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This paper presents the characteristics of HgCdTe mid-wavelength infrared (MWIR) electron-initiated avalanche photodiodes (e-APDs) as a function of temperature under different biases. The devices show a low dark current density of the order of ${10^{ - 7}} \text{A/cm}^2$ at 80 K when the reverse bias voltage is below 4 V, with an exponential gain above 100 at − 8 V. Low excess noise factor of around 1.2 is also demonstrated for the devices at 80 K. The dark current and gain characteristics at different temperatures are analyzed, along with the device simulation results. A varied-temperature impact ionization model for MWIR e-APD devices is adopted based on the experimental results. In addition, a significant increase of the dark current in the APD device is observed at high temperature under large reverse bias, which can be associated with the local electric field redistribution due to the accumulation of holes in the depletion region at high temperatures. The analysis presented in this work paves the way to achieve a high operating temperature (HOT) of the HgCdTe APD with further optimization.

High-speed photodetector operating at 850 nm wavelength with a large diameter and high quantum efficiency is desirable to meet the growing demands of short-reach optical links for high-performance computing systems. Zero-bias operation of the high-speed photodetectors can reduce power consumption, minimize system complexity of the optical transceivers and reduce the radiation damage in a harsh environment. Traditional p-i-n photodetectors for 850 nm applications often require a high reverse bias to accelerate the carrier transport for high-speed data transmission. In this work, we demonstrate a high-speed and low dark current modified uni-traveling-carrier photodiode based on GaAs/AlGaAs at 850 nm wavelength operating under zero bias with a quantum efficiency of 73%. The 3-dB bandwidth of the 20 μm and 40 μm diameter devices is 22.5 GHz and 13.3 GHz, respectively. A clear eye pattern is demonstrated at a 25.8 Gbit/s data rate for the device under zero-bias operation. To the best of our knowledge, this photodetector demonstrates the highest 3-dB bandwidth among all the zero-bias 850 nm photodetectors reported to date.

Seeking effective solutions to control and mitigate the interaction between drilling fluids and clay formations has been a challenge for many years, and various shale inhibitors have shown excellent results in problematic shale formations around the world. Herein, the hyperbranched polyamine (HBPA) inhibitor with a higher ratio of amine groups and obvious tendentiousness in protonation was successfully synthesized from ethylenediamine, acryloyl chloride and aziridine by five steps, in which the metal-organic framework (MOF) was employed as a catalyst for ring-open polycondensation (ROP). The structure and purity were confirmed by nuclear magnetic resonance hydrogen spectroscopy and high-performance liquid chromatography (HPLC) respectively. The HBPA displays more excellent performance than EDA and KCl widely applied in the oil field. After aging at 80°C and 180°C, the YP of a slurry system containing 25 wt.% bentonite and 2 wt.% HBPA are just 8.5 Pa and 5.5 Pa (wt.%: percentage of mass), respectively. The swelling lengths of 2 wt.% HBPA are estimated to be 1.78 mm, which falls by 70% compared with that of freshwater. Under a hot rolling aging temperature of 180°C, the HBPA system demonstrates a significant inhibition with more than 85% shale cuttings recovery rate and is superior to conventional EDA and KCl. Mechanism analysis further validates that the HBPA can help to increase the zeta potential.

Magnetic stiffness is one of the important stability parameters of high temperature superconducting levitation systems. Till to now, great efforts have been made to understand levitation properties including flux penetration, magnetization curves, levitation force, ac susceptibilities, etc. In this paper we present a quadratic approximation method for the limit of magnetic stiffness in a high temperature superconducting levitation system based on Kim’s critical state model and Ampère law. The system is composed with a cylindrical permanent magnet (PM) and a coaxial high temperature superconductor (HTS). It is found that the limit of magnetic stiffness depends upon both the penetration history of shielding currents distribution in HTS and applied magnetic field gradients. Furthermore, the influence of the physical parameters, such as critical current density in HTS and applied magnetic field, on the limits of magnetic stiffness is investigated in detail. The obtained results display that magnetic stiffness decreases with the increasing of critical current density, since shielding currents have not penetrated into the large portion of the HTS. With the increase of applied magnetic field, the magnetic stiffness obtain a larger magnification factor. It is related to the increase of the shielding current penetration volume and the internal magnetic field in HTS.

The linearity of high power photodetectors is the limiting factor to the dynamic range performance of analog optical links and microwave photonics applications. In this work, we characterized the third order intermodulation distortion (IMD3) of a uni-traveling carrier photodiode with InGaAs/GaAsSb type-II multiple quantum wells absorber. The 10 μm diameter photodiode shows a third order output intercept point of 36.6 dBm at 200 MHz and 12.9 dBm at 25 GHz, under reverse bias of −5 V and photo current of 15 mA. Combining with the measured device parameters, an equivalent circuit model based simulation is carried out, and the general trend of the simulated IMD3 is consistent with the measurement results. By separately involving the nonlinear mechanisms, the source of the nonlinearity is studied in detail.

