ON THE CONTRIBUTION OF DESIGN ATTRIBUTES TO THE CLASSIFICATION OF WEBSITES CATEGORIES

Doron Cohen -  M.Sc. student

The Department of Industrial Engineering, Tel-Aviv University, Israel

Abstract:

Web mining is the use of data mining techniques to automatically discover knowledge from the World Wide Web. One of the most challenges applications of web mining is detecting websites by their category and in particular – detecting malicious websites. Developing tools for website's categories detection is often required to be resources expensive as the enormous amount of information found in the web continues to rise rapidly. In this study we present an algorithm which is able to pull websites content and design by a given URL. We have activated the algorithm and processed the information of 450 websites. Then, we examined the websites information in front of their categories taken from "Google's top 1000 sites" and we built a prediction model using J48 tree with 10-folds cross validation. In the first experiment, we show that classification by design and HTML colors features only (with no use of text mining and other sophisticated tools) is able to predict five different websites categories (including malicious). In the second experiment, we show that adding attributes of design to other objective prediction method, can enhance predictability of malicious websites to high accuracy percentage of ~97.8%, with low resources usage and low run time. Furthermore, we have used T-test and we found significance enhancement. We conclude that colors have great importance when predicting websites categories.

This work was performed under the supervision of Prof. Irad E. Ben-Gal and Prof. Shulamith Kreitler

ההרצאה תתקיים ביום שלישי 9/12/14, בשעה 14:00 בחדר 206, בנין וולפסון הנדסה, הפקולטה להנדסה, אוניברסיטת תל-אביב.

SCHOOL OF MECHANICAL ENGINEERING SEMINAR
Wednesday, December 31, 2015 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Combustion of Methane Hydrates

Dr. Tali Bar-Kohany

NRCN

Gas-hydrates are ice-like crystalline solids, consisting of non-stoichiometric compounds of water cavities and guest gas molecules. At high pressures and low temperatures, different gases fill the cavities within the ice preventing hydrogen-bond strain and breakage.

Deep-ocean gas-hydrates, mainly methane, occur naturally along the edge of continental shelves, represent an enormous and tempting repository of fuel which might compare with or exceed the available energy from more conventional fossil fuels. Moreover, methane hydrates, is free of hazardous pollutants such as sulfur that may be found at conventional fossil fuels. Thus, utilizing this kind of energy is tempting, especially, if this could be done, in-situ. For example, if burning these gas-hydrates in high-pressure, following by sequestering the carbon-dioxide in the deep-ocean environment, could be done.

In the present seminar, a solution for the transient vaporization and quasi-steady combustion of methane-hydrate in a diffusion-controlled spherically symmetric, three-phase particle will be presented. A single, isolated particle is an ideal representation of the physical processes that the particle undergoes in a dilute region of a spray or any bulk.

Short Bio

Tali Bar-Kohany received her mechanical engineering degrees from the University of Ben-Gurion (Ph.D. 2004, A study of the mechanism of sprays formation by bi-component liquid flashing). She won the WOLF award for outstanding Master achievements in 2000 and the Kazir scholarship by the ministry of defense in 2004, and since then she is employed at the nuclear research center of the Negev. In 2010 she received an honorary fellowship from the Australian institute of high energetic materials. During 2013-2014 she spent a Sabbatical at the University of California, Irvine, working with Professors W.A. Sirignano and D.Dunn-Rankin on the subject of combustion of methane-hydrates, which will be the topic of her talk.

School of Mechanical Engineering Seminar
Wednesday, December 31, 2014 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Semi-Active Shape Control of a Hydraulic Micro Catheter

using Electrostatic Actuators

Meytal Gershkovich

MSc Student of Dr. Gabor Kosa and Prof. Slava Krylov

There is a significant interest in developing small, at the scale of several microns up to several millimeters, flexible catheter-type actuators able to perform complex spatial motions in a controllable way. This interest is motivated primarily by medical applications such as endoscopy, minimally invasive surgery and micro robotics. Existing tools are mechanically actuated by cables and are characterized by small number of degrees of freedom while an ability of their further miniaturization probably reached its limit.  Although several devices were reported based on shape memory alloys or electroactive polymers, actuation remains probably the main challenge in these types of systems mainly due to small forces developed by micro actuators which are typically not sufficient for direct shape control of the tool. Hydraulic/pneumatic actuation distinguished by relatively high forces represents an attractive alternative. However, shape control of hydraulic actuators is difficult and requires multiple pressure channels to be delivered to the tool.

