Results from the ORPHEUS dark matter detector

The ORPHEUS dark matter detector consists of 450 g superconducting tin granules with diameters of 28 and 36 μm. The detector has been operating in the shallow site of the underground laboratory in Bern (70 m.w.e). First preliminary results on WIMP detection sensitivity will be presented.     

The influence of oxygen vacancies on piezoelectricity in samarium-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics

A study of 0.71Pb(Mg_1/3Nb_2/3)O₃-0.29PbTiO₃ shows that, when it is doped with 2.5% Sm on the A-site, in addition to an almost threefold increase in piezoelectric charge coefficient and dielectric permittivity, there is a 2 order of magnitude reduction in conductivity, attributed to a decrease in oxygen vacancy concentration. An analysis of the nonlinearity of permittivity with respect to field amplitude shows that both the reversible and irreversible contributions increase significantly with Sm-doping, with simple models showing that these changes are consistent with a reduction in the concentration of dipolar defects that can inhibit both polarization rotation and domain wall translation. Contrary to the argument that doping increases heterogeneity, there is little change in the diffuseness of the peak in permittivity as a function temperature, whilst there is a 15% increase in spontaneous polarization with Sm addition. Through comparison of the Rayleigh law parameters with those published for other piezoelectric materials, it is concluded that a significant contribution to the observed increase in piezoelectric performance due to Sm-doping of PMN-PT is similar in origin to that seen in soft, donor-doped PZT and other conventional piezoelectric ceramics.     

Multipurpose modular experimental station for the DiProI beamline of Fermi@Elettra free electron laser

We present a compact modular apparatus with a flexible design that will be operated at the DiProI beamline of the Fermi@Elettra free electron laser (FEL) for performing static and time-resolved coherent diffraction imaging experiments, taking advantage of the full coherence and variable polarization of the short seeded FEL pulses. The apparatus has been assembled and the potential of the experimental setup is demonstrated by commissioning tests with coherent synchrotron radiation. This multipurpose experimental station will be open to general users after installation at the Fermi@Elettra free electron laser in 2011.     

改性γ-聚谷氨酸去除重金属Pb2+性能研究

研究了不同改性水平的γ-聚谷氨酸(以下简写为γ-PGA)吸附去除水体中重金属离子Pb2+的性能影响。研究结果表明,交联改性后的γ-PGA与未改性的γ-PGA相比,具有更好的Pb2+吸附性能,在将改性γ-PGA加入到含有Pb2+的水体中并均匀混合之后,随着交联度的提高,改性γ-PGA吸附Pb2+的性能逐渐增加,但在吸附最终结束时,不同改性的γ-PGA对Pb2+吸附去除率均在99%以上。在吸附去除Pb2+影响因素分析中发现Pb2+初始质量浓度和溶液pH对不同改性的γ-PGA吸附去除Pb2+性能的影响较大。随着Pb2+质量浓度的增加,不同改性水平γ-PGA对Pb2+的去除率均略有一定程度的下降。当溶液的pH控制在中性或者偏碱性时,25%改性γ-PGA对Pb2+的去除率能够保持在99%以上,当pH降至4.5和3时,Pb2+去除率分别降为90.76%和78.46%。     

Homogenization and crystallization of histidine ammonia-lyase by exchange of a surface cysteine residue

Histidase (histidine ammonia-lyase, EC 4.3.1.3) from Pseudomonasputida was expressed in Escherichia coli and purified. In theabsence of thiols the tetrameric enzyme gave rise to undefinedaggregates and suitable crystals could not be obtained. Thesolvent accessibility along the chain was predicted from theamino acid sequence. Among the seven cysteines, only one waslabeled as `solvent-exposed'. The exchange of this cysteineto alanine abolished all undefined aggregations and yieldedreadily crystals diffracting to 1.8 Å resolution.     

Search beam method

An interactive multi‐objective decision‐making (MODM) model based on the Search Beam Method (SBM) and a finite‐difference groundwater flow model (GWM), is developed for analysing groundwater resources development and management problems. The SBM utilizes one‐dimensional search in the objective space to (systematically) identify the non‐dominated solutions. The steady‐state GWM determines the aquifer response due to well withdrawals. Three competing objectives of maximizing total yield, minimizing maximum compression and minimizing total pumping cost are considered. Applicability of the MODM model is demonstrated on a simplified confined aquifer system resembling one of the water‐bearing layers underlying Bangkok.     

