A bibliometric study of differential item functioning

Summary This study presents a bibliometric analysis of scientific output in the area of Differential Item Functioning (DIF), the aim being to offer an overview of research activity in this field and characterise its most important aspects and their evolution over the last quarter of the 20th century, thus providing data regarding the basis on which this activity is being developed at the beginning of the 21st century. The analysis makes use of the Web of Science database, the search being restricted to articles published between 1975 and 2000 and which contain the terms differential item functioning, DIF or item bias. The various analyses focus on the presentation of publication frequencies and percentages, as well as on the application of Bradfords law of scattering and Lotkas law.     

Measuring national output in physics: Delimitation problems

In a study of the Dutch publication output in physics we tested methods of delimitating fields by journal categories in theScience Citation Index (SCI) compared to the classification of individual publications into subfields in the subject specific databasePhysics Briefs (PHYS). Different methods of measuring national scientific output were compared as well. In this paper we report the main findings on these issues, based on a study of six selected subfields in physics. The main conclusion with respect to the use of different classification methods is that in most of the selected fields in physics the method which delimitates fields by journal categories yields an incomplete picture of the output of a country. Particularly because this method neglects a considerable number of articles published in general journals. With respect to different methods of counting publications it was corroborated by the Dutch data inPhysics Briefs that: 1. so-called integer counted world shares are very much influenced by the degree of internationalisation and 2. first author counting gives a satisfactory approximation of fractional counting. Citation indicators based on first author counting, however, may be distorted in fields with a large fraction of international co-authored publications.     

Industrial research in India as viewed throughResearch & Industry

The paper examines the bibliometric characteristics of industrial research activity of India. The study reveals that public-funded R&D is the major contributor of research papers, inResearch & Industry while the contribution of in-house R&D centres is lacking. Among the two industrial sectors (Chemical and Engineering), much of the R&D activity, as reflected by published papers, has been in chemical and allied industries. However, there appears to be a significant change in emphasis during the decade studied, namely a decrease in R&D activity in engineering industries with a corresponding increase in miscellaneous industries. There is a significant increase in exploratory research. R&D and industry interface is found inadequate. Multiplicity of authorship is gradually increasing. Indian Industrial research is heavily dependent on foreign and non-patent literature.     

Systematic derivation of contour integration formulae for laplace and elastostatic gradient BIE's

A complete set of contour integrands is derived for the primary BIE's of elastostatics and potential flow. Because of surface-independent properties of vector potentials, these apply to nonplanar surfaces and can be differentiated at the fixed point, producing contour integrands for both the so-called hypersingular and Cauchy singular parts of the gradient BIE. The results are applicable to far field, near field and on surface cases. Numerical examples demonstrate exact agreement with surface quadrature, and contour plots are given showing variation of the hypersingular integrands in on surface cases.     

Cutting, by ‘pressing and slicing,’ of thin floppy slices of materials illustrated by experiments on cheddar cheese and salami

Why it is easier to cut with even the sharpest knife when pressing down and sliding than when merely pressing down alone is explained. A variety of cases of cutting where the blade and workpiece have different relative motions is analysed and it is shown that the greater the slice/push ratio given by (blade speed parallel to the cutting edge/blade speed perpendicular to the cutting edge), the lower the cutting forces. However, friction limits the reductions attainable at the highest . The analysis is applied to the geometry of a wheel cutting device (delicatessan slicer) and experiments with a cheddar cheese and a salami using such an instrumented device confirm the general predictions.     

A frequency distribution function derived from a stochastic model considering human behaviors and its comparison with an empirical bibliometric distribution

Simon's stochastic model is extended to take both selective and random factors in human behaviors into consideration. The resulting distribution function is of non-steadystate type and approaches the Poisson distribution at the random limit while the Yule (or Zipf) distribution at the selective limit. A comparison of the theoretical distribution with an observed one for classification items indexed in a bibliorgraphic database is made. The results give some insights into statistical features of a class in which the total number of elements is fixed.     

Mapping co-word structures: A comparison of multidimensional scaling and leximappe

The LEXIMAPPE method and Multidimensional Scaling (MDS) are discussed as methods to visualize (map) characteristics of structures of word-occurrence (co-word) relations. Utilization of MDS is proposed as an alternative mapping method able to circumvent problematic features of LEXIMAPPE maps of the total co-word structure. A comparison of both methods on the same real-life co-word matrix demonstrates topological advantages of an extended MDS-mapping.     

