294 research outputs found
Dipole Excitation of Dipositronium
The energy interval between the ground and the P-wave excited states of the
recently discovered positronium molecule Ps_2 is evaluated, including the
relativistic and the leading logarithmic radiative corrections, E_P-E_S = 0.181
586 7(8) a.u. The P-state, decaying usually via annihilation, is found to decay
into the ground state by an electric dipole transition 19 percent of the time.
Anticipated observation of this transition will provide insight into this
exotic system.Comment: 5 page
Extended Hylleraas three-electron integral
A closed form expression for the three-electron Hylleraas integral involving
the inverse quadratic power of one inter-particle coordinate is obtained, and
recursion relations are derived for positive powers of other coordinates. This
result is suited for high precision calculations of relativistic effects in
lithium and light lithium-like ions.Comment: Submited to Phys. Rev.
Relativistic, QED, and finite nuclear mass corrections for low-lying states of Li and Be
Accurate results for nonrelativistic energy, relativistic, QED, and finite
nuclear mass corrections are obtained for , and
states of the Li atom and Be ion. Our computational approach
uses the Hylleraas basis set with the analytic integration and recursion
relations. From comparison of experimental results for the isotope shifts to
theoretical predictions including nuclear polarizabilities, we obtain nuclear
charge radii for Li and Be isotopes.Comment: 19 pages, 8 tables, Phys. Rev. A in prin
Recursion relations for Hylleraas three-electron integral
Recursion relations for Hylleraas three-electron integral are obtained in a
closed form by using integration by parts identities. Numerically fast and well
stable algorithm for the calculation of the integral with high powers of
inter-electronic coordinates is presented.Comment: 12 pages, requires RevTeX4, submitted to Phys. Rev.
Photoperiodism in Hamsters: Abrupt Versus Gradual Changes in Day Length Differentially Entrain Morning and Evening Circadian Oscillators
In studies of photoperiodism, animals typically are transferred abruptly from a long (e.g., 16 h light per day [16L]) to a short (8L) photoperiod, and circadian oscillators that regulate pineal melatonin secretion are presumed to reentrain rapidly to the new photocycle. Among rats and Siberian hamsters, however, reentrainment rates vary depending on whether additional darkness is added to morning or evening, and a subset of hamsters (nonresponders) fails ever to reentrain normally to short photoperiods. The authors assessed whether several short-day responses occurred at different rates when darkness was extended into morning versus evening hours and the effectiveness of abrupt versus gradual shortening in day lengths (DLs). Entrainment patterns of photoresponsive hamsters also were compared to those of photononresponsive hamsters. Responsive hamsters transferred on a single day from 16L to 8L underwent more rapid gonadal regression, weight loss, decreases in follicle-stimulating hormone titers, and expansion of nocturnal locomotor activity when darkness was added to morning versus evening. When the dark phase was extended gradually by 8 h over 16 weeks, short-day responses occurred at the same rate whether darkness was appended to morning or evening or was added symmetrically. Darkness added to evening promoted more rapid short-day responses when it was added gradually rather than abruptly, despite the fact that average DLs were significantly shorter for the latter group. Among nonresponders, morning extensions of darkness transiently increased activity duration, whereas evening extensions did not. Gradual and abrupt decreases in DL differentially affect entrainment of evening and morning circadian oscillators. The authors argue for the incorporation of simulated natural photoperiods in studies of photoperiodism.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66702/2/10.1177_074873049701200204.pd
The Applicability of Global and Surface Sensitive Techniques to Characterization of Silver Nanoparticles for Ink-Jet Printing Technology
Ultracold mixtures of metastable He and Rb: scattering lengths from ab initio calculations and thermalization measurements
We have investigated the ultracold interspecies scattering properties of
metastable triplet He and Rb. We performed state-of-the-art ab initio
calculations of the relevant interaction potential, and measured the
interspecies elastic cross section for an ultracold mixture of metastable
triplet He and Rb in a quadrupole magnetic trap at a temperature of
0.5 mK. Our combined theoretical and experimental study gives an interspecies
scattering length , which prior to this work was
unknown. More general, our work shows the possibility of obtaining accurate
scattering lengths using ab initio calculations for a system containing a
heavy, many-electron atom, such as Rb.Comment: 11 pages, 11 figures, accepted for publication in Phys. Rev.
Avaliação de características fenotípicas para a determinação do rendimento foliar em espinheira-santa (Maytenus ilicifolia Martius).
A espinheira-santa (Maytenus ilieifolia) é uma espécie medicinal arbórea, nativa das formações de Floresta Ombrófila Mista do sul do Brasil, a qual vem sofrendo grande pressão de exploração nos seus ambientes naturais. Este trabalho teve como objetivo caracterizar o rendimento de indivíduos de diferentes populações naturais de espinheira-santa, por meio de características fenotípicas não destrutivas, a fim de contribuir para o processo de manejo sustentável. Para fins de determinação do rendimento, foram avaliados o número de ramos primários com e sem folhas, a altura, o diâmetro a altura do colo (DAC) e a altura da primeira ramificação, em 60 indivíduos de espinheira-santa de duas populações naturais, com características distintas. Estimou-se coeficientes de corre/ação entre estes parâmetros, bem como equações de regressão entre e o número de ramos primários com folhas (X) e o rendimento (R). As equações R = 0,75205 • X, para populações que ocorrem a pleno sol, e R = 1,53459 • X, para populações que ocorrem no sub-bosque de formações secundárias, são de uso prático e capazes de representar com elevada precisão o rendimento em populações com essas características ambientais
Princípio pagador-poluidor - como princípio norteador da cobrana pelo uso dos recursos hídricos
O presente trabalho objetiva conduzir uma análise detalhada do princípio poluidor-pagador,amplamente consagrado em diversos ordenamentos legais, com o intuito de aclarar sua interpretação de modo que possa ser aplicado uniformemente e,por conseguinte,mais freqüentemente. Este estudo enfoca a análise da doutrina,bem como de alguns artigos,visando ao exame dos aspectos econômicos e jurídicos do PPP,à investigação da relação entre o PPP e outros princípios ambientais,em especial, a responsabilidade civil pó danos ambientais e o chamado "princípio do usuário-pagador", de sua evolução,terminologia e finalidades ,sem deixar de mencionar a importância da adoção de instrumentos econômicos(mormente a cobrança pelo uso da água) para a proteção qualitativa e quantitativa dos recursos hídricos,a guiar a implementação efetiva do princípio em tela
Relativistic, QED, and nuclear mass effects in the magnetic shielding of He
The magnetic shielding of He is studied. The complete
relativistic corrections of order , leading QED corrections of
order , and finite nuclear mass effects of order
are calculated with high numerical precision. The resulting
theoretical predictions for are the most
accurate to date among all elements and support the use of He as a NMR
standard.Comment: 10 pages, corrected minor errors in Eqs.(6,7
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