Wasseruntersuchung

Ohne Zusammenfassung     

Messung der zirkularen Polarisation der Inneren Bremsstrahlung von90Y

The circular polarization of the Internal Bremsstrahlung (IB) of⁹⁰Y was measured with a Compton polarimeter according to Beard and Rose. The results are compatible with the theoretical predictions of Ford and Martin [8], who include “detour transitions” in their calculations of the circular polarization. Measurements ofΒ-γ-correlations of the IB of⁹⁰Y are discussed, which suggest the consideration of detour transitions too.     

Methode zur Brom-Bestimmung in Woll-Textilien mittels Röntgen-Fluoreszenz-Spektroskopie

Ohne Zusammenfassung     

Ein genaues und schnelles Verfahren zur kombinierten direkten Bestimmung der Oxydationsstufe des Vanadins und des Vanadingehalts von Metall-Vanadin-Sauerstoffverbindungen

Zusammenfassung Es wird ein Verfahren beschrieben, das es gestattet, in Metall- Vanadin-Sauerstoffverbindungen in einer Probe hintereinander die Oxydationsstufe des Vanadins und den Vanadingehalt auf maßanalytischem Wege mit großer Genauigkeit zu bestimmen. Zur Ermittlung der Oxydationsstufe wird mit einer bekannten Menge KMnO₄-Lösung oxydierend gelöst und mit FeSO₄-Lösung bis zum Vanadin(IV) zurücktitriert. Als Indicator wird Natrium-N-methyldiphenylamin-p-sulfonat verwendet. Anschließend wird mit KMnO₄ zum Vanadin(V) oxydiert, der KMnO₄-Überschuß mit Nitrit entfernt, das nicht umgesetzte Nitrit mit Harnstoff zerstört und der Vanadingehalt durch erneute Titration mit FeSO₄-Lösung bestimmt.     

A self-threaded "molecular 8"

A new type of [1]rotaxanes containing two aliphatic bridges between axle and wheel is obtained in 39% yield in a one-step synthesis starting from a [2]rotaxane which contained one sulfonamide group each in both the wheel and the axle. Temperature controlled chemoselective substitution reactions first at these sulfonamide nitrogens and then subsequently at the various other carboxamide nitrogens in the wheel and axle give rise to the formation of an isomeric mixture of three double-bridged [1]rotaxanes which could be separated by HPLC. Structure determination of the main product 3a was possible by NMR experiments supported by molecular modeling calculations. Using different reaction conditions, a double-substituted but not yet bridged [2]rotaxane 4 could be isolated as an intermediate giving further evidence for the assigned structure of 3a and the way of its formation. The shape of this double-bridged [1]rotaxane 3a reminds of a self-intertwining chiral "molecular 8", in which any possible racemization due to deslipping is hindered by the two stoppers originating from the former rotaxane axle. Hence, to the best of our knowledge this is the first example of a molecule in which both concepts, cycloenantiomerism and helical chirality, are realised in one structure. Enantiomer separation of the main product was possible by further HPLC using chiral stationary phases. The Cotton effects of the circular dichrograms are different to those of the already synthesized [1]rotaxanes bearing just one aliphatic bridge between axle and wheel.     

Charged-particle pseudorapidity density distributions from Au+Au collisions at sqrt[s(NN)]=130 GeV

The charged-particle pseudorapidity density dN(ch)/d eta has been measured for Au+Au collisions at sqrt[s(NN)] = 130 GeV at RHIC, using the PHOBOS apparatus. The total number of charged particles produced for the 3% most-central Au+Au collisions for /eta/相似文献   

Dibromodiphenylstannane: isolated centrosymmetric dimers as a new structure motif for the intermolecular association of diorganotin(IV) dihalides

