A Sub-wavelength Electro-optic Switch Based on Plasmonic T-Shaped Waveguide

A sub-wavelength electro-optic switch based on plasmonic T-shaped waveguide has been proposed and numerically investigated. The finite-difference time-domain simulation results reveal that the switch based on T-shaped waveguide with two U-shaped grooves can realize the function of switching single wavelength from one port to the other by an external voltage. The U-shaped structure is composed of two teeth filled with highly nonlinear organic EO material and one groove filled with 6H-SiC connecting the two teeth. The switch wavelength can be chosen by adjusting both lengths of the left and right teeth, and the switch voltage is 3.35 V for the wavelength of λ = 730 nm with the insertion loss around −2.6 dB and the extinction ratio around −20 dB at port 2.     

An Annular Plasmonic Lens Under Illumination of Circularly Polarized Light

In this paper, we consider a circular central aperture surrounded with annular depth-tuned grooves and investigate the beaming effect of the structure under illumination of a circularly polarized (CP) plane wave. As a CP plane wave is equivalent to the superposition of two linearly polarized plane waves (TM and TE) with a phase difference of π/2, the superposition of the electric field intensity, ( | E_x |² + | E_y |² ) \left( {{{\left| {E_x} \right|}^2} + {{\left| {E_y} \right|}^2}} \right) , is observed in the transmission field. In addition, two plasmonic modes are found at the resonant wavelengths λ ₁ and λ ₂ with each consisting of multiple wavelengths. At the wavelength λ ₁ = 420 nm, the significant near-field collimation is formed along the direction z, having a long propagation distance up to 1.75 μm (≈4λ) away from the exit plane of the new plasmonic lens.     

Scattering spectrum properties and their relationship to biogeochemical parameters: a case study in Taihu Lake

The scattering spectrum properties of highly turbid and eutrophic inland case 2 water from Taihu Lake were studied during three cruises from 2006 to 2007. The scattering [b _p(λ)] and backscattering [b _bp(λ)] coefficients and the backscattering probability (B) for Taihu Lake were found to show a clear spectral dependence, and this dependence was well simulated by a power-law function. This dependence, however, became weak when algae dominated the sample points. The mean values of the power-law index for b _p(λ), v, in Oct 2006, Mar 2007 and Nov 2007 were −0.6712, −0.8129 and −0.7600, respectively. To interpret the spectral characteristics and mechanisms of b _p(λ) and b _bp(λ), water samples were collected simultaneously for the biogeochemical characterization of suspended particles. The average values of the specific scattering coefficients for total suspended matter, inorganic suspended matter (ISPM) and organic suspended matter (OSPM) were 0.634 (550 nm), 1.057 (532 nm), and 0.396 g m⁻² (532 nm), respectively. The power-law index of b _bp(λ) (Y) was significantly related to ISPM/OSPM and b _bp(532 nm), but only weakly related to the particle size distribution index. The mean (spatial and wavelength) values of B in Oct 2006, Mar 2007, and Nov 2007 were 0.0108, 0.0138, and 0.0125, respectively. B decreases with increasing ISPM concentration because of the large contribution of ISPM to b _b(λ) and the strong restraint on b _bp(λ) caused by the multi-scattering effect under high-turbidity conditions.     

Numerical Investigation on Elliptic Cylindrical Nanowire Hybrid Plasmonic Waveguide–Based Polarization Beam Splitter

A novel design of elliptic cylindrical nanowire hybrid plasmonic waveguide (ECNHPW)–based polarization beam splitter (PBS) is proposed. In the proposed design, the ECNHPW arm acts as an input port and a bar port; on the other hand, a regular silicon wire (RSW) arm acts as a cross port. By selecting the physical parameters of the proposed PBS accurately, the transverse electric (TE) mode is merely satisfied with the phase-matching condition. In contrast, the transverse magnetic (TM) mode does not propagate to the RSW arm. Consequently, the TM input mode goes directly to the ECNHPW arm, while the TE input mode in ECNHPW is coupled with RSW arm. As a result, the two different polarization modes are meritoriously separated, and they pass through two different arms. For the proposed PBS, the insertion loss (IL) of both polarizations lies below 1 dB. For TE input, the value of the polarization extinction ratio (PER) is 27.2 dB, and for TM input, it is 23.9 dB at 1550 nm operating wavelength. Further optimization is implemented by varying the wavelength, thickness of SiO₂, and the gap between the waveguides using the finite element method (FEM). The proposed PBS is designed with 150 nm bandwidth, high PER, and low IL, which can be suitable for photonic integrated circuits (PICs).

