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We present experimental and numerical investigations of high-energy mid-infrared filamentation with multi-octave-spanning supercontinuum generation (SCG), pumped by a 2.4 μm, 250 fs Cr:ZnSe chirped-pulse laser amplifier. The SCG is demonstrated in both anomalous and normal dispersion regimes with YAG and polycrystalline ZnSe, respectively. The formation of stable and robust single filaments along with the visible-to-mid-infrared SCG is obtained with a pump energy of up to 100 μJ in a 6-mm-long YAG medium. To the best of the authors’ knowledge, this is the highest-energy multi-octave-spanning SCG from a laser filament in a solid. On the other hand, the SCG and even-harmonic generation based on random quasi-phase matching (RQPM) are simultaneously observed from the single filaments in a 6-mm-long polycrystalline ZnSe medium with a pump energy of up to 15 μJ. The numerical simulations based on unidirectional pulse propagation equation and RQPM show excellent agreement with the measured multi-octave-spanning SCG and even-harmonic generation. They also reveal the temporal structure of mid-infrared filaments, such as soliton-like self-compression in YAG and pulse broadening in ZnSe.
The Sewol ferry disaster is one of the most tragic events in Korea’s modern history. Among the 476 people on board, which included Danwon High School students (324) and teachers (14), 304 passengers died in the disaster (295 recovered corpses and 9 missing) and 172 survived. Of the rescued survivors, 72 were attending Danwon High School, located in Ansan City, and residing in a residence nearby. Because the students were young, emotionally susceptible adolescents, both the government and the parents requested the students be grouped together at a single hospital capable of appropriate psychiatric care. Korea University Ansan Hospital was the logical choice, as the only third-tier university-grade hospital with the necessary faculty and facilities within the residential area of the families of the students. We report the experiences and the lessons learned from the processes of preparing for and managing the surviving young students as a community-based hospital. (Disaster Med Public Health Preparedness. 2017;11:389–393)
Blackberry is a fruiting berry species with very high nutrient contents. With the recent increasing consumer demand for blackberries, new sources of germplasm and breeding techniques are required to improve blackberry production. This study was carried out to evaluate the genetic diversity (GD) and relationship among 55 blackberry (Rubus fruticosus) mutants derived from γ-ray treatment (52 lines) and N-methyl-N′-nitrosourea (MNU) treatment (three lines) using an inter-simple sequence repeat marker. A total of 18 bands were amplified with an average of 3.6 bands per primer. Among them, eight bands were identified to be polymorphic with a rate of 44.4%. In addition, the GD information content values were highest in the 60 Gy treatment population and the GD values were higher in the γ-ray treatment populations than in the MNU treatment population. According to a cluster analysis, all the mutant lines can be classified into five categories, and the genetic distance was greatest between the 80 Gy-irradiated population and other populations. These results indicate that mutant lines have high GD and can be effectively utilized for improving blackberry breeding.
To describe the incidence of recovery of both vancomycin-resistant enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA) from culture of a single clinical specimen, to describe the clinical characteristics of patients from whom these specimens were recovered, and to identify the risk factors of these patients.
A retrospective cohort and case-control study.
A tertiary care university hospital and referral center in Seoul, Korea.
We identified 61 case patients for whom a single clinical specimen yielded both VRE and MRSA on culture, and 122 control patients for whom any clinical specimen yielded only VRE on culture. The control patients were selected by matching 2 :1 with the case patients for age, sex, and first date of sampling that led to isolation of VRE or both VRE and MRSA among 1,536 VRE-colonized patients from January 1, 2003, through December 31, 2006. To identify patient risk factors for the recovery of both VRE and MRSA in a single clinical specimen, we performed univariate comparisons between the 2 groups and then multivariate logistic regression analysis.
The incidence of recovery of both VRE and MRSA from culture of a single clinical specimen was 3.97% (for 61 of 1,536 VRE-colonized patients) over 4 years. Among these 82 single clinical specimens, the most common type was wound specimens (26.8%), followed by lower respiratory tract specimens (18.3%), urine specimens (17.1%), and catheter tips (15.9%). Of the 61 case patients, 14 (23.0%) had 2 or more single clinical specimens that yielded both VRE and MRSA on culture, and the longest interval from the first sampling that yielded both organisms to the last sampling that yielded both was 174 days. Independent patient risk factors for the presence of both VRE and MRSA in a single clinical specimen were chronic renal disease (odds ratio [OR], 7.00; P = .012), urinary catheterization (OR, 3.36; P = .026), and longer total cumulative duration of hospital stay within the previous year (OR, 1.03; P < .001).
