168 research outputs found
Sub-structural Niching in Estimation of Distribution Algorithms
We propose a sub-structural niching method that fully exploits the problem
decomposition capability of linkage-learning methods such as the estimation of
distribution algorithms and concentrate on maintaining diversity at the
sub-structural level. The proposed method consists of three key components: (1)
Problem decomposition and sub-structure identification, (2) sub-structure
fitness estimation, and (3) sub-structural niche preservation. The
sub-structural niching method is compared to restricted tournament selection
(RTS)--a niching method used in hierarchical Bayesian optimization
algorithm--with special emphasis on sustained preservation of multiple global
solutions of a class of boundedly-difficult, additively-separable multimodal
problems. The results show that sub-structural niching successfully maintains
multiple global optima over large number of generations and does so with
significantly less population than RTS. Additionally, the market share of each
of the niche is much closer to the expected level in sub-structural niching
when compared to RTS
Multi-objective improvement of software using co-evolution and smart seeding
Optimising non-functional properties of software is an important part of the implementation process. One such property is execution time, and compilers target a reduction in execution time using a variety of optimisation techniques. Compiler optimisation is not always able to produce semantically equivalent alternatives that improve execution times, even if such alternatives are known to exist. Often, this is due to the local nature of such optimisations. In this paper we present a novel framework for optimising existing software using a hybrid of evolutionary optimisation techniques. Given as input the implementation of a program or function, we use Genetic Programming to evolve a new semantically equivalent version, optimised to reduce execution time subject to a given probability distribution of inputs. We employ a co-evolved population of test cases to encourage the preservation of the program’s semantics, and exploit the original program through seeding of the population in order to focus the search. We carry out experiments to identify the important factors in maximising efficiency gains. Although in this work we have optimised execution time, other non-functional criteria could be optimised in a similar manner
State Transition Algorithm
In terms of the concepts of state and state transition, a new heuristic
random search algorithm named state transition algorithm is proposed. For
continuous function optimization problems, four special transformation
operators called rotation, translation, expansion and axesion are designed.
Adjusting measures of the transformations are mainly studied to keep the
balance of exploration and exploitation. Convergence analysis is also discussed
about the algorithm based on random search theory. In the meanwhile, to
strengthen the search ability in high dimensional space, communication strategy
is introduced into the basic algorithm and intermittent exchange is presented
to prevent premature convergence. Finally, experiments are carried out for the
algorithms. With 10 common benchmark unconstrained continuous functions used to
test the performance, the results show that state transition algorithms are
promising algorithms due to their good global search capability and convergence
property when compared with some popular algorithms.Comment: 18 pages, 28 figure
Ultra-thin polymer foil cryogenic window for antiproton deceleration and storage
We present the design and characterization of a cryogenic window based on an ultra-thin aluminized biaxially oriented polyethylene terephthalate foil at T < 10 K, which can withstand a pressure difference larger than 1 bar at a leak rate < 1 × 1 0 − 9 mbar l/s. Its thickness of ∼1.7 μm makes it transparent to various types of particles over a broad energy range. To optimize the transfer of 100 keV antiprotons through the window, we tested the degrading properties of different aluminum coated polymer foils of thicknesses between 900 and 2160 nm, concluding that 1760 nm foil decelerates antiprotons to an average energy of 5 keV. We have also explicitly studied the permeation as a function of coating thickness and temperature and have performed extensive thermal and mechanical endurance and stress tests. Our final design integrated into the experiment has an effective open surface consisting of seven holes with a diameter of 1 mm and will transmit up to 2.5% of the injected 100 keV antiproton beam delivered by the Antiproton Decelerator and Extra Low ENergy Antiproton ring facility of CERN
Short Term Psychodynamic Psychotherapy (STPP) for Clients with Complex and Enduring Difficulties within NHS Mental Health Services:A Case Series
