Changes In Fraction Distribution Research Articles

Interfacial Structures in Bubbly-to-Slug Transition Flows in a Duct

As a critical closure equation to the two-fluid model and an important tool to characterize the two-phase-flow interfacial transport, the interfacial area transport equation (IATE) was formulated by taking various physical mechanisms causing interfacial area change into account. To fulfill the dynamic prediction advantage of IATE and further replace the flow regime–based constitutive relations, the IATE model should be validated by transition data to ensure model reliability and robustness. Air-water experiments are performed in bubbly-to-slug transition flows in a 200 × 10-mm narrow rectangular duct. Four-sensor conductivity probes are used to measure the local void fraction, interfacial area concentration (IAC), and bubble velocity at three axial locations. The void fraction distribution changes significantly with the flow developing. Flow conditions with a similar area-averaged void fraction but different superficial mixture velocities are compared, and it is found that the superficial mixture velocity significantly affects the IAC. In addition, the two-group IATE model for narrow rectangular channel is evaluated using the collected data. The average relative error for the total IAC prediction is 11.4%, but the group II IAC is overestimated for most flow conditions.

Sorption Characteristics and Fraction Distribution Changes of Selenite in Soil

Sorption properties play a key role in the mobility of selenium (Se) and fraction distribution changes, leading to the bioavailability of Se in the soil environment. Thus, the effect of soil physicochemical properties on the sorption of exogenous selenite was investigated to predict the rate and capacity of sorption. Correlation analysis and multiple linear regression were used to observe the relationship between sorption characteristics and soil properties. Sequential extraction was used to observe the fractions of Se at different ages in soil. Results indicated that sorption isotherms followed the Langmuir equation, and the sorption capacity ranged from 50.7 to 567 mg·kg−1 with pseudo-second-order sorption kinetics. The correlation and multiple linear regression analyses showed that sorption parameters were significantly positively correlated with dithionite–citrate–bicarbonate-extracted Fe (FeDCB), dithionite–citrate–bicarbonate-extracted Al (AlDCB), amorphous Fe (FeOX), and soil organic matter (SOM), whereas pH was negatively correlated. Sequential extraction analyses revealed that the fraction distribution of Se in soil varied with the age, and the content of elemental Se increased with prolonged aging. FeDCB, AlDCB, FeOX, pH, and SOM play important roles in selenite sorption onto soils. Selenite sorption onto soil can be reduced to a lower-state Se, such as elemental Se and selenides, during the aging process. This information on the environmental behavior of Se is used to develop agronomic strategies for increasing Se levels in food crops and improving human health.

Void fraction distribution in overburden disturbed by longwall mining of coal

Voids in overburden disturbed by coal mining provide channels for transfer of heat, methane, groundwater, oxygen, exhaust gas and fire-fighting materials in the underground environment. Based on expressions of strata and ground subsidence, a group of void fraction distribution models are proposed, including porosity in the caved zone, the fracture ratio in the bed separation zone and the fissure ratio in the ground subsidence zone. Combined with a case study of the Antaibao coal mine, China, theoretical calculation and numerical simulation indicate that porosity distribution in the caved zone is U-type and the transverse void fractions in the bed separation zone and ground subsidence zone have M-type distributions. Additionally, the longitudinal void fraction distribution changes from ∩-type to M-type along the strike and dip of the coalbed after the complete subsidence of ground. The distribution of fractures in the disturbed overburden of the goaf presents a “fractured arch”, and fracture density gradually decreases from arch foot to crown. Fire-prone zones, propagating paths of coalbed fires, areas prone to water influx and outlets of boreholes used for fire-fighting all usually appear around the perimeter of disturbed overburden. The transverse void fractions distribution in the bed separation zone changes from ∩-type to M-type with an increase in the size of the goaf. It is suggested that the inlets of gob vent boreholes should be arranged near the center of the bed separation zone in the early stages of longwall mining, and around the perimeter in middle to late stages of mining.

