Magnetization Process of Atacamite: A Case of Weakly Coupled S=1/2 Sawtooth Chains.

We present a combined experimental and theoretical study of the mineral atacamite Cu_{2}Cl(OH)_{3}. Density-functional theory yields a Hamiltonian describing anisotropic sawtooth chains with weak 3D connections. Experimentally, we fully characterize the antiferromagnetically ordered state. Magnetic order shows a complex evolution with the magnetic field, while, starting at 31.5 T, we observe a plateaulike magnetization at about M_{sat}/2. Based on complementary theoretical approaches, we show that the latter is unrelated to the known magnetization plateau of a sawtooth chain. Instead, we provide evidence that the magnetization process in atacamite is a field-driven canting of a 3D network of weakly coupled sawtooth chains that form giant moments.

MnSi nanostructures obtained from epitaxially grown thin films: magnetotransport and Hall effect.

We present a comparative study of the (magneto)transport properties, including Hall effect, of bulk, epitaxially grown thin film and nanostructured MnSi. In order to set our results in relation to published data we extensively characterize our materials, this way establishing a comparatively good sample quality. Our analysis reveals that in particular for thin film and nanostructured material, there are extrinsic and intrinsic contributions to the electronic transport properties, which by modeling the data we separate out. Finally, we discuss our Hall effect data of nanostructured MnSi under consideration of the extrinsic contributions and with respect to the question of the detection of a topological Hall effect in a skyrmionic lattice.

Direct observation of electron propagation and dielectric screening on the atomic length scale.

The propagation and transport of electrons in crystals is a fundamental process pertaining to the functioning of most electronic devices. Microscopic theories describe this phenomenon as being based on the motion of Bloch wave packets. These wave packets are superpositions of individual Bloch states with the group velocity determined by the dispersion of the electronic band structure near the central wavevector in momentum space. This concept has been verified experimentally in artificial superlattices by the observation of Bloch oscillations--periodic oscillations of electrons in real and momentum space. Here we present a direct observation of electron wave packet motion in a real-space and real-time experiment, on length and time scales shorter than the Bloch oscillation amplitude and period. We show that attosecond metrology (1 as = 10(-18) seconds) now enables quantitative insight into weakly disturbed electron wave packet propagation on the atomic length scale without being hampered by scattering effects, which inevitably occur over macroscopic propagation length scales. We use sub-femtosecond (less than 10(-15) seconds) extreme-ultraviolet light pulses to launch photoelectron wave packets inside a tungsten crystal that is covered by magnesium films of varied, well-defined thicknesses of a few ångströms. Probing the moment of arrival of the wave packets at the surface with attosecond precision reveals free-electron-like, ballistic propagation behaviour inside the magnesium adlayer--constituting the semi-classical limit of Bloch wave packet motion. Real-time access to electron transport through atomic layers and interfaces promises unprecedented insight into phenomena that may enable the scaling of electronic and photonic circuits to atomic dimensions. In addition, this experiment allows us to determine the penetration depth of electrical fields at optical frequencies at solid interfaces on the atomic scale.

The mechanically induced structural disorder in barium hexaferrite, BaFe12O19, and its impact on magnetism.

The response of the structure of the M-type barium hexaferrite (BaFe12O19) to mechanical action through high-energy milling and its impact on the magnetic behaviour of the ferrite are investigated. Due to the ability of the (57)Fe Mössbauer spectroscopic technique to probe the environment of the Fe nuclei, a valuable insight on a local atomic scale into the mechanically induced changes in the hexagonal structure of the material is obtained. It is revealed that the milling of BaFe12O19 results in the deformation of its constituent polyhedra (FeO6 octahedra, FeO4 tetrahedra and FeO5 triangular bi-pyramids) as well as in the mechanically triggered transition of the Fe(3+) cations from the regular 12k octahedral sites into the interstitial positions provided by the magnetoplumbite structure. The response of the hexaferrite to the mechanical treatment is found to be accompanied by the formation of a non-uniform nanostructure consisting of an ordered crystallite surrounded/separated by a structurally disordered surface shell/interface region. The distorted polyhedra and the non-equilibrium cation distribution are found to be confined to the amorphous near-surface layers of the ferrite nanoparticles with the thickness extending up to about 2 nm. The information on the mechanically induced short-range structural disorder in BaFe12O19 is complemented by an investigation of its magnetic behaviour on a macroscopic scale. It is demonstrated that the milled ferrite nanoparticles exhibit a pure superparamagnetism at room temperature. As a consequence of the far-from-equilibrium structural disorder in the surface shell of the nanoparticles, the mechanically treated BaFe12O19 exhibits a reduced magnetization and an enhanced coercivity.

