Small Intensity Changes Research Articles

A savanna response to precipitation intensity.

As the atmosphere warms, precipitation events are becoming less frequent but more intense. A three-year experiment in Kruger National Park, South Africa, found that fewer, more intense precipitation events encouraged woody plant encroachment. To test whether or not these treatment responses persisted over time, here, we report results from all five years of that experiment. Grass growth, woody plant growth, total fine root number and area and hydrologic tracer uptake by grasses and woody plants were measured in six treated plots (8 m by 8 m) and six control plots. Treatment effects on soil moisture were measured continuously in one treated and one control plot. During the fourth year, increased precipitation intensity treatments continued to decrease water flux in surface soils (0–10 cm), increase water flux in deeper soils (20+ cm), decrease grass growth and increase woody plant growth. Greater root numbers at 20–40 cm and greater woody plant uptake of a hydrological tracer from 45–60 cm suggested that woody plants increased growth by increasing root number and activity (but not root area) in deeper soils. During the fifth year, natural precipitation events were large and intense so treatments had little effect on precipitation intensity or plant available water. Consistent with this effective treatment removal, there was no difference in grass or woody growth rates between control and treated plots, although woody plant biomass remained higher in treated than control plots due to treatment effects in the previous four years. Across the five years of this experiment, we found that 1) small increases in precipitation intensity can result in large increases in deep (20–130 cm) soil water availability, 2) plant growth responses to precipitation intensity are rapid and disappear quickly, and 3) because woody plants accumulate biomass, occasional increases in precipitation intensity can result in long-term increases in woody plant biomass (i.e., shrub encroachment). While results are likely to be site-specific, they provide experimental evidence of large ecohydrological responses to small changes in precipitation intensity.

Proposal for dark exciton based chemical sensors

The rapidly increasing use of sensors throughout different research disciplines and the demand for more efficient devices with less power consumption depends critically on the emergence of new sensor materials and novel sensor concepts. Atomically thin transition metal dichalcogenides have a huge potential for sensor development within a wide range of applications. Their optimal surface-to-volume ratio combined with strong light–matter interaction results in a high sensitivity to changes in their surroundings. Here, we present a highly efficient sensing mechanism to detect molecules based on dark excitons in these materials. We show that the presence of molecules with a dipole moment transforms dark states into bright excitons, resulting in an additional pronounced peak in easy accessible optical spectra. This effect exhibits a huge potential for sensor applications, since it offers an unambiguous optical fingerprint for the detection of molecules—in contrast to common sensing schemes relying on small peak shifts and intensity changes.

The role of dynamic surface water‐groundwater exchange on streambed denitrification in a first‐order, low‐relief agricultural watershed

AbstractThe role of temporally varying surface water‐groundwater (SW‐GW) exchange on nitrate removal by streambed denitrification was examined along a reach of Leary Weber Ditch (LWD), Indiana, a small, first‐order, low‐relief agricultural watershed within the Upper Mississippi River basin, using data collected in 2004 and 2005. Stream stage, GW heads (H), and temperatures (T) were continuously monitored in streambed piezometers and stream bank wells for two transects across LWD accompanied by synoptic measurements of stream stage, H, T, and nitrate (NO3) concentrations along the reach. The H and T data were used to develop and calibrate vertical two‐dimensional, models of streambed water flow and heat transport across and along the axis of the stream. Model‐estimated SW‐GW exchange varied seasonally and in response to high‐streamflow events due to dynamic interactions between SW stage and GW H. Comparison of 2004 and 2005 conditions showed that small changes in precipitation amount and intensity, evapotranspiration, and/or nearby GW levels within a low‐relief watershed can readily impact SW‐GW interactions. The calibrated LWD flow models and observed stream and streambed NO3 concentrations were used to predict temporal variations in streambed NO3 removal in response to dynamic SW‐GW exchange. NO3 removal rates underwent slow seasonal changes, but also underwent rapid changes in response to high‐flow events. These findings suggest that increased temporal variability of SW‐GW exchange in low‐order, low‐relief watersheds may be a factor contributing their more efficient removal of NO3.

Effect of color visualization and display hardware on the visual assessment of pseudocolor medical images.

