Pulling Effect Research Articles

MOCVD Growth and Investigation of InGaN/GaN Heterostructure Grown on AlGaN/GaN-on-Si Template

The investigation of the III-V nitride-based driving circuits is in demand for the development of GaN-based power electronic devices. In this work, we aim to grow high-quality InGaN/GaN heterojunctions on the n-channel AlGaN/GaN-on-Si high electron mobility transistor (HEMT) templates to pursue the complementary p-channel conductivity to realize the monolithic integrated circuits. As the initial step, the epitaxial growth is optimized and the structure properties are investigated by comparing with the InGaN/GaN heterojunctions grown on GaN/sapphire templates. It is found that both the In composition and relaxation degree are higher for the InGaN/GaN on the HEMT template than that on the sapphire substrate. The crystalline quality is deteriorated for the InGaN grown on the HEMT template, which is attributed to the poor-quality GaN channel in the HEMT template. Further analysis indicates that the higher In incorporation in the InGaN layer on the HEMT template may be caused by the higher relaxation degree due to the compositional pulling effect. An increase in the growth temperature by 20 °C with optimized growth condition improves the crystalline quality of the InGaN, which is comparable to that on GaN/sapphire even if it is grown on a poor-quality GaN channel.

InGaN Platelets: Synthesis and Applications toward Green and Red Light-Emitting Diodes.

In this work, we present a method to synthesize arrays of hexagonal InGaN submicrometer platelets with a top c-plane area having an extension of a few hundred nanometers by selective area metal-organic vapor-phase epitaxy. The InGaN platelets were made by in situ annealing of InGaN pyramids, whereby InGaN from the pyramid apex was thermally etched away, leaving a c-plane surface, while the inclined {101̅1} planes of the pyramids were intact. The as-formed c-planes, which are rough with islands of a few tens of nanometers, can be flattened with InGaN regrowth, showing single bilayer steps and high-quality optical properties (full width at half-maximum of photoluminescence at room temperature: 107 meV for In0.09Ga0.91N and 151 meV for In0.18Ga0.82N). Such platelets offer surfaces having relaxed lattice constants, thus enabling shifting the quantum well emission from blue (as when grown on GaN) to green and red. For single InGaN quantum wells grown on the c-plane of such InGaN platelets, a sharp interface between the quantum well and the barriers was observed. The emission energy from the quantum well, grown under the same conditions, was shifted from 2.17 eV on In0.09Ga0.91N platelets to 1.95 eV on In0.18Ga0.82N platelets as a result of a thicker quantum well and a reduced indium pulling effect on In0.18Ga0.82N platelets. On the basis of this method, prototype light-emitting diodes were demonstrated with green emission on In0.09Ga0.91N platelets and red emission on In0.18Ga0.82N platelets.

Large-Signal Modeling and Experimental Design Automation of Self-Isolated Harmonic Oscillator for Pulling Effect Reduction

A class of self-isolated harmonic oscillator (SIHO) with a feedback-loop structure is able to significantly reduce the pulling effect without involving extra circuit complexity such as a buffer amplifier. In the first part of this paper, the operation principle of the SIHO is theoretically studied through equivalent circuit models and X-parameter techniques. Closed-form expressions are derived to represent the respective linear and nonlinear equivalent impedances of SIHO subnetworks perturbed by varied load and injected signals. A conventional feedback-loop oscillator structure delivering the fundamental tone is used for comparative study. Such a modeling technique reveals the physical principle and behavior parameters that have an impact on the pulling effect. The experimental verification of the SIHO operation principle and modeling is presented as the second part of this paper. To this end, a harmonic measurement and design system is proposed and implemented for the design of an exemplary SIHO, which delivers a 4-GHz signal with 16.6-dBm power, 28% dc-RF efficiency, and −136.5-dBc/Hz phase noise at 1-MHz offset. The design process does not rely on circuit simulation software packages or a prior knowledge of the large-signal model of transistors, thus demonstrating the concept of a model-free nonlinear circuit design automation based on the experimental optimization. The SIHO circuit model is validated with the measured X-parameters of its nonlinear subnetwork.

