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.

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.

Morbidity among persons employed in styrene production, polymerization and processing plants.

BASF has been producing styrene and polystyrene since 1931. An investigation of morbidity was undertaken for 84 workers employed in the styrene plant and exposed for 1--36 years and 93 workers employed in the polystyrene plant and exposed for 1--38 years. In all groups the concentration of styrene in the atmosphere was measured at various points of the workplace. All workers underwent a thorough physical examination and also extensive laboratory tests, including the determination of urinary mandelic acid. The absenteeism and accident rates were also taken into consideration in both plants. Blood samples were also taken and mandelic acid tests made on a small group of 16 persons employed in polyester processing plants not attached to the BASF.

Mutagenicity study of workers employed in the styrene and polystyrene processing and manufacturing industry.

Mutagenicity studies were undertaken on lymphocytes from the following groups of persons exposed to styrene or polystyrene: one group from a styrene manufacturing plant, one from a polystyrene plant, and three from plants processing unsaturated polyester resins with different manufacturing methods. For all the groups the concentration of styrene in the atmosphere of the workplace was measured at various points and the amount of urinary mandelic acid was determined. In each case 100 metaphases were analyzed for chromosomal aberrations. The results were compared with reference groups.

Survey of mortality among employees engaged in the manufacture of styrene and polystyrene at the BASF Ludwigshafen works.

A mortality survey of 1,960 employees currently or previously exposed to styrene at work has shown that the observed number of deaths from cancer or other causes is no higher than the number expected in the German population or in a group of BASF employees. Analyses of deaths occurring after a minimum period of five years in groups exposed for different durations (5 years, 10 years, 15 years, more than 15 years) indicated no increase in mortality with exposure time. This latter observation also applied to malignant tumors; therefore it may be inferred that prolonged exposure to styrene is not a cancer hazard.

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.

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.

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.

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.

Mutagenicity of vinyl chloride. External chromosome studies on persons with and without VC illness, and on VC exposed animals.

Chromosome analysis was undertaken on lymphocyte cultures taken from (1) six workers with estimated exposure to VC and four workers with monitored exposure to VC (employed in the BASF); (2) 20 workers showing symptoms of VC illness with unknown exposure and one angiosarcoma case, due to VC exposure (not employed in the BASF); and, (3) on bone marrow cells of Chinese hamsters after inhalation of 2,500 ppm or 5,000 ppm, or after intraperitoneal injections of 300 mg/kg or 600 mg/kg. The proband groups showing symptoms of VC illness, the only living angiosarcoma case, and the animal test show a significant increase in the rate of aberrations in comparison to the control group.

Analysis of chromosomes of workers exposed to acrylonitrile.

Examination of 18 workers who had been exposed to acrylonitrile for 15.3 years on average and 18 workers who had not been exposed to acrylonitrile showed no difference in the incidence of chromosome aberrations; for each person concerned 100 metaphases were evaluated.

Chromosome investigations on workers exposed to styrene/polystyrene.

Chromosomes investigations were undertaken on 12 employees with three to 34 years possible exposure to styrene in order to determine if there was a possibility of chromosome impairment. The data did not reveal any significant differences between persons exposed to styrene and members of the control group. The concentrations of styrene at the workplace were far below the MAC value and also the mandelic acid content of the urine was far below the norm.

[Women in the chemical industry. Occupational medicine problems]. / Die Frau in der chemischen Industrie. Arbeitsmedizinische Probleme.

Report on women working in the chemical industry. Attention is drawn to the occupational medicine problems: sex-specific physical differences, occupational protection for women, rate of sickness -- absences, accidents, problems regarding health, double amount of stress -- part-time employment, health awareness of the working women, precautional and rehabilitation measures, and measures beneficial to health.

[Occupational vitiligo caused by para-tertiary-butylphenol, a trias of vitiligo, hepatosis and struma]. / Berufsbedingte Vitiligo durch para-tertiär-Butylphenol, eine Trias von Vitiligo, Hepatose und Struma

In the period between 1956-1974 twelve cases of occupational vitiligo due to para-tertiary butylphenol were observed. In addition another 12 cases of vitiligo of other etiology occurred. Occupational vitiligo cannot be distinguished from ordinary vitiligo. 21 patients had, aside from their leukodermia a normal thyroid function, and 18 patients showed symptoms of chronic liver damage. The trias of vitiligo, hepatic disease and struma euthyreotica was noticeable. Autoimmunisation tests were positive in cases of vitiligo of unknown etiology. The localization of vitiligo may be compared to viscero-cutaneous reflexes.

[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.

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.

[The problems of lipid metabolism. Demands for diagnostically improved insight into the function of lipoproteins (author's transl)]. / Zur Problematik des Fettstoffwechsels. Anforderungen an Diagnostik - verbesserter Einblick in die Funktion der Lipoproteine.

In the course of a follow-up of 87 subjects with known hyperlipoproteinemia a new, simplified method was tested for quantification of the individual lipoprotein fractions capable of being performed by every larger laboratory, in contrast to the expensive ultracentrifugation. The LDL/HDL ratio proved to be the conclusive parameter for daily diagnosis in hospital and general practise. This enabled the most important aspects of the lipid metabolic situation of a patient to be recognized immediately.