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1.
The performance and lifetime of micro electro mechanical systems (MEMS) is strongly affected by friction and wear. We therefore
analysed the friction and wear characteristics of microstructures produced by the LIGA-process. The measurements were carried
out in a special designed microtribometer, which is capable to work inside a scanning electron microscope (SEM), and hence
offering the possibility of a high resolution in-situ observation of the microscopic tribological mechanism during operation
of the system.
The material combinations investigated were chosen in order to represent the most important tribological junctions occurring
in the ‘micro-motor’ and ‘micro-turbine’ currently produced by the LIGA-technique. We studied the tribological properties
of nickel-nickel micro components (LIGA-side-wall/LIGA-sidewall and LIGA-bottom side/LIGA-top side), as well as nickel micro
components (bottom side)-Al2O3-ceramic substrates (contact between rotor-base).
The results indicate a strong influence of the relative humidity level (RHL) on the friction and wear properties of the metal/ceramic
as well as of the metal/metal contacts appearing in the LIGA-MEMS, showing the lowest level of friction and wear at high RHL-values.
We also found out that the friction and wear parameters were highly influenced by the applied surface pressure. Changing the
surface pressure results in the formation of different kinds of wear debris accumulating or smearing out in the wear track.
The metal oxides produced hereby in the wear track can lower adhesion and thus reduce the friction of the system. 相似文献
2.
T. Bieger 《Microsystem Technologies》1997,3(4):155-163
The performance and lifetime of micro electro mechanical systems (MEMS) is strongly affected by friction and wear. Because
of the restrictions due to the fabrication process the variety of materials used for micro systems is not very manifold. This
results often is very poor tribological properties, since the tribological pairings are disadvantageous with regard to friction
and especially wear. We therefore investigated materials which can be fabricated by the process currently used for LIGA-microstructures,
and have the potential of better properties concerning friction and wear. The results of our tribologic experiments showed,
that nickel phosphorous alloys are a promising material for microsystems suffering wear, especially at high surface pressures
(high loading). Their absolute values of the wear intensity, are at least one order of magnitude lower than those of nickel
and copper, which are the materials mostly used today.
Received: 27 June 1996/Accepted:12 July 1996 相似文献
3.
R. Bandorf H. Lüthje K. Schiffmann T. Staedler A. Wortmann 《Microsystem Technologies》2002,8(1):51-54
This paper deals with the fabrication and characterisation of friction and wear reduced nano-films for micro actuator applications.
For this investigation films of diamond-like-carbon (DLC), metal doped Me-DLC, carbon-nitride CN
x
, boron-nitride BN and alumina Al2O3 films have been applied in the thickness range of 20–500 nm. The hardness of those coatings varied between 10 and 60 GPa.
Micromechanical and microtribological properties of nano-coatings have been characterized by a modified scanning probe microscope.
Besides this a novel micro tester for abrasive wear measurement of nano coatings was used. Friction of micro-contact areas
was measured by use of a pin-on-disc tester. It turned out, that friction was – besides other parameters – dependent on determination
method and load. Friction determined at areal DLC/DLC contact zones was generally much higher (μDLC 0.1) than diamond tip versus DLC (∼μ
DLC
0.06).
Received: 19 June 2001/Accepted: 15 September 2001 相似文献
4.
The miniaturisation of mechanical components and machines enables innovative future products. However, for the improvement of functionality, reliability and lifetime of those micro systems, micro tribological coatings with thicknesses in the sub-micron range are needed. To cover these needs, we investigated different submicron coatings with the aim to develop wear and friction optimized thin films for this application. The basis of this work has been the state of the art know how of well established macroscopic coatings which in general are in a thickness range of a few micrometers. It turned out, that particularly the surface topography and the substrate material influence the properties of very thin films. For investigations with single asperity contact, the coefficient of friction (COF) was reduced by lowering the tip radius and the hardness of the substrate material. In contrast, for larger contact radii (pin-on-disc), an increase of the COF with decreasing substrate Youngs modulus was found. With respect to wear, it turned out that the wear depth increased dramatically with increasing initial surface roughness (Ra).The authors gratefully acknowledge the financial support of the German Research Foundation by grant SFB 516. We also thank T. Staedler and A. Wortmann for their contributions through their respective PhD Theses on this topic. 相似文献
5.
