Changes In Deposition Rates Research Articles

Effect of wire deposition rate on macro and microscopic characteristics of laser weld-brazed AA5083 aluminum alloy to galvanized steel joints and their corrosion response

ABSTRACT In this study, dissimilar metals, such as aluminium (AA5083) and galvanised interstitial free steel, were laser-brazed in a flange configuration using eutectic filler aluminium wire (4047, Al-12%Si). To investigate the effects of wire deposition rate on the characteristics of laser-brazed joints and to understand the factors contributing to corrosion in these joints. The wire deposition rates were varied while keeping other laser parameters constant. Changes in wire deposition rate were observed to affect the flow behaviour of molten metal leading to variations in the geometrical characteristics of the brazed joints and interfacial reactions as revealed by macroscopic examination. A series of corrosion tests, including electrochemical, immersion, and salt spray tests, were conducted on the laser-brazed joints. It was demonstrated by Immersion corrosion tests that the wire rate influenced the corrosion results for the laser-brazed joints. However, the salt spray test showed no substantial effect on corrosion with respect to different wire deposition rates. Furthermore, the electrochemical results indicated significant changes in the corrosion response of the brazed zone due to the presence of chemically dissimilar phases. A correlative discussion between laser parameters, observed microstructure, and their effects on the corrosion performance of the brazed samples is presented.

A new look at an explanation of band gap of PECVD grown a-Si:H thin films using absorption spectra, spectroscopic ellipsometry, Raman, and FTIR spectrosopy

Amorphous silicon is seen to be among the most promising materials for solar cell applications because of its higher temperature coefficient of resistance, adjustable forbidden-band gap, enhanced optical absorption, and capacity to reduce solar module costs. Changes in deposition rate, absorption coefficient and optical band gap of a-Si:H films with varying silane flow rate show that SiH4 molecules density influence the plasma growth process. Silane flow rate affects the percentage of silicon atoms during processing. The deposition rate of a-Si: H films increased from 14.36 nm/min to 15.97 nm/min by increasing silane flow rate from 25 sccm to 45 sccm. Broadening of optical band is observed. Films deposited at 35 sccm of silane flow rate shows the higher absorption coefficient. All films are characterized by FTIR, Raman spectroscopy, spectroscopic ellipsometry and optical absorption to understand the changes in band gap. The band gap Eg of all films is correlated with microstructure factor, Q factor, bond angle deviation Δθ and width of Si–H2 mode to analyse the effect of defects, disorders and microvoids.

Paleo±Dust: quantifying uncertainty in paleo-dust deposition across archive types

Abstract. Mineral dust aerosol concentrations in the atmosphere varied greatly on glacial–interglacial timescales. The greatest changes in global dust activity occurred in response to changes in orbital parameters (which affect dust emission intensity through glacial activity) and the lifetime of dust in the atmosphere (caused by changes in the global hydrological cycle). Long-term changes in the surface dust deposition rate are registered in geological archives such as loess, peats, lakes, marine sediments, and ice. Data provided by these archives are crucial for guiding simulations of dust and for better understanding the natural global dust cycle. However, the methods employed to derive paleo-dust deposition rates differ markedly between archives and are subject to different sources of uncertainty. Here, we present Paleo±Dust, an updated compilation of bulk and <10 µm paleo-dust deposition rates with quantitative 1σ uncertainties that are inter-comparable among archive types. Paleo±Dust incorporates a total of 285 pre-industrial Holocene (pi-HOL) and 209 Last Glacial Maximum (LGM) dust flux constraints from studies published until December 2022, including, for the first time, peat records. We also recalculate previously published dust fluxes to exclude data from the last deglaciation and thus obtain more representative constraints for the last pre-industrial interglacial and glacial end-member climate states. Based on Paleo±Dust, the global LGM:pi-HOL ratio of <10 µm dust deposition rates is 3.1 ± 0.7 (1σ). We expect Paleo±Dust to be of use for future paleoclimate dust studies and simulations using Earth system models of high to intermediate complexity. Paleo±Dust is publicly accessible at https://doi.org/10.1594/PANGAEA.962969 (Cosentino et al., 2024).

