Granulation of Lactose in a Recording High-Speed Mixer, Diosna P25

When the conditions involved in the granulation process — inter alia liquid flow rate, atomization conditions, impeller and chopper speed, and amount of powder — were fixed, it was possible to determine the end-point of the graulation of lactose with a gelatin solution on the basis of rotation-rate changes affecting the main impeller shaft.     

Economic Comparison of NdFeB and Hard Ferrites in Automotive Applications

With the increasing use of electric motors in automobiles—in some cases as many as 100 electric motors per vehicle—alternatives to ferrite magnetic materials are under consideration. If more powerful magnetic materials could be implemented, size reductions in these motors could result in curb weight reductions that lead to improved fuel economy. NdFeB magnets are attractive as potential replacement materials, due to their higher flux density and thus smaller required size; however, high material costs have limited their implementation. To investigate the economic competitiveness of alternative magnetic materials, technical cost models (TCMs) were developed and used to examine the manufacturing economics related to the production of both NdFeB and ferrite magnets. Results from the TCMs are used to identify the cost drivers and opportunities for cost reductions. Subsequent investigations will include effects on vehicle fuel efficiency, and the environmental impact of magnet manufacture and disposal.     

The chemistry of micrometeoroid and space debris remnants captured on hubble space telescope solar cells

Prior to the retrieval in 1993 from low Earth orbit (LEO), the “—V2” Solar Array wing of the Hubble Space Telescope was exposed to hypervelocity impacts (micrometre to millimetre scale) from both micrometeoroids and space debris. The initial survey of the damage (100–3500μm diameter sized craters) identified that micrometeoroid remnants dominated the flux in the 100–1000μm size regime, with debris dominating>1000μm. These residues were composed of remnants of silicate minerals, calcite, metal sulfides and metals that often appeared as complex poly-mineralic melts within melt pits. A further survey of 10–100μm diameter craters identified that the most common chemistry was space debris with the crossover from meteoroids to debris being at around 30μm D_CO. Residues include remnants of specialised steels and paint fragments but the dominant type is aluminium and aluminium oxide, which are almost certainly remnants of solid rocket motor operations. It is found that the relative contribution of debris as a function of size, agrees remarkably with a prediction derived using flux data from Long Duration Exposure Facility and a meteoroid model.     

Effects of microstructural variables on the deformation behaviour of dual-phase steel

An expression for the stress of martensite in dual-phase steel was developed, which shows the interdependence of the stress of martensite and strain hardening in the ferrite matrix and the contribution of microstructural variables (the volume fraction of martensite f_m, ferrite grain size d_f, and martensite particle size d_m). The onset of plastic deformation of martensite in dual-phase steel was predicted to depend on its yield strength and the microstructural variables, and this was verified by the modified Crussard-Jaoul analysis. It was found that for this dual-phase steel, refining the grain size and increasing f_m increase the flow stress and raise the strain hardening rate at low strains, but little affect the strain hardening rate at high strains. The effect of the ferrite grain size on the flow stress of this dual-phase steel was found to obey the Hall-Petch relation, i.e. σ = σ₀^e + K^ed_f^−1/2, where the Hall-Petch intersection σ₀^e and slope K^e are functions of strain, f_m and d_m. The effects of the plastic deformation of martensite and the microstructural variables on the strain hardening rate and the Hall-Petch behaviour were analysed in terms of the densities of statistically stored dislocations and geometrically necessary dislocations using the previously developed theoretical model.     

A fatigue crack propagation model for strain hardening materials

In this paper a crack propagation model based on Tomkins concept (dl/dN ∝ Δε_p · ω) has been developed using the theoretically developed cyclic plastic zone sizes. The crack propagation rates are found to be functions of stress intensity factor, Elber's effective stress range ratio, cyclic yield strength of material, crack length, specimen width and cyclic strain hardening exponent. Suitably grouped to give the crack growth rate in terms of five constants termed as Loading Constant, Material constant, Crack size constant, specimen Width Constant and Stress Intensity Exponent. The crack growth rates found by theory are compared with the experimental results available in literature and a good agreement is found.     

Development of ultrafine microstructures and superplasticity in Hadfield manganese steels

Ultrafine grains were developed in Hadfield manganese steels through appropriate thermomechanical processing. The steels contained from 1.2 to 1.7 wt.% C and 12.3–16.3 wt.% Mn. The austenite grains. 2–8 μm in size, were stabilized against grain growth by a dispersion of fine carbides, typically less than 1 μm. The processed materials were evaluated for superplastic properties at elevated temperatures (750–900 °C). Values for the strain rate sensitivity exponent m in the expression ranged from 0.37 to 0.65. The value of m in the superplastic regime was found to depend on composition, grain size and temperature. At 23 °C, the fine-grain steels showed higher yield strengths and hardness values, but lower ductility, relative to values reported for commercially processed materials.     

