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1

Development and Characterization of a High Throughput Screen to investigate the delayed Effects of Radiations Commonly Encountered in Space  

NASA Astrophysics Data System (ADS)

Astronauts based on the space station or on long-term space missions will be exposed to high Z radiations in the cosmic environment In order to evaluate the potentially deleterious effects of exposure to radiations commonly encountered in space we have developed and characterized a high throughput assay to detect mutation deletion events and or hyperrecombination in the progeny of exposed cells This assay is based on a plasmid vector containing a green fluorescence protein reporter construct We have shown that after stable transfection of the vector into human or hamster cells this construct can identify mutations specifically base changes and deletions as well as recombination events e g gene conversion or homologous recombination occurring as a result of exposure to ionizing radiation Our focus has been on those events occurring in the progeny of an irradiated cell that are potentially associated with radiation induced genomic instability rather than the more conventional assays that evaluate the direct immediate effects of radiation exposure Considerable time has been spent automating analysis of surviving colonies as a function of time after irradiation in order to determine when delayed instability is induced and the consequences of this delayed instability The assay is now automated permitting the evaluation of potentially rare events associated with low dose low dose rate radiations commonly encountered in space

Morgan, W. F.

2

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. 4 figs.

Thacker, L.H.

1995-10-17

3

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. 4 figs.

Thacker, L.H.

1994-08-16

4

Semianalytical estimates of scattering thresholds and gravitational radiation in ultrarelativistic black hole encounters  

SciTech Connect

Ultrarelativistic collisions of black holes are ideal gedanken experiments to study the nonlinearities of general relativity. In this paper we use semianalytical tools to better understand the nature of these collisions and the emitted gravitational radiation. We explain many features of the energy spectra extracted from numerical relativity simulations using two complementary semianalytical calculations. In the first calculation we estimate the radiation by a 'zero-frequency limit' analysis of the collision of two point particles with finite impact parameter. In the second calculation we replace one of the black holes by a point particle plunging with arbitrary energy and impact parameter into a Schwarzschild black hole, and we explore the multipolar structure of the radiation paying particular attention to the near-critical regime. We also use a geodesic analogy to provide qualitative estimates of the dependence of the scattering threshold on the black hole spin and on the dimensionality of the spacetime.

Berti, Emanuele [Department of Physics and Astronomy, The University of Mississippi, University, Mississippi 38677 (United States); California Institute of Technology, Pasadena, California 91109 (United States); Cardoso, Vitor [Department of Physics and Astronomy, University of Mississippi, University, Mississippi 38677 (United States); CENTRA, Departamento de Fisica, Instituto Superior Tecnico, Avenida Rovisco Pais 1, 1049 Lisboa (Portugal); Hinderer, Tanja [California Institute of Technology, Pasadena, California 91109 (United States); Lemos, Madalena [CENTRA, Departamento de Fisica, Instituto Superior Tecnico, Avenida Rovisco Pais 1, 1049 Lisboa (Portugal); Pretorius, Frans; Yunes, Nicolas [Department of Physics, Princeton University, Princeton, New Jersey 08544 (United States); Sperhake, Ulrich [Department of Physics and Astronomy, The University of Mississippi, University, Mississippi 38677 (United States); California Institute of Technology, Pasadena, California 91109 (United States); Institut de Ciencies de l'Espai (CSIC-IEEC), Facultat de Ciencies, Campus UAB, Torre C5 parells, Bellaterra, 08193 (Spain)

2010-05-15

5

Small fields: Nonequilibrium radiation dosimetry  

SciTech Connect

Advances in radiation treatment with beamlet-based intensity modulation, image-guided radiation therapy, and stereotactic radiosurgery (including specialized equipments like CyberKnife, Gamma Knife, tomotherapy, and high-resolution multileaf collimating systems) have resulted in the use of reduced treatment fields to a subcentimeter scale. Compared to the traditional radiotherapy with fields {>=}4x4 cm{sup 2}, this can result in significant uncertainty in the accuracy of clinical dosimetry. The dosimetry of small fields is challenging due to nonequilibrium conditions created as a consequence of the secondary electron track lengths and the source size projected through the collimating system that are comparable to the treatment field size. It is further complicated by the prolonged electron tracks in the presence of low-density inhomogeneities. Also, radiation detectors introduced into such fields usually perturb the level of disequilibrium. Hence, the dosimetric accuracy previously achieved for standard radiotherapy applications is at risk for both absolute and relative dose determination. This article summarizes the present knowledge and gives an insight into the future procedures to handle the nonequilibrium radiation dosimetry problems. It is anticipated that new miniature detectors with controlled perturbations and corrections will be available to meet the demand for accurate measurements. It is also expected that the Monte Carlo techniques will increasingly be used in assessing the accuracy, verification, and calculation of dose, and will aid perturbation calculations of detectors used in small and highly conformal radiation beams.

Das, Indra J.; Ding, George X.; Ahnesjoe, Anders [Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States); Department of Radiation Oncology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232 (United States); Department of Oncology, Radiology and Clinical Immunology, Section of Oncology, Uppsala University, S-751 85 Uppsala and Nucletron AB, S-751 47 Uppsala (Sweden)

2008-01-15

6

Fields radiated by electrostatic discharges  

NASA Astrophysics Data System (ADS)

Electrostatic discharge (ESD) fields are examined both analytically and experimentally. Measurements indicate that the electric fields can be quite significant (150 V/m or more at a distance of 1.5 m, for example) for short periods of time (a few nanoseconds), particularly for relatively low-voltage events (6 kV or less). A relatively simple dipole model for an ESD spark is developed and used to predict the radiated fields. The agreement between theory and experiment is fair. The model may be used to predict ESD fields for a wide range of possible configurations, particularly in the near-field zone where no measurements are presently available.

Wilson, Perry F.; Ma, M. T.

1991-02-01

7

Relativistic theory for radiative forward electron emission in heavy ion-atom encounters  

NASA Astrophysics Data System (ADS)

The forward electron emission with simultaneous photon production during the scattering of relativistic, highly stripped projectiles from light target atoms is calculated within the Dirac theory. The method of calculation is a simplification of the impulse approximation and is based on the relation of the cross section for radiative capture to continuum of loosely bound electrons to the frame-transformed electron bremsstrahlung cross section. It is demonstrated that such an approximation is well justified in a large region of energies and photon emission angles, with the exception of the extreme forward and backward emission and the soft-photon energy limit. The cusp spectrum and the corresponding angular distribution are compared to recent experimental data for the collision system 90.38 MeV/amu U88+ + N2.

Jakubaßa-Amundsen, Doris; Müller, Robert; Surzhykov, Andrey; Yerokhin, Vladimir

2014-12-01

8

Electrifying Encounters  

NSDL National Science Digital Library

In this "electrifying encounter," fifth-grade students teamed up with elementary education students for a celebration of science and technology learning. A problem-solving-through-technology approach was used to give the preservice teachers valuable exper

Ebbers, Margaretha; Cross, Sandy

1999-09-01

9

In situ observations of reconnection Hall magnetic fields at Mars: Evidence for ion diffusion region encounters  

E-print Network

In situ observations of reconnection Hall magnetic fields at Mars: Evidence for ion diffusion. [1] We present Mars Global Surveyor measurements of bipolar out-of-plane magnetic fields at current (2009), In situ observations of reconnection Hall magnetic fields at Mars: Evidence for ion diffusion

California at Berkeley, University of

10

Quasi light fields: Extending the light field to coherent radiation  

E-print Network

Imaging technologies such as dynamic viewpoint generation are engineered for incoherent radiation using the traditional light field, and for coherent radiation using electromagnetic field theory. We present a model of ...

Accardi, Anthony J.

11

Quasi light fields: extending the light field to coherent radiation  

E-print Network

Quasi light fields: extending the light field to coherent radiation Anthony Accardi1,2 and Gregory light field, and for coherent radiation using electromagnetic field theory. We present a model of coherent image formation that strikes a balance between the utility of the light field

Wornell, Gregory W.

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. PMID:24885471

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

Nonclassical correlation properties of radiation fields  

E-print Network

A full characterization of nonclassical space-time dependent correlations of radiation is formulated in terms of normally and time-ordered field correlation functions. It describes not only the properties of initially prepared multimode radiation fields, but also the dynamics of radiation sources. Some of these correlation effects occur in the resonance fluorescence of a single two-level atom.

Werner Vogel

2008-01-12

15

Gravitational waves from galaxy encounters  

SciTech Connect

We discuss the emission of gravitational radiation produced in encounters of dark matter galactic halos. To this aim we perform a number of numerical simulations of typical galaxy mergers, computing the associated gravitational radiation waveforms as well as the energy released in the processes. Our simulations yield dimensionless gravitational wave amplitudes of the order of 10{sup -13} and gravitational wave frequencies of the order of 10{sup -16} Hz, when the galaxies are located at a distance of 10 Mpc. These values are of the same order as those arising in the gravitational radiation originated by strong variations of the gravitational field in the early Universe, and therefore, such gravitational waves cannot be directly observed by ground-based detectors. We discuss the feasibility of an indirect detection by means of the B-mode polarization of the cosmic microwave background (CMB) induced by such waves. Our results show that the gravitational waves from encounters of dark matter galactic halos leave much too small an imprint on the CMB polarization to be actually observed with ongoing and future missions.

Quilis, Vicent; Saez, Diego; Font, Jose A. [Departament d'Astronomia i Astrofisica, Universitat de Valencia, Dr. Moliner 50, 46100 Burjassot (Valencia) (Spain); Gonzalez-Garcia, A. Cesar [Instituto de Astrofisica de Canarias, Via Lactea s/n, La Laguna, 38200 (Spain); Departamento de Fisica Teorica, C-XI, Universidad Autonoma de Madrid, Madrid, 28049 (Spain)

2007-05-15

16

Gravitational waves from galaxy encounters  

E-print Network

We discuss the emission of gravitational radiation produced in encounters of dark matter galactic halos. To this aim we perform a number of numerical simulations of typical galaxy mergers, computing the associated gravitational radiation waveforms as well as the energy released in the processes. Our simulations yield dimensionless gravitational wave amplitudes of the order of $10^{-13}$ and gravitational wave frequencies of the order of $10^{-16}$ Hz, when the galaxies are located at a distance of 10 Mpc. These values are of the same order as those arising in the gravitational radiation originated by strong variations of the gravitational field in the early Universe, and therefore, such gravitational waves cannot be directly observed by ground-based detectors. We discuss the feasibility of an indirect detection by means of the B-mode polarization of the Cosmic Microwave Background (CMB) induced by such waves. Our results show that the gravitational waves from encounters of dark matter galactic halos leave much too small an imprint on the CMB polarization to be actually observed with ongoing and future missions.

V. Quilis; A. C. González-García; D. Sáez; J. A. Font

2007-04-23

17

Radiation Q of dipole-generated fields  

NASA Astrophysics Data System (ADS)

The radiation Q of several dipole fields in free space are determined using the time-dependent Poynting theorem. Earlier works on this subject, recently summarized by McLean [1996], are based upon the complex Poynting theorem. It was previously shown [Grimes and Grimes, 1997] that the full complex Poynting theorem is correct only for single-mode radiation fields. The time-dependent theorem shows that three numbers are necessary to completely specify time-varying power, and complex numbers supply but two; the third piece of information, a phase, is discarded when complex notation is formed. Omissions inherent in the complex Poynting theorem affect the calculated value of standing energy about an antenna and hence the calculated value of Q. To avoid such omissions, we develop a method of determining Q based upon the time-dependent Poynting theorem that builds upon and extends our earlier work [Grimes and Grimes, 1997]. The purposes of this paper are to (1) provide a time domain basis for calculating Q in mixed modal radiation fields, (2) determine the Q of electric and magnetic dipoles, alone and in combination, and (3) demonstrate how source structure and relative phasing affect the physics of several combinations of electric and magnetic dipole radiation fields. The primary conclusion of this work is that the minimum possible Q of a radiation source established by Chu [1948] does not extend to properly mixed and phased multimodal radiation fields. A radiation source is presented for which, by our analysis, the radiation Q is zero.

Grimes, Dale M.; Grimes, Craig A.

1999-03-01

18

Harmonic undulator radiations with constant magnetic field  

NASA Astrophysics Data System (ADS)

Harmonic undulators has been analysed in the presence of constant magnetic field along the direction of main undulator field. The spectrum modifications in harmonic undulator radiations and intensity degradation as a function of constant magnetic field magnitude at fundamental and third harmonics have been evaluated with a numerical integration method and generalised Bessel function. The role of harmonic field to overcome the intensity reduction due to constant magnetic field and energy spread in electron beam has also been demonstrated.

Jeevakhan, Hussain; Mishra, G.

2015-01-01

19

Scattering by an electromagnetic radiation field  

E-print Network

Motion of test particles in the gravitational field associated with an electromagnetic plane wave is investigated. The interaction with the radiation field is modeled by a force term {\\it \\`a la} Poynting-Robertson entering the equations of motion given by the 4-momentum density of radiation observed in the particle's rest frame with a multiplicative constant factor expressing the strength of the interaction itself. Explicit analytical solutions are obtained. Scattering of fields by the electromagnetic wave, i.e., scalar (spin 0), massless spin $\\frac12$ and electromagnetic (spin 1) fields, is studied too.

Donato Bini; Andrea Geralico

2014-08-21

20

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

21

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

22

Monte Carlo Simulation of the Radiation Environment Encountered by a Biochip During a Space Mission to Mars  

NASA Astrophysics Data System (ADS)

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.

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

23

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

24

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

25

Chiral-field microwave antennas (Chiral microwave near fields for far-field radiation)  

E-print Network

In a single-element structure we obtain a radiation pattern with a squint due to chiral microwave near fields originated from a magnetostatic-mode ferrite disk. At the magnetostatic resonances, one has strong subwavelength localization of energy of microwave radiation. Magnetostatic oscillations in a thin ferrite disk are characterized by unique topological properties: the Poynting-vector vortices and the field helicity. The chiral-topology near fields allow obtaining unique phase structure distribution for far-field microwave radiation.

Kamenetskii, E O; Shavit, R

2015-01-01

26

Radiation Effects on Current Field Programmable Technologies  

NASA Technical Reports Server (NTRS)

Manufacturers of field programmable gate arrays (FPGAS) take different technological and architectural approaches that directly affect radiation performance. Similar y technological and architectural features are used in related technologies such as programmable substrates and quick-turn application specific integrated circuits (ASICs). After analyzing current technologies and architectures and their radiation-effects implications, this paper includes extensive test data quantifying various devices total dose and single event susceptibilities, including performance degradation effects and temporary or permanent re-configuration faults. Test results will concentrate on recent technologies being used in space flight electronic systems and those being developed for use in the near term. This paper will provide the first extensive study of various configuration memories used in programmable devices. Radiation performance limits and their impacts will be discussed for each design. In addition, the interplay between device scaling, process, bias voltage, design, and architecture will be explored. Lastly, areas of ongoing research will be discussed.

Katz, R.; LaBel, K.; Wang, J. J.; Cronquist, B.; Koga, R.; Penzin, S.; Swift, G.

1997-01-01

27

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

28

Haemopoietic cell renewal in radiation fields  

NASA Astrophysics Data System (ADS)

Space flight activities are inevitably associated with a chronic exposure of astronauts to a complex mixture of ionising radiation. Although no acute radiation consequences are to be expected as a rule, the possibility of Solar Particle Events (SPE) associated with relatively high doses of radiation (1 or more Gray) cannot be excluded. It is the responsibility of physicians in charge of the health of astronauts to evaluate before, during and after space flight activities the functional status of haemopoietic cell renewal. Chronic low level exposure of dogs indicate that daily gamma-exposure doses below about 2 cGy are tolerated for several years as far as blood cell concentrations are concerned. However, the stem cell pool may be severely affected. The maintenance of sufficient blood cell counts is possible only through increased cell production to compensate for the radiation inflicted excess cell loss. This behaviour of haemopoietic cell renewal during chronic low level exposure can be simulated by bioengineering models of granulocytopoiesis. It is possible to define a ``turbulence region'' for cell loss rates, below which an prolonged adaptation to increased radiation fields can be expected to be tolerated. On the basis of these experimental results, it is recommended to develop new biological indicators to monitor haemopoietic cell renewal at the level of the stem cell pool using blood stem cells in addition to the determination of cytokine concentrations in the serum (and other novel approaches). To prepare for unexpected haemopoietic effects during prolonged space missions, research should be increased to modify the radiation sensitivity of haemopoietic stem cells (for instance by the application of certain regulatory molecules). In addition, a ``blood stem cell bank'' might be established for the autologous storage of stem cells and for use in space activities keeping them in a radiation protected container.

Fliedner, T. M.; Nothdurft, W.; Tibken, B.; Hofer, E.; Weiss, M.; Kindler, H.

1994-10-01

29

Competition Between Gravitational and Scalar Field Radiation  

NASA Astrophysics Data System (ADS)

Recent astrophysical observations have provided strong evidence that the present expansion of the universe is accelerating, powered by the energy density associated with a cosmological term. Assuming the latter to be not simply a constant term but a ``quintessence'' field, we study the radiation of quanta of such a quintessence field (``quintons'') by binary systems of different types and compare intensities to those of standard tensor gravitational wave emission. We consider both the case in which the quintessence field varies only over cosmological distances and the case in which it is modified spatially by (strong) gravitational fields, a condition that results in bounds on the gradient of the scalar field. We show that, in both the first case and, because of a bound we derive from the Hulse-Taylor pulsar, in the second, there is not sufficient quinton radiation to affect expected LISA and LIGO gravity wave signals from binary systems. We show that in the second case, the Large Hadron Collider is capable of setting a bound similar to that from the binary pulsar.

Kazanas, Demosthenes; Teplitz, Vigdor L.

2004-02-01

30

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

31

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

32

Near-field radiative cooling of nanostructures.  

PubMed

We measure near-field radiative cooling of a thermally isolated nanostructure up to a few degrees and show that in principle this process can efficiently cool down localized hotspots by tens of degrees at submicrometer gaps. This process of cooling is achieved without any physical contact, in contrast to heat transfer through conduction, thus enabling novel cooling capabilities. We show that the measured trend of radiative cooling agrees well theoretical predictions and is limited mainly by the geometry of the probe used here as well as the minimum separation that could be achieved in our setup. These results also pave the way for realizing other new effects based on resonant heat transfer, like thermal rectification and negative thermal conductance. PMID:22891815

Guha, Biswajeet; Otey, Clayton; Poitras, Carl B; Fan, Shanhui; Lipson, Michal

2012-09-12

33

Virtual radiation fields for ALARA determination  

SciTech Connect

As computing power has increased, so too has the ability to model and simulate complex systems and processes. In addition, virtual reality technology has made it possible to visualize and understand many complex scientific and engineering problems. For this reason, a virtual dosimetry program called Virtual Radiation Fields (VRF) is developed to model radiation dose rate and cumulative dose to a receptor operating in a virtual radiation environment. With the design and testing of many facilities and products taking place in the virtual world, this program facilitates the concurrent consideration of radiological concerns during the design process. Three-dimensional (3D) graphical presentation of the radiation environment is made possible through the use of IGRIP, a graphical modeling program developed by Deneb Robotics, Inc. The VRF simulation program was designed to model and display a virtual dosimeter. As a demonstration of the program`s capability, the Hanford tank, C-106, was modeled to predict radiation doses to robotic equipment used to remove radioactive waste from the tank. To validate VRF dose predictions, comparison was made with reported values for tank C-106, which showed agreement to within 0.5%. Graphical information is presented regarding the 3D dose rate variation inside the tank. Cumulative dose predictions were made for the cleanup operations of tank C-106. A four-dimensional dose rate map generated by VRF was used to model the dose rate not only in 3D space but also as a function of the amount of waste remaining in the tank. This allowed VRF to predict dose rate at any stage in the waste removal process for an accurate simulation of the radiological conditions throughout the tank cleanup procedure.

Knight, T.W.

1995-12-31

34

Radiation reaction in strong field QED  

NASA Astrophysics Data System (ADS)

We derive radiation reaction from QED in a strong background field. We identify, in general, the diagrams and processes contributing to recoil effects in the average momentum of a scattered electron, using perturbation theory in the Furry picture: we work to lowest nontrivial order in ?. For the explicit example of scattering in a plane wave background, we compare QED with classical electrodynamics in the limit ??0, finding agreement with the Lorentz-Abraham-Dirac and Landau-Lifshitz equations, and with Larmor's formula. The first quantum corrections are also presented.

Ilderton, Anton; Torgrimsson, Greger

2013-10-01

35

Electromagnetic radiation by quark-gluon plasma in magnetic field  

E-print Network

The electromagnetic radiation by quark-gluon plasma in strong magnetic field is calculated. The contributing processes are synchrotron radiation and one--photon annihilation. It is shown that in relativistic heavy--ion collisions at RHIC and LHC synchrotron radiation dominates over the annihilation. Moreover, it constitutes a significant part of all photons produced by the plasma at low transverse momenta; its magnitude depends on the plasma temperature and the magnetic field strength. Electromagnetic radiation in magnetic field is probably the missing piece that resolves a discrepancy between the theoretical models and the experimental data. It is argued that electromagnetic radiation increases with the magnetic field strength and plasma temperature.

Kirill Tuchin

2012-06-03

36

A method for characterizing photon radiation fields  

SciTech Connect

Uncertainty in dosimetric and exposure rate measurements can increase in areas where multi-directional and low-energy photons (< 100 keV) exist because of variations in energy and angular measurement response. Also, accurate measurement of external exposures in spatially non-uniform fields may require multiple dosimetry. Therefore, knowledge of the photon fields in the workplace is required for full understanding of the accuracy of dosimeters and instruments, and for determining the need for multiple dosimeters. This project was designed to develop methods to characterize photon radiation fields in the workplace, and to test the methods in a plutonium facility. The photon field at selected work locations was characterized using TLDs and a collimated NaI(Tl) detector from which spatial variations in photon energy distributions were calculated from measured spectra. Laboratory results showed the accuracy and utility of the method. Field measurement results combined with observed work patterns suggested the following: (1) workers are exposed from all directions, but not isotropically, (2) photon energy distributions were directionally dependent, (3) stuffing nearby gloves into the glovebox reduced exposure rates significantly, (4) dosimeter placement on the front of the chest provided for a reasonable estimate of the average dose equivalent to workers` torsos, (5) justifiable conclusions regarding the need for multiple dosimetry can be made using this quantitative method, and (6) measurements of the exposure rates with ionization chambers pointed with open beta windows toward the glovebox provided the highest measured rates, although absolute accuracy of the field measurements still needs to be assessed.

Whicker, J.J.; Hsu, H.H. [Los Alamos National Lab., NM (United States); Hsieh, F.H.; Borak, T.B. [Colorado State Univ., Fort Collins, CO (United States). Dept. of Radiological Health Sciences

1999-04-01

37

Electromagnetic field radiation model for lightning strokes to tall structures  

Microsoft Academic Search

This paper describes observation and analysis of electromagnetic field radiation from lightning strokes to tall structures. Electromagnetic field waveforms and current waveforms of lightning strokes to the CN Tower have been simultaneously measured since 1991. A new calculation model of electromagnetic field radiation is proposed. The proposed model consists of the lightning current propagation and distribution model and the electromagnetic

H. Motoyama; W. Janischewskyj; A. M. Hussein; W. A. Chisholm; J. S. Chang; R. Rusan

1996-01-01

38

Scattering of particles by radiation fields: a comparative analysis  

E-print Network

The features of the scattering of massive neutral particles propagating in the field of a gravitational plane wave are compared with those characterizing their interaction with an electromagnetic radiation field. The motion is geodesic in the former case, whereas in the case of an electromagnetic pulse it is accelerated by the radiation field filling the associated spacetime region. The interaction with the radiation field is modeled by a force term entering the equations of motion proportional to the 4-momentum density of radiation observed in the particle's rest frame. The corresponding classical scattering cross sections are evaluated too.

Donato Bini; Andrea Geralico; Maria Haney; Robert T. Jantzen

2014-08-22

39

Light-Cone Effect of Radiation Fields in Cosmological Radiative Transfer Simulations  

E-print Network

We present a novel method to implement time-delayed propagation of radiation fields in cosmological radiative transfer simulations. Time-delayed propagation of radiation fields requires construction of retarded-time fields by tracking the location and lifetime of radiation sources along the corresponding light-cones. Cosmological radiative transfer simulations have, until now, ignored this "light-cone effect" or implemented ray-tracing methods that are computationally demanding. We show that radiative transfer calculation of the time-delayed fields can be easily achieved in numerical simulations when periodic boundary conditions are used, by calculating the time-discretized retarded-time Green's function using the Fast Fourier Transform (FFT) method and convolving it with the source distribution. We also present a direct application of this method to the long-range radiation field of Lyman-Werner band photons, which is important in the high-redshift astrophysics with first stars.

Ahn, Kyungjin

2015-01-01

40

Near-Field Radiative Cooling of Nanostructures Biswajeet Guha,  

E-print Network

Near-Field Radiative Cooling of Nanostructures Biswajeet Guha, Clayton Otey, Carl B. Poitras, Shanhui Fan, and Michal Lipson*,,§ School of Electrical and Computer Engineering, Cornell University 14853, United States *S Supporting Information ABSTRACT: We measure near-field radiative cooling

Lipson, Michal

41

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

42

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. PMID:23918373

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

2013-01-01

43

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

44

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

45

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

46

Radiation of Electron in the Field of Plane Light Wave  

Microsoft Academic Search

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

I. Drebot; Yu. Grigor'ev; A. Zelinsky; O. Zvonar'ova; R. Tatchyn

2005-01-01

47

Radiation of Electron in the Field of Plane Light Wave  

Microsoft Academic Search

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. Zelinsky; I. V. Drebot; Yu. N. Grigorev; O. D. Zvonareva; R. Tatchyn

2006-01-01

48

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

49

Comments on 'Cellular response to modulated radiation fields'.  

PubMed

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. PMID:19204382

Ross, C K; Klassen, N V

2009-03-01

50

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

51

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

52

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. 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

53

Formation of neutron fields for radiation technologies  

NASA Astrophysics Data System (ADS)

The article considers the problem of forming a neutron field in the experimental channels of the water-cooled research reactors. Using the software package MCU5 we calculated a neutron field in different moderators which the experimental channel passes through. It is shown that the most appropriate moderator for neutron transmutation doping is the beryllium. The optimal location of the channel in the moderator was determined.

Varlachev, V. A.; Emets, E. G.; Kuznetsov, S. I.; Bogdan, A. M.; Varlacheva, N. V.

2014-11-01

54

Radiation fields of helical antenna in compressible electron plasma  

Microsoft Academic Search

Expressions for the radiation fields in a compressible electron plasma medium are derived pertaining to the helical antenna of finite size immersed in it. The current distribution on the helical antenna is assumed to be an out-going travelling wave with an arbitrary phase propagation constant. From these general expressions fields of circular loop and linear antennas can be deduced as

V. L. TALEKAR; K. R. SONI

1974-01-01

55

Electron trajectories in pulsed radiation fields  

SciTech Connect

The work reported here analyzes the dynamical behavior of an electron, initially at rest, when subjected to a radiation pulse of arbitrary, but integrable, shape. This is done by a general integration procedure that has been programmed in VAXIMA. Upon choosing a specific shape for the pulse, VAXIMA finds both the space-time trajectory and the four-momentum of the electron. These are obtained in analytic or numerical form - or both - at the choice of the user. Several examples of analytical and numerical solutions, for different pulse shapes, are given.

Einwohner, T.; Lippmann, B.A.

1987-05-01

56

Voyager Encounter Highlights  

NASA Technical Reports Server (NTRS)

The following are presented: computer animation of trajectories for both Voyagers 1 and 2; view of Jupiter during one orbit of Ganymede; computer animation of Voyager 2's encounter with Jupiter and its satellites; time lapse of the planet's rotation and its satellites; stroboscopic sequence of selected frames; cloud motion; Jupiter's Great Red Spot (4/25 - 5/24, 1979) through a violet filter; and the Great Red Spot through a blue filter by Voyager 1. The dynamics of Jupiter's clouds are shown - the whole planet is shown first, then two closer looks are repeated several times. Also included are pans of stills of Jupiter's satellites and a computer simulation tour of Saturn system from POV just behind Voyager, made of 116 images of Saturn through a green filter and of 516 images taken by Voyager 1 (9/12 - 9/14, 1980). Frames are enhanced to show the motion of features in Saturn's rings. Pans of stills of Saturn's satellites are shown. There is computer animation of the planet's system, rings, and Sigma Sagittari. Images on January 14, 1986 are through an orange filter. Uranus's satellites are shown as is computer animation of an August 1989 encounter.

1989-01-01

57

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

58

Synchrotron radiation in strongly coupled conformal field theories  

NASA Astrophysics Data System (ADS)

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 ?˜1/?. 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; Nickel, Dominik; Rajagopal, Krishna

2010-06-01

59

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

60

Teacher Educators Using Encounter Stories  

ERIC Educational Resources Information Center

Many prospective teachers are unaware of the encounters that Black, heterosexual women or White lesbians face. Here, we present encounter stories--individual narratives of poignant encounters and interactions that we have experienced with people unlike us--to identify with and ultimately draw on their experiences. Subsequently, the narratives…

Davis, Danné E.; Kellinger, Janna Jackson

2014-01-01

61

Towards Synchrotron Radiation Theory In Curved Magnetic Field Lines  

NASA Astrophysics Data System (ADS)

The radiation emission mechanism from an ultrarelativistic charged particle moving in a curved inhomogeneous magnetic field is analyzed. The power, angular distribution, spectral distribution and polarization properties of the radiation are obtained. Using a more accurate (than in drift approximation) particle's trajectory, we generalize the formulae for synchrocurvature radiation, which have been obtained earlier in [1-4], find out conditions of applicability and reveal new features of synchrocurvature radiation mechanism. Particularly, when the particle's velocity along magnetic field lines tends to the speed of light, there is a band of instantaneous characteristic frequencies instead of a single characteristic frequency for synchrotron or curvature radiation. If the velocity of centrifugal drift is approximately equal to the velocity of Larmor rotation, then it is necessary to use the formulae of synchrocurvature radiation mechanism. The conditions for applicability this radiation mechanism in radio sources are considered. 1. Cheng K.S., Zhang J.L. 1996, ApJ., 463, 271 2. Harko T., Cheng K.S., 2002, MNRAS, 335, 99 3. Sobolev Ya.M., 2000, Problems Atomic Sci. Technol., 2000, #1, 27; 2001, Kosmichna Nauka i Tekhnologiya, dodatok, 7, 89 4. Sobolev Ya.M., 2001, Radio Physics and Radio Astronomy, 6, 277

Sobolev, Ya. M.

2006-08-01

62

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

63

BPS Dyon in a Weak Electromagnetic Field: Equations of Motion and Radiation Fields  

E-print Network

Dynamics of a BPS dyon in a weak, constant, electromagnetic field is studied through a perturbative analysis of appropriate non-linear field equations. The full Lorentz force law for a BPS dyon is established. Also derived are the radiation fields accompanying the motion.

Dongsu Bak; Choonkyu Lee

1994-02-09

64

Magnetic fields and radiative feedback in the star formation process  

NASA Astrophysics Data System (ADS)

Star formation is a complex process involving the interplay of many physical effects, including gravity, turbulent gas dynamics, magnetic fields and radiation. Our understanding of the process has improved substantially in recent years, primarily as a result of our increased ability to incorporate the relevant physics in numerical calculations of the star formation process. In this contribution we present an overview of our recent studies of star cluster formation in turbulent, magnetised clouds using self-gravitating radiation-magnetohydrodynamicscalculations[1, 2]. Our incorporation of magnetic fields and radiative transfer into the Smoothed Particle Hydrodynamics method are discussed. We highlight how magnetic fields and radiative heating of the gas around newborn stars can solve several of the key puzzles in star formation, including an explanation for why star formation is such a slow and inefficient process. However, the presence of magnetic fields at observed strengths in collapsing protostellar cores also leads to problems on smaller scales, including a difficulty in forming protostellar discs and binary stars [3, 4], which suggests that our understanding of the role of magnetic fields in star formation is not yet complete.

Price, Daniel J.; Bate, Matthew R.

2010-06-01

65

Black Hole Evaporation and Nonequilibrium Thermodynamics for a Radiation Field  

E-print Network

When a black hole is put in an "empty" space (zero temperature space) on which there is no matter except the matter of the Hawking radiation (Hawking field), then an outgoing energy flow from the black hole into the empty space exists. By the way, an equilibrium between two arbitrary systems can not allow the existence of an energy (heat) flow from one system to another. Consequently, in the case of a black hole evaporation in the empty space, the Hawking field should be in a nonequilibrium state. Hence the total behaviour of the evaporation, for example the time evolution of the total entropy, should be analysed with a nonequilibrium thermodynamics for the Hawking field. This manuscript explains briefly the way of constructing a nonequilibrium thermodynamic theory for a radiation field, and apply it to a simplified model of a black hole evaporation to calculate the time evolution of the total entropy.

Hiromi Saida

2005-05-18

66

Electromagnetic Fields Radiated by a Circular Loop With Arbitrary Current  

NASA Astrophysics Data System (ADS)

We present a rigorous approach to compute the electromagnetic fields radiated by a thin circular loop with arbitrary current. We employ a polar transmission representation along with a Kontorovich-Lebedev transform to derive integral representations of the field in the interior and exterior regions of a sphere circumscribing the loop. The convergence of the obtained expressions is discussed and comparisons with full-wave simulation and other methods are shown.

Salem, Mohamed A.; Caloz, Christophe

2015-01-01

67

Radiation of the blackbody in the external field  

E-print Network

The blackbody is considered in the external general field. The additional coefficients of stimulated emission and absorption are introduced into the Einstein mechanism. Then, the generalized Planck formula is derived. The Einstein and Debye formula for the specific heat is possible to generalize. The application of the theory to the sonoluminescence, the relic radiation and solar spectrum is discussed.

Miroslav Pardy

2006-03-06

68

Multipole radiation from massive fields: Application to binary pulsar systems  

SciTech Connect

A general multipole expansion for radiation from massive vector and scalar fields is developed for periodic sources. This formalism is then combined with data on the binary pulsar PSR 1913+16 to set limits on the electric charge of astrophysical bodies, and on the coupling strengths of new weak forces.

Krause, D.E.; Kloor, H.T.; Fischbach, E. (Physics Department, Purdue University, West Lafayette, Indiana 47907-1396 (United States))

1994-06-15

69

S-76 high intensity radiated fields, volume 3  

Microsoft Academic Search

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

Jerry Blair

1993-01-01

70

S-76 high intensity radiated fields, volume 2  

Microsoft Academic Search

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

Jerry Blair

1993-01-01

71

S-76 high intensity radiated fields, volume 1  

Microsoft Academic Search

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

Jerry Blair

1993-01-01

72

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

Microsoft Academic Search

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

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

2011-01-01

73

Nanodosimetric Characterization of Mixed Radiation Fields: Status and Perspectives  

NASA Astrophysics Data System (ADS)

The nanodosimetric characterization of mixed radiation fields containing variable fluences of charged particles, neutrons, and photons with stochastic quantities related to the number of ionizations in biological targets of nanometric size is an active area of research and development. Applications include measurements in low-dose radiation environments, including outer space, for radiation protection as well as characterization of mixed radiation therapy fields present in particle therapy with protons, light ions, or neutrons. Approaches for the nanodosimetric characterization of mixed radiation fields should consist of balance of theoretical Monte Carlo simulations and experimental studies that can inform each other. The former should be carefully benchmarked with the latter, usually employing detectors filled with low-pressure gas in which nanodosimetric studies are possible. Research in experimental nanodosimetry has exploited the principle of low-pressure-gas scaling of mean interaction distances between energy transfer points up to a million-fold, thus allowing to collect single charges (ions or electrons) generated in cylindrical volumes equivalent to a short segment of DNA. When combined with arrival-time selection, position resolution of down to 5 nm, has been achieved for experimental track structure studies. The results of these experimental studies and Monte Carlo simulations using the Monte Carlo codes will be summarized. More recently, we have studied a new principle of 2D low-energy ion detection by impact ionization in a hole-pattern detector in combination with a low-pressure time projection chamber. First proof-of-principle and performance studies with this track-imaging detector and corresponding Monte Carlo simulations will be presented. The full potential of nanometric quantities in characterizing radiation quality for dosimetry of ionizing radiation is yet to be explored. The most significant signature of radiation quality may be the size and frequency of clustered ionization events in nanometric scales. Radiobiological evidence points to the importance of these clustered events and the hypothesis that the frequency of large clusters leading to irreparable events in DNA correlate with secondary cancer risk and other late effects of mixed radiation fields should be tested in the future.

Schulte, Reinhard; Bashkirov, Vladimir; Casiraghi, Margherita

74

Technology infusion in service encounters  

Microsoft Academic Search

Service encounters are critical in all industries, including those that have not been traditionally defined as service industries.\\u000a The increasing deployment of technology is altering the essence of service encounters formerly anchored in a “low-tech, high-touch”\\u000a paradigm. This article explores the changing nature of service, with an emphasis on how encounters can be improved through\\u000a the effective use of technology.

Mary Jo Bitner; Stephen W. Brown; Matthew L. Meuter

2000-01-01

75

Modulation of the earth's electric field by cosmic radiation  

NASA Astrophysics Data System (ADS)

Relationships between cosmic radiation levels and the ionospheric potential are investigated as a possible mechanism for solar effects on terrestrial meteorology not involving a heating process. Cosmic ray data obtained by the neutron monitor at Mount Washington, New Hampshire, and by the IMP 4 satellite were compared with measurements of ionospheric potential acquired by aircraft soundings in the Bahamas and balloon soundings primarily in Germany. A 10% change in ground level cosmic radiation is found to be associated with a 10 to 20% change in ionospheric potential, which is taken as an indicator of electric field intensity. In addition, it is found that the Bz component of the interplanetary magnetic field and the auroral geomagnetic index, which are related to magnetospheric-ionospheric coupling, are not correlated with the ionospheric potential data. It is concluded that solar modulation of the earth's electric field occurs through the regulation of ionizing radiation by magnetic discontinuities within the solar wind, with the ionizing radiation affecting atmospheric electrification through regulation of the current output of the global thunderstorm generator.

Markson, R.

