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As an economical energy recovery device, pump as turbine (PAT) is widely used in micro-hydropower stations and the chemical industry. The inlet and outlet pipelines connected to the double-suction pump are on the same horizontal line. As the pipeline layout is very convenient, in some chemical industries, the way of residual pressure energy utilization is increasing using the double-suction pump as a turbine. Based on numerical simulation, experimental verification, and entropy generation theory, the energy loss rule of each flow component in the pump mode and turbine mode under different flow rates is compared and analyzed. The results show that when the double-suction pump is used as a turbine, the flow rate at the best efficiency point (BEP) in the turbine mode shifts to a large flow rate by 30.89% and the BEP efficiency decreases by 1.30%. In the pump mode and turbine mode, the main energy loss component is the impeller, and the turbulent entropy generation power and the wall entropy generation power are the main sources of energy loss. The energy loss in the suction chamber and impeller increases sharply, and the energy loss is primarily enhanced in the blade trailing edge and the tongue near due to the unsteady flow in the turbine mode. Due to the complex structure, the spiral suction chamber is not suitable for the flow direction of the fluid flow out of the impeller, and the flow state inside the impeller is negatively affected by the suction chamber in the turbine mode. This paper provides a theoretical basis for the design and application of double-suction centrifugal PAT. [ABSTRACT FROM AUTHOR]

We demonstrate an optically tunable mode-locked fiber laser using long-period fiber grating (LPFG) coated with multi-walled carbon nanotubes (CNTs). The multi-walled CNTs can absorb light to convert it into thermal energy, and the resonance wavelength of the grating can be easily turned by varying the external modulated light power. This multi-walled CNT coated LPFG-based all-optical fast and efficient spectrum tunable filter enables continuous tuning of the central wavelength of the laser by manipulating the loss of the mode-locked laser, ensuring the stability of the mode-locking state. In the absence of modulated light on multi-walled CNTs, the soliton laser could generate 890 fs pulses at 1546.7 nm with a spectrum bandwidth of 3.26 nm and a signal-to-noise ratio of 73.1 dB. Through adjustment of the pump power of the modulation light on multi-walled CNTs, the mode-locked fiber laser can be continuously tuned from 1546.71 to 1563.15 nm. The response time of the optically tunable system was measured to be in the order of hundreds of milliseconds. The presented optical tuning filter shows great potential in the fiber laser system, offering a repeatable, straightforward, and rapidly responsive laser tuning technique. [ABSTRACT FROM AUTHOR]

Apart from the polarization and spatial mode, the degree of coherence (DoC), as a new degree of freedom (DoF), has actuated the control of structured optical fields beyond into a higher dimension. However, the control of DoC mainly focuses on the spatial coherence, and so far, there are no reports on the modulation of temporal coherence of the structured light. Here, a temporal coherence-tailorable vector fiber source is proposed and experimentally demonstrated. With a two-mode long-period fiber grating and polarization control, switchable transverse-mode outputs including azimuthally polarized mode TE01 and radially polarized mode TM01 are performed in an all-fiber compact regime. Benefitting from a tunable superfluorescent fiber source as the illumination of spatial mode control, the temporal coherence and the operating wavelength of vector beams can be simultaneously modulated. This work may not only advance a considerable protocol for creating and manipulating high-dimensional vectorial optical field, but also open up a promising avenue for potential applications in optical communication, high-resolution imaging, and particle trapping. [ABSTRACT FROM AUTHOR]

Due to the complex structure of a double-suction pump's suction chamber, the flow in the pump's cavity is often ignored in numerical simulations because of difficulties in structured hexahedral meshing. However, the wear ring clearance interlinking the pump chamber leads the fluid at the impeller inlet directly to the impeller area. This significantly impacts the pump's internal flow field, so the influence of the clearance on the internal flow of a double-suction pump cannot be ignored. This paper develops four three-dimensional double-suction pump models with different wear ring clearances to investigate their influence on pump performance, and structured hexahedral meshes were used for all the computational domains. The clearances varied from 0.2 to 0.5 mm in 0.1 mm increments. The influences of the clearance on the energy loss, external characteristics, and internal flow field distribution of the pump were simulated via a verified computational fluid dynamics method. The results show that the wear ring leakage decreases with the flow rate and increases with wear ring clearance. The increase in backflow leads to an internal flow disorder inside the impeller, resulting in a decreased head and efficiency. Energy loss is mainly caused by increasing the turbulence entropy production with an increasing wear ring clearance. Also, the low-pressure region in the pump cavity expands to the volute with increasing clearance, and the impeller outlet pressure decreases. This study's research on wear ring clearance provides a reference for the design and application of double-suction centrifugal pumps. [ABSTRACT FROM AUTHOR]

