Light-Driven Modulation of Electrical Current through DNA Sequences: Engineering of a Molecular Optical Switch.

Designing a molecular switch with bistable on/off states is of particular interest in molecular electronics. Motivated by experimental studies of molecular conductors, interplays of photons and electrons and their effects on electrical properties are studied theoretically. We have tried to model a molecular optical switch based on DNA sequences of the hepatitis delta virus and Toxocara canis parasite. The electrical response of chains to the light irradiation was examined to optimize the function of an optical switch. The switch turns on when the amplitude of incident irradiation and its frequency approach to 0.3 at the unit of (ℏc)/(er0) and 2 THz, respectively. We can modulate the switching of the system via the simultaneous variation of effective factors and obtain different islands in the parameter settings. The appearance of different islands in the parameter surface relates to the on/off states of electrical current, which can be verified and estimated through the multifractal analysis.

Study of encapsulated microbubble cluster based on association schemes perspective.

Ultrasound contrast agents have been recently utilized in therapeutical implementations for targeted delivery of pharmaceutical substances. Radial pulsations of a cluster of encapsulated microbubbles under the action of an ultrasound field are complex and highly nonlinear, particularly for drug and gene delivery applications with high acoustic pressure amplitudes. In this paper, based on Qin-Ferrara's model (Qin and Ferrara, 2010), the complete synchronization and cluster formation in targeted microbubbles network are studied. Also, association schemes as a novel approach are suggested for finding a relationship between coupled microbubbles elements which are immersed in blood or surrounding soft tissue. A significant advantage of this method is that the stability of the synchronized state (or symmetric eigenmode of mutual bubble oscillation) with respect to another state (another eigenmode) can now predict. More interestingly, we find a significant relationship between an isolated and multiple microbubbles. The results show that the problem of studying the dynamics of encapsulated microbubble cluster at synchronization state is dependent on the dynamical characteristics of isolated cases, shell thickness, density. Also, the distance between microbubbles has an important role in their synchronous modes.

Engineering DNA Molecule Bridge between Metal Electrodes for High-Performance Molecular Transistor: An Environmental Dependent Approach.

Molecule-based transistors have attracted much attention due to their exclusive properties. Creation of a molecular transistor as well as engineering its structure have become one of the greatest aims of scientists. We have focused on the environmental dependent behavior of a DNA-templated transistor. Using the statistical distribution of the energy levels, we were able to distinguish the delocalized states of charge carriers and the transition between the localized and delocalized behaviors. On the other hand, we can determine the stability conditions of our quantum dynamical system. The results are verified by the inverse participation ratio method. Therefore, the most appropriate parameters for designing the DNA transistor are chosen. The DNA sequence is an important factor for its transport properties, but the results have shown that in the presence of the bath, the bath parameters are important, too. As is shown, it is possible that via the adjustment of bath parameters, one can design a conductivity channel for all nucleotide contents. Thus, one can engineer a DNA based transistor simply through the setting of only one parameter.

Association schemes perspective of microbubble cluster in ultrasonic fields.

Dynamics of a cluster of chaotic oscillators on a network are studied using coupled maps. By introducing the association schemes, we obtain coupling strength in the adjacency matrices form, which satisfies Markov matrices property. We remark that in general, the stability region of the cluster of oscillators at the synchronization state is characterized by Lyapunov exponent which can be defined based on the N-coupled map. As a detailed physical example, dynamics of microbubble cluster in an ultrasonic field are studied using coupled maps. Microbubble cluster dynamics have an indicative highly active nonlinear phenomenon, were not easy to be explained. In this paper, a cluster of microbubbles with a thin elastic shell based on the modified Keller-Herring equation in an ultrasonic field is demonstrated in the framework of the globally coupled map. On the other hand, a relation between the microbubble elements is replaced by a relation between the vertices. Based on this method, the stability region of microbubbles pulsations at complete synchronization state has been obtained analytically. In this way, distances between microbubbles as coupling strength play the crucial role. In the stability region, we thus observe that the problem of study of dynamics of N-microbubble oscillators reduce to that of a single microbubble. Therefore, the important parameters of the isolated microbubble such as applied pressure, driving frequency and the initial radius have effective behavior on the synchronization state.

Modeling the electrical conduction in DNA nanowires: charge transfer and lattice fluctuation theories.

An analytical approach is proposed for the investigation of the conductivity properties of DNA. The charge mobility of DNA is studied based on an extended Peyrard-Bishop-Holstein model when the charge carrier is also subjected to an external electrical field. We have obtained the values of some of the system parameters, such as the electron-lattice coupling constant, by using the mean Lyapunov exponent method. On the other hand, the electrical current operator is calculated directly from the lattice operators. Also, we have studied Landauer resistance behavior with respect to the external field, which could serve as the interface between chaos theory tools and electronic concepts. We have examined the effect of two types of electrical fields (dc and ac) and variation of the field frequency on the current flowing through DNA. A study of the current-voltage (I-V) characteristic diagram reveals regions with a (quasi-)Ohmic property and other regions with negative differential resistance (NDR). NDR is a phenomenon that has been observed experimentally in DNA at room temperature. We have tried to study the affected agents in charge transfer phenomena in DNA to better design nanostructures.

Toll-like receptor 2 and 4 expression in the pregnant and non-pregnant human uterine cervix.

Pelvic infections and sexually transmitted diseases place a burden on health resources and may be associated with premature birth. The mechanisms by which the female reproductive tract (FRT) combats these infections remain ill understood, but are likely to involve the pattern recognition Toll-like receptors (TLR). We sought to compare the expression of TLR-2 and -4 by human pregnant and non-pregnant ectocervical epithelium as a prelude to the investigation of the function of these receptors in this tissue during pregnancy. Using the techniques of reverse-transcriptase polymer chain reaction (RT-PCR) and immunohistochemistry, the gene and protein expression of TLR-2 and -4 were studied in the biopsies of ectocervix obtained from non-pregnant premenopausal women (n=21) undergoing hysterectomy, women in the first trimester of pregnancy undergoing non-medically indicated suction pregnancy termination (n=6), and women at term undergoing elective caesarean section (n=11). The expression of TLR2 and TLR4 genes and proteins were upregulated in early and late pregnant ectocervical epithelium, compared with non-pregnant tissue. These findings suggest that the upregulation of TLR2 and TLR4 in the lower FRT may play a key role in the modulation of the innate immune and inflammatory mechanisms of the ectocervix during pregnancy, interacting with other neuroendocrine factors.

Multifractal analysis of thermal denaturation based on the Peyrard-Bishop-Dauxois model.

The theory of DNA dynamics is exceedingly complex and not easily explained. In the past two decades, by adapting methods of statistical physics, the dynamics of DNA in contact with a thermal bath is widely studied. In this paper, the thermal denaturation of DNA in the framework of the Peyrard-Bishop-Dauxois (PBD) model through the Rényi dimension is investigated. As a result, the Rényi dimension spectrum of the melting transition process reveals the multifractal nature of the dynamics of the Peyrard-Bishop-Dauxois model. Also, it can be concluded that the Rényi dimension (D(q)) at negative values of q is the characteristic signature of pre-melting and thermal denaturation of DNA. Furthermore, this approach is in excellent agreement with previous experimental studies.