1,136 research outputs found
Expected seismic performance of irregular isolated bridges
Bridge structures are usually built on irregular topographical surfaces which create substructures with pier heights of different lengths. Three height irregularity types of typical RC medium length
bridges are analyzed aimed at determining the best strength and stiffness parameters of an isolation system.
The models were located in a high seismicity zone of Mexico. The isolation system is composed by lead rubber bearings (LRB) located on each pile and abutment. The bridge and isolation parameters conducted to the nonlinear time history analysis (NLTHA) of 169 models. Ten seismic records representative of the subduction
zone in the Pacific Coast in Mexico were chosen to carry out the study. The maximum drift pier demands,
bending moments and shear forces were analyzed to identify the best isolation properties for improving the
bridges’ structural behavior, specially focused on looking for avoiding irregularity concentrations of shear forces on piers. Additionally, the seismic response of the bridges supported on traditional neoprene bearings was carried out
Effect of verbal task complexity in a working memory paradigm in patients with type 1 diabetes. A fMRI study.
Podeu consultar dades primàries associades a l'article a: http://hdl.handle.net/2445/109182Type 1 diabetes (T1D) is commonly diagnosed in childhood and adolescence, and the developing brain has to cope with its deleterious effects. Although brain adaptation to the disease may not result in evident cognitive dysfunction, the effects of T1D on neurodevelopment could alter the pattern of BOLD fMRI activation. The aim of this study was to explore the neural BOLD activation pattern in patients with T1D versus that of healthy matched controls while performing two visuospatial working memory tasks, which included a pair of assignments administered through a block design. In the first task (condition A), the subjects were shown a trial sequence of 3 or 4 white squares positioned pseudorandomly around a fixation point on a black background. After a fixed delay, a second corresponding sequence of 3 or 4 red squares was shown that either resembled (direct, 50%) or differed from (50%) the previous stimulation order. The subjects were required to press one button if the two spatial sequences were identical or a second button if they were not. In condition B, the participants had to determine whether the second sequence of red squares appeared in inverse order (inverse, 50%) or not (50%) and respond by pressing a button. If the latter sequence followed an order distinct from the inverse sequence, the subjects were instructed to press a different button. Sixteen patients with normal IQ and without diabetes complications and 16 healthy control subjects participated in the study. In the behavioral analysis, there were no significant differences between the groups in the pure visuo-spatial task, but the patients with diabetes exhibited poorer performance in the task with verbal stimuli (p < .001). However, fMRI analyses revealed that the patients with T1D showed significantly increased activation in the prefrontal inferior cortex, subcortical regions and the cerebellum (in general p < .001). These different activation patterns could be due to adaptive compensation mechanisms that are devoted to improving efficiency while solving more complex cognitive tasks
Quasi-free Compton Scattering and the Polarizabilities of the Neutron
Differential cross sections for quasi-free Compton scattering from the proton
and neutron bound in the deuteron have been measured using the Glasgow/Mainz
tagging spectrometer at the Mainz MAMI accelerator together with the Mainz 48
cm 64 cm NaI(Tl) photon detector and the G\"ottingen SENECA
recoil detector. The data cover photon energies ranging from 200 MeV to 400 MeV
at . Liquid deuterium and hydrogen targets
allowed direct comparison of free and quasi-free scattering from the proton.
The neutron detection efficiency of the SENECA detector was measured via the
reaction . The "free" proton Compton scattering cross
sections extracted from the bound proton data are in reasonable agreement with
those for the free proton which gives confidence in the method to extract the
differential cross section for free scattering from quasi-free data.
Differential cross sections on the free neutron have been extracted and the
difference of the electromagnetic polarizabilities of the neutron have been
obtained to be
in units . In combination with the polarizability sum deduced from photoabsorption data, the neutron electric and
magnetic polarizabilities, and
are obtained. The backward spin polarizability of the neutron was determined to
be
Adiabatic Formation of Rydberg Crystals with Chirped Laser Pulses
Ultracold atomic gases have been used extensively in recent years to realize
textbook examples of condensed matter phenomena. Recently, phase transitions to
ordered structures have been predicted for gases of highly excited, 'frozen'
Rydberg atoms. Such Rydberg crystals are a model for dilute metallic solids
with tunable lattice parameters, and provide access to a wide variety of
fundamental phenomena. We investigate theoretically how such structures can be
created in four distinct cold atomic systems, by using tailored
laser-excitation in the presence of strong Rydberg-Rydberg interactions. We
study in detail the experimental requirements and limitations for these
systems, and characterize the basic properties of small crystalline Rydberg
structures in one, two and three dimensions.Comment: 23 pages, 10 figures, MPIPKS-ITAMP Tandem Workshop, Cold Rydberg
Gases and Ultracold Plasmas (CRYP10), Sept. 6-17, 201
Neutron polarizabilities investigated by quasi-free Compton scattering from the deuteron
Measuring Compton scattered photons and recoil neutrons in coincidence,
quasi-free Compton scattering by the neutron has been investigated at MAMI
(Mainz) at in an energy range from 200 to 400 MeV.
From the data a polarizability difference of in units of has been
determined. In combination with the polarizability sum deduced from photo absorption data, the neutron electric and
magnetic polarizabilities, and ,
are obtained
Exclusive measurement of coherent eta photoproduction from the deuteron
Coherent photoproduction of eta mesons from the deuteron has been measured
from threshold up to incident photon energies of 750 MeV using the photon
spectrometer TAPS at the tagged photon facility at the Mainz microtron MAMI.
For the first time, differential coherent cross sections have been deduced from
the coincident detection of the eta meson and the recoil deuteron. A missing
energy analysis was used for the suppression of background events so that a
very clean identification of coherent eta-photoproduction was achieved. The
resulting cross sections agree with previous experimental results except for
angles around 90 deg in the photon-deuteron cm-system where they are smaller.
They are compared to various model calculations.Comment: 4 pages, 4 figure
Structural phase transitions in multipole traps
A small number of laser-cooled ions trapped in a linear radiofrequency
multipole trap forms a hollow tube structure. We have studied, by means of
molecular dynamics simulations, the structural transition from a double ring to
a single ring of ions. We show that the single-ring configuration has the
advantage to inhibit the thermal transfer from the rf-excited radial components
of the motion to the axial component, allowing to reach the Doppler limit
temperature along the direction of the trap axis. Once cooled in this
particular configuration, the ions experience an angular dependency of the
confinement if the local adiabaticity parameter exceeds the empirical limit.
Bunching of the ion structures can then be observed and an analytic expression
is proposed to take into account for this behaviour
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