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1.
A subwavelength metallic heterostructure is put forth for the purpose of suppressing sidelobes and improving superfocusing
at a quasi-far field region. Improvement has been made by means of optimization of the heterostructure composed of structured
Au and Ag thin films. By tuning thicknesses of both the structured Au and Ag films, we can modulate propagation distance of
the plasmonic lens and beam width of main lobe for the superfocusing. A finite-difference and time-domain (FDTD) algorithm-based
computational numerical calculation was carried out for analyzing the focusing performance and tuning ability of the metal
films. Our computational calculation results show that the sidelobes which play negative role for the focusing can be suppressed
significantly in the case of the metal film thicknesses of h
Au = 50 nm and h
Ag = 10 nm. Theoretically, the metallic structure with smaller thicknesses of the structured Au and Ag films is helpful for
improving the focusing performance. This heterostructure-based device is possible to be used as a superlens or nanoprobe in
data storage, nanometrology/inspection, and biosensing etc. 相似文献
2.
A polyhydroxyalkanote depolymerase gene from Thermobifida sp. isolate BCC23166 was cloned and expressed as a C-terminal His 6-tagged fusion in Pichia pastoris. Primary structure analysis revealed that the enzyme PhaZ-Th is a member of a proposed new subgroup of SCL-PHA depolymerase
containing a proline–serine repeat linker. PhaZ-Th was expressed as two glycosylated forms with apparent molecular weights
of 61 and 70 kDa, respectively. The enzyme showed esterase activity toward p-nitrophenyl alkanotes with V
max and K
m of 3.63 ± 0.16 μmol min −1 mg −1 and 0.79 ± 0.12 mM, respectively, on p-nitrophenyl butyrate with optimal activity at 50–55°C and pH 7–8. Surface plasmon resonance (SPR) analysis demonstrated that
PhaZ-Th catalyzed the degradation of poly-[( R)-3-hydroxybutyrate] (PHB) films, which was accelerated in ( R)-3-hydroxyvalerate copolymers with a maximum degradation rate of 882 ng cm −2 h −1 for poly[( R)-3-hydroxybutyrate-co-3-hydroxyvalerate] (12 mol% V). Surface deterioration, especially on the amorphous regions of PHB films
was observed after exposure to PhaZ-Th by atomic force microscopy. The use of P. pastoris as an alternative recombinant system for bioplastic degrading enzymes in secreted form and a sensitive SPR analytical technique
will be of utility for further study of bioplastic degradation. 相似文献
3.
The influence of TiO2 coating on resonant properties of gold nanoisland films deposited on silica substrates was studied numerically and in experiments. The model describing plasmonic properties of a metal truncated nanosphere placed on a substrate and covered by a thin dielectric layer has been developed. The model allows calculating a particle polarizability spectrum and, respectively, its surface plasmon resonance (SPR) wavelength for any given cover thickness, particle radius and truncation parameter, and dielectric functions of the particle, the substrate, the coating layer, and the surrounding medium. Dependence of the SPR position calculated for truncated gold nanospheres has coincided with the measured one for the gold nanoisland films covered with titania of different thicknesses. In the experiments, gold films with thickness of 5 nm were deposited on a silica glass substrate, annealed at 500 °C to form nanoislands of 20 nm in diameter, and covered with amorphous titania layers using atomic layer deposition technique. The resulting structures were characterized with scanning electron microscopy and optical absorption spectroscopy. The measured dependence of the SPR position on titania film thickness corresponded to the one calculated for truncated sphere-shaped nanoparticles with the truncation angle of ~50°. We demonstrated the possibility of tuning the SPR position within ~100 nm range by depositing to 30 nm thick titania layer. 相似文献
4.
The aim of the study is to examine thermal behavior of water within reticulated structure of bacterial cellulose (BC) films
by sub-ambient differential scanning calorimetry (DSC). BC films with different carbon source, either manitol (BC (a)) or
glycerol (BC (b)), were produced by Acetobacter xylinum using Hestrin and Shramm culture medium under static condition at 30 ± 0.2°C for 3 days. BC samples were characterized by
electron scanning microscopy and X-ray diffraction spectroscopy. The pore analysis was done by B.H.J. nitrogen adsorption.