1981-06-01

76

Quantum driven dissipative parametric oscillator in a blackbody radiation field  

SciTech Connect

We consider the general open system problem of a charged quantum oscillator confined in a harmonic trap, whose frequency can be arbitrarily modulated in time, that interacts with both an incoherent quantized (blackbody) radiation field and with an arbitrary coherent laser field. We assume that the oscillator is initially in thermodynamic equilibrium with its environment, a non-factorized initial density matrix of the system and the environment, and that at t = 0 the modulation of the frequency, the coupling to the incoherent and the coherent radiation are switched on. The subsequent dynamics, induced by the presence of the blackbody radiation, the laser field, and the frequency modulation, is studied in the framework of the influence functional approach. This approach allows incorporating, in analytic closed formulae, the non-Markovian character of the oscillator-environment interaction at any temperature as well the non-Markovian character of the blackbody radiation and its zero-point fluctuations. Expressions for the time evolution of the covariance matrix elements of the quantum fluctuations and the reduced density-operator are obtained.

Pachón, Leonardo A. [Grupo de Física Atómica y Molecular, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia) [Grupo de Física Atómica y Molecular, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Department of Chemistry and Center for Quantum Information and Quantum Control, Chemical Physics Theory Group, University of Toronto, Toronto, Ontario M5S 3H6 (Canada); Brumer, Paul [Department of Chemistry and Center for Quantum Information and Quantum Control, Chemical Physics Theory Group, University of Toronto, Toronto, Ontario M5S 3H6 (Canada)] [Department of Chemistry and Center for Quantum Information and Quantum Control, Chemical Physics Theory Group, University of Toronto, Toronto, Ontario M5S 3H6 (Canada)

2014-01-15

77

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

78

Radiative transfer model validations during the First ISLSCP Field Experiment  

NASA Technical Reports Server (NTRS)

Two simple radiative transfer models, the 5S model based on Tanre et al. (1985, 1986) and the wide-band model of Morcrette (1984) are validated by comparing their outputs with results obtained during the First ISLSCP Field Experiment on concomitant radiosonde, aerosol turbidity, and radiation measurements and sky photographs. Results showed that the 5S model overestimates the short-wave irradiance by 13.2 W/sq m, whereas the Morcrette model underestimated the long-wave irradiance by 7.4 W/sq m.

Frouin, Robert; Breon, Francois-Marie; Gautier, Catherine

1990-01-01

79

Anomalous Radiative Trapping in Laser Fields of Extreme Intensity  

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

80

Operation Sun Beam, Shots Little Feller II and Small Boy. Project Officer's report - Project 7. 16. Airborne E-field radiation measurements of electromagnetic-pulse phenomena  

SciTech Connect

Airborne measurements of the absolute vertical electric field (E-field) of the radiated electromagnetic pulse were attempted for Shots Little Feller II and Small Boy. Instrumentation included calibrated vertical whip antennas, wideband magnetic tape recorders, and photographs of oscilloscope traces. One instrumented aircraft participated in Little Feller II (C-131F); two aircraft participated in Small Boy (a C-131F and an A-3A). No detectable signals were recorded for either event. It is concluded that the vertical E-field intensities encountered were below the calibrated levels of the instrumentation or the method of instrumentation and calibration was inadequate for nonrepetitive pulse signals.

Butler, K.L.

1985-09-01

81

Close encounters with DNA  

NASA Astrophysics Data System (ADS)

Over the past ten years, the all-atom molecular dynamics method has grown in the scale of both systems and processes amenable to it and in its ability to make quantitative predictions about the behavior of experimental systems. The field of computational DNA research is no exception, witnessing a dramatic increase in the size of systems simulated with atomic resolution, the duration of individual simulations and the realism of the simulation outcomes. In this topical review, we describe the hallmark physical properties of DNA from the perspective of all-atom simulations. We demonstrate the amazing ability of such simulations to reveal the microscopic physical origins of experimentally observed phenomena. We also discuss the frustrating limitations associated with imperfections of present atomic force fields and inadequate sampling. The review is focused on the following four physical properties of DNA: effective electric charge, response to an external mechanical force, interaction with other DNA molecules and behavior in an external electric field.

Maffeo, C.; Yoo, J.; Comer, J.; Wells, D. B.; Luan, B.; Aksimentiev, A.

2014-10-01

82

Chemical composition of tropospheric air masses encountered during high altitude flights (>11.5 km) during the 2009 fall Operation Ice Bridge field campaign  

NASA Astrophysics Data System (ADS)

As part of the 2009 Operation Ice Bridge campaign, the NASA DC-8 aircraft was used to fill the data-time gap in laser observation of the changes in ice sheets, glaciers and sea ice between ICESat-I (Ice, Cloud, and land Elevation Satellite) and ICESat-II. Complementing the cryospheric instrument payload were four in situ atmospheric sampling instruments integrated onboard to measure trace gas concentrations of CO2, CO, N2O, CH4, water vapor and various VOCs (Volatile Organic Compounds). This paper examines two plumes encountered at high altitude (12 km) during the campaign; one during a southbound transit flight (13°S) and the other at 86°S over Antarctica. The data presented are especially significant as the Southern Hemisphere is heavily under-sampled during the austral spring, with few if any high-resolution airborne observations of atmospheric gases made over Antarctica. Strong enhancements of CO, CH4, N2O, CHCl3, OCS, C2H6, C2H2 and C3H8 were observed in the two intercepted air masses that exhibited variations in VOC composition suggesting different sources. The transport model FLEXPART showed that the 13°S plume contained predominately biomass burning emissions originating from Southeast Asia and South Africa, while both anthropogenic and biomass burning emissions were observed at 86°S with South America and South Africa as indicated source regions. The data presented here show evidence that boundary layer pollution is transported from lower latitudes toward the upper troposphere above the South Pole, which may not have been observed in the past.

Yang, Mei Ying Melissa; Vay, Stephanie A.; Stohl, Andreas; Choi, Yonghoon; Diskin, Glenn S.; Sachse, Glen W.; Blake, Donald R.

2012-09-01

83

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

84

Modern Classical Electrodynamics and Electromagnetic Radiation - Vacuum Field Theory Aspects  

E-print Network

The work is devoted to studying some new classical electrodynamics models of interacting charged point particles and related with them physical aspects. Based on the vacuum field theory no-geometry approach, developed in \\cite{BPT,BPT1}, the Lagrangian and Hamiltonian reformulations of some alternative classical electrodynamics models are devised. A problem closely related to the radiation reaction force is analyzed aiming to explain the Wheeler and Feynman reaction radiation mechanism, well known as the absorption radiation theory, and strongly dependent on the Mach type interaction of a charged point particle in an ambient vacuum electromagnetic medium. There are discussed some relationships between this problem and the one derived within the context of the vacuum field theory approach. The R. \\ Feynman's \\textquotedblleft heretical\\textquotedblright\\ approach \\cite{Dy1,Dy2} to deriving the Lorentz force based Maxwell electromagnetic equations is also revisited, its complete legacy is argued both by means of the geometric considerations and its deep relation with the vacuum field theory approach devised before in \\cite{BPT0,BPT1}. \\ Being completely classical, we reanalyze the Feynman's derivation from the classical Lagrangian and Hamiltonian points of view \\ and construct its nontrivial \\ relativistic generalization compatible with the mentioned above vacuum field theory approach.

N. N. Bogolubov; A. K. Prykarpatsky

2013-02-16

85

Synchrotron X-ray radiation in highly turbulent fields  

NASA Astrophysics Data System (ADS)

Synchrotron radiation is considered to be the main channel for the production of non-thermal emission in the energy band from radio to soft gamma rays. This emission component emerges from interaction of high energy electrons with magnetic field, and its spectral properties have been studied in detail both in the context of theoretical physics and astrophysics. However, to a large extend this concerns only the case when the magnetic field is homogeneous. Properties of emission which is produced when electrons interact with turbulent (or simply chaotic) magnetic field still remains a subject for theoretical and numerical studies. Here we focus on the implications of this radiation regime on production of X-ray emission in different astrophysical sources. We discuss the difference in the X-ray spectral slope and flux level as compared to the "conventional" one-zone model. In particular, it was found that the standard relations used to link the X-ray and gamma-ray components in synchrotron-inverse Compton models can be significantly disturbed by the chaotic nature of magnetic field. Also, we discuss how a case of chaotic magnetic field can be distinguished from the emission produced in several active zones characterised by different strength of magnetic field.

Khangulyan, D.; Aharonian, F.; Kelner, S.

2014-07-01

86

Stability of Toroidal Magnetic Fields in Rotating Stellar Radiation Zones  

E-print Network

The questions of how strong magnetic fields can be stored in rotating stellar radiative zones without being subjected to pinch-type instabilities and how much radial mixing is produced if the fields are unstable are addressed. Linear equations are derived for weak disturbances of magnetic and velocity fields which are global in horizontal dimensions but short--scaled in radius. The equations are solved to evaluate the stability of toroidal field patterns with one or two latitudinal belts under the influence of a rigid basic rotation. Hydrodynamic stability of latitudinal differential rotation is also considered. The magnetic instability is essentially three--dimensional. It does not exist in a 2D formulation with strictly horizontal disturbances on decoupled spherical shells. Only stable (magnetically modified) r-modes are found in this case. The instability recovers in 3D. The most rapidly growing modes for the Sun have radial scales smaller than 1 Mm. The finite thermal conductivity makes a strong destabilizing effect. The marginal field strength for the onset of the instability in the upper part of the solar radiative zone is about 600 G. The toroidal field can only slightly exceed this critical value for otherwise the radial mixing produced by the instability would be too strong to be compatible with the observed lithium abundance. Also the threshold for hydrodynamic instability of differential rotation which exists in 2D is lowered in 3D. When radial displacements are included, the value of 28% for critical shear is reduced to 21%.

L. L. Kitchatinov; G. Ruediger

2007-01-30

87

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

88

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

89

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.

90

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

91

Electrically-gated near-field radiative thermal transistor  

E-print Network

In this work, we propose a near-field radiative thermal transistor made of two graphene-covered silicon carbide (SiC) plates separated by a nanometer vacuum gap. Thick SiC plates serve as the thermal "source" and "drain", while graphene sheets function as the "gate" to modulate the near-field photon tunneling by tuning chemical potential with applied voltage biases symmetrically or asymmetrically. The radiative heat flux calculated from fluctuational electrodynamics significantly varies with graphene chemical potentials, which can tune the coupling between graphene plasmon across the vacuum gap. Thermal modulation, switching, and amplification, which are the key features required for a thermal transistor, are theoretically realized and analyzed. This work will pave the way to active thermal management, thermal circuits, and thermal computing.

Yang, Yue

2015-01-01

92

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

93

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

94

Modelling of radiation field around spent fuel container.  

PubMed

Operation of nuclear reactors leads to the production of spent nuclear fuel (SNF). There are two basic strategies of SNF management: ultimate disposal of SNF in geological formations and recycle or repeated utilisation of reprocessed SNF. In both options, there is an urgent necessity to study radiation properties of SNF. Information about SNF radiation properties is required at all stages of SNF management. In order to reach more effective utilisation of nuclear materials, new fuel cycles are under development based on uranium-plutonium, uranium-thorium and some other types of nuclear fuel. These promising types of nuclear fuel are characterised by quite different radiation properties at all the stages of nuclear fuel cycle (NFC) listed above. So, comparative analysis is required for radiation properties of different nuclear fuel types at different NFC stages. The results presented here were obtained from the numerical analysis of the radiation field around transport containers of different SNF types and in SNF storage. The calculations are carried out with the application of the computer code packages SCALE-4.3 and MCNP-4C. Comparison of the dose parameters obtained for different models of the transport container with experimental data allowed us to make certain conclusions about the errors of numerical results caused by the approximate geometrical description of the transport container. PMID:16604702

Kryuchkov, E F; Opalovsky, V A; Tikhomirov, G V

2005-01-01

95

Gravitational radiation in d>4 from effective field theory  

NASA Astrophysics Data System (ADS)

Some years ago, a new powerful technique, known as the classical effective field theory, was proposed to describe classical phenomena in gravitational systems. Here we show how this approach can be useful to investigate theoretically important issues, such as gravitational radiation in any spacetime dimension. In particular, we derive for the first time the Einstein-Infeld-Hoffman Lagrangian and we compute Einstein’s quadrupole formula for any number of flat spacetime dimensions.

Cardoso, Vitor; Dias, Óscar J. C.; Figueras, Pau

2008-11-01

96

Cosmological perturbations for an inflaton field coupled to radiation  

NASA Astrophysics Data System (ADS)

Within the framework of the interacting fluid formalism, we provide the numerical solution to the Boltzmann equation describing the evolution of an inflaton field coupled to radiation. We study the behavior of the system during the slow-roll regime, in the case in which an additional stochastic source term is included in the set of equations, and we recover the expression for the cosmological perturbations previously obtained in the Warm inflation scenarios.

Visinelli, Luca

2015-01-01

97

THz near-field imaging employing synchrotron radiation  

NASA Astrophysics Data System (ADS)

Terahertz scanning near-field infrared microscopy below 1 THz is demonstrated at an electron storage ring using coherent synchrotron radiation. Spatial resolution below the diffraction limit down to about ?/40 at 2 cm-1 is derived from the transmittance spectra of a conical aperture probe. The potential of the technique is exemplified by imaging wet biological samples. Strongly absorbing living leaves have been imaged in transmittance with a spatial resolution of 130 ?m at about 12 cm-1. The THz near-field images reveal distinct structural differences in the mesophytic and xerophytic leaves investigated.

Schade, U.; Holldack, K.; Kuske, P.; Wüstefeld, G.; Hübers, H.-W.

2004-02-01

98

Stability of Toroidal Magnetic Fields in Rotating Stellar Radiation Zones  

E-print Network

The questions of how strong magnetic fields can be stored in rotating stellar radiative zones without being subjected to pinch-type instabilities and how much radial mixing is produced if the fields are unstable are addressed. Linear equations are derived for weak disturbances of magnetic and velocity fields which are global in horizontal dimensions but short--scaled in radius. The equations are solved to evaluate the stability of toroidal field patterns with one or two latitudinal belts under the influence of a rigid basic rotation. Hydrodynamic stability of latitudinal differential rotation is also considered. The magnetic instability is essentially three--dimensional. It does not exist in a 2D formulation with strictly horizontal disturbances on decoupled spherical shells. Only stable (magnetically modified) r-modes are found in this case. The instability recovers in 3D. The most rapidly growing modes for the Sun have radial scales smaller than 1 Mm. The finite thermal conductivity makes a strong destabili...

Kitchatinov, L L

2007-01-01

99

Numerical simulations of protostellar encounters I. Star-disc encounters  

E-print Network

It appears that most stars are born in clusters, and that at birth most stars have circumstellar discs which are comparable in size to the separations between the stars. Interactions between neighbouring stars and discs are therefore likely to play a key role in determining disc lifetimes, stellar masses, and the separations and eccentricities of binary orbits. Such interactions may also cause fragmentation of the discs, thereby triggering the formation of additional stars. We have carried out a series of simulations of disc-star interactions using an SPH code which treats self-gravity, hydrodynamic and viscous forces. We find that interactions between discs and stars provide a mechanism for removing energy from, or adding energy to, the orbits of the stars, and for truncating the discs. However, capture during such encounters is unlikely to be an important binary formation mechanism. A more significant consequence of such encounters is that they can trigger fragmentation of the disc, via tidally and compressionally induced gravitational instabilities, leading to the formation of additional stars. When the disc-spins and stellar orbits are randomly oriented, encounters lead to the formation of new companions to the original star in 20% of encounters. If most encounters are prograde and coplanar, as suggested by simulations of dynamically-triggered star formation, then new companions are formed in approximately 50% of encounters.

H. M. J. Boffin; S. J. Watkins; A. S. Bhattal; N. Francis; A. P. Whitworth

1998-05-28

100

Monte Carlo simulation of the operational quantities at the realistic mixed neutron-photon radiation fields CANEL and SIGMA.  

PubMed

The Institute for Radiological Protection and Nuclear Safety owns two facilities producing realistic mixed neutron-photon radiation fields, CANEL, an accelerator driven moderator modular device, and SIGMA, a graphite moderated americium-beryllium assembly. These fields are representative of some of those encountered at nuclear workplaces, and the corresponding facilities are designed and used for calibration of various instruments, such as survey meters, personal dosimeters or spectrometric devices. In the framework of the European project EVIDOS, irradiations of personal dosimeters were performed at CANEL and SIGMA. Monte Carlo calculations were performed to estimate the reference values of the personal dose equivalent at both facilities. The Hp(10) values were calculated for three different angular positions, 0 degrees, 45 degrees and 75 degrees, of an ICRU phantom located at the position of irradiation. PMID:17578872

Lacoste, V; Gressier, V

2007-01-01

101

RADIATION FIELDS FOR SEMILINEAR WAVE EQUATIONS DEAN BASKIN AND ANT^ONIO SA BARRETO  

E-print Network

RADIATION FIELDS FOR SEMILINEAR WAVE EQUATIONS DEAN BASKIN AND ANT^ONIO S´A BARRETO Abstract. We define the radiation fields of solutions to critical semilinear wave equations in R3 and use them to define the scattering operator. We also prove a support theorem for the radiation fields with radial

Sá Barreto, Antônio

102

Asymptotic Electromagnetic Fields in Models of Quantum-Mechanical Matter Interacting with the Quantized Radiation Field  

E-print Network

In models of (non-relativistic and pseudo-relativistic) electrons interacting with static nuclei and with the (ultraviolet-cutoff) quantized radiation field, the existence of asymptotic electromagnetic fields is established. Our results yield some mathematically rigorous understanding of Rayleigh scattering and of the phenomenon of relaxation of isolated atoms to their ground states. Our proofs are based on propagation estimates for electrons inspired by similar estimates known from $N$-body scattering theory.

J. Froehlich; M. Griesemer; B. Schlein

2000-09-27

103

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

104

Generation of electromagnetic radiation based on nanotubes under a constant electric field and an electromagnetic wave field  

SciTech Connect

The possible generation of radiation in the millimeter range based on nanotubes by an alternating (rapidly oscillating) electric field under a constant (or nonstationary) electric field is studied. Radiation enhancement is based on a periodic dependence of the current in nanotubes in such electric fields. The results of a mathematical simulation are presented.

Sadykov, N. R., E-mail: sadykov@rambler.ru; Scorkin, N. A. [South Ural State University (Russian Federation)

2012-02-15

105

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

106

Intercomparison of radiation protection instrumentation in a pulsed neutron field  

NASA Astrophysics Data System (ADS)

In the framework of the EURADOS working group 11, an intercomparison of active neutron survey meters was performed in a pulsed neutron field (PNF). The aim of the exercise was to evaluate the performances of various neutron instruments, including commercially available rem-counters, personal dosemeters and instrument prototypes. The measurements took place at the cyclotron of the Helmholtz-Zentrum Berlin für Materialien und Energie GmbH. The cyclotron is routinely used for proton therapy of ocular tumours, but an experimental area is also available. For the therapy the machine accelerates protons to 68 MeV. The interaction of the proton beam with a thick tungsten target produces a neutron field with energy up to about 60 MeV. One interesting feature of the cyclotron is that the beam can be delivered in bursts, with the possibility to modify in a simple and flexible way the burst length and the ion current. Through this possibility one can obtain radiation bursts of variable duration and intensity. All instruments were placed in a reference position and irradiated with neutrons delivered in bursts of different intensity. The analysis of the instrument response as a function of the burst charge (the total electric charge of the protons in the burst shot onto the tungsten target) permitted to assess for each device the dose underestimation due to the time structure of the radiation field. The personal neutron dosemeters were exposed on a standard PMMA slab phantom and the response linearity was evaluated.

Caresana, M.; Denker, A.; Esposito, A.; Ferrarini, M.; Golnik, N.; Hohmann, E.; Leuschner, A.; Luszik-Bhadra, M.; Manessi, G.; Mayer, S.; Ott, K.; Röhrich, J.; Silari, M.; Trompier, F.; Volnhals, M.; Wielunski, M.

2014-02-01

107

Computation of High-Altitude Hypersonic Flow-Field Radiation.  

NASA Astrophysics Data System (ADS)

Accurate calculations of radiation on and from transatmospheric flight vehicles are currently a challenge to computational aerodynamicists. Due to combined effects of low density and hypersonic flight conditions, the gas in the shock-layer is in a state of thermal and chemical nonequilibrium. The present work aims at gathering existing ideas together about how such flows should be modeled and comparing them to recent, more accurate experiments that probe the separate energy modes of the different species of the gas in a more direct way than previously reported. Two recent Bow-Shock-Ultra-Violet flight experiments, and two recent shock-tube experiments are used to test the validity of the flow-field models implemented in the current state-of-the-art numerical codes. They involve highly non-equilibrium flow regimes in nitrogen and air with negligible ionization and provide detailed spectra emitted by the hot gas. A recent plasma torch experiment at Stanford, and the Cochise experiments at the Geophysics Directorate laboratories, have been the ideal experimental counterpart to test and improve the radiation calculation in the UV -visible spectral range and the IR region respectively. Each spectral region is used to probe several different aspects of the thermal and chemical nonequilibrium. A hierarchy of flow-field codes has been developed in conjunction with a greatly enhanced radiation code, termed NEQAIR2, to simulate these experiments. The flow -field codes involve axisymmetric Navier-Stokes and Burnett simulations around blunt-nose cones for the flight experiments and quasi-1D Euler simulations for the shock-tube experiments. They include between 5 and 8 chemical species and between 3 and 6 separate internal energy modes. The corresponding system of conservation equations are solved with finite volume, flux split algorithms. Gauss-Siedel line relaxation is used to increase efficiency of the fully-implicit method and exact numerical jacobians have been derived to increase the rate of convergence. The radiation code involves a collisional-radiative model based on a quasi-steady-state (QSS) approximation and a detailed line-by-line calculation for several atomic systems and molecular band systems. Comparisons of numerical spectra with the flight data show good agreement at the lower altitudes but the predictions are only within an order of magnitude at higher altitudes.

Moreau, Stephane

108

Localisation of atomic populations in the optical radiation field  

NASA Astrophysics Data System (ADS)

The possibility of two-dimensional spatial localisation of atomic populations under the influence of the travelling wave fields in the tripod-configuration of quantum states is studied for the first time. Three travelling waves propagating in the same plane at an angle of 120° to each other form a system of standing waves under the influence of which atomic populations are localised. The size of the region of spatial localisation of the populations, in principle, can be hundredths of a wavelength of optical radiation.

Efremova, E. A.; Gordeev, M. Yu; Rozhdestvensky, Yu V.

2014-10-01

109

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

110

Interaction of Electromagnetic Radiation with Supercritical Magnetic Field  

E-print Network

It is pointed, that effects of refraction of electromagnetic radiation in the medium, formed by the magnetized vacuum, become essential already for relatively soft photons, not hard enough to create an electron-positron pair, including those belonging to soft gamma-, X-ray, optic and radio- range, if the magnetic field B exceeds the critical value of Bcr=m^2/e=4.4 10^13 Gauss. Three leading terms in the asymptotic expansion of the one-loop polarization operator in a constant magnetic field are found for B>>Bcr, and the corresponding refraction index is shown to depend only on the propagation direction of the photon relative to the external field. It is established, that the refraction index for one of polarization modes unlimitedly grows with the field, while the other is saturated at a moderate level. The photon capture effect is extended to soft photons. The results may be essential in studying reflection, refraction and splitting of X-rays, light and radio waves by magnetic fields of magnetars, as well as in considering emission of such waves by charged particles .

A. E. Shabad

2004-01-12

111

Radiative Corrections from Heavy Fast-Roll Fields during Inflation  

E-print Network

We investigate radiative corrections to the inflaton potential from heavy fields undergoing a fast-roll phase transition. We find that a logarithmic one-loop correction to the inflaton potential involving this field can induce a temporary running of the spectral index. The induced running can be a short burst of strong running, which may be related to the observed anomalies on large scales in the cosmic microwave spectrum, or extend over many e-folds, sustaining an effectively constant running to be searched for in the future. We implement this in a general class of models, where effects are mediated through a heavy messenger field sitting in its minimum. Interestingly, within the present framework it is a generic outcome that a large running implies a small field model with a vanishing tensor-to-scalar ratio, circumventing the normal expectation that small field models typically lead to an unobservable small running of the spectral index. An observable level of tensor modes can also be accommodated, but, sur...

Jain, Rajeev Kumar; Sloth, Martin S

2015-01-01

112

Simulation of Van Allen Probes plasmapause encounters  

NASA Astrophysics Data System (ADS)

We use an E × B-driven plasmapause test particle (PTP) simulation to provide global contextual information for in situ measurements by the Van Allen Probes (Radiation Belt Storm Probes (RBSP)) during 15-20 January 2013. During 120 h of simulation time beginning on 15 January, geomagnetic activity produced three plumes. The third and largest simulated plume formed during enhanced convection on 17 January, and survived as a rotating, wrapped, residual plume for tens of hours. To validate the simulation, we compare its output with RBSP data. Virtual RBSP satellites recorded 28 virtual plasmapause encounters during 15-19 January. For 26 of 28 (92%) virtual crossings, there were corresponding actual RBSP encounters with plasmapause density gradients. The mean difference in encounter time between model and data is 36 min. The mean model-data difference in radial location is 0.40 ± 0.05 RE. The model-data agreement is better for strong convection than for quiet or weakly disturbed conditions. On 18 January, both RBSP spacecraft crossed a tenuous, detached plasma feature at approximately the same time and nightside location as a wrapped residual plume, predicted by the model to have formed 32 h earlier on 17 January. The agreement between simulation and data indicates that the model-provided global information is adequate to correctly interpret the RBSP density observations.

Goldstein, J.; Pascuale, S. De; Kletzing, C.; Kurth, W.; Genestreti, K. J.; Skoug, R. M.; Larsen, B. A.; Kistler, L. M.; Mouikis, C.; Spence, H.

2014-09-01

113

Measurement of neutron and gamma radiation in a mixed field.  

PubMed

This paper describes a study of dosimeters with a range of 0 to 0.2 mGy that were developed by the authors and built by the Federal Emergency Management Agency (FEMA). These instruments are a type of air-filled ion chamber that is self-reading by means of an internal carbon fiber electrometer. Two types of these dosimeters were constructed: one with an ion chamber wall made of a conductive hydrogenous material, and the other device made with a conductive wall lining of non-hydrogenous material. Both types of dosimeters have the same sensitivity for gamma radiation, but greatly different sensitivities for fast neutrons, thus making it possible to measure gamma radiation and neutron doses separately in a mixed radiation field. The results indicate that such pairs of dosimeters can be used for the first time to accurately monitor personnel for gamma ray and neutron doses in real time. Since the difference in neutron sensitivities is due to the properties of wall materials, periodic calibrations of the dosimeter system can be accomplished using only gamma rays after the material constants are measured. The absolute number of neutron induced transmutations in sulfur was required for this work. Methods and techniques which were applied to determine this quantity are described in the text. This approach was one of several dosimetric procedures utilized in this investigation. PMID:7558835

Kronenberg, S; Bechtel, E; Brucker, G J

1995-10-01

114

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

115

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

116

Further progress in the characterisation of complex radiation fields.  

PubMed

One of the topics which forms part of CONRAD project addresses the problems related to the dosimetry of complex-mixed radiation fields at workplaces. This topic was included in work package (WP) 6. WP 6 was established to co-ordinate research activities in two areas:the development of new techniques and the improvement of current techniques for characterisation of complex workplace fields (including high-energy fields and pulsed fields): measurement and calculation of particle energy and direction distributions (Subgroup A); and model improvements for dose assessment of solar particle events (Subgroup B). In both cases in order to aid the research, WP 6 increases the efficiency of resource utilisation, and facilitates the technology transfer to practical application and for the development of standards. This contribution presents a general overview of activities of SG A; specific results related to the benchmark experiment at GSI Darmstadt are presented separately, and will be published in other way. As far as the results acquired in the frame of the SG B activities, these are presented in the meeting held as part of EURADOS AM 2008. PMID:18718960

Spurny, Frantisek; Silari, Marco

2008-01-01

117

Experimental determination of radiated internal wave power without pressure field Frank M. Lee,1  

E-print Network

for tidal flow of a stratified fluid past a knife edge. The results for the radiated internal wave powerExperimental determination of radiated internal wave power without pressure field data Frank M. Lee to determine, using only velocity field data, the time-averaged energy flux J and total radiated power P

Morrison, Philip J.,

118

Radiative capture reactions in lattice effective field theory.  

PubMed

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. PMID:23909313

Rupak, Gautam; Lee, Dean

2013-07-19

119

Chemical Abundances and the Metagalactic Radiation Field at High Redshift  

E-print Network

We have carried out model calculations of the photoionized intergalactic medium (IGM) to determine the effects on the predicted ionic column densities due to uncertainties in the published dielectronic recombination (DR) rate coefficients. Based on our previous experimental work and a comparison of published theoretical DR rates, we estimate there is in general a factor of 2 uncertainty in existing DR rates used for modeling the IGM. We demonstrate that this uncertainty results in factors of ~1.9 uncertainty in the predicted N V and Si IV column densities, ~1.6 for O VI, and ~1.7 for C IV. We show that these systematic uncertainties translate into a systematic uncertainty of up to a factor of ~3.1 in the Si/C abundance ratio inferred from observations. The inferred IGM abundance ratio could thus be less than the solar Si/C ratio or greater than 3 times the solar ratio. If the latter is true, then it suggests the metagalactic radiation field is not due purely to active galactic nuclei, but includes a significant stellar component. Lastly, column density ratios of Si IV to C IV versus C II to C IV are often used to constrain the decrement in the metagalactic radiation field at the He II absorption edge. We show that the variation in the predicted Si IV to C IV ratio due to a factor of 2 uncertainty in the DR rates is almost as large as that due to a factor of 10 change in the decrement. Laboratory measurements of the relevant DR resonance strengths and energies are the only unambiguous method to remove the effects of these atomic physics uncertainties from models of the IGM.

Daniel Wolf Savin

1999-11-01

120

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

121

Magnetic field and radiative transfer modelling of a quiescent prominence  

NASA Astrophysics Data System (ADS)

Aims: The aim of this work is to analyse the multi-instrument observations of the June 22, 2010 prominence to study its structure in detail, including the prominence-corona transition region and the dark bubble located below the prominence body. Methods: We combined results of the 3D magnetic field modelling with 2D prominence fine structure radiative transfer models to fully exploit the available observations. Results: The 3D linear force-free field model with the unsheared bipole reproduces the morphology of the analysed prominence reasonably well, thus providing useful information about its magnetic field configuration and the location of the magnetic dips. The 2D models of the prominence fine structures provide a good representation of the local plasma configuration in the region dominated by the quasi-vertical threads. However, the low observed Lyman-? central intensities and the morphology of the analysed prominence suggest that its upper central part is not directly illuminated from the solar surface. Conclusions: This multi-disciplinary prominence study allows us to argue that a large part of the prominence-corona transition region plasma can be located inside the magnetic dips in small-scale features that surround the cool prominence material located in the dip centre. We also argue that the dark prominence bubbles can be formed because of perturbations of the prominence magnetic field by parasitic bipoles, causing them to be devoid of the magnetic dips. Magnetic dips, however, form thin layers that surround these bubbles, which might explain the occurrence of the cool prominence material in the lines of sight intersecting the prominence bubbles. Movie and Appendix A are available in electronic form at http://www.aanda.org

Gunár, S.; Schwartz, P.; Dudík, J.; Schmieder, B.; Heinzel, P.; Jur?ák, J.

2014-07-01

122

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

123

On the divergence difficulty of quantized field theories and the rigorous treatment of radiation reaction : with related additional papers   

E-print Network

By an orthodox application of the perturbation theory to the general case of a quantized field, it is shown that the divergence difficulty hitherto encountered arises from a faulty application of the expansion method. The ...

Peng, Hwan-Wu

124

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

125

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

126

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

127

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

128

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

PubMed Central

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. PMID:24320415

Kerns, James R.; Anand, Aman

2013-01-01

129

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

130

Normal tissue toxicity after small field hypofractionated stereotactic body radiation  

Microsoft Academic Search

Stereotactic body radiation (SBRT) is an emerging tool in radiation oncology in which the targeting accuracy is improved via the detection and processing of a three-dimensional coordinate system that is aligned to the target. With improved targeting accuracy, SBRT allows for the minimization of normal tissue volume exposed to high radiation dose as well as the escalation of fractional dose

Michael T Milano; Louis S Constine; Paul Okunieff

2008-01-01

131

Low-cost Shielding to Minimize Radiation Errors of Temperature Sensors in the Field  

Microsoft Academic Search

The importance of shielding temperature sensors from solar radiation is understood, but there is a lack of prescriptive advice for plant scientists to build inexpensive and effective shields for replicated field experiments. Using the general physical principles that govern radiation shielding, a number of low-cost, passively ventilated radiation shields built in-house was assessed for the measurement of air temperature against

Julie M. Tarara

2007-01-01

132

Radiation fields for nanoscale systems Ming Liang Zhang* and D. A. Drabold**  

E-print Network

Radiation fields for nanoscale systems Ming Liang Zhang* and D. A. Drabold** Department of Physics-classical radiation theory, temporal coarse graining * Corresponding author: e-mail zhangm@ohio.edu, Phone: (01) 740 semi-classical radiation theory (SCRT) with these sources, the microscopic Maxwell equations can

Drabold, David

133

Non-thermal continuous and modulated electromagnetic radiation fields effects on sleep EEG of rats?  

PubMed Central

In the present study, the alteration in the sleep EEG in rats due to chronic exposure to low-level non-thermal electromagnetic radiation was investigated. Two types of radiation fields were used; 900 MHz unmodulated wave and 900 MHz modulated at 8 and 16 Hz waves. Animals has exposed to radiation fields for 1 month (1 h/day). EEG power spectral analyses of exposed and control animals during slow wave sleep (SWS) and rapid eye movement sleep (REM sleep) revealed that the REM sleep is more susceptible to modulated radiofrequency radiation fields (RFR) than the SWS. The latency of REM sleep increased due to radiation exposure indicating a change in the ultradian rhythm of normal sleep cycles. The cumulative and irreversible effect of radiation exposure was proposed and the interaction of the extremely low frequency radiation with the similar EEG frequencies was suggested.

Mohammed, Haitham S.; Fahmy, Heba M.; Radwan, Nasr M.; Elsayed, Anwar A.

2012-01-01

134

Involved-Field Radiation Therapy for Locoregionally Recurrent Ovarian Cancer  

PubMed Central

Objective To evaluate the effectiveness of definitive involved-field radiation therapy (IFRT) for selected patients with locoregionally-recurrent ovarian cancer. Methods We retrospectively reviewed records of 102 epithelial ovarian cancer patients treated with definitive IFRT (?45 Gy). IFRT was directed to localized nodal (49%) and extranodal (51%) recurrences. Results The median time from diagnosis to IFRT was 36 months (range, 1–311), and the median follow-up after IFRT was 37 months (range, 1–123). Patients received a median of three chemotherapy courses before IFRT (range, 0–9). Five-year overall (OS) and progression-free survival (PFS) rates after IFRT were 40% and 24% respectively; the 5-year in-field disease control rate was 71%. Thirty-five patients (35%) had no evidence of disease at a median of 38 months after IFRT (range, 7–122), including 25 continuously without disease for a median of 61 months (range, 17–122) and 10 with salvage treatment following disease recurrence, disease-free for a median of 39 months after salvage treatment (range, 7–92). Eight clear cell carcinoma patients had higher 5-year OS (88% versus 37%; p=0.05) and PFS (75% versus 20%; p=0.01) rates than other patients. Patients sensitive to initial platinum chemotherapy had a higher 5-year OS rate than platinum-resistant patients (43% versus 27%, p=0.03). Patients who required chemotherapy for recurrence after IFRT often benefitted from longer chemotherapy-free intervals after than before IFRT. Conclusions Definitive IFRT can yield excellent local control, protracted disease-free intervals, and even cures in carefully selected patients. RT should be considered a tool in the curative management of locoregionally-recurrent ovarian cancer. PMID:23648467

Brown, Aaron P.; Jhingran, Anuja; Klopp, Ann H.; Schmeler, Kathleen M.; Ramirez, Pedro T.; Eifel, Patricia J.

2015-01-01

135

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

136

Practical method for evaluating the sound field radiated from a waveguide.  

PubMed

This letter presents a simple and practical method for evaluating the sound field radiated from a waveguide. By using the proposed method, detailed information about the radiated sound field can be obtained by measuring the sound field in the mouth of the baffled waveguide. To examine this method's effectiveness, the radiated sound pressure distribution in space was first evaluated by using the proposed method, and then it was measured directly for comparison. Experiments using two different waveguides showed good agreement between the evaluated and the measured radiated sound pressure distributions. PMID:25618097

Feng, Xuelei; Shen, Yong; Chen, Simiao; Zhao, Ye

2015-01-01

137

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. PMID:20724780

Haberthür, David; Hintermüller, Christoph; Marone, Federica; Schittny, Johannes C.; Stampanoni, Marco

2010-01-01

138

Analysis of Radiating Electric Field for Indoor Broadband Power Line Communication  

Microsoft Academic Search

Broadband power line communication (BPL) is a novel technology for constructing home networks. However, the electric field radiating from the power lines could change the indoor electromagnetic environment even disturb other radio communication services. Thus, a model based on four- port networks is proposed to evaluate the radiating field. Numerous branches of power lines are also taken into account. The

Yang Biao; Lv Ying-hua; Zhang Hong-xin

2007-01-01

139

Numerical Simulation of a Convective Turbulence Encounter  

NASA Technical Reports Server (NTRS)

A numerical simulation of a convective turbulence event is investigated and compared with observational data. The numerical results show severe turbulence of similar scale and intensity to that encountered during the test flight. This turbulence is associated with buoyant plumes that penetrate the upper-level thunderstorm outflow. The simulated radar reflectivity compares well with that obtained from the aircraft's onboard radar. Resolved scales of motion as small as 50 m are needed in order to accurately diagnose aircraft normal load accelerations. Given this requirement, realistic turbulence fields may be created by merging subgrid-scales of turbulence to a convective-cloud simulation. A hazard algorithm for use with model data sets is demonstrated. The algorithm diagnoses the RMS normal loads from second moments of the vertical velocity field and is independent of aircraft motion.

Proctor, Fred H.; Hamilton, David W.; Bowles, Roland L.

