Hyphenation of gas chromatography to microcoil 1H nuclear magnetic resonance spectroscopy

Whereas the hyphenation of gas chromatography (GC) with mass spectrometry is of great importance, little is known about the coupling to nuclear magnetic resonance spectroscopy (NMR). The investigation of this technique is an attractive proposition because of the valuable information given by NMR on molecular structure. The experiments shown here are to our knowledge the first hyphenating capillary GC to microcoil NMR. In contrast to liquids, gases have rarely been investigated by NMR, mainly due to the experimental difficulties in handling gases and the low signal-to-noise-ratio (SNR) of the NMR signal obtained at atmospheric pressure. With advances in NMR sensitivity (higher magnetic fields and solenoidal microprobes), this limitation can be largely overcome. In this paper, we describe the use of a custom-built solenoidal NMR microprobe with an active volume of 2 microL for the NMR detection of several compounds at 400 MHz, first in a mixture, and then with full coupling to capillary GC to identify them separately. The injected amounts of each analyte in the hyphenated experiments are in the range of 15-50 micromol, resulting in reasonable SNR for sample masses of 1-2 microg.     

Resource-Bounded Measure and Learnability

We consider the resource-bounded measure of polynomial-time learnable subclasses of polynomial-size circuits. We show that if EXP ≠ MA, then every PAC-learnable subclass of P/poly has EXP-measure zero. We introduce a nonuniformly computable variant of resource-bounded measure and show that, for every fixed polynomial q , any polynomial-time learnable subclass of circuits of size q has measure zero with respect to P/poly. We relate our results to the question of whether the class of Boolean circuits is polynomial-time learnable. Received July 15, 1998, and in final form September 9, 1999.     

Reciprocal expression of 17alpha-hydroxylase-C17,20-lyase and aromatase cytochrome P450 during bovine trophoblast differentiation: a two-cell system drives placental oestrogen synthesis

No definitive information is yet available on the steroidogenic capacity of the two morphologically distinct cell types forming the bovine trophoblast, the uninucleated trophoblast cells (UTCs) and the trophoblast giant cells (TGCs). Hence, in order to localise 17alpha-hydroxylase-C17,20-lyase (P450c17) on a cellular level and to monitor its expression as a function of gestational age, placentomes from pregnant (days 80-284; n = 19), prepartal (days 273-282; 24-36 h prior to the onset of labour; n = 3) and parturient cows (n = 5) were immunostained for P450c17 using an antiserum against the recombinant bovine enzyme. At all stages investigated, P450c17 was exclusively found in the UTCs of chorionic villi (CV), where staining was ubiquitous between days 80 and 160, but was largely restricted to primary CV and the branching sites of secondary CV between days 160 and 240. Thereafter, a distinct ubiquitous staining reoccurred in the UTCs of all CV in late pregnant, prepartal and parturient animals. Using an antiserum against human aromatase cytochrome P450 (P450arom), specific cytoplasmic staining was observed in TGCs. In placentomes from pregnant cows, staining intensity was higher in mature compared with immature TGCs and was more pronounced in the trophoblast covering big stem villi compared with the trophoblast at other sites of the villous tree. In placentomes of a parturient cow, specific staining was only found in mature TGCs that survived the normal, but substantial, prepartal decline in TGC numbers. These results clearly showed that bovine UTCs and TGCs exhibit different steroidogenic capacities, constituting a 'two-cell' organisation for oestrogen synthesis. P450c17 expression appears to be quickly down-regulated and P450arom is up-regulated when UTCs enter the TGC differentiation pathway.     

The glycosylation of pregnancy-associated glycoproteins and prolactin-related protein-I in bovine binucleate trophoblast giant cells changes before parturition

Binucleate trophoblast giant cells (BNC) in the bovine placenta produce glycoproteins, which are delivered into the mother after fusion of BNC with uterine epithelial cells. During most time of pregnancy, BNC produce pregnancy-associated glycoproteins (PAGs) and prolactin-related protein-I (PRP-I) with asparagine-linked lactosamine-type glycans terminating with N-acetyl-galactosamine. We show by lectin histochemistry that terminal N-acetyl-galactosamine (detected by Dolichos biflorus agglutinin, DBA) in placentomal BNC is greatly reduced prior to parturition, while lactosamine-type N-glycans (detected by Phaseolus vulgaris leucoagglutinin, PHA-L) remain unaltered. The change in DBA-staining showed no statistically significant differences between placentomes of cows with and without retention of fetal membranes. Western blots revealed that, at parturition the apparent molecular mass of PAGs and PRP-I is 1-2 kDa lower than in late pregnancy. These changes are due to alterations of asparagine-linked glycans, since the molecular weight of the peptide backbones after enzymatical release of asparagine-linked glycans is identical at late pregnancy and parturition. Lectin western blots showed a reduction of terminal N-acetyl-galactosamine on PAGs at parturition. A lectin sandwich-ELISAwas used to differentiate DBA- and PHA-L-binding PAGs in sera of pregnant and non-pregnant cows. The values for DBA-binding PAGs at parturition were not significantly different from non-pregnancy, while the values for PHA-L-binding PAGs were significantly higher at parturition. The peripartal changes of PAG- and PRP-I-glycosylation could alter functional properties of these proteins and might therefore be considered for functional studies. The differentiation of PAG glycoforms in maternal serum could be valuable for a further optimization of PAG-based pregnancy diagnosis in cattle.     

