Abrupt Concentration Changes Research Articles

A real-time monitoring of pre-overcharge in high‑nickel lithium ion batteries via plasma emission spectroscopy

Using the calibration-free atomic spectroscopic technique on lithium (Li) I with its wavelengths at 610.35, 610.65, and 670.79 nm, Li ion signals at varying state of charge (SOC) from high‑nickel (>88 %) batteries with NCA (Ni-Co-Al) cathode and SCN (silicon carbon nanocomposite) anode are detected in real-time (<3 s). The laser-induced plasma spectroscopy (LIPS) revealed that moderate changes in the concentrations of Li and metals (Ni, Co, and Al) during the normal charging underwent an abrupt concentration change in Li as the SOC reached above 75 %. Verified by using SEM-EDS (Scanning Electron Microscopy-Energy Dispersive Spectrometer), this sudden decrease of Li ions in cathode is deemed as being indicative of the state of overcharge. The present work is aimed at developing a new opto-chemical SOC sensor while the experimental set up offers a new method for detecting the state of pre-overcharge in nickel-rich Li-ion batteries.

Formation mechanism of Tb-rich shell in grain boundary diffusion processed Nd–Fe–B sintered magnets

We propose a new mechanism for the formation of Tb-rich shell in the Nd–Fe–B sintered magnet that was subjected to the grain boundary diffusion (GBD) process using TbH2. Tb-enriched liquid films form along grain boundaries during the GBD process, which migrate by chemically induced liquid film migration (CILFM) to form Tb-rich shells behind. As a result, the Tb-rich shell form asymmetrically along a grain boundary with an abrupt concentration change at a core/shell interface with a gradual decrease of Tb concentration toward a grain boundary. These microstructure features can be reproduced with phase-field simulations.

Laboratory observations of particle release in a porous medium using increasing ultrasound stimulation

Summary It is well established that seismic waves disperse into higher harmonics, thereby generating waves at ultrasonic frequencies within layers. Field tests and laboratory investigations have demonstrated that ultrasonic stimulation can enhance particle release in natural systems, but the intrinsic mechanisms of ultrasonic waves are not fully comprehended. We investigated the underlying mechanics of such waves by generating increasing ultrasound stimulation upon enhanced release of trapped particles from pores. Experiments were conducted using a novel soil column apparatus that is capable of applying ultrasonic waves, controlling the confining pressures, regulating the soil column height, and controlling the temperature of the soil column. Particles with median diameters of 9.63 μm in the range of 1–35 μm were evaluated in a series of tests under three flow rates. Stimulations were applied for 60 s at power levels of 600, 1000, 1400, and 1800 W. The particle concentration in the effluent during each test was recorded. The laboratory results showed that hydrodynamic drag was the dominant force in pre-stimulation particle release. However, the flow rate was found to be constant in pre- and post-stimulation phases, and cavitation caused by ultrasound stimulation was judged to be the most likely reason for post-stimulation particle release. Furthermore, the nature of the post-stimulation particle release was distinctly different from that of the pre-stimulation release, in that an abrupt concentration change was observed in each stimulation application. These abrupt concentration changes were attributed to ultrasound stimulation, but the release concentration and the duration of particle release were controlled by the power of the ultrasound stimulation and the quantity of particles deposited in the sand. Furthermore, the release rate coefficient first decreased and then increased as the number of ultrasound stimulations increased. Two mechanisms of particle release were identified that could explain the rate change: (1) only particles deposited in the porous medium by fouling mechanisms could be released by ultrasound stimulations at power levels below a certain critical value, or (2) ultrasound stimulations at power levels above a certain critical value are sufficient to change the structure of the porous medium, producing more dead-end pore openings that allow particle flow through the porous medium. The results presented are unique in indicating that successive particle release can be induced using increasing ultrasound stimulation.

