The translocation dynamics of the polymer through a conical pore: Non-stuck, weak-stuck, and strong-stuck modes.

The external voltage-driven polymer translocation through a conical pore (with a large opening at the entry and a small tip at the exit) is studied by using the Langevin dynamics simulation in this paper. The entire translocation process is divided into an approaching stage and a threading stage. First, the approaching stage starts from the polymer entering the large opening and ends up at a terminal monomer reaching the pore tip. In this stage, the polymer will undergo the conformation adjustment to fit the narrowed cross-sectional area of the pore, leading to three approaching modes: the non-stuck mode with a terminal monomer arriving at the pore tip smoothly, the weak-stuck mode for the polymer stuck inside the pore for a short duration with minor conformational adjustments, and the strong-stuck mode with major conformational changes and a long duration. The approaching times (the duration of the approaching stage) of the three approaching modes show different behavior as a function of the pore apex angle. Second, the threading stage describes that the polymer threads through the pore tip with a linear fashion. In this stage, an increase in the apex angle causes the reduction of the threading time (the duration of the threading stage) due to the increase in the driving force with the apex angle at the tip. Moreover, we also find that with the increase in the apex angle or the polymer length, the polymer threading dynamics will change from the quasi-equilibrium state to the non-equilibrium state.

Design and performance of a terahertz absorber based on patterned graphene.

Modern terahertz (THz) technology offers the advantage of enhanced target detection ability with high spatial and temporal resolutions in the THz band, which makes it a formidable threat to stealth targets. Consequently, THz absorbers have outstanding potential as an electromagnetic countermeasure. In this Letter, we design, fabricate, and characterize a THz absorber based on patterned graphene. We present the transfer, photolithography, and etching processes involved in graphene patterning, as well as the experimental measurements of the fabricated absorber. Our simulations show that with an increase in the Fermi energy, the performance of the designed absorber gradually improves and, finally, decreases slightly. Further, the absorption bandwidth first broadens and then narrows slightly. The effective bandwidth with absorption ≥90% ranges from 1.54 to 2.23 THz, with the relative bandwidth (RBW) reaching about 36.6%. Although the measured RBW (from ∼12% to ∼14% and then to ∼8%) slightly deviates from the simulated one, the position of the resonant frequency is well matched between theory and experiment. Moreover, we illuminate the absorption mechanism using the theory of destructive interference. This Letter can significantly contribute to the design, manufacture, and application of patterned graphene-based THz absorbers.

Theoretical study on the polymer translocation into an attractive sphere.

We report a non-sampling model, combining the blob method with the standard lattice-based approximation, to calculate the free energy for the polymer translocation into an attractive sphere (i.e., spherical confined trans side) through a small pore. The translocation time is then calculated by the Fokker-Planck equation based on the free energy profile. There is a competition between the confinement effect of the sphere and the polymer-sphere attraction. The translocation time is increased due to the confinement effect of the sphere, whereas it is reduced by the polymer-sphere attraction. The two effects offset each other at a special polymer-sphere attraction which is dependent on the sphere size, the polymer length, and the driving force. Moreover, the entire translocation process can be divided into an uncrowded stage where the polymer does not experience the confinement effect of the sphere and a crowded stage where the polymer is confined by the sphere. At the critical sphere radius, the durations of the two (uncrowded and crowded) stages are the same. The critical sphere radius R* has a scaling relation with the polymer length N as R* ∼ Nß. The calculation results show that the current model can effectively treat the translocation of a three-dimensional self-avoiding polymer into the spherical confined trans side.

Green synthesis of gold nanoparticles using Citrus maxima peel extract and their catalytic/antibacterial activities.

