Thresholds of bifurcation of the degree of circular polarization of the bremsstrahlung-generated pump field harmonics in plasma

It is established that, for a Maxwellian plasma in a monochromatic pump field, the phenomenon of bifurcation of the degree of circular polarization of the field harmonics is of a universal nature. A general equation determining the thresholds for this phenomenon for arbitrary harmonics is derived, and a set of its solutions is presented for illustrative purposes.     

Thermostability of Proteases and Lipases from a Number of Species of Psychrotrophic Bacteria of Dairy Origin

Proteases and lipases from a number of different species of psychrotrophic bacteria isolated from dairy products are resistant to heat treatments of 77°C for a holding time of 17 s and 140°C for a holding time of 5s. A further treatment combining the 77°C for 17 s heating process with a heat treatment involving a temperature of 55°C for 1 h was also examined. The proteases and, to a lesser extent, the lipases were also resistant to the treatments in combination. The resistance of proteases and lipases to inactivation by a treatment of 55°C for 1 h varied between and within species. Therefore, this treatment may not have a widespread practical application.     

The role of phadiatop in the screening of respiratory allergy

Phadiatop is a new in vitro screening test for respiratory allergy. This test, based on the RAST procedure, detects in serum, the presence of specific IgE to a mixture of common inhalent allergens. Among 70 patients (26 children and 44 adults) consulting for respiratory syndrome, Phadiatop was positive in 31 cases. There were a good correlation between this new test and skin tests (59% for adults and 92% for children), total IgE (70% for adults and 65% for children) and RAST (93% for adults and 96% for children). Phadiatop, with a specificity of 100%, a sensitivity of 82% (76% for adults and 92% for children) and an efficiency of 90% (86% for adults and 96% for children), is a more accurate test than total IgE and could be an excellent in vitro screening test for respiratory allergy.     

Study of the deglycosylation of various antibiotics of the vancomycin group

Conditions for deglycosylation of a number of antibiotics belonging to the vancomycin group were studied. A two-stage process including methanolysis followed by acidolysis in a mixture of trifluoracetic acid and HC1 in the presence of nucleophile was shown optimal for formation of a biologically active aglycone of ristomycin A while for formation of the vancomycin aglycone a one-stage process (trifluoracetic acid/HC1--acidolysis) was optimal. A scheme for isolation and purification of the aglycones of ristomycin A and vancomycin is presented.     

Comparison of models of insulin release

A model for insulin secretion with a storage and a labile compartment, as well as a provisionary factor, is combined with a signal model in which the signal can be the difference between an excitation and an inhibition, or the difference in concentrations inside and outside some cell components. The model, using a single set of values for the parameters, accounts in a semiquantitative manner for all of the regularly appearing features of the insulin secretion from thein vitro perfused pancreas to a wide range of patterns of glucose and tolbutamide stimulation. Among the features which can be accounted for are: early and late secretion of insulin as a function of glucose in terms of a single parameter; the apparent depletion and recovery during a pulsed pattern of stimulation by tolbutamide; the hypersecretion following a short period of rest during a prolonged stimulation by glucose; the negative spike which occurs when the concentration of glucose, which has been maintained for a period of time, is suddenly reduced to a lower level; and the appropriate responses to slow and fast ramp functions of glucose concentration.     

Characterization of the existence of galled-tree networks

In this paper, we give a complete characterization of the existence of a galled-tree network in the form of simple sufficient and necessary conditions for both root-known and root-unknown cases. As a by-product we obtain a simple algorithm for constructing galled-tree networks. We also introduce a new necessary condition for the existence of a galled-tree network similar to bi-convexity.     

