INVESTIGATION OF THE OPTICAL BISTABILITY IN A ONE-DIMENSIONAL LAYERED STRUCTURE CONTAINING THREE SYMMETRIC NONLINEAR DEFECT LAYERS

ABSTRACT In this paper, using the transfer matrix method, we investigate the dependence of threshold intensity of the optical bistability to distance between the defect layers for a symmetric (and also asymmetric) one-dimensional nonlinear layered structure, theoretically. The one-dimensional nonlinear layered structure under consideration in this paper contains three coupled nonlinear defect layers. Therefore, two coupled defect modes can be created in the photonic gap of this structure. The symmetric structure for minimum value of the distance between the defect layers is referred as the special geometry. It is shown that, for the shorter wavelength defect mode created in the special geometry of the symmetric structure, the minimum threshold intensity of the optical bistability can be achieved. KEYWORDS: Optical bistability; Nonlinear layered structure; Coupled defect layers; Threshold intensity; Transfer matrix method In the last few decades, the nonlinear responses of layered structures and also photonic crystals (PCs) have inspired considerable interest in both physics and engineering communications, because of their fantastic applications in the light control devices [1]. One finds a variety of these nonlinear responses (such as nonlinearity induced self-trapping [2-9], four-wave mixing [10][11][12], etc.) when these structures are illuminated by a highpower laser. The simplest example of such nonlinear responses is optical bistability (OB), in which one has situations with two (meta-) stable values for the light intensity transmitted through a nonlinear material for one value of the input intensity [12,13]. The OB is occurred because the dielectric constant of the material depends on the intensity of the electromagnetic wave [14][15][16]. The bistable behavior in the transmission was found to have a diode action, which may be quite useful in microwave nonlinear devices [17][18][19]. Also, the concept of optical bistability plays the main role in the design of alloptical transistors, switches, logical gates and optical memory devices [20, 21]. When a single nonlinear defect layer is introduced into a linear 1D PC, the OB phenomenon can be produced by the dynamic shifting of defect modes [22,23] as well. Also, the direct observation of defect modes shifting in experiment observed [24]. Further studies indicated that the basic way to obtain low switching threshold is to reach a nonlinear defect with proper physical parameters or increase the number of layers [25]. Moreover, P. Hou et al. introduced a 1D PC composed of two coupled nonlinear defect layers separated by a linear middle layer, recently [26]. In that paper, they investigated the effect of parameters variation of the linear layer on the modulation of OB threshold intensity. As far as reducing the OB threshold intensity is concerned, it is worth to introduce a structure that has lower switching threshold in comparison with the mentioned structures. To the best of our knowledge, the OB of a 1D layered structure composed of alternative linear and nonlinear layers containing three coupled nonlinear defect (TCND) layers has not been investigated. Therefore, in this paper, we investigate how the minimum value of the OB threshold intensity in the 1D TCND layered structure can be achieved. We believe that a new physics arises from the presented geometry of the structure under consideration in this paper. Also, the concluded results are appropriate for photon control devices based on 1D layered structures. Our paper is organized as follows. In Section 2, the theoretical analysis of the nonlinea

Delivery of curcumin by a pH-responsive chitosan mesoporous silica nanoparticles for cancer treatment

Mesoporous silica nanocarriers as accommodate drug molecule capsules were synthesized and capped by chitosan natural polymer. This nanocarrier acts as a pH-responsive shield to increase the solubility and improvement of anticancer properties of curcumin against U87MG glioblastoma cancer cell line. The encapsulation efficiency and drug-loading content were measured 88.1 ± 4.76 and 8.81 ± 0.47, respectively. The curcumin release from the CS-MCM-41 was slow and sustained at low pH (42.72 ± 2.29) compared to the environment pH (19.54 ± 1.36) in 96 h. The MTT evaluations showed that IC50 after 72 h treatment with free curcumin and curcumin-loaded CS-MCM-41 were 15.20 and 5.21 lg/mL (p<0.05). respectively. © 2017 Informa UK Limited, trading as Taylor & Francis Group

Preparation of a sepiolite/Cu-BDC nanocomposite and its application as an adsorbent in respirator cartridges for H2S removal

A newly developed Cu-BDC MOF nanocomposite based on natural sepiolite (Sep) was prepared and characterized using XRD, SEM, EDS, BET, and FTIR techniques. The surface areas of the sepiolite and the Sep/Cu-BDC nanocomposite were obtained as 105.5 m(2) g(-1) and 270.5 m(2) g(-1) with average micropore volumes of 0.39 and 0.32 cm(3) g(-1), respectively. The Sep/Cu-BDC nanocomposite was prepared from the Cu-BDC metal-organic framework with values of 10, 25, and 40 by weight. The synthesized nanocomposite was tested to estimate the adsorption capacity and breakthrough time under various temperature, humidity, and concentration conditions using a designed setup. The aeroqual S500 direct-reading sensor with 0.01 ppm accuracy was used to measure the exact amount of hydrogen sulfide gas (H2S). The produced Sep/Cu-BDC nanocomposites had an extremely high adsorption capacity compared to the primary sepiolite. Among the different adsorbents, the Sep/Cu-BDC (25 wt) nanocomposite exhibited the highest adsorption capacity of 55.13 mg g(-1) (SD = 0.70) and breakthrough time of 46.32 min (SD = 1.53), respectively. Also, the amount of adsorption and breakthrough time of H2S were decreased with increasing moisture and concentration. The pressure drop was also increased slightly. The nanocomposite with 40 wt of Cu-BDC showed a significant decrease in the adsorption capacity and breakthrough time of H2S. The Sep/Cu-BDC adsorbent was regenerated using thermal regeneration at 190 degrees C in N-2 flow for 4 h, and the results showed that the adsorbent could be used for three consecutive cycles exhibiting excellent recyclability and thermal stability