| 1. |
- Etman, Ahmed S., 1986-
(författare)
-
Aqueous Exfoliation of Transition Metal Oxides for Energy Storage and Photocatalysis Applications : Vanadium Oxide and Molybdenum Oxide Nanosheets
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Two-dimensional (2D) transition metal oxides (TMOs) are a category of materials which have unique physical and chemical properties compared to their bulk counterparts. However, the synthesis of 2D TMOs commonly includes the use of environmental threats such as organic solvents. In this thesis, we developed environmentally friendly strategies to fabricate TMO nanosheets from the commercially available bulk oxides. In particular, hydrated vanadium pentoxide (V2O5∙nH2O) nanosheets and oxygen deficient molybdenum trioxide (MoO3-x) nanosheets were prepared. The V2O5∙nH2O nanosheets were drop-cast onto multi-walled carbon nanotube (MWCNT) paper and applied as a free-standing electrode (FSE) for a lithium battery. The accessible capacity of the FSE was dependent on the electrode thickness; the thickest electrode delivered the lowest accessible capacity. Alternatively, a composite material of V2O5∙nH2O nanosheets with 10% MWCNT (VOx-CNT composite) was prepared and two types of electrodes, FSE and conventionally cast electrode (CCE), were employed as cathode materials for lithium batteries. A detailed comparison between these electrodes was presented. In addition, the VOx-CNT composite was applied as a negative electrode for a sodium-ion battery and showed a reversible capacity of about 140 mAh g-1. On the other hand, the MoO3-x nanosheets were employed as binder-free electrodes for supercapacitor application in an acidified Na2SO4 electrolyte. Furthermore, the MoO3-x nanosheets were used as photocatalysts for organic dye degradation. The simple eco-friendly synthesis methods coupled with the potential application of the TMO nanosheets reflect the significance of this thesis in both the synthesis and the energy-related applications of 2D materials.
|
|
| 2. |
- Hassan, Rebwar, 1959-
(författare)
-
Sediment Characteristics and Sedimentation Rate Estimation in the Dukan Reservoir
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Dukan Reservoir has been created from the construction of the Dukan Dam on the Lesser Zab River where it crosses the Khalakan Thrust Sheet (Khalakan Mountains) through a gorge 65 km northwest of Sulaimani and 295 km northeast of Baghdad. The Dukan Dam is a multi-purpose dam which was built from 1954 to 1959 to control the flooding of the Lesser Zab River, and to provide irrigation, hydroelectricity, and water storage. Reservoir sedimentation can significantly reduce reservoir storage capacity as dams become older. The Dukan Reservoir has been selected for this study to determine the nature and characteristics of the deposited sediment particles in the reservoir, as well as the estimation of the rate of sedimentation from 1959 to 2014 by using the bathymetric survey and the Soil and Water Assessment Tool (SWAT) model methods.Geologically, the Dukan Reservoir is located in the High Zagros Fold-Thrust Zone (High Folded Zone) of the northwestern segment of the Kurdistan Zagros Fold-Thrust Belt. This reservoir is a natural and structurally controlled depression located in the Btwen (Ranya) Agricultural Plain extending between the Ranya Thrust Sheet (Kewa-Rash Mountains) and the dam body itself. A geological survey was conducted for the study area and it has been concluded that the structural controls were more effective by dividing the Dukan Reservoir into two sub-reservoirs: a bigger triangle-shaped sub-reservoir in the north and a smaller irregularly shaped sub-reservoir in the south. The differences that exist in shapes, lengths, widths, surface areas, and shorelines between the two subreservoirs are also closely related to the structural and stratigraphical controls. The field observations and bathymetric survey indicate that bank sediment erosion is occurring in the two sub-reservoirs, but most of the sediment particles deposition takes place within the bigger sub-reservoir. Grain analyses of the 32 bed sediment samples show that the reservoir bed sediment consists of 15% gravel, 14% sand, 48% silt, and 23% clay. The sediments are composed of silty clay (77.6%), silty sandy clay (10%), sandy gravelly silty clay (1.2%) and gravelly sandy silty clay (1%). The reservoir bed is covered mainly with silt. Both silt and clay percentages increase towards the dam in the smaller sub-reservoir. This is attributable to the decreased water velocity in the reservoir, leading to the deposition of the suspended materials. The sediments are very finegrained, very poorly sorted, strongly coarse skewed, and mesokurtic. The depositedsediment along the Dukan Reservoir can be classified into topset bed (coarse particles) and bottomset bed (fine materials). The slope of the western bank of