Combining multiple investigative approaches to unravel functional responses to global change in the understorey of temperate forests

AbstractPlant communities are being exposed to changing environmental conditions all around the globe, leading to alterations in plant diversity, community composition, and ecosystem functioning. For herbaceous understorey communities in temperate forests, responses to global change are postulated to be complex, due to the presence of a tree layer that modulates understorey responses to external pressures such as climate change and changes in atmospheric nitrogen deposition rates. Multiple investigative approaches have been put forward as tools to detect, quantify and predict understorey responses to these global‐change drivers, including, among others, distributed resurvey studies and manipulative experiments. These investigative approaches are generally designed and reported upon in isolation, while integration across investigative approaches is rarely considered. In this study, we integrate three investigative approaches (two complementary resurvey approaches and one experimental approach) to investigate how climate warming and changes in nitrogen deposition affect the functional composition of the understorey and how functional responses in the understorey are modulated by canopy disturbance, that is, changes in overstorey canopy openness over time. Our resurvey data reveal that most changes in understorey functional characteristics represent responses to changes in canopy openness with shifts in macroclimate temperature and aerial nitrogen deposition playing secondary roles. Contrary to expectations, we found little evidence that these drivers interact. In addition, experimental findings deviated from the observational findings, suggesting that the forces driving understorey change at the regional scale differ from those driving change at the forest floor (i.e., the experimental treatments). Our study demonstrates that different approaches need to be integrated to acquire a full picture of how understorey communities respond to global change.

Sediment organic carbon and nitrogen trapping in a small reservoir within a typical agricultural granite catchment

Small reservoirs are more widely distributed globally than larger reservoirs, and they have characteristic sediment total organic carbon (TOC) and total nitrogen (TN) trapping patterns that differ from those of larger reservoirs. Few studies have quantified the TOC and TN trapping in a small reservoir within a catchment underlain by a single lithology, particularly in non-karst terrain, from the perspective of environmental change. Based on the chronologies established using 137Cs and 210Pbex, we assessed the temporal patterns of sediment TOC and TN trapping in a small reservoir within a typical agricultural granite catchment (Yimeng Mountains, China) by examining depth trends in TOC and TN concentrations in three sediment cores and temporal trends in TOC and TN deposition rates in the reservoir over the past ∼60 years. The TOC and TN concentrations and C/N ratios show an overall upward increase in the three cores. The TOC and TN deposition rates were relatively high during 1954–1962, decreased to the lowest rates during 1963–1972, and generally increased thereafter. Anthropogenic sources associated with agriculture were the dominant factor in the up-core increases in TOC and TN concentrations, although natural sources were the main contributor to TOC and TN deposition. The temporal changes in TOC and TN deposition rates were mainly due to the sediment yield rather than anthropogenic sources associated with agriculture. The changes in TOC and TN concentrations with depth, and temporal changes in the TOC and TN deposition rates determined from the three cores, reflect the temporal patterns of sediment TOC and TN trapping in the small reservoir over the past ∼60 years. Sediment yield exerted a greater effect on the TOC and TN deposition in the studied reservoir, as compared with a previously reported reservoir within a small agricultural limestone catchment, and the different results of the two studies originated from the contrasting lithologies in the two catchments. Moreover, a comparison with data obtained for a previously studied large reservoir suggests that differences in TOC and TN deposition (including concentrations, specific deposition rates, and temporal trends in deposition rates) are related to catchment size, and the comparison highlights the characteristic patterns of TOC and TN trapping in the small and large reservoirs. The present findings improve our understanding of the temporal patterns of sediment TOC and TN trapping in a small reservoir within a typical agricultural granite catchment in terms of environmental changes influenced by human activity. This study also enhances our knowledge of the barrier effects of a dam on the downstream transport of TOC and TN in a small catchment in a non-karst setting, and the redistribution of sediment TOC and TN in a large river, which can help guide strategies for water resource management on the river basin-scale.

