RF-MBE Grown AlGaN/GaN HEMT Structure with High Al Content

A Si doped AlGaN/GaN HEMT structure with high Al content (x=43%) in the barrier layer is grown on sapphire substrate by RF-MBE.The structural and electrical properties of the heterostructure are investigated by the triple axis X-ray diffraction and Van der Pauw-Hall measurement,respectively.The observed prominent Bragg peaks of the GaN and AlGaN and the Hall results show that the structure is of high quality with smooth interface.The high 2DEG mobility in excess of 1260cm2/(V·s) is achieved with an electron density of 1.429×10 13cm -2 at 297K,corresponding to a sheet-density-mobility product of 1.8×10 16V -1·s -1.Devices based on the structure are fabricated and characterized.Better DC characteristics,maximum drain current of 1.0A/mm and extrinsic transconductance of 218mS/mm are obtained when compared with HEMTs fabricated using structures with lower Al mole fraction in the AlGaN barrier layer.The results suggest that the high Al content in the AlGaN barrier layer is promising in improving material electrical properties and device performance.

Cross-Linked Crown Ether-SE-54 as Stationary Phase for Open-Tubular Column Gas Chromatography

The cross-linking of crown ether-SE-54 in fused-silica capillary columns were initiated by dicumyl peroxide(DCUP),azo-bis-isobutyronitrile (AIBN)and ozone(O_3).Parameters of evaluation such as polarity,selectivity, phase transition temperature and thermal stability were studied and compared with those of poly(crown ether)stationary phase.

Treatment of Cough and Dyspnea due to Acute Bronchitis by Plaster for Cough and Dyspnea——A Report of 735 Cases

In the light of the theory of treating the internal disease externally, an externally used plaster for treating cough and dyspnea due to acute bronchitis (Ke Chuan Yi Tie Kang [symbol: see text]-[symbol: see text]) was successfully applied to 735 cases of acute bronchitis (the treatment group), with the other 423 cases treated with routine western drugs as controls. The results showed that the cure rate in the treatment group was significantly higher than that in the control group (P

Sintering technology for micro heat pipe with sintered wick

In order to study reasonable sintering technological parameters and appropriate copper powder size range of micro heat pipe (MHP) with the sintered wick, the forming principle of copper powders in wicks and MHP's heat transfer capabilities were first analyzed, then copper powders with different cell sizes and dispersions were sintered in RXL-12-11 resistance furnace under the protection of the hydrogen at different sintering temperatures for different durations of sintering time, and finally the sintered wicks' scanning electron microscope (SEM) images and their heat transfer capabilities were analyzed. The results indicate that the wick sintered with copper powders of larger cell size or smaller size range has better sintering properties and larger heat transfer capabilities; and that the increase of either sintering temperatures or sintering time also helps to improve the wick's sintering properties and heat transfer capabilities, and the former affects more obviously than the latter. Considering both its manufacturing cost and performance requirements, it is recommended that copper powders with the size range of 140-170 μm are sintered at 900-950℃ for 30-60 min in practical manufacturing. In addition, two approaches to improve wick's porosity are also proposed through theoretical analysis, which suggests that the larger the wick's porosity, the better the heat transfer capabilities of the MHP.

House dust mite allergen Der f enhanced bronchial epithelial cell cytokine expression

