4,339 research outputs found
Inheritance-Based Diversity Measures for Explicit Convergence Control in Evolutionary Algorithms
Diversity is an important factor in evolutionary algorithms to prevent
premature convergence towards a single local optimum. In order to maintain
diversity throughout the process of evolution, various means exist in
literature. We analyze approaches to diversity that (a) have an explicit and
quantifiable influence on fitness at the individual level and (b) require no
(or very little) additional domain knowledge such as domain-specific distance
functions. We also introduce the concept of genealogical diversity in a broader
study. We show that employing these approaches can help evolutionary algorithms
for global optimization in many cases.Comment: GECCO '18: Genetic and Evolutionary Computation Conference, 2018,
Kyoto, Japa
Some remarks on quasi-Hermitian operators
A quasi-Hermitian operator is an operator that is similar to its adjoint in
some sense, via a metric operator, i.e., a strictly positive self-adjoint
operator. Whereas those metric operators are in general assumed to be bounded,
we analyze the structure generated by unbounded metric operators in a Hilbert
space. Following our previous work, we introduce several generalizations of the
notion of similarity between operators. Then we explore systematically the
various types of quasi-Hermitian operators, bounded or not. Finally we discuss
their application in the so-called pseudo-Hermitian quantum mechanics.Comment: 18page
Weak commutation relations of unbounded operators: nonlinear extensions
We continue our analysis of the consequences of the commutation relation
[S,T]=\Id, where and are two closable unbounded operators. The {\em
weak} sense of this commutator is given in terms of the inner product of the
Hilbert space \H where the operators act. {We also consider what we call,
adopting a physical terminology}, a {\em nonlinear} extension of the above
commutation relations
Thermodynamics of the three-dimensional Hubbard model: Implications for cooling cold atomic gases in optical lattices
We present a comprehensive study of the thermodynamic properties of the
three-dimensional fermionic Hubbard model, with application to cold fermionic
atoms subject to an optical lattice and a trapping potential. Our study is
focused on the temperature range of current experimental interest. We employ
two theoretical methods - dynamical mean-field theory and high-temperature
series - and perform comparative benchmarks to delimitate their respective
range of validity. Special attention is devoted to understand the implications
that thermodynamic properties of this system have on cooling. Considering the
distribution function of local occupancies in the inhomogeneous lattice, we
show that, under adiabatic evolution, the variation of any observable (e.g.,
temperature) can be conveniently disentangled into two distinct contributions.
The first contribution is due to the redistribution of atoms in the trap during
the evolution, while the second one comes from the intrinsic change of the
observable. Finally, we provide a simplified picture of the cooling procedure
recently proposed in J.-S. Bernier et al., Phys. Rev. A 79, 061601 (2009) by
applying this method to an idealized model.Comment: 17 pages, 27 figures, version published in PR
Carboplatin binding to a model protein in non-NaCl conditions to eliminate partial conversion to cisplatin, and the use of different criteria to choose the resolution limit
Hen egg white lysozyme (HEWL) co-crystallisation conditions of carboplatin
without sodium chloride (NaCl) have been utilised to eliminate partial
conversion of carboplatin to cisplatin observed previously. Tetragonal HEWL
crystals were successfully obtained in 65% MPD with 0.1M citric acid buffer at
pH 4.0 including DMSO. The X-ray diffraction data resolution to be used for the
model refinement was reviewed using several topical criteria together. The
CC1/2 criterion implemented in XDS led to data being significant to 2.0{\AA},
compared to the data only being able to be processed to 3.0{\AA} using the
Bruker software package (SAINT). Then using paired protein model refinements
and DPI values based on the FreeR value, the resolution limit was fine tuned to
be 2.3{\AA}. Interestingly this was compared with results from the EVAL
software package which gave a resolution limit of 2.2{\AA} solely using
crossing 2, but 2.8{\AA} based on the Rmerge values (60%). The
structural results showed that carboplatin bound to only the N{\delta} binding
site of His-15 one week after crystal growth, whereas five weeks after crystal
growth, two molecules of carboplatin are bound to the His-15 residue. In
summary several new results have emerged: - firstly non-NaCl conditions showed
a carboplatin molecule bound to His-15 of HEWL; secondly binding of one
molecule of carboplatin was seen after one week of crystal growth and two
molecules were bound after five weeks of crystal growth; and thirdly the use of
several criteria to determine the diffraction resolution limit led to the
successful use of data to higher resolution.Comment: 14 pages; submitted to Acta Cryst D Biological Crystallography
