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1

Encounters with Insects: Field and Classroom Activities.  

ERIC Educational Resources Information Center

Describes field and classroom activities to conduct investigations of insects that emphasize capture and release rather than capture for semipermanent collections. Provides contact information for the Young Entomologists' Society, Inc. (JRH)

McLure, John W.

1995-01-01

2

Enhancement of magnetic fields arising from galactic encounters  

NASA Astrophysics Data System (ADS)

Context. Galactic encounters are usually marked by a substantial increase in synchrotron emission of the interacting galaxies when compared with the typical emission from similar non-interacting galaxies. This increase is believed to be associated with an increase in the star formation rate and the turbulent magnetic fields resulting from the encounter, while the regular magnetic field is usually believed to decrease as a result of the encounter. Aims: We attempt to verify these expectations. Methods: We consider a simple, however rather realistic, mean-field galactic dynamo model where the effects of small-scale generation are represented by random injections of magnetic field resulting from star forming regions. We represent an encounter by the introduction of large-scale streaming velocities and by an increase in small-scale magnetic field injections. The latter describes the effect of an increase in the star formation rate caused by the encounter. Results: We demonstrate that large-scale streaming, with associated deviations in the rotation curve, can result in an enhancement of the anisotropic turbulent (ordered) magnetic field strength, mainly along the azimuthal direction. This leads to a significant temporary increase of the total magnetic energy during the encounter; the representation of an increase in star formation rate has an additional strong effect. In contrast to expectations, the large-scale (regular) magnetic field structure is not significantly destroyed by the encounter. It may be somewhat weakened for a relatively short period, and its direction after the encounter may be reversed. Conclusions: The encounter causes enhanced total and polarized emission without increase in the regular magnetic field strength. The increase in synchrotron emission caused by the large-scale streaming can be comparable to the effect of the increase in the star formation rate, depending on the choice of parameters. The effects of the encounter on the total magnetic field energy last only slightly longer than the duration of the encounter (ca. 1 Gyr). However, a long-lasting field reversal of the regular magnetic field may result.

Moss, D.; Sokoloff, D.; Beck, R.; Krause, M.

2014-06-01

3

Titan's magnetic field signature during the first Cassini encounter.  

PubMed

The magnetic field signature obtained by Cassini during its first close encounter with Titan on 26 October 2004 is presented and explained in terms of an advanced model. Titan was inside the saturnian magnetosphere. A magnetic field minimum before closest approach marked Cassini's entry into the magnetic ionopause layer. Cassini then left the northern and entered the southern magnetic tail lobe. The magnetic field before and after the encounter was approximately constant for approximately 20 Titan radii, but the field orientation changed exactly at the location of Titan's orbit. No evidence of an internal magnetic field at Titan was detected. PMID:15890875

Backes, Heiko; Neubauer, Fritz M; Dougherty, Michele K; Achilleos, Nicholas; André, Nicolas; Arridge, Christopher S; Bertucci, Cesar; Jones, Geraint H; Khurana, Krishan K; Russell, Christopher T; Wennmacher, Alexandre

2005-05-13

4

Astrophysical False Positives Encountered in Wide-Field Transit Searches  

NASA Astrophysics Data System (ADS)

Wide-field photometric transit surveys for Jupiter-sized planets are inundated by astrophysical false positives, namely systems that contain an eclipsing binary and mimic the desired photometric signature. We discuss several examples of such false alarms. These systems were initially identified as candidates by the PSST instrument at Lowell Observatory. For three of the examples, we present follow-up spectroscopy that demonstrates that these systems consist of (1) an M-dwarf in eclipse in front of a larger star, (2) two main-sequence stars presenting grazing-incidence eclipses, and (3) the blend of an eclipsing binary with the light of a third, brighter star. For an additional candidate, we present multi-color follow-up photometry during a subsequent time of eclipse, which reveals that this candidate consists of a blend of an eclipsing binary and a physically unassociated star. We discuss a couple indicators from publicly-available catalogs that can be used to identify which candidates are likely giant stars, a large source of the contaminants in such surveys.

Charbonneau, David; Brown, Timothy M.; Dunham, Edward W.; Latham, David W.; Looper, Dagny L.; Mandushev, Georgi

2004-06-01

5

Results of the international field trial with the Reason for Encounter Classification.  

PubMed

The Reason for Encounter Classification (RFEC) was designed by a WHO Working Party to classify the reasons why patients seek care at the primary care level. It is designed along two axes: Chapters and Components. Each chapter carries an alpha-code which is the first character of the basic 3-character alphanumeric code. Each chapter is subdivided into seven "components" carrying 2-digit numeric codes. The field trial was undertaken by family physicians and nurses in: Australia, Barbados, Brazil, Hungary, Malaysia, the Netherlands, Norway and the US. 90497 RFE's were analysed. Their distribution over the chapters and components characterize the content of international primary care. Listings with the most common RFE's in the participating countries reflect the cultural differences. It is concluded that the RFEC is not only feasible to classify reasons why patients seek care but also to classify the diagnosis and the process of primary care. As a result of this, the International Classification of Primary Care (ICPC) succeeds the RFEC. PMID:4002871

Lamberts, H; Meads, S; Wood, M

1985-01-01

6

Gamma radiation field intensity meter  

DOEpatents

A gamma radiation intensity meter measures dose rate of a radiation field. The gamma radiation intensity meter includes a tritium battery emitting beta rays generating a current which is essentially constant. Dose rate is correlated to an amount of movement of an electroscope element charged by the tritium battery. Ionizing radiation decreases the voltage at the element and causes movement. A bleed resistor is coupled between the electroscope support element or electrode and the ionization chamber wall electrode.

Thacker, Louis H. (Knoxville, TN)

1995-01-01

7

Gamma radiation field intensity meter  

DOEpatents

A gamma radiation intensity meter measures dose rate of a radiation field. The gamma radiation intensity meter includes a tritium battery emitting beta rays generating a current which is essentially constant. Dose rate is correlated to an amount of movement of an electroscope element charged by the tritium battery. Ionizing radiation decreases the voltage at the element and causes movement. A bleed resistor is coupled between the electroscope support element or electrode and the ionization chamber wall electrode.

Thacker, Louis H. (Knoxville, TN)

1994-01-01

8

All field simultaneous radiation therapy  

US Patent & Trademark Office Database

This invention describes a system for generating multiple simultaneous tunable electron and photon beams and monochromatic x-rays for all field simultaneous radiation therapy (AFSRT), tumor specific AFSRT and screening for concealed elements worn on to the body or contained in a container. Inverse Compton scattering renders variable energy spent electron and tunable monochromatic x-rays. It's spent electron beam is reused for radiation with electron beam or to generate photon beam. Tumor specific radiation with Auger transformation radiation is facilitated by exposing high affinity tumor bound heavy elements with external monochromatic x-rays. Heavy elements like directly iodinated steroid molecule that has high affinity binding to estrogen receptor in breast cancer and to iodinated testosterone in prostate cancer or with directly implanted nanoparticles into the tumor are exposed with tuned external monochromatic x-rays for tumor specific radiation therapy. Likewise, screening element's atom's k, l, m, n shell specific Auger transformation radiation generated by its exposure to external monochromatic x-rays is used to screen for concealed objects. Multiple beam segments from a beam storage ring or from octagonal beam lines are simultaneously switched on for simultaneous radiation with multiple beams. The beam on time to expose a tumor or an object is only a few seconds. It also facilitates breathing synchronized radiation therapy. The intensity modulated radiation therapy (IMRT) and intensity modulated screening for concealed objects (IMSFCO) is rendered by varying beam intensities of multiple simultaneous beams. The isocentric additive high dose rate from simultaneously converging multiple beams, the concomitant hyperthermia and chemotherapy and tumor specific radiation therapy and the AFSRT's very low radiation to the normal tissue all are used to treat a tumor with lower radiation dose and to treat a radioresistant and multiple times recurrent tumors that heave no other alternative treatments.

2012-05-08

9

Radiation Fields on Schwarzschild Spacetime  

NASA Astrophysics Data System (ADS)

In this paper we define the radiation field for the wave equation on the Schwarzschild black hole spacetime. In this context it has two components: the rescaled restriction of the time derivative of a solution to null infinity and to the event horizon. In the process, we establish some regularity properties of solutions of the wave equation on the spacetime. In particular, we prove that the regularity of the solution across the event horizon and across null infinity is determined by the regularity and decay rate of the initial data at the event horizon and at infinity. We also show that the radiation field is unitary with respect to the conserved energy and prove support theorems for each piece of the radiation field.

Baskin, Dean; Wang, Fang

2014-04-01

10

International Cometary Explorer encounter with Giacobini-Zinner - Magnetic field observations  

NASA Technical Reports Server (NTRS)

The vector helium magnetometer on the International Cometary Explorer observed the magnetic fields induced by the interaction of comet Giacobini-Zinner with the solar wind. A magnetic tail was penetrated about 7800 kilometers downstream from the comet and was found to be 10,000 kilometers wide. It consisted of two lobes, containing oppositely directed fields with strengths up to 60 nanoteslas, separated by a plasma sheet about 1000 kilometers thick containing a thin current sheet. The magnetotail was enclosed in an extended ionosheath characterized by intense hydromagnetic turbulence and interplanetary fields draped around the comet. A distant bow wave, which may or may not have been a bow shock, was observed at both edges of the ionoshpeath. Weak turbulence was observed well upstream of the bow wave.

Smith, E. J.; Tsurutani, B. T.; Slavin, J. A.; Jones, D. E.; Siscoe, G. L.

1986-01-01

11

Identifying the Discomfort: An Examination of Ethical Issues Encountered by MSW Students during Field Placement  

ERIC Educational Resources Information Center

The purpose of this descriptive study was to determine which ethical issues graduate social work students experienced most frequently during their field placement, the resources students used to resolve these issues, and whether such resources were helpful. The results indicate that conflicts concerning beneficence versus agency policy and…

Dodd, Sarah-Jane

2007-01-01

12

Encounters with fierce dogs and itchy bedbugs: why my first field work failed  

PubMed Central

This essay, which is the fifth in the series “Recollections, Reflections, and Revelations: Personal Experiences in Ethnobiology”, is a personal reminiscence by the researcher on his first field experience in Turkey in the late 1970s, which was a failure from an ethnobiological point of view but a success for a social scientist pursuing Turkic studies. The author later returned to ethnobiology during subsequent fieldwork on the Faroes.

2014-01-01

13

Encounters with fierce dogs and itchy bedbugs: why my first field work failed.  

PubMed

This essay, which is the fifth in the series "Recollections, Reflections, and Revelations: Personal Experiences in Ethnobiology", is a personal reminiscence by the researcher on his first field experience in Turkey in the late 1970s, which was a failure from an ethnobiological point of view but a success for a social scientist pursuing Turkic studies. The author later returned to ethnobiology during subsequent fieldwork on the Faroes. PMID:24885471

Svanberg, Ingvar

2014-01-01

14

Gravitational radiative corrections from effective field theory  

SciTech Connect

In this paper we construct an effective field theory (EFT) that describes long wavelength gravitational radiation from compact systems. To leading order, this EFT consists of the multipole expansion, which we describe in terms of a diffeomorphism invariant point particle Lagrangian. The EFT also systematically captures 'post-Minkowskian' corrections to the multipole expansion due to nonlinear terms in general relativity. Specifically, we compute long distance corrections from the coupling of the (mass) monopole moment to the quadrupole moment, including up to two mass insertions. Along the way, we encounter both logarithmic short distance (UV) and long wavelength (IR) divergences. We show that the UV divergences can be (1) absorbed into a renormalization of the multipole moments and (2) resummed via the renormalization group. The IR singularities are shown to cancel from properly defined physical observables. As a concrete example of the formalism, we use this EFT to reproduce a number of post-Newtonian corrections to the gravitational wave energy flux from nonrelativistic binaries, including long distance effects up to 3 post-Newtonian (v{sup 6}) order. Our results verify that the factorization of scales proposed in the NRGR framework of Goldberger and Rothstein is consistent up to order 3PN.

Goldberger, Walter D.; Ross, Andreas [Department of Physics, Yale University, New Haven, Connecticut 06520 (United States)

2010-06-15

15

Radiated fields from an electromagnetic pulse simulator  

Microsoft Academic Search

Simulators of electromagnetic pulses allow generation within a limited time of very high-intensity fields such as those produced in a nuclear explosion. These fields can be radiated out of the test zone at a lower but nevertheless significant level; if the intensity of these fields is sufficiently high, damage to humans and electronic equipment can result. An evaluation of the

M. Pelletier; G. Y. Delisle; S. Kashyap

1990-01-01

16

Radiated fields from an electromagnetic pulse simulator  

NASA Astrophysics Data System (ADS)

Simulators of electromagnetic pulses allow generation within a limited time of very high-intensity fields such as those produced in a nuclear explosion. These fields can be radiated out of the test zone at a lower but nevertheless significant level; if the intensity of these fields is sufficiently high, damage to humans and electronic equipment can result. An evaluation of the potential danger of these simulator emissions requires knowledge of the amplitude, duration, and the energy of the radiated impulses. A technique is presented for calculating the fields radiated by a parallel-plane electromagnetic pulse simulator. The same method can also be applied to a rhombic type simulator. Sample numerical results are presented along with the calculations of the energy and power density and a discussion of the formation of the field in the frequency domain.

Pelletier, M.; Delisle, G. Y.; Kashyap, S.

17

The Voyager 2 Neptune encounter  

SciTech Connect

The findings made by the Voyager 2 Neptune encounter are reviewed. Data on the bowshock, magnetic field, magnetosphere, rings, plasma sheet, aurora, moons, and dust of Neptune are discussed. Findings made concerning Triton are summarized.

Tsurutani, B.T. (JPL, Pasadena, CA (USA))

1989-10-01

18

Monte Carlo simulation of the radiation environment encountered by a biochip during a space mission to Mars.  

PubMed

Simulations with a Monte Carlo tool kit have been performed to determine the radiation environment a specific device, called a biochip, would face if it were placed into a rover bound to explore Mars' surface. A biochip is a miniaturized device that can be used to detect organic molecules in situ. Its specific detection part is constituted of proteins whose behavior under cosmic radiation is completely unknown and must be investigated to ensure a good functioning of the device under space conditions. The aim of this study is to define particle species and energy ranges that could be relevant to investigate during experiments on irradiation beam facilities. Several primary particles have been considered for galactic cosmic ray (GCR) and solar energetic particle (SEP) contributions. Ionizing doses accumulated in the biochip and differential fluxes of protons, alphas, neutrons, gammas, and electrons have been established for both the Earth-Mars transit and the journey at Mars' surface. Neutrons and gammas appear as dominant species on martian soil, whereas protons dominate during the interplanetary travel. Depending on solar event occurrence during the mission, an ionizing dose of around a few Grays (1 Gy = 100 rad) is expected. PMID:19368517

Le Postollec, A; Incerti, S; Dobrijevic, M; Desorgher, L; Santin, G; Moretto, P; Vandenabeele-Trambouze, O; Coussot, G; Dartnell, L; Nieminen, P

2009-04-01

19

New approach to the classical radiation fields of moving dipoles  

Microsoft Academic Search

We present an alternative approach for calculating classical radiation fields of moving point sources. This approach simplifies considerably the computation of the radiation fields of moving dipoles. As a novel application, we calculate the radiation fields of an arbitrarily moving toroid dipole. As a by-product, we derive new formulas for the radiated power and the radiation reaction force of nonrelativistic

José A. Heras

1998-01-01

20

The NASA High Intensity Radiated Fields Laboratory  

NASA Technical Reports Server (NTRS)

High Intensity Radiated Fields (HIRF) are the result of a multitude of intentional and nonintentional electromagnetic sources that currently exists in the world. Many of today's digital systems are susceptible to electronic upset if subjected to certain electromagnetic environments (EME). Modern aerospace designers and manufacturers increasingly rely on sophisticated digital electronic systems to provide critical flight control in both military, commercial, and general aviation aircraft. In an effort to understand and emulate the undesired environment that high energy RF provides modern electronics, the Electromagnetics Research Branch (ERB) of the Flight Electronics and Technology Division (FETD) conducts research on RF and microwave measurement methods related to the understanding of HIRF. In the High Intensity Radiated Fields Laboratory, the effects of high energy radiating electromagnetic fields on avionics and electronic systems are tested and studied.

Williams, Reuben A.

1997-01-01

21

A model of SVC radiation in magnetic dipole field and radiation varying with magnetic field. II - SVC radiation mechanism and radiation variation with magnetic field  

Microsoft Academic Search

The radio radiation and other radiative characteristics of the slowly varying component (SVC) are examined by means of a model of electron temperature and density and incorporating a dipole magnetic field. The model is based on recent EUV data regarding the chromosphere-corona transition region. The plasma electron temperature, density, and magnetic field are studied as a function of height above

Ren-Yang Zhao

1991-01-01

22

Polarized radiation diagnostics of stellar magnetic fields  

NASA Astrophysics Data System (ADS)

The main techniques used to diagnose magnetic fields in stars from polarimetric observations are presented. First, a summary of the physics of spectral line formation in the presence of a magnetic field is given. Departures from the simple case of linear Zeeman effect are briefly considered: partial Paschen-Back effect, contribution of hyperfine structure, and combined Stark and Zeeman effects. Important approximate solutions of the equation of transfer of polarized light in spectral lines are introduced. The procedure for disk-integration of emergent Stokes profiles, which is central to stellar magnetic field studies, is described, with special attention to the treatment of stellar rotation. This formalism is used to discuss the determination of the mean longitudinal magnetic field (through the photographic technique and through Balmer line photopolarimetry). This is done within the specific framework of Ap stars, which, with their unique large-scale organized magnetic fields, are an ideal laboratory for studies of stellar magnetism. Special attention is paid to those Ap stars whose magnetically split line components are resolved in high-dispersion Stokes I spectra, and to the determination of their mean magnetic field modulus. Various techniques of exploitation of the information contained in polarized spectral line profiles are reviewed: the moment technique (in particular, the determination of the crossover and of the mean quadratic field), Zeeman-Doppler imaging, and least-squares deconvolution. The prospects that these methods open for linear polarization studies are sketched. The way in which linear polarization diagnostics complement their Stokes I and V counterparts is emphasized by consideration of the results of broad band linear polarization measurements. Illustrations of the use of various diagnostics to derive properties of the magnetic fields of Ap stars are given. This is used to show the interest of deriving more physically realistic models of the geometric structure of these fields. How this can possibly be achieved is briefly discussed. An overview of the current status of polarimetric studies of magnetic fields in non-degenerate stars of other types is presented. The final section is devoted to magnetic fields of white dwarfs. Current knowledge of magnetic fields of isolated white dwarfs is briefly reviewed. Diagnostic techniques are discussed, with particular emphasis on the variety of physical processes to be considered for understanding of spectral line formation over the broad range of magnetic field strengths encountered in these stars.

Mathys, Gautier

23

AfricaArray International Geophysics Field School: Applications of Near Surface Geophysics to challenges encountered in mine planning  

NASA Astrophysics Data System (ADS)

Hard rock exploration and mining presents many opportunities for the effective use of near surface geophysics. For over 10 years the AfricaArray international geophysics field school has been hosted at a variety of mines in South Africa. While the main objective of the field school is practical training for the next generation of geophysicists, being hosted at a mine has allowed us to investigate applications of near surface geophysics in the early stages of mine planning and development as geophysics is often cheaper and faster than drilling. Several applications include: detailed delineation of dykes and stringer dykes, physical property measurements on drill core for modeling and marker horizons, determination of overburden thickness, locations of water and faults. Dolerite dykes are usually magnetic and are associated with loss of ground (i.e. where the dyke replaces the ore and thus reduces the amount of ore available) and safety/stability concerns. Thus the accurate mapping of dykes and narrow stringers that are associated with them are crucial to the safe planning of a mine. We have acquired several case studies where ground magnetic surveys have greatly improved on the resolution and detail of airborne magnetic surveys in regions of complicated dyke swarms. In many cases, thin stringer dykes of less than 5 cm have been detected. Physical property measurements of these dykes can be used to distinguish between different ages of dykes. It is important to accurately determine overburden thickness when planning an open pit mine as this directly affects the cost of development. Depending on the nature of the overburden, both refraction seismic and or DC resistivity can provide continuous profiling in the area of interest that fills in gaps between boreholes. DC resistivity is also effective for determining water associated with dykes and structures that may affect mine planning. The field school mainly addresses the training of a variety of students. The core students are the geophysics Honours students (~4th year undergraduates). In addition, up to 8 students from all over Africa are included in the program to help address practical training in Africa. The final cohort are minority students from the USA. Participants spend a week planning and costing out surveys, a week in the field collecting data using different methods including: gravity, DGPS, magnetics, resistivity, refraction seismic, EM methods, core logging and physical property measurements. The final week is spent interpreting and integrating their results. Graduate students are given the opportunity to instruct on the field school and manage the logistics for a particular method. The field school is unique in Africa and satisfies a need for practical training with limited resources, with a rare blend of cultural interactions!

Webb, S. J.; Jones, M. Q.; Durrheim, R. J.; Nyblade, A.; Snyman, Q.

2012-12-01

24

Reading the Other: Ethics of Encounter  

ERIC Educational Resources Information Center

Most scholarly fields, at least in the humanities, have been asking the same questions about the politics of encounter for hundreds of years: Should we try to find a way to encounter an other without appropriating it, without imposing ourselves on it? Is encountering-without-appropriating even possible? These questions are profuse and taken up…

Allen, Sarah

2008-01-01

25

The Pioneer of the Group Encounter Movement.  

ERIC Educational Resources Information Center

The purpose of this paper was to (1) identify the Pioneer of the Group Encounter Movement, and (2) expose and clarify some of the ambiguities, contradictions and backbiting evident in the Group Encounter Field. The origins of the group encounter movement are examined with a particularly strong emphasis on J. L. Moreno and his introduction of…

Treadwell, Thomas; Treadwell, Jean

26

Automatic field shaping for conformal radiation therapy.  

PubMed

A computer method has been developed to shape the radiation field to conform to the shape of the target as visualized through the beam's eye view (BEV) perspective for conformal radiation therapy. Initially, a series of 2D target contours to define the target size are input into the computer. These target contour data are mapped onto a 3D surface and thereafter projected onto a BEV plane. The projection's outer boundary of the target is auto-contoured. After auto-contouring, a margin is automatically added to define the radiation beam cross section. Since the BEV plane is arbitrarily oriented about the target, the beam orientation can be non-coplanar to the plane of the target contours. For a chosen beam orientation, the conformal treatment beam cross section can be generated automatically using this computer technique and output to either a laser printer, a plotter or stored on files for transfer to the linear accelerator computer system. PMID:7924269

Ayyangar, K

1994-04-01

27

Radiated fields in rail launchers operation  

Microsoft Academic Search

In this paper electromagnetic fields radiated from a railgun operating system with a plasma armature are investigated. A small-bore railgun has been fabricated in their laboratory, a capacitor bank (0.12 F-160 V) has been used as energy supply and an experimental setup has been implemented. Experiments have been performed in a remotely operated shielded semi-anechoic chamber in conformity with current

Andrea Tellini; Bernardo Tellini; Gianluca Genovesi

2001-01-01

28

Plasma wake field XUV radiation source  

DOEpatents

A XUV radiation source uses an interaction of electron beam pulses with a gas to create a plasma radiator. A flowing gas system (10) defines a circulation loop (12) with a device (14), such as a high pressure pump or the like, for circulating the gas. A nozzle or jet (16) produces a sonic atmospheric pressure flow and increases the density of the gas for interacting with an electron beam. An electron beam is formed by a conventional radio frequency (rf) accelerator (26) and electron pulses are conventionally formed by a beam buncher (28). The rf energy is thus converted to electron beam energy, the beam energy is used to create and then thermalize an atmospheric density flowing gas to a fully ionized plasma by interaction of beam pulses with the plasma wake field, and the energetic plasma then loses energy by line radiation at XUV wavelengths Collection and focusing optics (18) are used to collect XUV radiation emitted as line radiation when the high energy density plasma loses energy that was transferred from the electron beam pulses to the plasma.

Prono, Daniel S. (Los Alamos, NM); Jones, Michael E. (Los Alamos, NM)

1997-01-01

29

Cellular response to modulated radiation fields  

NASA Astrophysics Data System (ADS)

Cell survival following exposure to spatially modulated beams, as created by intensity-modulated radiotherapy (IMRT), is investigated. In vitro experiments were performed using malignant melanoma cells (MM576) exposed to a therapeutic megavoltage photon beam. We compared cell survival in modulated fields with cell survival in uniform control fields. Three different spatial modulations of the field were used: a control 'uniform' field in which all cells in a flask were uniformly exposed; a 'quarter' field in which 25% of cells at one end of the flask were exposed and a 'striped' field in which 25% of cells were exposed in three parallel stripes. The cell survival in both the shielded and unshielded regions of the modulated fields, as determined by a clonogenic assay, were compared to the cell survival in the uniform field. We have distinguished three ways in which cell survival is influenced by the fate of neighbouring cells. The first of these (type I effect) is the previously reported classical Bystander effect, where cell survival is reduced when communicating with irradiated cells. We find two new types of Bystander effect. The type II effect is an observed increase in cell survival when nearby cells receive a lethal dose. The type III effect is an increase in the survival of cells receiving a high dose of radiation, when nearby cells receive a low dose. These observations of the Bystander effects emphasize the need for improved radiobiological models, which include communicated effects and account for the effects of modulated dose distribution.

Claridge Mackonis, E.; Suchowerska, N.; Zhang, M.; Ebert, M.; McKenzie, D. R.; Jackson, M.

2007-09-01

30

Limited-field radiation for bifocal germinoma  

SciTech Connect

Purpose: To report the incidence, characteristics, treatment, and outcomes of bifocal germinomas treated with chemotherapy followed by focal radiation. Methods and Materials: This was a retrospective review. Inclusion criteria included radiologic diagnosis of bifocal germinoma involving the pineal and neurohypophyseal region, no evidence of dissemination on spinal MRI, negative results from cerebrospinal fluid cytologic evaluation, and negative tumor markers. Results: Between 1995 and 2004, 6 patients (5 male, 1 female; median age, 12.8 years) fulfilled the inclusion criteria. All had symptoms of diabetes insipidus at presentation. On MRI, 4 patients had a pineal and suprasellar mass, and 2 had a pineal mass associated with abnormal neurohypophyseal enhancement. All patients received chemotherapy followed by limited-field radiation and achieved complete remission after chemotherapy. The radiation field involved the whole ventricular system (range, 2,400-4,000 cGy) with or without a boost to the primary lesions. All patients remain in complete remission at a median follow-up of 48.1 months (range, 9-73.4 months). Conclusions: This experience suggests that bifocal germinoma can be considered a locoregional rather than a metastatic disease. Chemotherapy and focal radiotherapy might be sufficient to provide excellent outcomes. Staging refinement with new diagnostic tools will likely increase the incidence of the entity.

Lafay-Cousin, Lucie [Pediatric Brain Tumor Program, Hospital for Sick Children, Toronto, Ontario (Canada)]. E-mail: lucie.lafay-cousin@sickkids.ca; Millar, Barbara-Ann [Department of Radiation Oncology, Princess Margaret Hospital, Toronto, Ontario (Canada); Mabbott, Donald [Pediatric Brain Tumor Program, Hospital for Sick Children, Toronto, Ontario (Canada); Department of Psychology, Hospital for Sick Children, Toronto, Ontario (Canada); Spiegler, Brenda [Department of Psychology, Hospital for Sick Children, Toronto, Ontario (Canada); Drake, Jim [Department of Neurosurgery, Hospital for Sick Children, Toronto, Ontario (Canada); Bartels, Ute [Pediatric Brain Tumor Program, Hospital for Sick Children, Toronto, Ontario (Canada); Huang, Annie [Pediatric Brain Tumor Program, Hospital for Sick Children, Toronto, Ontario (Canada); Bouffet, Eric [Pediatric Brain Tumor Program, Hospital for Sick Children, Toronto, Ontario (Canada)

2006-06-01

31

Observations of the diffuse UV radiation field  

NASA Technical Reports Server (NTRS)

Spectra are presented for the diffuse UV radiation field between 1250 to 3100 A from eight different regions of the sky, which were obtained with the Johns Hopkins UVX experiment. UVX flew aboard the Space Shuttle Columbia (STS-61C) in January 1986 as part of the Get-Away Special project. The experiment consisted of two 1/4 m Ebert-Fastie spectrometers, covering the spectral range 1250 to 1700 A at 17 A resolution and 1600 to 3100 A at 27 A resolution, respectively, with a field of view of 4 x .25 deg, sufficiently small to pick out regions of the sky with no stars in the line of sight. Values were found for the diffuse cosmic background ranging in intensity from 300 to 900 photons/sq cm/sec/sr/A. The cosmic background is spectrally flat from 1250 to 3100 A, within the uncertainties of each spectrometer. The zodiacal light begins to play a significant role in the diffuse radiation field above 2000 A, and its brightness was determined relative to the solar emission. Observed brightnesses of the zodiacal light in the UV remain almost constant with ecliptic latitude, unlike the declining visible brightnesses, possibly indicating that those (smaller) grains responsible for the UV scattering have a much more uniform distribution with distance from the ecliptic plane than do those grains responsible for the visible scattering.

Murthy, Jayant; Henry, R. C.; Feldman, P. D.; Tennyson, P. D.

1989-01-01

32

The Submicrosecond Structure of Lightning Radiation Fields.  

NASA Astrophysics Data System (ADS)

Lightning electric field (E) and electric field derivative (dE/dt) signals have been recorded using sensors with 40 ns and 10 ns response times, respectively. Field propagation between the source and the recording antennas was entirely over salt water, so that distortions due to ground wave propagation were minimal below about 20 MHz. The fast-varying, initial portions of return stroke E fields have 10% to 90% risetimes which average 90 (+OR -) 40 ns. Peak dE/dt values range from 7 to 71 V/m/(mu)s, with a mean and standard deviation of 33 (+OR-) 14 V/m/(mu)s, when normalized to 100 km using an inverse distance dependence. The shapes of first and subsequent stroke fields are similar, but peak subsequent stroke dE/dts are larger than peak first stroke dE/dts in some flashes. The temporal structure of the fast varying fields produced by leader steps near the ground are very similar to return stroke fields. The mean maximum leader dE/dt, at 100 km, is 27 (+OR-) 9 V/m/(mu)s. Large amplitude radiation fields produced by cloud discharge processes tend to be bipolar, with either positive or negative initial polarity and usually have several, fast, unipolar pulses superimposed on the initial half cycle. Cloud discharge fields with positive initial polarity usually precede cloud-to-ground flashes and produce a mean maximum dE/dt of 16 (+OR-) 8 V/m/(mu)s. The field derivatives for all processes tend to be large when the amplitude of the associated fast field change is large. Estimates of lightning current derivatives, made using range normalized dE/dt measurements, average 155 (+OR-) 70 kA/(mu)s, 135 (+OR-) 45 kA/(mu)s, and 80 (+OR -) 40 kA/(mu)s, for return strokes, leader steps, and cloud discharges, respectively, and a current wavefront velocity of 1 x 10('8) m/s. These values are about 10 times larger than the maximum dI/dt recorded in strikes to instrumented towers. Lightning field amplitude spectra have been derived by Fourier analyzing dE/dt waveforms, and the spectral amplitudes decrease as 1/f('2) or faster with increasing frequency in the interval from about 6 to 20 MHz.

Weidman, Charles David

33

Experimental models of porcine post-weaning colibacillosis and their relationship to post-weaning diarrhoea and digestive disorders as encountered in the field.  

PubMed

The aim of this study was to develop a reliable model system of porcine post-weaning colibacillosis, and in doing so to assess the primary relationship of enterotoxigenic Escherichia coli to post-weaning diarrhoea and digestive disorders as encountered in the field. Six sequential experiments were carried out using 168 SPF piglets weaned into an optimal controlled environment at 28 days of age. The piglets were allocated to 23 treatment groups, 17 of which were inoculated either orally or intragastrically with enterotoxigenic strains of E. coli (LT+, STI+, STII+) possessing adhesive factors including K88 (F4). The piglets were challenged either once (Day 4 post-weaning) or on several days post-weaning, with the challenge load for each inoculation varying from 10(8) to 10(12) CFU. Overall 14.5% of inoculated pigs developed severe illness and died: these had lesions in their digestive tracts typical of colibacillosis. Diarrhoea occurred on at least 1 day in 50% of inoculated pigs, but was transient (1.7 days on average), appeared very soon after challenge (sometimes within half a day), and was accompanied by signs of depression and low weight gain. Generally a prompt recovery then occurred. In the second 2 weeks post-inoculation daily weight gain reached the same level in most inoculated groups of pigs as in the uninoculated controls. Only a small number of pigs developed a chronic enteritis lasting several days, as is typically observed in field cases. Diarrhoea was more common in the piglets that were tested adhesive positive to the K88 fimbriae receptor, but the disorders were no more severe in these animals. The response of all pigs depended primarily on the inoculum used, and especially on the challenge load. Although enterotoxigenic E. coli are clearly important in the aetiology of post-weaning diarrhoea, other factors are also required for the production of the chronic post-weaning digestive disorders and ill-thrift that are commonly encountered in commercial piggeries. PMID:10727839

Madec, F; Bridoux, N; Bounaix, S; Cariolet, R; Duval-Iflah, Y; Hampson, D J; Jestin, A

2000-03-15

34

Dosimetry in radiation fields around high-energy proton accelerators  

Microsoft Academic Search

Radiation dosimetry at high-energy proton accelerators is a difficult task because of the complexity of the stray radiation field. A good knowledge of this mixed radiation field is very important to be able to select the type of detectors (active and\\/or passive) to be employed for routine area monitoring and to choose the personal dosimeter legally required for estimating the

S. Agosteo; S. Rollet; M. Silari; C. Theis

2008-01-01

35

Radiation field characterization and shielding studies  

NASA Astrophysics Data System (ADS)

The ELI-Beamlines facility in the Czech Republic will offer to users versatile radiation sources in an unprecedented energy range. Laser-driven proton beams are expected to range between 50 MeV and 3 GeV. The number of particles delivered per laser shot is estimated to be 1010-1012. Starting from analytical calculations, as well as from dedicated simulations, the main proton fields produced in the laser-matter interaction have been described and used to characterize the "source terms" in full simulations with the Monte Carlo code FLUKA in order to assess a proper shielding. We present the results of this study and the proposed solutions together with a cross-check analysis performed with the Monte Carlo code GEANT4.

Ferrari, A.; Amato, E.; Margarone, D.

2013-07-01

36

Angry Birds Space Encounter  

NASA Video Gallery

At NASA's Kennedy Space Center Visitor Complex in Florida, a grand opening celebration was held for the new Angry Birds Space Encounter, March 22. Finland-based Rovio Entertainment, the creator of ...

37

Radiation field mapping using a mechanical-electronic detector  

NASA Astrophysics Data System (ADS)

A method of radiation field mapping of a scanned electron beam using a Faraday-type detector and an electromechanical linear translator is presented. Utilizing this arrangement, fluence and fluence rate measurements can be made at different locations within the radiation field. The Faraday-type detector used in these experiments differs from most as it consists of a hollow stainless steel sphere. Results are presented in two- and three-dimensional views of the radiation field.

Czayka, M.; Fisch, M.

2010-04-01

38

Radiation Hard Silicon Nanowire Field Effect Transistors  

Microsoft Academic Search

Silicon nanowire-based transistors were fabricated and tested for their radiation hardness by exposure to Co60 X-ray radiation at doses ranging from 50-250 kRad. Minor degradation of the transistor characteristics was observed at 250 kRad. Our results show the inherent radiation hardness of nanowire devices.

L. Tsakalakos; P. Losee; J. Balch; A. L. Bogorad; W. J. Taft; J. J. Likar; R. Herschitz

2008-01-01

39

The clinical encounter revisited.  

PubMed

The patient-physician encounter is the pivotal starting point of any healthcare delivery, but it is subject to multiple process breakdowns and prevalent suboptimal performance. An overview of the techniques and components of a successful encounter valid for every setting and readily applicable is presented, stressing 7 rules: (1) ensuring optimal environment, tools, and teamwork; (2) viewing each encounter not only as a cognitive/biomedical challenge, but also as a personal one, and a learning opportunity; (3) adopting an attitude of curiosity, concentration, compassion, and commitment, and maintaining a systematic, orderly approach; (4) "simple is beautiful"-making the most of the basic clinical data and their many unique advantages; (5) minding "the silent dimension"-being attentive to the patient's identity and emotions; (6) following the "Holy Trinity" of gathering all information, consulting databases/colleagues, and tailoring gained knowledge to the individual patient; and (7) using the encounter as a "window of opportunity" to further the patient's health-not just the major problem, by addressing screening and prevention; promoting health literacy and shared decision-making; and establishing proper follow-up. Barriers to implementation identified can be overcome by continuous educational interventions. A high-quality encounter sets a virtuous cycle of patient-provider interaction and results in increasing satisfaction, adherence, and improved health outcomes. PMID:24333201

Schattner, Ami

2014-04-01

40

Transient Radiated Fields from Sources Located on a Planar Surface.  

National Technical Information Service (NTIS)

Expressions for the transient radiated electric fields of a planar array of sources are developed for elements having known field distribution, as well as time delay, located on an infinite, perfectly conducting, ground plane. The analysis of such arrays ...

C. E. Smith

1977-01-01

41

Voyager's Last Encounter  

NASA Technical Reports Server (NTRS)

This video describes Voyager 2's encounter with Neptune. Computer animation and actual data convey Voyager's discoveries such as turbulent storms and dark spots in Neptune's atmosphere, six new moons, Neptune's three rings, and the presence of frozen methane on Triton, as researchers at NASA's Jet Propulsion Laboratory describe Voyager's achievements.

1989-01-01

42

Mysterious Earthly Encounters.  

ERIC Educational Resources Information Center

Examines the use of a storyline approach to integrated learning and provides a detailed example. The "Mysterious Encounters--Earth" program based on a detective storyline includes an intensive environmental experience at a local park and provides the springboard and framework to help teachers integrate environmental learning into classroom…

Warner, Alan; Taylor, George

1994-01-01

43

A Lakatosian Encounter  

ERIC Educational Resources Information Center

There is much to be learned and pondered by reading "Proofs and Refutations," by Imre Lakatos. It highlights the importance of mathematical definitions, and how definitions evolve to capture the essence of the object they are defining. It also provides an exhilarating encounter with the ups and downs of the mathematical reasoning process, where…

Chick, Helen

2010-01-01

44

Encounter Group Effects of Soccer Team Performance.  

ERIC Educational Resources Information Center

Suggests that a positive relationship exists between encounter group experience and the soccer team performance--a conclusion worthy of consideration in further research in the fields of psychology and sociology of sports. (Author)

Magen, Zipora

1980-01-01

45

Radiation Fields in the Vicinity of Compact Accelerator Neutron Generators  

SciTech Connect

Intense pulsed radiation fields emitted from sealed tube neutron generators provide a challenge for modern health physics survey instrumentation. The spectral sensitivity of these survey instruments requires calibration under realistic field conditions while the pulsed emission characteristics of neutron generators can vary from conditions of steady-state operation. As a general guide for assessing radiological conditions around neutron generators, experiments and modeling simulations have been performed to assess radiation fields near DD and DT neutron generators. The presence of other materials and material configurations can also have important effects on the radiation dose fields around compact accelerator neutron generators.

David L. Chichester; Brandon W. Blackburn; Augustine J. Caffrey

2006-10-01

46

Understanding metropolitan patterns of daily encounters  

PubMed Central

Understanding of the mechanisms driving our daily face-to-face encounters is still limited; the field lacks large-scale datasets describing both individual behaviors and their collective interactions. However, here, with the help of travel smart card data, we uncover such encounter mechanisms and structures by constructing a time-resolved in-vehicle social encounter network on public buses in a city (about 5 million residents). Using a population scale dataset, we find physical encounters display reproducible temporal patterns, indicating that repeated encounters are regular and identical. On an individual scale, we find that collective regularities dominate distinct encounters’ bounded nature. An individual’s encounter capability is rooted in his/her daily behavioral regularity, explaining the emergence of “familiar strangers” in daily life. Strikingly, we find individuals with repeated encounters are not grouped into small communities, but become strongly connected over time, resulting in a large, but imperceptible, small-world contact network or “structure of co-presence” across the whole metropolitan area. Revealing the encounter pattern and identifying this large-scale contact network are crucial to understanding the dynamics in patterns of social acquaintances, collective human behaviors, and—particularly—disclosing the impact of human behavior on various diffusion/spreading processes.

Sun, Lijun; Axhausen, Kay W.; Lee, Der-Horng; Huang, Xianfeng

2013-01-01

47

Understanding metropolitan patterns of daily encounters.  

PubMed

Understanding of the mechanisms driving our daily face-to-face encounters is still limited; the field lacks large-scale datasets describing both individual behaviors and their collective interactions. However, here, with the help of travel smart card data, we uncover such encounter mechanisms and structures by constructing a time-resolved in-vehicle social encounter network on public buses in a city (about 5 million residents). Using a population scale dataset, we find physical encounters display reproducible temporal patterns, indicating that repeated encounters are regular and identical. On an individual scale, we find that collective regularities dominate distinct encounters' bounded nature. An individual's encounter capability is rooted in his/her daily behavioral regularity, explaining the emergence of "familiar strangers" in daily life. Strikingly, we find individuals with repeated encounters are not grouped into small communities, but become strongly connected over time, resulting in a large, but imperceptible, small-world contact network or "structure of co-presence" across the whole metropolitan area. Revealing the encounter pattern and identifying this large-scale contact network are crucial to understanding the dynamics in patterns of social acquaintances, collective human behaviors, and--particularly--disclosing the impact of human behavior on various diffusion/spreading processes. PMID:23918373

Sun, Lijun; Axhausen, Kay W; Lee, Der-Horng; Huang, Xianfeng

2013-08-20

48

Measurement of Far-Field and Near-Field Radiation Patterns from Optical Fibers.  

National Technical Information Service (NTIS)

Systems are described for measuring the far- and near-field radiation patterns from optical fibers. Parameters which affect measurement precision, accuracy, resolution, and signal-to-noise ratio are discussed. Measurements using radiation patterns are cov...

E. M. Kim D. L. Franzen

1981-01-01

49

Radiation field associated with Hiroshima and Nagasaki  

SciTech Connect

Accuracy of dosimetric estimates can determine the value of the atomic bomb survivor experience in establishing radiation risks. The status of a major revision of this dosimetry, initiated in 1980, is assessed. 3 references, 6 figures.

Loewe, W.E.

1984-08-01

50

Radiation fields of open-cavity radiators and a backfire antenna  

Microsoft Academic Search

The radiation fields of an open-cavity radiator are studied theoretically and experimentally. This antenna consists of a simple open-ended circular cavity with a primary radiator, which includes a dipole, a dipole array, a terminated transmission line, and a loop, placed at an appropriate location inside the cavity. For the case of the dipole array exciter, because of the presence of

Min Hong; D. Nyquist; K. Chen

1970-01-01

51

New theory of radiative energy transfer in free electromagnetic fields  

Microsoft Academic Search

A theory of radiative transfer in free, statistically stationary electromagnetic fields is presented which provides a model for energy transport that is rigorous within the framework of the stochastic theory of the classical field as well as within the framework of the theory of the quantized field. The present theory emphasizes the need for characterizing energy transport by means of

E. Wolf

1976-01-01

52

COHERENT AND INCOHERENT STATES OF THE RADIATION FIELD  

Microsoft Academic Search

Methods are developed for discussing the photon statistics of arbitrary ; radiation fields in fully quantummechanical terms. In order to keep the ; classical limit of quantum electrodynamics plainly in view, extensive use is made ; of the coherent states of the field. These states, which reduce the field ; correlation functions to factorized forms, are shown to offer a

Roy Glauber

1963-01-01

53

NEAR-FIELD RADIATIVE TRANSFER: THERMAL RADIATION, THERMOPHOTOVOLTAIC POWER GENERATION AND OPTICAL CHARACTERIZATION  

Microsoft Academic Search

This dissertation focuses on near-field radiative transfer, which can be defined as the discipline concerned with energy transfer via electromagnetic waves at sub-wavelength distances. Three specific subjects related to this discipline are investigated, namely nearfield thermal radiation, nanoscale-gap thermophotovoltaic (nano-TPV) power generation and optical characterization. An algorithm for the solution of near-field thermal radiation problems in one-dimensional layered media is

Mathieu Francoeur

2010-01-01

54

Detection of alpha radiation in a beta radiation field  

DOEpatents

An apparatus and method for detecting alpha particles in the presence of high activities of beta particles utilizing an alpha spectrometer. The apparatus of the present invention utilizes a magnetic field applied around the sample in an alpha spectrometer to deflect the beta particles from the sample prior to reaching the detector, thus permitting detection of low concentrations of alpha particles. In the method of the invention, the strength of magnetic field required to adequately deflect the beta particles and permit alpha particle detection is given by an algorithm that controls the field strength as a function of sample beta energy and the distance of the sample to the detector.

Mohagheghi, Amir H. (Albuquerque, NM); Reese, Robert P. (Edgewood, NM)

2001-01-01

55

Theoretical investigation of non-equilibrium chemistry and optical radiation in hypersonic flow fields  

NASA Technical Reports Server (NTRS)

Future space vehicles returning from distant missions or high earth orbits may enter the upper regions of the atmosphere and use aerodynamic drag to reduce their velocity before they skip out of the atmosphere and enter low earth orbit. The Aeroassist Flight Experiment (AFE) is designed to explore the special problems encountered in such entries. A computer code was developed to calculate the radiative transport along line-or-sight in the general 3-D flow field about an arbitrary entry vehicle, if the temperatures and species concentrations along the line-of-sight are known. The radiative heating calculation at the stagnation point of the AFE vehicle along the entry trajectory was performed, including a detailed line-by-line accounting of the radiative transport in the vacuum ultraviolet (below 200 nm) by the atomic N and O lines. A method was developed for making measurements of the haze particles in the Titan atmosphere above 200 km altitude. Several other tasks of a continuing nature, to improve the technical ability to calculate the nonequilibrium gas dynamic flow field and radiative heating of entry vehicles, were completed or advanced.

Whiting, Ellis E.

1990-01-01

56

VOYAGER OBSERVATIONS OF THE DIFFUSE FAR-ULTRAVIOLET RADIATION FIELD  

SciTech Connect

The two Voyager spacecraft have completed their planetary exploration mission and are now probing the outer realms of the heliosphere. The Voyager ultraviolet spectrometers continued to operate well after the Voyager 2 Neptune encounter in 1989. We present a complete database of diffuse radiation observations made by both Voyagers: a total of 1943 spectra (500-1600 A) scattered throughout the sky. These include observations of dust-scattered starlight, emission lines from the hot interstellar medium, and a number of locations where no diffuse radiation was detected, with the very low upper limit of about 25 photons cm{sup -2} s{sup -1} sr{sup -1} A{sup -1}. Many of these observations were from late in the mission when there was significantly less contribution from interplanetary emission lines and thus less contamination of the interstellar signal.

Murthy, Jayant [Indian Institute of Astrophysics, Bengalooru 560 034 (India); Henry, Richard Conn [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Holberg, Jay B., E-mail: jmurthy@yahoo.com [Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States)

2012-03-01

57

Fiber optics in transient radiation fields  

SciTech Connect

Fiber optics have been utilized in a variety of sensor and data transmission roles, some of which are complicated by the presence of ionizing radiation. In this paper, transient radiation effects in fibers are reviewed. Both luminescence and absorption processes are discussed in this paper, with emphasis on the latter subject. Most discussions are on effects occurring below 100 ns, with limited data in the microsecond time regime. This paper is intended as a review paper and its scope is restricted to previously published work. Areas that will profit from further study are highlighted.

Lyons, P.B.

1985-01-01

58

On the field of antenna radiation circular the polarization  

Microsoft Academic Search

The article concerns submission of antenna radiation field in a circular polarization basis. A block diagram of measuring system for the investigation of amplitude and polarization directional diagrams is presented.

L. Y. Ilnytskiy; I. I. Mykhal'chuk

2010-01-01

59

Device for remote viewing of objects in ionizing radiation fields  

Microsoft Academic Search

A device is described for remote viewing of objects in ionizing radiation fields, wherein a fibre-optics channel for transmitting the image of an object under observation beyond the biological shield against ionizing radiation comprises an entrance lens in whose immediate vicinity there is placed one of the ends of a bundle of optic fibres, the other end of the bundle

B. I. Ivanov; N. M. Ivanov; I. K. Malakhov; J. D. Motin; I. A. Reformatsky; P. R. Sinitsyn

1980-01-01

60

The Electromagnetic Dipole Radiation Field through the Hamiltonian Approach  

ERIC Educational Resources Information Center

The dipole radiation from an oscillating charge is treated using the Hamiltonian approach to electrodynamics where the concept of cavity modes plays a central role. We show that the calculation of the radiation field can be obtained in a closed form within this approach by emphasizing the role of coherence between the cavity modes, which is…

Likar, A.; Razpet, N.

