No description available.

Pyroelectric energy scavenging is the process of converting wasted energy from a system to power another one, based on the pyroelectric effect of piezoelectric materials. Pyroelectrically generated power is a function of the surface of material, the pyroelectric coefficient, and the temporal temperature gradient. In the current project, a simple model is developed to predict the power generation based on the temporal change in temperature of material. In addition, a model is validated with experimental measurements from several piezoelectric materials. It is shown that energy generation can be enhanced by using piezoelectric materials with significantly higher pyroelectric coefficients such as pre-stressed piezoelectric materials or thin films. Meanwhile, a method of continuously harvesting energy from pyroelectric materials is demonstrated using an innovative cyclic heating scheme. Besides, simple analytic expressions are developed for ideal voltage, power and power densities as a function of pyroelectric constant, permittivity, surface area, thickness, temperature variation.

In recent years, there has been recent increase in the deployment of wireless sensor networks. These sensors are typically powered by a battery which has limited life span. This problem can be overcomed by using energy scavenging or power harvesting which is the process of converting ambient energy from the environment into usable electrical energy. It can be used in applications such as remote patient monitoring, implantable sensors, machinery/equipment monitoring and so on. The thesis presents the RF scavenging system and mainly focuses on the study of the rectifier architectures which is one of the key components in the RF scavenging system. The thesis also provides the design challenges while implementing the different rectifier structures, which are PMOS bridge rectifier, CMOS differential rectifier and charge pump. The functionality of the rectifier structures are studied by simulation using RF signal of 900 MHz and implemented in 0.35μm and 65 nm technologies to compare the results. The simulation results shows that there is a tradeoff between high output DC voltage and high power efficiency. Maximum DC output voltage of 1 V is obtained from input amplitude level of 0.16 V using 7-stage charge pump rectifier. In the other hand maximum power efficiency of 23 % is obtained using CMOS differential rectifier.

No description available.

Clouds strongly influence three-dimensional aerosol distributions by 1) wet scavenging and subsequent deposition to the earth's surface, and 2) processing and subsequent release to the atmosphere by evaporation processes. In this study, physically detailed size-dependent representations of below-cloud and in-cloud scavenging for mixed phase clouds are introduced into the ECHAM5-HAM global climate model. As well, a stratiform cloud aerosol processing scheme is extended to convective clouds. Below-cloud impaction scavenging is found to contribute strongly to the global and annual mean mass deposition for sulfate (14%), black carbon (13%), particulate organic matter (10%), sea salt (23%), and dust (24%). The modeled global mean aerosol optical depth, and sea salt burden are reduced by about 15% for the more vigorous size-dependent parameterization of below-cloud scavenging by rain and snow. In stratiform clouds, aerosol mass is found to be primarily (>90%) scavenged by cloud nucleation processes for all aerosol species, except for dust (50%). Uncertainties in the representation of in-cloud scavenging processes change the predicted annual, global mean aerosol mass burdens by 20 to 30%, and change the predicted aerosol mass concentrations by up to one order of magnitude in the middle troposphere where mixed phase clouds exist. Closer agreement with observations of black carbon profiles from aircraft is found for the new in-cloud scavenging scheme. Convective and stratiform clouds contribute about equally to the global, annual mean aerosol processing, but wet deposition is primarily attributed to stratiform clouds (75%). Sulfate and carbonaceous aerosols undergo 1-3 cloud cycles before deposition. Aerosol burdens and optical depth (AOD) increase by a factor of 3-5 with the explicit representation of cloud/precipitation evaporation. Revised sea salt emissions and more vigorous in-cloud impaction scavenging reduce the AOD by a factor of three to give closer agreement with satellite retrievals. Observed marine boundary layer accumulation mode size distributions, and vertically integrated aerosol size distributions from AERONET observations are more closely approximated with the aerosol processing scheme than for the standard ECHAM5-HAM.

No description available.

Thesis (Ph. D.)--Oregon Graduate Center, 1986.

The Ph.D. thesis enclosed focuses on various implications of scavenging by generalist predators on invertebrate cadavers. Comparison of the retention time for invertebrate cadavers in the field, with the detection period for decaying slug material in the guts of the predators is presented and indicates that PCR-based techniques are not able to distinguish between predated and scavenged food items. Disappearance rates for invertebrate cadavers in the field, together with generealist predator preference for dead prey were estimated and their implication on survival strategies of entomopathogenic and molluscicidal nematodes in the cadavers is discussed. Two different strategies were investigated and are presentd in the thesis.

No description available.

To better characterize the fundamentals of oxygen scavenging as a means to prepare high oxygen barrier polymer films, the oxidation of 1,4-polybutadiene, in the presence of a transition metal salt catalyst, cobalt neodecanoate, was studied at 30oC. 1,4-Polybutadiene was subjected to several purification steps to remove oxidation antioxidants that are typically added during the industrial scale preparation of this polymer. The importance of the purification method and residual antioxidant on oxidation was determined. Oxygen uptake of 1,4-polybutadiene films was measured as a function of cobalt neodecanoate concentration. In these samples, oxygen mass uptake values as high as 15 weight percent were observed, and the oxidation process occurred over approximately one week. Oxygen mass uptake was measured in 1,4-polybutadiene films of different thicknesses undergoing cobalt-catalyzed oxidation in air at 30ºC. FTIR and XPS analysis suggest that the oxidation was heterogeneous, with the film surface being highly oxidized and the film center being less oxidized. Interestingly, the oxygen uptake exhibited a maximum with catalyst loading, which is believed to be related to the heterogeneous nature of the oxidation process. Films thicker than approximately 50 µm showed a decrease in oxygen uptake per unit polymer mass as film thickness increased, while oxygen uptake per unit film area remained independent of thickness, suggesting that oxidation was heterogeneous and proceeded essentially as an oxidized front penetrating into the film from the surfaces exposed to oxygen. In contrast, oxidation in thin films appears to proceed homogeneously, with oxygen uptake per unit mass being essentially independent of thickness. The dividing line between thick and thin films, the so-called critical thickness for oxidation, appears to be about 28 µm. In oxidized samples, oxygen and nitrogen permeability decreased by more than two orders of magnitude relative to permeability values in unoxidized samples. A two-phase model was used to describe the permeability data. Experiments were also conducted at different temperatures and oxygen partial pressures. Thick films oxidized at 45ºC showed heterogeneous oxidation similar to that reported above, while films oxidized at 5ºC showed a much longer oxidation time scale and higher oxygen mass uptake value. SEM images demonstrated that the structures of cross sections in films oxidized at different temperatures were also different; the oxidized layer structure was not observed in samples oxidized at 5ºC. Oxygen partial pressure experiments were conducted under the conditions that environmental oxygen content was less than 21%. It is observed that increasing oxygen partial pressure leads to faster oxidation kinetics and higher oxygen mass uptake in polybutadiene films. / text