An experiment on stress intensity factors for an interface crack between epoxy and aluminum plates

A teflon tape (0.07 mm thickness) is placed at the center of an edge of an epoxy plate. The plate is used to fabricate a mold, and epoxy resin is cast in the mold so as to produce a cracked epoxy plate. A tensile test is conducted so as to determine the fracture toughness value of the epoxy plate. Next, a mold is fabricated from an aluminum plate having a teflon tape placed along its edge, and epoxy resin is cast in the mold so as to produce an epoxy-aluminum composite weakened by an interface crack. Tensile testing reveals that the crack always propagates into the epoxy plate at an angle measured from the interface. The stress intensity factor for an interface crack is defined in a manner similar to that for a crack in a homogeneous material, and is obtained for several values of a/h, 2a being the crack length and 2h being the width of the epoxy-aluminum composite.     

Intercept length distributions for several polygons

Abstract

Intercept length distribution curves were calculated or determined graphically for a variety of polygons and shapes as an initial step in ascertaining the nature of intercept distributions for statistical grain sections, an intermediate goal being to provide a method of calculating section diameters from the more easily measured intercept distributions determined by lineal analysis, but with the ultimate aim of determining the spatial distribution. The following shapes were selected: an ellipse, an equilateral and an irregular triangle, a square, a 60° rhombus, a rectangle, a pentagon, a hexagon, an irregular seven sided polygon, and an irregular five sided polygon having convex sides. If the intercept length is designated as q and the distribution function as f(q), it is concluded that f(q) of a statistical grain section would have the following characteristics: f(q) finite at q=0, df(q)/dq≠0 at low values of q, f(q) a maximum at q < q_max and f(q)=0 at q_max.

MST/1104     

Note on the Thermal Degradation of Polytetrafluoroethylene as a First-Order Reaction

Additional experiments on the rates of thermal degradation of polytetrafluoroethylene in a vacuum confirm an earlier conclusion that a first-order rate law is involved in the degradation reaction.In a study made by Madorsky, Hart, Straus, and Sedlak¹ on the rates and activation energy of thermal degradation of polytetrafluoroethylene in a vacuum, two methods were employed: a gravimetric method, using a very sensitive tungsten spring balance in a vacuum system to measure the rate of loss of weight of the degrading sample, and a pressure method, using a multiplying manometer to measure the pressure of the C₂F₄ formed in the reaction. The material that was used was in the form of a tape 0.07 mm thick. Weight of the sample was about 7 mg in the gravimetric experiments and 5 to 306 mg in the pressure experiments.The rates obtained by the gravimetric method are reproduced in figure 1, plotted as a function of percentage loss of weight of the sample for 480, 490, 500, and 510 °C. The initial rates were obtained by extrapolating the rate curves to the ordinate. The rate curves beyond the initial 5 to 18 percent loss of weight of the sample are straight lines, and when extended to the right they approach near the zero rate at 100 percent volatilization. The rates obtained by the pressure method were studied at 10 different temperatures ranging from 423.5 to 513.0 °C. Logarithms of the initial rates obtained by both methods are shown in figure 2 plotted against the inverse of absolute temperature.² From the Arrhenius equation the slope of the resulting straight line indicates an activation energy of 80.5 kcal/mole. From the appearance of the curves in figure 1 it seemed logical to conclude that the reaction involved in the thermal degradation of polytetrafluoroethylene in a vacuum follows a first-order law.Open in a separate windowFigure 1Rate of thermal degradation of polytetrafluoroethylene by the weight method as a function of percentage volatilization.Open in a separate windowFigure 2Activation energy slope for thermal degradation of polytetrafluoroethylene.●—weight method (see footnote ¹)○—pressure method (see footnote ¹)■—present work.At a later date Wall and Michaelson³ studied the rate of thermal degradation of polytetrafluoroethylene at 460 °C in a stream of nitrogen. They used a gravimetric method by heating 1-g samples of a powdered material and weighing the residues at intervals. They state that below about 480 °C the reaction is zero order, whereas above 510 °C they concede it is first order.In view of this result by Wall and Michaelson, it was deemed advisable to check further on the rate order involved in the thermal degradation of this material in a vacuum. Although experiments by the pressure method were carried out in our earlier work at temperatures below 480 °C, the extent of volatilization was at most only 6.4 percent. Degradation had not been carried far enough to determine accurately whether the percentage loss versus time plots were straight or curved lines, i.e., whether the indicated reaction is of zero or first order. Rate experiments were therefore carried out by the weight method at lower temperatures, namely at 460, 475, and 485 °C, and the results are shown in figure 3, where percentage loss of weight is plotted against time. The curves are definitely not straight lines, as would have been the case if the reaction had followed a zero order.Open in a separate windowFigure 3Pyrolysis of polytetrafluoroethylene at low temperatures.In our previous work (see footnote ¹) the rates were obtained by plotting the slopes between two neighboring experimental points in the volatilization-time plots. In the present work the slopes were calculated from the curves shown in figure 3, and the resulting rate curves based on these calculations are shown in figure 4. The same type of rate curves were obtained as in the earlier work. Values obtained for the initial rates at these three temperatures fit nicely into the Arrhenius plot, as shown by the squares in figure 2.Open in a separate windowFigure 4Rates of thermal degradation of polytetraduoroethylene at low temperatures.The present work therefore confirms our earlier conclusion that the degradation of polytetrafluoroethylene in a vacuum follows a first-order rate law, where the rate of volatilization, based on the sample, is directly proportional to the amount of residue.     

