10,651 research outputs found
Ex-ante measure of patent quality reveals intrinsic fitness for citation-network growth
We have constructed a fitness parameter, characterizing the intrinsic
attractiveness for patents to be cited, from attributes of the associated
inventions known at the time a patent is granted. This exogenously obtained
fitness is shown to determine the temporal growth of the citation network in
conjunction with mechanisms of preferential attachment and obsolescence-induced
ageing that operate without reference to characteristics of individual patents.
Our study opens a window on understanding quantitatively the interplay of the
rich-gets-richer and fit-gets-richer paradigms that have been suggested to
govern the growth dynamics of real-world complex networks.Comment: 6 pages, 3 figures, RevTex4.1, v2: minor changes, version to appear
as a Rapid Communication in Phys. Rev.
Unraveling the dynamics of growth, aging and inflation for citations to scientific articles from specific research fields
We analyze the time evolution of citations acquired by articles from journals
of the American Physical Society (PRA, PRB, PRC, PRD, PRE and PRL). The
observed change over time in the number of papers published in each journal is
considered an exogenously caused variation in citability that is accounted for
by a normalization. The appropriately inflation-adjusted citation rates are
found to be separable into a preferential-attachment-type growth kernel and a
purely obsolescence-related (i.e., monotonously decreasing as a function of
time since publication) aging function. Variations in the empirically extracted
parameters of the growth kernels and aging functions associated with different
journals point to research-field-specific characteristics of citation intensity
and knowledge flow. Comparison with analogous results for the citation dynamics
of technology-disaggregated cohorts of patents provides deeper insight into the
basic principles of information propagation as indicated by citing behavior.Comment: 13 pages, 6 figures, Elsevier style, v2: revised version to appear in
J. Informetric
Construction of nonlocal light-cone operators with definite twist
A systematic procedure is introduced to uniquely decompose nonlocal
LC-operators into harmonic operators of well defined geometric twist. The
method will be demonstrated for (pseudo)scalar, (axial) vector and skew tensor
bilocal quark light-ray operatorsComment: 4 pages, AMSTeX, Contribution to 7th Int. Workshop on Deep Inelastic
Scatterin and QCD, Zeuthen, April 1999 change of formulas 25 and 2
Origin Of the enhanced flexoelectricity of relaxor ferroelectrics
We have measured the bending-induced polarization of Pb(Mg1/3Nb2/3)O3-PbTiO3
single crystals with compositions at the relaxor-ferroelectric phase boundary.
The crystals display very large flexoelectricity, with flexocoupling
coefficients an order of magnitude bigger than the theoretical upper limit set
by the theories of Kogan and Tagantsev. This enhancement persists in the
paraphrase up to a temperature T* that coincides with the start of elastic
softening in the crystals. Analysis of the temperature dependence and
cross-correlation between flexoelectric, dielectric and elastic properties
indicates that the large bendinginduced polarization of relaxor ferroelectrics
is not caused by intrinsically giant flexoelectricity, but by the reorientation
of polar nanotwins that become ferroelastically active below T*
Dynamics of the Narrow-Line Region in the Seyfert 2 Galaxy NGC 1068
We present dynamical models based on a study of high-resolution long-slit
spectra of the narrow-line region (NLR) in NGC 1068 obtained with the Space
Telescope Imaging Spectrograph (STIS) aboard The Hubble Space Telescope (HST).
