We have studied the effects of proton irradiation on the AlGaN/GaN HEMTs with AlN buffer layer as well as conventional GaN buffer layer. It was found that a short time proton irradiation (~ 50 sec) can promote beneficial effects on device performances, which results in great reduction in the off-state leakage current and the gate leakage current without degrading the output current and transconductance. The pulsed I-V measurement demonstrated that both devices exhibit greatly improved current dispersion characteristics and, particularly, the device with AlN buffer layer shows stronger radiation hardness than that of the device with GaN buffer layer. These interesting results are believed to be due to the hydrogen passivation with thermal annealing effect during the proton irradiation. It is expected that the proper irradiation condition such as fluence, energy, and time is crucial to improve the device performances, rather than to deteriorate the performances.
Background: Chronic obstructive pulmonary disease(COPD) is categorized by the percentage of the predicted FEV1(Forced expiratory volume in 1 second) result which is highly correlated with disease severity(morbidity and mortality).In COPD patients, dyspnea seems to be different from disease severity.We investigated whether dyspnea is correlated with disease severity, as measured by FEV1, quality of life(QoL), occupation, and supporting level of family members and neighbors.Method: Thirty-six clinically stable patients with chronically irreversible airflow limitation were enrolled.We used the Medical Research Council(MRC) dyspnea scale to assess the level of dyspnea and the Korean St. Goerge's respiratory questionnaire(SGRQ) as measure the QoL.Result: The mean percentage of the predicted FEV1 was 32.0%.Dyspnea was not correlated with GOLD stage using FEV1(p=0.114).With deteriorating level of dyspnea the scores of symptoms(p=0.041),activity(p=0.004),impact(p=0.001), and total SGRQ score(p<0.001)were significantly increased.Dyspnea was not correlated with the level of occupation(p=0.259).The supporting level of family members and neighbors was significantly negatively correlated with dyspnea scale(p=0.011). Conclusion:In the management of COPD patients, we have to remember that the level of subjective dyspnea is correlated with QoL(symptom, activity and impact on society) and social supporting level as well as GOLD stage(FEV1).
Background: Pleural effusion develops in approximately 40% of pneumonia patients. In 5-10% of these cases, it progresses to complicated parapneumonic effusion (CPPE) or empyema that requires drainage. The prognostic factors of CPPE and empyema remain to be clarified. We examined the treatment outcomes of CPPE and empyema and elucidating their prognostic factors. Methods: One hundred and fifteen patients with CPPE or empyema, who were diagnosed and treated in Kyungpook National University Hospital (Daegu, Korea) between September 2001 and December 2005, were retrospectively analyzed. All the data was acquired from their chart review, and regarding treatment results, the time to defervescence and the length of hospital stay were analyzed. Results: The treatment was successful in 101 patients with a success rate of 87.8%. Multivariate analysis showed the level of pleural fluid lactate dehydrogenase (LDH) to be a significant prognostic factor (odds ratio [OR] 7.37; 95% confidence interval [CI], 1.63 to 33.37; p=0.009). Pussy pleural fluid (r=0.236; p=0.01) and the frequency of urokinase use (r=0.257; p=0.01) correlated with the time to defervescence. However, there was no clinical factor that correlated with the length of hospital stay. Conclusion: The pleural fluid LDH level is a useful prognostic factor for monitoring treatment results of CPPE and empyema.
Tuberculous pleural effusion (TPE) leads to residual pleural opacity (RPO) in a significant proportion of cases. The aim of this study was to investigate which TPE patients would have RPO following the treatment. This study was performed prospectively for a total of 60 TPE patients, who underwent pleural fluid analysis on the initial visit and chest radiographs and computed tomography (CT) scans before and after the administration of antituberculous medication. At the end of antituberculous medication, the incidence of RPO was 68.3% (41/60) on CT with a range of 2-50 mm. Compared with the non-RPO group, the RPO group had a longer symptom duration and lower pleural fluid glucose level. On initial CT, loculation, extrapleural fat proliferation, increased attenuation of extrapleural fat, and pleura-adjacent atelectasis were more frequent, and parietal pleura was thicker in the RPO group compared with the non-RPO group. By multivariate analysis, extrapleural fat proliferation, loculated effusion, and symptom duration were found to be predictors of RPO in TPE. In conclusion, RPO in TPE may be predicted by the clinico-radiologic parameters related to the chronicity of the effusion, such as symptom duration and extrapleural fat proliferation and loculated effusion on CT.