We confirmed that the recovery of VRE and MRSA from a single clinical specimen occurs continually. Because prolonged cell-to-cell contact can facilitate transfer of vanA, close observation and surveillance for vancomycin-resistant S. aureus, especially among patients with risk factors for the recovery of both VRE and MRSA from a single clinical specimen, should be continued.
We have investigated the shift of threshold voltage in the a-Si:H TFT due to the various negative pulse width stress. The drain bias dependent threshold voltage shift in the pulsed stress of a-Si:H TFT for AMOLED backplane is also measured and analyzed. When a positive gate and drain bias is applied to a-Si:H TFT (W/L = 200/4 Ým), VTH of a-Si:H TFT is increased during the stress time due to the defect state creation and charge trapping. VTH of a-Si:H TFT is increased from 1.645V to 2.53V (δVTH=0.885V) after the DC gate bias stress of VGS=15V, VDS=0V for 20,000sec. When the pulsed negative bias stress is applied to the gate electrode of the current driving a-Si:H TFT with the drain bias, VTH shift is considerably reduced due to the hole trapping into the gate insulator during the stress. When a negative pulse width is 16msec (pulse of 60Hz), the VTH is increased form 1.594V to 2.195V (δVTH=0.601V). When a negative pulse width increases from 16msec to 5sec without drain bias (VDS=0V), VTH is increased from 1.615V to 2.055V (δVTH=0.44V). When a drain bias is increased from 0V to 15V, VTH is slightly decreased from 1.58V to 1.529V (δVTH=-0.051V) due to large (-30V) VGD (VG=-15V, VD=15V) bias, while it is increased from 1.66V to 2.078V (δVTH=0.418V) width DC gate bias stress of VGS=15V, VDS=15V for 20,000sec.
The threshold voltage (VT) degradation of asymmetric source-drain a-Si:H TFTs due to the electrical stress has been investigated. In the absence of a drain bias (VG=15V, VD=0V), the threshold voltage (VT) shifts of asymmetric TFTs were similar to that of symmetric TFT. However, in the presence of drain bias (VG=15V, VD=20V), the VT shifts of asymmetric TFTs were less than symmetric TFT. The VT shifts of ‘L’ and ‘J’ shaped TFT were 0.29V, 0.24V respectively, while the VT shift of ‘I’ shaped TFT was 0.42V.
The less VT degradation of the asymmetric source-drain a-Si:H TFT compared with the symmetric TFT may be explained by the defect creation model. Since the actual drain width of asymmetric TFT is longer than symmetric TFT at the same W/L ratio, the charge depletion due to the drain bias is larger than that of the asymmetric TFT. Due to the less carrier concentration in the channel, the asymmetric a-Si:H TFT shows the less VT degradation compared with the symmetric TFT.
We propose a pre-electrical bias aging to reduce threshold voltage (Vth) shift of hydrogenated- amorphous silicon thin-film transistor (a-Si:H TFT) for AMOLED display. The quantity of Vth shift in the sample subjected to a bias-aging is reduced due to the reduction of created dangling bond density, compared with a sample without a bias-aging. When an identical stress duration of 50,000 sec is applied to a-Si:H TFT with or without a pre-electrical bias-aging, the created dangling bond density (ΔNDB) after a pre-electrical bias-aging is decreased from 1.38 × 1011/cm2 to 0.685 × 1011/cm2. Our experimental results indicate that after the pre-electrical bias aging, a newly created dangling bond during an electrical stress is decreased because a weak bond density and hydrogen diffusion may be decreased.