Quantitative analysis of the ion-dependent folding stability of DNA triplexes

A DNA triplex is formed through binding of a third strand to the major groove of a duplex. Due to the high charge density of a DNA triplex, metal ions are critical for its stability. We recently developed the tightly bound ion (TBI) model for ion-nucleic acids interactions. The model accounts for the potential correlation and fluctuations of the ion distribution. We now apply the TBI model to analyze the ion dependence of the thermodynamic stability for DNA triplexes. We focus on two experimentally studied systems: a 24-base DNA triplex and a pair of interacting 14-base triplexes. Our theoretical calculations for the number of bound ions indicate that the TBI model provides improved predictions for the number of bound ions than the classical Poisson-Boltzmann (PB) equation. The improvement is more significant for a triplex, which has a higher charge density than a duplex. This is possibly due to the higher ion concentration around the triplex and hence a stronger ion correlation effect for a triplex. In addition, our analysis for the free energy landscape for a pair of 14-mer triplexes immersed in an ionic solution shows that divalent ions could induce an attractive force between the triplexes. Furthermore, we investigate how the protonated cytosines in the triplexes affect the stability of the triplex helices.     

Isolation of cell surface antigen mutants of Myxococcus xanthus by use of monoclonal antibodies

Monoclonal antibodies (MAbs) with affinities for molecules on the cell surface of the procaryote Myxococcus xanthus were used in a screening strategy for the isolation of mutants lacking particular cell surface molecules. From a large library of independent mutants created by Tn5 transposon mutagenesis, mutants were isolated which lacked reactivities with MAb 1604 (a MAb specific for a cell surface protein) and MAbs 2600, 1733, 1514, 1412, and 783 (MAbs specific for carbohydrate epitopes on the O antigen of lipopolysaccharide [LPS]). The defect in antibody recognition was shown by genetic crosses and DNA hybridization experiments to be caused by the Tn5 transposon acting as a mutation at a single locus. Quantitative enzyme-linked immunosorbent assays showed that particular mutant strains had no detectable affinity for the specific MAb probe. LPS mutants were resistant to myxophage Mx8, and this provided a selection method for isolating a large number of new LPS mutants. A class of Mx8-resistant mutants lacked reactivity with MAb 1514 and therefore was defective in the O antigen of LPS. A class of Mx1-resistant mutants lacked reactivity with MAb 2254, a MAb specific for a carbohydrate epitope on the core of LPS. A comparison of MAb binding to different mutant strains revealed a principle for mapping epitopes and showed that MAbs 1514 and 2254 recognize side-chain carbohydrates rather than backbone carbohydrates within the LPS molecule.     

Synthesis of some analogs of estradiol

As part of a search for estradiol derivatives designed for conjugation to carboxyl or amine functions of anti-cancer agents or suitable derivatives thereof, estradiol analogs with side chains at the C-16 or -17 position were prepared for biological assay. These analogs include several which have a substituted nitrogenous function at C-17. The avidity of some of these analogs for binding to estrogen receptor was found to be of a low order.     

Affinity of corticosteroids for mineralocorticoid and glucocorticoid receptors of the rabbit kidney: effect of steroid substitution

Corticosteroid derivatives coupled in the C3, C7 or C17 position with a long aliphatic chain were synthesized in order to select a suitable ligand for the preparation of a biospecific affinity adsorbent for mineralocorticoid receptor purification. The affinity of these derivatives for mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) was explored in rabbit kidney cytosol. In this model, aldosterone bound to a single class of receptors with high affinity (Kd 1 nM) and mineralocorticoid specificity. RU26988, a highly specific ligand for GR, did not compete for these sites. The C7 and C17 positions were found to be of crucial importance in the steroid's interaction with the mineralocorticoid receptors, since the linkage of a long side chain in these positions induced complete loss of affinity. Hence, deoxycorticosterone no longer bound to MR after 17 beta substitution with a 9-carbon aliphatic chain. This loss of affinity was not observed for glucocorticoids. The 17 beta nonylamide derivative of dexamethasone still competed for GR. Increasing the length of the C7 side of the spirolactone SC26304 suppressed its affinity for MR. Finally, C3 was an appropriate position for steroid substitution. The 3-nonylamide of carboxymethyloxime deoxycorticosterone bound to MR but not to GR, and therefore constitutes a suitable ligand for the preparation of a mineralocorticoid adsorbent.     