     

Two X family DNA polymerases, λ and μ, in meiotic tissues of the basidiomycete, Coprinus cinereus

The X family DNA polymerases λ (CcPolλ) and μ (CcPolμ) were shown to be expressed during meiotic prophase in the basidiomycete, Coprinus cinereus. These two polymerases are the only members of the X family in the C. cinereus genome. The open reading frame of CcPolλ encoded a predicted product of 800 amino acid residues and that of CcPolμ of 621 amino acid residues. Both CcPolλ and CcPolμ required Mn²⁺ ions for activity, and both were strongly inhibited by dideoxythymidine triphosphate. Unlike their mammalian counterparts, CcPolλ and CcPolμ had no terminal deoxynucleotidyl transferase activity. Immunostaining analysis revealed that CcPolλ was present at meiotic prophase nuclei in zygotene and pachytene cells, which is the period when homologous chromosomes pair and recombine. CcPolμ was present in a slightly wider range of cell stages, zygotene to diplotene. In analyses using D-loop recombination intermediate substrates, we found that both CcPolλ and CcPolμ could promote primer extension of an invading strand in a D-loop structure. Moreover, both polymerases could fully extend the primer in the D-loop substrate, suggesting that D-loop extension is an activity intrinsic to CcPolλ and CcPolμ. Based on these data, we discuss the possible roles of these polymerases in meiosis.     

Development of optical criteria to discriminate various types of highly turbid lake waters

Our aim was to refine the optical classification of turbid waters in order to improve the performance of water color algorithms. Bio-optical measurements and sampling of optically active substances were performed in highly turbid lakes Taihu, Chaohu, and Dianchi, and in Three Gorges reservoir in China. Based on strong correlations between trough depths of remote sensing reflectance (R _rs(λ)) near 680 nm (denoted as TD680) and the ratios of inorganic suspended matter (ISM) to total suspended matter (TSM) concentrations, an empirical model was developed for water classification. In the 400–900 nm spectral range, different correlations between R _rs(λ), TSM and chlorophyll a (Chla) concentrations indicate discrepancies among the following ISM/TSM ranges: ISM/TSM ≤ 0.5, 0.5 < ISM/TSM < 0.8, and ISM/TSM ≥ 0.8. Corresponding findings support an important conclusion that only high ISM/TSM ratios, usually above 0.5, and using the more sensitive and stable near infrared spectral range (730–820 nm), can assure good performances of the TSM remote sensing algorithms. Meanwhile, the particulate absorption a _p(λ) and scattering b _p(λ) were strongly influenced by different ranges of ISM/TSM ratios. Typically the a _p(675) peaks became more and more vague as ISM/TSM increased, and the b _p(λ) values first decreased and then increased with a marked inflexion at ISM/TSM ≈ 0.5. The TD680 threshold values were derived to discriminate three types of turbid waters, i.e., Type 1 (TD680 ≥ 0.0082 sr⁻¹), Type 2 (0.0082 sr⁻¹ > TD680 > 0 sr⁻¹), and Type 3 (TD680 ≤ 0 sr⁻¹). This study provides a promising tool for identifying various types of highly turbid waters, and is significant for the development of class-based algorithms of water color remote sensing.     

