Experimental realization of a π/2 vortex mode converter for electrons using a spherical aberration corrector.

In light optics, beams with orbital angular momentum (OAM) can be produced by employing a properly-tuned two-cylinder-lens arrangement, also called π/2 mode converter. It is not possible to convey this concept directly to the beam in an electron microscope due to the non-existence of cylinder lenses in commercial transmission electron microscopes (TEMs). A viable work-around are readily-available electron optical elements in the form of quadrupole lenses. In a proof-of-principle experiment in 2012, it has been shown that a single quadrupole in combination with a Hilbert phase-plate produces a spatially-confined, transient vortex mode. Here, an analogue to an optical π/2 mode converter is realized by repurposing a CEOS DCOR probe corrector in an aberration corrected TEM in a way that it resembles a dual cylinder lens using two quadrupoles. In order to verify the presence of OAM in the output beam, a fork dislocation grating is used as an OAM analyser. The possibility to use magnetic quadrupole fields instead of, e.g., prefabricated fork dislocation gratings to produce electron beams carrying OAM enhances the beam brightness by almost an order of magnitude and delivers switchable high-mode purity vortex beams without unwanted side-bands.

On the residual six-fold astigmatism in DCOR/ASCOR.

After the introduction of the hexapole Cs-correctors for scanning transmission electron microscopes (STEM), the next big step forward was the strong reduction of the six-fold astigmatism A5 by means of an advanced hexapole design (DCOR/ASCOR). As a result all axial aberrations up to fifth order are sufficiently small to allow for large semi-aperture angles beyond 40 mrad for electron energies in the range of 30 to 300 kV without deterioration of the STEM resolution. In this paper we derive simple expressions for the optimum hexapole strength for minimum A5 and the size of the residual A5. Both quantities are intrinsic properties of the hexapoles and the transfer lens doublet in between. The optimum hexapole strength scales with the inverse of the electron wavelength, while the residual A5 does not depend on the electron energy directly, but on the spherical aberration Cs of the pole piece. With the given properties of the DCOR/ASCOR and typical values of Cs in the range of 0.5 to 2.7 mm, at all acceleration voltages A5 remains in the range from 0.03 to 0.4 mm, the latter even for a large-gap pole piece.

π/2 mode converters and vortex generators for electrons.

In optics, mode conversion is an elegant way to switch between Hermite Gaussian and Laguerre Gaussian beam profiles and thereby impart orbital angular momentum onto the beam and to create vortices. In optics such vortex beams can be produced in a setup consisting of two identical cylinder lenses. In electron optics, quadrupole lenses can be used for the same purpose. Here we investigate generalized asymmetric designs of a quadrupole mode converter that may be realized within the constraints of existing electron microscopes and can steer the development of dedicated vortex generators for high brilliance electron vortex probes of atomic scale.

Transmission electron microscopy at 20 kV for imaging and spectroscopy.

The electron optical performance of a transmission electron microscope (TEM) is characterized for direct spatial imaging and spectroscopy using electrons with energies as low as 20 keV. The highly stable instrument is equipped with an electrostatic monochromator and a C(S)-corrector. At 20 kV it shows high image contrast even for single-layer graphene with a lattice transfer of 213 pm (tilted illumination). For 4 nm thick Si, the 200 reflections (271.5 pm) were directly transferred (axial illumination). We show at 20 kV that radiation-sensitive fullerenes (C(60)) within a carbon nanotube container withstand an about two orders of magnitude higher electron dose than at 80 kV. In spectroscopy mode, the monochromated low-energy electron beam enables the acquisition of EELS spectra up to very high energy losses with exceptionally low background noise. Using Si and Ge, we show that 20 kV TEM allows the determination of dielectric properties and narrow band gaps, which were not accessible by TEM so far. These very first results demonstrate that low kV TEM is an exciting new tool for determination of structural and electronic properties of different types of nano-materials.

Double aberration correction in a low-energy electron microscope.

The lateral resolution of a surface sensitive low-energy electron microscope (LEEM) has been improved below 4 nm for the first time. This breakthrough has only been possible by simultaneously correcting the unavoidable spherical and chromatic aberrations of the lens system. We present an experimental criterion to quantify the aberration correction and to optimize the electron optical system. The obtained lateral resolution of 2.6 nm in LEEM enables the first surface sensitive, electron microscopic observation of the herringbone reconstruction on the Au(111) surface.

Information transfer in a TEM corrected for spherical and chromatic aberration.

