Trial and Error

A pac-learning algorithm is -space bounded, if it stores at most examples from the sample at any time. We characterize the -space learnable concept classes. For this purpose we introduce the compression parameter of a concept class and design our Trial and Error Learning Algorithm. We show : is -space learnable if and only if the compression parameter of is at most . This learning algorithm does not produce a hypothesis consistent with the whole sample as previous approaches e.g. by Floyd, who presents consistent space bounded learning algorithms, but has to restrict herself to very special concept classes. On the other hand our algorithm needs large samples; the compression parameter appears as exponent in the sample size. We present several examples of polynomial time space bounded learnable concept classes: – all intersection closed concept classes with finite VC–dimension. – convex -gons in . – halfspaces in . – unions of triangles in . We further relate the compression parameter to the VC–dimension, and discuss variants of this parameter. Received May 24, 1994 / July 4, 1995     

Maintainability defects detection and correction: a multi-objective approach

Software defects often lead to bugs, runtime errors and software maintenance difficulties. They should be systematically prevented, found, removed or fixed all along the software lifecycle. However, detecting and fixing these defects is still, to some extent, a difficult, time-consuming and manual process. In this paper, we propose a two-step automated approach to detect and then to correct various types of maintainability defects in source code. Using Genetic Programming, our approach allows automatic generation of rules to detect defects, thus relieving the designer from a fastidious manual rule definition task. Then, we correct the detected defects while minimizing the correction effort. A correction solution is defined as the combination of refactoring operations that should maximize as much as possible the number of corrected defects with minimal code modification effort. We use the Non-dominated Sorting Genetic Algorithm (NSGA-II) to find the best compromise. For six open source projects, we succeeded in detecting the majority of known defects, and the proposed corrections fixed most of them with minimal effort.     

Preparation of a hydrophobic recycled jute-based nonwoven using a titanium dioxide/stearic acid coating

This work aims at developing a hydrophobic treatment for jute fiber-based nonwovens. Three solutions of titanium dioxide (TiO₂) nanoparticles were prepared through a sol–gel method by varying the molar ratio of the various constituents. The nonwoven was pretreated with these solutions before being impregnated with different concentrations of stearic acid. The TiO₂ nanoparticles synthesized are amorphous; their size varies with the concentration of ethanol used as a solvent in the sol–gel method. The nanoparticle coating produced on the jute fibers is uniform. The nonwoven wettability was evaluated by measuring its water contact angle and retention time; the nonwoven became hydrophobic at the lowest fatty acid concentration tested. An increase in the stability of the hydrophobicity was observed when the TiO₂ nanoparticle pretreatment was used compared to the application of the stearic acid treatment only. No detrimental effect of the hydrophobic treatment on the nonwoven mechanical performance and thermal stability was observed. These results demonstrate the potential of the TiO₂ nanoparticle/stearic acid treatment as a fast method to provide a stable hydrophobicity to recycled jute-based nonwovens.     

Advances of nanofluids in heat exchangers—A review

Recently, many researchers have focused on their studies on the analysis of nanofluid flows due to their participation in the enhancement of heat transfer rates in industrial processes. The ordinary fluids, such as water, mineral oils, and so on, are known for their low thermal conductivity in heat transfer processes. A significant enhancement in the thermal properties of ordinary fluid may be obtained by adding nanoparticles having a diameter of less than 100 nm or suspension of fibers. Better spreading, wetting, dispersion, and stability and with acceptable viscosity are the main advantageous properties of nanofluids on a solid surface. The nanofluids are encountered in various thermal engineering systems such as in heat exchangers, refrigeration, thermal management of fuel cells, cooling of nuclear reactors, microelectromechanical systems, and others. In particular, the thermal conversion is known as a great application of nanotechnology, and many studies have been achieved with such fluids in heat exchangers. Therefore, this paper aims to present a global insight into the different applications of nanofluids in various heat exchangers, that is, heat pipe and plate-fin heat exchangers. All research works have been summarized into three main parts: laminar, transition, and turbulent nanofluid flow regimes.     

