361 research outputs found
Brief Communication: Early season snowpack loss and implications for oversnow vehicle recreation travel planning
Oversnow vehicle recreation contributes to rural
economies but requires a minimum snow depth to mitigate negative impacts on
the environment. Daily snow water equivalent (SWE) observations from weather
stations in the Lake Tahoe region (western USA) and a SWE reanalysis product
are used to estimate the onset dates of SWE corresponding to ∼30 cm in snow depth (SWEmin). Since 1985, median SWEmin onset has
shifted later by approximately 2 weeks. Potential proximal causes of
delayed onset are investigated; rainfall is increasing during
October–January with dry days becoming warmer and more frequent. Adaptation
strategies to address oversnow vehicle management challenges in recreation
travel planning are explored.</p
Replica symmetry breaking in the `small world' spin glass
We apply the cavity method to a spin glass model on a `small world' lattice,
a random bond graph super-imposed upon a 1-dimensional ferromagnetic ring. We
show the correspondence with a replicated transfer matrix approach, up to the
level of one step replica symmetry breaking (1RSB). Using the scheme developed
by M\'ezard & Parisi for the Bethe lattice, we evaluate observables for a model
with fixed connectivity and long range bonds. Our results agree with
numerical simulations significantly better than the replica symmetric (RS)
theory.Comment: 21 pages, 3 figure
Trading interactions for topology in scale-free networks
Scale-free networks with topology-dependent interactions are studied. It is
shown that the universality classes of critical behavior, which conventionally
depend only on topology, can also be explored by tuning the interactions. A
mapping, , describes how a shift of the
standard exponent of the degree distribution can absorb the
effect of degree-dependent pair interactions .
Replica technique, cavity method and Monte Carlo simulation support the
physical picture suggested by Landau theory for the critical exponents and by
the Bethe-Peierls approximation for the critical temperature. The equivalence
of topology and interaction holds for equilibrium and non-equilibrium systems,
and is illustrated with interdisciplinary applications.Comment: 4 pages, 5 figure
Derivatives and Credit Contagion in Interconnected Networks
The importance of adequately modeling credit risk has once again been
highlighted in the recent financial crisis. Defaults tend to cluster around
times of economic stress due to poor macro-economic conditions, {\em but also}
by directly triggering each other through contagion. Although credit default
swaps have radically altered the dynamics of contagion for more than a decade,
models quantifying their impact on systemic risk are still missing. Here, we
examine contagion through credit default swaps in a stylized economic network
of corporates and financial institutions. We analyse such a system using a
stochastic setting, which allows us to exploit limit theorems to exactly solve
the contagion dynamics for the entire system. Our analysis shows that, by
creating additional contagion channels, CDS can actually lead to greater
instability of the entire network in times of economic stress. This is
particularly pronounced when CDS are used by banks to expand their loan books
(arguing that CDS would offload the additional risks from their balance
sheets). Thus, even with complete hedging through CDS, a significant loan book
expansion can lead to considerably enhanced probabilities for the occurrence of
very large losses and very high default rates in the system. Our approach adds
a new dimension to research on credit contagion, and could feed into a rational
underpinning of an improved regulatory framework for credit derivatives.Comment: 26 pages, 7 multi-part figure
Theory of agent-based market models with controlled levels of greed and anxiety
We use generating functional analysis to study minority-game type market
models with generalized strategy valuation updates that control the psychology
of agents' actions. The agents' choice between trend following and contrarian
trading, and their vigor in each, depends on the overall state of the market.
