Formation of TiSi2 During Rapid Thermal Annealing: In Situ Resistance Measurements at Heating Rates From 1°C/S to 100°C/S

In VLSI technology, there is interest in monitoring the sequence of phase formation of TiSi2 (c-Ti ⇒ a-TiSi ⇒ C49 TiSi2 ⇒ C54 TiSi2), with the prospect of reducing the temperature of formation of the stable C54 TiSi2 phase. In this study, phase formation characteristics of TiSi2 during rapid thermal annealing(RTA) of Ti-Si bilayers are investigated by means of in situ four point probe resistance measurements. Ex situ X-ray diffraction(XRD) was used for phase identification and characterization. Results indicate that the same multi-step sequence of transformations precede the formation of the C54 TiSi2 phase for heating rates from 1°C/s to 100°C/s. Also, all intermediate and metastable phases which occur at l°C/s also occur at 100°C/s. Temperature dependence and kinetics of the C49 TiSi2 and the C54 TiSi2 phase formation were studied over a wide range of heating rates. Activation energies estimated for the two processes were ∼2eV and ∼5eV respectively. Finally, a new Electrical Thermal Annealing(ETA) technique for heating at rates up to 30000°C/s is introduced. Preliminary in situ resistivity measurement results of TiSi2 formation at these high heating rates are also presented.

Interdiffusion and Phase Relations in Ti-Aluminide/NB/Ti-Aluminide Composite Structures

We have studied interdiffusion and phase relations in two titanium aluminide/Nb/titanium aluminide composite structures at 1100 °C using solid state diffusion approach. The composite structures were prepared with two practical intermetallic alloys, γ (Ti-48Al-2Nb-0.3Ta, in at.%) alloy and super-α2 (Ti-25Al-10Nb-3V-1Mo, in at.%) alloy, and pure Nb sheet by diffusion bonding technique. The interfacial microstructures evolved during thermal diffusion annealing were characterized using optical microscopy, SEM, TEM and X-ray diffraction. The effect of Nb on the phase stabilities of two intermetallic alloys and the phase relations among different phases formed in the diffusion zone due to interdiffusion were analyzed in terms of rules of diffusion paths on the basis of the observed diffusion structures and experimental diffusion paths.

Microstructure Control for Thin Film Metallization

A strategy was developed for controlling hillock formation in thin metal films by controlling the fiber texture to be of a relatively “weak” orientation. Two-dimensional molecular dynamics (MD) simulations were performed to determine the parameter dependencies of texturing under ion beam assisted deposition. Simulations showed that even for film orientations that have a lower number of nearest neighbor surface bonds, the reduction in sputtering rate by ion channeling will favor the growth of the grains aligned with their channeling direction in the direction of the ion beam. Higher energies should result in greater sputtering and a higher surface roughness. Confirmatory experiments were performed by growing Al films using ion beam assisted deposition in which the Ne ion beam was normal to the substrate surface. For all energies above 0 eV/atom, the fiber texture contained a (220) component and, at high normalized energies, the fiber texture was heavily (220) dominated. Subsequent annealing at 450°C for 30 min. resulted in hillock formation in the PVD (physical vapor deposition) condition, a reduction in the hillock density by two orders of magnitude in the 120 eV/atom condition and complete elimination of hillocking above 800 eV/atom. Although the surface roughness increased with ion beam energy as modeled by MD, the surface became smoother during annealing. These results show that the fiber texture can be controlled in a thin metal film in such a way as to eliminate hillock formation, that molecular dynamics simulation is a valuable predictive tool for guiding experiments in the development of thin film microstructures and that ion beam assisted deposition is an effective, practical tool for controlling microstructures of thin metal films.

