A Meaningful MD5 Hash Collision Attack

It is now proved by Wang et al., that MD5 hash is no more secure, after they proposed an attack that would generate two different messages that gives the same MD5 sum. Many conditions need to be satisfied to attain this collision. Vlastimil Klima then proposed a more efficient and faster technique to implement this attack. We use these techniques to first create a collision attack and then use these collisions to implement meaningful collisions by creating two different packages that give identical MD5 hash, but when extracted, each gives out different files with contents specified by the atacker

Atypical presentation of visceral leishmaniasis from non-endemic region

A case of atypical and acute presentation of visceral leishmaniasis from non-endemic region, characterised by exudative pleural effusion and hepatitis is reporte

Coronal Structure and Abundances in Young Fast Rotators

AB Dor, Speedy Mic and Rst137B are in their early post-T Tauri evolutionary phase (<100Myr), at the age of fastest rotation in the life of late-type stars. They straddle the coronal saturation-supersaturation boundary first defined by young stars in open clusters. High resolution Chandra X-ray spectra have been analysed to study their coronal properties as a function of coronal activity parameters Rossby number, $L_X/L_{bol}$ and a coronal temperature index. Plasma emission measure distributions as a function of temperature show broad peaks at T~10e7K. Differences between stars suggest that as supersaturation is reached the DEM slope below the temperature of peak DEM becomes shallower, while the DEM drop-off above this temperature becomes more pronounced. A larger sample comprising our three targets and 22 active stars studied in the recent literature reveals a general increase of plasma at T>10e7 toward the saturated-supersaturated boundary but a decline beyond this among supersaturated stars. All three of the stars studied in detail here show lower coronal abundances of the low FIP elements Mg, Si and Fe, relative to the high FIP elements S, O and Ne, as compared to the solar mixture. The coronal Fe abundances of the stellar sample are inversely correlated with Lx/Lbol, declining slowly with rising Lx/Lbol, but with a much more sharp decline at Lx/Lbol>3x10e-4. For dwarfs the Fe abundance is also well-correlated with Rossby number. The coronal O/Fe ratios for dwarfs show a clear increase with decreasing Rossby number, apparently reaching saturation at [O/Fe]=0.5 at the coronal supersaturation boundary. Similar increases in O/Fe with increasing coronal temperature and $L_X/L_{bol}$ are seen.Comment: 22 pages, 8 figures, 6 tables. Accepted by Ap

PyCARL: A PyNN Interface for Hardware-Software Co-Simulation of Spiking Neural Network

We present PyCARL, a PyNN-based common Python programming interface for hardware-software co-simulation of spiking neural network (SNN). Through PyCARL, we make the following two key contributions. First, we provide an interface of PyNN to CARLsim, a computationally-efficient, GPU-accelerated and biophysically-detailed SNN simulator. PyCARL facilitates joint development of machine learning models and code sharing between CARLsim and PyNN users, promoting an integrated and larger neuromorphic community. Second, we integrate cycle-accurate models of state-of-the-art neuromorphic hardware such as TrueNorth, Loihi, and DynapSE in PyCARL, to accurately model hardware latencies that delay spikes between communicating neurons and degrade performance. PyCARL allows users to analyze and optimize the performance difference between software-only simulation and hardware-software co-simulation of their machine learning models. We show that system designers can also use PyCARL to perform design-space exploration early in the product development stage, facilitating faster time-to-deployment of neuromorphic products. We evaluate the memory usage and simulation time of PyCARL using functionality tests, synthetic SNNs, and realistic applications. Our results demonstrate that for large SNNs, PyCARL does not lead to any significant overhead compared to CARLsim. We also use PyCARL to analyze these SNNs for a state-of-the-art neuromorphic hardware and demonstrate a significant performance deviation from software-only simulations. PyCARL allows to evaluate and minimize such differences early during model development.Comment: 10 pages, 25 figures. Accepted for publication at International Joint Conference on Neural Networks (IJCNN) 202

