Neuronal interactions are an intricate part of cortical information processing generating internal representations of the environment beyond simple one-to-one mappings of the input parameter space. ...Here we examined functional ranges of interaction processes within ensembles of neurons in cat primary visual cortex. Seven "elementary" stimuli consisting of small squares of light were presented at contiguous horizontal positions. The population representation of these stimuli was compared to the representation of "composite" stimuli, consisting of two squares of light at varied separations. Based on receptive field measurements and by application of an Optimal Linear Estimator, the representation of retinal location was constructed as a distribution of population activation (DPA) in visual space. The spatiotemporal pattern of the DPA was investigated by obtaining the activity of each neuron for a sequence of time intervals. We found that the DPA of composite stimuli deviates from the superposition of its components because of distance-dependent (1) early excitation and (2) late inhibition. (3) The shape of the DPA of composite stimuli revealed a distance-dependent repulsion effect. We simulated these findings within the framework of dynamic neural fields. In the model, the feedforward response of neurons is modulated by spatial ranges of excitatory and inhibitory interactions within the population. A single set of model parameters was sufficient to describe the main experimental effects. Combined, our results indicate that the spatiotemporal processing of visual stimuli is characterized by a delicate, mutual interplay between stimulus-dependent and interaction-based strategies contributing to the formation of widespread cortical activation patterns.
Segmenting range data into semantic categories has become a more and more active field of research in robotics. In this paper, we advocate to view this task as a problem of fast, large-scale ...retrieval. Intuitively, given a dataset of millions of labeled scan points and their neighborhoods, we simply search for similar points in the datasets and use the labels of the retrieved ones to predict the labels of a novel point using some local prediction model such as majority vote or logistic regression. However, actually carrying this out requires highly efficient ways of (1) storing millions of scan points in memory and (2) quickly finding similar scan points to a target scan point. In this paper, we propose to address both issues by employing Weiss et al.'s recent spectral hashing. It represents each item in a database by a compact binary code that is constructed so that similar items will have similar binary code words. In turn, similar neighbors have codes within a small Hamming distance of the code for the query. Then, we learn a logistic regression model locally over all points with the same binary code word. Our experiments on real world 3D scans show that the resulting approach, called spectrally hashed logistic regression, can be ultra fast at prediction time and outperforms state-of-the art approaches such as logistic regression and nearest neighbor.
The selection of fouling resistances to design plate-and-frame heat exchangers is usually based on experience or guesswork. The primary aim of this study was to compare fouling resistances for plate ...heat exchangers with values obtained in a parallel double-pipe heat exchanger under comparable operating conditions. The double-pipe heat exchanger was selected because it represents a shell-and-tube heat exchanger in a simplified form. Correction factors for plate heat exchangers have been obtained by comparing the performance of the two heat exchanger types during calcium sulfate crystallization fouling. Fouling was investigated in both heat exchangers for two conditions: particles present in the process solution were allowed to enhance the crystallization process; particles present in the process solution were removed by an in-line 1-mum filter. For similar flow velocities, the plate heat exchanger was found to foul significantly less than the double-pipe heat exchanger, i.e., 20-25 times less in the presence of particles and around 15 times less when the particles were filtered out. When data for similar overall shear forces are compared, results for both heat exchanger types are much closer, even though the plate heat exchanger still seems to perform somewhat better. Fouling in plate-and-frame heat exchangers was also found to depend significantly on plate design. This will add a further complication in direct comparison with shell-and-tube heat exchangers.
Age is one of five prognostic parameters identified based on data of the trauma registry of the German Association for Trauma Surgery (DGU). We asked ourselves if the suggested prognostic model ...provides the same predictive power of data from an independent hospital. Furthermore, we investigated whether age itself or age-associated comorbidity causes an unfavorable prognostic effect.
The investigation was based on data of 103 multiply injured patients (67 male, 36 female, mean age 35,4+/-SD 19,0 years, ISS 36,8+/-10,9). Data were collected prospectively following the guidelines of the trauma registry of the German Association for Trauma Surgery. Based on documented comorbidities, a risk calculation was performed using the ASA classification. Correlation between age and ASA was analyzed using Spearman's method. The prognostic value of the original model in our patient pool with or without ASA classification, possible interactions, and the discriminatory power of the model were estimated using logistic regression.
Attributable mortality was 31,7% (95% CI 22,7-41,7%). Age, ISS, GCS and ASA were included into the final logistic model. Odds ratios of the origin model were reproducible nearly identical in our patinet pool (OR: age 1,048; ISS 1,066; GCS 0,822). In spite of the fact that we have found a strong correlation between age and ASA-Classification (rho=0,60, p<0,0001) there was no prognostic value of comorbidity.
The suggested prognostic model based on multicenter data evaluation can be applied to a single center with only minimal loss of discriminatory power. In this context, age seems to have a prognostic value independent of comorbidity.
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