95 research outputs found
Low-lying Pentaquark states in the Inherent Nodal Structure Analysis
The strangeness pentaquark states as clusters are
investigated in this letter. Starting from the inherent geometric symmetry, we
analyzed the inherent nodal structure of the system. As the nodeless states,
the low-lying states are picked out. Then the S-wave state and P-wave state may be the
candidates of low-lying pentaquark states. By comparing the accessibility of
the two states and referring the presently obtained K-N interaction potential,
we propose that the quantum numbers of the observed pentaquark state
may be and L=1.Comment: 15 pages, 2 figures, 4 tables. Revised version with detailed
description, expanded discussion and reference for the geometric
configuration to be proposed being adde
Dataplane Specialization for High-performance OpenFlow Software Switching
OpenFlow is an amazingly expressive dataplane program-
ming language, but this expressiveness comes at a severe
performance price as switches must do excessive packet clas-
sification in the fast path. The prevalent OpenFlow software
switch architecture is therefore built on flow caching, but
this imposes intricate limitations on the workloads that can
be supported efficiently and may even open the door to mali-
cious cache overflow attacks. In this paper we argue that in-
stead of enforcing the same universal flow cache semantics
to all OpenFlow applications and optimize for the common
case, a switch should rather automatically specialize its dat-
aplane piecemeal with respect to the configured workload.
We introduce ES WITCH , a novel switch architecture that
uses on-the-fly template-based code generation to compile
any OpenFlow pipeline into efficient machine code, which
can then be readily used as fast path. We present a proof-
of-concept prototype and we demonstrate on illustrative use
cases that ES WITCH yields a simpler architecture, superior
packet processing speed, improved latency and CPU scala-
bility, and predictable performance. Our prototype can eas-
ily scale beyond 100 Gbps on a single Intel blade even with
complex OpenFlow pipelines
Tuple Space Explosion: A Denial-of-Service Attack Against a Software Packet Classifier
Efficient and highly available packet classification is fundamental for various security primitives. In this paper, we evaluate whether the de facto Tuple Space Search (TSS) packet classification algorithm used in popular software networking stacks such as the Open vSwitch is robust against low-rate denial-of-service attacks. We present the Tuple Space Explosion (TSE) attack that exploits the fundamental space/time complexity of the TSS algorithm.
TSE can degrade the switch performance to 12% of its full capacity with a very low packet rate (0.7 Mbps) when the target only has simple policies such as, "allow some, but drop others". Worse, an adversary with additional partial knowledge of these policies can virtually bring down the target with the same low attack rate. Interestingly, TSE does not generate any specific traffic patterns but only requires arbitrary headers and payloads which makes it particularly hard to detect.
Due to the fundamental complexity characteristics of TSS, unfortunately, there seems to be no complete mitigation to the problem. As a long-term solution, we suggest the use of other algorithms (e.g., HaRP) that are not vulnerable to the TSE attack. As a short-term countermeasure, we propose MFCGuard that carefully manages the tuple space and keeps packet classification fast
Possible production of exotic baryonia in relativistic heavy-ion collisions
Properties of a hypothetical baryonium with the quark content
(uds\ov{u}\ov{d}\ov{s}) are discussed. The MIT bag model predicts its mass to
be unexpectedly low, approximately 1210 MeV. Possible hadronic decay modes of
this state are analyzed. Ultrarelativistic heavy-ion collisions provide
favorable conditions for the formation of such particles from the baryon-free
quark-gluon plasma. We estimate multiplicities of such exotic baryonia on the
basis of a simple thermal model.Comment: 8 pages, 1 figur
Baryon Washout, Electroweak Phase Transition, and Perturbation Theory
We analyze the conventional perturbative treatment of sphaleron-induced
baryon number washout relevant for electroweak baryogenesis and show that it is
not gauge-independent due to the failure of consistently implementing the
Nielsen identities order-by-order in perturbation theory. We provide a
gauge-independent criterion for baryon number preservation in place of the
conventional (gauge-dependent) criterion needed for successful electroweak
baryogenesis. We also review the arguments leading to the preservation
criterion and analyze several sources of theoretical uncertainties in obtaining
a numerical bound. In various beyond the standard model scenarios, a realistic
