530 research outputs found
Coherent control of enrichment and conversion of molecular spin isomers
A theoretical model of nuclear spin conversion in molecules controlled by an
external electromagnetic radiation resonant to rotational transition has been
developed. It has been shown that one can produce an enrichment of spin isomers
and influence their conversion rates in two ways, through coherences and
through level population change induced by radiation. Influence of conversion
is ranged from significant speed up to almost complete inhibition of the
process by proper choice of frequency and intensity of the external field.Comment: REVTEX, 13 pages + 6 eps figure
Violation of the I=1/2 rule in the nonmesonic weak decay of hypernuclei
Violations of the I=1/2 rule are investigated in the nonmesonic weak
hypernuclear decay using a weak NNN transition potential based on
meson exchange. While the weak I=3/2 matrix elements of baryons with
pseudoscalar mesons are known to be very small, the same matrix elements of
baryons with vector mesons, evaluated in the factorization approximation, are
found to be significant. Within the uncertainties of the factorization
approximation we find that the total rate increases by at most 6% lying within
the error bars of the more recent experimental result. The neutron- to
proton-induced rate, on the other hand, can change by up to a factor of two,
while the asymmetry parameter is strongly affected as well.Comment: 17 pages. Paper related to a contribution presented at the
International Conference on Hypernuclear and Strange Particle Physics
(HYP97). Submitted to Phys. Lett.
Asymmetries in Accessing Vowel Representations Are Driven by Phonological and Acoustic Properties: Neural and Behavioral Evidence From Natural German Minimal Pairs
In vowel discrimination, commonly found discrimination patterns are directional asymmetries where discrimination is faster (or easier) if differing vowels are presented in a certain sequence compared to the reversed sequence. Different models of speech sound processing try to account for these asymmetries based on either phonetic or phonological properties. In this study, we tested and compared two of those often-discussed models, namely the Featurally Underspecified Lexicon (FUL) model (Lahiri and Reetz, 2002) and the Natural Referent Vowel (NRV) framework (Polka and Bohn, 2011). While most studies presented isolated vowels, we investigated a large stimulus set of German vowels in a more naturalistic setting within minimal pairs. We conducted an mismatch negativity (MMN) study in a passive and a reaction time study in an active oddball paradigm. In both data sets, we found directional asymmetries that can be explained by either phonological or phonetic theories. While behaviorally, the vowel discrimination was based on phonological properties, both tested models failed to explain the found neural patterns comprehensively. Therefore, we additionally examined the influence of a variety of articulatory, acoustical, and lexical factors (e.g., formant structure, intensity, duration, and frequency of occurrence) but also the influence of factors beyond the well-known (perceived loudness of vowels, degree of openness) in depth via multiple regression analyses. The analyses revealed that the perceptual factor of perceived loudness has a greater impact than considered in the literature and should be taken stronger into consideration when analyzing preattentive natural vowel processing
An ISFET-based anion sensor for the potentiometric detection of organic acids in liquid chromatography
An ion-selective field effect transistor (ISFET) was applied as a potentiometric detector in liquid chromatography (LC) for the determination of organic acids. The ISFET was prepared by coating the gate insulator of the encapsulated transistor with a poly(vinyl chloride) (PVC) matrix membrane containing methyltridodecylammoniumchloride, which enables the detection of organic anions. The ISFET was tested for its applicability as detector for carboxylic acids in ion-exchange and reversed-phase chromatography. Its analytical characteristics were compared to those of a coated-wire electrode (CWE) and of a conventional type of ion-selective electrode (ISE)
ESC NN-Potentials in Momentum Space. I. PS-PS Exchange Potentials
A momentum space representation is derived for the Nijmegen
Extended-Soft-Core (ESC) interactions. The partial wave projection of this
representation is carried through, in principle for Two-Meson-Exchange (TME) in
general. Explicit results for the momentum space partial wave NN-potentials
from PS-PS-Exchange are given.Comment: 23 pages, 2 PostScript figures, revtex
Cluster models of Lambda-Lambda-6He and Lambda-9Be hypernuclei
Configuration space Faddeev calculations are performed for the binding energy
of Lambda-Lambda-6He and Lambda-9Be bound states, here considered as
alpha-Lambda-Lambda and alpha-alpha-Lambda clusters respectively, in order to
study the dependence of the calculated binding energy on the alpha-Lambda
potential input. For Lambda-Lambda-6He, using realistic interactions, the
uncertainty in extracting the Lambda-Lambda S=L=0 interaction strength does not
exceed 0.1 MeV, which is a fraction of the order of magnitude derived for other
theoretical uncertainties. For Lambda-9Be, the dependence of the calculated
binding energy on the alpha-Lambda potential is considerably larger, of order 1
MeV. Our results for Lambda-9Be suggest that the odd-state alpha-Lambda
interaction is substantially reduced with respect to the even-state component.Comment: 16 pages, including 4 figures, typos corrected, slightly revised,
accepted to Nuclear Physics
Energy level displacement of the excited nl state of pionic hydrogen
The energy level displacements of the excited nl states of pionic hydrogen
and the contribution of the ns -> 1s transitions and the (pi^-p)_Coul -> 1s
transitions of the pi^-p pair, coupled by the attractive Coulomb field in the
S-wave state with a continuous energy spectrum, to the shift of the energy
level of the ground state of pionic hydrogen, caused by strong low-energy
interactions, are calculated within a quantum field theoretic, relativistic
covariant and model-independent approach developed in nucl-th/0306047.Comment: 18 pages, no figures, latex, text is revised, references are adde
- …