Fracture mechanics approach to design analysis of notches, steps and internal cut-outs in planar components

A new approach to the assessment and optimization of geometric stress-concentrating features is proposed on the basis of the correspondence between sharp crack or corner stressfield intensity factors and conventional elastic stress concentration factors (SCFs) for radiused transitions. This approach complements the application of finite element analysis (FEA) and the use of standard SCF data from the literature. The method makes it possible to develop closed-form solutions for SCFs in cases where corresponding solutions for the sharp crack geometries exist. This is helpful in the context of design optimization. The analytical basis of the correspondence is shown, together with the limits on applicability where stress-free boundaries near the stress concentrating feature are present or adjacent features interact. Examples are given which compare parametric results derived from FEA with closed-form solutions based on the proposed method. New information is given on the stress state at a 90° corner or width step, where the magnitude of the stress field intensity is related to that of the corresponding crack geometry. This correspondence enables the user to extend further the application of crack-tip stress-field intensity information to square-cornered steps, external U-grooves, and internal cut-outs

Characteristics of ferroelectric-ferroelastic domains in N{\'e}el-type skyrmion host GaV4_4S8_8

GaV$_4$S$_8$ is a multiferroic semiconductor hosting N{\'e}el-type magnetic skyrmions dressed with electric polarization. At T$_s$ = 42K, the compound undergoes a structural phase transition of weakly first-order, from a non-centrosymmetric cubic phase at high temperatures to a polar rhombohedral structure at low temperatures. Below T$_s$, ferroelectric domains are formed with the electric polarization pointing along any of the four $\left< 111 \right>$ axes. Although in this material the size and the shape of the ferroelectric-ferroelastic domains may act as important limiting factors in the formation of the N{\'e}el-type skyrmion lattice emerging below T$_C$=13\:K, the characteristics of polar domains in GaV$_4$S$_8$ have not been studied yet. Here, we report on the inspection of the local-scale ferroelectric domain distribution in rhombohedral GaV$_4$S$_8$ using low-temperature piezoresponse force microscopy. We observed mechanically and electrically compatible lamellar domain patterns, where the lamellae are aligned parallel to the (100)-type planes with a typical spacing between 100 nm-1.2 $\mu$m. We expect that the control of ferroelectric domain size in polar skyrmion hosts can be exploited for the spatial confinement and manupulation of N{\'e}el-type skyrmions

Quantitative Antibiotic Use in Hospitals: Comparison of Measurements, Literature Review, and Recommendations for a Standard of Reporting

Abstract : Background: : Reports on antibiotic use often lack complete definitions of the units of measurement, hampering the comparison of data between hospitals or hospital units. Patients and Methods: : To compare methods of measures of in-hospital antimicrobial use, we determined aggregate in-hospital consumption data at a tertiary care university hospital using variations of nominators and denominators. Means of defined daily doses (DDD) of individual antimicrobials per 100 bed-days and per 100 admissions at each hospital and intensive care unit (ICU) were calculated. Furthermore, a literature review was performed for benchmarking purposes. Results: : Antibiotic use in different hospital units ranged from 0.105 to 323.37 DDD/100 bed-days and from 4.23 to 6737.92 DDD/100 admissions, respectively. Including the day of discharge in the denominator ‘bed-days' underestimated antibiotic use in various hospital wards by up to 27.7 DDD/100 bed-days (26.0%). Equating ‘numbers of patients admitted to the hospital' and ‘numbers of admissions' on a hospital level resulted in a difference of 192.6 DDD/100 admissions (64%) because patients transferred between hospital units accounted for multiple admissions. Likewise, reporting antimicrobial (Anatomical Therapeutic Chemical [ATC] group ‘J') instead of antibiotic (ATC group ‘J01') use led to a difference of 16.5 DDD/100 bed-days (19.3%). The literature review revealed underreporting of complete definitions of antibiotic use measurements. Conclusions: : Data on in-hospital antimicrobial use vary widely not only due to different antibiotic policies at different institutions but also due to different methods of measures. Adherence to the standard of reporting the methods of measurement is warranted for benchmarking and promotion of rational antimicrobial us

Two-path self-interference in PTCDA active waveguides maps the dispersion and refraction of a single waveguide mode

