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Chen, C. C.

Publications and source records attributed to Chen, C. C..

17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

The simulation of the sensitivity of the Antarctic Impulsive Transient Antenna (ANITA) to Askaryan radiation from cosmogenic neutrinos interacting in the Antarctic Ice

A Monte Carlo simulation program for the radio detection of Ultra High Energy (UHE) neutrino interactions in the Antarctic ice as viewed by the Antarctic Impulsive Transient Antenna (ANITA) is described in this article. The program, icemc, provides an input spectrum of UHE neutrinos, the parametrization of the Askaryan radiation generated by their interaction in the ice, and the propagation of the radiation through ice and air to a simulated model of the third and fourth ANITA flights. Lastly, this paper provides an overview of the icemc simulation, descriptions of the physics models used and of the ANITA electronics processing chain, data/simulation comparisons to validate the predicted performance, and a summary of the impact of published results.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Comprehensive analysis of anomalous ANITA events disfavors a diffuse tau-neutrino flux origin

Recently, the ANITA collaboration reported on two upward-going extensive air shower events consistent with a primary particle that emerges from the surface of the Antarctic ice sheet. These events may be of ν τ origin, in which the neutrino interacts within the Earth to produce a τ lepton that emerges from the Earth, decays in the atmosphere, and initiates an extensive air shower. In this paper we estimate an upper bound on the ANITA acceptance to a diffuse ν τ flux detected via τ-lepton-induced air showers within the bounds of standard model uncertainties. Furthermore, by comparing this estimate with the acceptance of Pierre Auger Observatory and IceCube and assuming standard model interactions, we conclude that a ν τ origin of these events would imply a neutrino flux at least two orders of magnitude above current bounds.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Observation of an Unusual Upward-Going Cosmic-Ray-like Event in the Third Flight of ANITA

We report here on an upward traveling, radio-detected cosmic-ray-like impulsive event with characteristics closely matching an extensive air shower. This event, observed in the third flight of the Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload, is consistent with a similar event reported in a previous flight. These events could be produced by the atmospheric decay of an upward-propagating τ lepton produced by a ν τ interaction, although their relatively steep arrival angles create tension with the standard model neutrino cross section. Each of the two events have a posteriori background estimates of ≲ 10 - 2 events. If these are generated by τ -lepton decay, then either the charged-current ν τ cross section is suppressed at EeV energies, or the events arise at moments when the peak flux of a transient neutrino source was much larger than the typical expected cosmogenic background neutrinos.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Constraints on the diffuse high-energy neutrino flux from the third flight of ANITA

The Antarctic Impulsive Transient Antenna, a NASA long-duration balloon payload, searches for radio emission from interactions of ultrahigh-energy neutrinos in polar ice. The third flight of the Antarctic Impulsive Transient Antenna was launched in December 2014 and completed a 22-day flight. Here, we present the results of three analyses searching for Askaryan radio emission of neutrino origin. In the most sensitive of the analyses, we find one event in the signal region on an expected background of 0.7$+0.5\atop{-0.3}$. Though consistent with the background estimate, the event remains compatible with a neutrino hypothesis even after additional postunblinding scrutiny.

47 OTHER INSTRUMENTATION↗
NASA NTRS2017

An Intercomparative Study of the Effects of Aircraft Emissions on Surface Air Quality