Fabrication by the ‘Laser-LIGA’ process of three-dimensional structures for micro-fluidic devices is investigated. Polymer
moulds are formed by projection ablation using an excimer laser operating at 248 nm wavelength. The moulds are replicated
by electroforming –as in conventional X-ray LIGA – to produce fixed and freely moving nickel microturbine parts with heights
of 150 μm, wall angles of 1.5° from vertical and surface roughnesses below 100 nm.
Received: 30 October 1995/Accepted: 4 March 1996 相似文献
6.
R. Küster R. Bandorf C. Henke H. Lüthje J.-H. Sick C. Neumeister A. Phataralaoha S. Büttgenbach H. H. Gatzen G. Bräuer 《Microsystem Technologies》2006,12(7):680-684
In this work the possibilities for the reduction of friction and wear in micro electro-mechanical systems (MEMS) are investigated. An improvement of the tribological behaviour of microsystems can be realized by optimizing the contact condition and by application of special coatings with low friction and low wear rates. For optimizing the contact condition a defined topography and surface profile is generated by photolithography. Furthermore tribological coatings with low friction and low wear rates are developed and investigated using nanoindentation and micro scratch experiments. Also novel results on micro structured surfaces coated with a-C:H and a-C films will be discussed. The results show the great potential of carbon-based coatings in combination with an optimized geometrical surface design. 相似文献
7.
Particular cases of nonlinear systems of delay Volterra integro-differential equations (denoted by DVIDEs) with constant delay
τ > 0, arise in mathematical modelling of ‘predator–prey’ dynamics in Ecology. In this paper, we give an analysis of the global
convergence and local superconvergence properties of piecewise polynomial collocation for systems of this type. Then, from
the perspective of applied mathematics, we consider the Volterra’s integro-differential system of ‘predator–prey’ dynamics
arising in Ecology. We analyze the numerical issues of the introduced collocation method applied to the ‘predator–prey’ system
and confirm that we can achieve the expected theoretical orders of convergence.
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8.
This article offers a research update on a 3-year programme initiated by the Kamloops Art Gallery and the University College
of the Cariboo in Kamloops, British Columbia. The programme is supported by a ‘Community–University Research Alliance’ grant
from the Social Sciences and Humanities Research Council of Canada, and the collaboration focuses on the cultural future of
small cities – on how cultural and arts organisations work together (or fail to work together) in a small city setting. If
not by definition, then certainly by default, ‘culture’ is associated with big city life: big cities are equated commonly
with ‘big culture’; small cities with something less. The Cultural Future of Small Cities research group seeks to provide
a more nuanced view of what constitutes culture in a small Canadian city. In particular, the researchers are exploring notions
of social capital and community asset building: in this context, ‘visual and verbal representation’, ‘home’, ‘community’ and
the need to define a local ‘sense of place’ have emerged as important themes. As the Small Cities programme begins its second
year, a unique but key aspect has become the artist-as-researcher.
Correspondence and offprint requests to: L. Dubinsky, Kamloops Art Gallery, 101–465 Victoria Street, Kamloops, BC V2C 2A9 Canada. Tel.: 250-828-3543; Email: ldubinsky@museums.ca 相似文献
9.
J. Rogalski 《Cognition, Technology & Work》1999,1(4):247-256
Managing dynamic environments often requires decision making under uncertainty and risk. Two types of uncertainty are involved:
uncertainty about the state and the evolution of the situation, and ‘openness’ of the possible actions to face possible consequences.
In an experimental study on risk management in dynamic situations, two contrasted ‘ecological’ scenarios – transposed from
effective situations of emergency management – were compared in order to identify the impact of their ‘openness’ in the subjects’
strategies for decision making. The ‘Lost Child’ scenario presented qualitative and irreversible consequences (child’s death)
and high uncertainty; it exerted high demands both in risk assessment (risk representation) and action elaboration and choice.
