Abrupt Changes In Intensity Research Articles

Leaf gas exchange responses to abrupt changes in light intensity for two invasive and two non-invasive C 4 grass species

Transient and steady state responses of leaf gas exchange (photosynthesis ( A) and stomatal conductance to water vapor ( g s)) to marked changes in photosynthetic photon flux density (PPFD) were studied for two invasive [ Cynodon dactylon (L.) Pers. and Sorghum halepense (L.) Pers.] and two non-invasive, native [ Bothriochloa ischaemum (L.) Keng and Chrysopogon gryllus (Torn.) Trin.] perennial C 4 grass species from semiarid temperate grasslands or croplands. Following an abrupt drop in PPFD from 1300 to 270 μmol photon m −2 s −1, the two invasive species reduced g s to a greater extent than A, resulting in higher intrinsic photosynthetic water use efficiency (PWUE = A/ g s) at low, compared to high-light conditions. For non-invasives, a comparable drop in g s and A led to invariant PWUE, which was lower than that for the invasive group under low light. The duration and speed of stomatal closure was similar for the four species. However, unlike the other grasses, the noxious weed S. halepense exhibited a negligible net loss in PWUE during the high-to-low light transition. Responses of the native B. ischaemum were mostly intermediate between those of the two invasive species and the non-invasive C. gryllus, which is in agreement with the species’ ecological intermediacy: non-invasive but often reaches local dominance following a disturbance. With a sudden reverse change in PPFD photosynthetic light induction was not faster for invasives than for non-invasives. These results indicate more efficient water use under variable light for invasive compared to non-invasive perennial C 4 grasses which may contribute to their success in semiarid temperate habitats with a heterogeneous light regime. Yet, rapid photosynthetic light induction appears to be of less importance in such environments.

Complex Spike-Event Pattern of Transienton-offRetinal Ganglion Cells

ON-OFF transient ganglion cells of the turtle retina show distinct spike-event patterns in response to abrupt intensity changes, such as during saccadic eye movements. These patterns consist of two main spike events, with the latency of each event showing a systematic dependency on stimulus contrast. Whereas the latency of the first event decreases monotonically with increasing contrast, as expected, the second event shows the shortest latency for intermediate contrasts and a longer latency for high and low contrasts. These spike-event patterns improve the discrimination of different light-intensity transitions based on ensemble responses of the ON-OFF transient ganglion cell subpopulation. Although the discrimination results are far better than chance using either spike counts or latencies of the first spikes, they are further improved by using properties of the second spike event. The best classification results are obtained when spike rates and latencies of both events are considered in combination. Thus spike counts and temporal structure of retinal ganglion cells carry complementary information about the stimulus condition, and thus spike-event patterns could be an important aspect of retinal coding. To investigate the origin of the spike-event patterns in retinal ganglion cells, two computational models of retinal processing are compared. A linear-nonlinear model consisting of separate filters for on and off response components fails to reproduce the spike-event patterns. A more complex cascade filter model, however, accurately predicts the timing of the spike events by using a combination of gain control loop and spike rate adaptation.

Grazing incidence reflection absorption Fourier transform infrared (GIRA-FTIR) spectroscopic studies on the ferroelectric behavior of poly(vinylidene fluoride–trifluoroethylene) ultrathin films

Grazing incidence reflection absorption Fourier transform infrared (GIRA-FTIR) spectroscopy was used to characterize the ferroelectric behavior of a thin poly(vinylidene fluoride–trifluoroethylene) P(VDF–TrFE) copolymer. The lab-built GIRA-FTIR apparatus allowed the heating and corona poling process to be carried out whilst collecting the GIRA spectra of the thin polymer film. The Curie transition from the ferroelectric to paraelectric phase was confirmed from the abrupt change in intensity of the 849 cm −1 band in the RA-FTIR spectrum. It was found that the Curie temperature dropped dramatically when the film thickness was lowered to below a certain critical value of approximately 100 nm. The switching of the CF 2 dipoles in the ferroelectric crystals after applying the external electric field could be determined by monitoring the change in the 849 cm −1 band intensity. For the 600 nm thick P(VDF–TrFE) film, the switching of the dipoles appears to occur almost instantaneously, while the kinetics of dipole switching of the 75 nm thick film were significantly retarded. The repeated switchability of the CF 2 dipoles upon the application of a bipolar cyclic electric field was also confirmed. The bistability of the film due to remnant polarization was also confirmed from the absorbance of the 849 cm −1 band after removing the applied voltage during corona poling.