Incomplete reprogramming of the donor cell nucleus after nuclear transfer (NT) probably leads to the abnormal expression of developmentally important genes. This may be responsible for the low efficiency of cloned animal production. Insulin-like growth factor 2 (IGF2) and IGF2 receptor (IGF2R) are imprinted genes that play important roles in preimplantation development. To obtain an insight into abnormal gene expression after nuclear transfer, we assessed the transcription patterns of IGF2-IGF2R in single in vitro fertilised and cloned embryos by reverse-transcription polymerase chain reaction (RT-PCR). IGF2R expression did not differ significantly but IGF2 was more highly expressed in cloned embryos than in IVF embryos (p < 0.05). This was confirmed by a quantitative RT-PCR method. Thus, incomplete reprogramming may induce abnormal transcription of IGF2 in cloned embryos.
A simple lateral grain growth of polysilicon employing single excimer laser irradiation is proposed. In order to increase the size of silicon grain and to control the location of the large lateral grain, the oxide trench is employed under the amorphous silicon film in the proposed method. The proposed oxide trench, which is shaped like a triangle or a polygon with an acute angle, induces temperature gradient on the molten silicon film during the solidification. It was verified by SEM that about 2 μm-long silicon grains are successfully achieved near the oxide trench edge and the locations of lateral grains are controlled by the angular points of the diagram.
Incomplete recrystallized junction defects of self-aligned, excimer laser annealed polycrystalline silicon (poly-Si) thin film transistor (TFT) was investigated by high-resolution transmission electron microscopy (HR-TEM). TEM observation and simulation result verify that the laser irradiation intensity decreased remarkably at the junction due to diffraction of laser beam at gate electrode edge. We proposed oblique-incidence excimer laser annealing method and successfully eliminated the residual junction defects.
We report a new poly-Si TFT, of which the troublesome implantation damage near the source/drain junction was eliminated, by performing source/drain ion implantation as well as excimer laser annealing (ELA) prior to the gate formation. The recrystallization of a-Si in the channel region and the dopant activation in the source/drain region were simultaneously accomplished by single ELA process step so that the implantation damage, which results in large leakage current of TFT, has been successfully eliminated. TEM image verifies that large poly-Si grains were successfully grown from the ion implanted source/drain region to the channel region. The proposed poly-Si TFT, of which mobility is 171 cm2/Vs, exhibits a large on/off current ratio exceeding 4.1 × 107 without LDD or offset structure while those of the conventional TFT, which has been fabricated simultaneously for the comparison purpose, are 86 cm2/Vs and 6.1 × 106.
A short channel polycrystalline silicon thin film transistor (poly-Si TFT), which has single grain boundary in the center of channel, is reported. The reported poly-Si TFT employs lateral grain growth method through aluminum patterns, which acts as a selective beam mask and a lateral heat sink during the laser irradiation, on an amorphous silicon layer. The electrical characteristics of the proposed poly-Si TFT have been considerably improved due to grain boundary density lowered. The reported short channel poly-Si TFT with single grain boundary exhibits high mobility as 222 cm2/Vsec and large on/off current ratio exceeding 1 × 108.
A high-quality silicon dioxide (SiO2) suitable for a gate oxide on plastic substrates is successfully deposited by e-gun evaporation at room temperature. The e-gun evaporated oxide film is free from troublesome hydrogen atoms and high-energy ion damage, which ensures good electrical characteristics. N2O/N2 plasma post-treatment was effective to reduce the flat band voltage and leakage current of the evaporated oxides due to the passivation of high-energy nitrogen and oxygen radicals. In the SiO2 film treated by N2O/N2 plasma for 1 minute, the flat band voltage has been reduced from −2.5V to about −0.5V and the leakage current has been decreased by more than one order. Our experimental results show that very low temperature SiO2 film suitable for a gate insulator of TFTs on the plastic substrates has been successfully obtained by the e-gun evaporation and N2O/N2 plasma post-treatment.
XeCl excimer laser was irradiated on metal induced laterally crystallized (MILC) polycrystalline silicon (poly-Si) film in order to eliminate the intra-grain defects of MILC poly-Si film which incorporated 2 μm wide metal induced crystallized (MIC) poly-Si line pattern. On the irradiation of the laser beams, different melt and recrystallization phenomena were observed in the MILC and the MIC poly-Si region due to the Ni content difference in each film. The transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) measurements indicated that the melting temperature of the poly-Si film decreased as the Ni content increased. With the laser irradiation energy density of 370 mJ/cm2, 2 μm long defect-free poly-Si grain was successfully grown in the MILC poly-Si due to the melting temperature variation at the MILC-MIC poly-Si boundary.
