Small Area Ratio Research Articles

Highly-efficient low-voltage electrodeposition of superhydrophobic diamond-like carbon films from N-methyl pyrrolidone

N-methyl pyrrolidone was proposed as a new carbon source for efficiently preparing the diamond-like carbon (DLC) films by a one-step electrodeposition technique at a low voltage. The responses of surface morphology, microstructure and surface wettability of the DLC films on the variation of the area ratio of anode to cathode were investigated in terms of current density in the process of electrodeposition. Especially, the dynamic behaviors of water droplets impacting on one of the superhydrophobic DLC films were studied in detail as a function of Weber number and inclined angle. Results revealed that either a larger or a smaller area ratio than 1.56 could facilitate the formation of hierarchical structure with more hydrocarbon features, which is in favor of creating superhydrophobicity with low surface adhesion. Further, it was found that a competitive strategy between deformation and movement depending on Weber number and inclined angle, where the movement is balanced by sliding with rolling, dominates the impact dynamics of water droplets. This work provides new insight and explanation for the efficient electrodeposition of DLC films at low voltage and the dynamic evolution of impacting droplets on the inclined superhydrophobic surface.

Research on key influencing factors of scrap tire-soil retaining wall

The emergence of STSW can reduce the amount of materials such as sand and gravel and improve its performance compared to conventional retaining walls. In order to investigate the key influencing factors of STSW, the compression modulus of Scrap tire-soil module (STSM) was obtained by designing a full-scale compression strength test. The shear strength was obtained through a scale-test of shear strength. On this basis, the gravity STSW was established by the finite element numerical simulation software, and the bearing capacity of STSW was analyzed. Further, the key influencing factors of the bearing capacity of STSW were analyzed by designing orthogonal tests, and suggestions for parameter selection for designing STSW were given. The results show that: the friction angle of STSW increases and becomes larger with the increase of area ratio, and the cohesion decreases and decreases with the increase of area ratio; with the increase of compression modulus and internal friction angle, the maximum shear stress inside the retaining wall increases, while the cohesive force has almost no effect on the maximum value of shear stress inside the retaining wall; when constructing retaining walls, it is recommended to use Internal filling material with large compression modulus, small area ratio and its in the range of [0.3–0.5] of STSM.

Comparative study on short-circuit and surge current capabilities of 1.2 kV SiC SBD-embedded MOSFETs

This paper presents a comparative study on the short-circuit and surge current withstanding capabilities and the static and turn-on switching characteristics of commercial 1.2 kV SiC Schottky barrier diode (SBD)-embedded metal–oxide–semiconductor field-effect transistors (MOSFETs). The results confirmed that MOSFETs with a larger SBD area ratio had higher leakage current through the SBD during short-circuit transients due to a higher electric field and lattice temperatures as high as roughly 1120 K at the SBD, which resulted in reduced short-circuit withstanding capabilities. It was also found that MOSFETs with a smaller SBD area ratio had reduced surge-current capabilities in embedded SBDs. We conclude that is not due to the small SBD area ratio but to a weak bipolar operation of the Junction Barrier and Schottky rectifiers even in high current regions.

Investigation on propagation characteristics and performances of RDE fueled by kerosene under low oxygen mass fraction

The application of rotating detonation chambers instead of traditional afterburners is expected to improve the overall performance of turbine engines. Based on the background, the effects of oxygen mass fractions, inlet temperatures, equivalent ratios and nozzle outlet areas on the propagation characteristics and performances of RDE under low oxygen mass fractions and lean fuel conditions are investigated. It is observed that increasing the inlet temperature can widen the lower boundary of the oxygen mass fraction maintaining the propagation of RDWs, but decrease the propagation stability of the detonation waves. Although increasing the equivalent ratio has little effect on the lower boundary of the oxygen mass fraction, the propagation stability of the detonation wave is enhanced. It is found that reducing the nozzle outlet area ratio can effectively broaden the lower boundary of the oxygen mass fraction. With the decrease of oxygen mass fraction, the total pressure gain and combustion efficiency show a decreasing trend. Reducing the inlet air temperature, increasing equivalent ratios and reducing the nozzle outlet area ratio are conducive to reducing the inlet pressure ratio, which in turn reduces the inlet air loss and improves the total pressure gain. Combustion efficiency is higher under conditions of high oxygen mass fractions, low inlet temperatures, low equivalent ratios and small outlet area ratios.

