氧化石墨烯功能化后含水甲基蓝中隐藏的驰豫通道

The mixture of graphene oxide (GO) and dye molecules may provide some new applications due to unique electronic, optical, and structural properties. Methylene blue (MB), a typical anionic dye, can attach on GO via π-π stacking and electrostatic interaction, and the molecule removal process on GO has been observed. However, it remains unclear about the ultrafast carrier dynamics and the internal energy transfer pathways of the system which is composed of GO and MB. We have employed ultrafast optical pump-probe spectroscopy to investigate the excited dynamics of the GO-MB system dispersed in water by exciting the samples at 400 nm pump pulse. The pristine MB and GO dynamics are also analyzed in t_andem for a direct comparison. Utilizing the global analysis to fit the measured signal via a sequential model, five lifetimes are acquired:(0.61±0.01) ps, (3.52±0.04) ps, (14.1±0.3) ps, (84±2) ps, and (3.66±0.08) ns. The ultrafast dynamics corresponding to these lifetimes was analyzed and the new relaxation processes were found in the GO-MB system, compared with the pristine MB. The results reveal that the functionalization of GO can alter the known decay pathways of MB via the energy transfer from GO to MB in system, the increased intermediate state, and the promoted energy transfer from triplet state MB to ground state oxygen molecules dissolved in aqueous sample.     

Kinetic Evidence for Methanol Trimer Assisted Proton Transfer: Transient Absorption Study on Excited Triplet State of 4-Hydroxy-4′-nitrobiphenyl

Hydroxyaromatic compounds have a wide range of applications in catalytic synthesis and biological processes due to their enhanced acidity upon photo-excitation. Most hydroxyaromatic compounds with a medium excited state acidity are unable to deprotonate in non-aqueous solvents such as alcohol due to their short-lived excited singlet states. The nitro group in 4-hydroxy-4'-nitrobiphenyl (NO₂-Bp-OH) increases the spin-orbit coupling between excited singlet states and the triplet state, resulting in ultrafast intersystem crossing and the formation of the long-lived lowest excited triplet state (T₁) with a high yield. Using transient absorption spectroscopy and kinetic analysis, we discover that, despite its moderate acidity, the T₁ state of NO₂-Bp-OH (³NO₂-Bp-OH) is able to transfer proton to methanol. Following the formation of the hydrogen-boned complex between ³NO₂-Bp-OH and three methanol molecules in a consecutive process, proton transfer occurs very fast. This finding suggests that the long lifetime of the photoacid excited state allows for the formation of alcohol oligomer with sufficient basicity to induce photoacid deprotonation.     

二硫化钼纳米点中的缺陷辅助载流子俘获超快动力学

二硫化钼纳米点正在成为有潜质的半导体材料用于光电设备的应用.然而,关于对其中激子动力学的研究却很少.本文利用飞秒瞬态吸收光谱学来研究二硫化钼纳米点的载流子动力学.结果显示,缺陷辅助的载流子再复合过程与观测到的动力学相符,通过俄歇散射对光激载流子进行俘获至少存在两种不同俘获速率的缺陷.四个过程参与了载流子驰豫,在受到光激发后,立即在~0.5 ps内载流子冷却,然后大部分载流子被缺陷快速俘获,随着泵浦能量的增加,该过程对应的时间从~4.9 ps增加到~9.2 ps,这可以用缺陷态的饱和来解释.接下来,拥有相对慢的载流子俘获速率的其它类型缺陷对小部分载流子进行俘获,该过程约65 ps.最后,剩余的少量载流子通过直接带间跃迁发生电子-空穴再复合,时间约为1 ns.研究结果可以深入了解二硫化钼纳米点中的载流子动力学基本原理,引导其更多的应用.     

MOL solution of DOM for transient radiative transfer in 3-D scattering media

A methodology based on the method of lines solution of discrete ordinates method for solution of the 3-D transient radiative transfer equation is introduced. The method is applied to the prediction of transient and steady state transmittances in a cubical enclosure containing purely scattering medium and validated against Monte Carlo solutions from the literature. The flexibility of the method for implementation of linear spatial differencing schemes, flux limiters and weighted essentially non-oscillatory methods is demonstrated. Van Leer flux limiter is found to provide stable, accurate and efficient solutions.     