The pre-treated with 100% relative humidity, at 30.0 ± 0.2°C for 7 days samples were subjected to a between 25 and −150°C-cooling–heating
cycle of DSC at 5.00°C/min rate. The pre-treated samples were also hydrated by adding 1 μl of water and thermally run with
identical conditions. It is observed that cellulose fibrils of BC (a) were thinner and reticulated to form slightly smaller
porosity than those of BC (b). They exhibited slightly but non-significantly different crystalline features. The freezable
bound water behaved as a water confinement within pores rather than a solvent of polymer which is possible to use thermoporosimetry
based on Gibb–Thomson equation to approach pore structure of BC. In comparison with nitrogen adsorption, it was found that
thermoporosimetry underestimated the BC porosity, i.e., the mean diameters of 23.0 nm vs. 27.8 nm and 27.9 nm vs. 33.9 nm for BC (a) and BC (b), respectively, by thermoporosimetry vs. B.H.J. nitrogen adsorption. It may be due to large non-freezable water fraction interacting with cellulose, and the validity
of pore range based on thermodynamic assumptions of Gibb–Thomson theory. 相似文献
5.
Water dispersible zinc sulfide quantum dots (ZnS QDs) with an average diameter of 2.9 nm were synthesized in an environment
friendly method using chitosan as stabilizing agent. These nanocrystals displayed characteristic absorption and emission spectra
having an absorbance edge at 300 nm and emission maxima ( λ
emission) at 427 nm. Citrate-capped silver nanoparticles (Ag NPs) of ca. 37-nm diameter were prepared by modified Turkevich process.
The fluorescence of ZnS QDs was significantly quenched in presence of Ag NPs in a concentration-dependent manner with K
sv value of 9 × 10 9 M −1. The quenching mechanism was analyzed using Stern–Volmer plot which indicated mixed nature of quenching. Static mechanism
was evident from the formation of electrostatic complex between positively charged ZnS QDs and negatively charged Ag NPs as
confirmed by absorbance study. Due to excellent overlap between ZnS QDs emission and surface plasmon resonance band of Ag
NPs, the role of energy transfer process as an additional quenching mechanism was investigated by time-resolved fluorescence
measurements. Time-correlated single-photon counting study demonstrated decrease in average lifetime of ZnS QDs fluorescence
in presence of Ag NPs. The corresponding F?rster distance for the present QD–NP pair was calculated to be 18.4 nm. 相似文献
6.
Vibrio anguillarum ghosts (VAG) were generated, for the first time, using a conjugation vector containing a ghost bacteria inducing cassette,
pRK-λP R-cI-Elysis, in which the expression of PhiX174 lysis gene E was controlled by the P
R
/ cI regulatory system of lambda phage. By scanning electron microscopy, holes ranging 80–200 nm in diameter were observed in
the VAG. To avoid the presence of bacterial genomic DNA and an antibiotic resistance gene in the final VAG product, we constructed
a new dual vector, pRK-λP R-cI-E-SNA, containing the E-mediated lysis cassette and the staphylococcal nuclease A ( SNA)-mediated DNA degradation cassette, and generated safety-enhanced VAG for use as a fish vaccine. 相似文献
7.