Thin film MnGe grown on Si(111).

MnGe has been grown as a thin film on Si(111) substrates by molecular beam epitaxy. A 10 Å layer of MnSi was used as the seed layer in order to establish the B20 crystal structure. Films of a thickness between 45 and 135 Å have been prepared and structurally characterized using reflection high-energy electron diffraction, atomic force microscopy and x-ray diffraction. These studies provided evidence that MnGe forms in the cubic B20 crystal structure as islands exhibit a very smooth surface. The islands become larger with increasing film thickness. A magnetic characterization reveals that the ordering temperature of MnGe thin films is enhanced compared to that for bulk material. The properties of the helical magnetic structure obtained from magnetization and magnetoresistivity measurements are compared with those of films of the related compound MnSi. The much stronger Dzyaloshinskii-Moriya interaction in MnGe results in a higher rigidity of the spin helix.

Chiral properties of structure and magnetism in Mn(1-x)Fe(x)Ge compounds: when the left and the right are fighting, who wins?

Magnetic susceptibility measurements have shown that the compounds Mn(1-x)Fe(x)Ge are magnetically ordered through the whole range of concentrations x = [0.0,1.0]. Small-angle neutron scattering reveals the helical nature of the spin structure with a wave vector, which changes from its maximum (|k| = 2.3 nm(-1)) for pure MnGe, through its minimum (|k| → 0) at x(c) ≈ 0.75, to the value of |k| = 0.09 nm(-1) for pure FeGe. The macroscopic magnetic measurements confirm the ferromagnetic nature of the compound with x = x(c). The observed transformation of the helix structure to the ferromagnet at x = x(c) is explained by different signs of chirality for the compounds with x > x(c) and x

Attosecond time-resolved photoemission from core and valence states of magnesium.

We report on laser-assisted attosecond photoemission from single-crystalline magnesium. In strong contrast to the previously investigated transition metal tungsten, photoelectron wave packets originating from the localized core level and delocalized valence-band states are launched simultaneously from the solid within the experimental uncertainty of 20 as. This phenomenon is shown to be compatible with a heuristic model based on free-particle-like propagation of the electron wave packets generated inside the crystal by the attosecond excitation pulse and their subsequent interaction with the assisting laser field at the metal-vacuum interface.

Safety and frequency of whole blood donations from elderly donors.

BACKGROUND: Within the coming decades, a steadily growing demand for blood products will face a shrinking blood donor population in many countries. After increasing the donor age of repeat donors for whole blood donation (WB) from 68 to 70 years in 2009 in our Blood Service, we investigated whether this is sufficient as a safe and effective strategy to sustain future blood supply. MATERIALS AND METHODS: Between 1 March 2009 and 28 February 2011, WB donations from donors aged between 69 and 70 and their proportion of total donations in 2010 were determined. We analysed adverse reaction rates in donors with respect to sex and age and calculated mean annual donation frequencies. RESULTS: Of all invited donors, 32·5% responded and contributed 0·98% (men) and 0·56% (women) to all WB units collected in 2010. The overall and systemic adverse reaction rate per 1·000 WB donations declined by age [men: 1·10 (95%CI: 0·84-1·35) vs. 0 (0-0·8), P < 0·0001; 0·99 (0·75-1·23) vs. 0 (0-0·8), P < 0·0001 and women: 1·80 (1·46-2·14) vs. 1·12 (0·1-2·66), P < 0·0001; 1·47 (1·17-1·78) vs. 1·12 (-0·43-2·66), P = 0·0004]. Mean donation frequencies were strongly correlated with increasing age (men: r = 0·953, P < 0·0001; women: r = 0·913, P < 0·0001) with peak values for 70-year-old male: 2·53 ± 1·37 vs. 1·79 ± 1·05, P < 0·0001 and female donors: 2·15 ± 1·06 vs. 1·52 ± 0·78, P < 0·0001. CONCLUSIONS: Elderly donors have very low adverse reaction frequencies and are highly committed to donate blood. Thus, we consider donations from repeat donors aged 69-70 safe and suggest it a powerful short- to midterm strategy to, at least partially, overcome the challenges of the demographic change.

