This qualitative study focused on four secondary school physics teachers in Bangladesh using semi-structured interviews and observations to explore their understanding about the relationship between practical work and developing students’ conceptual knowledge of physics. Recent studies indicate that practical work helps secondary science students easily and effectively learn the concepts and theories of physics. However, the secondary school physics teachers in Bangladesh in this study did not provide students with practical work during classroom teaching. Rather, they provided practical work in separate practical classes. Although the teachers believed that practical work made their teaching and also students’ learning easier and effective, they did not offer frequent practical demonstrations in teaching the contents of physics. The major findings of the study include that teachers used mostly transmissive pedagogy to assist students to understand physics concepts and theories. Even though there are clear and specific instructions for the teachers to do demonstrations in the secondary physics curriculum, there were constraints on teachers and on students trying to conduct practical work. Constraints included: a lack of sufficient equipment. Teachers and students in non-government schools faced comparatively more difficulties than those in government schools. Low teacher/student ratios and no positions for laboratory assistants were reasons given for teachers’ intense workloads. This study implies a need to provide government and non-government schools with necessary equipment for doing practical work; to appoint sufficient teachers with higher studies and training that includes practical work in physics; to create positions for laboratory assistants; to set up classrooms with a smaller number of students; and to develop awareness of the value of practical work among school administration and among physics teachers.

We live in an information hungry age, we generate and process information at a rate never before recorded in the history of mankind. Today’s computing platforms are run on Gigahertz multi-core processors churning out Gigabits streams of data that need to be transmitted as quickly as possible. Often times the source and the destination are mobile which means wired connections are not a choice. This has led to an ever increasing need to develop wireless access technologies that support high throughput regardless of the transmission environment. Till date, many proprietary solutions exist that seek to bridge this gap with little or no support for interoperability. For the sheer scale of development that is required, a standard based solution is the key. The IEEE 802.1x committee oversees the development of standards for wireless systems, it formed the 802.16 working group to develop a standards-based Wireless Metropolitan Area Network (MAN) solution. One of the fruits of this effort is the 802.16e standard fondly referred to as mobile WiMAX and it is the subject of study in this thesis. This thesis seeks to analyze the transmission characteristics of two of the antenna systems defined in the standard i.e. Adaptive Beamforming Systems and Multiple-Input Multiple-Output Systems. Multiple-Input Multiple-Output (MIMO): utilizes multiple antennas at the transmitter and receiver to provide diversity gain, multiplexing gain or both. Adaptive Antenna Systems (AAS): Adaptive array system uses an antenna array to generate in real-time radiation patterns with the main lobes and/or nulls dynamically tuned to specific directions in order to increase or suppress signal power in that direction. / Worldwide Interoperability for Microwave Access (WiMAX) is the acronym for Institute of Electrical and Electronics Engineers (IEEE) 802.16 set of standards governing Air Interface for Fixed Broadband Wireless Access Systems. In the history of wireless systems, WiMAX is revolutionary technology as affords its users the Wi-Fi grade throughput and cellular system level of mobility. With WiMAX, broadband technology (traditionally ADSL and Fiber) goes wireless and WiMAX users can basically enjoy triple-play application, and split-second download and upload rates. WIMAX also offers full mobility much as traditional cellular systems do with features like seamless hand-over and roaming at vehicular speed; this is made possible because the system design covers the access network to core network. For the operator, WiMAX is a welcome development because it merges traditional cellular networks with broadband technology thus opening them to more business offerings and a larger client base and all this at a reduced cost of deployment. Base stations are comparatively cheaper and do not require extensive planning typical of other cellular systems thus WiMAX is aptly suited for emerging markets where infrastructure cost is a major issue; little wonder a lot of 3rd world countries have signified interest in the technology.

