Contact System Research Articles

Equivalent Heat Source Model of Thermal Relay Contact Based on Surface Roughness of Silver–Magnesium–Nickel Contact

In a sealed electromagnetic relay, the change in the surface roughness mainly depends on the collision wear between the contact and the moving reed and the ablation effect of the arc on the contact surface based on the strong correlation between the contact resistance and the surface roughness of the Ag-Mg-Ni contact. With a change in contact resistance, the contact temperature increase in a hermetically sealed electromagnetic relay (HSER) is greatly affected. Under extreme overload conditions, the contact surface is severely ablated by the arc, and the roughness increases rapidly with the number of cycles, which greatly affects the contact resistance of the contact surface and the reliability of the relay. A thermal model of a relay contact system based on the surface roughness of Ag-Mg-Ni contacts was established in this paper by analyzing the effect of an arc on the surface roughness of Ag-Mg-Ni contacts under heavy overload conditions. The arc image of the Ag-Mg-Ni contact was recorded using a double-axis arc photographing platform, and the moving track of the arc center under overload conditions was drawn. This paper explored the patterns of arc center movement on the contact surface and the effects of the arc on the surface roughness of the contacts by analyzing the probabilities of the arc center appearing in various locations. A mathematical model correlating the number of contact cycles with contact resistance was established. Subsequently, a finite element simulation model for the equivalent heat source of the contact was developed. The theoretical model error was less than 10%. The accuracy of the equivalent heat source model was verified by comparing the measured data with the simulation results.

Comparison of suckling and artificial rearing on calf growth and milk requirements in pastoral dairy systems

Context Dairy calf-rearing practises have the potential to influence profitability through milk requirements at rearing, and affect lifetime productivity and market access from an animal-welfare perspective. Aims The aim of this research was to compare calf growth and milk requirements by using conventional artificial rearing (AR) and restricted milk allocation with AR and high milk allocation or suckled calves. Methods Forty-five Friesian × Jersey calves were allocated to be either AR on 6 L/calf.day, (ARC) or 12 L/calf.day, (ARH), or suckled with dams in a cow–calf contact system using partial contact (15 h/day, CCC). AR calves were fed, and intake measured, using an automatic feeder, whereas CCC calves had access to their dams between 1500 hours and 0600 hours. Calves were transitioned off milk, once they reached at least 75 kg liveweight (LW), by gradually reducing their milk allocation (AR) or reducing access to their dam (CCC). Key results Milk consumption for ARH was greater than for ARC calves (382 vs 450 L/calf, P < 0.05), whereas for CCC calves milk-yield difference between dams for the control and suckling groups during the suckling period and over the full season was 706 and 1048 L/cow respectively. There was no difference in weaning weight of calves (87 ± 1.7 kg LW), but, owing to differences in pre-weaning growth rate, age to weaning was youngest (P < 0.05) for CCC (55 days), followed by ARH (62 days) and ARC (73 days). Respective growth rates between birth and weaning (P < 0.001) for CCC, ARH and ARC calves were 0.955, 0.873 and 0.755 ± 0.028 kg/day. Although there was a growth check among CCC calves during the weaning period, there were no post-weaning differences in growth rate among the groups. Conclusions Increasing milk allowance had the benefit of improving calf pre-weaning growth rate, giving the option of weaning calves either earlier or when heavier. However, milk yield losses under suckling systems may be too high to warrant the elevated pre-weaning growth of calves. Implications The costs–benefits of high milk allocation or suckling systems need to be ascertained over the lifetime of the animals to assess long-term survival and productivity outcomes.

Don't forget the dams! Dairy cows' responses to two separation methods after 3 months of cow-calf contact

