Fluctuation Properties and Polar Emission Mapping of Pulsar B0834+06 at Decameter Wavelengths

Recent results regarding subpulse-drift in pulsar B0943+10 have led to the identification of a stable system of sub-beams circulating around the magnetic axis of the star. Here, we present single-pulse analysis of pulsar B0834+06 at 35 MHz, using observations from the Gauribidanur Radio Telescope. Certain signatures in the fluctuation spectra and correlations allow estimation of the circulation time and drift direction of the underlying emission pattern responsible for the observed modulation. We use the `cartographic transform' mapping technique to study the properties of the polar emission pattern. These properties are compared with those for the other known case of B0943+10, and the implications are discussed.Comment: (v3: minor changes); 9 pages, 6 figures (11 ps files); To appear in MNRA

Topology and Polarisation of Subbeams Associated With Pulsar B0943+10's `Drifting'-Subpulse Emission: II. Analysis of Gauribidanur 35-MHz Observations

In the previous paper of this series Deshpande & Rankin (2001) reported results regarding subpulse-drift phenomenon in pulsar B0943+10 at 430 MHz and 111 MHz. This study has led to the identification of a stable system of subbeams circulating around the magnetic axis of this star. Here, we present a single-pulse analysis of our observations of this pulsar at 35 MHz. The fluctuation properties seen at this low frequency, as well as our independent estimates of the number of subbeams required and their circulation time, agree remarkably well with the reported behavior at higher frequencies. We use the `cartographic'-transform mapping technique developed in Paper-I to study the emission pattern in the polar region of this pulsar. The significance of our results in the context of radio emission mechanisms is also discussed.Comment: 6 pages, 7 figures (2 color figs), MNRAS, 326 (4), 1249-1254 (2001

ISM Simulations: An Overview of Models

Until recently the dynamical evolution of the interstellar medium (ISM) was simulated using collisional ionization equilibrium (CIE) conditions. However, the ISM is a dynamical system, in which the plasma is naturally driven out of equilibrium due to atomic and dynamic processes operating on different timescales. A step forward in the field comprises a multi-fluid approach taking into account the joint thermal and dynamical evolutions of the ISM gas.Comment: Overview paper (3 pages) presented by M. Avillez at the Special Session "Modern views of the interstellar medium", XXVIIIth IAU General Assembly, August 27-30, 2012, Beijing. Chin

Fel Oscillators with Tapered Undulators: Inclusion of Harmonic Generation and Pulse Propagation

We review the theory of FEL oscillators operating with tapered undulators. We consider the case of a uniform tapering and introduce a parameter which characterizes the effect of the tapering on the gain and on the saturation intensity. We analyze the effect of the tapering on the FEL dynamics by including the pulse propagation effects too. We analyze the importance of tapering as a tool to model the optical pulse shapes and to control the higher harmonic intensities

Strasbaugh Nonconforming Report Optimization

This paper strives to convey the problems and proposed solutions for Strasbaugh’s Nonconforming Report (NCR) Optimization. Strasbaugh is a world leader in silicon wafer polisher and grinder technologies. After a significant down size to the company parts they used to manufacture now have to be purchased, and many of these incoming parts do not conform to Strasbaugh’s high standards. This has led to an increase in NCRs that need to be processed, which takes up time, resources and money. The objective therefore became to update the multi-sheet carbon copy paper system to better optimize the use of these reports and get to the root cause of the issue. This was done using Microsoft Access (per clients request) as a low cost solution with a quick implementation period. Higher cost web-based server solutions were also proposed for future use. The design of the database is simple, sleek and user friendly. The main menu gives options to view the percentage breakdown report, search for potential trends in NCR’s, export NCR entries to an excel file, as well as track trends to find faulty suppliers or other major issues. In addition to the database, three flowcharts were created to document the process for current employee use and aid in training future employees. Lastly, a cost breakdown was done to show Strasbaugh that by using the new procedure they would be able to save money in the long term. Ideally, Strasbaugh would be able to identify root causes by using the database and completely eliminating all NCRs. Realistically, they will be able to reduce somewhere between 25% and 50% of their NCRs. In reducing 25% Strasbaugh would save $11,250 in overtime caused by rework and$1,502.40 in time the Quality Engineer can spend doing someone else or even towards solving the root causes. With a 50% reduction, the savings would double. As Strasbaugh has more money and resources they can dedicate to improving this process, they can begin using a web-based server. This will allow them to easily send data within the company, input NCRs from multiple locations, and generate more in depth reports for management. With a web-based server, an administrative account could also be created so not all information is accessible and only the administrator will have editing capabilities. The following report will give a detailed analysis of the processes used and the end deliverables to be given to the client

