Additional Path Research Articles

Correlating shipping noise on multiple beams

There has been much interest in using transiting surface ships as sources of opportunity for tomography and geo acoustic inversion. In tomography, it would be valuable to increase the ranges at which ship signatures can be processed by measuring times of arrival at the output of beamforming processes, which provide spatial processing gain. This additional gain may enable fainter multipath arrivals to be identified and exploited as additional paths to sample the ocean water column. This seems readily achievable when cross-correlating multiple vertical beams formed on a single vertical line array for example. However, cross-correlating beams from multiple arrays, vertical or horizontal, raises questions. In both cases, different beams may have different Doppler, which is manageable with a correlation process that includes Doppler compensation. But obeserving a ship from different vantage points may be problematic, if the ship signature is due to horizontally displaced noise sources distributed around the ship. We will present results of processing surface ships observed on single and multiple arrays and assess the use of such processing in ambient noise tomography.

Role of ammonia addition on polycyclic aromatic hydrocarbon growth: A ReaxFF molecular dynamics study

Ammonia (NH3), one of the most promising carbon-free fuels, has received great research interest. In particular, NH3 is often blended with hydrocarbon fuels to achieve desired combustion characteristics. However, NH3 addition could affect soot formation, which has not been adequately understood. In this study, the effect of NH3 on the growth of polycyclic aromatic hydrocarbons (PAHs) is investigated with the reactive force field molecule dynamics (ReaxFF MD) simulations and quantum chemistry calculations. The simulation results indicate that NH3 addition slows down the growth of large carbon-containing species in the C2H4/O2 system. Novel path with HCN addition is discovered in the PAH growth, which inhibits the PAH growth compared to the conventional Hydrogen-Abstraction-Carbon-Addition (HACA) path via C2H2 addition. Moreover, quantum chemical calculations verified the rationality of this addition path and explained its inhibition on PAH growth by calculating the heat of reactions and reaction energy barriers. According to the present study, NH3 also has an inhibitory effect on both the HCN addition path and C2H2 addition path by providing H atoms to promote the generation of PAH radicals back to PAH molecules, and this effect is more significant for the C2H2 addition path. Results from the study provide a fundamental insight for the inhibition of PAH growth due to the NH3 addition from an atomistic insight, which helps to improve the understanding of the combustion of blends of NH3 and hydrocarbon fuels.

RIS-Aided 6G Communication System With Accurate Traceable User Mobility

Reconfigurable intelligent surface (RIS) can effectively improve the performance of 6G communication systems by providing additional LoS paths. Although the beam alignment is necessary in 6G communication system due to the user mobility, the deployment of RIS increases significantly the complexity of beam tracking, making it impractical to apply directly conventional schemes. To this end, we study a time-varying RIS-aided millimeter wave (mmWave) system, a robust complex-valued extended Kalman filter method is proposed to tackle the beam alignment problem. More specifically, the proposed scheme achieves 17% performance gain compared to conventional training-based method. The impact of the number of RIS elements is investigated, there exists corresponding optimal number of RIS elements in terms of the minimum of the mean square error of the estimated beam angle. A simple but efficient algorithm to obtain the optimal number of RIS elements is presented. Simulation results demonstrate that, by employing the RIS in mmWave communication systems, the performance of beam tracking can be enhanced by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {37\%}$</tex-math></inline-formula> with proposed algorithms.

Analysis of flux barrier effect of LCF PM in series hybrid magnet variable flux memory machine

Variable flux memory machines (VFMMs) with series hybrid magnets using both low coercive force (LCF) and high coercive force (HCF) permanent magnets (PMs) have been recognized as a viable candidate for wide-speed-range industrial applications due to the advantages of high torque density and wide speed range. Nevertheless, the adverse effects of LCF PM on the HCF PM in series-type VFMM under different magnetization states (MSs) are still unreported. In this paper, the flux barrier effect (FBE) of the LCF PM existing in series hybrid magnet VFMM is first revealed, and its causes are discussed as well as analyzed in depth on the basis of the equivalent magnetic circuit method and finite-element (FE) analyses. A topology of VFMM with dual-layer PMs is further developed to alleviate the FBE induced from LCF PMs. It can be found that the FBE can be effectively suppressed by employing the dual-layer (DL) PM arrangement and additional leakage flux paths. A prototype of the proposed design is built, and the theoretical and FE results are experimentally verified.

