29,508 research outputs found
Possible thermodynamic structure underlying the laws of Zipf and Benford
We show that the laws of Zipf and Benford, obeyed by scores of numerical data
generated by many and diverse kinds of natural phenomena and human activity are
related to the focal expression of a generalized thermodynamic structure. This
structure is obtained from a deformed type of statistical mechanics that arises
when configurational phase space is incompletely visited in a severe way.
Specifically, the restriction is that the accessible fraction of this space has
fractal properties. The focal expression is an (incomplete) Legendre transform
between two entropy (or Massieu) potentials that when particularized to first
digits leads to a previously existing generalization of Benford's law. The
inverse functional of this expression leads to Zipf's law; but it naturally
includes the bends or tails observed in real data for small and large rank.
Remarkably, we find that the entire problem is analogous to the transition to
chaos via intermittency exhibited by low-dimensional nonlinear maps. Our
results also explain the generic form of the degree distribution of scale-free
networks.Comment: To be published in European Physical Journal
Phase Space Models for Stochastic Nonlinear Parabolic Waves: Wave Spread and Singularity
We derive several kinetic equations to model the large scale, low Fresnel
number behavior of the nonlinear Schrodinger (NLS) equation with a rapidly
fluctuating random potential. There are three types of kinetic equations the
longitudinal, the transverse and the longitudinal with friction. For these
nonlinear kinetic equations we address two problems: the rate of dispersion and
the singularity formation.
For the problem of dispersion, we show that the kinetic equations of the
longitudinal type produce the cubic-in-time law, that the transverse type
produce the quadratic-in-time law and that the one with friction produces the
linear-in-time law for the variance prior to any singularity.
For the problem of singularity, we show that the singularity and blow-up
conditions in the transverse case remain the same as those for the homogeneous
NLS equation with critical or supercritical self-focusing nonlinearity, but
they have changed in the longitudinal case and in the frictional case due to
the evolution of the Hamiltonian
Micro-CT Characterization of Human Trabecular Bone in Osteogenesis Imperfecta
Osteogenesis imperfecta (OI) is a genetic syndrome affecting collagen synthesis and assembly. Its symptoms vary widely but commonly include bone fragility, reduced stature, and bone deformity. Because of the small size and paucity of human specimens, there is a lack of biomechanical data for OI bone. Most literature has focused on histomorphometric analyses, which rely on assumptions to extrapolate 3-D properties. In this study, a micro-computed tomography (μCT) system was used to directly measure structural and mineral properties in pediatric OI bone collected during routine surgical procedures. Surface renderings suggested a poorly organized, plate-like orientation. Patients with a history of bone-augmenting drugs exhibited increased bone volume fraction (BV/TV), trabecular number (Tb.N), and connectivity density (Eu.Conn.D). The latter two parameters appeared to be related to OI severity. Structural results were consistently higher than those reported in a previous histomorphometric study, but these differences can be attributed to factors such as specimen collection site, drug therapy, and assumptions associated with histomorphometry. Mineral testing revealed strong correlations with several structural parameters, highlighting the importance of a dual approach in trabecular bone testing. This study reports some of the first quantitative μCT data of human OI bone, and it suggests compelling possibilities for the future of OI bone assessment
A Case of Reactive Cervical Lymphadenopathy with Fat Necrosis Impinging on Adjacent Vascular Structures.
A tender neck mass in adults can be a diagnostic challenge due to a wide differential diagnosis, which ranges from reactive lymphadenopathy to malignancy. In this report, we describe a case of a young female with an unusually large and tender reactive lymph node with fat necrosis. The diagnostic imaging findings alone mimicked that of scrofula and malignancy, which prompted a complete workup. Additionally, the enlarged lymph node was compressing the internal jugular vein in the setting of oral contraceptive use by the patient, raising concern for Lemierre's syndrome or internal jugular vein thrombosis. This report shows how, in the appropriate clinical context, and especially with the involvement of adjacent respiratory or neurovascular structures, aggressive diagnostic testing can be indicated
Recent Topics on Very High Energy Gamma-ray Astronomy
With the advent of imaging atmospheric Cherenkov telescopes in late 1980's,
ground-based observation of TeV gamma-rays came into reality after struggling
trials by pioneers for twenty years, and the number of gamma-ray sources
detected at TeV energies has increased to be over seventy now. In this review,
recent findings from ground-based very-high-energy gamma-ray observations are
summarized (as of 2008 March), and up-to-date problems in this research field
are presented.Comment: 6 pages, 4 figures, Proceedings of the International Workshop on
Advances in Cosmic Ray Science, March 17-19, 2008, Waseda University, Tokyo,
Japan; to be published in Journal of the Physical Society of Japan
(supplement
Revealing hidden symmetries and gauge invariance of the massive Carroll-Field-Jackiw model
In this paper we have analyzed the improved version of the Gauge Unfixing
(GU) formalism of the massive Carroll-Field-Jackiw model, which breaks both the
Lorentz and gauge invariances, to disclose hidden symmetries to obtain gauge
invariance, the key stone of the Standard Model. In this process, as usual, we
have converted this second-class system into a first-class one and we have
obtained two gauge invariant models. We have verified that the Poisson brackets
involving the gauge invariant variables, obtained through the GU formalism,
coincide with the Dirac brackets between the original second-class variables of
the phase space. Finally, we have obtained two gauge invariant Lagrangians
where one of them represents the Stueckelberg form.Comment: revised version. To appear in Europhysics Letter
Avalanche-Induced Current Enhancement in Semiconducting Carbon Nanotubes
Semiconducting carbon nanotubes under high electric field stress (~10 V/um)
display a striking, exponential current increase due to avalanche generation of
free electrons and holes. Unlike in other materials, the avalanche process in
such 1D quantum wires involves access to the third sub-band, is insensitive to
temperature, but strongly dependent on diameter ~exp(-1/d^2). Comparison with a
theoretical model yields a novel approach to obtain the inelastic optical
phonon emission length, L_OP,ems ~ 15d nm. The combined results underscore the
importance of multi-band transport in 1D molecular wires
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