Stepwise photoconversion of an artificial light-harvesting array built from extended BODIPY units

The target light-harvesting antennae can be used to sensitize a solar cell in order to improve its performance.

High spatial resolution measurements of NO₂ applying Topographic Target Light scattering-Differential Optical Absorption Spectroscopy (ToTaL-DOAS)

Topographic Target Light scattering – Differential Optical Absorption Spectroscopy (ToTaL-DOAS), also called Target-DOAS, is a novel experimental procedure to retrieve trace gas concentrations present in the low atmosphere. Scattered sunlight (diffuse or specular) reflected from natural or artificial targets located at different distances are analyzed to retrieve the spatial distribution of the concentration of different trace gases like NO2, SO2 and others. We report high spatial resolution measurements of NO2 mixing ratios in the city of Montevideo (Uruguay) observing three buildings as targets with a Mini-DOAS instrument. Our instrument was 146 m, 196 m, and 280 m apart from three different buildings located along a main Avenue. We obtain temporal variation of NO2 mixing ratios between 30 ppb and 65 ppb from measurements of November 2007 and mixing ratios up to 50 ppb from measurements of August and September 2008. Our measurements demonstrate that ToTaL-DOAS observations can be made over relative short distances. In polluted air masses, the retrieved absorption signal was found to be sufficiently strong to allow measurements over distances in the range of several tens of meters.

High spatial resolution measurements of NO₂ applying Topographic Target Light scattering-Differential Optical Absorption Spectroscopy (ToTaL-DOAS)

Tomographic Target Light scattering – Differential Optical Absorption Spectroscopy (ToTaL-DOAS), also called Target-DOAS, is a novel experimental procedure to retrieve trace gas concentrations present in the low atmosphere. Scattered sunlight (partially or totally) reflected from natural or artificial targets of similar albedo located at different distances is analyzed to retrieve the concentration of different trace gases like NO2, SO2 and others. We report high spatial resolution measurements of NO2 mixing ratios in the city of Montevideo (Uruguay) observing three buildings as targets with a Mini-DOAS instrument. Our instrument was 146 m apart from the first building, 196 m from the second and 286 m from the third one. All three buildings are located along a main Avenue. We obtain temporal variation of NO2 mixing ratios between 30 ppb and 65 ppb (±2 ppb). Our measurements demonstrate that ToTaL-DOAS measurements can be made over very short distances. In polluted air masses, the retrieved absorption signal was found to be strong enough to allow measurements over distances in the range of several ten meters, and achieve a spatial resolution of 50 m approximately.

Interaction of smooth pursuit and the vestibuloocular reflex in three dimensions

1. What is the neural mechanism of vestibuloocular reflex (VOR) cancellation when a subject fixates a target moving with the head? One theory is that the moving target evokes pursuit eye movements that add to and cancel the VOR. A recent finding with implications for this theory is that eye velocity vectors of both pursuit and the VOR vary with eye position, but in different ways, because pursuit follows Listing's law whereas the VOR obeys a “half-Listing” strategy. As a result, pursuit cannot exactly cancel the VOR in most eye positions, and so the pursuit superposition theory predicts an eye-position-dependent pattern of residual eye velocities during cancellation. To test these predictions, we measured eye velocity vectors in humans during VOR, pursuit, and cancellation in response to torsional, vertical, and horizontal stimuli with the eyes in different positions. 2. For example, if a subject is rolling clockwise (CW, frequency 0.3 Hz, maximum speed 37.5 deg/s) while looking 20 deg up, the VOR generates an eye velocity that is mainly counterclockwise (CCW), but also leftward. If we then turn on a small target light, located 20 deg up and moving with the subject, then pursuit superposition predicts that the CCW component of eye velocity will shrink and the horizontal component will reverse, from leftward to rightward. This pattern was seen in all subjects. 3. Velocities depended on eye position in the predicted way; e.g., when subjects looked 20 deg down, instead of 20 deg up, during CW roll, the reversal of horizontal eye velocity went the other way, from rightward to leftward. And when gaze was 20 deg right or left, analogous reversals occurred in the vertical eye velocity, again as predicted. 4. Analogous predictions for horizontal and vertical stimulation were also borne out by the data. For example, when subjects rotated rightward while looking 20 deg up, the VOR response was leftward and CCW. When the target light switched on, the torsional component of the response reversed, becoming CW. And analogous predictions for other eye positions and for vertical stimulation also held. 5. For all axes of stimulation and all eye positions, eye velocity during cancellation was roughly parallel with the gaze line. This alignment is predicted by pursuit superposition and has the effect of reducing retinal image slip over the fovea. 6. The fact that the complex dependence of eye velocity on the stimulation axis and eye position predicted by pursuit superposition was seen in all subjects and conditions suggests strongly that the VOR indeed is canceled additively by pursuit. However, eye velocities during cancellation were consistently smaller than predicted. This shrinkage indicates that a second mechanism, besides pursuit superposition, attenuates eye velocities during cancellation. The results can be explained if VOR gain is reduced by approximately 30%, and if, in addition, pursuit is driven by retinal slip rather than reconstructed target velocity in space.

Effect of unilateral cerebral cortical lesions on ocular motor behavior in monkeys: saccades and quick phases

Saccades and quick phases of vestibular and optokinetic nystagmus were quantitated using the magnetic-field search coil technique before and during 1 yr after unilateral decortication in three rhesus monkeys. Saccades were examined during several different behavioral conditions: spontaneous saccades made in the light and in the dark; intentional saccades including visually guided saccades to a target light, predictive saccades to a target light stepped to a predictable location, and target-searching saccades when the monkey was rewarded to find and fixate the target light located in the defective visual hemifield; and reflexive saccades made to novel visual, auditory, and tactile stimuli. Quick phases of nystagmus and spontaneous saccades could be initiated immediately postoperatively, although those initiated away from the side of the lesion were reduced in amplitude and rarely moved the eyes into contralateral craniotopic space. Intentional and reflexive saccades could not be initiated away from the side of the lesion during the first postoperative week. Visually guided saccades and reflexive saccades to stationary or moving visual stimuli in the defective visual hemifield never recovered. Target-searching and predictive saccades directed away from the lesioned side recovered but were generated in a staircase pattern; those saccades from orbital positions further into craniotopic space on the side opposite the lesion had progressively higher latencies and smaller amplitudes. The amplitudes of visually guided saccades to targets stepped into the normal visual hemifield were increased in amplitude by approximately 15% but slowly returned to near preoperative values by 20 wk. Pure vertical visually guided saccades to targets stepped or moved in the vertical direction were not generated throughout the postoperative period. Instead, the animals generated oblique saccades, tilted 10-15 degrees toward the side of the lesion. Velocities of saccades and quick phases were significantly reduced at all amplitudes both away from (approximately 37%) and toward (approximately 22%) the side of the lesion. This deficit diminished with time but velocities were still low one yr postoperatively. Our results suggest that cortical areas in one hemisphere are involved in the initiation of contralaterally directed intentional and reflexive saccades but not in the initiation of spontaneous saccades or quick phases. In time, other structures can initiate contralaterally directed intentional and reflexive saccades, except those guided by vision.(ABSTRACT TRUNCATED AT 400 WORDS)