Near dipole-dipole effects on the propagation of few-cycle pulse in a dense two-level medium

The propagation behaviors, which include the carrier-envelope phase, the area evolution and the solitary pulse number of few-cycle pulses in a dense two-level medium, are investigated based on full-wave Maxwell-Bloch equations by taking Lorentz local field correction (LFC) into account. Several novel features are found: the difference of the carrier-envelope phase between the cases with and without LFC can go up to pi at some location; although the area of ultrashort solitary pulses is lager than 2 pi, the area of the effective Rabi frequency, which equals to that the Rabi frequency pluses the product of the strength of the near dipole-dipole (NDD) interaction and the polarization, is consistent with the standard area theorem and keeps 2 pi; the large area pulse penetrating into the medium produces several solitary pulses as usual, but the number of solitary pulses changes at certain condition. (C) 2005 Optical Society of America.

Propagation of an arbitrary elliptically polarized few-cycle ultrashort laser pulse in resonant two-level quantum systems

We investigate the propagation of an arbitrary elliptically polarized few-cycle ultrashort laser pulse in resonant two-level quantum systems using an iterative predictor-corrector finite-difference time-domain method. It is shown that when the initial effective area is equal to 2 pi, the effective area will remain invariant during the course of propagation, and a complete Rabi oscillation can be achieved. However, for an elliptically polarized few-cycle ultrashort laser pulse, polarization conversion can occur. Eventually, the laser pulse will evolve into two separate circularly polarized laser pulses with opposite helicities.

Propagation of a few-cycle laser pulse in a V-type three-level system

Propagation of a few-cycle laser pulse in a V-type three-level system (fine structure levels of rubidium) is investigated numerically. The full three-level Maxwell-Bloch equations without the rotating wave approximation and the standing slowly varying envelope approximation are solved by using a finite-difference time-domain method. It is shown that, when the usual unequal oscillator strengths are considered, self-induced transparency cannot be recovered and higher spectral components can be produced even for small-area pulses. (c) 2005 Pleiades Publishing, Inc.

Polarization evolution of a few-cycle ultrashort laser pulse propagating in a degenerate three-level medium

The propagation of an arbitrary polarized few-cycle ultrashort laser pulse in a degenerate three-level medium is investigated by using an iterative predictor-corrector finite-difference time-domain method. It is found that the polarization evolution of the ultrashort laser pulse is dependent not only on the initial atomic coherence of the medium but also on the polarization condition of the incident laser pulse. When the initial effective area is equal to 2 pi, complete linear-to-circular and circular-to-linear polarization conversion of few-cycle ultrashort laser pulses can be achieved due to the quantum interference effects between the two different transition paths.

A STUDY ON THE EFFECT OF LESIONS OF AREA-7 OF THE PARIETAL CORTEX ON THE SHORT-TERM VISUAL SPATIAL MEMORY OF RHESUS-MONKEYS (MACACA-MULATTA)

This research is focused on the contribution of area 7 to the short-term visual spatial memory. Three rhesus monkeys (Macaca mulatta) were trained in the direct delayed response task in which 5 delay intervals were used in each session. When each monkey reached the criterion of 90% correct responses in 5 successive sessions, two monkeys underwent a surgery while the other one received a sham operation as a control. In the first stage of the surgery, bilateral areas 7a, 7b and 7ip of the parietal cortex of two monkeys were precisely lesioned. After 7 days of recuperation, the monkeys were required to do the same task. The average percentage of correct responses in the lesioned animals decreased from 94.7% to 89.3% and 93.3% to 82.0% respectively (no significance, P > 0.05, n = 2). In addition, the monkeys' complex movements were mildly impaired. The lesioned monkeys were found to have difficulty picking up food from the wells. In the second stage, bilateral area 7m was lesioned. In the 5 postoperative sessions, the average percentage of correct responses in one monkey, with a relatively precise 7m lesion, decreased from 94.7% to 92.2% (no significance, P > 0.05), while the other monkey, with widely spread necrosis of lateral parietal cortex, showed an. obvious decline in performance, but still over the chance level. After 240 trials this monkey reattained the normal criterion. The results of this research suggest that the lesions of area 7 of the parietal cortex did not significantly affect the short-term visual spatial memory, which has been shown to be sensitive to lesions of the prefrontal cortex; they also support the notion of dissociation of spatial functions in the prefrontal and parietal cortices.

