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

Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

http://science.sciencemag.org/content/sci/345/6196/542.full.pdf

Interface engineering of highly efficient perovskite solar cells

A novel non-fullerene electron acceptor (ITIC) that overcomes some of the shortcomings of fullerene acceptors, for example, weak absorption in the visible spectral region and limited energy-level variability, is designed and synthesized. Fullerene-free polymer solar cells (PSCs) based on the ITIC acceptor are demonstrated to exhibit power conversion effi ciencies of up to 6.8%, a record for fullerene-free PSCs.

An electron acceptor challenging fullerenes for efficient polymer solar cells.

We introduce an external-load-assisted thin film channel crack growth technique to measure the subcritical crack growth properties of thin films (i.e., crack velocity, v, versus the strain energy release rate, G), and demonstrate it using 250-nm-thick SiNx films on poly(ethylene terephthalate) substrates. The main particularity of this technique is that it requires a polymer substrate to allow loading to large strains (in order to induce channel cracking) without substrate fracture. Its main advantages are to provide a full v-G curve with a single specimen while relying on a simple specimen preparation and straightforward crack growth characterization. Importantly, the technique can be employed for a much larger range of thin films compared to the residual-stress-driven, thin film channel crack growth tests, including ultrathin films and thin film with residual compressive stresses. The restrictions to a proper use of this technique, related to the (visco)plastic deformation of the substrate, are discussed.

Note: A single specimen channel crack growth technique applied to brittle thin films on polymer substrates

Activated gaseous species generated adjacent a carbon contaminated surface affords in-situ cleaning. A device for removing carbon contamination from a surface of the substrate includes (a) a housing defining a vacuum chamber in which the substrate is located; (b) a source of gaseous species; and (c) a source of electrons that are emitted to activate the gaseous species into activated gaseous species. The source of electrons preferably includes (i) a filament made of a material that generates thermionic electron emissions; (ii) a source of energy that is connected to the filament; and (iii) an electrode to which the emitted electrons are attracted. The device is particularly suited for photolithography systems with optic surfaces, e.g., mirrors, that are otherwise inaccessible unless the system is dismantled. A method of removing carbon contaminants from a substrate surface that is housed within a vacuum chamber is also disclosed. The method employs activated gaseous species that react with the carbon contaminants to form carbon containing gaseous byproducts.

Method for in-situ cleaning of carbon contaminated surfaces

In this work, we investigate several approaches to the development of encapsulation of organic electronics. A combination of plasma enhanced chemical vapor deposition, atomic layer deposition, and physical vapor deposition are used to make single layer and multilayer thin films and study the impact of structure on effective water vapor transmission rates. It was found that multilayer thin films consisting of organic and inorganic layers as well as inorganic nanolaminates provided the highest performance barrier films with effective water vapor transmission rates less than 5 × 10−5 g/m2/day. Materials such as atomic layer deposition deposited Al 2 O 3 also showed excellent initial performance, but were found to be susceptible to corrosion from water. Combining alumina with other materials was found to improve the long-term performance of the alumina films. Integration of these films into organic solar cell platforms was shown to effectively maintain shelf lifetime performance for more than 7000 h.

The development of thin film barriers for encapsulating organic electronics

Heterogeneous integration is important to create multi-functionality in future electronic devices. However, few thermal studies of the interfaces formed in these integrated devices have been reported before. Recently, integrated interfaces by surface-activated bonding were found to have high thermal boundary conductance, which provides a solution for heat dissipation of GaN and β-Ga2O3-based power electronics. Here, we review the recent progress on the interfacial thermal transport across heterogeneously integrated interfaces, including transferred van der Waals force bonded interfaces, surface-activated bonded interfaces, plasma bonded interfaces, and hydrophilic bonded interfaces. This Perspective specifically focuses on applications of thermal management strategies of electronics, especially power electronics. Finally, the challenges, such as high-throughput thermal measurements of buried interfaces, thermal property-structure relations of interfaces bonded under different conditions, theoretical understanding of interfacial thermal transport, and device demonstrations, are pointed out. 

Perspective on thermal conductance across heterogeneously integrated interfaces for wide and ultrawide bandgap electronics

We present a systematic study to investigate the effects of nonframework cations and the role of phonon scattering mechanisms on the thermal transport properties of zeolite LTA, via experiment and semiempirical lattice dynamics calculations. Our study is motivated by the increasing interest in accurate measurements and mechanistic understanding of the thermal transport properties of zeolite materials. The presence of a nanostructured pore network, extra-framework cations, and tunable framework structure and composition confer interesting thermophysical properties to these materials, making them a good model system to investigate thermal transport in complex materials. Continuous films of zeolite LTA with different nonframework cations (Na+, K+, and Ca+2) were synthesized and characterized. The thermal conductivity was measured using the three-omega method over a wide range of temperature (150–450 K). These are the first thermal conductivity measurements performed on bulk LTA, so they are more accurate tha...

Samuel Graham

Papers

Note: A single specimen channel crack growth technique applied to brittle thin films on polymer substrates

Method for in-situ cleaning of carbon contaminated surfaces

The development of thin film barriers for encapsulating organic electronics

Perspective on thermal conductance across heterogeneously integrated interfaces for wide and ultrawide bandgap electronics

Effects of nonframework metal cations and phonon scattering mechanisms on the thermal transport properties of polycrystalline zeolite LTA films