We report a high-speed partial-depleted-absorber photodiode based on GaAs/AlGaAs with 3-dB bandwidth of 17.9 GHz at 850nm wavelength. Device exhibits responsivity of 0.466 A/W and dark current of 1.09 pA under −3 V bias. © 2020 The Author(s)

High-speed, high power-handling photodiodes with sufficiently low amplitude-to-phase (AM-to-PM) conversion coefficients are critical components in the systems that generate ultra-stable microwave signals. This paper reports the AM-to-PM conversion in modified uni-traveling carrier photodiodes (MUTC-PDs) with 20 µm and 40 µm diameters. The contributions of AM-to-PM conversions from the carrier transit-time and impedance were quantified systematically based on a photocurrent-dependent nonlinear equivalent circuit model. It is found that the AM-to-PM conversion in 40 µm PD is dominated by the nonlinear impedance, while for 20 µm PD, the transit-time impacts the AM-to-PM conversion more significantly. These results imply that, for large PDs, the nonlinearity of the PDs’ photocurrent-dependent impedance is the critical reason causing AM-to-PM conversion.

We report the demonstration of a normal-incidence p-i-n germanium-tin ( Ge 0.951 Sn 0.049 ) photodetector on silicon-on-insulator substrate for 2 μm wavelength application. The DC and RF characteristics of the devices have been characterized. A dark current density under − 1 V bias of approximately 125 mA/ cm 2 is achieved at room temperature, and the optical responsivity of 14 mA/W is realized for illumination wavelength of 2 μm under − 1 V reverse bias. In addition, a 3 dB bandwidth ( f 3 dB ) of around 30 GHz is achieved at − 3 V , which is the highest reported value among all group III–V and group IV photodetectors working in the 2 μm wavelength range. This work illustrates that a GeSn photodetector has great prospects in 2 μm wavelength optical communication.

On the basis of the conventional PID control algorithm, a modified adaptive PID (MA-PID) control algorithm is presented to improve the steady-state and dynamic performance of closed-loop systems. The proposed method has a straightforward structure without excessively increasing the complexity and cost. It can adaptively adjust the values of the control parameters (Kp, Ki and Kd) by following a new control law. Simulation results show that the line transient response of the MA-PID is better than that of the adaptive digital PID because the differential coefficient Kd is introduced to changes. In addition, experimental results based on a FPGA indicate that the MA-PID control algorithm reduces the recovery time by 62.5% in response to a 1V line transient, 50% in response to a 500mA load transient, and 23.6% in response to a steady-state deviation, when compared with the conventional PID control algorithm.

The 'white pollution' produced by wasted flexible polyvinyl chloride (PVC) with poor degradation ability and the potential fire hazard of PVC with high flammability not only restrict their application but also cause serious environmental problem. Thus platinum-doped titanate nanotubes/reduced graphene oxide (denoted as Pt-TNTs/rGO) nanocomposites were prepared by a facile method in order to improve the visible photodegradation and get rid of the 'white pollution' as well as flame retardancy of PVC. The photodegradation activity and flame retardancy effect of the as-prepared Pt-TNTs/rGO nanocomposites were investigated by ultraviolet and visible light irradiation as well as cone calorimetry. Results show that the Pt-TNTs/rGO-PVC nanocomposites exhibit enhanced visible light photodegradation performance (with mass loss being 6.5%) during 15 day exposure to solar irradiation, and good flame retardancy (providing a 44% reduction of total smoke release as compared with that of PVC matrix). Besides, Pt-TNTs/rGO-PVC nanocomposites show suppressed smoke and reduced CO production as compared with the PVC matrix. These results demonstrate that Pt-TNTs/rGO not only get rid of the 'white pollution' as the photocatalyst but also improve the fire safety of PVC as the flame retardant. This could be ascribed to the combination effect between Pt-TNTs and rGO. The present research, hopefully, is to pave a potential pathway to constructing polymer-matrix composites with desired photodegradation activity and flame retardancy, thereby shedding light on simultaneously dealing with the 'white pollution' and high flammability of polymer matrix like PVC.

A single-input fuzzy PID (SIF-PID) controller is proposed in this paper to improve the dynamic performance of dc-dc buck converter. The fuzzy logic adjusts the three parameters of PID controller adaptively by detecting the output voltage. Establishment of double-input rule table with Toeplitz structure is presented by analysising the system response curve. One-dimension rule vectors are derived based on the slope λ of the parallel diagonal lines in rule table to reduce the computational burden. The genetic algorithm is utilized to optimize the coefficient λ to guarantee the simplified rule vectors are equivalent to the original rule table in terms of control performance. Effectiveness of the proposed controller is validated by simulation results.

