Comment on 'Stability of the semiclassical Einstein equation'

Some mathematical errors of the paper commented upon [W.-M. Suen, Phys. Rev. D 40, (1989) 315] are corrected.Comment: 3 pages, LaTeX, reprinted from Phys. Rev. D 50 (1994) 545

How to measure spatial distances?

The use of time--like geodesics to measure temporal distances is better justified than the use of space--like geodesics for a measurement of spatial distances. We give examples where a ''spatial distance'' cannot be appropriately determined by the length of a space--like geodesic.Comment: 4 pages, latex, no figure

Total synthesis of the cyclic monoterpenoid pyrano[3,2-a]carbazole alkaloids derived from 2-hydroxy-6-methylcarbazole

The synthesis of seven pyrano[3,2-a]carbazole alkaloids has been achieved using their putative biogenetic precursor 2-hydroxy-6-methylcarbazole as key intermediate

Phosphorus donors in highly strained silicon

The hyperfine interaction of phosphorus donors in fully strained Si thin films grown on virtual Si$_{1-x}$Ge$_x$ substrates with $x\leq 0.3$ is determined via electrically detected magnetic resonance. For highly strained epilayers, hyperfine interactions as low as 0.8 mT are observed, significantly below the limit predicted by valley repopulation. Within a Green's function approach, density functional theory (DFT) shows that the additional reduction is caused by the volume increase of the unit cell and a local relaxation of the Si ligands of the P donor.Comment: 12 pages, 3 figure

The tetralogy of Birkhoff theorems

We classify the existent Birkhoff-type theorems into four classes: First, in field theory, the theorem states the absence of helicity 0- and spin 0-parts of the gravitational field. Second, in relativistic astrophysics, it is the statement that the gravitational far-field of a spherically symmetric star carries, apart from its mass, no information about the star; therefore, a radially oscillating star has a static gravitational far-field. Third, in mathematical physics, Birkhoff's theorem reads: up to singular exceptions of measure zero, the spherically symmetric solutions of Einstein's vacuum field equation with Lambda = 0 can be expressed by the Schwarzschild metric; for Lambda unequal 0, it is the Schwarzschild-de Sitter metric instead. Fourth, in differential geometry, any statement of the type: every member of a family of pseudo-Riemannian space-times has more isometries than expected from the original metric ansatz, carries the name Birkhoff-type theorem. Within the fourth of these classes we present some new results with further values of dimension and signature of the related spaces; including them are some counterexamples: families of space-times where no Birkhoff-type theorem is valid. These counterexamples further confirm the conjecture, that the Birkhoff-type theorems have their origin in the property, that the two eigenvalues of the Ricci tensor of two-dimensional pseudo-Riemannian spaces always coincide, a property not having an analogy in higher dimensions. Hence, Birkhoff-type theorems exist only for those physical situations which are reducible to two dimensions.Comment: 26 pages, updated references, minor text changes, accepted by Gen. Relat. Gra

Spin echo formation in the presence of stochastic dynamics

Spin echo formation in magnetic field gradients in the presence of fast stochastic motion is studied for hyperpolarized He3 gas at different diffusivities. The fast translational motion leads to frequency shifts already during echo formation, which can be described analytically for a linear gradient. Despite complete signal loss at the position of the spin echo itself, considerable intensity can be preserved at an earlier time (2τ rather than 2τ, where τ is the pulse delay). Hence, the phenomenon is designated as a pseudo spin echo. © 2007 The American Physical Society.Fil: Zänker, Paul P.. Max Planck Institute For Polymer Research; AlemaniaFil: Schmidt, Jochen. Max Planck Institute For Polymer Research; AlemaniaFil: Schmiedeskamp, Jörg. Max Planck Institute For Polymer Research; AlemaniaFil: Acosta, Rodolfo Héctor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Spiess, Hans W.. Max Planck Institute For Polymer Research; Alemani

Long-term in vivo imaging of fibrillar tau in the retina of P301S transgenic mice.

Tauopathies are widespread neurodegenerative disorders characterised by the intracellular accumulation of hyperphosphorylated tau. Especially in Alzheimer's disease, pathological alterations in the retina are discussed as potential biomarkers to improve early diagnosis of the disease. Using mice expressing human mutant P301S tau, we demonstrate for the first time a straightforward optical approach for the in vivo detection of fibrillar tau in the retina. Longitudinal examinations of individual animals revealed the fate of single cells containing fibrillar tau and the progression of tau pathology over several months. This technique is most suitable to monitor therapeutic interventions aimed at reducing the accumulation of fibrillar tau. In order to evaluate if this approach can be translated to human diagnosis, we tried to detect fibrillar protein aggregates in the post-mortem retinas of patients that had suffered from Alzheimer's disease or Progressive Supranuclear Palsy. Even though we could detect hyperphosphorylated tau, we did not observe any fibrillar tau or Aß aggregates. In contradiction to previous studies, our observations do not support the notion that Aβ or tau in the retina are of diagnostic value in Alzheimer's disease

Військовополонені Першої світової війни в Кременчуцькому гарнізоні

У статті досліджено правове становище та умови перебування військовополонених Першої світової війни на території Кременчуцького гарнізону в другій половині 1916 року. На основі архівних даних визначено кількісний склад полонених, його розподіл за національною, соціальною та конфесійною ознаками. Досліджено динаміку чисельності, побутові умови та використання праці військовополонених.В статье исследовано правовое положение и условия пребывания военнопленных Первой мировой войны на территории Кременчугского гарнизона во второй половине 1916 года. На основе архивных данных определен количественный состав пленных, его распределение по национальной, социальной и конфессиональной принадлежности. Исследована динамика численности, бытовые условия и использования труда военнопленных.In article the legal status and conditions of stay of prisoners of war of the First World War in territory of the Kremenchug garrison in second half of 1916 is investigated. On the basis of contemporary records the quantitative structure captured, its distribution on a national, social and confessional accessory is defi ned. Dynamics of number, conditions of life and uses of work of prisoners of war is investigated