Spatial Sensitivity Distribution Research Articles

Parallel Magnetic Resonance Imaging

Parallel MRI started with the introduction of coil arrays in improving radiofrequency (RF) acquisition (what is called parallel imaging) and continued with an analogous development for RF transmission (parallel transmission). Based on differences in the spatial sensitivity distributions of the involved array elements, both techniques try to shorten the respective k-space trajectory. Parallel imaging refers to the acquisition of k-space data, whereas parallel transmission is dealing with the deposition of RF energy packages in the excitation k-space. However, parallel transmission is not simply the reciprocal of parallel imaging. The main goal of parallel imaging is the shortening of the acquisition time. The main goal of parallel transmission is the shortening of the pulse duration of spatially selective RF pulses. The present article describes the basic concept, the state of the art, and the similarities and differences of both technologies.

Quantifying energy savings in daylight responsive systems: The role of dimming electronic ballasts

The application of lighting control technologies with photosensors has led to an increase in public interest. Although these technologies have been promoted during the last years their successful use in buildings has been accomplished in a small percentage of new projects. One reason is the difficulty in quantifying the energy savings and thus the subsequent payback period. Daylight responsive dimming systems consist of three basic components: photosensor, controller, and dimming unit. Electronic dimming ballast (EDB) is one substantial component of these lighting control systems which can adjust the light output due to the transferred signal from the photosensor and lighting controller. The aim of this study is to quantify energy savings among different EDBs. Eighteen commercial EDBs were selected and various sets of electrical and illuminance measurements were taken for different dimming levels, in order to develop polynomial functions between light output and consumed power. Using the measured data, a set of simulations were performed for a photosensor with an ideal cosine spatial sensitivity distribution installed in a typical office room using two control algorithms, closed loop and integral reset, trying to quantify the relative differences in energy savings.

Homeostatic regulation of supercoiling sensitivity coordinates transcription of the bacterial genome

Regulation of cellular growth implies spatiotemporally coordinated programmes of gene transcription. A central question, therefore, is how global transcription is coordinated in the genome. The growth of the unicellular organism Escherichia coli is associated with changes in both the global superhelicity modulated by cellular topoisomerase activity and the relative proportions of the abundant DNA-architectural chromatin proteins. Using a DNA-microarray-based approach that combines mutations in the genes of two important chromatin proteins with induced changes of DNA superhelicity, we demonstrate that genomic transcription is tightly associated with the spatial distribution of supercoiling sensitivity, which in turn depends on chromatin proteins. We further demonstrate that essential metabolic pathways involved in the maintenance of growth respond distinctly to changes of superhelicity. We infer that a homeostatic mechanism organizing the supercoiling sensitivity is coordinating the growth-phase-dependent transcription of the genome.

Pressure pain sensitivity and hardness along human normal and sensitized muscle

The spatial distribution of pressure sensitivity and muscle hardness was examined on normal muscle tissue and muscle tissue after induction of delayed onset muscle soreness (DOMS). The pressure sensitivity and muscle hardness were assessed at nine sites on the tibialis muscle from the proximal to distal tendon on two separate days. In total 37 healthy volunteers participated in three experiments. In the first experiment pressure pain threshold (PPT) and pressure pain tolerance (PPTO) were assessed. Decreased PPT and PPTO were found on day 2, 7 days after day 1. Proximal and distal stimulation sites were harder compared to muscle belly sites. In a second experiment two different probe sizes were used. Variation in PPT between the nine sites was found for the large probe with muscle belly being less sensitive to pressure stimulation compared to proximal and distal sites. The most proximal stimulation site was harder compared to muscle belly sites. In a third experiment PPT and muscle hardness were assessed before and 48 h after eccentric exercise. PPT at two muscle belly sites was significantly decreased during DOMS. No specific sites were harder during DOMS, the average muscle hardness across sites was however significantly increased. Decreased PPT and increased muscle hardness did not correlate. In conclusion, within subjects the pressure sensitivity varies along the musculoskeletal unit. In DOMS, specific muscle belly sites were more sensitive to pressure stimulation. Muscle–tendon sites were harder compared to muscle belly sites.