2009-01-01

61

Radiation tolerant silicon nitride insulated gate field effect transistors  

NASA Technical Reports Server (NTRS)

Metal-Insulated-Semiconductor Field Effect Transistor /MISFET/ device uses a silicon nitride passivation layer over a thin silicon oxide layer to enhance the radiation tolerance. It is useful in electronic systems exposed to space radiation environment or the effects of nuclear weapons.

Newman, P. A.

1969-01-01

62

Effects of hypersonic field and anharmonic interactions on channelling radiation  

NASA Astrophysics Data System (ADS)

The effects of a hypersonic field on positron channelling radiation are considered. Anharmonic effects of the transverse potential induced by these longitudinal fields are incorporated and the wavefunction of the planar channelled positron is found by the solution of Dirac equation under the resonant influence of hypersound. An expression for the resonant frequency is estimated. The transition probabilities and the intensity of the channelling radiation are also calculated. It is found that the anharmonic effects change the spectral distributions considerably.

George, Juby; Pathak, Anand P.; Goteti, L. N. S. Prakash; Nagamani, G.

2007-03-01

63

Reconstruction of radiating sound fields using minimum energy method.  

PubMed

A method for reconstructing a pressure field at the surface of a radiating body or source is presented using recording data of a microphone array. The radiation is assumed to consist of many spherical radiators, as microphone positions are present in the array. These monopoles are weighted using a parameter alpha, which broadens or narrows the overall radiation directivity as an effective and highly intuitive parameter of the radiation characteristics. A radiation matrix is built out of these weighted monopole radiators, and for different assumed values of alpha, a linear equation solver reconstructs the pressure field at the body's surface. It appears that from these many arbitrary reconstructions, the correct one minimizes the reconstruction energy. The method is tested, localizing the radiation points of a Balinese suling flute, reconstructing complex radiation from a duff frame drum, and determining the radiation directivity for the first seven modes of an Usbek tambourine. Stability in terms of measurement noise is demonstrated for the plain method, and additional highly effective algorithm is added for a noise level up to 0 dB. The stability of alpha in terms of minimal reconstruction energy is shown over the whole range of possible values for alpha. Additionally, the treatment of unwanted room reflections is discussed, still leading to satisfactory results in many cases. PMID:20058977

Bader, Rolf

2010-01-01

64

Radiation fields of the short-backfire antenna  

Microsoft Academic Search

A method for the approximate calculation of the radiation fields of a short-backfire antenna is presented. This technique is based upon the assumption that the aperture field is distributed approximately cosinusoidally in both horizontal and vertical planes as evidenced by near-zone field measurements. It appears that the short-backfire antenna is essentially a circular aperture antenna with cosinusoidal aperture field, and

K. Chen; D. Nyquist; J. Lin

1968-01-01

65

The Geomagnetic Field and Radiation in Near-Earth Orbits  

NASA Technical Reports Server (NTRS)

This report shows, in detail, how the geomagnetic field interacts with the particle flux of the radiation belts to create a hazard to spacecraft and humans in near-Earth orbit. It illustrates the geometry of the geomagnetic field lines, especially around the area where the field strength is anomalously low in the South Atlantic Ocean. It discusses how the field will probably change in the future and the consequences that may have on hazards in near space.

Heirtzler, J. R.

1999-01-01

66

DNA Damage Responses following Exposure to Modulated Radiation Fields  

PubMed Central

During the delivery of advanced radiotherapy treatment techniques modulated beams are utilised to increase dose conformity across the target volume. Recent investigations have highlighted differential cellular responses to modulated radiation fields particularly in areas outside the primary treatment field that cannot be accounted for by scattered dose alone. In the present study, we determined the DNA damage response within the normal human fibroblast AG0-1522B and the prostate cancer cell line DU-145 utilising the DNA damage assay. Cells plated in slide flasks were exposed to 1 Gy uniform or modulated radiation fields. Modulated fields were delivered by shielding 25%, 50% or 75% of the flask during irradiation. The average number of 53BP1 or ?H2AX foci was measured in 2 mm intervals across the slide area. Following 30 minutes after modulated radiation field exposure an increase in the average number of foci out-of-field was observed when compared to non-irradiated controls. In-field, a non-uniform response was observed with a significant decrease in the average number of foci compared to uniformly irradiated cells. Following 24 hrs after exposure there is evidence for two populations of responding cells to bystander signals in-and out-of-field. There was no significant difference in DNA damage response between 25%, 50% or 75% modulated fields. The response was dependent on cellular secreted intercellular signalling as physical inhibition of intercellular communication abrogated the observed response. Elevated residual DNA damage observed within out-of-field regions decreased following addition of an inducible nitric oxide synthase inhibitor (Aminoguanidine). These data show, for the first time, differential DNA damage responses in-and out-of-field following modulated radiation field delivery. This study provides further evidence for a role of intercellular communication in mediating cellular radiobiological response to modulated radiation fields and may inform the refinement of existing radiobiological models for the optimization of advanced radiotherapy treatment plans.

Trainor, Colman; Butterworth, Karl T.; McGarry, Conor K.; McMahon, Stephen J.; O'Sullivan, Joe M.; Hounsell, Alan R.; Prise, Kevin M.

2012-01-01

67

DNA damage responses following exposure to modulated radiation fields.  

PubMed

During the delivery of advanced radiotherapy treatment techniques modulated beams are utilised to increase dose conformity across the target volume. Recent investigations have highlighted differential cellular responses to modulated radiation fields particularly in areas outside the primary treatment field that cannot be accounted for by scattered dose alone. In the present study, we determined the DNA damage response within the normal human fibroblast AG0-1522B and the prostate cancer cell line DU-145 utilising the DNA damage assay. Cells plated in slide flasks were exposed to 1 Gy uniform or modulated radiation fields. Modulated fields were delivered by shielding 25%, 50% or 75% of the flask during irradiation. The average number of 53BP1 or ?H2AX foci was measured in 2 mm intervals across the slide area. Following 30 minutes after modulated radiation field exposure an increase in the average number of foci out-of-field was observed when compared to non-irradiated controls. In-field, a non-uniform response was observed with a significant decrease in the average number of foci compared to uniformly irradiated cells. Following 24 hrs after exposure there is evidence for two populations of responding cells to bystander signals in-and out-of-field. There was no significant difference in DNA damage response between 25%, 50% or 75% modulated fields. The response was dependent on cellular secreted intercellular signalling as physical inhibition of intercellular communication abrogated the observed response. Elevated residual DNA damage observed within out-of-field regions decreased following addition of an inducible nitric oxide synthase inhibitor (Aminoguanidine). These data show, for the first time, differential DNA damage responses in-and out-of-field following modulated radiation field delivery. This study provides further evidence for a role of intercellular communication in mediating cellular radiobiological response to modulated radiation fields and may inform the refinement of existing radiobiological models for the optimization of advanced radiotherapy treatment plans. PMID:22912853

Trainor, Colman; Butterworth, Karl T; McGarry, Conor K; McMahon, Stephen J; O'Sullivan, Joe M; Hounsell, Alan R; Prise, Kevin M

2012-01-01

68

Radiation from Relativistic Shocks with Turbulent Magnetic Fields  

NASA Technical Reports Server (NTRS)

Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs at shocked region. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the shock. The "jitter" radiation from deflected electrons in turbulent magnetic fields has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. New recent calculation of spectra with various different Lorentz factors of jets (two electrons) and initial magnetic fields. New spectra based on small simulations will be presented.

Nishkawa, K.; Medvedev, M.; Zhang, B.; Hardee, P.; Niemiec, J.; Mizuno, A.; Nordlund, A.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Oka, M.; Fishman, J.

2009-01-01

69

Gravitational radiation from preheating with many fields  

NASA Astrophysics Data System (ADS)

Parametric resonances provide a mechanism by which particles can be created just after inflation. Thus far, attention has focused on a single or many inflaton fields coupled to a single scalar field. However, generically we expect the inflaton to couple to many other relativistic degrees of freedom present in the early universe. Using simulations in an expanding Friedmann-Lemaître-Robertson-Walker spacetime, in this paper we show how preheating is affected by the addition of multiple fields coupled to the inflaton. We focus our attention on gravitational wave production — an important potential observational signature of the preheating stage. We find that preheating and its gravitational wave signature is robust to the coupling of the inflaton to more matter fields.

Giblin, John T., Jr.; Price, Larry R.; Siemens, Xavier

2010-08-01

70

Radiation Fields in the Vicinity of Compact Accelerator Neutron Generators  

Microsoft Academic Search

Intense pulsed radiation fields emitted from sealed tube neutron generators provide a challenge for modern health physics survey instrumentation. The spectral sensitivity of these survey instruments requires calibration under realistic field conditions while the pulsed emission characteristics of neutron generators can vary from conditions of steady-state operation. As a general guide for assessing radiological conditions around neutron generators, experiments and

David L. Chichester; Brandon W. Blackburn; Augustine J. Caffrey

2008-01-01

71

Radiation Fields in the Vicinity of Compact Accelerator Neutron Generators  

Microsoft Academic Search

Intense pulsed radiation fields emitted from sealed tube neutron generators provide a challenge for modern health physics survey instrumentation. The spectral sensitivity of these survey instruments requires calibration under realistic field conditions while the pulsed emission characteristics of neutron generators can vary from conditions of steady-state operation. As a general guide for assessing radiological conditions around neutron generators, experiments and

David L. Chichester; Brandon W. Blackburn; Augustine J. Caffrey

2006-01-01

72

Field distribution in a generalized geometric radiation state  

NASA Astrophysics Data System (ADS)

Both the Wigner function and the field distribution function in the generalized geometric state of the radiation field, which were recently introduced by us [A.-S. F. Obada, S. S. Hassan, R. R. Puri, and M. S. Abdalla, Phys. Rev. A 48, 3174 (1993)], are calculated exactly and examined in both the phase-averaged and the nonaveraged cases.

Batarfi, H. A.; Abdalla, M. Sebawe; Obada, A.-S. F.; Hassan, S. S.

1995-03-01

73

Fields radiated by a nanoemitter in a graphene sheet  

Microsoft Academic Search

The extraordinary properties of graphene make it a very promising material for optoelectronics. However, basic attributes of the electromagnetic field in graphene are still unexplored. Here we report on the in-plane fields radiated by a nanoemitter lying on a graphene sheet in terahertz regime, which present a rich dependence on frequency, distance to the source, and orientation of the dipole

A. Yu. Nikitin; F. Guinea; F. J. Garcia-Vidal; L. Martin-Moreno

2011-01-01

74

Scientific results from the Pioneer Saturn encounter - Summary  

NASA Technical Reports Server (NTRS)

The scientific results of the Pioneer Saturn encounter with Saturn are summarized. The Pioneer mission was designed to image the planet, its satellites and rings, and measure its particulate environment and the magnetic field and photon and charged particle radiation by means of 11 operational scientific instruments and its 2.293-GHz telemetry carrier signal. Principle results of the mission include the discovery of an additional ring and a previously unidentified satellite, the further characterization of the physical properties of Saturn and its magnetic field, and the description of the planetary magnetosphere. The successful completion of the mission demonstrated the ability of spacecraft such as Voyager 1 and 2 to survive the particle environments of Saturn's rings and trapped radiation environments, and Pioneer Saturn is expected to continue transmitting information on the interplanetary medium and the solar wind interaction with the interstellar medium until the mid-1980's.

Opp, A. G.

1980-01-01

75

Corrosion of metals and alloys in high radiation fields  

SciTech Connect

Degradation in the properties of structural materials in high-energy proton accelerators will occur as a result of the radiation environment during routine accelerator operations. The potential for such degradation must be included in design and service life assessments of the materials and components. Structural materials in the window, target/blanket, and reflector regions of high-energy proton accelerators will be exposed to a mixed proton-neutron flux that will change the material's exposure environment and cause displacement damage and implant spallation products in the exposed metal. The effects of implantation and displacement damage on materials behavior have been studied on a more or less continuous basis for decades, while radiation effects on corrosion and corrosion related degradation processes has received relatively little attention. The high radiation fields will accelerate corrosion, enhance hydrogen uptake and permeation, and promote corrosion fatigue through environmental changes induced by radiolysis and the deposition of spallation products. Aluminum alloys are particularly susceptible to radiation-induced acceleration of corrosion, and may experience a decreased resistance to fatigue damage. The irradiation fields and the (n, p) reactions associated with tritium production will enhance the uptake and permeation of tritium through austenitic stainless. These radiation-induced effects must be considered in any realistic assessment of material performance in the APT target/blanket region. This paper rationalizes the impact of high radiation fields on corrosion, hydrogen embrittlement, and corrosion fatigue, and relates that impact to radiation-induced changes in chemical reactivity, hydrogen fugacity, and surface chemistry.

Sindelar, R.L.; Lam, P.S.; Louthan, M.R. Jr.; Iyer, N.C.

1999-09-01

76

Spontaneous Radiation Emission from Short, High Field Strength Insertion Devices  

SciTech Connect

Since the earliest papers on undulaters were published, it has been known how to calculate the spontaneous emission spectrum from ''short'' undulaters when the magnetic field strength parameter is small compared to unity, or in ''single'' frequency sinusoidal undulaters where the magnetic field strength parameter is comparable to or larger than unity, but where the magnetic field amplitude is constant throughout the undulater. Fewer general results have been obtained in the case where the insertion device is both short, i.e., the magnetic field strength parameter changes appreciably throughout the insertion device, and the magnetic field strength is high enough that ponderomotive effects, radiation retardation, and harmonic generation are important physical phenomena. In this paper a general method is presented for calculating the radiation spectrum for short, high-field insertion devices. It is used to calculate the emission from some insertion device designs of recent interest.

Geoffrey Krafft

2005-09-15

77

Field Testing of a Portable Radiation Detector and Mapping System  

SciTech Connect

Researchers at the Savannah River Site (SRS) have developed a man- portable radiation detector and mapping system (RADMAPS) which integrates the accumulation of radiation information with precise ground locations. RADMAPS provides field personnel with the ability to detect, locate, and characterize nuclear material at a site or facility by analyzing the gamma or neutron spectra and correlating them with position. the man-portable field unit records gamma or neutron count rate information and its location, along with date and time, using an embedded Global Positioning System (GPS). RADMAPS is an advancement in data fusion, integrating several off-the-shelf technologies with new computer software resulting in a system that is simple to deploy and provides information useful to field personnel in an easily understandable form. Decisions on subsequent actions can be made in the field to efficiently use available field resources. The technologies employed in this system include: recording GPS, radiation detection (typically scintillation detectors), pulse height analysis, analog-to-digital converters, removable solid-state (Flash or SRAM) memory cards, Geographic Information System (GIS) software and personal computers with CD-ROM supporting digital base maps. RADMAPS includes several field deployable data acquisition systems designed to simultaneously record radiation and geographic positions. This paper summarizes the capabilities of RADMAPS and some of the results of field tests performed with the system.

Hofstetter, K.J. [Westinghouse Savannah River Company, AIKEN, SC (United States); Hayes, D.W.; Eakle, R.F.

1998-03-01

78

Equilibrium correlations in charged fluids coupled to the radiation field  

SciTech Connect

We provide an exact microscopic statistical treatment of particle and field correlations in a system of quantum charges in equilibrium with a classical radiation field. Using the Feynman-Kac-Ito representation of the Gibbs weight, the system of particles is mapped onto a collection of random charged wires. The field degrees of freedom can be integrated out, providing an effective pairwise magnetic potential. We then calculate the contribution of the transverse field coupling to the large-distance particle correlations. The asymptotics of the field correlations in the plasma are also exactly determined.

El Boustani, Sami; Buenzli, Pascal R.; Martin, Philippe A. [Institute of Theoretical Physics, Swiss Federal Institute of Technology Lausanne, CH-1015, Lausanne EPFL (Switzerland)

2006-03-15

79

Forces on Dust Grains Exposed to Anisotropic Interstellar Radiation Fields  

Microsoft Academic Search

Grains exposed to anisotropic radiation fields are subjected to forces due to\\u000athe asymmetric photon-stimulated ejection of particles. These forces act in\\u000aaddition to the ``radiation pressure'' due to absorption and scattering. Here\\u000awe model the forces due to photoelectron emission and the photodesorption of\\u000aadatoms. The ``photoelectric'' force depends on the ambient conditions relevant\\u000ato grain charging. We find

Joseph C. Weingartner; B. T. Draine

2000-01-01

80

Synchrotron radiation in strongly coupled conformal field theories  

SciTech Connect

Using gauge/gravity duality, we compute the energy density and angular distribution of the power radiated by a quark undergoing circular motion in strongly coupled N=4 supersymmetric Yang-Mills theory. We compare the strong coupling results to those at weak coupling, finding them to be very similar. In both regimes, the angular distribution of the radiated power is in fact similar to that of synchrotron radiation produced by an electron in circular motion in classical electrodynamics: the quark emits radiation in a narrow beam along its velocity vector with a characteristic opening angle {alpha}{approx}1/{gamma}. To an observer far away from the quark, the emitted radiation appears as a short periodic burst, just like the light from a lighthouse does to a ship at sea. Our strong coupling results are valid for any strongly coupled conformal field theory with a dual classical gravity description.

Athanasiou, Christiana; Chesler, Paul M.; Liu, Hong; Rajagopal, Krishna [Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Nickel, Dominik [Institute for Nuclear Theory, University of Washington, Seattle, Washington 98195 (United States)

2010-06-15

81

IAEA programme in the field of radiation technology  

NASA Astrophysics Data System (ADS)

Radiation technologies applying gamma sources and electron accelerators for material modification are well-established processes. There are over 160 gamma industrial irradiators and 1300 electron industrial accelerators in operation worldwide. A new advancement in the field of radiation sources engineering is the development of high power direct e-/X conversion sources based on electron accelerators. Technologies to be developed beside environmental applications could be nanomaterials, structure engineered materials (sorbents, composites, ordered polymers, etc.) and natural polymers' processing. New products based on radiation-processed polysaccharides have already been commercialised in many countries of the East Asia and Pacific Region, especially in those being rich in natural polymers. Very important and promising applications concern environmental protection-radiation technology, being a clean and environment friendly process, helps to curb pollutants' emission as well. Industrial plants for flue gas treatment have been constructed in Poland and China. The pilot plant in Bulgaria using this technology has just started its operation. The Polish plant is equipped with accelerators of over 1 MW power, a breakthrough in radiation technology application. The industrial plant for wastewater treatment is under development in Korea and a pilot plant for sewage sludge irradiation has been in operation in India for many years. Due to recent developments, the Agency has restructured its programme and organized a Technical Meeting (TM) on "Emerging Applications of Radiation Technology for the 21st Century" at its Headquarters in Vienna, Austria, in April 2003, to review the present situation and possible developments of radiation technology to contribute to a sustainable development. This meeting provided the basic input to launch others in the most important fields of radiation technology applications: "Advances in Radiation Chemistry of Polymers" (Notre Dame, USA, September 2003), "Status of Industrial Scale Radiation Treatment of Wastewater" (Taejon, Republic of Korea, October 2003), "Radiation Processing of Polysaccharides" (Takasaki, Japan, November 2003), "Emerging Applications of Radiation in Nanotechnology" (Bologna, Italy, March 2004) and "Radiation Processing of Gaseous and Liquid Effluents" (Sofia, Bulgaria, September 2004). The Agency is presently supervising three Coordinated Research Projects on radiation wastewater treatment, radiation synthesis stimuli-responsive hydrogels for separation purposes and degradation effects of polymers. The role of this technology for a sustainable development is well illustrated by the fact that over 30 technical cooperation projects (including three regional ones) were accomplished in the years 2003-2004 and several new projects are being expected for the new cycle 2005-2006. Detailed analyses of the results of both, regular and TC programmes, laid the foundation for formulation of the new programme for the years 2006-2007. The emphasis will be put on nanotechnology, natural polymers, environment and health protection, including combat with hazardous bioagents.

Chmielewski, Andrzej G.; Haji-Saeid, Mohammad

2005-07-01

82

Radiation of Electron in the Field of Plane Light Wave  

SciTech Connect

Results of integration of a Lorentz equation for a relativistic electron moving in the field of running, plane, linear polarized electromagnetic wave are presented in the paper. It is shown that electron velocities in the field of the wave are almost periodic functions of time. For calculations of angular spectrum of electron radiation intensity expansion of the electromagnetic field in a wave zone into generalized Fourier series was used. Expressions for the radiation intensity spectrum are presented in the paper. Derived results are illustrated for electron and laser beam parameters of NSC KIPT X-ray generator NESTOR. It is shown that for low intensity of the interacting electromagnetic wave the results of energy and angular spectrum calculations in the frame of classical electrodynamics completely coincide with calculation results produced using quantum electrodynamics. Simultaneously, derived expressions give possibilities to investigate dependence of energy and angular Compton radiation spectrum on phase of interaction and the interacting wave intensity.

Zelinsky, A.; Drebot, I.V.; Grigorev, Yu.N.; Zvonareva, O.D.; /Kharkov, KIPT; Tatchyn, R.; /SLAC

2006-02-24

83

Cosmological fluctuations of a random field and radiation fluid  

NASA Astrophysics Data System (ADS)

A generalization of the random fluid hydrodynamic fluctuation theory due to Landau and Lifshitz is applied to describe cosmological fluctuations in systems with radiation and scalar fields. The viscous pressures, parametrized in terms of the bulk and shear viscosity coefficients, and the respective random fluctuations in the radiation fluid are combined with the stochastic and dissipative scalar evolution equation. This results in a complete set of equations describing the perturbations in both scalar and radiation fluids. These derived equations are then studied, as an example, in the context of warm inflation. Similar treatments can be done for other cosmological early universe scenarios involving thermal or statistical fluctuations.

Bastero-Gil, Mar; Berera, Arjun; Moss, Ian G.; Ramos, Rudnei O.

2014-05-01

84

The electromagnetic dipole radiation field through the Hamiltonian approach  

NASA Astrophysics Data System (ADS)

The dipole radiation from an oscillating charge is treated using the Hamiltonian approach to electrodynamics where the concept of cavity modes plays a central role. We show that the calculation of the radiation field can be obtained in a closed form within this approach by emphasizing the role of coherence between the cavity modes, which is discarded in the calculation of the radiation power. We believe that this simple case can elucidate some basic questions students pose when introduced to quantum electrodynamics or perturbation theory in quantum mechanics.

Likar, A.; Razpet, N.

2009-11-01

85

Near-field radiative transfer: Thermal radiation, thermophotovoltaic power generation and optical characterization  

NASA Astrophysics Data System (ADS)

This dissertation focuses on near-field radiative transfer, which can be defined as the discipline concerned with energy transfer via electromagnetic waves at sub-wavelength distances. Three specific subjects related to this discipline are investigated, namely near-field thermal radiation, nanoscale-gap thermophotovoltaic (nano-TPV) power generation and optical characterization. An algorithm for the solution of near-field thermal radiation problems in one-dimensional layered media is developed, and several tests are performed showing the accuracy, consistency and versatility of the procedure. The possibility of tuning near-field radiative heat transfer via thin films supporting surface phonon-polaritons (SPhPs) in the infrared is afterwards investigated via the computation of the local density of electromagnetic states and the radiative heat flux between two films. Results reveal that due to SPhP coupling, fine tuning of near-field radiative heat transfer is possible by solely varying the structure of the system, the structure being the film thicknesses and their distance of separation. The coexistence of two regimes of near-field thermal radiation between two thin films of silicon carbide is demonstrated via numerical simulations and an asymptotic analysis of the radiative heat transfer coefficient. The impacts of thermal effects on the performances of nano-TPV power generators are investigated via the solution of the coupled near-field thermal radiation, charge and heat transport problem. The viability of nano-TPV devices proposed so far in the literature, based on a tungsten radiator at 2000 K and indium gallium antimonide cell, is questioned due to excessive heating of the junction converting thermal radiation into electricity. Using a convective thermal management system, a heat transfer coefficient as high as 105 Wm-2K-1 is required to maintain the junction at room temperature. The possibility of characterizing non-intrusively, and potentially in real-time, nanoparticles from 5 nm to 100 nm in size via scattered surface wave is explored. The feasibility of the characterization framework is theoretically demonstrated via a sensitivity analysis of the scattering matrix elements. Measurements of the scattering matrix elements for 200 nm and 50 nm gold spherical particles show the great sensitivity of the characterization tool, although an ultimate calibration is difficult with the current version of the experimental set-up. KEYWORDS: Near-field thermal radiation, Surface phonon-polariton, Nanoscale-gap thermophotoltaic power generation, Optical characterization of nanoparticles, Scattering (Mueller) matrix

Francoeur, Mathieu

86

Effect of radiation reaction on particle motion and production in IZEST-strong fields  

NASA Astrophysics Data System (ADS)

We discuss radiation physics in fields approaching the Schwinger field. Among the leading effects in such strong fields are: (1) lepton production; (2) radiation effects from highly accelerated electrons; and (3) radiation back-reaction. Once applied to multi-TeV electrons, the intense electromagnetic fields could produce radiating muons.

Sokolov, I. V.; Mourou, G. A.; Naumova, N. M.

2014-05-01

87

STABILITY OF THE TOROIDAL MAGNETIC FIELD IN STELLAR RADIATION ZONES  

SciTech Connect

The stability of the magnetic field in radiation zones is of crucial importance for mixing, angular momentum transport, etc. We consider the stability properties of a star containing a predominant toroidal field in spherical geometry by means of a linear stability in the Boussinesq approximation taking into account the effect of thermal conductivity. We calculate the growth rate of instability and analyze in detail the effects of stable stratification and heat transport. We argue that the stabilizing influence of gravity can never entirely suppress the instability caused by electric currents in radiation zones. However, the stable stratification can essentially decrease the growth rate of instability.

Bonanno, Alfio [INAF, Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania (Italy); Urpin, Vadim, E-mail: alfio.bonanno@inaf.it, E-mail: vadim.urpin@uv.es [INFN, Sezione di Catania, Via S. Sofia 72, 95123 Catania (Italy)

2012-03-10

88

Near-field radiative energy transfer at nanometer distances  

NASA Astrophysics Data System (ADS)

Near-field thermal radiation which can exceed blackbody radiation by several orders of magnitude has potential applications in energy conversion devices, nanofabrication, and near-field imaging. The present dissertation provides a comprehensive and thorough investigation of near-field heat transfer between parallel plates at nanometer distances. The first part of this dissertation focuses on the fundamentals of nanoscale thermal radiation through a systematic study on the near-field heat transfer between doped Si plates. In order to calculate the near-field heat transfer, it is important to accurately predict the dielectric function of doped Si. The dielectric function of doped Si which is described by the Drude model is a function of carrier concentration and mobility. Hence, accurate ionization and carrier mobility models for both p- and n-type Si are identified after a careful review of the available literature. The radiative properties calculated using the improved dielectric function agrees to a good extent with measurements performed using a FTIR. The near-field heat transfer between doped Si plates at varying doping levels is then calculated using the improved dielectric functions. Several important and characteristic features of near-field radiation are revealed in the analysis. An interesting issue regarding the maximum achievable nanoscale thermal radiation arises out of the study on near-field heat transfer in doped Si. The second part of this dissertation investigates the maximum achievable nearfield thermal radiation between two plates at finite vacuum gaps. Initially, both the emitter and the receiver are assumed to have identical frequency-independent dielectric functions and a cut off in the order of the lattice spacing is set on the upper limit of the wavevector. The energy transfer is maximum when the real part of dielectric function is around -1 due to surface waves. On the other hand, there is a strong relationship between the imaginary part of the dielectric function and the vacuum gap. While the study using frequency independent dielectric function is not realistic, it lays down the guidelines for the parametric optimization of dielectric functions of real materials for achieving maximum near-field heat transfer. A parametric study of the different adjustable parameters in the Drude and Lorentz model is performed in order to analyze their effect on the near-field heat transfer. It is seen that the optimized Drude model always results in greater near-field heat transfer compared to the Lorentz model and the maximum achievable near-field heat transfer is nearly 1 order greater than that between real materials. In the third part of this dissertation, the unusual penetration depth and the energy streamlines in near-field thermal radiation are studied. It is seen that unlike far-field radiation, the penetration depth in near-field heat transfer is dependent on the vacuum gap. This unusual feature results in a 10 nm thick SiC film behaving as completely opaque when the vacuum gap is around 10 nm. The energy streamlines inside the emitter, receiver, and the vacuum gap are calculated using fluctuation electrodynamics and errors generated due to thin film optics are pointed out. It is seen that the lateral shift of the streamlines inside the emitter can be greater than that in the vacuum gap for SiC. However, for doped Si, the lateral shift is comparable in the different media. While the study on the penetration depth determines the thickness of the emitter, the streamlines determine the lateral dimension.

Basu, Soumyadipta

89

Axion radiation by nonrelativistic nondegenerate neutrons in a magnetic field  

NASA Astrophysics Data System (ADS)

The axion luminosity of magnetic neutron stars associated with the flip of the anomalous magnetic moment of nondegenerate nonrelativistic neutrons is calculated using the derived polarization matrix of neutron density in the magnetic field. It is shown that the foregoing mechanism of axion radiation is major for the magnetic-field induction B > (˜) 1018 G. For B ˜ 1017 G this is one of the primary mechanisms.

Skobelev, V. V.

2011-04-01

90

Universalist ethics in extraterrestrial encounter  

NASA Astrophysics Data System (ADS)

If humanity encounters an extraterrestrial civilization, or if two extraterrestrial civilizations encounter each other, then the outcome may depend not only on the civilizations' relative strength to destroy each other but also on what ethics are held by one or both civilizations. This paper explores outcomes of encounter scenarios in which one or both civilizations hold a universalist ethical framework. Several outcomes are possible in such scenarios, ranging from one civilization destroying the other to both civilizations racing to be the first to commit suicide. Thus, attention to the ethics of both humanity and extraterrestrials is warranted in human planning for such an encounter. Additionally, the possibility of such an encounter raises profound questions for contemporary human ethics, even if such an encounter never occurs.

Baum, Seth D.

2010-02-01

91

Radiation-Reaction Trapping of Electrons in Extreme Laser Fields  

NASA Astrophysics Data System (ADS)

A radiation-reaction trapping (RRT) of electrons is revealed in the near-QED regime of laser-plasma interaction. Electrons quivering in laser pulse experience radiation reaction (RR) recoil force by radiating photons. When the laser field reaches the threshold, the RR force becomes significant enough to compensate for the expelling laser ponderomotive force. Then electrons are trapped inside the laser pulse instead of being scattered off transversely and form a dense plasma bunch. The mechanism is demonstrated both by full three-dimensional particle-in-cell simulations using the QED photonic approach and numerical test-particle modeling based on the classical Landau-Lifshitz formula of RR force. Furthermore, the proposed analysis shows that the threshold of laser field amplitude for RRT is approximately the cubic root of laser wavelength over classical electron radius. Because of the pinching effect of the trapped electron bunch, the required laser intensity for RRT can be further reduced.

Ji, L. L.; Pukhov, A.; Kostyukov, I. Yu.; Shen, B. F.; Akli, K.

2014-04-01

92

Radiation-reaction trapping of electrons in extreme laser fields.  

PubMed

A radiation-reaction trapping (RRT) of electrons is revealed in the near-QED regime of laser-plasma interaction. Electrons quivering in laser pulse experience radiation reaction (RR) recoil force by radiating photons. When the laser field reaches the threshold, the RR force becomes significant enough to compensate for the expelling laser ponderomotive force. Then electrons are trapped inside the laser pulse instead of being scattered off transversely and form a dense plasma bunch. The mechanism is demonstrated both by full three-dimensional particle-in-cell simulations using the QED photonic approach and numerical test-particle modeling based on the classical Landau-Lifshitz formula of RR force. Furthermore, the proposed analysis shows that the threshold of laser field amplitude for RRT is approximately the cubic root of laser wavelength over classical electron radius. Because of the pinching effect of the trapped electron bunch, the required laser intensity for RRT can be further reduced. PMID:24765978

Ji, L L; Pukhov, A; Kostyukov, I Yu; Shen, B F; Akli, K

2014-04-11

93

Simulation studies of field shaping in rotational radiation therapy  

Microsoft Academic Search

This article presents simulation studies of field shaping in rotational radiation therapy by means of two categories of beam modifying devices: protectors and shapers. The protectors used are diminished copies of the organs at risk (OARs) and stay parallel to them during gantry rotation. Thus, each protector always keeps the corresponding OAR in its shadow, significantly reducing the irradiation. The

T. Ivanova; K. Bliznakova; N. Pallikarakis

2006-01-01

94

Short backfire antenna far-field radiation pattern  

Microsoft Academic Search

An analytical expression of the far-field radiation pattern of a short backfire antenna has been derived in terms of aperture illumination assuming multiple reflection of electromagnetic waves between the two conducting planes. Some results are computed from this theory and compared with the experimental results as obtained by Nielsen and Pontoppidan (1970).

C. D. PATEL

1971-01-01

95

Graphene field effect transistor as a radiation and photodetector  

NASA Astrophysics Data System (ADS)

We exploit the dependence of the electrical conductivity of graphene on a local electric field, which can be abruptly changed by charge carriers generated by ionizing radiation in an absorber material, to develop novel highperformance radiation sensors for detection of photons and other kinds of ionizing radiation. This new detection concept is implemented by configuring graphene as a field effect transistor (FET) on a radiation-absorbing undoped semiconductor substrate and applying a gate voltage across the sensor to drift charge carriers created by incident photons to the neighborhood of graphene, which gives rise to local electric field perturbations that change graphene resistance. Promising results have been obtained with CVD graphene FETs fabricated on various semiconductor substrates that have different bandgaps and stopping powers to address different application regimes. In particular, graphene FETs made on SiC have exhibited a ~200% increase in graphene resistance at a gate voltage of 50 V when exposed to room light at room temperature. Systematic studies have proven that the observed response is a field effect.

Koybasi, Ozhan; Childres, Isaac; Jovanovic, Igor; Chen, Yong P.

2012-05-01

96

Radiation effects in materials - field-ion microscope characterizations  

Microsoft Academic Search

Atomic-level analyses of radiation effects in metals and alloys, utilizing field ion microscopy (FIM) has shed much light into the various irradiation-induced phenomena exhibited in the form of point defects, point defects clusters and voids of small sizes (less than 10 nm). The study presented summarized FIM research done on crystalline as well as amorphous materials exposed to explosive shock,

O. T. Inal; W. F. Sommer

1985-01-01

97

Synchrotron Radiation X Ray Topography Study of Lateral Field Resonators.  

National Technical Information Service (NTIS)

Using synchrotron radiation, plano-convex AT resonators excited by a lateral field were studied by the X-ray topography technique. Different overtones and anharmonics of the three types of the thickness modes were observed. The study showed that it is pos...

B. Capelle, J. Detaint, J. Schwartzel, Y. Zheng, A. Zarka

1992-01-01

98

Multimodal Far-Field Acoustic Radiation Pattern: An Approximate Equation.  

National Technical Information Service (NTIS)

The far-field sound radiation theory for a circular duct was studied for both single mode and multimodal inputs. The investigation was intended to develop a method to determine the acoustic power produced by turbofans as a function of mode cut-off ratio. ...

E. J. Rice

1977-01-01

99

Attainment of Large Accelerating Gradients Using Near Field Synchrotron Radiation.  

National Technical Information Service (NTIS)

Lienard-Wiechert potentials are used to find the electromagnetic field everywhere in free space resulting from a point charge moving on a helical trajectory. The total power emitted as synchrotron radiation from a particle on a circular path is calculated...

G. Decker

1989-01-01

100

Neutron Radiation Fields Outside Shielding at the Fermilab Tevatron  

Microsoft Academic Search

The present measurements characterize the neutron radiation fields outside shielding in two different experimental areas at Fermilab, the Neutrino West (NWA) and the Proton Center (PC-4) beam lines. At NWA, a beam stop, constructed out of a series of iron slabs, was used as absorbing material for the incident beam. The particles incident on this beam stop were negative pions

Marcia Maria Campos Torres

1996-01-01

101

Measuring the radiation field and radiation hard detectors at JET: Recent developments  

NASA Astrophysics Data System (ADS)

Since in ITER the radiation field will be much more demanding than that of present day devices, research programmes at JET are aimed at developing radiation hard diagnostics and related components. Initially, significant efforts are devoted to determining the radiation field of both the plasma and in the immediate environment with better accuracy. New developments in MCNP calculations and dedicated measurements provide useful information about the radiation field in the Torus Hall, even during non-operational periods. The effect of using Beryllium in the near future for JET first wall, is being assessed. New materials for activation samples are under consideration and will be tested to improve the calibration accuracy of JET neutron diagnostics. The long-term goal of this work is to obtain spectrometric information from an appropriate combination of different materials. Several studies are under way to modify the radiation field at the detectors by using LiH or pure water as neutron filters, to alleviate the problem of the background in ?-ray measurements. A suite of radiation hard detectors for neutrons, magnetic field and charged particles are being developed. Super-heated fluid neutron detectors, used for yield and imaging, are being upgraded, in order to provide a broad-band spectrometric capability. Chemical vapour deposited diamond diodes are being qualified as counters and as spectrometers. Prototypes of Hall probes made of InSb have been installed on the machine and have provided some preliminary results. Si-on-insulator detectors are under development for use in neutral particle analysers and are currently being bench-tested. Some attention is being devoted to optical components, fibres and mirrors, and to investigating radiation hard electronics using reconfigurable Field Programmable Gate Arrays.

Murari, A.; Edlington, T.; Angelone, M.; Bertalot, L.; Bolshakova, I.; Bonheure, G.; Brzozowski, J.; Coccorese, V.; Holyaka, R.; Kiptily, V.; Lengar, I.; Morgan, P.; Pillon, M.; Popovichev, S.; Prior, P.; Prokopowicz, R.; Quercia, A.; Rubel, M.; Santala, M.; Shevelev, A.; Syme, B.; Vagliasindi, G.; Villari, R.; Zoita, V. L.; JET-EFDA Contributors

102

Simulation of the radiation fields from ionizing radiation sources inside the containment in an accident  

SciTech Connect

In the present work, a set of codes used for simulations of the radiation fields from ionizing radiation sources inside the containment in an accident is described. A method of evaluating the gamma dose rate from a space and energy distributed source is given. The dose rate is calculated by means of the design point kernel method and using buildup factors. The code MCU-REA with the ORIMCU module is used for the burnup calculations.

Kalugin, M. A., E-mail: kalugin@adis.vver.kiae.ru [Russian Research Center Kurchatov Institute (Russian Federation)

2010-12-15

103

Further characteristics of positive radiation fields from lightning in sweden  

NASA Astrophysics Data System (ADS)

Characteristics of the fields radiated by lightning in Sweden have been reported recently by Cooray and Lundquist (1982). That study is supplemented here by presenting additional characteristics of those fields that are hypothesized to be produced by positive return strokes. The new data presented here indicate that the currents in the sources of these radiation fields are either similar in duration to the currents in negative return strokes or of longer duration. This is based on the observation that the duration of these radiation fields are either similar to that of negative return strokes or of longer duration. During the first 50-100 ?s both normal and long-duration waveforms, and hence the inferred currents, seem to behave in a similar manner. That is, there is an initial peak in the first few tens of microseconds and then a decay. After this the field and the inferred currents in some positive strokes continue to decay and in others start to increase again and reach a second peak in a few hundred microseconds. While the current is flowing, in some cases, a burst of electromagnetic pulses with a separation between pulses of about 3 ?s or less occur. The shape of the inferred long-duration currents are similar to the shapes of the positive return stroke currents measured in lightning strikes to high towers.

Cooray, Vernon

1984-12-01

104

High field CdS detector for infrared radiation  

NASA Technical Reports Server (NTRS)

An infrared radiation detector including a cadmium sulfide platelet having a cathode formed on one of its ends and an anode formed on its other end is presented. The platelet is suitably doped such that stationary high-field domains are formed adjacent the cathode when based in the negative differential conductivity region. A negative potential is applied to the cathode such that a high-field domain is formed adjacent to the cathode. A potential measuring probe is located between the cathode and the anode at the edge of the high-field domain and means are provided for measuring the potential at the probe whereby this measurement is indicative of the infrared radiation striking the platelet.

Tyagi, R. C.; Robertson, J. B.; Boer, K. W.; Hadley, H. C., Jr. (inventors)

1974-01-01

105

Two encounters with the flank low-latitude boundary layer - Further evidence for closed field topology and investigation of the internal structure  

NASA Technical Reports Server (NTRS)

The structure of the flank low-latitude boundary layer (LLBL) is examined through differential energy spectra and particle angular anisotropies for traversals of the dawn flank (December 19, 1977) and dusk flank (July 7, 1978) during periods of predominantly northward magnetosheath field orientation. Spectra are presented that were obtained from combined ISEE 1 low-energy-proton and electron-differential-energy-analyzer and medium-energy-particle-instrument data extending over the 200-eV/q to 2-MeV energy range for the plasma sheet, stagnation region, outer LLBL, and magnetosheath regions. The stagnation region and the outer LLBL are each a mixture of plasma-sheet and magnetosheath populations, but the stagnation region contains a relatively higher fraction of plasma sheet particles, consistent with its placement earthward of the outer LLBL. Evidence for energization of thermal electrons appears during the dusk flank crossing. Bidirectional field-aligned ion distributions are observed with typically 5-to-1 enhancement of the flux along the magnetic field during certain portions of the dusk flank crossing.

Traver, D. P.; Mitchell, D. G.; Williams, D. J.; Frank, L. A.; Huang, C. Y.

1991-01-01

106

Successful I.D. Encounters.  

ERIC Educational Resources Information Center

Instructional Development (I.D.) encounters are dependent for success on such variables as power, politics, promotion, and organizational placement. I.D. consultants must be aware of power bases or orientation of other personnel and clients, e.g., these four "power personalities" which affect their efforts in managing I.D. encounters: the gate…

Poorman, Margaret J.

107

High field magnetic resonance imaging-based gel dosimetry for small radiation fields  

NASA Astrophysics Data System (ADS)

Small megavoltage photon radiation fields (< 3cm diameter) are used in advanced radiation therapy techniques, such as intensity modulated radiotherapy, and stereotactic radiosurgery, as well as for cellular and preclinical radiobiology studies (very small fields, <1 mm diameter). Radiation dose characteristics for these small fields are difficult to determine in multiple dimensions because of steep dose gradients (30--40% per mm) and conditions of electronic disequilibrium. Conventional radiation dosimetry techniques have limitations for small fields because detector size may be large compared to radiation field size and/or dose acquisition may be restricted to one or two dimensions. Polymer gel dosimetry, is a three-dimensional (3D) dosimeter based on radiation-induced polymerization of tissue equivalent gelatin. Polymer gel dosimeters can be read using magnetic resonance imaging (MRI), which detects changes in relaxivity due to gel polymerization. Spatial resolution for dose readout is limited to 0.25--0.5mm pixel size because of available the magnetic field strengths (1.5T and 3T) and the stability of polymer gelatin at room temperature. A reliable glucose-based MAGIC (methacrylic and ascorbic acid in gelatine initiated by copper) gel dosimeter was formulated and evaluated for small field 3D dosimetry using 3T and 7T high field MRI for dose readout. The melting point of the original recipe MAGIC gel was increased by 4°C by adding 10% glucose to improve gel stability. Excellent spatial resolution of 79um (1.5 hr scan) and 39um (12 hr scan) was achieved using 7T MRI, proving gel stability for long scan times and high resolution 3D dosimetry.

Ding, Xuanfeng

108

Anomalous radiative trapping in laser fields of extreme intensity.  

PubMed

We demonstrate that charged particles in a sufficiently intense standing wave are compressed toward, and oscillate synchronously at, the antinodes of the electric field. We call this unusual behavior anomalous radiative trapping (ART). We show using dipole pulses, which offer a path to increased laser intensity, that ART opens up new possibilities for the generation of radiation and particle beams, both of which are high energy, directed, and collimated. ART also provides a mechanism for particle control in high-intensity quantum-electrodynamics experiments. PMID:25032929

Gonoskov, A; Bashinov, A; Gonoskov, I; Harvey, C; Ilderton, A; Kim, A; Marklund, M; Mourou, G; Sergeev, A

2014-07-01

109

Compliance with High-Intensity Radiated Fields Regulations - Emitter's Perspective  

NASA Technical Reports Server (NTRS)

NASA's Deep Space Network (DSN) uses high-power transmitters on its large antennas to communicate with spacecraft of NASA and its partner agencies. The prime reflectors of the DSN antennas are parabolic, at 34m and 70m in diameter. The DSN transmitters radiate Continuous Wave (CW) signals at 20 kW - 500 kW at X-band and S-band frequencies. The combination of antenna reflector size and high frequency results in a very narrow beam with extensive oscillating near-field pattern. Another unique feature of the DSN antennas is that they (and the radiated beam) move mostly at very slow sidereal rate, essentially identical in magnitude and at the opposite direction of Earth rotation.The DSN is in the process of revamping its documentation to provide analysis of the High Intensity Radiation Fields (HIRF) environment resulting from radio frequency radiation from DSN antennas for comparison to FAA regulations regarding certification of HIRF protection as outlined in the FAA regulations on HIRF protection for aircraft electrical and electronic systems (Title 14, Code of Federal Regulations (14 CFR) [section sign][section sign] 23.1308, 25.1317, 27.1317, and 29.1317).This paper presents work done at JPL, in consultation with the FAA. The work includes analysis of the radiated field structure created by the unique DSN emitters (combination of transmitters and antennas) and comparing it to the fields defined in the environments in the FAA regulations. The paper identifies areas that required special attention, including the implications of the very narrow beam of the DSN emitters and the sidereal rate motion. The paper derives the maximum emitter power allowed without mitigation and the mitigation zones, where required.Finally, the paper presents summary of the results of the analyses of the DSN emitters and the resulting DSN process documentation.

Statman, Joseph; Jamnejad, Vahraz; Nguyen, Lee

2012-01-01

110

Radiation from relativistic shocks in turbulent magnetic fields  

NASA Astrophysics Data System (ADS)

Using our new 3-D relativistic particle-in-cell (PIC) code parallelized with MPI, we investigated long-term particle acceleration associated with a relativistic electron-positron jet propagating in an unmagnetized ambient electron-positron plasma. The simulations were performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks. Acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value as predicted by hydrodynamic shock compression. In the jet (reverse) shock behind the bow (forward) shock the strongest electromagnetic fields are generated. These fields may lead to time dependent afterglow emission. In order to calculate radiation from first principles that goes beyond the standard synchrotron model used in astrophysical objects we have used PIC simulations. Initially we calculated radiation from electrons propagating in a uniform parallel magnetic field to verify the technique. We then used the technique to calculate emission from electrons in a small simulation system. From these simulations we obtained spectra which are consistent with those generated from electrons propagating in turbulent magnetic fields with red noise. This turbulent magnetic field is similar to the magnetic field generated at an early nonlinear stage of the Weibel instability. A fully developed shock within a larger simulation system may generate a jitter/synchrotron spectrum.

Nishikawa, K.-I.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Nordlund, A.; Frederiksen, J.; Mizuno, Y.; Sol, H.; Pohl, M.; Hartmann, D. H.; Oka, M.; Fishman, G. J.

2011-04-01

111

A Computational Model of Cellular Response to Modulated Radiation Fields  

SciTech Connect

Purpose: To develop a model to describe the response of cell populations to spatially modulated radiation exposures of relevance to advanced radiotherapies. Materials and Methods: A Monte Carlo model of cellular radiation response was developed. This model incorporated damage from both direct radiation and intercellular communication including bystander signaling. The predictions of this model were compared to previously measured survival curves for a normal human fibroblast line (AGO1522) and prostate tumor cells (DU145) exposed to spatially modulated fields. Results: The model was found to be able to accurately reproduce cell survival both in populations which were directly exposed to radiation and those which were outside the primary treatment field. The model predicts that the bystander effect makes a significant contribution to cell killing even in uniformly irradiated cells. The bystander effect contribution varies strongly with dose, falling from a high of 80% at low doses to 25% and 50% at 4 Gy for AGO1522 and DU145 cells, respectively. This was verified using the inducible nitric oxide synthase inhibitor aminoguanidine to inhibit the bystander effect in cells exposed to different doses, which showed significantly larger reductions in cell killing at lower doses. Conclusions: The model presented in this work accurately reproduces cell survival following modulated radiation exposures, both in and out of the primary treatment field, by incorporating a bystander component. In addition, the model suggests that the bystander effect is responsible for a significant portion of cell killing in uniformly irradiated cells, 50% and 70% at doses of 2 Gy in AGO1522 and DU145 cells, respectively. This description is a significant departure from accepted radiobiological models and may have a significant impact on optimization of treatment planning approaches if proven to be applicable in vivo.

