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Tethered Chains in Poor Solvent Conditions: An Experimental Study Involving Langmuir Diblock Copolymer Monolayers
No full textWe have employed Langmuir monolayer of highly asymmetric polydimethylsiloxane- polystyrene (PDMS-PS) diblock copolymers on dioctyl phthalate (DOP) at temperatures ranging from 22 "C to -35 `C as a model system for tethered chains in poor solvent conditions. The thicknesses of the tethered PS layers extending into the DOP subphase, measured by neutron reflection, decrease with decreasing temperature (T) over this entire r~ge. However, the v~iation with T becomes weak below -20 "C. At the ]owest T, the layer thicknesses are contracted 55 % -75 `% of their values at the theta condition (T8 = 22 "C), but are still quite swollen compared to the fully collapsed, nonsolvent limit. The contraction of the layer with decreasing T is determined as a function of surface density and molecular weight. These data are compared to universal scaling forms. The PS segments are depleted from the air surface over the entire T range, the thickness of the depletion layer increasing slightly with decreasing T. The free energy of the surface layer is probed by surface tension measurements. Negative surface pressures are observed at low coverages for both PDMS-PS and PDMS monolayer, indicating metastability toward lateral phase separation. Evidence for a trruisition from a dispersed phase to a condensed phase with decreasing T was observed in the reflectivity at very low PDMS-PS coverage
Massively Parallel Linear Stability Analysis with P_ARPACK for 3D Fluid Flow Modeled with MPSalsa
No full textWe are interested in the stability of three-dimensional fluid flows to small dkturbances. One computational approach is to solve a sequence of large sparse generalized eigenvalue problems for the leading modes that arise from discretizating the differential equations modeling the flow. The modes of interest are the eigenvalues of largest real part and their associated eigenvectors. We discuss our work to develop an effi- cient and reliable eigensolver for use by the massively parallel simulation code MPSalsa. MPSalsa allows simulation of complex 3D fluid flow, heat transfer, and mass transfer with detailed bulk fluid and surface chemical reaction kinetics
Self-Organized Growth of Alloy Superlattices
No full textWe predict theoretically and demonstrate experimentally the spontaneous formation of a superlattice during crystal growth. When a strained alloy grows by "step flow", the steps at the surface form periodic bunches. The resulting modulated strain biases the incorporation of the respective alloy components at different steps in the bunch, leading to the formation of a superlattice. X-ray diffraction and electron microscopy for SiGe grown on Si give clear evidence for such spontaneous superlattice formation
An automatic coastline detector for use with SAR images
No full textSAR imagery for coastline detection has many potential advantages over conventional optical stereoscopic techniques. For example, SAR does not have restrictions on being collected during daylight or when there is no cloud cover. In addition, the techniques for coastline detection witth SAR images can be automated. In this paper, we present the algorithmic development of an automatic coastline detector for use with SAR imagery. Three main algorithms comprise the automatic coastline detection algorithm, The first algorithm considers the image pre-processing steps that must occur on the original image in order to accentuate the land/water boundary. The second algorithm automatically follows along the accentuated land/water boundary and produces a single-pixel-wide coastline. The third algorithm identifies islands and marks them. This report describes in detail the development of these three algorithms. Examples of imagery are used throughout the paper to illustrate the various steps in algorithms. Actual code is included in appendices. The algorithms presented are preliminary versions that can be applied to automatic coastline detection in SAR imagery. There are many variations and additions to the algorithms that can be made to improve robustness and automation, as required by a particular application
Simulations of the Penetration of 6061-T6511 Aluminum Targets by Spherical-Nosed VAR 4340 Steel Projectiles
No full textIn certain penetration events it is proposed that the primary mode of deformation of the target can be approximated by known analytical expressions. In the context of an analysis code, this approximation eliminates the need for discretizing the target as well as the need for a contact algorithm. Thus, this method substantially reduces the computer time and memory requirements. In this paper a forcing function which is derived from a spherical-cavity expansion (SCE) analysis has been implemented in a transient dynamic finite element code. This irnplementation is capable of computing the structural and component responses of a projectile due to a three dimensional penetration event. Simulations are presented for 7.1 l-mm-diameter, 74.7-mm-long, spherical-nose, vacuum- arc-remelted (VAR) 4340 steel projectiles that penetrate 6061-T6511 aluminum targets. Final projectile configurations obtained from the simulations are compared with post-test radiographs obtained from the corresponding experiments. It is shown that the simulations accurately predict the permanent projectile deformation for three dimensional loadings due to incident pitch and yaw over a wide range of striking velocities
Micromachine Wedge Stepping Motor