2002-01-01

140

The Solar and Thermal Radiation Field Below the Venus Clouds  

NASA Astrophysics Data System (ADS)

Even though the H2SO4 clouds that shroud Venus reflect ~80% of the incident sunlight and absorb more than half of the rest, entry probes show that the atmosphere is well illuminated between the cloud base ( ~47.5 km) and the surface. For example, the Pioneer Venus Large Probe entered near the dawn terminator (7:38 AM) and measured downward solar fluxes decreasing from ~200 W/m2 to ~20 W/m2 between the cloud base and surface (Tomasko et al., JGR, 85, 1980). The Venera spectrophotometers showed that the sunlight is most intense at 0.5 1 ? m, except in the near-IR spectral windows at 1.0, 1.1, 1.18, 1.27, 1.31, 1.74, and 2.3 ? m. The sub-cloud region is also illuminated by thermal emission from hot surface and lower atmosphere. This emission is most intense in these spectral windows, where it contributes 0.1 to 1 W/m2/sr/ ? m. A spectrum resolving multiple scattering model was used to study the spectral and angular distribution of this radiation to assess the feasibility of descent imaging from entry probes. The radiation field is azimuthally uniform everywhere below the clouds, even when the sun is on the horizon. At ? < 0.6 ? m, Rayleigh scattering optical depths between the cloud base and the surface are comparable to the optical depth of the main cloud deck (? R ~25 at 0.5 ? m). This scattering will dramatically reduce the contrast in high-altitude (>10 km) images of the surface at visible wavelengths. Fortunately, Rayleigh scattering decreases as 1/? 4, such that ? R<1 at 1.0? m. This spectral region is also relatively free of absorption by gases. It therefore may provide the best opportunity to image the surface from a falling probe. This work is supported by the NASA Planetary Atmospheres Program.

Crisp, D.

2000-10-01

141

Stellar orbit evolution in close circumstellar disc encounters  

NASA Astrophysics Data System (ADS)

The formation and early evolution of circumstellar discs often occurs within dense, newborn stellar clusters. For the first time, we apply the moving-mesh code AREPO, to circumstellar discs in 3D, focusing on disc-disc interactions that result from stellar flybys. Although a small fraction of stars are expected to undergo close approaches, the outcomes of the most violent encounters might leave an imprint on the discs and host stars that will influence both their orbits and their ability to form planets. We first construct well-behaved 3D models of self-gravitating discs, and then create a suite of numerical experiments of parabolic encounters, exploring the effects of pericentre separation rp, disc orientation and disc-star mass ratio (Md/M*) on the orbital evolution of the host stars. Close encounters (2rp ? disc radius) can truncate discs on very short time-scales. If discs are massive, close encounters facilitate enough orbital angular momentum extraction to induce stellar capture. We find that for realistic primordial disc masses Md ? 0.1M*, non-colliding encounters induce minor orbital changes, which is consistent with analytic calculations of encounters in the linear regime. The same disc masses produce entirely different results for grazing/colliding encounters. In the latter case, rapidly cooling discs lose orbital energy by radiating away the energy excess of the shock-heated gas, thus causing capture of the host stars into a bound orbit. In rare cases, a tight binary with a circumbinary disc forms as a result of this encounter.

Muñoz, D. J.; Kratter, K.; Vogelsberger, M.; Hernquist, L.; Springel, V.

2015-01-01

142

THz near-field imaging of biological tissues employing synchrotron radiation  

E-print Network

THz near-field imaging of biological tissues employing synchrotron radiation Ulrich Schadea scanning near-field infrared microscopy (SNIM) below 1 THz is demonstrated. The near-field tech- nique (0.06 THz) is derived from the transmittance spectra of the near-field probes. The potential

143

A new solution to waveguide excitation suppressing the effects of the radiated field. Application to the Y-junction  

Microsoft Academic Search

When an integrated optical component is asymmetrically excited, a radiated field is generated. Most of the time, the energy carried by the radiated field is lost. However, with high-level integration structures, this field can couple back into another waveguide and then disturb the operating conditions of the whole component. An original waveguide geometry that rapidly removes this radiated field is

Philippe Gérard; Alain Morand; Pierre Lemaître-Auger

1998-01-01

144

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...

145

COMET ENCOUNTERS AND CARBON 14  

SciTech Connect

The {sup 14}C production of shock-accelerated particles is calculated in terms of the total energy released in energetic particles. The recently reported 1.2% jump in the {sup 14}C content of the atmosphere in the year C.E. 775, it is found, would require {approx}> 10{sup 34} erg in energetic particles, less than first estimates but far more than any known solar flare on record. It is noted that the superflare from a large comet (comparable to C/Hale-Bopp) colliding with the sun could produce shock-accelerated GeV cosmic rays in the solar corona and/or solar wind, and possibly account for the C.E. 775 event. Several additional predictions of cometary encounters with the sun and other stars may be observable in the future.

Eichler, David; Mordecai, David, E-mail: eichler.david@gmail.com [Physics Department, Ben-Gurion University, Be'er-Sheva 84105 (Israel)

2012-12-20

146

Graphene-assisted near-field radiative heat transfer between corrugated polar materials  

SciTech Connect

Graphene has attracted great attention in nanoelectronics, optics, and energy harvesting. Here, the near-field radiative heat transfer between graphene-covered corrugated silica is investigated based on the exact scattering theory. It is found that graphene can improve the radiative heat flux between silica gratings by more than one order of magnitude and alleviate the performance sensitivity to lateral shift. The underlying mechanism is mainly attributed to the improved photon tunneling of modes away from phonon resonances. Besides, coating with graphene leads to nonlocal radiative transfer that breaks Derjaguin's proximity approximation and enables corrugated silica to outperform bulk silica in near-field radiation.

Liu, X. L.; Zhang, Z. M., E-mail: zhuomin.zhang@me.gatech.edu [G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

2014-06-23

147

Virtual radiation fields -- A virtual environment tool for radiological analysis and simulation  

SciTech Connect

A virtual reality system was developed for computational and graphical modeling and simulation of radiation environments. This system, called Virtual Radiation Fields (VRF), demonstrates the usefulness of radiological analysis in simulation-based design for predicting radiation doses for robotic equipment and personnel working in a radiation environment. The system was developed for use in determining the radiation doses for robotic equipment to be used in tank-waste retrieval operations at the Hanford National Laboratory. As a reference case, specific application is made to simulate cleanup operations for Hanford tank C-106. A three-dimensional model representation of the tank and its predicted radiation levels are presented and analyzed. Tank cleanup operations were simulated to understand how radiation levels change during the cleanup phase and to predict cumulative radiation doses to robotic equipment to aid in the development of maintenance and replacement schedules.

Knight, T.W.; Dalton, G.R.; Tulenko, J.S. [Univ. of Florida, Gainesville, FL (United States). Dept. of Nuclear Engineering Sciences

1997-02-01

148

Evaluation of the trade-offs encountered in planning and treating locally advanced head and neck cancer: intensity-modulated radiation therapy vs dual-arc volumetric-modulated arc therapy  

PubMed Central

Objective The primary purpose of this study was to assess the practical trade-offs between intensity-modulated radiation therapy (IMRT) and dual-arc volumetric-modulated arc therapy (DA-VMAT) for locally advanced head and neck cancer (HNC). Methods For 15 locally advanced HNC data sets, nine-field step-and-shoot IMRT plans and two full-rotation DA-VMAT treatment plans were created in the Pinnacle3 v. 9.0 (Philips Medical Systems, Fitchburg, WI) treatment planning environment and then delivered on a Clinac iX (Varian Medical Systems, Palo Alto, CA) to a cylindrical detector array. The treatment planning goals were organised into four groups based on their importance: (1) spinal cord, brainstem, optical structures; (2) planning target volumes; (3) parotids, mandible, larynx and brachial plexus; and (4) normal tissues. Results Compared with IMRT, DA-VMAT plans were of equal plan quality (p>0.05 for each group), able to be delivered in a shorter time (3.1 min vs 8.3 min, p<0.0001), delivered fewer monitor units (on average 28% fewer, p<0.0001) and produced similar delivery accuracy (p>0.05 at ?2%/2mm and ?3%/3mm). However, the VMAT plans took more planning time (28.9 min vs 7.7 min per cycle, p<0.0001) and required more data for a three-dimensional dose (20 times more, p<0.0001). Conclusions Nine-field step-and-shoot IMRT and DA-VMAT are both capable of meeting the majority of planning goals for locally advanced HNC. The main trade-offs between the techniques are shorter treatment time for DA-VMAT but longer planning time and the additional resources required for implementation of a new technology. Based on this study, our clinic has incorporated DA-VMAT for locally advanced HNC. Advances in knowledge DA-VMAT is a suitable alternative to IMRT for locally advanced HNC. PMID:22806619

Oliver, M; McConnell, D; Romani, M; McAllister, A; Pearce, A; Andronowski, A; Wang, X; Leszczynski, K

2012-01-01

149

Synchrotron radiation in strongly coupled conformal field theories  

E-print Network

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 ...

Athanasiou, Christiana

150

Analysis of the failures and corrective actions for the LHC cryogenics radiation tolerant electronics and its field instruments  

SciTech Connect

The LHC cryogenic system radiation tolerant electronics and their associated field instruments have been in nominal conditions since before the commissioning of the first LHC beams in September 2008. This system is made of about 15’000 field instruments (thermometers, pressure sensors, liquid helium level gauges, electrical heaters and position switches), 7’500 electronic cards and 853 electronic crates. Since mid-2008 a software tool has been deployed, this allows an operator to report a problem and then lists the corrective actions. The tool is a great help in detecting recurrent problems that may be tackled by a hardware or software consolidation. The corrective actions range from simple resets, exchange of defective equipment, repair of electrical connectors, etc. However a recurrent problem that heals by itself is present on some channels. This type of fault is extremely difficult to diagnose and it appears as a temporary opening of an electrical circuit; its duration can range from a few minutes to several months. This paper presents the main type of problems encountered during the last four years, their evolution over time, the various hardware or software consolidations that have resulted and whether they have had an impact in the availability of the LHC beam.

Balle, Christoph; Casas, Juan; Vauthier, Nicolas [CERN, TE Department, 1211 Geneva (Switzerland)

2014-01-29

151

Brief encounters: Assembling cosmetic surgery tourism.  

PubMed

This paper reports findings from a large-scale, multi-disciplinary, mixed methods project which explores empirically and theoretically the rapidly growing but poorly understood (and barely regulated) phenomenon of cosmetic surgery tourism (CST). We explore CST by drawing on theories of flows, networks and assemblages, aiming to produce a fuller and more nuanced account of - and accounting for - CST. This enables us to conceptualise CST as an interplay of places, people, things, ideas and practices. Through specific instances of assembling cosmetic surgery that we encountered in the field, and that we illustrate with material from interviews with patients, facilitators and surgeons, our analysis advances understandings and theorisations of medical mobilities, globalisation and assemblage thinking. PMID:24985788

Holliday, Ruth; Bell, David; Cheung, Olive; Jones, Meredith; Probyn, Elspeth

2015-01-01

152

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

Microsoft Academic Search

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

James J. Greene; William J. Skowronski; J. Michael Mullins; Roland M. Nardone; Miguel Penafiel; Robert Meister

1991-01-01

153

The electromagnetic fields and the radiation of a spatio-temporally varying electric current loop  

E-print Network

The electric and magnetic fields of a spatio-temporally varying electric current loop are calculated using the Jefimenko equations. The radiation and the nonradiation parts of the electromagnetic fields are derived in the framework of Maxwell's theory of electromagnetic fields. In this way, a new, exact, analytical solution of the Maxwell equation is found.

Markus Lazar

2013-04-12

154

Magnetic fields in extragalactic jets. II. Specific models and radiative processes  

Microsoft Academic Search

The authors previously calculated magnetic fields produced in axisymmetric charged particle beams (jets) in which electrons (electrons and positrons) have drift velocities with respect to protons. In the present paper numerical solutions are compared with Bessel function and helical magnetic field solutions. Magnetic fields are calculated within mildly relativistic, relativistic, and ultrarelativistic jets interacting with the 2.7 K background radiation.

William K. Rose

1989-01-01

155

Magnetic fields in extragalactic jets. II - Specific models and radiative processes  

Microsoft Academic Search

The authors previously calculated magnetic fields produced in axisymmetric charged particle beams (jets) in which electrons (electrons and positrons) have drift velocities with respect to protons. In the present paper numerical solutions are compared with Bessel function and helical magnetic field solutions. Magnetic fields are calculated within mildly relativistic, relativistic, and ultrarelativistic jets interacting with the 2.7 K background radiation.

William K. Rose

1989-01-01

156

Thermodynamics and energy conversion of near-field thermal radiation: Maximum work and efficiency bounds  

NASA Astrophysics Data System (ADS)

We analyse the process of conversion of near-field thermal radiation into usable work by considering the radiation emitted between two planar sources supporting surface phonon-polaritons. The maximum work flux that can be extracted from the radiation is obtained taking into account that the spectral flux of modes is mainly dominated by these surface modes. The thermodynamic efficiencies are discussed and an upper bound for the first law efficiency is obtained for this process.

Latella, Ivan; Pérez-Madrid, Agustín; Rubi, J. Miguel

2014-12-01

157

Scatter radiation intensities around full-field digital mammography units  

PubMed Central

ABSTRACT The aim of this study was to investigate the scatter radiation intensity around digital mammography systems and apply these data to standard shielding calculations to reveal whether shielding design of existing breast screening rooms is adequate for the use of digital mammography systems. Three digital mammography systems from GE Healthcare, Hologic and Philips were employed in the study. A breast-equivalent phantom was imaged under clinical workload conditions and scatter radiation intensities around the digital mammography systems were measured for a range of angles in three planes using an ionisation chamber. The results were compared with those from previous studies of film-screen systems. It may be deduced from the results that scattering in the backward direction is significant for all three systems, while scattering in the forward direction can be significant for some planes around the GE and Hologic systems. Measurements at typical clinical settings on each system revealed the Philips system to have markedly lower scatter radiation intensities than the other systems. Substituting the measured scattered radiation intensity into shielding calculations yielded barrier requirements similar to those already in place at the screening centres operating these systems. Current radiation protection requirements based on film-screen technology remain sufficient when applied to rooms with digital mammography installations and no alteration is required to the structural shielding. PMID:23239693

Judge, M A; Keavey, E; Phelan, N

2013-01-01

158

Tuning near field radiative heat flux through surface excitations with a metal insulator transition.  

PubMed

The control of heat flow is a formidable challenge due to lack of good thermal insulators. Promising new opportunities for heat flow control were recently theoretically discovered for radiative heat flow in near field, where large heat flow contrasts may be achieved by tuning electronic excitations on surfaces. Here we show experimentally that the phase transition of VO2 entails a change of surface polariton states that significantly affects radiative heat transfer in near field. In all cases the Derjaguin approximation correctly predicted radiative heat transfer in near field, but it underestimated the far field limit. Our results indicate that heat flow contrasts can be realized in near field that can be larger than those obtained in far field. PMID:23003960

van Zwol, P J; Ranno, L; Chevrier, J

2012-06-01

159

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

Microsoft Academic Search

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

D. M. Le Vine; R. Meneghini

1978-01-01

160

Gas pressure on the surface of condensed phase in a resonance radiation field  

Microsoft Academic Search

The influence of resonance radiation on the pressure exerted by gas on the surface of a condensed phase is studied. The effects, which are associated with a change in the recoil pressure of molecules escaping from the surface in a radiation field, are considered. Combined manifestation of thermal and resonance effects is analyzed, as well as the influence of a

V. V. Levdansky

1999-01-01

161

Particle acceleration and radiation by direct electric fields in flaring complex solar active regions  

E-print Network

Particle acceleration and radiation by direct electric fields in flaring complex solar active-Meudon, 92195 Meudon Cedex, FRANCE Abstract The acceleration and radiation of solar energetic particles with the existing observations. 1 Introduction The approach used for particle acceleration models proposed for solar

Anastasiadis, Anastasios

162

Polarization of atomic radiation in stochastic plasma fields V. I. Savchenko and N. J. Fisch  

E-print Network

Polarization of atomic radiation in stochastic plasma fields V. I. Savchenko and N. J. Fisch a laser pulse of certain polarization or an electron beam excites atoms in a plasma, the atomic spectrum of the radiation emitted by the atoms exhibits differently polarized line core and line wings. This unusual effect

163

AIP/123-QED Experimental determination of radiated internal wave power without pressure field  

E-print Network

AIP/123-QED Experimental determination of radiated internal wave power without pressure field data-dimensional internal gravity waves. Both J and P are determined from expressions involving only a scalar function of a stratified fluid past a knife edge. The results for the radiated internal wave power given by the stream

Texas at Austin. University of

164

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

165

Low-Cost Shielding to Minimize Radiation Errors of Temperature Sensors in the Field  

Technology Transfer Automated Retrieval System (TEKTRAN)

The importance of shielding temperature sensors from solar radiation is understood, but there is a lack of prescriptive advice for plant scientists to build inexpensive, effective shields for replicated field experiments. Using general physical principles that govern radiation shielding, a number of...

166

Pioneer Saturn Encounter. [Pioneer 11 space probe  

NASA Technical Reports Server (NTRS)

The Pioneer Saturn Spacecraft, which began its journey as Pioneer 11, provided the first close view of the rings of Saturn as well as its system of moons. Its payload of 11 operating instruments obtained or confirmed data about the mass, temperature, composition, radiation belts, and atmosphere of the planet and its larger satellite, Titan. It made photometric and polarization measurements of lapetus, Rhea, Dione, and Tethys, as well as discovered additional rings. Scientific highlights of the mission are summarized. Color imagery provided by the photopolarimeter is included along with illustrations of the planet's magnetic field and radiation belts.

1979-01-01

167

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

168

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

Code of Federal Regulations, 2014 CFR

...be accompanied by a description of the site where the measurements were made showing the location of any possible source of reflections which might distort the field strength measurements. Information submitted shall include the relative radiated power...

2014-10-01

169

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

Code of Federal Regulations, 2010 CFR

...be accompanied by a description of the site where the measurements were made showing the location of any possible source of reflections which might distort the field strength measurements. Information submitted shall include the relative radiated power...

2010-10-01

170

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

Code of Federal Regulations, 2012 CFR

...be accompanied by a description of the site where the measurements were made showing the location of any possible source of reflections which might distort the field strength measurements. Information submitted shall include the relative radiated power...

2012-10-01

171

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

Code of Federal Regulations, 2013 CFR

...be accompanied by a description of the site where the measurements were made showing the location of any possible source of reflections which might distort the field strength measurements. Information submitted shall include the relative radiated power...

2013-10-01

172

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

Code of Federal Regulations, 2011 CFR

...be accompanied by a description of the site where the measurements were made showing the location of any possible source of reflections which might distort the field strength measurements. Information submitted shall include the relative radiated power...

2011-10-01

173

Gravitational waves from stellar encounters  

E-print Network

The emission of gravitational waves from a system of massive objects interacting on elliptical, hyperbolic and parabolic orbits is studied in the quadrupole approximation. Analytical expressions are then derived for the gravitational wave luminosity, the total energy output and gravitational radiation amplitude. A crude estimate of the expected number of events towards peculiar targets (i.e. globular clusters) is also given. In particular, the rate of events per year is obtained for the dense stellar cluster at the Galactic Center.

Salvatore Capozziello; Mariafelicia De Laurentis

2008-06-25

174

Strong-field perspective on high-harmonic radiation from bulk solids.  

PubMed

Mechanisms of high-harmonic generation from crystals are described by treating the electric field of a laser as a quasistatic strong field. Under the quasistatic electric field, electrons in periodic potentials form dressed states, known as Wannier-Stark states. The energy differences between the dressed states determine the frequencies of the radiation. The radiation yield is determined by the magnitudes of the interband and intraband current matrix elements between the dressed states. The generation of attosecond pulses from solids is predicted. Ramifications for strong-field physics are discussed. PMID:25479494

Higuchi, Takuya; Stockman, Mark I; Hommelhoff, Peter

2014-11-21

175

Computation of High-Altitude Hypersonic Flow-Field Radiation  

Microsoft Academic Search

Accurate calculations of radiation on and from transatmospheric flight vehicles are currently a challenge to computational aerodynamicists. Due to combined effects of low density and hypersonic flight conditions, the gas in the shock-layer is in a state of thermal and chemical nonequilibrium. The present work aims at gathering existing ideas together about how such flows should be modeled and comparing

Stephane Moreau

1994-01-01

176

Electric-field distribution near rectangular microstrip radiators for hyperthermia heating: Theory versus experiment in water  

SciTech Connect

A rectangular microstrip antenna radiator is investigated for its near-zone radiation characteristics in water. Calculations of a cavity model theory are compared with the electric-field measurements of a miniature nonperturbing diode dipole E-field probe whose 3 mm tip was positioned by an automatic three-axis scanning system. These comparisons have implications for the use of microstrip antennas in a multielement microwave hyperthermia applicator. Half-wavelength rectangular microstrip patches were designed to radiate in water at 915 MHz. Both low ([epsilon][sub r] = 10) and high ([epsilon][sub r] = 85) dielectric constant substrates were tested. Normal and tangential components of the near-zone radiated electric field were discriminated by appropriate orientation of the E-field probe. Low normal to transverse electric-field ratios ar 3.0 cm depth indicate that the radiators may be useful for hyperthermia heating with an intervening water bolus. Electric-field pattern addition from a three-element linear array of these elements in water indicates that phase and amplitude adjustment can achieve some limited control over the distribution of radiated power.

Underwood, H.R. (Wheaton College, IL (United States)); Peterson, A.F. (Georgia Institute of Technology, Atlanta (United States)); Magin, R.L. (University of Illinois, Urbana (United States))

1992-02-01

177

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

178

Shear Wave Field Radiated by an Electromagnetic Acoustic Transducer  

NASA Astrophysics Data System (ADS)

The horizontally polarized ultrasonic shear wave field emitted by an electromagnetic acoustic transducer (EMAT) is studied by the surface force distribution on the EMAT approximately described as an inhomogeneous horizontal shear force. The shear wave directivity pattern is plotted by numerical calculations based on our strictly analytic solutions of the wave field we presented previously. An experimental system of EMAT generation and piezoelectric transducer reception is set up to check the predictions of the theoretical wave field by measuring the ultrasonic signals through aluminium block. The directivity pattern of the wave field obtained from the experimental results conforms the theoretical prediction, which lays a foundation for engineering applications of EMATs.

Wu, Di; Li, Ming-Xuan; Wang, Xiao-Min

2006-12-01

179

Absorption cross section and Hawking radiation of the electromagnetic field with Weyl corrections  

E-print Network

We have investigated the absorption cross section and the Hawking radiation of electromagnetic field with Weyl correction in the background of a four-dimensional Schwarzschild black hole spacetime. Our results show that the properties of the absorption cross section and the Hawking radiation depend not only on the Weyl correction parameter, but also on the parity of the electromagnetic field, which is quite different from those of the usual electromagnetic field without Weyl correction in the four-dimensional spacetime. With increase of Weyl correction parameter, the absorption probability, the absorption cross section, the power emission spectra and the luminosity of Hawking radiation decreases with Weyl correction parameter for the odd-parity electromagnetic field and increases with the event-parity electromagnetic field.

Hao Liao; Songbai Chen; Jiliang Jing

2013-12-19

180

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

181

Position sensitive detection of neutrons in high radiation background field  

SciTech Connect

We present the development of a high-resolution position sensitive device for detection of slow neutrons in the environment of extremely high ? and e{sup ?} radiation background. We make use of a planar silicon pixelated (pixel size: 55 × 55 ?m{sup 2}) spectroscopic Timepix detector adapted for neutron detection utilizing very thin {sup 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{sup ?4}.

Vavrik, D., E-mail: vavrik@itam.cas.cz [Institute of Experimental and Applied Physics, Czech Technical University in Prague, Horska 3a/22, Prague (Czech Republic); Institute of Theoretical and Applied Mechanics, Academy of Sciences of the Czech Republic, Prosecka 76, 190 00 Prague 9 (Czech Republic); Jakubek, J.; Pospisil, S. [Institute of Theoretical and Applied Mechanics, Academy of Sciences of the Czech Republic, Prosecka 76, 190 00 Prague 9 (Czech Republic)] [Institute of Theoretical and Applied Mechanics, Academy of Sciences of the Czech Republic, Prosecka 76, 190 00 Prague 9 (Czech Republic); Vacik, J. [Nuclear Physics Institute, Academy of Sciences of the Czech Republic, Rez, 250 68 Prague, Czech Republic (Czech Republic)] [Nuclear Physics Institute, Academy of Sciences of the Czech Republic, Rez, 250 68 Prague, Czech Republic (Czech Republic)

2014-01-15

182

Basic physics of accretion disks : advection, radiation and magnetic fields  

NASA Astrophysics Data System (ADS)

This book provides the first extensive examination of various aspects of advection-dominated disks. Topics discussed include the global disk structure, thermal stability, two-temperature regimes, electron-positron pair production, disk spectra, the relation to the outburst behaviour of X-ray transients and hard - soft spectral transitions, the effect of radiation drag force, jet formation and possible nucleosynthesis in advection-dominated disks.

Kato, S.; Inagaki, S.; Mineshige, S.; Fukue, J.

183

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

184

Synchro-Curvature Radiation of Charged Particles in the Strong Curved Magnetic Fields  

NASA Astrophysics Data System (ADS)

It is generally believed that the radiation of relativistic particles in a curved magnetic field proceeds in either the synchrotron or the curvature radiation modes. In this paper we show that in strong curved magnetic fields a significant fraction of the energy of relativistic electrons can be radiated away in the intermediate, the so-called synchro-curvature regime. Because of the persistent change of the trajectory curvature, the radiation varies with the frequency of particle gyration. While this effect can be ignored in the synchrotron and curvature regimes, the variability plays a key role in the formation of the synchro-curvature radiation. Using the Hamiltonian formalism, we find that the particle trajectory has the form of a helix wound around the drift trajectory. This allows us to calculate analytically the intensity and energy distribution of prompt radiation in the general case of magnetic bremsstrahlung in the curved magnetic field. We show that the transition to the limit of the synchrotron and curvature radiation regimes is determined by the relation between the drift velocity and the component of the particle velocity perpendicular to the drift trajectory. The detailed numerical calculations, which take into account the energy losses of particles, confirm the principal conclusions based on the simplified analytical treatment of the problem, and allow us to analyze quantitatively the transition between different radiation regimes for a broad range of initial pitch angles. These calculations demonstrate that even very small pitch angles may lead to significant deviations from the spectrum of the standard curvature radiation when it is formally assumed that a charged particle moves strictly along the magnetic line. We argue that in the case of realization of specific configurations of the electric and magnetic fields, the gamma-ray emission of the pulsar magnetospheres can be dominated by the component radiated in the synchro-curvature regime.

Kelner, S. R.; Prosekin, A. Yu.; Aharonian, F. A.

2015-01-01

185

Use of an electric field in an electrostatic liquid film radiator.  

PubMed

Experimental and numerical work was performed to further the understanding of an electrostatic liquid film radiator (ELFR) that was originally proposed by Kim et al.(1) The ELFR design utilizes an electric field that exerts a normal force on the interface of a flowing film. The field lowers the pressure under the film in a space radiator and, thereby, prevents leakage through a puncture in the radiator wall. The flowing film is subject to the Taylor cone instability, whereby a cone of fluid forms underneath an electrode and sharpens until a jet of fluid is pulled toward the electrode and disintegrates into droplets. The critical potential for the instability is shown to be as much as an order of magnitude higher than that used in previous designs.(2) Furthermore, leak stoppage experiments indicate that the critical field is adequate to stop leaks in a working radiator. PMID:12446309

Bankoff, S G; Griffing, E M; Schluter, R A

2002-10-01

186

Gain and electric field radiation pattern approximations for the E-plane horn antenna  

SciTech Connect

A gain and electric (E) field radiation pattern approximation can be used to avoid the complex mathematics and computation methods typically required to calculate the gain and E field radiation pattern of the E-plane horn antenna. Using conventional techniques, the calculation of these antenna parameters involves solving the Fresnel integrals and the use of numerical integration. With the approximation model developed by the author, an estimate of the gain and E-plane radiation pattern can be determined using simple trigonometric terms. The criterion used to evaluate the accuracy of the approximations was that the approximated values fall within 3 dB of the calculated values. Under this criterion, the results showed that the gain approximation holds for a flare angle of less than 10/degree/ for typical antenna dimensions and the E field radiation pattern approximation holds until the antenna's phase error approaches 60/degree/. 4 refs., 20 figs., 12 tabs.

Ewing, P.D.

1988-12-01

187

Inefficient star formation: the combined effects of magnetic fields and radiative feedback  

NASA Astrophysics Data System (ADS)

We investigate the effects of magnetic fields and radiative protostellar feedback on the star formation process using self-gravitating radiation magnetohydrodynamical calculations. We present results from a series of calculations of the collapse of 50Msolar molecular clouds with various magnetic field strengths and with and without radiative transfer. We find that both magnetic fields and radiation have a dramatic impact on star formation, though the two effects are in many ways complementary. Magnetic fields primarily provide support on large scales to low-density gas, whereas radiation is found to strongly suppress small-scale fragmentation by increasing the temperature in the high-density material near the protostars. With strong magnetic fields and radiative feedback, the net result is an inefficient star formation process with a star formation rate of <~10 per cent per free-fall time that approaches the observed rate, although we have only been able to follow the calculations for 1/3 of a free-fall time beyond the onset of star formation.

Price, Daniel J.; Bate, Matthew R.

2009-09-01

188

Electromagnetic field radiated from broadband signal transmission on power line carrier channels  

Microsoft Academic Search

A rigorous procedure is presented for the evaluation of the rectangular components of the electromagnetic field radiated by excited carrier channels on multiconductor overhead power lines above a lossy ground. The proposed full wave approach, based on the use of Hertz potentials, allows to carry out the high-frequency analysis of a spread spectrum transmission system. Field sources are the current

M. S. Sarto

1997-01-01

189

Sub-THz Beam-forming using Near-field Coupling of Distributed Active Radiator Arrays  

E-print Network

Sub-THz Beam-forming using Near-field Coupling of Distributed Active Radiator Arrays Kaushik of beam-forming at sub-THz frequencies in CMOS. Near-field coupling is shown to be a scalable method and industrial safety. However, generation of high enough THz power in silicon has been a major bottleneck

Hajimiri, Ali

190

Bounds on the Magnetic Fields in the Radiative Zone of the Sun  

Microsoft Academic Search

We discuss bounds on the strength of the magnetic fields that could be buried in the radiative zone of the Sun. The field profiles and decay times are computed for all axisymmetric toroidal ohmic decay eigenmodes with lifetimes exceeding the age of the Sun. The measurements of the solar oblateness yield a bound of <~7 MG on the strength of

Alexander Friedland; Andrei Gruzinov

2004-01-01

191

The radiation field characteristics of piezoelectric polymer membrane transducers when operating into air  

Microsoft Academic Search

This paper describes the evaluation of the radiation field characteristics of PVDF membrane transducers, whereby the active area is defined by an appropriate electrode pattern when operating into air. Measurement, including conventional scanning of the fields and laser vibrometry, is supplemented by finite element modeling over the frequency range 500 kHz to 1.1 MHz. Contrary to expectation, the surface displacements

Gordon Hayward; Graham Benny; R. Banks; W. Galbraith

2000-01-01

192

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

193

Please report any Smalltooth Sawfish encounter!  

E-print Network

. The International Sawfish Encounter Database (ISED) was established as a sawfish tracking database to assist Carvalho Tel: (352) 392-2360 Cell: (352) 871-8230 International Sawfish Encounter Database Florida Program greatly help conservation efforts by providing the following information: · Your name, phone number, and e

Watson, Craig A.

194

Encounter with Jupiter. [Pioneer 10 space probe  

NASA Technical Reports Server (NTRS)

Pioneer 10 space probe's encounter with the Jupiter is discussed in detail. Tables are presented which include data on the distances during the encounter, times of crossing satellite orbits, important events in the flight near Jupiter, and time of experiments. Educational study projects are also included.

1975-01-01

195

THE SCOTTISH ENCOUNTER WITH TROPICAL DISEASE  

E-print Network

and his former Glasgow University pupil James Watt (1736-1819) invented the steam engine. Scottish-17 The Filariases 18-19 The Scottish Encounter with Filariases 20-21 Parasitic Flukes 22-23 The Scottish Encounter elsewhere. Two of the most influential early European explorers of Africa were James Bruce (1730-1794), who

Schnaufer, Achim

196

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

197

Electromagnetic signatures of far-field gravitational radiation in the 1+3 approach  

E-print Network

Gravitational waves from astrophysical sources can interact with background electromagnetic fields, giving rise to distinctive and potentially detectable electromagnetic signatures. In this paper, we study such interactions for far-field gravitational radiation using the 1+3 approach to relativity. Linearised equations for the electromagnetic field on perturbed Minkowski space are derived and solved analytically. The inverse Gertsenshtein conversion of gravitational waves in a static electromagnetic field is rederived, and the resultant electromagnetic radiation is shown to be significant for highly magnetised pulsars in compact binary systems. We also obtain a variety of nonlinear interference effects for interacting gravitational and electromagnetic waves, although wave-wave resonances previously described in the literature are absent when the electric-magnetic self-interaction is taken into account. The fluctuation and amplification of electromagnetic energy flux as the gravitational wave strength increases towards the gravitational-electromagnetic frequency ratio is a possible signature of gravitational radiation from extended astrophysical sources.

Alvin J. K. Chua; Priscilla Cañizares; Jonathan R. Gair

2014-06-14

198

Electromagnetic signatures of far-field gravitational radiation in the 1 + 3 approach  

NASA Astrophysics Data System (ADS)

Gravitational waves (GWs) from astrophysical sources can interact with background electromagnetic fields, giving rise to distinctive and potentially detectable electromagnetic signatures. In this paper, we study such interactions for far-field gravitational radiation using the 1 + 3 approach to relativity. Linearized equations for the electromagnetic field on perturbed Minkowski space are derived and solved analytically. The inverse Gertsenshte?n conversion of GWs in a static electromagnetic field is rederived, and the resultant electromagnetic radiation is shown to be significant for highly magnetized pulsars in compact binary systems. We also obtain a variety of nonlinear interference effects for interacting gravitational and electromagnetic waves, although wave–wave resonances previously described in the literature are absent when the electric–magnetic self-interaction is taken into account. The fluctuation and amplification of electromagnetic energy flux as the GW strength increases towards the gravitational–electromagnetic frequency ratio is a possible signature of gravitational radiation from extended astrophysical sources.

Chua, Alvin J. K.; Cañizares, Priscilla; Gair, Jonathan R.

2015-01-01

199

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. PMID:23385413

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

2013-01-01

200

The Gravitational Field of a Radiating Electromagnetic Dipole  

E-print Network

We begin with the time-dependent electric and magnetic dipole solution of Maxwell's equations in Minkowski space. This Maxwell field is then used to determine the behavior of the gravitational field (the Weyl tensor) as a second-order perturbation off of the Minkowski background. From the Weyl tensor we go on and find the spin-coefficients and the full metric in this approximation. The physical meaning of many of the relations is discussed. In particular we can identify the conservation law of angular momentum that contains an angular momentum flux term.

Tim Adamo; Ezra T Newman

2008-07-22

201

Two-temperature steady-state thermodynamics for a radiation field  

NASA Astrophysics Data System (ADS)

A candidate for a consistent steady-state thermodynamics is constructed for a radiation field in vacuum sandwiched by two black bodies of different temperatures. Because of the collisionless nature of photons, a steady state of a radiation field is completely determined by the temperatures of the two black bodies. Then the zeroth, first, second and third laws can be extended to steady states, where the idea of local steady states plays an important role in the system whose geometrical shape is anisotropic and inhomogeneous. The thermodynamic formalism presented in this paper does not include an energy flux as a state variable. This is consistent with the notable conclusion by [C. Essex, Adv. Thermodyn. 3 (1990) 435; Planet. Space. Sci. 32 (1984) 1035] that, contrary to the success in the irreversible thermodynamics for dissipative systems, a nonequilibrium radiation field does not obey the bilinear formalism of the entropy production rate using an energy flux and its conjugate force. Although the formalism given in this paper may be unique to a radiation field, a nonequilibrium order parameter of steady states of a radiation field is explicitly defined. This order parameter denotes that the geometrical shape of the system determines how a steady state is far from an equilibrium. The higher the geometrical symmetry, the more distant the steady state.

Saida, Hiromi

2005-10-01

202

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

203

11/5/2007 M. Holdridge 1 New Horizons Pluto EncounterNew Horizons Pluto Encounter  

E-print Network

11/5/2007 M. Holdridge 1 New Horizons Pluto EncounterNew Horizons Pluto Encounter Baseline Review not conclude the concept development phase of planning the Pluto encounter. Continued analysis and trades, we are finding the Pluto flyby is a very unique flyby in terms of geometry and goals

Young, Leslie A.

204

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 A. Hodge, Ding Yuan, Raymond P. Keegan, Michael A. Krstich

2007-07-09

205

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

206

Radiative signature of magnetic fields in internal shocks  

NASA Astrophysics Data System (ADS)

Common models of blazars and gamma-ray bursts assume that the plasma underlying the observed phenomenology is magnetized to some extent. Within this context, radiative signatures of dissipation of kinetic and conversion of magnetic energy in internal shocks of relativistic magnetized outflows are studied. We model internal shocks as being caused by collisions of homogeneous plasma shells. We compute the flow state after the shell interaction by solving Riemann problems at the contact surface between the colliding shells, and then compute the emission from the resulting shocks. Under the assumption of a constant flow luminosity, we find that there is a clear difference between the models where both shells are weakly magnetized (?? 10-2) and those where, at least, one shell has ?? 10-2. We obtain that the radiative efficiency is largest for models in which, regardless of the ordering, one shell is weakly and the other strongly magnetized. Substantial differences between weakly and strongly magnetized shell collisions are observed in the inverse-Compton part of the spectrum, as well as in the optical, X-ray and 1-GeV light curves. We propose a way to distinguish observationally between weakly magnetized and strongly magnetized internal shocks by comparing the maximum frequency of the inverse-Compton part and synchrotron part of the spectrum to the ratio of the inverse-Compton to synchrotron fluence. Finally, our results suggest that low-frequency peaked blazars (LBL) may correspond to barely magnetized flows, while high-frequency peaked blazars (HBL) could correspond to moderately magnetized ones. Indeed, by comparing with actual blazar observations, we conclude that the magnetization of typical blazars is ?? 0.01 for the internal shock model to be valid in these sources.

Mimica, P.; Aloy, M. A.

