2,476 research outputs found
Photon Counting Using Edge-Detection Algorithm
New applications such as high-datarate, photon-starved, free-space optical communications require photon counting at flux rates into gigaphoton-per-second regimes coupled with subnanosecond timing accuracy. Current single-photon detectors that are capable of handling such operating conditions are designed in an array format and produce output pulses that span multiple sample times. In order to discern one pulse from another and not to overcount the number of incoming photons, a detection algorithm must be applied to the sampled detector output pulses. As flux rates increase, the ability to implement such a detection algorithm becomes difficult within a digital processor that may reside within a field-programmable gate array (FPGA). Systems have been developed and implemented to both characterize gigahertz bandwidth single-photon detectors, as well as process photon count signals at rates into gigaphotons per second in order to implement communications links at SCPPM (serial concatenated pulse position modulation) encoded data rates exceeding 100 megabits per second with efficiencies greater than two bits per detected photon. A hardware edge-detection algorithm and corresponding signal combining and deserialization hardware were developed to meet these requirements at sample rates up to 10 GHz. The photon discriminator deserializer hardware board accepts four inputs, which allows for the ability to take inputs from a quadphoton counting detector, to support requirements for optical tracking with a reduced number of hardware components. The four inputs are hardware leading-edge detected independently. After leading-edge detection, the resultant samples are ORed together prior to deserialization. The deserialization is performed to reduce the rate at which data is passed to a digital signal processor, perhaps residing within an FPGA. The hardware implements four separate analog inputs that are connected through RF connectors. Each analog input is fed to a high-speed 1-bit comparator, which digitizes the input referenced to an adjustable threshold value. This results in four independent serial sample streams of binary 1s and 0s, which are ORed together at rates up to 10 GHz. This single serial stream is then deserialized by a factor of 16 to create 16 signal lines at a rate of 622.5 MHz or lower for input to a high-speed digital processor assembly. The new design and corresponding hardware can be employed with a quad-photon counting detector capable of handling photon rates on the order of multi-gigaphotons per second, whereas prior art was only capable of handling a single input at 1/4 the flux rate. Additionally, the hardware edge-detection algorithm has provided the ability to process 3-10 higher photon flux rates than previously possible by removing the limitation that photoncounting detector output pulses on multiple channels being ORed not overlap. Now, only the leading edges of the pulses are required to not overlap. This new photon counting digitizer hardware architecture supports a universal front end for an optical communications receiver operating at data rates from kilobits to over one gigabit per second to meet increased mission data volume requirements
Early Advanced LIGO binary neutron-star sky localization and parameter estimation
2015 will see the first observations of Advanced LIGO and the start of the
gravitational-wave (GW) advanced-detector era. One of the most promising
sources for ground-based GW detectors are binary neutron-star (BNS)
coalescences. In order to use any detections for astrophysics, we must
understand the capabilities of our parameter-estimation analysis. By simulating
the GWs from an astrophysically motivated population of BNSs, we examine the
accuracy of parameter inferences in the early advanced-detector era. We find
that sky location, which is important for electromagnetic follow-up, can be
determined rapidly (~5 s), but that sky areas may be hundreds of square
degrees. The degeneracy between component mass and spin means there is
significant uncertainty for measurements of the individual masses and spins;
however, the chirp mass is well measured (typically better than 0.1%).Comment: 4 pages, 2 figures. Published in the proceedings of Amaldi 1
Supplement: Going the Distance: Mapping Host Galaxies of LIGO and Virgo Sources in Three Dimensions Using Local Cosmography and Targeted Follow-up
This is a supplement to the Letter of Singer et al.
(https://arxiv.org/abs/1603.07333), in which we demonstrated a rapid algorithm
for obtaining joint 3D estimates of sky location and luminosity distance from
observations of binary neutron star mergers with Advanced LIGO and Virgo. We
argued that combining the reconstructed volumes with positions and redshifts of
possible host galaxies can provide large-aperture but small field of view
instruments with a manageable list of targets to search for optical or infrared
emission. In this Supplement, we document the new HEALPix-based file format for
3D localizations of gravitational-wave transients. We include Python sample
code to show the reader how to perform simple manipulations of the 3D sky maps
and extract ranked lists of likely host galaxies. Finally, we include
mathematical details of the rapid volume reconstruction algorithm.Comment: For associated data release, see
http://asd.gsfc.nasa.gov/Leo.Singer/going-the-distanc
An observational study of individual child journeys through autism diagnostic pathways, and associated costs, in the UK National Health Service
High-Speed Operation of Interband Cascade Lasers