Effects of nitric acid passivation on the physicochemical properties of stainless steel 316 and its reactivity with highly concentrated hydrogen peroxide

Stainless steel 316 (SUS316) tanks and tubes for the storage of highly concentrated hydrogen peroxide, which is used as a clean propellant in rocket systems, are passivated with nitric acid to suppress hydrogen peroxide decomposition and increase its storability. However, the physicochemical changes to the surface of passivated SUS316 due to nitric acid passivation remain unexplored, and the surface properties of SUS316 that determine the rate of hydrogen peroxide decomposition have not been clearly identified. Therefore, developing the optimal passivation process to maximize the storage of hydrogen peroxide is challenging. To this end, we investigated the effects of nitric acid passivation on the physicochemical properties of the SUS316 surface and the decomposition rate of hydrogen peroxide stored using SUS316. Moreover, a novel method, which measures pressure changes caused by the decomposition of hydrogen peroxide, enabled a quantitative evaluation of the decomposition rate that was ≥10 times faster than the conventional measurement of active oxygen loss. Scanning electron microscopy and contact surface profiling analysis revealed that nitric acid passivation reduced the roughness of the SUS316 surface, rendering it smooth, and reduced the surface area that promoted the decomposition of hydrogen peroxide. X-ray photoelectron spectroscopy showed that nitric acid passivation decreased the ratio of Cr(VI)/Cr(III) on the SUS316 surface. Cr(VI) and Cr(III) were dominantly in the CrO3 and Cr2O3 phases, respectively. In addition, direct reaction studies indicated that CrO3 promoted the decomposition of hydrogen peroxide at a rate of approximately 100 thousand times higher than those of Cr2O3 and Fe2O3. Therefore, a small surface area and low ratio of Cr(VI)/Cr(III) on SUS316 may be key in enhancing the storabilities of hydrogen peroxide in SUS316 tanks or tubes.

Suppression of pressure feedback of the rotating detonation combustor by a Tesla inlet configuration

With the increase in the inlet throat area, the rotating detonation combustor (RDC) can obtain higher pressure gain. However, the pressure feedback caused by the rotating detonation wave (RDW) can affect the upstream components of combustion chamber and interfere with the stable operation of RDC. Therefore, to obtain outstanding performance, it is imperative to investigate the suppression of pressure feedback. In this study, kerosene and 28.5% oxygen-enriched air (at room temperature) were taken as the propellant, and the tesla valve inlet configuration was applied to RDC, and the effect was compared with that of the traditional inlet configuration to suppress pressure feedback. A series of experiments were conducted to examine the operation characteristics of Tesla RDC and the effect and mechanism of suppressing pressure feedback. Under similar conditions, Tesla RDC can effectively transform the longitudinal pulsed detonation (LPD) mode into the rotating detonation (RD) mode, thus expanding the operating range of RDC. RDC under the exit nozzle with a small area ratio (0.25) was successfully realized. The operating range of Tesla RDC can be expanded by 300% and 94.7% at an exit area ratio of 0.5 and 0.65, respectively. The bypass channel in Tesla valve inlet configuration is the key to expanding the operating range. Directing pressure feedback to the bypass channel can effectively weaken the influence on the main inlet channel and shorten the inlet recovery time. Two quantitative evaluation indexes of pressure feedback were established; one is the percentage of the pressure fluctuating amplitude in the air plenum to the pressure amplitude of the detonation wave (PFdw), and the other is the static pressure of the air plenum, PFap. By analyzing the dynamic pressure signal upstream of the combustor, it was found that pressure disturbance is in the form of a pressure wave during the upstream return of the combustor, and the return speed is close to the local sound speed. Pressure feedback is mainly suppressed at the inlet throat, and PFdw is reduced by approximately 14% due to drainage of the bypass channel. Tesla RDC exhibits a good suppression effect on LPD mode, PFdw is significantly lower in the large exit nozzle area ratio, and the minimum value is 23%. PFap has an approximately linear relationship with the equivalence ratio, and the minimum value is 7.7%. Overall, this study demonstrates that Tesla RDC has excellent potential in widening the operation range and suppressing the pressure feedback, providing an innovative method for improving the performance of RDC.

