Engineering topics

Kim, K. C.

Publications and source records attributed to Kim, K. C..

14 records

NASA NTRS2018

Observations of the Interaction and Transport of Fine Mode Aerosols With Cloud and/or Fog in Northeast Asia From Aerosol Robotic Network and Satellite Remote Sensing

Analysis of Sun photometer measured and satellite retrieved aerosol optical depth (AOD) datahas shown that major aerosol pollution events with very highfine mode AOD (>1.0 in midvisible) in theChina/Korea/Japan region are often observed to be associated with significant cloud cover. This makesremote sensing of these events difficult even for high temporal resolution Sun photometer measurements.Possible physical mechanisms for these events that have high AOD include a combination of aerosolhumidification, cloud processing, and meteorological covariation with atmospheric stability andconvergence. The new development of Aerosol Robotic Network Version 3 Level 2 AOD with improved cloudscreening algorithms now allow for unprecedented ability to monitor these extremefine mode pollutionevents. Further, the spectral deconvolution algorithm (SDA) applied to Level 1 data (L1; no cloud screening)provides an even more comprehensive assessment offine mode AOD than L2 in current and previous dataversions. Studying the 2012 winter-summer period, comparisons of Aerosol Robotic Network L1 SDA dailyaveragefine mode AOD data showed that Moderate Resolution Imaging Spectroradiometer satellite remotesensing of AOD often did not retrieve and/or identify some of the highestfine mode AOD events in thisregion. Also, compared to models that include data assimilation of satellite retrieved AOD, the L1 SDAfinemode AOD was significantly higher in magnitude, particularly for the highest AOD events that were oftenassociated with significant cloudiness.

Eck, T. F.↗

NASA NTRS2013

Time Variations of Cosmic-Ray Helium Isotopes with BESS-Polar I

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) is configured with a solenoidal superconducting magnet and a suite of precision particle detectors, including time-of-flight hodoscopes based on plastic scintillators, a silica-aerogel Cherenkov detector, and a high resolution tracking system with a central jet-type drift chamber. The charges of incident particles are determined from energy losses in the scintillators. Their magnetic rigidities (momentum/charge) are measured by reconstructing each particle trajectory in the magnetic field, and their velocities are obtained by using the time-of-flight system. Together, these measurements can accurately identify helium isotopes among the incoming cosmic-ray helium nuclei up to energies in the GeV per nucleon region. The BESS-Polar I instrument flew for 8.5 days over Antarctica from December 13th to December 21st, 2004. Its long-duration flight and large geometric acceptance allow the time variations of isotopic fluxes to be studied for the first time. The time variations of helium isotope fluxes are presented here for rigidities from 1.2 to 2.5 GV and results are compared to previously reported proton data and neutron monitor data.

Cosmic-ray flux time variations↗

NASA NTRS2012

Measurement of the Cosmic-Ray Antiproton Spectrum at Solar Minimum with a Long-Duration Balloon Flight over Antarctica

The energy spectrum of cosmic-ray antiprotons (p-bar's) from 0.17 to 3.5 GeV has been measured using 7886 p-bar's detected by BESS-Polar II during a long-duration flight over Antarctica near solar minimum in December 2007 and January 2008. This shows good consistency with secondary p-bar calculations. Cosmologically primary p-bar's have been investigated by comparing measured and calculated p-bar spectra. BESS-Polar II data.show no evidence of primary p-bar's from the evaporation of primordial black holes.

Abe, K.↗

NASA NTRS2012

Search for Antihelium with the BESS-Polar Spectrometer

In two long-duration balloon flights over Antarctica, the BESS-Polar collaboration has searched for antihelium in the cosmic radiation with higher sensitivity than any reported investigation. BESSPolar I flew in 2004, observing for 8.5 days. BESS-Polar II flew in 2007-2008, observing for 24.5 days. No antihelium candidate was found in BESS-Polar I data among 8.4 x 10(exp 6) [Z] = 2 nuclei from 1.0 to 20 GV or in BESS-Polar II data among 4.0 x 10(exp 7) [Z] = 2 nuclei from 1.0 to 14 GV. Assuming antihelium to have the same spectral shape as helium, a 95% confidence upper limit of 6.9 x 10(exp -8) was determined by combining all the BESS data, including the two BESS-Polar flights. With no assumed antihelium spectrum and a weighted average of the lowest antihelium efficiencies from 1.6 to 14 GV, an upper limit of 1.0 x 10(exp -7) was determined for the combined BESS-Polar data. These are the most stringent limits obtained to date.

