23,070 research outputs found
A luminous blue kilonova and an off-axis jet from a compact binary merger at z=0.1341
The recent discovery of a faint gamma-ray burst (GRB) coincident with the
gravitational wave (GW) event GW 170817 revealed the existence of a population
of low-luminosity short duration gamma-ray transients produced by neutron star
mergers in the nearby Universe. These events could be routinely detected by
existing gamma-ray monitors, yet previous observations failed to identify them
without the aid of GW triggers. Here we show that GRB150101B was an analogue of
GRB170817A located at a cosmological distance. GRB 150101B was a faint short
duration GRB characterized by a bright optical counterpart and a long-lived
X-ray afterglow. These properties are unusual for standard short GRBs and are
instead consistent with an explosion viewed off-axis: the optical light is
produced by a luminous kilonova component, while the observed X-rays trace the
GRB afterglow viewed at an angle of ~13 degrees. Our findings suggest that
these properties could be common among future electromagnetic counterparts of
GW sources.Comment: 28 pages, 8 figures, 2 tables. Accepted for publicatio
Focusing and Compression of Ultrashort Pulses through Scattering Media
Light scattering in inhomogeneous media induces wavefront distortions which
pose an inherent limitation in many optical applications. Examples range from
microscopy and nanosurgery to astronomy. In recent years, ongoing efforts have
made the correction of spatial distortions possible by wavefront shaping
techniques. However, when ultrashort pulses are employed scattering induces
temporal distortions which hinder their use in nonlinear processes such as in
multiphoton microscopy and quantum control experiments. Here we show that
correction of both spatial and temporal distortions can be attained by
manipulating only the spatial degrees of freedom of the incident wavefront.
Moreover, by optimizing a nonlinear signal the refocused pulse can be shorter
than the input pulse. We demonstrate focusing of 100fs pulses through a 1mm
thick brain tissue, and 1000-fold enhancement of a localized two-photon
fluorescence signal. Our results open up new possibilities for optical
manipulation and nonlinear imaging in scattering media
Measuring Accuracy of Automated Parsing and Categorization Tools and Processes in Digital Investigations
This work presents a method for the measurement of the accuracy of evidential
artifact extraction and categorization tasks in digital forensic
investigations. Instead of focusing on the measurement of accuracy and errors
in the functions of digital forensic tools, this work proposes the application
of information retrieval measurement techniques that allow the incorporation of
errors introduced by tools and analysis processes. This method uses a `gold
standard' that is the collection of evidential objects determined by a digital
investigator from suspect data with an unknown ground truth. This work proposes
that the accuracy of tools and investigation processes can be evaluated
compared to the derived gold standard using common precision and recall values.
Two example case studies are presented showing the measurement of the accuracy
of automated analysis tools as compared to an in-depth analysis by an expert.
It is shown that such measurement can allow investigators to determine changes
in accuracy of their processes over time, and determine if such a change is
caused by their tools or knowledge.Comment: 17 pages, 2 appendices, 1 figure, 5th International Conference on
Digital Forensics and Cyber Crime; Digital Forensics and Cyber Crime, pp.
147-169, 201
The North Ecliptic Pole Wide survey of AKARI: a near- and mid-infrared source catalog
We present a photometric catalog of infrared (IR) sources based on the North
Ecliptic PoleWide field (NEP-Wide) survey of AKARI, which is an infrared space
telescope launched by Japan. The NEP-Wide survey covered 5.4 deg2 area, a
nearly circular shape centered on the North Ecliptic Pole, using nine
photometric filter-bands from 2 - 25 {\mu}m of the Infrared Camera (IRC).
