Spectra of Modular Random Graphs

We compute spectra of symmetric random matrices defined on graphs exhibiting a modular structure. Modules are initially introduced as fully connected sub-units of a graph. By contrast, inter-module connectivity is taken to be incomplete. Two different types of inter-module connectivity are considered, one where the number of intermodule connections per-node diverges, and one where this number remains finite in the infinite module-size limit. In the first case, results can be understood as a perturbation of a superposition of semicircular spectral densities one would obtain for uncoupled modules. In the second case, matters can be more involved, and depend in detail on inter-module connectivities. For suitable parameters we even find near-triangular shaped spectral densities, similar to those observed in certain scale-free networks, in a system of consisting of just two coupled modules. Analytic results are presented for the infinite module-size limit; they are well corroborated by numerical simulations.Comment: 16 pages, 4 figures. to appear in J. Phys.

Growing random networks with fitness

Three models of growing random networks with fitness dependent growth rates are analysed using the rate equations for the distribution of their connectivities. In the first model (A), a network is built by connecting incoming nodes to nodes of connectivity $k$ and random additive fitness $\eta$, with rate $(k-1)+ \eta$. For $\eta >0$ we find the connectivity distribution is power law with exponent $\gamma=+2$. In the second model (B), the network is built by connecting nodes to nodes of connectivity $k$, random additive fitness $\eta$ and random multiplicative fitness $\zeta$ with rate $\zeta(k-1)+\eta$. This model also has a power law connectivity distribution, but with an exponent which depends on the multiplicative fitness at each node. In the third model (C), a directed graph is considered and is built by the addition of nodes and the creation of links. A node with fitness $(\alpha, \beta)$, $i$ incoming links and $j$ outgoing links gains a new incoming link with rate $\alpha(i+1)$, and a new outgoing link with rate $\beta(j+1)$. The distributions of the number of incoming and outgoing links both scale as power laws, with inverse logarithmic corrections

Tail index estimation: quantile driven threshold selection

The selection of upper order statistics in tail estimation is notoriously difficult. Most methods are based on asymptotic arguments, like minimizing the asymptotic mse, that do not perform well in finite samples. Here we advance a data driven method that minimizes the maximum distance between the fitted Pareto type tail and the observed quantile. To analyse the finite sample properties of the metric we organize a horse race between the other methods. In most cases the finite sample based methods perform best. To demonstrate the economic relevance of choosing the proper methodology we use daily equity return data from the CRSP database and find economic relevant variation between the tail index estimates

Observations of whistler mode waves with nonlinear parallel electric fields near the dayside magnetic reconnection separatrix by the Magnetospheric Multiscale mission

We show observations from the Magnetospheric Multiscale (MMS) mission of whistler mode waves in the Earth's low-latitude boundary layer (LLBL) during a magnetic reconnection event. The waves propagated obliquely to the magnetic field toward the X line and were confined to the edge of a southward jet in the LLBL. Bipolar parallel electric fields interpreted as electrostatic solitary waves (ESW) are observed intermittently and appear to be in phase with the parallel component of the whistler oscillations. The polarity of the ESWs suggests that if they propagate with the waves, they are electron enhancements as opposed to electron holes. The reduced electron distribution shows a shoulder in the distribution for parallel velocities between 17,000 and 22,000 km/s, which persisted during the interval when ESWs were observed, and is near the phase velocity of the whistlers. This shoulder can drive Langmuir waves, which were observed in the high-frequency parallel electric field data

Electron beam induced radio emission from ultracool dwarfs

We present the numerical simulations for an electron-beam-driven and loss-cone-driven electron-cyclotron maser (ECM) with different plasma parameters and different magnetic field strengths for a relatively small region and short time-scale in an attempt to interpret the recent discovered intense radio emission from ultracool dwarfs. We find that a large amount of electromagnetic field energy can be effectively released from the beam-driven ECM, which rapidly heats the surrounding plasma. A rapidly developed high-energy tail of electrons in velocity space (resulting from the heating process of the ECM) may produce the radio continuum depending on the initial strength of the external magnetic field and the electron beam current. Both significant linear polarization and circular polarization of electromagnetic waves can be obtained from the simulations. The spectral energy distributions of the simulated radio waves show that harmonics may appear from 10 to 70$\nu_{\rm pe}$ ($\nu_{\rm pe}$ is the electron plasma frequency) in the non-relativistic case and from 10 to 600$\nu_{\rm pe}$ in the relativistic case, which makes it difficult to find the fundamental cyclotron frequency in the observed radio frequencies. A wide frequency band should therefore be covered by future radio observations.Comment: 10 pages, 19 figures, accepted for publication in the Astrophysical Journa