Rate sensitivity of mechanical properties and fracture characteristics of two-phase titanium alloys subjected to thermal cycles of diffusion welding

The effect of strain rate on mechanical properties and fracture characteristics of two dual-phase titanium alloys was studied using standard test equipment. The alloys had been subjected to various thermal cycles, simulating diffusion welding.

It is shown that diffusion welding is possible within the alloys β phase region without serious loss of service characteristics provided service temperature and rate of stress application are accounted for. A service temperature (which also depends on loading rate) of between 60 and 100°C is suggested for titanium articles — commensurable in size with that studied — to be diffusion welded in the β region.     

Transient response of plates to travelling loads with application to slamming damage

There is a considerable range of slamming loads on hull plating which cause either elastic response or elastic-plastic response where the plastic deformation is of the same order as the elastic deformation. Failure criteria for plate design can likely be from pulses causing this range of deformation.

This paper summarizes the author's Master's thesis which gives a detailed analysis of the elastic response of hull plating to slamming pulses. A finite difference model of a plate strip is developed which accounts for membrane effects. The analysis shows detailed stress and deflection response to various pulses. The results of the elastic analysis give the combinations of typical pulses of 207–1380 K Pa peak pressures and decay times of 0.001–0.5 s leading to, but not exceeding, incipient yield at 276 and 414 MPa (40 000 and 60 000 psi) in various plate sizes.

The plate strip concept is then extended to the elastic-plastic range. The model is made of two rigid sections with deformable hinges at the center and ends. These hinges are comprised of layers of bar elements with elastic—plastic characteristics. The results of this analysis give the permanent deflections from pulses of two—six times those which cause incipient yield. Unexpected resonances of 5–30% occur in the elastic—plastic range, not noted in the elastic range.

While the slamming load is a pressure wave which propagates across a plate at some finite velocity, it is common in the analysis of hull plate slamming response to assume a spatially constant load. This paper gives justification for the approximation by analyzing the response to a travelling pressure front and specifies the criterion for which the approximation remains valid.     

Improvement on the light yield of a high-Z inorganic scintillator GSO(Ce)

Cerium-doped gadolinium silicic dioxide crystal, GSO(Ce), is a high-Z non-hydroscopic scintillator that gives higher light yield than BGO, and can potentially replace NaI(Tl), CsI(Tl) and BGO in many applications. Its production cost, however, has been substantially higher than any of them, while its energy resolution has been worse than that of NaI(Tl) or CsI(Tl). The merit did not overcome these deficiencies except in limited applications.

We developed a low background phoswich counter (the well-type phoswich counter) for the Hard X-ray Detector of the Astro-E project based on GSO scintillator. In the developmental work, we have succeeded in improving the light yield of GSO(Ce) by 40–50%. For energies above 500 keV, a large GSO(Ce) crystal (4.5 cm×4.5φ cm) now gives energy resolution comparable to or better than the best NaI(Tl) when read out with a phototube. With a small GSO(Ce) crystal (5×5×5 mm³) and a photodiode, an energy resolution comparable to or better than the best CsI(Tl) has been obtained. With this improved performance, we find that the much higher photopeak efficiency and the shorter scintillation decay time of GSO(Ce) offsets its higher cost for many applications.

We summarize our past developmental work to decrease radioactive contamination and to increase light yield of GSO(Ce) for astronomical hard X-ray detection. Included also are measurements done after the unsuccessful launch of the Astro-E mission. The work is still continuing for the remake version of Astro-E Hard X-ray Detector.     

Sensitivity of Optimum Workforce Size to Employee Absenteeism in Stochastic Workload Situations

This paper presents the results of a simulation model developed to explore the relationship between unit cost and a number of primary production variables for a large warehouse operation of a major national retailer. The output of the simulation model includes a plot of total cost per completed unit for each combination of workforce size. Results indicate that under the conditions studied the total cost per completed unit is not particularly sensitive to workforce size and absenteeism patterns, and therefore insensitive to traditional managerial measures (such as over-staffing) to reduce these unit costs. This result is counter-intuitive and leads to the conclusion that the “fine turning” of staff levels as currently being attempted is perhaps not necessary.     