McMahon, Stephen J., E-mail: stephen.mcmahon@qub.ac.uk [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom); Butterworth, Karl T. [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom)] [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom); McGarry, Conor K. [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom) [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom); Radiotherapy Physics, Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, Northern Ireland (United Kingdom); Trainor, Colman [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom)] [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom); O'Sullivan, Joe M. [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom) [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom); Clinical Oncology, Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, Belfast, Northern Ireland (United Kingdom); Hounsell, Alan R. [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom) [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom); Radiotherapy Physics, Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, Northern Ireland (United Kingdom); Prise, Kevin M. [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom)] [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom)

2012-09-01

112

Interaction of relativistic dust grains with the solar radiation field  

NASA Astrophysics Data System (ADS)

The effects of the solar radiation field on the propagation of relativistic dust grains are evaluated. It is concluded that relativistic iron grains with energies about 10 exp 19 eV will melt in the solar radiation field before they reach the Earth's orbit around the sun. However iron grains with lower energies will reach the Earth's orbit but grains travelling from the direction of the sun will melt. This directional anisotropy or fingerprint may be used to search for relativistic dust grains in the primary cosmic rays. The fact that no significant solar system anisotropy has been detected places constraints on the hypothesis that the initiating particles of the extensive air showers are relativistic iron grains.

McBreen, B.; Plunkett, S.; Lambert, C. J.

1993-07-01

113

Local field and radiative relaxation rate in a dielectric medium  

SciTech Connect

The effect of macroscopic parameters of a substance on the optical characteristics of impurity particles is investigated. A generalized control equation is derived for two-level emitters forming an ensemble of optical centers in a transparent dielectric medium. In this equation, the effective values of the acting pump field and the radiative relaxation rate of an optical center are taken into account. The formalism developed here is a completely microscopic approach based on the chain of the Bogoliubov-Born-Green-Kirkwood-Yvon equations for reduced density matrices and correlation operators for material particles and modes of a quantized radiation field. The method used here makes it possible to take into account the effects of individual and collective behavior of emitters, which are associated with the presence of an intermediate medium, consistently without using phenomenological procedures. It is shown that the resultant analytic expression for the effective lifetime of the excited state of an optical center conforms with experimental data.

Kuznetsov, D. V., E-mail: dkusnet@yandex.ru; Roerich, Vl. K. [Troitsk Institute for Innovation and Fusion Research (SRC RF TRINITI), State Research Center of Russian Federation (Russian Federation); Gladush, M. G., E-mail: mglad@isan.troitsk.ru [Vladimir State University (Russian Federation)

2011-10-15

114

Potential theoretic methods for far field sound radiation calculations  

NASA Technical Reports Server (NTRS)

In the area of computational acoustics, procedures which accurately predict the far-field sound radiation are much sought after. A systematic development of such procedures are found in a sequence of papers by Atassi. The method presented here is an alternate approach to predicting far field sound based on simple layer potential theoretic methods. The main advantages of this method are: it requires only a simple free space Green's function, it can accommodate arbitrary shapes of Kirchoff surfaces, and is readily extendable to three-dimensional problems. Moreover, the procedure presented here, though tested for unsteady lifting airfoil problems, can easily be adapted to other areas of interest, such as jet noise radiation problems. Results are presented for lifting airfoil problems and comparisons are made with the results reported by Atassi. Direct comparisons are also made for the flat plate case.

Hariharan, S. I.; Stenger, Edward J.; Scott, J. R.

1995-01-01

115

Near-field radiative heat transfer between metamaterial thin films.  

PubMed

We investigate near-field radiative heat transfer between two thin films made of metamaterials. The impact of film thickness on magnetic and electric surface polaritons (ESPs) is analyzed. It is found that the strength as well as the location of magnetic resonance does not change with film thickness until the film behaves as semi-infinite for the dielectric function chosen in this study. When the film is thinner than vacuum gap, both electric and magnetic polaritons contribute evenly to near-field radiative heat transfer. At larger film thicknesses, ESPs dominate heat transfer due to excitation of a larger number of modes. Results obtained from this study will facilitate applications of metamaterials as thin-film coatings for energy systems. PMID:24690723

Basu, Soumyadipta; Francoeur, Mathieu

2014-03-01

116

Radiation from electrons in magnetic field turbulence astrophysical scenarios  

Microsoft Academic Search

Radiation emission from gamma-ray bursts is a hot topic in astrophysics. Both the Weibel and the Kelvin-Helmoltz instabilities have been proposed as mechanisms involved in the generation of magnetic fields in turbulent scenarios relevant to this context. In this work we explore scenarios of Weibel and Kelvin-Helmoltz generated turbulence through 3D particle-in-cell (PIC) simulations performed with OSIRIS 2.0. We analyze

Joana L. Martins; Samuel F. Martins; Eduardo P. Alves; Ricardo A. Fonseca; Luis O. Silva

2010-01-01

117

Radiation effects in materials - field-ion microscope characterizations  

SciTech Connect

Atomic-level analyses of radiation effects in metals and alloys, utilizing field ion microscopy (FIM) has shed much light into the various irradiation-induced phenomena exhibited in the form of point defects, point defects clusters and voids of small sizes (less than 10 nm). The study presented summarized FIM research done on crystalline as well as amorphous materials exposed to explosive shock, laser, and charged (proton) and uncharged (neutron) particle irradiation at room temperature. Also included is an in situ study of gaseous plasma-introduced defects on preimaged field emission end forms, to further emphasize the capability of this analysis technique. 37 references.

Inal, O.T.; Sommer, W.F.

1985-03-01

118

Field profile tailoring in a-Si:H radiation detectors  

SciTech Connect

The capability of tailoring the field profile in reverse-biased a-Si:H diodes by doping and/or manipulating electrode shapes opens a way to many interesting device structures. Charge collection in a-Si:H radiation detectors is improved for high LET particle detection by inserting thin doped layers into the i-layer of the usual p-i-n diode. This buried p-i-n structure enables us to apply higher reverse-bias and the electric field is enhanced in the mid i-layer. Field profiles of the new structures are calculated and the improved charge collection process is discussed. Also discussed is the possibility of field profile tailoring by utilizing the fixed space charges in i-layers and/or manipulating electrode shapes of the reverse-biased p-i-n diodes. 10 refs., 7 figs.

Fujieda, I.; Cho, G.; Conti, M.; Drewery, J.; Kaplan, S.N.; Perez-Mendez, V.; Quershi, S.; Wildermuth, D. (Lawrence Berkeley Lab., CA (USA)); Street, R.A. (Xerox Palo Alto Research Center, CA (USA))

1990-03-01

119

Radiation hydrodynamics of triggered star formation: the effect of the diffuse radiation field  

NASA Astrophysics Data System (ADS)

We investigate the effect of including diffuse field radiation when modelling the radiatively driven implosion of a Bonnor-Ebert sphere (BES). Radiation-hydrodynamical calculations are performed by using operator splitting to combine Monte Carlo photoionization with grid-based Eulerian hydrodynamics that includes self-gravity. It is found that the diffuse field has a significant effect on the nature of radiatively driven collapse which is strongly coupled to the strength of the driving shock that is established before impacting the BES. This can result in either slower or more rapid star formation than expected using the on-the-spot approximation depending on the distance of the BES from the source object. As well as directly compressing the BES, stronger shocks increase the thickness and density in the shell of accumulated material, which leads to short, strong, photoevaporative ejections that reinforce the compression whenever it slows. This happens particularly effectively when the diffuse field is included as rocket motion is induced over a larger area of the shell surface. The formation and evolution of 'elephant trunks' via instability is also found to vary significantly when the diffuse field is included. Since the perturbations that seed instabilities are smeared out elephant trunks form less readily and, once formed, are exposed to enhanced thermal compression.

Haworth, Thomas J.; Harries, Tim J.

2012-02-01

120

THE RADIATIVE TRANSFER OF SYNCHROTRON RADIATION THROUGH A COMPRESSED RANDOM MAGNETIC FIELD  

SciTech Connect

This paper examines the radiative transfer of synchrotron radiation in the presence of a magnetic field configuration resulting from the compression of a highly disordered magnetic field. It is shown that, provided Faraday rotation and circular polarization can be neglected, the radiative transfer equations for synchrotron radiation separate for this configuration, and the intensities and polarization values for sources that are uniform on large scales can be found straightforwardly in the case where opacity is significant. Although the emission and absorption coefficients must, in general, be obtained numerically, the process is much simpler than a full numerical solution to the transfer equations. Some illustrative results are given and an interesting effect, whereby the polarization increases while the magnetic field distribution becomes less strongly confined to the plane of compression, is discussed. The results are of importance for the interpretation of polarization near the edges of lobes in radio galaxies and of bright features in the parsec-scale jets of active galactic nuclei, where such magnetic field configurations are believed to exist.

Cawthorne, T. V. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston, Lancashire PR1 2HE (United Kingdom); Hughes, P. A. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1042 (United States)

2013-07-01

121

Voyager encounters Saturn: Scientific highlights  

NASA Technical Reports Server (NTRS)

Observations generated by Voyager 1's encounter with Saturn are disclosed. Atmospheric conditions, the rings, new moons and the five inner moons are described. Titan, Hyperion and Iapetus are discussed in detail, as is Saturn's magnetosphere.

1980-01-01

122

Radiation pressure and the linear momentum of the electromagnetic field.  

PubMed

We derive the force of the electromagnetic radiation on material objects by a direct application of the Lorentz law of classical electrodynamics. The derivation is straightforward in the case of solid metals and solid dielectrics, where the mass density and the optical constants of the media are assumed to remain unchanged under internal and external pressures, and where material flow and deformation can be ignored. For metallic mirrors, we separate the contribution to the radiation pressure of the electrical charge density from that of the current density of the conduction electrons. In the case of dielectric media, we examine the forces experienced by bound charges and currents, and determine the contribution of each to the radiation pressure. These analyses reveal the existence of a lateral radiation pressure inside the dielectric media, one that is exerted at and around the edges of a finite-diameter light beam. The lateral pressure turns out to be compressive for s-polarized light and expansive for p-polarized light. Along the way, we derive an expression for the momentum density of the light field inside dielectric media, one that has equal contributions from the traditional Minkowski and Abraham forms. This new expression for the momentum density, which contains both electromagnetic and mechanical terms, is used to explain the behavior of light pulses and individual photons upon entering and exiting a dielectric slab. In all the cases considered, the net forces and torques experienced by material bodies are consistent with the relevant conservation laws. Our method of calculating the radiation pressure can be used in conjunction with numerical simulations to yield the distribution of fields and forces in diverse systems of practical interest. PMID:19484099

Mansuripur, Masud

2004-11-01

123

47 CFR 2.1053 - Measurements required: Field strength of spurious radiation.  

Code of Federal Regulations, 2010 CFR

...Measurements required: Field strength of spurious radiation. 2.1053 Section 2...Measurements required: Field strength of spurious radiation. (a) Measurements shall be made to detect spurious emissions that may be...

2009-10-01

124

47 CFR 2.1053 - Measurements required: Field strength of spurious radiation.  

Code of Federal Regulations, 2010 CFR

...Measurements required: Field strength of spurious radiation. 2.1053 Section 2...Measurements required: Field strength of spurious radiation. (a) Measurements shall be made to detect spurious emissions that may be...

2010-10-01

125

47 CFR 2.1053 - Measurements required: Field strength of spurious radiation.  

Code of Federal Regulations, 2013 CFR

...false Measurements required: Field strength of spurious radiation. 2.1053 Section 2.1053 Telecommunication FEDERAL...1053 Measurements required: Field strength of spurious radiation. (a) Measurements shall be made to...

2013-10-01

126

Microwave background radiation anisotropy from scalar field gradients  

NASA Astrophysics Data System (ADS)

Analytic calculations of the cosmological density fluctuations and microwave background radiation anisotropies induced by gradients in a topologically trivial scalar field are presented. This anlaytic solution should provide a good test for numerical simulations of microwave anisotropy from scalar fields. To the extent that these results generalize to other scalar field models and configurations, they imply that (1) MBR measurements limit large-scale primordial variations greater than about 5×1016 GeV within our horizon, (2) the total scalar field variation is a fair predictor of the magnitude of the MBR anisotropy, but is only accurate to within a factor of about three, (3) scalar fields as well as other models of seeded perturbations produce a few times more anisotropy ?T/T for a given density fluctuation ??/? (on the same scale) than do primordial adiabatic perturbations, (4) models of scalar field seeds which produce a scale-invariant spectrum of perturbations seem to require galaxies to be more clustered than the mass on small scales, and (5) scalar fields do not ``tilt'' the Universe.

Stebbins, Albert; Veeraraghavan, Shoba

1993-09-01

127

Radiation from Relativistic Shocks with Turbulent Magnetic Fields  

NASA Astrophysics Data System (ADS)

Using our new 3D relativistic electromagnetic particle (REMP) code parallelized with MPI, we investigated long-term particle acceleration associated with a relativistic electron-positron jet propagating in an unmagnetized ambient electron-positron plasma. We have also performed simulations with electron-ion jets. The simulations were performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability for electron-positron jets and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks for pair plasma case. Acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value for pair plasmas. Behind the bow shock in the jet shock strong electromagnetic fields are generated. These fields may lead to time-dependent afterglow emission. We calculated radiation from electrons propagating in a uniform parallel magnetic field to verify the technique. We also used the new technique to calculate emission from electrons based on simulations with a small system with two different cases for Lorentz factors (15 and 100). We obtained spectra which are consistent with those generated from electrons propagating in turbulent magnetic fields with red noise. This turbulent magnetic field is similar to the magnetic field generated at an early nonlinear stage of the Weibel instability.

Nishikawa, K.-I.; Nimiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Mizuno, Y.; Nordlund, Å.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Oka, M.; Fishman, J. F.

128

Frame-dragging fields and spin 1 gravitomagnetic radiation  

NASA Astrophysics Data System (ADS)

Experimental results published in 2004 (Ciufolini and Pavlis in Nature 431:958-960, 2004) and 2011 (Everitt et al. in Phys Rev Lett 106:221101, 1-5, 2011) have confirmed the frame-dragging phenomenon for a spinning earth predicted by Einstein's field equations. Since this is observed as a precession caused by the gravitomagnetic (GM) field of the rotating body, these experiments may be viewed as measurements of a GM field. The effect is encapsulated in the classic steady state solution for the vector potential field ? of a spinning sphere-a solution applying to a sphere with angular momentum J and describing a field filling space for all time (Weinberg in Gravitation and Cosmology, Wiley, New York, 1972). In a laboratory setting one may visualise the case of a sphere at rest (? =0, { t}<0), being spun up by an external torque at { t}=0 to the angular momentum J: the ? field of the textbook solution cannot establish itself instantaneously over all space at { t}=0, but must propagate with the velocity c, implying the existence of a travelling GM wave field yielding the textbook ? field for large enough t (Tolstoy in Int J Theor Phys 40(5):1021-1031, 2001). The linearized GM field equations of the post-Newtonian approximation being isomorphic with Maxwell's equations (Braginsky et al. in Phys Rev D 15(6):2047-2060, 1977), such GM waves are dipole waves of spin 1. It is well known that in purely gravitating systems conservation of angular momentum forbids the existence of dipole radiation (Misner et al. in Gravitation, Freeman & Co., New York, 1997); but this rule does not prohibit the insertion of angular momentum into the system from an external source-e.g., by applying a torque to our laboratory sphere.

Tolstoy, Ivan

2012-12-01

129

A model of SVC radiation in magnetic dipole field and radiation varying with magnetic field. I - Active region model and SVC radiation source model  

Microsoft Academic Search

The present model of slowly-varying-component (SVC) radiation in a magnetic dipole field employs the latest EUV data on the chromosphere-corona transition region. It is assumed that the plasma conditions above an active region are varying continuously from the center of the region to the adjacent quiet region. The plasma's three physical parameters (electron temperature and density, and magnetic field) are

Ren-Yang Zhao

1991-01-01

130

Field-deployable gamma-radiation detectors for DHS use  

NASA Astrophysics Data System (ADS)

Recently, the Department of Homeland Security (DHS) has integrated all nuclear detection research, development, testing, evaluation, acquisition, and operational support into a single office: the Domestic Nuclear Detection Office (DNDO). The DNDO has specific requirements set for all commercial off-the-shelf and government off-the-shelf radiation detection equipment and data acquisition systems. This article would investigate several recent developments in field deployable gamma radiation detectors that are attempting to meet the DNDO specifications. Commercially available, transportable, handheld radio isotope identification devices (RIID) are inadequate for DHS' requirements in terms of sensitivity, resolution, response time, and reach-back capability. The leading commercial vendor manufacturing handheld gamma spectrometer in the United States is Thermo Electron Corporation. Thermo Electron's identiFINDERTM, which primarily uses sodium iodide crystals (3.18 x 2.54cm cylinders) as gamma detectors, has a Full-Width-at-Half-Maximum energy resolution of 7 percent at 662 keV. Thermo Electron has just recently come up with a reach-back capability patented as RadReachBackTM that enables emergency personnel to obtain real-time technical analysis of radiation samples they find in the field1. The current project has the goal to build a prototype handheld gamma spectrometer, equipped with a digital camera and an embedded cell phone to be used as an RIID with higher sensitivity, better resolution, and faster response time (able to detect the presence of gamma-emitting radio isotopes within 5 seconds of approach), which will make it useful as a field deployable tool. The handheld equipment continuously monitors the ambient gamma radiation, and, if it comes across any radiation anomalies with higher than normal gamma gross counts, it sets an alarm condition. When a substantial alarm level is reached, the system automatically triggers the saving of relevant spectral data and software-triggers the digital camera to take a snapshot. The spectral data including in situ analysis and the imagery data will be packaged in a suitable format and sent to a command post using an imbedded cell phone.

Mukhopadhyay, Sanjoy

2007-09-01

131

Field Deployable Gamma Radiation Detectors for DHS Use  

SciTech Connect

Recently, the U.S. Department of Homeland Security (DHS) has integrated all nuclear detection research, development, testing, evaluation, acquisition, and operational support into a single office: the Domestic Nuclear Detection Office (DNDO). The DNDO has specific requirements set for all commercial and government off-the-shelf radiation detection equipment and data acquisition systems. This article would investigate several recent developments in field deployable gamma radiation detectors that are attempting to meet the DNDO specifications. Commercially available, transportable, handheld radio isotope identification devices (RIID) are inadequate for DHS’s requirements in terms of sensitivity, resolution, response time and reach back capability. The leading commercial vendor manufacturing handheld gamma spectrometer in the United States is Thermo Electron Corporation. Thermo Electron’s identiFINDER™, which primarily uses sodium iodide crystals (3.18-cm x 2.54-cm cylinders) as gamma detector, has a Full-Width-at-Half-Maximum energy resolution of 7 percent at 662 keV. Thermo Electron has just recently come up with a reach-back capability patented as RadReachBack™ that enables emergency personnel to obtain real-time technical analysis of radiation samples they find in the field. The current project has the goal to build a prototype handheld gamma spectrometer, equipped with a digital camera and an embedded cell phone to be used as an RIID with higher sensitivity (comparable to that of a 7.62-cm x 7.62-cm sodium iodide crystal at low gamma energy ranging from 30 keV to 3,000 keV), better resolution (< 3.0 percent at 662 keV), faster response time (able to detect the presence of gamma-emitting radio isotopes within 5 seconds of approach), which will make it useful as a field deployable tool. The handheld equipment continuously monitors the ambient gamma radiation and, if it comes across any radiation anomalies with higher than normal gamma gross counts, it sets an alarm condition. When a substantial alarm level is reached, the system auto triggers saving of relevant spectral data and software-triggers the digital camera to take a snapshot. The spectral data including in situ analysis and the imagery data will be packaged in a suitable format and sent to a command post using an imbedded cell phone.

Sanjoy Mukhopadhyay

2007-08-31

132

Field Deployable Gamma Radiation Detectors for DHS Use  

SciTech Connect

Recently, the Department of Homeland Security (DHS) has integrated all nuclear detection research, development, testing, evaluation, acquisition, and operational support into a single office: the Domestic Nuclear Detection Office (DNDO). The DNDO has specific requirements set for all commercial off-the-shelf and government off-the-shelf radiation detection equipment and data acquisition systems. This article would investigate several recent developments in field deployable gamma radiation detectors that are attempting to meet the DNDO specifications. Commercially available, transportable, handheld radio isotope identification devices (RIID) are inadequate for DHS requirements in terms of sensitivity, resolution, response time, and reach-back capability. The leading commercial vendor manufacturing handheld gamma spectrometer in the United States is Thermo Electron Corporation. Thermo Electron's identiFINDER{trademark}, which primarily uses sodium iodide crystals (3.18 x 2.54cm cylinders) as gamma detectors, has a Full-Width-at-Half-Maximum energy resolution of 7 percent at 662 keV. Thermo Electron has just recently come up with a reach-back capability patented as RadReachBack{trademark} that enables emergency personnel to obtain real-time technical analysis of radiation samples they find in the field. The current project has the goal to build a prototype handheld gamma spectrometer, equipped with a digital camera and an embedded cell phone to be used as an RIID with higher sensitivity, better resolution, and faster response time (able to detect the presence of gamma-emitting radio isotopes within 5 seconds of approach), which will make it useful as a field deployable tool. The handheld equipment continuously monitors the ambient gamma radiation, and, if it comes across any radiation anomalies with higher than normal gamma gross counts, it sets an alarm condition. When a substantial alarm level is reached, the system automatically triggers the saving of relevant spectral data and software-triggers the digital camera to take a snapshot. The spectral data including in situ analysis and the imagery data will be packaged in a suitable format and sent to a command post using an imbedded cell phone.

Sanjoy Mukhopadhyay

2007-08-01

133

Guest-Host Encounters in Diaspora-Heritage Tourism: The Taglit-Birthright Israel Mifgash (Encounter)  

ERIC Educational Resources Information Center

More than 300,000 diaspora Jewish young adults and tens of thousands of their Israeli peers have participated in structured, cross-cultural encounters--"mifgashim"--in the context of an experiential education program known as Taglit-Birthright Israel. Drawing on field observations, interviews, and surveys, the formal and informal components of the…

Sasson, Theodore; Mittelberg, David; Hecht, Shahar; Saxe, Leonard

2011-01-01

134

BINARY ASTEROID ENCOUNTERS WITH TERRESTRIAL PLANETS: TIMESCALES AND EFFECTS  

SciTech Connect

Many asteroids that make close encounters with terrestrial planets are in a binary configuration. Here, we calculate the relevant encounter timescales and investigate the effects of encounters on a binary's mutual orbit. We use a combination of analytical and numerical approaches with a wide range of initial conditions. Our test cases include generic binaries with close, moderate, and wide separations, as well as seven well-characterized near-Earth binaries. We find that close approaches (<10 Earth radii) occur for almost all binaries on 1-10 million year timescales. At such distances, our results suggest substantial modifications to a binary's semimajor axis, eccentricity, and inclination, which we quantify. Encounters within 30 Earth radii typically occur on sub-million year timescales and significantly affect the wider binaries. Important processes in the lives of near-Earth binaries, such as tidal and radiative evolution, can be altered or stopped by planetary encounters.

Fang, Julia; Margot, Jean-Luc [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)

2012-01-15

135

Tail terms in gravitational radiation reaction via effective field theory  

NASA Astrophysics Data System (ADS)

Gravitational radiation reaction affects the dynamics of gravitationally bound binary systems. Here we focus on the leading “tail” term which modifies binary dynamics at fourth post-Newtonian order, as first computed by Blanchet and Damour. We reproduce this result using effective field theory techniques in the framework of the Lagrangian formalism suitably extended to include dissipation effects. We recover the known logarithmic tail term, consistently with the recent interpretation of the logarithmic tail term in the mass parameter, as a renormalization group effect of the Bondi mass of the system.

Foffa, Stefano; Sturani, Riccardo

2013-02-01

136

Cosmic Radiation Fields: Sources in the early Universe  

NASA Astrophysics Data System (ADS)

The workshop "Cosmic Radiation Fields - Sources in the Early Universe" (CRF 2010) focuses on the connection between the extragalactic infrared background and sources in the early universe, in particular stars powered by dark matter burning (Dark Stars; DS). The workshop covers the following topics: the cosmic infrared background, formation of early stars, dark stars, effect of dark matter in the early universe, dark matter halos, primordial star formation rate, and reionization. Further information can be found on the conference webpage: http://www.desy.de/crf2010/. Organizing committee: Tanja Kneiske, Martin Raue, Dominik Elsaesser, Alexander Gewering-Peine, Peter Hausschildt, Dieter Horns, and Andreas Maurer.

Raue, Martin; Kneiske, Tanja; Horns, Dieter; Elsaesser, Dominik; Hauschildt, Peter

137

Satisfaction with the outpatient encounter  

Microsoft Academic Search

OBJECTIVE: To compare patients’ and physicians’ visit-specific satisfaction in an internal medicine outpatient setting, and to explain\\u000a their respective views.\\u000a \\u000a \\u000a DESIGN: Patients’ and physicians’ background characteristics were assessed prior to outpatient encounters. Immediately after the\\u000a encounter, both patients and physicians completed a questionnaire assessing satisfaction with the visit.\\u000a \\u000a \\u000a \\u000a \\u000a SETTING: The outpatient division of an academic teaching hospital.\\u000a \\u000a \\u000a \\u000a \\u000a PARTICIPANTS: Thirty residents

Linda C. Zandbelt; Ellen M. A. Smets; Frans J. Oort; Mieke H. Godfried

2004-01-01

138

Predicting the Earth encounters of (99942) Apophis  

NASA Technical Reports Server (NTRS)

Arecibo delay-Doppler measurements of (99942) Apophis in 2005 and 2006 resulted in a five standard-deviation trajectory correction to the optically predicted close approach distance to Earth in 2029. The radar measurements reduced the volume of the statistical uncertainty region entering the encounter to 7.3% of the pre-radar solution, but increased the trajectory uncertainty growth rate across the encounter by 800% due to the closer predicted approach to the Earth. A small estimated Earth impact probability remained for 2036. With standard-deviation plane-of-sky position uncertainties for 2007-2010 already less than 0.2 arcsec, the best near-term ground-based optical astrometry can only weakly affect the trajectory estimate. While the potential for impact in 2036 will likely be excluded in 2013 (if not 2011) using ground-based optical measurements, approximations within the Standard Dynamical Model (SDM) used to estimate and predict the trajectory from the current era are sufficient to obscure the difference between a predicted impact and a miss in 2036 by altering the dynamics leading into the 2029 encounter. Normal impact probability assessments based on the SDM become problematic without knowledge of the object's physical properties; impact could be excluded while the actual dynamics still permit it. Calibrated position uncertainty intervals are developed to compensate for this by characterizing the minimum and maximum effect of physical parameters on the trajectory. Uncertainty in accelerations related to solar radiation can cause between 82 and 4720 Earth-radii of trajectory change relative to the SDM by 2036. If an actionable hazard exists, alteration by 2-10% of Apophis' total absorption of solar radiation in 2018 could be sufficient to produce a six standard-deviation trajectory change by 2036 given physical characterization; even a 0.5% change could produce a trajectory shift of one Earth-radius by 2036 for all possible spin-poles and likely masses. Planetary ephemeris uncertainties are the next greatest source of systematic error, causing up to 23 Earth-radii of uncertainty. The SDM Earth point-mass assumption introduces an additional 2.9 Earth-radii of prediction error by 2036. Unmodeled asteroid perturbations produce as much as 2.3 Earth-radii of error. We find no future small-body encounters likely to yield an Apophis mass determination prior to 2029. However, asteroid (144898) 2004 VD17, itself having a statistical Earth impact in 2102, will probably encounter Apophis at 6.7 lunar distances in 2034, their uncertainty regions coming as close as 1.6 lunar distances near the center of both SDM probability distributions.

Giorgini, Jon D.; Benner, Lance A. M.; Ostro, Steven J.; Nolan, Michael C.; Busch, Michael W.

2007-01-01

139

Predicting the Earth encounters of (99942) Apophis  

NASA Astrophysics Data System (ADS)

Arecibo delay-Doppler measurements of (99942) Apophis in 2005 and 2006 resulted in a five standard-deviation trajectory correction to the optically predicted close approach distance to Earth in 2029. The radar measurements reduced the volume of the statistical uncertainty region entering the encounter to 7.3% of the pre-radar solution, but increased the trajectory uncertainty growth rate across the encounter by 800% due to the closer predicted approach to the Earth. A small estimated Earth impact probability remained for 2036. With standard-deviation plane-of-sky position uncertainties for 2007-2010 already less than 0.2 arcsec, the best near-term ground-based optical astrometry can only weakly affect the trajectory estimate. While the potential for impact in 2036 will likely be excluded in 2013 (if not 2011) using ground-based optical measurements, approximations within the Standard Dynamical Model (SDM) used to estimate and predict the trajectory from the current era are sufficient to obscure the difference between a predicted impact and a miss in 2036 by altering the dynamics leading into the 2029 encounter. Normal impact probability assessments based on the SDM become problematic without knowledge of the object's physical properties; impact could be excluded while the actual dynamics still permit it. Calibrated position uncertainty intervals are developed to compensate for this by characterizing the minimum and maximum effect of physical parameters on the trajectory. Uncertainty in accelerations related to solar radiation can cause between 82 and 4720 Earth-radii of trajectory change relative to the SDM by 2036. If an actionable hazard exists, alteration by 2-10% of Apophis' total absorption of solar radiation in 2018 could be sufficient to produce a six standard-deviation trajectory change by 2036 given physical characterization; even a 0.5% change could produce a trajectory shift of one Earth-radius by 2036 for all possible spin-poles and likely masses. Planetary ephemeris uncertainties are the next greatest source of systematic error, causing up to 23 Earth-radii of uncertainty. The SDM Earth point-mass assumption introduces an additional 2.9 Earth-radii of prediction error by 2036. Unmodeled asteroid perturbations produce as much as 2.3 Earth-radii of error. We find no future small-body encounters likely to yield an Apophis mass determination prior to 2029. However, asteroid (144898) 2004 VD17, itself having a statistical Earth impact in 2102, will probably encounter Apophis at 6.7 lunar distances in 2034, their uncertainty regions coming as close as 1.6 lunar distances near the center of both SDM probability distributions.

Giorgini, Jon D.; Benner, Lance A. M.; Ostro, Steven J.; Nolan, Michael C.; Busch, Michael W.

2008-01-01

140

Novel properties of the q-analogue quantized radiation field  

NASA Technical Reports Server (NTRS)

The 'classical limit' of the q-analog quantized radiation field is studied paralleling conventional quantum optics analyses. The q-generalizations of the phase operator of Susskind and Glogower and that of Pegg and Barnett are constructed. Both generalizations and their associated number-phase uncertainty relations are manifestly q-independent in the n greater than g number basis. However, in the q-coherent state z greater than q basis, the variance of the generic electric field, (delta(E))(sup 2) is found to be increased by a factor lambda(z) where lambda(z) greater than 1 if q not equal to 1. At large amplitudes, the amplitude itself would be quantized if the available resolution of unity for the q-analog coherent states is accepted in the formulation. These consequences are remarkable versus the conventional q = 1 limit.

Nelson, Charles A.

1993-01-01

141

Investigations on dynamic intensity modulated photon fields in radiation therapy  

NASA Astrophysics Data System (ADS)

The objective of this thesis is to investigate the validity of a class of intensity modulated radiation beam delivery (IMRT) with the view towards its clinical implementation. Intensity modulated photon beam (IMB) delivery is a new radiation delivery technique in external beam radiation therapy. The technique is complex in planning, delivery and verification and frequently requires a large number of beams to achieve a desired dose distribution. Therefore, an important consideration in exploiting the advantages offered by this new technology is to study the degree of accuracy with which highly conformal dose distributions can be achieved. A methodology appropriate to dosimetry and quality assurance (QA) of dynamic fields is proposed in this thesis and the theoretical modeling was improved based on the results of this work. Dynamic fields utilizing the motion of multileaf collimators (MLCs) and backup diaphragms were used to produce 1 and 2D intensity maps arbitrary in orientation with respect to collimator axis. Dynamic wedge dose profiles produced by moving diaphragms are accurate to within +/-1% of those produced with conventional techniques. The accuracy of the omni wedge with arbitrary field orientations are found within +/-2° of calculations. A dosimetric verification technique used to monitor the dynamic beam delivery for IMRT plans is introduced. The design considerations and clinical evaluation of a QA phantom, facilitating the measurement of IMRT dose distribution and conversion of photon fluence to machine deliverable monitor units are described. Benchmark tests and clinical examples for IMRT dose verification techniques are carried out to demonstrate the accuracy of the technique. in-vitro and in-vivo dose measurements of dynamic IMB's were in good agreements with the calculation model. A theoretical error analysis on the influence of systematic and random field perturbations in highly conformal beam deliveries with emphasis on its dosimetric effects is also presented. It is shown that field inaccuracies in dynamic deliveries in the order of +/-1.0 mm could lead to dose errors of 20% or more. Based on the findings of our study, we have proposed a QA procedure unique to the delivery of dynamic beams.

Parsai, Homayon

142

A Lakatosian Encounter with Probability  

ERIC Educational Resources Information Center

There is much to be learned and pondered by reading "Proofs and Refutations" by Imre Lakatos (Lakatos, 1976). It highlights the importance of mathematical definitions, and how definitions evolve to capture the essence of the object they are defining. It also provides an exhilarating encounter with the ups and downs of the mathematical reasoning…

Chick, Helen

2010-01-01

143

Dialogic Encounters as Art Education  

ERIC Educational Resources Information Center

Although educators believe in the importance of dialogue and dialogic encounters, and often propose to engage their students in "discussion," dialogic communication is rarely used in the classroom. Rather than through relational and substantive conversation, most educational dialogue in public schools is limited to telling, asking one-way…

Miles, Adetty Perez

2010-01-01

144

Difficulties Japanese Gay Youth Encounter  

ERIC Educational Resources Information Center

This feature is a collection of brief essays recently written by Japanese and Chinese gay youth, followed by commentary from several leading educators and scholars. Akihiko Komiya's "Difficulties Japanese Gay Youth Encounter" provides excerpts from the stories of six gay youth and their everyday lives, based on their letters in "Buddy", a magazine…

Komiya, Akihiko; Ofuji, Keiko

2003-01-01

145

Successful I.D. Encounters.  

National Technical Information Service (NTIS)

Instructional Development (I.D.) encounters are dependent for success on such variables as power, politics, promotion, and organizational placement, I.D. consultants must be aware of power bases or orientation of other personnel and clients, e.g., these f...

M. J. Poorman

1979-01-01

146

Mathilde Encounter: June 27, 1997  

NSDL National Science Digital Library

This site presents a brief account of the Near Earth Asteroid Rendezvous (NEAR) flyby of the asteroid 253 Mathilde. Materials include descriptions of the NEAR mission, pre-encounter optical navigation, science objectives, images, and animations. Links to related topics are included.

147

Development of a Characterized Radiation Field for Evaluating Sensor Performance  

SciTech Connect

Numerous efforts are funded by US agencies (DOE, DoD, DHS) for development of novel radiation sensing and measurement systems. An effort has been undertaken to develop a flexible shielding system compatible with a variety of sources (beta, X-ray, gamma, and neutron) that can be highly characterized using conventional radiation detection and measurement systems. Sources available for use in this system include americium-beryllium (AmBe), plutonium-beryllium (PuBe), strontium-90 (Sr-90), californium-252 (Cf-252), krypton-85 (Kr-85), americium-241 (Am-241), and depleted uranium (DU). Shielding can be varied by utilization of materials that include lexan, water, oil, lead, and polyethylene. Arrangements and geometries of source(s) and shielding can produce symmetrical or asymmetrical radiation fields. The system has been developed to facilitate accurately repeatable configurations. Measurement positions are similarly capable of being accurately re-created. Stand-off measurement positions can be accurately re-established using differential global positioning system (GPS) navigation. Instruments used to characterize individual measurement locations include a variety of sodium iodide (NaI(Tl)) (3 x 3 inch, 4 x 4 x 16 inch, Fidler) and lithium iodide (LiI(Eu)) detectors (for use with multichannel analyzer software) and detectors for use with traditional hand held survey meters such as boron trifluoride (BF{sub 3}), helium-3 ({sup 3}He), and Geiger-Mueller (GM) tubes. Also available are Global Dosimetry thermoluminescent dosimeters (TLDs), CR39 neutron chips, and film badges. Data will be presented comparing measurement techniques with shielding/source configurations. The system is demonstrated to provide a highly functional process for comparison/characterization of various detector types relative to controllable radiation types and levels. Particular attention has been paid to use of neutron sources and measurements. (authors)

Rogers, D.M.; Coggins, T.L.; Marsh, J.; Mann, St.D.; Waggoner, Ch.A. [Institute for Clean Energy Technology (ICET) and Office of Regulatory Compliance, Mississippi State University, Starkville, MS (United States)

2008-07-01

148

Hazard Criteria for Wake Vortex Encounters.  

National Technical Information Service (NTIS)

A piloted, motion-base simulation was conducted to evaluate the ability of simulators to produce realistic vortex encounters and to develop criteria to define hazardous encounters. Evaluation of the simulation by pilots experienced in vortex encounters co...

R. I. Sammonds G. W. Stinnett

1975-01-01

149

Space radiation dosimetry in low-Earth orbit and beyond  

Microsoft Academic Search

Space radiation dosimetry presents one of the greatest challenges in the discipline of radiation protection. This is a result of both the highly complex nature of the radiation fields encountered in low-Earth orbit (LEO) and interplanetary space and of the constraints imposed by spaceflight on instrument design. This paper reviews the sources and composition of the space radiation environment in

E. R. Benton; E. V. Benton

2001-01-01

150

A simple method to quantify the coincidence between portal image graticules and radiation field centers or radiation isocenter  

SciTech Connect

Purpose: The aim of this study was to develop a computerized method to quantify the coincidence between portal image graticules and radiation field centers or radiation isocenter. Three types of graticules were included in this study: Megavoltage (MV) mechanical graticule, MV electronic portal imaging device digital graticule, and kilovoltage (kV) on-board imaging digital graticule. Methods: A metal ball bearing (BB) was imaged with MV and kV x-ray beams in a procedure similar to a Winston-Lutz test. The radiation fields, graticules, and BB were localized in eight portal images using Hough transform-based computer algorithms. The center of the BB served as a static reference point in the 3D space so that the distances between the graticule centers and the radiation field centers were calculated. The radiation isocenter was determined from the radiation field centers at different gantry angles. Results: Misalignments of MV and kV portal imaging graticules varied with the gantry or x-ray source angle as a result of mechanical imperfections of the linear accelerator and its imaging system. While the three graticules in this study were aligned to the radiation field centers and the radiation isocenter within 2.0 mm, misalignments of 1.5-2.0 mm were found at certain gantry angles. These misalignments were highly reproducible with the gantry rotation. Conclusions: A simple method was developed to quantify the alignments of portal image graticules directly against the radiation field centers or the radiation isocenter. The advantage of this method is that it does not require the BB to be placed exactly at the radiation isocenter through a precalibrated surrogating device such as room lasers or light field crosshairs. The present method is useful for radiation therapy modalities that require high-precision portal imaging such as image-guided stereotactic radiotherapy.

Du Weiliang; Yang, James; Luo Dershan; Martel, Mary [Department of Radiation Physics, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030 (United States)

2010-05-15

151

Classical calculation of radiative lifetimes of atomic hydrogen in a homogeneous magnetic field  

NASA Astrophysics Data System (ADS)

Radiative lifetimes of hydrogenic atoms in a homogeneous magnetic field of moderate strength are calculated on the basis of classical radiation. The modifications of the Keplerian orbits due to the magnetic field are incorporated by classical perturbation theory. The model is complemented by a classical radiative decay calculation using the radiated Larmor power. A recently derived highly accurate formula for the transition rate of a field-free hydrogenic state is averaged over the angular momentum oscillations caused by the magnetic field. The resulting radiative lifetimes for diamagnetic eigenstates classified by n,m and the diamagnetic energy shift C compare well with quantum results.

Horbatsch, M. W.; Hessels, E. A.; Horbatsch, M.

2005-09-01

152

Measurement of the radiation field surrounding the Collider Detector at Fermilab  

SciTech Connect

We present here the first direct and detailed measurements of the spatial distribution of the ionizing radiation surrounding a hadron collider experiment. Using data from two different exposures we measure the effect of additional shielding on the radiation field around the Collider Detector at Fermilab (CDF). Employing a simple model we parameterize the ionizing radiation field surrounding the detector.

K. Kordas et al.

2004-01-28

153

Radiation Field of Cosmic Rays Measured in Low Earth Orbit by CR39 Detectors  

Microsoft Academic Search

In low earth orbit (LEO) astronauts are exposed to a radiation field composed of galactic cosmic rays, solar particles, particles in the Earth's radiation belts and albedo neutrons and protons from the Earth's atmosphere. LET spectra have been measured for the STS-108, STS-112 and ISS-7S missions. Measurement of the radiation fields is based on accurate measurements of recoils produced in

D. Zhou; D. O'Sullivan; E. Semones; W. Heinrich

2004-01-01

154

Dose equivalent measurements in mixed and time varying radiation fields around high-energy accelerators  

Microsoft Academic Search

Measurements of ambient dose equivalent in stray radiation fields behind the shielding of high-energy accelerators are a challenging task. Several radiation components (photons, neutrons, charged particles, muons, etc.), spanning a wide range of energies, contribute to the total dose equivalent. The radiation fields are produced by beam losses interacting with structural material during the acceleration or at the ejection to

S Mayer; T Otto

2003-01-01

155

Out-of-Field Cell Survival Following Exposure to Intensity-Modulated Radiation Fields  

SciTech Connect

Purpose: To determine the in-field and out-of-field cell survival of cells irradiated with either primary field or scattered radiation in the presence and absence of intercellular communication. Methods and Materials: Cell survival was determined by clonogenic assay in human prostate cancer (DU145) and primary fibroblast (AGO1552) cells following exposure to different field configurations delivered using a 6-MV photon beam produced with a Varian linear accelerator. Results: Nonuniform dose distributions were delivered using a multileaf collimator (MLC) in which half of the cell population was shielded. Clonogenic survival in the shielded region was significantly lower than that predicted from the linear quadratic model. In both cell lines, the out-of-field responses appeared to saturate at 40%-50% survival at a scattered dose of 0.70 Gy in DU-145 cells and 0.24 Gy in AGO1522 cells. There was an approximately eightfold difference in the initial slopes of the out-of-field response compared with the {alpha}-component of the uniform field response. In contrast, cells in the exposed part of the field showed increased survival. These observations were abrogated by direct physical inhibition of cellular communication and by the addition of the inducible nitric oxide synthase inhibitor aminoguanidine known to inhibit intercellular bystander effects. Additional studies showed the proportion of cells irradiated and dose delivered to the shielded and exposed regions of the field to impact on response. Conclusions: These data demonstrate out-of-field effects as important determinants of cell survival following exposure to modulated irradiation fields with cellular communication between differentially irradiated cell populations playing an important role. Validation of these observations in additional cell models may facilitate the refinement of existing radiobiological models and the observations considered important determinants of cell survival.

Butterworth, Karl T., E-mail: k.butterworth@qub.ac.u [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom); McGarry, Conor K. [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom); Radiotherapy Physics, Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, Northern Ireland (United Kingdom); Trainor, Colman [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom); O'Sullivan, Joe M. [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom); Clinical Oncology, Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, Belfast, Northern Ireland (United Kingdom); Hounsell, Alan R. [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom); Radiotherapy Physics, Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, Northern Ireland (United Kingdom); Prise, Kevin M. [Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland (United Kingdom)

2011-04-01

156

OUT-OF-FIELD CELL SURVIVAL FOLLOWING EXPOSURE TO INTENSITY-MODULATED RADIATION FIELDS  

PubMed Central

Purpose To determine the in-field and out-of-field cell survival of cells irradiated with either primary field or scattered radiation in the presence and absence of intercellular communication. Methods and Materials Cell survival was determined by clonogenic assay in human prostate cancer (DU145) and primary fibroblast (AGO1552) cells following exposure to different field configurations delivered using a 6-MV photon beam produced with a Varian linear accelerator. Results Nonuniform dose distributions were delivered using a multileaf collimator (MLC) in which half of the cell population was shielded. Clonogenic survival in the shielded region was significantly lower than that predicted from the linear quadratic model. In both cell lines, the out-of-field responses appeared to saturate at 40%–50% survival at a scattered dose of 0.70 Gy in DU-145 cells and 0.24 Gy in AGO1522 cells. There was an approximately eightfold difference in the initial slopes of the out-of-field response compared with the ?-component of the uniform field response. In contrast, cells in the exposed part of the field showed increased survival. These observations were abrogated by direct physical inhibition of cellular communication and by the addition of the inducible nitric oxide synthase inhibitor aminoguanidine known to inhibit intercellular bystander effects. Additional studies showed the proportion of cells irradiated and dose delivered to the shielded and exposed regions of the field to impact on response. Conclusions These data demonstrate out-of-field effects as important determinants of cell survival following exposure to modulated irradiation fields with cellular communication between differentially irradiated cell populations playing an important role. Validation of these observations in additional cell models may facilitate the refinement of existing radiobiological models and the observations considered important determinants of cell survival.

Butterworth, Karl T.; McGarry, Conor K.; Trainor, Colman; O'Sullivan, Joe M.; Hounsell, Alan R.; Prise, Kevin M.

2011-01-01

157

Radiative Capture Reactions in Lattice Effective Field Theory  

NASA Astrophysics Data System (ADS)

We outline a general method for computing nuclear capture reactions on the lattice. The method consists of two major parts. In this study we detail the second part which consists of calculating an effective two-body capture reaction on the lattice at finite volume. We solve this problem by calculating the two-point Green’s function using an infrared regulator and the capture amplitude to a two-body bound state. We demonstrate the details of this method by calculating on the lattice the leading M1 contribution to the radiative neutron capture on proton at low energies using pionless effective field theory. We find good agreement with exact continuum results. The approach we outline here can be used in a wide range of applications including few-body reactions in cold atomic systems and hadronic reactions in lattice quantum chromodynamics.

Rupak, Gautam; Lee, Dean

2013-07-01

158

Nanobeacons: Far-field-radiating nanoscale optical waveguides  

NASA Astrophysics Data System (ADS)

Some of us have recently demonstrated that visible light can be transmitted through coaxial waveguides having subwavelength transverse dimensions [1]. Here, we used focused ion beam-assisted (FIB) deposition to precisely position and fabricate vertical nanopillars that will function as inner conductors of nanocoaxial optical waveguides. The coax annuli were prepared by atomic layer deposition of a 100 nm thick conformal oxide coating, with sputtered metal used for the outer electrodes. Using high resolution optical microscopy, we successfully demonstrated the transmission of visible light into, along and out of these subwavelength nanocoaxes prepared by this in situ FIB method. The macroscopic distance between the coax termini and the detecting microscope confirms that the nanocoaxes are functioning as ``nanobeacons'', radiating far-field light.[4pt][1] J. Rybczynski, K. Kempa, A. Herczynski, Y. Wang, M.J. Naughton, Z.F. Ren, Z.P. Huang, D. Cai, and M. Giersig, Appl. Phys. Lett. 90, 021104 (2007).

Dhakal, Pashupati; Peng, Yun; McMahon, G.; Kempa, K.; Naughton, M. J.

2010-03-01

159

High-resolution optical telescope for ultraviolet /UV/ radiation field  

NASA Technical Reports Server (NTRS)

Design techniques are discussed for all-reflecting optics from first-order system considerations and applications currently utilized in the field of astronomical optics. The solution of the Dall-Karkham design problem is described, showing the advantage of inexpensive construction as compared with higher order surfaces. The design process reported here is a F/5 collecting system which quickly mates directly with the spectrometer; it is capable of achieving desired high resolution and sensitivity requirements. The theoretical limit of aberration tolerances is achieved with less than 1/8 of a wavelength at final focus (OPD). The design of spectrometer for ultra-violet (UV) radiation and its mechanism is included in this study.

Karayan, W. W.

1979-01-01

160

Correlated Measurements of UHF Radar Signatures, RF Radiation and Electric Field Changes from Lightning.  