Quality inspection of cube beam splitters by awhite light interferometric approach.

Beam splitters have a wide range of applications as a key component in optical systems. Adopting beam splitters with geometric defects in an optical system, e.g., an interferometric measurement system, may cause additional optical path difference and degrade the measurement accuracy. The quality inspection of beam splitters is essential to meet the accuracy requirements for modern optical systems. Most of the current quality inspection methods rely on inefficient and inaccurate manual observation. Therefore, for commonly used cube beam splitters (CBSs), we propose a digital method to quantify the geometric quality based on the white light interferometric principle. A Fourier domain analysis is used to calculate the CBS misalignment error and perpendicularity error. This method is verified by inspecting six different CBS samples. The experimental results show that all samples have varying degrees of misalignment and perpendicularity errors. The maximum perpendicularity error is 0.93°, and three of the six samples have misalignment errors larger than 50µm. Nanometer level precision of the misalignment measurement can be achieved.

Optimization of communication topology for persistent formation in case of communication faults

To address the optimization problem of communication topology for persistent formation in the case of communication faults such as link interruption, transmitter failure, and receiver failure a two-stage model including fast reconstruction of communication topology and re-optimization of communication topology is constructed. Then, a fast reconstruction algorithm of communication topology for persistent formation (FRA-CT-PF), based on optimally rigid graph, arc addition operation, and path reversal operation, is proposed, which can quickly generate a feasible reconstructed communication topology after communication faults, thus ensuring the safety of the agents and maintaining the formation shape of persistent formation. Furthermore, a re-optimization algorithm of communication topology for persistent formation (ROA-CT-PF), based on agent position exchange, is proposed, which can further obtain a reoptimized communication topology to minimize the formation communication cost while still maintaining the formation shape of persistent formation. The time complexities of these two algorithms are also analyzed. Finally, the effectiveness of the above algorithms is verified by numerical experiments. Compared with existing algorithms, FRA-CT-PF can always obtain feasible reconstructed communication topology in much less time under all communication fault scenarios, and ROA-CT-PF can obtain a reoptimized communication topology to further reduce the formation communication cost in a shorter time.

Localization of Transmitters and Scatterers by Single Receiver

Localization by single receiver is attractive in practice. This paper exploits the additional propagation paths from scatterers for the localization of transmitters, using the time differences of arrival between the direct and scattered signals and their angles of arrival observed at the receiver. Localization is possible only if there are at least two transmitters and at least two scatterers, which may not happen in a real scenario. We explore the utilization of intentional transmitter or scatterer at known position to assist in the localization, thereby enabling localization with arbitrary number of transmitters or scatterers. The challenge for this problem is that the positions of the unintentional scatterers are not known and they need to be estimated in conjunction with the transmitter positions. A non-iterative localization algorithm based on the integration of several minimal measurement solutions is proposed, with the analysis in supporting the Cramer-Rao Lower Bound performance for Gaussian noise over the small error region. The optimum placement of single intentional transmitter is derived for the 2-D and 3-D scenarios, as well as for single intentional scatterer. Simulation confirms the expected performance of the proposed positioning solution and validates the optimum placement.

