Active vibration suppression of smart beams

In this paper an active vibration control technique for a smart beam is presented. The structure is made of two layers of piezoelectric material (PZT8) embedded on the surface of an aluminium beam. The active control is inserted into the finite element model by using programming tools of the general purpose code used here. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Certified reference material IAEA-418: 129I in Mediterranean Sea water

A certified reference material designed for the determination of ¹²⁹I in seawater, IAEA-418 (Mediterranean Sea water) is described and the results of certification are presented. The median of ¹²⁹I concentration with 95% confidence interval was chosen as the most reliable estimates of the true value. The median, given as the certified value, is 2.28 × 10⁸ atom L^?1 (95% confidence interval is (2.16–2.73) 10⁸ atom L^?1), or 3.19 × 10^?7 Bq L^?1 (95% confidence interval is (3.02–3.82) × 10^?7 Bq L^?1). The material is intended to be used for standardization procedures applied in accelerator mass spectrometric laboratories. It is available in 1 L units and may be ordered via IAEA web side (www.iaea.org).     

Charge transfer between isomer domains on n(+)-doped Si(111)-2?×?1: energetic stabilization

Domains of different surface reconstruction-negatively or positively buckled isomers-have been previously observed on highly n-doped Si(111)-2?×?1 surfaces by angle-resolved ultraviolet photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. At low temperature, separate domains of the two isomer types are apparent in the data. It was argued in the previous work that the negative isomers have a lower energy of their empty surface states than the positive isomers, providing a driving force for the formation of the negative isomers. In this work we show that the relative abundance of these two isomers shows considerable variation from sample to sample, and it is argued that the size of the isomer domains is likely to be related to this variation. A model is introduced in which the electrostatic effect of charge transfer between the domains is computed, yielding total energy differences between the two types of isomer. It is found that the transfer of electrons from domains of positive isomers to negative ones leads to an energetic stabilization of the negative isomers. The model predicts a dependence of the isomer populations on doping that is in agreement with most experimental results. Furthermore, it accounts, at least qualitatively, for the marked lineshape variation from sample to sample observed in photoemission spectra.     

Time-resolved measurements of hot-electron equilibration dynamics in high-intensity laser interactions with thin-foil solid targets

Time-resolved K(α) spectroscopy has been used to infer the hot-electron equilibration dynamics in high-intensity laser interactions with picosecond pulses and thin-foil solid targets. The measured K(α)-emission pulse width increases from ~3 to 6 ps for laser intensities from ~10(18) to 10(19) W/cm(2). Collisional energy-transfer model calculations suggest that hot electrons with mean energies from ~0.8 to 2 MeV are contained inside the target. The inferred mean hot-electron energies are broadly consistent with ponderomotive scaling over the relevant intensity range.     

Cosmological solutions in a spontaneously broken gauge theory

We consider solutions of the Yang-Mills-Higgs system coupled to gravity in asymptotically de Sitter space-time. The basic features of two classes of solutions are discussed, one of them corresponding to magnetic monopoles, the other one to sphalerons. We find that although the total mass within the cosmological horizon of these configurations is finite, their mass evaluated at timelike infinity generically diverges for most values of the cosmological constant. Also, no solutions exist in the absence of a Higgs potential.     

Development of a SIMS Method for Isotopic Measurements in Nuclear Forensic Applications

 Methodologies based on secondary ion mass spectrometry (SIMS) for isotopic measurements in nuclear forensic applications relevant to the age determination of Pu particles and isotopic composition of oxygen for geolocation assignment are described. For the age determination of Pu particles, a relative sensitivity factor (RSF) to correct for the different ionisation efficiencies of U and Pu, was obtained by analysing standard Pu materials with known ages. An RSF of 2.41±0.05 was obtained for PuO₂ from measurements on samples with different Pu/U ratios. In a sample of known origin, using this RSF value, the age calculated from the ²³⁸Pu/²³⁴U and ²⁴⁰Pu/²³⁶U ratios agreed well with the reported age of 2.3 years. For geolocation assignment, a new approach based on the measurement of differences in the natural abundance of ¹⁸O and ¹⁶O isotopes and their ratio was developed. The instrumental mass discrimination of the ¹⁸O/¹⁶O ratio was determined using three O-isotope samples of different chemical composition. The measured precision (the standard error of 100 cycles/analysis) obtained for the oxygen isotopic measurement on the samples was typically ±1.1‰.     

Isotopic abundance measurements on solid nuclear-type samples by glow discharge mass spectrometry

A double-focusing Glow Discharge Mass Spectrometer (GDMS) installed in a glovebox for nuclear sample screening has been employed for isotopic measurements. Isotopic compositions of zirconium, silicon, lithium, boron, uranium and plutonium which are elements of nuclear concern have been determined. Interferences arising from the matrix sample and the discharge gas (Ar) for each of these elements are discussed. The GDMS results are compared with those from Thermal Ionization Mass Spectrometry (TIMS). For boron and lithium at microg/g-ng/g levels, the two methods gave results in good agreement. In samples containing uranium the isotopic composition obtained by GDMS was in agreement with those from TIMS independently of the enrichment. Attempts for the determination of plutonium isotopic composition were also made. In this case, due to the interferences of uranium at mass 238 and americium at mass 241, the GDMS raw data are complementary with those values obtained from physical non-destructive techniques.     

Comparison between the use of direct current glow discharge mass spectrometry and inductively coupled plasma quadrupole mass spectrometry for the analysis of trace elements in nuclear samples

The quantitative determination of trace elements in nuclear samples by GDMS and ICP-MS is presented and compared. Spectral interferences, matrix effects, detection limits, precision and accuracy are discussed. Results for selected samples demonstrated that both techniques are complementary. The use of a multi-standard solution provides the most accurate results in ICP-MS, whereas in GDMS this is achieved by relative sensitivity factors (RSF) matrix matched. Nevertheless, the use of standard RSF allows a fast screening.     

Comparison between the use of direct current glow discharge mass spectrometry and inductively coupled plasma quadrupole mass spectrometry for the analysis of trace elements in nuclear samples

The quantitative determination of trace elements in nuclear samples by GDMS and ICP-MS is presented and compared. Spectral interferences, matrix effects, detection limits, precision and accuracy are discussed. Results for selected samples demonstrated that both techniques are complementary. The use of a multi-standard solution provides the most accurate results in ICP-MS, whereas in GDMS this is achieved by relative sensitivity factors (RSF) matrix matched. Nevertheless, the use of standard RSF allows a fast screening.