Correlation of fermentation redox potential and induction of recombinant E. coli expression system

Currently, Escherichia coli (E. coli) is widely adopted as a host for recombinant genes to overexpress. It is common to regard optical density (OD) reading as an indicator to guide IPTG induction of recombinant E. coli and harvest them at an empirical moment. However, it is found that OD reading cannot truly reflect the actively growing cells in the culture. With labor involvement, the frequent sampling for monitoring fermentation progress is prone to result in contamination. Besides, with an improperly designed sampling schedule, the optimal induction moment may be missed. Due to these reasons, a new measurement using redox potential (ORP) to replace OD as a more appropriate method to monitor the fermentation of recombinant E. coli was proposed, implemented and validated. ORP is known as an instantaneous reflection of organisms, either oxidized or reduced, which is related to the fermentation dissolved oxygen (DO) level and the intracellular metabolic reactions. During the culture of recombinant E. coli at 16 ºC, OD ORP and DO profiles were collected and compared. ORP profile was found as a portrait of a real-time growth stage of recombinant cells. And this relationship has been verified to be reproducible and reliable. With the cells rapid build up at the start of exponential phase, ORP declines promptly. Then ORP stayed at this minimal level for over sixty hours until E. coli grew to the end of stationary phase. When the culture was ready for harvest, ORP raised noticeably in a short period of time due to a living cell reduction. In addition, two special features of ORP profile were related to the crucial moments of E. coli growth. Specifically, the fluctuation during the decreasing phase of ORP was recognized as a certain timing for induction. Besides, harvesting cells when ORP increased rapidly was known as an optimal period for both enlarging the protein expression and improving the enzyme activity. DO supply was then noticed insufficient during the fermentation which had a negative effect on cells’ growth. Two methods increasing agitation rate and aeration rate were implemented in order to improve and control DO level. The results demonstrated that DO level was able to be controlled at a sufficient amount by combining these two methods. Comparing the fermentation technology developed in this research with the typical recombinant cell cultivation technique when OD is chosen to guide the IPTG addition, the expression level of prolinase of both techniques was compatible. Our fermentation technology (compared to the conventional cultivation technology) has various advantages, including less prone to culture contamination, less labor involvement, and low operating cost. This proposed technology can be further improved to become an automatic fermentation process towards the production of recombinant products

Numerical simulation for mold-filling of thin-walled aluminum alloy castings in traveling magnetic field

The numeical simulation for mold-filling of thin-walled aluminum alloy castins in horizontal traveling magnetic field is performed. A force model of Al alloy melt in the traveling magnetic field is founded by analyzing traveling magnetic field carefully. Numerical model of Al alloy mold-filling is founded based on N-S equation, which was suitable for traveling magnetic field. By using acryl glass mold with indium as alloy melt, the experiment testiied the filling state of alloy in traveling magnetic field. The results of numerical simulation indicate that the mold-filling ability of gallium melt increases continually with the incease of the input ampere turns

Economic optimization on two time scales for a hybrid energy system based on virtual storage

Abstract This paper proposes an economic optimization method with two time scales for a hybrid energy system based on the virtual storage characteristic of a thermostatically controlled load (TCL). The optimization process includes two time scales in order to ensure accuracy and efficiency. Based on the forecast load and energy supply of the system, the first time scale is day-ahead economic operating optimization, carried out to determine the minimum operating cost for the whole day, and to find the period of greatest cost to which the second time scale optimization is applied. Using the virtual storage characteristic, the second time scale is short term detailed optimization carried out for these particular hours. By dispatching thermal load in this period and adjusting energy supply accordingly, we can find the optimal economic performance, and customer requests are taken into account to ensure satisfaction. A case study in Tianjin illustrates the effectiveness of this method and proves that a TCL can make a great contribution to improving the economic performance of a hybrid energy system

Effect of hafnium addition on solidifi cation structure of cast Ti-46Al alloys

To investigate the effect of hafnium addition on the solidifi cation structure, Ti-46Al alloys with nominal compositions of Ti-46Al-xHf (x = 0, 3, 5, 7) (at.%) were arc-melted into small ingots in an argon atmosphere. The characteristics of the macrostructures and microstructures were studied using a linear intercept method, OM, SEM (BSE), XRD and TEM. The results showed that the ingots with Hf have near lamellar microstructure in columnar and dendrite morphology. The hafnium concentration has a strong effect on the columnar spacing refi nement. Increasing Hf from 0 to 7 (at.%), the columnar spacing can be reduced from ~ 1000 to ~ 400 μm. Constitute phases of the ingots are α2, a small amount of B2 and c. Most of the B2 phases, richer in Hf and leaner in Al and Ti, exist on the node of the dendrite core in block shape and a little across the lamellar colonies in stick shape. The c phases exist on the boundaries of lamellar colonies in small cellular shape. There also exists a segregation of Hf on the columnar and dendrite core. Particularly, both the α- and β-phase form from the melt as prior phases. The possible phase sequencing during solidifi cation and solid-state transformations with Hf is given in this paper

Effect of growth rate on characteristic lengths of microstructure in directionally solidified

The microstructure of TiAl based alloys is sensitive to growth rates. In this paper, Bridgman directional solidification of Ti-46Al-2Cr-2Nb-0.2B (at.%) alloy was carried out at a constant temperature gradient (G) to investigate the effects of various growth rates (v) on characteristic lengths (primary dendritic arm spacing, secondary dendritic arm spacing and lamellar spacing) of the microstructure. Results show that under the experimental conditions of G = 18 K·m-1 and v = 15 μm·s-1 to 70 μm·s-1, the primary phase of directionally solidified Ti-46Al-2Cr-2Nb-0.2B alloy is α phase, the values of primary dendritic arm spacing (λ1), secondary dendritic arm spacing (λ2) and lamellar spacing (λ1a) decrease with the increase in growth rate. The results were compared with theoretical models and similar experimental results of TiAl based alloys. The Bouchard-Kirkaldy model agrees well with the relationship between primary dendritic arm spacing and growth rate obtained in the experiment; the relationship between them can be expressed by λ1 = 758.6v-0.39. The relationship between the secondary dendritic arm spacing and the growth rate can be expressed by λ2 = 113.9v-0.45, while the relationship between the lamellar spacing and growth rate can be expressed by λ1a = 22.88v-0.94

Electromagnetic characteristics of square cold crucible designed for silicon preparation

In the present work, the strength and distribution of electromagnetic field in the square cold crucible that designed for casting multicrystalline silicon were measured and analyzed by using a small coil method. The results show that in the perpendicular direction the maximum of magnetic flux density (B) appears at the position slightly above the middle of the coil, and then B attenuates toward both sides, and decreases more to the bottom of the crucible. In the horizontal direction, from the edge (corner) to the center, B firstly decreases gradually, and then slightly increases in the center. While along the inner sides of the crucible, the distribution is relatively uniform, especially in the effective acting range. B increases with the increasing of the input power. Moving the coil to the top of the crucible, B increases and the effective acting range of the electromagnetic field becomes bigger. For the coils with different turns, the five turns coil can induce the highest magnetic flux density