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This study evaluated the benefits of Open Graded Friction Course (OGFC) via two field projects constructed by the Nevada Department of Transportation: one project was in Elko, and the other was in Las Vegas. Each project included both the OGFC and Dense-Graded Hot Mix Asphalt (DGHMA) sections. The Elko project was located in the town area of Elko while the Las Vegas project was constructed in a rural area on I-15 interstate highway. Laboratory tests were performed to evaluate the durability, rutting, and moisture-susceptibility of OGFC mixtures. The selected test methods included the Cantabro test, Tensile Strength Ratio test, and Hamburg Wheel-Track test (HWTT). The laboratory test results showed that the Las Vegas OGFC mixture passed all the performance criteria, but the Elko Mixture failed to satisfy the HWTT criterion. The field performance tests were conducted to assess the permeability, friction, and noise functionality over time. The selected test methods included the NCAT falling head permeameter test, locked-wheel skid trailer test, and On-Board Sound Intensity test. The field performance results demonstrated that the Las Vegas OGFC pavement exhibited benefits in permeability, friction, and noise reduction compared to the DGHMA pavement, while the Elko OGFC pavement showed comparable performance with the DGHMA pavement after 2-years of service. Finally, a cost-benefit analysis was conducted to monetize the advantages and disadvantages of OGFC pavements. As demonstrated in the economic analysis, the OGFC pavement in Las Vegas reduced the net present value of OGFC costs by 36%, while the OGFC pavement in Elko increased the net present value of costs by 86%. This indicates that the implementation of OGFC is cost-effective in rural highways but impractical in urban or town areas. High speed traffic is generally needed to help keep the interconnected voids of an OGFC pavement from becoming clogged over time. As a result of the reduced speed on the Elko project, the permeability functionality was lost after one year and the noise reduction benefit was lost after thirty two months.

The use of porous friction course (PFC) provides numerous safety benefits and improves the noise quality of surrounding areas. Many agencies once used PFC for these reasons, but have since stopped using PFC due to performance issues. PFC pavements have reportedly been prone to ravelling and cracking, which leads to reduced service life. In addition, PFC is also typically more expensive than a dense-graded mix due to its use of high-quality aggregates, modified asphalt binder, and higher asphalt binder contents. Research is needed to extend the service life of PFC pavements in order to encourage agencies to start, or continue, use of PFC for its safety benefits. The objective of this research is to address the ravelling and cracking distresses commonly seen by adjusting the asphalt and dust content of PFC mixes to improve durability. This was accomplished by using an array of performance tests to evaluate the effect of additional fine aggregate passing the 0.075 mm (P−0.075) sieve on two PFC mixtures: one ...

Open-graded friction courses (OGFC) are special purpose thin surface mixtures used to reduce the risk of hydroplaning, wet skidding, splash and spray, pavement noise, and improve night and wet weat...

Since the late 1970s there has been much research performed to understand better the stripping phenomenon in asphalt mixtures. As a result, there have been changes in both materials and technology over the past 30 years to improve the resistance to moisture damage and the ability to test for performance under adverse moisture conditions. Because of the changes in materials and technologies related to the development and improvement of antistrip agents, this research study was conducted to evaluate the effectiveness of current antistrip agents used in hot-mix asphalt pavements. The objectives of this project were to construct a field test section that used three different antistrip agents in a conventional Superpave® surface mixture and conduct a series of laboratory performance test comparisons using different aging periods to make long-term comparisons of the effectiveness of hydrated lime, liquid additive, and warm-mix asphalt antistrip additives. Multiple freeze–thaw cycles of zero, one, five, and 10 cycles were used for a portion of the research study. The results showed that hydrated lime had the highest tensile strength and highest tensile strength ratio (TSR) values and was the only additive treatment to meet the minimum of 80% TSR for all freeze–thaw cycle combinations. Both five and 10 freeze–thaw cycles were significantly more discriminating for moisture susceptibility than one freeze–thaw cycle alone. Warm-mix asphalt treated mixtures produced low initial tensile strengths, but the strength of these mixtures improved with time.

