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Modification of the National Weather Service Distributed Hydrologic Model for subsurface water exchanges between grids
To account for spatial variability of precipitation, as well as basin physiographic properties, the National Weather Service (NWS) has developed a distributed version of its hydrologic component, termed the Hydrology Laboratory-Research Distributed Hydrologic Model (HL-RDHM). Because channels are the only source of water exchange between neighboring computational elements, the absence of such exchange has been identified as a weakness in the model. The primary objective of this paper is to modify the model structure to account for subsurface water exchanges without dramatically altering the conceptual framework of the water balance module. The subsurface exchanges are established by partitioning the slow response components released from the lower layer storages into two parts: the first part involves the grid's conceptual channel, while the second is added to the lower layer storages of the downstream pixel. Realizing the deficiency of the water balance module to locate the lower zone layers in sufficient depths, a complementary study is conducted to test the feasibility of further improvement in the modified model by equally shifting downward the lower zone layers of all pixels over the basin. The Baron Fork at Eldon, Oklahoma, is chosen as the test basin. Ten years of grid-based multisensor precipitation data are used to investigate the effects of the modification, plus shifting the lower zone layers on model performance. The results show that the modified-shifted HL-RDHM can markedly improve the streamflow simulations at the interior point, as well as very high peak-flow simulations at the basin's outlet. Copyright 2011 by the American Geophysical Union
Inhibition causes ceaseless dynamics in networks of excitable nodes
The collective dynamics of a network of excitable nodes changes dramatically
when inhibitory nodes are introduced. We consider inhibitory nodes which may be
activated just like excitatory nodes but, upon activating, decrease the
probability of activation of network neighbors. We show that, although the
direct effect of inhibitory nodes is to decrease activity, the collective
dynamics becomes self-sustaining. We explain this counterintuitive result by
defining and analyzing a "branching function" which may be thought of as an
activity-dependent branching ratio. The shape of the branching function implies
that for a range of global coupling parameters dynamics are self-sustaining.
Within the self-sustaining region of parameter space lies a critical line along
which dynamics take the form of avalanches with universal scaling of size and
duration, embedded in ceaseless timeseries of activity. Our analyses, confirmed
by numerical simulation, suggest that inhibition may play a counterintuitive
role in excitable networks.Comment: 11 pages, 6 figure
The Spin-Orbit Evolution of GJ 667C System: The Effect of Composition and Other Planet's Perturbations
Potentially habitable planets within the habitable zone of M-dwarfs are
affected by tidal interaction. We studied the tidal evolution in GJ 667C using
a numerical code we call TIDEV. We reviewed the problem of the dynamical
evolution focusing on the effects that a rheological treatment, different
compositions and the inclusion of orbital perturbations, have on the spin-down
time and the probability to be trapped in a low spin-orbit resonance.
Composition have a strong effect on the spin-down time, changing, in some
cases, by almost a factor of 2 with respect to the value estimated for a
reference Earth-like model. We calculated the time to reach a low resonance
value (3:2) for the configuration of 6 planets. Capture probabilities are
affected when assuming different compositions and eccentricities variations. We
chose planets b and c to evaluate the probabilities of capture in resonances
below 5:2 for two compositions: Earth-like and Waterworld planets. We found
that perturbations, although having a secular effect on eccentricities, have a
low impact on capture probabilities and noth- ing on spin-down times. The
implications of the eccentricity variations and actual habitability of the GJ
667C system are discussed.Comment: 15 pages, 9 figures, 4 tables. Accepted for publication in MNRAS - V
Negative-energy perturbations in cylindrical equilibria with a radial electric field
The impact of an equilibrium radial electric field on negative-energy
perturbations (NEPs) (which are potentially dangerous because they can lead to
either linear or nonlinear explosive instabilities) in cylindrical equilibria
of magnetically confined plasmas is investigated within the framework of
Maxwell-drift kinetic theory. It turns out that for wave vectors with a
non-vanishing component parallel to the magnetic field the conditions for the
existence of NEPs in equilibria with E=0 [G. N. Throumoulopoulos and D.
