No description available.

<p>Energy recovering techniques for air conditioning has increased in recent years and new prod- </p><p>ucts have been introduced to the market where the Membrane-based Energy Recovery Ventilator </p><p>(ERV) is one promising product. The aim of this study was to evaluate a new type of membrane </p><p>material for an ERV and give an analysis of the need for digital control of the air flow rate to </p><p>improve efficiency. A prototype counter-flow ERV was used in the test to validate the performance under different </p><p>flow conditions. The result was promising for the tested membrane material with high moisture </p><p>and heat transfer. The optimisation of the flow rate was found to be superfluous, since the relation </p><p>between the energy transferred by the ERV and the air flow rate was almost linear.</p>

Energy recovering techniques for air conditioning has increased in recent years and new prod- ucts have been introduced to the market where the Membrane-based Energy Recovery Ventilator (ERV) is one promising product. The aim of this study was to evaluate a new type of membrane material for an ERV and give an analysis of the need for digital control of the air flow rate to improve efficiency. A prototype counter-flow ERV was used in the test to validate the performance under different flow conditions. The result was promising for the tested membrane material with high moisture and heat transfer. The optimisation of the flow rate was found to be superfluous, since the relation between the energy transferred by the ERV and the air flow rate was almost linear.

No description available.

No description available.

Hair cell structures are one of the most common forms of sensing elements found in nature. In humans, approximately 16,000 auditory hair cells can be found in the cochlea of the ear. Each hair cell contains a stereocilia, which is the primary structure for sound transduction. This study looks to develop and characterize a bilayer lipid membrane (BLM) operated artificial hair cell sensor that resembles the stereocilia of the human ear. To develop this sensor, a flexible substrate with internal compartments for hosting the biomolecules and mating cap are constructed and experimentally characterized. The regulated attachment method (RAM) is used to form bilayers within the sealed device. Capacitance measurements of the encapsulated bilayer show that the sealing cap slightly compresses the bottom insert and reduces the size of the enclosed bilayer. Single channel measurements of alamethicin peptides further verify that the encapsulated device can be used to detect the gating activity of transmembrane proteins in the membrane. The flexible substrate was incorporated into a low-noise, portable test fixture. The response of the sensor and tip velocity of the hair were measured with respect to an impulse input on the test fixture and several frequency response functions (FRFs) were created. The FRF between the sensor and the tip velocity was used to show that the hair vibration was transmitted to the bilayer for certain hair lengths. The transfer function between the sensor and the input was used to show the effect of membrane potential on sensor response. / Master of Science

