Matrix-enhanced secondary ion mass spectrometry: a method for molecular analysis of solid surfaces

A new methodology, matrix-enhanced secondary ion mass spectrometry (ME-SIMS), is reported for the molecular analysis of biomaterials. The technique applies static secondary ion mass spectrometry (SSIMS) techniques to samples prepared in a solid organic matrix similar to sample preparations used in matrix-assisted laser desorption/ionization (MALDI). Molecular ions are observed in this ion beam sputtering of organic mixtures for peptides and oligonucleotides up to masses on the order of 10?000 Da. This matrix-enhanced SIMS exhibits substantial increases in the ionization efficiency of selected analyte molecules compared to conventional SSIMS processes. Thus, higher mass peptides, proteins, and nucleic acids become accessible to near-surface analysis by ion beam techniques, and subpicomole sensitivity has been demonstrated. A number of matrices were examined for their efficiency in ME-SIMS applications, and these initial matrix studies focused on common MALDI matrices and their isomers. The results of this survey indicate that 2,5-dihydroxybenzoic acid provides the best general enhancement of molecular secondary ions emitted from analyte/matrix mixtures.     

Steel and nickel alloys at high temperatures: Part D of ‘The requirements for and limitations of materials at high temperatures’

The range of steels considered includes corrosion resistant ferritic and austenitic steels and low alloy, martensitic 12% Cr and austenitic steels for higher strength applications. Nickel superalloys are discussed under the gas turbine applications for which they were largely developed. Nickel alloys for corrosion resistant applications are discussed and a short section on the refractory materials Mo, Nb, Tn and W is included.     

A branch and bound algorithm for scheduling problem of a robot‐centered manufacturing cell

Abstract

An alternative formulation of the scheduling problem in a robot‐centered manufacturing cell has been described here, which was originally formulated by Lin et al. [7] as a mixed integer programming problem. An efficient procedure based on the branch and bound technique has been proposed. In order to reduce the complexity of the branching procedure, several sequencing rules [4] have been imbedded into the proposed procedure and an integrated algorithm has then been presented. The computational results have indicated the proposed algorithm to be efficient. Finally, conclusions and some suggestions are given.     

Consolidation of Al2O3–GdAlo3 eutectic powder prepared from induction-melted solid and strength at high temperatures

A eutectic powder of Al₂0₃–GdA10₃ was melted using a Mo crucible by induction heating. The melt was slowly solidified, resulting in a eutectic solid with coarse Al₂0₃ and GdAl0₃ phases. The eutectic solid was ground and sieved into 3–44 µm and 64–124 µm particles. The powders were consolidated to produce a eutectic composite by spark plasma sintering. Mechanical properties of the consolidated eutectic composite were measured at room temperature. High temperature strength was obtained at temperatures up to 1673 K. Superplastic deformation of the eutectic composite was not observed on stress–strain curves at 1673 K, but did occur in the case of a conventional composite at 1573 K.     

Consolidation of Al2O3–GdAlO3 eutectic powder prepared from induction-melted solid and strength at high temperatures

A eutectic powder of Al₂O₃–GdAlO₃ was melted using a Mo crucible by induction heating. The melt was slowly solidified, resulting in a eutectic solid with coarse Al₂O₃ and GdAlO₃ phases. The eutectic solid was ground and sieved into 3–44 μm and 64–124 μm particles. The powders were consolidated to produce a eutectic composite by spark plasma sintering. Mechanical properties of the consolidated eutectic composite were measured at room temperature. High temperature strength was obtained at temperatures up to 1673 K. Superplastic deformation of the eutectic composite was not observed on stress–strain curves at 1673 K, but did occur in the case of a conventional composite at 1573 K.     

The structure of shock and interphase layers for a heat conducting Maxwellian rate-type approach to solid–solid phase transitions

