In metabolic engineering, unbalanced microbial carbon distribution has long blocked the further improvement in yield and productivity of high-volume natural metabolites. Current studies mostly focus ...on regulating desired biosynthetic pathways, whereas few strategies are available to maximize L-threonine efficiently. Here, we present a strategy to guarantee the supply of reduced cofactors and actualize L-threonine maximization by regulating cellular carbon distribution in central metabolic pathways. A thermal switch system was designed and applied to divide the whole fermentation process into two stages: growth and production. This system could rebalance carbon substrates between pyruvate and oxaloacetate by controlling the heterogenous expression of pyruvate carboxylase and oxaloacetate decarboxylation that responds to temperature. The system was tested in an L-threonine producer Escherichia coli TWF001, and the resulting strain TWF106/pFT24rp overproduced L-threonine from glucose with 111.78% molar yield. The thermal switch system was then employed to switch off the L-alanine synthesis pathway, resulting in the highest L-threonine yield of 124.03%, which exceeds the best reported yield (87.88%) and the maximum available theoretical value of L-threonine production (122.47%). This inducer-free genetic circuit design can be also developed for other biosynthetic pathways to increase product conversion rates and shorten production cycles.
•A strategy was exploited to dynamically regulate carbon distribution in E. coli.•The redox metabolism was rebalanced to appropriately reduce the cofactor supply.•A thermal switch system was designed for improving E. coli industrial production.•Significant threonine production was gained using the system.•Maximum threonine yield was obtained by switching off the alanine synthesis pathway.
•Energy simulation of AIS using experimentally validated thermal resistances.•AIS evaluation at varying orientations, climate zones, and switching ratios.•Investigation of AIS switching and wall ...thermal conductivity/heat transfer.•Application of freeze timer to reduce the number of switches of AIS.
Active insulation systems (AISs) in buildings are envelopes that integrate thermal insulation, thermal energy storage, and controls. Although different designs for AISs have been proposed in the literature, a comprehensive analysis of feasible AISs is lacking. This paper discusses the energy performance, peak demand reduction potential, and performance characteristics of an AIS that uses a concrete wall as thermal mass sandwiched between two solid-state thermal switches (STSs). These STSs change their thermal conductivity using an on/off metal switch to create or break a thermal bridge across the STS. This paper first describes the experimental setup, used to determine the ratio of thermal resistance during R-high (low thermal conductivity) and R-low (high thermal conductivity) states of the STSs. This ratio was then used in whole-building energy simulations to evaluate the performance of AIS walls across different climate zones with/without a freeze timer of 60 min. The timer was added to reduce the number of switches of STSs from one state to another, and hence the energy needed for these switches. Analysis of the switching frequency and interval of STSs, thermal conductivity of walls, impact of wall orientation, and heat transfer through the wall from the use of AIS at different climate zones/locations were performed. The simulation results show that the AIS can achieve energy savings ranging from ∼ 980 to 2,290 kWh in a single-family home with a floor area of ∼ 220 m2 compared with an IECC 2018 baseline. The energy savings was higher in dry climate zones which represent 17% of residential buildings in the United States, compared to humid or marine climate.
Organic material-based thermal switch is drawing much attention as one of the key thermal management devices in organic electronic devices. This study aims at tuning the switching temperature (T S) ...of thermal conductivity by using liquid crystalline block copolymers (BCs) with different order–order transition temperature (T tr) related to the types of mesogens in the side chain. The BC films with low T tr of 363 K and high T tr of 395 K exhibit reversible thermal conductivity switching behaviors at T S of ∼360 K and ∼390 K, respectively. The BC films also exhibit thermal conductivity variation originating from the anisotropy of the internal structures: poly(ethylene oxide) domains and liquid crystals. These results demonstrate that the switching behavior is attributed to an order–order transition between BC films with vertically arranged cylinder domains and the ones with ordered sphere domains. This highlights that BCs become a promising thermal conductivity switching material with tailored T S.
Heat transfer and thermal management have garnered widespread attention due to their industrial applications, particularly for thermal and electronics devices. Therefore, new thermal management ...solutions are urgently required to maintain optimum temperature and efficiency of the systems. Herein, Fe3O4 magnetic nanofluid was prepared to establish the quick heat conduction channel between heat source and heat sink relying on the high thermal conductivity. And a magneto-responsive remote-controlled heat transfer method was presented by controlling the external physical field and material property. The appearance and disappearance of magnetic “needle-like protuberance” could be tuned by external magnetism ON or OFF. The magnetic responsiveness, adjustability and recyclability of heat transfer have been demonstrated experimentally. The Nusselt number at 30 mT has an enhancement of 112.4% compared to that without magnetic field. And the overheating protection experiments in the heat sink showed that it can effectively reduce the working temperature of electronic components, and the steady temperature decreased by 22.6% using Fe3O4 magnetic nanofluid when applying a magnetic field. This research exhibited a novel approach to achieve excellent heat exchange characteristics by tuning the magnetic field intensities for the utilization of thermal management.