Even though the use of color in the interpretation of medical images has increased significantly in recent years, the ad hoc manner in which color is handled and the lack of standard approaches have been associated with suboptimal and inconsistent diagnostic decisions with a negative impact on patient treatment and prognosis. The purpose of this study is to determine if the choice of color scale and display device hardware affects the visual assessment of patterns that have the characteristics of functional medical images. Perfusion magnetic resonance imaging (MRI) was the basis for designing and performing experiments. Synthetic images resembling brain dynamic-contrast enhanced MRI consisting of scaled mixtures of white, lumpy, and clustered backgrounds were used to assess the performance of a rainbow ("jet"), a heated black-body ("hot"), and a gray ("gray") color scale with display devices of different quality on the detection of small changes in color intensity. The authors used a two-alternative, forced-choice design where readers were presented with 600 pairs of images. Each pair consisted of two images of the same pattern flipped along the vertical axis with a small difference in intensity. Readers were asked to select the image with the highest intensity. Three differences in intensity were tested on four display devices: a medical-grade three-million-pixel display, a consumer-grade monitor, a tablet device, and a phone. The estimates of percent correct show that jet outperformed hot and gray in the high and low range of the color scales for all devices with a maximum difference in performance of 18% (confidence intervals: 6%, 30%). Performance with hot was different for high and low intensity, comparable to jet for the high range, and worse than gray for lower intensity values. Similar performance was seen between devices using jet and hot, while gray performance was better for handheld devices. Time of performance was shorter with jet. Our findings demonstrate that the choice of color scale and display hardware affects the visual comparative analysis of pseudocolor images. Follow-up studies in clinical settings are being considered to confirm the results with patient images.

Detection of Small Changes in Psoriasis Intensity with PrecisePASI

Background: The Psoriasis Area and Severity Index (PASI) is the score of choice to grade psoriasis severity and detect clinical changes. Due to low resolution based on the calculation of the score by fixed area classes, PASI scores <10 have little value. Methods: At 756 patient examinations, psoriasis activity was measured with both PASI and PrecisePASI. Results: PrecisePASI has a linear increase while PASI has a staircase pattern. Both scores meet at the endpoint-relevant values of body surface area (BSA) 10, 30, 50, 70 and 90%. PASI and PrecisePASI correlate significantly over the whole range of BSA. In the region of BSA <5%, PrecisePASI shows a significantly higher resolution (p < 0.0001). Conclusion: The calculation of PrecisePASI corrects the undesired inaccuracies of PASI in the lower BSA ranges and is a tool to use as an endpoint in trials aiming to detect differences in the lower ranges of BSA.

Postpartum hypernatremic cerebral encephalopathy with osmotic myelinolysis: Report of two cases and review with emphasis on magnetic resonance imaging findings

Postpartum complications are diverse. Electrolyte imbalance with hypernatremia can occur secondary to underlying postpartum complication or can arise de novo. Hypernatremia causes demyelination similar to hyponatremia but predominantly involves extra-pontine structures. Here, we present two cases, one classical and another a variant of a recently described entity called postpartum hypernatremic encephalopathy with osmotic demyelination. The more classical appearance is altered signal intensity changes in the posterior limb of internal capsules, external capsule, crus cerebri, corticopontine tracts, middle cerebellar peduncle, hippocampus, fornix, and cerebellar white matter with classical wine glass appearance on coronal T2-weighted images. The nonclassical case shows a different and atypical imaging finding of the same disease with small focal transient altered signal intensity changes in the splenium of corpus callosum. Both the patients recovered with conservative management of the electrolyte imbalance.

