No abstract is provided for this article.
The "beads-on-a-string" model for folding of polymers is a cornerstone of theoretical polymer science. This communication describes a physical model of beads-on-a-string, based on the folding of flexible strings of electrostatically charged beads in two dimensions. The system comprises millimeter-scale Teflon and Nylon-6,6 (spherical or cylindrical) beads (approximately 6 mm in diameter) separated by smaller (approximately 3 mm) poly(methyl methacrylate) (PMMA) spherical beads, threaded on a flexible string. The smaller, uncharged beads define the distances between the larger beads, and control the flexibility of the string. During agitation of the sequence of beads on a planar, horizontal paper surface, tribocharging generates opposite electrostatic charges on the larger Nylon and Teflon beads, but leaves the smaller PMMA beads essentially uncharged; the resulting electrostatic interactions cause the string to fold. Examination and comparison of two models--one physical and one theoretical--may offer a new approach to understanding folding, collapse, and molecular recognition at an abstract level, with particular opportunity to explore the influence of the flexibility of the string and the shape of the beads on the pattern and rate of folding. The physical system is, thus, an analog computer, simulating the theoretical beads-on-a-string model in two dimensions; this system makes it possible to test hypotheses connecting "sequence" to "folding", rapidly and conveniently, while exploring nonlinearities and other complexities omitted from the theoretical model.
Low-grade inflammation might mediate associations between size at birth, early life growth, excessive weight gain, and subsequent risk of cardiovascular disease in adult life. Our aim was to investigate relationships between fetal growth, weight over the life course, and low-grade inflammation measured by serum high sensitivity C-reactive protein (CRP) levels at 31 years. General population-based northern Finland 1966 Birth Cohort study of 5840 participants attending a clinical examination at 31 years, including measurement of CRP. Weight and height were assessed at birth, 12 months, and 14 and 31 years of age. CRP levels at 31 years were 16% [95% confidence interval (CI) 8, 23] higher per 1 kg lower birth weight, 21% (95% CI 2, 37) higher per 10 cm lower birth length, and 24% (95% CI 10, 36) higher per 1 kg/m3 lower ponderal index, after adjustment for potential confounders. Participants with highest tertile body mass index (BMI) at 31 years and lowest tertile birth weight had the highest average CRP levels. Per unit increase in BMI from 14 to 31 years was associated with 16% (95% CI 14, 17) higher CRP levels; the association was larger for those in the top BMI tertile at age 14 years. Systemic low-grade inflammation may lie on the causal pathway that relates impaired fetal growth and weight gain from childhood to adulthood to adverse adult cardiovascular health. Lifestyle changes from early life might be an important step in reducing cardiovascular risk in adults.
No abstract is provided for this article.
This paper investigates the hypothesis that localization of deformation into a shear band may be considered a result of an instability in the constitutive description of homogeneous deformation. General conditions for a bifurcation, corresponding to the localization of deformation into a planar band, are derived. Although the analysis is general and applications to other localization phenomena are noted, the constitutive relations which are examined in application of the criterion for localization are intended to model the behavior of brittle rock masses under compressive principal stresses. These relations are strongly pressure-sensitive since inelasticity results from frictional sliding on an array of fissures; the resulting inelastic response is dilatant, owing to uplift in sliding at asperities and to local tensile cracking from fissure tips. The appropriate constitutive descriptions involve non-normality of plastic strain increments to the yield hyper-surface. Also, it is argued that the subsequent yield surfaces will develop a vertex-like structure. Both of these features are shown to be destabilizing and to strongly influence the resulting predictions for localization by comparison to predictions based on classical plasticity idealizations, involving normality and smooth yield surfaces. These results seem widely applicable to discussions of the inception of rupture as a constitutive instability.
▪ Abstract Soft lithography, a set of techniques for microfabrication, is based on printing and molding using elastomeric stamps with the patterns of interest in bas-relief. As a technique for fabricating microstructures for biological applications, soft lithography overcomes many of the shortcomings of photolithography. In particular, soft lithography offers the ability to control the molecular structure of surfaces and to pattern the complex molecules relevant to biology, to fabricate channel structures appropriate for microfluidics, and to pattern and manipulate cells. For the relatively large feature sizes used in biology (≥50 μm), production of prototype patterns and structures is convenient, inexpensive, and rapid. Self-assembled monolayers of alkanethiolates on gold are particularly easy to pattern by soft lithography, and they provide exquisite control over surface biochemistry.