We have proposed and fabricated a novel poly-Si TFT that is integrated into the gate-data line-crossover in order to increase aperture ratio and to decrease signal delay of AMLCD panel and electrical characteristics of TFT integrated into gate-data line-crossover almost are identical to conventional TFT. The aperture ratio of AMLCD panel was increased considerably because the TFT was located under the opaque metal line. We employed a low dielectric air-gap between the gate-data line crossover, which reduced a capacitance between the gate and data lines so that the RC signal delay of the data line is decreased significantly. Our experimental result shows that the fabricated TFT was successfully operated and the proposed structure found to reduce the RC signal delay has been reduced by factor of 9 compared with conventional AMLCD panel that employs SiO2 for insulator between gate and data lines.
We report new lateral grain growth mechanism by XeCl excimer laser annealing on a-Si film with pre-patterned Al layer. 2000Å-thick Al pattern on 800Å-thick PECVD a-Si film successfully reflects the incident laser beam and results in temperature gradient during the recrystallization process. The TEM images show that grain growth near the boundary between the liquid and the solid region exhibits a different mechanism compared with the conventional ELA. About 1.5 m-long lateral grain has been successfully obtained by single laser irradiation
A poly-Si TFT with single grain boundary in the channel has been fabricated by the proposed excimer laser annealing. An excellent device characteristics such as mobility more than 250cm2/Vsec, high On/Off current ratio of 6.3×106 and low threshold voltage less than 1 V has been obtained. The experimental results show that the mobility, threshold voltage and sub-threshold slope of proposed TFTs are superior to those of the conventional TFTs.
A new excimer laser recrystallization method of amorphous silicon is proposed to increase the grain size and control the grain boundary locations in polycrystalline silicon films. The proposed method is based on the lateral grain growth which occurs at the interface between molten and unmolten regions. To obtain selectively molten regions, the proposed method employs aluminum patterns on amorphous silicon. The aluminum patterns act as the beam shield during the laser irradiation as well as the lateral heat sink during the solidification period. The high reflectance of aluminum at the wavelength of XeCl excimer laser offers stable beam shielding property, and the high thermal conductivity enhances the lateral heat flow by the quick draining of laterally propagated heat. TEM observation has revealed that the well arranged large grains were successfully obtained.
Anew excimer laser recrystallization method of a-Si film to increase the grain size of poly-Si film has been proposed. Excimer laser energy was locally modulated by being irradiated on stepped substrate with 500 nm deep trench on which a-Si film was deposited. Fairly large poly-Si grains (over 1 µm) were obtained due to lateral thermal gradient which resulted from the laser energy difference on the vertical wall and on the horizontal bottom plane of the trench without altering laser energy density elaborately.
We have proposed and fabricated a new poly-Si TFT that employs selectively doped regions between the source and drain in order to reduce leakage current without the sacrifice of the on current. In the proposed poly-Si TFTs, the selectively doped regions where doping concentration is identical to that of source/drain, reduce the effective channel length during the on state. Under the off state, the selectively doped regions may reduce the lateral electric field induced in the depletion region near drain so that the leakage current reduces considerably. The experimental data of the proposed TFT shows that it has the high on-current, low leakage current and low threshold voltage when compared with conventional TFT. The fabrication steps for the proposed TFT are reduced because ion-implantation for source/drain and selectively doped regions is performed simultaneously prior to an excimer laser irradiation. It should be noted that, in the proposed TFT, only one excimer laser annealing is required while two excimer laser annealing steps are required in conventional TFT.
A simple low-temperature excimer-laser doping process employing phosphosilicate glass (PSG) and borosilicate glass (BSG) films as dopant sources is proposed in order to form source and drain regions for polycrystalline silicon thin film transistors (poly-Si TFTs). We have successfully controlled sheet resistance and dopant depth profile of doped poly-Si films by varying PH3/SiH4 flow ratio, laser energy density and the number of laser pulses. The penetration depth and the surface concentration of dopants were increased with increasing laser energy density and the number of laser pulses. The minimum sheet resistance of 450ω/ for phosphorus (P) doping and 1100ω/ for boron (B) doping were successfully obtained. Our experimental results show that the proposed laser-doping process is suitable for source/drain formation of poly-Si TFTs.