This research had several objectives: measure the dynamic modulus of commonly used hot-mix asphalt mix types, two aggregate base courses, and two soils that represent high and low values; compare the results of using measured moduli with Mechanistic–Empirical Pavement Design Guide (MEPDG) Level 3 default moduli for the subgrade and aggregate base material; and compare design results using the AASHTO 1972 Interim Guide for Pavement Design currently being used by the Georgia Department of Transportation (GDOT) with the MEPDG results. The research showed that the MEPDG Level 3 default values for resilient modulus of both soil and aggregate materials are significantly higher than the actual values determined from laboratory test results. Use of actual material properties and load spectra resulted in significantly greater structures being recommended than when Level 3 default values were used for the MEPDG design program. On the basis of these results, GDOT is cautioned against using the default values built into the MEPDG software and should conduct a thorough calibration study using Georgia materials before implementing the MEPDG design procedure.

The objective of this project was to evaluate the performance of Georgia's mixes designed by using the Superpave® gyratory compactor. Mixes designed with numbers of design gyrations that are too high would be rut resistant but may be difficult to compact adequately in the field and may lack sufficient durability because of reduced asphalt binder content. The following conclusions were made on the basis of an evaluation of field projects and from laboratory volumetric and performance testing with various aggregate sources and gyration levels: (a) It is unlikely that Superpave mixtures will reach the design air voids of 4.0% during the life of the pavement. After nearly 5 years, the average air voids measured in the wheelpaths were 5.7% for Superpave projects and 3.8% for Marshall projects. On the basis of volumetric comparisons, 66 gyrations with the laboratory-produced mix gave approximately the same density achieved on the Superpave projects in the field. (b) The difference between 4-in.-diameter Marshall samples and 6-in.-diameter gyratory samples for moisture susceptibility was not statistically significant enough to assign a relationship between the tensile strength ratio (TSR) for samples with a diameter of 4 in. and the TSR for samples with a diameter of 6 in. (c) Although the asphalt binder content was an important factor in extending fatigue life, aggregate source and strain level were the most significant variables affecting fatigue results.

This research evaluated the effect of reclaimed asphalt pavement (RAP) on the combined overall performance of stone matrix asphalt mixtures in Georgia. Four types of RAP were combined at four levels (0%, 10%, 20%, and 30%) with four aggregate sources, with the use of a one-fourth fraction factorial design. Granite materials common to Georgia were used exclusively in this study for both RAP and virgin aggregate. Testing was performed to evaluate the binder effect on resistance to moisture susceptibility, rutting potential, thermal cracking potential, and fatigue life of the recycled mixtures. The following main findings are applicable only to the RAP and virgin aggregates used in this study. Virgin aggregate had a greater effect on Los Angeles abrasion loss and percent flat and elongated particles than did the addition of RAP. Increasing RAP content resulted in higher tensile strengths (conditioned and unconditioned) for moisture susceptibility testing. Up to 20% RAP can be used without significantly affecting performance. Only fatigue life (at high strain levels) decreased significantly with the addition of 30% RAP. Fine-graded RAP reduced virgin binder requirements, which translates into increased economic benefits. However, mixes are stiffer because they have higher aged-to-virgin binder ratios and may be more susceptible to fatigue cracking. Adding up to 30% RAP had little effect on low-temperature performance grade properties, which may indicate that the grade of virgin binder does not have to be adjusted to provide the desired low-temperature binder properties.

