The rectification of electromagnetic waves to direct currents is a crucial process for energy harvesting, beyond-5G wireless communications, ultra-fast science, and observational astronomy. As the ...radiation frequency is raised to the sub-terahertz (THz) domain, ac-to-dc conversion by conventional electronics becomes challenging and requires alternative rectification protocols. Here, we address this challenge by tunnel field-effect transistors made of bilayer graphene (BLG). Taking advantage of BLG's electrically tunable band structure, we create a lateral tunnel junction and couple it to an antenna exposed to THz radiation. The incoming radiation is then down-converted by the tunnel junction nonlinearity, resulting in high responsivity (>4 kV/W) and low-noise (0.2 pW/Formula: see text) detection. We demonstrate how switching from intraband Ohmic to interband tunneling regime can raise detectors' responsivity by few orders of magnitude, in agreement with the developed theory. Our work demonstrates a potential application of tunnel transistors for THz detection and reveals BLG as a promising platform therefor.
Fast radio bursts (FRBs) are bright, millisecond-duration radio transients originating from sources at extragalactic distances
, the origin of which is unknown. Some FRB sources emit repeat bursts, ...ruling out cataclysmic origins for those events
. Despite searches for periodicity in repeat burst arrival times on timescales from milliseconds to many days
, these bursts have hitherto been observed to appear sporadically and-although clustered
-without a regular pattern. Here we report observations of a 16.35 ± 0.15 day periodicity (or possibly a higher-frequency alias of that periodicity) from the repeating FRB 180916.J0158+65 detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project
. In 38 bursts recorded from 16 September 2018 to 4 February 2020 UTC, we find that all bursts arrive in a five-day phase window, and 50 per cent of the bursts arrive in a 0.6-day phase window. Our results suggest a mechanism for periodic modulation either of the burst emission itself or through external amplification or absorption, and disfavour models invoking purely sporadic processes.
Hydrogen has been inferred to occur in enhanced concentrations within permanently shadowed regions and, hence, the coldest areas of the lunar poles. The Lunar Crater Observation and Sensing Satellite ...(LCROSS) mission was designed to detect hydrogen-bearing volatiles directly. Neutron flux measurements of the Moon's south polar region from the Lunar Exploration Neutron Detector (LEND) on the Lunar Reconnaissance Orbiter (LRO) spacecraft were used to select the optimal impact site for LCROSS. LEND data show several regions where the epithermal neutron flux from the surface is suppressed, which is indicative of enhanced hydrogen content. These regions are not spatially coincident with permanently shadowed regions of the Moon. The LCROSS impact site inside the Cabeus crater demonstrates the highest hydrogen concentration in the lunar south polar region, corresponding to an estimated content of 0.5 to 4.0% water ice by weight, depending on the thickness of any overlying dry regolith layer. The distribution of hydrogen across the region is consistent with buried water ice from cometary impacts, hydrogen implantation from the solar wind, and/or other as yet unknown sources.
The CHIME Pulsar Project: System Overview Amiri, M.; Bandura, K. M.; Boyle, P. J. ...
The Astrophysical journal. Supplement series,
07/2021, Letnik:
255, Številka:
1
Journal Article
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Abstract
We present the design, implementation, and performance of the digital pulsar observing system constructed for the Canadian Hydrogen Intensity Mapping Experiment (CHIME). Using accelerated ...computing, this system processes independent, digitally steered beams formed by the CHIME correlator to simultaneously observe up to 10 radio pulsars and transient sources. Each of these independent streams is processed by the CHIME/Pulsar back-end system, which can coherently dedisperse, in real time, up to dispersion measure values of 2500 pc cm
−3
. The tracking beams and real-time analysis system are autonomously controlled by a priority-based algorithm that schedules both known sources and positions of interest for observation with observing cadences as rapid as 1 day. Given the distribution of known pulsars and radio-transient sources and the dynamic scheduling, the CHIME/Pulsar system can monitor 400–500 positions once per sidereal day and observe most sources with declinations greater than −20° once every ∼4 weeks. We also discuss the extensive science program enabled through the current modes of data acquisition for CHIME/Pulsar that centers on timing and searching experiments.
Abstract
The Pulsar backend of the Canadian Hydrogen Intensity Mapping Experiment has monitored hundreds of known pulsars in the northern sky since fall 2018, providing a rich data set for the study ...of temporal variations in pulsar emission. Using a matched filtering technique, we report, for the first time, nulling behavior in five pulsars as well as mode switching in nine pulsars. Only one of the pulsars is observed to show both nulling and moding signals. These new nulling and mode-switching pulsars appear to come from a population with relatively long spin periods, in agreement with previous findings in the literature.
