Showing papers by "Tulane University published in 1980"

Theory of nonuniform electronic systems. I. Analysis of the gradient approximation and a generalization that works

Abstract: A complete wave-vector analysis has been made of the gradient coefficient for the exchange-correlation energy of a nonuniform electronic system. It is shown that the majority of the contribution comes from a very small but universal region of $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ space near the origin. From this it can be concluded that random-phase-approximation-like calculations, like the present one or that of Rasolt and Geldart, which treat this region correctly, are likely to provide accurate results for the gradient coefficient and hence for the energy and structure of a system whose density is truly slowly varying. However, it also shows that the criterion for the validity of the gradient approximation itself is much more severe than previously supposed, so that the usual type of application, to say a surface or bulk material, is incorrect. For the surface case this is verified in unequivocal detail. On the other hand, a generalization of the gradient scheme based on an average slope instead of a local slope is proposed. This gives good agreement with limiting cases where they exist, and rough agreement with the interpolation scheme proposed previously by the authors.

Quantitative reversed-phase high performance liquid chromatographic determination of major and modified deoxyribonucleosides in DNA

Abstract: We have developed a method to accurately determine (< 3% RSD) the complete major and modified base composition of a few micrograms of unlabeled DNA. The DNA samples were quantitatively hydrolyzed with DNase 1, Nuclease P1, and bacterial alkaline phosphatase. The resulting deoxyribonucleosides were directly separated in 70 min by reversed-phase high performance liquid chromatography with detection by ultraviolet absorption at 254 nm and 280 nm (RP-HPLC). The highly sensitive and selective dual wavelength quantitation greatly enhances the precision and accuracy of the chromatographic analysis. Contamination of DNA preparations with RNA does not interfere with the DNA analysis due to the high resolution of the chromatography. We have used this method for the quantitation of m5dCyd in 5 microgram of calf thymus and salmon sperm DNA in which the m5dCyd comprises only 1 to 2% of the total bases. This method should be a useful research tool in studies on various DNAs and DNA subfractions and should help to elucidate the functions of methylation of DNA.

Comparison of bisulfite modification of 5-methyldeoxycytidine and deoxycytidine residues

Abstract: Sodium bisulfite is a mutagen which can specifically deaminate more than 96% of the cytosine residues in single-stranded DNA via formation of a 5,6-dihydrocytosine-6-sulfonate intermediate. Under the same reaction conditions, only 2-3% of the 5-methylcytosine (m5Cyt) residues in single-stranded XP-12 DNA, which has 34 mole% m5Cyt, was converted to thymine (Thy) residues. In contrast, at the deoxynucleoside and free base levels, the same treatment with bisulfite and then alkali converted 51% and > 95%, respectively, of the m5Cyt to the corresponding Thy derivatives. However, the rate of reaction of m5Cyt and its deoxyribonucleoside was much slower than that of the analogous quantitative conversion of cytosine or deoxycytidine to uracil or deoxyuridine, respectively. The much lower reactivity of m5Cyt and its derivatives compared to that of the unmethylated analogs is primarily due to a decrease in the rate of formation of the sulfonate adduct.

Neuron Loss in the Aging Visual Cortex of Man

Abstract: Measured by a cell dispersion technique, the neuron population densities of the macular projection areas of 23 individuals aged 20 to 87 years fell from about 46 million neurons per gram of tissue of age 20 to about 24 million neurons per gram at age 80. A corresponding increase in glial cells was found in the gray and subjacent white matter. Since the older brains showed a significant decrease in mass, the decrease in neuron population density could only reflect an absolute loss of neurons proportional to or greater than the nearly 50% loss indicated by these data. Neuron death in the macular projection area of the human visual cortex is evidently a major factor in the loss of visual acuity in old age.

Constructing Lens Spaces by Surgery on Knots.

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Splanchnic somatostatin: a hormonal regulator of nutrient homeostasis.

Abstract: Free (approximately 1600 daltons) somatostatin-like immunoreactivity was identified in arterial plasma of dogs that had received a test meal. Neutralization of circulating somatostatin while the dogs were consuming a fatty meal increased the plasma concentrations of triglycerides, gastrin, pancreatic polypeptide, and insulin after the meal. It is concluded that, in the dog, somatostatin is a true hormone that regulates the movement of nutrients from the gut to the internal environment.

The diagnosis and treatment of renal cell carcinoma.

