Effect of Laser Processing Parameters on the Formation of Intermetallic Compounds in Fe-Al Dissimilar Welding

Fusion welding of steel to aluminum is difficult due to formation of different types of Fe-Al intermetallics (IMs). In this work, 2 mm-thick steel was joined to 6 mm aluminum in overlap configuration using a 8 kW CW fiber laser. A defocused laser beam was used to control the energy input and allow melting of the aluminum alone and form the bond by wetting of the steel substrate. Experimentally, the process energy was varied by changing the power density (PD) and interaction time separately to understand the influence of each of these parameters on the IM formation. It was observed that the IM formation is a complex function of PD and interaction time. It was also found that the mechanical strength of such joint could not be simply correlated to the IM layer thickness but also depends on the area of wetting of the steel substrate by molten aluminum. In order to form a viable joint, PD needs to be over a threshold value where although IM growth will increase, the strength will be better due to increased wetting. Any increase in interaction time, with PD over the threshold, will have negative effect on the bond strength.     

Non-linear unit root properties of crude oil production

While there is good reason to expect crude oil production to be non-linear, previous studies that have examined the stochastic properties of crude oil production have assumed that crude oil production follows a linear process. If crude oil production is a non-linear process, conventional unit root tests, which assume linear and systematic adjustment, could interpret departure from linearity as permanent stochastic disturbances. The objective of this paper is to test for non-linearities and unit roots in crude oil production. To realize our objective, this study applies a threshold autoregressive model with an autoregressive unit root to monthly crude oil production for 17 OPEC and non-OPEC countries over the period January 1973 to December 2007. Specifically, first we test for the presence of non-linearities (threshold effects) in the production of crude oil in two regimes. Second, we test for a unit root against a non-linear stationary process in two regimes and a partial unit root process when the unit root is present in one regime only. We find that crude oil production is characterized by threshold effects. We find that for eleven of the countries a unit root was present in both regimes, while for the others a partial unit root was found to be present in either the first regime or second regime.     

On the power of deep pushdown stacks

Inspired by recent work of Meduna on deep pushdown automata, we consider the computational power of a class of basic program schemes, NPSDS _s , based around assignments, while-loops and non-deterministic guessing but with access to a deep pushdown stack which, apart from having the usual push and pop instructions, also has deep-push instructions which allow elements to be pushed to stack locations deep within the stack. We syntactically define sub-classes of NPSDS _s by restricting the occurrences of pops, pushes and deep-pushes and capture the complexity classes NP and PSPACE. Furthermore, we show that all problems accepted by program schemes of NPSDS _s are in EXPTIME.     

Design Guidelines for Polyethylene Pipe Interface Shear Resistance

Polyethylene pipes are commonly used in pipeline systems. Current methods used to determine the pipe pullout capacity do not consider the effects of diameter changes and cyclic movements that the pipelines may experience. Laboratory tests were performed to study the interface shearing resistance of polyethylene pipes under varying conditions. The tests were performed in a temperature-controlled room, where properties were investigated for thermal variations expected in the field. Two types of tests were performed: pull/push tests and cyclic tests. Test results indicated that reductions in pipe diameter affect the interface shear resistance that develops between the pipe and soil. As the pipe diameter gets smaller, the normal contact stresses at the interface decreases, causing a reduction in the interface shearing resistance directly proportional to the normal stress changes. Cyclic pipe movements also cause significant reduction in pipe pullout resistance. The test results indicated that the polyethylene pipe interface shear resistance can be significantly lower than the one determined using the current methods. This paper presents the test results, findings, and design recommendations for the pullout resistance of buried polyethylene pipes.     

Blood lead (Pb) levels: Further evidence for an environmental mechanism explaining the association between socioeconomic status and psychophysiological dysregulation in children.

