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Recently, in an intercomparison of the Hohenheim German oak chronology (Becker 1993) and the Göttingen chronology (Leuschner and Delorme 1988), an error was discovered in the former (Leuschner, in preparation). Due to an error in adding sections at 5241 bc, 41 yr are missing in the published Hohenheim chronology. After correction of the error, the two chronologies synchronize over their entire common length, back to 7200 bc.
We present the first speckle interferometric observations of R CrB, the prototype of a class of peculiar stars which undergo irregular declines in their visible light curves. The observations were carried out with the 6 m telescope at the Special Astrophysical Observatory near maximum light (V = 7, 1996 Oct. 1) and at minimum light (V = 10.61, 1999 Sep. 28). A spatial resolution of 75 mas was achieved in the K-band. The dust shell around R CrB is partially resolved, and the visibility is approximately 0.8 at a spatial frequency of 10 cycles/arcsec. The two-dimensional power spectra obtained at both epochs do not show any significant deviation from circular symmetry. The visibility function and spectral energy distribution obtained near maximum light can be simultaneously fitted with a model consisting of the central star and an optically thin dust shell with density proportional to r−2 and amorphous carbon as its constituent. The inner boundary of the shell is found to be 82 R* (19 mas) with a temperature of 920 K near maximum light. However, this simple model fails to simultaneously reproduce the visibility and spectral energy distribution obtained at minimum light. We show that this discrepancy can be attributed to thermal emission from a newly formed optically thick dust cloud. Simultaneous fits of the observed SED and visibility with models including a thermally emitting dust cloud suggest the presence of a newly formed dust cloud as hot as 1200 K with a radius of 4 – 5R*, in addition to an optically thin dust shell whose inner boundary is ~ 170 R* with a temperature of ~ 690 K. Alternatively the discrepancy can be attributed to an unusual extinction curve of dust grains in the obscuring cloud which was present in front of the star at minimum light. The details of the observations and modeling are described in Ohnaka et al. (2001, A&A 380, 212).
The center of the stellar association in 30 Doradus, R136 (HD 38268), is an unusually high concentration of massive and bright O, B and Wolf-Rayet stars and represents the closest example of an intense starburst region.
Observations of a fairly regular sunspot penumbra near disk center have been carried out using a Stokes V polarimeter at the German Vacuum-Tower-Telescope in Izaña, Tenerife. We obtained two-dimensional spectral data by scanning the limb oriented sector of the penumbra in steps of 1” with the slit parallel to the solar limb. From Stokes V and Stokes I spectra of four magnetic sensitive lines (Fe I 5247.1, Cr I 5247.6, Fe I 5250.2, and Fe I 5250.7) obtained with 1024 × 1024 pixel CCDs we have determined Doppler shifts and several magnetic parameters. The results of a correlation analysis point out a clear relation between continuum brightness and magnetic field inclination in the sense of steeper field lines in the bright penumbral filaments. There is also a doubtless connection between intensity and Doppler shift. We did find indications for a correlation between field strength and brightness which is not uniform across the penumbra, though.
The Hawthorne Effect is a prevalent observer effect that causes behavioral changes among participants of epidemiological studies or infection control interventions. The purpose of the review is to describe the origins of the Hawthorne Effect, to understand the term in relation to current scientific literature, to describe characteristics of the Hawthorne effect, and to discuss methods to quantify and overcome limitations associated with the Hawthorne Effect.
Infect. Control Hosp. Epidemiol. 2015;36(12):1444–1450
The presence of multiple fields during inflation might seed a detectable amount of non-Gaussianity in the curvature perturbations, which in turn becomes observable in present data sets like the cosmic microwave background (CMB) or the large scale structure (LSS). Within this proceeding we present a fully analytic method to infer inflationary parameters from observations by exploiting higher-order statistics of the curvature perturbations. To keep this analyticity, and thereby to dispense with numerically expensive sampling techniques, a saddle-point approximation is introduced whose precision has been validated for a numerical toy example. Applied to real data, this approach might enable to discriminate among the still viable models of inflation.
