287,712 research outputs found
Password Cracking and Countermeasures in Computer Security: A Survey
With the rapid development of internet technologies, social networks, and
other related areas, user authentication becomes more and more important to
protect the data of the users. Password authentication is one of the widely
used methods to achieve authentication for legal users and defense against
intruders. There have been many password cracking methods developed during the
past years, and people have been designing the countermeasures against password
cracking all the time. However, we find that the survey work on the password
cracking research has not been done very much. This paper is mainly to give a
brief review of the password cracking methods, import technologies of password
cracking, and the countermeasures against password cracking that are usually
designed at two stages including the password design stage (e.g. user
education, dynamic password, use of tokens, computer generations) and after the
design (e.g. reactive password checking, proactive password checking, password
encryption, access control). The main objective of this work is offering the
abecedarian IT security professionals and the common audiences with some
knowledge about the computer security and password cracking, and promoting the
development of this area.Comment: add copyright to the tables to the original authors, add
acknowledgement to helpe
Evaluation of the techniques to mitigate early shrinkage cracking through an image analysis methodology
This is the accepted version of the following article: [Ruiz-Ripoll, L., Barragán, B. E., Moro, S., and Turmo, J. (2016) Evaluation of the Techniques to Mitigate Early Shrinkage Cracking through an Image Analysis Methodology. Strain, 52: 492–502. doi: 10.1111/str.12191], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/str.12191/abstractNowadays, new products are introduced in concrete mixes to reduce the effects of shrinkage, which are the main reason of most of early age cracking phenomena, especially when curing is not performed in accordance to best practices. The lack of a standardized methodology to quantify concrete cracking complicates the determination of the effectiveness of different solutions and comparison between them. This research presents an evaluation through images of the suitability of fibres and shrinkage-reducing admixtures to control early shrinkage cracking in slab-type concrete elements. The use of this technique has permitted quantifying the typical cracking parameters objectively and analyse probabilistically the average crack width. Results show a delay and reduction of cracking after adding shrinkage-reducing admixtures and fibres in concrete, especially 1kgm-3 of polymeric microfibres. The incorporation of these components directly into the mix modified the behaviour of concrete, reducing shrinkage cracking from the beginning of moisture losses.Peer ReviewedPostprint (author's final draft
The Role of Shrinkage Strains Causing Early-Age Cracking in Cast-in-Place Concrete Bridge Decks
Early-age cracking in cast-in-place reinforced concrete bridge decks is occurring more frequently now than three decades ago and principle factors that lead to early-age deck cracking are not fully understood. A finite element (FE) simulation methodology for assessing the role of shrinkage-induced strains in generating early-age bridge deck cracking is described. The simulations conducted indicate that drying shrinkage appears to be capable of causing transverse (and possibly longitudinal) bridge deck cracks as early as 9 to II days after bridge deck placement. The drying-shrinkage induced stresses would result in transverse cracking over interior pier supports in a typical bridge superstructure considered in the finite element simulations conducted
Lattice Modeling of Early-Age Behavior of Structural Concrete.
The susceptibility of structural concrete to early-age cracking depends on material composition, methods of processing, structural boundary conditions, and a variety of environmental factors. Computational modeling offers a means for identifying primary factors and strategies for reducing cracking potential. Herein, lattice models are shown to be adept at simulating the thermal-hygral-mechanical phenomena that influence early-age cracking. In particular, this paper presents a lattice-based approach that utilizes a model of cementitious materials hydration to control the development of concrete properties, including stiffness, strength, and creep resistance. The approach is validated and used to simulate early-age cracking in concrete bridge decks. Structural configuration plays a key role in determining the magnitude and distribution of stresses caused by volume instabilities of the concrete material. Under restrained conditions, both thermal and hygral effects are found to be primary contributors to cracking potential
Cracking Piles of Brittle Grains
A model which accounts for cracking avalanches in piles of grains subject to
external load is introduced and numerically simulated. The stress is
stochastically transferred from higher layers to lower ones. Cracked areas
exhibit various morphologies, depending on the degree of randomness in the
packing and on the ductility of the grains. The external force necessary to
continue the cracking process is constant in wide range of values of the
fraction of already cracked grains. If the grains are very brittle, the force
fluctuations become periodic in early stages of cracking. Distribution of
cracking avalanches obeys a power law with exponent .Comment: RevTeX, 6 pages, 7 postscript figures, submitted to Phys. Rev.
