Neutron spin-flip scattering of nanocrystalline cobalt.

We report results of longitudinal (one-dimensional) neutron polarization analysis on polycrystalline bulk Co with an average crystallite size of D = 10 nm. The spin-flip small-angle neutron scattering (SANS) data are analyzed in the approach-to-saturation regime within the framework of micromagnetic theory. In particular, we provide a closed-form expression for the spin-flip SANS cross section [Formula: see text]. From the data analysis, we find a room-temperature value of A = (2.6 ± 0.1) × 10( - 11) J m( - 1) for the exchange-stiffness constant, which agrees well with earlier data.

Dipolar structures in magnetite ferrofluids studied with small-angle neutron scattering with and without applied magnetic field.

Field-induced structure formation in a ferrofluid with well-defined magnetite nanoparticles with a permanent magnetic dipole moment was studied with small-angle neutron scattering (SANS) as a function of the magnetic interactions. The interactions were tuned by adjusting the size of the well-defined, single-magnetic-domain magnetite (Fe3O4) particles and by applying an external magnetic field. For decreasing particle dipole moments, the data show a progressive distortion of the hexagonal symmetry, resulting from the formation of magnetic sheets. The SANS data show qualitative agreement with recent cryogenic transmission electron microscopy results obtained in 2D [Klokkenburg, Phys. Rev. Lett. 97, 185702 (2006)] on the same ferrofluids.

Field-induced pseudocrystalline ordering in concentrated ferrofluids.

Concentrated surfactant stabilized cobalt ferrofluids up to 6 vol % Co have been studied by small-angle scattering using polarized neutrons and synchrotron x rays. The combination of these techniques allowed the magnetic and nuclear form factors to be reliably separated from the structure factors. Above 1 vol % Co, inter particle interactions are induced by an applied external magnetic field that gives rise to pseudocrystalline ordering of cobalt core-shell particles. Particles are arranged in hexagonal planes, with the magnetic moments aligned parallel to the [110] direction. Two types of equivalent textures were found to be present simultaneously, corresponding to a stacking of the hexagonal planes in horizontal and vertical direction. The in-plane nearest-neighbor distance is almost independent of the concentration and temperatures, whereas the distance between the neighboring planes, c, strongly varies from sample to sample. In addition, segments of chains of particles with parallel moments are aligned along the magnetic field and frozen-in when the carrier liquid is solidified. The field induced pseudocrystalline lamellar hexagonal particle arrangement, observed experimentally in colloidal magnetic liquids, confirms predictions from molecular-dynamics and Monte Carlo simulations.

Occurrence and levels of indicator bacteriophages in bathing waters throughout Europe.

Somatic coliphages, F-specific RNA bacteriophages, bacteriophages infecting Bacteroides fragilis, Escherichia coli and enterococci were counted in bathing waters in the late spring and summer. We tested fresh and marine bathing waters from North, South, East and West Europe expected to contain between 100 and 500 E. coli per 100 ml, although wider ranges were sometimes found. Bacteriophages were counted after concentration, since a preliminary study proved that this step was necessary to obtain positive counts. During monitoring, a first-line quality control with reference materials for bacteria and bacteriophages was performed by all the laboratories participating in the study. The same microbes were also counted in raw sewage samples from various areas in Europe, where the bacterial indicators and the three groups of bacteriophages were detected in roughly the same numbers. All groups of bacteriophages were detected in both fresh and marine bathing waters throughout Europe. Reliable and complete results from 147 samples showed that for log-transformed values, E. coli and bacteriophages were slightly correlated. However, the slope of the regression line changed according to E. coli concentration and the correlation diminished when this concentration was close to zero per 100 ml. The ratios between E. coli and phages in bathing waters differed significantly from those in sewage. The relative amounts of bacteriophages, mainly somatic coliphages and phages infecting Bact. fragilis RYC2056, increased in bathing waters with low E. coli concentration, especially in seawater samples containing < 100 E. coli per 100 ml. The relationship of bacteriophages with respect to enterococci paralleled that of bacteriophages with respect to E. coli. Somatic coliphages and bacteriophages infecting Bact. fragilis are useful to predict the presence of some pathogens with the same origin as present bacterial indicators but with higher survival rates.