2012-04-01

207

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

208

[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

209

Evanescent field enhancement and dipole radiation in the presence of multilayer thin films  

NASA Astrophysics Data System (ADS)

Weak optical signals, e.g., Raman scattering, fluorescence emission, etc., are typically enhanced by increasing both the excitation field and the collection efficiency. Near a surface, signals can be resonantly enhanced using either surface plasmon polaritons or a resonant dielectric waveguide, provided the sources lie within an evanescent decay length of the surface. We have studied both of these strategies experimentally and also via numerical simulations. The evanescent field can be enhanced by an order of magnitude via surface plasmon resonance, and by several orders with a resonant dielectric waveguide. On the other hand, in order to efficiently collect the resulting emissions, we must know how they are distributed spatially, i.e. we must understand how the outgoing energy flux (the Poynting vector) depends on the radial distance and the polar and azimuthal angles of the observation point relative to the source, which we model as an electric dipole having some specified orientation. We have carried out calculations of these "radiation patterns" using the exact Sommerfeld integral formalism, generalized to apply to a multilayer system, which yields the field intensities at an arbitrary point relative to the source. We have also employed a computationally simpler approach based on the Lorentz reciprocity theorem that yields the fields in the asymptotic limit where the observation point is far from the source point; here only the radiation fields survive. We have compared the radiation patterns calculated by the above two methods for a single dipole positioned above a dielectric half space. We have also conducted a series of optical measurements to determine the dipole radiation patterns associated with embedded rhodamine B dye molecules in various multilayer structures. The radiation patterns are highly structured. Good agreement was achieved between the far-field simulations and the experimental results. A possible setup is proposed for utilizing both the enhanced evanescent field and the structured radiation pattern.

Luan, Lan

210

Lightning electromagnetic radiation field spectra in the interval from 0. 2 to 20 MHz  

Microsoft Academic Search

Average energy spectral densities are presented for the fast transitions in most of the components that produce large radiation field impulses from cloud-to-ground lightning; first and subsequent return strokes; stepped, dart-stepped, and 'chaotic' leaders; and 'characteristic' cloud pulses. A disagreement in the previous literature about the spectral energy radiated by return strokes at high frequencies is noted and explained. The

J. C. Willett; J. C. Bailey; C. Leteinturier; E. P. Krider

1990-01-01

211

Thermodynamic structure of field equations near apparent horizon for radiating black holes  

E-print Network

We study the intriguing analogy between gravitational dynamics of the horizon and thermodynamics for the case of nonstationary radiating spherically symmetric black holes both in four dimensions and higher dimensions. By defining all kinematical parameters of nonstationary radiating black holes in terms of null vectors, we demonstrate that it is possible to interpret the Einstein field equations near the apparent horizon in the form of a thermodynamical identity $TdS=dE+PdV$.

Uma Papnoi; Megan Govender; Sushant G Ghosh

2014-11-10

212

Determination of ¹N gamma radiation fields at BWR nuclear power stations  

Microsoft Academic Search

Measurements of environmental gamma radiation fields produced by ¹N in components above the floor in the turbine buildings of two large BWR power plants were carried out in April 1975, using pressurized argon ionization chambers and NaI(Tl) and Ge(Li) spectrometers. Both turbine buildings are heavily side-shielded, so that the bulk of the radiation outside the buildings is skyshine. The shapes

W. M. Lowder; P. D. Raft; G. deP Burke

1976-01-01

213

Modeling of Ionizing Radiation-Induced Degradation in Multiple Gate Field Effect Transistors  

Microsoft Academic Search

The radiation response of advanced non-planar mul- tiple gate field effect transistors (MuGFETs) has been shown to have a strong dependence on fin width . The incorporation of total ionizing dose (TID) effects into a physics-based surface-po- tential compact model allows for the effects of radiation-induced degradation in MuGFET devices to be modeled in circuit sim- ulators, e.g., SPICE. A

Ivan Sanchez Esqueda; Hugh J. Barnaby; Keith E. Holbert; Farah El-Mamouni; Ronald D. Schrimpf

2011-01-01

214

Gravitational radiation generated by cosmological phase transition magnetic fields  

SciTech Connect

We study gravitational waves generated by the cosmological magnetic fields induced via bubble collisions during the electroweak (EW) and QCD phase transitions. The magnetic field generation mechanisms considered here are based on the use of the fundamental EW minimal supersymmetric and QCD Lagrangians. The gravitational waves spectrum is computed using a magnetohydrodynamic turbulence model. We find that the gravitational wave spectrum amplitude generated by the EW phase transition peaks at a frequency of approximately 1-2 mHz, and is of the order of 10{sup -20}-10{sup -21}; thus this signal is possibly detectable by the Laser Interferometer Space Antenna (LISA). The gravitational waves generated during the QCD phase transition, however, are outside the LISA sensitivity bands.

Kahniashvili, Tina [McWilliams Center for Cosmology and Department of Physics, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Department of Physics, Laurentian University, Sudbury, Ontario P3E 2C6 (Canada); National Astrophysical Observatory, Ilia Chavchavadze State University, Tbilisi, GE-0160 (Georgia); Kisslinger, Leonard [McWilliams Center for Cosmology and Department of Physics, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Stevens, Trevor [Department of Physics, West Virginia Wesleyan College, Buckhannon, West Virginia 26201 (United States)

2010-01-15

215

A Study of High Altitude Hypersonic Flow-Field Radiation  

NASA Technical Reports Server (NTRS)

This paper presents the results of the works carried out jointly at Stanford University and Ames Research Center under a grant from the Ballistic Missile Defense Organization (BMDO) (formerly the Strategic Defense Initiative Organization) to explain and understand the results of the two flight experiments, Bow Shock Ultra-Violet 1 and Bow Shock Ultra-Violet 2, carried out by the Organization. A portion of the material contained in this paper has been reported elsewhere in open literature. However, this paper provides (1) the details of scientific contents not available in those literature, (2) the links among those and the logical order of the efforts involved, and (3) some materials not contained in any open literature. The first author is responsible for execution of the work; the second author directed the work of the first author. In the two flight experiments mentioned above, the spectra of radiation in the ultraviolet wavelength range incident on the stagnation point of a blunt body were measured at the flight speeds of 3.8 and 5.2 km/sec over a wide range of altitudes. The results were compared first with the calculations made using the original version of the NEQAIR/STRAP codes written earlier by the second author. At low altitudes, the calculations agreed with the measurement. However, at high altitudes, the calculations underestimated the intensity of the radiation by several orders of magnitudes. A shock tube experiment was carried out at CALSPAN and a plasma-torch experiment was carried out at Stanford University to produce experimental data to help explain the discrepancy. In addition, the shock tube experiment at Ames Research Center carried out independently of the BMDO was also found to be relevant to this question. In this paper, several theoretical models are developed and calculations using the models were carried out to explain the results not only of the flight experiments but also of the CALSPAN, Stanford, and Ames experiments. The are: (1) the diffusion model for the rotational mode to explain the slowness of rotational excitation, (2) assignment of different vibrational temperatures and different relaxation rates for different molecules, and (3) the modification of the NEQAIR code to accommodate the new experimental data. This paper shows that the discrepancy between the flight data and calculation is smaller with the present model, but is still substantial.

Moreau, Stephane; Park, Chul; Edwards, Thomas A. (Technical Monitor)

1994-01-01

216

Synchro-curvature radiation of charged particles in the strong curved magnetic fields  

E-print Network

It is generally believed that the radiation of relativistic particles in a curved magnetic field proceeds in either the synchrotron or the curvature radiation modes. In this paper we show that in strong curved magnetic fields a significant fraction of the energy of relativistic electrons can be radiated away in the intermediate, the so-called synchro-curvature regime. Because of the persistent change of the trajectory curvature, the radiation varies with the frequency of particle gyration. While this effect can be ignored in the synchrotron and curvature regimes, the variability plays a key role in the formation of the synchro-curvature radiation. Using the Hamiltonian formalism, we find that the particle trajectory has the form of a helix wound around the drift trajectory. This allows us to calculate analytically the intensity and energy distribution of prompt radiation in the general case of magnetic bremsstrahlung in the curved magnetic field. We show that the transition to the limit of the synchrotron and...

Kelner, S R; Aharonian, F A

2015-01-01

217

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

218

Lightning electromagnetic radiation over a stratified conducting ground: Formulation and numerical evaluation of the electromagnetic fields  

NASA Astrophysics Data System (ADS)

The formulation describing the electromagnetic field radiated by a lightning return stroke over a two-layered conducting ground is presented in this paper. The derivation of the Green's functions required to solve the problem is first discussed in detail, and the expressions for the lightning electromagnetic fields are determined. Afterward, an efficient method for the numerical evaluation of the electromagnetic field is proposed. The proposed method is based on a suitable modification of a previously developed model for the evaluation of the fields in the presence of a lossy but homogeneous soil. Particular attention is devoted to the soil reflection coefficient properties, both from a physical and from a mathematical point of view. In part 2 of the paper, the developed approach and numerical algorithms will be used to evaluate the effect of the soil stratification on the radiated fields and to perform the validity assessment of simplified approaches proposed in the literature.

Delfino, Federico; Procopio, Renato; Rossi, Mansueto; Shoory, Abdolhamid; Rachidi, Farhad

2011-02-01

219

Passive Lossless Huygens Metasurfaces for Conversion of Arbitrary Source Field to Directive Radiation  

E-print Network

We present a semi-analytical formulation of the interaction between a given source field and a scalar Huygens metasurface (HMS), a recently introduced promising concept for wavefront manipulation based on a sheet of orthogonal electric and magnetic dipoles. Utilizing the equivalent surface impedance representation of these metasurfaces, we establish that an arbitrary source field can be converted into directive radiation via a passive lossless HMS if two physical conditions are met: local power conservation and local impedance equalization. Expressing the fields via their plane-wave spectrum and harnessing the slowly-varying envelope approximation we obtain semi-analytical formulae for the scattered fields, and prescribe the surface reactance required for the metasurface implementation. The resultant design procedure indicates that the local impedance equalization induces a Fresnel-like reflection, while local power conservation forms a radiating virtual aperture which follows the total excitation field magni...

Epstein, Ariel

2014-01-01

220

OPTICAL FIELD PARAMETERS: Estimate of the minimal coherence length of probe optical radiation in interferometry  

NASA Astrophysics Data System (ADS)

The minimal coherence length of probe optical radiation sufficient for formation of a homogeneous interference structure is estimated. The estimate is based on the analysis of the interference structure in the intensity distribution of the field scattered by rough surfaces and point objects and also formed in interferometers. Analysis was performed for the field intensity detected for the time T > 10?c (under the condition that the coherence time of the probe radiation is ?c > 3/?0, where ?0 is the central frequency of the emission spectrum). It is shown that the minimal coherence length Lc of the probe radiation, at which the homogeneous stratified interference structure of the scattered field can be still formed, is 8? (? is the central wavelength). The possibility of using this result for determining the maximal information content of the method of low-coherence optical tomography is analysed.

Bakut, P. A.; Mandrosov, V. I.

2007-01-01

221

Radiation drag in the field of a non-spherical source  

NASA Astrophysics Data System (ADS)

The motion of a test particle in the gravitational field of a non-spherical source endowed with both mass and mass quadrupole moment is investigated when a test radiation field is also present. The background is described by the Erez-Rosen solution, which is a static space-time belonging to the Weyl class of solutions to the vacuum Einstein's field equations, and reduces to the familiar Schwarzschild solution when the quadrupole parameter vanishes. The radiation flux has a fixed but arbitrary (non-zero) angular momentum. The interaction with the radiation field is assumed to be Thomson-like, i.e. the particles absorb and re-emit radiation, thus suffering for a friction-like drag force. Such an additional force is responsible for the Poynting-Robertson effect, which is well established in the framework of Newtonian gravity and has been recently extended to the general theory of relativity. The balance between gravitational attraction, centrifugal force and radiation drag leads to the occurrence of equilibrium circular orbits which are attractors for the surrounding matter for every fixed value of the interaction strength. The presence of the quadrupolar structure of the source introduces a further degree of freedom: there exists a whole family of equilibrium orbits parametrized by the quadrupole parameter, generalizing previous works. This scenario is expected to play a role in the context of accretion matter around compact objects.

Bini, D.; Geralico, A.; Passamonti, A.

2015-01-01

222

Radiation drag in the field of a non-spherical source  

E-print Network

The motion of a test particle in the gravitational field of a non-spherical source endowed with both mass and mass quadrupole moment is investigated when a test radiation field is also present. The background is described by the Erez-Rosen solution, which is a static spacetime belonging to the Weyl class of solutions to the vacuum Einstein's field equations, and reduces to the familiar Schwarzschild solution when the quadrupole parameter vanishes. The radiation flux has a fixed but arbitrary (non-zero) angular momentum. The interaction with the radiation field is assumed to be Thomson-like, i.e., the particles absorb and re-emit radiation, thus suffering for a friction-like drag force. Such an additional force is responsible for the Poynting-Robertson effect, which is well established in the framework of Newtonian gravity and has been recently extended to the general theory of relativity. The balance between gravitational attraction, centrifugal force and radiation drag leads to the occurrence of equilibrium circular orbits which are attractors for the surrounding matter for every fixed value of the interaction strength. The presence of the quadrupolar structure of the source introduces a further degree of freedom: there exists a whole family of equilibrium orbits parametrized by the quadrupole parameter, generalizing previous works. This scenario is expected to play a role in the context of accretion matter around compact objects.

Donato Bini; Andrea Geralico; Andrea Passamonti

2014-10-12

223

Radiation field in a superstrong magnetoactive electron plasma.  

PubMed

Using the language of quantum field theory, we present a concise derivation for the electromagnetic vector potential A(mu), which is valid for an anisotropic superstrong magnetoactive electron plasma. It is shown that the expression for the vector potential A(mu) can be reduced to various known limits. Applications to important problems in astrophysics are briefly discussed. The relevance of our result to the recent development of the collective interaction between intense neutrino fluxes and stellar plasmas is briefly stressed. PMID:11970505

Chou, C K

1999-11-01

224

Elastic orthonormal beams and localized fields with applications to control laser radiation  

NASA Astrophysics Data System (ADS)

Unique elastic fields, beams defined by a given set of orthonormal scalar functions on a two-dimensional or three- dimensional beam manifold, are treated. The proposed approach enables one to obtain sets of orthonormal beams and various families of localized fields in both isotropic and anisotropic solids. This can be applied also to sound beams in liquids. By way of illustration, the fields defined by the spherical harmonics are considered. The families of orthonormal beams can be used as functional bases for complex elastic fields. The obtained localized elastic fields include storms, whirls, and tornadoes, i.e., the localized fields for which time average energy flux is identically zero at all points, azimuthal, and spiral, respectively. It is shown that these fields can be combined into a complex field structure, such as an ultrasonic diffraction grating. This makes them promising tools to control laser radiation.

Borzdov, George N.

2001-07-01

225

Voyager 1 encounter with the Saturnian system  

NASA Technical Reports Server (NTRS)

The Voyager 1 Saturn flyby mission of March 1979 is reviewed, with brief discussions of its flight, trajectory, science plan formulation and telemetered data. Analytical results of such data with respect to Saturn's atmosphere, rings, icy satellites, Titan satellite atmosphere and the Saturn magnetosphere, are summarized. The Voyager science investigations comprise imaging science (ISS), infrared radiation (IRIS), photopolarimetry (PPS), ultraviolet spectroscopy (UVS), radio science (RSS), magnetic fields (MAG), plasma particles (PLS), plasma waves (PWS), planetary radio astronomy (PRA), low energy charged particles (LECP), and cosmic-ray particles (CRS).

Stone, E. C.; Miner, E. D.

1981-01-01

226

Entanglement and nonclassicality for multimode radiation-field states  

SciTech Connect

Nonclassicality in the sense of quantum optics is a prerequisite for entanglement in multimode radiation states. In this work we bring out the possibilities of passing from the former to the latter, via action of classicality preserving systems like beam splitters, in a transparent manner. For single-mode states, a complete description of nonclassicality is available via the classical theory of moments, as a set of necessary and sufficient conditions on the photon number distribution. We show that when the mode is coupled to an ancilla in any coherent state, and the system is then acted upon by a beam splitter, these conditions turn exactly into signatures of negativity under partial transpose (NPT) entanglement of the output state. Since the classical moment problem does not generalize to two or more modes, we turn in these cases to other familiar sufficient but not necessary conditions for nonclassicality, namely the Mandel parameter criterion and its extensions. We generalize the Mandel matrix from one-mode states to the two-mode situation, leading to a natural classification of states with varying levels of nonclassicality. For two-mode states we present a single test that can, if successful, simultaneously show nonclassicality as well as NPT entanglement. We also develop a test for NPT entanglement after beam-splitter action on a nonclassical state, tracing carefully the way in which it goes beyond the Mandel nonclassicality test. The result of three-mode beam-splitter action after coupling to an ancilla in the ground state is treated in the same spirit. The concept of genuine tripartite entanglement, and scalar measures of nonclassicality at the Mandel level for two-mode systems, are discussed. Numerous examples illustrating all these concepts are presented.

Ivan, J. Solomon; Chaturvedi, S.; Ercolessi, E.; Marmo, G.; Morandi, G.; Mukunda, N.; Simon, R. [Raman Research Institute, C. V. Raman Avenue, Sadashivanagar, Bangalore 560 080 (India); School of Physics, University of Hyderabad, Hyderabad 500 046 (India); Physics Department, University of Bologna, CNISM and INFN, 46 v.Irnerio, I-40126 Bologna (Italy); Dipartimento di Scienze Fisiche, University of Napoli and INFN, v.Cinzia, I-80126 Naples (Italy); Physics Department, University of Bologna, CNISM and INFN, 6/2 v.le Berti Pichat, I-40127 Bologna (Italy); Centre for High Energy Physics, Indian Institute of Science, Bangalore 560 012 (India); The Institute of Mathematical Sciences, C.I.T Campus, Chennai 600 113 (India)

2011-03-15

227

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

228

Time Dependence of the Ultraviolet Radiation Field in the Local Interstellar Medium  

NASA Astrophysics Data System (ADS)

Far-ultraviolet (FUV, 6eVradiation has been suggested as the main source of heating of the neutral interstellar gas, and, in this case, it determines whether the thermal balance of the neutral gas results in cold (T~50-100 K) clouds (cold neutral material [CNM]), warm (T~104 K) clouds (warm neutral material [WNM]), or a combination of the two. For gas at fixed mean density, high FUV fields convert the neutral gas to WNM, while low fields result in CNM. The main sources of interstellar FUV radiation are short-lived massive stars in associations that form in giant molecular clouds. Using McKee & Williams' distribution of birthrates for OB associations in the Galaxy, we determine the expected behavior of the time-dependent FUV field for random positions in the ISM at the solar circle. The FUV field is calculated in two bands (912-1100 and 912-2070 Å) and at the wavelength 1400 Å. In terms of U-17?U/(10-17ergscm-3Å- 1), where U is the energy density of the radiation field in some band, we find (mean, median) values at the solar circle of U-17=(15.7,7.4) and (14.2, 7.2) for the 912-1100 and 912-2070 Å bands, respectively. At 1400 Å we find (mean, median) values of U-17=(14.4,7.5). Our median value for the 912-2070 Å band is G0=1.6 times Habing's value for the radiation field at the solar circle in this band and quite close to Draine's value, G0=1.7. Habing and Draine's values are based on observations of sources of FUV radiation in the solar neighborhood, so all three values are close to observed values. Because of attenuation by dust, only associations within about 500 pc contribute significantly to the energy density at a given point. Large-angle scattering produces a diffuse field that is about 10% of the field produced by the sum of direct and small-angle (<5°) scattering from discrete sources (the associations), as observed. At a point exposed to the median radiation field, the brightest association typically produces about 20% of the total energy density. At a point exposed to an above average radiation field, the brightest association produces most of the energy density. Therefore, the FUV field is asymmetric at a given point, and the asymmetry grows for higher fields. The FUV field fluctuates with a variety of amplitudes, the larger ones being less frequent. The mean field is about twice the median field because of these fluctuations, or spikes, in the radiation field. These spikes, which last ~30 Myr, are caused by the infrequent birth of nearby associations. For spikes that are significantly higher than the mean field, the time interval between spikes is ~2U3/2-15 Gyr. We also model shorter duration spikes caused by runaway OB stars. The presence of a fluctuating heating rate created by the fluctuating FUV field converts CNM to WNM and vice versa.

Parravano, Antonio; Hollenbach, David J.; McKee, Christopher F.

2003-02-01

229

Pioneer to encounter Saturn on September 1  

NASA Technical Reports Server (NTRS)

The encounter of the Pioneer 11 Spacecraft with Saturn, designed to provide information on the evolution of the Sun and its planets, is described. Photographs and measurements of Saturn, its rings, and several of its 10 satellites, including Titan, to be taken by Pioneer instruments, are emphasized. The encounter sequence and spacecraft trajectory are discussed. A description of Saturn and its atmosphere is included. Onboard instruments and experiments are also described.

1979-01-01

230

TOPICAL REVIEW: Strong field interaction of laser radiation  

NASA Astrophysics Data System (ADS)

The Review covers recent progress in laser-matter interaction at intensities above 1018 W cm-2. At these intensities electrons swing in the laser pulse with relativistic energies. The laser electric field is already much stronger than the atomic fields, and any material is instantaneously ionized, creating plasma. The physics of relativistic laser-plasma is highly non-linear and kinetic. The best numerical tools applicable here are particle-in-cell (PIC) codes, which provide the most fundamental plasma model as an ensemble of charged particles. The three-dimensional (3D) PIC code Virtual Laser-Plasma Laboratory runs on a massively parallel computer tracking trajectories of up to 109 particles simultaneously. This allows one to simulate real laser-plasma experiments for the first time. When the relativistically intense laser pulses propagate through plasma, a bunch of new physical effects appears. The laser pulses are subject to relativistic self-channelling and filamentation. The gigabar ponderomotive pressure of the laser pulse drives strong currents of plasma electrons in the laser propagation direction; these currents reach the Alfvén limit and generate 100 MG quasistatic magnetic fields. These magnetic fields, in turn, lead to the mutual filament attraction and super-channel formation. The electrons in the channels are accelerated up to gigaelectronvolt energies and the ions gain multi-MeV energies. We discuss different mechanisms of particle acceleration and compare numerical simulations with experimental data. One of the very important applications of the relativistically strong laser beams is the fast ignition (FI) concept for the inertial fusion energy (IFE). Petawatt-class lasers may provide enough energy to isochorically ignite a pre-compressed target consisting of thermonuclear fuel. The FI approach would ease dramatically the constraints on the implosion symmetry and improve the energy gain. However, there is a set of problems to solve before the FI will work. The laser pulse cannot reach the dense core of the target directly. The laser energy must be converted into fast particles first and then transported through the overdense plasma region. The energy spectra of the laser-generated particle beams, their emittance and transport problems are discussed here. The laser-particle interaction at relativistic intensities is highly non-linear and higher laser harmonics are generated. In plasma, the high-harmonic generation is a collective effect - it appears to be quite effective when an intense laser pulse is reflected from the overdense plasma layer. The plasma boundary is then driven by the laser ponderomotive force and works as a relativistically oscillating mirror. Another interesting application is the amplification of short-pulse laser in plasma by a counter-propagating pump pulse. 3D PIC simulations suggest that multi-terawatt pulses of sub-10 fs duration can be generated this way.

Pukhov, Alexander

2003-01-01

231

Encounters between binaries and neutron stars  

NASA Technical Reports Server (NTRS)

We simulated encounters between a neutron star and primordial and tidal-capture binaries. In the case of encounters involving a tidal-capture binary, comprising a white dwarf and a main-sequence star, we find that most exchange encounters will produce a single merged object with the white dwarf and neutron star engulfed in a common envelope of gas donated by the main-sequence primary of the original binary. A small fraction of exchanges induce a merger of the white dwarf and main-sequence star, with this object being unbound to the neutron star, and the two objects having a large relative speed at infinity. For encounters involving a primordial binary, fewer encounters require the inclusion of hydrodynamical effects. Those involving collisions or close encounters tend to produce a binary comprised of the two merged stars (now forming one star) and the third star. The binaries produced typically have large enough separations to prevent the formation of a single merged object until subsequent stellar evolution of one of the components causes it to fill its Roche lobe. Clean exchanges produce binaries with large eccentricities; they are typically sufficiently wide to avoid circularization.

Davies, M. B.; Benz, W.; Hills, J. G.

1993-01-01

232

Boundary conditions for polarized radiative transfer with incident radiation  

NASA Astrophysics Data System (ADS)

Context. Polarized radiative transfer in the presence of scattering in spectral lines and/or in continua may be cast in a reduced form for six reduced components of the radiation field. In this formalism, the six components of the reduced source function are angle-independent quantities. It thus drastically reduces the storage requirement of numerical codes and it is very well suited to solving polarized non-local thermodynamic equilibrium radiative transfer problems in 3D media. Aims: This approach encounters a fundamental problem when the medium is illuminated by a polarized incident radiation, because there is a priori no way of relating the known (and measurable) Stokes parameters of the incident radiation to boundary conditions for the reduced equations. The origin of this problem is that there is no unique way of deriving the radiation-reduced components from its Stokes parameters (only the inverse operation is clearly defined). The method proposed here aims at enabling to work with arbitrary incident radiation field (polarized or unpolarized). Methods: In previous studies, an ad-hoc treatment of the boundary conditions, applied to cases where the incident radiation is unpolarized, has been used. In this paper, we show that it is possible to account for the incident radiation in a rigorous way without any assumption on its properties by expressing the radiation field as the sum of a directly transmitted radiation and of a diffuse radiation. This approach was first used by Chandrasekhar to solve the problem of diffuse reflection by planetary atmospheres illuminated by their host star. Results: The diffuse radiation field obeys a transfer equation with no incident radiation that may be solved in the reduced form. The first scattering of the incident radiation introduces primary creation terms in the six components of the reduced source function. Once the reduced polarized transfer problem is solved for the diffuse radiation field, its Stokes parameters can be computed. The full radiation field is then obtained by adding the directly transmitted radiation field computed in the Stokes formalism. Conclusions: In the case of an unpolarized incident radiation, the diffuse field approach allows us to validate the previously introduced ad-hoc expressions. The diffuse field approach however leads to more accurate computation of the source terms in the case where the incident radiation is anisotropic. It is the only possible approach when the incident radiation field is polarized. We perform numerical computations of test cases, showing that the emergent line-polarization may be significantly affected by the polarization of the incident radiation.

Faurobert, M.; Mili?, I.; Atanackovi?, O.

2013-11-01

233

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

234

Terahertz radiation from carbon nanorings in external collinear constant and varying electric fields  

NASA Astrophysics Data System (ADS)

We consider the response of a quasi-one-dimensional ballistic carbon ring to the field of an electromagnetic wave propagating along the normal to the ring plane in the presence of a constant electric field collinear to the field of the wave. The dipole moment and the radiation intensity of the ring are calculated for the ballistic motion of a conduction electron. The possibility of implementation of regular periodic and chaotic regimes of ring emission under the action of external fields is demonstrated. The radiation spectrum of the ring is analyzed, and the dependence of the scattering cross section for an electromagnetic wave incident on the ring on its frequency and amplitude is calculated.

Fedorov, E. G.; Yanyushkina, N. N.; Belonenko, M. B.

2013-04-01

235

Testing of Performance of Optical Fibers Under Irradiation in Intense Radiation Fields, When Subjected to Very High Temperatures  

SciTech Connect

The primary objective of this project is to measure and model the performance of optical fibers in intense radiation fields when subjected to very high temperatures. This research will pave the way for fiber optic and optically based sensors under conditions expected in future high-temperature gas-cooled reactors. Sensor life and signal-to-noise ratios are susceptible to attenuation of the light signal due to scattering and absorbance in the fibers. This project will provide an experimental and theoretical study of the darkening of optical fibers in high-radiation and high-temperature environments. Although optical fibers have been studied for moderate radiation fluence and flux levels, the results of irradiation at very high temperatures have not been published for extended in-core exposures. Several previous multi-scale modeling efforts have studied irradiation effects on the mechanical properties of materials. However, model-based prediction of irradiation-induced changes in silica�s optical transport properties has only recently started to receive attention due to possible applications as optical transmission components in fusion reactors. Nearly all damage-modeling studies have been performed in the molecular-dynamics domain, limited to very short times and small systems. Extended-time modeling, however, is crucial to predicting the long-term effects of irradiation at high temperatures, since the experimental testing may not encompass the displacement rate that the fibers will encounter if they are deployed in the VHTR. The project team will pursue such extended-time modeling, including the effects of the ambient and recrystallization. The process will be based on kinetic MC modeling using the concept of amorphous material consisting of building blocks of defect-pairs or clusters, which has been successfully applied to kinetic modeling in amorphized and recrystallized silicon. Using this procedure, the team will model compensation for rate effects, and the interplay of rate effects with the effects of annealing, to accurately predict the fibers� reliability and expected lifetime

Blue, Thomas; Windl, Wolfgang; Dickerson, Bryan

2013-01-03

236

Quasinormal modes, scattering, and Hawking radiation of Kerr-Newman black holes in a magnetic field  

SciTech Connect

We perform a comprehensive analysis of the spectrum of proper oscillations (quasinormal modes), transmission/reflection coefficients, and Hawking radiation for a massive charged scalar field in the background of the Kerr-Newman black hole immersed in an asymptotically homogeneous magnetic field. There are two main effects: the Zeeman shift of the particle energy in the magnetic field and the difference of values of an electromagnetic potential between the horizon and infinity, i.e. the Faraday induction. We have shown that 'turning on' the magnetic field induces a stronger energy-emission rate and leads to 'recharging' of the black hole. Thus, a black hole immersed in a magnetic field evaporates much quicker, achieving thereby an extremal state in a shorter period of time. Quasinormal modes are moderately affected by the presence of a magnetic field which is assumed to be relatively small compared to the gravitational field of the black hole.

Kokkotas, K. D.; Konoplya, R. A.; Zhidenko, A. [Theoretical Astrophysics, Eberhard-Karls University of Tuebingen, Tuebingen 72076 (Germany); Centro de Matematica, Computacao e Cognicao, Universidade Federal do ABC, Rua Santa Adelia, 166, 09210-170, Santo Andre, Sao Paulo (Brazil)

2011-01-15

237

Radiative properties of a plasma moving across a magnetic field. II: Numerical results  

SciTech Connect

A theoretical analysis developed in a companion paper to treat the early-time evolution of plasmas moving across a background magnetic field is applied to the modeling of low-beta, barium chemical releases in the magnetosphere. The results indicate that radiation damping plays an important role in defining the plasma cloud evolution, causing a rapid decay of the polarization field and a loss of plasma kinetic energy and momentum on time scales comparable to several ion gyroperiods. The radiation spectrum consists of a burst of chirped, high-frequency (in the range of the cloud plasma frequencies) waves, followed by a pulse of whistler waves, and subsequently by ion cyclotron emission. Scaling laws are derived for the plasma momentum and energy loss rates and predictions for the braking time, the amplitude and spectrum of the radiation field, and the total radiated power are presented for conditions relevant to the recent Combined Release and Radiation Effects Satellite (CRRES) experiments [Phys. Fluids B [bold 4], 2249 (1992)].

Roussel-Dupre, R. (Space Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)); Miller, R.H. (Space Physics Research Laboratory, Department of Atmospheric, Oceanic and Space Sciences, The University of Michigan, Ann Arbor, Michigan 48109-2143 (United States))

1993-04-01

238

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

239

Transient quantum coherent response to a partially coherent radiation field  

SciTech Connect

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.

Sadeq, Zaheen S.; Brumer, Paul, E-mail: pbrumer@chem.utoronto.ca [Department of Chemistry and Center for Quantum Information and Quantum Control, Chemical Physics Theory Group, University of Toronto, Toronto, Ontario M5S 3H6 (Canada)] [Department of Chemistry and Center for Quantum Information and Quantum Control, Chemical Physics Theory Group, University of Toronto, Toronto, Ontario M5S 3H6 (Canada)

2014-02-21

240

Radiation field consideration of biconical horn antenna with different flare angles  

Microsoft Academic Search

The radiation fields of a biconical horn antenna with different flare angles are computed from both the fields of an equivalent Huygens source on the spherical-surface aperture and the infinite biconical horn antenna with spherical TEM wave. Experimental results are first presented for the symmetrical biconical horn antenna, ka = 1.57 and 3.14 (where k is the propagation constant and

Koji Nagasawa; Isamu Matsuzuka

1988-01-01

241

Simulation of relativistic shocks and associated radiation from turbulent magnetic fields  

Microsoft Academic Search

Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs in the shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and for particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The ``jitter'' radiation from deflected

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

2011-01-01

242

On Consideration of Radiated Power in RF Field Simulations for MRI  

PubMed Central

In numerical analyses of 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.

2012-01-01

243

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. PMID:21731221

Taylor, Michael L.; Kron, Tomas

2011-01-01

244

Correction of MODIS aerosol retrieval for 3D radiative effects in broken cloud fields  

NASA Astrophysics Data System (ADS)

Retrieval of aerosol properties near clouds from reflected sunlight is rather challenging. Sunlight reflected from clouds can effectively enhance the reflectance from clear regions nearby. Ignoring cloud 3D radiative adjacency effects can lead to large biases in aerosol retrievals, resulting incorrect interpretation of satellite observations for aerosolcloud interaction. We have developed a simple model to compute cloud-induced radiance enhancement due to radiative interaction between boundary layer clouds and the molecular layer above it. Here we apply this method to broken cloud fields acquired from MODIS. We use CERES observations combined with radiative transfer models to derive visible narrowband radiative fluxes for estimating the radiance enhancement. With the corrected spectral radiances as input to the MODIS aerosol retrieval algorithm, we compute the corrected aerosol optical thicknesses (AOT). We compare the corrected AOT with the original ones to assess the performance of our approach. We further discuss issues in the current correction method and plans to validate the algorithm.

Wen, Guoyong; Marshak, Alexander; Remer, Lorraine; Levy, Robert; Loeb, Norman; Várnai, Tamás; Cahalan, Robert F.

2013-05-01

245

Cirrus microphysics and radiative transfer: Cloud field study on October 28, 1986  

NASA Technical Reports Server (NTRS)

The radiative properties of cirrus clouds present one of the unresolved problems in weather and climate research. Uncertainties in ice particle amount and size and, also, the general inability to model the single scattering properties of their usually complex particle shapes, prevent accurate model predictions. For an improved understanding of cirrus radiative effects, field experiments, as those of the Cirrus IFO of FIRE, are necessary. Simultaneous measurements of radiative fluxes and cirrus microphysics at multiple cirrus cloud altitudes allows the pitting of calculated versus measured vertical flux profiles; with the potential to judge current cirrus cloud modeling. Most of the problems in this study are linked to the inhomogeneity of the cloud field. Thus, only studies on more homogeneous cirrus cloud cases promises a possibility to improve current cirrus parameterizations. Still, the current inability to detect small ice particles will remain as a considerable handicap.

Kinne, Stefan; Ackerman, Thomas P.; Heymsfield, Andrew J.; Valero, Francisco P. J.; Sassen, Kenneth; Spinhirne, James D.

1990-01-01

246

Application of whole-body personal TL dosemeters in mixed field beta-gamma radiation.  

PubMed

Application of whole-body personal TL dosemeters based on a high-sensitivity LiF:Mg,Cu,P (MCP-N) in mixed field beta-gamma radiation has been characterised. The measurements were carried out with (90)Sr/(90)Y, (85)Kr and (137)Cs point sources to calculate the energy response and linearity of the TLD response in a dose range of 0.1-30 mSv. From the result, calibration curves were obtained, enabling the readout of individual dose equivalent Hp(10) from gamma radiation and Hp(0.07) from beta radiation in mixed field beta-gamma. Limitation of the methodology and its application are presented and discussed. PMID:25009188

Ciupek, K; Aksamit, D; Wo?oszczuk, K

2014-11-01

247

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

248

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

249

A Study of an N Molecule Quantized-Radiation-Field Hamiltonian  

E-print Network

In this dissertation a simple Hamiltonian for a system of inter-acting molecules and radiation field is developed from a model of N Two-Level Molecules interacting, via a dipole approximation, with a single mode, quantized radiation field. The exact eigenvalues and eigenvectors of this Hamiltonian are compared with analytical results obtained from several different approximation schemes applied to the simple model. The consequence of this comparison is the development of validity criteria for the utilization of these approximation schemes to more difficult problems. For example, an analysis done here indicates that using an independent molecule approximation in an explanation of the "build up" of coherent radiation in a gas laser (maser) may be inappropriate.

Michael Thomas Tavis

2012-06-01

250

Radiation field of cosmic rays measured in low Earth orbit by CR-39 detectors  

NASA Astrophysics Data System (ADS)

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 and fragments produced in CR-39 detectors by cosmic ray primary and secondary protons and heavier nuclei and by secondary neutrons. The measured LET spectra were used to determine the corresponding absorbed dose and dose equivalent. Total flux of Z ? 2 was estimated and a charge spectrum was measured for STS-108 and STS-112 missions. Comparisons are made with the predictions of cosmic ray transport models.

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

251

Radiation Field of Cosmic Rays Measured in Low Earth Orbit by CR-39 Detectors  

NASA Astrophysics Data System (ADS)

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 CR-39 detectors by cosmic ray primary and secondary protons and heavier nuclei and by secondary neutrons. The measured LET spectra were used to determine the corresponding absorbed dose and dose equivalent. Total flux of Z?2 was estimated and a charge spectrum was measured for STS-108 and STS-112 missions. Comparisons are made with the predictions of cosmic ray transport models.

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

252

Response of alanine and radio-photo-luminescence dosemeters to mixed high-energy radiation fields.  

PubMed

Alanine and Radio-Photo-Luminescence (RPL) dosemeters are passive dosemeters used to monitor absorbed dose in all kind of radiation fields. However, up to now both dosemeter types are calibrated to photon sources only. In order to study the response of RPL and alanine dosemeters to mixed high-energy particle fields like those occurring at CERN's accelerators, an irradiation campaign at the CERN-EC High-Energy Reference field Facility (CERF-field) was performed. In this facility a copper target is irradiated by hadrons with a momentum of 120 GeV/c. Dosemeters were exposed to various mixed radiation fields by placing them at various positions on the surface of the target. In addition to the experiment FLUKA Monte Carlo simulations were carried out, which provide information concerning the energy deposition at the dosemeter locations. This paper compares the measurements with the simulation results and discusses the radiation field compositions present at the various dosemeter positions on the target. PMID:17369266

Vincke, H; Brunner, I; Floret, I; Forkel-Wirth, D; Fuerstner, M; Mayer, S; Theis, C

2007-01-01

253

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

254

Generating High-Intensity Electromagnetic Fields for Radiated-Susceptibility Test  

Microsoft Academic Search

This paper discusses a feasibility study covering the generation of high-intensity electromagnetic fields for radiated susceptibility or ordnance hazard tests. A new type of antenna using an elliptic-cylinder reflector is discussed. The results of laboratory measurements made with such an antenna are displayed graphically and discussed in the text of the paper. The advantages and limitations of this device are

Victor P. Musil

1968-01-01

255

Would be the photon a composed particle? quantization of field fluxes in electromagnetic radiation  

E-print Network

[En] Here it is made a comparative analysis between the classical and the quantum expressions for the energy of electromagnetic radiation (ER). The comparison points to the possibility of the quantization of the magnetic and the electric field fluxes in the ER.