Current stone matrix asphalt (SMA) design guidelines list two compaction options to design SMA, 50 blows Marshall or 100 gyrations with the Superpave® gyratory compactor (SGC). However, some states have found that 100 gyrations with the SGC is excessive for their materials. In this study a lower compaction level of 65 gyrations was used to compare with the standard 100 gyrations to design SMA mixtures. Results showed that mixtures designed by 65 gyrations had an average of 0.7% higher optimum asphalt content and 1.5% higher voids in mineral aggregate (VMA) than those designed by 100 gyrations. All mixtures designed by 65 gyrations met the minimum asphalt content and VMA requirements for SMA, whereas only eight of 15 mixtures designed by 100 gyrations met those two requirements. Compaction at 100 gyrations resulted in an additional 0.62% average aggregate breakdown at the critical sieve as compared with 65 gyrations. SMA mixtures designed by 65 gyrations and 100 gyrations had an average asphalt pavement analyzer rut depth of 3.9 mm and 3.1 mm, respectively. Thirteen of 15 mixtures designed by 65 gyrations performed well if 5.0 mm was set as the maximum allowed rut depth. On the basis of this study, 65 gyrations can be used to design a more durable SMA mixture, while still maintaining the good rutting resistance that SMA mixtures are noted for. The successful design by 65 gyrations for all five aggregates in this study indicates that a lower design compaction level may allow the use of more aggregate sources for SMA mixtures.

The Alabama Department of Transportation specifies the Superpave® design system for most of its dense-graded HMA mixes. However, there is concern that the number of design gyrations ( NDesign) may be too high for specified traffic levels. Mixes designed with an NDesign level that is too high would be rut resistant but may be difficult to compact in the field and may suffer from durability problems such as premature cracking and raveling. The objective of this project is to evaluate the performance of Alabama's mixes designed according to Superpave criteria and compare them to the performance of Alabama's Marshall-designed mixes to determine whether current NDesign levels should be adjusted. The following conclusions are based on an evaluation of 25 Marshall and Superpave projects placed about the same time and serving under approximately the same traffic conditions: ( a) Generally, both Marshall and Superpave mixtures are performing quite well with little rutting and cracking after a period of about 4 years. ( b) It is likely that most Marshall and Superpave mixtures will not reach the design air voids of 4.0% during the life of the pavement. After 4 years, the average air voids measured in the wheelpaths was 5.3% for Marshall mixes and 5.9% for Superpave mixtures. ( c) It appears that the durability of Superpave mixtures can be improved, without adversely affecting the rutting resistance, by increasing the asphalt content. Practitioners, however, are cautioned to monitor rutting indicators closely during mixture design, production, and construction.

Several lab tests were used in this study to evaluate mixture properties. A draindown test, Cantabro stone loss test, a permeability test, and a modified version of AASHTO T-283 were used to evaluate laboratory performance of open-graded friction course (OGFC) mixes. Some of the more pertinent conclusions were as follows. The CoreLok procedure appears to be a more accurate method of determining bulk specific gravity of compacted specimens than the dimensional method. The minimum air voids content for new-generation OGFC mixtures should be 18% on the basis of the dimensional method and 16% on the basis of the CoreLok method. The addition of fiber stabilizers significantly reduced the potential for draindown. Superpaver; gyratory compactor (SGC)-compacted samples can be used for the Cantabro stone loss procedure. Unconditioned SGC samples should have stone loss of no more than 20%. If an aging process is used, the maximum amount of stone loss should be limited to 24%. Because there is not a significant difference between unaged and aged sample results, the aging procedure is not necessary. Results from this study show no significant difference in tensile strength when one, three, and five freeze-thaw cycles are used in the moisture-conditioning procedure. Therefore, only one freeze-thaw cycle is needed.

During NCHRP Project 9-8, Designing Stone Matrix Asphalt Mixtures, the voids in coarse aggregate (VCA) concept was selected as the preferred method to determine whether stone-on-stone contact existed in stone matrix mixtures. It is believed that stone-on-stone contact is important for open-graded friction course (OGFC) mixes to minimize the potential for rutting. Therefore, the same VCA requirements were adopted for OGFC mixes as had been developed for stone matrix asphalt mixtures. The objective of this study was to verify the VCA concept for defining stone-on-stone contact within OGFC mixtures by using digital imaging techniques such as analyzing particle contacts and the air voids size distribution. The effect of aggregate breakdown on stone-on-stone contact by the VCA method was also evaluated. The following conclusions are based on the information presented in this study. ( a) A general guideline for determining the critical breakpoint sieve would be to select the finest sieve for which there is at least 10% of the total aggregate retained. This sieve size also should differentiate between the aggregate skeleton and filler particles. ( b) Digital imaging provides a scientific method for identifying when stone-on-stone contact exists and supports the VCA. An advantage of digital imaging is that it can quantify the number of contacts between aggregate particles.

