22,625 research outputs found
Monte Carlo Simulations of Hadronic Fragmentation Functions using NJL-Jet Model
The recently developed Nambu-Jona-Lasinio (NJL) - Jet model is used as an
effective chiral quark theory to calculate the quark fragmentation functions to
pions, kaons, nucleons, and antinucleons. The effects of the vector mesons rho,
K* and phi on the production of secondary pions and kaons are included. The
fragmentation processes to nucleons and antinucleons are described by using the
quark-diquark picture, which has been shown to give a reasonable description of
quark distribution functions. We incorporate effects of next-to-leading order
(NLO) in the Q^2 evolution, and compare our results with the empirical
fragmentation functions.Comment: 27 pages, 13 figure
Medium Modifications of Hadron Properties and Partonic Processes
Chiral symmetry is one of the most fundamental symmetries in QCD. It is
closely connected to hadron properties in the nuclear medium via the reduction
of the quark condensate , manifesting the partial restoration of
chiral symmetry. To better understand this important issue, a number of
Jefferson Lab experiments over the past decade have focused on understanding
properties of mesons and nucleons in the nuclear medium, often benefiting from
the high polarization and luminosity of the CEBAF accelerator. In particular, a
novel, accurate, polarization transfer measurement technique revealed for the
first time a strong indication that the bound proton electromagnetic form
factors in 4He may be modified compared to those in the vacuum. Second, the
photoproduction of vector mesons on various nuclei has been measured via their
decay to e+e- to study possible in-medium effects on the properties of the rho
meson. In this experiment, no significant mass shift and some broadening
consistent with expected collisional broadening for the rho meson has been
observed, providing tight constraints on model calculations. Finally, processes
involving in-medium parton propagation have been studied. The medium
modifications of the quark fragmentation functions have been extracted with
much higher statistical accuracy than previously possible.Comment: to appear in J. Phys.: Conf. Proc. "New Insights into the Structure
of Matter: The First Decade of Science at Jefferson Lab", eds. D.
Higinbotham, W. Melnitchouk, A. Thomas; added reference
Observations of Transient Active Region Heating with Hinode
We present observations of transient active region heating events observed
with the Extreme Ultraviolet Imaging Spectrometer (EIS) and X-ray Telescope
(XRT) on Hinode. This initial investigation focuses on NOAA active region 10940
as observed by Hinode on February 1, 2007 between 12 and 19 UT. In these
observations we find numerous examples of transient heating events within the
active region. The high spatial resolution and broad temperature coverage of
these instruments allows us to track the evolution of coronal plasma. The
evolution of the emission observed with XRT and EIS during these events is
generally consistent with loops that have been heated and are cooling. We have
analyzed the most energetic heating event observed during this period, a small
GOES B-class flare, in some detail and present some of the spectral signatures
of the event, such as relative Doppler shifts at one of the loop footpoints and
enhanced line widths during the rise phase of the event. While the analysis of
these transient events has the potential to yield insights into the coronal
heating mechanism, these observations do not rule out the possibility that
there is a strong steady heating level in the active region. Detailed
statistical analysis will be required to address this question definitively
Particulate and aerosol detector
A device is described for counting aerosols and sorting them according to either size, mass or energy. The component parts are an accelerator, a capacitor sensor and a readout. The accelerator is a means for accelerating the aerosols toward the face of the capacitor sensor with such force that they partially penetrate the capacitor sensor, momentarily discharging it. The readout device is a means for counting the number of discharges of the capacitor sensor and measuring the amplitudes of these different discharges. The aerosols are accelerated by the accelerator in the direction of the metal layer with such force that they penetrate the metal and damage the oxide layers, thereby allowing the electrical charge on the capacitor to discharge through the damaged region. Each incident aerosol initiates a discharge path through the capacitor in such a fashion as to vaporize the conducting path. Once the discharge action is complete, the low resistance path no longer exists between the two capacitor plates and the capacitor is again able to accept a charge. The active area of the capacitor is reduced in size by the damaged area each time a discharge occurs
An Optimal Linear Time Algorithm for Quasi-Monotonic Segmentation
Monotonicity is a simple yet significant qualitative characteristic. We
consider the problem of segmenting a sequence in up to K segments. We want
segments to be as monotonic as possible and to alternate signs. We propose a
quality metric for this problem using the l_inf norm, and we present an optimal
linear time algorithm based on novel formalism. Moreover, given a
precomputation in time O(n log n) consisting of a labeling of all extrema, we
compute any optimal segmentation in constant time. We compare experimentally
its performance to two piecewise linear segmentation heuristics (top-down and
bottom-up). We show that our algorithm is faster and more accurate.
Applications include pattern recognition and qualitative modeling.Comment: This is the extended version of our ICDM'05 paper (arXiv:cs/0702142
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