Weaning and separation remain among some of the biggest challenges for cow-calf contact systems, making the development of practical and low stress separation methods mandatory for future success of these systems. This study aimed to compare behavioral and physiological responses of dairy cows to separation from their calves after 3 mo of full-time contact with either the 2-step method (NF, 2 wks full-time contact while calves wore a nose flap, 1 wk fence-line contact before total separation, n = 18) or by gradual reduction of contact time between cow and calf (GR, 1 wk half day contact, 1 wk morning contact, 1 wk fence-line contact before total separation, n = 18). Vocalizations and searching behavior were observed on 4 d/wk from 1 wk before separation until 1 wk after total separation. During the same period, lying behavior and rumination time was automatically assessed via accelerometers and pressure sensors. Fecal and blood samples were collected twice/wk from day -1 till +23 relative to separation start for analysis of fecal cortisol metabolites and the immune response. Milk yield in the parlor was continuously recorded. Statistical analysis was conducted using linear mixed effects models. We found no difference between the 2 separation methods in any of the examined behavioral and physiological response variables. However, a significant increase in vocalizations and searching behavior compared with baseline was present with both methods. Further, there was a transient increase in physiological distress markers and a short-lived retention of milk yield at initiation of treatments, indicating that both methods induced distress for the cows. Descriptively, there were large inter-individual differences between cows as well as a different temporal distribution in occurrence of behavioral responses, as GR cows vocalized most frequently during the week with fence-line contact and after total separation from the calf, while NF cows reacted strongest during the 2 wks while calves wore the nose flap. Milk yield was higher in NF than GR cows during the 2 wks while GR calves had time-restricted access to their dams and NF calves were prevented from suckling, but showed no difference afterward anymore. However, similar evening milk yields of GR cows in the weeks with half day and morning contact, indicated that the weekly reductions in contact time worked in a rather stepwise than gradual manner, which warrants further improvement of the GR method. Taken together, results showed that cows experienced distress during separation with the GR method, when implemented over 3 wks in 3 steps, as well as with the NF method, but differences between individuals were considerable.

Variational inequalities of multilayer elastic contact systems with interlayer friction: Existence and uniqueness of solution and convergence of numerical solution

Inspired by the layered structure models in pavement mechanics research, in this study, a class of multilayer elastic contact systems with interlayer frictional contact conditions and deformable supporting frictional contact conditions on the foundation has been constructed. Based on the nonlinear elastic constitutive equations, the corresponding system of partial differential equations and variational inequalities are respectively introduced. Under the framework of variational inequalities, the existence and uniqueness of solutions for such models, along with the approximation properties of finite element numerical solutions, are proven and analyzed. The aforementioned conclusions provide fundamental and broadly applicable theoretical support for addressing mechanical problems in multilayer elastic contact systems within the framework of variational inequalities. Finally, the numerical experimental results based on the mixed finite element method also substantiate our theoretical conclusions.

A Possible Explanation of W-type Phenomena in V694 Peg

Three sets of complete multicolor light curves of V694 Peg observed in 2013, 2015, and 2019 were presented and analyzed. Our photometric solutions show that this system was an A-type shallow contact binary in 2013 and 2015 while it converted to a W-type one in 2019. A large cool spot on the component of this binary could explain the conversion, implying the W-type phenomena may be caused by the magnetic activity of the components. We have collected available data on this binary and calculated 505 times of light minimum, which spans 17 yr. The orbital period investigation based on these timings shows there is a long-term period increase at a rate of dP/dt = 4.3(±0.3)×10−9 day yr−1 superposed on a periodic variation with a period of 11.81(±0.06) yr. The cyclic orbital variation may be the result of magnetic activity cycles or the existence of a third body. Until now, only eight transformed systems, including V694 Peg, have been reported. Compared with other converting contact systems between A-type and W-type, V694 Peg is recorded as the shortest-period one. All of these converting systems are late-type (later than F7) contact binaries with the O’Connell effect and show cyclic period variation, which indicates that magnetic activity may be the reason for the conversion between the two types of contact binaries. For investigating the nature of A-type and W-type phenomena, the discovery of more converting contact binaries is essential.

Research on wheel–rail impact dynamics due to combined rail weld irregularities and polygonal wheel effects considering 3D contact geometry

The geometric irregularities of rail welds and polygonal wheels are common defects observed in high-speed railways, leading to the generation of high-frequency impact forces and vibrations in the wheel–rail contact system. This research establishes a novel vehicle-track coupled dynamic model that incorporates a 3D wheel–rail contact model using meshing grid and conjugate gradient methods to study the high-magnitude wheel–rail impact forces caused by rail weld irregularities and polygonal wheel combinations. The primary objective of this study is to develop a precise 3D contact model that incorporates the actual geometry of wheel and rail surface irregularities into the calculation of vehicle-track dynamic interactions. The study evaluates the effects of 3D rail weld irregularities and polygonal wheels on wheel–rail dynamic interaction by comparing results with those obtained from a conventional vehicle-track coupled model that considers a 2D contact model. The results show that the lengths and depths of polygonal wheels and rail weld irregularities, as well as vehicle speeds, significantly increase the wheel/rail dynamic impact forces. The results also indicate that the widening of irregularities not only significantly affects the wheel–rail contact force but also has an important influence on the contact stiffness.

