8,466 research outputs found
Nylon-6/rubber blends: 8. Influence of the molecular weight of the matrix on the impact behaviour
Blends of nylon-6 with polybutadiene were prepared with comparable morphology and different molecular weights of the matrix. These specimens were tested using the notched Izod impact test and the notched tensile impact test. An increase in molecular weight resulted in a shift of the brittle-to-tough transition temperature of 40°C to lower temperatures. In the notched tensile impact tests, especially in the high-speed region, pronounced differences between blends with different molecular weights of the matrix were observed
Motor action and emotional memory
Can simple motor actions affect how efficiently people retrieve emotional memories, and influence what they choose to remember? In Experiment 1, participants were prompted to retell autobiographical memories with either positive or negative valence, while moving marbles either upward or downward. They retrieved memories faster when the direction of movement was congruent with the valence of the memory (upward for positive, downward for negative memories). Given neutral-valence prompts in Experiment 2, participants retrieved more positive memories when instructed to move marbles up, and more negative memories when instructed to move them down, demonstrating a causal link from motion to emotion. Results suggest that positive and negative life experiences are implicitly associated with schematic representations of upward and downward motion, consistent with theories of metaphorical mental representation. Beyond influencing the efficiency of memory retrieval, the direction of irrelevant, repetitive motor actions can also partly determine the emotional content of the memories people retrieve: moving marbles upward (an ostensibly meaningless action) can cause people to think more positive thoughts
Polyamide-rubber blends: micrscopic studies of the deformation zone
The morphology of injection moulded samples of polyamide—polybutadiene blends (85.15) with an average particle size of 0.3 μm was studied. The samples were fractured in a notched tensile test at crosshead speeds of 10−4 and 1 ms −1 and the structure of the deformation zone was studied using various techniques: polarized light microscopy, scanning electron microscopy, transmission electron microscopy on stained cut samples and carbon replicas, and selected area electron diffraction transmission electron microscopy. The deformation zone of samples tested at 10−4 ms−1 was found to consist of two layers. Far from the fracture surface a layer was observed with more or less round cavities and with cavities in the rubber particles, while near the fracture surface a layer with strongly deformed cavities (length/diameter ratio of 5–10) could be seen. In the samples tested at 1 ms−1 the deformation zone was found to have three layers. In addition to the two previous layers an extra layer next to the fracture plane was found. This layer was 2–3 μm thick with round rubber particles and no orientation of the matrix material. This indicates that, at the high deformation speed of the test, relaxation in the melt took place, suggesting that the material around the crack tip was molten during fracture.\u
Nylon-6/rubber blends: 6. Notched tensile impact testing of nylon-6(ethylene-propylene rubber) blends
The deformation and fracture behaviour of nylon-6/EPR (ethylene-propylene rubber) blends is studied as a function of strain rate and rubber content. Therefore, tensile experiments are conducted on notched specimens over a broad range of draw speeds (including strain rates as encountered in normal tensile tests and in impact tests). The blends with a high rubber content show super-tough behaviour at low and high speeds. In the intermediate-speed regime the fracture energy reaches a minimum (with a level comparable with that of unmodified nylon). The blends with a low rubber content show a transition from tough to brittle behaviour with increasing strain rate. The sudden rise in fracture energy with rising strain rate is believed to be caused by a transition from isothermal to adiabatic deformation. In the adiabatic regime the rise in temperature is high enough to melt the material around the crack tip. This thermal blunting mechanism causes crack propagation to be stable at high strain rates. This mechanism is affirmed by scanning electron microscope studies of the deformation zone
On the relation between adjacent inviscid cell type solutions to the rotating-disk equations
Over a large range of the axial coordinate a typical higher-branch solution of the rotating-disk equations consists of a chain of inviscid cells separated from each other by viscous interlayers. In this paper the leading-order relation between two adjacent cells will be established by matched asymptotic expansions for general values of the parameter appearing in the equations. It is found that the relation between the solutions in the two cells crucially depends on the behaviour of the tangential velocity in the viscous interlayer. The results of the theory are compared with accurate numerical solutions and good agreement is obtained
