Quickly routing searches without having to move content

Abstract. A great deal of work has been done to improve peer-to-peer routing by strategically moving or replicating content. However, there are many applications for which a peer-to-peer architecture might be appropriate, but in which content movement is not feasible. We argue that even in such applications, progress can be made in developing techniques that ensure efficient searches. We present several such techniques. First, we show that organizing the network into a square-root topology, where peer degrees are proportional to the square root of the popularity of their content, provides much better performance than power-law networks. Second, we present routing optimizations based on the amount of content stored at peers, and tracking the “best ” peers, that can further improve performance. These and other techniques can make searches efficient, even when content movement or replication is not feasible.

Multiple chiral doublets in four-j shells particle rotor model: Five possible chiral doublets in 60136Nd76

A particle rotor model, which couples nucleons in four single-j shells to a triaxial rotor core, is developed to investigate the five pairs of nearly degenerate doublet bands recently reported in the even-even nucleus 136Nd. The experimental energy spectra and available B(M1)/B(E2) values are successfully reproduced. The angular momentum geometries of the valence nucleons and the core support the chiral rotation interpretations not only for the previously reported chiral doublet, but also for the other four candidates. Hence, 136Nd is the first even-even candidate nucleus in which the multiple chiral doublets exist. Five pairs of chiral doublet bands in a single nucleus is also a new record in the study of nuclear chirality

New excited 2+{2}^{+} and 3−{3}^{{-}} two-proton states in 84210Po126_{\phantom{\rule{0.28em}{0ex}}\phantom{\rule{0.28em}{0ex}}84}^{210}\mathrm{Po}_{126} populated by two-proton transfer

International audienceFive new 2+ levels have been established in the semimagic Po210 nucleus from a Pb208(C12,Be10) two-proton transfer experiment, performed at energies close to the Coulomb barrier at JAEA Tokai. A setup combining Ge, LaBr3, and Si telescopes was used to detect both in-beam γ rays and ejectile residues. The new 2+ states have been established by means of the transitions toward the 0+ ground state which are present in the γ spectra produced by properly selecting the excitation energy in Po210 after kinematical reconstruction. (f7/2)2, h9/2⊗f5/2, (i13/2)2, f7/2⊗p3/2, and f7/2⊗f5/2 two-proton configurations are assigned to these states. In addition, a new 3− level has also been established in this nucleus, very likely originating from the f7/2⊗i13/2 configuration. Shell-model calculations strongly support these assignments

Lifetime of the recently identified 10+^+ isomeric state at 3279 keV in the 136^{136}Nd nucleus

International audienceBackground: The γ softness of Nd136 makes it possible to study the shape changes induced by two-proton or two-neutron excitation. Purpose: We measure the lifetimes of two-quasiparticle states of the bands based on the 10+ states at 3296 and 3279 keV to investigate the shape change induced by the alignment of two protons or two neutrons in the h11/2 orbital. Methods: The recoil-distance Doppler shift method was used for the study of Nd136 studies, which was formed by the fusion reaction Sn120(Ne20,4n)Nd136, at Ebeam=85 MeV. Calculations were performed within the microscopic-macroscopic approach, based on the deformed Woods-Saxon single-particle potential and the Yukawa-plus-exponential macroscopic energy. Results: The lifetime of the 10+ state at 3279 keV of Nd136 was measured to be T1/210+=1.63(9) ns. The lifetimes of the 2+ state at 374 keV and of the 12+ state at 3686 keV of the ground band were also measured to be T1/22+=26.5(14) ps and T1/212+=22.5(14) ps. Conclusions: The measured lifetime of 10+ the state at 3279 keV together with other observables confirm the structure change in Nd136. A rather small reduced hindrance of the electromagnetic decay of the 10+ state at 3279 keV would be consistent with its K-mixed character

Probing the nature of the conjectured low-spin wobbling bands in atomic nuclei

International audienceThe precession of an atomic nucleus can be approximately described as wobbling motion, arising from the coupling of a rotation and a harmonic vibration. Recently, a number of wobbling bands were reported at low spin, which violate the wobbling approximation that can be valid only at high spin. In the present work, we explore the nature of the reported low-spin wobbling bands. Via a new experiment including both angular correlation and linear polarization measurements, we demonstrate that one such band in 187Au is generated by dominant single-particle excitation rather than by the excitation of a wobbling phonon. Assessing the experimental proofs and discussions to assign the reported low-spin wobbling bands, we further point out that the imperfect research paradigm used previously would lead to unreliable identification of low-spin wobbling bands

