Room temperature pretreatment of pubescens by AlCl_3 aqueous solution

Room temperature(about 16°C)pretreatment of pubescens by Al Cl_3aqueous solution with different concentrations was studied.In the presence of 20 wt%Al Cl_3for pretreatment within 24 h,the degradation of hemicellulose reached 19.5 wt%without obvious degradation of cellulose and lignin(2.7 wt%and2.4 wt%,respectively).The extracted hemicellulose from pubescens could be divided into two parts,i.e.,small molecular weight products(saccharides and carboxylic acid,which occupy approximately 28.2%)and oligomers(approximately 71.8%).Low concentration of AlCl_3(<10 wt%)slightly promoted the formation of oligomers with molecular weight in the range of 200–1000 Da,while high concentration of Al Cl_3(10–20 wt%)promoted the formation of oligomers in the molecular weight range above 20,000 Da.The conversion of hemicellulose with acceptable selectivity resulted in the cleavage of bond between hemicellulose and lignin yielding three classical Lignin-Carbohydrate complexes.

Influences of mass flow rate on heat and mass transfer performances of water sublimator combined with fluid loop

For spacecraft working in vacuum environment, sublimator is an effective heat rejection approach to reject system's peak heat load, and supplement spacecraft radiation heat rejection. For a spacecraft active fluid loop thermal control system combined with sublimator, waste heat generated from multi-point distributed heat sources could be collected by the fluid loop efficiently. However, the heat and mass transfer performances of the sublimator combined with fluid loop have not been adequately studied in previous research, especially for the influences of the heat load. Since work fluid mass flow rate is the main factor affecting heat load of the fluid loop, this context experimentally studied influences of the fluid loop mass flow rate on sublimator start-up transient characteristics, including heat transfer performances, response time, and work stability. Results indicated that the fluid loop mass flow rate affected the sublimator heat and mass transfer performances obviously, but the heat rejection ability is not always increase with the increasing of the fluid loop mass flow rate. In addition, we obtained the condition to judge whether there is a positive correlation between heat rejection ability and fluid loop mass flow rate.

Theoretical Analysis on the Air-Condition Cabin Technique for Satellite Temperature Adjustment on the Ground

The aim of this paper is to study the heat transfer mechanism of the air-condition cabin technique for satellite temperature adjustment on the ground before the launch of those satellites with pressurized structure. By the study, the temperature of the satellite can be set appropriately, and this is very important to the initial satellite temperature after the satellite operates in orbit. In the paper, the simplified physical model is provided and the mathematical equations are obtained, thereafter, the experimental data are compared with the theoretical analysis. The quantitative conclusions from the theoretical analysis can be used to direct the design or the experiment of the temperature adjustment. Finally, we can conclude that, the temperature variation rule of the satellite is exponential, and the temperature adjustment process can be predicted by the exponential formula, which is obtained from the theoretical analysis.

State-of-the-art development about cryogenic technologies to support space-based infrared detection

As a key technology for space-based Earth observation and astronomical exploration,cooled mid-wavelength and long-wavelength Infrared(IR)detection is widely used in national defense,astronomy exploration,medical imaging,environmental monitoring,agricultural and other areas.The performances of IR detectors,including cut-off wavelength,detectivity,sensitivity and temperature resolution,plays a significant role in efficiently observing and tracking the low-temperature far-distance moving targets.Achieving optimal detection performance requires the IR detectors to operate at cryogenic temperatures.The future development of space-based applications relies heavily on the mid-wavelength and long-wavelength IR detection technologies,which should be enabled by the long-life cryogenic refrigeration and high-efficiency energy transportation system operating below 40 K,to support the Earth observation and astronomical detection.However,the efficiency degradation caused by the super low temperature brings tremendous challenges to the life time of cryogenic refrigeration and energy transportation systems.This paper evaluates the influence of cryogenic temperature on the infrared detector performances,reviews the features,development and space applications of cryogenic cooling technologies,as well as the cryogenic energy transportation approaches.Additionally,it analyzes the future development trends and challenges in supporting the space-based IR detection.

Construction of Chiral All-Carbon Quaternary Stereocenters by Asymmetric Friedel-Crafts Reaction of Isatin Derivatives

Un der the catalysis of chiral Cu(ll)complex,C2 and C3 alkylati on of pyrrole and C3 alkylation of in dole were realized simulta neously.The chiral oxindole skeleton with an all-carb on quater nary stereogenic cen ter at the C3-position could be obtai ned exclusively with high yields(up to 95%)and excellent enantioselectivities(up to>99%).

Lewis acid-catalyzed enantioselective Friedel-Crafts reaction of pyrazole-4,5-diones withβ-naphthol

A series of pyrazolone derivatives bearing a tetrasubstituted chiral center were prepared by virtue of a Lewis acid-catalyzed Friedel-Crafts reaction,in which a chiral copper complex was employed as the catalyst.This reaction can be carried out smoothly under mild condition to afford the pyrazolone derivatives with high yields(up to 85%)and excellent enantioselectivities(up to 99%).In addition,the gram scale synthesis proved the practicality of this reaction.

Investigation on low total temperature combustion characteristics of kerosene-fueled supersonic combustor

In this paper,the combustion characteristics of kerosene-fueled supersonic combustor under the conditions of Mach number 2.0,the total temperature at 700 K and the total pressure at 520 k Pa(simulated flight Mach number at 3.5)were studied by using the flame stabilizing method of cavity and strut from three aspects such as blockage ratios,kerosene equivalence ratios,location and quantity of injection holes.The results showed that:(A)The combustor with the strut realized the independent and stable combustion of kerosene.The combustion-induced back pressure in the block test with blockage ratio of 20%and 10%destroyed the inlet flow conditions;while the blockage ratio was 7.3%and 5%,the incoming flow conditions when kerosene was burned stably were not destroyed.(B)The kerosene Equivalence Ratio(ER)was more likely to be disturbed upstream than the induced back pressure when it rose,and an excessively high-ER would reduce the combustion efficiency;when the equivalence ratio was constant,the combustion efficiency of the blockage ratio of 7.3%was higher than the blockage ratio of 5%.The combustion efficiencies were 0.86(ER=0.13)and 0.78(ER=0.19)when the blockage ratio was 5%,respectively;the combustion efficiencies were 0.89(ER=0.16)and 0.82(ER=0.19)when the blockage ratio was 7.3%,respectively;the combustion efficiencies were 0.51(ER=0.25),0.81(ER=0.3),0.65(ER=0.34)and0.62(ER=0.42)when the blockage ratio was 20%,respectively.(C)The porous injection provided behind the strut was beneficial to the atomization of kerosene and improved the combustion efficiency of kerosene;the second injection after the cavity would reduce the combustion efficiency due to insufficient oxygen and combustion space.This study expanded the working range of ramjet and provided a reference fuel injection scheme for Turbine-Based Combined Cycle(TBCC)engine.

Loading experiment and thermal analysis for conduction cooled magnet of SMES system

China’s first 35 kJ high temperature superconducting magnetic energy storage(SMES)system with an experiment equipment was depicted.The dynamic heat analysis of the magnet of the SMES was conducted through the current load test on the directly cooled conduction magnet.The research results were as follows:when the converter charges and discharges the magnet for energy storage,the hysteresis loss is the main part of power loss,and contributes significantly to temperature rise;reducing the current frequency at the side of direct current is conducive to restraining temperature rise.The optimizing factors of the cool-guide structure were analyzed based on the heat stability theory,and it was found that the heat transfer of its key part(at the top of the magnet)must be strengthened to reduce the axial temperature difference of the magnet.