Formation of surface color centers at differently coordinated sites: MgO/Ag(1,1,19)

In order to find criteria for discrimination between surface color centers at terraces and steps, and bulk color centers, the characteristic losses of these centers have been investigated by electron energy loss spectroscopy on an epitaxial MgO film grown on a Ag (1,1,19) surface. This film contains a significantly higher step density compared with a film grown on Ag(100). The generation of four distinct losses at 2.0, 2.4, 2.8, and 3.4 eV and a broad loss centered at 5.5 eV have been observed that are induced by electron bombardment of the MgO surface. The latter loss is attributed to bulk color centers (Fb centers). By comparing the measured loss energies with experiments performed on MgO/Ag(100) and with theoretical literature data, the observed losses at 2.0 and 2.8 eV can be consistently assigned to transitions of color centers located on step sites, whereas those at 2.4 and 3.4 eV are attributed to terrace sites. The kinetics of color center formation during electron bombardment, as well as the annihilation of F centers by simple exposure to O2 gas at room temperature, was determined and compared for differently coordinated color centers. While all surface color centers follow the same kinetics, we show that the Fb centers can only decay as long as the existence of surface color centers provides active sites for dissociating oxygen molecules. This corroborates the assignment of Fb centers. © 2003 The American Physical Societ

Prostaglandin-independent protection by furosemide from oliguric ischemic renal failure in conscious rats

Prostaglandin-independent protection by furosemide from oliguric ischemic renal failure in conscious rats. In 38 conscious rats divided into seven groups, acute unilateral ischemic renal failure was induced by 1 hour of complete occlusion of the left renal artery while the contralateral kidney remained intact. Renal excretory function of the left kidney was monitored up to 144 hours after ischemia and revealed a typical course of oliguric renal failure with oligoanuria persisting for more than 48 hours. Urinary osmolality and sodium concentration became plasma isotonic after release of renal artery occlusion and approximated control values on day 6 after ischemia. In nine rats, the i.v. infusion of furosemide before (6 µg/min/100g body wt) and after (12 µg/min/ 100g body wt) renal artery occlusion protected the ischemic kidney from oligoanuria with endogenous creatinine clearance of 0.42 ± 0.11 ml/min/g kidney wt 5 hours after ischemia. Tubular absorption of sodium and water was at least partially preserved 36 hours after ischemia when infusion of furosemide was stopped. The loop diuretic significantly (P < 0.01) increased total urinary prostaglandin (PG) E2 excretion before and after renal artery occlusion; and 5 hours after ischemia, PGE2 excretion from the ischemic kidney significantly exceeded that from the intact kidney (P < 0.05). Indomethacin (1 mg/100g body wt) administered in six animals markedly suppressed control PGE2 excretion (P < 0.05) as well as the furosemide-induced rise in urinary PG excretion before and after ischemia but did not modify the protective effect of the diuretic in this experimental model. Inhibition of PG synthesis, however, reduced urinary flow rate and sodium and potassium excretion of the contralateral intact kidney and almost completely prevented its compensatory rise in creatinine clearance. The results indicate that mechanisms other than the intrarenal prostaglandin system must be considered to mediate the protective effects of furosemide in acute ischemic renal failure.Protection par le furosemide, indépendante des prostaglandins, de l'insuffisance rénale oligurique et ischémique chez le rat éveillé. Trente huit rats éveillés, répartis en sept groupes, ont été mis en insuffisance rénale aiguë ischémique unilatérale par occlusion complète de l'artère rénale gauche pendant 1 heure alors que le rein controlatéral était intact. La fonction excrétoire du rein a été surveillée pendant 144 heures après l'ischémie et elle a subi l'évolution typique de l'insuffisance rénale oligurique avec persistance de l'oligo-anurie pendant plus de 48 heures. L'osmolalité urinaire et la concentration de sodium sont devenues égales à celles du plasma après la levée de l'occlusion artérielle rénale et se sont rapprochées des valeurs contrôles au sixième jour après l'ischémie. Chez neuf rats la perfusion de furosemide avant (6 µg/min/100g poids corporel) et après (12 µg/ min/100g poids corporel) l'occlusion de l'artère rénale a protégé le rein ischémique de l'oligo-anurie, avec des clearances de la créatinine de 0,42 ± 0,11 ml/min/g de rein 5 heures après l'ischémie. La réabsorption tubulaire de sodium et d'eau était au moins partiellement préservée 36 heures après l'ischémie quand la perfusion de furosemide était arrêtée. Ce diurétique augmente significativement (P < 0,01) l'excrétion urinaire de prostaglan-dines (PG) E2 avant et après l'occlusion de l'artère rénale; 5 heures après l'ischémie l'excrétion de PGE2 par le rein lésé est significativement supérieure à celle du rein intact (P < 0,05). L'indométhacine (1 mg/100g poids corporel) administrée à six animaux diminue considérablement l'excrétion basale de PGE2 (P < 0,05) de même que l'augmentation, dépendante du furosémide, de l'excrétion urinaire de PG avant et après l'ischémie, mais ne change pas l'effet protecteur du diurétique dans ce modèle expérimental. L'inhibition de la synthèse de PG, cependant, diminue le débit urinaire et l'excrétion de sodium et de potassium du rein intact et empêche presque complètement l'augmentation compensatrice de la clearance de la créatinine. Ces résultats indiquent que d'autres mécanismes que le système des prostaglandines intrarénales doivent être invoqués comme médiateurs des effets protecteurs du furosémide dans l'insuffisance rénale aiguë ischémique

Impaired response of the denervated kidney to endothelin receptor blockade in normotensive and spontaneously hypertensive rats