Structural features of the 5’ flanking region of the Yak (Bos grunniens) growth hormone receptor (GHR) gene (Brief Report)

Abstract. Yak (Bos grunniens) is a species of the Bovidae family living on the Qinghai-Tibetan Plateau and its adjacent territories at altitudes from 2 000–5 000 m (LUO et al. 2005, MA et al. 2009). As a multi-purpose domestic animal, yaks are indispensable to the local animal husbandry development because it can provide life necessities such as meat, milk, fur, velour manufacturing, transportation and manure for fuel to the local herdsmen. There are twelve yak populations numbered around 13.3 million in China and the Bazhou yak is one of Chinese yak populations (WIENER et al. 2003). The Growth Hormone Receptor (GHR) gene was identified as a candidate gene affecting key quantitative traits, like growth, milk yield and composition in livestock. At present, only investigations were carried out on the genetic variation in Exon-8, Intron-8 and Exon-10 of the yak GHR gene (VARVIO et al. 2008), no other information on the yak GHR gene is available. The purposes of this study were to – analyze the structural features of the 5’ flanking region of the yak GHR gene – compare the 5’ flanking region of yak GHR gene with that of other species of the Bovidae family and – construct the phylogenetic tree to indicate the evolutionary relationship among them.

p66(Shc) restrains Ras hyperactivation and suppresses metastatic behavior

Normal tissue cells survive and proliferate only while anchored to solid substrate. Conversely, transformed cells both survive and proliferate following detachment, having lost attachment context through unclear mechanisms. p66(Shc) is a focal adhesion-associated protein that reports cell attachment through a RhoA-dependent mechanosensory test. We find that human small cell lung cancer (SCLC) cells and mouse Lewis lung carcinoma (LLC), which display aggressive metastatic behavior, lack both p66(Shc) and retinoblastoma (pRB) and bypass anoikis. Re-expression of p66(Shc) in these cells restores anoikis and provides striking protection from metastasis by LLC cells in vivo. Notably, knockdown of p66(Shc) in normal epithelial cells leads to unrestrained Ras activation, preventing anoikis through downstream suppression of RhoA but blocking proliferation in a pRB-dependent manner, thus mimicking oncogenic Ras. Conversely, LLC and SCLC cells display constitutive Ras activation necessary to bypass anoikis, which is reversed by re-expression of p66(Shc). p66(Shc) therefore coordinates Ras-dependent control of proliferation and anchorage sensation, which can be defeated in the evolution of highly metastatic tumors by combined loss of both p66(Shc) and pRB.

Genotyping of the polymorphism within exon 1 of <i>Hormone Sensitive Lipase (LIPE)</i> Gene in three Chinese Yak (<i>Bos grunniens</i>) breeds by PCR-RFLP (Brief Report)

Abstract. The yak (Bos grunniens), a herbivore living on the Qinghai-Tibetan Plateau and its adjacent territories, is one of world’s most remarkable domestic animals. Over the past decades, research has been done on properties of yak meat at physiological and biochemical levels. In recent years, some candidate genes associating with meat quality and lipid metabolism in yak have been studied (MA et al. 2007, ZHONG et al. 2007). The Hormone Sensitive Lipase (LIPE) gene has been regarded as a candidate gene associating with lipid metabolism and meat quality. Several studies have reported the genetic variations in the LIPE genes of human and pig (TALMUD et al. 1998, KNOLL et al. 1998, WU et al. 1998, HARBITZ et al. 1999), whereas the yak LIPE gene polymorphism has not been investigated and no information is available. The aim of this study was to identify and characterize the genetic variation in Chinese yak LIPE at the DNA sequence level and genotyping of the polymorphism within LIPE in different yak breeds.

Engineered Saccharomyces cerevisiae that produces 1,3-propanediol from D-glucose

AIMS

Saccharomyces cerevisiae is a safe micro-organism used in fermentation industry. 1,3-Propanediol is an important chemical widely used in polymer production, but its availability is being restricted owing to its expensively chemical synthesis. The aim of this study is to engineer a S. cerevisiae strain that can produce 1,3-propanediol at low cost.

METHODS AND RESULTS

By using D-glucose as a feedstock, S. cerevisiae could produce glycerol, but not 1,3-propanediol. In this study, we have cloned two genes yqhD and dhaB required for the production of 1,3-propanediol from glycerol, and integrated them into the chromosome of S. cerevisiae W303-1A by Agrobacterium tumefaciens-mediated transformation. Both genes yqhD and dhaB functioned in the engineered S. cerevisiae and led to the production of 1,3-propanediol from D-glucose.