Celso de Araujo Duarte

2013-12-02

256

The energy distribution of atoms in the field of thermal radiation  

E-print Network

Using the principle of detailed balance and the assumption on the absorption cross-section consistent with available astrophysical data, we obtain the energy distribution of atoms in the field of thermal blackbody radiation and show that this distribution diverges from the Boltzmann law. There is an inversion of the high energy level population at sufficiently high temperatures.

F. V. Prigara

2003-11-24

257

The energy distribution of atoms in the field of thermal blackbody radiation  

E-print Network

Using the principle of detailed balance and the assumption on the absorption cross-section consistent with available astrophysical data, we obtain the energy distribution of atoms in the field of thermal blackbody radiation and show that this distribution diverges from the Boltzmann law.

F. V. Prigara

2002-02-06

258

A new approach to calculate the field radiated from arbitrarily structured transducer arrays  

Microsoft Academic Search

A efficient time-domain algorithm, based on the spatial pulse response approach, is proposed for the determination of the acoustic fields radiated by means of acoustical sources. The computations are performed by the discrete representation array modelling (DREAM) procedure, specially adapted to study the planar and arbitrarily structured multielement transducer arrays. DREAM, based on the discrete representation computational concept, acts as

Bogdan Piwakowski; Khalid Sbai

1999-01-01

259

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...

260

The Physical Reality of Space and Surface Waves in the Radiation Field of Radio Antennas  

Microsoft Academic Search

Evidence is presented which indicates that, notwithstanding the change in sign made by Sommerfeld in his 1926 paper on radio wave propagation, the radiation field of a vertical electric dipole may be separated into space and surface wave components. Sommerfeld's original concepts as to the characteristics of two such waves in radio transmission are largely substantiated. It is shown that

K. A. Norton

1937-01-01

261

Measurement of neutron dose equivalent to proton therapy patients outside of the proton radiation field  

Microsoft Academic Search

Measurements of neutron dose equivalent values and neutron spectral fluences close to but outside of the therapeutic proton radiation field are presented. The neutron spectral fluences were determined at five locations with Bonner sphere measurements and established by unfolding techniques. More than 50 additional neutron dose equivalent values were measured with LiI and BF3 thermal neutron detectors surrounded by a

X Yan; U Titt; A. M Koehler; W. D Newhauser

2002-01-01

262

Hawking radiation for a scalar field conformally coupled to an AdS black hole  

E-print Network

The decomposition in normal modes of a scalar field conformally coupled to an AdS black hole leads to a Heun equation with simple coefficients thanks to conformal invariance. By applying the Damour-Ruffini method we can relate the critical exponent of the radial part at the horizon surface to the Hawking radiation of scalar particles.

Valtancoli, P

2015-01-01

263

Negative Binomial States of the Radiation Field and their Excitations are Nonlinear Coherent States  

E-print Network

We show that the well-known negative binomial states of the radiation field and their excitations are nonlinear coherent states. Excited nonlinear coherent state are still nonlinear coherent states with different nonlinear functions. We finally give exponential form of the nonlinear coherent states and remark that the binomial states are not nonlinear coherent states.

Xiao-Guang Wang; Hong-Chen Fu

1999-03-03

264

Tidal Disruptions of White Dwarfs from Ultra-Close Encounters with Intermediate Mass Spinning Black Holes  

E-print Network

We present numerical relativity results of tidal disruptions of white dwarfs from ultra-close encounters with a spinning, intermediate mass black hole. These encounters require a full general relativistic treatment of gravity. We show that the disruption process and prompt accretion of the debris strongly depend on the magnitude and orientation of the black hole spin. However, the late-time accretion onto the black hole follows the same decay, $\\dot{M}$ ~ t^{-5/3}, estimated from Newtonian gravity disruption studies. We compute the spectrum of the disk formed from the fallback material using a slim disk model. The disk spectrum peaks in the soft X-rays and sustains Eddington luminosity for 1-3 yrs after the disruption. For arbitrary black hole spin orientations, the disrupted material is scattered away from the orbital plane by relativistic frame dragging, which often leads to obscuration of the inner fallback disk by the outflowing debris. The disruption events also yield bursts of gravitational radiation with characteristic frequencies of ~3.2 Hz and strain amplitudes of ~10^{-18} for galactic intermediate mass black holes. The optimistic rate of considered ultra-close disruptions is consistent with no sources found in ROSAT all-sky survey. The future missions like Wide-Field X-ray Telescope (WFXT) could observe dozens of events.

Roland Haas; Roman V. Shcherbakov; Tanja Bode; Pablo Laguna

2012-01-20

265

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

266

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

SciTech Connect

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. [Interdisciplinary Research Center, Yokohama National University, Yokohama 240-8501 (Japan); Shimosato, H.; Bito, M.; Furusawa, K. [Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531 (Japan); Adachi, M.; Zen, H.; Kimura, S.; Katoh, M. [UVSOR, Institute of Molecular Science, Okazaki 444-8585 (Japan); School of Physical Sciences, Graduate Universities for Advanced Studies (SOKENDAI), Okazaki 444-8585 (Japan); Shimada, M. [High Energy Accelerator Research Organization, KEK, Tsukuba 305-0801 (Japan); Yamamoto, N.; Hosaka, M. [Graduate School of Engineering, Nagoya University, Nagoya 464-8603 (Japan); Ashida, M. [Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531 (Japan); PRESTO, JST (Japan)

2012-03-12

267

Polarization-dependent heating of the cosmic microwave background radiation by a magnetic field  

NASA Astrophysics Data System (ADS)

The changes in the cosmic microwave background (CMB) spectrum seen as an increase of temperature due to a strong magnetic field are determined and their influence on the polarization of the radiation is exhibited. The effect is due to the coupling of the CMB photons to the magnetic field in the QED vacuum via the interaction with virtual pairs. In spite of the fact that the distortion of the CMB spectrum for magnetic fields that exist in the vicinity of magnetars is quite large, this effect is very difficult to detect at present because the required angular resolutions is not yet available.

Bialynicka-Birula, Zofia; Bialynicki-Birula, Iwo

2014-12-01

268

Polarization-dependent heating of the cosmic microwave background radiation by a magnetic field  

E-print Network

The changes in the cosmic microwave background (CMB) spectrum seen as an increase of temperature due to a strong magnetic field are determined and their influence on the polarization of the radiation is exhibited. The effect is due to the coupling of the CMB photons to the magnetic field in the QED vacuum via the interaction with virtual pairs. In spite of the fact that the distortion of the CMB spectrum for magnetic fields that exist in the vicinity of magnetars is quite large, this effect is very difficult to detect at present because the required angular resolutions is not yet available.

Bialynicka-Birula, Zofia

2014-01-01

269

Far field and energy flux caused by a radiating source in an anisotropic medium  

NASA Astrophysics Data System (ADS)

The Lighthill-Giles (1960, 1978), method is extended to evaluate the far field resulting from a moving radiating source in an anisotropic and dispersive medium, and the result thus obtained has a retardation interpretation. The radiation energy flux derived from the J-E method, only after a modification resulting from anisotropy of the medium and a correction factor resulting from retardation, is found to be compatible with that directly calculated from the far field, provided interference may be neglected. While the interference, which arises from the mixed product of any two far-field terms of different wave vectors, is demonstrated to be completely null in a uniaxial medium for a stationary source, it is shown to exist in a gyrotropic magnetoplasma, and the total Poynting vector could be substantially nonradial in certain special cases.

Lai, H. M.; Chan, P. K.

1986-06-01

270

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

271

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

272

Contribution of backscattering to radiation fields in the Source Projector Facility  

SciTech Connect

The Radiation Physics Source Projection Facility at Fermilab employs three collimated {sup 137}Cs sources for different calibration purposes. This facility is used to calibrate many of the instruments used at Fermilab to measure both prompt and residual radiation fields due to accelerator operations. A study was done using three air ion chambers (2.5 ml, 80 ml, and 1000 ml) to measure field uniformity within the radiation cone and separately the contribution of backscatter. The field uniformity was measured by extracting the deviations of the gamma ray intensity from the inverse square law. Then by positioning the ion chambers at different location in the calibration cave, both inside and outside the effective radiation cone, the room scattered fraction has been extracted and compared to the calculations. It is found that the deviation from the inverse square law near the source is mainly due to scattering off the source collimator and at the far end is primarily due to scattering off the walls.

Marshall, E.; Vaziri, K.; Krueger, F.; Cossairt, D.

1996-10-01

273

Estimation of the radiation field homogeneity in 60Co blood irradiator  

NASA Astrophysics Data System (ADS)

The aim of this work is to estimate the homogeneity of the radiation field in various configurations and relative activities of the “disposed” but still relatively highly active (approximately thousands of Curies, i.e. tens of TBq) sources for their potential use in irradiation of blood (or blood derivatives). Small dose rate, which is already unusable/inappropriate for the teletherapy, may be still utilized by simultaneous use of multiple sources or reducing the distance to the irradiated object (blood unit). To estimate the homogeneity of the radiation field a modeling approach has been chosen in which Monte Carlo code MCNP has been employed. (In-) homogeneity of the radiation field has been estimated on the basis of isodoses in the water phantom and for various configurations and relative activities of the 60Co sources. The results of simulations are also discussed with regard to further optimization (homogeneity of the sample irradiation, costs, radiation protection of service staff, availability of a sufficient number of resources, etc.).

Urban, Tomas

2014-11-01

274

Response of dosemeters in the radiation field generated by a TW-class laser system.  

PubMed

State-of-the-art laser systems are able to generate ionising radiation of significantly high energies by focusing ultra-short and intense pulses onto targets. Thus, measures ensuring the radiation protection of both working personnel and the general public are required. However, commercially available dosemeters are primarily designed for measurement in continuous fields. Therefore, it is important to explore their response to very short pulses. In this study, the responses of dosemeters in a radiation field generated by iodine high-power and Ti:Sapphire laser systems are examined in proton and electron acceleration experiments. Within these experiments, electron bunches of femtosecond pulse duration and 100-MeV energy and proton bunches with sub-nanosecond pulse duration and energy of several megaelectronvolts were generated in single-shot regimes. Responses of typical detectors (TLD, films and electronic personal dosemeter) were analysed and compared. Further, a first attempt was carried out to characterise the radiation field generated by TW-class laser systems. PMID:24563524

Olšovcová, V; Klír, D; Krása, J; Kr?s, M; Velyhan, A; Zelenka, Z; Rus, B

2014-10-01

275

Characterization of ALS undulator radiation—High K, taper, and the near field effect  

NASA Astrophysics Data System (ADS)

The results of the measurements of spectral and angular distribution of the U5.0 (5 cm period) and U8.0 (8 cm period) Advanced Light Source (ALS) undulators are described. The spectra of on-axis undulator radiation were measured for various values of the deflection parameter K. In particular, the high K case was studied, representing the region between the undulator and wiggler limits. Good agreement in harmonic peak flux and width is found between the measurements and the computations that include the real magnetic field, the electron beam energy spread, and the electron beam emittance. The effect of the undulator taper on the spectral characteristics of the radiation was analyzed. At small taper (˜0.5% gap variation) significant reduction in peak brightness and flux of the fifth harmonic was observed with small effect on the fundamental. The near field effect in the undulator radiation was studied by measuring the off-axis spectral and angular distributions of the radiation. The broadening and the fine structure in the distributions at large off-axis angles were observed, resulting from the near field effect.

Mossessian, D. A.; Heimann, P. A.

1995-11-01

276

Polarized Radiation Diagnostics for Measuring the Magnetic Field of the Outer Solar Atmosphere  

NASA Astrophysics Data System (ADS)

The basic idea of optical pumping, for which Alfred Kastler received the 1966 Nobel Prize in physics, is that the absorption and scattering of light that is near-resonant with an optical transition can produce large population imbalances among the magnetic sublevels of atomic ground states as well as in excited states. The degree of this radiatively-induced atomic level polarization, which is very sensitive to the presence of magnetic fields, can be determined by observing the polarization of the scattered or transmitted spectral line radiation. Probably, the most important point for solar physics is that the outer solar atmosphere is indeed an optically pumped vapor and that the polarization of the emergent spectral line radiation can be exploited for detecting magnetic fields that are too weak and/or too tangled so as to produce measurable Zeeman polarization signals. In this talk we review some recent radiative transfer simulations of the polarization produced by optical pumping in selected IR, FUV and EUV spectral lines, showing that their sensitivity to the Hanle effect is very suitable for magnetic field measurements in the outer solar atmosphere. We argue that solar magnetometry using the spectral lines of optically pumped atoms in the chromosphere, transition region and corona should be a high-priority goal for large aperture solar telescopes, such as ATST, EST and SOLAR-C.

Trujillo Bueno, J.

2012-12-01

277

Characterisation of radiation field for irradiation of biological samples at nuclear reactor-comparison of twin detector and recombination methods.  

PubMed

Central Laboratory for Radiological Protection is involved in achieving scientific project on biological dosimetry. The project includes irradiation of blood samples in radiation fields of nuclear reactor. A simple facility for irradiation of biological samples has been prepared at horizontal channel of the nuclear reactor MARIA in NCBJ in Poland. The radiation field, composed mainly of gamma radiation and thermal neutrons, has been characterised in terms of tissue kerma using twin-detector technique and recombination chambers. PMID:24366246

Golnik, N; Gryzi?ski, M A; Kowalska, M; Meronka, K; Tulik, P

2014-10-01

278

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

279

Homeless women's experiences of service provider encounters.  

PubMed

Service providers are gatekeepers to health-sustaining services and resources, although little is known about service encounters from the perspective of homeless women. We conducted in-depth semistructured interviews with 15 homeless women to better understand their experiences of service encounters. Using a phenomenological method, 160 significant statements were extracted from participant transcripts; more positive than negative interactions were reported. The 10 themes that emerged fall along a dehumanizing/humanizing continuum primarily separated by the power participants experienced in the interaction and the trust they felt in the service provider. Implications for nursing practice and research are offered. PMID:24528122

Biederman, Donna J; Nichols, Tracy R

2014-01-01

280

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

281

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

282

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

283

High-field half-cycle terahertz radiation from relativistic laser interaction with thin solid targets  

SciTech Connect

It is found that half-cycle terahertz (THz) pulses with the peak field over 100 MV/cm can be produced in ultrashort intense laser interactions with thin solid targets. These THz pulses are shown to emit from both the front and rear sides of the solid target and are attributed to the coherent transition radiation by laser-produced ultrashort fast electron bunches. After the primary THz pulses, subsequent secondary half-cycle pulses are generated while some refluxing electrons cross the vacuum-target interfaces. Since such strong THz radiation is well synchronized with the driving lasers, it is particularly suitable for applications in various pump-probe experiments.

Ding, W. J.; Koh, W. S. [A-STAR Institute of High Performance Computing, Singapore 138632 (Singapore)] [A-STAR Institute of High Performance Computing, Singapore 138632 (Singapore); Sheng, Z. M. [Key Laboratory for Laser Plasmas (MoE) and Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China) [Key Laboratory for Laser Plasmas (MoE) and Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); SUPA, Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom)

2013-11-11

284

Double-probe measurements in field-aligned irregularities produced by intense electromagnetic radiation  

NASA Astrophysics Data System (ADS)

We present the signature of filamentary field-aligned irregularities (FAI) in the artificially modified ionosphere using data from a rocket-borne floating double-probe gathered near the critical layer of the Arecibo HF heater beam. We model the double-probe signature as proportional to each filament's density gradient, in the plane perpendicular to the geomagnetic field. We find that this signature is consistent with the presence of a radially directed effective electric field Eeff within each of the over 180 filaments. The direction of Eeff is consistent with that of an ambipolar electric field associated with the rapid perpendicular diffusion of ions out of each filament, or with an apparent electric field due to an inward electron temperature gradient associated with the presence of hotter plasma inside each filament. Our model also gives an estimate of the impact parameter at which each filament is encountered. The mean square impact parameter shows the correct relation to the mean square filament transit time, assuming cylindrical field-aligned filaments. The consistency of these results confirms that the previously reported density depletions are quasi-steady, cylindrically symmetric, spatial structures. A small shift in the apparent angle between the double-probe boom and the filament-rocket velocity places a lower limit on the Earth-frame drift velocity of the filaments, away from the heater beam. Since the filaments are observed near the westward edge of the heater beam, well away from the bulk of the heater Poynting flux, we expect that the filaments are observed in the process of decaying, that is, that ions are diffusing inward rather than outward. Thus we identify Eeff as a temperature gradient and use it to estimate a minimum filament temperature enhancement of ~100 K.

Peria, W. J.; Kelley, M. C.; Franz, T.

1999-04-01

285

Intense THz radiation produced in organic salt crystals for high-field applications  

NASA Astrophysics Data System (ADS)

Organic stilbazolium salt crystals pumped by intense, ultrashort mid-infrared laser have been investigated for efficient THz generation by optical rectification. In this paper we present our latest results in view of the generation of single-cycle and high-field THz transient in the THz gap (0.1-10 THz). The organic rectifiers like DAST, OH1 and DSTMS combine extremely large optical susceptibility with excellent velocity matching between the infrared pump and the THz radiation. Our simple collinear conversion scheme provides THz beams with excellent focusing properties and single cycle electric field larger than 1.5 MV/cm and magnetic field strength beyond 0.5 Tesla. The source can potentially cover the full THz gap at field strength which is barely provided by other THz sources. The THz pulse is carrier-envelope phase stable and the polarity of the field can be easily inverted.

Vicario, C.; Ruchert, C.; Hauri, C. P.

2013-03-01

286

Superkicks in ultrarelativistic encounters of spinning black holes  

SciTech Connect

We study ultrarelativistic encounters of two spinning, equal-mass black holes through simulations in full numerical relativity. Two initial data sequences are studied in detail: one that leads to scattering and one that leads to a grazing collision and merger. In all cases, the initial black hole spins lie in the orbital plane, a configuration that leads to the so-called superkicks. In astrophysical, quasicircular inspirals, such kicks can be as large as {approx}3000 km/s; here, we find configurations that exceed {approx}15 000 km/s. We find that the maximum recoil is to a good approximation proportional to the total amount of energy radiated in gravitational waves, but largely independent of whether a merger occurs or not. This shows that the mechanism predominantly responsible for the superkick is not related to merger dynamics. Rather, a consistent explanation is that the ''bobbing'' motion of the orbit causes an asymmetric beaming of the radiation produced by the in-plane orbital motion of the binary, and the net asymmetry is balanced by a recoil. We use our results to formulate some conjectures on the ultimate kick achievable in any black hole encounter.

Sperhake, Ulrich [Institut de Ciencies de l'Espai (CSIC-IEEC), Facultat de Ciencies, Campus UAB, E-08193 Bellaterra (Spain); California Institute of Technology, Pasadena, California 91125 (United States); Department of Physics and Astronomy, The University of Mississippi, University, Mississippi 38677 (United States); Berti, Emanuele [Department of Physics and Astronomy, The University of Mississippi, University, Mississippi 38677 (United States); California Institute of Technology, Pasadena, California 91125 (United States); Cardoso, Vitor [CENTRA, Departamento de Fisica, Instituto Superior Tecnico, Universidade Tecnica de Lisboa-UTL, Av. Rovisco Pais 1, 1049 Lisboa (Portugal); Department of Physics and Astronomy, The University of Mississippi, University, Mississippi 38677 (United States); Pretorius, Frans [Department of Physics, Princeton University, Princeton, New Jersey 08544 (United States); Yunes, Nicolas [Department of Physics, Princeton University, Princeton, New Jersey 08544 (United States); Department of Physics and MIT Kavli Institute, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States); Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States)

2011-01-15

287

Particle Acceleration and Radiation associated with Magnetic Field Generation from Relativistic Collisionless Shocks  

E-print Network

Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The ``jitter'' radiation from deflected electrons 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.

K. -I. Nishikawa; P. Hardee; G. Richardson; R. Preece; H. Sol; G. J. Fishman

2003-12-03

288

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

289

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

290

Problems Encountered by Novice Pair Programmers  

ERIC Educational Resources Information Center

In a study of the types of problems encountered by students that led them to seek assistance, Robins et al. [2006] found that the most common problems were related to trivial mechanics. The students in this study worked by themselves on their programming exercises. This article discusses a replication of the Robins et al. study in which the…

Hanks, Brian

2008-01-01

291

EPOXI COMET ENCOUNTER Nov. 2, 2010  

E-print Network

1 EPOXI COMET ENCOUNTER FACT SHEET Nov. 2, 2010 Quick Facts Flyby Spacecraft Dimensions: 3.3 meters metric tons Nucleus rotation period: About 18 hours Nucleus composition: Water ice, carbon dioxide ice the sun. Frozen balls of ice, rocks and dust, they are the undercooked leftovers that remained after

Gruner, Daniel S.

292

Entering a Crack: An Encounter with Gossip  

ERIC Educational Resources Information Center

In this paper, I enter a crack to think otherwise about the concept "gossip". Drawing on previous scholarship engaging with Deleuzian concepts to inform research methodologies, this paper builds on this body of work. Following Deleuze and Guattari, the paper undertakes a mapping of gossip, subsequent to an encounter with a crack.…

Henderson, Linda

2014-01-01

293

The Landscape Encountered and Experienced While Hiking  

Microsoft Academic Search

An operational definition is developed for the landscape encountered and experienced while hiking a natural area. Participant photography and experience sampling methods were combined and modified to enable sampling and exploration of this landscape. At various times during a hike, people were interrupted and instructed to photograph what they were looking at, to rate the scenic beauty of the view

R. Bruce Hull; William P. Stewart

1995-01-01

294

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

295

Occupational radiation exposure history of Idaho Field Office Operations at the INEL  

SciTech Connect

An extensive review has been made of the occupational radiation exposure records of workers at the Idaho National Engineering Laboratory (INEL) over the period of 1951 through 1990. The focus has been on workers employed by contractors and employees of the Idaho Field Operations Office (ID) of the United States Department of Energy (USDOE) and does not include the Naval Reactors Facility (NRF), the Argonne National Laboratory (ANL), or other operations field offices at the INEL. The radiation protection guides have decreased from 15 rem/year to 5 rem/year in 1990 for whole body penetrating radiation exposure. During these 40 years of nuclear operations (in excess of 200,000 man-years of work), a total of twelve individuals involved in four accidents exceeded the annual guidelines for exposure; nine of these exposures were received during life saving efforts on January 3, 1961 following the SL-1 reactor accident which killed three military personnel. These exposures ranged from 8 to 27 rem. Only one individual has exceeded the annual whole body penetrating radiation protection guidelines in the last 29 years.

Horan, J.R.; Braun, J.B.

1993-10-01

296

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

297

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

298

Spectrally enhancing near-field radiative heat transfer by exciting magnetic polariton in SiC gratings  

E-print Network

In the present work, we theoretically demonstrate, for the first time, that near field radiative transport between 1D periodic grating microstructures separated by subwavelength vacuum gaps can be significantly enhanced by exciting magnetic resonance or polariton. Fluctuational electrodynamics that incorporates scattering matrix theory with rigorous coupled wave analysis is employed to exactly calculate the near field radiative heat flux between two SiC gratings. Besides the well known coupled surface phonon polaritons (SPhP), an additional spectral radiative heat flux peak, which is due to magnetic polariton, is found within the phonon absorption band of SiC. The mechanisms, behaviors and interplays between magnetic polariton, coupled SPhP, single interface SPhP, and Wood's anomaly in the near field radiative transport are elucidated in detail. The findings will open up a new way to control near field radiative heat transfer by magnetic resonance with micro or nanostructured metamaterials.

Yang, Yue

2015-01-01

299

Effect of Spatial Organization on Solar Radiative Transfer in Three-Dimensional Idealized Stratocumulus Cloud Fields  

Microsoft Academic Search

To relate the error associated with 1D radiative calculations to the geometrical scales of cloud organization and\\/or in-cloud optical inhomogeneities, a new idealized methodology, based on a Fourier statistical technique, has been developed. Three-dimensional cloud fields with variability over a selected range of horizontal spatial scales and consistent vertical structure can be obtained and controlled by a small number of

F. Di Giuseppe; A. M. Tompkins

2003-01-01

300

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

301

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

302

Proton radiation effects in XC4036XLA field programmable gate arrays  

Microsoft Academic Search

We have measured the proton-induced single-event upset (SEU) cross section of Xilinx XC4036XLA field programmable gate arrays. The threshold energy for SEU was determined to be (22±2) MeV. The upset cross section saturated at a value of (2.7±0.2)×10-9 cm2\\/device. We have demonstrated that Bendel models are unable to describe the upset cross section. The effects of the radiation environment of

N. J. Buchanan; D. M. Gingrich

2003-01-01

303

Methodology For Establishment Of The Radiation Control System At The Karachaganak Oil Gas-Condensate Field  

Microsoft Academic Search

\\u000a At the present time radiological contamination by natural radionuclides of industrial platforms of oil-fields is well-known,\\u000a but far from being resolved problem for many countries. Problem as a whole has gained an environmental-technological value.\\u000a The solution of the problem given requires an introduction at the oil-and-gas production facilities of the complex measures\\u000a on normalization of radiation - ecological conditions, decrease

S. V. Reznikov; K. K. Kadyrzhanov; A. Zh. Tuleushev; Zh. N. Marabaev; S. N. Lukashenko; V. P. Solodukhin; I. V. Kazachevskiy; T. I. Ageyeva

304

Magnetic Fields and the Polarization of Astrophysical Maser Radiation: A Review  

E-print Network

Basic aspects of the relationship between the magnetic field and polarized maser radiation are described with the emphasis on interpreting the observed spectra. Special attention is given to three issues--the limitations on the applicability of the classic solutions of Goldreich, Keeley & Kwan (1973), inferring the strength of the magnetic field from the circular polarization when the Zeeman splitting is much less than the spectral linebreadth (especially for SiO masers), and the significance of the absence of components of the Zeeman triplet in the spectra of OH masers in regions of star formation.

William D. Watson

2008-11-10

305

Application of the TLD albedo technique for monitoring and interpretation of neutron stray radiation fields  

NASA Astrophysics Data System (ADS)

A single sphere albedo technique with TLD 600/TLD 700 detectors has been applied in neutron monitoring to calibrate albedo dosimeters and to interpret neutron stray radiation fields in terms of neutron dose equivalent separated for the energy groups below 0.4 eV, 0.4-10 keV and 10 keV-10 MeV, and Eeff for fast neutrons. The paper describes the technique for field and personnel monitoring under the aspect of an on-line computer program for data recording and processing.

Piesch, E.; Burgkhardt, B.

1980-09-01

306

Near-field thermal radiation between hyperbolic metamaterials: Graphite and carbon nanotubes  

SciTech Connect

The near-field radiative heat transfer for two hyperbolic metamaterials, namely, graphite and vertically aligned carbon nanotubes (CNTs), is investigated. Graphite is a naturally existing uniaxial medium, while CNT arrays can be modeled as an effective anisotropic medium. Different hyperbolic modes can be separately supported by these materials in certain infrared regions, resulting in a strong enhancement in near-field heat transfer. It is predicted that the heat flux between two CNT arrays can exceed that between SiC plates at any vacuum gap distance and is about 10 times higher with a 10?nm gap.

Liu, X. L.; Zhang, R. Z.; Zhang, Z. M., E-mail: zhuomin.zhang@me.gatech.edu [G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

2013-11-18

307

Electromagnetic field and radiation for a charge moving along a helical trajectory inside a waveguide with dielectric filling  

E-print Network

We investigate the electromagnetic field generated by a point charge moving along a helical trajectory inside a circular waveguide with conducting walls filled by homogeneous dielectric. The parts corresponding to the radiation field are separated and the formulae for the radiation intensity are derived for both TE and TM waves. It is shown that the main part of the radiated quanta is emitted in the form of the TE waves. Various limiting cases are considered. The results of the numerical calculations show that the insertion of the waveguide provides an additional mechanism for tuning the characteristics of the emitted radiation by choosing the parameters of the waveguide and filling medium.

A. S. Kotanjyan; A. A. Saharian

2007-08-27

308

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

309

Influence of Electric Field Distribution on High-Power Array Antenna Radiation Pattern with Rectangular Aperture  

NASA Astrophysics Data System (ADS)

The antenna element with rectangular aperture is one of the main forms of the array antenna. The electric field amplitude distribution of the rectangular aperture, as well as the phase distribution is the most important parameter that affects the radiation gain and beam direction of the array antenna. In this work, a theoretical study is carried out on array antennae for high-power microwave (HPM) applications. An electric integration method is applied to obtain the far-field radiation pattern with different kinds of electric field distributions. Moreover, the influence of the electric field amplitude and phase on the performance of the array antenna is analyzed. For one antenna element, uniform electric field distribution is not the best choice. However, the uniform distribution has specific advantages for an array antenna consisting of combined antenna elements. The phase deviation has more significant influence on the performance of the array antenna than the amplitude deviation. It indicates that a good working phase shifter with high-power capacity and time-adjusting capability is very important.

Yang, Yi-Ming; Yuan, Cheng-Wei; Qian, Bao-Liang

2014-06-01

310

The influence of magnetic fields, turbulence, and UV radiation on the formation of supermassive black holes  

NASA Astrophysics Data System (ADS)

Context. The seeds of the supermassive black holes with masses of ~109M? observed already at z ~ 6 may have formed through the direct collapse of primordial gas in Tvir ? 104 K halos, whereby the gas must stay hot (~104 K) in order to avoid fragmentation. Aims: The interplay between magnetic fields, turbulence, and a UV radiation background during the gravitational collapse of primordial gas in a halo is explored; in particular, the possibilities for avoiding fragmentation are examined. Methods: Using an analytical one-zone model, the evolution of a cloud of primordial gas is followed from its initial cosmic expansion through turnaround, virialization, and collapse up to a density of 107 cm-3. Results: It was found that in halos with no significant turbulence, the critical UV background intensity (J21crit) for keeping the gas hot is lower by a factor ~10 for an initial comoving magnetic field B0 ~ 2 nG than for the zero-field case, and even lower for stronger fields. In turbulent halos, J21crit is found to be a factor ~10 lower than for the zero-field-zero-turbulence case, and the stronger the turbulence (more massive halo and/or stronger turbulent heating), the lower J21crit. Conclusions: The reduction in J21crit is particularly important, since it exponentially increases the number of halos exposed to a supercritical radiation background.

Van Borm, C.; Spaans, M.

2013-05-01

311

Study of magnetic field expansion using a plasma generator for space radiation active protection  

NASA Astrophysics Data System (ADS)

There are many active protecting methods including Electrostatic Fields, Confined Magnetic Field, Unconfined Magnetic Field and Plasma Shielding etc. for defending the high-energy solar particle events (SPE) and Galactic Cosmic Rays (GCR) in deep space exploration. The concept of using cold plasma to expand a magnetic field is the best one of all possible methods so far. The magnetic field expansion caused by plasma can improve its protective efficiency of space particles. One kind of plasma generator has been developed and installed into the cylindrical permanent magnet in the eccentric. A plasma stream is produced using a helical-shaped antenna driven by a radio-frequency (RF) power supply of 13.56 MHz, which exits from both sides of the magnet and makes the magnetic field expand on one side. The discharging belts phenomenon is similar to the Earth's radiation belt, but the mechanism has yet to be understood. A magnetic probe is used to measure the magnetic field expansion distributions, and the results indicate that the magnetic field intensity increases under higher increments of the discharge power.

Jia, Xiang-Hong; Jia, Shao-Xia; Xu, Feng; Bai, Yan-Qiang; Wan, Jun; Liu, Hong-Tao; Jiang, Rui; Ma, Hong-Bo; Wang, Shou-Guo

2013-09-01

312

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

313

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

314

Lightning-channel morphology by return-stroke radiation field waveforms  

NASA Technical Reports Server (NTRS)

Simultaneous video and wideband electric field recordings of 32 cloud-to-ground lightning flashes in Florida were analyzed to show 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 to identify each waveform with a visible channel to ground. Fifty-five correlated waveforms and channel images were obtained. Of these, all 34 first-stroke waveforms (multiple jagged E peaks, noisy dE/dt), 8 of which were not radiated by the chronologically first stroke in the flash, came from new channels to ground (not previously seen on video). All 18 subsequent-stroke waveforms (smoothly rounded E and quiet dE/dt after initial peak) were radiated by old channels (illuminated by a previous stroke). Two double-ground waveforms (two distinct first-return-stroke pulses separated by tens of microseconds or less) coincided with video fields showing two new channels. One `anomalous-stroke' waveform (beginning like a first stroke and ending like a subsequent) was produced by a new channel segment to ground branching off an old channel. This waveform classification depends on the presence or absence of high-frequency fine structure. Fourier analysis shows that first-stroke waveforms contain about 18 dB more spectral power in the frequency interval from 500 kHz to at least 7 MHz than subsequent-stroke waveforms for at least 13 microseconds after the main peak.

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

1995-01-01

315

Determination of High-Frequency Current Distribution Using EMTP-Based Transmission Line Models with Resulting Radiated Electromagnetic Fields  

SciTech Connect

Application of BPL technologies to existing overhead high-voltage power lines would benefit greatly from improved simulation tools capable of predicting performance - such as the electromagnetic fields radiated from such lines. Existing EMTP-based frequency-dependent line models are attractive since their parameters are derived from physical design dimensions which are easily obtained. However, to calculate the radiated electromagnetic fields, detailed current distributions need to be determined. This paper presents a method of using EMTP line models to determine the current distribution on the lines, as well as a technique for using these current distributions to determine the radiated electromagnetic fields.

Mork, B; Nelson, R; Kirkendall, B; Stenvig, N

2009-11-30

316

Numerical Study of a Convective Turbulence Encounter  

NASA Technical Reports Server (NTRS)

A numerical simulation of a convective turbulence event is investigated and compared with observational data. The specific case was encountered during one of NASA's flight tests and was characterized by severe turbulence. The event was associated with overshooting convective turrets that contained low to moderate radar reflectivity. Model comparisons with observations are quite favorable. Turbulence hazard metrics are proposed and applied to the numerical data set. Issues such as adequate grid size are examined.

Proctor, Fred H.; Hamilton, David W.; Bowles, Roland L.

2002-01-01

317

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

318

The radiation fields around a proton therapy facility: A comparison of Monte Carlo simulations  

NASA Astrophysics Data System (ADS)

A proton therapy test facility with a beam current lower than 10 nA in average, and an energy up to 150 MeV, is planned to be sited at the Frascati ENEA Research Center, in Italy. The accelerator is composed of a sequence of linear sections. The first one is a commercial 7 MeV proton linac, from which the beam is injected in a SCDTL (Side Coupled Drift Tube Linac) structure reaching the energy of 52 MeV. Then a conventional CCL (coupled Cavity Linac) with side coupling cavities completes the accelerator. The linear structure has the important advantage that the main radiation losses during the acceleration process occur to protons with energy below 20 MeV, with a consequent low production of neutrons and secondary radiation. From the radiation protection point of view the source of radiation for this facility is then almost completely located at the final target. Physical and geometrical models of the device have been developed and implemented into radiation transport computer codes based on the Monte Carlo method. The scope is the assessment of the radiation field around the main source for supporting the safety analysis. For the assessment independent researchers used two different Monte Carlo computer codes named FLUKA (FLUktuierende KAskade) and MCNPX (Monte Carlo N-Particle eXtended) respectively. Both are general purpose tools for calculations of particle transport and interactions with matter, covering an extended range of applications including proton beam analysis. Nevertheless each one utilizes its own nuclear cross section libraries and uses specific physics models for particle types and energies. The models implemented into the codes are described and the results are presented. The differences between the two calculations are reported and discussed pointing out disadvantages and advantages of each code in the specific application.

Ottaviano, G.; Picardi, L.; Pillon, M.; Ronsivalle, C.; Sandri, S.

2014-02-01

319

PHYSICAL REVIEW B 85, 155422 (2012) Near-field thermal radiation transfer controlled by plasmons in graphene  

E-print Network

-field transfer offers the promise of an externally controllable thermal switch as well as a novel hybrid graphene-graphene in graphene Ognjen Ilic,1,* Marinko Jablan,2 John D. Joannopoulos,1 Ivan Celanovic,3 Hrvoje Buljan,2 and Marin-field radiation transfer between two closely separated graphene sheets. The dependence of near-field heat exchange

Soljaèiæ, Marin

320

Radiation  

Cancer.gov

DCEG researchers carry out a broad-based research program designed to identify, understand, and quantify the risk of cancer in populations exposed to medical, occupational, or environmental radiation. They study ionizing radiation exposures (e.g., x-rays,

321

Analysis of near-field radiation transfer within nano-gaps using FDTD method  

NASA Astrophysics Data System (ADS)

Enhancement of near-field radiative emission via coupling of surface plasmons in nano-gaps formed between thin films is important for understanding and implementation of energy harvesting using nano-thermophotovoltaic cells. Design and construction of such cells need to be carried out along with detailed modeling studies, necessitating accurate calculation of near-field emission within thin films. The objective of this paper is to provide a methodology based on finite difference time domain analysis for the calculation of the near-field thermal radiation emission based on local density of electromagnetic states. Near-field thermal emission is investigated within the nano-gap formed between thin silicon carbide layers where both support surface phonon polaritons. Modeling of this problem with the FDTD method is not trivial particularly for establishing the Drude-Lorentz permittivity model and the selection of the right boundary conditions. We present an effective boundary condition, for calculation of Local Density Of electromagnetic States (LDOS) via Finite Difference Time Domain Method (FDTD) for applications to nano-scale geometries. We conclude that Convolutional Perfectly Matched Layer (CPML) is the optimum boundary condition that gives the most accurate results compared against the other methodologies for parallel plates separated by nano-gaps. This boundary condition allows more streamlined simulations to be carried out when working with sub-wavelength structures. The challenges and the possible solutions to overcome these difficulties are discussed in detail.

Didari, Azadeh; Mengüç, M. Pinar

2014-10-01

322

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

323

Radiative properties of a plasma moving across a magnetic field. I: Theoretical analysis  

SciTech Connect

The early-time evolution of plasmas moving across a background magnetic field is addressed with a two-dimensional model in which a plasma cloud is assumed to have formed instantaneously with a velocity across a uniform background magnetic field and with a Gaussian density profile in the two dimensions perpendicular to the direction of motion. This model treats both the dynamics associated with the formation of a polarization field and the generation and propagation of electromagnetic waves. In general, the results indicate that, to zeroth order, the plasma cloud behaves like a large dipole antenna oriented in the direction of the polarization field which oscillates at frequencies defined by the normal mode of the system. The magnitude of the radiation field and the amount of plasma momentum and energy carried away by and stored instantaneously in the fields are discussed only qualitatively in this paper, quantitative results for specific cloud parameters and scaling laws for the magnitude of the fields and the slowing down of the plasma cloud are presented in a companion manuscript.