Even in `fake history' models, the theory now involves an effective overall bid
process (coupled to the effective agent process) which can exhibit profound
remanence effects and new phase transitions. For some models the bid process
can be solved directly, others require Maxwell-construction type
approximations.Comment: 30 pages, 10 figure
Survey propagation for the cascading Sourlas code
We investigate how insights from statistical physics, namely survey
propagation, can improve decoding of a particular class of sparse error
correcting codes. We show that a recently proposed algorithm, time averaged
belief propagation, is in fact intimately linked to a specific survey
propagation for which Parisi's replica symmetry breaking parameter is set to
zero, and that the latter is always superior to belief propagation in the high
connectivity limit. We briefly look at further improvements available by going
to the second level of replica symmetry breaking.Comment: 14 pages, 5 figure
Neutron time-of-flight measurements of charged-particle energy loss in inertial confinement fusion plasmas
Neutron spectra from secondary ^{3}H(d,n)α reactions produced by an implosion of a deuterium-gas capsule at the National Ignition Facility have been measured with order-of-magnitude improvements in statistics and resolution over past experiments. These new data and their sensitivity to the energy loss of fast tritons emitted from thermal ^{2}H(d,p)^{3}H reactions enable the first statistically significant investigation of charged-particle stopping via the emitted neutron spectrum. Radiation-hydrodynamic simulations, constrained to match a number of observables from the implosion, were used to predict the neutron spectra while employing two different energy loss models. This analysis represents the first test of stopping models under inertial confinement fusion conditions, covering plasma temperatures of k_{B}T≈1-4 keV and particle densities of n≈(12-2)×10^{24} cm^{-3}. Under these conditions, we find significant deviations of our data from a theory employing classical collisions whereas the theory including quantum diffraction agrees with our data
The Cavity Approach to Parallel Dynamics of Ising Spins on a Graph
We use the cavity method to study parallel dynamics of disordered Ising
models on a graph. In particular, we derive a set of recursive equations in
single site probabilities of paths propagating along the edges of the graph.
These equations are analogous to the cavity equations for equilibrium models
and are exact on a tree. On graphs with exclusively directed edges we find an
exact expression for the stationary distribution of the spins. We present the
phase diagrams for an Ising model on an asymmetric Bethe lattice and for a
neural network with Hebbian interactions on an asymmetric scale-free graph. For
graphs with a nonzero fraction of symmetric edges the equations can be solved
for a finite number of time steps. Theoretical predictions are confirmed by
simulation results. Using a heuristic method, the cavity equations are extended
to a set of equations that determine the marginals of the stationary
distribution of Ising models on graphs with a nonzero fraction of symmetric
edges. The results of this method are discussed and compared with simulations
Registration of ‘Hallam’ Wheat
‘Hallam’ (Reg. no. CV-983, PI 638790) is a hard red winter wheat (Triticum aestivum L.) cultivar developed cooperatively by the Nebraska Agricultural Experiment Station and the USDA-ARS and released in 2005 by the developing institutions. Hallam was released primarily for its superior adaptation to rainfed wheat production systems in eastern Nebraska. The name Hallam was chosen to honor Hallam, NE, a town and its people rebuilding after a tornado.
Hallam was selected from the cross ‘Brule’ (Schmidt et al., 1983)/‘Bennett’ (Schmidt et al., 1981)//‘Niobrara’ (Baenziger et al., 1996) that was made in 1992. The F1 generation was grown in the greenhouse and the F2 to F3 generations were advanced using the bulk breeding method in the field at Mead, NE. In 1995, single F3:4 rows were planted for selection. Hallam was selected in the F4 and there was no further selection thereafter.
Hallam was evaluated as NE98471 in Nebraska yield nurseries starting in 1999, in the Northern Regional Performance Nursery in 2001 and 2002, and in Nebraska cultivar performance trials from 2002 to 2004. In the Nebraska cultivar performance trials, it was narrowly adapted and performs best in eastern Nebraska. The average Nebraska rainfed yield of Hallam of 4110 kg ha-1 (41 environments from 2002 to 2004) was greater than the yields of ‘Wahoo’ (4030 kg ha-1; Baenziger et al., 2002), ‘Alliance’ (3880 kg ha-1; Baenziger et al., 1995), and ‘Harry’ (4000 kg ha-1; Baenziger et al., 2004b), but was lower than ‘Millennium’ (4180 kg ha-1; Baenziger et al., 2001) and ‘Wesley’ (4210 kg ha-1; Peterson et al., 2001). In its primary area of adaptation (eastern Nebraska), Hallam has yielded 4540 kg ha-1 (five environments), which was greater than Wesley (4150 kg ha-1), Millennium (4250 kg ha-1), Wahoo (3940 kg ha-1), and Alliance (3900 kg ha21). In the Northern Regional Performance Nursery, Hallam ranked 14th of 30 in 2001 (12 environments) and fourth of 25 entries in 2002 (13 environments) and averaged 100 kg ha-1 more grain yield than ‘Nekota’ (Haley et al., 1996). Hallam is not recommended for use in irrigated production systems where other wheat cultivars with superior performance, especially with better straw strength (described below), would be recommended.