Divergence temporal dynamics of a Q-switched laser

I address the influence of the direct coupling of the average lattice strains to the active ions on the pulse shape and the far-field beam spreading of a Q-switched laser. Calculations are made for the Cr(3+): sapphire system. The dynamic behavior of laser divergence as the pulse develops is studied without and with an internal aperture. The results can be used to search for similar effects in lasers involving other ions, such as Ti(3+) and Cr(4+).     

Effect of vegetable and synthetic fibers on mechanical performance and durability of Metakaolin-based mortars

The use of vegetable fibers has regained interest in different fields. In fact, fibers may represent an alternative to traditional fibers incorporated in building materials, such as polypropylene fibers. Sustainable development requires the adoption of ecofriendly and natural materials. In this approach, using vegetable fibers as reinforcement for cementitious materials represents an interesting option for concrete industry. Thus, this article studies mechanical performances and transfer properties of cementitious mortars reinforced with vegetable fibers. The used fibers were Dis (DS), Alfa (AF), Date palm (DP) and Hemp (HE). They were subjected to prior treatment with calcium hydroxide. The results show that reinforced mortars with vegetable fibers represent a better deformation capacity than the control mortar without fibers; the best bending strength was recorded for hemp and date palm mortars; the addition of vegetable fibers leads to thermal conductivity decrease by 15% for a content of 0.1%. However, greater carbonation depths were recorded for vegetable fibers based mixes. These findings, for us, are promising for the use of vegetable fibers in cementitious materials.     

Effect of the Inclination of Baffles on the Power Consumption and Fluid Flows in a Vessel Stirred by a Rushton Turbine

The role of baffles in mechanically stirred tanks is to promote the stability of power drawn by the impeller and to avoid the fluid swirling, thus enhancing mixing. The present paper numerically investigates the baffles effects in a vessel stirred by a Rushton turbine. The geometric factor of interest is the baffle inclination which is varying between 25°, 32.5°, 45°, 70° and 90° at different impeller rotational speeds. The impeller rotational direction has also been varied. The vortex size and power consumption were evaluated for each geometrical configuration. It was found that the best configuration is the baffle inclination by α = 70° at a negative angular velocity.     

Two-Variable Refined Plate Theory for Thermoelastic Bending Analysis of Functionally Graded Sandwich Plates

The thermoelastic bending analysis of functionally graded sandwich plates using the two-variable refined plate theory is presented in this paper. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory presented is variationally consistent, has strong similarity with classical plate theory in many aspects, does not require shear correction factor, and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. The sandwich plate faces are assumed to have isotropic, two-constituent material distribution through the thickness, and the modulus of elasticity, Poisson's ratio of the faces, and thermal expansion coefficients are assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic ceramic material. Several kinds of sandwich plates are used taking into account the symmetry of the plate and the thickness of each layer. The influences played by the transverse shear deformation, thermal load, plate aspect ratio, and volume fraction distribution are studied. Numerical results for deflections and stresses of functionally graded metal–ceramic plates are investigated. It can be concluded that the proposed theory is accurate and simple in solving the thermoelastic bending behavior of functionally graded plates.     

A generic approach to detect design patterns in model transformations using a string-matching algorithm

Software and Systems Modeling - Maintaining software artifacts is a complex and time-consuming task. Like any other program, model transformations are subject to maintenance. In a maintenance...     

Coxiella burnetti infectious endocarditis. Apropos of a case

Chronic forms of Q fever (endocarditis) are rare, but are responsible for severe and desperately recurrent infections, resulting in multiple valve replacements with a reserved prognosis. The authors report the case of a 35-year-old patient with a known history of rheumatic fever, who developed blood culture negative infectious endocarditis on a mitral bioprosthesis. The diagnosis of Q fever was based on serological arguments. Despite long-term antibiotic therapy, serology remained strongly positive and was associated with repeated mitral valve disinsertion. The patient died immediately after the fourth operation in a context of haemodynamic failure. This clinical case emphasizes the importance of performing Q fever serology in any case of culture negative endocarditis and the therapeutic difficulties encountered in chronic recurrent endocarditis.