Distributed MEMS Sensors Using Plasmonic Antenna Array Embedded Sagnac Interferometer

A micro Sagnac interferometer is proposed for electron cloud distributed sensors formed by an integrated (micro-electro-mechanical systems) MEMS resonator structure. The Sagnac interferometer consists of four microring probes integrated into a Sagnac loop. Each of the microring probes is embedded with the silver bars to form the plasmonic wave oscillation. The polarized light of 1.50 µm wavelength is input into the interferometer, which is polarized randomly into upstream and downstream directions. The polarization outputs can be controlled by the space–time input at the Sagnac port. Electrons are trapped and oscillated by the whispering gallery modes (WGMs), where the plasmonic antennas are established and applied for wireless fidelity (WiFi) and light fidelity (LiFi) sensing probes, respectively. Four antenna gains are 2.59 dB, 0.93 dB, 1.75 dB, and 1.16 dB, respectively. In manipulation, the sensing probe electron densities are changed by input source power variation. When the electron cloud is excited by the microscopic medium, the change in electron density is obtained and reflected to the required parameters. Such a system is a novel device that can be applied for brain-device interfering with the dual-mode sensing probes. The obtained WGM sensors are 1.35 µm^?2, 0.90 µm^?2, 0.97 µm^?2, and 0.81 µm^?2, respectively. The WGMs behave as a four-point probe for the electron cloud distributed sensors, where the electron cloud sensitivities of 2.31 prads^?1mm³ (electrons)^?1, 2.27 prads^?1mm³ (electrons)^?1, 2.22 prads^?1mm³(electrons)^?1, and 2.38 prads^?1mm³(electrons)^?1 are obtained, respectively.

     

A Simple and Sensitive SPRS Method for Trace H2O2 Based on the TiO2+ Complex and Gold Nanoparticles Aggregation Reactions

In the medium of H₂SO₄ and in the presence of TiO²⁺, gold nanoparticles in size of 10 nm exhibited a weak surface plasmon resonance scattering (SPRS) peak at 775 nm. Upon addition of trace H₂O₂, the yellow complex [TiO(H₂O₂)]²⁺ formed that cause the gold nanoparticles aggregations to form bigger gold nanoparticle clusters in size of about 900 nm, and the SPRS intensity at 775 nm (I) enhanced greatly. The enhanced intensity ΔI was linear to the H₂O₂ concentration in the range of 0.025–48.7 μg/mL, with a detection limit of 0.014 μg/mL H₂O₂. This SPRS method was applied to determining H₂O₂ in water samples with satisfactory results.     

A Novel Polarization Filter Based on Photonic Crystal Fiber with a Single Au-Coated Air Hole and Semi-Hourglass Structure

A polarization filter that has a novel photonic crystal fiber structure of semi-hourglass part and Au-coated film is proposed. We simulated the performance of the structure by the finite element method. The numerical simulation results show that altering the structure parameters and the thickness of Au film can lead to an optimal parameter combination with remarkable features, owing to the semi-hourglass part that induced huge asymmetry factor into the structure. On the one hand, when the thickness of Au film is controlled to be 18.7 nm, we can get the confinement loss 1304.02 dB/cm and 3.96 dB/cm on y-polarization and x-polarization respectively at λ = 1.55 μm. On the other hand, controlling the thickness to 35 nm, the confinement loss on y-polarization and x-polarization is 848.87 dB/cm and 1.31 dB/cm respectively at λ = 1.31 μm. In addition, the bandwidth with crosstalk smaller than − 20 dB is 680 nm and 800 nm at λ = 1.55 μm and 1.31 μm, respectively, when the fiber length is 500 μm. This structure, as a reference, can provide a new idea when designing a photonic crystal fiber structure applied in optical communication and sensor system.

     

High Efficient Far-Field Nanofocusing with Tunable Focus Under Radial Polarization Illumination

We design a new nanofocusing lens for far-field practical applications. The constructively interference of cylindrical surface plasmon launched by the subwavelength metallic structure can form a subdiffraction-limited focus, which is modulated by the dielectric grating from the near field to the far field. The principle of designing such a far-field nanofocusing lens is elucidated in details. The numerical simulations demonstrated that nanoscale focal spot (0.12λ ²) can be realized with 3.6λ in depth of focus and 4.5λ in focal length by reasonably designing parameters of the grating. The focusing efficiency can be 7.335, which is much higher than that of plasmonic microzone plate-like lenses. A blocking chip can enhance the focusing efficiency further as the reflected waves at the entrance would be recollected at the focus. By controlling the number of the grooves in the grating, the focal length can be tuned easily. This design method paved the road for utilizing the plasmonic lens in high-density optical storage, nanolithography, superresolution optical microscopic imaging, optical measurement, and sensing.     