One continues the qualitative analysis started in Part I (F?ciu and Molinari in Acta Mech) concerning the thermomechanical characteristics of a steady, structured moving phase boundary in a shape memory alloy (SMA) by a quantitative investigation. The internal structure of these interphase layers is governed by a Maxwellian rate-type constitutive equation coupled or not with the Fourier heat conduction law. We consider as equilibrium stress–strain–temperature response function for the Maxwellian model an explicit piecewise linear thermoelastic relation for an SMA bar which can exist in the austenite phase A and in two variants of martensite M ^±. Its thermal properties are built in agreement with experimental results on NiTi. This equilibrium relation has the atypical property that not only the derivative of the stress response function with respect to the strain changes its sign, but also the derivative with respect to the temperature. Considerable temperature variation is generated by impact-induced phase transformations due to the large amount of latent heat released (absorbed) inside the transition layer. One gets strong heating (cooling) across a compressive A→ M ^? (expansive M ^? → A) propagating interphase layer. A significant lower (larger) temperature than that at the front and Hugoniot back state is obtained inside an impact-induced M ⁺→ M ^? (M ^?→ M ⁺) interphase layer. The experimental finding of this phenomenon of temperature undershoot (overshoot) could be a valuable indication for the existence of an interphase layer.     

The structure of shock and interphase layers for a heat conducting Maxwellian rate-type approach to solid–solid phase transitions

We consider a thermoelastic model for phase transforming materials which can adequately describe the evolution with respect to the temperature of the hysteresis loop both in compression and tension tests. The specificity of this model is that the Grüneisen coefficient changes its sign. The model is augmented by considering a dissipative mechanism governed by a Maxwellian rate-type constitutive equation that can describe stress relaxation phenomena toward equilibrium between phases. Existence and uniqueness of traveling wave solutions are investigated. One derives that the admissibility condition induced by the Maxwellian rate-type approach, coupled or not with Fourier heat conduction law is related to the chord criterion with respect to the Hugoniot locus. We investigate the structure of profile layers, and we focus on their thermodynamic properties. The influence of the exothermic or endothermic character of phase transitions on the inner structure of interphase layers is captured. A phenomenon of temperature overshoot/undershoot with respect to the front state temperature and Hugoniot back state temperature inside an interphase layer is revealed.     

Development and Characterization of Microcalorimeters for a Next Generation 187Re Beta-Decay Experiment

It has been demonstrated in the past that observing the β-decay spectrum of ¹⁸⁷Re with microbolometers provides a suitable method to determine the mass of the electron anti-neutrino from β-endpoint measurements. In a first step, with the experiment MIBETA a sensitivity of m _νe≤15 eV/c² was achieved. To compete with the sensitivity of m _νe≤2.2 eV/c² established by the Mainz/Troitsk tritium β-decay experiment and the limit of m _νe≤0.2 eV/c² aimed at with KATRIN, a new experiment MARE has been initiated. As a first stage (MARE-1), 300 detectors consisting of silicon implanted thermistors, produced by NASA/GSFC, and absorbers of AgReO₄ crystals will be mounted. To optimize the experimental setup, a test array was equipped with 10 AgReO₄ crystals of various size and shape. The influence of the crystal quality as well as of different types of resin on rise time and energy resolution was investigated.      

Exergy analysis and performance of a counter flow Ranque–Hilsch vortex tube having various nozzle numbers at different inlet pressures of oxygen and air

An experimental investigation is made to determine the effects of the orifice nozzle number and the inlet pressure on the heating and cooling performance of the counter flow Ranque–Hilsch vortex tube when air and oxygen used as a fluid. The orifices used at these experiments are made of the polyamide plastic material. The thermal conductivity of polyamide plastic material is 0.25 W/m °C. Five orifices with nozzle numbers of 2, 3, 4, 5 and 6 have been manufactured and used during the experiments. For each one of the orifices (nozzle numbers) when used with two different fluids, inlet pressures were adjusted from 150 kPa to 700 kPa with 50 kPa increments, and the exergy efficiency was determined. During the experiments, a vortex tube is used with an L/D ratio of 15, and cold mass fraction is held constant at 0.5. As a result of the experimental study, it is determined that the temperature gradient between the hot and cold fluid is decreased with increasing of the orifice nozzle number.     

In situ preparation of a SiC–TiB2 composite and its wear fracture mechanism at high temperatures

Journal of Materials Science - The unsatisfactory high-temperature performance of commonly used silicon carbide (SiC)-based ceramics calls for a novel approach for their reinforcement. We present...     

Ion–solid interactions at the extremes of electronic energy loss: Examples for amorphous semiconductors and embedded nanostructures

A selection of ion–solid interactions in the swift heavy-ion irradiation regime is reviewed. We consider the effects of electronic energy loss at tens of keV/nm on both bulk material and nanostructures embedded in a matrix. Specific examples include ion track formation at low ion fluences in bulk Si and Ge and porous layer formation at high ion fluences in bulk Ge. In addition, the intriguing shape and phase transformations observable at high ion fluences in Ge and metallic nanoparticles embedded in bulk SiO₂ are examined and compared. Experiment, modelling and simulation are combined synergistically as we seek fundamental atomistic insight into these unique yet poorly understood processes operative only at the extremes of electronic energy loss.     