Characterization of Polarization Pulling in Fiber Optical Parametric Amplifiers

In fiber optical parametric amplifiers (FOPAs), the output states of polarization (SOPs) of both the signal and the idler are affected by the pump SOP through the polarization pulling effect. We proposed a normalized model to characterize the general dynamics of polarization pulling in degenerated pump FOPAs. By using this model, we determined the relationship between the output degree of polarization (DOP) and the gain of the FOPAs over three orders of magnitude changes in polarization-mode dispersion (PMD) coefficient. We demonstrated numerically that when fibers with typical PMD coefficients are used, the output signals of the FOPAs can achieve higher DOP than those of co-propagating fiber Raman amplifiers, which depends on whether the parametric gain is sufficiently large to compensate the PMD-induced phase mismatch. We also found that for FOPAs using different types of fibers with moderate PMD coefficients, this DOP-gain relationship exhibits highly similar behaviors. We thus adopted a set of modified empirical formulas to analyze this relationship. This formula can also describe the relationship between the output DOP and the conversion efficiency of the idler. The results indicate that in all cases studied, FOPAs achieve much stronger polarization pulling to the idlers than the signals.

Study on the Influence of Monetary Policy on Real Estate Price in China

The real estate industry has been in a stage of rapid development since 2000, and its pulling effect on economic growth is very significant, but it has continued to develop at a rapid pace over the years. The rising prices that follow have also had a lot of impact on all aspects of society and economy. However, a country’s macroeconomic control policy, especially monetary policy, has a very important impact on the development of the real estate industry. For example, the expansionary monetary policy since 2008 has increased the money supply, so that the real estate market investment and consumption rising, house prices accelerated. Although there are also a lot of restrictions of macroeconomic policy on the rise of house prices, the effect is not obvious. Therefore, it is necessary to make use of the policy means to regulate the real estate industry in order to achieve healthy development. This paper first analyzes the mechanism of monetary policy influencing real estate price, and then discusses the effect of monetary policy on real estate market by using empirical research method. It is found that both money supply and interest rate will have an impact on real estate price. Finally, combined with the conclusion of the analysis, some policy suggestions are put forward to improve the monetary policy system for the healthy development of the real estate industry.

Nonconjugated α,ω-Diolefin/Propylene Copolymerization to Long Chain-Branched Polypropylene by Ziegler–Natta Catalyst: Overcoming Steric Hindrance by Introducing an Extra Electronic Pulling Effect

Synthesis of long chain-branched polypropylene (LCB-PP) by propylene copolymerization with nonconjugated α,ω-diolefin is a steric hindrance-prevailing reaction process which involves in copolymeriz...

What the CO2 Siphon Tells Us

The debate over the mechanisms responsible for the flow rates of simple tube siphons (Fig. 1) has received much attention in the physics education and general physics literature in the past decade. Particularly with regard to the driving mechanism for water siphons, some suggested explanations emphasize contributions, or lack thereof, from the atmospheric pressure on the tank supply-side, while other sources argue for, and against, the pulling effect of the weight of the water in the long side of the siphon, in a chain-like action via intermolecular forces, as the dominant mechanism driving the siphoning action. What is more, the atmospheric model has recently become the principal competitor to the chain pulling model, neither of which in our assessment supplies the essential explanation of the dominant driving mechanism of simple tube siphons, nor in any way accounts for their near steady-state flow rates.

Effect of strain modification on crystallinity and luminescence of InGaN/GaN multiple quantum wells grown by MOCVD

The effects of compressive strain modification on green-emitting InGaN/GaN multiple quantum wells (MQWs) are comprehensively investigated by inserting a bulk InGaN prestrain underlying layer with different indium doping contents. Systematic measurements of the structural, morphological and optical properties are conducted. Better crystallinities are obtained for both modified samples, in which the density of V-pits is reduced from 4.0 × 108 /cm2 in the original sample to 1.9 × 108 /cm2 and 3.3 × 108 /cm2. Compared with the conventional InGaN/GaN MQWs, the photoluminescence (PL) emission wavelength of the strain-modified MQW structure with an InGaN (In = 0.03) prestrain layer is blueshifted by ~ 6 nm as a result of the reduced built-in piezoelectric field, while the other MQW structure with an InGaN (In = 0.1) layer has an ~ 15 nm redshift, which is attributed to not only the ~ 1% increase in the In content in the QWs and the ~ 0.6 nm increase in the well width due to the composition pulling effect, but also the ~ 0.19 degree of strain relaxation in the InGaN QWs. The low-temperature PL (LTPL) intensities of both samples are approximately twice as large as that of the conventional one, whereas the internal quantum efficiency is three times larger at the maximum. These tremendous improvements are mainly due to the weakened quantum confined stark effect and stronger carrier localization states, as confirmed by LTPL and temperature-dependent PL (TDPL) measurements.

