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The Helmholtz Zentrum München is a member of the Helmholtz Association of German Research Centres and is responsible for studying environmental health issues. Founded in 1964, it is a joint project of the Federal Ministry of Education and Research and Bavaria's Finance Ministry. The Helmholtz Zentrum München's focus is to investigate chronic diseases like diabetes, cancer, lung diseases, illnesses of the immune system or mechanisms of neurodegenerative diseases.The head office of the center is located in Neuherberg to the north of Munich. Helmholtz Zentrum München has 1700 staff members. Helmholtz Zentrum München belongs to the Helmholtz Association, a German research organization with 16 scientific-technical and medical-biological research centers. Wikipedia.

Exposure of ion bombarded solids to Cs gives rise to a very strong enhancement of the yields of negatively charged secondary ions and, concurrently, to a lowering of positive ion yields. The phenomena have been explored in a large number of experimental and theoretical studies but attempts to clarify the mechanism of ion formation were not as successful as assumed. This review examines the state of the art in Cs controlled secondary ion mass spectrometry (SIMS) in great detail, with due consideration of low-energy alkali-ion scattering. In very basic studies on alkali induced secondary ion yield changes, sub-monolayer quantities of Cs or Li were deposited on the sample surface, followed by low-fluence ion bombardment, to avoid significant damage. If SIMS is applied to characterise the composition of solid materials, the simplest approach to achieving sample erosion as well as high negative-ion yields is bombardment with primary ions of Cs. Two other methods of sample loading with Cs provide more flexibility, (i) exposure to a collimated beam of Cs vapour and concurrent bombardment with high-energy non-Cs ions and (ii) the mixed-beam approach involving quasi-simultaneous bombardment with Cs and Xe ions. Both concepts have the advantage that undesirable sample overload with Cs can be avoided. High Cs concentrations reduce the formation probability of target specific molecular ions and lower the yields of all types of positive secondary ions, including Cs+, M+, X+, MCs + and XCs+ (M and X denoting matrix and impurity elements). Quantitative SIMS analysis using MCs+ and XCs+ ions appears feasible, provided the Cs coverage is kept below about 5%. The semi-classical model of resonant charge transfer, also known as the tunnelling model, has long been considered a solid framework for the interpretation of Cs and Li based SIMS data. The model predicts ionisation probabilities for cases in which, at shallow distances from the surface, the affinity (ionisation) level of the departing atom is shifted below (above) the Fermi level. Ion yields should be controlled by the work function (WF) of the sample, Φ, and the normal velocity of the ejected ions. To explore the predicted velocity dependence, the performance characteristics of the employed SIMS instrument need to be known. The Cs induced negative-ion yield enhancement observed with pure metal and alloy targets often exceeded five orders of magnitude, with enhancement factors essentially independent of the emission energy. This absence of a velocity dependence is at variance with the predictions of the tunnelling model. Previous theoretical attempts to model the Φ-dependence and the apparent velocity effect for the overrated case of O-emission from Li and Cs exposed oxidised metal surfaces must be considered a meander. The experimental data, recorded with a quadrupole based instrument of inadequate extraction geometry, may alternatively be rationalised in terms of alkali induced changes in the energy spectrum of sputtered atoms. Another important finding is that secondary ion yield changes do not correlate with the absolute magnitude of the (macroscopic) WF but often with WF changes, ΔΦ. The frequently used method of determining ΔΦ in situ from the shift of the leading edge of secondary ion energy spectra rests on the assumption, taken for granted or not even appreciated, that Cs induced yield changes are independent of the ion's emission velocity. Hence the approach is only applicable if the tunnelling model is not valid. The local character of alkali induced WF changes, which might provide a route to an understanding of previously unexplained phenomena, has been explored using photoemission of adsorbed inert gases, scanning tunneling microscopy and low-energy ion scattering spectrometry. At room temperature, the Cs coverage is limited to one layer of adatoms. Close similarities are identified between WF changes generated by Cs vapour deposition and by bombardment with Cs ions. This finding implies that sub-monolayer quantities of Cs adatoms grow at the surface of Cs bombarded samples. The process has been studied in-situ by medium-energy ion scattering spectrometry. The stationary Cs coverage, NCs, is controlled by the efficiency of active transport of implanted atoms to the surface, the bulk retention properties of the sample and the cross section for sputtering of adatoms. Unearthing immobile implanted Cs atoms by sputter erosion usually provides only a minor contribution to the stationary coverage. Cs adatoms are mobile; the time required for final adatom rearrangement may be on the order of minutes at room temperature. Exposure of Cs bombarded samples to oxygen gives rise to oxidation of the substrate as well as to the formation of oxide layers of complex composition. Intercalation should be taken into account as a possible route of alkali transport into analysed samples. An important aspect ignored in prior work is that the alkali coverage required to produce a certain WF change is five to seven times higher if Li is deposited instead of Cs. Studies involving the use of Li thus provide no advantage compared to Cs. Furthermore, migration of the tiny Li atoms into the sample and metallisation effects aggrevate data interpretation. Literature data for ΔΦ (NCs), measured using Cs vapour deposition, can be converted to calibration curves, N Cs (ΔΦ), for calculating the coverage established in implantation studies, a method referred to as ΔΦ→NCs conversion. This concept may be carried even further, as shown convincingly for silicon, the material examined most frequently in basic SIMS studies: Si - ion fractions, P(Si-), derived from yields measured under vastly different conditions of Cs supply, exhibit essentially the same ΔΦ dependence. Inverting the data one can produce calibration functions for ΔΦ versus P(Si-), denoted P(Si -)→ΔΦ, or, more generally, P(M-) →ΔΦ conversion. On this basis, transient yields measured during Cs implantation can be evaluated as a function of Cs coverage. The summarised results imply that secondary ions are commonly not formed by charge transfer between an escaping atom and the electronic system of the sample but are already emitted as ions. The probability of ion formation appears to be controlled by the local ionic character of the alkali-target atom bonds, i.e., by the difference in electronegativity between the involved elements as well as by the electron affinity and the ionisation potential of the departing atom. This idea is supported by the finding that Si- yields exhibit the same very strong dependence on Cs coverage as Si+ and O- yields on the oxygen fraction in oxygen loaded Si. Most challenging to theoreticians is the finding that the ionisation probability is independent of the emission velocity of sputtered ions. This phenomenon cannot be rationalised along established routes of thinking. Different concepts need to be explored. An old, somewhat exotic idea takes account of the heavy perturbation created for a very short period of time at the site of ion emission (dynamic randomisation). Molecular dynamics simulations are desirable to clarify the issue. Ultimately it may be possible to describe all phenomena of enhanced or suppressed secondary ion formation, produced either by surface loading with alkali atoms or by enforced surface oxidation, on the basis of a single universal model. There is plenty of room for exciting new studies. © 2012 Elsevier B.V. Source

