP (r = −0.80; p < 0.001). Furthermore, the relationship between CRF and BP remained significant after adjusting for the changes in the proportion of total abdominal fat gained as visceral fat.

Discussion: These findings suggest that higher levels of CRF are associated with a smaller increase in BP with weight gain, independently of changes in abdominal visceral fat.
Energy Imbalance Underlying the Development of Childhood Obesity
Authors: Butte Nancy F. , Christiansen Edmund , Sørensen Thorkild I. A.
Published: July 2008

Objective: To develop a model based on empirical data and human energetics to predict the total energy cost of weight gain and obligatory increase in energy intake and/or decrease in physical activity level associated with weight gain in children and adolescents.

Research Methods and Procedures: One‐year changes in weight and body composition and basal metabolic rate (BMR) were measured in 488 Hispanic children and adolescents. Fat‐free mass (FFM) and fat mass (FM) were measured by DXA and BMR by calorimetry. Model specifications include the following: body mass (BM) = FFM + FM, each with a specific energy content, cff (1.07 kcal/g FFM) and cf (9.25 kcal/g FM), basal energy expenditure (EE), kff and kf, and energetic conversion efficiency, eff (0.42) for FFM and ef (0.85) for FM. Total energy cost of weight gain is equal to the sum of energy storage, EE associated with increased BM, conversion energy (CE), and diet‐induced EE (DIEE).

Results: Sex‐ and Tanner stage–specific values are indicated for the basal EE of FFM (kff) and the fat fraction in added tissue (fr). Total energy cost of weight gain is partitioned into energy storage (24% to 36%), increase in EE (40% to 57%), CE (8% to 13%), and DIEE (10%). Observed median (10th to 90th percentile) weight gain of 6.1 kg/yr (2.4 to 11.4 kg/yr) corresponds at physical activity level (PAL) = 1.5, 1.75, and 2.0 to a total energy cost of weight gain of 244 (93 to 448 kcal/d), 267 (101 to 485 kcal/d), and 290 kcal/d (110 to 527 kcal/d), respectively, and to a total energy intake of 2695 (1890 to 3730), 3127 (2191 to 4335), and 3551 (2487 to 4930) kcal/d, respectively. If weight gain is caused by a change in PAL alone and PAL0 = 1.5 at baseline t = 0, the model indicates a drop in PAL of 0.22 (0.08 to 0.34) units, which is equivalent to 60 (18 to 105) min/d of walking at 2.5 mph.

Discussion: Halting the development or progression of childhood obesity, as observed in these Hispanic children and adolescents, by counteracting its total energy costs will require a sizable decrease in energy intake and/or reciprocal increase in physical activity.
Adolescents’ Perceived Weight Associated With Depression in Young Adulthood: A Longitudinal Study
Authors: Al Mamun Abdullah , Cramb Susanna , McDermott Brett M. , O'Callaghan Michael , Najman Jake M. , Williams Gail M.
Published: July 2008

Objective: The objective of this study is to examine whether adolescents’ measured BMI and self‐ or mother's perception of weight status at age 14 are associated with depression at age 21.

Research Methods and Procedures: The study participants were a subsample of 2017 participants of the Mater–University of Queensland Study of Pregnancy and Its Outcomes, a population‐based birth cohort study, which commenced in 1981 in Brisbane, Australia, for whom measured BMI at ages 14 and 21 and information on self‐reported mental health problems were available at the age 21 follow‐up. A total of 1802 individuals had measured BMI and reported weight perception in a supplementary questionnaire at 14 years, and their self‐reported mental health problems were reported at 21 years. Mental health was measured using Center for Epidemiology Studies Depression Scale and Young Adults Self‐Reported depression/anxiety at 21 years of age.

Results: We found that both young adult males and females who perceived themselves as overweight at age 14 had more mental health problems compared with those who perceived themselves as the right weight. When we combined adolescents’ weight perception with their measured BMI categories, weight perception but not measured overweight was associated with mental health problems for males and females at age 21. This association remained after adjusting for potential confounders, including adolescents’ behavioral problems, family meals, diet, physical activity, and television watching.