We have successfully grown AlGaN/GaN high electron mobility transistor (HEMT) structure on the high-quality undoped thick AlN buffer layer with large band offset to replace the conventional high-resistivity GaN buffer layer. The AlGaN/GaN HEMT fabricated on this AlN buffer layer exhibits low OFF-state leakage current with high I \scriptscriptstyle ON /I \scriptscriptstyle OFF of ~ 10 6 due to enhanced confinement of the electrons in the 2-D electron gas (2-DEG) channel. The undoped AlN buffer layer is responsible for suppressing the trapping effects to greatly reduce the current dispersion in pulsed I \text D - V \text D characteristics, which is hardly avoided in conventional deep acceptor-doped GaN buffer layer. The device also demonstrates high breakdown voltage of 2154 V with very high figure of merit (FOM) of ~1.8 GV $^{2-1}$ cm $^{-{2}}$ , one of the highest ever reported, suggesting that the AlGaN/GaN-based Hemts WITH AlN buffer layer are promising for high-performance RF and power applications.
In this work, threshold voltage modulation realized by adjusting fin width and dielectric layer were investigated through MIS-FinFETs. As fin width decreases from 120 to 30 nm, threshold voltage shifts toward positive direction and finally becomes positive value while maintaining SS smaller than 60 mV/dec. The phenomenon of achieving sub-60 mV/dec characteristics were illustrated by simulation and the concept of effective channel length. As for dielectric layer, by 20 nm-thick SiO 2 dielectric layer, device with fin width of 90 nm exhibits a threshold voltage of -0.5 V with SS as small as 50 mV/dec. Even when fin width is 30 nm, drain leakage is still not small enough when VG = 0, which indicates that the gate is not able to totally deplete the fin structure. In order to further increase threshold voltage and enhance the gate controllability, by 10 nm-thick Al 2 O 3 dielectric layer, a threshold voltage of 2 V is achieved when fin width is 40 nm with SS as small as 52 mV/dec due to the higher dielectric constant and thinner thickness of Al 2 O 3 compared with SiO 2 . Therefore, by the modulation of fin width, dielectric layer type, and dielectric thickness, threshold voltage can be carefully designed according to the application requirements while maintaining SS below 60 mV/dec.
The effects of interface charges on the performances of gate-all-around (GAA) GaN vertical nanowire MOSFETs with different geometries have been studied. Geometrical effect on the gate current of vertical GAA GaN nanowire MOSFET has also been analysed for the first time. In the ideal condition, the circular geometry nanowire (CGN) MOSFET exhibits the best performance with subthreshold swing (SS) of 62 mV/dec, drain-induced barrier lowering (DIBL) of 14 mV/V, and ON/OFF current ratio ( I ON /I OFF ) of ~10 8 . The triangular or hexagonal geometry nanowire (TGN or HGN) MOSFET suffer from large gate leakage current due to the field enhancement at sidewall corners. It is also known that interface traps at the sidewall surface of vertical nanowires deteriorate the overall device performance. The HGN MOSFET with m-plane sidewall demonstrates the best performance with SS of 69 mV/dec and DIBL of 13 mV/V, while the TGN MOSFET with a-plane sidewall exhibits the worst performance with SS of 112 mV/dec and DIBL of 101 mV/V.
The transforms of two oriented parallel strands to a k-half twist of two strands are called t k -move and [Formula: see text]-move respectively depending on the orientations of the two strands. In this paper we give criterions to detect whether a knot K can be transformed to a knot K' by t 2k -moves and [Formula: see text]-moves respectively and if so, we give some results on how many moves are needed in these transformations respectively, by using some Vassiliev invariants. Moreover we give a relation between the Δ-move and the t 2k -move by considering the coefficient of z 2 in the Conway polynomial of a knot, which is a Vassiliev invariant of degree 2.
A search for pair production of fourth-generation sequential leptons in ${e}^{+}{e}^{\ensuremath{-}}$ annihilation at a center-of-mass energy $\sqrt{s}=56$ GeV is reported. Event topologies corresponding to the cases where one particle decays leptonically while the other decays hadronically as well as those where both particles decay hadronically were explored. We set a 95%-confidence-level lower limit of 27.6 GeV/${\mathit{c}}^{2}$ for the mass of a fourth-generation lepton.
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