Investigations on the location and construction of a low background gamma-spectrometer

The underground radiation conditions in the mining district of Freiberg and in a rock salt environment of the Werra district were investigated. In a salt mine a very low natural activity level can be found. For selection of proper shielding materials a low-level -spectrometer and an optimum sample geometry must be used. The photopeak differences between sample and blank are small in most cases. Considerable differences can be found in the continuous background below 0.7 MeV.     

Influence of column length and pore size on high-performance ion-exchange chromatography of estrogen and progestin receptors

A high-performance liquid chromatographic (HPLC) procedure has been evaluated to establish a routine test in the clinical laboratory for measuring the profiles of estrogen and progestin receptor isoforms in human breast and endometrial tumors. This procedure will be used to determine if there is a relationship between particular isoform profiles and response to various endocrine therapies. Evaluation of various HPLC modes has shown that high-performance ion-exchange chromatography (HPIEC) with silica-based anion exchangers offers a promising approach. In this paper, we have compared HPIEC columns of different lengths (10 and 25 cm) and pore sizes (300, 500 and 1,000 A) in order to obtain an optimal separation procedure. Because of receptor lability, all investigations were performed at 4 degrees C. The mobile phase consisted of 10-500 mM phosphate buffer, supplemented with the stabilizing agent, sodium molybdate at pH 7.4. Recoveries from each of the columns were between 70-100%. The length of the column did not influence significantly the retention time and salt concentration required for elution of receptor proteins. However, pore sizes appeared to alter these parameters. With a larger pore size (1,000 A), the retention of proteins was lower (elution with 50 mM phosphate) than that observed with the 500-A pore size column (elution with 100 mM phosphate) or of the 300-A pore size column (elution with 150 mM phosphate). Based solely on recovery patterns and peak shape, we conclude that separation of receptor isoforms on a 1,000-A, 25-cm column is best suited for clinical analysis.     

Influence of Morphological Homogeneity of Superspherical Gold Nanoparticles on Plasmonic Photothermal Heat Generation

The plasmonic photothermal (PPT) characteristics of gold nanostructures have been extensively investigated theoretically and experimentally due to their potential for use materials science and industry. The management of the size and shape of gold nanoparticles has been a key issue in the development of better solutions for PPT heat generation because their size and shape determine their resultant photothermal properties. However, the light absorption of gold nanostructures is mainly dependent on the wavelength and orientation of the incident light; hence, maintaining uniform size and shape is critical for achieving maximum photothermal energy. Morphologically homogeneous spherical gold nanoparticles, or super gold nanospheres prepared by slowly etching uniform octahedral gold nanoparticles, demonstrate better PPT heat generation compared with commercially available nonsmooth gold nanoparticles (GNSs). The PPT heating experiments show a maximum temperature difference of 5.7 °C between the super and ordinary GNSs with the same average maximum Feret's diameters, which result from the more efficient PPT heat power generation (20.6%) of the super GNSs. In an electromagnetic‐wave simulation, the super GNSs show lower polarization dependence and a 24.6% higher absorption cross‐section than ordinary GNSs.     

A Paper‐Based Platform for Long‐Term Deposition of Nanoparticles with Exceptional Redispersibility,Stability, and Functionality

Although nanoparticles (NPs) can be carefully engineered to have maximal stability and functionality desirable for use in diverse applications, they are generally not suitable for long‐term storage in solution. It is also difficult to store NPs in a dry state because dried NPs generally become aggregated and cannot easily be redispersed. Thus, a new strategy allowing long‐term storage of NPs with high stability, redispersibility, and functionality is highly demanded. By passivating the 13 nm gold nanoparticle (AuNP) surface with stabilizing agents and treating a paper substrate with both bovine serum albumin and sucrose after coating with a hydrophobic polyvinyl butyral layer, it is possible to fully redisperse (≈100%) dried AuNPs with colloidal stability comparable to that of as‐prepared AuNPs. Furthermore, AuNPs physically stabilized with polyvinylpyrrolidone can react with thiol‐containing compounds, such as 1,4‐dithiothreitol (DTT). Taking advantage of the oxidation reaction of hypochlorous acid with DTT, it is possible to demonstrate a paper‐based colorimetric sensor for detection of residual chlorine in water. Since this strategy is applicable to large‐sized AuNPs (30–90 nm), silver NPs, oleic acid‐capped magnetic NPs, and cetrimonium bromide‐passivated gold nanorods, it can be used for diverse NPs requiring long‐term storage for many applications.     

