Minimum Mismatch Research Articles

A multi-layer constrained spectral k-embedded clustering methodology approach for intelligent partitioning of power grid to enhance resiliency in transmission networks

The intentional controlled islanding by intelligent partitioning of the power grid is considered as essential to protect the grid from cascading events, faults, and High Impact Low Probability (HILP) events. To enhance the resilience, stability, and security of the power grid, the proposed model in this paper intentionally divides the affected power network into islands. This paper presents an intelligent partitioning approach to create an islanding solution through multilayer graphs using spectral clustering. The controlled islanding algorithm uses a multi-criteria objective function that considers the correlation coefficients among the frequency of the buses and minimal disturbances in the real and reactive power. The proposed control technique is implemented in two phases. The first phase employs correlation coefficients between frequency of the buses and modularity clustering to identify clusters of coherent buses. During the second stage, all nodes are categorised into groups using Multi-level constrained Spectral Clustering (ML-CSC) to determine the solution for Intentional controlled Islanding that satisfies bus coherency with the minimum level of disruptions to real and reactive power flows across the boundaries. The proposed algorithm for resolving the generator coherency issue and an intelligent islanding solution is demonstrated by simulation experiments conducted on an IEEE 39-bus transmission test system developed in DIGSILENT Powerfactory version 2023. The MATLAB version R2023a is used to construct the ML-CSC control method. The results demonstrated that the proposed ML-CSC algorithm substantially impacts the functioning of the power system, enabling the formation of intelligent islanding during abnormal conditions. Also, the results clearly show that instead of using single-layer spectral clustering, the multi-layer spectral clustering yields a better intentional islanding solution with minimum power flow mismatch which enhances the transient stability of the islands.

GR.4 Circadian rhythm influences ischemic core and penumbra volumes in pediatric and young adult populations

Background: Circadian rhythms are implicated in timing of stroke onset and infarct progression in adults, but this has not been studied in pediatric/young adult populations. Methods: We queried the RAPID Insights database from centers in USA for unique patients <25 years with a CTP (10/05/2018-09/29/2023) and a minimum ischemic core volume (defined as relative cerebral blood flow (rCBF) reduction of <30%) of >0 cc and minimum mismatch of >0 cc. Imaging time was subdivided into three epochs: Nigh (23:00 h-06:59 h), Day (07:00 h-14:59 h), and Evening (15:00 h-22:59 h). We analyzed age by pre-defined strata: <2 years, 2-5, 6-11, 12-18 and 19-25. Perfusion parameters (core, perfusion volume, mismatch ratio) were analyzed using descriptive statistics. Results: 836 patients were included; 52.3% were in the 19-25 category. Median ischemic cores were larger during the Night (23.0cc [10.0 – 58.0]) compared to Day (19.0cc [8.0-42.0]) or Evening (15.0cc [7.0-33.0]), p=0.009. There was a trend towards larger perfusion volumes in the Night epoch. In the 19-25 group, perfusion volumes were significantly larger at Night (127.5cc [51.5 – 203.5]) compared to Day (74.0cc [33.0 – 139.0]) or Evening (76.0cc [38.0 – 157.5]), with larger mismatch volumes at Night. Conclusions: This is the first study to demonstrate diurnal fluctuations in perfusion parameters in a predominantly pediatric cohort.

Establish a Graded Method to Avoid HLA Class I Antibodies Corresponding Antigen and Combining HLAMatchmaker Application in Improving the CCI Value after Platelet Transfusion for Patients with IPTR