A case report of false negative Legionella test results in a chlorinated public hot water distribution system due to the lack of sodium thiosulfate in sampling bottles.

We examined samples from the showers and the central water distribution system of a public building with an indoor swimming pool. The pool was used for school and recreational activities and as a sports therapy facility for patients with coronary heart disease. The building's hot water system was contaminated with Legionella pneumophila. Due to the building's intricate piping system, several attempts to completely eliminate legionellae by thermal and chemical disinfection had failed, so an external sanitation company was charged with the installation of a continuous chlorination device in order to keep Legionella concentrations low. The laboratory which was contracted by the sanitation company to monitor bacteria levels after installation of the chlorination device used sampling bottles without sodium thiosulfate and repeatedly reported an absence of Legionella. However, up to 69,000 colony forming particles (CFP) of Legionella pneumophila (Lp) per litre and up to 171 CFP/ml of heterotrophic bacteria could be detected when parallel samples were collected in bottles containing sodium thiosulfate at standard concentrations. Laboratories, epidemiologists, public health officials and technical staff who may be in charge of delivering, preparing or using sterile sampling devices for the collection of environmental samples to be tested for legionellae should be aware that cultures can return false negative results if the sampling containers used to collect chlorinated drinking water or chlorinated pool water samples do not contain a neutralizing agent to instantly inactivate residual halogen biocides. False negative results may lead to a false sense of security regarding the safety of water systems or the success of disinfection measures, and may thus endanger public health or even hinder the epidemiological clarification of outbreaks.

Economic factors and the rates of suicide in Germany between 1881 and 1989.

The potential consequence of economic stress most frequently cited in the literature of medical sociology is the increase in the rate of suicide, it probably being the most valid and reliable indicator of collective mental health. To assess the probability of such being the consequence of current economic realignment in the Federal Republic of Germany, we deemed it promising to evaluate the extent to and manner in which economic factors have to date affected the frequency of suicide in Germany. The current study analyzed the effects of four economic variables (growth of the economy, average real income, unemployment and frequency of bankruptcy) on the rates of suicide in Germany from 1881 to 1989. We set the commencement date of the period analyzed as early as possible to include long-term developments as well as the effects of different moderator variables. The annual fluctuations of all four variables, in conformity with our hypothesis, correlated both in the period preceding World War II as well as in the postwar period with those in the rates of suicide. The strongest correlations held for the rate of unemployment and for the frequency of bankruptcy in times of obvious social disintegration coupled with diminished state safeguards against unemployment. Our hypothesis that the effects of economic factors would more strongly influence the rates of suicide by men as opposed to women could not be corroborated.

Dynamics of field-induced ordering in magnetic colloids studied by new time-resolved small-angle neutron-scattering techniques.

The reversal of magnetic moments of nanoparticles in concentrated Co ferrofluids was monitored in an oscillating magnetic field by new time-resolved stroboscopic small-angle neutron-scattering techniques. Time resolution in the micros range was achieved by using a pulsed beam technique, TISANE, while in continuous mode resolution was limited by the wavelength spread to about 1 ms. The frequency dependence of anisotropic scattering patterns has been modeled using Langevin dynamics. The dynamics follows a two step mechanism: field-induced ordering is governed by fast Brownian rotation of nanoparticles with a characteristic time of about 160 micros. Magnetic relaxation of locally ordered domains of about 100 nm in size takes place within a few seconds by Brownian rotation or by Néel type rotation of magnetic moments.

[The EU Bathing Water Directive. Risk assessment and standards]. / Die Novelle der EU-Badegewässerrichtlinie. Aspekte der Risikobewertung bei der Grenzwertsetzung.

