The First Two Months

This chapter describes the development of the fetus in the first 2 months of pregnancy following conception, including the development of the zygote as it travels down the fallopian tube, cell migration and differentiation, and a discussion of stem cells. As the author starts to experience pregnancy for the very first time, she describes common symptoms of pregnancy, including morning sickness, headaches, breast tenderness, increased hunger, frequent urination, and fatigue. She also discusses the high incidence of miscarriages—which are common of 10–20% of known pregnancies—and their frequency in the first trimester. Finally, she describes a mother’s very first sonogram, or internal ultrasound.

How does genome size affect the evolution of pollen tube growth rate, a haploid performance trait?

ABSTRACTPremise of the StudyMale gametophytes of most seed plants deliver sperm to eggs via a pollen tube. Pollen tube growth rates (PTGRs) of angiosperms are exceptionally rapid, a pattern attributed to more effective haploid selection under stronger pollen competition. Paradoxically, whole genome duplication (WGD) has been common in angiosperms but rare in gymnosperms. Pollen tube polyploidy should initially accelerate PTGR because increased heterozygosity and gene dosage should increase metabolic rates, however polyploidy should also independently increase tube cell size, causing more work which should decelerate growth. We asked how genome size changes have affected the evolution of seed plant PTGRs.MethodsWe assembled a phylogenetic tree of 451 species with known PTGRs. We then used comparative phylogenetic methods to detect effects of neo-polyploidy (within-genus origins), DNA content, and WGD history on PTGR, and correlated evolution of PTGR and DNA content.Key ResultsGymnosperms had significantly higher DNA content and slower PTGR optima than angiosperms, and their PTGR and DNA content were negatively correlated. For angiosperms, 89% of model weight favored Ornstein-Uhlenbeck models with a faster PTGR optimum for neo-polyploids, but PTGR and DNA content were not correlated. In comparisons of within-genus and intraspecific-cytotype pairs, PTGRs of neo-polyploids ≤ paleo-polyploids.ConclusionsGenome size increases should negatively affect PTGR when genetic consequences of WGDs are minimized, as found in intra-specific autopolyploids (low heterosis) and gymnosperms (few WGDs). But in angiosperms, the higher PTGR optimum of neo-polyploids and non-negative PTGR-DNA content correlation suggest that recurrent WGDs have caused substantial PTGR evolution in a non-haploid state.

Comparative Study of Thermal-Hydraulic Behavior of the DFR Using U-Pu and TRU Salt Fuels

The Dual Fluid Reactor is a molten salt fast reactor developed by the IFK1 based on the Gen-IV Molten-Salt Reactor (MSR) and the Liquid-Metal Cooled Reactor (SFR, LFR) concepts. Based on previous researches an analysis focusing on the simulation on different dimensions of the DFR system with transuranium (TRU) salt fuel option is performed. The zero-dimensional point-kinetics model coupled with the zero-dimensional heat-transfer model constructed by SIMULINK will be set up first. The radial power profile of the fuel salts inside of the fuel tube cell is described by a two-dimensional system which focuses on the single fuel unit cell of the DFR with the equivalent cylindrical model instead of the original hexagonal prismatic shape. The comparison between the results is then discussed.

Crush dynamics of rubber tube under low velocity impact

It is proved that hyperelastic honeycomb coatings can attenuate underwater blast loads impinged on the ship hull. The crush behavior of a unit tube cell of the coating made of rubber material is investigated in this study. A series of tests are conducted to investigate the crush dynamic behavior of the tube under low velocity impact loads. Numerical analyses are carried out to explore the impact process of the rubber tube and the role of some dynamic parameters, thereby serve as a reference in the design of new coating. Some characteristics, such as the geometric imperfections, nonlinear elasticity and material viscosity, are analyzed. The results of simulation and experiments show that the geometric imperfections not only attenuate the shock force in the buckling and the force plateau stages, but also enhance the shock force in the densification stage greatly and promote the global peak force initiation, while the material viscosity enhances the force plateau and attenuates the shock force in the densification stage greatly. These effects are illustrated and quantified with the aid of experiments and numerical calculations.