6,521 research outputs found
Morphology Development in Model Polyethylene via Two-Dimensional Correlation Analysis
Two-dimensional (2D) correlation analysis is applied to synchrotron X-ray scattering data to characterize
morphological regimes during nonisothermal crystallization of a model ethylene copolymer (hydrogenated polybutadiene,
HPBD). The 2D correlation patterns highlight relationships
among multiple characteristics of structure evolution, particularly the extent to which separate features change simultaneously versus sequentially. By visualizing these relationships during cooling, evidence is obtained for two separate physical processes occurring in what is known as “irreversible crystallization” in random ethylene copolymers. Initial growth of primarily lamellae into unconstrained melt (“primary-irreversible crystallization”) is distinguished from subsequent secondary lamellae formation in the constrained, noncrystalline regions
between the primary lamellae (“secondary-irreversible crystallization”). At successively lower temperatures (“reversible crystallization”), growth of the crystalline reflections is found to occur simultaneously with the change in shape of the amorphous halo, which is inconsistent with the formation of an additional phase. Rather, the synchronous character supports the view that growth of frustrated crystals distorts the adjacent noncrystalline material. Furthermore, heterocorrelation analysis of small-angle and wideangle X-ray scattering data from the reversible crystallization regime reveals that the size of new crystals is consistent with fringedmicellar structures (~9 nm). Thus, 2D correlation analysis provides new insights into morphology development in polymeric systems
Explanation of the Normal Winter Anomaly from the Seasonal Variation of Short Wave Absorption
The frequency dependence of the winter anomaly (WA) of radio wave absorption indicates the altitude range where the considered seasonal variation of absorption, L, takes place: 75-95 km. In this height region considerable seasonal variations of ionic composition and effective recombination coefficient, alpha sub e, exist, which can cause seasonal variations of electron concentration, N, and absorption, L. An attempt to render a qualitative estimation of the normal WA, i.e., the increased ratio of winter over summer absorption, L sub w/L sub s, at medium latitudes 40 deg and 50 deg, for solar zenith angles CHi = 60 deg and 75 deg is made. This is compared with existing experimental data
Probing scattering phase shifts by attosecond streaking
Attosecond streaking is one of the most fundamental processes in attosecond
science allowing for a mapping of temporal (i.e. phase) information on the
energy domain. We show that on the single-particle level attosecond streaking
time shifts contain spectral phase information associated with the
Eisenbud-Wigner-Smith (EWS) time delay, provided the influence of the streaking
infrared field is properly accounted for. While the streaking phase shifts for
short-ranged potentials agree with the associated EWS delays, Coulomb
potentials require special care. We show that the interaction between the
outgoing electron and the combined Coulomb and IR laser fields lead to a
streaking phase shift that can be described classically
The NorduGrid architecture and tools
The NorduGrid project designed a Grid architecture with the primary goal to
meet the requirements of production tasks of the LHC experiments. While it is
meant to be a rather generic Grid system, it puts emphasis on batch processing
suitable for problems encountered in High Energy Physics. The NorduGrid
architecture implementation uses the \globus{} as the foundation for various
components, developed by the project. While introducing new services, the
NorduGrid does not modify the Globus tools, such that the two can eventually
co-exist. The NorduGrid topology is decentralized, avoiding a single point of
failure. The NorduGrid architecture is thus a light-weight, non-invasive and
dynamic one, while robust and scalable, capable of meeting most challenging
tasks of High Energy Physics.Comment: Talk from the 2003 Computing in High Energy Physics and Nuclear
Physics (CHEP03), La Jolla, Ca, USA, March 2003, 9 pages,LaTeX, 4 figures.
PSN MOAT00
Time-resolved photoemission by attosecond streaking: extraction of time information
Attosecond streaking of atomic photoemission holds the promise to provide
unprecedented information on the release time of the photoelectron. We show
that attosecond streaking phase shifts indeed contain timing (or spectral
phase) information associated with the Eisenbud-Wigner-Smith time delay matrix
of quantum scattering. However, this is only accessible if the influence of the
streaking infrared (IR) field on the emission process is properly accounted
for. The IR probe field can strongly modify the observed streaking phase shift.