perturbative treatment will likely require knowledge of the complete two-loop
finite temperature effective potential and the one-loop sphaleron rate.Comment: 25 pages, 9 figures; v2 minor typos correcte
Heavy and Light Pentaquark Chiral Lagrangian
Using the SU(3) flavor symmetry, we construct the chiral Lagrangians for the
light and heavy pentaquarks. The correction from the nonzero quark is taken
into account perturbatively. We derive the Gell-MannOkubo type relations for
various pentaquark multiplet masses and Coleman-Glashow relations for
anti-sextet heavy pentaquark magnetic moments. We study possible decays of
pentaquarks into conventional hadrons. We also study the interactions between
and within various pentaquark multiplets and derive their coupling constants in
the symmetry limit. Possible kinematically allowed pionic decay modes are
pointed out
Spatial fluctuations in transient creep deformation
We study the spatial fluctuations of transient creep deformation of materials
as a function of time, both by Digital Image Correlation (DIC) measurements of
paper samples and by numerical simulations of a crystal plasticity or discrete
dislocation dynamics model. This model has a jamming or yielding phase
transition, around which power-law or Andrade creep is found. During primary
creep, the relative strength of the strain rate fluctuations increases with
time in both cases - the spatially averaged creep rate obeys the Andrade law
, while the time dependence of the spatial
fluctuations of the local creep rates is given by . A similar scaling for the fluctuations is found in the logarithmic
creep regime that is typically observed for lower applied stresses. We review
briefly some classical theories of Andrade creep from the point of view of such
spatial fluctuations. We consider these phenomenological, time-dependent creep
laws in terms of a description based on a non-equilibrium phase transition
separating evolving and frozen states of the system when the externally applied
load is varied. Such an interpretation is discussed further by the data
collapse of the local deformations in the spirit of absorbing state/depinning
phase transitions, as well as deformation-deformation correlations and the
width of the cumulative strain distributions. The results are also compared
with the order parameter fluctuations observed close to the depinning
transition of the 2 Linear Interface Model or the quenched Edwards-Wilkinson
equation.Comment: 27 pages, 18 figure
The Skyrme model predictions for the mass spectrum and the - mass splittings
The -plet mass spectrum and the - mass splittings are computed in the framework of the minimal SU(3)
extended Skyrme model. As functions of the Skyrme charge and the SU(3)
symmetry breaking parameters the predictions are presented in tabular form. The
predicted mass splitting - is the smallest among
all SU(3) baryonic multiplets.Comment: 4 pages, 2 tables, version to appear in Phys. Rev.
Probing the partonic structure of pentaquarks in hard electroproduction
Exclusive electroproduction of a K or K* meson on the nucleon can give a
Theta+ pentaquark in the final state. This reaction offers an opportunity to
investigate the structure of pentaquark baryons at parton level. We discuss the
generalized parton distributions for the N-->Theta+ transition and give the
leading order amplitude for electroproduction in the Bjorken regime. Different
production channels contain complementary information about the distribution of
partons in a pentaquark compared with their distribution in the nucleon.
Measurement of these processes may thus provide deeper insight into the very
nature of pentaquarks.Comment: 17 pages, 8 figures. v2: minor clarifications, references adde
Yielding and irreversible deformation below the microscale: Surface effects and non-mean-field plastic avalanches
Nanoindentation techniques recently developed to measure the mechanical
response of crystals under external loading conditions reveal new phenomena
upon decreasing sample size below the microscale. At small length scales,
material resistance to irreversible deformation depends on sample morphology.
Here we study the mechanisms of yield and plastic flow in inherently small
crystals under uniaxial compression. Discrete structural rearrangements emerge
as series of abrupt discontinuities in stress-strain curves. We obtain the
theoretical dependence of the yield stress on system size and geometry and
elucidate the statistical properties of plastic deformation at such scales. Our
results show that the absence of dislocation storage leads to crucial effects
on the statistics of plastic events, ultimately affecting the universal scaling
behavior observed at larger scales.Comment: Supporting Videos available at
http://dx.plos.org/10.1371/journal.pone.002041
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