Mechanisms of Ar release from Himalayan metamorphic hornblende

Changes in hornblende samples that occur during stepwise 39Ar/40Ar analysis were studied experimentally and mineralogically. A complex succession of reactions was seen (hornblende ~ oxyhornblende ~ clinopyroxene-structured phase ~ fine-grained reaction products ~ glasses) in the temperature range 750-1300 °C. The release of Ar from hornblende in the vacuum furnace appeared to occur by fundamentally different processes from those resulting in Ar loss during metamorphism. Simple diffusional interpretations of the release patterns are, therefore, not capable of revealing the thermal history of samples. In principle, some useful information may be obtained if long-standing fractures andother defects control both natural Ar loss and mineral reactions within the laboratory

UV emission from young and middle-aged pulsars: Connecting X-rays with the optical

We present the UV spectroscopy and timing of three nearby pulsars (Vela, B0656+14 and Geminga) recently observed with the Space Telescope Imaging Spectrograph. We also review the optical and X-ray properties of these pulsars and establish their connection with the UV properties. We show that the multiwavelengths properties of neutron stars (NSs) vary significantly within the sample of middle-aged pulsars. Even larger differences are found between the thermal components of Ge-minga and B0656+14 as compared to those of radio-quiet isolated NSs. These differences could be attributed to different properties of the NS surface layers.Comment: To appear in Astrophysics and Space Science, Proceedings of "Isolated Neutron Stars: from the Interior to the Surface", eds. D. Page, R. Turolla and S. Zane; 10 pages, 4 figures, 3 table

Context-Aware Multifactor Authentication Based on Dynamic Pin

An innovative context-aware multi-factor authentication scheme based on a dynamic PIN is presented. The scheme is based on graphical passwords where a challenge is dynamically produced based on contextual factors and client device constraints while balancing security assurance and usability. The approach utilizes a new methodology where the cryptographic transformation used to produce the Dynamic PIN changes dynamically based on the user input, history of authentications, and available authentication factors at the client device