Conclusions: This study suggests that the perception of being overweight during adolescence is a significant risk factor for depression in young adult men and women. The perception of being overweight during adolescence should be considered a possible target for a prevention intervention.
Lifestyle Factors and Incident Mobility Limitation in Obese and Non‐obese Older Adults
Authors: Koster Annemarie , Penninx Brenda W. J. H. , Newman Anne B. , Visser Marjolein , van Gool Coen H. , Harris Tamara B. , van Eijk Jacques Th. M. , Kempen Gertrudis I. J. M. , Brach Jennifer S. , Simonsick Eleanor M. , Houston Denise K. , Tylavsky Frances A. , Rubin Susan M. , Kritchevsky Stephen B.
Published: July 2008

Objective: This study examines the association between incident mobility limitation and 4 lifestyle factors: smoking, alcohol intake, physical activity, and diet in well‐functioning obese (n = 667) and non‐obese (n = 2027) older adults.

Research Methods and Procedures: Data were from men and women, 70 to 79 years of age from Pittsburgh, PA and Memphis, TN, participating in the Health, Aging and Body Composition (Health ABC) study. In addition to individual lifestyle practices, a high‐risk lifestyle score (0 to 4) was calculated indicating the total number of unhealthy lifestyle practices per person. Mobility limitation was defined as reported difficulty walking 1/4 mile or climbing 10 steps during two consecutive semiannual assessments over 6.5 years.

Results: In non‐obese older persons, significant risk factors for incident mobility limitation after adjustment for socio‐demographics and health‐related variables were current and former smoking [hazard ratio (HR) = 1.51; 95% confidence interval (CI), 1.20 to 1.89; HR = 1.40; 95% CI, 1.12 to 1.74), former alcohol intake (HR = 1.30; 95% CI, 1.05 to 1.60), low and medium physical activity (HR = 1.78; 95% CI, 1.45 to 2.18; HR = 1.29, 95% CI, 1.07 to 1.54), and eating an unhealthy diet (HR = 1.57; 95% CI, 1.17 to 2.10). In the obese, only low physical activity was associated with a significantly increased risk of mobility limitation (HR = 1.44; 95% CI, 1.08 to 1.92). Having two or more unhealthy lifestyle factors was a strong predictor of mobility limitation in the non‐obese only (HR = 1.98; 95% CI, 1.61 to 2.43). Overall, obese persons had a significantly higher risk of mobility limitation compared with non‐obese persons, independent of lifestyle factors (HR = 1.73; 95% CI, 1.52 to 1.96).

Conclusions: These results underscore the importance of a healthy lifestyle for maintaining function among non‐obese older adults. However, a healthy lifestyle cannot overcome the effect of obesity in obese older adults; this stresses the importance of preventing obesity to protect against mobility loss in older persons.
Association of Maternal Lifestyles Including Smoking During Pregnancy with Childhood Obesity
Authors: Mizutani Takashi , Suzuki Kohta , Kondo Naoki , Yamagata Zentaro
Published: July 2008

Objective: To examine the extent to which maternal smoking during early pregnancy and other prepregnancy lifestyle habits are associated with obesity and overweight in 5‐year‐old Japanese children.

Research Method and Procedures: We studied 1417 mother‐child pairs enrolled in Project Enzan—a prospective cohort study. The dependent variables, childhood overweight and obesity, were defined with an international cut‐off value. Maternal smoking during early pregnancy and other prepregnancy lifestyle habits were used as independent variables.

Results: Maternal smoking habits were associated with overweight in the 5‐year‐old children [adjusted odds ratio (OR): 2.15; 95% confidence interval (CI): 1.12 to 4.11]. Maternal sleep duration of ≥8 h/d negatively affected childhood overweight (adjusted OR: 0.71; 95% CI: 0.49 to 1.04). Children whose mothers skipped breakfast were likely to become overweight (adjusted OR: 1.78; 95% CI: 1.14 to 2.77). The results of childhood obesity analysis were similar to those of childhood overweight analysis.

Discussion: The results of this study suggest that there are effects of smoking during early pregnancy and other maternal lifestyle habits on the onset of childhood obesity in Japan. Therefore, interventions in maternal lifestyle habits are required to prevent childhood obesity, and these interventions should be initiated before pregnancy.
The Extended Relationship between Child Cardiovascular Risks and Academic Performance Measures
Authors: Cottrell Lesley A. , Northrup Karen , Wittberg Richard
Published: July 2008

Objective: To examine the relationship between children's overweight status and other cardiovascular risk fitness factors and academic performance among fifth‐grade students.