Situation awareness: some conditions of possibility

Situation awareness (SA) has become a ubiquitous object of knowledge in our discourses of human performance and accident explanation. Based on Michel Foucault's archaeological approach, in this paper, we examine SA by mapping the ‘conditions of possibility’ for this object to emerge. By highlighting the logic that SA builds upon, the political need that it intends to address, and the knowledges that delimitate it in its constitution, we aim to display the contingent nature of this object. Ultimately, we argue that as a discursive object, SA has effects.     

Time-dependent toxicity of fluoranthene to freshwater invertebrates and the role of biotransformation on lethal body residues

The time-dependent toxicity of fluoranthene was examined for Hyalella azteca, Chironomus tentans, and Diporeia spp. C. tentans appeared to be the most sensitive species, and Diporeia was the least sensitive. Incipient LC50 values, the concentration at which the LC50 reaches an asymptote and does not change with increasing duration of exposure, for H. azteca and C. tentans were approximately 60 and 40 microg x L(-1), respectively. Incipient levels were not reached for Diporeia; however, the 28-d LC50 concentration was 95.5 microg x L(-1). There was a temporal relationship with respect to lethal body residues for each of the test species. For H. azteca, the LR50, the median lethal residue at an identified exposure time required to cause 50% mortality, based on total fluoranthene equivalents (parent + metabolite compounds) decreased from 3.19 micromol x g(-1) at 5 d to 0.80 micromol x g(-1) at 28 d. For C. tentans, the LR50 decreased from 0.43 to 0.17 micromol x g(-1) from 2 to 10 d. The 10-d LR50 for Diporeia was 9.97 micromol x g(-1), and the 28-d value was 3.67 micromol x g(-1). The toxicokinetics are not sufficient to address the temporal changes in LR50 values. Thus, the data were fit to a Damage Assessment Model that also accounts for toxicodynamic processes. This analysis provides estimates of the incipient lethal residues for H. azteca, C. tentans, and Diporeia: 0.84, 0.21, and 3.00 micromol x g(-1), respectively. When comparing the relative sensitivity among species using lethal body residues, special attention should be given to ensure that comparisons are made at a common point in relation to exposure duration (i.e., time to steady state, Tss). When the LR50(lipid) values among the three species were compared at steady state, C. tentans is more sensitive than H. azteca and Diporeia spp.; however, there are no significant differences between the amphipod species. The greater sensitivity of C. tentans to fluoranthene as compared to the amphipods may be due, in part, to a potential toxic metabolite.     

Penetration length studies of supercritical water jets submerged in a subcritical water environment using a novel optical Schlieren method

In hydrothermal spallation deep drilling a high-velocity, hot, supercritical water jet is directed towards the rock to induce fragmentation. One major challenge in the realization of this novel technique is the entrainment of comparatively cool, aqueous drilling fluid by the hot water jet, which can lead to significant heat losses before the hot jet's energy can be transferred to the rock. The present work quantifies such entrainment effects by determining penetration lengths of supercritical water jets injected into a cool, subcritical environment using a novel optical Schlieren method. Penetration lengths of supercritical jets were found to be equal to the injector's nozzle diameter and almost independent of the jet's temperature at the nozzle exit and the jet's mass flow under almost all experimental conditions investigated. A semi-empirical model adapted from steam jet studies confirmed these findings and indicates that heat and mass transfer are primarily controlled by turbulent mixing.     

Improved Determination of Bimodal Size Distributions from Measurements with Diffusional Size Classification

The size distribution of the unattached fraction of the short-lived radon progeny is reported in the literature to have a bimodal structure. Due to the weak size resolution of diffusional size classification, a wide variety of bimodal size distributions yields similar measurement results, obstructing the reconstruction of size distribution parameters from measured data. For example, it could be shown that although 2 of the commonly used nonlinear approximation algorithms per formed well for the reconstruction of a monomodal size distribution, the reproduc tion of parameters of a bimodal size distribution was unsatisfactory. In conse quence, a "random walk" approach is presented. The basic idea for this approach consists of probing the complete parameter space as an ideal method for locating the best set of parameters. Additionally, 2 steps are introduced for the reduction of computation time to render the ideal approach to an applicable method. The range of geometric standard deviations for the calculation was restricted to values between 1 and 5. The range of median diameters was limited according to the penetration functions of the diffusional samplers. This restricted volume of param eter space was subdivided into 10⁴ cells. During the calculation, cells with exceptionally large values of the minimization functional were eliminated from further computation. Compared to the results of EM and Simplex algorithms, this ''random walk'' method was able to retrieve parameters of both monomodal and bimodal size distributions with improved accuracy.