Factors affecting the voxel-based analysis of diffusion tensor imaging

Diffusion tensor imaging (DTI) provides a unique method to reveal the integrity of white matter microstructure noninvasively. Voxel-based analysis (VBA), which is a highly reproducible and user-independent technique, has been used to analyze DTI data in a number of studies. Fractional anisotropy (FA), which is derived from DTI, is the most frequently used parameter. The parameter setting during the DTI data preprocessing might affect the FA analysis results. However, there is no reliable evidence on how the parameters affect the results of FA analysis. This study sought to quantitatively investigate the factors that might affect the voxel-based analysis of FA; these include the interpolation during spatial normalization, smoothing kernel and statistical threshold. Because it is difficult to obtain the true information of the lesion in the patients, we simulated lesions on the healthy FA maps. The DTI data were obtained from 20 healthy subjects. The FA maps were calculated using DTIStudio. We randomly divided these FA maps into two groups. One was used as a model patient group, and the other was used as a normal control group. Simulated lesions were added to the model patient group by decreasing the FA intensities in a specified region by 5 %-50 %. The model patient group and the normal control group were compared by two-sample t test statistic analysis voxel-by-voxel to detect the simulated lesions. We evaluated these factors by comparing the difference between the detected lesion through VBA and the simulated lesion. The result showed that the space normalization of FA image should use the trilinear interpolation, and the smoothing kernel should be 2-3 times the voxel size of spatially normalized FA image. For lesions with small intensity change, FWE correction must be cautiously used. This study provided an important reference to the analysis of FA with VBA method.

Examination of synaptic vesicle recycling using FM dyes during evoked, spontaneous, and miniature synaptic activities.

Synaptic vesicles in functional nerve terminals undergo exocytosis and endocytosis. This synaptic vesicle recycling can be effectively analyzed using styryl FM dyes, which reveal membrane turnover. Conventional protocols for the use of FM dyes were designed for analyzing neurons following stimulated (evoked) synaptic activity. Recently, protocols have become available for analyzing the FM signals that accompany weaker synaptic activities, such as spontaneous or miniature synaptic events. Analysis of these small changes in FM signals requires that the imaging system is sufficiently sensitive to detect small changes in intensity, yet that artifactual changes of large amplitude are suppressed. Here we describe a protocol that can be applied to evoked, spontaneous, and miniature synaptic activities, and use cultured hippocampal neurons as an example. This protocol also incorporates a means of assessing the rate of photobleaching of FM dyes, as this is a significant source of artifacts when imaging small changes in intensity.

DYNAMICS OF CORONAL RAIN AND DESCENDING PLASMA BLOBS IN SOLAR PROMINENCES. I. FULLY IONIZED CASE

Observations of active regions and limb prominences often show cold, dense blobs descending with an acceleration smaller than that of free fall. The dynamics of these condensations falling in the solar corona is investigated in this paper using a simple fully ionised plasma model. We find that the presence of a heavy condensation gives rise to a dynamical rearrangement of the coronal pressure that results in the formation of a large pressure gradient that opposes gravity. Eventually this pressure gradient becomes so large that the blob acceleration vanishes or even points upwards. Then, the blob descent is characterised by an initial acceleration phase followed by an essentially constant velocity phase. These two stages can be identified in published time-distance diagrams of coronal rain events. Both the duration of the first stage and the velocity attained by the blob increase for larger values of the ratio of blob to coronal density, for larger blob mass, and for smaller coronal temperature. Dense blobs are characterised by a detectable density growth (up to 60% in our calculations) and by a steepening of the density in their lower part, that could lead to the formation of a shock. They also emit sound waves that could be detected as small intensity changes with periods of the order of 100 s and lasting between a few and about ten periods. Finally, the curvature of the falling path is only relevant when a very dense blob falls along inclined magnetic field lines.

Direct and Indirect Effects of UV-B Exposure on Litter Decomposition: A Meta-Analysis

Ultraviolet-B (UV-B) exposure in the course of litter decomposition may have a direct effect on decomposition rates via changing states of photodegradation or decomposer constitution in litter while UV-B exposure during growth periods may alter chemical compositions and physical properties of plants. Consequently, these changes will indirectly affect subsequent litter decomposition processes in soil. Although studies are available on both the positive and negative effects (including no observable effects) of UV-B exposure on litter decomposition, a comprehensive analysis leading to an adequate understanding remains unresolved. Using data from 93 studies across six biomes, this introductory meta-analysis found that elevated UV-B directly increased litter decomposition rates by 7% and indirectly by 12% while attenuated UV-B directly decreased litter decomposition rates by 23% and indirectly increased litter decomposition rates by 7%. However, neither positive nor negative effects were statistically significant. Woody plant litter decomposition seemed more sensitive to UV-B than herbaceous plant litter except under conditions of indirect effects of elevated UV-B. Furthermore, levels of UV-B intensity significantly affected litter decomposition response to UV-B (P<0.05). UV-B effects on litter decomposition were to a large degree compounded by climatic factors (e.g., MAP and MAT) (P<0.05) and litter chemistry (e.g., lignin content) (P<0.01). Results suggest these factors likely have a bearing on masking the important role of UV-B on litter decomposition. No significant differences in UV-B effects on litter decomposition were found between study types (field experiment vs. laboratory incubation), litter forms (leaf vs. needle), and decay duration. Indirect effects of elevated UV-B on litter decomposition significantly increased with decay duration (P<0.001). Additionally, relatively small changes in UV-B exposure intensity (30%) had significant direct effects on litter decomposition (P<0.05). The intent of this meta-analysis was to improve our understanding of the overall effects of UV-B on litter decomposition.

