Analysis of the accuracy of actuation electronics in the laser interferometer space antenna pathfinder

The Laser Interferometer Space Antenna Pathfinder (LPF) main observable, labeled Δg, is the differential force per unit mass acting on the two test masses under free fall conditions after the contribution of all non-gravitational forces has been compensated. At low frequencies, the differential force is compensated by an applied electrostatic actuation force, which then must be subtracted from the measured acceleration to obtain Δg. Any inaccuracy in the actuation force contaminates the residual acceleration. This study investigates the accuracy of the electrostatic actuation system and its impact on the LPF main observable. It is shown that the inaccuracy is mainly caused by the rounding errors in the waveform processing and also by the random error caused by the analog to digital converter random noise in the control loop. Both errors are one order of magnitude smaller than the resolution of the commanded voltages. We developed a simulator based on the LPF design to compute the close-to-reality actuation voltages and, consequently, the resulting actuation forces. The simulator is applied during post-processing the LPF data

Design of an on-line dynamic magnetic flux analyzer based on double-buffer sliding DFT

An on-line dynamic magnetic flux analyzer for magnetic measurement is presented. The instrument achieves on-line harmonic analysis by means of an improved implementation of the sliding DFT algorithm on the basis of the Fast Digital Integrator [1]. In particular, the round-off error, unacceptable in digital integrators, is corrected by employing two buffers alternatively. Details about the structure of the instrument and the algorithm implementation are pointed out, and some experimental results are analyzed in order to validate the proposal

Palaeoenvironmental reconstructions through compositional data analysis: the CoDaMAT method

We present a modern analog technique (CoDaMAT) based on compositional data analysis (Aitchison, 2003). In order to reconstruct palaeoenvironmental parameters, CoDaMAT adopts the Aitchison distance (Aitchison, 2000; 2003), obtained from relative abundances expressed in log-ratios (logarithm of ratios), as a “natural” measure of similarity between modern and fossil assemblages. The number of modern analogs from which obtain the palaeoestimates was determined through cross-validation techniques taking modern assemblages as the training data set. Atypicality index was considered to detect past no-analog conditions. The average of distances and expected maximum estimate errors were taken into account to evaluate the quality of palaeoestimates. The method has been tested on Mediterranean and Atlantic planktonic foraminiferal assemblages to reconstruct past sea surface temperatures (SST). Due to the peculiar oceanographical asset of the Mediterranean, no-analog conditions may represent an important problem in attempting the reconstruction of glacial SST. Keeping in mind these limitations, we obtained for the Tyrrhenian sea, at 15 ka BP (during the Greenland stadial GS2-a), summer and winter SST estimates respectively 12°C and 6°C lower than present. These are the lowest values reached during the last 34 ka. In the coldest interval of the Greenland stadial GS1 (Younger Dryas), reconstructed summer and winter SST were respectively 11°C and 5°C lower than present. In comparison with previous foraminiferal based reconstructions (de Abreu et al., 2003), the CoDaMAT palaeoestimates of Atlantic ocean surface temperatures for the last 200 ka show a stronger coherence with the alkenones and stable isotope record (Pailler and Bard, 2002)

Microstructural stability in LPE Ga{sub x}In{sub (1{minus}x)}As{sub y}Sb{sub (1{minus}y)}/GaSb heterostructures

The morphological and structural characteristics associated with the growth of lattice matched In{sub x}Ga{sub (1{minus}x)}As{sub y}Sb{sub (1{minus}y)}/GaSb (100) heterostructures is presented. The experiments focused on studying the effect of growth on vicinal surfaces tilted from the exact (100) orientation as well as variations in epilayer chemistry. It was found that variations in these process parameters had very strong effects on both the nucleation characteristics of the epilayer and the atomistic scale homogeneity of the alloy. The and variants in compositional modulation/phase separation were detected, as well as the evolution of weak (110) ordering. These results are discussed in the context of other studies on phase stability in III-V epitaxial structures, especially in terms of surface reconstruction and kinetic effects near conditions of spinodal decomposition

Microbial biofilms associated with biliary stent clogging

Endoscopic stenting is a palliative approach for the treatment of diseases involving biliary obstruction. Its major limitation is represented by stent occlusion, followed by life-threatening cholangitis, often requiring stent removal and replacement. Although it has been suggested that microbial colonization of biliary stents could play a role in the clogging process, the so far available data, particularly on the role of anaerobic bacteria, are not enough for a comprehensive description of this phenomenon. Our study was focused on the analysis of 28 explanted biliary stents by culturing, denaturing gradient gel electrophoresis and scanning electron microscopy to identify all the aerobic/anaerobic bacteria and fungi involved in the colonization of devices and to verify the ability of isolated anaerobic bacterial strains to form a biofilm in order to better understand the mechanisms of stent clogging