Removing particles dispersed in fluid through drops is widely presented in various fields, and the critical factor is particles captured by droplets. Drop rotation effects play a dominant role in the capture process. However, their influences on collection characteristics remain unclear. Thus, a particle collection model was developed to simultaneously consider rotation and translation effects on fine particles captured by an individual droplet. The finite volume method was used to solve for flow field and collection efficiency, and the proposed model was verified by comparison with experimental and published results. The Liutex method was used to identify the vortex structure, on which dimensionless droplet rotation rates ranged from 0 to 0.1. Velocity, drag coefficient, radial position, and captured particle velocity distribution and collection efficiency were also investigated in relation to the rotation effect. The results show that the established model is reasonable. Vortex strength increases with increased rotation speed where the increment can be up to 480, and fluid rotation strength depends on the competitive relation between the increase in the rotation rate and the vortex movement. Radial velocity increases in regions where the angle between the positive x axis and the normal vector of drop surface ranges from 115° to 180° but decreases in regions where the angle ranges from −180° to −120°, and corresponding regions produce a comparative relation for improving particle capture. Increasing the rotation rate can increase the drag force coefficient by about 0.025, hindering droplet–particle collision. Average radial velocity of particles with higher than 3.7 mm/s is necessary at high rotation rates, while collection efficiency decreases at increased droplet rotation rates. [ABSTRACT FROM AUTHOR]

The internal conversion and intramolecular vibrational relaxation processes of nitro-tri-tert-butylphthalocyanine, tetra-phenylporphyrin (TPP), and tetra-tert-butylphthalocyanine (BuPc) in chloroform solution were investigated with an ultrafast time-resolved fluorescence depletion method. A regular fluorescence depletion was observed, indicating that the vibrational relaxation in the S1 state takes a few hundred femtoseconds to several picoseconds. For TPP and BuPc, an additional sharp dip superposes on the regular depletion. It is explained by an ultrafast internal conversion process from the S2 state to the S1 state with a time of a few tens of femtoseconds. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Here, we study hierarchy of graphene wrinkles induced by thermal strain engineering and demonstrate that the wrinkling hierarchy can be accounted for by the wrinklon theory. We derive an equation λ = (ky)0.5, explaining evolution of wrinkling wavelength λ with the distance to the edge y observed in our experiment by considering both bending energy and stretching energy of the graphene flakes. The prefactor k in the equation is determined to be about 55 nm. Our experimental result indicates that the classical membrane behavior of graphene persists down to about 100 nm of the wrinkling wavelength. [ABSTRACT FROM AUTHOR]

Bottom-gate bottom-contact (BGBC) organic thin film transistors (OTFTs) based on N,N′-ditridecyl perylene diimide exhibit electron mobility as high as 3.54 cm2 V-1 s-1 in nitrogen, higher than that (1 cm2 V-1 s-1) of bottom-gate top-contact devices. The better performance of BGBC configuration in N2 is attributed to lower contact resistance, which is further reduced by thermal annealing. After thermally annealing the BGBC OTFTs at 180 °C, electron mobility as high as 3.5 cm2 V-1 s-1, current on/off ratio of 106 and threshold voltage of 9 V are achieved in air, and the mobility retains above 1 cm2 V-1 s-1 after storage for two months in air. Thermal treatment enhanced crystalline grains, reduced grain boundaries, and suppressed the adsorption of H2O and O2, leading to excellent performance in air. [ABSTRACT FROM AUTHOR]

The authors reported organic phototransistors (PTs) with octadecyltrichlorosilane treated SiO2/Si substrate based on anthra[2,3-b]benzo[d]thiophene. The organic PTs show a high mobility of 0.4 cm2 V-1 s-1, a maximum photoresponsivity of about 1000 A/W, and photocurrent/dark-current ratio of around 800 under white light irradiation with 30 μW/cm2. The data are comparable with those of PTs based on amorphous silicon. Meanwhile, it is interesting to see that the devices show a high air-stable property and high photosensitivity via electric-field enhanced process. All these phenomena were attributed to the intrinsic optic-electronic property of the organic semiconductor and optic-electric field effect. [ABSTRACT FROM AUTHOR]

