6,110 research outputs found
Person to Person in England
While still in the midst of their study abroad experiences, students at Linfield College write reflective essays. Their essays address issues of cultural similarity and difference, compare lifestyles, mores, norms, and habits between their host countries and home, and examine changes in perceptions about their host countries and the United States. In this essay, Lisa Ekstrom describes her observations during her study abroad program at the University of Nottingham in England
Report on Phase 2.3, Investigation of Welded Highway Bridges. Project IHR-64
The object of this investigation was to study the effect of internal flaws
on the fatigue behavior of butt-welded connections in mild structural steel, the
initiation of fatigue cracks from these flaws and the propagation rates of these
cracks in the connections. Since internal flaws occur in many welds it is essential
to obtain a better understanding of the behavior of flawed connections so that adequate,
yet realistic, code requirements can be established.
The study is limited to two major types of defects, porosity and incomplete
penetration. The porosity was further subdivided into two categories based on
the severity of the defect. The specimens with incomplete penetration were made
with an initial 3/16" centrally located crack the full width of the- specimen.
The fatigue behavior of the connections with the defects is compared with
that of sound welds to observe the effects of the defects on the fatigue strength
of the connections. The data are compared with result~ of similar studies found in
the literature and also with the AASHO 1970 Specification design requirements.
Three of the specimens with incomplete penetration were examined radiographically
during the fatigue testing to determine when initiation of the fatigue
cracks occurred, and how rapidly they propagated. The results of the crack propagation
tests are compared with similar relationships developed for high strength
steels. A relationship that better fits the data for mild steel has been developed
in a manner similar to that used for the high strength steels.State of Illinois. Department of Transportation. Division of HighwaysU.S. Department of Transportation. Federal Highway Administratio
The spectro-contextual encoding and retrieval theory of episodic memory.
The spectral fingerprint hypothesis, which posits that different frequencies of oscillations underlie different cognitive operations, provides one account for how interactions between brain regions support perceptual and attentive processes (Siegel etal., 2012). Here, we explore and extend this idea to the domain of human episodic memory encoding and retrieval. Incorporating findings from the synaptic to cognitive levels of organization, we argue that spectrally precise cross-frequency coupling and phase-synchronization promote the formation of hippocampal-neocortical cell assemblies that form the basis for episodic memory. We suggest that both cell assembly firing patterns as well as the global pattern of brain oscillatory activity within hippocampal-neocortical networks represents the contents of a particular memory. Drawing upon the ideas of context reinstatement and multiple trace theory, we argue that memory retrieval is driven by internal and/or external factors which recreate these frequency-specific oscillatory patterns which occur during episodic encoding. These ideas are synthesized into a novel model of episodic memory (the spectro-contextual encoding and retrieval theory, or "SCERT") that provides several testable predictions for future research
On the value of optimal stopping games
We show, under weaker assumptions than in the previous literature, that a
perpetual optimal stopping game always has a value. We also show that there
exists an optimal stopping time for the seller, but not necessarily for the
buyer. Moreover, conditions are provided under which the existence of an
optimal stopping time for the buyer is guaranteed. The results are illustrated
explicitly in two examples.Comment: Published at http://dx.doi.org/10.1214/105051606000000204 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
Differential recruitment of brain networks following route and cartographic map learning of spatial environments.
An extensive neuroimaging literature has helped characterize the brain regions involved in navigating a spatial environment. Far less is known, however, about the brain networks involved when learning a spatial layout from a cartographic map. To compare the two means of acquiring a spatial representation, participants learned spatial environments either by directly navigating them or learning them from an aerial-view map. While undergoing functional magnetic resonance imaging (fMRI), participants then performed two different tasks to assess knowledge of the spatial environment: a scene and orientation dependent perceptual (SOP) pointing task and a judgment of relative direction (JRD) of landmarks pointing task. We found three brain regions showing significant effects of route vs. map learning during the two tasks. Parahippocampal and retrosplenial cortex showed greater activation following route compared to map learning during the JRD but not SOP task while inferior frontal gyrus showed greater activation following map compared to route learning during the SOP but not JRD task. We interpret our results to suggest that parahippocampal and retrosplenial cortex were involved in translating scene and orientation dependent coordinate information acquired during route learning to a landmark-referenced representation while inferior frontal gyrus played a role in converting primarily landmark-referenced coordinates acquired during map learning to a scene and orientation dependent coordinate system. Together, our results provide novel insight into the different brain networks underlying spatial representations formed during navigation vs. cartographic map learning and provide additional constraints on theoretical models of the neural basis of human spatial representation
Progenitors of supernova Ibc: a single Wolf-Rayet star as the possible progenitor of the SN Ib iPTF13bvn
Core-collapse supernova (SN) explosions mark the end of the tumultuous life
of massive stars. Determining the nature of their progenitors is a crucial step
towards understanding the properties of SNe. Until recently, no progenitor has
been directly detected for SN of type Ibc, which are believed to come from
massive stars that lose their hydrogen envelope through stellar winds and from
binary systems where the companion has stripped the H envelope from the
primary. Here we analyze recently reported observations of iPTF13bvn, which
could possibly be the first detection of a SN Ib progenitor based on
pre-explosion images. Very interestingly, the recently published Geneva models
of single stars can reproduce the observed photometry of the progenitor
candidate and its mass-loss rate, confirming a recently proposed scenario. We
find that a single WR star with initial mass in the range 31-35 Msun fits the
observed photometry of the progenitor of iPTF13bvn. The progenitor likely has a
luminosity of log (L/Lsun)~5.55, surface temperature ~45000 K, and mass of
~10.9 Msun at the time of explosion. Our non-rotating 32 Msun model
overestimates the derived radius of the progenitor, although this could likely
be reconciled with a fine-tuned model of a more massive (between 40 and 50
Msun), hotter, and luminous progenitor. Our models indicate a very uncertain
ejecta mass of ~8 Msun, which is higher than the average of the SN Ib ejecta
mass that is derived from the lightcurve (2-4 Msun). This possibly high ejecta
mass could produce detectable effects in the iPTF13bvn lightcurve and spectrum.
If the candidate is indeed confirmed to be the progenitor, our results suggest
that stars with relatively high initial masses (>30 Msun) can produce visible
SN explosions at their deaths and do not collapse directly to a black hole.Comment: 4 pages, 2 figures, accepted for publication in A&
- …