2,978 research outputs found
Alarm-Based Prescriptive Process Monitoring
Predictive process monitoring is concerned with the analysis of events
produced during the execution of a process in order to predict the future state
of ongoing cases thereof. Existing techniques in this field are able to
predict, at each step of a case, the likelihood that the case will end up in an
undesired outcome. These techniques, however, do not take into account what
process workers may do with the generated predictions in order to decrease the
likelihood of undesired outcomes. This paper proposes a framework for
prescriptive process monitoring, which extends predictive process monitoring
approaches with the concepts of alarms, interventions, compensations, and
mitigation effects. The framework incorporates a parameterized cost model to
assess the cost-benefit tradeoffs of applying prescriptive process monitoring
in a given setting. The paper also outlines an approach to optimize the
generation of alarms given a dataset and a set of cost model parameters. The
proposed approach is empirically evaluated using a range of real-life event
logs
Leonardo's rule, self-similarity and wind-induced stresses in trees
Examining botanical trees, Leonardo da Vinci noted that the total
cross-section of branches is conserved across branching nodes. In this Letter,
it is proposed that this rule is a consequence of the tree skeleton having a
self-similar structure and the branch diameters being adjusted to resist
wind-induced loads
Hyperaccreting Disks around Magnetars for Gamma-Ray Bursts: Effects of Strong Magnetic Fields
(Abridged) The hyperaccreting neutron star or magnetar disks cooled via
neutrino emission can be a candidate of gamma-ray burst (GRB) central engines.
The strong field G of the magnetar can play a significant
role in affecting the disk properties and even lead to the funnel accretion
process. We investigate the effects of strong fields on the disks around
magnetars, and discuss implications of such accreting magnetar systems for GRB
and GRB-like events. We discuss quantum effects of the strong fields on the
disk, and use the MHD conservation equations to describe the behavior of the
disk flow coupled with a large scale field, which is generated by the star-disk
interaction. In general, stronger fields give higher disk densities, pressures,
temperatures and neutrino luminosity, and change the electron fraction and
degeneracy state significantly. A magnetized disk is always viscously stable
outside the Alfv\'{e}n radius, but will be thermally unstable near the
Alfv\'{e}n radius where the magnetic field plays a more important role in
transferring the angular momentum and heating the disk than the viscous stress.
The funnel accretion process will be only important for an extremely strong
field, which creates a magnetosphere inside the Alfv\'{e}n radius and truncates
the plane disk. Because of higher temperature and more concentrated neutrino
emission of the magnetar surface ring-like belt region covered by funnel
accretion, the neutrino annihilation rate from the accreting magnetars can be
much higher than that from accreting neutron stars without fields. Furthermore,
the neutrino annihilation mechanism and the magnetically-driven pulsar wind
from the magnetar surface can work together to generate and feed an
ultra-relativistic jet along the stellar magnetic poles.Comment: 62 pages, 14 figures, 4 tables, improved version following the
referee's comments, accepted for publication in Ap
Hyperaccreting Neutron-Star Disks and Neutrino Annihilation
Newborn neutron stars surrounded by hyperaccreting and neutrino-cooled disks
may exist in some gamma-ray bursts (GRBs) and/or supernovae (SNe). In this
paper we further study the structure of such a neutron-star disk based on the
two-region (i.e., inner & outer) disk scenario following our previous work, and
calculate the neutrino annihilation luminosity from the disk in various cases.
We investigate the effects of the viscosity parameter, energy parameter
(measuring the neutrino cooling efficiency of the inner disk) and outflow
strength on the structure of the entire disk as well as the effect of emission
from the neutron star surface boundary emission on the total neutrino
annihilation rate. The inner disk satisfies the entropy-conservation or the
advection-dominated self-similar structure depending on the energy parameter.
An outflow from the disk decreases the density and pressure but increases the
thickness of the disk. Moreover, compared with the black-hole disk, the
neutrino annihilation luminosity above the neutron-star disk is higher, and the
neutrino emission from the boundary layer could increase the neutrino
annihilation luminosity by about one order of magnitude higher than the disk
without boundary emission. The neutron-star disk with the advection-dominated
inner disk could produce the highest neutrino luminosity while the disk with an
outflow has the lowest. Although a heavily mass-loaded outflow from the neutron
star surface at early times of neutron star formation prevents the outflow
material from being accelerated to a high bulk Lorentz factor, an energetic
ultrarelativistic jet via neutrino annihilation can be produced above the
stellar polar region at late times if the disk accretion rate and the neutrino
emission luminosity from the surface boundary layer are sufficiently high.Comment: 46 pages, 11 figures, 4 tables, improved version following the
referee's comments, accepted for publication in Ap
Electron transport through dipyrimidinyl-diphenyl diblock molecular wire: protonation effect
Recently, rectifying direction inversion has been observed in
dipyrimidinyl-diphenyl (PMPH) diblock molecular wire [J. Am. Chem. Soc. (2005)
127, 10456], and a protonation mechanism was suggested to explain this
interesting phenomena. In this paper, we study the protonation effect on
transport properties of PMPH molecule by first principles calculations. No
significant rectification is found for the pristine diblock molecular wire.
