SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Suspension

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The objectives of this study were to compare the effects of a newly designed magnetic suspension system with that of two existing suspension methods on pistoning inside the prosthetic socket and to compare satisfaction and perceived problems among transtibial amputees.

Concepts: Psychology, Comparison, Suspension

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Abstract Background: Air-jet atomization is a common technique used for the generation of therapeutic aerosols from liposome suspensions for drug delivery to the lungs. Although the technique does not use an electric field, the aerosols generated by this technique are still charged, and this may affect respiratory drug deposition. Methods: In this study, the charge distribution of liposomes aerosolized by an air-jet atomizer was measured using a tandem differential mobility analyzer (TDMA) technique. The liposomes, composed of a mixture of two amphiphilic lipids and cholesterol, were synthesized by the dehydration-rehydration vesicle method. The effect of the precursor suspension properties, such as medium composition, pH, conductivity, and lipid mass concentration, on the charge distribution of the liposome aerosols was studied. Results and Conclusions: Results showed that the atomized liposomes have a bipolar charge distribution, and the number-fraction of charged liposome aerosols was influenced strongly by properties of the precursor solution under investigation. Liposomes synthesized in deionized water were observed to carry much higher charges than those synthesized in phosphate-buffered saline (PBS). Increasing the lipid mass concentration in the precursor suspension resulted in a decrease in the charge on the aerosols. Thus, the precursor suspension properties-composition, pH, and conductivity-can be used to control the magnitude of charge on liposome aerosols and to synthesize engineered liposome particles for the pulmonary delivery of drugs with controlled alveolar deposition and controlled delivery to alveolar macrophages.

Concepts: Electric charge, Membrane biology, Solution, Aerosol, Lipid bilayer, Suspension, Atomization, Atomic spectroscopy

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Flocculation of microalgae is a promising technique to reduce the costs and energy required for harvesting microalgae. Harvesting marine microalgae requires suitable flocculants to induce the flocculation under marine conditions. This study demonstrates that cationic polymeric flocculants can be used to harvest marine microalgae. Different organic flocculants were tested to flocculate Phaeodactylum tricornutum and Neochloris oleoabundans grown under marine conditions. Addition of 10 ppm of the commercial available flocculants Zetag 7557 and Synthofloc 5080H to P. tricornutum showed a recovery of, respectively, 98% ± 2.0 and 94% ± 2.9 after flocculation followed by 2h sedimentation. Using the same flocculants and dosage for harvesting N. oleoabundans resulted in a recovery of 52% ± 1.5 and 36% ± 11.3. This study shows that cationic polymeric flocculants are a viable option to pre-concentrate marine cultivated microalgae via flocculation prior to further dewatering.

Concepts: Agriculture, Phaeodactylum tricornutum, Suspension, Flocculation, Sedimentation

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The functionalization of nanoparticles has primarily been used as a means to impart stability in nanoparticle suspensions. In most cases even the most advanced nanomaterials lose their function should suspensions aggregate and settle, but with the capping agents designed for specific solution chemistries, functionalized nanomaterials generally remain monodisperse in order to maintain their function. The importance of this cannot be underestimated in light of the growing use of functionalized nanomaterials for wide range of applications. Advanced functionalization schemes seek to exert fine control over suspension stability with small adjustments to a single, controllable variable. This review is specific to functionalized nanoparticles and highlights the synthesis and attachment of novel functionalization schemes whose design is meant to affect controllable aggregation. Some examples of these materials include stimulus responsive polymers for functionalization which rely on a bulk solution physicochemical threshold (temperature or pH) to transition from a stable (monodisperse) to aggregated state. Also discussed herein are the primary methods for measuring the kinetics of particle aggregation and theoretical descriptions of conventional and novel models which have demonstrated the most promise for the appropriate reduction of experimental data. Also highlighted are the additional factors that control nanoparticle stability such as the core composition, surface chemistry and solution condition. For completeness, a case study of gold nanoparticles functionalized using homologous block copolymers is discussed to demonstrate fine control over the aggregation state of this type of material.