Temperature dependence of surface impedance Z(T, ω) and mean free paths I(T) of YBCO-superconductors

The surface impedance Z(T,) at 10 and 145 GHz and between 4 and 300 K is obtained experimentally. Z(T_aTT_c) is quantitatively fitted by the BCS theory with a mean free path I(T) increasing rapidely below T_c. This I-increase in the frame of the BCS-theory is limited at T_a by inelastic surface scattering at weak or strong links, e.g., by twin boundaries in distances a_TW which dominates scattering for a_Tw2I(T_a). Below T_a the enforced energy transfer from YBCO-crystallites to weak links may enhance Z(Ta) until at T T* the weak link surface impedance dominates Z_res(T相似文献   

Two Outfalls in an Estuary: Cooperative Pollution Minimization

Two outfalls, each with given tidally averaged discharge rates, are discharging into the same narrow (rapidly mixed) estuary. The lowest achievable concentration peak (in position and time) for the principal contaminant species is attained with an all or nothing discharging policy. The discharge rate is either all that is allowed by concentration peak or is nothing. The nothing regime corresponds to the water from the less vulnerable outfall with the relatively small discharge load, which would otherwise have had the greatest pollution impact at the more vulnerable outfall. Constructive (exact) algorithms are presented for the all or nothing partition and for the cooperative discharge rates at the two outfalls.     

A note on the utility of international publication data

This note focuses on a possible limitation of international publication data as a measure of research activity. It is argued that differences in the pressure and/or capacity to publish may exist between countries which would necessitate the standardization of publication data on a country basis. The argument is supported by statistical tests performed on data recently utilized to measure agricultural scientific research activity.     

Information behaviour in a scientific-technical environment: A survey with innovation engineers

A small written survey with innovation engineers in a large company is discussed, giving some figures on both behaviour and attitudes with respect to 1) information gathering, 2) information production/dissemination and 3) information storage and management. Most results confirm the trends in other research with R & D engineers: the use and management of information is rather improvised with low levels of sophistication. High tech information techniques (databases, online...) are only marginally important in this high-tech environment. Only younger engineers do some structured efforts. The general attitude is to rely mostly on oral, personal and occasional information sources. By combining positive attitudes and behaviour aspects towards information in the job, a measure of information-orientation was constructed, which can be seen as an extension of the classical concept of gate-keepers in a company. A few questions to reconstruct a critical incident with respect to information problems reveal that information situations can be very time- and money-consuming but again solutions depend on occasional and unstructured information work. However the restricted written approach did not prove to be a good one for this kind of analysis. More in-depth interview-techniques will be necessary for analysis within the critical incident theory-frame.This article is compiled from the full report (in Dutch): Informatiegedrag bij innovators, published as a major project these for the postgraduate in Documentation and Library Science of the Antwerp University by A.D'Espallier (Wilrijk (Belgium), September, 1989); the survey's supervising and technical aspects were conducted by the author.     

On the equivalence of integral formulations for certain exterior and interior boundary value problems in mechanics

A procedure is given which relates various linear boundary value problems. It is shown that a relations exists between certain exterior and interior problems. For computational purposes an interior problem is more desirable. The method is restricted by the requirement that the Neumann function, or its equivalent, be known for the problem being considered.Dedicated to Professor Menahem M. Schiffer, with reverence and gratitude     

On postulates of plasticity in classical elastoplasticity

Summary. It is commonly known that Druckers postulate of plasticity in stress space is applicable to hardening materials only, but not to softening materials, and, on the other hand, that Ilyushins postulate of plasticity in strain space is applicable to both softening and hardening materials. Accordingly, it is usually thought that the latter would be less restrictive and hence more general than the former. In this work, we introduce the notions of standard elastoplastic stress and strain cycles, each starting at a point inside the yield surface and incorporating only one infinitesimal plastic strain increment. We show that these standard cycles always exist for a yield function depending continuously on stress and plastic strain history. By means of these standard cycles, we propose respective weakened forms of Druckers and Ilyushins postulates. These two weakened forms are less restrictive in two respects. One is that, unlike Druckers and Ilyushins postulates, they are not concerned with stress and strain cycles starting at points on the yield surface. The second is that they are formulated in terms of the rates of change of the net stress work and the stress work when the plastic strain increment incorporated tends to vanish. We demonstrate that either of the proposed weakened forms is adequate to result in the normality rule for the plastic strain rate and the convexity of the yield surface, as does either Druckers or Ilyushins postulate. These suggest that, in a less restrictive sense and hence in a broader scope, the two proposed weakened forms not only apply to both hardening and softening materials, but also ensure the same consequences.     

Problems of Heat Conduction for an Angular Region with an Internal Source

Exact solutions of nonstationary problems of heat conduction have been obtained for an unbounded rectangular region when the opening angle is equal to /(2n + 1), where n is any natural number. By passage to the limit it has been shown that no stationary regime is possible for the rectangular region in the case of action of a constant internal source. The exact solution of the stationary problem for an angular region with an arbitrary opening angle ₀ has been given. It has been proved that in the presence of a constant heat source the stationary regime is possible just for the acute angle ₀ /2, while for the right or obtuse angles ₀ /2 the stationary regime is impossible, since the temperature increases without bound at internal points.     