Friction in soft biological systems and surface self-organization: the role of viscoelasticity

AbstractFriction is a critical factor in the proper functioning of human organs as well as in the potential development of disease. It is also important for the design of diagnostic and interventional medical devices. Nanoscale surface roughness, viscoelastic or plastic deformations, wear, and lubrication all influence the functions of individual cells. The effects of friction in soft matter systems are quantified using different types of frictional coefficients, including the dynamic friction coefficient, friction-skin drag, and pressure drag. These coefficients are determined by the viscoelastic properties of the two systems in contact and their relative velocity. In this review, several biological systems are considered, including (i) epithelial tissues in contact with soft hydrogel-like implants, (ii) the collective migration of epithelial monolayers on substrate matrices, (iii) blood flow through blood vessels, and (iv) the movement of cancer cells past epithelial clusters along with the migration of epithelial cells within the cluster.

Achieving bifacial photovoltaic performance in PTB7-based organic solar cell by integrating transparent contact for emerging semi-transparent applications

In this study, the design, fabrication and detailed analysis of semi-transparent bifacial organic solar cells (ST-OSC) based on MoO3/Ag/WO3 (10/dm/dod nm) dielectric/metal/dielectric (DMD) transparent contact system integrated with PTB7 polymer were investigated. The study emphasizes the importance of designing transparent contact systems to optimize the solar cells’ transparency (average visible transmittance, AVT), color rendering (color rendering index, CRI), efficiency (power conversion efficiency, PCE), and bifaciality. The performance of three distinct configurations was examined in the AVTmax (47.14% AVT, 3.93% PCE), (CRIext)max (23.82% AVT, 6.21% PCE), and Extreme Color (26.34% AVT, 5.81% PCE). The theoretically predicted AVTs for these configurations were 48.75%, 22.29%, and 25.15%, respectively. The strong agreement between theoretical and observed outcomes confirmed the accuracy of the Transfer Matrix Model (TMM). Furthermore, the assessment of bifaciality performance exhibited that the AVTmax had a bifaciality factor of 0.94, with a PCE of 3.67% under top illumination and 3.93% under bottom illumination. The high bifaciality of the structure designed with TMM to maximize the AVT demonstrates the value of calculations prior to solar cell structure fabricating and the possibility of constructing high bifaciality structures using this technique.

Unraveling the thrombin–Alzheimer’s connection: Oral anticoagulants as potential neuroprotective therapeutics

In Alzheimer’s disease (AD), toxic amyloids formed by amyloid-β (Aβ) proteins and tau are implicated in the development of inflammatory, vascular, and neurodegenerative brain disorders. Thrombin has also been recognized as a proteopathic factor involved in Aβ-induced neurovascular dysfunction. Vascular Aβ activates the contact system in the blood, stimulating the production of inflammatory bradykinin and procoagulant thrombin. Thrombin, in turn, triggers inflammation, platelet activation, and the formation of fibrinolysis-resistant, Aβ-containing fibrin clots, leading to Aß-type cerebral amyloid angiopathy and associated neuropathology. Targeting thrombin with oral anticoagulants can normalize proinflammatory and prothrombotic states, counteracting the neurovascular consequences of AD. Pre-clinical studies have shown that such interventions preserve vascular and blood–brain barrier integrity, improve cerebral blood flow and brain perfusion, and reduce parenchymal accumulations of toxic Aβ, tau, fibrin(ogen), and thrombin. These effects mitigate neuroinflammatory and neurodegenerative processes, ultimately preserving cognitive functions for a longer period. Recent observational clinical studies in patients with atrial fibrillation (AF) demonstrated that treatment with direct oral anticoagulants (DOACs) or vitamin K antagonists (VKAs) reduced the risk of dementia by up to 48% compared to non-users. The anti-dementia effects were most prominent in elderly patients but were also observed in individuals with low AF risk or newly diagnosed AF. In addition, DOACs reduced the risk of intracranial hemorrhage by approximately 50% compared to VKAs. The current review highlights the potential neuroprotective role of DOACs in AD. By preventing excessive thrombin generation caused by Aβ pathology, DOACs could protect vascular and neuronal functions, thereby slowing cognitive decline. DOACs, such as dabigatran, apixaban, and rivaroxaban, warrant further clinical investigation for their potential repurposing as disease-modifying therapeutics in AD.

