Effect of contact induced states on minimum conductivity in graphene

The objective of this paper is to point out that contact induced states can help explain the structure dependence of the minimum conductivity observed experimentally even if the samples were purely ballistic. Contact induced states are similar to the well-known metal induced gap states (MIGS) in metal-semiconductor Schottky junctions, which typically penetrate only a few atomic lengths into the semiconductor, while the depth of penetration decreases with increasing band gap. However, in graphene we find that these states penetrate a much longer distance of the order of the width of the contacts. As a result, ballistic graphene samples with a length less than their width can exhibit a resistance proportional to length that is not Ohmic in origin, but arises from a reduced role of contact-induced states. While actual samples are probably not ballistic and involve scattering processes, our results show that these contact induced effects need to be taken into account in interpreting experiments and minimum conductivity depends strongly on the structure and configuration (two- vs. four-terminal) used.Comment: 4 pages, 4 figure

Conductance of graphene nanoribbon junctions and the tight binding model

Planar carbon-based electronic devices, including metal/semiconductor junctions, transistors and interconnects, can now be formed from patterned sheets of graphene. Most simulations of charge transport within graphene-based electronic devices assume an energy band structure based on a nearest-neighbour tight binding analysis. In this paper, the energy band structure and conductance of graphene nanoribbons and metal/semiconductor junctions are obtained using a third nearest-neighbour tight binding analysis in conjunction with an efficient nonequilibrium Green’s function formalism. We find significant differences in both the energy band structure and conductance obtained with the two approximations

Report of the parasitoid wasp, Cotesia plutellae (Hym.: Braconidae), from Iran

This paper reports the occurrence of the hymenoterous parasitoid of the diamondback moth larvae in Iran. One species of Braconidae, Cotesia plutellae (Kurdjumov), was collected from larvae of Plutella xylostella (L.) (Lep.: Plutellidae). This parasitoid, which belongs to the subfamily Microgastrinae, is newly recorded from Iran

Report of the parasitoid wasp, Oomyzus sokolowskii (Hym.: Eulophidae), from Iran

One species of Eulophidae, Oomyzus sokolowskii (Kurdjumov), was collected from larvae of the diamondback moth, Plutella xylostella (L.) (Lep.: Plutellidae). This parasitoid is a major gregarious larval-pupal endoparasitoid of P. xylostella that prefers ovipositing into host larvae but depositing its eggs in host prepupae too. This is the first report of the occurrence of this species from Iran

Report of the parasitoid wasp, Diadegma anurum (Hym.: Ichneumonidae), from Iran

This paper reports the occurrence of the hymenoterous parasitoid of the diamondback moth larvae in Iran. One species of Ichneumonidae, Diadegma anurum (Thomson), was collected from larvae of Plutella xylostella (L.) (Lep.: Plutellidae). This parasitoid, which belongs to the subfamily Campopleginae and tribe Limneriini, is a new record for Iran

Lethal and sublethal effects of dinotefuran and thiamethoxam on the population growth parameters of the green lacewing, Chrysoperla carnea (Neu.: Chrysopidae), under laboratory conditions

