Think Positive: Phase Separation Enables a Positively Charged Additive to Induce Dramatic Changes in Calcium Carbonate Morphology

Soluble macromolecules are essential to Nature's control over biomineral formation. Following early studies where macromolecules rich in aspartic and glutamic acid were extracted from nacre, research has focused on the use of negatively charged additives to control calcium carbonate precipitation. It is demonstrated that the positively charged additive poly(allylamine hydrochloride) (PAH) can also cause dramatic changes in calcite morphologies, yielding thin films and fibers of CaCO₃ analogous to those produced with poly(aspartic acid) via a so‐called PILP (polymer‐induced liquid precursor) phase. The mechanism by which PAH induces these effects is investigated using a range of techniques including cryo transmission electron microscopy (TEM), Raman microscopy, and thermogravimetric analysis, and the data show that hydrated Ca²⁺/PAH/CO₃^2? droplets initially form in solution, before coalescing and ultimately crystallizing to give calcite, together with small quantities of vaterite. It is suggested that it is the initial formation of hydrated Ca²⁺/PAH/CO₃^2? droplets that is key to this process, rather than a specific polymer/mineral interaction. These results are discussed in terms of their relevance to biomineralization processes and highlight the opportunity for using counter‐ion‐induced phase separation of polyelectrolytes as a method for generating minerals with non‐crystallographic morphologies.     

Effect of anions from calcium sources on the synthesis of nano-sized xonotlite fibers

The xonotlite fibers were synthesized via the hydrothermal synthesis method with CaO and SiO2 as the raw materials and the molar ratio of Si/Ca of 1.0. Effect of anions from various calcium sources on the microstructure of the xonotlite fibers is studied in this paper. These obtained products were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM) techniques to investigate their crystalline phase, crystal structure and morphology. The results indicate that anion from various calcium sources has little influence on the crystalline phases of xonotlite fibers but poses a great impact on their morphologies. Xonotlite fibers with single crystal characteristics and large aspect ratio of 50—100 were successfully fabricated from CaCl2 as calcium material at 225 °C for 15 h. The existence of Cl? anion in the CaO-SiO2-H2O system significantly contributes to the formation of xonotlite crystal.     

Time resolved study on Co/Ni/a-Si phase transition during isothermal annealing at 400 °C

An approach based on in situ sheet resistance analyses during isothermal annealing processes is proposed to find out the critical stages of Co/Ni phase transition on amorphous silicon. Unlike the case of conventional Co/Si systems, it was found that Co/Ni/Si reaction produces a double-peak in the resistance versus time curve. This behaviour was studied by energy filtered transmission electron microscopy (EFTEM), energy dispersive X-ray spectroscopy (EDS) and selected area electron diffraction (SAED) analyses. It was found that cobalt atoms prefer to diffuse through the grain boundaries of the underlying Ni₂Si layer that forms at very low temperature in contact with silicon. The diffusion process stops when cobalt atoms reach the deeper NiSi layer which is located at the interface with the substrate. Finally, CoSi and NiSi phases form separately, and Co(Ni)Si₂ grains nucleate in contact with silicon differently from what is known for thick layer systems.     

纯硅芯光纤的空间辐照环境适应性

研究了光纤的辐照损伤机理,对纯硅芯光纤与传统芯层掺杂光纤的结构特点进行了系统地分析,从结构组成特点上分析了两者的抗辐照性能差异。研究了国内外关于光纤的抗辐照试验标准,对各标准中剂量率、总剂量等试验条件差异进行了对比,并对不同剂量率对光纤辐照试验结果的影响进行了分析,给出了光纤在空间辐照环境条件下应用的辐照试验条件的选择原则。最后,采用0.1 rad（Si）/s剂量率对某国产纯硅芯光纤的抗辐照性能进行了试验评估,光纤在20 k rad（Si）总剂量辐照后光纤损耗为1.934 dB/km。空间辐照性能评估结果满足该项目的宇航型号的空间环境使用需求,辐照评估结论为可用。     

