A software controllable modular RF signal generator with multichannel transmission capabilities.

A software controllable system which generates and transmits user defined RF signals is discussed. The system is implemented with multiple, modular transmitting channels that allow the user to easily replace parts such as amplifiers or antennas. Each channel is comprised of a data pattern generator (DPG), a digital to analog converter (DAC), a power amplifier, and a transmitting antenna. All channels are controlled through a host PC and synchronized through a master clock signal provided to each DAC by an external clock source. Signals to be transmitted are generated through the DPG control software on the PC or can be created by the user in a numerical computing environment. Three experiments are discussed using a two- and four-channel antenna array incorporating Chebyshev tapered TEM horn antennas. Transmitting distinct sets of nonperiodic bipolar impulses through each of the antennas in the array enabled synthesizing a sinusoidal signal of specific frequency in free space. Opposite to the standard phased array approach, each antenna radiates a distinctly different signal rather than the same signal simply phase shifted. The presented approach may be employed as a physical layer of encryption dependent on the position of the receiving antenna.

Robust Zero-Field Skyrmion Formation in FeGe Epitaxial Thin Films.

B20 phase magnetic materials have been of significant interest because they enable magnetic Skyrmions. One major effort in this emerging field is the stabilization of Skyrmions at room temperature and zero magnetic field. We grow phase-pure, high crystalline quality FeGe epitaxial films on Si(111). Hall effect measurements reveal a strong topological Hall effect after subtracting the ordinary and anomalous Hall effects, demonstrating the formation of high density Skyrmions in FeGe films between 5 and 275 K. In particular, a substantial topological Hall effect was observed at a zero magnetic field, showing a robust Skyrmion phase without the need of an external magnetic field.

On the origin of extraordinary cyclic strengthening of the austenitic stainless steel Sanicro 25 during fatigue at 700°C.

The origin of the extraordinary strengthening of the highly-alloyed austenitic stainless steel Sanicro 25 during cyclic loading at 700°C was investigated by use of advanced scanning transmission electron microscopy (STEM). Along with substantial change of dislocation structure, nucleation of two distinct populations of nanoparticles was revealed. Fully coherent Cu-rich nanoparticles were observed homogeneously dispersed with high density along with nanometer-sized incoherent NbC carbides precipitating on dislocations during cyclic loading. Probe-corrected HAADF STEM imaging was used to characterize the atomic structure of nanoparticles. Compositional analysis was conducted using both EELS and high spatial resolution EDS. High temperature exposure induced precipitation of a high density of coherent Cu-rich nanoparticles while strain-induced nucleation of incoherent NbC nanoparticles leads to retardation of dislocation movement. The pinning effects and associated obstacles to dislocation motion prevent recovery and formation of the localized low-energy cellular structures. As a consequence, the alloy exhibits remarkable cyclic hardening at elevated temperature.

Phase transformation strengthening of high-temperature superalloys.

Decades of research has been focused on improving the high-temperature properties of nickel-based superalloys, an essential class of materials used in the hot section of jet turbine engines, allowing increased engine efficiency and reduced CO2 emissions. Here we introduce a new 'phase-transformation strengthening' mechanism that resists high-temperature creep deformation in nickel-based superalloys, where specific alloying elements inhibit the deleterious deformation mode of nanotwinning at temperatures above 700 °C. Ultra-high-resolution structure and composition analysis via scanning transmission electron microscopy, combined with density functional theory calculations, reveals that a superalloy with higher concentrations of the elements titanium, tantalum and niobium encourage a shear-induced solid-state transformation from the γ' to η phase along stacking faults in γ' precipitates, which would normally be the precursors of deformation twins. This nanoscale η phase creates a low-energy structure that inhibits thickening of stacking faults into twins, leading to significant improvement in creep properties.

Quantitative STEM Imaging of Order-Disorder Phenomena in Double Perovskite Thin Films.

Using aberration-corrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), we investigate ordering phenomena in epitaxial thin films of the double perovskite Sr_{2}CrReO_{6}. Experimental and simulated imaging and diffraction are used to identify antiphase domains in the films. Image simulation provides insight into the effects of atomic-scale ordering along the beam direction on HAADF-STEM intensity. We show that probe channeling results in ±20% variation in intensity for a given composition, allowing 3D ordering information to be probed using quantitative STEM.

Epitaxial growth of iridate pyrochlore Nd2Ir2O7 films.

Epitaxial films of the pyrochlore Nd2Ir2O7 have been grown on (111)-oriented yttria-stabilized zirconia (YSZ) substrates by off-axis sputtering followed by post-growth annealing. X-ray diffraction (XRD) results demonstrate phase-pure epitaxial growth of the pyrochlore films on YSZ. Scanning transmission electron microscopy (STEM) investigation of an Nd2Ir2O7 film with a short post-annealing provides insight into the mechanism for crystallization of Nd2Ir2O7 during the post-annealing process. STEM images reveal clear pyrochlore ordering of Nd and Ir in the films. The epitaxial relationship between the YSZ and Nd2Ir2O7 is observed clearly while some interfacial regions show a thin region with polycrystalline Ir nanocrystals.

