Low percolation threshold of graphene/polymer composites prepared by solvothermal reduction of graphene oxide in the polymer solution

Graphene/polyvinylidene fluoride (PVDF) composites were prepared using in-situ solvothermal reduction of graphene oxide in the PVDF solution. The electrical conductivity of the composites was greatly improved by doping with graphene sheets. The percolation threshold of such composite was determined to be 0.31 vol.%, being much smaller than that of the composites prepared via blending reduced graphene sheets with polymer matrix. This is attributed to the large aspect ratio of the SRG sheets and their uniform dispersion in the polymer matrix. The dielectric constant of PVDF showed a marked increase from 7 to about 105 with only 0.5 vol.% loading of SRG content. Like the other conductor-insulator systems, the AC conductivity of the system also obeyed the universal dynamic response. In addition, the SRG/PVDF composite shows a much stronger nonlinear conduction behavior than carbon nanotube/nanofiber based polymer composite, owing to intense Zener tunneling between the SRG sheets. The strong electrical nonlinearity provides further support for a homogeneous dispersion of SRG sheets in the polymer matrix.     

High-speed dual-modulus prescaler architecture for programmabledigital frequency dividers

A new high-speed architecture for a dual-modulus prescaler N/N+1 divider is presented and compared to the widely used Johnson counter, in addition to some other approaches that have inherent limitations of speed when the '+1' of the N+1 divider is processed. This high-speed structure allows a speed similar to that of a simple divider-by-two from which it derives     

Circulating lupus coagulants. A paradox in vascular pathology]

Lupus anticoagulants (LA) are acquired inhibitors of coagulation related to the antiphospholipid antibodies. Paradoxically, these anticoagulants do not expose patients to the risk of hemorrhage but, on the contrary, to a thrombotic risk. The association in a patient of an antiphospholipid antibody and a clinical manifestation (thrombosis or equivalent) defines the antiphospholipid syndrome. This syndrome is termed primary or secondary according to whether it appears as an isolated disorder or is associated with an identified disease, frequently autoimmune (systemic lupus erythematous or lupus related syndrome). Clinical complications of LA are arterial or venous thrombosis at various sites. They are frequently recurrent, and deep venous thrombosis of leg, oculo-cerebral ischemic lesions and heart valve complications have all been well documented. Thrombosis of the microcirculation can cause tissue or organ disfunction, the most characteristic effect being repeated abortions. Laboratory demonstration of LA is difficult when the inhibitor is weak, and this should be completed by tests for other antiphospholipid antibodies. Clinical studies are necessary to assess the thrombotic risk of the LA in different clinical conditions and to evaluate the need and type of antithrombotic treatment. The LA are heterogeneous and only a small proportion of patients with LA will develop thrombosis. New tests capable of predicting the thrombotic risk, bases on the physiopathological mechanisms with which LA interfere in vivo, are currently being investigated.     

Recent progress in the development and properties of novel metal matrix nanocomposites reinforced with carbon nanotubes and graphene nanosheets

One-dimensional carbon nanotubes and two-dimensional graphene nanosheets with unique electrical, mechanical and thermal properties are attractive reinforcements for fabricating light weight, high strength and high performance metal-matrix composites. Rapid advances of nanotechnology in recent years enable the development of advanced metal matrix nanocomposites for structural engineering and functional device applications. This review focuses on the recent development in the synthesis, property characterization and application of aluminum, magnesium, and transition metal-based composites reinforced with carbon nanotubes and graphene nanosheets. These include processing strategies of carbonaceous nanomaterials and their composites, mechanical and tribological responses, corrosion, electrical and thermal properties as well as hydrogen storage and electrocatalytic behaviors. The effects of nanomaterial dispersion in the metal matrix and the formation of interfacial precipitates on these properties are also addressed. Particular attention is paid to the fundamentals and the structure–property relationships of such novel nanocomposites.     