On the straightness of eigenvalue interactions

Solutions to eigenvalue problems come in two parts, an eigenvalue and an eigenvector, and these solution pairs occur at discrete points in the range of possible eigenvalues. Multiparameter eigenvalue problems similarly have solutions that have a dimension smaller by 1 than the space of the eigenvalues - solutions to a 2-parameter problem are discrete curves in a plane, and in general, solutions to an n-parameter problem are hypersurfaces in an n dimensional space. These curves/surfaces/hypersurfaces are eigenvalue interaction curves (/surfaces, etc.), and they might be flat. An unchanging eigenvector leads to a flat interaction, almost trivially. This paper addresses the question if an interaction is flat (in particular, if an interaction curve is straight), what conditions does this place on the eigenvector?     

Absolute Configuration and Chemical Topology

The stereochemistry of catenanes, knotted molecules, and Borromean rings is discussed. An augmentation of the Cahn-Ingold-Prelog convention for designating absolute configuration is proposed. A convention is proposed for designating the absolute configuration of knotted molecules. A suggestion is made concerning the citing of the absolute configuration of molecularly dissymmetric diastereomers.Proposals of rules for designating absolute configuration have been put forth by Cahn, Ingold, and Prelog¹ and by Terentiev and Potapov.² The rules of the latter workers are deliberately linked to nomenclature. Those of the former workers rely entirely on structure and have found wide acceptance among organic chemists. In their closely reasoned paper Cahn, Ingold, and Prelog properly claim to have covered by their rules all known types of dissymmetry deriving from tetracovalent and tricovalent atoms.Work aiming toward the establishment of a major system for handling chemical information requires the ability precisely to designate chemical structures without recourse to structural formulas. A number of notation systems have been devised for representing chemical structures by linear arrays of symbols,³ although none of the systems has yet been perfected even for organic compounds.⁴ Since an adequate information handling system must accommodate not only all known structural types but also those structural types which have to date been merely speculated on, an examination of more esoteric stereochemistry was undertaken. I now wish to propose an augmentation of the Cahn-Ingold-Prelog (C-I-P) rules and the addition of a new (specialized) set of rules to cover a wider range of molecularly dissymmetric structural types.The molecularly dissymmetric structures for which further rules are necessary are of two types: (1) substituted catenanes,⁵ which are stereochemically related to substituted allenes and spiro compounds, and (2) knots,⁶, ⁷ compounds whose dissymmetry is due entirely to topology, independent of substitution. ^{6, 7} The C-I-P convention is inapplicable to knots and before being applied to catenanes requires a further convention for defining the “near groups”.     

Hydroxyapatite-Derived Heterogeneous Ru-Ru2P Electrocatalyst and Environmentally-Friendly Membrane Electrode toward Efficient Alkaline Electrolyzer

Alkaline membrane water electrolysis is a promising production technology, and advanced electrocatalyst and membrane electrode design have always been the core technology. Herein, an ion-exchange method and an environmentally friendly in situ green phosphating strategy are successively employed to fabricate Ru-Ru₂P heterogeneous nanoparticles by using hydroxyapatite (HAP) as a phosphorus source, which is an exceptionally active electrocatalyst for hydrogen evolution reaction (HER). Density functional theory calculation results reveal that strong electronic redistribution occurs at the heterointerface of Ru-Ru₂P, which modulates the electronic structure to achieve an optimized hydrogen adsorption strength. The obtained Ru-Ru₂P possesses excellent HER performance (24 mV at 10 mA cm⁻²) and robust stability (1000 mA cm⁻² for 120 h) in alkaline media. Furthermore, an environmentally friendly membrane electrode with a sandwich structure is assembled by HAP nanowires as an alkaline membrane, Ru-Ru₂P as a cathodic catalyst, and NiFe-LDH as an anodic catalyst, respectively. The voltage of (−) Ru-Ru₂P || NiFe-LDH/CNTs (+) (1.53 V at 10 mA cm⁻²) is lower than that of (−) 20 wt% Pt/C || RuO₂ (+) (1.60 V at 10 mA cm⁻²) for overall water splitting. Overall, the studies not only design an efficient catalyst but also provide a new route to achieve a high-stability electrolyzer for industrial H₂ production.     

