Stability and Noise Performance of Various Rubidium Standards Among the well-known time and frequency standards from Hewlett Packard and other vendors, the HP A rubidium vapor frequency standard offers the best medium-term frequency stability of any device that the casual or even hardcore "time nut" is likely to encounter.
The Interstate Technology and Regulatory Council ITRC has written a vapor-intrusion guideline document that is currently out for review and is due to be released in early ASTM International has entered into the fray and has convened a workgroup to amend the Phase I guidance to include assessment of the vapor-intrusion pathway and to write a standard on how to do it.
Many others are working on their own guidance. The concern about vapor intrusion extends to the United Kingdom U. Since soil-gas data are preferred by the majority of agencies in evaluating the pathway, much debate has surfaced over some of the collection and analytical procedures.
In this article, I present some of the results from recent studies that address some of the pertinent issues. I refer you to Parts 1 LUSTLine 42 and 3 in this series for a good introduction to this article and for more information on some of the topics covered herein.
The Two Most Common Market equilibration process paper Vapors and vapor intrusion are unfamiliar territories for many practitioners in this field regulators, stakeholders, consultants, subcontractors, attorneys. Here are two of the most common errors that people make with soil-gas programs or data.
The units are not equivalent, and the conversion depends on the molecular weight of the compound. Converting between units e. As I advised in Part 3, make your life simpler by: Required Soil-Gas Target Levels The other error I see too often is the regulator or consultant using incorrect soil-gas target levels.
Residential values are erroneously applied at commercial sites, incorrect attenuation factors are being used to determine target values, or values determined from predictive models are incorrect.
The soil-gas target level ultimately determines the required analytical method and the need for additional assessment. Determining the proper value is often an unfamiliar exercise for both regulator and consultant.
So, consultants need to ensure that regulators are asking for the proper values, and regulators need to ensure that consultants are proposing the proper value. Sample-Collection Issues Probe Installation Method I have not seen a significant difference in results among samples collected either through the probe rod while the rod is still in place or through tubes that are buried in the ground after the rod is removed.
This observation is based on data from hundreds of sites where we have made repeated measurements using different methods. While I have never compiled these data, a recent report by U.
EPA DiGiulio et al. Although small differences were detected, the study showed that data collected using hand-driven probes, direct-push rods, and buried tubes show good agreement, generally about the same as analytical precision. The bottom line is that the probe installation technique does not matter so long as you do it right.
So, the choice of which method to use should depend upon the site, access, and project goals. Typically, sampling through the probe rod is faster and less likely to disturb the insitu soil gas. For limited-access areas, a hand probe may be all that is applicable. For deeper depths, direct-push probes are more convenient.
For repeated sampling, burial of smalldiameter tubes offers advantages. If the probe-rod methods are used, samples should be collected through small-diameter inert tubing that runs down the probe rod so the sample does not contact the inside of the probe rod.
Extraction Volume Three published studies are now out that compare soil-gas concentrations collected from volumes ranging from 0.
The results of these studies, done in relatively coarse-grained soils, show no significant difference in concentrations. I have reviewed data from countless sites comparing on-site analysis from 50cc syringe samples to off-site analysis done on samples collected in canisters 1L to 6L.
I rarely see differences greater than 20 percent. However, in finer-grained soils, large volumes are often not possible or difficult to collect. If larger sample volumes are attempted, the potential for leaks around fittings increases.
I also have witnessed higher concentrations where large volumes are "forced" from tight soils, presumably due to contaminant desorption off the soils.
Finally, the larger the volume extracted, the greater the uncertainty of where the sample is located.Aas, H., Klepp, K., Laberg, J. C., & Aaro, L. E. (). Predicting adolescents' intentions to drink alcohol: Outcome expectancies and self-efficacy.
Macro Notes 3: Money Demand Demand for Money The notion of a demand for money may strike you at first glance as bizarre. Don't you just want as much as you can get?
This paper discusses market equilibrium associated with the supply and demand of sugar cane in Brazil. The writer will discourse the jurisprudence of supply and demand with the hurts of demand and supply.
describe efficient markets theory. and explain excess and deficit. View Homework Help - Market Equilibration Process Pape2 from QRB QRB/ at University of Phoenix. 1 Market Equilibration Process Paper Shari Kraus Eco/ December 14, M DE Point 2 The market. Type or paste a DOI name into the text box.
Your browser will take you to a Web page (URL) associated with that DOI name. Send questions or comments to doi. Aas, H., Klepp, K., Laberg, J.
C., & Aaro, L. E. (). Predicting adolescents' intentions to drink alcohol: Outcome expectancies and self-efficacy.