Geostatistical analysis of tritium, groundwater age and other noble gas derived parameters in California.

Key characteristics of California groundwater systems related to aquifer vulnerability, sustainability, recharge locations and mechanisms, and anthropogenic impact on recharge are revealed in a spatial geostatistical analysis of a unique data set of tritium, noble gases and other isotopic analyses unprecedented in size at nearly 4000 samples. The correlation length of key groundwater residence time parameters varies between tens of kilometers ((3)H; age) to the order of a hundred kilometers ((4)Heter; (14)C; (3)Hetrit). The correlation length of parameters related to climate, topography and atmospheric processes is on the order of several hundred kilometers (recharge temperature; δ(18)O). Young groundwater ages that highlight regional recharge areas are located in the eastern San Joaquin Valley, in the southern Santa Clara Valley Basin, in the upper LA basin and along unlined canals carrying Colorado River water, showing that much of the recent recharge in central and southern California is dominated by river recharge and managed aquifer recharge. Modern groundwater is found in wells with the top open intervals below 60 m depth in the southeastern San Joaquin Valley, Santa Clara Valley and Los Angeles basin, as the result of intensive pumping and/or managed aquifer recharge operations.

Saturated zone denitrification: potential for natural attenuation of nitrate contamination in shallow groundwater under dairy operations.

We present results from field studies at two central California dairies that demonstrate the prevalence of saturated-zone denitrification in shallow groundwater with 3H/ 3He apparent ages of < 35 years. Concentrated animal feeding operations are suspected to be major contributors of nitrate to groundwater, but saturated zone denitrification could mitigate their impact to groundwater quality. Denitrification is identified and quantified using N and O stable isotope compositions of nitrate coupled with measurements of excess N2 and residual NO3(-) concentrations. Nitrate in dairy groundwater from this study has delta15N values (4.3-61 per thousand), and delta18O values (-4.5-24.5 per thousand) that plot with delta18O/delta15N slopes of 0.47-0.66, consistent with denitrification. Noble gas mass spectrometry is used to quantify recharge temperature and excess air content. Dissolved N2 is found at concentrations well above those expected for equilibrium with air or incorporation of excess air, consistent with reduction of nitrate to N2. Fractionation factors for nitrogen and oxygen isotopes in nitrate appear to be highly variable at a dairy site where denitrification is found in a laterally extensive anoxic zone 5 m below the water table, and at a second dairy site where denitrification occurs near the water table and is strongly influenced by localized lagoon seepage.

Pre-concentration and measurement of low levels of gamma-ray emitting radioisotopes in coastal waters.

We describe extensive testing of a large-volume, high-speed water sampler for the concentration and measurement of radionuclides using high-resolution gamma ray spectrometry. The sampler processed hundreds to thousands of liters of natural waters with variable suspended sediment and salinity loads at flow rates of 10-201/min. Extraction of most radionuclides in the water column was accomplished through the combination of physical filtration down to 0.1 microm particle size and chemical separation of dissolved species on cellulose-based inorganic sorbent beds without recourse to complex, or hazardous chemistry. Performance and extraction efficiencies for suites of radioisotopes were determined in the laboratory and in the field with river and coastal ocean water samples. Extraction and recovery efficiencies are better than 90% for most fission and activation product radioisotopes. This methodology has broad application to the study of the distribution and fate of radioisotopes in coastal waterways.

The biologic activity of mast cell granules. VIII. In vivo and in vitro characterization of mast cell granule-derived inflammatory factors involved in rat late-phase reactions.

Intradermal injections of isolated mast cell granules (MCGs), as well as solubilized high-molecular-weight (HMW) (greater than 10,000 daltons) and low-molecular-weight (LMW) (10,000 greater than MW greater than 500 daltons) fractionated granule constituents, can produce inflammatory responses termed late-phase reactions (LPRs). The identity and mechanism of action of various inflammatory factor(s) contained within these fractions is incompletely established. Since rat LPRs are neutrophil-dependent responses, we analyzed the inherent neutrophil chemoattractant potential of HMW and LMW granule fractions using a 48-well microchemotaxis chamber. Although both HMW and LMW fractions attracted rat neutrophils, the LMW fraction was less active at equivalent protein concentrations. Checkerboard analysis demonstrated that the HMW fraction enhanced random migration of neutrophils, indicating that the HMW fraction contains factors that are primarily chemokinetic. To analyze further the HMW fraction, solubilized MCGs were sequentially fractionated with XM300 (MW greater than 300,000 daltons), and YM100 (300,000 greater than MW greater than 100,000 daltons), XM50 (100,000 greater than MW greater than 50,000 daltons), and YM10 (50,000 greater than MW greater than 10,000 daltons) ultrafiltration membranes. This process revealed that most in vivo inflammation-provoking activity as well as the in vitro chemoattractant activity resided in the XM300 and YM100 retentate fractions. Two of the major constituents of the HMW fraction, heparin and chymase, were evaluated for their contribution to the chemoattraction. Purified MCG heparin did not evoke neutrophil migratory responses in vitro or in vivo. Sepharose 4B chromatography of solubilized MCG demonstrated a peak of inflammation-provoking activity beginning at the void volume and tapering off near the 400,000 MW range. This in vivo activity was clearly separable from the chymase activity and represents the HMW inflammatory factors. These results demonstrate that both HMW and LMW granule fractions contain inflammatory activities capable of producing LPR in vivo and suggest that enhancement of neutrophil migration at sites of mast cell degranulation is one mechanism of action.

