Development of a microbalance suitable for space application

The tapered element oscillating microbalance (TEOM), an ultrasensitive mass measurement device which is suitable for both particulate and vapor deposition measurements is described. The device can be used in contamination measurements, surface reaction studies, particulate monitoring systems or any microweighing activity where either laboratory or field monitoring capability is desired. The active element of the TEOM consists of a tube or reed constructed of a material with high mechanical quality factor and having a special taper. The element is firmly mounted at the wide end while the other end supports a substrate surface which can be composed of virtually any material. The tapered element with the substrate at the free (narrow) end is set into oscillation in a clamped free mode. A feedback system maintains the oscillation whose natural frequency will change in relation to the mass deposited on the substrate

Ice in space: An experimental and theoretical investigation

Basic knowledge is provided on the behavior of ice and ice particles under a wide variety of conditions including those of interplanetary space. This information and, in particular, the lifetime of ice particles as a function of solar distance is an absolute requirement for a proper interpretation of photometric profiles in comets. Because fundamental properties of ice and ice particles are developed in this report, the applicability of this information extends beyond the realm of comets into any area where volatile particles exist, be it in space or in the earth's atmosphere

Bond Orientational Order, Molecular Motion and Free Energy of High Density DNA Mesophases

By equilibrating condensed DNA arrays against reservoirs of known osmotic stress and examining them with several structural probes, it has been possible to achieve a detailed thermodynamic and structural characterization of the change between two distinct regions on the liquid crystalline phase digram: a higher-density hexagonally packed region with long-range bond orientational order in the plane perpendicular to the average molecular direction; and a lower-density cholesteric region with fluid-like positional order. X-rays scattering on highly ordered DNA arrays at high density and with the helical axis oriented parallel to the incoming beam showed a six-fold azimuthal modulation of the first order diffraction peak that reflects the macroscopic bond-orientational order. Transition to the less-dense cholesteric phase through osmotically controlled swelling shows the loss of this bond orientational order that had been expected from the change in optical birefringence patterns and that is consistent with a rapid onset of molecular positional disorder. This change in motion was previously inferred from intermolecular force measurements and is now confirmed by $\rm ^{31}P$ NMR. Controlled reversible swelling and compaction under osmotic stress, spanning a range of densities between $\sim 120$ mg/ml to $\sim 600$ mg/ml, allows measurement of the free energy changes throughout each phase and at the phase transition, essential information for theories of liquid-crystalline states.Comment: 14 pages, 3 figures in gif format available at http://abulafia.mgsl.dcrt.nih.gov/pics.html E-mail: [email protected]

Sharp interface limit for a phase field model in structural optimization

We formulate a general shape and topology optimization problem in structural optimization by using a phase field approach. This problem is considered in view of well-posedness and we derive optimality conditions. We relate the diffuse interface problem to a perimeter penalized sharp interface shape optimization problem in the sense of $\Gamma$-convergence of the reduced objective functional. Additionally, convergence of the equations of the first variation can be shown. The limit equations can also be derived directly from the problem in the sharp interface setting. Numerical computations demonstrate that the approach can be applied for complex structural optimization problems

Localisation in water wave and thin plate problems

Simulations obtained for water waves over rough seabed and waves in rough in vacuo plate. Attenuation rates of effective and individual wave fields extracted, compared and found to differ

Emitter-site selective photoelectron circular dichroism of trifluoromethyloxirane

The angle-resolved inner-shell photoionization of R-trifluoromethyloxirane, C3H3F3O, is studied experimentally and theoretically. Thereby, we investigate the photoelectron circular dichroism (PECD) for nearly-symmetric O 1s and F 1s electronic orbitals, which are localized on different molecular sites. The respective dichroic $\beta_{1}$ and angular distribution $\beta_{2}$ parameters are measured at the photoelectron kinetic energies from 1 to 16 eV by using variably polarized synchrotron radiation and velocity map imaging spectroscopy. The present experimental results are in good agreement with the outcome of ab initio electronic structure calculations. We report a sizable chiral asymmetry $\beta_{1}$ of up to about 9% for the K-shell photoionization of oxygen atom. For the individual fluorine atoms, the present calculations predict asymmetries of similar size. However, being averaged over all fluorine atoms, it drops down to about 2%, as also observed in the present experiment. Our study demonstrates a strong emitter- and site-sensitivity of PECD in the one-photon inner-shell ionization of this chiral molecule