Several combinations of mix type, aggregate type, asphalt binder type, and layer thickness are in place at the National Center for Asphalt Technology (NCAT) test track. It was desirable to examine the effects these various combinations may have on temperatures within the pavement. The purpose of this study was to evaluate measured versus predicted temperatures, evaluate the effect of mix type on pavement temperature, and compare the effect of surface layer thickness on pavement temperatures. On the basis of temperature data from the NCAT test track, some of the general conclusions are that ( a) both the Strategic Highway Research Program (SHRP) and Long-Term Pavement Performance (LTPP) temperature models slightly underpredicted high pavement temperatures at 50% reliability and slightly overpredicted temperatures at 98% reliability and ( b) the low-temperature models for SHRP overpredicteded low pavement temperatures for both 50% and 98% reliability. The LTPP models were also overly conservative at 98% reliability. These results indicate that asphalt binders may not need to be as soft as specified in the Superpaver; performance grading system for low-temperature performance.

Open-graded friction course (OGFC) has been used in the United States for more than 50 years. In 2000, National Center for Asphalt Technology (NCAT) research led to a recommended mix design procedure for a new-generation OGFC, but the work involved only one aggregate source. Therefore, NCAT is in the process of refining this design procedure to ensure that it is applicable to other aggregate types used in surface mixes throughout the United States. The objectives of NCAT's current research are to refine and field validate the new-generation OGFC mix design procedure. This work has led to several experiments. Several objectives have been identified that need to be addressed. Superpave® technology and use of the Superpave gyratory compactor (SGC) need to be incorporated into the mix design procedure. The Cantabro test for durability and resistance to stone loss needs to be adapted to SGC-prepared specimens and performance parameters established. The asphalt draindown test (AASHTO T 305-97), which was developed for stone-matrix asphalt mixtures, also needs to be evaluated for applicability to OGFC mixtures. In addition, a method for effectively evaluating air void criteria needs to be investigated. On the basis of the research conducted in this study, 50 gyrations of the SGC was selected as the design compactive effort during mix design. Also, the use of SGC-prepared samples during the Cantabro test appears to be a reasonable alternative to use of Marshall-compacted samples.

Stone matrix asphalt (SMA) and Superpave® represent relatively new mix design technologies in the United States. Therefore, a condition survey was conducted of mixes that had been in service for several years to evaluate the long-term performance of SMA and Superpave projects. This study is a follow-up to a 1995 review of SMA projects and a 1998 review of Superpave projects. Both SMA and Superpave are acknowledged to be rut-resistant mixes, and this resistance was shown to be the case during this project review. However, a significant amount of cracking occurred early in the life of some of these mixtures. Overall, the SMA mixtures appeared to be more durable than the Superpave mixtures evaluated. The SMA mixtures have been in place about 2½ years longer than the Superpave mixtures, but the overall condition is about the same. Some of the primary conclusions from the survey are as follows: both SMA and Superpave mixtures were shown to be rut-resistant even when placed on facilities with high traffic volume; much of the observed cracking, especially load cracking, appeared to be more related to problems other than mix design or material properties; and SMA mixtures can be expected to last longer than Superpave mixtures before reaching the same condition level.

Open-graded friction courses (OGFCs) are special-purpose mixes used to improve friction, minimize hydroplaning, reduce splash and spray, improve night visibility, and lower pavement noise levels. OGFCs typically utilize a gap grading for aggregates and a low percentage of filler. The asphalt content for OGFCs is generally slightly higher than that for dense-graded mixes. The combination of uniform grading, low filler, and normal OGFC asphalt content can lead to the draining of asphalt binder from a mix (typically called draindown) during transportation and laydown procedures. States that use OGFC typically utilize fibers to help prevent draindown. Generally, these states have specified mineral fibers over organic fibers because of concern that organic fibers (cellulose) would absorb water and lead to moisture problems in the field. A study was conducted to evaluate the use of cellulose fibers in OGFC mixes. The study entailed both a field phase and a laboratory phase. Field work entailed conducting a visual distress survey of six experimental OGFC pavements placed in Georgia during 1992. These pavements contained six different combinations of binder polymer and additives. Laboratory work entailed preparing OGFC mixes with both cellulose and mineral fibers and performing numerous moisture sensitivity tests. Results indicated that cellulose fibers performed as well as mineral fibers in OGFC mixes.

