4,871 research outputs found
Cosmic ray records in Antarctic meteorites
The cosmogenic radionuclides Be(10), Al(26), and Mn(53) and noble gases were determined in more than 28 meteorites from Antarctica by nuclear analytical techniques and static mass spectrometry, respectively. The summarized results are listed. The concentrations of Al(26) and Mn(53) are normalized to the repective main target elements and given in dpm/kg Si sub eq and dpm/kg Fe. The errors stated include statistical as well as systematical errors. For noble gas concentrations estimated errors are 5% and for isotopic ratios 1.5%. Cosmic ray exposure ages T sub 21 were calculated by the noble gas concentrations and the terrestrial residence time (T) on the basis of the spallogenic nuclide Al(26). The suggested pairing of the LL6 chondrite RKPA 80238 and RKPA 80248 and the eucrites ALHA 76005 and ALHA 79017 is confirmed not only by the noble gas data but also by the concentrations of the spallation produced radionuclides. Futhermore, ALHA 80122, clasified as an H6 chondrite, has a noble gas pattern which suggest that this meteorite belongs to the ALHA 80111 shower
Nuclear spin-lattice relaxation in p-type GaAs
Spin-lattice relaxation of the nuclear spin system in p-type GaAs is studied
using a three-stage experimental protocol including optical pumping and
measuring the difference of the nuclear spin polarization before and after a
dark interval of variable length. This method allows us to measure the
spin-lattice relaxation time of optically pumped nuclei "in the dark",
that is, in the absence of illumination. The measured values fall into
the sub-second time range, being three orders of magnitude shorter than in
earlier studied n-type GaAs. The drastic difference is further emphasized by
magnetic-field and temperature dependences of in p-GaAs, showing no
similarity to those in n-GaAs. This unexpected behavior is explained within a
developed theoretical model involving quadrupole relaxation of nuclear spins,
which is induced by electric fields within closely spaced donor-acceptor pairs.Comment: 9 pages, 8 figure
Quantitative complementarity between local and nonlocal character of quantum states in a three-qubit system
Local or nonlocal character of quantum states can be quantified and is
subject to various bounds that can be formulated as complementarity relations.
Here, we investigate the local vs. nonlocal character of pure three-qubit
states by a four-way interferometer. The complete entanglement in the system
can be measured as the entanglement of a specific qubit with the subsystem
consisting of the other two qubits. The quantitative complementarity relations
are verified experimentally in an NMR quantum information processor.Comment: 10 pages, 10 figure
Quantum information processing using strongly-dipolar coupled nuclear spins
Dipolar coupled homonuclear spins present challenging, yet useful systems for
quantum information processing. In such systems, eigenbasis of the system
Hamiltonian is the appropriate computational basis and coherent control can be
achieved by specially designed strongly modulating pulses. In this letter we
describe the first experimental implementation of the quantum algorithm for
numerical gradient estimation on the eigenbasis of a four spin system.Comment: 5 pages, 5 figures, Accepted in PR
Perioperative Nerve Blockade: Clues from the Bench
Peripheral and
neuraxial nerve blockades are widely used in the
perioperative period. Their values to diminish
acute postoperative pain are established but
other important outcomes such as chronic
postoperative pain, or newly, cancer recurrence,
or infections could also be influenced. The
long-term effects of perioperative nerve
blockade are still controversial. We will review
current knowledge of the effects of blocking
peripheral electrical activity in different
animal models of pain. We will first go over the
mechanisms of pain development and evaluate
which types of fibers are activated after an
injury. In the light of experimental results, we
will propose some hypotheses explaining the
mitigated results obtained in clinical studies
on chronic postoperative pain. Finally, we will
discuss three major disadvantages of the current
blockade: the absence of blockade of myelinated
fibers, the inappropriate duration of blockade,
and the existence of activity-independent
mechanisms
An ab initio and dynamics study of the photodissociation of nitric acid HNO3
We investigated the photodissociation of HNO3 within the first (300 nm) and the third (200 nm) absorption band. The relevant S1 and S3 potential energy surfaces were calculated by taking into account the N-O single bond and N=O “double” bond distances. The striking feature of the dynamical analysis is a bifurcation of the wave packet on the S3 surface which explains the branching into the two
reaction pathways with the products OH+NO2 and O+HONO found in experiments. Dissociation on the S1 surface is predicted to proceed along a single channel leading to OH+NO2, both in their electronic ground states.
Corresponding author
I.V. LABETALOL IN THE TREATMENT OF HYPERTENSION FOLLOWING CORONARY-ARTERY SURGERY
SUMMARY The cardiovascular effects of incremental fixed i.v. doses of labetalol were evaluated in 10 normovolaemic sedated patients presenting with hypertension and tachycardia in the early period after myocardial revas-cularizaoon. A first dose of 20 mg was sufficient to provoke a (P < 0.01) mean decrease in systolic (−9.3%), diastolic (−8.2%) and mean arterial (−7.9%) pressure (AP) and in the rate-pressure product (RPP) (−13.1%). The mean heart rate (HR) did not change significantly, but a linear correlation could be established between the change at 2 min and the value before injection (r = 0.73). A second dose of labetalol 40 mg given S min later did not decrease AP further, but a significant decrease in HR was noted. A marked difference in the individual response among patients was found as the range of effective total doses per kg body weight was 0.6-4.1 mg kg−1 (mean 2.2). Apart from one patient, no patient needed vagolytic or sympathomimetic drugs to oppose the alpha or beta actions of labetalol during the 24-h follow-up perio
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