Gamma-ray radiation effects on hydroxyl absorption increase in optical fibers

This paper presents gamma-ray irradiation effects on OH-loss increase due to the chemical reaction of H2for GeO2-doped and GeO2. P2O5-doped fibers. When H2diffuses into irradiated fibers (γ-H2treatment), OH-loss increase occurs even at room temperature. Moreover, OH-loss increases due to dissolved H2in irradiated fibers are larger than those in unirradiated fibers at high temperatures. These OH-loss increases are attributed to irradiation-induced defects with which H2reacts to form OH ions. When H2-dissolved fibers are irradiated, the OH-loss increases are larger than those in the γ-H2-treated fibers at room temperature. These larger loss increases are thought to be caused by the reaction of the unstable radical and dissolved H2, which are excited by the irradiation.     

Effects of regional stimulation using a miniature stimulatorimplanted in feline posterior biceps femoris

The effects of placement of a miniature implantable stimulator on motor unit recruitment were examined in the posterior head of cat biceps femoris. The implantable stimulator (13-mm long×2-mm diameter) was injected either proximally near the main nerve branch, or distally near the muscle insertion, through a 12-gauge hypodermic needle. Glycogen-depletion methods were used to map the distribution of fibers activated by electrical stimulation. Muscle fibers were found to be depleted at most or all proximodistal levels of the muscle, but the density of depleted fibers varied transversely according to the stimulus strength and proximity of the device to the nerve-entry site. Thus, muscle cross sections often had a “patchy” appearance produced because different proportions of depleted fibers intermingled with undepleted fibers in different parts of the cross section. In other preparations, the force of muscle contraction was measured when stimuli of varying strengths were delivered by the stimulator positioned at the same proximal or distal sites within the muscle. Devices placed close to the nerve-entry site produced the greatest forces. Those placed more distally produced less force. As stimulus current and/or pulse width increased, muscle force increased, often in steps, until a maximum was reached, which was usually limited by the compliance voltage of the device to less than the force produced by whole nerve stimulation     

Spectrally Resolved Transmission Loss in Gamma Irradiated Yb-Doped Optical Fibers

Yb³⁺-doped silicate fibers are commonly employed in optical systems utilizing fiber lasers and amplifiers. Deployment of such materials and systems in space-based and other adverse radiation environments requires knowledge of their response to fluxes of ionizing radiation. This paper reports the results of gamma radiation exposures on a suite of passive, modern, highly Yb³⁺-doped aluminosilicate fibers. Of interest are the effects of total dose and dose rate as well as the development of radiation-induced absorption across a broad spectral window (1.0-1.7 mum). Results indicate that these fibers exhibit reasonable radiation resistance to gamma exposures typical of a five-year low-Earth-orbit environment. Maximum transmittance losses of less than 10% in the 1.0-1.7-mum spectral region for total gamma exposures of 2-5 krad (Si) were observed. In addition, it was found that the dependence of transmittance on radiation dose generally followed a power law that was dependent on dose rate.     

Gamma-ray radiation hardened properties of pure silica coresingle-mode fiber and its data link system in radioactive environments

The radiation resistances of pure silica core single-mode optical fiber (Si-SMF) and its data link module at 1.30 μm were investigated. It was found that the induced loss of fibers exposed to γ-rays at a low dose rate was proportional to the 0.54 power of total dose from the result of a low dose rate irradiation test for 3 years, and the induced loss for 40 years aging at 1 R/h was estimated to be 1.8 dB/km. It was ascertained that transmission is achievable at a bit rate of 125 Mb/s even under high dose rate irradiation to a total dose of 10⁸ R, which corresponds to the postulated maximum γ-ray exposure in nuclear power plants     