Structural performance of 1 way and 2 way setback with the soft first story using ddbd

Irregular building structures increasingly varied, such as setback buildings and buildings with soft level stiffness irregularity on the first floor of the building (soft first story). High-rise buildings are at risk of collapse due to earthquakes. Designing efficiency requires a Direct Displacement Based Design (DDBD) method. In this study, the DDBD method uses pushover analysis on soft first-story buildings without a setback,1-way setback, and 2-way setback. This study aims to obtain the value software's value of displacement, story drift, ductility, plastic hinge response, and performance levels study indicates that the displacement value of the soft first-story building without setback is smaller than the setback building. In addition, the value of displacement and story drift in the setback building with a soft first story is influenced by the small setback area ratio. The highest displacement and story drift values in the X direction are 1-way setback buildings, which are 0.422 m and 0.0147 m, while in the Y-direction, the 2-way setback buildings are 0.44 m and 0.0167 m. The most significant value of actual ductility is a building without setbacks with a soft first-story. The plastic hinge response in all three buildings shows a strong column weak beam. The level of structural performance in all three buildings is at the level of Immediate Occupancy, where the value of the performance level of the FEMA 356 method is greater than the ATC 40 method.

Research progress on the seed plasma disk magnetohydrodynamic generator

To fully and clearly understand the development status and key research problems of the seed plasma disk magnetohydrodynamic (MHD) generator, this study reviews the development process of the seed plasma disk MHD generator. The development of the disk MHD generator has experienced the stages of suppressing the ionization instability of nonequilibrium plasma, revealing the characteristics of stable nonequilibrium plasma based on the concept of seed full ionization, and proving the high performance of the disk MHD generator. At present, there are attempts to use a small area ratio disk MHD generator to obtain a high entropy efficiency at a high enthalpy extraction rate with cesium added inert gas as the working fluid. Moreover, the research progress is described from two aspects of numerical simulation and experimental research, and the key technologies and problems to be solved and the development prospects of the seed plasma disk MHD generator are analysed. It is shown that the future theoretical research still will be focused on the generation and ionization process of nonequilibrium plasma. The key technology in the future is still aimed to obtain high-quality, uniform and stable non-equilibrium plasma. Therefore, in the future, it is expected to become a high-power static power supply with a compact structure and high-power conversion efficiency. Tables 2, Figs 9, Refs 153.

Experimental Investigation of the Fatigue Damage and Strength Characteristics of Heterogeneous Rock Mass under Cyclic Loading

Rock fractures filled with cementation inevitably lead to rock mass heterogeneity and affect its mechanical properties. The cementation is usually regarded as a defect due to its strength is lower than that of the surrounding rock. To investigate the influence of the defect on fatigue damage and strength of the rock mass under cyclic loading, the defect area ratio was obtained and a series of static and cyclic loading uniaxial tests were carried out. The experimental results reveal that tensile failure with few secondary cracks occurs under static loading. However, microcracks are widely developed in the samples after cyclic loading, especially at the defect interface. The compressive strength decreases with increasing defect area ratio. During cyclic loading, the fatigue damage for samples with small defect area ratios (<10%) is similar to that of intact rock. However, multiple sudden increases in the residual strain and dissipation energy occur when the defect area ratio is greater than 10%. In addition, cumulative residual strain, cumulative acoustic emission (AE) count and cumulative dissipation energy increase with increasing defect area ratio. Cyclic loadings significantly reduce the rock mass strength, and the strength reduction increases with increasing defect area ratio. It is inferred that the incompatible deformation in the heterogeneous rock mass is the main reason for the sample damage and the strength reduction, and the unloading has an essential effect on the initiation, propagation and coalescence of microcracks.