Collectivity of the 2p-2h proton intruder band of 116^{116}Sn

International audienceThe half-life of the 42+ state of the 2p-2h proton intruder band of Sn116 has been measured with the fast-timing technique. The lifetime of T1/2=29(10) ps leads to a transition probability BE2;42+→22+=40(13) Weisskopf units, which is in very good agreement with the large BE2;22+→03+ value measured previously and provides strong support for the 03+ state as the bandhead of the intruder configuration and for the shape coexistence in the semimagic Sn116 nucleus. IBM-2 calculations with mixing reproduce the experimental data very well, giving insight into the degree of mixing between the different states

Low-spin states in <math><mmultiscripts><mi>Sn</mi><mprescripts/><none/><mn>118</mn></mmultiscripts></math> populated by the radiative capture of thermal neutrons

International audienceBackground: γ-ray spectroscopy studies of the Sn isotopes provide important information on nuclear structure and shell evolution across the long isotopic chain between the doubly-magic Sn100 and Sn132 nuclei. These studies also offer great value to test and tune nuclear models which can then be applied to other regions of the nuclear chart.Purpose: We aim to expand the level scheme of Sn118 by populating low-spin states in the range of 3–5 MeV and determine their angular momentum for the possible connection of these states to pygmy quadrupole Resonances, a new phenomenon observed in the neighboring Sn112,114,124 isotopes as a resonance-like structure in the 3–5 MeV range.Method: Excited states in Sn118 were populated via the Sn117(n,γ)Sn118 reaction at the Institut Laue-Langevin in Grenoble, France. The FIssion Product Prompt gamma-ray Spectrometer (FIPPS), an array of eight n-type high purity Germanium clover detectors augmented with eight additional clover detectors from IFIN “Horia Hulubei” were used to detect γ rays from excited states in Sn118. The array provides a superior efficiency for γ-ray detection and nearly 4π coverage for the measurements of angular correlations for spin assignment of excited nuclear levels.Results: Through γ-γ coincidences, 112 excited states were identified with 57 being newly placed in the level scheme. From these states, 567 γ-ray transitions were observed with 501 being newly identified. Many levels were identified in the 3–5 MeV region. Further, an indirect measurement of the E0 transition which decays from the 03+ state to the 2p-2h, 02+ state was performed and the qK2(E0/E2) and X(E0/E2) for this transition were determined to be 12.7(11) and 6.3(5), respectively. The 103×ρ2(E0) was determined to be &gt;38 based on a half-life limit of &lt;200 ps of the 2057-keV, 03+ level.Conclusions: The abundant spectroscopic information on Sn118 obtained in the present experiment is an important input to the theoretical description of nuclei in the region and highlights the capabilities of the FIPPS array at ILL in conjunction with neutron capture reactions. Many states identified in the 3–5 MeV region could very likely have J=2+ and contribute to the pygmy quadrupole resonances

Evidence of oblate-prolate shape coexistence in the strongly-deformed nucleus 119Cs

International audienceProlate-oblate shape coexistence close to the ground state in the strongly-deformed proton-rich A≈120 nuclei is reported for the first time. One of the four reported bands in 119Cs, built on a 11/2− state at 670 keV, consists of nearly degenerate signature partners, and has properties which unequivocally indicate the strongly-coupled πh11/2[505]11/2− configuration associated with oblate shape. Together with the decoupled πh11/2[541]3/2− band built on the 11/2− prolate state at 110 keV, for which a half-life of T1/2=55(5)μs has been measured, the new bands bring evidence of shape coexistence at low spin in the proton-rich strongly deformed A≈120 nuclei, a phenomenon predicted since long time, but not yet observed. Calculations using the particle-number conserving cranked shell model and two dimensional tilted axis cranking covariant density functional theory support and well reproduce the observed oblate and prolate coexisting low-energy states in 119Cs