Hexagonal Lattice Pattern Research Articles

A graphene/Au/TiO2 coated dual-core PCF SPR biosensor with improved design and performance for early cancer cell detection of with high sensitivity

Nowadays, the second most common disease in the world is cancer and in recent years, the mortality rate from cancer has increased. A biomarker-based approach to diagnosis might significantly improve cancer early detection and subsequent therapy. For the identification or detection of biomarkers, Biosensors are most suitable and crucial tools. An outstanding technique to enable the detection of bioanalytes without the need for labels, using optical methods, is Surface Plasmon Resonance (SPR) technology. This research proposes a biosensor based on SPR technology that exhibits enhanced sensitivity and capabilities for the identification of cancerous cells that is based on hybrid Graphene, Au, and TiO2 layer. Our prototype's fibre has a hexagonal lattice pattern that is perforated with round air holes, that improves sensor performance. The COMSOL Multiphysics Simulation tool's approach known as Finite Element Model (FEM) was used for the numerical study. Using the wavelength-interrogation and amplitude-interrogation techniques, the refractive-index (ri) alterations of malignance cells are identified. After optimising the fibre parameters and utilising the numerical results of the amplitude and spectrum interrogation methodologies, we discovered that this biosensor demonstrated a maximum sensitivity of 5714.29 nm RIU−1 for MCF7 cells when subjected to spectral interrogation. When subjected to amplitude-interrogation techniques, the biosensor exhibited a sensitivity of 599.53 1/RIU for MCF7 cells. Additionally, the biosensor demonstrated a value of 4.0 × 10−5 RIU for Basal cells as higher resolution.

Design and analysis of a photonic crystal-based biosensor for the detection of chikungunya virus

A two-dimensional photonic crystal biosensor is theoretically demonstrated and investigated based on refractive index sensing. It detects the chikungunya virus (CHIKV) in the various blood components with high sensitivity of 421.5 nm/RIU. Simulation and various analyses are done with both normal and infected blood constituents (uric acid, platelets and plasma) to detect CHIKV. The sensor operates within the wavelength range of 1230–1560 nm. The important optical parameters such as sensitivity and quality factor are analyzed and numerical investigations are done with the finite difference time domain method. The sensor is built with a circular array of holes etched on a silicon slab in a hexagonal lattice pattern. A nanohole resonant sensing cavity is placed at the center of two waveguides, enhancing the light–matter interaction of the analyte and trapping the optical mode at the nanohole of the sensor. When the sensor is completely submerged in blood constituents infected with CHIKV (plasma, platelets and uric acid), the resonating modes undergo a shift as the refractive index of each analyte is unique. The sensor has a very high sensitivity of 421.5 nm RIU−1, and a good quality factor of 229.68 for the different blood constituents is obtained. A maximum transmission of 89.25% with a detection limit of 0.01 are obtained and reported in this work.

DMD-based compact SIM system with hexagonal-lattice-structured illumination.

In this study, we developed a novel, compact, and efficient structured illumination microscopy (SIM) system, to our best knowledge. A binary hexagonal lattice pattern was designed and implemented on a digital micromirror device (DMD), resulting in a projection-based structured-light generation. By leveraging the combination of the high-speed switching capability of the DMD with a high-speed CMOS camera, the system can capture 1024×1024 pixels images at a 200fps frame rate when provided with sufficient illumination power. The loading of the hexagonal lattice pattern reduces the number of images required for reconstruction to seven, and by utilizing the DMD modulating characteristics on the illumination path, there is no need to use bulky mechanical structures for phase shifting. We designed a compact system with 110m m×150m m×170m m dimensions that displayed a 1.61 resolution enhancement for fluorescent particle and biological sample imaging.

Structural phase transitions of optical patterns in atomic gases with microwave-controlled Rydberg interactions

Spontaneous symmetry breaking and formation of self-organized structures in nonlinear systems are intriguing and important phenomena in nature. Advancing such research to new nonlinear optical regimes is of much interest for both fundamental physics and practical applications. Here we propose a scheme to realize optical pattern formation in a cold Rydberg atomic gas via electromagnetically induced transparency. We show that, by coupling two Rydberg states with a microwave field (microwave dressing), the nonlocal Kerr nonlinearity of the Rydberg gas can be enhanced significantly and may be tuned actively. Based on such nonlocal Kerr nonlinearity, we demonstrate that a plane-wave state of probe laser field can undergo a modulation instability (MI) and hence spontaneous symmetry breaking, which may result in the emergence of various self-organized optical patterns. Especially, we find that a hexagonal lattice pattern (which is the only optical pattern when the microwave dressing is absent) may develop into several types of square lattice ones when the microwave dressing is applied; moreover, as a outcome of the MI the formation of nonlocal optical solitons is also possible in the system. Different from earlier studies, the optical patterns and nonlocal optical solitons found here can be flexibly manipulated by adjusting the effective probe-field intensity, nonlocality degree of the Kerr nonlinearity, and the strength of the microwave field. Our work opens a route for versatile controls of self-organizations and structural phase transitions of laser light, which may have potential applications in optical information processing and transmission.

