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Cycling exercise initiated early in pregnancy and performed at least 30 minutes, 3 times per week, is associated with a significant reduction in the frequency of gestational diabetes mellitus in overweight/obese pregnant women. And this effect is very relevant to that exercise at the beginning of pregnancy decreases the gestational weight gain before the mid-second trimester. Furthermore, there was no evidence that the exercise prescribed in this study increased the risk of preterm birth or reduced the mean gestational age at birth.

OBJECTIVETo evaluate the value of fasting plasma glucose (FPG) value in the first prenatal visit to diagnose gestational diabetes mellitus (GDM).RESEARCH DESIGN AND METHODSMedical records of 17,186 pregnant women attending prenatal clinics in 13 hospitals in China, including the Peking University First Hospital (PUFH), were examined. Patients with pre-GDM were excluded; data for FPG at the first prenatal visit and one-step GDM screening with 75-g oral glucose tolerance test (OGTT) performed between 24 and 28 weeks of gestation were collected and analyzed.RESULTSThe median ± SD FPG value was 4.58 ± 0.437. FPG decreased with increasing gestational age. FPG level at the first prenatal visit was strongly correlated with GDM diagnosed at 24–28 gestational weeks (χ2 = 959.3, P < 0.001). The incidences of GDM were 37.0, 52.7, and 66.2%, respectively, for women with FPG at the first prenatal visit between 5.10 and 5.59, 5.60 and 6.09, and 6.10–6.99 mmol/L. The data of PUFH were not statistically different from other hospitals.CONCLUSIONSPregnant women (6.10 ≤ FPG < 7.00 mmol/L) should be considered and treated as GDM to improve outcomes; for women with FPG between 5.10 and 6.09 mmol/L, nutrition and exercise advice should be provided. An OGTT should be performed at 24–28 weeks to confirm or rule out GDM. Based on our data, we cannot support an FPG value ≥5.10 mmol/L at the first prenatal visit as the criterion for diagnosis of GDM.

Mode I steady-state crack growth is analysed under plane strain conditions in small scale yielding. The elastic-plastic solid is characterized by a generalization of JZ flow theory which accounts for the influence of the gradients of plastic strains on hardening. The constitutive model involves one new parameter, a material length 1, specifying the scale of nonuniform deformation at which hardening elevation owing to strain gradients becomes important. Gradients of plastic strain at a sharp crack tip result in a substantial increase in tractions ahead of the tip. This has important consequences for crack growth in materials that fail by decohesion or cleavage at the atomic scale. The new constitutive law is used in conjunction with a model which represents the fracture process by an embedded traction-separation relation applied on the plane ahead of the crack tip. The ratio of the macroscopic work of fracture to the work of the fracture process is calculated as a function of the parameters characterizing the fracture process and the solid, with particular emphasis on the role of 1. 0 1997 Elsevier Science Ltd

Monolayer two-dimensional (2D) crystals exhibit a host of intriguing properties, but the most exciting applications may come from stacking them into multilayer structures. Interlayer and interfacial shear interactions could play a crucial role in the performance and reliability of these applications, but little is known about the key parameters controlling shear deformation across the layers and interfaces between 2D materials. Herein, we report the first measurement of the interlayer shear stress of bilayer graphene based on pressurized microscale bubble loading devices. We demonstrate continuous growth of an interlayer shear zone outside the bubble edge and extract an interlayer shear stress of 40 kPa based on a membrane analysis for bilayer graphene bubbles. Meanwhile, a much higher interfacial shear stress of 1.64 MPa was determined for monolayer graphene on a silicon oxide substrate. Our results not only provide insights into the interfacial shear responses of the thinnest structures possible, but also establish an experimental method for characterizing the fundamental interlayer shear properties of the emerging 2D materials for potential applications in multilayer systems.

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This letter addresses the issue of deformation mechanisms and mechanical tensile behavior of the twinned metal nanowires using atomistic simulations. Free surfaces are always the preferential dislocation nucleation sites in the initial inelastic deformation stage, while with further plastic deformation, twin boundary interfaces will act as sources of dislocations with the assistance of the newly formed defects. The smaller the twin boundary spacing, the higher the yielding stresses of the twinned nanowires. Twin boundaries, which serve both as obstacles to dislocation motion and dislocation sources, can lead to hardening effects and contribute to the tensile ductility. This work illustrates that the mechanical properties of metal nanowires could be controlled by tailoring internal growth twin structures. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2721367͔Due to the unique mechanical, electrical, and optical properties, materials with nanometer-sized structure have attracted a great deal of interest in the past few decades [1][2][3] Many researchers have demonstrated, through both experiments and analysis, that the structure and properties of nanowires can be quite different from those of bulk materials due to the effects of larger free surfaces. [4][5][6][7][8][9][10][11][12][13][14] Simulations reported in the previous literatures are generally defect-free and the sizes of the modeled wires are usually smaller than 6 nm. [6][7][8][9][10][11][12][13][14] Meanwhile experimentally, twins, a class of planar defects, are observed most often in single-crystal metal ͑copper, silver, and gold͒ nanowires with a ͓111͔ growth orientation. 15,16 Because twin boundaries ͑TBs͒ in nanowires will strongly affect the physical properties of nanowires, it is of great significance to investigate the details of twin structures and their roles in metal nanowires. Until now, there are still some key issues about twin related deformation which are not quite clear and need fundamental understanding. For example, what is the role of TBs in mechanical deformation? Does it act as grain boundaries or surfaces? In our recent work, the mechanical behavior of fivefold twinned nanowires is studied. 17 We found that the strengthening mechanism in the fivefold twinned nanowires is due to the TBs as obstacles to the dislocation motion. In this letter, we address the effect of TBs on inelastic deformation of the twinned nanowires using atomistic simulations.In this work we focus on twinned Cu nanowires with ͗111͘ growth orientation and nearly square cross section as indicated from the experimental observations. 15,16 The initial configuration of the twinned nanowires is constructed by repeating ⌺3 coherent twins in the ͗111͘ axis orientation. 18 Four samples are prepared for the simulations. The first one consists of two twins, the second consists of four twins, and the third contains five twins. The twin boundary spacings ͑TBSs͒ of the first, second, and third wires are 14 nm ͑sample I͒, 7 nm ͑sample II͒, and 5 nm ͑sample III͒, respect...

ÐThe adhesion at interfaces between dissimilar materials is strongly aected by both segregation and the extent of plasticity in the adjoining material, particularly when one of these is a metal (or thermoplastic). It will be shown that these interfaces when clean, are generally strong and tough, such that failure occurs in one of the adjoining materials, rather than at the interface. However, segregrants and contaminants often embrittle and weaken the interface, especially in combination with ambient moisture. The embrittlement is obviated either by alloying with elements that``getter'' the contaminants or by using aǹ`a dhesion layer'' that has essentially the same eect: Cr and Ti are particularly eective gettering elements. Models that relate these eects to fundamental material parameters through non-dimensional indices are described. They comprise linkages between atomistic and continuum, enabled by implementation of a plasticity length scale, within the context of a crack growth simulation routine. Comparison with the experimental results is conducted, leading to suggestions for development of a predictive scheme.