For the transmission electron aberration-corrected microscope (TEAM) initiative of five U.S. Department of Energy laboratories in the United States, a correction system for the simultaneous compensation of the primary axial aberrations, the spherical aberration Cs, and the chromatic aberration Cc has been developed and successfully installed. The performance of the resulting Cc /Cs-corrected TEAM instrument has been investigated thoroughly. A significant improvement of the linear contrast transfer can be demonstrated. The information about the instrument one obtains using Young's fringe method is compared for uncorrected, Cs-corrected, and Cc /Cs-corrected instruments. The experimental results agree well with simulations. The conclusions might be useful to others in understanding the process of image formation in a Cc /Cs-corrected transmission electron microscope.

Current and future aberration correctors for the improvement of resolution in electron microscopy.

The achievable resolution of a modern transmission electron microscope (TEM) is mainly limited by the inherent aberrations of the objective lens. Hence, one major goal over the past decade has been the development of aberration correctors to compensate the spherical aberration. Such a correction system is now available and it is possible to improve the resolution with this corrector. When high resolution in a TEM is required, one important parameter, the field of view, also has to be considered. In addition, especially for the large cameras now available, the compensation of off-axial aberrations is also an important task. A correction system to compensate the spherical aberration and the off-axial coma is under development. The next step to follow towards ultra-high resolution will be a correction system to compensate the chromatic aberration. With such a correction system, a new area will be opened for applications for which the chromatic aberration defines the achievable resolution, even if the spherical aberration is corrected. This is the case, for example, for low-voltage electron microscopy (EM) for the investigation of beam-sensitive materials, for dynamic EM or for in-situ EM.

Detection of single atoms and buried defects in three dimensions by aberration-corrected electron microscope with 0.5-A information limit.

The ability of electron microscopes to analyze all the atoms in individual nanostructures is limited by lens aberrations. However, recent advances in aberration-correcting electron optics have led to greatly enhanced instrument performance and new techniques of electron microscopy. The development of an ultrastable electron microscope with aberration-correcting optics and a monochromated high-brightness source has significantly improved instrument resolution and contrast. In the present work, we report information transfer beyond 50 pm and show images of single gold atoms with a signal-to-noise ratio as large as 10. The instrument's new capabilities were exploited to detect a buried Sigma3 {112} grain boundary and observe the dynamic arrangements of single atoms and atom pairs with sub-angstrom resolution. These results mark an important step toward meeting the challenge of determining the three-dimensional atomic-scale structure of nanomaterials.

Sorption and transport of 17beta-estradiol and testosterone in undisturbed soil columns.

Land-applied domestic animal wastes contain appreciable amounts of 17beta-estradiol (henceforth, estradiol) and testosterone. These sex hormones may be transported through soil to groundwater and streams, where they may adversely affect the environment. Previous column transport studies with these hormones used repacked soil and did not consider preferential flow. We, therefore, determined the sorption and transport characteristics of estradiol and testosterone in undisturbed soil columns (15-cm i.d. by 32-cm height). In the sorption experiment, isotherms for estradiol and testosterone were nonlinear with Freundlich exponents (n) less than one. Sorption of both hormones decreased with soil depth, and estradiol sorbed more strongly than testosterone. Average estradiol Freundlich sorption coefficients (K(f)) values were 36.9 microg(1 - n) mL(n) g(-1) for the 0- to 10-cm soil depth and 25.7 microg(1 - n) mL(n) g(-1) for the 20- to 30-cm soil depth. Average testosterone K(f) values were 26.7 microg(1 - n) mL(n) g(-1) for the 0- to 10-cm soil depth and 14.0 microg(1 - n) mL(n) g(-1) for the 20- to 30-cm soil depth. In the transport experiment, 27% of the estradiol and 42% of the testosterone leached through the soil columns. Approximately 50% of the remaining soil-bound hormones were sorbed in the top 10 cm of soil. In almost all instances, breakthrough concentrations of estradiol, testosterone, and a chloride tracer peaked simultaneously. Simultaneous breakthrough and HYDRUS-1D transport parameters indicated both chemical and physical nonequilibrium processes affected hormone transport. This suggests hormones placed on soil surfaces may contaminate groundwater under conditions of preferential flow.

Phytoremediation of pyrene in a Cecil soil under field conditions.