Concepts: Nanoparticle, Chemistry, Nanotechnology, Nanomaterials, Sol-gel, Colloid, Gold, Suspension

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This paper proposes adaptive control designs for vehicle active suspension systems with unknown nonlinear dynamics (e.g., nonlinear spring and piece-wise linear damper dynamics). An adaptive control is first proposed to stabilize the vertical vehicle displacement and thus to improve the ride comfort and to guarantee other suspension requirements (e.g., road holding and suspension space limitation) concerning the vehicle safety and mechanical constraints. An augmented neural network is developed to online compensate for the unknown nonlinearities, and a novel adaptive law is developed to estimate both NN weights and uncertain model parameters (e.g., sprung mass), where the parameter estimation error is used as a leakage term superimposed on the classical adaptations. To further improve the control performance and simplify the parameter tuning, a prescribed performance function (PPF) characterizing the error convergence rate, maximum overshoot and steady-state error is used to propose another adaptive control. The stability for the closed-loop system is proved and particular performance requirements are analyzed. Simulations are included to illustrate the effectiveness of the proposed control schemes.

Concepts: Mathematics, Systems theory, Control theory, Proposal, Proposals, Suspension, Nonlinear system, Active suspension

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Laboratory experiments were carried out to study the effects of slow mixing conditions on magnesium hydroxide floc size and strength and to determine the turbidity and total suspended solid (TSS) removal efficiencies during coagulation of highly turbid suspensions. A highly turbid kaolin clay suspension (1,213 ± 36 nephelometric turbidity units (NTU)) was alkalized to pH 10.5 using a 5 M NaOH solution; liquid bittern (LB) equivalent to 536 mg/L of Mg(2+) was added as a coagulant, and the suspension was then subjected to previously optimized fast mixing conditions of 100 rpm and 60 s. Slow mixing speed (20, 30, 40, and 50 rpm) and time (10, 20, and 30 min) were then varied, while the temperature was maintained at 20.7 ± 1 °C. The standard practice for coagulation-flocculation jar test ASTM D2035-13 (2013) was followed in all experiments. Relative floc size was monitored using an optical measuring device, photometric dispersion analyzer (PDA 2000). Larger and more shear resistant flocs were obtained at 20 rpm for both 20- and 30-min slow mixing times; however, given the shorter duration for the former, the 20-min slow mixing time was considered to be more energy efficient. For slow mixing camp number (Gt) values in the range of 8,400-90,000, it was found that the mixing speed affected floc size and strength more than the time. Higher-turbidity removal efficiencies were achieved at 20 and 30 rpm, while TSS removal efficiency was higher for the 50-rpm slow mixing speed. Extended slow mixing time of 30 min yielded better turbidity and TSS removal efficiencies at the slower speeds.

Concepts: Colloid, Physical quantities, Calcium hydroxide, Suspension, Total suspended solids, Flocculation, Turbidity, Settling

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Microalgae represent a promising source of renewable biomass for the production of biofuels and valuable chemicals. However, energy efficient cultivation and harvesting technologies are necessary to improve economic viability. A Tris-Acetate-Phosphate-Pluronic (TAPP) medium that undergoes a thermoreversible sol-gel transition is developed to efficiently culture and harvest microalgae without affecting the productivity as compared to that in traditional culture in a well-mixed suspension. After seeding microalgae in the TAPP medium in a solution phase at 15 °C, the temperature is increased by 7 °C to induce gelation. Within the gel, microalgae are observed to grow in large clusters rather than as isolated cells. The settling velocity of the microalgal clusters is approximately ten times larger than that of individual cells cultured in typical solution media. Such clusters are easily harvested gravimetrically by decreasing the temperature to bring the medium to a solution phase.

