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The use of high-intensity, 8Kw, x-ray sources (Rigaku rotating-anode generator and wide - angle goniometer for this study) provides both opportunities and challenges. With high - intensity x-ray sources, detection limits can be lowered significantly while still offering count times of practical duration. On the other hand, the availability of high intensity x-ray sources puts greater demands on information extraction procedures and on the mechanical preciseness of sample containment and support. In particular we addressed the use of a cylindrical aluminum sample cell with a 0.010’’ polycrystalline (cold rolled) beryllium window electron –beam welded to an aluminum frame. See Figure 1. This cell permitted analysis of various air-sensitive specimens. The sample was pressed against the back of the beryllium window by a spring-loaded backing plate.
Thin-section (micromorphological) analysis of samples from the upper 1.5 m of a core obtained in 2007 from Anderson Pond, Tennessee, reveals a coherent but discontinuous record of late Pleistocene and Holocene climate change that supports some interpretations from previous pollen and charcoal analyses but indicates a revised Holocene chronology for this classic pollen site. Legacy sediments recording anthropogenic disturbance compose the upper 65 cm of the core (<160 cal yr BP) and are characterized by mixed, darker-colored, and coarser-grained deposits containing reworked soil aggregates, which sharply overlie finer-grained and lighter-colored, rooted middle Holocene sediments interpreted as a paleosol. These mid-Holocene sediments (95–65 cm; 7100–5600 cal yr BP) record extensive warm-dry subaerial soil conditions during the middle Holocene thermal maximum, manifested by illuviated clay lining root pores, and also contain abundant charcoal. Late Pleistocene sediments (150–95 cm), dark-colored and organic-rich, record open-water conditions and include siliceous aggregate grains at 143–116 cm (14,300–13,900 cal yr BP), recording intense fires. Thin sections are not commonly used in studies of paleoclimate from Quaternary lacustrine sediments, but we advocate for their inclusion in multianalytical approaches because they enhance resolution of depositional and pedogenic processes.
The objective of the present study was to assess the effect of adding specific prebiotics to standard formula feeding on the number of fever episodes in the first year of life. In the present randomised, double-blind, placebo-controlled trial in seven centres in five West European countries, 830 healthy term infants, without a first-degree family history of allergic disease, of mothers who indicated to give only formula feeding were randomised either to receive a standard non-hydrolysed cows' milk-based formula to which a mixture of specific oligosaccharides was added (prebiotics group (PG)), or to receive a similar formula without oligosaccharides (control group (CG)). A separate reference group consisted of 300 breast-fed infants. The primary outcome was the number of fever episodes prospectively documented by the parents. There was no difference in the number of fever episodes between the PG (median value 1·19; 25th–75th percentile 0·09–2·34) and CG (1·16; 25th–75th percentile 0·06–2·38). The median number of fever episodes in the separate breast-feeding reference group was 1·24 (25th–75th percentile 0·51–3·45). There was no effect of adding specific prebiotics to standard formula feeding in reducing the number of fever episodes in the present study.
We are studying the boron nitride system by using a pulsed excimer laser to ablate from hexagonal BN (hBN) targets to form cubic BN (cBN) films. We are depositing BN films on heated (25 - 800°C) Si (100) surfaces and are using a broad-beam ion source operated with Ar and N2 source gasses to produce BN films with a high percentage of sp3-bonded cBN. In order to understand and optimize the growth and nucleation of cBN films, parametric studies of the growth parameters have been performed. The best films to date show >85% sp3-bonded BN as determined from Fourier-transform infrared (FTIR) reflection spectroscopy. High resolution transmission electron microscopy (TEM) and selected area electron diffraction confirm the presence of cBN in these samples. The films are polycrystalline and show grain sizes up to 30- 40 nm. We find from both the FTIR and TEM analyses that the cBN content in these films evolves with growth time. Initially, the films are deposited as hBN and the cBN nucleates on this hBN underlayer. Importantly, the position of the cBN IR phonon also changes with growth time. Initially this mode appears near 1130 cm-1 and the position decreases with growth time to a constant value of 1085 cm-1. Since in bulk cBN this IR mode appears at 1065 cm-1, a large compressive stress induced by the ion bombardment is suggested. In addition, we report on the variation in cBN percentage with temperature.