Protonation leads to conductance enhancement and rectification. However, for
all considered junctions with rectifying effect, the preferential current
directions are samely from dipyrimidinyl side to diphenyl side. Effect of
molecule-electrode anchoring geometry is studied, and it is not responsible for
the discrepancy between experiment and theory.Comment: 17 pages, 8 figure
A strongly first order electroweak phase transition from strong symmetry-breaking interactions
We argue that a strongly first order electroweak phase transition is natural
in the presence of strong symmetry-breaking interactions, such as technicolor.
We demonstrate this using an effective linear scalar theory of the
symmetry-breaking sector.Comment: LaTex, 15 pages, 3 figures in EPS format. Phys. Rev. D approved
Typographically Correct version, minor grammatical change
The influence of collective neutrino oscillations on a supernova r-process
Recently, it has been demonstrated that neutrinos in a supernova oscillate
collectively. This process occurs much deeper than the conventional
matter-induced MSW effect and hence may have an impact on nucleosynthesis. In
this paper we explore the effects of collective neutrino oscillations on the
r-process, using representative late-time neutrino spectra and outflow models.
We find that accurate modeling of the collective oscillations is essential for
this analysis. As an illustration, the often-used "single-angle" approximation
makes grossly inaccurate predictions for the yields in our setup. With the
proper multiangle treatment, the effect of the oscillations is found to be less
dramatic, but still significant. Since the oscillation patterns are sensitive
to the details of the emitted fluxes and the sign of the neutrino mass
hierarchy, so are the r-process yields. The magnitude of the effect also
depends sensitively on the astrophysical conditions - in particular on the
interplay between the time when nuclei begin to exist in significant numbers
and the time when the collective oscillation begins. A more definitive
understanding of the astrophysical conditions, and accurate modeling of the
collective oscillations for those conditions, is necessary.Comment: 27 pages, 10 figure
Phase diagrams of magnetopolariton gases
The magnetic field effect on phase transitions in electrically neutral
bosonic systems is much less studied than those in fermionic systems, such as
superconducting or ferromagnetic phase transitions. Nevertheless, composite
bosons are strongly sensitive to magnetic fields: both their internal structure
and motion as whole particles may be affected. A joint effort of ten
laboratories has been focused on studies of polariton lasers, where
non-equilibrium Bose-Einstein condensates of bosonic quasiparticles,
exciton-polaritons, may appear or disappear under an effect of applied magnetic
fields. Polariton lasers based on pillar or planar microcavities were excited
both optically and electrically. In all cases a pronounced dependence of the
onset to lasing on the magnetic field has been observed. For the sake of
comparison, photon lasing (lasing by an electron-hole plasma) in the presence
of a magnetic field has been studied on the same samples as polariton lasing.
The threshold to photon lasing is essentially governed by the excitonic Mott
transition which appears to be sensitive to magnetic fields too. All the
observed experimental features are qualitatively described within a uniform
model based on coupled diffusion equations for electrons, holes and excitons
and the Gross-Pitaevskii equation for exciton-polariton condensates. Our
research sheds more light on the physics of non-equilibrium Bose-Einstein
condensates and the results manifest high potentiality of polariton lasers for
spin-based quantum logic applications.Comment: 21 pages, 11 figure
Orbital Interaction Mechanisms of Conductance Enhancement and Rectification by Dithiocarboxylate Anchoring Group
We study computationally the electron transport properties of
dithiocarboxylate terminated molecular junctions. Transport properties are
computed self-consistently within density functional theory and nonequilibrium
Green's functions formalism. A microscopic origin of the experimentally
observed current amplification by dithiocarboxylate anchoring groups is
established. For the 4,4'-biphenyl bis(dithiocarboxylate) junction, we find
that the interaction of the lowest unoccupied molecular orbital (LUMO) of the
dithiocarboxylate anchoring group with LUMO and highest occupied molecular
orbital (HOMO) of the biphenyl part results in bonding and antibonding
resonances in the transmission spectrum in the vicinity of the electrode Fermi
energy. A new microscopic mechanism of rectification is predicted based on the
electronic structure of asymmetrical anchoring groups. We show that the peaks
in the transmission spectra of 4'-thiolato-biphenyl-4-dithiocarboxylate
junction respond differently to the applied voltage. Depending upon the origin
of a transmission resonance in the orbital interaction picture, its energy can
be shifted along with the chemical potential of the electrode to which the
molecule is more strongly or more weakly coupled
Pump-seed synchronization for MHz repetition rate, high-power optical parametric chirped pulse amplification
We report on an active synchronization between two independent mode-locked lasers using a combined electronic-optical feedback. With this scheme, seed pulses at MHz repetition rate were amplified in a non-collinear optical parametric chirped pulse amplifier (OPCPA). The amplifier was seeded with stretched 1.5 nJ pulses from a femtosecond Ti:Sapphire oscillator, while pumped with the 1 ps, 2.9 µJ frequency-doubled output of an Yb:YAG thin-disk oscillator. The residual timing jitter between the two oscillators was suppressed to 120 fs (RMS), allowing for an efficient and broadband amplification at 11.5 MHz to a pulse energy of 700 nJ and an average power of 8 W. First compression experiment with 240 nJ amplified pulse energy resulted in a pulse duration of ~10 fs
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