Optical Gas Sensors Using Terahertz Waves in the Layered Media

Terahertz (THz) wave propagation in the layered media is presented based on the waveguide and artificial-material configurations to sense the gas molecules. The single dielectric layer with a cylindrical conformation works as a pipe waveguide in the wave frequency of 0.1–1 THz. For a long-distance propagation over 10 cm of the pipe, resonant modes are characterized from the transmission power dips. The pipe-waveguide resonator works for a THz refractive-index sensor when the resonance frequency is monitored to sense vapor molecules inside the pipe core. Besides of the waveguide configuration, a multilayer microporous polymer structure (MPS) is considered an artificial material to transmit THz waves for sensing gaseous molecules. The MPS is not only transparent to THz waves but also enhances the detection resolution of THz absorption for the vapor molecules. The porous structure provides a large hydrophilic surface area and numerous micropores to adsorb or fill vapors, thereby leading to greatly enhanced wave-analyte interaction with an apparent THz signal change. Different concentrations of toxic methanol adulterated in alcoholic aqueous solutions are thus identified in their vapor phases by using the MPS-based THz sensor

Terahertz Fiber Sensing

Terahertz fibers used for optical-sensing applications are introduced in this chapter, including the dielectric wires, ribbons and pipes. Different analyte conformations of the liquid, solid particle, thin film and vapor gas are successfully integrated with suitable fibers to perform high sensitivities. Based on the optimal sensitivities, analyte recognitions limited in traditional terahertz spectroscopy are experimentally demonstrated by the terahertz fiber sensors. Using the cladding index-dependent waveguide dispersion and high fractional cladding power of terahertz wire fiber, 20 ppm concentration between polyethylene and melamine particles can be distinguished. When the evanescent mode field of a terahertz ribbon fiber is controlled by a diffraction metal grating, subwavelength-confined surface terahertz waves potentially enable the near-field recognition for nano-thin films. Resonance waveguide field surrounding the terahertz pipe fiber is able to identify the macromolecule deposition in subwavelength-scaled thickness, approximately λ/225. For inner core-confined resonance waveguide field inside the terahertz pipe fiber, low physical density of the vaporized molecules around 1.6 nano-mole/mm3 can also be discriminated

Terahertz scanning imaging with a subwavelength plastic fiber

[[abstract]]The feasibility to perform terahertz imaging utilizing a terahertz subwavelength plastic fiber is investigated. Dour study shows that, With a low (<1%) fractional power inside the fiber score, the bending loss of the terahertz subwavelength fiber is acceptable to enable large area scanning without seriously sacrificing the signal-to-noise ratio of the acquired image. With a transmission geometry, this feasibility is demonstrated by direct two-dimensional scanning of the terahertz subwavelength fiber output end to image different biological samples and concealed substances.[[fileno]]2010144010155[[department]]物理

Investigation of spectral properties and lateral confinement of THz waves on a metal-rod-array-based photonic crystal waveguide

Terahertz (THz) waves laterally confined in a 1 mm-thick microstructured planar waveguide are demonstrated on a free-standing metal rod array (MRA), and one apparent rejection band of a transmission spectrum, resembling the bandgap of a photonic crystal, is found in 0.1–0.6 THz. The visibility of the photonic bandgap in the spectral width and power distinction can be manipulated by changing the MRA geometry parameters, including the rod diameter, the interspace between adjacent rods, and the propagation length based on the interactive MRA-layer number. THz transmission ratio enhanced by a large interactive length is verified in 30 MRA layers due to the longitudinally resonant guidance of transverse-magnetic-polarized waveguide modes along the MRA length, which is critical to the interspace width of adjacent rods and the metal coating of the rod surface. For an MRA with respective rod diameter and interspace dimensions of about 0.16 and 0.26 mm, the highest transmission of the guided resonant THz waves are performed at 0.505–0.512 THz frequency with strong confinement on the metal rod tips and a low scattering loss of 0.003 cm−1

Pinning synchronization of delayed neural networks

2008-2009 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Re-expression of ARHI (DIRAS3) induces autophagy in breast cancer cells and enhances the inhibitory effect of paclitaxel

