1,721,070 research outputs found
Ntab, a novel non-coding RNA abundantly expressed in rat brain
No full textWe have identified a novel transcript that is abundantly and specifically expressed in both the adult and developing rat CNS. Within the full-length cDNA sequence we were unable to identify a clear open reading frame. Moreover, we were unable to detect any protein product derived from the full-length cDNA sequence using an in vitro translation assay. Therefore, we suggest this gene is one of a growing number of non-coding mRNA-like RNA transcripts that exert their cellular functions directly as an RNA. We have named this novel gene Ntab for non-coding transcript abundantly expressed in brain (accession number AY035551). In addition, in some regions of the brain we find evidence for RNA accumulation in cellular processes at some distance from the soma. These findings suggest that Ntab is actively transported and may function within cellular processes. Since Ntab is a targeted non-coding RNA, such cellular functions could include the targeting and/or regulation of localised translation of other mRNA species
A novel method for nanoprecision alignment in wafer bonding applications
Full text linkWafer bonding has been identified as a promising technique to enable fabrication of many advanced semiconductor devices such as three dimensional integrated circuits (3D IC) and micro/nano systems. However, with the device dimensions already in the nanometer range, the lack of approaches to achieve high precision bonding alignment has restricted many applications. With this increasing demand for wafer bonding applications, a novel mechanical passive alignment technique is described in this work aiming at nanoprecision alignment based on kinematic and elastic averaging effects. A number of cantilever supported pyramid and V-pit microstructures have been incorporated into the outer circumference area of the to-be-bonded Si chips, respectively. The engagement between the convex pyramids and concave V-pits and the compliance of the support cantilever flexures result in micromechanical passive alignment which is followed by direct bonding between the Si chips. The subsequent infrared (IR) and scanning electron microscopy (SEM) inspections repeatedly confirmed the achievement of the alignment accuracy of better than 200nm at the bonding interface with good bonding quality. The impact and potential applications of the developed alignment technique are also discussed
From MEMS to NEMS: Scaling Cantilever Sensors
No full textThis thesis studies the effects of scaling on the characterisation and readout of micro-electro mechanical systems (MEMS) to nano-electro mechanical systems (NEMS). In particular it focuses on cantilever, which is a basic device building block and an important transducer in many sensing applications. This thesis presents an overview of major scaling effects and discusses their scaling factors. It includes scaling analysis on physical property aspects such as quality factor, Young’s modulus, thermal noise and elastic non-linearity. It also includes scaling analysis on practical aspects such as sensitivity, mass-stiffness decoupling and surface contamination. Furthermore, it studies the scaling of different cantilever detection techniques, in particular the laser deflection, hard contact, field emission and piezoresistive sensing techniques. Down-scaling a cantilever sensor is an intuitive way of increasing its sensitivity and responsiveness. However the advantages gained must be weighed against other effects which also became significant due to the scaling. For this reason, this thesis provides the necessary information, analysis and methods that help assessing the advantages and disadvantages of scaling.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Micro and Nanofluidic devices: For Single cell and DNA analysis
No full textResearch in the field of Micro/nanofluidics has been extensively carried out for the last few years. With the available technological advancements today many complex systems can be fabricated in a more efficient and simpler way. Conventional methods in a laboratory consumes a lot of time, chemicals and in turn generates a lot of waste unlike the Lab-on-a-chip (LOC) devices where all the processes are carried out on a small chip with small drops of chemicals, negligible wastes and in minimum time. Most of all this is very efficient and inexpensive. Most of the work in this project was concentrated on developing and optimizing the technologies for the fabrication of micro and nanofluidic devices. Conventional soft-lithography was used initially to fabricate the microfluidic devices using PDMS. Realizing the limitations in working with PDMS the choice was made to replace PDMS with TMMF S2030 dry film photoresist (DFR) which turned out to be fruitful. Working with DFR is inexpensive, more accurate and easier compared to working with PDMS in microfluidics. Dry film photoresist (DFR) is a new type of photoresists, which is gaining importance in semiconductor industry. These are generally negative tone photoresists in the form of a thin foil protected by PET (Polyethylene terephthalate) on both sides. They are differentiated into permanent and non-permanent resists. The minimum known thickness of the available dry films is 15 µm and the maximum reaching to few hundreds of microns. They can potentially replace soft lithographic materials, since they are easier to process. Dry film photoresists have a big role to play in microfluidics, which is yet to be completely explored. Manipulating a single cell has been an interesting topic for the researchers in the field of microfluidics for a long time. Our design fulfils the idea of trapping, cell