Short Contact Time Research Articles

An innovative compact system for advanced treatment of combined sewer overflows (CSOs) discharged into large lakes: Pilot-scale validation

Combined sewer overflows discharging into natural water bodies could potentially contaminate them in terms of conventional wastewater parameters and coliform bacteria. When green water infrastructures are not technically feasible or practically sustainable for stormwater management, innovative compact and effective end-of-pipe systems can be of interest. This study presents long-term and real-environment validated data of a compact and rapid treatment system specifically applicable to CSOs that consists of a dynamic rotating belt filter, adsorption on granular activated carbon and UV disinfection steps. The results of treatment for Lake Garda in Italy, showed great potential for TSS, COD and E. coli removal efficiencies with more than 90%, 69% and 99% respectively. Due to the short contact time of GAC adsorption, nutrients removals were not very high. TN and TP removal of around 41% and 19% were observed respectively that suggests further specific nutrients removal processes are required for achieving higher efficiencies. The treatment system, due to its compactness and rapidness could be a great asset for water utilities in different EU catchments that are dealing with the frequent CSO events. In addition, the possibility of using different combinations of treatment steps allows the choice of different treatment scenarios depending on the treatment goals for any specific catchment.

Adsorption of Hydrogen Sulphide by Commercialized Rice Husk Biochar (RHB) & Hydrogel Biochar Composite (RH-HBC)

Hydrogen sulfide (H2S) is a naturally occurring component found during microbial disintegration and processing of natural gas & oil which can cause wellbeing and condition issue if being discharged into a climate at high fixation. Activated carbon which cost a lot in manufacturing is used as an adsorbent for removing these hazardous gases. As an alternative, the abundance waste of biomass available can be converted into good use. Biochar is one of the most practical and promising adsorbents that shows incredible potential as an adsorbent for the expulsion of contaminants in wastewater and gas treatment. This study covered on the characteristics and adsorption performance of two adsorbents Activated Rice Husk Biochar (RHB) and Rice Husk Hydrogel Composite (RH-HBC) on hydrogen sulfide. RHB is prepared by treating grinded rice husk biochar using aqueous Zinc Chloride (ZnCl2) and hydrochloric acid (HCl) solution to increase the size of pores of active sites and remove the impurities present in on the adsorbents. Polymerization is conducted by using initiator (ammonium persulfate, APS), monomer (acrylamide, AAm) and crosslinker (N,N'-methylenebisacrylamide,MBA) to create treated hydrogel biochar (RH-HBC). The adsorption performance is done to evaluate the effect of sorbent weight (20 g, 25 g, 30 g), H2S gas flow rate (200 L/hr, 150 L/hr, 100 L/hr) and temperature (30℃, 50℃, 70℃). RHB shows better porosity compared to RH-HBC where it has a higher surface area (222.85m2/g) compared to RH-HBC (8.68m2/g). While the presence of alkene group C=C in RH-HBC gives more stability to withstand high temperature compared to RHB. From the result, it can be concluded that the increased the sorbent weight, give an increased in adsorption capacity. When increased the gas flow rate, it gives a shorter contact time between gas and adsorbent which result in less adsorption capacity. RH-HBC give longest breakthrough time and highest adsorption capacity compared with RHB in all experiment.

Leidenfrost suppression and contact time reduction of a drop impacting on silicon nanowire array-coated surfaces

Drop impacting on a superheated surface is of practical concern in several thermal systems. When the surface temperature is higher than the Leidenfrost point (LFP), a stable vapor cushion forms on the solid surface and the drop hovers over the thin vapor layer. This results in a drastic reduction in heat and mass transfer due to the thermally insulating vapor layer. The contact time of an impacting drop is the amount of time during which the drop comes in contact with the solid surface. A short contact time enhances heat transfer. Thus, a high LFP and a short drop contact time are of interest to researchers. The present study revealed substantial Leidenfrost suppression and contact time reduction on a superheated superhydrophilic silicon nanowire (SiNW) array-coated surface. For an impacting drop of 14 μL with a Weber number (We) of 2.0, a LFP of 655 ± 14 °C was obtained on the SiNW array-coated surface with a nanowire height of 90 μm. This LFP was the highest reported value in the literature. A theoretical modeling revealed that the elevated LFP was caused by a superior capillary force and a strong vapor dispersion into the nanowire array. In addition, contact time was substantially reduced on the superheated SiNW surface in the jet-bouncing regime. The contact time of 1.3 ± 0.1 ms was 91% lower than the capillary–inertia limit. It was also the lowest reported value in the literature. The contact time reduction on the superheated SiNW surface resulted from the application of an upward thrust on the impacting drop generated by the vigorous bubbling on the SiNW surface.

