Two-particle dark state cooling of a nanomechanical resonator

The steady-state cooling of a nanomechanical resonator interacting with three coupled quantum dots is studied. General conditions for the cooling to the ground state with single and two-electron dark states are obtained. The results show that in the case of the interaction of the resonator with a single-electron dark state, no cooling of the resonator occurs unless the quantum dots are not identical. The steady-state cooling is possible only if the energy state of the quantum dot coupled to the drain electrode is detuned from the energy states of the dots coupled to the electron source electrode. The detuning has the effect of unequal shifting of the effective dressed states of the system that the cooling and heating processes occur at different frequencies. For the case of two electrons injected to the quantum dot system, the creation of a two-particle dark state is established to be possible with spin-antiparallel electrons. The results predict that with the two-particle dark state, an effective cooling can be achieved even with identical quantum dots subject of an asymmetry only in the charging potential energies coupling the injected electrons. It is found that similar to the case of the single-electron dark state, the asymmetries result in the cooling and heating processes to occur at different frequencies. However, an important difference between the single and two-particle dark state cases is that the cooling process occurs at significantly different frequencies. This indicates that the frequency at which the resonator could be cooled to its ground state can be changed by switching from the one-electron to the two-electron Coulomb blockade process.Comment: Published versio

An Evacuation Model for Passenger Ships That Includes the Influence of Obstacles in Cabins

Passenger behavior and ship environment are the key factors affecting evacuation efficiency. However, current studies ignore the interior layout of passenger ship cabins and treat the cabins as empty rooms. To investigate the influence of obstacles (e.g., tables and stools) on cabin evacuation, we propose an agent-based social force model for advanced evacuation analysis of passenger ships; this model uses a goal-driven submodel to determine a plan and an extended social force submodel to govern the movement of passengers. The extended social force submodel considers the interaction forces between the passengers, crew, and obstacles and minimises the range of these forces to improve computational efficiency. We drew the following conclusions based on a series of evacuation simulations conducted in this study: (1) the proposed model endows the passenger with the behaviors of bypassing and crossing obstacles, (2) funnel-shaped exits from cabins can improve evacuation efficiency, and (3) as the exit angle increases, the evacuation time also increases. These findings offer ship designers some insight towards increasing the safety of large passenger ships

Non-classical non-Gaussian state of a mechanical resonator via selectively incoherent damping in three-mode optomechanical systems

We theoretically propose a scheme for the generation of a non-classical single-mode motional state of a mechanical resonator (MR) in the three-mode optomechanical systems, in which two optical modes of the cavities are linearly coupled to each other and one mechanical mode of the MR is optomechanically coupled to the two optical modes with the same coupling strength simultaneously. One cavity is driven by a coherent laser light. By properly tuning the frequency of the weak driving field, we obtain engineered Liouvillian superoperator via engineering the selective interaction Hamiltonian confined to the Fock subspaces. In this case, the motional state of the MR can be prepared into a non-Gaussian state, which possesses the sub-Poisson statistics although its Wigner function is positive.Comment: 6 pages, 5 figure

Ordered mesoporous SiO₂ nanoparticles as charge storage sites for enhanced triboelectric nanogenerators

Triboelectric nanogenerators (TENGs) have demonstrated great prospects in energy harvesting and self-powered sensing. However, the surface triboelectric charges are very easy to dissipate in the air atmosphere, especially after the contact electrification stops. Here, we propose ordered mesoporous SiO2 (OMS) nanoparticles with a large specific surface area (SSA) as effective body charge storage sites inside polydimethylsiloxane (OMS-PDMS) to enhance the output performance of TENGs. With the addition of 1 wt% OMS nanoparticles, the transferred charges of the TENG showed a sharp enhancement, rising from 21 nC to 60 nC. The enhancement effect of OMS nanoparticles on the output increased linearly with SSA. In addition, the OMS-PDMS also demonstrated a superior charge retention ability, with 68 % of the voltage being retained over a long time after the contact separation motion stopped, while that of the pure PDMS quickly dropped to near zero. The instantaneous output power density of the TENG with OMS-PDMS reached 5.26 W/m2, which is a 25-fold enhancement. This work proposed OMS nanoparticles with a large SSA as effective charge storage sites to enhance the output performance of TENGs.</p

Effects of drought and rehydration on the growth and physiological characteristics of mustard seedlings

The mustard variety Felicia was used to analyze the response and compensation effects of growth and physiology under drought stress and rehydration conditions at the seedling stage. The seedlings were exposed to different levels of drought stress simulated by polyethylene glycol (PEG). The growth parameters, fresh weight, chlorophyll fluorescence, and antioxidant system were measured. The results showed that drought stress inhibited the growth of roots and shoots and reduced the performance of photosystem II (PS II). After rehydration, the root length and fresh weight of plants rapidly increased, and the performance index (PIABS) was found to be higher compared with the control, which suggested a compensative effect. The chlorophyll content was significantly reduced under moderate and severe drought stress. However, it increased under mild stress conditions. After rehydration, the chlorophyll content under moderate and severe stress did not return to the levels of control, and there was no significant difference between mild stress and the control. Under drought stress, the activities of antioxidant enzymes and content of malondialdehyde (MDA) increased significantly in the leaves. After rehydration, MDA and the activities of antioxidant enzyme were higher than those of the control group, particularly under moderate and severe stress. Therefore, these results suggest that mustard is strongly adapted to mild drought stress through the efficient activities of antioxidant enzymes activity and photosynthesis, as well as its rapid recovery after rehydration