Loss of gametophytic self-incompatibility with evolution of inbreeding depression

Gametophytic self-incompatibility (SI) in plants is a widespread mechanism preventing self-fertilization and the ensuing inbreeding depression, but it often evolves to self-compatibility. We analyze genetic mechanisms for the breakdown of gametophytic SI, incorporating a dynamic model for the evolution of inbreeding depression allowing for partial purging of nearly recessive lethal mutations by selfing, and accounting for pollen limitation and sheltered load linked to the S-locus. We consider two mechanisms for the breakdown of gametophytic SI: a nonfunctional S-allele and an unlinked modifier locus that inactivates the S-locus. We show that, under a wide range of conditions, self-compatible alleles can invade a self-incompatible population. Conditions for invasion are always less stringent for a nonfunctional S-allele than for a modifier locus. The spread of self-compatible genotypes is favored by extremely high or low selfing rates, a small number of S-alleles, and pollen limitation. Observed parameter values suggest that the maintenance of gametophytic SI is caused by a combination of high inbreeding depression in self-incompatible populations coupled with intermediate selfing rates of the self-compatible genotypes and sheltered load linked to the S-locus.     

Likelihood of a particular order of genetic markers and the construction of genetic maps

We model the recombination process of fungal systems via chromatid exchange in meiosis, which accounts for any type of bivalent configuration in a genetic interval in any specified order of genetic markers, for both random spore and tetrad data. First, a probability model framework is developed for two genes and then generalized for an arbitrary number of genes. Maximum likelihood estimators (MLEs) for both random and tetrad data are developed. It is shown that the MLE of recombination for tetrad data is uniformly more efficient over that from random spore data by a factor of at least 4 usually. The MLE for the generalized probability framework is computed using the expectation-maximization (EM) algorithm. Pearson's chi-squared statistic is computed as a measure of goodness of fit using a product-multinomial setup. We implement our model with genetic marker data on the whole genome of Neurospora crassa. Simulated annealing is used to search for the best order of genetic markers for each chromosome, and the goodness of fit value is evaluated for model assumptions. Inferred map orders are corroborated by genomic sequence, with the exception of linkage groups I, II, and V.     

Exact tests of goodness of fit of log-linear models for rates

We propose Metropolis-Hastings sampling methods for estimating the exact conditional p-value for tests of goodness of fit of log-linear models for mortality rates and standardized mortality ratios. We focus on two-way tables, where the required conditional distribution is a multivariate noncentral hypergeometric distribution with known noncentrality parameter. Two examples are presented: a 2 x 3 table, where the exact results, obtained by enumeration, are available for comparison, and a 9 x 7 table, where Monte Carlo methods provide the only feasible approach for exact inference.     

Quantitative evaluation of the allometric transformation of of biological structures

Detection and quantification of allometry is a crucial problem in understanding morphological changes, both for systematic and morphogenetic purposes. A section of S.A.M. (Shape Analytical Morphometry) software system was used for this attempt. It consists of the following steps: a) boundary detection; b) starting point detection; c) size normalization; d) extraction of the fundamental shape by Kth order polynomials; e) finding of symmetry evaluator (S.A.E.) by means of a second degree equation. This last procedure gives an arc-chord complex that expresses a vector for allometry where intercept value was for application point, first degree coefficient was for direction and second degree coefficient was for modulus and versus. The main parameters, isometry fraction and allometry fraction may be understood referring them to morphogenetic models.     

