Strain engineering of graphene nanoribbons: pseudomagnetic versus external magnetic fields

Bandgap opening due to strain engineering is a key architect for making graphene’s optoelectronic, straintronic, and spintronic devices. We study the bandgap opening due to strain induced ripple waves and investigate the interplay between pseudomagnetic fields and externally applied magnetic fields on the band structures and spin relaxation in graphene nanoribbons (GNRs). We show that electron-hole bands of GNRs are highly influenced (i.e. level crossing of the bands are possible) by coupling two combined effects: pseudomagnetic fields (PMF) originating from strain tensor and external magnetic fields. In particular, we show that the tuning of the spin-splitting band extends to large externally applied magnetic fields with increasing values of pseudomagnetic fields. Level crossings of the bands in strained GNRs can also be observed due to the interplay between pseudomagnetic fields and externally applied magnetic fields. We also investigate the influence of this interplay on the electromagnetic field mediated spin relaxation mechanism in GNRs. In particular, we show that the spin hot spot can be observed at approximately B = 65 T (the externally applied magnetic field) and B₀ = 53 T (the magnitude of induced pseudomagnetic field due to ripple waves) which may not be considered as an ideal location for the design of straintronic devices. Our analysis might be used for tuning the bandgaps in strained GNRs and utilized to design the optoelectronic devices for straintronic applications.     

Effect of internal viscosity on Brownian dynamics of DNA molecules in shear flow

The results of Brownian dynamics simulations of a single DNA molecule in shear flow are presented taking into account the effect of internal viscosity. The dissipative mechanism of internal viscosity is proved necessary in the research of DNA dynamics. A stochastic model is derived on the basis of the balance equation for forces acting on the chain. The Euler method is applied to the solution of the model. The extensions of DNA molecules for different Weissenberg numbers are analyzed. Comparison with the experimental results available in the literature is carried out to estimate the contribution of the effect of internal viscosity.     

紫外光子在星周天体化学中的作用

介于1到8个太阳质量之间的恒星在演化后期的渐近巨星分支(AGB)阶段,会以气体和尘埃的形式损失大量物质. AGB星提供了星际介质中高达35%的尘埃,其中包含形成太阳系所需要的物质. 此外,AGB星周包层是复杂有机化学所发生的重要场所之一,在其中已探测到的有机分子已超过80多个. 这里展示了AGB星自身或者其近距离的伴星所辐射的紫外光子会显著地改变星周包层的化学特性,尤其是具有团块结构的星周包层. 研究发现,在恒星存在伴星(例如白矮星)的情况下,高通量的紫外光子会破坏富碳AGB星周包层内部的H₂O分子,使其含量低于观测到的水平,并且在星周包层内部产生C⁺等物质,这与以往的星周化学模型的研究结果是不同的.     

Dynamic, electronically controlled angle steering of spatial solitons in AlGaAs slab waveguides

We demonstrate experimentally that spatial solitons in AlGaAs slab waveguides can be deflected by an electronically induced prism. We also show that a weak signal beam can be guided and steered by the solitons, thus demonstrating the feasibility of a dynamically reconfigurable optical interconnect.     

Calibration of NO sensors for in-vivo voltammetry: laboratory synthesis of NO and the use of UV–visible spectroscopy for determining stock concentrations

The increasing scientific interest in nitric oxide (NO) necessitates the development of novel and simple methods of synthesising NO on a laboratory scale. In this study we have refined and developed a method of NO synthesis, using the neutral Griess reagent, which is inexpensive, simple to perform, and provides a reliable method of generating NO gas for in-vivo sensor calibration. The concentration of the generated NO stock solution was determined using UV–visible spectroscopy to be 0.28±0.01 mmol L^–1. The level of NO₂^– contaminant, also determined using spectroscopy, was found to be 0.67±0.21 mmol L^–1. However, this is not sufficient to cause any considerable increase in oxidation current when the NO stock solution is used for electrochemical sensor calibration over physiologically relevant concentrations; the NO sensitivity of bare Pt-disk electrodes operating at +900 mV (vs. SCE) was 1.08 nA mol^–1 L, while that for NO₂^– was 5.9×10^–3 nA mol^–1 L. The stability of the NO stock solution was also monitored for up to 2 h after synthesis and 30 min was found to be the time limit within which calibrations should be performed.     

Synthese neuer Nonafulvene

Synthesis of New Nonafulvenes Nonafulvenes 1c and 1m – s are prepared by the following methods: (a) Elimination of AcOH from acetoxyalkyl-cyclononatetraenes (Scheme 2; 1m ); (b) alkylation of nonafulvenolates (Scheme 3; 1c , 1n ); (c) elimination of alcohol from di- and trialkoxymethyl-cyclononatetraenes (Scheme 5; 1o , 1p , 1q ); (d) deprotonation of intermediary formed formamidiniumcyclononatetraenes (Scheme 6; 1r , 1s ). Scope and limitations of these preparative sequences are discussed and compared with the corresponding pentafulvene syntheses.     

Electronic interaction in an outer-sphere mixed-valence double salt: a polarized neutron diffraction study of K(3)(MnO(4))(2)

The mixed-valence double salt K(3)(MnO(4))(2) crystallizes in space group P2(1)/m with Z = 2. The manganese centers Mn1 and Mn2 constitute discrete "permanganate", [Mn(VII)O(4)](-), and "manganate", [Mn(VI)O(4)](2-), ions, respectively. There is a spin-ordering transition to an antiferromagnetic state at ca. T = 5 K. The spin-density distribution in the paramagnetic phase at T = 10 K has been determined by polarized neutron diffraction, confirming that unpaired spin is largely confined to the nominal manganate ion Mn2. Through use of both Fourier refinement and maximum entropy methods, the spin on Mn1 is estimated as 1.75 +/- 1% of one unpaired electron with an upper limit of 2.5%.     

PHOTOCHEMICAL QUANTUM EFFICIENCY AND ABSORPTION SPECTRA OF REACTION CENTERS FROM RHODOPSEUDOMONAS SPHAEROIDES AT LOW TEMPERATURE

Abstract— The quantum efficiency of bacteriochlorophyll photo-oxidation in reaction centers from Rhodopseudomonas sphaeroides is independent of temperature, within experimental accuracy of ± 15%, from 300 K to 5 K. Absorption spectra at low temperature show maxima at 532 and 544 nm corresponding to the two molecules of bacteriopheophytin in the reaction center. Comparison with the spectrum of the transient light-induced state P ^F indicates that of these two molecules, only the one absorbing at 544 nm participates in forming P ^F.