Phosphorus Addition Reduces Seedling Growth and Survival for the Arbuscular Mycorrhizal Tree Cinnamomum camphora (Lauraceae) and Ectomycorrhizal Tree Castanopsis sclerophylla (Fagaceae) in Fragmented Forests in Eastern China.

Global changes in nutrient deposition rates and habitat fragmentation are likely to have profound effects on plant communities, particularly in the nutrient-limited systems of the tropics and subtropics. However, it remains unclear how increased phosphorus (P) supply affects seedling growth in P-deficient subtropical fragmented forests. To explore this, we applied P to 11 islands in a subtropical Chinese archipelago and examined the results in combination with a contemporary greenhouse experiment to test the influence of P addition on seedling growth and survival. We measured the growth (i.e., base area) and mortality rate of seedlings for one arbuscular mycorrhizal (AM) and one ectomycorrhizal (EcM) tree species separately and calculated their relative growth rate and mortality when compared with P addition and control treatment on each island. We also measured three functional traits and the biomass of seedlings in the greenhouse experiment. Results showed that P addition significantly increased the mortality of AM and EcM seedlings and reduced the growth rate of EcM seedlings. The relative growth rate of AM seedlings, but not EcM seedlings, significantly decreased as the island area decreased, suggesting that P addition could promote the relative growth rate of AM seedlings on larger islands. The greenhouse experiment showed that P addition could reduce the specific root length of AM and EcM seedlings and reduce the aboveground and total biomass of seedlings, indicating that P addition may affect the resource acquisition of seedlings, thereby affecting their survival and growth. Our study reveals the synergistic influence of habitat fragmentation and P deposition, which may affect the regeneration of forest communities and biodiversity maintenance in fragmented habitats.

Annualized changes in rate of amyloid deposition and neurodegeneration are greater in participants who become amyloid positive than those who remain amyloid negative

This study longitudinally examined participants in the Alzheimer’s Disease Neuroimaging Initiative (ADNI) who underwent a conversion in amyloid-beta (Aβ) status in comparison to a group of ADNI participants who did not show a change in amyloid status over the same follow-up period. Participants included 136 ADNI dementia-free participants with 2 florbetapir positron emission tomography (PET) scans. Of these participants, 68 showed amyloid conversion as measured on florbetapir PET, and the other 68 did not. Amyloid converters and non-converters were chosen to have representative demographic data (age, education, sex, diagnostic status, and race). The amyloid converter group showed increased prevalence of APOE ε4 (p < 0.001), greater annualized percent volume loss in selected magnetic resonance imaging (MRI) regions (p < 0.05), lower cerebrospinal fluid Aβ1–42 (p < 0.001), and greater amyloid retention (as measured by standard uptake value ratios) on florbetapir PET scans (p < 0.001) in comparison to the non-converter group. These results provide compelling evidence that important neuropathological changes are occurring alongside amyloid conversion.

Effect of low-cost recirculating portable air filtration on aerosol particle deposition and concentration in a conference room: Experiment, theory, and simulation comparison

Respiratory particles exhaled when an individual speaks and breathes can facilitate respiratory virus transmission. Portable air purification units can potentially reduce transmission risk by decreasing the overall infectious particle concentration in a room. This is particularly important for rooms with an inability to be ventilated with adequate amounts of filtered or outdoor air. While the efficacy of portable air filtration units on particle concentrations has been well-studied, the impact of portable air purification units on particle deposition and, hence, indirect aerosol transmission, has received lesser study but may be important for smaller spaces with greater surface area-to-volume ratios. We conducted a series of experiments in a simulated, small conference room (34.4 m3, mimicking a common office meeting room) assessing (1) particle removal rates and (2) changes in deposition rate owing to the presence of a low-cost box fan air purifier (BFAP). To mimic an infectious aerosol source, a breathing simulator manikin was utilized in these experiments, which ejected fluorescein tagged particles in the 1–3 μm size range throughout each experimental condition, with a prescribed, periodic, breathing waveform mimicking human exhalation. We measured deposition flux on upward- and downward-facing horizontal surfaces throughout the room and determined aerosol mass concentrations using impingers; combined, these data enabled estimates of surface-specific deposition velocities. Aerosol size distributions within the room were also quantified using an optical particle spectrometer. CFD simulations and theoretical calculations were simultaneously conducted for comparison to the experimental data. Results suggested the BFAP unit, which had an effective clean air delivery rate of 540 m3 h−1, increased the effective air exchange rate by 4.4x over baseline (20.1 vs. 4.5 h−1). Notably, BFAP unit operation introduced greater deposition to surfaces near the breathing simulator manikin vs. baseline, with deposition velocities within 2 m of the breathing simulator being 100 cm s−1 during BFAP operation, compared to 10−2 cm s−1 during baseline. Deposition velocities and air exchange rates generated from the CFD and theoretical calculations largely agreed with those derived from experiments. Taken together, data suggest that in smaller rooms, such as conference rooms, deposition is not negligible as a mechanism of aerosol clearance, even for particles near 1–3 μm in diameter.