viability, manipulation, sensing and detection. The devices were equipped with different channels for different applications like, providing nutrients to the cell, to hold the cell with suction and to collect the reaction by-products, sense and detect them. Di-electrophoresis is a well known technique for manipulating neutral particles/cells in fluids and it is widely used in micro fluidic systems for forcing particles to desired trajectories. Since the particle has to be moved in the horizontal plane, the width and the introduction point of the particle are more critical variables. Presorter electrodes were introduced more upstream in the entrance channel which will bring far-off particles to the trapping range and also a minimum distance between presorter and trapping electrodes should be regarded. One more important goal is to keep the cell in the reservoir once it is there. This can be achieved by a simple electrode pair blocking the outlet of the hole. The particle is repelled from the resulting field. The same repelling force will prevent other particles to enter the hole. The geometry of electrodes was designed so that it is only necessary to modify the applied voltage according to the entrance speed. Experiments for trapping polystyrene beads followed by E.coli bacteria were successfully carried out with the help of a dedicated holder and an Olympus inverted microscope. Research stops nowhere. Following the path from microfluidic devices for single cell analysis, we have concentrated on developing nanofluidic devices for DNA analysis. Lot of research has been carried out in nanofluidics for DNA, protein and nucleic acid analysis studies. Existing devices have electrodes placed at the ends of microchannels and a potential is applied to move the particles into the nanochannels. The devices we aimed at have electrodes embedded within the nanochannels along with electrodes at the junctions of micro and nanochannels. The main idea in designing and fabricating these devices with embedded electrodes is to study the behavior of the biomolecules in a localized electrical field. Devices were fabricated by a conventional anodic bonding process and a completely new single silicon wafer process. To our knowledge this is the first time that nanofluidic devices (200 nm deep channels and integrated electrodes) were fabricated on a single silicon wafer. The nanochannels in this case were defined by sacrificial etching. Electrodes were patterned on the top side of the nanochannels. Microchannels were etched from the back side of the silicon wafer connecting to the nanochannels through a membrane of silicon nitride. Initial experiments were carried out with rhodamine + ethanol solution to prove the opening of nanochannels without any leakage followed by trapping carboxylate modified fluorescent polystyrene beads to confirm the working of embedded electrodes. Further experiments were carried out with DNA molecules tagged with a fluorescent dye. DNA molecules were injected into the microchannel and once the channels were filled completely, electrodes in the microchannels were switched on to drag the DNA molecule towards the entrance of the nanochannel. Then the EOF voltage over the nanochannel was switched on to drag the DNA through the nanochannel. A single DNA molecule was successfully tracked over the length of the nanochannel. Time and the distance travelled by the molecule were calculated. Using microfluidic devices further experiments on sensing and detection can be carried out with single cells. Behavior of different lengths of DNA within the electrical double layer in a localized electric field can be studied with the help of the fabricated nanofluidic devices. Experiments were also carried out to define the best etch mask to etch completely through a glass wafer. Amorphous silicon turned out to be the best etch mask material to etch the glass in 40% HF. Even though slight pin holes were observed by using PECVD amorphous silicon, we recommend that thick layers sputtered in batches will resolve this problem and a clear surface can be achieved. It is recommended that LPCVD amorphous silicon would be the best etch mask if it can be sputtered at lower temperatures. Along with amorphous silicon, Molybdenum can also be a good etch mask if more research has been done on improving the adhesion of ‘Mo’ to glass substrates.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc
Evanescent Waveguide Sensors for Biomedical Applications
No full textThe American Cancer Society reported that the major public health problem is cancer. Based on the report, colonic cancer is the major cancer type in the digestive system. In addition, the percentage of death rate due to this cancer is 50%. Surgery to remove the part of the colon infected by the cancer and then reconnect the healthy one is called anastomosis. However, after the anastomosis, there is sometimes leakage that gives an opportunity for bacteria inside the colon (E. coli) into leak to the abdominal cavity and cause infections, multiple organ failure or even mortality. The leakage is serious problem but unfortunately it is difficult to predict early. Consequently it is often too late to take action for the patients. The leakage can be examined by detecting bacteria in drain fluid. However by using conventional methods, it will take long time. In this thesis, a new approach to diagnose the leakage by detecting E. coli in drain fluid was demonstrated. The approach uses sensor based on evanescent waves during the propagation of light in a waveguide. The wave propagates on the waveguide surface and it is a very good candidate for this application because it is very sensitive to environmental changes. In general, there are three aspects to be