The house dust mites (Dermatophagoides farinae, Derf) are the major source of aeroaller gens implicated in the expression of atopic disorders, including asthma, allergic rhinitis and atopic dermatitis. In particular, strong circumstantial evidence suggests that house dust mite antigens are important precipitating factors of asthma. Many house dust mite allergens are proteases that can elicit airway inflammation by stimulating the release of cytokines from bronchial epithelial cells. To investigate whether Der f allergen proteases induced cytokine production from the epithelial cell line BEAS-2B, BEAS-2B cells were cultured with 4 different concentrations of Derf (0.02, 0.2, 2, 20μg/ml) for 24-96 h, after which supernatants were assayed for interleukin (IL)-6 and IL-8 with ELISA. Reverse transcription-PCR was also performed. The cell sheets were intact throughout the observation in control group without any exposure to Der f antigen. In the experimental groups cells treated with Der f allergen showed changes in the anchorage status of the monolayer. There was a significant increase in the level of cytokine production compared with the untreated sample. The release of IL-6 and IL-8 increased in a concentration-dependent manner (P <0.05, respectively) with the addition of increasing dosage of Der f to the cell sheets. Levels of IL-6 and IL-8 began to rise at 24 h and 48 h after allergen exposure, and they increased significantly in the supematants at 72 h and 96 h. At the same time the concentration dependence of induction of IL-6 and IL-8 expression as well as an increase in the expression of IL-6 and IL-8 mRNA manifested evidently. HDM-induced airway inflammation may include Der f-mediated release of inflammatory mediators, and the proteolytic activity of an allergen may stimulate the release of proinflammatory cytokines from human bronchial epithelium. It is suggested that IL-6 and IL-8 production by bronchial epithelial cells may play a role in the pathogenesis of allergic asthma.

CIRCULATING INTERCELLULAR ADHESION MOLECULE 1 LEVELS IN SERA OF BRONCHIAL ASTHMA

Objective The aim of the study was to determine whether bronchial asthma was associated with increased levels of soluble intercellular adhesion molecule 1(sICAM 1) in serum, which might be valuble data for the effective therapy of these patients Patients and methods The concentrations of sICAM 1 were determined in sera of healthy donors and asthmatic patients using a sensitive enzyme immunoassay Results The mean(±SD) levels of serum sICAM 1 of 26 asthmatic patients (205±72 0 μg/L)was significantly higher than that of the 30 healthy volunteers (154±63 9 μg/L,P<0 01) There was no much difference between the serum levels in 12 patients suffering from atopic asthma and the levels in 14 patients with nonatopic asthma The serum concentrations of sICAM 1 were higher during asthma attacks than that during remissions in the same patients (P<0 05) Conclusion These results suggest that sICAM 1 may play a certain role in the pathophysiology of bronchial asthma,and might be signals for successful treatment

Cloning and polymorphism analysis of IL-4 proximal promoter in asthmatic children

OBJECTIVE: To clone and study the polymorphism within interleukin-4 (IL-4) proximal promoter of asthmatic children. METHODS: The IL-4 proximal promoter segments were amplified and selected by polymerase chain reaction (PCR) and single strand conformation polymorphism (SSCP) with genomic DNA from ten healthy children and forty patients with dominantly allergic familial histories as templates. The selected PCR segments were cloned into recombinant plasmids pIL-4-Jx2. The PCR inserts were sequenced by dideoxy chain termination method. RESULTS: Seven aberrant bands were found in SSCP analysis from forty asthmatic patients. The sequencing results showed that four variant sites were found within or adjacent to the known IL-4 regulatory element. A C to A transversion located at -229 position was just within the positive regulatory element-I (PRE-I) in one patient. A C to T transition adjacent to the negative regulatory element-II (NRE-II) and an extra G adjacent to TATA box were found in two patients. A five base nucleotide deletion was found near signal transducers and activators of transcription-6 responsive element (STAT-6 RE) in one patient. CONCLUSION: There were polymorphisms within the IL-4 proximal promoter of allergic asthmatic patients and these polymorphisms might result in aberrant expression of IL-4 gene and asthma.

自行车

老年人爱回忆。工作之余,我总是爱回忆。有时候想得出神入化,生怕别人打乱。今天我突然想到了自行车的事,掐指一算,从我拥有第一辆自行车开始,总共换了21台。1949年解放以后,我15岁,就迷恋上自行车了。

Alteration of surfactant proteins A and D in bronchoalveolar lavage fluid of pneumocystis carinii pneumonia