Heavily doped Si:Ga has been prepared by liquid phase epitaxy (LPE) and by ionimplantation with rapid thermal annealing (RTA) or laser annealing (LA). Peak substitutional Ga concentrations obtained by each technique were 1.5, 2.5 and 2.9 ×1020cm-3, respectively. Substitutional fractions (>90%) were similar in the three types of samples, and the conductivity scaled with the total Ga concentration. A lattice expansion per substitutional Ga atom in Si of +0.9 ± 0. l×10-24cm3 /atom was measured by double crystal x-ray diffraction. The average nearest neighbor Si-Ga bond length measured with extended x-ray absorption fine structure (EXAFS) was 0.237 ± 0.004 nm, indistinguishable, to within experimental error, from the intrinsic Si-Si bond lngth, 0.235 nm. Combining these two results the lattice strain per hole in the Si valence band was calculated, +0.4 ± 0.8x10G-cm3. This result complements the lattice contraction per electron in the Si conduction band (-1.8 ± 0.4x10-24cm 3) already reported for Si:As [G. S. Cargill III, J. Angilelloand K. L. Kavanagh, Phys. Rev. Letters 61, 1748 (1988)].
The effect of thermal cycling under a constant tensile load on the transformation temperatures (TTs) of NiTi-based shape memory alloys (SMAs) is investigated. Three SMAs are examined in this study: a near equiatomic binary Ni49Ti51 alloy and two ternary Ni49Ti51-xHfx alloys with 1 at% and 3 at% Hf. The SMAs are in the form of wires with 40% cold work (reduction in area) and heat treated between 300°C and 600°C. These SMA wires are thermally cycled between their martensite (M) and austenite (A) phases for 100 cycles under an axial tensile stress of 206.8MPa (30Ksi) in air. Results show that the effect of thermal cycling on the M and A TTs depends on heat treatment (HT) temperature and composition in a complex manner. For example, the M TT, of the binary NiTi SMA heat treated between 300°C and 450°C, increases during thermal cycling. However, with HT temperatures between 500°C and 600°C, the M TIT decreases slightly during thermal cycling. For the NiTi-based SMAs that contain 1 at% and 3 at% Hf, the M TT increases during thermal cycling for HT temperatures up to 500°C, and the M TT decreases during thermal cycling when heat treated at 600°C. These results are due to changes in internal stress and structure, such as dislocation density and arrangement, which are affected by HT temperature and thermal cycling. The influence of Hf content on the changes in the M and A TTs during thermal cycling is also shown.
The development of monolithic silicon photonic systems has been the subject of intense research over the last decade. In addition to passive waveguiding structures suitable for DWDM applications, integration of electrical and optical functionality has yielded devices with the ability to dynamically attenuate, switch and modulate optical signals. Despite this significant progress, much higher levels of integration and increased functionality are required if silicon is to dominate as a substrate for photonic circuit fabrication as it does in the microelectronic industry. In particular, there exists a requirement for efficient silicon-based optical sources and detectors which are compatible with wavelengths of 1.3 and 1.5μm. While a great deal of work has focussed on the development of silicon-based optical sources, there has been less concentrated effort on the development of a simple, easily integrated detector technology. We describe here the design, fabrication and characterization of a wholly monolithic silicon waveguide optical detector, utilizing an integrated p+-u-n+ diode, which has significant response to optical signals at the communication wavelength of 1.54μm. Measurable infra-red response is induced via the controlled introduction of mid-gap electronic levels within the rib waveguide. This approach is completely compatible with ULSI fabrication. The requirement for the detectors to be integrated with a rib waveguide and hence the guarantee of a long optical signal-device interaction, results in electrical signals of several μAs, even for deep-levels with a small optical absorption cross-section. Further, the rise and fall time of the detectors is compatible with current monolithic, silicon device based, optical switching and modulation operating in the MHz regime. These results suggest that these detectors offer a cost-effective route to signal monitoring in integrated photonic circuits.
Color information is commonly captured by silicon sensor arrays covered by a mosaic of color filters. However, the detection of the colors red, green and blue at different spatial positions of the sensor arrays leads to color aliasing or color moiré effects. This effect inherently limits conventional sensor arrays. In order to overcome this limitation we have realized color sensors based on vertically integrated thin-film structures. The complete color information can be detected at the same position of a sensor array without using optical filters. The sensors consist of a multilayer thin-film system based on amorphous silicon and its alloys. The spectral sensitivity of the sensors can be controlled by the optical and optoelectronic properties of the employed materials and the applied bias voltages. The working principle of the thin-film sensors and the sensor arrays will be presented. For the first time a large area three color sensor array was realized without using optical filters.