The Twin-Probe Method: Improving Langmuir Probe Measurements on Small Spacecraft

The Langmuir probe (LP) is generally accepted as an effective and relatively simple <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> space plasma instrument (plasma density, electron temperature, and spacecraft potential). As LPs transition to small spacecraft, their implementation encounters new technical challenges. For example, a negative charge is induced on the spacecraft while positively biasing an LP due to the small surface area ratios (spacecraft surface area to probe surface area ≪ 1000). This results in a varying spacecraft potential that degrades the accuracy of electron temperature and electron density measurements, reducing the LP’s effectiveness as a diagnostic tool. To mitigate the effects of this spacecraft charging, the twin-probe method (TPM) was developed. The TPM corrects LP measurements with tracked spacecraft potentials, measured by a separate high-impedance probe. By accounting for the changes in the spacecraft potential, the LP sweeps can be reconstructed to provide more accurate measurements of the ambient plasma’s properties. Here, we detail the TPM and present laboratory experiments that study its effectiveness and summarize constraints. Through these experiments, we found that it is possible to correct for spacecraft charging effects that can cause deviations in temperature and density as large as 20% and 136%, respectively. Furthermore, we will demonstrate a clear correlation between area ratio, spacecraft charging, and the negative impact on temperature and density measurement accuracy.

Heterophase Boundary for Active Hydrogen Evolution in MoTe2

AbstractThe phase engineering of transition metal dichalcogenides (TMDs) is considered a promising strategy for promoting efficient catalysis, such as the hydrogen evolution reaction (HER). While theoretical studies predict the presence of catalytically active atomic sites at heterophase boundaries in TMDs, conventional bulk HER measurements are not able to precisely explore these 1D heterophase regions for HER. Here, one reports on active HER occurring at heterophase boundaries between the semiconducting 2H and metallic 1T’ phases in large‐scale MoTe2 grown via chemical vapor deposition. Microreactors are used to investigate the local HER at varying lengths of 1D heterophase boundaries, and the results are systematically compared with the HER performance at the pristine basal planes of MoTe2. Despite the small area ratio between the 1D heterophase boundary and the open region for local HER, a clear improvement in HER is observed with a turnover frequency of 317 s–1. The Kelvin probe force microscopy determines a surface potential difference of 50 mV across the heterophase boundary, which supports sharp band bending and local charge accumulation as the basis for the TMDs’ efficient electrochemical catalysis.

Numerical Prediction of Homogeneity of Gas Flow through Perforated Plates

Vanes and baffles are often used as flow distributors where uniform flow is required in the apparatus of large cross-section surface areas. As an alternative, perforated plates with a range of open area ratios are applied to produce required gas flow homogeneity. Usually, the plates with various open area ratios are combined into large panels, of which total surface area can reach hundreds of square meters for large-sized industrial apparatus. Numerical modelling of the flow through such panels can be thought of as overly complex, time-consuming, and inefficient due to numerous small open area ratios in the plates and large differences in dimensions between open area ratios and free-stream areas. For this reason, numerical models of gas flow are limited to single plates only with constant open area ratios. A new indirect modelling approach of gas flow through the perforated plates panel with structural elements and various open area ratios with application of the porous media model is proposed. A perforated plate was experimentally investigated in terms of pressure drop and velocity distribution. The data obtained were used for the validation of the numerical results, which differed from the experimental results by less than 5%. In the next step, numerical analyses were performed for plates with open area ratios in the range of 30 to 70% for gas velocities of 5 and 10 m/s. A general correlation for pressure drop as a function of open area ratio was proposed. Finally, systematic numerical studies of the flow through both perforated and porous plates including structural elements were performed. The internal resistance of the porous core was calculated by means of a developed correlation. A good agreement between results with an error lower than 15% was observed.