The peel of Citrus maxima (C. maxima) is the primary byproducts during the process of fruit or juice in food industries, and it was always considered as biomass waste for further treatments. In this study, the authors reported a simple and eco-friendly method to synthesise gold nanoparticles (AuNPs) using C. maxima peel extract as reducing and capping agents. The synthesised AuNPs were characterised by UV-visible spectrum, X-ray diffraction (XRD), transmission electron microscope (TEM) and Fourier-transform infrared spectroscopy (FTIR). The UV-visible spectrum of the AuNPs colloid showed a characteristic peak at 540 nm. The peaks of XRD analysis at (2θ) 38.30°, 44.28°, 64.62°, 77.57° and 81.75° were assigned to (111), (200), (220), (311) and (222) planes of the face-centered cubic (fcc) lattice of gold. The TEM images showed that AuNPs were nearly spherical in shape with the size of 8-25 nm. The FTIR spectrum revealed that some bioactive compounds capped the surface of synthesised AuNPs. The biosynthesised AuNPs performed strong catalytic activity in degradation of 4-nitrophenol to 4-aminophenol and good antibacterial activity against both gram negative (Escherichia coli) and gram positive (Staphylococcus aureus) bacterium. The synthesis procedure was proved simple, cost effective and environment friendly.

Ultra-wideband surface plasmonic Y-splitter.

We present an ultra-wideband Y-splitter based on planar THz plasmonic metamaterials, which consists of a straight waveguide with composite H-shaped structure and two branch waveguides with H-shaped structure. The spoof surface plasmonic polaritons (SSPPs) supported by the straight waveguide occupy the similar dispersion relation and mode characteristic to the ones confined by the branch waveguides. Attributing to these features, the two branch waveguides can equally separate the SSPPs wave propagating along the straight plasmonic waveguide to form a 3dB power divider in an ultra-wideband frequency range. To verify the functionality and performance of the proposed Y-splitter, we scaled down the working frequency to microwave and implemented microwave experiments. The tested device performances have clearly validated the functionality of our designs. It is believed to be applicable for future plasmonic circuit in microwave and THz ranges.

Translocation of polymers into crowded media with dynamic attractive nanoparticles.

The translocation of polymers through a small pore into crowded media with dynamic attractive nanoparticles is simulated. Results show that the nanoparticles at the trans side can affect the translocation by influencing the free-energy landscape and the diffusion of polymers. Thus the translocation time τ is dependent on the polymer-nanoparticle attraction strength ɛ and the mobility of nanoparticles V. We observe a power-law relation of τ with V, but the exponent is dependent on ɛ and nanoparticle concentration. In addition, we find that the effect of attractive dynamic nanoparticles on the dynamics of polymers is dependent on the time scale. At a short time scale, subnormal diffusion is observed at strong attraction and the diffusion is slowed down by the dynamic nanoparticles. However, the diffusion of polymers is normal at a long time scale and the diffusion constant increases with the increase in V.

A 90° fair circular waveguide bend.

We propose a synthesis method to design a 90° bent fair circular waveguide TE01 mode transition based on the non-uniform rational B-spline technique. The transition by this method has advantages of small geometry, high transmission with wide band and high profile fairness. An example of design of such a transition is presented. The simulation shows that the transition exhibits a transmission as high as 99.3% at the central frequency 35 GHz and has a bandwidth of 16.7% when keeping the transmission over 95%. Furthermore, the profile is extremely fair, which meets the requirements to decrease the geometry errors between actual device and its design, to reduce the machining difficulty in the machining process. The hot test data indicate that good transmission of the TE01 mode is obtained.

Influence of polymer-pore interaction on the translocation of a polymer through a nanopore.

The translocation of a bond fluctuation polymer through an interacting nanopore is studied using dynamic Monte Carlo simulation. A driving force F is applied only for monomers inside the pore. The influence of polymer-pore interaction on the scaling relation τ~N(α) is studied for both unbiased and biased translocations, with τ the translocation time and N the polymer length. Results show that the exponent α is dependent on the polymer-pore interaction. For a noninteracting pore, we find α=2.48 for unbiased translocation and α=1.35 for strong biased translocation; for strong attraction, we find α=2.35 for unbiased translocation and α=1.22 for strong biased translocation. The unbiased translocation corresponds to the low-NF regime whereas the strong biased translocation corresponds to the high-NF regime.

