A regularization term to avoid the saturation of the sigmoids in multilayer neural networks.

In this paper we propose a new method to prevent the saturation of any set of hidden units of a multilayer neural network. This method is implemented by adding a regularization term to the standard quadratic error function, which is based on a repulsive action between pairs of patterns.

Use of multilayer feedforward neural nets as a display method for multidimensional distributions.

We present a new method based on multilayer feedforward neural nets for displaying an n-dimensional distribution in a projected space of 1, 2 or 3 dimensions. A fully nonlinear net with several hidden layers is used. Efficient learning is achieved using multi-seed backpropagation. As a principal component analysis (PCA), the proposed method is useful for extracting information on the structure of the data set, but unlike the PCA, the transformation between the original distribution and the projected one is not restricted to be linear. Artificial examples and a real application are presented in order to show the reliability and potential of the method.

[Polyphosphate and ATP content of Propionibacterium shermanii cells in nitrogen starvation]. / Soderzhanie polifosfatov i ATF v kletkakh Prionibacterium shermanii v usloviiakh azotnogo golodaniia.

When Propionibacterium shermanii was cultivated in a medium with glucose under the conditions of nitrogen deficiency, the content of high molecular weight polyphosphates (salt-soluble fraction, alkali-soluble fraction, and fraction extracted with hot perchloric acid) decreased. In contrast, it rose in a medium with lactate within two and three days of starvation. The culture growth stopped after a day under these conditions, the energy substrate was assimilated during the entire process of starvation, and the content of ATP continuously decreased. When ammonium sulfate was added after two and three days of starvation, the intracellular content of polyphosphates (in all of the three fractions) increased in the medium with glucose. If ammonium sulfate was added after three days of starvation in the medium with lactate, the content of polyphosphates rose in the fraction extracted with hot perchloric acid while the content of salt-soluble and alkali-soluble polyphosphates decreased. The culture started to grow again and the content of ATP in its cells rose abruptly when ammonium sulfate was added under these conditions. If the culture was grown in the medium with glucose and ammonium sulfate, the content of acid-insoluble polyphosphates increased twofold during the first day and dropped to the initial level by the third day of growth.

[ATP pool in Propionibacterium shermanii cells under various culture conditions]. / Pul ATF v kletkakh Propionibacterium shermanii v raznykh usloviiakh kul'tivirovaniia.

During batch cultivation of Propionibacterium shermanii in a medium with glucose, ATP content in the cells (nmoles per 1 mg of dry biomass) increased up to the middle of the log phase, and decreased abruptly by the end of the log phase. When the culture was grown in a medium with lactate, the maximal level of ATP (3 nmoles/mg) was lower than in a medium with glucose (5 nmoles/mg). Nitrogen starvation of the culture was accompanied with a decrease in the level of ATP. If ammonium sulphate was added to such a culture, first the level of ATP increased and then the growth began. Addition of ammonium sulphate, after 72 h, to the nitrogen--deficient culture, the original density of whose cell suspension was over 0.25 mg/ml, did not induce the growth, although the level of ATP also increased.

[Ribonucleotide reductase in Propionibacterium shermani]. / Ribonukleotidreduktaza Propionibacterium shermani

The cell-free extract of Propionibacterium shermanii was found to contain B12-dependent ribonucleotide reductase. The extract of the cells grown under the conditions of the inhibited synthesis of vitamin B12 reduces ribonucleotides with the participation of B12-independent enzyme. The synthesis of B12-dependent apoenzyme of ribonucleotide reductase is partially maintained under these conditions. Both enzymes reduce preferably ribonucleoside diphosphates. The reducing agent of nucleotides in vitro is lipoic acid or dithiothreitol, in the B12-dependent pathway, and NADPH and thioredoxin, in the B12-independent pathway. Only B12-independent ribonucleotide reductase requires Mg2+ ions. Vitamin B12 in the coenzyme form inhibits the activity of B12-independent enzyme.