8,319 research outputs found
The Kolmogorov-Smirnov test and its use for the identification of fireball fragmentation
We propose an application of the Kolmogorov-Smirnov test for rapidity
distributions of individual events in ultrarelativistic heavy ion collisions.
The test is particularly suitable to recognise non-statistical differences
between the events. Thus when applied to a narrow centrality class it could
indicate differences between events which would not be expected if all events
evolve according to the same scenario. In particular, as an example we assume
here a possible fragmentation of the fireball into smaller pieces at the
quark/hadron phase transition. Quantitative studies are performed with a Monte
Carlo model capable of simulating such a distribution of hadrons. We conclude
that the Kolmogorov-Smirnov test is a very powerful tool for the identification
of the fragmentation process.Comment: 9 pages, 10 figure
Experimental Predictions of The Functional Response of A Freshwater Fish
The functional response is the relationship between the feeding rate of an animal and its food density. It is reliant on two basic parameters; the volume searched for prey per unit time (searching rate) and the time taken to consume each prey item (handling time). As fish functional responses can be difficult to determine directly, it may be more feasible to measure their underlying behavioural parameters in controlled conditions and use these to predict the functional response. Here, we tested how accurately a Type II functional response model predicted the observed functional response of roach Rutilus rutilus, a visually foraging fish, and compared it with Type I functional response. Foraging experiments were performed by exposing fish in tank aquaria to a range of food densities, with their response captured using a two-camera videography system. This system was validated and was able to accurately measure fish behaviour in the aquaria, and enabled estimates of fish reaction distance, swimming speed (from which searching rate was calculated) and handling time to be measured. The parameterised Type II functional response model accurately predicted the observed functional response and was superior to the Type I model. These outputs suggest it will be possible to accurately measure behavioural parameters in other animal species and use these to predict the functional response in situations where it cannot be observed directly
Test of Nuclear Wave Functions for Pseudospin Symmetry
Using the fact that pseudospin is an approximate symmetry of the Dirac
Hamiltonian with realistic scalar and vector mean fields, we derive the wave
functions of the pseudospin partners of eigenstates of a realistic Dirac
Hamiltonian and compare these wave functions with the wave functions of the
Dirac eigenstates.Comment: 11 pages, 4 figures, minor changes in text and figures to conform
with PRL requirement
Testing Magnetic Field Models for the Class 0 Protostar L1527
For the Class 0 protostar, L1527, we compare 131 polarization vectors from
SCUPOL/JCMT, SHARP/CSO and TADPOL/CARMA observations with the corresponding
model polarization vectors of four ideal-MHD, non-turbulent, cloud core
collapse models. These four models differ by their initial magnetic fields
before collapse; two initially have aligned fields (strong and weak) and two
initially have orthogonal fields (strong and weak) with respect to the rotation
axis of the L1527 core. Only the initial weak orthogonal field model produces
the observed circumstellar disk within L1527. This is a characteristic of
nearly all ideal-MHD, non-turbulent, core collapse models. In this paper we
test whether this weak orthogonal model also has the best agreement between its
magnetic field structure and that inferred from the polarimetry observations of
L1527. We found that this is not the case; based on the polarimetry
observations the most favored model of the four is the weak aligned model.
