Absorption isotherms for H2(D2)–Pd0.8Ag0.2 (198–323 K)

Isotherms for H₂/D₂–Pd_0.8Ag_0.2 systems have been measured over a low temperature range, 198–323 K. Such low temperature data for this system have not been obtained previously. The absorption kinetics was found to be fast. The isotherms at low temperatures are compared with literature values at or above 313 K, as well as those for H₂(D₂)–Pd systems. The H/D isotope effect and the separation factors in the plateau range over Pd_0.8Ag_0.2 are calculated at various temperatures and discussed, based on the isotherms. Enthalpies are extracted from van’t Hoff plots and compared with calorimetric values and the results from the literature for both absorption and desorption processes. A method is given for using isotherm information from single isotope systems to estimate the separation factor for the mixed isotope systems and this is a helpful tool.The challenge of measuring absorption isotherms at low temperatures and low pressures is discussed. Sample pre-treatment, non-soluble impurity accumulation in an absorption process and thermal transpiration effects are examined.     

Biogeochemical cycles for the chemical elements in Nymphaea odorata ait. and the aphid Rhopalosiphum nymphaeae (L.) living in Linsley Pond

A hydrogeochemical study to determine the abundance of the chemical elements in the water of Linsley Pond, North Branford, Conn., U.S.A., was initiated in 1965. As the investigation progressed, it became clear that the aquatic macrophytes, associated sediments, and the soils and rocks of the basin had to be examined chemically in order to elucidate the biogeochemical cycle of the elements in the water. This aspect of the study concerns the elemental chemical composition of Nymphaea odorata Ait. and the aphid Rhopalosiphum nymphaeae (L.) feeding on its leaves. Thirty-five elements were detected in the water but fifty-four were found in this water-lily and its aphid. Those not encountered in lake water concentrated twenty-fold were Cs, Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Ge, Zr, Hf, Th, As, Nb and Se. The water-lily, the aphid, the lake sediment and the soils and rocks of the basin all contained detectable quantities of the rare earths, though beyond Sm only those of even atomic number were encountered. The aphids contained more Na, Li, Cs, Ba, Zn, Al, Ga, Si, Ge, Pb, Ti, Hf, P, Bi, S, Se, Cr, Mo, I, Fe, Co, Ni, Mn, Y, La, Ce, Pr and Sm than the leaves upon which they feed. The water-lily leaves contain more Ag, Ca, Mg, Cd, Hg, B, Sn, Zr, Th, Cl, Br, Nd and Sc than the aphids. The amount of Be, Gd, Dy, Er, Yb, K, Rb, Cu, Sr, As, V and F is essentially the same in the insects as in the leaves which support them. Pertinent comparative data from other sources are also presented.     

Systemic arterial blood pressure and urine protein/creatinine ratio in dogs with hyperadrenocorticism

OBJECTIVE: To determine prevalence and severity of systemic arterial hypertension and proteinuria in dogs with naturally developing hyperadrenocorticism and to determine whether these abnormalities resolve with adequate management of the disease. DESIGN: Case series and cohort study. ANIMALS: 77 dogs with naturally developing hyper-adrenocorticism examined once; 15 dogs examined before and after treatment. RESULTS: Among dogs examined only once, hypertension was diagnosed in 21 of 26 dogs with untreated pituitary-dependent hyperadrenocorticism (PDH), 17 of 21 with inadequately controlled PDH, 8 of 16 with well-controlled PDH, 10 of 10 with an untreated adrenocortical tumor, and 0 of 4 that had undergone adrenalectomy because of an adrenocortical tumor. Untreated dogs and dogs with inadequately controlled PDH had significantly higher blood pressures than did other dogs. Proteinuria was documented in 12 of 26 dogs with untreated PDH, 5 of 16 with inadequately controlled PDH, 3 of 14 with well-controlled PDH, 5 of 8 with an untreated adrenocortical tumor, and 1 of 3 that had undergone adrenalectomy. Dogs with untreated PDH and dogs with an untreated adrenocortical tumor had higher urine protein/creatinine ratios than did dogs with well-controlled PDH. Among dogs evaluated before and after treatment, blood pressure and urine protein/creatinine ratio did not change in 8 dogs with inadequately controlled hyperadrenocorticism, but decreased in 7 dogs with well-controlled disease. CLINICAL IMPLICATIONS: Results suggest that systemic hypertension and proteinuria are common in dogs with untreated hyperadrenocorticism and that successful treatment of hyperadrenocorticism will result in resolution of these abnormalities in many, but not all, dogs.     

The effect of coatings on deuterium retention and permeation in aluminum 6061-T6 APT tritium production tubes

The accelerator production of tritium project will utilize spallation neutrons incident on thousands of ³He gas filled metal tubes to produce tritium by way of the exothermic ³He(n,p)³H reaction. Tritons with energies up to 192 keV and protons with energies up to 576 keV are directly implanted into the tube walls. To minimize tritium retention in the tubes and permeation into the coolant surrounding the tubes, it is desirable to have the implanted tritium migrate back to the inner surface of the tubes and rapidly recombine to be released as T₂ and HT. Aluminum alloy (Al 6061-T6) is the primary candidate material for fabrication of the tubes. Aluminum alloy samples implanted with deuterons and protons to fluences as high as 3×10²² D (and p)/m² were studied. Deuterium retention was measured by mass spectrometry during thermal desorption. Approximately 10% of the implanted deuterium was retained. Copper, nickel and anodized coatings on aluminum alloy were studied as possible methods of reducing retention and permeation of the tritium. In these experiments, the Cu and Ni coatings reduced the retention significantly, whereas retention increased in the anodized coated sample.     