Influence of Coronal Abundance Variations

The PI of this project was Jeff Scargle of NASA/Ames. Co-I's were Alma Connors of Eureka Scientific/Wellesley, and myself. Part of the work was subcontracted to Eureka Scientific via SAO, with Vinay Kashyap as PI. This project was originally assigned grant number NCC2-1206, and was later changed to NCC2-1350 for administrative reasons. The goal of the project was to obtain, derive, and develop statistical and data analysis tools that would be of use in the analyses of high-resolution, high-sensitivity data that are becoming available with new instruments. This is envisioned as a cross-disciplinary effort with a number of "collaborators" including some at SA0 (Aneta Siemiginowska, Peter Freeman) and at the Harvard Statistics department (David van Dyk, Rostislav Protassov, Xiao-li Meng, Epaminondas Sourlas, et al). We have developed a new tool to reliably measure the metallicities of thermal plasma. It is unfeasible to obtain high-resolution grating spectra for most stars, and one must make the best possible determination based on lower-resolution, CCD-type spectra. It has been noticed that most analyses of such spectra have resulted in measured metallicities that were significantly lower than when compared with analyses of high- resolution grating data where available (see, e.g., Brickhouse et al., 2000, ApJ 530,387). Such results have led to the proposal of the existence of so-called Metal Abundance Deficient, or "MAD" stars (e.g., Drake, J.J., 1996, Cool Stars 9, ASP Conf.Ser. 109, 203). We however find that much of these analyses may be systematically underestimating the metallicities, and using a newly developed method to correctly treat the low-counts regime at the high-energy tail of the stellar spectra (van Dyk et al. 2001, ApJ 548,224), have found that the metallicities of these stars are generally comparable to their photospheric values. The results were reported at the AAS (Sourlas, Yu, van Dyk, Kashyap, and Drake, 2000, BAAS 196, v32, #54.02), and at the conference on Statistical Challenges in Modem Astronomy (Sourlas, van Dyk, Kashyap, Drake, and Pease, 2003, SCMA 111, Eds. E.D.Feigelson, G.J.Babu, New York:Springer, p489-490). We also described the limitations of one of the most egregiously misused and misapplied statistical tests in astrophysical literature, the F-test for verifying model components (Protassov, van Dyk, Connors, Kashyap, and Siemiginowska, 2002, ApJ, 571,545). Indeed, a search through the ApJ archives turned up 170 papers in the 5 previous years that used the F-test explicitly in some form or the other, and with the vast majority of them not using it correctly! Indeed, looking at just 4 issues of the ApJ in 2001, we found 13 instances of its use, of which nine were demonstrably incorrect. Clearly, it is difficult to understate the importance of this issue. We also worked on speeding up Bayes Blocks and Sparse Bayes Blocks algorithms to make them more tractable for large searches. We also supported staistics students and postdocs in both explicit physics- model-based (spectra with tens of thousands of atomic lines) and "model-free" -- i.e. non-parametric or semi-parametric -- algorithms. Work on using more of the latter is just beginning; while using multi-scale methods for Poisson imaging has come to hition. In fact, "An Image Restoration Technique with Error Estimates", by D. Esch, A. Connors, M. Karovska, and D. van Dyk, was published by ApJ (Esch et a1.2004, ApJ, 610, 1213). The code has been delivered to M. Karovska for CXC; and is available for beta-testing upon request. The other large project we worked on was on the self-consistent modeling of logN-logs curves in the Poisson limit. logN-logs curves are a fundamental tool in the study of source populations, luminosity functions, and cosmological parameters. However, their determination is hampered by statistical effects such as the Eddington bias, incompleteness due to detection efficiency, faint source flux fluctuations, etc. We have develed a new and powerful method using the full Poisson machinery that allows us to model the logN-logs distribution of X-ray sources in a self-consistent manner. Because we properly account for all the above statistical effects, our modeling is valid over the full range of the data, and not just for strong sources, as is normally done. Using a Bayesian approach and modeling the fluxes with known functional forms such as simple or broken power-laws, and conditioning the expected photon counts on the fluxes, the background contamination, effective area, detector vignetting, and detection probability, we can delve deeply into the low counts regime and extend the usefulness of medium sensitivity surveys such as ChAMP by orders of magnitude. The built-in flexibility of the algorithm also allows a simultaneous analysis of multiple datasets. We have applied this analysis to a set a Chandra observations (Sourlas, Kashyap, Zezas, van Dyk, 2004, HEAD #8, #16.32