Niobium (Nb) and tantalum (Ta) are found in the same group (VB) of the periodic table of elements and therefore have similar chemical properties, which is the reason why they are difficult to separate. They are usually found together in various minerals of which the most important are columbite ((Fe, Mn, Mg)(Nb, Ta)2O6) and tantalite ((Fe, Mn)(Nb, Ta)2O6). Several methods have been used to separate Nb and Ta. Most methods use very high concentrations of hydrofluoric acid (HF) and sulphuric acid (H2SO4) as the aqueous phase, tributyl phosphate (TBP) as the extractant and methyl isobutyl ketone (MIBK) as the organic phase. High extraction can be achieved, but the reagents used are hazardous. With the increasing demand of both pure Ta and Nb, as well as stricter environmental requirements, a need exists to develop a more efficient and safer technique to separate Ta and Nb. In this project the focus was on the solvent extraction (SX) of Ta and Nb with the possible application in a membrane-based solvent extraction (MBSX) process. For this purpose, eight different extractants were investigated, namely the cation exchangers di-iso-octyl-phosphinic acid (PA) and di-(2-ethylhexyl)-phosphoric acid (D2EHPA), the neutral solvating extractant 2-thenoyl-trifluoro- acetone (TTA), and the anion exchangers Alamine 336, Aliquat 336, 1-octanol, 2-octanol and 3-octanol. The extractant to metal ratio was varied from 0.1:1 to 10:1, while cyclohexane was used as diluent and 3% v/v 1-octanol was used as modifier for the organic phase. In addition, four different acids, hydrochloric acid (HCl), nitric acid (HNO3), sulphuric (H2SO4) and perchloric acid (HClO4), were used at different concentrations to determine the best combination for extraction. First, fluoride salts of Ta and Nb (Ta(Nb)F5) were tested and the optimum results showed that the highest extraction was obtained with PA and D2EHPA, irrespective of the type of acid used. Similarly, irrespective of the acid used, extraction with PA and D2EHPA increased with increasing acid concentration, followed by Alamine 336, Aliquat 336 and then TTA and the octanols. Extraction values of 97% Ta at 15 mol/dm3 and 85% Nb between 12 and 15 mol/dm3 were obtained. Although extraction of both Ta and Nb was achieved with all the acids tested, only H2SO4 showed sufficient separation (log D = 3) of the two metals in the 0 to 2 mol/dm3 acid range and 15 mol/dm3 for PA and D2EHPA, respectively. Precipitation, probably due to hydrolysis of the metals, occurred in the absence of acid when using Alamine 336, Aliquat 336 and TTA. The octanols showed the least amount of extraction of Ta and Nb, irrespective of the acid investigated. The optimum extraction was achieved with an E/M ratio of 3:1 of PA and D2EHPA as the extractant and 10 mol/dm3 H2SO4 in the aqueous phase. The NH4Ta(Nb)F6 salt solution was investigated using the optimum conditions for maximum extraction obtained from the Ta(Nb)F5 experiments, i.e. 4 mol/dm3 H2SO4 with an E/M ratio above 3:1 for the extractant PA and 4 mol/dm3 H2SO4 with an E/M ratio of 20:1 for the extractant D2EHPA. Kinetic equilibrium for PA was reached after 10 minutes and for D2EHPA after 20 minutes. The highest extraction of Ta (100%) above 3 mol/dm3 H2SO4 and Nb (54%) at 8 mol/dm3 with the highest separation factor of 4.7 with PA was achieved, followed by the 100% extraction of Ta above 5 mol/dm3 and 40% Nb at 10 mol/dm3 with the highest separation factor of 4.9 in D2EHPA. Although the aim of this study was the extraction and separation of Ta and Nb, the recovery or back extraction of the metals from the organic phase, as well as the membrane-based solvent extraction (MBSX) was briefly investigated. From the preliminary results obtained it became apparent that further research into the different aspects, including the type of stripping agent used, stripping agent concentration, effect of Ta to Nb ratio and different sources of Ta and Nb is needed to obtain the optimum conditions for the MBSX process and the subsequent recovery of Ta and Nb. / Thesis (MSc (Chemistry))--North-West University, Potchefstroom Campus, 2013.

