Possible contributions of volatile-producing bacteria to soil fungistasis

Soil fungistasis can adversely affect the germination and growth of most fungal species in the field. Among the inhibitors, volatiles of microbial origins are potentially very important. In this study, we investigated the frequency and identity of bacteria producing fungistatic volatiles. Among the 1018 bacterial isolates tested, 328 were found to produce antifungal volatiles that could inhibit spore germination and mycelial growth of two nematicidal fungi Paecilomyces lilacinus and Pochonia chlamydosporia. A phylogenetic analysis based on restriction fragment length polymorphism (RFLP) and 16S rDNA sequence placed the 328 bacteria in five groups: Alcaligenaceae, Bacillales, Micrococcaceae, Rhizobiaceae and Xanthomonadaceae. Volatile compounds of 39 bacterial isolates were identified by gas chromatography/mass spectrum (GC/MS). Tests with commercially available antifungal compounds suggested that seven volatile compounds of bacterial origins (acetamide, benzaldehyde, benzothiazole, 1-butanamine, methanamine, phenylacetaldehyde and 1-decene) likely play important roles in soil fungistasis.     

Antioxidant activity of a flavonoid-rich extract of Hypericum perforatum L. in vitro

A flavonoid-rich extract of Hypericum perforatum L. (FEHP) was prepared by adsorption on macroporous resin and desorption by ethanol. Total flavonoid content of FEHP was determined by a colorimetric method. The major constituents of FEHP, including rutin, hyperoside, isoquercitrin, avicularin, quercitrin, and quercetin, were determined by HPLC analysis and confirmed by LC-MS. Different antioxidant assays were utilized to evaluate free radical scavenging activity and antioxidant activity of FEHP. FEHP was an effective scavenger in quenching DPPH and superoxide radical with IC50 of 10.63 microg/mL and 54.3 microg/mL, respectively. A linear correlation between concentration of FEHP and reducing power was observed with a coefficient of r2 = 0.9991. Addition of 150 microg of FEHP obviously decreased the peroxidation of linoleic acid during 84 h incubation, but the amount of FEHP over 150 microg did not show statistically significant inhibitory effect of peroxidation of linoliec acid (p > 0.05). FEHP exhibited inhibitory effect of peroxidation of liposome induced both by hydroxyl radical generated with iron-ascorbic acid system and peroxyl radical and showed prominent inhibitory effect of deoxyribose degradation in a concentration-dependent manner in site-specific assay but poor effect in non-site-specific assay, which suggested that chelation of metal ion was the main antioxidant action. According to the results obtained in the present study, the antioxidant mechanism of FEHP might be attributed to its free radical scavenging activity, metal-chelation activity, and reactive oxygen quenching activity.     

荔枝鲜果挤压力学特性

为减小荔枝在收获、储运过程中的机械损伤,给荔枝作业装备设计提供依据,试验测定了荔枝鲜果的几何特征,对其果实进行了不同加载条件的挤压试验,并对其果壳进行了拉伸试验。试验得到妃子笑、桂味2种荔枝鲜果在5种加载速率和2种压缩方向下的破裂力分别为76.46～112.90?N和38.67～53.83?N、破裂相对变形分别为27.93%～32.57%和18.87%～21.27%、弹性模量分别为2.52～4.69×105?Pa和4.26～5.93×105?Pa。试验表明,荔枝果实的抗挤压能力具有各向异性,其纵向大于横向;妃子笑的各向异性比桂味显著,且抗挤压能力大于桂味;试验范围内加载速率对果实的抗挤压能力影响不显著。荔枝果实可简化为果核呈长椭球体、厚度均匀薄壳球体,利用其简化结构及果壳强度各向异性对其挤压力学特性和裂壳特征的力学原理进行了分析。研究结果可为荔枝收获、加工和运输等提供理论依据。     

基于CFD的下沉式日光温室保温性能分析

为了深入了解下沉式日光温室的保温性能,该文基于非稳态传热模型,采用计算流体力学(computational fluid dynamics,CFD)软件模拟盖帘状态下下沉式日光温室的温度场,并采用试验对CFD模拟温室内的温度场进行验证,验证结果表明,CFD对下沉式日光温室盖帘状态下温度场的模拟具有较高的可信度.为了提高下沉式日光温室的保温效率,使用CFD软件对不同盖帘时间的下沉式日光温室的温度场进行模拟,并分析其对热能分布的影响.结果表明,不同盖帘时刻对下沉式日光温室夜间温度的影响差异显著;在午后弱光、室内外温差较大条件下,提前盖帘可以显著提高日光温室内夜间温度.该研究为CFD在下沉式日光温室研究中的应用及下沉式日光温室盖帘管理提供参考.     