Research Methods and Procedures: Using a sample of 968 fifth‐grade students (50.7% boys; mean age = 10.6 years), children's cardiovascular risks (BMI, blood pressure, acanthosis nigricans) and fitness measures were compared with their mean group performance scores across four subscales (mathematics, reading/language arts, science, and social studies) of a statewide standardized academic performance test.

Results: Of this sample, 39% were either at risk for being overweight or were already overweight; slightly over one half were of normal weight. Initial findings revealed a significant relationship between children's weight category and their reading/language arts, mathematics, and science test scores even after controlling for a proxy of socioeconomic status. When additional cardiovascular risk and fitness measures were included in the model, however, children's BMI status had no association. Instead, a composite fitness index, children's blood pressure, sex, and proxy of socioeconomic status were significantly associated with children's academic test scores.

Discussion: This study expanded our understanding of the connection between children's overweight risks and academic performance by examining the impact of other cardiovascular risk factors such as high blood pressure and measures of fitness. These findings support the development and implementation of childhood cardiovascular risk surveillance programs that evaluate not only children's overweight risks but also their fitness, risk for type 2 diabetes, and/or high blood pressure by showing a relationship between some of these risks and children's academic test performance.
The effect of the water/methane interface on methane hydrate cages: The potential of mean force and cage lifetimes
Authors: Mastny Ethan A. , Miller Clark A. , de Pablo Juan J.
Published: July 2008

Molecular dynamics simulations were used to determine the influence of a methane-water interface on the position and stability of methane hydrate cages. A potential of mean force was calculated as a function of the separation of a methane hydrate cage and a methane-water interface. The hydrate cages are found to be strongly repelled from the methane gas into the water phase. At low enough temperatures, however, the most favorable location for the hydrate cage is at the interface on the water side. Cage lifetime simulations were performed in bulk water and near a methane-water interface. The methane-water interface increases the cage lifetime by almost a factor of 2 compared to cage lifetimes of cages in bulk water. The potential of mean force and the cage lifetime results give additional explanations for the proposed nucleation of gas hydrates at gas-water interfaces.
Investigation on the intergranular interaction of the soft magnetic granular films by δM(H) curves
Authors: Yao Dongsheng , Ge Shihui , Zhou Xueyun , Zuo Huaping
Published: July 2008

( Fe 65 Co 35 ) x ( SiO 2 ) 1 − x granular films with various volume fraction (x) of Fe65Co35 alloy were fabricated by magnetron sputtering, and the interaction between granules was explored by δM(H) plots. Research results show that δM(H) is positive for the samples in a wide range of 0.42<x<0.86, indicating that exchange coupling exists among granules. Further research revels that δM(H)max increases gradually with decreasing x, reaching the maximum value at x=0.57, then decreases after x<0.57. Since δM(H)max can effectively reflect the intensity of exchange coupling, the intergranular exchange coupling also increases first, then decreases as x decreases. The microstructure is analyzed with help of the high-resolution transmission electron microscopy, and results show that the variation of exchange coupling with metal volume fraction x is dominated by the change of microstructure of samples. The microstructure of the sample with x=0.57 satisfy the optimization for realizing exchange coupling, leading to excellent soft magnetic properties.
Nanometer strain profiling through Si/SiGe quantum layers
Authors: Agaiby R. M. B. , Olsen S. H. , Dobrosz P. , Coulson H. , Bull S. J. , O’Neill A. G.
Published: July 2008

For the first time, nanometer-scale strain resolution is demonstrated using conventional Raman spectroscopy to profile strain through thin epitaxial Si/SiGe layers used as high mobility metal oxide field effect transistor channels. The strained layers were grown using ultrahigh vacuum chemical vapor deposition on relaxed SiGe virtual substrates. We observe how strain varies through the layer with 1.2 nm depth resolution. This is achieved by shallow angle (0.7°) bevelling. Tensile strain is found to be maximum at the buried Si/SiGe interface and decreases toward the surface. The partial surface strain relaxation is considered to be due to the imminence of the critical thickness. The bevel process has been characterized and does not impact results. SiGe composition and strained layer thickness are also determined and are in excellent agreement with secondary ion mass spectroscopy and x-ray diffraction data. The technique is proven to have 1 nm resolution in thickness measurements. Strain throughout the epitaxial layer stack has also been investigated. We show that the undulating surface morphology characteristic of relaxed SiGe alloys generated using compositional grading relates to periodic fluctuations in the strain fields in the SiGe virtual substrate, which are transferred to the overlying tensile strained Si. The resulting peak-peak variation in the tensile strained Si is determined to be 0.1%.
Modification of local order in FePd films by low energy He+ irradiation
Authors: Merkel D. G. , Tanczikó F. , Sajti Sz. , Major M. , Németh A. , Bottyán L. , Horváth Z. E. , Waizinger J. , Stankov S. , Kovács A.
Published: July 2008

