Validation of bibliometric indicators in the field of mathematics

Bibliometric analyses of scientific publications provide quantitative information that enables evaluators to obtain a useful picture of a team's research visibility. In combination with peer judgements and other qualitative background knowledge, these analyses can serve as a basis for discussions about research performance quality. However, many mathematicians are not convinced that citation counts do in fact provide useful information in the field of mathematics. According to these mathematicians, citation and publication habits differ completely from scholarly fields such as chemistry or physics. Therefore, it is impossible to derive valid information regarding research performance from citation counts. The aim of this study is to obtain more insight into the significance of citation-based indicators in the field of mathematics. To which extent do citation-scores mirror to the opinions of experts concerning the quality of a paper or a journal? A survey was conducted to answer this question.Top journals, as qualified by experts, receive significantly higher citation rates thangood journals. Thesegood journals, in turn, have significantly higher scores than journals with the qualificationless good. Top publications, recorded in the ISI database, receive on the average 15 times more citations than the mean score within the field of mathematics as a whole. In conclusion, the experts' views on top publications or top journals correspond very well to bibliometric indicators based on citation counts.     

Dispersion measures for h-index: a study of the Brazilian researchers in the field of mathematics

Although the h-index is considered a significant indicator to evaluate the researchers' performance, as it simultaneously measures aspects related to their scientific productivity and citation impact, several studies have pointed out its deficiencies and limitations. In this context, this study aims to evaluate the contribution of dci and dco indicators, two Hirsch-type indices, to measure the reasonableness of the h-index as a representation of the researcher’s scientific performance. The universe of analysis consisted of 116 Brazilian mathematicians holding CNPq grants. For each researcher, the number of articles, the number of citations per article and the year of publication were collected in the Scopus database. Then, for each researcher, the h-index and dci and dco indices were calculated. The dci and dco indicators allowed selective and productive researchers to be to distinguished more accurately. In addition, they contributed to estimate the possibility of the researcher to increase his/her h-index. The study concludes that the dci and dco indices were able to reliably measure the distribution dispersion of the researchers' citation impact together with their h-index. Consequently, they managed to estimate the representativeness of h-index as an indicator of the researchers' scientific performance in the field of mathematics in Brazil.

     

Investigations on the stress intensity factor field for unstable dynamic crack growth

In this study, the unstable dynamic crack propagation due to static loading in an elastic material is analyzed for both antiplane and inplane conditions. Of particular concern is the investigation of limitations on the assumption that the stress intensity factor field is fully established over a region of given size near the tip of a growing crack. The transient analysis of the stress for a material particle at a small fixed distance from the moving crack tip is examined in detail. Some estimations are made of the time required for the stress at a point near the moving crack tip to reach the value it would have if the stress field were actually given by the near tip stress intensity factor field. In addition, a simple formulation obtained from the equivalent static problem is proposed which can be used as a good approximation to the associated complicated dynamic transient problem.     

Uncertainty of the thyroid dose conversion factor for inhalation intakes of 131I and its parametric uncertainty

Inhalation exposures of 131I may occur in the physical form of a gas as well as a particulate. The physical characteristics pertaining to these different types of releases influence the intake and subsequent dose to an exposed individual. The thyroid dose received is influenced by the route through which 131I enters the body and its subsequent clearance, absorption and movement throughout the body. The radioactive iodine taken up in the gas-exchange tissues is cleared to other tissues or absorbed into the bloodstream of the individual and transferred to other organs. Iodine in the circulatory system is then taken up by the thyroid gland with resulting dose to that tissue. The magnitude of and uncertainty in the thyroid dose is important to the assessment of individuals exposed to airborne releases of radioiodine. Age- and gender-specific modelling parameters have resulted in significant differences between gas uptake, particulate deposition and inhalation dose conversion factors for each age and gender group. Inhalation dose conversion factors and their inherent uncertainty are markedly affected by the type of iodine intake. These differences are expected due to the modelling of particulate deposition versus uptake of gas in the respiratory tract. Inhalation dose estimates via iodine gases are very similar and separate classifications may not be necessarily based on this assessment.     

Electromagnetic field attractor made of gradient index metamaterials

We present a device that is designed with varying permittivity ε(r) such that an electromagnetic wave in the K-band of the microwave regime entering it will bend inward towards the core. The core is made of silicon composites. We follow the distribution formula of the permittivity for the device derived by Narimanov and Kildishev using the optical-mechanical analogy. The diameter of the device is 14 cm, and it is constructed out of 21 rings of two different types of etched printed circuit boards, as well as dielectric powders as adding filling materials. The experimental wave intensity profile, based on parallel plate measurements for the cases where the incident plane wave is slightly displaced to the top of the center of the device and the case of on center incidence, are presented and discussed. In spite of some mismatch of the core and metamaterial structures of the device found, approximately 80% of the wave still manages to reach the core of the device and gets trapped and absorbed. Broadband properties of the device are also investigated.     