To establish a graded method to avoid mean fluorescence intensity (MFI) threshold of HLA Class I antibodies corresponding antigen, and the HLAMatchmaker program has been used to select the minimum mismatch value of donor-patient epitopes. Evaluate the application value of combining both methods in selecting HLA compatible platelets (PTL) for patients with immune platelet transfusion failure (IPTR) in improving platelet the corrected count increment (CCI). A total 7 807 PLT cross-matching compatible were performed by the solid-phase red cell adherence (SPRCA) method for 51 IPTR patients. The Luminex single antigen flow cytometry was used to detect HLA Class I antibodies in patients, and detected the MFI value for different specificity antigens of HLA Class I antibodies, was graded into strong positive group (MFI>4 000, level 1), medium positive group (1 000< MFI≤4 000, 2), weak positive group (500< MFI≤1 000, 3), and one negative control group (MFI≤500). The results of 7 807 SPRCA their negative/positive reaction wells were enrolled and statistically analyzed in different grades and the four groups, the statistical differences between the four groups were compared. Multiple applications for the select HLA Class I compatible donor events were made for patients in two cases, and HLAMatchmaker program was used to calculate the number of HLA Class I epitopes mismatches between the donors and patients. The donor with the minimum number of epitopes mismatches was selected, while avoiding the corresponding antigens of HLA Class I antibodies in levels 1 and 2, the provision of HLA compatible platelets for IPTR. After the transfusions, the CCI value of the platelet transfusion efficacy evaluation index was calculated, and the clinical evaluation of the transfusion effect was obtained through statistical analysis. There were statistically significant differences in the positive results of SPRCA immunoassay among the strong positive group, medium positive group, and weak positive group of 51 IPTR patients with different specific of HLA -I class antibodies and corresponding antigens(all P <0.001). The positive results showed a range from high to low, with strong positive group>medium positive group>weak positive group. There were a statistical difference among between the strongly positive or moderately positive groups and the negative control group(P <0.001). There was no statistical difference between the weakly positive group and the negative control group(P >0.05). The strong positive group was set as the corresponding specific HLA Class I site corresponding antigen grade 1 avoidance threshold, the medium positive group as the grade 2 avoidance thresholds, and the weak positive group as the grade 3 avoidance threshold. In the case of donor platelet shortage, it is not necessary to avoid the weak positive group. Avoiding the strategy of donor antigens and HLAMatchmaker program scores ≤7 corresponding to HLA Class I antibodies of levels 1 and 2, with CCI values>4.5×109/L within 24 hours, can obtain effective clinical platelet transfusion conclusions. When selecting HLA Class I compatible donors for IPTR patients, the grading avoids HLA Class I antibodies corresponding to donor antigens, and the donor selection strategy with the minimum scores of HLAMatchmaker program is comprehensively selected. The negative result confirmed by platelet cross-matching experiments has certain practical application value for improving platelet count in IPTR patients.

Voltage-controlled cryogenic Boolean logic gates based on ferroelectric SQUID and heater cryotron

The recent progress in quantum computing and space exploration led to a surge in interest in cryogenic electronics. Superconducting devices such as Josephson junction, Josephson field effect transistor, cryotron, and superconducting quantum interference device (SQUID) are traditionally used to build cryogenic logic gates. However, due to the superconducting nature, gate-voltage-based control of these devices is extremely difficult. Even more challenging is to cascade the logic gates because most of these devices require current bias for their operation. Therefore, these devices are not as convenient as the semiconducting transistors to design logic gates. Here, to overcome these challenges, we propose a ferroelectric SQUID (FeSQUID) based voltage-controlled logic gates. FeSQUID exhibits two different critical current levels for two different voltage-switchable polarization states of the ferroelectric. We utilize the polarization-dependent (hence, voltage-controllable) superconducting to resistive switching of FeSQUID to design Boolean logic gates such as Copy, NOT, AND, and OR gates. The operations of these gates are verified using a Verilog-A-based compact model of FeSQUID. Finally, to demonstrate the fanning out capability of FeSQUID-based logic family, we simulate a two-input XOR gate using FeSQUID-based NOT, AND, and OR gates. Together with the ongoing progress on FeSQUID-based non-volatile memory, our designed FeSQUID-based logic family will enable all FeSQUID-based cryogenic computer, ensuring minimum mismatch between logic and memory blocks in terms of speed, power consumption, and fabrication process.

Controlled dynamic variation of interfacial electronic and optical properties of lithium intercalated ZrO2/MoS2 vdW heterostructure