A pyruvate carbon flux tugging strategy for increasing 2,3-butanediol production and reducing ethanol subgeneration in the yeast Saccharomyces cerevisiae

BackgroundThe yeast Saccharomyces cerevisiae is a promising host cell for producing a wide range of chemicals. However, attempts to metabolically engineer Crabtree-positive S. cerevisiae invariably face a common issue: how to reduce dominant ethanol production. Here, we propose a yeast metabolic engineering strategy for decreasing ethanol subgeneration involving tugging the carbon flux at an important hub branching point (e.g., pyruvate). Tugging flux at a central glycolytic overflow metabolism point arising from high glycolytic activity may substantially increase higher alcohol production in S. cerevisiae. We validated this possibility by testing 2,3-butanediol (2,3-BDO) production, which is routed via pyruvate as the important hub compound.ResultsBy searching for high-activity acetolactate synthase (ALS) enzymes that catalyze the important first-step reaction in 2,3-BDO biosynthesis, and tuning several fermentation conditions, we demonstrated that a stronger pyruvate pulling effect (tugging of pyruvate carbon flux) is very effective for increasing 2,3-BDO production and reducing ethanol subgeneration by S. cerevisiae. To further confirm the validity of the pyruvate carbon flux tugging strategy, we constructed an evolved pyruvate decarboxylase (PDC)-deficient yeast (PDCΔ) strain that lacked three isozymes of PDC. In parallel with re-sequencing to identify genomic mutations, liquid chromatography–tandem mass spectrometry analysis of intermediate metabolites revealed significant accumulation of pyruvate and NADH in the evolved PDCΔ strain. Harnessing the high-activity ALS and additional downstream enzymes in the evolved PDCΔ strain resulted in a high yield of 2,3-BDO (a maximum of 0.41 g g−1 glucose consumed) and no ethanol subgeneration, thereby confirming the utility of our strategy. Using this engineered strain, we demonstrated a high 2,3-BDO titer (81.0 g L−1) in a fed-batch fermentation using a high concentration of glucose as the sole carbon source.ConclusionsWe demonstrated that the pyruvate carbon flux tugging strategy is very effective for increasing 2,3-BDO production and decreasing ethanol subgeneration in Crabtree-positive S. cerevisiae. High activity of the common first-step enzyme for the conversion of pyruvate, which links to both the TCA cycle and amino acid biosynthesis, is likely important for the production of various chemicals by S. cerevisiae.

Molecular mechanism of viscoelastic polymer enhanced oil recovery in nanopores.

Polymer flooding is a promising chemical enhanced oil recovery (EOR) method, which realizes more efficient extraction in porous formations characterized with nanoscale porosity and complicated interfaces. Understanding the molecular mechanism of viscoelastic polymer EOR in nanopores is of great significance for the advancement of oil exploitation. Using molecular dynamics simulations, we investigated the detailed process of a viscoelastic polymer displacing oil at the atomic scale. We found that the interactions between polymer chains and oil provide an additional pulling effect on extracting the residual oil trapped in dead-end nanopores, which plays a key role in increasing the oil displacement efficiency. Our results also demonstrate that the oil displacement ability of polymer can be reinforced with the increasing chain length and viscoelasticity. In particular, a polymer with longer chain length exhibits stronger elastic property, which enhances the foregoing pulling effect. These findings can help to enrich our understanding on the molecular mechanism of polymer enhanced oil recovery and provide guidance for oil extraction engineering.

Intrinsic frequency tuning of terahertz quantum-cascade lasers

We have studied the intrinsic frequency tuning of several terahertz (THz) quantum-cascade lasers (QCLs) based on a hybrid design. With increasing driving current, most QCLs exhibit either a redshift or a blueshift, while some QCLs show both. An oscillator model describes the observed behavior. The accuracy of the model is affected by the complexity of the current-dependent gain spectra of the THz QCLs. Numerical simulations demonstrate a cavity pulling effect insofar as the tuning behavior depends on the resonator losses and on the width of the gain spectra.

Ultrasound-guided sialo-irrigation with a saline-air mixture as the contrast medium.