Perceived timing of first- and second-order changes in vision and hearing

Simultaneous changes in visual stimulus attributes (such as motion or color) are often perceived to occur at different times, a fact usually attributed to differences in neural processing times of those attributes. However, other studies suggest that perceptual misalignments are not due to stimulus attributes, but to the type of change, first- or second-order. To test whether this idea generalizes across modalities, we studied perceptual synchrony of acoustic and of audiovisual cross-modal stimuli, which varied in a first- or second-order fashion. First-order changes were abrupt changes in tone intensity or frequency (auditory), or spatial position (visual), while second-order changes were an inversion of the direction of change, such as a turning point when a rising tone starts falling or a translating visual blob reverses. For both pure acoustic and cross-modal stimuli, first-order changes were systematically perceived before second-order changes. However, when both changes were first-order, or both were second-order, little or no difference in perceptual delay was found between them, regardless of attribute or modality. This shows that the type of attribute change, as well as latency differences, is a strong determinant of subjective temporal alignments. We also performed an analysis of reaction times (RTs) to the first- and second-order attribute changes used in these temporal alignment experiments. RT differences between these stimuli did not correspond with our temporal alignment data, suggesting that subjective alignments cannot be accounted for by a simple latency-based explanation.

Degree of Micelle Ionization and Micellar Growth for Gemini Surfactants Detected by 6-Methoxy-N-(3-sulfopropyl)quinolinium Fluorescence Quenching

The degree of micelle ionization of gemini surfactants has been investigated by using halide-sensitive fluorescence probes (e.g., 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ)). The fluorescence is quenched by the free bromide ions dissociated from surfactants. The degree of micelle ionization increased with increasing spacer chain length, but it decreased with increasing surfactant concentration. The Stern-Volmer plot gave two inflection points (i.e., not only at the cmc but also far above the cmc). The second inflection point suggested spherocylindrical micellar growth with decreases in the degree of micelle ionization. The spherocylindrical micellar growth was depressed with increasing spacer chain length, whereas it was enhanced with increasing tail chain length. The degree of micelle ionization of spherocylindrical micelles depended on the concentration and chain length of gemini surfactants. The change in SPQ fluorescence spectra upon hydrogenation was utilized to evaluate the solubilization site in micelle solutions. The dissolved SPQ in water was instantly reduced by the addition of NaBH4, resulting in abrupt changes in fluorescence intensity and spectral shift. All of the SPQ in micelle solution was also instantly reduced by NaBH4, indicating the existence of SPQ in the water bulk phase, but its fluorescence intensity increased upon the solubilization of hydrogenated SPQ into micelles.

Conformation and Energy Transfer in a Single Luminescent Conjugated Polymer

The photophysics and conformation of single long-chain 2,5-dioctyloxy-p-phenylenevinylene (DOO-PPV) polymers are investigated. The fluorescence intensity−time trace of an individual polymer contains abrupt quantized intensity changes superimposed on small gradual changes. Under the same processing conditions, the size of abrupt changes varies from individual to individual, varying between 0 and 100% of the total intensity. Polarization modulation indicates considerable orientation of absorption dipoles within the polymer. Time-dependent measurements indicate that, in the majority of polymers, absorption dipoles in those regions of the polymer responsible for abrupt intensity changes are arranged less anisotropically than in regions responsible for the gradual changes. Spectroscopic measurements show a greater spectral variation accompanying jumps than that accompanying gradual decay. This can be explained by the coexistence of extended regions and a core region. The first is characterized by a relatively greater alignment of absorption dipoles and multiple emitters, while in the second, absorption dipoles are more isotropically distributed and energy is efficiently funneled to a few emitting excitons. Within a single processing batch, the ratio of these two regions varies from individual to individual.

Task-Based Profile of Vocal Intensity Decline in Parkinson’s Disease

This study examines intensity decay in the phonation of persons with Parkinson’s disease (PD). The decline in vocal intensity (determined by linear regression of the intensity envelope) was compared across the following tasks: vowel prolongation, syllable repetition (diadochokinesis, DDK), isolated sentences and conversation. In contrast to previous studies, PD speakers demonstrated no significant differences in intensity decline from healthy speakers in vowel prolongation. The vocal intensity of speakers with PD declined more rapidly than that of controls in DDK tasks. While intensity slopes in conversation were more variable in both groups, some participants with PD exhibited abrupt changes in intensity. Results indicate that the DDK is particularly useful for describing intensity decay associated with PD. However, considering the inconsistent group differences across tasks, and the discrepant findings from previous studies, intensity decay is not a robust symptom of PD.