A less open situation (‘Hydrocarbon Fire’) required a main choice between two contrasted actions, with quantitative computable
consequences. The strategies of ‘experimental subjects’ (university students) and ‘operative subjects’ (professional fire-fighter
officers) were compared in order to evaluate the ecological validity of experimental research in this field, from the point
of view of the subjects themselves. The two scenarios appeared to be independent, so that quite different models of decision
making have to be hypothesised, differing by the importance of assessing risk and defining possible actions on the one hand,
and by the process of choice on the other. ‘Experimental’ subjects dramatically differed from ‘operative’ subjects when confronted
with the same scenario, particularly for the less technical but more demanding scenario. It is hypothesised that three components
might account for the effect of the situations and for the differences between and within groups of subjects: importance of
situation assessment, spatial abilities, and global orientation of activity in managing dynamic risk. 相似文献
10.
The notion of P-simple points was introduced by Bertrand to conceive parallel thinning algorithms. In ‘A 3D fully parallel thinning algorithm
for generating medial faces’ (Pattern Recogn. Lett. 16:83–87, 1995), Ma proposed an algorithm for which there are objects whose topology is not preserved. In this paper, we propose a new application
of P-simple points: to automatically correct Ma’s algorithm. 相似文献
11.
Previous work has demonstrated that the use of structured abstracts can lead to greater completeness and clarity of information,
making it easier for researchers to extract information about a study. In academic year 2007/08, Durham University’s Computer Science Department revised the format of
the project report that final year students were required to write, from a ‘traditional dissertation’ format, using a conventional
abstract, to that of a 20-page technical paper, together with a structured abstract. This study set out to determine whether
inexperienced authors (students writing their final project reports for computing topics) find it easier to produce good abstracts, in terms of completeness and clarity, when using a structured form rather than a conventional form. We performed
a controlled quasi-experiment in which a set of ‘judges’ each assessed one conventional and one structured abstract for its
completeness and clarity. These abstracts were drawn from those produced by four cohorts of final year students: two preceding
the change, and the two following. The assessments were performed using a form of checklist that is similar to those used
for previous experimental studies. We used 40 abstracts (10 per cohort) and 20 student ‘judges’ to perform the evaluation.
Scored on a scale of 0.1–1.0, the mean for completeness increased from 0.37 to 0.61 when using a structured form. For clarity,
using a scale of 1–10, the mean score increased from 5.1 to 7.2. For a minimum goal of scoring 50% for both completeness and
clarity, only 3 from 19 conventional abstracts achieved this level, while only 3 from 20 structured abstracts failed to reach
it. We conclude that the use of a structured form for organising the material of an abstract can assist inexperienced authors
with writing technical abstracts that are clearer and more complete than those produced without the framework provided by
such a mechanism. 相似文献
12.
David Martin Jacki O’neill Dave Randall Mark Rouncefield 《Computer Supported Cooperative Work (CSCW)》2007,16(3):231-264
As a comparatively novel but increasingly pervasive organizational arrangement, call centres have been a focus for much recent
research. This paper identifies lessons for organizational and technological design through an examination of call centres
and ‘classification work’ – explicating what Star [1992, Systems/Practice vol. 5, pp. 395–410] terms the ‘open black box’. Classification is a central means by which organizations standardize procedure,
assess productivity, develop services and re-organize their business. Nevertheless, as Bowker and Star [1999, Sorting Things Out: Classification and Its Consequences. Cambridge MA: MIT Press] have pointed out, we know relatively little about the work that goes into making classification
schema what they are. We will suggest that a focus on classification ‘work’ in this context is a useful exemplar of the need
for some kind of ‘meta-analysis’ in ethnographic work also. If standardization is a major ambition for organizations under
late capitalism, then comparison might be seen as a related but as-yet unrealized one for ethnographers. In this paper, we
attempt an initial cut at a comparative approach, focusing on classification because it seemed to be the primary issue that
emerged when we compared studies. Moreover, if technology is the principal means through which procedure and practice is implemented
and if, as we believe, classifications are becoming ever more explicitly embedded within it (for instance with the development
of so-called ‘semantic web’ and associated approaches to ontology-based design), then there is clearly a case for identifying
some themes which might underpin classification work in a given domain. 相似文献
13.