Global Dust Cycle and Direct Radiative Effect in E3SM Version 1: Impact of Increasing Model Resolution

AbstractQuantification of dust aerosols in Earth System Models (ESMs) has important implications for water cycle and biogeochemistry studies. This study examines the global life cycle and direct radiative effects (DREs) of dust in the U.S. Department of Energy's Energy Exascale Earth System Model version 1 (E3SMv1), and the impact of increasing model resolution both horizontally and vertically. The default 1° E3SMv1 captures the spatial and temporal variability in the observed dust aerosol optical depth (DAOD) reasonably well, but overpredicts dust absorption in the shortwave (SW). Simulations underestimate the dust vertical and long‐range transport, compared with the satellite dust extinction profiles. After updating dust refractive indices and correcting for a bias in partitioning size‐segregated emissions, both SW cooling and longwave (LW) warming of dust simulated by E3SMv1 are increased and agree better with other recent studies. The estimated net dust DRE of −0.42 Wm−2 represents a stronger cooling effect than the observationally based estimate −0.2 Wm−2 (−0.48 to +0.2), due to a smaller LW warming. Constrained by a global mean DAOD, model sensitivity studies of increasing horizontal and vertical resolution show strong influences on the simulated global dust burden and lifetime primarily through the change of dust dry deposition rate; there are also remarkable differences in simulated spatial distributions of DAOD, DRE, and deposition fluxes. Thus, constraining the global DAOD is insufficient for accurate representation of dust climate effects, especially in transitioning to higher‐ or variable‐resolution ESMs. Better observational constraints of dust vertical profiles, dry deposition, size, and LW properties are needed.

Observations and modelling of glyoxal in the tropical Atlantic marine boundary layer

