排序方式: 共有46条查询结果,搜索用时 123 毫秒
1.
Wi SG Chung BY Kim JS Kim JH Baek MH Lee JW Kim YS 《Micron (Oxford, England : 1993)》2007,38(6):553-564
This review discusses the morphological changes and biological responses of plants irradiated with gamma rays. Seedlings exposed to relatively low doses of gamma rays (1-5 Gy) developed normally, while the growth of plants irradiated with a high dose gamma ray (50 Gy) was significantly inhibited. Based on TEM observations, chloroplasts were extremely sensitive to gamma irradiation compared to other cell organelles, particularly thylakoids being heavily swollen. In addition, some portions of the mitochondria and endoplasmic reticulum were structurally altered, for example, distortion and swelling. The cerium perhydroxide deposition, as a maker for H(2)O(2) deposition, was typically manifest on the plasma membranes and cell walls of the tissues from both the control and irradiated plants. However, the intensities of cerium perhydroxide deposits (CPDs) were remarkably increased in the plasma membranes and cell walls of pumpkin tissues such as petiole, cotyledon, hypocotyl and especially leaf after gamma irradiation. These observations are in good agreement with the results of H(2)O(2) content in all tissues. The immuno-localization analysis for peroxidase (POD) on the tissues from pumpkin plant showed the same pattern between the control and irradiated plants, but the density of gold particles as indication of POD localization was significantly increased on the cell corner middle lamellae of parenchyma cells, especially in the petiole after gamma irradiation. However, accumulation and localization of H(2)O(2) and POD in vessels were not significantly different between both plants. The accumulation and localization of both H(2)O(2) and POD were differentially affected by gamma irradiation depending on the different tissue types. The deposition of both H(2)O(2) and POD in parenchyma cells appeared much higher than in vessels, suggesting that the former is more sensitive than the latter against gamma rays. 相似文献
2.
Zhenqiang Ma Bhattacharya P. Jae-Sung Rieh Ponchak G.E. Alterovitz S.A. Croke E.T. 《Microwave and Wireless Components Letters, IEEE》2001,11(10):401-403
The degradation behavior of NPN Si/SiGe/Si heterojunction bipolar transistors, grown by solid-source molecular beam epitaxy (MBE), has been studied by accelerated lifetime testing at different ambient temperatures. The degradations of the dc current gain and the microwave performance of the devices are explained in terms of recombination enhanced impurity diffusion (REID) of boron atoms from the base region and the subsequent formation of parasitic energy barriers at the base-emitter and base-collector junctions 相似文献
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4.
Jea‐Shik Shin Insang Song Chul‐Soo Kim Moon‐Chul Lee Sang Uk Son Duck‐Hwan Kim Ho‐Soo Park Sungwoo Hwang Jae‐Sung Rieh 《ETRI Journal》2014,36(2):317-320
A balanced RF duplexer with low interference in an extremely narrow bandgap is proposed. The Long‐Term Evolution band‐7 duplexer should be designed to prevent the co‐existence problem with the WiFi band, whose fractional bandgap corresponds to only 0.7%. By implementing a hybrid bulk acoustic wave (BAW) structure, the temperature coefficient of frequency (TCF) value of the duplexer is successfully reduced and the suppressed interference for the narrow bandgap is performed. To achieve an RF duplexer with balanced Rx output topology, we also propose a novel balanced BAW Rx topology and RF circuit block. The novel balanced Rx filter is designed with both lattice‐ and ladder‐type configurations to ensure excellent attenuation. The RF circuit block, which is located between the antenna and the Rx filter, is developed to simultaneously function as a balance‐to‐unbalance transformer and a phase shift network. The size of the fabricated duplexer is as small as 2.0 mm × 1.6 mm. The maximum insertion loss of the duplexer is as low as 2.4 dB in the Tx band, and the minimum attenuation in the WiFi band is as high as 36.8 dB. The TCF value is considerably lowered to ?16.9 ppm/°C. 相似文献
5.
Jagannathan B. Khater M. Pagette F. Rieh J.-S. Angell D. Chen H. Florkey J. Golan F. Greenberg D.R. Groves R. Jeng S.J. Johnson J. Mengistu E. Schonenberg K.T. Schnabel C.M. Smith P. Stricker A. Ahlgren D. Freeman G. Stein K. Subbanna S. 《Electron Device Letters, IEEE》2002,23(5):258-260
This paper reports on SiGe NPN HBTs with unity gain cutoff frequency (fT) of 207 GHz and an fMAX extrapolated from Mason's unilateral gain of 285 GHz. fMAX extrapolated from maximum available gain is 194 GHz. Transistors sized 0.12×2.5 μm2 have these characteristics at a linear current of 1.0 mA/μm (8.3 mA/μm2). Smaller transistors (0.12×0.5 μm2) have an fT of 180 GHz at 800 μA current. The devices have a pinched base sheet resistance of 2.5 kΩ/sq. and an open-base breakdown voltage BVCEO of 1.7 V. The improved performance is a result of a new self-aligned device structure that minimizes parasitic resistance and capacitance without affecting fT at small lateral dimensions 相似文献
6.
