Study on collection and retention efficiencies of a new integrated collector storage solar water heating system using a planar thermal diode: an experimental study.

Thermal diodes are a novel method to rectify the heat transfer mechanism and help reduce heat losses in solar thermal collectors during non-collection periods. The current study introduces and analyzes a new planar thermal diode integrated collector storage (ICS) solar water heating system using an experimental approach. This thermal diode ICS system has a simple, affordable structure composed of two parallel plates. Water serves as a phase change material to transfer heat through evaporation and condensation inside the diode. Three scenarios were considered to assess the dynamics of the thermal diode ICS: atmospheric pressure, depressurized thermal diodes, and Ppartial = 0, - 0.2, and - 0.4 bar. The water temperature reached 40 °C, 46 °C, and 42 °C in Ppartial = 0, - 0.2, and - 0.4 bar, respectively. The heat gain coefficients are 38.61, 40.65, and 39.26 W/K, while the heat loss coefficients are 9.56, 5.16, and 7.03 W/K in Ppartial = 0, - 0.2, and - 0.4 bar, respectively. The optimum heat collection and retention efficiencies are 45.3% and 33.5% in Ppartial = - 0.2 bar. Hence, there is an optimum partial pressure to achieve the best performance, equal to - 0.2 bar. The acquired results illustrate the robustness of the planar thermal diode in reducing heat losses and rectifying the heat transfer mechanism. Furthermore, despite the simple structure of the planar thermal diode, its efficiency is as high as that of other types of thermal diodes analyzed in recent studies.

Universal Behavior of the Coulomb-Coupled Fermionic Thermal Diode.

We propose a minimal model of a Coulomb-coupled fermionic quantum dot thermal diode that can act as an efficient thermal switch and exhibit complete rectification behavior, even in the presence of a small temperature gradient. Using two well-defined dimensionless system parameters, universal characteristics of the optimal heat current conditions are identified. It is shown to be independent of any system parameter and is obtained only at the mean transitions point "-0.5", associated with the equilibrium distribution of the two fermionic reservoirs, tacitly referred to as "universal magic mean".

Positive temperature coefficient of the thermal conductivity above room temperature in a perovskite cobaltite.

The thermal conductivity above room temperature is investigated for LaCoO3-based materials showing spin-state and insulator-metal crossovers. A positive temperature coefficient (PTC) of the thermal conductivity is observed during the insulator-metal crossover around 500 K. Our analysis indicates that the phononic thermal transport is also enhanced in addition to the electronic contribution as the insulator-metal crossover takes place. The enhancement of the phononic component is ascribed to the reduction of the incoherent local lattice distortion coupled with the spin/orbital state of each Co3+ ion, which is induced by the enhanced spin-state fluctuation between low and excited spin-states. Moreover, fine tunability for the PTC of the thermal conductivity is demonstrated via doping hole-type carriers into LaCoO3. The observed enhancement ratio of the thermal conductivity κ T (773 K) / κ T (323 K) = 2.6 in La0.95Sr0.05CoO3 is the largest value among oxide materials which exhibit a PTC of their thermal conductivity above room temperature. The thermal rectification ratio is estimated to reach 61% for a hypothetical thermal diode consisting of La0.95Sr0.05CoO3 and LaGaO3, the latter of which is a typical band insulator. These results indicate that utilizing spin-state and orbital degrees of freedom in strongly correlated materials is a useful strategy for tuning thermal transport properties, especially for designing thermal diodes.

Non-equilibrium thermoelectric transport across normal metal-quantum dot-superconductor hybrid system within the Coulomb blockade regime.

