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

Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

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

Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

We developed micro-structured thin films with ultra-low coefficient of thermal expansion. These low-weight, flexible, thermally stable films are expected to be a useful tool in aerospace applications, for example, as a reflective layers of deformable space telescope mirrors. The low-CTE films are composed of a Ti frame supporting hexagonal Al plates arranged in a two-dimensional periodic lattice. The effective CTE of these materials can be controlled by selecting the appropriate constitutent material properties of the frame and plates, and the geometry of the lattice. Aluminum and titanium were selected as constituent materials to create thin films with a CTE close to zero. The 2D bi-metallic lattice was microfabricated, and characterized for its thermal and optical functionalities. The effective CTE was confirmed to be ultra-low (-0.6×10^(-6)/°C), and the imaging capability of this metallic layer was evaluated in the range of temperature from room temperature to 150 °C.

Engineered thin films with ultra-low thermal expansion coefficient for deployable or deformable space structures

The ionic conductivity of CaCl2-crosslinked pectin was found to exhibit a record-high temperature response, suggesting its potential applications in wearable devices and infrared sensors [R. Di Giacomo et al., Sci. Rob. 2, eaai9251 (2017)]. However, little was known about its ion conduction mechanisms and the origin of its high-temperature sensitivity. In this study, we perform controlled experiments and identify calcium ions as the dominant current carriers. By analyzing infrared spectra at different temperatures, we find that the temperature response is due to changes in ion mobility, rather than variations in ion number density. We compare measurements and modeling results of nine different multivalent ions and find a positive correlation between their temperature responses and their binding energy to pectin. While these findings are fundamental in nature, they provide relevant guidance for the future design of temperature-sensitive polymers and other materials for organic electronics.

Ion transport in thermally responsive pectin film

A tunable frequency acoustic rectifier that is a granular crystal composed of a statically compressed one-dimensional array of particles in contact, containing a light mass defect near a boundary. The tunable frequency acoustic rectifier is nonlinear and contains tunable pass and stop bands in their dispersion relation. Vibrations at selected frequencies applied to the granular crystal from the side near the defect will cause the system to bifurcate at a critical input amplitude and subsequently jump to quasiperiodic and chaotic states with broadband frequency content. Some of this frequency content lies within the pass bands and will propagate through the crystal. Vibrations at the same frequencies applied to the other side of the granular crystal will not bifurcate, and little energy is transmitted.

Bifurcation-based acoustic switch and rectifier

We present a tabletop-scale realization of a tunable metamaterial platform to control surface acoustic waves (SAWs). The platform comprises an array of ferromagnetic beads controlled with permanent magnets, arranged atop an elastic substrate. We demonstrate the possibility of shifting the beads resonances and, in turn, tuning the SAWs bandgaps.

Controlling surface acoustic waves via magnetically-modulated contact resonances

In this letter, we provide the first experimental demonstration of amplitude-dependent dispersion tuning of surface acoustic waves interacting with nonlinear resonators. Leveraging the similarity between the dispersion properties of plate edge waves and surface waves propagating in a semi-infinite medium, we use a setup consisting of a plate with a periodic arrangement of bead-magnet resonators along one of its edges. Nonlinear contact between the ferromagnetic beads and magnets is exploited to realize nonlinear local resonance effects. First, we experimentally demonstrate the nonlinear softening nature and amplitude-dependent dynamics of a single bead-magnet resonator on both rigid and compliant substrates. Next, the dispersion properties of the system in the linear regime are investigated. Finally, we demonstrate how the interplay of nonlinear local resonances with plate edge waves gives rise to amplitude-dependent dispersion properties. The findings will inform the design of more versatile surface acoustic wave devices that can passively adapt to loading conditions.

Chiara Daraio

Papers

Engineered thin films with ultra-low thermal expansion coefficient for deployable or deformable space structures

Ion transport in thermally responsive pectin film

Bifurcation-based acoustic switch and rectifier

Controlling surface acoustic waves via magnetically-modulated contact resonances

Experimental Evidence of Amplitude-Dependent Surface Wave Dispersion via Nonlinear Contact Resonances