Contamination and distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in agriculture fields in Ya-Er Lake area, China

The contamination and distribution of polychlorinated dibeinizo-p-dioxins and dibenzofurans (PCDD/Fs) from two agricultural fields of a heavily polluted lake area in China (Ya-Er Lake) are presented. The vertical distribution pattern of total PCDD/Fs in soil cores reveals that the maximum concentration was in the layer of 20-30 cm. The concentrations in the top layer of soil at the two sites were similar (17.48 ng/kg at Site 1 and 18.10 ng/kg at Site 2), but the maximum concentration of Site 1 (120.8 ng/kg) was two times higher than that of Site 2 (64.39 ng/kg). The maximum concentration of PCDD/Fs in mud cores in rice fields (0-50 cm) at Sites 1 and 2 was in the layer of 0-10 cm. The maximum PCDD/F concentration in the top layer in mud at Site 1 (203.1 ng/kg) was higher than that at Site 2: (143.3 ng/kg). Significant correlations were found between the mind PCDD/Fs and the organic carbon content (R = 0.9743, P< 0,05 at Site 1; R = 0.9821, P< 0.05 at Site 2), the two variables being highly correlated (R = 0.9049, P< 0.05, at Site 1; R = 0.9916, P< 0.05 at Site 2). All correlation coefficients were significant at the 95% level. Concentrations were highly correlated with organic carbon, indicating that sorption to organic carbon was the dominant mechanism. Using principal component analysis, the homologue profiles of soil, mud, and plants (rice and radish) were compared. The PCDD/F patterns in plants were found not to be correlated to those in soil and mud. This suggests that atmospheric deposition may be the main source of PCDD/Fs in rice grain. However, mixed exposure involving uptake mechanisms and atmospheric deposition is considered main the source of PCDD/F pollution in radishes. (C) 2002 Elsevier Science (USA).

Study on the photosynthetic performances of Enteromorpha prolifera collected from the surface and bottom of the sea of Qingdao sea area

In this work, the photosynthetic performances of Enteromorpha prolifera thalli collected from the surface and bottom of the sea of Qingdao sea area were studied with chlorophyll fluorescence and oxygraph technology. The samples with the highest photosynthetic activity among their kinds, the floating thalli from the sea surface of the south of the Qingdao Olympic Sailing Center and the sedimentary thalli from the mud surface of the bottom Tuandao bay, were chosen as representatives of surface thalli and bottom thalli, respectively. The results showed that the maximal PSII quantum yield of the floating thalli was significantly lower than the normal level although their photosynthetic activities were relatively high; the photosynthetic potential of the thalli form the mud surface was extremely low. Thus, it is indicated that the floating thalli are seriously stressed by their environment and the thalli from the mud surface are already dead or are dying. On the other hand, the results of the laboratory cultivation showed that the sedimentary thalli cannot regain normal photosynthetic activity even under normal illumination conditions. Thus, the thalli from the mud surface cannot become reproductive source of the alga even if they can reach sea surface again. Therefore, a preliminary conclusion can be reached that, up to mid-July 2008, the environmental conditions of the Qingdao sea area are not suitable for the growth of the alga E. prolifera and for this reason the biomass of E. prolifera, in the area, could be declining.

The change of characteristics of tidal wave in the Changjiang River mouth area since the post-glacial transgression maximum

During the period of the post-glacial transgression maximum (PGTM), there was a huge trumpet estuary in the modern Changjiang River Delta area. The location and the shape of the Paleo-Changjiang River Estuary (PCRE) were much different from those of the present Changjiang River Estuary. The study on the change of characteristics of tidal wave in the Changjiang River mouth area since the PGTM can help to understand better the dynamic development of the Changjiang River Delta. The course curves of tidal level and tidal current velocity during a single tidal cycle for 35 points are calculated, and characteristics of tidal waves in the PCRE and its adjacent area are compared with those of tidal waves in the modern Changjiang River mouth area. The results show that the tidal waves within the PCRE and in its adjacent area during the period of the PGTM belonged to standing wave or a mixture of standing wave and progressive wave. Since then, the tidal wave in the Changjiang River mouth become gradually to be progressive wave with the PCRE being filled and the Changjiang River mouth shifting southeastwards.

Radioactivity Concentrations in Soils in the Qingdao Area, China

The specific activity concentrations of radionuclides U-238, Th-212, and K-40 of 2300 sampling points in the Qingdao area were measured by an FD-3022 gamma-ray spectrometer. The radioactivity concentrations of U-238, Th-232, and K-40 ranged from 3.3 to 185.3, from 6.9 to 157.2, and from 15.8 to 7834.4 Bq kg(-1), respectively. The air-absorbed dose at I meter above ground, effective annual dose, external hazard index, and radium equivalent activity were also calculated to systematically evaluate the radiological hazards of the natural radioactivity in Qingdao. The air-absorbed dose, effective annual dose, external hazard index, and radium equivalent activity in the study area were 98.6 nGy h(-1), 0.12 mSv, 0.56, 197 Bq kg(-1), respectively. Compared with the worldwide value, the air-absorbed dose is slightly high, but the other factors are all lower than the recommended value. The natural external exposure will not pose significant radiological threat to the population. In conclusion, the Qingdao area is safe with regard to the radiological level and suitable for living.