电子束真空辐射固化技术基础研究

提出了电子束真空辐射固化技术新概念，并对该技术的固化机理等进行了阐述。通过对液态低聚物辐射固化条件和SDS-Ⅱ型曝光机的加速电压、曝光剂量等曝光参数的分析研究，得出SDS-Ⅱ型曝光机可以用于液态低聚物辐射固化的结论。在此基础上使用SDS-Ⅱ型曝光机在20kV的加速电压、2μC／em^2的曝光剂量下，对经真空挥发处理过的三羟甲基丙烷三丙烯酸酯(TMPTA)液态低聚物进行了曝光试验，得到了固化结构。基本上证明了电子束真空辐射固化液态低聚物的可行性，为微机电三维微结构的加工提供了一种新方法。     

Liquid phase epitaxy for the production of YBa2Cu3O7-δ coated conductor

The liquid phase epitaxy (LPE), which is performed under ambient pressure with simple growth apparatus, allows us to fabricate high-Jc YBa₂Cu₃O_7-δ (YBCO) crystalline thick films at high growth rate. We propose that the LPE growth of YBCO films on single crystalline oxide fibers is another way to produce YBCO-coated conductors for power application. In the conventional case of using BaO–CuO melt as a solvent, by which the YBCO crystals grow at about 1000°C, YBCO coating on yttria-stabilized zirconia (YSZ) or SrTiO₃ (STO) single crystalline fibers has not been successfully achieved because of their reaction with the solvent. Recently we have discovered that BaF₂ added as a solution decreases the crystallization temperature of YBCO down to 900°C and suppress the reactivity with no degradation of superconductivity of the YBCO crystal. The YBCO-coated fibers are successfully prepared using this solution. The behavior of critical current under magnetic fields shows that these YBCO-coated fibers have the potential to be used under a high magnetic field at the temperature of liquid nitrogen.     

Experimental investigation of the factors influencing temperature dependence of radiation-induced attenuation in optical fiber

The effects of transmission wavelength, total dose and light source power on temperature dependence of radiation-induced attenuation (RIA) in Ge–P co-doped fibers were investigated. Three fibers irradiated up to total dose of 100 Gy and 10,000 Gy were used as test samples. A test system for temperature dependence of RIA was built up. The influence of transmission wavelength, total dose and light power on temperature sensitivity and linearity of RIA in three irradiated fibers were researched. The test results show that temperature sensitivity and linearity of RIA in optical fibers could be improved by adjusting total dose and selecting transmission wavelength. The light source power does not have obvious influence on temperature sensitivity and linearity. The Ge–P co-doped fiber at 850 nm transmission wavelength with higher total dose is a very promising candidate for fiber-optic temperature sensor.     

Detection of neuromuscular junctions on isolated branched muscle fibers: application of nitric acid fiber digestion method for scanning electron microscopy.

Three-dimensional morphology and neuromuscular junctions of the branched muscle fibers of the rat skeletal muscles isolated from the rat were examined by application of the nitric acid digestion method for scanning electron microscopy. Treatment with fifteen percent nitric acid and a supersonic wave bath were effective in isolating the branched muscle fibers and for detecting their innervations by scanning electron microscopy. Mean numbers of total and branched fibers in the rat plantaris muscles were 11,130 +/- 314 and 32.4 +/- 4.8 (n = 12), respectively. Bifurcation of these fibers resembled either the letter X (X type) or letter Y (Y type). The Y type fibers were most frequently seen (84% of total branched fibers), and X types accounted for 14%. The remaining 2% of the fibers were subtypes of X and Y with overlapping bifurcation. These branched fibers were differentiated by their length from the bifurcated point, i.e., short, medium and long branches. Neuromuscular junctions on these branched fibers were located almost at the center of their length. The number of innervations was decided by the number of bifurcating fibers across the central part of the length.     