A detailed investigation of the non-equilibrium steady-state electric and thermoelectric transport properties of a quantum dot (QD) coupled to the normal metallic and s-wave superconducting reservoirs (N-QD-S) are provided within the Coulomb blockade regime. Using non-equilibrium Keldysh Green's function formalism, initially, various model parameter dependences of thermoelectric transport properties are analysed within the linear response regime. It is observed that the single-particle tunnelling close to the superconducting gap edge can generate a relatively large thermopower and figure of merit. Moreover, the Andreev tunnelling plays a significant role in the suppression of thermopower and figure of merit within the gap region. Further, within the non-linear regime, we discuss two different situations, i.e., the finite voltage biasing between isothermal reservoirs and the finite thermal gradient in the context of thermoelectric heat engine. In the former case, it is shown that the sub-gap Andreev heat current can become finite beyond the linear response regime and play a vital role in asymmetric heat dissipation and thermal rectification effect for low voltage biasing. The rectification of heat current is enhanced for strong on-dot Coulomb interaction and at low background thermal energy. In the latter case, we study the variation of thermovoltage, thermopower, maximum power output, and corresponding efficiency with the applied thermal gradient. These results illustrate that hybrid superconductor-QD nanostructures are promising candidates for the low-temperature thermal applications.

A Thermal Diode Based on Nanoscale Thermal Radiation.

In this work we demonstrate thermal rectification at the nanoscale between doped Si and VO2 surfaces. Specifically, we show that the metal-insulator transition of VO2 makes it possible to achieve large differences in the heat flow between Si and VO2 when the direction of the temperature gradient is reversed. We further show that this rectification increases at nanoscale separations, with a maximum rectification coefficient exceeding 50% at ∼140 nm gaps and a temperature difference of 70 K. Our modeling indicates that this high rectification coefficient arises due to broadband enhancement of heat transfer between metallic VO2 and doped Si surfaces, as compared to narrower-band exchange that occurs when VO2 is in its insulating state. This work demonstrates the feasibility of accomplishing near-field-based rectification of heat, which is a key component for creating nanoscale radiation-based information processing devices and thermal management approaches.

Very large thermal rectification in bulk composites consisting partly of icosahedral quasicrystals.

The bulk thermal rectifiers usable at a high temperature above 300 K were developed by making full use of the unusual electron thermal conductivity of icosahedral quasicrystals. The unusual electron thermal conductivity was caused by a synergy effect of quasiperiodicity and by a narrow pseudogap at the Fermi level. The rectification ratio, defined by TRR = [Formula: see text], reached vary large values exceeding 2.0. This significant thermal rectification would lead to new practical applications for the heat management.

The Short-term Results of Photodynamic Therapy for Choroidal Neovascularization

PURPOSE: To evaluate the short-term results of photodynamic therapy with Verteporfin for the patients with choroidal neovascularization. METHODS: We performed photodynamic therapy with Verteporfin in 19 patients (19 eyes) who were diagnosed as subfoveal CNV. The range of age was from 27 to 81 years, and 57 years on average. Twelve patients were male and seven were female. The pretreatment visual acuity with ETDRS chart was from 20/200 to 20/32. On FAG, predominantly classic type were fourteen eyes, minimally classic were four eyes, and no classic was one eye. Visudyne(R) of 6 mg per body surface area was infused intravenously for 10 minutes, and then non-thermal diode laser of 689 nm wavelength was applied for 83 seconds with 600 Mw/Cm2 intensity. We followed up 1 month, 3 months after treatment, thereafter every 3 months. The follow up period was ranged from 3 months to 11 months, 4 months on average. We performed retreatment with the same method when any leakage was found on FAG which is performed every 3 month. RESULTS: Threes months after treatment, only one eye showed visual acuity decrease of more than 3 lines with ETDRS chart, and mean visual acuity change was increased by 0.94 lines. At the same time there was one eye which presented no leakage on FAG, seven eyes showed minimal leakage, ten eyes showed moderate leakage, and only one eye showed progression. Out of twelve eyes which could be followed up more than 6 months, only eye showed decreased visual acuity of more than 3 lines. On FAG, no leakage was not found, minimal leakage in nine eyes, moderate leakage in two eyes and one eye showed progression. CONCLUSION: The above results indicates that the short-term results of photodynamic therapy for subfoveal CNV from various causes were encouraging as a good treatment modality to reduce the risk of visual loss and further study with longer follow-up and large number of cases will be necessary to decide the effect of photodynamic therapy in Korea.