There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

A polyacrylamide hydrogel exhibits near-perfect elasticity: its stress-stretch curve is rate-independent and has negligible hysteresis. The near-perfect elasticity results from the large amount of water between the polymer chains. Water has low viscosity and lubricates polymer chains. Here we report that the polyacrylamide hydrogel exhibits rate-dependent toughness when the polymer chains are long. We interpret this finding as follows. Toughness is measured by rupturing a hydrogel containing a precut crack. When the hydrogel is stretched, at the crack tip, some polymer chains slide relative to others. Before a polymer chain breaks, high tension is distributed over a long length of the chain. Breaking the chain releases the energy stored in the long length of the chain. It is this deconcentration of tension that toughens the hydrogel. When the hydrogel is stretched at a high rate, however, the polymer chain at the crack tip does not have time to slip fully, so that the high tension only transmits over a short segment of the chain. Breaking the chain will lead to a lower toughness. Consequently, the toughness decreases as the stretch rate increases. We invoke a shear lag model and find that the toughness scales with stretch rate as Gc ∼ (dλ/dt)−1/4.

Polyacrylamide hydrogels. IV. Near-perfect elasticity and rate-dependent toughness

Elastomeric seals are widely used to block fluids of high pressure. When multiple seals are installed in series and the spaces between the seals contain compressible fluids (e.g., gas or gas–liquid mixture), the seals often damage sequentially, one after another. Here, we demonstrate that the serial seals achieve high sealing capacity if individual seals undergo elastic leak, without material damage. When individual seals leak elastically, fluid fills the spaces between the seals. Instead of damage one after another, all the seals share the load. The elastic leak of individual seals greatly amplifies collective sealing capacity of serial seals.

Elastic Leak for a Better Seal

Hydrogel compositions, and corresponding methods of making, are provided. The hydrogels do not freeze, or only partially freeze, over a wide range of temperatures below the freezing temperature of water. Concurrently, these hydrogels also retain their room temperature mechanical properties (e.g., strength, modulus, elasticity) over a wide range of temperatures, including temperatures below the freezing temperature of water. The hydrogels are synthesized by adding a suitable amount of a salt together with previously cross-linked polymer gel. Hydration of the gel with aqueous solutions containing the prescribed salts not only depresses the hydrogel freezing point but protects the structure. For example, the salts do not allow the hydrogel to completely freeze, thus protecting the hydrogel from brittle failure. Whether the hydrogels partially freeze or remain non-frozen when chilled below the freezing temperature of water is determined by concentration of salt within the hydrogel.

Hydrogels with improved mechanical properties below water freezing temperature

Synergy of noncovalent interlink and covalent toughener for tough hydrogel adhesion

This paper describes our recent progress in developing a finite element method for simulating interface motion. Attention is focused on two mass transport mechanisms: interface migration and surface diffusion. A classical theory states that, for interface migration, the local normal velocity of an interface is proportional to the free energy reduction associated with a unit volume of atoms detach from one side of the interface and attach to the other side. We express this theory into a weak statement, in which the normal velocity and any arbitrary virtual motion of the interface relate to the free energy change associated with the virtual motion. An example with two degrees of freedom shows how the weak statement works. For a general case, we divide the interface into many elements, and use the positions of the nodes as the generalized coordinates. The variations of the free energy associated with the variations of the nodal positions define the generalized forces. The weak statement connects the velocity components at all the nodes to the generalized forces. A symmetric, positive-definite matrix appears, which we call the viscosity matrix. A set of nonlinear ordinary differential equations evolve the nodal positions. We then treat combined surface diffusion and evaporation-condensation in a similar method with generalized coordinates including both nodal positions and mass fluxes. Three numerical examples are included. The first example shows the capability of the method in dealing with anisotropic surface energy. The second example is pore-grain boundary separation in the final stage of ceramic sintering. The third example relates to the process of mass reflow in VLSI fabrication.

Zhigang Suo

Papers

Polyacrylamide hydrogels. IV. Near-perfect elasticity and rate-dependent toughness

Elastic Leak for a Better Seal

Hydrogels with improved mechanical properties below water freezing temperature

Synergy of noncovalent interlink and covalent toughener for tough hydrogel adhesion

A finite element method for simulating interface motion