Subwavelength Focusing Using Plasmonic Wavelength-Launched Zone Plate Lenses

We propose a plasmonic wavelength-launched Fresnel zone plate structure for subwavelength focusing. The plasmonic structure consists of a central circular groove surrounded by 12 transparent and opaque zones. All the zones with widths smaller than one half of the incident wavelength are used to enhance the field of evanescent waves in the transmission. Based on the finite-difference time-domain analysis, a focus spot with a full-width at half-maximum of 270 nm (= 0.4λ _in ) can be achieved, accompanied by a largely reduced depolarization effect. The sharp waistline indicates that the surface waves are largely converged in the region of focus.     

A novel and sensitive resonance scattering assay for detection of urea in serum coupled urease catalytic reaction and NH4 + associated particle reaction

In the pH 6.6 Na₂HPO₄–NaH₂PO₄ buffer solutions and in the presence of urease catalyst, urea can be decomposed to form NH₄ ⁺. The NH₄ ⁺ reacted with sodium tetraphenyl boron (NaTPB) to form the association particles that exhibited a resonance scattering (RS) peak at 474 nm. When the urea concentration increased, NH₄ ⁺ increased, and RS intensity at 474 nm enhanced linearly. Under the chosen conditions, the increased RS intensity (ΔI _474 nm) had a linear response to the urea concentration in the range of 0.125–15 μM, with a detection limit of 0.058 μM urea, and a regression equation of ΔI _474 nm = 31.6C + 2.1, a correlation coefficient of 0.9986. This catalytic RS method was applied for the detection of urea in human serum sample, with good selectivity and sensitivity, and the results were consistent with the reference method.     

Development of a colorimetric assay for rapid quantitative measurement of clavulanic acid in microbial samples

We developed a colorimetric assay to quantify clavulanic acid (CA) in culture broth of Streptomyces clavuligerus, to facilitate screening of a large number of S. clavuligerus mutants. The assay is based on a β-lactamase-catalyzed reaction, in which the yellow substrate nitrocefin (λ _max=390 nm) is converted to a red product (λ _max=486 nm). Since CA can irreversibly inhibit β-lactamase activity, the level of CA in a sample can be measured as a function of the A ₃₉₀/A ₄₈₆ ratio in the assay mixture. The sensitivity and detection window of the assay were determined to be 50 μg L⁻¹ and 50 μg L⁻¹ to 10 mg L⁻¹, respectively. The reliability of the assay was confirmed by comparing assay results with those obtained by HPLC. The assay was used to screen a pool of 65 S. clavuligerus mutants and was reliable for identifying CA over-producing mutants. Therefore, the assay saves time and labor in large-scale mutant screening and evaluation tasks. The detection window and the reliability of this assay are markedly better than those of previously reported CA assays. This assay method is suitable for high throughput screening of microbial samples and allows direct visual observation of CA levels on agar plates.     

Characterization of PSI recovery after chilling-induced photoinhibition in cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.) leaves

By simultaneously analyzing the chlorophyll a fluorescence transient and light absorbance at 820 nm as well as chlorophyll fluorescence quenching, we investigated the effects of different photon flux densities (0, 15, 200 μmol m⁻² s⁻¹) with or without 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on the repair process of cucumber (Cucumis sativus L.) leaves after treatment with low temperature (6°C) combined with moderate photon flux density (200 μmol m⁻² s⁻¹) for 6 h. Both the maximal photochemical efficiency of Photosystem II (PSII) (F _v/F _m) and the content of active P700 (ΔI/I _o) significantly decreased after chilling treatment under 200 μmol m⁻² s⁻¹ light. After the leaves were transferred to 25°C, F _v/F _m recovered quickly under both 200 and 15 μmol m⁻² s⁻¹ light. ΔI/I _o recovered quickly under 15 μmol m⁻² s⁻¹ light, but the recovery rate of ΔI/I _o was slower than that of F _v/F _m. The cyclic electron transport was inhibited by chilling-light treatment obviously. The recovery of ΔI/I _o was severely suppressed by 200 μmol m⁻² s⁻¹ light, whereas a pretreatment with DCMU effectively relieved this suppression. The cyclic electron transport around PSI recovered in a similar way as the active P700 content did, and the recovery of them was both accelerated by pretreatment with DCMU. The results indicate that limiting electron transport from PSII to PSI protected PSI from further photoinhibition, accelerating the recovery of PSI. Under a given photon flux density, faster recovery of PSII compared to PSI was detrimental to the recovery of PSI or even to the whole photosystem.     