National Technical Information Service (NTIS)

During Storm Hazards - 82, simultaneous measurements are made of radar echoes, fast and slow field changes and RF radiation from lightning. Radio frequency radiation and radar echoes are also obtained during periods when the research aircraft is struck by...

D. M. Levine, V. Mazur

1983-01-01

161

Field test of a post-closure radiation monitor  

SciTech Connect

The DOE is conducting remedial actions at many sites contaminated with radioactive materials. After closure of these sites, long-term subsurface monitoring is typically required by law. This monitoring is generally labor intensive and expensive using conventional sampling and analysis techniques. The U.S. Department of Energy`s Morgantown Energy Technology Center (METC) has contracted with Babcock and Wilcox to develop a Long-Term Post-Closure Radiation Monitoring System (LPRMS) to reduce these monitoring costs. A prototype LPRMS probe was built, and B&W and FERMCO field tested this monitoring probe at the Fernald Environmental Management Project in the fall of 1994 with funding from the DOE`s Office of Technology Development (EM-50) through METC. The system was used to measure soil and water with known uranium contamination levels, both in drums and in situ at depths up to 3 meters. For comparison purposes, measurements were also performed using a more conventional survey probe with a sodium iodide scintillator directly butt-coupled to detection electronics. This paper presents a description and the results of the field tests. The results were used to characterize the lower detection limits, precision and bias of the system, which allowed the DOE to judge the monitoring system`s ability to meet its long-term post-closure radiation monitoring needs. Based on the test results, the monitoring system has been redesigned for fabrication and testing in a potential Phase III of this program. If the DOE feels that this system can meet its needs and chooses to continue into Phase III of this program, this redesigned full scale prototype system will be built and tested for a period of approximately a year. Such a system can be used at a variety of radioactively contaminated sites.

Reed, S. [Babcock & Wilcox, Alliance, OH (United States); Christy, C.E. [Morgantown Energy Technology Center, WV (United States); Heath, R.E. [FERMCO, Cincinnati, OH (United States)

1995-12-01

162

Radiation fields backscattered from material interfaces: I. Biological effectiveness.  

PubMed

Confluent cultures of CHO-K1 and CHO-xrs5 cells were irradiated attached to 6 microm Mylar with 137Cs gamma rays and 200 kVp X rays adjacent to scattering materials consisting of polystyrene, glass, aluminum, copper, tin and lead. The absorbed dose in cell nuclei was estimated from measurements of backscattered dose made with a parallel-plate ion chamber with a 5-microm Mylar window and a gas volume whose thickness was equivalent to approximately 2.6 microm of cells or tissue. Cell inactivation after various doses was measured by clonogenic assays after trypsinization and enumeration. Survival curves constructed from data pooled from at least two independent experiments were best fitted to a linear-quadratic (LQ) or a linear equation for CHO-K1 and CHO-xrs5 cells, respectively. An average distance of 9.3+/-1.9 microm from the scattering surfaces to the midline of nuclei for both the cell lines was estimated from electron micrographs of fixed cell sections. The major differences in biological effect observed when the cells were irradiated adjacent to these materials could be largely explained by the differences in the physical dose. Further analyses using the LQ equation suggested additional biological effects with implications for the mechanisms involved. CHO-K1 cells showed a small but consistent increase in the low-dose (alpha-inactivation coefficient) mechanism for both radiations scattered from high-Z material. An increased value of the alpha coefficient suggests an increase in RBE which could be associated with a higher proportion of low-energy and track-end electrons in these fields. The radiation fields which produced maximum single-hit killing in CHO-K1 cells also produced less killing by the quadratic (beta-inactivation coefficient) mechanism. In contrast, when similarly irradiated, CHO-xrs5 cells exhibited significantly lower alpha coefficients of inactivation. The mechanistic basis for this opposite effect of backscattered radiations in these cell lines is as yet unknown. PMID:9768854

Zellmer, D L; Chapman, J D; Stobbe, C C; Xu, F; Das, I J

1998-10-01

163

Extractable proteins from field radiation vulcanized natural rubber latex  

NASA Astrophysics Data System (ADS)

The type I allergy associated with the use of natural rubber latex (NRL) products is caused by the NRL proteins leached by the sweat or other body fluids. Makuuchi's group proposed for the first time the proteins removal by the addition of water-soluble polymers (WSP) on radiation vulcanization of natural rubber latex (RVNRL) that is a promising process under development in many countries. In this study, Brazilian field natural rubber was irradiated with a 60Co gamma source to reduce the content of WSP in the final product. WSP was used as additive to improve the extraction of protein. After irradiation the RVNRL was centrifuged to extract the WSP and proteins. The analytical methodology for protein content was based on the modified Lowry method according to ASTM D5712. Protein determination was carried out in serum of latex and in the extracts of the gloves. The concentration of extractable water-soluble proteins in serum of irradiated field NRL (NRL1), not irradiated one (NRL2); of twice centrifuged sample with polymer additive NRL (NRL3) and of the glove manufactured (NRLG) are compared with commercial glove (CG). The irradiation process increases the extractable water-soluble proteins, EP, as reported in the literature. In this study the use of polymeric additive on the bi-centrifugation process to remove protein was successful and the EP of the glove obtained in NRL3 was at around 40% of the commercial glove.

Parra, Duclerc F.; Pinto Martins, Carlos Felipe; Collantes, Hugo D. C.; Lugao, Ademar B.

2005-07-01

164

S-76 high intensity radiated fields, volume 3  

NASA Astrophysics Data System (ADS)

The Federal Aviation Administration (FAA) Technical Center sponsored a series of High Intensity Radiated Fields (HIRF) tests on a Sikorsky S-76 rotorcraft. The project was conducted to evaluate the practically of performing aircraft level HIRF tests, determine the effects of HIRF on a specific rotorcraft with the potential to obtain information on rotorcraft in general, and evaluate the effects of exposure to 'real world' HIRF emitters. HIRF ground and flight tests were conducted to achieve the objective of the project. Site calibration (SCAL) measurements were made in the test area to determine the levels at which the S-76 would be irradiated when placed in the test area. Ground tests consisted of Low Level Swept Coupling (LLSC) and Low Level Swept Fields (LLSF) tests. The flight tests were flown directly into the main beam of a variety of pulsed and continuous wave (CW) transmitters including the Over the Horizon Back Scatter (OTHB), PAVE PAWS, ASR-9, FPS-65, and FPS-16 radars. Results of the S-76 tests added credibility to the existence of HIRF as a flight safety hazard. In the evaluation of the emitters, the flight tests showed repeatable instances where exposure resulted in instrumentation disruptions. It should however be noted that all the observed disruptions were of a non-critical nature.

Blair, Jerry

1993-10-01

165

S-76 high intensity radiated fields, volume 1  

NASA Astrophysics Data System (ADS)

The Federal Aviation Administration (FAA) Technical Center sponsored a series of High Intensity Radiated Fields (HIRF) test on a Sikorsky S-76 rotorcraft. The project was conducted to evaluate the practicality of performing aircraft level HIRF tests, determine the effects of HIRF on a specific rotorcraft with the potential to obtain information on rotorcraft in general, and evaluate the effects of exposure to real world HIRF emitters. HIRF ground and flight tests were conducted to achieve the objective of the project. Site calibration (SCAL) measurements were made in the test area to determine the levels at which the S-76 would be irradiated when placed in the test area. Ground tests consisted of Low Level Swept Coupling (LLSC) and Low Level Swept Fields (LLSF) tests. The flight tests were flown directly into the main beam of a variety of pulsed and continuous wave (CW) transmitters including the Over the Horizon Back Scatter (OTHB), PAVE PAWS, ASR-9, FPS-65, and FPS-16 radars. Results of the S-76 tests added credibility to the existence of HIRF as a flight safety hazard. In the evaluation of the emitters, the flight tests showed repeatable instances where exposure resulted in instrumentation disruptions. It should be noted that all the observed disruptions were of a non-critical nature.

Blair, Jerry

1993-10-01

166

S-76 high intensity radiated fields, volume 2  

NASA Astrophysics Data System (ADS)

The Federal Aviation Administration (FAA) Technical Center sponsored a series of High Intensity Radiated Fields (HIRF) test on a Sikorsky S-76 rotorcraft. The project was conducted to evaluate the practically of performing aircraft level HIRF tests, determine the effects of HIRF on a specific rotorcraft with the potential to obtain information on rotorcraft in general, and evaluate the effects of exposure to real world HIRF emitters. HIRF ground and flight tests were conducted to achieve the objective of the project. Site calibration (SCAL) measurements were made in the test area to determine the levels at which the S-76 would be irradiated when placed in the test area. Ground tests consisted of Low Level Swept Coupling (LLSC) and Low Level Swept Fields (LLSF) tests. The flight tests were flown directly into the main beam of a variety of pulsed and continuous wave (CW) transmitters including the Over the Horizon Back Scatter (OTHB), PAVE PAWS, ASR-9, FPS-65, and FPS-16 radars. Results of the S-76 tests added credibility to the existence of HIRF as a flight safety hazard. In the evaluation of the emitters, the flight tests showed repeatable instances where exposure resulted in instrumentation disruptions. It should be noted that all the observed disruptions were of a non-critical nature.

Blair, Jerry

1993-10-01

167

Simplified field-in-field technique for a large-scale implementation in breast radiation treatment  

SciTech Connect

We wanted to evaluate a simplified 'field-in-field' technique (SFF) that was implemented in our department of Radiation Oncology for breast treatment. This study evaluated 15 consecutive patients treated with a simplified field in field technique after breast-conserving surgery for early-stage breast cancer. Radiotherapy consisted of whole-breast irradiation to the total dose of 50 Gy in 25 fractions, and a boost of 16 Gy in 8 fractions to the tumor bed. We compared dosimetric outcomes of SFF to state-of-the-art electronic surface compensation (ESC) with dynamic leaves. An analysis of early skin toxicity of a population of 15 patients was performed. The median volume receiving at least 95% of the prescribed dose was 763 mL (range, 347-1472) for SFF vs. 779 mL (range, 349-1494) for ESC. The median residual 107% isodose was 0.1 mL (range, 0-63) for SFF and 1.9 mL (range, 0-57) for ESC. Monitor units were on average 25% higher in ESC plans compared with SFF. No patient treated with SFF had acute side effects superior to grade 1-NCI scale. SFF created homogenous 3D dose distributions equivalent to electronic surface compensation with dynamic leaves. It allowed the integration of a forward planned concomitant tumor bed boost as an additional multileaf collimator subfield of the tangential fields. Compared with electronic surface compensation with dynamic leaves, shorter treatment times allowed better radiation protection to the patient. Low-grade acute toxicity evaluated weekly during treatment and 2 months after treatment completion justified the pursuit of this technique for all breast patients in our department.

Fournier-Bidoz, Nathalie [Department of Medical Physics, Institut Curie, Paris (France); Department of Radiation Oncology, Institut Curie, Paris (France); Kirova, Youlia M., E-mail: youlia.kirova@curie.net [Department of Radiation Oncology, Institut Curie, Paris (France); Campana, Francois; Dendale, Remi; Fourquet, Alain [Department of Radiation Oncology, Institut Curie, Paris (France)

2012-07-01

168

Simplified field-in-field technique for a large-scale implementation in breast radiation treatment.  

PubMed

We wanted to evaluate a simplified "field-in-field" technique (SFF) that was implemented in our department of Radiation Oncology for breast treatment. This study evaluated 15 consecutive patients treated with a simplified field in field technique after breast-conserving surgery for early-stage breast cancer. Radiotherapy consisted of whole-breast irradiation to the total dose of 50 Gy in 25 fractions, and a boost of 16 Gy in 8 fractions to the tumor bed. We compared dosimetric outcomes of SFF to state-of-the-art electronic surface compensation (ESC) with dynamic leaves. An analysis of early skin toxicity of a population of 15 patients was performed. The median volume receiving at least 95% of the prescribed dose was 763 mL (range, 347-1472) for SFF vs. 779 mL (range, 349-1494) for ESC. The median residual 107% isodose was 0.1 mL (range, 0-63) for SFF and 1.9 mL (range, 0-57) for ESC. Monitor units were on average 25% higher in ESC plans compared with SFF. No patient treated with SFF had acute side effects superior to grade 1-NCI scale. SFF created homogenous 3D dose distributions equivalent to electronic surface compensation with dynamic leaves. It allowed the integration of a forward planned concomitant tumor bed boost as an additional multileaf collimator subfield of the tangential fields. Compared with electronic surface compensation with dynamic leaves, shorter treatment times allowed better radiation protection to the patient. Low-grade acute toxicity evaluated weekly during treatment and 2 months after treatment completion justified the pursuit of this technique for all breast patients in our department. PMID:21945169

Fournier-Bidoz, Nathalie; Kirova, Youlia M; Campana, Francois; Dendale, Rémi; Fourquet, Alain

2012-01-01

169

Simulation studies of field shaping in rotational radiation therapy.  

PubMed

This article presents simulation studies of field shaping in rotational radiation therapy by means of two categories of beam modifying devices: protectors and shapers. The protectors used are diminished copies of the organs at risk (OARs) and stay parallel to them during gantry rotation. Thus, each protector always keeps the corresponding OAR in its shadow, significantly reducing the irradiation. The shapers are used in order to obtain a more uniform dose distribution in the planning target volume (PTV) while preserving their initial orientation during gantry rotation. Thus, the use of beam modifying devices allows modulation of the beam intensity, to better fit irradiation requirements, at every gantry position. A software tool for calculations of geometrical position and dimensions of the beam modifying devices, using information about the shape, size, and position of the protected organ or area at risk as input, was developed. This tool was integrated into the in-house-developed Monte Carlo radiation therapy simulator (MCRTS), used to simulate the particle transport through the designed system. The verification of the software tool showed good agreement between experimental and simulation data, with discrepancies of less than 3%. Dose distributions in solid-geometry and voxel-based neck models were evaluated. Furthermore, the effectiveness of the shapers to modify the dose distribution outside the protected area was studied. Results demonstrated that the use of the shapers effectively improves dose uniformity. Studies using shapers of different materials were also carried out and resulted in similar dose distributions. The results of the simulation studies with a voxel-based model showed that rotational therapy with beam modifying devices offers adequate protection of the OAR and a uniform dose distribution outside the protected region. PMID:17153407

Ivanova, T; Bliznakova, K; Pallikarakis, N

2006-11-01

170

Simulation studies of field shaping in rotational radiation therapy  

SciTech Connect

This article presents simulation studies of field shaping in rotational radiation therapy by means of two categories of beam modifying devices: protectors and shapers. The protectors used are diminished copies of the organs at risk (OARs) and stay parallel to them during gantry rotation. Thus, each protector always keeps the corresponding OAR in its shadow, significantly reducing the irradiation. The shapers are used in order to obtain a more uniform dose distribution in the planning target volume (PTV) while preserving their initial orientation during gantry rotation. Thus, the use of beam modifying devices allows modulation of the beam intensity, to better fit irradiation requirements, at every gantry position. A software tool for calculations of geometrical position and dimensions of the beam modifying devices, using information about the shape, size, and position of the protected organ or area at risk as input, was developed. This tool was integrated into the in-house-developed Monte Carlo radiation therapy simulator (MCRTS), used to simulate the particle transport through the designed system. The verification of the software tool showed good agreement between experimental and simulation data, with discrepancies of less than 3%. Dose distributions in solid-geometry and voxel-based neck models were evaluated. Furthermore, the effectiveness of the shapers to modify the dose distribution outside the protected area was studied. Results demonstrated that the use of the shapers effectively improves dose uniformity. Studies using shapers of different materials were also carried out and resulted in similar dose distributions. The results of the simulation studies with a voxel-based model showed that rotational therapy with beam modifying devices offers adequate protection of the OAR and a uniform dose distribution outside the protected region.

Ivanova, T.; Bliznakova, K.; Pallikarakis, N. [Department of Medical Physics, School of Medicine, University of Patras, 26500, Rio- Patras (Greece)

2006-11-15

171

Radiation-Field Control by Single Steam Generator Cooldowns.  

National Technical Information Service (NTIS)

Steam generator radiation levels were compiled for several power reactor cooldowns executed using a single steam generator while the second generator's secondary side was isolated. These radiation levels were compared with normal cooldowns done using both...

J. K. Schmotzer

1982-01-01

172

Violin f-hole contribution to far-field radiation via patch near-field acoustical holography.  

PubMed

The violin radiates either from dual ports (f-holes) or via surface motion of the corpus (top+ribs+back), with no clear delineation between these sources. Combining "patch" near-field acoustical holography over just the f-hole region of a violin with far-field radiativity measurements over a sphere, it was possible to separate f-hole from surface motion contributions to the total radiation of the corpus below 2.6 kHz. A0, the Helmholtz-like lowest cavity resonance, radiated essentially entirely through the f-holes as expected while A1, the first longitudinal cavity mode with a node at the f-holes, had no significant f-hole radiation. The observed A1 radiation comes from an indirect radiation mechanism, induced corpus motion approximately mirroring the cavity pressure profile seen for violinlike bowed string instruments across a wide range of sizes. The first estimates of the fraction of radiation from the f-holes F(f) indicate that some low frequency corpus modes thought to radiate only via surface motion (notably the first corpus bending modes) had significant radiation through the f-holes, in agreement with net volume changes estimated from experimental modal analysis. F(f) generally trended lower with increasing frequency, following corpus mobility decreases. The f-hole directivity (top/back radiativity ratio) was generally higher than whole-violin directivity. PMID:17552736

Bissinger, George; Williams, Earl G; Valdivia, Nicolas

2007-06-01

173

The use of computed radiography plates to determine light and radiation field coincidence  

SciTech Connect

Purpose: Photo-stimulable phosphor computed radiography (CR) has characteristics that allow the output to be manipulated by both radiation and optical light. The authors have developed a method that uses these characteristics to carry out radiation field and light field coincidence quality assurance on linear accelerators.Methods: CR detectors from Kodak were used outside their cassettes to measure both radiation and light field edges from a Varian linear accelerator. The CR detector was first exposed to a radiation field and then to a slightly smaller light field. The light impinged on the detector's latent image, removing to an extent the portion exposed to the light field. The detector was then digitally scanned. A MATLAB-based algorithm was developed to automatically analyze the images and determine the edges of the light and radiation fields, the vector between the field centers, and the crosshair center. Radiographic film was also used as a control to confirm the radiation field size.Results: Analysis showed a high degree of repeatability with the proposed method. Results between the proposed method and radiographic film showed excellent agreement of the radiation field. The effect of varying monitor units and light exposure time was tested and found to be very small. Radiation and light field sizes were determined with an uncertainty of less than 1 mm, and light and crosshair centers were determined within 0.1 mm.Conclusions: A new method was developed to digitally determine the radiation and light field size using CR photo-stimulable phosphor plates. The method is quick and reproducible, allowing for the streamlined and robust assessment of light and radiation field coincidence, with no observer interpretation needed.

Kerns, James R. [Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 and Graduate School of Biomedical Sciences, The University of Texas Health Science Center Houston, Houston, Texas 77030 (United States)] [Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 and Graduate School of Biomedical Sciences, The University of Texas Health Science Center Houston, Houston, Texas 77030 (United States); Anand, Aman [Department of Radiation Oncology, Mayo Clinic, Scottsdale, Arizona 85259 (United States)] [Department of Radiation Oncology, Mayo Clinic, Scottsdale, Arizona 85259 (United States)

2013-11-15

174

Effect of a Strong Radiation Field on an Electron Moving in a Plane Electromagnetic Wave.  

National Technical Information Service (NTIS)

The effect of an external radiation field with arbitrary spectral composition on an electron which is moving in the field of a monochromatic plane electromagnetic wave (first wave) is considered. The change in the average energy of a relativistic electron...

I. M. Ternov V. R. Khalilov A. F. Zhuravlev G. A. Chizhov

1973-01-01

175

Characteristic of the radiation field in low Earth orbit and in deep space.  

PubMed

The radiation exposure in space by cosmic radiation can be reduced through careful mission planning and constructive measures as example the provision of a radiation shelter, but it cannot be completely avoided. The reason for that are the extreme high energies of particles in this field and the herewith connected high penetration depth in matter. For missions outside the magnetosphere ionizing radiation is recognized as the key factor through its impact on crew health and performance. In absence of sporadic solar particle events the radiation exposure in Low Earth orbit (LEO) inside Spacecraft is determined by the galactic cosmic radiation (protons and heavier ions) and by the protons inside the South Atlantic Anomaly (SAA), an area where the radiation belt comes closer to the earth surface due to a displacement of the magnetic dipole axes from the Earth's center. In addition there is an albedo source of neutrons produced as interaction products of the primary galactic particles with the atoms of the earth atmosphere. Outside the spacecraft the dose is dominated by the electrons of the horns of the radiation belt located at about 60" latitude in Polar Regions. The radiation field has spatial and temporal variations in dependence of the Earth magnetic field and the solar cycle. The complexity of the radiation field inside a spacecraft is further increased through the interaction of the high energy components with the spacecraft shielding material and with the body of the astronauts. In interplanetary missions the radiation belt will be crossed in a couple of minutes and therefore its contribution to their radiation exposure is quite small, but subsequently the protection by the Earth magnetic field is lost, leaving only shielding measures as exposure reduction means. The report intends to describe the radiation field in space, the interaction of the particles with the magnetic field and shielding material and give some numbers on the radiation exposure in low earth orbits and in interplanetary missions. PMID:19205293

Reitz, Guenther

2008-01-01

176

Reverberation Chamber Uniformity Validation and Radiated Susceptibility Test Procedures for the NASA High Intensity Radiated Fields Laboratory  

NASA Technical Reports Server (NTRS)

The NASA Langley Research Center's High Intensity Radiated Fields Laboratory has developed a capability based on the RTCA/DO-160F Section 20 guidelines for radiated electromagnetic susceptibility testing in reverberation chambers. Phase 1 of the test procedure utilizes mode-tuned stirrer techniques and E-field probe measurements to validate chamber uniformity, determines chamber loading effects, and defines a radiated susceptibility test process. The test procedure is segmented into numbered operations that are largely software controlled. This document is intended as a laboratory test reference and includes diagrams of test setups, equipment lists, as well as test results and analysis. Phase 2 of development is discussed.

Koppen, Sandra V.; Nguyen, Truong X.; Mielnik, John J.

2010-01-01

177

Characteristic of the radiation field in low earth orbit and in deep space  

Microsoft Academic Search

The radiation exposure in space by cosmic radiation can be reduced through careful mission planning and constructive measures as example the provision of a radiation shelter, but it cannot be completely avoided. The reason for that are the extreme high energies of particles in this field and the herewith connected high penetration depth in matter. For missions outside the magnetosphere

Guenther Reitz

2008-01-01

178

Applying BEM to calculations of temperature fields in bodies containing radiating enclosures  

NASA Astrophysics Data System (ADS)

The BEM is applied here to calculate temperature fields in a body containing a radiating enclosure. The medium is isothermal and can be treated as a gray emitter and absorber of radiation energy. The equations of radiation and conduction and the boundary conditions are presented, and the discretization is shown. The solution strategy is discussed, and a numerical example is given.

Bialecki, R.

179

Performance Tests of Survey Instruments used in Radiation Fields Around High-Energy Accelerators  

Microsoft Academic Search

Measurements of ambient dose equivalent in stray radiation fields behind the shielding of high-energy accelerators are a challenging task. Several radiation components (photons, neutrons, charged particles), spanning a wide range of energies, contribute to the total dose equivalent. Usually for measurements of the total dose equivalent, a set of radiation detectors consisting of ionisation chambers and so-called REM counters is

S. Mayer; D. Forkel-Wirth; M. Fuerstner; H. G. Menzel; S. Roesler; C. Theis; H. Vincke

2005-01-01

180

Deformation field validation and inversion applied to adaptive radiation therapy  

NASA Astrophysics Data System (ADS)

Development and implementation of chronological and anti-chronological adaptive dose accumulation strategies in adaptive intensity-modulated radiation therapy (IMRT) for head-and-neck cancer. An algorithm based on Newton iterations was implemented to efficiently compute inverse deformation fields (DFs). Four verification steps were performed to ensure a valid dose propagation: intra-cell folding detection finds zero or negative Jacobian determinants in the input DF; inter-cell folding detection is implemented on the resolution of the output DF; a region growing algorithm detects undefined values in the output DF; DF domains can be composed and displayed on the CT data. In 2011, one patient with nonmetastatic head and neck cancer selected from a three phase adaptive DPBN study was used to illustrate the algorithms implemented for adaptive chronological and anti-chronological dose accumulation. The patient received three 18F-FDG-PET/CTs prior to each treatment phase and one CT after finalizing treatment. Contour propagation and DF generation between two consecutive CTs was performed in Atlas-based autosegmentation (ABAS). Deformable image registration based dose accumulations were performed on CT1 and CT4. Dose propagation was done using combinations of DFs or their inversions. We have implemented a chronological and anti-chronological dose accumulation algorithm based on DF inversion. Algorithms were designed and implemented to detect cell folding.

Vercauteren, Tom; De Gersem, Werner; Olteanu, Luiza A. M.; Madani, Indira; Duprez, Fréderic; Berwouts, Dieter; Speleers, Bruno; De Neve, Wilfried

2013-08-01

181

Vibration analysis and sound field characteristics of a tubular ultrasonic radiator.  

PubMed

A sort of tubular ultrasonic radiator used in ultrasonic liquid processing is studied. The frequency equation of the tubular radiator is derived, and its radiated sound field in cylindrical reactor is calculated using finite element method and recorded by means of aluminum foil erosion. The results indicate that sound field of tubular ultrasonic radiator in cylindrical reactor appears standing waves along both its radial direction and axial direction, and amplitudes of standing waves decrease gradually along its radial direction, and the numbers of standing waves along its axial direction are equal to the axial wave numbers of tubular radiator. The experimental results are in good agreement with calculated results. PMID:16987537

Liang, Zhaofeng; Zhou, Guangping; Zhang, Yihui; Li, Zhengzhong; Lin, Shuyu

2006-12-01

182

Terahertz spectroscopy of the reactive and radiative near-field zones of split ring resonator.  

PubMed

A terahertz microscope has been used to excite and observe the resonant modes of a single split ring resonator in the reactive and radiative near-field zones. The two lowest resonant modes of an isolated split ring resonator with their corresponding radiation patterns are reported; they showed good agreement to simulations. The passage from the reactive to radiative near-field zone is also discussed. Further, our result introduced a novel technique to perform terahertz time-domain spectroscopy of samples a few tens of micrometers in size by measuring the in-plane radiative near-field zone. PMID:23038582

Blanchard, F; Ooi, K; Tanaka, T; Doi, A; Tanaka, K

2012-08-13

183

Conversion of radiated field strength at different distance in semi-anechoic chamber  

Microsoft Academic Search

The conversion of radiated field strength at different distance in semi-anechoic chamber is analyzed. Firstly, the empirical model based on the logarithmic distance path loss is introduced. Secondly, theoretical models of radiation field in the same site or the different site at different distance are obtained through calculating the difference of normalized site attenuation (NSA) with different transmit \\/ receive

Luo-quan Hu

2010-01-01

184

Radiated Electric Field from a Solar Cell Module Set on the Ground Plane  

Microsoft Academic Search

Radiated electric field from a solar cell module set on the ground plane has been studied experimentally and theoretically in order to clarify the antenna effect of the solar cell module. In experimental examination, the radiated electric field characteristics of the thin-film Si solar cell module were measured by using the semi-anechoic chamber including the ground plane. In theoretical examination,

Ryosuke Hasegawa; Mariko Tomisawa; Masamitsu Tokuda

2010-01-01

185

Radiation field of cosmic rays measured in low Earth orbit by CR39 detectors  

Microsoft Academic Search

In low Earth orbit astronauts are exposed to a radiation field composed of galactic cosmic rays, solar particles, particles in the Earth’s radiation belts and albedo neutrons and protons from the Earth’s atmosphere. Linear Energy Transfer (LET) spectra have been measured for the STS-108, STS-112 and ISS-7S missions. Measurement of the radiation fields is based on accurate measurements of recoils

D. Zhou; D. O’Sullivan; E. Semones; W. Heinrich

2006-01-01

186

Radiation dose optimized lateral expansion of the field of view in synchrotron radiation X-ray tomographic microscopy  

PubMed Central

Volumetric data at micrometer level resolution can be acquired within a few minutes using synchrotron-radiation-based tomographic microscopy. The field of view along the rotation axis of the sample can easily be increased by stacking several tomograms, allowing the investigation of long and thin objects at high resolution. On the contrary, an extension of the field of view in the perpendicular direction is non-trivial. This paper presents an acquisition protocol which increases the field of view of the tomographic dataset perpendicular to its rotation axis. The acquisition protocol can be tuned as a function of the reconstruction quality and scanning time. Since the scanning time is proportional to the radiation dose imparted to the sample, this method can be used to increase the field of view of tomographic microscopy instruments while optimizing the radiation dose for radiation-sensitive samples and keeping the quality of the tomographic dataset on the required level. This approach, dubbed wide-field synchrotron radiation tomographic microscopy, can increase the lateral field of view up to five times. The method has been successfully applied for the three-dimensional imaging of entire rat lung acini with a diameter of 4.1?mm at a voxel size of 1.48?µm.

Haberthur, David; Hintermuller, Christoph; Marone, Federica; Schittny, Johannes C.; Stampanoni, Marco

2010-01-01

187

Far-field radiation of aft turbofan noise  

NASA Technical Reports Server (NTRS)

Approximate expressions were developed for the noise radiation from the aft duct. The results of approximate aft radiation equation compare favorably to more exact Wiener-Hopf radiation results. Refraction as well as convective effects in the multiple flow streams is considered. The peak in the radiation pattern, which occurs nearly at engine sideline, is composed of modes with relatively large cut-off ratios. This implies that aft fan radiation will be inherently more difficult to suppress that the fan inlet noise. The theoretical multimodal radiation pattern is compared to experimental data for the first two harmonics of blade passage frequency for three full scale fans at two speeds. The agreement between theory and experiment is quite good.

Rice, E. J.; Saule, A. V.

1980-01-01

188

Shielding distribution for anisotropic radiation in low earth orbit  

Microsoft Academic Search

The highly directional nature of radiation encountered in low earth orbit (LEO) can be a basis for distributing mass for spacecraft radiation shielding. Trapped (Van Allen) radiation at low altitudes is concentrated within a plane perpendicular to the local geometric field lines. Trapped high-energy protons (which penetrate the relatively thin shielding required for electrons) have a pronounced east-west asymmetry at

M. W. Henley

1986-01-01

189

Preliminary science results of Voyager 1 Saturn encounter  

NASA Technical Reports Server (NTRS)

Preliminary science results of the Voyager 1 encounter of the planet Saturn are reported. On August 22, 1980, the spacecraft was 109 million km (68 million mi) from Saturn. Closest approach to Saturn took place on November 12, at 3:46 p.m. (PDT), when the spacecraft passed 126,000 km (78,000 mi) from the cloud tops. Measurements of the atmosphere, wind speed, radiation, six surrounding rings, and the planet's old and newly found satellites were recorded. The encounter ended December 15, 1980. The spacecraft took more than 17,500 photographs of Saturn and its satellites.

Bane, D.

1981-01-01

190

A model of SVC radiation in magnetic dipole field and radiation varying with magnetic field. I. Active region model and SVC radiation source model  

Microsoft Academic Search

According to the combined mechanism including both the gyroresonance radiation and the bremsstrahlung, the author has calculated the radio radiation of the slowly varying component (SVC) and studied the radiative characteristics of the SVC radiation (such as the spectra of flux density, polarization degree, and brightness temperature, and the brightness distribution) and the geometrical features of the SVC radiation source

Renyang Zhao

1991-01-01

191

Development of a Characterized Radiation Field for Evaluating Sensor Performance  

Microsoft Academic Search

Numerous efforts are funded by US agencies (DOE, DoD, DHS) for development of novel radiation sensing and measurement systems. An effort has been undertaken to develop a flexible shielding system compatible with a variety of sources (beta, X-ray, gamma, and neutron) that can be highly characterized using conventional radiation detection and measurement systems. Sources available for use in this system

D. M. Rogers; T. L. Coggins; J. Marsh; St. D. Mann; Ch. A. Waggoner

2008-01-01

192

Estimating the Reliability of Electronic Parts in High Radiation Fields  

NASA Technical Reports Server (NTRS)

Radiation effects on materials and electronic parts constrain the lifetime of flight systems visiting Europa. Understanding mission lifetime limits is critical to the design and planning of such a mission. Therefore, the operational aspects of radiation dose are a mission success issue. To predict and manage mission lifetime in a high radiation environment, system engineers need capable tools to trade radiation design choices against system design and reliability, and science achievements. Conventional tools and approaches provided past missions with conservative designs without the ability to predict their lifetime beyond the baseline mission.This paper describes a more systematic approach to understanding spacecraft design margin, allowing better prediction of spacecraft lifetime. This is possible because of newly available electronic parts radiation effects statistics and an enhanced spacecraft system reliability methodology. This new approach can be used in conjunction with traditional approaches for mission design. This paper describes the fundamentals of the new methodology.

Everline, Chester; Clark, Karla; Man, Guy; Rasmussen, Robert; Johnston, Allan; Kohlhase, Charles; Paulos, Todd

2008-01-01

193

Icing Encounter Duration Sensitivity Study  

NASA Technical Reports Server (NTRS)

This paper describes a study performed to investigate how aerodynamic performance degradation progresses with time throughout an exposure to icing conditions. It is one of the first documented studies of the effects of ice contamination on aerodynamic performance at various points in time throughout an icing encounter. Both a 1.5 and 6 ft chord, two-dimensional, NACA-23012 airfoils were subjected to icing conditions in the NASA Icing Research Tunnel for varying lengths of time. At the end of each run, lift, drag, and pitching moment measurements were made. Measurements with the 1.5 ft chord model showed that maximum lift and pitching moment degraded more rapidly early in the exposure and degraded more slowly as time progressed. Drag for the 1.5 ft chord model degraded more linearly with time, although drag for very short exposure durations was slightly higher than expected. Only drag measurements were made with the 6 ft chord airfoil. Here, drag for the long exposures was higher than expected. Novel comparison of drag measurements versus an icing scaling parameter, accumulation parameter times collection efficiency was used to compare the data from the two different size model. The comparisons provided a means of assessing the level of fidelity needed for accurate icing simulation.

Addy, Harold E., Jr.; Lee, Sam

2011-01-01

194

Observation of the transition from the near-field to the far-field region for broadband terahertz radiation  

Microsoft Academic Search

Summary form only given. In the antenna theory, it has long been well known that the space surrounding an antenna can be divided into the near- and far-field region. But in the terahertz (THz) optoelectronics community, this had not received much attention until recently when Budiarto et al. (1998) observed the near-field effect in the measurement of THz radiation from

S.-G. Park; M. R. Melloch; A. M. Weiner

1999-01-01

195

ESTIMATING SOLAR RADIATION EXPOSURE IN WETLANDS USING RADIATION MODELS, FIELD DATA, AND GEOGRAPHIC INFORMATION SYSTEMS  

EPA Science Inventory

This seminar will describe development of methods for the estimation of solar radiation doses in wetlands. The methodology presents a novel approach to incorporating aspects of solar radiation dosimetry that have historically received limited attention. These include effects of a...

196

Radiation fields in star-forming galaxies: the disc, thin disc and bulge  

NASA Astrophysics Data System (ADS)

We provide and describe a library of diffuse stellar radiation fields in spiral galaxies derived using calculations of the transfer of stellar radiation from the main morphological components - discs, thin discs and bulges - through the dusty interstellar medium. These radiation fields are self-consistent with the solutions for the integrated panchromatic spectral energy distributions (SEDs) previously presented using the same model. Because of this, observables calculated from the radiation fields, such as gamma-ray or radio emission, can be self-consistently combined with the solutions for the ultraviolet/optical/submillimetre SEDs, thus expanding the range of applicability of the radiation transfer model to a broader range of wavelengths and physical quantities. We also give analytic solutions for radiation fields in optically thin stellar discs, in stellar discs with one dust disc and in stellar discs with two dust discs. The analytic solutions for the direct light are exact and can be used as benchmarks. The analytic solutions with scattering are only approximate, becoming exact only in the extreme optically thick limit. We find strongly contrasting solutions for the spatial distribution of the radiation fields for discs, thin discs and bulges. For bulges, we find a strong dependence of the radiation fields on the Sérsic index.

Popescu, Cristina C.; Tuffs, Richard J.

2013-12-01

197

Acetylcholinesterase: diffusional encounter rate constants for dumbbell models of ligand.  

PubMed Central

For some enzymes, virtually every substrate molecule that encounters the entrance to the active site proceeds to reaction, at low substrate concentrations. Such diffusion-limited enzymes display high apparent bimolecular rate constants ((kcat/KM)), which depend strongly upon solvent viscosity. Some experimental studies provide evidence that acetylcholinesterase falls into this category. Interestingly, the asymmetric charge distribution of acetylcholinesterase, apparent from the crystallographic structure, suggests that its electrostatic field accelerates the encounter of its cationic substrate, acetylcholine, with the entrance to the active site. Here we report simulations of the diffusion of substrate in the electrostatic field of acetylcholinesterase. We find that the field indeed guides the substrate to the mouth of the active site. The computed encounter rate constants depend upon the particular relative geometries of substrate and enzyme that are considered to represent successful encounters. With loose reaction criteria, the computed rates exceed those measured experimentally, but the rate constants vary appropriately with ionic strength. Although more restrictive reaction criteria lower the computed rates, they also lead to unrealistic variation of the rate constants with ionic strength. That these simulations do not agree well with experiment suggests that the simple diffusion model is incomplete. Structural fluctuations in the enzyme or events after the encounter may well contribute to rate limitation. Images FIGURE 1

Antosiewicz, J; Gilson, M K; Lee, I H; McCammon, J A

1995-01-01

198

The effects of the diffuse radiation fields due to multiple scattering and thermal reradiation by dust on the dynamics and thermodynamics of a dusty cometary atmosphere  

NASA Technical Reports Server (NTRS)

A self-consistent model of a dirty, clathrate cometary nucleus is extended to account for diffuse radiation fields caused by multiple scattering and thermal reradiation of the solar continuum by dust. The model is configured to fit conditions expected for the various spacecraft which will encounter Halley's comet at 0.89 AU. The atmosphere is assumed a chemically reactive dust-gas mixture in quasi-steady spherically symmetric expansion. The effect of electron-neutral ion collisions is accounted for, along with rate constants of the various species of clathrate ice particles and radiative transfer of the solar input in the UV, visible and near-IR intervals. The opacity of the circumnuclear dust is projected to be an order of magnitude greater than previous estimates, which severely impacts the potential visibility of the nucleus to the cameras of the flyby satellites.

Marconi, M. L.; Mendis, D. A.

1984-01-01

199

Reduction of the Background Magnetic Field Inhibits Ability of Drosophila melanogaster to Survive Ionizing Radiation  

PubMed Central

The effects of exposure to an environment where the background magnetic field has been reduced were studied on wild-type Drosophila melanogaster by measuring its ability to survive a single exposure to ionizing radiation during its larval stage. The experimental design presented shows a timeframe, ionizing radiation dose and background magnetic field parameters that will cause a significant and reproducible reduction of survival on this insect model. These results suggest that background magnetic fields may play a fundamental role in the recovery or harm of a biological system that is exposed to single doses of ionizing radiation.

Portelli, Lucas; Madapatha, Dinu; Martino, Carlos; Hernandez, Mark; Barnes, Frank

2012-01-01

200

The impact of atmospheric aerosol interactions with the solar radiation field on the radiation absorption efficiency of a forest canopy  

NASA Astrophysics Data System (ADS)

Aerosols (small atmospheric particulate matter originating from different source types) attract a growing interest from atmospheric scientists with regard to their impact on pollution as well as the global climate. A hypothesis, less investigated, is whether atmospheric aerosol interactions in the solar radiation field affect the amount of radiation absorbed by vegetation canopies and hence agricultural productivity. Typically, aerosols may affect vegetation canopy radiation absorption efficiency by altering the physical characteristics of solar radiation impinging on for example a forest canopy. It has been well illustrated, that increasing mixing ratio's of atmospheric particulate matter lead to more diffuse sunlight. It can be demonstrated, based on the application of atmospheric (MODTRAN) and canopy radiative transfer models (5-Scale), that radiation absorption efficiency (and hence productivity) of forests increases with increasing levels of diffuse radiation. It can be documented - on a theoretical basis - that increasing aerosols loads in the atmosphere, enhance canopy photosynthesis. From our study it can even be suggested, that aerosol interactions in the atmosphere have to be taken into account when estimating vegetation gross primary productivity responses to actual and future aerosol climatology. Modelling results indicate that atmospheric aerosol load has a significant impact on photosynthetically active radiation absorbed by for example a forest canopy. This suggests that forest CO2 sink magnitude may increase with increasing atmospheric aerosol loads

Veroustraete, F.; Verstraeten, W. W.

2009-04-01

201

The Magnetic Field of a Model Radiation Belt, Numerically Computed  

Microsoft Academic Search

The magnetic field of a model ring-current belt encircling the earth symmetri- cally is numerically calculated, to a first approximation, for a particular model belt already discussed by Akasou and Chapman (1961a). They calculated the first approximation to the field only for points in the equatorial plane. The whole distribution of the field is here dis- cussed, and for a

Syuh-Ichi Akasofu; Joseph C. Cain; Sydney Chapman

1961-01-01

202

Hazard criteria for wake vortex encounters  

NASA Technical Reports Server (NTRS)

A piloted, motion-base simulation was conducted to evaluate the ability of simulators to produce realistic vortex encounters and to develop criteria to define hazardous encounters. Evaluation of the simulation by pilots experienced in vortex encounters confirmed the capability of the simulator to realistically reproduce wake vortex encounters. A boundary for encounter hazard based on subjective pilot opinion was identified in terms of maximum bank angle. For encounter altitudes from 200 to 500 ft (61.0 to 152.4 m), tentative hazard criteria established for visual flight conditions indicated that the acceptable upset magnitude increased nearly linearly with increasing altitude. The data suggest that the allowable upsets under instrument conditions no greater than 50 percent of that allowable under visual conditions.

Sammonds, R. I.; Stinnett, G. W., Jr.

1975-01-01

203

Miniature CdZnTe Detectors for application in high intensity radiation fields  

Microsoft Academic Search

Presently room-temperature CdZnTe (CZT) nuclear radiation detectors of various designs and sizes are widely used for spectrometric measurements of X and gamma-radiations. In most cases the spectrometric detectors with highest efficiency are required1. But there are tasks where good spectrometric detectors with a low efficiency should be applied. Those are tasks connected with spectrometric measurements in strong radiation fields where

V. Ivanov; L. Aleksejeva; P. Dorogov; A. Loutchanski

2008-01-01

204

Sapphire-bonded photonic Crystal microcavity lasers and their far-field radiation patterns  

Microsoft Academic Search

Room-temperature continuous-wave lasing was demonstrated in photonic crystal microcavities with diameters of approximately 3.2 ?m. Far-field radiation patterns of these lasers were experimentally measured and compared with numerical simulation predictions.

J. R. Cao; Wan Kuang; Zhi-Jian Wei; Sang-Jun Choi; Haixia Yu; Mahmood Bagheri; J. D. O'Brien; P. D. Dapkus

2005-01-01

205

Radiation Damage of Myoglobin Crystals in Weak Stationary Electric and Magnetic Fields  

NASA Astrophysics Data System (ADS)

Radiation damage is one of the bottlenecks in the field of structural biology. Cryo-cooling of protein crystals provided a breakthrough in the 1980s and resulted in significant reductions in radiation damage. Other factors positively influencing the progression of damage include the application of radical scavengers and reductions in the experimental beam size. Here we study the impact on radiation damage of applying static magnetic and electric fields during protein diffraction experiments, ultimately probing the Lorenz force effect on primary photoelectrons and secondary Auger electrons, which both contribute to the damage process. The design of a special mounting pin using graphene for applying electric fields on a crystalline sample is described. Analyses of myoglobin protein crystals exposed to the fields of ~40 mT and -300 V show a slower global radiation damage rate and also changes in the progression of specific damage process on the molecular level, in particular at doses extending beyond the Garman limit of 30 MGy.

Trame, C. B.; Dragovic, M.; Chiu, H.-J.

2014-03-01

206

Attenuation of VHE Gamma Rays by the Milky Way Interstellar Radiation Field  

SciTech Connect

The attenuation of very high energy gamma rays by pair production on the Galactic interstellar radiation field has long been thought of as negligible. However, a new calculation of the interstellar radiation field consistent with multi-wavelength observations by DIRBE and FIRAS indicates that the energy density of the Galactic interstellar radiation field is higher, particularly in the Galactic center, than previously thought. We have made a calculation of the attenuation of very high energy gamma rays in the Galaxy using this new interstellar radiation field which takes into account its nonuniform spatial and angular distributions. We find that the maximum attenuation occurs around 100 TeV at the level of about 25% for sources located at the Galactic center, and is important for both Galactic and extragalactic sources.

Moskalenko, Igor V.; /Stanford U., HEPL; Porter, Troy A.; /Louisiana State U.; Strong, Andrew W.; /Garching, Max Planck Inst., MPE

2006-04-19

207

The effects of emitter-tied field plates on lateral PNP ionizing radiation response  

SciTech Connect

Radiation response comparisons of lateral PNP bipolar technologies reveal that device hardening may be achieved by extending the emitter contact over the active base. The emitter-tied field plate suppresses recombination of carriers with interface traps.

Barnaby, H.J.; Schrimpf, R.D.; Cirba, C.R. [Vanderbilt Univ., Nashville, TN (United States); Pease, R.L. [RLP Research, Inc., Albuquerque, NM (United States); Fleetwood, D.M. [Sandia National Labs., Albuquerque, NM (United States); Kosier, S.L. [VTC Inc., Bloomington, MN (United States)

1998-03-01

208

Optical Absorption in Commercial Single Mode Optical Fibers in a High Energy Physics Radiation Field  

Microsoft Academic Search

This paper reports on the radiation induced attenuation of light at 1310 nm and 1550 nm in 12 commercially available single mode (SM) optical fibers. The fiber samples are exposed to gamma rays from a 60Co source and to a high energy physics radiation field. The attenuation is studied as a function of total dose, dose rate, light power and

Thijs Wijnands; Luit Koert De Jonge; Jochen Kuhnhenn; Stefan Klaus Hoeffgen; Udo Weinand

2008-01-01

209

LETTER TO THE EDITOR: Comments on 'Cellular response to modulated radiation fields'  

NASA Astrophysics Data System (ADS)

The authors of a recent paper (Claridge Mackonis et al 2007 Phys. Med. Biol. 52 5469-82) measured cell survival in spatially modulated radiation fields. They claim to have identified two new types of radiation-induced bystander effect. We conclude that their claims are not supported by their data.

Ross, C. K.; Klassen, N. V.

2009-03-01

210

Analytical formulation of the radiation field of printed antennas in the presence of artificial magnetic superstrates  

NASA Astrophysics Data System (ADS)

In this paper, the cavity model of a microstrip patch antenna in conjunction with the reciprocity theorem is used to develop a fast analytical solution for the radiation field of a microstrip patch antenna loaded with a novel artificial magnetic superstrate and to investigate the effect of the engineered superstrate layer on the directivity and radiation pattern of the printed patch antenna.

Attia, Hussein; Yousefi, Leila; Siddiqui, Omar; Ramahi, Omar M.

2011-06-01

211

RHrFPGA Radiation-Hardened Re-programmable Field-Programmable Gate Array  

NASA Technical Reports Server (NTRS)

Viewgraphs on the development of the Radiation-Hardened Re-programmable Field-Programmable Gate Array (RHrFPGA) are presented. The topics include: 1) Radiation Test Suite; 2) Testing Interface; 3) Test Configuration; 4) Facilities; 5) Test Programs; 6) Test Procedure; and 7) Test Results. A summary of heavy ion and proton testing is also included.

Sanders, A. B.; LaBel, K. A.; McCabe, J. F.; Gardner, G. A.; Lintz, J.; Ross, C.; Golke, K.; Burns, B.; Carts, M. A.; Kim, H. S.

2004-01-01

212

Dose, dose-rate and field size effects on cell survival following exposure to non-uniform radiation fields.  

