Evaluation of Cold Resistance and Semi-lethal Low Temperature(LT_(50))of Nine Pear Cultivars

[Objectives]To evaluate the cold resistance and semi-lethal temperature of pear cultivars,and provide a theoretical basis for the regional extension and breeding of cold-resistant pear cultivars.[Methods]Nine pear cultivars were used to study the changes in relative conductivity and cell injury rate of pear branches under low temperature stress,and the semi-lethal temperature(LT_(50))of pear branches was analyzed by fitting Logistic equation.[Results]The relative conductivity and cell injury rate of pear branches took on the trend of slow increase,rapid increase,and slow increase the decrease of treatment temperature.The LC_(50) of the nine pear cultivars were as follows:Nanguo pear-33.9℃,Wanyu-32.3℃,Red D Anjou-31.8℃,Jinfeng-31.3℃,Wujiuxiang-29.2℃,20 th Century Pear-29.1℃,Hanxiang-35.1℃,Yuluxiang-27.9℃ and Korla Fragrant Pear-29.2℃.[Conclusions]The semi-lethal temperature could reflect the cold resistance of pear trees,and Wanxiang had better cold resistance.The evaluation of cold resistance and semi-lethal temperature of pear cultivars can provide theoretical basis for regional extension and breeding of cold-resistant pear cultivars.

Thin Film Chip Resistors with High Resistance and Low Temperature Coefficient of Resistance

High resistance thin film chip resistors(0603 type) were studied,and the specifications are as follows:1 k? with tolerance about ±0.1% after laser trimming and temperature coefficient of resistance(TCR) less than ±15×10-6/℃.Cr-Si-Ta-Al films were prepared with Ar flow rate and sputtering power fixed at 20 standard-state cubic centimeter per minute(sccm) and 100 W,respectively.The experiment shows that the electrical properties of Cr-SiTa-Al deposition films can meet the specification requirements of 0603 ty...

Effects of mechanical boundary conditions on thermal shock resistance of ultra-high temperature ceramics

The effects of mechanical boundary conditions, often encountered in thermalstructural engineering, on the thermal shock resistance（TSR） of ultra-high temperature ceramics（UHTCs） are studied by investigating the TSR of a UHTC plate with various types of constraints under the first, second, and third type of thermal boundary conditions. The TSR of UHTCs is strongly dependent on the heat transfer modes and severity of the thermal environments. Constraining the displacement of the lower surface in the thickness direction can significantly decrease the TSR of the UHTC plate, which is subject to the thermal shock at the upper surface. In contrast, the TSR of the UHTC plate with simply supported edges or clamped edges around the lower surface is much better.

Abnormality of Magnetic Behavior and Resistivity of La_(0.7-x)Dy_x Sr_(0.3)MnO_3 (0.00≤x≤0.30)System at Low Temperature

By measuring M-T curves, ρ-T curves and MR-T curves of the samples under different temperatures, the influence of Dy doping （0.00 ≤ x ≤0.30） on the magnetic and electric properties of La0.7-xDyxSr0.3MnO3 has been studied. The experimental results show that, with the increase of the Dy content, the system undergoes a transition from long range ferromagnetic order to the cluster-spin glass state and further to antiferromagnetic order. For the samples with x=0.20 and 0.30, their magnetic behaviors are abnormal at low temperature, and their resistivities at low temperature have a minimum value. These peculiar phenomena not only come from the lattice effect induced by doping, but also from extra magnetic coupling induced by doping.

Variety Test on Low Temperature-resistant Pleurotus ostreatus Strains in Beijing Area

With 7 familiar Pleurotus ostreatus strains in Beijing region as the test materials,the randomized block design method was adopted to analyze the antagonistic effects,mycelial growth rate,yield of mushroom at low temperature season,total biological efficiency and agronomic characteristics of fruit bodies.The results showed that there were antagonistic effects and differences in all the tested items between all the tested strains,of which the strain PL5 had the shortest spawn age,the strain PL3 showed the highest total biological efficiency,and the fructification of the strain PL7 tasted crisp and tender.

