Atmospheric transmittance of an absorbing gas. 4. OPTRAN: a computationally fast and accurate transmittance model for absorbing gases with fixed and with variable mixing ratios at variable viewing angles

A fast and accurate method for the generation of atmospheric transmittances, optical path transmittance (OPTRAN), is described. Results from OPTRAN are compared with those produced by other currently used methods. OPTRAN produces transmittances that can be used to generate brightness temperatures that are accurate to better than 0.2 K, well over 10 times as accurate as the current methods. This is significant because it brings the accuracy of transmittance computation to a level at which it will not adversely affect atmospheric retrievals. OPTRAN is the product of an evolution of approaches developed earlier at the National Environmental Satellite, Data, and Information Service. A major feature of OPTRAN that contributes to its accuracy is that transmittance is obtained as a function of the absorber amount rather than the pressure.     

Antimicrobial enzymes: Applications and future potential in the food industry

Antimicrobial enzymes are ubiquitous in nature, playing a significant role in the defense mechanisms of living organisms against infection by bacteria and fungi. Hydrolytic antimicrobial enzymes function by degrading key structural components of the cell walls of bacteria and/or fungi, whereas antimicrobial oxidoreductases exert their effects by the generation in situ of reactive molecules. The potential of these enzymes in food preservation is still far from realized at present.     

Mutational analysis of the Vibrio fischeri LuxI polypeptide: critical regions of an autoinducer synthase

Synthesis of the Vibrio fischeri autoinducer, a signal involved in the cell density-dependent activation of bioluminescence, is directed by the luxI gene product. The LuxI protein catalyzes the synthesis of N-acyl-homoserine lactones from S-adenosylmethionine and acylated-acyl carrier protein. We have gained an appreciation of the LuxI regions and amino acid residues involved in autoinducer synthesis by isolating and analyzing mutations generated by random and site-specific mutagenesis of luxI. By random mutagenesis we isolated 13 different single amino acid substitutions in the LuxI polypeptide. Eleven of these substitutions resulted in no detectable autoinducer synthase activity, while the remaining two amino acid substitutions resulted in reduced but detectable activity. The substitutions that resulted in no detectable autoinducer synthase activity mapped to two small regions of LuxI. In Escherichia coli, wild-type luxI showed dominance over all of the mutations. Because autoinducer synthesis has been proposed to involve formation of a covalent bond between an acyl group and an active-site cysteine, we constructed site-directed mutations that altered each of the three cysteine residues in LuxI. All of the cysteine mutants retained substantial activity as an autoinducer synthase in E. coli. Based on the analysis of random mutations we propose a model in which there are two critical regions of LuxI, at least one of which is an intimate part of an active site, and based on the analysis of site-directed mutations we conclude that an active-site cysteine is not essential for autoinducer synthase activity.     

Synthesis,characterisation and use of 2-tetradecylcyclobutanone together with other cyclobutanones as markers for irradiated liquid whole egg

The synthesis and characterisation of 2-tetradecylcyclobutanone (TCB) is described. Both 2-dodecykyclobutanone and TCB were shown to be present in liquid whole egg irradiated at doses of 2.5 and 10.0 kGy. These compounds were absent from the unirradiated pasteurised samples. Using gas chromatography and infrared spectroscopy, there was also evidence for the presence in irradiated egg of 2-tetradeccnyl- and 2-tetradecadienylyclobutanone which are formed from oleic and linoleic acids, respectively. Authentic standards for these unsaturated cyclobutanones were not available commercially but the presence of 2-tetra-decenylcyclobutanone was substantiated by hydrogenating the egg extracts so converting this unsaturated cyclobutanone to TCB. Saturated and unsaturated cyclobutanones appear to be specific products of irradiation and are potential markers for detection of irradiated liquid egg and probably other fat-containing foods.     

Simplified linearly polarised contoured beam reflector antenna for a European coverage requirement

The design of a linearly polarised contoured beam reflector antenna for a European coverage requirement is described. The antenna is a 1.1 m offset reflector, fed by an array of only five rectangular feed horns, operating in a 10.7?11.7 GHz band. The minimum gain requirement of 28 dBi for the contoured beam, in contrast to the current ECS-1 CEPT (Conference Europeenne de Poste et Telecommunication) elliptical Eurobeam gain requirement of 25 dBi, is achieved.     