Here, we report for the first time the synthesis of bismuth-coated silver nanoparticles in dichroic bismuth glass nanocomposites
by a novel and simple one-step melt quench technique without using any external reducing agent. The metallic silver nanoparticles
(Ag NPs) were generated first, and subsequently, metallic bismuth was deposited on the Ag NPs and formed a thick layer. The
reduction of Bi 3+ to Bi o and subsequently its deposition on the Ag NPs (which were formed earlier than Bi o) in the K 2O–Bi 2O 3–B 2O 3 (KBB) glass system have been explained by their standard reduction potentials. The UV–vis absorption spectra show a prominent
surface plasmon resonance (SPR) absorption band at 575 nm at lower concentrations (up to 0.01 wt%); three bands at 569, 624
and 780 nm at medium concentration (0.02–0.03 wt%); and two weak bands at 619 and 817 nm at highest concentration (0.06 wt%)
of silver. They have been explained by the electrodynamics theories. TEM images reveal the conversion of spheroidal (5–15 nm)
to hexagonal (10–35 nm) shaped Ag NPs with the increase in concentration of silver (up to 0.06 wt%). SAED pattern confirms
the crystalline planes of rhombohedral bismuth and cubic silver. Thermal treatment at 360 °C, which is the glass transformation
temperature ( T
g) of the sample containing lower concentration of silver (0.007 wt%), shows red-shifted SPR band due to increase in size of
NPs. Whereas the sample containing higher concentration (0.06 wt%) of silver under similar treatment exhibited changes in
SPR spectral profile happened due to conversion to spherical NPs from hexagonal shape and reduction in size (10–20 nm) of
NPs after heat treatment for 65 h. HRTEM images corroborate the different orientations of the NPs. FESEM images reveal hexagonal
disk like structure having different orientations. Dichroic nature of the nanocomposites has been explained with the size
and shape of Ag nanoparticles. We believe that this work will create new avenues in the area of nanometal–glass hybrid nanocomposites
and the materials have significant applications in the field of optoelectronics and nanophotonics. 相似文献
8.
( R)-ethyl-3-hydroxyglutarate with highly optical purity (≥99%) can be used as a novel precursor for synthesis of chiral side
chain of rosuvastatin. In this study, a novel synthesis route of ( R)-ethyl-3-hydroxyglutarate by whole microorganism cells from racemic ethyl 4-cyano-3-hydroxybutyate was created. A strain
ZJB-0910 capable of transforming racemic β-hydroxy aliphatic nitrile was isolated by employing a screening method based on
a colorimetric reaction of Co 2+ ion with ammonia, and identified as Rhodococcus erythropolis based on its morphology, physiological tests, Biolog, and the 16S rDNA sequence. After cultivation in a sterilized medium
with composition of 20 g glucose, 5 g yeast extract, 0.5 g KH 2PO 4, 0.5 g K 2HPO 4, 0.2 g MgSO 4·7H 2O per liter at 30°C and 150 rpm for 48 h, the whole cells of R. erythropolis ZJB-0910 were prepared as a catalyst in ( R)-enantioselective hydrolysis of racemic ethyl 4-cyano-3-hydroxybutyate for synthesis of ( R)-ethyl-3-hydroxyglutarate, without bearing hydrolase activity for the ester bond of ethyl 4-cyano-3-hydroxybutyate. Under
the optimized biotransformation conditions of pH 7.5, 30°C, and 20 mM substrate concentration, ( R)-ethyl-3-hydroxyglutarate with 46.2% yield ( ee > 99%) was afforded, and its chemical structure was determined by ESI-MS, NMR, and IR. The apparent Michaelis constant K
m and maximum rate V
max for this biocatalytic reaction were 0.01 M and 85.6 μmol min −1 g −1, respectively. 相似文献
9.
We report the deposition of highly uniform thin silver films on plastic materials using a wet-chemistry method, suitable for
surface plasmon-coupled emission (SPCE). This approach is reproducible for diverse low-cost applications and versatile to
generate silver surfaces on various plastics substrates. An oxygen plasma pretreatment of the plastic provides for rapid silvering,
leading to a 47-nm-thick continuous film for SPCE applications. The surface smoothness and thickness of the films have been
estimated using atomic force microscope. The higher refractive index of polycarbonate, resulted in an SPCE angle of θ
F = 47 0 for Rhodamine B, compared to glass ( θ
F = 50 0). The current study presents details on film deposition conditions, appropriate choice of index matching fluids, substrates,
and light sources that play a vital role to augment SPCE emission intensity. 相似文献
10.