Objective To understand the interaction between surfactant proteins and pneumocystis carinii pneumonia (PCP),and the impact of corticosteriods on surfactant proteins.Methods We established rat models of PCP and bacterial pneumonia induced by subcutaneous injection of 25mg cortisone acetate.At 8- 12 wk,the bronchoalveolar lavage fluid(BALF)of rats was collected.Total nucleated cells of BALF were counted and differentiated,and the concentrations of surfactant protein A(SP-A)and surfactant protein D(SP-D)were measured by immunoblotting assay.The rats were divided into three immunosuppressive groups and a normal control group.Group I,normal control(n = 6),consisted of healthy SD rats;group Ⅱ,negative control(n = 6),consisted of rats with cortisone acetate injection for over 8 wk without lung infection;group Ⅲ,bacterial pneumonia(n = 11),rats were injected with cortisone acetate over 8 wk that resulted in bacterial pneumonia without other pathogens isolated;and group Ⅳ,PCP(n = 14),rats with injected cortisone acetate for 8 - 12 wk and developed PCP without other pathogens isolated.Results Our results indicated that the total cell count in BALF in the negative control group was lower than that in the normal control group(P ＜ 0.001).During PCP infection,the total cell count and the percentage of polymorphonuclearcytes(PMNs)in BALF were significantly increased(P ＜ 0.01),but were lower than those in the bacterial pneumonia group.The concentration of SP-A of BALF in PCP(45.1 ± 22.1 μg/ml)was significantly increased in comparison with that in the negative control(16.2 ± 9.9 μg/ml,P ＜ 0.05)and bacterial pneumonia groups(6.2 ± 5.6 μg/ml,P ＜ 0.001).We also found that the relative content of SP-D was significantly higher in PCP(24249 ±4780 grey values)than that in the negative control (13 384 ± 2887 grey values,P ＜ 0.001)and that in bacterial pneumonia(11 989 ± 2750 grey values,P＜0.001).SP-A and SP-D were also higher in the moderate to heavy group of PCP than those seen in the mild group(P ＜ 0.01,P ＜ 0.001).SP-A and SP-D were higher in the negative control group than those in the normal control group,but there was no significant difference between the 2 groups.Conclusion These results suggest that the concentrations of SP-A and SP-D in BALF are increased by pneumocystis carinii specific stimulation,but the alteration is not related to the corticosteriod usage.

Nuclear factor-κB in signal conduction of protein kinase C in T lymphocytes from an asthmatic guinea pig model

Objective To explore the role of nuclear factor κB (NF κB) in the signal conduction of protein kinase C (PKC) regulated proliferation, apoptosis and expression of Th2 cytokines - interleukin 4 (IL 4) and interleukin 5 (IL 5) of T lymphocytes in the bronchial alveolus lavage fluid (BALF) Methods T lymphocytes were isolated and purified from BALF of asthmatic guinea pigs in normal and asthmatic groups, and were stimulated with PKC agitator phorbol 12 myristate 13 acetate (PMA) and NF κB inhibitor pyrrolidine dithiocarbamate (PDTC), respectively The expressions of NF κB, IL 4 and IL 5 mRNA and protein, the proliferation and apoptosis of T lymphocytes were observed by immunohistochemistry, in situ hybridization, ELISA, MTT and TUNEL, respectively Results The activation of NF κB, proliferation response, and expression of IL 4 and IL 5 mRNA and protein in T lymphocytes stimulated by PMA were significantly higher than those of their blank control ( P 【0 01), while those indexes of T lymphocytes stimulated by PMA and PDTC simultaneously were significantly lower than those stimulated by PMA alone ( P 【0 01) The apoptotic index of T lymphocytes stimulated with PMA were significantly lower than that of their blank control ( P 【0 01), and the apoptotic index of asthmatic guinea pig T lymphocytes stimulated with PMA and PDTC simultaneously were significantly higher than that stimulated by PMA alone ( P 【0 01) The significant positive correlations were found between the activation of NF κB and the proliferation ( r =0 64, P 【0 001), and the expression of IL 4 and IL 5 mRNA and protein of T lymphocytes, respectively ( r =0 55-0 68, P 【0 001) There was also significant negative correlation between the activation of NF κB and apoptosis of T lymphocytes ( r =0 62, P 【0 001) Conclusions NF κB may participate in the signal conduction of PKC regulated proliferation, apoptosis and expression of IL 4 and IL 5 of T lymphocytes in asthma The activation of NF κB in PKC signal conduction pathway of T lymphocytes may play an important role in the pathogenesis of asthma

