25,792 research outputs found
Spectrum of low-lying configurations with negative parity
Spectrum of low-lying five-quark configurations with strangeness quantum
number and negative parity is studied in three kinds of constituent
quark models, namely the one gluon exchange, Goldstone Boson exchange, and
instanton-induced hyperfine interaction models, respectively. Our numerical
results show that the lowest energy states in all the three employed models are
lying at 1800 MeV, about 200 MeV lower than predictions of various
quenched three-quark models. In addition, it is very interesting that the state
with the lowest energy in one gluon exchange model is with spin 3/2, but 1/2 in
the other two models.Comment: Version published in Phys. Rev.
A rapid cosmic-ray increase in BC 3372-3371 from ancient buried tree rings in China
Cosmic rays interact with the Earth's atmosphere to produce C, which
can be absorbed by trees. Therefore, rapid increases of C in tree rings
can be used to probe previous cosmic-ray events. By this method, three C
rapidly increasing events have been found. Plausible causes of these events
include large solar proton events, supernovae or short gamma-ray bursts.
However, due to the lack of measurements of C by year, the occurrence
frequency of such C rapidly increasing events is poorly known. In
addition, rapid increases may be hidden in the IntCal13 data with five-year
resolution. Here we report the result of C measurements using an ancient
buried tree during the period between BC 3388 and 3358. We find a rapid
increase of about 9\textperthousand~ in the C content from BC 3372 to BC
3371. We suggest that this event could originate from a large solar proton
event.Comment: 23 pages, 3 figures, 2 tables, published in Nature Communication
Spectral responses in granular compaction
The slow compaction of a gently tapped granular packing is reminiscent of the
low-temperature dynamics of structural and spin glasses. Here, I probe the
dynamical spectrum of granular compaction by measuring a complex
(frequency-dependent) volumetric susceptibility . While the
packing density displays glass-like slow relaxations (aging) and
history-dependence (memory) at low tapping amplitudes, the susceptibility
displays very weak aging effects, and its spectrum shows no
sign of a rapidly growing timescale. These features place in
sharp contrast to its dielectric and magnetic counterparts in structural and
spin glasses; instead, bears close similarities to the complex
specific heat of spin glasses. This, I suggest, indicates the glass-like
dynamics in granular compaction are governed by statistically rare relaxation
processes that become increasingly separated in timescale from the typical
relaxations of the system. Finally, I examine the effect of finite system size
on the spectrum of compaction dynamics. Starting from the ansatz that low
frequency processes correspond to large scale particle rearrangements, I
suggest the observed finite size effects are consistent with the suppression of
large-scale collective rearrangements in small systems.Comment: 18 pages, 17 figures. Submitted to PR
Comment on ``Superconducting PrBa_2Cu_3O_x''
Recently, Zou et al. (Phys. Rev. Lett. 80, 1074, 1998) reported the
observation of bulk superconductivity (SC) for a PrBa_2Cu_3O_x (Pr123) single
crystal grown by the traveling-solvent floating zone (TSFZ) method. The aim of
this Comment is to show the inconsistency of the value of effective magnetic
moment \mu_{eff} reported by Zou et al. (2.92\mu_B) with their magnetic
susceptibility data. The estimation made directly from their data points gives
a considerably smaller value of \mu_{eff}=2.09\mu_B. At the same time the
values of mu_{eff}=2.9\mu_B and 3.1\mu_B were obtained for our Pr123 single
crystals grown by flux method for H||ab-plane and H||c-axis, respectively. This
suggests that Pr occupies only about a half of the RE sites in TSFZ crystal.
The other half of the RE sites is occupied most probably by the nonmagnetic Ba.
Noteworthy, SC with T_c=43 K was observed earlier for
Pr_{0.5}Ca_{0.5}Ba_2Cu_3O_{7-y} thin films. Ba^{2+} has a larger ionic radius
than Pr^{3+} and so the substitution of Ba for Pr could give a natural
explanation not only for the SC in TSFZ Pr123 but also for the elongation of
the distance between the CuO_2 planes observed by Zou et al.Comment: Slightly extended version of Comment accepted to Phys. Rev. Lett.
(v.81, N24, 1998), tentatevely to be publ. 14Dec98. 1 page, REVTex; 1 EPS fi
Linear optics substituting scheme for multi-mode operations
We propose a scheme allowing a conditional implementation of suitably
truncated general single- or multi-mode operators acting on states of traveling
optical signal modes. The scheme solely relies on single-photon and coherent
states and applies beam splitters and zero- and single-photon detections. The
signal flow of the setup resembles that of a multi-mode quantum teleportation
scheme thus allowing the individual signal modes to be spatially separated from
each other. Some examples such as the realization of cross-Kerr nonlinearities,
multi-mode mirrors, and the preparation of multi-photon entangled states are
considered.Comment: 11 pages, 4 eps-figures, using revtex
Evidence for Quasiparticle Decay in Photoemission from Underdoped Cuprates
I argue that the ``gap'' recently observed at the Brillouin zone face of
cuprate superconductors in photoemission by Marshall et al [Phys. Rev. Lett.
76, 4841 (1996)] and Ding et al [Nature 382, 54 (1996)] is evidence for the
decay of the injected hole into a spinon-holon pair.Comment: 4 pages of ReVTeX, 3 eps figure
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