The influence of conduit processes on changes in style of basaltic Plinian eruptions: Tarawera 1886 and Etna 122 BC

Basaltic volcanism is most typically thought to produce effusion of lava, with the most explosive manifestations ranging from mild Strombolian activity to more energetic fire fountain eruptions. However, some basaltic eruptions are now recognized as extremely violent, i.e., generating widespread phreatomagmatic, subplinian and Plinian fall deposits. We focus here on the influence of conduit processes, especially partial open-system degassing, in triggering abrupt changes in style and intensity that occurred during two examples of basaltic Plinian volcanism. We use the 1886 eruption of Tarawera, New Zealand, the youngest known basaltic Plinian eruption and the only one for which there are detailed written eyewitness accounts, and the well-documented 122 BC eruption of Mount Etna, Italy, and present new grain size and vesicularity data from the proximal deposits. These data show that even during extremely powerful basaltic eruptions, conduit processes play a critical role in modifying the form of the eruptions. Even with very high discharge, and presumably ascent, rates, partial open-system behaviour of basaltic melts becomes a critical factor that leads to development of domains of largely stagnant and outgassed melt that restricts the effective radius of the conduit. The exact path taken in the waning stages of the eruptions varied, in response to factors which included conduit geometry, efficiency and extent of outgassing and availability of ground water, but a relatively abrupt cessation to sustained high-intensity discharge was an inevitable consequence of the degassing processes.

Estimation of S-wave site response in and around Delhi region from weak motion data

Site response in and around Delhi is studied using digital seismograms recorded by a thirteen-station VSAT-based 24-bit digital Delhi telemetry network of the India Meteorological Department. Nine local (M l ≥ 2.3) and nine regional (M l ≥ 3.9) earthquakes are selected for the estimation of site amplification factor using the classical standard spectral ratio for regional events (Ridge Delhi Observatory being the reference station), normalized standard spectral ratio for local events, horizontal-to-vertical spectral ratio or receiver function and the generalized inversion techniques in the frequency range of 0.5 to 7.5 Hz. Site response curves at all the thirteen stations exhibit station to station variation of the site amplification factor reflecting the changes in geologic/geotectonic/soil conditions. A comparison of the site response values obtained by the generalized inversion with those computed using receiver function technique shows a large scatter even though the pattern of the curves remain more or less similar. However, the site effects computed by generalized inversion and standard spectral ratio exhibit a good 1:1 correspondence. The peaks yielded by all the methods have been observed to occur at the same frequencies. It is evident that the softer fluvial deposits of the newer alluvium of the east Yamuna sector show steeper site amplification gradient at lower frequencies, while the greater Delhi experiences moderate site amplification. The variation of site response corroborates the abrupt changes in intensity from one location to another due to local site condition.

Automated detection of sperm whale sounds as a function of abrupt changes in sound intensity

An algorithm designed to detect abrupt changes in sound intensity was developed and used to identify and count sperm whale vocalizations and to measure boat noise. The algorithm is a Matlab routine that counts the number of occurrences for which the change in intensity level exceeds a threshold. The algorithm also permits the setting of a ‘‘dead time’’ interval to prevent the counting of multiple pulses within a single sperm whale click. This algorithm was used to analyze digitally sampled recordings of ambient noise obtained from the Gulf of Mexico using near bottom mounted EARS buoys deployed as part of the Littoral Acoustic Demonstration Center experiment. Because the background in these data varied slowly, the result of the application of the algorithm was automated detection of sperm whale clicks and creaks with results that agreed well with those obtained by trained human listeners. [Research supported by ONR.]

Insights into the photo-physics of single luminescent conjugated polymers of PPV derivatives using single molecule techniques

The time dependent photo-luminescent behavior of PPV derivatives is studied. Insights gained from short-chain analogues are used to aid in interpretation. Emission is characterized by periods of constant intensity emission punctuated by abrupt intensity changes. A model in which exciton migration is dominated by three-dimensional effects is shown to adequately explain experimental results.

