ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 1767-1774 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A description and analysis of the solution of a two-dimensional model for a HV breakdown of a short gap is presented. The model consists of the electron, ion, and excited-atom conservation and Poisson equations and is applied to a plane-parallel gap with an electrode separation of 0.48 mm in helium gas at atmospheric pressure and a temperature of 293 K subjected to an electrical field of 10 kV cm−1. Two-dimensional plots of the charged and excited-particle densities and electric field components are presented and discussed. It is shown that in the first, diffusion-controlled, stage density profiles are close to a Gaussian distribution with an effective radius increasing in time. The subsequent stage is controlled by the space-charge field, causing prominent constriction of the electron density channel. In consequence, a high ionization near the discharge axis results in a virtual narrowing of the ion and excited-atom profiles as well, and the forming conductive chanel exhibits a tendency towards constriction. Calculations were conducted up to a maximum time of t=1139 ns, when maximum electron, ion, and excited-atom densities reached values of 3.1×1010, 3.7×1011, and 2.5×1012 cm−3. Among the ionization processes the direct and Penning interactions are dominant, accounting at average for approximately 70% and 30% of the total at time t=1139 ns; ionization frequencies are substantially affected by space-charge field and vary considerably in time and space near the end of calculations.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 5791-5797 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An empirical relationship for the breakdown voltage in a nonuniform field in SF6 is derived with the help of a correlation of experimental data for a rod-plane geometry. The model is based on the hypothesis that the corona shielding radius and the critical corona length are related by a simple formula. In the first approximation this formula depends on the rod radius and the critical corona length at critical pressure; for small gap lengths a correction term, dependent on the gap length, is suggested.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 2570-2575 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An effective set of collisional cross sections of c-C4F8 was determined by fitting the transport coefficients, i.e., drift velocity, diffusion, ionization, and attachment coefficients, to available experimental data. The best fit was obtained for the following values: a total momentum transfer cross section of 8×10−15 cm2 for electron energies of z≤4 eV dropping to 1.75×10−15 cm2 for z〉12 eV, a maximum vibrational cross section of 8×10−15 cm2 at 0.4 eV, and an excitation cross section of about 4×10−16 cm2 between 9 and 20 eV. Ionization and attachment cross sections based on measurements by M. V. Kurepa [Transactions of the 3rd Czechoslovak Conference on Electronics and Vacuum Physics (Academia, Prague, 1967), p. 107] were used; the ionization cross section was multiplied by a correction factor of 0.59, while the attachment cross sections were readjusted according to measurements by C. Lifshitz and R. Grajower [Int. J. Mass Spectrom. Ion Phys. 10, 25 (1972/73)] and I. Sauers, L. G. Christophorou, and J. G. Carter [J. Chem. Phys. 71, 3016 (1979)]. Calculations of the transport coefficients of N2-c-C4F8 mixtures were also performed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 4719-4724 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple experimental arrangement consisting of two arcs burning in series has been devised for measurement of the voltage gradient in the discharge column. The method is based on reciprocal variation of the length of the discharges so that the total length during the measurement is constant. Experiments have been performed in the current range between 20 mA and 4 A in dry air at pressures between 20 and 150 kPa. In the arc mode the current dependence of the field can be approximated by the power function E∝Iα, where the exponent α for pressures between 60 and 150 kPa is −0.54 and slightly higher at lower pressures. The pressure dependence (at constant current) can be expressed in similar form E∝pm with the exponent m equal to 0.15 and 0.24 for currents of 1 and 4 A, respectively, and for pressures above 40 kPa. Average values of the zero-length voltage were obtained in the arc and glow discharge modes, namely, 14.5 V in the case of the arc and 367, 346, 331, and 331 V for the glow discharge at pressures of 20, 60 100, and 150 kPa, respectively.