A flexible apparatus for attosecond photoelectron spectroscopy of solids and surfaces.

We describe an apparatus for attosecond photoelectron spectroscopy of solids and surfaces, which combines the generation of isolated attosecond extreme-ultraviolet (XUV) laser pulses by high harmonic generation in gases with time-resolved photoelectron detection and surface science techniques in an ultrahigh vacuum environment. This versatile setup provides isolated attosecond pulses with photon energies of up to 140 eV and few-cycle near infrared pulses for studying ultrafast electron dynamics in a large variety of surfaces and interfaces. The samples can be prepared and characterized on an atomic scale in a dedicated flexible surface science end station. The extensive possibilities offered by this apparatus are demonstrated by applying attosecond XUV pulses with a central photon energy of ∼125 eV in an attosecond streaking experiment of a xenon multilayer grown on a Re(0001) substrate.

[Management of complex thrombocytopenia with thrombelastometry : a case of simultaneous posttransfusion purpura and heparin-induced thrombocytopenia]. / Management einer komplexen Thrombozytopenie mithilfe der Thrombelastometrie : Koinzidenz von posttransfusioneller Purpura und Heparin-induzierter Thrombozytopenie.

The case presented describes the combined onset of heparin-induced thrombocytopenia II (HIT) and post-transfusion purpura (PTP) 5-10 days following exposure to heparin and blood transfusion during aortic dissection repair. On day 4 the platelet count decreased by 40% and D-dimers started to increase again. Despite a low clinical probability for HIT-II at this time (4T score of 3) serological testing was done the next day and yielded a negative test result. Following a transient rise after platelet transfusion another 40% decrease in platelet count occurred on day 8. To increase precision of the 4T score, screening ultrasonography was performed and identified a clinically unapparent jugular vein thrombosis. As this increased the 4T score to 6 points, serological testing was repeated and now showed the presence of HIT-II antibodies. Despite switching from heparin to argatroban the platelet count continued to decrease to <5×10(3)/µl. Conventional clotting tests showed a prolonged prothrombin time and severe hypofibrinogenemia. Because of the female sex, age >50 years, history of pregnancy and transfusion 8 days before, PTP was suspected. The alteration of the plasmatic coagulation, however, could not be explained by PTP. Therefore, disseminated intravascular coagulation (DIC) and interference of argatroban with conventional clotting tests were considered as alternative diagnoses. In order to differentiate between the two alternatives rotational thrombelastometry (ROTEM®) was performed and revealed an increased functional fibrinogen level without signs of hyperfibrinolysis. This argued for an interference of argatroban with the Clauss method of fibrinogen measurement and rendered DIC unlikely. Under suspicion of PTP, treatment with immunoglobulin was initiated and blood transfusions were avoided. Detection of PTP antibodies 1 day later confirmed the combined presence of PTP and HIT-II. As hyperfibrinogenemia compensated for the effects of thrombocytopenia on clot firmness in ROTEM®, anticoagulation with lepirudin was started at 9×10(3) platelets/µl only. The next day the platelet count increased to 32×10(3)/µl and clot firmness returned to normal. No thromboembolic complications and no relevant bleeding were observed. In summary, this case shows for the first time that HIT-II and PTP can occur in parallel in patients with simultaneous exposure to heparin and blood transfusions. Confounding effects of argatroban on conventional clotting tests may mimic DIC under these circumstances and make diagnosis difficult. Careful evaluation of the time-related magnitude in platelet decrease, patient history, course of D-dimers, screening ultrasonography and ROTEM® seem to be helpful to initiate early appropriate therapy before serological test results become available. In contrast to the Clauss method of fibrinogen measurement, assessment of clot firmness in ROTEM® is not influenced by argatroban. Moreover, ROTEM® reveals the compensatory effects of increased functional fibrinogen on clot firmness during severe thrombocytopenia as an important variable for anticoagulation therapy during thrombocytopenia with increased thromboembolic risk.