IgE antibody mediated inflammation of rat lung: histologic and bronchoalveolar lavage assessment.

Pulmonary antigen challenge in sensitized individuals elicits immediate and late phase responses (LPR). While mast cells and tissue inflammation are thought to be vital to the development of the LPR, the precise pathogenesis of these responses remains under investigation. Using the Sprague-Dawley rat as a model to study cutaneous LPR, we have previously demonstrated that rat cutaneous LPR are mast cell-dependent and are histologically characterized by early (1-8 h) neutrophil-rich and late (8-24 h) mononuclear cell-rich infiltrates. To compare and contrast this cutaneous response with IgE-dependent pulmonary inflammatory responses, we performed bronchoalveolar lavage (BAL) analyses of pulmonary inflammation following specific antigen challenge in actively immunized [IgE anti-ovalbumin (OA) antibody] and BAL and histologic analyses in passively sensitized [mouse hybridoma anti-dinitrophenyl (DNP) IgE antibody] rats. Following direct insufflation of OA into the trachea, actively sensitized animals demonstrated an increased number of polymorphonuclear leukocytes (PMNs) at 4 h in BAL fluid. These cell numbers were significantly increased over controls by 24 h following challenge. In addition, rats passively sensitized for 72 h with anti-DNP IgE hybridoma antibody (PCA = 1:10,000) were challenged with DNP-BSA aerosols. Examination of BAL fluid 1 to 2 h following challenge revealed significantly increased numbers of PMNs which returned to normal levels by 24 h. Numbers of lymphocytes and macrophages were unchanged compared to controls. Microscopic examination of lung tissue revealed alveolar and interstitial edema at 2 h following challenge and a focal peribronchiolitis characterized by a predominantly mononuclear cell infiltrate.(ABSTRACT TRUNCATED AT 250 WORDS)

[Course and prognosis of the rehabilitation of patients following acute polyneuritis]. / Verlauf und Prognose der Rehabilitation von Patienten nach akuter Polyneuritis.

Presented are 31 patients who had been admitted to our clinic for physical medicine for post-acute rehabilitation treatment. On admission, 25 of them suffered from incomplete tetraparesis. All patients were able to walk at discharge, some still having to rely on aids. 29 patients had achieved full independence in ADL tasks. Further gains in muscular strength and functional capacity were achieved over a period of up to two years of continued treatment on an outpatient basis.

In vivo and in vitro assessment of the role of leukotriene B4 as a mediator of rat cutaneous late-phase reactions.

Mast cell-dependent late-phase reactions (LPR) occur in rat skin and are characterized histologically by an early (1 to 8 hours) neutrophil-rich infiltrate, which is essential to a later (24 hours) infiltration by mononuclear cells. Although the ability of preformed mast cell-granule constituents alone to elicit LPR is clearly established, the relative pathogenetic contributions of newly generated lipid mediators to rat LPR are unknown. Leukotriene B4 (LTB4) may be generated by stimulated mast cells in a number of species and might potentially contribute to the neutrophil ingress. In order to examine this possibility in a well-characterized animal model of LPR, the capacity of LTB4 to influence rat cutaneous inflammation was studied. LTB4 (0.1 to 100 ng) alone did not induce vasopermeability in rat skin nor potentiate the blueing response to histamine. Intracutaneous LTB4 (0.1 to 100 ng) did not cause significant infiltration of neutrophils 3 to 4, 6 to 8, or 24 hours after injection; increased numbers of mononuclear leukocytes were not appreciated through 24 hours. In the same animals intracutaneous anti-IgE and intact mast cell granules both produced intense biphasic infiltration characteristic of rat LPR. In order to examine if rat polymorphonuclear leukocytes were capable of responding to LTB4, several in vitro studies were performed. Rat peritoneal and peripheral blood neutrophils migrated toward formyl-methionyl-leucyl-phenyl-alanine in vitro but not to purified human or synthetic LTB4. Rat peripheral blood and elicited peritoneal neutrophils bound only 32% and 27%, respectively, of the quantity of [3H]LTB4 bound by human neutrophils.(ABSTRACT TRUNCATED AT 250 WORDS)

[Rehabilitation following surgery of intraspinal tumors of the thoracic spine]. / Rehabilitation nach Operation intraspinaler Tumoren im BWS-Bereich.

17 patients were operated on because of a spinal compression by tumour. Postoperatively, all patients had an incomplete paraparesis, 11 patients were bed-ridden and needing care, 12 had a rectovesical incontinence. On an average 3 months after intensive physiotherapy, 14 patients could walk without or with little help, only 2 had no control of faeces or urine. In general, the postoperative rehabilitation needs a long time, but has an encouraging prognosis.