Concepts: Solubility, Colloid, Harvest, Viticulture, Biomass, Suspension, Aerogel, Annual growth cycle of grapevines

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The efficient concentration and separation of microorganisms from dilute culture suspensions is crucial to the success and productivity of many biotechnological processes. This article presents the design and characterization of polyamphoteric flocculants with a tunable, zwitterionic character for the enhanced separation of biocolloidal suspensions of yeast, wastewater, microalgae, and potentially other cellular systems. The polyamphoteric flocculants have overall molecular charges dependent upon the system pH, thereby providing a strong electrostatic attraction to the diverse but predominantly negatively-charged cellular surfaces of the biological suspensions. The polyamphoteric flocculants with tailored charge character are shown to have higher flocculation efficiencies than comparable cationic polyelectrolytes, and have an enhanced ability to 1) adsorb to the diverse range of charge character in cellular suspensions, 2) operate over an extended range of suspension pHs, and 3) operate at lower flocculant concentrations. These enhanced flocculation properties are shown to arise, perhaps counterintuitively, due to interactions between the negatively-charged functionality on the flocculant and the predominantly negatively-charged biocolloids.

Concepts: Bacteria, Electric charge, Biotechnology, Colloid, Solution, Suspension, Flocculation, Sedimentation

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Aerosol generation and characterization are critical components in the assessment of the inhalation hazards of engineered nanomaterials (NMs). An extensive review was conducted on aerosol generation and exposure apparatus as part of an international expert workshop convened to discuss the design of an in vitro testing strategy to assess pulmonary toxicity following exposure to aerosolized particles. More specifically, this workshop focused on the design of an in vitro method to predict the development of pulmonary fibrosis in humans following exposure to multi-walled carbon nanotubes (MWCNTs). Aerosol generators, for dry or liquid particle suspension aerosolization, and exposure chambers, including both commercially available systems and those developed by independent researchers, were evaluated. Additionally, characterization methods that can be used and the time points at which characterization can be conducted in order to interpret in vitro exposure results were assessed. Summarized below is the information presented and discussed regarding the relevance of various aerosol generation and characterization techniques specific to aerosolized MWCNTs exposed to cells cultured at the air-liquid interface (ALI). The generation of MWCNT aerosols relevant to human exposures and their characterization throughout exposure in an ALI system is critical for extrapolation of in vitro results to toxicological outcomes in humans.

Concepts: Carbon, Assessment, In vitro, Particulate, Aerosol, Suspension, Aerosol spray, CS gas

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Covalent organic frameworks (COFs) are two- or three-dimensional (2D or 3D) polymer networks with designed topology and chemical functionality, permanent porosity, and high surface areas. These features are potentially useful for a broad range of applications, including catalysis, optoelectronics, and energy storage devices. But current COF syntheses offer poor control over the material’s morphology and final form, generally providing insoluble and unprocessable microcrystalline powder aggregates. COF polymerizations are often performed under conditions in which the monomers are only partially soluble in the reaction solvent, and this heterogeneity has hindered understanding of their polymerization or crystallization processes. Here we report homogeneous polymerization conditions for boronate ester-linked, 2D COFs that inhibit crystallite precipitation, resulting in stable colloidal suspensions of 2D COF nanoparticles. The hexagonal, layered structures of the colloids are confirmed by small-angle and wide-angle X-ray scattering, and kinetic characterization provides insight into the growth process. The colloid size is modulated by solvent conditions, and the technique is demonstrated for four 2D boronate ester-linked COFs. The diameter of individual COF nanoparticles in solution is monitored and quantified during COF growth and stabilization at elevated temperature using in situ variable-temperature liquid cell transmission electron microscopy imaging, a new characterization technique that complements conventional bulk scattering techniques. Solution casting of the colloids yields a free-standing transparent COF film with retained crystallinity and porosity, as well as preferential crystallite orientation. Collectively this structural control provides new opportunities for understanding COF formation and designing morphologies for device applications.

Concepts: Electron, Crystal, Nanoparticle, Solubility, Colloid, Liquid, Solution, Suspension