We have simulated the performance of heterojunction with intrinsic thin-layer (HIT) solar cells on n-type c-Si substrates using the numerical simulator automat for simulation of heterostructures ...(AFORS-HET), with emphasis on the effect of density of defect states (DOS) in both p-type hydrogenated amorphous silicon ( a -Si:H) emitter and intrinsic a -Si:H buffer layers. A detailed and accurate DOS distribution, including both bandtail states and deep dangling-bond states, has been established in a -Si:H layers based on existing experimental results of a -Si:H films in the literature. The changes of DOS distribution for differently doped thin a -Si:H layers, depending on their doping concentrations (from intrinsic to highly doped), have explicitly been considered. With this DOS distribution model, we have calculated the charge trapped in defect states, which understands the mechanism of trapping effect, i.e., how the DOS influences the built-in field, space-charge region, and the cell performance within HIT solar cell structures. It is found that the DOS in the p-type a -Si:H emitter layer can cause an unfavorable trapping effect, which becomes more serious and even difficult to avoid in case of high doping concentration beyond 1 × 10 20 cm -3 . In contrast, the DOS in the intrinsic a -Si:H buffer layer will not sufficiently suppress the cell output until the density of dangling-bond states reaches 5 × 10 18 cm -3 . This paper presents a clear physical picture for the mechanism of trapping effect and concludes the suggestive DOS required for the high efficiency of HIT cells above 20%.
Conventional undoped gallium nitride (GaN) surface was treated with trimethylgallium (TMGa) flow for 100 s in the ambient of H2 and low ammonia at 500 °C and 500 Torr followed by thermal annealing at ...1050 °C. On the Gallium droplets and GaN nanoislands patterned layer-structured surface, droplet homoepitaxy of thin GaN layers was realized by flowing the surface with TMGa and low ammonia at 1035 °C for 400 s in the ambient of H2. By such an in situ three-step surface modification, the surface stoichiometry (Ga/N) changed from nonstoichiometry (N-rich, 0.92) to close-to-stoichiometry (slightly Ga-rich, 1.04) with very thin nanoislands (20 nm in diameter and 1 nm in height) patterning on the smooth layer-structured surface. Photoluminescence studies show significant reduction of yellow/blue emissions, which suggests improvement of surface/interface qualities of GaN films.
In this paper, we propose using a terahertz quantum-well photodetector (THz QWP) in combination with a terahertz source to realize a detection system with photon-noise limited performance (PLIP) at ...high temperatures. Systematical investigations on the high-temperature performances of THz QWPs, including required signal power density for PLIP, detectivity, and the signal-to-noise ratio, have been carried out by elaborating their dark current mechanism and photocurrent response both experimentally and theoretically. We also present the optimal doping concentration of THz QWPs designed for different peak wavelengths and the resulting optimum performance regarding the above three key parameters. Numerical results show that optimal designed QWP with peak response frequency of 5.5 THz is expected to achieve PLIP at 77 K at signal power density at 819 W/cm 2 and above. This work gives a precise description of PLIP performance of THz QWPs and will open ways for new applications for high-temperature detection in the THz regime.
The fruit flesh color of papaya is an important nutritional quality trait and is due to the accumulation of carotenoid. To elucidate the carotenoid biosynthesis pathway in
Carica papaya
, the ...phytoene desaturase (PDS) and the ζ-carotene desaturase (ZDS) genes were isolated from papaya (named
CpPDS
and
CpZDS
) using the rapid amplification of cDNA ends (RACE) approach, and their expression levels were investigated in red- and yellow-fleshed papaya varieties.
CpPDS
contains a 1749 bp open reading frame coding for 583 amino acids, while
CpZDS
contains a 1716 bp open reading frame coding for 572 amino acids. The deduced CpPDS and CpZDS proteins contain a conserved dinucleotide-binding site at the N-terminus and a carotenoid-binding domain at the C-terminus. Papaya genome sequence analysis revealed that
CpPDS
and
CpZDS
are single copy; the
CpPDS
was mapped to papaya chromosome LG6, and the
CpZDS
was mapped to chromosome LG3. Quantitative PCR showed that both
CpPDS
and
CpZDS
were expressed in all tissues examined with the highest expression in maturing fruits, and that the expression of
CpPDS
and
CpZDS
were higher in red-fleshed fruits than in yellow-fleshed fruits. These results indicated that the differential accumulation of carotenoids in red- and yellow-fleshed papaya varieties might be partly explained by the transcriptional level of
CpPDS
and
CpZDS
.