场效应管X射线剂量增强的实验测量

为了实验精确测量场效应管的X射线剂量增强系数,介绍了如何改进剂量增强系数实验测量的方法和实验测量装置,以及实验测量的详细过程.得到了两种不同类型场效应管的辐照数据,根据实验数据计算了其剂量增强系数.剂量增强效应十分明显,IRF540场效应管在阈电压1.5 V时相对剂量增强系数为16,IRF9530要小些,在阈电压为4v时相对剂量增强系数约7.5.     

Identification of nosean in sodalite and conversion of nosean to sodalite

Sodalite (Na₆Al₆Si₆O₂₄·2NaBr) grown hydrothermally in insufficient solvent concentrations contains a second phase. This additional phase is identified, using X-ray diffraction, as basic nosean (Na₆Al₆Si₆O₂₄·2NaOH·nH_2O). A low-temperature reaction (LTR) process which converts the nosean phase to sodalite by removing H₂O from the structure was developed and is discussed. The LTR process enhances the coloration sensitivity of sodalite grown by hydrothermal and solid sintering techniques by increasing the degree of crystallinity of the material.     

The effect of an electric field on the carbon sulfide conversion in ionized air

The effect of an electric field on the process of carbon sulfide conversion was studied by modeling the process in a mixture of nitrogen and oxygen ionized under the action of nanosecond high-current or microsecond low-current electron beams. Depending on the method of ionization, the electric field influences the conversion efficiency either by inducing the synthesis of nitrogen oxides or by changing the rate of cluster ion formation.     

Refractive index of doped polymers modified by electrical field

Polymethylmethacrylate (PMMA) and polystyrene (PS) were doped from a solution with 3-(1,2-dimethyl imidazole)-borane dipolar compound to 0–10 wt.%. From the pristine and doped polymers, 200-nm thick films were prepared by spin coating onto a silicon substrate. The film deposition proceeded either without external electrical field or under DC electrical field of 2.5 kV cm⁻¹. Refractive index (n) of the films in spectral region from 200–1100 nm was determined by a refractometer. It was demonstrated that, under the external electrical field, both polymer composites behave differently. While for PS based composite the refractive index increases, for doped polar PMMA, application of an external electrical field results in refractive index declination.     

基于可靠指标的稳定安全系数探讨

桥梁结构当第一类稳定安全系数取4时,能否保证结构在更可能出现的第二类失稳发生时的可靠指标达到目标可靠指标值得研究。对单层单跨刚架桥分别进行了第一类和第二类稳定计算,以第一类稳定计算得到的临界荷载,取第一类稳定安全系数为4,采用一次可靠度方法编制程序得出可靠指标。进而采用第一类稳定可靠指标计算时的荷载效应和第二类临界荷载来计算第二类可靠指标。根据可靠指标探讨结构稳定安全系数取值的合理性。在此基础上,对两类稳定临界荷载进行了参数分析,研究临界荷载的变化对可靠指标的影响。结果表明:稳定分析应区分失稳状态,第一类稳定安全系数取4,但当结构发生第二类失稳时,有些情况下不足以保证可靠指标达到目标可靠指标。     

直剪作用下再生混凝土力学性能及强度指标换算

以再生粗骨料取代率为变化参数,通过75个再生混凝土(RAC)试件的直剪、抗压与劈裂抗拉试验,揭示了RAC的直剪破坏机制及不同强度指标之间的换算规律。结果表明:RAC在直剪作用下为明显的脆性破坏,粗骨料和水泥基体均被剪断;随着取代率的增加,RAC直剪强度较普通混凝土变化不大,总体上呈降低趋势,但50%取代率(按质量)时直剪强度有所增大;峰值剪切变形随取代率的增大,总体呈增大趋势,平均提高了18.85%;初始剪切变形模量随取代率的增大,总体呈降低的趋势,平均降低了8.97%;最后,基于试验数据提出了RAC剪切强度与抗压、劈裂抗拉强度的换算关系式,计算结果与试验值吻合较好。      

Stress intensity factor error index for finite element analysis with singular elements

An error index for the stress intensity factor (SIF) obtained from the finite element analysis results using singular elements is proposed. The index was developed by considering the facts that the analytical function shape of the crack tip displacement is known and that the SIF can be evaluated from the displacements only. The advantage of the error index is that it has the dimension of the SIF and converges to zero when the actual error of the SIF by displacement correlation technique converges to zero. Numerical examples for some typical crack problems, including a mixed mode crack, whose analytical solutions are known, indicated the validity of the index. The degree of actual SIF error seems to be approximated by the value of the proposed index.     

Stress intensity factor error index for finite element analysis with singular elements

An error index for the stress intensity factor (SIF) obtained from the finite element analysis results using singular elements is proposed. The index was developed by considering the facts that the analytical function shape of the crack tip displacement is known and that the SIF can be evaluated from the displacements only. The advantage of the error index is that it has the dimension of the SIF and converges to zero when the actual error of the SIF by displacement correlation technique converges to zero. Numerical examples for some typical crack problems, including a mixed mode crack, whose analytical solutions are known, indicated the validity of the index. The degree of actual SIF error seems to be approximated by the value of the proposed index.