Niobium (Nb) and tantalum (Ta) are found in the same group (VB) of the periodic table of elements and therefore have similar chemical properties, which is the reason why they are difficult to separate. They are usually found together in various minerals of which the most important are columbite ((Fe, Mn, Mg)(Nb, Ta)2O6) and tantalite ((Fe, Mn)(Nb, Ta)2O6). Several methods have been used to separate Nb and Ta. Most methods use very high concentrations of hydrofluoric acid (HF) and sulphuric acid (H2SO4) as the aqueous phase, tributyl phosphate (TBP) as the extractant and methyl isobutyl ketone (MIBK) as the organic phase. High extraction can be achieved, but the reagents used are hazardous. With the increasing demand of both pure Ta and Nb, as well as stricter environmental requirements, a need exists to develop a more efficient and safer technique to separate Ta and Nb. In this project the focus was on the solvent extraction (SX) of Ta and Nb with the possible application in a membrane-based solvent extraction (MBSX) process. For this purpose, eight different extractants were investigated, namely the cation exchangers di-iso-octyl-phosphinic acid (PA) and di-(2-ethylhexyl)-phosphoric acid (D2EHPA), the neutral solvating extractant 2-thenoyl-trifluoro- acetone (TTA), and the anion exchangers Alamine 336, Aliquat 336, 1-octanol, 2-octanol and 3-octanol. The extractant to metal ratio was varied from 0.1:1 to 10:1, while cyclohexane was used as diluent and 3% v/v 1-octanol was used as modifier for the organic phase. In addition, four different acids, hydrochloric acid (HCl), nitric acid (HNO3), sulphuric (H2SO4) and perchloric acid (HClO4), were used at different concentrations to determine the best combination for extraction. First, fluoride salts of Ta and Nb (Ta(Nb)F5) were tested and the optimum results showed that the highest extraction was obtained with PA and D2EHPA, irrespective of the type of acid used. Similarly, irrespective of the acid used, extraction with PA and D2EHPA increased with increasing acid concentration, followed by Alamine 336, Aliquat 336 and then TTA and the octanols. Extraction values of 97% Ta at 15 mol/dm3 and 85% Nb between 12 and 15 mol/dm3 were obtained. Although extraction of both Ta and Nb was achieved with all the acids tested, only H2SO4 showed sufficient separation (log D = 3) of the two metals in the 0 to 2 mol/dm3 acid range and 15 mol/dm3 for PA and D2EHPA, respectively. Precipitation, probably due to hydrolysis of the metals, occurred in the absence of acid when using Alamine 336, Aliquat 336 and TTA. The octanols showed the least amount of extraction of Ta and Nb, irrespective of the acid investigated. The optimum extraction was achieved with an E/M ratio of 3:1 of PA and D2EHPA as the extractant and 10 mol/dm3 H2SO4 in the aqueous phase. The NH4Ta(Nb)F6 salt solution was investigated using the optimum conditions for maximum extraction obtained from the Ta(Nb)F5 experiments, i.e. 4 mol/dm3 H2SO4 with an E/M ratio above 3:1 for the extractant PA and 4 mol/dm3 H2SO4 with an E/M ratio of 20:1 for the extractant D2EHPA. Kinetic equilibrium for PA was reached after 10 minutes and for D2EHPA after 20 minutes. The highest extraction of Ta (100%) above 3 mol/dm3 H2SO4 and Nb (54%) at 8 mol/dm3 with the highest separation factor of 4.7 with PA was achieved, followed by the 100% extraction of Ta above 5 mol/dm3 and 40% Nb at 10 mol/dm3 with the highest separation factor of 4.9 in D2EHPA. Although the aim of this study was the extraction and separation of Ta and Nb, the recovery or back extraction of the metals from the organic phase, as well as the membrane-based solvent extraction (MBSX) was briefly investigated. From the preliminary results obtained it became apparent that further research into the different aspects, including the type of stripping agent used, stripping agent concentration, effect of Ta to Nb ratio and different sources of Ta and Nb is needed to obtain the optimum conditions for the MBSX process and the subsequent recovery of Ta and Nb. / Thesis (MSc (Chemistry))--North-West University, Potchefstroom Campus, 2013.