PubMed

For the delivery of intensity-modulated radiation therapy (IMRT), highly modulated fields are used to achieve dose conformity across a target tumour volume. Recent in vitro evidence has demonstrated significant alterations in cell survival occurring out-of-field which cannot be accounted for on the basis of scattered dose. The radiobiological effect of area, dose and dose-rate on out-of-field cell survival responses following exposure to intensity-modulated radiation fields is presented in this study. Cell survival was determined by clonogenic assay in human prostate cancer (DU-145) and primary fibroblast (AG0-1522) cells following exposure to different modulated field configurations delivered using a X-Rad 225 kVp x-ray source. Uniform survival responses were compared to in- and out-of-field responses in which 25-99% of the cell population was shielded. Dose delivered to the out-of-field region was varied from 1.6-37.2% of that delivered to the in-field region using different levels of brass shielding. Dose rate effects were determined for 0.2-4 Gy min?¹ for uniform and modulated exposures with no effect seen in- or out-of-field. Survival responses showed little dependence on dose rate and area in- and out-of-field with a trend towards increased survival with decreased in-field area. Out-of-field survival responses were shown to scale in proportion to dose delivered to the in-field region and also local dose delivered out-of-field. Mathematical modelling of these findings has shown survival response to be highly dependent on dose delivered in- and out-of-field but not on area or dose rate. These data provide further insight into the radiobiological parameters impacting on cell survival following exposure to modulated irradiation fields highlighting the need for refinement of existing radiobiological models to incorporate non-targeted effects and modulated dose distributions. PMID:22546687

Butterworth, Karl T; McGarry, Conor K; Trainor, Colman; McMahon, Stephen J; O'Sullivan, Joe M; Schettino, Giuseppe; Hounsell, Alan R; Prise, Kevin M

2012-05-21

213

Traffic encounters and Hocman: Associating motorcycle ethnography with design  

Microsoft Academic Search

Brief encounters between acquainted and unacquainted motorcyclists are enjoyable moments. This truly mobile form of social interaction is difficult to study through traditional ethnographic fieldwork. However, the method is applicable when integrated in a design approach where the participants collaborate to integrate the field study, the design and the evaluation. This has made it possible to generate a novel mobile

Mattias Esbjörnsson; Oskar Juhlin; Mattias Östergren

2004-01-01

214

A simple ionizing radiation spectrometer/dosimeter based on radiation sensing field effect transistors (RadFETs)  

SciTech Connect

This paper reports on the processing steps in a silicon foundry leading to improved performance of the Radiation Sensing Field Effect Transistor (RadFET) and the use of multiple RadFETs in a handheld, battery operated, combination spectrometer/dosimeter.

Moreno, D.J.; Hughes, R.C.; Jenkins, M.W.; Drumm, C.R.

1997-05-01

215

A search for advanced fields in electro-magnetic radiation  

Microsoft Academic Search

An experiment to search for an advanced component of electromagnetic radiation, as suggested by the time symmetry of Maxwell's equations was conducted. A dipole transmitting antenna was driven periodically with 10.2 GHz microwave pulses of 12 ns duration and 4 watt instantaneous power. A receiving dipole antenna at a distance R = 10m away was instrumented to search for power

J. D. Schmidt

1980-01-01

216

Angular momentum loss of primordial gas in Ly? radiation field  

NASA Astrophysics Data System (ADS)

We present results on the radiation drag exerted by an isotropic and homogeneous background of Ly? photons on neutral gas clouds orbiting within H II regions around Population III stars of different masses. The Doppler shift causes a frequency difference between photons moving in the direction of the cloud and opposite to it resulting in a net momentum loss of the cloud in the direction of motion. We find that half of the angular momentum of gas with v? ? 20 km s-1 near (r ? 3 kpc) a Population III star of 120 M? at z = 20 is lost within ˜106 yr. The radiation drag is a strong function of cloud velocity that peaks at v ˜ 20 km s-1 reflecting the frequency dependence of the photon cross-section. Clouds moving with velocities larger than ˜100 km s-1 lose their angular momentum on time-scales of ˜108 yr. At lower redshifts radiation drag becomes inefficient as the Ly? photon density in H II regions decreases by a factor (1 + z)3 and angular momentum is lost on time-scales ? 108 yr even for low-velocity clouds. Our results suggest that a sweet spot exists for the loss of angular momentum by radiation drag for gas clouds at z > 10 and with v ˜ 20 km s-1. Comparison to dynamical friction forces acting on typical gas clouds suggest that radiation drag is the dominant effect impacting the orbit. We propose that this effect can suppress the formation of extended gas discs in the first galaxies and help gas accretion near galactic centres and central black holes.

Yajima, Hidenobu; Khochfar, Sadegh

2014-06-01

217

Radiation hardness tests performed high gamma field sources. ... measured survive ionizing radiation order Murad survive ...... en Dependence transmission coefficients CCl crystals collared hard .  

EPA Pesticide Factsheets

Did you mean: Radiation hardness tests performed high gamma field sources. ... measured survive ionizing radiation order Murad survive ...... en Dependence transmission coefficients CCl crystals collared hard . ?

218

Local field effects and stimulated multimode scattering of resonance radiation in a two-level medium  

Microsoft Academic Search

Scattering of resonance radiation in a dense two-level medium is considered with allowance for the local field effects. The\\u000a system is studied in the framework of the mean-field approximation for a modified hierarchy of the Bogoliubov-Born-Green-Kirkwood-Yvon\\u000a equations for reduced density matrices of an ensemble of atoms and modes of a quantized electromagnetic field. The local field\\u000a correction is consistently derived

M. G. Gladush; A. A. Panteleev; Vl. C. Roerich

2006-01-01

219

Lightning-channel morphology revealed by return-stroke radiation field waveforms  

Microsoft Academic Search

Simultaneous video and wideband electric field recordings of 32 cloud-to-ground lightning flashes in Florida were analyzed to show that the formation of new channels to ground can be detected by examination of the return-stroke radiation fields alone. The return-stroke E and dE\\/dt waveforms were subjectively classified according to their fine structure. Then the video images were examined field by field

J. C. Willett; D. M. Le Vine; V. P. Idone

1995-01-01

220

Radiation of Electron in the Field of Plane Light Wave.  

National Technical Information Service (NTIS)

Results of integration of a Lorentz equation for a relativistic electron moving in the field of running, plane, linear polarized electromagnetic wave are presented in the paper. It is shown that electron velocities in the field of the wave are almost peri...

I. Drebot Y. Grigorev A. Zelinsky O. Zvonarova R. Tatchyn

2006-01-01

221

INSREC: Computational System for Quantitative Analysis of Radiation Effects Covering All Radiation Field  

SciTech Connect

In the nuclear energy field, there are so many difficult things that even people who are working in this field are not much familiar with, such as, Dose evaluation, Dose management, etc. Thus, so many efforts have been done to achieve the knowledge and data for understanding. Although some data had been achieved, the applications of these data to necessary cases were more difficult job. Moreover, the type of Dose evaluation program until now was 'Console type' which is not easy enough to use for the beginners. To overcome the above causes of difficulties, the window-based integrated program and database management were developed in our research lab. The program, called as INSREC, consists of four sub-programs as follow; INSREC-NOM, INSREC-ACT, INSREC-MED, and INSREC-EXI. In ICONE 11 conference, INSREC-program(ICONE-36203) which can evaluates on/off-site dose of nuclear power plant in normal operation was introduced. Upgraded INSREC-program which will be presented in ICONE 14 conference has three additional codes comparing with pre-presented INSREC-program. Those subprograms can evaluate on/off-site Dose of nuclear power plant in accident cases. And they also have the functions of 'Dose evaluation and management' in the hospital and provide the 'Expert system' based on knowledge related to nuclear energy/radiation field. The INSREC-NOM, one of subprograms, is composed of 'Source term evaluation program', 'Atmospheric diffusion factor evaluation program', 'Off-site dose evaluation program', and 'On-site database program'. The INSREC-ACT is composed of 'On/Off-site dose evaluation program' and 'Result analysis program' and the INSREC-MED is composed of 'Workers/patients dose database program' and 'Dose evaluation program for treatment room'. The final one, INSREC-EXI, is composed of 'Database searching program based on artificial intelligence', 'Instruction program,' and 'FAQ/Q and A boards'. Each program was developed by using of Visual C++, Microsoft Access mainly. To verify the reliability, some suitable programs were selected such as AZAP and Stardose programs for the comparison. The AZAP program was selected for the on/off-site dose evaluation during the normal operation of nuclear reactor and Stardose program was used for the on/off-site dose evaluation in accident. The MCNP code was used for the dose evaluation and management in the hospital. Each comparison result was acceptable in errors analysis. According to the reliable verification results, it was concluded that INSREC program had an acceptable reliability for dose calculation and could give many proper dada for the sites. To serve the INSREC to people, the proper server system was constructed. We gave chances for the people (user) to utilize the INSREC through network connected to server system. The reactions were pretty much good enough to be satisfied. For the future work, many efforts will be given to improve the better user-interface and more necessary data will be provided to more people through database supplement and management. (authors)

Dong Hoon Shin; Young Wook Lee; Young Ho Cho; Hyun Seok Ko; SukHoon Kim; YoungMin Kim; Chang Sun Kang [Seoul National University, 599 Gwanangno, Gwanak-gu, Seoul, 151-742 (Korea, Republic of)

2006-07-01

222

Position sensitive detection of neutrons in high radiation background field.  

PubMed

We present the development of a high-resolution position sensitive device for detection of slow neutrons in the environment of extremely high ? and e(-) radiation background. We make use of a planar silicon pixelated (pixel size: 55 × 55 ?m(2)) spectroscopic Timepix detector adapted for neutron detection utilizing very thin (10)B converter placed onto detector surface. We demonstrate that electromagnetic radiation background can be discriminated from the neutron signal utilizing the fact that each particle type produces characteristic ionization tracks in the pixelated detector. Particular tracks can be distinguished by their 2D shape (in the detector plane) and spectroscopic response using single event analysis. A Cd sheet served as thermal neutron stopper as well as intensive source of gamma rays and energetic electrons. Highly efficient discrimination was successful even at very low neutron to electromagnetic background ratio about 10(-4). PMID:24517756

Vavrik, D; Jakubek, J; Pospisil, S; Vacik, J

2014-01-01

223

ANOLE Portable Radiation Detection System Field Test and Evaluation Campaign  

SciTech Connect

Handheld, backpack, and mobile sensors are elements of the Global Nuclear Detection System for the interdiction and control of illicit radiological and nuclear materials. They are used by the U.S. Department of Homeland Security (DHS) and other government agencies and organizations in various roles for border protection, law enforcement, and nonproliferation monitoring. In order to systematically document the operational performance of the common commercial off-the-shelf portable radiation detection systems, the DHS Domestic Nuclear Detection Office conducted a test and evaluation campaign conducted at the Nevada Test Site from January 18 to February 27, 2006. Named “Anole,” it was the first test of its kind in terms of technical design and test complexities. The Anole test results offer users information for selecting appropriate mission-specific portable radiation detection systems. The campaign also offered manufacturers the opportunity to submit their equipment for independent operationally relevant testing to subsequently improve their detector performance. This paper will present the design, execution, and methodologies of the DHS Anole portable radiation detection system test campaign.

Chris A. Hodge

2007-07-12

224

Radiation Isotope Identification Device (RIIDs) Field Test and Evaluation Campaign  

SciTech Connect

Handheld, backpack, and mobile sensors are elements of the Global Nuclear Detection System for the interdiction and control of illicit radiological and nuclear materials. They are used by the U.S. Department of Homeland Security (DHS) and other government agencies and organizations in various roles for border protection, law enforcement, and nonproliferation monitoring. In order to systematically document the operational performance of the common commercial off-the-shelf portable radiation detection systems, the DHS Domestic Nuclear Detection Office conducted a test and evaluation campaign conducted at the Nevada Test Site from January 18 to February 27, 2006. Named 'Anole', it was the first test of its kind in terms of technical design and test complexities. The Anole test results offer users information for selecting appropriate mission-specific portable radiation detection systems. The campaign also offered manufacturers the opportunity to submit their equipment for independent operationally relevant testing to subsequently improve their detector performance. This paper will present the design, execution, and methodologies of the DHS Anole portable radiation detection system test campaign.

Christopher Hodge, Raymond Keegan

2007-08-01

225

The Challenges Encountered by Immigrated Elite Athletes  

Microsoft Academic Search

Sport psychology consultants and coaches in sport sometimes work with athletes who re-locate from other countries. Though immigrated athletes encounter many transition and adjustment issues linked to their relocation, little is known about what those challenges are and subsequently, how they might be overcome. This article identifies some of the challenges encountered by this group of athletes, post-relocation, and subsequently

Robert J. Schinke; David Yukelson; Gina Bartolacci; Randy C. Battochio; Katherine Johnstone

2011-01-01

226

Encountering Death: Structured Activities for Death Awareness.  

ERIC Educational Resources Information Center

This book is intended to be used as a supplement to standard textbooks on death and dying for college students. Chapter 1 "Encountering Death in the Self" builds the foundation for increased self-awareness for the study of death and dying. Chapter 2 "Encountering Death in the Family" provides activities which are appropriate for a wide variety of…

Welch, Ira David; And Others

227

Basic theory for polarized, astrophysical maser radiation in a magnetic field  

NASA Technical Reports Server (NTRS)

Fundamental alterations in the theory and resulting behavior of polarized, astrophysical maser radiation in the presence of a magnetic field have been asserted based on a calculation of instabilities in the radiative transfer. I reconsider the radiative transfer and find that the relevant instabilities do not occur. Calculational errors in the previous investigation are identified. In addition, such instabilities would have appeared -- but did not -- in the numerous numerical solutions to the same radiative transfer equations that have been presented in the literature. As a result, all modifications that have been presented in a recent series of papers (Elitzur 1991, 1993) to the theory for polarized maser radiation in the presence of a magnetic field are invalid. The basic theory is thus clarified.

Watson, William D.

1994-01-01

228

Involved field radiation for Hodgkin's lymphoma: the actual dose to breasts in close proximity.  

PubMed

To decrease the risk of late toxicities in Hodgkin's lymphoma (HL) patients treated with radiation therapy (RT) (HL), involved field radiation therapy (IFRT) has largely replaced the extended fields. To determine the out-of-field dose delivered from a typical IFRT to surrounding critical structures, we measured the dose at various points in an anthropomorphic phantom. The phantom is divided into 1-inch-thick slices with the ability to insert TLDs at 3-cm intervals grid spacing. Two treatment fields were designed, and a total of 45 TLDs were placed (equally spaced) at the margin of the each of the 2 radiation fields. After performing a computed tomography simulation, 2 treatment plans targeting the mediastinum, a typical treatment field in patients with early stage HL, were generated. A total dose of 3060 cGy was delivered to the gross tumor volume for each field consecutively. The highest measured dose detected at 1 cm from the field edge in the planning target volume was 496 cGy, equivalent to 16% of the isocentric dose. The dose dropped significantly with increasing distance from the field edge. It ranged from 1.1-3.9% of the isocentric dose at a distance of 3.2-4 cm to <1.6% at a distance of >6 cm. Although the computer treatment planning system (CTPS) frequently underestimated the dose delivered, the difference in dose between measured and generated by CTPS was <2.5% in 90 positions measured. The collateral dose of radiation to breasts from IFRT is minimal. The out-of-field dose, although mildly underestimated by CTPS, becomes insignificant at >3 cm from the field edge of the radiation field. PMID:22513213

Dabaja, Bouthaina; Wang, Zhonglo; Stovall, Marilyn; Baker, Jamie S; Smith, Susan A; Khan, Meena; Ballas, Leslie; Salehpour, Mohammad R

2012-01-01

229

Involved field radiation for Hodgkin's lymphoma: The actual dose to breasts in close proximity  

SciTech Connect

To decrease the risk of late toxicities in Hodgkin's lymphoma (HL) patients treated with radiation therapy (RT) (HL), involved field radiation therapy (IFRT) has largely replaced the extended fields. To determine the out-of-field dose delivered from a typical IFRT to surrounding critical structures, we measured the dose at various points in an anthropomorphic phantom. The phantom is divided into 1-inch-thick slices with the ability to insert TLDs at 3-cm intervals grid spacing. Two treatment fields were designed, and a total of 45 TLDs were placed (equally spaced) at the margin of the each of the 2 radiation fields. After performing a computed tomography simulation, 2 treatment plans targeting the mediastinum, a typical treatment field in patients with early stage HL, were generated. A total dose of 3060 cGy was delivered to the gross tumor volume for each field consecutively. The highest measured dose detected at 1 cm from the field edge in the planning target volume was 496 cGy, equivalent to 16% of the isocentric dose. The dose dropped significantly with increasing distance from the field edge. It ranged from 1.1-3.9% of the isocentric dose at a distance of 3.2-4 cm to <1.6% at a distance of >6 cm. Although the computer treatment planning system (CTPS) frequently underestimated the dose delivered, the difference in dose between measured and generated by CTPS was <2.5% in 90 positions measured. The collateral dose of radiation to breasts from IFRT is minimal. The out-of-field dose, although mildly underestimated by CTPS, becomes insignificant at >3 cm from the field edge of the radiation field.

Dabaja, Bouthaina, E-mail: bdabaja@mdanderson.org [Departments of Radiation Oncology, Radiation Physics at University of Texas MD Anderson Cancer Center, Houston, TX (United States); Wang Zhonglo; Stovall, Marilyn; Baker, Jamie S.; Smith, Susan A.; Khan, Meena; Ballas, Leslie; Salehpour, Mohammad R. [Departments of Radiation Oncology, Radiation Physics at University of Texas MD Anderson Cancer Center, Houston, TX (United States)

2012-01-01

230

[An encounter with extraterrestrial intelligence].  

PubMed

It is much easier to find extraterrestrial intelligence than to detect simple organisms living on other planets. However, it is hard to communicate with such intelligence without the mutual understanding of inter-stellar communication protocol. The radio SETI (The Search for Extra-Terrestrial Intelligence) was initiated with the pioneering work of F. Drake in 1960, one year after the historical SETI paper by Cocconi and Morrison. This talk explains that SETI evolves with two bases of science; the understanding of our universe and the development of technology. Since SETI has had strong connection with radio astronomy from its early beginning, the impacts of radio astronomical findings and technological breakthrough can be seen in many aspects of the SETI history. Topics of this talk include the detection of microwave 3 K background radiation in the universe. Interstellar atomic and molecular lines found in radio-wave spectra provide the evidence of pre-biotic chemical evolution in such region. Radio telescope imaging and spectral technique are closely associated with methodology of SETI. Topics of the talk extend to new Allen Telescope Array and projected Square Kilometer Array. Recent optical SETI and the discoveries of extra solar planets are also explained. In the end, the recent understanding of our universe is briefly introduced in terms of matter, dark matter and dark energy. Even our understanding of the universe has been evolutionarily revolved and accumulated after 1960, we must recognize that our universe is still poorly understood and that astronomy and SETI are required to proceed hand in hand. PMID:15136757

Hisabayashi, Hisashi

2003-12-01

231

Prediction of the field radiated at one meter from PCB's and microprocessors from near EM field cartography  

Microsoft Academic Search

The paper shows a near field scanning method to characterize chips that leads to the prediction of the coupling phenomena on the electronic board and to the evaluation of the radiated emission at one meter. A theoretical model is first given for simple circuits. An estimation of the scalar and vector potentials is found with the EM scan. Using these

F. de Daran; J. Chollet-Ricard; F. Lafon; O. Maurice

2003-01-01

232

Radiation from relativistic jets in turbulent magnetic fields  

SciTech Connect

Using our new 3-D relativistic electromagnetic particle (REMP) code parallelized with MPI, we have investigated long-term particle acceleration associated with an relativistic electron-positron jet propagating in an unmagnetized ambient electron-positron plasma. The simulations have been performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks. The acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value. Behind the bow shock in the jet shock strong electromagnetic fields are generated. These fields may lead to the afterglow emission. We have calculated the time evolution of the spectrum from two electrons propagating in a uniform parallel magnetic field to verify the technique.

Nishikawa, K.-I.; Mizuno, Y. [National Space Science and Technology Center, Huntsville, AL 35805 (United States); Medvedev, M. [Department of Physics and Astronomy, University of Kansas, KS 66045 (United States); Zhang, B. [Department of Physics, University of Nevada, Las Vegas, NV 89154 (United States); Hardee, P. [Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487 (United States); Niemiec, J. [Institute of Nuclear Physics PAN, ul. Radzikowskiego 152, 31-342 Krakow (Poland); Nordlund, A.; Frederiksen, J. [Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Oe (Denmark); Sol, H. [LUTH, Observatore de Paris-Meudon, 5 place Jules Jansen, 92195 Meudon Cedex (France); Fishman, G. J. [NASA/MSFC, Huntsville, AL 35805 (United States)

2009-05-25

233

Cherenkov Radiation Induced by Cosmogenic Neutrinos in Near-Field  

NASA Astrophysics Data System (ADS)

The radio technique of cosmogenic neutrino detection, which relies on the Cherenkov signals coherently emitted from the particle showers in dense medium, has now become a mature field. We present an alternative approach to calculate such Cherenkov pulse by a numerical code based on the finite difference time-domain (FDTD) method that does not rely on the far-field approximation. We show that for a shower elongated by the LPM (Landau-Pomeranchuk-Migdal) effect and thus with a multi-peak structure, the generated Cherenkov signal will always be a bipolar and asymmetric waveform in the near-field regime regardless of the specific variations of the multi-peak structure, which makes it a generic and distinctive feature. This should provide an important characteristic signature for the identification of ultra-high energy cosmogenic neutrinos.

Hu, Chia-Yu; Chen, Chih-Ching; Chen, Pisin

2013-12-01

234

Collective modes in free plasmas subjected to a radiation field  

NASA Astrophysics Data System (ADS)

In this study we report the effects of an electromagnetic field on the physical properties of free plasmas3.The calculations are carried out in the semi-classical approximation, i.e., the electromagnetic field is treated classically and the electrons from a quantum mechanical viewpoint. The results show that the collective modes are damped away more smoothly and in a smaller frequency range than those reported by previous studies. An exponential-like decay of the frequencies is readily observable from the plot of the plasmon frequency as a function of the external field amplitude. We successfully recreate the results of previous studies. We also obtain that the single photon processes has a pronounced effect on the decrease of the frequency range of modulation.

Ribeiro, B. V.; Santos, D. D. A.; Amato, M. A.; Fonseca, A. L. A.

2014-05-01

235

Gravitational field and radiation in general relativity and cosmology  

SciTech Connect

Properties of specific particle-like and cosmological solutions of general relativity are studied. In the first part, solution for the NUT geodesics was studied to help understand the physical interpretation of the NUT parameter. It is shown that the properties of the NUT geodesics are similar to the properties of the trajectories of a charged particle in a potential created by a magnetic monopole. The properties of the NUT geodesics are summarized. The second part of this dissertation is the study of an inhomogeneous generalization of the Bianchi I cosmological solution which contains gravitational waves. This model considers the interaction of the initial inhomogeneities with the evolution of the background geometry, electromagnetic radiation, gravity waves, and matter. In this model the initial inhomogeneities evolve at late times into gravitational waves, which are propagating through a smooth Bianchi I background. As the wave evolves it interacts with the global shear and different forms of energy. Around the origin the propagation of the wave is governed by the shear, where as, at later times the influence of the shear decreases and the radiation density dominates the solution.

Yaghoubi-Shahir, B.

1987-01-01

236

Simulation of Relativistic Shocks and Associated Radiation from Turbulent Magnetic Fields  

NASA Technical Reports Server (NTRS)

Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs at shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The jitter'' radiation from deflected electrons in turbulent magnetic fields has different properties than synchrotron radiation, which is calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets in general, and supernova remnants. We will present detailed spectra for conditions relevant of various astrophysical sites of shock formation via the Weibel instability. In particular we will discuss the application to GRBs and SNRs

Nishikawa, K.-I.; Mizuno, Y.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Fishman, G. J.

2010-01-01

237

Near Field Radiation Characteristics of Implantable Square Spiral Chip Inductor Antennas for Bio-Sensors  

NASA Technical Reports Server (NTRS)

The near field radiation characteristics of implantable Square Spiral Chip Inductor Antennas (SSCIA) for Bio-Sensors have been measured. Our results indicate that the measured near field relative signal strength of these antennas agrees with simulated results and confirm that in the near field region the radiation field is fairly uniform in all directions. The effects of parameters such as ground-plane, number of turns and microstrip-gap width on the performance of the SSCIA are presented. Furthermore, the SSCIA antenna with serrated ground plane produce a broad radiation pattern, with a relative signal strength detectable at distances within the range of operation of hand-held devices for self-diagnosis.

Nessel, James A.; Simons, Rainee N.; Miranda, Felix A.

2007-01-01

238

Calculation of sound field radiated by oscillating cascade  

NASA Astrophysics Data System (ADS)

In the present aeroacoustic model of an oscillating cascade, the frequency and propagation characteristics of the sound generated are analyzed by combining the model with the calculation of the cascade's unsteady field. Bending and tortion vibration, and coupled bending-tortion vibration, are all dependent on the relative Mach number of the inlet flow and the frequency of blade vibration, in addition to the geometrical parameters of the fan or compressor in question. Steady blade forces produce higher sound pressure levels than the unsteady blade forces in the acoustic near-field.

Wang, Shu-Hua; Sun, Xiao-Feng; Cao, Chuan-Jun

239

Radiation Field Wave Forms Produced by Lightning Stepped Leaders  

Microsoft Academic Search

Broad band electric field data are presented which show stepped leader wave forms preceding records of distant lightning return strokes. The majority of leader pulses are characterized by a large initial peak with a small and slow opposite overshoot. Total pulse durations range from 15-40 us several milliseconds before the return stroke to 2-10 us immediately preceding the return stroke.

E. Philip Krider; George J. Radda

1975-01-01

240

High field CdS detector for infrared radiation  

NASA Technical Reports Server (NTRS)

New and highly sensitive method of detecting infrared irradiation makes possible solid state infrared detector which is more sensitive near room temperature than usual photoconductive low band gap semiconductor devices. Reconfiguration of high field domains in cadmium sulphide crystals provides basis for discovery.

Tyagi, R. C.; Boer, K. W.; Hadley, H. C.; Robertson, J. B.

1972-01-01

241

A MEMS Device Capable of Measuring Near-Field Thermal Radiation between Membranes  

PubMed Central

For sensors constructed by freestanding membranes, when the gap between a freestanding membrane and the substrate or between membranes is at micron scale, the effects of near-field radiative heat transfer on the sensors' thermal performance should be considered during sensor design. The radiative heat flux is transferred from a membrane to a plane or from a membrane to a membrane. In the current study of the near-field thermal radiation, the scanning probe technology has difficulty in making a membrane separated at micron scale parallel to a plane or another membrane. A novel MEMS (micro electromechanical system) device was developed by sacrificial layer technique in this work to realize a double parallel freestanding membrane structure. Each freestanding membrane has a platinum thin-film resistor and the distance between the two membranes is 1 ?m. After evaluating the electrical and thermal characteristics of the lower freestanding membrane,experimental measurements of near-field radiative heat transfer between the lower membrane and the upper membrane were carried out by setting the lower membrane as a heat emitter and the upper membrane as a heat receiver. The near-field radiative heat transfer between the two membranes was validated by finding a larger-than-blackbody radiative heat transfer based on the experimental data.

Feng, Chong; Tang, Zhenan; Yu, Jun; Sun, Changyu

2013-01-01

242

ASRS Reports on Wake Vortex Encounters  

NASA Technical Reports Server (NTRS)

ASRS is conducting a structured callback research project of wake vortex incidents reported to the ASRS at all US airports, as well as wake encounters in the enroute environment. This study has three objectives: (1) Utilize the established ASRS supplemental data collection methodology and provide ongoing analysis of wake vortex encounter reports; (2) Document event dynamics and contributing factors underlying wake vortex encounter events; and (3) Support ongoing FAA efforts to address pre-emptive wake vortex risk reduction by utilizing ASRS reporting contributions.

Connell, Linda J.; Taube, Elisa Ann; Drew, Charles Robert; Barclay, Tommy Earl

2010-01-01

243

Techniques to maximize software reliability in radiation fields  

SciTech Connect

Microprocessor system failures due to memory corruption by single event upsets (SEUs) and/or latch-up in RAM or ROM memory are common in environments where there is high radiation flux. Traditional methods to harden microcomputer systems against SEUs and memory latch-up have usually involved expensive large scale hardware redundancy. Such systems offer higher reliability, but they tend to be more complex and non-standard. At the Space Astronomy Laboratory the authors have developed general programming techniques for producing software which is resistant to such memory failures. These techniques, which may be applied to standard off-the-shelf hardware, as well as custom designs, include an implementation of Maximally Redundant Software (MRS) model, error detection algorithms and memory verification and management.

Eichhorn, G.; Piercey, R.B.

1986-08-01

244

BOBCAT Personal Radiation Detector Field Test and Evaluation Campaign  

SciTech Connect

Following the success of the Anole test of portable detection system, the U.S. Department of Homeland Security (DHS) Domestic Nuclear Detection Office organized a test and evaluation campaign for personal radiation detectors (PRDs), also known as “Pagers.” This test, “Bobcat,” was conducted from July 17 to August 8, 2006, at the Nevada Test Site. The Bobcat test was designed to evaluate the performance of PRDs under various operational scenarios, such as pedestrian surveying, mobile surveying, cargo container screening, and pedestrian chokepoint monitoring. Under these testing scenarios, many operational characteristics of the PRDs, such as gamma and neutron sensitivities, positive detection and false alarm rates, response delay times, minimum detectable activities, and source localization errors, were analyzed. This paper will present the design, execution, and methodologies used to test this equipment for the DHS.

Chris Hodge

2008-03-01

245

Fan Noise Prediction System Development: Source/Radiation Field Coupling and Workstation Conversion for the Acoustic Radiation Code  

NASA Technical Reports Server (NTRS)

The Acoustic Radiation Code (ARC) is a finite element program used on the IBM mainframe to predict far-field acoustic radiation from a turbofan engine inlet. In this report, requirements for developers of internal aerodynamic codes regarding use of their program output an input for the ARC are discussed. More specifically, the particular input needed from the Bolt, Beranek and Newman/Pratt and Whitney (turbofan source noise generation) Code (BBN/PWC) is described. In a separate analysis, a method of coupling the source and radiation models, that recognizes waves crossing the interface in both directions, has been derived. A preliminary version of the coupled code has been developed and used for initial evaluation of coupling issues. Results thus far have shown that reflection from the inlet is sufficient to indicate that full coupling of the source and radiation fields is needed for accurate noise predictions ' Also, for this contract, the ARC has been modified for use on the Sun and Silicon Graphics Iris UNIX workstations. Changes and additions involved in this effort are described in an appendix.

Meyer, H. D.

1993-01-01

246

Microwave radiation power of relativistic electron beam with virtual cathode in the external magnetic field  

SciTech Connect

The study of the output power of the electromagnetic radiation of the relativistic electron beam (REB) with virtual cathode in the presence of external magnetic field has been found out. The typical dependencies of the output microwave power of the vircator versus external magnetic field have been analyzed by means of 3D electromagnetic simulation. It has been shown that the power of vircator demonstrates several maxima with external magnetic field growth. The characteristic features of the power behavior are determined by the conditions of the virtual cathode formation in the presence of the external transversal magnetic field and the REB self-magnetic fields.

Kurkin, S. A.; Hramov, A. E.; Koronovskii, A. A. [Saratov State University, Astrakhanskaja 83, Saratov 410012 (Russian Federation) [Saratov State University, Astrakhanskaja 83, Saratov 410012 (Russian Federation); Saratov State Technical University, Politechnicheskaja 77, Saratov 410028 (Russian Federation)

2013-07-22

247

Far-field radiation pattern of tunable diode lasers  

NASA Technical Reports Server (NTRS)

Technique rapidly determines far-field spatial energy distribution. Method takes about 3 minutes. It is optically simple and is economical, using standard laboratory parts and equipment. It records automatically without operator control and is easily adaptable to computer control of input instructions and computer treatment of output data. Degree of data resolution is limted only by width of recorder pen, and data are repeatable.

Lash, T. J.

1980-01-01

248

A CLOSER ENCOUNTER WITH MARS  

NASA Technical Reports Server (NTRS)

Taking advantage of Mars's closest approach to Earth in eight years, astronomers using NASA's Hubble Space Telescope have taken the space-based observatory's sharpest views yet of the Red Planet. NASA is releasing these images to commemorate the second anniversary of the Mars Pathfinder landing. The lander and its rover, Sojourner, touched down on the Red Planet's rolling hills on July 4, 1997, embarking on an historic three-month mission to gather information on the planet's atmosphere, climate, and geology. The telescope's Wide Field and Planetary Camera 2 snapped these images between April 27 and May 6, when Mars was 54 million miles (87 million kilometers) from Earth. From this distance the telescope could see Martian features as small as 12 miles (19 kilometers) wide. The telescope obtained four images, which, together, show the entire planet. Each view depicts the planet as it completes one quarter of its daily rotation. In these views the north polar cap is tilted toward the Earth and is visible prominently at the top of each picture. The images were taken in the middle of the Martian northern summer, when the polar cap had shrunk to its smallest size. During this season the Sun shines continuously on the polar cap. Previous telescopic and spacecraft observations have shown that this summertime 'residual' polar cap is composed of water ice, just like Earth's polar caps. These Hubble telescope snapshots reveal that substantial changes in the bright and dark markings on Mars have occurred in the 20 years since the NASA Viking spacecraft missions first mapped the planet. The Martian surface is dynamic and ever changing. Some regions that were dark 20 years ago are now bright red; some areas that were bright red are now dark. Winds move sand and dust from region to region, often in spectacular dust storms. Over long timescales many of the larger bright and dark markings remain stable, but smaller details come and go as they are covered and then uncovered by sand and dust. The upper-left image is centered near the location of the Pathfinder landing site. Dark sand dunes that surround the polar cap merge into a large, dark region called Acidalia. This area, as shown by images from the Hubble telescope and other spacecraft, is composed of dark, sand-sized grains of pulverized volcanic rock. Below and to the left of Acidalia are the massive Martian canyon systems of Valles Marineris, some of which form long linear markings that were once thought by some to be canals. Early morning clouds can be seen along the left limb of the planet, and a large cyclonic storm composed of water ice is churning near the polar cap. The upper-right image is centered on the region of the planet known as Tharsis, home of the largest volcanoes in the solar system. The bright, ring-like feature just to the left of center is the volcano Olympus Mons, which is more than 340 miles (550 kilometers) across and 17 miles (27 kilometers) high. Thick deposits of fine-grained, windblown dust cover most of this hemisphere. The colors indicate that the dust is heavily oxidized ('rusted'), and millions (or perhaps billions) of years of dust storms have homogenized its composition. Prominent late afternoon clouds along the right limb of the planet can be seen. The lower-left image is centered near another volcanic region known as Elysium. This area shows many small, dark markings that have been observed by the Hubble telescope and other spacecraft to change as a result of the movement of sand and dust across the Martian surface. In the upper left of this image, at high northern latitudes, a large chevron-shaped area of water ice clouds mark a storm front. Along the right limb, a large cloud system has formed around the Olympus Mons volcano. The lower-right image is centered on the dark feature known as Syrtis Major, first seen telescopically by the astronomer Christiaan Huygens in the 17th century. Many small, dark, circular impact craters can be seen in this region, attesting to the Hubble telescope's ability to reveal fine detail on the planet's surface. To

2002-01-01

249

The magneto-Coulomb radiation of ultrarelativistic electrons in a strong magnetic field  

NASA Astrophysics Data System (ADS)

The propagation of ultrarelativistic (TeV or higher) electrons along the lines of an intense (TG) magnetic field and the resulting generation of hard gamma radiation by the Joint action of matter and the magnetic field (the magneto-Coulomb mechanism, MCM, proposed by Kel'ner and Kotov, 1985) are investigated analytically. In the MCM, the particles undergo Coulomb collisions with the target matter and are raised to excited Landau states, and gamma photons are generated as they undergo radiative transition to lower levels. The MCM cross sections for the case of a fully ionized plasma target are calculated, and the spectrum, angular distribution, and polarization of the MCM radiation are determined. It is shown that the electron energy loss due to MCM radiation is dominant for conditions consistent with the two-level approximation employed. The implications of the MCM for the gamma emission of neutron stars are considered.

Kotov, Y. D.; Kelner, S. R.

1985-12-01

250

On the radiative part of the Maxwell tensor for a Liénard - Wiechert field  

NASA Astrophysics Data System (ADS)

The Maxwell energy-momentum tensor associated with the Liénard - Wiechert field of a point charge in arbitrary motion splits naturally into a bounded and a radiative part. It is known that the bounded part of the Maxwell tensor does not contribute to the energy-momentum balance between matter and field which is completely accounted for by its radiative part only. In this paper we show that the purely radiative part of the Maxwell tensor can be further decomposed as the sum of a term, again not contributing to the energy-momentum balance, plus a part which is completely responsible for it. Furthermore, we also manage to find that the full radiative part of the Maxwell tensor can be generated by a superpotential that has to be regarded as non-local since its definition involves integration over a finite section of the charge's world line.

Núñez-Yépez, H. N.; López-Bonilla, J. L.; Salas-Brito, A. L.

1997-05-01

251

Mechanism of Radiation Coupling to Plasma Wave Field Effect Transistor Sub-THz Detectors  

NASA Astrophysics Data System (ADS)

Detection of 100 GHz and 285 GHz electromagnetic radiation by GaAs/AlGaAs field effect transistors with the gate length of 150 nm was investigated at 300 K as a function of the angle ? between the direction of linear polarization of the radiation and the symmetry axis of the field effect transistors. The angular dependence of the detected signal was found to be Acos2(?-?0)+C. A response of the transistor chip (including bonding wires and the substrate) to the radiation was numerically simulated. Calculations confirmed experimentally observed dependences and allowed to investigate the role of bonding wires and contact pads in coupling of the radiation to the transistor channel.

Sakowicz, M.; ?usakowski, J.; Karpierz, K.; Grynberg, M.; Gwarek, W.; Knap, W.; Boubanga, S.

2008-11-01

252

A NUMERICAL TREATMENT OF ANISOTROPIC RADIATION FIELDS COUPLED WITH RELATIVISTIC RESISTIVE MAGNETOFLUIDS  

SciTech Connect

We develop a numerical scheme for solving fully special relativistic, resistive radiation magnetohydrodynamics. Our code guarantees conservation of total mass, momentum, and energy. The radiation energy density and the radiation flux are consistently updated using the M-1 closure method, which can resolve an anisotropic radiation field, in contrast to the Eddington approximation, as well as the flux-limited diffusion approximation. For the resistive part, we adopt a simple form of Ohm's law. The advection terms are explicitly solved with an approximate Riemann solver, mainly the Harten-Lax-van Leer scheme; the HLLC and HLLD schemes are also solved for some tests. The source terms, which describe the gas-radiation interaction and the magnetic energy dissipation, are implicitly integrated, relaxing the Courant-Friedrichs-Lewy condition even in an optically thick regime or a large magnetic Reynolds number regime. Although we need to invert 4 Multiplication-Sign 4 matrices (for the gas-radiation interaction) and 3 Multiplication-Sign 3 matrices (for the magnetic energy dissipation) at each grid point for implicit integration, they are obtained analytically without preventing massive parallel computing. We show that our code gives reasonable outcomes in numerical tests for ideal magnetohydrodynamics, propagating radiation, and radiation hydrodynamics. We also applied our resistive code to the relativistic Petschek-type magnetic reconnection, revealing the reduction of the reconnection rate via radiation drag.

Takahashi, Hiroyuki R. [Center for Computational Astrophysics, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Ohsuga, Ken [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan)

2013-08-01

253

First-Year Principal Encounters Homophobia  

ERIC Educational Resources Information Center

A 1st-year principal encounters homonegativity and an ethical dilemma when she attempts to terminate a teacher because of the teacher's inadequate and ineffective teaching. The teacher responds by threatening to "out" Ms. L. to the parents.

Retelle, Ellen

2011-01-01

254

Exploring Digital Encounters in the Public Arena  

NASA Astrophysics Data System (ADS)

In this chapter, we explore the types of encounters that technology enables. We consider the differences between digital and nondigital encounters through two pilot studies carried out in the city of Bath, United Kingdom. We investigate how technology can be appropriated for shared interactions that support conscious (or unconscious) social encounters, and highlight the importance of space and the role of place in providing temporal and spatial mechanisms facilitating different types of shared encounters. Here, we apply a method based on intervention through "sensing and projecting" Bluetooth names and digital identity in the public arena, and describe initial observations about people's reaction toward the projection of their Bluetooth names in public. In particular, we note the significance of constructing socially meaningful relations between people mediated by these technologies. We discuss initial results and outline issues raised in detail before finally describing the ongoing work.

Schieck, Ava Fatah Gen.; Kostakos, Vassilis; Penn, Alan

255

Compendium of Material Composition Data for Radiation Transport Modeling  

Microsoft Academic Search

Introduction Meaningful simulations of radiation transport applications require realistic definitions of material composition and densities. When seeking that information for applications in fields such as homeland security, radiation shielding and protection, and criticality safety, researchers usually encounter a variety of materials for which elemental compositions are not readily available or densities are not defined. Publication of the Compendium of Material

Ronald J. McConn; Christopher J. Gesh; Richard T. Pagh; Robert A. Rucker; Robert Williams

2011-01-01

256

Modelling net radiation in a High Arctic environment using summer field camp data  

Microsoft Academic Search

A model is presented that uses easily obtained twice-daily field data (cloud-type, amount, temperature, wind speed at 2 m) to estimate net radiation for horizontal and slope sites in a High Arctic setting. Incoming shortwave radiation is estimated using a cloud-layer model, sensible and latent heat fluxes are determined using temperature and wind data, and the surface heat flux is

Kathy L. Young; Ming-Ko Woo

1997-01-01

257

Plasma wave instability and amplification of terahertz radiation in field-effect-transistor arrays.  

PubMed

We show that the strong amplification of terahertz radiation takes place in an array of field-effect transistors at small DC drain currents due to hydrodynamic plasmon instability of the collective plasmon mode. Planar designs compatible with standard integrated circuit fabrication processes and strong coupling of terahertz radiation to plasmon modes in FET arrays make such arrays very attractive for potential applications in solid-state terahertz amplifiers and emitters. PMID:21693816

Popov, V V; Tsymbalov, G M; Shur, M S

2008-09-24

258

Larmor radiation from the ultra-intense field ionization of atoms  

Microsoft Academic Search

The angle- and energy-resolved Larmor radiation from atomic ionization in the focus of ultra-intense laser field is calculated using a semi-classical, trajectory ensemble model of ionization. We find that including the quantum nature of the atomic ionization decreases the radiation yield by an order of magnitude compared to a classical electron calculation due to interference effects in the extended probability

Enam A Chowdhury; Isaac Ghebregziabiher; Barry C Walker

2005-01-01

259

Ultraviolet-B radiation and nitrogen affect the photosynthesis of maize: a Mediterranean field study  

Microsoft Academic Search

The effects of UV-B radiation on the gas exchange rates, chlorophyll fluorescence, pigmentation, soluble sugars, starch, soluble proteins and carboxylating enzyme activities of maize (Zea mays L.) were investigated at four levels of applied nitrogen (0, 100, 200 and 300kgha?1 of N) under Mediterranean field conditions. The experiment simulated a 20% stratospheric ozone depletion over Portugal. Supplementary UV-B radiation and

Carlos M. Correia; José M. Moutinho Pereira; João F. Coutinho; Lars O. Björn; José M. G. Torres-Pereira

2005-01-01

260

Dynamics of self-gravitating shells driven by radiation pressure from the field stars  

NASA Astrophysics Data System (ADS)

It is shown that self-gravitating shells can be accelerated only when the energy density of the stellar radiation exceeds the critical value of 3.6 x 10 to the -13th J/cu m. It is thus concluded that the acceleration mechanism for self-gravitating shells connected with radiation pressure from the field stars is not effective for systems with Galaxy parameters.

Pas'ko, V. P.; Silich, S. A.

1988-04-01

261

Exposure to extremely-low-frequency electromagnetic fields and radiofrequency radiation: cardiovascular effects in humans  

Microsoft Academic Search

Cardiovascular changes in humans exposed to nonionizing radiation [including extremely-low-frequency electromagnetic fields\\u000a (ELF EMFs) and radiofrequency radiation (RFR)] are reviewed. Both acute and long-term effects have been investigated. In general,\\u000a if heating does not occur during exposure, current flow appears to be necessary for major cardiovascular effects to ensue,\\u000a such as those due to electric shock. Whereas most studies have

James R. Jauchem

1997-01-01

262

Microdosimetric measurements in the secondary radiation field produced in 12 C-therapy irradiations  

Microsoft Academic Search

The ambient dose equivalent from the secondary radiation produced during irradiation of a cylindrical water phantom with 200 MeV\\/u\\u000a 12C-ions was investigated at the biophysics cave at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Pencil-like\\u000a ion beams were delivered by the heavy-ion synchrotron SIS18 using the slow extraction mode. Since the secondary radiation\\u000a field outside the phantom is complex in its

F. Wissmann; U. Giesen; T. Klages; D. Schardt; G. Martino; C. Sunil

2010-01-01

263

History-Enriched Spaces for Shared Encounters  

Microsoft Academic Search

\\u000a We discuss “history-enriched spaces” that use historical data to support shared encounters. We first examine our experiences\\u000a with DeaiExplorer, a social network display that uses RFID and a historical database to support social interactions at academic conferences.\\u000a This leads to our discussions on three complementary approaches to addressing the issues of supporting social encounters:\\u000a (1) embedding historical data in embodied

Shin’ichi Konomi; Kaoru Sezaki; Masaru Kitsuregawa

2010-01-01

264

Predicting the Earth encounters of (99942) Apophis  

Microsoft Academic Search

Arecibo delay–Doppler measurements of (99942) Apophis in 2005 and 2006 resulted in a five standard-deviation trajectory correction to the optically predicted close approach distance to Earth in 2029. The radar measurements reduced the volume of the statistical uncertainty region entering the encounter to 7.3% of the pre-radar solution, but increased the trajectory uncertainty growth rate across the encounter by 800%

Jon D. Giorgini; Lance A. M. Benner; Steven J. Ostro; Michael C. Nolan; Michael W. Busch

2008-01-01

265

Predicting the Earth encounters of (99942) Apophis  

Microsoft Academic Search

Arecibo delay Doppler measurements of (99942) Apophis in 2005 and 2006 resulted in a five standard-deviation trajectory correction to the optically predicted close approach distance to Earth in 2029. The radar measurements reduced the volume of the statistical uncertainty region entering the encounter to 7.3% of the pre-radar solution, but increased the trajectory uncertainty growth rate across the encounter by

Jon D. Giorgini; Lance A. M. Benner; Steven J. Ostro; Michael C. Nolan; Michael W. Busch

2008-01-01

266

Predicting the Earth encounters of (99942) Apophis  

Microsoft Academic Search

Arecibo delay-Doppler measurements of (99942) Apophis in 2005 and 2006 resulted in a five standard-deviation trajectory correction to the optically predicted close approach distance to Earth in 2029. The radar measurements reduced the volume of the statistical uncertainty region entering the encounter to 7.3% of the pre-radar solution, but increased the trajectory uncertainty growth rate across the encounter by 800%

Jon D. Giorgini; Lance A. M. Benner; J. Ostro; Michael C. Nolan; Michael W. Busch

2008-01-01

267

Miniature scintillating detector for small field radiation therapy.  

PubMed

In planning stereotactic radiosurgery treatments, depth dose curves, profiles, and dose rate of treatment beams are difficult to obtain with conventional detectors because of loss of lateral electronic equilibrium and volume averaging. A scintillating detector with high spatial resolution and good reliability has been developed to overcome this problem. The miniature dosimeter consists of two identical radiation-resistant 10 m long silica optical fibers, each connected to an independent silicon photodiode. A small cylindrical polystyrene scintillator (3.9 mm3) is optically glued to the detection fiber. The light seen by the photodiode connected to this fiber arises from fluorescence of the scintillator and from the Cerenkov effect produced in silica. The reference signal produced by the fiber without scintillator is used to subtract the Cerenkov light contribution from the raw detector response. The sensitive volume of the scintillating detector is nearly water-equivalent and thus minimizes dose distribution perturbation in water. The miniature dosimeter has a spatial resolution comparable to the film-densitometer system. Profiles of 1 cm diam, 6 MV photon beam measured with both systems show very similar shapes. Furthermore, the use of photodiodes instead of photomultiplier tubes gives a better stability response and offers the possibility to perform absolute dosimetry. PMID:10619239

Létourneau, D; Pouliot, J; Roy, R

1999-12-01

268

On the magnetic field signal radiated by an atmospheric pressure room temperature plasma jet  

SciTech Connect

In this paper, the magnetic field signal radiated from an atmospheric pressure room temperature plasma plume is measured. It's found that the magnetic field signal has similar waveform as the current carried by the plasma plume. By calibration of the magnetic field signal, the plasma plume current is obtained by measuring the magnetic field signal radiated by the plasma plume. In addition, it is found that, when gas flow modes changes from laminar regime to turbulence regime, the magnetic field signal waveforms appears different, it changes from a smooth curve to a curve with multiple spikes. Furthermore, it is confirmed that the plasma plume generated by a single electrode (without ground electrode) plasma jet device carries higher current than that with ground electrode.