In the present research silver nanoparticle was fabricated by chemical reduction of silver salt (Silver nitrate, AgNO 3) solution. Sodium citrate was used as a reducer. The formation of silver nanoparticle was observed visually by color change
(greenish yellow). The surface plasmon resonance peak in absorption spectra of silver nanoparticle showed an absorption maximum
at 420 nm in UV-VIS spectrometry. The X-ray diffraction pattern showed the presence of sharp reflections at 111, 200, 220,
and 311. This would indicate the presence of silver nanoparticle. The scanning electron micrograph revealed that the average
size of silver nanoparticle was 21.22 ± 5.17 nm. Silver nanoparticle exhibited better antimicrobial activity against Staphylococcus aureus than the other bacterial pathogens. The correlation coefficient between silver nanoparticles and selected bacterial pathogens
revealed that there is a strong negative correlation with Escherichia coli, S. aureus and Klebsiella pneumonia (r = −0.975, −0.993, and −0.998, respectively). 相似文献
11.
Polyacrylonitrile film (PAN) surfaces were modified with chemical polymerization of conductive polyaniline (PANI) in the presence
of potassium dichromate as an oxidizing agent. The conductive films were used for immobilization of uricase. The surface resistance
of the conductive film in this work was found to be 0.97 kΩ/cm. The maximum amount of immobilized enzyme on conductive film
containing 2.4% PANI was about 216 μg/cm 2. The optimum pH for free and immobilized enzymes was observed at 7.0 and 7.5, respectively. The K
m values for free and immobilized uricase were found to be 94 and 138 μM, respectively. V
max values were calculated as 1.87 and 1.63 U/mg protein for the free and immobilized enzymes, respectively. Immobilized uricase
exhibited ~68% of its original activity even after 2 months of storage at 4 °C while the free enzyme lost its initial activity
within 4 weeks. 相似文献
12.
To investigate annual variation in soil respiration ( R
S) and its components [autotrophic ( R
A) and heterotrophic ( R
H)] in relation to seasonal changes in soil temperature (ST) and soil water content (SWC) in an Abies holophylla stand (stand A) and a Quercus-dominated stand (stand Q), we set up trenched plots and measured R
S, ST and SWC for 2 years. The mean annual rate of R
S was 436 mg CO 2 m −2 h −1, ranging from 76 to 1,170 mg CO 2 m −2 h −1, in stand A and 376 mg CO 2 m −2 h −1, ranging from 82 to 1,133 mg CO 2 m −2 h −1, in stand Q. A significant relationship between R
S and its components and ST was observed over the 2 years in both stands, whereas a significant correlation between R
A and SWC was detected only in stand Q. On average over the 2 years, R
A accounted for approximately 34% (range 17–67%) and 31% (15–82%) of the variation in R
S in stands A and Q, respectively. Our results suggested that vegetation type did not significantly affect the annual mean
contributions of R
A or R
H, but did affect the pattern of seasonal change in the contribution of R
A to R
S. 相似文献
13.
Measurements of chlorophyll fluorescence and hyperspectral reflectance were used to detect salinity stress in Suaeda salsa L ., beach of Dongtai, Jiangsu Province, China. Three experimental sites were used in our study, which belong to low salinity,
middle salinity and high salinity. The results showed that leaf chlorophyll fluorescence changed along salinity gradient.
To select the sensitive hyperspectral ranges of leaf chlorophyll fluorescence, the correlationship between leaf chlorophyll
fluorescence and hyperspectral reflectance was regressed and analyzed. Statistical results indicated that the 680 and 935 nm
were the most sensitive hyperspectral bands for estimating leaf chlorophyll fluorescence. Then, 11 relative hyperspectral
indices were selected based on the sensitive bands and previous literature. ( R
680 − R
935)/( R
680 + R
935) and R
680/ R
935 have higher correlationship coefficient ( R) and lower root mean square error, may be used for detecting chlorophyll fluorescence, such as F
o, F
m, F
v/ F
m, qP, and ΦPSII, while NPQ may be detected by ( R
780 − R
710)/( R
780 − R
680). These results suggest that chlorophyll fluorescence of halophyte response to salinity stress could be identified by remote
sensing. 相似文献
14.
