392 research outputs found
The Perception of Distance on a Real Geographic Slope
Ooi, Wu, and He (2001) have shown that for objects resting on flat, horizontal surfaces, those that appear in the lower sector of the visual field are perceived as close to the observer and objects located near the visual horizon are perceived as further from the observer. Researchers have hypothesized that observers utilize the angle subtended between the horizon and the line of sight to the target object as information for distance.In a previous investigation Hajnal, Bunch, and Kelty-Stephen (2014) showed that an object’s physical angle of declination below the horizon is not uniquely utilized when making distance estimates to objects placed on a sloped surface. In that experiment a flat, horizontal surface was visible in the background when viewing objects placed on the sloped surface. To further investigate the possible utility of the angular declination below the horizon hypothesis we have replicated the findings of the previous study on a natural hillside where a flat, horizontal surface is not visible in the background. This setup has allowed us to evaluate whether observers rely on the same information to perceive distance on ramps versus real hills. The present research may have implications for the hypothesis which claims that perceived effort influences space perception (Proffitt, 2006a, 2006b) in addition to optical variables
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Potential Design, Implementation, and Benefits of a Feebate Program for New Passenger Vehicles in California: Interim Statement of Research Findings
A comprehensive study was undertaken to assess the potential design, implementation, and benefits of a feebate program in California as well as possible stakeholder responses. A feebate is a market- based policy for encouraging greenhouse gas (GHG) emission reductions from new passenger vehicles by levying fees on relatively high-emitting vehicles and providing rebates to lower-emitting vehicles. This study finds that feebate policies can be used in California to achieve additional reductions in greenhouse gases from new passenger vehicles beyond those projected from emission standards alone. Specifically, feebate policies affect the average emissions levels for the new vehicle fleet sold in each model year. The amount will depend on the design features of the feebate policy and other modeling assumptions. For the period 2011-2025, a moderate feebate program based on a footprint system with average rebates of 700 yields a 3 percent improvement, or about 2 percent of the reductions needed to achieve the AB 32 target
Monolayer MoS2 strained to 1.3% with a microelectromechanical system
We report on a modified transfer technique for atomically thin materials integrated onto microelectromechanical
systems (MEMS) for studying strain physics and creating strain-based devices. Our method tolerates the non-planar
structures and fragility of MEMS, while still providing precise positioning and crack free transfer of flakes. Further,
our method used the transfer polymer to anchor the 2D crystal to the MEMS, which reduces the fabrication time,
increases the yield, and allowed us to exploit the strong mechanical coupling between 2D crystal and polymer to
strain the atomically thin system. We successfully strained single atomic layers of molybdenum disulfide (MoS2) with
MEMS devices for the first time and achieved greater than 1.3% strain, marking a major milestone for incorporating
2D materials with MEMS We used the established strain response of MoS2 Raman and Photoluminescence spectra to
deduce the strain in our crystals and provide a consistency check. We found good comparison between our experiment
and literature.Published versio
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Factors Affecting Demand for Plug-in Charging Infrastructure: An Analysis of Plug-in Electric Vehicle Commuters
The public sector and the private sector, which includes automakers and charging network companies, are increasingly investing in building charging infrastructure to encourage the adoption and use of plug-in electric vehicles (PEVs) and to ensure that current facilities are not congested. However, building infrastructure is costly and, as with road congestion, when there is significant uptake of PEVs, we may not be able to “build out of congestion.” We modelled the choice of charging location that more than 3000 PEV drivers make when given the options of home, work, and public locations. Our study focused on understanding the importance of factors driving demand such as: the cost of charging, driver characteristics, access to charging infrastructure, and vehicle characteristics. We found that differences in the cost of charging play an important role in the demand for charging location. PEV drivers tend to substitute workplace charging for home charging when they pay a higher electricity rate at home, more so when the former is free. Additionally, socio-demographic factors like dwelling type and gender, as well as vehicle technology factors like electric range, influence the choice of charging location
The inflationary prediction for primordial non-gaussianity
We extend the \delta N formalism so that it gives all of the stochastic
properties of the primordial curvature perturbation \zeta if the initial field
perturbations are gaussian. The calculation requires only the knowledge of some
family of unperturbed universes. A formula is given for the normalisation \fnl
of the bispectrum of \zeta, which is the main signal of non-gaussianity.