Transparent and Conductive Polyethylene Oxide Film by the Introduction of Individualized Single‐Walled Carbon Nanotubes

It is demonstrated that an optically transparent and electrically conductive polyethylene oxide (PEO) film is fabricated by the introduction of individualized single‐walled carbon nanotubes (SWNTs). The incorporated SWNTs in the PEO film sustain their intrinsic electronic and optical properties and, in addition, the intrinsic properties of the polymer matrix are retained. The individualized SWNTs with smaller diameter provide high transmittance as well as good electrical conductivity in PEO films.

     

Luminescent characteristics of CaTiO3:Pr thin films prepared by pulsed laser deposition method with various substrates

CaTiO₃:Pr³⁺ films were deposited on different substrates such as Al₂O₃ (0 0 0 1), Si (1 0 0), MgO (1 0 0), and fused silica using pulsed laser deposition method. The crystallinity and surface morphology of these films were investigated by XRD and SEM measurements. The films grown on the different substrates have different crystallinity and morphology. The FWHM of (2 0 0) peak are 0.18, 0.25, 0.28, and 0.30 for Al₂O₃ (0 0 0 1), Si (1 0 0), MgO (1 0 0), and fused silica, respectively. The grain sizes of phosphors grown on different substrates were estimated by using Scherrer's formula and the maximum crystallite size observed for the thin film grown on Al₂O₃ (0 0 0 1). The room temperature PL spectra exhibit only the red emission peak at 613 nm radiated from the transition of (¹D₂ → ³H₄) and the maximum PL intensity for the films grown on the Al₂O₃ (0 0 0 1) is 1.1, 1.4, and 3.7 times higher than that of the CaTiO₃:Pr³⁺ films grown on MgO (1 0 0), Si (1 0 0), and fused Sillica substrates, respectively. The crystallinity, surface morphology and luminescence spectra of thin-film phosphors were highly dependent on substrates.     

Growth of carbon nanotubes on stainless steel substrates by DC-PECVD

We report on the fabrication of carbon nanotubes (CNTs) on Ni-coated stainless steel (SUS) substrates by using dc plasma enhanced chemical vapor deposition. The synthesized CNTs have the diameter of about 30 nm and the length of about 1.2 μm. To verify the effects of SUS substrates on the growth of CNTs, CNTs had also been grown on Ni-coated Si substrates. CNTs grown on the SUS substrates were more uniform compared with those grown on the Si substrates. Field emission properties of the CNT films were measured in the diode configuration, and the turn-on electric field of 3.87 V/μm and field enhancement factor β of about 1737 were obtained from the synthesized CNTs at the gap of 500 μm between the SUS substrate and the anode. These results have not only clarified the effects of the substrate on the growth of CNTs, but also shown the potential of CNTs in field emission applications, especially CNT-based cold-cathode X-ray tubes.     

Effects of correlated disorder on the magneto‐transport in colossal magnetoresistance manganites

Monte‐Carlo simulations predict that a local correlated disorder is responsible for many of the novel transport and magnetic properties of colossal magnetoresistance (CMR) materials such as manganites. One important prediction of these models is that the resistivity at the metal–insulator transition (MIT) in manganites depends strongly on the correlated quenched disorder. However, experimental confirmation has been challenging since it is difficult to control the amount of disorder in these compounds. We carried out experiments on Sm_0.55Sr_0.45MnO₃, a prototypical CMR manganite with a sharp MIT, whereby the oxygen‐related disorder is systematically enhanced by low temperature thermal activation. We observe dramatic changes in the temperature dependence of resistivity at the MIT as the amount of quenched disorder is increased, occurring in a manner that is in agreement with theoretical predictions.