Identification and characterization of the S-layer formed on the sheath of Thiothrix nivea.

Thiothrix nivea is a filamentous sulfur-oxidizing bacterium common in activated sludge and its filament is covered with a polysaccharide layer called sheath. In this study, we found that T. nivea aggregates under acidic conditions. A hexagonal lattice pattern, a typical morphological feature of proteinaceous S-layers, was newly observed on the surface of the sheath by transmission electron microscopy. The pattern and the acid-dependent aggregation were not observed in T. fructosivorans, a relative sheath-forming bacterium of T. nivea. The putative S-layer of T. nivea was detached by washing with unbuffered tris(hydroxymethyl)aminomethane base (Tris) solution and a protein of 160kDa was detected by electrophoresis. Based on partial amino acid sequences of the protein, its structural gene was identified. The gene encodes an acidic protein which has a putative secretion signal and a Ca2+-binding domain. The protein was solubilized with urea followed by dialysis in the presence of calcium. A hexagonal lattice pattern was observed in the aggregates formed during dialysis, revealing that the protein is responsible for S-layer formation. Biosorption ability of copper, zinc, and cadmium onto the T. nivea filament decreased upon pretreatment with Tris, demonstrating that the S-layer was involved in metal adsorption. Moreover, aggregation of Escherichia coli was promoted by acidification in the presence of the S-layer protein, suggesting that the protein is potentially applicable as an acid-driven flocculant for other bacteria.

Negatively Charged Lipids Are Essential for Functional and Structural Switch of Human 2-Cys Peroxiredoxin II

The function of ubiquitous 2-Cys peroxiredoxins (Prxs) can be converted alternatively from peroxidases to molecular chaperones. This conversion has been reported to occur by the formation of high-molecular-weight (HMW) complexes upon overoxidation of or ATP/ADP binding to 2-Cys Prxs, but its mechanism is not well understood. Here, we show that upon binding to phosphatidylserine or phosphatidylglycerol dimeric human 2-Cys PrxII (hPrxII) is assembled to trefoil-shaped small oligomers (possibly hexamers) with full chaperone and null peroxidase activities. Spherical HMW complexes are formed, only when phosphatidylserine or phosphatidylglycerol is bound to overoxidized or ATP/ADP-bound hPrxII. The spherical HMW complexes are lipid vesicles covered with trefoil-shaped oligomers arranged in a hexagonal lattice pattern. Thus, these lipids with a net negative charge, which can be supplied by increased membrane trafficking under oxidative stress, are essential for the structural and functional switch of hPrxII and possibly most 2-Cys Prxs.

Probing the magnetization reversal process of permalloy nano-rings with high wall height-to-thickness ratios

We report a study of magnetization reversal process on a tall magnetic nano-ring with a wall height-to-thickness ratio of up to 21. Samples in a hexagonal lattice pattern of ring array with an outer/inner diameter of 300/260 nm and a ring height of 420 nm are fabricated using electron beam lithography in conjunction with an ion beam etching technique. A longitudinal magneto-optical Kerr effect (MOKE) measurement reveals that meta-stable states exist during the magnetization reversal process. In particular, the exact magnetization configurations at the top end of the nano-ring are illustrated using magnetic force microscopy (MFM) that is facilitated with a photoresist etch-back technique. Most interestingly, MFM images of two sets of head-to-head (H2H)/tail-to-tail (T2T) domain walls are captured during the magnetization reversal process. It is believed that the domain walls formation and evolution processes at the top end of the nano-ring are mediated by the anti-symmetrical distribution of the vortex domain wall on the tubular sidewalls. Simulation results using Object Oriented Micromagnetic Framework confirm the MOKE hysteresis loop and MFM imaging.

