Extremal black holes that are not extremal: maximal warm holes

We study a family of four-dimensional, asymptotically flat, charged black holes that develop (charged) scalar hair as one increases their charge at fixed mass. Surprisingly, the maximum charge for given mass is a nonsingular hairy black hole with nonzero Hawking temperature. The implications for Hawking evaporation are discussed.

Synthesis and Computational Characterization of Organic UV-Dyes for Cosensitization of Transparent Dye-Sensitized Solar Cells

The fabrication of colorless and see-through dye-sensitized solar cells (DSCs) requires the photosensitizers to have little or no absorption in the visible light region of the solar spectrum. However, a trade-off between transparency and power conversion efficiency (PCE) has to be tackled, since most transparent DSCs are showing low PCE when compared to colorful and opaque DSCs. One strategy to increase PCE is applying two cosensitizers with selective conversion of the UV and NIR radiation, therefore, the non-visible part only is absorbed. In this study, we report synthesis of novel five UV-selective absorbers, based on diimide and Schiff bases incorporating carboxyl and pyridyl anchoring groups. A systematic computational investigation using density functional theory (DFT) and time-dependent DFT approaches was employed to evaluate their prospect of application in transparent DSCs. Experimental UV/Vis absorption spectra showed that all dyes exhibit an absorption band covering the mid/near-UV region of solar spectrum, with a bathochromic shift and a hyperchromic shifts for Py-1 dye. Computational results showed that the studied dyes satisfied the basic photophysical and energetics requirements of operating DSC as well as the stability and thermodynamical spontaneity of adsorption onto surface of TiO2. However, results revealed outperformance of the thienothiophene core-containing Py-1 UV-dye, owing to its advantageous structural attributes, improved conjugation, intense emission, large Stokes shift and maximum charge transferred to the anchor. Chemical compatibility of Py-1 dye was then theoretically investigated as a potential cosensitizer of a reference VG20-C2 NIR-dye. By the judicious selection of pyridyl anchor-based UV-absorber (Py-1) and carboxyl anchor-based NIR-absorber (VG20), the advantage of the optical complementarity and selectivity of different TiO2-adsorption-site (Lewis- and Bronsted-acidic) can be achieved. An improved overall PCE is estimated accordingly.

PPV and Frequency Characteristics of Tunnel Blast-Induced Vibrations on Tunnel Surfaces and Tunnel Entrance Slope Faces

Tunnel blast-induced vibration probably causes damage to the rock mass surrounding the tunnel surface and also to the rock mass of the slope at the tunnel entrance. It is important to simultaneously monitor the vibration on the tunnel surface and on the tunnel entrance slope face, especially when the blasting work face is close to tunnel entrance. During blasting excavation of the traffic tunnel at Baihetan hydropower station, vibration monitors were installed both on the tunnel surface and on the tunnel entrance slope face. Based on the monitoring data, a comparative study is conducted on the peak particle velocity (PPV) and frequency characteristics of the vibrations at these two locations. A three-dimensional FEM simulation of the tunnel blast is then performed to verify the field test results. The field monitoring and the numerical simulation show that there is significant difference between the vibration on the tunnel surface and that on the tunnel entrance slope face. The vibration on the tunnel surface has greater PPV and faster attenuation, while the tunnel entrance slope face has higher frequency and faster reduction rate in the center frequency. These differences are attributed to the different wave types and wave propagation paths. The tunnel surface is mainly surface waves transmitted through the damaged rock mass around the tunnel profile, while the tunnel entrance slope face originates mainly from the body waves transmitted via the undamaged rock mass inside the mountain. The comparisons of the monitored vibrations with the velocity limits specified in the Chinese standard show that the most dangerous vibration that may exceed the limit occurs on the tunnel surface. Therefore, the maximum charge weight used in the tunnel blast is determined by the vibration on the tunnel surface. Under different control standards, the allowable maximum charge weight per delay is further discussed.