Electromagnetically Induced Transparency and Refractive Index Sensing for a Plasmonic Waveguide with a Stub Coupled Ring Resonator

A plasmonic refractive index sensor based on electromagnetically induced transparency (EIT) composed of a metal-insulator-metal (MIM) waveguide with stub resonators and a ring resonator is presented. The transmission properties and the refractive index sensitivity are numerically studied with the finite element method (FEM). The results revealed an EIT-like transmission spectrum with an asymmetric line profile and a refractive index sensitivity of 1057 nm/RIU are obtained. The coupled mode theory (CMT) based on transmission line theory is adopted to illustrate the EIT-like phenomenon. Multiple EIT-like peaks are observed in the transmission spectrum of the derived structures based on the MIM waveguide with stub resonator coupled ring resonator. To analyze the multiple EIT-like modes of the derived structures, the H _z field distribution is calculated. In addition, the effect of the structural parameters on the EIT-like effect is also studied. These results provide a new method for the dynamic control of light in the nanoscale.     

Variation of chromophoric dissolved organic matter and possible attenuation depth of ultraviolet radiation in Yunnan Plateau lakes

The increase of ultraviolet radiation (UVR, 280–400 nm) caused by stratospheric ozone depletion has profound effects on aquatic ecosystems. High-altitude lakes in the Yunnan Plateau are exposed to high intensities of UVR and contain low concentrations of chromophoric dissolved organic matter (CDOM). Thirty-eight lakes in the Yunnan Plateau with elevations from 1291 to 3809 m above sea level were investigated to study CDOM concentrations and possible effects of UVR on the lake ecosystem. The attenuation of UVR in the Yunnan Plateau lakes was calculated from the absorption coefficient of CDOM based on an empirical relationship from lakes in the Alps and Pyrenees mountains. Absorption coefficients [α(λ)] at 320 nm [α(320)] ranged from 0.52 to 14.05 m⁻¹ (mean ± standard deviation, 4.40 ± 3.85 m⁻¹) and at 380 nm [α(380)] from 0.05 to 4.51 m⁻¹ (1.40 ± 1.30 m⁻¹). The exponential slope coefficient for the relationship of wavelength to α(λ) ranged from 16.2 to 41.4 μm⁻¹ (21.74 ± 4.93 μm⁻¹) over the 280–400 nm interval. Normalized fluorescence emission (NFLU) at 450 nm from an excitation wavelength of 355 nm, F _n(355), averaged 7.93 ± 3.22 NFLU. A significant positive relationship was found between α(355) and F _n(355). The estimated diffuse attenuation coefficients of UV-B (320 nm) and UV-A (380 nm) ranged from 0.55 to 15.77 m⁻¹ and from 0.24 to 6.73 m⁻¹; the corresponding 1% attenuation depths ranged from 0.29 to 8.44 m and from 0.68 to 19.12 m. Twenty-five of 38 lakes had 1% UV-B attenuation depths of 1.5 m or more. The median 1% attenuation depth was 28.8% of the sampling depth for UV-B radiation and 60% for UV-A. In addition to CDOM, chlorophyll α (Chla) and total suspended matter (TSM) also may contribute to attenuation of UVR.     

Relationship between the wavelength maximum of a protein and the temperature dependence of its intrinsic tryptophan fluorescence intensity

Proper determination of the temperature dependence of intrinsic tryptophan fluorescence intensity in native and denatured states is an essential prerequisite for extracting the free energy of protein unfolding from the thermal denaturation profile. The most common method employed in determining the temperature dependence of these conformations is through the determination of slopes of pre- and post-transition baselines. However, simulations of protein unfolding profiles suggest that this method does not work for marginally stable proteins. We show herein that the temperature dependence of the fluorescence intensity of N-acetyl tryptophanamide (NATA) in organic solvents and water may be used to represent the temperature dependence of the fluorescence intensity of tryptophan in native and denatured conformations of a protein, respectively. The wavelength of the emission maximum, λ _max, of N-acetyl tryptophanamide (NATA) in a particular solvent or tryptophan in proteins is related to the temperature dependence (m) of its fluorescence intensity by the equation: m (K⁻¹) = (−0.000299 ± 2.2 × 10⁻⁵ K⁻¹ nm⁻¹) × λ _max (nm) + (0.0919 ± 0.0025 K⁻¹).     

