ALBERT

Notes: Quantum coherence and its dephasing by coupling to a dissipative environment play an important role in time-resolved nonlinear optical response as well as nonadiabatic transitions in the condensed phase. We have discussed nonlinear optical processes on a multi-state one-dimensional system with Morse potential surfaces in a dissipative environment. This was based on a numerical study using the multi-state quantum Fokker–Planck equation for a colored Gaussian–Markovian noise bath, which was expressed as a hierarchy of kinetic equations. This equation can treat strong system-bath interactions at a low temperature heat bath, where quantum effects play a major role. The approach applies to linear absorption measurements as well as four-wave mixing including pump-probe spectroscopy. Laser induced photodissociation and predissociation have been studied for the potential surfaces of Cs2. We have calculated nuclear wave packets in Wigner representation and their monitoring by femtosecond pump-probe spectroscopy for various displacements of potentials and heat-bath parameters. Numerical calculations of probe absorption spectra for strong pump pulse are also presented and discussed. The results show dynamical Stark splitting, but, in contrast to the Bloch equations which contain an infinite-temperature dephasing, we find that at finite temperature their peaks have different heights even when the pump pulse is on resonance. © 1997 American Institute of Physics.

Notes: Ab initio total energy calculation and molecular dynamics simulation on the process of dopant insertion into carbon nanotubes are carried out on the basis of the all-electron mixed basis approach within the local density approximation. First, an upper bound for the height of the potential barrier which is seen by typical alkali metals (Na and K) going through the center of a hexagonal ring of the nanotube is estimated to be 40 eV for Na and 90 eV for K. Next, such an insertion process is simulated with a suitable kinetic energy of the dopant (70 eV for Na and 150 eV for K). It is observed that the carbon atoms are pushed to open the hexagonal ring wider and the dopant passes through. After encapsulation, the hexagonal ring restores its initial configuration, while the impact shock propagates along the nanotube and gradually decays. © 1999 American Institute of Physics.

Notes: A dissipative particle dynamics (DPD) simulation has been used to study the spontaneous vesicle formation of amphiphilic molecules in aqueous solution. The amphiphilic molecule is represented by a coarse-grained model, which contains a hydrophilic head group and a hydrophobic tail. Water is also modeled by the same size particle as adopted in the amphiphile model, corresponding to a group of several H2O molecules. In the DPD simulation, from both a randomly dispersed system and a bilayer structure of the amphiphile for the initial condition, a spontaneous vesicle formation is observed through the intermediate state of an oblate micelle or a bilayer membrane. The membrane fluctuates and encapsulates water particles and then closes to form a vesicle. During the process of vesicle formation, the hydrophobic interaction energy between the amphiphile and water is diminishing. It is also recognized that the aggregation process is faster in two-tailed amphiphiles than those in the case of single-tailed ones. © 2002 American Institute of Physics.

Notes: © 2002 American Institute of Physics.

Notes: The seasonal changes in photosynthetic properties in 1-year-old needles of Sakhalin spruce (Picea glehnii) were measured using the chlorophyll fluorescence technique at various temperatures (5, 10, 20, 25 and 30°C). In the course of seasonal change, a temporary decrease in the quantum yield of PSII electron transport (ΦPSII) was observed just before budbreak. A decline in photochemical quenching (qP) was observed at the same time as that of ΦPSII but only at the two lowest temperatures (5 and 10°C). Photochemical efficiency of open PSII (Fv′/Fm′) also declined just before budbreak at 25 and 30°C. An increase in thermal energy dissipation as indicated by a decrease in Fv′/Fm′ before budbreak was not significant at lower temperatures (5 and 10°C) in spite of the declines in qP. This implies that thermal energy dissipation necessitated by the decline in ΦPSII might not be sufficiently strong to prevent a decline in qP at lower temperatures. On the other hand, at higher temperatures no decline was observed in qP because ΦPSII decreased to a relatively small extent, therefore thermal energy dissipation is sufficient in coping with the excessive energy accumulation in PSII. Seedlings of Sakhalin spruce exposed to ambient air temperature below 10°C before budbreak exhibited photoinhibition indicated by a decrease in the maximal photochemical efficiency of PSII (Fv/Fm) after an overnight dark adaptation. The present study suggests that 1-year-old shoots of Sakhalin spruce have an increased susceptibility to photoinhibition at low temperature just before budbreak.

Notes: The influence of long-term drought stress on photosynthesis of Japanese mountain birch (Betula ermanii Cham.) was examined using chlorophyll fluorescence and gas exchange measurements. Drought stress was imposed in potted plants by reducing irrigation frequency from daily (control) to twice-weekly and once-weekly. Thirty-day-old leaves, which had developed under fully stressed conditions, were used for the measurements. The decline in net CO2 assimilation rate (A) observed in situ in drought-stressed plants resulted from a lower intercellular CO2 concentration (Ci) due to stomatal closure but the carboxylation efficiency was not affected as there was no difference in the initial slope of the A/Ci response after watering. Although there were no treatment differences in A at Ci below 270 μmol mol−1 (with ambient air at 360 μmol mol−1 CO2), higher electron transport rate (ETR), photochemical quenching (qP) and the efficiency of energy conversion of open PSII (Fv′/Fm′), and similar or even lower non-photochemical quenching (NPQ) were observed at a given Ci in drought-stressed plants (of both twice- and once-weekly irrigation), suggesting a higher fraction of open PSII resulting from energy dissipation achieved through higher electron flow rather than through thermal dissipation in PSII antennae. The once-weekly watered plants showed a lower ratio of gross carbon assimilation rate to ETR (A*/ETR), suggesting an enhanced alternative pathway of electron flow probably involving the Mehler-peroxidase (MP) reaction as indicated by a higher ΦPSII at a given ΦCO2 under non-photorespiratory conditions. On the other hand, plants of twice-weekly watering exhibited almost the same A*/ETR and ΦPSII–ΦCO2 relationship as control plants, indicating no enhanced alternative pathways under mild drought stress.