Efficient strategies for modifying the characteristics of van der Waals (vdW) layered materials in a precise and reversible mode remain challenging. Our suggested method for customization entails the implementation of layer-sliding and intercalation. In this work, a norm-conserving approach within the context of density functional theory has been used to examine the electronic and optical properties of two-dimensional (2D) van der Waals heterostructure (vdWHS), which is modeled by using 2D zirconium dioxide (1T-ZrO2) and molybdenum disulfide (1T-MoS2) monolayers of similar phase. Both contributing monolayers have similar lattice structures, with a minimum lattice mismatch of 0.83 %, and have corrugation on both sides that can successfully retain foreign species at the vdW-gap. In the next step, interfacial engineering through Li-intercalation and layer-sliding was employed to modify physical properties of the vdWHS. It is the worth mentioning that a narrow bandgap of 0.102 eV (0.22 eV) has been observed in the unintercalated ZrO2/MoS2 vdWHS when employing PW-LDA (hybrid-functional). Li-intercalation and sliding process significantly influenced the electronic properties of the studied vdWHS. Furthermore, un-slided and fully-slided Li-intercalated vdWHS exhibit an increase in the vdW-gap by 3.78 % and 27.14 %, respectively, as compared to unintercalated vdWHS. To further understand the electrical behaviour at the interface of contributing monolayers, a comparative study has also been made for the variation in the planar average charge density difference, charge transfer, and interface dipole moment for unintercalated and intercalated vdWHS. In the unintercalated vdWHS, the calculated values of ΔQ and μ(z) provide evidence of significant charge transfer from 1T-ZrO2 to 1T-MoS2 before sliding, whereas in the fully-slided vdWHS, there is 80.11 % more charge transfer from 1T-MoS2 to 1T-ZrO2. Li-intercalation increases the magnitude of ΔQ (by 90.27 %) near 1T-MoS2, indicating a sufficient quantity of charge transfer from the 1T-MoS2 monolayer. The results of the anisotropic analysis show that the calculated in-plane and out-of-plane components of the real and imaginary parts of the dielectric function differ significantly. The optical absorption and energy losses of Li-intercalated vdWHS experience a substantial decrease of about 90 % and 50 %, respectively, as compared to unintercalated vdWHS. Our employed method promotes the notion that interfacial engineering through simultaneous layer-sliding and intercalation approach can be used to regulate and modify the physical properties of 2D insulator/metal based vdWHS.

Effect of Mg Addition on Inclusions in the Welding Heat-Affected Zone of Pressure Vessel Steels

With the development of the pressure vessel industry, high-energy wire welding has a great future. However, this means higher demands on the weldability of pressure vessel steels. Controlling inclusions via oxidative metallurgy is a reliable method of improving the weldability of pressure vessel steels. Hence, in this paper, experimental steels with different Mg element mass fractions were prepared using vacuum metallurgy. Simulated welding for high-heat input welding was carried out using the Gleeble-2000 welding thermal simulation test machine. The inclusions in the welding heat-affected zone (HAZ) in the experimental steels were observed using an optical microscope (OM) and scanning electron microscope (SEM). The compositions of the inclusions were analyzed using an energy-dispersive spectrometer (EDS). The research results indicated that the addition of Mg could increase the number density of the inclusions in the welding HAZ. With the addition of Mg from 0 to 5 wt.%, the total number density of the inclusions increased from 133 to 687 pieces/mm2, and the number density of the inclusions with a size of 0–5 μm2 increased from 122 to 579 pieces/mm2. The inclusions in the experimental steel welding HAZ with Mg elements were mainly elliptical composite inclusions composed of (Mg-Zr-O) + MnS. Moreover, MnS precipitated on the surface of the Mg-containing inclusions in the welding HAZ. Intragranular acicular ferrite (IAF) nucleation was primarily induced via the minimum lattice mismatch mechanism, supplemented with stress-strain energy and inert interface energy mechanisms.

High-throughput interface prediction and generation scheme: The case of β -Ga2O3/AlN interfaces

Solid–solid interfaces play a critical role in determining the performance of materials and devices. However, both experimental and theoretical determinations of interface structures are very challenging. In this Letter, we develop a high-throughput interface prediction and generation (IPG) scheme to predict the atomic structure of interfaces. To demonstrate the performance of the IPG, we apply it to the β-Ga2O3/AlN interface, which has attracted a great deal of attention for its promising application in power devices. Six β-Ga2O3/AlN interfaces are screened from thousands of candidates with the minimum mismatch and area tolerance. All these interfaces are modeled to satisfy the electron counting rules and then optimized by the minimum hopping method. The band alignments at the β-Ga2O3/AlN interfaces are in accordance with the available theoretical and experimental results. The results provide the basis for designing optical and electronic devices based on β-Ga2O3/AlN interfaces.