Other measurements of performance from comparison trials show that Hallam is moderately early in maturity (142 d after January 1, five environments), about 2.5 d and 1.2 d earlier flowering than Millennium and Wesley, respectively. Hallam is a semidwarf wheat cultivar. Hallam has a medium short coleoptile (46 mm), as expected for a semidwarf wheat cultivar, and is shorter than ‘Goodstreak’ (61 mm; Baenziger et al., 2004a) and slightly longer than semidwarf wheat cultivars such as Harry (36 mm). The mature plant height of Hallam (86 cm) is 3 cm shorter than Millennium and 6 cm taller than Wesley (41 environments). Hallam has moderate straw strength (45% lodged), similar to Wahoo (46% lodged), but worse than Wesley (34% lodged) in those environments (3) where severe lodging was found. The winter hardiness of Hallamis good to very good, similar to ‘Abilene’ (PI 511307) and comparable to other winter wheat cultivars adapted and commonly grown in Nebraska
Registration of ‘Hallam’ Wheat
‘Hallam’ (Reg. no. CV-983, PI 638790) is a hard red winter wheat (Triticum aestivum L.) cultivar developed cooperatively by the Nebraska Agricultural Experiment Station and the USDA-ARS and released in 2005 by the developing institutions. Hallam was released primarily for its superior adaptation to rainfed wheat production systems in eastern Nebraska. The name Hallam was chosen to honor Hallam, NE, a town and its people rebuilding after a tornado.
Hallam was selected from the cross ‘Brule’ (Schmidt et al., 1983)/‘Bennett’ (Schmidt et al., 1981)//‘Niobrara’ (Baenziger et al., 1996) that was made in 1992. The F1 generation was grown in the greenhouse and the F2 to F3 generations were advanced using the bulk breeding method in the field at Mead, NE. In 1995, single F3:4 rows were planted for selection. Hallam was selected in the F4 and there was no further selection thereafter.
Hallam was evaluated as NE98471 in Nebraska yield nurseries starting in 1999, in the Northern Regional Performance Nursery in 2001 and 2002, and in Nebraska cultivar performance trials from 2002 to 2004. In the Nebraska cultivar performance trials, it was narrowly adapted and performs best in eastern Nebraska. The average Nebraska rainfed yield of Hallam of 4110 kg ha-1 (41 environments from 2002 to 2004) was greater than the yields of ‘Wahoo’ (4030 kg ha-1; Baenziger et al., 2002), ‘Alliance’ (3880 kg ha-1; Baenziger et al., 1995), and ‘Harry’ (4000 kg ha-1; Baenziger et al., 2004b), but was lower than ‘Millennium’ (4180 kg ha-1; Baenziger et al., 2001) and ‘Wesley’ (4210 kg ha-1; Peterson et al., 2001). In its primary area of adaptation (eastern Nebraska), Hallam has yielded 4540 kg ha-1 (five environments), which was greater than Wesley (4150 kg ha-1), Millennium (4250 kg ha-1), Wahoo (3940 kg ha-1), and Alliance (3900 kg ha21). In the Northern Regional Performance Nursery, Hallam ranked 14th of 30 in 2001 (12 environments) and fourth of 25 entries in 2002 (13 environments) and averaged 100 kg ha-1 more grain yield than ‘Nekota’ (Haley et al., 1996). Hallam is not recommended for use in irrigated production systems where other wheat cultivars with superior performance, especially with better straw strength (described below), would be recommended.
Other measurements of performance from comparison trials show that Hallam is moderately early in maturity (142 d after January 1, five environments), about 2.5 d and 1.2 d earlier flowering than Millennium and Wesley, respectively. Hallam is a semidwarf wheat cultivar. Hallam has a medium short coleoptile (46 mm), as expected for a semidwarf wheat cultivar, and is shorter than ‘Goodstreak’ (61 mm; Baenziger et al., 2004a) and slightly longer than semidwarf wheat cultivars such as Harry (36 mm). The mature plant height of Hallam (86 cm) is 3 cm shorter than Millennium and 6 cm taller than Wesley (41 environments). Hallam has moderate straw strength (45% lodged), similar to Wahoo (46% lodged), but worse than Wesley (34% lodged) in those environments (3) where severe lodging was found. The winter hardiness of Hallamis good to very good, similar to ‘Abilene’ (PI 511307) and comparable to other winter wheat cultivars adapted and commonly grown in Nebraska
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