<p>Abstract</p> <p>Background</p> <p><it>ARHI </it>is a Ras-related imprinted gene that inhibits cancer cell growth and motility. ARHI is downregulated in the majority of breast cancers, and loss of its expression is associated with its progression from ductal carcinoma <it>in situ </it>(DCIS) to invasive disease. In ovarian cancer, re-expression of ARHI induces autophagy and leads to autophagic death in cell culture; however, ARHI re-expression enables ovarian cancer cells to remain dormant when they are grown in mice as xenografts. The purpose of this study is to examine whether ARHI induces autophagy in breast cancer cells and to evaluate the effects of ARHI gene re-expression in combination with paclitaxel.</p> <p>Methods</p> <p>Re-expression of ARHI was achieved by transfection, by treatment with trichostatin A (TSA) or by a combination of TSA and 5-aza-2'-deoxycytidine (DAC) in breast cancer cell cultures and by liposomal delivery of ARHI in breast tumor xenografts.</p> <p>Results</p> <p>ARHI re-expression induces autophagy in breast cancer cells, and ARHI is essential for the induction of autophagy. When ARHI was re-expressed in breast cancer cells treated with paclitaxel, the growth inhibitory effect of paclitaxel was enhanced in both the cell culture and the xenografts. Although paclitaxel alone did not induce autophagy in breast cancer cells, it enhanced ARHI-induced autophagy. Conversely, ARHI re-expression promoted paclitaxel-induced apoptosis and G2/M cell cycle arrest.</p> <p>Conclusions</p> <p>ARHI re-expression induces autophagic cell death in breast cancer cells and enhances the inhibitory effects of paclitaxel by promoting autophagy, apoptosis, and G2/M cell cycle arrest.</p

Geometry-dependent modal field properties of metal-rod-array-based terahertz waveguides

One terahertz (THz) waveguide based on the metal rod array (MRA) structure is numerically demonstrated in 0.1–1 THz, including the fundamental and high-order transverse magnetic (TM) modes. The high-order TM-mode THz waves are strictly confined inside the MRA structure and are thus sensitive to the metal rod interspace for their spectral positions, bandwidths, transmittances, and attenuation coefficients. Arranging metal rods with fine-tuning the interspaces across the optic axis is presented as the critical stratagem to optimize the transportation efficiency of THz waves through an MRA structure. The maximum propagation length of MRA-confined THz waves is over 30 mm with the lowest attenuation coefficients of approximately 0.05–0.1 cm−1. The MRA is, therefore, applicable as one deformable artificial structure in THz frequency region because simply one-axial adjustment of the metal-rod interspace enables the modulation purpose without uniform adjustment on the two-dimensional metal rod interspace

Variational Methods for Biomolecular Modeling

Structure, function and dynamics of many biomolecular systems can be characterized by the energetic variational principle and the corresponding systems of partial differential equations (PDEs). This principle allows us to focus on the identification of essential energetic components, the optimal parametrization of energies, and the efficient computational implementation of energy variation or minimization. Given the fact that complex biomolecular systems are structurally non-uniform and their interactions occur through contact interfaces, their free energies are associated with various interfaces as well, such as solute-solvent interface, molecular binding interface, lipid domain interface, and membrane surfaces. This fact motivates the inclusion of interface geometry, particular its curvatures, to the parametrization of free energies. Applications of such interface geometry based energetic variational principles are illustrated through three concrete topics: the multiscale modeling of biomolecular electrostatics and solvation that includes the curvature energy of the molecular surface, the formation of microdomains on lipid membrane due to the geometric and molecular mechanics at the lipid interface, and the mean curvature driven protein localization on membrane surfaces. By further implicitly representing the interface using a phase field function over the entire domain, one can simulate the dynamics of the interface and the corresponding energy variation by evolving the phase field function, achieving significant reduction of the number of degrees of freedom and computational complexity. Strategies for improving the efficiency of computational implementations and for extending applications to coarse-graining or multiscale molecular simulations are outlined.Comment: 36 page

Nanocomposite ZnO–SnO2 Nanofibers Synthesized by Electrospinning Method

We report the characterization of mixed oxides nanocomposite nanofibers of (1 − x) ZnO-(x)SnO2 (x ≤ 0.45) synthesized by electrospinning technique. The diameter of calcined nanofibers depends on Sn content. Other phases like SnO, ZnSnO3, and Zn2SnO4 were absent. Photoluminescence studies show that there is a change in the blue/violet luminescence confirming the presence of Sn in Zn-rich composition. Present study shows that the crystalline nanocomposite nanofibers with stoichiometry of (1 − x)ZnO-(x)SnO2 (x ≤ 0.45) stabilize after the calcination and possess some morphological and optical properties that strongly depend on Sn content