However, this model does not produce a circumstellar disk, so our result
implies that a non-turbulent, ideal-MHD global collapse model probably does not
represent the core collapse that has occurred in L1527. Our study also
illustrates the importance of using polarization vectors covering a large area
of a cloud core to determine the initial magnetic field orientation before
collapse; the inner core magnetic field structure can be highly altered by a
collapse and so measurements from this region alone can give unreliable
estimates of the initial field configuration before collapse.Comment: 43 pages, 9 figures, 4 tables. Accepted by the Astrophysical Journa
Middle School Students’ Conceptual Understanding of Equations: Evidence from Writing Story Problems
This study investigated middle school students’ conceptual understanding of algebraic equations. 257 sixth- and seventh-grade students solved algebraic equations and generated story problems to correspond with given equations. Aspects of the equations’ structures, including number of operations and position of the unknown, influenced students’ performance on both tasks. On the story-writing task, students’ performance on two-operator equations was poorer than would be expected on the basis of their performance on one-operator equations. Students made a wide variety of errors on the story-writing task, including (1) generating story contexts that reflect operations different from the operations in the given equations, (2) failing to provide a story context for some element of the given equations, (3) failing to include mathematical content from the given equations in their stories, and (4) including mathematical content in their stories that was not present in the given equations. The nature of students’ story-writing errors suggests two main gaps in students’ conceptual understanding. First, students lacked a robust understanding of the connection between the operation of multiplication and its symbolic representation. Second, students demonstrated difficulty combining multiple mathematical operations into coherent stories. The findings highlight the importance of fostering connections between symbols and their referents
Unraveling critical dynamics: The formation and evolution of topological textures
We study the formation of topological textures in a nonequilibrium phase
transition of an overdamped classical O(3) model in 2+1 dimensions. The phase
transition is triggered through an external, time-dependent effective mass,
parameterized by quench timescale \tau. When measured near the end of the
transition the texture separation and the texture width scale respectively as
\tau^(0.39 \pm 0.02) and \tau^(0.46 \pm 0.04), significantly larger than
\tau^(0.25) predicted from the Kibble-Zurek mechanism. We show that
Kibble-Zurek scaling is recovered at very early times but that by the end of
the transition the power-laws result instead from a competition between the
length scale determined at freeze-out and the ordering dynamics of a textured
system. In the context of phase ordering these results suggest that the
multiple length scales characteristic of the late-time ordering of a textured
system derive from the critical dynamics of a single nonequilibrium correlation
length. In the context of defect formation these results imply that significant
evolution of the defect network can occur before the end of the phase
transition. Therefore a quantitative understanding of the defect network at the
end of the phase transition generally requires an understanding of both
critical dynamics and the interactions among topological defects.Comment: 12 pages, revtex, 9 figures in eps forma
The Schwinger Mechanism, the Unruh Effect and the Production of Accelerated Black Holes
We compute the corrections to the transition amplitudes of an accelerated
Unruh ``box'' that arise when the accelerated box is replaced by a ``two level
ion'' immersed in a constant electric field and treated in second quantization.
There are two kinds of corrections, those due to recoil effects induced by the
momentum transfers and those due to pair creation. Taken together, these
corrections show that there is a direct relationship between pair creation
amplitudes described by the Heisenberg-Euler-Schwinger mechanism and the Unruh
effect, i.e. the thermalisation of accelerated systems at temperature where is the acceleration. In particular, there is a thermodynamical
consistency between both effects whose origin is that the euclidean action
governing pair creation rates acts as an entropy in delivering the Unruh
temperature. Upon considering pair creation of charged black holes in an
electric field, these relationships explain why black holes are created from
vacuum in thermal equilibrium, i.e. with their Hawking temperature equal to
their Unruh temperature.Comment: Revised version: expanded introduction and discussion of pair
creation of black holes, 2figures added, 22 pages, Late
New black holes in the brane-world?
It is known that the Einstein field equations in five dimensions admit more
general spherically symmetric black holes on the brane than four-dimensional
general relativity. We propose two families of analytic solutions (with
g_tt\not=-1/g_rr), parameterized by the ADM mass and the PPN parameter beta,
which reduce to Schwarzschild for beta=1. Agreement with observations requires
|\beta-1| |\eta|<<1. The sign of eta plays a key role in the global causal
structure, separating metrics which behave like Schwarzschild (eta<0) from
those similar to Reissner-Nordstroem (eta>0). In the latter case, we find a
family of black hole space-times completely regular.Comment: 4 pages, RevTeX, 3 eps figures, final version to appear in Phys. Rev.
- …