Геополитические реалии российско-американских отношений

The article examines the key aspects of the geopolitical realities in Russian-American relations at the present stage. The current state of the global system of international contacts is analyzed. Particular attention is paid to the factors determining the strategic interests of Russia and the United States, as well as the impact of regional conflicts on the dynamics of interaction between the two powers. The economic, military-political and information aspects of the confrontation are being investigated. Based on a comprehensive analysis, practical recommendations are offered for stabilizing Russian-American relations and adapting the system of international contacts to the realities of the emerging multipolar world. It is noted that Russia in the modern geopolitical space has several vectors of development, characterized by an increasing influence on global processes determined by strategies for the realization of national interests in the context of a transforming system of international relations. The complexity and inconsistency of modern relations between the two powers is emphasized, as well as the need to find ways of cooperation to solve global problems.

Methodology for Testing Selected Parameters of Low-Current Vacuum Electric Arc

This article presents the author’s methodology for testing selected parameters of a low-current vacuum arc, implemented using an innovative test stand based on a vacuum discharge chamber with a contact system mounted inside. In order to verify the validity of the adopted research methodology, as well as the correctness of the operation of the developed laboratory bench, measurements and calculations were made, among other things, of the energy and burning time of the vacuum arc, depending on selected factors, such as pressure and the delay time of the contact opening, calculated from the “passage through zero” of the sinusoid of the current flowing through the system. The tests were performed at 230 V and a current of 5 A for two pressure values: p1 = 1.00 × 105 Pa (atmospheric pressure) and p2 = 4.00 × 10−3 Pa (high vacuum environment). It was found that the vacuum insulation technique allows a significant reduction in the value of the arc energy and the burning time of the arc. It was also observed that in the case of a high vacuum environment, the ignition of the vacuum arc occurs after a time equal to about 3 ms from the “passage through zero” of the current flowing through the system. Below this value, the phenomenon did not occur. The results obtained provide an opportunity for the design and manufacturing of vacuum switchgear, where there is the prospect of reducing the negative effects associated with the arc burning process in the contact gap.

Research Progress on Current-Carrying Friction with High Stability and Excellent Tribological Behavior

Current-carrying friction affects electrical contact systems like switches, motors, and slip rings, which determines their performance and lifespan. Researchers have found that current-carrying friction is influenced by various factors, including material type, contact form, and operating environment. This article first reviews commonly used materials, such as graphite, copper, silver, gold, and their composites. Then different contact forms like reciprocating, rotational, sliding, rolling, vibration, and their composite contact form are also summarized. Finally, their environmental conditions are also analyzed, such as air, vacuum, and humidity, on frictional force and contact resistance. Additionally, through experimental testing and theoretical analysis, it is found that factors such as arcing, thermal effects, material properties, contact pressure, and lubrication significantly influence current-carrying friction. The key mechanisms of current-carrying friction are revealed under different current conditions, including no current, low current, and high current, thereby highlighting the roles of frictional force, material migration, and electroerosion. The findings suggest that material selection, surface treatment, and lubrication techniques are effective in enhancing current-carrying friction performance. Future research should focus on developing new materials, intelligent lubrication systems, stronger adaptability in extreme environments, and low friction at the microscale. Moreover, exploring stability and durability in extreme environments and further refining theoretical models are essential to providing a scientific basis for designing efficient and long-lasting current-carrying friction systems.

An evolutionary mixed variational problem with time‐dependent Tresca friction arising from multi‐layer viscoelastic contact systems

An evolutionary mixed variational problem with time‐dependent Tresca friction arising from multi‐layer viscoelastic contact systems

A reinvestigation on combined dry and wet adhesive contact considering surface tension

The present study theoretically explores combined dry and wet adhesive contact between a rigid sphere and elastic semi-half substrate, in which dry contact is encircled by liquid bridge. We consider threefold effects of liquid bridge on contact behavior, namely Laplace pressure induced by the curved surface of liquid meniscus, surface tension at the triple-phase junction and alternation of adhesion energy between solid surfaces ascribed to liquid immersion. A clear novelty in this study is the investigation on the effect of surface tension at the vapor-liquid-solid junction on the adhesive contact response, in contrast to previous studies. The model solution predicts that the contact behavior and adhesive strength are strongly dependent on surface wettability (manifested by contact angle), liquid volume and the contact system's rapidity in achieving thermodynamic equilibrium. It is found that the transition of the pull-off force is evidently different from Maugis-Dugdale model in terms of a couple of interesting characteristics. Moreover, it is unveiled that the jump instabilities and hysteresis of force-separation curves are highly affected by surface wettability and liquid volume. These theoretical results can not only shed lights on the mechanism of liquid-mediated adhesion employed by animals and plants, but also provide us inspiration for development of biomimetic adhesive devices.

