Helicopter-borne NMR for detection of oil under sea-ice

Mobile nuclear magnetic resonance (NMR) operating in Earth's magnetic field is adapted to detect leaked or spilled oil trapped in or under sea ice without the need to place any personnel on the ice. A helicopter placed a 6-meter diameter NMR coil system weighing approximately 1000 kg on 92 cm-thick ice surrogate and detected the equivalent of 1 cm thick oil under the ice surrogate in 3-1/2 min.

Internal magnetic gradient fields in glass bead packs from numerical simulations and constant time diffusion spin echo measurements

Internal magnetic field gradients in water saturated glass bead packs were studied by numerical simulations and a constant time spin echo (CTSE) experiment. The CTSE is comprised of two spin echo refocusing periods where each of the two evolution periods, tau1 and tau2, is varied so that the total evolution, 2(tau1 + tau2), is held constant. The experiment is similar to that introduced by Norwood and Quilter and allows the effects of dephasing due to diffusion in a magnetic field gradient to be separated from other relaxation mechanisms. In our experiments, the magnetic susceptibility difference between the pore fluid and glass beads creates the internal field gradient. CTSE measurements were performed at 7 T (300 MHz 1H) for water saturated in 50 microm diameter glass bead pack. We find that the internal gradients in the center of the pore bodies, where free diffusion applies, is in the range of 10 to 100 G/cm. This fluid volume accounts for < or =10% of the total pore volume. From direct numerical simulations of the internal magnetic field based on a first principles calculation, we find that the major fraction, >90%, of the pore volume has internal gradients of order 500 to 5,000 G/cm. Signals from water in these large gradients is not observed in our CTSE measurements.

Observation of electro-osmotic flow echoes in porous media by nuclear magnetic resonance

A method for assessing the time reversibility of molecular displacements in fluids is presented. The method utilizes pulsed field gradient NMR experiments, in which the flow driving force is inverted during the magnetization lifetime in each measurement cycle. The method is suitable for opaque three-dimensional systems and short displacements, and provides inherent separation between thermal diffusion and displacements driven by externally controlled forces. This approach was applied to study the time reversibility of an electric-field-driven flow of water in natural sand samples, over time scales of up to 0.4 s and displacement scales of the order of one particle diameter. It is demonstrated that the intensity loss of the NMR signal, caused by flow-induced phase dispersion, is fully refocused upon inversion of the polarity of the applied electric field, resulting in flow echoes.

NMR T2 distributions and two phase flow simulations from x-ray micro-tomography images of sandstones

The distribution of fluids in the pore space of a series of sandstones is calculated as a function of capillary pressure using a two phase flow simulation model. The pore space is represented by a system of channels and nodes which are derived from x-ray micro-tomography images of sandstones. The sandstones studied varied in permeability from approximately 40 to 3,000 mD. The simulation results illustrate the significance of the pore level by-pass phenomena in controlling the location of fluids within the pore structure. The implications of these results on the interpretation of NMR T(2) distributions to determine the irreducible water saturation are discussed.

Combined proton T1N and CPMG T2N studies of water saturated sandstone core plugs

Diffusion dynamics for water in a series of sandstone core plugs with a broad range of permeabilities was studied using both the Carr-Purcell-Meiboom-Gill (CPMG) and inversion recovery experiments. Both the transverse and longitudinal magnetization curves were found to fit well to stretched exponential relaxation kinetics. At short times, the transverse magnetization is well described by an expression for free diffusion averaged over a distribution of pore sizes. The stretch exponents for the transverse and longitudinal magnetization are shown to be simply related to the width of the pore size distribution. A cross over from free to restricted diffusion is evident in the dependence of T2 with increasing diffusion time set by the interpulse spacing tau in the CPMG experiment. The T2(tau) data is fit to a model which interpolates between the limits of free and restricted diffusion. A length derived from this model is shown to provide a simple estimate of the absolute fluid flow permeability.

