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1.
ABSTRACT Copolymers of 1,5-dioxepan-2-one (DXO) and e-caprolactone (?-CL), δ-valerolactone (δ-VL) or L-lactide (LLA) have been synthesized and characterized. High molecular weight copolymers were obtained using stannous-2-ethyl hexanoate as catalyst in bulk. Reactivity ratios for the copolymerization of DXO and δ-VL were determined at 110°C as rVL=0.5 and rDXO=2.3. At high conversion, depolymerization of δ-VL occurred, resulting in lower molecular weight and variations in the copolymer composition. Physical properties, such as crystallinity and melting temperature of the DXO-copolymers proved to be strongly dependent on the choice of comonomer and on the molar composition of the copolymers. DXO appears to be incorporated into the poly-?-caprolactone (PCL) crystals and to some extent into the poly-δ-valerolactone (PVL) crystals, resulting in a more gradual decrease in crystallinity with increasing amount of DXO. 相似文献
2.
A Mukherjee M Dasgupta DJ Hinde CR Morton AC Berriman RD Butt JO Newton H Timmers 《Pramana》2001,57(1):195-198
Fusion cross-sections for the 7Li + 12C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy
evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their
contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections
due to the breakup of 7Li may not be significant for 7Li + 12C reaction at energies around the barrier. 相似文献
3.
RD Harris WS Baker Van Stipdonk MJ RM Crooks EA Schweikert 《Rapid communications in mass spectrometry : RCM》1999,13(14):1374-1380
A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd. 相似文献
4.
Ackermann M Ajello M Albert A Atwood WB Baldini L Ballet J Barbiellini G Bastieri D Bechtol K Bellazzini R Berenji B Blandford RD Bloom ED Bonamente E Borgland AW Bregeon J Brigida M Bruel P Buehler R Burnett TH Buson S Caliandro GA Cameron RA Cañadas B Caraveo PA Casandjian JM Cecchi C Charles E Chekhtman A Chiang J Ciprini S Claus R Cohen-Tanugi J Conrad J Cutini S de Angelis A de Palma F Dermer CD Digel SW do Couto e Silva E Drell PS Drlica-Wagner A Falletti L Favuzzi C Fegan SJ Ferrara EC 《Physical review letters》2011,107(24):241302
Satellite galaxies of the Milky Way are among the most promising targets for dark matter searches in gamma rays. We present a search for dark matter consisting of weakly interacting massive particles, applying a joint likelihood analysis to 10 satellite galaxies with 24 months of data of the Fermi Large Area Telescope. No dark matter signal is detected. Including the uncertainty in the dark matter distribution, robust upper limits are placed on dark matter annihilation cross sections. The 95% confidence level upper limits range from about 10(-26) cm3 s(-1) at 5 GeV to about 5×10(-23) cm3 s(-1) at 1 TeV, depending on the dark matter annihilation final state. For the first time, using gamma rays, we are able to rule out models with the most generic cross section (~3×10(-26) cm3 s(-1) for a purely s-wave cross section), without assuming additional boost factors. 相似文献
5.
Chae KH Biggs AD Blandford RD Browne IW De Bruyn AG Fassnacht CD Helbig P Jackson NJ King LJ Koopmans LV Mao S Marlow DR McKean JP Myers ST Norbury M Pearson TJ Phillips PM Readhead AC Rusin D Sykes CM Wilkinson PN Xanthopoulos E York T 《Physical review letters》2002,89(15):151301
We derive constraints on cosmological parameters and the properties of the lensing galaxies from gravitational lens statistics based on the final Cosmic Lens All Sky Survey data. For a flat universe with a classical cosmological constant, we find that the present matter fraction of the critical density is Omega(m)=0.31(+0.27)(-0.14) (68%)+0.12-0.10 (syst). For a flat universe with a constant equation of state for dark energy w=p(x)(pressure)/rho(x)(energy density), we find w<-0.55(+0.18)(-0.11) (68%). 相似文献
6.
Measurement of separate cosmic-ray electron and positron spectra with the fermi large area telescope
Ackermann M Ajello M Allafort A Atwood WB Baldini L Barbiellini G Bastieri D Bechtol K Bellazzini R Berenji B Blandford RD Bloom ED Bonamente E Borgland AW Bouvier A Bregeon J Brigida M Bruel P Buehler R Buson S Caliandro GA Cameron RA Caraveo PA Casandjian JM Cecchi C Charles E Chekhtman A Cheung CC Chiang J Ciprini S Claus R Cohen-Tanugi J Conrad J Cutini S de Angelis A de Palma F Dermer CD Digel SW do Couto E Silva E Drell PS Drlica-Wagner A Favuzzi C Fegan SJ Ferrara EC Focke WB Fortin P 《Physical review letters》2012,108(1):011103
We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting Earth's shadow, which is offset in opposite directions for opposite charges due to Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 and 200?GeV. We confirm that the fraction rises with energy in the 20-100?GeV range. The three new spectral points between 100 and 200?GeV are consistent with a fraction that is continuing to rise with energy. 相似文献
7.
LANGLEY J. K. 《中国科学 数学(英文版)》2010,(3)
We determine all real meromorphic functions f in the plane such that f has finitely many zeros, the poles of f have bounded multiplicities, and f and F have finitely many non-real zeros, where F is a linear differential polynomial given by F = f (k) +Σk-1j=0ajf(j) , in which k≥2 and the coefficients aj are real numbers with a0≠0. 相似文献
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9.
George E. Blandford 《Finite Elements in Analysis and Design》1985,1(3):271-285
The nonlinear thermoelastic behavior of orthotropic layered slabs and cylinders including radiation boundaries, temperature-dependent material properties, and stress-dependent layer interface conditions is investigated. A one-dimensional finite element formulation employing quadratic layer and linear interface elements is used to perform the analyses. The transient heat conduction portion of the program is temporally discretized via an implicit linear time interpolation algorithm which includes Crank-Nicolson, Galerkin, and Euler backward differencing. The nonlinear heat conduction equations are iteratively evaluated using a modified Newton-Raphson scheme. Direct iteration between heat conduction and stress analysis is employed when stress-dependent interface thermal resistance coefficients are utilized. Verification problems are presented to demonstrate the accuracy of the finite element code. 相似文献
10.
M. Paolucci D. Kossman R. Conte P. Lukowicz P. Argyrakis A. Blandford G. Bonelli S. Anderson S. de Freitas B. Edmonds N. Gilbert M. Gross J. Kohlhammer P. Koumoutsakos A. Krause B. -O. Linnér P. Slusallek O. Sorkine R. W. Sumner D. Helbing 《The European physical journal. Special topics》2012,214(1):77-108