Magnetoresistance anisotropy in a hexagonal lattice of Co antidots obtained by thermal evaporation

Patterned soft magnetic materials are eligible for use in magnetic random access memories. A hexagonal-lattice pattern of circular antidots was produced by optical lithography in a Co film. In order to test the effect of geometry on the local magnetisation configuration of such a structure, we performed room-temperature angle-resolved magnetisation measurements aimed to check the pinning of domain walls by the pattern's lattice. Magnetoresistance (MR) room-temperature measurements were performed at various angles between the magnetic field direction and the macroscopic electrical current vector, to clarify whether and how the local current density configuration affects the MR response. We found that the magnetoresistance is of anisotropic type (AMR) and has a local origin. Furthermore, the largely unsaturating behaviour of MR at high fields may be explained only by considering that tiny portions of the pattern constitute highly frustrated regions and align their magnetisation at rather high fields. A simplified model based on a local anisotropy term is shown to account for the experimental results for both M and MR.

English

Hexagonal lattice pattern formed by helical and circumferential ribs is the most common among different possible lattice patterns. An energy-based smeared stiffener model (SSM) is developed to obtain equivalent stiffness coefficients of a composite lattice cylindrical shell with such hexagonal lattice patterns. Using the equivalent stiffness coefficients, Ritz buckling analysis was carried out. Extensive finite element modelling covering different representative sizes have been carried out. SSM is validated by comparing the estimated buckling loads. Variation of material properties of rib unidirectional composites from those of normal unidirectional composites is accounted for in the energy formulations. Defence Science Journal, 2009, 59(3), pp.230-238 , DOI:http://dx.doi.org/10.14429/dsj.59.1516

Enhanced external quantum efficiency of light emitting diodes by fabricating two-dimensional photonic crystal sapphire substrate with holographic technique

Investigation in fabricating two-dimensional (2D) photonic crystal (PC) on sapphire substrates for enhancing external efficiency of GaN based light emitting diodes (LEDs) is presented. 2D-PC was fabricated on a sapphire substrate using holographic lithography and inductively coupled plasma (ICP) dry etching. LEDs with 2μm thick n-GaN layer，four pairs of InGaN/GaN quantum well structures and 200nm thick p-GaN layer were grown on the patterned sapphire substrate (PSS) by metal organic chemical vapor deposition (MOCVD). The PC fabricated on PSS has 2D hexagonal lattice pattern，with 3.8μm lattice constant and 800nm depth. LED output measurement shows 100% increase in the average luminous intensity of PSS-LEDs compared with that of conventioanl LEDs. The measured X-ray rocking curves of (0002) diffraction for GaN layers grown on patterned and non-patterned sapphire substrates indicate that the quality of GaN crystal grown on PSS is not improved，which implies that the large enhancement of external quantum efficiency of PSS-LED is not caused by the increase in internal efficiency but possibly by the increase in extraction efficiency，which results from the scattering of the PSS.

GaN-Based Light-Emitting Diodes Grown on Photonic Crystal-Patterned Sapphire Substrates by Nanosphere Lithography

GaN-based light-emitting diodes (LEDs) grown on photonic crystal-patterned sapphire substrates (PCPSS) have been demonstrated. PCPSS was fabricated by nanosphere lithography, and the photonic crystal structure was the hexagonal-lattice pattern. The forward voltages of PCPSS and patterned sapphire substrates (PSS) LEDs were smaller than that of conventional sapphire substrates (CSS) LED, and it infers the epitaxial film quality of PCPSS and PSS LEDs has been slightly improved. The luminance intensity of PCPSS LED was 1.63 and 1.51 times higher than those of CSS and PSS LED at 20 mA injection current. The enhancement in the luminance intensity of PCPSS LED is attributed to the photonic crystal structure.

Phosphorylation-dependent Translocation of Glycogen Synthase to a Novel Structure during Glycogen Resynthesis

Glycogen metabolism has been the subject of extensive research, but the mechanisms by which it is regulated are still not fully understood. It is well accepted that the rate-limiting enzymes in glycogenesis and glycogenolysis are glycogen synthase (GS) and glycogen phosphorylase (GPh), respectively. Both enzymes are regulated by reversible phosphorylation and by allosteric effectors. However, evidence in the literature indicates that changes in muscle GS and GPh intracellular distribution may constitute a new regulatory mechanism of glycogen metabolism. Already in the 1960s, it was proposed that glycogen was present in dynamic cellular organelles that were termed glycosomas but no such cellular entities have ever been demonstrated. The aim of this study was to characterize muscle GS and GPh intracellular distribution and to identify possible translocation processes of both enzymes. Using in situ stimulation of rabbit tibialis anterior muscle, we show GS and GPh intracellular redistribution at the beginning of glycogen resynthesis after contraction-induced glycogen depletion. We identify a new "player," a new intracellular compartment involved in skeletal muscle glycogen metabolism. They are spherical structures that were not present in basal muscle, and we present evidence that indicate that they are products of actin cytoskeleton remodeling. Furthermore, for the first time, we show a phosphorylation-dependent intracellular distribution of GS. Here, we present evidence of a new regulatory mechanism of skeletal muscle glycogen metabolism based on glycogen enzyme intracellular compartmentalization.

