| 1. |
- Kim, Jung Hun, et al.
(author)
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Production of β-carotene by recombinant Escherichia coli with engineered whole mevalonate pathway in batch and fed-batch cultures
- 2009
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In: Biotechnology and Bioprocess Engineering. - : Springer Science and Business Media LLC. - 1226-8372 .- 1976-3816. ; 14:5, s. 559-564
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Journal article (peer-reviewed)abstract
- Recombinant Escherichia coli engineered to contain the whole mevalonate pathway and foreign genes for β-carotene biosynthesis, was utilized for production of β-carotene in bioreactor cultures. Optimum culture conditions were established in batch and pH-stat fed-batch cultures to determine the optimal feeding strategy thereby improving production yield. The specific growth rate and volumetric productivity in batch cultures at 37°C were 1.7-fold and 2-fold higher, respectively, than those at 28°C. Glycerol was superior to glucose as a carbon source. Maximum β-carotene production (titer of 663 mg/L and overall volumetric productivity of 24.6 mg/L × h) resulted from the simultaneous addition of 500 g/L glycerol and 50 g/L yeast extract in pH-stat fed-batch culture.
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| 2. |
- Amann-Winkel, Katrin, et al.
(author)
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Liquid-liquid phase separation in supercooled water from ultrafast heating of low-density amorphous ice
- 2023
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In: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Journal article (peer-reviewed)abstract
- Recent experiments continue to find evidence for a liquid-liquid phase transition (LLPT) in supercooled water, which would unify our understanding of the anomalous properties of liquid water and amorphous ice. These experiments are challenging because the proposed LLPT occurs under extreme metastable conditions where the liquid freezes to a crystal on a very short time scale. Here, we analyze models for the LLPT to show that coexistence of distinct high-density and low-density liquid phases may be observed by subjecting low-density amorphous (LDA) ice to ultrafast heating. We then describe experiments in which we heat LDA ice to near the predicted critical point of the LLPT by an ultrafast infrared laser pulse, following which we measure the structure factor using femtosecond x-ray laser pulses. Consistent with our predictions, we observe a LLPT occurring on a time scale < 100 ns and widely separated from ice formation, which begins at times >1 mu s. Obtaining experimental evidence of a liquid-liquid phase transition in supercooled water is challenging due to the rapid crystallization. Here the authors drive low-density amorphous ice to the conditions of liquid-liquid coexistence using ultrafast laser heating and observe the liquid-liquid phase transition with femtosecond x-ray laser pulses.
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| 3. |
- Kim, Kyung Hwan, et al.
(author)
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Experimental observation of the liquid-liquid transition in bulk supercooled water under pressure
- 2020
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 370:6519, s. 978-982
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Journal article (peer-reviewed)abstract
- We prepared bulk samples of supercooled liquid water under pressure by isochoric heating of high-density amorphous ice to temperatures of 205 ± 10 kelvin, using an infrared femtosecond laser. Because the sample density is preserved during the ultrafast heating, we could estimate an initial internal pressure of 2.5 to 3.5 kilobar in the high-density liquid phase. After heating, the sample expanded rapidly, and we captured the resulting decompression process with femtosecond x-ray laser pulses at different pump-probe delay times. A discontinuous structural change occurred in which low-density liquid domains appeared and grew on time scales between 20 nanoseconds to 3 microseconds, whereas crystallization occurs on time scales of 3 to 50 microseconds. The dynamics of the two processes being separated by more than one order of magnitude provides support for a liquid-liquid transition in bulk supercooled water.
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| 4. |
- Ladd-Parada, Marjorie, et al.
(author)
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Following the Crystallization of Amorphous Ice after Ultrafast Laser Heating
- 2022
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 126:11, s. 2299-2307
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Journal article (peer-reviewed)abstract
- Using time-resolved wide-angle X-ray scattering, we investigated the early stages (10 μs–1 ms) of crystallization of supercooled water, obtained by the ultrafast heating of high- and low-density amorphous ice (HDA and LDA) up to a temperature T = 205 K ± 10 K. We have determined that the crystallizing phase is stacking disordered ice (Isd), with a maximum cubicity of χ = 0.6, in agreement with predictions from molecular dynamics simulations at similar temperatures. However, we note that a growing small portion of hexagonal ice (Ih) was also observed, suggesting that within our timeframe, Isd starts annealing into Ih. The onset of crystallization, in both amorphous ice, occurs at a similar temperature, but the observed final crystalline fraction in the LDA sample is considerably lower than that in the HDA sample. We attribute this discrepancy to the thickness difference between the two samples.
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| 5. |
- Ladd-Parada, Marjorie, 1985-, et al.
(author)
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Following the Crystallization of Amorphous Ice after Ultrafast Laser Heating
- 2022
-
In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 126:11, s. 2299-2307
-
Journal article (peer-reviewed)abstract
- Using time-resolved wide-angle X-ray scattering, we investigated the early stages (10 μs–1 ms) of crystallization of supercooled water, obtained by the ultrafast heating of high- and low-density amorphous ice (HDA and LDA) up to a temperature T = 205 K ± 10 K. We have determined that the crystallizing phase is stacking disordered ice (Isd), with a maximum cubicity of χ = 0.6, in agreement with predictions from molecular dynamics simulations at similar temperatures. However, we note that a growing small portion of hexagonal ice (Ih) was also observed, suggesting that within our timeframe, Isd starts annealing into Ih. The onset of crystallization, in both amorphous ice, occurs at a similar temperature, but the observed final crystalline fraction in the LDA sample is considerably lower than that in the HDA sample. We attribute this discrepancy to the thickness difference between the two samples.
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| 6. |
- Yang, Cheolhee, et al.
(author)
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Melting domain size and recrystallization dynamics of ice revealed by time-resolved x-ray scattering
- 2023
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In: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Journal article (peer-reviewed)abstract
- The phase transition between water and ice is ubiquitous and one of the most important phenomena in nature. Here, we performed time-resolved x-ray scattering experiments capturing the melting and recrystallization dynamics of ice. The ultrafast heating of ice I is induced by an IR laser pulse and probed with an intense x-ray pulse which provided us with direct structural information on different length scales. From the wide-angle x-ray scattering (WAXS) patterns, the molten fraction, as well as the corresponding temperature at each delay, were determined. The small-angle x-ray scattering (SAXS) patterns, together with the information extracted from the WAXS analysis, provided the time-dependent change of the size and the number of liquid domains. The results show partial melting (~13%) and superheating of ice occurring at around 20 ns. After 100 ns, the average size of the liquid domains grows from about 2.5 nm to 4.5 nm by the coalescence of approximately six adjacent domains. Subsequently, we capture the recrystallization of the liquid domains, which occurs on microsecond timescales due to the cooling by heat dissipation and results to a decrease of the average liquid domain size.
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| 7. |
- Yang, Jae-Jin, et al.
(author)
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사회보장재원구성에 관한 기초연구
- 2019
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Reports (other academic/artistic)
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