Inhibiting creep in nanograined alloys with stable grain boundary networks.

Creep, the time-dependent deformation of materials stressed below the yield strength, is responsible for a great number of component failures at high temperatures. Because grain boundaries (GBs) in materials usually facilitate diffusional processes in creep, eliminating GBs is a primary approach to resisting high-temperature creep in metals, such as in single-crystal superalloy turbo blades. We report a different strategy to inhibiting creep by use of stable GB networks. Plastic deformation triggered structural relaxation of high-density GBs in nanograined single-phased nickel-cobalt-chromium alloys, forming networks of stable GBs interlocked with abundant twin boundaries. The stable GB networks effectively inhibit diffusional creep processes at high temperatures. We obtained an unprecedented creep resistance, with creep rates of ~10-7 per second under gigapascal stress at 700°C (~61% melting point), outperforming that of conventional superalloys.

Swept-source endoscopic optical coherence tomography real-time imaging system based on GPU acceleration for axial megahertz high-speed scanning.

OBJECTIVE: In order to solve the problem of image real-time processing and correction for high-speed endoscopic swept-source optical coherence tomography (SS-OCT), we highly optimize a computer-unified device architecture-based platform and use a field-programmable gate array to summarize the application experience. MATERIALS AND METHODS: We use the Half-Sync/Half-Asyn mode to optimize memory in order to build a high-throughput data thread pool for CPU. We use asynchronous streaming architecture to multiplex multiple threads at high speed to accelerate data processing. At the same time, we design a rotary scanning position information encoding feedback module to suppress image drift, which can realize 25ns logic-timing sequence synchronization control through FPGA 40MHz clock. RESULTS: The maximum complete attainable axial-scan-processing rate (including memory transfer and display of B-scan frames) is 3.52 MHz for a 16-bit pixel depth and A-scans/s of 1024 pixels. To our knowledge, this is the fastest processing rate reported to date with a single-chip graphical processing unit for SS-OCT. Finally, the established high-speed SS-OCT is used to image mouse esophagus and human fingers, and the output images are stable. When the image size is 1024 × 1024 pixels, the real-time imaging rate is 200 frames per second. CONCLUSIONS: This paper develops a real-time image processing and reconstruction technology suitable for high-throughput SS-OCT systems, which can have high-density operation and efficient parallelism, while suppressing high-speed image drift. It lays the foundation for the non-destructive, in vivo, non-staining, fast and convenient early tumor diagnosis of high-speed endoscopic SS-OCT.

Selective induction of LTP and LTD by postsynaptic [Ca2+]i elevation.

Long-term potentiation (LTP) and long-term depression (LTD), two prominent forms of synaptic plasticity at glutamatergic afferents to CA1 hippocampal pyramidal cells, are both triggered by the elevation of postsynaptic intracellular calcium concentration ([Ca2+]i). To understand how one signaling molecule can be responsible for triggering two opposing forms of synaptic modulation, different postsynaptic [Ca2+]i elevation patterns were generated by a new caged calcium compound nitrophenyl-ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid in CA1 pyramidal cells. We found that specific patterns of [Ca2+]i elevation selectively activate LTP or LTD. In particular, only LTP was triggered by a brief increase of [Ca2+]i with relatively high magnitude, which mimics the [Ca2+]i rise during electrical stimulation typically used to induce LTP. In contrast, a prolonged modest rise of [Ca2+]i reliably induced LTD. An important implication of the results is that both the amplitude and the duration of an intracellular chemical signal can carry significant biological information.

Effects of muscle electrical activity on the transmission of developing neuromuscular junction.

Miniature endplate potentials (MEPPS) caused by the spontaneous release of ACh from the growth cone of cholinergic neurons, are recorded by the whole-cell patch-clamp technique on a large number of 1-day cultured myoballs which have contact neurites of co-cultured neurons. Both muscle cell and neuron are dissociated from the 1-day-old (about stage 20) Xenopus embryo. Frequency and/or amplitude of MEPPs can obviously increase after the repetitive high-level depolarization caused by the stimuli on muscle cells. No detectable changes of single ACh receptor channel property are observed by using the single-channel recording technique. These results suggest that the mechanism of the increase of MEPPs after electrical activity of postsynaptic muscle cells probably involve some alteration of presynaptic membrane.

The effects of glutamate and GABA (gamma-amino-butyric-acid) on spontaneous acetylcholine release at the neuromuscular junction in Xenopus laevis embryo cell cultures.

The miniature endplate currents (MEPC's) were recorded at the neuromuscular junction of Xenopus laevis embryo neuron-muscle co-cultured cells. These MEPC's were due to the spontaneous release of acetylcholine from the nerve terminal. After perfusion with glutamate (10 mumol/L), both frequency and amplitude of the MEPC's increased. After washing away of glutamate, this effect persisted. We named this phenomena "Long-Term Facilitation". GABA (20 mumol/L) on the other hand had an inhibitory effect on both frequency and amplitude of the MEPC's. After washing away of GABA, the MEPC frequency and amplitude increased. We named this effect "Post-Potentiation". Local perfusion experiments furthermore indicated that the effect of glutamate was restricted to the neuromuscular junction, the effect of GABA was restricted to the soma.

Endothelium-derived relaxing factor activates calcium-activated potassium channels of resistance vessel smooth muscle cells.

Direct observation was made by using the patch-clamp technique with a specially designed microperfusion system to investigate the effect of acetylcholine (Ach 10(-6) mol/L) elicited endothelium-derived relaxing factor (EDRF) on the calcium-activated potassium channel (IK(Ca)) in the smooth muscle cells of mesenteric resistance vessels in Wistar rats. Activation of IK(Ca) was firstly observed by inducing the elicited EDRF or sodium nitroprusside (SNP 10(-8) mol/L) under various clamping voltages in cell-attached configuration. While the pipette solution contained KCl 126 mmol/L and the bath solution contained KCl 5.9 mmol/L, two types of conductances of calcium-activated potassium current being 76.4 +/- 2.3 pS (mean +/- S.E. n = 7) and 160.3 +/- 7.5 pS (mean +/- S.E. n = 7) were recorded during the EDRF activation, one type of conductance being 100.5 +/- 2.8 pS (mean +/- S.E. n = 6) was activated by nitric oxide (NO) which is an effective component from SNP. Differences in kinetic characteristics of these channels between EDRF and NO activation were found, particularly the probability of the channel being open in EDRF activation was obviously greater than that in NO stimulation. It has been shown that the potassium channel mechanisms involved in the EDRF and NO actions might be different.