Ntziachristos V.,Helmholtz Center Munich
Nature Methods | Year: 2010

Optical microscopy has been a fundamental tool of biological discovery for more than three centuries, but its in vivo tissue imaging ability has been restricted by light scattering to superficial investigations, even when confocal or multiphoton methods are used. Recent advances in optical and optoacoustic (photoacoustic) imaging now allow imaging at depths and resolutions unprecedented for optical methods. These abilities are increasingly important to understand the dynamic interactions of cellular processes at different systems levels, a major challenge of postgenome biology. This Review discusses promising photonic methods that have the ability to visualize cellular and subcellular components in tissues across different penetration scales. The methods are classified into microscopic, mesoscopic and macroscopic approaches, according to the tissue depth at which they operate. Key characteristics associated with different imaging implementations are described and the potential of these technologies in biological applications is discussed. © 2010 Nature America, Inc. All rights reserved. Source

Helmholtz Center Munich | Date: 2013-08-13

The present invention relates to a method of identifying a predisposition for developing type 2 diabetes mellitus in a subject, said method comprising the step of assessing in a sample obtained from said subject the amount of one or more metabolite(s) selected from (a) a first group comprising the metabolites glycine, lysoPhosphatidylcholine acyl C18:2, lysoPhosphatidylcholine acyl C17:0, lysoPhosphatidylcholine acyl C18:0, lysoPhosphatidylcholine acyl C18:1, phosphatidylcholine acyl-alkyl C34:2, phosphatidylcholine acyl-alkyl C36:2, phosphatidylcholine acyl-alkyl C36:3 and isobaric metabolites having the same molecular mass as glycine, lysoPhosphatidylcholine acyl C18:2, lysoPhosphatidylcholine acyl C17:0, lysoPhosphatidylcholine acyl C18:0, lysoPhosphatidylcholine acyl C18:1, phosphatidylcholine acyl-alkyl C34:2, phosphatidylcholine acyl-alkyl C36:2 or phosphatidylcholine acyl-alkyl C36:3 but different chemical formula; and/or (b) a second group comprising the metabolite acetylcarnitine C2 and an isobaric metabolite having the same molecular weight as acetylcarnitine C2 but different chemical formula; wherein a decrease in the amount of a metabolite selected from said first group or an increase in the amount of a metabolite selected from said second group as compared to the amount of the corresponding metabolite(s) of a control is indicative of a predisposition to develop type 2 diabetes mellitus. Further, the invention relates to a method of identifying a compound capable of preventing type 2 diabetes mellitus and diseases associated therewith or serving as a lead compound for developing a compound capable of preventing type 2 diabetes mellitus and diseases associated therewith and a method of selecting a therapy to prevent type 2 diabetes mellitus. Also, the invention relates to a kit.

A method for detecting radiation during the examination of a sample (

Helmholtz Center Munich | Date: 2014-02-06

The invention relates to a method for in vitro maturation of at least one immate dendritic cell, comprising stimulating said immature dendritic cell with TNF, IL-1, IFN, a TLR7/8 agonist and prostaglandin E2(PG). Furthermore, the invention elates to a composition comprising these factors as well as to mature dendritic cells produced by a method of the invention.

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