Touchpoints and systems for unmanned autonomous urban ferry operation

Abstract Currently, both experimental and commercial autonomous ferry services have a safety operator onboard who monitors the ferry systems, takes care of the passengers’ safety, and gives them the necessary information. Service touchpoints are all the interaction points between the autonomous ferry and the passengers throughout the passenger journey, from planning the trip to reaching their destination. To reach a state where the ferry service can be unmanned, by moving the safety operator into a remote operation centre, several additional systems and service touchpoints are needed to support the passengers’ safety and provide them with necessary information. This article discusses (1) the service touchpoints and systems needed for an autonomous urban ferry service, (2) how these touchpoints provide the passengers with the necessary information to foster trust and perceived safety, and (3) shows some examples and design suggestions for the experimental autonomous urban ferry milliAmpere2. The service touchpoints presented are (1) a ticket system, (2) an automatic ferry ordering system for on-demand operation, (3) an automatic passenger handling system for safe boarding of the ferry, (4) a passenger information system to provide visual and audio feedback about the ferry service, and (5) a passenger-operator communication system in case contact between the ferry and the remote operation centre need to be established.

Optical Measurement System for Monitoring Railway Infrastructure—A Review

Rail infrastructure plays an important role in fulfilling the demand for freight and passenger transportation. Increases in traffic volume, heavier axles and vehicles, higher speeds, and increasing climate extremes all contribute to the constant strain on the infrastructure. Due to their major importance in the transportation of people and freight, they are subject to continuous condition monitoring. This is an essential requirement for the selective planning of maintenance tasks and ultimately for safe and reliable operation. Various measuring systems have been developed for this purpose. These must measure precisely, quickly, and robustly under difficult conditions. Whether installed from mobile or stationary platforms, they have to cope with a wide range of ambient temperatures and lighting conditions, harsh environmental influences, and varying degrees of reflection. Despite these circumstances, railway operators require precise measurement data, high data densities even at high traveling speeds, and a user-friendly presentation of the results. Photogrammetry, laser scanning, and fiber optics are light-based measurement methods that are used in this sector. They are able to record with high precision rail infrastructure such as overhead contact systems, clearance profiles, rail tracks, and much more. This article provides an overview of the established and modern optical sensing methods, as well as the use of artificial intelligence as an evaluation method, and highlights their advantages and disadvantages.

Dairy calves' time spent in the cow herd in a calf-driven cow-calf contact system during two-step separation with a nose flap

Although originally developed for weaning of beef calves, nose flaps are also used on dairy farms nowadays to wean calves which are reared with contact to their dam or a foster cow. These calves are often weaned younger than beef calves and the time they wear nose flaps is highly variable, since it is unknown for how long younger calves need to wear the nose flap in order to induce an effective weaning. The aim of our study was therefore to track changes in dam-contact initiated by dairy calves after insertion of a nose flap in order to determine the minimum duration a nose flap needs to be worn to effectively reduce suckling motivation of calves. The study was conducted in two sequential experiments using 3-month-old dairy calves that were reared with full-time dam contact. Calves were weaned with a nose flap over either 14 (experiment I, 9 calves in herd A and 9 calves in herd B) or 7 days (experiment II, 11 calves in herd A and 12 calves in herd B) before they were fence-line separated from their dams. The total time a calf spent within the cow herd (TIC) per day was determined from continuous video recordings during 7 days before nose flap insertion (baseline), as well as during the 7 or 14 days in which calves had free access to the cow area while wearing the nose flap. Statistical analysis was conducted using linear mixed effects models. Results from both experiments showed that calves reduced their TIC at the fourth day of wearing the nose flap compared to their individual baseline (p=0.03 and p=0.001 respectively). In experiment I, calves showed a further numerical reduction in TIC from day 4 to day 5, while in experiment II, calves showed no further reduction in TIC after the 4 days of wearing the nose flap. After these 4 or 5 days respectively, TIC of calves in both experiments stayed at a constant low level of several hours per day. Taken together, these results indicate that in 3-month-old dairy calves it needs at least 4 days until the motivation to spend time with the cow decreases after insertion of a nose flap, while there seems to be no further decrease in motivation when using a nose flap longer than this time. However, results were subject to considerable inter-individual variability already during the baseline week and need replication in a pasture-based setting with less space-restrictions.