Wu, S.; Huang, Q.; Wang, Z.; Lu, X. [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)

2013-01-28

269

The electric field changes and UHF radiations caused by the triggered lightning in Japan  

NASA Astrophysics Data System (ADS)

The electric field changes, the magnetic field changes, and UHF radiation were observed during the rocket-triggered lightning experiment in winter storms. A remarkable discrepancy is noticed between electromagnetic field changes of flashes triggered with a rocket and an isolated wire that struck a power tower and flashes with a rocket and a grounded wire. Flashes to tower have a distinguishable first pulse of a large amplitude, which, we speculate, occurs at the moment of attachment of a downward leader to the tower. The UHF radiation measurements indicate that the triggered lightning process starts with a pulse series resembling a negative stepped leader. The electric field change records of rockettriggered lightning in winter storms do not show the presence of rapid field variations typical for return strokes in natural cloud-to-ground flashes.

Kawasaki, Zen-Ichiro; Kanao, Tadashi; Matsuura, Kenji; Nakano, Minoru; Horii, Kenji; Nakamura, Koh-Ichi

1991-09-01

270

Do planetary encounters reset surfaces of near Earth asteroids?  

NASA Astrophysics Data System (ADS)

Processes such as the solar wind sputtering and micrometeorite impacts can modify optical properties of surfaces of airless bodies. This explains why spectra of the main belt asteroids, exposed to these 'space weathering' processes over eons, do not match the laboratory spectra of ordinary chondrite (OC) meteorites. In contrast, an important fraction of Near Earth Asteroids (NEAs), defined as Q-types in the asteroid taxonomy, display spectral attributes that are a good match to OCs. Here we study the possibility that the Q-type NEAs underwent recent encounters with the terrestrial planets and that the tidal gravity (or other effects) during these encounters exposed fresh OC material on the surface (thus giving it the Q-type spectral properties). We used numerical integrations to determine the statistics of encounters of NEAs to planets. The results were used to calculate the fraction and orbital distribution of Q-type asteroids expected in the model as a function of the space weathering timescale, tsw (see main text for definition), and maximum distance, r?, at which planetary encounters can reset the surface. We found that tsw ˜ 10 6 yr (at 1 AU) and r? ˜ 5 Rpl, where Rpl is the planetary radius, best fit the data. Values tsw < 10 5 yr would require that r? > 20 Rpl, which is probably implausible because these very distant encounters should be irrelevant. Also, the fraction of Q-type NEAs would be probably much larger than the one observed if tsw > 10 7 yr. We found that tsw ? q2, where q is the perihelion distance, expected if the solar wind sputtering controls tsw, provides a better match to the orbital distribution of Q-type NEAs than models with fixed tsw. We also discuss how the Earth magnetosphere and radiation effects such as YORP can influence the spectral properties of NEAs.

Nesvorný, David; Bottke, William F.; Vokrouhlický, David; Chapman, Clark R.; Rafkin, Scot

2010-10-01

271

Simulation studies of wide and medium field of view earth radiation data analysis  

NASA Technical Reports Server (NTRS)

A parameter estimation technique is presented to estimate the radiative flux distribution over the earth from radiometer measurements at satellite altitude. The technique analyzes measurements from a wide field of view (WFOV), horizon to horizon, nadir pointing sensor with a mathematical technique to derive the radiative flux estimates at the top of the atmosphere for resolution elements smaller than the sensor field of view. A computer simulation of the data analysis technique is presented for both earth-emitted and reflected radiation. Zonal resolutions are considered as well as the global integration of plane flux. An estimate of the equator-to-pole gradient is obtained from the zonal estimates. Sensitivity studies of the derived flux distribution to directional model errors are also presented. In addition to the WFOV results, medium field of view results are presented.

Green, R. N.

1978-01-01

272

Electromagnetic fields radiated from a lightning return stroke - Application of an exact solution to Maxwell's equations  

NASA Technical Reports Server (NTRS)

A solution is presented for the electromagnetic fields radiated by an arbitrarily oriented current filament over a conducting ground plane in the case where the current propagates along the filament at the speed of light, and this solution is interpreted in terms of radiation from lightning return strokes. The solution is exact in the fullest sense; no mathematical approximations are made, and the governing differential equations and boundary conditions are satisfied. The solution has the additional attribute of being specified in closed form in terms of elementary functions. This solution is discussed from the point of view of deducing lightning current wave forms from measurements of the electromagnetic fields and understanding the effects of channel tortuosity on the radiated fields. In addition, it is compared with two approximate solutions, the traditional moment approximation and the Fraunhofer approximation, and a set of criteria describing their applicability are presented and interpreted.

Le Vine, D. M.; Meneghini, R.

1978-01-01

273

Design of the beam loss monitoring system in strong prompt radiation field  

NASA Astrophysics Data System (ADS)

It is inescapable that some electrons will be lost when they are accelerated or transported in the accelerator vacuum chamber. A beam loss monitoring (BLM) system, which works by the radiation measurement, has been successfully installed on the storage ring. Next on the schedule is design of the BLM system for LINAC and transport line. The radiation field around the LINAC and transport line consists of a strong prompt mixed (gamma, neutron) one. Its duty factor is only 10 -6 at Hefei Light Source (HLS). A detector based on counting cannot be used here, while one based on integral charge may be suitable in such a field. The most effective detected objects for estimating beam loss by radiation measurement are shower electrons because they can indicate the beam loss position more clearly than ? rays. The detector also should have the ability to decrease stray radiation influence in strong prompt radiation field. For the requirements mentioned above, a new kind of photodiode detector is being developed. We analyzed the beam transportation process and calculated relevant parameters. Then the positions where the detectors should be fixed were determined. The CAN bus mode we use for the storage ring BLM system is out of date because of the rapid development in the communication field. TCP/IP communication is used for the new system.

Juexin, Li; Yuxiong, Li; Weimin, Li; Guanghua, Gong; Zhengguo, Zhao

2007-08-01

274

Ultraviolet radiation penetrating vehicle glass: a field based comparative study.  

PubMed

The solar UV transmitted through automobile glass was measured in the field in two cars using a spectroradiometer. The two cars were identical except that one of the cars had all of the windows (except the windshield) tinted. The measured spectral erythemal UV on a horizontal plane with the windows fully closed was reduced in the tinted car by a factor of 42 when compared with the erythemal UV measured in the untinted car. The ambient UVA irradiances at various locations within four different makes of car and a tractor were also measured with a broad band UVA handheld meter. The average normalized daily UVA exposure (measured with a broad band UVA meter) was 1.3 times higher in a large family sedan when compared with that in a small hatchback and the UVA exposure in a car with tinted windows was 3.8 times less than in a similar untinted car. PMID:10232805

Kimlin, M G; Parisi, A V

1999-04-01

275

EPR dosimetry in a mixed neutron and gamma radiation field.  

PubMed

Suitability of Electron Paramagnetic Resonance (EPR) spectroscopy for criticality dosimetry was evaluated for tooth enamel, mannose and alanine pellets during the 'international intercomparison of criticality dosimetry techniques' at the SILENE reactor held in Valduc in June 2002, France. These three materials were irradiated in neutron and gamma-ray fields of various relative intensities and spectral distributions in order to evaluate their neutron sensitivity. The neutron response was found to be around 10% for tooth enamel, 45% for mannose and between 40 and 90% for alanine pellets according their type. According to the IAEA recommendations on the early estimate of criticality accident absorbed dose, analyzed results show the EPR potentiality and complementarity with regular criticality techniques. PMID:15353687

Trompier, F; Fattibene, P; Tikunov, D; Bartolotta, A; Carosi, A; Doca, M C

2004-01-01

276

Rotation and Stability of the Toroidal Magnetic Field in Stellar Radiation Zones  

NASA Astrophysics Data System (ADS)

The stability of the magnetic field in radiation zones is of crucial importance for mixing and angular momentum transport in the stellar interior. We consider the stability properties of stars containing a predominant toroidal field in spherical geometry by means of a linear stability in the Boussinesq approximation taking into account the effect of thermal conductivity. We calculate the growth rate of instability and analyze in detail the effects of stable stratification and heat transport. We argue that the stabilizing influence of gravity can never entirely suppress the instability caused by electric currents in radiation zones. However, the stable stratification can essentially decrease the growth rate of instability.

Bonanno, Alfio; Urpin, Vadim

2013-03-01

277

Deconvolution of wide-field-of-view measurements of reflected solar radiation  

NASA Technical Reports Server (NTRS)

Wide-field-of-view (WFOV) radiometers have been flown as part of the Earth Radiation Budget instrument on the Nimbus 6 and 7 spacecraft and as part of the Earth Radiation Budget Experiment (ERBE) instruments aboard the ERBE spacecraft and also the NOAA 9 and 10 operational spacecraft. The measurement is the integral of the reflected solar flux distribution at the top of the earth-atmosphere system over the field-of-view of the radiometer. This paper develops the solution to this two-dimensional integral equation for the albedo distribution in terms of the measurements.

Smith, G. Louis; Rutan, David

1990-01-01

278

Radiative multipole moments of integer-spin fields in curved spacetime  

NASA Astrophysics Data System (ADS)

Radiative multipole moments of scalar, electromagnetic, and linearized gravitational fields in Schwarzschild spacetime are computed to third order in v in a weak-field, slow-motion approximation, where v is a characteristic velocity associated with the motion of the source. These moments are defined for all three types of radiation by relations of the form ?(t,x-->)=r-1?lmMlm(u)Ylm(?,?), where ? is the radiation field at infinity and Mlm are the radiative moments, functions of retarded time u=t-r-2Mln(r/2M-1); M is the mass parameter of the Schwarzschild spacetime and (t,x-->)=(t,r,?,?) are the usual Schwarzschild coordinates. For all three types of radiation the moments share the same mathematical structure: To zeroth order in v, the radiative moments are given by relations of the form Mlm(u)~(d/du)l??(u,x-->)rlY¯lm(?,?)dx-->, where ? is the source of the radiation. A radiative moment of order l is therefore given by the corresponding source moment differentiated l times with respect to retarded time. To second order in v, additional terms appear inside the spatial integrals, and the radiative moments become Mlm(u)~(d/du)l?[1+O(r2?2u)+O(M/r)]?rlY¯lm dx-->. The term involving r2?2u can be interpreted as a special-relativistic correction to the wave-generation problem. The term involving M/r comes from general relativity. These correction terms of order v2 are near-zone corrections which depend on the detailed behavior of the source. Furthermore, the radiative multipole moments are still local functions of u, as they depend on the state of the source at retarded time u only. To third order in v, the radiative moments become Mlm(u)-->Mlm(u)+2M?u-?[ln(u-u')+const]M ¨lm(u') du', where overdots indicate differentiation with respect to u'. This expression shows that the O(v3) correction terms occur outside the spatial integrals, so that they do not depend on the detailed behavior of the source. Furthermore, the radiative multipole moments now display a nonlocality in time, as they depend on the state of the source at all times prior to the retarded time u, with the factor ln(u-u') assigning most of the weight to the source's recent past. (The term involving the constant is actually local.) The correction terms of order v3 are wave-propagation corrections which are heuristically understood as arising from the scattering of the radiation by the spacetime curvature surrounding the source. The radiative multipole moments are computed explicitly for all three types of radiation by taking advantage of the symmetries of the Schwarzschild metric to separate the variables in the wave equations. Our calculations show that the truly nonlocal wave-propagation correction - the term involving ln(u-u') - takes a universal form which is independent of multipole order and field type. We also show that in general relativity, temporal and spatial curvatures contribute equally to the wave-propagation corrections. Finally, we produce an alternative derivation of the radiative moments of a scalar field based on the retarded Green's function of DeWitt and Brehme. This calculation shows that the tail part of the Green's function is entirely responsible for the wave-propagation corrections in the radiative moments.

Leonard, Stephen W.; Poisson, Eric

1997-10-01

279

On Whether Angular Momentum in Electric and Magnetic Fields Radiates to Infinity  

NASA Technical Reports Server (NTRS)

The Feynman Disk experiment and a related thought experiment with a static magnetic field and capacitor are studied. The mechanical torque integrated over time (angular impulse) is related to the angular momentum in the electric/magnetic field. This is not called an electromagnetic field since quasi-static as well as electromagnetic effects are included. The angular momentum in the electric/magnetic field is examined to determine its static and radiative components. This comparison was then examined to see if it clarified the Abraham-Minkowski paradox.

Canning, Francis X.; Knudsen, Steven

2006-01-01

280

Does the Helmholtz theorem of vector decomposition apply to the wave fields of electromagnetic radiation?  

NASA Astrophysics Data System (ADS)

The derivation of the Helmholtz theorem of vector decomposition of a three-vector field requires that the field satisfy certain convergence properties at spatial infinity. This paper investigates if time-dependent electromagnetic radiation wave fields of point sources, which are of long range, satisfy these requirements. It is found that the requirements are satisfied because the fields give rise to integrals over the radial distance r of integrands of the form sin(kr)/r and cos(kr)/r. These Dirichlet integrals converge at infinity as required.

Stewart, A. M.

2014-06-01

281

Modeling of Lorentz forces and radiated wave fields for bulk wave electromagnetic acoustic transducers  

NASA Astrophysics Data System (ADS)

Currently, the finite element method (FEM) and analytical calculation are widely employed for the modeling of electromagnetic acoustic transducers (EMATs). However, it takes long time for finite element calculation. Previous analytical models for bulk wave EMATs are generally considered separately and incompletely, and expressions of radiated wave fields contain infinite integrations and multiple singular points, which result in complex numerical computation. A complete model containing the Lorentz force and radiated wave field calculation for the EMAT with a spiral coil and a NdFeB permanent magnet is established. By introducing a current loop instead of the permanent magnet and adopting the truncated region eigenfunction expansion (TREE) method, the distributions of static and dynamic magnetic fields and their generated Lorentz forces are calculated. A series expansion method is proposed for the computation of radiated wave fields, which replaces the integration by series operation and avoids the solutions of singular points effectively. The Lorentz forces and radiated wave fields of a typical transducer are computed. The validity of the model is verified by FEM and experiments. Their good agreements verify the accuracy and validity of the model.

Zhai, Guofu; Wang, Kaican; Wang, Yakun; Su, Riliang; Kang, Lei

2013-08-01

282

Transient quantum coherent response to a partially coherent radiation field.  

PubMed

The response of an arbitrary closed quantum system to a partially coherent electric field is investigated, with a focus on the transient coherences in the system. As a model we examine, both perturbatively and numerically, the coherences induced in a three level V system. Both rapid turn-on and pulsed turn-on effects are investigated. The effect of a long and incoherent pulse is also considered, demonstrating that during the pulse the system shows a coherent response which reduces after the pulse is over. Both the pulsed scenario and the thermally broadened CW case approach a mixed state in the long time limit, with rates dictated by the adjacent level spacings and the coherence time of the light, and via a mechanism that is distinctly different from traditional decoherence. These two excitation scenarios are also explored for a minimal "toy" model of the electronic levels in pigment protein complex PC645 by both a collisionally broadened CW laser and by a noisy pulse, where unexpectedly long transient coherence times are observed and explained. The significance of environmentally induced decoherence is noted. PMID:24559335

Sadeq, Zaheen S; Brumer, Paul

2014-02-21

283

Delineation of electric and magnetic field effects of extremely low frequency electromagnetic radiation on transcription  

SciTech Connect

The relative effects of the electric and magnetic field components of extremely low frequency electromagnetic radiation (ELF) on transcription were examined in human leukemia HL-60 cells. Delineation of the individual field contributions was achieved by irradiating cells in separate concentric compartments of a culture dish within a solenoid chamber. This exposure system produced a homogeneous magnetic field with a coincident electric field whose strength varied directly with distance from the center of the culture dish. Irradiation of HL-60 cells with sine wave ELF at 60 Hz and a field strength of 10 Gauss produced a transient increase in the transcriptional rates which reached a maximum of 50-60% enhancement at 30-120 minutes of irradiation and declined to near basal levels by 18 hours. Comparison of transcription responses to ELF of cells in different concentric compartments revealed that the transcriptional effects were primarily the result of the electric field component with little or no contribution from the magnetic field.

Greene, J.J.; Skowronski, W.J.; Mullins, J.M.; Nardone, R.M.; Penafiel, M.; Meister, R. (Catholic Univ. of America, Washington, DC (USA))

1991-01-31

284

Evaluation of dosimetric characteristics of multi-leaf and conventional collimated radiation fields using a scanning liquid ionization chamber EPID.  

PubMed

The characteristics of radiation fields set up using conventional and Multi-Leaf collimators were investigated using a Scanning Liquid Ionization Chamber Electronic Portal Imaging Device (SLIC-EPID). Results showed that the radiation fields set up using MLCs are generally larger than those set up using conventional collimators. A significant difference was observed between the penumbra width for conventional and MLC radiation fields. SLIC-EPID was found to be a sensitive device to evaluate the characteristics of the radiation fields generated with MLCs. PMID:19239054

Mohammadi, M; Bezak, E

2008-12-01

285

Local field effects and stimulated multimode scattering of resonance radiation in a two-level medium  

SciTech Connect

Scattering of resonance radiation in a dense two-level medium is considered with allowance for the local field effects. The system is studied in the framework of the mean-field approximation for a modified hierarchy of the Bogoliubov-Born-Green-Kirkwood-Yvon equations for reduced density matrices of an ensemble of atoms and modes of a quantized electromagnetic field. The local field correction is consistently derived from the initial Hamiltonian of the system. The problem of scattering of a short rectangular pulse from a quasi-point sample is considered numerically and theoretically. The possibility of a multimode spectrum of scattered radiation with frequencies multiple of the Rabi frequency and with other intermediate frequencies is demonstrated. The relative intensities of spectral lines are determined.

Gladush, M. G., E-mail: mglad@triniti.ru; Panteleev, A. A.; Roerich, Vl. C. [Russian Federation State Research Center TRINITI (Russian Federation)

2006-08-15

286

Excitation of surface waves and the scattered radiation fields by rough surfaces of arbitrary slope  

NASA Astrophysics Data System (ADS)

Surface waves as well as lateral waves are excited when a rough surface is illuminated by the radiation fields. In view of shadowing, these terms of the complete field expansions contribute significantly to the total fields when the transmitter or receiver are near the rough surface. In this work explicit expressions are derived for the coupling between the radiation fields and the surface waves which are guided at the irregular interface between two media. In the analysis, the slope of the rough surface is not restricted and the solutions for both the horizontally and vertically polarized waves are shown to satisfy reciprocity and duality relationships in electromagnetic theory. Special consideration is given to Brewster angles of incidence and scatter and stationary phase techniques. The full-wave solutions are also applied to random and periodic rough surfaces.

Bahar, E.

1980-09-01

287

Field distribution and radiation field of finite axial slots on circular waveguides  

Microsoft Academic Search

The field distribution on a finite axial slot is determined from that of a semi-infinite axial slot, using a multiple reflection technique. It involves enforcing the continuity of the transverse field components, at the common boundaries between the solid and the slotted sections of the waveguides, to determine the mode coefficients of reflected and transmitted waves. The steps for determining

L. Shafai; E. E. M. Hassan

1981-01-01

288

Polarized Atomic Radiative Emission in the Presence of Electric and Magnetic Fields  

NASA Astrophysics Data System (ADS)

A reduced-density-matrix approach provides a very general framework for the theoretical description of polarized radiative emission during single-photon transitions from bound and autoionizing states of atomic systems in the presence of a general arrangement of static (or quasistatic) electric and magnetic fields. Polarized radiative emission from partially ionized atomic systems in plasmas can occur as a result of the excitation of the radiating atomic states by electrons with an anisotropic velocity distribution, which can be produced in an electron—ion beam experiment, in a nonequilibrium plasma environment, and in an electromagnetic field that is sufficiently intense in the relevant spectral region. Polarized radiative emission can also be produced or modified during the excitation of the atomic system in the presence of electric and magnetic fields and electromagnetic fields. In electric and magnetic fields, the normally overlapping angular-momentum-projection components of atomic spectral lines can be substantially shifted from their field-free positions and split into spectroscopically resolvable (and inherently polarized) features. Due to the breakdown of the field-free angular-momentum and parity selection rules, otherwise forbidden components of atomic spectral lines can be generated. Spectral patterns and polarizations produced by either a uniform static electric or magnetic field have been extensively investigated, and the individual Stark and Zeeman effects have been treated in both the weak-field (perturbative) and strong-field (nonperturbative) regimes. The more complex Stark—Zeeman patterns have been investigated primarily for simple atomic systems, including hydrogen-like or high-Rydberg atoms, and for special applied-field configurations, including parallel and perpendicular electric and magnetic fields. In the theoretical description of the polarized atomic radiative emission, it is advantageous to consider the coherent excitation of a particular subspace of the initial atomic bound or autoionizing states, which can occur as a result of sufficiently intense electromagnetic interactions. A general expression for the matrix elements of the detected-photon density operator provides a unified framework for the analysis of the spectral intensity, angular distribution, and polarization of the Stark—Zeeman patterns. From a unified development of time-domain (equation-of-motion) and frequencydomain (resolvent-operator) formulations of the more comprehensive reduceddensity-matrix approach, the nonequilibrium atomic-state kinetics and the homogeneous spectral-line shapes can be systematically and self-consistently described.

Jacobs, V. L.

289

Small radiation field dosimetry with 2-methylalanine miniature dosimeters at K-band electron paramagnetic resonance  

Microsoft Academic Search

Minidosimeters of 2-methyalanine (2MA) with millimeter dimensions were produced and tested for small radiation field dosimetry. Their performance was assessed by measuring the relative output factor (ROF), beam profile (BP) and penumbra width values and were determined for square fields of 0.5×0.5, 1×1, 3×3, 5×5 and 10×10cm2. These results were compared with those obtained for Kodak X-Omat V radiographic film.

F. Chen; C. S. Guzmán Calcina; A. de Almeida; C. E. de Almeida; O. Baffa

2007-01-01

290

Predictions of mixed non-Gaussian cosmological density fields for the cosmic microwave background radiation  

Microsoft Academic Search

We present simulations of the Cosmic Microwave Background Radiation (CMBR)\\u000apower spectrum for a class of mixed, non-Gaussian, primordial random fields. We\\u000aassume a skew positive mixed model with adiabatic inflation perturbations plus\\u000aadditional isocurvature perturbations possibly produced by topological defects.\\u000aThe joint probability distribution used in this context is a weighted\\u000acombination of Gaussian and non-Gaussian random fields, such

Ana Paula Andrade; Carlos Alexandre Wuensche; Andre Luiz B. Ribeiro

2003-01-01

291

Predictions of Mixed Non-Gaussian Cosmological Density Fields for the Cosmic Microwave Background Radiation  

Microsoft Academic Search

We present simulations of the cosmic microwave background radiation (CMBR) power spectrum for a class of mixed, non-Gaussian, primordial random fields. We assume a skew-positive mixed model with adiabatic inflation perturbations plus additional isocurvature perturbations possibly produced by topological defects. The joint probability distribution used in this context is a weighted combination of Gaussian and non-Gaussian random fields, such as

A. P. A. Andrade; C. A. Wuensche; A. L. B. Ribeiro

2004-01-01

292

Correction of Magnetic Field Distribution within the Optical Radiation Coverage Zone of Magnetic Laser Therapy Apparatuses  

Microsoft Academic Search

Methods for correction of magnetic field distribution within the optical radiation coverage zone of magnetic laser therapy\\u000a apparatuses were developed. These methods in medical apparatuses provide a 3.5–4.0-fold decrease in the magnetic induction\\u000a in the therapeutic zone of ring magnets. Magnetic field strength was optimized using magnetic tips made of soft magnetic materials.\\u000a Engineering solution of magnetotherapeutic apparatuses provides optimal

V. Yu. Plavskii

2011-01-01

293

Measurement of temperature field in the region near to the radiator by using digital holography  

NASA Astrophysics Data System (ADS)

A simple method for measurement of temperature field in the region near to the metal plate of the radiator is demonstrated by using digital holography in the Lensless Fourier transform configuration (LFT). The temperature is measured within the boundary layer of the convective flow field. The deviation of the temperature produced by this method, from that obtained by the thermocouple is rather small. It has shown that the method is reasonable and efficient.

Li, Yan; Wang, Dayong; Wang, Guangjun; Zhang, Yizhuo; Liu, Changgeng

2009-07-01

294

Axionic dark radiation and the Milky Way's magnetic field  

NASA Astrophysics Data System (ADS)

Recently it has been suggested that dark radiation in the form of axions produced during the decay of string theory moduli fields could be responsible for the soft x-ray excess in galaxy clusters. These soft x-ray photons come about due to the conversion of these axions into photons in the magnetic fields of the clusters. In this work we calculate the conversion of axionic dark radiation into x-ray photons in the magnetic field of our own Galaxy. We consider ?N?˜0.5 worth of dark radiation made up of axions with energy of order 0.1-1 keV. We show that it is possible, if a little optimistic, to explain the large regions of x-ray emission located above and below the center of the Galactic plane detected in the 3/4 keV ROSAT all-sky map completely due to the conversion of dark radiation into photons with an inverse axion-photon coupling of M ˜3×1013 GeV and an axion mass of m ?10-12 eV. Different parameter values could explain both these features and the 3/4 keV x-ray background. More conservatively, these x-ray observations are a good way to constrain such models of axionic dark radiation.

Fairbairn, Malcolm

2014-03-01

295

Development of a cryogenic radiation detector for mapping radio frequency superconducting cavity field emissions  

SciTech Connect

Field emissions in a super conducting helium cooled RF cavity and the production of radiation (mostly X-Rays) have been measured externally on cryomodules at Jefferson Lab since 1991. External measurements are limited to radiation energies above 100 keV due to shielding of the stainless steel cryogenic body. To measure the onset of and to map field emissions from a superconducting cavity requires the detecting instrument be inside the shield and within the liquid Helium. Two possible measurement systems are undergoing testing at JLab. A CsI detector array set on photodiodes and an X-Ray film camera with a fixed aperture. Several devices were tested in the cell with liquid Helium without success. The lone survivor, a CsI array, worked but saturated at high power levels due to backscatter. The array was encased in a lead shield with a slit opening set to measure the radiation emitted directly from the cell eliminating a large portion of the backscatter. This is a work in progress and te sting should be complete before the PAC 05. The second system being tested is passive. It is a shielded box with an aperture to expose radiation diagnostic film located inside to direct radiation from the cell. Developing a technique for mapping field emissions in cryogenic cells will assist scientists and engineers in pinpointing any surface imperfections for examination.

Danny Dotson; John Mammosser

2005-05-01

296

Mission design challenges posed by the Voyager 2 Neptune encounter  

NASA Technical Reports Server (NTRS)

A major challenge for the Voyager 2 Neptune encounter lies in the detailed design of a trajectory that achieves science objectives at the planet as well as at its large satellite, Triton. This achievement demands a close flyby of the primary, whereas the planet's great distance makes such an undertaking especially challenging. Changing estimates and uncertainties of parameters characterizing the Neptune environment, particularly ring, atmosphere and radiation models, affect the mission design. These effects are investigated and trade-offs among candidate trajectories are examined with respect to spacecraft performance, avoidance of risk and science objective achievement.

Cesarone, R. J.; Potts, C. L.; Francis, K.; Kosmann, W. J.; Matousek, S. E.

1988-01-01

297

Theoretical model for sound radiation from annular jet pipes: far- and near-field solutions  

NASA Astrophysics Data System (ADS)

An analytical model is presented for sound radiation from a semi-infinite unflanged annular duct. The duct carries a jet which issues into a uniform mean flow while an inner cylindrical centre body extends downstream from the duct exit. This geometrical arrangement forms an idealized representation of a turbofan exhaust where noise propagates along the annular bypass duct, refracts through the external bypass stream and radiates to the far field. The instability wave of the vortex sheet and its interaction with the acoustic field are accounted for in an exact way in the current solution. Efficient numerical procedures are presented for evaluating near-field and far-field solutions, and these are used as the basis for a parametric study to illustrate the effect of varying the hub tip ratio, and the ratio of jet velocity to external flow velocity. Since the ‘Kutta’ condition can be turned on and off in the current solution, this capability is used to assess the effect of vortex shedding on noise radiation. Far-field directivity patterns are presented for single modes and also for a multi-mode ‘broadband’ source model in which all cut-on modes are assumed to be present with equal modal power. Good agreement is found between analytical solutions and experimental data. Near-field pressure maps of the acoustic and instability portions of the solution are generated for selected tones.

Gabard, G.; Astley, R. J.

298

Star Formation in the Galaxy and the Fluctuating UV Radiation Field  

NASA Technical Reports Server (NTRS)

We examine the formation of massive stars in the Galaxy, the resultant fluctuating UV radiation field, and the effect of this Field on the star-forming interstellar medium. Following previous researchers such as Habing (1968), we calculate the average interstellar radiation field at the Solar Circle of the Galaxy. However, our new calculations follow more closely the time dependence of the field at any point. We show that there is a significant difference between the mean field and the median field, and that there are substantial fluctuations of the field (on timescales of order 100 million years) at a given point. Far Ultraviolet Radiation (FUV, photon energies of 6 eV - 13.6 eV) has been recognized as the main source of heating of the neutral interstellar gas. Given the pressure of the interstellar medium (ISM) the FUV field determines whether the thermal balance of the neutral gas results in cold (T approximately 50 - 100 K) clouds (CNM), warm (T about 10,000 K) (WNM), for a combination of the two (the two phase ISM) We present results for the time history of the FUV field for points in the local ISM of the Milky Way Galaxy. The presence of this fluctuating heating rate converts CNM to WNM and vice versa. We show how to calculate the average fractions of the gas in the CNM and WNM when the interstellar gas is subject to this fluctuating FUV field. The knowledge of how these fractions depend on the gas properties (i.e. mean density and composition) and on the FUV-sources (i.e. the star formation rate, or the IMF, or the size distribution of associations) is a basic step in building any detailed model of the large scale behavior of the ISM and the mutual relation between the ISM and the SFR.

Hollenbach, David; Parravano, A.; McKee, C.; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

299

Hydrogen in intense laser fields: Radiative close-coupling equations and quantum-defect parametrization  

SciTech Connect

A system of radiative close-coupling equations for a hydrogen atom in a circularly polarized intense laser field is derived. The radiative scattering matrix is parametrized within a multichannel quantum-defect formalism. The quasienergy spectrum corresponding to nonperturbative shifts and ionization widths of the bound atomic states is computed from the poles of the radiative scattering matrix. For an intensity range up to {alpha}{sub 0}{approx}1.5{ital a}{sub 0} (with {alpha}{sub 0} the oscillation amplitude of the free electron in the laser and {ital a}{sub 0} the Bohr radius), numerical results are presented in the frequency regime where two-photon ionization and above-threshold ionization of the ground state is possible. For one-photon transitions a stabilization of the atomic states for strong fields is predicted.

Marte, P.; Zoller, P. (Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria (AT))

1991-02-01

300

Design of organic scintillators for non-standard radiation field dosimetry: Experimental setup.  

PubMed

This paper describes an experimental setup designed for sensing the luminescent light coming from an organic plastic scintillator stimulated with ionizing radiation. This device is intended to be a part of a complete dosimeter system for characterization of small radiation fields which is the project of the doctoral thesis of the medical physicist at the Radiation Oncology facility of Hospital San Vicente Fundación in conjunction with the Universidad de Antioquia of Medellín Colombia. Some preliminary results predict a good performance of the unit, but further studies must be conducted in order to have a completed evaluation of the system. This is the first step in the development of an accuracy tool for measurement of non-standard fields in the Radiotherapy or Radiosurgery processes. PMID:24110369

Norman H, Machado R; Maximiliano, Trujillo T; Javier E, Garcia G; Diana C, Narvaez G; Paula A, Marin M; Robinson A, Torres V

2013-01-01

301

On the electromagnetic fields, Poynting vector, and peak power radiated by lightning return strokes  

NASA Technical Reports Server (NTRS)

The initial radiation fields, Poynting vector, and total electromagnetic power that a vertical return stroke radiates into the upper half space have been computed when the speed of the stroke, nu, is a significant fraction of the speed of light, c, assuming that at large distances and early times the source is an infinitesimal dipole. The initial current is also assumed to satisfy the transmission-line model with a constant nu and to be perpendicular to an infinite, perfectly conducting ground. The effect of a large nu is to increase the radiation fields by a factor of (1-beta-sq cos-sq theta) exp -1, where beta = nu/c and theta is measured from the vertical, and the Poynting vector by a factor of (1-beta-sq cos-sq theta) exp -2.

Krider, E. P.

1992-01-01

302

The photoevaporation of a neutral structure by an EUV+FUV radiation field  

NASA Astrophysics Data System (ADS)

The EUV photoionizing radiation and FUV dissociating radiation from newly born stars photoevaporate their parental neutral cloud, leading to the formation of dense clumps that could eventually form additional stars. We study the effects of including a photodissociating FUV flux in models of the fragmentation of a photoevaporating, self-gravitating molecular cloud. We compute 3D simulations of the interaction of an inhomogeneous, neutral, self-gravitating cloud with external EUV and FUV radiation fields, and calculate the number of collapsing clumps and their mass. We find that the presence of an outer photodissociation region has an important effect on the formation of dense structures due to the expansion of an H II region. In particular, including a FUV field leads to the earlier formation of a larger number of dense clumps, which might lead to the formation of more stars.

Lora, V.; Vasconcelos, M. J.; Raga, A. C.; Esquivel, A.; Cerqueira, A. H.

2013-10-01

303

Consideration of the radiation dose delivered away from the treatment field to patients in radiotherapy  

PubMed Central

Radiation delivery to cancer patients for radiotherapy is invariably accompanied by unwanted radiation to other parts of the patient’s body. Traditionally, considerable effort has been made to calculate and measure the radiation dose to the target as well as to nearby critical structures. Only recently has attention been focused also on the relatively low doses that exist far from the primary radiation beams. In several clinical scenarios, such doses have been associated with cardiac toxicity as well as an increased risk of secondary cancer induction. Out-of-field dose is a result of leakage and scatter and generally difficult to predict accurately. The present review aims to present existing data, from measurements and calculations, and discuss its implications for radiotherapy.

Taylor, Michael L.; Kron, Tomas

2011-01-01

304

On consideration of radiated power in RF field simulations for MRI.  

PubMed

In numerical analyses of radiofrequency (RF) fields for MRI, RF power is often permitted to radiate out of the problem region. In reality, RF power will be confined by the magnet bore and RF screen enclosing the magnet room. We present numerical calculations at different frequencies for various surface and volume coils, with samples from simple spheres to the human body in environments from free space to a shielded RF room. Results for calculations within a limited problem region show radiated power increases with frequency. When the magnet room RF screen is included, nearly all the power is dissipated in the human subject. For limited problem regions, inclusion of a term for radiation loss results in an underestimation of transmit efficiency compared to results including the complete bore and RF screen. If the term for radiated power is not included, calculated coil efficiencies are slightly overestimated compared to the complete case. PMID:22473620

Liu, Wanzhan; Kao, Chien-ping; Collins, Christopher M; Smith, Michael B; Yang, Qing X

2013-01-01

305

Study of shockwave method for diagnosing the radiation fields of laser-driven gold hohlraums  

NASA Astrophysics Data System (ADS)

Besides the routinely used broad-band x-ray spectrometer (Dante or SXS), ablative shock-wave method is often used to diagnose the radiation fields of laser-driven Hohlraums. The x-ray ablation process of Aluminum and Titanium is studied numerically with a 1-D radiation hydrodynamic code RDMG [F. Tinggui et al., Chin. J. Comput. Phys. 16, 199 (1999)], based on which a new scaling relation of the equivalent radiation temperature with the ablative shock velocity in Aluminum plates is proposed, and a novel method is developed for determining simultaneously the radiation temperature and the M-band (2-4 keV) fraction in laser-driven gold Hohlraums.

Li, Yongsheng; Lan, Ke; Huo, Wenyi; Lai, Dongxian; Gao, Yaoming; Pei, Wenbing

2013-11-01

306

VEGA Pathfinder navigation for Giotto Halley encounter  

NASA Technical Reports Server (NTRS)

Results of the VEGA Pathfinder concept which was used to successfully target the European Space Agnecy's Giotto spacecraft to a 600 km encounter with the comet Halley are presented. Pathfinder was an international cooperative navigation activity involving USSR, European and U.S. space agencies. The final Giotto targeting maneuver was based on a comet location determined from optical data acquired by the earlier arriving Soviet VEGA spacecraft. Inertial pointing angles extracted from optical images of the comet nucleus were combined with a precise estimate of the VEGA encounter orbits determined using VLBI data acquired by NASA's Deep Space Network to predict the location of Halley at Giotto encounter. This article describes the VLBI techniques used to determine the VEGA orbits and shows that the insensitivity of the VLBI data strategy to unmodeled dynamic error sources resulted in estimates of the VEGA orbits with an accuracy of 50 km.

Ellis, J.; Mcelrath, T. P.

1986-01-01

307

On the motion of a charged particle in a uniform electric field with radiation reaction  

Microsoft Academic Search

It is shown that the motion of a charged particle in a uniform electric field, obeying Dirac-Lorentz relativistic equation of motion with radiation reaction, is confined in a plane. Further, the component of velocity normal to the lines of force continuously decreases to zero. Thus, the motion asymptotically tends to a rectilinear motion along the line of force. The motion

N. D. Sen Gupta

1971-01-01

308

An analysis of the radiation field beneath a bank of tubular quartz lamps  

NASA Technical Reports Server (NTRS)

Equations governing the incident heat flux distribution beneath a lamp-reflector system were developed. Analysis of a particular radiant heating facility showed good agreement between theory and experiment when a lamp power loss correction was used. In addition, the theory was employed to estimate thermal disruption in the radiation field caused by a protruding probe.

Ash, Robert L.

1972-01-01

309

EFFECTS OF UV-B RADIATION ON SOYBEAN YIELD AND SEED QUALITY: A 6-YEAR FIELD  

EPA Science Inventory

Two soybean, [Glycine max (L.) Merr.] cultivars, Essex and Williams, were grown in the field for 6 consecutive seasons under ambient and supplemental levels of ultraviolet B radiation to determine the potential for alterations in yield or seed quality with a reduction in the stra...

310

Waves in plasmas generated by a rotating magnetic field and implications to radiation belts  

Microsoft Academic Search

The interaction of rotating magnetic fields (RMF) with magnetized plasmas is a fundamental plasma physics problem with implications to a wide range of areas, including laboratory and space plasma physics. Despite the importance of the topic the basic physics of the phenomenon remains unexplored. An important application of a RMF is its potential use as an efficient radiation source of

Alexey V. Karavaev

2010-01-01

311

Genetic Algorithms for Predicting Antenna Radiation Patterns from Near-Field Measurements in a Screened Room  

Microsoft Academic Search

A method for echo cancelling in a screened room is presented in this work. The method obtains an Antenna Under Test (AUT) radiation pattern in terms of a set of infinitesimal electric and\\/or magnetic dipoles, placed on the surface of a volume containing the AUT. For this purpose, some measured near-field samples taken around the antenna and a genetic algorithm

J. R. Perez; J. Basterrechea

2001-01-01

312

Inverse method predicting spinning modes radiated by a ducted fan from free-field measurements  

Microsoft Academic Search

In the study the inverse problem of deducing the modal structure of the acoustic field generated by a ducted turbofan is addressed using conventional farfield directivity measurements. The final objective is to make input data available for predicting noise radiation in other configurations that would not have been tested. The present paper is devoted to the analytical part of that

Serge Lewy

2005-01-01

313

Cerenkov Radiation from Charged Particles in a Plasma in a Magnetic Field  

Microsoft Academic Search

The Cerenkov radiation from electrons in a plasma in a magnetic field has been calculated by Kolomenskii, who determined the allowed frequency regions and the energy loss. It is shown here that his results are in error. The allowed frequency regions have a much more complicated dependence on the plasma frequency, gyrofrequency, and electron velocity than he indicates, and he

W. Sollfrey; H. T. Yura

1965-01-01

314

The Acoustic Field of the Near Radiation Zone Formed upon EMAC in Metals  

Microsoft Academic Search

This paper analyzes the behavior of bulk types of waves generated by a circular bus with current by the magnetostriction mechanism in a normal polarizing field in a magnetic high-conductivity halfspace in relative proximity to a media boundary. Calculated dependences of the module of the amplitude and the angle characterizing the direction of radiation of bulk waves in the near

V. A. Komarov

2004-01-01

315

Radiation field in the troposphere and stratosphere-II. Numerical analysis  

Microsoft Academic Search

The results of calculations of the multiply-scattered solar-induced radiation field in the troposphere and stratosphere are presented for direct application to photochemical models. The enhancement factors due to multiple scattering are given for the heights, solar zenith angles and wavelengths (between 800 and 300 nm) which play a role in the photodissociation of various atmospheric constituents.

M. Nicolet; R. R. Meier; D. E. Anderson

1982-01-01

316

Measurement of Near-Field Thermal Radiation through a Nanometer-Sized Gap  

NASA Astrophysics Data System (ADS)

Radiation heat transfer in nanostructures can differ significantly from that in macrostructures due to wave effects. Theory has predicted that thermal radiation heat transfer between two surfaces separated by tens of nanometers can exceed that of Planck's blackbody radiation law by several orders of magnitude. Our AFM-inspired heat flux sensor, comprising of a sphere attached to the tip of a bimetallic cantilever, can measure the radiation exchange across nanometer-scale gaps between a sphere and a flat surface. The objective of this work is to experimentally study thermal radiative transfer at very small separation gaps. In previous experiment, our group has successfully measured near-field radiative heat transfer through gap as small as 30 nm. In this work, we extend this technique to decrease the gap down to a few nanometers and show that existing fluctuating electrodynamics theory cannot predict experimental results in the extreme limit of small separation between two surfaces. Our experiments raise interesting question on the convergence of radiation heat transfer mechanism and interfacial heat conduction mechanism. Theoretical approaches bridging these two regimes will be discussed.

Mavrokefalos, Anastassios; Sambegoro, Poetro; Chen, Gang

2012-02-01

317

The Voyager 2 encounter with Uranus  

NASA Technical Reports Server (NTRS)

The instruments and science investigations of the Voyager 2 payload are listed in tables and illustrated with a drawing, and a general overview of the encounter with Uranus in January 1986 is given. The spacecraft approached to within 107,100 km of the center of Uranus, and to within 29,000 km of the Uranian satellite Miranda before continuing on for an encounter with Neptune in 1989; the trajectory also permitted radio occultation studies of the Uranian rings and radio and UV occultation studies of the planet's atmosphere. Diagrams of the trajectory are provided.

Stone, E. C.

1987-01-01

318

Evaluation of Breast Sentinel Lymph Node Coverage by Standard Radiation Therapy Fields  

SciTech Connect

Background: Biopsy of the breast sentinel lymph node (SLN) is now a standard staging procedure for early-stage invasive breast cancer. The anatomic location of the breast SLN and its relationship to standard radiation fields has not been described. Methods and Materials: A retrospective review of radiotherapy treatment planning data sets was performed in patients with breast cancer who had undergone SLN biopsy, and those with a surgical clip at the SLN biopsy site were identified. The location of the clip was evaluated relative to vertebral body level on an anterior-posterior digitally reconstructed radiograph, treated whole-breast tangential radiation fields, and standard axillary fields in 106 data sets meeting these criteria. Results: The breast SLN varied in vertebral body level position, ranging from T2 to T7 but most commonly opposite T4. The SLN clip was located below the base of the clavicle in 90%, and hence would be excluded from standard axillary radiotherapy fields where the inferior border is placed at this level. The clip was within the irradiated whole-breast tangent fields in 78%, beneath the superior-posterior corner multileaf collimators in 12%, and outside the tangent field borders in 10%. Conclusions: Standard axillary fields do not encompass the lymph nodes at highest risk of containing tumor in breast cancer patients. Elimination of the superior-posterior corner MLCs from the tangent field design would result in inclusion of the breast SLN in 90% of patients treated with standard whole-breast irradiation.

Rabinovitch, Rachel [Department of Radiation Oncology, University of Colorado Cancer Center, Aurora, CO (United States)], E-mail: Rachel.rabinovitch@uchsc.edu; Ballonoff, Ari; Newman, Francis M.S. [Department of Radiation Oncology, University of Colorado Cancer Center, Aurora, CO (United States); Finlayson, Christina [Department of GI, Tumor, and Endocrine Surgery, University of Colorado Cancer Center, Aurora, CO (United States)

2008-04-01

319

Radiation effects on junction field-effect transistors (JFETS), MOSFETs, and bipolar transistors, as related to SSC circuit design.  

National Technical Information Service (NTIS)

Some results of radiation effects on selected junction field-effect transistors, MOS field-effect transistors, and bipolar junction transistors are presented. The evaluations include dc parameters, as well as capacitive variations and noise evaluations. T...

E. J. Kennedy G. T. Alley C. L. Britton P. L. Skubic B. Gray

1990-01-01

320

Electric field detection of coherent synchrotron radiation in a storage ring generated using laser bunch slicing  

NASA Astrophysics Data System (ADS)

The electric field of coherent synchrotron radiation (CSR) generated by laser bunch slicing in a storage ring has been detected by an electro-optic sampling method. The gate pulses for sampling are sent through a large-mode-area photonic-crystal fiber. The observed electric field profile of the CSR is in good agreement with the spectrum of the CSR observed using Fourier transform far-infrared spectrometry, indicating good phase stability in the CSR. The longitudinal density profiles of electrons modulated by laser pulses were evaluated from the electric field profile.

Katayama, I.; Shimosato, H.; Bito, M.; Furusawa, K.; Adachi, M.; Shimada, M.; Zen, H.; Kimura, S.; Yamamoto, N.; Hosaka, M.; Katoh, M.; Ashida, M.

2012-03-01

321

Comparison of curricula in radiation technology in the field of radiotherapy in selected European Union countries  

PubMed Central

Background Radiation technology is a discipline of medical science which deals with diagnostics, imaging and radiotherapy, that is treatment by ionizing radiation. Aim To present and compare the existing curricula of radiation technology in selected EU countries. Materials and methods The research work done for the purpose of the comparative analysis was based on the methods of diagnostic test and document analysis. Results The comparison of curricula in selected countries, namely Austria, France, the Netherlands and Poland, showed that admission criteria to radiation technology courses are varied and depend on regulations of respective Ministries of Health. The most restrictive conditions, including written tests in biology, chemistry and physics, and psychometric test, are those in France. Contents of basic and specialist subject groups are very similar in all the countries. The difference is in the number of ECT points assigned to particular subjects and the number of course hours offered. The longest practical training is provided in the Netherlands and the shortest one in Poland. The duration of studies in the Netherlands is 4 years, while in Poland it is 3 years. Austria is the only country to offer extra practical training in quality management. Conclusion Graduates in the compared EU countries have similar level of qualifications in the fields of operation of radiological equipment, radiotherapy, nuclear medicine, foreign language and specialist terminology in the field of medical and physical sciences, general knowledge of medical and physical sciences, and detailed knowledge of radiation technology.

Janaszczyk, Agnieszka; Bogusz-Czerniewicz, Marta

2011-01-01

322

Encounter: A Picture Book for Any Classroom.  

ERIC Educational Resources Information Center

Describes the content of the picture book, "Encounter," written by Jane Yolen and illustrated by David Shannon. States that it focuses on the arrival of Christopher Columbus to San Salvador (El Salvador) from a boy's perspective. Includes questions for use when discussing the messages and content of the book. (CMK)

Hazler, Kitty Y.

