The influence of random removal of sources and items on the h-index

If we have two information production processes with the same h-index, random removal of items causes one system to have a higher h-index than the other system while random removal of sources causes the opposite effect. In a Lotkaian framework we prove formulae for the h-index in case of random removal of items and in case of random removal of sources. In conclusion, we warn for the use of the h-index in case of incomplete data sets.     

Carbon particle phase stability as a function of size

The stability of particulate carbon formed in the detonation of high explosives has been investigated with first-principles and semiempirical molecular orbital calculations carried out on atomic clusters designed to represent the graphite and diamond phases. In order to compare the accuracy of different computational approximations, the dangling bonds were first capped with hydrogen atoms to maintain the sp2 or sp3 hybridization at the surface and then the surface contributions were removed by extrapolating the cohesive energies as a function of the cluster size. Calculations were also carried out on geometry optimized carbon clusters without capping atoms, resulting in reconstructed surfaces that may be a more realistic model for carbon formed under the extreme conditions of detonation. Comparison of the calculated heat of formation of graphite and diamond particles as a function of size predicts that the graphite phase becomes more stable for 104–105 carbon atoms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Publication rate as a function of the laboratory/group size

In view of conflict with the conclusions of several earlier studies, a fresh analysis has been made ofCohen's data on publication-rate for various lab. group sizes in the National Cancer Institute (USA) and the National Institute of Medical Research (U.K.) for 1976–77. The present analysis is based on subdividing the data into successive ranges of lab. group size, 1–3, 4–6, 7–9 ... and calculating the relevant publication rate person (R) for each range.When plotted, this yields graphs with aninitial linear rise of per-capita publication rate, R, followed by well-marked maxima of publication rates (maxima/minima 1.6) at group size of 6,16, and 27±2 persons, which are confirmed through analyses with ranges of two different group sizes. The group size at the peaks presumably correspond to optimum efficiency, in general agreement with the findings of the present author on samples from various countries published several years ago. Our conclusions fall somewhere between the findings ofCohen (publication rate independent of size) and those ofWallmark et al. (research efficiency increases exponentially with size).     

Detachment frequency as a function of size for vapor bubbles

It is assumed that the bubble detachment frequency for the heater surface is determined by the oscillation frequency of the particles in the surrounding liquid. A relation is drawn up between the frequency and the detachment diameter for bubbles.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 6, pp. 988–994, June, 1971.     

Reliability and true-score measures of binary items as a function of their Rasch difficulty parameter

This article provides formulas for expected true-score measures and reliability of binary items as a function of their Rasch difficulty when the trait (ability) distribution is normal or logistic. The proposed formulas have theoretical value and can be useful in test development, score analysis, and simulation studies. Once the items are calibrated with the dichotomous Rasch model, one can estimate (without further data collection) the expected values for true-score measures (e.g., domain score, true score variance, and error variance for the number-right score) and reliability for both norm-referenced and criterion-referenced interpretations. Thus, given a bank of Rasch calibrated items, one can develop a test with desirable values of population true-score measures and reliability or compare such measures for subsets of items that are grouped by substantive characteristics (e.g., content areas or strands of learning outcomes). An illustrative example for using the proposed formulas is also provided.     

Lineal energy as a function of site size for HZE radiation

Monte Carlo calculations have been used to estimate the frequency and magnitude of energy deposition events produced by delta rays originating with high atomic number, high-energy, primary particles. The results show that the spectrum of delta rays incident on small targets is relatively insensitive to primary particle velocity or distance to the primary track. They suggest that measurements of energy deposition in different size sites can be used to characterise the velocity of the incident particle.     

Publication rate as a function of laboratory size in a biomedical research institution

At the Rockefeller University in 1977–78, the number of all publications of a research group in a year was approximately proportional to the number of individuals in that group during the year. The number of primary research publications of a group in a year was also approximately proportional to the number of individuals in that group during the year. The observed frequency distribution of laboratory size was statistically indistinguishable from a 0-truncated negative binomial distribution, which is the equilibrium frequency distribution of size predicted by stochastic models for the dynamics of freely-forming primate social groups.     

Predictability in a highly stochastic system: final size of measles epidemics in small populations

A standard assumption in the modelling of epidemic dynamics is that the population of interest is well mixed, and that no clusters of metapopulations exist. The well-known and oft-used SIR model, arguably the most important compartmental model in theoretical epidemiology, assumes that the disease being modelled is strongly immunizing, directly transmitted and has a well-defined period of infection, in addition to these population mixing assumptions. Childhood infections, such as measles, are prime examples of diseases that fit the SIR-like mechanism. These infections have been well studied for many systems with large, well-mixed populations with endemic infection. Here, we consider a setting where populations are small and isolated. The dynamics of infection are driven by stochastic extinction–recolonization events, producing large, sudden and short-lived epidemics before rapidly dying out from a lack of susceptible hosts. Using a TSIR model, we fit prevaccination measles incidence and demographic data in Bornholm, the Faroe Islands and four districts of Iceland, between 1901 and 1965. The datasets for each of these countries suffer from different levels of data heterogeneity and sparsity. We explore the potential for prediction of this model: given historical incidence data and up-to-date demographic information, and knowing that a new epidemic has just begun, can we predict how large it will be? We show that, despite a lack of significant seasonality in the incidence of measles cases, and potentially severe heterogeneity at the population level, we are able to estimate the size of upcoming epidemics, conditioned on the first time step, to within reasonable confidence. Our results have potential implications for possible control measures for the early stages of new epidemics in small populations.     