Illumination of exciton migration in rodlike luminescent conjugated polymers by single-molecule spectroscopy

Single-molecule spectroscopy is used to study the time-dependent spectral behavior of a short rodlike Poly(phenylene vinylene) (PPV) derivative polymer spin cast in a polystyrene matrix. The fluorescent time trace is characterized by stepwise intensity emission with constant spectral composition, punctuated by abrupt intensity changes, which are usually accompanied by abrupt spectral changes. In contrast to coiled long chain polymers, defect-free rodlike polymers exhibit multiple-emission sites, each with its characteristic invariant spectrum. The distribution of spectral jumps in the emission spectrum reflects the distribution of the effective conjugation length. This implies the energy transfer (i.e., thermalized exciton migration) along the polymer backbone is inefficient. A static disorder induced conjugation length distribution model with limited energy transfer can be used in understanding the photophysics of an isolated polymer.

Time-resolved study of SrTiO3 homoepitaxial pulsed-laser deposition using surface x-ray diffraction

Homoepitaxy of SrTiO3 by pulsed-laser deposition has been studied using in situ time-resolved surface x-ray diffraction in the temperature range of 310 °C to 780 °C. Using a two-detector configuration, surface x-ray diffraction intensities were monitored simultaneously at the (0 0 12) specular and the (0 1 12) off-specular truncation rod positions. Abrupt intensity changes in both the specular and off-specular rods after laser pulses indicated prompt crystallization into SrTiO3 layers followed by slower intra- and interlayer surface rearrangements on time scales of seconds. Specular rod intensity oscillations indicated layer-by-layer growth, while off-specular rod intensity measurements suggested the presence of transient in-plane lattice distortions for depositions above 600 °C.

Determination of S-Wave Site Response in the Garhwal Himalaya from the Aftershock Sequence of the 1999 Chamoli Earthquake

Site response in the Garhwal Himalaya is studied using digital seismograms recorded by a five-station 24-bit digital microearthquake network established to monitor the aftershocks of the 28 March 1999 Chamoli earthquake ( m b 6.3). Fifteen aftershocks ( M d ≥2.0) are chosen for the site response estimation using horizontal-to-vertical spectral ratio and generalized inversion techniques. Site response curves at all the five sites show station-to-station variation of the site factor reflecting the changes in geologic/geotectonic/soil conditions. A comparison of the site response values obtained by the inversion with those computed using receiver function technique show a large scatter even though the pattern of the curves remains more or less similar. The peaks yielded by both the methods have been observed to occur at the same frequencies. The variation of site response corroborates the abrupt changes in intensity from one location to another due to local site condition. Manuscript received 22 September 2000.

Local time features of geomagnetic jerks

The geomagnetic jerk amplitudes, which are defined as abruptness of changes in the trends of geomagnetic time series, are investigated with geomagnetic monthly means computed from hourly mean values at each local time. A statistical time series model in which the trend component is expressed by a second order spline function with variable knots is constructed for each time series. The optimum parameter values of the model including positions of knots are estimated by the maximum likelihood method, and the optimum number of parameters including the number of knots are determined based on the Akaike Information Criterion (AIC). The jerks are detected objectively and automatically by regarding the optimized positions of knots as the occurrence epochs. This analysis reveals that the spatial distributions of jerk amplitudes essentially do not depend on the local time, which indicates that the jerks cannot be explained by abrupt changes in intensities of latitudinally flowing external currents such as the field-aligned currents. Longitudinally flowing currents, on the other hand, such as the ring current could explain the distributions. The abrupt changes of the ring current intensity are estimated from the distributions of jerk amplitudes in the eastward component in 1969, 1978, and 1991 supposing that an abrupt change in the ring current intensity causes a jerk. However those estimated changes cannot consistently explain the distributions of the jerks in the northward and downward components. Therefore it is plausible that the jerks which occurred in 1969, 1978, and 1991 are not caused by external sources but internal ones. It is also confirmed that the occurrence epochs of jerks in the southern hemisphere are a few years after those of the 1969 and 1978 jerks in the northern hemisphere, and it is also found that the jerk in the southern hemisphere occurred a few years after the occurrence of the 1991 jerk in Europe. Taking these time lags in occurrence epochs into account, it can be said that the 1969, 1978, and 1991 jerks are global phenomena.