In an attempt to reduce the risk of infection in natural bathing waters the European Union is in the process of improving the Bathing Water Directive 76/160/EWG, which regulates the safety of such waters. The proposal contains several positive innovations which will improve the protection of the bathers: (1) health-related indicators, (2) harmonized detection methods, (3) requirements for active bathing water management, and (4) stricter standards for coastal waters. One of the most salient features of the current draft is the introduction of bacterial standards that are more stringent for coastal than for fresh waters. This decision on different standards seems unjustified: it was taken solely on the grounds that in two epidemiological studies-one carried out in coastal, the other in fresh waters-the maximum excess rate of gastroenteritis among bathers in coastal waters was higher than among bathers in fresh waters. However, it was not taken into account that the concentrations of bacterial indicators at which the gastroenteritis rate began to increase was nearly identical in both studies. The ratio between the standard concentrations of E. coli and intestinal enterococci in the draft was set at 2.5. This value does not correspond to the ratio found in German surface waters with low pollution levels, with ratios ranging from 2.7 to 4.0, and to the even higher ratios found in raw and treated sewage effluents. As a consequence in a majority of cases the non-compliance of bathing waters in Germany would be caused exclusively by a violation of E. coli standards. In assessing risks of infection it must also be taken into account that the adequacy of E. coli and intestinal enterococci for signaling the presence of viruses in water is far from optimal. The decay of viruses in water-estimated by the decay of bacteriophages-was found to be substantially slower than the die-off of indicator bacteria.

The impact of availability, attraction and lethality of suicide methods on suicide rates in Germany.

Substantial fluctuations have prevailed in both the rate and particular methods of suicide in the Federal Republic of Germany during the past 40 years. The current study examines the extent to which the availability, attraction and lethality of particular methods of suicide affect suicide rates. A close relationship existed in the period from 1949 and 1989 between the peaks of the suicide rate and the percentage of low threshold suicide methods according to De Catanzaro, whereby suicide in this context is understood to mean suicide by shooting or intake of solid, liquid or gaseous poisons. Our hypothetically expected lesser compensation between high and low threshold methods for women was confirmed. Between 1963 and 1976 the rate of suicide committed using domestic gas receded dramatically. Within the same period, however, the rate of suicide committed using other poisons rose accordingly.

Testing Durkheim's theory of suicide: additional results from Germany.

In a recent study of 14 European countries, Lester (1993), using inference statistical techniques, confirmed Durkheim's (1897) observation that lower birth rates were associated with higher suicide rates in 1870 and 1980. Due to changes in national boundaries, Germany was excluded from these analyses. Among the federal states of Germany, Bavaria most suitably lends itself to a study of the relationship between suicide and familial integration over time. A long-term analysis of the years between 1865 and 1980 reveals a prominent reciprocal relationship (r = -0.87; P < 0.001) between rates of suicide and birth in Bavaria. Marriage rates, on the other hand, correlate only minimally (r = -0.19 ns) with rates of suicide. Our results accord with Durkheim's view that unlike birth rates, higher marriage rates per se are only slightly associated with suicide rates.

[Enterobacteria as quality criteria in unprocessed, drinking and swimming pool water. Comparative study of the occurrence of enterobacteria, Escherichia coli, coliforms, colony count, fecal streptococci and Pseudomonas aeruginosa]. / Enterobakterien als Qualitätskriterium bei Roh-, Trink- und Badewasser. Vergleichende Untersuchung über das Vorkommen von Enterobakterien, Escherichia coli, coliformen Keimen, Koloniezahl, Fäkalstreptokokken und Pseudomonas aeruginosa.

Between 1985 and 1986 2064 samples of raw-, drinking- and swimming-pool-waters from Southwest-Germany have been examined according to German Drinking-Water Standards as well as for the occurrence of Enterobacteria, fecal streptococci and Pseudomonas aeruginosa. With the exception of Pseudomonas aeruginosa all parameters showed a statistically verified dependence on each others occurrence, which was most significant between the two criteria "Escherichia coli" and "fecal streptococci". The results of the investigation increased the doubts concerning the value of "coliforms" as a quality criterion. Enterobacteria seem to be a suitable quality criterion for waters which have received a disinfecting treatment.

