Detecting structural variances of Co3O4 catalysts by controlling beam-induced sample alterations in the vacuum of a transmission electron microscope.

This article summarizes core aspects of beam-sample interactions in research that aims at exploiting the ability to detect single atoms at atomic resolution by mid-voltage transmission electron microscopy. Investigating the atomic structure of catalytic Co3O4 nanocrystals underscores how indispensable it is to rigorously control electron dose rates and total doses to understand native material properties on this scale. We apply in-line holography with variable dose rates to achieve this goal. Genuine object structures can be maintained if dose rates below ~100 e/Å2s are used and the contrast required for detection of single atoms is generated by capturing large image series. Threshold doses for the detection of single atoms are estimated. An increase of electron dose rates and total doses to common values for high resolution imaging of solids stimulates object excitations that restructure surfaces, interfaces, and defects and cause grain reorientation or growth. We observe a variety of previously unknown atom configurations in surface proximity of the Co3O4 spinel structure. These are hidden behind broadened diffraction patterns in reciprocal space but become visible in real space by solving the phase problem. An exposure of the Co3O4 spinel structure to water vapor or other gases induces drastic structure alterations that can be captured in this manner.

Maintaining the genuine structure of 2D materials and catalytic nanoparticles at atomic resolution.

The recent development of atomic resolution, low dose-rate electron microscopy allows investigating 2D materials as well as catalytic nano particles without compromising their structural integrity. For graphene and a variety of nanoparticle compositions, it is shown that a critical dose rate exists of <100 e(-)/Å(2) s at 80 keV of electron acceleration that allows maintaining the genuine object structures including their surfaces and edges even if particles are only 3 nm large or smaller. Moreover, it is demonstrated that electron beam-induced phonon excitation from outside the field of view contributes to a contrast degradation in recorded images. These degradation effects can be eliminated by delivering electrons onto the imaged area, only, by using a Nilsonian illumination scheme in combination with a suitable aperture at the electron gun/monochromator assembly.

Observing gas-catalyst dynamics at atomic resolution and single-atom sensitivity.

Transmission electron microscopy (TEM) has become an indispensable technique for studying heterogeneous catalysts. In particular, advancements of aberration-corrected electron optics and data acquisition schemes have made TEM capable of delivering images of catalysts with sub-Ångström resolution and single-atom sensitivity. Parallel developments of differentially pumped electron microscopes and of gas cells enable in situ observations of catalysts during the exposure to reactive gas environments at pressures of up to atmospheric levels and temperatures of up to several hundred centigrade. Here, we outline how to take advantage of the emerging state-of-the-art instrumentation and methodologies to study surface structures and dynamics to improve the understanding of structure-sensitive catalytic functionality. The concept of using low electron dose-rates in TEM in conjunction with in-line holography and aberration-correction at low voltage (80 kV) is introduced to allow maintaining atomic resolution and sensitivity during in situ observations of catalysts. Benefits are illustrated by exit wave reconstructions of TEM images of a nanocrystalline Co3O4 catalyst material acquired in situ during their exposure to either a reducing or oxidizing gas environment.

Instrumental requirements for the detection of electron beam-induced object excitations at the single atom level in high-resolution transmission electron microscopy.

This contribution touches on essential requirements for instrument stability and resolution that allows operating advanced electron microscopes at the edge to technological capabilities. They enable the detection of single atoms and their dynamic behavior on a length scale of picometers in real time. It is understood that the observed atom dynamic is intimately linked to the relaxation and thermalization of electron beam-induced sample excitation. Resulting contrast fluctuations are beam current dependent and largely contribute to a contrast mismatch between experiments and theory if not considered. If explored, they open the possibility to study functional behavior of nanocrystals and single molecules at the atomic level in real time.

Global and regional parameters to visualize the 'best' PEEP during a PEEP trial in a porcine model with and without acute lung injury.

BACKGROUND: Setting the optimal level of positive end-expiratory pressure (PEEP) in critically ill patients remains a matter of debate. "Best" PEEP is regarded as minimal lung collapse and overdistention to prevent lung injury. In this study, global and regional variables were evaluated in a porcine model to identify which variables should be used to visualize "best" PEEP. METHODS: Eight pigs (28-31 kg) were studied during an incremental and decremental PEEP trial before and after the induction of acute lung injury (ALI) with oleic acid. Arterial oxygenation, compliance, lung volume, dead space, esophageal pressure and electrical impedance tomography (EIT) were recorded at the end of each PEEP step. RESULTS: After ALI, "best" PEEP was comparable at 15 cmH2O between regional compliance of the dorsal lung region by EIT and the global indicators: dynamic compliance, arterial oxygenation, alveolar dead space and venous admixture. After ALI, the intratidal gas distribution was able to detect regional overdistention at 15 cmH2O PEEP. "Best" PEEP based on transpulmonary pressure was lower and no optimal level could be found based on lung volume measurements alone. In addition, the recruitment phase significantly improved end-expiratory lung volume, PaO2, venous admixture and regional and global compliance, both in ALI and the "healthy" lung. CONCLUSION: Most of the evaluated parameters indicate comparable 'best' PEEP levels. However, a combination of these parameters, and especially EIT-derived intratidal gas distribution, might provide additional information. The application of lung recruitment was beneficial in both ALI and the "healthy" lung.