Analysis of the characteristics of time-resolved signals for transient radiative transfer in scattering participating media

Transient radiative transfer (TRT) in one-dimensional (1-D) homogeneous and inhomogeneous media with ultra-short pulse laser irradiated is investigated by means of the finite volume method (FVM) in the present research. Comparing with the steady radiative transfer (SRT), the extra time-resolved information can be obtained in TRT. Meanwhile, the propagation speed of short-pulse laser and the geometric thickness of the media should be considered in the simulation of TRT problem besides the optical thickness. A new nondimensional number ζ=ct_p/L is presented. For the homogeneous media, the temporal signals would overlap one another with different combinations of the pulse duration and the thickness of the media with the same ζ. Furthermore, in two-layer media, the influence of the scattering albedo, optical thickness and the geometric thickness of the participating media on ‘dual-peak’ are studied thoroughly. The improved expression of the ‘local minimum’ in the ‘dual-peak’ and the interface location of the multi-layer media are provided.     

Transient radiation and conduction heat transfer inside a plane-parallel participating gray medium with boundaries having different reflecting characteristics

A hybrid ray-tracing method is developed for the solution to the radiative transfer in a plane-parallel participating medium having one specular surface and another diffuse surface. By this method, radiative transfer coefficients (RTCs) for specular–diffuse (S–D) surfaces are deduced. The medium surfaces are considered to be semitransparent. The effects of convection–radiation parameter, conduction–radiation parameter and refractive index on transient coupled heat transfer are investigated. Results show that the temperature curves of the medium having S–D surfaces is higher than those of the medium having S–S surfaces (two specular surfaces); the total heat flux at steady state for the S–D surfaces is lower than that for the S–S surfaces.     

Transient times,resonances and drifts of attractors in dissipative rotational dynamics

In a dissipative system the time to reach an attractor is often influenced by the peculiarities of the model and in particular by the strength of the dissipation. As a dissipative model we consider the spin–orbit problem providing the dynamics of a triaxial satellite orbiting around a central planet and affected by tidal torques. The model is ruled by the oblateness parameter of the satellite, the orbital eccentricity, the dissipative parameter and the drift term. We devise a method which provides a reliable indication on the transient time which is needed to reach an attractor in the spin–orbit model; the method is based on an analytical result, precisely a suitable normal form construction. This method provides also information about the frequency of motion. A variant of such normal form used to parameterize invariant attractors provides a specific formula for the drift parameter, which in turn yields a constraint – which might be of interest in astronomical problems – between the oblateness of the satellite and its orbital eccentricity.     

Ramanujan theta functions and birth and death processes

This paper discusses birth and death processes that are related to the celebrated Ramanujan’s theta functions. The pertinent transient system size probabilities are calculated numerically via a truncation of continued fractions.     

The maximum number of infected individuals in SIS epidemic models: Computational techniques and quasi-stationary distributions

We study the maximum number of infected individuals observed during an epidemic for a Susceptible-Infected-Susceptible (SIS) model which corresponds to a birth-death process with an absorbing state. We develop computational schemes for the corresponding distributions in a transient regime and till absorption. Moreover, we study the distribution of the current number of infected individuals given that the maximum number during the epidemic has not exceeded a given threshold. In this sense, some quasi-stationary distributions of a related process are also discussed.     

Photoinitiated Energy Transfer in Porous-Cage-Stabilised Silver Nanoparticles

We report a new composite material consisting of silver nanoparticles decorated with three-dimensional molecular organic cages based on light-absorbing porphyrins. The porphyrin cages serve to both stabilize the particles and allow diffusion and trapping of small molecules close to the metallic surface. Combining these two photoactive components results in a Fano-resonant interaction between the porphyrin Soret band and the nanoparticle-localised surface-plasmon resonance. Time-resolved spectroscopy revealed the silver nanoparticles transfer up to 37 % of their excited-state energy to the stabilising layer of porphyrin cages. These unusual photophysics cause a 2-fold current increase in photoelectrochemical water-splitting measurements. The composite structure provides a compelling proof of concept for advanced photosensitiser systems with intrinsic porosity for photocatalytic and sensing applications.