Resonating Valence Bond Mechanism of Impurity Band Superconductivity in Diamond

Superconductivity in an uncompensated boron doped diamond, a very recent observation, is strikingly close to an earlier observation of Anderson–Mott insulator to metal transition, prompting us to suggest an electron correlation driven superconductivity in an impurity band. Random coulomb potential remove a three fold orbital degeneracy of boron acceptor states, resulting in an effective single, narrow, tight binding and half-filled band of holes. Singlet coupling between spins of neighboring neutral acceptors B ⁰–B ⁰ is the seed of pairing. Across the insulator to metal transition, a small and equal fraction of charged B ⁺ and B ⁻ states (free carriers) get spontaneously generated and delocalize. Thereupon neutral singlets resonate and get charged resulting in a resonating valence bond (RVB) superconducting state.     

Qualitative analysis of the possibility of ignition of controllable thermonuclear fusion

Results of a preliminary experiment on excitation of gaseous active media by hard radiation of an uncontrolled thermonuclear explosion are presented. Pulsed lasing of an HF laser with an energy output of ≈10 kJ and efficiency of ≈3% and of an excimer XeF laser with an output of ≈1 kJ and efficiency of ≈9% with a pulse duration of ≈2 nsec is obtaned. Ya. Kupala Grodno State University, Grodno, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 72, No. 4, pp. 739–740, July–August, 1999.     

Note on the Preparation of Sodium Amalgam in the Form of Pellets

A procedure is described for the preparation of sodium amalgam in the form of pellets.In connection with the development of methods for the synthesis of radioactive carbohydrates,¹ a procedure and apparatus were previously described [1, 2, 3]² for the reduction of semimicro quantities of aldonic lactones to sugars. The method employs sodium amalgam together with a slightly soluble, acid salt (sodium binoxalate) as buffer.³ The amalgam is used in the form of pellets made by dropping the molten amalgam into a “shot tower” of oil. Because other workers have had difficulty in making these pellets, the procedure is now given in detail.The amalgam is prepared in a 500-ml, round-bottomed, stainless-steel flask having a single neck, with a 24/40 standard-taper joint (outer),⁴ and a thermometer inlet. The joint is fitted with a stainless-steel stopper, which has an inlet tube bent at right angles to the stopper and covered with asbestos for convenience in handling. The flask is held in a sturdy, asbestos-covered clamp, which serves as a handle for the vessel during the heating step. An alundum (Soxhlet extraction) thimble 45 mm in diam, in the bottom of which six 1.5-mm holes have been drilled, is held in a second asbestos-covered clamp. The oil bath is a thick-walled heat-resistant glass jar, 6 in. in diam and 18 in. high, containing paraffin oil to within 3 in. of the top (see fig. 1).Open in a separate windowFigure 1Apparatus used in the preparation of sodium amalgam pellets.To prepare the amalgam, a weighed amount of mercury is placed in the flask, into which a continuous stream of dry nitrogen is passed by means of the inlet tube of the stopper. The required amount of sodium⁵ is weighed under paraffin oil, and then cut into pieces just small enough to be readily slipped through the neck of the flask. Each piece is rinsed in a hydrocarbon solvent, such as heptane or toluene, quickly blotted dry, and dropped through the neck of the flask into the mercury; the stopper is immediately replaced. The sodium reacts quickly with the mercury and may be added fairly rapidly because of the atomosphere of nitrogen. After the addition of the sodium is completed, the flask is heated with a Meeker burner until the amalgam is entirely molten. (The presence of remaining solid particles in the amalgam maybe detected by the sound of their impact on the walls of the flask when it is given a gentle, swirling motion.) While the amalgam is being prepared, the alundum thimble is heated over another Meeker burner by a second operator. The hot thimble is then so clamped that its bottom is 1 to 2 in. above the surface of the oil, and the molten amalgam is poured into the thimble from the thermometer inlet of the flask. The amalgam flows through the holes in the bottom of the thimble, drops through the oil, and collects at the bottom of the oil bath as small, rather flat pellets.Optimal conditions for the production of smooth pellets must be determined by trial. If the flask and thimble have not been sufficiently heated, the amalgam may solidify in the thimble. If the holes in the thimble are too large, the product may be somewhat “thready.” However, once the optimal conditions have been established, the procedure may be repeated without difficulty.The entire operation must be performed in an efficient hood. The amalgam is stored under paraffin oil in a wide-mouthed, screw-capped bottle (see fig. 2). Pellets are removed as needed, weighed under oil, and rinsed with an inert, volatile solvent immediately before use.Open in a separate windowFigure 2Sodium amalgam pellets.     