Acinic Cell Carcinoma of the Lower Lip: a Case Report

Karcinom acinusnih stanica rijetka je bolest – to je tumor žlijezda slinovnica niskog stupnja malignosti. Najčešće se nalazi u velikim žlijezdama slinovnicama, gotovo uvijek u parotidnoj žlijezdi, a rijetko u malim žlijezdama slinovnicama. U ovom opisu predstavljamo slučaj muškarca u dobi od 64 godine s perzistentnom dvogodišnjom oteklinom u sluznici donje usnice u ravnini očnjaka. Lezija je bila bezbolna, meke teksture, nalikovala je na mukokelu, bila je veličine 1x1,5 cm te pokrivena sluznicom normalne boje. Kirurški je uklonjena te je histopatološki potvrđen karcinom acinusnih stanica.Acinic cell carcinoma is a rare, low grade malignant tumor of the salivary glands. Most frequently it originates from major salivary glands almost exclusively in parotid gland and rarely from minor salivary glands. In this report we present a case of 64-year-old man with a persistent swelling within the mucosa of the lower lip at the line of the canine tooth for two years. The lesion was painless, soft in texture, mimicked a mucocel and had the dimensions of 1x1.5 cm with an overlying mucosa normal in color. Surgical excision of the lesion is performed and histopathological confirmation revealed acinic cell carcinoma

Spectral density of random graphs with topological constraints

The spectral density of random graphs with topological constraints is analysed using the replica method. We consider graph ensembles featuring generalised degree-degree correlations, as well as those with a community structure. In each case an exact solution is found for the spectral density in the form of consistency equations depending on the statistical properties of the graph ensemble in question. We highlight the effect of these topological constraints on the resulting spectral density.Comment: 24 pages, 6 figure

A Mini-survey of Ultracool Dwarfs at 4.9 GHz

A selection of ultracool dwarfs are known to be radio active, with both gyrosynchrotron emission and the electron cyclotron maser instability being given as likely emission mechanisms. To explore whether ultracool dwarfs previously undetected at 8.5 GHz may be detectable at a lower frequency. We select a sample of fast rotating ultracool dwarfs with no detectable radio activity at 8.5 GHz, observing each of them at 4.9 GHz. From the 8 dwarfs in our sample, we detect emission from 2MASS J07464256+2000321, with a mean flux level of 286 $\pm$ 24 $\mu Jy$. The light-curve of 2MASS J07464256+2000321, is dominated towards the end of the observation by a very bright, $\approx$100 % left circularly polarized burst during which the flux reached 2.4 mJy. The burst was preceded by a raise in the level of activity, with the average flux being $\approx$ 160 $\mu Jy$ in the first hour of observation rising to $\approx$ 400 $\mu Jy$ in the 40 minutes before the burst. During both periods, there is significant variability. The detection of 100% circular polarization in the emission at 4.9 GHz points towards the electron cyclotron maser as the emission mechanism. However, the observations at 4.9 GHz and 8.5 GHz were not simultaneous, thus the actual fraction of dwarfs capable of producing radio emission, as well as the fraction of those that show periodic pulsations is still unclear, as indeed are the relative roles played by the electron cyclotron maser instability versus gyrosynchrotron emission, therefore we cannot assert if the previous non-detection at 8.5 GHz was due to a cut-off in emission between 4.9 and 8.4 GHz, or due to long term variability

Laparoscopic Splenectomy in Children

BACKGROUND: Laparoscopic splenectomy is being performed more commonly in children, although its advantages are not clear. We sought to determine whether laparoscopic splenectomy was superior to open splenectomy. METHODS: The records of all pediatric patients undergoing splenectomy without significant comorbidities over a 12-year period were examined. The patients were divided into those undergoing laparoscopic splenectomy and those undergoing open splenectomy. Demographics, operative time, estimated blood loss, spleen size, length of stay, and total charges were compared between the groups. RESULTS: Eighty-one (58%) children underwent laparoscopic splenectomy, and 59 (42%) children underwent open splenectomy. The groups were similar in age and sex; hereditary spherocytosis was more common in the LS group. Operating time was longer in the laparoscopic splenectomy group (231 +/- 10 min vs 138 +/- 9 min; P\u3c0.001), but blood loss and complication rates were similar. Twelve (15%) conversions were necessary primarily due to spleen size. Although children undergoing LS had a shorter length of stay (2.4 +/- 0.1 vs 4.1 +/- 0.3 days; P\u3c0.001), they incurred higher charges (dollars 21199 +/- 664 vs dollars 15723 +/- 1737; P\u3c0.002). CONCLUSION: Laparoscopic splenectomy is a safe procedure in children, resulting in shorter hospital stay, which may translate into earlier return to activity and a smaller burden on the child\u27s caretakers