7,346 research outputs found
Polyimide processing additives
A process for preparing polyimides having enhanced melt flow properties is described. The process consists of heating a mixture of a high molecular weight poly-(amic acid) or polyimide with a low molecular weight amic acid or imide additive in the range of 0.05 to 15 percent by weight of additive. The polyimide powders so obtained show improved processability, as evidenced by lower melt viscosity by capillary rheometry. Likewise, films prepared from mixtures of polymers with additives show improved processability with earlier onset of stretching by TMA
Measuring Transport Resilience: A Manawatu-Wanganui Region Case Study
The resilience of transport networks is attracting greater scrutiny at the international,
national and sub-national levels. This research report explores the current state of
knowledge about measuring transport resilience and presents a case study to address the
question is: How resilient is the road and rail infrastructure in the Manawatu-Wanganui
Region? This region in New Zealand’s lower North Island provides an interesting case
study due to its strategic location in the North Island’s and indeed New Zealand’s
transport network. In addition, it has experienced significant disruptions in the recent
past, most notably widespread failures caused by flooding in 2004, and the lengthy
closure of a significant inter-regional road connection, the Manawatu Gorge State
Highway 3 road, due to a landslide in 2011-2012. It also provides an opportunity to
explore this topic outside of a major metropolitan region. The region’s transport networks
and infrastructure also have important social and economic functions.
This research report is structured around a proposed Transport Resilience Indicator
Framework (RIF) which explores six key dimensions of transport infrastructure resilience:
engineering, services, ecological, social, economic and institutional. This holistic approach
to measuring transport resilience and is envisaged to accommodate both qualitative and
quantitative indicators. Within this framework, data were gathered via analysis of
secondary sources and nine key informant interviews. The interview participants were
from public sector agencies responsible for managing aspects of the region’s transport
network, the private sector and one social service provider. The participants had
considerable knowledge relating to the planning of the road network and/or its economic
and social significance. They also had knowledge of the impacts and/or management of
recent disruptions.
The institutions responsible for managing the region’s transport network can identify
vulnerabilities in the network, but can also collaborate and learn from past disruptions.
Concerns were expressed about the level of funding for maintaining and upgrading the
region’s transport networks, particularly for territorial authorities with large networks and
small rates bases. The region is strongly dependent on the roading network, with limited
alternatives during roading network disruptions. It proved difficult to quantify the
environmental impacts of transport disruptions. A case study of the response of a local
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health shuttle service provided an example of how a community, by drawing on social
capital, was able to adapt and respond appropriately to a transport disruption.
One key area identified for further research is assessing the capacity of private
contractors to respond to natural hazard events of varying magnitudes. The RIF could
also be strengthened by the use of indicators based on quantitative data, in addition to
qualitative data. It is suggested that one method of achieving this could this could be to
adopt a multi-disciplinary approach, drawing on expertise, methods and perspectives
from related professions, such as engineering and economics. [Executive summary
Yes, You Can Control Crabgrass!
A combination of cultural and chemical control practices works best in getting rid of this pest. Two new chemicals, in particular, show promise in preventing crabgrass seed germination and seedling establishment
Contact Atomic Structure and Electron Transport Through Molecules
Using benzene sandwiched between two Au leads as a model system, we
investigate from first principles the change in molecular conductance caused by
different atomic structures around the metal-molecule contact. Our motivation
is the variable situations that may arise in break junction experiments; our
approach is a combined density functional theory and Green function technique.
We focus on effects caused by (1) the presence of an additional Au atom at the
contact and (2) possible changes in the molecule-lead separation. The effects
of contact atomic relaxation and two different lead orientations are fully
considered. We find that the presence of an additional Au atom at each of the
two contacts will increase the equilibrium conductance by up to two orders of
magnitude regardless of either the lead orientation or different group-VI
anchoring atoms. This is due to a LUMO-like resonance peak near the Fermi
energy. In the non-equilibrium properties, the resonance peak manifests itself
in a large negative differential conductance. We find that the dependence of
the equilibrium conductance on the molecule-lead separation can be quite
subtle: either very weak or very strong depending on the separation regime.Comment: 8 pages, 6 figure
Interaction-Induced Strong Localization in Quantum Dots
We argue that Coulomb blockade phenomena are a useful probe of the cross-over
to strong correlation in quantum dots. Through calculations at low density
using variational and diffusion quantum Monte Carlo (up to r_s ~ 55), we find
that the addition energy shows a clear progression from features associated
with shell structure to those caused by commensurability of a Wigner crystal.