2002-01-01

323

Encountering Pedagogy through Relational Art Practices  

ERIC Educational Resources Information Center

Two artists involved in "socially engaged art" practice were invited to work with art education teacher candidates and instructors in an effort to rethink notions of teaching, learning and art. We initiated this residency, which we called "The Summerhill Residency", to examine how learning encounters might create environments for meaningful…

Irwin, Rita L.; O'Donoghue, Donal

2012-01-01

324

The Voyager 2 encounter with Uranus  

Microsoft Academic Search

The instruments and science investigations of the Voyager 2 payload are listed in tables and illustrated with a drawing, and a general overview of the encounter with Uranus in January 1986 is given. The spacecraft approached to within 107,100 km of the center of Uranus, and to within 29,000 km of the Uranian satellite Miranda before continuing on for an

E. C. Stone

1987-01-01

325

Consumerism, reflexivity and the medical encounter  

Microsoft Academic Search

Much emphasis has been placed recently in sociological, policy and popular discourses on changes in lay people's attitudes towards the medical profession that have been labelled by some as a move towards the embracing of “consumerism”. Notions of consumerism tend to assume that lay people act as “rational” actors in the context of the medical encounter. They align with broader

Deborah Lupton

1997-01-01

326

Socially Driven Instruction: Developing Learning Encounters Online  

ERIC Educational Resources Information Center

Face-to-face library instruction sessions for academic courses usually have a captive audience because of required attendance, while online sessions for distance learners are often optional. Is it possible to provide such a great online learning encounter that students (both on campus and distance) will choose to attend even an optional session?…

Mathews, Brian S.

2009-01-01

327

The Expression of Differences in Intercultural Encounters.  

ERIC Educational Resources Information Center

Participants in an intercultural encounter bring with them differences in values, beliefs, attitudes, and world views. The communication of these differences often results in threatening and defensive behavior. The facilitating attitudes of open-mindedness and nonevaluation promote understanding and a respect for differing experience and…

Broome, Benjamin J.

328

Mixed encounters, limited perception and optimal foraging.  

PubMed

This article demonstrates how perceptual constraints of predators and the possibility that predators encounter prey both sequentially (one prey type at a time) and simultaneously (two or more prey types at a time) may influence the predator attack decisions, diet composition and functional response of a behavioural predator-prey system. Individuals of a predator species are assumed to forage optimally on two prey types and to have exact knowledge of prey population numbers (or densities) only in a neighbourhood of their actual spatial location. The system characteristics are inspected by means of a discrete-time, discrete-space, individual-based model of the one-predator-two-prey interaction. Model predictions are compared with ones that have been obtained by assuming only sequential encounters of predators with prey and/or omniscient predators aware of prey population densities in the whole environment. It is shown that the zero-one prey choice rule, optimal for sequential encounters and omniscient predators, shifts to abruptly changing partial preferences for both prey types in the case of omniscient predators faced with both types of prey encounters. The latter, in turn, become gradually changing partial preferences when predator omniscience is considered only local. PMID:11016087

Berec, L

2000-09-01

329

Voyager Program: Voyager 2 Encounter at Saturn.  

National Technical Information Service (NTIS)

The planned sequence of events for the encounter are presented. The current status of the Voyager flight and ground systems, and the mission success criteria are summarized. Key Voyager team members are identified. Changes to the plan described may be exp...

1981-01-01

330

Spherical galaxy collisions - Head-on encounters  

Microsoft Academic Search

A series of N-body simulations was performed in order to investigate head-on encounters between equal mass spherical galaxies of similar structure. Two different types of galaxy models were used in the experiments, differing mainly in the velocity distribution and central concentration: in the first kind of model, most of the particles moved predominantly along eccentric orbits, while in the second

Julio F. Navarro; Mirta B. Mosconi

1989-01-01

331

Spherical galaxy collisions - head-on encounters  

Microsoft Academic Search

A series of N-body simulations was performed in order to investigate head-on encounters between equal mass spherical galaxies of similar structure. Two different types of galaxy models were used in the experiments, differing mainly in the velocity distribution and central concentration: in the first kind of model, most of the particles moved predominantly along eccentric orbits, while in the second

Julio F. Navarro; Mirta B. Mosconi

1989-01-01

332

An experimental investigation into the radiation field offset of a dynamic multileaf collimator  

NASA Astrophysics Data System (ADS)

In this study we investigate the characteristics of a rounded leaf end multileaf collimator (MLC) that is used for delivering intensity-modulated radiotherapy (IMRT) with a Varian linear accelerator. The rounded leaf end MLC design results in an offset between the radiation field edge (the physical leaf position) and the light field (the geometric leaf position). We call this the radiation field offset (RFO). The leaf position is calibrated to the leaf tip at the mid-leaf plane. There is an additional offset between the geometric leaf position and the projected leaf tip position that varies as a function of distance from the collimator central axis due to the MLC geometry. We call this the leaf position offset (LPO). There is a lack of consistency in the interpretation and implementation of the RFO and the LPO in the literature. We investigated the RFO and the LPO on Varian's 600 C/D and 21 EX linear accelerators. We used a combination of film and ion chamber measurements of static, segmental MLC (SMLC) and dynamic MLC (DMLC) fields to quantify the leaf offsets across the range of leaf positions. We were able to improve the dosimetry at large off-axis positions with minor adjustments to the vendor's LPO file. The RFO was determined to within 0.1 mm accuracy at the collimator central axis. The measured RFO value depends on whether the method is based on the radiation field edge position or on an integral dose measurement. The integral dose method results in an RFO that is approximately 0.2 mm greater than the radiation field edge method. The difference is due to the MLC penumbra shape. We propose a methodology for measuring and implementing MLC leaf offsets that is suitable for both SMLC and DMLC IMRT. In addition, we propose some definitions that more clearly describe the MLC leaf position for accurate IMRT dosimetry.

Vial, Philip; Oliver, Lyn; Greer, Peter B.; Baldock, Clive

2006-11-01

333

Analysis of vertical radiation loss and far-field pattern for microcylinder lasers with an output waveguide.  

PubMed

Vertical radiation loss and far-field pattern are investigated for microcylinder lasers by 3D FDTD simulation and experimentally. The numerical results show that an output waveguide connected to the microcylinder resonator can result in additional vertical radiation loss for high Q coupled modes and affect the far field pattern. The vertical radiation loss can be controlled by adjusting the up cladding layer thickness. Furthermore, two lobes of vertical far-field patterns are observed for a 15-?m-radius microcylinder laser connected with an output waveguide, which confirms the vertical radiation loss. PMID:23842394

Lv, Xiao-Meng; Huang, Yong-Zhen; Yang, Yue-De; Long, Heng; Zou, Ling-Xiu; Yao, Qi-Feng; Jin, Xin; Xiao, Jin-Long; Du, Yun

2013-07-01

334

A new multistack radiation boundary condition for FDTD based on self-teleportation of fields  

SciTech Connect

In [Electromagnetics 23 (2003) 187], a technique for injecting perfect plane waves into finite regions of space in FDTD was reported. The essence of the technique, called Field Teleportation, is to invoke the principle of equivalent sources using FDTDs discrete definition of the curl to copy any field propagating in one FDTD domain to a finite region of another domain. In this paper, we apply this technique of Field Teleportation to the original domain itself to create a transparent boundary across which any outward traveling FDTD field produces an exact negative copy of itself. When this copied field is teleported one cell ahead and one cell forward in time it causes significant self-cancelation of the original field. Illustrative experiments in two-dimensions show that a two-layer (10-cell thick) multi-stack Radiation Boundary Condition (RBC) with a simplest Huygens's termination readily yields reflection coefficients of the order of -80 dB up to grazing incidence for all the fields radiated by a harmonic point source ({lambda} = 30 cells) in free space located 20 cells away from the boundary. Similarly low levels of artificial reflection are demonstrated for a case in which the RBC cuts through five different magnetodielectric materials.

Diaz, Rodolfo E. [Material-Wave Interaction Laboratory, Electrical Engineering Department, Arizona State University, Tempe Center, 951 S. Mill Ave., Suite no. 199, Tempe, AZ 85287-9509 (United States); Scherbatko, Igor [Material-Wave Interaction Laboratory, Electrical Engineering Department, Arizona State University, Tempe Center, 951 S. Mill Ave., Suite no. 199, Tempe, AZ 85287-9509 (United States)]. E-mail: igor_s@asu.edu

2005-02-10

335

EVOLUTION OF X-RAY AND FAR-ULTRAVIOLET DISK-DISPERSING RADIATION FIELDS  

SciTech Connect

We present new X-ray and far-ultraviolet (FUV) observations of T Tauri stars covering the age range 1-10 Myr. Our goals are to observationally constrain the intensity of radiation fields responsible for evaporating gas from the circumstellar disk and to assess the feasibility of current photoevaporation models, focusing on X-ray and UV radiation. We greatly increase the number of 7-10 Myr old T Tauri stars observed in X-rays by including observations of the well-populated 25 Ori aggregate in the Orion OB1a subassociation. With these new 7-10 Myr objects, we confirm that X-ray emission remains constant from 1 to 10 Myr. We also show, for the first time, observational evidence for the evolution of FUV radiation fields with a sample of 56 accreting and non-accreting young stars spanning 1 Myr to 1 Gyr. We find that the FUV emission decreases on timescales consistent with the decline of accretion in classical T Tauri stars until reaching the chromospheric level in weak T Tauri stars and debris disks. Overall, we find that the observed strength of high-energy radiation is consistent with that required by photoevaporation models to dissipate the disks in timescales of approximately 10 Myr. Finally, we find that the high-energy fields that affect gas evolution are not similarly affecting dust evolution; in particular, we find that disks with inner clearings, transitional disks, have similar levels of FUV emission as full disks.

Ingleby, Laura; Calvet, Nuria; Miller, Jon; Bergin, Edwin; Hartmann, Lee [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Hernandez, Jesus; Briceno, Cesar [Centro de Investigaciones de Astronomia (CIDA), Merida, 5101-A (Venezuela, Bolivarian Republic of); Espaillat, Catherine, E-mail: lingleby@umich.edu, E-mail: ncalvet@umich.edu, E-mail: jonmm@umich.edu, E-mail: ebergin@umich.edu, E-mail: lhartm@umich.edu, E-mail: jesush@cida.ve, E-mail: briceno@cida.ve, E-mail: cespaillat@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States)

2011-04-15

336

Behaviour of BeCu dynode photomultiplier tubes in high radiation fields and their use in fast neutron detection  

Microsoft Academic Search

In the course of conducting tests on photomultiplier tubes (PMT) for use in the ZEUS detector, it was observed that the dark noise current of the PMT's increased significantly when they were operated in high radiation fields. The behaviour of the RCA 8575 was studied in mixed radiation fields consisting of protons, neutrons, and gamma rays which were produced by

J. K. Mayer; J. J. G. Durocher; G. R. Smith

1988-01-01

337

Distribution of /sup 32/P in laboratory colonies of Solenopsis invicta (Hymenoptera: Formicidae) after feeding on labeled Heliothis zeal (Lepidoptera: Noctuidae) eggs: an explanation of discrepancies encountered in field predation experiments  

SciTech Connect

Factors responsible for low recovery rates of radioactive Solenopsis invicta Buren following placement of /sup 32/P-labeled Heliothis zea (Boddie) eggs on cotton in field predation tests were investigated using laboratory colonies of the ants. S. invicta workers became radioactive while handling labeled eggs by rupturing the egg chorion or by picking up labeled substances present on the surface of eggs. Foragers that removed the eggs from the plants picked up significantly more of the label than did workers that were sampled from the colonies between 12 and 72 h after egg introduction. Percentage of workers that became labeled over time was much lower with the solid live food than in other studies that used powdered food sources. Problems in finding labeled ants in the field may have been associated with low mean levels of /sup 32/P per ant, together with difficulty in locating and isolating labeled ants from the population. Results indicate that egg predation rates estimated from counts per minute per predator have high variability, and suggest fairly large errors in estimates of eggs consumed per ant. Use of recovery rates of labeled predators to improve estimation of predation rates is discussed.

Nuessly, G.S.; Sterling, W.L.

1986-12-01

338

Strong field-induced frequency conversion of laser radiation in plasma plumes: recent achievements.  

PubMed

New findings in plasma harmonics studies using strong laser fields are reviewed. We discuss recent achievements in the growth of the efficiency of coherent extreme ultraviolet (XUV) radiation sources based on frequency conversion of the ultrashort pulses in the laser-produced plasmas, which allowed for the spectral and structural studies of matter through the high-order harmonic generation (HHG) spectroscopy. These studies showed that plasma HHG can open new opportunities in many unexpected areas of laser-matter interaction. Besides being considered as an alternative method for generation of coherent XUV radiation, it can be used as a powerful tool for various spectroscopic and analytical applications. PMID:23864818

Ganeev, R A

2013-01-01

339

Development of a proposed international standard for certification of aircraft to High Intensity Radiated Fields (HIRF)  

NASA Technical Reports Server (NTRS)

Avionic systems performing critical functions in modern aircraft are potentially susceptible to the hazards of electromagnetic radiation from ground and airborne transmitters. The Federal Aviation Administration (FAA) requested that the Society of Automotive Engineers (SAE) coordinate the development of procedures and guidance material which can be used during the aircraft certification process to ensure adequate protection against high intensity radiated fields (HIRF). This paper addresses both the technical challenge of drafting a certification procedure and guidance standard as well as the management process used by the SAE subcommittee AE4R to converge a diverse range of opinions by its international membership in the shortest possible time.

Sargent, Noel B.

1993-01-01

340

Plasma wave detection of terahertz radiation by silicon field effects transistors: Responsivity and noise equivalent power  

NASA Astrophysics Data System (ADS)

Si metal oxide semiconductor field effect transistors (MOSFETs) with the gate lengths of 120-300 nm have been studied as room temperature plasma wave detectors of 0.7 THz electromagnetic radiation. In agreement with the plasma wave detection theory, the response was found to depend on the gate length and the gate bias. The obtained values of responsivity (<=200 V/W) and noise equivalent power (>=10-10 W/Hz0.5) demonstrate the potential of Si MOSFETs as sensitive detectors of terahertz radiation.

Tauk, R.; Teppe, F.; Boubanga, S.; Coquillat, D.; Knap, W.; Meziani, Y. M.; Gallon, C.; Boeuf, F.; Skotnicki, T.; Fenouillet-Beranger, C.; Maude, D. K.; Rumyantsev, S.; Shur, M. S.

2006-12-01

341

Correlated measurements of UHF radar signatures, RF radiation, and electric field changes from lightning  

NASA Technical Reports Server (NTRS)

During Storm Hazards - 82, simultaneous measurements were made of radar echoes, fast and slow field changes and RF radiation from lightning near the Wallops Flight Facility. RF radiation and radar echoes were also obtained during periods when the NASA F106 research aircraft was struck by lightning. These data are presently being used to better understand the electrical processes which occur during strikes to the aircraft. Preliminary conclusions based on data obtained in 1982 verify that the events recorded aboard the aircraft occurred during lightning but also indicate that they occur with surprising frequency very early in the flash.

Levine, D. M.; Mazur, V.

1983-01-01

342

Correlated measurements of UHF radar signatures, RF radiation and electric field changes from lightning  

NASA Astrophysics Data System (ADS)

During Storm Hazards - 82, simultaneous measurements are made of radar echoes, fast and slow field changes and RF radiation from lightning. Radio frequency radiation and radar echoes are also obtained during periods when the research aircraft is struck by lightning. These data are presently used to better understand the electrical processes which occur during strikes to the aircraft. Preliminary conclusions verify that the events recorded aboard the aircraft occurred during lightning but also indicate that they occur with surprising frequency very early in the flash.

Levine, D. M.; Mazur, V.

343

Correlated measurements of UHF radar signatures, RF radiation and electric field changes from lightning  

NASA Technical Reports Server (NTRS)

During Storm Hazards - 82, simultaneous measurements are made of radar echoes, fast and slow field changes and RF radiation from lightning. Radio frequency radiation and radar echoes are also obtained during periods when the research aircraft is struck by lightning. These data are presently used to better understand the electrical processes which occur during strikes to the aircraft. Preliminary conclusions verify that the events recorded aboard the aircraft occurred during lightning but also indicate that they occur with surprising frequency very early in the flash.

Levine, D. M.; Mazur, V.

1983-01-01

344

Correlated measurements of UHF radar signatures, RF radiation, and electric field changes from lightning  

NASA Astrophysics Data System (ADS)

During Storm Hazards - 82, simultaneous measurements were made of radar echoes, fast and slow field changes and RF radiation from lightning near the Wallops Flight Facility. RF radiation and radar echoes were also obtained during periods when the NASA F106 research aircraft was struck by lightning. These data are presently being used to better understand the electrical processes which occur during strikes to the aircraft. Preliminary conclusions based on data obtained in 1982 verify that the events recorded aboard the aircraft occurred during lightning but also indicate that they occur with surprising frequency very early in the flash.

Levine, D. M.; Mazur, V.

1983-06-01

345

Simple far-field radiative thermal rectifier using Fabry-Perot cavities based infrared selective emitters.  

PubMed

We present a thermal rectification device concept based on far-field radiative exchange between two selective emitters. Rectification is achieved due to a large contrast between the two selective emitters' thermo-optical properties. A simple device constituted by two multilayer samples made of metallic (Au) and semiconductor (Si and HDSi) thin films is proposed. This device shows a rectification ratio increasing with temperature up to 19% for a temperature difference of ?T=370??K. Further optimization would allow larger rectification values. The presented results might be useful for energy conversion devices, engineering of smart radiative coolers/insulators, and development of thermal logical circuits. PMID:24922424

Nefzaoui, E; Drevillon, J; Ezzahri, Y; Joulain, K

2014-06-01

346

Impact of magnetic field inhomogeneity on electron cyclotron radiative loss in tokamak reactors  

NASA Astrophysics Data System (ADS)

The potential importance of electron cyclotron (EC) emission in the local electron power balance in the steady-state regimes of ITER operation with high temperatures, as well as in the DEMO reactor, requires accurate calculation of the one-dimensional (over magnetic surfaces) distribution of the net radiated power density, P EC(?). When the central electron temperature increases to ˜30 keV, the local EC radiative loss comprises a substantial fraction of the heating power from fusion alphas and is close to the total auxiliary NBI heating power, P EC(0) ? 0.3 P ?(0) ? P aux(0). In the present paper, the model of EC radiative transport in an axisymmetric toroidal plasma is extended to the case of an inhomogeneous magnetic field B( R, Z). The impact of such inhomogeneity on local and total power losses is analyzed in the framework of this model by using the CYNEQ code. It is shown that, for the magnetic field B, temperature T e , density n e , and wall reflection coefficient R w expected in ITER and DEMO, accurate simulations of the EC radiative loss require self-consistent 1.5D transport analysis (i.e., one-dimensional simulations of plasma transport and two-dimensional simulations of plasma equilibrium). It is shown that EC radiative transport can be described with good accuracy in the 1D approximation with the surface-averaged magnetic field, B(?) = < B( R, Z)> ms . This makes it possible to substantially reduce the computational time required for time-dependent self-consistent 1.5D transport analysis. Benchmarking of the CYNEQ results with available results of the RAYTEC, EXACTEC, and CYTRAN codes is performed for various approximations of the magnetic field.

Kukushkin, A. B.; Minashin, P. V.; Polevoi, A. R.

2012-03-01

347

Impact of magnetic field inhomogeneity on electron cyclotron radiative loss in tokamak reactors  

SciTech Connect

The potential importance of electron cyclotron (EC) emission in the local electron power balance in the steady-state regimes of ITER operation with high temperatures, as well as in the DEMO reactor, requires accurate calculation of the one-dimensional (over magnetic surfaces) distribution of the net radiated power density, P{sub EC}({rho}). When the central electron temperature increases to {approx}30 keV, the local EC radiative loss comprises a substantial fraction of the heating power from fusion alphas and is close to the total auxiliary NBI heating power, P{sub EC}(0) Asymptotically-Equal-To 0.3P{sub {alpha}}(0) Asymptotically-Equal-To P{sub aux}(0). In the present paper, the model of EC radiative transport in an axisymmetric toroidal plasma is extended to the case of an inhomogeneous magnetic field B(R, Z). The impact of such inhomogeneity on local and total power losses is analyzed in the framework of this model by using the CYNEQ code. It is shown that, for the magnetic field B, temperature T{sub e}, density n{sub e}, and wall reflection coefficient R{sub w} expected in ITER and DEMO, accurate simulations of the EC radiative loss require self-consistent 1.5D transport analysis (i.e., one-dimensional simulations of plasma transport and two-dimensional simulations of plasma equilibrium). It is shown that EC radiative transport can be described with good accuracy in the 1D approximation with the surface-averaged magnetic field, B({rho}) = Left-Pointing-Angle-Bracket B(R, Z) Right-Pointing-Angle-Bracket {sub ms}. This makes it possible to substantially reduce the computational time required for time-dependent self-consistent 1.5D transport analysis. Benchmarking of the CYNEQ results with available results of the RAYTEC, EXACTEC, and CYTRAN codes is performed for various approximations of the magnetic field.

Kukushkin, A. B.; Minashin, P. V. [National Research Centre Kurchatov Institute, Tokamak Physics Institute (Russian Federation); Polevoi, A. R. [Route de Vinon sur Verdon, ITER Organization (France)

2012-03-15

348

Evaluating a radiation monitor for mixed-field environments based on SRAM technology  

NASA Astrophysics Data System (ADS)

Instruments operating in particle accelerators and colliders are exposed to radiations that are composed of particles of different types and energies. Several of these instruments often embed devices that are not hardened against radiation effects. Thus, there is a strong need for monitoring the levels of radiation inside the mixed-field radiation areas, throughout different positions. Different metrics exist for measuring the radiation damage induced to electronic devices, such as the Total Ionizing Dose (TID), the Displacement Damage (DD) and of course the fluence of particles for estimating the error rates of the electronic devices among other applications. In this paper, we propose an SRAM based monitor, that is used to define the fluence of High Energy Hadrons (HEH) by detecting Single Event Upsets in the memory array. We evaluated the device by testing it inside the H4IRRAD area of CERN, a test area that reproduces the radiation conditions inside the Large Hadron Collider (LHC) tunnel and its shielded areas. By using stability estimation methods and presenting experimental data, we prove that this device is proper to be used for such a purpose.

Tsiligiannis, G.; Dilillo, L.; Bosio, A.; Girard, P.; Pravossoudovitch, S.; Todri, A.; Virazel, A.; Mekki, J.; Brugger, M.; Wrobel, F.; Saigne, F.

2014-05-01

349

Intercomparison of radiation protection devices in a high-energy stray neutron field, Part II: Bonner sphere spectrometry  

Microsoft Academic Search

The European Commission has funded within its 6th Framework Programme a three-year project (2005–2007) called CONRAD, COordinated Network for RAdiation Dosimetry. A major task of the CONRAD Work Package “complex mixed radiation fields at workplaces” was to organise a benchmark exercise in a workplace field at a high-energy particle accelerator where neutrons are the dominant radiation component. The CONRAD benchmark

B. Wiegel; S. Agosteo; R. Bedogni; M. Caresana; A. Esposito; G. Fehrenbacher; M. Ferrarini; E. Hohmann; C. Hranitzky; A. Kasper; S. Khurana; V. Mares; M. Reginatto; S. Rollet; W. Rühm; D. Schardt; M. Silari; G. Simmer; E. Weitzenegger

2009-01-01

350

Quantizing remote sensing radiation field research based on J-C model  

NASA Astrophysics Data System (ADS)

Remote sensing provides a powerful tool for human to explore the environment around us from multidimensional perspective and macroscopic view. As marrow of remote sensing, remote sensing information is about the message of light or electromagnetic wave obtained by remote sensing platform. Quantum remote sensing reveals remote sensing theories and methods in quantum level. Quantum remote sensing information is about how to express and transmit information by quantum state. Quantizing remote sensing radiation field is its main basis. Based on J-C model, which describes interaction between single mode light field and a two-level atom, expressions of operators correlated with light field can be obtained through state vector of atom-light field coupling system and Schrodinger equation. Both analysis and calculations show that quantum fluctuation of the light field can be squeezed. Numerical simulation is used to study the variation of quantum fluctuation, which deepens our understanding of quantum remote sensing information.

Zhen, Ming; Bi, Siwen

2014-03-01

351

Tunnel ionization of highly excited atoms in a noncoherent laser radiation field  

SciTech Connect

A theory is developed of the ionization of highly excited atomic states by a low-frequency field of noncoherent laser radiation with a large number of modes. Analytic formulas are obtained for the probability of the tunnel ionization in such a field. An analysis is made of the case of the hydrogen atom when the parabolic quantum numbers are sufficiently good in the low-frequency limit, as well as of the case of highly excited states of complex atoms when these states are characterized by a definite orbital momentum and parity. It is concluded that the statistical factor representing the ratio of the probability in a stochastic field to the probability in a monochromatic field decreases, compared with the case of a short-range potential, if the ''Coulomb tail'' is included. It is shown that at a given field intensity the statistical factor decreases on increase in the principal quantum number of the state being ionized.

Krainov, V.P.; Todirashku, S.S.

1982-10-01

352

Signals of cosmic magnetic fields from the cosmic microwave background radiation  

NASA Astrophysics Data System (ADS)

The Cosmic Microwave Background Radiation (CMBR) is the cleanest and most direct source of information about the physical processes in the universe at the recombination era. It also has the potential to give us indirect information about the very early universe. Depending on the ionization history of the universe, CMBR studies can help us understand physical processes in the post recombination era. I start with the introduction to CMBR. I then present a brief discussion on causes of its anisotropy and polarization. Divergence-free velocity fields in baryons lead to characteristic signatures in the polarization (B-type polarization) of the CMBR. Normally such fields decay with cosmological expansion. However in the presence of tangled magnetic fields such divergence velocity fields can be sustained. I will discuss as to how, by studying the nature of polarization of the CMBR, and the non-Gaussianity of the temperature anisotropy, we can understand the strength and behavior of cosmic magnetic fields.

Seshadri, T. R.

2012-03-01

353

Internal Electric Field Behavior of Cadmium Zinc Telluride Radiation Detectors Under High Carrier Injection  

SciTech Connect

The behavior of the internal electric-field of nuclear-radiation detectors substantially affects the detector's performance. We investigated the distribution of the internal field in cadmium zinc telluride (CZT) detectors under high carrier injection. We noted the build-up of a space charge region near the cathode that produces a built-in field opposing the applied field. Its presence entails the collapse of the electric field in the rest of detector, other than the portion near the cathode. Such a space-charge region originates from serious hole-trapping in CZT. The device's operating temperature greatly affects the width of the space-charge region. With increasing temperature from 5 C to 35 C, its width expanded from about 1/6 to 1/2 of the total depth of the detector.

Yang, G.; Bolotnikov, A.E.; Camarda, G.S.; Cui, Y.; Hossain, A.; Kim, K.H.; Gul, R.; and James, R.B.

2010-10-26

354

Would Larger Radiation Fields Lead to a Faster Onset of Pain Relief in the Palliation of Bone Metastases?  

SciTech Connect

Purpose: Hemibody irradiation has been shown to relieve bony metastatic pain within 24-48 hours of treatment, whereas for local external beam radiation, onset of pain relief is 1-4 weeks after radiation. The primary objective of this study is to examine whether there is a relationship between the areas of radiation treatment and onset of pain relief. Methods and Materials: From Jan 1999 to Jan 2002, a total of 653 patients with symptomatic bone metastases were treated with external beam radiation. Pain scores and analgesic consumption were recorded at baseline and Weeks 1, 2, 4, 8, and 12. The areas of radiation treatment for all patients were calculated, then correlated with the response and analyzed in various ways. We first compared pain score alone with mean radiation field size. Second, we combined pain score and analgesic consumption. Last, we implemented the International Consensus end points for pain score and analgesic intake. Results: Assessment of 653 patients showed no significant correlation comparing pain scores alone with radiation field area, with the exception of Week 4 for partial responders. Again, no significant correlation was found when combining both analgesic intake and pain score against radiation field size. Even when implementing the International Consensus end point definitions for radiation response, the only significant correlation between radiation field size and response was observed in Week 2 for partial response. Conclusion: There was no statistical significance between mean areas of radiation treatment with the onset of pain relief.

Chow, Edward [Rapid Response Radiotherapy Program, Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Toronto (Canada)], E-mail: edward.chow@sunnybrook.ca; Makhani, Leila; Culleton, Shaelyn; Makhani, Nadiya; Davis, Lori; Campos, Sarah; Sinclair, Emily [Rapid Response Radiotherapy Program, Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Toronto (Canada)

2009-08-01

355

Simulation of Relativistic Shocks and Associated Radiation from Turbulent Magnetic Fields  

NASA Technical Reports Server (NTRS)

Plasma instabilities excited in collisionless shocks are responsible for particle acceleration. We have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic-like shock structure. In the leading shock, electron density increases by a factor of about 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. These magnetic fields contribute to the electron's transverse deflection behind the shock. The jitter'' radiation from deflected electrons in turbulent magnetic fields has different properties than synchrotron radiation, which is calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets in general, and supernova remnants. New spectra based on simulations will be presented.

Nishikawa, K.-I.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Mizuno, Y.; Nordlund, A.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Fishman, J. F.

2009-01-01

356

The electric field changes and UHF radiations caused by the triggered lightning in Japan  

NASA Technical Reports Server (NTRS)

In the rocket triggered lightning experiment of fiscal 1989, researchers observed electromagnetic field changes and UHF electromagnetic radiation accompanying rocket triggered lightning. It was found that no rapid changes corresponding to the return stroke of natural lightning were observed in the electric field changes accompanying rocket triggered lightning. However, continuous currents were present. In the case of rocket triggered lightning to the tower, electromagnetic field changes corresponding to the initiation of triggered lightning showed a bipolar pulse of a relatively large amplitude. In contrast, the rocket triggered lightning to the ground did not have such a bipolar pulse. The UHF radiation accompanying the rocket triggered lightning preceded the waveform portions corresponding to the first changes in electromagnetic fields. The number of isolated pulses in the UHF radiation showed a correlation with the time duration from rocket launching up to triggered lightning. The time interval between consecutive isolated pulses tended to get shorter with the passage of time, just like the stepped leaders of natural lightning.

Kawasaki, Zen-Ichiro; Kanao, Tadashi; Matsuura, Kenji; Nakano, Minoru; Horii, Kenji; Nakamura, Koichi

1991-01-01

357

Radiated Electric Field from a Solar Cell Module Set on the Ground Plane  

NASA Astrophysics Data System (ADS)

Radiated electric field from a solar cell module set on the ground plane has been studied experimentally and theoretically in order to clarify the antenna effect of the solar cell module. In experimental examination, the radiated electric field characteristics of the thin-film Si solar cell module were measured by using the semi-anechoic chamber including the ground plane. In theoretical examination, the solar cell was assumed as a conducting wire, which has limited electric conductivity. And the radiated electric field of a solar cell was analyzed by using the method of moment. In both examinations, the maximum value of electric field strength for every frequency was measured or calculated when the solar cell module was rotated by 360 degree. Consequently the calculation value agreed with the measurement one within 3dB at the whole frequency region from 30MHz to 300MHz. As the results, we confirmed the availability and the validity of the calculation method by assuming the solar cell module as the conducting wire in the semi-anechoic chamber with the ground plane.

Hasegawa, Ryosuke; Tomisawa, Mariko; Tokuda, Masamitsu

358

Simulation of Relativistic Shocks and Associated Radiation from Turbulent Magnetic Fields  

NASA Astrophysics Data System (ADS)

Using our new 3-D relativistic particle-in-cell (PIC) code, we investigated long-term particle acceleration associated with a relativistic electron-positron jet propagating in an unmagnetized ambient electron-positron plasma. The simulations were performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks. Acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value as predicted by the hydrodynamic compression. Behind the bow shock, in the jet shock, strong electromagnetic fields are generated. These fields may lead to time dependent afterglow emission. In order to go beyond the standard synchrotron model used in astrophysical objects we have used PIC simulations and calculated radiation based on the first principles. We calculated radiation from electrons propagating in a uniform parallel magnetic field to verify the technique. We also used the technique to calculate emission from electrons based on simulations with a small system. We obtained spectra which are consistent with those generated from electrons propagating in turbulent magnetic fields. This turbulent magnetic field is similar to the magnetic field generated at an early nonlinear stage of the Weibel instability. A fully developed shock within a larger system may generate a jitter/synchrotron spectrum.

Nishikawa, K.-I.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Mizuno, Y.; Nordlund, A.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Fishman, G. J.

2011-10-01

359

Simulation of relativistic shocks and associated radiation from turbulent magnetic fields  

NASA Astrophysics Data System (ADS)

Using our new 3-D relativistic particle-in-cell (PIC) code, we investigated long-term particle acceleration associated with a relativistic electron-positron jet propagating in an unmagnetized ambient electron-positron plasma. The simulations were performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks. Acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value as predicted by hydrodynamic compression. Behind the bow shock, in the jet shock, strong electromagnetic fields are generated. These fields may lead to time dependent afterglow emission. In order to go beyond the standard synchrotron model used in astrophysical objects we have used PIC simulations and calculated radiation based on first principles. We calculated radiation from electrons propagating in a uniform parallel magnetic field to verify the technique. We also used the technique to calculate emission from electrons based on simulations with a small system. We obtain spectra which are consistent with those generated from electrons propagating in turbulent magnetic fields. This turbulent magnetic field is similar to the magnetic field generated at an early nonlinear stage of the Weibel instability. A fully developed shock within a larger system may generate a jitter/synchrotron spectrum.

Nishikawa, K.-I.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Nordlund, A.?.; Frederiksen, J.; Mizuno, Y.; Sol, H.; Pohl, M.; Hartmann, D. H.; Fishman, G. J.

2011-08-01

360

Simulation of Relativistic Shocks and Associated Radiation from Turbulent Magnetic Fields  

NASA Technical Reports Server (NTRS)

Using our new 3-D relativistic particle-in-cell (PIC) code, we investigated long-term particle acceleration associated with a relativistic electron-positron jet propagating in an unmagnetized ambient electron-positron plasma. The simulations were performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks. Acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value as predicted by hydrodynamic compression. Behind the bow shock, in the jet shock, strong electromagnetic fields are generated. These fields may lead to time dependent afterglow emission. In order to go beyond the standard synchrotron model used in astrophysical objects we have used PIC simulations and calculated radiation based on first principles. We calculated radiation from electrons propagating in a uniform parallel magnetic field to verify the technique. We also used the technique to calculate emission from electrons based on simulations with a small system. We obtain spectra which are consistent with those generated from electrons propagating in turbulent magnetic fields. This turbulent magnetic field is similar to the magnetic field generated at an early nonlinear stage of the Weibel instability. A fully developed shock within a larger system may generate a jitter/synchrotron spectrum.

Nishikawa, K.-I.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Nordlund, A.; Frederiksen, J.; Mizuno, Y.; Sol, H.; Pohl, M.; Hartmann, D. H.; Fishman, G. J.

2011-01-01

361

Acoustic radiation potential on a sphere in plane, cylindrical, and spherical standing wave fields  

NASA Technical Reports Server (NTRS)

The method of Gor'kov is applied for deriving the acoustic radiation potential on a sphere in an arbitrary sound field. Generalized potential and force expressions are derived for arbitrary standing wave modes in rectangular, cylindrical, and spherical geometries for the case where the sphere radius is much smaller than the wavelength. Criteria for determining radiation-potential minima are derived and examples of characteristic spatial radiation-potential profiles are presented. Single modes that can sustain stable positioning are discussed for each geometry. The localizing force strengths for representative standing wave modes in the three geometries are also compared. The positioning of samples due to acoustic forces only are considered. However, the method developed is general and is extended to include gravity or other external forces.

Barmatz, M.; Collas, P.

1985-01-01

362

Study of high speed complex number algorithms. [for determining antenna for field radiation patterns  

NASA Technical Reports Server (NTRS)

A method of evaluating the radiation integral on the curved surface of a reflecting antenna is presented. A three dimensional Fourier transform approach is used to generate a two dimensional radiation cross-section along a planer cut at any angle phi through the far field pattern. Salient to the method is an algorithm for evaluating a subset of the total three dimensional discrete Fourier transform results. The subset elements are selectively evaluated to yield data along a geometric plane of constant. The algorithm is extremely efficient so that computation of the induced surface currents via the physical optics approximation dominates the computer time required to compute a radiation pattern. Application to paraboloid reflectors with off-focus feeds in presented, but the method is easily extended to offset antenna systems and reflectors of arbitrary shapes. Numerical results were computed for both gain and phase and are compared with other published work.

Heisler, R.

1981-01-01

363

Effects of radiation damping on the dynamics of electrons in ELI intensity laser fields  

SciTech Connect

An electron in the presence of a high intensity laser field, such as that anticipated at ELI, will be accelerated so strongly that its own radiation emission may significantly affect its motion. This opens up the possibility of testing experimentally the classical theory of radiation reaction in such a context. We therefore explore the effects of radiation damping on the dynamics of electrons in optical laser pulses. In the case of high intensities and high initial electron energies, the trajectories and net energy changes of the electrons are found to be significantly altered. These effects are found to become increasingly significant the closer one gets to a directly head on collision between the laser and electrons.

Harvey, Christopher; Marklund, Mattias [Department of Physics, Umea University, SE-90187 Umea (Sweden)

2012-07-09

364

Polarization sensitive detection of 100 GHz radiation by high mobility field-effect transistors  

NASA Astrophysics Data System (ADS)

Detection of 100 GHz electromagnetic radiation by a GaAs/AlGaAs high electron mobility field-effect transistor was investigated at 300 K as a function of the angle ? between the direction of linear polarization of the radiation and the symmetry axis of the transistor. The angular dependence of the detected signal was found to be A0 cos2(?-?0)+C with A0, ?0, and C dependent on the electrical polarization of the transistor gate. This dependence is interpreted as due to excitation of two crossed phase-shifted oscillators. A response of the transistor chip (including bonding wires and the substrate) to 100 GHz radiation was numerically simulated. Results of calculations confirmed experimentally observed dependencies and showed that the two oscillators result from an interplay of 100 GHz currents defined by the transistor impedance together with bonding wires and substrate related modes.

Sakowicz, M.; ?usakowski, J.; Karpierz, K.; Grynberg, M.; Knap, W.; Gwarek, W.

2008-07-01

365

Radiation hardening of MOS devices by boron. [for stabilizing gate threshold potential of field effect device  

NASA Technical Reports Server (NTRS)

A technique is described for radiation hardening of MOS devices and specifically for stabilizing the gate threshold potential at room temperature of a radiation subjected MOS field-effect device with a semiconductor substrate, an insulating layer of oxide on the substrate, and a gate electrode disposed on the insulating layer. The boron is introduced within a layer of the oxide of about 100 A-300 A thickness immediately adjacent the semiconductor-insulator interface. The concentration of boron in the oxide layer is preferably maintained on the order of 10 to the 18th power atoms/cu cm. The technique serves to reduce and substantially annihilate radiation induced positive gate charge accumulations.

Danchenko, V. (inventor)

1974-01-01

366

Assessment of radiation-induced second cancer risks in proton therapy and IMRT for organs inside the primary radiation field  

NASA Astrophysics Data System (ADS)

There is clinical evidence that second malignancies in radiation therapy occur mainly within the beam path, i.e. in the medium or high-dose region. The purpose of this study was to assess the risk for developing a radiation-induced tumor within the treated volume and to compare this risk for proton therapy and intensity-modulated photon therapy (IMRT). Instead of using data for specific patients we have created a representative scenario. Fully contoured age- and gender-specific whole body phantoms (4 year and 14 year old) were uploaded into a treatment planning system and tumor volumes were contoured based on patients treated for optic glioma and vertebral body Ewing's sarcoma. Treatment plans for IMRT and proton therapy treatments were generated. Lifetime attributable risks (LARs) for developing a second malignancy were calculated using a risk model considering cell kill, mutation, repopulation, as well as inhomogeneous organ doses. For standard fractionation schemes, the LAR for developing a second malignancy from radiation therapy alone was found to be up to 2.7% for a 4 year old optic glioma patient treated with IMRT considering a soft-tissue carcinoma risk model only. Sarcoma risks were found to be below 1% in all cases. For a 14 year old, risks were found to be about a factor of 2 lower. For Ewing's sarcoma cases the risks based on a sarcoma model were typically higher than the carcinoma risks, i.e. LAR up to 1.3% for soft-tissue sarcoma. In all cases, the risk from proton therapy turned out to be lower by at least a factor of 2 and up to a factor of 10. This is mainly due to lower total energy deposited in the patient when using proton beams. However, the comparison of a three-field and four-field proton plan also shows that the distribution of the dose, i.e. the particular treatment plan, plays a role. When using different fractionation schemes, the estimated risks roughly scale with the total dose difference in%. In conclusion, proton therapy can significantly reduce the risk for developing an in-field second malignancy. The risk depends on treatment planning parameters, i.e. an analysis based on our formalism could be applied within treatment planning programs to guide treatment plans for pediatric patients.

Paganetti, Harald; Athar, Basit S.; Moteabbed, Maryam; Adams, Judith A.; Schneider, Uwe; Yock, Torunn I.

2012-10-01

367

GLOBAL ELECTROMAGNETIC RADIATION POLLUTION: RISK ASSESSMENT FROM FIELD MEASUREMENTS AND ANIMAL EXPERIMENTS  

NASA Astrophysics Data System (ADS)

The extended use of wireless technology throughout the globe in almost all developed and non-developed countries has forced a large number of scientists to get involved in the investigation of the effects. The major issue is that unlike other forms of radiation exposure, this “non-ionizing electromagnetic radiation” was not present throughout the evolution of life in earth and therefore there are no adaptive mechanisms evolved. All organisms are vulnerable to the possible effects of radiation depending on the actual exposure level. “Safety limits” on the power density have been proposed but ongoing research has shown that these limits are not really safe for humans, not mentioning the entire population of living creatures on earth. The so called “Electrosmog Pollution” originating from the numerous radio and TV stations, communication satellite emission, but most importantly from mobile phone mast antennas, are of major concern, because it is gradually increasing at exponential rate. Therefore the key question is, do living organisms react upon their exposure to fields of non ionizing electromagnetic radiation? To have this question answered extensive research is being performed in various laboratories. One approach of our research includes field measurements within houses and classrooms, since a considerable proportion of the population in each country is exposed to the radiation coming from the nearby mast stations, in order to make a risk assessment. The measurements showed that in many cases the actual radiation present was potentially harmful. In other words, although the measured values were below the national safety levels, nevertheless they were above the levels of other countries. Therefore it has been suggested that a new cellular network should be constructed in order to minimize radiation levels in living areas and schools. Our experimental work is focusing on the elucidation of the effects of non-ionizing EMFs on mice exposed to mobile phone and wireless DECT phone radiation and especially on the brain tissues. The brain is the major organ of the body that if affected by environmentally derived radiation, several cognitive - related functions shall be altered, such as memory and learning. We have approached this issue by means of behavioural tests (i.e. Morris water maze) and also by proteomics analysis (very precise separation and identification of the brain proteins by sophisticated techniques). Both ways of approaches have shown important deficits, suggesting that the normal use of the mobile and wireless phone next to the brain should be avoided and that new safety guidelines must be established.

Fragkopoulou, A. F.; Margaritis, L. H.

2009-12-01

368

Mobbing behaviors encountered by nurse teaching staff.  

PubMed

The term 'mobbing' is defined as antagonistic behaviors with unethical communication directed systematically at one individual by one or more individuals in the workplace. This cross-sectional and descriptive study was conducted for the purpose of determining the mobbing behaviors encountered by nursing school teaching staff in Turkey, its effect on them, and their responses to them. A large percentage (91%) of the nursing school employees who participated in this study reported that they had encountered mobbing behaviors in the institution where they work and 17% that they had been directly exposed to mobbing in the workplace. The academic staff who had been exposed to mobbing behaviors experienced various physiological, emotional and social reactions. They frequently 'worked harder and [were] more organized and worked very carefully to avoid criticism' to escape from mobbing. In addition, 9% of the participants stated that they 'thought about suicide occasionally'. PMID:17562724

Yildirim, Dilek; Yildirim, Aytolan; Timucin, Arzu

2007-07-01

369

Minimum radiation force target size for power measurements in focused ultrasonic fields with circular symmetry.  

PubMed

The time-averaged ultrasonic power emitted by medical ultrasonic equipment is mostly measured using a radiation force balance, and the question of the necessary target size is of practical importance. The question is answered here by calculations based on a Rayleigh integral algorithm for fields from circular, focusing transducers. This case occurs particularly in the field of high-intensity therapeutic ultrasound. The calculation yields the necessary size of an absorbing target so that the radiation force is 98% of that exerted on an absorber of infinite lateral size, and this as a function of the transducer-to-target distance, of the transducer radius in comparison with the wavelength and of the focus (half-)angle. Several distributions of the transducer vibration amplitude are considered. The Rayleigh integral strictly applies only to planar transducers, but among the amplitude distributions there is also one that allows the simulation of the spherically curved transducer type often found in practice. PMID:21218869

Beissner, K

2010-12-01

370

A method to detect ultra high energy electrons using earth's magnetic field as a radiator  

NASA Technical Reports Server (NTRS)

It is pointed out that the detection of electrons with energies exceeding a few TeV, which lose energy rapidly through synchrotron and inverse Compton processes, would provide valuable information on the distribution of sources and on the propagation of cosmic rays in the solar neighborhood. However, it would not be possible to measure the energy spectrum beyond a few TeV with any of the existing experimental techniques. The present investigation is, therefore concerned with the possibility of detecting electrons with energies exceeding a few TeV on the basis of the photons emitted through synchrotron radiation in the earth's magnetic field. Attention is given to the synchrotron radiation of electrons in the earth's magnetic field, detector response and energy estimation, and the characteristics of an ideal detector, capable of detecting photons with energies equal to or greater than 20 keV.

Stephens, S. A.; Balasubrahmanyan, V. K.

1983-01-01

371

A comparison of collimator geometries for imaging mixed radiation fields with fast liquid organic scintillators  

SciTech Connect

As a result of recent advances in digital pulse-shape discrimination methods it has become possible to image mixed fields (radiation environments compromising both neutrons and gamma rays) relatively quickly with a single, organic liquid 'fast' scintillator within a heavy metal collimator. The use of a liquid scintillator has significant benefits over other techniques for imaging radiation environments as the acquired data can be analysed to provide separate information about the gamma and neutron emissions from a source (or sources) in a single scan. The imaging resolution achieved is fundamentally related to the detector efficiency and to the collimator geometry. In this paper the impact of using two different geometries of tungsten collimator are compared experimentally and three different materials considered in the Monte Carlo simulation, in order to determine the optimum set-up for mixed-field imaging. The measurements were performed in the low-scatter facility of the National Physical Laboratory, Teddington. (authors)

Gamage, K. A. A.; Joyce, M. J. [Engineering Dept., Lancaster Univ., Lancaster, Lancashire, LA1 4YR (United Kingdom); Taylor, G. C. [Neutron Metrology Group, National Physical Laboratory, Teddington, Middlesex, TW11 0LW (United Kingdom)

2011-07-01

372

On the relativistic classical motion of a radiating spinning particle in a magnetic field  

SciTech Connect

Research Highlights: > We propose classical equations of motion for a charged particle with magnetic moment. > We account for radiation reaction as well. > Unlike previous proposals we do not have runaway solutions. > We find that the particle loses energy even in a constant magnetic field for a particular spin-polarized state. - Abstract: We propose classical equations of motion for a charged particle with magnetic moment, taking radiation reaction into account. This generalizes the Landau-Lifshitz equations for the spinless case. In the special case of spin-polarized motion in a constant magnetic field (synchrotron motion) we verify that the particle does lose energy. Previous proposals did not predict dissipation of energy and also suffered from runaway solutions analogous to those of the Lorentz-Dirac equations of motion.

Kar, Arnab, E-mail: arnabkar@pas.rochester.edu [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Rajeev, S.G. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States)

2011-04-15

373

Strong near-field enhancement of radiative heat transfer between metallic surfaces.  

PubMed

Near-field heat transfer across a gap between plane-parallel tungsten layers in vacuo was studied experimentally with the temperature of the cold sample near 5 K and the temperature of the hot sample in the range 10-40 K as a function of the gap size d. At gaps smaller than one-third of the peak wavelength ?(m) given by Wien's displacement law, the near-field effect was observed. In comparison with blackbody radiation, hundred times higher values of heat flux were achieved at d?1 ?m. Heat flux normalized to the radiative power transferred between black surfaces showed scaling (?(m)/d)(n), where n?2.6. This Letter describes the results of experiment and a comparison with present theory over 4 orders of magnitude of heat flux. PMID:23368126

Kralik, Tomas; Hanzelka, Pavel; Zobac, Martin; Musilova, Vera; Fort, Tomas; Horak, Michal

2012-11-30

374

Reverse electric field Monte Carlo simulation for vector radiative transfer in the atmosphere  

NASA Astrophysics Data System (ADS)

In this paper, a reverse electric field Monte Carlo (REMC) method is proposed to study the vector radiation transfer in the atmosphere. The REMC is based on tracing the multiply scattered electric field to simulate the vector transmitted radiance. The reflected intensities with different total optical depth values are obtained, which accord well with the results in the previous research. Stokes vector and the degree of polarization are numerically investigated. The simulation result shows that when the solar zenith angle is determined, the zenith angle of detector has two points, of which the degree of polarization does not change with the ground albedo and the optical depth. The two points change regularly with the solar zenith angle. Moreover, our REMC method can be applied to the vector radiative transfer in the atmosphere—ocean system.