Fate of Electromagnetic Field on the Cracking of PSR J1614-2230 in Quadratic Regime
In this paper, we study the cracking of compact object PSR J1614-2230 in
quadratic regime with electromagnetic field. For this purpose, we develop a
general formalism to determine the cracking of charged compact objects. We
apply the local density perturbations to the hydrostatic equilibrium equation
as well as all the physical variables involve in the model. We plot the force
distribution function against radius of the star with different values of model
parameters both with and without charge. It is found that PSR J1614-2230
remains stable (no cracking) corresponding to different values of parameters
when charge is zero, while it exhibit cracking (unstable) when charge is
introduced. We conclude that stability region increases as amount of charge
increases.Comment: 21 pages, 8 figures, version to appear in advances in high energy
physic
Stochastic Database Cracking: Towards Robust Adaptive Indexing in Main-Memory Column-Stores
Modern business applications and scientific databases call for inherently
dynamic data storage environments. Such environments are characterized by two
challenging features: (a) they have little idle system time to devote on
physical design; and (b) there is little, if any, a priori workload knowledge,
while the query and data workload keeps changing dynamically. In such
environments, traditional approaches to index building and maintenance cannot
apply. Database cracking has been proposed as a solution that allows on-the-fly
physical data reorganization, as a collateral effect of query processing.
Cracking aims to continuously and automatically adapt indexes to the workload
at hand, without human intervention. Indexes are built incrementally,
adaptively, and on demand. Nevertheless, as we show, existing adaptive indexing
methods fail to deliver workload-robustness; they perform much better with
random workloads than with others. This frailty derives from the inelasticity
with which these approaches interpret each query as a hint on how data should
be stored. Current cracking schemes blindly reorganize the data within each
query's range, even if that results into successive expensive operations with
minimal indexing benefit. In this paper, we introduce stochastic cracking, a
significantly more resilient approach to adaptive indexing. Stochastic cracking
also uses each query as a hint on how to reorganize data, but not blindly so;
it gains resilience and avoids performance bottlenecks by deliberately applying
certain arbitrary choices in its decision-making. Thereby, we bring adaptive
indexing forward to a mature formulation that confers the workload-robustness
previous approaches lacked. Our extensive experimental study verifies that
stochastic cracking maintains the desired properties of original database
cracking while at the same time it performs well with diverse realistic
workloads.Comment: VLDB201
A fracture mechanics-based method for prediction of cracking of circular and elliptical concrete rings under restrained shrinkage
A new experimental method, utilizing elliptical ring specimens, is developed for assessing the likelihood of cracking and cracking age of concrete subject to restrained shrinkage. To investigate the mechanism of this new ring test, a fracture mechanics-based numerical approach is proposed to predict crack initiation in restrained concrete rings by using the R-curve method. It has been found that numerical results accord well with experimental results in terms of cracking ages for both circular and elliptical concrete rings, indicating that the proposed fracture mechanics-based numerical approach is reliable for analyzing cracking in concrete ring specimens subject to restrained condition.UK Engineering and Physical Sciences Research Council under the grant of EP/I031952/1, and the National Natural Science Foundation of China under the grant of NSFC 51121005/5110902
Cracking of Charged Polytropes with Generalized Polytropic Equation of State
We discuss the occurrence of cracking in charged anisotropic polytropes with
generalized polytropic equation of state through two different assumptions; (i)
by carrying out local density perturbations under conformally flat condition
(ii) by perturbing anisotropy, polytropic index and charge parameters. For this
purpose, we consider two different definitions of polytropes exist in
literature. We conclude that under local density perturbations scheme cracking
does not appears in both types of polytropes and stable configuration are
observed, while with second kind of perturbation cracking appears in both types
of polytropes under certain conditions.Comment: 24 pages, 11 figure
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