The outer and inner hair cells of the mammalian cochlea perform different functions. In response to changes in membrane potential, the cylindrical outer hair cell rapidly alters its length and ...stiffness. These mechanical changes, driven by putative molecular motors, are assumed to produce amplification of vibrations in the cochlea that are transduced by inner hair cells. Here we have identified an abundant complementary DNA from a gene, designated Prestin, which is specifically expressed in outer hair cells. Regions of the encoded protein show moderate sequence similarity to pendrin and related sulphate/anion transport proteins. Voltage-induced shape changes can be elicited in cultured human kidney cells that express prestin. The mechanical response of outer hair cells to voltage change is accompanied by a 'gating current', which is manifested as nonlinear capacitance. We also demonstrate this nonlinear capacitance in transfected kidney cells. We conclude that prestin is the motor protein of the cochlear outer hair cell.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Low-frequency noise (LFN) measurements were performed on hydrogenated nanocrystalline silicon (nc-Si:H)/crystalline-silicon heterojunction diodes for the forward- and reverse-biased currents I . The ...1/ f γ noise with γ ~ 1.3 (for low I ) or 0.6 (for high I ) was observed to dominate the LFN, and the noise power spectral density Si showed a power-law behavior ( Si ~ I α , where α ~ 2). This quadratic behavior may indicate the 1/ f γ noise to stem from the carrier number fluctuations mediated by deep trap states (for γ ~ 1.3) or band tail states (for γ ~ 0.6) of nc-Si:H. Also, the band tail width of nc-Si:H was estimated to be ~ 65 meV.
Ag/0.7 wt% Nb-doped SrTiO
3
(Nb:STO)/Ti structure was prepared by sputtering Ag and Ti electrodes on a Nb:STO single crystal substrate and the resistance switching (RS) properties were investigated. ...Reversible multilevel resistance switching behavior was obtained by applying different voltages. The resistance switching (RS) effect comes from the Schottky barrier existed between Ag and Nb:STO interface. The multilevel switching mechanism may be related to the different number of electrons trapped or detrapped by oxygen vacancies (V
o
2+
) at the Ag/Nb:STO interface, which can change the width of depletion layer. The temperature dependence on resistance of Ag/Nb:STO/Ti suggests that both high resistance state (HRS) and low resistance state (LRS) are of semiconductor behavior. Substrate annealing in vacuum degrades the RS properties of Ag/Nb:STO/Ti structure due to the increase of V
o
2+
in Nb:STO.
Under optimal conditions, most of the light energy is used to drive electron transport. However, when the light energy exceeds the capacity of photosynthesis, the overall photosynthetic efficiency ...drops down. The present study investigated the effects of high light on rice photooxidation-prone mutant 812HS, characterized by a mutation of leaf photooxidation 1 gene, and its wild type 812S under field conditions. Our results showed no significant difference between 812HS and 812S before exposure to high sunlight. However, during exposure to high light, shoot tips of 812HS turned yellow and their chlorophyll (Chl) content decreased. Transmission electron microscopy showed that photooxidation resulted in significant damage of chloroplast ultrastructure. It was confirmed also by inhibited photophosphorylation and reduced ATP content. The decreased coupling factor of ATP, Ca
2+
-ATPase and Mg
2+
-ATPase activities also verified these results. Further, significantly enhanced activities of antioxidative enzymes were observed during photooxidation. Malondialdehyde, hydrogen peroxide, and the superoxide generation rates also increased. Chl
a
fluorescence analysis found that the performance index and maximum quantum yield of PSII declined on August 4, 20 days after high-light treatment. Net photosynthetic rate also decreased and substomatal CO
2
concentration increased in 812HS at the same time. In conclusion, our findings indicated that excessive energy triggered the production of toxic reactive oxygen species and promoted lipid peroxidation in 812HS plants, causing severe damage to cell membranes, degradation of photosynthetic pigments and proteins, and ultimately inhibition of photosynthesis.
RNA-mediated virus resistance based on natural antiviral RNA silencing has been exploited as a powerful tool for engineering virus resistance in plants. In this study, a conserved 3'-region ...(positions 9839-10117, 279 nt) of the capsid protein (CP) gene of papaya ringspot virus (PRSV), designated CP279, was used to generate an intron-containing hairpin RNA (ihpRNA) construct by one-step, zero-background ligation-independent cloning (OZ-LIC). The RNaseIII-deficient Escherichia coli strain M-JM109lacY was identified as the best choice for producing large quantities of specific ihpRNA-CP279. Resistance analyses and ELISA data verified that most papaya plants mechanically co-inoculated with TRIzol-extracted ihpRNA-CP279 and PRSV were resistant to PRSV, and resistance was maintained throughout the test period (>2 months post-inoculation). In contrast, a 1-2 day interval between sequential inoculation of PRSV and ihpRNA-CP279 did not result in complete protection against PRSV infection, but delayed the appearance of viral symptoms by 3 to 4 days. These findings indicate that direct mechanical inoculation of papaya plants with bacterially-expressed ihpRNA-CP279 targeting the PRSV CP gene can interfere with virus infection. This work lays a foundation for developing a non-transgenic approach to control PRSV by directly spraying plants with ihpRNA or crude bacterial extract preparations.
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