In this seminar we present the new operational principle, modeling and design of a simple large stroke high force hydraulic actuator, which is able to perform complex spatial motions while operated by only one pressure channel. The approach is based on the active changing of the structure’s bending stiffness by varying the effective properties of the catheter’s section. The device is built as a flexible tube with a pressurized internal volume. Flexible cantilever-type electrodes made of a material much stiffer than that of the tube are located on the outer surface of the tube. The electrodes can be in two digital states ON and OFF. In an initial unactuated OFF state the electrodes are detached from the tube and do not contribute to its effective bending stiffness.  By means of electrostatic actuation the cantilevers are selectively attached to the tube’s surface resulting in an increase of its effective bending stiffness in a desired non-symmetric way.  The combination of the mentioned effect with the inner pressure inside the tube creates the bending of the actuator. By strategically actuating the electrodes at different locations on the tube, complex three dimensional curves of the catheter can be achieved. We present the electromechanical model of the devices, demonstrate its functionality using the model and evaluate possible design parameters and expected performance of the tool.  We find the possible combinations of the electrodes which should be actuated to provide a required shape of the catheter. Finally we demonstrate how the actuator can follow a path of an arbitrary function.

THE DESIGN AND OPERATION OF Flexible Job-Shop FOR MAKESPAN MINIMIZATION

M.Sc. student - Oshrat Lalush Yechiel

Abstract

Nowadays, firms are facing competitive and dynamic environments, where it is required to customize products while providing high service level and utilization of resources. Flexibility is an important tool to achieve those goals, as operations can be routed to multiple machines that were configured to perform various tasks. As a result, machine utilization is improved and jobs completion times might be shortened. In this talk, we address the problem of simultaneously determining the machine flexibility and job scheduling in a job-shop environment. The problem is combined of two inter-related well studied problems which so far were examined separately. The first involves selecting a process flexibility configuration, while the second consists of assigning and scheduling job operations to machines, given the chosen flexibility. The solution to each of these problems has a major impact on the other, therefore it is important to examine them simultaneously. Our work first investigates the symmetric case, for which an optimal analytical solution with an interesting structure is detected. When generalizing the problem to asymmetric cases, we show that some of them can still be solved to optimality by the same procedure, while others are shown to be NP-Hard. For an important class of asymmetric cases, a heuristic is developed, which is shown to perform very well.

This work was performed under the supervision of Prof. Yossi Bukchin and Prof. Michal Tzur.

ההרצאה תתקיים ביום חמישי 4/12/14, בשעה 12:00 בחדר 206, בנין וולפסון הנדסה, הפקולטה להנדסה, אוניברסיטת תל-אביב.

School of Mechanical Engineering Seminar
Wednesday, December 24, 2014 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Natural Convection in Non-Uniformly Heated Open-Ended Channels

Prof. Victoria Timchenko

MSc/PhD Student of Prof. Supervisor

School of Mechanical and Manufacturing Engineering,

  University of New South Wales, Sydney, Australia.

To improve understanding of the flow and heat transfer phenomena in narrow, open-ended, channel formed by the double skin façade numerical and experimental investigations have been undertaken. Non-uniform heating configurations in which heat sources alternated with unheated zones on both walls were studied to simulate opaque PV arrays and glazed panes/windows of the building. Heat transfer and flow measurements were obtained for periodicity 1/15 of heated/unheated zones and heat input, 220 W/m² as well as large-eddy simulation has been utilized to capture the flow behaviour and possible transition to turbulence in similar non-uniform heating configuration. Several kinds of flow structures have been identified both experimentally and numerically. Intermittent flow structures are observed disrupting the thermal boundary layer allowing to increase heat transfer and to induce high levels of mixing. Vortices in corners of the channel promote horizontal heat transfer from the panels to the lateral walls. Recirculation zone caused by unheated area at the channel entrance contributes to the periodicity of flow within the channel and lower average temperatures. It has been shown that disturbances introduced at the system inlet improve mixing and heat transfer. In comparison to uniformly heating configuration, non-uniformly heating configuration enhances both convective heat transfer and chimney effect. This enhancement may reach 34% in the heat transfer and 12% in mass flow rate. Concerning the physical mechanisms involved, the results show that the flow does not necessarily undergo transition to turbulence but two walls non-uniformly heated arrangement induces better mixing and higher turbulence production in the channel.