Reactions of NaSCPh 3 with (R 3tacn)Cu(OTf) 2 (R is Me, iPr; tacn is 1,4,7-triazacyclononane; OTf is CF 3SO 3
−) yield blue complexes identified as ((R 3tacn)CuSCPh 3)(OTf) on the basis of UV–vis, resonance Raman, and electron paramagnetic resonance (EPR) spectroscopy and electrospray ionization
mass spectrometry. These complexes exhibit spectroscopic properties typical of type 1 copper sites in proteins, including
diagnostic S π → Cu( dx2 - y2 ) (d_{{x^{2} - y^{2} }} ) ligand-to-metal charge transfer transitions at approximately 610–630 nm and small A
|| values in EPR spectra of less than 100 × 10 −4 cm −1. Cyclic voltammetry experiments revealed redox potentials for the complexes similar to those of several low-potential type
1 copper proteins (e.g., azurin, stellacyanin) and approximately 0.5 V higher than those of previously reported model compounds.
Thus, the new complexes mimic key aspects of both the structure and the function of type 1 copper sites. 相似文献
15.
Vegetation water content (VWC) is an important variable for both agriculture and forest fire management. Remote sensing technology
offers an instantaneous and non-destructive method for VWC assessment provided we can relate in situ measurements of VWC to
spectral reflectance in a reliable way. In this paper, based on radiative transfer models, three new normalized difference
water indices (NDWI) are proposed for VWC [fuel moisture content (FMC), and equivalent water thickness (EWT)] estimation,
taking both leaf internal structure and dry matter content into account. Reflectance at 1,200, 1,450 and 1,940 nm were selected
and normalized with reflectance at 860 nm to establish three water indices, NDWI 1200, NDWI 1450 and NDWI 1940. Good correlations were observed between FMC ( R
2 = 0.65–0.80) and EWT (both at the leaf scale, R
2 = 0.75–0.81 for EWT L and at the canopy scale, R
2 = 0.80–0.83 for EWT C) at various stages of wheat crop development. 相似文献
16.
We investigated the influence of stand density [938 tree ha −1 for high stand density (HD), 600 tree ha −1 for medium stand density (MD), and 375 tree ha −1 for low stand density (LD)] on soil CO 2 efflux ( R
S) in a 70-year-old natural Pinus densiflora S. et Z. forest in central Korea. Concurrent with R
S measurements, we measured litterfall, total belowground carbon allocation (TBCA), leaf area index (LAI), soil temperature
(ST), soil water content (SWC), and soil nitrogen (N) concentration over a 2-year period. The R
S (t C ha −1 year −1) and leaf litterfall (t C ha −1 year −1) values varied with stand density: 6.21 and 2.03 for HD, 7.45 and 2.37 for MD, and 6.96 and 2.23 for LD, respectively. In
addition, R
S was correlated with ST ( R
2 = 0.77–0.80, P < 0.001) and SWC ( R
2 = 0.31–0.35, P < 0.001). It appeared that stand density influenced R
S via changes in leaf litterfall, LAI and SWC. Leaf litterfall ( R
2 = 0.71), TBCA ( R
2 = 0.64–0.87), and total soil N contents in 2007 ( R
2 = 0.94) explained a significant amount of the variance in R
S ( P < 0.01). The current study showed that stand density is one of the key factors influencing R
S due to the changing biophysical and environmental factors in P. densiflora. 相似文献
17.
We present an analysis of X-ray-induced damage in ΦX174 plasmid DNA, applying doses between D = 250 and 1,500 Gy. To analyse this damage in detail, the distribution of plasmid fragments after irradiation have been determined
by scanning force microscopy. The results show that even for the lowest dose of D = 250 Gy, a significant amount of double-strand breaks are observed. For increasing dose, the percentage of small fragments
increases and is accompanied by a shortening of the average fragment length from < L> = 1,400 nm for a dose of D = 250 Gy to < L> = 1,080 nm after irradiation with D = 1,500 Gy. The most crucial parameter, the average number of double-strand breaks per broken plasmid (<DSB b> ) has been determined for the first time for the applied doses. The results show that the average number of DSBs per broken
plasmid <DSB b> increases almost linearly from a value of <DSB b> = 1.3 after irradiation with D = 250 Gy to <DSB b> = 1.7 after exposure to D = 1,500 Gy. The presented results show that the amount of DSBs induced by X-ray radiation in plasmid DNA can be calculated
with high accuracy by means of scanning force microscopy, providing relevant information regarding the interaction of X-rays
with DNA molecules.