Abstract: Surgical excision remains the only method of curing renal cell carcinoma. Early ligation of the renal artery and vein, followed by radical nephrectomy with regional lymphadenectomy, seems to offer the best method of cure for patients with localized disease. Results of more extensive surgery have been encouraging, and surgical extirpation should be attempted even when the tumor involves the vena cava, adjacent organs, or a solitary kidney. Radiotherapy as a post-operative adjuvant has not been effective, and when used pre-operatively, may decrease local recurrence but does not appear to improve five-year survival. A chemotherapeutic agent capable of significantly altering the course of metastastic renal cell carcinoma has not been identified. Vinblastine, the most effective currently available drug, rarely produces tumor regression. Progestational agents seldom, if ever, cause tumor regression, though newer hormonal agents may be more promising. Data continue to accumulate documenting altered immune mechanisms in renal cancer patients. These studies have provided impetus for continued trials of immunotherapy, and several agents are being studied. The management of patients with metastases at the time of diagnosis remains controversial. A better understanding of the natural history of these patients suggests that palliative nephrectomy may be inappropriate except for severe symptoms and patients with resectable metastases. Intraarterial infarction, fellowed by palliative nephrectomy, may improve survival, perhaps by stimulating a general immune response.

Many-body quantum mechanics as a symplectic dynamical system

Abstract: An approach is formulated to the problem of obtaining approximate solutions to many-body quantum mechanics. The starting point is the representation of quantum mechanics as Hamiltonian mechanics on a symplectic manifold (phase space). It is shown that Dirac's variation of an action integral provides a natural mechanism for constraining the dynamics to symplectic submanifolds and gives rise to a hierarchy of approximate many-body theories of which Hartree-Fock, random-phase approximation, time-dependent Hartree-Fock, and the double commutator equations of motion formalism are special cases.

Chemotherapy Programs of the National Prostatic Cancer Project (NPCP).

Abstract: Results of the first nationally randomized trial of the National Prostatic Cancer Project revealed a demonstrable advantage for chemotherapy in the management of advanced disease (Stage D in relapse from endocrine therapy). Both cyclophosphamide and 5-Fluorouracil showed improved activity over standard therapy. A second trial for patients previously irradiated, with less tolerance to myelosuppressive agents, revealed an advantage for estramustine phosphate and streptozotocin over standard therapy. Subsequently completed trials have revealed activity for prednimustine and imidazole carboxamide (DTIC). Trials currently underway for newly-diagnosed Stage D and for Stage D disease clinically stable to diethylstilbestrol (DES) show promising activity for DES combined with cyclophosphamide. Current trials with single agents in advanced disease are comparing methyl-CCNU and hydroxyurea with cyclophosphamide; another is evaluating estramustine phosphate and vincristine alone and in combination. The use of chemotherapy in earlier staged patients as adjuvants to definitive surgery or irradiation is underway in two clinical trials, where the effect of cyclophosphamide and estramustine phosphate as long-term therapies is compared with no additional treatment.

Implant‐bone interface characteristics of bioglass dental implants

Abstract: Three-dimensional finite element analysis (FEA) has been used to determine the implant-bone interface characteristics of bioglass dental implants. The results of the FEA were verified by comparison with the results of mechanical testing performed on animal implant specimens. The results of the study showed that the assumption of a discontinuous change of elastic properties at the bone-implant interface was a poor assumption for the bioglass implants. Interface elastic moduli of 354.0, 155.0, and 47.0 MPa for conditions of 25, 50, and 100% tissue attachment were determined for the bioglass implants.

Recent Approaches to Fertility Control Based on Derivatives of LH-RH

Abstract: Publisher Summary This chapter discusses the recent approaches to fertility control based on derivatives of luteinizing hormone-releasing hormone (LH-RH). The most recent advances on antisera to LH-RH and the agonistic and antagonistic analogs of this hormone are reviewed. Among several contraceptive approaches presently being considered and developed is one based on analogs and derivatives of the hypothalamic hormone that controls the secretion of both LH and follicle-stimulating hormone (FSH) from the pituitary. The work with antisera to LH-RH should be continued to investigate the possibilities of temporary active immunization against LH-RH. The development of contraceptives based on inhibitory analogs of LH-RH that could be conveniently applied as a nasal spray and that would be free of undesirable side effects. Basic and clinical research should also be continued on the phenomena of paradoxical fertility inhibition by large doses of superactive long-acting LH-RH analogs. The possible use of various derivatives of LH-RH for fertility control is also emphasized in the chapter.

Identification of averantin as an aflatoxin B1 precursor: placement in the biosynthetic pathway.

Abstract: A new blocked mutant of Aspergillus parasiticus produces no detectable aflatoxin B1, but accumulates several polyhydroxyanthraquinones. One of these pigments was identified as averantin. This is the first report of its formation by A. parasiticus. Radiotracer studies with [14C]averantin showed that 15.3% of label from averantin was incorporated into aflatoxin B1. This incorporation was blocked by dichlorvos. With radiotracers and other mutants, averantin was placed after norsolorinic acid and before averufin in the biosynthetic pathway in which the general steps are norsolorinic acid leads to averantin leads to averufin leads to versiconal hemiacetal acetate leads to versicolorin A leads to sterigmatocystin leads to aflatoxin B1.