We evaluated the effects of annual ryegrass (Lolium multiflorum Lam.) and phosphorus (P) availability on the dissipation of pyrene added at a concentration of approximately 600 mg kg-1 dry soil in the top 7.5 cm of a Cecil loamy sand (fine, kaolinitic, thermic Typic Kanhapludults) in a 10-month experiment under field conditions in Clemson, South Carolina. Plastic canopies were installed to prevent flooding of plots and raindrop dispersion of pyrene. Treatment factors were pyrene, vegetation, and available P levels. Each of the eight treatments had four replicates. The soil was adjusted to low and high P concentrations (an average of 41 and 66 kg extractable P ha-1, respectively). After a 175-d lag period for all treatments, the rate of pyrene removal followed first-order kinetics. The first-order rate constant was significantly higher in nonvegetated (0.098 d-1) than vegetated treatments (0.034 d-1). These data suggest that the presence of easily biodegradable organic matter from plant roots slowed the removal rate of pyrene. The levels of available P did not affect the rate of pyrene dissipation. Pyrene decreased below the detection limit of 6.25 mg kg-1 dry soil in all treatments after 301 d.

Putative temporal variability of Escherichia coli ribotypes from yearling steers.

Escherichia coli is a ubiquitous component of the intestinal microflora of warm-blooded animals, and is an indicator of fecal contamination of surface waters. Ribotype profiling of E. coli is one of several genotypic methods that has been developed to determine the host origin of fecal bacteria. Like most genotypic methods of source tracking, ribotyping requires a host origin database to identify environmental isolates. To determine the extent of temporal variability of ribotypes and its effect on a host origin database, E. coli isolates were obtained from fecal samples of two herds of Black Angus steers at a long-term experimental site at four sampling times from October 1999 to July 2000. Fecal samples were taken from six randomly chosen steers at each time. At a similarity index of 90% as calculated by unweighted pair-group method using arithmetic averages (UPGMA), 240 ribotypes were identified from 451 E. coli isolates. Only 20 ribotypes (8.3%), comprising 33% of the total isolates, were shared among sampling times and were considered resident ribotypes. Two of the twenty resident ribotypes appeared at three sampling times, and the remaining eighteen appeared at two. The majority of the ribotypes, therefore, were transient and unique to each sampling time and steer. Both the apparent turnover of E. coli ribotypes and a clonal diversity index of 0.97 (indicative of extensive ribotype variability) suggest the necessity of ribotyping a large number E. coli isolates per host to establish a host origin database that is independent of temporal variability, or complete enough to be effective.

Association of carbon disulfide with plants in the family Fabaceae.

We examined 40 taxa from nine genera within the subfamily Mimosoideae; 29 (73%) from six genera produced carbon disulfide (CS2). In addition, 19 of 40 taxa (48%) produced carbonyl sulfide (OCS). Of nine mimosoid taxa that produced CS2, all possessed a djenkolic acid and a cysteine lyase. Of three mimosoid taxa that did not produce CS2, two lacked a cysteine lyase and one lacked both a lyase and a djenkolic acid. Of 16 taxa from 14 genera from the other two subfamilies of the Fabaceae, the Caesalpinioideae and Papilionoideae, none produced CS2. The results suggest that CS2 production is common in the Mimosoideae and uncommon in the Caesalpinioideae and Papilionoideae and that plants in the Mimosoideae that do produce CS2 must possess both a djenkolic acid and a cysteine lyase for this production to occur.

Finance modeling in the delivery of medical care in tertiary-care hospitals in the Department of Veterans Affairs.