Sizing of giant unilamellar vesicles using a metal mesh with a high opening ratio

Size control of giant unilamellar vesicles (GUVs) has been challenged extensively for realizing quantitative assays within these biomimetic reactors. Although microfluidics-based monodisperse GUV generation methods have shown tremendous progress, they are often difficult and still not available for general users. Meanwhile, the conventional bulk methods, which are more flexible in compositions, only generate polydisperse GUVs with a linear dimension ranging more than two orders of magnitude. Here, we characterized the sizing protocol of GUVs using the metal mesh with a large opening area ratio (>35%). Unlike the conventional track-etched membrane filters with a small opening area ratio (<10%), the present method enabled fast filtration (<10 min) to remove GUVs smaller than the mesh size without delicate flow control. We demonstrated that the combination of extrusion and filtration with selected filters produced GUV populations with fairly narrow size distributions (<30% C.V. in diameter).

Experiments and modeling of boiling heat transfer on hybrid-wettability surfaces

This paper studies pool boiling heat transfer on the hybrid-wettability surfaces, i.e., hydrophobic dot/stripe patterns fabricated on a superhydrophilic substrate. It is shown that the nucleate boiling heat transfer coefficient for the hybrid surface is improved compared to both the substrate and plain copper reference, but the critical heat flux (CHF) on the enhanced surface is very complex. The pattern-to-substrate contact angle difference is also concerned: CHF for the hybrid surface increases remarkably with increasing the contact angle difference, but the nucleate boiling heat transfer coefficient declines. Combining the results for both dot and stripe patterns, it is revealed that CHF on the hybrid surfaces is closely associated with the pattern-to-surface area ratio and the pattern-to-pattern spacing: it declines generally with increasing the area ratio; its dependence on the pattern spacing is minor at large area ratios; however, at small area ratios, the pattern spacing plays an increasingly important role because it dominates both vapor-liquid instabilities and surface rewetting, and the optimal pattern spacing for maximal pool boiling heat transfer enhancement can be estimated using the capillary length. A modified theoretical model is proposed to predicting CHF on both homogenous- and hybrid-wettability surfaces.

An approximate point-based alternative for the estimation of variance under big BAF sampling

BackgroundA new variance estimator is derived and tested for big BAF (Basal Area Factor) sampling which is a forest inventory system that utilizes Bitterlich sampling (point sampling) with two BAF sizes, a small BAF for tree counts and a larger BAF on which tree measurements are made usually including DBHs and heights needed for volume estimation.MethodsThe new estimator is derived using the Delta method from an existing formulation of the big BAF estimator as consisting of three sample means. The new formula is compared to existing big BAF estimators including a popular estimator based on Bruce’s formula.ResultsSeveral computer simulation studies were conducted comparing the new variance estimator to all known variance estimators for big BAF currently in the forest inventory literature. In simulations the new estimator performed well and comparably to existing variance formulas.ConclusionsA possible advantage of the new estimator is that it does not require the assumption of negligible correlation between basal area counts on the small BAF factor and volume-basal area ratios based on the large BAF factor selection trees, an assumption required by all previous big BAF variance estimation formulas. Although this correlation was negligible on the simulation stands used in this study, it is conceivable that the correlation could be significant in some forest types, such as those in which the DBH-height relationship can be affected substantially by density perhaps through competition. We derived a formula that can be used to estimate the covariance between estimates of mean basal area and the ratio of estimates of mean volume and mean basal area. We also mathematically derived expressions for bias in the big BAF estimator that can be used to show the bias approaches zero in large samples on the order of frac {1}{n} where n is the number of sample points.

