43,343 research outputs found
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Multi-Material Ultrasonic Consolidation
Ultrasonic consolidation (UC) is a recently developed direct metal solid freeform
fabrication process. While the process has been well-demonstrated for part fabrication in Al alloy
3003 H18, including with intricate cooling channels, some of the potential strengths of the
process have not been fully exploited. One of them is its flexibility with build materials and the
other is its suitability for fabrication of multi-material and functionally graded material parts with
enhanced functional or mechanical properties. Capitalizing on these capabilities is critical for
broadening the application range and commercial utilization of the process. In the current work,
UC was used to investigate ultrasonic bonding of a broad range of engineering materials, which
included stainless steels, Ni-base alloys, brass, Al alloys, and Al alloy composites. UC multimaterial part fabrication was examined using Al alloy 3003 as the bulk part material and the
above mentioned materials as performance enhancement materials. Studies were focused on
microstructural aspects to evaluate interface characteristics between dissimilar material layers.
The results showed that most of these materials can be successfully bonded to Al alloy 3003 and
vice versa using the ultrasonic consolidation process. Bond formation and interface
characteristics between various material combinations are discussed based on oxide layer
characteristics, material properties, and others.Mechanical Engineerin
Children's suggestibility in relation to their understanding about sources of knowledge
In the experiments reported here, children chose either to maintain their initial belief about an object's identity or to accept the experimenter's contradicting suggestion. Both 3â to 4âyearâolds and 4â to 5âyearâolds were good at accepting the suggestion only when the experimenter was better informed than they were (implicit source monitoring). They were less accurate at recalling both their own and the experimenter's information access (explicit recall of experience), though they performed well above chance. Children were least accurate at reporting whether their final belief was based on what they were told or on what they experienced directly (explicit source monitoring). Contrasting results emerged when children decided between contradictory suggestions from two differentially informed adults: Threeâ to 4âyearâolds were more accurate at reporting the knowledge source of the adult they believed than at deciding which suggestion was reliable. Decision making in this observation task may require reflective understanding akin to that required for explicit source judgments when the child participates in the task
Are cocaine-seeking âhabitsâ necessary for the development of addiction-like behavior in rats?
Drug self-administration models of addiction typically require animals to make the same response (e.g., a lever-press or nose-poke) over and over to procure and take drugs. By their design, such procedures often produce behavior controlled by stimulus-response (S-R) habits. This has supported the notion of addiction as a âdrug habitâ, and has led to considerable advances in our understanding of the neurobiological basis of such behavior. However, for addicts to procure drugs, like cocaine, often requires considerable ingenuity and flexibility in seeking behavior, which, by definition, precludes the development of habits. To better model drug-seeking behavior in addicts we first developed a novel cocaine self-administration procedure (the Puzzle Self-Administration Procedure; PSAP) that required rats to solve a new puzzle every day to gain access to cocaine, which they then self-administered on an Intermittent Access (IntA) schedule. Such daily problem-solving precluded the development of S-R seeking habits. We then asked whether prolonged PSAP/IntA experience would nevertheless produce âsymptoms of addictionâ. It did, including escalation of intake, sensitized motivation for drug, continued drug use in the face of adverse consequences and very robust cue-induced reinstatement of drug-seeking, especially in a subset of âaddiction-proneâ rats. Furthermore, drug-seeking behavior continued to require dopamine neurotransmission in the core of the nucleus accumbens (but not the dorsolateral striatum). We conclude that the development of S-R seeking habits is not necessary for the development of cocaine addiction-like behavior in rats
Field research on the spectral properties of crops and soils, volume 1
The experiment design, data acquisition and preprocessing, data base management, analysis results and development of instrumentation for the AgRISTARS Supporting Research Project, Field Research task are described. Results of several investigations on the spectral reflectance of corn and soybean canopies as influenced by cultural practices, development stage and nitrogen nutrition are reported as well as results of analyses of the spectral properties of crop canopies as a function of canopy geometry, row orientation, sensor view angle and solar illumination angle are presented. The objectives, experiment designs and data acquired in 1980 for field research experiments are described. The development and performance characteristics of a prototype multiband radiometer, data logger, and aerial tower for field research are discussed
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Improving Linear Weld Density in Ultrasonically Consolidated Parts
Ultrasonic consolidation is a novel additive manufacturing process with immense
potential for fabrication of complex shaped three-dimensional metallic objects from metal foils.