Synergistic QTL interactions between Rf-1 and Rf-3 increase renal damage susceptibility in double congenic rats.

The FHH (fawn-hooded hypertensive) rat is a model of hypertension-associated chronic kidney damage. Five interacting quantitative trait loci (QTLs), named Rf-1-Rf-5, determine the high renal susceptibility. The aim of the present study was to investigate a possible interaction between Rf-1 and Rf-3. Differences in renal susceptibility between ACI (August x Copenhagen Irish) controls, Rf-1A and Rf-3 single congenics, and Rf-1A+3 double congenic rats were assessed using four different treatments: two-kidney control (2K), 2K plus N(omega)-nitro-L-arginine methyl ester (L-NAME)-induced hypertension (2K+L-NAME), unilateral nephrectomy (UNX), and UNX plus L-NAME-induced hypertension (UNX+L-NAME). Proteinuria (UPV) and systolic blood pressure (SBP) were assessed after 6, 12, and 18 weeks, while the incidence of glomerulosclerosis (%FGS) was determined at the end of the experiment. In a separate experiment, renal autoregulation was assessed in 13-15-week old 2K rats of all four strains. Compared to ACI rats, small increases in renal susceptibility were found in Rf-1A and Rf-3 single congenics following 2K+L-NAME, UNX, and UNX+L-NAME treatments. However, in the Rf-1A+3 double congenics, a major increase in renal susceptibility was found with all four treatments. Both Rf-1A and Rf-1A+3 congenic rats had an impaired renal autoregulation. In contrast, the Rf-3 had a normal autoregulation, similar to that of the ACI rat. These findings indicate that Rf-1 and Rf-3 alone slightly increase the susceptibility to the development of renal damage. However, a synergistic interaction between these two QTLs markedly enhances renal susceptibility. In contrast to the Rf-1 region, the Rf-3 region does not carry genes influencing renal autoregulation.

Distortion and segregation in a dislocation core region at atomic resolution.

The structure of an isolated, Ga terminated, 30 degree partial dislocation in GaAs:Be is determined by high resolution transmission electron microscopes and focal series reconstruction. The positions of atomic columns in the core region are measured to an accuracy of better than 10 pm. A quantitative comparison of the structure predicted by an ab initio electronic structure total energy calculation to the experiment indicates that theory and experiment agree to within 20 pm. Further analysis shows the deviations between theory and experiment appear to be systematic. Electron energy loss spectroscopy establishes that defects segregate to the core region, thus accounting for the systematic deviations.

Direct compositional analysis of AlGaAs/GaAs heterostructures by the reciprocal space segmentation of high-resolution micrographs.

A detailed description of a combined reciprocal and real space technique for the mapping of layer compositions across interior interfaces from high-resolution electron micrographs is presented. The analysis is based on the reciprocal space extraction of chemically sensitive image information encoded in lattice images of AlGaAs/GaAs heterostructures taken under optimized imaging conditions. Analysis procedures include centering a set of apertures around chemically sensitive reflections in the Fourier transform of lattice images and performing an inverse transformation, thus extracting composition related information from experimental micrographs. It is demonstrated that this approach is characterized by the same spatial resolution as real space techniques but by improved capabilities with respect to analysing images characterized by a minor signal-to-noise ratio. For illustration purposes the stability of AlAs/GaAs multiple quantum wells grown under low-temperature conditions against thermal treatment as expressed by interfacial roughness parameters is investigated.

Computer graphics interface to a complex simulation.

The program "Cardio VascularCat" is a simulation of a laboratory experiment on the cardiovascular system of the cat, for students of physiology or pharmacology. There are two important innovations in this version, utilizing the "Macintosh environment": 1) The functioning of the program is highly interactive with the student. Any manipulation almost immediately produces some result in the (simulated) experimental animal. 2) The input from the student, and the output to the student, are handled in simple and intuitive ways. The mouse and menu system are utilized to simplify the control of the program. The keyboard is eliminated. The Macintosh graphics capabilities provide for an output display that is easily and quickly interpreted by the student. The program has been tested with a small sample of medical students. As measured by an objective test, the results are equivalent to learning from a textbook. An attitude survey revealed that the Macintosh program is clearly superior for reenforcement and review.