Optimisation of a microfluidic analysis chamber for the placement of microelectrodes

The behaviour of droplets entering a microfluidic chamber designed to house microelectrode detectors for real time analysis of clinical microdialysate is described. We have designed an analysis chamber to collect the droplets produced by multiphase flows of oil and artificial cerebral spinal fluid. The coalescence chamber creates a constant aqueous environment ideal for the placement of microelectrodes avoiding the contamination of the microelectrode surface by oil. A stream of alternating light and dark coloured droplets were filmed as they passed through the chamber using a high speed camera. Image analysis of these videos shows the colour change evolution at each point along the chamber length. The flow in the chamber was simulated using the general solution for Poiseuille flow in a rectangular chamber. It is shown that on the centre line the velocity profile is very close to parabolic, and an expression is presented for the ratio between this centre line velocity and the mean flow velocity as a function of channel aspect ratio. If this aspect ratio of width/height is 2, the ratio of flow velocities closely matches that of Poiseuille flow in a circular tube, with implications for connections between microfluidic channels and connection tubing. The droplets are well mixed as the surface tension at the interface with the oil dominates the viscous forces. However once the droplet coalesces with the solution held in the chamber, the no-slip condition at the walls allows Poiseuille flow to take over. The meniscus at the back of the droplet continues to mix the droplet and acts as a piston until the meniscus stops moving. We have found that the no-slip conditions at the walls of the chamber, create a banding effect which records the history of previous drops. The optimal position for sensors is to be placed at the plane of droplet coalescence ideally at the centre of the channel, where there is an abrupt concentration change leading to a response time ≪16 ms, the compressed frame rate of the video. Further away from this point the response time and sensitivity decrease due to convective dispersion.

Origin of the Sphere-to-Rod Transition in Cationic Micelles with Aromatic Counterions: Specific Ion Hydration in the Interfacial Region Matters

Sphere-to-rod transitions of cetyltrimethylammonium (CTA+) micelles with dichlorobenzoate counterions are remarkably substituent dependent. Simultaneous estimates of the interfacial molarities of H2O, MeOH, and Cl- and 2,6- and 3,5-dichlorobenzoate (2,6OBz and 3,5OBz) counterions were obtained by the chemical trapping method in mixed micelles of CTACl/CTA3,5OBz and CTACl/CTA2,6OBz without added salt. Increasing the CTA3,5OBz mole fraction produces a marked concurrent increase in interfacial 3,5OBz- and a decrease in interfacial H2O concentrations through the sphere-to-rod transition. No abrupt concentration changes are observed with increasing CTA2,6OBz mole fraction. Counterion-specific changes in the interfacial water concentration may be a major contributor to the delicate balance of forces governing micellar morphology.

Seasonal variability of greenhouse gases in the lower troposphere above the eastern European taiga (Syktyvkar, Russia)

A three year long record of regular vertical aircraft profiling for continuous atmospheric CO2 mixing ratio measurements as well as for flask sampling to derive the climatology of other greenhouse gases (CH4, SF6 and N2O), is presented. Measurements were undertaken in the lower troposphere between 100 and 3000 m over the eastern European taiga about 100 km south east of the city of Syktyvkar(61°24′N, 52°18′E). From the continuous profiles mean CO2 mixing ratios were calculated for the atmospheric boundary layer (ABL) and for the “free troposphere” up to 3000 m. The amplitudes of the respective seasonal cycles are 22.1 ± 3.5 and 14.0 ± 2.1 ppm. ABL mixing ratios are generally larger than free tropospheric values during the winter period, and smaller during the summer due to the change of the continental biosphere from a source to a sink. The phasing of the seasonal cycles is slightly different between the two height intervals (by about 30 days), with the ABL extremes occurring earlier. Very abrupt concentration changes up to 8 ppm are observed in the free troposphere associated with changes in air mass origin. Mean CO2 mixing ratios derived from flask samples at 3000 m compare well with the respective integrated values measured in the continuous profiles above the ABL (ΔCO2 = 0.3 ± 1.6 ppm). CH4 mixing ratios also show a pronounced seasonality, and winter time vertical gradients correlate well with those of CO2. Similarly, SF6 vertical gradients are correlated with CO2 gradients possibly pointing to some anthropogenic origin of the boundary layer CO2 signal during winter. N2O and SF6 also show a slight seasonality with almost the same phasing. The main reasons for the seasonality of both gases are probably transport processes with a possible contribution from stratosphere/troposphere exchange.