We show that the part of the phase shift ("time shift") due to the interaction
between the outgoing electron and the combined Coulomb and IR laser fields can
be described classically. By contrast, the strong initial-state dependence of
the streaking phase shift is only revealed through the solution of the
time-dependent Schr\"odinger equation in its full dimensionality. We find a
time delay between the hydrogenic 2s and 2p initial states in He+ exceeding
20as for a wide range of IR intensities and XUV energies
Scattering and Diffraction in Magnetospheres of Fast Pulsars
We apply a theory of wave propagation through a turbulent medium to the
scattering of radio waves in pulsar magnetospheres. We find that under
conditions of strong density modulation the effects of magnetospheric
scintillations in diffractive and refractive regimes may be observable. The
most distinctive feature of the magnetospheric scintillations is their
independence on frequency.
Results based on diffractive scattering due to small scale inhomogeneities
give a scattering angle that may be as large as 0.1 radians, and a typical
decorrelation time of seconds.
Refractive scattering due to large scale inhomogeneities is also possible,
with a typical angle of radians and a correlation time of the order
of seconds. Temporal variation in the plasma density may also result
in a delay time of the order of seconds. The different scaling of the
above quantities with frequency may allow one to distinguish the effects of
propagation through a pulsar magnetosphere from the interstellar medium. In
particular, we expect that the magnetospheric scintillations are relatively
more important for nearby pulsars when observed at high frequencies.Comment: 19 pages, 1 Figur
Atlas Data-Challenge 1 on NorduGrid
The first LHC application ever to be executed in a computational Grid
environment is the so-called ATLAS Data-Challenge 1, more specifically, the
part assigned to the Scandinavian members of the ATLAS Collaboration. Taking
advantage of the NorduGrid testbed and tools, physicists from Denmark, Norway
and Sweden were able to participate in the overall exercise starting in July
2002 and continuing through the rest of 2002 and the first part of 2003 using
solely the NorduGrid environment. This allowed to distribute input data over a
wide area, and rely on the NorduGrid resource discovery mechanism to find an
optimal cluster for job submission. During the whole Data-Challenge 1, more
than 2 TB of input data was processed and more than 2.5 TB of output data was
produced by more than 4750 Grid jobs.Comment: Talk from the 2003 Computing in High Energy Physics and Nuclear
Physics (CHEP03), La Jolla, Ca, USA, March 2003, 7 pages, 3 ps figure
Phase and Intensity Distributions of Individual Pulses of PSR B0950+08
The distribution of the intensities of individual pulses of PSR B0950+08 as a
function of the longitudes at which they appear is analyzed. The flux density
of the pulsar at 111 MHz varies strongly from day to day (by up to a factor of
13) due to the passage of the radiation through the interstellar plasma
(interstellar scintillation). The intensities of individual pulses can exceed
the amplitude of the mean pulse profile, obtained by accumulating 770 pulses,
by more than an order of magnitude. The intensity distribution along the mean
profile is very different for weak and strong pulses. The differential
distribution function for the intensities is a power law with index n = -1.1 +-
0.06 up to peak flux densities for individual pulses of the order of 160 Jy
Shell-model description of monopole shift in neutron-rich Cu
Variations in the nuclear mean-field, in neutron-rich nuclei, are
investigated within the framework of the nuclear shell model. The change is
identified to originate mainly from the monopole part of the effective two-body
proton-neutron interaction. Applications for the low-lying states in odd- Cu
nuclei are presented. We compare the results using both schematic and realistic
forces. We also compare the monopole shifts with the results obtained from
large-scale shell-model calculations, using the same realistic interaction, in
order to study two-body correlations beyond the proton mean-field variations.Comment: Phys. Rev. C (in press
- …