Jupiter’s zonal winds and their variability studied with small-size telescopes

Context. The general circulation of Jupiter’s atmosphere at cloud level is dominated by a system of zonal jets that alternate in direction with latitude. The winds, measured in high-resolution images obtained by different space missions and the Hubble Space Telescope, are overall stable in their latitude location with small changes in intensity at particular jets. However, the atmosphere experiences repetitive changes in the albedo of particular belts and zones that are subject to large-scale intense disturbances that may locally influence the profile.Aims. The lack of high-resolution images has not allowed the wind system to be studied with the regularity required to assess its stability with respect to these major changes or to other types of variations (e.g., seasonality). To amend that, we present a study of the zonal wind profile of Jupiter using images acquired around the 2011 opposition by a network of observers operating small-size telescopes with apertures in the range 0.20−1 m.Methods. Using an automatic correlation technique, we demonstrate the capability to extract the mean zonal winds in observing periods close to the opposition. A broad collaboration with skilled amateur astronomers opens the possibility to regularly study short- and long-term changes in the jets of Jupiter.Results. We compare the 2011 Jovian wind profile to those previously obtained. The winds did not experience significant short-term changes over 2011 but show noteworthy variations at particular latitudes when compared with wind profiles from previous years. Most of these variations are related to major changes in the cloud morphology of the planet, in particular at 7° N where an intense eastward jet varies around 40 ms-1 in its intensity according to the development or not of the “dark projection” features, confirming previous results.

Swift heavy ion induced modifications in structural, optical & magnetic properties of pure and V doped ZnO films

The effect of swift heavy ion irradiation on structural, optical and magnetic properties of pure ZnO, Zn0.95V0.05O and Zn0.90V0.10O films prepared by RF sputtering are studied. X-ray diffraction (XRD) analysis reveals no significant change in the ZnO crystal structure except a small change in intensity and peak broadening on irradiation. Raman spectra reveal the degradation of crystalline quality upon ion irradiation. Atomic force microscopy (AFM) study shows the formation of smaller sized nanostructures on ion irradiation. Photoluminescence (PL) spectra of ZnO films reveal the increase of defects such as oxygen vacancy in the films upon ion irradiation. The irradiated V doped ZnO films exhibit room temperature ferromagnetic behaviour. An increase in oxygen vacancy on ion irradiation together with V ion concentration favours enhanced ferromagnetic behaviour in irradiated V doped ZnO films.

Electrochemically Induced Far-Infrared Difference Spectroscopy on Metalloproteins Using Advanced Synchrotron Technology

New information on a protein's structure, intra- and intermolecular hydrogen bonds, or metal-ligand bond properties can be unraveled in the far-infrared (far-IR)-terahertz-domain (600-3 cm(-1) or 18-0.1 THz). In this study, we compare the performances of thermal sources with synchrotron far-IR to record reaction-induced Fourier transform infrared (FT-IR) difference signals with proteins in solution. Using the model protein Cu-azurin placed in a short path length electrochemical cell adapted for transmission spectroscopy in vacuum-purged optics, we show that minute spectral shifts induced by metal isotope labeling or temperature changes are detected using the far-IR beamline AILES of the synchrotron SOLEIL. On one hand, these data allow us to identify modes involving Cu-ligand vibrations and pave the way for the analysis of metal sites or metal redox states of proteins not amenable to resonance Raman spectroscopy. On another hand, small band shifts or changes in band intensity upon temperature modifications show that far-IR difference spectroscopy allows one to extract from a complex background hydrogen-bonding signatures directly relevant to the protein function. For Cu-azurin, a temperature-sensitive IR mode involving Cu(II)-His vibrations points to the role of a hydrogen bond between a Cu histidine ligand and the water solvent in tuning the Cu(II)-histidine bond properties. Furthermore, these experimental data support the possible role of a His117-water interaction in electron-transfer activity of Cu-azurin proposed by theoretical studies.