Seasonal variability of greenhouse gases in the lower troposphere above the eastern European taiga (Syktyvkar, Russia)

A three year long record of regular vertical aircraft profiling for continuous atmospheric CO2 mixing ratio measurements as well as for flask sampling to derive the climatology of other greenhouse gases (CH4, SF6 and N2O), is presented. Measurements were undertaken in the lower troposphere between 100 and 3000 m over the eastern European taiga about 100 km south east of the city of Syktyvkar(61°24′N, 52°18′E). From the continuous profiles mean CO2 mixing ratios were calculated for the atmospheric boundary layer (ABL) and for the “free troposphere” up to 3000 m. The amplitudes of the respective seasonal cycles are 22.1 ± 3.5 and 14.0 ± 2.1 ppm. ABL mixing ratios are generally larger than free tropospheric values during the winter period, and smaller during the summer due to the change of the continental biosphere from a source to a sink. The phasing of the seasonal cycles is slightly different between the two height intervals (by about 30 days), with the ABL extremes occurring earlier. Very abrupt concentration changes up to 8 ppm are observed in the free troposphere associated with changes in air mass origin. Mean CO2 mixing ratios derived from flask samples at 3000 m compare well with the respective integrated values measured in the continuous profiles above the ABL (ΔCO2 = 0.3 ± 1.6 ppm). CH4 mixing ratios also show a pronounced seasonality, and winter time vertical gradients correlate well with those of CO2. Similarly, SF6 vertical gradients are correlated with CO2 gradients possibly pointing to some anthropogenic origin of the boundary layer CO2 signal during winter. N2O and SF6 also show a slight seasonality with almost the same phasing. The main reasons for the seasonality of both gases are probably transport processes with a possible contribution from stratosphere/troposphere exchange.

Distribution of individual components in thermoplastic olefins: step-scan FT-IR photoacoustic phase analysis

A method to determine surface stratification of components within a thermoplastic olefin (TPO) compound is developed using Fourier transform infrared (FT-IR) step-scan photoacoustic spectroscopy (S 2 PAS). Infrared bands attributed to magnesium silicate (talc), polypropylene (PP), and ethylene–propylene rubber (EPR) are used as analytical depth-profiling probes to establish the origin of the photoacoustic (PA) signal. This was accomplished by performing a series of experiments at various modulation frequencies, and subsequent monitoring of phase spectra and phase rotated spectra generated from signals collected at 0° ( I) and 90° ( Q) phase shifted from the light source. Utilizing phase analysis data, a TPO compound stratification model was developed, which consists of four distinct layers extending by 0–12 μm from the sample surface. Layer I (0–3 μm) shows evidence of a large change in talc and PP concentration, while layer II (3–6 μm) shows a significant decrease in both of these components. Within this same layer, evidence of discrete individual EPR particles are shown by an abrupt concentration change from 2.67 to 5.35 μm, followed by a large decrease from 5.35 to 6.55 μm. Further into the sample at 6–9 μm from the surface (layer III), all three components reach their highest maximums for all four layers, with talc serving as the local maximum. Approaching layer IV, talc concentration diminishes until it is no longer apparent further than a distance of 8.40 μm from the surface. In addition, both EPR and PP concentration are detected within this layer (9–12 μm), showing decreases in concentration with depth. The proposed depth profiling technique also shows potential applications to various systems displaying stratification near the surface.

Determination of trace elements in tree rings ofPinus by neutron activation analysis

The elemental composition of pine trees as a function of age was achieved by the tree-ring method. By using instrumental neutron activation analysis, trace elements were determined in individual rings ofPinus elliottii var.elliottii of 32, 14 and 9 years, from an implanted forest ofPinus sp., Buri, Sao Paulo, far away from industrial pollution. Different components of the system such as needles, pith, bark, soil and litter were also analyzed for 18 elements (As, Br, Ce, Co, Cs, Eu, Fe, Hf, K, La, Mn, Na, Rb, Sc, Sm, Yb, Zn, and Zr). Al, B, Ba, Ca, Fe, K, Mg, and P concentrations were determined by atomic absorption and/or emission spectrometry (AAS; ICP-AES). Some elements have showed similar radial distribution of the concentration for the three ages. Abrupt concentration changes in the pith and ring-bark boundary corresponding to the first and last growth rings were observed.