Arsenic accumulation and chemical fraction distribution changes in sludge in a low-sludge wastewater treatment system

This paper investigated the accumulation of arsenic and its chemical fraction distributions in a low-sludge wastewater treatment system using “sonication-cryptic growth” method. Subsequent bio-reactors (SBR) were used; one SBR without sonication was used for control. Results showed that “sonication-cryptic growth” technique cut sludge production in SBR by 50%. The accumulation of arsenic in sludge occurred in both reactors; the accumulation was low in 0–60 days and showed a sharp increase in 60–90 days. The final sludge arsenic content in the low-sludge system was 1.23 times of that in the control system. However, the higher arsenic content in the low-sludge treatment system did not impact the COD removal and the sludge bioactivity. The low-sludge system had higher COD removal efficiency and higher sludge activity than those of the control. Further analyses of the chemical fraction distribution of arsenic showed that arsenic existed in different forms in the two systems. In the control system, the major form of arsenic in sludge was the organically bound fraction during 0–60 days, and the chemical fractions were redistributed during 60–90 days and the Fe/Mn oxide fraction and organically bound fraction were the main fractions. In the low-sludge system, the major form of arsenic in sludge was Fe/Mn oxides bound fraction during the whole operation duration.

Modification of placenta blood serum proteins under low temperature effect

Changes in environmental physical and chemical factors upon freeze-thawing and low temperature storage of biological samples can result in impairments of protein structures. This work specifies spontaneous and diamide-induced protein aggregations of placenta blood serum stored at -20 degrees and -196 degrees C during 2 years with SDS-PAGE. It was shown that storage of placenta blood serum at low temperatures did not cause any quantitative and qualitative changes in fraction distribution of proteins denatured with SDS in comparison to the native samples which were not frozen. Application of beta-mercaptoethanol revealed that placenta blood serum proteins upon freeze-thawing did not form spontaneous aggregates linked by disulphide bridges. Oxidation of amino acid sulfhydryl groups induced by diamide and accompanied by high molecular aggregate formation proved to be a quite effective way for indirect estimation of structural changes in protein upon low temperature effects. In samples thawed after low temperature storage the protein aggregation with 4 microM diamide was significantly higher than in native serum. These discrepancies between native and frozen-thawed samples are stipulated by impairments of protein structure under low temperature and increased in accessibility of reactive SH-groups of proteins for oxidation with diamide. Structural changes in placenta blood serum proteins, which caused by low temperatures and revealed by elevated sensibility to diamide-induced aggregate formation, did not depend on temperature (-20 degrees and -196 degrees C) and storage terms (2 years and 3 weeks). They reflect protein reaction to freeze-thawing processes and could be sequence of ice crystal formation which takes place in unprotected media.

Fate and chemical fraction distribution changes of arsenic and mercury during ultrasonic sludge treatment process

Abstract Arsenic and mercury are typical elements with high toxicity found in sewage sludge, and only low content of them could cause severe environmental risks. Therefore, changes of arsenic and mercury during sludge treatment and disposal should be concerned. In this study, ultrasound irradiation was used for sludge treatment. The contents and chemical fraction changes of arsenic and mercury during sludge sonication were investigated in detail. Results showed that arsenic and mercury were released from sewage sludge into the aqueous phase by sonication. The concentrations of arsenic and mercury in the aqueous phase increased steadily during 30 min of sonication. The release of arsenic was higher than that of mercury (58% vs. 26%), since the content of unsteady chemical fractions of arsenic in sludge was high. Sonication enhanced the stability of arsenic and mercury in sludge. For arsenic, the unsteady fraction decreased from 85.0% to 0.0% and transformed into a stable fraction after 30 min of sonication...

Modification of placental blood serum proteins induced by low temperatures

Changes in physical and chemical factors appeared in response to freeze-thawing and low temperature storage of biological samples can result in impairments of protein structures. Spontaneous and diamide-induced protein aggregation of placenta blood serum stored at −20 and −196°C up to 2 years has been investigated by SDS-PAGE. It was shown that storage of placental blood serum at low temperatures did not cause any quantitative and qualitative changes in fraction distribution of proteins denatured by SDS compared with native (unfrozen) samples. Application of β-mercaptoethanol revealed that during freeze-thawing placental blood serum proteins did not form spontaneous aggregates cross-linked by disulphide bridges. Oxidation of amino acid sulfhydryl groups induced by diamide and accompanied by formation of high molecular aggregates was a reasonably effective approach for indirect assessment of structural changes in protein molecules induced by low temperatures. In the samples exposed to low temperature storage protein aggregation induced by 4 mM diamide was significantly higher than in native serum. The structural changes in serum proteins caused by low temperatures and recognized by discrepant susceptibility to diamide-induced protein aggregate formation did not depend on temperature (−20 and −196°C) and time-length of storage (2 years and 3 weeks). These changes do reflect protein reaction to freeze-thawing processes and could originate from ice crystal formation which takes place in unprotected media.