Optical sources operating in the atmospheric window of 3-5 microns are of particular interest for the development of free-space optical communication link. It is more advantageous to operate the free-space optical communication link in 3-5-microns atmospheric transmission window than at the telecom wavelength of 1.5 m due to lower optical scattering, scintillation, and background radiation. However, the realization of optical communications at the longer wavelength has encountered significant difficulties due to lack of adequate optical sources and detectors operating in the desirable wavelength regions. Interband Cascade (IC) lasers are novel semiconductor lasers that have a great potential for the realization of high-power, room-temperature optical sources in the 3-5-microns wavelength region, yet no experimental work, until this one, was done on high-speed direct modulation of IC lasers. Here, highspeed interband cascade laser, operating at wavelength 3.0 m, has been developed and the first direct measurement of the laser modulation bandwidth has been performed using a unique, highspeed quantum well infrared photodetector (QWIP). The developed laser has modulation bandwidth exceeding 3 GHz. This constitutes a significant increase of the IC laser modulation bandwidth over currently existing devices. This result has demonstrated suitability of IC lasers as a mid-IR light source for multi-GHz free-space optical communications link
Highly multimode memory in a crystal
We experimentally demonstrate the storage of 1060 temporal modes onto a
thulium-doped crystal using an atomic frequency comb (AFC). The comb covers
0.93 GHz defining the storage bandwidth. As compared to previous AFC
preparation methods (pulse sequences i.e. amplitude modulation), we only use
frequency modulation to produce the desired optical pumping spectrum. To ensure
an accurate spectrally selective optical pumping, the frequency modulated laser
is self-locked on the atomic comb. Our approach is general and should be
applicable to a wide range of rare-earth doped material in the context of
multimode quantum memory
Formation of the black-hole binary M33 X-7 via mass-exchange in a tight massive system
M33 X-7 is among the most massive X-Ray binary stellar systems known, hosting
a rapidly spinning 15.65 Msun black hole orbiting an underluminous 70 Msun Main
Sequence companion in a slightly eccentric 3.45 day orbit. Although
post-main-sequence mass transfer explains the masses and tight orbit, it leaves
unexplained the observed X-Ray luminosity, star's underluminosity, black hole's
spin, and eccentricity. A common envelope phase, or rotational mixing, could
explain the orbit, but the former would lead to a merger and the latter to an
overluminous companion. A merger would also ensue if mass transfer to the black
hole were invoked for its spin-up. Here we report that, if M33 X-7 started as a
primary of 85-99 Msun and a secondary of 28-32 Msun, in a 2.8-3.1 day orbit,
its observed properties can be consistently explained. In this model, the Main
Sequence primary transferred part of its envelope to the secondary and lost the
rest in a wind; it ended its life as a ~16 Msun He star with a Fe-Ni core which
collapsed to a black hole (with or without an accompanying supernova). The
release of binding energy and, possibly, collapse asymmetries "kicked" the
nascent black hole into an eccentric orbit. Wind accretion explains the X-Ray
luminosity, while the black hole spin can be natal.Comment: Manuscript: 18 pages, 2 tables, 2 figure. Supplementary Information:
34 pages, 6 figures. Advance Online Publication (AOP) on
http://www.nature.com/nature on October 20, 2010. To Appear in Nature on
November 4, 201
Notch-Deficient Skin Induces a Lethal Systemic B-Lymphoproliferative Disorder by Secreting TSLP, a Sentinel for Epidermal Integrity
Epidermal keratinocytes form a highly organized stratified epithelium and sustain a competent barrier function together with dermal and hematopoietic cells. The Notch signaling pathway is a critical regulator of epidermal integrity. Here, we show that keratinocyte-specific deletion of total Notch signaling triggered a severe systemic B-lymphoproliferative disorder, causing death. RBP-j is the DNA binding partner of Notch, but both RBP-j–dependent and independent Notch signaling were necessary for proper epidermal differentiation and lipid deposition. Loss of both pathways caused a persistent defect in skin differentiation/barrier formation. In response, high levels of thymic stromal lymphopoietin (TSLP) were released into systemic circulation by Notch-deficient keratinocytes that failed to differentiate, starting in utero. Exposure to high TSLP levels during neonatal hematopoiesis resulted in drastic expansion of peripheral pre- and immature B-lymphocytes, causing B-lymphoproliferative disorder associated with major organ infiltration and subsequent death, a previously unappreciated systemic effect of TSLP. These observations demonstrate that local skin perturbations can drive a lethal systemic disease and have important implications for a wide range of humoral and autoimmune diseases with skin manifestations
Persistent elastic behavior above a megathrust rupture patch: Nias island, West Sumatra
We quantify fore-arc deformation using fossil reefs to test the assumption commonly made in seismic cycle models that anelastic deformation of the fore arc is negligible. Elevated coral microatolls, paleoreef flats, and chenier plains show that the Sumatran outer arc island of Nias has experienced a complex pattern of relatively slow long-term uplift and subsidence during the Holocene epoch. This same island rose up to 2.9 m during the Mw 8.7 Sunda megathrust rupture in 2005. The mismatch between the 2005 and Holocene uplift patterns, along with the overall low rates of Holocene deformation, reflects the dominance of elastic strain accumulation and release along this section of the Sunda outer arc high and the relatively subordinate role of upper plate deformation in accommodating long-term plate convergence. The fraction of 2005 uplift that will be retained permanently is generally <4% for sites that experienced more than 0.25 m of coseismic uplift. Average uplift rates since the mid-Holocene range from 1.5 to −0.2 mm/a and are highest on the eastern coast of Nias, where coseismic uplift was nearly zero in 2005. The pattern of long-term uplift and subsidence is consistent with slow deformation of Nias along closely spaced folds in the north and trenchward dipping back thrusts in the southeast. Low Holocene tectonic uplift rates provide for excellent geomorphic and stratigraphic preservation of the mid-Holocene relative sea level high, which was under way by ∼7.3 ka and persisted until ∼2 ka
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