considered to develop high quality sensors i.e fabrication, sensitivity, and selectivity. Simulation using effective index method (EIM) and calculation were conducted to estimate the optimum dimensions of the sensor so that it affects the existence of the evanescent wave positively and influences the sensitivity of the sensor. In addition, to enhance the sensitivity, the structure of the sensor was designed as freestanding so that both surfaces are able to react to the surrounding. Material development consists of thin film deposition of TiO2 using atomic layer deposition (ALD) and characterisation of the thin film: surface roughness, thin film stress and optical properties. Based on the characterisations of the TiO2-ALD, the material was found to have good properties as waveguide sensor material. Lithography-based micromachining by combining bulk and surface micromachining was used to fabricate the waveguide in the cleanroom and MEMS-lab. The advantage of the method is in the integration aspect, so that the device can be integrated with other platforms such as CMOS, optical systems, and microfluidic systems. Drain fluid is a highly complex fluid which consists of bacteria, plasma, fluids etcetera. The sensor must be able to detect the target of interest in the complex fluid. Consequently, selectivity is an important property in the development of the sensor. In order to enhance selectivity, the evanescentwaveguide sensor surfaces were functionalised using antibody for E. coli. In this treatment, self-assembly monolayers (SAM) and coupling agents (protein-A and EDC) were deposited on the surface prior to antibody deposition to increase bonding between the waveguide surface and antibodies. The sensor sensitivity was evaluated using isopropyl alcohol (IPA) by measuring the evaporation rate of several different concentrations of IPA in water. Functionalised sensor sensitivity was tested using solutions of E. coli K12 in LB medium. Furthermore, selectivity of the sensor was also examined in this experiment. Solutions that consist of constant E. coli and several different concentrations of Bacillus Subtilis in LB medium were used for this testing. The sensor responses show that the variation of Bacillus does not affect the output signal of the sensor. Different concentrations of drain fluid from patients were also used to evaluate the operation of the sensor. In the experiments using drain fluid, the different concentrations of drain fluid could be detected by the sensor. The results show that the sensor has good sensitivity and selectivity for chemical and biological applications. Finally, to evaluate the reusability of the sensor, the reproducibility and repeatability of the sensor was investigated. By using several samples and measuring the samples in two conditions (load and unload) several times, the reproducibility of the sensor was determined.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc
Modal wavefront correctors based on nematic liquid crystals
No full textModal wavefront correctors are active optical components for the compensation of aberrated optical wavefronts in a smooth and continuous way. They are traditionally represented by membrane and continuous faceplate deformable mirrors. This thesis is dedicated to the investigation and development of modal wavefront correctors based on nematic liquid crystals. The thesis introduces a new method for evaluating the average static correction performance of a wavefront corrector applied to compensation of random phase aberrations. Statistics of the random wavefronts are described by Kolmogorov's theory. The method allows a comparison of the static correction performances of different types of deformable mirrors and different actuator structures. A range of modal liquid crystal (LC) devices is considered, including adaptive spherical and cylindrical LC lenses and three different types of multi-element wavefront correctors. The research is focused on electro-optics of the devices, consideration of potentially useful control modes, development of algorithms of optimization and control, and alternative technologies for modal addressing of LCs. A control algorithm and software have been developed for a system for practical calibration of modal LC lenses. Feasibility of control using several degrees of freedom per actuator is demonstrated for both adaptive LC lenses and multi-element modal wavefront correctors. Two new approaches to forming of the modal-type phase profiles in LC layers are considered. The first one is based on spreading of the electric field in a thick dielectric substrate and the second one is based on a passive resistive network formed in a semiconductor silicon substrate. These approaches are illustrated with practically implemented devices. Comparison of the new technologies to a previously studied one is presented.Electrical Engineering, Mathematics and Computer Scienc
Methods and sensors for accurate wavefront measurements
No full textThe wavefront measurement is an important part both in adaptive optics and in optical shop testing. A number of wavefront sensors based on interferometric or on Hartmann principle is known; this thesis investigates particular technologies that can help to increase the accuracy and/or speed of existing wavefront sensors either by optimising the wavefront reconstruction algorithm or by optimising the hardware. The topics discussed are interferogram analysis, optimising of the Hartmann mask geometry, and design of a 2D heterodyne phase detector.Electrical Engineering, Mathematics and Computer Scienc
Reliability of micromechanical thin-film resonators
No full textElectrical Engineering, Mathematics and Computer Scienc
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