Comprehensive study of group III-nitride light emitting diode structures based on sapphire and ScAlMgO4 (0001) substrate for high intensity green emission

To mitigate the green gap problems existing in GaN/InGaN/AlGaN system on sapphire substrate, an In0.17Ga0.83N/InxGa1–xN/AlyGa1–yN based LED structure on ScAlMgO4 (0001) substrate has been introduced for green light (525…565 nm) emission. On ScAlMgO4 (0001) substrate, 35% of In composition with 1.6 nm well thickness and only 15% of Al composition with 1.1 nm thick AlGaN as capping layer on top provide the best LED structure. It provides minimum equivalent lattice mismatch (0.01%) with reasonable overall elastic energy value (0.47 J/m2). Most importantly, it provides at least 10% brighter green light emission than that of sapphire based LED structure.

Numerical-relativity-informed effective-one-body model for black-hole–neutron-star mergers with higher modes and spin precession

We present the first effective-one-body (EOB) model for generic-spins quasi-circular black-hole--neutron-star (BHNS) inspiral-merger-ringdown gravitational waveforms (GWs). Our model is based on a new numerical-relativity (NR) informed expression of the BH remnant and its ringdown. It reproduces the NR $(\ell,m)=(2,2)$ waveform with typical phase agreement of ${\lesssim0.5}\,$rad (${\lesssim1}\,$rad) to merger (ringdown). The maximum (minimum) mismatch between the $(2,2)$ and the NR data is 4% (0.6%). Higher modes (HMs) $(2,1)$, $(3,2)$, $(3,3)$, $(4,4)$ and $(5,5)$ are included and their mismatch with the available NR waveforms are up to (down to) a 60% (1%) depending on the inclination. Phase comparison with a 16 orbit precessing simulation shows differences within the NR uncertainties. We demonstrate the applicability of the model in GW parameter estimation by perfoming the first BHNS Bayesian analysis with HMs (and non-precessing spins) of the event GW190814, together with new $(2,2)$-mode analysis of GW200105 and GW200115. For the GW190814 study, the inclusion of HMs gives tighter parameter posteriors. The Bayes factors of our analyses on this event show decisive evidence for the presence of HMs, but no clear preference for a BHNS or a binary black hole (BBH) source. Similarly, we confirm GW200105 and GW200115 show no evidence for tidal effects.

A Robust Cathode Structure for Eco-Friendly Li-Ion Battery: NMC Coated Li-Rich LMO Cathode

Remarkable efforts have been put forth for the development of environmentally benign, abundant, low-cost and high-performance cathode materials for Li-ion batteries. Spinel LiMn2O4 has been considered as the most promising cathode among the many candidates for next-generation energy storage systems due to afore-mentioned advantages[1]. However, there are some challenges associated to this cathode that inhibit its practical usage for future applications. During cycling, the structural change from cubic to tetragonal takes place, in the Mn3+ configuration due to Jahn-teller distortion followed by Mn2+ dissolution under the influence of acidic electrolyte which destabilises the cathode structure[2]. These changes lead to cathode’s structural transformation and particle cracking resulting in active material loss and capacity fading. The deposition of soluble Mn2+ on anode's SEI results in increased cell’s impedance[3]. Moreover, severe capacity fading at elevated temperatures is still an issue hindering its full-scale commercial development due surface manganese dissolution in the electrolyte at those temperatures[4]. Ever since the emergence of LiMn2O4, various strategies have been employed to exploit its potential. Among many techniques, surface-coating, material composites and doping have been widely used[5]. Most of these techniques focus either on the restriction of direct contact between the active material and electrolyte via coating or the structural enhancement to accommodate for the anisotropic volume changes caused due to disproportionation reaction. Although, these strategies have shown some positive impact on the cycle life of the LMO based Li-ion battery but, in most of the cases the protection from the acidic electrolyte and structural strengthening of LMO has not been addressed simultaneously. Therefore, In order to develop a practical LMO based Li-ion battery, the active material requires a robust protection from the acidic electrolyte contact via a continuous, uniform and Li-ion permeable coating with minimum mismatch while enhancing the structural stability simultaneously to mitigate the irreversible phase transitions.Herein, we report a novel heterostructure design; NMC layered Li-ion permeable phase grown on the surface of Lithium-rich LiMn2O4 octahedra. The layered surface phase protects the host spinel from being directly exposed to the acidic electrolyte during electrochemical cycling. In addition, it provides an efficient path for the ionic and electronic mobility resulting in improved kinetics due to its Li-ion permeability. On the other hand, the excess Li in LMO contributes to the structural enhancement during cycling to accommodate anisotropic volume changes, thus resulting in a robust cathode for high-voltage Li-ion batteries. In comparison to spinel LMO, the newly modified LMO displays an enhanced cyclic performance with superior charge-discharge rate capability. The uniquely developed LiMn2O4 phase surface coated with layered structure demonstrated discharge capacity of 120 mAh g-1 at 20 ℃ temperature while retaining >97% of its initial capacity after 300 cycles at 0.5C. Further, The cathode was tested at elevated temperatures of 60 °C, showing stabilised reversible specific capacity of 113 m Ah g-1 at 0.2 C-rate ensuring energy density of 452 W h kg-1. The full-cell utilising MCMB anode and newly modified LMO cathode showed the areal capacity of 1.22 m Ah cm-2, after 100 cycles with a capacity retention of 95.3% at 0.44 mA cm-2 while maintaining its trend till 300 cycles.