Saccharomyces mating-type switching results from replacement by gene conversion of the MAT locus with sequences copied from one of two unexpressed donor loci, HML or HMR. MATa cells recombine with HMLα ∼90% of the time, whereas MATα cells choose HMRa 80%–90% of the time. HML preference in MATa is controlled by the cis-acting recombination enhancer (RE) that regulates recombination along the entire left arm of chromosome III. Comparison of RE sequences between S. cerevisiae, S. carlsbergensis, and S. bayanus defines four highly conserved regions (A, B, C, and D) within a 270-bp minimum RE. An adjacent E region enhances RE activity. Multimers of region A, D, or E are sufficient to promote selective use of HML. Regions A, D, and E each bind in vivo the transcription activator forkhead proteins Fkh1p and Fkh2p and their associated Ndd1p, although there are no adjacent open reading frames (ORFs). Deletion of FKH1significantly reduces MATa's use of HML, as does mutation of the Fkh1/Fkh2-binding sites in a multimer of region A. We conclude that Fkh1p regulates MATa donor preference through direct interaction with RE.

In order to learn about the evolutionary conservation of the recombination enhancer (RE) that controls donor preference during mating type switching in Saccharomyces cerevisiae, we have cloned a 13 kb region from S. servazzii. We find that the order of four genes surrounding the RE in S. cerevisiae (PRD1, KAR4, SPB1 and PBN1) is preserved in S.servazzii. However, there is an additional ORF in S. servazzii between PRD1 and KAR4 that is not homologous to any gene in S. cerevisiae or to genes in other organisms. Despite a 75–79% amino acid identity for KAR4 and SPB1, respectively, the S. servazzii sequence did not carry a well-conserved RE sequence and these sequences lacked RE function when introduced into S. cerevisiae. The S. servazzii region contains a sequence that supports autonomous DNA replication in S. cerevisiae and may represent a homologue of ARS304. The S. servazziii sequence has Genbank Accession No. BankIt359091 AF307954. Copyright © 2001 John Wiley & Sons, Ltd.

This paper introduces a hydraulic pumping unit for offshore platform that has been developed by Shengli Petroleum Administration and successfully applied to the oil field. This pumping unit adopts closed return circuit. In order to reclaim power and save energy, two sets of accumulators are set respectively at the entrance and exit of the hydraulic power pump. The energy is stored in the accumulators during the down stroke and the stored energy is released to lift the oil well load during the lift stroke. This pumping unit adopts the unique full hydraulic reversing and controlling return circuit, the hydraulic cylinder is set in the working barrel under the wellhead. In order to collect the signal of the piston arriving the top and bottom dead center, the both stroke holes are set in the inner tube of the hydraulic cylinder. The wellhead's installation area and height are equivalent to the flowing wellhead's. The height of this wellhead is less than 3 meters measuring from casing head. The structure of the hydraulic station is compact, the area that it contains is small, so it can be used on the offshore platform which area is limited. By developing of the hydraulic pumping unit for offshore platform, the mature technology in sucker rode oil production mode will be applied to offshore oil production, its application will greatly extend well repair cycle and obtain enormously economic benefit.

Abstract In order to raise the recovery ratio of maturing field, Shengli Petroleum Administration has carried out a project of sidetracking horizontal wells in existing straight wells from the latter of 1995. This paper will introduce the completion technique used to sidetrack horizontal wells within 5 1/2in casing including geologic condition, reservoir type, selection and design of completion type, researches and design of completion tubing along with downhole tools and wellbore treatment etc.. In addition, the question of reservoir protection is discussed, and a few conclusions were made. P. 399

Background Enzymatic biodiesel production by transesterification in solvent media has been investigated intensively, but glycerol, as a by-product, could block the immobilized enzyme and excess n-hexane, as a solution aid, would reduce the productivity of the enzyme. Esterification, a solvent-free and no-glycerol-release system for biodiesel production, has been developed, and two-step catalysis of soybean oil, hydrolysis followed by esterification, with Yarrowia lipolytica lipase is reported in this paper. Results First, soybean oil was hydrolyzed at 40°C by 100 U of lipase broth per 1 g of oil with approximately 30% to 60% (vol/vol) water. The free fatty acid (FFA) distilled from this hydrolysis mixture was used for the esterification of FFA to fatty acid ethyl ester by immobilized lipase. A mixture of 2.82 g of FFA and equimolar ethanol (addition in three steps) were shaken at 30°C with 18 U of lipase per 1 gram of FFA. The degree of esterification reached 85% after 3 hours. The lipase membranes were taken out, dehydrated and subjected to fresh esterification so that over 82% of esterification was maintained, even though the esterification was repeated every 3 hours for 25 batches. Conclusion The two-step enzymatic process without glycerol released and solvent-free demonstrated higher efficiency and safety than enzymatic transesterification, which seems very promising for lipase-catalyzed, large-scale production of biodiesel, especially from high acid value waste oil.