Abstract: A method for preparing the modified polyester. The modified polyester segments include terephthalic acid segment, ethylene glycol diol segment and branched diol segment, in which the branched diol segment refers to a diol segment in which a branch is located on a non-terminal carbon in the glycol segment and the branch is a linear carbon chain having 5 to 10 carbon atoms. The method includes preparing terephthalic acid glycol ester through the esterification of terephthalic acid and branched diol using the concentrated sulfuric acid as the catalyst. Then get ethylene terephthalate through the esterification of terephthalic acid and ethylene glycol. After stirring and mixing the two, the modified polyester can be obtained through polycondensation reaction of a low vacuum stage and a high vacuum stage using the catalyst and stabilizer.

Abstract: A nanoparticle-resin coated frac sand composition is provided. The nanoparticle-resin coated frac sand composition includes a silica sand, an epoxy resin, methanol, a hardener, and nanoparticles. The nanoparticles may be silica nanoparticles, alumina nanoparticles, zinc oxide (ZnO) nanoparticles, or titanium oxide (TiO2) nanoparticles. The methanol is used as a diluent for the epoxy resin. The nanoparticle-resin coated frac sand composition may be used as a proppant in a hydraulic fracturing operation, such by injecting a hydraulic fracturing fluid having the composition into a subterranean formation. Methods of manufacturing the composition and hydraulic fracturing of a subterranean formation are also provided.

Abstract: A high-modulus low-shrinkage polyester industrial yarn obtained by subjecting a polyester to dissolution, washing and solid state polycondensation followed by spinning. The high-modulus low-shrinkage polyester industrial yarn has a dry heat shrinkage rate of 2.0±0.25% under test conditions of 177° C.×10 min×0.05 cN/dtex. The average value of the crystal volume VC of the high-modulus low-shrinkage polyester industrial yarn is larger than 230 mm3. The high-modulus low-shrinkage polyester industrial yarn has a fiber modulus of ?100 cN/dtex. The polycondensation catalyst consists of magnesium ethylene glycol and antimony ethylene glycol, which has a small thermal degradation coefficient.

Abstract: A polyester obtained by the esterification of terephthalic acid and ethylene glycol and the polycondensation catalysed by a mixture of magnesium ethylene glycol and antimony ethylene glycol followed by granulation. In the polyester sections, the carboxyl end group is less than 15 mol/t, the mass percentage of oligomer is lower than 0.5%, and weight percentage of diethylene glycol is lower than 0.5%.

Abstract: A method for data transmission is disclosed. The method includes: performing, by a system, resource element mapping on modulation symbols which include data to be transmitted and reference signals and which are allocated to antenna ports of a designated type; performing antenna port mapping on the modulation symbols which are through the resource element mapping; and generating Orthogonal Frequency Division Multiplexing (OFDM) signals based on the modulation symbols which are through the antenna port mapping and transmitting the OFDM signals via physical antennas. The present invention also discloses an apparatus for data transmission. In the method and apparatus provided by the present invention, through establishing a mapping relationship between physical antenna elements and antenna ports, beamforming weights are added to modulation symbols of users at the same time. Thus, beamforming operation of the users is implemented.

Abstract: A method for data transmission is disclosed. The method includes: performing, by a system, resource element mapping on modulation symbols which include data to be transmitted and reference signals and which are allocated to antenna ports of a designated type; performing antenna port mapping on the modulation symbols which are through the resource element mapping; and generating Orthogonal Frequency Division Multiplexing (OFDM) signals based on the modulation symbols which are through the antenna port mapping and transmitting the OFDM signals via physical antennas. The present invention also discloses an apparatus for data transmission. In the method and apparatus provided by the present invention, through establishing a mapping relationship between physical antenna elements and antenna ports, beamforming weights are added to modulation symbols of users at the same time. Thus, beamforming operation of the users is implemented.