CONCLUSION

Saccharomyces cerevisiae can be engineered to produce 1,3-propanediol from low-cost feedstock D-glucose.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our knowledge, this is the first report on developing S. cerevisiae to produce 1,3-propanediol by using A. tumefaciens-mediated transformation. This study might lead to a safe and cost-efficient method for industrial production of 1,3-propanediol.

Molecular characterization of toxigenic and atoxigenic Aspergillus flavus isolates, collected from peanut fields in China

AIMS

The objectives of this study were to assess the genetic relationships between toxigenic and atoxigenic isolates of Aspergillus flavus collected from peanut fields in China, and to analyse deletions within the aflatoxin biosynthetic gene cluster for the atoxigenic isolates.

METHODS AND RESULTS

Analysis of random-amplified polymorphic DNA and microsatellite-primed PCR data showed that the toxigenic and atoxigenic isolates of A. flavus were not clustered based on their regions and their ability of aflatoxin and sclerotial production. These results were further supported by DNA sequence of ITS, pksA and omtA genes. PCR assays showed that 24 of 35 isolates containing no detectable aflatoxins had the entire aflatoxin gene cluster. Eleven atoxigenic isolates had five different deletion patterns in the cluster.

CONCLUSIONS

Toxigenic and atoxigenic isolates of A. flavus are genetically similar, but some atoxigenic isolates having deletions within the aflatoxin gene cluster can be identified readily by PCR assays.

SIGNIFICANCE AND IMPACT OF THE STUDY

Because the extensive deletions within the aflatoxin gene cluster are not rare in the atoxigenic isolates, analysis of deletion within the cluster would be an effective method for the rapid screening of atoxigenic isolates for developing biocontrol agents.

Plasminogen activator inhibitor-1 and asthma: role in the pathogenesis and molecular regulation

Plasminogen activator inhibitor (PAI)-1 is a major inhibitor of the fibrinolytic system. PAI-1 levels are markedly increased in asthmatic airways, and mast cells (MCs), a pivotal cell type in the pathogenesis of asthma, are one of the main sources of PAI-1 production. Recent studies suggest that PAI-1 may promote the development of asthma by regulating airway remodelling, airway hyperresponsiveness (AHR), and allergic inflammation. The single guanosine nucleotide deletion/insertion polymorphism (4G/5G) at -675 bp of the PAI-1 gene is the major genetic determinant of PAI-1 expression. Plasma PAI-1 level is higher in people with the 4G/4G genotype than in those with the 5G/5G genotype. A strong association between the 4G/5G polymorphism and the risk and the severity of asthma has been suggested. Levels of plasma IgE and PAI-1 and severity of AHR are greater in asthmatic patients with the 4G/4G genotype than in those with the 5G/5G genotype. The PAI-1 promoter with the 4G allele renders higher transcription activity than the PAI-1 promoter with the 5G allele in stimulated MCs. The molecular mechanism for the 4G allele-mediated higher PAI-1 expression is associated with greater binding of upstream stimulatory factor-1 to the E-box adjacent to the 4G site (E-4G) than to the E-5G. In summary, PAI-1 may play an important role in the pathogenesis of asthma. Further studies evaluating the mechanisms of PAI-1 action and regulation may lead to the development of a novel prognostic factor and therapeutic target for the treatment and prevention of asthma and other PAI-1-associated diseases.