Effects of an attractive wall on the translocation of polymer under driving.

The effects of an attractive wall at the trans side on the translocation of an eight-site bond-fluctuation model (BFM) polymer through a pore in a membrane under driving are simulated by the dynamic Monte Carlo method. The attractive wall shows two contrary effects: its excluded volume effect reduces configuration entropy and thus hinders the translocation of the polymer, while its attraction decreases the energy and thus accelerates the translocation. At a critical polymer-wall interaction ε* ≈- 1, we find that the two effects compensate each other and the translocation time τ is roughly independent of the separation distance between the wall and the pore. The value ε* ≈- 1 is roughly equal to the critical adsorption point for the BFM polymer. Moreover, the value of the critical attraction is roughly independent of chain length N and chemical potential difference Δµ. At last, a scaling relation τ âˆ¼ N(α) is observed for polymer translocation at a high value of NΔµ. Though the translocation time is highly dependent on the polymer-wall interaction and pore-wall separation distance, the exponent α is always about 1.30 ± 0.05 so long as NΔµ is large enough.

Translocation properties of copolymer (A(n)B(m))(l) through an interacting pore.

The translocation of a copolymer (A(n)B(m))(l) through an interacting pore was investigated by Monte Carlo simulation on a three-dimensional cubic lattice. Interactions between monomer A and pore ɛ(A) and between monomer B and pore ɛ(B) were considered. The difference between two translocation orientations, orientation A with monomer A entering the pore first and orientation B with monomer B first, was studied. Both the orientation probability and translocation time are dependent on monomer-pore interactions, block length, and fractions of monomers. The separation of different copolymers using translocation was also discussed. The results were explained qualitatively from the view of the free energy landscape of the copolymer translocation.

Monte Carlo simulation on polymer translocation in crowded environment.

The effect of crowded environment with static obstacles on the translocation of a three-dimensional self-avoiding polymer through a small pore is studied using dynamic Monte Carlo simulation. The translocation time τ is dependent on polymer-obstacle interaction and obstacle concentration. The influence of obstacles on the polymer translocation is explained qualitatively by the free energy landscape. There exists a special polymer-obstacle interaction at which the translocation time is roughly independent of the obstacle concentration at low obstacle concentration, and the strength of the special interaction is roughly independent of chain length N. Scaling relation τ ~ N(1.25) is observed for strong driving translocations. The diffusion property of polymer chain is also influenced by obstacles. Normal diffusion is only observed in dilute solution without obstacles or in a crowded environment with weak polymer-obstacle attraction. Otherwise, subdiffusion behavior of polymer is observed.

Simulation study on the translocation of diblock copolymer A(n)B(n) through interacting nanopores.

Translocation of diblock copolymer A(n)B(n) through an interacting nanopore is studied using a dynamic Monte Carlo method on a simple three-dimensional cubic lattice. The probabilities and translocation times of two translocation orientations of copolymer, orientation A with block A translocating first and orientation B with block B first, are mainly dependent on the segment-pore interactions ε(A) and ε(B). We find that both the probability and the translocation time are larger for the orientation with stronger attraction. The dynamic behaviors of copolymer translocation at different ε(A) and ε(B) can be explained based on the free energy landscapes of homopolymer at different polymer-pore interaction. The results reveal a complicated free energy landscape for copolymer translocation.

Free energy landscape for the translocation of polymer through an interacting pore.

Free energy landscapes for polymer chain translocating through an interacting pore are calculated by using exact enumeration method. A potential barrier exists at weak attractive or repulsive polymer-pore interaction and it changes to a potential well with the increase in the attraction. The result reveals that there is a free translocation point where polymer is free of energy barrier. Using the free energy landscape, the translocation time tau for polymer worming through the pore and the migration time tau(m) for polymer migrating from cis side to trans side are calculated with the Fokker-Plank equation. It shows that a moderate attractive polymer-pore interaction accelerates the migration of polymer from cis side to trans side.

[Impact of proportion of adding raw wastewater on post-treatment of digested piggery wastewater].