Hybrid MCM-41 grafted by a general microwave-assisted procedure: a characterization study

Hybrid materials obtained through a Microwave-assisted grafting of organic functional groups on mesoporous silica (MCM-41 type) have been characterized by X-ray powder diffraction, TG-DSC, N₂ adsorption, solid state ¹³C- and ²⁹Si-NMR, TEM and SEM. The studied grafting procedure is effective in the preparation of hybrid organosilicas under solvent-free conditions. Microwaves allows an ultra-fast and clean functionalization of the mesoporous materials and the method has been applied to produce a wide series of functional materials. The hybrid materials maintain the original mesoporous structure when the loading of linked organic groups does not exceed 10 %. In this cases, the slight pore volume reduction is linearly correlated to the organic amount in the product. If functional groups able to interact among them through hydrogen bond are used, hybrid materials exhibit high Organic/SiO₂ ratios and low pore volumes due to the formation of a network occluding the pores, where functional groups of free organosilane molecules interacts with the functional groups of molecules linked to the matrix. NMR data confirm that the network is composed by organosilane molecules linked or not to the framework. Acid washing is able to labilize hydrogen bond and open the network. In the case of bulky but chemically inert functionalising agents the network is not produced.     

Smoothing spectral power distribution of daylights

CIE Division 1 entrusted TC 1–74 to investigate the possibility to develop a smooth curve version of the D illuminants. This article investigates the possibility to create such smoothed curves with minimal colorimetric error. Six different smoothing algorithms were investigated; the best method, using a locally weighted regression and smoothing algorithm, enabled a smooth function, where the worst colour difference for a 100 000 sample set was less than ΔE_ab^* = 0.5, comparing calculations using the CIE standard daylight spectrum and the smoothed function. Thus, the smoothed function can be recommended for redefining the daylight spectra for colorimetry without loosing continuity to results using the current calculation tables and for designing daylight simulator spectra. © 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 316–321, 2013     

Conversion of N2O to N2 on TiO2(1 1 0)

In this study, we examine the interaction of N₂O with TiO₂(1 1 0) in an effort to better understand the conversion of NO_x species to N₂ over TiO₂-based catalysts. The TiO₂(1 1 0) surface was chosen as a model system because this material is commonly used as a support and because oxygen vacancies on this surface are perhaps the best available models for the role of electronic defects in catalysis. Annealing TiO₂(1 1 0) in vacuum at high temperature (above about 800 K) generates oxygen vacancy sites that are associated with reduced surface cations (Ti³⁺ sites) and that are easily quantified using temperature programmed desorption (TPD) of water. Using TPD, X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS), we found that the majority of N₂O molecules adsorbed at 90 K on TiO₂(1 1 0) are weakly held and desorb from the surface at 130 K. However, a small fraction of the N₂O molecules exposed to TiO₂(1 1 0) at 90 K decompose to N₂ via one of two channels, both of which are vacancy-mediated. One channel occurs at 90 K, and results in N₂ ejection from the surface and vacancy oxidation. We propose that this channel involves N₂O molecules bound at vacancies with the O-end of the molecule in the vacancy. The second channel results from an adsorbed state of N₂O that decomposes at 170 K to liberate N₂ in the gas phase and deposit oxygen adatoms at non-defect Ti⁴⁺ sites. The presence of these O adatoms is clearly evident in subsequent water TPD measurements. We propose that this channel involves N₂O molecules that are bound at vacancies with the N-end of the molecule in the vacancy, which permits the O-end of the molecule to interact with an adjacent Ti⁴⁺ site. The partitioning between these two channels is roughly 1:1 for adsorption at 90 K, but neither is observed to occur for moderate N₂O exposures at temperatures above 200 K. EELS data indicate that vacancies readily transfer charge to N₂O at 90 K, and this charge transfer facilitates N₂O decomposition. Based on these results, it appears that the decomposition of N₂O to N₂ requires trapping of the molecule at vacancies and that the lifetime of the N₂O–vacancy interaction may be key to the conversion of N₂O to N₂.     

Electrochemically Stimulated Release from Liposomes Embedded in a Polyelectrolyte Multilayer

Triggered release of an entrapped dye from vesicles embedded in a polyelectrolyte multilayer (PEM), as a consequence of the electrochemically induced local pH change in the vicinity of the electrode, is reported. The PEM was deposited on an indium tin oxide (ITO) electrode wherein lipid vesicles filled with a fluorescent dye were embedded. The use of vesicles with a strong negative charge and the polyelectrolyte species of the PEM matrix with a polycation as topmost layer enabled the generation of a stable layer of liposomes in the PEM.