Endothelium-dependent relaxant effect of neurokinins on rabbit aorta is mediated by the NK1 receptor

Several neurokinins, namely substance P, neurokinin A, neurokinin B, [beta-Ala8]neurokinin A-(4-10) and senktide, were tested on noradrenaline-precontracted rabbit aortic rings to characterize the receptor mediating their endothelium-dependent relaxant effect in this preparation. CP-96,345, the new nonpeptide antagonist selective for the NK1 receptor, was also studied. Substance P, neurokinin A and neurokinin B, in that order of potency, were effective in relaxing precontracted rings, indicating the involvement of the NK1 receptor; [beta-Ala8]neurokinin A-(4-10) and senktide, which are selective agonists for NK2 and NK3 receptors, respectively, had no significant relaxant effect. The relaxant effects of substance P, neurokinin A and neurokinin B were competitively antagonized by nanomolar concentrations of CP-96,345. These findings support the view that the NK1 receptor mediates the endothelium-dependent relaxant effect of the neurokinins in rabbit aorta.

Sensitivity and reactivity to endothelin-1 in mesenteric beds and aortic rings of 4-week-old spontaneously hypertensive rats

The vasoconstrictor effects of endothelin-1 were studied in perfused mesenteric vascular beds (MVB) and aortic rings of 4-week-old spontaneously hypertensive rats (SHR) and age-matched Wistar Kyoto rats (WKY). Mean blood pressure (124 +/- 4 vs. 97 +/- 3 mmHg) and initial perfusion pressure in the MVBs (25 +/- 2 vs. 19.7 +/- 1.2) were significantly higher in SHR. Reactivity to endothelin-1 was increased in MVBs of SHR, as indicated by the maximum perfusion pressure obtained (223 +/- 8 vs 155 +/- 7 mmHg, p less than 0.001), whereas there was no significant difference in sensitivity between the two strains (EC50 values: 50 +/- 12 and 80 +/- 15 pmol, respectively). By contrast, in aortic rings reactivity and sensitivity to endothelin-1 were similar in both strains, (EC50s: 1.8 +/- 0.12 and 1.4 +/- 0.1 nM). Reactivity to norepinephrine was increased in MVBs, but reduced in aortic rings of SHR. The unchanged sensitivity to endothelin-1 and the unspecifically increased reactivity in the MVBs of SHR to endothelin-1 and norepinephrine indicate rather a change in vascular structure and not a functional abnormality. These results suggest that hyperreactivity to endothelin-1 may not be a primary hypertensive mechanism in genetic hypertension.

N coordination of FeMo cofactor requires His-195 of the MoFe protein alpha subunit and is essential for biological nitrogen fixation

Electron spin echo envelope modulation (ESEEM) spectroscopy, a pulsed electron spin resonance technique, was used to analyze the N coordination of the iron-molybdenum (FeMo) cofactor contained within the nitrogenase MoFe protein. Comparison of spectra obtained from whole cells and purified MoFe protein established that the N coordination of the FeMo cofactor provided by the MoFe-protein polypeptide matrix can be unambiguously recognized in whole cells. ESEEM spectra of altered MoFe proteins, which were produced in certain mutant strains of Azotobacter vinelandii, showed that the N coordination to FeMo cofactor requires His-195 of the MoFe protein alpha subunit. Moreover, this requirement for His-195 was shown to be essential for biological nitrogen fixation.

Effect of covalent dimer conjugates of angiotensin II on receptor affinity and activity in vitro

Angiotensin II [1-8 or 2-8] analogues and [4-8] fragments were dimerized through the amino- or carboxy-terminal groups in order to try to increase their potency as reported for other hormones. The binding affinity to the angiotensin II receptor subtypes A (A IIA) and B (A IIB) was tested and compared to the potency in rabbit aortic ring. The [2-8] dimers coupled through the N-terminus show no significant change in potency in aortic ring. The [4-8] fragments coupled through the N-terminus are inactive in the ring. They have however a significantly increased affinity for the A IIA receptor, the specific function of which has not yet been reported. When angiotensin II analogues or fragments are coupled through the C-terminus, there was a significant drop in affinity and potency, confirming the importance of the free carboxyl group in position 8 for binding and activity. It is concluded that binding to the A IIB receptor correlates well with the effectiveness in aortic ring. However, in contrast to the beneficial effect reported for a large number of other hormones, dimerization of angiotensin II or its fragments is not accompanied by an increased biological activity in aortic ring.