Requirements for and factors affecting high temperature capability: Part A of ‘The Requirements for the Limitations of Materials at High Temperatures’

Examples where high temperature technology is important are given. Aspects such as melting temperature, crystal structure, deformation, creep and fatigue are covered. Environmental effects such as oxidation, corrosion, erosion and wear are also considered.     

Dynamics and ‘normal stress’ evaluation of dilute suspensions of periodically forced prolate spheroids in a quiescent Newtonian fluid at low Reynolds numbers

The problem of determining the force acting on a particle in a fluid where the motion of the fluid and the particle is given has been considered in some detail in the literature. In this work, we propose an example of a new class of problems where, the fluid is quiescent and the effect of an external periodic force on the motion of the particle is determined at low non-zero Reynolds numbers. We present an analysis of the dynamics of dilute suspensions of periodically forced prolate spheroids in a quiescent Newtonian fluid at low Reynolds numbers including the effects of both convective and unsteady inertia. The inclusion of both forms of inertia leads to a nonlinear integro — differential equation which is solved numerically for the velocity and displacement of the individual particle. We show that a ‘normal stress’ like parameter can be evaluated using standard techniques of Batchelor. Hence this system allows for an experimentally accessible measurable macroscopic parameter, analogous to the ‘normal stress’, which can be related to the dynamics of individual particles. We note that this ‘normal stress’ arises from the internal fluctuations induced by the periodic force. In addition, a preliminary analysis leading to a possible application of separating particles by shape is presented. We feel that our results show possibilities of being technologically important since the ‘normal stress’ depends strongly on the controllable parameters and our results may lead to insights in the development of active dampeners and smart fluids. Since we see complex behaviour even in this simple system, it is expected that the macroscopic behaviour of such suspensions may be much more complex in more complex flows.     

Burnett PVT Measurements of Hydrogen and the Development of a Virial Equation of State at Pressures up to 100 MPa

PVT properties were measured for hydrogen by the Burnett method in the temperature range from 353 K to 473 K and at pressures up to 100 MPa. In the present Burnett method, the pressure measurement was simplified by using an absolute pressure transducer instead of a differential pressure transducer, which is traditionally used. The experimental procedures become easier, but the absolute pressure transducer is set outside the constant temperature bath because of the difficulty of its use in the bath, and the data acquisition procedure is revised by taking into account the effects of the dead space in the absolute pressure transducer. The measurement uncertainties in temperature, pressure, and density are 20 mK, 28 kPa, and 0.07 % to 0.24 % (k = 2), respectively. Based on the present data and other experimental data at low temperatures, a virial equation of state (EOS) from 220 K to 473 K and up to 100 MPa was developed for hydrogen with uncertainties in density of 0.15 % (k = 2) at P ≤ 15 MPa, 0.20 % at 15 MPa < P ≤ 40 MPa, and 0.24 % at P > 40 MPa, and this EOS shows physically reasonable behavior of the second and third virial coefficients. Isochoric heat capacities were also calculated from the virial EOS and were compared with the latest EOS of hydrogen. The calculated isochoric heat capacities agree well with the latest EOS within 0.5 % above 300 K and up to 100 MPa, while at lower temperatures, as the pressure increases, the deviations become larger (up to 1.5 %).     

Dry Coupling Ultrasonic High Frequency (10–100 MHz) Sensors for Detection of Surface and Tribological Properties at a Submicrometric Scale

Acoustic plane sensors adequately pressed against materials are suitable to measure elastic constants from flight-time measurement, without any coupling fluid for high temperature, with longitudinal and transverse acoustic waves in the megacycle range. Soft delay lines are generally used to match the sample roughness and to make mechanical play correction easier. At the opposite, our sensors use a hard delay line with a mirror-polished end surface. An experimental set-up is presented to perform acoustic reflection measurement in various contact conditions by increasing the applied mechanical load. The frequency dependence of this parameter is also measured in the 10- to 100-MHz range. Reproducibility tests are presented to validate this experimental set-up, but the main results concern the surprising ability of this technique to detect surface property modifications limited to thickness less than 1 m. Indeed, surface modification induced by different solvents on glass substrates has been detected by this means. This technique has also been used to detect surface property modifications of lixiviated glasses. In this case, atomic force microscopy and inductively coupled plasma analyses have demonstrated that the earlier stage of the surface damage had been detected whereas the thickness altered by ionic diffusion was less than 100 nm with almost no roughness variation. Similarly, tests on mechanically scratched glasses have shown that samples with an average roughness, respectively, of 4 and 120 nm were easily identified from their reflection coefficient versus load curves. Moreover, the pressure dependence of the acoustic reflection is used to estimate the contact stiffness and the contact area between the sensor and the material as a function of the applied compressive stress for contact, adhesion, and friction investigations.     