BACKGROUND: In the mid-1990s, the Department of Veterans Affairs (DVA) implemented the Veterans Equitable Resource Allocation (VERA), a new financial model developed to attempt to better distribute the approximately $18 billion annual budget among roughly 170 Veterans Administration Medical Centers (VAMCs). VERA is based on a Health Maintenance Organization (HMO) model. VERA provides reimbursement to each of the 22 regional Veterans Integrated Service Networks (VISNs), and subsequent VISN distribution to individual VAMCs is based on an individual medical center's enrollment of unique social security numbers (uniques). In HMO vocabulary these are individual "covered lives." METHODS: Currently available demographic and staffing information regarding the DVA's 23 tertiary hospital systems (Category 7 hospitals) on the KLF database (DVA Austin Data Base) and published information on the DVA website were reviewed. The following was obtained: (1) staffing information-physician and nurse full-time employment equivalent (FTEE) staffing; (2) patient demographics and hospital workload-facility uniques (u), outpatient facility uniques, average daily census (ADC), discharges, and outpatient clinic visits. The following staffing ratios were calculated for both physician and nursing: FTEE/(u/1000), FTEE/(discharges/1000), FTEE/(clinic visits/1000), FTEE/ADC. For all categories the means +/- SD were calculated and correlation coefficients were calculated on pertinent pairings. RESULTS: Although categorized as similar tertiary care facilities, the 23 "Group 7" VA hospitals are anything but equivalent when reviewed using the VERA financing model with respect to physician staffing, nurse staffing, and facility uniques. Using VERA methodology, average physician FTEE and total nursing FTEE staffing/(u/1000) are 3.67 +/- 0.89 and 15.53 +/- 3.77, respectively. Correlation statistics of staffing versus unique SSNs demonstrated correlation coefficients of 0.46 and 0.59 with respect to physician and nurse staffing, respectively. On the other hand, when physician FTEE and nursing FTEE staffing were compared with VAMC workload parameters (total ADC, discharges, and outpatient visits), correlation coefficients were more consistent, ranging from 0.62 to 0.86. CONCLUSIONS: In the VERA model, the reward of a larger annual budget for an individual VAMC or the regional VISN is realized when staffing of VAMCs is minimized, overall provided medical services (especially costly tertiary services) are limited, and the number of covered lives is maximized. A VAMC staffing system that equates medical services delivered in a tertiary VAMC setting based on an HMO model like VERA (where the user population is skewed toward the sicker, older patient) shows decreased correlation when compared with VAMC workload model parameters.

[Plastic surgery treatment of blepharochalasia with ptosis]. / Die plastisch-chirurgische Behandlung der ptosiformen Blepharochalasis.

Ptosiform blepharochalasis is not only an esthetic but also a functional problem for the elderly patient. In clinical terms there is an extension of the lid skin over upper-lid margin, a relaxation of the orbicularis muscle and a large amount of periorbital fat. The operation involves resection of the excess skin by an elliptical excision, shortening of the orbicularis muscle, and resection of the fat pads from two compartments. Postoperatively there is only edema, but no pain, which is important for the elderly.

Presence of a Vanadium Nitrogenase in Azotobacter paspali.

There have been no previous studies on the genetics of Azotobacter paspali, an aerobic bacterium which forms a highly specific diazotrophic association with Bahia grass (Paspalum notatum). We constructed A. paspali strains defective in the molybdenum nitrogenase so that alternative N(2)ases could be studied. The cosmid vector pTBE and genomic DNA fragments ( approximately 50 kb) of A. paspali ATCC 23367 were used to construct a gene library in Escherichia coli. Recombinant cosmids containing sequences homologous to molybdenum nitrogenase nifDK structural genes were identified by hybridization. A 2.9-kb fragment bearing the putative nifDK genes of A. paspali was subcloned and mutagenized in vitro by the insertion of a kanamycin resistance gene cassette. The mutation was recombined into the chromosome of A. paspali with the suicide vector pCU101. One resultant mutant strain, AP2, was incapable of diazotrophic growth in a molybdenum-containing medium (Nif) without vanadium but grew well in a molybdenum-deficient medium with vanadium. The nitrogenase system in AP2 reduced acetylene to ethylene and produced ethane as 2.4% of the total products. Molybdenum levels as low as 10 nM prevented the diazotrophic growth of AP2, even in the presence of vanadium at levels up to 10 muM. These results are consistent with the existence of a vanadium nitrogenase system in A. paspali.

The Role of Microbes Associated with Chicken Litter in the Suppression of Meloidogyne arenaria.

The role of microbes associated with chicken litter in the suppression of Meloidogyne arenaria in amended soil was investigated. Amended soil treatments were prepared, including combinations of sterile and nonsterile chicken litter and soil. Microbial biomass in different treatments was compared by measuring carbon dioxide evolution. There was less CO evolved in sterile litter than in nonsterile litter treatments. Tomato seedlings cv. Rutgers were transplanted into soil mixtures and inoculated with 2,000 M. arenaria eggs. After 10 days, fewer second-stage juveniles (J2) had penetrated the roots in soils amended with nonsterile litter than sterile litter. The effects of sterile and nonsterile litter-amended soil solutions on M. arenaria eggs and J2 were observed over a period of 6 days. A lower percentage of eggs remained apparently healthy in nonsterile than in sterile-amended soil solutions over 6 days. Microbial degradation of the egg shells was apparent. Fewer J2 survived in sterile- and nonsterile-amended-soil solutions as compared to water controls.