Crystal handedness and spin helix chirality in Fe1-xCoxSi.

We show, with the help of polarized neutrons, that the cubic magnets Fe1-xCoxSi with Dzyaloshinskii-Moriya interaction can be switched between left (for x=0.1, 0.15) and right (for x=0.2, 0.25, 0.3, 0.5) chiral states of the spin helix. The absolute structure was evaluated using x-ray diffraction. The crystals are shown to be enantiopure and the structural chirality changes from right handed for x<0.2 to left handed for x>0.2. These compounds are compared with the etalon sample of MnSi which is identified as having the left-handed chirality both in the magnetic and crystallographic sense.

O- and H-induced surface core level shifts on Ru(0001): prevalence of the additivity rule.

In previous work on adsorbate-induced surface core level shifts (SCLSs), the effects caused by O atom adsorption on Rh(111) and Ru(0001) were found to be additive: the measured shifts for first-layer Ru atoms depended linearly on the number of directly coordinated O atoms. Density-functional theory calculations quantitatively reproduced this effect, allowed separation of initial- and final-state contributions, and provided an explanation in terms of a roughly constant charge transfer per O atom. We have now conducted similar measurements and calculations for three well-defined adsorbate and coadsorbate layers containing O and H atoms: (1 × 1)-H, (2 × 2)-(O+H) and (2 × 2)-(O+3H) on Ru(0001). As H is stabilized in fcc sites in the prior two structures and in hcp sites in the latter, this enables us to not only study coverage and coadsorption effects on the adsorbate-induced SCLSs, but also the sensitivity to similar adsorption sites. Remarkably good agreement is obtained between experiment and calculations for the energies and geometries of the layers, as well as for all aspects of the SCLS values. The additivity of the next-neighbor adsorbate-induced SCLSs is found to prevail even for the coadsorbate structures. While this confirms the suggested use of SCLSs as fingerprints of the adsorbate configuration, their sensitivity is further demonstrated by the slightly different shifts unambiguously determined for H adsorption in either fcc or hcp hollow sites.

Evidence for itineracy in the anticipated Kondo insulator FeSi: a quantitative determination of the band renormalization.

A comparison of high-resolution, angle-resolved photoemission spectroscopy (ARPES) data with ab initio band-structure calculations by density functional theory for the anticipated Kondo insulator FeSi shows that the experimental dispersions can quantitatively be described by an itinerant behavior provided that an appropriate self-energy correction is included, whose real part describes the band renormalization due to interactions of the Fe 3d electrons. The imaginary part of the self-energy, on the other hand, determines the linewidth of the quasiparticle peaks in the ARPES data. We use a model self-energy which consistently describes both the renormalized single-particle dispersion and the energy-dependent linewidth of the Fe 3d bands. These results are clear evidence that FeSi is an itinerant semiconductor whose properties can be explained without a local Kondo-like interaction.

Concentrations of acute-phase proteins in dogs with steroid responsive meningitis-arteritis.