Adsorptive removal of cobalt(II) from aqueous solutions using multi-walled carbon nanotubes and γ-alumina as novel adsorbents: Modelling and optimization based on response surface methodology and artificial neural network

The efficiency of new and nano-scale adsorbents including multi-walled carbon nanotubes (MWCNTs) and γ-alumina in the removal of cobalt(II) from aqueous solutions was experimentally evaluated in a batch-system reactor. To the best of our knowledge, no previous study has specifically attempted to introduce a hybrid strategy based on artificial neural network and genetic algorithm techniques for modelling and optimizing adsorptive removal of cobalt(II) from aqueous solutions via the proposed nanoparticles. The analyses of SEM, TEM, and FTIR were used to characterize both adsorbents. The response surface methodology (RSM) approach suggested a second-order polynomial model with a p-value < 0.0001 and R2 of 0.9980 for MWCNTs adsorbent and a p-value < 0.0001 and R2 of 0.9992 for γ-alumina adsorbent. The artificial neural network (ANN) approach suggested a three-layered feed-forward backpropagation model with R2 of 0.9794 for MWCNTs adsorbent and R2 of 0.9823 for γ-alumina adsorbent. The results linked to optimization by RSM showed that the maximum cobalt(II) removal efficiency of about 90% was achieved in the case of the MWCNTs adsorbent under the conditions of pH = 10, contact time = 38.6 min, MWCNTs dosage = 1.57 mg/L, and initial cobalt(II) concentration = 56.57 mg/L. About 93% of cobalt(II) removal could be obtained in the case of γ-alumina adsorbent under the conditions of pH = 10, contact time = 35.5 min, γ-alumina dosage = 1.63 g/L, and initial cobalt(II) concentration = 52.15 mg/L. The optimization values using the genetic algorithm (GA) technique were almost the same as those obtained from the RSM method. The kinetic model of Ho and McKay's pseudo-second order (PSO) and the isotherm model of Dubinin–Radushkevich were found to be the best-fitted to the experimental for both MWCNTs and γ-alumina. In addition, the maximum monolayer adsorption capacity of MWCNTs and γ-alumina adsorbents for the adsorption of cobalt(II) was 78.94 mg/g and 75.78 mg/g, respectively. Also, a thermodynamic study exhibited a favorable and spontaneous adsorption process for both materials. The present study clearly concluded that the proposed adsorbents could be effectively used for the removal of cobalt(II) from aqueous solutions at lower adsorbent dose and shorter contact times than various adsorbents reported in literature.

Efficient hydrodeoxygenation of guaiacol and fast-pyrolysis oil from rice straw over PtNiMo/SBA-15 catalyst for co-processing in fluid catalytic cracking process

Fast pyrolysis of renewable biomass is an attractive approach to convert solid biomass into a liquid which has higher energy density. However, pyrolysis oil has high acidity, low energy value, high viscocity and instability that limit end-user applications. This study focuses on the upgrading of pyrolysis oil using hydrodeoxygenation (HDO) process to produce a suitable bio-oil that can be further co-processed in standard refinery. In the first part, Pt was added to NiMo/SBA-15 catalyst in order to improve the HDO activity of guaiacol (GUA) and of fast pyrolysis oil from rice straw. Pt addition leads to important increases in both GUA conversion and HDO degree, and more interestingly, to the domination of saturated cyclic compounds (80–95 %) among formed products. Temperature programed reduction analysis proved that the reduction of Ni and Mo species occurred at lower temperatures with the presence of Pt. The use of 0.7 PtNiMo/SBA-15 catalyst resulted in the very high GUA conversion (94.5 %), high HDO degree (98.7 %), and high saturated cyclic compounds selectivity (97.4 %). In addition, the HDO treatment of fast pyrolysis oil over this catalyst at 300 °C, 12 MPa leads to a decrease in oxygen content from 44 wt.% to 20 wt.%. Then, the second part of this work has shown that HDO bio-oil obtained can be co-processed (up to 20 wt.% of bio-oil) with vacuum gasoil (VGO) in fluid catalytic cracking lab-scale unit (short contact time micro-activity unit, SCT-MAT) without significant change of the yield of profitable products: liquid petroleum gas, gasoline and light cycle oil.

