Mechanism of void growth in irradiated NaCl based on exiton-induced formation of divacancies at dislocations

We propose a mechanism of void growth in di-atomic ionic crystals due to agglomeration of divacancies produced by interactions between dislocations and excitons. An exciton can cause movement of nearby dislocation jogs, resulting in the creation of equal numbers of anion and cation vacancies (Schottky defects). Owing to the heat generated locally during the exciton annihilation, the jog can be displaced while a divacancy arises in the lattice. Subsequent diffusion and agglomeration of divacancies can result in void formation and growth. We evaluate the void nucleation and growth rates in electron irradiated NaCl. (C) 2004 Elsevier B.V. All rights reserved

Effect of sitagliptin on cardiovascular outcomes in type 2 diabetes

BACKGROUND: Data are lacking on the long-term effect on cardiovascular events of adding sitagliptin, a dipeptidyl peptidase 4 inhibitor, to usual care in patients with type 2 diabetes and cardiovascular disease. METHODS: In this randomized, double-blind study, we assigned 14,671 patients to add either sitagliptin or placebo to their existing therapy. Open-label use of antihyperglycemic therapy was encouraged as required, aimed at reaching individually appropriate glycemic targets in all patients. To determine whether sitagliptin was noninferior to placebo, we used a relative risk of 1.3 as the marginal upper boundary. The primary cardiovascular outcome was a composite of cardiovascular death, nonfatal myocardial infarction, nonfatal stroke, or hospitalization for unstable angina. RESULTS: During a median follow-up of 3.0 years, there was a small difference in glycated hemoglobin levels (least-squares mean difference for sitagliptin vs. placebo, -0.29 percentage points; 95% confidence interval [CI], -0.32 to -0.27). Overall, the primary outcome occurred in 839 patients in the sitagliptin group (11.4%; 4.06 per 100 person-years) and 851 patients in the placebo group (11.6%; 4.17 per 100 person-years). Sitagliptin was noninferior to placebo for the primary composite cardiovascular outcome (hazard ratio, 0.98; 95% CI, 0.88 to 1.09; P<0.001). Rates of hospitalization for heart failure did not differ between the two groups (hazard ratio, 1.00; 95% CI, 0.83 to 1.20; P = 0.98). There were no significant between-group differences in rates of acute pancreatitis (P = 0.07) or pancreatic cancer (P = 0.32). CONCLUSIONS: Among patients with type 2 diabetes and established cardiovascular disease, adding sitagliptin to usual care did not appear to increase the risk of major adverse cardiovascular events, hospitalization for heart failure, or other adverse events

Stored energy of heavily irradiated NaCl

Radiolysis of NaCl at moderate temperatures (50-150 degrees C) is a rather complicated process, which is affected by the dose, dose rate, irradiation temperature, impurities, dislocations, etc. In the literature until now the attention was focused at the development during irradiation of F-, and F-aggregate centers, colloids, hole centers such as H, V-k, V-F-centers, etc, and dislocation lines and structures. We have observed colloid fractions as high as 15% in some of the heavily irradiated NaCl samples. For several doped samples the production of colloids is not in agreement with the (modified) Jain-Lidiard model. In addition, this model does not account for the production of voids during irradiation. In this paper some characteristic features of the production of the stored energy associated with the radiation-induced defects will be presented

Dipoles in solid solutions Sr1-xGdxF2+x

In this paper we present new results on the dielectric relaxation behavior of solid solutions of the type Sr1-xGdxF2+x. Attention will be paid to dipole relaxation peaks associated with two different complexes: (a) the nearest-neighbor (NN) Gd3+-Fi- dipole and (b) the next-nearest-neighbor (NNN) Gd3+-Fi- center. The experiments have been carried out in the frequency range from 100 to 3×104 Hz. From the behavior of the NN and NNN dipole relaxation bands as a function of the excitation frequency, we have determined the energy difference between the two different dipole configurations to be about 0.050 eV. In addition, we have studied the intensity of the dipole bands as a function of the concentration (x) of Gd3+ ions. It is possible to explain the observed behavior of the intensity of the dipole relaxation peaks as a function of x without the need of assuming that there is extensive clustering of Gd3+ impurities. We propose to divide the dipoles into two different groups: The first one contains dipoles that are not disturbed severely by extremely close dipoles, contributing to the dipole relaxation peak; the second group of dipoles, which are at close distances from at least a second dipole, contributes significantly to the dc-ionic-conduction process

Depolarization experiments on space charges in concentrated solid solutions of NdF3 in SrF2

The influence of the defect concentration on the relaxation of space charges in Sr1-xNdxF2+x solid solutions has been investigated with the ionic-thermocurrent technique. A concentration domain of 0.004 up to 45 mol% has been used. As in the system Ba1-xLaxF2+x the space-charge relaxation band (high-temperature band) shifts to lower temperatures with increasing RF3 concentration. A percolation model has been used to explain these shifts. Most of the differences between the systems Sr1-xNdxF2+x and Ba1-xLaxF2+x are reducible to different dipolelike jumps supporting the charge transport: nearest-neighbor dipolelike jumps in Sr1-xNdxF2+x and next-nearest-neighbor dipolelike jumps in Ba1-xLaxF2+x. The charge transport may be interpreted qualitatively with a percolation mechanism

Radiation damage in NaCl. I. Optical-absorption experiments on heavily irradiated samples

Results of optical-absorption experiments on heavily irradiated NaCl single crystals are presented. The dose rates were between 4 and 250 Mrad/h; the doses between 1 and 7 Grad. The irradiation temperatures were in the range of 20-150-degrees-C. Because of the intense optical bands, the thickness of the samples had to be reduced to values between 2 and 100 mum using a thinning device. With this device we are able to investigate samples containing about 1 mol % Na and Cl2. The optical spectra of the samples, irradiated at low temperatures, show intense F, M, R, and N bands. The positions of the optical bands of the electron excess centers are in agreement with the literature. With increasing irradiation temperature, the contribution of these centers to the total amount of radiation damage decreases due to coagulation to colloidal Na particles. The colloid band, however, is much wider than the literature values; in addition, it is located at longer wavelengths. These observations can be explained by assuming that we are dealing with extremely small colloids, showing appreciable quantum size effects

Kinetics of back reaction between radiolytic products initiated by radiation-induced voids in NaC1

A time-dependent model is formulated for the chemical reaction between sodium colloids and gas bubbles, which are brought into contact with each other by the growing voids. It is shown that in this exothermic reaction, heat is released much faster than it is dissipated by conduction to the surrounding salt. This results in a large and sudden temperature and pressure increase in the void, which is analysed in detail. The effect on the mechanical stability of NaCl under irradiation is discussed