Sarmesin is a partial agonist of angiotensin-II receptors in rabbit, but not in rat, aortic rings

Sarmesin, [Sar1, Tyr(Me)4]angiotensinII], has been reported to be a competitive angiotensin II (AII) receptor antagonist in rat smooth muscle preparations (Scanlon et al., (1984), Life Science 34, 317-321). In the present study, sarmesin displaced AII from its binding sites in rat aortic smooth muscle cells and in a rabbit aorta membrane preparation (IC50 5 and 6 nM resp.; Ki 4.1 and 5.3 resp.) In rabbit aortic rings, sarmesin (0.003-3 microM) produced concentration-dependent contractions (ED50 89 nM) and this effect was inhibited by saralasin. No contraction was observed in the rat aorta up to 100 microM. In rabbit aortic rings, sarmesin, at the same concentrations that produced contraction, inhibited contractions induced by AII in a competitive manner (pA2 7, 26). These results indicate that, in rabbit aortic rings sarmesin is a partial agonist of AII receptors.

Reactivity and sensitivity of mesenteric vascular beds and aortic rings of spontaneously hypertensive rats to endothelin: effects of calcium entry blockers

1. The vasoconstrictor effects of endothelin-1 were studied in perfused mesenteric vascular beds (MVB) and aortic rings of 14-16 week-old spontaneously hypertensive rats (SHR) and age-matched Wistar Kyoto rats (WKY). 2. Reactivity to endothelin-1 was increased in MVBs of SHR, as indicated by the maximum perfusion pressure obtained (264 +/- 8 and 141 +/- 9 mmHg respectively) (P less than 0.001), whereas sensitivity was not significantly different between the two strains (EC50 171 +/- 21 and 102 +/- 19, respectively). 3. In aortic rings, in contrast, reactivity to endothelin-1 was reduced in SHR as compared to WKY, whereas sensitivity was similar (EC50 0.78 +/- 0.08 and 0.87 +/- 0.09 nM). 4. As with endothelin-1, reactivity to noradrenaline and potassium chloride was increased in MVBs, but not in aortic rings of SHR. Endothelin-1 was 30 times more potent than noradrenaline in MVBs of SHR, and 15 times more potent than noradrenaline in aortic rings. 5. In both strains, nifedipine and nitrendipine almost completely blocked potassium-induced contractions in MVB and aortic rings, respectively, whereas contractions induced by endothelin-1 or noradrenaline were only partially inhibited. 6. It is concluded that calcium influx via the voltage-operated calcium channel is only partially responsible for the vasoconstrictor action of endothelin-1 in MVBs and aortic rings of SHR and WKY rats. The increased reactivity of the MVB of SHR to endothelin-1 at this stage of the hypertensive process is most likely to be the result of a change in vascular structure rather than due to a primary hypertensive mechanism.

Binding characteristics and vascular effects of various angiotensin II antagonists

Subtypes of angiotensin II (Ang II) receptors have been recently identified using specific ligands (see Whitebread et al. Biochem Biophys Res Comm 1989; 163:284-291). The present study compares the binding characteristics of different structural classes of Ang II receptor ligands in rat aortic smooth muscle cells (Ang IIB subtype) and in human uterus (Ang IIA subtype) and their effects on the constrictor response to Ang II in isolated rabbit aortic rings. Saralasin and [Sar1 Ile8]-Ang II displayed similar affinity for the two subtypes. In contrast, CGP 42112A bound with high affinity to the uterus (Ki 0.24 nM), but showed a low affinity for the aortic receptor (Ki 1,760 nM). Compound 89 displayed affinity for the aortic receptor only (Ki 26 nM) whereas Ex 169 recognized specifically the uterus receptor (Ki 310 nM). In rabbit aortic rings, saralasin, [Sar1 Ile8]Ang II, CGP42112A and compound 89 inhibited Ang II-induced contractions at concentrations similar to those required to bind to the Ang IIB receptor subtype. IC50s were 3, 0.7, 1,850, and 23 nM respectively. Ex 169 was ineffective in concentrations up to 100 microM. There was a highly significant correlation between inhibition of Ang II-induced contraction in aortic rings and binding to smooth muscle cells. This correlation does not exist with human uterus. Our results indicate that the Ang IIB receptor subtype is responsible for vascular contractions. Antagonists of this vascular receptor subtype are potential antihypertensive agents.