Environmental noise at high levels and inappropriate construction techniques used in conventional buildings in Brazil claim for a transition to better construction systems. Recently the Brazilian standard NBR 15575:2013 established for the first time parameters and criteria for residential building performance. In standard minimum requirements for sound insulation are given, for example for external walls and roof structures. This way it is of fundamental importance to have sound transmission loss data for diferente types of such elements at hand. Taking into account that there is very little information on the sound transmission loss of external walls of the light steel frame (LSF) type measurements of sound insulation of different vertical external LSF walls typically used in Brazil were carried out. Eighteen different LSF walls were mounted in the sound transmission measurement chamber of the Federal University of Santa Maria and measurements were carried out in accordance with ISO 10140:2010. Sound insulation was characterized by means of the sound reduction index R, the weighted sound reduction index Rw and the sound transmission class, making it possible to compare the sound insulation of the LSF walls with data from the literature. The LSF walls under investigation in this study used different materials such as OSB panels, cement boards, plaster boards, Smartside panels, PVC panels, XPS panels and magnesium oxide boards for the outer face. The influence of resilient channels and sponge tape, placed between the outer face and the metalic studes, were also evaluated. The sound insulation of the diferente LSF walls were found to be 43 dB ≤ Rw ≤ 50 dB and 45 dB ≤ STC ≤ 52 dB. Within the LSF walls measured the one which used magnesium oxide boards on the outer face showed to have the highest weight sound reduction index (Rw = 50 dB). Resilient channels, fabricated especially for this study, and sponge tape were able to provide an increase of Rw and STC up to 5 dB compared to the same wall without this resilient elements, and provide better sound insulation especially for frequencies higher than 400 Hz. From the data it can be concluded that LSF walls are more efficient regarding the sound insulation than single walls of the same surface mass and in some cases even better than single walls of superior surface mass, such as walls made of massive brick or concrete blocks. / O excesso de ruído ambiental e as inadequadas técnicas construtivas dos sistemas convencionais utilizados no mercado da construção civil brasileira, fazem com que seja necessária a introdução de novas tecnologias construtivas mais racionais e produtivas. A partir da entrada em vigor da NBR 15575:2013 foram estabelecidos diversos parâmetros de desempenho para edificações habitacionais. A referida norma também estabelece exigências mínimas de isolamento acústico para os sistemas que compõem as edificações, entre eles, as vedações verticais. Desta forma, informações sobre o isolamento acústico providenciado pelos diferentes sistemas construtivos tornaram-se de fundamental importância. Tendo em vista a pouca informação existente na literatura sobre o isolamento sonoro de paredes externas em light steel frame (LSF), foram realizadas medições de perda de transmissão sonora em paredes externas executadas neste sistema construtivo, usadas tipicamente no mercado brasileiro. Dezoito composições de paredes em LSF foram montadas na câmara reverberante de transmissão sonora da UFSM para realização dos ensaios de perda de transmissão conforme procedimentos propostos pela ISO 10140:2010. O isolamento sonoro foi quantificado a partir dos espectros do índice de redução sonora R, pelo índice de redução sonora ponderado Rw e pela classe de transmissão sonora STC, facilitando a comparação entre diferentes composições de parede e dados de isolamento sonoro encontrados na bibliografia. Os principais materiais utilizados no revestimento das paredes LSF foram paineis OSB, placas cimentícias, placas de gesso acartonado, réguas Smartside, réguas de siding vinílico, painéis XPS e placas de óxido de magnésio. A influência da utilização de barras resilientes e fitas de espuma de PVC, entre as placas de revestimento e a estrutura metálica, também foi avaliada. Determinou-se que o isolamento sonoro das diferentes paredes LSF avaliadas é de 43 dB ≤ Rw ≤ 50 dB e 45 dB ≤ STC ≤ 52 dB. Dentre as paredes externas em LSF, aquela que utilizou placas de óxido de magnésio na face exterior apresentou o maior Rw = 50 dB. As barras resilientes e fitas de espuma de PVC foram capazes de aumentar o Rw e STC em até 5 dB, se comparado à parede semelhante sem estes dispositivos, especialmente nas frequências a partir de 400 Hz. A partir da análise dos dados, concluiu-se que as paredes LSF consideradas paredes duplas são mais eficientes no isolamento sonoro quando comparadas às paredes simples ou homogêneas de mesma massa e até do que algumas paredes com massa muito superior, como paredes de tijolos maciços, de blocos de concreto ou de blocos cerâmicos.

It is well known that communication systems employing multiple transmit and multiple receive antennas provide high data rates along with increased reliability. It has been shown that coding across both spatial and temporal domains together, called Space-Time Coding (STC), achieves, a diversity order equal to the product of the number of transmit and receive antennas. Space-Time Block Codes (STBC) achieving the maximum diversity is called full-diversity STBCs. An STBC is called information-lossless, if the structure of it is such that the maximum mutual information of the resulting equivalent channel is equal to the capacity of the channel. This thesis deals with high-rate and information-lossless STBCs obtained from certain matrix algebras called Crossed-Product Algebras. First we give constructions of high-rate STBCs using both commutative and non-commutative matrix algebras obtained from appropriate representations of extensions of the field of rational numbers. In the case of commutative algebras, we restrict ourselves to fields and call the STBCs obtained from them as STBCs from field extensions. In the case of non-commutative algebras, we consider only the class of crossed-product algebras. For the case of field extensions, we first construct high-rate; full-diversity STBCs for arbitrary number of transmit antennas, over arbitrary apriori specified signal sets. Then we obtain a closed form expression for the coding gain of these STBCs and give a tight lower bound on the coding gain of some of these STBCs. This lower bound in certain cases indicates that some of the STBCs from field extensions are optimal m the sense of coding gain. We then show that the STBCs from field extensions are information-lossy. However, we also show that the finite-signal-set capacity of the STBCs from field extensions can be improved by increasing the symbol rate of the STBCs. The simulation results presented show that our high-rate STBCs perform better than the rate-1 STBCs in terms of the bit error rate performance. Then we proceed to present a construction of high-rate STBCs from crossed-product algebras. After giving a sufficient condition on the crossed-product algebras under which the resulting STBCs are information-lossless, we identify few classes of crossed-product algebras that satisfy this sufficient condition and also some classes of crossed-product algebras which are division algebras which lead to full-diversity STBCs. We present simulation results to show that the STBCs from crossed-product algebras perform better than the well-known codes m terms of the bit error rate. Finally, we introduce the notion of asymptotic-information-lossless (AILL) designs and give a necessary and sufficient condition under which a linear design is an AILL design. Analogous to the condition that a design has to be a full-rank design to achieve the point corresponding to the maximum diversity of the optimal diversity-multiplexing tradeoff, we show that a design has to be AILL to achieve the point corresponding to the maximum multiplexing gain of the optimal diversity-multiplexing tradeoff. Using the notion of AILL designs, we give a lower bound on the diversity-multiplexing tradeoff achieved by the STBCs from both field extensions and division algebras. The lower bound for STBCs obtained from division algebras indicates that they achieve the two extreme points, 1 e, zero multiplexing gain and zero diversity gain, of the optimal diversity-multiplexing tradeoff. Also, we show by simulation results that STBCs from division algebras achieves all the points on the optimal diversity-multiplexing tradeoff for n transmit and n receive antennas, where n = 2, 3, 4.

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