On the modelling of biological effects on morphology in estuaries and seas

Morphological modelling aims to explain and predict the changes in rivers, seas and estuaries due to these interaction. In recent history, a lot of progress has been made, especially with stability analysis approaches. However, so far only the physical interactions have been taken into account. It is known however, that biological factors are important to the dynamics of the water systems. In this paper a first step is made in the inclusion of biology into the morphodynamic models. This inclusion is based on the effect that benthic organisms have on the erodibility of the bed. This can easily be included by a change of the critical bed shear stress. These changes in the critical bed shear stress then influence the morphology. This idea has been applied to two cases. The results of the first case indicate that this approach can reproduce the influence of benthic organisms on the mud content of the bed in estuaries. The second case shows that even low numbers of organisms can influence the characteristics of large bed forms

Modelling the variability of 1ES1218+30.4

The blazar 1ES1218+30.4 has been previously detected by the VERITAS and MAGIC telescopes in the very high energies. The new detection of VERITAS from December 2008 to April 2009 proves that 1ES1218+30.4 is not static, but shows short-time variability. We show that the time variability may be explained in the context of a self-consistent synchrotron-self Compton model, while the long time observation do not necessarily require a time-resolved treatment. The kinetic equations for electrons and photons in a plasma blob are solved numerically including Fermi acceleration for electrons as well as synchrotron radiation and Compton scattering. The light curve observed by VERITAS can be reproduced in our model by assuming a changing level of electron injection compared to the constant state of 1ES1218+30.4. The multiwavelength behaviour during an outburst becomes comprehensible by the model. The long time measurements of VERITAS are still explainable via a constant emission in the SSC context, but the short outbursts each require a time-resolved treatment.Comment: 4 pages, 3 figures; accepted in A&A; AA/2010/1429

Radio Luminosities and Classificatory Criteria of BL Lacertae Objects

Using the sample of radio selected BL Lacertae objects (RBLs) and X-ray selected BL Lacertae objects (XBLs) presented by Sambruna et al. (1996), we calculated the luminosities of radio, optical and X-ray of each source and made the statistical analysis among the luminosities at different wave-bands, broad-band spectral indices from radio to X-ray ($\alpha_{\rm rx}$) and peak frequencies ($\nu_p$). Our results are as follows: (i) there is a positive correlation between radio luminosity $L_{\rm r}$ and $\alpha_{\rm rx}$ and a negative correlation between $L_{\rm r}$ and $\nu_p$. High-energy peak BL Lacs (HBLs) and low-energy peak BL Lacs (LBLs) can be distinguished very well, the dividing lines are probably those of $\log {L_{\rm r}}=43.25$ (erg/sec) and $\alpha_{\rm rx}>$(or $\leq$)0.75 for $L_{\rm r}$ - $\alpha_{\rm rx}$ plot and those of $\log {L_{\rm r}}\leq 43.25$ (erg/sec) and $\log {\nu_p}>14.7$ for the $L_{\rm r}$ - $\nu_p$ plot; (ii) there is a weak positive correlation between optical luminosity $L_o$ and $\alpha_{\rm rx}$ and a negatively weak correlation between $L_{\rm o}$ and $\nu_p$; (iii) there is no correlation between X-ray luminosity $L_X$ and $\alpha_{\rm rx}$ or between $L_X$ and $\nu_p$. From our analysis, we find that synchrotron radiation is the main X-ray radiation mechanism for HBLs while inverse Compton scattering for LBLs.Comment: 9 pages, 3 figures. Submitted to A&

Knowledge-base black holes: the next (small) big thing?

Hydraulic EngineeringCivil Engineering and Geoscience

MICROGRID RESILIENCE ANALYSIS SOFTWARE DEVELOPMENT

Military installation microgrids need to be resilient to a variety of potential disruptions (storms, attacks, et cetera). Various metrics for assessing microgrid resilience have been described in literature, and multiple tools for simulating microgrid performance have been constructed; however, it is often left to system owners and maintainers to bring these efforts together to identify and realize effective, efficient improvement strategies. Military microgrid stakeholders have expressed a desire for an integrated, unified platform that provides these multiple capabilities in a coordinated fashion. In support of these endeavors, analysis methods developed by NPS and NAVFAC Expeditionary Warfare Center researchers for measuring microgrid resilience have been integrated into an existing web-based microgrid power flow simulation and distributed energy resource rightsizing software tool. This was achieved by the development of additional functions and methods within the existing software platform code base, and expansion of the application programming interface (API). These API additions enabled access to the new calculation and analysis capabilities, as well as increased control over power flow simulation parameters. These analytical and functional contributions were validated through a design of experiments, including comparison to independently generated data, and factorial analysis.Outstanding ThesisCivilian, Department of the NavyCivilian, Department of the NavyCivilian, Department of the NavyCivilian, Department of the NavyCivilian, Department of the NavyApproved for public release. Distribution is unlimited

Radio observations of the planetary nebula around the OH/IR Star OH354.88-0.54 (V1018 Sco)

We present radio observations of the unique, recently formed, planetary nebula (PN) associated with a very long-period OH/IR variable star V1018 Sco that is unequivocally still in its asymptoticgiant branch phase. Two regions within the optical nebula are clearly detected in nonthermal radio continuum emission, with radio spectral indices comparable to those seen in colliding-wind Wolf-Rayet binaries. We suggest that these represent shocked interactions between the hot, fast stellar wind and the cold nebular shell that represents the PN's slow wind moving away from the central star. This same interface produces both synchrotron radio continuum and the optical PN emission. The fast wind is neither spherical in geometry nor aligned withany obvious optical or radio axis. We also report the detection of transient H2O maser emission in this nebula.Comment: 11 pages, LaTeX (mn2e.cls), incl. 9 PostScript (ps or eps) figures and 2 tables. Accepted by MNRA

The HRX-BL Lac sample - evolution of BL Lac objects

The unification of X-ray and radio selected BL Lacs has been an outstanding problem in the blazar research in the past years. Recent investigations have shown that the gap between the two classes can be filled with intermediate objects and that apparently all differences can be explained by mutual shifts of the peak frequencies of the synchrotron and inverse Compton component of the emission. We study the consequences of this scheme using a new sample of X-ray selected BL Lac objects comprising 104 objects with z<0.9 and a mean redshift z=0.34. 77 BL Lacs, of which the redshift could be determined for 64 (83%) objects, form a complete sample. The new data could not confirm our earlier result, drawn from a subsample, that the negative evolution vanishes below a synchrotron peak frequency log (peak-frequency) = 16.5. The complete sample shows negative evolution at the 2 sigma level ( = 0.42 +- 0.04). We conclude that the observed properties of the HRX BL Lac sample show typical behaviour for X-ray selected BL Lacs. They support an evolutionary model, in which flat-spectrum radio quasars (FSRQ) with high energetic jets evolve towards low frequency peaked (mostly radio-selected) BL Lac objects and later on to high frequency peaked (mostly X-ray selected) BL Lacs.Comment: 24 pages, 35 figures, accepted by A&