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M Mehring

Publications and source records attributed to M Mehring.

At least 19 recordsLinked to original sources
PubMed2005

Indirect detection of selective nuclear spin-spin interactions in a hostile environment.

We present a number of techniques which may be used to obtain precise values of selective spin-spin interactions between two nuclear spins in a hostile environment. Such an environment may be characterized by very fast relaxation and decoherence, e.g. due to the strong coupling of the two spins of interest to electron spins in their vicinity as well as other nuclei. Here, we used dilute paramagnetic Ce(3+) centers hosted in a single crystal of CaF(2). Selected (19)F internuclear interactions were measured indirectly by applying different electron nuclear double resonance (ENDOR) pulse sequences.

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PubMed2004

Pseudoentanglement of spin states in the multilevel 15N@C60 system.

We have prepared combined electron and nuclear spin pseudoentangled states Psi+/-27 and Phi+/-18 out of the total number of eight quantum states in the multilevel quantum system of a nitrogen atom with electron spin 3/2 and nuclear spin 1/2 encaged in the endohedral fullerene (15)N@C(60). Density matrix tomography was applied to verify the degree of entanglement.

Journal Article↗
PubMed2003

Entanglement between an electron and a nuclear spin 1/2.

We report on the preparation and detection of entangled states between an electron spin 1/2 and a nuclear spin 1/2 in a molecular single crystal. These were created by applying pulses at ESR (9.5 GHz) and NMR (21 MHz, 46 MHz) frequencies. Entanglement was detected by using a special entanglement detector sequence based on a unitary back transformation including phase rotation.

Journal Article↗
PubMed2001

[Prognostic factors for development of peritoneal carcinosis in stomach carcinoma].

OBJECTIVE: Several adjuvant therapy concepts have been developed to improve the treatment of gastric cancer patients. Dealing with intraperitoneal chemotherapy, it seems to be useful to determine suitable prognostic factors for the occurrence of peritoneal carcinosis, as it is possible to select patients who may profit from this therapy. METHODS: Between June 1975 and December 1999 resection of gastric cancer was performed in 575 patients. From 1 January 1986 clinical data were recorded prospectively, before that time, retrospectively. The complete data concerning preoperative diagnosis, operation, histology, postoperative course and survival time were documented in an Excel file for statistical analysis. Multivariate analysis was performed using the chi-squared logistic regression test. RESULTS: Significant correlation was found between the occurrence of peritoneal dissemination and tumour stage pT3, pN2, G3, cancer of the whole stomach and cancer at the anastomotic site after partial gastric resection. Lauren classification, signet-ring cell cancer, liver metastasis and tumour localisation in the distal or proximal stomach showed no significant correlation to peritoneal carcinosis in the multivariate analysis. However, only one-third of patients with liver metastasis had simultaneous peritoneal dissemination. CONCLUSION: The results show a clinical correlation of tumour localisation, infiltration of the serosa, lymph node metastasis and grading with peritoneal dissemination. The present data serve as a basis for further histochemical and molecular biological investigations e.g. of the expression of adhesion molecules to determine the risk of peritoneal tumour dissemination after gastric cancer.

Adult↗
PubMed2000

Syntheses, characterizations, and single-crystal X-ray structures of soluble titanium alkoxide phosphonates.

Reactions of Ti(OiPr)4 with different phosphonic acids RPO3H2 (R = Ph, 4-CNPh, Me, tBu) in organic solvents have been investigated. In the presence of small amounts of water, the new molecular titanium oxide alkoxide phosphonates [Ti4(mu 3-O)(OiPr)5(mu-OiPr)3(RPO3)3].DMSO [R = Ph (1), Me (2), tBu (3), 4-CNPh (4)] were isolated. The single-crystal X-ray structure analyses of 1 and 2 revealed hexacoordinated titanium atoms and a connectivity of (111) for each phosphonate. Under rigorous exclusion of water, the reaction of Ti(OiPr)4 with tert-butylphosphonic acid in toluene gave the titanium phosphonate tetramer [Ti(OiPr)2(tBuPO3)]4 (5). A single-crystal X-ray structure analysis of 5 revealed a 5 + 1 coordination of the titanium atoms as a result of the (112) connectivity of each phosphonate; such a coordination mode has never been reported for a titanium phosphate, phosphonate, or phosphinate. Compounds 1-5 were characterized by FT-IR, 31P MAS NMR, and solution multinuclear NMR (1H, 13C(1H,) 31P(1H)) spectroscopies. 13C CP MAS NMR experiments were carried out on arylphosphonates 1 and 4. Solution NMR experiments were also used to investigate the exchange reaction between 1 and 2 and the conversion of 5 to [Ti4(mu 3-O)(OiPr)5(mu-OiPr)3(tBuPO3)3].iPrOH by partial hydrolysis in the presence of Ti(OiPr)4. The phosphonate clusters 1-5 are soluble in organic solvents and are likely intermediates in the sol-gel processing of inorganic-organic hybrids based on titanium oxide and phosphonate groups that we are currently developing.

Journal Article↗
PubMed2000

Charge-order-driven spin-peierls transition in alpha(')-NaxV2O5

We conclude from 23Na and 51V NMR measurements in alpha(')-NaxV2O5 (x = 0.996) (i) a charge-ordering transition starting at T</=37 K and preceding the lattice distortion and (ii) the formation of a spin gap Delta = 106 K at T(c) = 34.7 K. Above T(c), only a single Na site is observed in agreement with the Pmmn space group of this first 1/4-filled ladder system. Below T(c) = 34.7 K, this line evolves into eight distinct 23Na quadrupolar split lines, which evidences a lattice distortion with, at least, a doubling of the unit cell in the (a,b) plane. A model for this unique transition, implying both charge density wave and spin-Peierls order, is discussed.

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PubMed2000

Electron spin density distribution in the polymer phase of CsC60: assignment of the NMR spectrum.

We present high resolution 133Cs-13C double resonance NMR data and 13C-13C NMR correlation spectra of 13C enriched samples of the polymeric phase of CsC60. These data lead to a partial assignment of the lines in the 13C NMR spectrum of CsC60 to the carbon positions on the C60 molecule. A plausible completion of the assignment can be made on the basis of an ab initio calculation. The data support the view that the conduction electron density is concentrated at the C60 "equator," away from the interfullerene bonds.

Journal Article↗
PubMed2000

Production of volatile derivatives of metal(loid)s by microflora involved in anaerobic digestion of sewage sludge.

Gases released from anaerobic wastewater treatment facilities contain considerable amounts of volatile methyl and hydride derivatives of metals and metalloids, such as arsine (AsH(3)), monomethylarsine, dimethylarsine, trimethylarsine, trimethylbismuth (TMBi), elemental mercury (Hg(0)), trimethylstibine, dimethyltellurium, and tetramethyltin. Most of these compounds could be shown to be produced by pure cultures of microorganisms which are representatives of the anaerobic sewage sludge microflora, i.e., methanogenic archaea (Methanobacterium formicicum, Methanosarcina barkeri, Methanobacterium thermoautotrophicum), sulfate-reducing bacteria (Desulfovibrio vulgaris, D. gigas), and a peptolytic bacterium (Clostridium collagenovorans). Additionally, dimethylselenium and dimethyldiselenium could be detected in the headspace of most of the pure cultures. This is the first report of the production of TMBi, stibine, monomethylstibine, and dimethylstibine by a pure culture of M. formicicum.

Anaerobiosis↗