The dynamical models consider the radiative force due to the active galactic
nucleus (AGN), gravitational forces from the supermassive black hole (SMBH),
nuclear stellar cluster, and galactic bulge, and a drag force due to the NLR
clouds interacting with a hot ambient medium. The derived velocity profile of
the NLR gas is compared to that obtained from our previous kinematic models of
the NLR using a simple biconical geometry for the outflowing NLR clouds. The
results show that the acceleration profile due to radiative line driving is too
steep to fit the data and that gravitational forces along cannot slow the
clouds down, but with drag forces included, the clouds can slow down to the
systemic velocity over the range 100--400 pc, as observed. However, we are not
able to match the gradual acceleration of the NLR clouds from ~0 to ~100 pc,
indicating the need for additional dynamical studies.Comment: Paper prepared by emulateapj version 10/09/06 and accepted for print
in Ap
On the relation between nuclear and nucleon Structure Functions and their moments
Calculations of nuclear Structure Functions (SF) F_k^A(x,Q^2) routinely
exploit a generalized convolution, involving the SF for nucleons F_k^N and the
linking SF f^{PN,A} of a fictitious nucleus, composed of point-particles, with
the latter usually expressed in terms of hadronic degrees of freedom. For
finite Q^2 the approach seemed to be lacking a solid justification and the same
is the case for recently proposed, effective nuclear parton distribution
functions (pdf), which exactly reproduce the above-mentioned hadronically
computed F_k^A. Many years ago Jaffe and West proved the above convolution in
the Plane Wave Impulse Approximation (PWIA) for the nuclear components in the
convolution. In the present note we extend the above proof to include classes
of nuclear Final State Interactions (FSI). One and the same function appears to
relate parton distribution functions (pdf) in nuclei and nucleons, and SF for
nuclear targets and for nucleons. That relation is the previously conjectured
one,with an entirely different interpretation of f^{PN,A}. We conclude with an
extensive analysis of moments of nuclear SF based on the generalized
convolution. Characteristics of those moments are shown to be quite similar to
the same for a nucleon. We conclude that the above evidences asymptotic freedom
of a nucleon in a medium and not of a composite nucleus.Comment: 18 pages, 9 figure
Inhibition of Friend erythroleukaemia-cell tumours in vivo by a synthetic analogue of prostaglandin E2.
The effect of 16,16-dimethyl-PGE2-methyl ester (di-M-PGE2), a long-acting synthetic analogue of prostaglandin E2, on the replication of Friend erythroleukaemia cells (FLC) in vivo has been studied. Pre-treatment in vitro of both undifferentiated and differentiated FLC with di-M-PGE2 (1 microgram/ml) did not alter rates of tumour appearance or growth, but increased the median survival of DBA/2J mice. Systemic administration of di-M-PGE2 (10 microgram/mouse/day) was not toxic to the mice, but significantly inhibited tumour growth and increased median survival in mice injected s.c. with undifferentiated FLC. These effects of di-M-PGE2 were much more pronounced in mice receiving differentiated (DMSO-treated) FLC. In this latter group, the appearance of tumour was also significantly delayed by di-M-PGE2. The different effects of di-M-PGE2 treatment on tumours derived from undifferentiated and differentiated cells suggest that the analogue is acting directly on tumour-cell replication rather than on factors related to the host response
Effect of manganese doping on the size effect of lead zirconate titanate thin films and the extrinsic nature of dead layers
We have investigated the size effect in lead zirconate titanate (PZT) thin
films with a range of manganese (Mn) doping concentrations. We found that the
size effect in the conventional Pt/PZT/Pt thin-film capacitors could be
systematically reduced and almost completely eliminated by increasing Mn doping
concentration. The interfacial layer at the electrode-film interface appears to
disappear almost entirely for the PZT films with 2% Mn doping levels, confirmed
by the fits using the conventional in-series capacitor model. Our work
indicates that the size effect in ferroelectrics is extrinsic in nature,
supporting the work by Saad et al. Other implications of our results have also
been discussed. By comparing a variety of experimental studies in the
literature we propose a scenario that the dead layer between PZT (or barium
strontium titanate, BST) and metal electrodes such as Pt and Au might have a
defective pyrochlore/fluorite structure (possibly with a small portion of
ferroelectric perovskite phase).Comment: 21 pages, 6 figure
Einstein's mirror revisited
We describe a simple geometrical derivation of the formula for reflection of
light from a uniformly moving plane mirror directly from the postulates of
special relativity.Comment: 4 pages, 5 figures, RevTeX4, comments welcome; V2: corrected Fig. 5
and the discussion associated with it, co-author include
Novel Quark Fragmentation Functions and the Nucleon's Transversity Distribution
We define twist-two and twist-three quark fragmentation functions in Quantum
Chromodynamics (QCD) and study their physical implications. Using this
formalism we show how the nucleon's transversity distribution can be measured
in single pion inclusive electroproduction.Comment: 10 pages, uses PHYZZX macro package, 2 PostScript figures (added
using FIGURES). MIT-CTP-215
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