Ultrasound (US)-guided salivary gland irrigation is a popular conservative treatment method that improves the success rate and reduces complications of the sialo-irrigation procedure. US is routinely used for evaluation of various salivary gland diseases because of its easy accessibility and absence of ionizing radiation. US also allows dynamic studies with real-time imaging during diagnostic or surgical procedures. However, conventional US images have limitations in salivary duct visualization. Although US images acquired with saline irrigation have improved visualization because of ductal system dilation by the pulling effect, the resultant image quality remains insufficient for diagnosis. Therefore, contrast agents are required during US-guided sialo-irrigation procedures to produce diagnostic image quality. Air bubbles in saline solution have high echogenicity and enhance image quality by acting as a US contrast agent. The aim of this study was to assess the clinical significance of US-guided sialo-irrigation with a saline-air contrast medium, to estimate its diagnostic and treatment efficacy, and to examine the procedure in two patients. In the study, two patients underwent US-guided salivary gland irrigation with air-bubble mixed saline solution. During the procedure, we were able to visualize the salivary gland duct and subsequently irrigate and clean the inside of the duct. As a result, the patients' symptoms were relieved and saline solution mixed with air bubbles was confirmed to be an effective contrast agent.

Asymmetric and partial injection locking of a three-terminal spin-torque oscillator

We measure the injection locking of a three-terminal spin-torque oscillator (STO) excited by spin-orbit torque. The device consists of a magnetic tunnel junction on top of a Pt wire. A DC and an AC current are applied through the Pt wire to induce the oscillations and injection lock the STO, respectively. The injection locking is studied at fMW ≈ f0 or at fMW ≈ 2f0, where fMW is the microwave frequency and f0 is the free running frequency of the STO. The frequency response is qualitatively different from the injection locking in STOs generally reported experimentally and theoretically. Whereas typical phase-locking behavior is observed at fMW ≈ 2f0, the injection locking at fMW ≈ f0 is only partial and exhibits a strongly asymmetric frequency response. Defining the frequency deviation range as the frequency range where the STO differs from its free running frequency, we show that the asymmetric interaction is characterized by a pulling effect present on only one side of the frequency deviation range, the presence of a sideband inside the frequency deviation range, and an interaction of the STO with the microwave current that is wider than the frequency deviation range.

Reaching a few 10-15 long-term stability of integrating sphere cold atom clock

We present the long-term stability of the integrating sphere cold atom clock (ISCAC) and analyze its systematic limitations. The relative frequency instability of 2.6×10−15 is reached for an averaging time of 2×105 s. The second-order Zeeman effect and the cavity pulling effect in ISCAC, which would induce the frequency drift from the clock transition, are analyzed. The analytical and experimental results indicate that the cavity pulling effect is the main contribution to the long-term frequency instability of the ISCAC. Further technical improvements to the microwave cavity are also discussed.

An Empirical Study of the Economic Impact of the MICE Industry in China Using Interregional Input-output Models

In the field of event activities, the study on the economic impact of MICE is relatively weak compared to sports activities. How to integrate all the industries and regions related to the MICE to avoid distortion and leakage is one of the difficulties in the study of the economy impact of the MICE. This study is the first time to use the interregional input-output model (IRI0) to calculate the intraregional and interregional influence power of the MICE industry in 30 provinces by merging the 12 industrial sectors that related to MICE. Taking the Canton Fair as a case, we have an empirical analysis of the indirect economic impact of the MICE. The research results show that China's MICE industry has a strong pulling effect on the national economy, and almost all regions will have a mutual diffusion effect. As for total output, the influence power of the MICE industry shows obvious differences in the East Coast and Midwest. There is still room for development in China's MICE industry. Case studies show that the indirect economic impact of the 104th Canton Fair is about 16.243 billion yuan (the highest proportion in Guangdong, 35.09%), the ratio of direct and indirect impact is 1:2.94, five industrial sectors such as wholesale and retail trade affected by the Canton Fair, the total proportion is 77%.

Viscous flow around spherical particles in different arrangements

Viscous flow past two or more spherical particles in direction parallel or perpendicular to the line connecting the body centers is studied numerically at Reynolds number up to 200. The FEM is used to simulate the flow structure for different arrangements and diameters of the spheres. The drag and lift coefficients are calculated as functions of the flow velocity and the distance between the spheres. The results show the downstream spheres face a reduced drag compared to a single sphere and that the upstream one changes its drag coefficient according to the distance between the bodies. In the case of side by side arranged spheres, an effect of repulsion exists up to a certain separation distance and after that a weak pulling effect appears. A configuration of three (or more) spherical particles arranged in „V“ formation was examined where one body is set to be a leading and the others are located symmetrically up and down behind it. The flow characteristics are studied when the angle behind the leading sphere vary from 40° to 180°. This configuration supposes stronger interaction between the bodies due to the influence of the wakes behind the first sphere to the downstream ones and to the lift forces appeared.

A study of the influence of regional environmental expenditure on air quality in China: the effectiveness of environmental policy.