Implantation and activation of high concentrations of boron in Germanium

There is renewed interest in the development of Ge-based devices. Implantation and dopant activation are critical process steps for future Ge devices fabrication. Boron is a common p-type dopant, which remarkably is active immediately after implantation in Ge at low doses. This paper examines the effect of increasing dose (i.e., 5/spl times/10/sup 13/-5/spl times/10/sup 16/ cm/sup -2/) and subsequent annealing (400/spl deg/C-800/spl deg/C for 3 h in nitrogen) on activation and diffusion of boron in Ge. Secondary ion mass spectrometry (SIMS), spreading resistance profiling (SRP), high resolution X-ray diffraction (HRXRD), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA) are used to characterize the implants before and after annealing. It is found that very high fractions of the boron dose (/spl sim/5%-55%) can be incorporated substitutionally immediately after implantation leading to very high hole concentrations, /spl ges/2/spl times/10/sup 20/ cm/sup -3/, deduced from SRP. Small increases in activation after annealing are observed, however, 100% activation is not indicated by either SRP or NRA. Negligible diffusion after annealing at either 400/spl deg/C or 600/spl deg/C for 3 h was, furthermore, observed.     

脉冲γ射线对光纤的辐射感生损耗

研究了光纤受射线辐照响应机制,计算了光纤对射线吸收率、效应截面、Compton电子的能通量及角度分布;提出了瞬态辐射感生损耗的测量方法,采用波长分别为405、660、850、1 310、1 550 nm的模拟宽带光纤传输系统,设计了瞬态辐射感生损耗的实验测量系统。在平均光子能量0.3 MeV、剂量率2.03107 Gy/s和平均光子能量1.0 MeV、剂量率5.32109 Gy/s的两种脉冲射线辐照条件下,获得了4种光纤瞬态辐射感生损耗与剂量的关系、永久性感生损耗的谱分布和折射率变化结果:（1）脉冲射线对光纤的瞬态辐射感生损耗随探测波长在近红外到可见光范围内的减小而增大;（2）在相同辐照条件下,多模光纤的瞬态辐射感生损耗稍大于单模光纤;（3）辐射致光纤折射率降低;（4）在一定剂量范围内,多模光纤瞬态辐射感生损耗和剂量呈近似线性关系。研究表明,射线导致光纤基质原子产生新的色心和光纤折射率降低,色心对传输光子的共振吸收导致光纤吸收损耗增加,折射率降低导致光纤波导损耗增加,感生损耗是两种机制共同作用的结果。     

Behavioral Suppression by 383-MHz Radiation (Short Papers)

The heads of two rhesus monkeys were irradiated in a 383-MHz resonant cavity immediately before and during performance of a four-choice forced-choice serial reaction task. CW radiation at integral dose rates of 0.001 -17.5 W were delivered to the head. No effects were observed below a critical dose level (/spl ap/23 W/kg) derived from integral dose rate and body mass. Above this level, behavioral suppression occurred, i.e., correct response rate was profoundly altered. The effect was completely reversible and repeatable in one of the subjects---the other subject did not recover completely and was sacrificed for histological examination which revealed no gross or microscopic damage. The nature of the effect suggests a neurochemical rather than an electrical or mechanical basis for the results.     

A further observation of the structural changes of microvessels in the extensor digitorum longus muscle of the aged rat

We further examined the structural changes of microvessels in the extensor digitorum longus muscle of the aged (18 months) rat. Muscle bundles in this aged muscle constantly consisted of numerous large muscle fibers 50-60 mum in diameter and a few small muscle fibers <30 mum in diameter. Neuromuscular junctions (NMJs) in large muscle fibers often showed degenerative figures, thus degenerating muscle fibers. On the other hand, NMJs in small muscle fibers were mainly characterized by sparse and short junctional folds, being possibly in the course of regeneration. In some muscle bundles, the extracellular matrix was a little widened. Microvascular networks from arterioles to venules via capillaries seemed to vary in structural features between muscle bundles. In addition to the normal microvascular network consisting of microvessels with a round or oval vascular lumen during their course, two different types of microvascular networks were found. One type was characterized by the constriction of arterioles, capillaries and venules, probably representing a degenerative process of the microvascular network. In fact, uneven and compressed scaffolds of basal laminae of capillaries were often observed around these constricted microvessels. The other type consisted of arterioles and capillaries with an irregular slit-like vascular lumen and venules with a round or oval vascular lumen, and these capillaries had thick or two-layered basal laminae, being probably in the course of remodeling of the microvascular network. From these findings, it is suggested that the constriction and/or contraction of microvessels by smooth muscle cells and pericytes may be involved in the degeneration and remodeling of the microvascular network in the muscle bundles following degeneration and regeneration of the muscle fibers.     