An epoxy polysulfone binder modified with an active diluent, furfuryl glycidyl ether (FGE), is studied. The addition of FGE significantly improves the technological parameters of the high-viscosity ...binder. The processing temperature of modified binders varies in the range of 80 to 120°C depending on the FGE concentration. The phase decomposition of the binder during its preparation is not observed, but occurred during curing. The glass transition temperature of matrices based on the obtained binder remains at a high level: 100–107°С. The type of phase structure formed during the curing of the hybrid binder depends on the concentration of FGE and polysulfone PSK-1.
The microwave properties of the components of the waveguide structure of a heterodyne receiver in the range 211–275 GHz with sideband separation based on a pair of ...superconductor–insulator–superconductor (SIS) tunnel junctions are described. The following elements of the waveguide structure have been studied: a hybrid four-port splitter, a directional coupler, a T-shaped splitter, and a waveguide absorber. S parameters for all elements are calculated. For the hybrid divider, the phase balance is additionally shown, which has deviations of less than 0.4 deg, and the amplitude balance is within 1 dB. The expected level of quality of band separation in a receiver with band separation when using the studied waveguide elements is analyzed, its value is more than –25 dB. Waveguide elements are designed taking into account that the block will be manufactured by precision milling; the minimum dimensions of the waveguide structure are limited by the diameter of the cutter used; in our case, 100 µm was chosen. All numerical calculations were performed by the finite interval method in the HFSS package.
The physical-mechanical properties of epoxy matrices modified with polyethersulfone (PES) and unidirectional glass- and carbon-fiber-reinforced plastics (GFRP and CFRP) based on them were ...investigated. The fracture toughness of epoxy matrices modified with 20 wt% PES, increased by 4.3 times. The delamination energy of GFRP and CFRP with this content of PES in the matrix increases by 50 and 65%, respectively. A correlation between the fracture toughness of modified matrices and the delamination toughness of GFRP and CFRP was established, and the influence of structure of the matrices on the fracture toughness of the reinforced plastics was demonstrated. A significant increase in the fracture toughness of the matrices and reinforced plastics was also observed during the formation of extended phases enriched with PES.
We present results from a new incoherent-beam fast radio burst (FRB) search on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder. Its large instantaneous field of view (FoV) and ...relative thermal insensitivity allow us to probe the ultra-bright tail of the FRB distribution, and to test a recent claim that this distribution's slope, , is quite small. A 256-input incoherent beamformer was deployed on the CHIME Pathfinder for this purpose. If the FRB distribution were described by a single power law with = 0.7, we would expect an FRB detection every few days, making this the fastest survey on the sky at present. We collected 1268 hr of data, amounting to one of the largest exposures of any FRB survey, with over 2.4 × 105 deg2 hr. Having seen no bursts, we have constrained the rate of extremely bright events to <13 sky−1 day−1 above for τ between 1.3 and 100 ms, at 400-800 MHz. The non-detection also allows us to rule out 0.9 with 95% confidence, after marginalizing over uncertainties in the GBT rate at 700-900 MHz, though we show that for a cosmological population and a large dynamic range in flux density, is brightness dependent. Since FRBs now extend to large enough distances that non-Euclidean effects are significant, there is still expected to be a dearth of faint events and relative excess of bright events. Nevertheless we have constrained the allowed number of ultra-intense FRBs. While this does not have significant implications for deeper, large-FoV surveys like full CHIME and APERTIF, it does have important consequences for other wide-field, small dish experiments.
Iron-containing composites with nanoparticles are synthesized by the method of thermal decomposition of pentacarbonyl and iron formate in a polyethylene melt. The synthesized nanoparticles are ...characterized by transmission electron microscopy (TEM), X-ray phase analysis, and Mössbauer spectroscopy. The size of nanoparticles synthesized from iron pentacarbonyl and iron formate is 5.3 and 11.5 nm, respectively. It follows from the diffraction patterns that the particles have a complex composition. Composite materials are obtained based on iron nanoparticles and high-density polyethylene (HDPE). According to dynamic mechanical analysis, the elastic modulus of HDPE filled with particles obtained from iron pentacarbonyl is higher than for matrices containing iron formate. The biocidity test showed that the particle-modified matrix inhibits the growth of microorganisms more effectively than pure polyethylene.
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