Owing to their strong perpendicular magnetic anisotropy, FePd, CoPd, and their Co(Fe)Pt counterparts are candidate materials for ultrahigh density magnetic recording. The stability and magnetic properties of such films are largely dependent on the orientation and local distribution of the L10 FePd phase fraction. Therefore, the formation and transformation of the L10 phase in such thin films have been the subject of continued interest. Highly ordered epitaxial FePd(001) thin films (with an L10 phase fraction of 0.81) were prepared by molecular-beam epitaxy on a MgO(001) substrate. The effect of postgrown room temperature, 130 keV He+ irradiation was investigated at fluences up to 14.9×1015 ions/cm2. X-ray diffraction and conversion electron Mössbauer spectroscopy revealed that with increasing fluence, the L10 FePd phase decomposes into the face centered cubic phase with random Fe and Pd occupation of the sites. A partially ordered local environment exhibiting a large hyperfine magnetic field also develops. Upon He+ irradiation, the lattice parameter c of the FePd L10 structure increases and the long range order parameter S steeply decreases. The Fe–Fe nearest-neighbor coordination in the Fe-containing environments increases on average from Fe47Pd53 to Fe54Pd46, indicating a tendency of formation iron-rich clusters. The equilibrium parameters corresponding to the equiatomic L10 phase were found at different fluences by conversion electron Mössbauer spectroscopy and by x-ray diffraction a difference, from which a plane-perpendicular compressive stress and a corresponding in-plane tensile stress are conjectured. The steep increase in the interface roughness above 7.4×1015 ions/cm2 is interpreted as a percolation-type behavior related to the high diffusion anisotropy in the L10 phase.
Strain-induced modulation of band structure of silicon
Authors: Karazhanov S. Zh. , Davletova A. , Ulyashin A.
Published: July 2008

This work presents ab initio study of strain-induced modulation of band structure of Si. It is shown that at straining pressures >12GPa, band structure of Si can be turned from indirect to direct. Both the bottommost conduction band and topmost valence band are located at the Γ point. The conduction band minimum at the Γ point of the strained Si is found to be much more dispersive than that at the X point of the unstressed Si. Consequently, electrical conductivity through the Γ valley is suggested to be more superior than the X point of the unstressed Si. Barrier height, which is needed to transfer electrons in the Γ point to X∕L points or from Γ point to X∕L to Γ point have been calculated. The results have been applied to explain peculiarities of electronic structure and light emission of Si based materials containing dislocations and voids.
Becchi-Rouet-Stora-Tyutin operators for W algebras
Authors: Isaev A. P. , Krivonos S. O. , Ogievetsky O. V.
Published: July 2008

The study of quantum Lie algebras motivates a use of noncanonical ghosts and antighosts for nonlinear algebras, such as W-algebras. This leads, for the W3 and W3(2) algebras, to the Becchi-Rouet-Stora-Tyutin operator having the conventional cubic form.
Physically based kinetic Monte Carlo modeling of arsenic-interstitial interaction and arsenic uphill diffusion during ultrashallow junction formation
Authors: Kong Ning , Kirichenko Taras A. , Kim Yonghyun , Foisy Mark C. , Banerjee Sanjay K.
Published: July 2008