Sexual Dimorphism, Female Reproductive Characteristics and Egg Incubation in an Oviparous Forest Skink (Sphenomorphus incognitus) from South China

We studied sexual dimorphism and female reproduction in an oviparous forest skink (Sphenomorphus incognitus) from South China. We incubated eggs under five thermal regimes (22, 25, 28, 25 ± 3 and 27 ± 5 °C) to examine the effects of constant versus fluctuating temperatures on incubation length and hatchling morphology. In our sample the largest male and female were 110 mm and 108 mm snout-vent length (SVL), respectively. Adult males and females did not differ in mean SVL; adult males were larger in head size (both length and width), longer in fore- and hind-limb lengths and shorter in abdomen length than females of the same SVL. Accordingly, we conclude that S. incognitus is a sexually monomorphic species in terms of SVL but shows sexual dimorphism in head size, abdomen length and appendage length. Females laid a single clutch of 3−10 eggs per breeding season from early May to mid-August, with larger females generally laying more (but not always larger) eggs per clutch than did smaller ones. Embryonic stages at laying ranged from Dufaure and Hubert’s (1961) stage 31 to 32, with a mean stage of 31.3. The positive relationship between clutch mass and female SVL was not significant. The offspring size-number trade-off does not exist in S. incognitus, as revealed by the fact that egg mass was independent of relative fecundity. Incubation length decreased as temperature increased, and stable temperatures resulted in delayed hatching. Hatchlings incubated under the five thermal regimes did not differ from each other in any examined trait, suggesting that S. incognitus is among oviparous reptilian species where incubation temperature has no role in modifying hatchling morphology as long as eggs are not exposed to extreme temperatures for prolonged periods of time

Numerical study on the effects of intake charge on oxy-fuel combustion in a dual-injection spark ignition engine at economical oxygen-fuel ratios

In order to achieve carbon neutrality by decreasing Carbon Dioxide (CO2) emissions, Oxy-Fuel Combustion (OFC) technology with Carbon Capture and Storage (CCS) is becoming a hot topic in the field of Internal Combustion Engine (ICE). However, almost no research has been reported about the implementation of OFC in dual-injection Spark Ignition (SI) engine. This article presents a numerical study about the effects of Water Injection (WI) strategies on OFC in a dual-injection Spark Ignition (SI) engine, with Gasoline Direct Injection (GDI), Port Fuel Injection (PFI) and P50-G50 (50% PFI and 50% GDI) three injection strategies. The results show that compared to Conventional Air Combustion (CAC), there is a significant increase in BSFC under OFC. θ_F is significantly prolonged, and the spark timing is obviously advanced. The θ_C of PFI is a bit shorter than that of GDI and P50-G50. There is a small benefit to BSFC under low R_wf. However, with the further increase of R_wf from 0.2 to 0.9, there is an increment of 4.29%, 3.6% and 3.77% in BSFC for GDI, P50-G50 and PFI, respectively. As t_WI postpones to around -30 °CA under the conditions of R_wf ≥ 0.8, BSFC has a sharp decrease of more than 6 g/kWh, and this decline is more evident under GDI injection strategy. The variation of Pmax and φ_CA50 is less affected by T_WI compared to the effects of R_wf or t_WI. BSFC just has a small decline with the increase of T_WI from 298K to 368K regardless of the injection strategy. Consequently, it is feasible to implement appropriate WI strategies to control OFC characteristics in a dual-injection SI engine, but the benefit in fuel economy is limited

Enhanced triboelectric nanogenerators based on 2D smectite clay nanosheets with a strong intrinsic negative surface charge

Triboelectric nanogenerators (TENGs) have demonstrated their huge potential in micro/nano energy harvesting for self-powered systems. The output performance of TENGs is largely dependent on the surface charge density of the triboelectric materials. Here, for the first time, we propose 2D smectite clay (SC) nanosheets with a strong intrinsic negative surface charge for improving the charge density of traditional triboelectric-negative materials. A single-layer 2D SC nanosheet (∼1.1 nm thick) showed a strong negative surface potential (−14.3 mV), and the SC was confirmed to have a strong triboelectric negativity close to that of polytetrafluoroethylene (PTFE). 2D SC nanosheets were blended into polyvinylidene fluoride (SC-PVDF), based on which the SC-TENG demonstrated a significantly enhanced output performance, with the transferred charge increasing from 14 nC to 35 nC at the optimal SC concentration of 5 wt%. At higher SC concentrations, the influence of decreased effective contact area because of severe aggregation of SC nanosheets began to outperform the effect of increased interior charge. The instantaneous output power density of the SC-TENG was enormously improved to 1450 mW/m2 from that of the pristine TENG (15 mW/m2). This work proposed a new 2D material, SC, with a strong intrinsic negative surface charge, which has huge prospects in enhancing the output performance of TENGs.</p