6,899 research outputs found
Gamma-ray burst beaming: a universal configuration with a standard energy reservoir?
We consider a gamma-ray burst (GRB) model based on an anisotropic fireball
with an axisymmetric power-law distribution of the energy per solid angle with
index -k, and allow for the observer's viewing direction being at an arbitrary
angle with respect to the jet axis. This model can reproduce the key features
expected from the conventional on-axis uniform jet models, with the novelty
that the achromatic break time in the broadband afterglow lightcurves
corresponds to the epoch when the relativistic beaming angle is equal to the
viewing angle rather than to the jet half opening angle. If all the GRB
fireballs have such a similar energy distribution form with 1.5 < k < (or \sim)
2, GRBs may be modeled by a quasi-universal beaming configuration, and an
approximately standard energy reservoir. The conclusion also holds for some
other forms of angular energy distributions, such as the Gaussian function.Comment: Slightly expanded version accepted for publication in Ap
Pion charge form factor and constraints from space-time translations
The role of Poincar\'e covariant space-time translations is investigated in
the case of a relativistic quantum mechanics approach to the pion charge form
factor. It is shown that the related constraints are generally inconsistent
with the assumption of a single-particle current, which is most often referred
to. The only exception is the front-form approach with . How accounting
for the related constraints, as well as restoring the equivalence of different
RQM approaches in estimating form factors, is discussed. Some extensions of
this work and, in particular, the relationship with a dispersion-relation
approach, are presented. Conclusions relative to the underlying dynamics are
given.Comment: 6 pages, 2 figures, proceedings of the QNP2009 international
conference (Beijing, oct. 2009), to be published in Chinese Physics
Chiral expansion of the decay width
A chiral field theory of mesons has been applied to study the contribution of
the current quark masses to the decay width at
the next leading order. enhancement has been predicted and there is no
new parameter.Comment: 9 page
Multiplier-continuation algorthms for constrained optimization
Several path following algorithms based on the combination of three smooth penalty functions, the quadratic penalty for equality constraints and the quadratic loss and log barrier for inequality constraints, their modern counterparts, augmented Lagrangian or multiplier methods, sequential quadratic programming, and predictor-corrector continuation are described. In the first phase of this methodology, one minimizes the unconstrained or linearly constrained penalty function or augmented Lagrangian. A homotopy path generated from the functions is then followed to optimality using efficient predictor-corrector continuation methods. The continuation steps are asymptotic to those taken by sequential quadratic programming which can be used in the final steps. Numerical test results show the method to be efficient, robust, and a competitive alternative to sequential quadratic programming
Probing the birth of fast rotating magnetars through high-energy neutrinos
We investigate the high-energy neutrino emission expected from newly born
magnetars surrounded by their stellar ejecta. Protons might be accelerated up
to 0.1-100 EeV energies possibly by, e.g., the wave dissipation in the winds,
leading to hadronic interactions in the stellar ejecta. The resulting PeV-EeV
neutrinos can be detected by IceCube/KM3Net with a typical peak time scale of a
few days after the birth of magnetars, making the characteristic soft-hard-soft
behavior. Detections would be important as a clue to the formation mechanism of
magnetars, although there are ambiguities coming from uncertainties of several
parameters such as velocity of the ejecta. Non-detections would also lead to
useful constraints on the scenario.Comment: 5 pages, 3 figures, accepted for publication in PR
Periodic Variation of Stress in Sputter Deposited Si/WSi2 Multilayers
A tension increment after sputter deposition of 1 nm of WSi2 onto sputtered
Si was observed at low Ar gas pressures. Wafer curvature data on multilayers
were found to have a periodic variation corresponding to the multilayer period,
and this permitted statistical analyses to improve the sensitivity to small
stresses. The observation of tension instead of compression in the initial
stage of growth is new and a model invoking surface rearrangement is invoked.
The data also bear on an unusual surface smoothing phenomena for sputtered Si
surfaces caused by the sputter deposition of WSi2 . We furthermore report that
for low Ar pressures the Si layers are the predominant source of built-up
stress
Highly Charged Ion (HCI) Clocks: Frontier candidates for testing variation of fine-structure constant
Attempts are made to unify gravity with the other three fundamental forces of
nature. As suggested by higher dimensional models, this unification may require
space and time variation of some dimensionless fundamental constants. In this
scenario, probing temporal variation of the electromagnetic fine structure
constant () in low energy regimes at the
cosmological time scale is of immense interest. Atomic clocks are ideal
candidates for probing variation because their transition frequencies
are measured to ultra-high precision accuracy. Since atomic transition
frequencies are functions of , measurements of clock frequencies at
different temporal and spatial locations can yield signatures to ascertain such
conjecture. Electrons in highly charged ions (HCIs) experience unusually
enhanced relativistic effects. Hence level-crossings can be observed often in
these ions compared to their isoelectronic neutral or singly charged atomic
systems. Such a process features by their more significant relativistic
sensitive coefficients () of atomic transitions. For unambiguous detection
of subtle changes in the transition frequencies due to variation, it
would be judicious to contemplate transitions for which values are
enormous. HCIs are considered one of the most suitable candidates for making
atomic clocks as they are the least sensitive to external electromagnetic
fields owing to their exceptionally contracted orbitals. The first HCI clock
has been realized, but its accuracy is much less than the counter optical
clocks based on neutral atoms and singly charged ions. The realization of HCI
clocks can add an extra dimension to investigating fundamental physics. In this
work, we survey HCIs suitable for clock candidates on the grounds of general
features, including their potential to probe temporal variation of .Comment: 35 pages, 12 table
Perancangan Buku Essay Foto Kerajinan Cukli Lombok
Indonesia merupakan Negara yang kaya akan berbagai sumber daya alam. Keindahan alamnya pun luar biasa dan tidak semua Negara memiliki keindahan dan kekayaan alam seperti yang dimiliki oleh Negara ini.Begitu juga dengan pulau Lombok yang memiliki keindahan alam dan memiliki berbagai kerajinan yang memanjakan mata.Kerajinan Cukli merupakan kerajinan asli dari Lombok dan sangat digemari oleh turis mancanegara.Sayangnya masyarakat lokal banyak yang tidak mengetahui tentang adanya kerajinan ini. Oleh karena itu dibuatlah perancangan ini yang bertujuan untuk mengenalkan kerajinan Cukli Lombok pada masyarakat yang tidak mengetahui apa kerajinan Cukli tersebut
Testing Microfluidic Fully Programmable Valve Arrays (FPVAs)
Fully Programmable Valve Array (FPVA) has emerged as a new architecture for
the next-generation flow-based microfluidic biochips. This 2D-array consists of
regularly-arranged valves, which can be dynamically configured by users to
realize microfluidic devices of different shapes and sizes as well as
interconnections. Additionally, the regularity of the underlying structure
renders FPVAs easier to integrate on a tiny chip. However, these arrays may
suffer from various manufacturing defects such as blockage and leakage in
control and flow channels. Unfortunately, no efficient method is yet known for
testing such a general-purpose architecture. In this paper, we present a novel
formulation using the concept of flow paths and cut-sets, and describe an
ILP-based hierarchical strategy for generating compact test sets that can
detect multiple faults in FPVAs. Simulation results demonstrate the efficacy of
the proposed method in detecting manufacturing faults with only a small number
of test vectors.Comment: Design, Automation and Test in Europe (DATE), March 201
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