HPGe detectors for low-temperature nuclear orientation

Using the Low-Temperature Nuclear Orientation (LTNO) technique one can study various interesting properties of atomic nuclei and nuclear decay which can be deduced from the measurements of the angular distributions of charged particles emitted during the decay. However, the use of particle detectors working in conditions of LTNO devices (which are generally not available commercially) is a necessary precondition for the realization of these experiments.

Planar HPGe detectors for detection of charged particles at “liquid helium” temperatures were developed and produced at NPI e . Relatively simple technology using vacuum evaporation and diffusion was employed. The performance of detectors at low temperatures was tested and their characteristics measured in a testing cryostat before using them in real experiments.

The HPGe detectors were extensively used in a whole range of LTNO experiments with various physical objectives — in offline (IKS Leuven) as well as online (CERN-ISOLDE, Louvain-la-Neuve — LISOL) experiments. In frame of the project “Meson-Exchange Enhancement of First-Forbidden Beta Transitions in the Lead Region”, the measurements of angular distribution of emitted β-particles allowed to determine experimentally the “meson-exchange currents” contribution to the β-decay. In the project “Isospin Mixing in NZ nuclei”, the isospin-forbidden β-transitions of the nuclei in region (A=50–100) were studied in order to obtain information on the isospin structure of the nuclear states. A new project looking for the possible presence of the tensor currents contribution to the β-decay is being prepared for the CERN-ISOLDE facility.     

Variational stability of infinite-dimensional optimal control problems

In this paper we examine the variational stability of infinite-dimensional optimal control problems governed by nonlinear evolution equations. Our tools are the Kuratowski—Mosco convergence of sets and the corresponding τ-convergence of functions. We prove the τ-convergence of cost functional and the convergence of the values of the problems, and we examine the variational stability of the solution and reachable sets. These results are then applied to a sequence of nonlinear parabolic distributed-parameter optimal control problems     

Some effects of yield strength on the stress corrosion cracking behaviour of low alloy steels in aqueous environments at ambient temperatures

The present paper describes the results of a literature review on the effects of material yield strength on the threshold stress corrosion cracking (SCC) condition known as K_1SCC, of a series of low alloy steels in various aqueous environments at ambient temperatures. It has been shown that an increase in yield strength reduced the value of K_1SCC and that this effect was more significant over the lower yield strength range 600–1200 MPa; at higher yield strength levels the effects of yield strength were much less evident. A review of the results indicated that SCC transgranular fracture was seen at yield strength values below around 1200 MPa while above this value the fracture path was exclusively intergranular in nature. Note that the transition point between transgranular and intergranular SCC coincided with the point at which yield strength effects were much reduced. A series of models reported in the literature, which attempted to explain the effects of yield strength on K_1SCC in terms of a fracture mechanics framework were examined with the introduction of a critical distance concept. Finally, the predictions of a grain size effect on the point at which the fracture path changed from transgranular to intergranular were taken from one model and used to show that the large data scatter in the region where transgranular fracture was operative, viz., the lower yield strength region of 600–1200 MPa, could be the result of grain size variations between the different reported studies.     

A Relational Approach to Organization Design

The paper criticizes the currently dominant view of organization forms as “discrete alternatives” and “coherent” set attributes, and proposes a more refined and micro-analytic view of organization forms as particular combinations of coordination mechanisms and rights allocations. This view is relevant for understanding and devising “new” forms and proposing solutions for governing the composite and fast changing systems of today. The view is “relational” as it offers a procedure for devising “superior” configurations as combinations—relations between organizational components—in a quasi-continuous space of possibilities. The approach is sustained by the quantitative methods of network analysis as applied to relations among firm's resources and activities. Theoretically, the approach revisits organization design, integrating classic organization theory tenets with the new inputs provided by organizational economics. Substantively, it is argued that a mix of much differentiated coordination mechanisms is usually superior to the codified, “packaged”, allegedly “coherent”, forms of organization. The procedure presented in the paper is applied to a field experiment in a medium size firm.1     

Scalability of a Hybrid Extended Compact Genetic Algorithm for Ground State Optimization of Clusters

We analyze the utility and scalability of extended compact genetic algorithm (eCGA)—a genetic algorithm (GA) that automatically and adaptively mines the regularities of the fitness landscape using machine learning methods and information theoretic measures—for ground state optimization of clusters. In order to reduce the computational time requirements while retaining the high reliability of predicting near-optimal structures, we employ two efficiency-enhancement techniques: (1) hybridizing eCGA with a local search method, and (2) seeding the initial population with lowest energy structures of a smaller cluster. The proposed method is exemplified by optimizing silicon clusters with 4-20 atoms. The results indicate that the population size required to obtain near-optimal solutions with 98% probability scales sub linearly (as Θ(n^0.83)) with the cluster size. The total number of function evaluations (cluster energy calculations) scales sub-cubically (as Θ(n^2.45)), which is a significant improvement over exponential scaling of poorly designed evolutionary algorithms.     

