Gamma-ray emission from globular clusters

Over the last few years, the data obtained using the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope has provided new insights on high-energy processes in globular clusters, particularly those involving compact objects such as Millisecond Pulsars (MSPs). Gamma-ray emission in the 100 MeV to 10 GeV range has been detected from more than a dozen globular clusters in our galaxy, including 47 Tucanae and Terzan 5. Based on a sample of known gamma-ray globular clusters, the empirical relations between gamma-ray luminosity and properties of globular clusters such as their stellar encounter rate, metallicity, and possible optical and infrared photon energy densities, have been derived. The measured gamma-ray spectra are generally described by a power law with a cut-off at a few gigaelectronvolts. Together with the detection of pulsed gamma-rays from two MSPs in two different globular clusters, such spectral signature lends support to the hypothesis that gamma-rays from globular clusters represent collective curvature emission from magnetospheres of MSPs in the clusters. Alternative models, involving Inverse-Compton (IC) emission of relativistic electrons that are accelerated close to MSPs or pulsar wind nebula shocks, have also been suggested. Observations at >100 GeV by using Fermi/LAT and atmospheric Cherenkov telescopes such as H.E.S.S.-II, MAGIC-II, VERITAS, and CTA will help to settle some questions unanswered by current data.Comment: 11 pages, 7 figures, 2 tables, J. Astron. Space Sci., in pres

Program Design and Student Outcomes in Graduate Education

Doctoral programs in the humanities and related social sciences are characterized by high attrition and long time-to-degree. In response to these long-standing problems, the Andrew W. Mellon Foundation launched the Graduate Education Initiative (GEI) to improve the structure and organization of PhD programs, and in turn reduce attrition and shorten time-to-degree. Over a 10-year period starting in 1991, the Foundation provided a total of $80 million to 51 departments at 10 major research universities. This paper estimates the impact of the GEI on attrition rates and time-to-degree. Our analysis is based on a competing-risk duration model and student-level data spanning the start of the GEI, including data on students at a set of control departments. We estimate that, on average, the GEI had modest impacts on student outcomes in the expected directions: reducing attrition rates, reducing time-to-degree, and increasing completion rates. The overall impacts of the GEI appear to have been driven in part by reductions in cohort size, increases in financial aid, and increases in student quality

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

Investigation of CTA 1 with Suzaku Observation

We report on an 105 ks Suzaku observation of the supernova remnant CTA 1 (G119.5+10.2). The Suzaku soft X-ray observation was carried out with both timing mode and imaging mode. A ~ 10' extended feature, which is interpreted as a bow-shock component of the pulsar wind nebula (PWN), is revealed in this deep observation for the first time. The nebular spectrum can be modelled by a power-law with a photon index of ~ 1.8 which suggests a slow synchrotron cooling scenario. The photon index is approximately constant across this extended feature. We compare and discuss our observations of this complex nebula with previous X-ray investigations. We do not obtain any significant pulsation from the central pulsar in the soft (0.2-12 keV) and hard (10-60 keV) X-ray data. The non-detection is mainly due to the loss of the precise imaging ability to accurately determine the source contribution. The spectra of XIS and HXD can be directly connected without a significant spectral break according to our analysis. Future observations of NuSTAR and Astro-H would be able to resolve the contamination and provide an accurate hard X-ray measurement of CTA 1.Comment: 9 pages, 7 figures, accepted by MNRA

Using schema transformation pathways for data lineage tracing

With the increasing amount and diversity of information available on the Internet, there has been a huge growth in information systems that need to integrate data from distributed, heterogeneous data sources. Tracing the lineage of the integrated data is one of the problems being addressed in data warehousing research. This paper presents a data lineage tracing approach based on schema transformation pathways. Our approach is not limited to one specific data model or query language, and would be useful in any data transformation/integration framework based on sequences of primitive schema transformations

Extracting topological features from dynamical measures in networks of Kuramoto oscillators

The Kuramoto model for an ensemble of coupled oscillators provides a paradigmatic example of non-equilibrium transitions between an incoherent and a synchronized state. Here we analyze populations of almost identical oscillators in arbitrary interaction networks. Our aim is to extract topological features of the connectivity pattern from purely dynamical measures, based on the fact that in a heterogeneous network the global dynamics is not only affected by the distribution of the natural frequencies, but also by the location of the different values. In order to perform a quantitative study we focused on a very simple frequency distribution considering that all the frequencies are equal but one, that of the pacemaker node. We then analyze the dynamical behavior of the system at the transition point and slightly above it, as well as very far from the critical point, when it is in a highly incoherent state. The gathered topological information ranges from local features, such as the single node connectivity, to the hierarchical structure of functional clusters, and even to the entire adjacency matrix.Comment: 11 pages, 10 figure

Sistem Pelacakan dan Pengamanan Kendaraan Berbasis GPS dengan Menggunakan Komunikasi GPRS

Sistem pelacakan kendaraan berbasis GPS dengan menggunakan komunikasi GPRS (GPS based vehicle tracking and security system over GPRS) merupakan sebuah sistem dimana posisi sebuah kendaraan dapat diketahui secara pasti. Sistem pelacakan ini menggunakan teknologi GPS (Global Positioning System) untuk menentukan posisi kendaraan tersebut dan perangkat GPRS untuk berkomunikasi dengan server di Internet melalui jaringan nirkabel telepon seluler. Modul komunikasi GPRS dan perangkat GPS untuk keperluan ini menggunakan Simcom SIM908. Kendaraan yang dilengkapi dengan sebuah GPS – sistem koordinat dengan bantuan sinyal satelit dan dengan konsep trianggulasi – maka lokasi kendaraan dapat dideteksi dengan baik. Sistem GPS mengguakan prototol NMEA-0183 untuk berkomunikasi dengan mikrokontroler ATMEGA164PA dan juga sebuah modem GPRS untuk berkomunikasi dengan sebuah server basis data. Mikrokontroler ATMega164PA digunakan untuk menghubungkan system GPS (menggunakan protocol NMA-0183) dan GPRS melalui komunikasi serial TTL (UART). Mikrokontroler bertugas memilah data yang dikirimkan modul GPS untuk kemudian dikirimkan kepada server menggunakan komunikasi GPRS. Mikrokontroler melalui protokol AT+Command memerintahkan modul GSM untuk mengirimkan data-data tersebut kedalam databse server. Pengiriman data kepada server menggunakan protokol HTTP dengan metode GET yang dibangun didalam protocol TCP/IP pada layer applikasi. Koordinat lokasi kendaraan yang telah disimpan didalam database ditampilkan pada halaman web yang telah dilengkapi dengan peta (menggunakan Google Map) dan didalamnya disertai marker posisi kendaraan. Pengendara dapat memberitau keadaan darurat di kendaraan kepada operator dengan menekan tombol darurat (emergency) lebih dari dua kali dalam satu detik. Perangkat ini telah dibuat dan diimplementasikan dengan baik. Pada halaman web telah dapat ditampilkan posisi kendaraan dan informasi lain. Pada saat tombol darurat ditekan, terlihat adanya tanda darurat pada halaman web tersebut