Pest Control Expert System for Tomato (PCEST) 总被引:4,自引:0,他引:4
This paper presents a real-life pest control expert system for tomato. The system involves two main subtasks, namely: ‘diagnose’
and ‘treat’. The ‘diagnose’ subtask finds out the causes of the growers' complaints, while the ‘treat’ subtask finds out a
treatment plan for these causes. CommonKADS methodology has been used to develop the system. Dependency network is used as
one of our knowledge representation schemes in both subtasks. An expert system evaluation methodology has been suggested and
applied to the developed system.
Received May 1998 / Revised January 1999 / Accepted in revised form May 1999 相似文献
14.
Nanotribological characterization of perfluoroalkylphosphonate self-assembled monolayers deposited on aluminum-coated silicon substrates 总被引:1,自引:0,他引:1
Bharat Bhushan Michal Cichomski Enamul Hoque James A. DeRose Patrik Hoffmann Hans J. Mathieu 《Microsystem Technologies》2006,12(6):588-596
Aluminum-coated silicon substrates are commonly used for various micro/nanooptoelectromechanical systems (MOEMS/NOEMS) including Digital Micromirror Devices (DMD®). For efficient and failure proof operation of these devices, ultra-thin lubricant films of self-assembled monolayers (SAMs) are increasingly being employed. Fluorinated molecules are known to exhibit low surface energy, adhesion, and friction, desirable for tribological applications. In this study, we investigate contact angle, surface energy, friction, adhesion, and wear properties of a perfluoroalkylphosphonate SAM and compare them with those of alkylphosphonate SAMs. The influence of relative humidity, temperature, and sliding velocity on the friction and adhesion behavior is studied. Failure mechanisms of SAMs are investigated by wear tests. These studies are expected to aid in the design and selection of proper lubricants for MOEMS/NOEMS. 相似文献
15.
Thomas Velten Frank Bauerfeld Herbert Schuck Sabine Scherbaum Christof Landesberger Karlheinz Bock 《Microsystem Technologies》2011,17(4):619-627
In this paper we present a new roll-to-roll embossing process allowing the replication of micro patterns with feature sizes
down to 0.5 μm. The embossing process can be run in ‘continuous mode’ as well as in ‘discontinuous mode’. Continuous hot embossing
is suitable for the continuous output of micro patterned structures. Discontinuous hot embossing has the advantage that it
is not accompanied by waste produced during the initial hot embossing phase. This is because in ‘discontinuous mode’, embossing
does not start before the foil has reached the target temperature. The foil rests between two parallel heating plates and
foil movement and embossing starts only after the part of the foil resting between the heating plates has reached a thermal
steady state. A new type of embossing master is used which is based on flexible silicon substrates. The embossing pattern
with sub-μm topographic resolution is prepared on silicon wafers by state of the art lithography and dry etching techniques.
The wafers are thinned down to a thickness of 40 μm, which guarantees the mechanical flexibility of the embossing masters.
Up to 20 individual chips with a size of 20 × 20 mm2 were assembled on a roller. Embossing experiments with COC foils showed
a good replication of the silicon master structures in the foil. The maximum depth of the embossed holes was about 70% of
the master height. 相似文献
16.
DSM as a knowledge capture tool in CODE environment 总被引:1,自引:0,他引:1
A design structure matrix (DSM) provides a simple, compact, and visual representation of a complex system/ process. This paper
shows how DSM, a system engineering tool, is applied as a knowledge capture (acquisition) tool in a generic NPD process. The
acquired knowledge (identified in the DSM) is provided in the form of Questionnaires, which are organized into five performance
indicators of the organization namely ‘Marketing’, ‘Technical’, ‘Financial’, ‘Resource Management’, and ‘Project Management’.