BACKGROUND: Measurement of concentrations of acute-phase proteins (APPs) is used as an aid in the diagnosis of a variety of diseases in animals. OBJECTIVE: To determine the concentration of APPs in dogs with steroid responsive meningitis-arteritis (SRMA) and other neurologic diseases. ANIMALS: One hundred and thirty-three dogs with neurologic diseases, 6 dogs with sepsis, and 8 healthy dogs were included in the study. Thirty-six dogs had SRMA (31 of which had monitoring), 14 dogs had other meningoencephalitides (ME), 32 had disk disease (IVDD/DLSS), 26 had tumors affecting the central nervous system (TCNS), and 25 had idiopathic epilepsy (IE). METHODS: Prospective, observational study: C-reactive protein (CRP), alpha(2)-macroglobulin (AMG), and albumin concentrations were determined in the serum or plasma. CRP was also measured in the cerebrospinal fluid. RESULTS: Serum CRP was significantly higher in dogs with SRMA (x=142 microg/mL+/-75) and sepsis (x=114 microg/mL+/-67) in comparison with dogs with other neurologic diseases (x=2.3-21 microg/mL; P< .001). There was no significant difference detected in AMG between groups. Serum albumin concentration was significantly lower (P< .01) in dogs with SRMA (x=3.2 g/dL+/-0.41) than in other groups (x=3.6-3.9 g/dL). Serum CRP concentration of SRMA dogs correlated with alkaline phosphatase levels (r=0.515, P= .003). CONCLUSIONS AND CLINICAL IMPORTANCE: CRP concentrations in serum are useful in diagnosis of dogs with SRMA. Serum CRP could be used as a monitoring parameter in treatment management of these dogs.

Low-energy electron-induced processes in fluorinated copper phthalocyanine films observed by F- desorption: why so little damage?

As an indication of damage induced by hot electrons in an organic electronic material, the desorption of F- ions from a thin perfluorinated copper phthalocyanide film on SiO2 under low-energy (0-25 eV) electron impact has been recorded mass spectrometrically. Yields and damage cross sections are very low. No strong features due to negative ion resonances are found in the electron energy dependence of the desorption yield; rather the yield function rises from a threshold at about 5-6 eV continuously (with some weak structure) throughout the measured range. We discuss these findings in terms of the electronic structure of the film, as well as parameters influencing the relevant bond breaking process. We emphasize the strong influence of energy redistribution, which quenches normally long-lived negative ion resonances and selects localized and strongly repulsive excitations, as often observed in electronically induced bond breaking at surfaces. The improved understanding should be helpful in the selection of low-damage materials for organic semiconductor devices and for selection of operation parameters.

Adsorption and thermal evolution of SO2 on Ru(0001).

Using high resolution S 2p and O 1s x-ray photoelectron spectroscopies, the adsorption of SO2 and its surface bound reaction products on Ru(0001) have been investigated simultaneously while dosing SO2 and while heating the adsorbed species. SO2 is found to adsorb on Ru(0001) at 100 K molecularly in two variants as well as dissociatively and to react to SO3, SO4, SO, and S with increasing coverage. After the monolayer has been saturated, SO2 adsorbs molecularly in multilayers. When heating adsorbed SO2 from 100 K, SO, SO2, and SO4 decompose in a wide temperature range up to 305 K. In contrast SO3 is found to be stable bound to Ru(0001) up to 300 K and to disappear from the surface to below 325 K. At 550 K the surface remains with a saturated atomic sulfur and oxygen layer and some sulfur species in a second layer. Our quantitative analysis of the sulfur amount bound to the surface supports a simple desorption process only for SO4. All other species mainly or partly decompose on the surface.

Cell-type-specific disruption and recovery of the cytoskeleton in Arabidopsis thaliana epidermal root cells upon heat shock stress.

The cytoskeleton in plant cells plays an important role in controlling cell shape and mediating intracellular signalling. However, almost nothing is known about the reactions of cytoskeletal elements to heat stress, which represents one of the major environmental challenges for plants. Here we show that living epidermal root cells of Arabidopsis thaliana could cope with short-term heat shock stress showing disruption and subsequent recovery of microtubules and actin microfilaments in a time-dependent manner. Time-lapse imaging revealed a very dynamic behavior of both cytoskeletal elements including transient depolymerization and disassembly upon heat shock (40-41 degrees C) followed by full recovery at room temperature (20 degrees C) within 1-3 h. Reaction of microtubules, but not actin filaments, to heat shock was dependent on cell type and developmental stage. On the other hand, recovery of actin filaments, but not microtubules, from heat shock stress was dependent on the same parameters. The relevance of this adaptive cytoskeletal behavior to intracellular signalling is discussed.

