429,609 research outputs found
How Scale Affects Structure in Java Programs
Many internal software metrics and external quality attributes of Java
programs correlate strongly with program size. This knowledge has been used
pervasively in quantitative studies of software through practices such as
normalization on size metrics. This paper reports size-related super- and
sublinear effects that have not been known before. Findings obtained on a very
large collection of Java programs -- 30,911 projects hosted at Google Code as
of Summer 2011 -- unveils how certain characteristics of programs vary
disproportionately with program size, sometimes even non-monotonically. Many of
the specific parameters of nonlinear relations are reported. This result gives
further insights for the differences of "programming in the small" vs.
"programming in the large." The reported findings carry important consequences
for OO software metrics, and software research in general: metrics that have
been known to correlate with size can now be properly normalized so that all
the information that is left in them is size-independent.Comment: ACM Conference on Object-Oriented Programming, Systems, Languages and
Applications (OOPSLA), October 2015. (Preprint
Depinning with dynamic stress overshoots: A hybrid of critical and pseudohysteretic behavior
A model of an elastic manifold driven through a random medium by an applied
force F is studied focussing on the effects of inertia and elastic waves, in
particular {\it stress overshoots} in which motion of one segment of the
manifold causes a temporary stress on its neighboring segments in addition to
the static stress. Such stress overshoots decrease the critical force for
depinning and make the depinning transition hysteretic. We find that the steady
state velocity of the moving phase is nevertheless history independent and the
critical behavior as the force is decreased is in the same universality class
as in the absence of stress overshoots: the dissipative limit which has been
studied analytically. To reach this conclusion, finite-size scaling analyses of
a variety of quantities have been supplemented by heuristic arguments.
If the force is increased slowly from zero, the spectrum of avalanche sizes
that occurs appears to be quite different from the dissipative limit. After
stopping from the moving phase, the restarting involves both fractal and
bubble-like nucleation. Hysteresis loops can be understood in terms of a
depletion layer caused by the stress overshoots, but surprisingly, in the limit
of very large samples the hysteresis loops vanish. We argue that, although
there can be striking differences over a wide range of length scales, the
universality class governing this pseudohysteresis is again that of the
dissipative limit. Consequences of this picture for the statistics and dynamics
of earthquakes on geological faults are briefly discussed.Comment: 43 pages, 57 figures (yes, that's a five followed by a seven), revte
A Consistency Test of EFT Power Countings from Residual Cutoff Dependence
A method to quantitatively assess the consistency of power-counting proposals
in Effective Field Theories (EFT) which are non-perturbative at leading order
is presented. The Renormalisation Group evolution of an observable predicts the
functional form of its residual cutoff dependence on the breakdown scale of an
EFT, on the low-momentum scales, and on the order of the calculation. Passing
this test is a necessary but not sufficient consistency criterion for a
suggested power counting whose exact nature is disputed. In Chiral Effective
Field Theory (ChiEFT) with more than one nucleon, a lack of universally
accepted analytic solutions obfuscates the convergence pattern in results. This
led to proposals which predict different sets of Low Energy Coefficients (LECs)
at the same chiral order, and at times even predict a different ordering
long-range contributions. The method may independently check whether an
observable is renormalised at a given order, and proves estimates of both the
breakdown scale and the momentum-dependent order-by-order convergence pattern.
Conversely, it helps identify those LECs (and long-range pieces) which ensure
renormalised observables at a given order. I also discuss assumptions and the
relation to Wilson's Renormalisation Group; useful observable and cutoff
choices; the momentum window with likely best signals; its dependence on the
values and forms of cutoffs as well as on the EFT parameters; the impact of
fitting LECs to data; and caveats as well as limitations. Since the test is
designed to minimise the use of data, it quantitatively falsifies if the EFT
has been renormalised consistently. This complements other tests which quantify
how an EFT compares to experiment. Its application in particular to the 3P0 and
P2-3F2 partial waves of NN scattering in ChiEFT may elucidate persistent
power-counting issues.Comment: 15 pages LaTeX2e (pdflatex) including 5 figures as .pdf files using
includegraphics. Final version to appear in Europ. J. Phys. A topical issue
"The Tower of Effective (Field) Theories and the Emergence of Nuclear
Phenomena". arXiv admin note: substantial text overlap with arXiv:1511.00490
Author's note: substantial corrections in key argument and expansions.
Version appearing in Eur Phys J
An analysis of the evolving comoving number density of galaxies in hydrodynamical simulations
The cumulative comoving number-density of galaxies as a function of stellar
mass or central velocity dispersion is commonly used to link galaxy populations
across different epochs. By assuming that galaxies preserve their
number-density in time, one can infer the evolution of their properties, such
as masses, sizes, and morphologies. However, this assumption does not hold in
the presence of galaxy mergers or when rank ordering is broken owing to
variable stellar growth rates. We present an analysis of the evolving comoving
number density of galaxy populations found in the Illustris cosmological
hydrodynamical simulation focused on the redshift range . Our
primary results are as follows: 1) The inferred average stellar mass evolution
obtained via a constant comoving number density assumption is systematically
biased compared to the merger tree results at the factor of 2(4) level
when tracking galaxies from redshift out to redshift ; 2) The
median number density evolution for galaxy populations tracked forward in time
is shallower than for galaxy populations tracked backward in time; 3) A similar
evolution in the median number density of tracked galaxy populations is found
regardless of whether number density is assigned via stellar mass, stellar
velocity dispersion, or dark matter halo mass; 4) Explicit tracking reveals a
large diversity in galaxies' assembly histories that cannot be captured by
constant number-density analyses; 5) The significant scatter in galaxy linking
methods is only marginally reduced by considering a number of additional
physical and observable galaxy properties as realized in our simulation. We
provide fits for the forward and backward median evolution in stellar mass and
number density and discuss implications of our analysis for interpreting
multi-epoch galaxy property observations.Comment: 18 pages, 11 figures, submitted to MNRAS, comments welcom
What is a Cool-Core Cluster? A Detailed Analysis of the Cores of the X-ray Flux-Limited HIFLUGCS Cluster Sample
We use the largest complete sample of 64 galaxy clusters (HIghest X-ray FLUx
Galaxy Cluster Sample) with available high-quality X-ray data from Chandra, and
apply 16 cool-core diagnostics to them, some of them new. We also correlate
optical properties of brightest cluster galaxies (BCGs) with X-ray properties.
To segregate cool core and non-cool-core clusters, we find that central cooling
time, t_cool, is the best parameter for low redshift clusters with high quality
data, and that cuspiness is the best parameter for high redshift clusters. 72%
of clusters in our sample have a cool core (t_cool < 7.7 h_{71}^{-1/2} Gyr) and
44% have strong cool cores (t_cool <1.0 h_{71}^{-1/2} Gyr). For the first time
we show quantitatively that the discrepancy in classical and spectroscopic mass
deposition rates can not be explained with a recent formation of the cool
cores, demonstrating the need for a heating mechanism to explain the cooling
flow problem. [Abridged]Comment: 45 pages, 19 figures, 7 tables. Accepted for publication in A&A.
Contact Person: Rupal Mittal ([email protected]
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