Inverse modeling for seawater intrusion in coastal aquifers: Insights about parameter sensitivities, variances, correlations and estimation procedures derived from the Henry problem

Inverse modeling studies employing data collected from the classic Henry seawater intrusion problem give insight into several important aspects of inverse modeling of seawater intrusion problems and effective measurement strategies for estimation of parameters for seawater intrusion. Despite the simplicity of the Henry problem, it embodies the behavior of a typical seawater intrusion situation in a single aquifer. Data collected from the numerical problem solution are employed without added noise in order to focus on the aspects of inverse modeling strategies dictated by the physics of variable-density flow and solute transport during seawater intrusion. Covariances of model parameters that can be estimated are strongly dependent on the physics. The insights gained from this type of analysis may be directly applied to field problems in the presence of data errors, using standard inverse modeling approaches to deal with uncertainty in data. Covariance analysis of the Henry problem indicates that in order to generally reduce variance of parameter estimates, the ideal places to measure pressure are as far away from the coast as possible, at any depth, and the ideal places to measure concentration are near the bottom of the aquifer between the center of the transition zone and its inland fringe. These observations are located in and near high-sensitivity regions of system parameters, which may be identified in a sensitivity analysis with respect to several parameters. However, both the form of error distribution in the observations and the observation weights impact the spatial sensitivity distributions, and different choices for error distributions or weights can result in significantly different regions of high sensitivity. Thus, in order to design effective sampling networks, the error form and weights must be carefully considered. For the Henry problem, permeability and freshwater inflow can be estimated with low estimation variance from only pressure or only concentration observations. Permeability, freshwater inflow, solute molecular diffusivity, and porosity can be estimated with roughly equivalent confidence using observations of only the logarithm of concentration. Furthermore, covariance analysis allows a logical reduction of the number of estimated parameters for ill-posed inverse seawater intrusion problems. Ill-posed problems may exhibit poor estimation convergence, have a non-unique solution, have multiple minima, or require excessive computational effort, and the condition often occurs when estimating too many or co-dependent parameters. For the Henry problem, such analysis allows selection of the two parameters that control system physics from among all possible system parameters.

The development of visual sensitivity to words in ventral occipito-temporal sulcus

INTRO Left ventral Occipito-Temporal Sulcus (OTS) responds more powerfully to visual words than to checkerboards (Cohen et al., 2003). We have shown that BOLD response to words in this region decreases with increasing amounts of noise. In this study, we ask how early this sensitivity develops. METHODS We measured BOLD signals while 7–12y children with varying reading skills viewed word stimuli in an implicit reading task. Subjects judged the color of a fixation cross in the center of each word. Word visibility was parametrically manipulated by forming a convex sum of the word with a phase scrambled version of itself. Stimuli were presented in 12s (6 items) blocks, alternating with fixation blocks. Twenty-six 2.5×2.5×3 mm axial slices were acquired (3T GE Signa, spiral acquisition) covering occipito-temporal cortex. To assess the spatial distribution of noise sensitivity, we computed a GLM and created contrast maps for the high visibility vs. low visibility conditions in each brain. We measured the size of the BOLD response to words as a function of noise level within left OTS, defined anatomically and functionally by contrasting word conditions vs. fixation. RESULTS We found robust activation in left OTS in 20 out of 22 children (some as young as 7y) for high vs. low visibility words. ROI analysis revealed that individual response functions in this region decreased with increasing amounts of noise, but the shape of this function varied between subjects. Response decrease to added noise was not found in early visual areas (V1/2/3). CONCLUSIONS Sensitivity for words in visual noise develops as early as age 7, and manifests in similar brain regions as in the adult reader. This is in agreement with behavioral data showing a ‘viewing position effect’ for words in children at the end of the first grade (Aghababian and Nazir, 2000). Correlating individual response functions with behavioral reading measures will further elucidate the functional significance of this early perceptual sensitivity for words.

Assessment and spatial distribution of sensitivity of soil erosion in Tibet

Based on Universal Soil Loss Equation and methods of mathematics model and GIS analysis, this study classified influence of precipitation, soil, topography and vegetation upon sensitivity of soil erosion into five different degrees which are extreme sensitivity, quite sensitivity, sensitivity, less sensitivity and no sensitivity. Assessment map of each factor was generated separately. Integrated assessment map of sensitivity of soil erosion has also been drawn by overlapping function with Arcinfo. Furthermore, the study analyzed distribution characteristics and spatial difference of sensitivity of soil erosion under special plateau environment of Tibet. According to sensitivity degree, some important controlling regions was confirmed so that departments of water conservancy, traffic management and agriculture could make scientific and reasonable decisions for their respective subject planning.