the reservoir is steeper than the eastern and northern banks. Land slope is the most effective factor in erosion and sediment transport. From the bathymetric survey, it has been also concluded that the minimum elevation which reaches 430 m.a.s.l. is located at the southern part of the bigger sub- reservoir. Based on different bulk densities of the deposited sediment at different water elevations, i.e., 1855 kg/m3 at 470 m.a.s.l., 1855 kg/m3 at 480 m.a.s.l., and 1200 kg/m3 at 480 m.a.s.l., the annual sedimentation rates in the reservoir are estimated to be about 3.8 MCM, 7 MCM, and 6.6 MCM, respectively. This estimation has been supported by the SWAT model method, which shows that the annual sediment load delivered to the Dukan Reservoir from the watershed is estimated to be about 1.3 MCM, representingabout 34% of the total sediments deposited in the reservoir.The reduction in storage capacity of the bigger sub-reservoir from 1952 to 2014 at water elevations 440 m.a.s.l., 460 m.a.s.l, and 480 m.a.s.l. are 72%, 48%, and 24%, respectively. The volume of the deposited sediment is estimated to be around 274 MCM. The percentage of the smaller sub-reservoir area as a percentage of the whole reservoir area varied in 1952 from 4% at water level 520 m.a.s.l. to 100% at 420 m.a.s.l. The author predicts that the estimated annual deposition rate of 6.6 MCM and the projected useful lifespan might extend for another 155 years until 2169, when the sediment will fully occupy the live storages.
|
|
| 3. |
- Shami, Muhammad Ali, 1980-
(författare)
-
Dynamically Reconfigurable Resource Array
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The goals set by the International Technology Roadmap for Semiconductors (ITRS) for the consumer portable category, to be realized by 2020, are 1000X improvement in performance with only 40\% increase in power budget and no increase in design team size. To meet these goals, the challenges facing the VLSI community are gaps in architecture efficacy, design productivity and battery capacity.As the causes of the gaps in architecture efficacy and battery capacity, this thesis identifies: a) instruction granularity mismatch, b) bit-width granularity mismatch, c) silicon granularity mismatch and d) parallelism mismatch. Field Programmable Gate Array(FPGA) technology can address instruction/bit-width granularity and parallelism mismatch but suffers from silicon granularity mismatch due to high reconfiguration overheads. The ultimate design goal of a system-on-chip is to achieve an ASIC-like performance and FPGA-like flexibility, design time and cost. Coarse Grain Reconfigurable Architectures (CGRAs) are a compromise between ASIC and FPGA since they provide better computational efficiency compared to FPGAs and better engineering efficiency compared to ASIC. However, the current generation of CGRAs lack many architectural properties that would enable them to replace ASIC and/or FPGA by mainstream industry.To objectively discuss these properties, in the first part of the thesis a classification scheme has been proposed that classifies parallel computing machines into 47 classes and propose how they can be graded in terms of flexibility. We apply this classification scheme on academic and industrial reconfigurable architectures to compare them for their similarities and differences. We identify an instruction flow spatial computing class to be used for a CGRA fabric called Dynamically Reconfigurable Resource Array (DRRA) presented in the second part of this thesis. The DRRA fabric is a Parallel Distributed Digital Signal Processing (PDDSP) fabric with distributed arithmetic, logic, interconnect and control resources. Problems associated with the distributed control model of DRRA are identified and architectural solutions that can be exploited by the compiler tools are presented.After logical and physical synthesis, DRRA shows a peak performance of 21 GOPS and peak silicon efficiency of 16.03 GOPS/mm\textsuperscript{2}. We further performed a three-level validation of the DRRA fabric. At first level, we mapped a number of signal and compute intensive algorithms to demonstrate the flexibility of the DRRA fabric. At second level, we measured the gap between ASIC, DRRA and FPGA. On average DRRA shows 22.87x area, 10.75x power consumption, 852x configuration bits, 959x configuration cycles, 63,94x silicon efficiency, 4.78x computational efficiency, and 6.15E+10x better energy-delay product improvements compared to FPGA. Finally, at third level we present the use of DRRA for a real world example of implementing a 128-, 256-, 512-, 1024-, 2048-point configurable FFT processor. For 1024 point FFT, in terms of computational efficiency, DRRA outperforms all CGRAs by at least 2x and is worse than ASIC by 3.45x. As regards silicon efficiency, although dedicated processors perform 1.6x better, DRRA is better than all other CGRAs.
|
|
