Hybrid Qm/Mm Simulation Of The Hydration Phenomena Of Dipalmitoylphosphatidylcholine Headgroup

The polar headgroup of dipalmitoylphosphatidylcholine (DPPC) molecule both in gas phase and aqueous Solution is investigated by the hybrid quantum mechanical/molecular mechanical (QM/MM) method, in which the polar head of DPPC molecule and the bound water molecules are treated with density functional theory (DFT), while the apolar hydrocarbon chain of DPPC molecule is treated with MM method. It is demonstrated that the hybrid QM/MM method is both accurate and efficient to describe the conformations of DPPC headgroup. Folded structures of headgroup are found in gas phase calculations. In this work, both monohydration and polyhydration phenomena are investigated. In monohydration, different water association sites are studied. Both the hydration energy and the quantum properties of DPPC and water molecules are calculated at the DFT level of theory after geometry optimization. The binding force of monohydration is estimated by using the scan method. In polyhydration, more extended conformations are found and hydration energies in different polyhydration styles are estimated. (C) 2008 Elsevier Inc. All rights reserved.

Self-healing Techniques for RF and mm-Wave Transmitters and Receivers

With continuing advances in CMOS technology, feature sizes of modern Silicon chip-sets have gone down drastically over the past decade. In addition to desktops and laptop processors, a vast majority of these chips are also being deployed in mobile communication devices like smart-phones and tablets, where multiple radio-frequency integrated circuits (RFICs) must be integrated into one device to cater to a wide variety of applications such as Wi-Fi, Bluetooth, NFC, wireless charging, etc. While a small feature size enables higher integration levels leading to billions of transistors co-existing on a single chip, it also makes these Silicon ICs more susceptible to variations. A part of these variations can be attributed to the manufacturing process itself, particularly due to the stringent dimensional tolerances associated with the lithographic steps in modern processes. Additionally, RF or millimeter-wave communication chip-sets are subject to another type of variation caused by dynamic changes in the operating environment. Another bottleneck in the development of high performance RF/mm-wave Silicon ICs is the lack of accurate analog/high-frequency models in nanometer CMOS processes. This can be primarily attributed to the fact that most cutting edge processes are geared towards digital system implementation and as such there is little model-to-hardware correlation at RF frequencies.

All these issues have significantly degraded yield of high performance mm-wave and RF CMOS systems which often require multiple trial-and-error based Silicon validations, thereby incurring additional production costs. This dissertation proposes a low overhead technique which attempts to counter the detrimental effects of these variations, thereby improving both performance and yield of chips post fabrication in a systematic way. The key idea behind this approach is to dynamically sense the performance of the system, identify when a problem has occurred, and then actuate it back to its desired performance level through an intelligent on-chip optimization algorithm. We term this technique as self-healing drawing inspiration from nature's own way of healing the body against adverse environmental effects. To effectively demonstrate the efficacy of self-healing in CMOS systems, several representative examples are designed, fabricated, and measured against a variety of operating conditions.

We demonstrate a high-power mm-wave segmented power mixer array based transmitter architecture that is capable of generating high-speed and non-constant envelope modulations at higher efficiencies compared to existing conventional designs. We then incorporate several sensors and actuators into the design and demonstrate closed-loop healing against a wide variety of non-ideal operating conditions. We also demonstrate fully-integrated self-healing in the context of another mm-wave power amplifier, where measurements were performed across several chips, showing significant improvements in performance as well as reduced variability in the presence of process variations and load impedance mismatch, as well as catastrophic transistor failure. Finally, on the receiver side, a closed-loop self-healing phase synthesis scheme is demonstrated in conjunction with a wide-band voltage controlled oscillator to generate phase shifter local oscillator (LO) signals for a phased array receiver. The system is shown to heal against non-idealities in the LO signal generation and distribution, significantly reducing phase errors across a wide range of frequencies.