Influence of Cr element on impact fracture process of ductile Ni-resistant alloyed iron at low temperature

In this study, in order to investigate the influence of Cr element on the impact fracture process of ductile Ni-resistant alloyed iron at low temperature, different contents of Cr element were added to ductile Ni-resistant(DNR) austenitic alloyed iron. The experimental results show that Cr addition can increase the hardness of the DNR alloyed iron, but it has an destructive effect on low-temperature impact properties. Through the analysis of the dynamic load and absorbed energy of samples with different Cr contents in the impact fracture process, and the comparison of the impact fracture process at room and low temperatures, it reveals that Cr addition into the DNR alloyed iron can facilitate the formation of the carbide mixture in Mn23C6 and Cr23C6 with homogeneous and discontinuous distribution. Meanwhile, Cr addition also can improve the the maximum dynamic load and crack initiation energy at low temperature, but has no obvious effect on the yield behavior of the DNR alloyed iron in the impact fracture process. Compared with the impact crack propagation process at room temperature, the metastable propagation energy at low temperature declines significantly with an increase in Cr content. This is because the micro-cracks that caused by the carbides weaken the matrix, resulting in the decline of impact crack propagation resistance. The fracture analysis results also show that the impact fracture mechanism gradually transforms from ductile to brittle with an increase in Cr content at low temperature. It explains that too much Cr addition can lead to brittle fracture even though the austenitic matrix has a good toughness at low temperature.

Effect of linear carboxylic ester on low temperature performance of LiMn_2O_4-graphite cells

To improve the low-temperature performances of Li-ion cells, three types of linear carboxylic ester-based electrolyte, such as EC/EMC/EA（1：1：2, mass ratio）, EC/EMC/EP（1：1：2, mass ratio） and EC/EMC/EB（1：1：2, mass ratio）, were prepared to substitute for industrial electrolyte（EC/EMC/DMC）. Then, 18650-type Li Mn2O4-graphite cells（nominal capacity of 1150 mA ·h） were assembled and studied. Results show that the cells containing three types of electrolyte are able to undertake 5C discharging current with above 93% capacity retention at-20 °C. Electrochemical impedance spectra show that the discharge capacity fading of Li-ion cells at low temperature is mainly ascribed to the charge transfer resistance increasing with temperature decreasing. In comparison, the cells containing electrolyte of 1.0 mol/L LiPF6 in EC/EMC/EA（1：1：2, mass ratio） have the highest capacity retention of 90% at-40 °C and 44.41% at-60 °C, due to its lowest charge-transfer resistance.

Novel Cascade Refrigeration Cycle for Cold Supply Chain of COVID-19 Vaccines at Ultra-Low Temperature -80°C Using Ethane (R170) Based Hydrocarbon Pair

Several media report highlight on that the pharmaceutical companies require ultra-low temperatures -80°C to transport and store its COVID-19 vaccines. This research presents the thermodynamic analysis on cascade refrigeration system (CRS) with several refrigerant pairs which are R32/R170, R123/R170, R134a/R170, R404A/R170, R407c/R170, R410/R170, and the hydrocarbon (HC) refrigerant pair Propane/Ethane, namely R290/R170. Besides, the results of R22/R170 pair, which is not recommended to be used due to phase out of R22 as per Montréal Protocol, are included as base case to compare the novel hydrocarbon pairs in CRS and the old trend of refrigerant pairs. Thermodynamic properties of all these pairs were investigated and compared under different intermediate temperature used in CRS heat exchanger, which thermally connected both the Low and High temperature cycles (LTC) and (HTC). By applying the first law of thermodynamics, the coefficients of performance (COPs) and the specific power consumptions (SPC) in kW/TR are presented and compared. In addition, by applying the second law of thermodynamics the exergetic efficiencies were estimated. The results reveal the promising opportunity of using the HC pair (R290/R170). The minimum SPC in kW/TR is recorded for the pair R123/R170. One the other hand, the highest exegetic efficiency values are observed to be 40%, 38%, and 35% for the pairs R123/R170, R290/R170, and R134/R170, respectively. This research concludes that the HC pair (R290/R170) is highly recommended for CRS applications either to transport the COVID-19 or store it in cold storage rooms in hospitals and clinics. All precautionary measures should be carefully applied in design and operation of HC pair (R290/R170) due to its flammability hazard.

