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  • 2010-2014  (12,959)
  • 2005-2009  (5,654)
  • 1960-1964  (85)
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  • 1
    Series available for loan
    Series available for loan
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
    Associated volumes
    Call number: ZSP-202-103
    In: Research report / Cold Regions Research and Engineering Laboratory, 103
    Description / Table of Contents: Summary: The effect of air flow on the thermal conductivity of snow was investigated. Steady-state temperature measurements were made along the edge and axis of a cylindrical bed of snow to determine the effective axial thermal conductivity of snow. Unconsolidated snow samples were used, with densities ranging from 0.376 to 0.472 g/cm^3 and corresponding snow particle sizes of 0.065 to 0.219 cm nominal diameter; the mass flow rates employed ranged from approximately 10-40 x 10^-4g/cm^2 sec. Snow density and sample size apparently have opposite effects on the effective thermal conductivity because of the flow of fluid in snow. The test apparatus is described in detail and is illustrated. The results of the experiments are tabulated, and a least square equation is given which represents the results well.
    Type of Medium: Series available for loan
    Pages: iv, 14, A2 Seiten , Illustrationen
    Series Statement: Research report / Cold Regions Research and Engineering Laboratory 103
    Language: English
    Note: CONTENTS Preface Summary Introduction Theory Apparatus and experimental procedure Results and discussion References Appendix A: Sample calculations of a and ke
    Location: AWI Archive
    Branch Library: AWI Library
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  • 2
    Series available for loan
    Series available for loan
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
    Associated volumes
    Call number: ZSP-202-95
    In: Research report / Cold Regions Research and Engineering Laboratory, 95
    Description / Table of Contents: Summary: An investigation was conducted at Camp Century, Greenland, to study the feasibility of using air wells to cool undersnow structures in the arctic during the summer months. From results obtained during the summers of 1959,and 1960 and late November, 1960, it was found that the air well is a practical and effective means of providing a -20°C air supply at volumetric flow rates of 1200 to 1700 ft^3/min. The extent and rate of warming of the snow beneath the trench floor by heat exchange between the air and the snow foundation was found to depend upon trench air temperature, fan capacity, fan arrangement, and casing length. For example, in a well cased to a depth of 17. 5 ft and equipped with a 5 hp fan drawing in air at a rate of 1700 ft^3/min, the maximum warming was found to be 12.5°C during a 42-day period. Snow temperature differences of about 7°C were found between similar trenches with and without a fan installation. The minimum permissible distance between two adjacent fans to eliminate, overlap in warming up the snow foundation is approximately 80 ft.
    Type of Medium: Series available for loan
    Pages: iv, 17 Seiten , Illustrationen
    Series Statement: Research report / Cold Regions Research and Engineering Laboratory 95
    Language: English
    Note: CONTENTS Preface Summary Theoretical background Test method and equipment Test operations Effectiveness of the air well Estimation of fan capacity Natural cooling in winter Change of trench foundation temperature Trench wall warm-up Conclusions and recommendations
    Location: AWI Archive
    Branch Library: AWI Library
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  • 3
    Keywords: Chemistry ; Chemistry, Physical organic ; Chemistry ; Mathematics ; Computer simulation
    ISBN: 9781402036903
    Language: English
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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
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