34,847 research outputs found
Dynamic response of phenolic resin and its carbon-nanotube composites to shock wave loading
We investigate with nonreactive molecular dynamics simulations the dynamic response of phenolic resin and its carbon-nanotube (CNT) composites to shock wave compression. For phenolic resin, our simulations yield shock states in agreement with experiments on similar polymers except the
āphase changeā observed in experiments, indicating that such phase change is chemical in nature. The elasticāplastic transition is characterized by shear stress relaxation and atomic-level slip, and phenolic resin shows strong strain hardening. Shock loading of the CNT-resin composites is applied parallel or perpendicular to the CNT axis, and the composites demonstrate anisotropy in wave
propagation, yield and CNT deformation. The CNTs induce stress concentrations in the composites and may increase the yield strength. Our simulations suggest that the bulk shock response of the composites depends on the volume fraction, length ratio, impact cross-section, and geometry of the CNT components; the short CNTs in current simulations have insignificant effect on the bulk
response of resin polymer
Transition Density and Pressure at the Inner Edge of Neutron Star Crusts
Using the nuclear symmetry energy that has been recently constrained by the
isospin diffusion data in intermediate-energy heavy ion collisions, we have
studied the transition density and pressure at the inner edge of neutron star
crusts, and they are found to be 0.040 fm
fm and 0.01 MeV/fm MeV/fm,
respectively, in both the dynamical and thermodynamical approaches. We have
also found that the widely used parabolic approximation to the equation of
state of asymmetric nuclear matter gives significantly higher values of
core-crust transition density and pressure, especially for stiff symmetry
energies. With these newly determined transition density and pressure, we have
obtained an improved relation between the mass and radius of neutron stars.Comment: 7 pages, 3 figures, proceeding of "The International Workshop on
Nuclear Dynamics in Heavy-Ion Reactions and the Symmetry Energy (IWND2009)
Effect of Intermittent Pneumatic Foot Compression on Popliteal Artery Haemodynamics
AbstractPurpose: the aim was to investigate the effect of intermittent pneumatic foot compression (IPCfoot) on popliteal artery haemodynamics in normal individuals and in patients with intermittent claudication due to peripheral vascular disease (PVD) (Fontaine stage II). Material and methods: popliteal artery volume flow [vFl], pulsatility index [PI], mean velocity [mV], peak systolic [PSV] and end diastolic velocity [EDV], in 25 limbs of 20 normal subjects and 40 limbs of 32 stable claudicants were obtained in the sitting position before, during and within 30 seconds after the application of IPCfoot(applied pressure: 120 mmHg; inflation time: 3 seconds; deflation time: 17 seconds) using colour-flow duplex imaging (CFDI). The reproducibility of flow velocity estimations using CFDI in the horizontal [hor] (recovery) and sitting [sit] positions was evaluated in 20 limbs of normal controls and 20 limbs of claudicants. Results: popliteal artery vFl, mV, PSV and PI measurements were performed with a coefficient of variation (CV) of less than 14.6% among claudicants and of less than 13.3% in normal subjects. EDV is the least reproducible parameter with an overall CV range of 10.2ā21.5% in normal controls and 9.1ā18.6% in arteriopaths. On application of IPCfootpopliteal artery vFl increased by 111% in the control group (p<0.001) and by 51% in the claudicants (p<0.001). Within 30 seconds of the cessation of pump action flow decreased significantly in both groups (p<0.001), but maintained a significantly higher level than that at baseline (p<0.001, in both groups). The mV, PSV and EDV showed a similar pattern of significant changes. Both in normals and claudicants, the PI decreased with IPCfoot(p<0.001) and increased post-compression; however, it was significantly lower than baseline (p<0.005) within 30 seconds of impulse delivery. Conclusions: current CFDI technology enables a reproducible estimation of popliteal artery flow velocities. IPCfootcan significantly augment arterial calf inflow on an acute basis both in normals and claudicants. The increase of EDV and decrease of PI indicate that attenuation of peripheral resistance to flow is the main mechanism underlying the popliteal artery vFl enhancement on application of IPCfoot. Prospective trials on the long-term effect of IPCfootin the management of patients with PVD are indicated from the results of this study
Extracting non-linear integrate-and-fire models from experimental data using dynamic IāV curves
