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Annealing of both cold-drawn atactic polystyrene and cold-drawn poly-methylmethacrylate at temperatures ranging from 50°C to their respective Tg's and for times ranging from 1 to 6 days gradually but completely eliminates the orientation arcing from the wide-angle X-ray diffraction pattern but induces only ~25% recovery of the cold-drawn deformation (as calculated from dimensional shrinkage). Analogous studies show that the birefringence of cold-drawn polystyrene is reduced by 57% during the annealing treatment. The results are evidence for segmental molecular motion below Tg and suggest that the molecular alignment responsible for the wide-angle X-ray diffraction arcing is not necessarily the same molecular orientation required for dimensional recovery. We have tentatively interpreted these results in terms of our recently proposed structural model consisting of both ordered domains and connecting disordered regions in the amorphous polymeric solid state. Annealing below Tg can produce chain backbone motion within the disordered regions and cause disorientation of the aligned ordered domains brought about by the initial cold-draw process. 相似文献
3.
Yuliy Baryshnikov Wil Brady Andrew Bressler Robin Pemantle 《Journal of statistical physics》2011,142(1):78-107
We analyze several families of two-dimensional quantum random walks. The feasible region (the region where probabilities do
not decay exponentially with time) grows linearly with time, as is the case with one-dimensional QRW. The limiting shape of
the feasible region is, however, quite different. The limit region turns out to be an algebraic set, which we characterize
as the rational image of a compact algebraic variety. We also compute the probability profile within the limit region, which
is essentially a negative power of the Gaussian curvature of the same algebraic variety. Our methods are based on analysis
of the space-time generating function, following the methods of Pemantle and Wilson (J. Comb. Theory, Ser. A 97(1):129–161,
2002). 相似文献
4.
Evan Xuguang Chen Michael Gehm Ryan Danell Mitch Wells Jeffrey T. Glass David Brady 《Journal of the American Society for Mass Spectrometry》2014,25(7):1295-1304
Conventionally, quadrupole ion trap mass spectrometers eject ions of different mass-to-charge ratio (m/z) in a sequential fashion by performing a scan of the rf trapping voltage amplitude. Due to the inherent sparsity of most mass spectra, the detector measures no signal for much of the scan time. By exploiting this sparsity property, we propose a new compressive and multiplexed mass analysis approach—multi Resonant Frequency Excitation (mRFE) ejection. This new approach divides the mass spectrum into several mass subranges and detects all the subrange spectra in parallel for increased mass analysis speed. Mathematical estimation of standard mass spectrum is demonstrated while statistical classification on the parallel measurements remains viable because of the sparse nature of the mass spectra. This method can reduce mass analysis time by a factor of 3–6 and increase system duty cycle by 2×. The combination of reduced analysis time and accurate compound classification is demonstrated in a commercial quadrupole ion trap (QIT) system. Figure
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In this paper we derive a general analytical solution for a monocentric lens system and present a global optimization method combining sequential design for global optimization and an expected improvement algorithm for global optimization for the design and analysis of a layered monocentric lens system, which provides an “intelligent” way to search the optimization space based on accumulated experience. We then apply these methods to an example of monocentric lens design, and explore the improvement in system performance obtained through increasing the system volume. 相似文献
8.
Ridgers CP Brady CS Duclous R Kirk JG Bennett K Arber TD Robinson AP Bell AR 《Physical review letters》2012,108(16):165006
In simulations of a 10 PW laser striking a solid, we demonstrate the possibility of producing a pure electron-positron plasma by the same processes as those thought to operate in high-energy astrophysical environments. A maximum positron density of 10(26) m(-3) can be achieved, 7 orders of magnitude greater than achieved in previous experiments. Additionally, 35% of the laser energy is converted to a burst of γ rays of intensity 10(22) W cm(-2), potentially the most intense γ-ray source available in the laboratory. This absorption results in a strong feedback between both pair and γ-ray production and classical plasma physics in the new "QED-plasma" regime. 相似文献
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There is only one gap in the isoperimetric spectrum 总被引:1,自引:0,他引:1