Sedge meadow response to various experimental treatments

Plant density, species diversity, and the biomass of sedge meadow species were measured in mesocosms treated with one of two levels of four treatments in a randomized block experiment: stratified or not stratified seed, high or low groundwater level, high or low seeding density, and a complete set of all species or a split-set where non-aggressive species were seeded in the spring and aggressive species were seeded the following fall. The study was conducted at Iowa State University’s Hinds Research Farm in Ames, IA from 2013-2016. The high groundwater level had the greatest impact on increasing the plant density, diversity, and biomass of sedge meadow species. Stratifying seed also had a significant impact, but to a lesser extent. Seed density was found to have no effect on sedge meadow species response. The split-set of seeded species increased the plant density and biomass of many non-aggressive sedge species, but only a few grasses or forbs. The split-set also significantly reduced the number of aggressive species present at the end of three years. In a follow-up study from 2015-2016 at the same research site, plant density and species diversity of sedge meadow species were measured in mesocosms treated with varying fine-scale groundwater levels and seeding dates. The groundwater levels were 0, 5, 10, and 20 cm measured below soil surface. The seeding dates were June 16, June 30, and July 14, 2016. The plant density of forb species increased by 0.6 plants/ 0.4 m2 soil surface / cm decrease in groundwater level (p \u3c0.001). The seeding date of June 30 resulted in the highest average plant density of forbs at 6.9 per m2 soil surface (p \u3c0.05). S. tabernaemontani decreased at the rate of -0.1 plants/ 0.4 m2 soil surface/ cm decrease in groundwater level (p \u3c0.001). High numbers of S. tabernaemontani corresponded with decreased plant density of other species and decreased diversity

Closed-form expressions for the numerical dispersion and reflection in FEM simulations involving biaxial materials

Closed-form expressions for the numerical errors caused by finite-element discretization of problems involving materials of biaxial permittivity and permeability tensors are developed. In particular, we derive expressions for the numerical dispersion and reflection in both first-order node and edge basis function finite-element formulations in an equilateral triangular mesh. Results using these closed-form expressions are compared to practical numerical simulations. The application of these expressions to the analysis of the performance of the perfectly matched layer boundary is suggeste

Effect of physician reminders on preventive care: meta-analysis of randomized clinical trials

pre-printThe objective of this study was to assess the clinical value of the physician reminder, an information intervention, in increasing compliance for selected preventive health care measures. Meta-analysis was used to combine the quantitative evidence from randomized controlled clinical trials meeting the eligibility criteria. The trials included in this meta-analysis were conducted in a family or internal medicine clinic. Physician reminders were used in the trials to influence utilization and compliance of preventive health care activities. The use of physician reminders for preventive health care activities resulted in a homogeneous effect for the subcategories of cervical cancer screening (test for heterogeneity X22 = 4.122, non significant) and tetanus immunization (test for heterogeneity X22 = 3.139, non-significant). Similarly, the odds ratio from the combination of evidence from the three cervical cancer screening trials was significant (1.180, 95 percent CI: 1.020 to 1.339). The resulting odds ratio from the combination of evidence from the three tetanus immunization trials was significant (2.819, 95 percent CI: 2.664 to 2.975). The results of the meta-analyses for cervical cancer screening and tetanus immunizations indicate that physician reminders are an effective information intervention and can improve compliance for these two preventive health care procedures. Based on the results of this meta-analysis, further trials testing the effect of physician reminders on tetanus immunization would be unnecessary and probably unethical

Optical mode size control by MgO indiffusion in Ti:LiNbO3 waveguides

In this paper, the use of magnesium oxide (MgO) indiffusion in combination with Ti:LiNbO<sub>3</sub> through appropriate control of pre- and post-diffusion parameters is investigated as a way of controlling optical mode size. The co-diffusion of pre-patterned Ti with various patterned MgO films on LiNbO<sub>3</sub> has been compared experimentally. This method has been applied to study straight waveguides and couplers. The waveguides were optically characterized by near-field mode size and loss measurements methods at a wavelength of 1.55 μm. Reduction of inter-mode coupling between adjacent waveguides with the introduction of MgO has been observed

A novel wide-band tunable RF phase shifter using a variable optical directional coupler

We present a novel RF phase-shifter design with a usable bandwidth of 80:1. The design is verified through demonstration of a proof of concept device, consisting of a readily available voltage variable optical coupler fabricated from LiNbO3, combined with an fiber-optic delay line. The design is analyzed theoretically and measurement of the device confirms the predicted range of operation. Methods of extension of this range of operation are discusse

Systematic design approach for optimized resonantly enhanced Mach-Zehnder modulators

A systematic design approach using the developed numerical model for the investigation of any arbitrary electrooptic modulator configuration is described, and its application to the simulation and synthesis of resonantly enhanced Mach-Zehnder modulators (RE-MZMs) is demonstrated. The tool is implemented using equivalent circuit model using transmission lines, lumped elements, and N-port S-parameters. The numerical tool is used to simulate the modulation enhancement factor and radio frequency (RF) return loss of a number of theoretically and experimentally demonstrated examples. Finally, the design tool is used to synthesize a new optimized RE-MZM. This RE-MZM is fabricated and measured, and predicted results are compared

Using Infrared Spectroscopy and Ellipsometry to Study Fluorination and Ligand-Exchange Reactions During Etching of Oxides and Nitrides

Over the last 60 years, the etching of materials has become a necessity for advancements in integrated circuits. As critical dimensions decrease it has become important to control the thicknesses of various features to the nanometer scale. Atomic layer etching (ALE) is a technique that has gained significance over the last 15 years. Recently thermally based atomic layer etching systems have been developed for many materials relevant for semiconductor manufacturing.First, the fluorination reaction during the ALE of aluminum oxide with HF and BCl3 is studied. Spectroscopic ellipsometry showed that the etch rate of Al2O3 can be controlled by increasing the pressure of the HF exposure. X-ray photoelectron spectroscopy (XPS) was used to model the fluoride thickness during HF fluorination and found good agreement between the fluoride thickness and etch rate. Infrared spectroscopy was also used to monitor the conversation of aluminum oxide to aluminum fluoride. Etching of ALD grown AlN was done with sequential exposures of HF and BCl3. Infrared difference spectra argued for fluorination and ligand exchange reactions. Single-crystal AlN was etched by XeF2 and static exposures of BCl3 with an etch rate of 0.62 Å/cycle. XPS was used to monitor the Al 2p region as well as contaminants left from the etching process. Quadrupole mass spectrometry (QMS) was also used to study the volatile etch products. AlCl3 was seen with BClxFy compounds. The etching of Al2O3 was investigated with HF and BCl3. Linear etching of Al2O3 was observed using infrared spectroscopy. Initial exposures of BCl3 showed a conversion reaction from Al2O3 to B2O3 but further cycles showed fluorination and ligand-exchange reactions. QMS results showed the etch product AlCl3 when cycling HF and BCl3. Spontaneous etching of B2O3 and TiO2 are studied as well. Infrared spectroscopy was utilized to monitor the ALD growth of B2O3 with BCl3 and H2O. Spontaneous etching was seen with sequential HF exposures. IR spectra during B2O3 etching showed there was B-F on the surface. B2O3 was able to be spontaneously etched down to 40ºC. Theory predicted etching at all temperatures down to 110K. QMS studies observed BF3 as the main volatile etch product. TiO2 ALD was done with TiCl4 and H2O. Etching was seen at temperatures of 100ºC and greater. Surface Ti-F bonding was seen during the spontaneous etching. QMS showed TiF4 was the main product during etching