Highly-ordered GaAs/AlGaAs quantum-dot arrays on GaAs (001) substrates grown by molecular-beam epitaxy using nanochannel alumina masks

Highly-ordered GaAs/AlGaAs quantum-dot arrays (QDA) were grown by molecular-beam epitaxy on GaAs (001) using masks of anodic nanochannel alumina (NCA). The QDA replicated the hexagonal lattice pattern of the NCA masks with period spacing of 100 nm. The circular disk-like dots were defined by the nanohole channels of NCA masks with size adjustable between 45 and 85 nm. Both single- and double-well GaAs/AlGaAs QDA exhibited strong photoluminescence. The single-well QDA showed a narrow peak at 1.64 eV with full width at half maximum of only 16 meV, indicating good size uniformity and crystal quality for the QDA. NCA masked epitaxial growth is thus shown to be a promising general approach for fabricating various heterostructure QDA, including both strained and lattice-matched heterostructures.

Molecular beam epitaxial growth studies of ordered GaAs nanodot arrays using anodic alumina masks

Highly ordered GaAs nanodot arrays were successfully grown on GaAs (0 0 1) substrates through anodic nanochannel alumina masks using molecular beam epitaxy. These nanodot arrays replicate the hexagonal lattice pattern with period spacing of 100 nm on the nanochannel alumina mask. The dots also retain the circular shape and good size uniformity of the nanopores on the mask, and the dot size is adjustable by controlling the pore size of the mask. The selectivity of GaAs growth on the GaAs surface exposed under the nanoholes compared with GaAs deposition on the Al 2O 3 mask increases with reducing growth rate. This approach provides a low cost means for fabricating novel arrays of quantum nanostructures.

Spatial resonances and superposition patterns in a reaction-diffusion model with interacting Turing modes.

Spatial resonances leading to superlattice hexagonal patterns, known as "black-eyes," and superposition patterns combining stripes and/or spots are studied in a reaction-diffusion model of two interacting Turing modes with different wavelengths. A three-phase oscillatory interlacing hexagonal lattice pattern is also found, and its appearance is attributed to resonance between a Turing mode and its subharmonic.

Asymmetric structure of the Si(111)- [formula omitted]× [formula omitted]-Ag surface

The atomic and electronic structures of the Si(111)- 3 × 3 -Ag surface are studied by first-principles calculations based on the density functional theory. It is found that a structural model consisting of two inequivalent Ag triangles is energetically more favorable than the well-established honeycomb-chained-triangle (HCT) model. The new structure should yield an empty-state STM image with a hexagonal-lattice pattern, rather than a honeycomb pattern, which is confirmed by low-temperature STM observations.

Control of microtubule pattern during the development of a large organelle in the ciliate Nassula

Bundles of hexagonally arranged microtubules in the cytopharynx of Nassula develop abnormally during colchicine treatment. Some of the tubules undergo a microtubule-macrotubule transition. Portions of tubules that assemble during the treatment fail to grow along straight paths and are irregularly arranged. Portions of the same tubules which assemble after treatment are arranged hexagonally. Comparisons of normal development with that occurring during and after colchicine treatment indicate that several procedures are involved in defining microtubule arrangement. It seems that highly ordered arrays of microtubule nucleating sites form against the proximal ends of basal bodies. Each array of sites apparently determines the cross-sectional shape of a bundle and the orientation of the hexagonal lattice pattern in which its tubules are arranged by specifying the positions in which tubules start to assemble fairly exactly. The term microtubule-nucleating-template is proposed for arrays of sites that act in this way. A special close-packing-effect may maintain the hexagonal pattern as tubules lengthen until tubules are connected by links. Links mainly attach to particular binding points on tubule walls. Since links can project in a variety of directions from these points, links probably do not play an important role in establishing tubule arrangement in this organelle.