Sasaki, M.↗

NASA NTRS2011

Search for Cosmic-Ray Antiproton Origins and for Cosmological Antimatter with BESS

The balloon-borne experiment with a superconducting spectrometer (BESS) has performed cosmic-ray observations as a US-Japan cooperative space science program, and has provided fundamental data on cosmic rays to study elementary particle phenomena in the early Universe. The BESS experiment has measured the energy spectra of cosmic-ray antiprotons to investigate signatures of possible exotic origins such as dark matter candidates or primordial black holes. and searched for heavier antinuclei that might reach Earth from antimatter domains formed in the early Universe. The apex of the BESS program was reached with the Antarctic flight of BESS-Polar II, during the 2007- 2008 Austral Summer, that obtained over 4.7 billion cosmic-ray events from 24.5 days of observation. The flight took place at the expected solar minimum, when the sensitivity of the low-energy antiproton measurements to a primary source is greatest. Here, we report the scientific restults, focusing on the long-duration flights of BESS-Polar I (2004) and BESS-Polar II (2007-2008).

Yamamoto, A.↗

NASA NTRS2011

Measurement of Cosmic-Ray Antiproton Spectrum at Solar Minimum with a Long-Duration Balloon Flight in Antarctica

The energy spectrum of cosmic-ray antiprotons (p(raised bar)'s) collected by the BESS-Polar II instrument during a long-duration flight over Antarctica in the solar minimum period of December 2007 through January 2008. The p(raised bar) spectrum measured by BESS-Polar II shows good consistency with secondary p(raised bar) calculations. Cosmologically primary p(raised bar)'s have been searched for by comparing the observed and calculated p(raised bar) spectra. The BESSPolar II result shows no evidence of primary p(raised bar)'s originating from the evaporation of PBH.

Abe, K.↗

NASA NTRS2009

Systematics in the Electron Spectrum Measured by ATIC

An analysis of different parameters to separate electrons from protons in the ATIC experiment has been performed. Five separate discriminants were studied by different Monte Carlo programs, leading to a variety of results. Application to the ATIC data indicates the range of variation possible in the interpretation of the data. The results of this analysis, when compared with the published results [5], show good agreement in the most interesting region of energy (from 90 GeV to 600 GeV). The measured electron spectrum is compared with the recent data reported by Fermi/LAT, and there is no major disagreement between ATIC s results and Fermi/LAT. Finally, possible systematics-free, short energy scale features of the ATIC electron spectrum are mentioned. Keywords: ATIC, electron spectrum, fine structure

Panov, A. D.↗

NASA NTRS2009

Determining the Detection Efficiency and Background Level of ATIC Electron Observation from Flight Data

Observations of Cosmic-ray electrons are difficult due to the large flux of cosmic ray hadrons. The event selection efficiency and background levels can be estimated from flight data for the ATIC instrument. This reduces the dependence upon Monte Carlo simulations, which show differences between different codes, thereby reducing the systematic errors resulting from analyses that only use simulations. This paper discusses some of the methods used in the ATIC analysis to determine the detection efficiency and background level for the flight data.

Chang, J.↗

NASA NTRS2009

Observations of High Energy Cosmic Ray Electrons by the ATIC Balloon Experiment

Recently the Advanced Thin Ionization Calorimeter (ATIC) balloon experiment reported observations of high energy cosmic ray electrons over the energy range 300 to 800 GeV, indicating a feature or "bump" in the otherwise smoothly decreasing energy spectrum. The severe energy losses that occur as these high energy particles traverse the galaxy render the cosmic ray electron spectrum sensitive to local (a few kiloparsecs) sources and hence very interesting. The ATIC results are the first time that such a cosmic ray spectrum anomaly has been observed at high energy. Potential sources of this electron excess include pulsars, microquasars, supernovae remnants as well as the annihilation of exotic dark matter candidate particles. ATIC has had three successful high altitude flights over the continent of Antarctica 2000-2001, 2002-2003 and 2007-2008. Only results from the first two flights have been reported so far. During this talk we will discuss the ATIC experiment, the electron observations (including preliminary results from the most recent ATIC flight), examine the merits of the various source models and compare the ATIC observations with other recent measurements.