Intramolecular Electron Transfers in Donor/Acceptor Linked Molecules Based on Endohedral Lanthanide Metallofullerenes

Chemical syntheses and intramolecular electron transferring behaviors in the electron donor/acceptor conjugates based on endohedral metallofullerenes, La₂@C₈₀ and La@C₈₂, are overviewed. A study on the photo-induced excited states of a La₂@C₈₀ derivative connected with an electron donor revealed the formation of a distinct radical ion pair state. A La@C₈₂ derivative linked with an electron donor demonstrated an unprecedented ion/anion pair state, and La₂@C₈₀ tethered with an acceptor showed a fullerene donor system, in which the fullerene acts as an electron donor. Using endohedral lanthanide metallofullerenes for intramolecular electron transferring systems opens a new door for developing novel molecular materials.     

Detecting <Emphasis Type="Italic">h</Emphasis>-index manipulation through self-citation analysis

The h-index has received an enormous attention for being an indicator that measures the quality of researchers and organizations. We investigate to what degree authors can inflate their h-index through strategic self-citations with the help of a simulation. We extended Burrell’s publication model with a procedure for placing self-citations, following three different strategies: random self-citation, recent self-citations and h-manipulating self-citations. The results show that authors can considerably inflate their h-index through self-citations. We propose the q-index as an indicator for how strategically an author has placed self-citations, and which serves as a tool to detect possible manipulation of the h-index. The results also show that the best strategy for an high h-index is publishing papers that are highly cited by others. The productivity has also a positive effect on the h-index.     

Some fires and explosions in liquids of high flash point

Many fires and explosions have occurred because of a failure to realise that heavy oils, once they are hot, catch fire or explode as easily as petrol.Some incidents are described, together with the precautions necessary to prevent them happening again.The incidents described are: an explosion in a distillation column; several explosions while demolishing storage tanks; a fire while demolishing an old pipeline; a plant destroyed when a spillage of solvent caught fire; an explosion in a lorry wheel; an explosion in a cargo of bananas; a fire while filling a road tank wagon.     

Physical properties of multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWNTs), which were prepared by hydrogen arc discharge, were purified by using an infrared radiation heating system. The morphology, structure, vibrational modes and crystalline perfection of purified MWNTs were investigated by using scanning electron microscopy, high-resolution transmission electron microscopy, an X-ray diffractometer and a Raman spectrometer. Moreover, the electrical conductivity of individual purified MWNTs was measured using a two-probe method using a micro manipulator system. It turned out that the MWNTs had a high degree of graphitization, an electrical conductivity of about 1.85×10³ S cm⁻¹ along the long axis, and an enormous current density of more than 10⁷ A cm⁻².     

Subnanosecond pulsed X-ray source based on nanosecond discharge in air at atmospheric pressure

We have studied the characteristics of an X-ray source based on a gas diode filled with air at atmospheric pressure. Driven by a SLEP-150 pulser with a maximum voltage amplitude of ∼140 kV, a pulse full width at half maximum (FWHM) of ∼1 ns, and a leading front width of ∼0.3 ns, a soft X-ray source produces subnanosecond pulses with an FWHM not exceeding 600 ps and an exposure dose of ∼3 mR per pulse. It is shown that the main contribution to the measured exposure dose is due to X-ray quanta with an effective energy of ∼7.5 keV.     

Mitigating Ion Migration with an Ultrathin Self-Assembled Ionic Insulating Layer Affords Efficient and Stable Wide-Bandgap Inverted Perovskite Solar Cells

Wide-bandgap perovskite solar cells (PSCs) are attracting increasing attention because they play an irreplaceable role in tandem solar cells. Nevertheless, wide-bandgap PSCs suffer large open-circuit voltage (V_OC) loss and instability due to photoinduced halide segregation, significantly limiting their application. Herein, a bile salt (sodium glycochenodeoxycholate, GCDC, a natural product), is used to construct an ultrathin self-assembled ionic insulating layer firmly coating the perovskite film, which suppresses halide phase separation, reduces V_OC loss, and improves device stability. As a result, 1.68 eV wide-bandgap devices with an inverted structure deliver a V_OC of 1.20 V with an efficiency of 20.38%. The unencapsulated GCDC-treated devices are considerably more stable than the control devices, retaining 92% of their initial efficiency after 1392 h storage under ambient conditions and retaining 93% after heating at 65 °C for 1128 h in an N₂ atmosphere. This strategy of mitigating ion migration via anchoring a nonconductive layer provides a simple approach to achieving efficient and stable wide-bandgap PSCs.     