InAlN/GaN HEMT With n+GaN Contact Ledge Structure for Millimeter-Wave Low Voltage Applications

In this work, high performance InAlN/GaN HEMT based on the n+GaN regrown ohmic contact with n+GaN contact ledge structure is proposed. The regrown ohmic contact of InAlN/GaN HEMT is formed by MBE n+GaN regrowth and selfstopping etching, which makes the total ohmic contact resistance between the 2DEG channel and the ohmic metal decrease to 0.12 Ωmm and forms n+GaN contact ledge structure. Owing to the n+GaN contact ledge on the InAlN barrier, with the increasing of drain-source voltage (VDS), an additional current path comes into being between the n+GaN contact ledge on the InAlN barrier and the 2DEG channel, which can “shorten” the device effective drainsource distance, thus further reducing the parasitic resistance. Compared with regrown InAlN/GaN HEMT without n+GaN contact ledge structure, the peak transconductance (Gm.max) of regrown InAlN/GaN HEMT with n+GaN contact ledge structure increases from 747 mS/mm to 874 mS/mm, and the saturation current density (ID.max) increases from 2.6 A/mm to 2.9 A/mm. Besides, the self-stopping etching on the access region does not induce extra defects, and negligible current collapse is obtained. As the results of low parasitic resistance, high output current density, low knee voltage and negligible current collapse, poweradded-efficiency (PAE) of 44% together with output power density (Pout) of 2.5 W/mm is achieved at 30 GHz and VDS of 10 V, which indicates regrown InAlN/GaN HEMT with n+GaN contact ledge structure has great potential for millimeter-wave low voltage applications. Additionally, the transfer and schottky gate characteristics show negligible degradation after OFF/ON-state electrical stress tests.

Application of lamellar nickel hydroxide membrane as a tunable platform for ionic thermoelectric studies.

The recent trend in thermoelectric literature suggests that ionic thermoelectric (i-TE) materials are ideal for directly converting low-grade waste heat into electricity. Here, we developed a unique platform for i-TE studies by stacking two-dimensional sheets of β-Ni(OH)2 prepared by a bottom-up method. The lamellar membrane of β-Ni(OH)2 (Ni-M) itself does not display significant thermovoltages, but when doped with mobile anion-generating species (like aminopropyl functionalized magnesium phyllosilicate or organic halide salts), it exhibits significant negative Seebeck coefficient (up to -13.7 ± 0.2 mV K-1). Similarly, upon doping with cation-generating species like poly(4-styrene sulfonic acid) (PSS), it displays positive Seebeck coefficient values (up to +12 ± 1.9 mV K-1). The positive and negative i-TE materials prepared by doping Ni-M are assembled into ionic thermopiles capable of generating thermovoltages up to 1 V, at ΔT = 12 K. The Ni-M-based nanofluidic systems demonstrated an additional path of electricity harvesting by connecting colder zones of the positive and negative i-TE materials with other ion conducting membranes. In contrast to organic polymer-based i-TE systems, the Ni-M based system exhibited consistent performance despite being exposed to high temperatures (∼200 °C, 5 minutes).

Corrosion behavior of Yb4Hf3O12 ceramics exposed to Calcium-Ferrum-Alumina-Silicate (CFAS) coupled with water vapor at 1400 °C

In this work, the corrosion behavior of Yb4Hf3O12 ceramics under CFAS coupled with water vapor environment at 1400 °C for 2–50 h was investigated. Results show that the CFAS were rapidly dissolved into ceramics under test environment, and then the Yb-Ca-Si apatite and Hf-rich fluorite phases were re-precipitated. Simultaneously, the water vapor corrosion mainly induced grain surface corrosion, resulting in the formation of corrosion pits and ridge-like structures. Moreover, the pores and microcracks caused by water vapor corrosion offer additional penetration path for CFAS melt.

Principle and performance analysis of low-power, high-speed, low-noise comparators

This paper studies three different structures proposed in recent years and discusses their advantages and properties respectively. A modified strong-arm latch voltage comparator is adapted to 3GHz operating frequency through additional current paths in the pre-amplifier. A latch-type comparator with a dynamic-biased pre-amplifier (DA) greatly reduces energy and improves noise performance through the stabilization of the input common-mode voltage. An FIA comparator further reduces energy and noise and greatly enhances the delay performance and the robustness of the comparator against different input common-mode voltage.