Some European satellite-antenna developments and trends

The environment, as well as the mass and available power limitations specific to space missions, add special constraints. These lead to the use of exotic low-mass, high-stability materials, with advanced mechanical and thermal designs. Also, antenna front ends must be tailored for optimum efficiency and power handling. Researchers and engineers in universities, research institutes, and industrial laboratories, from the 14 member states of the European Space Agency (ESA), together with staff from the European Space Agency's Technology Centre (ESTEC) antenna section and from project teams, have studied and developed software-modeling tools, critical reflector and array technologies, novel antenna architectures, and special measurement techniques to cope with these requirements. This paper presents an overview of some of the latest antenna-design tools and technology developments, supported by ESA for space applications. The following topics are covered reflectors, feed systems, and direct-radiating arrays. Some trends and developments in space antenna requirements and technologies are outlined     

Reciprocal inhibition in man

Reciprocal inhibition is the automatic antagonist alpha motor neurone inhibition which is evoked by contraction of the agonist muscle. This so-called natural reciprocal inhibition is a ubiquitous and pronounced phenomenon in man and must be suspected of playing a major role in the control of voluntary movements. The spinal pathways underlying this inhibitory phenomenon were studied. The disynaptic reciprocal Ia inhibitory pathway between the tibial anterior muscle and the soleus alpha motor neurones was identified and described in man. It was shown that the inhibition can be evoked in most healthy subjects at rest, but the degree of inhibition varies considerably from one subject to another. It was concluded that it corresponds to the disynaptic reciprocal Ia inhibitory pathway which has been extensively described in animal experiments. The disynaptic reciprocal inhibition was shown to increase during the dynamic phase of a dorsiflexion movement of the foot, but not during the tonic phase. However, when the peripheral afferent feedback from the contracting muscle was blocked by ischaemia, an increase of the inhibition was revealed also during the tonic phase of the dorsiflexion. The concealment of this increase during unrestrained peripheral feedback from the muscle was thought to be due to the post-activation depression mechanism; a mechanism which was described further and which probably involves reduced transmitter release at Ia afferent terminals as a result of previous activation of these afferent fibers. Hence the hypothesis was supported that alpha motor neurones and the corresponding inhibitory interneurones, which project reciprocal inhibition to the antagonist motor neurones, are activated in parallel during voluntary contraction of agonist muscles. An additional reciprocal inhibitory mechanism, the long latency reciprocal inhibition, was described between the tibial anterior muscle and the soleus alpha motor neurones. It was shown to be evoked by group I afferent activity and it was seen at a conditioning-test interval of 3-6 msec. It was initiated by supraspinal pathways and it was seen only during dorsiflexion of the foot. The pathway underlying this inhibitory mechanism is unknown, but it was suggested that it was mediated by a propriospinal pathway. The possible contribution to reciprocal inhibition of presynaptic inhibition of soleus Ia afferent fibers was studied by an indirect method. It was concluded that this presynaptic inhibition was increased during even slight dorsiflexion of the foot and that the increase was mainly dependent upon the peripheral afferent input from the contracting muscle.(ABSTRACT TRUNCATED AT 400 WORDS)     

Pathological features of the placenta in fetal death

Few studies of the histopathological features of the placenta in cases of fetal death are available. We will describe the placental findings from 24 midtrimester spontaneous abortions and 54 stillborn infants of more than 28 weeks' gestation. In almost 100% of midtrimester abortions and in 48% of the placentas from stillborn infants of more than 28 weeks' gestation, chorioamnionitis, deciduitis, and/or villitis were present. Because of this very high percentage of lesions, which suggests an infectious causation, it is mandatory that studies be performed that might identify pathogens. One third of the stillborn infants of more than 28 weeks' gestation were associated with maternal complications (diabetes, preeclampsia, and urinary tract infection), in addition to placental fetal vasculopathy, ischemia, infarcts, and chorangiosis (villous capillary hyperplasia). We emphasize the use of the placenta for the recognition of maternal diabetes.