Properties and microstructure of Ti6Al4V by deformation accelerated low temperature plasma nitriding

An integrated low-temperature nitriding process was carried out for Ti6Al4V to investigateitseffect on microstructure and properties.The process was designed to enhance the nitriding kinetics in low-temperature（500℃） nitriding by deformation, and to strengthen Ti6Al4V alloybydispersionat the same time. Specimens of Ti6Al4V alloyweretreated through the process of solid solutionstrengthening-cold deformation-nitriding at 500℃. The white nitriding layeris formed after some time and then kept stable, changing little withthedeformationdegreeand time. The effect of aging on substrate is significant. Surface hardness and substrate hardnessincrease with deformation increasing. The construction was investigated by XRD.The surface nitridesare TiN, Ti2N, Ti4N3-Xand Ti3N1.29,and thenitridesin cross-section are Ti3N1.29and TiN0.3. The wear tests of specimens after nitriding, aging and deformation were carried out,andthetest data show that the nitrided pieces have the best wear resistance.

Microstructure and Properties of Low Temperature Composite Chromized Layer on H13 Tool Steel

Low temperature composite chromizing is a process composed of a plain ion-carbonitriding or ion-nitriding at 550-580℃, followed by a low-temperature chromizing in a salt-bath of 590℃. The microstructure and properties of the low temperature composite chromized layer on H13 tool steel were investigated using metallography, X-ray diffraction, microanalysis, hardness and wear tests. It was found that this low temperature process was thermo-dynamically and kinetically possible, and the composite chromized layer on H13 steel, with a thickness of 3-6 μm, consisted of three sub-layers (bands), viz. the outer Cr-rich one, the intermediate (black) one, and the inner, original white layer. After chromizing, the former diffusion layer was thickened. The results of X-ray diffraction showed that the composite chromized layer contained such nitrides and carbides of chromium as CrN, Cr2N, (Cr, Fe)23C6, and (Cr, Fe)7C3, as well as plain α-(Fe, Cr). A high surface microhardness of 1450-1550 HV0.025, which is much higher than that obtained by the conventional ion carbonitriding and ion nitriding, was obtained. In addition, an excellent wear resistance was gained on the composite chromized layer.

Effect of Introducing Conductive Organic Carrier on Properties of Low-Temperature Conductive Silver Paste

The poly(epoxy-N-methylaniline)conductive organic carrier was used as the bonding phase of the low-temperature conductive silver paste.Then,this was mixed with different proportions of silver powder to prepare the low-temperature conductive silver paste.Afterwards,the effect of the conductive organic carrier on the properties of the low-temperature conductive silver paste was determined by IR,DMA and SEM.The results revealed that the prepared conductive paste has good conductivity,film-forming performance,printing performance,low-temperature curing performance,and anti-aging performance.When the mass percentage of the bonding phase/conductive phase was 40/60,the lowest volume resistivity of the conductive silver paste was 4.9×10^(−6)Ω⋅cm,and the conductivity was the best.

Preparation of aluminide coatings at relatively low temperatures

A method was presented to prepare aluminide coatings on metals by combining the pack aluminizing with the ball impact process. This technique applied mechanical vibration to a retort, which was loaded with pack-aluminizing powder, specimens and alloy balls. Pack aluminizing was carried out with repeated ball impact, which accelerated chemical reactions and atomic diffusion. Aluminide coatings were formed at a relatively lower temperature (below 600 ℃) and in a shorter treatment time, compared with the conventional pack aluminizing. The effects of the operation temperature and the treatment time on the formation of the coatings were analysed. The SEM, EDS and XRD analysis results show that the aluminide coatings appear to be homogeneous, with a high density and free of porosity, and have excellent adherence to the substrate. The coatings mainly consist of Al-rich phases such as η-Fe2Al5, θ-FeAl3 and ?CrAl5. Oxidation resistance was studied by high-temperature tests. The formation mechanism of the Al-coatings was also investigated. This technique provides a new approach for industrial diffusion coatings with great energy and time savings.

