Surface active agents

Površinski aktivne tvari ili surfaktanti su spojevi koji smanjuju površinsku napetost adsorpcijom na međupovršine te stvaraju strukture koloidnih dimenzija u otopini, što je posljedica njihove amfipatske prirode. Surfaktanti se mogu podijeliti na više načina: s obzirom na primjenu, s obzirom na fizikalna svojstva te s obzirom na kemijsku strukturu. Imaju veoma raznoliku primjenu kako u industriji tako i u svakodnevnom životu. Najviše istraživane su vodene otopine površinski aktivnih tvaru, a od oblika koji mogu nastati u otopini, nabolje su proučene micele. Otopine površinski akrivnih tvari u kojima dolazi do stvaranja micela mogu se okarakterizirati trima veličinama: kritičnom micelizacijskom koncentracijom (CMC), Krafftovom temperaturom i agregacijskim brojem (N). Iznad kritične micelizacijske koncentracije dolazi do nagle promjene brojnih fizikalno-kemijskih svojstvava poput površinske napetosti, molarne provodnosti otopine itd. Te promjene ukazuju na to da su u otopini ispod odn. iznad CMC prisutne različite vrste. Ispod kritične micelizacijske koncentracije prisutni su samo monomeri površinski aktivne tvari, dok su iznad te koncentracije prisutne micele građene od N monomera, a nalaze se u ravnoteži sa slobodnim monomerima. Struktura micela koje nastaju u razrjeđenim vodenim otopinama sastoji se od dva osnovna dijela: od nepolarnog sloja kojeg čine ugljikovodični dijelovi molekula površinski aktivnih tvari, te od polarnog sloja u kojem su prisutne i molekule vode. Nadalje, u slučaju ionskih micela postoji i tredi sloj koji se sastoji od vezanih protuiona, bududi da ionske micele sadrže nabijene skupine u polarnom sloju. Pri opisu micelizacije koriste se dva termodinamička modela: agregacijski model i model separacije faza. Promjena Gibbsove energije za proces micelizacije, kao ni izrazi za ostale termodinamičke veličine, ne ovise o modelu na temelju kojeg su izvedeni. Vrijednosti za entalpiju i entropiju micelizacije ukazuju na dominantan doprinos entropije spontanosti procesa agregacije, što se naziva hidrofobnim efektom

Pressure jump interface law for the Stokes-Darcy coupling: Confirmation by direct numerical simulations

It is generally accepted that the effective velocity of a viscous flow over a porous bed satisfies the Beavers-Joseph slip law. To the contrary, interface law for the effective stress has been a subject of controversy. Recently, a pressure jump interface law has been rigorously derived by Marciniak-Czochra and Mikeli\'c. In this paper, we provide a confirmation of the analytical result using direct numerical simulation of the flow at the microscopic level.Comment: 25 pages, preprin

Our Experience in Oral Treatment of Handicapped Children and Young People by the Application of General Anaesthesia

Budući da je postojala niska razina stomatološke skrbi za djecu s teškoćama u razvoju na području današnje Splitsko-dalmatinske županije, 70-ih godina prošloga stoljeća počelo se sustavno školovati kadrove i osiguravati im prostor i opremu. Većina populacije koju smo obrađivali sastojala se od djece i mladeži s teškoćama u razvoju smještene u odgovarajućim ustanovama ili kod svojih roditelja uglavnom s navedenoga podruja. Stomatološku sanaciju uglavnom je obavljao temeljni tim liječnika specijalista sastavljen od pedodonta, oralnog kirurga i anesteziologa sa suradnicima. Njima su se po potrebi pridruživali ostali stomatolozi specijalisti. Sve naše bolesnike tretirali smo u općoj inhalacijskoj anesteziji uz nužnu kliničku i laboratorijsku obradbu, te uz pismeni pristanak roditelja ili skrbnika. U minulih dvadeset godina stomatološki smo obradili 680 pacijenata. U prosjeku smo obrađivali 3 pacijenta po operativnom danu. U početku su prevladavali konzervativno-protetski zahvati, a poslije su bili češći konzervativno-restorativni. Iz našega iskustva metodu endotrahealne anestezije smatramo vrlo prihvatljivom za djecu i mladež s teškoćama u razvoju.Because of the low level of dental care for handicapped children in the Split-Dalmatian district systematic training of staff and procurement of space and equipment was initiated during the 1970s. The majority of the population treated consisted of handicapped children and young people, in relevant institutions or with their families, mainly from this area. A team of specialists, consisting of a pedodontist, oral surgeon, anaesthesiologist and co-workers usually performed dental treatment. When necessary they were joined by other dental specialists. All our patients were treated under general inhalation anaesthesia with the necessary clinical and laboratory tests and written consent of the families or guardians. During a period of twenty years 680 patients were treated. We treated three patients on average in one operative day. Initially the operations were conservative-prosthetic operations, and later this changed to more frequent conservative-restorative procedures. From our experience we consider that the method of endotracheal anaesthesia is particularly suitable for handicapped children and young people

On the Roughness-Induced Effective Boundary Conditions for an Incompressible Viscous Flow