To improve the safety of motorists on Georgia highways, the Georgia Department of Transportation (GDOT) has continued to use the most advanced and effective pavements available, including the open-graded friction course (OGFC). Since OGFCs were conceived in the 1950s and 1960s, GDOT has used these mixes as thin porous wearing layers primarily on Interstate highways. In the past, GDOT encountered problems with OGFC use, including asphalt cement (AC) draindown, rapid oxidation, raveling, and stripping of underlying layers. Consequently, GDOT placed a moratorium on OGFC use in 1982. Since that time, however, several modifications have been made to improve the performance of OGFC mixes. Hydrated lime is added as an antistripping agent to OGFC and to all other mixes used on the Georgia state route system, including dense-graded mixes that underlie OGFC. Fibers are added to eliminate AC draindown. Polymer-modified AC is added to improve the durability of the pavement by reducing problems associated with premature oxidation and raveling. Production temperatures are increased to more thoroughly dry aggregate components and thus improve AC adhesion. Finally, coarser gradations and thicker layers are used to improve permeability. With the modifications made to these mixes in the last few years, significant improvements in mix performance have already been noted. Agencies that have used this mix in the past and experienced problems similar to those experienced by GDOT should consider using this modified OGFC on high-volume traffic facilities.

Microsurface mix, or microsurfacing, can be used for sealing and providing a friction surface for cracked and deteriorated surface mixes. This mix, essentially consisting of 9.5-mm (0.37-in.) screenings bonded by a polymer-modified asphalt emulsion, is economical and can be placed very swiftly. Microsurfacing is also aesthetically pleasing because of its resemblance to hot-mix asphalt. In 1990–1991, the Georgia Department of Transportation (GDOT) successfully used microsurfacing in a test section on I-75 in Henry County, which had high traffic volumes and a heavy truck concentration. Two varieties of the mix were used, and both showed little deterioration after 2 years. In 1996, GDOT opted to use microsurfacing for a 9.2-km (5.7-mi) section of I-285 in Atlanta between Conley Road and Old National Highway. This 92 lane-km (57-lane-mi) project was initiated to address the raveling and cracking in the section and improve its appearance before the 1996 summer Olympics. The I-285 project began in late May 1996 and was completed in 1 month. The microsurfacing used on I-285 has performed quite well since the project was completed. No additional problems with raveling or load cracking have been encountered. The mix has provided excellent smoothness and good friction, with a minimal increase in pavement noise levels. Microsurfacing may be suitable for use on cracked pavements in lieu of more conventional rehabilitation methods such as crack sealing, leveling, and double surface treatments.

Reuse of roofing shingle waste not only minimizes the environmental problems related to the disposal of waste in landfills, but also reduces the amount of virgin asphalt cement and fine aggregate required in hot mix asphaltic concrete (HMAC), thus creating the potential for cost savings. The Georgia Department of Transportation (GDOT) has experimented with the recycling of roofing shingles in HMAC by constructing two test sections in 1994 and 1995. The source of the roofing shingles used in both test sections was waste generated by a roofing manufacturer; this generally consisted of discolored or damaged shingles. One test section was constructed on Chatham Parkway in Chatham County and one on State Route 21 in Effingham County. GAF Building Materials, Inc., located in Savannah, provided the waste shingle material; APAC Georgia, Inc., also located in Savannah, produced and placed these experimental mixtures. To date, both test sections are performing well compared with the unmodified control sections. Based on the performance of these test sections, shingle manufacturing waste is allowed as a recycling material in HMAC, just as reclaimed asphalt pavement is, for GDOT projects. A specification allowing postconsumer roofing shingle waste to be used is also being proposed.

