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  • Articles  (5,670)
  • 2005-2009  (5,590)
  • 1960-1964  (80)
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  • 1
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 329 (Jan. 2007), p. 391-396 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Rotary ultrasonic machining (RUM) is considered to be a very effective and relativelyaccurate way to drill deep holes in brittle materials. Although brittle fracture (micro chipping) is thedominant material removal mechanism utilized by the RUM process, poor surface roughness anddeep penetrated cracks are the consequence if the machining parameters are not properly controlled.To ensure the quality of the generated surface and to improve the process efficiency, efforts havebeen made in this study to correlate the material removal mechanisms, surface integrity and tool wearinvolved in the RUM process. Diamond-impregnated tools were used in the experiment and theultrasonic vibration frequency was kept at 20 kHz. Three major material removal modes namely,impact mode, grinding mode and erosion mode were found to be the dominant removal processes atthe tool tip, around the diamond wheel and around the steel sleeve respectively. It was also foundthat, during the grinding/erosion processes, the bonding material of the wheel was first eroded awayand left big part of diamond grits well-exposed. Pull-out and/or fracture are normally theconsequence of these exposed diamond grits due to the lack of support and protection
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Genetics 39 (2005), S. 537-559 
    ISSN: 0066-4197
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Ciliated protozoan are unicellular eukaryotes. Most species in this diverse group display nuclear dualism, a special feature that supports both somatic and germline nuclei in the same cell. Probably due to this unique life style, they exhibit unusual nuclear characteristics that have intrigued researchers for decades. Among them are large-scale DNA rearrangements, which restructure the somatic genome to become drastically different from its germline origin. They resemble the classical phenomenon of chromatin diminution in some nematodes discovered more than a century ago. The mechanisms of such rearrangements, their biological roles, and their evolutionary origins have been difficult to understand. Recent studies have revealed a clear link to RNA interference, and begin to shed light on these issues. Using the simple ciliate Tetrahymena as a model, this chapter summarizes the physical characterization of these processes, describes recent findings that connect them to RNA interference, and discusses the details of their mechanisms, potential roles in genome defense, and possible occurrences in other organisms.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 364-366 (Dec. 2007), p. 601-606 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Stainless steel and other ferrous metals are normally classified as not diamond turnablefor the unacceptable tool wear caused by the thermal-chemical reaction between diamond andferrous metals. In the present research, stainless steel specimens were plasma nitrided at a relativelylow temperature (〈450oC) to prevent the depletion of Cr content at the austenite matrix and to givea hardened layer where Fe atoms are bonded to nitrogen atom to form γ’-Fe4N. Diamond turningexperiments were subsequently carried out under the following machining conditions: single crystaldiamond tool, cutting speed up to 180 m/min, cut depth up to 5μm and light mineral oil as thecutting fluid. The results showed that, given the same machining conditions, while rapid tool wearand poor surface finish were obtained when turning the as-received stainless steel, surfaces with Rabetter than 3nm and no obvious tool wear were achieved when turning the plasma nitridedspecimens
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Advanced materials research Vol. 55-57 (Aug. 2008), p. 321-324 
    ISSN: 1662-8985
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Electrospinning is common used in manufacturing ultrafine fibers from a polymer solution. With a high specific surface area, high porosity and good biocompatibility, the elecrospun membranes have extensive applications as biomaterials such as tissue scaffolds and for drug delivery. Silk fibroins (SF), gelatin (G) both have good biocompatibility and are non-toxic. And in previous literature, gelatin nanofiber can be successfully prepared by electrospinning, which was dissolved in formic acid. Tencel, which is extracted from wood pulp, is biodegradable, has a smooth fiber structure, can protect wounds and is irritation-free. Consequently, SF, G and Tencel are widely used in biomedical applications, such as for wound dressings and scaffolds for tissue engineering and so on. In this study, we discussed the applications of different shapes of electrospun membrane such as film, web. After that, the electrospun membrane was combined with Tencel nonwoven to fabricate composite nonwoven. Electrospinning of SF/ G was performed using formic acid as the spinning solvent. Parameters, such as electrical field (15~11 kV), spinning distance (15~7 cm), and volume ratio of SF and G, were analyzed to investigate their effects on electrospinnability and morphology of nanofiber membranes. The morphology of electrospun SF/ G nanofibers was investigated by scanning electron microscopy (SEM). Analytical demonstrate that the optimal electrospinning condition was fibers with an average diameter of 200–300 nm