Experimental and Numerical Investigation of CMT Wire and Arc Additive Manufacturing of 2205 Duplex Stainless Steel

In this paper, the mechanical properties, microhardness and metallographic structure of 2205 duplex stainless steel by cold metal transfer (CMT) wire and arc additive manufacturing process are studied. The results show that the ultimate tensile strength, yield strength and elongation at break of reciprocating additive along building direction (BD) are 856.73 MPa, 710.5 MPa and 42.35%, respectively. In addition, the same direction motion (SDM) and reciprocating motion (RM) is selected as parameter variables in the experiment, and the finite element model is established by ABAQUS software, and the temperature and residual stress field of the additive forming at different paths are tested and simulated. Firstly, the accuracy of the selected finite element model was verified by comparing the experimental results from the simulation results to the macroscopic morphology of the cross-section of the single-pass additive specimen. The numerical simulation results show that due to the difference of the additive scanning paths, the distribution of the temperature field has a large difference, and with the increase of the deposited layer, the heat accumulation of the SDM additive is larger than that of the RM, so that the end collapses of the SDM additive will occur in the actual additive specimen. By simulating and comparing the equivalent stress distribution of different paths, the equivalent stress distribution of SDM and RM is approximately the same in the vertical direction, and the minimum of equivalent stress appears at the bottom of the deposition layers, about 116.5 MPa, and the maximum of equivalent stress appears at 8 mm from the top, about 348 MPa.

A Novel AMOLED Pixel Circuit to Alleviate Effects of Leakage Current using Additional Compensation Leakage Current Path

A Novel AMOLED Pixel Circuit to Alleviate Effects of Leakage Current using Additional Compensation Leakage Current Path

Electrochemical Impedance Spectroscropy Study on the Behavior of Reinforced Concrete Elements under Loading

Concrete is a material of porous nature that, when humidified, becomes an ionic conductor whose apparent conductivity depends on the ionic load (typically based on OH−, Ca2+, Na+, and K+) and the amount of available free water. Under conditions of partial pore-saturation, the amount of free water can be modulated by an external load, which leads to observable changes in electrical properties such as conductivity and capacitance. Moreover, metallic reinforcements, either as bars or fibers, represent an additional parallel conduction path but of an electronic nature in this case. The free water develops a double-layer capacitance structure at the metallic interfaces, with associated charge-transfer resistance, representing an additional contribution to the capacitive behavior that can be modulated with an external load. The dependence that the electrical and/or ionic conducting properties of concrete and reinforced concrete elements have on the available free water makes them suitable for transductors in various sensing and self-sensing applications discussed in the text.

Trust Black Women: Using Photovoice to Amplify the Voices of Black Women to Identify and Address Barriers to Breastfeeding in Southeast Georgia.

Barriers to breastfeeding for Black mothers are well documented in the literature. Local context is crucial for understanding and addressing barriers. Our research used the photovoice method to amplify the voices of Black mothers in Chatham County, Georgia. Guided by the sociol-ecological model, this photovoice project explored and identified the social, cultural, and physical barriers to breastfeeding that the mothers experienced. Two additional themes emerged through data analysis: personal comfort with public breastfeeding and the women's recommendations for breastfeeding support and normalization. Lack of physical spaces, lack of peer and family support, the need to overcome the stigma associated with breastfeeding, and advocating for more lactation spaces were commonly stated by the participants. These results led to the creation of a policy toolkit, a breastfeeding policy template, a proclamation to make the City of Savannah a Breastfeeding Family Friendly Community, an online photobook to share the experiences of the mothers, and additional paths of dialogue to increase inclusivity and expand health equity within Chatham County.