The palaeoclimatic and palaeoceanographic history of the Gulf of Taranto (Mediterranean Sea) in the last 15 ky

A multidisciplinary study, which includes micropaleontology, sedimentology and geochemistry, was carried out on the TEA-C6 core, raised in the Gulf of Taranto (north-western Ionian Sea). The chronological framework was yielded by tephrostratigraphy combined with ecostratigraphy and AMS ⁠14C dating. New results allowed surface and bottom conditions in the Gulf of Taranto during the last 15 ky to be reconstructed, thus providing a detailed and age-constrained paleoclimate and paleocological record for this sector of the Mediterranean Sea. The quantitative record of past sea surface temperatures (SST) was obtained by means of Compositional Data Analysis (CoDA) methods applied to planktonic foraminifera assemblages. High-resolution analyses allowed the Sapropel S1 event to be characterised at centennial-scale resolution. The main interval of the sapropel S1, here dated between 10.2calka and 7.8calka, is preceded and followed by transition phases spanning several centuries and prevailing anoxic bottom conditions are punctuated by several episodes of partial oxygen recovery. The S1a interval corresponds to high summer SST, whereas an SST drop of about 2.5° took place towards the end of the S1b interval. New tephrochronological data record the signature of eruptive events from Italian volcanoes which were not documented on land up to date

Phase stability in Ga{sub x}In{sub 1{minus}x}As{sub y}Sb{sub 1{minus}y}/GaSb heterostructures

The crystallographic and microstructural characteristics of liquid phase epitaxy lattice-matched In{sub x}Ga{sub (1{minus}x)}As{sub y}Sb{sub (1{minus}y)}/GaSb (100) heterostructures is presented. Using both transmission electron microscopy and high resolution X-ray diffraction, a variety of diffusional based phase transformations in the epitaxial films are observed, including: spinodal decomposition, compositional modulations of the order of 30 nm, and weak long range ordering. These results are interpreted in terms of the possible influence of substrate surface structure on the phase stability of epitaxial layers

The TEA C6 record: a reference archive from the Gulf of Taranto (Ionian Sea) for the last 15 ka

An integrated stratigraphic analysis was carried out on the TEA C6 gravity core raised from the Amendolara basin in the Gulf of Taranto. The 4.5 m long succession was investigated by means of sedimentology and textural analysis, petrophysics, micropaleontology and geochemistry with a refined dating framework provided by oxygen isotope, tephrochronology and 14C AMS ages. Textural and micropaleontological data were analysed by means of Compositional data analysis. The results pointed to a deep marine record with no or little disturbance and they aimed to contribute to the reconstruction of the palaeoceanographical and paleoclimatic changes occurred in this sector of the Central Mediterranean during the last 15 ka BP. In particular, data obtained along the sapropelitic interval corresponding to the Sapropel S1 deposition (9.6-7.5 ka BP), offered a detailed insight on the conditions that characterised the study area during this phase. The deposit was sampled with a continuous step of 1 cm-slides of sediment and this allowed to have resolution even in the order of 50 years. During the early Holocene, before the onset of Sapropel deposition, foraminifera show evidence of several centuries characterised by persistence of winter mixing and likely summer eutrophication. The weakening of winter mixing is simultaneous with a change in bottom conditions, leading to the dominance of oxygen resistant species and then to the establishment of anoxic conditions. During this phase, truly onoxic conditions alternate with periods of partial recovery of benthic faunas, the longest of which correspond to the Sapropel S1 interruption. This moment is time fixed by the occurrence of a tephra layer interbedded within the marine deposit. The end of the Sapropel S1 phase coincides with the re-establishment of winter mixing, although eutrophication persists during a transition interval 400 years long. Dynamics and duration of Sapropel S1 in the Gulf of Taranto show similarities with those of the Adriatic Sea. Sea Surface Temperatures (SST) recontructions obtained from planktonic foraminifera by means of CoDaMAT indicate during the stadial GS1 (Younger Dryas) summer and winter SST about 12°C and 7°C lower than present, respectively, and Holocene SST fluctuations in the range of 2°C. According to the results, TEA C6 core might represent a reference archive for the Gulf of Taranto in terms of response of the sedimentary environment to palaeoceanographical and paleoclimatic changes from the late glacial to the late Holocene