Characterization of interfacial failure in SiC reinforced Si3N4 matrix composite material by both fiber push-out testing and Auger electron spectroscopy

An investigation into the mechanical/chemical properties of the fiber/matrix interface in an SCS-6 SiC reinforced reaction bonded Si3N4 composite is made using a fiber push-out test for determining interfacial shear strength and Auger electron spectroscopy (AES) depth profiling for elemental composition in the interface region. Special emphasis is placed on locating the weak point where interfacial failure occurs. Fiber push-out tests determined the interfacial frictional shear stress to have an average value of 8 MPa and was found to depend only on frictional stresses. AES depth profiles were obtained for composite fracture surfaces as well as pushed-out fibers. For both composite fracture and fiber push-outs, the interfacial failure was determined to occur either between the two C-rich coatings that are present on the double-coated SCS-6 SiC fibers or between the inner C-rich coating and the SiC fiber. Failure was not observed between the outer C-rich coating and the matrix. AES depth profiles indicated that interface failure occurs at points of very abrupt concentration changes. Evidence is presented for substantial mass transport within the fiber coating during composite fabrication.

The effect of abrupt changes in the concentration and frequency of feeding milk-substitute diets on the voluntary food intake of calves

1. To examine the relations between short- and long-term regulation of food intake in calves given milk-substitute diets, abrupt changes were made in the dry matter (DM) concentration of the diet (Expt 1) and in the frequency of feeding (Expts 2 and 3). 2. When calves, fed once daily, had the DM concentration of their diet changed, they drank the same volume of milk on the 1st day they received the new diet as they had on the previous days; so the DM intakes changed in proportion to the change in milk DM concentration. Over the subsequent 6 d, milk intake progressively increased when milk DM concentration was reduced. When the DM concentration of milk was increased the volume of milk drunk was reduced to a minimum value 2-3 d after the change in diet and increased thereafter. The size of the changes was dependent on the initial and changed DM concentrations of the milk. 3. In calves receiving milk-substitute diets containing 80-260 g DM/kg, milk intakes were reduced by up to 30% on the 1st day that calves were fed once daily instead of twice daily. Over the subsequent 13 d of once-daily feeding, milk intakes increased, particularly for calves given diets of low DM concentration. 4. Feeding the calves once daily reduced the digestibility of DM in Expt 2 but not the digestibility of crude protein (nitrogen x 6.25) and fat; diets containing lower concentrations of DM were particularly affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Phase diagrams and crystal growth

Phase diagrams are briefly treated as generalized property-composition relationships, with respect to crystal technology optimization. The treatment is based on mutual interaction of three systems related to semiconductors: (a) the semiconducting material systems, (b0 the data bank, (c) the system of crystallization methods. A model is proposed enabling optimatization on the path from application requirements to the desired material. Further, several examples of the selection as to the composition of LED and laser diode material are given. Some of molten-solution-zone methods are being successfully introduced for this purpose. Common features of these methods, the application of phase diagrams, and their pecularities compared with other crystallization methods are illustrated by schematic diagrams and by examples. LPE methods, particularly the steady-state LPE methods such as Woodall's ISM and Nishizawa's TDM-CVP, and the CAM-S (Crystallization Method Providing Composition Autocontrol in Situ) have been chosen as examples. Another approach of exploiting phase diagrams for optimal material selection and for determination of growth condition before experimentation through a simple calculation is presented on InP-GaP solid solutions. Ternary phase diagrams are visualized in space through calculation and constructions based on the corresponding thermodynamic models and anaglyphs. These make it easy to observe and qualitatively analyze the crystallization of every composition. Phase diagrams can be also used as a powerful tool for the deduction of new crystallization methods. Eutectic crystallization is an example of such an approach where a modified molten-solution-zone method can give a sandwich structure with an abrupt concentration change. The concentration of a component can range from 0 to 100% in the different solid phases.

Sensory adaptation mutants of E. coli

The ability of E. coli to adapt to constant levels of attractant and repellent chemicals was studied by examining the patterns of flagellar movement in cells subjected to abrupt concentration changes. Wild-type bacteria exhibited transient responses to such stimuli, in support of previous findings. Nonchemotactic mutants of the cheX class responded to both attractants and repellents, but were unable to terminate these behavioral changes as long as the stimulating chemical was present. The sensory adaptation defect of cheX strains may be due to an inability to methylate several cytoplasmic membrane proteins that initiate changes in flagellar movement in response to chemoreceptor signals. Based on these results, possible mechanisms of stimulus transduction and sensory adaptation during chemotaxis are discussed.

