Condensation heat transfer of R22, R410A and R32 inside a multiport mini-channel tube

In the present study, the heat transfer coefficients are investigated experimentally for condensation of R22, R410A, and R32 inside a horizontal multiport rectangular mini-channel tube. The multiport tube having nine channels in 0.969mm of hydraulic diameter, the experimental measurements were carried out at the fixed saturation temperature of 48oC, by the varying refrigerant mass flux from 50 to 500kg/m2s, and the heat flux range from 3 to 15kW/m2. The test section was a double tube of counter-flow type; the refrigerant was flowed condensation inside the test tube by heat exchange with cooling water flowing in the annular side. The temperature and pressure of refrigerant were measured at the inlet and outlet of the test section, and the surface temperature of tubes was measured. The effect of vapor quality, mass flux and heat flux on condensation characteristics is clarified. The experiment results were compared with the existing heat transfer coefficient correlations, and a new correlation was proposed using the present data with good prediction

In-situ micromotion compensation of trapped ions by Rabi oscillation and direct scanning of dc voltages

Micromotion is detrimental to accurate qubit control of trapped ions, thus measuring and minimizing it is crucial. In this paper, we present a simple method to measure and minimize micromotion of trapped ions by Rabi oscillation combined with direct scanning of dc voltages. The approach utilizes the qubit control scheme itself, and eliminates the need to install additional experimental setups, or compromise the trapping stability by adjusting the intensity or frequency of the trapping lasers or fields. Accordingly, the method enables in-situ measurement of micromotion during qubit controls of the ions, while achieving a comparable level of sensitivity to commonly used techniques.Comment: 11 pages, 6 figures, submitted to Optics Expres

Implementation and Performance Evaluation of the LRFU Replacement Policy

Recently, a new block replacement policy called the LRFU (Least Recently/Frequently Used) policy was proposed that subsumes both the LRU and LFU policies, and provides a spectrum of replacement policies between them. In this paper, we describe an implementation of the LRFU replacement policy in the FreeBSD 2.1.5 and present a performance evaluation of the implementation using the SPEC SDET benchmark. The results show that the new policy gives up to a 30% performance improvement over the LRU block replacement policy. 1: Introduction The speed gap between processors and disks is becoming wider as VLSI technologies advance at an enormous rate. One solution to overcoming this speed gap is to use a caching technique which keeps disk blocks that are likely to be accessed in the near future in DRAM memory. For example, in the UNIX operating system, a portion of DRAM memory, commonly called the buffer cache [2], is reserved for that specific purpose. Since the buffer cache size is necessaril..

Implementation and performance evaluation of the LRFU replacement policy

Recently, a new block replacement policy called the LRFU (Least Recently/Frequently Used) policy was proposed that subsumes both the LRU and LFU policies, and provides a spectrum of replacement policies between them. In this paper, we describe an implementation of the LRFU replacement policy in the FreeBSD 2.1.5 and present a performance evaluation of the implementation using the SPEC SDET benchmark. The results show that the new policy gives up to a 30% performance improvement over the LRU block replacement policy

Transparent and Colorless Polyimides Containing Multiple Trifluoromethyl Groups as Gate Insulators for Flexible Organic Transistors with Superior Electrical Stability

A suitable insulating polymer material that is compatible with the fabrication process of organic transistors and has excellent electrical properties is critically required for the next-generation flexible organic electronics. In this study, using a one-step polymerization method, we synthesized two different solution-processable polyimides (PIs) incorporated with abundant trifluoromethyl groups. Not only were the two resulting PIs.termed 6FDA-6FDAM-PI and 6FDA-TFMB-PI.well soluble in organic solvents, but also they showed transparent and colorless optical properties. The fluorinated PI films showed smooth surface topographies and surface energy values that were appropriate for their use in bottom-gate organic transistors. Organic transistors separately fabricated with 6FDA-6FDAM-PI and 6FDA-TFMB-PI as the gate insulators showed excellent device performance and electrical stability under various testing conditions, especially for pentacene-based devices. The excellent performance of the devices with fluorinated PIs was attributed to the enhanced microstructure of the organic semiconductor and the fluorine-rich characteristic of the underlying gate insulator. Furthermore, organic complementary circuits including the basic logic gates of NOT, NOR, and NAND were demonstrated using these devices

Chain Vacancies in 2D Crystals

Defects in bulk crystals can be classified into vacancies, interstitials, grain boundaries, stacking faults, dislocations, and so forth. In particular, the vacancy in semiconductors is a primary defect that governs electrical transport. Concentration of vacancies depends mainly on the growth conditions. Individual vacancies instead of aggregated vacancies are usually energetically more favorable at room temperature because of the entropy contribution. This phenomenon is not guaranteed in van der Waals 2D materials due to the reduced dimensionality (reduced entropy). Here, it is reported that the 1D connected/aggregated vacancies are energetically stable at room temperature. Transmission electron microscopy observations demonstrate the preferential alignment direction of the vacancy chains varies in different 2D crystals: MoS2 and WS2 prefer 11> direction, while MoTe2 prefers 10> direction. This difference is mainly caused by the different strain effect near the chalcogen vacancies. Black phosphorous also exhibits directional double- chain vacancies along direction. Density functional theory calculations predict that the chain vacancies act as extended gap (conductive) states. The observation of the chain vacancies in 2D crystals directly explains the origin of n-type behavior in MoTe2 devices in recent experiments and offers new opportunities for electronic structure engineering with various 2D materials © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim4

Regioregular Low Bandgap Polymer with Controlled Thieno[3,4-b]thiophene Orientation for High-Efficiency Polymer Solar Cells

The regioregular p-type copolymer PBDTTT-C-T composed of TT-BDT-TT-BDT repeating units (TT = thieno[3,4-b]thiophene, BDT = benzo[1,2-b:4,5-b']dithoiphene) and perfectly controlled TT orientation was synthesized. The optical, thermal, and electrochemical properties of the regioregular PBDTTT-C-T were characterized and compared with the random PBDTTT-C-T without structural regioregularity. The regioregular PBDTTT-C-T showed lower optical bandgap (1.55 eV) and higher degree of crystallinity compared to the random PBDTTT-C-T. The inverted bulk heterojunction PSCs based on the regioregular PBDTTT-C-T exhibited a power conversion efficiency as high as 7.79%, which is 19% higher than the random PBDTTT-C-T-based PSCs. It was found that the improved photoabsorption and increase in charge carrier mobility due to high regioregularity of conjugated polymer backbones and effective ordering between polymer chains are the most likely reasons for enhancement of power conversion efficiency in PSCs. © 2015 American Chemical Society.