Quasi-TEM modes in rectangular waveguides: a study based on the properties of PMC and hard surfaces

Hard surfaces or magnetic surfaces can be used to propagate quasi-TEM modes inside closed waveguides. The interesting feature of these modes is an almost uniform field distribution inside the waveguide. But the mechanisms governing how these surfaces act, how they can be characterized, and further how the modes propagate are not detailed in the literature. In this paper, we try to answer these questions. We give some basic rules that govern the propagation of the quasi-TEM modes, and show that many of their characteristics (i.e. their dispersion curves) can be deduced from the simple analysis of the reflection properties of the involved surfaces

Non-singular arbitrary cloaks dressing three-dimensional anisotropic obstacles

We design three dimensional electromagnetic cloaks, starting from a small region of complex shape instead of a point. We derive the expression of a transformation matrix describing an objet with a surface of revolution and its associated non-singular cloak. We note that while none of the eigenvalues vanish inside the cloak, they suffer a discontinuity on its inner surface. Moreover, all three eigenvalues are independent upon the radius in the concealed object. The validity of our analytical results is confirmed by finite edge-elements computations showing scattering is much reduced when the object is dressed with the cloak. We note that neither the object nor the cloak are invisible on their own.Comment: 7 pages, 4 figure

The enigmatic core L1451-mm: a first hydrostatic core? or a hidden VeLLO?

We present the detection of a dust continuum source at 3-mm (CARMA) and 1.3-mm (SMA), and 12CO(2-1) emission (SMA) towards the L1451-mm dense core. These detections suggest a compact object and an outflow where no point source at mid-infrared wavelengths is detected using Spitzer. An upper limit for the dense core bolometric luminosity of 0.05 Lsun is obtained. By modeling the broadband SED and the continuum interferometric visibilities simultaneously, we confirm that a central source of heating is needed to explain the observations. This modeling also shows that the data can be well fitted by a dense core with a YSO and disk, or by a dense core with a central First Hydrostatic Core (FHSC). Unfortunately, we are not able to decide between these two models, which produce similar fits. We also detect 12CO(2-1) emission with red- and blue-shifted emission suggesting the presence of a slow and poorly collimated outflow, in opposition to what is usually found towards young stellar objects but in agreement with prediction from simulations of a FHSC. This presents the best candidate, so far, for a FHSC, an object that has been identified in simulations of collapsing dense cores. Whatever the true nature of the central object in L1451-mm, this core presents an excellent laboratory to study the earliest phases of low-mass star formation.Comment: 15 pages, 9 figures, emulateapj. Accepted by Ap

Intravital Imaging of Cellular Response due to Traumatic Brain Injury Using Confocal Microscopy

Introduction: Cellular reaction to traumatic brain injury is complex and involves considerable interactions between cells and reactivity to foreign bodies. Our objective was to assess neurons, microglia, astrocytes, and intracellular Ca2+ signaling by creating a novel confocal microscopy technique involving an air immersed lens that does not sacrifice resolution and limits signal attenuation. This study aimed to create a consistent dynamic methodology to observe the cortical cellular response using real-time intravital imaging as trauma is being induced. Methods: Once surgical plane was achieved, rodent cortices were exposed via craniotomy and blunt insertion with a silicone shunt catheter into the lateral ventricle was performed at a controlled rate. Neurons, microglia, astrocytes, and intracellular Ca+2signaling were fluorescently tagged with DiD (4-chlorobenzenesulfonate), tomato lectin from lycopersicon esculentum, sulforhodamine B, and Cal 520 AM, respectively. Activity tracking of fluorescently tagged markers 700 microns from blunt insertion TBI was performed using upright resonant scanning confocal microscopy. Results: Neurons, microglia, astrocytes, and Ca2+ signaling were identified at a depth of 100 microns from the meninges. Gross movement of cells was visualized during shunting by identifying specific cells and tracking movement over time. Preliminary data shows that astrocytes are in closest proximity to the inserted shunt catheter. Conclusion: This novel method identified cell types and tracked gross movement. Although preliminary data and other post-hoc studies indicate primarily astrocytic involvement, it shows that we can successfully record immediate cell involvement around the shunt catheter for the first time. Future studies will improve cellular tracking and imaging resolution