IR-Detectors Based on IN2O3-Anode Oxide-CDxHg1-xTe

High sensitive IR detectors were developed by using noncompensated CdxHg1-xTe (x=0.25÷0.3) with the field-effect electrode from InxO3, which were received by magnetron spattering onto the anodized surface of the single crystal. Photoelectric properties (spectral distribution of the photoconductivity, time-response, the uniformity of the spatial distribution of sensitivity) were investigated under different potential applied to the field-effect electrode. For high sensitive material the detectivity D* = 8·1011 cm Hz1/2 W-1was obtained at the wavelength of 5 μm in the aperture angle of 30°. It was shown that the semitransparent field-effect electrode made from In2O3 allows to rule the output parameters of the detector in a wide range.

Analysis of the spatial distribution of detector sensitivity in a multilayer randomly inhomogeneous medium with strong light scattering and absorption by the Monte Carlo method

The spatial distribution of sensitivity in the domain of detection of a fiber-optic sensor used for spectrophotometric studies of skin and other biological tissues is studied. The method and results of modeling the propagation of optical radiation in multilayer randomly inhomogeneous media with strong light scattering and absorption are presented. Owing to the small distances between the source and detector (100–800 μm), the propagation of radiation in the medium under study is modeled by the Monte Carlo method combining the calculation of true paths and the use of statistical weights. For the same reason, we represent the surface and interfaces of layers of skin as rough randomly periodic surfaces corresponding to the actual structure of human skin. The method presented can be recommended as a means for the optimum selection of an arrangement for radiation incoupling and outcoupling.

Computer modeling of dual-band HgCdTe photovoltaic detectors

The performance of middle wavelength/long wavelength (MW/LW) dual-band HgCdTe photovoltaic detectors was examined theoretically. An original iteration scheme was used to solve the system of nonlinear continuity equations and the Poisson equation. The effect of composition and doping profiles on the heterojunction detector parameters is presented. It is assumed that the performance of photodiodes is due to thermal generation governed by the Auger mechanism. All quantities are functions of the electric potential and Fermi quasi-levels. The results of calculations are presented as maps showing spatial distribution of electrical potential, photoelectrical gain, sensitivity, and density of noise generation. The theoretical predictions of heterojunction device parameters are compared with available experimental data.

Critical loads for nitrogen deposition and their exceedance at European scale

In Europe serious problems associated with emissions of nitrogen oxides and ammonia are related to eutrophication and acidification. Impacts of eutrophication in terrestrial ecosystems are associated with changes in floristic composition and in ecosystem function and stability. Various activities have been initiated to assess the risk posed by nitrogen deposition for negotiations concerning the UN/ECE NO x Protocol. As there are difficulties in mapping critical loads for nitrogen, two different methods are presented here at European scale. One method uses a sensitivity approach linked to data for empirically derived critical loads; the other method uses a nitrogen saturation approach which sums quantitative values for acceptable long-term removal rates of nitrogen from the ecosystem and accumulation in soil organic matter. Resulting critical load maps show significant areas across Europe that are potentially sensitive to nitrogen deposition. Generally, the spatial distribution of sensitivity shows similarities using both approaches. However, the range of empirical critical loads in the literature determined for certain vegetation types is greater than those calculated using the saturation approach. A comparison with 1990 total nitrogen deposition does reveal a similar distribution of exceedance, but only when the lower end of the empirical critical load range is used. There are uncertainties associated with both methods nevertheless they do illustrate that substantial areas across Europe may be at risk from deleterious impacts caused by nitrogen deposition.

Measurement of thermal diffusivity parallel to the surface of platelike specimen by the laser pulse heating method

A new method has been developed to measure the thermal diffusivity parallel to the surface of a platelike specimen using laser pulse heating. A pulsed laser beam which has a circular cross section is irradiated onto the front surface of the specimen. The time dependence of the temperature response of a circular area on the back surface at a certain distance from the irradiated area is determined using a radiation detector for which the spatial distribution of sensitivity is experimentally determined. The geometry of the apparatus is determined using standard specimens the thermal diffusivity of which is known. For isotropic samples, the values parallel to the surface obtained by the present method agree within 10% with those perpendicular to the surface obtained by the conventional pulse heating method.