Limits of platelet aggregation tests for investigating thromboses (author's transl)

Three methods--spontaneous aggregation, ADP-induced aggregation and levels of circulating platelet aggregates--were used to test for platelet hyperaggregation in 87 adult patients divided into three groups. Group A comprised 26 patients with severe arterial diseases, including cerebral vascular accidents (16) and peripheral thrombosis (10) ; group B consisted of 31 patients with venous conditions, including deep phlebitis (22) and recurrent thrombo-embolic disease (9) ; group C, which served as control, comprised 30 patients with various non-vascular disorders. Spontaneous aggregation and enhanced reactivity to ADP correlated well with each other and were more frequent in patients with vascular diseases. However, one-third of patients in group C had pathological results, while one-third of patients in groups A and B had normal results, independently of any clinical particularity or therapeutic regimen. There were no significant differences between the three groups with regard to circulating platelet aggregates. These tests, therefore, appear to be of statistical and epidemiological interest, but of questionable practical value.     

The shell middle distillate synthesis process (SMDS)

Since the early 1970s Shell's research has been involved in syngas chemistry with special focus on routes to convert (remote) natural gas into easily transportable liquid hydrocarbons. This has resulted in the development of the SMDS process. The world's first commercial SMDS plant is being constructed on a site adjoining the Bintulu LNG plant in Sarawak, Malaysia, and will come on stream in the last quarter of 1992.The heart of SMDS is an enhanced Fischer-Tropsch process. However, direct FT synthesis does not allow the selective production of materials of narrow carbon number range. To overcome this limitation the flexible two-stage concept of SMDS has been developed, which combines the chain-length-independent FT chain-growth reaction with a chain-length-dependent cracking process. Naphtha, kerosene and gas oil yield ratios can be varied from 152560 to 255025. Both the kerosene and gas oil show excellent combustion properties: the smoke point of the kerosene can be over 45 mm and the gas oil has a cetane number in excess of 70.Further attention is paid to the production of the synthesis gas because of its impact on overall process efficiency, to the selection of multitubular FT reactors, and to the environmental merits of the SMDS process and its clean, aromatics-free products.Prepared for presentation at the AIChE Spring National Meeting, Orlando, Florida, USA, 18–22 March 1990.     

Some aspects of electron beam welded and laser welded ferritic Fe-22Cr-3Mo-5Ni-0.3Ru alloy

Ferritic Fe-22Cr-3Mo-5Ni-0.3Ru alloy was welded by electron beam (EB) and laser techniques. Tensile tests, impact tests, oxalic acid etch, electrochemical potentiokinetic reactivation (EPR) and potential-time measurements were employed to investigate the mechanical properties, microstructural features and corrosion behaviour of the EB and laser welded metals. The oxalic acid etch tests revealed that the microstructure of the EB and laser welded metals consisted of columnar grains and cells, respectively. These structures were formed directly from the substrate by epitaxial solidification. Furthermore, the oxalic acid tests also showed that the EB and laser welded metals were immune to intergranular corrosion. Similar results were obtained by double loop EPR tests.     

Laboratory-scale coal reactivity testing for entrained gasification

A relatively simple and rapid micro-gasification test has been developed for measuring gasification reactivities of carbonaceous materials under conditions which are more or less representative of an entrained gasification process, such as the Shell coal gasification process. Coal particles of < 100 μm are heated within a few seconds to a predetermined temperature level of 1000–2000 °C, which is subsequently maintained. Gasification is carried out with either CO₂ or H₂O. It is shown that gasification reactivity increases with decreasing coal rank. The CO₂ and H₂O gasification reactions of lignite, bituminous coal and fluid petroleum coke are probably controlled by diffusion at temperatures 1300–1400 °C. Below these temperatures, the CO₂ gasification reaction has an activation energy of about 100 kJ mol^?1 for lignite and 220–230 kJ mol^?1 for bituminous coals and fluid petroleum coke. The activation energies for H₂O gasification are about 100 kJ mol^?1 for lignite, 290–360 kJ mol^?1 for bituminous coals and about 200 kJ mol^?1 for fluid petroleum coke. Relative ranking of feedstocks with the micro-gasification test is in general agreement with 6 t/d plant results.