Based on the panel data model, data on environmental expenditures, the air quality index, economic aggregates, industrial structures, etc., of seven seriously polluted cities in China, from the period 2007-2015, were collected, and this paper estimates the general relationship between environmental expenditures and the air quality index. Besides, the impact of the fuel tax policy on air quality as well as on the relationship between environmental expenditure and the air quality index is tested using the method of regression discontinuity. We find that there is a long-term equilibrium relationship between environmental expenditure and air quality index as well as a 0.0507% positive effect of the former on the latter. Second, for Beijing, Taiyuan, Chongqing, and Lanzhou, a 1% increase in environmental expenditure leads to 0.0773, 0.0125, 0.0965, and 0.0912% decreases in the air quality index, respectively; however, for Shijiazhuang, Ji'nan, and Urumqi, effect of environmental expenditure on air quality is insignificant. Third, both economic growth and optimization of the industrial structure can lead to an improvement of air quality. Fourth, since the implementation of the fuel tax policy in 2009, the air quality of the sample cities has improved, and the pulling effect of environmental expenditure on the air quality index has decreased from 0.0507 to 0.0048%. Our findings cannot only clarify the effect of environmental expenditures on air quality but can also objectively judge the effectiveness of environmental policies of China to a certain extent. It may benefit Chinese government to effectively govern air pollution with fiscal tools in conjunction with economic and environmental characteristics.

Spatial Econometric Research on the Relationship between Highway Construction and Regional Economic Growth in China: Evidence from the Nationwide Panel Data

Based on spatial panel data from 2010 to 2016 in China, this paper makes an empirical analysis on the relationship between highway construction and regional economic growth by means of spatial econometric model. The results show that there is positive spatial correlation on regional economic growth in China, and strong spatial dependences between some provinces and cities appear, specifically, Hebei, Beijing, Tianjin, Shanghai, Zhejiang and other eastern coastal areas show high-high agglomeration trend, the Pearl River Delta region presents high-low agglomeration trend; In terms of nationwide provinces and municipalities, a province’s highway construction investment for their own province and the neighboring provinces has pulling effect on economic growth to a certain extent, and the direct effect is more obvious.

Multipulse dynamics of a passively mode-locked semiconductor laser with delayed optical feedback.

Passively mode-locked semiconductor lasers are compact, inexpensive sources of short light pulses of high repetition rates. In this work, we investigate the dynamics and bifurcations arising in such a device under the influence of time delayed optical feedback. This laser system is modelled by a system of delay differential equations, which includes delay terms associated with the laser cavity and feedback loop. We make use of specialised path continuation software for delay differential equations to analyse the regime of short feedback delays. Specifically, we consider how the dynamics and bifurcations depend on the pump current of the laser, the feedback strength, and the feedback delay time. We show that an important role is played by resonances between the mode-locking frequencies and the feedback delay time. We find feedback-induced harmonic mode locking and show that a mismatch between the fundamental frequency of the laser and that of the feedback cavity can lead to multi-pulse or quasiperiodic dynamics. The quasiperiodic dynamics exhibit a slow modulation, on the time scale of the gain recovery rate, which results from a beating with the frequency introduced in the associated torus bifurcations and leads to gain competition between multiple pulse trains within the laser cavity. Our results also have implications for the case of large feedback delay times, where a complete bifurcation analysis is not practical. Namely, for increasing delay, there is an ever-increasing degree of multistability between mode-locked solutions due to the frequency pulling effect.

An experimental study of the performance of low-molecular weight polymer for enhanced heavy oil recovery in a heterogeneous media

The goal of enhanced oil recovery is to improve sweep efficiency in the reservoir by the injection of artificial materials in order to reduce the trapped oil saturation. In this study, the application of an anionic polyacrylamide polymer was investigated for heavy oil recovery based on the results of rheological measurements and oil recovery experiments. The properties of the polymer solution were interpreted by the use of well-known rheological models and oil recovery experiments were performed using a heterogeneous two-dimensional glass micromodel saturated with heavy oil of 270 cP. To provide a better understanding of the microscopic efficiency of the process, analysis of continuously provided pictures during the experiments by the use of image processing technique was performed. Rheological results combined with microscopic observations revealed that the non-Newtonian behavior of the solution enhances the sweep efficiency of the both pore throats and pore bodies. Macroscopic observations showed the ultimate oil recovery of 56% and dramatic improvement in breakthrough time during polymer flood in comparison to water flood. In addition, the microscopic pictures disclosed that the pulling effect and stripping mechanisms are responsible mechanisms for the high microscopic sweep efficiency during polymer flooding.