Measuring hypervelocity impact velocity from micrometeoroid crater geometry

Guided by half-space computer simulations showing hypervelocity impact crater formation for an iron particle impacting an aluminum target and characteristic crater geometry changes with impact velocity over the range 8–40 km s⁻¹, we examined normal surface crater views and cross-sectional views through craters (>0.5 mm diameter) from samples retrieved from the NASA LDEF satellite and examined in the scanning electron microscope (SEM). While geometrical features suggested in the computer simulations were indeed observed for micrometeoroid craters in 6061-T6 aluminum targets and 303 stainless steel targets, there was no consistent estimate for impact velocities in any of the experimental samples, and velocity estimates based on measuring ratios of ejecta width/crater diameter and ejecta height/crater depth as well as ejecta height/crater diameter varied from 8 to 42 km s⁻¹; over the same range simulated. These results point to the need to create reference data from actual hypervelocity impact experiments in the laboratory, and systematic observation of residual crater geometries in the SEM. These experiments also demonstrate the uncertainty in assuming a fixed impact velocity for all impact craters in space materials as well as an apparent futility in attempting to correlate impacting particle velocity with post-mortem characteristics of a given crater.     

Measuring the impact of passenger restrictions on new teenage drivers

Passenger restrictions for new teenage drivers that became law in 1998 in California provide an opportunity to study the effectiveness of such laws in reducing the number of passengers as well as the influence of teenage passengers on novice drivers. Using fatal and injury crash data from California's Statewide Integrated Traffic Records System, this study found that teenage passengers are a causal factor in crashes of 16-year-old drivers and that in the three years following implementation of the new law, the average number of teenage passengers carried by 16-year-olds decreased by approximately 25%. Without considering the beneficial effect of a decrease in the crash rate, the decrease in the number of teenage passengers in actual crashes resulted in an estimated saving of eight lives and the prevention of 684 injuries over a three-year period.     

Measuring international knowledge flows and scholarly impact of scientific research

We introduce a new quantitative measure of international scholarly impact of countries by using bibliometric techniques based on publication and citation data. We present a case study to illustrate the use of our proposed measure in the subject area Energy during 1996–2009. We also present geographical maps to visualize knowledge flows among countries. Finally, using correlation analysis between publication output and international scholarly impact, we study the explanatory power of the applied measure.     

Measuring impact by a full option method and the notion of bibliometric spectra

A full option method for determining impact takes into account citations to all cited publications, instead of limiting the analysis to ISI-publications only, as usually done in the standard method. The method was tested for the 258 early Ghent professors, teaching in 6 different faculties. The impact of monographs is, in general, much larger than the impact of articles (whether of ISI-type or not). This result remains valid for all six faculties separately. Limiting the bibliometric visibility to ISI-publications reduces the number of citations to only 16%. Bibliometric spectra are presented, in which citations, cited publications and their impact are shown in function of the year of publication. The number of cited publications is always important to expose the influence of activity (production) upon bibliometric scores. For the faculty of Arts, the citations to early professors are compared with those obtained for the presentday generation: the bibliometric spectrum for the former group is rather discontinuous (showing a large erosion in the number of citations by year), whereas that of the latter is continuous. The Ghent citation data are also compared with those given internationally in the same period.     

Measuring the impact of scientific publications. The case of the biomedical sciences

The bibliometric indicators currently used to assess scientific production have a serious flaw: a notable bias is produced when different subfields are compared. In this paper we demonstrate the existence of this bias using the impact factor (IF) indicator. The impact factor is related to the quality of a published article, but only when each specific subfield is taken separately: only 15.6% of the subfields we studied were found to have homogeneous means. The bias involved can be very misleading when bibliometric estimators are used as a basis for assigning research funds. To improve this situation, we propose a new estimator, the RPU, based on a normalization of the impact factor that minimizes bias and permits comparison among subfields. The RPU of a journal is calculated with the formula: RPU=10(1-exp (-IF/x)), where IF is the impact factor of the journal and x the mean IF for the subfield in which the journal belongs. The RPU retains the advantages of the impact factor: simplicity of calculation, immediacy and objectivity, and increases homogeneous subfields from 15.6% to 93.7%.     

Measuring the citation impact of research journals in clinical neurology: A structural equation modelling analysis

This study develops and tests an integrated conceptual model of journal evaluation from varying perspectives of citation analysis. The main objective is to obtain a more complete understanding of the external factors affecting journal citation impact; that is, a theoretical construct measured by a number of citation indicators. Structural equation modelling (SEM) with partial least squares (PLS) is used to test the conceptual model with empirical data from journals in clinical neurology. Interrelationships among journal citation impact and four external factors (journal characteristics, journal accessibility, journal visibility and journal internationality) have been successfully explored, and the conceptual model of journal evaluation has been examined. This revised version was published online in June 2006 with corrections to the Cover Date.     

双光束法测速度时测量角产生的影响

本文讲述了利用双光束法进行无接触流速的测量。并着重讨论和分析了不同测量角所带来的不同影响,以及最佳测量角的选定。     

表面粗糙度仪的测量系统分析

本文以JB-1C型表面粗糙度测试仪组成的测景系统为研究对象,制定了表面粗糙度仪测量系统分析计划.采用均值-极差法对测量系统的重复性与再现性的分析步骤、计算过程、计算结果做了详尽的剖析和讨论.认为该测量系统的偏倚、线性和稳定性能满足要求,其重复性与再现性指标10%≤%R&R=17.9%<30%.测量系统可以接受.     

一种新型的质心测量机构与测量方法

分析了不平衡力矩和多点称重测质心方法,探讨了一种高精度质心测量方法.采用大、小量程十字分布传感器支撑旋转轴系, 设计了一种新型的质心测量机构.利用旋转轴作为质心测量基准,大量程传感器作为等效刀口,小量程传感器测量偏心力,提高了测量灵敏度.进行了测量方法的误差来源分析,结合现有的形心测量技术,研制了一台高精度质心测量设备,并成功应用于产品实测.