Abstract. In situ field measurements of glyoxal at the surface in the tropical marine boundary layer have been made with a temporal resolution of a few minutes during two 4-week campaigns in June–July and August–September 2014 at the Cape Verde Atmospheric Observatory (CVAO; 16∘52′ N, 24∘52′ W). Using laser-induced phosphorescence spectroscopy with an instrumental detection limit of ∼1 pptv (1 h averaging), volume mixing ratios up to ∼10 pptv were observed, with 24 h averaged mixing ratios of 4.9 and 6.3 pptv observed during the first and second campaigns, respectively. Some diel behaviour was observed, but this was not marked. A box model using the detailed Master Chemical Mechanism (version 3.2) and constrained with detailed observations of a suite of species co-measured at the observatory was used to calculate glyoxal mixing ratios. There is a general model underestimation of the glyoxal observations during both campaigns, with mean midday (11:00–13:00) observed-to-modelled ratios for glyoxal of 3.2 and 4.2 for the two campaigns, respectively, and higher ratios at night. A rate of production analysis shows the dominant sources of glyoxal in this environment to be the reactions of OH with glycolaldehyde and acetylene, with a significant contribution from the reaction of OH with the peroxide HC(O)CH2OOH, which itself derives from OH oxidation of acetaldehyde. Increased mixing ratios of acetaldehyde, which is unconstrained and potentially underestimated in the base model, can significantly improve the agreement between the observed and modelled glyoxal during the day. Mean midday observed-to-modelled glyoxal ratios decreased to 1.3 and 1.8 for campaigns 1 and 2, respectively, on constraint to a fixed acetaldehyde mixing ratio of 200 pptv, which is consistent with recent airborne measurements near CVAO. However, a significant model under-prediction remains at night. The model showed limited sensitivity to changes in deposition rates of model intermediates and the uptake of glyoxal onto aerosol compared with sensitivity to uncertainties in chemical precursors. The midday (11:00–13:00) mean modelled glyoxal mixing ratio decreased by factors of 0.87 and 0.90 on doubling the deposition rates of model intermediates and aerosol uptake of glyoxal, respectively, and increased by factors of 1.10 and 1.06 on halving the deposition rates of model intermediates and aerosol uptake of glyoxal, respectively. Although measured levels of monoterpenes at the site (total of ∼1 pptv) do not significantly influence the model calculated levels of glyoxal, transport of air from a source region with high monoterpene emissions to the site has the potential to give elevated mixing ratios of glyoxal from monoterpene oxidation products, but the values are highly sensitive to the deposition rates of these oxidised intermediates. A source of glyoxal derived from production in the ocean surface organic microlayer cannot be ruled out on the basis of this work and may be significant at night.

Real-time monitoring of electrochemically induced calcium carbonate depositions: Kinetics and mechanisms

Calcium carbonate (CaCO3) deposition plays a significant role in processes such as scale formation in power plants and in oil or gas production wells. The development of appropriate methods based on well suitable in situ sensors is important to evaluate and predict the deposition process. In this study, a combination of electrochemical techniques and quartz crystal microbalance with dissipation monitoring (QCM-D) in one analysis setup (EQCM-D) was used for the first time to monitor the CaCO3 deposition in real time and provide kinetic details of the CaCO3 deposition process. Through recording the frequency change of quartz crystal sensors, it allows us to perform a quantitative analysis of the morphology, coverage, deposition rate, and mass changes with nanogram sensitivity. By varying the applied voltage, it was found that a lower applied voltage resulted in more deposition of CaCO3 mass and increase of the thickness of the deposited layer. Under the absence of flow, the CaCO3 growth rate switched from accelerating to decelerating and this point is characterized by an inflection point (IP). A lower applied voltage resulted in a lower IP. Increasing Ca2+ and HCO3− concentrations, both the deposited amount of CaCO3 mass and coating thickness increased correspondingly. With the addition of 50 mM Mg2+, a reduction in the deposition rate of CaCO3 as high as 73% was achieved. The higher the Mg2+ concentration, the larger the deposition rate reduction, which was attributed to the incorporation of Mg2+ into the growing CaCO3 mineral, resulting in the reduction of growth sites (inhibiting effect). The obtained results contribute to a better understanding of electrochemically induced CaCO3 deposition and provide valuable insights into the determination of optimal precipitation parameters, with the aim to optimize industry scaling and anti-scaling processes.

Reconstruction of temporal and spatial trends of atmospheric pollution based on polychlorinated biphenyls concentration changes in ombrotrophic bogs