The friction of rocks in the laboratory is a function of time, velocity of sliding, and displacement. Al- though the processes responsible for these dependencies are unknown, constitutive equations have been developed that do a reasonable job of describing the laboratory behavior. These constitutive laws have been used to create a model of earth. quakes at Parkfield, CA, by using boundary conditions ap- propriate for the section of the fault that slips in magnitude 6 earthquakes every 20-30 years. The behavior of this model prior to the earthquakes is investigated to determine whether or not the model earthquakes could be predicted in the real world by using realistic instruments and instrument locations. Premonitory slip does occur in the model, but it is relatively restricted in time and space and detecting it from the surface may be difficult. The magnitude of the strain rate at the earth's surface due to this accelerating slip seems lower than the detectability limit of instruments in the presence of earth noise. Although not specifically modeled, microseismicity related to the accelerating creep and to creep events in the model should be detectable. In fact the logarithm of the moment rate on the hypocentral cell of the fault due to slip increases linearly with minus the logarithm of the time to the earthquake. This could conceivably be used to determine when the earthquake was going to occur. An unresolved question is whether this pattern of accelerating slip could be recognized from the microseismicity, given the discrete nature of seismic events. Nevertheless, the model results suggest that the most likely solution to earthquake prediction is to look for a pattern of acceleration in microseismicity and thereby identify the microearthquakes as foreshocks.
OBJECTIVE—Inflammation is associated with both chronic kidney dysfunction and type 2 diabetes. Adiponectin, a novel circulating anti-inflammatory protein made by adipocytes, has been reported to be lower in diabetic than nondiabetic subjects. In contrast, serum levels of adiponectin are elevated in end-stage renal disease. We sought to investigate the relation between adiponectin and mild to moderate renal dysfunction in men with type 2 diabetes. RESEARCH DESIGN AND METHODS—Multivariate logistic regression was used to evaluate the relation between serum adiponectin concentrations and the presence of renal dysfunction (estimated glomerular filtration rate [eGFR] <60 ml/min per 1.73 m2 by the four-variable Modification of Diet in Renal Disease equation) in participants with type 2 diabetes in the Health Professionals’ Follow-Up Study. A total of 733 men were included in this cross-sectional analysis. RESULTS—Adiponectin was positively correlated with age (Spearman coefficient, r = 0.19, P < 0.001) and negatively correlated with weight (Spearman coefficient, r = −0.18, P < 0.001). Those with adiponectin in the second quartile or higher (>10 μg/ml) compared with those in the first quartile had a reduced odds for renal dysfunction (multivariate odds ratio 0.48 [95% CI 0.28–0.81]). These results were unchanged when serum lipids were included in the multivariate model. CONCLUSIONS—We conclude that a higher serum adiponectin concentration is associated with reduced odds of moderate renal dysfunction in men with type 2 diabetes.
The role of geometrically necessary dislocations in providing macroscopic strengthening is reviewed with particle reinforcement as an example. The general relation between the Nye tensor and slip along a curvilinear slip line net is derived to emphasise the importance of curvature of slip lines upon the rate of dislocation storage.
Excessive postpartum weight retention puts women at risk for health problems. This study aimed to investigate the effects of dairy foods on weight retention and risk of obesity in postpartum women in the Nurses’ Health Study II. Weight was reported every 2 years. We identified the pre-pregnancy and postpartum exams that were approximately 2 years before and after the birth year. Dairy consumption was averaged during these 4 years. Linear models were used to assess postpartum weight retention. Multivariable models were used to estimate risk of obesity. Women with higher yogurt (≥2 servings/week vs. <1 serving/month) intakes had 0.61 pounds less postpartum weight retention. Consuming ≥ 5 cheese servings/week was associated with 0.63 pounds less weight retention than the lowest intake. Among sedentary women, only yogurt intake was associated with lower risk of postpartum obesity (RR: 0.84; 95% CI: 0.71–1.00), though of borderline statistical significance. Among women with less healthy diets, yogurt consumption was also associated with lower postpartum obesity risk (RR: 0.70; 95% CI: 0.57–0.85). In sum, higher yogurt and cheese intakes were associated with less postpartum weight retention and among higher risk women (sedentary or lower diet quality) greater yogurt intake was associated with lower risks of postpartum obesity.