Notes: Fragmentation and ion-scattering processes in the low-energy (0–200 eV) collisions of Agn+ (n=1–4) with a highly oriented pyrolytic graphite (HOPG) surface have been investigated by employing a tandem time-of-flight mass spectrometer. It was found that the fragmentation of scattered cluster ions is due to unimolecular dissociation in the energy range studied. A marked difference between the fragmentation pattern of incident Ag3+ and that of Ag4+ has been found: The intact scattered cluster ion was observed for Ag3+ while only fragment ions for Ag4+. From the incident energy dependence of fragment ion intensities, it was deduced that internal energies of the scattered parent ions have upper and lower limits. These limitations are probably due to the adsorption and the implantation of the projectile clusters on the surface. Ion-scattering yield was found to increase with cluster size. Both the incident energy and cluster size dependencies of ion-scattering yields were reproduced by a model calculation in which the hole survival and sticking probabilities of the clusters, and the incident energy spread of the projectile ions are incorporated. The hole survival probability was evaluated from the time-dependent electron transfer rate for a elastically scattered sphere with an equivalent volume to that of the incident cluster ion. The calculation indicates that the average hole–surface distance at the moment of impact, which is determined by the dimensions of the incident cluster, is important for the hole survival in the cluster–surface collisions. © 2000 American Institute of Physics.

Notes: The effects of strong light in combination with elevated temperatures on the photosynthetic system were examined in 4 dipterocarp tree species with ecologically different habitats. The 4 dipterocarp tree species were: Shorea platyclados originated from upper dipterocarp forests, Shorea parvifolia– lowland and hill dipterocarp forests, Shorea assamica– lowland dipterocarp forests, and Dipterocarpus oblongifolius– riparian fringes. S. platyclados and D. oblongifolius have higher growth and survival rates in open sites than S. parvifolia and S. assamica. Tolerance of high temperature among the species was assessed by determining the critical temperatures (Tc) at which the minimal fluorescence (Fo) began to rise sharply. This was measured by exposing plants to an increasing temperature of about 1°C min−1. The intrinsic thermotolerance of the thylakoid membrane appears to be the highest for D. oblongifolius (Tc=46.4°C), intermediate for S. platyclados (45.7°C), and lowest for S. parvifolia and S. assamica (45.2 and 45.3°C, respectively). The temperature-dependent efficiency of PSII electron transport (ΔF/F′m), photochemical quenching (qP), and the efficiency of light capture of open PSII (F′v/F′m) were measured at the photosynthetic steady state at least 10 min after the light exposure (180 μmol m−2 s−1 PFD). Stable temperature responses of ΔF/F′m and qP were observed in S. platyclados and D. oblongifolius, while those in S. parvifolia and S. assamica were more temperature-dependent and severely affected at 45°C. Little difference was observed in temperature-dependent F′v/F′m among species. Photoinhibitory light exposure (1600 μmol m−2 s−1 PFD) for 2 h at 40°C had little effect on the recovery kinetics from photoinhibition of S. platyclados and D. oblongifolius compared with those at 35°C. In contrast, the recovery from photoinhibition was retarded in S. parvifolia and S. assamica. These findings suggest that even at 40°C, a temperature below Tc, an exposure to strong light exacerbated photoinhibition in S. parvifolia and S. assamica corresponding to the closure of PSII reaction centers, as indicated by the decrease in qP at this temperature. Thus, S. platyclados and D. oblongifolius, which occur at uplands and riparian fringes with frequent disturbances, are suggested to have higher photosynthetic tolerance to elevated temperatures contributing to a circumvention of photoinhibition.

Notes: Elevated atmospheric CO2 concentration [CO2] and different levels of nitrogen (N) nutrition can influence the amount of excess excitation energy in photosystem (PS) II and related photosynthetic properties. The interactive effect of two [CO2] levels (ambient: 360 µM M−1 and elevated: 720 µM M−1) and two N levels (high: 700 mg N plant−1 and low: 100 mg N plant−1) on these properties was examined in seedlings of Japanese white birch (Betula platyphylla var. japonica) using simultaneous measurements of gas exchange and chlorophyll fluorescence. Photosynthetic acclimation to elevated [CO2], as indicated by a decline in carboxylation efficiency (CE), was observed in plants grown at elevated [CO2] especially under low N. Elevated [CO2] resulted in a decrease in area-based leaf N content (Narea) irrespective of N treatment. The adverse effect of elevated [CO2] and low N on CE may have been exacerbated by a greater accumulation of leaf sugar and starch contents in these plants leading to a lower electron transport rate (ETR). While these plants also showed higher non-photochemical quenching (NqP) that could offset the reduction in energy dissipation through ETR to some extent, they still have a higher risk of photoinhibition from excessive excitation energy in PSII as indicated by a decrease in photochemical quenching (qP). However, chronic photoinhibition was not observed in plant grown at elevated [CO2] and low N because they showed no difference in Fv/Fm (the maximum photochemical efficiency of PSII) from those grown at ambient [CO2] and low N after an overnight dark adaptation. High levels of NqP in plants grown at elevated [CO2] and low N reflect a near saturation of thermal energy dissipation. This impaired capacity of photoprotection would render these plants more vulnerable to photoinhibition in the event of additional environmental stresses such as drought, low or high temperature.