Design of newly effective grain refiner for aluminum based on medium-entropy metal diboride

In this paper, medium-entropy metal diboride (Ti1/3Cr1/3V1/3)B2 with a hexagonal TiB2-type crystal structure were synthesized via molten salt reaction, and its effect on refining pure aluminum grains was investigated. Compared with TiB2, the minimum lattice mismatch between Al and (Ti1/3Cr1/3V1/3)B2 is reduced from 5.6% to 3.7%, effectively reducing undercooling required for nucleation. By just adding 1.5 vol% (Ti1/3Cr1/3V1/3)B2, the average grain size of commercial pure aluminum is reduced to ∼32 μm. The synthesized particles are expected to be used in grain refinement during additive manufacturing and rapid solidification, and in the preparation of aluminum matrix composites. This study opens up a new direction in designing new compounds for grain refinement by tailoring lattice matching within multi-component composition space.

Real time power management strategy for an all‐electric ship using a predictive control model

This study proposes a power management strategy (PMS) that can efficiently and accurately address the nonlinear dynamics of ship power systems for all-electric ships (AESs). The design of a PMS can be considered naturally in a model predictive control framework. However, the control error caused by a model mismatch is a challenge of the PMS for physical system implementation. The proposed PMS is based on a complex system-level nonlinear model that ensures a minimum mismatch. In addition, an efficient optimization algorithm is proposed to efficiently apply the PMS. The proposed method is verified using real-time simulations with physical systems in various scenarios. The experimental results demonstrate the superior efficiency of the proposed optimization algorithm and the accuracy of the developed PMS for physical system implementation.

Performance Enhancement of Partial Shaded Photovoltaic System With the Novel Screw Pattern Array Configuration Scheme

The performance of the solar photovoltaic system is affected by the unpredictable phenomenon of partial shading. This causes the mismatch losses that suppress the power generation of healthy PV modules in it. The objective of the proposed work in this paper is to bring out the maximum power from each PV module in the PV array by reducing the mismatch losses. A new array configuration method is proposed in this paper, which follows the screw pattern in the row formation. Each PV row is created with distinct PV modules from the rows of the conventional array configuration. This proposed work allows the PV system to operate with minimum mismatch losses by even shade dispersion over the PV array. The proper mathematical expression with all necessary constraints was derived for the array formation of the proposed work. The output analysis is been validated in the simulation of the <inline-formula> <tex-math notation="LaTeX">$9\times 9$ </tex-math></inline-formula> PV array in MATLAB/Simulink &#x24C7;. The mismatch loss generation and output power enhancement are measured and compared with the various conventional array configuration methods under six kinds of partial shading patterns. The proposed array configuration is 40&#x0025; more efficient than the conventional series-parallel array configuration and also performs better than the total cross-tied and sudoku puzzle pattern methods. The shade dispersion rate of the proposed array configuration has highly reduced the mismatch losses in the PV system and hence, it improves the power output.

Numerical modeling, simulation and evaluation of conventional and hybrid photovoltaic modules interconnection configurations under partial shading conditions