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 400-402 (Oct. 2008), p. 453-457 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The polymer sulphoaluminate cement is composed of styrene-acrylic emulsion and sulphoaluminate cement. The resistance to sulfate attack, impermeability and mechanical performance are studied in the paper. The hardened paste microstructure of the polymer sulphoaluminate cement is studied by means of SEM. The experiment shows that the impermeability of the cement is improved with the increase of styrene-acrylic emulsion. When the ratio of polymer to cement increases from 0% to 15%, the permeate height of the hardened cement paste decreases by 70%. The resistance to sulfate attack of the cement is also improved with the increase of styrene-acrylic emulsion. Styrene-acrylic emulsion has little effect on the flexural strength of sulphoaluminate cement. When the ratio of polymer to cement is less than 15%, the flexural strength of the cement at 28d curing ages are all above 7.1MPa. As shown from SEM photographs, the cement becomes more close-grained when the ratio of polymer to cement increases
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 505-507 (Jan. 2006), p. 367-372 
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Precise and efficient tool setting technique and accurate tool shape monitoring are ofessential importance in ultra-precision diamond turning operation. The traditional way of tool setting are typically laborious, inefficient and rely heavily on experience. A big part of the tool setting is done by using a contact probe such as LVDT. The contact tool setting station can normally, depending on the resolution of the probes, place the tool tip to within a 1~10μm positioning accuracy. However, it isrunning the risk of damage the delicate tool tip and has the ambiguity introduced by contact point of tool and touch probe. The optical/non-contact way of setting the tool do have the advantage of not having to touch the tool, but its resolution is limited by the optical diffraction limit and the resolution of the CCD device used (mm/pixel). A non-contact precision tool setting system is developed and built in this study using edge-detection image processing and sub-pixel dividing techniques inconjunction with CNC controller of the precision turning machine to improve the system presently available. Depending on the sampling distance of the images, the error band gets wider when the sampling step becomes larger. In the case of 0.1μm sampling distance the obtained error band was within ±0.1μm and the results showed that tools of different shapes namely round, half-round and sharp tool could all be positioned to within an error band of ±0.1μm by using the developed toolsetting system
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2006-10-11
    Print ISSN: 0178-2762
    Electronic ISSN: 1432-0789
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Springer
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  • 8
    Publication Date: 2007-09-08
    Print ISSN: 0178-2762
    Electronic ISSN: 1432-0789
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Springer
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  • 9
  • 10
    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 2009. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 126 (2009): 451-459, doi:10.1121/1.3132525.
    Description: In this article, a pitch tracking algorithm [named discrete logarithmic Fourier transformation-pitch detection algorithm (DLFT-PDA)], originally designed for human telephone speech, was modified for killer whale vocalizations. The multiple frequency components of some of these vocalizations demand a spectral (rather than temporal) approach to pitch tracking. The DLFT-PDA algorithm derives reliable estimations of pitch and the temporal change of pitch from the harmonic structure of the vocal signal. Scores from both estimations are combined in a dynamic programming search to find a smooth pitch track. The algorithm is capable of tracking killer whale calls that contain simultaneous low and high frequency components and compares favorably across most signal to noise ratio ranges to the peak-picking and sidewinder algorithms that have been used for tracking killer whale vocalizations previously.
    Description: C.W. was supported by DARPA under Contract No. N66001-96-C-8526, monitored through Naval Command, Control, and Ocean Surveillance Center and by the National Science Foundation under Grant No. IRI-9618731. A.D.S. was supported by a National Defense Science and Engineering Graduate Fellowship.
    Keywords: Acoustic signal detection ; Biocommunications ; Fourier transforms ; Target tracking
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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