Dynamical Casimir Effect in Optically Modulated Cavities

Cavities with periodically oscillating mirrors have been predicted to excite photon pairs out of the quantum vacuum in a process known as the Dynamical Casimir effect. Here we propose and analyse an experimental layout that can provide an efficient modulation of the effective optical length of a cavity mode in the near-infrared spectral region. An analytical model of the dynamical Casimir emission is developed and compared to the predictions of a direct numerical solution of Maxwell's equations in real time. A sizeable intensity of dynamical Casimir emission is anticipated for realistic operating parameters. In the presence of an external coherent seed beam, we predict amplification of the seed beam and the appearance of an additional phase-conjugate beam as a consequence of stimulated dynamical Casimir processes.Comment: 6 pages, 5 figure

Deposing the Cool Corona of KPD 0005+5106

The ROSAT PSPC pulse height spectrum of the peculiar He-rich hot white dwarf KPD 0005+5106 provided a great surprise when first analysed by Fleming, Werner & Barstow (1993). It defied the best non-LTE modelling attempts in terms of photospheric emission from He-dominated atmospheres including C, N and O and was instead interpreted as the first evidence for a coronal plasma around a white dwarf. We show here that a recent high resolution Chandra LETGS spectrum has more structure than expected from a thermal bremsstrahlung continuum and lacks the narrow lines of H-like and He-like C expected from a coronal plasma. Moreover, a coronal model requires a total luminosity more than two orders of magnitude larger than that of the star itself. Instead, the observed 20-80 AA flux is consistent with photospheric models containing trace amounts of heavier elements such as Fe. The soft X-ray flux is highly sensitive to the adopted metal abundance and provides a metal abundance diagnostic. The weak X-ray emission at 1 keV announced by O'Dwyer et al (2003) instead cannot arise from the photosphere and requires alternative explanations. We echo earlier speculation that such emission arises in a shocked wind. Despite the presence of UV-optical O VIII lines from transitions between levels n=7-10, no X-ray O VIII Ly alpha flux is detected. We show that O VIII Lyman photons can be trapped by resonant scattering within the emitting plasma and destroyed by photoelectric absorption.Comment: 15 Pages, 4 figures. Accepted for the Astrophysical Journa

Effect of an atom on a quantum guided field in a weakly driven fiber-Bragg-grating cavity

We study the interaction of an atom with a quantum guided field in a weakly driven fiber-Bragg-grating (FBG) cavity. We present an effective Hamiltonian and derive the density-matrix equations for the combined atom-cavity system. We calculate the mean photon number, the second-order photon correlation function, and the atomic excited-state population. We show that, due to the confinement of the guided cavity field in the fiber cross-section plane and in the space between the FBG mirrors, the presence of the atom in the FBG cavity can significantly affect the mean photon number and the photon statistics even though the cavity finesse is moderate, the cavity is long, and the probe field is weak.Comment: Accepted for Phys. Rev.

FK Comae Berenices, King of Spin: The COCOA-PUFS Project

COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast spinning, heavily spotted, yellow giant FK Com (HD117555; G4 III). This single star is thought to be a recent binary merger, and is exceptionally active by measure of its intense ultraviolet and X-ray emissions, and proclivity to flare. COCOA-PUFS was carried out with Hubble Space Telescope in the UV (120-300 nm), using mainly its high-performance Cosmic Origins Spectrograph, but also high-precision Space Telescope Imaging Spectrograph; Chandra X-ray Observatory in the soft X-rays (0.5-10 keV), utilizing its High-Energy Transmission Grating Spectrometer; together with supporting photometry and spectropolarimetry in the visible from the ground. This is an introductory report on the project. FK Com displayed variability on a wide range of time scales, over all wavelengths, during the week-long main campaign, including a large X-ray flare; "super-rotational broadening" of the far-ultraviolet "hot-lines" (e.g., Si IV 139 nm (T~80,000 K) together with chromospheric Mg II 280 nm and C II 133 nm (10,000-30,000 K); large Doppler swings suggestive of bright regions alternately on advancing and retreating limbs of the star; and substantial redshifts of the epoch-average emission profiles. These behaviors paint a picture of a highly extended, dynamic, hot (10 MK) coronal magnetosphere around the star, threaded by cooler structures perhaps analogous to solar prominences, and replenished continually by surface activity and flares. Suppression of angular momentum loss by the confining magnetosphere could temporarily postpone the inevitable stellar spindown, thereby lengthening this highly volatile stage of coronal evolution.Comment: to be published in ApJ