Research on Insulation State of 10kV XLPPE Fault Cable Based on Qt Technology

The cross-linked polyethylene cable will undergo thermal aging during service, which will seriously affect the service life of the cable. The current integration method can analyze the charge injection and conduction parameters from the dynamic change rate of the charge over time, and then analyze the insulation state of the polymer. Aiming at the field 10KV fault breakdown cable, this paper uses the current integration method to compare the dynamic change characteristics of the charge of the faulty cable and the new cable, and uses the ratio of Q(t) at t=600s and t=4s to study Charge injection and accumulation situation. Through analysis, it is found that the fault breakdown of the cable, the maximum charge accumulation under high voltage is 9000 Q/nC, the charge change rate is about 2, and the dielectric constant is 3.1, which is much greater than that of the new cable, indicating that the breakdown of the three-phase cable is mainly caused by the cable. It is caused by aging and eventually leads to insulation deterioration and breakdown.

Prediction of BlastInduced Ground Vibration (BIGV) of Metro Construction Using Difference Evolution AlgorithmOptimized Gaussian Process (DE-GP)

Rock blasting often has an irreversible impact on the surrounding environment and threatens the safety of life and property. Therefore, accurate prediction of blast-induced ground vibration (BIGV) is a prerequisite for safe construction. In view of the fact that traditional blasting peak particle velocity (PPV) empirical formulas cannot be accurately predicted, this study selected 88 sets of blasting monitoring data, based on distance from the blast-face, maximum charge per delay, total charge, hole depth, spacing, burden, stemming length, and powder factor being used as input variables and PPV being used as output variable to characterize BIGV. First, a nonlinear mapping relationship between input variables and output variable is established through the Gaussian process (GP). The differential evolution algorithm (DE) is used to optimize the hyperparameters σf, σn, and l of the GP, and a blasting PPV model based on the DE-GP is constructed. The proposed model is compared with the empirical formulas, least square support vector machine (LSSVM), artificial neural network (ANN), and GP model, and its prediction performance is evaluated by statistical indicators such as root mean square error (RMSE). Finally, the cosine amplitude method (CAM) is used to analyze the sensitivity of blasting parameters. The results show that the DE-GP algorithm for blasting vibration velocity prediction has higher precision and accuracy, which is significantly better than other models, and is the closest to the measured PPV. Distance from the blast-face, total charge, and maximum charge per delay have a greater impact on the prediction of PPV, while stemming length and powder factor have a smaller impact on the prediction of PPV. The DE-GP model proposed by this research has certain reference value for the prediction and control of PPV in blasting construction.

An Insight to the Degradation Behaviour of the Parallel Connected Lithium-Ion Battery Cells

In an electric vehicle, a large number of lithium-ion cells are connected in parallel. While cells in parallel increase the reliability of the battery pack, it increases the probability of current imbalance between the parallel branches, thus ageing gradient. The current peak in a cell also can exceed the maximum charge current capability of the cell; leading to lithium plating, therefore a safety issue. The temperature gradient within a battery pack amplifies this issue. This work reports the impact of such temperature gradient on current imbalance within parallel connected cells, their long-term impact on degradation and evaluation of current distribution with degradation. Employing a real-world relevant experimental setup, a total of 1400 cycles were performed on a module with four cells in parallel. A temperature gradient of 10 °C was introduced among the cells, and current in individual parallel branches was measured employing Hall-effect sensors. Over the course of the experiment, module capacity decreased by 23.6%. Cells at higher temperature/lower exposure to active cooling experienced higher degradation. However, the cell with the lowest starting capacity, although exposed to nominal module temperature and cooling experienced the highest current amplitude towards the end of discharge/charge and thus the highest resistance degradation. It was found that current in an individual parallel branch was exceeding the maximum rated charge/discharge current by 53%.