Guzik, T. G.↗

NASA NTRS2008

The Cosmic Ray Electron Excess

This slide presentation reviews the possible sources for the apparent excess of Cosmic Ray Electrons. The presentation reviews the Advanced Thin Ionization Calorimeter (ATIC) instrument, the various parts, how cosmic ray electrons are measured, and shows graphs that review the results of the ATIC instrument measurement. A review of Cosmic Ray Electrons models is explored, along with the source candidates. Scenarios for the excess are reviewed: Supernova remnants (SNR) Pulsar Wind nebulae, or Microquasars. Each of these has some problem that mitigates the argument. The last possibility discussed is Dark Matter. The Anti-Matter Exploration and Light-nuclei Astrophysics (PAMELA) mission is to search for evidence of annihilations of dark matter particles, to search for anti-nuclei, to test cosmic-ray propagation models, and to measure electron and positron spectra. There are slides explaining the results of Pamela and how to compare these with those of the ATIC experiment. Dark matter annihilation is then reviewed, which represent two types of dark matter: Neutralinos, and kaluza-Kline (KK) particles, which are next explained. The future astrophysical measurements, those from GLAST LAT, the Alpha Magnetic Spectrometer (AMS), and HEPCAT are reviewed, in light of assisting in finding an explanation for the observed excess. Also the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) could help by revealing if there are extra dimensions.

Chang, J.↗

NASA NTRS2007

Revised Energy Spectra for Primary Elements, H - Si, above 50 GeV from the ATIC-2 Science Flight

The Advanced Thin Ionization Calorimeter (ATIC) long duration balloon experiment had a successful science flight accumulating 18 days of data (12/02 - 1/03) during a single circumnavigation in Antarctica. ATIC measures the energy spectra of elements from H to Fe in primary cosmic rays using a fully active Bismuth Germanate calorimeter preceded by a carbon target, with embedded scintillator hodoscopes, and a silicon matrix charge detector at the top. Preliminary results from ATIC have been reported in previous conferences. The revised results reported here are derived from a new analysis of the data with improved charge resolution, lower background and revised energy calibration. The raw energy deposit spectra are de-convolved into primary energy spectra and extrapolated to the top of the atmosphere. We compare these revised results to previous data and comment upon the astrophysical interpretation of the results.

Wefel, J. P.↗

NASA NTRS2007

Relative Fluxes of Primary Particles in B-C-N-O Group from the ATIC Experiment (Science Flight)

The ATIC balloon-born experiment measures the energy spectra of elements from H to Fe in primary cosmic rays from about 100 GeV to 100 TeV. ATIC is comprised of a fully active bismuth germinate calorimeter, a carbon target with embedded scintillator hodoscopes, and a silicon matrix that is used as a main charge detector. The silicon matrix produces good charge resolution for the protons and helium but only a partial resolution for heavier nuclei. In the present paper a charge resolution of ATIC device was improved and backgrounds were reduced in the region from Be to Si by means of the upper layer of the scintillator hodoscope that was used as charge detector together with silicon matrix. Relative fluxes of nuclei B, C, N, O in the energy region from about 20 GeV/nucleon to 200 GeV/nucleon that were obtained from new high-resolution and high-quality charge spectra of nuclei are presented.

Panov, A. D.↗

NASA NTRS2002

Advanced Thin Ionization Calorimeter (ATIC) Update

The Advanced Thin Ionization Calorimeter (ATIC) experiment is designed to measure the composition and energy spectra of Z = 1 to 28 cosmic rays over the energy range of approximately 10 GeV - 100 TeV. ATIC is comprised of an eight-layer, 18 radiation length deep Bismuth Germanate (BGO) calorimeter, downstream of a 0.75 nuclear interaction length graphite target and an approximately 1 sq m finely segmented silicon charge detector. Interleaved with the graphite layers are three scintillator strip hodoscopes for pre-triggering and tracking. ATIC flew for the first time on a Long Duration Balloon (LDB) launched from McMurdo, Antarctica in January 2001. During its 16-day flight ATIC collected more than 30 million science events, along with housekeeping, calibration, and rate data. This presentation will describe the ATIC data processing, including calibration and efficiency corrections, and show results from analysis of this dataset. The next launch is planned for December 2002.

Ahn, H. S.↗

NASA NTRS2000

Particle Identification in the ACCESS Mission

ACCESS (Assembly Concept for Construction of Erectable Space Structures) is a planned Space Station mission to measure the elemental energy spectra of Galactic cosmic rays at energies above 100 GeV/nuc. ACCESS consists of a transition radiation detector (TRD) mounted on top of an ionization calorimeter (IC). A silicon matrix detector placed on top of the IC determines the elemental identity of each cosmic ray measured by the IC. The silicon matrix must be designed to identify each cosmic ray in the presence of backscatter from the calorimeter. Because the TRD is mounted above the IC, the matrix must also recognize cosmic rays that have interacted within the TRD before reaching the IC. We will report the results of detailed GEANT simulations of the silicon matrix in ACCESS. Results will be presented on backscatter interference with charge identification and the ability of the matrix to recognize cosmic rays that interacted in the TRD.

Wang, J. Z.↗