In the crystalline state, the low‐melting title compound [common name: diphenyltin(IV) dibromide], [SnBr₂(C₆H₅)₂], consists of distorted tetrahedral molecules with compressed halide and enlarged carbon opening angles of 102.741 (9) and 123.53 (8)°, respectively, and Sn—C and Sn—Br bond lengths of 2.109 (2)/2.113 (2) and 2.4710 (3)/2.4947 (3) Å, respectively. Intermolecular Sn...Br interactions, typical for diorganotin(IV) dihalides, R₂SnHal₂ (with Hal = Cl, Br, I), and sterically less demanding organic groups lead to the formation of a hitherto unknown association pattern consisting of centrosymmetric dimers with an antiparallel orientation of the dipole moments and two weak intermolecular Sn...Br distances of 3.8482 (3) Å between one of the two Br atoms and its neighbouring Sn atom, and vice versa. The second Br atom is not involved in intermolecular interactions and lies somewhat outside the association plane that, therefore, is not coplanar [interplanar angle = 1.750 (2)°] with the tin–halide plane. The new structure motif of intermolecular tin–halide interaction can be classified as 2a_i, which indicates the number of molecules (i.e. `2') composing the oligomer, the antiparallel orientation (i.e. `a') of their dipole moments and the centre of symmetry (i.e. `i') giving rise to the association pattern.     

1,7‐Dideaza‐2′‐deoxy‐6‐nitronebularine: a pyrrolo[2,3‐b]pyridine nucleoside with an intramolecular hydrogen bond stabilizing the syn conformation

The title compound [systematic name: 1‐(2‐deoxy‐β‐D‐erythro‐pentofuranosyl)‐4‐nitro‐1H‐pyrrolo[2,3‐b]pyridine], C₁₂H₁₃N₃O₅, forms an intramolecular hydrogen bond between the pyridine N atom as acceptor and the 5′‐hydroxy group of the sugar residue as donor. Consequently, the N‐glycosylic bond exhibits a syn conformation, with a χ torsion angle of 61.6 (2)°, and the pentofuranosyl residue adopts a C2′‐endo envelope conformation (²E, S‐type), with P = 162.1 (1)° and τ_m = 36.2 (1)°. The orientation of the exocyclic C4′—C5′ bond is +sc (gauche, gauche), with a torsion angle γ = 49.1 (2)°. The title nucleoside forms an ordered and stacked three‐dimensional network. The pyrrole ring of one layer faces the pyridine ring of an adjacent layer. Additionally, intermolecular O—H...O and C—H...O hydrogen bonds stabilize the crystal structure.     

Is it necessary to penalize impulsive noise +5 dB due to higher risk of hearing damage?

It is studied whether the +5 dB penalty for impulsiveness established by ISO 1999:1990 accounts for a higher risk of noise-induced hearing loss. A total of 16 normal-hearing human subjects were exposed for 10 min to two types of binaural industrial-recordings: (1) a continuous broad-band noise normalized to L(EX,8 h)=80 dBA and (2) the combination of the previous stimulus with an impulsive noise normalized to L(EX,8 h)=75+5(db penalty)=80 dBA (peak level 117 dBC and repetition rate of 0.5 impacts per second). Distortion product otoacoustic emissions (DPOAEs) were measured in a broad frequency range before and in the following 90 min after the exposure. The group results show that the continuous exposure had a bigger impact on DPOAE levels, with a maximum DPOAE shift of approximately 5 dB in the frequency range of 2-3.15 kHz during the first 10 min of the recovery. No evident DPOAE shift is seen for the impulsive + continuous stimulus. The results indicate that the penalty overestimated the effects on DPOAE levels and support the concept that the risk of hearing loss from low-level impulses may be predicted on an equal-energy basis.     

Bimetric renormalization group flows in quantum Einstein gravity

The formulation of an exact functional renormalization group equation for quantum Einstein gravity necessitates that the underlying effective average action depends on two metrics, a dynamical metric giving the vacuum expectation value of the quantum field, and a background metric supplying the coarse graining scale. The central requirement of “background independence” is met by leaving the background metric completely arbitrary. This bimetric structure entails that the effective average action may contain three classes of interactions: those built from the dynamical metric only, terms which are purely background, and those involving a mixture of both metrics. This work initiates the first study of the full-fledged gravitational RG flow, which explicitly accounts for this bimetric structure, by considering an ansatz for the effective average action which includes all three classes of interactions. It is shown that the non-trivial gravitational RG fixed point central to the asymptotic safety program persists upon disentangling the dynamical and background terms. Moreover, upon including the mixed terms, a second non-trivial fixed point emerges, which may control the theory’s IR behavior.