Fine Structural Analysis of Brefeldin A-Induced Compartment Formation After High-Pressure Freeze Fixation of Maize Root Epidermis: Compound Exocytosis Resembling Cell Plate Formation during Cytokinesis.

Formation of large perinuclear brefeldin A (BFA)-induced compartments is a characteristic feature of root apex cells, but it does not occur in shoot apex cells. BFA-induced compartments have been studied mostly using low resolution fluorescence microscopy techniques. Here, we have employed a high-resolution ultrastructural method based on ultra rapid freeze fixation of samples in order to study the formation of BFA-induced compartments in intact maize root epidermis cells in detail. This approach reveals five novel findings. Firstly, plant TGN/PGN elements are not tubular networks, as generally assumed, but rather vesicular compartments. Secondly, TGN/PGN vesicles interact with one another extensively via stalk-like connections and even fuse together via bridge-like structures. Thirdly, BFA-induced compartments are formed via extensive homotypic fusions of the TGN/PGN vesicles. Fourthly, multivesicular bodies (MVBs) are present within the BFA-induced compartments. Fifthly, mitochondria and small vacuoles accummulate abundantly around the large perinuclear BFA-induced compartments.

Poly(A)+ RNA and cytoskeleton during cyst formation in the cap ray of Acetabularia peniculus.

The configuration and distribution of polyadenylated RNA (poly(A)+ RNA) during cyst formation in the cap rays of Acetabularia peniculus were demonstrated by fluorescence in situ hybridization using oligo(dT) as a probe, and the spatial and functional relationships between poly(A)+ RNA and microtubules or actin filaments were examined by immunofluorescence microscopy and cytoskeletal inhibitor treatment. Poly(A)+ RNA striations were present in the cytoplasm of early cap rays and associated with longitudinal actin bundles. Cytochalasin D destroyed the actin filaments and caused a dispersal of the striations. Poly(A)+ RNA striations occurred in the cytoplasm of the cap rays up to the stage when secondary nuclei migrated into the cap rays, but they disappeared after the secondary nuclei were settled in their positions. At that time, a mass of poly(A)+ RNA was present around each of the secondary nuclei and accumulated rRNA. This mass colocalized with microtubules radiating from the surface of each secondary nucleus and disappeared when the microtubules were depolymerized by butamifos, which did not affect the configuration of actin filaments. These masses of poly(A)+ RNA continued to exist even after the cap ray cytoplasm divided into cyst domains. Thus two distinct forms of poly(A)+ RNA population, striations and masses, appear in turn at consecutive stages of cyst formation and are associated with distinct cytoskeletal elements, actin filaments and microtubules, respectively.

Cell wall pectins and xyloglucans are internalized into dividing root cells and accumulate within cell plates during cytokinesis.

Recently, we have reported that cell wall pectins are internalized into apical meristem root cells. In cells exposed to the fungal metabolite brefeldin A, all secretory pathways were inhibited, while endocytic pathways remained intact, resulting in accumulation of internalized cell wall pectins within brefeldin A-induced compartments. Here we report that, in addition to the already published cell wall epitopes, rhamnogalacturonan I and xyloglucans also undergo large-scale internalization into dividing root cells. Interestingly, multilamellar endosomes were identified as compartments internalizing arabinan cell wall pectins reactive to the 6D7 antibody, while large vacuole-like endosomes internalized homogalacturonans reactive to the 2F4 antibody. As all endosomes belong topographically to the exocellular space, cell wall pectins deposited in these "cell wall islands", enclosed by the plasma-membrane-derived membrane, are ideally suited to act as temporary stores for rapid formation of cell wall and generation of new plasma membrane. In accordance with this notion, we report that all cell wall pectins and xyloglucans that internalize into endosomes are highly enriched within cytokinetic cell plates and accumulate within brefeldin A compartments. On the other hand, only small amounts of the pectins reactive to the JIM7 antibody, which are produced in the Golgi apparatus, localize to cell plates and they do not accumulate within brefeldin A compartments. In conclusion, meristematic root cells have developed pathways for internalization and recycling of cell wall molecules which are relevant for plant-specific cytokinesis.