Fracture toughness and hardness of zinc sulphide as a function of grain size

The erosion properties of brittle materials depend upon plastic deformation and crack generation at an impact or indented site. Vickers indentations have been used to investigate the plastic processes and crack systems in chemical vapour deposited zinc sulphide of different grain sizes. The hardness,H, and the local fracture toughnessK _c, are dependent upon the grain size of the material. For small grain size material (<50 m) the Vickers hardness was found to increase with decreasing grain size in accord with the Petch mechanism, i.e.H=H ₀ +kd ^–1/2 wherek andH ₀ are constants andd is the grain diameter. A maximum hardness of ca. 4 GPa has been observed for material with an average 0.5 m grain diameter. In large grain size material, hardness anisotropy within the grains causes significant experimental scatter in the hardness measurements because the plastic impression formed by the indenter (load 10 N and 100 N) is smaller than the grain diameter. The values ofK _c obtained using an indentation technique show that for grain sizes less than 8 mK _c decreases with decreasing grain size. For materials with a grain size in the range 500 m to 8 m, well developed median cracks were not observed, however, the radius of the fracture zone was measured in order to estimate an effectiveK _c. The effectiveK _c was found to increase approximately linearly with the reciprocal root of the grain size. Consideration of the models for elastic/plastic impact and micromechanics of crack nucleation in conjuction with the variation ofK _c andH, indicate that zinc sulphide with a mean grain size of 8 m will give the optimum solid particle and rain erosion resistance.     

Publication rate as a function of laboratory size in three biomedical research institutions

In three biomedical research institutions, there is no indication of a single laboratory size at which the number of publications per scientist is maximal or minimal. In a scattergram of the number of publications of a laboratory against laboratory size, the horizontal coordinate measures the number of scientists in a laboratory, the vertical axis measures the number of publications from the laboratory (counting each publication once regardless of the number of authors), and each laboratory is represented by one point. Scattergrams for the Rockefeller University (RU), New York, the National Institute for Medical Research (NIMR), London, and the National Cancer Institute (NCI), Bethesda, are each described well by a straight line through the origin. The slopes of the lines for the three institutions are not significantly different. In these laboratories, ranging in size from 1 to 46 scientists, one additional scientist increases the expected annual number of publications of a laboratory by approximately 1.1, regardless of the size of the laboratory. Although the three institutions have significantly different mean laboratory sizes, the frequency distribution of laboratory size in each institution is described well by a 0-truncated negative binomial distribution, as predicted by a simple model of laboratory population dynamics.     

Light-scattering efficiency of starch acetate pigments as a function of size and packing density

We study theoretically the light-scattering efficiency of paper coatings made of starch acetate pigments. For the light-scattering code we use a discrete dipole approximation method. The coating layer is assumed to consists of roughly equal-sized spherical pigments packed either at a packing density of 50% (large cylindrical slabs) or at 37% or 57% (large spheres). Because the scanning electron microscope images of starch acetate samples show either a particulate or a porous structure, we model the coatings in two complementary ways. The material can be either inside the constituent spheres (particulate case) or outside of those (cheeselike, porous medium). For the packing of our spheres we use either a simulated annealing or a dropping code. We can estimate, among other things, that the ideal sphere diameter is in the range 0.25-0.4 microm.     

The effect of sample size for estimating Rasch/IRT parameters with dichotomous items

Thirteen samples were randomly drawn from the normative database for the latest edition of Knox's Cube Test-Revised (KCT-R). Parameter estimates for the Rasch model and two and three parameter logistic models were derived and compared. Sample size influenced these estimates as might be expected. Rasch parameter estimates consistently showed the smallest values by sample size using a goodness of fit index.     

Critical heat flux as a function of heater size for a liquid boiling in a large enclosure

Results are presented of an experimental investigation to determine q_* for ethanol boiling under free convection on surfaces insulated on both sides.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 5, pp. 802–806, November, 1977.     

The sensitivity and characteristic size of a hydrophone in the frequency band when there are sources of reflections

The sensitivity of a hydrophone in the frequency band when there is a source of reflections which increases the characteristic size of the hydrophone is considered. The effect of the width of the frequency band on the change in the characteristic size is investigated. It is shown that the characteristic size of the hydrophone may be reduced considerably and that far-field conditions can be ensured for measurements in a hydroacoustic basin when it is calibrated in 1/3-octave frequency bands. __________ Translated from Izmeritel’naya Tekhnika, No. 12, pp. 53–57, December 2005.     

The design of a highly reliable safety critical emergency shutdown system

An emergency shutdown system (ESD) by its nature should be fail-safe. That is, in case of failure in any of its operations, in order to safeguard human life, property and the environment, it should shut down the plant that it controls. However, a complete shutdown, for example, of a petrochemical or nuclear plant is extremely costly. Therefore, as an alternative, the design of highly reliable emergency shutdown systems should be investigated.The major difference between a shutdown system and other control systems is the degree of tolerable operational integrity. A malfunction in the latter is immediately visible and the system can be replaced by a fully operational one. A shutdown system on the other hand is usually, sometimes for years and hopefully forever, `dormant'. When, however, a true emergency situation arises and real demand is placed on it, it must be fully functional. Reliability is of paramount importance. Therefore, besides applying structured design techniques and improved testability other design methods will also need to be incorporated in the final system in order to increase its reliability.