Characteristics of alternating current hopping conductivity in DNA sequences

This paper presents a model to describe alternating current （AC） conductivity of DNA sequences, in which DNA is considered as a one-dimensional （1D） disordered system, and electrons transport via hopping between localized states. It finds that AC conductivity in DNA sequences increases as the frequency of the external electric field rises, and it takes the form of σac（ω） - ω2 ln^2（1/ω）. Also AC conductivity of DNA sequences increases with the increase of temperature, this phenomenon presents characteristics of weak temperature-dependence. Meanwhile, the AC conductivity in an offdiagonally correlated case is much larger than that in the uncorrelated case of the Anderson limit in low temperatures, which indicates that the off-diagonal correlations in DNA sequences have a great effect on the AC conductivity, while at high temperature the off-diagonal correlations no longer play a vital role in electric transport. In addition, the proportion of nucleotide pairs p also plays an important role in AC electron transport of DNA sequences. For p 〈 0.5, the conductivity of DNA sequence decreases with the increase of p, while for p ≥ 0.5, the conductivity increases with the increase of p.

Direct current hopping conductance in one-dimensional diagonal disordered systems

Based on a tight-binding disordered model describing a single electron band, we establish a direct current （de） electronic hopping transport conductance model of one-dimensional diagonal disordered systems, and also derive a dc conductance formula. By calculating the dc conductivity, the relationships between electric field and conductivity and between temperature and conductivity are analysed, and the role played by the degree of disorder in electronic transport is studied. The results indicate the conductivity of systems decreasing with the increase of the degree of disorder, characteristics of negative differential dependence of resistance on temperature at, low temperatures in diagonal disordered systems, and the conductivity of systems decreasing with the increase of electric field, featuring the non-Ohm＇s law conductivity.

Features of the Conductivity of the Ag8Ge1-xMnxTe6 Solid Solutions

Samples of Ag8Ge1-xMnxTe6 solid solutions with different manganese content (x = 0, 0.05, 0.1, 0.2) were prepared by fusing and further pressing their powders under the pressure of 0.6 GPa. In addition of Mn atoms to the Ag8GeTe6 compound leads to compression of their lattice. All p-type samples acquire a high resistance below the transition at temperatures of 180 - 220 K. The electrical conductivity of all compositions in the range of 220 - 300 K increases due to hopping mechanism, and at temperatures T > 320 K, a semiconductor characteristic is observed. By studying impedance spectra of samples, it was established that at 80 K solid solutions behave like a homogeneous dielectric material. At high temperatures and frequencies of an external electric field, a significant role of grain boundaries in conductivity was revealed. The dielectric anomaly occurring at low frequencies is also associated with an effect that manifests itself in the grain boundary.

Conduction Mechanism and Conductivity Behaviour of Pure Polypropylene (PP) and Polypropylene-Banana Fiber (PP-B) Composites

Fibers reinforced composite materials offer a combination of strength and modulus that are either comparable to or better than many traditional metallic materials.The research on natural fiber based composite materials fit well into this ecological image.This paper reports the conduction mechanism and ac conductivity,activation energy behavior of Polypropylene and banana fiber reinforced thermoplastic composites.Polypropylene[-CH_(2)-CH_(2)-CH_(2)-]n and different fiber content(wt.%)of polypropylene-banana fibers(natural fiber)composites were fabricated using a hot-press molding system.The optimum fabrication parameters were established(initial pressure,temp.etc.).These composite test samples were fabricated so the short fibers were randomly oriented in the matrix.The detail investigation of the a.c.conductivity and conduction mechanism of polymer composites would provide information about the relaxation processes,activation energy etc.which are dependent on frequency,temperature and time.The activation energy involved in the above processes can also be estimated from this study.The measurements were performed over a wide range of frequency of 60 Hz to 3 MHz and temperature range from 30℃(303°K)to 110℃(383°K).Experimental results of the ac properties of pure polypropylene and polypropylene-natural banana fiber composites were compared.It has been established that the fabricated composition changes its insulating property after adding the natural fibers and gives the better conductivity properties.