We employed passive particle-tracking microrheology to map the micromechanical structure of the hyaluronan-rich pericellular coat enveloping chondrocytes. Therefor we exploited the technique's position sensitivity to gain radial information on the coat. We observed a linear increase in viscoelasticity from the coat's rim towards the cell membrane. This gradient corresponds to hyaluronan concentration profiles observed in confocal fluorescent microscopy with small, specific hyaluronan markers. These results suggest that the structural basis of the pericellular coat is formed by grafted hyaluronan of different effective lengths stretched out by a homogenous decoration with hyaladherins such as aggrecan. The different effective lengths could be caused either by different lengths of the HA chains or by “side-on” attachments within the chain. Remarkably, the hyaluronan-rich coat increases the viscosity of the pericellular space only by about a factor of about two at 100 and at 20 Hz compared to pure media and an increasing elastic component is observed. Both the viscoelasticity as well as the hyaluronan concentration decrease linearly or slightly exponential from the cell membrane towards the PCC's rim. These observations could be obtained on living cells exploiting this unintrusive measurement techniques.
Monolithic integration of sensing devices usually requires sharing the CMOS chip floor space between sensors and their readout electronics. Vertical integration of the sensor on top of the electronics allows one to have the full chip area dedicated to sensing. For light detection, the deposition of hydrogenated amorphous silicon (a-Si:H) photodiodes on top of CMOS readout circuits offers several advantages compared to standard CMOS imagers. The issues regarding the design of a-Si:H photodiodes, their integration and the influence of the CMOS chip design (i.e. its surface morphology) on a-Si:H diode performance are discussed. Examples of TFA sensors for vision and particle detection are also presented.
Image and particle sensors based on thin film on CMOS (TFC) technology, where a-Si:H detectors are vertically integrated on top of a CMOS chip, basically provide high sensitivity and low dark current densities (Jdark). However, as shown in previous work and as confirmed by the actual measurements, Jdark values depend on the topology of the chip and on the detector structure used.
The present paper describes a systematic study carried out, both with test structures on glass and also with a dedicated CMOS test chip designed by CERN. The increase in Jdark is shown to be related to border effects, and especially on the detailed structure of the pixel periphery. In all cases, lower Jdark are obtained when one uses metal-i-p instead of n-i-p configuration detectors. Transferring these results to the standard TFC sensors used by them, the authors have obtained values of Jdark as low as 20 pA/cm2 at -1 V reverse bias.
Low temperature pulsed electrically detected magnetic resonance (pEDMR) measurements of charge trapping and recombination transitions involving Pb centers at the c-Si (111)/SiO2 interface are presented. The results of these experiments show that when a conduction electron is trapped, it forms a strongly coupled spin pair with the defect electron prior to its readjustment into the charged Pb ground state. The data reveals that the Landé factors of the two electrons within these pairs are almost identical (difference < 0.002) and that they are, within the measurement accuracy, identical to the Landé factor of the uncharged, singly occupied Pb center. From this, it is concluded that trapping and recombination at Pb defects is dominated by direct charge capture and not by tunneling or hopping transitions from other localized states. Different cross sections attributed in previous studies to different interface defects at the c-Si/SiO2 interface can be explained by readjustment out of different spin configurations of the charged Pb-* defect.
Zinc oxide (ZnO) films were deposited on polyimide-based substrates by pulsed laser deposition. The ZnO films and the underlying polymer layers were studied using Fourier Transform Infrared (FTIR) and Photoluminescence (PL) spectroscopies. FTIR measurements in structurally well-characterized samples exhibiting all X-ray reflections of crystalline hexagonal ZnO show absorbance bands around 405 cm-1(Zn-O stretching vibration) and 1110 cm-1 (in-plane C-H vibrations on aromatic rings of polyimide). Observed shifts in both absorption features as a function of deposition temperatures can probably be attributed to thermal stress in the layers. PL measurements showed broad spectra centered around 3.35 eV from ZnO excitonic emission and a broader PL band from 2.7 to 3.1 eV defect complex emissions. The appearance of these peaks was consistent for depositions of ZnO on non-organic substrates, which indicates that the integration of ZnO thin films on polymer based substrate preserved the characteristic optical properties of ZnO.