Aggregate degradation during gyratory compaction may cause changes in the original gradation of the aggregate, and it may also affect volumetric requirements for Superpave Level I mix design. The effect of aggregate degradation on the design gradation and final volumetric properties of the asphalt mix compacted by the Superpave gyratory and Astec vibratory compactors was evaluated. Because vibratory compaction is an alternative compaction method that simulates field compaction, a vibratory compactor developed by Astec Industries, Inc., was used for comparison with the Superpave gyratory compactor. Aggregates with high and low Los Angeles abrasion losses were used to evaluate the effect of aggregate toughness or abrasion resistance on gradation change and volumetric properties. The changes in the amount of material passing the 0.075-mm sieve due to aggregate degradation during compaction were not significant enough to prevent specimens from meeting dust proportion requirements, regardless of whether low-or high-abrasion loss aggregates were used. A mix containing high-abrasion aggregate was less likely to meet restricted zone requirements than a mix using low-abrasion aggregate after degradation resulting from compaction.

Guidelines for the new hot-mix asphalt design system, Superpave, were developed under the Strategic Highway Research Program. One of the most controversial components of this system is the aggregate gradation restricted zone. This restricted zone was adopted as a gradation specification primarily to deter the use of high levels of natural sand in high-performance mixes. By designing mixes with gradations that avoid the restricted zone (i.e., limit natural sand), the internal strength provided by internal friction could be improved. Some agencies question the validity of the restricted zone. The specified gradations of many current mixes contain bands that enter the restricted zone, but the mixes have performed well for years in actual field conditions. The Georgia Department of Transportation (GDOT) currently specifies several standard mixes with gradations that enter the restricted zone and still perform well. These high-performance mixes contain good quality, 100 percent manufactured aggregates and no natural sand. GDOT recommends that the Georgia loaded wheel tester or some other proof tester be incorporated into the mix design process to screen mixes before rejecting them solely because their combined gradation enters the restricted zone. If mixes having combined gradations that enter the restricted zone are categorically rejected, mixes that are economical for the purpose intended may be rejected in the process.

In 1991, the Georgia Department of Transportation (GDOT) began to evaluate the production and placement of crumb rubber hot-mix asphalt. The crumb rubber mix (CRM) used by GDOT was produced by adding ground tire rubber to hot-mix asphalt using the wet process. A test section of CRM was placed on I-75 in Henry County, just south of Atlanta, consisting of a surface mix containing 6 percent crumb rubber by weight of asphalt cement (AC). The test section was evaluated from 1991 to 1995. The test section indicated that the CRM became very brittle over time, as indicated by a large increase in viscosity and decrease in penetration, and by a large amount of transverse reflective cracking. Compared with the control mix, the CRM did not reduce rutting and was more than twice as expensive to place. In addition to the test section, two contract projects were initiated using CRM. These two projects indicated that CRM could be produced and placed using conventional equipment requiring only a few modifications. On-site blending units were used to combine the crumb rubber at a dosage rate of 16 percent by weight of AC. Pump and metering equipment was modified to accurately meter the stiff asphalt material, and correction factors were established for determining the AC content by vacuum extraction, since some of the rubber particles were retained in the aggregate portion of the sample.

This report identifies improved test methods for determining laboratory mixing and compaction temperatures of modified and unmodified asphalt binders. The report will be of immediate interest to materials engineers in state highway agencies and the hot-mix asphalt (HMA) construction industry.

Sir John Eccles wrote that Descartes’ dualist-interactionism guided his scientific career, yet his scientific work reached far beyond the bounds of this or any other philosophical proposition. Indeed, the untestable, metaphysical foundation of dualism in all its forms conflict with scientific thinking. Thus, if Eccles had concentrated on spirit as distinct from matter, he would have positioned himself to discover a scientific theory of the self. To illustrate how this is possible, we compare such a theory–the Theory of Enformed Systems–with dualist-interactionism.

First, about fifty principles, rules, definitions, test methods, etc., are surveyed “from A to Z” under the heading “Real and Conceptual Tools: Definitions.” This is not a glossary of ESD terms but a limited list of those that are especially important to our approach; definitions of other terms, such as abbreviations for types of devices, can be found in textbooks on electronics.