Fluorescence and the structure of proteins. XXII. Fluorescence of aminotyrosyl residues formed in ribonuclease A

1. Tyrosyl residues on ribonuclease A were nitrated with tetranitromethane and then reduced to aminotyrosyl residues. By variation of reaction conditions and degree of exposure of tyrosyl residues it was possible to convert from 1 to all 6 tyrosyl to aminotyrosyl residues. 2. At the lower levels of 1-3 aminated tyrosyl residues/molecule the change in conformation seemed minor and 70% of the enzymatic activity was retained. When the three buried tyrosyl residues or all six residues were aminated only 5% of the enzymatic activity was retained. 3. Titration data, susceptibility to urea denaturation, and fluorescence characteristics indicated that some of the aminotyrosyl residues were buried in the interior and others were exposed on the surface of the protein. On the basis of the activation/emission wavelengths it was possible to distinguish buried (288/320 nm) and exposed (288/365-395 nm) aminotyrosyl residues as well as exposed tyrosyl residues (275-305 nm). 4. The modification of specific tyrosyl residues on a protein to aminotyrosyl residues appears to have some promise for observation of changes in environment of the residues that accompany various conformation changes by monitoring the fluorescence.     

Assessing the reactivity of TiCl3 and TiF3 with hydrogen

TiCl₃ and TiF₃ additives are known to facilitate hydrogenation and dehydrogenation in a variety of hydrogen storage materials, yet the associated mechanism remains under debate. Here, experimental and computational studies are reported for the reactivity with hydrogen gas of bulk and ball-milled TiCl₃ and TiF₃ at the temperatures and pressures for which these additives are observed to accelerate reactions when added to hydrogen storage materials. TiCl₃, in either the α or δ polymorphic forms and of varying crystallite size ranging from ～5 to 95 nm, shows no detectable reaction with prolonged exposure to hydrogen gas at elevated pressures (～120 bar) and temperatures (up to 200 °C). Similarly, TiF₃ with varying crystallite size from ～4 to 25 nm exhibits no detectable reaction with hydrogen gas. Post-exposure vibrational and electronic structure investigations using Fourier transform infrared spectroscopy and x-ray absorption spectroscopy confirm this analysis. Moreover, there is no significant promotion of H₂ dissociation at either interior or exterior surfaces, as demonstrated by H₂/D₂ exchange studies on pure TiF₃. The computed energy landscape confirms that dissociative adsorption of H₂ on TiF₃ surfaces is thermodynamically inhibited. However, Ti-based additives could potentially promote H₂ dissociation at interfaces where structural and compositional varieties are expected, or else by way of subsequent chemical transformations. At interfaces, metallic states could be formed intrinsically or extrinsically, possibly enabling hydrogen-coupled electronic transfer by donating electrons.     

Applications and outcome of hemodialysis in cats: a review of 29 cases

Hemodialysis (HD) has been used in the management of renal failure in dogs, but its feasibility has not been reported for uremic cats. Therefore, we investigated the technical possibility, efficacy, and complications of intermittent HD in cats with severe uremia. A total of 160 HD treatments were performed on 29 cats with acute renal failure (ARF) (n = 15), chronic renal failure (CRF) (n = 6), or acute on CRF (n = 8) between November 1993 and June 1996. Hemodialysis treatments were performed with transcutaneous dialysis catheters using a bicarbonate-based delivery system, sodium modeling, and volumetric-controlled ultrafiltration. Presenting serum chemistries (mean +/- SD) for all cats were creatinine, 16.4 +/- 7.5 mg/dL; blood urea nitrogen (BUN), 229 +/- 87 mg/dL; phosphate, 15.4 +/- 5.4 mg/dL; potassium, 6.0 +/- 1.6 mEq/L; and HCO3-, 16.0 +/- 4.4 mEq/L. For intensive HD treatments, pre-HD versus post-HD creatinine changed from 10.3 +/- 4.4 to 1.6 +/- 0.9 mg/dL and BUN from 105 +/- 33 to 8 +/- 10 mg/dL. One or more adverse events occurred during 111 (69%) treatments. Dialysis-related events included hypotension, dialysis dysequilibrium, clotting, and bleeding. Nine of 15 (60%) cats with ARF and 1 cat with CRF recovered sufficiently to survive without ongoing need for HD. For the remaining cats, the proximate causes of death were dialysis related in 9 cats, uremia related in 6 cats, and iatrogenic or unknown in 4 cats. Hemodialysis is technically feasible and effectively controls the biochemical disturbances of uremic cats. It is especially valuable for the management of severe ARF, permitting recovery in a large number of cats refractory to conventional therapy. Technical complications and chronic debility, however, may limit its usefulness for cats with advanced CRF.