CRYSTALLIZATION OF A NaCl SOLUTION IN A VACUUM CENTRIFUGAL FILM DISTILLER

Проблематика. Использование центробежных сил в теплообменных аппаратах обеспечивает высокую эффективность процессов тепломассообмена и позволяет создать аппараты, которые работоспособны в условиях микрогравитации, характерных для космических аппаратов. Малое время контакта раствора с теплообменной поверхностью предупреждает отложение растворенных веществ при повышении концентрации раствора. В результате центробежный дистилляционный аппарат может работать в режиме кристаллизатора, что обеспечивает увеличение коэффициента регенерации воды в системах жизнеобеспечения пилотируемых космических аппаратов. Цель исследования. Исследование работы одноступенчатого центробежного дистиллятора взрывного вскипания при концентрировании раствора NaCl. Методика реализации. Экспериментальные исследования на опытном образце центробежного вакуумного одноступенчатого дистиллятора. Результаты исследования. Получены результаты при концентрировании раствора NaCl, в т.ч. в режиме кристаллизации (когда начинается выпадение растворенных кристаллов NaCl). Определена физико-химическая температурная депрессия в зависимости от концентрации раствора и давления в аппарате с контролем качества полученного дистиллята. Проведено сравнение полученных результатов с данными других авторов. Показано хорошее совпадение. Использование фильтра в горячем контуре позволяет работать в режиме кристаллизатора без появления отложений на конструктивных элементах аппарата. Выводы. Интенсивный теплообмен в центробежном аппарате обеспечивает полное срабатывание перегрева раствора, что позволяет использовать его для изучения физико-химической температурной депрессии растворов при разных давлениях. При этом качество дистиллята не зависит от концентрации растворенных веществ в горячем контуре (в т.ч. в режиме кристаллизации). Использование фильтра в горячем контуре обеспечивает возможность работы системы в режиме кристаллизатора до забивания фильтра. После замены фильтра процесс может быть продлен.

Towards understanding of phenolic compounds impact on Ni- and V-USY zeolites during bio-oils co-processing in FCC units

In this work, the n-heptane transformation was carried out in absence and presence of 1.2 wt% of guaiacol over Ni- and V-impregnated zeolites at 450 °C, to evaluate the influence of these metals on the poisoning effect of phenolic molecules during bio-oils and traditional Fluid Catalytic Cracking (FCC) feedstocks co-processing. Impregnation of the metals slightly decreased the Brønsted acid sites, but importantly increased the Lewis acidity. Notably, guaiacol was found to be less poisonous at shorter time-on-streams when Ni or V were present on the zeolite, as the metal-induced Lewis acidity seems to promote guaiacol transformation, which slows down coke formation from n-heptane. Simultaneously, unconverted guaiacol molecules adsorb mainly on the Lewis acid sites, resulting in a higher number of Brønsted acid sites available for the cracking reactions. Influence of Ni on the attenuation of the guaiacol deactivating effect was more important owing to the generation of a higher amount of metal-induced Lewis acid sites. Hence, taking into account the short contact times in the FCC riser, the presence of metal contaminants, such as Ni and V, on the FCC catalysts appears to be beneficial for the co-processing, being possibly one of the explanations for the lower impact of the phenolic compounds on the FCC equilibrium catalyst when compared to pure ultra-stable Y zeolites.

A new honeycomb carbon monolith for CO2 capture by rapid temperature swing adsorption using steam regeneration

A rapid process for CO2 capture is of key importance for the economic feasibility of the process in industry, consequently short adsorption/desorption cycles are crucial. With this aim in mind, a carbon based honeycomb monolith was evaluated for CO2 capture in a thermal swing adsorption process at short contact times. The effect of (1) regeneration time, (2) presence of water vapor during adsorption and desorption and (3) regeneration method (steam versus hot air) on CO2 adsorption was studied. The monolith was characterized in terms of porosity and CO2, N2, and H2O isotherms. Cyclic adsorption/desorption experiments were performed using different synthetic gas mixtures with concentrations of CO2 ranging between 6 and 15 vol%. The effect of water vapor in the synthetic gas mixture on adsorption capacity was limited but increases with relative humidity. Steam of 120 °C was used to heat the monolith and desorb CO2. Advantages of steam usage are the facile separation of steam and concentrated CO2 and the low (waste) heating energy cost of steam. It was demonstrated that the steam allows very fast heating and cooling of the monolith. However, the presence of residual condensation water after the cooling step reduces the cyclic adsorption capacity, requiring an additional drying step with hot or cold air.