Selective detection of viable Cryptosporidium oocysts by PCR.

Although the diagnosis of cryptosporidiosis in diarrheic patients is relatively simple, as large amounts of oocysts are usually shed, environmental samples can contain only few oocysts which have a comparatively high epidemiological relevance. Very sensitive detection methods are therefore requested in environmental hygiene. Additionally these methods should allow a statement about the viability of the detected organisms. The combination of a DNA-digest and a viability assay followed by a PCR might reveal a very promising method. A DNA-digest destroys free DNA in the sample. In the following excystation protocol only viable sporozoites excyst. A PCR carried out now gives definitive proof of viable oocysts. Dead sporozoites within intact oocyst-walls are not detected.

Expression of the fragile site Xq27 in fibroblasts. I. Detection of fra(X)(q27) in fibroblast clones from males with X-linked mental retardation.

Twelve fibroblast clones from two males with X-linked mental retardation expressed the fragile site Xq27 in 3%-38% of metaphases analyzed. The number of in vitro doublings during the cloning procedure had no evident influence on the induction of fragile X expression. The variability of fragile X expression seems to depend on cell properties acquired during culture rather than on properties originally inherent in the cells.

Manifestation of the fragile site Xq27 in fibroblasts. III. A method to demonstrate R-type replication patterns and the fragile site.

A protocol is reported which allows the efficient induction of bromodeoxyuridine (BrdU)-induced R-type replication patterns in fibroblast cultures prepared to demonstrate the fragile site fra(X)(q27). The technique includes partial synchronization of the culture by fluorodeoxyuridine (FdU) blocking at the G1/S transition. This block does not impair the induction of the fragile site in medium 199 containing methotrexate. The marked increase of the mitotic index in the synchronized culture may be an advantage in the study of folic acid sensitive fragile sites in fibroblasts. Adding BrdU after block removal leads to an efficient labeling of replicating chromosomes without severely impairing the manifestation of fra(X)(q27).

Structural changes of the Escherichia coli GroEL-GroES chaperonins upon complex formation in solution: a neutron small angle scattering study.

We applied neutron scattering in conjunction with deuterium (D-) labeling in order to obtain information about the domain structure of GroEL and GroES isolated and in the complex. Each subunit of the heptameric GroES consists of two domains, a core domain (Met1 to Lys15 and Lys34 to Ala97) and an intervening loop region (Glu16 to Ala33). Neutron scattering shows that both regions change their conformation upon GroEL/GroES complex formation. The interdomain angle between the core regions of the heptameric GroES increases from 120 to 140 degrees, leading to a less dome-like shape of GroES, and the loop regions turn inwards by 75 degrees. The 23 C-terminal amino acids of the 14 GroEL subunits (Lys526 to Met548), which are unresolved in the crystal structure, are located either at the bottom of the cavity formed by the seven-membered GroEL ring or at the inner wall of the cavity. Upon complex formation the apical domains of GroEL move outwards, which facilitates binding of GroES at a Gro-EL-GroES center-to-center distance of (87 +/- 8) A. These structural changes may be important for the dissociation of the unfolded protein bound to the central cavity upon GroES binding. The overall structure determined by neutron scattering in solution tallies with the crystallographic model published after completion of this study. Differences in the conformation of GroES observed in the complex by the two methods support the view that the chaperonin complex is a flexible molecule which might switch in solution between different conformations.

The Surface Geometry of Vycor

The interface geometry of Vycor porous glass was examined by adsorption of water in conjunction with small-angle scattering of X rays and neutrons. When the sample is dry, a fractal surface with a fractal dimension D approximately 2.5 was detected. When wet, a soft hydrogel is formed, resulting in a diffuse boundary. To observe a fractal surface, thorough drying of the sample is necessary, however. It was shown that a small amount of water, 3% w/w, is sufficient to render the surface smooth. Copyright 1997Academic Press