A differential, membrane-based nanocalorimeter has been designed and constructed for thermal studies of mesoscopic samples at low temperatures. The calorimeter is intended for sample masses from mg to sub-μg and a broad temperature range from above room temperature down to the sub-K region. It allows concurrent use of ac steady state and relaxation methods. Effort was spent to achieve good absolute accuracy to enable investigations of the electronic contribution to the heat capacity of superconductors. The calorimeter consists of a pair of cells, each of which is a stack of heaters and thermometer in the center of a silicon nitride membrane, in total giving a background heat capacity less than 100 nJ/K at 300 K, decreasing to 10 pJ/K at 1 K. The device has several distinctive features: i) The resistive thermometer, made of a GeAu alloy, displays a high sensitivity, dlnR/dlnT ≈ −1 over the entire temperature range. ii) The sample is placed in direct contact with the thermometer, which is allowed to self-heat. The thermometer can thus be operated at high dc current to increase the resolution. iii) Data are acquired with a set of eight synchronized lock-in amplifiers measuring dc, 1st and 2nd harmonic signals of heaters and thermometer. iv) Absolute accuracy is achieved via a novel variable-frequency fixed-phase technique in which the measurement frequency is automatically adjusted during ac-calorimetry measurements to account for the temperature variation of the sample specific heat and the device thermal conductance. The properties of the empty cell and the effect of the thermal link between sample and cell were analytically studied. Practical expressions for describing the frequency dependence of heat capacity, thermal conductance, and temperature oscillation amplitude of the system were formulated. Comparisons with measurements and numerical simulations show excellent agreement. Calibration procedures are simple, but care should be taken to minimize thermal radiation effects. The experimental setup is operated with self-regulation of heater powers and thermometer bias, including compensation to zero the differential dc signal. As a result its high resolution and compact format, the calorimeter is well suited for studies of phase transitions and phase diagrams as well as electronic specific heat. The performance of the device is demonstrated by a study of the superconducting state of a small lead crystal. / En differentiell, membran-baserad nanocalorimeter har designats och tillverkats för termiska studier av mesoskopiska prover vid låg temperatur. Kalorimetern är avsedd för provmassor från mg till sub-μg och ett brett temperaturområde från över rumstemperatur till under 1 K. Den tillåter samtidig användning av både ac steady state och relaxations-metod. Fokus har lagts på att uppnå en god absolut noggrannhet för att möjliggöra studier av det elektroniska bidraget till värmekapaciteten hos supraledare. Kalorimetern består av två celler, var och en uppbyggd som en stack med värmeelement och termometer i mitten av ett kiselnitrid-membran, med en total bakgrundsvärmekapacitet på mindre än 100 nJ/K vid 300 K, minskande till 10 pJ/K vid 1 K. Kalorimetern har flera särdrag: i) Den resistiva termometern, gjord av en GeAu legering, visar en hög känslighet, dlnR/dlnT ≈ −1 över hela temperaturområdet. ii) Provet placeras i direkt kontakt med termometern, som tillåts att självvärma. Termometern kan alltså användas vid hög dc ström för att öka upplösningen. iii) Mätningarna genomförs med en uppsättning av åtta synkroniserade lock-in förstärkare, som mäter dc, grundfrekvens och 1:a övertonen hos värme-element och termometer. iv) Absolut noggrannhet uppnås genom en ny variabel-frekvens konstant-fas teknik där mätfrekvensen justeras automatiskt under ac-kalorimetrimätningar för att kompensera temperaturberoendet hos provets specifika värmekapacitet och kalorimetercellens värmeledningsförmåga. Egenskaperna hos den tomma cellen och inverkan av den termiska länken mellan prov och cell studerades analytiskt. Praktiska uttryck för att beskriva frekvens beroendet hos systemets värmekapacitet, värmeledningsförmåga, och temperaturoscillationer har formulerats. Jämförelser mellan mätningar och numeriska simuleringar visar mycket bra överensstämmelse. Kalibreringsförfarandet är enkelt, men försiktighet bör vidtas för att minimera värmestrålningseffekter. Experimentuppställningen drivs med självreglering av värmare och termometer, inklusive kompensation för att nollställa den differentiella dc signalen. Som en följd av dess höga upplösning och kompakta format är kalorimetern väl lämpad för studier av fasövergångar och fasdiagram såväl som det elektroniska specifika värmet. Kalorimeterns prestanda demonstreras genom en studie av det supraledande tillståndet hos en liten blykristall. / At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Accepted.

Clonal haematopoiesis of indeterminate potential, or CHIP are a family of mutations present in the general population. CHIP-mutations are prevalent in the haematopoietic stem cells and in the more mature cell populations, T-lymphocytes, B-lymphocytes and myeloid cells (CD3+, CD19+ and CD33+ cells) in blood. By separating these cell populations using magnetic isolation, extracting DNA from the cell populations, and detecting the same mutation in all cell populations, one can prove the presence of CHIP-mutations in a hematopoietic stem cell. At least 50 ng good quality DNA is needed for the gene analysis to detect CHIP-mutations. The magnet separated cell population may be very small, so the DNA extraction method must be optimized to achieve enough DNA yield. The main purpose of the method development was to compare two storage methods before DNA-extractions, and then three different DNA-quantification methods after the DNA-extractions. After the best storage and quantification methods were identified, five samples of cryo-preserved viable cells were used to isolate cell populations using magnetic beads covered in specific antibodies and a magnetic field, and then quantified. Results of the study showed that the best way was to store the cells in ATL-buffer and Proteinase K. To quantify DNA, qPCR was the most accurate method, since the other methods showed incorrect results because of the low DNA concentrations. Magnet cell separation was partly successful. All except one of the DNA yields from the cell separation protocols reached the critical amount of DNA, but some yields were not pure yields of the sought-after cell population. In general, the method must be worked on more with further research.