Highly photosensitive nanoswitches with a structure of indium tin oxide/organic insulator/metal have been fabricated. Electric current in the photoswitches is sensitive to ultraviolet (UV) radiation, and can be inhibited and recovered by exposing the photoswitch to, or shielding it from, UV radiation, respectively. Photoswitches with a very high on/off ratio exceeding 106, which is the highest ratio recorded for all reported organic photoswitches, have been demonstrated under UV radiation even with a low power density (∼10-5 W/cm2). [ABSTRACT FROM AUTHOR]

The aim of this study is to establish the structure-properties relationship of tetrathiafulvalene (TTF). After this study (1) TTF crystals with α and β phases were controllably obtained by the cast method with careful selection of the solvents, and (2) organic field-effect transistors (OFETs) of α and β phases both exhibited field-effect performance, and the performance of α phase was much better than that of β phase. The highest mobility of α phase reached 1.2 cm2 V-1 s-1, while β phase showed the maximum mobility only about 0.23 cm2 V-1 s-1, indicating the strong performance dependence of OFETs performance on the crystal phases. [ABSTRACT FROM AUTHOR]

The authors report a simple approach to reduce power consumption of organic light-emitting diodes. Introducing a 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline layer into the emissive layer can dramatically improve the carrier recombination efficiency. The presence of an interlayer of tris(8-quinolinolato)aluminum (Alq3) within the hole-transport layer also gives rise to the similar phenomenon. Furthermore, they modified the anode with the ultrathin hexadecafluorocopper phthalocyanine layer in order to further enhance the electroluminescent properties. They obtained the high performance light-emitting diodes using Alq3 as the emissive layer with a high current efficiency of 7.63 cd/A and a low turn-on voltage of 2.89 V. [ABSTRACT FROM AUTHOR]

We prepared a large quantity of multiwall nanotubes with intramolecular junctions (CNx/C) by pyrolysis of iron phthalocyanine with or without an inlet of ammonia gas. The nanotubes consist of two sections, one section made of carbon nitride featuring bamboo-like structure and the other one made of carbon featuring empty hollow cylinder structure, and thus the intramolecular junctions were formed in the middle as a result of being doped or undoped with nitrogen. Nanodiode based on a single CNx/C junction shows reproducible rectifying behavior with a rectification ratio of 1.3×103 at ±2 V. In addition, the nanodiode demonstrated as a half-wave rectifier worked at an input sine wave of 1 kHz. Two CNx/C junctions were configured together to exhibit functions of OR and AND logic gates. Moreover, after substituting the wave-detection silicon diode in common transistor radio set with our nanodiode, the radio set still worked normally, representing an important step toward the potential application for nano-scale devices. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Thin-film transistors based on aligned carbon nanotubes (CNTs) were fabricated by directly growing highly ordered CNTs on silicon dioxide surface. The transistor shows a pronounced field effect. Electric transport through the aligned carbon nanotubes is dominated by the holes at room temperature. A hole mobility (μ[SUBp]) of the CNT thin-film transistor was estimated to be as high as 61.6 cm[SUP2]/V s. Such a mobility is comparable to that of heavily doped n-Si and is larger than individual CNT field-effect transistor. Thus, it reveals a potential application of the aligned CNTs in electronics. [ABSTRACT FROM AUTHOR]

The solubility of fullerene (C[sub 60]) is improved by combining it with an alkyl group of substituted copper (II) phthalocyanine (CuPc) through Diels-Alder reaction. Optical limiting properties of this compound were investigated by using a double frequency Nd:YAG laser system at a wavelength of 532 nm with pulse duration of 45 ps. The results show that there are two separated conjugation systems in this kind of molecule. Both of them independently contribute to the reverse saturable absorption. Broadband optical limiting materials might be designed based on the combination of various optical limiting molecules through covalent bonds. Phase separation problems existing in the mixture of various materials can be avoided. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Resonant rings which can amplify RF power through the coupling of waves are used for high power breakdown tests, unidirectional filters, or pulse-shaping techniques. Usually, the RF output terminal of a resonant ring is connected to a matched load. For the resonant ring at Peking University, the matched load has been replaced by a waveguide shorting plate to obtain higher conditioning power for the 1.3 GHz capacitive type power couplers. The power gain is increased significantly with this short termination with the same input RF power. Working mechanism analysis, experiments, and results of this modified resonant ring will be presented. [ABSTRACT FROM AUTHOR]