Microscopic formation mechanism of Si/Tl5Al1/TiN ohmic contact on non-recessed i-InAlN/GaN heterostructures with ultra-low resistance

In this work, we use Si/Tl5Al1/TiN for a source/drain ohmic contact to demonstrate an ultra-low contact resistance of 0.11 Ω mm (ρc = 2.62 × 10−7 Ω cm2) on non-recessed i-InAlN/GaN heterostructures. The Ti5Al1 alloy was used to suppress the out-diffusion of Al and extract N from the InAlN layer, which aided the formation of ohmic contact by improving the tunneling efficiency of electrons, as we have reported in the past work. A thin Si inter-layer combined with the Ti5Al1 alloy is proposed to further reduce contact resistance. A heavy n-type InAlN layer was obtained through doping with Si atoms to improve the tunneling transport of electrons. Furthermore, the TiN inclusions penetrated into the GaN channel because the in-diffused Si promoted the decomposition of GaN at a high annealing temperature and the in-diffused Ti reacted with GaN. These TiN inclusions provided direct contact with two-dimensional electron gas, offering an additional path for the injection of electrons into the channel. The tunneling and spike mechanism worked alternately to lower the contact resistance at different annealing temperatures (dividing at 900 °C), implying that the joint effect of tunneling and the spike mechanism was initially promoted in the formation of ohmic contact. The mechanism of this Si/Ti5Al1/TiN ohmic contact was fully understood through microscopic and thermodynamic analyses. These results shed light on the mechanism for the formation of ohmic contact in a gold-free metal stack for GaN-based HEMTs.

A Single-Event Burnout Hardened Super-Junction Trench SOI LDMOS with Additional Hole Leakage Paths

In this paper, a novel super-junction trench silicon-on-insulator laterally-diffused metal-oxide-semiconductor (SJT SOI LDMOS) power device with additional hole leakage paths to improve single-event burnout (SEB) performance under high liner energy transfer (LET) is proposed for the first time. The electrical characteristics and SEB performance of the proposed SJT SOI LDMOS are both enhanced effectively. The replacement of a lightly doped N drift region with a heavily doped P pillar and N pillar considerably improves the tradeoff between breakdown voltage (BVDS) and specific on-resistance (Ron,sp). Compared with the conventional trench SOI LDMOS (CT SOI LDMOS), the static figures of merit (FOM, BVDS2/Ron,sp) of the SJT SOI LDMOS increases by 239%. The SEB performance of the SJT SOI LDMOS is significantly improved as the holes induced by the heavy ion can be quickly absorbed to the trench source metal through the heavily doped P+ region and P buried region rather than the base resistor of the parasitic bipolar junction transistor (BJT). The SEB threshold voltage (VSEB) of the CT SOI LDMOS is 58 V (39% of the BVDS) and that of the SJT SOI LDMOS is up to 173 V (87% of the BVDS) at high LET of 1 pC/μm.

Solid phase microextraction of benzenes in river water by pomelo peel biochar

Pomelo peel, as a by-product of pomelo consumption, is rich in various fiber and functional compounds. The utilization of the valuable components found in pomelo peel may mitigate environmental concerns. In this study, pomelo peel rich in lignin and oxygen-containing functional groups was used to prepare pomelo peel biochar (PPB) via temperature-programmed pyrolysis at different temperatures (800 ℃ and 1000 ℃). Their structures were investigated by N2 adsorption-desorption isotherms and BJH pore size distribution. The results showed that PPB1000 (pomelo peel biochar prepared at 1000 ℃) had a higher specific surface area (749.9 m2/g), larger pore volume (0.42 cm3/g), more concentrated pore size distribution (2-3 nm), and better adsorption performance than commercial activated carbon. PPB1000 exhibited excellent capability to capture benzenes (BTEX, including benzene (B), toluene (T), ethylbenzene (E), and xylene (X)) through hydrogen bonds, π-π, and electrostatic interactions. Additionally, their honeycomb porous structure could provide additional adsorption sites and material transport paths. PPB1000 was coated on iron wire using the sol-gel method to prepare chemically and mechanically stable solid phase microextraction (SPME) fibers. By combining PPB1000-based SPME analysis with gas chromatography-flame ionization detection (GC-FID), an effective method was developed for the extraction and determination of BTEX. The optimized method had low LODs (0.004-0.032 μg/L), wide linear range (1-100 μg/L), and good linear relationship (determination coefficients, r2≥0.9919). The RSDs of the intra-batch (n=6) and inter-batch (n=5) precisions were 1.04%-6.56% and 1.03%-12.42%, respectively. The method validation results showed that PPB1000 had good stability. Compared with the commercial reagent polydimethylsiloxane (7 μm), PPB1000 had a higher extraction efficiency. When applied to the analysis of BTEX in natural water samples, trace levels of ethylbenzene (4.80 μg/L), o-xylene (3. 00 μg/L), and m-xylene and p-xylene (2.46 μg/L) were detected. Recovery tests were performed to validate the reliability of the method, and recoveries were between 75.7% and 117.6%. This effective pretreatment process combined with GC-FID could realize the rapid detection of BTEX and is promising for the analysis of BTEX in complex matrixes in the future.