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 552-558 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ionization and attachment coefficients for CCl2F2/SF6 mixtures were determined from measurements of prebreakdown ionization currents in a steady-state Townsend discharge at a pressure p25=4 Torr and temperature of 25 °C. The curves representing the ionization coefficient (α) for reduced fields in the range from 110 to 180 V cm−1 Torr−1 exhibit a small maximum at about 15% of CCl2F2, while those representing the attachment coefficient (η) flatten out between 0% and 50% CCl2F2 and decrease at higher partial densities. The limit field obtained using the condition α=η shows two extrema, i.e., a minimum at approximately 20% and a maximum at 75% of CCl2F2, while the curves obtained from the breakdown-potential measurements available in the literature show only a maximum, at roughly the same position. Theoretical values of the transport coefficients were obtained by numerically solving the Boltzmann equation using previously determined effective sets of electron collision cross sections [J. P. Novak and M. F. Fréchette, J. Appl. Phys. 55, 107 (1984); 57, 4368 (1985)]. The good agreement between the calculated and the experimental values provides supporting evidence for the applicability of the present calculation method and collisional cross sections to analyze electron swarms in the range of fields comparable in magnitude to the limit field.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 924-934 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Densities of the negative and positive ions of SF6 in a 110-liter Pyrex container were measured using a Gerdien ion counter. The current-voltage characteristics were obtained for gas flows ranging from 40 to 200 cm3 s−1. A quantitative model of the counter was developed to interpret the measured data. The model includes appropriate representation of the developing gas flow and the electric field distribution near the ends of the accelerating electrode. The best-fit value for the negative-ion mobility was μn =0.38 cm2 V−1 s−1, as derived from a comparison of the calculated and the measured characteristics. The mobility of the positive ions was found to equal that of the negative ions within the limits of dispersion of experimental data. The negative-ion density at a pressure of 760 Torr evaluated at the counter entry plane was 3000 cm−3; the value of the positive-ion density was practically identical.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 3605-3615 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-dimensional model of the high-voltage breakdown has been developed, consisting of the Poisson equation and the conservation equations for electrons, ions, and excited particles. The model is based on the assumption of a low degree of ionization, so that the transport coefficients of the gas are uniquely determined by the local electric field, i.e., the model is limited to the initial stages of the channel formation. It is applied to a short plane-parallel gap in He at atmospheric pressure. The discharge is started by releasing the cloud of electrons near the cathode, and its sequence is followed up to 1.11 μs. Cathode emission is taken to include that due to ion and metastable impact and the photoeffect. The discharge develops from the initial Townsend-type discharge governed by cathode emission and the direct and Penning volume ionization, and progresses to the space-charge dominated stage. At the moment when the calculations are terminated, the maximum densities have already attained values of 1.6×1010, 2.5×1011, and 1.8×1012 cm−3 for the electrons, ions, and excited particles, respectively. The maximum axial component of the space-charge electric field is approximately 3.3 kV cm−1.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 4368-4376 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A set of effective electron collision cross sections, including momentum transfer, vibration, and electron excitation collisions has been determined for CCl2F2 gas: the momentum transfer is approximately 2×10−15 cm2 with the highest maximum about 4×10−15 at 6 eV, two vibrational maxima with thresholds of 0.11 and 0.14 eV are about 9 and 4 (10−16 cm2) at 0.2 and 0.25 eV and two excitation maxima with thresholds of 7.0 and 9.8 eV are 2.8 and 5.1 (10−16 cm2) at 11 and 18 eV, respectively. The calculated transport coefficients are in satisfactory agreement with measured values, except for the attachment coefficient, which is too high at low (below 90 V cm−1 Torr−1) and high (above 180 V cm−1 Torr−1) reduced fields. The possibility of comparison in the case of N2-CCl2F2 mixtures is limited and agreement is less satisfactory than in the case of pure CCl2F2. Deviations for medium fields are within about 30% for the D/μ ratio and ionization coefficients. The attachment coefficients agree well at high partial density of CCl2F2 (above approximately 50%) but the experimental values are much higher than predicted at low CCl2F2 content. Calculated values of the limit fields agree well with the values obtained from breakdown potential measurements available in the literature.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 2002-2004 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We examine the factors that govern the stability of imaging using single-wall C nanotubes as probes for atomic force microscopy. Nonvertical alignment of the nanotubes causes such probes to bend in response to the surface–nanotube interaction forces during imaging. For long nanotubes, this elastic response causes the nanotube tip to jump into contact with the surface and renders it unsuitable for imaging. For short nanotubes, stable noncontact-mode imaging can be achieved using a small cantilever vibration amplitude. However, the bending response is enhanced on highly textured surfaces, which limits the ability to image nonplanar features. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 255 (1977), S. 198-198 
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...