Contractile proteins and nonerythroid spectrin in oogenesis of Xenopus laevis.

The distribution of contractile proteins, actin and myosin, and an actin-binding protein, spectrin, was studied in oogenesis of Xenopus laevis. These proteins are present in oocytes already at the previtellogenic stages, which are characterized by their diffuse distribution. The localization of proteins changed with the beginning of vitellogenesis. At all vitellogenic stages, including the fully grown oocyte, animal-vegetal differences were noted in localization of actin and myosin: in the animal hemisphere they appear as fibrillar-like structures, while in the vegetal one they are localized around the yolk platelets. By the end of the oocyte's growth, a cortical gradient appeared: predominant localization of actin and myosin in the cortical area. As the oocyte maturation proceeded, the distribution of actin and myosin again became diffuse and nonuniform, so that a cortical gradient appears. At the beginning of vitellogenesis spectrin is distributed as a network all over the ooplasm, while in the fully grown oocyte it is localized mostly in the subcortical area of the animal hemisphere and, as individual inclusions, in other regions of the oocyte. No spectrin is found by the end of maturation. Actin, myosin, and spectrin are also present in the oocyte's nuclei. Changes in the distribution of contractile proteins and spectrin during oocyte maturation are discussed with respect to the development of cortical contractility, as well as to the changes in spatial distribution of yolk platelets and regional sensitivity of the maturing oocyte to cytochalasin B.

Neural circuit tuning fly visual interneurons to motion of small objects. I. Dissection of the circuit by pharmacological and photoinactivation techniques.

1. Visual interneurons tuned to the motion of small objects are found in many animal species and are assumed to be the neuronal basis of figure-ground discrimination by relative motion. A well-examined example is the FD1-cell in the third visual neuropil of blowflies. This cell type responds best to motion of small objects. Motion of extended patterns elicits only small responses. As a neuronal mechanism that leads to such a response characteristic, it was proposed that the FD1-cell is inhibited by the two presumably GABAergic and, thus, inhibitory CH-cells, the VCH- and the DCH-cell. The CH-cells respond best to exactly that type of motion by which the activity of the FD1-cell is reduced. The hypothesis that the CH-cells inhibit the FD1-cell and, thus, mediate its selectivity to small moving objects was tested by ablating the CH-cells either pharmacologically or by photoinactivation. 2. After application of the gamma-aminobutyric acid (GABA) antagonist picrotoxinin, the FD1-cell responds more strongly to large-field than to small-field motion, i.e., it has lost its small-field selectivity. This suggests that the tuning of the FD1-cell to small moving objects relies on a GABAergic mechanism and, thus, most likely on the CH-cells. 3. The role of each CH-cell for small-field tuning was determined by inactivating them individually. They were injected with a fluorescent dye and then ablated by laser illumination. Only photoinactivation of the VCH-cell eliminated the specific selectivity of the FD1-cell for small-field motion. Ablation of the DCH-cell did not significantly change the response characteristic of the FD1-cell. This reveals the important role of the VCH-cells in mediating the characteristic sensitivity of the FD1-cell to motion of small objects. 4. The FD1-cell is most sensitive to motion of small objects in the ventral part of the ipsilateral visual field, whereas motion in the dorsal part influences the cell only weakly. This specific feature fits well to the sensitivity of the VCH-cell to ipsilateral motion that is most pronounced in the ventral part of the visual field. The spatial sensitivity distribution of the FD1-cell matches also the characteristics of figure-ground discrimination and fixation behavior.