Electric properties of La_(0.8)Sr_(0.2)CoO_3 nanoceramics

The electric measurements were carried out for La0.8Sr0.2CoO3 nanoceramics by using impedance spectroscopy methods. The resistance of sample was practically independent of frequency in measurement range. Its dependence on reciprocal temperature showed quite complicated mechanism of conduction. The most striking property of investigated sample was its resistance decreasing with increasing applied polarization.

Substituting Effect of Y in La_(0.5) Ba_(0.5) CoO_3

La 0.5- x Y x Ba 0.5 CoO 3 polycrystals were prepared by solid state reaction. The substituting effects of Y for La on the magnetic and transport properties of the materials were studied systematically. The results indicate that substitution of Y induces two effects. Firstly, the charge transfer from Y to 3d orbital of Co happens. This causes the molecular magnetic moment to decrease. Secondly, the antiferromagnetic exchange interaction of Co ions appears. When the content of Y is less than or equal to 30%, the non colinear structure of spins in materials is observed. When the content of Y is greater than 30%, the materials transit from predominant ferromagnetic state to predominant antiferromagnetic one. The conductive mechanism for the materials with different content of Y belongs to the variable range hopping conduction of polarons. The resistivity of materials increases sharply with increasing Y content.

Multiphonon hopping conduction in carbon-nickel composite films at different deposition time

In this work, the electrical properties of car- bon-nickel composite films deposited at different time （50-600 s） were investigated. The films were grown by radio frequency magnetron sputtering on glass substrates at room temperature. The electrical conductivity of the films was investigated in the temperature range of 15-500 K. The conductivity data in the temperature range of 400-500 K show the extended state conduction mecha- nism, while the multiphonon hopping （MPH） conduction is found to dominate the electrical transport in the tempera- ture range of 150-300 K. The films deposited at 180 s have the maximum conductivity. The conductivity at T 〈 60 K could be described in terms of variable range hopping （VRH） conduction. The localized state density around Fermi level （N（EF）） at low temperature for the films deposited at 180 s has the minimum value of about 4.02 × 10^21 cm^-3.eV^-1. The average hopping distance （Rhop） for the films deposited at 180 s has the maximum value of about 3.51 × 10^-7 cm.

A critical path approach for elucidating the temperature dependence of granular hopping conduction

We revisit the classical problem of granular hopping conduction＇s σ∝exp[-（To/T）1/2] temperature dependence, where a denotes conductivity, T is temperature, and To is a sample-dependent constant. By using the hopping conduction formulation in conjunction with the incorporation of the random potential that has been shown to exist in insulator-conductor composites, it is demonstrated that the widely observed temperature dependence of granular hopping conduction emerges very naturally through the immediate-neighbor critical-path argument. Here, immediate-neighbor pairs are defined to be those where a line connecting two grains does not cross or by-pass other grains, and the critical-path argument denotes the derivation of sample conductance based on the geometric percolation condition that is marked by the critical conduction path in a random granular composite. Simulations based on the exact electrical network evaluation of finite-sample conductance show that the configuration- averaged results agree well with those obtained using the immediate-neighbor critical-path method. Furthermore, the results obtained using both these methods show good agreement with experimental data on hopping conduction in a sputtered metal-insulator composite Agx（SnO2）1-x, where x denotes the metal volume fraction. The present approach offers a relatively straightforward and simple expla- nation for the temperature behavior that has been widely observed over diverse material systems, but which has remained a puzzle in spite of the various efforts made to explain this phenomenon.

Progress and challenges in blocked impurity band infrared detectors for space-based astronomy

Astronomical detection at infrared wavelengths is crucial in astrophysics due to the critical information in this wavelength range.Blocked impurity band(BIB) infrared detectors are desirable for space-based astronomical observation due to their broad response range, low dark currents, high quantum efficiencies, and excellent radiation resistance. In this review, typical BIB device structures and device physics development are first introduced. Subsequently, we discuss progress in Si-based BIB detectors with different doping types and emphasize their applications in space-based infrared detection. Additionally, we discuss recent efforts on pixel performance optimization, response extension, and higher operating temperature devices. Finally,we conclude by proposing the challenges and perspectives of BIB detectors with improved detection performances.