Closed-form solution for process-induced stresses and deformation of a composite part cured on a solid tool: Part II – Curved geometries

In this study, closed-form expressions are developed that provide insight into the mechanisms that lead to the stress development in curved composite parts undergoing autoclave processing. Despite many assumptions that are made in the course of the analytical development, the closed-form predictions agree well with the more sophisticated finite element results. It is shown that stresses in a curved part develop mainly due to the thermo-chemical strain mismatch between the part and the tool in the tangential and radial directions. The unbalanced moment which causes the deformation due to the thermo-chemical strain mismatch in the tangential direction develops mostly at the early stages (heat-up) of the curing process when the part shear modulus is very low compared to its axial modulus. In contrast, the unbalanced moment due to the thermo-chemical strain mismatch in the radial direction develops mostly at the final stages (cool-down) of the cure cycle when the part shear modulus is relatively high.     

Optimization and performance experiments of a MnCl2/CaCl2–NH3 two-stage solid sorption freezing system for a refrigerated truck

Based on the earlier-established MnCl₂/CaCl₂–NH₃ two-stage solid sorption freezing system for a refrigerated truck, a series of optimization designs are conducted in this prototype system. For sorption beds consisting of many unit tubes, the arrangement mode is changed to the staggered arrangement. Off-the-shelf heat exchangers from refrigeration industries are chosen as the evaporator and the condenser, and an expansion valve is also used. The total mass of the optimized system is reduced to approximately 150 kg. Firstly, different refrigerating temperatures ranging from −25 °C to 0 °C are investigated, and experimental results show the optimized system can easily satisfy requirement even for transporting frozen goods. The earlier-established system can only satisfy requirement for transporting fresh goods. Simultaneously, the cycle time can be reduced to 45 min. Through the optimization, both the refrigerating capacity and the total mass of the system can satisfy requirement of this refrigerated truck.     

Optical properties of amorphous (GeS)1 − x Bi x (0 ≤ x ≤ 0.15) films and a tentative cluster model for their structure

This paper examines the effect of Bi doping on the optical properties of amorphous (GeS)_{1 ? x} Bi _x (0 ≤ x ≤ 0.15) films. Experimental data in conjunction with first-principles electronic structure calculations for Ge _n S _m and Bi _n S _m clusters are used to derive a cluster model for the structure of the amorphous (GeS)_{1 ? x} Bi _x films.     

Optically Induced Measurement of Electron and Hole Drift Velocities in a Germanium 〈100〉 CDMS Detector at 50 mK

We report on precise drift velocity measurements of electrons and holes in 50 mK, ultrapure (≈10¹⁰ net shallow impurities per?cm³) germanium 〈100〉 CDMS dark matter detectors as a function of electric field up to 4?V/cm. A laser diode connected to an optical fiber extending from room-temperature to the detector creates electron-hole pairs on one surface of the crystal. High-speed electronics measure the drift current as the generated carriers travel to the opposite face of the crystal. CDMS detectors measure the ionization and phonon response of particle interactions within the crystal. Stable charge collection is necessary for successful background discrimination when looking for a possible dark matter signal. While biased, however, ionization performance degrades over time due to the build-up of space charge. Free electrons and holes created by particle interactions are subject to drift-diffusion dynamics occurring simultaneously with the trapping of carriers to localized surface and bulk states. The combination of these processes determine the evolution of space charge within the crystal, making it important that we understand carrier transport under our unique operating condition of low-temperature and low-field. We find good agreement between our measured drift velocities and our theoretical predictions, indicating carrier scattering is dominated by spontaneous phonon emission. In addition, we present preliminary measurements of effective longitudinal carrier trapping lengths for both n-type and p-type crystals at 50?mK.