Assessing the Performance of the Diffusion Monte Carlo Method as Applied to the Water Monomer, Dimer, and Hexamer

The Diffusion Monte Carlo (DMC) method is applied to the water monomer, dimer, and hexamer, using q-TIP4P/F, one of the most simple, empirical water models with flexible monomers. The bias in the time step ($\Delta\tau$) and population size ($N_w$) is investigated. For the binding energies, the bias in $\Delta\tau$ cancels nearly completely, while a noticeable bias in $N_w$ still remains. However, for the isotope shift, (e.g, in the dimer binding energies between (H$_2$O)$_2$ and (D$_2$O)$_2$) the systematic errors in $N_w$ do cancel. Consequently, very accurate results for the latter (within $\sim 0.01$ kcal/mol) are obtained with relatively moderate numerical effort ($N_w\sim 10^3$). For the water hexamer and its (D$_2$O)$_6$ isotopomer the DMC results as a function of $N_w$ are examined for the cage and prism isomers. For a given isomer, the issue of the walker population leaking out of the corresponding basin of attraction is addressed by using appropriate geometric constraints. The population size bias for the hexamer is more severe, and in order to maintain accuracy similar to that of the dimer, the population size $N_w$ must be increased by about two orders of magnitude. Fortunately, when the energy difference between cage and prism is taken, the biases cancel, thereby reducing the systematic errors to within $\sim 0.01$ kcal/mol when using a population of $N_w=4.8\times 10^5$ walkers. Consequently, a very accurate result for the isotope shift is also obtained. Notably, both the quantum and the isotope effects for the prism-cage energy difference are small.Comment: 11 pages, 5 figures, 36 references. Submitted to the Journal of Physical Chemistr

Boston Hospitality Review: Spring 2018

Table of contents: Sustainability In Hospitality? How Legality and Authenticity Impact the Rationale for Integrating Sustainable Practices By Christian E. Hardigree, J.D. -- The Digital Future of the Tourism & Hospitality Industry By Martin Zsarnoczky -- Cutting Through the Online Hospitality Clutter, Part II: Best Practices for Paid Digital Marketing By Leora Lanz and Namrata Sridhar -- Blending Theory and Practice: Experiential Learning in Hospitality Curriculum: A Case Study of Student Projects for Industry Clients By Michael Oshins and Joel Brown

Endangered Species Responses to Natural Habitat Declines: Nebraska’s Interior Least Terns (\u3ci\u3eSternula antillarum athalassos\u3c/i\u3e) and Piping Plovers (\u3ci\u3eCharadrius melodus\u3c/i\u3e) Nesting in a Human-Created Habitat

Formerly, state and federally endangered Interior Least Terns (Sternula antillarum athalassos) and state and federally threatened Piping Plovers (Charadrius melodus) nested on sandbars in rivers as well as on other sandy beach habitat (Hardy 1957; Haig 1992; Kirsch 1992; Ziewitz et al. 1992; Thompson et al. 1997). In Nebraska, the birds primarily used sandbars in the Platte, Loup, Elkhorn, Niobrara, and Missouri rivers (Sharpe et al. 2001). These sandbars were created and maintained by river flow and regular flooding events. Despite the frequent scouring, reshaping, and relocation of the sandbars, nesting habitat was consistently available to the birds in these river systems. With recent human-caused modifications to annual river flow, river bed and bank structure, and emergent vegetation, the number of river sandbars that are suitable for nesting has been greatly reduced (Haig 1992; Ziewitz et al. 1992; Wilson et al. 1993; Thompson et al. 1997; NRC 2005). In recent decades, Least Terns and Piping Plovers have used human-created habitats for nesting, although they still use river sandbars when they are available (Haig 1992; Thompson et al. 1997). During the last several decades, the birds have nested on human-created sites such as sand spill piles at sand and gravel mines, fly-ash piles at electrical power-generating plants, gravel and tar rooftops, and lakeshore-sandy beach housing developments (Ducey 1982; Haig 1992; Kirsch 1992; Ziewitz et al. 1992; Wilson et al.1993; Thompson et al. 1997; Forys and Borboen-Abrams 2006). In eastern Nebraska, economic growth near human population centers has increased the attractiveness of lakeshore housing developments to investors. In the past, retired sand and gravel mines were converted into lakeshore housing developments. Recently, however, developers have bypassed the mine stage and are excavating the lakes directly for housing developments. As terns and plovers use human-created and human-dominated habitats with increasing frequency, the importance of these areas to conservation and management becomes more critical. Threats to nests, chicks, and adults may be quite different at these sites than at river nesting sites or sand and gravel mines because of different human uses. Reliable nesting data are essential for the development of effective protocols to secure and recover the populations of these two protected species. Here we report the results of one nesting season at a human-created site along the lower Platte River