To reconstruct the deposition rate of polychlorinated biphenyls (PCBs) in different historical periods and to examine the temporal and spatial trend of PCBs pollution, we analyzed the changes of PCBs concentration and deposition rate in peat cores and lake sediments, and evaluated the suitability of peat cores and lake sediments for studying PCBs deposition trend. Through the dating analysis of all samples, we found that peat bog could well record the historical sedimentation of PCBs. PCBs did not degrade in peat, and it was thus feasible to use peatland to examine the settlement of PCBs. In this study, the reconstruction time of ∑11PCBs in peat was from the beginning of 19th century to the beginning of 21st century. The mean inventory of ∑11PCBs in three peat cores of each bog changed between (37.0±5.4) and (47.2 ±27.8) μg·m-2, with the standard deviation between 14.9% and 58.9%. The highest concentration of ∑11PCBs was 6.8 ng·g-1DW, while the maximum deposition rate of reconstructed PCBs was up to 989.7 ng·m-2·a-1. The trend of deposition rate was first increasing and then decreasing. After the year 1980, the deposition rate was substantially decreasing, which was consistent with the prohibition of PCBs production in the United States in 1979. Meanwhile, the analysis of sediment samples in the lake near bog showed that concentration and maximum deposition rate of the lake sediment were comparable to those of the nearby bog. The concentrations of Di- to Hepta-PCB congeners were evenly distributed along the sediment profile. Therefore, lake sediments could not be used to analyze the historical sedimentary model of low order PCBs. This study reconstructed temporal and spatial variation of PCBs in atmospheric environment in different historical periods, which could provide basic data for the evaluation of regional environmental quality.

Study of silicon nitride deposition in III-N MOVPE reactors

Si3N4 deposition from silane and ammonia in a number of III-N MOVPE reactors of various sizes was studied in a wide range of reactor conditions. It was revealed that Si3N4 deposition rate depends on temperature, pressure, carrier gas type, and ammonia concentration. Deposition rate rises with temperature up to 1050–1100 °C in a manner typical for temperature-activated processes, but under any studied conditions, including the 800–850 °C range, it is strictly linear with SiH4 concentration indicating the absence of high-order parasitic reactions at high temperature and surface passivation at low temperature. For a low-volume reactor the higher the pressure is, the faster the deposition is both for N2 and H2 carrier gases. For large reactors the dependence is non-monotonic. At temperature above 900 °C using H2 as a carrier gas results in a higher Si3N4 deposition rate than when using N2. If nitrogen is used as a carrier gas, deposition rate gradually rises with ammonia concentration. If hydrogen is used, deposition rate rapidly rises with ammonia concentration and then gradually falls. If hydrogen-nitrogen mixture is used as a carrier gas, deposition rate changes in a linear manner with the mole fraction of hydrogen in the carrier gas.

Sedimentation Patterns of Multiple Finnish Lakes Reveal the Main Environmental Stressors and the Role of Peat Extraction in Lake Sedimentation

Human land-use activities, especially in the peatlands, are under consideration as the mitigation and lowering of CO2 emissions from land-use practices is needed to address climate change. In Finland, approximately one third of the land surface is covered by peatlands, and around 50% of peatlands are ditched for forestry. Another 3% of peatlands are used for agriculture and approximately 1% for peat extraction. The effects of these different land-use practices, including changes in sediment depositional rates and sediment quality, need to be identified. This study analyzed 51 lakes that were subdivided into two groups: (1) a group of impacted lakes in which peat was recently extracted from the catchments and (2) a reference group consisting of lakes where peat had not been extracted from the basin, but in which other land-use activities had occurred. The overall aim of the study was to investigate if peat extraction caused excessive delivery and deposition of dry and organic matter in lakes that are located in their immediate downstream catchment areas. Differences in sediment accumulation were defined by comparing the overall sediment thickness and recent (post 1986) sedimentation levels to identify if there were differences in the sediment chemical composition or rate of organic matter deposition between groups and to identify possible land-use stressors that could explain the possible differences in sediment chemical assemblages or sedimentation rates. The results show moderate (cm scale) sedimentation rates in both impacted and reference lakes after 1986, while sediment chemical assemblages indicated the erosion and input of mineral soils to all of the studied lakes, rather than the input of organic materials. No statistically significant correlations were observed between selected environmental variables and the recent accumulation rates of carbon and dry matter. Moreover, significant changes in the stressors potentially affecting the chemical assemblages of pre- and post-disturbance sediments were not observed.