First, take an hour to skim through the Appendix and read the abstracts and conclusions carefully. Note the locations of detailed information, e.g., description of test methods, for future reference.

By the Basic Rule, an ESDS item must always be in an SSZ. This SSZ will be in (1) an SSP, (2) an SSW, or (3) elsewhere under continuous operator supervision (paragraph 3.5.2 of Model Specification 1 in Chapter 9). An example of “elsewhere” is an open tote box being carried between SSWs by an operator whose wrist-strap cord is connected to an overhead grounded trolley.

First, let’s define “ESD.” Electrostatic discharge (ESD) means a discharge (flow of electrons) to or from a charge (deficit or surplus of electrons) that formerly had been static (immobile).

As of this writing, MIL-STD-1686, like many other government specifications and standards, may be on the way out (see Chapter 10). Some government contracts already exclude MIL-STD-1686 and, of course, it has never controlled commercial work. But watchdogs such as government agencies, not to mention critically minded customers, will continue to demand a well-documented ESD-control program. The purpose of this chapter is to sketch the paperwork required.

As mentioned at the start of Chapter 6, an ESDS item must always be in an SSZ. This chapter is concerned with the means of maintaining an SSZ inside an SSW.

Troubleshooting, by which we mean the solving of unique problems as they arise, is done using one or more of three approaches (analysis, standard test, or special test) with the aid of other real or conceptual tools from Chapter 4. In the following actual case histories, we describe each problem and state which of the above three approaches was used. Then we present the solution in enough detail to illustrate the reasoning process.

This is a vital subject when expensive products, e.g., modules worth $100,000 each, might have to be scrapped because of ESD damage that is measured or even only suspected.

This chapter includes several topics: reasons for an ESD-control program; history of ESD control and purpose of this chapter; objectives and overview of program; what? when? and how?; cost-effectiveness; plan of action; the enforcement problem; advice to small companies; the role of the program coordinator; and safety.

This model was born in 1974 with the proposal by Speakman that a part such as an integrated circuit might be damaged or destroyed by rapid discharge of static electricity accumulated on the part’s own body (Ref. 5-1). In 1980, the CDM was judged the predominant failure mode at AT&T, as typified by dual-in-line packages (DIPs) sliding within their plastic packaging tubes to become triboelectrically charged with most of the charge residing on the lead frame (Ref. 5-2). In 1992, it was said, “It has become clear in the past five years that the CDM, not the HBM, is responsible for the vast majority of ESD damage, certainly to discrete devices and probably to entire circuit cards and assemblies” (Ref. 5-3). Reflecting industry concern about the CDM, certain packaging materials are now being advertised as “CDM-safe.”

Summary A thermomagnetic balance has been constructed which enables gasmixing and continuous monitoring of oxygen fugacity. By means of this system, f(O2)'s can be varied from about 10−3 to 10−28 atmosphere, making it possible to adequately maintain almost all magnetic or potentially magnetic minerals in their stability fields throughout the experiment, or to vary the oxygen fugacity so as to obtain a special result. The system is easy to use and the difficulties inherent in a vacuum system are avoided. Moreover, because of the small sample size, the duration of the experiment is short.

Electropotential differences between the cell interior and the external medium have been studied with intracellular microelectrodes in ovarian oocytes, ovulated unfertilized eggs and fertilized eggs of R. pipiens. In ovarian oocytes the cytoplasm was 50 to 80 mV negative, relative to isotonic Ringer's solution. In contrast, electrode penetration of the oocyte nucleus in situ indicated that the nucleoplasm was about 25 mV positive, relative to the cytoplasm. After ovulation, the cortical cytoplasm became 20 to 50 mV positive with regard to an external solution of 0.1 strength Ringer's solution (ca. pond water). Penetration of the cytoplasm at levels from 0.3 to 0.6 mm below the egg surface revealed an inner zone with a potential which was about 15 mV negative, relative to the cortical cytoplasm. A slow hyperpolarization of the cortical membrane occurred at activation, with the potential returning to that of the ovulated unfertilized egg within ten minutes. After fertilization, the egg cytoplasm remained positive until the first cleavage. As division proceeded, the cytoplasm slowly depolarized and became 50 to 60 mV negative, relative to 0.1 strength Ringer's solution.