Obesity and sedentary lifestyle are associated with increased oxidative stress, inflammation and vessel dysfunction. Previous research has shown that an encapsulated fruit/berry/vegetable juice powder (FBV) supplement or controlled exercise training improve the markers of redox biology, low-grade inflammation and circulation. The aim of the present study was to assess the effects of 8 weeks of supplementation with FBV or placebo, and a single bout of controlled walking on the markers of oxidation, inflammation and skin capillary microcirculation in forty-two obese pre-menopausal women (41 (sd 5) years, non-smokers and BMI 34·5 (sd 3·8) kg/m2) using a randomised, double-blind, placebo-controlled design. All assessments were made before and after 8 weeks of capsule supplementation, and pre- and post-30 min of controlled treadmill walking at 70 % of VO2max. Venous blood was collected for the determination of carbonyl proteins (CP), oxidised LDL (ox-LDL), total oxidation status (TOS) of lipids, malondialdehyde, TNF-α and IL-6. Capillary blood flow, O2 saturation of Hb (SO2Hb) and the relative concentration of Hb (rHb) were assessed at a 2 mm skin depth. Following 8 weeks of supplementation, compared with placebo, the FBV group had a significant (P< 0·05) reduction in CP, ox-LDL, TOS and TNF-α, and a significant increase in blood flow, SO2Hb and rHb. Independent of supplementation, moderate exercise significantly increased blood flow and rHb, with a trend towards increased SO2Hb. Compared with placebo, 8 weeks of supplementation with FBV decreased the markers of systemic oxidation and inflammation. Both FBV supplementation and a single walking bout improved the markers of the microcirculation in these obese women.
We present an infrared spectroscopic ellipsometry investigation of SixNy films deposited on textured Si substrates employed for photovoltaic cells. A multiple-sample data analysis scheme is used in order to determine the SixNy dielectric function and thickness parameters regardless of the surface morphology of the substrate. We observe changes in the dielectric function of the silicon nitride film which suggest variations in the chemical composition of the films depending on the substrate morphology.
Stoichiometric FePt nanoparticles with sizes in the range 3 – 6 nm were prepared in the gas-phase and thermally sintered prior to deposition. Whereas unsintered particles exhibit irregular shapes and a low degree of crystallinity, the majority of the sintered particles are multiply twinned and have predominantly icosahedral structure. There is no indication for the occurance of L10 ordering in the gas-phase sintered particles, although previous post-deposition annealing experiments of unsintered particles had shown the occurrence of partial formation of the L10 FePt intermetallic phase. On the other hand, analysis of the structural data obtained from (high resolution) electron microscopy shows that the relative amount of icosahedral particles increases with increasing sintering temperature. This result is discussed on the basis of a structure model of an irregular icosahedron, which is built up from distorted tetrahedral building blocks. The distortion in each tetrahedron is in accordance with the tetragonally compressed unit cell of the L10-phase.
Octanethiol-stabilized Si nanocrystals, ranging from 2 to 8 nm in diameter, were synthesized in cyclohexane heated and pressurized above its critical point at temperatures ranging from 400°C to 500°C. The nanocrystals exhibit crystalline cores and photoluminesce with relatively high efficiencies. These nanocrystals are suitable for single particle spectroscopic measurements that reveal optical information about the individual chromophores that are buried in ensemble measurements. The sterically-stabilized Si nanocrystals emit with relatively narrow emission spectra at room temperature, characteristic of molecules.
We report the synthesis of a series of highly functional metal chelated silyl- and tert-butyl-protected 2, 3-diaminomethyl norbornene derivatives. Subsequent alterations to the previously synthesized norbornene adducts afford many other derivatives containing such functionalities as alkyl, cyano, esters, and ethers. These derivatives are then subjected to ring-opening metathesis polymerization (ROMP) employing a ruthenium homogeneous catalyst to afford phase separated block polymers. The block polymers formed serve as unique templates for the formation of size controlled metal nanoclusters having a narrow dispersion. These metal nanoclusters containing diblock polymers are evaluated as unique electrical and optical materials.
The defect properties of as-etched, annealed and thermally oxidized nano-porous Si as well as self supporting macro-porous silicon layers are studied by electron paramagnetic resonance (EPR), photoluminescence (PL), optically detected magnetic resonance (ODMR), and electron nuclear double resonance (ENDOR). The paramagnetic defects observed are dangling bonds closely related to the Pb-center, the Si/SiO2 interfacial defect. In EPR a minimum defect density of 1016 cm−3 is observed for as-etched material, it reaches a maximum of 8 x 1018 cm−3 for samples annealed around 400°C. We quantitatively correlate the defect density with hydrogen desorption data and luminescence efficiency. In the ODMR experiments the same dangling bond centers are observed on the 1.7 eV luminescence band, but with increased sensitivity in the infra-red emission band at 1.15 eV. Electron nuclear double resonance experiments show that the dangling bonds are not solely bonded to Si neighbors but involve hydrogen and fluorine.
