[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).

Laser Material Processing

This review article attempts to provide a comprehensive review of the recent progress in the so-called resistive random access memories (RRAMs) First, a brief introduction is presented to describe the construction and development of RRAMs, their potential for broad applications in the fields of nonvolatile memory, unconventional computing and logic devices, and the focus of research concerning RRAMs over the past decade Second, both inorganic and organic materials used in RRAMs are summarized, and their respective advantages and shortcomings are discussed Third, the important switching mechanisms are discussed in depth and are classified into ion migration, charge trapping/de-trapping, thermochemical reaction, exclusive mechanisms in inorganics, and exclusive mechanisms in organics Fourth, attention is given to the application of RRAMs for data storage, including their current performance, methods for performance enhancement, sneak-path issue and possible solutions, and demonstrations of 2-D and 3-D crossbar arrays Fifth, prospective applications of RRAMs in unconventional computing, as well as logic devices and multi-functionalization of RRAMs, are comprehensively summarized and thoroughly discussed The present review article ends with a short discussion concerning the challenges and future prospects of the RRAMs

Recent progress in resistive random access memories: Materials, switching mechanisms, and performance

Semiconductor-based photocatalysts and photoelectrochemical cells for solar fuel generation: a review

In this study, a memristor with the simple structure Ag/poly(3,4-ethylenedioxythiophene):poly (styrenesulphonate) (PEDOT:PSS)/Ta was fabricated. Essential synaptic plasticity and learning behaviours were emulated using this memristor, including short-term plasticity, long-term plasticity, spike-timing-dependent plasticity and spike-rate-dependent plasticity. Important time constants were extracted from these synaptic modifications, which are associated with brain learning and memory functions. It was clearly demonstrated that the movement of the Ag interface upon the initiation of a redox reaction accounts for the resistive switching mechanism of our memristor. The conducting path in the polymer layer and the elastic effect of the polymer matrix were suggested to be considered in the memory and learning processes. Moreover, the energy band diagram of our memristor was drawn after the cross-sectional transmission electron microscopy images were analysed. It was found that a natural p–n junction in the PEDOT:PSS/Ta compound was formed. This resulted in rectifying, high resistance and low power consumption. Our device structure may be considered a feasible prototype for integrating memristors into a large-scale neuromorphic circuit.

Synaptic plasticity and learning behaviours mimicked through Ag interface movement in an Ag/conducting polymer/Ta memristive system

The electrocaloric effect (ECE) of BaTiO3multilayer thick film was investigated by direct calorimetric measurement. The ECE increases monotonically with the enhancement of applied field. The maximum ECE occurs above T c and shifts to higher temperature with increasing applied field. Under an ultrahigh field of 800 kV/cm, it exhibits a giant ECE of ΔT  = 7.1 K and ΔS  = 10.1 J/kg · K at 80 °C. The ECE heat follows a general power-law relation with the varying rate of applied field within a certain range. A high cooling power (∼50 W/kg) is achieved based on the net-cooling resulting from the different varying rates of rising and falling fields.

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The giant electrocaloric effect and high effective cooling power near room temperature for BaTiO₃ thick film

BaTiO 3 ceramics were prepared by conventional sintering technique with a special emphasis on the effects of sintering temperature (1100–1230 °C) on the crystalline structure and piezoelectric properties. XRD patterns indicated that the crystallographic structure changed from tetragonal phase to orthorhombic one with raising sintering temperature from 1160 °C to 1180 °C. Domains were shaped in a stripe and a herringbone in orthorhombic samples for BaTiO 3 ceramics. The domain width and domain density increased with raising sintering temperature. The BaTiO 3 ceramic sintered at 1190 °C showed the excellent electrical properties, d 33  = 355 pC/N, k p  = 40%, P r  = 10.2 μC/cm 2 , respectively, which are originated to the contributions of both the crystallographic structure transition and nano-domain.

Phase structure and nano-domain in high performance of BaTiO3 piezoelectric ceramics

This paper presents a systematic exploration of modifying the electrocaloric effect (ECE) in BaTiO3 ceramics by rare-earth substitution (Ba0.94R0.04TiO3, R = La, Ce, Nd, Sm, Eu, Gd, Dy, Er). All samples exhibit a dense microstructure after sintering in the temperature range of 1350–1450 °C, and they exhibit a high resistivity of ∼1011 Ω cm except for Er doped samples due to the amphoteric incorporation of Er. The rare-earth doping changes the lattice symmetry where the tetragonal distortion enhances with the decrease in the rare-earth ionic radius. Accordingly, the ferroelectric and ECE properties are modified and the first-order phase transition is diffused. The Curie temperature and latent heat increases, and the polarization intensity is strengthened with the decrease of the doping ionic radius, while the peak of ECE ΔT widens and shifts to a higher temperature. The samples show a large ECE value of ∼0.35 K m MV−1 over a wide temperature range from room temperature to 140 °C, which provides a series of top-level ECE materials.

A systematic modification of the large electrocaloric effect within a broad temperature range in rare-earth doped BaTiO3 ceramics

Pentacene thin film transistors (TFTs) were fabricated by the organic molecular beam deposition method. The TFTs were characterized in order to study the effect of thermal annealing on the morphology and carrier mobility of the transistors. For all the TFT samples the mobility exhibited an Arrhenius relationship with temperature, indicating a thermally activated transport that could be explained by the carrier trap and thermal release transport mechanism. Therefore, in order to investigate the annealing effect, we tested the data for a significant period of time after annealing until the temperature recovered to room temperature, so that the thermal activation effect was screened and possible effects of thermal expansion and stress were also ruled out. As a result, we found that only with a temperature below a critical temperature of approximately 45°C could annealing improve the mobility, while annealing with T>50°C would decrease the mobility compared to the value before annealing. Atomic force microsco...

Dong Guo

Papers

Synaptic plasticity and learning behaviours mimicked through Ag interface movement in an Ag/conducting polymer/Ta memristive system

The giant electrocaloric effect and high effective cooling power near room temperature for BaTiO₃ thick film

Phase structure and nano-domain in high performance of BaTiO3 piezoelectric ceramics

A systematic modification of the large electrocaloric effect within a broad temperature range in rare-earth doped BaTiO3 ceramics

Effect of annealing on the mobility and morphology of thermally activated pentacene thin film transistors