Validity and Reliability of the Session-RPE Method for Quantifying Training in Australian Football

The purpose of this study was to examine and compare the criterion validity and test-retest reliability of the CR10 and CR100 rating of perceived exertion (RPE) scales for team sport athletes that undertake high-intensity, intermittent exercise. Twenty-one male Australian football (AF) players (age: 19.0 ± 1.8 years, body mass: 83.92 ± 7.88 kg) participated the first part (part A) of this study, which examined the construct validity of the session-RPE (sRPE) method for quantifying training load in AF. Ten male athletes (age: 16.1 ± 0.5 years) participated in the second part of the study (part B), which compared the test-retest reliability of the CR10 and CR100 RPE scales. In part A, the validity of the sRPE method was assessed by examining the relationships between sRPE, and objective measures of internal (i.e., heart rate) and external training load (i.e., distance traveled), collected from AF training sessions. Part B of the study assessed the reliability of sRPE through examining the test-retest reliability of sRPE during 3 different intensities of controlled intermittent running (10, 11.5, and 13 km·h(-1)). Results from part A demonstrated strong correlations for CR10- and CR100-derived sRPE with measures of internal training load (Banisters TRIMP and Edwards TRIMP) (CR10: r = 0.83 and 0.83, and CR100: r = 0.80 and 0.81, p < 0.05). Correlations between sRPE and external training load (distance, higher speed running and player load) for both the CR10 (r = 0.81, 0.71, and 0.83) and CR100 (r = 0.78, 0.69, and 0.80) were significant (p < 0.05). Results from part B demonstrated poor reliability for both the CR10 (31.9% CV) and CR100 (38.6% CV) RPE scales after short bouts of intermittent running. Collectively, these results suggest both CR10- and CR100-derived sRPE methods have good construct validity for assessing training load in AF. The poor levels of reliability revealed under field testing indicate that the sRPE method may not be sensible to detecting small changes in exercise intensity during brief intermittent running bouts. Despite this limitation, the sRPE remains a valid method to quantify training loads in high-intensity, intermittent team sport.

Assessing the role of spectral and intensity cues in spectral ripple detection and discrimination in cochlear-implant users

Measures of spectral ripple resolution have become widely used psychophysical tools for assessing spectral resolution in cochlear-implant (CI) listeners. The objective of this study was to compare spectral ripple discrimination and detection in the same group of CI listeners. Ripple detection thresholds were measured over a range of ripple frequencies and were compared to spectral ripple discrimination thresholds previously obtained from the same CI listeners. The data showed that performance on the two measures was correlated, but that individual subjects' thresholds (at a constant spectral modulation depth) for the two tasks were not equivalent. In addition, spectral ripple detection was often found to be possible at higher rates than expected based on the available spectral cues, making it likely that temporal-envelope cues played a role at higher ripple rates. Finally, spectral ripple detection thresholds were compared to previously obtained speech-perception measures. Results confirmed earlier reports of a robust relationship between detection of widely spaced ripples and measures of speech recognition. In contrast, intensity difference limens for broadband noise did not correlate with spectral ripple detection measures, suggesting a dissociation between the ability to detect small changes in intensity across frequency and across time.