Finite element analysis on a circular wedge prism with 400 mm diameter

The paper comprehensively analyzes the distortions of a circular wedge prism with 400 mm diameter in a scanner by method of optical-mechanical-thermal integrating analysis. The structure and intensity of the prism assembly is verified and checked, and the surface deformations of the prism under gravity load, as well as the thermo-elastic distortions of the prism, are analyzed in detail and evaluated, which is finally contrasted with the measured values of Zygo Mark interferometer. The results show: the maximal distortion of the prism assembly is 10 nm magnitude and the maximal stress is 0.441 Mpa, which has much tolerance to the precision requirement of structure and the admissible stress of material; the influence of heat effect on the surface deformations of prism is proved to be far greater than the influence of gravity load, so some strict temperature-controlled measures are to be considered when the scanner is used. (c) 2006 Elsevier GmbH. All rights reserved.

Phi 140 mm sapphire crystal growth by temperature gradient techniques and its color centers

Sapphire crystals, 140 mm in diameter and 90 turn in height, have been grown by temperature gradient techniques (TGT). The growth direction of the boule was fixed by means of Lane X-ray diffraction. A prominent 204 nm absorption band in TGT-Al2O3. which does not appear in single crystals grown by Czochralski method has been studied. Analysis further substantiates the F-center model of this band. Two relatively weaker bands absorbing at 232 nm and 254 nm were ascribed to F+ centers. F-type centers concentration was determined using Smakula's equation. (c) 2005 Elsevier B.V. All rights reserved.

Spectral hole-burning of Eu3+: Y2SiO5 crystal at 579.62 mm

By using an Ar+ ion laser, a tunable Rh 6G dye laser(Linewidth : 0.5 cm(-1)) and a Coherent 899-21 dye laser as light sources and using a monochromator and a phase-locking amplifier, the optical properties of Eu3+ : Y2SiO5 crystal were detected. Persistent spectral hole burning (PSHB) were also observed in (5)Do-(7)Fo transition in the crystal at the temperature of 16 K. For 15 mW dye laser (Wavelength : 579.62 nm) burning the crystal for 0.1 s a spectral hole with about 80 MHz hole width were detected and the hole can been keep for longer than 10 h.

Evaluating boundary dependent errors in QM/MM simulations.

Hybrid quantum mechanics/molecular mechanics (QM/MM) simulations provide a powerful tool for studying chemical reactions, especially in complex biochemical systems. In most works to date, the quantum region is kept fixed throughout the simulation and is defined in an ad hoc way based on chemical intuition and available computational resources. The simulation errors associated with a given choice of the quantum region are, however, rarely assessed in a systematic manner. Here we study the dependence of two relevant quantities on the QM region size: the force error at the center of the QM region and the free energy of a proton transfer reaction. Taking lysozyme as our model system, we find that in an apolar region the average force error rapidly decreases with increasing QM region size. In contrast, the average force error at the polar active site is considerably higher, exhibits large oscillations and decreases more slowly, and may not fall below acceptable limits even for a quantum region radius of 9.0 A. Although computation of free energies could only be afforded until 6.0 A, results were found to change considerably within these limits. These errors demonstrate that the results of QM/MM calculations are heavily affected by the definition of the QM region (not only its size), and a convergence test is proposed to be a part of setting up QM/MM simulations.

Import substitution of combination wire rope. Part 2. Production and standardisation of 17 mm dia combination wire rope.

The prototype combination wire rope (Cift-CWR 1) developed for deep sea trawling was further studied for improvement, optimisation of efficiency and standardization. A series of improved prototype combination wire ropes (Cift-CWR 2 to 6) were twisted and evaluated their mechanical properties and reported in this paper with recommendations for a standard 17mm dia combination wire rope of 6S (7C+8+1 Scr) + 6 Crs(6+1+1 Crc) construction.

QM/MM simulation of liquid water with an adaptive quantum region.

