1,147 research outputs found
Sequential model to describe the nicotinic synaptic current
An analytical formula is derived to describe the synaptic end plate current (epc) at the nicotinic receptor. Various concurrently occurring underlying processes, including (a) diffusion, (b) hydrolysis of acetylcholine, and (c) its binding to the dimeric receptor, were considered in order to develop the equation. Numeric solution of the equations that describe the events underlying the epc showed that these events occur in sequence, rather than concurrently. This sequential occurrence of the processes allowed for simplifications, which were used as the basis for the new description of the epc. The resulting formula serves as a tool for evaluating the relative contribution of the various processes in formation of the natural occurring transient epc
Punctuated Equilibrium in Software Evolution
The approach based on paradigm of self-organized criticality proposed for
experimental investigation and theoretical modelling of software evolution. The
dynamics of modifications studied for three free, open source programs Mozilla,
Free-BSD and Emacs using the data from version control systems. Scaling laws
typical for the self-organization criticality found. The model of software
evolution presenting the natural selection principle is proposed. The results
of numerical and analytical investigation of the model are presented. They are
in a good agreement with the data collected for the real-world software.Comment: 4 pages, LaTeX, 2 Postscript figure
Delikli Kompozit Yapıların Sonlu Elemanlar Yöntemiyle Analizi
Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2015Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2015Burada delikli ileri kompozit yapılarda hasarın doğru tahmini için yapılan bir çalışmanın sonuçları sunulmuştur. Çalışmanın ilk bölümünde, kullanılan kompozitlerin ilgili mekanik özelliklerini belirlemek için kupon ve çatlak ilerleme testlerinden oluşan bir malzeme test programı yürütülmüştür. Daha sonra, delikli kompozit yapıları incelemek için bir sonlu elemanlar analizi modeli oluşturulmuştur. Sürekli ortam kabuk elemanları (continuum shell) kullanarak delaminasyonu (tabaka ayrılmasını) hesaba katan ve katmayan sonlu eleman modelleri oluşturuldu. Gerçekçi bir simülasyon elde edebilmek için ilerlemeli hasar analizi yapılmıştır. En uygun modeli belirlemek amacıyla, test sonuçları ve simülasyonlardan elde edilen sonuçlar ayrıntılı olarak tartışılmıştır.The results of a study for the prediction of failure behavior in advanced composite structures with holes are presented here. In the first part of the study, a materials test program based on coupon and fracture tests is conducted to obtain related mechanical properties. A finite element model is then constructed for simulating the behavior of advanced composite laminates with hole under tension. Two finite element models using continuum shell elements, one with and the other without the delamination failure were developed. In order to have a realistic simulation, the progressive failure analysis is applied. For an optimum model, test results and simulation results are discussed, thoroughly
Contracts in Practice
Contracts are a form of lightweight formal specification embedded in the
program text. Being executable parts of the code, they encourage programmers to
devote proper attention to specifications, and help maintain consistency
between specification and implementation as the program evolves. The present
study investigates how contracts are used in the practice of software
development. Based on an extensive empirical analysis of 21 contract-equipped
Eiffel, C#, and Java projects totaling more than 260 million lines of code over
7700 revisions, it explores, among other questions: 1) which kinds of contract
elements (preconditions, postconditions, class invariants) are used more often;
2) how contracts evolve over time; 3) the relationship between implementation
changes and contract changes; and 4) the role of inheritance in the process. It
has found, among other results, that: the percentage of program elements that
include contracts is above 33% for most projects and tends to be stable over
time; there is no strong preference for a certain type of contract element;
contracts are quite stable compared to implementations; and inheritance does
not significantly affect qualitative trends of contract usage
Sublinear-Time Algorithms for Monomer-Dimer Systems on Bounded Degree Graphs
For a graph , let be the partition function of the
monomer-dimer system defined by , where is the
number of matchings of size in . We consider graphs of bounded degree
and develop a sublinear-time algorithm for estimating at an
arbitrary value within additive error with high
probability. The query complexity of our algorithm does not depend on the size
of and is polynomial in , and we also provide a lower bound
quadratic in for this problem. This is the first analysis of a
sublinear-time approximation algorithm for a # P-complete problem. Our
approach is based on the correlation decay of the Gibbs distribution associated
with . We show that our algorithm approximates the probability
for a vertex to be covered by a matching, sampled according to this Gibbs
distribution, in a near-optimal sublinear time. We extend our results to
approximate the average size and the entropy of such a matching within an
additive error with high probability, where again the query complexity is
polynomial in and the lower bound is quadratic in .
Our algorithms are simple to implement and of practical use when dealing with
massive datasets. Our results extend to other systems where the correlation
decay is known to hold as for the independent set problem up to the critical
activity
Testing probability distributions underlying aggregated data
In this paper, we analyze and study a hybrid model for testing and learning
probability distributions. Here, in addition to samples, the testing algorithm
is provided with one of two different types of oracles to the unknown
distribution over . More precisely, we define both the dual and
cumulative dual access models, in which the algorithm can both sample from
and respectively, for any ,
- query the probability mass (query access); or
- get the total mass of , i.e. (cumulative
access)
These two models, by generalizing the previously studied sampling and query
oracle models, allow us to bypass the strong lower bounds established for a
number of problems in these settings, while capturing several interesting
aspects of these problems -- and providing new insight on the limitations of
the models. Finally, we show that while the testing algorithms can be in most
cases strictly more efficient, some tasks remain hard even with this additional
power
Can we avoid high coupling?
It is considered good software design practice to organize source code into modules and to favour within-module connections (cohesion) over between-module connections (coupling), leading to the oft-repeated maxim "low coupling/high cohesion". Prior research into network theory and its application to software systems has found evidence that many important properties in real software systems exhibit approximately scale-free structure, including coupling; researchers have claimed that such scale-free structures are ubiquitous. This implies that high coupling must be unavoidable, statistically speaking, apparently contradicting standard ideas about software structure. We present a model that leads to the simple predictions that approximately scale-free structures ought to arise both for between-module connectivity and overall connectivity, and not as the result of poor design or optimization shortcuts. These predictions are borne out by our large-scale empirical study. Hence we conclude that high coupling is not avoidable--and that this is in fact quite reasonable
Coordination Implications of Software Coupling in Open Source Projects
The effect of software coupling on the quality of software has been studied quite widely since the seminal paper on software modularity by Parnas [1]. However, the effect of the increase in software coupling on the coordination of the developers has not been researched as much. In commercial software development environments there normally are coordination mechanisms in place to manage the coordination requirements due to software dependencies. But, in the case of Open Source software such coordination mechanisms are harder to implement, as the developers tend to rely solely on electronic means of communication. Hence, an understanding of the changing coordination requirements is essential to the management of an Open Source project. In this paper we study the effect of changes in software coupling on the coordination requirements in a case study of a popular Open Source project called JBoss
Return of the Great Spaghetti Monster : Learnings from a Twelve-Year Adventure in Web Software Development
The widespread adoption of the World Wide Web has fundamentally changed the landscape of software development. Only ten years ago, very few developers would write software for the Web, let alone consider using JavaScript or other web technologies for writing any serious software applications. In this paper, we reflect upon a twelve-year adventure in web development that began with the development of the Lively Kernel system at Sun Microsystems Labs in 2006. Back then, we also published some papers that identified important challenges in web-based software development based on established software engineering principles. We will revisit our earlier findings and compare the state of the art in web development today to our earlier learnings, followed by some reflections and suggestions for the road forward.Peer reviewe
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