Computational fluid dynamics simulation to compare large volume irrigation and continuous spraying during nasal irrigation.

Nasal irrigation is now widely recognized as a treatment for chronic rhinosinusitis and during the postoperative period. However, there are no guidelines for performing irrigation. This study used computational fluid dynamics (CFD) simulation objective physical parameters to optimize and increase the efficiency of nasal irrigation and to compare large-volume, manual, and gravity pressure irrigation vs small-volume continuous spraying. A 3-dimensional (3D) sinonasal model was constructed from a healthy adult high-resolution computed tomography (CT) scan. The 3D nasal model was constructed using a tetrahedral and hex-dominant mesh grid with TGRID™ 16 (ANSYS Inc., Villeurbanne, France) software. A structured hex mesh was created inside the domain using the Hexcore meshing method. The final mesh had a total of 9.6 × 106 cells with an average size of 0.29 mm3 , or an average volume of 2.42 × 10-2 mm3 . Navier-Stokes equations were resolved with the standard k - ε model. Large-volume irrigation (15 mL/s) covered all zones (136 to 310 cm2 ) rapidly with strong shear stress and prolonged contact time (310 mPa 3.26 seconds for gravity mode and 280 mPa 3.35 seconds for manual pressure mode). Continuous spraying (3 mL/second) covered all areas (76 to 310 cm2 ) but with far less volume, more slowly, with low shear stress (50 mPa), and with shorter contact time (1.84 seconds). The surface wetted by time in contact was 135.4, 113.9, and 46.6 cm2 for gravity, manual pressure mode, and continuous spraying, respectively. CFD simulation visualizes the circulation of water during nasal irrigation and makes it possible to determine objective parameters to decide which mode of irrigation may be used.

Inactivation of Rhizoctonia solani in fertigation water using regenerative in situ electrochemical hypochlorination

The capture and re-use of greenhouse fertigation water is an efficient use of fertilizer and limited water resources, although the practice is not without risk. Plant pathogens and chemical contaminants can build up over successive capture and re-use cycles; if not properly managed they can lead to reduced productivity or crop loss. There are numerous established and emerging water treatment technologies available to treat fertigation water. Electrochemical processes are emerging as effective means for controlling pathogens via in situ regenerative hypochlorination; a process that is demonstrated here to achieve pathogen control in fertigation solutions without leading to the accumulation of potentially phytotoxic free chlorine residuals associated with other chlorination processes. An electrochemical flow cell (EFC) outfitted with ruthenium dioxide (RuO2) dimensionally stable anodes (DSA) was characterized and evaluated for free chlorine production and Rhizoctonia solani inactivation in both irrigation and fertigation solutions. Pathogen inactivation was achieved at low current densities and short residence or cell contact times. Effluent free chlorine concentrations were significantly lower than commonly reported phytotoxic threshold values (approximately 2.5 mg/L) when fertilizer (containing ammonium) was present in the test solution; an effect attributable to reactions associated with breakpoint chlorination, including chloramine formation, as well as the presence of other oxidizable compounds in the fertilizer. Chloride concentrations were stable under the test conditions suggesting that the EFC was operating as a regenerative in situ electrochemical hypochlorination system. No significant changes to macronutrient concentrations were found following passage through the EFC.

Effects of newly devised plasma lice comb on human hair

A plasma device was developed showing high potential for a pesticide-free treatment of pediculosis. As a first safety assessment of the device was presented earlier, this present paper focuses on the damage introduced to human hair during a plasma treatment for pediculosis control. Therefore, human hairs were treated repeatedly to assess the possible occurring damage developing with increasing treatment durations. To analyse the inflicted changes on human hair examinations using x-ray photoelectron spectroscopy (XPS/ESCA), scanning nearfield optical microscopy (SNOM) and scanning electron microscopy were conducted, to compare the modifications of surface chemistry and mechanical alterations. The investigations revealed a mild impact on the surface chemistry (XPS/SNOM), while more distinct morphological changes on the hair surface could be observed. The authors conclude that an effect of the plasma comb device on the hair during a real-life treatment is negligible, due to the very short contact times during a standard combing procedure for pediculosis control.