Little Ice Age glacier extent and temporal changes in annual mass balance (2016–2019) of Pensilungpa Glacier, Zanskar Himalaya

Glaciers and climate are known to exhibit positive feedbacks that are important for comprehending the overall glacier state. This relation is poorly understood in the relatively unexplored terrain like the Zanskar Himalaya. We have studied the impact of climate change regarding the past and present response of the Pensilungpa Glacier (PG), Zanskar Himalaya. Reconstructing the recent changes in the mass balance (2016–2019) along with the Little Ice Age (LIA) extent of the PG shows that the PG was joined by the five tributary glaciers during the LIA having an area of ~ 18 km2 and extended ~ 3 km downstream from its present-day snout located at 4470 ± 1 m.a.s.l. Since the LIA, the PG has retreated ~ 2941 ± 75 m, at an average rate of 5.6 ± 0.15 m a−1. Field observations for the last 4 years (2015–2019) show that the glacier now is retreating by ~ 27 ± 11 m at an average rate of 6.7 ± 3 m a−1, which is similar to the one since the LIA. The glaciers in the study area (Suru River valley) are mostly nourished by the Western Disturbances (during the December, January, and February) with maximum solid precipitation, and melt during the ablation period (May–October). The observed recessional trends of the PG may, therefore, be attributed to an increase in the temperature and decrease in precipitation during accumulation period. The ablation data reveal the significant influence of debris-cover on the mass balance and terminus retreat of the PG. Furthermore, the mass balance data for the last 3 years (2016–2019) show a negative trend with a small accumulation area ratio (AAR) (43%). The average net annual mass balance is estimated to be ~ − 3.67 × 106 m3 w.e. a−1 with the − 0.36 m w.e. a−1 specific balance between 2016 and 2019. During the period 2016–2019, the PG has lost ~ 11.03 × 106 m3 w.e. ice volume. The slower retreat rate and low AAR of the PG, compared to other glaciers in the area, suggest that its terrain characteristics (hypsometry, size, aspect, and slope) control the glacier dynamics and the glacier continues to adjust geometrically in response to the negative mass balance.

Future projection of greenhouse gas emissions due to permafrost degradation using a simple numerical scheme with a global land surface model

The Yedoma layer, a permafrost layer containing a massive amount of underground ice in the Arctic regions, is reported to be rapidly thawing. In this study, we develop the Permafrost Degradation and Greenhouse gasses Emission Model (PDGEM), which describes the thawing of the Arctic permafrost including the Yedoma layer due to climate change and the greenhouse gas (GHG) emissions. The PDGEM includes the processes by which high-concentration GHGs (CO2 and CH4) contained in the pores of the Yedoma layer are released directly by dynamic degradation, as well as the processes by which GHGs are released by the decomposition of organic matter in the Yedoma layer and other permafrost. Our model simulations show that the total GHG emissions from permafrost degradation in the RCP8.5 scenario was estimated to be 31-63 PgC for CO2 and 1261-2821 TgCH4 for CH4 (68th percentile of the perturbed model simulations, corresponding to a global average surface air temperature change of 0.05–0.11 °C), and 14-28 PgC for CO2 and 618-1341 TgCH4 for CH4 (0.03–0.07 °C) in the RCP2.6 scenario. GHG emissions resulting from the dynamic degradation of the Yedoma layer were estimated to be less than 1% of the total emissions from the permafrost in both scenarios, possibly because of the small area ratio of the Yedoma layer. An advantage of PDGEM is that geographical distributions of GHG emissions can be estimated by combining a state-of-the-art land surface model featuring detailed physical processes with a GHG release model using a simple scheme, enabling us to consider a broad range of uncertainty regarding model parameters. In regions with large GHG emissions due to permafrost thawing, it may be possible to help reduce GHG emissions by taking measures such as restraining land development.

Influence of Nozzle Type, Divergence Angle and Area Ratio on Impulse of Pulse Detonation Engine

The influence of nozzle geometry on the impulse produced by the single cycle Pulse detonation engine (PDE) was experimentally investigated. For each experiment the nozzles were attached at the end of the engine. The impulse produced by the pulse detonation engine was calculated from the measured thrust. The thrust measurement was done by sliding the engine on the central bar of the thrust stand. The main structure of the basic PDE has a detonation tube with one terminal closed, a Schelkin spiral used as deflagration to detonation device, and a thrust stand to support the structure. Stoichiometric acetylene and oxygen mixture were used as detonation mixture. Various nozzles with a range of divergent angle and area ratios were tested. The calculations of the impulse were made from the thrust pulse for the duration it lasted. The effect of the type of nozzle, divergent angle and area ratio were observed. The bell shaped nozzle with large angle of divergence produced maximum specific impulse of 80 Sec with 20° divergence angle and area ratio of 6.942; maximum impulse was produced by the bell shaped nozzle with a small area ratio of 2.969 and 10° divergence angle. The maximum total impulse obtained was 1200 N-sec.