Blockade of endothelin-induced contractions by dichlorobenzamil: mechanism of action

Contractions of intact rat aortic rings induced by endothelin were totally inhibited by the amiloride analogue dichlorobenzamil (DCB) at concentrations known to block Na-Ca exchange (IC50 = 30 microM). Amiloride (100 microM) was ineffective. Ca-channel blockers and a K-channel opener elicited only partial inhibition. These results could indicate that the Na-Ca exchanger plays an important role in endothelin-induced contractions. Endothelin, however, had no effect on the kinetics of the exchanger, and, in addition, contractions also occurred in Na-depleted vessels. The endothelin-induced contractions produced by Ca release from intracellular pools were also completely inhibited by DCB. In fact, the latter compound was found to block contractions induced by Ca itself in the presence of Ca ionophore or detergent. We conclude that DCB acts directly on Ca-induced activation of myofilaments in smooth muscle.

[Reasonableness of surgical interventions and compliance responsibilities in various insurance fields and under the social compensation law]

According to the German Social Legal Code I (I. Sozialgesetzbuch, SGB I) the recipient of social benefits is under obligation to submit to medical treatment if such treatment would result in an improvement of his/her condition or in the prevention of further deterioration (section 63 SGB I). In certain situations, lack of cooperation may result in total or partial refusalor withdrawal of benefits (section 66 SGB I). This social law parallels the civil law which can recognize, in the area of private liability, co-delinquency in cases of refusal of reasonable treatment (section 157. section 242 and 254 GBG). In private liability insurance, the acceptance of reasonable medical treatments is contractually anchored. - In practice, the underwriter is generally unable to enforce surgical interventions. In the administration of social benefits surgical measures are exempt from the obligation of cooperation through administrative rules and guidelines of the regional state departments. The entitlement to pensions for the visually handicapped ("Blindengeld"), based on the Federal Social Benefit Law (BSHG), is regulated at the state level through state organizations. The corresponding state laws do not provide for the termination of support in cases of refusal of reasonable and prognostically promising operations. The recipients of pensions for the blind are not addressed in SGB I. Benefit recipients are therefore not penalized for refusing reasonable medical measures. - In legal accident insurance and legal social security insurance there exist, under certain conditions, obligations to cooperate in line with SGB I.(ABSTRACT TRUNCATED AT 250 WORDS)

[Evaluation of eyeglasses in private accident insurance]

In a ruling issued on 27 April 1983 the Bundesgerichtshof (the supreme court of the Federal Republic of Germany) clarified the question as to the extent to which the need for spectacles has to be taken into consideration in private accident insurance. Spectacles are not a prosthesis; the diminution of usability is assessed according to the wearer's visual acuity with correction; the need for spectacles has to be taken into account when determining the diminution of usability (as a pre-existent infirmity or as an injury caused by an accident). Concerning the premium surcharges and rebates demanded, which were not laid down by the BGH, the authors, continuing earlier discussions with a team from the German association of private accident insurers, came to the following agreements, which are recommended for general use: lower and medium grades of correction up to +10 D and -13 D (in cylindrical glasses in the meridian with higher refraction) are to be assessed as a 3% disablement; where the degree of correction is higher, i.e., more than +10 D and -13 D, the degree of disablement is assessed at 5%.

[Assessment of eye damage for private accident insurance]

Together with a team from the HUK association (an association of liability, accident, transport and legal protection insurance-companies) the authors discussed a new assessment table for diminution of vision and have recommended its use by private accident insurance companies. The table was worked out on the basis of guidelines issued by the Deutsche Ophthalmologische Gesellschaft in 1981. In cases of bilateral eye damage the total extent of the disability - based on the specific diminution of usability of each eye - should be calculated according to the conditions of the insurance companies and not by a medical expert. Further proposals for the assessment of visual field defects and other kinds of eye damage covered by private accident insurance were also brought into line with the recommendations issued by the Deutsche Ophthalmologische Gesellschaft in 1981.