Li, Xu-You; Sun, Bo; Yu, Ying-Ying

2014-06-01

375

DOE Task Force meeting on Electrical Breakdown of Insulating Ceramics in a High Radiation Field  

SciTech Connect

This volume contains the abstracts and presentation material from the Research Assistance Task Force Meeting Electrical Breakdown of Insulating Ceramics in a High-Radiation Field.'' The meeting was jointly sponsored by the Office of Basic Energy Sciences and the Office of Fusion Energy of the US Department of Energy in Vail, Colorado, May 28--June 1, 1991. The 26 participants represented expertise in fusion, radiation damage, electrical breakdown, ceramics, and semiconductor and electronic structures. These participants came from universities, industries, national laboratories, and government. The attendees represented eight nations. The Task Force meeting was organized in response to the recent discovery that a combination of temperature, electric field, and radiation for an extended period of time has an unexplained adverse effect in ceramics, termed radiation-enhanced electrical degradation (REED). REED occurs after an incubation period and continues to accelerate with irradiation until the ceramics can no longer be regarded as insulators. It appears that REED is irreversible and the ceramic insulators cannot be readily annealed or otherwise repaired for future services. This effect poses a serious threat for fusion reactors, which require electrical insulators in diagnostic devices, in radio frequency and neutral beam systems, and in magnetic assemblies. The problem of selecting suitable electrical insulating materials in thus far more serious than previously anticipated.

Green, P.H. (comp.) [comp.

1991-08-01

376

Winnicott and Lacan: a missed encounter?  

PubMed

Winnicott was able to say that Lacan's paper on the mirror stage "had certainly influenced" him, while Lacan argued that he found his object a in Winnicott's transitional object. By following the development of their personal relations, as well as of their theoretical discussions, it is possible to argue that this was a missed encounter--yet a happily missed one, since the misunderstandings of their theoretical exchanges allowed each of them to clarify concepts otherwise difficult to discern. PMID:22768481

Vanier, Alain

2012-04-01

377

Children's contributions to pediatric outpatient encounters  

Microsoft Academic Search

Objective: Generally, increasing attention is being paid to the quality of doctor-patient communication. However, children's contributions have been, until now, primarily ignored in communication research, although there are indications that considering their views increases satisfaction and compliance. In the communication during outpatient pediatric encounters and what factors were associated with children's contributions. Patients: Twenty-one consulting pediatricians video-taped a total of

A. M. van Dulmen

1998-01-01

378

White phosphorus poisoning--explosive encounter.  

PubMed

Poisoning by white or yellow phosphorus is reported in various forms and also in ages varying from infants to adults, but spontaneous combustion and explosion during its management has never been described. This incidence occurred while attempting to pass a Ryle's tube. Its free end first exhibited a yellow flame and this later on led to an explosive encounter. Role of static electricity generated while handling plastic materials leading to ignition and explosion cannot be overlooked. PMID:15636320

Pande, T K; Pandey, S

2004-03-01

379

The Radiation Field Wave Forms Produced by Intracloud Lightning Discharge Processes  

Microsoft Academic Search

The large-amplitude radiation field pulses produced by intracloud lightning discharge processes have been recorded with submicrosecond time resolution. The wave forms are distinctly different from those produced by return strokes in cloud-to-ground lightning, yet they are surprisingly alike within a discharge and in different discharges. The shapes tend to be bipolar, with two or three narrow, fast-rising pulses superimposed on

Charles D. Weidman; E. Philip Krider

1979-01-01

380

Calibration of acoustic radiation pressure field inside microchannels using microparticle zeta potential measurement  

Microsoft Academic Search

We present a new method to extract acoustic radiation field inside a PZT-glass capillary microfluidic actuator, used for collection and separation of micro-nano-particles and biological entities. By focusing particles in a small volume, acoustic forces counteract against natural dispersive forces. Investigation of these dispersive forces related to zeta potential enables calculation of the acoustic force inside the complex microfluidic system.

Muhammet Kursad Araz; Amit Lal

2005-01-01

381

Radiation by ultrarelativistic electrons entering a dense medium in a strong magnetic field  

NASA Astrophysics Data System (ADS)

The synchrotron radiation of electrons with zero pitch angle before entering the matter is studied. Pitch-angle distribution occurs due to multiple scattering. It is shown that in the magnetic fields that are characteristic of pulsars the mechanism considered makes a main contribution to the electron energy losses in a wide range of the initial energies of the particles and concentrations of the nuclei.

Kotov, Y. D.; Kelner, S. R.; Bogovalov, S. V.

1986-06-01

382

NOTE: Measurement of ionizing radiation using carbon nanotube field effect transistor  

Microsoft Academic Search

Single-walled carbon nanotubes (SWNTs) are a new class of highly promising nanomaterials for future nano-electronics. Here, we present an initial investigation of the feasibility of using SWNT field effect transistors (SWNT-FETs) formed on silicon-oxide substrates and suspended FETs for radiation dosimetry applications. Electrical measurements and atomic force microscopy (AFM) revealed the intactness of SWNT-FET devices after exposure to over 1

Xiao-Wu Tang; Yong Yang; Woong Kim; Qian Wang; Pengfei Qi; Hongjie Dai; Lei Xing

2005-01-01

383

Near-field measurement of radiation levels of extended spatially uncorrelated sound sources  

NASA Astrophysics Data System (ADS)

A method is considered for measuring the radiation levels of extended spatially uncorrelated sound sources in the near field in the case of their imprecise positioning with respect to the measurement system—a linear antenna array. An algorithm is proposed for synthesizing the vector of weight coefficients ensuring the given value of methodological measurement error under maximum suppression of external noise. Examples are given of numerical modeling and experimental testing of the method in natural conditions.

Orlov, D. A.; Turchin, V. I.; Fiks, G. E.; Fiks, I. Sh.

2012-05-01

384

Models of performances of dosimetric telescopes in the anisotropic radiation field in low earth orbit  

Microsoft Academic Search

In the case of the International Space Station (ISS), the attitude of which is usually stabilized in the local vertical reference frame (airplane-like attitude), the anisotropies in the radiation field, such as the effect of the Earth's shadow, the angular dependence of the geomagnetic transmission factors and the East–West asymmetry in the South Atlantic Anomaly (SAA), cannot be ignored. One-dimensional

Attila Hirn

2010-01-01

385

Cell phone electromagnetic field radiations affect rhizogenesis through impairment of biochemical processes  

Microsoft Academic Search

Indiscriminate adoption and use of cell phone technology has tremendously increased the levels of electromagnetic field radiations\\u000a (EMFr) in the natural environment. It has raised the concerns among the scientists regarding the possible risks of EMFr to\\u000a living organisms. However, not much has been done to assess the damage caused to plants that are continuously exposed to EMFr\\u000a present in

Harminder Pal Singh; Ved Parkash Sharma; Daizy Rani Batish; Ravinder Kumar Kohli

386

Stellar Encounters with the ? Pictoris Planetesimal System  

NASA Astrophysics Data System (ADS)

We use data from the Hipparcos catalog and the Barbier-Brossat & Figon catalog of stellar radial velocities to test the hypothesis that the ? Pic planetesimal disk was disrupted by a close stellar encounter. We trace the space motions of 21,497 stars and discover 18 that have passed within 5 pc of ? Pic in the past 1 Myr. ? Pic's closest encounter is with the K2 III star HIP 27628 (~0.6 pc), but dynamically the most important encounter is with the F7 V star HIP 23693 (~0.9 pc). We calculate the velocity and eccentricity changes induced by the 18 perturbations and conclude that they are dynamically significant if planetesimals exist in a ? Pic Oort cloud. We provide a first-order estimate for the evolutionary state of a ? Pic Oort cloud and conclude that the primary role of these stellar perturbations would be to help build a comet cloud rather than destroy a preexisting structure. The stellar sample is ~20% complete and motivates future work to identify less common close interactions that would significantly modify the observed circumstellar disk. For future radial velocity study, we identify six stars in the Hipparcos catalog that may have approached ? Pic to within 0.1 pc and therefore remain as candidate disk perturbers.

Kalas, Paul; Deltorn, Jean-Marc; Larwood, John

2001-05-01

387

Magnetic Field Generation through Angular Momentum Exchange between Circularly Polarized Radiation and Charged Particles  

SciTech Connect

The interaction between circularly polarized (CP) radiation and charged particles can lead to generation of magnetic field through an inverse Faraday effect. The spin of the circularly polarized electromagnetic wave can be converted into the angular momentum of the charged particles so long as there is dissipation. We demonstrate this by considering two mechanisms of angular momentum absorption relevant for laser-plasma interactions: electron-ion collisions and ionization. The precise dissipative mechanism, however, plays a role in determining the efficiency of the magnetic field generation.

G. Shvets; N.J. Fisch; J.-M. Rax

2002-01-18

388

Initial Field Measurements with the Multisensor Airborne Radiation Survey (MARS) High Purity Germanium (HPGe) Detector Array  

SciTech Connect

Abstract: The Multi-sensor Airborne Radiation Survey (MARS) project has developed a new single cryostat detector array design for high purity germanium (HPGe) gamma ray spectrometers that achieves the high detection efficiency required for stand-off detection and actionable characterization of radiological threats. This approach is necessary since a high efficiency HPGe detector can only be built as an array due to limitations in growing large germanium crystals. The system is ruggedized and shock mounted for use in a variety of field applications. This paper reports on results from initial field measurements conducted in a truck and on two different boats.

Fast, James E.; Bonebrake, Christopher A.; Dorow, Kevin E.; Glasgow, Brian D.; Jensen, Jeffrey L.; Morris, Scott J.; Orrell, John L.; Pitts, W. Karl; Rohrer, John S.; Todd, Lindsay C.

2010-06-29

389

Magnetic field generation through angular momentum exchange between circularly polarized radiation and charged particles.  

PubMed

The interaction between circularly polarized radiation and charged particles can lead to generation of magnetic field through an inverse Faraday effect. The spin of the circularly polarized electromagnetic wave can be converted into the angular momentum of the charged particles so long as there is dissipation. We demonstrate this by considering two mechanisms of angular momentum absorption relevant for laser-plasma interactions: electron-ion collisions and ionization. The precise dissipative mechanism, however, plays a role in determining the efficiency of the magnetic-field generation. PMID:12006019

Shvets, G; Fisch, N J; Rax, J-M

2002-04-01

390

Theory of thermal nonequilibrium entropy in near-field thermal radiation  

NASA Astrophysics Data System (ADS)

We propose a theoretical formalism to evaluate the entropy density and entropy flux that takes into account near-field effects, i.e., interference, diffraction, and tunneling of waves. Using the fluctuation-dissipation theorem, expressions for entropy density and entropy flux in a vacuum cavity between planar multilayered media are derived in terms of local density of photons, local density of accessible microscopic states, and velocity of energy transmission. The proposed method is used to determine the maximum work that can be extracted and a thermodynamic limit of the energy conversion efficiency that can be obtained in near-field thermal radiation.

Narayanaswamy, Arvind; Zheng, Yi

2013-08-01

391

Advances in Quantifying the Radiative Effects of Aerosol Particles on Climate from Airborne Field Studies  

NASA Astrophysics Data System (ADS)

In the fourth assessment report of the Intergovernmental Panel on Climate Change, large uncertainties persist in estimates of climate forcing by aerosol particles. One contributor to this uncertainty is the poorly quantified vertical distribution of solar radiation absorbed by aerosol particles, from the regional to global scale. Another is the spectral and spatial variability of surface albedo, an effect that can dominate the top-of-atmosphere perturbations due to aerosol scattering and absorption, particularly over land. Over the past three years a number of intensive airborne field experiments (ICARTT, MILAGRO, GoMACCS) have contributed significantly to our understanding of the impact of pollution outflow from urban-industrial centers on radiative forcing, using spectrally resolved radiometric measurements and novel observationally-based methods to derive forcing efficiency and flux divergence. We present an overview of some of the most significant advances in direct radiative forcing realized by these studies, and recommendations on where the greatest challenges remain. In addition we present findings from these experiments on the influence of aerosol particles on cloud radiative properties, a potentially greater effect but even more uncertain than direct radiative forcing.

Pilewskie, P.; Schmidt, K. S.; Coddington, O.; Bergstrom, R.; Redemann, J.

2007-12-01

392

The Effects of Aerosol on Atmospheric UV Radiation: Measurements and Modeling from the MILAGRO Field Campaign  

NASA Astrophysics Data System (ADS)

The MILAGRO field campaign took place in and near Mexico City 1-30 March 2006. A comprehensive data set was obtained on atmospheric chemical composition (gas and aerosol), aerosol microphysics, spectral radiation, and meteorology from surface-, aircraft-, and satellite-based instruments. For much of this time, the lower atmosphere was laden with large amounts of aerosols originating from urban and industrial sources, biomass fires, and wind-blown dust. Spectral radiation measurements are available from filter radiometers and spectroradiometers, and span ultraviolet (UV) wavelengths important to surface biota and tropospheric photochemistry. By combining the spectral radiation measurements, aerosol composition, optical, and microphysical measurements, and modeling, an assessment is now possible on how aerosols affect surface UV radiation (e.g. DNA damage, erythema, vitamin-D production) and vertical profiles of photolysis frequencies (e.g. JNO2, JO3(O1D), JCH2O, JHONO). Interactions between aerosol-scattered radiation and absorption by gaseous pollutants (esp. O3, SO2, and NO2) can also be evaluated. Implications for human health and photochemical oxidant formation will be discussed.

Madronich, S.; Hall, S.; Shetter, R.; Slusser, J.; Arnott, P.

2007-05-01

393

A space weather index for the radiation field at aviation altitudes  

NASA Astrophysics Data System (ADS)

The additional dose contribution to the radiation exposure at aviation altitudes during Solar Particle Events (SPEs) has been a matter of concern for many years. After the Halloween storms in 2003 several airlines began to implement mitigation measures such as rerouting and lowering flight altitudes in response to alerts on the NOAA S-scale regarding solar radiation storms. These alerts are based on the integral proton flux above 10 MeV measured aboard the corresponding GOES-satellite which is operated outside the Earth's atmosphere in a geosynchronous orbit. This integral proton flux has, however, been proved to be an insufficient parameter to apply to the radiation field at aviation altitudes without an accompanying analysis of the shape of the energy spectrum. Consequently, false alarms and corresponding disproportionate reactions ensued. Since mitigating measures can be quite cost-intensive, there has been a demand for appropriate space weather information among responsible airline managers for about a decade. Against this background, we propose the introduction of a new Space Weather index D, based on dose rates at aviation altitudes produced by solar protons during solar radiation storms, as the relevant parameter for the assessment of corresponding radiation exposure. The Space Weather index D is a natural number given by a graduated table of ranges of dose rates in ascending order which is derived by an equation depending on the dose rate of solar protons.

Meier, Matthias M.; Matthiä, Daniel

2014-04-01

394

Control of whistler radiation efficiency of a loop antenna by generation of ambient magnetic field irregularities  

SciTech Connect

Electrodynamic means for the control of loop antenna radiation efficiency in plasma is proposed, which can be used in the whistler frequency band. The method is based on the generation, without perturbing the plasma density, of localized ambient magnetic field irregularities in the vicinity of the antenna. In order to produce such irregularities, it is suggested to feed the antenna with additional dc current along with the rf current. Experiments performed in a large laboratory magnetoplasma showed that the generation of localized magnetic field enhancements provides the possibility of increasing the amplitude of the whistlers emitted by the loop antenna. Moreover, experiments have shown that the amplification of the whistlers' signals from the receiving loop antenna fed with additional dc current is observed when a static magnetic field enhancement is generated in the vicinity of the receiver. The experimental data are in good agreement with the theoretical results obtained for comparatively weak ambient magnetic field perturbations.

Gushchin, M. E.; Korobkov, S. V.; Kostrov, A. V.; Strikovsky, A. V.; Koldanov, V. A. [Institute of Applied Physics, 603950 Nizhny Novgorod (Russian Federation); Zaboronkova, T. M. [Department of Applied Physics, Technical University of Nizhny Novgorod, 603950 Nizhny Novgorod (Russian Federation); Krafft, C. [Laboratoire de Physique et Technologie des Plasmas, Ecole Polytechnique, 91128 Palaiseau (France)

2008-05-15

395

Star Formation In the Galaxy and the Fluctuating UV Radiation Field  

NASA Technical Reports Server (NTRS)

We examine the formation of massive stars in the Galaxy, the resultant fluctuating UV (ultraviolet) radiation field, and the effect of this field on the star-forming interstellar medium. There are substantial fluctuations of the UV radiation field in space (scales of 100's of parsecs) and time (time-scales of order 100 million years). The FUV (far ultraviolet) (6 eV less than hv less than 13.6 eV) field and the pressure determines whether the thermal balance of the neutral gas results in cold clouds or warm (T approx. 10(exp 4) K) neutral medium. We show how to calculate the average fractions of the gas in the cold and warm phases when the interstellar gas is subject to this fluctuating FUV field. The knowledge of how these fractions depend on the gas properties and on the FUV sources is a basic step in building a model of the large scale behavior of the ISM (interstellar medium) and the mutual relation between the ISM and the star formation rate.

Hollenbach, David; Parravano, Antonio; McKee, Christopher H.; DeVincenzi, D. (Technical Monitor)

2002-01-01

396

Star Formation in the Galaxy and the Fluctuating UV Radiation Field  

NASA Technical Reports Server (NTRS)

We examine the formation of massive stars in the Galaxy, the resultant fluctuating UV radiation field, and the effect of this field on the star-forming interstellar medium (ISM). There are substantial fluctuations of the UV radiation field in space (scales of 100's of parsecs) and time (time-scales of order 100 million years) at the solar circle. The Far Ultraviolet (FUV) (6 eV< hv < 13.6 eV) field and the pressure determines whether the thermal balance of the neutral gas results in cold clouds or warm (T - 10(exp 4) neutral medium. We show how to calculate the average fractions of the gas in the cold and warm phases when the interstellar gas is subject to this fluctuating FUV field. The knowledge of how these fractions depend on the gas properties and on the FUV sources is a basic step in building a model of the large scale behavior of the ISM and the mutual relation between the ISM and the star formation rate. Application is made to observations of spiral galaxies which correlate the star formation rate per unit area with the surface density of the gas. We acknowledge support from the NASA Astrophysical Theory program.

Hollenbach, David; Parravano, Antonio; McKee, Christopher H.; Fonda, Mark (Technical Monitor)

2001-01-01

397

COMPLEX SCATTERED RADIATION FIELDS AND MULTIPLE MAGNETIC FIELDS IN THE PROTOSTELLAR CLUSTER IN NGC 2264  

SciTech Connect

Near-infrared imaging polarimetry in the J, H, and K{sub s} bands has been carried out for the protostellar cluster region around NGC 2264 IRS 2 in the Monoceros OB1 molecular cloud. Various infrared reflection nebula clusters (IRNCs) associated with NGC 2264 IRS 2 and the IRAS 12 S1 core, as well as local infrared reflection nebulae (IRNe), were detected. The illuminating sources of the IRNe were identified with known or new near- and mid-infrared sources. In addition, 314 point-like sources were detected in all three bands and their aperture polarimetry was studied. Using a color-color diagram, reddened field stars and diskless pre-main-sequence stars were selected to trace the magnetic field (MF) structure of the molecular cloud. The mean polarization position angle of the point-like sources is 81 Degree-Sign {+-} 29 Degree-Sign in the cluster core, and 58 Degree-Sign {+-} 24 Degree-Sign in the perimeter of the cluster core, which is interpreted as the projected direction on the sky of the MF in the observed region of the cloud. The Chandrasekhar-Fermi method gives a rough estimate of the MF strength to be about 100 {mu}G. A comparison with recent numerical simulations of the cluster formation implies that the cloud dynamics is controlled by the relatively strong MF. The local MF direction is well associated with that of CO outflow for IRAS 12 S1 and consistent with that inferred from submillimeter polarimetry. In contrast, the local MF direction runs roughly perpendicular to the Galactic MF direction.

Kwon, Jungmi; Tamura, Motohide; Kandori, Ryo; Kusakabe, Nobuhiko; Hashimoto, Jun; Nakajima, Yasushi; Nakamura, Fumitaka [National Astronomical Observatory of Japan, Tokyo 181-8588 (Japan); Nagayama, Takahiro [Department of Astrophysics, Nagoya University, Nagoya 464-8602 (Japan); Nagata, Tetsuya [Department of Astronomy, Kyoto University, Kyoto 606-8502 (Japan); Hough, James H. [Centre for Astrophysics Research, University of Hertfordshire, Hatfield, Herts AL10 9AB (United Kingdom); Werner, Michael W. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Teixeira, Paula S., E-mail: jungmi.kwon@nao.ac.jp [European Southern Observatory, D-85748 Garching bei Muenchen (Germany)

2011-11-01

398

Sterilization of liquid foods by pulsed electric fields  

Microsoft Academic Search

Recent advances in the field of high-voltage pulse power technology have provided scope for the development of nonthermal sterilization methods free from the disadvantages commonly encountered with existing physical, chemical, or radiation sterilization. The flexibility allowed in the application of electrical energy can make high-field sterilization economical, compact, energy efficient, and environmentally acceptable. The main thrust of present research in

Shesha H. Jayaram

2000-01-01

399

An analysis of the radiation field characteristics for extremity dose assessment during maintenance periods at nuclear power plants in Korea.  

PubMed

Workers who maintain the water chambers of steam generators during maintenance periods in nuclear power plants (NPPs) have a higher likelihood of high radiation exposure, even if they are exposed for a short period of time. In particular, it is expected that the hands of workers would receive the highest radiation exposure as a consequence of hand contact with radioactive materials. In this study, a characteristic analysis of inhomogeneous radiation fields for contact operations was conducted using thermoluminescent dosemeters for the whole body and extremities during maintenance periods at Korean NPPs. It was observed that inhomogeneous radiation fields for contact operations at NPPs were dominated by high-energy photons. PMID:22628525

Kim, Hee Geun; Kong, Tae Young

2012-12-01

400

Galileo early cruise, including Venus, First Earth, and Gaspra encounters  

NASA Technical Reports Server (NTRS)

This article documents DSN support for the Galileo cruise to Jupiter. The mission's unique trajectory affords multiple encounters during this cruise phase. Each encounter had or will have unique requirements for data acquisition and DSN support configurations. An overview of the cruise and its encounters, up through the asteroid Gaspra encounter, is provided.

Beyer, P. E.; Oconnor, R. C.; Mudgway, D. J.

1992-01-01

401

Galileo early cruise, including Venus, first Earth, and Gaspra encounters  

NASA Technical Reports Server (NTRS)

This article documents Deep Space Network (DSN) support for the Galileo cruise to Jupiter. The unique trajectory affords multiple encounters during this cruise phase. Each encounter had or will have unique requirements for data acquisition and DSN support configurations. An overview of the cruise and encounters through the asteroid Gaspra encounter is provided.

Beyer, P. E.; Oconnor, R. C.; Mudgway, D. J.

1992-01-01

402

Effect of organ size and position on out-of-field dose distributions during radiation therapy  

NASA Astrophysics Data System (ADS)

Mantle field irradiation has historically been the standard radiation treatment for Hodgkin lymphoma. It involves treating large regions of the chest and neck with high doses of radiation (up to 30 Gy). Previous epidemiological studies on the incidence of second malignancies following radiation therapy for Hodgkin lymphoma have revealed an increased incidence of second tumors in various organs, including lung, breast, thyroid and digestive tract. Multiple other studies, including the Surveillance, Epidemiology and End Results, indicated an increased incidence in digestive tract including stomach cancers following mantle field radiotherapy. Assessment of stomach dose is challenging because the stomach is outside the treatment field but very near the treatment border where there are steep dose gradients. In addition, the stomach can vary greatly in size and position. We sought to evaluate the dosimetric impact of the size and variable position of the stomach relative to the field border for a typical Hodgkin lymphoma mantle field irradiation. The mean stomach dose was measured using thermoluminescent dosimetry for nine variations in stomach size and position. The mean doses to the nine stomach variations ranged from 0.43 to 0.83 Gy when 30 Gy was delivered to the treatment isocenter. Statistical analyses indicated that there were no significant differences in the mean stomach dose when the stomach was symmetrically expanded up to 3 cm or shifted laterally (medial, anterior or posterior shifts) by up to 3 cm. There was, however, a significant (P > 0.01) difference in the mean dose when the stomach was shifted superiorly or inferiorly by >=2.5 cm.

Scarboro, Sarah B.; Stovall, Marilyn; White, Allen; Smith, Susan A.; Yaldo, Derek; Kry, Stephen F.; Howell, Rebecca M.

2010-12-01

403

Analysis of the Radiated Field in an Electromagnetic Reverberation Chamber as an Upset-Inducing Stimulus for Digital Systems  

NASA Technical Reports Server (NTRS)

Preliminary data analysis for a physical fault injection experiment of a digital system exposed to High Intensity Radiated Fields (HIRF) in an electromagnetic reverberation chamber suggests a direct causal relation between the time profile of the field strength amplitude in the chamber and the severity of observed effects at the outputs of the radiated system. This report presents an analysis of the field strength modulation induced by the movement of the field stirrers in the reverberation chamber. The analysis is framed as a characterization of the discrete features of the field strength waveform responsible for the faults experienced by a radiated digital system. The results presented here will serve as a basis to refine the approach for a detailed analysis of HIRF-induced upsets observed during the radiation experiment. This work offers a novel perspective into the use of an electromagnetic reverberation chamber to generate upset-inducing stimuli for the study of fault effects in digital systems.

Torres-Pomales, Wilfredo

2012-01-01

404

Stellar encounters in the context of outburst phenomena  

NASA Astrophysics Data System (ADS)

Young stellar systems are known to undergo outbursts, where the star experiences an increased accretion rate, and the system's luminosity increases accordingly. The archetype is the FU Orionis (FU Ori) outburst, where the accretion rate can increase by three orders of magnitude (and the brightness of the system by five magnitudes). The cause appears to be instability in the circumstellar disc, but there is currently some debate as to the nature of this instability (e.g. thermal, gravitational, magneto-rotational). This paper details high-resolution smoothed particle hydrodynamics (SPH) simulations that were carried out to investigate the influence of stellar encounters on disc dynamics. Star-star encounters (where the primary has a self-gravitating, marginally stable protostellar disc) were simulated with various orbital parameters to investigate the resulting disc structure and dynamics. Crucially, the simulations include the effects of radiative transfer to realistically model the resulting thermodynamics. Our results show that the accretion history and luminosity of the system during the encounter display many of the features of outburst phenomena. In particular, the magnitudes and decay times seen are comparable to those of FU Ori. There are two caveats to this assertion: the first is that these events are not expected to occur frequently enough to explain all FU Ori or EX Lupi; the second is that the inner discs of these simulations are subject to numerical viscosity, which will act to reduce the accretion rate (although it has less of an effect on the total mass accreted). In short, these results cannot rule out binary interactions as a potential source of some FU Ori-esque outbursts.

Forgan, Duncan; Rice, Ken

2010-02-01

405

Radiation field characterization and shielding studies for the ELI Beamlines facility  

NASA Astrophysics Data System (ADS)

The ELI (Extreme Light Infrastructure) Beamlines facility in the Czech Republic, which is planned to complete the installation in 2015, is one of the four pillars of the ELI European project. Several laser beamlines with ultrahigh intensities and ultrashort pulses are foreseen, offering versatile radiation sources in an unprecedented energy range: laser-driven particle beams are expected to range between 1 and 50 GeV for electrons and from 100 MeV up to 3 GeV for protons. The number of particles delivered per laser shot is estimated to be 109-1010 for the electron beams and 1010-1012 for the proton beams. The high energy and current values of the produced particles, together with the potentiality to operate at 10 Hz laser repetition rate, require an accurate study of the primary and secondary radiation fields to optimize appropriate shielding solutions: this is a key issue to minimize prompt and residual doses in order to protect the personnel, reduce the radiation damage of electronic devices and avoid strong limitations in the operational time. A general shielding study for the 10 PW (0.016 Hz) and 2 PW (10 Hz) laser beamlines is presented here. Starting from analytical calculations, as well as from dedicated simulations, the main electron and proton fields produced in the laser-matter interaction have been described and used to characterize the "source terms" in full simulations with the Monte Carlo code FLUKA. The secondary radiation fields have been then analyzed to assess a proper shielding. The results of this study and the proposed solutions for the beam dumps of the high energy beamlines, together with a cross-check analysis performed with the Monte Carlo code GEANT4, are presented.

Ferrari, A.; Amato, E.; Margarone, D.; Cowan, T.; Korn, G.

2013-05-01

406

Fractionated Wide-Field Radiation Therapy Followed by Fractionated Local-Field Irradiation for Treating Widespread Painful Bone Metastasis  

SciTech Connect

Purpose: Wide-field radiation therapy (WFRT) is an effective treatment for widespread bone metastasis. We evaluated local-field irradiation (LFI) after fractionated WFRT (f-WFRT) for treating the patients with multiple painful bone lesions. Methods and Materials: From 1998 to 2007, 32 patients with multiple bone metastases were treated with fractionated LFI (f-LFI) after f-WFRT. All patients initially received 15 Gy in 5 fractions to a wide field, followed by LFI (9-15 Gy in 3 Gy fractions). Response was assessed by evaluating the degree of pain relief using a visual analog scale before radiotherapy, after f-WFRT, and after f-LFI. Results: Fractionated LFI following f-WFRT yielded an overall relief rate of 93.8% and a complete relief rate of 43.8%. The rate of the appearance of new disease was 6.3% for the patients with complete relief, 20.5% for the patients with a partial relief, and 50% for the patients with no relief. Conclusion: Fractionated LFI after f-WFRT is a well-tolerated and effective treatment for multiple metastatic bone disease.

Ki, Yongkan [Department of Radiation Oncology, Medical Research Institute, Pusan National University Hospital, Pusan National University School of Medicine, Busan (Korea, Republic of); Kim, Wontaek, E-mail: rokwt@hanmail.ne [Department of Radiation Oncology, Medical Research Institute, Pusan National University Hospital, Pusan National University School of Medicine, Busan (Korea, Republic of); Nam, Jiho; Kim, Donghyun; Jeon, Hosang; Park, Dahl; Kim, Dongwon [Department of Radiation Oncology, Medical Research Institute, Pusan National University Hospital, Pusan National University School of Medicine, Busan (Korea, Republic of)

2011-01-01

407

Influence of induced axial magnetic field on plasma dynamics and radiative characteristics of Z pinches.  

PubMed

The influence of an induced axial magnetic field on plasma dynamics and radiative characteristics of Z pinches is investigated. An axial magnetic field was induced in a novel Z-pinch load: a double planar wire array with skewed wires (DPWAsk), which represents a planar wire array in an open magnetic configuration. The induced axial magnetic field suppressed magneto-Rayleigh-Taylor (MRT) instabilities (with m = 0 and m = 1 instability modes) in the Z-pinch plasma. The influence of the initial axial magnetic field on the structure of the plasma column at stagnation was manifested through the formation of a more uniform plasma column compared to a standard double planar wire array (DPWA) load [V. L. Kantsyrev et al., Phys. Plasmas 15, 030704 (2008)]. The DPWAsk load is characterized by suppression of MRT instabilities and by the formation of the sub-keV radiation pulse that occurs before the main x-ray peak. Gradients in plasma parameters along the cathode-anode gap were observed and analyzed for DPWAsk loads made from low atomic number Z (Al) and mid-Z (brass) wires. PMID:22181284

Kantsyrev, V L; Esaulov, A A; Safronova, A S; Velikovich, A L; Rudakov, L I; Osborne, G C; Shrestha, I; Weller, M E; Williamson, K M; Stafford, A; Shlyaptseva, V V

2011-10-01

408

Influence of induced axial magnetic field on plasma dynamics and radiative characteristics of Z pinches  

SciTech Connect

The influence of an induced axial magnetic field on plasma dynamics and radiative characteristics of Z pinches is investigated. An axial magnetic field was induced in a novel Z-pinch load: a double planar wire array with skewed wires (DPWAsk), which represents a planar wire array in an open magnetic configuration. The induced axial magnetic field suppressed magneto-Rayleigh-Taylor (MRT) instabilities (with m = 0 and m = 1 instability modes) in the Z-pinch plasma. The influence of the initial axial magnetic field on the structure of the plasma column at stagnation was manifested through the formation of a more uniform plasma column compared to a standard double planar wire array (DPWA) load [V. L. Kantsyrev et al., Phys. Plasmas 15, 030704 (2008)]. The DPWAsk load is characterized by suppression of MRT instabilities and by the formation of the sub-keV radiation pulse that occurs before the main x-ray peak. Gradients in plasma parameters along the cathode-anode gap were observed and analyzed for DPWAsk loads made from low atomic number Z (Al) and mid-Z (brass) wires.

Kantsyrev, V. L.; Esaulov, A. A.; Safronova, A. S.; Osborne, G. C.; Shrestha, I.; Weller, M. E.; Stafford, A.; Shlyaptseva, V. V. [Physics Department, University of Nevada, Reno, Nevada 89557 (United States); Velikovich, A. L. [Plasma Physics Division, Naval Research Laboratory, Washington, D.C. 20375 (United States); Rudakov, L. I. [Icarus Research Inc., Bethesda, Maryland 20824 (United States); Williamson, K. M. [Physics Department, University of Nevada, Reno, Nevada 89557 (United States); Plasma Engineering Research Laboratory, Texas A and M University, Corpus Christi, TX 78412 (United States)

2011-10-15

409

Triple Collision and Close Triple Encounters  

NASA Astrophysics Data System (ADS)

In gravitational systems of point masses binary collisions are mathematically simple and well understood. Collisions of three or more particles are much more complicated, i.e. a dramatic increase of complexity occurs when the number N of particles involved in a collision increases from 2 to 3. Collisions of more than three particles seem to be of the same complexity as triple collisions. However, there are still unanswered questions concerning general N-body collisions.The reason for the complexity of triple collision is the inherent sensitivity to initial conditions for solutions passing near triple collision, even after a short time. Specifically, a solution passing near triple collision may change dramatically if the initial conditions prior to the close encounter are modified infinitesimally. In contrast, this is not the case for a binary collision.We use the planar three-body problem as a model in order to discuss the main features of triple collision of point masses and of its realistic counterpart, the close triple encounter. This comparatively simple model allows us to study all important aspects of close encounters of N > 2 gravitationally interacting point masses.In Chapters 1 and 2 we discuss classical results, beginning with the equations of motion, then studying relationships between the total angular momentum and triple collision. C. L. Siegel's famous series for triple collision solutions, one time considered the highlight of the theory of triple collision, conclude the traditional part of these lectures.Chapter 3 is devoted to studying the relationship between solutions engaging in a sharp triple collision and neighbouring solutions. The variational equation gives a rough idea of what is happening. A complete understanding can be achieved by means of R. McGehee's concept of the collision manifold, which arises by introducing special coordinates blowing up all possible states close to triple collision. In this context, possibilities of regularizing triple collision will be considered.The close triple encounter may be seen as a particle accelerator that allows to accelerate point masses to arbitrarily large velocities. This is the key to the existence of the long-sought non-collision singularities in the motion of a sufficient number of gravitationally interacting point masses.

Waldvogel, Joerg

410

Reciprocity theory of binary inelastic encounters  

NASA Astrophysics Data System (ADS)

Since the Direct Simulation Monte Carlo (DSMC) method has established itself as a standard technique for numerically computing rarefied gas flows it follows that to develop the theory of rarefied gas dynamics a framework for its fundamental microscopic processes needs to be formulated, i.e., intermolecular collisions and gas surface interactions, which lead to rigorous statistical models that can be utilized in the code. In this report, attention is focussed on the binary inelastic encounter for which a statistical theory is exposed based on the principle of reciprocity at equilibrium.

Agbormbai, Adolf A.

1989-08-01

411

Comet Hyakutake's close encounter with the Sun  

NASA Astrophysics Data System (ADS)

LASCO is a joint project between NRL (USA), the Max Planck Institut für Aeronomie (Germany), the Laboratoire d'Astronomie Spatiale (France), and the School of Physics and Space Research at the University of Birmingham (UK). "Such observations require a special instrument in space to suppress the glare of the Sun and reveal the comet and its tails", said Dr. Guenter Brueckner, NRL's principal investigator for LASCO. Scattering of sunlight in the Earth's atmosphere prevented good views from the ground during the comet's "perihelion passage" when it was closest to the Sun. The orbital period of Comet Hyakutake has been estimated to be 10,000 years. Hyakutake is called a "new" comet because it was not seen when, and if, it last visited the solar system. As Hyakutake approaches the Sun, it is being heated enormously. If this is the first visit of the comet, it could be broken into pieces, according to scientists. Images captured by the LASCO instrument have shown that this did not happen when the comet was in LASCO's field of view, which is approximately the size of the constellation Orion. "Comet Hyakutake could have passed through the solar system many times before", said Dr. Brueckner, who is also head of the NRL's Solar Physics Branch. "How many times remains a mystery". Hyakutake's orbit carries it back into the so-called "Oort Cloud" a vast collection of billions of comets that is located 1.4 light years away from the solar system. These comets are presumably the remnants of the cloud from which the solar system were formed billions of years ago. When the comet enters the outer atmosphere of the Sun, it begins to react with the Sun's environment and can be used as a "probe" of the solar corona. LASCO images show the head of the comet, and clearly visible are three separate tails that behave differently as Hyakutake swings around the Sun. These tails are made of different materials ; dust of different sizes, perhaps chunks of ice and atomic particles, each of which reacts differently with their environment. The heavy particles follow the comet in its orbit without being redirected by an outside force while the light dust particles are lining up away from the Sun and are driven by the Sun's intensive radiation. Finally, the atomic particles are repelled from the comet by the solar wind and presumably line up with the magnetic field of the solar corona. As the comet speeds through the corona at 37 miles per second, these forces have direct influence on its tails, which could clearly be seen changing their relative direction over the seven-day observation period. Coronal mass ejections were also observed by LASCO, in which hot gases were expelled and accelerated by the corona's magnetic field to travel through the interplanetary medium. A strong reaction between such a solar high-speed cloud and the portion of the comet's tails made of atomic particles is expected when Hyakutake crosses the equatorial plane of the Sun. The comet was out of LASCO's field of view during this crossing, but the scientists will have another opportunity when Hyakutake reappears from behind the Sun and can be seen later in the southern hemisphere's night sky with ordinary telescopes. Researchers expect to learn more about the tails of the comet and the surrounding solar corona with more detailed analysis. SOHO is a project of international cooperation between ESA and NASA. More information can be found on the LASCO Comet Hyakutake page on the World Wide Web http://lasco-www.nrl.navy.mil/b2-1996.html and on the SOHO home page http://sohowww.nascom.nasa.gov.

1996-05-01

412

Nonadiabatic behavior of the polarization of electric-field-induced Lyman-? radiation  

NASA Astrophysics Data System (ADS)

The linear polarization of Lyman-? radiation emitted when hydrogen atoms in the metastable 2s1/2 state traverse an external electric field is studied as a function of the effective rise time of the field for field strengths extending from very small values up to 6 keV/cm. With decreasing rise time, the measured polarization exhibits a transition from adiabatic to sudden behavior. The transition region is centered at a rise time which is approximately equal to the characteristic time associated with the 2s1/2-2p1/2 Lamb splitting in the unperturbed hydrogen system. The experimental data are well described by the results of a time-dependent theory.

Plotzke, O.; Wille, U.; Hippler, R.; Lutz, H. O.

1990-12-01

413

Relating the radiated piano sound field to the vibrational modes of the soundboard  

NASA Astrophysics Data System (ADS)

The sound field near a piano sound board is determined by moving a microphone over a grid of points above and below the sound board as well as in a plane in front of the piano using the experimental techniques of modal analysis with soundboard excitation at a bridge point by a swept sine signal. Since the standard modal analysis signal processing technique relies on tracking phase relations between excitation and response, it is possible to relate the sound field in terms of the vibrating structure which radiated it. Animations of sound board motion and sound field pressure variations are shown for the lowest four modes. It is noted that in all modes the locations of maximal excursion correlate with the sound pressure maxima or minima, respectively.

Hansen, Uwe J.; Bork, Ingolf; Rossing, Thomas D.

2003-10-01

414

Inverse method predicting spinning modes radiated by a ducted fan from free-field measurements.  

PubMed

In the study the inverse problem of deducing the modal structure of the acoustic field generated by a ducted turbofan is addressed using conventional farfield directivity measurements. The final objective is to make input data available for predicting noise radiation in other configurations that would not have been tested. The present paper is devoted to the analytical part of that study. The proposed method is based on the equations governing ducted sound propagation and free-field radiation. It leads to fast computations checked on Rolls-Royce tests made in the framework of previous European projects. Results seem to be reliable although the system of equations to be solved is generally underdetermined (more propagating modes than acoustic measurements). A limited number of modes are thus selected according to any a priori knowledge of the sources. A first guess of the source amplitudes is obtained by adjusting the calculated maximum of radiation of each mode to the measured sound pressure level at the same angle. A least squares fitting gives the final solution. A simple correction can be made to take account of the mean flow velocity inside the nacelle which shifts the directivity patterns. It consists of modifying the actual frequency to keep the cut-off ratios unchanged. PMID:15759694

Lewy, Serge

2005-02-01

415

Convergence of vector spherical wave expansion method applied to near-field radiative transfer.  

PubMed

Near-field radiative transfer between two objects can be computed using Rytov's theory of fluctuational electrodynamics in which the strength of electromagnetic sources is related to temperature through the fluctuation-dissipation theorem, and the resultant energy transfer is described using the dyadic Green's function of the vector Helmholtz equation. When the two objects are spheres, the dyadic Green's function can be expanded in a series of vector spherical waves. Based on comparison with the convergence criterion for the case of radiative transfer between two parallel surfaces, we derive a relation for the number of vector spherical waves required for convergence in the case of radiative transfer between two spheres. We show that when electromagnetic surface waves are active at a frequency the number of vector spherical waves required for convergence is proportional to Rmax/d when d/Rmax ? 0, where Rmax is the radius of the larger sphere, and d is the smallest gap between the two spheres. This criterion for convergence applies equally well to other near-field electromagnetic scattering problems. PMID:21747546

Sasihithlu, Karthik; Narayanaswamy, Arvind

2011-07-01

416

Radiating two-fluid universe coupled with rotation interacting with a scalar field  

NASA Astrophysics Data System (ADS)

The solution of three new interesting studies, a rotating anisotropic two-fluid universe coupled with radiation and a scalar field, are studied here, where the anisotropic pressure is generated by the presence of two non-interacting perfect fluids which are in relative motion with respect to each other. In this problem, special discussion is made of the physically interesting class of models in which one fluid is a perfect comoving radiative fluid which is taken to model the cosmic microwave background and the second a perfect non-comoving fluid which will model the observed material content of the universe. Studying the different aspects of these model universes, the role of the radiation and scalar fields in defining the physical and dynamical properties of these models is specifically discussed. Analysis of the rotational perturbations is also made, in the course of which the amount of anisotropy induced in the pressure distribution by a small deviation from the Friedmann metric is also investigated, and it is observed that such anisotropies could grow faster than the expansion of the universe. All the models obtained in this problem are found to be theoretically satisfactory and thereby substantiate the possibilities of the existence of such astrophysical objects in this universe.

Manihar Singh, Koijam; Priyokumar Singh, Kangujam; Jairam Singh, Thiyam

2011-03-01

417

Twisted pair of optic fibers for background removal in radiation fields.  

PubMed

In many situations in which an optic fiber carries a signal through a radiation field, an unwanted background signal is produced consisting of fluorescent and/or Cerenkov light. This presents a major problem in the measurement of the light signal, for example, in scintillation dosimetry of medical therapeutic beams. In this paper, we demonstrate a new method of measuring and removing the background signal through the use of a twisted pair of optic fibers. The twisted pair consists of a fiber carrying the scintillation signal that is twisted with a second optic fiber to form a double helix. The two twisted fibers will experience the same radiation environment provided the periodicity of the twist is correlated to the dose rate gradient. An expression for the required twist periodicity is presented. A scintillation dosimeter with a twisted pair optic fiber was tested in a megavoltage beam and found to accurately measure its beam characteristics. The twisted pair approach is not restricted to medical applications and can be used in many situations in which optical signals are carried through radiation fields. PMID:23913071

Liu, P Z Y; Suchowerska, N; McKenzie, D R

2013-08-01

418

Inverse method predicting spinning modes radiated by a ducted fan from free-field measurements  

NASA Astrophysics Data System (ADS)

In the study the inverse problem of deducing the modal structure of the acoustic field generated by a ducted turbofan is addressed using conventional farfield directivity measurements. The final objective is to make input data available for predicting noise radiation in other configurations that would not have been tested. The present paper is devoted to the analytical part of that study. The proposed method is based on the equations governing ducted sound propagation and free-field radiation. It leads to fast computations checked on Rolls-Royce tests made in the framework of previous European projects. Results seem to be reliable although the system of equations to be solved is generally underdetermined (more propagating modes than acoustic measurements). A limited number of modes are thus selected according to any a priori knowledge of the sources. A first guess of the source amplitudes is obtained by adjusting the calculated maximum of radiation of each mode to the measured sound pressure level at the same angle. A least squares fitting gives the final solution. A simple correction can be made to take account of the mean flow velocity inside the nacelle which shifts the directivity patterns. It consists of modifying the actual frequency to keep the cut-off ratios unchanged. .

Lewy, Serge

2005-02-01

419

Near-field radiative transfer between two unequal sized spheres with large size disparities.  

PubMed

We compute near-field radiative transfer between two spheres of unequal radii R1 and R2 such that R2 ? 40R1. For R2 = 40R1, the smallest gap to which we have been able to compute radiative transfer is d = 0.016R1. To accomplish these computations, we have had to modify existing methods for computing near-field radiative transfer between two spheres in the following ways: (1) exact calculations of coefficients of vector translation theorem are replaced by approximations valid for the limit d ? R1, and (2) recursion relations for a normalized form of translation coefficients are derived which enable us to replace computations of spherical Bessel and Hankel functions by computations of ratios of spherical Bessel or spherical Hankel functions. The results are then compared with the predictions of the modified proximity approximation. PMID:24977544

Sasihithlu, Karthik; Narayanaswamy, Arvind

2014-06-16

420

Experimental determination of radiated internal wave power without pressure field data  

NASA Astrophysics Data System (ADS)

We present a method to determine, using only velocity field data, the time-averaged energy flux <{J}> and total radiated power P for two-dimensional internal gravity waves. Both <{J}> and P are determined from expressions involving only a scalar function, the stream function ?. We test the method using data from a direct numerical simulation for tidal flow of a stratified fluid past a knife edge. The results for the radiated internal wave power given by the stream function method agree to within 0.5% with results obtained using pressure and velocity data from the numerical simulation. The results for the radiated power computed from the stream function agree well with power computed from the velocity and pressure if the starting point for the stream function computation is on a solid boundary, but if a boundary point is not available, care must be taken to choose an appropriate starting point. We also test the stream function method by applying it to laboratory data for tidal flow past a knife edge, and the results are found to agree with the direct numerical simulation. The supplementary material includes a Matlab code with a graphical user interface that can be used to compute the energy flux and power from two-dimensional velocity field data.

Lee, Frank M.; Paoletti, M. S.; Swinney, Harry L.; Morrison, P. J.

2014-04-01

421

Fast-cooling synchrotron radiation in a decaying magnetic field and ?-ray burst emission mechanism  

NASA Astrophysics Data System (ADS)

Synchrotron radiation of relativistic electrons is an important radiation mechanism in many astrophysical sources. In the sources where the synchrotron cooling timescale is shorter than the dynamical timescale, electrons are cooled down below the minimum injection energy. It has been believed that such `fast cooling’ electrons have a power-law distribution in energy with an index -2, and their synchrotron radiation has a photon spectral index-1.5. On the other hand, in a transient expanding astrophysical source, such as a ?-ray burst (GRB), the magnetic field strength in the emission region continuously decreases with radius. Here we study such a system, and find that in a certain parameter regime, the fast-cooling electrons can have a harder energy spectrum. We apply this new physical regime to GRBs, and suggest that the GRB prompt emission spectra whose low-energy photon spectral index has a typical value-1 could be due to synchrotron radiation in this moderately fast-cooling regime.

Uhm, Z. Lucas; Zhang, Bing

2014-05-01