High performance floating self-excited sliding triboelectric nanogenerator for micro mechanical energy harvesting

Non-contact triboelectric nanogenerator (TENG) enabled for both high conversion efficiency and durability is appropriate to harvest random micro energy owing to the advantage of low driving force. However, the low output (<10 μC m−2) of non-contact TENG caused by the drastic charge decay limits its application. Here, we propose a floating self-excited sliding TENG (FSS-TENG) by a self-excited amplification between rotator and stator to achieve self-increased charge density, and the air breakdown model of non-contact TENG is given for a maximum charge density. The charge density up to 71.53 μC m−2 is achieved, 5.46 times as that of the traditional floating TENG. Besides, the high output enables it to continuously power small electronics at 3 m s−1 weak wind. This work provides an effective strategy to address the low output of floating sliding TENG, and can be easily adapted to capture the varied micro mechanical energies anywhere.

Strategi Pengisian Baterai pada Sistem Panel Surya Standalone Berbasis Kontrol PI Multi-Loop

This study discusses the power control strategy in a standalone photovoltaic-battery hybrid system. The life-time of the battery will be shorter if the battery is often charged with high current and exceeds its State-of-Charge (SoC). Therefore, a control method is needed to control the power flow on the DC bus and the charging current as well as the SoC of the battery so that the battery has a long life-time. The proposed system uses two dc-dc converters to connect photovoltaic (PV) and lead-acid batteries to the load. The unidirectional DC-DC converter is used as the interface between the PV and the DC bus, the bidirectional DC-DC converter is used as the interface between the battery and the DC bus. The control strategy plays a role in controlling the power flow between the converter and the load to maintain the balance of power in the system and controlling the battery to support PV when the available PV power is not enough to meet the load. The multi-loop control strategy is proposed in this study, one of the loops is used to maintain the SoC of the battery in order to control the PV output power to avoid over-charging. Another loop is used to ensure the balance of the system's power when the battery is charging at its maximum charge current. The proposed control system is implemented without requiring any conditions for the control to operate. The simulation results show that the proposed multi-loop control can control the power flow in the system while maintaining the maximum charging current and battery SoC limits.

Blasting Vibration Control Using an Improved Artificial Neural Network in the Ashele Copper Mine

Blasting is currently the most important method for rock fragmentation in metal mines. However, blast-induced ground vibration causes many negative effects, including great damage to surrounding rock masses and projects and even casualties in severe cases. Therefore, prediction of the peak particle velocity (PPV) caused by blasting plays an important role in reducing safety threats. In this paper, a genetic algorithm (GA) and an artificial neural network (ANN) algorithm were jointly used to construct a neural network model with a 4-5-1 topology to predict the PPV. For this model, the ANN parameters were optimized using the GA, and the deviating direction, horizontal distance, vertical distance, Euclidean distance, explosive type, burden, hole spacing, and maximum charge per delay were used as input information. Moreover, principal component analysis (PCA) was used to extract the first four principal components from the eight input factors as the four inputs of the ANN model. The model was successfully applied to protect an underground crushing cave from blasting vibration damage by adjusting the blasting parameters. Compared with several widely used empirical equations, the GA-ANN PPV prediction model produced significantly better results, while the Ambraseys–Hedron method was the best of the empirical methods. Therefore, the improved GA-ANN model can be used to predict the PPV on site and provide a reference for the control of blasting vibration in field production.

Physics and Modelling of Tri-Layered Strained Channel for Development of Double Gate n-channel FET

The strain silicon technology with FET is a dominant technology providing enrichment in carrier velocity in nanoscaled device by change of band structure arrangement. Leakage reduction while enhancement in drain current is another major objective therefore, designing a nano-regime double gate FET with strained channel is perceived. So, design and implementation of a double gate strained heterostructure on insulator (DG-SHOI) FET with tri-layered channel (s-Si/s-SiGe/s-Si) is the core. Biaxial strain is created in channel by inculcating three layers with optimal thicknesses while narrow channel depletion regions are strongly controlled by equipotential gates. Consequently, maximum charge carriers accumulate in channel due to quantum carrier confinement instigating ballistic transport across the 22 nm channel length device leading to lessening of intervalley scattering. In comparison to existing 22 nm DGSOI FET, drain current augmentation of 56% and transconductance amplification of 87.6% is observed while DIBL is prudently reduced for this newly designed and implemented DG-SHOI FET, signifying advancement in microelectronic technology.