Aeration challenge in high BSG suspended fermentation: Impact of stirred-tank bioreactor scale

The high loading of lignocellulosic substrates could merge the advantages of solid-state and submerged fermentations. However, high solid loading in bioreactors could result in oxygen mass transfer complications and caused extra waste of inlet air. In this work, the effects of Brewer's Spent Grain (BSG) loading on enzyme production, oxygen transfer rate (OTR) and carbon dioxide evolution rate (CER) were investigated at 50, 75 and 100 g L−1 BSG in a 2.5-L stirred tank bioreactor. However, in small-scale bioreactor, the short contact time and inadequate mixing of bubbles in liquids affected the OTR and gas holdup negatively. Therefore, xylanase production in a 14-L vessel with 100 g L−1 BSG has been studied. In a larger bioreactor, a remarkable improvement in OTR and a significant reduction in total air consumption were recorded. Furthermore, the enzyme production per 1 L of consumed air was four times greater than 2.5-L vessels. As a result, the energy consumption for aeration was less in the larger bioreactor with high solid loading. Additionally, the residual xylan content monitoring during enzyme production has revealed that the BSG's xylan content decreased in the first 12 h of cultivation and then it remained approximately constant that probably means further xylanase induction is influenced by the concentration of BSG's hydrolysis products. Concisely, it seems that initial higher solid loading could be used as a practical alternative to solid substrate feeding during the fermentation. These findings would be useful for the fermentation of high loading lignocellulosic material in the industrial-scale bioreactor.

Formation of metastable disinfection byproducts during free and combined aspartic acid chlorination: Effect of peptide bonds and impact on toxicity

The formation and occurrence of haloacetonitriles (HANs) in drinking water is of increasing concern because recent data have shown that they are the major contributors to DBP-associated toxicity of disinfected waters. Earlier research on HAN formation had established free amino acids as important HAN precursors due to their high reactivity with chlorine. However, free amino acids are unlikely to be the primary precursors for HANs in natural waters, mainly because the actual concentrations of these compounds are too low to sufficiently account for observed HAN formation. On the other hand, combined amino acids (i.e., peptides and proteins) are of much higher abundance even though it is unclear if they can contribute to HAN formation given that nearly all the amino nitrogen is tied up in peptide linkages. In order to clarify the reactivity of combined amino acids with chlorine to form HANs, dichloroacetonitrile (DCAN) formation kinetics was compared between free aspartic acid and two aspartyl-containing tetrapeptides (i.e., Asp-Asp-Asp-Asp and Arg-Gly-Asp-Ser). Results indicated that aspartyl residue could also lead to DCAN formation upon chlorination, whereas the rate of DCAN formation was much slower compared to that from free aspartic acid chlorination. Moreover, DCAN formation from the two model peptides was catalyzed by high pH. This is because chlorine-induced peptide backbone degradation is the key to DCAN formation from the chlorination of combined amino acids and this slow stepwise process is base-catalyzed. Perhaps most importantly, regardless of the precursors, DCAN was continuously formed but simultaneously degraded especially at alkaline pHs, leaving the corresponding N-chloro-2,2-dichloroacetamide (N–Cl-DCAM) and dichloroacetic acid (DCAA) as major end products. It was observed that over increasing chlorine exposure, there exists an important transition from initial organic precursors through metastable chlorination intermediates (e.g., DCAN and N–Cl-DCAM) and finally to stable end products (e.g., DCAA). By weighting DBP concentrations by their respective cytotoxic potencies, it is estimated that the aggregate cytotoxicity of chlorinated water would reach its maximum at relatively short chlorine contact times. In general, shorter water age and lower pH both resulted in higher levels of metastable intermediates (i.e., DCAN) and thus higher levels of aggregate calculated cytotoxicity. The resulting toxicity profile is different from the prevailing notion that supports current DBP regulations. Therefore, there is a risk that by placing regulatory limits and control strategies exclusively on regulated end products (e.g., HAAs), the overall toxicity of drinking water might be inadvertently elevated.