An Application of Facilities Location Theory to the Design of Forest Harvesting Areas

The problem of designing forest harvesting units and assigning logging equipment to those units can be formulated as a facilities location problem which exhibits a unique structure that has not previously appeared in the literature. This structure is referred to here as a “cascading fixed charge” structure; for small problems, exact solutions can be obtained by means of 0-1 integer programming systems. Problems of practical size for use in forest planning, however, would involve thousands of 0-1 variables and constraints. Such problems are intractable for presently available integer programming codes. This paper presents an approximation algorithm which has been developed to solve facilities location problems exhibiting the special cascading fixed charge structure. Experience with an application of the algorithm to an actual forest planning area is cited.     

A comparison of different methods to determine the threshold of fatigue crack propagation

Three different methods for determining the threshold value for fatigue crack growth — the load-shedding technique, the stepwise increase of load amplitude on specimens precracked in cyclic compression, and decrease of stress intensity range at a constant maximum stress intensity — were applied to a high-strength aluminium alloy. The load-shedding technique tended to lead to higher values of the threshold, especially at low R-ratios. The threshold determined with decreasing stress intensity range at a constant maximum stress intensity was larger than the effective threshold determined with stepwise increasing of load amplitude on specimens precracked in cyclic compression.     

Bending behavior of mortar reinforced with steel meshes and polymeric fibers

The main purpose of this research was to study the effects of combining reinforcing steel meshes with discontinuous fibers as reinforcement in thin walled Portland cement based mortar beams. The term ‘thin’ implies thicknesses of less than about 25 mm. The underlying idea behind this combination is to satisfy the ultimate strength limit state through the steel mesh reinforcement (main reinforcement) and to control cracking under service loads through fiber reinforcement (secondary reinforcement).

An extensive experimental program with bending tests was undertaken. Specimens were 127 × 457 × 12.7 mm. The following variables were investigated: (a) the reference mesh size — 25.4 × 25.4 mm and 50.8 × 50.8 mm; (b) the transverse wire spacing — 25.4 mm, 50.8 mm, and no transverse wires; (c) the type of fibers — polyvinylalcohol (PVA) and polypropylene (PP); and (d) the fiber volume fraction — 1 and 2% for PVA fibers, and 0.5 and 1% for PP fibers.

Some of the main conclusions are: (a) for the same fiber volume fraction, the use of PVA fibers led to a better overall performance than that of PP fibers; (b) an increase in cracking moment and a decrease in crack spacing was observed when 1% PVA, 2% PVA, and 1% PP fibers were used; (c) when 0.5% PP fiber was used, no noticeable change in behavior was observed in comparison to specimens without fibers; and (d) for 1% PVA fibers the transverse wire spacing had little effect on the crack spacing and for 2% PVA fibers, the transverse wire had no influence.     

Distorted yield surfaces – modelling by higher order anisotropic hardening tensors

Most of the constitutive models for metallic materials assume yield functions of von Mises or generalized Tsai–Wu type. Isotropic and/or kinematic evolutions are developed for hardening, which correspond to affin expansions or simple shifting of original yield surfaces, whereas experimental results show a distinctive change of the shape of yield surfaces (rotated or dented) depending on loading conditions and load paths. To cover the material behaviour with distorted yield surfaces a hierarchical expansion of yield functions to hardening tensors of the fourth and the sixth order is proposed. Parameters of corresponding evolutionary equations are determined by model parameter optimization. The extended model is investigated comparing numerical results to cyclic experimental data in biaxial σ–τ space.     

Size of Administrative Units—Some Criteria and Decision Rules

This study determined an optimum size range for the basic organizational unit—the Ranger District—in the U. S. Forest Service. Organization size for the Ranger District was defined as a weighted numerical composite of three variables describing various aspects of organizational complexity. The study attempted to make organizational effectiveness the criterion for size determination where organizational effectiveness was evaluated by means of objective and subjective measures. This, and a simulation study of operating cost changes associated with changes of size, yielded a decision rule for determining an optimum size range.