Pulsed Laser Deposition of Photoresponsive Two‐Dimensional GaSe Nanosheet Networks

Synthesis of functional metal chalcogenide (GaSe) nanosheet networks by stoichiometric transfer of laser‐vaporized material from bulk GaSe targets is presented. Uniform coverage of interconnected, crystalline, and photoresponsive GaSe nanosheets in both in‐plane and out‐of‐plane orientations are achieved under different ablation conditions. The propagation of the laser‐vaporized material is characterized by in situ ICCD‐imaging. High (1 Torr) Ar background gas pressure is found to be crucial for the stoichiometric growth of GaSe nanosheet networks. Individual 1–3 layer GaSe triangular nanosheets of ≈200 nm domain size are formed within 30 laser pulses, coalescing to form nanosheet networks in as few as 100 laser pulses. The thickness of the deposited networks increases linearly with pulse number, adding layers in a two‐dimensional (2D) growth mode. GaSe nanosheet networks show p‐type semiconducting characteristics with mobilities reaching as high as 0.1 cm²V^?1s^?1. Spectrally‐resolved photoresponsivities and external quantum efficiencies range from 0.4 AW^?1 and 100% at 700 nm, to 1.4 AW^?1 and 600% at 240 nm, respectively. Pulsed laser deposition under these conditions appears to provide a versatile and rapid approach to stoichiometrically transfer and deposit functional networks of 2D nanosheets with digital thickness control and uniformity for a variety of applications.     

Constellation Rearrangement: Enhancement for Multilevel Modulation Formats and Transmit Diversity

Radio link adaptivity will be a key feature of the air interfaces of future mobile communication systems. This adaptivity includes techniques such as fast scheduling, hybrid ARQ, transmit diversity and adaptive modulation and coding. The performance of adaptive modulation generally suffers from the power inefficiencies of multilevel modulation formats. This is due to the variations in bit reliabilities caused by the bit-mapping onto the signal constellation. This article presents a concept, called constellation rearrangement (CoRe), which improves the multilevel modulation power efficiency by the joint application with transmit diversity schemes. It is shown by a theoretical analysis for 16-QAM that the presented concept can equalize variations in bit reliabilities by employing different mapping rules for the transmission over the diversity branches. This significantly improves the receiver block error rate performance and, hence, the performance of the adaptive modulation and coding. This is proven by simulations at link-level in a multicarrier CDMA system for AWGN and fading channels employing turbo coded transmission.     

Safety and security of programmable network infrastructures

Safety and security are two reliability properties of a system. A “safe” system provides protection against errors of trusted users, while a “secure” system protects against errors introduced by untrusted users. There is considerable overlap between mechanisms to support each property. Requirements for rapid service creation have stimulated the development of programmable network infrastructures, where end users or service providers can customize the properties of a network infrastructure while it continues to operate. A central concern of potential users of such systems is their reliability and, most specifically, their safety and security. In this article we explain the impact the network service model and architecture have on safety and security, and provide a model with which policies can be translated into restrictions of a general system. We illustrate these ideas with the Secure Active Network Environment (SANE) architecture, which provides a means of controlling access to the functions provided by any programmable infrastructure     

Random sequence multisets for synchronous code-divisionmultiple-access channels

The effect of using randomly selected sequence multisets for the uplink of a synchronous code-division multiple-access channel is considered. A tight lower bound on the expected value of the sum capacity over the ensemble of randomly selected sequence multisets is given. For large systems, the sum rate penalty for using randomly selected multisets is shown to be at most 1 nat and to vanish as the number of users becomes large, compared to the sequence length     

New Acceleration Principle of Charged Particles for Electronic Applications. The General Hierarchic Description

A new principle of acceleration of changed particles and quasineutral plasma beams is proposed and theoretically substantiated. The essence of this new acceleration principle is die utilization of EH-undulated fields, which resemble those of EH free-electron laser pumping systems. Here the charged particles are moving in a superposition of crossed magnetic and electric vortex undulated fields (EH-accelerator). The advantage of such systems is that both negative (electrons) and positive (ions) charged particles are accelerated simultaneously in the same longitudinal direction. In addition to the concept of the EH-accelerators, a new theoretical approach (the theory of hierarchic oscillations and waves) is given further development here. This approach has been used as a basis for the general nonlinear theory of the EH-accelerators and some other similar isochronous electronic devices with long-time interactions. In addition, several new calculation methods are presented, including the method for nonlinear current density calculations (called the averaged current-density equation hierarchic method) and two versions of hierarchic asymptotic algorithms for the integration of Maxwell's equations.     

Should Russia increase domestic prices for natural gas?

Previous analyses of Russia's dual pricing system and hidden subsidies for natural gas, have neglected to assess the dual pricing system as a domestic environmental policy. If dual pricing is considered as a policy to reduce conventional air pollutants, it is more than economically justified in Russia on the basis of avoided health risks. In the short term, the substitution of coal for natural gas may result in significant additional human health risk, which translates into economic damage. An alternative abatement possibility is expensive and unlikely enforceable, due to weak environmental regulation. The authors conclude that while the price differential can be expected to diminish over time, as Russia increasingly moves to a market economy, in the near-term, dual pricing of natural gas remains the most efficient environmental policy for Russia.     

High-Gain Chemically Gated Organic Electrochemical Transistor

Organic electrochemical transistors (OECTs) have exhibited promising performance as transducers and amplifiers of low potentials due to their exceptional transconductance, enabled by the volumetric charging of organic mixed ionic/electronic conductors (OMIECs) employed as the channel material. OECT performance in aqueous electrolytes as well as the OMIECs’ redox activity has spurred a myriad of studies employing OECTs as chemical transducers. However, the OECT's large (potentiometrically derived) transconductance is not fully leveraged in common approaches that directly conduct chemical reactions amperometrically within the OECT electrolyte with direct charge transfer between the analyte and the OMIEC, which results in sub-unity transduction of gate to drain current. Hence, amperometric OECTs do not truly display current gains in the traditional sense, falling short of the expected transistor performance. This study demonstrates an alternative device architecture that separates chemical transduction and amplification processes on two different electrochemical cells. This approach fully utilizes the OECT's large transconductance to achieve current gains of 10³ and current modulations of four orders of magnitude. This transduction mechanism represents a general approach enabling high-gain chemical OECT transducers.     

Gerfried Zeichen — Aus Anlass seiner Emeritierung

Ohne Zusammenfassung     

On Chiroptical Spectroscopy of Turbid Media with Optically Soft, Large Spherical Particles

The influence of the size of particles on the circular dichroism and optical rotatory dispersion spectra of turbid layers with globules of chiral substances is studied. Simple equations for large chiral particles with the refractive index close to the refractive index of the surrounding medium are obtained and analyzed. Formulae derived can be used for the solution of the inverse problem, namely for obtaining intrinsic spectra of substances inside small particles from measurements of spectra for turbid layers.