Performance of dissolved organic matter removal from membrane bioreactor effluent by magnetic powdered activated carbon

Magnetic powdered activated carbon (Mag-PAC) was successfully developed and applied as an adsorbent for dissolved organic matter (DOM) removal from the effluent of a membrane bioreactor (MBR) using batch experiments. The results show that a coating of iron oxide particles is consistently distributed on the surface of powdered activated carbon (PAC), resulting in a decrease in the specific surface area and in the pH at the point of zero charge, even though the particle sizes of Mag-PAC and PAC were similar. A Mag-PAC dosage of 4 g/L exhibited efficient and fast DOM adsorption with a relatively short contact time of 5 min. The iron oxide coating on the surface of PAC may play an important role in the DOM removal efficiency. Temkin isotherm and pseudo-second order kinetic models well described the DOM adsorption, suggesting that the adsorption of DOM onto Mag-PAC could be mainly governed by a chemisorption mechanism. Humic acid- and fulvic acid-like compounds and aromatic DOM with molecular weights (MWs) between 2610 Da and 3030 Da were efficiently removed by Mag-PAC, whereas aromatic DOM with an MW of 1760 Da was poorly removed. Our results demonstrate that the application of Mag-PAC for DOM adsorption is attractive and yields benefits as a posttreatment system for MBR effluent due to its efficient and fast DOM adsorption.

Short Contact Time Catalytic Partial Oxidation of Methane over Rhodium Supported on Ceria Based 3-D Printed Supports

Three different ceria containing catalyst supports and an alumina (control) support have been deposited with rhodium and used in the short contact time catalytic partial oxidation of methane. The g...

Solute and water transport along an inner medullary collecting duct undergoing peristaltic contractions.

The mechanism by which solutes accumulate in the inner medulla of the mammalian kidney has remained incompletely understood. That persistent mystery has led to hypotheses based on the peristaltic contractions of the pelvic wall smooth muscles. It has been demonstrated the peristaltic contractions propel fluid down the collecting duct in boluses. In antidiuresis, boluses are sufficiently short that collecting ducts may be collapsed most of the time. In this study, we investigated the mechanism by which about half of the bolus volume is reabsorbed into the collecting duct cells despite the short contact time. To accomplish this, we developed a dynamic mathematical model of solute and water transport along a collecting duct of a rat papilla undergoing peristaltic contractions. The model predicts that, given preexisting axial concentration gradients along the loops of Henle, ∼40% of the bolus volume is reabsorbed as the bolus flows down the inner medullary collecting duct. Additionally, simulation results suggest that while the contraction-induced luminal hydrostatic pressure facilitates water extraction from the bolus, that pressure is not necessary to concentrate the bolus. Also, neither the negative interstitial pressure generated during the relaxation phase nor the concentrating effect of hyaluronic acid has a significant effect on bolus concentration. Taken together, these findings indicate that the high collecting duct apical water permeability allows a substantial amount of water to be extracted from the bolus, despite its short transit time. However, the potential role of the peristaltic waves in the urine-concentrating mechanism remains to be revealed.

A satellite mission concept for high drag environments

The United States scientific, military, and academic communities need the ability to maintain a presence within the vast gap in altitudes between where airplanes can fly and where satellites can be sustained in Low Earth Orbit (LEO). The list of potential stakeholders that could benefit from such a platform is long and includes a broad array of interests. The National Oceanic and Atmospheric Administration provides weather forecasts critical to disaster preparedness and response. The military and defense communities provide Signals Intelligence (SIGINT) and imagery (IMINT) that deepen our awareness and preparedness for potential threats to our nation and liberties. Colleges and universities conducting space weather research provide advances in our knowledge of the physical and chemical processes that inform our understanding of our environment on scales ranging from elemental to universal. As satellite altitudes decrease below 300 km, their orbits decay more rapidly due to the decelerating effects of rarefied gas interactions with satellite surfaces, as the satellite passes thought the upper layers of the Earth's atmosphere. The F region of the Earth's Ionosphere extends upward from about 160 km and is characterized by significant concentrations of free electrons. Densities of both neutral rarefied gases and charged particles in these regions vary by orders of magnitude. Day-night variations cycle over roughly 24-hour periods, and long-term variations occur due to the approximately eleven year span between solar maxima and minima. Due to the variability of these atmospheric constituents, many challenges exist for mission designers, ranging from how best to counter drag forces, to protecting against unwanted spacecraft charging. Mission designers are also faced with other inherent challenges because of these low altitude regimes, like Atomic Oxygen (AO) erosion of spacecraft materials, and short contact times. This paper examines the lower bound of satellite flight from a system perspective, presents previous research in the area, and discusses methods that may be able to narrow the gap by implementing sustained force in the satellite's orbital ram direction designed to reduce or eliminate the effect of drag, while minimizing the amount of stored propellant, thereby lengthening satellite lifetimes in these regions and enabling innovative new missions within our scientific, military, and academic communities. The classical Systems Engineering process is used to compare historical mission concepts and present a candidate satellite mission point design.