Impaired response of the denervated kidney to endothelin receptor blockade in normotensive and spontaneously hypertensive rats.BackgroundAs yet, there are only limited data available on the exact role of endothelin (ET) acting through endothelin-A (ETA) receptors in renal sodium and water regulation and the potential functional implications of an interaction of the renal ET system with renal nerves in normotensive and spontaneously hypertensive rats.MethodsExperiments were carried out in 64 male conscious spontaneously hypertensive rats and in 56 normotensive Wistar-Kyoto (WKY) rats. Bilateral renal denervation (BRD) was performed in 32 spontaneously hypertensive rats and 28 WKY rats 7days before the experiments. The ETA receptor antagonist, BQ-123 (16.4nmol/kg.min intravenously) or the endothelin-B (ETB) receptor antagonist, BQ-788 (25nmol/kg.min intravenously) were infused at a rate of 25 μL/min for 50 minutes.ResultsRenal papillary ET-1 concentration in intact spontaneously hypertensive rats was 67.8% lower than in intact WKY rats (154 ± 40 fmol/mg protein vs. 478 ± 62 fmol/mg protein, P < 0.01). BRD decreased papillary ET-1 by 73.5% in WKY rats to 127 ± 19 fmol/mg protein (P < 0.001), but had no effect in spontaneously hypertensive rats (122 ± 37 fmol/mg protein). BRD, BQ-123, or BQ-788 did not affect glomerular filtration rate (GFR) or renal blood flow (RBF) in any of the groups. In intact WKY, BQ-123 decreased urine flow rate (V) from 4.65 ± 0.44 μL/min.100g body weight to 2.44 ± 0.35 μL/min.100g body weight (P < 0.01), urinary excretion of sodium (UNaV) from 238.2 ± 27.4 to 100.2 ± 17.0 (P < 0.01) and potassium (UKV) from 532.1 ± 62.6nmol/min.100g body weight to 243.0 ± 34.2nmol/min.100g body weight (P < 0.001), whereas BQ-788 decreased only V and UNaV. In renal denervated WKY, BQ-123 or BQ-788 did not alter V, UNaV, or UKV. In intact spontaneously hypertensive rats BQ-123 but not BQ-788 decreased V from 3.94 ± 0.48 μL/min.100g body weight to 2.55 ± 0.44 μL/min.100g body weight (P < 0.05). In renal denervated spontaneously hypertensive rats neither BQ-123 nor BQ-788 affected V, UNaV, or UKV.ConclusionAn interaction between ET and renal nerves is involved in the control of renal function. Moreover, renal nerves participate in the regulation of ET-1 production within the kidney. Finally, decreased synthesis of ET-1 in the renal papilla of spontaneously hypertensive rats may contribute to development and/or maintenance of hypertension due to modulation of renal excretory function

Comparative case study of change in the electricity industries in New Zealand and The Gambia

This thesis examines the content and process of change associated with deregulation of the electricity industries in New Zealand and The Gambia by studying the scope of change, the process of implementation, the obstacles to change and the outcomes of change. The study employs a case study methodology using semi-structured interviews for primary data collection. A total of fifty-one respondents comprising senior managers, consultants and administrators were interviewed in both countries. Both manual and computer-aided analyses was carried out. Apart from providing a better understanding of the change process, the study makes three contributions to the literature on organisational change. First, it shows that internally initiated, controlled and implemented change processes are more likely to achieve their desired outcomes compared to change processes initiated, controlled and implemented from outside the organisation. Second, it demonstrates the crucial role of trust in facilitating effective change. Third, it illustrates the importance of the selection process in establishing and nurturing trust in organisations

Lyapunov exponents, one-dimensional Anderson localisation and products of random matrices

The concept of Lyapunov exponent has long occupied a central place in the theory of Anderson localisation; its interest in this particular context is that it provides a reasonable measure of the localisation length. The Lyapunov exponent also features prominently in the theory of products of random matrices pioneered by Furstenberg. After a brief historical survey, we describe some recent work that exploits the close connections between these topics. We review the known solvable cases of disordered quantum mechanics involving random point scatterers and discuss a new solvable case. Finally, we point out some limitations of the Lyapunov exponent as a means of studying localisation properties.Comment: LaTeX, 23 pages, 3 pdf figures ; review for a special issue on "Lyapunov analysis" ; v2 : typo corrected in eq.(3) & minor change

Centerscope

Centerscope, formerly Scope, was published by the Boston University Medical Center "to communicate the concern of the Medical Center for the development and maintenance of improved health care in contemporary society.

Evaluation Research and Institutional Pressures: Challenges in Public-Nonprofit Contracting

This article examines the connection between program evaluation research and decision-making by public managers. Drawing on neo-institutional theory, a framework is presented for diagnosing the pressures and conditions that lead alternatively toward or away the rational use of evaluation research. Three cases of public-nonprofit contracting for the delivery of major programs are presented to clarify the way coercive, mimetic, and normative pressures interfere with a sound connection being made between research and implementation. The article concludes by considering how public managers can respond to the isomorphic pressures in their environment that make it hard to act on data relating to program performance.This publication is Hauser Center Working Paper No. 23. The Hauser Center Working Paper Series was launched during the summer of 2000. The Series enables the Hauser Center to share with a broad audience important works-in-progress written by Hauser Center scholars and researchers

Bostonia: The Boston University Alumni Magazine. Volume 10

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

Реконструкция котла ПК-38 на Назаровской ГРЭС в г. Назарово Красноярского края

В работе рассматривается реконструкция котла ПК-38, работающего на твердом топливе Назаровского месторождения. Приведены конструктивные характеристики топки и всех поверхностей нагрева, произведен поверочный расчет котельного агрегата.The paper reviews the reconstruction of the PK-38 boiler, which operates on solid fuel at the Nazarovo deposit. The design characteristics of the furnace and all heating surfaces are presented, and the boiler unit is calibrate