Roussel-Dupre, R. (Space Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)); Miller, R.H. (Space Physics Research Laboratory, Department of Atmospheric, Oceanic and Space Sciences, The University of Michigan, Ann Arbor, Michigan 48109-2143 (United States))

1993-04-01

324

Influences of cosmic radiation, artificial radioactivity and aerosol concentration upon the fair-weather atmospheric electric field in Lisbon (1955–1991)  

Microsoft Academic Search

The atmospheric electric field is influenced by cosmic radiation, radioactivity and aerosols. In this work we investigate the existence of: (i) correlations between relative anomalies of annual values of atmospheric electric field and cosmic radiation intensity, artificial radioactivity and aerosol concentration; (ii) seasonal correlations between relative anomalies of the atmospheric electric field and cosmic radiation intensity. We used data of

Cláudia Serrano; A. Heitor Reis; Rui Rosa; Paulo S. Lucio

2006-01-01

325

Influences of cosmic radiation, artificial radioactivity and aerosol concentration upon the fair-weather atmospheric electric field in Lisbon (1955 1991)  

Microsoft Academic Search

The atmospheric electric field is influenced by cosmic radiation, radioactivity and aerosols. In this work we investigate the existence of: (i) correlations between relative anomalies of annual values of atmospheric electric field and cosmic radiation intensity, artificial radioactivity and aerosol concentration; (ii) seasonal correlations between relative anomalies of the atmospheric electric field and cosmic radiation intensity. We used data of

Cláudia Serrano; A. Heitor Reis; Rui Rosa; Paulo S. Lucio

2006-01-01

326

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 left<{J}right> and total radiated power P for two-dimensional internal gravity waves. Both left<{J}right> 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

327

Experimental determination of radiated internal wave power without pressure field data  

SciTech Connect

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.; Morrison, P. J. [Physics Department and Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712–1192 (United States)] [Physics Department and Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712–1192 (United States); Paoletti, M. S.; Swinney, Harry L. [Physics Department, The University of Texas at Austin, Austin, Texas 78712–1192 (United States)] [Physics Department, The University of Texas at Austin, Austin, Texas 78712–1192 (United States)

2014-04-15

328

Radiative corrections to the Casimir Pressure under the influence of temperature and external fields  

SciTech Connect

Generalizing the quantum field theory (QFT) with boundary conditions in covariant gauge to the case of finite temperature, we develop the quantum electrodynamics (QED) with boundary conditions in the Matsubara approach as well as in the thermofield formulation. We rederive the known results of the free-field theory for the pressure and the free energy of the Casimir problem. For infinitely thin plates we calculate the radiative corrections in second-order perturbation theory at finite temperature. Thereby it turns out that the calculation in of the vacuum energy at the vanishing temperature via the Z functional is much simplier than the calculation via the energy momentum tensor. This observation allows determination of the influence of static electromagnetic fields on the Casimir problem. copyright 1987 Academic Press, Inc.

Robaschik, D.; Scharonhorst, K.; Wieczorek, E.

1987-03-01

329

The statistical properties of electromagnetic fields with application to radiation and scattering  

SciTech Connect

Determining the relationships between different average values is an important step in any physics-based statistical theory. If these relationships exist and exhibit certain properties, then probability densities or distributions can be assigned to the field variables and the transition from an average-value theory'' to a statistical theory'' is complete. For electromagnetics, no such average-value relationships have been demonstrated to exist. The derivation of these relationships and their range of validity are the subject of consideration here. For purposes of this discussion, we limit our attention to the fields inside a complex cavity, but with the ultimate goal of deriving the statistics of the far radiated and scattered fields of complex envelopes.

Lehman, T.H. (Lehman (T.H.), Albuquerque, NM (USA)); Miller, E.K. (Los Alamos National Lab., NM (USA))

1991-01-01

330

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

331

Equivalent-radius scatter-air ratio model for inhomogeneity and irregular field corrections in radiation teletherapy  

Microsoft Academic Search

In the field of medical radiation therapy, a goal of the health professionals is to be able to treat the patient with that amount of radiation dose prescribed by the oncologist. The calculation of the treatment time required on a given therapy machine is not a simple, straightforward task, and involves the consideration of location of the treatment area, patient

Erb

1985-01-01

332

Active control of far-field sound radiation by a beam with piezoelectric control transducers: physical system analysis  

Microsoft Academic Search

This paper analytically demonstrates the use of piezoelectric actuators and PVDF sensors to actively control the far-field sound radiation from a simply-supported beam in an infinite rigid baffle. The beam is assumed to be subjected to a harmonic point force. The piezoelectric patches which are attached to the beam serve as actuators to control the sound radiated from the beam

Bor-Tsuen Wang

1994-01-01

333

Dosimetry in steep dose-rate gradient radiation fields: A challenge in clinical applications  

NASA Astrophysics Data System (ADS)

The fundamental goal of radiotherapy is to reduce the damage to normal tissue and optimize the dose to the tumor with an associated high probability of cure. Because of this, an accurate and precise knowledge of the radiation dose distribution delivered around the tumor volume during radiotherapy treatments such as stereotactic radiosurgery, intensity modulated radiotherapy or brachytherapy with low-energy X-ray and beta particle sources is of great importance. However, in each of these radiation fields, there exists a steep dose-rate gradient which makes it very difficult to perform accurate dose measurements. In this work, the physics phenomena involved in the energy absorption for each of these situations are discussed, and a brief revision of what the Medical Physics community is doing is presented.

Massillon-JL, G.

2010-12-01

334

Silicon field-effect transistors as radiation detectors for the Sub-THz range  

SciTech Connect

The nonresonance response of silicon metal-oxide-semiconductor field-effect transistors (Si-MOSFETs) with a long channel (1-20 {mu}m) to radiation in the frequency range 43-135 GHz is studied. The transistors are fabricated by the standard CMOS technology with 1-{mu}m design rules. The volt-watt sensitivity and the noise equivalent power (NEP) for such detectors are estimated with the calculated effective area of the detecting element taken into account. It is shown that such transistors can operate at room temperature as broadband direct detectors of sub-THz radiation. In the 4-5 mm range of wavelengths, the volt-watt sensitivity can be as high as tens of kV/W and the NEP can amount to 10{sup -11} - 10{sup -12}W/{radical}Hz . The parameters of detectors under study can be improved by the optimization of planar antennas.

But, D. B., E-mail: but.dmitry@gmail.com; Golenkov, O. G.; Sakhno, N. V.; Sizov, F. F.; Korinets, S. V.; Gumenjuk-Sichevska, J. V.; Reva, V. P.; Bunchuk, S. G. [National Academy of Sciences of Ukraine, Lashkaryov Institute of Semiconductor Physics (Ukraine)

2012-05-15

335

Dosimetry in steep dose-rate gradient radiation fields: A challenge in clinical applications  

SciTech Connect

The fundamental goal of radiotherapy is to reduce the damage to normal tissue and optimize the dose to the tumor with an associated high probability of cure. Because of this, an accurate and precise knowledge of the radiation dose distribution delivered around the tumor volume during radiotherapy treatments such as stereotactic radiosurgery, intensity modulated radiotherapy or brachytherapy with low-energy X-ray and beta particle sources is of great importance. However, in each of these radiation fields, there exists a steep dose-rate gradient which makes it very difficult to perform accurate dose measurements. In this work, the physics phenomena involved in the energy absorption for each of these situations are discussed, and a brief revision of what the Medical Physics community is doing is presented.

Massillon-JL, G. [Instituto de Fisica, Universidad Nacional Autonoma de Mexico, A.P. 20-364, 01000 DF (Mexico)

2010-12-07

336

Analysis and design of photobioreactors for microalgae production I: method and parameters for radiation field simulation.  

PubMed

Having capabilities for the simulation of the radiation field in suspensions of microalgae constitutes a great asset for the analysis, optimization and scaling-up of photobioreactors. In this study, a combined experimental and computational procedure is presented, specifically devised for the assessment of the coefficients of absorption and scattering, needed for the simulation of such fields. The experimental procedure consists in measuring the radiant energy transmitted through samples of suspensions of microalgae of different biomass concentrations, as well as the forward and backward scattered light. At a microscopic level, suspensions of microalgae are complex heterogeneous media and due to this complexity, in this study they are modeled as a pseudocontinuum, with centers of absorption and scattering randomly distributed throughout its volume. This model was tested on suspensions of two algal species of dissimilar cell shapes: Chlorella sp. and Scenedesmus quadricauda. The Monte Carlo simulation algorithm developed in this study, when used as a supporting subroutine of a main optimization program based on a genetic algorithm, permits the assessment of the physical parameters of the radiation field model. The Monte Carlo algorithm simulates the experiments, reproducing the events that photons can undergo while they propagate through culture samples or at its physical boundaries. PMID:22417291

Heinrich, Josué Miguel; Niizawa, Ignacio; Botta, Fausto Adrián; Trombert, Alejandro Raúl; Irazoqui, Horacio Antonio

2012-01-01

337

The analysis of complex mixed-radiation fields using near real-time imaging.  

PubMed

A new mixed-field imaging system has been constructed at Lancaster University using the principles of collimation and back projection to passively locate and assess sources of neutron and gamma-ray radiation. The system was set up at the University of Manchester where three radiation sources: (252)Cf, a lead-shielded (241)Am/Be and a (22)Na source were imaged. Real-time discrimination was used to find the respective components of the neutron and gamma-ray fields detected by a single EJ-301 liquid scintillator, allowing separate images of neutron and gamma-ray emitters to be formed. (252)Cf and (22)Na were successfully observed and located in the gamma-ray image; however, the (241)Am/Be was not seen owing to surrounding lead shielding. The (252)Cf and (241)Am/Be neutron sources were seen clearly in the neutron image, demonstrating the advantage of this mixed-field technique over a gamma-ray-only image where the (241)Am/Be source would have gone undetected. PMID:24782559

Beaumont, Jonathan; Mellor, Matthew P; Joyce, Malcolm J

2014-10-01

338

Ethogram of selected behaviors initiated by free-ranging short-finned pilot whales ( Globicephala macrorhynchus ) and directed to human swimmers during open water encounters  

Microsoft Academic Search

In order to establish an ethogram of interactive behaviors initiated by free- ranging short-finned pilot whales (Globice phala macrorhynchus) and directed to human swimmers, we initiated encounters with non-habituated pilot whale groups during open water encounters southwest of Tenerife, Canary Islands, over two field seasons (1996 and 2001). Human swim- mers followed a precautionary set of rules during approaches. Encounters

Michael Scheer; Bianka Hofmann; Itay P. Behr

2004-01-01

339

New Horizons: Encountering Pluto and KBOs  

NASA Astrophysics Data System (ADS)

New Horizons is a NASA mission to explore the Pluto system and the Kuiper Belt. The spacecraft was launched on 19 January 2006 and will begin its encounter studies of Pluto in early 2015, culminating on 14 July 2015 with a close approach just 12,500 km from Pluto. The spacecraft carries panchromatic and color images, IR and UV mapping spectrometers, a radio science package, two in situ plasma instruments, and a dust counter. We describe the capabilities of this instrument suite and the spacecraft, the observations planned for Pluto and its system of satellites, and our plans for KBO flybys to take place late in the 2010s.

Young, Leslie A.; Stern, S. Alan

340

The intriguing encounters of Pavlov and Cushing.  

PubMed

Ivan Petrovich Pavlov and Harvey William Cushing were two of the most prominent neuroscientists of the early 20th century. Their contributions helped advance the understanding of the brain and its disorders, and propelled neuroscience into a new era of research and treatment. Although separated geographically and culturally, Pavlov and Cushing exchanged letters and followed one another's careers from afar. They met only a few times, during international scientific gatherings in the US and abroad. These encounters were captured in journal entries, letters, and photographs, and provide a glimpse into the lives of these two great men and the history of neuroscience at the turn of the last century. PMID:15035298

Shahlaie, Kiarash; Watson, Joseph C; Benson, Daniel R

2004-03-01

341

First spacecraft encounter with an asteroid approaches  

NASA Technical Reports Server (NTRS)

During the course of the Galileo spacecraft's journey to Jupiter it will make two excursions through the steroid belt situated between Mars and Jupiter. The first excursion involves an encounter with the asteroid 951 Gaspra, which will take place on October 29, 1991. Gaspra is a small (about 15 km diameter) asteroid near the outer edge of the main asteroid belt. It's spectral classification is S, suggesting a composition similar to those of stony-iron meteorites. A figure is given showing the brightness of this asteroid as a function of time.

Tholen, David J.

1991-01-01

342

Mode Content Determination of Terahertz Corrugated Waveguides Using Experimentally Measured Radiated Field Patterns  

PubMed Central

This work focuses on the accuracy of the mode content measurements in an overmoded corrugated waveguide using measured radiated field patterns. Experimental results were obtained at 250 GHz using a vector network analyzer with over 70 dB of dynamic range. The intensity and phase profiles of the fields radiated from the end of the 19 mm diameter helically tapped brass waveguide were measured on planes at 7, 10, and 13 cm from the waveguide end. The measured fields were back propagated to the waveguide aperture to provide three independent estimates of the field at the waveguide exit aperture. Projecting that field onto the modes of the guide determined the waveguide mode content. The three independent mode content estimates were found to agree with one another to an accuracy of better than ±0.3%. These direct determinations of the mode content were compared with indirect measurements using the experimentally measured amplitude in three planes, with the phase determined by a phase retrieval algorithm. The phase retrieval technique using the planes at 7, 10, and 13 cm yielded a mode content estimate in excellent agreement, within 0.3%, of the direct measurements. Phase retrieval results using planes at 10, 20, and 30 cm were less accurate due to truncation of the measurement in the transverse plane. The reported measurements benefited greatly from a precise mechanical alignment of the scanner with respect to the waveguide axis. These results will help to understand the accuracy of mode content measurements made directly in cold test and indirectly in hot test using the phase retrieval technique. PMID:25264391

Jawla, Sudheer K.; Nanni, Emilio A.; Shapiro, Michael A.; Woskov, Paul P.; Temkin, Richard J.

2012-01-01

343

Newton’s second law, radiation reaction and type II Einstein-Maxwell fields  

NASA Astrophysics Data System (ADS)

Considering perturbations of the Reissner-Nordström metric while keeping the perturbations in the class of type II Einstein-Maxwell metrics, we perform a spherical harmonic expansion of all the variables up to the quadrupole term. This leads to rather surprising results. Referring to the source of the metric as a type II particle (analogous to referring to a Schwarzschild-Reissner-Nordström or Kerr-Newman particle), we see immediately that the Bondi momentum of the particle takes the classical form of mass times velocity plus an electromagnetic radiation reaction term, while the Bondi mass loss equation becomes the classical gravitational and electromagnetic (electric and magnetic) dipole and quadrupole radiation. The Bondi momentum loss equation turns into Newton’s second law of motion containing the Abraham-Lorentz-Dirac radiation reaction force plus a momentum recoil (rocket) force, while the reality condition on the Bondi mass aspect yields the conservation of angular momentum. Two things must be pointed out: (1) these results, (equations of motion, etc) take place, not in the spacetime of the type II metric but in an auxiliary space referred to as {H}-space, whose physical meaning is rather obscure and (2) this analysis of the type II field equations is a very special case of a similar analysis of the general asymptotically flat Einstein-Maxwell equations. Although the final results are similar (though not the same), the analysis uses different equations (specifically, the type II field equations) and is vastly simpler than the general case. Without a great deal of the technical structures needed in the general case, one can see rather easily where the basic results reside in the type II field equations.

Newman, Ezra T.

2011-12-01

344

Modeling the response of thermoluminescence detectors exposed to low- and high-LET radiation fields.  

PubMed

Lithium fluoride thermoluminescence (TL) detectors, with different Li composition (Li-6 and Li-7) and various activators (LiF:Mg,Ti, LiF:Mg,Cu,P), are widely used for dosimetry in space. The primary radiation field in space is composed of fast electrons, protons and heavy charged particles (HCP). By its interaction with the structures of the spacecraft, this field may be modified inside the crew cabin. Therefore, calibration of TL detectors against a dose of gamma-rays is not sufficient for relating the TL readout to absorbed dose or to quantities relevant in radiation protection, without suitable correction. We introduce and calculate the detection efficiency, eta, relative to gamma-ray dose, of lithium fluoride detectors after proton and heavy charged particle (HCP) irradiation. We calculate eta for MCP-N (LiF:Mg,Cu,P) and for MTS-N (LiF:Mg,Ti) using microdosimetric models. The microdosimetric distributions used in these models (for HCP of charges between Z=1 to Z=8 and in the energy range between 0.3 MeV/amu and 20 MeV/amu) are calculated using an analytical model, based on the results of Monte Carlo simulated charged particle tracks using the MOCA-14 code. The ratio etaMCP-N/etaMTS-N for protons of stopping power (in water) below 10 keV/microm lies in the range between 0.65 and 1.0 and for HCP with Z>1--between 0.3 and 0.6. The stopping power of the particle is found not to be a unique parameter to scale the response of TL detectors. The combination of response of LiF:Mg,Cu,P and LiF:Mg,Cu,P detectors can be more suitable for a dose correction in space radiation fields. PMID:12793731

Olko, Pawel; Bilski, Pawel; Budzanowski, Maciej; Waligórski, Michael Patrick Russell; Reitz, Guenther

2002-12-01

345

Photoinduced processes in solid polymer solutions of dyes in an interference field of laser radiation  

SciTech Connect

An investigation was made of the relationships governing the photochemical mechanism of formation of light-induced gratings in solid polymer solutions of a dye with a high quantum yield of the triplet states. The combined analysis of the results of real and numerical experiments was made for a solution of eosin K in gelatin. The protonation rate constant of the dye was measured and the dependence of the diffraction efficiency on the duration of irradiation was explained taking diffusion of the dye into account. A method was proposed for determination of the duffusion coefficient in a spatially modified interference field of the laser radiation. The diffusion coefficients were found. (nonlinear optical phenomena)

Sizykh, A G; Tarakanova, E A [Quantum Electronics Division, Krasnoyarsk State University, Krasnoyarsk (Russian Federation)

1998-12-31

346

Dynamic characteristics of far-field radiation of current modulated phase-locked diode laser arrays  

NASA Technical Reports Server (NTRS)

A versatile and powerful streak camera/frame grabber system for studying the evolution of the near and far field radiation patterns of diode lasers was assembled and tested. Software needed to analyze and display the data acquired with the steak camera/frame grabber system was written and the total package used to record and perform preliminary analyses on the behavior of two types of laser, a ten emitter gain guided array and a flared waveguide Y-coupled array. Examples of the information which can be gathered with this system are presented.

Elliott, R. A.; Hartnett, K.

1987-01-01

347

The limitations of using vertical cutoff rigidities determined from the IGRF magnetic field models for computing aircraft radiation dose.  

PubMed

Vertical cutoff rigidities derived from the International Geomagnetic Reference Fields (IGRF) are normally used to compute the radiation dose at a specific location and to organize the radiation dose measurements acquired at aircraft altitudes. This paper presents some of the usually ignored limits on the accuracy of the vertical cutoff rigidity models and describes some of the computational artifacts present in these models. It is noted that recent aircraft surveys of the radiation dose experienced along specific flight paths is sufficiently precise that the secular variation of the geomagnetic field is observable. PMID:14727668

Smart, D F; Shea, M A

2003-01-01

348

On the reciprocity relationship between direct field radiation and diffuse reverberant loading  

NASA Astrophysics Data System (ADS)

This analysis is concerned with the derivation of a ``diffuse field'' reciprocity relationship between the diffuse field excitation of a connection to a structural or acoustic subsystem and the radiation impedance of the connection. Such a relationship has been derived previously for connections described by a single degree of freedom. In the present work it is shown that the diffuse-field reciprocity relationship also arises when describing the ensemble average response of connections to structural or acoustic subsystems with uncertain boundaries. Furthermore, it is shown that the existing diffuse-field reciprocity relationship can be extended to encompass connections that possess an arbitrary number of degrees of freedom. The present work has application to (i) the calculation of the diffuse field response of structural-acoustic systems modeled by Finite Elements, Boundary Elements, and Infinite Elements; (ii) the general calculation of the Coupling Loss Factors employed in Statistical Energy Analysis (SEA); and (iii) the derivation of an alternative analysis method for describing the dynamic interactions of coupled subsystems with uncertain boundaries (a generalized ``boundary'' approach to SEA). .

Shorter, P. J.; Langley, R. S.

2005-01-01

349

Experimental Verification of Isotropic Radiation from a Coherent Dipole Source via Electric-Field-Driven LC Resonator Metamaterials  

NASA Astrophysics Data System (ADS)

It has long been conjectured that isotropic radiation by a simple coherent source is impossible due to changes in polarization. Though hypothetical, the isotropic source is usually taken as the reference for determining a radiator’s gain and directivity. Here, we demonstrate both theoretically and experimentally that an isotropic radiator can be made of a simple and finite source surrounded by electric-field-driven LC resonator metamaterials designed by space manipulation. As a proof-of-concept demonstration, we show the first isotropic source with omnidirectional radiation from a dipole source (applicable to all distributed sources), which can open up several possibilities in axion electrodynamics, optical illusion, novel transformation-optic devices, wireless communication, and antenna engineering. Owing to the electric- field-driven LC resonator realization scheme, this principle can be readily applied to higher frequency regimes where magnetism is usually not present.

Tichit, Paul-Henri; Burokur, Shah Nawaz; Qiu, Cheng-Wei; de Lustrac, André

2013-09-01

350

Envisioning invertebrates and other aquatic encounters  

NASA Astrophysics Data System (ADS)

To "envision" animals is to visualize, to experience, to figure, to image, kinds of species, discourses, representations, institutions, histories, epistemologies; and, to "imagine possible" a set of material and ethical relationships between species. This dissertation explores the "envisioning of animals" that takes place through/across/between the interfaces of seawater/visuality/experience/biology/technology/phyla---as illustrated in the documentary works of Jean Painleve (scientist and filmmaker), Genevieve Hamon (filmmaker and set-designer), Leni Riefenstahl (filmmaker and photographer), and David Powell (scientist and aquarist). In each case, aesthetic conceptions of beauty and/or ambiguity coupled with biological epistemology and phenomenology of the organisms themselves compete over "what gets to count as culture and nature," and in doing so, construct a host of hybridized and enmeshed "encounters." In the process the following questions are raised: What is the role of the ocean---it's ecosystems and semiotics---in the production of "envisioning"? How are animals used---and in turn shape and reshape the users---to construct tropes of encounter? What theories can be used to understand the phenomenological, semiotic, material, and rhetorical use/miss-use of animals in the articulation of history, economy, biology, narrativity, and representation? How does this motley crew of documentarians answer differently "the animal question," and challenge and/or reinforce anthropocentrism? Divided into two parts, the dissertation first develops a set of methodological questions derived from critical appraisal of "envisioning," encountering, and embodying through science studies, as well as an account of the use and misuse of animals as only "stand ins" for human intentionality; secondly, the dissertation analyses the work of the documentarians in question. Jean Painleve and Genevieve Hamon are shown to critique traditions of representation in nature/science films, particularly through challenging anthropocentrism with a "toolkit" of surrealist strategies and a biological knowledge of octopuses. Soft and hard corals (anthrozoans) are shown to enact a "biosemiotics" or "zoosemiotics" that "presses against" Leni Riefenstahl's "fascist (and humanist) aesthetic," which desires to memorialize "beautiful and unpolluted" coral communities. "The Drifter's Gallery," the primary designer being David Powell, at the Monterey Bay Aquarium, is shown to install a promise of immediate and luminous experience of "jellyfish otherness," but delivers an account of jellyfish as historically situated "actors" with in biocapitalism. The work of these documentarians is particularly prescient, considering the growing international concern about coral bleaching, anthropogenic pollution, over-harvesting, and commercialization of the oceans' resources. As a form of "situated knowledge," this dissertation expands the boundaries of "who/what gets to count?" to encompass an ethical concern about systems of power that constitutively produce animal and human actors. If we are to be committed to understanding the encounters and formations of encounters between non-human animals and human animals, then projects that bridge---rather than divide---disciplines are necessary endeavors for more inhabitable futures; this project attempts such a bridge.

Hayward, Eva

2007-12-01

351

Numerical simulations of protostellar encounters II. Coplanar disc-disc encounters  

E-print Network

It is expected that an average protostar will undergo at least one impulsive interaction with a neighbouring protostar whilst a large fraction of its mass is still in a massive, extended disc. Such interactions must have a significant impact upon the evolution of the protostars and their discs. We have carried out a series of simulations of coplanar encounters between two stars, each possessing a massive circumstellar disc, using an SPH code that models gravitational, hydrodynamic and viscous forces. We find that during a coplanar encounter, disc material is swept up into a shock layer between the two interacting stars, and the layer then fragments to produce new protostellar condensations. The truncated remains of the discs may subsequently fragment; and the outer regions of the discs may be thrown off to form circumbinary disc-like structures around the stars. Thus coplanar disc-disc encounters lead efficiently to the formation of multiple star systems and small-N clusters.

S. J. Watkins; A. S. Bhattal; H. M. J. Boffin; N. Francis; A. P. Whitworth

1998-05-28

352

A novel coaxial Ku-band transit radiation oscillator without external guiding magnetic field  

NASA Astrophysics Data System (ADS)

A novel coaxial transit radiation oscillator without external guiding magnetic field is designed to generate high power microwave at Ku-band. By using a coaxial structure, the space-charge potential energy is suppressed significantly, that is good for enhancing efficient beam-wave interaction. In order to improve the transmission stability of the unmagnetized intense relativistic electron beam, a Pierce-like cathode is employed in the novel device. By contrast with conventional relativistic microwave generators, this kind of device has the advantages of high stability, non-guiding magnetic field, and high efficiency. Moreover, with the coaxial design, it is possible to improve the power-handing capacity by increasing the radial dimension of the Ku-band device. With a 550 keV and 7.5 kA electron beam, a 1.25 GW microwave pulse at 12.08 GHz has been obtained in the simulation. The power conversion efficiency is about 30%.

Ling, Junpu; Zhang, Jiande; He, Juntao; Jiang, Tao

2014-02-01

353

Near-Field Radiative Heat Transfer between Metamaterials coated with Silicon Carbide Film  

E-print Network

In this letter, we study the near-field radiative heat transfer between two metamaterial substrates coated with silicon carbide (SiC) thin films. It is known that metamaterials can enhance the near-field heat transfer over ordinary materials due to excitation of magnetic plasmons associated with s polarization, while strong surface phonon polariton exists for SiC.By careful tuning of the optical properties of metamaterial it is possible to excite electrical and magnetic resonance for the metamaterial and surface phonon polaritons for SiC at different spectral regions, resulting in the enhanced heat transfer. The effect of the SiC film thickness at different vacuum gaps is investigated. Results obtained from this study will be beneficial for application of thin film coatings for energy harvesting.

Basu, Soumyadipta; Wang, Liping

2014-01-01

354

Polarized radiance fields under a dynamic ocean surface: a three-dimensional radiative transfer solution  

SciTech Connect

The hybrid matrix operator, Monte Carlo (HMOMC) method previously reported [Appl. Opt.47, 1063-1071 (2008)APOPAI0003-693510.1364/AO.47.001063] is improved by neglecting higher-order terms in the coupling of the matrix operators and by introducing a dual grid scheme. The computational efficiency for solving the vector radiative transfer equation in a full 3D coupled atmosphere-surface-ocean system is substantially improved, and, thus, large-scale simulations of the radiance distribution become feasible. The improved method is applied to the computation of the polarized radiance field under realistic surface waves simulated by the power spectral density method. To the authors' best knowledge, this is the first time that the polarized radiance field under a dynamic ocean surface and the underwater image of an object above such an ocean surface have been reported.

You Yu; Zhai Pengwang; Kattawar, George W.; Yang Ping

2009-06-01

355

Evidence of Saturn's magnetic field anomaly from Saturnian kilometric radiation high-frequency limit  

SciTech Connect

The detailed analysis of Voyager observations of Saturn kilometric radiation (SKR), taking into account the polarization response of the planetary radio astronomy experiment, has allowed the authors to study separately the high-frequency limit of SKR emitted from the northern and southern auroral regions of the planet. Interpretation of the variations of these high-frequency limits, in the frame of a model inspired by the cyclotron maser mechanism, has allowed them to demonstrate unambiguously the existence of a magnetic anomaly, postulated for years, in the near-surface Saturnian field. Its location and amplitude are estimated, and it is shown that, although it accounts for the observed SKR modulation, it could not be detected by the spacecraft-borne magnetometers which passed too far from the planetary surface. This demonstrates that the current degree of comprehension of planetary radio emissions makes them a unique and very pertinent tool for the fine study of planetary magnetic fields.

Galopeau, P.; Zarka, P. (Observatoire de Paris, Meudon (France)); Ortega-Molina, A.

1991-08-01

356

A novel coaxial Ku-band transit radiation oscillator without external guiding magnetic field  

SciTech Connect

A novel coaxial transit radiation oscillator without external guiding magnetic field is designed to generate high power microwave at Ku-band. By using a coaxial structure, the space-charge potential energy is suppressed significantly, that is good for enhancing efficient beam-wave interaction. In order to improve the transmission stability of the unmagnetized intense relativistic electron beam, a Pierce-like cathode is employed in the novel device. By contrast with conventional relativistic microwave generators, this kind of device has the advantages of high stability, non-guiding magnetic field, and high efficiency. Moreover, with the coaxial design, it is possible to improve the power-handing capacity by increasing the radial dimension of the Ku-band device. With a 550?keV and 7.5?kA electron beam, a 1.25?GW microwave pulse at 12.08?GHz has been obtained in the simulation. The power conversion efficiency is about 30%.

Ling, Junpu, E-mail: lingjunpu@163.com; Zhang, Jiande; He, Juntao; Jiang, Tao [College of Photoelectric Science and Engineering, National University of Defense Technology, Changsha 410073 (China)] [College of Photoelectric Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2014-02-15

357

Near-field radiative heat transfer between metamaterials coated with silicon carbide thin films  

NASA Astrophysics Data System (ADS)

In this letter, we study the near-field radiative heat transfer between two metamaterial substrates coated with silicon carbide (SiC) thin films. It is known that metamaterials can enhance the near-field heat transfer over ordinary materials due to excitation of magnetic plasmons associated with s polarization, while strong surface phonon polariton exists for SiC. By careful tuning of the optical properties of metamaterial, it is possible to excite electrical and magnetic resonances for the metamaterial and surface phonon polaritons for SiC at different spectral regions, resulting in the enhanced heat transfer. The effect of the SiC film thickness at different vacuum gaps is investigated. Results obtained from this study will be beneficial for application of thin film coatings for energy harvesting.

Basu, Soumyadipta; Yang, Yue; Wang, Liping

2015-01-01

358

Thermal radiation fields in time-dependent linear media at finite temperature  

NASA Astrophysics Data System (ADS)

The properties of thermal radiation fields in linear media which have time-dependent parameters are investigated on the basis of the invariant operator method. For quantum mechanical description of the electromagnetic waves whose amplitude and/or frequency vary with time, we introduce a quadratic invariant operator that is constructed according to its exact definition. The density operator of the system, being considered signal plus noise, is obtained via maximization of the entropy. The expectation values of the energy operator, the Hamiltonian, and the invariant operator are obtained in the thermal state and their thermal behaviours are illustrated in detail. It is shown that the fluctuations of the electric and the magnetic fields do not depend on signal plus noise and dissipate with time due to the conductivity in media. Our theory of wave propagation in time-varying media is applied to describe the biophoton signal in order to promote the understanding of our developments.

Ryeol Choi, Jeong

2013-10-01

359

Predicting age of ovarian failure after radiation to a field that includes the ovaries  

SciTech Connect

Purpose: To predict the age at which ovarian failure is likely to develop after radiation to a field that includes the ovary in women treated for cancer. Methods and Materials: Modern computed tomography radiotherapy planning allows determination of the effective dose of radiation received by the ovaries. Together with our recent assessment of the radiosensitivity of the human oocyte, the effective surviving fraction of primordial oocytes can be determined and the age of ovarian failure, with 95% confidence limits, predicted for any given dose of radiotherapy. Results: The effective sterilizing dose (ESD: dose of fractionated radiotherapy [Gy] at which premature ovarian failure occurs immediately after treatment in 97.5% of patients) decreases with increasing age at treatment. ESD at birth is 20.3 Gy; at 10 years 18.4 Gy, at 20 years 16.5 Gy, and at 30 years 14.3 Gy. We have calculated 95% confidence limits for age at premature ovarian failure for estimated radiation doses to the ovary from 1 Gy to the ESD from birth to 50 years. Conclusions: We report the first model to reliably predict the age of ovarian failure after treatment with a known dose of radiotherapy. Clinical application of this model will enable physicians to counsel women on their reproductive potential following successful treatment.

Wallace, W. Hamish B. [Section of Child Life and Health, Department of Reproductive and Developmental Sciences, University of Edinburgh, Edinburgh, Scotland (United Kingdom)]. E-mail: Hamish.Wallace@ed.ac.uk; Thomson, Angela B. [Royal Hospital for Sick Children, Yorkhill, Glasgow, Scotland (United Kingdom); Saran, Frank [Royal Marsden NHS Trust Foundation, Sutton (United Kingdom); Kelsey, Tom W. [School of Computer Science, University of St. Andrews, St. Andrews, Scotland (United Kingdom)

2005-07-01

360

Effective field theory calculation of two-deuteron radiative capture reaction at astrophysical energies  

NASA Astrophysics Data System (ADS)

Two-deuteron radiative capture reaction is one of the deuterium-burning processes that the cross section is not well known at very low-energies. We develop the formalism based on pionless Effective Field Theory (EFT) for deuteron-deuteron ( dd) scattering to derive the cross section of two-deuteron radiative capture. Within this formalism the two- and three-body forces, should also be included in the capture cross section calculations. The aim of the present work is to calculate the observables of the low-energy dd photonuclear reactions. The cross section and the astrophysical S-factor for the 2H( d, ?)4He reaction have been calculated. The 4He is studied as four-body bound states in the pionless EFT. The theoretical uncertainties for observables are estimated based on the variation of the cutoffs. The astrophysical S-factor is accurately determined to be 6.9×10-6 keV b (6.1×10-6 keV b) for two-body (two- and three-body) at zero energy. A satisfactory agreement between theory and experiment for dd radiative capture observables up to order of calculation has been found by insertion of three-body force.

Sadeghi, H.; Khalili, H.

2014-08-01

361

[Saccharomyces cerevisiae as a model organism for studying the carcinogenicity of non-ionizing electromagnetic fields and radiation].  

PubMed

Medical and biological aspects of the effects of non-ionizing electromagnetic (EM) fields and radiation on human health are the important issues that have arisen as a result of anthropogenic impact on the biosphere. Safe use of man-made sources of non-ionizing electromagnetic fields and radiation in a broad range of frequencies--static, radio-frequency and microwave--is a subject of discussions and speculations. The main problem is the lack of understanding of the mechanism(s) of reception of EMFs by living organisms. In this review we have analyzed the existing literature data regarding the effects of the electromagnetic radiation on the model eukaryotic organism--yeast Saccharomyces cerevisiae. An attempt was made to estimate the probability of induction of carcinogenesis in humans under the influence of magnetic fields and electromagnetic radiation of extremely low frequency, radio frequency and microwave ranges. PMID:24800516

Vo?chuk, S I

2014-01-01

362

Near-field radiative heat transfer across a pore and its effects on thermal conductivity of mesoporous silica  

NASA Astrophysics Data System (ADS)

Mesoporous silica substrate consists of uniformly distributed, unconnected cylindrical or spherical pores. Since the diameters of the pores are less than the wavelength, near-field radiative heat transfer across a cylindrical or spherical pore was simulated by employing the fluctuation dissipation theorem and Green function. Such factors as the diameter of the pore, and the temperature of the material were analyzed. It turned out that when the diameter is greater than 1 nm and less than 50 nm, the radiative heat flux at the mesoscale is 2-6 orders higher than the value at the macroscale, and decreases exponentially with the pore radius increasing for both cylindrical and spherical pore. The thermal conductivity of the mesoporous silica was modified with consideration of near-field radiation. It was concluded that the combined thermal conductivities of mesoporous silica which considering near-field radiation can agree with the experimental results more properly than non-considering near-field radiation. The smaller the pore diameter, the more significant the near-field radiation effect. The combined thermal conductivities of mesoporous silica decrease gradually with the pore diameter increasing, while increase smoothly with the temperature increasing.

Li, Jing; Feng, Yanhui; Zhang, Xinxin; Huang, Congliang; Wang, Ge

2015-01-01

363

A prototype scintillation dosimeter customized for small and dynamic megavoltage radiation fields.  

PubMed

A prototype plastic scintillation dosimeter has been developed with a small sensitive volume, rapid response and good dosimetric performance. The novelty of this design is the use of an air core light guide to transport the scintillation signal out of the primary radiation field. The significance of this innovation is that it eliminates the Cerenkov background signal that is generated in conventional optical fibres. The dosimeter performance was compared to existing commercial dosimeters in 6 MV and 18 MV photon beams and 6 MeV and 20 MeV electron beams, in both static and dynamic fields. The dosimeter was tested in small static fields and in dynamically delivered fields where the detector volume is shielded, while the stem is irradiated. The depth dose measurements for the photon beams agreed with ionization chamber measurements to within 1.6%, except in the build-up region due to positional uncertainty. For the 6 MeV and 20 MeV electron beams, the percentage depth dose measurements agreed with the ionization chamber measurements to within 3.6% and 4.5%, respectively. For field sizes of 1 cm x 1 cm and greater, the air core dosimeter readings agreed with diamond detector readings to within 1.2%. The air core dosimeter was accurate in dynamically delivered fields and had no measurable stem effect. The air core dosimeter was accurate over a range of field sizes, energies and dose rates, confirming that it is a sensitive and accurate dosimeter with high spatial resolution suitable for use in megavoltage photon and electron beams. PMID:20107251

Lambert, Jamil; Yin, Yongbai; McKenzie, David R; Law, Susan H; Ralston, Anna; Suchowerska, Natalka

2010-02-21

364

Africa on My Mind: Encounters in the Field  

E-print Network

: Prentice-Hall. Gans, He~bert J. 1?8~. "Sociology in America: The Discipline and the Public." . . Alnenc~n SOCiological Review 54 (February):1-16. Sunon, David R. and D. Stanley Eitzen.. 1990;-Elite.·Deviance.-·3rd·,ed. Bosten. Allyn and Bacon, forthcoming...~). While grappling with the project focus, I was, s~ultane~~l'y faced .~th dissonance over personal demographics. It wasn t Just. the initial suspicion social scientists' commonly face, or the natural apprehension of people in an authoritarian society...