No full textA wedge stepping motor, which will index a mechanism, has been designed and fabricated in the surface rnicromachine SUMMiT process. This device has demonstrated the ability to index one gear tooth at a time with speeds up to 205 teeth/see. The wedge stepper motor has the following features, whi:h will be useful in a number of applications. o The ability to precisely position mechanical components. . Simple pulse signals can be used for operation. o Only 2 drive signals are requixed for operation. o Torque and precision capabilities increase with device size . The device to be indexed is restrained at all times by the wedge shaped tooth that is used for actuation. This paper will discuss the theory of operation and desi=m of the wedge stepping motor. The fabrication and testing of I he device will also be presented
Reformulation of Elasticity Theory for Discontinuities and Long-Range Forces
No full textSome materials may naturally form discontinuities such as cracks as a result of deformation. As an aid to the modeling of such materials, a new framework for the basic equations of continuum mechanics, called the "peridynamic" formulation, is proposed. The propagation of linear stress waves in the new theory is discussed, and wave dispersion relations are derived. Material stability and its connection with wave propagation is investigated. It is demonstrated by an example that the reformulated approach permits the solution of fracture problems using the same equations either on or off the crack surface or crack tip. This is an advantage for modeling problems in which the location of a crack is not known in advance
Task 1.13 - Data Collection and Database Development for Clean Coal Technology By-Products Characteristics and Management Practices
No full textInformation from DOE projects and commercial endeavors in fluidized-bed combustion (FBC) and coal gasification is the focus of the task reported here. The primary goal is to provide an easily accessible compilation of characterization information on the by-products from these processes to government agencies and industry to facilitate sound regulatory and management decisions. Additional written documentation will facilitate the preparation of an updated final version of the DOE report to Congress on barriers to CCB utilization. The information assembled will be valuable to the U.S. Environmental Protection Agency (EPA) in its upcoming decision on the waste status of FBC by-products and had to be submitted to EPA by April 1997. This effort facilitates interaction between DOE and industry regarding input to EPA. The effort of DOE FETC to provide this type of information to EPA is consistent with the recommendation in the DOE Report to Congress on ash barriers that a determination placing CCT by-products under RCRA Subtitle D for solid wastes is needed if these materials are to be utilized. Several DOE projects have already investigated utilization of these materials, so this is an opportunity to give this information the emphasis it deserves
Atomic Structure and Properties of Extended Defects in Silicon
No full textThe Z-contrast technique represents a new approach to high-resolution electron microscopy allowing for the first time incoherent imaging of materials on the atomic scale. The key advantages of the technique, an intrinsically higher resolution limit and directly interpretable, compositionally sensitive imaging, allow a new level of insight into the atomic configurations of extended defects in silicon. This experimental technique has been combined with theoretical calculations (a combination of first principles, tight binding, and classical methods) to extend this level of insight by obtaining the energetic and electronic structure of the defects
Closure Report for CAU No. 430: Buried Depleted Uraniuim Artillery Round No. 1, Tonopah Test Range, Revision 0
No full text1.1 Purpose This Closure Report presents the information obtained from investigative actions performed to justify the decision for clean closure of CAU 430 through "No Further Action." The investigative actions were performed per the Streamlined Approach for Environmental Restoration Plan, CA UNO. 430: Buried Depleted Uranium Artille~ Round No. 1, Tonopah Test Range (DOE/NV, 1996a) (hereafter referred to as the SAFER Plan). The Buried DU Artillery Round No. 1 is located approximately 1.1 kilometers (km) (0.7 mile [mi]) south of Avenue 13 in the test area south of Area 9 (Figure 1-2). The site was thought to consist of a potentially unexploded W-79 Joint Test Assembly (JTA) test artillery projectile with high explosives (HE) and DU. The DU was substituted for Special Nuclear Material to prevent a nuclear explosion and yet retain the physical characteristics of uranium for ballistic and other mechanical tests. The projectile was reportedly buried in one pit, approximately 5 to 10 feet (ft) deep (Smith, 1993; Smith, 1996; Quas, 1996). The exact location of the burial pit is unknown; however, three disturbed areas (Sites A, B, and C) were identified through geophysical surveys, site visits, and employee interviews as possible locations of the test projectile (Figure 1-3). Results of the investigation are summarized within this Closure Report. Additional information about the site and investigation activities may be found in the SAFER Plan (DOE/NV, 1996a). 1.2 Scope The objectives of the SAFER Plan (DOE/NV, 1996a) activities were to prepare the site for closure through locating and identi~ing the projectile (Buried DU Artillery Round No. 1), destroying the projectile and any remaining components, collecting soil samples to detect residual contamination resulting from projectile destruction, and finally, remediating residual contamination