The green lacewing, Chrysoperla carnea (Stephens), is a common natural enemy of various agricultural pestsand widely used as a biocontrol agent in integrated pest management (IPM) programs. The lethal and sublethal effects of the insecticides dinotefuran and thiamethoxam on the first instar larvae of C. carnea was assessed in the laboratory conditions at 25 ± 1°C, 60 ± 5% RH and a photoperiod of 16: 8 (L: D). The LC50 values for dinotefuran and thiamethoxam were 19.382 and 9.880 mg ai/l, respectively, that showed the high toxicity of thiamethoxam on the first instar larvae of C. carnea. To assess the sublethal effects, the first instar larvae were treated with the LC30 for dinotefuran and thiamethoxam at 3.532 and 1.692 mg ai/l, respectively. The estimated rm values in the control, dinotefuran and thiamethoxam were 0.185, 0.186 and 0.143 day-1, respectively. Finite rate of increase (λ) in the control, dinotefuran and thiamethoxam were 1.204, 1.204 and 1.154 day-1. Generation time and doubling time values in the control, dinotefuran and thiamethoxam were 30.77, 30.46 and 35.14 as well as 3.73, 3.72 and 4.82 days, respectively. The gross and net reproductive rates in the control, dinotefuran and thiamethoxam were 459.89, 439.08 and 309.42, and also 298.01, 278.45 and 155.03 (female/female/generation), respectively. Dinotefuran caused no significant adverse effects on the population growth parameters of C. carnea. If similar results are obtained for dinotefuran in the field, it might be an insecticide with low toxicity to C. carnea by using the reduced doses of the insecticide in IPM context. Studies under the laboratory conditions can help us to select some insecticides for additional studies under more natural conditions and for application of suitable insecticides along with natural enemies in pest management

Fabrication of multifunctional microfibrous and nanofibrous cellulose carriers and comparison of cell adhesion and spreading potential on them

Fibrous biomaterials have received much attention in tissue engineering and regenerative medicine due to their morphology, resembling extracellular matrix. In comparison to synthetic fibers, cellulose based fibers have interesting properties for cellular applications such as biodegradability, biocompatibility, simple preparation and their potential for chemical modification. Among cellulose derivatives, carboxymethyl cellulose and quaternized cellulose are the most important and valuable cellulose ethers which have anionic and cationic surface charge. In this research, we report the fabrication of multifunctional cellulose microfibrous and nanofibrous scaffolds and the comparison of adhesion and spreading potential of human fibroblast cell on them. The fabricated fibrous scaffolds were characterized by several instrumental techniques. The results showed that multifunctional cellulose nanofibers and microfiber had 8.6 and 8.2 mV surface potential, 7.1 and 6.8 MPa tensile strength, 560 and 510 MPa Young modules, 610 and 595 water uptake and 41o and 44o contact angle, respectively. The MTT assay showed that proliferation of fibroblast cells was enhanced in nanofibrous, compared to microfibrous mat. The SEM analysis of fixed cells on scaffolds showed that cells spreading on nanofibrous samples became more noticeable than microfibrous ones. © 2020 by the authors

Kinetic investigation on extrinsic spin Hall effect induced by skew scattering

The kinetics of the extrinsic spin Hall conductivity induced by the skew scattering is performed from the fully microscopic kinetic spin Bloch equation approach in $(001)$ GaAs symmetric quantum well. In the steady state, the extrinsic spin Hall current/conductivity vanishes for the linear-$\mathbf k$ dependent spin-orbit coupling and is very small for the cubic-$\mathbf k$ dependent spin-orbit coupling. The spin precession induced by the Dresselhaus/Rashba spin-orbit coupling plays a very important role in the vanishment of the extrinsic spin Hall conductivity in the steady state. An in-plane spin polarization is induced by the skew scattering, with the help of the spin-orbit coupling. This spin polarization is very different from the current-induced spin polarization.Comment: 5 pages, 2 figures, to be published in JPC

How close can one approach the Dirac point in graphene experimentally?

The above question is frequently asked by theorists who are interested in graphene as a model system, especially in context of relativistic quantum physics. We offer an experimental answer by describing electron transport in suspended devices with carrier mobilities of several 10^6 cm^2V^-1s^-1 and with the onset of Landau quantization occurring in fields below 5 mT. The observed charge inhomogeneity is as low as \approx10^8 cm^-2, allowing a neutral state with a few charge carriers per entire micron-scale device. Above liquid helium temperatures, the electronic properties of such devices are intrinsic, being governed by thermal excitations only. This yields that the Dirac point can be approached within 1 meV, a limit currently set by the remaining charge inhomogeneity. No sign of an insulating state is observed down to 1 K, which establishes the upper limit on a possible bandgap