Short Term Psychodynamic Psychotherapy (STPP) has been demonstrated as an effective treatment for several mental health difficulties. However, its implementation in secondary mental health services in the National Health Service (NHS) is scarce. The aim of this study was to bridge the gap between controlled trials and practice-based evidence, by exploring an initial estimate of the therapeutic effects of this intervention as well as its safety in a secondary care NHS community mental health setting. Method: The study followed a quantitative case series design. Eight clients with complex, enduring mental health difficulties, supported by a community secondary mental health service received a course of STPP. They completed outcome measures at the start, at the end and eight-weeks following completion of therapy. Results: All participants but one completed the therapy and attendance rates were high (>75%). No adverse effects were reported. All participants but two reported improvement in the CORE-OM, BSI and the PHQ-9 and these were maintained at follow-up. Conclusions: The results suggested that STPP was a safe and acceptable intervention, that may have contributed to clinical and reliable improvement for 4 participants, non-reliable improvement for 2 and non-reliable deterioration for one participant who finished the treatment
A 16 Parts per Trillion Comparison of the Antiproton-to-Proton q/m Ratios
The Standard Model (SM) of particle physics is both incredibly successful and
glaringly incomplete. Among the questions left open is the striking imbalance
of matter and antimatter in the observable universe which inspires experiments
to compare the fundamental properties of matter/antimatter conjugates with high
precision. Our experiments deal with direct investigations of the fundamental
properties of protons and antiprotons, performing spectroscopy in advanced
cryogenic Penning-trap systems. For instance, we compared the proton/antiproton
magnetic moments with 1.5 ppb fractional precision, which improved upon
previous best measurements by a factor of >3000. Here we report on a new
comparison of the proton/antiproton charge-to-mass ratios with a fractional
uncertainty of 16ppt. Our result is based on the combination of four
independent long term studies, recorded in a total time span of 1.5 years. We
use different measurement methods and experimental setups incorporating
different systematic effects. The final result,
= ,
is consistent with the fundamental charge-parity-time (CPT) reversal
invariance, and improves the precision of our previous best measurement by a
factor of 4.3. The measurement tests the SM at an energy scale of
GeV (CL 0.68), and improves 10 coefficients of the
Standard Model Extension (SME). Our cyclotron-clock-study also constrains
hypothetical interactions mediating violations of the clock weak equivalence
principle (WEP) for antimatter to a level of , and enables the first differential test of the WEP
using antiprotons \cite{hughes1991constraints}. From this interpretation we
constrain the differential WEP-violating coefficient to
Ultra thin polymer foil cryogenic window for antiproton deceleration and storage
We present the design and characterisation of a cryogenic window based on an
ultra-thin aluminised PET foil at T < 10K, which can withstand a pressure
difference larger than 1bar at a leak rate < mbar l/s.
Its thickness of approximately 1.7 m makes it transparent to various types
of particles over a broad energy range. To optimise the transfer of 100keV
antiprotons through the window, we tested the degrading properties of different
aluminium coated PET foils of thicknesses between 900nm and 2160nm, concluding
that 1760nm foil decelerates antiprotons to an average energy of 5 keV. We have
also explicitly studied the permeation as a function of coating thickness and
temperature, and have performed extensive thermal and mechanical endurance and
stress tests. Our final design integrated into the experiment has an effective
open surface consisting of 7 holes with 1 mm diameter and will transmit up to
2.5% of the injected 100keV antiproton beam delivered by the AD/ELENA-facility
of CERN
BASE-STEP: A transportable antiproton reservoir for fundamental interaction studies
Currently, the only worldwide source of low-energy antiprotons is the
AD/ELENA facility located at CERN. To date, all precision measurements on
single antiprotons have been conducted at this facility and provide stringent
tests of the fundamental interactions and their symmetries. However, the
magnetic field fluctuations from the facility operation limit the precision of
upcoming measurements. To overcome this limitation, we have designed the
transportable antiproton trap system BASE-STEP to relocate antiprotons to
laboratories with a calm magnetic environment. We anticipate that the
transportable antiproton trap will facilitate enhanced tests of CPT invariance
with antiprotons, and provide new experimental possibilities of using
transported antiprotons and other accelerator-produced exotic ions. We present
here the technical design of the transportable trap system. This includes the
transportable superconducting magnet, the cryogenic inlay consisting of the
trap stack and the detection systems, and the differential pumping section to
suppress the residual gas flow into the cryogenic trap chamber.Comment: To be submitted to Rev. Sci. Instrument
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