Muons probe strong hydrogen interactions with defective graphene

Here, we present the first muon spectroscopy investigation of graphene, focused on chemically produced, gram-scale samples, appropriate to the large muon penetration depth. We have observed an evident muon spin precession, usually the fingerprint of magnetic order, but here demonstrated to originate from muon-hydrogen nuclear dipolar interactions. This is attributed to the formation of CHMu (analogous to CH(2)) groups, stable up to 1250 K where the signal still persists. The relatively large signal amplitude demonstrates an extraordinary hydrogen capture cross section of CH units. These results also rule out the formation of ferromagnetic or antiferromagnetic order in chemically synthesized graphene samples.     

Time-domain ab initio study of Auger and phonon-assisted auger processes in a semiconductor quantum dot

We developed time-domain ab initio simulation of Auger phenomena, including multiple exciton generation (MEG) and recombination (MER). It is the first approach describing phonon-assisted processes and early dynamics. MEG starts below the electronic threshold, strongly accelerating with energy. Ligands are particularly important to phonon-assisted MEG, which therefore can be probed with infrared spectroscopy. Short-time gaussian component gives 5-10% of MEG, justifying rate theories that assume exponential dynamics. MER is preceded by electron-phonon relaxation to low energies.     

Tailoring the diameter of single-walled carbon nanotubes for optical applications

Single-walled carbon nanotubes (SWCNTs) with specific diameters are required for various applications particularly in electronics and photonics, since the diameter is an essential characteristic determining their electronic and optical properties. In this work, the selective growth of SWCNTs with a certain mean diameter is achieved by the addition of appropriate amounts of CO₂ mixed with the carbon source (CO) into the aerosol (floating catalyst) chemical vapor deposition reactor. The noticeable shift of the peaks in the absorption spectra reveals that the mean diameters of the as-deposited SWCNTs are efficiently altered from 1.2 to 1.9 nm with increasing CO₂ concentration. It is believed that CO₂ acts as an etching agent and can selectively etch small diameter tubes due to their highly curved carbon surfaces. Polymer-free as-deposited SWCNT films with the desired diameters are used as saturable absorbers after stamping onto a highly reflecting Ag-mirror using a simple dry-transfer technique. Sub-picosecond mode-locked fiber laser operations at ∼1.56 μm and ∼2 μm are demonstrated, showing improvements in the performance after the optimization of the SWCNT properties.      

温度对碳热还原/氮化法合成氮化硅的影响

碳热还原/氮化合成Si3N4在1 300~1 600℃下N2或N2-H2混合气中进行。反应物由非晶Si O2与C粉以1∶4.5摩尔比混合、压片。产生的CO由红外传感器监测,样品中氧、氮、碳含量由LECO元素分析仪测得,混合物各相由X射线衍射(XRD)检测。Si O2还原反应在1 300℃以下开始,速率随温度升高增大;温度高于1 570℃时,速率因反应物表面被生成物覆盖降低。由于还原产物CO平衡分压差别小,选择生成Si3N4或Si C的临界温度不明显。碳热还原/氮化法合成氮化硅的原理需进一步探讨。     

Detonation Spraying of Ti–Al Intermetallics: Phase and Microstructure Development of the Coatings

The goal of this work was to study the phase and microstructure changes involved in the process of coating formation by detonation spraying of Ti₃Al, TiAl, and TiAl₃ intermetallics. The O₂/C₂H₂ ratio was varied between 1.1 and 2.0, and the explosive charge was 30–40% of the barrel volume. In most experiments air was used as a carrier gas; selected experiments were performed with argon. We found that depending on the spraying parameters, TiAl₃ essentially retains in the coatings or partially decomposes forming TiAl and Ti₃Al as minor phases. Detonation sprayed Ti₃Al reacts with nitrogen and oxygen partially transforming into titanium nitrides TiN/Ti₂N and titanium oxynitrides TiN_xO_y. TiAl partially decomposes forming Ti₃Al, which further reacts with oxygen and nitrogen as the particle temperature and the content of oxygen in the explosive mixture increase. The in situ formed titanium nitrides and oxynitrides show a reinforcing effect increasing the hardness of the coatings.     

Combined power and inter-cell interference control for LTE based on role game approach

In this paper the application of Role Game Theory to Power Control (PC) and Inter-Cell Interference Control (ICIC) for Long Term Evolution (LTE) is considered. The authors propose an approach based on defining different roles of the users within a cell of the LTE network. The main idea is to apply different methods and algorithms for PC and ICIC depending on the classified by role subscriber. Such an approach will give the possibility for flexible application and combination of different PC and ICIC methods for achieving better performance.     

Perspektiven der Säure‐Base‐Methode zur Untersuchung der Oberflächeneigenschaften von Polymeren

Modern methods for determining the surface free energy and their parameters were analyzed in the context of the presented investigations. The method of Berger and van Oss‐Chaudhury‐Good were found as the most suitable method for the determination of wetting solid polymer surfaces. Methods of nonlinear systems by Della Volpe and Siboni were evaluated and adapted. Various data of the surface free energy as well as its components have been identified for a number of polymer surfaces by application of spatial equation solutions.     

Investigation of upper oligotrophic mires in the middle Ob basin (West Siberia)

The paper presents results of research into the upper ecosystems and convex forms of peat mires of moss (oligotrophic) type in the Ob basin area. We have determined four types of upper mire ecosystems, and have described their morphometric, botanical and hydro-chemical properties. These studies allow us to evaluate the structure and functioning of the upper mire ecosystems.