High-resolution electron energy loss spectroscopy is used to study surface phonons in the direction of
qG
on Ag(111). The gap mode (S2) at
in the surface Brillouin zone is measured for the first time. We have also measured the Rayleigh mode and the resonance mode up to the zone boundary. The results are complementary to the earlier He atom scattering measurements and are in good agreement with the first-principles calculations performed recently. 相似文献
7.
Kim HM Yang PR Seo MS Yi JS Hong JH Jeon SJ Ko YG Lee KJ Cho BR 《The Journal of organic chemistry》2007,72(6):2088-2096
A novel, two-photon probe for the detection of free Mg2+ ions in living cells and live tissues has been developed. The probe can be excited by 880 nm laser photons, emits strong two-photon excited fluorescence in response to Mg2+ ions, can be easily loaded into the cell and tissue, shows high photostability, and can measure the Mg2+ ion concentration without interference by Ca2+ ions in living cells. The intracellular dissociation constant (Kdi) for Mg2+ determined by the two-photon process is 2.5 mM, which is suitable for dynamic Mg2+ concentration measurement. In addition, the probe is capable of imaging endogenous stores of free Mg2+ at a few hundred micrometers depth in live tissues using two-photon microscopy (TPM). 相似文献
8.
Baoyin Han Sai-Anand Gopalan Kwang-Don Lee Byoung-Ho Kang Sang-Won Lee Jae-Sung Lee Dae-Hyuk Kwon Seung-Ha Lee Shin-Won Kang 《Current Applied Physics》2014,14(11):1443-1450
In this study, we explored the ability of a preheated solvent (methanol) to induce characteristic changes at the organic active layer/metal interface, thereby improving the performance of fabricated organic photovoltaic (OPV) cells composed of poly(3-hexylthiopene) (P3HT) and a [6,6]-phenyl-C71-butyric acid methyl ester (PCBM) photoactive blend. Our results demonstrate that exposure to methanol (at room temperature, or preheated at 45 °C or 65 °C) improves the performance of the fabricated OPV cells. After preheated methanol exposure, the P3HT:PCBM thin films were tested for crystallinity, morphology, mobility, and photovoltaic characteristics. Our results revealed that use of the preheated solvent on the organic active layer significantly influences the micro/nano scale morphology and phase segregation of the P3HT:PCBM thin films, as well as the charge carrier mobility. It is hypothesized that the side chain ordering of P3HT and redistribution of PCBM could be results of the modified active layer. Consequently, OPV cells modified with the methanol preheated at 65 °C exhibited a power conversion efficiency (PCE) of 3.36%, with open-circuit voltage of 0.59 V, short-circuit current density of 13.83 mA/cm2, and fill-factor of 0.41. In contrast, the unmodified P3HT:PCBM thin film (without methanol exposure) showed a PCE of only 2.13%. 相似文献
9.
Jeng S.J. Jagannathan B. Rieh J.-S. Johnson J. Schonenberg K.T. Greenberg D. Stricker A. Chen H. Khater M. Ahlgren D. Freeman G. Stein K. Subbanna S. 《Electron Device Letters, IEEE》2001,22(11):542-544
A record 210-GHz fT SiGe heterojunction bipolar transistor at a collector current density of 6-9 mA/μm2 is fabricated with a new nonself-aligned (NSA) structure based on 0.18 μm technology. This NSA structure has a low-complexity emitter and extrinsic base process which reduces overall thermal cycle and minimizes transient enhanced diffusion. A low-power performance has been achieved which requires only 1 mA collector current to reach 200-GHz fT. The performance is a result of narrow base width and reduced parasitics in the device. Detailed comparison is made to a 120-GHz self-aligned production device 相似文献
10.
The diffraction image patterns of small particles are referred to as their point spread function (PSF); these patterns vary
distinctively with the refractive index (RI) of a transparent test medium when the particles are imaged through the medium.
The RI correlates directly with the mixture concentration, so proper inversion of measured PSFs can provide full-field information
on the mixture concentration field. In this study, fluorescent nanoparticles of 500 nm diameter are fixed on a glass surface
by means of evaporative self-assembly, and the time-varying test mixture is placed in front of the glass surface. The time-varying
and full-field PSF distributions are imaged and digitally analyzed to determine the local RI values as well as the local mixture
concentrations. Both immiscible water/oil mixture and miscible water/glycerol mixture are imaged. The present method shows
an RI measurement to have an uncertainty of ±5 × 10−3 RIU and the mixture concentration measurements to have uncertainty of approximately 4%. 相似文献