Measurement and prediction of Young’s modulus of a Pb-free solder

Accurate and reproducible measurements of the Youngs modulus of solders are complicated by the early onset of yielding, microporosity, and variations in cooling rate. In this study, we report measurements of Youngs modulus of an Sn–3.5 wt % Ag solder by two techniques: (a) loading–unloading measurements in tension, and (b) non-destructive resonant ultrasound spectroscopy. Both techniques yielded similar values of Youngs modulus. The modulus decreased with increasing microporosity, in accordance with predicted values. Cooling rate affected the Ag₃Sn intermetallic morphology, but not Youngs modulus since the distribution of the particles was relatively random. This result was confirmed by microstructure-based finite element modeling.     

Follow-up angle-to-digital converter with self-adjusting two-phase angle sensor

We consider a slave angle-to-digital amplitude converter structure in which the initial conversion accuracy that decreases with use is adjusted automatically.Translated from Izmeritelnaya Tekhnika, No. 11, pp. 25–27, November, 2004.     

Modelling of dimensional changes during polymer-ceramic conversion for bulk component fabrication

Shrinkage and porosity generation during conversion of polymer-filler systems into ceramic bodies during pyrolysis is examined. In the presence of an inert filler phase such as Si₃N₄ or SiC powder dispersed in an organosilicon polymeric matrix only porous microstructures may be obtained without any shrinkage. By using an active filler phase such as carbide- or nitride-forming transition metals, however, shrinkage of the polymer matrix may be compensated by appropriate expansion of the filler phase. A model is derived to predict the critical volume fractions of various potential active filler systems in inert and reactive gas atmospheres, which can be effective in controlling shrinkage and porosity during the fabrication of ceramic components from polymer-derived precursor materials.Nomenclature P Polymer phase - C Condensed polymer pyrolysis product (ceramic) - G Gaseous polymer decomposition product - F Inert filler phase - T Active filler phase (e.g. transition metal) - M Reaction product of active filler phase (e.g. carbide, nitride) - m Mass - V Volume fraction - V _F,T ^max Maximum packing density of an inert (F) or active (T) filler powder - V _F,t ^* Critical volume fraction of an inert (F) or active (T) filler powder in the starting polymer-filler mixture - V _v Residual porosity in the polymer pyrolysis product - V _v ^pf Residual porosity in the polymer-inert filler system after pyrolysis - Ceramic yield of polymer after pyrolysis - Weight change of active filler phase during reaction pyrolysis - Density ratio of polymer to polymer pyrolysis (ceramic) product - Density ratio of active filler to filler reaction product - ^P Linear shrinkage of the polymer phase during pyrolysis - ^pf Linear shrinkage of a polymer-inert filler system during pyrolysis - ^paf Linear shrinkage of a polymer-active filler system during reaction pyrolysis - Linear shrinkage/expansion of the filler phase during reaction - Density     

Cohesive crack models for semi-brittle materials derived from localization of damage coupled to plasticity

Based on discontinuous displacement approximation of the continuum and shear band kinematics, two cohesive crack models are derived within the constitutive framework of coupled damage and plasticity. The models employ the Rankine fracture criterion, and the model parameters are determined from a uniaxial tension test (mode I cracking). Bifurcation analysis is used in order to diagnose critical directions along which the crack will gradually develop and propagate. These directions depend on the actual stress state and are kept fixed after fracture has initiated, whereby a fixed crack model is obtained. A discrete crack strategy is employed at the finite element implementation in the sense that interfaces (that represent the cohesive crack) are introduced along inter-element boundaries. This implementation strategy calls for gradual realignment of the mesh as a key feature of the algorithm. Numerical results from the analysis of mixed mode fracture in a notched concrete plate are presented.     

Response to the discussion by I.V. Rokach of the paper entitled: “Analysis of the dynamic responses for a pre-cracked three-point bend specimen”

The following response to the discussion of the above mentioned paper is divided into two parts: (1) a response to the issue of our comparison of the apparent period of specimen oscillation, , and the natural vibration period of a cracked specimen, T, and (2) a verification of the applicability of our model to short time-to-fracture tests, which Rokach has questioned, due to a lack of knowledge of Hopkinson bar techniques.     

The structure and superconducting behavior of some V-Al binary alloys and of ternary ‘β-W’ alloys based on the V-Al system

Results are given for the structure and superconducting behavior of binary V-Al alloys and of -W ternary alloys based on V₃X-V₃Al where X=Si, Ge, Sn, Ga, and Sb. No -W phase was observed in the binary V-Al system at 25 at. % Al. Instead the alloys were bcc. However, some evidence was found for a martensitic transformation in alloys rapidly quenched from high temperatures. Solid solubility of Al in the -W phase V₃X was restricted as would be expected from the absence of a binary -W V₃Al phase. The superconducting transition temperatures varied systematically with composition in a manner consistent with the phase structure of the alloys.