Closing volume--a test of small airway function?

Abstract Closing volume has been defined as that lung volume at which airways begin to close in the dependent zones of the lungs. The technique used for estimating closing volume is a modification of the single-breath nitrogen washout test adapted for use with other marker gases. A bolus of marker gas in inhaled at the start of inspiration from residual volume to total lung capacity. The concentration of the marker gas in the subsequently expired gases is recorded at the mouth and is displayed against a simultaneous measure of expired gas volume on an XY recorder. An abrupt change in concentration of the marker gas is observed towards the end of expiration, and this marks the point from which closing volume is measured. The form of the closing volume trace is critically influenced by gravity and by variations in inspiratory and expiratory flow rates. It has been suggested that the shape of the marker gas/expired volume curve may depend on airway narrowing caused by dynamic compression (trapping) rather than on total closure of the airways concerned. Reproducible estimations of the size of closing volume have been obtained in normal subjects and in patients with some diseases; estimations may not be reproducible in more severe airways obstructions. Some patients with chronic bronchitis or bronchial asthma record closing volume traces which are uninterpretable by simple methods. In normal subjects there is a progressive increase in size of closing volume with age. To calculate normal ranges for the size of closing volume at any age will require larger population samples than those reported so far. It is concluded that further developmental studies are required before measurement of the closing volume can be used as a routine clinical test of pulmonary function.

Silicic acid column chromatography: Parameters for a binary solvent system

AbstractThe elution characteristics of methanol‐benzene solvent systems were determined by separating a mixture of polar and nonpolar fatty methyl esters by liquid chromatography on silicic acid columns. A series of curves were plotted showing the relationship between the elution volume of each component and methanol concentration of the stationary phase. The resulting graphs serve as a basis for predicting elution conditions for separating other polar materials. Adsorption isotherms were plotted from equilibrium studies of methanol‐benzene systems on silicic acid. Methanol concentrations of the effluents from various columns were determined by refractive index. An abrupt concentration change occurs in the methanol content of the effluent when the mobile solvent is either richer or poorer in methanol than the equilibrated solvent. Elution position of this abrupt change depends upon the concentration of methanol in both the mobile and the stationary phases. The procedure has been rigorously standardized because small variations in the amount of methanol on the column create large differences in elution volumes.

Regularities in the structural formation of the chromed layer in iron-chromenickel alloys

1. The relation of the depth of chroming of iron-chrome-nickel alloys to the structure of an isothermic section of the ternary phase diagram has been indicated. 2. It has been established that during usual chroming of an alloy containing 35% Ni (KhN35VT steel) the change in chemical composition of the surface layer in the diffusion zone principally corresponds in the isothermic section of the diagram to the direction of a radial section joining the composition point of this alloy with the vertex of the concentration triangle belonging to chromium. 3. In chroming the same alloy (KhN35VT) under identical conditions but with the use of an accelerator, the appreciable acceleration of chromium diffusion is related to the fact that the chemical composition of the surface layer in the diffusion zone is characterized by a sharp rise in the ratio of iron to nickel as compared to this same ratio in the base metal. This leads to deviation of the composition points of the surface layer in the isothermic section of the diagram from the direction of the radial section and occasions the formation in the structure of the layer of a zone of α-phase in which the coefficient of chromium diffusion is greater than in the γ-phase. 4. It has been shown that during usual chroming of KhN35VT steel with powders in hermetic containers a transfer not only of atoms of iron but also of nickel atoms from the metal to ghe gas medium takes plase. 5. The existence of a zone of metastable austenite has been established when chroming an alloy containing 35% Ni (KhN35VT steel); this is explained by the absence on the chromium concentration curve of an abrupt change in concentration in the interval of values corresponding to the intermediate region in the isothermic section of the ternary diagram.

Effect of abrupt concentration changes on the motion of free drops

Effect of abrupt concentration changes on the motion of free drops