Computer simulation of the precordial QRS complex: effects of simulated changes in ventricular wall thickness and volume

Over a 4-year period 40,923 operations and 44,716 surgical admissions were monitored for both community and hospital onset infections. One thousand eight hundred sixty-five patients had 1966 surgical wound infections and 2056 remote infections including 1652 hospital onset and 404 community onset infections. One thousand one hudnred forty-four patients with multiple infections averaged 40 days in the hospital contrasted with 24 days for 721 patients with a single wound infection. The total excess cost of hospitalization for these patients was $951,150. A statistically significant reduction occurred for urinary tract infections, lower respiratory infections and clean and contaminated surgical wound infections. It is suggested that these are all inter-related and a significant reduction in surgical wound infections can be achieved through control of infections at remote sites, particularly those associated with medical devices. The coagulase positive staphylococcus is still the most important single bacterial species in the primary etiology of surgical wound infections. When the gastrointestinal tract is entered or "supra" infecting organisms appear, gram negative bacteria and mixed gram negative and gram positive infections are dominant. Reduction in remote site infections occurring in surgical patients is necessary to reduce the incidence of surgical wound infections, suggest preventive and control measures, and document the effectiveness of such measures.     

Defect studies in Cu2ZnSnSe4 and Cu2ZnSn(Se0.75S0.25)4 by admittance and photoluminescence spectroscopy

To achieve higher record efficiencies for solar cells containing Cu₂ZnSnSe₄ (CZTSe), Cu₂ZnSnS₄ (CZTS) or their solid solution Cu₂ZnSn(Se_xS_1?x)₄ (CZTSSe) as an absorber, it is necessary to obtain more knowledge about defect structure of these materials. In this work, admittance spectroscopy (AS) and low temperature photoluminescence spectroscopy (PL) were used for defect studies. Admittance spectroscopy in the frequency range from 20 Hz to 10 MHz was used for studies of CZTSe/CdS and CZTSSe/CdS monograin layer heterojunctions. The measurement temperature varied from 140 K to 245 K. Two defect states (labelled E_A1 and E_A2) were found in Cu₂ZnSnSe₄ and Cu₂ZnSn(Se_0.75S_0.25)₄. In different CZTSe/CdS heterojunctions the E_A2 state was present at 74 meV, but the second E_A1 defect state changed from 87 meV to 100 meV during time and had varying properties. In Cu₂ZnSn(Se_0.75S_0.25)₄ the E_A2 state was found at 25 meV. The E_A1 state at 154 meV showed the same properties as the two defect levels in CZTSe. In both cases the E_A2 defect state was attributed to an acceptor defect and the E_A1 state with changing properties to interface states. The detected PL bands were at 0.946 eV in CZTSe and at 1.028 eV in Cu₂ZnSn(Se_0.75S_0.25)₄. Obtained by PL measurements, defect states at 69 meV in CZTSe and at 39 meV in Cu₂ZnSn(Se_0.75S_0.25)₄ were attributed to the same acceptor defect that was found from the AS measurements.     

Ion Chromatographic Analysis of Ammonium Dinitramide–Oxidizer for Propellant and Pyrotechnic Applications

Analysis of ammonium dinitramide (ADN), the advance rocket propellant oxidizer, in pure form as well as in mixtures was carried out by ion chromatography (IC). The purity of ammonium dinitramide was directly determined by estimating the dinitramide ions and indirectly by estimating the impurities. Both methods gave results comparable with those determined by Differential Scanning Calorimetry and UV spectroscopy. The chemical composition of ADN in mixtures containing nitrate, chromate, chlorate, perchlorate, and thiocyanate ions was quantitatively estimated in the same solution without any interferences or prior separation of analyte ions. The newly developed ion chromatographic methods for the analysis of ADN are simple and fast with good accuracy and precision when compared to other analytical techniques. The IC methods are found to be highly suitable for quality control analysis of ADN containing compositions and for the online process monitoring of the formation of ADN in the reaction mixture.     

An improved method for localizing electric brain dipoles

Methods for localizing electrical dipolar sources in the brain differ from one another by the models they use to represent the head, the specific formulas used in the calculation of the scalp potentials, the way that the reference electrode is treated, and by the algorithm employed to find the least-squares fit between the measured and calculated EEG potentials. The model presented here is based on some of the most advanced features found in other models, and on some improvements. The head is represented by a three-layer spherical model. The potential on any point on the scalp due to any source is found by a closed formula, which is not based on matrix rotations. The formulas will accept any surface electrode as the reference electrode. The least-squares procedure is based on optimal dipoles, reducing the number of unknowns in the iterations from six to three. The new method was evaluated by localizing five implanted dipolar sources in human sensorimotor cortex. The distances between the locations of the sources as calculated by the method, and the actual locations were between 0.4 and 2.0 cm. The sensitivity of the method to uncertainties encountered whenever a real head has to be modeled by a three-layer model has also been assessed.     

Classification of multispectral image data by the binary diamondneural network and by nonparametric, pixel-by-pixel methods

The study deals with the application of nonparametric pixel-by-pixel classification methods in the classification of pixels, based on their multispectral data. A neural network, the binary diamond, is introduced, and its performance is compared with a nearest neighbor algorithm and a back-propagation network. The binary diamond is a multilayer, feedforward neural network, which learns from examples in unsupervised one-shot mode. It recruits its neurons according to the actual training set, as it learns. The comparisons of the algorithms were done using a realistic database, consisting of approximately 90000 Landsat 4 Thematic Mapper pixels. The binary diamond and the nearest neighbor performances were close, with some advantages to the binary diamond. The performance of the back-propagation network lagged behind. An efficient nearest neighbor algorithm, the binned nearest neighbor, is described. Ways for improving the performances, such as merging categories and analyzing nonboundary pixels, are addressed and evaluated     

Computer simulations of learning in neural systems

Recent experiments have shown that, in some cases, strengths of synaptic ties are being modified in learning. However, it is not known what the rules that control those modifications are, especially what determines which synapses will be modified and which will remain unchanged during a learning episode. Two postulated rules that may solve that problem are introduced. To check their effectiveness, the rules are tested in many computer models that simulate learning in neural systems. The simulations demonstrate that, theoretically, the two postulated rules are effective in organizing the synaptic changes. If they are found to also exist in biological systems, these postulated rules may be an important element in the learning process.     

Orthogonal surface lead recordings of His-Purkinje activity: comparison of actual and simulated waveforms

Noninvasive His-Purkinje system (HPS) recordings can be obtained using high amplification and signal averaging. However, this technique lacks the firm underpinnings necessary for its establishment as a useful clinical tool for the study of the electrical activity of the heart. Previous work has been incomplete resulting in fragmented knowledge of the body surface HPS activity and the nature of the HPS as an electrical source.     

Implementing a Consistency Criterion in Numerical Solution of the Bioelectric Forward Problem

The bioelectric forward problem is frequently formulated as an integral equation that relates unknown surface potentials with their known current generators, in a given volume conductor. The matrix of the discretized equations is singular, and this may cause difficulties in obtaining a numerical solution to the problem. A consistency criterion for the discretized equations is utilized in a new algorithm for the forward problem. Some examples of sources in a uniform spherical volume conductor were solved employing the new algorithm. It was found that the algorithm is reliable even when the number of discretized elements was relatively small. A comparison with the deflation method was done. In some examples the results were very close to each other. In other examples the results of the new algorithm were better.