Sequencing batch reactor (SBR) was used to treat digested piggery wastewater, in order to investigate the impact of proportion of adding raw wastewater. In consecutive experiments, the reactor with adding 30% raw wastewater could get low ammonia nitrogen (NH3-N), usually less than 10 mg/L in the effluent, while the reactors with adding 10% or 20% raw wastewater, concentration of NH3-N increased by degrees until reached 300 mg/L or 80 mg/L respectively at end of experiment. These can be explained by the facts that the reactor with adding 30% raw wastewater could maintain stable pH (about 7.7), whereas pH in the reactors with adding 10% or 20% raw wastewater decreased gradually until to below 5.5. Performance monitoring of a cycle of SBR indicate that the peak value of nitrite nitrogen (NO2(-)-N) and valley value of ammonia nitrogen (NH3-N) occur in the fourth, third and second hour after aeration beginning for the reactors with adding 10%, 20% and 30% raw wastewater respectively, which imply that the more is the proportion of adding raw wastewater, the fast does the ammonia oxidized. These results can be attributed to the facts the higher proportion of adding raw wastewater brought better denitrification resulting in stable and high pH. The batch experiment shows that the rate of denitrification has positive correlation with ratio of BOD5 to TN in influent. The consecutive and batch experiment all prove the proportion of adding raw wastewater must reach more than 30% for normal operation of post-treatment of digested piggery wastewater.

Caspase-1 dependent macrophage death induced by Burkholderia pseudomallei.

Burkholderia pseudomallei is the causative agent for melioidosis, an infectious disease endemic in South-east Asia and northern Australia. Infection can result in a wide spectrum of clinical outcomes, including asymtomatic, acute or chronic conditions. The ability of the bacteria to survive intracellularly within phagocytes and non-phagocytes is postulated to help this pathogen persist in the body during latent chronic conditions. In some Gram-negative bacteria, such as Shigella and Salmonella, the ability to evade macrophage killing involves inducing rapid macrophage cell death. In several of these instances, these bacteria activate cellular caspase-1 to induce cell death, which is increasingly described to exhibit features more characteristic of oncosis than classical apoptosis. We found that B. pseudomallei is also capable of inducing caspase-1 dependent death in macrophages and this process requires a functional bsa Type III Secretion System (TTSS). Bacterial internalization and pore formation in the cell membrane is necessary for death. Furthermore, cell death is accompanied by the release of IL-1beta and IL-18. We believe that this novel description of macrophage death induced by B. pseudomallei could shed light on the pathogenesis of the bacteria in disease.

Embryonic cell lines with endothelial potential: an in vitro system for studying endothelial differentiation.

OBJECTIVE: Endothelial differentiation is a fundamental process in angiogenesis and vasculogenesis with implications in development, normal physiology, and pathology. To better understand this process, an in vitro cellular system that recapitulates endothelial differentiation and is amenable to experimental manipulations is required. METHODS AND RESULTS: Embryonic cell lines that differentiate exclusively into endothelial cells were derived from early mouse embryos using empirical but reproducible culture techniques without viral or chemical transformation. The cells were not pluripotent and expressed reduced levels of Oct 4 and Rex-1. They were non-tumorigenic with a population doubling time of approximately 15 hours. When plated on matrigel, they readily differentiated to form patent tubular structures with diameters of 30 to 150 microm. The differentiated cells endocytosed acetylated low-density lipoprotein (LDL) and began to express endothelial-specific markers such as CD34, CD31, Flk-1, TIE2, P-selectin, Sca-1, and thy-1. They also expressed genes essential for differentiation and maintenance of endothelial lineages, eg, Flk-1, vascular endothelial growth factor (VEGF), and angiopoietin-1. When transplanted into animal models, these cells incorporated into host vasculature. CONCLUSIONS: These cell lines can undergo in vitro and in vivo endothelial differentiation that recapitulated known endothelial differentiation pathways. Therefore, they are ideal for establishing an in vitro cellular system to study endothelial differentiation.