Among the A/B stars, about 5% host large-scale organised magnetic fields. These magnetic stars show also abundance anomalies in their spectra, and are therefore called the magnetic Ap/Bp stars. Most of these stars are also slow rotators compared to the normal A and B stars.
Today, one of the greatest challenges concerning the Ap/Bp stars is to understand the origin of their slow rotation and their magnetic fields. The favoured hypothesis for the latter is that the fields are fosils, which implies that the magnetic fields subsist throughout the different evolutionary phases, and in particular during the pre-main sequence phase. The existence of magnetic fields at the pre-main sequence phase is also required to explain the slow rotation of Ap/Bp stars. During the last 3 years we performed a spectropolarimetric survey of the Herbig Ae/Be stars in the field and in young clusters, in order to investigate their magnetism and rotation. These investigations have resulted in the detection and/or confirmation of magnetic fields in 8 Herbig Ae/Be stars, ranging in mass from 2 to nearly 15 solar masses. In this paper I will present the results of our survey, as well as their implications for the origin and evolution of the magnetic fields and rotation of the A and B stars.
We present the adaptive optics assisted, near-infrared VLTI instrument GRAVITY for precision narrow-angle astrometry and interferometric phase referenced imaging of faint objects. With its two fibers per telescope beam, its internal wavefront sensors and fringe tracker, and a novel metrology concept, GRAVITY will not only push the sensitivity far beyond what is offered today, but will also advance the astrometric accuracy for UTs to 10 μas. GRAVITY is designed to work with four telescopes, thus providing phase referenced imaging and astrometry for 6 baselines simultaneously. Its unique capabilities and sensitivity will open a new window for the observation of a wide range of objects, and — amongst others — will allow the study of motion within a few times the event horizon size of the Galactic Center black hole.
Studies of stellar magnetism at the pre-main sequence phase can provide important new insights into the detailed physics of the late stages of star formation, and into the observed properties of main sequence stars. This is especially true at intermediate stellar masses, where magnetic fields are strong and globally organised, and therefore most amenable to direct study. This talk reviews recent high-precision ESPaDOnS observations of pre-main sequence Herbig Ae-Be stars, which are yielding qualitatively new information about intermediate-mass stars: the origin and evolution of their magnetic fields, the role of magnetic fields in generating their spectroscopic activity and in mediating accretion in their late formative stages, and the factors influencing their rotational angular momentum.
Fructo-oligosaccharides (FOS) are widely used in commercial food products. Most studies on FOS concern the health benefits, but some negative effects were recently reported concerning thefaecal cytotoxicity and excretion of mucin-type oligosaccharides in combination with a Ca-restricted diet. The present study was performed to investigate whether these effects of FOS are observed in adults consuming a regular diet unrestricted in Ca. The study was a randomised, double-blind, placebo-controlled crossover trial, involving eleven healthy adults, who consumed 25–30g FOS or maltodextrin (control) in a random order for 2 weeks in addition to their regular diet. Stools were collected for analysis of pH and SCFA (as markers of fermentation), for the assessment of faecal water cytotoxicity, and for the analysis of alkaline phosphataseactivity (as a marker of epithelial cell turnover) andO-linked oligosaccharides (to estimate the excretion of mucin-type oligosaccharides). FOS consumption significantly altered bacterial fermentation (increased percentage of acetate, decreased percentage of butyrate) and tended to decrease stool pH. Furthermore, FOS consumption resulted in a significantly higher stool frequency and in significantly more complaints of flatulence. No significant differences between the control and FOS period were observed in the mean cytotoxicity of faecal water (37·5 (sem 6·9) % v. 18·5 (sem 6·9) % P=0·084), in mean alkaline phosphatase activity (27·7 (sem 2·9) v. 24·6 (sem 3·2) U/g dry faeces; P=0·496) or in the mean excretion of mucin-type oligosaccharides (49·9 (sem 4·0)v. 53·5 (sem 4·3) mg/g dry faeces; P=0·553). We conclude that dietary FOS in a dose up to 25–30g/d altered the bacterial fermentation pattern but did not affect faecal cytotoxicity or the faecal concentration of mucin-type oligosaccharides in human adults consuming a regular diet.