相似文献
18.
The proposal in this study was to evaluate the physical properties of different biopolymers films. The materials used were:
pectin, carboxyl methylcellulose, methylcellulose, hydroxyl propylcellulose, hydroxypropyl-methylcellulose, and corn waxy
starch; from these polysaccharides aqueous dispersions were prepared to 3% ( w/ v) for obtained films. In these biopolymer films, the thermal diffusivities (α) was evaluated by the Open Photoacoustic Cell
method; also, their mechanical properties as tensile strength, elongation, and Young’s modulus were measured, their crystallinity
percentage was evaluated by X-ray diffraction and microstructure through atomic force microscopy in contact mode. From the
polysaccharide films, it was observed that most of them were flexible and transparent. In the case of the films, mechanical
properties were found that the highest value of tensile strength and Young’s modulus corresponded to carboxyl methylcellulose
with 69.17 and 1,912.20 MPa values, respectively. Also, Open Photoacoustic Cell method and X-ray diffraction measurements
showed that there exist a correlation between the thermal diffusivity values and the crystallinity measured in the biopolymer
films. It was also observed that α values of cellulose derived was affected by the substitution group in the molecule, reaching
the highest α value, the films of carboxyl methylcellulose. Regarding the microstructural of the films, starch showed the
highest roughness value (88.6 nm) whereas hydroxypropyl-methylcellulose resulted with the lowest roughness value (7.67 nm). 相似文献
19.
Phototransformation of P R to P FR in a 1,0007,000 x gpelletable fraction (17 KP), which was extracted fromdark-grown pea shoots that had been irradiated by red then far-redlight, was studied by low temperature spectrophotometry. Redlight irradiation of P R in 17 KP at 160°Cinduced an absorption increase at 695696 nm with a concomitant,small decrease of P R absorption at 670 nm. These changes werepartially photoreversed when the sample was irradiated subsequentlywith 700-nm light. At 55°C, red light irradiationof P R resulted mainly in bleaching and consequently in a reductionof the P R peak, accompanied by minor absorbance increases around695 nm. The intermediates formed at 165°C by 660-nmlight irradiation partly reverted back to P R or formed a bleachedintermediate (probably the same bleached intermediate describedabove) in the dark, when the pellets were warmed to 60°C.The bleached intermediate was transformed to P FR in the darkat 10°C or above. These characteristics of P R transformation observed in the pelletablephytochrome were essentially the same as those observed in invivo or soluble phytochrome. (Received December 24, 1982; Accepted July 28, 1983) 相似文献
20.
In this paper, a new glucose biosensor was prepared. At first, Prussian blue (PB) was electrodeposited on a glassy carbon
electrode (GCE) modified by titanium dioxide-multiwall carbon nanotubes-chitosan (TiO 2-MWNTs-CS) composite, and then gold nanoparticles functionalized by poly(diallyldimethylammonium chloride) (PDDA-Au) were
adsorbed on the PB film. Finally, the negatively charged glucose oxidase (GOD) was self-assembled on to the positively charged
PDDA-Au. The electrochemical performances of the modified electrodes had been studied by cyclic voltammetry (CV) and amperometric
methods, respectively. In addition, the stepwise fabrication process of the as-prepared biosensor was characterized by scanning
electron microscopy. PDDA-Au nanoparticles were characterized by ultraviolet–vis absorption spectroscopy and transmission
electron microscopy. Under the optimal conditions, the as-prepared biosensor exhibited a good response performance to glucose
with a linear range from 6 μM to 1.2 mM with a detection limit of 0.1 μM glucose ( S/ N = 3). In addition, this work indicated that TiO 2-MWNTs-CS composite and PDDA-Au nanoparticles held great potential for constructing biosensors. 相似文献
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