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•A nanofluid channel was established for quickly heat transfer between heat source and heat sink.•The heat transfer effect of nanofluid channel could be controlled by magnetism ON or OFF.•The magnetic responsiveness, adjustability and recyclability of heat transfer were demonstrated.•Heat exchange efficiency has enhancement of 112.4% using magneto-accelerated method.
Dynamical control of thermal transport at the nanoscale provides a time-domain strategy for optimizing thermal management in nanoelectronics, magnetic devices, and thermoelectric devices. However, ...the rate of change available for thermal switches and regulators is limited to millisecond time scales, calling for a faster modulation speed. Here, time-resolved X-ray diffraction measurements and thermal transport modeling reveal an ultrafast modulation of the interfacial thermal conductance of an FeRh/MgO heterostructure as a result of a structural phase transition driven by optical excitation. Within 90 ps after optical excitation, the interfacial thermal conductance is reduced by a factor of 5 and lasts for a few nanoseconds, in comparison to the value at the equilibrium FeRh/MgO interface. The experimental results combined with thermal transport calculations suggest that the reduced interfacial thermal conductance results from enhanced phonon scattering at the interface where the lattice experiences transient in-plane biaxial stress due to the structural phase transition of FeRh. Our results suggest that optically driven phase transitions can be utilized for ultrafast nanoscale thermal switches for device application.
Materials with either high or low lattice thermal conductivity are remarkable for thermal management with applying in high-power electronic, optoelectronic, and thermoelectric devices. The ...realization of thermal switch between high and low thermal conductivities can greatly promote the ability of thermal energy control. Here, based on first-principles calculations, we propose that ferroelastic PdSe2 can achieve continuous switchable thermal conductivity through strain-driven structural phase transition. Thermal switch we explored mainly stems from soft mechanical properties and strong anharmonicity of the structure after ferroelastic phase transition. We demonstrate that the maximum ratio of thermal switch can reach an order of magnitude, indicating PdSe2 as a promising candidate in thermal devices.
A convenient, reversible, fast, and wide-range switching of thermal conductivity is desired for efficient heat energy management. However, traditional methods, such as temperature-induced phase ...transition and chemical doping, have many limitations, e.g., the lack of continuous tunability over a wide temperature range and low switching speed. In this work, a strategy of electric field-driven crystal symmetry engineering to efficiently modulate thermal conductivity is reported with first-principles calculations. By simply changing the direction of an external electric field loaded in ferroelectric PbZr0.5Ti0.5O3, near the morphotropic phase boundary composition, we obtain the largest switching of thermal conductivity for ferroelectric materials at room temperature based on the dual-phonon theory, i.e., normal and diffuson-like phonons, with three different criteria. The calculation results indicate that with decreasing crystal symmetry, the degeneracy of phonon modes reduces and the avoid-crossing behavior of phonon branches enhances, leading to the increase of diffuson-like phonons and weighted phonon–phonon scattering phase space. A thermal switch prototype based on PbZr0.5Ti0.5O3 is further shown that can protect the Li-ion battery by modulating its temperature up to 17.5 °C. Our studies would pave the way for designing next-generation thermal switch with high speed, a wide temperature range, and a large switching ratio.
Controlling transport in quantum systems holds the key to many promising quantum technologies. Here we review the power of symmetry as a resource to manipulate quantum transport and apply these ideas ...to engineer novel quantum devices. Using tools from open quantum systems and large deviation theory, we show that symmetry-mediated control of transport is enabled by a pair of twin dynamic phase transitions in current statistics, accompanied by a coexistence of different transport channels. By playing with the symmetry decomposition of the initial state, one can modulate the importance of the different transport channels and hence control the flowing current. Motivated by the problem of energy harvesting, we illustrate these ideas in open quantum networks, an analysis that leads to the design of a symmetry-controlled quantum thermal switch. We review an experimental setup recently proposed for symmetry-mediated quantum control in the lab based on a linear array of atom-doped optical cavities, and the possibility of using transport as a probe to uncover hidden symmetries, as recently demonstrated in molecular junctions, is also discussed. Other symmetry-mediated control mechanisms are also described. Overall, these results demonstrate the importance of symmetry not only as an organizing principle in physics but also as a tool to control quantum systems.
An active convective 4He heat switch May, Andrew J.; Azzoni, Susanna; Melhuish, Simon ...
Cryogenics (Guildford),
December 2022, Volume:
128
Journal Article
Peer reviewed
Open access
•Design, modelling, and experimental demonstration of novel cryogenic switch.•Switch based on convective heat transfer inside a permanently sealed switch.•Switch is actively controlled by the heating ...of a charcoal cryopump.•We report the experimental demonstration of the switch.•We report CFD analysis of the switch.•Novel analytical model which shows far better agreement than previous models.
The design and experimental demonstration are reported of an active convective heat switch suitable for use at cryogenic temperatures. The switch is mechanically simple, relatively inexpensive, and requires no moving parts, instead being operated entirely using heaters. The working gas used is 4He in a closed cycle and, as such, the switch requires no external gas connections. Closed conductances on the order of 50 mW/K have been demonstrated with residual open conductances on the order of 0.4 mW/K. Novel modelling is presented which shows excellent agreement with the experimental data and significant improvement over existing models.
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