This study intercompares, among five global models, the potential impacts of all commercial aircraft emissions worldwide on surface ozone and particulate matter (PM (sub 2.5)). The models include climate-response models (CRMs) with interactive meteorology, chemical-transport models (CTMs) with prescribed meteorology, and models that integrate aspects of both. Model inputs are harmonized in an effort to achieve a consensus about the state of understanding of impacts of 2006 commercial aviation emissions. Models find that aircraft increase near-surface ozone (0.3 to 1.9 percent globally), with qualitatively similar spatial distributions, highest in the Northern Hemisphere. Annual changes in surface-level PM (sub 2.5) in the CTMs (0.14 to 0.4 percent) and CRMs (-1.9 to 1.2 percent) depend on differences in nonaircraft baseline aerosol fields among models and the inclusion of feedbacks between aircraft emissions and changes in meteorology. The CTMs tend to result in an increase in surface PM (sub 2.5) primarily over high-traffic regions in the North American midlatitudes. The CRMs, on the other hand, demonstrate the effects of aviation emissions on changing meteorological fields that result in large perturbations over regions where natural emissions (e.g., soil dust and sea spray) occur. The changes in ozone and PM (sub 2.5) found here may be used to contextualize previous estimates of impacts of aircraft emissions on human health.

Air quality↗
DOE OSTI2016

Kiloparsec-scale dust disks in high-redshift luminous submillimeter galaxies

We present high-resolution (0.″16) 870 μm Atacama Large Millimeter/submillimeter Array (ALMA) imaging of 16 luminous (L{sub IR}∼4×10{sup 12} L{sub ⊙}) submillimeter galaxies (SMGs) from the ALESS survey of the Extended Chandra Deep Field South. This dust imaging traces the dust-obscured star formation in these z∼2.5 galaxies on ∼1.3 kpc scales. The emission has a median effective radius of R {sub e} = 0.″24 ± 0.″02, corresponding to a typical physical size of R{sub e}= 1.8 ± 0.2 kpc. We derive a median Sérsic index of n = 0.9 ± 0.2, implying that the dust emission is remarkably disk-like at the current resolution and sensitivity. We use different weighting schemes with the visibilities to search for clumps on 0.″12 (∼1.0 kpc) scales, but we find no significant evidence for clumping in the majority of cases. Indeed, we demonstrate using simulations that the observed morphologies are generally consistent with smooth exponential disks, suggesting that caution should be exercised when identifying candidate clumps in even moderate signal-to-noise ratio interferometric data. We compare our maps to comparable-resolution Hubble Space Telescope H{sub 160}-band images, finding that the stellar morphologies appear significantly more extended and disturbed, and suggesting that major mergers may be responsible for driving the formation of the compact dust disks we observe. The stark contrast between the obscured and unobscured morphologies may also have implications for SED fitting routines that assume the dust is co-located with the optical/near-IR continuum emission. Finally, we discuss the potential of the current bursts of star formation to transform the observed galaxy sizes and light profiles, showing that the z∼0 descendants of these SMGs are expected to have stellar masses, effective radii, and gas surface densities consistent with the most compact massive (M{sub ∗} ∼ 1–2 × 10{sup 11} M{sub ⊙}) early-type galaxies observed locally.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Charge disproportionation in La{sub 1-x}Ca{sub x}FeO{sub 3−δ} (x = 0.4 and 0.5) investigated by mechanical spectroscopy

The nature of charge disproportionation in orthorhombic lanthanum orthoferrites La{sub 1-x}Ca{sub x}FeO{sub 3-δ} (x = 0.4 and 0.5) has been investigated by kilohertz mechanical spectroscopy. Contrast to rhombohedral La{sub 1-x}Sr{sub x}FeO{sub 3-δ} (x = 0.5), no elastic softening was observed in La{sub 1-x}Ca{sub x}FeO{sub 3-δ} above charge disproportionation. This different behavior of elastic modulus in La{sub 1-x}Ca{sub x}FeO{sub 3-δ} and La{sub 1-x}Sr{sub x}FeO{sub 3-δ} unveils the implicit orbital effect. Below charge disproportionation, an internal friction peak around 140 K was observed in La{sub 1-x}Ca{sub x}FeO{sub 3-δ}, which is similar to that in La{sub 1-x}Sr{sub x}FeO{sub 3-δ}. This peak is ascribed to an elastic manifestation of charge freezing and can be used as an indirect indication of CD in doped LaFeO{sub 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Viscosity-dependent drain current noise of AlGaN/GaN high electron mobility transistor in polar liquids