This cross-over (which occurs near r_s ~ 20 for spin-polarized electrons) is,
then, a signature of interaction-driven localization. As the addition energy is
directly measurable in Coulomb blockade conductance experiments, this provides
a direct probe of localization in the low density electron gas.Comment: 4 pages, published version, revised discussio
Context-awareness for mobile sensing: a survey and future directions
The evolution of smartphones together with increasing computational power have empowered developers to create innovative context-aware applications for recognizing user related social and cognitive activities in any situation and at any location. The existence and awareness of the context provides the capability of being conscious of physical environments or situations around mobile device users. This allows network services to respond proactively and intelligently based on such awareness. The key idea behind context-aware applications is to encourage users to collect, analyze and share local sensory knowledge in the purpose for a large scale community use by creating a smart network. The desired network is capable of making autonomous logical decisions to actuate environmental objects, and also assist individuals. However, many open challenges remain, which are mostly arisen due to the middleware services provided in mobile devices have limited resources in terms of power, memory and bandwidth. Thus, it becomes critically important to study how the drawbacks can be elaborated and resolved, and at the same time better understand the opportunities for the research community to contribute to the context-awareness. To this end, this paper surveys the literature over the period of 1991-2014 from the emerging concepts to applications of context-awareness in mobile platforms by providing up-to-date research and future research directions. Moreover, it points out the challenges faced in this regard and enlighten them by proposing possible solutions
On the Distribution of a Second Class Particle in the Asymmetric Simple Exclusion Process
We give an exact expression for the distribution of the position X(t) of a
single second class particle in the asymmetric simple exclusion process (ASEP)
where initially the second class particle is located at the origin and the
first class particles occupy the sites {1,2,...}
Enhancing the Mass Sensitivity of Graphene Nanoresonators Via Nonlinear Oscillations: The Effective Strain Mechanism
We perform classical molecular dynamics simulations to investigate the
enhancement of the mass sensitivity and resonant frequency of graphene
nanomechanical resonators that is achieved by driving them into the nonlinear
oscillation regime. The mass sensitivity as measured by the resonant frequency
shift is found to triple if the actuation energy is about 2.5 times the initial
kinetic energy of the nanoresonator. The mechanism underlying the enhanced mass
sensitivity is found to be the effective strain that is induced in the
nanoresonator due to the nonlinear oscillations, where we obtain an analytic
relationship between the induced effective strain and the actuation energy that
is applied to the graphene nanoresonator. An important implication of this work
is that there is no need for experimentalists to apply tensile strain to the
resonators before actuation in order to enhance the mass sensitivity. Instead,
enhanced mass sensitivity can be obtained by the far simpler technique of
actuating nonlinear oscillations of an existing graphene nanoresonator.Comment: published versio
Search for Mars lander/rover/sample-return sites: A status review
Ten Mars sites were studied in the USA for four years. The sites are the Chasma Boreale (North Pole), Planum Australe (South Pole), Olympus Rupes, Mangala Valles, Memnonia Sulci, Candor Chasma, Kasel Valles, Nilosyrtis Mensae, Elysium Montes, and Apollinaris Patera. Seven sites are being studied by the USSR; their prime sites are located at the east mouth of Kasel Valles and near Uranius Patera. Thirteen geological maps of the first six USA sites are compiled and in review. Maps of the Mangala East and West sites at 1:1/2 million scale and a 1:2 million scale map show evidence of three episodes of small-channel formation interspersed with episodes of volcanism and tectonism that span the period from 3.5 to 0.6 b.y. ago. The tectonic and geological history of Mars, both ancient and modern, can be elucidated by sampling volcanic and fluvial geologic units at equatorial sites and layered deposits at polar sites. The evidence appears clear for multiple episodes of fluvial channeling, including some that are quite recent; this evidence contrasts with the theses of Baker and Partridge (1986) and many others that all channels are ancient. Verification of this hypothesis by Mars Observer will be an important step forward in the perception of the history of Mars
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