14,549 research outputs found
Selective extinction of marine plankton at the end of the Mesozoic era: The fossil and stable isotope record
Floral, faunal and stable isotope evidence in a continuous sequence of latest Cretaceous and earliest Tertiary shallow water marine deposits in the Mangyshlak Peninsula, USSR suggest severe environmental changes at the Cretaceous/Tertiary (K/T) boundary. Time frame is provided by nanno, micro and macrofossils as well as by magnetic stratigraphy and an iridium spike. Oxygen isotopic analyses of the bulk sediments, composed of nanno and microplankton skeletal remains, show a sharp positive spike at the K/T boundary. This shift is primarily attributed to severe cooling possibly accompanied by increased salinities of the surface mixed layer. Floral and faunal extinctions were selective, affecting approximately 90 percent of the warm water calcareous phyto and zooplankton genera in the Tethyan-Paratethyan regions. These highly diverse taxa with many endemic representatives were at the peak of their evolutionary development. Geologic evidence indicates that the terminal Cretaceous temperature decline was coeval with widespread and intense volcanic activity which reached a peak at the close of the Mesozoic Era. Increased acidity temporarily prohibited calcite nucleation of the surface dwelling warm-water plankton. Superimposed upon decreased alkalinity, severe and rapid climatic changes caused the extinction of calcareous phyto and zooplankton
Graded ferroelectric capacitors with robust temperature characteristics
Ferroelectric thin films offer the possibility of engineering the dielectric response for tunable components in frequency-agile rf and microwave devices. However, this approach often leads to an undesired temperature sensitivity. Compositionally graded ferroelectric films have been explored as a means of redressing this sensitivity, but experimental observations vary depending on geometry and other details. In this paper, we present a continuum model to calculate the capacitive response of graded ferroelectric films with realistic electrode geometries by accurately accounting for the polarization distribution and long-range electrostatic interactions. We show that graded c-axis poled BaxSr_(1−xT)iO_3 BST parallel plate capacitors are ineffective while graded a-axis poled BST coplanar capacitors with interdigitated electrodes are extremely effective in obtaining high and temperature-stable dielectric properties
Longitudinal correlation of the triangular flow event plane in a hybrid approach with hadron and parton cascade initial conditions
The longitudinal long-range correlations of the triangular flow event plane
angles are calculated in a Boltzmann + hydrodynamics hybrid approach. The
potential to disentangle different energy deposition scenarios is explored by
utilizing two different transport approaches for the early non-equilibrium
evolution. In the hadronic transport approach the particle production in high
energy heavy ion reactions is mainly governed by string excitation and
fragmentation processes which are absent in the parton cascade approach. We
find that in both approaches the initial state shows a strong longitudinal
correlation of the event plane angles which is diluted but still persists in
the final state momentum space distributions of the produced particles. A
ridge-like structure can also be caused by near-collinear gluon radiation in a
parton cascade approach and does not necessarily prove longitudinal flux tubes
in the initial state.Comment: 5 pages, 6 figures, replaced with new version with correct labels and
added references, conclusions are unchange
Flavor-oscillation clocks, continuous quantum measurements and a violation of Einstein equivalence principle
The relation between Einstein equivalence principle and a continuous quantum
measurement is analyzed in the context of the recently proposed
flavor-oscillation clocks, an idea pioneered by Ahluwalia and Burgard (Gen. Rel
Grav. Errata 29, 681 (1997)). We will calculate the measurement outputs if a
flavor-oscillation clock, which is immersed in a gravitational field, is
subject to a continuous quantum measurement. Afterwards, resorting to the weak
equivalence principle, we obtain the corresponding quantities in a freely
falling reference frame. Finally, comparing this last result with the
measurement outputs that would appear in a Minkowskian spacetime it will be
found that they do not coincide, in other words, we have a violation of
Einstein equivalence principle. This violation appears in two different forms,
namely: (i) the oscillation frequency in a freely falling reference frame does
not match with the case predicted by general relativity, a feature previously
obtained by Ahluwalia; (ii) the probability distribution of the measurement
outputs, obtained by an observer in a freely falling reference frame, does not
coincide with the results that would appear in the case of a Minkowskian
spacetime.Comment: 16 pages, accepted in Mod. Phys. Letts.
Percolation Transition in the Heterogeneous Vortex State in NbSe2
A percolation transition in the vortex state of a superconducting 2H-NbSe2
crystal is observed in the regime where vortices form a heterogeneous phase
consisting of ordered and disordered domains. The transition is signaled by a
sharp increase in critical current that occurs when the volume fraction of
disordered domains, obtained from pulsed measurements of the current-voltage
characteristics, reaches the value Pc= 0.26. Measurements on different vortex
states show that while the temperature of the transition depends on history and
measurement speed, the value of Pc and the critical exponent characterizing the
approach to it, r =1.97 0.66, are universal
Weak value of Dwell time for Quantum Dissipative spin-1/2 System
The dwell time is calculated within the framework of time dependent weak
measurement considering dissipative interaction between a spin half system and
the environment. Caldirola and Montaldi's method of retarded Schroedinger
equation is used to study the dissipative system. The result shows that
inclusion of dissipative interaction prevents zero time tunneling.Comment: This work is original. arXiv admin note: text overlap with
arXiv:0807.1357, arXiv:quant-ph/9611018, arXiv:quant-ph/9501015 by other
author
Hyperpolarized ^1H NMR employing low γ nucleus for spin polarization storage
The PASADENA (parahydrogen and synthesis allow dramatically enhanced nuclear alignment)(1, 2) and DNP (Dynamic Nuclear Polarization)(3) methods efficiently hyperpolarize biologically relevant nuclei such as 1^H, (31)^P, (13)^C, (15)^N achieving signal enhancement by a factor of ~ 100000 on currently utilized MRI scanners. Recently, many groups have demonstrated the utility of hyperpolarized MR in biological systems using hyperpolarized (13)^C biomarkers with a relatively long spin lattice relaxation time T_1 on the order of tens of seconds.(4-7) Moreover, hyperpolarized (15)^N for biomedical MR has been proposed due to even longer spin lattice relaxations times.(8) An additional increase of up to tens of minutes in the lifetime of hyperpolarized agent in vivo could be achieved by using the singlet states of low gamma (γ) nuclei.(9) However, as NMR receptivity scales as γ^3 for spin 1/2 nuclei, direct NMR detection of low γ nuclei results in a lower signal-to-noise ratio compared to proton detection. While protons are better nuclei for detection, short spin lattice relaxation times prevent direct 1^H hyperpolarized MR in biomedical applications
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