The drain current fluctuation of ungated AlGaN/GaN high electron mobility transistors (HEMTs) measured in different fluids at a drain-source voltage of 0.5 V was investigated. The HEMTs with metal on the gate region showed good current stability in deionized water, while a large fluctuation in drain current was observed for HEMTs without gate metal. The fluctuation in drain current for the HEMTs without gate metal was observed and calculated as standard deviation from a real-time measurement in air, deionized water, ethanol, dimethyl sulfoxide, ethylene glycol, 1,2-butanediol, and glycerol. At room temperature, the fluctuation in drain current for the HEMTs without gate metal was found to be relevant to the dipole moment and the viscosity of the liquids. A liquid with a larger viscosity showed a smaller fluctuation in drain current. The viscosity-dependent fluctuation of the drain current was ascribed to the Brownian motions of the liquid molecules, which induced a variation in the surface dipole of the gate region. This study uncovers the causes of the fluctuation in drain current of HEMTs in fluids. The results show that the AlGaN/GaN HEMTs may be used as sensors to measure the viscosity of liquids within a certain range of viscosity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Effect of magnetic field profile on the uniformity of a distributed electron cyclotron resonance plasma

This study extensively measured the uniformity of an electron cyclotron resonance (ECR) plasma versus the magnetic field distribution. The influence of magnetic field distribution on the generation of uniform ECR plasma was examined. It is suggested that in addition to the uniformity of the magnetic field distribution at ECR zone and at the downstream zone near the substrate, the transition of the magnetic field between these two zones is also crucial. A uniform ECR plasma with the electron density uniformity of ±7.7% over 500 × 500 mm{sup 2} was measured at the downstream. The idea of generating uniform ECR plasma can be scaled up to a much larger area by using an n × n microwave input array and a well-designed magnetic system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Generating electron cyclotron resonance plasma using distributed scheme

This study employs a distributed microwave input system and permanent magnets to generate large-area electron cyclotron resonance (ECR) plasma. ECR plasmas were generated with nitrogen gas, and the plasma density was measured by Langmuir probe. A uniform ECR plasma with the electron density fluctuation of {+-}9.8% over 500 mm Multiplication-Sign 500 mm was reported. The proposed idea of generating uniform ECR plasma can be scaled to a much larger area by using n Multiplication-Sign n microwave input array system together with well-designed permanent magnets.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1987

Comparison of direct and heterodyne detection optical intersatellite communication links

The performance of direct and heterodyne detection optical intersatellite communication links are evaluated and compared. It is shown that the performance of optical links is very sensitive to the pointing and tracking errors at the transmitter and receiver. In the presence of random pointing and tracking errors, optimal antenna gains exist that will minimize the required transmitter power. In addition to limiting the antenna gains, random pointing and tracking errors also impose a power penalty in the link budget. This power penalty is between 1.6 to 3 dB for a direct detection QPPM link, and 3 to 5 dB for a heterodyne QFSK system. For the heterodyne systems, the carrier phase noise presents another major factor of performance degradation that must be considered. In contrast, the loss due to synchronization error is small. The link budgets for direct and heterodyne detection systems are evaluated. It is shown that, for systems with large pointing and tracking errors, the link budget is dominated by the spatial tracking error, and the direct detection system shows a superior performance because it is less sensitive to the spatial tracking error. On the other hand, for systems with small pointing and tracking jitters, the antenna gains are in general limited by the launch cost, and suboptimal antenna gains are often used in practice. In which case, the heterodyne system has a slightly higher power margin because of higher receiver sensitivity.