Low-Temperature Selective Catalytic Reduction of NO with NH_3 over Fe–Ce–O_x Catalysts

In this study, we used a simple impregnation method to prepare Fe-Ce-O x catalysts and tested them regarding their low-temperature (200-300 °C) selective catalytic reduction (SCR) of NO using NH3. We investigated the effects of Fe/Ce molar ratio, the gas hourly space velocity (GHSV), the stability and SO2/H2O resistance of the catalysts. The results showed that the FeCe(1:6)O x (Ce/Fe molar ratio is 1:6) catalyst, which has some ordered parallel channels, exhibited good SCR performance. The FeCe(1:6)O x catalyst had the highest NO conversion with an activity of 94-99% at temperatures between 200 and 300 °C at a space velocity of 28,800 h−1. The NO conversion for the FeCe(1:6)O x catalyst also reached 80-98% between 200 and 300 °C at a space velocity of 204,000 h−1. In addition, the FeCe(1:6)O x catalyst demonstrated good stability in a 10-h SCR reaction at 200-300 °C. Even in the presence of SO2 and H2O, the FeCe(1:6)O x catalyst exhibited good SCR performance.

Effect of processing temperatures on characteristics of surface layers of low temperature plasma nitrocarburized AISI 204Cu austenitic stainless steel

The influence of processing temperatures on the surface characteristics of AISI 204Cu austenitic stainless steel was investigated during a low temperature plasma nitrocarburizing.The resultant layer was a dual-layer structure,which comprises a N-enriched layer on the top of C-enriched layer.The surface hardness and the layer thickness increase up to about HV 0.05 1000 and 20μm with increasing temperature.The specimen treated at 400°C shows a much enhanced corrosion resistance compared to the untreated steel.A loss in corrosion resistance was observed for specimens treated at temperatures above 430°C due to the formation of Cr2N.

Comparison of Genetic Diversity and Growth Performance between the Selected Population and Hybridized Population of Litopenaeus vannamei at Low Temperature

[Objective] This study was conducted to compare the genetic diversity and growth performance of two Litopenaeus vannamei populations at low temperature. [Method] One population（selected population, SP） was produced through inbreeding and 3 years of selection from seven popula- tions of L. vannamei introduced from the United States and Singapore. The other population （hybridized population, HP） was the F1 generation of the crosses between Population SP and some excellent populations introduced from South Korea and Singapore. The growth performance of the two populations at low temperature was compared, and the genetic diversity and genetic differentiation between the two populations were assessed using 13 microsatellite loci. [Result] The shrimps of population HP had better growth performance than those of population SP. The average body weight （BW） for population HP, which was （13.18±3.65） g/ind., was significantly higher than that of population SP, which was （12.20±3.14） g/ind. The coefficient of variation in body weight for population SP was 25.74%, and that for population HP was 27.69%. The other growth indices of popula- tion HP were all higher than those of population SP. One-way analysis of variance （ANOVA） indicated that there were highly significant differences in both BW and width of third abdominal segment （WTAS） between HP and SP（P〈0.001）. The specific growth rate （SGR） and absolute growth rate （AGR） for population HP were （5.09±0.61） %/d and （0.26±0.60） g/d, respectively, while the SGR and AGR for population SP were （4.94±0.57） %/d and （0.24±0.63） g/d., both significantly lower than those of population HP （P〈0.001）. Genetic diversity analysis revealed that the number of alleles （Na） of population HP （Na=7.9） was slightly higher than that of population SP （Na=7.6）. The average polymorphic information content （PIC） of HP and SP populations was similar 0.63 and 0.62, both indicating high level of genetic diversity. The average observed heterozygosity （HQ） of HP and SP was 0.492 and 0.483, and the expected heterozygosity（He） was 0.675 and 0.663, respectively. Both Ho and He of population HP were higher than those of population SP, suggesting that HP had higher genetic diversity than population SP. Moreover, the mean of FsT values at the 13 microsatellite loci between HP and SP was 0.155 6, suggesting there was a significant genetic differentiation between the two populations. [Conclusion] Our results provide a theoretical basis for the breeding of new L. vannamei strains that are resistant to low temperature.