Finite element modelling of multielectrode capacitive systems for flow imaging

The CAD of a complex multielectrode arrangement for flow imaging is explored using the finite element method (FEM). This electrode arrangement forms the primary sensor subsystem for an electrical capacitive tomography (ECT) system. Results are presented in the form of sensor's performance parameters as functions of its various geometric parameters. The performance parameters include the standing and normalised capacitances, ratio of the maximum to minimum capacitance of the sensor (Kc) and the sensor's spatial sensitivity distributions. Extensive computer simulation studies were undertaken in calculating these parameters, and the techniques in finite element (FE) model definition, mesh generation and refinement, error minimisation and checking are highlighted in the paper in relation to the effective and efficient use of the FEM. Detailed results for a particular sensor design are compared with an experimental prototype and found to give good agreement. The response of the sensor to various flow regimes is also presented and analysed to optimise its performance for image reconstruction.

The spatial distribution of excitatory and inhibitory inputs to ganglion cell dendrites in the tiger salamander retina

In response to focal stimuli, ganglion cell dendrites receive excitation over a relatively narrow extent of the inner plexiform layer (IPL). This excitation is embedded in 2 wider lateral inhibitory regions. Here we estimate the lateral dimensions of the inhibitory regions. Ganglion cells were whole-cell patch-clamped and dendrites were identified and located in retinal slices using Lucifer yellow in the pipettes. The spatial distribution of ganglion cell dendritic sensitivity was measured with puffs of transmitter substances applied at different distances along the dendrites. All ganglion cell dendrites were sensitive to glutamate, GABA, and glycine across their full extent. The responses to puffs decreased with lateral distance from the soma and were well fit by Gaussians. The responses to puffs of potassium showed a similar decrement with distance. Since potassium channels are probably uniformly distributed along the dendrites, the similarity in profiles suggests that receptor density is also uniform along the dendrites. The spatial distribution of responses of ganglion cells to excitatory and inhibitory synaptic inputs was measured by depolarizing local populations of bipolar terminals (and subsequently local populations of amacrine cells) with transretinal current (TRC). TRC-stimulating electrodes were displaced laterally, with respect to the ganglion cell soma, to generate response profiles. We estimated the dimensions of the inhibitory and excitatory signals received by the ganglion cells by removing the contributions of their dendrites, the stimulus, and other interneurons from the response profiles. The excitatory signal extended less than 100 microns, the approximate dimensions of the ganglion cell dendrites, and corresponds roughly to the width of the bipolar inputs. The GABAergic signal extended, on average, 253 microns and glycinergic signal extended, on average, 315 microns. These inhibitory signal dimensions correspond to the width of classes of amacrine cell processes measured in other studies.

Study on the spatial distribution of sensitivity in crossing-type concave array microphone system

Study on the spatial distribution of sensitivity in crossing-type concave array microphone system

放射計視野内感度分布の変化に基づく拡散特性の計測法

放射計視野内感度分布の変化に基づく拡散特性の計測法

Experimental study on the spatial distribution of sensitivity in arc-arrayed microphone system : Analysis of deterioration factors

Experimental study on the spatial distribution of sensitivity in arc-arrayed microphone system : Analysis of deterioration factors

Response properties of horizontal cells in the isolated retina of wild- type and pearl mutant mice

Intracellular recordings were made from axon bearing horizontal cells in isolated retinas (with retinal pigment epithelium removed) of normal and pearl mutant mice superfused with mammalian Ringer's solution. Cells were injected with Lucifer yellow and identified by their morphology and their response wave-forms. On impalement, we measured a dark, resting voltage of 25-35 mV. All cells had similar spectral sensitivities that were consistent with the CIE scotopic relative spectral luminosity function. For stimuli of high irradiance, two types of responses could be distinguished, based on their waveform at stimulus offset. One consisted of a rapid and wavelength-dependent repolarization followed by a small, slow hyperpolarization. The other consisted of a large, long-lived, and wavelength-independent after-hyperpolarization. The former were recorded from the somatic end and the latter from the axon terminal arborization. The spatial distribution of sensitivity was measured in over 100 locations within the receptive field using small stimuli. The area within which sensitivity of the soma was within 0.1 log unit of the maximal sensitivity was larger than that of the soma dendritic field, but the sizes were nearly equal for the terminal arborization. No secondary maximum of sensitivity was noted over the dendritic field of the unimpaled part of the cell. For the terminal arborization, the half-saturating irradiance for diffuse 502 nm stimuli was about 180 photons micron-2 sec-1, about one-tenth that for the soma. These values are in good agreement with those for cat and rabbit.(ABSTRACT TRUNCATED AT 250 WORDS)