Thin-disk laser pump schemes for large number of passes and moderate pump source quality

Novel thin-disk laser pump layouts are proposed yielding an increased number of passes for a given pump module size and pump source quality. These novel layouts result from a general scheme which bases on merging two simpler pump optics arrangements. Some peculiar examples can be realized by adapting standard commercially available pump optics simply by intro ducing an additional mirror-pair. More pump passes yield better efficiency, opening the way for usage of active materials with low absorption. In a standard multi-pass pump design, scaling of the number of beam passes brings ab out an increase of the overall size of the optical arrangement or an increase of the pump source quality requirements. Such increases are minimized in our scheme, making them eligible for industrial applicationsComment: 16 pages, 9 figure

Compact 20-pass thin-disk amplifier insensitive to thermal lensing

We present a multi-pass amplifier which passively compensates for distortions of the spherical phase front occurring in the active medium. The design is based on the Fourier transform propagation which makes the output beam parameters insensitive to variation of thermal lens effects in the active medium. The realized system allows for 20 reflections on the active medium and delivers a small signal gain of 30 with M$^2$ = 1.16. Its novel geometry combining Fourier transform propagations with 4f-imaging stages as well as a compact array of adjustable mirrors allows for a layout with a footprint of 400 mm x 1000 mm.Comment: 7 pages, 6 figure

Hydration and the true water content of swellable clay minerals

Water affects biological, chemical and transportation processes as well as mechanical properties of soils. Thereby, clay mineral content determines the moisture balance of soils. In-situ moisture measurements depend on reliable calibration based on the true water content. Drying the soil at 105 °C is the most common procedure to determine the water content although it is known, swellable clay minerals retain hydration water up to much higher temperatures. The amplified water uptake and retention by swellable clay minerals results from hydration of interlayer cations. Thereby, the water binding mechanisms are complex due to structural heterogeneity and are determined by layer charge density and location of substitutions. While several experimental studies deal with the maximum water uptake of selected smectites and heating conditions for full dehydration a comprehensive understanding of the relation between the structure of smectites and water uptake/release is still missing. The Na-saturated smectite / water interface for the montmorillonite-beidellite series is investigated in the present work within the density functional theory (DFT). Layer charge is varied between 0.125 and 0.5 per formula unit [O10(OH)2] by substitution of Al3+ by Mg2+ in the octahedral sheet (montmorillonites) and by substitution of Si4+ by Al3+ in the tetrahedral sheets (beidellites). Starting from the water free supercells (with integer molar ratios), the number of water molecules is increased discretely. Stable hydration states (1H to 3H) do not necessarily correspond to the formation of water layers (1W to 3W) in the interlayer, which is deduced from the development of the basal spaces during hydration. With the help of ab initio thermodynamics, the energy states are related to temperature, and partial pressure of H2O and the resulting phase diagrams revealed hydration state in dependence of relative humidity (RH) as well as necessary temperatures for full dehydration to determine the true water content. Thereby it was shown that 2:1 layer silicates with a layer charge of 0.125 are swellable but reach only the 1H state even at 100% RH, but the removal of water molecules from the interlayer requires temperatures >110 °C and partial pressures of water <100 Pa. In contrast water uptake of smectites with layer charge 0.375 requires RH of >11% at room temperature, but dehydration occurs at moderate heating

Electrical stimulation of the mesencephalic locomotor region attenuates neuronal loss and cytokine expression in the perifocal region of photothrombotic stroke in rats

Deep brain stimulation of the mesencephalic locomotor region (MLR) improves the motor symptoms in Parkinson’s disease and experimental stroke by intervening in the motor cerebral network. Whether high-frequency stimulation (HFS) of the MLR is involved in non-motor processes, such as neuroprotection and inflammation in the area surrounding the photothrombotic lesion, has not been elucidated. This study evaluates whether MLR-HFS exerts an anti-apoptotic and anti-inflammatory effect on the border zone of cerebral photothrombotic stroke. Rats underwent photothrombotic stroke of the right sensorimotor cortex and the implantation of a microelectrode into the ipsilesional MLR. After intervention, either HFS or sham stimulation of the MLR was applied for 24 h. The infarct volumes were calculated from consecutive brain sections. Neuronal apoptosis was analyzed by TUNEL staining. Flow cytometry and immunohistochemistry determined the perilesional inflammatory response. Neuronal apoptosis was significantly reduced in the ischemic penumbra after MLR-HFS, whereas the infarct volumes did not differ between the groups. MLR-HFS significantly reduced the release of cytokines and chemokines within the ischemic penumbra. MLR-HFS is neuroprotective and it reduces pro-inflammatory mediators in the area that surrounds the photothrombotic stroke without changing the number of immune cells, which indicates that MLR-HFS enables the function of inflammatory cells to be altered on a molecular level

In‐situ characterization of deposits in ceramic hollow fiber membranes by compressed sensing RARE‐MRI

Ultrafiltration with ceramic hollow fiber membranes was investigated by compressed sensing rapid acquisition relaxation enhancement (CS-RARE) magnetic resonance imaging (MRI) to characterize filtration mechanisms. Sodium alginate was used as a model substance for extracellular polymeric substances. Dependent on the concentration of divalent ions like Ca21 in an aqueous alginate solution, the characteristics of the filtration change from concentration polarization to a gel layer. The fouling inside the membrane lumen could be measured by MRI with a CS-RARE pulse sequence. Contrast agents have been used to get an appropriate contrast between deposit and feed. The lumen was analyzed quantitatively by exploring the membrane’s radial symmetry, and the resulting intensity could be modeled. Thus, different fouling mechanisms could be distinguished. CS-RARE-MRI was proven to be an appropriate in situ tool to quantitatively characterize the deposit formation during in-out filtration processes. The results were underlined by flux interruption experiments and length dependent studies, which make it possible to differentiate between gel layer or cake filtration and concentration polarization filtration processes

Solubility of precursors and carbonation of waterglass-free geopolymers

Geopolymers have the potential to function as an environmentally friendly substitute for ordinary Portland cement, with up to 80% less CO$_{2}$ emission during production. The effect is best utilized for geopolymers prepared with amorphous silica instead of waterglass (Na$_{2x}$Si$_{y}$O$_{2y+x}$) to adjust the Si:Al ratio. The reactivity of the precursors with the alkaline activator affects the final mineralogical properties of the binder. The purpose of the present study was to investigate the amount of different phases formed during geopolymerization and to understand the quantitative evolution of carbonation during geopolymer synthesis by determining the solubility of metakaolinite and amorphous SiO$_{2}$ in NaOH at various concentrations. The solubility was studied by ICP-OES measurements. X-ray diffraction was used for qualitative and quantitative phase analysis of the geopolymers. The solubility of the precursors increased with calcination temperature of metakaolinite, reaction time for amorphous SiO$_{2}$, and at higher NaOH concentrations. Partial dissolution resulted in free Na$^{+}$, which is a source for the formation of carbonates in the geopolymers. Thermonatrite occurred prior to trona formation in all samples