Influence of the Germanium content on the amorphization of silicon–germanium alloys during ion implantation

We have studied by transmission electron microscopy the amorphization of silicon–germanium (SiGe) alloys by Ge⁺ implantation. We show that when implanted with the same amorphization dose, the resulting amorphous layers get narrower when the Ge content increases. The experimental results can be simulated using the critical damage energy density model assuming that the amorphization threshold rises linearly with the Ge content from 3 eV/at for pure Si to 5 eV/at for pure Ge. These results and simulations are needed to optimize the fabrication of highly doped regions in SiGe alloys.     

Deuterium post-metal annealing of MOSFET's for improved hot carrierreliability

Low-temperature post-metallization anneals in hydrogen ambients are critical to CMOS fabrication technologies in reducing Si/SiO₂ interface trap charge densities by hydrogen passivation. In this letter we show that the hot carrier reliability (lifetime) of NMOS transistors can be increased by an order of magnitude when wafers are annealed in a deuterium ambient. This phenomenon can be understood as a kinetic isotope effect. The chemical reaction rates involving the heavier isotopes are reduced, and consequently, under hot electron stress, bonds to deuterium are more difficult to break than bonds to protium (H). However, the static chemical bonding (i.e., binding energies and excited states) is evidently the same for both hydrogen and deuterium. We measure identical transistor function after hydrogen and deuterium treatment before hot electron dynamics and resultant damage. Therefore, deuterium and hydrogen post-metal anneal processes are compatible with each other in semiconductor manufacturing. SIMS analysis proves that at typical anneal temperatures (400-450°C), deuterium diffuses rapidly through the interlevel oxides and accumulates at Si/SiO ₂ interfaces. Transistor speed versus reliability trade-off in CMOS device design is discussed in light of the findings of this study     

Mechanical and optical properties of the chalcogenide glass system As2Se3-xTex

Chalcogenide glasses of As2Se3-xTex(0 leq x leq 3) were fabricated with special care to avoid traces of oxygen, using very pure raw materials. From part of these materials, special plates were made, and from the rest fibers were pulled. From transmittance measurements, the existence of absorption bands was shown, corresponding to the presence of small crystallites of As2O3. The attenuation in the infrared of these plates increased from 14 dB/m for As2Se3to 29 dB/m for As2Se0.5Te2.5. Conversely, a decrease of microhardness VHwas observed. The attenuation of CO2laser light (lambda = 10.6 mum) transmitted through the pulled fibers was measured as a function of the Te(x) content. and an increase of the attenuation was observed from 18.1 dB/m for As2Se3to 66.7 dB/m for As5Se1.5Te1.5. The surface of each fiber was examined in the scanning electron microscope and an increase of the defects (e.g., crystallites) when the Te content was increased, was observed. These defects (crystallites) are the main factors for finding an increase in the absorption in IR.     

Effect of natural radioactivity on optical fibers of underseacables

For undersea cables radiation doses between 2.5 and 25 rad are to be expected during a working life of 25 years. The majority of previous investigations of the radiation sensitivity of optical fibers, however, apply dose rates ≳1 rad/s and total dose values ≳3×10 ³ rad. The present paper describes ⁶⁰Co irradiations of a Ge-doped single mode fiber with dose rates between 10 ^-4 and 20 rad/s. Expected loss increase of an undersea optical fiber cable at 1550 nm wavelength with a temperature of 2°C is derived by three different methods. The most comfortable and reliable one, the `dose rate transformation method', yields, for example, a loss of only 0.0244 dB/100 km after 25 years of irradiation with a dose rate of 0.4 rad/s. This method could be the basis of a standard test procedure for the effect of natural radioactivity on optical fibers for very long repeaterless terrestrial and undersea cables