Making FORS2 fit for exoplanet observations (again)

For about three years, it was known that precision spectrophotometry with FORS2 suffered from systematic errors that made quantitative observations of planetary transits impossible. We identified the Longitudinal Atmospheric Dispersion Compensator (LADC) as the most likely culprit, and therefore engaged in a project to exchange the LADC prisms with the uncoated ones from FORS1. This led to a significant improvement in the depth of FORS2 zero points, a reduction in the systematic noise, and should make FORS2 again competitive for transmission spectroscopy of exoplanets.Comment: To appear in the March issue of the ESO Messenge

NGC 3628: Ejection Activity Associated with Quasars

NGC3628 is a well-studied starburst/low level AGN galaxy in the Leo Triplet noted for its extensive outgassed plumes of neutral hydrogen. QSOs are shown to be concentrated around NGC3628 and aligned with the HI plumes. The closest high redshift quasar has z=2.15 and is at the tip of an X-ray filament emerging along the minor axis HI plume. Location at this point has an accidental probability of ~2x10^-4. In addition a coincident chain of optical objects coming out along the minor axis ends on this quasar. More recent measures on a pair of strong X-ray sources situated at 3.2 and 5.4 arcmin on either side of NGC3628 along its minor axis, reveal that they have nearly identical redshifts of z=0.995 and 0.981. The closer quasar lies directly in the same X-ray filament which extends from the nucleus out 4.1 arcmin to end on the quasar of z=2.15. The chain of objects SW along the minor axis of NGC3628 has been imaged in four colors with the VLT. Images and spectra of individual objects within the filament are reported. It is suggested that material in various physical states and differing intrinsic redshifts is ejected out along the minor axis of this active, disturbed galaxy.Comment: 8 pages, 5 figures. Accepted for publication in A&A. Postscript file including full resolution figures at http://www.eso.org/~fpatat/ngc3628/paper_ngc3628.ps.g

How to deal with non-detectable and outlying values in biomarker research: Best practices and recommendations for univariate imputation approaches

Non-detectable (ND) and outlying concentration values (OV) are a common challenge of biomarker investigations. However, best practices on how to aptly deal with the affected cases are still missing. The high methodological heterogeneity in biomarker-oriented research, as for example, in the field of psychoneuroendocrinology, and the statistical bias in some of the applied methods may compromise the robustness, comparability, and generalizability of research findings. In this paper, we describe the occurrence of ND and OV in terms of a model that considers them as censored data, for instance due to measurement error cutoffs. We then present common univariate approaches in handling ND and OV by highlighting their respective strengths and drawbacks. In a simulation study with lognormal distributed data, we compare the performance of six selected methods, ranging from simple and commonly used to more sophisticated imputation procedures, in four scenarios with varying patterns of censored values as well as for a broad range of cutoffs. Especially deletion, but also fixed-value imputations bear a high risk of biased and pseudo-precise parameter estimates. We also introduce censored regressions as a more sophisticated option for a direct modeling of the censored data. Our analyses demonstrate the impact of ND and OV handling methods on the results of biomarker-oriented research, supporting the need for transparent reporting and the implementation of best practices. In our simulations, the use of imputed data from the censored intervals of a fitted lognormal distribution shows preferable properties regarding our established criteria. We provide the algorithm for this favored routine for a direct application in R on the Open Science Framework (https://osf.io/spgtv). Further research is needed to evaluate the performance of the algorithm in various contexts, for example when the underlying assumptions do not hold. We conclude with recommendations and potential further improvements for the field