The proportion of bonded area to unbonded area along the layer interface, termed linear weld
density (LWD), is perhaps the most important quality attribute of ultrasonically consolidated
parts. Part mechanical properties largely depend on LWD and a high level of LWD must be
ensured in parts intended for load-bearing structural applications. It is therefore necessary to
understand what factors influence LWD or defect formation and devise methods to enhance bond
formation during ultrasonic consolidation. The current work examines these issues and proposes
strategies to ensure near 100% LWD in ultrasonically consolidated aluminum alloy 3003 parts.
The work elucidates the effects of various process parameters on LWD and a qualitative
understanding of the effects of process parameters on bond formation during ultrasonic
consolidation is presented. The beneficial effects of using elevated substrate temperatures and its
implications on overall manufacturing flexibility are discussed. A preliminary understanding of
defect morphologies and defect formation is presented, based on which a method (involving
surface machining) for minimizing defect incidence during ultrasonic consolidation is proposed
and demonstrated. Finally, trade-offs between part quality and build time are discussed.Mechanical Engineerin
Large-scale educational telecommunications systems for the US: An analysis of educational needs and technological opportunities
The needs to be served, the subsectors in which the system might be used, the technology employed, and the prospects for future utilization of an educational telecommunications delivery system are described and analyzed. Educational subsectors are analyzed with emphasis on the current status and trends within each subsector. Issues which affect future development, and prospects for future use of media, technology, and large-scale electronic delivery within each subsector are included. Information on technology utilization is presented. Educational telecommunications services are identified and grouped into categories: public television and radio, instructional television, computer aided instruction, computer resource sharing, and information resource sharing. Technology based services, their current utilization, and factors which affect future development are stressed. The role of communications satellites in providing these services is discussed. Efforts to analyze and estimate future utilization of large-scale educational telecommunications are summarized. Factors which affect future utilization are identified. Conclusions are presented
On the controversy concerning the definition of quark and gluon angular momentum
A major controversy has arisen in QCD as to how to split the total angular
momentum into separate quark and gluon contributions, and as to whether the
gluon angular momentum can itself be split, in a gauge invariant way, into a
spin and orbital part. Several authors have proposed various answers to these
questions and offered a variety of different expressions for the relevant
operators. I argue that none of these is acceptable and suggest that the
canonical expression for the momentum and angular momentum operators is the
correct and physically meaningful one. It is then an inescapable fact that the
gluon angular momentum operator cannot, in general, be split in a gauge
invariant way into a spin and orbital part. However, the projection of the
gluon spin onto its direction of motion i.e. its helicity is gauge invariant
and is measured in deep inelastic scattering on nucleons. The Ji sum rule,
relating the quark angular momentum to generalized parton distributions, though
not based on the canonical operators, is shown to be correct, if interpreted
with due care. I also draw attention to several interesting aspects of QED and
QCD, which, to the best of my knowledge, are not commented upon in the standard
textbooks on Field Theory.Comment: 41 pages; Some incorrect statements have been rectified and a
detailed discussion has been added concerning the momentum carried by quarks
and the Ji sum rule for the angular momentu
Atlas of soil reflectance properties
A compendium of soil spectral reflectance curves together with soil test results and site information is presented in an abbreviated manner listing those soil properties most important in influencing soil reflectance. Results are presented for 251 soils from 39 states and Brazil. A narrative key describes relationships between soil parameters and reflectance curves. All soils are classified according to the U.S. soil taxonomy and soil series name for ease of identification
Quasiperiodicity and non-computability in tilings
We study tilings of the plane that combine strong properties of different
nature: combinatorial and algorithmic. We prove existence of a tile set that
accepts only quasiperiodic and non-recursive tilings. Our construction is based
on the fixed point construction; we improve this general technique and make it
enforce the property of local regularity of tilings needed for
quasiperiodicity. We prove also a stronger result: any effectively closed set
can be recursively transformed into a tile set so that the Turing degrees of
the resulted tilings consists exactly of the upper cone based on the Turing
degrees of the later.Comment: v3: the version accepted to MFCS 201
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