Partial shading on solar photovoltaic (PV) arrays is a prevalent problem in photovoltaic systems that impair the performance of PV modules and is responsible for reduced power output as compared to that in standard irradiance conditions thereby resulting in the appearance of multiple maximas on panel output power characteristics. These maxims contribute to mismatch power losses among PV modules. The mismatch losses depend on shading characteristics together with different interconnected configuration schemes of PV modules. The research presents a comparative analysis of partial shading effects on a 4 × 4 PV array system connected in series (S), parallel (P), serries-parallel (SP), total-cross-tied (TCT), central-cross-tied (CCT), bridge-linked (BL), bridge-linked total cross-tied (BLTCT), honey-comb (HC), honey-comb total-cross-tied (HCTCT) and ladder (LD) configurations using MATLAB/Simulink. The PV module SPR-X20-250-BLK was used for modeling and simulation analysis. Each module is comprised of 72 number of PV cells and a combination of 16 PV modules was employed for the contextual analysis. Accurate mathematical modeling for the HCTCT configuration under partial shading conditions (PSCs) is provided for the first time and is verified from the simulation. The different configuration schemes were investigated under short-narrow, short-wide, long-narrow, long-wide, diagonal, entire row distribution, and entire column distribution partial shading condition patterns with mathematical implementation and simulation of passing clouds. The performance of array configurations is compared in terms of maximum power generated (Pmp), mismatch power loss (ΔPml), relative power loss (Prl) and the fill factor (FF). It was inferred that on average, TCT configuration yielded maximum power generation under all shading patterns among all PV modules interconnection configurations with minimum mismatch power losses followed by hybrid and conventional PV array configurations respectively.

An integrated 0.0625–4 GHz quadrature-output fractional-N frequency synthesizer for software-defined radios

This paper presents a compact 0.0625–4 GHz fractional-N frequency synthesizer with quadrature phase output for software-defined radios (SDRs). Four voltage controlled oscillators (VCOs) and six cascaded dividers are used for wideband operation. Second harmonic filtering and high frequency noise suppression techniques are applied in VCO for phase noise optimization. Inverter switch and cascade switch buffers are combined for channel selection enhancement and output amplitude improvement. A large output voltage dynamic range with minimum current variation and mismatch is achieved by enabling transistors to work in triode region in charge pump. Implemented in a 55 nm CMOS process, the synthesizer demonstrates continuous frequency coverage from 62.5 to 4000 MHz with orthogonal output signals greater than 2 dBm while consuming 125 mW of power and provides the phase noise performance of −96.3/-127.7 dBc/Hz at 10 kHz/1 MHz offsets under a 2 GHz carrier. The chip area including all the pads and IOs is 3.34 mm2.

A novel arithmetic sequence pattern reconfiguration technique for line loss reduction of photovoltaic array under non-uniform irradiance

Partial shading causes unwanted impact on the output produced by the photovoltaic arrays. This occurs because some modules in the array are covered by shade while others are not in the same array. As a result of this phenomenon, multiple peaks arise in the P–V characteristics of the photovoltaic array along with sudden and severe row current changes. Both factors impede the array performance. This manuscript presents a novel static reconfiguration technique (i.e., arithmetic sequence pattern configuration) and verifies it using an experimental work bench to reduce the shading effect on the array. This novel approach reconfigures the conventional total cross tied array in the arithmetic sequence pattern that helps to reduce the shading effect on a specific point and distributes it evenly across all the rows and increases the overall energy output. This manuscript examines and compares different techniques such as SuDoKu, futoshiki SuDoKu, improved SuDoKu, skyscraper SuDoKu and modified SuDoKu interconnections based on various factors like fill factor, mismatch power loss, efficiency, and global maximum power points. Finally, the present work concludes that the suggested arithmetic sequence pattern topology effectively reduces the shading effect and wiring losses. It provides better power output in reference to the other topologies. The proposed topology provides a maximum reduction of 37.98% in wire length as compared to skyscraper SuDoKu and minimum mismatch power loss of 594.8 W lesser as compared to the other configurations.

Tuning single-walled aligned carbon nanotubes for optimal terahertz pulse generation through optical rectification of ultrashort laser pulses.

Terahertz radiation by optical rectification in single-walled highly aligned chiral carbon nanotubes (SWCNTs) irradiated by ultrashort laser pulses is comprehensively studied. We take into account the structural properties of SWCNTs, including the filling factor, alignment, and chirality, as well as the laser pulse parameters including the pulse duration and the wavelength. The second-order nonlinear susceptibility tensor and, consequently, polarization responsible for optical rectification in SWCNTs are derived based on symmetrical features.The effective dielectric constants of SWCNTs are also extracted using the effective medium approximation. Then, the propagation effects in terms of the group velocity dispersion and absorption at both pump and terahertz pulse frequency regions are investigated. By adjusting the laser and the structure effective parameters among those practically feasible, minimum velocity mismatch required for optimum optical rectification and coherent amplification at terahertz frequencies in SWCNTs are introduced. Comparing the electric field waveform and the spectrum of the generated terahertz pulses under various conditions reveals that SWCNTs with higher alignment and lower filling factor at chirality (6,4) irradiated by an ultrashort laser pulse with the wavelength of 1550 nm could provide the conditions for maximum terahertz radiation generation.