Extensive efforts were made to reduce possible false objects due to cosmic ray
hits, multiplexer bleeding phenomena around bright sources, and other
artifacts. The number of detected sources varied depending on the filter band:
with about 109,000 sources being cataloged in the near-IR bands at 2 - 5
{\mu}m, about 20,000 sources in the shorter parts of the mid-IR bands between 7
- 11 {\mu}m, and about 16,000 sources in the longer parts of the mid-IR bands,
with \sim 4,000 sources at 24 {\mu}m. The estimated 5? detection limits are
approximately 21 magnitude (mag) in the 2 - 5 {\mu}m bands, 19.5 - 19 mag in
the 7 - 11 {\mu}m, and 18.8 - 18.5 mag in the 15 - 24 {\mu}m bands in the AB
magnitude scale. The completenesses for those bands were evaluated as a
function of magnitude: the 50% completeness limits are about 19.8 mag at 3
{\mu}m, 18.6 mag at 9 {\mu}m, and 18 mag at 18 {\mu}m band, respectively. To
construct a reliable source catalog, all of the detected sources were examined
by matching them with those in other wavelength data, including optical and
ground-based near-IR bands. The final band-merged catalog contains about
114,800 sources detected in the IRC filter bands. The properties of the sources
are presented in terms of the distributions in various color-color diagrams.Comment: Accepted for publication in A&A, 23 pages, 27 figure
Understanding suicide attempts among gay men from their self-perceived causes
Gay men are at higher risk of suicidality. This paper describes the causes of suicide attempts as perceived by the men themselves and analyzes their impact on severity and recidivism. Mental health surveys conducted among gay men in Geneva, Switzerland, from two probability-based time-space samples in 2007 and 2011, were merged to yield a combined sample N = 762. Suicide ideation, plans, and attempts were assessed, and respondents who had ever attempted suicide answered open questions about perceived causes which were coded and categorized for analysis within the framework of cultural epidemiology. In all, 16.7% of the respondents reported a suicide attempt in their lifetime (59.5% of them with multiple attempts). At their latest attempt, over two thirds asserted intent to die, and half required medical assistance. There was a wide variety of perceived causes, with most individuals reporting multiple causes and many of the most common causes cited at both the first and most recent subsequent attempts. Social/inter-personal problems constitute the most prominent category. Problems with love/relationship and accepting one's homosexuality figure consistently among the top three causes. Whereas the former tend to be associated with weaker intent to die, the latter are associated with the strongest intent to die and reported at multiple attempts. Problems with family are among the most common perceived causes at first attempt but not at the most recent subsequent attempt. Nevertheless, they tend to be related to the strongest intent to die and the greatest medical severity of all the perceived causes. Ten percent of men attempting suicide cited depression as a cause. Although it tended to be associated with weaker intent to die, depression was most likely to be reported at multiple attempts. Respondent-driven assessment yielded both common and idiosyncratic causes of suicide and their distinct effects. Some of these perceived causes are not prominent in the curren literature, yet they have important implications for understanding risk and preventing suicide among gay men
Multi-Attribute SCADA-Specific Intrusion Detection System for Power Networks
The increased interconnectivity and complexity of supervisory control and data acquisition (SCADA) systems in power system networks has exposed the systems to a multitude of potential vulnerabilities. In this paper, we present a novel approach for a next-generation SCADA-specific intrusion detection system (IDS). The proposed system analyzes multiple attributes in order to provide a comprehensive solution that is able to mitigate varied cyber-attack threats. The multiattribute IDS comprises a heterogeneous white list and behavior-based concept in order to make SCADA cybersystems more secure. This paper also proposes a multilayer cyber-security framework based on IDS for protecting SCADA cybersecurity in smart grids without compromising the availability of normal data. In addition, this paper presents a SCADA-specific cybersecurity testbed to investigate simulated attacks, which has been used in this paper to validate the proposed approach
Magnetic Field-Induced Superconductor-Insulator-Metal Transition in an Organic Conductor: An Infrared Magneto-Optical Imaging Spectroscopy
The magnetic field-induced superconductor-insulator-metal transition (SIMT)
in partially deuterated -(BEDT-TTF)Cu[N(CN)]Br, which is just
on the Mott boundary, has been observed using the infrared magneto-optical
imaging spectroscopy. The infrared reflectivity image on the sample surface
revealed that the metallic (or superconducting) and insulating phases coexist
and they have different magnetic field dependences. One of the magnetic field
dependence is SIMT that appeared on part of the sample surface. The SIMT was
concluded to originate from the balance of the inhomogenity in the sample
itself and the disorder of the ethylene end groups resulting from fast cooling.Comment: 5 pages, 5 figures, to appear in Phys. Rev.
Predicting the visco-elastic properties of polystyrene/SIS composite blends using simple analytical micromechanics models
This paper is concerned with the prediction of the viscoelastic properties of rubber filled polymer blends. The question asked was as follows. Can the temperature dependent viscoelastic properties of phase separated polymer blends be adequately predicted using only a rational two phase micromechanics based analytical model with no empirical fitting parameters? In particular using only a knowledge of the individual bulk phase properties and the blend microstructure, but without any further detailed polymer physics knowledge such as the presence of an interphase region or any additional nanoscale structures within the separated rubber phase with the properties different from those of the two bulk phases? Blends of a polystyrene matrix and phase separated rubber inclusions (a polystyrene-polyisoprene-polystyrene triblock polymer (SIS)) were manufactured in a range of blend fractions (up to 20 vol % of the triblock co-polymer). Experimental measurements, for the storage modulus Gā² and the loss tangent tanĪ“, of both the individual phases and the blends, were made using dynamic mechanical tests over a range of temperatures from ā50 to +70 Ā°C. Numerical predictions, of the same parameters, were first obtained using the generalised self-consistent Christensen and Lo model which uses a simple representative volume element (RVE) of an isolated sphere of the minority rubber component in a surrounding sheath of polystyrene matrix embedded in a homogeneous effective medium. The agreement between the Christensen and Lo model and the experimental measurements, for Gā² and tanĪ“, was found to be excellent for rubber contents up to 10%. For a 20% rubber content, an improved prediction was obtained by altering the RVE to include the observed effect of having a polystyrene central core in a number of the dispersed rubber zones at this rubber fraction, using the Herve and Zaoui generalization of the Christensen and Lo model. Although conjoined (and therefore non-spherical) zones became more prevalent at the highest rubber content, use of the Tandon and Weng model showed that this shape anisotropy would not be expected to affect the viscoelastic properties
- ā¦