Bound waveguide modes propagating along nanostructures are of high importance since they offer low-loss energy-/signal-transport for future integrated photonic circuits. Particularly, the dispersion relation of these modes is of fundamental interest for the understanding of light propagation in waveguides as well as of light-matter interactions. However, for a bound waveguide mode, it is experimentally very challenging to determine the dispersion relation. Here, we apply a two-path interference experiment on microstructured single-mode active organic waveguides that is able to directly visualize the dispersion of the waveguide mode in energy-momentum space. Furthermore, we are able to observe the refraction of this mode at a structure edge by detecting directional interference patterns in the back-focal plane

Optical Diagnostics on Helical Flux Compression Generators

Explosively driven magnetic flux compression (MFC) has been object of research for more than three decades. Actual interest in the basic physical picture of flux compression has been heightened by a newly started Department of Defense (DoD) Multi-University Research Initiative. The emphasis is on helical flux compression generators comprising a hollow cylindrical metal liner filled with high explosives and at least one helical coil surrounding the liner. After the application of a seed current, magnetic flux is trapped and high current is generated by moving, i.e., expanding, the liner explosively along the winding of the helical coil. Several key factors involved in the temporal development can be addresses by optical diagnostics. 1) The uniformity of liner expansion is captured by framing camera photography and supplemented by laser illuminated high spatial and temporal resolution imaging. Also, X-ray flash photography is insensitive to possible image blur by shockwaves coming from the exploding liner. 2) The thermodynamic state of the shocked gas is assessed by spatially and temporally resolved emission spectroscopy. 3) The moving liner-coil contact point is a possible source of high electric losses and is preferentially monitored also by emission spectroscopy. Since optical access to the region between liner and coil is not always guaranteed, optical fibers can he used to extract light from the generator. The information so gained will give, together with detailed electrical diagnostics, more insight in the physical loss mechanisms involved in MFC

Photoemission spectra of many-polaron systems

The cross over from low to high carrier densities in a many-polaron system is studied in the framework of the one-dimensional spinless Holstein model, using unbiased numerical methods. Combining a novel quantum Monte Carlo approach and exact diagonalization, accurate results for the single-particle spectrum and the electronic kinetic energy on fairly large systems are obtained. A detailed investigation of the quality of the Monte Carlo data is presented. In the physically most important adiabatic intermediate electron-phonon coupling regime, for which no analytical results are available, we observe a dissociation of polarons with increasing band filling, leading to normal metallic behavior, while for parameters favoring small polarons, no such density-driven changes occur. The present work points towards the inadequacy of single-polaron theories for a number of polaronic materials such as the manganites.Comment: 15 pages, 13 figures; final version, accepted for publication in Phys. Rev.

Ground-based lidar measurements from Ny-Ålesund during ASTAR 2007

During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) in March and April 2007, measurements obtained at the AWIPEV Arctic Research Base in Ny-Ålesund, Spitsbergen at 78.9&amp;deg; N, 11.9&amp;deg; E (operated by the Alfred Wegener Institute for Polar and Marine Research – AWI and the Institut polaire français Paul-Emile Victor – IPEV), supported the airborne campaign. This included lidar data from the Koldewey Aerosol Raman Lidar (KARL) and the Micro Pulse Lidar (MPL), located in the atmospheric observatory as well as photometer data and the daily launched radiosonde. The MPL features nearly continuous measurements; the KARL was switched on whenever weather conditions allowed observations (145 h in 61 days). From 1 March to 30 April, 71 meteorological balloon soundings were performed and compared with the concurrent MPL measurements; photometer measurements are available from 18 March. For the KARL data, a statistical overview of particle detection based on their optical properties backscatter ratio and volume depolarization can be given. The altitudes of the occurrence of the named features (subvisible and visible ice and water as well as mixed-phase clouds, aerosol layers) as well as their dependence on different air mass origins are analyzed. Although the spring 2007 was characterized by rather clean conditions, diverse case studies of cloud and aerosol occurrence during March and April 2007 are presented in more detail, including temporal development and main optical properties as depolarization, backscatter and extinction coefficients. Links between air mass origins and optical properties can be presumed but need further evidence