The dynamic IāV curve method was recently introduced for the efficient experimental generation of reduced neuron models. The method extracts the response properties of a neuron while it is subject to a naturalistic stimulus that mimics in vivo-like fluctuating synaptic drive. The resulting history-dependent, transmembrane current is then projected onto a one-dimensional currentāvoltage relation that provides the basis for a tractable non-linear integrate-and-fire model. An attractive feature of the method is that it can be used in spike-triggered mode to quantify the distinct patterns of post-spike refractoriness seen in different classes of cortical neuron. The method is first illustrated using a conductance-based model and is then applied experimentally to generate reduced models of cortical layer-5 pyramidal cells and interneurons, in injected-current and injected- conductance protocols. The resulting low-dimensional neuron modelsāof the refractory exponential integrate-and-fire typeāprovide highly accurate predictions for spike-times. The method therefore provides a useful tool for the construction of tractable models and rapid experimental classification of cortical neurons
Optimal interdiction of urban criminals with the aid of real-time information
Most violent crimes happen in urban and suburban cities. With emerging tracking techniques, law enforcement officers can have real-time location information of the escaping criminals and dynamically adjust the security resource allocation to interdict them. Unfortunately, existing work on urban network security games largely ignores such information. This paper addresses this omission. First, we show that ignoring the real-time information can cause an arbitrarily large loss of efficiency. To mitigate this loss, we propose a novel NEtwork purSuiT game (NEST) model that captures the interaction between an escaping adversary and a defender with multiple resources and real-time information available. Second, solving NEST is proven to be NP-hard. Third, after transforming the non-convex program of solving NEST to a linear program, we propose our incremental strategy generation algorithm, including: (i) novel pruning techniques in our best response oracle; and (ii) novel techniques for mapping strategies between subgames and adding multiple best response strategies at one iteration to solve extremely large problems. Finally, extensive experiments show the effectiveness of our approach, which scales up to realistic problem sizes with hundreds of nodes on networks including the real network of Manhattan
Systematics of g factors of 2_1^+ states in even-even nuclei from Gd to Pt: A microscopic description by the projected shell model
The systematics of g factor of first excited 2^+ state vs neutron number N is
studied by the projected shell model. The study covers the even-even nuclei of
all isotopic chains from Gd to Pt. g factors are calculated by using the
many-body wavefunctions that reproduces well the energy levels and B(E2)'s of
the ground-state bands. For Gd to W isotopes the characteristic feature of the
g factor data along an isotopic chain is described by the present model.
Deficiency of the model in the g factor description for the heavier Os and Pt
isotopes is discussed.Comment: 9 pages, 5 figure
Flocculation on a chip: a novel screening approach to determine floc growth rates and select flocculating agents
Flocculation is a key purification step in cell-based processes for the food and pharmaceutical industry
where the removal of cells and cellular debris is aided by adding flocculating agents. However, finding the
best suited flocculating agent and optimal conditions to achieve rapid and effective flocculation is a nontrivial
task. In conventional analytical systems, turbulent mixing creates a dynamic equilibrium between floc
growth and breakage, constraining the determination of floc formation rates. Furthermore, these systems
typically rely on end-point measurements only. We have successfully developed for the first time a microfluidic
system for the study of flocculation under well controlled conditions. In our microfluidic device
(Ī¼FLOC), floc sizes and growth rates were monitored in real time using high-speed imaging and computational
image analysis. The on-line and in situ detection allowed quantification of floc sizes and their growth
kinetics. This eliminated the issues of sample handling, sample dispersion, and end-point measurements.
We demonstrated the power of this approach by quantifying the growth rates of floc formation under forty
different growth conditions by varying industrially relevant flocculating agents (pDADMAC, PEI, PEG), their
concentration and dosage. Growth rates between 12.2 Ī¼m sā1 for a strongly cationic flocculant (pDADMAC)
and 0.6 Ī¼m sā1 for a non-ionic flocculant (PEG) were observed, demonstrating the potential to rank flocculating
conditions in a quantitative way. We have therefore created a screening tool to efficiently compare
flocculating agents and rapidly find the best flocculating condition, which will significantly accelerate early
bioprocess development
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