A reverse-to-normal geomagnetic transition has been recorded in a sequence of Late Miocene volcanics dated at about 15 my in the Santa Rosa Range, northcentral Nevada. This transition, probably the same as that previously described in southern Oregon, exhibits large-scale east-west oscillations of the local field directions. A composite transition path, made by combining those of Oregon and Nevada, is sufficiently complete to permit analysis of the relative contributions of the dipole and non-dipole components during the reversal through mathematical modeling. Conclusions are that the non-dipole components predominated for most of the transition period and that the best estimate of the minimum time required for the reversal is 2000 yr.

Since the discovery of the phenomenally high urea content of the body fluids of cartilaginous fishes by Staedeler and Frerichs (1858), the unique osmoregulatory system of this vertebrate class has been studied by many investigators. In broad outline, the mechanisms are essentially similar in all three of the major subtaxa: the selachians, the batoids, and the holocephalans. A single exception is the genus Potamotrygon (fresh-water stingrays of South America and Africa), which has apparently lost the ability to concentrate urea even when transferred to salt water (Thorson, Cowan, and Watson 1967; Thorson 1970; Goldstein and Forster 1971b). Since the Chondrichthyes are primarily marine animals, research on them has centered mainly upon marine species, either in their natural environment or following transfer to various dilutions of seawater. These studies have been reviewed by Smith (1931b, 1936)

All previously reported species of Chondrichthyes, from both marine and fresh water, have contained urea at concentrations ranging from about 300 to 1300 milligrams of urea nitrogen per 100 milliliters of fluid. Body fluids from two species of Potamotrygon, permanent residents of the Amazon basin, contained only 2 to 3 milligrams of urea nitrogen per 100 milliliters. Although they have abandoned the retention of urea exhibited by other chondrichthyans, the extent to which they have lost the mechanisms of retaining and tolerating urea in a hypertonic medium has not been determined.

A precision constant-current supply designed to deliver up to 600 mA at 18 V dc is described. Short-term stability (

Electrophysiological studies using micro-electrodes have shown that the blastocoel fluid of the Rana pipiens embryo was 35 to 40 mV positive with respect to an external solution of 0.1 strength Ringer's. There was no significant change in potential difference from developmental stage 8 to stage 10. Replacement of external sodium ion with choline ion was followed by a slow decrease in potential suggesting that the potential is a result of sodium transfer from the medium into the blastocoel fluid. The potential was also sensitive to antidiuretic hormone, increasing 20 per cent when 10 milli- units of Pitressin were added per ml of medium. The results suggest that the late blastula and early gastrula have a mechanism for accumulating sodium from a low external concentration similar to that reported for adult frog skin.

Electropotential differences between the cytoplasm and external medium have been compared in the mature R. pipiens occyte and the ovulated unfertilized egg as a function of [Na]o, [K]o, [Ca]o and [Cl]o. In solutions containing 1.0 mM Ca++ the oocyte behaved as though it were predominantly permeable to K+ and Cl−, i.e., like a KCl electrode. However, the steady potential decreased with decreasing [Ca]o and in 5 × 10−4 mM [Ca]o the oocyte membrane behaved like a NaCl electrode. Studies on the steady potential as a function of [Na]o, [K]o and [Cl]o in 1.0 mM Ca++ or Ca-free solutions suggest that Ca++ controls the passive permeability of the oocyte membrane to Na+ and Cl−. In the ovulated unfertilized egg the K+ selectivity of the cell membrane disappeared and the system behaved like a NaCl electrode. No effect of external Ca++ or K+ concentration changes on the steady potential was observed. These results indicate that the ion permeability properties of the ovulated egg are similar to that of the ovarian oocyte in Ca-deficient medium, and suggests that the mechanism of ovulation may involve the removal of Ca++ regulation of ion permeability of the egg cell membrane.

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