Evaluating ultra-low volume ground applications of malathion against Aedes aegypti using landing counts in Puerto Rico, 1980-84.

Landing counts made in a residential area in San Juan, Puerto Rico during the 5-year period, 1980-84 indicated that malathion ULV applied by LECO Fog Generators was not effective against Aedes aegypti. Of 25 applications only 6 resulted in a decrease on the first day after treatment and only one remained much less than the pretreatment count on the second and third days after treatment. Daily, the number of mosquitoes landing for a 5-minute period at each of 2 stations was recorded. An ideal year created by averaging the monthly data suggested that the seasonal variation of mosquitoes was inverse to that of reported dengue incidence.

Correlation of agonist structure with acetylcholine receptor kinetics: studies on the frog end-plate and on chick embryo muscle.

The apparent lifetimes of frog end-plate channels activated by several nicotinic agonists have been determined with voltage-jump and fluctuation analysis techniques. The agonists were monoquaternary, N-substituted derivatives of trimethylammonium (TMA). Methyl TMA activated channels which had apparent lifetimes about 3-4 times shorter than acetylcholine (ACh)-activated channels. This result was confirmed with single-channel recordings from embryonic chick skeletal muscle. Channel conductance and voltage dependence of channel lifetime were similar for methyl TMA- and ACh-activated channels. Methyl TMA showed no signs of blocking open end-plate channels. Ethyl TMA, acetylthiocholine, cholinethiol and carbamylcholine all activated channels similar to methyl TMA-activated channels with regard to lifetime. None of these agonists appeared to block end-plate channels in the employed concentrations. 4-ketopentyl TMA, which contains a methylene group in place of the ether oxygen of ACh, sometimes opened end-plate channels with similar apparent lifetimes as those opened by ACh. Single-channel recordings showed that bursts of current from channels activated by 4-ketopentyl TMA have similar durations as do those activated by ACh. Pentyl TMA and benzyl TMA block open end-plate channels even when delivered at doses which elicit very small currents. It is concluded that the ester moiety of ACh serves to stabilize the open conformation of the channel.

Automatic control of potential and agonist-induced current across the endplate membrane by drug electrophoresis.

Two techniques are described that are designed to elicit long and constant postsynaptic depolarizations or agonist-induced currents by the electrophoretic application of agonists to endplate membranes. In the first technique, which can be described as a "pharmacologic voltage clamp," the current flowing through the agonist pipette is controlled by the potential across the endplate membrane. Sustained depolarizations of constant amplitude can be obtained in this manner, while the agonist current needed to produce and maintain the response is recorded. The second technique uses a signal proportional to the current flowing across a voltage-clamped endplate membrane to control the delivery of agonist. This allows control of the intensity of the agonist-induced current. The possible application of these techniques in studying receptor desensitization and obtaining samples of post-synaptic current noise for spectral analysis is discussed.

Phase-plane analysis of action potentials in uterine smooth muscle.

Action potentials were recorded by microelectrode from narrow strips of pregnant rat uterus in vitro. The phase-plane display (V vs dV/dt) of selected action potentials was analysed by the method of Jenerick (1964) to yield the ionic current. From this membrane current data, various parameters of the action potential were calculated. In comparison to skeletal muscle action potentials, the ionic currents were 30-100 times smaller in the uterus action potential. Epinephrine hyperpolarized the resting potentials and suppressed spontaneous activity, but did not cause any significant changes in the stimulated action potential. The after-potential may have been affected by epinephrine, preventing repetitive firing, but the data were inconclusive. The phase-plane analysis results were similar to the results of the double sucrose gap voltage clamp method on the same tissue (Kao and McCullough, 1975).

Propagation of stimulated slow waves in cat intestinal muscle.

This study was designed to examine the propagation and propagation failure of the slow wave. Spontaneous slow waves and action potentials were recorded from the longitudinal muscle layer of small strips of cat jejunum. Slow waves could be stimulated electrically at intervals shorter than the spontaneous interval, and the velocity of propagation of these slow waves was slower than the spontaneous slow waves. The velocity of propagation was approximately proportional to the time between slow waves. At intervals about one-half the normal spontaneous interval the propagation became slow and unstable, which would result in the periodic failure of a single slow wave. This type of failure may underlie the formation of the slow-wave frequency gradient observed in the intact intestine. The wave shape of the external recording of the slow wave, together with the measurement of electrotonic current spread in strips of isolated muscle, suggest that the slow wave propagates by local circuit currents in an electrically excitable cablelike tissue.