Exocytosis in the Dissociated Pancreatic Acinar Cells of the Guinea Pig Directly Visualized by VEC-DIC Microscopy

To elucidate the detailed process of exocytosis at the highest possible accuracy, we dissociated the pancreatic acinus of the guinea pig and observed zymogen granules under a video-enhanced contrast differential interference contrast (VEC-DIC) microscope. The preparation was thin enough to resolve each zymogen granule with the best clarity. When acinar cells were stimulated with ACh (20 μM), many zymogen granules near the lumen showed an abrupt light intensity change. For a period of 10 s immediately before exocytosis, zymogen granules neither shifted their position nor altered their shape within an accuracy of 38 nm. The time required for individual granules to change the light intensity (the releasing time) ranged from 0.15 to 0.70 s. After each response, the granule maintained its altered contrast for a few seconds until it was retrieved to a planar membrane. No compound exocytosis including granule-granule fusion was observed. We concluded that the exocytosis is not directly initiated by any supramolecular change but by a purely molecular event.

A TEST OF TWO POSSIBLE MECHANISMS FOR PHOTOTACTIC STEERING IN VOLVOX CARTERI (CHLOROPHYCEAE)

We tested two competing models that could explain how differential flagellar activity leads to phototactic turning in spheroids of Volvox carteri f. weismannia (Powers) Iyengar. In one model, turning results from the flagella of anterior cells in the lighted and shadowed hemispheres beating at different frequencies. In a competing model, turning results from a change in beat direction in these flagella. Both models successfully explain phototactic steering under constant illumination, but they make different predictions when colonies are exposed to abrupt changes in light intensity. If turning is due to control of flagellar beat frequency, both progression and rotation rates will change in the same direction and with similar magnitudes. If spheroid turning is due to a change in flagellar beat direction, a decreased rate of progression will accompany an increased rate of rotation and vice versa. We used video‐microscopy to observe the behavior of positively phototactic V. carteri spheroids exposed to 10× step‐up and step‐down stimuli. After a step‐up stimulus, spheroids slow their progression and rotation by equal amounts. No significant changes are reported in these parameters after the reciprocal step‐down response. These observations are consistent with the variable flagellar frequency model and inconsistent with the variable flagellar direction model for phototactic turning. Switching the direction of light stimulus by 180° results in reorientation of positively phototactic spheroids. The kinetics of this reorientation did not precisely match the predictions of either model.

Partial Emergence of the Bivalve Donax Vittatus in Response to Abrupt Changes in Light Intensity and before Spawning

Buried individuals of the bivalve Donax vittatus (Bivalvia: Donacidae) respond to change in incident light intensity by adjusting their position in the sediment. Video recordings of activity in aquarium tanks in natural daylight revealed that individuals responded to shading by moving upwards, causing some to partially emerge from the sand. Subsequent removal of the shading stimulated reburial to the normal position. Recordings in laboratory aquaria show similar upward movement and partial emergence occurring when illumination in the visible range is switched off. Upward movement and partial emergence of D. vittatus has also been observed to take place prior to spawning.

Hysteresis Curve of X-Ray Diffraction Peak Intensity in Lead Zirconate Titanate Ceramics

A new system has been developed for the measurement of motion of ferroelectric domains under high electric field driving in ferroelectric materials. This system can simultaneously measure the hysteresis curves of (hkl) X-ray diffraction peak intensity (I(hkl)), field-induced polarization (D), and switching current (I current) as a function of electric field. In a poled tetragonal lead zirconate titanate ceramic, it was found that the peak of I current occurs before the abrupt change in X-ray diffraction intensity of I002 (=I(002)/{I(002)+I(200)}) in the negative direction of the poling axis, whereas the peak of I current in the positive direction of the poling axis occurs at the same electric field as the abrupt change in the X-ray diffraction intensity of I002 under ±2000 V/mm triangular-waveform high electric field at a frequency of 1 mHz. Domain motion is suggested as follows: 180 deg domain walls move before 90 deg domain walls in the negative direction of the poling axis, and 180 deg domain walls move together with 90 deg domain walls in the positive direction of the poling axis near coercive electric fields. This is probably due to the existence of asymmetry of internal bias electric/stress field. Several discussions are given on the relationships among the hysteresis curves of X-ray diffraction peak intensity, field-induced strain, dielectric coefficient, and piezoelectric d33 coefficient in the tetragonal ceramics.

Structural phase transition in (BEDT-TTF) 3CuBr 4 at 60 K

Low temperature X-ray diffraction study for organic semiconductor (BEDT-TTF) 3CuBr 4 revealed structural phase transition from P2 1 c to Pc by losing inversion and screw symmetries at 60.2 K where the magnetic susceptibility shows a steep decrease. Abrupt changes in (0 k 0) X-ray reflection intensity and lattice parameters proved that this phase transition has first-order nature. Structure analysis at 65.9 K verified that the average coordination number of Br around Cu is four.