短序与阔叶十大功劳化学组分及小檗碱含量的FTIR比较研究

为快速评价短序与阔叶十大功劳不同部位化学成分差异,本研究运用FTIR采集短序和阔叶十大功劳不同部位的红外光谱并比较短序与阔叶十大功劳不同部位盐酸小檗碱含量差异。研究结果显示,生物碱、黄酮和丁香酯等化学成分,短序十大功劳根、茎及叶片中均较阔叶十大功劳丰富,但是,多糖和苷类含量在两种十大功劳根中相当,在茎和叶片中均以阔叶十大功劳含量高,尤其是叶片中这种差异更明显。最后,与盐酸小檗碱标准品比较发现,2种十大功劳中盐酸小檗碱含量均以茎中最高,叶片中含量最低;2种十大功劳比较各部位盐酸小檗碱含量均以短序十大功劳中高。故运用FTIR技术可以快速找出2种十大功劳化学成分的差异,本研究结果将为十大功劳属植物资源合理开发利用及良种选育提供参考。     

冰水混合间接换热系统中换热器参数试验

利用北方地区冬冷夏热的特点,冬季冻冰蓄冷,夏季利用。采用间接换热冷量交换系统,有利于低碳节能和保护环境。该文对系统中换热器的参数进行了优化试验。以热交换器中的风速、流量、迎风面积、热管长度为影响因素,以热交换器的换热效率为目标,得到换热效率84%以上的较佳参数组合为风速2.54～2.93 m/s,流量0.72～0.80 m3/h,迎风面积11.93～13.51 dm2,热管有效长度7.99～9.95 m。该研究为利用自然冷资源间接换热冷量交换系统中热交换器的设计和应用提供依据。     

Phenotypic and genotypic characterization of β-lactam resistance in Klebsiella pneumoniae isolated from swine

Little is known about the antimicrobial resistance mechanisms in Klebsiella pneumoniae from swine in China. Thus, this paper aims to demonstrate the β-lactam resistance phenotypes and genotypes of K. pneumoniae isolates from swine in southwestern China, detect possible new β-lactamase variants, and determine whether or not the variants differ in their antibiotic resistance. Isolates from 58 unrelated diseased swine were collected from 61 pig farms in southwestern China from 2007 to 2009. Among the 58 isolates, 75.8-100% were resistant to β-lactam, 62.0-68.97% to fluoroquinolone, 44.8-46.55% to aminoglycoside, and 8.62-17.24% to β-lactam inhibitors. PCR amplification and DNA sequencing showed that bla(TEM-1) was detected in 100% (n=58) of the isolates, bla(SHV) in 82.76% (n=48), bla(CTX-M) in 39.66% (n=23), and bla(OKP) in 17.24% (n=10). The bla(SHV) types included bla(SHV-1), bla(SHV-11), bla(SHV-12), and bla(SHV-27). None of the isolates harbored bla(KPC), bla(LEN), or bla(GES) gene. Four novel variants (bla(OKP-A-13), bla(OKP-A-14), bla(OKP-A-15), and bla(OKP-A-16)) were identified among the 10 OKP β-lactamase-producing K. pneumoniae isolates resistant to ampicillin, amoxicillin, oxacillin, cefalexin, and cefadroxil. Plasmid analysis and PCR amplification indicated that bla(TEM-1) genes were detected in the total plasmid. Molecular typing by pulsed-field gel electrophoresis revealed the presence of 10 distinct pulsotypes of OKP producer isolates. Plasmid DNA digested with XbaI yielded two to six bands of ca. 0.15-30 kb. Transformants of the 10 OKP producer isolates showed no differences in their antibiotic susceptibility, except for the pulsotype B transformant, which carried bla(CTX-M). In China, β-lactam resistance appeared to be common among K. pneumoniae isolates from swine, suggesting that K. pneumoniae may be a reservoir for the dissemination of β-lactam resistance among Chinese pig farms.     

澳洲坚果物理参数试验研究

对澳洲坚果千粒质量、含水率、果实及果仁三径尺寸、壳厚度、壳仁间隙和出仁率等基本物理参数进行了测定.结果表明:在相同条件下,坚果的外形尺寸呈正态分布,63%的果实分布在24~26mm范围内;不同位置果壳厚度差异较大,果壳底部最厚,中部最薄;壳仁间隙为1.20mm.     

轿车性能分析与优化研究

首先对发动机的外特性和万有特性进行研究并建立相应数学模型.其次结合汽车相关理论,阐述计算整车动力性和经济性的一般方法.以动力性和经济模拟计算为基础,根据变速器传动比优化的思路和方法,结合某款实车进行速比优化的工作.模拟计算结果表明,经过优化整车的动力性和经济性都有一定程度的提高.     

Chemical characterization of a procyanidin-rich extract from sorghum bran and its effect on oxidative stress and tumor inhibition in vivo

The present study was to characterize a procyanidin-rich extract (PARE) from sorghum ( Sorghum bicolor (L.) Moench) bran and assess its biological activities. The procyanidin oligomers were separated and identified by normal-phase HPLC equipped with fluorescence (FLD) and mass spectrometry (MS) detectors. In addition, the effects of PARE on oxidative stress in mice induced by D-galactose as well as tumor inhibition in C57BL/6J mice bearing Lewis lung cancer were investigated. Administration of D-galactose significantly (p < 0.05) lowered the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). This was accompanied by a significant (p < 0.05) increase in malondialdehyde (MDA) levels in both liver and serum. Administration of PARE (150 mg/kg) significantly (p < 0.05) reversed the d-galactose-induced oxidative stress by enhancing the activities of antioxidant enzymes. Furthermore, PARE administration inhibited tumor growth and metastasis formation by suppressing vascular endothelial growth factor (VEGF) production. The results suggested that PARE had antioxidant and antitumor activities.