reference number tz504
Toward a Holistic Agricultural Student Recruitment Model: A National Analysis of the Factors Affecting Students’ Decision to Pursue an Agricultural Related Degree
Currently, the agricultural industry struggles to fill positions with qualified agricultural workers. Therefore, it is critical to attract high caliber individuals to agricultural degree programs that are prepared to enter the workforce with the skills needed to navigate complex issues and problems. The purpose of this national study was to identify key factors that influence the recruitment of agriculture students at land-grant and non-land-grant universities. Using Chapman’s model of student success as our conceptual lens, we tested 66 factors identified in the literature as successful recruitment strategies for colleges of agriculture based on students’ personal characteristics as well as key external influences. We discovered statistically significant (p \u3c .05) differences existed based on students’ gender and race/ethnicity. To better operationalize the findings from this study for U.S. colleges of agriculture, we developed the agricultural student recruitment model (ASRM). The model visually represents the distinct but intersecting factors that most profoundly influence students’ academic degree decisions. Moving forward, we recommend colleges of agriculture use the ASRM as a tool to better resonate with populations that may lack representation in their degree programs and the state’s agricultural industry
Propagation on networks: an exact alternative perspective
By generating the specifics of a network structure only when needed
(on-the-fly), we derive a simple stochastic process that exactly models the
time evolution of susceptible-infectious dynamics on finite-size networks. The
small number of dynamical variables of this birth-death Markov process greatly
simplifies analytical calculations. We show how a dual analytical description,
treating large scale epidemics with a Gaussian approximations and small
outbreaks with a branching process, provides an accurate approximation of the
distribution even for rather small networks. The approach also offers important
computational advantages and generalizes to a vast class of systems.Comment: 8 pages, 4 figure
Experimental limits of ghost diffraction: Popper’s thought experiment
Quantum ghost diffraction harnesses quantum correlations to record diffraction or interference features using photons that have never interacted with the diffractive element. By designing an optical system in which the diffraction pattern can be produced by double slits of variable width either through a conventional diffraction scheme or a ghost diffraction scheme, we can explore the transition between the case where ghost diffraction behaves as conventional diffraction and the case where it does not. For conventional diffraction the angular extent increases as the scale of the diffracting object is reduced. By contrast, we show that no matter how small the scale of the diffracting object, the angular extent of the ghost diffraction is limited (by the transverse extent of the spatial correlations between beams). Our study is an experimental realisation of Popper’s thought experiment on the validity of the Copenhagen interpretation of quantum mechanics. We discuss the implication of our results in this context and explain that it is compatible with, but not proof of, the Copenhagen interpretation
Search for universality in one-dimensional ballistic annihilation kinetics
We study the kinetics of ballistic annihilation for a one-dimensional ideal
gas with continuous velocity distribution. A dynamical scaling theory for the
long time behavior of the system is derived. Its validity is supported by
extensive numerical simulations for several velocity distributions. This leads
us to the conjecture that all the continuous velocity distributions \phi(v)
which are symmetric, regular and such that \phi(0) does not vanish, are
attracted in the long time regime towards the same Gaussian distribution and
thus belong to the same universality class. Moreover, it is found that the
particle density decays as n(t)~t^{-\alpha}, with \alpha=0.785 +/- 0.005.Comment: 8 pages, needs multicol, epsf and revtex. 8 postscript figures
included. Submitted to Phys. Rev. E. Also avaiable at
http://mykonos.unige.ch/~rey/publi.html#Secon
How do electronic carriers cross Si-bound alkyl monolayers?
Electron transport through Si-C bound alkyl chains, sandwiched between n-Si
and Hg, is characterized by two distinct types of barriers, each dominating in
a different voltage range. At low voltage, current depends strongly on
temperature but not on molecular length, suggesting transport by thermionic
emission over a barrier in the Si. At higher voltage, the current decreases
exponentially with molecular length, suggesting tunneling through the
molecules. The tunnel barrier is estimated, from transport and photoemission
data, to be ~1.5 eV with a 0.25me effective mass.Comment: 13 pages, 3 figure
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