Antivibrio compounds produced by <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. W3: characterisation and assessment of their safety to shrimps

In order to explore compounds naturallly inhibitory to shrimp pathogenic vibrios, a culture filtrate of Pseudomonas sp. W3 at a pH of 2 was extracted with ethyl acetate (EtOAc) to produce 82.15 mg/l of a yellow–brown extract (EtOAc-W3) that had MIC values of 225-450 μg/ml against the growth of 18 shrimp pathogenic Vibrio harveyi strains. The MIC of EtOAc-W3 against the most pathogenic strain PSU 2015 was 450 μg/ml and this strain had the lowest LD₅₀ (50% lethal dose) to pacific white shrimp (Litopenaeus vannamei, PL 21). At this MIC value, EtOAc-W3 in artificial sea water (ASW) killed strain PSU 2015; however in natural sea water, only a partial growth inhibition was observed. The toxicity to pacific white shrimp and antivibrio activity of the EtOAc-W3 were investigated by conducting an experiment with 4 sets; native control (commercial ASW), EtOAc-W3 control (MIC/10, 45 μg/ml), challenge (inoculation 6.0 × 10⁶ c.f.u./ml PSU 2015) and treatment (6.0 × 10⁶ c.f.u./ml PSU 2015 + 45 μg/ml EtOAc-W3). The same experiment was repeated by increasing the dose of EtOAc-W3 to 90 μg/ml (MIC/5). Both concentrations of EtOAc-W3 tested had no toxicity to postlarval shrimps. A significant decrease in shrimp mortality was observed over a 72 h period as approximately 80% of the shrimps died in each challenge set but only 63 and 23% died in the presence of 45 and 90 μg/ml EtOAc-W3. The major component of EtOAc-W3 was supposed to be 2-heptyl-4-quinolone (HHQ) by FAB-MS and ¹H-NMR analyses of the purified fraction.     

A Hybrid Plasmonic Modulator Based on Graphene on Channel Plasmonic Polariton Waveguide

A hybrid plasmonic modulator based on graphene on channel plasmonic polariton waveguide was proposed to overcome the difficulty in achieving high-speed modulation on the nanometric plasmonic waveguide platform. The extinction ratio and the figure of merit of the proposed modulator were analyzed in detail, and a tradeoff between them was found due to the intrinsic loss of the channel plasmonic polariton waveguide. And an optimized hybrid plasmonic modulator with large modulation bandwidth of 0.662 THz, low power consumption of 118.7 fJ/bit, and short device length of 7.680 μm was obtained theoretically. In addition, the proposed hybrid plasmonic modulator based on graphene on channel plasmonic polariton waveguide is easy to fabricate and provides a potential solution for the high-speed plasmonic modulator.

     

Light-Dependency of Growth and Secondary Metabolite Production in the Captive Zooxanthellate Soft Coral Sinularia flexibilis

The branching zooxanthellate soft coral Sinularia flexibillis releases antimicrobial and toxic compounds with potential pharmaceutical importance. As photosynthesis by the symbiotic algae is vital to the host, the light-dependency of the coral, including its specific growth rate (μ day⁻¹) and the physiological response to a range of light intensities (10–1,000 μmol quanta m⁻² s⁻¹) was studied for 12 weeks. Although a range of irradiances from 100 to 400 μmol quanta m⁻² s⁻¹ was favorable for S. flexibilis, based on chlorophyll content, a light intensity around 100 μmol quanta m⁻² s⁻¹ was found to be optimal. The contents of both zooxanthellae and chlorophyll a were highest at 100 μmol quanta m⁻² s⁻¹. The specific budding rate showed almost the same pattern as the specific growth rate. The concentration of the terpene flexibilide, produced by this species, increased at high light intensities (200–600 μmol quanta m⁻² s⁻¹).