The simulation of complex chemical systems often requires a multi-level description, in which a region of special interest is treated using a computationally expensive quantum mechanical (QM) model while its environment is described by a faster, simpler molecular mechanical (MM) model. Furthermore, studying dynamic effects in solvated systems or bio-molecules requires a variable definition of the two regions, so that atoms or molecules can be dynamically re-assigned between the QM and MM descriptions during the course of the simulation. Such reassignments pose a problem for traditional QM/MM schemes by exacerbating the errors that stem from switching the model at the boundary. Here we show that stable, long adaptive simulations can be carried out using density functional theory with the BLYP exchange-correlation functional for the QM model and a flexible TIP3P force field for the MM model without requiring adjustments of either. Using a primary benchmark system of pure water, we investigate the convergence of the liquid structure with the size of the QM region, and demonstrate that by using a sufficiently large QM region (with radius 6 Å) it is possible to obtain radial and angular distributions that, in the QM region, match the results of fully quantum mechanical calculations with periodic boundary conditions, and, after a smooth transition, also agree with fully MM calculations in the MM region. The key ingredient is the accurate evaluation of forces in the QM subsystem which we achieve by including an extended buffer region in the QM calculations. We also show that our buffered-force QM/MM scheme is transferable by simulating the solvated Cl(-) ion.

Tests of an adaptive QM/MM calculation on free energy profiles of chemical reactions in solution.

We present reaction free energy calculations using the adaptive buffered force mixing quantum mechanics/molecular mechanics (bf-QM/MM) method. The bf-QM/MM method combines nonadaptive electrostatic embedding QM/MM calculations with extended and reduced QM regions to calculate accurate forces on all atoms, which can be used in free energy calculation methods that require only the forces and not the energy. We calculate the free energy profiles of two reactions in aqueous solution: the nucleophilic substitution reaction of methyl chloride with a chloride anion and the deprotonation reaction of the tyrosine side chain. We validate the bf-QM/MM method against a full QM simulation, and show that it correctly reproduces both geometrical properties and free energy profiles of the QM model, while the electrostatic embedding QM/MM method using a static QM region comprising only the solute is unable to do so. The bf-QM/MM method is not explicitly dependent on the details of the QM and MM methods, so long as it is possible to compute QM forces in a small region and MM forces in the rest of the system, as in a conventional QM/MM calculation. It is simple, with only a few parameters needed to control the QM calculation sizes, and allows (but does not require) a varying and adapting QM region which is necessary for simulating solutions.

Measuring the composition of AlGaN layers in GaN based structures grown on 150 mm Si substrates using (2 0 5) reciprocal space maps

A critical element for the successful growth of GaN device layers on Si is accurate control of the AlGaN buffer layers used to manage strain. Here we present a method for measuring the composition of the AlGaN buffer layers in device structures which makes use of a one-dimensional x-ray detector to provide efficient measurement of a reciprocal space map which covers the full compositional range from AlN to GaN. Combining this with a suitable x-ray reflection with low strain sensitivity it is possible to accurately determine the Al fraction of the buffer layers independent of their relaxation state. © 2013 IOP Publishing Ltd.

Growth kinetics of 1-2 mm and 3-4 mm colonies of Nostoc sphaeroides (Cyanophyta) in outdoor culture

Nostoc sphaeroides Kutzing was cultivated in paddlewheel-driven raceway ponds and the growth kinetics of 1-2 mm and 3-4 mm colonies of N. sphaeroides was studied. The biomass productivities in 2.5 m(2) raceway ponds inoculated with 1-2 mm and 3-4 mm colonies were 5.2 and 0.25 g dry wt m(-2) stop d(-1), respectively. Furthermore, differently sized colonies showed different relative water content, total soluble carbohydrates, chlorophyll a content and density of filaments. This is the first report on mass culture of N. sphaeroides under outdoor conditions.

GaAs基InAlAs/InGaAs MM-HEMT材料生长与器件制作

Submitted by zhangdi (zhangdi@red.semi.ac.cn) on 2009-04-13T11:45:31Z

GaAs 基InAlAs/InGaAs MM-HEMT 材料生长与器件制作

Submitted by zhangdi (zhangdi@red.semi.ac.cn) on 2009-04-13T11:45:31Z