Examples of the use of the formula are given, and its relation to cosmological
perturbation theory is explained.Comment: Revtex Latex file. 4 pages, no figures. v4: minor changes, typos
corrected, references added and updated. Version published in Physical Review
Letter
Adhesion, Stiffness and Instability in Atomically Thin MoS2 Bubbles
We measured the work of separation of single and few-layer MoS2 membranes
from a SiOx substrate using a mechanical blister test, and found a value of 220
+- 35 mJ/m^2. Our measurements were also used to determine the 2D Young's
modulus of a single MoS2 layer to be 160 +- 40 N/m. We then studied the
delamination mechanics of pressurized MoS2 bubles, demonstrating both stable
and unstable transitions between the bubbles' laminated and delaminated states
as the bubbles were inflated. When they were deflated, we observed edge pinning
and a snap-in transition which are not accounted for by the previously reported
models. We attribute this result to adhesion hysteresis and use our results to
estimate the work of adhesion of our membranes to be 42 +- 20 mJ/m^2
Adhesion of 2D MoS to Graphite and Metal Substrates Measured by a Blister Test
Using a blister test, we measured the work of separation between MoS
membranes from metal, semiconductor, and graphite substrates. We found a work
of separation ranging from 0.11 +- 0.05 J/m^2 for chromium to 0.39 +- 0.1 J/m^2
for graphite substrates. In addition, we measured the work of adhesion of
MoS membranes over these substrates and observed a dramatic difference
between the work of separation and adhesion which we attribute to adhesion
hysteresis. Due to the prominent role that adhesive forces play in the
fabrication and functionality of devices made from 2D materials, an
experimental determination of the work of separation and adhesion as provided
here will help guide their development
Voltage gated inter-cation selective ion channels from graphene nanopores
With the ability to selectively control ionic flux, biological protein ion
channels perform a fundamental role in many physiological processes. For
practical applications that require the functionality of a biological ion
channel, graphene provides a promising solid-state alternative, due to its
atomic thinness and mechanical strength. Here, we demonstrate that nanopores
introduced into graphene membranes, as large as 50 nm in diameter, exhibit
inter-cation selectivity with a ~20x preference for K+ over divalent cations
and can be modulated by an applied gate voltage. Liquid atomic force microscopy
of the graphene devices reveals surface nanobubbles near the pore to be
responsible for the observed selective behavior. Molecular dynamics simulations
indicate that translocation of ions across the pore likely occurs via a thin
water layer at the edge of the pore and the nanobubble. Our results demonstrate
a significant improvement in the inter-cation selectivity displayed by a
solid-state nanopore device and by utilizing the pores in a de-wetted state,
offers an approach to fabricating selective graphene membranes that does not
rely on the fabrication of sub-nm pores
Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2
We demonstrate the continuous and reversible tuning of the optical band gap
of suspended monolayer MoS2 membranes by as much as 500 meV by applying very
large biaxial strains. By using chemical vapor deposition (CVD) to grow
crystals that are highly impermeable to gas, we are able to apply a pressure
difference across suspended membranes to induce biaxial strains. We observe the
effect of strain on the energy and intensity of the peaks in the
photoluminescence (PL) spectrum, and find a linear tuning rate of the optical
band gap of 99 meV/%. This method is then used to study the PL spectra of
bilayer and trilayer devices under strain, and to find the shift rates and
Gr\"uneisen parameters of two Raman modes in monolayer MoS2. Finally, we use
this result to show that we can apply biaxial strains as large as 5.6% across
micron sized areas, and report evidence for the strain tuning of higher level
optical transitions.Comment: Nano Lett., Article ASA
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