Passive Islanding Detection Based on Angular Velocity Harmonic Patterns with Perceptron Neural Network

Traditional islanding detection methods present improper action when the power mismatch between generation and load in the islanding system is small. The minimum power mismatch for correct islanding detection defines the limits os a Non-Detection Zone. This paper proposes an efficient method for islanding detection based on angular velocity harmonic patterns. To accomplish this, the measured frequency is decomposed by a Fourier Transform and applied to a Perceptron artificial neural network for pattern classification. The performance of the proposed method is evaluated by tests on a modified IEEE 34 node test system. Several islanding and non-islanding cases were simulated. The proposed method achived a performance of 88.16% in the classification of harmonic patterns with a small training set. Compared with the Under/Over frequency method, the proposed method represents a performance improvement of 17%.

Microstructure evolution and properties of in-situ TiC reinforced titanium matrix composites coating by plasma transferred arc welding (PTAW)

In-situ TiC reinforced titanium matrix composites coating was prepared on the surface of Ti6Al4V by plasma transfer arc welding using pure Ti powder and Cr 3 C 2 powder. The obtained TMCs coating is dense, no porosity and forms a good metallurgical bond with the substrate. There are obvious composition differences in the coating along the direction of temperature gradient: Mixture structures of TiC dendrites, β-Ti, needle-like α-Ti and TiCr 2 phases were formed at the top of the coating due to heat accumulation and slow cooling rate, and the formation mechanism of these phases was analyzed in detail. The cavitation erosion resistance, corrosion resistance , microhardness and wear resistance of Ti6Al4V substrate and TMCs coating were compared and clarified. The TiC ceramic phase generated in situ is anchored by β-Ti, so that the TMCs coating is both tough and hard. The microhardness of the top of the coating reaches 1325 HV 0.2 , which is 4 times that of the substrate. In addition, the α-Ti + TiCr 2 phase precipitates along the minimum mismatch crystal orientation and presents a certain crystallographic orientation relationship with β-Ti. The TMCs coating exhibits higher resistance to wear and corrosion than Ti6Al4V substrate. Therefore, the surface modified TMCs coating prepared in this study is expected to apply in the surface protection of Ti6Al4V under the working conditions of wear and sea water erosion corrosion in the field of ocean engineering. • In situ TiC reinforced surface modified coatings were prepared by PTAW. • The formation mechanism of each phase in the coating was analyzed in detail. • Revealed the anti-cavitation erosion mechanism of TMCs coating. • The passivation kinetics of TMCs coating and Ti6Al4V coating were compared. • Revealed the wear mechanism of TMCs coating and Ti6Al4V substrate.

Directly visualizing the crossover from incoherent to coherent phonons in two-dimensional periodic MoS2/MoSe2 arrayed heterostructure

Recently, massive efforts have been done on controlling thermal transport via coherent phonons in the various periodic nanostructures. However, the intrinsic lattice difference between the constituent materials inevitably generates the disorder at the interfaces, thus limiting the opportunity of directly observing the coherent phonon transport. Here, we investigate the controllability and visualization of the coherent phonon transport in a periodic MoS2/MoSe2 arrayed heterostructure with minimum lattice mismatching using non-equilibrium molecular dynamics simulation. It is found that the coherent phonon transport can be destroyed and rebuilt through adjusting the density of MoSe2 nanodot arrays. The phonon localization induced by the destruction of correlation is visualized based on the spatial energy distribution and anharmonic analysis. Furthermore, the eigen vector diagrams provide a distinct visualization of the localized phonon modes. Besides, the correlation of phonon can be rebuilt by reducing the period length, which is verified by the enhanced group velocities extracted from phonon dispersion curves. Interestingly, the crossover from incoherent to coherent phonon transport is directly observed by the spatial energy distributions and the spectral phonon transmission coefficients. Finally, the size and temperature dependence of thermal conductivity are also discussed. This study of the phonon coherence and its visualizing manipulation on thermal conductivity will be beneficial to fine heat control and management in the real applications.