A kinetic arsenic-interstitial interaction model has been developed to study and predict arsenic transient enhanced diffusion (TED) and deactivation behavior during ultrashallow junction (USJ) formation. This model is based on density functional theory and has been verified by previous experiments in which the significant role of interstitial mechanism in arsenic TED was revealed. The mechanism of enhanced and retarded arsenic diffusion in different point defect environments is investigated by utilizing this model in kinetic Monte Carlo simulation. The arsenic-interstitial pair, with low binding energy and low migration energy, is shown to be the major contributor to arsenic TED in silicon interstitial-rich situations. In addition, by using this model, we demonstrate the transient existence of arsenic-interstitial clusters (AsnIm) during postimplant annealing and propose their possible role in deactivation for short time annealings such as laser annealing and spike annealing. Moreover, we have developed a novel surface-trap based kinetic Monte Carlo model to simulate arsenic uphill diffusion in proximity of the Si∕SiO2 interface. The simulation results show that the activation behavior of the uphill portion of arsenic has considerable impact on the junction sheet resistance. The activation behavior of this arsenic is expected to become more important when USJ depth is scaled down further.
Microcalorimetric study of thermal unfolding of lysozyme in water/glycerol mixtures: An analysis by solvent exchange model
Authors: Spinozzi Francesco , Ortore Maria Grazia , Sinibaldi Raffaele , Mariani Paolo , Esposito Alessandro , Cinelli Stefania , Onori Giuseppe
Published: July 2008

Folded protein stabilization or destabilization induced by cosolvent in mixed aqueous solutions has been studied by differential scanning microcalorimetry and related to difference in preferential solvation of native and denatured states. In particular, the thermal denaturation of a model system formed by lysozyme dissolved in water in the presence of the stabilizing cosolvent glycerol has been considered. Transition temperatures and enthalpies, heat capacity, and standard free energy changes have been determined when applying a two-state denaturation model to microcalorimetric data. Thermodynamic parameters show an unexpected, not linear, trend as a function of solvent composition; in particular, the lysozyme thermodynamic stability shows a maximum centered at water molar fraction of about 0.6. Using a thermodynamic hydration model based on the exchange equilibrium between glycerol and water molecules from the protein solvation layer to the bulk, the contribution of protein-solvent interactions to the unfolding free energy and the changes of this contribution with solvent composition have been derived. The preferential solvation data indicate that lysozyme unfolding involves an increase in the solvation surface, with a small reduction of the protein-preferential hydration. Moreover, the derived changes in the excess solvation numbers at denaturation show that only few solvent molecules are responsible for the variation of lysozyme stability in relation to the solvent composition.
Influence of emissivity on behavior of metallic dust particles in plasmas
Authors: Tanaka Y. , Smirnov R. D. , Pigarov A. Yu. , Rosenberg M.
Published: July 2008

Influence of thermal radiation emissivity on the lifetime of a dust particle in plasmas is investigated for different fusion relevant metals (Li, Be, Mo, and W). The thermal radiation is one of main cooling mechanisms of the dust in plasmas especially for dust with evaporation temperature higher than 2500K. In this paper, the temperature- and radius-dependent emissivity of dust particles is calculated using Mie theory and temperature-dependent optical constants for the above metallic materials. The lifetime of a dust particle in uniform plasmas is estimated with the calculated emissivity using the dust transport code DUSTT [A. Pigarov et al., Physics of Plasmas 12, 122508 (2005)], considering other dust cooling and destruction processes such as physical and chemical sputtering, melting and evaporation, electron emission etc. The use of temperature-dependent emissivity calculated with Mie theory provides a longer lifetime of the refractory metal dust particle compared with that obtained using conventional emissivity constants in the literature. The dynamics of heavy metal dust particles are also presented using the calculated emissivity in a tokamak plasma.
Magnetoelectric effect in rare earth ferrites, LnFe2O4
Authors: Serrao Claudy Rayan , Sahu Jyoti Ranjan , Ramesha K. , Rao C. N. R.
Published: July 2008

Dielectric and magnetic properties of selected rare earth ferrites, LnFe2O4 (Ln=Y,Er,Yb), have been investigated. All these materials show ferroelectricity near the ferrimagnetic transition temperature around 250 K. More importantly, they exhibit a change in the dielectric behavior on the application of magnetic fields.
The thermoelectric properties of bulk crystalline n- and p-type Mg2Si prepared by the vertical Bridgman method
Authors: Akasaka Masayasu , Iida Tsutomu , Matsumoto Atsunobu , Yamanaka Kohei , Takanashi Yoshifumi , Imai Tomohiro , Hamada Noriaki
Published: July 2008