A 92-year-old man with retropharyngeal hematoma caused by an injury of the anterior longitudinal ligament

Traumatic retropharyngeal hematoma is a rare condition and may be lethal in some cases. In patients with this condition, the absence of a vertebral fracture or a major vascular injury is extremely rare. We present the case of a 92-year-old man who hit his forehead by slipping on the floor in his house. He had no symptoms at the time; however, he experienced throat pain and dyspnea at 6 hours after the injury. On arrival, he complained of severe dyspnea; therefore, an emergency endotracheal intubation was performed. A lateral neck roentgenogram after intubation showed dilatation of the retropharyngeal and retrotracheal space and no evidence of a cervical vertebral fracture. Cervical computed tomography （CT） with contrast medium revealed a massive hematoma extending from the retropharyngeal to the superior mediastinal space but no evidence of contrast medium extravasation or a vertebral fracture. However, sagittal magnetic resonance imaging （MRI） revealed an anterior longitudinal ligament （C4-5 levels） injury. We determined that the cause of the hematoma was an anterior longitudinal ligament injury and a minor vascular injury around the injured ligament. Therefore, we recommend that patients with retropharyngeal hematoma undergo sagittal cervical MRI when roentgenography and CT reveal no evidenee of injury.

Synthesis and acetone gas sensing properties of α-Fe_2O_3 nanotubes

α-Fe2O3 nanotubes was successfully prepared by single nozzle electrospinning method. Scanning electron microscope （SEM） was used to characterize the morphology of α-Fe2O3 nanotubes. The gas sensing properties of α-Fe2O3 nanotubes were investigated in detail. The results exhibit relatively good sensing properties to acetone at 240℃. The response and recovery times are about 3 and 5 s, respectively. The structure of nanotubes is beneficial to the gas sensing properties, which will enlarge the surface-to-volume ratio of α-Fe2O3 and then be available for the transfer of gas, and thus improved the sensor performance consequentially.

The effect of MWCNTs on the performance of α-sexithiophene OTFT device and its gas-sensing property

In this paper,bottom contact organic thin-film transistor(OTFT)gas sensors were prepared.Silicon dioxide(SiO2)and titanium/aurum(Ti/Au)were used as the insulating layer and the electrode for the device,respectively.The multi-walled carbon nanotubes(MWCNTs)/α-sexithiophene(α-6T)bilayer films were used as the active layer,andα-6T single layer sensitive film was also prepared for comparison purpose.The electrical and trace NO2-sening properties of these two OTFT gas sensors were tested and analyzed.The results showed that,the OTFT device based on MWCNTs/α-6T bilayer had obviously better electrical properties,better stabilities and higher NO2-sening response values than the device withα-6T single layer,in which both the carrier mobility(μ)and on/off current ratio enhanced two order of magnitude.The improved performance of bilayer OTFT can be explained that MWCNTs acted as highly conducting bridges connecting the crystalline terraces in theα-6T film.Threshold voltage(VT),carrier mobility,on/off current ratio and grid current which showed extremely similar variation trend as source-drain current,were optional parameters to reveal the gas-sensing characteristic of OTFT gas sensors.Morphology analysis showed that the special feature of MWCNTs had certain influence on the gas-sensing properties.

The effects of proton irradiation on the electrical properties of NbAlO/AlGaN/GaN MIS-HEMT

AlGaN/GaN metal-insulator-semiconductor high electron-mobility transistors （MIS-HEMTs） with atomic layer deposited （ALD） NbA10 gate dielectric were investigated using 3 MeV proton irradiation at a fluence of 1015 p/crn2. It was found that the proton irradiation damage caused degradation in DC performance and a flatband voltage shift in the capacitance-voltage curve. Gate-drain conductance measurements indicated that new traps were introduced in GaN from the irradiation, and the trap densities increased from 1.18×10^12 cm-2.eV-1 to 1.82×10^12 cm-2.eV-1 in MIS-HEMTs after irradiation. However, these increases in trap densities caused by irradiation in MIS-HEMT are less than those in HEMT, which can be attributed to the protection of the A1GaN surface by the NbA10 dielectric layer.