Dual-parameter optimisation of the elastic properties of skin

This paper presents a procedure for characterising the mechanical properties of skin using stochastic inverse identification. It is based on the minimisation of a cost function relative to the comparison between experimental suction experiments and their corresponding finite element models. Two different models are compared: a classical single-layer approach and a dual-layer medium which account for both the dermis and the hypodermis. Finite element results are used to construct the pre-optimisation database which is required for the inverse analysis. To compare the calculations, the entire identification is based on a dual-parameter optimisation procedure: for the single-layer approach a quadratic hyperelastic constitutive equation is used, whereas for the dual-layer medium a simple neo-Hookean potential is used. Theoretical conclusions, which are developed first, are then compared with actual case studies.     

三角梅属植物的生物学研究进展

三角梅属(Bougainvil lea)属于紫茉莉科(Nyctaginaceae), 有14个种。该文综述了三角梅属植物的生物学特性, 展望了该属植物在增进人类健康、丰富精神生活以及保护环境等方面的应用前景。三角梅属植物因其苞片的形态色彩以及植株形态的变化而具有独特的观赏价值。三角梅属植物不仅作为花卉备受关注, 近年来, 有关三角梅其它应用价值的研究使人们对其有了新的认识。从三角梅叶片中分离得到具有类胰岛素功能的松醇(D-pini tol )对替代胰岛素治疗糖尿病以及减轻胰岛素疗法带来的副作用具有重要意义。研究还表明, 三角梅叶片和根中至少含有2种抗病毒蛋白——BAPI和 Bouganin, 它们对于多种植物病毒具有不同程度的抑制作用。这些研究结果对于开发低毒高效的生物农药具有十分积极的意义。三角梅还是研究甜菜色素代谢的重要模式植物之一, 其甜菜色素的种类和含量之丰富为开发安全的天然食用色素开辟了广阔的前景。这些相关研究展示了三角梅作为资源植物的多元价值, 为进一步开发三角梅的观赏、医药、生物农药价值和作为天然食用色素以及发挥环境修复作用提供了充分的科学依据。     

Cloning of the genes of the chitin utilization regulon of Serratia liquefaciens.

The set of genes that determine the expression of the enzymes involved in chitin degradation by Serratia liquefaciens was cloned. The role of each gene was investigated, and for the first time regulatory genes were identified in this system. The chiA and chiB genes coded for separate chitinase activities. The chiC region coded for a chitobiase activity, but it was not formally separated from chiB. Transposon mutagenesis and deletion analysis identified a region, chiD, whose absence led to higher expression of chiA, chiB, and chiC. chiD may therefore be a gene that codes for a repressor. Loss of function of another adjacent region, chiE, prevented induction unless a chiE+ strain was a near neighbor, suggesting that this gene may code for a protein that is involved in the synthesis of the inducer. chiB, chiC, chiD, and chiE are closely linked, while chiA is in a separate location on the chromosome.     

Influence of ejaculation frequency of stallions on characteristics of semen and output of spermatozoa.

Approximately 1 week was required to stabilize the extragonadal sperm reserves in stallions ejaculated daily for 10 weeks. The true daily sperm output of a stallion was equal to the mean daily sperm output of seven ejaculates +/- 1-35 X 10(9) spermatozoa. Mean concentrations of spermatozoa/ml and number of spermatozoa/ejaculate were higher (P less than 0-01) for X1 and X3/week ejaculation frequencies than for a X6/week frequency. Sperm output/week was nearly identical for a X6/week frequency. Sperm output/week was nearly identical for the X3 and X6 frequencies and higher (P less than 0-01) than the X1 frequency. Increase of ejaculation frequency from one to two ejaculates/day twice weekly significantly (P less than 0-01) raised the output of spermatozoa/week. Gel-free semen volume, spermatozoa/ml, and number of spermatozoa/ejaculate were higher (P less than 0-01) in the first, than in the second, ejaculate. Collection of semen on alternate days would be a practical ejaculation frequency for inseminating mares. Two ejaculates collected twice a week would be a practical ejaculation frequency for long-term storage of stallion semen.