Objective: The authors recently reported that blood lead (Pb) was a significant mediator for the positive association between socioeconomic status (SES) and peripheral vascular responses to acute stress in children (B. B. Gump et al., 2007). The present study considers the possibility that Pb may also mediate an association between SES and cortisol responses to acute stress. Design: Early childhood Pb exposure was tested as a mediator for cross-sectional associations between SES and cortisol responses. Main Outcome Measures: The primary outcome was cortisol responses to acute stress in 9.5-year-old children (N = 108). Results: Lower family income was associated with significantly greater cortisol levels following an acute stress task. A mediational analysis confirmed that Pb was a significant mediator for this association. Conclusion: These results reaffirm the importance of considering the chemical environment as well as social and psychological environment when evaluating psychophysiological effects of low SES. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Absorption isotherms for H2(D2)–Pd0.8Ag0.2 (198–323 K)

Isotherms for H₂/D₂–Pd_0.8Ag_0.2 systems have been measured over a low temperature range, 198–323 K. Such low temperature data for this system have not been obtained previously. The absorption kinetics was found to be fast. The isotherms at low temperatures are compared with literature values at or above 313 K, as well as those for H₂(D₂)–Pd systems. The H/D isotope effect and the separation factors in the plateau range over Pd_0.8Ag_0.2 are calculated at various temperatures and discussed, based on the isotherms. Enthalpies are extracted from van’t Hoff plots and compared with calorimetric values and the results from the literature for both absorption and desorption processes. A method is given for using isotherm information from single isotope systems to estimate the separation factor for the mixed isotope systems and this is a helpful tool.The challenge of measuring absorption isotherms at low temperatures and low pressures is discussed. Sample pre-treatment, non-soluble impurity accumulation in an absorption process and thermal transpiration effects are examined.     

NMR SPECTROSCOPY IN THE CHARACTERIZATION OF EIGHT SELECTED ASPHALTS

ABSTRACT

Nuclear Magnetic Resonance (NMR) spectroscopy has been used to partially characterize eight selected asphalts. This report describes the initial efforts in this endeavor. Proton and carbon spectra have been collected and analyzed for percent aromatic content as well as aromatic substitution. DEFT results, chemical shifts and literature precedent have been used to assign the major resonances in the aliphatic region to chemical entities. Finally, using elemental analysis data, molecular weight data and NMR results, average structures for the eight asphalts have been derived     

Chinook salmon and rainbow trout catch and temperature distributions in Lake Ontario

We determined the distributions of Chinook salmon and rainbow trout by describing seasonal mean vertical and bathymetric catch depths from 1997 to 2005 using angler creel surveys. We developed and applied a cross-validated model of Lake Ontario temperatures to determine the water temperatures associated with these distributions. During April, Chinook salmon and rainbow trout were found nearshore at a bathymetric depth of 20 m. However, rainbow trout were caught at shallower vertical depths (4 to 6 m) than Chinook salmon (8 to 10 m). Both species moved deeper and farther offshore during May, June, and July. Vertical catch depths were similar, but rainbow trout were found further offshore (40 to 65 m bathymetric depth) than Chinook salmon (35 to 50 m bathymetric depth) during June, July and August. During September, Chinook salmon moved closer to shore (25 to 35 m bathymetric depth) and to shallower depths (9 to 12 m), consistent with river mouth staging associated with spawning. Rainbow trout remained offshore (45 to 60 m bathymetric depth) in deeper water (11 to 16 m). The species occupied significantly different spatial habitats during April, August, and September. Mean catch temperatures of both species were similar and increased seasonally to 13 to 14 °C during August and September. Rainbow trout were caught at cooler temperatures than Chinook salmon during June and July. The estimated temperature distributions agree with independent field studies but are different then previously assumed in bioenergetic models.     

A Plan for the Development of Fusion Energy

This is the final report of a panel set up by the U.S. Department of Energy (DOE) Fusion Energy Sciences Advisory Committee (FESAC) in response to a charge letter dated September 10, 2002 from Dr. Ray Orbach, Director of the DOE's Office of Science. In that letter, Dr. Orbach asked FESAC to develop a plan with the end goal of the start of operation of a demonstration power plant in approximately 35 years. This report, submitted March 5, 2003, presents such a plan, leading to commercial application of fusion energy by mid-century. The plan is derived from the necessary features of a demonstration fusion power plant and from the time scale defined by President Bush. It identifies critical milestones, key decision points, needed major facilities and required budgets. The report also responds to a request from DOE to FESAC to describe what new or upgraded fusion facilities will best serve our purposes over a time frame of the next twenty years.