Industrial application is carried out for knowledge validation. It is found form the application that the acquired knowledge
helps NPD teams, managers and stakeholders to benchmark their NPD endeavor and select areas to focus their improvement efforts
(up to 80% valid). 相似文献
17.
Martin Colbert 《Personal and Ubiquitous Computing》2005,9(6):404-412
This paper reports a diary study of the use of mobile telephones for rendezvousing by young adults (aged 18–30) and mature
adults (aged 31–45) in the UK. A number of age differences were found. Specifically, 31–45s more frequently: (1) attributed
problems rendezvousing to the overrunning of previous activities, and to the spontaneous performance of additional tasks (‘side-stepping’);
(2) reported that ‘problem’ rendezvous resulted in unnecessary sacrifices; and (3) changed plans for the rendezvous. These
differences arose, because additional family commitments encouraged 31–45s to pack their daily programme of activities more
tightly than 18–30s. Mobile phones might better target 31–45s, if they, for example, enhanced To Do Lists with context-sensitive
reminders, in the first instance, reminders triggered by location (GSM network cellID) and logging off from PCs.
相似文献
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18.
Stuart Jackson Nuala Brady Fred Cummins Kenneth Monaghan 《Artificial Intelligence Review》2006,26(1-2):141-154
Recent findings in neuroscience suggest an overlap between those brain regions involved in the control and execution of movement
and those activated during the perception of another’s movement. This so called ‘mirror neuron’ system is thought to underlie
our ability to automatically infer the goals and intentions of others by observing their actions. Kilner et al. (Curr Biol
13(6):522–525, 2003) provide evidence for a human ‘mirror neuron’ system by showing that the execution of simple arm movements
is affected by the simultaneous perception of another’s movement. Specifically, observation of ‘incongruent’ movements made
by another human, but not by a robotic arm, leads to greater variability in the movement trajectory than observation of movements
in the same direction. In this study we ask which aspects of the observed motion are crucial to this interference effect by
comparing the efficacy of real human movement to that of sparse ‘point-light displays’. Eight participants performed whole
arm movements in both horizontal and vertical directions while observing either the experimenter or a virtual ‘point-light’
figure making arm movements in the same or in a different direction. Our results, however, failed to show an effect of ‘congruency’
of the observed movement on movement variability, regardless of whether a human actor or point-light figure was observed.
The findings are discussed, and future directions for studies of perception-action coupling are considered. 相似文献
19.
Miklós Erdélyi-Szabó László Kálmán Agi Kurucz 《Journal of Logic, Language and Information》2008,17(1):1-17
The paper sets out to offer an alternative to the function/argument approach to the most essential aspects of natural language
meanings. That is, we question the assumption that semantic completeness (of, e.g., propositions) or incompleteness (of, e.g.,
predicates) exactly replicate the corresponding grammatical concepts (of, e.g., sentences and verbs, respectively). We argue
that even if one gives up this assumption, it is still possible to keep the compositionality of the semantic interpretation
of simple predicate/argument structures. In our opinion, compositionality presupposes that we are able to compare arbitrary
meanings in term of information content. This is why our proposal relies on an ‘intrinsically’ type free algebraic semantic
theory. The basic entities in our models are neither individuals, nor eventualities, nor their properties, but ‘pieces of
evidence’ for believing in the ‘truth’ or ‘existence’ or ‘identity’ of any kind of phenomenon. Our formal language contains
a single binary non-associative constructor used for creating structured complex terms representing arbitrary phenomena. We
give a finite Hilbert-style axiomatisation and a decision algorithm for the entailment problem of the suggested system. 相似文献
20.
Satinder P. Gill 《AI & Society》2008,22(3):283-300
Socio-ethics covers the relation of the individual with the group and with society, as the individual acquires the skills
for social life with others and the conduct of ‘normal responsible behaviour’ (Leal in AI Soc 9:29–32, 1995) that guides moral action. For a consideration of what it means to be socially skilled in everyday human interaction and
the ethical issues arising from the new conditions of interaction that come with the integration of intelligent interactive
artefacts, we will provide an analysis at multiple levels of these phenomena and draw on a variety of application domains,
for example, healthcare and interactive media. 相似文献