AbstractWe consider the laminar viscous channel flow with the lateral surface of the channel containing surface irregularities. It is supposed that a uniform pressure gradient is maintained in the longitudinal direction of the channel. After studying the corresponding boundary layers, we obtain rigorously the Navier friction condition. It is valid when the size and amplitude of the imperfections tend to zero. Furthermore, the coefficient in the law is determined through an auxiliary boundary-layer type problem, and the tangential drag force and the effective mass flow are determined up to order O(ε3/2). The value of the effective coefficient is shown to be independent with respect to the position of the mean surface in the range of O(ε)

Service e-Learning Project : State Graduation Online Demo Exam

The service e-learning project described in this paper presents the online demo exam in informatics designed as a preparatory step for the state graduation. It was created in the midst of turbulence caused by the introduction of the state graduation at the end of secondary education in Croatia. With this project we wanted to engage grammar school students in service e-learning and present them with the opportunity to design their own test materials through the collaboration with college students who are experts in the field. We also aimed to gain our own benefit of connecting the theory learned during the study with new practical experiences while at the same time helping the students to achieve at a high level in the state graduation exam. Finally, since its free available online, our project should benefit everyone who wants to test their knowledge in informatics and/or learn something new in an easy and interesting way

Service Learning in Information Science : Web for the Blind

The biggest problem to blind and visually impaired people poses the integration in various aspects of the social life. Since computer technology with its dominantly visual interface increasingly becomes the prime media for communication, these people are faced with a new obstacle – the ability to work on a computer and use it to communicate with others. Technologies that enable the blind to use the computer do exist, both hardware and software, but they have difficulty learning to use them. The reason for this is lack of standardized educational program so that computer education of blind is usually left to themselves and a few associations that do not have sufficiently qualified staff for such a task. Our service learning project offers the first step to possible solution of the current situation. Service learning is a methodology where learning occurs when students apply what they learn to community problems. It was introduced into information science curriculum in the academic year 2006/07 for the first time in Croatian University with the goal to transform the old teaching style, give the final year students more place to apply the theory they learned through the study and, most important, to provide an important service to the local community. “Web for the Blind” is the service learning project that provides a first step towards an optimal solution. The main goal of this student project was to establish an adequate model on which all future projects in this field could be based. At the moment “Web for the Blind” is a stand-alone application that provides the blind and visually impaired with the guides on how to install a web browser, familiarizes them with its interface and gives them some basic information on surfing the web. The application can be used without a mouse and with or without screen-reader software because it contains the tutorials in textual and audio format. The next phase of the project involves intensive testing in the field. It is to be presented to as much users as possible for the evaluation purpose. Finally, the contents of the tutorials need to be gradually updated in both quality and quantity

Project of Developing the Multimedia Software Supporting Teaching and Learning English Vocabulary

Since the Academic Year 2005-2006 we have worked on a project of developing the interactive multimedia software for learning English vocabulary. The software was tested on junior learners in elementary school within the English language course lesson. The results were measured by comparing the test results from the computer-aided lesson with the ones from a traditional one and they showed a great level of disparity both regarding the learners’ knowledge and their motivation. Vocabulary of a language does not only consist of separate contextually independent words, but also of contextually bound lexical items, such as collocations. In 2006-2007 we have expanded the software by adding the feature for multimedia collocations. By terms of imitating reality, we have been designing multimedia animated presentations of English collocations comprising picture, text and sound. Our past, present and future phases of the project have purpose of examining the use of animation in educational settings

Framework of the Language Learning Environment for Assisting Foreigners in Learning Croatian (AFILC)

The goal of this paper is to present the development framework of the interactive multimedia project AFILC (Assisting Foreigners in Learning Croatian). The purpose of the AFILC is to develop language learning materials that will motivate foreigners to learn the Croatian language and help them cope with its grammatical richness. Interesting graphics, motivating user-friendly interface, educational character and interactivity are the characteristics that will enhance the process of mastering the Croatian language for foreigners. In the AFILC the users will be able to almost completely control and manage the process of learning at their own pace

Service Learning in Information Science : Web for the Blind

The biggest problem to blind and visually impaired people poses the integration in various aspects of the social life. Since computer technology with its dominantly visual interface increasingly becomes the prime media for communication, these people are faced with a new obstacle – the ability to work on a computer and use it to communicate with others. Technologies that enable the blind to use the computer do exist, both hardware and software, but they have difficulty learning to use them. The reason for this is lack of standardized educational program so that computer education of blind is usually left to themselves and a few associations that do not have sufficiently qualified staff for such a task. Our service learning project offers the first step to possible solution of the current situation. Service learning is a methodology where learning occurs when students apply what they learn to community problems. It was introduced into information science curriculum in the academic year 2006/07 for the first time in Croatian University with the goal to transform the old teaching style, give the final year students more place to apply the theory they learned through the study and, most important, to provide an important service to the local community. “Web for the Blind” is the service learning project that provides a first step towards an optimal solution. The main goal of this student project was to establish an adequate model on which all future projects in this field could be based. At the moment “Web for the Blind” is a stand-alone application that provides the blind and visually impaired with the guides on how to install a web browser, familiarizes them with its interface and gives them some basic information on surfing the web. The application can be used without a mouse and with or without screen-reader software because it contains the tutorials in textual and audio format. The next phase of the project involves intensive testing in the field. It is to be presented to as much users as possible for the evaluation purpose. Finally, the contents of the tutorials need to be gradually updated in both quality and quantity