Pfirsch, Phys. Rev. E 53, 2767 (1996)] remain valid, while the condition for
the existence of perpendicular NEPs, which are found to be the most important
perturbations, is modified. For ( is the
electrostatic potential) and ( is
the total plasma pressure), a case which is of operational interest in magnetic
confinement systems, the existence of perpendicular NEPs depends on ,
where is the charge of the particle species . In this case the
electric field can reduce the NEPs activity in the edge region of tokamaklike
and stellaratorlike equilibria with identical parabolic pressure profiles, the
reduction of electron NEPs being more pronounced than that of ion NEPs.Comment: 30 pages, late
Finding the Higgs Boson through Supersymmetry
The study of displaced vertices containing two b--jets may provide a double
discovery at the Large Hadron Collider (LHC): we show how it may not only
reveal evidence for supersymmetry, but also provide a way to uncover the Higgs
boson necessary in the formulation of the electroweak theory in a large region
of the parameter space. We quantify this explicitly using the simplest minimal
supergravity model with bilinear breaking of R-parity, which accounts for the
observed pattern of neutrino masses and mixings seen in neutrino oscillation
experiments.Comment: 7 pages, 7 figures. Final version to appear at PRD. Discussion and
results were enlarge
Statistical Properties of Avalanches in Networks
We characterize the distributions of size and duration of avalanches
propagating in complex networks. By an avalanche we mean the sequence of events
initiated by the externally stimulated `excitation' of a network node, which
may, with some probability, then stimulate subsequent firings of the nodes to
which it is connected, resulting in a cascade of firings. This type of process
is relevant to a wide variety of situations, including neuroscience, cascading
failures on electrical power grids, and epidemology. We find that the
statistics of avalanches can be characterized in terms of the largest
eigenvalue and corresponding eigenvector of an appropriate adjacency matrix
which encodes the structure of the network. By using mean-field analyses,
previous studies of avalanches in networks have not considered the effect of
network structure on the distribution of size and duration of avalanches. Our
results apply to individual networks (rather than network ensembles) and
provide expressions for the distributions of size and duration of avalanches
starting at particular nodes in the network. These findings might find
application in the analysis of branching processes in networks, such as
cascading power grid failures and critical brain dynamics. In particular, our
results show that some experimental signatures of critical brain dynamics
(i.e., power-law distributions of size and duration of neuronal avalanches),
are robust to complex underlying network topologies.Comment: 11 pages, 7 figure
Predicting criticality and dynamic range in complex networks: effects of topology
The collective dynamics of a network of coupled excitable systems in response
to an external stimulus depends on the topology of the connections in the
network. Here we develop a general theoretical approach to study the effects of
network topology on dynamic range, which quantifies the range of stimulus
intensities resulting in distinguishable network responses. We find that the
largest eigenvalue of the weighted network adjacency matrix governs the network
dynamic range. Specifically, a largest eigenvalue equal to one corresponds to a
critical regime with maximum dynamic range. We gain deeper insight on the
effects of network topology using a nonlinear analysis in terms of additional
spectral properties of the adjacency matrix. We find that homogeneous networks
can reach a higher dynamic range than those with heterogeneous topology. Our
analysis, confirmed by numerical simulations, generalizes previous studies in
terms of the largest eigenvalue of the adjacency matrix.Comment: 4 pages, 3 figure
Antigenic variation in vector-borne pathogens.
Several pathogens of humans and domestic animals depend on hematophagous arthropods to transmit them from one vertebrate reservoir host to another and maintain them in an environment. These pathogens use antigenic variation to prolong their circulation in the blood and thus increase the likelihood of transmission. By convergent evolution, bacterial and protozoal vector-borne pathogens have acquired similar genetic mechanisms for successful antigenic variation. Borrelia spp. and Anaplasma marginale (among bacteria) and African trypanosomes, Plasmodium falciparum, and Babesia bovis (among parasites) are examples of pathogens using these mechanisms. Antigenic variation poses a challenge in the development of vaccines against vector-borne pathogens
Negative-Energy Perturbations in Circularly Cylindrical Equilibria within the Framework of Maxwell-Drift Kinetic Theory
The conditions for the existence of negative-energy perturbations (which
could be nonlinearly unstable and cause anomalous transport) are investigated
in the framework of linearized collisionless Maxwell-drift kinetic theory for
the case of equilibria of magnetically confined, circularly cylindrical plasmas
and vanishing initial field perturbations. For wave vectors with a
non-vanishing component parallel to the magnetic field, the plane equilibrium
conditions (derived by Throumoulopoulos and Pfirsch [Phys Rev. E {\bf 49}, 3290
(1994)]) are shown to remain valid, while the condition for perpendicular
perturbations (which are found to be the most important modes) is modified.
Consequently, besides the tokamak equilibrium regime in which the existence of
negative-energy perturbations is related to the threshold value of 2/3 of the
quantity , a new
regime appears, not present in plane equilibria, in which negative-energy
perturbations exist for {\em any} value of . For various analytic
cold-ion tokamak equilibria a substantial fraction of thermal electrons are
associated with negative-energy perturbations (active particles). In
particular, for linearly stable equilibria of a paramagnetic plasma with flat
electron temperature profile (), the entire velocity space is
occupied by active electrons. The part of the velocity space occupied by active
particles increases from the center to the plasma edge and is larger in a
paramagnetic plasma than in a diamagnetic plasma with the same pressure
profile. It is also shown that, unlike in plane equilibria, negative-energy
perturbations exist in force-free reversed-field pinch equilibria with a
substantial fraction of active particles.Comment: 31 pages, late
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