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  • 1
    Publication Date: 2016-07-29
    Description: Ion acceleration in near-critical plasmas driven by intense laser pulses is investigated theoretically and numerically. A theoretical model has been given for clarification of the ion acceleration dynamics in relation to different laser and target parameters. Two distinct regimes have been identified, where ions are accelerated by, respectively, the laser-induced shock wave in the weakly driven regime (comparatively low laser intensity) and the nonlinear solitary wave in the strongly driven regime (comparatively high laser intensity). Two-dimensional particle-in-cell simulations show that quasi-monoenergetic proton beams with a peak energy of 94.6 MeV and an energy spread 15.8% are obtained by intense laser pulses at intensity I 0  = 3 × 10 20  W/cm 2 and pulse duration τ  = 0.5 ps in the strongly driven regime, which is more advantageous than that got in the weakly driven regime. In addition, 233 MeV proton beams with narrow spread can be produced by extending τ to 1.0 ps in the strongly driven regime.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 2
    Publication Date: 2015-01-31
    Description: We present experimental studies on ion acceleration from diamond-like carbon (DLC) foils irradiated by 800 nm, linearly polarized laser pulses with peak intensity of 1.7 × 10 19  W/cm 2 to 3.5 × 10 19  W/cm 2 at oblique incidence. Diamond-like carbon foils are heated by the prepulse of a high-contrast laser pulse and expand to form plasmas of near-critical density caused by thermal effect before the arrival of the main pulse. It is demonstrated that carbon ions are accelerated by a collisionless shock wave in slightly overdense plasma excited by forward-moving hot electrons generated by the main pulse.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 3
    Publication Date: 2015-07-07
    Description: A new scheme for proton acceleration by cascaded collisionless electrostatic shock (CES) is proposed. By irradiating a foil target with a moderate high-intensity laser beam, a stable CES field can be induced, which is employed as the accelerating field for the booster stage of proton acceleration. The mechanism is studied through simulations and theoretical analysis, showing that a 55 MeV seed proton beam can be further accelerated to 265 MeV while keeping a good energy spread. This scheme offers a feasible approach to produce proton beams with energy of hundreds of MeV by existing available high-intensity laser facilities.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 4
    Publication Date: 2014-12-11
    Description: In a long subcritical density plasma, an ultrashort ultraintense laser pulse can self-organize into a fast but sub-relativistic propagating structure consisting of the modulated laser light and a large number of trapped electrons from the plasma. Upon impact of the structure with a solid foil target placed in the latter, the remaining laser light is reflected, but the dense and hot trapped electrons pass through the foil, together with the impact-generated target-frontsurface electrons to form a dense hot electron cloud at the back of the target suitable for enhancing target normal sheath acceleration of the target-backsurface ions. The accelerated ions are well collimated and of high charge and energy densities, with peak energies a full order of magnitude higher than that from target normal sheath acceleration without the subcritical density plasma. In the latter case, the space-charge field accelerating the ions is limited since they are formed only by the target-frontsurface electrons during the very short instant of laser reflection.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 5
    Publication Date: 2016-05-27
    Description: Two-dimensional tailoring of a proton beam is realized by a “particle lens” in our experiment. A large quantity of electrons, generated by an intense femtosecond laser irradiating a polymer target, produces an electric field strong enough to change the trajectory and distribution of energetic protons flying through the electron area. The experiment shows that a strip pattern of the proton beam appears when hot electrons initially converge inside the plastic plate. Then the shape of the proton beam changes to a “fountain-like” pattern when these hot electrons diffuse after propagating a distance.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 5126-5131 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Excitation spectra for the 4pπ 3Πg–a 3Σu〈sup ARRANGE="STAGGER"〉+ system in 20Ne2 and 22Ne2 have been used to characterize the v=0 through v=3 levels in both electronic states. This is the first time levels with v〉1 have been characterized experimentally in either dimer. Rotational analyses lead to Be- and αe-values of 0.5638 cm−1 and −0.9000×10−2 cm−1 and of 0.5113 cm−1 and −0.6651×10−2 cm−1 for the a 3Σu〈sup ARRANGE="STAGGER"〉+ states in 20Ne2 and 22Ne2, respectively. The Be- and αe-values are, respectively, 0.5716 cm−1 and −0.6429×10−2 cm−1 (20Ne2) and 0.5201 cm−1 and −0.4172×10−2 cm−1 (22Ne2) for the 4pπ 3Πg state. The vibrational parameters ωe, xωe are found to be 556.2, 10.2 cm−1, and 593.2, 7.5 cm−1 for the a 3Σu〈sup ARRANGE="STAGGER"〉+ state and 4pπ 3Πg state, respectively, in 20Ne2 with corresponding values of 529.5, 9.75 cm−1, and 567, 7.5 cm−1 in 22Ne2. The observed vibrational level differences [ΔG(v+1/2)-values] for the 4pπ 3Πg state are within 0.5% of analogous spacings for the ground electronic state (X 2Σu〈sup ARRANGE="STAGGER"〉+) of Ne2〈sup ARRANGE="STAGGER"〉+ reported by Kim et al. [Phys. Rev. Lett. 68, 1311 (1992)]. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3332-3334 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear optical responses of laser-ablated Si nanoclusters were measured at λ=532 nm. Re{χ(3)} values as high as −(1.33±0.33)×10−3 esu were measured for films that were only 200 nm thick. The response time for this nonlinearity was as short as 3.5±0.5 ns, limited by our laser pulse duration. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 1063-1077 
    ISSN: 0887-6266
    Keywords: peroxide crosslinking ; gamma irradiation ; ultrahigh molecular weight polyethylene ; wear behavior ; orthopedic prosthetics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Acetabular cups for artificial hip joints were prepared by compression molding of ultrahigh molecular weight polyethylene in the presence of peroxide. Peroxide crosslinking led to a decrease in the degree of crystallinity, peak melting temperature, and recrystallization temperature, as well as decreased crystal perfection and size. Peroxide crosslinked cups were sterilized with gamma rays at room temperature in air atmosphere to an average dose of 3.4 Mrad. Irradiation produced further crosslinking in amorphous regions plus extensive chain scission of taut tie molecules and led to increased crystallinity and crystal perfection. A significant increase in carbonyl concentration was determined for irradiated specimens. In general, peroxide crosslinking reduces the effect of irradiation on the crosslinked network, because chemical crosslinking stabilizes chain fragments resulting from radiolytic scission and suppresses recrystallization of broken chains from amorphous regions. Wear rates were much lower for chemically crosslinked cups, which showed about one-fifth of the wear of control cups for the period from 0.5 to 1.0 million cycles. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 41 (1998), S. 71-78 
    ISSN: 0021-9304
    Keywords: peroxide crosslinking ; wear ; γ-irradiation ; ultrahigh molecular weight polyethylene ; polymer processing ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Morphological characterization of chemically crosslinked ultrahigh molecular weight polyethylene was performed by differential scanning calorimetry and scanning electron microscopy. The lamellar thickness of nascent UHMWPE inferred from DSC endotherms showed a very broad distribution, which was reduced significantly after melting and recrystallizing in DSC. Peroxide crosslinking further reduced the lamellar thickness distribution compared to uncrosslinked samples. After γ-irradiation, a slowly cooled peroxide-free sample showed a greater increase in lamellar thickness distribution. Examination of the morphology of freeze-fractured surfaces by SEM showed that a slowly cooled peroxide-free UHMWPE exhibited a rougher fracture while chemically crosslinked samples showed a smoother fracture. After compression molding at 300°C for 2 h, the grain boundaries between particles disappeared for all UHMWPE samples, indicating a complete fusion of the original flakes. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 71-78, 1998.
    Additional Material: 5 Ill.
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  • 10
    Publication Date: 2014-12-19
    Description: We present an effective approach to improve the sensitivity of inductance coil sensors by designing a sensor core that consists of multiple soft ferromagnetic microwires. A systematic study of the longitudinally excited magneto-inductive (LEMI) effect has been performed in a non-magnetic copper wire coil with a filler composed of multiple Co-rich amorphous microwires. Melt-extracted microwires of Co 68.2 Fe 4.3 B 15 Si 12.5 and glass-coated microwires of Co 68 B 15 Si 10 Mn 7 with excellent soft magnetic properties were used for this study. We have shown that the LEMI ratio and field sensitivity of an inductive coil depend strongly upon the filler-to-air ratio inside the coil, the magnetic softness, and the anisotropy axis distribution of the microwire. Relative to a single-microwire based sensor, the LEMI ratio and field sensitivity of a multi-microwire based sensor are enhanced by three to four times, when varying the number of microwires inside the inductive coil. The sensitivity of the sensor using four glass-coated Co 68 B 15 Si 10 Mn 7 microwires in the core reaches a maximum value of 1957%/Oe. Our study paves a pathway for the development of novel room-temperature electric contact free magnetic sensors for use in industry, biomagnetism, space science, and geoscience.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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