Crystal Structures and Conduction Paths of Sc-Doped CaTiO3 Fast Oxide-Ion Conductors with Orthorhombic Symmetry

The crystal structures and electron density distributions (EDDs) of Ca-deficient Sc-doped CaTiO3 fast oxide-ion conductors, Ca0.97(Ti0.97Sc0.03)O3-δ (CTS3) and Ca0.96(Ti0.9Sc0.1)O3-δ (CTS10), were investigated in the temperature range of 298-1173 K in N2 to analyze the effect of composition on the perovskite structure and oxide-ion transport mechanism. CTS3 and CTS10 exhibited orthorhombic Pnma symmetry in temperature ranges of 298-1173 K and 973-1173 K, respectively, with CTS10 exhibiting lower symmetry and reduction in oxide-ion conductivity below 973 K. The EDDs of CTS3 and CTS10 at 1173 K indicated unique chemical bonds and conduction paths. CTS3 and CTS10 showed covalent bonds between (Ti,Sc) and O1 (or O2) sites. CTS3, with a lower oxide-ion conductivity than that of CTS10, exhibited pseudo-one-dimensional (1D) zig-zag curved conduction paths for oxide-ions along the a-axis, unlike previously reported curved migration paths along the b-axis in CaTiO3, and chemical bonds between Ca and O1 sites, indicating oxide-ion conduction suppression. In CTS10, additional conduction paths were observed along the a-axis, forming three-dimensional (3D) zig-zag curved conduction paths in the ac-plane and along the b-axis, with the weakening of the chemical bonds between the Ca and O1 sites. The oxide-ion conductivity and mobile oxide-ion concentration of CTS10 were 3.6 and 2.0 times those of CTS3, respectively, at 1173 K; the higher oxide-ion conductivity of CTS10 could be attributed to an increase in the mobile oxide-ion concentration and mobility with a 1D to 3D change in the conduction paths and a weakening of chemical bonds between the Ca and O1 sites.

Improving the Performance of Lithium‐Ion Batteries Using a Two‐Layer, Hard Carbon‐Containing Silicon Anode for Use in High‐Energy Electrodes

Lithium‐ion battery cells with high‐energy density and good fast charging properties are subject of current research. One approach to achieve high‐energy densities is the use of higher mass loadings. The challenges of these so called “thick” electrodes are transport limitations: lithium ions cannot reach all layers of the electrode, which results in a drop of performance. Possible concepts to overcome these limitations are the use of different active materials (silicon oxide, graphite, and hard carbon (HC)), and a two‐layer coating of the anode to create a defined pore network, which reduces the ionic resistance and ensure better fast charging capability even at higher mass loadings (8 mAh cm−2). It could be demonstrated that by using a two‐layered anode with HC in the upper layer, the electrical conductivity could be increased by a factor of 10 compared to the reference anode. Furthermore, the interporous HC leads to a capacity retention increase up to 20% with no loss of capacity at moderate C‐rates and a low electrode density. This can be explained by the low tortuosity that results in additional conductive paths for the ions through the coating, reduces the ionic resistance, and ultimately enables faster lithiation of the anode.