Burgess, Elaine

1990-01-01

365

A Systematic Global Mapping of the Radiation Field at Aviation Altitudes  

NASA Technical Reports Server (NTRS)

This paper presents early results from aircraft measurements made by a Low-LET Radiation Spectrometer (LoLRS), as part of a long-range effort to study the complex dynamics of the atmospheric radiation field. For this purpose, a comprehensive data base is being generated to enable a multivariable global mapping (and eventually modeling) of doses and Linear-Energy-Transfer (LET) spectra at aviation altitudes. To accomplish this, a methodical collection of data from the LoLRS (and other instruments), is planned over extended periods of time, in a manner that complements some previous isolated and sporadic measurements by other workers, with the objective to generate a detailed long-range description of the cosmic-ray induced particle environment and to study its variability and dependence on atmospheric thickness, magnetic latitude, L-shell or rigidity, space weather, solar particle events, solar cycle effects, magnetic field variation, diurnal and seasonal effects, and atmospheric weather. Analysis of initial data indicates that the dose is rising with increasing altitude and increasing magnetic latitude. Comparison of total doses with predictions is in good agreement.

Stassinopoulos, E. G.; Stauffer, C. A.; Brucker, G. J.

2003-01-01

366

The development of low level coastal flow fields when solar radiation is blocked by smoke  

SciTech Connect

Thick layers of smoke, injected into the atmosphere by fires ignited by a nuclear exchange, would block the incident solar radiation and allow continental regions to cool while oceanic areas remain at constant temperature. It has been suggested that the resultant horizontal temperature gradient could initiate precipitation along the coastline that would rapidly scavenge the smoke. This hypothesis is being investigated using an enhanced version of the Colorado State University mesoscale model to simulate the flow field in the vicinity of continental coastlines. The model has been modified to include cloud formation and the effects of these clouds on the transfer of infrared radiation as well as improving the basic long wave radiation parameterization. For moderate westerly winds over the east coast (offshore flow), a layer of fog forms just above the ground that, after about 2 days, evolves into a stratus cloud. Over the ocean a similar stratus cloud forms because of upward mixing of water vapor and radiative cooling. Once these similar cloud layers form, the cooling rates over land and sea become nearly the same eliminating the proposed mechanism for development of convective precipitation and scavenging of mid- or high-level smoke. For the same westerly winds on the west coast (onshore flow), the sequence is similar but evolves more quickly because more moisture is present in the upwind maritime air. In both cases, the formation of ground fog prevents the air temperature in the surface layer from falling below the temperature at which saturation occurs. Before the temperature decreases further, moisture must be removed from the layer.

Molenkamp, C.R.

1987-08-01

367

ROLE FOR THE MAGNETIC FIELD IN THE RADIATION-INDUCED EFFLUX OF CALCIUM IONS FROM BRAIN TISSUE 'IN VITRO'  

EPA Science Inventory

Two independent laboratories have demonstrated that specific frequencies of electromagnetic radiation can cause a change in the efflux of calcium ions from brain tissue in vitro. Under a static magnetic field intensity of 38 microTesla (microT) due to the earth's magnetic field, ...

368

Gynogenesis in carp, Cyprinus Carpio L. and tench, Tinca Tinca L. induced by 60Co radiation in highly homogeneous radiating field  

NASA Astrophysics Data System (ADS)

The paper deals with a method of fertility inactivation of fish spermatozoa by gamma radiation. Spermatozoa motility remained unchanged after irradiation. Irradiated sperm has been utilized to induced gynogenesis by means of retention of the second polar body and of mitotic gynogenesis, realized in carp for the first time. Homogeneity of gamma-rays field was + - 1 %.

Pipota, J.; Linhart, O.

369

Generalized Reference Fields and Source Interpolation for the Difference Formulation of Radiation Transport  

SciTech Connect

In the difference formulation for the transport of thermally emitted photons, the photon intensity is defined relative to a reference field, the black body at the local material temperature. This choice of reference field combines the separate emission and absorption terms that nearly cancel, removing the dominant cause of noise in the Monte Carlo solution of thick systems, but introduces time and space derivative source terms that can not be determined until the end of the time step. The space derivative source term can also lead to noise induced crashes under certain conditions where the real physical photon intensity differs strongly from a black body at the local material temperature. In this paper, we consider a difference formulation relative to the material temperature at the beginning of the time step, or in cases where an alternative temperature better describes the radiation field, that temperature. The result is a method where iterative solution of the material energy equation is efficient and noise induced crashes are avoided. We couple our generalized reference field scheme with an ad hoc interpolation of the space derivative source, resulting in an algorithm that produces the correct flux between zones as the physical system approaches the thick limit.

Luu, T C; Brooks, E D; Szoke, A

2009-02-05

370

The effect of cumulus cloud field anisotropy on solar radiative fluxes and atmospheric heating rates  

NASA Astrophysics Data System (ADS)

The effect of fair-weather cumulus cloud field anisotropy on domain average surface fluxes and atmospheric heating profiles was studied. Causes of anisotropy were investigated using a large-eddy simulation (LES) model. Cloud formation under a variety of environmental conditions was simulated and the degree of anisotropy in the output fields was calculated. Wind shear was found to be the single greatest factor in the development of both vertically tilted and horizontally stretched cloud structures. A stochastic field generation algorithm was used to produce twenty three-dimensional liquid water content fields based on the statistical properties of the LES cloud scenes. Progressively greater degrees of tilt and stretching were imposed on each of these scenes, so that an ensemble of scenes were produced for each level of distortion. The resulting scenes were used as input to a three-dimensional Monte Carlo model. Domain-average transmission, reflection, and absorption of broadband solar radiation were computed for each scene along with the average heating rate profile. Both tilt and horizontal stretching were found to significantly affect calculated fluxes, with the amount and sign of flux differences depending strongly on sun position relative to cloud distortion geometry. For nearly all solar geometries, domain-averaged fluxes and atmospheric heating rate profiles calculated using the Independent Pixel Approximation differed substantially from the corresponding three-dimensional Monte Carlo results.

Hinkelman, Laura M.

371

Investigating Undergraduate Students’ Conceptions of Radiation  

NASA Astrophysics Data System (ADS)

Radiation is an essential topic to the physical sciences yet is often misunderstood by the general public. The last time most people have formal instruction about radiation is as students in high school and this knowledge will be carried into adulthood. Peoples’ conceptions of radiation influence their attitude towards research regarding radiation, radioactivity, and other work where radiation is prevalent. In order to understand students’ ideas about radiation after having left high school, we collected science surveys from nearly 12,000 undergraduates enrolled in introductory science courses over a span of 25 years. This research investigates the relationship between students’ conceptions of radiation and students’ personal beliefs and academic field of study.Our results show that many students in the sample were unable to adequately describe radiation. Responses were typically vague, brief, and emotionally driven. Students’ field of study was found to significantly correlate with their conceptions. Students pursuing STEM majors were 60% more likely to describe radiation as an emission and/or form of energy and cited atomic or radioactive sources of radiation twice as often as non-STEM students. Additionally, students’ personal beliefs also appear to relate to their conceptions of radiation. The most prominent misconception shown was that radiation is a generically harmful substance, which was found to be consistent throughout the duration of the study. In particular, non-science majors in our sample had higher rates of misconceptions, often generalized the idea of radiation into a broad singular topic, and had difficulty properly identifying sources.Generalized ideas of radiation and the inability to properly recognize sources of radiation may contribute to the prevalent misconception that radiation is an inexplicably dangerous substance. A basic understanding of both electromagnetic and particulate radiation and the existence of radiation at various energy levels may substantially deter fear-based generalizations and increase students’ abilities to make rational decisions when encountering various types of radiation in daily life.

Romine, James M.; Buxner, Sanlyn; Impey, Chris; Nieberding, Megan; Antonellis, Jessie C.

2014-11-01

372

Field effects of cadmium contamination in the radiation characteristics of maize  

NASA Astrophysics Data System (ADS)

Cadmium is one of the most common toxic heavy metals in our environment. Cadmium is a particularly dangerous element, because it dissolves readily, making it easily available to plants. It is thus able to accumulate in various links in the food chain, finally reaching humans, at the end of the chain. Adverse effects on human body was reported in 1858 at first. If it enters the body, damage to health, cause changes and can also cause cancer. Our study was designated to simulate the effects of cadmium on maize in field conditions, during the 2011 growing season. The impact of cadmium on maize was investigated at the Agro-meteorological Research Station in Keszthely. A Swiss-bred maize hybrid, Sperlona (FAO 340), with a short vegetation period, was sown in the experiments at the plant density (70,000 plants per hectare) widely used under Hungarian climatic conditions for growing grain maize. Effects of cadmium on corn life were studied under two water supplies. Evapotranspirometers of the Thornthwaite type were used for the "ad libitum" treatment and the the rainfed variant was sown in field plots. 0,5 M concentration of cadmium was used, which was sprayed weekly. The aim of the investigation was to simulate impact of atmospheric pollution of traffic origin (low and frequent doses in the field). Plant height was registered weekly similarly to leaf area index (LAI). Albedo was measured by pyranometers of the CMA-11 type (Kipp & Zonen, Vaisala). From this the most important radiative properties were calculated, so the net radiation balance, latent heat, sensible heat and the Bowen ratio. The values of LAI for the cadmium contaminated maize were significantly lower compared to the control maize. The net radiation balance was about the same in both treatments. Cadmium causes the latent heat decreased, while the sensible heat increased compared to the control treatment. The Bowen ratio in the polluted crops was higher, than the cadmium-untreated area. The yield of maize declined as a result of cadmium pollution. The number of distorted cobs increased on a very high extent. It means that both the quantity and quality of yield deteriorated in cadmium polluted fields. This article was made under the project TÁMOP-4.2.1/B-09/1/KONV-2010-0003 and TÁMOP-4.2.2/B-10/1-2010-0025. These projects are supported by the European Union and co-financed by the European Social Fund.

Illes, B.; Anda, A.

2012-04-01

373

Voyager program. Voyager 1 encounter at Jupiter, 5 March 1979  

NASA Technical Reports Server (NTRS)

Highlights of Voyager 1 activity during the observatory and far-encounter phases are summarized. Daily sequence of events for the spacecraft during the period of greatest encounter activity (Feb. 26 through Mar. 7) the near-encounter phase is given. Times shown designate the time of signal reception at Deep Space Network stations. Events listed emphasize activities pertaining to the four remote sensing instruments on the scan platforms. However, the other 7 experiments will continuously collect data throughout the encounter period.

1979-01-01

374

Voyager engineering improvements for Uranus encounter  

NASA Technical Reports Server (NTRS)

Engineering changes made on the Voyager spacecraft during their explorations of the outer solar system are discussed. A recovery from a scan actuator fault, achieved by ground testing, in flight capability enhancement and testing, conservation of actuator usage and a set of contingency plans to substitute roll motion of the spacecraft for motion of the scan platform in the AZ direction, is discussed. General engineering improvements made are addressed, including a scan platform anticreep patch modification, an improvement of dynamic performance during maneuvers, and adaptive control of the attitude control deadband. Changes made in the power management are described. Finally, engineering improvements made in order to enhance scientific findings at the Uranus encounter are reviewed in detail. The two most important were the increased gyro drift turn rate capability to accommodate image motion compensation for the close fly-by of Miranda and the reduction in spacecraft rates to accommodate increased imaging exposure times without incurring excessive image smear.

Marderness, H. P.

1986-01-01

375

Voyager Briefing: Expectations of the Neptune Encounter  

NASA Astrophysics Data System (ADS)

This NASA KSC video release presents a news briefing held Aug. 4, 1989 at NASA Headquarters three weeks after Voyager 2's official "encounter" with Neptune began. The video is comprised of two slide presentations followed by a short question and answer period. The press conference is moderated by Charles Redmond, (NASA Public Affairs), includes an introduction by Dr. Geoffrey A Briggs (Dir., Solar System Exploration Div.), and features Norman R. Haynes (Voyager Project Manager, JPL) and Dr. Edward C. Stone (Voyager Project Scientist, Cal Tech). Mr. Haynes' presentation centers on Voyager's history, engineering changes, and spacecraft trajectories while Dr. Stone presents the scientific aspects of Voyager, including the 11 scientific investigations planned for the mission, instruments used, and imaging techniques.

1989-08-01

376

Voyager Briefing: Expectations of the Neptune Encounter  

NASA Technical Reports Server (NTRS)

This NASA KSC video release presents a news briefing held Aug. 4, 1989 at NASA Headquarters three weeks after Voyager 2's official "encounter" with Neptune began. The video is comprised of two slide presentations followed by a short question and answer period. The press conference is moderated by Charles Redmond, (NASA Public Affairs), includes an introduction by Dr. Geoffrey A Briggs (Dir., Solar System Exploration Div.), and features Norman R. Haynes (Voyager Project Manager, JPL) and Dr. Edward C. Stone (Voyager Project Scientist, Cal Tech). Mr. Haynes' presentation centers on Voyager's history, engineering changes, and spacecraft trajectories while Dr. Stone presents the scientific aspects of Voyager, including the 11 scientific investigations planned for the mission, instruments used, and imaging techniques.

1989-01-01

377

Analysis of vortex wake encounter upsets  

NASA Technical Reports Server (NTRS)

The problem of an airplane being upset by encountering the vortex wake of a large transport on takeoff or landing is currently receiving considerable attention. This report describes the technique and results of a study to assess the effectiveness of automatic control systems in alleviating vortex wake upsets. A six-degree-of-freedom nonlinear digital simulation was used for this purpose. The analysis included establishing the disturbance input due to penetrating a vortex wake from an arbitrary position and angle. Simulations were computed for both a general aviation airplane and a commercial jet transport. Dynamic responses were obtained for the penetrating aircraft with no augmentation, and with various command augmentation systems, as well as with human pilot control. The results of this preliminary study indicate that attitude command augmentation systems can provide significant alleviation of vortex wake upsets; and can do it better than a human pilot.

Johnson, W. A.; Teper, G. L.

1974-01-01

378

Angular distribution of binary encounter electrons  

SciTech Connect

The double differential cross section, DDCS, of the binary encounter electrons (BEe) in 1 MeV/u F{sup q+} + H{sub 2} (q = 4, 6, 8, 9) is measured from 0 to 70 degrees with respect to the beam direction. At 0{degrees} the data confirm the decrease of the cross section with increasing projectile charge state. At larger observation angles, the data are in fair agreement with the prediction proposed by Shingal et al. where the ratio of the DDCS for 6+ ions to bare ions is less than 1 for {theta}{sub lab} > 30{degrees} and greater than 1 for {theta}{sub lab} < 30{degrees} as recently observed for C{sup q+}. We also observed that the energies of the BEe peak are charge state, q, independent at 0{degrees} observation angle, but q dependent at larger observation angles.

Liao, C.; Richard, P.; Grabbe, S. [Kansas State Univ., Manhattan, KS (United States)] [and others

1993-05-01

379

Exposure of arctic field scientists to ultraviolet radiation evaluated using personal dosimeters.  

PubMed

During July 2000 we used an electronic personal dosimeter (X-2000) and a biological dosimeter (Deutsches Zentrum für Luft- und Raumfahrt: Biofilm) to characterize the UV radiation exposure of arctic field scientists involved in biological and geological fieldwork. These personnel were working at the Haughton impact structure on Devon Island (75 degrees N) in the Canadian High Arctic under a 24 h photoperiod. During a typical day of field activities under a clear sky, the total daily erythemally weighted exposure, as measured by electronic dosimetry, was up to 5.8 standard erythemal dose (SED). Overcast skies (typically 7-8 okta of stratus) reduced exposures by a mean of 54%. We estimate that during a month of field activity in July a typical field scientist at this latitude could potentially receive approximately 80 SED to the face. Because of body movements the upper body was exposed to a UV regimen that often changed on second-to-second time-scales as assessed by electronic dosimetry. Over a typical 10 min period on vehicle traverse, we found that erythemal exposure could vary to up to 87% of the mean exposure. Time-integrated exposures showed that the type of outdoor field activities in the treeless expanse of the polar desert had little effect on the exposure received. Although absolute exposure changed in accordance with the time of day, the exposure ratio (dose received over horizontal dose) did not vary much over the day. Under clear skies the mean exposure ratio was 0.35 +/- 0.12 for individual activities at different times of the day assessed using electronic dosimetry. Biological dosimetry showed that the occupation was important in determining daily exposures. In our study, scientists in the field received an approximately two-fold higher dose than individuals, such as medics and computer scientists, who spent the majority of their time in tents. PMID:11683037

Cockell, C S; Scherer, K; Horneck, G; Rettberg, P; Facius, R; Gugg-Helminger, A; Driscoll, C; Lee, P

2001-10-01

380

Exposures involving perturbations of the EM field have non-linear effects on radiation response and can alter the expression of radiation induced bystander effects  

NASA Astrophysics Data System (ADS)

Our recent data suggest there is a physical component to the bystander signal induced by radiation exposure and that alternative medicine techniques such as Reiki and acupuncture or exposures to weak EM fields alter the response of cells to direct irradiation and either altered bystander signal production or altered the response of cells receiving bystander signals. Our proposed mechanism to explain these findings is that perturbation of electromagnetic (EM) fields is central to the induction of low radiation dose responses especially non-targeted bystander effects. In this presentation we review the alternative medicine data and other data sets from our laboratory which test our hypothesis that perturbation of bio-fields will modulate radiation response in the low dose region. The other data sets include exposure to MRI, shielding using lead and or Faraday cages, the use of physical barriers to bystander signal transmission and the use of membrane channel blockers. The data taken together strongly suggest that EM field perturbation can modulate low dose response and that in fact the EM field rather than the targeted deposition of ionizing energy in the DNA may be the key determinant of dose response in a cell or organism The results also lead us to suspect that at least when chemical transmission is blocked, bystander signals can be transmitted by other means. Our recent experiments suggest light signals and volatiles are not likely. We conclude that alternative medicine and other techniques involving electromagnetic perturbations can modify the response of cells to low doses of ionizing radiation and can induce bystander effects similar to those seen in medium transfer experiments. In addition to the obvious implications for mechanistic studies of low dose effects, this could perhaps provide a novel target to exploit in space radiation protection and in optimizing therapeutic gain during radiotherapy.

Mothersill, Carmel; Seymour, Colin

2012-07-01

381

The Electric Field and Waves Instruments on the Radiation Belt Storm Probes Mission  

NASA Astrophysics Data System (ADS)

The Electric Fields and Waves (EFW) Instruments on the two Radiation Belt Storm Probe (RBSP) spacecraft (recently renamed the Van Allen Probes) are designed to measure three dimensional quasi-static and low frequency electric fields and waves associated with the major mechanisms responsible for the acceleration of energetic charged particles in the inner magnetosphere of the Earth. For this measurement, the instrument uses two pairs of spherical double probe sensors at the ends of orthogonal centripetally deployed booms in the spin plane with tip-to-tip separations of 100 meters. The third component of the electric field is measured by two spherical sensors separated by ˜15 m, deployed at the ends of two stacer booms oppositely directed along the spin axis of the spacecraft. The instrument provides a continuous stream of measurements over the entire orbit of the low frequency electric field vector at 32 samples/s in a survey mode. This survey mode also includes measurements of spacecraft potential to provide information on thermal electron plasma variations and structure. Survey mode spectral information allows the continuous evaluation of the peak value and spectral power in electric, magnetic and density fluctuations from several Hz to 6.5 kHz. On-board cross-spectral data allows the calculation of field-aligned wave Poynting flux along the magnetic field. For higher frequency waveform information, two different programmable burst memories are used with nominal sampling rates of 512 samples/s and 16 k samples/s. The EFW burst modes provide targeted measurements over brief time intervals of 3-d electric fields, 3-d wave magnetic fields (from the EMFISIS magnetic search coil sensors), and spacecraft potential. In the burst modes all six sensor-spacecraft potential measurements are telemetered enabling interferometric timing of small-scale plasma structures. In the first burst mode, the instrument stores all or a substantial fraction of the high frequency measurements in a 32 gigabyte burst memory. The sub-intervals to be downloaded are uplinked by ground command after inspection of instrument survey data and other information available on the ground. The second burst mode involves autonomous storing and playback of data controlled by flight software algorithms, which assess the "highest quality" events on the basis of instrument measurements and information from other instruments available on orbit. The EFW instrument provides 3-d wave electric field signals with a frequency response up to 400 kHz to the EMFISIS instrument for analysis and telemetry (Kletzing et al. Space Sci. Rev. 2013).

Wygant, J. R.; Bonnell, J. W.; Goetz, K.; Ergun, R. E.; Mozer, F. S.; Bale, S. D.; Ludlam, M.; Turin, P.; Harvey, P. R.; Hochmann, R.; Harps, K.; Dalton, G.; McCauley, J.; Rachelson, W.; Gordon, D.; Donakowski, B.; Shultz, C.; Smith, C.; Diaz-Aguado, M.; Fischer, J.; Heavner, S.; Berg, P.; Malsapina, D. M.; Bolton, M. K.; Hudson, M.; Strangeway, R. J.; Baker, D. N.; Li, X.; Albert, J.; Foster, J. C.; Chaston, C. C.; Mann, I.; Donovan, E.; Cully, C. M.; Cattell, C. A.; Krasnoselskikh, V.; Kersten, K.; Brenneman, A.; Tao, J. B.

2013-11-01

382

Isotope selective photodissociation of N2 by the interstellar radiation field and cosmic rays  

NASA Astrophysics Data System (ADS)

Context. Photodissociation of 14N2 and 14N 15N occurs in interstellar clouds, circumstellar envelopes, protoplanetary discs, and other environments due to ultraviolet radiation originating from stellar sources and the presence of cosmic rays. This source of N atoms initiates the formation of more complex N-bearing species and may influence their isotopic composition. Aims: We study the photodissociation rates of 14N 15N by ultraviolet continuum radiation and both isotopologues in a field of cosmic ray induced photons. To determine the effect of these on the isotopic composition of more complex molecules. Methods: High-resolution theoretical photodissociation cross sections of N2 are used from an accurate and comprehensive quantum-mechanical model of the molecule based on laboratory experiments. A similarly high-resolution spectrum of H2 emission following interactions with cosmic rays has been constructed. The spectroscopic data are used to calculate photodissociation rates which are then input into isotopically differentiated chemical models, describing an interstellar cloud and a protoplanetary disc. Results: The photodissociation rate of 14N 15N in a Draine field assuming 30 K excitation is 1.73 × 10-10 s-1, within 4% of the rate for 14N2, and the rate due to cosmic ray induced photons assuming an H2 ionisation rate of ? = 10-16 s-1 is about 10-15 s-1, with up to a factor of 10 difference between isotopologues. Shielding functions for 14N15N by 14N2, H2, and H are presented. Incorporating these into an interstellar cloud model, an enhancement of the atomic 15N/14N ratio over the elemental value is obtained due to the self-shielding of external radiation at an extinction of about 1.5 mag. This effect is larger where assumed grain growth has reduced the opacity of dust to ultraviolet radiation. The transfer of photolytic isotopic fractionation of N and N2 to other molecules is demonstrated to be significant in a protoplanetary disc model with grain growth, and is species dependent with 15N enhancement approaching a factor of 10 for HCN. The cosmic ray induced dissociation of CO is revisited employing a more recent photodissociation cross section, leading to a rate that is ~40% lower than previously calculated.

Heays, Alan N.; Visser, Ruud; Gredel, Roland; Ubachs, Wim; Lewis, Brenton R.; Gibson, Stephen T.; van Dishoeck, Ewine F.

2014-02-01

383

TIDAL DISRUPTIONS OF WHITE DWARFS FROM ULTRA-CLOSE ENCOUNTERS WITH INTERMEDIATE-MASS SPINNING BLACK HOLES  

SciTech Connect

We present numerical relativity results of tidal disruptions of white dwarfs from ultra-close encounters with a spinning, intermediate-mass black hole (IMBH). These encounters require a full general relativistic treatment of gravity. We show that the disruption process and prompt accretion of the debris strongly depend on the magnitude and orientation of the black hole (BH) spin. However, the late-time accretion onto the BH follows the same decay, M-dot {proportional_to} t{sup -5/3}, estimated from Newtonian gravity disruption studies. We compute the spectrum of the disk formed from the fallback material using a slim disk model. The disk spectrum peaks in the soft X-rays and sustains Eddington luminosity for 1-3 yr after the disruption. For arbitrary BH spin orientations, the disrupted material is scattered away from the orbital plane by relativistic frame dragging, which often leads to obscuration of the inner fallback disk by the outflowing debris. The disruption events also yield bursts of gravitational radiation with characteristic frequencies of {approx}3.2 Hz and strain amplitudes of {approx}10{sup -18} for galactic IMBHs. The optimistic rate of considered ultra-close disruptions is consistent with no sources found in the ROSAT all-sky survey. Future missions like Wide-Field X-ray Telescope could observe dozens of events.

Haas, Roland; Bode, Tanja; Laguna, Pablo [Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Shcherbakov, Roman V. [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States)

2012-04-20

384

Tidal Disruptions of White Dwarfs from Ultra-close Encounters with Intermediate-mass Spinning Black Holes  

NASA Astrophysics Data System (ADS)

We present numerical relativity results of tidal disruptions of white dwarfs from ultra-close encounters with a spinning, intermediate-mass black hole (IMBH). These encounters require a full general relativistic treatment of gravity. We show that the disruption process and prompt accretion of the debris strongly depend on the magnitude and orientation of the black hole (BH) spin. However, the late-time accretion onto the BH follows the same decay, \\dot{M} \\propto \\,t^{-5/3}, estimated from Newtonian gravity disruption studies. We compute the spectrum of the disk formed from the fallback material using a slim disk model. The disk spectrum peaks in the soft X-rays and sustains Eddington luminosity for 1-3 yr after the disruption. For arbitrary BH spin orientations, the disrupted material is scattered away from the orbital plane by relativistic frame dragging, which often leads to obscuration of the inner fallback disk by the outflowing debris. The disruption events also yield bursts of gravitational radiation with characteristic frequencies of ~3.2 Hz and strain amplitudes of ~10-18 for galactic IMBHs. The optimistic rate of considered ultra-close disruptions is consistent with no sources found in the ROSAT all-sky survey. Future missions like Wide-Field X-ray Telescope could observe dozens of events.

Haas, Roland; Shcherbakov, Roman V.; Bode, Tanja; Laguna, Pablo

2012-04-01

385

The Measurements of Neutron and Gamma Dose Rates in Mixed Radiation Fields, Using a Liquid Scintillation Counter.  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Measurements of neutron and gamma dose rates in mixed radiation fields, and gamma dose rates from calibrated gamma sources, were performed using a liquid scintillation counter NE213 with a pulse shape discrimination technique based on the charge comparison method. A computer program was used to analyse the experimental data. The radiation field was obtained from a ^{241}Am-^9Be source. There was general agreement between measured and calculated neutron and gamma dose rates in the mixed radiation field, but some disagreement in the measurements of gamma dose rates for gamma sources, due to the dark current of the photomultiplier and the effect of the perturbation of the radiation field by the detector. An optical fibre bundle was used to couple an NE213 scintillator to a photomultipler, in an attempt to minimise these effects. This produced an improvement in the results for gamma sources. However, the optically coupled detector system could not be used for neutron and gamma dose rate measurements in mixed radiation fields. The pulse shape discrimination system became ineffective as a consequence of the slower time response of the detector system.

Shakshak, Bashir Ibrahim Omar

386

Busting Up Binaries: Encounters Between Compact Binaries and a Supermassive Black Hole  

E-print Network

Given the stellar density near the galactic center, close encounters between compact object binaries and the supermassive black hole are a plausible occurrence. We present results from a numerical study of close to 13 million such encounters. Consistent with previous studies, we corroborate that, for binary systems tidally disrupted by the black hole, the component of the binary remaining bound to the hole has eccentricity ~ 0.97 and circularizes dramatically by the time it enters the classical LISA band. Our results also show that the population of surviving binaries merits attention. These binary systems experience perturbations to their internal orbital parameters with potentially interesting observational consequences. We investigated the regions of parameter space for survival and estimated the distribution of orbital parameters post-encounter. We found that surviving binaries harden and their eccentricity increases, thus accelerating their merger due gravitational radiation emission and increasing the p...

Addison, Eric; Larson, Shane

2015-01-01

387

Simulator study of vortex encounters by a twin-engine, commercial, jet transport airplane  

NASA Technical Reports Server (NTRS)

A simulator study of vortex encounters was conducted for a twin-engine, commercial, jet transport airplane encountering the vortex flow field of a heavy, four-engine, commercial, jet transport airplane in the final-approach configuration. The encounters were conducted with fixed controls and with a pilot using a state-of-the-art, manual-control system. Piloted encounters with the base-line vortex flow field out of ground effect (unattenuated) resulted in initial bank-angle excursions greater than 40 deg, coupled with initial sideslip-angle excursions greater than 10 deg. The severity of these initial upsets was significantly reduced when the vortex center was moved laterally or vertically away from the flight path of the encountering airplane. Smaller reductions occurred when the flow field was attenuated by the flight spoilers on the generating airplane. The largest reduction in the severity of the initial upsets, however, was from aging in ground effect. The severity of the initial upsets of the following airplane was relatively unaffected by the approach speed. Increasing the lift coefficient of the generating airplane resulted in an increase in the severity of the initial upsets.

Hastings, E. C., Jr.; Keyser, G. L., Jr.

1982-01-01

388

On momentum and energy of a non-radiating electromagnetic field  

E-print Network

This paper inspects more closely the problem of the momentum and energy of a bound (non-radiating) electromagnetic (EM) field. It has been shown that for an isolated system of non-relativistic mechanically free charged particles a transformation of mechanical to EM momentum and vice versa occurs in accordance with the requirement PG=const, where PG is the canonical momentum. If such a system contains bound charges, fixed on insulators then, according to the assumption of a number of authors, a so-called "hidden" momentum can contribute into the total momentum of the system. The problem of "hidden momentum" (pro and contra) is also examined in the paper, as well as the law of conservation of total energy for different static configurations of the system "magnetic dipole plus charged particle". Analyzing two expressions for electromagnetic momentum of a bound EM field, qA and the Poynting expression, we emphasize that they coincide with each other for quasi-static configurations, but give a discrepancy for rapid dynamical processes. We conclude that neither the first, nor the second expressions provide a continuous implementation of the momentum conservation law. Finally, we consider the energy flux in a bound EM field, using the Umov vector. It has been shown that Umov vector can be directly derived from Maxwell equations. A new form of the momentum-energy tensor, which explicitly unites the mechanical and EM masses, has been proposed.

Alexander L. Kholmetskii

2005-01-31

389

A Topological Structure in the Set of Classical Free Radiation Electromagnetic Fields  

E-print Network

The aim of this work is to proceed with the development of a model of topological electromagnetism in empty space, proposed by one of us some time ago and based on the existence of a topological structure associated with the radiation fields in standard Maxwell's theory. This structure consists in pairs of complex scalar fields, say $\\phi$ and $\\theta$, that can be interpreted as maps $\\phi,\\theta: S^3\\mapsto S^2$, the level lines of which are orthogonal to one another, where $S^3$ is the compactified physical 3-space $R^3$, with only one point at infinity, and $S^2$ is the 2-sphere identified with the complete complex plane. These maps were discovered and studied in 1931 by the German mathematician H. Hopf, who showed that the set of all of them can be ordered in homotopy classes, labeled by the so called Hopf index, equal to $\\gamma=\\pm 1,\\,\\pm 2,\\,\\cdots ,\\, \\pm k,...$ but without $\\gamma=0$. In the model presented here and at the level of the scalars $\\phi$ and $\\theta$, the equations of motion are highly nonlinear; however there is a transformation of variables that converts exactly these equations (not by truncation!) into the linear Maxwell's ones for the magnetic and electric fields $\\B$ and $\\E$.

A. F. Ranada; A. Tiemblo

2014-07-29

390

Near-field radiative thermal transfer between a nanostructured periodic material and a planar substrate  

NASA Astrophysics Data System (ADS)

This paper provides a method based on rigorous coupled wave analysis for the calculation of the radiative thermal conductance between a layer that is patterned with arbitrary, periodically repeating features and a planar substrate. This method is applied to study the transfer from an array of beams with a rectangular cross section. The impact of the structure size and spacing on the thermal conductance are investigated. These calculations are compared to an effective medium theory, which becomes increasingly accurate as the structure sizes fall well below the relevant resonance wavelengths of materials and structures. Moreover, comparisons are made with a modified proximity approximation and the far-field approximation, which become valid for small and large spacings, respectively. Results show that new levels of control over the magnitude and spectral contributions to thermal conductance can be achieved with corrugated structures relative to planar ones. Specifically, we show for SiC arrays with rectangular cross sections and with the same filling fraction, that the use of a smaller periodicity leads to a lowered far-field thermal transfer and an increased near-field thermal transfer.

Chalabi, Hamidreza; Hasman, Erez; Brongersma, Mark L.

2015-01-01

391

BWR radiation assessment and control program: assessment and control of BWR radiation fields. Volume 2. Final report  

Microsoft Academic Search

This report covers work on the BWR Radiation Assessment and Control (BRAC) Program from 1978 to 1982. The major activities during this report period were assessment of the radiation-level trends in BWRs, evaluation of the effects of forward-pumped heater drains on BWR water quality, installation and operation of a corrosion-product deposition loop in an operating BWR, and analyzation of fuel

Marble

1983-01-01

392

BWR Radiation Assessment and Control Program: assessment and control of BWR radiation fields. Volume 1. Executive summary  

Microsoft Academic Search

This report covers work on the BWR Radiation Assessment and Control (BRAC) Program from 1978 to 1982. The major activities during this report period were assessment of the radiation-level trends in BWRs, evaluation of the effects of forward-pumped heater drains on BWR water quality, installation and operation of a corrosion-product deposition loop in an operating BWR, and analyzation of fuel-deposit

Anstine

1983-01-01

393

Effect of the ionizing radiation on the rain-time atmospheric electric field  

NASA Astrophysics Data System (ADS)

The atmospheric electric field, or potential gradient (PG) at Kakioka, 150 southwest of the Fukushima Nuclear Power Plant (NPP) shows peculiar behaviors after the accident, March 2012 due to the conductivity enhancement in the air by the ionizing radiation. This means that the PG provides significant information on the dynamics of the radioactive materials. During last EGU assembly 2012, we showed that the fine-weather PG decreased by one-two orders of magnitudes at the arrival of the radioactive plume, and that the PG recovered in various way depending on various types of re-suspension processes in addition to the physical decay of the deposited radioactive materials. We extended this work to the rain-time PG, which is very simple because of high variability of the PG depending on the cloud types and distribution. We yet found a statistical difference between rain-time PGs before and after the Fukushima NPP Accident: one-hour averaged rain-time PG during the first 45 days after the accident is not as much scattered to the negative side as those during the same period of different years or during 40 days before accident. Further examination of one-minute averaged data (1 Hz sampling) during the second half March for 2006-2012 revealed that this difference comes from short time-spans of negative peaks rather than the peak value after the accident compared to those before the accident. On the other hand, characteristics of positive peaks (cloud without rain) are unchanged. The results suggest either (1) the effect on the local charges in the rain cloud is narrowed under high dose of ionized radiation, making positive charges in the cloud less shielded by the negative charges, or (2) negative charge of ionized aerosol decays much faster under higher dose of ionized radiation due to the shortened time constant of the ionized aerosol (? 1-?, where ? is the atmospheric electric conductivity).

Yamauchi, Masatoshi; Takeda, Masahiko; Makino, Masahiko; Owada, Takeshi

2013-04-01

394

Encounters in Home-Based Nursing Care - Registered Nurses’ Experiences  

PubMed Central

The encounter between registered nurses and persons in need of healthcare has been described as fundamental in nursing care. This encounter can take place face-to-face in physical meetings and through meetings via distance-spanning technology. A strong view expressed in the literature is that the face-to-face encounter is important and cannot entirely be replaced by remote encounters. The encounter has been studied in various healthcare contexts but there is a lack of studies with specific focus on the encounter in home-based nursing care. The aim of this study was to explore the encounter in home-based nursing care based on registered nurses’ experiences. Individual interviews were performed with 24 nurses working in home-based nursing care. The transcribed interviews were analyzed using thematic content analysis and six themes were identified: Follows special rules, Needs some doing, Provides unique information and understanding, Facilitates by being known, Brings energy and relieves anxiety, and Can reach a spirit of community. The encounter includes dimensions of being private, being personal and being professional. A good encounter contains dimensions of being personal and being professional and that there is a good balance between these. This is an encounter between two human beings, where the nurse faces the person with herself and the profession steadily and securely in the back. Being personal and professional at the same time could encourage nurses to focus on doing and being during the encounter in home-based nursing care. PMID:23847697

Wälivaara, Britt-Marie; Sävenstedt, Stefan; Axelsson, Karin

2013-01-01

395

Magnetic coordinates for the Pioneer 10 Jupiter encounter  

NASA Technical Reports Server (NTRS)

The magnetic coordinates of the Pioneer 10 spacecraft and the five innermost satellites are reported for the Jupiter encounter. The D sub 2 offset is used to make the calculations. Magnetic coordinates are needed for the interpretation of the trapped particle measurements, including the absorption effects of the satellites. Contours of constant field magnitude and magnetic latitude are given at the surface of Jupiter for the D sub 2 model. The system 3 longitude of a spacecraft at Jupiter is derived, and formulas given for the relationships between system 1, 2, and 3 longitudes. The longitude of the magnetic dipole increases by about 3 deg per year, due to the inaccurate rotation rate used to define system 3 longitude.

Mead, G. D.

1974-01-01

396

CLOSE STELLAR ENCOUNTERS IN YOUNG, SUBSTRUCTURED, DISSOLVING STAR CLUSTERS: STATISTICS AND EFFECTS ON PLANETARY SYSTEMS  

SciTech Connect

Both simulations and observations indicate that stars form in filamentary, hierarchically clustered associations, most of which disperse into their galactic field once feedback destroys their parent clouds. However, during their early evolution in these substructured environments, stars can undergo close encounters with one another that might have significant impacts on their protoplanetary disks or young planetary systems. We perform N-body simulations of the early evolution of dissolving, substructured clusters with a wide range of properties, with the aim of quantifying the expected number and orbital element distributions of encounters as a function of cluster properties. We show that the presence of substructure both boosts the encounter rate and modifies the distribution of encounter velocities compared to what would be expected for a dynamically relaxed cluster. However, the boost only lasts for a dynamical time, and as a result the overall number of encounters expected remains low enough that gravitational stripping is unlikely to be a significant effect for the vast majority of star-forming environments in the Galaxy. We briefly discuss the implications of this result for models of the origin of the solar system, and of free-floating planets. We also provide tabulated encounter rates and orbital element distributions suitable for inclusion in population synthesis models of planet formation in a clustered environment.