Chen, C. C.↗
NASA NTRS1986

Loss factors associated with spatial and temporal tracking errors in intersatellite PPM communication links

The performance of an optical PPM intersatellite link in the presence of spatial and temporal tracking errors is investigated. It is shown that for a given rms spatial tracking error, an optimal transmitter beamwidth exists which minimizes the probability of bit error. The power penalty associated with the spatial tracking error when the transmitter beamwidth is adjusted to achieve optimal performance is shown to be large (greater than 9 dB) when the rms pointing jitter becomes a significant fraction (greater than 30 percent) of the diffraction limited beamwidth. The power penalty due to temporal tracking error, on the other hand, is relatively small (less than 0.1 dB) when the tracking loop bandwidth is less than 0.1 percent of the slot frequency. By properly allocating losses to spatial and temporal tracking errors, it is seen that a 10 to the -9th error rate can be achieved for a realistic link design with an approximately 3 dB signal power margin.

Chen, C. C.↗
NASA NTRS1985

Phase locked loop synchronization for direct detection optical PPM communication systems

Receiver timing synchronization of an optical pulse position modulation (PPM) communication system can be achieved using a phase locked loop (PLL) if the photodetector output is properly processed. The synchronization performance is shown to improve with increasing signal power and decreasing loop bandwidth. Bit error rate (BER) of the PLL synchronized PPM system is analyzed and compared to that for the perfectly synchronized system. It is shown that the increase in signal power needed to compensate for the imperfect synchronization is small (less than 0.1 dB) for loop bandwidths less than 0.1% of the slot frequency.

Chen, C. C.↗
NASA NTRS1983

Advanced 30/20 GHz multiple beam antenna for future communications satellites

The technologies which will be implemented in advanced satellite communications systems being studied by NASA and the intended coverage scenarios are described. The systems will function at 30/20 GHz with 2.5 GHz bandwidth for the uplink and downlink. Subfrequencies will have 500 MHz bandwidth and operations will include TDMA modes. Sample scan patterns are presented for the centerminous U.S. The signals will be broadcast from a multibeam offset Cassegrain reflector antenna to obtain a low sidelobe, wide angle scan. Three contiguous low sidelobe beams will be generated with a diplex feed cluster and a 19 element scanning beam-forming network. The same technology will be used to double the capacity of current 14/12 GHz satellites.

Chen, C. C.↗
NASA NTRS1982

Advanced 30/20 GHz multiple beam antenna for future communications satellites

A multiple offset reflector system is being used to provide multiple fixed and scanning beams at 30 GHz by means of a polarization grid diplexer to separate two orthogonally polarized feed assemblies. Each feed assembly consists of multiple fixed and scanning beam feeds. The technology developments required for successful operation of this proposed system are presented. These technologies include: (1) an offset Cassegrain system for low sidelobe wide angle scan beams; (2) a diplexed beam forming network for overlapping low sidelobe beams; (3) a fast switching network for scanning beams; and (4) fabrication of precision feed components and large offset reflectors.

Chen, C. C.↗
NASA NTRS1980

Ku-band multiple beam antenna

The frequency reuse capability is demonstrated for a Ku-band multiple beam antenna which provides contiguous low sidelobe spot beams for point-to-point communications between any two points within the continental United States (CONUS), or regional coverage beams for direct broadcast systems. A spot beam antenna in the 14/21 GHz band which provides contiguous overlapping beams covering CONUS and two discrete beams covering Hawaii and Alaska were designed, developed, and tested. Two reflector antennas are required for providing contiguous coverage of CONUS. Each is comprised of one offset parabolic reflector, one flat polarization diplexer, and two separate planar array feeds. This antenna system provides contiguous spot beam coverage of CONUS, utilizing 15 beams. Also designed, developed and demonstrated was a shaped contoured beam antenna system which provides contiguous four time zone coverage of CONUS from a single offset parabolic reflector incorporating one flat polarization diplexer and two separate planar array feeds. The beams which illuminate the eastern time zone and the mountain time zone are horizontally polarized, while the beams which illuminate the central time zone and the pacific time zone are vertically polarized. Frequency reuse is achieved by amplitude and polarization isolation.

Chen, C. C.↗