Accuracy in finite element computation for eigenfrequencies

In this paper we propose an original numerical method to get upper and lower bounds for the eigenfrequencies of an elastic structure. This method is based on a ‘static’ formulation for eigenvalue problems built up from a new quotient R_s which is defined on a load space. From R_s properties, upper and lower bounds for the exact eigenfrequencies are proved. The application of the method requires the solution of an eigenvalue problem of finite dimension and the computation of a constant which is characteristic of the discretization subspace. Results of numerical tests are given for the vibration problem of an elastic clamped membrane.     

A discrete spectral analysis for determining quasi-linear viscoelastic properties of biological materials

The viscoelastic behaviour of a biological material is central to its functioning and is an indicator of its health. The Fung quasi-linear viscoelastic (QLV) model, a standard tool for characterizing biological materials, provides excellent fits to most stress–relaxation data by imposing a simple form upon a material''s temporal relaxation spectrum. However, model identification is challenging because the Fung QLV model''s ‘box’-shaped relaxation spectrum, predominant in biomechanics applications, can provide an excellent fit even when it is not a reasonable representation of a material''s relaxation spectrum. Here, we present a robust and simple discrete approach for identifying a material''s temporal relaxation spectrum from stress–relaxation data in an unbiased way. Our ‘discrete QLV’ (DQLV) approach identifies ranges of time constants over which the Fung QLV model''s typical box spectrum provides an accurate representation of a particular material''s temporal relaxation spectrum, and is effective at providing a fit to this model. The DQLV spectrum also reveals when other forms or discrete time constants are more suitable than a box spectrum. After validating the approach against idealized and noisy data, we applied the methods to analyse medial collateral ligament stress–relaxation data and identify the strengths and weaknesses of an optimal Fung QLV fit.     

Fabrication of high quality zinc-oxide layers through electrohydrodynamic atomization

Zinc oxide (ZnO) is a useful material in the fabrication of many electronic devices because of its wide band-gap, excellent transparency and high electron mobility. Thin films of ZnO have been fabricated where an alcosol solution containing 7 wt.% ZnO nano-particles was synthesized and subjected to controlled flow through a metal capillary exposed to an electric field at the ambient temperature to generate an electrohydrodynamic jet, which subsequently disintegrated into droplets thereby depositing a uniform thin film of zinc oxide on the glass substrates with an average thickness of 115 nm at a constant substrate speed of 0.25 mm/s. Pure and perfectly uniform transparent films with an average transmittance of 88% have been deposited with wurtzite crystal structure and an electrical resistivity of approximately 64 Ω.cm.     

Simulation d'une machine frigorifique à absorption fonctionnant avec des mélanges d'alcanes

We propose in this article an absorption chiller operating with binary alkane mixtures as an alternative to compression machines. It is an installation using low-level energy at a temperature below 150 °C (waste heat or solar energy) and operating with environmentally friendly fluids. Ten mixtures are considered and compared with two cooling mediums of the condenser and the absorber: the ambient air at 35 °C and the water at 25 °C. For an air-cooled chiller, the COP reaches 0.37 for the n-butane/octane system. This value remains 27% lower than that of an ammonia/water installation operating under the same conditions. For a water-cooling chiller, the n-butane/octane and propane/octane systems give a COP of about 0.63, which is comparable to that of the ammonia/water system. When n-butane is used as refrigerant, the machine works at a pressure under 5 bars, which is an advantage compared with machines working with ammonia/water mixtures.     

Measuring co-authors’ contribution to an article’s visibility

The visibility of an article depends to a large extent on its authors. We study the question how each co-author’s relative contribution to the visibility of the article can be determined and quantified using an indicator, referring to such an indicator as a CAV-indicator. A two-step procedure is elaborated, whereby one first chooses an indicator (e.g. total number of citations, h-index …) and subsequently one of two possible approaches. The case where the indicator is an h-type index is elaborated in a Lotkaian framework. Different examples illustrate the procedure and the choices involved in determining a CAV-indicator.