Do sex and body structure influence spatiotemporal step characteristics in endurance runners?

Summary Objectives To examine the influence of sex and anthropometric characteristics of recreationally-trained endurance athletes on spatiotemporal parameters during running at a constant velocity. Equipments and methods In all, 97 runners (52 men and 45 women) performed a running protocol on a treadmill at 12 km.h−1. Spatiotemporal parameters were measured using the OptoGait system and anthropometric characteristics were assessed by determining body mass, height, leg length and torso length. Results Partial correlation analysis, adjusted by sex, revealed some significant correlations between anthropometric and spatiotemporal characteristics. Cluster k-means analysis grouped participants according to the body height, leg length and body mass. A 1-way Anova showed no between sex differences (P ≥ 0.05) in any spatiotemporal parameters; whereas some differences were found between created sub-groups. Shorter contact time (CT) and step length (SL) and higher step frequency (SF) were obtained by the shorter group (P

Microscopic description of pair transfer between two superfluid Fermi systems. II. Quantum mixing of time-dependent Hartree-Fock-Bogolyubov trajectories

While superfluidity is accurately grasped with a state that explicitly breaks the particle number symmetry, a precise description of phenomena like the particle transfer during heavy-ion reactions can only be achieved by considering systems with good particle numbers. We investigate the possibility to restore particle number in many-body dynamical problems by mixing-up several Time-Dependent Hartree-Fock Bogolyubov (TDHFB) trajectories. In our approach, each trajectory is independent from the others and the quantum mixing between trajectories is deduced from a variational principle. The associated theory can be seen as a simplified version of the Multi-Configuration TDHFB (MC-TDHFB) theory. Its accuracy to tackle the problem of symmetry restoration in dynamical problems is illustrated for the case of two superfluid systems that exchange particles during a short time. In Ref. [Phys. Rev. C 97, 034627 (2018)], using a schematic model where two systems initially described by a pairing Hamiltonians are coupled during a short contact time, it was demonstrated that statistical mixing of TDHFB trajectories can only qualitatively describe the transfer process and that a fully quantum treatment is mandatory. We show here that the present MC-TDHFB approach gives an excellent agreement with the exact solution when the two superfluids are the same (symmetric case) or different (asymmetric case) and from weak to strong interaction strength. Finally, we discuss the benefits and bottleneck of this method in view of its application to realistic systems.

Formation of iodinated trihalomethanes and noniodinated disinfection byproducts during chloramination of algal organic matter extracted from Microcystis aeruginosa

The increasing occurrence of harmful algal blooms in surface waters may increase the input of algal organic matter (AOM) to the dissolved organic matter pool. The formation of iodinated trihalomethanes (I-THMs) and noniodinated disinfection byproducts (DBPs) in synthetic waters containing AOM extracted from Microcystis aeruginosa was investigated in chloramination (preformed and in-situ formed chloramine, NH2Cl and Cl2-NH2Cl, respectively) and chlorination (Cl2) processes. AOM is much more favorable for iodine incorporation than natural organic matter (NOM). For example, the formation of I-THM from AOM is much higher than NOM isolate extracted from treated water (e.g., 3.5 times higher in the NH2Cl process), and thus higher iodine utilization and substitution factors from AOM were observed. Short contact time (2 min) chlorination in Cl2-NH2Cl process leading to the formation of halogenated intermediates favored I-THM formation, compared with NH2Cl process. However, further increasing chlorine contact time from 5 min to 24 h facilitated the conversion from iodide to iodate and thus I-THM formation decreased. Meanwhile, the formation of noniodinated THM4, haloacetonitriles (HANs), and haloacetaldehydes (HALs) increased. Factors including concentrations of AOM and bromide, pH, and chlorine/nitrogen ratios influenced the formation of I-THMs and noniodinated DBPs. To evaluate the benefit of mitigating I-THM formation over the risk of noniodinated DBP formation, measured DBPs were weighed against their mammalian cell toxicity indexes. Increasing the chlorine exposure increased the calculated cytotoxicity based on concentrations of measured I-THMs and noniodinated DBPs since unregulated HANs and HALs were the controlling agents.