Dense Regular Packings of Irregular Non-Convex Particles
We present a new numerical scheme to study systems of non-convex, irregular,
and punctured particles in an efficient manner. We employ this method to
analyze regular packings of odd-shaped bodies, not only from a nanoparticle but
also both from a computational geometry perspective. Besides determining
close-packed structures for many shapes, we also discover a new denser
configuration for Truncated Tetrahedra. Moreover, we consider recently
synthesized nanoparticles and colloids, where we focus on the excluded volume
interactions, to show the applicability of our method in the investigation of
their crystal structures and phase behavior. Extensions to the presented scheme
include the incorporation of soft particle-particle interactions, the study of
quasicrystalline systems, and random packings.Comment: 4 pages, 3 figure
Lyman Alpha Radiation From Collapsing Protogalaxies II: Observational Evidence for Gas Infall
We model the spectra and surface brightness distributions for the Lyman alpha
(Lya) radiation expected from protogalaxies that are caught in the early stages
of their assembly. We use the results of a companion paper to characterize the
radiation emerging from spherically collapsing gas clouds. We then modify the
intrinsic spectra to incorporate the effect of subsequent resonant scattering
in the intergalactic medium (IGM). Using these models, we interpret a number of
recent observations of extended Lya blobs (LABs) at high redshift. We suggest,
based on the angular size, energetics, as well as the relatively shallow
surface brightness profiles, and double-peaked spectra, that several of these
LABs may be associated with collapsing protogalaxies. We suggest two follow-up
observations to diagnose the presence of gas infall. High S/N spectra of LABs
should reveal a preferential flattening of the surface brightness profile at
the red side of the line. Complementary imaging of the blobs at redshifted
Balmer alpha wavelengths should reveal the intrinsic Lya emissivity and allow
its separation from radiative transfer effects. We show that Lya scattering by
infalling gas can reproduce the observed spectrum of Steidel et al's LAB2 as
accurately as a recently proposed outflow model. Finally, we find similar
evidence for infall in the spectra of point-like Lyman alpha emitters. The
presence of scattering by the infalling gas implies that the intrinsic Lya
luminosities, and derived quantities, such as the star-formation rate, in these
objects may have been underestimated by about an order of magnitude.Comment: Accepted for Publication in ApJ, 11 emulateapj pages with 6 figures,
together with a companion pape
A positive relationship between the abundance of ammonia oxidizing archaea and natural abundance δ15N of ecosystems
We present a significant relationship between the natural abundance isotopic composition of ecosystem pools and the abundance of a microbial gene. Natural abundance 15N of soils and soil DNA were analysed and compared with archaeal ammonia oxidizer abundance along an elevation gradient in northern Arizona and along a substrate age gradient in Hawai'i. There was a significant positive correlation between the abundance of archaeal amoA genes and natural abundance δ15N of total soil or DNA suggesting that ammonia oxidizing archaea play an important role in ecosystem N release. © 2013 Elsevier Ltd
Derivation of Delay Equation Climate Models Using the Mori-Zwanzig Formalism
Models incorporating delay have been frequently used to understand climate
variability phenomena, but often the delay is introduced through an ad-hoc
physical reasoning, such as the propagation time of waves. In this paper, the
Mori-Zwanzig formalism is introduced as a way to systematically derive delay
models from systems of partial differential equations and hence provides a
better justification for using these delay-type models. The Mori-Zwanzig
technique gives a formal rewriting of the system using a projection onto a set
of resolved variables, where the rewritten system contains a memory term. The
computation of this memory term requires solving the orthogonal dynamics
equation, which represents the unresolved dynamics. For nonlinear systems, it
is often not possible to obtain an analytical solution to the orthogonal
dynamics and an approximate solution needs to be found. Here, we demonstrate
the Mori-Zwanzig technique for a two-strip model of the El Nino Southern
Oscillation (ENSO) and explore methods to solve the orthogonal dynamics. The
resulting nonlinear delay model contains an additional term compared to
previously proposed ad-hoc conceptual models. This new term leads to a larger
ENSO period, which is closer to that seen in observations.Comment: Submitted to Proceedings of the Royal Society A, 25 pages, 10 figure
- …