Electro-responsive superabsorbent hydrogel based on carboxymethyl cellulose as a draw agent for forward osmosis desalination

To explore a simple and energy-efficient approach to regenerate draw agent is a key challenge for forward osmosis (FO) desalination. Electro-responsive hydrogels have attracted great attention due to their reversible swelling-shrinking behaviors under an electric stimulus. However, the developed electro-sensitive hydrogels based on 2-acrylamido-2-methyl-l-propanesulfonic acid (AMPS) so far exhibit low reusability due to their unstable electro-sensitive properties and poor degradability with potential environmental impact. This study explored the use of an electro-responsive superabsorbent hydrogel as a draw agent by grafting acrylic acid (AA) and acrylamide (AM) onto sodium carboxymethyl cellulose (CMC). The grafted hydrogel’s morphology and structure were investigated by FTIR and SEM. The swelling behaviors and deswelling properties in an electrode contact system were examined. The swelling kinetics of the hydrogel could be well described by the Schott's pseudo-second-order model with a theoretical swelling ratio of 452.5 g/g. The grafted hydrogel exhibited stable electro-sensitive characteristics with a decrease of 7.3 % in the equilibrium swelling ratio after undergoing three cycles of deswelling and swelling. During the FO test, the dry hydrogel particles produced a water flux of 1.55 L·m−2·h−1 within the first hour, surpassing the performance of other carboxylic acid-based hydrogels used as draw agents. Significantly, it exhibited encouraging water recovery capabilities in the five recycling FO processes, retaining around 84 % of its initial water recovery ratio after 40 min of exposure to a voltage of 15 V. This indicated that the grafted hydrogel could be considered as an effective and sustainable draw agent for FO desalination.

Exploration of immunomodulatory mechanism of caprine Wharton’s jelly derived mesenchymal stem cells

The present study was aimed to explore the possible mechanisms by which caprine Wharton’s jelly-derived MSCs (WJ-MSCs) perform their immunomodulatory function. WJ-MSCs were isolated through explants culture and characterized as per ISCT criteria using culture behavior, expression of surface markers by PCR, FACS and immunocytochemical localization (ICC), trilineage differentiation potential etc. Secretory behavior for important biomolecules (IDO, TGFβ1, VEGF, IL6) was evaluated by ICC and western blot assay. Cell-to-cell communication was studied by culturing cells in cell–cell contact and trans-well system. The MSCs when co-cultured with activated Tc and Th cells, down-regulation of T cell cytokine as well as upregulation of immunomodulatory factors (VEGF A, IL10, IL6, IDO, iNOS, PTGS2, HGF, TGFβ, CXCL10, CXCL11) was noticed in both cell–cell contact and trans-well culture system which was significantly higher in cell–cell contact system. Trilineage differentiation of MSCs showed significant upregulation of MHC I (CAHI) and MHC II (CLA DRB3) molecules suggesting better clinical applications of MSCs without differentiation to avoid immune rejection. It can be concluded that WJ-MSCs perform their immunomodulation through the secretion of a battery of biomolecules and work in both cell–cell contact manner and through their secretome.

Pros and Cons of (NH4)2S Solution Treatment of p-GaN/Metallization Interface: Perspectives for Laser Diode.

The impact of wet treatment using an (NH4)2S-alcohol solution on the interface state of the p-GaN/Ni/Au/Pt contact system and laser diode processing was investigated. Sulfur wet cleaning resulted in reduced surface roughness and contact resistivity. The lowest specific contact resistance (ρc < 1 × 10-4 Ω·cm2) was achieved with samples treated with an (NH4)2S-isopropanol solution, whereas the highest resistivity (ρc = 3.3 × 10-4 Ω·cm2) and surface roughness (Ra = 16 nm) were observed in samples prepared by standard methods. Annealing the contact system in an N2 + O2 + H2O atmosphere caused degradation through species inter-diffusion and metal-metal solid solution formation, irrespective of the preparation method. Standard prepared substrates developed a thin GaN-Au intermediate layer at the interface after heat treatment. Enhanced adhesion and the absence of GaN decomposition were observed in samples additionally cleaned with the (NH4)2S-solvent solution. Complete oxidation of nickel to NiO was observed in samples that underwent additional sulfur solution treatment. The intensity of metal species mixing and nickel oxidation was influenced by the metal diffusion rate and was affected by the initial state of the GaN substrate obtained through different wet treatment methods.