19,667 research outputs found
Pressure Dependence of Wall Relaxation in Polarized He Gaseous Cells
We have observed a linear pressure dependence of longitudinal relaxation time
() at 4.2 K and 295 K in gaseous He cells made of either bare pyrex
glass or Cs/Rb-coated pyrex due to paramagnetic sites in the cell wall. The
paramagnetic wall relaxation is previously thought to be independent of He
pressure. We develop a model to interpret the observed wall relaxation by
taking into account the diffusion process, and our model gives a good
description of the data
Topological energy gaps in the [111]-oriented InAs/GaSb and GaSb/InAs core-shell nanowires
The [111]-oriented InAs/GaSb and GaSb/InAs core-shell nanowires have been
studied by the Luttinger-Kohn Hamiltonian to
search for non-vanishing fundamental gaps between inverted electron and hole
bands. We focus on the variations of the topologically nontrivial fundamental
gap, the hybridization gap, and the effective gap with the core radius and
shell thickness of the nanowires. The evolutions of all the energy gaps with
the structural parameters are shown to be dominantly governed by quantum size
effects. With a fixed core radius, a topologically nontrivial fundamental gap
exists only at intermediate shell thicknesses. The maximum gap is
meV for GaSb/InAs and meV for InAs/GaSb core-shell nanowires, and
for the GaSb/InAs core-shell nanowires the gap persists over a wider range of
geometrical parameters. The intrinsic reason for these differences between the
two types of nanowires is that in the shell the electron-like states of InAs is
more delocalized than the hole-like state of GaSb, while in the core the
hole-like state of GaSb is more delocalized than the electron-like state of
InAs, and both features favor stronger electron-hole hybridization. Since
similar features of the electron- and hole-like states have been found in
nanowires of other materials, it could serve as a common rule to put the
hole-like state in the core while the electron-like state in the shell of a
core-shell nanowire to achieve better topological properties.Comment: 10 pages, 10 figure
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A review of net zero energy buildings in hot and humid climates: Experience learned from 34 case study buildings
Sustainable development in the building sector requires the integration of energy efficiency and renewable energy utilization in buildings. In recent years, the concept of net zero energy buildings (NZEBs) has become a potential plausible solution to improve efficiency and reduce energy consumption in buildings. To achieve an NZEB goal, building systems and design strategies must be integrated and optimized based on local climatic conditions. This paper provides a comprehensive review of NZEBs and their current development in hot and humid regions. Through investigating 34 NZEB cases around the world, this study summarized NZEB key design strategies, technology choices and energy performance. The study found that passive design and technologies such as daylighting and natural ventilation are often adopted for NZEBs in hot and humid climates, together with other energy efficient and renewable energy technologies. Most NZEB cases demonstrated site annual energy consumption intensity less than 100 kW-hours (kWh) per square meter of floor space, and some buildings even achieved “net-positive energy” (that is, they generate more energy locally than they consume). However, the analysis also shows that not all NZEBs are energy efficient buildings, and buildings with ample renewable energy adoption can still achieve NZEB status even with high energy use intensity. This paper provides in-depth case-study-driven analysis to evaluate NZEB energy performance and summarize best practices for high performance NZEBs. This review provides critical technical information as well as policy recommendations for net zero energy building development in hot and humid climates
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