Bulk Mg2Si crystals were grown using the vertical Bridgman melt growth method. The n-type and p-type dopants, bismuth (Bi) and silver (Ag), respectively, were incorporated during the growth. X-ray powder diffraction analysis revealed clear peaks of Mg2Si with no peaks associated with the metallic Mg and Si phases. Residual impurities and process induced contaminants were investigated by using glow discharge mass spectrometry (GDMS). A comparison between the results of GDMS and Hall effect measurements indicated that electrical activation of the Bi doping in the Mg2Si was sufficient, while activation of the Ag doping was relatively smaller. It was shown that an undoped n-type specimen contained a certain amount of aluminum (Al), which was due either to residual impurities in the Mg source or the incorporation of process-induced impurities. Thermoelectric properties such as the Seebeck coefficient and the electrical and thermal conductivities were measured as a function of temperature up to 850 K. The dimensionless figures of merit for Bi-doped and Ag-doped samples were 0.65 at 840 K and 0.1 at 566 K, respectively. Temperature dependence of the observed Seebeck coefficient was fitted well by the two-carrier model. The first-principles calculations were carried out by using the all-electron band-structure calculation package (ABCAP) in which the full-potential linearized augmented-plane-wave method was employed. The ABCAP calculation adequately presents characteristics of the Seebeck coefficients for the undoped and heavily Bi-doped samples over the whole measured temperature range from room temperature to 850 K. The agreement between the theory and the experiment is poorer for the Ag-doped p-type samples.
Integrable discrete systems on R and related dispersionless systems
Authors: Błaszak Maciej , Gürses Metin , Silindir Burcu , Szablikowski Błażej M.
Published: July 2008

A general framework for integrable discrete systems on R, in particular, containing lattice soliton systems and their q-deformed analogs, is presented. The concept of regular grain structures on R, generated by discrete one-parameter groups of diffeomorphisms, in terms of which one can define algebra of shift operators is introduced. Two integrable hierarchies of discrete chains together with bi-Hamiltonian structures and their continuous limits are constructed. The inverse problem based on the deformation quantization scheme is considered.
Deposition of aluminum oxide layer on GaN using diethyl aluminum ethoxide as a precursor
Authors: Uesugi Tsutomu , Kachi Tetsu , Sugimoto Masahiro , Matsuyama Tetsuya , Mizue Chihoko , Hashizume Tamotsu
Published: July 2008

We performed a feasibility study on the deposition of aluminum oxides (AlOx) on GaN using diethyl aluminum ethoxide [(C2H5)2AlOC2H5] as a precursor by electron-cyclotron-resonance-assisted chemical vapor deposition. We determined the refractive index and permittivity of the deposited AlOx layer to be 1.59 and 8.3, respectively. An x-ray photoelectron spectroscopy (XPS) study showed that the energy positions of the Al- and O-core levels were very close to those of the reference crystalline Al2O3 and that there was no significant peak related to carbon in the AlOx film. XPS also indicated a bandgap of 7.0 eV and oxygen composition of 1.48 for the AlOx layer deposited on GaN. We found good capacitance-voltage (C-V) behavior for the Ni/AlOx/n-GaN diode including accumulation and depletion behavior at room temperature. Even at high temperatures, the C-V slope remained unchanged indicating relatively low interface state densities near the midgap.
Titanium doped silicon layers with very high concentration
Authors: Olea J. , Toledano-Luque M. , Pastor D. , González-Díaz G. , Mártil I.
Published: July 2008

Ion implantation of Ti into Si at high doses has been performed. After laser annealing the maximum average of substitutional Ti atoms is about 1018 cm−3. Hall effect measurements show n-type samples with mobility values of about 400 cm2/V s at room temperature. These results clearly indicate that Ti solid solubility limit in Si has been exceeded by far without the formation of a titanium silicide layer. This is a promising result toward obtaining of an intermediate band into Si that allows the design of a new generation of high efficiency solar cell using Ti implanted Si wafers.
Effect of pore morphology on the electrochemical properties of electric double layer carbon cryogel supercapacitors
Authors: Batalla García Betzaida , Feaver Aaron M. , Zhang Qifeng , Champion Richard D. , Cao Guozhong , Fister Tim T. , Nagle Ken P. , Seidler Gerald T.
Published: July 2008