Characterization of sterol demethylation inhibitor-resistant isolates of Fusarium asiaticum and F. graminearum collected from wheat in China

Fusarium asiaticum and F. graminearum are the primary causal agents of Fusarium head blight (FHB) of wheat in China. In this study, sensitivities of 159 F. asiaticum and F. graminearum isolates to a benzimidazole fungicide carbendazim (MBC) and to sterol demethylation inhibitors (DMIs) tebuconazole and prochloraz were determined. Among the 159 isolates, 9 were resistant to MBC and designated as MBC-R isolates. Three showed resistance to tebuconazole and prochloraz and designated as DMI-R isolates. There was no cross-resistance between MBC and DMI. Genetic analysis by microsatellite-primed polymerase chain reaction (PCR) showed that MBC-R or DMI-R isolates had different genotypes, which indicated that they originated from different wild-type parents. Analysis of two 14alpha-demethylase (cyp51) homologous genes (cyp51A and cyp51B) showed that the F. asiaticum isolates could be distinguished from F. graminearum isolates based on the sequence of cyp51A. Analysis of deduced amino acid sequence of cyp51A and cyp51B suggested that no mutations were associated with DMI resistance. Real-time PCR analysis showed that the DMI resistance was not related to the expression of cyp51A and cyp51B in F. asiaticum and F. graminearum, but expressions of both genes were induced greatly by the tebuconazole. Results of this study indicated that cyp51A would be an informative marker for analysis of population structure of F. asiaticum and F. graminearum, and the existence of homologous cyp51 genes in F. asiaticum and F. graminearum could provide new insights into DMI resistance in phytopathogenic fungi.

Simultaneous detection of Fusarium asiaticum and Fusarium graminearum in wheat seeds using a real-time PCR method

AIMS

To develop a PCR-based method for quantitative detection of Fusarium asiaticum (Fa) and Fusarium graminearum (Fg) in wheat seeds.

METHODS AND RESULTS

Based on the sequences of the cyp51A gene, two primer pairs FaF + FaR and FgF + FgR were developed for the species-specific detection of Fa and Fg, respectively. To simultaneously detect these two phylogenetic species, a pair of primers FgaF + FgaR was developed based on the first and the second introns of beta-tubulin gene. This primer pair amplified a 228-bp fragment only from Fa and Fg isolates, but not from 22 other Fusarium spp. and 13 other fungal species. A real-time PCR with this primer pair was able to quantify minute amounts of Fa and Fg DNA in wheat seeds rapidly.

CONCLUSIONS

PCR primers designed based on the sequence of cyp51A or intron region of beta-tubulin gene could allow differentiation of genetically related fungal species.

SIGNIFICANCE AND IMPACT OF THE STUDY

The sensitive and quantitative detection method can be readily used in epidemiological studies and in assessing risk of Fusarium mycotoxin contamination in wheat samples.

Management of delayed intrathoracic esophageal perforation with modified intraluminal esophageal stent

In this article, we reviewed our experience of treatment of the delayed intrathoracic nonmalignant esophageal perforation employing modified intraluminal esophageal stent. Between February 1990 and August 2006, eight patients were included in this study. Five patients experienced sepsis. The interval time between perforation and stent placement ranged from 36 h to 27 days (average, 8.6 days). Esophageal stenting and throracotomy for foreign body removal were performed in four patients. The remaining four patients underwent stent placement and thoracostomy. Nutrition was initiated through gastrostomy after 7 to 10 days after the stenting. The stent was removed after the patients resumed oral intake of food and the esophagogram showed that perforation was closed. There was no death in this group. Signs of sepsis remitted 1 week after stent placement. Complications included stress ulcer, stimulative cough, and pneumonia each. Stent removal ranged 32 to 120 days (average 66.7) after its placement. The stent was kept in place for 4 months to prevent formation of esophageal stricture in one patient with caustic esophageal burns. The follow-up was completed in all the patients. The mean follow-up period was 59 months (range 12-180). One patient with caustic esophageal burn underwent cicatricial esophagectomy and gastric transposition 3 years later due to the esophageal stricture. Barium swallow demonstrated that there was a diverticulum-like outpouching in one patient and slight esophageal stricture at T2 and T3 level in another. One patient developed reflux esophagitis 5 years after stent removal. All the patients finally had a normal intake of food. Modified esophageal stenting is an effective method to manage the delayed intrathoracic esophageal perforation. Prevention of stent migration and its convenient adjustment might be the major advantages of this method.