Fraction Distribution Changes of Heavy Metals in Co-Pyrolysis of Sewage Sludge and Corn Straw

Maiz’s short sequential extraction procedure was used to extract the heavy metals in the carbon residues made from sewage sludge by co-pyrolysis with corn straw. The content of heavy metals in the residues was determined by ICP-MS to study the fraction distribution changes of heavy metals. It is concluded that the content of mobile and mobilization heavy metals exsisted in the residue decrease and the content of residual heavy metals increase due to the co-pyrolysis. The co-pyrolysis temperature has great effect on the fraction distribution changes of heavy metals. The content of residual fraction for Cr, Ni, Pb is up to the top at 700°C and for Cd、Cu、Zn is at 500°C. The carbon residues are unhazardous and safe.

The development of the structure of water – air bubble grid turbulence

The development of the turbulent flow field generated due to the interaction of grid turbulence with a swarm of bubbles is investigated experimentally, in a vertical channel of rectangular cross section. Void fraction and streamwise mean and rms velocity distributions have been measured at several distances from the grid, with an optical probe and Laser Doppler Velocimetry, in relation to the air flow rate ratio. The obtained results indicate that close to the grid the void fraction and velocity distributions are dictated by the bubble injectors’ location on the grid. Downstream the void fraction distribution changes to a double peak pattern. The velocity distribution is characterized by a shear layer between the wall area and the central area of the channel. The extend of this shear layer is increasing as the distance from the grid and the gas flow rate ratio are increasing, and is associated with a corresponding increase of the turbulence fluctuations. Autocorrelation and spectra measurements at the centre of the channel show a reduction of the flow scales for low void fraction. Consistently, power spectra distributions indicate that bubbles cause a redistribution of energy manifested by the relative enhancement of the intermediate scales’ energy content and a consequent reduction in the larger scales. These trends are gradually alleviated and reversed at large distances from the grid, as the air flow rate is increased.

Effect of bubble deformability in turbulent bubbly upflow in a vertical channel

As bubbles rising in a vertical channel with upflow become bigger, it is well known that the void fraction distribution changes in a fundamental way, from a wall peak for small bubbles to a maximum void fraction at the channel center for larger bubbles. Here, we use direct numerical simulations of buoyant bubbles in a turbulent flow to show that it is not the size of the bubbles that matters, but their deformability.

Circulatory effects of acute or chronic endotoxemia in rats.

A study was made of the effects of acute (4 h) infusion of Escherichia coli endotoxin on cardiovascular function in rats. Rats with acute endotoxemia had a reduced cardiac output but maintained their arterial blood pressure. Fractional distribution of the cardiac output was increased to the liver and reduced to the gastorintestinal tract and skin. No changes in fractional distribution to the kidneys, lungs, or heart were observed although absolute blood flow to these areas was reduced. Rats with chronic endotoxemia had a reduced cardiac output and hypotension with no change in peripheral resistance. Other changes resembled those seen in acute endotoxemia apart from a low renal fraction of the cardiac output. Calculation and interpretation of blood flow changes in these animals was difficult because of a large fall in hematocrit and changes in organ weight.

The Effect of Angiotensin-Converting Enzyme Inhibition on Regional Blood Flow in Salt-Depleted and Salt-Loaded Normotensive Conscious Rats

The effect of angiotensin-converting enzyme inhibition on regional blood flow was studied in a total of 21 normotensive Wistar rats fed on either low or high salt diet. A new potent angiotensin-converting enzyme inhibitor (CEI), SQ 14,225 was administered intravenously in a dose of 2 mg/Kg to the conscious animals, and changes in fractional distribution of cardiac output were determined with a microsphere method. Prior to administration of CEI, there was no significant difference in mean arterial pressure (MAP) or regional blood flow between salt-depleted and salt-loaded rats. With CEI, MAP did not change significantly in either group. Fractional distribution of cardiac output increased to the kidneys (p less than 0.002), and decreased to the stomach, spleen, and skeletal muscle (p less than 0.02, p less than 0.002, and p less than 0.01, respectively) in the salt-depleted group, while a pattern of blood flow distribution was not changed in the salt-loaded group. These results suggest that angiotensin II plays an important role in regulating regional blood flow in salt-depleted conscious animals, but not in salt-loaded ones.