In this study, a group of carbon cryogels have been synthesized using resorcinol formaldehyde as precursors, and altered via catalysis and activation, to obtain varied nanostructures and pore size distributions. To understand the relation between structure and electrochemical properties, an alternate approach to de Levi’s cylindrical pore, transmission line method was utilized. Using electrochemical impedance spectroscopy, the capacitor can be studied as a dielectric system composed of a porous electrode and the electrolyte (tetraethylammonium tetrafluoroborate in propylene carbonate). The complex capacitance and power are used to study the behavior of the system below the relaxation frequency f0 (φ=−45°). Therefore, the relaxation of the capacitor system at the low frequency range, f<f0, may be used as a measure of pore/electrolyte interaction. The approach proposed here also allows for a direct experimental characterization of the capacitance and power at low frequencies, where small pores are likely to affect the diffusion kinetics and dynamics of the electrolyte molecules. The results suggest a correlation between the occurrence of small micropores and that of high power losses that are related to the resistive element at the low frequency range. Moreover, the impact of the micropore structure on the supercapacitor’s performance is apparent in its capacitance and energy as well. In addition to the complex power and capacitance, other measurements including nitrogen physisorption, cyclic voltammetry, galvanic cycling, and x-ray Raman scattering were used to characterize the samples and support these results.
Highly localized mode in a pair structure made of epsilon-negative and mu-negative metamaterials
Authors: Feng Tuanhui , Li Yunhui , Guo Jiyong , He Li , Li Hongqiang , Zhang Yewen , Shi Yunlong , Chen Hong
Published: July 2008

In this paper, the tunneling phenomenon occurring in a pair structure made of epsilon-negative (ENG) and mu-negative (MNG) metamaterials is experimentally studied. The ENG and MNG metamaterials are fabricated using coplanar waveguide loading with lumped-element series capacitors and shunt inductors. The properties of the tunneling mode are investigated by means of the transfer-matrix method, based on the experiment parameters of effective permittivity and permeability. The results show that the tunneling frequency is independent of the pair length and the electric field is highly localized at the interface of the ENG-MNG pair. These features illustrate that the pair behaves as a cavity with strongly enhanced electric field and with dimensions beyond the half-wavelength limit.
Oxidation of SiC investigated by ellipsometry and Rutherford backscattering spectrometry
Authors: Szilágyi E. , Petrik P. , Lohner T. , Koós A. A. , Fried M. , Battistig G.
Published: July 2008

Oxidation of SiC was performed in Ar–O2 mixture of atmospheric pressure at 1100 °C and compared with that of Si. The partial pressure of O2 varied from 100 to 1000 mbar, while the oxidation time ranged from 0.5 to 45 h. The thickness of the oxide films was determined by spectroscopic ellipsometry and Rutherford backscattering spectrometry. The time and the pressure dependence of the oxidation kinetics of SiC are well described by the modified Deal–Grove model. In the diffusion-limited region, even for the faster case, the oxidation kinetics of the C-terminated face of SiC is not clearly limited by oxygen indiffusion, as for pure silicon. To interpret the ellipsometry spectra, two models of possible structure were used. In the case of the one-layer model, for layer thicknesses above 30 nm, the refractive index of the oxide layers is identical to that of thermally oxidized Si, and it increases rapidly with decreasing thickness below about 15 nm. This increase is significantly larger for C-terminated than for Si-terminated faces, and this difference can be explained by a transition layer introduced into the two-layer model. This model contains a pure SiO2 layer and a transition layer modeled by a mixture of 50 % SiO2 and 50 % SiC. The transition layer is thicker on the C-terminated surface than on the Si-terminated one. The thickness ratio of the transition layers is slightly larger than the surface roughness ratio on the two different sides determined by atomic force microscopy. The density of the oxide films, which can be determined from the backscattering and spectroscopic ellipsometry spectra, decreases with decreasing thickness below about 30 nm. For thicker films, the density of the oxide is equal to the bulk density of SiO2.
Lattice Boltzmann simulation of surface roughness effect on gaseous flow in a microchannel
Authors: Chai Zhenhua , Guo Zhaoli , Zheng Lin , Shi Baochang
Published: July 2008

At the microscale level, it is impossible to obtain a completely smooth wall surface, and the effect of surface roughness may be a main factor responsible for some different characteristics between fluid flow in the microchannels and that in conventional size channels. In the present work, the lattice Boltzmann method is applied to investigate the gaseous flow in a microchannel with surface roughness which is modeled by an array of rectangular modules. The effects of relative surface roughness, roughness distribution, and rarefaction on gaseous flow are studied, but the compressibility effect is neglected since the Mach number is less than 0.2. It was shown that the surface roughness had an important influence on friction factor and mass flow rate. In particular, this effect becomes more significant with the decrease of the Knudsen number. This is because the rarefaction reduces the interaction between the gas molecules and the channel walls, which results in reduction of the surface roughness effect.