The effect of wire size on high deposition rate wire and plasma arc additive manufacture of Ti-6Al-4V

Wire + arc additive manufacture (WAAM) is suitable for building large-scale components with high deposition rate. However, in order to further increase the deposition rate of Ti-6Al-4V to improve productivity and reduce manufacture costs without significantly compromising the quality, some fundamental process characteristics need to be investigated. In this paper, the effect of wire size on the limitation of deposition rate and bead shape in plasma arc additive manufacture was studied along with the process tolerance and melting characteristics, such as the effect of current and nozzle size on keyhole behaviour and the effect of wire feeding position on deposition process. The results show that with the same heat input the deposition rate increases linearly with the wire size due to the increasing melting efficiency. The bead geometry obtained with a thinner wire has a higher aspect ratio, which can be attributed to the difference in the distribution of the energy between wire and workpiece. The likelihood of keyhole increases with increasing current and decreasing nozzle size, and it can be mitigated by using thicker wires. The wire feeding position plays a significant role in determining the metal transfer mode, which has a great impact on the bead shape and process stability. Also, as the deposition rate changes thin wire is more sensitive to wire feeding position than thick wire in terms of metal transfer behaviour.

Optimization of passivation in AlGaN/GaN heterostructure microwave transistor fabrication by ICP CVD

We have studied the effect of silicon nitride (SiN) dielectric passivating film deposition by inductively coupled plasma chemical vapor deposition (ICP CVD) on the parameters of AlGaN/GaN heterostructure high electron mobility transistors (HEMT). Study of the parameters of the dielectric layers has allowed us to determine the effect of RF and ICP power and working gas flow ratio on film growth rate and structural perfection, and on the current vs voltage curves of the passivated HEMT. The deposition rate changes but slightly with an increase in RF power but increases with an increase in ICP power. Transistor slope declines considerably with an increase in RF power: it is the greatest at minimum power RF = 1 W. In the beginning of growth even at a low RF power (3 W) the transistor structure becomes completely inoperable. Dielectric deposition for HEMT passivation should be started at minimum RF power. We have developed an AlGaN/GaN microwave HEMT passivation process providing for conformal films and low closed transistor drain–source currents without compromise in open state transistor performance: within 15 and 100 mA, respectively, for a 1.25 and 5 mm common T-gate (Ug = –8 V and Ud-s = 50 V).

Antibacterial Efficiency of Stainless-Steel Grids Coated with Cu-Ag by Thermionic Vacuum Arc Method

Autonomous smart natural ventilation systems (SVS) attached to the glass façade of living quarters and office buildings can help reducing the carbon footprint of city buildings in the future, especially during warm seasons and can represent an alternative to the conventional mechanical ventilation systems. The work performed in this manuscript focuses on the investigation of bacteria trapping and killing efficiency of stainless steel grids coated with a mixed layer of Cu-Ag. These grids are to be employed as decontamination filters for a smart natural ventilation prototype that we are currently building in our laboratory. The tested grids were coated with a mixed Cu-Ag layer using thermionic vacuum arc plasma processing technology. The fixed deposition geometry allowed the variation of Cu and Ag atomic concentration in coated layers as a function of substrate position in relation to plasma sources. The test conducted with air contaminated with a pathogen strain of staphylococcus aureus indicated that the filtering efficiency is influenced by two parameters: the pore size dimension and the coating layer composition. The results show that the highest filtering efficiency of 100% was obtained for fine pore (0.5 × 0.5 mm) grids coated with a mixed metallic layer composed of 65 at% Cu and 35 at% Ag. The second test performed only on reference grids and Cu-Ag (65–35 at%) under working conditions, confirm a similar filtering efficiency for the relevant microbiological markers. This particular sample was investigated from morphological, structural, and compositional point of view. The results show that the layer has a high surface roughness with good wear resistance and adhesion to the substrate. The depth profiles presented a uniform composition of Cu and Ag in the layer with small variations caused by changes in deposition rates during the coating process. Identification of the two metallic phases of the Cu and Ag in the layers evidences their crystalline nature. The calculated grain size of the nanocrystalline was in the range 14–21 nm.

