Effect of magnetism and light sp-dopants on chain creation in Ir and Pt break junctions.

Applying the generalization of the model for chain formation in break-junctions (Di Napoli et al 2012 J. Phys.: Condens. Matter 24 135501), we study the effect of light impurities on the energetics and elongation properties of Pt and Ir chains. Our model enables us to develop a tool ideal for detailed analysis of impurity-assisted chain formation, in which zigzag bonds play an important role. In particular we focus on H (s-like) and O (p-like) impurities and assume, for simplicity, that the presence of impurity atoms in experiments results in a ..M-X-M-X-... (M: metal, X: impurity) chain structure in between the metallic leads. Feeding our model with material-specific parameters from systematic full-potential first-principles calculations, we find that the presence of such impurities strongly affects the binding properties of the chains. We find that, while both types of impurities enhance the probability of chains being elongated, the s-like impurities lower the chain's stability. We also analyze the effect of magnetism and spin-orbit interaction on the growth properties of the chains.

Role of vacancies in metal-insulator transitions of crystalline phase-change materials.

The study of metal-insulator transitions (MITs) in crystalline solids is a subject of paramount importance, both from the fundamental point of view and for its relevance to the transport properties of materials. Recently, a MIT governed by disorder was observed in crystalline phase-change materials. Here we report on calculations employing density functional theory, which identify the microscopic mechanism that localizes the wavefunctions and is driving this transition. We show that, in the insulating phase, the electronic states responsible for charge transport are localized inside regions having large vacancy concentrations. The transition to the metallic state is driven by the dissolution of these vacancy clusters and the formation of ordered vacancy layers. These results provide important insights on controlling the wavefunction localization, which should help to develop conceptually new devices based on multiple resistance states.

Modeling impurity-assisted chain creation in noble-metal break junctions.

In this work we present the generalization of the model for chain formation in break junctions, introduced by Thiess et al (2008 Nano Lett. 8 2144), to zigzag transition-metal chains with s and p impurities. We apply this extended model to study the producibility trends for noble-metal chains with impurities, often present in break junction experiments, namely, Cu, Ag and Au chains with H, C, O and N adatoms. Providing the material-specific parameters for our model from systematic full-potential linearized augmented plane-wave first-principles calculations, we find that the presence of such impurities crucially affects the binding properties of the noble-metal chains. We reveal that both the impurity-induced bond strengthening and the formation of zigzag bonds can lead to a significantly enhanced probability for chain formation in break junctions.

Magnetically hindered chain formation in transition-metal break junctions.

Based on first-principles calculations, we demonstrate that magnetism impedes the formation of long chains in break junctions. We find a distinct softening of the binding energy of atomic chains due to the creation of magnetic moments that crucially reduces the probability of successful chain formation. Thereby, we are able to explain the long standing puzzle why most of the transition metals do not assemble as long chains in break junctions and thus provide indirect evidence that in general suspended atomic chains in transition-metal break junctions are magnetic.

Theory and application of chain formation in break junctions.

We introduce a generic model of chain formation in break junctions by formulating criteria for the stability and producibility of suspended monatomic chains based on total energy arguments. Using ab initio calculations including spin-polarization and spin-orbit coupling, we apply our model to the formation of monatomic 4d and 5d transition metal (TM) chains. We explain the physical origin of the experimentally observed general trend of increasing probability for the creation of long chains for late 5d TMs and suppressed chain formation for 4d TMs. We also clarify why the probability of chain elongation can be greatly enhanced by the presence of adsorbates in experiments.

[Helminth findings in indigenous raccoon dogs Nyctereutes procyonoides (Gray, 1843)]. / Helminthenfunde beim einheimischen Marderhund Nyctereutes procyonoides (Gray, 1834).

Internal organs of 74 racoon dogs originating from the eastern districts of the Federal Land Brandenburg were subjected to a complete helminthological dissection. In addition, samples of diaphragma muscles from 46 further animals were examined for Trichinella larvae. Altogether 3 trematode- (Alaria alata, Isthmiophora melis, Metorchis bilis), 3 cestode- (Mesocestoides sp., Echinococcus multilocularis, Taenia polyacantha) and 7 nematode species (Capillaria aerophila, C. plica, Trichinella spiralis, Uncinaria stenocephala, Molineus patens, Crenosoma vulpis, Toxocara canis) could be identified. Thereby, the racoon dog has a comparable helminth spectrum as well known in red foxes. Differences in the frequency of the occurrence of helminths in both hosts can be explained by different food preferences.

Occupational health experience with organic additives.

For many decades, interest in occupational medicine has been focused on the wide variety of organic additives, which includes a large number of substances, for example, dyestuffs, pigments, and auxiliaries for the textile, leather, and paper industries. The reason is that, if the recommended precautions are not observed, there is a risk of exposure to most of these substances during both production and use. Moreover, over the years, some additives have caused concern and aroused suspicion regarding adverse effects on health. In order to deal with health problems in this field, it is important to be aware of how, what, and where occupational diseases or accidents arise. Much knowledge has been gained about these, and it would be an impossible task to give a systematic survey of the data that have accumulated, especially since it is necessary to take account of the problem of exposure to more than one substance. Thus an attempt is made to report on occupational health experience in general, and to demonstrate how an industrial hygienist may approach the many and various problems. Some epidemiological studies on organic additives (auramine, anthraquinone dyestuffs, organic dyes, etc.) are discussed.

Chromosome investigations of workers exposed to cadmium in the manufacturing of cadmium stabilizers and pigments.

Chromosome analyses were undertaken on 14 workers exposed to cadmium and the results were compared with a corresponding control group. All probands have been employed for many years in cadmium pigment and stabilizer production plants (between 6 and 25 years). The results of the clinical investigations were, for the most part, unspecific, although at the same time some parameters were above the normal (transaminase, beta 2-microglobulin deposit in the urine, as well as cadmium in the blood and urine). The chromosome analyses were undertaken on the lymphocytes of the peripheral blood with the aid of the so-called "micromethod." Metaphases, 150 per person, were analyzed. The statistical evaluation was made according to the Fisher-Yates test. The chromosome aberration rate of the group investigated was not higher than that of the control group, inclusive and exclusive of gaps.

Mortality study of persons exposed to dioxin in a trichlorophenol-process accident that occurred in the BASF AG on November 17, 1953.

Twenty-seven years after an accident which occurred in the BASF, Ludwigshafen plan in 1953, a mortality study of persons exposed to dioxin in an uncontrolled reaction during a trichlorophenol process was undertaken. The follow-up was 100% successful and involved 74 persons. Overall mortality (21 deaths) did not differ in this group from the rate expected in three external reference populations or from that observed in two internal comparison groups, where 18-20 deaths were observed. Of the 21 deceased persons, 7 had cancer, compared with 4.1 expected. In addition, two other cases of cancer (one bronchial carcinoma, and one carcinoma of the prostate) are still alive. Three deaths due to stomach cancer, at ages 64, 66, and 69 years, were found, compared with 0.6 expected from regional mortality data. One stomach cancer occurred among 148 individuals in the two comparison cohorts.