Hazard Assessment of Polymeric Nanobiomaterials for Drug Delivery: What Can We Learn From Literature So Far.

The physicochemical properties of nanobiomaterials, such as their small size and high surface area ratio, make them attractive, novel drug-carriers, with increased cellular interaction and increased permeation through several biological barriers. However, these same properties hinder any extrapolation of knowledge from the toxicity of their raw material. Though, as suggested by the Safe-by-Design (SbD) concept, the hazard assessment should be the starting point for the formulation development. This may enable us to select the most promising candidates of polymeric nanobiomaterials for safe drug-delivery in an early phase of innovation. Nowadays the majority of reports on polymeric nanomaterials are focused in optimizing the nanocarrier features, such as size, physical stability and drug loading efficacy, and in performing preliminary cytocompatibility testing and proving effectiveness of the drug loaded formulation, using the most diverse cell lines. Toxicological studies exploring the biological effects of the polymeric nanomaterials, particularly regarding immune system interaction are often disregarded. The objective of this review is to illustrate what is known about the biological effects of polymeric nanomaterials and to see if trends in toxicity and general links between physicochemical properties of nanobiomaterials and their effects may be derived. For that, data on chitosan, polylactic acid (PLA), polyhydroxyalkanoate (PHA), poly(lactic-co-glycolic acid) (PLGA) and policaprolactone (PCL) nanomaterials will be evaluated regarding acute and repeated dose toxicity, inflammation, oxidative stress, genotoxicity, toxicity on reproduction and hemocompatibility. We further intend to identify the analytical and biological tests described in the literature used to assess polymeric nanomaterials toxicity, to evaluate and interpret the available results and to expose the obstacles and challenges related to the nanomaterial testing. At the present time, considering all the information collected, the hazard assessment and thus also the SbD of polymeric nanomaterials is still dependent on a case-by-case evaluation. The identified obstacles prevent the identification of toxicity trends and the generation of an assertive toxicity database. In the future, in vitro and in vivo harmonized toxicity studies using unloaded polymeric nanomaterials, extensively characterized regarding their intrinsic and extrinsic properties should allow to generate such database. Such a database would enable us to apply the SbD approach more efficiently.

Pump absorption, laser amplification, and effective length in double-clad ytterbium-doped fibers with small area ratio.

We use numerical simulations with the beam propagation method (BPM) and rate equations to investigate the pump absorption and amplification characteristics in double-clad ytterbium-doped fibers with small cladding-to-core area ratios, in the range 1-3. The presence of modes with low overlap with the doped region (or alternatively, skew rays) hampers the pump absorption in a circular geometry, but we find that the effect is small for area ratios of ∼2.5 or less. We derive ray-based expressions for the small-signal absorption which show similar results. However, even when the small-signal absorption scales nearly ideally with the inverse of the area ratio, the absorption in an operating amplifier is much lower, and the dependence on the area ratio much weaker, when a large fraction of the Yb-ions is excited in a small-area-ratio fiber. We derive equations which show this, and that in contrast to conventional area ratios of, e.g., 100, the fiber length depends more strongly on the required gain than on the required pump absorption. However, fibers substantially shorter than 1 m still allow for adequate pump absorption and gain. The effective length for nonlinear interactions is less affected by this, since the Yb-excitation is low where the signal power is high. Although we treat single-mode cores, the BPM amplifier simulations show there are a few percent of the signal power in cladding-guided modes with high overlap with the Yb-doped core. Nevertheless, according to our simulations, it is possible to achieve high efficiency and mode purity with a small-area-ratio circularly symmetric double-clad fiber.