Uniqueness and Non-uniqueness in the Einstein Constraints

The conformal thin sandwich (CTS) equations are a set of four of the Einstein equations, which generalize the Laplace-Poisson equation of Newton's theory. We examine numerically solutions of the CTS equations describing perturbed Minkowski space, and find only one solution. However, we find {\em two} distinct solutions, one even containing a black hole, when the lapse is determined by a fifth elliptic equation through specification of the mean curvature. While the relationship of the two systems and their solutions is a fundamental property of general relativity, this fairly simple example of an elliptic system with non-unique solutions is also of broader interest.Comment: 4 pages, 4 figures; abstract and introduction rewritte

E2F4 regulates transcriptional activation in mouse embryonic stem cells independently of the RB family.

E2F transcription factors are central regulators of cell division and cell fate decisions. E2F4 often represents the predominant E2F activity in cells. E2F4 is a transcriptional repressor implicated in cell cycle arrest and whose repressive activity depends on its interaction with members of the RB family. Here we show that E2F4 is important for the proliferation and the survival of mouse embryonic stem cells. In these cells, E2F4 acts in part as a transcriptional activator that promotes the expression of cell cycle genes. This role for E2F4 is independent of the RB family. Furthermore, E2F4 functionally interacts with chromatin regulators associated with gene activation and we observed decreased histone acetylation at the promoters of cell cycle genes and E2F targets upon loss of E2F4 in RB family-mutant cells. Taken together, our findings uncover a non-canonical role for E2F4 that provide insights into the biology of rapidly dividing cells

PCB 47, 51, 68 – Bestimmung von PCB 47, 51, 68 in der Luft am Arbeitsplatz mittels Gaschromatographie (GC-ECD)

This analytical method is a validated measurement procedure for the determination of the three tetrachlorinated biphenyls PCB 47 [2437-79-8], PCB 51 [68194-04-7] and PCB 68 [73575-52-7] in workplace air in a concentration range of 0.16 to 0.62 μg/m3. It was developed to detect PCB that only may be generated during the manufacture of silicone products with peroxidic crosslinking with bis(2,4-dichlorobenzoyl) peroxide. By measurement in manufacturing plants it could be proven that the PCB to be investigated are present exclusively in vapour form. For this reason, the method was only validated for vaporous samples. There are currently no valid evaluation criteria for these PCB. Therefore, the German Occupational Exposure Limit Value for the sum of all PCB (5 × sum of the 6 indicator PCB [28, 52, 101, 138, 152, 180]) of 3 μg/m3 was used as the assessment standard for each congener. For sampling, a defined volume of air is drawn through a sorbent tube filled with Florisil. The flow rate is set to 1 l/min and sampling duration is 4 hours (which correspond to a sampling volume of 240 l). The PCB are extracted with n-hexane at 40 °C in an ultrasonic bath and subsequently analysed using gas chromatography with electron capture detection. The quantitative determination is based on a calibration function. The limit of quantification is 0.11 μg/m3 based on an air sample volume of 240 l. The mean recovery is 96% and the expanded uncertainty for the validation range of 0.16 to 0.62 μg/m3 is 22 to 24%

Acrylonitrile – Determination of acrylonitrile in workplace air using gas chromatography (GC-MS)

This analytical method is a validated measurement procedure for the determination of acrylonitrile [107-13-1] after personal or stationary sampling. Sampling is performed by drawing a defined volume of air through an adsorption tube made of stainless steel packed with Chromosorb 106 using a suitable flow-regulated pump. After thermal desorption, the acrylonitrile retained on the adsorbent is analysed using gas chromatography with flame ionisation detection and mass spectrometry. The relative limit of quantification (LOQ) is 0.0042 mg acrylonitrile/m3 for an air sample volume of 2.4 l. The mean recovery for acrylonitrile was 104%. The concentration-dependent expanded uncertainty was 26.0% to 26.6%. This analytical method has been accredited by the accident insurance companies for the detection in workplace air of substances that are carcinogenic, mutagenic or toxic to reproduction. This method has been tested and recommended for the determination of acrylonitrile in work areas by the GermanSocial Accident Insurance (DGUV). Both personal and stationary sampling can be performed for measurements in order to evaluate work area

1,2-Dichloroethane – Method for the determination of 1,2-dichloroethane in workplace air using gas chromatography (GC-MS)

This analytical method is a validated measurement procedure for the determination of 1,2-dichloroethane [107-06-2] after personal or stationary sampling. Sampling is performed by drawing a defined volume of air through an adsorption tube made of stainless steel packed with Chromosorb 106 using a suitable flow-regulated pump. After thermal desorption, the 1,2-dichloroethane retained on the adsorbens is analysed using gas chromatography with flame ionisation detection and mass spectrometry. The relative limit of quantification (LOQ) is 0.009 mg 1,2-dichloroethane/m3 for an air sample volume of 1.2 l. The mean recovery for 1,2-dichloroethane was 101%. The concentration-dependent expanded uncertainty was 20% to 21%. This analytical method has been accredited by the accident insurance companies for the detection in workplace air of substances that are carcinogenic, mutagenic or toxic to reproduction. This method has been tested and recommended for the determination of 1,2-dichloroethane in work areas by the German Social Accident Insurance (DGUV). Both personal and stationary sampling can be performed for measurements in order to evaluate work areas

Bisphenol A, bisphenol F, and bisphenol S – Determination of bisphenol A, bisphenol F, and bisphenol S in urine by UPLC-ESI-MS/MS

The working group “Analyses in Biological Materials” of the Permanent Senate Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area developed and verified the presented biomonitoring method. Bisphenol A (BPA), bisphenol F (BPF), and bisphenol S (BPS) are co-monomers for producing engineering plastics used in the automotive, food, and household sectors and are also used in paper chemicals and leather-tanning agents. Due to the wide range of applications, exposure to these bisphenols can occur both at the workplace and via the environment. The aim of this work was to develop a selective method for the determination of BPA, BPF, and BPS in human urine. This method has been comprehensively verified, and the reliability data have been confirmed by replication and validation of the procedure in a second, independent laboratory. The internal standards are added to the buffered urine samples, which are then subjected to enzymatic hydrolysis and processed via dispersive liquid-liquid microextraction (DLLME). The analytes are separated from matrix components by liquid chromatography and detected by tandem mass spectrometry using electrospray ionisation. Quantitative evaluation is carried out via external calibration in water. The good precision and accuracy data show that the method provides reliable and accurate measurement values. The method is selective and sensitive, and the quantitation limits of 0.25 μg/l, 0.10 μg/l, and 0.05 μg/l urine for BPA, BPF, and BPS, respectively, are sufficient to determine occupational as well as background exposure