The Effect of Environment on the X-Ray Emission from Early-Type Galaxies

In order to help understand the phenomena of X-ray emission from early-type galaxies, we obtained an optically flux-limited sample of 34 early-type galaxies, observed with ROSAT. A previous analysis of this sample suggested that the most X-ray luminous galaxies were in rich environments. Here we investigate environmental influences quantitatively, and find a positive correlation between L_B/L_X and the local galaxy density. We suggest that this correlation occurs because the X-ray luminosity is enhanced either through accretion of the intergalactic gas or because the ambient medium stifles galactic winds. When the ambient medium is unimportant, partial or global galactic winds can occur, reducing L_B/L_X. These effects lead to the large observed dispersion in L_X at fixed L_B. We argue that the transition from global winds to partial winds is one of the principle reasons for the steep relationship between L_X and L_B. We discuss details of the data reduction not previously presented, and examine the dependence of L_X on the choice of outer source radius and background location. Effects of Malmquist bias are shown not to be important for the issues addressed. Finally, we compare the temperature deduced for these galaxies from different analyses of ROSAT and ASCA data.Comment: 29 pages, including 6 figures (ps); AASTeX 12pt,aaspp4 format; submitted to Ap

Endangered Species Responses to Natural Habitat Declines: Nebraska’s Interior Least Terns (\u3ci\u3eSternula antillarum athalassos\u3c/i\u3e) and Piping Plovers (\u3ci\u3eCharadrius melodus\u3c/i\u3e) Nesting in a Human-Created Habitat

Formerly, state and federally endangered Interior Least Terns (Sternula antillarum athalassos) and state and federally threatened Piping Plovers (Charadrius melodus) nested on sandbars in rivers as well as on other sandy beach habitat (Hardy 1957; Haig 1992; Kirsch 1992; Ziewitz et al. 1992; Thompson et al. 1997). In Nebraska, the birds primarily used sandbars in the Platte, Loup, Elkhorn, Niobrara, and Missouri rivers (Sharpe et al. 2001). These sandbars were created and maintained by river flow and regular flooding events. Despite the frequent scouring, reshaping, and relocation of the sandbars, nesting habitat was consistently available to the birds in these river systems. With recent human-caused modifications to annual river flow, river bed and bank structure, and emergent vegetation, the number of river sandbars that are suitable for nesting has been greatly reduced (Haig 1992; Ziewitz et al. 1992; Wilson et al. 1993; Thompson et al. 1997; NRC 2005). In recent decades, Least Terns and Piping Plovers have used human-created habitats for nesting, although they still use river sandbars when they are available (Haig 1992; Thompson et al. 1997). During the last several decades, the birds have nested on human-created sites such as sand spill piles at sand and gravel mines, fly-ash piles at electrical power-generating plants, gravel and tar rooftops, and lakeshore-sandy beach housing developments (Ducey 1982; Haig 1992; Kirsch 1992; Ziewitz et al. 1992; Wilson et al.1993; Thompson et al. 1997; Forys and Borboen-Abrams 2006). In eastern Nebraska, economic growth near human population centers has increased the attractiveness of lakeshore housing developments to investors. In the past, retired sand and gravel mines were converted into lakeshore housing developments. Recently, however, developers have bypassed the mine stage and are excavating the lakes directly for housing developments. As terns and plovers use human-created and human-dominated habitats with increasing frequency, the importance of these areas to conservation and management becomes more critical. Threats to nests, chicks, and adults may be quite different at these sites than at river nesting sites or sand and gravel mines because of different human uses. Reliable nesting data are essential for the development of effective protocols to secure and recover the populations of these two protected species. Here we report the results of one nesting season at a human-created site along the lower Platte River

Glaucoma surgery calculator: limited additive IOP effect of phacoemulsification on Ab Interno Trabeculectomy

Purpose: To compare reduction of intraocular pressure (IOP) after Trabectome in pseudophakic patients and Trabectome combined with phacoemulsification (Trabectome-phaco) in phakic patients. Methods: Cases were excluded if patients were followed for less than 12 months, diagnosed with neovascular glaucoma, or required additional glaucoma surgery within 12 months after Trabectome or Trabectome-phaco. Missing data such as type of glaucoma, gender, or age was imputed by generating 5 similar but non-identical datasets. Groups were matched using Coarsened Exact Matching based on age, gender, type of glaucoma, race, preoperative number of glaucoma medications and baseline IOP. Linear regression was used to examine IOP reduction after surgery. Results: A total of 612 cases were included in the study with 248 Trabectome cases and 364 Trabectome-phaco cases. Baseline IOP was found to be statistically significant. An average of 0.73±0.03 mmHg IOP reduction is associated with an increment of 1 mmHg in baseline IOP. Type of surgery was not statistically significant after adjusting for baseline IOP, age, baseline number of glaucoma medications and type of glaucoma. Conclusion: Patients with higher baseline IOP are expected to have a greater IOP reduction