Craig, Jonathan; Krumholz, Mark R., E-mail: krumholz@ucolick.org [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

2013-06-01

397

Analysis of rat testicular proteome following 30-day exposure to 900 MHz electromagnetic field radiation.  

PubMed

The use of electromagnetic field (EMF) generating apparatuses such as cell phones is increasing, and has caused an interest in the investigations of its effects on human health. We analyzed proteome in preparations from the whole testis in adult male Sprague-Dawley rats that were exposed to 900 MHz EMF radiation for 1, 2, or 4 h/day for 30 consecutive days, simulating a range of possible human cell phone use. Subjects were sacrificed immediately after the end of the experiment and testes fractions were solubilized and separated via high-resolution 2D electrophoresis, and gel patterns were scanned, digitized, and processed. Thirteen proteins, which were found only in sham or in exposure groups, were identified by MALDI-TOF/TOF-MS. Among them, heat shock proteins, superoxide dismutase, peroxiredoxin-1, and other proteins related to misfolding of proteins and/or stress were identified. These results demonstrate significant effects of radio frequency modulated EMFs exposure on proteome, particularly in protein species in the rodent testis, and suggest that a 30-day exposure to EMF radiation induces nonthermal stress in testicular tissue. The functional implication of the identified proteins was discussed. PMID:25146694

Sepehrimanesh, Masood; Kazemipour, Nasrin; Saeb, Mehdi; Nazifi, Saeed

2014-12-01

398

Measurements and simulations of the BLM response to a radiation field inside the CERF target area  

E-print Network

The CERN-EU high-energy reference field (CERF) facility is installed in one of the secondary beam lines (H6) of the Super Proton Synchrotron (SPS), in the North Experimental Area at CERN. This facility is used as a reference for testing, inter-comparing and calibrating passive and active instruments. In May 2009, the SPS provided a mixed hadron beam (protons, pions and kaons) during a few days, in order to perform several measurements with different devices such as the Radiation Protection Monitor used for residual dose rates due to Induced Radioactivity in the LHC (PMI), the Secondary Emission Monitor used for high beam losses (SEM), the Radiation Monitor for electronics (RadMon), and the Beam Loss Monitor for the LHC (BLM). This report focuses on the measurements of the BLM response during this year’s operation at CERF. The measurements evaluate the sensitivity of the BLM signal to the particle energy spectrum, with special attention to the contribution coming from thermal neutrons. For this purpose, meas...

Lebbos, E; Dehning, B; Effinger, E; Ferrari, A; Kramer, D; Nordt, A; Roeed, K; Roesler, S; Sapinski, M; Vlachoudis, V

2010-01-01

399

Quantum correlations and violation of the Bell inequality induced by an external field in a two-photon radiative cascade  

SciTech Connect

We study the polarization-dependent second-order correlation of a pair of photons emitted in a four-level radiative cascade driven by an external field. It is found that the quantum correlations of the emitted photons, degraded by the energy splitting of the intermediate levels in the radiative cascade, can be efficiently revived by a far-detuned external field. The physics of this revival is linked to an induced Stark shift and the formation of dressed states in the system by the nonresonant external field. Furthermore, we investigated the competition between the effect of the coherent external field and incoherent dephasing of the intermediate levels. We find that the degradation of quantum correlations due to the incoherent dephasing can be contained for small dephasing with the external field. We also studied the nonlocality of the correlations by evaluating the Bell inequality in the linear polarization basis for the radiative cascade. We find that the Bell parameter decreases rapidly with increase in the intermediate-level energy splitting or incoherent dephasing rate to the extent that there is no violation. However, the presence of an external field leads to control over the degrading mechanisms and preservation of nonlocal correlation among the photons. This in turn can induce a violation of Bell's inequality in the radiative cascade for arbitrary intermediate-level splitting and small incoherent dephasing.

Yuan Luqi; Das, Sumanta [Institute for Quantum Science and Engineering and Department of Physics and Astronomy, Texas A and M University, College Station, Texas 77843 (United States)

2011-06-15

400

New Results from Space and Field Observations on the Aerosol Direct and Indirect Radiative Forcing  

NASA Technical Reports Server (NTRS)

New space observations from the MODIS instrument on board the Terra satellite and analysis of POLDER data flown on the ADEOS satellite, show in great details the spatial and seasonal variability of the global aerosol system. These spaceborne instruments distinguish fine aerosol from man-made regional pollution and biomass burning from mostly natural coarse dust and sea salt aerosol. E.g. fine regional pollution in and around the Indian sub-continent, Europe and North America; smoke from biomass burning in Southern Africa and Southern America; coarse dust from West Africa and mixed dust pollution and smoke from West and central Africa and East Asia. These regions were also studied extensively in focused field experiments and by the distributed AERONET network. The results generate the first climatologies of the aerosol system, are used to derive the aerosol radiative effects and to estimate the anthropogenic component. The measurements are also used to evaluate each other and constrain aerosol transport models.

Kaufman, Yoram J.; Remer, Lorraine; Tanre, Didier; Boucher, Olivier; Chin, Mian; Dubovik, Oleg; Holben, Brent

2002-01-01

401

Reduction of the scatter dose to the testicle outside the radiation treatment fields  

SciTech Connect

A technique is described to reduce the dose to the contralateral testicle of patients with testis tumors during retroperitoneal therapy with 10 MV X-rays. When a conventional clam-shell shielding device was used, the dose to the testis from the photons scattered by the patient and the collimator jaws was found to be about 1.6% of the prescribed midplane dose. A more substantial gonadal shield made of low melting Ostalloy, that reduced further the dose from internal scattered X rays, was therefore designed. A 10 cm thick lead scrotal block above the scrotum immediately outside the field is shown to reduce the external scattered radiation to negligible levels. Using the shield and the block, it is possible to reduce the dose to the testicle to one-tenth of one percent of the prescribed midplane dose.

Kubo, H.; Shipley, W.U.

1982-10-01

402

Reduction of the scatter dose to the testicle outside the radiation treatment fields  

SciTech Connect

A technique is described to reduce the dose to the contralateral testicle of patients with testis tumors during retroperitoneal therapy with 10 MV X rays. When a conventional clam-shell shielding device was used, the dose to the testis from the photons scattered by the patient and collimator jaws was found to be about 1.6% of the prescribed midplane dose. A more substantial gonadal shield made of low melting point Ostalloy, that reduced further the dose from internal scattered X rays, was therefore designed. A 10 cm thick lead scrotal block above the scrotum immediately outside the field is shown to reduce the external scattering radiation to negligible levels. Using the shield and the block, it is possible to reduce the dose to the testicle to one-tenth of one percent of the prescribed midplane dose.

Kubo, H.; Shipley, W.U.

1982-10-01

403

Sampling and Analysis of Impact Crater Residues Found on the Wide Field Planetary Camera-2 Radiator  

NASA Technical Reports Server (NTRS)

After nearly 16 years in low Earth orbit (LEO), the Wide Field Planetary Camera-2 (WFPC2) was recovered from the Hubble Space Telescope (HST) in May 2009, during the 12 day shuttle mission designated STS-125. The WFPC-2 radiator had been struck by approximately 700 impactors producing crater features 300 microns and larger in size. Following optical inspection in 2009, agreement was reached for joint NASA-ESA study of crater residues, in 2011. Over 480 impact features were extracted at NASA Johnson Space Center's (JSC) Space Exposed Hardware clean-room and curation facility during 2012, and were shared between NASA and ESA. We describe analyses conducted using scanning electron microscopy (SEM) - energy dispersive X-ray spectrometry (EDX): by NASA at JSC's Astromaterials Research and Exploration Science (ARES) Division; and for ESA at the Natural History Museum (NHM), with Ion beam analysis (IBA) using a scanned proton microbeam at the University of Surrey Ion Beam Centre (IBC).

Kearsley, A. T.; Grime, G. W.; Colaux, J. L.; Jeynes, C.; Palitsin, V. V.; Webb, R, P.; Griffin, T. J.; Reed, B. B.; Anz-Meador, P. D.; Kou, J.-C.; Robinson, G. A.; Opiela, J. N.; Gerlach, L.

2013-01-01

404

Nuclear Radiation Fields on the Mars Surface: Risk Analysis for Long-term Living Environment  

NASA Technical Reports Server (NTRS)

Mars, our nearest planet outward from the sun, has been targeted for several decades as a prospective site for expanded human habitation. Background space radiation exposures on Mars are expected to be orders of magnitude higher than on Earth. Recent risk analysis procedures based on detailed dosimetric techniques applicable to sensitive human organs have been developed along with experimental data regarding cell mutation rates resulting from exposures to a broad range of particle types and energy spectra. In this context, simulated exposure and subsequent risk for humans in residence on Mars are examined. A conceptual habitat structure, CAD-modeled with duly considered inherent shielding properties, has been implemented. Body self-shielding is evaluated using NASA standard computerized male and female models. The background environment is taken to consist not only of exposure from incident cosmic ray ions and their secondaries, but also include the contribution from secondary neutron fields produced in the tenuous atmosphere and the underlying regolith.

Anderson, Brooke M.; Clowdsley, Martha S.; Qualls, Garry D.; Nealy, John E.

2005-01-01

405

The attainment of large accelerating gradients using near field synchrotron radiation  

SciTech Connect

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. The point charge results are generalized to the case of a line charge, and formulae are presented which can easily be evaluated numerically. A useful gradient of 80 MeV/m per kA of peak driving beam current over a distance of 1 cm is calculated using two 5 MeV driving beams moving on 1 cm radius helical orbits with bunch length 1 mm. 11 refs., 5 figs.

Decker, G.

1989-01-01

406

Energy streamlines in near-field radiative heat transfer between hyperbolic metamaterials.  

PubMed

Metallodielectric photonic crystals having hyperbolic dispersions are called indefinite materials because of their ability to guide modes with extremely large lateral wavevectors. While this is useful for enhancing near-field radiative heat transfer, it could also give rise to large lateral displacements of the energy pathways. The energy streamlines can be used to depict the flow of electromagnetic energy through a structure when wave propagation does not follow ray optics. We obtain the energy streamlines through two semi-infinite uniaxial anisotropic effective medium structures, separated by a small vacuum gap, using the Green functions and fluctuation-dissipation theorem. The lateral shifts are determined from the streamlines within two penetration depths. For hyperbolic modes, the predicted lateral shift can be several thousand times of the vacuum gap width. PMID:24978074

Bright, T J; Liu, X L; Zhang, Z M

2014-06-30

407

A beaming model of the Io-independent Jovian decameter radiation based on multipole models of the Jovian magnetic field  

NASA Technical Reports Server (NTRS)

A geometrical model is presented in which the apparent source locations of the Io-independent decameter radiation are computed. The calculations assume that the radiation is produced by stably trapped electrons radiating near the electron gyrofrequency and that the emission is then beamed onto a conical surface. The maximum occurrence probability of noise storms is associated with regions in the Jovian magnetosphere where the axis of the emission cone is most inclined toward the Jovian equatorial plane. The calculations utilize and compare two of the octupole spherical harmonic expansions of the Jovian magnetic field constructed from data accumulated by the fluxgate and vector helium magnetometers on board Pioneer 11.

Goldstein, M. L.; Eviatar, A.; Thieman, J. R.

1978-01-01

408

Cytokinesis block micronucleus assay in field plants for monitoring radiation-induced genotoxicity of the environment.  

PubMed

Effective biomonitoring for detection of radiation-induced genotoxicity of contaminants in natural environments involves testing of field plants for cytogenetic changes. To increase the efficiency and precision of cytogenetic analyses of field plants that have naturally high individual variability, an improved micronucleus assay is proposed that employs a cytokinesis block technique similar to the lymphocyte test system used in mammals. In seed embryonic meristems of the Japanese cedar, application of a methylxanthine derivative, 3-isobutyl-1-methylxanthine (IBMX), was found to be effective in inhibiting cytokinesis to make once-divided cells easily recognizable by their binucleate appearance. In the meristem of IBMX-treated seminal roots from X-ray-irradiated seeds, variation in micronucleus frequency in the binucleate cell population was reduced compared to that in the total cell population. The highest efficiency of measurement of micronucleus frequencies was obtained in the root meristems where 0.2- to 1.5-mm-long seminal roots were incubated with IBMX for 24 h. This result indicated that this root elongation stage corresponded to the first divisions of the root meristematic cells, and was therefore suitable for obtaining reliable estimations of accumulated genetic damage in the seeds. This cytokinesis block assay applied specifically at the root elongation stage was then used to examine dose-response relationships in Japanese cedar seeds irradiated either acutely with X-rays or chronically with ?-rays. The resulting dose-response curve for the acute X-ray irradiation was fitted onto a linear-quadratic regression curve, whereas the dose-response curve for the chronic ?-irradiation matched a linear regression line better. Both dose-response curves were consistent with the target theory of classical radiation biology. The good agreement of the micronucleus data to a simple dose-response model indicates the proposed accuracy of the cytokinesis block micronucleus assay for plant monitoring. PMID:25440909

Watanabe, Yoshito; Kubota, Yoshihisa; Fuma, Shoichi; Kouichi, Maruyama; Ichikawa, San'ei; Kubota, Masahide; Yoshida, Satoshi

2014-11-01

409

OBSERVATIONAL CONSTRAINTS ON THE STELLAR RADIATION FIELD IMPINGING ON TRANSITIONAL DISK ATMOSPHERES  

SciTech Connect

Mid-infrared atomic and ionic line ratios measured in spectra of pre-main-sequence stars are sensitive indicators of the hardness of the radiation field impinging on the disk surface. We present a low-resolution Spitzer IRS search for [Ar II] at 6.98 {mu}m, [Ne II] at 12.81 {mu}m, and [Ne III] 15.55 {mu}m lines in 56 transitional disks. These objects, characterized by reduced near-infrared but strong far-infrared excess emission, are ideal targets to set constraints on the stellar radiation field onto the disk, because their spectra are not contaminated by shock emission from jets/outflows or by molecular emission lines. After demonstrating that we can detect [Ne II] lines and recover their fluxes from the low-resolution spectra, here we report the first detections of [Ar II] lines toward protoplanetary disks. We did not detect [Ne III] emission in any of our sources. Our [Ne II]/[Ne III] line flux ratios combined with literature data suggest that a soft-EUV or X-ray spectrum produces these gas lines. Furthermore, the [Ar II]/[Ne II] line flux ratios point to a soft X-ray and/or soft-EUV stellar spectrum as the ionization source of the [Ar II] and [Ne II] emitting layer of the disk. If the soft X-ray component dominates over the EUV, then we would expect larger photoevaporation rates and, hence, a reduction of the time available to form planets.

Szulagyi, Judit [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Pascucci, Ilaria [Lunar and Planetary Laboratory, University of Arizona, 1629 East University Boulevard, Tucson, AZ 85721 (United States); Abraham, Peter; Moor, Attila [Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege Miklos ut 15-17, H-1121 Budapest (Hungary); Apai, Daniel [Department of Astronomy, The University of Arizona, 933 N Cherry Avenue, Tucson, AZ 85721 (United States); Bouwman, Jeroen, E-mail: szulagyi@konkoly.hu [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany)

2012-11-01

410

Acoustic field modeling for physiotherapy ultrasound applicators by using approximated functions of measured non-uniform radiation distributions.  

PubMed

The strongest therapeutic effects in ultrasonic physiotherapy are mainly produced at the first centimeters, i.e. close to the applicator surface and, in general, only in the near-field zone. The acoustic field produced in practice by this type of transducers differs from the classical models because the vibration distribution on the real transducer surfaces is non-uniform. However, neither models using uniform distribution, nor those using typical non-uniform distribution patterns for the source accurately represent the radiation of this kind of transducers. Although this therapy is widely used and many efforts have been made in experimentally studying the patterns of ultrasound radiation produced during physiotherapy applications (IEC-61689, 1998), additional modeling researches still would be needed in order to achieve improved models giving field patterns closer to the measured ultrasonic results. In this paper, acoustic patterns produced from two source radiation functions are proposed and evaluated for field modeling of physiotherapy applicators. Both the functions are approximations to the pressure distribution measured close to the emitting surface and they are based on the modulation of the classical simply-supported function using either sinusoidal or Bessel-type distributions. The simply-supported function is accounted for the radiator-fixing condition and the modulation function simulates the complex vibration distribution of this kind of transducer. The modulator Bessel function is based on reports about Bessel-type vibration distributions found in piezoelectric disk resonators. The use of a selected sinusoidal segment represents another analytical option for obtaining an approximated behavior of the measured data in a real applicator. Both the field models are implemented using the finite element method (FEM) to obtain the numerical solution of wave equation at each point in the radiated space. The solution is reached by considering axisymmetric radiation in attenuation-free media. The results indicate the viability of applying an adequate model for acoustic field calculation by simulating the radiating distribution on the emitting surface as either sinusoidal or Bessel-modulated functions. Models using both the functions describe reasonably real behaviors, but those based on Bessel functions are better correlated with the measurements. The results for three commercial applicators indicate the possibility of representing, with adequate verisimilitude, the acoustic field radiated by physiotherapy ultrasound transducers using linear combinations of Bessel profiles describing the radiation source. PMID:22405588

Gutiérrez, Mario Ibrahín; Calás, Héctor; Ramos, Antonio; Vera, Arturo; Leija, Lorenzo

2012-08-01

411

Optimal aircraft performance during microburst encounter  

NASA Technical Reports Server (NTRS)

The effects of microburst characteristics on the optimal penetration performance of jet transport and general aviation aircraft are presented. The purpose is to determine the best possible performance that can be achieved in a broad range of microbursts. A secondary goal is to illustrate good strategies for dealing with a range of microbursts during takeoff and landing. Over 1100 optimal trajectories were computed for two aircraft types flying through idealized microbursts using a Successive Quadratic Programs trajectory optimization algorithm. Contours of safety metrics are plotted as functions of the length scales, magnitudes, and locations of horizontal wind shears and vertical downdrafts. These performance contours show three length-scale regimes for optimal microburst penetration. At short length scales, hazards usually associated with gustiness predominate (e.g., high normal load factor, rotational upset). At intermediate length scales, a degraded ability to maintain flight path and/or vertical velocity poses the most serious threat. At very long microburst length scales, excessive touchdown velocities may result. The ability to transit a microburst successfully also varies strongly with microburst location. The results show that both aircraft types could penetrate some very severe microbursts if optimal control histories were followed. Nevertheless, these control strategies assume perfect prior knowledge of the wind, and practical limits to successful encounter with real-time control capabilities would be lower. The optimally controlled jet transport can successfully penetrate higher intensity microbursts than can the general aviation aircraft.

Psiaki, Mark L.; Stengel, Robert F.

1991-01-01

412

Simulating black hole white dwarf encounters  

NASA Astrophysics Data System (ADS)

The existence of supermassive black holes lurking in the centers of galaxies and of stellar binary systems containing a black hole with a few solar masses has been established beyond reasonable doubt. The idea that black holes of intermediate masses (˜1000M) may exist in globular star clusters has gained credence over recent years but no conclusive evidence has been established yet. An attractive feature of this hypothesis is the potential to not only disrupt solar-type stars but also compact white dwarf stars. In close encounters the white dwarfs can be sufficiently compressed to thermonuclearly explode. The detection of an underluminous thermonuclear explosion accompanied by a soft, transient X-ray signal would be compelling evidence for the presence of intermediate mass black holes in stellar clusters. In this paper we focus on the numerical techniques used to simulate the entire disruption process from the initial parabolic orbit, over the nuclear energy release during tidal compression, the subsequent ejection of freshly synthesized material and the formation process of an accretion disk around the black hole.

Rosswog, Stephan; Ramirez-Ruiz, Enrico; Hix, W. Raphael; Dan, M.

2008-07-01

413

Aging and Osteoarthritis: An Inevitable Encounter?  

PubMed Central

Osteoarthritis (OA) is a major health burden of our time. Age is the most prominent risk factor for the development and progression of OA. The mechanistic influence of aging on OA has different facets. On a molecular level, matrix proteins such as collagen or proteoglycans are modified, which alters cartilage function. Collagen cross-linking within the bone results in impaired plasticity and increased stiffness. Synovial or fat tissue, menisci but also ligaments and muscles play an important role in the pathogenesis of OA. In the elderly, sarcopenia or other causes of muscle atrophy are frequently encountered, leading to a decreased stability of the joint. Inflammation in form of cellular infiltration of synovial tissue or subchondral bone and expression of inflammatory cytokines is more and more recognized as trigger of OA. It has been demonstrated that joint movement can exhibit anti-inflammatory mechanisms. Therefore physical activity or physiotherapy in the elderly should be encouraged, also in order to increase the muscle mass. A reduced stem cell capacity in the elderly is likely associated with a decrease of repair mechanisms of the musculoskeletal system. New treatment strategies, for example with mesenchymal stem cells (MSC) are investigated, despite clear evidence for their efficacy is lacking. PMID:22720159

Hügle, Thomas; Geurts, Jeroen; Nüesch, Corina; Müller-Gerbl, Magdalena; Valderrabano, Victor

2012-01-01

414

An Almost Linear Time Algorithm for Field Splitting in Radiation Therapy?  

PubMed Central

In this paper, we study an interesting geometric partition problem, called optimal field splitting, which arises in Intensity-Modulated Radiation Therapy (IMRT). In current clinical practice, a multi-leaf collimator (MLC) with a maximum leaf spread constraint is used to deliver the prescribed intensity maps (IMs). However, the maximum leaf spread of an MLC may require to split a large intensity map into several overlapping sub-IMs with each being delivered separately. We develop a close-to-linear time algorithm for solving the field splitting problem while minimizing the total complexity of the resulting sub-IMs, thus improving the treatment delivery efficiency. Meanwhile, our algorithm strives to minimize the maximum beam-on time of those sub-IMs. Our basic idea is to formulate the field splitting problem as computing a shortest path in a directed acyclic graph, which expresses a special “layered” structure. The edge weights of the graph satisfy the Monge property, which enables us to solve this shortest path problem by examining only a small portion of the graph, yielding a close-to-linear time algorithm. To minimize the maximum beam-on time of the resulting sub-IMs, we consider an interesting min-max slope path problem in a monotone polygon which is solvable in linear time. The min-max slope path problem may be of interest in its own right. Experimental results based on real medical data and computer generated IMs showed that our new algorithm runs fast and produces high quality field splitting results. PMID:24999294

Wu, Xiaodong; Dou, Xin; Bayouth, John E.; Buatti, John M.

2014-01-01

415

An Almost Linear Time Algorithm for Field Splitting in Radiation Therapy.  

PubMed

In this paper, we study an interesting geometric partition problem, called optimal field splitting, which arises in Intensity-Modulated Radiation Therapy (IMRT). In current clinical practice, a multi-leaf collimator (MLC) with a maximum leaf spread constraint is used to deliver the prescribed intensity maps (IMs). However, the maximum leaf spread of an MLC may require to split a large intensity map into several overlapping sub-IMs with each being delivered separately. We develop a close-to-linear time algorithm for solving the field splitting problem while minimizing the total complexity of the resulting sub-IMs, thus improving the treatment delivery efficiency. Meanwhile, our algorithm strives to minimize the maximum beam-on time of those sub-IMs. Our basic idea is to formulate the field splitting problem as computing a shortest path in a directed acyclic graph, which expresses a special "layered" structure. The edge weights of the graph satisfy the Monge property, which enables us to solve this shortest path problem by examining only a small portion of the graph, yielding a close-to-linear time algorithm. To minimize the maximum beam-on time of the resulting sub-IMs, we consider an interesting min-max slope path problem in a monotone polygon which is solvable in linear time. The min-max slope path problem may be of interest in its own right. Experimental results based on real medical data and computer generated IMs showed that our new algorithm runs fast and produces high quality field splitting results. PMID:24999294

Wu, Xiaodong; Dou, Xin; Bayouth, John E; Buatti, John M

2013-08-01

416

VISCOUS EVOLUTION AND PHOTOEVAPORATION OF CIRCUMSTELLAR DISKS DUE TO EXTERNAL FAR ULTRAVIOLET RADIATION FIELDS  

SciTech Connect

This paper explores the effects of FUV radiation fields from external stars on circumstellar disk evolution. Disks residing in young clusters can be exposed to extreme levels of FUV flux from nearby OB stars, and observations show that disks in such environments are being actively photoevaporated. Typical FUV flux levels can be factors of {approx}10{sup 2}-10{sup 4} higher than the interstellar value. These fields are effective in driving mass loss from circumstellar disks because they act at large radial distance from the host star, i.e., where most of the disk mass is located, and where the gravitational potential well is shallow. We combine viscous evolution (an {alpha}-disk model) with an existing FUV photoevaporation model to derive constraints on disk lifetimes, and to determine disk properties as functions of time, including mass-loss rates, disk masses, and radii. We also consider the effects of X-ray photoevaporation from the host star using an existing model, and show that for disks around solar-mass stars, externally generated FUV fields are often the dominant mechanism in depleting disk material. For sufficiently large viscosities, FUV fields can efficiently photoevaporate disks over the entire range of parameter space. Disks with viscosity parameter {alpha} = 10{sup -3} are effectively dispersed within 1-3 Myr; for higher viscosities ({alpha} = 10{sup -2}) disks are dispersed within {approx}0.25-0.5 Myr. Furthermore, disk radii are truncated to less than {approx}100 AU, which can possibly affect the formation of planets. Our model predictions are consistent with the range of observed masses and radii of proplyds in the Orion Nebula Cluster.

Anderson, Kassandra R.; Adams, Fred C. [Physics Department, University of Michigan, Ann Arbor, MI 48109 (United States); Calvet, Nuria [Astronomy Department, University of Michigan, Ann Arbor, MI 48109 (United States)

2013-09-01

417

Hot accretion disks with pairs: Effects of magnetic field and thermal cyclocsynchrotron radiation  

NASA Technical Reports Server (NTRS)

We show the effects of thermal cyclosynchrotron radiation and magnetic viscosity on the structure of hot, two-temperature accretion disks. Magnetic field, B, is assumed to be randomly oriented and the ratio of magnetic pressure to either gas pressure, alpha = P(sub mag)/P(sub gas), or the sum of the gas and radiation pressures, alpha = (P(sub mag)/P(sub gas) + P(sub rad)), is fixed. We find those effects do not change the qualitative properties of the disks, i.e., there are still two critical accretion rates related to production of e(sup +/-) pairs, (M dot)((sup U)(sub cr)) and (M dot)((sup L)(sub cr)), that affect the number of local and global disk solutions, as recently found by Bjoernsson and Svensson for the case with B = 0. However, a critical value of the alpha-viscosity parameter above which those critical accretion rates disappear becomes smaller than alpha(sub cr) = 1 found in the case of B = 0, for P(sub mag) = alpha(P(sub gas) + P(sub rad)). If P(sub mag) = alpha P(sub gas), on the other hand, alpha(sub cr) is still about unity. Moreover, when Comptonized cyclosynchrotron radiation dominates Comptonized bremsstrahlung, radiation from the disk obeys a power law with the energy spectral index of approximately 0.5, in a qualitative agreement with X-ray observations of active galactic nuclei (AGNS) and Galactic black hole candidates. We also extend the hot disk solutions for P(sub mag) = alpha(P(sub gas) + P(sub rad)) to the effectively optically thick region, where they merge with the standard cold disk solutions. We find that the mapping method by Bjoernsson and Svensson gives a good approximation to the disk structure in the hot region and show where it breaks in the transition region. Finally, we find a region in the disk parameter space with no solutions due to the inability of Coulomb heating to supply enough energy to electrons.

Kusunose, Masaaki; Zdziarski, Andrzej A.

1994-01-01

418

Far-Field Energy Radiation From a Building Under Harmonic Excitation  

NASA Astrophysics Data System (ADS)

A nine story building on the Caltech campus (Millikan Library) was harmonically excited at its East-West (EW) and North-South (NS) natural frequencies to determine the behavior of the far-field radiated waves emanating from the building. The building's natural frequencies are ~ 1.12 Hz. and ~ 1.64 Hz. for the EW and NS directions respectively, and the individual building shakes lasted approximately four hours each. We use the data recorded by the Southern California TriNet stations, and the building's signal can be observed at distances larger than 300 kilometers. By using 36 USGS owned FBA-11 accelerometers located in the building to compute the forces in each floor, we can estimate the maximum applied forces/overturning moments that the building imparts on the soil to be: Shear Force ~ 2.2e+5 N (4.9e+4 lbf) and Overturning Moment ~ 7.0e+6 Nm (5.2e+6 lbf ft) for the EW shake, and Shear Force ~ 5.2e+5 N (1.2e+5 lbf) and Overturning Moment ~ 1.6e+7 Nm (1.2e+7 lbf ft) for the NS shake. Furthermore, by using the roof displacement and the force being applied to the building, we estimate the horsepower being used by the motor that powers the shaker as ~ 12 J/sec (0.02 hp) for the EW shake, and ~ 40 J/sec (0.05 hp) for the NS shake. The units used above are as follows: N = Newton, lbf = Pound Force, m = Meter, ft = Feet, J = Joule, sec = Second, and hp = Horsepower. From the measured signals, we produce maximum amplitude plots (as the measured waves are harmonic) for each component as well as the vector sum of the components, and we find the best fitting distance decay rates for the data. We observe very little radiation pattern in the radiated waves, which is contrary to the simple half-space models and we explore the lack of azimuthal radiation patterns from the building. It is interesting to note that the best fitting distance decay rate changes at a distance of approximately 50 kilometers. This approach is nondestructive and repeatable and thus is suitable for establishing (monochromatic) amplitude response curves of the crust and mantle structure in Southern California. Furthermore, this may also be a powerful tool to monitor temporary variations of site response changes if they ever occur.

Favela, J.; Heaton, T. H.; Tanimoto, T.

2002-12-01

419

Far-field sound radiation of a submerged cylindrical shell at finite depth from the free surface.  

PubMed

The far-field sound radiation behavior of a circular cylindrical shell submerged at finite depth from the free surface is studied. Based on the Flügge shell theory and the Helmholtz equation, the structure-acoustic coupling equation is established. An image method is applied so that the sound boundary condition of the free surface can be satisfied. Analytical expression of the far-field sound pressure is obtained using the stationary phase method and the Graf's addition theorem. In order to evaluate the effect of the submerged depth on sound radiation, the results of the submerged cylindrical shell at finite depth from the free surface are compared with those of the submerged cylindrical shell in the infinite fluid. The characteristics of the far-field sound pressure with the change of the depth are investigated. It is found that the submerged depth has a significant influence on the far-field sound pressure radiated from the submerged cylindrical shell due to the free surface effects. The work provides more understanding on the sound radiation properties of the submerged circular cylindrical shell without assuming infinite fluid field, which was commonly used in previous studies. PMID:25190381

Li, T Y; Miao, Y Y; Ye, W B; Zhu, X; Zhu, X M

2014-09-01

420

Design and testing of indigenous cost effective three dimensional radiation field analyser (3D RFA).  

PubMed

The aim of the study is to design and validate an indigenous three dimensional Radiation Field Analyser (3D RFA). The feed system made for X, Y and Z axis movements is of lead screw with deep ball bearing mechanism made up of stain less steel driven by stepper motors with accuracy less than 0.5 mm. The telescopic column lifting unit was designed using linear actuation technology for lifting the water phantom. The acrylic phantom with dimensions of 800 x 750 x 570 mm was made with thickness of 15 mm. The software was developed in visual basic programming language, classified into two types, viz. beam analyzer software and beam acquisition software. The premeasurement checks were performed as per TG 106 recommendations. The physical parameters of photon PDDs such as Dmax, D10, D20 and Quality Index (QI), and the electron PDDs such as R50, Rp, E0, Epo and X-ray contamination values can be obtained instantaneously by using the developed RFA system. Also the results for profile data such as field size, central axis deviation, penumbra, flatness and symmetry calculated according to various protocols can be obtained for both photon and electron beams. The result of PDDs for photon beams were compared with BJR25 supplement values and the profile data were compared with TG 40 recommendation. The results were in agreement with standard protocols. PMID:23919396

Ganesh, K M; Pichandi, A; Nehru, R M; Ravikumar, M

2014-06-01

421

Azimuthal Patterns of the Radiated Sound Field from a Turbofan Model  

NASA Technical Reports Server (NTRS)

The azimuthal directivity of a scale fan model was measured extensively. The model is a 12 inch diameter fan with 16 rotors and 40 stator vanes and tests were done at a tip speed of 905 ft/sec. Tests were conducted in an anechoic chamber with an inflow control device installed on the stationary fan model. The acoustic far field of the fan was surveyed with a circular hoop, with a diameter of six fan diameters, centered on the fan axis and was moved along the fan axis at polar angles from 20 to 110 degrees in increments of 10 degrees. The hoop, with 16 microphones evenly spaced at intervals of 22.5 degrees was rotated in 24 increments in the azimuthal direction for a total 384 points. From this extensive mapping of the directivity it is shown that the azimuthal directivity of the fundamental and first two harmonics is significant and can vary up to 15 dB. The broadband can also have an azimuthal directivity with as much as a 4 dB variation. A theory is proposed with relates the radiated modes with the generation of the far field patterns which produce the azimuthal directivity.

Thomas, R. H.; Farassat, F.; Clark, L. R.; Gerhold, C. H.

1997-01-01

422

Regular and Chaotic Quantum Dynamics of Two-Level Atoms in a Selfconsistent Radiation Field  

NASA Technical Reports Server (NTRS)

Dynamics of two-level atoms interacting with their own radiation field in a single-mode high-quality resonator is considered. The dynamical system consists of two second-order differential equations, one for the atomic SU(2) dynamical-group parameter and another for the field strength. With the help of the maximal Lyapunov exponent for this set, we numerically investigate transitions from regularity to deterministic quantum chaos in such a simple model. Increasing the collective coupling constant b is identical with 8(pi)N(sub 0)(d(exp 2))/hw, we observed for initially unexcited atoms a usual sharp transition to chaos at b(sub c) approx. equal to 1. If we take the dimensionless individual Rabi frequency a = Omega/2w as a control parameter, then a sequence of order-to-chaos transitions has been observed starting with the critical value a(sub c) approx. equal to 0.25 at the same initial conditions.

Konkov, L. E.; Prants, S. V.

1996-01-01

423

Thirty-sixth Lauriston S. Taylor Lecture on radiation protection and measurements--from the field to the laboratory and back: the what ifs, wows, and who cares of radiation biology.  

PubMed

My scientific journey started at the University of Utah chasing fallout. It was on everything, in everything, and was distributed throughout the ecosystem. This resulted in radiation doses to humans and caused me great concern. From this concern I asked the question, "Are there health effects from these radiation doses and levels of radioactive contamination?" I have invested my scientific career trying to address this basic question. While conducting research, I got acquainted with many of the What ifs of radiation biology. The major What if in my research was, "What if we have underestimated the radiation risk for internally-deposited radioactive material?" While conducting research to address this important question, many other What ifs came up related to dose, dose rate, and dose distribution. I also encountered a large number of Wows. One of the first was when I went from conducting environmental fallout studies to research in a controlled laboratory. The activity in fallout was expressed as pCi L?¹, whereas it was necessary to inject laboratory animals with ?Ci g?¹ body weight to induce measurable biological changes, chromosome aberrations, and cancer. Wow! That is seven to nine orders of magnitude above the activity levels found in the environment. Other Wows have made it necessary for the field of radiation biology to make important paradigm shifts. For example, one shift involved changing from "hit theory" to total tissue responses as the result of bystander effects. Finally, Who cares? While working at U.S. Department of Energy headquarters and serving on many scientific committees, I found that science does not drive regulatory and funding decisions. Public perception and politics seem to be major driving forces. If scientific data suggested that risk had been underestimated, everyone cared. When science suggested that risk had been overestimated, no one cared. This result-dependent Who cares? was demonstrated as we tried to generate interactions by holding meetings with individuals involved in basic low-dose research, regulators, and the news media. As the scientists presented their "exciting data" that suggested that risk was overestimated, many of the regulators simply said, "We cannot use such data." The newspaper people said, "It is not possible to get such information by my editors." In spite of these difficulties, research results from basic science must be made available and considered by members of the public as well as by those that make regulatory recommendations. Public outreach of the data is critical and must continue to be a future focus to address properly the question of, "Who cares?" My journey in science, like many of yours, has been a mixture of chasing money, beatings, and the joys of unique and interesting research results. Perhaps through our experiences, we can improve research environments, funding, and use of the valuable information that is generated. Scientists that study at all levels of biological organization, from the environment to the laboratory and human epidemiology, must share expertise and data to address the What Ifs, Wows, and Who Cares of radiation biology. PMID:24077038

Brooks, Antone L

2013-11-01

424

Schistosomes and snails: a molecular encounter  

PubMed Central

Biomphalaria glabrata snails play an integral role in the transmission of Schistosoma mansoni, the causative agent for human schistosomiasis in the Western hemisphere. For the past two decades, tremendous advances have been made in research aimed at elucidating the molecular basis of the snail/parasite interaction. The growing concern that there is no vaccine to prevent schistosomiasis and only one effective drug in existence provides the impetus to develop new control strategies based on eliminating schistosomes at the snail-stage of the life cycle. To elucidate why a given snail is not always compatible to each and every schistosome it encounters, B. glabrata that are either resistant or susceptible to a given strain of S. mansoni have been employed to track molecular mechanisms governing the snail/schistosome relationship. With such snails, genetic markers for resistance and susceptibility were identified. Additionally, differential gene expression studies have led to the identification of genes that underlie these phenotypes. Lately, the role of schistosomes in mediating non-random relocation of gene loci has been identified for the first time, making B. glabrata a model organism where chromatin regulation by changes in nuclear architecture, known as spatial epigenetics, orchestrated by a major human parasite can now be investigated. This review will highlight the progress that has been made in using molecular approaches to describe snail/schistosome compatibility issues. Uncovering the signaling networks triggered by schistosomes that provide the impulse to turn genes on and off in the snail host, thereby controlling the outcome of infection, could also yield new insights into anti-parasite mechanism(s) that operate in the human host as well. PMID:25101114

Knight, Matty; Arican-Goktas, Halime D.; Ittiprasert, Wannaporn; Odoemelam, Edwin C.; Miller, André N.; Bridger, Joanna M.

2014-01-01