Long-term Evolution of Protostellar and Protoplanetary Disks. I. Outbursts

As an initial investigation into the long-term evolution of protostellar disks, we explore the conditions required to explain the large outbursts of disk accretion seen in some young stellar objects. We use one-dimensional time-dependent disk models with a phenomenological treatment of the magnetorotational instability (MRI) and gravitational torques to follow disk evolution over long timescales. Comparison with our previous two-dimensional disk model calculations (Zhu et al. 2009b, Z2009b) indicates that the neglect of radial effects and two-dimensional disk structure in the one-dimensional case makes only modest differences in the results; this allows us to use the simpler models to explore parameter space efficiently. We find that the mass infall rates typically estimated for low-mass protostars generally result in AU-scale disk accretion outbursts, as predicted by our previous analysis (Zhu et al. 2009a,Z2009a). We also confirm quasi-steady accretion behavior for high mass infall rates if the values of $\alpha$-parameter for the magnetorotational instability is small, while at this high accretion rate convection from the thermal instability may lead to some variations. We further constrain the combinations of the $\alpha$-parameter and the MRI critical temperature, which can reproduce observed outburst behavior. Our results suggest that dust sublimation may be connected with full activation of the MRI. This is consistent with the idea that small dust captures ions and electrons to suppress the MRI. In a later paper we will explore both long-term outburst and disk evolution with this model, allowing for infall from protostellar envelopes with differing angular momenta.Comment: Accepted to publish in Ap

A statistical study of the mass and density structure of Infrared Dark Clouds

How and when the mass distribution of stars in the Galaxy is set is one of the main issues of modern astronomy. Here we present a statistical study of mass and density distributions of infrared dark clouds (IRDCs) and fragments within them. These regions are pristine molecular gas structures and progenitors of stars and so provide insights into the initial conditions of star formation. This study makes use of a IRDC catalogue (Peretto & Fuller 2009), the largest sample of IRDC column density maps to date, containing a total of ~11,000 IRDCs with column densities exceeding N_{H2} = 1 X10^{22} cm^{-2} and over 50,000 single peaked IRDC fragments. The large number of objects constitutes an important strength of this study, allowing detailed analysis of the completeness of the sample and so statistically robust conclusions. Using a statistical approach to assigning distances to clouds, the mass and density distributions of the clouds and the fragments within them are constructed. The mass distributions show a steepening of the slope when switching from IRDCs to fragments, in agreement with previous results of similar structures. IRDCs and fragments are divided into unbound/bound objects by assuming Larson's relation and calculating their virial parameter. IRDCs are mostly gravitationally bound, while a significant fraction of the fragments are not. The density distribution of gravitationally unbound fragments shows a steep characteristic slope. (see paper for full Abstract).Comment: 15 pages, accepted for publication in Ap

Park and ride: Lessons from the UK experience

Park and Ride schemes using dedicated bus services have become particularly popular over the last 40 years with UK policymakers. This popularity can largely be attributed to the UK policy context and the advocating of Park and Ride to tackle increasing car use, congestion and traffic-related emissions. The aim of this paper is to use existing evidence on the degree to which this has been achieved and provide lessons on how bus-based Park and Ride can be used effectively. From this, lessons are provided that will benefit stakeholders internationally on the use of dedicated link-mode Park and Ride schemes operating at the edge of urban areas. It is found that although Park and Ride has been popular amongst motorists, it has also attracted users of existing public transport services and has generated additional trips, resulting in a counter-productive effect. It is concluded that for Park and Ride to be successful, it should be implemented in tandem with other supply-side measures and alongside sufficiently rigorous restraint instruments. Also, despite the use of frequent and dedicated bus-link services providing a key feature that attracts motorists who would not otherwise use public transport, their use needs to be carefully monitored to avoid low load-factors decreasing levels of efficiency