Superradiant Undulator Radiation for Selective THz Control Experiments at XFELs

The generation of frequency-tunable, narrow-bandwidth and carrier-envelope-phase stable THz pulses with fields in the MV/cm regime that can be appropriately timed to the femtosecond X-ray pulses from free-electron-lasers is of highest scientific interest. It will enable to follow the electronic and structural dynamics stimulated by (non)linear selective excitations of matter on few femtosecond time and {\AA}ngstrom length scales. In this article, a scheme based on superradiant undulator radiation generated just after the XFEL is proposed. The concept utilizes cutting edge superconducting undulator technology and provides THz pulses in a frequency range between 3 and 30 THz with exceptional THz pulse energies. Relevant aspects for realization and operation are discussed point by point on the example of the European XFEL

ISM simulations: an overview of models

Until recently the dynamical evolution of the interstellar medium (ISM) was simu- lated using collisional ionization equilibrium (CIE) conditions. However, the ISM is a dynamical system, in which the plasma is naturally driven out of equilibrium due to atomic and dynamic processes operating on different timescales. A step forward in the field comprises a multi-fluid approach taking into account the joint thermal and dynamical evolutions of the ISM gas

Drifting subpulses and inner acceleration regions in radio pulsars

The classical vacuum gap model of Ruderman & Sutherland, in which spark-associated subbeams of subpulse emission circulate around the magnetic axis due to the EB drift, provides a natural and plausible physical mechanism of the subpulse drift phenomenon. Recent progress in the analysis of drifting subpulses in pulsars has provided a strong support to this model by revealing a number of subbeams circulating around the magnetic axis in a manner compatible with theoretical predictions. However, a more detailed analysis revealed that the circulation speed in a pure vacuum gap is too high when compared with observations. Moreover, some pulsars demonstrate significant time variations of the drift rate, including a change of the apparent drift direction, which is obviously inconsistent with the EB drift scenario in a pure vacuum gap. We resolved these discrepancies by considering a partial flow of iron ions from the positively charged polar cap, coexisting with the production of outflowing electron-positron plasmas. By fitting the observationally deduced drift-rates to the theoretical values, we managed to estimate polar cap surface temperatures in a number of pulsars. The estimated surface temperatures correspond to a small charge depletion of the order of a few percent of the corotational charge density. We also argue that if the thermionic electron outflow from the surface of a negatively charged polar cap is slightly below the Goldreich-Julian density, then the resulting small charge depletion will have similar consequences as in the case of the ions outflow. We thus believe that the sparking discharge of a partially shielded acceleration potential drop occurs in all pulsars, with both positively (``pulsars'') and negatively (``anti-pulsars'') charged polar caps

Electron Distribution in the Galactic Disk - Results From a Non-Equilibrium Ionization Model of the ISM

Using three-dimensional non-equilibrium ionization (NEI) hydrodynamical simulation of the interstellar medium (ISM), we study the electron density, $n_{e}$, in the Galactic disk and compare it with the values derived from dispersion measures towards pulsars with known distances located up to 200 pc on either side of the Galactic midplane. The simulation results, consistent with observations, can be summarized as follows: (i) the DMs in the simulated disk lie between the maximum and minimum observed values, (ii) the log derived from lines of sight crossing the simulated disk follows a Gaussian distribution centered at \mu=-1.4 with a dispersion \sigma=0.21, thus, the Galactic midplane =0.04\pm 0.01$cm$^{-3}$, (iii) the highest electron concentration by mass (up to 80%) is in the thermally unstable regime (200<T<10^{3.9} K), (iv) the volume occupation fraction of the warm ionized medium is 4.9-6%, and (v) the electrons have a clumpy distribution along the lines of sight.Comment: Letter accepted for publication in Monthly Notices of the Royal Astronomical Societ