The Standard Model for Perceived Magnitude: A Framework for (Almost) Everything Known About It

The psychophysics of perceived magnitude entails three aspects of sensory systems: range of sensitivity (dynamic range [DR]), resolving power (the capacity to resolve small changes in stimulus intensity), and the form of the function relating perceived magnitude to signal strength throughout the DR. A simple model is proposed that integrates what is known about all three aspects into a single framework. According to the model, perceived magnitude is a power function of stimulus strength (S. S. Stevens, 1956), and both the exponent of that function and a measure of resolving power are inversely related to the log of DR (R. Teghtsoonian, 1971). The DR is thought to have a characteristic value for each sensory system and may be estimated directly by measurement of upper and lower limits, or indirectly by estimating the exponent of the power function under optimal conditions. A central feature of the model is that all DRs are assumed to be subjectively equal. It is also suggested that the impression of perceived magnitude may be mediated by a single mechanism, regardless of the sensory system that is activated. It remains to be seen whether brain science is able to identify a neural basis for such a mechanism.

Identification of intensity ratio break points from photon arrival trajectories in ratiometric single molecule spectroscopy.

We describe a statistical method to analyze dual-channel photon arrival trajectories from single molecule spectroscopy model-free to identify break points in the intensity ratio. Photons are binned with a short bin size to calculate the logarithm of the intensity ratio for each bin. Stochastic photon counting noise leads to a near-normal distribution of this logarithm and the standard student t-test is used to find statistically significant changes in this quantity. In stochastic simulations we determine the significance threshold for the t-test’s p-value at a given level of confidence. We test the method’s sensitivity and accuracy indicating that the analysis reliably locates break points with significant changes in the intensity ratio with little or no error in realistic trajectories with large numbers of small change points, while still identifying a large fraction of the frequent break points with small intensity changes. Based on these results we present an approach to estimate confidence intervals for the identified break point locations and recommend a bin size to choose for the analysis. The method proves powerful and reliable in the analysis of simulated and actual data of single molecule reorientation in a glassy matrix.

Topographic Effects on the Tropical Land and Sea Breeze

Abstract The effect of an inland plateau on the tropical sea breeze is considered in terms of idealized numerical experiments, with a particular emphasis on offshore effects. The sea breeze is modeled as the response to an oscillating interior heat source over land. The parameter space for the calculations is defined by a nondimensional wind speed, a scaled plateau height, and the nondimensional heating amplitude. The experiments show that the inland plateau tends to significantly strengthen the land-breeze part of the circulation, as compared to the case without terrain. The strengthening of the land breeze is tied to blocking of the sea-breeze density current during the warm phase of the cycle. The blocked sea breeze produces a pool of relatively cold, stagnant air at the base of the plateau, which in turn produces a stronger land-breeze density current the following morning. Experiments show that the strength of the land breeze increases with the terrain height, at least for moderate values of the height. For very large terrain, the sea breeze is apparently blocked entirely, and further increases in terrain height lead to only small changes in land-breeze intensity and propagation. Details of the dynamics are described in terms of the transition from linear to nonlinear heating amplitudes, as well as for cases with and without background winds. The results show that for the present experiments, significant offshore effects are tied to nonlinear frontal propagation, as opposed to quasi-linear wave features.

Prebreakdown excitation of crystals at double multiphoton resonance: III. Forbidden transitions

Within the three-band model of a crystal, we calculated the probabilities of forbidden-allowed four-photon transitions between the valence band and the conduction band under conditions of two-photon resonance on the adjacent transition between two conduction bands. We show that the transformation of the electronic band spectrum under the action of high-power light of a prebreakdown intensity leads to a nonmonotonic dependence of the rate of photogeneration electron-hole pairs on the radiation intensity. We determined conditions under which a small change in the intensity in the range 1011–1013 W/cm2 leads to an increase in the generation rate of electron-hole pairs by more than an order of magnitude, which can cause an increase in the number of nonequilibrium carriers to values sufficient to trigger processes of destruction of the material.

Head-mountable high speed camera for optical neural recording

We report a head-mountable CMOS camera for recording rapid neuronal activity in freely moving rodents using fluorescent activity reporters. This small, lightweight camera is capable of detecting small changes in light intensity (0.2% Δ I/ I) at 500 fps. The camera has a resolution of 32 × 32, sensitivity of 0.62 V/lx s, conversion gain of 0.52 μV/e − and well capacity of 2.1 Me −. The camera, containing intensity offset subtraction circuitry within the imaging chip, is part of a miniaturized epi-fluorescent microscope and represents a first generation, mobile scientific-grade, physiology imaging camera.