Ventilation strategies and indoor particulate matter in a classroom

Particle mass and number concentrations were measured in a mechanically ventilated classroom as part of a study of ventilation strategies for energy conservation. The ventilation system was operated either continuously, intermittently, or shut down during nights while it was on during workdays. It appears that the nighttime ventilation scheme is not important for indoor particle concentrations the following day if fans are operated to give five air exchanges in advance of the workday. The highest concentrations of PM₁₀ were found during and after workdays and were due to human activity in the classroom. The average workday PM₁₀ concentration was 14 μg/m³, well below the WHO guideline values. The number concentration of particles with diameter <0.750 μm was typically between 0.5 × 10³ and 3.5 × 10³ particle/cm³. These concentrations were largely independent of the occupants. Transient formation of small particles was observed when ventilation was shut down. Then remaining ozone reacted with terpenes emitted by indoor sources and gave up to 8 × 10³ particle/cm³ before formation stopped due to lack of ozone. The intermittent ventilation regime was found least favorable for the indoor air quality in the classroom.     

Characterizations,relationship, and potential sources of outdoor and indoor particulate matter bound polycyclic aromatic hydrocarbons (PAHs) in a community of Tianjin,Northern China

Polycyclic aromatic hydrocarbons (PAHs) are among the most toxic air pollutants in China. However, because there are unsubstantial data on indoor and outdoor particulate PAHs, efforts in assessing inhalation exposure and cancer risk to PAHs are limited in China. This study measured 12 individual PAHs in indoor and outdoor environments at 36 homes during the non‐heating period and heating period in 2009. Indoor PAH concentrations were comparable with outdoor environments in the non‐heating period, but were lower in the heating period. The average indoor/outdoor ratios in both sampling periods were lower than 1, while the ratios in the non‐heating period were higher than those in the heating period. Correlation analysis and coefficient of divergence also verified the difference between indoor and outdoor PAHs, which could be caused by high ventilation in the non‐heating period. To support this conclusion, linear and robust regressions were used to estimate the infiltration factor to compare outdoor PAHs to indoor PAHs. The calculated infiltration factors obtained by the two models were similar in the non‐heating period but varied greatly in the heating period, which may have been caused by the influence of ventilation. Potential sources were distinguished using a diagnostic ratio and a mixture of coal combustion and traffic emission, which are major sources of PAHs.     

Design and achieving mechanism of upconversion white emission based on Yb/Tm/Er tri-doped KY3F10 nanocrystals

KY₃F₁₀:Yb³⁺/Tm³⁺/Er³⁺ upconversion nanocrystals are synthesized via a simple hydrothermal procedure. The nanocrystals emit the near equal energy white light with high brightness and favorable color balance when excited using a 980 nm continuous wave diode laser. The research of upconversion mechanism indicates that in addition to the energy transfer processes from Yb³⁺ to Tm³⁺ and Er³⁺, respectively, there exists a new process ¹G₄ (Tm³⁺) + ⁴I_11/2 (Er³⁺) → ³H₄ (Tm³⁺) + ⁴S_3/2 (Er³⁺).     

10KV配电网的线损管理及降损措施

电力网线损率是评价供电企业经济效益的主要技术经济指标,10kV配电网线损的程度直接反应了一个供电企业运营能力的好坏,因此加强10kV强配电网线损的管理和降损工作尤为重要。     

ADC10压铸铝合金变速箱体硬质点缺陷分析及预防

通过宏观和微观检验、化学成分分析、硬度测试以及能谱分析等方法,对ADC10压铸铝合金汽车变速箱体中出现硬质点的原因进行了分析。结果表明:硬质点的产生是由于熔融铝液中的氧化物或含钛型金属化合物在压铸过程中随同铝液一起注射进入模具型腔并最终保留在零件内部。其后机械加工时,硬质点的存在致使刀具损坏,机械加工难以正常进行,严重时导致变速箱体报废。最后提出改进铝液的前处理工艺,避免氧化物或金属化合物进入模具型腔,可有效防止硬质点的产生。     

冷却速度对X12CrMoWVNbN10-1-1耐热钢的力学性能影响

采用力学性能测试、金相分析以及TEM微观结构分析,研究了淬火和回火冷却速度对X12CrMoWVNbN10-1-1耐热钢力学性能的影响,并探讨了脆化机制,结果表明:在相同的回火工艺下,随淬火冷却速度的降低,强度降低,塑性变化不大,但冲击值增加,其主要原因是缓冷降低了马氏体基体的再结晶温度,导致基体的回复与再结晶程度增加;...     

Synthesis, characterization and DNA binding of the complexes of rare earth with phenanthroline and demethylcantharate

Three novel rare earth complexes, [Ln2(DCA)2(phen)2](NO3)2·6H2O (Ln(III)=Sm(III)(1), Er(III)(2), Yb(III)(3); DCA2-=de-methylcantharate, 7-oxabicyclo[2.2.1] heptane-2,3-dicarboxylate, C8H8O52-; phen=1,10-phenanthroline, C12H8N2) were synthesized. The structures were characterized by elemental analysis, molar conductance, IR and TGA. The results suggested that the structural features of the complexes were: in each DCA2-, one carboxylate group, as bidentate bridging group, connected two rare earth ions; the other carboxylate group, as bidentate chelate group took part in the coordination with rare earth ion. And cyclic ether oxygen of DCA2- and nitrogen atoms of phen took part in the coordination. The probable coordination number was seven. The interaction of the complexes with DNA was studied by UV-spectra, fluorescence spectra and viscosity measurements. Following increasing the concentration of DNA, the UV absorption bands nearby 265 nm of the three complexes appeared hypochromism and red-shift phenomena. And the values of binding constants Kb were 1.89×105 L/mol (1), 3.54×104 L/mol (2) and 3.83×104 L/mol (3). The complexes could quench the fluorescence of EB-DNA system, and the values of equilibrium constants Ksq were 1.72(1), 0.56(2) and 1.09(3). The relative viscosity of DNA steadily decreased with increasing the concentration of complexes. So, we could infer that the complexes may partially insert into DNA. The study of agarose gel electrophoresis showed that the complexes could cleave plasmid DNA, and the process of the reaction was through unclassical redox mechanism.     

Copper‐Catalyzed Domino Synthesis of Benzo[4,5]imidazo[1,2‐a]pyrimidin‐4(10H)‐ones using Cyanamide as a Building Block

An efficient and practical copper‐catalyzed domino synthesis of benzo[4,5]imidazo[1,2‐a]pyrimidin‐4(10H)‐ones has been developed. The protocol uses N‐(2‐halophenyl)‐3‐alkylpropiolamides and cyanamide as the starting materials, inexpensive copper(I) iodide and pipecolinic acid as the catalyst and ligand, and the corresponding products were obtained in moderate to good yields.

     

5Cu/(10NiO-NiFe2O4)金属陶瓷惰性阳极钠钾混合电解质电解腐蚀研究

采用传统粉末冶金技术制备了铝电解用5Cu/(NiFe2O4-10NiO)金属陶瓷惰性阳极,对其在钠钾冰晶石混合冰晶石中进行电解腐蚀。研究结果表明,从微观来看,阳极存在腐蚀现象。电解过程的槽电压波动剧烈。Fe、Ni和Cu组元的平衡浓度分别为150×10-6、42×10-6及40×10-6,腐蚀速率比常规电解条件下的低。