Effect of Low Temperature Stress on Protein Content of Toona Sinensis Seedlings and Expression of Specific Protein

[Objective] The paper was to study the changes of protein content and component in leaves of Toona Sinensis under low-temperature stress.[Method] Potted experiment was adopted,and SDS-PAGE electrophoresis was also used to analyze the dynamic changes of protein in T.Sinensis leaves.[Result] Low temperature stress could change the content and component in leaves of T.Sinensis,but different provenances had different performance under different temperatures,so did the same provenance under different stress periods.SDS-PAGE electrophoresis results indicated that the change law of provenances of Xixia of Henan and Nanjing of Jiangsu with stronger cold resistance was similar,showing the change trend of "increase-decrease-increase".Protein was greatly expressed after stress for 1 d,the color of band became darker;the content gradually decreased in the following second and third day,and the color of bands was lighter;the content began to increase at the forth day.Two provenances induced the specific proteins with molecular weights of 27.6 and 22.5 kD,respectively.The soluble protein content of provenance of Xiapu of Fujian with relatively weak cold resistance was gradually increased,but no new protein bands were induced.The changes of protein band color of various provenances in SDS-PAGE electrophoresis was basically consistent with the changes of protein content,the provenance with stronger cold resistance could induce the production of specific proteins.[Conclusion] The study provided theoretical basis for under the molecular mechanism of plant cold resistance,which had great significance in theory and practice.

Synthesis of N-Alkane Mixture Microcapsule and Its Application in Low-Temperature Protective Fabric

We investigated synthesis and characterization of melamine-urea-formaldehyde（MUF） microcapsules containing n-alkane mixture as phase change core material for thermal energy storage and low-temperature protection. The phase change microcapsules（microPCMs） were prepared by an in situ polymerization using sodium dodecyl sulfate（SDS） and polyvinyl alcohol（PVA） as emulsifiers. Surface morphology, particle size, chemical structure, and thermal properties of microPCMs were, respectively, characterized by using scanning electron microscopy（SEM）, field emission scanning electron microscopy（FESEM）, Fourier transform infrared spectroscopy（FT-IR）, differential scanning calorimetry（DSC）, and thermal gravimetric analysis（TGA）. Low-temperature resistance performances were measured at-15,-30,-45, and-60 ℃ after microPCMs were coated on a cotton fabric by foaming technology. The results showed that spherical microPCMs had 4.4 μm diameter and 100 nm wall thickness. The melting and freezing temperatures and the latent heats of the microPCMs were determined as 28.9 and 29.6 ℃ as well as 110.0 and 115.7 J/g, respectively. Encapsulation of n-alkane mixture achieved 84.9 %. TGA analysis indicated that the microPCMs had good chemical stability below 250 ℃. The results showed that the microencapsulated n-alkane mixture had good energy storage potential. After the addition of 10 % microPCMs, low-temperature resistance duration was prolonged by 126.9%, 145.5%, 128.6%, and 87.5% in environment of-15,-30,-45 and-60 ℃, respectively as compared to pure fabric. Based on the results, phase change microcapsule plays an effective role in lowtemperature protection field for the human body.

Effect of heat treatment on microstructure and mechanical properties of Ti-containing low alloy martensitic wear-resistant steel

Effects of quenching temperature and cooling conditions(water cooling and 10%NaCl cooling)on microstructure and mechanical properties of a 0.2%Ti low alloy martensitic wear-resistant steel used for die casting ejector plate were investigated.The results show that lath martensite can be obtained after austenitizing in the range of 860-980℃and then water cooling.With an increase in austenitizing temperature,the precipitate content gradually decreases.The precipitates are mainly composed of TiC and Ti4C2S2,and their total content is between 1.15wt.%and 1.64wt.%.The precipitate phase concentration by water-cooling is higher than that by10%NaCl cooling due to the lower cooling rate of water cooling.As the austeniting temperature increases,the hardness and tensile strength of both water cooled and 10%NaCl cooled steels firstly increase and then decrease.The experimental steel exhibits the best comprehensive mechanical properties after being austenitized at 900℃,cooled by 10%NaCl,and then tempered at 200℃.Its hardness,ultimate tensile strength,and wear rate reach551.4 HBW,1,438.2 MPa,and 0.48×10^(-2)mg·m^(-1),respectively.

Wear resistance of TC4 by deformation accelerated plasma nitriding at 400 °C

An integrated low temperature nitriding process for TC4（Ti6Al4V） has been developed and the effect on wear resistance has been investigated. Through the process of solid solution strengthening—cold deformation—nitriding at 400℃, the TC4 alloy is nitrided on surface and dispersion strengthened in bulk at the same time. The white nitriding layer is formed after some time of nitriding. The nitriding speed increases with the deformation degree. The construction was investigated by XRD and the nitride is Ti3N（2-X）. The wear test was carried out and results exhibit that the nitrided samples have better wear resistance.