The synthesis of silicon nitride powder by the reaction between silica, carbon and nitrogen is the economically most interesting route. Only this route makes possible the use of very cheap raw materials as well as the use of a simple production process. On the other side, the properties of the powders are within the limit of the technical requirements of the ceramic part manufacturer. The aim of this paper is to show that an optimized carbothermal Si3N4 powder synthesis leads to a product which fulfills the economical (low price) as well as the technical requirements. After a short introduction regarding the economical requirements, an overview of the carbothermal synthesis will be given. The influence of raw material, conditions of synthesis and removal of excess carbon on the powder properties will be discussed. Also, the properties of the powder as well as the sintering behaviour of Si3Ns4 powders, produced by Si-direct nitridation, Si-diimide process and the carbothermal route, will be compared in detail.
Both the cadmium vacancy (Vcd) and the tellurium vacancy (VTe) in CdTe are identified by means of electron paramagnetic resonance (EPR). The VCd is a double acceptor and the EPR spectrum is observed in its single negative charge state. The symmetry is found to be trigonal, which can be explained in a model in which the hole occupies a dangling bond t2 orbital and the orbital degeneracy is removed by a static Jahn-Teller distortion. The hyperfine interaction shows that the hole is localised on one of the four Te neighbours. The EPR spectrum of VTe+ reveals cubic (unperturbed) symmetry and the hyperfine structure shows that the unpaired electron is equally spread over the four Cd neighbours.
Photo-EPR measurements locate the 0/+ state of VTe at Ev + 0.2 eV and the 2−/− acceptor level of VCd to be situated less than 0.47 eV above the valence band.
Ga0.5In0.5P has been investigated using optically detected cyclotron resonance and photoluminescence techniques. For the disordered alloy, the electron mass is determined to m*=0.092 m0, and for ordered material (band gap reduction ~ 50 meV) the value m*=0.088 m0 is found. The experimentally deduced values are compared with those obtained from a five-band kp calculation.
Both the cadmium vacancy (Vcd) and the tellurium vacancy (VTe) in CdTe are identified by means of electron paramagnetic resonance (EPR). The Vcd is a double acceptor and the EPR spectrum is observed in its single negative charge state. The symmetry is found to be trigonal, which can be explained in a model in which the hole occupies a dangling bond t2 orbital and the orbital degeneracy is removed by a static Jahn-Teller distortion. The hyperfine interaction shows that the hole is localised on one of the four Te neighbours. The EPR spectrum of VTe+ reveals cubic (unperturbed) symmetry and the hyperfine structure shows that the unpaired electron is equally spread over the four Cd neighbours
Photo-EPR measurements locate the 0/+ state of VTe at Ev + 0.2 eV and the 2-/- acceptor level of VCd to be situated less than 0.47 eV above the valence band.
The process conditions during SiC bulk crystal growth by physical vapor transport (PVT) are studied both theoretically and experimentally focussing on the magnitude of achievable growth rates V and possible correlations with defect formation. An increase of micropipe density with crystallization rate is observed. Growth parameters determining V are identified allowing a general non-dimensional representation of the dependencies of growth rate from kinetics, mass transport and heat transfer. It can be shown that at conventional process conditions of SiC growth by sublimation in graphite environment (5 mbar ≤p≤ 100 mbar, 2400K ≤T≤ 2600K) growth is limited by diffusion and kinetics for very short crystal lengths L and by heat transfer for geometries L> 1 mm. Including possible destabilizing effects due to constitutional supercooling an augmentation of V without deteriorating crystal quality should be conducted by stochiometry control for supression of graphitization and control of the thermal field tailoring the axial heat transfer with process time. Finally SiC growth from the liquid phase is introduced to promise a growth technique for specific SiC material as, in contrast to PVT growth, the closing of micropipes is demonstrated to be feasible.
Polycapillary optics, shaped arrays consisting of hundreds of thousands of hollow glass capillary tubes, can be used to redirect, collimate, or focus x-ray beams from conventional, laboratory-based sources. Multifiber polycapillary collimating optics were placed without system optimization into a number of diffractometer systems. Strain and texture measurements were performed. Measurements on thin films with and without the lens yielded gains of 8–100. Gains are higher in comparison with systems employing pinhole rather than one-dimensional slit collimation. The collimation also resulted in peak symmetrization, which simplified peak shape analysis.
Focused beam optics provide even larger gains. Gains of 100 have been demonstrated using polycapillary optics with spot sizes as small 20 μm. This is of particular significance for providing spatial resolution for low signal applications such as thin films. The inverse dependence of the critical angle for total external reflection on photon energy also results in suppression of high energy photons. This suppression of Bremsstrahlung can allow use of higher tube potentials to increase characteristic line emission. Background suppression from a polycapillary optic ″soller slit″ is also enhanced due to the two dimensional collimation and much smaller acceptance angle of the polycapillary optics. Polycapillary optic alignment is also faster and more convenient than the usual parafocusing geometry. The combination of background suppression, intensity gain and increased tube emission by employing polycapillary optics greatly increases the signal to noise ratio for thin film stress analysis.