The influence of the extent of excluded volume interactions on the linear viscoelastic properties of dilute polymer solutions

The Rouse model has recently been modified to take into account the excluded volume interactions that exist between various parts of a polymer chain by incorporating a narrow Gaussian repulsive potential between pairs of beads on the Rouse chain (cond-mat/0002448). The narrow Gaussian potential is characterized by two parameters: z* - which accounts for the strength of the interaction, and d* - which accounts for the extent of the interaction. In the limit of d* going to zero, the narrow Gaussian potential tends to the more commonly used delta-function repulsive potential. The influence of the parameter d*, in the limit of infinite chain length, on equilibrium and linear viscoelastic properties, and on universal ratios involving these properties, is examined here. A renormalization group calculation of the end-to-end vector suggests that the value chosen for the variable d* will not affect critical exponents, or universal ratios. A similar trend is also observed for results obtained with an approximate solution, which is based on the assumption that the non-equilibrium configurational distribution function is Gaussian.Comment: 23 pages, 6 figures, LaTe

Post-Earthquake Home Reconstruction in the Surrounding Hills of Kathmandu Valley, Nepal, PRP 200

In April of 2015, a 7.6 magnitude earthquake struck the Kathmandu Valley at the center of Nepal. Within the following year, Kathmandu was struck by a 7.3 magnitude earthquake and multiple aftershocks. The initial earthquake caused the deaths of 8,856 people, injured 22,309, and affected eight million more. Many agencies around the world came together to fund reconstruction efforts as part of a Nepal and a Multi-Donor Trust Fund (MDTF). The MDTF conducted an Earthquake Housing Damage and Characteristics Survey (EHDC) which led to the creation of Nepal Rural Housing Reconstruction Program (NRHRP), which sought to reconstruct earthquake-resistant homes. The NRHRP developed a homeowner-driven grant process and established the National Reconstruction Authority (NRA) to distribute housing reconstruction grants to families. Those grants were to be paid out via three tranches, each after the completion of a specific construction phase. During 2017, an international collaborative effort began among four parties: Hiroshima University (HU); Tribhuvan University (TU); Nepal’s Alternative Energy Promotion Center (AEPC); and the Lyndon B. Johnson School of Public Affairs (LBJ) of the University of Texas at Austin (UT). The team investigated the challenges and opportunities for reconstruction of homes in rural areas damaged by the 2015 earthquake in and around the hinterland of Kathmandu Valley, Nepal. Within the context of a university course, students began by studying alternative building technologies (ABTs) being implemented in Nepal by local nongovernmental organizations (NGOs). When project members visited Nepal in March 2017, they interviewed rural residents to identify barriers to home reconstruction. During a field study, the students also met with local governmental officials and NGO representatives. This report describes students’ field investigation in Nepal, background research on alternative building technologies (ABTs) for home reconstruction, and recommendations developed from consultation with stakeholders and technical advisors. The first chapter starts with the earthquake and its associated damage and describes the response of the Government of Nepal (GON) and the international community in forming the MDTF, the NRHRP, and the NRA. The second chapter discusses different alternative building technologies (ABTs) considered by the GON, including bamboo, hempcrete, rammed earth, Compressed Stabilized Earth Brick (CSEB), earthbags, and modified conventional housing. Each section describes the type of building style, its construction, materials and labor required, estimates of construction time (if available), costs, and a brief section on comparative advantages and disadvantages. The third chapter describes the 2017 field study in Nepal, included the locations of the field study and interviews and discussions with local NGOs, the governmental agencies, and local residents. The research group sought to learn whether a lack of affordable and appropriate building methods could explain why many villagers still live in temporary shelters. Village residents discussed barriers to housing reconstruction unrelated to the type of home being built. The final chapter presents conclusions from 2017 field study observations of the three villages. Researchers found four common barriers to reconstruction: the cost of transportation and materials; insufficient reconstruction incentives; grant processes with many procedural barriers to funding; and the need for consistent interaction of the community with governmental agencies. One suggestion is to evaluate the home reconstruction program to assess its procedures and outcomes. A second suggestion is for Nepal to enhance the number and authority of mobile teams of professionals to assist villagers seeking to reconstruct homes.Public Affair

Spontaneous Recovery of Superhydrophobicity on Nanotextured Surfaces

Rough or textured hydrophobic surfaces are dubbed superhydrophobic due to their numerous desirable properties, such as water repellency and interfacial slip. Superhydrophobicity stems from an aversion for water to wet the surface texture, so that a water droplet in the superhydrophobic "Cassie state", contacts only the tips of the rough hydrophobic surface. However, superhydrophobicity is remarkably fragile, and can break down due to the wetting of the surface texture to yield the "Wenzel state" under various conditions, such as elevated pressures or droplet impact. Moreover, due to large energetic barriers that impede the reverse (dewetting) transition, this breakdown in superhydrophobicity is widely believed to be irreversible. Using molecular simulations in conjunction with enhanced sampling techniques, here we show that on surfaces with nanoscale texture, water density fluctuations can lead to a reduction in the free energetic barriers to dewetting by circumventing the classical dewetting pathways. In particular, the fluctuation-mediated dewetting pathway involves a number of transitions between distinct dewetted morphologies, with each transition lowering the resistance to dewetting. Importantly, an understanding of the mechanistic pathways to dewetting and their dependence on pressure, allows us to augment the surface texture design, so that the barriers to dewetting are eliminated altogether and the Wenzel state becomes unstable at ambient conditions. Such robust surfaces, which defy classical expectations and can spontaneously recover their superhydrophobicity, could have widespread importance, from underwater operation to phase change heat transfer applications

Kaon Condensation in Neutron Star Matter with Hyperons

Based on the Kaplan-Nelson Lagrangian, we investigate kaon condensation in dense neutron star matter allowing for the explicit presence of hyperons. Using various models we find that the condensate threshold is sensitive to the behavior of the scalar density; the more rapidly it increases with baryon density, the lower is the threshold for condensation. The presence of hyperons, particularly the $\Sigma^-$, shifts the threshold for $K^-$ condensation to a higher density. In the mean field approach, with hyperons, the condensate amplitude grows sufficiently rapidly that the nucleon effective mass vanishes at a finite density and a satisfactory treatment of the thermodynamics cannot be achieved. Thus, calculations of kaon-baryon interactions beyond the mean field level appear to be necessary.Comment: 13 pages, latex, 3 figures by fax/mail from [email protected]