Effect of frequency and pulse-on time of high power impulse magnetron sputtering on deposition rate and morphology of titanium nitride using response surface methodology

Abstract Titanium nitride thin films were deposited on silicon by high power impulse magnetron sputtering (HiPIMS) method at different frequencies (162−637 Hz) and pulse-on time (60−322 μs). Response surface methodology (RSM) was employed to study the simultaneous effect of frequency and pulse-on time on the current waveforms and the crystallographic orientation, microstructure, and in particular, the deposition rate of titanium nitride at constant time and average power equal to 250 W. The crystallographic structure and morphology of deposited films were analyzed using XRD and FESEM, respectively. It is found that the deposition rate of HiPIMS samples is tremendously dependent on pulse-on time and frequency of pulses where the deposition rate changes from 4.5 to 14.5 nm/min. The regression equations and analyses of variance (ANOVA) reveal that the maximum deposition rate (equal to (17±0.8) nm/min) occurs when the frequency is 537 Hz and pulse-on time is 212 μs. The experimental measurement of the deposition rate under this condition gives rise to the deposition rate of 16.7 nm/min that is in good agreement with the predicted value.

Time-richness and phosphatic microsteinkern accumulation in the Cincinnatian (Katian) Ordovician, USA: An example of polycyclic phosphogenic condensation

Millimeter-scale phosphatic steinkern preservation is a feature of the taxonomically enigmatic Early Cambrian “small shelly faunas”, but this style of preservation is not unique to the Cambrian; it is ubiquitous, if infrequently reported, from the Phanerozoic record. The polycyclic phosphogenic condensation (PPC) model envisions both the genesis and concentration of phosphatic microsteinkerns as natural outcomes of shell bed genesis through episodic sediment starvation. This model predicts that more reworked and condensed shell bed limestones will contain more phosphatic microsteinkerns, but that even the least reworked limestones may contain some phosphatic particles. We test this model through examination of vertical thin sections densely collected through a 10-meter interval from the classic Cincinnatian (upper Katian, middle Maysvillian North American Stage) upper Fairview Formation, Miamitown Shale, and lower Grant Lake formations at four localities near Cincinnati, Ohio. For each of approximately 50 distinguishable limestone depositional units in each locality, a 2 × 2 cm square was selected for study. Each square was assigned a textural classification (mud content of intergranular space) and a breakage rank (pristine to comminuted). Phosphatic particle distribution was quantified both by visual estimation and by particle counting, with counts ranging from none detected to over 1000 per 4 cm2. Our analyses show a strong positive relationship between phosphate content and both textural maturity and fragmentation. This positive relationship is consistent with the PPC model and confirms that textural maturity can reflect the degree of condensation as well as depth-related environmental energy. This finding suggests that shell bed processes of repeated deposition and reworking make a significant contribution to the generation and accumulation of phosphatic particles. If local-scale sedimentary processes and conditions can control this accumulation, temporal changes in phosphatic sediment deposition rates may be linked to earth changes more complexly than through changing ocean chemistry on a global scale.

Disentangling dust and sand deposition using a peat record in CE Europe (northern Romania): A multiproxy approach

Aeolian sediments play an important role in the global climatic system and occur in the atmosphere due to soil and bedrock erosion. Here, we applied three different methods: geochemical (XRF), manual and laser-based particle size analysis to an ombrotrophic peat profile in the Carpathian Mountains to determine changes in aeolian deposition and wind/storm activity over the last 7800 years. The results show the following changes in aeolian fluxes (dust and sand) over time: 7800–4150 cal. yr BP – generally low dust fluxes with a periodic intensification of sand fluxes; 4150–2300 cal. yr BP – intense deposition of both dust and sand; 2300–150 cal. yr BP – fluctuating dust and sand fluxes; the last 200 years – the highest amplitude of both sand and dust fluxes. This study found that patterns in aeolian fluxes were influenced by a combination of climate and human impact, but with anthropogenic drivers, such as disturbance by fire, becoming more important in recent times. We also found a good agreement with other studies of dust fluxes for the earlier part of this record, but an increasing divergence over the last 3500 years. In terms of a methodological approach, we suggest that the three approaches each have both advantages and disadvantages; though overall laser-based particle size dust and sand reconstruction appears to best capture the most complex changes in both aeolian deposition rates and sources.